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PhD
projects for Entry in October 2010
This page gives a list of PhD projects available in the
Department of Materials Science. Most of the projects listed above are
available only to UK and EU nationals (fees only) although some awards
may be available for high-calibre graduates from outside Europe.
For details of the application process follow this link.
For general information on studentships follow this link.
For other information, please contact Dr Rosie Ward, Department of Materials
Science and Metallurgy, University of Cambridge, Pembroke Street, Cambridge,
CB2 3QZ, tel +44 1223 331955, fax +44 1223 762088, remw2@msm.cam.ac.uk
Please include a CV and state your project(s) of interest
Biomaterials
Optimisation of calcium phosphate
bone cements for defect filling
The current, widely used methods of implant fixation and
bone defect filling are still far from ideal and in response to this need
for improvement the use of calcium phosphate bone cements (CPBCs) has
developed. The materials consist of a powder phase which forms a plastic
paste upon mixing with a liquid. The eventual phase which results from
the reaction in the cement is hydroxyapatite (HA, (Ca10(PO4) 6(OH)2) which
is one of a series of highly biocompatible calcium phosphates and closely
resembles the mineral component of bone. Although these materials are
extremely promising in terms of the in-vivo bioactivity, there still remains
a great deal of room for improvement both biologically and in terms of
mechanical stability with time. This project will involve the development
of cements which provide reproducible and enhanced properties in terms
of phase composition, crystallinity and biological and mechanical performance
and, by incorporating or engineering the evolution of novel substituted
apatites with compositions more closely matched to bone mineral than hydroxyapatite,
a method of increasing bone integration may be developed. For further
information contact Dr. Serena Best (smb51@cam.ac.uk).
Mechanical characterisation and
processing of substituted apatites
The benefits of "susbtituted apatites" (hydroxyapatite-based
materials with physiologically relevant (bone-like) ionic lattice substitutions)
have now been established. Although the materials are now on the verge
of clinical application and technology transfer to industry, there is
still a great deal more work which needs to be conducted to fully understand
the structural and mechanical implications of the ionic susbtitutions.
Detailed investigations are required to provide data on the static and
dynamic mechanical behaviour and processing properties of the materials
to take them forward from granules for defect filling towards a whole
raft of different applications ranging from bioactive porous orbits to
middle ear implants. For further information contact Dr. Serena Best (smb51@cam.ac.uk).
Calcium phosphate Gels as injectable
bone repair systems
Current figures show that only 8% of the bone graft market
is comprised of synthetic materials and of these, the main commercially
available source of hydroxyapatite (HA) is from coralline and bovine sources.
There is a great deal of scope for improvement of materials developed
for defect filling and augmentation. The development of highly bioactive,
injectable calcium phosphate materials will be investigated using physical,
chemical and biological analyses. The materials will be investigated as
purely synthetic systems but also with a view to the incorporation of
biological moieties. The systems developed will be studied in-vitro using
the unique wet system capabilities provided by environmental scanning
electron microscopy and confocal microscopy. For further information contact
Dr. Serena Best (smb51@cam.ac.uk).
Thin film substituted calcium phosphate
coatings
In the search for bioactive implants for major load bearing
applications, interest has been directed towards the use of calcium phosphate
coatings on metallic substrates. The vast majority of research and development
has been concentrated on plasma sprayed coatings and these are widely
used in the orthopaedics industry. However, the disadvantage of plasma
sprayed coatings is that they often contain microstructural defects and
may have variable phase compositions and crystallinity. RF-Magnetron Sputtering
offers the potential to apply thin coatings of controlled chemistry and
phase composition to metallic and polymeric substrates. The project will
involve the deposition and characterisation of hydroxyapatite and substituted
apatite coatings using scanning electron microscopy (SEM), transmission
electron microscopy (TEM), X-ray diffraction (XRD) and FT-infrared spectroscopy
and coating evaluation using biological testing techniques. For further
information contact Dr. Serena Best (smb51@cam.ac.uk).
Formulation and production of bioactive
glass ceramics
There is an ever expanding range of possible applications
for materials produced through the glass ceramics route. As a class of
materials, ceramics alone allow the selection and optimisation of material
composition to enhance bioactivity. This project will encompass the advantages
of near net shape forming, the ability to produce fully dense ceramic
components with controlled microstructures and optimisation of chemical
composition the development of bioactive glass ceramics. Through research
into new formulations. a new family of strong, tough, bioactive materials
with potential for application in major load bearing applications will
be developed. For further information contact Dr. Serena Best (smb51@cam.ac.uk).
Mechanical evaluation of ceramic
articulating surfaces
The orthopaedics industry has highlighted as a priority
the need for the improvement of the wear performance of the articulating
surfaces in hips and knees. Current solutions include the use of ceramic
femoral heads and knee surfaces, but there are still major problems in
terms of implant lifetimes. There is a need for the development of improved
materials and processes that must be economically viable in industry.
Areas of investigation will include optimisation of the performance of
ceramic / ceramic systems and investigation of the potential for functionally
graded metal / ceramic components. The scope of the project will range
from mechanical evaluation through to ultramicroscopic examination of
structures using electron microscopy. For further information contact
Dr. Serena Best (smb51@cam.ac.uk).
3D structures from resorbable polymers
Poly(glycolic acid) is a biocompatible, biodegradable,
semi-crystalline polymer which is approved for use in the body. It is
used to make resorbable sutures and recent and ongoing research in this
lab has focused on its development as a controlled drug delivery matrix.
This project will centre on the production and properties of controlled
foams of poly(glycolic) acid and other biocompatible resorbable polymers.
The physical properties of the foams, their potential as a drug carrier
and the relationships between microstructure and release will be examined.
Sintering of foam particles will be explored with the aim of producing
degradable foam structures for mechanical wound support or tissue engineering
applications. A wide range of physical techniques will be applied. For
further information contact Dr Ruth Cameron 01223 334324, rec11@cam.ac.uk.
Modelling of resorbable polymers:
interplay of microstructure, reaction and diffusion
Newly developed hierarchical computer modelling procedures
will be employed to model the behaviour and consequent drug release profiles
in resorbable polymer systems. These procedures involve molecular dynamic
regimes (atomic level), lattice mesoscale models with chain detail and
fully macroscopic models (such as those used to model Case II diffusion).
Our experimental results on poly(glycolic acid) have allowed us to develop
a conceptual model of the interplay between diffusion, reaction and drug
release profile. The model is in some senses similar to Case II diffusion.
By changing the boundary conditions of the model, it should be possible
to explore the behaviour of other resorbable polymers in the poly(glycolic
acid) / poly(lactic acid) system. This will be a mainly computational
project, but will involve close liaison with experimental groups. For
further information contact Dr Ruth Cameron 01223 334324, rec11@cam.ac.uk.
Drug delivery from biocompatible
coatings
Biocompatible coatings can enhance to performance of a
range of medical devices by facilitating a functional interface between
the implant and the body. This project takes the further step of considering
the incorporation and release of drug molecules from such coatings, designed
to give highly localised and controlled delivery of drugs around the device.
Physical, chemical and biological information will be combined to gain
the understanding required to design devices with appropriate tailored
drug release profiles. For further information contact Dr Ruth Cameron
01223 334324, rec11@cam.ac.uk.
Composite Materials
Characterisation of the Adhesion of Single Cells
to Ti-based Surfaces, using Forced Liquid Flow
This study will be carried out using bovine chondrocyte (cartilege) cells
and human bone cells from an established osteoblast cell line.
These cells will be distributed onto pure titanium and Ti-6Al-4V substrates,
after they have been subjected to several different surface treatments.
The cells will be left for a short period in a nutrient solution,
to allow cell attachment to occur. Flow of liquid over the surface
will then be stimulated, and observations made about the relationship
between the flow conditions (velocity profile) and the cell detachment
behaviour. Analytical and numerical modelling of the flow pattern
will be carried out, taking account of cell shape, so that the detachment
characteristics can be translated into mechanical adhesion parameters.
Correlations will be sought with results from an ongoing project
in which the force necessary to detach single cells is being measured
directly. For further information contact Prof TW Clyne (twc10@cam.ac.uk)
or Dr AE Markaki
High Strain Rate Superelastic Behaviour of NiTi
Shape Memory Alloys
There is interest in the mechanical behaviour of shape memory (NiTi)
alloys under high imposed strain rates [1, 2]. An attractive tool
for study of the superelastic deformation of such alloys is the nanoindenter.
There have been several recent studies [3, 4] of the nanoindentation
response of NiTi, and it has been shown [4] that nanoindentation data
can be used to establish whether deformation is occurring via superelasticity.
Multiple impact indentation modes, transiently generating high
local strain rates, will be used to explore high strain rate superelasticity
in this way. Some exploratory work has been done [5], but more
systematic studies are now needed, covering effects, such as adiabatic
heating, which have not previously been considered. Comprensive
FEM modelling of the strain field during indentation will be undertaken,
building on previous work [4-6]. NiTi specimens will be subjected
to static and multiple impact nanoindentation, over a range of effective
strain rates. Further experiments will be carried out using a simple coiled
spring specimen geometry, with loading via a servo-hydraulic testing machine,
over a range of frequency. Monitoring of whether purely superelastic
deformation has occurred will be by checking whether there is any residual
plastic strain on unloading, for various imposed strain amplitudes.
This testing geometry has the advantage that the strain field is much
simpler than that during nanoindentation. For further information contact
Prof TW Clyne (twc10@cam.ac.uk).
1. Millett, JCF, Bourne,
NK and Gray, G , Behaviour of the Shape Memory Alloy NiTi during One
Dimensional Shock Loading , J. Appl. Phys. , vol. 92 (2002)
p.3107-3110.
2. Meziere, Y, Millett,
J and Bourne, N , Equation of State and Mechanical Response of NiTi
during One-dimensional Shock Loading , J. Appl. Phys. , vol. 100
(2006) p.Art. 033513.
3. Shaw, GA, Stone,
DS, Johnson, AD, Ellis, AB and Crone, WC , Shape Memory Effect in
Nanoindentation of Nickel-Titanium Thin Films , Appl. Phys. Letts.
, vol. 83 (2003) p.257-259.
4. Muir Wood, AJ and
Clyne, TW , Measurement and Modelling of the Nanoindentation Response
of Shape Memory Alloys , Acta Materialia , vol. 54 (2006)
p.5607-5615.
5. Ma, X-G and Komvopoulos,
K , Pseudoelasticity of Shape Memory Titanium-Nickel Films subjected
to Dynamic Nanoindentation , Appl. Phys. Letts. , vol. 84
(2004) p.4274-4276.
6. Zhang, Y, Cheng,
Y and Grummon, D, Finite element modeling of indentation-induced superelastic
effect using a three-dimensional constitutive model for shape memory materials
with plasticity , J. Appl. Phys. , vol. 101 (2007)
Art. 053507 .
Microstructure, Hardness and Tribological
Characteristics of PEO Coatings
Plasma electrolytic oxidation (PEO) is a novel surface engineering technology,
allowing thick oxide coatings to be formed on metal components.
It is based on electrolysis within an aqueous electrolyte, with dielectric
breakdown of the growing oxide film occurring via a series of local discharge
events, allowing production of films as thick as 100 µm or
more. The discharge events have a profound effect on coating microstructure,
and hence on the physical and mechanical properties of the coating.
The process is particularly effective on aluminium and magnesium.
Empirical process optimisation has led to coatings with good tribological
characteristics [1-3]. There is now a pressing need for improved
understanding of the fundamentals, particularly relationships between
electrolyte and alloy composition, coating microstructure/composition,
hardness and wear resistance. Some of the work will build on recent
progress [4-6] on correlations between production conditions, microstructural
features and thermo-physical properties. Coatings will be produced
in Cambridge. Initial work will focus on 1000, 2000, 5000 and 6000
series Al alloys. Porosity characteristics will be investigated
by precision densitometry, mercury porosimetry, BET analysis and He pycnometry.
Both global and local responses to indentation will be examined,
over a range of temperature. The macroscopic hardness will be used
as a general guide to the mechanical strength of the coatings, while a
nanoindenter will be used to explore local variations in hardness and
also to study the multiple impact response. Preliminary indications
have already been obtained that the coating hardness varies with alloy
composition and such variations will be systematically explored.
Both pin-on-disk and erosive wear experiments will be carried out, and
results will be correlated with both static hardness and dynamic nanoindentation
results. For further information contact Prof TW Clyne (twc10@cam.ac.uk)
1. Nie, X, Meletis,
EI, Jiang, JC, Leyland, A, Yerokhin, AL and Matthews, A , Abrasive
Wear/corrosion Properties and TEM Analysis of Al 2 O 3 Coatings Fabricated
using Plasma Electrolysis , Surf. & Coat. Techn. , vol. 149
(2002) p.245-251.
2. Rama-Krishna, L,
Somaraju, KRC and Sundararajan, G , The Tribological Performance of
Ultra-hard Ceramic Composite Coatings obtained through Microarc Oxidation
, Surf. Coat. Techn. , vol. 163-164 (2003)
p.484-490.
3. Wei, T, Yan, F and
Tian, J , Characterization and Wear- and Corrosion-resistance of Microarc
Oxidation Ceramic Coatings on Aluminum Alloy , J. Alloys and Compounds
, vol. 389 (2004) p.169-176.
4. Curran, JA and Clyne,
TW , Thermo-physical Properties of Plasma Electrolytic Oxide Coatings
on Aluminium , Surf. & Coat. Techn. , vol. 199 (2005)
p.168-176.
5. Curran, JA and Clyne,
TW , The Thermal Conductivity of Plasma Electrolytic Oxide Coatings
on Aluminium and Magnesium , Surf. & Coat. Techn. , vol. 199
(2005) p.177-183.
6. Curran, JA and Clyne,
TW , Porosity in Plasma Electrolytic Oxide Coatings , Acta Mater.
, vol. 54 (2006) p.1985-1993.
Mechanical Stability and Biocompatibility of PEO
Coatings on Titanium Substrates
Plasma electrolytic oxidation (PEO) is a novel surface engineering technology,
allowing thick oxide coatings to be formed on metal components.
It is based on electrolysis within an aqueous electrolyte, with dielectric
breakdown of the growing oxide film occurring via a series of local discharge
events, allowing production of films as thick as 100 µm or
more. Recent work in the Gordon Laboratory [2, 3] has led to improved
understanding of the relationships between production conditions, microstructural
features and thermo-physical properties. There is also growing
interest in the potential for their use in various biomedical applications,
since it has already become clear that high biocompatibility and bioactivity
levels can be generated [4, 5]. PEO coatings will be produced on
Ti-6Al-4V substrates, using a range of conditions designed to generate
HA, or closely similar compounds, within the microstructure. These
will be characterised in terms of density, pore structure, phase constitution
and mechanical properties. Their biocompatibility will be assessed
in the Cell Culture facility within the Gordon Laboratory, using bovine
chondrocyte and human osteoblast cells. For further information contact
Prof TW Clyne (twc10@cam.ac.uk) or Dr AE Markaki.
1. Curran, JA and Clyne, TW, Thermo-physical Properties
of Plasma Electrolytic Oxide Coatings on Aluminium , Surf. &
Coat. Techn. , vol.199 (2005) p.168-176.
2. Curran, JA and Clyne, TW, The Thermal Conductivity
of Plasma Electrolytic Oxide Coatings on Aluminium and Magnesium ,
Surf. & Coat. Techn. , vol.199 (2005) p.177-183.
3. Han, Y, Hong, SH and Xu, KW, Structure and In Vitro
Bioactivity of Titania-based Films by Micro-arc Oxidation , Surf.
Coat. Techn. , vol.168 (2003) p.249-258.
4. Huang, P, Xu, KW and Han, Y, Preparation and apatite
layer formation of plasma electrolytic oxidation film on titanium for
biomedical application , Materials Letters , vol.59 (2005) p.185-189.
Electrical Discharge Characteristics of Plasma Electrolytic
Oxide (PEO) Coatings
Substantial advances have been made recently in understanding of the
process-microstructure-property relationships in PEO coatings [1-4].
These coatings, which can be relatively thick (~100 µm), are
formed in aqueous electrolytes by repeated local dielectric breakdown
events, with charge transfer and chemical changes occuring within the
associated plasma channels. Microstructural features include a
very fine grain size, the presence of an amorphous phase and relatively
high levels of ultra-fine, inter-connected porosity. There is considerable
interest in the dielectric properties of these coatings, over a range
of frequencies and under both wet and dry conditions. This partly
arises from possible use of these coatings for electrical insulation purposes,
but these characteristics are also expected to give valuable insights
into the way that the coatings are formed. Electrical characteristics
of PEO coatings on aluminium alloys, particularly the voltage and current
profiles during each cycle, will be studied over a range of conditions
and correlations will be established with microstructural features. For
further information contact Prof TW Clyne (twc10@cam.ac.uk).
1. Curran, JA and Clyne, TW, Thermo-physical
Properties of Plasma Electrolytic Oxide Coatings on Aluminium , Surf.
& Coat. Techn. , vol. 199 (2005) p.168-176.
2. Curran, JA and Clyne, TW, The
Thermal Conductivity of Plasma Electrolytic Oxide Coatings on Aluminium
and Magnesium , Surf. & Coat. Techn . , vol. 199
(2005) p.177-183.
3. Curran, JA and Clyne, TW, Porosity
in Plasma Electrolytic Oxide Coatings , Acta Materialia , vol. 54
(2006) p.1985-1993.
4. Curran, JA, Kalkanc?, H, Magurova,
Y and Clyne, TW, Mullite-rich Plasma Electrolytic Oxide Coatings for
Thermal Barrier Applications , Surf. Coat. Technol. , vol. 201
(2007) p.8683-8687.
Colloidal films for complex multilayer structures
A major problem in the development of complex multilayer microsystems
is the cracking during the drying of the colloidal layers. Such cracking
also occurs in many other processes, both industrial and natural, such
as the patterns that form in the polar regions of the earth and Mars,
in photonic crystals, even cosmetics. Surprisingly the forces that drive
this cracking and even the resistance to it are not understood, so that
attempts to control cracking are all very empirical, although some variables.
Such cracks often grow in a stable manner with a well-defined crack spacing.
The project will involve studying the cracking in-situ using existing
equipment to enable measurements of crack velocity, crack spacing and
the distances between the various fronts associated with the overall process.
Shape changes and crack opening will also be measured using profilometry
and SEM to understand how the stresses and strains build up, the nature
of this type of cracking and the underlying processes that drive it. The
project forms part of a collaborative project funded by the EU at the
level of fees for an EU student. For further information please contact
Dr Bill Clegg, wjc1000@cam.ac.uk,
01223 334470.
Microstructural changes in thin film AlOx
sensors
Measurement of water vapour is important in sophisticated manufacturing
processes, such as silicon chip fabrication, where moisture levels of
parts-per-trillion are important, in energy efficient buildings and, as
water vapour is one of the main greenhouse gases, in helping to develop
accurate models for climate change (see Bell et al, Int. J. Thermophysics,
2008.) The principal problem with existing sensors is the long-term drift
that occurs during use and which, at present, requires continued recalibration
of the sensor. Most humidity sensors are based on porous alumina membranes,
typically 1 µm thick made by anodising aluminium. Our initial work
with one of the leading manufacturers of these sensors has suggested that
that the drift is caused by changes in the porous structure of the film
by a process analogous to liquid-phase sintering. The aim of the project
is to investigate, in collaboration with the company involved, whether
such structural changes do occur and how they might be minimised, perhaps
by limiting the solubility of alumina in water. Tests will be carried
out on alumina films aged in controlled environments and cycles to study
how the properties change with time. The properties and structure will
be studied using a variety of techniques such as impedance and capacitance
measurements, ellipsometry, nanoindentation and a range of electron optical
techniques to investigate how these mechanisms are influenced by the structure
of the film and how the structure changes in service. For further information
please contact Dr Bill Clegg, wjc1000@cam.ac.uk,
01223 334470 .
Deformation and friction in layered oxides for solid
lubricants
Rotating components operating at high temperatures or in vacuum, where
the usual liquid lubricants would decompose or vaporise, require solid
lubricants. There are a surprising number of layered structures, such
as vanadium oxides that might be suitable for low friction uses, due to
the very weak bonding across the plates and although they are used their
properties and the structural features that control them are not well
understood. Dislocations and plastic flow are known to be important in
other layered structures, but it is not known how the bonding might be
manipulated to produce materials with low friction coefficients for use
as solid lubricants. The aim of this project is to investigate the deformation,
friction and wear behaviour of the vanadium oxides (and the related titanium
sub-oxides) and other chalcogenides. The project is a collaboration with
the University of Aachen and will use suitably oriented micropillars and
nanoindentation as a function of temperature to characterise the deformation
behaviour, as well as nanoscratch for wear and friction measurements,
combined with transmission electron microscopy. For further information
please contact Dr Bill Clegg, wjc1000@cam.ac.uk,
01223 334470.
Novel zinc oxide varistors
Varistors derive their non-linear current-voltage characteristics
from the addition of low levels of transition and heavy metal oxides.
It is usual for commercial compositions to have five or six oxide additions.
However, recent work here at Cambridge has shown that ZnO with additions
of MnO2 and V2O5 alone exhibits varistor behaviour rivalling that of commercial
material. This Ph.D. project will establish microstructure-electrical
property relationships in this ternary system by examining a range of
ZnO-rich pellets by X-ray diffraction and transmission electron microscopy.
An area of particular interest will be mapping of the electrical barriers
at zinc oxide grain boundaries using electron holography and Fresnel fringe
analyses. For further information, please contact Dr Kevin Knowles, telephone
+44 1223 334312, kmk10@cam.ac.uk
Electrostatic bonding
Electrostatic bonding is a common process in microelectromechanical
systems (MEMS). For example, it is used to manufacture pressure sensors.
The two materials, such as silicon and pyrex, are bonded together by applying
a high d.c. voltage across the bond at a temperature of ~ 400 ˚C.
In this example, pyrex, the poorer electrical conductor, is cathodic with
respect to silicon. A requirement of electrostatic bonding is that the
ceramic material used in the process is a sufficiently good electrical
conductor at the temperature used to make the bond.
In this PhD project the principle of electrostatic bonding will be applied
to the bonding of metals (e.g., Nb, Cu, Ni and Al) to other ceramics and
glasses, such as beta-alumina, soda-lime-silica glass and zirconia. The
aims of the project will be to specify the range of temperature and d.c.
voltage conditions within which good bonds can be formed between the metals
and the beta-alumina and to characterise these bonds using a range of
transmission electron microscopy techniques. For further information,
please contact Dr Kevin Knowles, telephone +44 1223 334312, kmk10@cam.ac.uk
High temperature brazing of engineering
ceramics
The aim of this PhD project is to examine by X-ray diffraction,
scanning electron microscopy and transmission electron microscopy, the
microstructure of novel particle-reinforced brazes for joining engineering
ceramics such as alumina, silicon carbide and silicon nitride to metallic
materials such as nickel, so that the joints can be used at service temperatures
of >500 ˚C. Experience at Cambridge with brazes for bonding SiC
has shown that the introduction of small SiC particulates to high temperature
braze compositions is beneficial for joining SiC to itself, producing
mechanically sound joints. It is proposed to extend this methodology to
other systems of engineering significance. For further information, please
contact Dr Kevin Knowles, telephone +44 1223 334312, kmk10@cam.ac.uk
Device Materials
Combinatorial thin film growth
Many new materials targeted for specific applications have multiple components
or critical doping levels within a complicated phase diagram. Combinatorial
materials synthesis, in which a continuous composition spread is deposited
on a single substrate, coupled with high throughput analysis can lead
to discovery and optimisation of a desired materials property in the shortest
possible time. We have developed pulsed laser deposition combinatorial
techniques to produce a variation of properties on a single substrate.
The aim of this project is to extend combinatorial studies to other parameter
spaces through the development of artificial substrates whose lattice
parameter varies as a function of position; this will enable us to investigate
continuous variation of lattice mismatch-induced strain in films grown
on these substrates. We will develop this technique through the study
of perovskite systems in which it is already clear that strain considerably
modifies the electronic and magnetic behaviour of the film and sometimes
can reveal properties which do not occur at ambient pressure in the bulk.
Spin injection devices
The ability to inject, manipulate and detect electron spin will enable
the development of spintronics devices. In order to inject and detect
spins from a ferromagnetic metal into a semiconductor, the resistivity
mismatch problem has to be overcome. This can be achieved by inserting
a tunnel or Schottky barrier to create a large resistance at the interface.
Tunnelling through a thin barrier is more attractive than a Schottky contact
because an artificial tunnel barrier also offers symmetric behaviour under
forward and reverse bias; however, oxide tunnel barriers must be absolutely
free of pin-holes and other defects and are known to be difficult to deposit
on semiconductors. The aim of this project is to investigate the deposition
of semiconductors onto preformed tunnel barriers on either superconductors
or ferromagnets in order that the tunnel barrier properties can be optimised
independently of the type of semiconductor used.
Magnetic vortex cutting in superconductors
The behaviour of quantised magnetic vortices in type II superconductors
is of enormous practical significance for applications and is of fundamental
interest because many of their interactions are still not properly understood.
In particular, there is a great deal of interest in the behaviour of non-parallel
vortices if they are forced towards each other. This specific question can
be visualised as two pieces of elastic being pushed together at an angle
to each other - do they entangle and stretch or is there a process by which
they can pass through each other? The aim of this project is to study a
new experimental geometry which will enable us to test directly the many
theoretical models of this behaviour which have emerged in recent years.
Electric field effects in oxide
magnetic materials
In semiconductor devices the field effect is used to change
the carrier density in the channel linking the source and drain and
hence control the conductivity of the device. There is considerable
potential for modifiying the properties of many oxide magnetic materials
by changing the electric field across them because the number of carriers
is rather low. Since the magnetism in many systems is linked to the
carrier density it might be possible to control the Curie temperature
of some of these oxides electronically which would give considerable
scope for magnetoelectronic devices. The aim of this project is to develop
field-effect devices which can be used to investigate such effects.
For further information, please contact Prof. Mark Blamire, telephone
+44 1223 334359, mb52@cam.ac.uk.
Spin torque devices
In ferromagnetic materials an electric current transports
spin as well as charge. There are many ways in which this effect can
be used including so-called spin transistors and light emitting diodes
which emit polarised light. In the last few years it has been shown
that the spin carried by an electric current can be used to rotate the
moment of a thin ferromagnetic layer; this “spin torque”
effect can in principle be used as a means of storing data and performing
logic operations. However the current densities required in the current
devices are far too high, indeed they are close to the currents at which
devices melt. The aim of this project is to investigate novel device
geometries which might significantly reduce the current densities required.
For further information, please contact Prof. Mark Blamire, telephone
+44 1223 334359, mb52@cam.ac.uk.
The development of ion enhanced
deposition techniques
We have considerable experience of magnetron sputter deposition
of a very wide range of films and heterostructures, and wish to develop
this deposition technique further. For example, by the addition of an
rf plasma between the source and substrates, we can increase control of
the depositing flux through ionisation. Other methods for the production
of highly ionised plasmas during film growth include the use of ultra
high power pulsed sputter sources, structured hollow cathode targets,
and dual gas injection methods.
Plasma diagnostic techniques, such as optical emission spectroscopy
and probe studies, are required to study the deposition environment, whilst
deposited films may be characterised using, for example, electron microcopy,
X-ray diffraction and atomic force microscopy.
For further information, please contact Dr Zoe Barber, telephone +44 1223
334326, zb10@cam.ac.uk.
Ferromagnetic semiconductor / insulator
thin films
There is much current interest in the properties and potential applications
of dilute magnetic semiconductors (DMS), e.g. magnetically doped nitrides
such as GaN and AlN which offer great potential for room temperature
(and higher) applications. In a preliminary programme we have fabricated,
by sputter deposition, Cr-doped AlN films which have a significant fraction
of magnetically active Cr and the highest Curie temperature yet reported
in a DMS system (> 630 degrees C). We plan to explore the role of
crystallinity, stoichiometry and the potential for other dopants (both
magnetic and non-magnetic) on the magnetic and electrical properties
of ferromagnetic AlN. Hence we will gain a better understanding of the
nature of the magnetic coupling mechanism in these materials and the
degree to which the Curie temperature and exchange energy are controllable.
In addition, there is the opportunity to explore the potential for using
this doped AlN as a tunnel barrier in spin electronic devices. Further
information on this project can be obtained from Dr Z H Barber (zb10@cam.ac.uk)
or Professor M G Blamire (mb52@cam.ac.uk).
Ferroelectric thin film growth
There is much current interest in thin film ferroelectrics:
for example, for future memory applications. The properties of ferroelectric
films are greatly influenced by their crystallographic orientation and
microstructure which, in turn, are functions of the deposition parameters
during growth. A fuller understanding of the relation between film growth
and the resulting film properties is essential for their exploitation.
Films, and ferroelectric/electrode combinations, will be deposited (principally
by Pulsed Laser Deposition) and characterised using structural and electrical
techniques.
We are also working on the development and optimisation of new ferroelectric
materials, and are studying the effect of a range of dopant additions
on ferroelectric film properties. In addition to the use of PLD, thin
film composition is being studied through the use of sol gel processing
for rapid property assessment.
For further information,please contact Dr Zoe Barber, telephone +44 1223
334326, zb10@cam.ac.uk.
Nanocomposite coatings
Recent reports of extremely high hardness in "nanocomposite"
thin films, consisting of nanocrystallites within an amorphous matrix,
offer great promise for the development of new, hard wear-resistant coatings.
We wish to develop techniques for the fabrication of such coatings, and
the control of their structures, and are also interested in other possible
applications for such materials. This will require the development of
thin film deposition techniques, as well as sensitive characterisation
methods for assessing such fine-scale features.
For further information, please contact Dr Zoe Barber, telephone +44 1223
334326, zb10@cam.ac.uk.
Multiferroic thin film devices
Ferromagnets tend to be metallic, and ferroelectrics must be insulating
or else they depolarise. Surprisingly, a few materials are both ferromagnetic
and ferroelectric, i.e. "multiferroic". The aim of this project is to
enhance the properties of thin film candidate materials, and fabricate
devices in order to investigate the coupling of the ferromagnetic and
ferroelectric order parameters, e.g. to switch the magnetic state by applying
an electric field. Appropriate oxide films, grown by pulsed laser deposition,
will be electrically and magnetically characterised using a range of techniques,
including local probes in the form of piezoforce microscopy and magnetic
force microscopy (both of these techniques use an appropriately configured
atomic force microscope). Contact Dr ND Mathur (ndm12@cus.cam.ac.uk).
Mesoscopic texture in manganites
Radically different phases can coexist over radically different lengthscales
in the manganites [1,2]. This is because the magnetic, electronic and
crystal structures of these exotic oxides of manganese interact strongly
with one another. Surprising new phases [3] and surprises about the old
phases [4] make this field exciting. The aim is to create patches of one
phase within another at controlled locations in thin film devices. In
this project, such patches will be examined using magnetometry and electrical
transport measurements. Contact Dr ND Mathur (ndm12@cus.cam.ac.uk).
[1] "Mesoscopic texture in manganites", Neil Mathur and Peter Littlewood,
Physics Today 56 (January 2003) 25-30
[2] "Nanotechnology: The Third Way", Neil Mathur and Peter Littlewood,
Nature Materials 3 (2004) 207-209
[3] "Charge-ordered ferromagnetic phase in La 0.5 Ca 0.5 MnO 3 ", JC
Loudon, ND Mathur and PA Midgley
Nature 420 (2002) 797-800
[4] "Weak charge-lattice coupling requires reinterpretation of stripes
of charge order in (La,Ca)MnO 3 ", JC Loudon, S Cox, AJ Williams,
JP Attfield, PB Littlewood, PA Midgley and ND Mathur, available at
http://lanl.arxiv.org/abs/cond-mat/0308581
Development of high magnetic
field high critical current A-15 conductors for use in NMR and cryogen
free magnets utilisation of the novel reduction of oxides process
The ternary alloyed Nb3Al intermetallic is recognised
by the superconductivity community as an excellent source for future
superconducting multifilamentary conductors capable of operation at
magnetic fields of much higher than 25 Tesla and under extreme mechanical
and irradiation conditions such as will occur in the International Thermomolecular
Experimental Reactor. The development of high-critical-current superconducting
A-15 conductors able to carry a current in very high magnetic fields
(25-30T) is recognised as an enabling technology for the construction
of second-generation NMR magnets operating at frequencies well above
1GHz. This project will involve the study of changes of critical temperature
(Tc), critical current (Jc (B)) and lattice parameters of the Nb3(Al,Ge)
phase formed during the diffusion process of wires manufactured by advanced
infiltration processes of the porous Nb-based rods manufactured by Direct
Electrochemical Reduction in collaboration with Prof. D.Fray. The understanding
of the correlation between the diffusion of Al and Ge from an internal
reservoir to the niobium filaments, and of the uniform properties of
intermetallic diffusion Nb3(Al,Ge) layers formed during multistage heat
treatment, is essential for further improvement of the superconducting
properties of conductors manufactured world-wide. This project if continued
as a PhD project will involve interaction with numerous International
companies and research institution including visits to two famous Japanese
Research Centres. This project is expected to have a full industrial
support. For further details please contact Dr Bartek Glowacki on tel.
+44 1223 331738, e-mail bag10@cus.cam.ac.uk.
The continuous infrared zone
melting process for production of superconducting coatings
Yttrium-based superconducting coatings, such as YBa2Cu3O7-?
can be successfully fabricated using a semi-wet extrusion process and
on-line infrared zone melting technique. The aim of this project is
to achieve continuous superconducting coating, characterised by a high
transport critical current.
The study will consist of optimising the phase composition, microstructure,
texture and electromagnetic properties of coatings by varying the processing
parameters, such as, melting velocity, and temperature and atmosphere
of post-annealing. The successful, optimised process for manufacture
of the coatings, characterised by the highest transport critical current,
will be publicised and could be used to wind the first high Tc superconducting
YBCO conductor for underground energy power transmission. For further
details please contact Dr Bartek Glowacki on tel. +44 1223 331738, e-mail
bag10@cus.cam.ac.uk.
Development of High Critical
Temperature Superconducting and Magnetic coatings by ink-jet printing
Continuous spray pyrolysis and sol-gel ink-jet printing
of superconducting suspensions on metallic substrates is one of the
cheapest and successful methods of making superconducting tapes which
are capable of carrying very high currents in a high magnetic field.
The technique appears to be very promising and is covered by a patent.
The novel technique of deposition of acid solutions (nitric, propionic
and acetic) of nitrate salts of "YBCO" and "Bi-2212"
composition, has been developed on the base of commercially available
ink-jet printing equipment. This project will involve detailed study
of the influence of the chemical composition of the solutions to optimise
the nominal cation stoichiometry in respect to minimising the amount
of the impurity phase and maximisation of the critical temperature using
combinatorial methodology. Optimisation of the quality of the high temperature
superconducting films will need to take thermodynamics, and the structure
and chemistry of the matching materials into account. At the same time
a great deal of fundamental work is needed to understand the mechanisms
of textured growth. The deposition technique will be fully computerised
with the existing interface unit to create a virtual laboratory working
environment. Wide applicability of the developed technology can be easily
transferred to other area of electroceramic devices and even rapid prototyping.
This project will involve research visits to Gent University and participation
in EU funded Interdisciplinary and international Brite-Euram project.
This project is expected to have a full industrial support. For further
details please contact Dr Bartek Glowacki on tel. +44 1223 331738, e-mail
bag10@cus.cam.ac.uk.
Formation of native cube textured
oxide on a flexible NiFe tape substrate for superconducting coated conductor
applications
The oxidation behaviour of NiFe tape with a well developed
cubic (100)<1001> texture will be investigated in an attempt to
develop buffer layers suitable for deposition of well aligned superconductors.
An initial research conducted in the vacuum chamber indicates that reoxidation
of the tape leads to the formation of a nickel-iron oxide with an excellent
cube texture, having in-plane and out-of-plane X-ray FWHMs of around
8 degrees. The project will demonstrate how an oxide layer with an excellent
cube texture may be produced on the surface of the NiFe tape by a simple
two-stage oxidation process. For further details please contact Dr Bartek
Glowacki on tel. +44 1223 331738, e-mail bag10@cus.cam.ac.uk.
Changes of critical temperature
and stoichiometry of the superconducting Nb3Sn phase formed during the
reactive diffusion process in superconducting wire
A multilayer jelly-roll wire manufactured by the "internal
tin" will be investigated. The project involves in-situ studies
of the formation of the superconducting Nb3Sn layers (using differential
thermal analysis and electriconic measurements) in relation to critical
temperature (measured by ac susceptibility) and conductor morphology.
The results will be assessed on the basis of microscopic observations
of the development of Nb-Sn phases during multi-stage diffusion processes.
Magnetic properties, in correlation with the cross-sectional microstructure,
will be studied in order to define interfilamentary bridging and phase
formation during heat treatment. The results will be published as a
part of the on-going research on the development of a new generation
of intermetallic low temperature superconducting conductors for the
Large Hadron Collider in CERN. For further details please contact Dr
Bartek Glowacki on tel. +44 1223 331738, e-mail bag10@cus.cam.ac.uk.
Superconducting properties of
Cu-MgB2 and Fe-MgB2 conductors
The new exciting class of recently discovered Mg-B superconducting
conductors will be prepared using the standard in-situ and ex-situ powder-in-tube,
PIT, method where Mg+2B mixture will be used to fill the copper and
iron tubes. Study of the intergranular current, grain connectivity and
superconducting phases in wires were conducted by AC susceptibility
measurements and direct four point transport measurements. Using SQUID
magnetometer, magnetisation versus magnetic field (M-H) curves of the
round wires after reactive diffusion will be measured at temperatures
5K and magnetic field up to 5T to define the magnetic critical current
density Jcmag. The direct current density measurements of the in-situ
Cu-MgB2 and Fe-MgB2 will be performed at 4.2K and expected in the range
of 1010 Am-2. The results will be published as a part of the on-going
research on the development of a new generation of intermetallic medium
temperature superconducting conductors Magnetic Resonance Imaging, MRI
magnets. For further details please contact Dr Bartek Glowacki on tel.
+44 1223 331738, e-mail bag10@cus.cam.ac.uk.
Development of a simultaneous
pulse transport current and pulse magnetic field measurements method
for characterisation of high field superconductors
The high temperature superconducting, HTS, conductors
are already used in hybrid magnets to produce fields enhancing the fields
of conventional magnets made from A-15 type low temperature superconducting,
LTS, wires. Therefore for usage of HTS superconductors in high-field
applications, it is vital that the interdependence of the critical parameters
such as critical current vs magnetic field can be mapped under high
field and high current conditions. However, the latest superconductors
have high currents even at fields over 20T, making accurate measurements
very difficult due to the thermal and mechanical problems. This project
is focused on further development of the pulse-pulse system where analysis
of the voltage signal from superconducting conductors and samples in
pulsed conditions may be used to extract the critical current density
in quasi-stationary conditions. This innovative pulsed high transport
current and pulsed high field technique will be compared with DC current
and DC magnetic field measurements using a Bitter type magnet. This
project will involve research visits to Clarendon Lab, Oxford University
and International Laboratory of High Magnetic Fields and Low Temperatures
in Poland. For further details please contact Dr Bartek Glowacki on
tel. +44 1223 331738, e-mail bag10@cus.cam.ac.uk.
Magnetic semiconductor oxides
The field of microelectronics could be revolutionised
if devices could be made in which spin polarised electrons are injected
into semiconductors at room temperature. This field of spintronics allow
the exploitation of the spin degree of freedom in the semiconductor
and it promises new logic devices with enhanced functionality, higher
speeds and reduced power consumption. A spin injector material is required
which is highly spin polarised, has a Curie temperature above room temperature,
is chemically compatible with semiconductors and can be grown at low
temperatures. No ideal system has yet been identified although a range
of dilute magnetic semiconductors have been investigated. Doped- ZnO
is a promising candidate ferromagnetic spin injector material. The route
by which it is processed appears to be critical to properties. This
project will involve producing well-controlled, doped material in bulk
and epitaxial film form by using low temperature chemical and electrochemical
solution routes.
For further information, please contact Dr Judith Driscoll, telephone
+44 1223 334468, jld35@cam.ac.uk.
Pinning in Superconductor Films
There are numerous potential applications for superconducting
tapes, based on YBa2Cu3O7-x (YBCO) films coated onto metallic substrates.
A long established goal of more than 15 years has been to understand
the magnetic flux pinning mechanisms which allow films to maintain high
current densities out to high magnetic fields. In fact, films carry
1-2 orders of magnitude higher current densities than any other form
of the material. For this reason, the idea of further improving pinning
has received little attention. Now that commercialisation of conductors
is much closer, for both better performance and lower fabrication costs,
an important goal is to achieve enhanced pinning in a practical way.
We have demonstrated, for the first time, more than one simple and industrially
scaleable route which yields 2 to 5-fold improvements in the in-field
critical current densities of already-high-quality conductors. There
is the potential to improve this further. The project will deal with
nano-structuring of the material combined with detailed microstructural
characterisation and will involve collaboration with Los Alamos National
Laboratory. For further information, please contact Dr Judith Driscoll,
telephone +44 1223 334468, jld35@cam.ac.uk.
Novel Magnetic oxides with high spin polarisation
Highly spin polarised oxides are required for different
magnetic sensor devices (e.g. MRAM) and in spintronics. A variety of
magnetic oxides have recently been identified and studies, e.g CrO2,
Fe3O4, Sr2FeMoO6 ,Fe3O4 and doped- ZnO, SnO2, and TiO2. None of these
ideally fulfil the functional requirements. There are other potential
semiconducting oxides with easily tuneable electrical properties, and
these are potential candidates for doping with magnetic ions, in the
hope of retaining the magnetic properties as well as coupling to the
electronic states. The project will investigate new materials, and will
involve bulk and film growth, as well as electrical and microstructural
characterisation. For further information, please contact Dr Judith
Driscoll, telephone +44 1223 334468, jld35@cam.ac.uk
Nano-wires of functional materials
by vapour-liquid-solid growth
Nano-wires are expected to play an important role both
as interconnects and functional components. Their proven enhanced mechanical,
low threshold lasing, gas sensing, and photoelectrochemical properties
already make them very interesting. One of the most important routes
for fabrication nano-wires is by vapour-liquid-solid growth (v-l-s).
The v-l-s routes studied, so far, involve the formation of metal-alloy
droplets at relatively high temperature, followed by cooling to increase
supersaturation of one species in the alloy. This leads to nucleation
and growth of the desired species in nano-form (either as pure element
or oxide). Many aspects of the process are poorly controlled or poorly
understood at present and there is a great potential to achieve better
process control through basic studies. In this project, new alloy droplet
catalyts will be investigated. Hence, there will be the possibility
of growing materials of more complex compositions than the usual unaries
or binaries. There will also be the potential to better control the
nano-wire dimensionality. For further information, please contact Dr
Judith Driscoll, telephone +44 1223 334468, jld35@cam.ac.uk
Device applications of single InGaN quantum
dots
Quantum dots are nanoscale crystals which exhibit atom-like properties.
We aim to exploit these characteristics and in the development of optoelectronic
devices based on single InGaN quantum dots. For example, we have recently
demonstrated the first quantum dot single photon source emitting in the
blue spectral region. This device is based on the quantised nature of
the energy levels in the InGaN quantum dot structure, which prevent it
from emitting multiple photons simultaneously. However, in order to develop
a practical device from our prototype, we must greatly improve the efficiency
with which photons are extracted from the device. Hence, this project
will involve the design and development of three-dimensional microcavities
based on micropillars or photonic crystals, and incorporation on quantum
dots into such cavities in order to achieve improved single photon source
operation. For further information, please contact Dr Rachel Oliver, rao28@cam.ac.uk
Nanoscale imaging of the electrical and optical
properties of nitride semiconductors
Nitride semiconductors have widespread application in optoelectronic
devices and are being developed for high power electronic devices. In
order to improve the performance of these devices we need to understand
their structural and electrical properties on a micro- to nano-metre scale.
In this project, studies of the variation in electrical properties in
nitride materials and devices will be performed using techniques based
on atomic force microscopy and will be compared with cathodoluminescence
data, which will reveal the spatial variation in lumoinescence intensity
from these materials. In this may, we hope to understand the correlations
between electrical and optical properties and hence to develop better
devices. For further information, please contact Dr Rachel Oliver, rao28@cam.ac.uk
Growth and characterisation of
GaN-based high temperature devices
Gallium nitride not only emits intense light, it should
also be possible to make transistors from this material, which operate
at a much higher temperature than Si or GaAs transistors. There is a considerable
need for such transistors to be used as the control electronics in high
temperature aerospace engines, for example. This project is to study the
materials factors that limit the high temperature operation of GaN-based
devices and to grow such devices in our GaN growth system, and to characterise
the materials using advanced electron microscopy and other techniques.
This is an exciting project to produce transistors which operate at much
higher temperatures than Si transistors. For further details contact Professor
Colin Humphreys, telephone +44 (0)1223 334457, colin.humphreys@msm.cam.ac.uk
Atomic resolution studies of gate
oxides and Interfaces in devices
As semiconductor devices shrink in size it becomes increasingly
important to measure gate oxide thicknesses, for example, with atomic
scale precision. It is also necessary to understand in detail the bonding
at the interface between Si and its oxide. In this project a highly focused
electron beam will be used to image interfaces in semiconductor materials
as atomic resolution, and electron energy loss spectroscopy will be used
to determine the changes in chemistry and bonding on going across interfaces
in semiconductor devices. The research will be performed in part on state-of-the-art
electron microscopes in our Department, and will also use state-of-the-art
electron microscopes at a new facility which has recently been constructed
at Daresbury Laboratory. This exciting project combines electron microscopy
and analysis at atomic resolution with state-of-the-art electronic devices
in which the gate oxide thicknesses are only about 1nm thick. For further
details contact Professor Colin Humphreys, telephone +44 (0)1223 334457,
colin.humphreys@msm.cam.ac.uk
Growth and characterisation of
ultra-bright GaN-based LEDs
Gallium nitride is probably the most important new semiconductor
material since silicon, and it is generating huge international interest.
The department has recently had installed the latest state-of-the-art
growth system for GaN (a Thomas Swan MOCVD system) and this project is
to grow ultra-bright LEDs. GaN emits intense blue light, and if alloyed
with In to produce InGaN, light of any colour can be produced. Red, yellow
and green LEDs are already more efficient than thermionic light bulbs
and are being used in traffic lights. However, white LEDs are currently
less efficient than light bulbs. This exciting project is to study how
to increase the efficiency of white LEDs, and to make such devices. The
device structures will be characterised by advanced electron microscopy
and other techniques. If really successful, this project will enable all
the light bulbs in the world to be replaced with GaN-based LEDs! These
last 100 times longer than light bulbs and will consume less energy thus
reducing electricity consumption and CO2 emissions from power stations.
For further details contact Professor Colin Humphreys, telephone +44 (0)1223
334457, colin.humphreys@msm.cam.ac.uk.
Contacts to GaN-based devices
An absolutely key element of fabricating devices is the
metal-semiconductor contact. To obtain good contacts on GaN and AlGaN,
multilayer metals such as Au/Ni/Ti/Al must be deposited on top of the
GaN or AlGaN and then annealed. The metals react with each other and with
the GaN to form a rangeof compounds (for example TiN, NiAl, etc.), and
the reason why a particular contact is good is poorly understood. This
project will use a range of advanced electron microscope techniques to
characterise the complex microstructures and phases present in contacts
on GaN/AlGaN and to understand the factors that are important in producing
good ohmic contacts, so that these contacts can be optimised. For further
details contact Professor Colin Humphreys, telephone +44 (0)1223 334457,
colin.humphreys@msm.cam.ac.uk.
Electron holography of GaN structures
GaN and InGaN are piezo electric and when internal strains
are present in the materials, internal voltages are developed. Hence voltages
are developed at dislocations, which are highly charged, at strained quantum
well layers of InGaN grown in GaN, etc. The effect is very strong in GaN
and it is important to understand this for its effect on device operation.
Electron holography is a powerful method of measuring the internal electric
fields present in materials, and this exciting project will apply the
technique of electron holography to solve a variety of problems in gallium
nitride-based structures. For further details contact Professor Colin
Humphreys, telephone +44 (0)1223 334457, colin.humphreys@msm.cam.ac.uk.
Electron energy loss spectroscopy
(EELS) of defects in GaN
Dislocations and other defects in gallium nitride are
believed to have states in the band gap which act as recombination centres
and reduce the light emission. This project will use EELS to measure these
defect states. This important project will require a very good understanding
of the theory of EELS and very careful experiments using our state-of-the-art
equipment. For further details contact Professor Colin Humphreys, telephone
+44 (0)1223 334457, colin.humphreys@msm.cam.ac.uk.
Doping contrast from semiconductors
As semiconductor devices shrink in size it becomes increasingly
important to develop new techniques to measure doping levels, and image
p-n junctions, from very small regions. Recently a new technique has been
developed for this, which is causing considerable world-wide interest,
which uses a field emission gun scanning electron microscope (SEM). The
intensity of the secondary electrons scattered from a semiconductor is
a very sensitive function of the doping concentration, and p-n junctions
can be mapped out using this technique. However, the theory of what is
happening is not well understood and the technique is not yet quantitative.
This project is to develop the theory and make the effect quantitative.
For further details contact Professor Colin Humphreys, telephone +44 (0)1223
334457, colin.humphreys@msm.cam.ac.uk.
Fabricating nanowires and nanostructures
using electron beams
This exciting project is to make nanowires possibly only one atom thick.
If wires are very thin, their electrical properties change dramatically,
for example, even a law as fundamental as Ohm's Law no longer holds
for very thin wires. The wires will be fabricated using intense electron
beams in an electron microscope. Their electrical properties will then
be measured. It is then planned to make single electron transistors
(SETs) using such wires which will operate at room temperature. These
nanoscale devices may replace 'conventional' Si chips in future computers
etc. because they will be much smaller and much faster than current
devices. For further details contact Professor Colin Humphreys, telephone
+44 (0)1223 334457, colin.humphreys@msm.cam.ac.uk.
Electron microscopy
The crystal structure of pharmaceutical
crystals
The vast majority of pharmaceutical crystal structures remain unknown.
Potentially useful and important drugs may never come to market because
their crystal structure cannot be solved using conventional x-ray diffraction.
The reason is often that the pharmaceutical is produced in multi-phase
or polymorphic form and the lack of spatial resolution in most x-ray
diffraction experiments means that it is difficult, if not impossible,
to deconvolve the crystal structure of interest from other crystals
in the sample. Electron microscopy offers very high spatial resolution
with the ability to form diffraction patterns from very small (nanometre-sized)
regions of the sample. Recent developments in new methods of electron
diffraction (e.g. electron precession) and new algorithms for structure
solution (e.g. charge flipping) may lead to new insights into the structures
of pharmaceutical crystals. This project would concentrate on acquiring
high quality electron diffraction patterns from a number of unknown
crystal structures and, in conjunction with a small team in the EM Group,
develop and apply new structure solution algorithms suited especially
to electron diffraction. For further information please contact Prof
Paul Midgley, tel: 01223 334561, email: pam33@cam.ac.uk.
3D structure of semiconductor devices
As individual components within modern integrated circuits become ever
smaller, the fine scale composition and structure of the device becomes
increasingly critical. For many years transmission electron microscopy
(TEM) has been used to investigate the fidelity of semiconductor structures
and to determine the precision of the manufactured device. A conventional
'slice' through the device for TEM examination may be 100nm thick and
a single micrograph is a projection through that slice. Any variation
through that thickness would be difficult to visualise in the image
of the slice. This has led the microelectronics industry to consider
electron tomography as a means to investigate the 3D structure of devices
without possible mis-interpretation from projecting fine scale detail.
This project would be to develop techniques to investigate semiconductor
devices, taken in the form of a 'core sample' from wafers. Relatively
thick samples would be imaged using new TEM imaging modes (such as incoherent
BF imaging) to understand large-scale 3D structures, with higher resolution
tomography (using HAADF imaging) used following further dual beam ion
thinning. For further information please contact Prof Paul Midgley,
tel: 01223 334561, email: pam33@cam.ac.uk.
3D electrostatic potentials
Off-axis electron holography is a TEM technique that allows the projected
electrostatic potential of a sample to be reconstructed quantitatively.
For example, holography can be used to measure the spatial variation
in the potential across a semiconductor junction and hence determine
the electric field across that junction and the related space charge
regions. Many devices are becoming 3-dimensional in design and one of
the major barriers to designing successful 3D devices is the current
inability to map potentials (and dopants) in 3D with high spatial resolution
(~5nm). Combining electron holography with electron tomography offers
a means to reconstruct electrostatic potentials in 3D with very high
spatial resolution. The student would work together with Dr Alison Harrison
of the EM Group to further develop this holo-tomography technique and
to establish it as a reliable and quantitative tool for the microelectronics
industry. For further information please contact Prof Paul Midgley,
tel: 01223 334561, email: pam33@cam.ac.uk.
High Resolution Electron Energy Loss Spectroscopy
The Department will shortly take delivery of a new generation transmission
electron microscope which has aberration correction on the probe forming
lens to enable sub Angstrom spatial resolution and an electron monochromator
to allow energy loss spectra to be acquired with better than 0.25 eV
resolution. The combination of high spatial and high spectral resolution
enables new experiments to be undertaken on a variety of important materials,
especially modern semiconductor heterostructure devices. By choosing
ternary and quaternary alloys, semiconductor bandgaps can be engineered
to high precision. A technique is needed to map the band gaps of such
heterostructures and high resolution EELS is the primary candidate.
Further, the details of the low loss spectrum beyond the band edge can
reveal a remarkable array of other electron transitions, such as band
to band transitions, Cerernkov radiation and surface and waveguide modes
that are potentially of great importance in device communication in
optical computers. These modes can be 'hidden' within the overall plasmon
loss using conventional energy loss spectroscopy but implementing the
monochromator, coupled with the ability to disperse the spectrum in
momentum (or k-) space, can reveal spectral detail, and hence information
about the electronic structure, not normally seen. For further information
please contact Prof Paul Midgley, tel: 01223 334561, email: pam33@cam.ac.uk.
3-Dimensional Atomic Resolution
Electron tomography has now established itself firmly as a key technique
in materials science for the study of structures in 3D at nanometre
resolution. The 'holy grail' however is to push the resolution still
further to achieve true atomic resolution in 3 dimensions. To reach
this goal, a combination of two techniques is probably needed. Firstly
to use a conventional tilt series approach, to investigate the atomic
structure from different viewpoints and secondly to use a confocal method
whereby an optical section of the sample is recorded by minimising the
depth of field, analogous to confocal optical microscopy. In order to
sample the whole structure a through-focal series is recorded. However
the sampling resolution is far from isotropic, with perhaps sub-Angstrom
resolution in the lateral plane but with nanometre resolution in the
perpendicular plane. Methods need to be developed to combine the two
approaches such that atomic resolution may be achieved in all 3 dimensions.
The project will involve the use of a state-of-the-art aberration-corrected
TEM, to be delivered to Cambridge in the near future, and computer simulations
to optimise the methods and understand the results. For further information
please contact Prof Paul Midgley, tel: 01223 334561, email: pam33@cam.ac.uk.
3-Dimensional Mesoscale Imaging and Analysis in
the Dual Beam Microscope
The dual beam microscope is essentially a scanning electron microscope
(SEM) with an additional ion column that allows ion beam thinning (and
imaging) to be combined with simultaneous SEM studies. In the summer
of 2007 the Department will take deliver of a new dual beam microscope
that will allow a so-called 'slice-and-view' method to achieve a 3D
reconstruction slice by slice. More than that, each freshly exposed
face can be studied using electron backscattered diffraction and energy-dispersive
X-ray analysis. At each image pixel, a diffraction pattern and an x-ray
spectrum can be recorded such that the orientation (strain), composition
and microstructure can be mapped in 3 dimensions with <100nm resolution
over cubic microns of sample. Using key materials structures, especially
deformed polycrystalline metal alloys, this project will focus on acquisition
technology, methods to best interpret and analyse such a large data
set, and to develop new image processing and data mining tools. This
project will likely involve close collaboration with the instrument
manufacturer. For further information please contact Prof Paul Midgley,
tel: 01223 334561, email: pam33@cam.ac.uk.
Scanning Transmission Electron Microscopy in a
Scanning Electron Microscope
The Department will shortly have installed a dual beam microscope based
on a high resolution field emission scanning electron microscope. Importantly
the microscope has post-specimen detectors which enables forward scattered
electrons to be recorded. By scanning the electron beam, BF and DF STEM
images can be recorded with beam voltages at 30kV and below. For materials
composed of low atomic number species (e.g. carbon nanotubes), low voltage
operation minimises knock-on beam damage. This project will develop
low voltage STEM imaging in the dual beam microscope, optimising the
performance of the SEM column to achieve sub nm resolution and understanding
the contrast seen in the images at low voltage operation. This project
will likely involve close collaboration with the instrument manufacturer.
For further information please contact Prof Paul Midgley, tel: 01223
334561, email: pam33@cam.ac.uk.
Materials Chemistry
Fabrication of a new class of biosensors
This research project is concerned with developing composite ionic and
electrodic materials for a new class of "biosensor" aimed at better monitoring
of a disease to clinical treatment. In this project there will be opportunity
to work in close collaboration with the Institute of Biotechnology at
University of Cambridge and Department of Chemistry at Queen Mary University
of London. It is aimed to use this glucose sensor as the model for the
next generation of biosensors for detecting cancer using synthetically
derived detecting agents ("synzymes") which are currently being developed.
For further information, please contact Dr Vasant Kumar, rvk10@cam.ac.uk
High conductivity solid electrolytes for solid
oxide fuel cells for operating at a low temperature
The aim of this research project is to investigate the possibility of
developing a suitable solid electrolyte system that can help lower the
operating temperatures of solid oxide fuel cells from over 1200 K to possibly
lower than 1050 K. This will allow the replacement of expensive and fragile
ceramic interconnects with metallic interconnects in a fuel cell stack
making substantial differences to the capital and the operating costs.
It is envisaged that the electrolyte systems will be based upon multi-doping
and/or multi-layering.. Multi-doping will be used to optimize the defect
chemistry such that ionic conductivity is maximized, while multi-layering
can provide the opportunity to select the most stable layer for contacting
the fuel at the anode and the oxidant at the cathode with the intermediate
layers for grading. Industrial collaboration is available with Henson
Ceramics Ltd. For further information, please contact Dr Vasant Kumar,
rvk10@cam.ac.uk
A novel type of CO sensors
Despite a great progress in gas sensing technology, there is no suitable
CO sensor available that can be used for in-situ detection of CO in gas
mixtures, such as in hot exhaust gases in automobiles or stacks. Using
a novel approach, CO will be measured indirectly by allowing CO to react
and come to equilibrium with oxygen adsorbed on a catalytic surface attached
via an electrode to a suitable solid electrolyte. In this project, an
optimum combination of the solid electrolyte, electrode containing the
catalyst and the operating temperature will be developed. Such a sensor,
it is envisaged, will result in rapid industrial usage. Industrial collaboration
with Environmental Monitoring & Control Ltd is available. For further
information, please contact Dr Vasant Kumar, rvk10@cam.ac.uk
Opto-ionic Sensors
A novel approach is being investigated that can utilize the optical properties
of ionic compounds for non-destructively evaluating the performance, quality
and properties of ceramic coatings. A doping strategy will be evaluated
for a selected ceramic such as partially or fully stabilized zirconia.
This new method can have a major impact in manufacturing, operation and
maintenance in many areas such as fuel cells, turbine blades, sensors
and other engineering structures/ components. For further information,
please contact Dr Vasant Kumar, rvk10@cam.ac.uk
Li-S Battery
Using novel ideas , batteries using Li anode and Sulphur
cathode will be developed in order to achieve ultra high levels of energy
and power density for the next generation of applications. Particular
focus will be made on optimising the S composite cathode using nano-particles
with a view to increase sulphur utilization and minimize fading with cycle
life. This work will be carried out in close collaboration with Oxis Energy
Ltd. For further information, please contact Dr Vasant Kumar, rvk10@cam.ac.uk
Light Weight Lead Batteries?
There is so much emphasis on producing Li base batteries for Electrical
Vehicles that the most established automotive battery over 100 years has
not been seriously considered for the next generation of EVs and HEVs.
It is surprising given the cost advantages are by a factor of 10. Of course
Pb is heavy and Li is light. In reality the active component is not lead
but oxides. The heavy lead grid in the battery only serves to hold the
paste and conduct electricity and can be replaced by a light modern advanced
material. The active lead oxide can be made super-efficient by using nano-particles
in the paste. In this project, foundations will be laid for the next generation
of low-cost, light weight and high energy density lead based batteries.
For further information, please contact Dr Vasant Kumar, rvk10@cam.ac.uk
Sustainable Lead Batteries
Lead Acid batteries represent a recycling success story; in that 90%
are already recycled and over 50% of new batteries are produced using
recycled lead. However, the processes used to recover lead are in themselves
environmentally unfriendly. The most common method involves smelting the
battery at a high temperature ( > 1000 o C) to decompose the PbSO 4
in the spent battery and releasing large quantities of sulphur dioxide
and Pb fumes along with CO 2 into the atmosphere. Other new solutions
being trialed involve dissolving the battery with highly toxic and corrosive
chemicals, and recovering the lead using capital and electrically intensive
processes. Due to the environmental costs of the processes, batteries
are increasingly shipped across continents for processing in countries
with less stringent environmental regulations, a step which simply moves
the environmental damage and which may also be restricted in the near
future by EU legislation on the transport of toxic materials. A new patented
process is being developed in this Department, which chemically leaches
and crystallizes the battery contents into a form that can, by a simple
combustion-calcination, be used directly in the manufacture of new batteries.
The reactants arise from biological sources, making the process nearly
C-neutral. This method was designed with the dual goals of being environmentally
sound and being cost-effective to operate either locally on a small scale
or on larger industrial scales. For further information, please contact
Dr Vasant Kumar, rvk10@cam.ac.uk
Novel sulphurous sensors
Despite more than 2 decades of research using solid electrolytes, sulphurous
sensors for detection of gases such as SO 2 , SO 3 , H 2 S have not progressed
beyond the laboratory. Some recent developments in this Department has offered
new opportunity for translating the scientific work into an industrial practice.
In collaboration with Environmental Monitoring & Control Ltd and Greenbank
Ltd, it is intended in this project to develop the sulphur suite sensors
for application in exhaust gases. For further information, please contact
Dr Vasant Kumar, rvk10@cam.ac.uk
The aluminium/air battery
The aluminium/air battery is a device which is capable of supplying
high currents. Its anodic reaction consists of oxidising aluminium
to give dissolved aluminium ions, the cathode being reduction of oxygen
from air. In order to dissolve the aluminium, aggressive electrolytes
are used; typically these would be chloride solutions or strongly caustic
solutions. Because of the high energy density and power density
of aluminium, the battery has potential applications in a variety of
fields. This project will investigate both the aluminium anode
and the air cathode reactions with the object of improving the devices.
Aluminium anode will be made of designed alloy composition in
order to lower the anode potential as much as possible, as well as to
raise the anodic current. One of the problems with activating
the anode too far is that a degree of self-corrosion can dominate the
reaction. Self corrosion is caused by cathodic decomposition
of water and dissolution of aluminium. This parasitic reaction
reduces the anode efficiency and its lifetime. By suitable alloy
design and electrolyte composition, the self corrosion process can be
reduced significantly. The project is suitable for graduates
in materials science, metallurgy or chemistry. Applicants should
have an interest in electrochemistry. The supervisor will be
Prof G T Burstein, from whom further information can be obtained via
gtb1000@cus.cam.ac.uk.
New methods of detection and measurement
of sensitisation of stainless steels.
Stainless steels are notoriously prone to sensitisation of the grain
boundaries to corrosion. The phenomenon arises because under
appropriate heat treatment, the carbon and chromium components precipitate
in the metal phase to form chromium carbides, and an associated depletion
in chromium in the alloy matrix around the precipitate. The problem
is exacerbated by the presence of a high carbon content, but can be
observed in lower carbon steels as well. Such sensitised steels
are prone to intergranular corrosion and to stress-corrosion cracking.
Because the grain boundary region can show composition variation
over very small dimensions, testing for sensitisation can sometimes
be difficult. The present project will investigate new methods
of measuring sensitisation. The work will focus on the behav
iour of microelectrodes in aggressive solutions. Measurement
of the thermal response of the corrosion system will also be carried
out using a technique specially developed in the laboratory.
The research will generate new methods of analysis, more sensitive than
has hitherto been possible. It will also develop a better understanding
of the mechanisms involved. The research will be carried
out in the corrosion laboratory under the supervision of Prof G T Burstein,
from whom further information can be obtained via gtb1000@cus.cam.ac.uk.
Electrocatalysts made from base materials
as electrodes for fuel cells
Low temperature fuel cells currently require platinum based materials
to function as the electrocatalyst, both for the anodic oxidation of
the fuel and for the cathodic reduction of oxygen. Whilst
these catalysts work well, they suffer from some disadvantages.
The cost of platinum is huge, and large-scale use of the metal as might
be anticipated by for example, fuel-cell powered vehicles, would make
the cost even higher. One potential solution to this is to research
into possible electrocatalysts made from base materials. This
difficult task requires the candidate materials to have a number of
properties. Apart from catalytic activity, the material much
also be resistant to corrosion in the potentially aggressive fuel-cell
electrolyte. Resistance to corrosion for an acidic electrolyte
requires passivity. This project will carry out research into
possible electrocatalysts made from base materials which are both electrocatalytic
towards the reactant, as well as passive towards corrosion. Preliminary
work has shown that materials based on metal carbides can show a low
degree of electrocatalytic activity. Although the electrocatalytic
activity is currently very low, the mechanisms of anodic oxidation of
fuel are different for these materials, and further developments can
be made. For example, some can be tailored to catalysis for hydrogen
or for methanol. These materials also show a remarkable degree
of resistance to poisoning by carbon monoxide, a problem that arises
with platinum based catalysts. The research will be supervised
by Prof G T Burstein, from whom further information can be obtained
via gtb1000@cus.cam.ac.uk.
Corrosion in reinforced concrete in oil wells
This project will investigate corrosion of steel as well as some other
materials as might be used in oil wells. Of particular interest
is the behaviour within the concrete well casing, and the interaction
with sea water at elevated temperature. The research will consist
of electrochemical examination of the problem, including anode and cathode
reactions, as well as analytical methods of microscopy and x-ray diffraction.
Some aspects of systems design will also be involved. Possible
methods of inhibition will be investigated through variations in alloy
composition as well as by modification of the concrete mix. This
project is of interest to anyone with a first degree in metallurgy, materials
science or chemistry, with an interest in electrochemistry and/or corrosion.
The research will be supervised by Prof G T Burstein, from whom
further information can be obtained via gtb1000@cus.cam.ac.uk.
Materials Modelling
Computational modelling of GaN
and related alloys
Atomic level modelling has a crucial role to play in understanding
how the defect structure and chemistry of GaN influences its opto-electronic
properties. Using high performance computers and state-of-the-art atomistic
and electronic structure methods the physics and chemistry of the (Ga,
Al, In)N system will be investigated. The project will focus on several
aspects of this system which are poorly understood such as the incorporation
and diffusion of impurities and the nature of impurity clusters. The microscopic
properties of other defects will also be investigated including heterostructures.
The work will be closely coupled to ongoing experimental investigations
within the Cambridge GaN Research Centre. This important project will
require a good understanding of semiconductor materials and condensed
matter theory as well as a familiarity with the use of computers and programming.
For further details contact Dr Paul Bristowe, telephone +44 (0)1223 334305,
pdb1000@cus.cam.ac.uk.
Computer modelling of interfaces
in electroceramic materials
Varistors and boundary-layer capacitors are made from
polycrystalline electroceramic materials where internal interfaces such
as grain boundaries control the functionality of the device. The interfaces
act as Schottky barriers to charge transport but the precise mechanisms
at the microscopic level are unclear. It is believed that interfacial
segregation, native point defects and the formation of new intergranular
phases play an important role. Using high performance computers and state-of-the-art
atomistic and electronic structure methods the properties of grain boundaries
and impurities in ZnO and SrTiO3 will be investigated. The work will be
closely coupled to ongoing experimental investigations on these materials
within the department. This important project will require a good understanding
of ceramic materials and condensed matter theory and also a familiarity
with the use of computers and programming. For further details contact
Dr Paul Bristowe, telephone +44 (0)1223 334305, pdb1000@cus.cam.ac.uk.
Computer modelling of hydrogen
storage in carbon nanostructures
One of the most exciting, but also controversial, applications
of nanotubes and nanofibres is in the storage of hydrogen. So far a wide
range of experimental values for hydrogen uptake in carbon nanostructures
have been reported ranging from the completely negative to the wildly
optimistic. Modelling and theoretical considerations have yet to provide
a plausible explanation for significant gas storage. However, we believe
that some interesting avenues remain to be explored that could throw some
light on this issue. Using high performance computers and state-of-the-art
electronic structure methods this project will focus on investigating
novel hydrogen chemisorption processes. Our aim is to search for new reaction
mechanisms that will lead to C-H bonds with strengths intermediate between
those produced by physisorption and those expected from conventional covalent
bonds. The project will have strong links to DERA and the departments
ongoing experimental work to measure hydrogen storage and will require
a good understanding of condensed matter theory and a familiarity with
the use of computers and programming. For further details contact Dr Paul
Bristowe, telephone +44 (0)1223 334305, pdb1000@cus.cam.ac.uk
Constitutive Modelling of Deformation
Mechanisms in Single Crystal Superalloys
In recent years many detailed models of the deformation
of single crystal superalloys have been developed based upon a number
of deformation mechanisms identified in these alloys. Each mechanism
gives rise to distinctive mechanical responses. However the stress and
temperature ranges over which these mechanisms operate, the effect of
micro-structural instabilities such as anisotropic g' growth (rafting)
and TCP precipitation and how they combine with prior damage are not
well understood.
Detailed observations in the TEM and SEM of the dislocation
mechanisms operating in a small number of representative alloys will
provide the basis for constitutive models of deformation over a range
of conditions of stress and temperature critical to engine components.
Central to this is an understanding of the 'deformation mechanism maps'
of an alloy. This describes the temperature, stress and strain rate
range over which various mechanisms operate. These include: diffusion
controlled climb/glide by FCC dislocations in the g matrix, shear of
the g and g' by combinations of partials and stacking faults, micro-structural
instabilities such as rafting and the processes leading to fracture
such as raft cutting and porosity at topologically close packed (TCP)
phases. Moreover, the boundaries between the different mechanisms are
a sensitive function of the alloy parameters such as g' size and volume
fraction, misfit, solid solution hardening and stacking fault energy
in both g and g'. For further information contact Dr CA Rae.
Physical Metallurgy
Lifing of Electron Beam Physical Vapor
Deposition (EBPVD) Thermal Barrier Coatings (TBCs)
Modern aeroengine turbines operate under extremely high
temperatures and pressures. Traditionally, single crystal Ni-base superalloys
were typically used under these severe environments. However, demands
for higher efficiency and power output resulted in large temperature increases
in the hot gases entering the turbine. With current gas temperatures exceeding
the melting point of the single crystal alloy, ceramic coatings are necessary
to minimize metal temperatures and prevent failure. The ceramic coatings
are applied onto the turbine blades in a complex series of processes.
With spallation of the coatings leading to the premature failure of the
blade, developing a mechanistic understanding of the failure modes is
critical in blade design and extending the useful lifetime of the components.
Rejuvenation of Ni-Base Single Crystal
Superalloy Components
Large costs are associated with the manufacture of turbine
engines and components for both power generation and aerospace applications.
Consequently, service and repair of used components is a growing worldwide
business. Due to the extreme operating conditions of the turbine engine
environment, plastic deformation and microstructural changes often occur
in components that have seen service. Careful thermal-mechanical treatments
have shown great promise in restoring both the mechanical properties and
the original microstructure of the component. When dealing with single
crystal components, great care has to be taken to prevent recrystallization
during these thermal treatments. This project will focus on investigating
both the micro and macrostructural changes that occur in these complex
Ni-base systems during service and the subsequent rejuvenation treatment.
Electronic Metallization for Extreme
Environments
Reactions at contacts in electronic devices for service in extreme conditions.
This project is part of a "Faraday" consortium
involving several universities and companies. It is concerned with developing
the metallic interconnects, wires and contacts for electronic devices
to be embedded in aeroengines, oil-drill bits, etc. The main part of the
work will be microscopy and analysis of metal contacts, looking at the
influence of various factors (including electromigration) on the interdiffusion
and reactions at the contacts. For further details contact Professor A
L Greer, +44 1223 334398, alg13@hermes.cam.ac.uk.
Chalcogenide Alloys for Data Recording
This is intended to be a CASE award with a local company
Plasmon Data Systems (based in Melbourn Cambs and in California) to work
on various issues associated with the phase-change material in CD-RWs
and DVDs. This might include looking at the possibilities for exploiting
this technology other than in discs. The project will involve electron
microscopy and analysis of phase-change kinetics. For further details
contact Professor A L Greer, +44 1223 334398, alg13@hermes.cam.ac.uk.
Low-k dielectric materials
This is intended to be a CASE award with Trikon Technologies
in Newport, Gwent. The speed of modern integrated circuits is limited
by the RC time delays. The resistance R of the interconnect lines is reduced
by having Cu lines rather than Al. The capacitance C can be reduced by
having an insulator of lower dielectric constant than the silica which
is used at present. These low-k materials are porous on a nm scale, and
the aim of the project is to characterize their structure and properties.
For further details contact Professor A L Greer, +44 1223 334398, alg13@hermes.cam.ac.uk.
Solidification and Microstructure in Al Alloys
This project (CASE award under negotiation) is on the control
of microstructure in Al alloys, involving microstructural characterization
and modelling, with a strong emphasis on developing predictive models.
For further details contact Professor A L Greer, +44 1223 334398, alg13@hermes.cam.ac.uk.
Polymers and carbon nanotubes
Smart carbon nanotubes fibres
Modern intelligent materials, or smart materials , are materials
especially designed to respond to an external stimulus, which could be
mechanical, electrical, chemical, thermal or magnetic. Examples include
shape memory alloys, photonic fibres and polymer electronics. On the other
hand, carbon nanotubes have been well recognized as one of the most promising
emerging materials for the next generation of commercial products. This
project aims to exploit the potential of carbon nanotube fibres prepared
by a unique process developed in this Department to be used as smart fibres.
In particular, the project is aimed at understanding the coupling
between mechanical stress and electrical and thermal conductivities,
in terms of the internal structure of the nanotube fibres. Such knowledge
is an essential precursor to opening up the market potential for sensor
and actuator applications. Physical properties of the carbon nanotube
fibres will be measured as a function of process parameters and the relationship
between these properties will be assessed. Microstructural changes will
be followed by scanning and transmission electron microscopy, X-ray diffraction
and Raman spectroscopy. Supervisors: either Prof A H Windle
Nanotube fibers spun from liquid crystalline suspensions
It has recently been demonstrated in this laboratory that suspensions
of carbon nanotubes can form liquid crystalline phases. This project aims
to develop a process to spin nanotube fibers from liquid crystalline suspensions,
which is similar to that used in making the world's strongest widely available
polymer fiber, Kevlar. One application for nanotube liquid crystals is
high tensile strength fibers. The objective of this project is
to develop our understanding of liquid crystallinity of nanotube suspensions
with the objective of developing a new route to nanotube fibres.
Defect interactions, rheologies and external field effects will be studied
in the context of the appropriate phase diagram using microscopic, Raman
and scattering techniques. Exploring the parameter
space of processing conditions will provide key factors to control nanotube
alignments in the fibres. Supervisors: either Prof A H Windle
Nano materials for the hydrogen
economy
Global warming is becoming a key issue which is beginning to influence
national science strategies. The problem with CO 2
emissions from motor vehicles is that it is not as economic to trap the
CO 2 as at centralised power stations. There is thus
a drive towards hydrogen fuelled fuel cell powered vehicles.
The challenge is to find a sensible, on board, hydrogen storage technology.
Nanotubes and nanofibrous materials have opened up the possibility
of using lightweight, nano-scale structures for the purification and storage
of gases. If realised, these high surface area materials could be used
in a variety of environments as filters and/or membranes, or as sponge-like
materials storing gaseous products as part of a storage system.
Apparatus that has been purpose built for the investigation of gas storage
properties will be used to identify those structures capable of reversibly
adsorbing combustible gases at room temperature. The objective
is now to explore the gas absorption (and adsorption) properties a wide
range of nano materials, many of which are being synthesised in the department.
The project will involve the development of measurement techniques,
the modifications of nanoparticular materials, and their structural and
chemical characterisation. Supervisors: either Prof A H
Windle
Electro-magnetic energy transfer into the carbon
nanotubes
Many standard thermoplastic materials that could be used for enclosure
of electronic systems (computers, televisions, mobile phones, etc.) are
transparent to the low frequency electromagnetic radiation (eg. radio
frequency). The fascinating property of electro-magnetic energy adsorption
by carbon fibre materials have been already exploited in many applications
ranging from computers to building structures. There is initial evidence
that carbon nanotubes, especially single wall carbon nanotubes, could
be extraordinarily effective material for electromagnetic energy transfer.
If this prediction is correct, it will significantly affect the
packing and casing industry since shielding could be produced easily and
cheaply from injection moulded nanotube-polymer composites. However,
the work may suggest new, ultra -efficient ways of heating polymers, and
also has relevance where the modification of radar absorbency might be
of interest. The conversion of low frequency electromagnetic radiation
into the thermal energy within a range of carbon nanotube materials will
be measured as a function of nanotube loadings and structure.
The objective will be to create materials with very high levels of coupling
into radio frequency energy, and develop a robust method of making such
measurements. Supervisors: either Prof A H Windle
Development of the physical properties of carbon
nanotube fibres by post-spinning treatments
The newly developed continuous spinning process for carbon nanotube fibres,
generates fibre which has promising mechanical and electrical properties.
One objective is the creation of a cheap electrical conductor where
the promising levels of electrical conductivity are balanced by high strength.
Attention is now focusing on the improvement of these properties,
in the quest to move the fibre performance up to the levels of the strongest
types of fibres know. One strategy is to back diffuse a polymer into the
directly spun fibre with a solvent to achieve two objectives. The
first is to obtain a measure of self order in the form of a liquid crystalline
lyotropic phase. The second is to exploit the enhanced mobility
provided by the solvent to enable the nanotubes to align with the tensile
axis on further drawing. The objective is to optimise electrical conductivity
and strength through the development of structure and alignment in the
continuous nanotube fibres. Supervisors: either Prof A H
Windle
Production of functionalised, aligned carbon nanotubes
by substrate growth.
Carbon nanotubes show considerable promise for a wide range of applications
due to their unique combination of properties. However, there are still
significant challenges in realising these applications due to the difficulties
in producing straight, unentangled nanotubes, functionalising them and
then processing them into the desired structures. One successful approach
has been growing mats of aligned nanotubes by the decomposition of ferrocene
and a hydrocarbon . These mats have subsequently been used in composites
and supercapacitors.
This project will build upon the success of this production route by
developing methods for producing single-walled mats rather than the conventional
multiwalled mats. Furthermore, the mats represent a useful surface and
studies will be made on functionalising the nanotubes without destroying
their arrangement. Finally, the science of the mat growth will be investigated,
with the benefit of learning on how to keep catalyst activated and hence
grow as long nanotubes as possible. This PhD will use a broad
range of experimental techniques, including catalytic vapour deposition,
TEM, SEM, TGA and Raman spectroscopy. Supervisors: either Prof
A H Windle
SKF University Technology Centre for Steels
Developing nanostructured steels of exceptional strength, formability and toughness
Severe plastic deformation technologies allow the controlled formation of ultra-fine structures at the micrometre level. These foster alloy toughening while producing a structure with a high density of crystallographic defects (e.g. grain boundaries and dislocations). At an even lower scale, low-temperature isothermal bainitic transformation has shown exceptionally high strength and ductility, but at the cost of very lengthy heat treatments. By combining both technologies, the driving force for the formation of bainite can be manipulated, raising the temperature at which bainitic transformation takes place, and therefore its pace, while inhibiting long sheaves via a high density of high angle boundaries. This will allow Carbon content to decrease, enhancing weldability. It is wished to model both processes so as to determine optimal deformation strain, strain rates and temperatures for alloy compositions amenable to bainite formation. Irreversible thermodynamics will be used to predict the optimal dislocation density, while equilibrium thermodynamics and phase kinetics will aid in tailoring the nanobainitic structures. The designed alloys will be cast to specification, severely deformed and heat treated by our partners in the Central Iron & Steel Research Institute, Beijing, PRC. Candidates should have an interest in phase transformation theory, alloy processing and characterization. For further information please contact Dr Pedro Rivera on Tel +44 1223 331538, email pejr2@cam.ac.uk.
Mechanisms controlling the formation of ε carbide in high performance steels
Recent research has shown the possibility to achieve steels with yield strength and ductility in excess of 2 GPa and 25% elongation. The formation of ε carbide is hold responsible for such outstanding properties in certain steel families. Upon quenching from high temperature where austenite prevails, marteniste and ε form. ε size can be further controlled upon tempering at low temperatures so as to reach peak hardness. There is still controversy as to the mechanisms controlling the formation of ε, which may either occur displacively or diffusionaly. Moreover, there are no quantitative models predicting such formation, and hence aiding in its control and tailoring. The purpose of the project is to develop the fundamental knowledge required to explain the nature of ε formation, and to express this mathematically in terms of the relevant heat treatment parameters necessary for improving the extraordinary mechanical properties reported in the literature. The project will be performed in cooperation with CENIM in Spain, aiding in the alloy characterization. The ideal candidate should have knowledge (and preferably experience) in computational thermo dynamics and phase kinetics modelling. Interest in high resolution electron microscopy as well as atomistic modelling will be an asset. For further information please contact Dr Pedro Rivera on Tel +44 1223 331538, email pejr2@cam.ac.uk.
Irreversible thermodynamics prediction of high and low temperature deformation and fatigue damage accumulation
Very recent theoretical work has been able to relate the combined effects of temperature, strain rate and composition in a physically-based model rooted in irreversible thermodynamics. The model postulates that the rate-controlling parameter in describing the deformation of single crystals, polycrystals, ultra-fine grained and nano-crytalline metallic alloys is the activation energy for dislocation annihilation. Independent work has demonstrated this to be a key parameter for controlling room temperature fatigue behaviour. The project is aimed at developing the necessary theory to describe the damage accumulation on physically-based grounds. The methodology will include the assessment of the energetics of dislocation glide, formation, climb, as well as the interaction of these with crystal defects such as vacancies and interstitial atoms. Such energies will be used as an input to an irreversible thermodynamics approach to control steady state fatigue behaviour of high performance engineering alloys. Candidates with interest in solid state physics and plasticity theory are welcome to apply. This project will be performed in collaboration with Prof Jilt Sietsma in Delft University of Technology. For further information please contact Dr Pedro Rivera on Tel +44 1223 331538, email pejr2@cam.ac.uk.
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