List of Final Year Projects 2008-2009
Go here for the new site:http://www2.surrey.ac.uk/physics
Catching light with FROGs and SPIDERs: measuring the amplitude and phase of femtosecond laser pulses (phs3ja_001)
Supervisor: Professor Jeremy Allam
Type of project: Experiment
Course: BSc in Physics
Academic year: 2008-2009
Project Description:
Modern ultrafast lasers produce intense, tunable light pulses with duration of only a few femtoseconds. This is short enough to time chemical reactions, vibrations of molecules or crystals, electron motion in semiconductors? in fact these lasers have revolutionised areas of physics, metrology (Nobel Prize 2005), chemistry (Nobel Prize 1999), and biology. Measuring the properties of these femtosecond pulses is essential if they are to be used, but you have to be quick - they are gone after 10-14 seconds! It's usually done by arranging for two pulses to arrive almost simultaneously in a material that has a non-linear response to the light intensity.
We know from Fourier transform theory (or from the Uncertainty Principle) that such a short pulse (t small) contains a spread of energies or wavelengths (E large), so we need to measure the spectrum as well as the duration. Over the last few years, several spectral-temporal characterisation methods have been shown such as Frequency-Resolved Optical Gating (FROG) and Spectral Phase Interferometery for Direct Electric field Reconstruction (SPIDER). MI-FROG is a version using multiple pulses to remove ambiguities in the phase determination. GRENOUILLE is an experimentally-simple variation of FROG with no moving parts (and is also an extremely contrived acronym!). There are also SEA-SPIDERs, TADPOLEs and POLLIWOGs?.
In the Advanced Technology Institute at Surrey we have installed state-of-the-art femtosecond lasers and we want to know the pulse characteristics. The student working on this project will construct a GRENOUILLE system from available parts, and will use it to study pulses from our femtosecond laser, and analyse the results to find the pulse duration, spectral bandwidth and 'frequency chirp'. The student might also study how these properties are changed when the light pulse passes through optical fibres, semiconductor waveguides, or other materials. The merits of different approaches - especially MI-FROG - will be compared.
This project is a chance to work with sophisticated equipment and methods in a hot research field. The student will need to have a good track record in laboratory work.
WRITE-BRIGHT-LIGHT: Laser engineering of optical structures (phs3ja_002)
Supervisor: Professor Jeremy Allam
Type of project: Experiment
Course: BSc in Physics
Academic year: 2008-2009
Project Description:
Integrated photonic circuits, with applications in communications, sensing, etc, require the formation of optical waveguides, resonators, filters, etc. Control of the light is achieved by changing the refractive index of the material, either by physically removing material or by changing its dielectric properties in some way. Common substrates for these circuits include silica glass, and silicon and III-V semiconductors.
One way to change the dielectric properties of a material is to illuminate it with a focused high power laser, exploiting various mechanisms including recrystallisation, thermal damage, laser-induced diffusion, etc. The focused laser spot is scanned across the surface to generate the desired shape of waveguide or other device.
Ultrashort pulse lasers are attracting interest for material modification. For pulse durations of picoseconds or less, the interaction mechanism of light with matter is dramatically different than for CW lasers, or even pulsed lasers of durations down to nanoseconds. Direct ablation of material replaces melting, and acoustic shock replaces thermal damage. In some circumstances this leads to more controllable modification of material, and this is being exploited in industry and medicine.
In this project, the student will "write" simple waveguides and structures into glass or silicon waveguides, using a focused high power ultrashort pulse laser. The student will find ways to characterise the material modification and therefore to assess this method of direct writing of waveguides using pulsed lasers.
This experimental project make use of an advanced, high-power ultrashort pulse laser system. The number of users is strictly limited, the equipment is fragile and expensive, and careful attention to safety is required. This project is therefore restricted to those who have a strong record of achievement in undergraduate practical laboratories.
Two-photon microscopy of quantum dots and meningitis bacteria (phs3ja_100)
Supervisor: Professor Jeremy Allam
Type of project: Experiment
Course: MSc in Nanotechnology & Nanoelectronic Devices
Academic year: 2008-2009
Project Description:
In two-photon microscopy, chromophores (light emitting molecules) are detected by the absorption of two photons from an intense femtosecond laser followed by the re-emission of a single photon of twice the energy. The non-linear absorption occurs only at the focus of the laser beam, allowing background-free, low-damage, three-dimensional imaging with sub-micron resolution. This two-photon absorption (TPA) microscopy has become an important technique in biology. The chromophore (e.g. green-fluorescing protein, or more recently, semiconductor quantum dots) can be selectively attached to different biochemical species and therefore placed as a marker within the cell.
In this project, the student will use a recently-constructed TPA microscope in conjunction with the femtosecond lasers recently installed in the Advanced Technology Institute at Surrey. Semiconductor quantum dots, crystallized in suspension and deposited on various electrode structures, will be studied. Samples of meningitis bacteria (dead!) tagged with green-fluorescing protein have been provided by collaborators in the School of Biomedical and Molecular Sciences.
The student will gain experience in the design and construction of advanced optical systems, in the use of high-power femtosecond lasers, and in the use of photonics in biomedical applications.
This experimental project make use of an advanced, high-power ultrashort pulse laser system. The number of users is strictly limited, the equipment is fragile and expensive, and careful attention to safety is mandatory. This project is therefore restricted to those who have a strong record of achievement in undergraduate practical laboratories.
Exciting the rainbow: supercontinuum generation with high-power lasers (phs3ja_179)
Supervisor: Professor Jeremy Allam
Type of project: Experiment
Course: BSc in Physics
Academic year: 2008-2009
Project Description:
Supercontuum generation from an optical fibre excited by an ultrashort laser pulse, taken from http://www.physics.usyd.edu.au/current/tsp/Martijn_deSterke.pdf
Normally, if you shine red light through a piece of glass, you get red light out at the other end. The speed of light and the wavelength are modified within the glass - but the photon energy stays the same. This all changes when the light intensity becomes very bright, for example if we use a high-intensity laser beam. Various nonlinear optical effects come into play which can change the photon energy. We can arrange to convert photons of one energy to photons of a different energy (parametric conversion), for example changing red light into blue. Or we can generate a broad spectrum of colours - a "supercontinuum" or "laser rainbow".
Modern ultrafast lasers concentrate their optical power into short pulses whose duration is measured in femtoseconds (10-15s). The light intensity in these pulses is very high and a supercontinuum can be generated just by focusing through a piece of glass a few mm thick, producing femtosecond pulses of white light. This has a several important applications. In spectroscopy, we can measure the absorption of a material at many different wavelengths simultaneously and so find out how the population of electrons in different energy states evolves in its first femtoseconds of existence. Supercontinuum radiation is also important in imaging techniques such as Optical Coherence Tomography.
In this project, you will investigate supercontinuum generation by the nonlinear process of self-phase modulation. You will use an amplified titanium-sapphire laser system located in the Advanced Technology Institute to irradiate different materials and optical fibres, and study how the spectral width and the generation efficiency depend on the intensity, wavelength and other properties of the laser pulse. This will help us to improve our white-light spectroscopy system which we are using to study optical properties of materials such as carbon nanotubes.
This project will suit someone who is confident around advanced experimental apparatus and who has a good track record in undergraduate laboratories. You will receive training on the safe use of high power lasers.
For more information on supercontinuum generation with lasers, have a look at the Encyclopedia of Laser Physics and Technology at http://www.rp-photonics.com/supercontinuum_generation.html .
Quantum Genesis: Coherent Control with Genetic Algorithms (phs3ja_186)
Supervisor: Professor Jeremy Allam
Type of project: Theory/Computational Modelling
Course: BSc in Physics
Academic year: 2008-2009
Project Description:
In coherent control, femtosecond laser pulses with customized pulse shape interact with a quantum mechanical system such as an atom or molecule.
On these timescales, the phase memory of the system is long compared with the laser pulse. The atom remembers the phase imprinted by the parts of the light pulse which arrive early, and so there is a phase-coherent interaction with the late-arriving parts of the light pulse. By controlling the energy and phase of a sequence of light pulses such that subsequent pulses interfere constructively with the remembered optical phase, the interaction with the atom can be maximised. This technique is used in photochemistry to selectively break bonds, therefore determining which pathway a chemical reaction will take (Ahmed Zewail got the Nobel prize in 1999 for this!).
A suitable pulse sequence can be produced by 'spectral-domain filtering': an ultrashort light pulse is dispersed by a prism, passed through a liquid-crystal modulator which controls the transmission of the different colours, and recombined in a second prism. Adjusting the pixels in the liquid crystal modulator produces a pulse sequence with the desired energy and phase to control a particular atomic transition. In situations where the optimum pulse sequence is not known, the pixels can be varied stochastically until the interaction of the light and atom is maximised.
This project will use stochastic methods to calculate the modulator transmission required to generate pulse sequences suitable for coherent control of various quantum mechanical systems. The effects of imperfect and misaligned optics will be included. Different stochastic methods including 'stimulated annealing' and 'genetic algorithms' will be compared. The calculation will also required numerical Fourier transforms.
The student will need to be able to write 'from scratch' a computer programme to implement the numerical techniques mentioned above.
Identifying the Structure of Carbon Nanotubes using Optical Spectroscopy (phs3ja_188)
Supervisor: Professor Jeremy Allam
Type of project: Experiment
Course: BSc in Physics
Academic year: 2008-2009
Project Description:
Figure 1. Optical absorption of carbon nanotubes. The fit (red line) is a set of peaks centred on the known transition energies. The units should be in microns or 1000nm !
This is an experimental project to measure the light absorption and emission from carbon nanotubes.
Carbon nanotubes (CNT) have attracted great interest for their outstanding mechanical and electrical properties. There is now growing interest in their optical properties. They absorb light at wavelengths which are important for technological applications, and the particular wavelength absorbed depends on the precise size and structure of the tube. They also have strong optical nonlinearities which have already been used in a commercially-available pulsed laser. However, the way in which the optical properties depend on the structure, and on other phenomena such as electron-electron interactions, is not yet well understood.
Carbon nanotubes can be considered as rolled up individual sheets of graphene. The size of the tube and the degree of chirality (the extent to which the carbon bonds spiral around the tube) determine the wavelength at which light is absorbed. Single-walled carbon nanotubes with diameters of a few microns are in many ways ideal one-dimensional systems of electrons, and so their properties are determined by quantum mechanics. Figure 1 shows the absorption of a solution of carbon nanotubes: each peak corresponds to a tube of different diameter or chirality. Because the solution contains a mix of many tubes of different size, the different peaks tend to overlap.
Figure 2. Excitation luminesence from a solution of carbon nanotubes , from Bachilo et al., Science 298, p2351 (2002). The peaks within the white oval represent individual tubes excited on E2 and probed on E1.
Spectral features unique to individual species of nanotube can be obtained by a technique known as excitation photoluminesence. A source of monochromatic light is tuned so as to excite electrons from the valence band into the first excited electron state (E2 ). They then lose energy and relax to the ground electronic state (E1 ) before returning to the valence band by emitting a photon of characteristic energy. Hence light emission only occurs when both the excitation and detection wavelengths are resonant with electronic transitions. Figure 2 shows the results for a solution of nanotubes; each red spot corresponds to a tube of particular size and structure.
In this project, you will set up a double spectrometer to perform this kind of measurement. A high quality detection system is available (a spectrometer with cryogenically-cooled photodiode array). You will construct the excitation system from a white light source and a computer-controlled scanning-grating monochromator. You will need to learn a simple graphical programming language called Labview (now the industry standard software for control of experiments). You will analyse the spectra to identify the different nanotubes present in the sample, and deduce their size and chirality. You will take spectra of carbon nanotubes which have been made soluble by different means, including wrapping them with DNA or RNA, and compare the results.
This project is linked to our EPSRC-funded research programme on nonlinear optics in carbon nanotubes, and depending on your progress there may be opportunities to be involved with nonlinear measurements of the same samples, using a high power laser.
Drunken Walks in One Dimension: Exciton Annhilation in Carbon Nanotubes (phs3ja_212)
Supervisor: Professor Jeremy Allam
Type of project: Theory/Computational Modelling
Course: BSc in Physics
Academic year: 2008-2009
Project Description:
This project will use computer simulation to model our recent experimental results on exciton annihilation in carbon nanotubes.
The annihilation (A+A->0) and coagulation (A+A->A) of diffusing reactants (A) is of great importance in many areas of physics as well as in chemistry, biology, geology, ecology, etc. The random walk of the reactants can lead to formation of complex spatial and temporal patterns in the reactant concentration and in some cases to chaotic behaviour 1. When reactants are close to each other, the reaction rate is limited by the reaction time, whereas when they are far apart it is limited by the diffusion time. Initial fluctuations in the distribution of reactants can lead to large-scale ordering, which is enhanced in systems of low dimensionality.2 These systems have been much studied using stochastic (Monte Carlo) simulations. Analytic solutions can be found in some cases if both physical and mathematical approximations are made.3
We have been studying experimentally the optical properties of carbon nanotubes (CNTs) which can be regarded as individual sheets of graphene, one atom thick, rolled up to form a hollow tube whose diameter is of the order of nanometers. Because this diameter is smaller than the de Broglie wavelength of electrons in carbon, the electrons can only move freely in the direction of the tube's axis: they live in a one-dimensional world. When infrared light is shone on the nanotubes, electrons are excited from the valance band to the conduction band, leaving positively-charged 'holes' in the otherwise full valance band. Because the electron and hole are confined to the nanometer-sized tube, they always form an electrostatically-bound pair called an exciton. It is the decay of these excitons which controls the recovery time of the CNT after illumination, which is an important consideration for practical applications such as light emitters and nonlinear optical switches. We have found that the main decay process is exciton-exciton annihilation, and we can clearly identify reaction-limited and diffusion-limited regimes in our experimental data (see figure, right).
The purpose of this project is to simulate the generation, diffusion and annhilation of excitons on carbon nanotubes, using a Monte Carlo simulation of the exciton's random walk. Particular features which will need to be considered include:
- the random distribution of excitons created on each nanotube
- the ensemble of nanotubes of varying length
- the finite nanotube length and initial exciton density (eventually there is only one exciton per tube and exciton annihilation can no longer occur)
- the finite reaction probability of overlapping excitons
- the widely different timescales required to observe the different regimes
The project will involve writing a computer simulation 'from scratch', and will suit a student who excels in writing computer simulations and interpreting their results. You will get in-depth experience in an important computational technique and become familiar with a 'hot topic' in current nanotechnology research. This project is linked to an ongoing EPSRC-funded research programme on nonlinear optics in carbon nanotubes.
1 Alan Turing, 'The Chemical Basis of Morphogenesis', Phil. Trans. R. Soc. London B 237 pp 37-72 (1952).
2 D. Toussaint and F. A. Wilzcek, 'Particle–antiparticle annihilation in diffusive motion', J.Chem.Phys, 78, 2642 (1983)
3 D. X. Zhong & D. Benavraham, 'Diffusion-Limited Coalescence with Finite Reaction Rates in One Dimension', J. Phys. A, 28, 33 (1995)
Pseudopotentials for energy bands in semiconductors (phs3ja_213)
Supervisor: Professor Jeremy Allam
Type of project: Theory/Computational Modelling
Course: BSc in Physics
Academic year: 2008-2009
Project Description:
The properties of the electronic and optoelectronic devices in our computers, CD players and telephone systems, made of semiconductor crystals such as silicon (Si) and gallium arsenide (GaAs), are largely determined by the allowed energy bands for electrons. The calculation of these energy bands is therefore very important in designing devices with improved properties.
'First principles' quantum mechanical calculations are difficult because there are very many interacting electrons in a crystal, although such calculations are becoming possible with modern computers. A simpler empirical approach is often used where the electrostatic potential of the constituent atoms is described approximately (the 'pseudopotential'); the energy of a crystalline arrangement of atoms can then be found. The empirical parameters are adjusted until the calculated energy bands agree with measured optical characteristics. Remarkably, only 3 adjustable parameters are needed to give a very good description of the energy bands in silicon.
Figure 1. Electronic bandstructure of GaAs and Ge for wavevectors in the (100) and (111) directions, calculated using the model pseudopoetntial method.
Although we can go on and find the parameters to describe the bands of any given semiconductor material, we know that many electronic properties of semiconductors vary smoothly with atomic number or position in the Periodic Table - so presumably the atomic potentials do as well. A 'model pseudopotential' makes use of this information.
In this project, the student will examine different model potentials and calculate energy bands for a wide range of semiconductors. The scaling of electronic and optical properties with atomic number will be studied. If things go well, the simple model potential could be extended to incorporate 'nonlocal' effects.
This project will suit a student who is strong in computational modelling methods and in programming using FORTRAN. Although the programme to calculate energy bandstructure will be provided, the student will need to calculate the model potentials and to interface with the bandstructure calculation. The student will gain knowledge and experience of computational methods, quantum theory of solids, and the electronic and optical properties of semiconductors.
Band structure engineering in quantum well structures (phs2aa_012)
Supervisor: Dr Aleksey D Andreev
Type of project: Theory/Computational Modelling
Course: BSc in Physics
Academic year: 2008-2009
Project Description:
Modern semiconductor technology allows fabricating the pre-defined semiconductor structures where the thickness and composition of each layer can be controlled with the accuracy of a single atomic layer. This opens a possibility for band structure engineering in semiconductor structures. The composition and thickness of each layer can be optimised to give better device characteristics and then the optimised structure can be fabricated.
The simplest semiconductor structure with quantum well consists of three layers. This however gives quite small freedom to change the carrier states in such a structure. Recently a quantum well structure with 5 layers has been used for creating a new mid-infrared laser. The potential of this structure is shaped like the letter "W".
The project is to study energy levels and carrier wavefunctions in "W" quantum well structures that consists of 5 layers. The Schrödinger equation for a W-shaped one-dimensional quantum well should be solved. The project will require both analytical and computational work.
Quantum cascade lasers for medical applications (phs2aa_013)
Supervisor: Dr Aleksey D Andreev
Type of project: Theory/Computational Modelling
Course: BSc in Physics
Academic year: 2008-2009
Project Description:
Recent developments of a new type of the devices like quantum cascade lasers operating in mid-infrared and far-infrared spectral regions open new possible applications in medicine. In contrast to the interband lasers, where the photon is generated due to the electron-hole recombination, in quantum cascade lasers many photons can be generated due to the consequent electron optical transitions in a cascade structure. A novel principle in the structure design allows fabrication of the laser with the required emission wavelength. This may be very valuable especially for medical applications, for example for laser surgery on different tissues.
The project includes the following:
- Literature survey on existing and future medical applications of the quantum cascade lasers (to find out what lasers and with what wavelength and emission powers can be used for medical applications).
- Identifying the material combination required for the design of the chosen laser structure. Calculations of corresponding material parameters.
- Calculations of the energy levels in the quantum cascade laser structures using the approximations to be agreed during the project.
Quantum computers based on quantum dots (phs2aa_014)
Supervisor: Dr Aleksey D Andreev
Type of project: Theory/Computational Modelling
Course: BSc in Physics
Academic year: 2008-2009
Project Description:
Semiconductor structures with quantum dots are among major objects of the research in the area of solid-state physics. The energy of the electrons localized in these structures is quantized along all three spatial directions and therefore quantum dots can be considered as artificial atoms. Recently it has been discovered that electron and/or hole states in quantum dots may be used as a quantum bit (or qubit) - the basic element of the quantum computers. There are different possibilities of the realization of the qubit, for example the charge or spin states in a quantum dot or coupled quantum dots (quantum dot molecule) The project includes the following:
- Literature survey on possible ways of the qubit implementation using semiconductor quantum dots and quantum dot molecules.
- To review the case of the quantum dot exciton qubit in details
- To calculate the exciton binding energy and other parameters of the exciton qubit using the approximation to be agreed during the project.
Electronic structure of spherical quantum shell (phs2aa_015)
Supervisor: Dr Aleksey D Andreev
Type of project: Theory/Computational Modelling
Course: BSc in Physics
Academic year: 2008-2009
Project Description:
A small insertion of one semiconductor material into another is usually called a quantum dot. The simplest variant of the quantum dot is a spherical inclusion. Quantum dots are analogous to artificial atoms, since the carrier energy levels there are discrete. Semiconductor spherical quantum dot embedded in glass matrix has only one geometrical parameter that determines its properties - the radius. An interesting object is formed by covering the sphere of one material with another material and embedding it in a glass matrix. As a result, one gets a quantum shell with spherical symmetry, but its properties are now controlled by two geometrical parameters - the total radius and the width of the shell. Such an object provides some freedom in optimisation of the quantum dot properties with the aim of potential device applications.
The project is to calculate the electronic structure and wave functions in the spherical quantum shell. The potential barriers inside and outside the shell are assumed to be infinite. Using spherical symmetry of the potential, the Schrödinger equation in three dimensions should be solved. The dependence of the ground state dipole matrix element of the shell geometry should be calculated. The project will require both analytical and computational work, and, of course, some quantum mechanics knowledge.
Optical transitions in quantum dots of different shape (phs2aa_016)
Supervisor: Dr Aleksey D Andreev
Type of project: Theory/Computational Modelling
Course: BSc in Physics
Academic year: 2008-2009
Project Description:
Modern semiconductor structures contain low-dimensional objects, where the energy spectrum is quantized in one or several directions. In quantum dot the particles are localised in all three directions and have discrete energy levels. The electronic structure of a quantum dot depends on size and shape. By changing the shape of semiconductor quantum dot one can increase or decrease the overlap between electron and hole ground states. This is one of the ways to optimise the optoelectronic devices based on quantum dots.
The project is to calculate the electronic structure and optical matrix elements for the semiconductor quantum dots of three different shapes: sphere, cube and cylinder. The model with infinite barriers will be used for simplification. The aim is then to compare the optical matrix elements for the quantum dots of different shape, but with the same ground state energy. The project requires an analytical solution of the three-dimensional Schrödinger equation, but the results should be obtained using simple computational skills.
Semiconductor cluster band structure using SIESTA (phs2aa_110)
Supervisor: Dr Aleksey D Andreev
Type of project: Theory/Computational Modelling
Course: MSc in Nanotechnology & Nanoelectronic Devices
Academic year: 2008-2009
Project Description:
To use SIESTA code (density-functional theory based computer program) to calculate the band structure of bulk semiconductors and small clusters. Possible link to experiments in the UK and abroad
Modelling of extraordinary magnetoresistance in narrow band gap structures (phs2aa_111)
Supervisor: Dr Aleksey D Andreev
Type of project: Theory/Computational Modelling
Course: MSc in Nanotechnology & Nanoelectronic Devices
Academic year: 2008-2009
Project Description:
This is project is related to modelling of a new effect recently observed in semiconductor-metal structures and it is related to change of the resistance of the structure in the magnetic field. The effect has a potential applications to the new generation of computer hard drive read-heads. Link with experimentalists in Cambridge is possible.
Modelling of semiconductor quantum dots using tight-binding methods (phs2aa_112)
Supervisor: Dr Aleksey D Andreev
Type of project: Theory/Computational Modelling
Course: MSc in Nanotechnology & Nanoelectronic Devices
Academic year: 2008-2009
Project Description:
The project is to use a simple modification of the tight-binding model to compute and study the energy band structure of a semiconductor quantum dot.
Quantum computation using quantum dot molecules (phs2aa_114)
Supervisor: Dr Aleksey D Andreev
Type of project: Experiment
Course: MSc in Nanotechnology & Nanoelectronic Devices
Academic year: 2008-2009
Project Description:
The project is about using a simple model to study the basic operations of the building block of a quantum computer, a qubit, in a configuration using "molecules" of quantum dots ("artificial atoms").
Carbot nanotube: electronic structure in view of solar cell applications (phs2aa_222)
Supervisor: Dr Aleksey D Andreev
Type of project: Theory/Computational Modelling
Course: BSc in Physics
Academic year: 2008-2009
Project Description:
The aim of the project is use a simple version of the tight-binding method to reproduce the band structure of single wall carbot nanotubes. The results will then be used to look at the requirements to nanotubes for solar cell applications. The student taking this project must be prepared to do some (simple!!!) analytical calculations to derive the relevant equations to be used in (simple!!!) Fortran code development. The project has also got an element of the literature review - to find out the requirements for solar cell applications. The two sides of the project (modelling and literature review) can be adjusted according the student's needs.
Organic materials for light emission applications (phs2aa_223)
Supervisor: Dr Aleksey D Andreev
Type of project: Literature Review
Course: BSc in Physics
Academic year: 2008-2009
Project Description:
This is a literature review on the applications of the organic semiconductors for light emission devices. The project may also involve an element of modelling; the portion of modelling can be adjusted according to student's needs. The project would involve the following steps:
1) review and understanding of the organic semiconductor materials and principles of operation of the light emitting devices of their base
2) A detailed literature survey of the subject using various sources ( including internet search engines, WoK database and cross-references related to main papers of the field)
3) a simple graphical analysis of the data obtained in 2), which may involve some very simple graph plotting and programming (i.e. statistics on papers, the improvemnet in main benchmark parameters, etc.)
Solid State Drives vs Hard Disks: current trends and perspectives (phs2aa_224)
Supervisor: Dr Aleksey D Andreev
Type of project: Literature Review
Course: BSc in Physics
Academic year: 2008-2009
Project Description:
The aims of this project is to do a brief overview of the main parameters in the Solid State Disks and Hard Drive Disks from a physicist's point of view. The key parameters of the devices and potential limitations in terms of the size of the elementary memory cells may be discussed. The student may wish to carry out as part of the project a simple modelling of the particular characteristics of the devices.
The results of the projects may be discussed (if necessary) with the key researchers in Hitachi Global Storage Technologies in California.
Carbon Nanotube Based Smart Tongues and Noses (phs1ad_132)
Supervisor: Dr. Alan Dalton
Type of project: Experiment
Course: BSc in Physics
Academic year: 2008-2009
Project Description:
Carbon nanotubes have extraordinary mechanical, thermal and electrical properties and have been hailed as the wonder material of the new nanotechnology revolution. A particularly fascinating property of nanotube arrays is that they respond to chemicals adsorbed on their surface by actuating like muscles.
In this project we will use arrays of carbon nanotubes to sense components in gases or liquids and to automatically act like billions of nanoscale muscles which could be eventually used to regulate microvalves, close vents, or make clothing impermeable to harmful agents. For example, textiles that become non-porous on contact with hazardous chemicals might be used for the clothing of fireman and other first responders. Knowledge of chemically induced actuation is also potentially important for understanding how chemical processing during nanoscale device fabrication might produce disastrous performance-degrading mechanical strains.
It is challenging to understand the surprisingly large observed chemical actuation for carbon nanotubes arrays. For instance, the adsorption of chemicals on the surface of nanotubes or nanotube bundles may change the degree of charge transfer to the nanotubes, which changes the length of the nanotubes since nanotube tube length depends on charge transfer.
The project will use ellipsometry, an optical technique that studies the change in the state of polarisation of light after reflecting from a surface or interface, to monitor the dimensional response of the carbon nanotube arrays to chemical exposure.
In this project we will use arrays of carbon nanotubes to sense components in gases or liquids and to automatically act like billions of nanoscale muscles which could be eventually used to regulate microvalves, close vents, or make clothing impermeable to harmful agents.
For example, textiles that become non-porous on contact with hazardous chemicals might be used for the clothing of fireman and other first responders. Knowledge of chemically induced actuation is also potentially important for understanding how chemical processing during nanoscale device fabrication might produce disastrous performance-degrading mechanical strains.
Surface Enhanced Raman Spectroscopy of carbon nanotubes (phs1ad_225)
Supervisor: Dr. Alan Dalton
Co-Supervisors: Dr. Simon Henley
Type of project: Experiment
Course: BSc in Physics
Academic year: 2008-2009
Raman Spectroscopy of Damaged Collagen (phs1ad_226)
Supervisor: Dr. Alan Dalton
Co-Supervisors: Dr. David Bradley
Type of project: Experiment
Course: BSc in Physics
Academic year: 2008-2009
Simulation of Nano-Lasers (phs1oh_028)
Supervisor: Professor Ortwin Hess
Type of project: Theory/Computational Modelling
Course: BSc in Physics
Academic year: 2008-2009
Project Description:
The project aims at exploring the absolute limit of nano-lasers as well as examining the quantum properties of spontaneous emission.
FDTD Simulation of Photonic Structures on High-performance Parallel Compute Clusters (phs1oh_030)
Supervisor: Professor Ortwin Hess
Type of project: Theory/Computational Modelling
Course: BSc in Physics
Academic year: 2008-2009
Project Description:
Novel materials for integrated photonics like photonic crystals or photonic band-gap fibers need extensive "design" before starting any technology. The FDTD simulation method offers a very general approach to simulation of this novel class of photonic materials that allows to simulate many real world properties. The project aims to use sophisticated computer simulation codes that have been written by the group as well as develop new parallel numerical approaches on the high-performance parallel computing clusters of the group.
Modelling Slow Light in Negative-Index Metamaterials (phs1oh_078)
Supervisor: Professor Ortwin Hess
Type of project: Theory/Computational Modelling
Course: BSc in Physics
Academic year: 2008-2009
Project Description:
Stopping light all-optically may evolve to become one of the major applications of photonic crystals and optical metamaterials. Coupled with recent advances in the fabrication techniques left-handed metamaterials can conceivably lead to the creation of optical waveguides that will be able to trap or dramatically slow-down light and increase light-trapping for use in novel photoelectric devices.
The project will build on a scheme that uses the unique properties of metamaterial heterostructures for achieving a control of the group velocity of the light. In metamaterial heterostructures this may be realized by varying the thickness of the core waveguide. The realization of broadband slow light at optical frequencies for exploitation in next generation solar cells will be explored. Finite-difference time-domain (FDTD) codes will be used for the accurate analysis and wideband performance characterisation of composite left-handed materials.
Infra-red Spectrometer for Narrow-gap Semiconductors (phs1th_207)
Supervisor: Dr Jeff Hosea
Type of project: Experiment
Course: BSc in Physics
Academic year: 2008-2009
Project Description:
Characterisation of semiconductor band structure is essential in order to understand their optical properties for device applications. Several popular techniques, such as photoluminescence (PL) or transmission spectroscopy, involve using diffraction-grating spectrometers to provide a method of wavelength selection. There are two experiments in the teaching laboratories that use exactly these techniques and you may already have performed one of these experiments in Level 2.
In transmission spectroscopy, a white light source is shone into the entrance slit of a grating spectrometer and, by angling the grating, one can select which, essentially monochromatic, wavelengths escape out of the exit slit. By measuring the transmission of this monochromatic light through a semiconductor sample, as a function of increasing wavelength, one can find the wavelength at which the sample changes from being opaque to transparent. At this key l the incident photon energy is just that required to excite electrons from the valence band (VB) into the conduction band (CB). Therefore, this provides a measure of its fundamental bandgap energy Eg - i.e. the energy-width of the forbidden gap between the VB and CB : a parameter of vital importance in the characterisation of semiconductors.
In PL, on the other hand, a laser is shone onto the sample which excites electrons from the VB into the CB. When these excited electrons recombine with the holes they left behind in the VB, photons are emitted of energy closely-related to Eg . By using the spectrometer to measure this emitted light as a function of l, a peak at the wavelength corresponding to the band gap Eg can be found.
In either technique, there is a need for a spectrometer capable of measuring, or providing, wavelengths of the desired range. Up until recently most semiconductors in the industry have operated in the visible to near-infra-red wavelength range. However, there is now an increased interest in studying semiconductors that can operate further into the infra-red, and therefore have narrow band gaps. One reason is because many pollutant and greenhouse gases have “signature” absorptions in the infra-red and there is increasing need to build semiconductor-based emitters and detectors that operate at these key wavelengths
The project involves the use of a small Jobin-Yvon grating spectrometer, capable of operating in the infra-red out to wavelengths as long as ~4 microns. The first part of the project will involve linking the spectrometer to a PC in order that it can be controlled by already existing software. A set-up capable of measuring the infra-red transmission and/or PL spectra of various narrow gap semiconductors will then need to be built. If successful the project will culminate in measuring the band gaps of example topical narrow-gap semiconductors.
Can Gold Nanoparticles Make Adhesives Stronger? (phs1jk_211)
Supervisor: Professor Joe Keddie
Co-Supervisors: &;Dr. Antonios Kanaras, University of Southampton
Type of project: Experiment
Course: BSc in Physics
Academic year: 2008-2009
Project Description:
One application of polymers is in adhesives, which are commonly used to fasten together objects. Previous research in the Soft Matter Physics Group has investigated what properties a polymer needs in order to give it a sticky surface and to adhere strongly to surfaces. This project will investigate the effect of adding gold nanoparticles (with diameters less than 100 nm) on the properties of adhesives. The particles will be made by collaborators at the University of Southampton. If it is of interest, the project student may travel to Southampton to assist with the synthesis of the particles. In the Soft Matter laboratory at Surrey, the student will blend the nanoparticles with polymer particles in water. This mixture will be cast on surfaces to create an adhesive. Specialised equipment will be used to measure the adhesion force and the energy of adhesion as a function of the gold nanoparticle concentration and size. There is also the possibility that the nano-scale structure of the adhesives could be studied by atomic force microscopy.
Atomic force microscopy of polymer-peptide conjugates (phs1jk_232)
Supervisor: Professor Joe Keddie
Type of project: Experiment
Course: BSc in Physics
Academic year: 2008-2009
Project Description:
Atomic force microscopy (AFM) provides information at the nano-scale on the structure and mechanical properties of surfaces. In the intermittent contact mode of operation, an ultra-sharp tip on a cantilever oscillates up and down near its resonant frequency, so that it "taps" the surface. Maintaining a constant amplitude of oscillation while scanning across a surface provides information on changes in the surface height (i.e. topography), while changes in the phase lag of the oscillation in relation to the driver electronics provide information on energy dissipation and hence the viscoelastic properties.
This project will be carried out in collaboration with nanoscience researchers at the University of Reading. They are creating a new type of material from the building blocks of proteins (peptides) and polymers. These hybrid molecules are able to assemble into structures, such as fibrils, at the nano- and micrometer scale. These materials have applications in drug delivery and in tissue engineering. The student will use AFM to determine the dimensions and level of orientational order in polymer-peptide structures, and these measurements will be correlated with type of peptide and with the polymer characteristics, such as its molecular weight. This project is particularly well suited for a student with an A-level qualification in biology and an interest in the application of physics to biological problems.
Magnetic resonance relaxation of water in carbon nanotubes (phs1pm_210)
Supervisor: Professor Peter McDonald
Co-Supervisors: Dr David Faux, Professor Ortwin Hess
Type of project: Experiment
Course: BSc in Physics
Academic year: 2008-2009
Project Description:
Theorists in the ATI have performed molecular dynamics simulations of water in Carbon nanotubes. These calculations have yielded some startling results and predictions that this project aims to test experimentally.
The experiments to be performed are hydrogen NMR measurments of spin-lattice (T1) and spin-spin (T2) relaxation times of water - carbon nanotube mixtures. It is to be expected that the relaxation times of free water around the tubes will be much longer than that of water confined within them. To measure these times will, in itself, be interesting.
However, it is then proposed to move on and use recently suggested two dimensional relaxation experiments. In these experiments, two measurments of relaxation times are made in quick succession - with an intermediate delay Tdelay. The relaxation time measured in both experiments will be the same unless, of course, the water enters or leaves the nanotube during Tdelay in which case the first measurement will yield a "long" relaxation time and the second "short" (if enetring) or vice-versa if exiting. Correlating the fraction of long-long; long-short; short-long and short-short results will yield extremely valuable information on the water dynamics to test the theories.
In doing this project, a student will:
1: Learn how to prepare colloidal smaples of nanotubes in water
2: Learn how operate an NMR spectrometer and be introduced to T1 and T2 measurments widely used in iundustrial appliactions of NMR.
3: Be exposed to an area of real scientific interest and challenge that could yet lead to a publication.
Nuclear Deformation with the Mottelson-Nilsson Model (phs2mo_166)
Supervisor: Dr. Makito Oi
Type of project: Theory/Computational Modelling
Course: BSc in Physics
Academic year: 2008-2009
Project Description:
Using the simple 3D harmonic oscillator, nuclear deformation energy and the corresponding single-particle energy levels are calculated as a function of the anisotropic parameters (i.e. deformation parameter).
Equilibrium shape of a nucleus is given as a minimum of the deformation potential. By calculating the potential for many types of nuclei, systematic studies will be performed to gain an insight how nuclear shape changes as more neutrons and protons are added to the system. If time allows, the effect of nuclear pairing correlation to nuclear deformation is also investigated.
Requires knowledge on Quantum Mechanics and Nuclear Physics.
Wobbling Motion in Classical and Quantum Mechanics (phs2mo_167)
Supervisor: Dr. Makito Oi
Type of project: Theory/Computational Modelling
Course: BSc in Physics
Academic year: 2008-2009
Project Description:
Breaking axial symmetry, a rigid rotor will show a novel 3D rotation, called nutation and wobbling motion. Considering both a classical and quantum rigid motor, the wobbling of such a body will be investigated.
For the classical wobbling, time-dependance in the orientation of the angular momentum vector is mainly investigated through the Euler equation.
As for the quantum wobbling, the Bohr-Mottelson model for the wobbling is applied, and the energy spectrum and the structure of the corresponding wave functions are analyised through the diagonalisation method.
If time allows, a full microscopic calculation based on the generator coordinate method could be attempted, which is in the current frontier in the nuclear structure physics research.
Requires knowledge on Quantum Mechanics and Classical Mechanics on a Rigid motor.
Review Project: Dawn of Quantum Mechanics (on the particle-wave duality) (phs2mo_168)
Supervisor: Dr. Makito Oi
Type of project: Theory/Computational Modelling
Course: BSc in Physics
Academic year: 2008-2009
Project Description:
This is a review project to study the particle-wave duality heavily discussed in the early days of Quantum Mechanics. With the three typical phenomena that cannot be explained with the classical mechanics, which are the black body radiation, the Compton effect, and the photo-electric effect, the efforts and achievements done in the early 20th century to develop Quantum Mechanics are reviewed.
Requires knowledge of Quantum Mechanics; Theory of Relativity; Thermodynamics and Statistical Mechanics.
Nuclear Waste Management Worldwide (phs1zp_170)
Supervisor: Dr Zsolt Podolyak
Type of project: Experiment
Course: BSc in Physics
Academic year: 2008-2009
Project Description:
Nuclear power is firmly back on the agenda in the UK and other countries around the world. This possible renaissance of nuclear power is related to global warming, the need to cut CO2 emission.
The main argument against building new nuclear power stations is the environmental hazard associated to there usage and the problems related to the produced long-lived radioactive waste.
The present project is essentially a literature review. Its aim to compare the solutions, both short term and log term, suggested and sometimes used in different countries (UK, France, USA, Japan, Russia, Scandinavia etc.). A critical evaluation of the proposed solutions to waste management, from the point of view of the physics behind, is required (for example depending on the composition of the waste).
What are the Long-Term Dangers of Radiation Fallout from Nuclear Weapons Testing? (phs1pr_042)
Supervisor: Prof. Paddy Regan
Type of project: Literature Review
Course: BSc in Physics with Nuclear Astrophysics
Academic year: 2008-2009
Project Description:
Many nuclear weapons tests took place above ground in the 1950s and 60s by the US, USSR, French and British governments. These 'atmosperic' tests released significant amounts of radioactive nuclear material into the earth's atmosphere, leading to measureable ammounts of 'excess' radioactivity around the globe. What were the long-term health affects on the world's population of such testing ?. This project will review the mechanism in by which this radiation was released; the different types of radiation fallout released, their differeing biological effects on humans and other living things and the measurement scenarios in place to determine the potential effects of this radiation both at the time of the tests and now. . The potential longer-term issues arising from fallout from weapons testing with respect to health risks associated with exposure of large populations to ionizing radiation will be assessed. This literature survey will include use of sources from the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) , unclassified reports from the Atomic Weapons Research Establishment (AWE, formerly AWRE) and recent reports and studies by the UK Health Protection Agency. It would be an excellent project for students thinking of a future career in the radiation protection/health physics industries.
Establishing Nuclear Decays in the Nanosecond Time Regime (phs1pr_043)
Supervisor: Prof. Paddy Regan
Co-Supervisors: Professor William Gelletly, Dr Zsolt Podolyak
Type of project: Experiment
Course: BSc in Physics with Nuclear Astrophysics
Academic year: 2008-2009
Project Description:
This is an experimental project based on utilising state of the art BaF2 and LaBr3(Cl) scintilation detectors to perform high-accuracy nuclear spectriscopy experiments making a series of measurements of decay half-lives in radioactive nuclei at the 1nanosecond (10-9 s) scale. The project involves an initial short literature survey on the use of 'fast timing' scintilators for nuclear spectroscopy and willl be followed by a series of specialist measurements within the physics department's new bespoke radiation laboratories. The project will demonstrate how nuclear state lifetimes on the nanosecond scale and below can be measured and how these can be related to fundamental quanities such as the shape of the atomic nucleus. The project would best suit a student who is interested in 'hands on 'experimental laboratory work and will be part of the Surrey group's new Decay Spectroscopy (DESPEC) research project (which was recently funded via a ~£9m multi-instittional grant from the Science and Technologies Facilities Council). This would be an excellent proiject for students considering either a future PhD in nuclear physics and/or someone interested in working in the nuclear/radiation/health physics industries following graduation.
Measuring thicknesses with gamma-rays. (phs1pr_044)
Supervisor: Prof. Paddy Regan
Co-Supervisors: Professor William Gelletly, Dr Zsolt Podolyak
Type of project: Experiment
Course: BSc in Physics with Nuclear Astrophysics
Academic year: 2008-2009
Project Description:
This project uses gamma-ray spectroscopic techniques to measure thicknesses and deduce densities of materials by measuring the atteunation of discrete energy gamma-rays from mixed, characteristic radiation sources using hyper-pure germanium detectors. The project will involve an initial determination of the response characteristics of the gamma-ray detection system and follow this with a series of laboratory experiments to determine the effect of different thicknesses of differing materials. In addition to experience in nuclear spectroscopic measurements, the student wil gain an understanding of the main concepts behind radiation shielding issues which have numerous applicationsin the medical and nuclear industries. This would be a good project for a student with an experimental bent and an interest in nuclear/radiation issues.
Dosimetry response of Plastic Ionisation Chambers (phs2ps_200)
Supervisor: Dr Paul Sellin
Co-Supervisors:
Type of project: Experiment
Course: BSc in Physics
Academic year: 2008-2009
Project Description:
Plastic Ionisation Chambers (PICs) are a new type of radiation dosimetry detector which combine the dosimetric response of a conventional ion chamber with the small size and high sensitivity of a silicon photodiode. PICs have recently been developed at the University of Surrey, and are attractive as tissue equivalent dosimetry detectors because of their all-plastic construction.
In this project you will carry out a range of calibration measurements on PIC detectors using megavoltage (MV) linac beams at the Royal Surrey County Hospital. It will be of particular interest to measure the time response of PIC devices to the microsecond pulsed linac signal. Students should have an interest in radiation and/or nuclear physics, and be willing to carry out experimental work at the hospital, possibly with some work during after-hours periods.
Tensor Forces in Nuclei (phs3ps_176)
Supervisor: Dr Paul Stevenson
Type of project: Theory/Computational Modelling
Course: BSc in Physics
Academic year: 2008-2009
Project Description:
fig: effect of including tensor term on the splitting of single-particle states as calcuated in a mean-field model. Model GT2 includes the tensor force and agrees with the experimental data much better than model D1S which does not include it. Figure from [2]
Many of the properties of atomic nuclei can be described by the Nuclear Shell Model, in which nucleons occupy orbitals much like in atoms, though with somewhat different properties. In its original formulation, these orbitals occurred at fixed energies, no matter what the nucleus, but it has been found recently that for “exotic” nuclei (those with unusual combinations of neutron number and proton number) the levels can rearrange [1].
One mechanism for causing the level change is the tensor force. In this project you will find out how the tensor force causes an interaction between nuclear levels, and perform calculations to see how the structure of nuclei changes far away from the familiar region of stable and nearly-stable nuclei.
No programming will be involved, but the calculations will be computer based, using existing programs. You should be taking 3NSR in the Autumn semester to take this project.
[1] http://www.nature.com/physics/highlights/7045-2.html
[2] Journal of Physics: Conference Series 49 (2006) 41–42
Darwin meets Schrödinger (phs3ps_185)
Supervisor: Dr Paul Stevenson
Type of project: Theory/Computational Modelling
Course: BSc in Physics
Academic year: 2008-2009
Project Description:
Genetic Algorithms borrow ideas from natural selection to solve optimisation problems in various areas of science. One possible use is to solve equations, either by using the information in the simulated genes to encode directly the value of the solution function at various points, or to encode parameters in a trial function.
In this project, you will use genetic algorhithms to solve the Schrödinger equation for simple systems (oscillator, square well etc...) and evaluate how well it works both in directly representing the solution function and in representing the parameters in a trial wavefunction.
This is a computational project which will require a good standard of programming ability, along with a good grasp of quantum mechanics and the solution of differential equations by 'normal' means.
Some previous work along these lines can be found in Saha et al., Physics Letters A 291 (2001) 397-406.
Nuclear fusion reaction dynamics (phs1jt_071)
Supervisor: Professor Jeff Tostevin
Type of project: Theory/Computational Modelling
Course: BSc in Physics
Academic year: 2008-2009
Project Description:
The attractive strong nuclear forces, combined with the repulsive Coulomb interaction between nuclei, produce a potential (Coulomb) barrier. When two nuclei collide with a relative kinetic energy near to the height of this barrier then they can fuse (i) by passing over the barrier or, (ii) at lower energy, by quantum mechanical tunelling through the barrier. The extents to which such tunelling can take place at energies just below the height of the barrier is very sensitive indeed to its width - and hence to the detailed shape of the nuclear potential as the two nuclear surfaces approach each other.
This project will investigate (a) the sensitivity of the fusion reaction cross sections to the assumed geometry of the surface of the nuclear potentials and (b) to which radii the experimental data are most sensitive as a function of the collision energy, by applying a perturbation to the nuclear potentials.
The project will involve solution of the appropriate Schrödinger equation in the presence of an arbitrary nuclear plus Coulomb potential well and will therefore require both analysis and computational work,
References:
[1] M. Dasgupta, et al., Annu. Rev. Nucl. Part. Sci. 48, (1998) 401.
[2] M. Beckerman, Rep. Prog. Phys. 51, (1988) 1047.
Scattering with quantum decoherence (phs1jt_214)
Supervisor: Professor Jeff Tostevin
Type of project: Theory/Computational Modelling
Course: BSc in Physics
Academic year: 2008-2009
Project Description:
In quantum mechanical elastic scattering, treatment of the excitation of the objects being scattered is often approximated by including an imaginary part in their interaction potential, U(r)=V(r)+iW(r) [1]. This introduces an absorption (or a loss of flux from the wave function describing their relative motion). An alternative quantum formulation [2] treats such excitations as due to irreversible interactions between the scattering systems with numerous (very
complicated) states, thought of as an external environment, and that leads to quantum decoherence.
This project involves some formalism but is largely numerical in nature. It will involve writing a code for the time-evolution of the scattering, treated using a wave packet description, and comparing this with Schrodinger predictions that use the imaginary potential approximation. Confidence in programming and a good knowledge of undergraduate quantum mechanics are necessary.
1. e.g. D.F. Jackson, Nuclear Reactions (Methuen, London, 1970).
2. see e.g. http://arxiv.org/PS_cache/arxiv/pdf/0809/0809.4403v1.pdf
