Physics
La Trobe University
Victoria 3086
AUSTRALIA
Tel: +61 3 9479 2622
Fax: +61 3 9479 1552
Email: physics@
latrobe.edu.au

Projects related to the ARC Centre of Excellence for Coherent X-Ray Science are asterisked

A. Coherent X-ray Science*

The diffraction pattern from a non-crystalline sample can be used to obtain information about the structure of that sample. This is particularly useful for x-ray diffraction where the diffraction limit allows extremely small objects (< 1 nm) to be resolved. Under the right conditions the diffraction pattern from a non-crystalline sample can also be inverted to produce a high-resolution image of the sample. Recent demonstrations of the so-called oversampling method using x-rays (Miao, J. Charalambous, P., Kirz, J. and Sayre, D. Nature, 400, 342 (1999) and Miao et al Proc. Nat. Acad. Sci. USA 100, 110 (2003)) have led to a belief that single molecule imaging may be possible. This is the technique upon which the Centre for Coherent X-ray Science is based.

Joint Project with Biochemistry – Contrast from Enhanced Diffraction*

This project will interact with a parallel project within the department of Biochemistry and will use certain cells of research interest, such as malaria parasite infected red blood cells, mammalian cells as well as simpler organisms such as bacterium. Using standard chemical procedures the cell or bacteria will be arrayed with gold particles (or other X-ray dense matter) around the surface of the cell. Additionally, the feasibility of introducing the heavy metal particles inside the cell will be investigated. The samples will be assessed using scanning and transmission electron microscopy. The student from physics will use computational methods to make a numerical model of the cell (both doped and undoped) and the expected diffraction pattern from the cell under x-ray illumination will be generated. This will allow an assessment of whether separate features in cells (with or without doping) can produce resolvable contrast in the resulting diffraction pattern.

This project will require strong computational and analytical skills.

Project – Visible analogue of curved beam diffraction*

This project will undertake a visible wavelength analogue experiment of the x-ray oversampling method – but with a difference. Whereas normally the incident wavefield on the sample is required to be a plane wave, we will perform the experiment under conditions where the wavefield is highly curved. Recent work has speculated that curved wavefields can greatly aid in the reconstruction of the sample information. The aim of this project is to see whether this can be demonstrated.

The project will require experimental skills and involves an optical bench setup using lasers and some optical elements. The data analysis will require some computing ability and will use some existing software.

Project – Astigmatic diffraction*

		Using the oversampling method there are problems with the uniqueness of the sample that is retrieved from the measured diffraction pattern. One type of object is particularly problematic – the optical singularity or vortex. An optical vortex is a state of light where the equi-phase surfaces form a helix that spirals along the direction of propagation of the carrier beam. After reconstruction by the standard oversampling method it is impossible to say whether the vortex is spiraling in a clockwise or anti-clockwise fashion. The aim of this project is to build upon recent work investigating the quality of vortices created using a computer generated hologram to create a vortex at visible wavelengths and then, using the recently proposed method of astigmatic diffraction (K.A.Nugent, A.G.Peele, H.N.Chapman and A.P.Mancuso, “Unique Phase Recovery for Non-Periodic Objects,” Phys. Rev. Lett., 91, 203902 (2003)), attempt to uniquely reconstruct the sense of rotation of that vortex.
Interferogram of a high charge vortex state produced using 6 keV x-rays. The characteristic multiple forks of a vortex

The project will require experimental skills and involves an optical bench setup using lasers and some optical elements. The data analysis will require some computing ability and will use some existing software.

Project – Sample Mounting

We wish to image samples that are < 10 μm in size. Cryogenic cooling will be implemented to reduce damage for biological samples. This project will involve the construction and integration of a dedicated sample mount and manipulation stages. The mount will be incorporated into a vacuum endstation.

This project will require strong experimental and technical skills including computer control of stages and vacuum equipment.

B. Lobster-eye

The lobster-eye telescope is a novel x-ray telescope that will give wide field of view coverage of the x-ray sky (W. C. Priedhorsky, A. G. Peele, and K. A. Nugent, "X-ray all-sky monitor with extraordinary sensitivity," MNRAS 279, 733 (1996)). An on-going project is attempting to model the telescope in its orbiting environment on the International Space Station or on a small satellite.

Project - modelling

In previous work an extensive simulation package (A. G. Peele, H. Lyngsjo, R. M. Crocker, J. Markham, N. Bannister, K. A. Nugent, “Modeling of the Lobster-ISS x-ray telescope in orbit,” in UV and Gamma-Ray Space Telescope Systems, G. Hasinger and M. J. L. Turner Eds, Proc SPIE 5488, 232 – 241 (2004).) has been written which models the orbit of the telescope and generates a synthetic data set that mimics what the lobster-eye telescope will observe in operation. In this project the computer code will be enhanced so that data products corresponding to the current planned configuration for the telescope will be produced. Those products will then be used to design efficient data recovery strategies and to predict the likely sensitivity and resolution of the operational telescope.

This project will require an able programmer with skills in C++ and an ability to design and implement data processing algorithms.

Project – Lobster materials

		The lobster-eye telescope is based around a glass object known as a micro-channel plate (MCP). These MCPs consist of thousands of small square channels arrayed in a regular fashion. The channels are very deep (6 mm – 300 µm) compared to their diameter (200 µm – 10 µm). In the Lobster geometry x-rays reflect off the interior walls of these channels. Just how well they reflect depends (in part) on the chemical composition of the glass. The aim of this project is to look at the chemical composition of the glass on these interior walls. The measurements will be made using surface analytical techniques (XPS, TOF-SIMS) that have been developed in the Centre for Materials and Surface Science. There is a catch! The size of the channels is smaller than the analysis spot size of the XPS instrument so methods will have to be developed (breaking and cleaning channels?) to allow several channels to be analysed at once.
X-ray focus produced by a lobster-eye lens

The project will require strong experimental skills involving working with small (and expensive) objects.

C. X-ray Tomography

In a research grouping led by the Victorian Centre for Advanced Manufacturing and Materials, we have recently been funded by the Victorian State Government to purchase a laboratory-based x-ray tomography system. This system will be commissioned in 2006. It will allow extremely high-resolution 3D images of samples to be produced. In addition the source is sufficiently small that phase contrast methods can be pursued (A. G. Peele, P.J. McMahon, F. DeCarlo, B. B. Dhal, K. A. Nugent, "X-ray phase contrast tomography with a bending magnet source" Rev. Sci. Instrum. 76, 083707 (2005) and P.J.McMahon, A.G.Peele, D.Paterson, K.A.Nugent, A.Snigirev, T.Weitkamp, C.Rau, “X-Ray Tomographic Imaging of the Complex Refractive Index,” Appl. Phys. Lett., 83, 1480-1482 (2003))

Structural Characterisation Projects

In cooperation with the research goals of various partners samples will be characterised using the best imaging techniques for those samples. Sample projects include: Structural characterisation of blood vessels in rats brains and structural characterisation of porous Aluminium samples.

These projects require good experimental skills an ability to present data and to interact with other researchers.

Project – Analysis of synchrotron data

		This project will utilize existing data obtained at the Advanced Photon Source and will investigate the analytical methods necessary to optimize a data set for presentation. The data sets available include metallurgical samples, phase images of test objects such as microspheres and images of rat brains where the goal is to image the blood vessels.
Tomographic reconstruction of a plastic rotor part.

This project will require strong computational skills and a high degree of organization to deal with the large data sets involved.

D. Small Scale Patterning

It is becoming increasingly important to be able to make structures that can interact with micron scale samples and also to manipulate the x-ray wavefields that we use in our imaging work. We have recently been investigating methods in x-ray lithography for construction of extremely tall microstructures (K. D. Vora, B. Y. Shew, E. C. Harvey, J. P. Hayes and A. G. Peele, “Specification of mechanical support structures to prevent SU-8 stiction in high aspect ratio structures,” J. Micromech.. Microeng. 15, 978-983 (2005)). As part of the Centre of Excellence funding we will acquire additional small scale fabrication patterning capability. For instance, by using e-beam lithography we plane to make optical devices that will act as a hologram for x-ray radiation to produce structured wavefields such as vortices. Some example projects are as follows.

Project – Fabrication of a computer generated hologram to create vortices in x-ray wavefields*

A. G. Peele, K. A. Nugent, A. P. Mancuso, D. Paterson, I. McNulty, J. P. Hayes, “X-Ray Vortices: Theory and Experiment,” J. Opt. Soc. Am. A, 21, 1575-1584 (2004)

Project – Fabrication of a computer generated holograms to create structured illumination for lithography

Project – Fabrication of patterned surfaces for array and orientation of proteins

Project – Fabrication and testing of strongly diffracting test samples for coherent diffractive imaging*

All of these projects will require exceptional laboratory skills and a high degree of organisation. The ability to set and follow experimental protocols is essential.