ARC Centre of Excellence for Antimatter and Matter Studies (CAMS) Sergei Samarin1. Positron studies of thin films and surfaces. The positron studies are complementary to those using electron beams as probes for which UWA has an international facility comprising spin-polarised electron-pair (e,2e) spectroscopy in addition to most single electron spectroscopies, such as SEM, LEED, Auger, EELS, XPS, UPS, SPLEED as well as an optical ellipsometer. The combined use of these techniques enables their overlapping and complementary information to establish a better understanding of many surface phenomena. Specific projects include (i) characterizing the emission of secondary electron production, (ii) positron re-emission as a function of surface properties, (iii) design and construction of an electrostatic positron beam facility, (iv) positron annihilation lifetime spectroscopy and (v) positron detection of cracks, voids etc in materials. Project (iv) and (v) can involve interaction with ANSTO if you wish. Our positron experiments are part of the ARC Centre of Excellence for Antimatter and Matter Studies (CAMS) with colleagues at the ANU. See http://atom.uwa.edu.au Extensive collaboration exists with international partners in USA, UK, Europe and Japan on leading edge science and technology. See http://www.positron.edu.au/ 2. Electronic structure and magnetic properties of solid surfaces and thin films. Many solid-state (semiconductor) devices are based on a contact (interface) between two materials. The knowledge of the electronic and structural properties of solid surfaces is very important for the fabrication of devices. We will study these properties of metal single crystals (W, Cu, Fe) and semiconductors (Si, GaAs) and thin films deposited on surfaces. Experimental conditions assume ultra-high vacuum (10^(-11) Torr). The techniques to be applied include: a) Two-electron coincidence spectroscopy (electronic structure); b) Low Energy Electron Diffraction (crystal surface structure, film growth); c) Auger-electron Spectroscopy (element-specific analysis of the surface); d) Surface Magneto-optic Kerr Effect (magnetic properties). 3. Electron impact excitation and ionisation of atoms, with astronomical applications. Atomic states, with linear combinations of bound and/or continuum states of even or odd spin multiplicity, and formed in electron impact scattering processes, will be observed through their spatial and/or angular correlations. We want to find which individual components of a linear superposition of single electron configuration states with different LS mixing coefficients (for example) can be preferentially excited. The atoms may be free or confined in macromolecules. Significant questions are, for example: - How do the observable superpositions change with collision process and for what times? - When are the combinations coherent or incoherent? - Will that approach also separate direct, exchange and spin-dependent interactions? The answers may indicate how atomic structures can be built. Experiments will describe the energy, angular and polarisation correlations which reflect the characteristic structure and dynamic properties, how those properties depend on the filling of subshells, configuration interaction, multipole moments and the effective angular momentum coupling between incident, target and scattered electrons. 4. Techniques of atomic and surface physics. - Ultra high vacuum (10^(-11) Torr). Turbo and ion pumps. Electron optics, electron energy analysis, time-of-flight electron energy analysers, electron-pair methods, metal vapour beams - Spin-polarised electron production via (laser) photoemission from GaAs crystals using circularly polarised laser. - Surface science methods including LEED, Auger, X-ray techniques, fast (KeV) ion beam methods, ellipsometry, thin magnetic films, adsorbed molecules. - Stokes' parameter (polarization) analysis of photons, liquid crystal polariser and phase retarder, acoustic-opto-tunable wavelength filter. - Positron production and detection. - Single pulse counting (100 MHz), Coincidence techniques. Angular correlation analysis. Position-sensitive-detection (imaging), Multidimensional histogramming techniques. Spectrum pulse height analysis, Computer automation of experiments. 5. Other current activities Dr Vladimir Petrov, from St Petersburg University, is collaborating on studies using our new Mott detector of electron spin on out Scanning Electron Microscope. Dr Debashis, from the Institute of technology, Calcutta, has received a DEST (Australian Dept of Education and Science) Endeavour Research Fellowship to join our surface physics experiments from November 2008. Paul Guagliardo, honours 2006 and now a PhD student, spent 6 weeks at the University of Texas, Arlington during 2007 to acquire new research techniques and experience using positrons. Also Paul sent four weeks during July and August attending the Slow Positron Conference at Orleans, France, the International Conference on Electronic, Atomic Collisions in Freiburg and the Positron Conference in Reading, UK. Expenses were paid by the research group funding. He is now spending several months at ANSTO on PALS (positron annihilation lifetime spectroscopy) of wool fibres and other materials. Peter Wilkie has started a PhD project on positron energy moderation. Alex Semenov will arrive in January 2009 to start PhD studies. 2007 and 2008 have been our best years ever with 14 research papers published in international journals and 12 papers presented at international conferences. |