The University of Surrey hosts the EPSRC national ion beam facility, upgraded in 2002 by the installation of a new 3 MV Tandetron accelerator.
The accelerator is housed within the Surrey Centre for Ion Beam Imaging (SCRIBA), part of the EPSRC funded national ion beam facility. Ion beam research at Surrey specialises in the use of highly focusing ion beams in the form of a nuclear microprobe, which is scanned over the sample surface. This enables spatially-resolved analysis on a micron scale. This process is analogous to the scanning electron microscope except that because an ion beam is so much heavier than an electron beam, it scatters much less when it hits the sample, allowing spatially-resolved analysis of thick or buried layers with high spatial resolution.
Ion Beam Analysis
Ion beam analysis consists of several inter-related techniques that provide information about the distribution of elements within a substance. For example, Rutherford Backscattering Spectrometry (RBS) is used to obtain depth profiles of elements. The technique measures the energy at which high energy (MeV) particles (usually 4He+ ions) are elastically scattered from the atoms in a target material. RBS has been particularly successful in determining the distribution of ionic surfactant molecules (such as sodium dodecyl sulfate) in latex films. In many cases, the surfactant segregates near a surface, and RBS can determine the thickness and composition of the surface layer.
Nuclear reaction analysis (NRA) is another technique used widely at Surrey, which is particularly sensitive for the detection of deuterium. This capability makes NRA ideal for studies of polymer blends in which deuterium is substituted for hydrogen in one type of molecule. NRA can be performed with a scanning microbeam to create a two-dimensional map of deuterium across a surface. The group has used a microbeam in NRA experiments to find out how soap molecules were distributed around and in a single strand of human hair.
Contact Tony Clough for more information about NRA research.
Ion Beam Induced Charge (IBIC)
The new accelerator is also equipped with an Oxford Microbeams nuclear microbeam line, which allows imaging with beam sizes as small as 1 micrometer. Using this facility, Ion Beam Induced Charge (IBIC) imaging has been extensively developed for the study of charge transport and trapping phenomena in bulk semiconductor materials for radiation detector applications.
IBIC is currently carried out using proton and helium beams, with energies of up to 3 MeV and 6 MeV respectively, with a beam spot size of 1 micron. Event rates of the focussed beam on the sample can be reduced as low as 100 Hz, allowing event-by-event acquisition and analysis. Conversely for high flux operation, the maximum beam current is typically 1 microamp. IBIC is used in both regular 'analogue' mode and also in a time resolved 'digital' mode. Time resolved IBIC allows high resolution mapping of drift mobility, charge emission from traps, and other aspects of charge transport dynamics.
Contact Paul Sellin for more information about the IBIC facility.