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Characterisation of the Physical, Chemical and Electronic Properties of Solids on the Nanometre Scale




Positron Annihilation Spectroscopy

The experimental technique is based on the measurement of the Doppler broadening of the 511keV annihilation gamma line as a function of incident positron energy (typically in the range 0.1 - 35keV, probing depths from a few nm up to several m m below a surface). The measured, broadened linewidth is a linear combination of contributions from annihilations at the surface and from all possible subsurface positron states. Reliable data analysis rests upon the accurate description of positron thermalisation and diffusion in the materials studied; our collaboration with theorist colleagues is an important feature of this aspect of the research.

CAD Drawing of new PAS Beam Chamber

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The magnetically confined beam for PAS experiments


The Bath positron group  has two computer-controlled magnetic-transport positron beam systems, one of which is used exclusively for slow positron implantation spectroscopy of subsurface defect structures. Sample temperatures can be controlled between 16 and 1500K.  Past studies in the group have used electrostatic positron beams for rapid whole-wafer mapping or the study of small (mm) samples, positron re-emission spectroscopy and microscopy.

Examples of experimental studies in recent years are:

  • surface modification of polymer films by laser or plasma treatment
  • defects in relaxed SiGe epilayers
  • subsurface electric fields in doped Cz-Si
  • oxygen agglomerates in doped Si epilayers
  • carbon impurities in edge-defined film-fed growth Si (grown for solar cells)
  • defects caused by the implantation of Ge ions into SiC
  • transition region between SiO2 and Si
  • oxygen-related defects in as-grown Cz-Si
  • defect tails in Ge-implanted Si
  • surface damage in laser-irradiated SiC
  • fluorine diffusion, complexing and agglomeration in Si
  • interfaces between nanocrystals of Si and a silica matrix
  • high-resolution depth profiling of vacancies in ion-implanted Si
  • defects in ferroelectric films
  • defects in high dielectric constant films
  • pilot studies on spin-polarised positron beam spectroscopy
  • phase and pore studies of ice films


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