| A positron microscope has been constructed and is nearing the conclusion of its assembly and testing. The instrument is designed to perform positron and electron microscopy in both scanning and magnifying modes. In scanning mode, a small beam of particles is rastered across the target and the amplitude of a positron or electron related signal is recorded as a function of position. For positrons this signal may come from Doppler Broadening Spectroscopy, Reemitted Positron Spectroscopy or Positron Annihilation Lifetime Spectroscopy. For electrons this signal may come from the number of secondary electrons or Auger Electron Spectroscopy. In magnifying mode an incident beam of particles is directed onto the target and emitted particles, either secondary electrons or reemitted positrons, are magnified to form an image. As a positron microscope the instrument will primarily operate in magnifying mode, as a positron reemission microscope. As an electron microscope the instrument will be able to operate in both magnifying and scanning modes.;Depth-profiled Doppler Broadening Spectroscopy studies using a non-microscopic low-energy positron beam have also been performed on a series of samples to ascertain the applicability of positron spectroscopies and/or microscopy to their study. All samples have sub-micron film and/or feature size and thus are only susceptible to positron study with low-energy beams. Several stoichiometries and crystallinities of chalcogenide thin films (which can be optically reversibly switched between crystalline states) were studied and a correlation was found to exist between the amorphous/FCC S-parameter difference and the amorphous/FCC switching time. Amorphous silicon films were studied in an attempt to observe the well-established Staebler-Wronski effect as well as the more controversial photodilatation effect. However, DBS was not able to detect either effect. The passive oxide films on titanium and aluminum were studied in an attempt to verify the Point Defect Model, a detailed, but as yet microscopically unconfirmed, theory of the corrosive breakdown of passive films. DBS results supportive of the PDM were observed. Graphitic carbon fibers were also studied and DBS indicated the presence of a 200 nm thick outer fiber skin possibly characterized by a high degree of graphitic crystallite alignment. |
