Showing papers by "Tolek Tyliszczak published in 1990"

Near‐edge electron energy loss fine structure: Core excitation of chemisorbed molecules in the laboratory

Abstract: Reflection near‐edge electron energy‐loss fine structure (NEELFS) has been used to study C 1s and N 1s core excitation spectra of pyridine chemisorbed on Ag(100) and Ag(111) surfaces at submonolayer and monolayer coverages. The N 1s spectra of pyridine on both Ag surfaces show dramatic changes with exposures between 1 and 5 L, which correspond to coverages in the submonolayer region. The spectral changes track a shift in the average orientation of the pyridine molecules from a small to a large tilt angle relative to the surface. The NEELFS spectra of pyridine on Ag(111) were found to be similar to the corresponding near edge x‐ray absorption fine structure (NEXAFS) spectra. These results demonstrate that NEELFS spectra recorded by small‐angle reflection electron‐energy‐loss (EELS) are sensitive to molecular orientation. With improved large‐angle performance, the angular dependence of NEELFS should allow experimental determination of molecular orientation in a manner analogous to polarization‐dependent NEXAFS.

X‐ray absorption of As low‐energy ion implanted into Si(100) grown by molecular‐beam epitaxy

Abstract: Information about the local environment of dopants in semiconductor materials is required to understand and help optimize the electrical activity in highly doped samples. The near‐edge (XANES) and extended x‐ray absorption fine structure (EXAFS) components of x‐ray absorption spectra provide detailed information on local geometric and electronic structure about selected atoms. Electron yield and fluorescence detection of As K EXAFS and XANES, with sample rotation to eliminate substrate diffraction, have been used to study the As sites in Si(As) epilayers grown by molecular‐beam epitaxy (MBE) and doped in situ by low‐energy As implantation. Marked differences are found in both the near edge and EXAFS signals between samples prepared under low temperature (460 °C) growth/implantation conditions and those prepared under the preferred, higher temperature (700 °C) growth conditions. The EXAFS analysis indicates that As is located primarily in the substitutional site in the optimal (700 °C) sample but that a la...