Auger KLL and Is photoelectron spectra of silicon have been studied from samples of Si delta doped layers in GaAs with very thin capping layers. By tuning the exciting photon energy through the Si K edge resonant Auger spectra were obtained. A comparison of the x-ray absorption spectra (XAS) in the vicinity of the Si K edges with the energy dependence of the resonant Auger spectra indicates that in each material the resonant process involves a narrow state in the GaAs band gap localized at the Si sites. The energy dispersion of the resonant peak sheds light on the nature of these localized states and XAS data around the Si K edge indicates that they are located in the GaAs band gap. The results yield information on the positions and widths of the localized states.

The (2 × 4) reconstruction of the (001) surface of GaAs has been studied using scanning tunnelling microscopy (STM) and spectroscopy. The images, produced at several biases, show coexisting two dimer and three dimer surface unit cell reconstructions. By examining line profiles across the dimers, we find an asymmetry in the two dimer surface unit cell reconstruction which changes with the sample bias. The images of the three dimer surface unit cell reconstruction are also shown to be different at different biases. A spectroscopic spectrum is presented which gives insight into the origin and characteristics of negative and positive bias tunnelling. Our results are compared to theoretical studies of the expected appearance of STM images under different bias conditions and the implications of the findings are discussed.

As-terminated Si surfaces are model semiconductor interface systems with a wide range of technological applications. We have studied As-terminated Si (001) surfaces with scanning tunneling microscopy which reveals that it is possible to produce a well ordered surface. Some characteristic types of defects do occur on this surface, however, which are found to be of particular interest. These include antiphase domain boundaries, step edges, and long, atomically straight trenches running perpendicular to the dimer rows across the surface. The nature and origin of these defects are discussed.

We have generated scanning tunneling microscopy images of the reconstructed GaAs(001) surface using an ab initio pseudopotential method and the Bardeen tansfer Hamiltonian approximation. These images are compared with observed images for different bias voltages. We find that there is a strong correlation between theory and experiment.

Chemical shifts in the core level photoelectron spectra and Auger spectra of atoms provide insight into the nature of the chemical bonding and the local electronic structure. Recent progress has been made in the development of a core potential model for chemical shifts which treats implicitly the effects of electron relaxation, charge transfer, screening and polarisation. Here we present calculated potential model parameters for the elements LiAr. A parameter related to electronegativity is introduced which depends on the charge state and orbital character of the valence electrons of these elements. The physical meanings of the parameters and their trends across the period are discussed.

The interphase between a polyimide and a metal substrate was modeled by depositing phthalic anhydride (PA) onto a gold substrate pretreated with 4-aminophenyldisulfide (APDS) and then curing in a mixture of acetic anhydride and pyridine or triethylamine. Surface-enhanced Raman scattering (SERS) and reflection-absorption infrared spectroscopy (PAIR) were used to characterize the model interphases. It was found that APDS was adsorbed dissociatively onto Au substrates through the sulfur atoms. The average tilt angle for APDS molecules adsorbed onto gold substrates was determined, using RAIR, to be approximately 46 degrees. However, there was no preferred rotational angle of the adsorbed APDS molecules about the long molecular axes. When PA was deposited onto APDS-primed Au substrates, anhydride groups of PA reacted with amino groups of APDS to form amic acids. Curing these thin amic acid films in acetic anhydride catalyzed with pyridine produced mainly isoimide species, while curing in the presence of triethylamine gave imide as the major product. The relative amount of isoimide and imide thus depended strongly on the catalyst used in the chemical curing processes.

The GaAs(111)A-(2 × 2) surface has been examined using scanning tunnelling microscopy (STM), and found to exhibit two phases with the same periodicity. At high surface As concentrations images consistent with an As-trimer structure are seen, which transforms into a Ga-vacancy structure as the excess As desorbs at higher temperatures. Both filled and empty state images of the vacancy structure are of atomic resolution, and reveal a relaxation in the surface bilayer in agreement with predictions.

The molecular structure of interphases formed by curing the polyamic acid of pyromellitic dianhydride (PMDA) and 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (4-BDAF) against silver substrates was determined by surface-enhanced Raman scattering (SERS) and reflection-absorption infrared spectroscopy (RAIR). Bands characteristic of amide, imide, and carboxylate groups were observed in the SERS spectra of the polyamic acid after curing, indicating that curing of the polyamic acid to the polyimide was inhibited by interaction of acid groups with the silver substrate. These conclusions were substantiated by results obtained from RAIR spectra of thin films of the polyamic acid cured against silver substrates. As the thickness of the polymer films decreased, bands characteristic of imide groups and C6H4 rings became weaker and bands characteristic of carboxylate groups appeared. For films having a thickness of approximately 15 angstrom, bands related to the imide groups almost completely disappeared, while those related to the carboxylate groups became relatively strong. A band assigned to the ether COC asymmetric stretching mode was strong regardless of the film thickness. Changes in the RAIR spectra as a function of film thickness were related to chemical interaction between the polyamic acid and the substrate and to preferential orientation of polymer segments near the interface. It was concluded that acid groups in the PMDA moieties formed carboxylate sets with silver ions from the substrate, thus inhibiting curing of the polymer adjacent to the substrate. It was also concluded that the planes of the PMDA moieties were parallel to the surface and that the planes of the carboxylate groups were perpendicular to those of the PMDA moieties and the silver surface. Approximately half of the C6H4 rings in the 4-BDAF moieties were parallel to the surface, but the planes of the COC groups were perpendicular to the surface.

A two-band transfer matrix method has been developed to study tunneling currents in narrow gap and interband tunnel structures. This relatively simple model gives good agreement with recently reported experimental results for InAs/AlSb/InAs/AlSb/InAs double-barrier heterostructures and InAs/AlSb/GaSb/AlSb/InAs resonant interband tunneling devices, and should be useful in the design of new interband tunneling devices.