Photoemission studies of adsorbed oxygen and oxide layers

A critical review is given of a new technique, developed during the past several years, for surface crystallography. The technique is based on the observation that X-ray photoelectrons and Auger electrons with kinetic energies of a few hundred electron volts and above exhibit enhanced intensities along internuclear axes, or bond directions, connecting the emitting atom with its nearest and next-nearest neighbor atoms. This affect is a result of forward scattering, or forward focusing, of the outgoing electron wave by the potential of atoms overlying the emitter. As a corollary, atoms present in the top atomic layer do not exhibit such forward-scattering enhancements. Consequently, this effect is an excellent diagnostic of whether or not an atom is in the top layer, and if not, it is an excellent diagnostic of the local structural environment around the emitting atom. As a new probe of short-range order, this technique finds important applications in areas such as the orientation of adsorbed molec...

X-Ray photoelectron and auger electroo forward scattering: A new tool for surface crystallography

The use of position‐sensitive detectors (PSDs) has become common in many spectroscopies. The increased signal provided by the parallel detection of many spectral elements affords increases in sensitivity and/or time resolution. Recently, the use of a PSD to increase the temporal resolution of an electron energy loss (EEL) spectrometer has been demonstrated in our laboratory. This article summarizes the present development of EEL spectrometers and then presents a detailed review of four classes of PSDs in the context of their potential application to EEL spectroscopy (EELS). The four classes considered are (a) discrete channel detectors, (b) coincidence array detectors, (c) charge division detectors, and (d) optical detectors imaging phosphor screens. All four designs, as typically implemented, utilize microchannel plates (MCPs) as spatially imaging electron multipliers. The performance of MCPs is reviewed and the constraints that MCP behavior at the high count rates achievable in EELS places on acceptable...

Position-sensitive detector performance and relevance to time-resolved electron energy loss spectroscopy

Ion bombardment often leads to compositional changes in the surface layers of multicomponent targets. Such changes due to noble gas ion sputtering are discussed for InP and GaAs. The analyses show that the compositional change in InP (i.e., indium enrichment) is mainly due to preferential sputtering. In the case of GaAs. the changes are due to radiation-induced diffusion and segregation effects. Brief mention is made of compositional changes in a few other systems. The discussion on sputter-induced topography development deals mainly with InP because ion bombardment leads to dramatic topographical effects in this material. Ripple development on GaAs is also briefly discussed. Radiation damage has been well researched, and its mechanism and effects usually differ substantially when going from one semiconductor group to another. Bombardment-induced damage is briefly discussed for InP, GaAs, SiC, some II-VI semiconductors, and HgCdTe.

Sputtering of compound semiconductor surfaces. II: Compositional changes and radiation-induced topography and damage

A knowledge of the atomic identities, positions, and bonding mechanisms within the first 3–5 layers of a surface is essential to any quantitative microscopic understanding of surface phenomena. This implies knowing bond directions, bond distances, site symmetries, coordination numbers, and the degree of both short-range and long-range order present in this selvedge region. A number of surface-structure probes have thus been developed in recent years in an attempt to provide this information.1 Each of these methods has certain unique advantages and disadvantages, and they are often complementary to one another.

The Study of Surface Structures by Photoelectron Diffraction and Auger Electron Diffraction

Photoelectron diffraction effects in XPS angular distributions from GaAs(110) and Ge(110) single crystals

Estimation of Surface Crystal Regularity by Utilizing X-Ray Photoelectron Diffraction (XPED) Effects

X-ray photoelectron diffraction (XPED) patterns from: III-V compound mixed crystals (Ga1-xAlxAs AND GaAs1-yPy). Comparison of experiment and single scattering calculations

A position sensitive detector system composed of a channel plate, a vidicon TV camera, and a computer is utilized for multichannel detection of ESCA spectra. It is demonstrated that the system achieves a marked improvement of measurement speed, S/N ratio, and sensitivity. The system also realized an improvement of spatial resolution while retaining energy resolution.

Computer controlled ESCA for nondestructive surface characterization utilizing a TV-type position sensitive detector.

It is known that angle-resolved x-ray photoelectron spectroscopy (ARXPS) provides, in addition to ordinary XPS information, quite new information concerning the crystal regularity of the surface layers. This technique was used to characterize the initial crystal growth of gold films evaporated on GaAs (110) surfaces to a thickness about 5-6A. The angular distribution curve (ADC) of Au 4f photoelectron intensity showed some clear fine structure after the heat treatment for 30 minutes at 350-400°C. Taking the results of chemical state analysis into consideration, it can be concluded that the Au atoms grew epitaxially in an island-like fashion. When the annealing temperature was raised over 450°C, the fine structure of ADC from the Au 4f peak disappeared, implying diffusion of Au atoms into the bulk GaAs crystal. In summary it is shown that ARXPS has quite useful applicability for investigation of the initial crystal growth of very thin films evaporated on semiconductor surfaces.

https://www.jstage.jst.go.jp/article/jsssj1980/1/1/1_1_48/_pdf

Masahiro Kudo

Papers

Photoelectron diffraction effects in XPS angular distributions from GaAs(110) and Ge(110) single crystals

Estimation of Surface Crystal Regularity by Utilizing X-Ray Photoelectron Diffraction (XPED) Effects

X-ray photoelectron diffraction (XPED) patterns from: III-V compound mixed crystals (Ga1-xAlxAs AND GaAs1-yPy). Comparison of experiment and single scattering calculations

Computer controlled ESCA for nondestructive surface characterization utilizing a TV-type position sensitive detector.

Angle-Resolved XPS Studies of the Thin Gold Films Evaporated on GaAs (110) Surfaces