P. L. Cowan

Extended x-ray absorption fine structure and x-ray standing wave study of the clean InP(110) surface relaxation

Through a unique combination of surface sensitive extended x‐ray absorption fine structure (EXAFS) and x‐ray standing waves (XSW), we have determined the pertinent structural parameters of the clean InP(110) surface reconstruction. We find a rotation angle of 27° between the P–In chains, no change of the first neighbor P–In bond length, and a small but measurable, ∼0.1 A, expansion of the average P–P second neighbor distance. The general application of the EXAFS and XSW techniques to the study of clean surfaces will be discussed.

Adatom location on the Si(111) 7×7 and Si(111) √3×√3–In surfaces by the x‐ray standing wave and photoemission techniques

The x‐ray standing wave technique has been used to determine the adatom positions on the Si(111) 7×7 and Si(111) √3×√3–In surfaces. By monitoring the intensity of the surface sensitive Si 1s photopeak as a function of photon energy around the Si(111) Bragg backreflection condition, we determine the Si adatoms of the clean 7×7 surface to reside 1.69±0.1 A above the extrapolated Si(111) bulk plane. In contrast, the In adatoms on the 1/3 monolayer √3×√3–In surface are found to remove the Si displacements and lie at a position of 2.11±0.05 A. High‐resolution Si 2p core‐level measurements support the T4 geometry for the In adatom location.

Determination of the geometrical configuration of Bi on GaAs (110) by x‐ray standing wave triangulation

Triangulation from x‐ray standing wave applied to three Bragg planes, together with symmetry considerations, have established the geometrical structure of epitaxial Bi overlayers on GaAs (110). Our results are consistent with the epitaxial continued layer structure model. Our analysis is based on prior experimental results that indicate two equally populated Bi sites.

X‐ray standing wave study of the Sb/GaAs(110) interface structure*

The x‐ray standing wave technique has been used to determine the geometric structure of the monolayer Sb/GaAs(110) interface. Using the backreflection diffraction geometry, we find the average perpendicular distance of Sb atoms from the (220), (400), and (111) diffracting planes to be 2.27±0.05, 1.60±0.05, and 3.00±0.1 A, respectively. On the basis of these data, the atomic coordinates of the overlayer have been quantitatively established. The results are in agreement with theoretical calculations for the epitaxial continued layer structure and inconsistent with other models of zigzag chains.

Performance of InSb/KDP monochromator crystal pair

Abstract We report on the performance of an InSb/KDP monochromator mismatched crystal pair in use on beamline X24A at the National Synchrotron Light Source. This crystal pair provides extremely high spectral resolving power and throughput in the photon energy range 1750 to 2100 eV, which is below the physical limit of Si(111). By measuring the back-reflection from a Si(111) single crystal, we determine the resolution of the mismatched pair to be 0.40±0.05 eV at 1977 eV. The first Si 1s absorption spectrum (1840 eV) recorded with resolution better than the core-hole lifetime is also reported.

Geometrical structure of the Bi/GaP (110) interface: An x‐ray standing wave triangulation study of a nonideal system

The locally ordered structure formed by one monolayer of Bi on GaP (110) is studied by x‐ray standing wave triangulation applied to three Bragg planes. This system has a larger lattice mismatch than other V/III–V interfaces (e.g., Sb/GaAs, Sb/InP, and Bi/InP), and does not grow epitaxially as those other systems. Prior scanning tunneling microscopy studies of the Bi/GaP interface show that Bi grows in chains along the (110) direction interrupted by vacancies. The large difference in the atomic radii induces the formation of vacancies to allow relaxation. Nevertheless, our results indicate that the interface structure resembles the epitaxial continued layer structure, as in the better matched systems.