B. A. Karlin

Design and performance of the Advanced Light Source double‐crystal monochromator

A new ‘‘Cowan type’’ double‐crystal monochromator, based on the boomerang design used at National Synchrotron Light Source (NSLS) beamline X‐24A, has been developed for beamline 9.3.1 at the Advanced Light Source (ALS), a windowless ultrahigh vacuum beamline covering the 1–6 keV photon‐energy range. Beamline 9.3.1 is designed to simultaneously achieve the goals of high energy resolution, high flux, and high brightness at the sample. The mechanical design of the monochromator has been simplified, and recent developments in technology have been included. Measured mechanical precision of the monochromator shows significant improvement over existing designs. In tests with x‐rays at NSLS beamline X‐23A2, maximum deviations in the intensity of monochromatic light were just 7% during scans of several hundred eV in the vicinity of the Cr K edge (6 keV) with the monochromator operating without intensity feedback. Such precision is essential because of the high brightness of the ALS radiation and the overall length...

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.

X‐ray, soft x‐ray, and VUV beam position monitor

An x‐ray beam position monitor has been developed and is currently operational at the NIST beam line X‐24A of the National Synchrotron Light Source. It was developed to accurately measure the vertical position of the synchrotron beam and to allow precise positioning of beam line optics. It is an area‐type monitor positioned 5.6 m from the tangent point and precedes all beam line instrumentation. Vertical beam position is given by the differential photoemission current from two grids mounted on a Macor frame. The monitor also senses the total photon beam flux.

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.

Synchrotron x‐ray standing‐wave study of Sb on GaAs(110) and InP(110)

The soft x‐ray standing‐wave technique has been used to study ordered monolayers of Sb on GaAs(110) and InP(110). Using the back‐reflection diffraction geometry from (220) planes, we determine the perpendicular distances of Sb atoms to the substrate and compare these with theoretical calculations and elastic low‐energy electron diffraction determinations. The various models of Sb chemisorption are evaluated on the basis of our data.

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.

Design and performance of the ALS double-crystal monochromator

A new ``Cowan type`` double-crystal monochromator, based on the boomerang design used at NSLS beamline X-24A, has been developed for beamline 9.3.1 at the ALS, a windowless UHV beamline covering the 1-6 keV photon-energy range. Beamline 9.3.1 is designed to simultaneously achieve the goals of high energy resolution, high flux, and high brightness at the sample. The mechanical design has been simplified, and recent developments in technology have been included. Measured mechanical precision of the monochromator shows significant improvement over existing designs. In tests with x-rays at NSLS beamline X-A, maximum deviations in the intensity of monochromatic light were just 7% during scans of several hundred eV in the vicinity of the Cr K edge (6 keV) with the monochromator operating without intensity feedback. Such precision is essential because of the high brightness of the ALS radiation and the overall length of beamline 9.3.1 (26 m).