E.D. Crozier

Angular scanning stage for glancing‐incidence surface EXAFS

In this paper a simple and inexpensive angular positioning apparatus is described which can be applied to measurements of x‐ray reflectivity and extended x‐ray absorption fine structure (EXAFS) at glancing angles of incidence. An efficient interactive alignment procedure is discussed and the performance of the device is given.

Application of various XAFS techniques to the investigation of structurally damaged materials

Abstract We have applied several XAFS techniques to study materials which have been structurally modified in a variety of ways. These techniques include conventional absorption and fluorescence methods as well as electron yield at atmospheric pressure, grazing incidence and optical EXAFS. The method used depended upon the sample to be investigated and the information desired. The various samples examined and the approaches used are discussed for natural metamict minerals, Pu doped zirconolite, 50/200 KeV Pb implanted SrTiO3 and Mn containing glass.

Ultrahigh vacuum-compatible fluorescence x-ray absorption fine structure detector

The design and operation of an ultrahigh vacuum (UHV) compatible ionization chamber for fluorescent x-ray detection in the hard-x-ray regime is described. The detector is comprised of two main components: an UHV compatible, bakeable housing and multiple, 90% transparent, nickel wire-mesh internal collectors. The detector has been used successfully to study molecular beam epitaxy prepared metal thin films in situ.

The valence transition in SmSe

Introduction The Sm monochalcogenides, which crystallize in the NaCl crystal structure, undergo pressure-induced mixed valence transitions. These isostructural phase transitions are of first order in SmS and continuous in SmSe and SmTe. It has been suggested’ that these transitions may all be of first order at low enough temperature. Thus we investigated the valence transition at 77K in order to observe a possible sharpening. Another reason for the low-temperature work was the reduction of the temperature-dependent part of the EXAFS DebyeWailer factor in order to observe better a possible structural disorder. For maximum resolution in R-space we measured the Se K-edge EXAFS up to 24 A-1. While previous work2 already indicated an anomaly in the DebyeWaller factor in the region of the phase transition we now try to determine whether this anomaly can be interpreted as being due to a splitting of the nn Se-Sm distance into two Se-Sm distances according to the different ionic radii of the rare earth ion.

X-ray absorption spectrum of compressed copper

Abstract X-ray absorption spectrum of compressed copper is studied using synchrotron radiation. Copper is suggested to be a suitable pressure calibrant for high pressure X-ray absorption experiments.

Extended X-Ray Absorption Fine Structure Studies at High Pressure

It is the purpose of this paper to review the problems and possibilities offered by EXAFS studies of materials at high pressures. This is a new field for which high pressure techniques must be refined. Cell designs and methods of measuring the pressure in situ which we have used are indicated. It will be seen that we are currently concerned with the accuracy in measuring bond lengths as a function of pressure and, learning what EXAFS can tell us about pressure-induced structural or electronic phase changes.

The Pd/Fe Interface in the Epitaxial System Pd/Fe/GaAs(001)‐ 4 × 6

Magnetic properties of thin magnetic films are strongly affected by the nature of the interface between magnetic and non‐magnetic layers. In spintronic devices the extent to which spins are scattered at an interface depends upon interfacial roughness, alloying, and impurities. We present a polarization‐dependent XAFS study of a 1Pd/9Fe/GaAs(001)‐(4×6) structure grown in situ in the MBE facility at the PNC/XOR, APS. To increase the interfacial roughness, the 1ML Pd was grown on the 9 ML Fe without first sputtering and annealing the Fe. An estimate of interfacial roughness, evidence for formation of Pd islands, their height, and the amount of As floating to the Pd surface from the GaAs are given.

Characteristics of the MBE1 End-Station at PNC/XOR

An end‐station for in‐situ characterization of thin films at the PNC/XOR undulator beamline, Sector 20 of the Advanced Photon Source, is detailed. The ability to study films in‐situ on a beamline enables examination of surfaces and interfaces on freshly‐prepared films, without the influence of a capping layer. The MBE1 molecular beam epitaxy system was designed with this in mind. Now in routine operation and available for General Users on a collaborative basis, the primary function of MBE1 is to undertake polarization‐dependent XAFS studies on fresh or stored films, but it also has the capability to do X‐ray Standing Wave and Reflectivity measurements. The characteristics of the MBE1 system — its ranges of motions and detector options — are described in detail, with example data illustrating its functionality.

High pressure x-ray absorption studies of phase transitions

The application of high pressure to a substance generally changes all of its properties to some degree. One of the most striking changes is a pressure-induced phase transition. Here we review how such phase changes reveal themselves in x-ray absorption spectra. The examples given are from our own work at SSRL, the experimental details having been previously reported [1]. The EXAFS-derived bond compression of a standard are used to determine the pressure.

XANES at High-Pressure Phase Transitions

For the past several years our group has been observing the effects of high pressure on x-ray absorption spectra. The EXAFS has been shown to be quite sensitive to pressure due to the changing bond lengths and atom-pair, mean-square displacements [1–3]. We have also reported some of the effects of pressure on the XANES. However, these reports have been mainly directed to the high pressure community [4,5]. Our purpose here is to summarize such effects for those interested in XANES, per se.