A differential anomalous x-ray scattering technique has been developed for structural studies of disordered and amorphous systems. The results on amorphous GeSe 2 are consistent with the twofold coordination of Se and the fourfold coordination of Ge. The results on amorphous GeSe are consistent with threefold-coordinated models of the structure but not with the fourfold-twofold models.

The radial distribution function (RDF) of liquid water has been determined by x-ray scattering. Using a free-standing water jet and a diffracted beam analyzer to separate the Compton from the elastic scattering experimentally, several significant sources of error have been eliminated in the experiment. These have enabled the collection of quality data out to 19.7 A(-1). Data were collected both at 278 K and at 296 K. Our RDF presents fine structure, particularly, a distinct peak at 3.4 A and a peak split at 4.5 A. These features cannot be interpreted by a simple tetrahedral configuration suggested by continuum models. The uncertainties due to the truncation effects and the choice of scattering factors are found to have little influence on the RDF at intermolecular distances.

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The characteri=tion of nanometer-de phase sepamtion in sputterd amorphous meti-Ge and Fe-Si films has led to the observation of a new microstructure that extends through the meti-insulator transition. The phase separated regions, which are depndent on deposition conditions, are well-correlated and of the order of 1 nm in the growth plane but poorly-correlated and 1.5-2.0 nm in the growth direction. The resdts suggest that fluctuations during film growth play a pivoti role in preventing anticipate columnar structures, probably l~ing to unusti percolation properties.-. Vapor-depositi amorphous meti-germanium and meti-silicon films have been the subject : of extensive study over the past decade. Much of the effort is aired at understanding the meMinsulator (M-I) transition, since many view the films as relatively unique examples of homogeneous materials which undergo a continuous structural transition as the meti concentration is increased:: In contrast, Kortright and Bienenstoekl inferred from their structural study of amorphous MoCGel-c that films with &c4.23 consist of aGe and a Me-modified material that coexist on a size scak of less than 4 nm. These authors were unable to confirm their supposition definitively with small-angle x-ray scattering (SAXS), however, since the observed intensity patterns could arise from either defecm or such phase separation. In addition, they reference an unsuccessful attempt to detect phase separation with transmission electron microscopy. Subsequently, Yoshizumi et al.2 and Mael et d.3 notd that their observation of a metallic low tempemture specific heat in insulating (cd. 1) amorphous MoCGel-Cfilms is consistent with the coexistence proposal. Recently, Rice et d.4 have used anomalous small-angle x-my mttering (ASAXS) to show, definitively that a variety of Ge-nch amorphous meti-germanium films have SAXS patterns that arise _from composition fluctuations or phase separation, rather than from defec~. E1-tron microscopy has been used in the past to observe composition modulations in, for example, the Work supported in part by~epartment of Energy Contract DE-AC03-76S~515.