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An ultrahigh-vacuum environmental chamber for surface X-ray diffraction on Station 9.4 at the Synchrotron Radiation Source, Daresbury Laboratory, is described. Film growth can be monitored by simultaneously recording the Auger signal and the X-ray intensity at a particular point in reciprocal space. Such in situ measurements are essential for understanding the dynamic processes that occur during adsorption. An example is given in which the specularly reflected X-ray signal is correlated with Auger plots, during growth of Tl on Cu(001). In addition, the diffractometer and chamber combination allow large reconstructions to be investigated as shown by the in-plane structural analysis of the c(4×4) InSb surface. A study of the layer structure of Cr on Ag(001), in which an extended out-of-plane detector assembly was used, is also presented.

The first experimental observation of diffraction from a thin surface layer at a 90 Bragg reflection is reported. A thin (< 1 mm) InGaAs film deposited on a GaAs(800) substrate was studied near the 90 Bragg position. Slight, less than 0.1%, difference in the lattice spacing between the layer and the substrate, has allowed, for the first time, a direct and exclusive observation of the diffraction profile from a thin layer as if it was a ªfree-standingº thin crystal.

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