PEAK PROFILES IN SUPERSATURATED SOLID SOLUTIONSlocated in the region 3 < q < 10. Therefore, the presence of this feature in observed peak profiles, resulting from samples where a demixing process has probably occurred, will make the use of the aforesaid analytical expression quite advantageous. From a numerical point of view, in fact, the use of (19) is only slightly more complicated than that of pseudo-Voigt functions. Besides, with 8 = 8LSW, it involves only one parameter, Do or equivalently De. This result is interesting for three reasons: (a) it makes it possible to test whether the conditions underlying the LSW theory are met or not, directly using WAXS results; (b) one could use SAXS experimental results for testing the applicability of the LSW model. In the affirmative case, one knows the ideal WAXS profiles. Thus any deviation ought to be ascribed to disorder effects; (c) with 8 as a free parameter, one has another simple expression for fitting peak profiles. If it turns out that the overall agreement is better than that obtained by using Voigt functions, one would find a v.f.w.d, skewed in a direction opposite to the ones so far observed.Financial support from the Italian Ministry of University and Scientific Research through 40% funds is acknowledged.References BENEDE'I-FI, A., CICCARIELLO, S. & FAGHERAZZI, G. (1988 AbstractA method is described for the least-squares refinement of the atomic parameters of the ordered part of a crystal structure in the presence of disordered solvent areas. Potential solvent regions are identified automatically. The contribution of the observed contents to the total structure factor is calculated via a discrete Fourier transformation, and incorporated in a further least-squares refinement of the ordered part of the structure. The procedure is iterated a few times to convergence. It is found that this mixed discreteatom and continuous solvent-area model refinement approach greatly improves the quality of discrete * Author to whom correspondence should be addressed.0108-7673/90/030194-08503.00 atomic parameters, i.e. the geometry and the e.s.d.'s. An electron count over the solvent region in the final difference electron-density map provides a convenient estimate for the number of solvent molecules present in the unit cell. The application of the method to four structures is described.

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The growth of III-V semiconductors on silicon would allow the integration of their superior (opto-)electronic properties with silicon technology. But fundamental issues such as lattice and thermal expansion mismatch and the formation of antiphase domains have prevented the epitaxial integration of III-V with group IV semiconductors. Here we demonstrate the principle of epitaxial growth of III-V nanowires on a group IV substrate. We have grown InP nanowires on germanium substrates by a vapour-liquid-solid method. Although the crystal lattice mismatch is large (3.7%), the as-grown wires are monocrystalline and virtually free of dislocations. X-ray diffraction unambiguously demonstrates the heteroepitaxial growth of the nanowires. In addition, we show that a low-resistance electrical contact can be obtained between the wires and the substrate.

It is shown that thin layers of palladium coated magnesium lanthanide alloys reversibly go through an optical transition by variation of the hydrogen concentration, just as has recently been shown for pure lanthanides. With these layers optical switches can be constructed that exhibit three different optical states: a color-neutral transparent state at high hydrogen concentration, a nontransparent dark absorbing state at intermediate hydrogen pressures, and a highly reflective metallic state at low hydrogen pressures. The ratio in transmission between the transparent state and the reflecting state is more than 1000.