Knoop hardness anisotropy on {001} faces of germanium and gallium arsenide
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M. Endo Shinshu University, Nagano-shi 380, Japan
T. Enoki Institute for Molecular Science, Okazaki 444, Japan (Received 5 August 1985; accepted 31 October 1985) The in-plane and c-axis structure of K H , -GIC's and KD,-GIC's is studied using transmission electron microscopy (TEM) and x-ray diffraction as a function of intercalation temperature and time. With the TEM, two commensurate in-plane phases are found to coexist in these compounds with relative concentrations depending on intercalation conditions. When the direct intercalation method is used, the first step of intercalation is the formation of a stage n potassium-GIC and the final compound is a stage n KH^-GIC (or K D , - G I C ) . Highresolution (00/) lattice images show direct evidence for intermediate phases in the intercalation process. These intermediate phases are hydrogen (deuterium) deficient and are found at the boundary between pure potassium regions and regions with high hydrogen (deuterium) content. A comparison of the structure for the two methods of intercalation of KH is also presented. I. INTRODUCTION High-resolution transmission electron microscopy (TEM) provides information about the structure of materials at a microscopic level that cannot be obtained by other methods such as x-ray diffraction, Raman scattering spectroscopy, neutron scattering, etc. In this work we apply the TEM technique to study the structure and process of intercalation of KH and KD into graphite. Complementary x-ray measurements are also reported. Graphite intercalation compounds (GIC's) are prepared by the insertion of layers of foreign species between the graphite layers. In these compounds, n (the stage index) graphite layers separate two neighboring intercalate layers.1 In addition to the superlattice structure perpendicular to the layer planes, some of the intercalants form in-plane superlattices that are commensurate with the graphite lattice. Often several phases are found to coexist in the same sample. In general, the method used to synthesize GIC's depends on the intercalant and on the desired stage. Synthesis of KH X -GIC's or KD, -GIC's can be achieved by direct intercalation2 of KH (KD) or by chemical absorption3 of hydrogen (deuterium) intopotassium-GIC's. However, stage 1 KH X -(KD > ,)-GIC's have only been prepared by the direct intercalation of KH (KD). For the stage 2 compound which can be prepared by either technique, the stoichiometry of the compound depends on the intercalation process, with a higher hydrogen (deuterium) uptake for the direct intercalation2 ofKH x ( K D , ) [ X ( J 0 < 0 . 8 ] than for the a>
Present address: General Motors Research Lab, Warren, Michigan 48090-9055.
J. Mater. Res. 1 (1), Jan/Feb 1986
http://journals.cambridge.org
chemical absorption4 of hydrogen (deuterium) into stage 1 potassium-GIC [;t(j0
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