On diamond-hexagonal germanium
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Diamond-hexagonal (dh) Ge has been produced by Vickers micro-indentation of a Ge single crystal and investigated by high resolution transmission electron microscopy (HREM). The results are consistent with the mechanisms that have been proposed earlier for the generation of dh Si. The hexagonal phase of these elemental semiconductors may be produced by two related mechanisms: (a) secondary twinning or (b) the intersection of two twins. The hexagonal germanium produced by both of these mechanisms has been observed and is presented in the present paper.
I. INTRODUCTION The generation of hexagonal phase of Si during high temperature indentation of (diamond cubic) Si was first noted by Eremenko and Nikitenko.1 This was confirmed by Tan et al.2 who repeated the experiments of Eremenko and Nikitenko.1 A more extensive investigation of hot indentations in Si, and the generation of hexagonal Si, was made later.3"9 In the latter work, a mechanism was proposed for the generation of the dh structure where it was shown that this phase forms by a martensitic transformation of the diamond cubic (dc) lattice. The transformation was one way of accommodating the strain that is produced in the region of twin intersections. More recently, Cerva has studied dh Si in polycrystalline silicon deposited by low pressure chemical vapor deposition,10 and Wegscheider et al.n have proposed an elegant dislocation model for twin intersections and the formation of hexagonal phase. In Refs. 3 - 9 , the requirements for the phase transformation were proposed to be intermediate temperatures where twinning is a prevalent mode of deformation in semiconducting materials and the appropriate stress conditions. Thus, in intrinsic Si, the indentation temperatures at which the phase transition occurred were found to be in the range of 400-700 °C. In the present work, Ge has been indented at temperatures of 330 °C and 360 °C and bands of the dh material found to be produced. In addition, dh Ge was observed at the intersection of twins with different habit planes. II. EXPERIMENTAL Disks 3 mm in diameter with a (110) normal were cut from an ingot of p-type Ge single crystal. The disks were polished to a thickness of 170 ^m with the final polishing done on a 1 fj,m diamond paste. Indentations were performed under vacuum (~10~5 Torr) in a Nikon High-Temperature Microhardness Tester (Model QM, Nikon Inc., Garden City, NJ), and 10 x 10 arrays of 1406 http://journals.cambridge.org
J. Mater. Res., Vol. 7, No. 6, Jun 1992
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indents were made on Ge disks heated to 330 °C and 360 °C, respectively, using a load of 50 g. Subsequently, the disks were polished to a thickness of 30 /im from the back side (i.e., the side opposite to the indentations) and ion beam milled at 4 kV to electron transparency. The ion milling was also carried out from the back side, although, at the final stages of the thinning, after the appearance of the first perforations, the milling was carried out for 2 h from both sides at a reduced voltage of 2 kV in order to clean
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