Hexagotnal Silicon: A New Hrem Study
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HEXAGOtNAL SILICON: A NEW HREM STUDY P. Pirouz, J. Yang, F. Ernst, and H.-J. K51ler, Department of Materials Science and Engineering, Case Western Reserve University, Cleveland, OH 44106. ABSTRACT A new high resolution electron microscopy investigation of indentationinduced hexagonal silicon has been carried out using the JEOL 4000EX The better resolution of the microscope enables one to electron microscope. extract more structural information about this intriguing phase and its interface with the cubic phase. A new structural model for the cubic/hexagonal interface is presented. Image simlations are carried out over a wide range of thickness and defocus for the new model and also a previous model due to Tan et al. INTRODUCTION Hexagonal silicon has now been observed using a number of experimental techniques: high temperature indentation [1-3], ion-implantation [2,4-7], Additionally, Bourret [9] has and low temperature compression (8]. suggested that the Ribbon-like defects (RLDs) in annealed Czochralski silicon are thin bands of hexagonal silicon. This has been recently supported by Bender and Vanhellemont [10]. The bonding in hexagonal silicon, as in diamond cubic (dc) silicon, is of the covalent sp3 tetrahedral type. However its space group is P6 /mmc instead of the Fdm3 of dc silicon. Basically the only difference between the two is a change in stacking sequence from the cubic ... ABCABC... to the hexagonal ... ABAB....
Because the bond length does not change,
the c/a
Hence, in analogy with the diamond ratio is ideal and equal to (8/3)1/2. cubic phase, it has been termed "diamond hexagonal" (dh) silicon [11]. Probably what is most intriguing about this phase is its habit plane with dc From a simple change in the Si, ( 5 1 1 }d , and its orientation relationship. 11 ld 11(0001)4h' da 11[1210] h stacking sequence, one expects a orientation relationship. This can be achieved by glide oý 1/6
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