International audienceWe evidence the influence of the quality of the starting Si surface on the III-V/Si interface abruptness and on the formation of defects during the growth of III-V/Si heterogeneous crystal, using high resolution transmission electron microscopy and scanning transmission electron microscopy. GaP layers were grown by molecular beam epitaxy on vicinal Si (001). The strong effect of the Si substrate chemical preparation is first demonstrated by studying structural properties of both Si homoepitaxial layer and GaP/Si heterostructure. It is then shown that choosing adequate chemical preparation conditions and subsequent III-V regrowth conditions enables the quasi-suppression of micro-twins in the epilayer. Finally, the abruptness of GaP/Si interface is found to be very sensitive to the Si chemical preparation and is improved by the use of a bistepped Si buffer prior to III-V overgrowth
The molecular weights of a series of unfractionated polyvinyl acetates of low degrees of polymerization have been measured by determining the lowering of the vapor pressure of their solutions. An approsimate ~nolecular-weight range of 5000-40,000 was examined. While most of the determinations were made in berrze~le solutions a t 55O C., other solvents and temperatures were used. Anomalous results were obtained with one sample of fractionated material.
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