The epitaxial growth and structure of metal overlayers on oriented substrates studied by surface x-ray diffraction.

摘要

The growth mode and structure of metal overlayers, stabilised by molecular beam epitaxy, on oriented semiconductor and metal substrates, was investigated using surface x-ray diffraction and synchrotron radiation. The growth of the metastable fee phase of Fe on Cu(001) at 300 K followed a layer- by-layer mode with limited atomic intermixing of Fe and Cu at the overlayer-substrate interface. Relaxation to the bulk bcc Fe structure occurred at a critical coverage dependent on the growth conditions. Fe deposition at higher substrate temperatures was characterised by strong Fe-Cu intermixing giving poor layer development. The growth was diffusion limited at low temperature. The vertical morphology of clean Cu(00l) and adsorbate-covered surfaces at specific Fe coverages was determined from kinematical analysis of intensity measurements perpendicular to the surface and showed changes in the surface interlayer spacing with film thickness. The metastable bcc phase of Co grown on GaAs(001) evolved in a predominantly three-dimensional manner with significant disruption of the semiconductor substrate, causing inclusion of As and Ga into the growing metal film. The structure of the Co film, determined from x-ray specular reflectivity measurements, was consistent with bcc Co. The behaviour of Fe deposited on GaAs(001) was similar, although the overlayer formation was better ordered. In deposited on the Si(001)2x1 surface at substrate temperatures between 300 to 623 K exhibited a Stranski-Krastanov growth mode, that is the formation of one or two atomic monolayers (ML), followed by three-dimensional island formation. The metal induced a series of coverage and temperature dependent surface reconstructions. Deposition of In at 300 K caused only minimal substrate disruption, whereas In and Ga interacted strongly with the dimerised Si(001)2x1 surface at a substrate temperature of 373 K. During formation of the Si(001)2x1-In surface reconstruction the dimerised Si structure was partly destroyed and replaced by In dimers.