tailieunhanh - Báo cáo hóa học: " Ultra-steep side facets in multi-faceted SiGe/Si(001) Stranski-Krastanow islands"

Tuyển tập báo cáo các nghiên cứu khoa học quốc tế ngành hóa học dành cho các bạn yêu hóa học tham khảo đề tài: Ultra-steep side facets in multi-faceted SiGe/Si(001) Stranski-Krastanow islands | Brehm et al. Nanoscale Research Letters 2011 6 70 http content 6 1 70 o Nanoscale Research Letters a SpringerOpen Journal NANO EXPRESS Open Access Ultra-steep side facets in multi-faceted SiGe Si 001 Stranski-Krastanow islands Moritz Brehm Herbert Lichtenberger Thomas Fromherz Gunther Springholz Abstract For the prototypical Ge Si 001 system we show that at high growth temperature a new type of Stranski-Krastanow islands is formed with side facets steeper than 111 and high aspect ratio. Nano-goniometric analysis of the island shapes reveals the presence of six new facet groups in addition to those previously found for dome or barn-shaped islands. Due to the highly multi-faceted island shape and high aspect ratio the new island types are named cupola islands and their steepest 12 5 3 side facet is inclined by 68 to the substrate surface. Assessing the relative stability of the new facets from surface area analysis we find that their stability is similar to that of 113 and 15 3 23 facets of dome islands. The comparison of the different island shapes shows that they form a hierarchical class of geometrical structures in which the lower aspect ratio islands of barns domes and pyramids are directly derived from the cupola islands by successive truncation of the pedestal bases without facet rearrangements. The results underline the key role of surface faceting in the process of island formation which is as crucial for understanding the island s growth evolution as it is important for device applications. Introduction SiGe islands grown on Si 001 substrates exhibit a large variety of shapes that strongly depend on the Ge growth temperature and thus the thermal energy provided to the system 1 . For very low growth temperatures of TGe 400 C atom surface diffusivity is low . Ge atoms are incorporated before they can form three-dimensional 3D island clusters and the elastic energy stored in the 2D film is relaxed by misfit dislocation formation 2 .