1,721,081 research outputs found
ELECTRONIC STATES AT THE FERMI-LEVEL OF DOPED C-60
No full textThe density of states of the lowest unoccupied molecular orbital band as a function of K doping was investigated by yield spectroscopy excited with visible and near-uv photons. The Fermi level position was determined at each composition with high precision. The superconducting phase K3Co60 exhibits a clear metallic edge, although the Fermi level is positioned at low state density [N(E(f))=0.8 +/- 0.2 states/eV molecule] past the band maximum. The K4C60 phase is insulating. Correlation effects are necessary to explain the data as a function of doping
ELECTRONIC-STRUCTURE OF A-SI1-XCX-H ALLOYS
No full textThe valence band states of a-Si1-xCx:H have been studied by combining photoemission and Auger spectroscopies. It was possible to establish the relative positions of the onsets and of the maxima of the local electronic-state density at C and Si atoms. It was also found that heteronuclear Si-C bonds are strongly favoured
Spontaneous ordering of self-assembled-Ge island
No full textSelf-assembled quantum dots can be the building blocks of a variety of mesoscopic devices. However, in order to use these structures in large-scale integrated devices, accurate control over their spatial positioning is required. We show here that, by a suitable engineering of the deposition process, it is possible to obtain self-organization resulting in well ordered clusters composed of regularly disposed nano-sized islands. Elastically relaxed Ge islands act as a stressor for a Si layer subsequently deposited (Ge has a 4 % larger lattice cell). This effect results in a modulation of the lattice parameter and strain field in the Si over-layer. In particular the Si lattice in the columnar region on top of the buried islands is tensile strained and will act as preferential nucleation site for the subsequent Ge island growth. We have generated a square array of tensile-strained regions oriented along the [010]-[100] directions on the Si(001) surface exploiting the self-ordering occurring in the growth at 750 degrees C of Ge island multi-layers used as a template. The strain field intensity and shape was modified by changing the thickness of the template Si over-layer: the thicker the overlayer the wider and less intense the strain field in the Si tensile regions. On this template we have grown a Ge island layer at the lower temperature of 600 degrees C. At this growth temperature the islands are much smaller than the lateral extension of the strain field on the Si surface of the template and the nucleation and evolution of several islands inside a single tensile-strained regions is promoted. Upon decreasing the template Si over-layer thickness from 200 to 35 nm the Ge island spatial distribution changes from random to a well-ordered square lattice of multi-island clusters. At intermediate Si over-layer thickness (65 nm), the Ge islands are confined in cluster regions only at the first stage of their evolution (pyramids), while for thinner over-layer (35 nm) islands are assembled in clusters up to the last stage their growth dynamics (relaxed domes). The strong dome-to-dome interaction within a cluster, due to their small mutual separation, has impact also on the dome size by reducing their mean base width of about 35%. (c) 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Ge/Si(100) islands: Growth dynamics versus growth rate
No full textThe effect of the deposition rate on the size, density, and uniformity of Ge islands grown on Si(100) is investigated. Upon changing the growth rate from 4 to 110 ML/min the island density increases by one order of magnitude and the strained dome base decreases from 84 to 55 nm. A narrowing of the island size distribution was also observed. We discuss these experimental findings by taking into account island-island interaction effects. (C) 2003 American Institute of Physics
Island and wetting-layer intermixing in the Ge/Si(001) system upon capping
No full textIn this paper we present an atomic force microscopy and X-ray photoemission spectroscopy study of the composition and shape evolution of self-assembled Ge/Si(001) islands upon capping with Si. We found that the islands undergo a reverse Straski-Krastanov shape evolution, with a progressive Si-enrichment of both the wetting layer and the islands. We demonstrate that the island shape evolves at constant volume with silicon atom incorporation occurring in the absence of lateral diffusion of Ge and Si atoms from the wetting layer to the islands themselves. (C) 2008 Elsevier Ltd. All rights reserved
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