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Supported Two-Dimensional Metal Clusters
Published in Klaus D. Sattler, st Century Nanoscience – A Handbook, 2020
In previous sections, we focused on the morphology of 2D metal clusters. In the following, we will demonstrate how to use the substrate as a template to control the location and orientation of clusters. Clean surfaces have a tendency to reconstruct, and one of the consequences of surface reconstruction is the formation of a strain-relief network within the top atomic layer. The strain-relief pattern can be used to control the nucleation of clusters. Among the many surfaces with strain-relief patterns, the Au(111) surface is the most extensively studied.
Planar and Nanostructured Semiconductor Junctions
Published in Juan Bisquert, The Physics of Solar Energy Conversion, 2020
In general, a rearrangement of atoms occurs at the semiconductor surface, with respect to the bulk, in order to reduce the total energy of the surface, and this modification is termed surface reconstruction. The reconstruction involves the outward or inward displacement of surface atoms, which leads to the change of the surface dipole layer accompanied by a change of the effective affinity, as discussed in Chapter 2. These effects may produce a considerable variation of the electron affinity up to ≥1 eV. For example, for metal oxides, a metal termination leads to a low and an oxygen termination to a high electron affinity (Klein, 2012). At semiconductor–semiconductor interfaces, the interface reconstruction will be different than the surface reconstruction. In these cases a dipole occurs at the interface and the electron affinity rule does not hold true. Measurements of XPS and UPS are necessary to obtain an accurate energy diagram of the heterojunction.
Semiconductor Materials
Published in Jerry C. Whitaker, Microelectronics, 2018
If one imagines slicing a single crystal along a crystallographic plane, a very high density of atomic bonds is broken between the two halves. Such dangling bonds would represent the surface of the crystal, if the crystal structure extended fully to the surface. The atomic lattice and broken bonds implied by the slicing, however, do not represent a minimum energy state for the surface. As a result, there is a reordering of bonds and atomic sites at the surface to achieve a minimum energy structure. The process is called surface reconstruction and leads to a substantially different lattice structure at the surface. This surface reconstruction will be highly sensitive to a variety of conditions, making the surface structure in real semiconductor crystals quite complex. Particularly important are any surface layers (e.g., the native oxide on Si semiconductors) that can incorporate atoms different from the semiconductor’s basis atoms. The importance of surfaces is clearly seen in Si MOS transistors, where surface interfaces with low defect densities are now readily achieved. The reconstructed surface can significantly impact electrical properties of several devices. For example, mobilities of carriers moving in the surface region can be substantially reduced compared to bulk mobilities. In addition, MOS devices are sensitive to fixed charge and trap sites that can moderate the voltage appearing at the semiconductor surface relative to the applied gate voltage.
Chemical modification of group IV graphene analogs
Published in Science and Technology of Advanced Materials, 2018
Hideyuki Nakano, Hiroyuki Tetsuka, Michelle J. S. Spencer, Tetsuya Morishita
Morishita et al. carried out a series of DFT-MD calculations to investigate the stability of BHS at 300 K [138]. They found that either the AA or AB stacking structure is transformed to a bilayer structure exhibiting novel surface reconstructions. It is well known that the cleaved Si(1 1 1) surface reconstructs at finite temperature in vacuum, creating a 7 × 7 or 2 × 1 surface structure. Such surface reconstruction is triggered by the driving force to reduce the number of dangling bonds on the surface, which also applies to BHS. Thus, BHS can be easily transformed to other bilayer structures as demonstrated in the DFT-MD simulations.