Enhanced Vibrations at Surfaces with Back-Bonds Nearly Parallel to the Surface

Abstract

It has been discovered that several very different surfaces exhibit a common property:unusually large vibration amplitudes of the outermost atoms, well beyond the enhancement normally expected at typical clean surfaces. These special surfaces are: ice (010) and Si(111)-(2x1). The root-mean-square vibration amplitudes in these surfaces are at least double the bulk values. The common cause that may explain these vibration amplitudes is that the surface atoms (or molecules in the case of ice) only have back-bonds that are nearly parallel to the surface. In this geometry, vibrations, especially perpendicular to the surface, involve primarily bond bending rather than bond stretching/compression: since bond bending is relatively soft, the corresponding vibration modes can have larger amplitudes. It is suggested that theory examine and confirm this cause of enhanced surface vibration amplitudes, and explore its implication for other phenomena such as adsorption and catalysis.

Depth Profiling of Melting and Metallization in Si(111) and Si(001) Surfaces

“…3). These results can possibly be rationalized in light of the previous observations and calculations showing that enhanced vibrations for specific surface geometries [26], as well as a poorer surface packing and first-neighbor bonding and coordination [1,5], favor surface melting. In our case, the backbonds nearly parallel to the surface Si(111) are able to induce surface premelting through large anisotropic vibrations, as also observed for other surfaces including ice (see Ref.…”

Bandgap and Structure Engineering via Cation Exchange: From Binary Ag2S to Ternary AgInS2, Quaternary AgZnInS alloy and AgZnInS/ZnS Core/Shell Fluorescent Nanocrystals for Bioimaging

“…This illustrates that, after the incorporation of zinc, low symmetry monoclinic acanthite Ag 2 S undergoes rearrangement to higher symmetry orthorhombic and cubic AIS. The transformation of the crystals structure have been observed in many cases, which may be the comprehensive result of free energy, diffusion rate and cationic radius. , Structural relationship among monoclinic Ag 2 S, orthorhombic AIS, and cubic AIS is demonstrated in Figure S4.…”

“…The transformation of the crystals structure have been observed in many cases, which may be the comprehensive result of free energy, diffusion rate and cationic radius. 48,49 Structural relationship among monoclinic Ag 2 S, orthorhombic AIS, and cubic AIS is demonstrated in Figure S4.…”

Size- and Shape-Dependent Transformation of Nanosized Titanate into Analogous Anatase Titania Nanostructures

“…7 It has been observed that, at the nanoscale, there are changes in the reaction free energy and the height of the reaction barrier, relative to the bulk. 27,28 For instance, by analogy to quantum dots, in the thin precursor protonic titanate nanotubes, the width of the reaction zone can become comparable in dimension to the whole width of the nanotube, due to the relatively small number of atomic layers present within a few nanometers of the structure. Hence, the slow propagation of the reaction front, driven by the gradient of the local chemical potential at or near the reaction zone, may no longer be the rate-limiting step of the reaction.…”