Thermodynamic properties and atomistic structure of the dry amorphous silica surface from a reactive force field model

Abstract

Thermodynamic properties and atomistic structure of the dry amorphous silica surface from a reactive force field model Cabriolu, R., & Ballone, P. (2010). Thermodynamic properties and atomistic structure of the dry amorphous silica surface from a reactive force field model. Physical Review B (Condensed Matter), 81 (15) A force field model of the Keating type supplemented by rules to break, form, and interchange bonds is applied to investigate thermodynamic and structural properties of the amorphous SiO 2 surface. A simulated quench from the liquid phase has been carried out for a silica sample made of 3888 silicon and 7776 oxygen atoms arranged on a slab ϳ40 Å thick, periodically repeated along two directions. The quench results into an amorphous sample, exposing two parallel square surfaces of ϳ42 nm 2 area each. Thermal averages computed during the quench allow us to determine the surface thermodynamic properties as a function of temperature. The surface tension turns out to be ␥ = 310Ϯ 20 erg/ cm 2 at room temperature and ␥ = 270Ϯ 30 at T = 2000 K, in fair agreement with available experimental estimates. The entropy contribution Ts s to the surface tension is relatively low at all temperatures, representing at most ϳ20% of the surface energy. Almost without exceptions, Si atoms are fourfold coordinated and oxygen atoms are twofold coordinated. Twofold and threefold rings appear only at low concentration and are preferentially found in proximity of the surface. Above the glass temperature T g = 1660Ϯ 50 K, the mobility of surface atoms is, as expected, slightly higher than that of bulk atoms. The computation of the height-height correlation function shows that the silica surface is rough in the equilibrium and undercooled liquid phase, becoming smooth below the glass temperature T g .

Probing of 2 dimensional confinement-induced structural transitions in amorphous oxide thin film

“…These studies, together with studies of glass surfaces, suggest that the degree of structural disorder in amorphous oxide thin film may increase with decreasing thickness89101112: the increase in elastic modulus of amorphous SiO 2 was attributed to an increase in the fraction of smaller-membered rings, indicating an increase in the structural disorder and defect concentration at surfaces9101112 as also suggested for the surfaces of amorphous selenium thin film13. In contrast, enhanced mobility at surfaces suggested for amorphous polymer thin film (e.g 14. )…”

Rotation‐Misfit‐Free Heteroepitaxial Stacking and Stitching Growth of Hexagonal Transition‐Metal Dichalcogenide Monolayers by Nucleation Kinetics Controls

“…In the case of WS 2 ML wetting on MoS 2 ML, indicated as “(1)” in Figure a, () will be very small, because the interfacial energy between the two ML crystals, , is negligible and the and are nearly the same in the range of about 70–75 mJ m −2 . Meanwhile, for the case of MoS 2 ML wetting on SiO 2 , indicated as “(2)” in Figure a, can be significant due to larger surface energy of SiO 2 (≈ 300–400 mJ m −2 ), provided that the other factors are invariant at same nucleus size. This sets a condition that a larger must be overcome for MoS 2 ML lateral stitching growth, compared to the vertical stacking growth of WS 2 ML on MoS 2 MLs.…”

Frank–van der Merwe Growth versus Volmer–Weber Growth in Successive Stacking of a Few‐Layer Bi2Te3/Sb2Te3 by van der Waals Heteroepitaxy: The Critical Roles of Finite Lattice‐Mismatch with Seed Substrates

“…Consequently, at the growth front, adatoms randomly incorporate onto nucleus edges, and therefore form irregular crystal shapes instead of thermodynamically stable facets. This assumption is qualitatively valid considering the lower surface energy of h ‐BN, γ h ‐BN ≈ 65–75 mJ m −2 , which lacks dangling bonds, than that of SiO 2 , ≈ 300–400 mJ m −2 , as similarly discussed elsewhere . On SiO 2 /Si substrates adatom diffusion is relatively slow, due to surface roughness and dangling bonds of amorphous SiO 2 (i.e., D s, h ‐BN > >), and crystal growth is limited by the incorporation reaction rate into nucleus.…”

“…This difference in crystal shapes implies that underlying substrates critically influence the vapor phase growth mode. This assumption is qualitatively valid considering the lower surface energy of h-BN, γ h-BN ≈ 65-75 mJ m −2 , which lacks dangling bonds, than that of SiO 2 , SiO2 γ ≈ 300-400 mJ m −2 , [33][34][35] as similarly discussed elsewhere. [31,32] In general, within the framework of the nucleation kinetics model, a gas-phase growth reaction can be divided into two steps: (1) adsorption of vaporized precursors onto substrates and diffusion to the preferential growth sites and (2) incorporation of precursors into existing nuclei.…”