Two-Membered Silicon Rings on the Dehydroxylated Surface of Silica

Abstract

We present extensive modeling of the amorphous silica surface, aimed at connecting its structural and chemical features. beta-cristobalite surfaces are initially studied to model the hydroxylated surfaces. A model reconstruction of the (111) surface is used to define a path leading to the formation of two-membered silicon rings upon dehydroxylation. Subsequently, a realistic model of the amorphous dehydroxylated (dry) surface is produced, by full ab initio annealing of an initial model generated by classical simulation. The presence of surface two-membered silicon rings emerges naturally. A calculation of IR activity yields an associated peak doublet in agreement with experimental data.

Sodium diffusion through amorphous silica surfaces: A molecular dynamics study

“…Also in the external region, the 2 and 3-fold rings (that are still present) are oriented perpendicularly to the surfaces (FIG. 4(b)) as observed at the ASF surfaces 28,49 . We have also analyzed the dynamics of the Na + cations and compared the results obtained in the present 'NS10' system with those obtained in a NS4 glass.…”

Fully Coordinated Silica Nanoclusters:(SiO2)NMolecular Rings

“…Cluster DF calculations using hydrogen-terminated two-rings yield relatively high estimates (0:72 eV=SiO 2 [16]) but neglect the stabilizing effect of an extended silica bonding environment [17]. Periodic DF calculations on two-rings in a relaxed amorphous silica surface give a value of 0:69 eV=SiO 2 [6], while similar calculations comparing the energy of silica-w to that of -quartz, yield 0:62 eV=SiO 2 [18]. Using the latter value, and adding it to the cyclic strain in our molecular rings, gives an estimate of the formation energy of our rings with respect to -quartz per SiO 2 unit, E Q!R ; see Table II.…”

“…Two-rings at silica surfaces form, at temperatures above 900 K, from the condensation of vicinal hydroxyl groups but are strained species, which are readily reversibly hydrolyzed [1,2]. At higher temperatures (1400 -1700 K), in the absence of water, thermodynamic rearrangement of the pure silica structure favors the formation of two-rings at the surface [3][4][5][6][7]. The elevated temperatures of this process cause the surface to be more flexible and potentially allows for more stable two-rings to form within a relaxed environment.…”

“…Recent studies have provided a wealth of evidence confirming that two-rings exist at the surfaces of amorphous and crystalline silica [1][2][3][4][5][6][7]. Two-rings at silica surfaces form, at temperatures above 900 K, from the condensation of vicinal hydroxyl groups but are strained species, which are readily reversibly hydrolyzed [1,2].…”

Modelling of silica film growth by chemical vapour deposition : Influence of the interface properties

“…Thus, it may be useful to perform different structural and chemical analyses of both sets of films. In this regard it is important to note that it is well-established [27][28][29][30][31] that among the active sites for silicon dioxide growth (i.e. SiH bonds, SiOH groups and two-and three-membered siloxane rings) SiR groups and twomembered siloxane rings are the most active ones within our temperature range.…”