Structure of rings in vitreous<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">SiO</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>

Rino, José Pedro; Ebbsjö, Ingvar; Kalia, Rajiv K.; Nakano, Aiichiro; Vashishta, Priya

doi:10.1103/physrevb.47.3053

Cited by 225 publications

(137 citation statements)

References 31 publications

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“…The model devel-oped by Nakano et al has been successfully employed to describe the bulk and the surface of disordered phases of SiO 2 , viz. amorphous and porous silica, 10,13,[36][37][38][39][40][41] which are evidently relevant to the present problem. In this model, silicon is assumed to be coordinated to four oxygen atoms, that is, the network is chemically ordered.…”

Section: Computational Detailsmentioning

confidence: 88%

“…In the present model, the fraction of three-and fourmembered rings is about 0.1 and 0.15 per deposited silicon atom, respectively, roughly ten and two times that of normal a-SiO 2 . 10 The mean value of the Si-OSi bond angle is 139 • . These results are consistent with the above-mentioned experimental results for evaporated films.…”

Section: Resultsmentioning

confidence: 99%

“…In this way, proper conclusions on the atomic mechanisms that mediate bombardment-induced densification can be drawn. Thus, for instance, models help understanding how changes in the medium-range structure of amorphous silica (a-SiO 2 ) influence the Si-O-Si bond-angle, 10 which in turn is related to such properties as the density, the optical index or the amount of built-in stress. 1,5,7,11 It is useful to discuss the structure of a-SiO 2 in terms of short-range order (SRO) and medium-range order (MRO) correlations, 12 at length scales ≤ 4Å and in the range 4-10Å, respectively.…”

Section: Introductionmentioning

confidence: 99%

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Structural properties of silicon dioxide thin films densified by medium-energy particles

et al. 2001

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Classical molecular-dynamics simulations have been carried out to investigate densification mechanisms in silicon dioxide thin films deposited on an amorphous silica surface, according to a simplified ion-beam assisted deposition (IBAD) scenario. We compare the structures resulting from the deposition of near-thermal (1 eV) SiO2 particles to those obtained with increasing fraction of 30 eV SiO2 particles. Our results show that there is an energy interval -between 12 and 15 eV per condensing SiO2 unit on average -for which the growth leads to a dense, low-stress amorphous structure, in satisfactory agreement with the results of low-energy ion-beam experiments. We also find that the crossover between low-and high-density films is associated with a tensile to compressive stress transition, and a simultaneous healing of structural defects of the a-SiO2 network, namely threeand four-fold rings. It is observed, finally, that densification proceeds through significant changes at intermediate length scales (4-10Å), leaving essentially unchanged the "building blocks" of the network, viz. the Si(O 1/2 )4 tetrahedra. This latter result is in qualitative agreement with the mechanism proposed to explain the irreversible densification of amorphous silica recovered from high pressures (∼ 15-20 GPa).

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Section: Computational Detailsmentioning

confidence: 88%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Structural properties of silicon dioxide thin films densified by medium-energy particles

et al. 2001

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“…These models were generated by different simulation techniques: classical and ab initio molecular dynamics, Monte-Carlo, and cluster simulations. [5][6][7] Among these different simulations, ab intio molecular dynamics simulations employing periodic boundary conditions are the most accurate as they reflect the quantum nature of the interatomic forces. As such, they more accurately represent changes in hybridization and charge transfer effects as bonds break and reform in dynamical simulations.…”

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confidence: 99%

Simulating liquid and amorphous silicon dioxide using real-space pseudopotentials

2012

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We present ab initio molecular dynamics simulations of liquid and amorphous silicon dioxide. The interatomic forces in our simulations are calculated using real-space pseudopotentials, which were constructed using density-functional theory. Our simulations are carried out using BornOppenheimer molecular dynamics, i.e., the electronic structure problem is solved by performing fully self-consistent calculations for each time step. Using a subspace filtering iteration technique, we avoid solving the Kohn-Sham eigenvalue with "standard" diagonalization methods. We consider systems with up to 192 atoms (64 SiO2 units) in a periodic supercell for simulations over 20 ps. The liquid and amorphous ensembles are formed by thermally quenching random configurations of silicon and oxygen atoms. We compare our liquid and amorphous simulations with previously performed Car-Parrinello molecular dynamic simulations and with experiment. In particular, we examine the possible formation of two-fold rings, which were not observed in previous simulations using quantum forces. We attribute this difference to a "biased" initial configuration, which inhibits the formation of two-fold rings. We also compare the structural properties of our simulated amorphous systems with neutron diffraction measurements and find good agreement.

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“…The short-and medium-range topology of a-SiC has been studied by MD simulations. 9 In this Letter, we study nanoindentation-induced deformations of amorphous silicon carbide ͑a-SiC͒ by means of MD. The maximum indentation pressure of 30 GPa is consistent with experimental values of hardness for a-SiC (Ref.…”

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confidence: 99%

Atomistic processes during nanoindentation of amorphous silicon carbide

Szlufarska

Kalia

Nakano

et al. 2005

Applied Physics Letters

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Atomistic mechanisms of nanoindentation of a-SiC have been studied by molecular dynamics simulations. The load displacement curve exhibits a series of load drops, reflecting the short-range topological order similar to crystalline 3C-SiC. In contrast to 3C-SiC, the load drops are irregularly spaced and less pronounced. The damage is spatially more extended than in 3C-SiC, and it exhibits long-range oscillations consistent with the indenter size. Hardness is ϳ60% lower than in 3C-SiC and is in agreement with experiment. The onset of plastic deformation occurs at depth ϳ75% lower than in 3C-SiC. © 2005 American Institute of Physics. [DOI: 10.1063/1.1849843] Nanoindentation is widely used to study mechanical properties of materials at the nanometer scale. [1][2][3][4] In crystalline solids, many experimental 5 and theoretical 6,7 studies show that the nanoindentation load-displacement ͑P -h͒ curve is correlated with the nucleation of subsurface defects in crystalline solids. For example, a molecular dynamics (MD) simulation has shown 8 that nucleation and coalescence of dislocations under an indenter lead to amorphization.Amorphous materials lack a long-range order of topological network and hence there is no clear notion of dislocations. For this reason, understanding atomistic processes during nanoindentation in amorphous materials presents a great challenge. MD simulations provide trajectories of all the atoms and are expected to shed light on the question of deformations in amorphous materials. The short-and medium-range topology of a-SiC has been studied by MD simulations. 9In this Letter, we study nanoindentation-induced deformations of amorphous silicon carbide ͑a-SiC͒ by means of MD. The maximum indentation pressure of 30 GPa is consistent with experimental values of hardness for a-SiC (Ref. 10) and is only ϳ40% of that in a zinc-blende crystalline 3C-SiC. 8 The indentation damage is spatially less localized in comparison with 3C-SiC. The onset of plasticity occurs at a depth only 25% of that in 3C-SiC. The P -h curve in a -SiC exhibits a series of load drops in the plastic regime. The magnitudes of load drops are less than in 3C-SiC due to less accumulated pressure under the indenter. The load drops are related to changes in structural correlations, which are analyzed through local rearrangements of atoms, local pressure and shear stress distribution, and bond-angle distribution.The interatomic potential used here consists of two-and three-body terms, which include steric repulsion, charge transfer, electronic polarizability, van der Waals interaction, and covalent bonding effects. The calculated lattice constant, melting temperature, elastic constants, and cohesive energy are in good agreement with experiments. 11 This potential has been used also to predict a new mechanism for a reversible zinc-blende-to-rocksalt transformation of SiC under pressure, 12 which was later confirmed by first-principles calculations. 13 We start from a perfect zinc-blende bulk ͑N = 1 048 320 atoms͒ at the experimental SiC ...

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Structure of rings in vitreousSiO2

Cited by 225 publications

References 31 publications

Structural properties of silicon dioxide thin films densified by medium-energy particles

Structural properties of silicon dioxide thin films densified by medium-energy particles

Simulating liquid and amorphous silicon dioxide using real-space pseudopotentials

Atomistic processes during nanoindentation of amorphous silicon carbide

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