Local vibrational densities of states in glasses: Numerical study of a model of amorphous silicon

Ishibashi, Kiyoshi; Tsumuraya, Kazuo; Nakata, Satoshi

doi:10.1063/1.467764

Cited by 4 publications

(5 citation statements)

References 27 publications

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“…However, for models with equal numbers of defects the decrease of the TO VDOS peak is larger for models with larger total strain energy. These results confirm the conclusions from previous studies that the height of the TO peak is related to the concentration of defects [2,5] and the degree of distortion of the Si tetrahedra [5,6]. We observe also slight increase of the linewidth of the LA VDOS peak with increasing number of coordination defects and total strain energy.…”

Section: Resultssupporting

confidence: 92%

“…The results for the jump in PQ(ω), the number of strongly localized modes and their correlation lengths as a function of the defect concentration quantitatively demonstrate that the character of the vibrational modes of a-Si depends on the concentration of coordination defects and tetrahedra with large local strains. Previous calculations of the partial VDOS of fourcoordinated Si atoms, using the recursion method [5], also show that increasing the number of five-coordinated nearest neighbours around a regular tetrahedron, i.e. increasing the size of the D 5 defect clusters, depresses the height of the TO peak in the partial VDOS.…”

Section: Discussionmentioning

confidence: 92%

“…Despite the great influence of coordination defects on the width of the band gap in a-Si [3], there are only a few qualitative studies of their effect on the vibrational spectra which are restricted only to the vibrational density of states and the participation ratio of the vibrational modes [4][5][6][7]. Studies of the effects of the network topology on the vibrational spectra, with the exception of [8] and [9], where the effect of voids on the VDOS was studied, are practically nonexistent.…”

Section: Introductionmentioning

confidence: 99%

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Dependence of the vibrational spectra of amorphous silicon on the defect concentration and ring distribution

Zotov

Marinov²,

Mousseau

et al. 1999

J. Phys.: Condens. Matter

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The Raman spectra of nine 216-atom models of amorphous silicon (a-Si) are calculated using the bond polarizability approximation of Raman scattering. These a-Si models, generated by the activation relaxation technique, have different concentrations of coordination defects, ring statistics and local strain distributions, which cause changes in the vibrational density of states and the Raman scattering. Analysis of the vibrational modes indicates that an increase in the number of coordination defects leads to an increase in the high-frequency localization and to mixing of the TA modes with other high-frequency modes. Calculation of partial Raman spectra indicates that five-coordinated Si atoms enhance the high-frequency part of the LO Raman peak at about 400 cm −1 and lead to characteristic band at about 600 cm −1 on the high-frequency side of the TO Raman peak. For their part, the three-coordinated Si atoms contribute to the low-frequency part of the LO peak. A weak correlation between the number of four-membered rings and the intensity of the LO Raman peak is also established although there is no correlation between the number of three-and four-membered rings and the total strain energy.

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Section: Resultssupporting

confidence: 92%

Section: Discussionmentioning

confidence: 92%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Dependence of the vibrational spectra of amorphous silicon on the defect concentration and ring distribution

Zotov

Marinov²,

Mousseau

et al. 1999

J. Phys.: Condens. Matter

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show abstract

“…59 Significant growth in the population of five-fold coordinated atoms was observed in simulations when the a-Si network was exposed to strains above a certain threshold (which may be affected by temperature and shear velocity). 2 In theoretical studies, an increase in the number of five-fold coordinated atoms has been linked to losses in intensity 7,15,24,27,55 and widening of the TO band. 6,24,27,55 In the present work, a decrease in the relative intensity of the TO band (see FIG 5b) and a sizable change in the width (see FIG 6) was observed at load L3.…”

Section: Discussionmentioning

confidence: 99%

In situspectroscopic study of the plastic deformation of amorphous silicon under nonhydrostatic conditions induced by indentation

et al. 2015

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Indentation-induced plastic deformation of amorphous silicon (a-Si) thin films was studied by in situ Raman imaging of the deformed contact region of an indented sample, employing a Raman spectroscopy-enhanced instrumented indentation technique. Quantitative analyses of the generated in situ Raman maps provide unique, new insight into the phase behavior of as-implanted a-Si. In particular, the occurrence and evolving spatial distribution of changes in the a-Si structure caused by processes, such as polyamorphization and crystallization, induced by indentation loading were measured. The experimental results are linked with previously published work on the plastic deformation of a-Si under hydrostatic compression and shear deformation to establish a sequence for the development of deformation of a-Si under indentation loading. The sequence involves three distinct deformation mechanisms of a-Si: (1) reversible deformation, (2) increase in coordination defects (onset of plastic deformation), and (3) phase transformation. Estimated conditions for the occurrence of these mechanisms are given with respect to relevant intrinsic and extrinsic parameters, such as indentation stress, volumetric strain, and bond angle distribution (a measure for the structural order of the amorphous network). The induced volumetric strains are accommodated solely by reversible deformation of the tetrahedral network when exposed to small indentation stresses. At greater indentation stresses, the increased volumetric strains in the tetrahedral network lead to the formation of predominately five-fold coordination defects, which seems to mark the onset of irreversible or plastic deformation of the a-Si thin film. Further increase in the indentation stress appears to initiate the formation of six-fold coordinated atomic arrangements. These six-fold coordinated arrangements may maintain their amorphous tetrahedral structure with a high density of coordination defects or nucleate as a new crystalline β-tin phase within the a-Si network.

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“…7,8 The calculated VDOS also compares well with previous VDOS calculations for a-Si models constructed by different methods using various potentials. 36,[41][42][43][44][45][46] As in crystalline Si, the peak at ϳ175 cm Ϫ1 is commonly assigned to transverse acoustic ͑TA͒-like vibrations, the weak peak at ϳ325 cm Ϫ1 to longitudinal acoustic ͑LA͒-like vibrations, the weak shoulder at ϳ400 cm Ϫ1 to longitudinal optic ͑LO͒-like vibrations, and the high-frequency peak at ϳ500 cm Ϫ1 to transverse optic ͑TO͒-like vibrations. In the SW models, the TA peak practically does not change position with increasing PC MRO, while the TO peak shifts to slightly lower frequencies in PC-K2.…”

Section: B Vibrational Modesmentioning

confidence: 99%

Structure and physical properties of paracrystalline atomistic models of amorphous silicon

Voyles

Zotov

Nakhmanson

et al. 2001

Journal of Applied Physics

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We have examined the structure and physical properties of paracrystalline molecular dynamics models of amorphous silicon. Simulations from these models show qualitative agreement with the results of recent mesoscale fluctuation electron microscopy experiments on amorphous silicon and germanium. Such agreement is not found in simulations from continuous random network models. The paracrystalline models consist of topologically crystalline grains which are strongly strained and a disordered matrix between them. We present extensive structural and topological characterization of the medium range order present in the paracrystalline models and examine their physical properties, such as the vibrational density of states, Raman spectra, and electron density of states. We show by direct simulation that the ratio of the transverse acoustic mode to transverse optical mode intensities I TA /I TO in the vibrational density of states and the Raman spectrum can provide a measure of medium range order. In general, we conclude that the current paracrystalline models are a good qualitative representation of the paracrystalline structures observed in the experiment and thus provide guidelines toward understanding structure and properties of medium-range-ordered structures of amorphous semiconductors as well as other amorphous materials.

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Local vibrational densities of states in glasses: Numerical study of a model of amorphous silicon

Cited by 4 publications

References 27 publications

Dependence of the vibrational spectra of amorphous silicon on the defect concentration and ring distribution

Dependence of the vibrational spectra of amorphous silicon on the defect concentration and ring distribution

In situspectroscopic study of the plastic deformation of amorphous silicon under nonhydrostatic conditions induced by indentation

Structure and physical properties of paracrystalline atomistic models of amorphous silicon

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