Shau Grossman’s research while affiliated with Central Michigan University and other places

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Publications (6)


Chain formation and the origin of structure in the Raman spectrum of a-SiSe_ {2}
  • Article

December 2001

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9 Reads

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16 Citations

Physical Review B

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Shau Grossman

We have used a first-principles method based on the density functional theory to investigate the Raman spectrum of a-SiSe2.{}{\mathrm{SiSe}}_{2}. By calculating vibrational frequencies and associated Raman intensities for a series of cluster models, we arrive at an interpretation of the observed spectrum that directly links spectral features to structural units in the glass. The results indicate that edge-sharing chains containing three tetrahedra are a dominant structural motif in the stoichiometric glass.


The origin of structure in the Raman spectrum of SiSe_2

March 2001

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11 Reads

We have performed systematic calculations on a series of cluster models to investigate the Raman spectrum of SiSe_2. The spectrum of SiSe2 is superficially similar to that of its chemical analogue, GeSe_2, but the main spectral features have additional structure not present in the GeSe2 spectrum. The first-principles calculations are based on the density functional theory in the local density approximation. We compute the full vibrational spectrum for each cluster model. To make connection with experimental data, we also compute the Raman scattering strength of each mode, using a new, first-principles method (see Jackson et al., Phys. Rev. B 60, R14 985 (1999)). A simulated spectrum based on the calculations is in excellent agreement with the recent observations of Selvanathan et al. (Phys. Rev. B 61, 15061 (2000)). The calculations suggest that the additional structure in the spectrum is due to the formation of chains of edge-sharing tetrahedra in the material.


First principles study of the Raman spectra of SiS2 and SiSe_2

March 2000

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104 Reads

Raman spectroscopy has long been used as a probe of the atomic structure of chalcogenide glasses. Sharp features in the spectra indicate the presence of characteristic structural units, but the Raman measurements alone cannot directly determine the atomic arrangements in these units. In this presentation we discuss calculations based on the density functional theory (DFT) that are aimed at interpreting the spectral peaks in atomistic terms. The calculations yield both the frequencies and Raman spectral intensities for the vibrational modes of cluster models of the materials. We create simulated spectra by combining results of several cluster calculations. Here we focus on SiS2 and SiSe_2. The simulated spectra for these materials are in good agreement with experiment. We contast the results for these glasses with previous calculations for the Ge-analogues, GeS2 and GeSe2 and discuss the structural implications of the differences. Work supported by Research Corporation and NSF DMR-9972333


Raman-Active Modes of a-GeSe2 and a-GeS2: A First-Principles Study

December 1999

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59 Reads

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226 Citations

Physical Review B

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Arlin Briley

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Shau Grossman

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[...]

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We have used a recently developed computational technique based on density-functional theory to study the Raman-active modes of amorphous GeSe2 and GeS2. Vibrational modes and the associated Raman activities for three cluster building blocks of the glasses are calculated directly from first principles. The positions of the calculated symmetric-stretch modes in the cluster models are in excellent agreement with sharp features in the observed spectra. Moreover, simulated spectra based on the cluster results are in good agreement with experiment, accounting for all the observed features in the bond-stretch region of the spectra. The cluster results suggest a new interpretation for the 250 cm-1 mode appearing in the spectra of Ge-rich samples in the GexS1-x family.



First-principles Raman intensities for chalcogenide glasses

18 Reads

We have conducted a series of calculations on cluster models of the chalcogenide glasses GeSe2 and SiSe_2. The clusters include the edge-sharing (ES) and corner-sharing (CS) units that are expected to be important in the glasses. We have computed the vibrational modes of the clusters and the corresponding absolute Raman intensities, using a recently developed technique based on density functional theory. We find the positions of the Raman-active modes calculated for these cluster models to be in excellent agreement with corresponding experimental peaks. Using experimental intensity data and our absolute Raman intensities, we predict the relative concentrations of the structural units in the glasses.

Citations (2)


... Glasses with rich GeSe 2 exhibit a broad band in the 170-240 cm −1 region, with major peaks observed at 203 and 215 cm −1 , corresponding to the A 1 symmetric stretching mode of corner-sharing [GeSe 4/2 ] tetrahedrons and the A 1 c vibrational mode (companion mode) of edge-sharing [GeSe 4/2 ] tetrahedrons, respectively. 16 The characteristic peak at 195 cm −1 is due to the vibration of Sb-Se bonds in SbSe 3/2 pyramids. 17 A Raman band at ∼160 cm −1 corresponds to Sb-Sb vibration in Se 2 Sb-SbSe 2 entities. ...

Reference:

Impact of structural changes of Ge–Sb–Se chalcogenide glasses on their acousto‐optic properties
Raman-Active Modes of a-GeSe2 and a-GeS2: A First-Principles Study
  • Citing Article
  • December 1999

Physical Review B

... When counting the triads of tetrahedra within the network, we realized that the restriction to only one kind of intertetrahedral connection (the ES one) is very unrealistic, since both ES and CS occur in a non-negligible number of configurations. The set of results presented above is an outstanding example of the added value of the FPMD approach applied to chalcogenide glasses when one correctly considers them (as it should) as three-dimensional structures, as opposed to methodologies (cluster calculations [24]) not accounting for the actual spatial extension of the network. 4 . ...

Chain formation and the origin of structure in the Raman spectrum of a-SiSe_ {2}
  • Citing Article
  • December 2001

Physical Review B