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Title: Shedding Synchrotron Light on a Puzzle of Glasses

Vibrational dynamics of glasses remains a point of controversial discussions. In particular, the density of vibrational states (DOS) reveals an excess of states above the Debye model called "boson pemore »ak." Despite the fact that this universal feature for all glasses has been known for more than 35 years, the nature of the boson peak is still not understood. The application of nuclear inelastic scattering via synchrotron radiation perhaps provides a clearer, more consistent picture of the subject. The distinguishing features of nuclear inelastic scattering relative to, e.g., neutron inelastic scattering, are ideal momentum integration and exact scaling of the DOS in absolute units. This allows for reliable comparison to data from other techniques such as Brillouin light scattering. Another strong point is ideal isotope selectivity: the DOS is measured for a single isotope with a specific low-energy nuclear transition. This allows for special "design" of an experiment to study, for instance, the dynamics of only center-of-mass motions. Recently, we have investigated the transformation of the DOS as a function of several key parameters such as temperature, cooling rate, and density. In all cases the transformation of the DOS is sufficiently well described by a transformation of the continuous medium, in particular, by changes of the macroscopic density and the sound velocity. These results suggest a collective sound-like nature of vibrational dynamics in glasses and cast doubts on microscopic models of glass dynamics. Further insight can be obtained in combined studies of glass with nuclear inelastic and inelastic neutron scattering. Applying two techniques, we have measured the energy dependence of the characteristic correlation length of atomic motions. The data do not reveal localization of atomic vibrations at the energy of the boson peak. Once again, the results suggest that special features of glass dynamics are related to extended motions and not to local models.« less
Title: Shedding Synchrotron Light on a Puzzle of Glasses
Publication Date: 2007-12-05
OSTI Identifier: 987273
DOE Contract Number: ACO2-06CH11357
Other Number(s): Other: 20071205-150214-1
Resource Type: Multimedia
Specific Type: Multimedia Presentation
Resource Relation: Conference: APS Colloquium Series, Advanced Photon Source (APS) at Argonne National Laboratory, Argonne, Illinois (United States), presented on December 05, 2007
Research Org: ANL-APS (Argonne National Laboratory-Advanced Photon Source (United States))
Sponsoring Org: USDOE Office of Science (SC)
Publisher: Advanced Photon Source (APS) Colloquium Series Video Collection
Country of Publication: United States
Language: English
Run Time: 0:39:38
System Entry Date: 2016-01-27