CERL ERDC

Champaign, IL, United States

CERL ERDC

Champaign, IL, United States
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Mantey K.,University of Illinois at Urbana - Champaign | Zhu A.,University of Illinois at Urbana - Champaign | Boparai J.,University of Illinois at Urbana - Champaign | Nayfeh M.,University of Illinois at Urbana - Champaign | And 2 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

In bulk single-crystal silicon, the semiconducting diamond-to-metallic ß-Sn phase transformation nucleates on defects, and is manifested by a sharp uptake in light absorption at a threshold of ∼11 Gpa, accompanied with the creation of nanosized (20-50 nm) fragmentation domains. We report on the observation of linear uptakes in the absorption and in the luminescence and with insignificant spectral change in ultrasmall 1-nm Si particles. We associate the gradual absorption uptake and luminescence yield with silicon-metal transformation on the surface. The insignificant change in the spectral content of the luminescence points to surface stability for particles, which are smaller than the bulk fragmentation domain. First-principles atomistic calculations yield absorption behavior that exhibits gradual uptake followed by sharp uptake at ∼9-11 Gpa. The results point to the conclusion that two-dimensional surface-like phase transformations are manifested by linear uptake in absorption and luminescence. © 2012 American Physical Society.


Ford K.B.,CERL ERDC | Collins M.K.,CERL ERDC | Ajami N.E.,CERL ERDC | Dowds D.,CERL ERDC | And 4 more authors.
Materials Letters | Year: 2013

Recent discoveries of pressure dependence in quantum dot (QD) fluorescence wavelength has led to work pursuing QD-based systems for strain and pressure-sensing applications. However, the spectral shift of QDs tends to be fairly insensitive, typically requiring applied pressure on the order of gigapascals before any change can be detected. We present a QD-epoxy nanocomposite whose spectral intensity response to pressure can be used to quantitatively detect pressure changes in the megapascal range. The intensity of QD fluorescence is compared to the intensity of a reference to provide meaningful intensity data, which provides a bright signal that is quantitatively indicative of material stress. We believe that further optimization and characterization of this nanocomposite may be useful in the development of sensitive optical strain sensors. © 2013 Elsevier B.V.

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