Showing papers by "James A. Forrest published in 1995"
TL;DR: In this paper, Brillouin light scattering (BLS) was used to measure the glass transition temperature of thin, freely-standing poly(styrene) (PS) films, which were prepared by spincoating solutions of PS in toluene onto glass substrates, annealing the supported films in vacuum, and then using a water surface transfer technique to place the films across a 3 mm diameter orifice.
Abstract: We have used Brillouin light scattering (BLS) to measure the glass transition temperature of thin, freely-standing poly(styrene) (PS) films. The freely-standing films were prepared by spincoating solutions of PS in toluene onto glass substrates, annealing the supported films in vacuum, and then using a water surface transfer technique to place the films across a 3 mm diameter orifice. Ellipsometry measurements of similar floated films transferred to Si(001) wafers allow the determination of the film thicknesses. Atomic force microscopy measurements revealed that the films have an rms roughness of less than 10 A˚. With the freely-standing films placed in an optical furnace, we performed BLS measurements of the films using a high-contrast, multipassed, tandem Fabry-Perot interferometer. We obtained a reliable, reproducible measure of the glass transition temperature, Tg, from the large changes in the frequencies of the thermally-excited, viscoelastic, film-guided waves within the PS films as the films were heated above Tg. BLS results for bulk PS and a 1800 A˚ thick, freely-standing PS film are presented. We find the same glass transition temperature for the 1800 A˚ thick film as the bulk PS sample. This Tg value is the same as that obtained using differential scanning calorimetry (DSC).
20 citations
01 Jan 1995
TL;DR: In this paper, the authors summarize the understanding of charge-induced absorption spectra, its associated model, and attempts to include optical flashes within this model, including flashes and thermal spikes.
Abstract: Spectroscopic studies of irradiated solid hydrogens have utilized electron-beam excitation of thin samples, tritium doping for in-situ irradiation, and proton-beam excitation of bulk samples. All of these techniques have allowed the observation of a broad emission spectrum near 800 nm whose origin is uncertain. Additionally, at temperatures below 4.2 K, flashes and thermal spikes have been observed. While previous studies have unambiguously linked the occurrence of thermal spikes to a rapid decrease in the atom concentration inside the solid, the mechanism responsible for the optical flashes is uncertain. This paper will summarize our understanding of charge-induced absorption spectra, its associated model, and attempts to include optical flashes within this model.