129 I and 119 Sn Mössbauer spectroscopy , reversibility window and nanoscale phase separation in binary Ge x Se 1 x glasses
The molecular structure of the prototypical chalcogenide glass system—GexSe1 x in the 0oxo3 range, has received much scrutiny over the years. These glasses have been probed by modulated DSC, Raman scattering, Sn absorption and I emission Mössbauer spectroscopy, and neutron scattering. The I measurements utilize Te parent as a dopant in glasses, and reveal a bimodal (A, B) distribution of sites, with the site intensity ratio, IB/IA (x), tracking changes in glass structure as a function of x. At low x (o0.15) Senchains are stochastically cross-linked by Ge additive, and IB/IA (x) sharply declines with x. But at x40:15, rigid regions nucleate at the expense of floppy ones, and the ratio IB/IA (x) reverses slope to display a global maximum in the 0:20oxo0:25 range. The latter coincides with the reversibility window usually taken as signature of self-organization of these networks. At x40:26, these glasses enter a stressed-rigid elastic phase and in the 0:31oxo1 3 range nanoscale phase separate into Se-rich and Ge-rich regions. The signature of the latter is saturation of IB/IA (x) at a high value of 1.5 at x 1⁄4 13. Sn Mossbauer spectroscopy measurements independently support the picture of broken chemical order of the stoichiometric glass inferred from the I Mössbauer experiments. These observations using local probes are well correlated to Raman scattering, modulated differential scanning calorimetric and diffraction measurements. r 2006 Elsevier B.V. All rights reserved. PACS: 61.40.Fs; 63.50.+x; 78.30.Ly; 76.80.+y
Femtosecond Laser Deposition of Germanium Selenide onto Silicon Platform at Different Substrate Temperatures
Germanium selenide (GeSe) thin films were fabricated by employing femtosecond pulsed-laser deposition (fs-PLD) on silicon (100) substrates at various substrate temperatures, ranging from 25 °C to 600 °C. The thin films’ surface morphology qualities and optical properties were studied by utilising transmission electron microscopy (TEM) and X-ray diffraction (XRD). The X-ray diffraction result signifies that the thin films deposited on the silicon at a substrate temperature below 400 °C were amorphous Ge-Se. In contrast, those grown at 400 °C and above exhibited crystallised peaks of Ge-Se orthorhombic and tetragonal structures. The deposition growth rate of the thin films was also found to decrease substantially with increasing substrate temperature. These results show that the fs-PLD process has great potential for fabricating good quality Ge-Se thin film. This technique could enable the manufacture of modern optoelectronic devices for applications in optical communication, sensing, and ovonic threshold switching for the high-density crossbar memory array.
A natural language discourse model to explain linear programming models and solutions
Abstract This paper presents a natural language (i.e., English) discourse model to explain a linear programming model and, possibly, its computed solution (which need not be optimal). Drawing from earlier syntactic translations, a semantic model is presented, based on economic input-output relations commonly found in large-scale linear programs. These are then shown how to form rule-driven explanations, which comprises a fundamental component of an intelligent mathematical programming system.