Dynamics at the crystal-melt interface in a supercooled chalcogenide liquid near the glass transition.

Direct quantitative measurements of nanoscale dynamical processes associated with structural relaxation and crystallization near the glass transition are a major experimental challenge. These type of processes have been primarily treated as macroscopic phenomena within the framework of phenomenological models and bulk experiments. Here, we report x-ray photon correlation spectroscopy measurements of dynamics at the crystal-melt interface during the radiation induced formation of Se nano-crystallites in pure Se and in binary AsSe4 glass-forming liquids near their glass transition temperature. We observe a heterogeneous dynamical behaviour where the intensity correlation functions g2(q, t) exhibits either a compressed or a stretched exponential decay, depending on the size of the Se nano-crystallites. The corresponding relaxation timescale for the AsSe4 liquid increases as the temperature is raised, which can be attributed to changes in the chemical composition of the melt at the crystal-melt interface with the growth of the Se nano-crystallites

Coherent X-ray Scattering Reveals Nanoscale Fluctuations in Hydrated Proteins

Hydrated proteins undergo a transition in the deeply supercooled regime, which is attributed to rapid changes in hydration water and protein structural dynamics. Here, we investigate the nanoscale stress relaxation in hydrated lysozyme proteins stimulated and probed by X-ray Photon Correlation Spectroscopy (XPCS). This approach allows us to access the nanoscale dynamic response in the deeply supercooled regime (T = 180 K) which is typically not accessible through equilibrium methods. The relaxation time constants exhibit Arrhenius temperature dependence upon cooling with a minimum in the Kohlrausch-Williams-Watts exponent at T = 227 K. The observed minimum is attributed to an increase in dynamical heterogeneity, which coincides with enhanced fluctuations observed in the two-time correlation functions and a maximum in the dynamic susceptibility quantified by the normalised variance $\chi_T$. Our study provides new insights into X-ray stimulated stress relaxation and the underlying mechanisms behind spatio-temporal fluctuations in biological granular materials

Growth, processing, and optical properties of epitaxial Er_2O_3 on silicon

Erbium-doped materials have been investigated for generating and amplifying light in low-power chip-scale optical networks on silicon, but several effects limit their performance in dense microphotonic applications. Stoichiometric ionic crystals are a potential alternative that achieve an Er^(3+) density 100× greater. We report the growth, processing, material characterization, and optical properties of single-crystal Er_2O_3 epitaxially grown on silicon. A peak Er^(3+) resonant absorption of 364 dB/cm at 1535nm with minimal background loss places a high limit on potential gain. Using high-quality microdisk resonators, we conduct thorough C/L-band radiative efficiency and lifetime measurements and observe strong upconverted luminescence near 550 and 670 nm

Structural And Thermophysical Property Studies Of Metallic Liquids And Glasses Using The Beamline Electrostatic Levitation Technique

An accurate description of atomic structures is at the heart of an improved understanding of the properties of condensed solids. By correlating structural information from high energy synchrotron X-ray diffraction with thermophysical properties important insights have been gained into the role of local structural evolution in undercooling and glass formation. Here, the results of a number of investigations into the structures and properties of some amorphous phases will be presented and analyzed. Phase separation in Al88Y7Fe5 is identified prior to devitrification and is proposed as an explanation for extremely high observed nucleation rates. The development and construction of the Beamline Electrostatic Levitation Technique: BESL), which has shown increased utility over the past several years as an important probe of metallic systems, will be presented. Using BESL, atomic structures in equilibrium and supercooled liquids of Zr80Pt20 are explored using Reverse Monte Carlo methods, which indicate the presence of medium range atomic order that is dominated by Pt-Pt correlations. The thermophysical properties and atomic structures in the bulk metallic glass forming Ni-Nb and Ni-Nb-Ta liquids are examined. The high glass formability and low glass formability compositions are compared and important differences are discussed. Finally, the X-ray structure factors and densities for liquid aluminum from 1123K to 1273K are presented and atomic structures as a function of temperature have been constructed from the diffraction data with Reverse Monte Carlo fits

Preparation and characterization of lithium thiogermanate thin films using RF magnetron sputtering

Commercially developed in 1991, lithium ion batteries have long attracted the attention of scientists because of the high electropositivity of lithium. As power requirements become more demanding, batteries are also expected to provide the high energy densities necessary to keep pace. Chalcogenide glasses have long held an interest in battery applications because of the polarizability of the sulfide anion which is believed to be the cause of its superior conductivities. This class of materials exhibits room temperature conductivities on the order of 10-2 S/cm. Targets in the Li2S-GeS2 binary system have been sputtered in Argon and Nitrogen atmospheres using an RF magnetron sputtering technique with the hope of creating a new class of electrolytes with increased conductivity and stability in contact with litium. Films were characterized using IR, Raman and X-ray photoelectron spectroscopies in order to evaluate their structure. Our progress in producing and characterizaing these ion conducting sulfide thin films will be reported