Strongly correlated phases exhibit collective carrier dynamics that if properly harnessed can enable novel functionalities and applications. In this article, we investigate the phenomenon of electrical oscillations in a prototypical MIT system, vanadium dioxide (VO2). We show that the key to such oscillatory behaviour is the ability to induce and stabilize a non-hysteretic and spontaneously reversible phase transition using a negative feedback mechanism. Further, we investigate the synchronization and coupling dynamics of such VO2 based relaxation oscillators and show, via experiment and simulation, that this coupled oscillator system exhibits rich non-linear dynamics including charge oscillations that are synchronized in both frequency and phase. Our approach of harnessing a non-hysteretic reversible phase transition region is applicable to other correlated systems exhibiting metal-insulator transitions and can be a potential candidate for oscillator based non-Boolean computing.

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We report the growth of (001)-oriented VO2 films as thin as 1.5 nm with abrupt and reproducible metal-insulator transitions (MIT) without a capping layer. Limitations to the growth of thinner films with sharp MITs are discussed, including the Volmer-Weber type growth mode due to the high energy of the (001) VO2 surface. Another key limitation is interdiffusion with the (001) TiO2 substrate, which we quantify using low angle annular dark field scanning transmission electron microscopy in conjunction with electron energy loss spectroscopy. We find that controlling island coalescence on the (001) surface and minimization of cation interdiffusion by using a low growth temperature followed by a brief anneal at higher temperature are crucial for realizing ultrathin VO2 films with abrupt MIT behavior.

these estimates is caused by the need to make certain assumptions, such as the thickness of the contaminated layer. However, for the period evaluated, the trends in parameters suggest a relatively constant level of contamination, but with some variability. At the 618-11 sub-region, monitoring results since 1999 show decreasing tritium concentrations at wells closest to the source and variable concentrations at wells along the downgradient migration pathway. This plume has not reached the Energy Northwest water supply wells, nor the Columbia River. At the 316-4/618-10 sub-region, COPC are currently at levels below the drinking water standards, except for very recent samples from two wells near the 316-4 cribs excavation site that show concentrations near the 30-ug/L standard for uranium. A revised strategy for categorizing waste constituents in groundwater as a COC or COPC, along with the implications for remedial actions and regulatory decisions, is proposed. As a result, the lists developed during the remedial investigation have been shortened, primarily because of improving conditions and lack of evidence suggesting unacceptable risk. Conceptual Site Model for 300 Area Uranium. The 300 Area uranium plume can be characterized as persistent, i.e., the area and concentrations have remained similar to early 1990 conditions. There has been variability in spatial and temporal distribution patterns, primarily as a consequence of (a) cessation of liquid waste disposal to the ground, (b) large-scale source excavation activities, (c) unusually high and prolonged water table conditions during 1996 and 1997, and (d) seasonality because of river-stage fluctuations. During the most recent years, the plume appears to be relatively stable, with evidence showing gradual downgradient migration to the Columbia River. The highest concentrations observed currently are along the shoreline, and probably reflect the last significant input from beneath former major waste sites, such as the 316-5 process trenches. Uranium is lost from the plume via discharge to the river and groundwater withdrawal at a water supply well. Some amount of re-supply to the plume is believed to occur as a consequence of long-term release of uranium that has been sequestered on vadose zone and aquifer solids. The mobility of uranium and controls on dissolved concentrations are influenced by the geochemistry of the original waste effluent, the receiving sediment, and pore fluids, all of which vary in the 300 Area environment. The compositional and spatial variability leads to complexity in computer models designed for predicting plume behavior. The heterogeneity in conditions also drives the need for more field data on the locations, inventory, and geochemical characteristics of uranium in potential source zones. Conceptual Site Model for 618-11 Tritium. The tritium plume associated with the 618-11 sub-region has apparently been created by episodic release of tritium gas from irradiated materials in the burial ground. The gas interacts with moisture in the vad...

Materials exhibiting electronic phase transitions have attracted widespread attention. By switching between metallic and insulating states under external stimuli, the accompanying changes in the electrical and optical properties can be harnessed in novel electronic and optical applications. In this work, a laterally confined conductive pattern is inscribed into an otherwise insulating VO2 thin film using ultraviolet light, inducing an almost four orders of magnitude decrease in electrical resistivity of the exposed area. The metallic imprint remains in VO2 after ultraviolet light exposure and can be completely erased by a short low temperature anneal. The ability to optically pattern confined metallic structures provides new opportunities for reconfigurable photonic and plasmonic structures, as well as re‐writable electric circuitry.