A cryogenic Quadraprobe scanning tunneling microscope system with fabrication capability for nanotransport research

We describe the development and the capabilities of an advanced system for nanoscale electrical transport studies. This system consists of a low temperature four-probe scanning tunneling microscope (STM) and a high-resolution scanning electron microscope coupled to a molecular-beam epitaxy sample preparation chamber. The four STM probes can be manipulated independently with subnanometer precision, enabling atomic resolution STM imaging and four-point electrical transport study of surface electronic systems and nanostructured materials at temperatures down to 10 K. Additionally, an integrated energy analyzer allows for scanning Auger microscopy to probe chemical species of nanostructures. Some testing results are presented.     

Neutron sputtering yields from Nb,Au and Co

Employing a neutron source based on the ⁹Be (d, n) reaction, high energy neutron sputtering yields have been determined for Nb, Au and Co. Two experiments have been conducted. In the first, graphite catcher foils were used and in the second, polished Si wafers. From data collected in the first experiment the neutron sputtering yields of Nb, Au and Co were determined to be in the range of 10^?5 to 10^?4 particles per incident neutron. Examination of the collector foils from the second experiment did not show any evidence of large particle (> 1 μm) ejection from the Nb targets.     

The application of tris buffer and copper sulfate for the preservation of phenylurea pesticides analyzed using U.S. EPA method 532 in the UCMR Survey

A high performance liquid chromatographic method was developed to meetthe U.S. Environmental Protection Agency's (EPA) Unregulated Contaminant Monitoring Rule (UCMR) Survey need for the analysis of phenylurea pesticides in drinking waters. Many of these phenylurea compounds were demonstrated to degrade rapidly in the presence of the residual chlorine disinfectant in drinking waters. This degradation was halted by the addition of a tris buffer, which was initially chosen to optimize the sample pH prior to extraction. Copper sulfate was found to prevent the regrowth of microorganisms in surface waters, which was observed upon dechlorination. Tris buffer provided the additional benefit of keeping the copper sulfate preservative in solution even in groundwater matrices that caused precipitation of copper in its absence. A C18 solid phase, in cartridge or disk form, was used to efficiently extract target compounds from the preserved drinking water matrices. A 21-day storage stability study, together with precision and accuracy studies, demonstrated thatthis method had suitable sensitivity, selectivity, accuracy, precision, and ruggedness for use in the EPA's UCMR drinking water occurrence survey.     

Novel formation and decay mechanisms of nanostructures on surface

For decades research on thin-film growth has attracted a lot of attention as these kinds of materials have the potential in new generation device application. It is known that the nuclei at initial stage of the islands are more stable than others and certain atoms are inert while others are active. In this paper, we will show that, when a surfactant layer is used to mediate the growth, a counter-intuitive fractal-to-compact island shape transition can be induced by increasing deposition flux or decreasing growth temperature. Specifically, we introduce a reaction-limited aggregation (RLA) theory, where the physical process controlling the island shape transition is the shielding effect of adatoms stuck to stable islands on incoming adatoms. Also discussed are the origin of a transition from triangular to hexagonal then to inverted triangular and the decay characteristics of 3D islands on surface, and connections of our unique predictions with recent experiments. Furthermore, we will present a novel idea to make use of the condensation energy of adatoms to control the island evolution along special direction.     

Lithotripsy for retained common duct stones: a quasi-urological procedure

A protocol for bile duct lithotripsy was formulated in early 1988 after review of the literature and encouragement by gastroenterologists. Seven cases have been treated at our center and are being reported to explain our current concept of this therapy. Failure of the Food and Drug Administration to approve gallstone lithotripsy has complicated the promulgation of this procedure.