An analysis of SEM techniques used to profile chemical etching on the semiconductor Hg1-xCdxTe

Various methods have been used to obtain accurate cross-sectional profiles of Hg_1-xCd_xTe devices after etching. Preliminary measurements from different etching techniques are also presented. Techniques used were scanning electron microscopy with stereo pairs and cleaved cross-sections, topography SEM (multiple detector SEM) and atomic force microscopy.     

The direct formation of ketones by reaction of methyl- and aryl-(carbonyl)(iodo)pentamethylcyclopentadienylrhodium complexes with organic iodides

[C₅Me₅Rh(aryl)(CO)I] reacts with methyl iodide to give [(C₅Me₅RhI₂)₂] and arylCOMe; similar reactions occur between [C₅Me₅Rh(Me)(CO)I] and RI to give the ketones RCOMe (R = Ph, Me, Et, or Pr).     

Plasma Photocathodes

Plasma wakefield accelerators offer accelerating and focusing electric fields three to four orders of magnitude larger than state-of-the-art radiofrequency cavity-based accelerators. Plasma photocathodes can release ultracold electron populations within such plasma waves and thus open a path toward tunable production of well-defined, compact electron beams with normalized emittance and brightness many orders of magnitude better than state-of-the-art. Such beams will have far-reaching impact for applications such as light sources, but also open up new vistas on high energy and high field physics. This paper reviews the innovation of plasma photocathodes, and reports on the experimental progress, challenges, and future prospects of the approach. Details of the proof-of-concept demonstration of a plasma photocathode in 90° geometry at SLAC FACET within the E-210: Trojan Horse program are described. Using this experience, alongside theoretical and simulation-supported advances, an outlook is given on future realizations of plasma photocathodes such as the upcoming E-310: Trojan Horse-II program at FACET-II with prospects toward excellent witness beam parameter quality, tunability, and stability. Future installations of plasma photocathodes also at compact, hybrid plasma wakefield accelerators, will then boost capacities and open up novel capabilities for experiments at the forefront of interaction of high brightness electron and photon beams.     

The Kinematic Flow Structure for the Gvirtzman–Gorelick In Situ VOC Remediation System

Potential theory and Stokes' stream function techniques are used to investigate the flow structure around the recirculation system developed by Gvirtzman and Gorelick (1992, 1993), which consists of an extraction well and a gallery (trench) for the recharge of treated water to the aquifer. Analytical formulas are derived for the drawdown, velocity, and stream function for a model in which the extraction well is modeled as a uniformly distributed line sink and the gallery is modeled as a uniformly distributed ring source. Travel times are reported for water particles traveling along the streamlines containing 50 and 90% of the flow for various degrees of well penetration and various radii of the ring source. The travel times along the streamline resulting in the shortest travel time (not necessarily the shortest path) are also reported for various degrees of well penetration and various radii of the ring source. The method completely eliminates the use of numerical finite-difference or finite-element methods and can be used for optimization of technological parameters of this remediation system.     

Generation of quaternary centers by reductive cross-coupling: shifting of regioselectivity in a subset of allylic alcohol-based coupling reactions

Regioselective titanium alkoxide-mediated reductive cross-coupling reactions of allylic alcohols with vinylsilanes and imines have previously been demonstrated to proceed with allylic transposition by formal metallo-[3,3]-rearrangement [thought to proceed by a sequence of: (1) directed carbometalation, and (2) syn-elimination]. While many examples have been described that support this reaction path, a collection of substrates have recently been identified that react by way of an alternative pathway, delivering a concise convergent route to coupled products bearing a quaternary center.     

DNA-templated photonic arrays and assemblies: design principles and future opportunities

Molecular photonics is a rapidly developing and multi-disciplinary field of research involving the construction of molecular assemblies comprising photoactive building blocks that are responsive to a light stimulus. A salient challenge in this field is the controlled assembly of these building blocks with nanoscale precision. DNA exhibits considerable promise as an architecture for the templated assembly of photoactive materials. In this Concept Article we describe the progress that has been made in the area of DNA photonics, in which DNA acts as a platform for the construction of optoelectronic assemblies, thin films and devices.     

Collapse of a two-state sticky hard sphere chain

The collapse of a homopolymer gaussian chain into a globule is represented as a transition between two states, viz., extended and collapsed. Appropriately, this model has been labeled as the all-or-none view of chain collapse. In the collapsed state, the single polymer partition function is expressed by a single Mayer diagram with the maximum number of f-bonds arising from nonbonded square well interactions. Our target is the dependence of the transition temperature on chain length and the interaction range of the square well, as indicated through the behavior of the radius of gyration and the constant volume heat capacity. Properties of the collapse transition are calculated exactly for chains with three to six backbone atoms and heuristically for long chains using arguments derived from the small chains and from conditions of integrability. Comparison with simulation studies is made.