A diode device combining lateral field-effect transport and vertical tunneling in a multi-quantum-well heterostructure

The authors discuss an electronic device with asymmetric contacts to a InGaAs-InP multilayer heterostructure. Current enters via an alloyed ohmic contact into the quantum wells (QWs) and flows laterally along capacitively coupled channels. It leaves via tunneling between the layers and through a forward-biased surface Schottky contact. A step-like I-V dependence is observed and interpreted by a model calculation

Robust surface electronic properties of topological insulators: Bi2Te3 films grown by molecular beam epitaxy

The surface electronic properties of the important topological insulator Bi2Te3 are shown to be robust under an extended surface preparation procedure which includes exposure to atmosphere and subsequent cleaning and recrystallization by an optimized in-situ sputter-anneal procedure under ultra high vacuum conditions. Clear Dirac-cone features are displayed in high-resolution angle-resolved photoemission spectra from the resulting samples, indicating remarkable insensitivity of the topological surface state to cleaning-induced surface roughness.Comment: 3 pages, 3 figure

Los Alamos Plutonium Facility Waste Management System

This paper describes the new computer-based transuranic (TRU) Waste Management System (WMS) being implemented at the Plutonium Facility at Los Alamos National Laboratory (LANL). The Waste Management System is a distributed computer processing system stored in a Sybase database and accessed by a graphical user interface (GUI) written in Omnis7. It resides on the local area network at the Plutonium Facility and is accessible by authorized TRU waste originators, count room personnel, radiation protection technicians (RPTs), quality assurance personnel, and waste management personnel for data input and verification. Future goals include bringing outside groups like the LANL Waste Management Facility on-line to participate in this streamlined system. The WMS is changing the TRU paper trail into a computer trail, saving time and eliminating errors and inconsistencies in the process

Quantum Information Processing with Ferroelectrically Coupled Quantum Dots

I describe a proposal to construct a quantum information processor using ferroelectrically coupled Ge/Si quantum dots. The spin of single electrons form the fundamental qubits. Small (<10 nm diameter) Ge quantum dots are optically excited to create spin polarized electrons in Si. The static polarization of an epitaxial ferroelectric thin film confines electrons laterally in the semiconductor; spin interactions between nearest neighbor electrons are mediated by the nonlinear process of optical rectification. Single qubit operations are achieved through "g-factor engineering" in the Ge/Si structures; spin-spin interactions occur through Heisenberg exchange, controlled by ferroelectric gates. A method for reading out the final state, while required for quantum computing, is not described; electronic approaches involving single electron transistors may prove fruitful in satisfying this requirement.Comment: 10 pages, 3 figure

Watch and Learn: Seeing Is Better than Doing when Acquiring Consecutive Motor Tasks

During motor adaptation learning, consecutive physical practice of two different tasks compromises the retention of the first. However, there is evidence that observational practice, while still effectively aiding acquisition, will not lead to interference and hence prove to be a better practice method. Observers and Actors practised in a clockwise (Task A) followed by a counterclockwise (Task B) visually rotated environment, and retention was immediately assessed. An Observe-all and Act-all group were compared to two groups who both physically practised Task A, but then only observed (ObsB) or did not see or practice Task B (NoB). The two observer groups and the NoB control group better retained Task A than Actors, although importantly only the observer groups learnt Task B. RT data and explicit awareness of the rotation suggested that the observers had acquired their respective tasks in a more strategic manner than Actor and Control groups. We conclude that observational practice benefits learning of multiple tasks more than physical practice due to the lack of updating of implicit, internal models for aiming in the former

A Survey of Monitoring and Assay Systems for Release of Metals from Radiation Controlled Areas at LANL Los Alamos NATIONAL LABORATORY A SURVEY OF MONITORING AND ASSAY SYSTEMS FOR RELEASE OF METALS FROM RADIATION CONTROLLED AREAS AT LANL

Abstract At Los Alamos National Laboratory (LANL), a recent effort in waste minimization has focused on scrap metal from radiological controlled areas (RCAs). In particular, scrap metal from RCAs needs to be dispositioned in a reasonable and cost effective manner. Recycling of DOE scrap metals from RCAs is currently under a self-imposed moratorium. Since recycling is not available and reuse is difficult, often metal waste from RCAs, which could otherwise be recycled, is disposed of as low-level waste. Estimates at LANL put the cost of low-level waste disposal at $550 to$4000 per cubic meter, depending on the type of waste and the disposal site. If the waste is mixed, the cost for treatment and disposal can be as high as $50,000 per cubic meter. Disposal of scrap metal as low-level waste uses up valuable space in the low-level waste disposal areas and requires transportation to the disposal site under Department of Transportation (DOT) regulations for low-level waste. In contrast, disposal as non-radioactive waste costs as little as$2 per cubic meter. While recycling is unavailable, disposing of the metal at an industrial waste site could be the best solution for this waste stream. A Green Is Clean (GIC) type verification program needs to be in place to provide the greatest assurance that the waste does not contain DOE added radioactivity. This paper is a review of available and emerging radiation monitoring and assay systems that could be used for scrap metal as part of the LANL GIC program

New measurement technique for waveguide losses based on photoluminescence

A new technique has been developed to measure optical losses of waveguide devices fabricated in III-V semiconductors by optical excitation of an integrated twinguide structure, which is nondestructive and also applicable to multimode waveguides and multiport waveguide devices. Reproducibility of excitation was found to be better than 0.2 d

MOVPE im System Ga-In-As-P. Ein Beitrag zur Technologie und Charakterisierung von Quantentoepfen

SIGLEAvailable from TIB Hannover: DW 5528 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Investigation of the local Ge concentration in Si/SiGe nanostructures by convergent-beam electron diffraction

SiGe multi quantum well structures were investigated by convergent-beam electron diffraction (CBED) measurements. Detailed layer characterizations were performed by acquiring series of bright field CBED patterns in the form of a line scan across the nanostructures in scanning transmission electron microscopy (STEM) mode. From the higher order Laue zone (HOLZ) lines the local lattice parameters were deduced. The Ge concentration corresponding to these lattice parameters was determined by means of the elasticity theory. In this work it is shown that the lattice constants can be determined locally with an accuracy of about +/- 0.001 to +/- 0.003 angstrom which leads to an accuracy of the corresponding Ge concentration of about 1-2%. The characteristics of the focused electron probe and its influence on the experimental data were used for an estimation of the spatial resolution of the CBED method. For comparison, experimental values regarding the spatial resolution were determined by investigating the abrupt interface between Si(1 1 1) and AlN(0 0 0 1). (C) 2010 Elsevier B.V. All rights reserved