A comparative materials study of magnetron ion etched GaAs using Freon-12, SiCl4 and BCl3

Etch characteristics and residual damage incurred via magnetron ion etching of GaAs using three different etch gases, namely, freon-12, SiCl₄ and BCl₃, at two different power levels has been studied. Transmission electron microscopy, scanning electron microscopy, Auger electron spectroscopy, and Schottky diode measurements were employed to determine the suitability of the processed surfaces for device fabrication. Lattice damage was incurred in all processing situations in the form of small dislocation loops. Samples etched in freon-12 at the highest power density exhibited the roughest surface morphology, while those etched in SiCl₄ and BCl₃ resulted in planar surfaces. The Schottky barrier diode characteristics, for all etch gases, degraded with increasing power density. The electrical quality of the BCl₃-etched GaAs at the lowest power density was superior to that of the other etch gases at all power levels. The etched profiles of SiCl₄ and BCl₃ yielded vertical sidewalls, whereas freon-12 yielded a negative undercut. The BCl₃-etched GaAs surfaces were residue-free, while those of freon-12 and SiCl₄ exhibited surface or sidewall contamination. Our results have demonstrated that magnetron ion etching with BCl₃ yields planar residue-free surfaces with minimum material surface damage and superior electrical integrity compared with GaAs etched with freon-12 or SiCl₄.     

An extended shear angle model derived from in situ strain measurements during orthogonal cutting

There are numerous cutting models which describe the chip formation process. However, they are based on a number of simplifying assumptions. In order to verify these assumptions and to get a better understanding of the cutting process, the different stress states in the chip formation zone were determined by means of diffraction experiments with monochromatic high-energy synchrotron X-radiation during orthogonal, quasistatic cutting of the material C45E. The results from the experiments are compared with simulated stresses. The experimental data indicate that the assumption of a free chip flow according to the shear angle model of Opitz and Hucks is not valid. The model was therefore extended considering the normal stresses in direction of the chip flow.     

Austenitic stainless steel for separating safeguards: development of an FEA-model for the simulation of impact tests in reference to material specific parameters

Austenitic stainless steels have a high potential for the use in separating safeguards of machine tools based on the TRIP (Transformation Induced Plasticity) effect. The problem with these materials is the high variance of the alloy composition. Therefore, the specific penetration resistance W _D,spec varies significantly. The presented research analyses the impact of material specific parameters on the specific penetration resistance W _D,spec and the FEA simulation of impact tests. The result of the project is the knowledge of the penetration resistance and hence the security (factor of safety) against penetration.     

Machining of micro rotational parts by wire electrical discharge grinding

Micro rotational parts are used in several industrial sectors. Well-known applications are micro shafts of gears, ejector pins in forming tools, pin electrodes for micro electrical discharge drilling or micro stamping dies. Depending on the geometrical complexity of micro rotational parts different process variants of micro electrical discharge machining characterized by a rotating work piece can be used: wire electrical discharge grinding (WEDG) with fine wire electrodes, electrical discharge turning (EDT) with micro structured tool electrode, cylindrical electrical discharge grinding (CEDG) with micro profiled disk electrode. Characteristic to these process variants is the superimposed relative motion between the rotating electrodes and the feed. This relative motion can be varied in a wide circumferential velocity range to improve the material removal process. The paper gives an overview of kinematic and technological restrictions and requirements of the WEDG process influencing the process behavior with respect to the technological requirements of micromachining.     

The National Ignition Facility neutron time-of-flight system and its initial performance (invited)

The National Ignition Facility (NIF) successfully completed its first inertial confinement fusion (ICF) campaign in 2009. A neutron time-of-flight (nTOF) system was part of the nuclear diagnostics used in this campaign. The nTOF technique has been used for decades on ICF facilities to infer the ion temperature of hot deuterium (D(2)) and deuterium-tritium (DT) plasmas based on the temporal Doppler broadening of the primary neutron peak. Once calibrated for absolute neutron sensitivity, the nTOF detectors can be used to measure the yield with high accuracy. The NIF nTOF system is designed to measure neutron yield and ion temperature over 11 orders of magnitude (from 10(8) to 10(19)), neutron bang time in DT implosions between 10(12) and 10(16), and to infer areal density for DT yields above 10(12). During the 2009 campaign, the three most sensitive neutron time-of-flight detectors were installed and used to measure the primary neutron yield and ion temperature from 25 high-convergence implosions using D(2) fuel. The OMEGA yield calibration of these detectors was successfully transferred to the NIF.     

视觉景观研究——回顾与展望

阐述了视觉景观研究的回顾与展望。在2个对立学派的基础上形成视觉景观质量评估。客观主义者或物理学派(基于专家的方式方法)认为视觉景观质量是其自身物质特性的内在表现。主观主义者或心理学派(基于个人的方式方法)认为景观美是客体或视觉媒介和观察者的相互作用。如照片、草图、模型、三维可视化等景观表达可以协助实施现场或遥感评估。评估方法包括例如明智的配对比较法、分类法,还有其他分级或排序法。大多数的研究脱离现实环境而实施,容易忽视人们动态地感知世界。在虚拟现实影院里,景观身临其境的体验为观众提供了自由探索这个虚拟环境的机会。移动增强现实技术的最新发展进一步提供了这种可能:现存环境的影像与被数字可视化的未来变化影像相叠合,如同现场体验一般,从而提供了全方位的感官体验,这将为景观评估提供新的途径。     

Kilopixel X-ray Microcalorimeter Arrays for Astrophysics: Device Performance and Uniformity

We are developing kilopixel arrays of TES microcalorimeters to enable high-resolution x-ray imaging spectrometers for future x-ray observatories and laboratory astrophysics experiments. Our current array design was targeted as a prototype for the X-ray Microcalorimeter Spectrometer proposed for the International X-ray Observatory, which calls for a 40×40-pixel core array of 300?μm devices with 2.5?eV energy resolution (at 6?keV). Here we present device characterization of our 32×32 arrays, including x-ray spectral performance of individual pixels within the array. We present our results in light of the understanding that our Mo/Au TESs act as weak superconducting links, causing the TES critical current (I _c ) and transition shape to oscillate with applied magnetic field (B). We show I _c (B) measurements and discuss the uniformity of these measurements across the array, as well as implications regarding the uniformity of device noise and response. In addition, we are working to reduce pixel-to-pixel electrical and thermal crosstalk; we present recent test results from an array that has microstrip wiring and an angle-evaporated copper backside heatsinking layer, which provides copper coverage on the four sidewalls of the silicon wells beneath each pixel.     

Implications of Weak Link Effects on Thermal Characteristics of Transition-Edge Sensors

Weak link behavior in transition-edge sensor (TES) microcalorimeters creates the need for a more careful characterization of a device’s thermal characteristics through its transition. This is particularly true for small TESs where a small change in the bias current results in large changes in effective transition temperature. To correctly interpret measurements, especially complex impedance, it is crucial to know the temperature-dependent thermal conductance, G(T), and heat capacity, C(T), at each point through the transition. We present data illustrating these effects and discuss how we overcome the challenges that are present in accurately determining G and T from I–V curves. We also show how these weak link effects vary with TES size. Additionally, we use this improved understanding of G(T) to determine that, for these TES microcalorimeters, Kaptiza boundary resistance dominates the G of devices with absorbers while the electron-phonon coupling also needs to be considered when determining G for devices without absorbers