Electron Sources for Future Lightsources, Summary and Conclusions for the Activities during FLS 2012

This paper summarizes the discussions, presentations, and activity of the Future Light Sources Workshop 2012 (FLS 2012) working group dedicated to Electron Sources. The focus of the working group was to discuss concepts and technologies that might enable much higher peak and average brightness from electron beam sources. Furthermore the working group was asked to consider methods to greatly improve the robustness of operation and lower the costs of providing electrons.Comment: 11 pages, 7 figures, summary paper from working group Future Light Sources 2012 Workshop at Newport News, Virginia, USA (http://www.jlab.org/conferences/FLS2012/

A review of advances in pixel detectors for experiments with high rate and radiation

The Large Hadron Collider (LHC) experiments ATLAS and CMS have established hybrid pixel detectors as the instrument of choice for particle tracking and vertexing in high rate and radiation environments, as they operate close to the LHC interaction points. With the High Luminosity-LHC upgrade now in sight, for which the tracking detectors will be completely replaced, new generations of pixel detectors are being devised. They have to address enormous challenges in terms of data throughput and radiation levels, ionizing and non-ionizing, that harm the sensing and readout parts of pixel detectors alike. Advances in microelectronics and microprocessing technologies now enable large scale detector designs with unprecedented performance in measurement precision (space and time), radiation hard sensors and readout chips, hybridization techniques, lightweight supports, and fully monolithic approaches to meet these challenges. This paper reviews the world-wide effort on these developments.Comment: 84 pages with 46 figures. Review article.For submission to Rep. Prog. Phy

High Quality Silicon Carbide Epitaxial Growth by Novel Fluorosilane Gas Chemistry For Next Generation High Power Electronics

High quality, thick (~100µm), low doped and low defect density SiC epitaxial films are essential for high voltage (blocking voltage \u3e10kV), light, compact and reliable next generation power devices. One of the significant challenges in obtaining high quality thick SiC epitaxial films is to restrict/eliminate the Si gas-phase nucleation or aerosol formation during growth. The generated aerosol particles adversely influence growth by reducing the growth rate due to precursor losses, and also affect crystal quality, since the Si droplets are carried to the crystal growth surface. Moreover, liquid aerosol particles adhere to the various reactor parts (parasitic deposition), and contribute to their severe degradation during epitaxial growth. These parasitic depositions are generally loosely bound, and can be carried to the growth surface during growth as particulates, resulting in degradation of crystal quality by introducing defects in the growing epitaxial layers. The aforesaid condition is specifically severe at higher precursor gas flow rates or in long duration growth required to achieve high quality thick epitaxy since parasitic deposition and related particulate formation are also increased at these growth conditions. At this parasitic deposition enhanced condition, the cost of growth is also expected to increase due to frequent replacement of degraded reactor parts. Hence, cost effective, high quality thick epitaxy is not achievable until the particle generation in the reactor is suppressed effectively in high temperature SiC CVD. To investigate the critical issues of parasitic deposition and nucleation related particle generation, intensive comparative study was performed for the first time for different conventional silane and chloro-silane gases. Based on the study of these precursors, a novel Si precursor gas tetrafluorosilane (SiF4) was proposed to be a superior Si precursor gas specifically suitable for high temperature SiC CVD. Initially, SiF4 is compared to DCS without any propane addition during growth. It was found that without propane SiF4 with only hydrogen, no Si deposition takes place in the reactor (only etches the SiC), whereas DCS deposits severe Si on the surface making the reactor parts unusable. The ability of SiF4 not to deposit Si in the reactor is unique and found to be very useful to achieve high quality SiC epitaxy at high temperatures in the cleanest possible growth environment. The chemistry of SiF4 gas precursor is utilized to eliminate Si gas phase nucleation and Si parasitic deposition during silicon carbide (SiC) epitaxial growth, otherwise unachievable in similar growth conditions using conventional silane (SiH4) and dichlorosilane (SiCl2H2/DCS) precursors. Higher Si-F bond strength (565 kJ/mol) in SiF4 prevents early gas decomposition and Si cluster formation, essential for high temperature SiC CVD, and yet enables growth of high quality epitaxy in an improved particulate suppressed growth condition. High quality, thick 4H-SiC epilayers \u3e100 um have been demonstrated using SiF4 with excellent surface morphology, polytype uniformity, crystallinity and low defect density needed for reliable high power devices

Electro-spinning/netting: A strategy for the fabrication of three-dimensional polymer nano-fiber/nets.

Since 2006, a rapid development has been achieved in a subject area, so called electro-spinning/netting (ESN), which comprises the conventional electrospinning process and a unique electro-netting process. Electro-netting overcomes the bottleneck problem of electrospinning technique and provides a versatile method for generating spider-web-like nano-nets with ultrafine fiber diameter less than 20 nm. Nano-nets, supported by the conventional electrospun nanofibers in the nano-fiber/nets (NFN) membranes, exhibit numerious attractive characteristics such as extremely small diameter, high porosity, and Steiner tree network geometry, which make NFN membranes optimal candidates for many significant applications. The progress made during the last few years in the field of ESN is highlighted in this review, with particular emphasis on results obtained in the author's research units. After a brief description of the development of the electrospinning and ESN techniques, several fundamental properties of NFN nanomaterials are addressed. Subsequently, the used polymers and the state-of-the-art strategies for the controllable fabrication of NFN membranes are highlighted in terms of the ESN process. Additionally, we highlight some potential applications associated with the remarkable features of NFN nanostructure. Our discussion is concluded with some personal perspectives on the future development in which this wonderful technique could be pursued

Analysis, Design and Fabrication of Micromixers, Volume II

Micromixers are an important component in micrototal analysis systems and lab-on-a-chip platforms which are widely used for sample preparation and analysis, drug delivery, and biological and chemical synthesis. The Special Issue "Analysis, Design and Fabrication of Micromixers II" published in Micromachines covers new mechanisms, numerical and/or experimental mixing analysis, design, and fabrication of various micromixers. This reprint includes an editorial, two review papers, and eleven research papers reporting on five active and six passive micromixers. Three of the active micromixers have electrokinetic driving force, but the other two are activated by mechanical mechanism and acoustic streaming. Three studies employs non-Newtonian working fluids, one of which deals with nano-non-Newtonian fluids. Most of the cases investigated micromixer design

High Quality Low Offcut 4h-Sic Epitaxy and Integrated Growth of Epitaxial Graphene for Hybrid Graphene/Sic Devices

Power electronic semiconductor devices are critical components in next-generation power systems such as hybrid electric vehicles and smart grid power controls enabling reduction in system size, weight, and cost. Wide bandgap materials such as SiC, GaN, and diamond have been investigated to replace silicon, due to their superior material properties. Of these, 4H-SiC is considered the most viable candidate beyond 3kV due to its technological maturity, its wide band gap (3.23 eV), high breakdown field (4×106 V/cm), high thermal conductivity (5 W/cm/K) and, more importantly, its indirect bandgap. The main contribution of my research relates to the development and investigating the methods for growing high-quality SiC homoepitaxial layers with low defect density, particularly basal plane dislocations (BPDs) which severely affects the SiC bipolar device yield in high scale environments. The first approach of eliminating BPDs was to produce high quality SiC epilayers using a novel Si precursor Tetrafluorosilane (TFS) on nearly on-axis substrates (0.5° offcut) which inherently suppress BPD formation, by identifying a unique growth regime that promotes step flow growth in a nearly on-axis surface which is considered a major challenge in SiC epitaxy. As an alternate solution to BPD elimination in the most common 4º subtsrtaes, we developed a composite growth structure to produce 100% BPD free SiC epilayers over a wide range of C/Si ratios (1 to 1.8), introducing a minimal specific on-resistance of Final part of this work is integrating the high quality SiC epilayers for fabricating hybrid EG/SiC Schottky structures with epitaxial graphene as an in-situ high temperature metal contact grown using TFS under Argon ambience. The EG/SiC Schottky devices fabricated exhibited an excellent ideality of 1.1 and a barrier height of 0.85 eV. These EG/SiC Schottky devices were tested as photodetectors for sensing UV light owing to graphene’s transparent optical property and 4H-SiC bandgap which is in the range of UV spectrum. With these contributions made towards increasing the material quality and yield of SiC and SiC-graphene devices, SiC can be envisioned as a versatile and reliable material for power electronics and harsh environment sensor applications in the near future