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Conference on Optoelectronic and Microelectronic Materials and Devices

作者： J. Valentine P. Moitra Y. Yang W. Wang Department of Mechanical Engineering Vanderbilt University Nashville TN USA Interdisciplinary Program in Materials Science Vanderbilt University Nashville TN USA Department of Electrical Engineering and Computer Science Vanderbilt University Nashville TN USA

Dielectric metamaterials offer a potential low-loss alternative to plasmonic metamaterials at optical frequencies. However, demonstrations of dielectric metamaterials have so far been limited to microwave and mid-infrared frequencies. In this work, we outline the development of purely dielectric zero-index metamaterials operating at optical frequencies. The metamaterial, formed from silicon rods, exhibits impedance matching with air, resulting in unity transmission at the zero-index point. Design and experimental realization of the metamaterials is presented. The metamaterials can potentially be used for a number of applications including compact lens systems, directional emitters, and transformation optics devices.

关键词： Metamaterials Magnetic materials Silicon Optical device fabrication Dielectrics Optical refraction

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Intrinsic defects and conduction characteristics of Sc2O3 in thermionic cathode systems

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Physical Review B 2012年第5期86卷 054106-054106页

作者： Ryan M. Jacobs John H. Booske Dane Morgan Interdisciplinary Materials Science Program University of Wisconsin–Madison 1509 University Avenue Madison Wisconsin 53706 USA Department of Electrical and Computer Engineering University of Wisconsin–Madison 1415 Engineering Drive Madison Wisconsin 53706 USA Department of Materials Science and Engineering University of Wisconsin–Madison 1509 University Avenue Madison Wisconsin 53706 USA

Recent experimental observations indicate that bulk Sc2O3 (∼200 nm thick), an insulator at room temperature and pressure, must act as a good electronic conductor during thermionic cathode operation, leading to the observed high emitted current densities and overall superior emission properties over conventional thermionic emitters which do not contain Sc2O3. Here, we employ ab initio methods using both semilocal and hybrid functionals to calculate the intrinsic defect energetics of Sc and O vacancies and interstitials and their effects on the electronic properties of Sc2O3 in an effort to explain the good conduction of Sc2O3 observed in experiment. The defect energetics were used in an equilibrium defect model to calculate the concentrations of defects and their compensating electron and hole concentrations at equilibrium. Overall, our results indicate that the conductivity of Sc2O3 solely due to the presence of intrinsic defects in the cathode operating environment is unlikely to be high enough to maintain the magnitude of emitted current densities obtained from experiment, and that the presence of impurities is necessary to raise the conductivity of Sc2O3 to a high enough value to explain the current densities observed in experiment. The necessary minimum impurity concentration to impart sufficient electronic conduction is very small (approximately 7.5 × 10−3 ppm) and is probably present in all experiments.

关键词： SCANDIUM oxides CATHODES PRESSURE ELECTRIC conductors POINT defects PHYSICS experiments EQUILIBRIUM

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On the interference due to cooperative cognitive radios in the presence of multiple low-power primary users

On the interference due to cooperative cognitive radios in t...

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2011 49th Annual Allerton Conference on Communication, Control, and Computing, Allerton 2011

作者： Madhusudhanan, Prasanna Brown, Timothy X. Liu, Youjian Department of Electrical Computer and Energy Engineering University of Colorado Boulder CO 80309-0425 United States Interdisciplinary Telecommunications Program University of Colorado Boulder CO 80309-0425 United States

ISBN: (纸本)9781457718168

We analyze a cognitive radio network where the low-power primary users and cognitive radio (CR) devices are distributed according to two independent homogeneous Poisson processes over the k-dimensional space, where k = 1, 2, 3. The CRs cooperate among themselves in detecting the beacons transmitted by the primary users, to ensure that they cause reduced interference at the primary users. A range of cooperative sensing schemes including the no (NC), partial (PC) and full cooperation (FC) scenarios are analyzed. Using the concepts of stochastic geometry, we assess the impact of the presence of the multiple primary users on the distribution of the signal-to-interference-plus-noise ratio (SINR) at a given primary user, for each cooperation scheme. Further, we characterize the improvement in the spectrum usage due to the CR operation in the licensed frequency band in terms of the probability, denoted by rho, that a CR is able to operate within the k-dimensional space. Using our calculations of the SINR at the primary user and rho, it is shown that the PC scheme achieves enhanced spectrum usage vis-a-vis the FC scheme and an improved SINR as compared to the NC scheme. Moreover, the PC scheme can be tuned in such a way that any desired value for spectrum usage and SINR is achievable. © 2011 IEEE.

关键词： Cognitive radio

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Accelerated oxidation of silicon due to x-ray irradiation

Accelerated oxidation of silicon due to x-ray irradiation

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12th European Conference on Radiation and Its Effects on Component and Systems, RADECS 2011

作者： Bhandaru, Shweta Zhang, En Xia Fleetwood, Daniel M. Reed, Robert A. Weller, Robert A. Weiss, Sharon M. Interdisciplinary Graduate Program in Material Science Vanderbilt University Nashville TN 37235 United States Department of Electrical Engineering and Computer Science Vanderbilt University Nashville TN 37235 United States

Enhanced rates of oxide growth have been observed on silicon when exposed to high-energy x-ray irradiation. This observed effect could potentially be utilized for remote total ionizing dose-sensing applications. ©... 详细信息

ISBN: (纸本)9781457705878

关键词： Silicon

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On the interference due to cooperative cognitive radios in the presence of multiple low-power primary users

On the interference due to cooperative cognitive radios in t...

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Annual Allerton Conference on Communication, Control, and Computing

作者： Prasanna Madhusudhanan Timothy X Brown Youjian Liu Department of Electrical Computer and Energy Engineering University of Colorado Boulder CO USA Department of Electrical Computer and Energy Engineering Interdisciplinary Telecommunications Program University of Colorado Boulder CO USA

ISBN: (纸本)9781457718175

We analyze a cognitive radio network where the low-power primary users and cognitive radio (CR) devices are distributed according to two independent homogeneous Poisson processes over the k- dimensional space, where k = 1, 2, 3. The CRs cooperate among themselves in detecting the beacons transmitted by the primary users, to ensure that they cause reduced interference at the primary users. A range of cooperative sensing schemes including the no (NC), partial (PC) and full cooperation (FC) scenarios are analyzed. Using the concepts of stochastic geometry, we assess the impact of the presence of the multiple primary users on the distribution of the signal-to-interference-plus-noise ratio (SINR) at a given primary user, for each cooperation scheme. Further, we characterize the improvement in the spectrum usage due to the CR operation in the licensed frequency band in terms of the probability, denoted by rho, that a CR is able to operate within the k-dimensional space. Using our calculations of the SINR at the primary user and rho, it is shown that the PC scheme achieves enhanced spectrum usage vis-a-vis the FC scheme and an improved SINR as compared to the NC scheme. Moreover, the PC scheme can be tuned in such a way that any desired value for spectrum usage and SINR is achievable.

关键词： Interference Receivers PSNR Silicon Cognitive radio Random variables

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Multi-Tier Network Performance Analysis Using a Shotgun Cellular System

Multi-Tier Network Performance Analysis Using a Shotgun Cell...

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2011 IEEE Global Telecommunications Conference - GLOBECOM 2011

作者： Prasanna Madhusudhanan Juan G. Restrepo Youjian Liu Timothy X. Brown Kenneth R. Baker Department of Electrical Computer and Energy Engineering University of Colorado Boulder CO USA Department of Applied Mathematics University of Colorado Boulder CO USA Department of Electrical Computer and Energy Engineering Interdisciplinary Telecommunications Program University of Colorado Boulder CO USA Interdisciplinary Telecommunications Program University of Colorado Boulder CO USA

This paper studies the carrier-to-interference ratio (CIR) and carrier-to-interference-plus-noise ratio (CINR) performance at the mobile station (MS) within a multi-tier network composed of M tiers of wireless networks, with each tier modeled as the homogeneous n-dimensional (n-D, n=1,2, and 3) shotgun cellular system, where the base station (BS) distribution is given by the homogeneous Poisson point process in n-D. The CIR and CINR at the MS in a single tier network are thoroughly analyzed to simplify the analysis of the multi-tier network. For the multi-tier network with given system parameters, the following are the main results of this paper: (1) semi-analytical expressions for the tail probabilities of CIR and CINR; (2) a closed form expression for the tail probability of CIR in the range [1,infinity); (3) a closed form expression for the tail probability of an approximation to CINR in the entire range [0,infinity); (4) a lookup table based approach for obtaining the tail probability of CINR, and (5) the study of the effect of shadow fading and BSs with ideal sectorized antennas on the CIR and CINR. Based on these results, it is shown that, in a practical cellular system, the installation of additional wireless networks (microcells, picocells and femtocells) with low power BSs over the already existing macrocell network will always improve the CINR performance at the MS.

关键词： Fading Noise Approximation methods Random variables Closed-form solutions Macrocell networks Femtocells

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Stabilization of hydroxyl-terminated silanes in porous silicon for in-situ DNA synthesis

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Physica Status Solidi (C) Current Topics in Solid State Physics 2011年第6期8卷 1851-1855页

作者： Lawrie, Jenifer L. Weiss, Sharon M. Interdisciplinary Graduate Program in Materials Science Vanderbilt University Nashville TN United States Department of Electrical Engineering and Computer Science Vanderbilt University Nashville TN United States

Passivation of porous silicon sensors is a critical issue for achieving high sensitivity and selectivity toward biomolecule targets that may be detected in complex physiologic solution. Without appropriate passivation, degradation of the porous silicon matrix inhibits the repeatability of optical measurements and limits applications in complex media. In this work, we present a method for stabilizing TEOS-HBA monolayers in porous silicon. Annealing of the silane at 200°C for 16 hours, followed by a deionized water wash for a minimum of one hour, results in a porous silicon surface that is highly stable in a number of solvents. Annealing improves cross-linking of surface-attached silane molecules for added stability, and hydrolyzing facilitates removal of weakly bound multilayers. This surface treatment procedure is of considerable interest in applications such as DNA synthesis where hydroxyl functionality is critical and a thick silane surface coating is not desired. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

关键词： Passivation

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Accelerated oxidation of silicon due to x-ray irradiation

Accelerated oxidation of silicon due to x-ray irradiation

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European Conference on Radiation and its Effects on Components and Systems (RADECS)

作者： Shweta Bhandaru En Xia Zhang Daniel M. Fleetwood Robert A. Reed Robert A. Weller Sharon M. Weiss Interdisciplinary Graduate Program in Material Science Vanderbilt University Nashville TN USA Department of Electrical Engineering and Computer Science Vanderbilt University Nashville TN USA

关键词： Silicon Radiation effects Oxidation Atomic measurements Temperature measurement Optical sensors Atomic layer deposition

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Optimization of defect hole placement in resonant cavities

Optimization of defect hole placement in resonant cavities

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作者： Kang, Christopher Weiss, Sharon M. Vlasov, Yurii A. Assefa, Solomon Interdisciplinary Graduate Program in Materials Science Vanderbilt University Nashville TN 37235 United States Department of Physics and Astronomy Vanderbilt University Nashville TN 37235 United States Department of Electrical Engineering and Computer Science Vanderbilt University 37235 United States IBM T.J. Watson Research Center Yorktown Heights NY 10536 United States

We demonstrate the resonance wavelength and quality factor dependence of 50nm defect-hole placement within photonic crystal L3 microcavities. Proper placement of defect-holes leads to a 12% increase in photonic crysta... 详细信息

ISBN: (纸本)9781557529107

关键词： Photonic crystals

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Optimization of defect hole placement in resonant cavities

Optimization of defect hole placement in resonant cavities

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Conference on Lasers and Electro-Optics (CLEO)

作者： Christopher Kang Sharon M. Weiss Yurii A. Vlasov Solomon Assefa Interdisciplinary Graduate Program in Materials Science Vanderbilt University Nashville TN USA Department of Electrical Engineering and Computer Science Vanderbilt University USA IBM T.J Watson Research Center Yorktown Heights NY USA

ISBN: (纸本)9781557529107

关键词： Cavity resonators Lattices Photonic crystals Optical waveguides Sensitivity Slabs Q factor

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