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Full-Text Articles in Engineering
The Electrostatic Interaction Of Charged, Dust-Particle Pairs In Plasmas, M. E. Markes, P. F. Williams
The Electrostatic Interaction Of Charged, Dust-Particle Pairs In Plasmas, M. E. Markes, P. F. Williams
Department of Electrical and Computer Engineering: Faculty Publications
We report the results of a study of the electrostatic interaction between negatively charged particles in a plasma. The goal of the study was to investigate the possibility of an attractive interaction which would make possible the formation of “molecules” of particles. For all approximations relating the positive ion density to the local electrostatic potential that we examined, we find that the interaction is repulsive for all particle separations.
Infrared Switching Electrochromic Devices Based On Tungsten Oxide, E. B. Franke, C. L. Trimble, J. S. Hale, Mathias Schubert, John A. Woollam
Infrared Switching Electrochromic Devices Based On Tungsten Oxide, E. B. Franke, C. L. Trimble, J. S. Hale, Mathias Schubert, John A. Woollam
Department of Electrical and Computer Engineering: Faculty Publications
Different types of electrochromic devices for thermal emittance modulation were developed in the spectral region from mid- to far-infrared (2–40 μm). In all devices polycrystalline and amorphous tungsten oxide have been used as electrochromic and ion storage layer, respectively. Two types of all-solid-state devices were designed, one with a metal grid for the top and bottom electrode deposited on a highly emissive glass substrate, and another with a top metal grid electrode and a highly reflecting bottom metal electrode layer. Tantalum oxide is used as an ion conductor in both device types. The third device type consists of a polymeric …
Thickness Analysis Of Silicon Membranes For Stencil Masks, E. Sossna, R. Kassing, I. W. Rangelow, C. M. Herzinger, T. E. Tiwald, John A. Woollam, Th. Wagner
Thickness Analysis Of Silicon Membranes For Stencil Masks, E. Sossna, R. Kassing, I. W. Rangelow, C. M. Herzinger, T. E. Tiwald, John A. Woollam, Th. Wagner
Department of Electrical and Computer Engineering: Faculty Publications
Stencil masks are key to charged particle projection lithography, in particular for ion projection lithography. To fulfill pattern printing requirements in the sub-70 nm regime, excellent thickness uniformity and thermal emissivity control are critical parameters for high quality stencil mask fabrication. We propose and demonstrate a technique based on infrared variable angle spectroscopic ellipsometry (IR-VASE) to measure these parameters with adequate accuracy and precision. The refractive index of the Si membrane was evaluated using a Sellmeier dispersion model combined with a Drude model. Because of its spectral range from 2 to 33 μm, the IR-VASE method is sensitive to the …
Dielectric Function Of Amorphous Tantalum Oxide From The Far Infrared To The Deep Ultraviolet Spectral Region Measured By Spectroscopic Ellipsometry, Eva Franke, C. L. Trimble, M. J. Devries, John A. Woollam, Mathias Schubert, F. Frost
Dielectric Function Of Amorphous Tantalum Oxide From The Far Infrared To The Deep Ultraviolet Spectral Region Measured By Spectroscopic Ellipsometry, Eva Franke, C. L. Trimble, M. J. Devries, John A. Woollam, Mathias Schubert, F. Frost
Department of Electrical and Computer Engineering: Faculty Publications
Amorphous tantalum oxide thin films were deposited by reactive rf magnetron sputtering onto [001] silicon substrates. Growth temperature, oxygen partial pressure, and total gas pressure have been varied to obtain thin films with different densities. The thin films were analyzed by glancing angle-of-incidence x-ray diffraction, atomic force microscopy, and variable angle-of-incidence spectroscopic ellipsometry in the near infrared to vacuum ultraviolet spectral region for photon energies from E=1 to 8.5 eV, and in the infrared region from E=0.03 to 1 eV. We present the dielectric function of amorphous tantalum oxide obtained by line shape analysis of the experimental ellipsometric …
Self-Organization In Porous 6h–Sic, S. Zangooie, John A. Woollam, H. Arwin
Self-Organization In Porous 6h–Sic, S. Zangooie, John A. Woollam, H. Arwin
Department of Electrical and Computer Engineering: Faculty Publications
Pores in porous 6H–SiC were found to propagate first nearly parallel with the basal plane and gradually change direction and align with the c axis. As a consequence, well-defined columnar pores were formed. It was shown that the rate of change of propagation directions was influenced by the etching parameters, such as hydrofluoric acid concentration and current density. Larger currents resulted in formation of larger pores. Pore sizes were found to increase with depth due to a decrease of the acid concentration. In addition, due to chemical etching effects, larger pore sizes were obtained close to the sample surface.
Dielectric Tensor For Interfaces And Individual Layers In Magnetic Multilayer Structures, Xiang Gao, Michael J. Devries, Daniel W. Thompson, John A. Woollam
Dielectric Tensor For Interfaces And Individual Layers In Magnetic Multilayer Structures, Xiang Gao, Michael J. Devries, Daniel W. Thompson, John A. Woollam
Department of Electrical and Computer Engineering: Faculty Publications
The magneto-optical Kerr response of metallic magnetic multilayers has been studied by determining the dielectric tensors (dielectric functions) for individual layers, including the magnetic and nonmagnetic interfacial layers. The diagonal components of these tensors were determined using in situ ellipsometric analysis, where the ellipsometric data were taken in real time during multilayer deposition. The off-diagonal components were determined by regression fitting magneto-optic polar Kerr rotation and ellipticity data to models supported by electromagnetic theory. The Voigt parameters (ratio between off-diagonal and diagonal components of dielectric tensors) were determined from these model fits. Higher magnitudes for the Voigt parameters were found …
All-Solid-State Electrochromic Reflectance Device For Emittance Modulation In The Far-Infrared Spectral Region, E. B. Franke, C. L. Trimble, Mathias Schubert, John A. Woollam
All-Solid-State Electrochromic Reflectance Device For Emittance Modulation In The Far-Infrared Spectral Region, E. B. Franke, C. L. Trimble, Mathias Schubert, John A. Woollam
Department of Electrical and Computer Engineering: Faculty Publications
All-solid-state electrochromic reflectance devices for thermal emittance modulation were designed for operation in the spectral region from mid- to far-infrared wavelengths (2–40 μm). All device constituent layers were grown by magnetron sputtering. The electrochromic (polycrystalline WO3), ion conductor (Ta2O5), and Li+ ion-storage layer (amorphous WO3), optimized for their infrared (IR) optical thicknesses, are sandwiched between a highly IR reflecting Al mirror, and a 90% IR transmissive Al grid top electrode, thereby meeting the requirements for a reversible Li+ ion insertion electrochromic device to operate within the 300 K blackbody emission …
Optical Properties Of Bulk And Thin-Film Srtio3 On Si And Pt, Stefan Zollner, A. A. Demkov, R. Liu, P. L. Fejes, R.B. Gregory, Prasad Alluri, J. A. Curless, Z. Yu, J. Ramdani, R. Droopad, T. E. Tiwald, J. N. Hilfiker, John A. Woollam
Optical Properties Of Bulk And Thin-Film Srtio3 On Si And Pt, Stefan Zollner, A. A. Demkov, R. Liu, P. L. Fejes, R.B. Gregory, Prasad Alluri, J. A. Curless, Z. Yu, J. Ramdani, R. Droopad, T. E. Tiwald, J. N. Hilfiker, John A. Woollam
Department of Electrical and Computer Engineering: Faculty Publications
We have studied the optical properties (complex dielectric function) of bulk SrTiO3 and thin films on Si and Pt using spectroscopic ellipsometry over a very broad spectral range, starting at 0.03 eV [using Fourier transform infrared (FTIR) ellipsometry] to 8.7 eV. In the bulk crystals, we analyze the interband transitions in the spectra to determine the critical-point parameters. To interpret these transitions, we performed band structure calculations based on ab initio pseudopotentials within the local-density approximation. The dielectric function was also calculated within this framework and compared with our ellipsometry data. In the FTIR ellipsometry data, we notice a …
In Situ Ellipsometry Growth Characterization Of Dual Ion Beam Deposited Boron Nitride Thin Films, E. Franke, Mathias Schubert, John A. Woollam, J.-D. Hecht, G. Wagner, H. Neumann, F. Bigl
In Situ Ellipsometry Growth Characterization Of Dual Ion Beam Deposited Boron Nitride Thin Films, E. Franke, Mathias Schubert, John A. Woollam, J.-D. Hecht, G. Wagner, H. Neumann, F. Bigl
Department of Electrical and Computer Engineering: Faculty Publications
Pure hexagonal h, as well as mixed-phase cubic/hexagonal c/h boron nitride (BN) thin films were deposited onto [001] silicon substrates using the dual ion beam deposition technique. The BN thin films were grown under UHV conditions at different substrate temperatures and ion beam bombarding parameters. Thin-film growth was monitored using in situ spectroscopic ellipsometry at 44 wavelengths between 420 and 761 nm. The in situ ellipsometric Ψ and Δ data were compared with two-layer growth model calculations for the mixed-phase c/h BN, and with one-layer growth model calculations for pure h-BN growth. In situ data provide information on …
Ambiguity Function Of An Ultrawideband Random Noise Radar, Muhammad Dawood, Ram M. Narayanan
Ambiguity Function Of An Ultrawideband Random Noise Radar, Muhammad Dawood, Ram M. Narayanan
Department of Electrical and Computer Engineering: Faculty Publications
The University of Nebraska has developed an ultra-wideband (UWB) random noise radar system which transmits an ultra-wideband random noise (Gaussian) waveform with a uniform power spectral density (PSD) in the 1-2 GHz frequency range. The ability of the system to characterize the Doppler shift of moving targets exhibiting varying linear and rotational velocities was clearly demonstrated [l, 2]. In this paper, we look at the range and range rate resolution issues by analyzing the Woodward’s ambiguity function [3]. In general, the radar signal ambiguity function is defined as the normalized response of a filter matched to a return signal with …
Class Project On Airborne Radar System Design And Development For Remote Sensing Applications, Ram M. Narayanan, K. Jon Ranson
Class Project On Airborne Radar System Design And Development For Remote Sensing Applications, Ram M. Narayanan, K. Jon Ranson
Department of Electrical and Computer Engineering: Faculty Publications
A unique experiment on remote sensing education has recently been undertaken involving an educational institution (University of Nebraska-Lincoln) and a government agency involved in remote sensing (NASA Goddard Space Flight Center). The centerpiece of this experiment is the assignment of an airborne radar system design project to students enrolled in a senior undergraduate and graduate level class on Radar Systems. The class was split into two competing teams. A fictitious request for proposal (RFP) was issued by NASA GSFC, and the teams responded to the RFF’ by proposing and defending competing designs. The teams also prepared final design reports, and …
Doppler Estimation Using A Coherent Ultrawide-Band Random Noise Radar, Ram M. Narayanan, Muhammad Dawood
Doppler Estimation Using A Coherent Ultrawide-Band Random Noise Radar, Ram M. Narayanan, Muhammad Dawood
Department of Electrical and Computer Engineering: Faculty Publications
The University of Nebraska has developed an ultrawide- band (UWB) coherent random noise radar operating over the 1–2 GHz frequency range. The system achieves phase coherence by using heterodyne correlation of the received signal with a time-delayed frequency-shifted replica of the transmit waveform. Knowledge of the phase of the received signal and its time dependence due to target motion permits the extraction of the mean Doppler frequency from which the target speed can be inferred. Theoretical analysis, simulation studies, and laboratory measurements using a microwave delay line showed that it was possible to estimate the Doppler frequency from targets with …
A Comparative Study Of Uwb Fopen Radar Imaging Using Step-Frequency And Random Noise Waveforms, Xiaojian Xu, Ram M. Narayanan
A Comparative Study Of Uwb Fopen Radar Imaging Using Step-Frequency And Random Noise Waveforms, Xiaojian Xu, Ram M. Narayanan
Department of Electrical and Computer Engineering: Faculty Publications
The detection and identification of targets that are obscured by foliage have been topics of great interest. Several experimental developments of such ultrawideband (UWB) radars have been published. By operating in the VHF and UHF frequency bands and using either LFM or step-frequency waveforms, these radars have demonstrated promising images of terrain and man-made objects obscured by dense foliage [l]. The University of Nebraska has developed a new technique that permits coherent processing of backscatter data acquired by a radar that transmits UWB random noise signals. This technique has been used in various applications, such as ground penetration detection of …
Sar Imaging Using Fully Random Bandlimited Signals, Dmitriy S. Garmatyuk, Ram M. Narayanan
Sar Imaging Using Fully Random Bandlimited Signals, Dmitriy S. Garmatyuk, Ram M. Narayanan
Department of Electrical and Computer Engineering: Faculty Publications
A coherent ultrawideband (UWB) random noise synthetic aperture radar (SAR) has been developed and tested at the University of Nebraska. It has been experimentally shown that this type of radar is capable of extracting the phase and the amplitude of the backscattered signal, thus enabling us to create target profiles in the frequency domain. The use of fully random waveforms (bandlimited noise) as the transmit signal is analyzed in this paper. A UWB signal model is developed and radar signal processing is simulated to yield statistical characteristics of image formation using stochastic waveforms. The influence of UWB signal characteristics on …