Electrical and Computer Engineering Commons^™

Thin-Film Hermeticity: A Quantitative Analysis Of Diamond-Like Carbon Using Variable Angle Spectroscopic Ellipsometry, S. Orzeszko, Bhola N. De, John A. Woollam, John J. Pouch, Samuel A. Alterovitz, David C. Ingram

Department of Electrical and Computer Engineering: Faculty Publications

The purpose of this paper is twofold. First, we report on the successful application of variable angle spectroscopic ellipsometry to quantitative thin-film hermeticity evaluation. Secondly, it is shown that under a variety of film preparations and moisture introduction conditions water penetrates only a very thin diamondlike carbon (DLC) top surface-roughness region. Thus DLC is an excellent candidate for use as protective coatings in adverse chemical and aqueous environments.

Variable Angle Of Incidence Spectroscopic Ellipsometric Characterization Of Tio2/Ag/Tio2 Optical Coatings, Kazem Memarzadeh, John A. Woollam, Abe Belkind

Department of Electrical and Computer Engineering: Faculty Publications

Optical constants (3000–8000 Å) and layer thicknesses of TiO₂/Ag/TiO₂ optical coatings are determined using variable angle of incidence spectroscopic ellipsometry. Ellipsometrically determined silver layer thicknesses agree well with those obtained by cross-sectional transmission electron microscopy. Also, spectral characteristics, absent in bulk silver data, are observed in n and k spectra for the thin silver layers. It is suggested that these structures may be caused by plasmon effects from the silver layers.

Physical Mechanism Of Triggering In Trigatron Spark Gaps, F. E. Peterkin, P. F. Williams

P. F. (Paul Frazer) Williams Publications

Since the first trigatron spark gap was described by J. D. Craggs, M. E. Haine, and J. M. Meek [J. Inst. Electr. Eng. 93A, 963 (1946)], there has been controversy about the physical mechanism responsible for triggering the devices. In this letter we present experimental evidence that directly shows the sequence of physical events responsible for triggering in the gap we studied, and we present a model for trigatron triggering based on this information. We believe this model to be general and discuss it in light of existing literature. We briefly discuss the implications of the model for the engineering …

Two-Dimensionat Studies Of Streamers Fn Gases, S. K. Dhali, P. F. Williams

P. F. (Paul Frazer) Williams Publications

We present the results of two-dimensional computer simulations of streamer initiation and propagation in atmospheric pressure N₂. The simulation algorithm makes use of flux-corrected transport techniques and was used as a tool to study the solutions of the transport equations under conditions suitable for streamers, for which realistic analytic solutions are not known. We present and discuss conclusions about streamer transport based on the results of these studies. Finally, we present a novel method of checking on the numerical accuracy with which the algorithm solves the transport equations.

Influence Of Photodetachment On The Switching Characteristics Of Diffuse Discharges Containing Oxygen, G. Schaefer, G. Z. Hutcheson, K. H. Schoenbach, P. F. Williams

P. F. (Paul Frazer) Williams Publications

Externally sustained discharges can be used as opening and closing switches in pulsed power systems. Admixtures of attachers allow rapid opening when the external sustaining source is terminated; however, they will increase losses in the closing phase. Photodetachment has been proposed as an additional control mechanism to overcome these losses. This letter presents measurements on photoionization sustained discharges in argon and nitrogen containing admixtures of oxygen under the influence of laser radiation. Strong changes of the voltage-current characteristics have been observed. The influence of parameters such as percentage of O₂, laser power, laser pulse width, and circuit impedance …

Field-Enhancement Calculations For A Field-Distortion Triggered Spark Gap, B. Pashale, G. Schaefer, K. H. Schoenbach, P. F. Williams

P. F. (Paul Frazer) Williams Publications

We present the results of numerical field calculation which supplement a recent article in which we described a new design concept for field-distortion triggered spark gaps. The calculations verify the shielding and field enhancement assumptions made in the article, and they provide insight into the interaction of the design tradeoffs associated with simultaneously maximizing the holdoff voltage and the triggering capability of the gap.

An Exact Analysis For Efficient Computation Of Random-Pattern Testability In Combinational Circuits, Sharad C. Seth, Bhargab B. Bhattacharya, Vishwani Agrawal

School of Computing: Conference and Workshop Papers

Experimental evidence shows that low testability in a typical circuit is much more likely due to poor observability than poor controllability. Thus, from theoretical and practical standpoints, it is important to develop an accurate model for observability computation. One such model, in terms of supergates, is proposed in the first part of this paper thus complimenting our earlier work. It is now possible to obtain exact random-pattern testability for each line in a circuit.

The second part of the paper analyzes the supegate structure of a circuit from a graph theoretic viewpoint. Finding a supergate is related to determining the …

Identification Of Defect Centers In Hg1-XCdXTe Using Their Energy Ievel Composition Dependence, Charles W. Myles, P. F. Williams, R. A. Chapman, E. G. Bylander

P. F. (Paul Frazer) Williams Publications

We have extended the Kobayashi, Sankey, and Dow [Phys. Rev. B 25,6367 (1982)] theory of deep levels in Hg_1-xCd_xTe to include (vacancy, impurity) nearest-neighbor pairs. In qualitative agreement with the results obtained by these workers for isolated point defects, we find that the composition dependences (dE /dx) of the defect energy levels associated with such complexes depend on the site occupied by the impurity atom. Furthermore, we find that the composition dependences of some of the defect levels produced by such a complex are very different than the dE /dx of levels associated with …

A New Design Concept For Field Distortion Trigger Spark Gaps, G. Schaefer, B. Pashale, P. F. Williams, K. H. Schoenbach, H. Krompholz

P. F. (Paul Frazer) Williams Publications

A common field distortion triggered spark gap utilizing geometric field enhancement at sharp edges usually operates in a cascade mode via the trigger electrode. A new trigger concept is proposed allowing strong field enhancement and direct breakdown between the two main electrodes. A test setup was designed to prove the feasibility of this concept. Experimental results on delay and jitter depending on percent breakdown voltage are presented. Best results achieved are a delay of 9 ns and a jitter of 2 ns at a self-breakdown voltage of 15 kV.

Numerical Simulation Of Streamer Propagation In Nitrogen At Atmospheric Pressure, S. K. Dhali, P. F. Williams

P. F. (Paul Frazer) Williams Publications

Results of the application of flux-corrected transport techniques to a two-dimensional numerical simulation of streamer propagation are presented. Characteristics such as diameter, velocity, shape, and density gradient of the head, and ionization in the body of the propagating streamer are determined. These results provide new insight into streamer propagation.

Study Of Mo, Au, And Ni Implanted Molybdenum Laser Mirrors By Spectroscopic Ellipsometry, Paul G. Snyder, George H. Bu-Abbud, Jae Oh, John A. Woollam, David Poker, D. E. Aspnes, David Ingram, Peter Pronko

Department of Electrical and Computer Engineering: Faculty Publications

The implantation of 150 kev molybdenum ions into polished molybdenum laser mirrors is found to increase the complex dielectric constant in the visible spectrum. Analysis using the Bruggeman effective medium approximation demonstrates that the increase is due to surface smoothing and that the surface is made nearly atomically smooth by a fluence of 5 x 10¹⁵ /cm². Implantation of Au at 1Mev caused considerable microscopic roughening, as well as a change in the bulk optical properties. 3 MeV Ni ion implantation caused only a slight surface roughening. A thin dielectric film (probably a hydrocarbon) is found to …

Photodetachment As A Control Mechanism For Diffuse Discharge Switches, Gerhard Schaefer, P. F. Williams, Karl H. Schoenbach, John T. Moseley

P. F. (Paul Frazer) Williams Publications

Photodetachment is considered as a control mechanism for diffuse discharge switches. Experiments have been performed on photodetachment of ions in the flowing afterglow of a dc glow discharge in oxygen. Experiments with different laser wavelengths and the dependence of the optogalvanic signal on the laser energy flux indicate that 0^- is the dominant negative ion. For an energy flux of 35 mJ/cm², 50 percent of the 0^- ions can be photodetached.

Interfacial Electrical Properties Of Ion-Beam Sputter Deposited Amorphous Carbon On Silicon, A. Azim Khan, John A. Woollam, Y. Chung, B. Banks

Department of Electrical and Computer Engineering: Faculty Publications

Amorphous, “diamond-like” Carbon films have been deposited on Si substrates, using ion-beam sputtering. The interfacial properties are studied using capacitance and conductance measurements. Data are analyzed using existing theories for interfacial electrical properties. The density of electronic states at the interface, along with corresponding time constants are determined, and the density of interface states is unusually low for an as yet unoptimized

Time-Resolved Two-Dimensional Imaging Of Ground-State Species Using Laser-Induced Fluorescence, R. A. Dougal, P. F. Williams, D. C. Pease

P. F. (Paul Frazer) Williams Publications

Laser-induced fluorescence has been employed to obtain two-dimensional images of the spatial distribution of a vapor in the ground state with nanosecond resolution. The method has a wide range of potential applications, as it can be used to observe any species which has energy levels accessible to tunable laser systems. In the application we describe, aluminum vapor was observed jetting from spark gap electrodes and diffusing throughout the gap volume.

Efficient Infrared Upconversion In Gap, M. A. Gundersen, T. A. Yocom, P. G. Snyder, P. F. Williams

P. F. (Paul Frazer) Williams Publications

Mechanisms for linear conversion of infrared to visible were investigated in extrinsic Gap. Efficient (1 %) conversion of 10 micron to visible was observed in GaP:Zn,O. Several device applications are discussed and a quantum counter scheme involving 111-V photocathodes is presented.

Simple Powerful Tunable Single-Mode And Mode-Locked Tea Co2 Laser, R. A. Dougal, M. A. Gunderson, P. F. Williams

P. F. (Paul Frazer) Williams Publications

A simple method for constructing a single longitudinal-mode CO₂ laser that is tunable within individual rotational transitions is presented. Useful power levels, typically 0.3 J per pulse in a single-mode beam, are obtained from a single-stage device. Mode-locked output can also be obtained from the laser. In addition, design and construction of a local oscillator for making absolute in situ frequency measurements is described.

Electron Densities In Laser-Triggered Hydrogen Sparks, S. K. Dhali, P. F. Williams, M. A. Gundersen, R. J. Crumley

P. F. (Paul Frazer) Williams Publications

We have used Stark broadening measurements of the H_β emission line to determine the temporally and spatially resolved electron density in laser-triggered hydrogen sparks. In this paper the results of this work are presented and compared with earlier work on conventional overvolted sparks.

New Infrared Laser Lines In Argon, Krypton, And Xenon, E. L. Brown, M. A. Gundersen, P. F. Williams

P. F. (Paul Frazer) Williams Publications

Fourteen new infrared laser transitions in Ar, Kr, and Xe ranging from 3.725 to 17.233 pm are reported. All of the Kr laser transitions and all but one of the Ar and Xe transitions have upper levels in the s or d state: the majority of the transitions satisfy the condition ΔK = ΔJ. Identification of a previously observed, unidentified laser line at 5.804 μm in Ar is given.

Atomic Hydrogen Storage, John A. Woollam

Department of Electrical and Computer Engineering: Faculty Publications

Atomic hydrogen, for use as a fuel or as an explosive, is stored in the presence of a strong magnetic field in exfoliated layered compounds such as molybdenum disulfide or an elemental layer material such as graphite. The compound is maintained at liquid temperatures and the atomic hydrogen is collected on the surfaces of the layered compound which are exposed during delamination (exfoliation). The strong magnetic field and the low temperature combine to prevent the atoms of hydrogen from recombining to form molecules.

Optics At Texas Tech University: Learning By Doing, John F. Walkup, P. F. Williams, Martin A. Gundersen

P. F. (Paul Frazer) Williams Publications

In both the undergraduate and graduate educational programs of the Department of Electrical Engineering at Texas Tech University, students are strongly encouraged to learn by active participation. Both programs have benefited from a vigorous faculty involvement in a wide range of funded research projects in various areas of modern optics.

Electronic Properties Of Metal Chloride Intercalants Of Graphite*, **, John A. Woollam, M. B. Dowell, A. Yavrouian, A. G. Lozier, G. Matulka

Department of Electrical and Computer Engineering: Faculty Publications

The Shubnikov-deHaas (SdH) effect has been used to study the electronic properties of graphite intercalated with PdC1₂ (stage 3), FeC1₃ (stages 2, 4, 6, and 11), CuC1₂ (stage 1), and WC1₆ (stage 5). For the palladium chloride, ferric chloride, and copper chloride intercalants the SdH spectra are similar: these show frequencies of approximately, 27, 80, 380, and 550 Tesla for fields parallel to the c-axis. The effective masses have been measured for each of these carriers, and are of the order of 0.1 m₀, where m₀ is the free electron mass. These carriers …

Atomic Hydrogen Storage Method And Apparatus, John A. Woollam

Department of Electrical and Computer Engineering: Faculty Publications

Atomic hydrogen, for use as a fuel or as an explosive, is stored in the presence of a strong magnetic field in exfoliated layered compounds such as molybdenum disulfide or an elemental layer material such as graphite. The compound is maintained at liquid helium temperatures and the atomic hydrogen is collected on the surfaces of the layered compound which are exposed during delamination (exfoliation). The strong magnetic field and the low temperature combine to prevent the atoms of hydrogen from recombining to form molecules.

Sio2-Si Film-Substrate Single-Reflection Retarders For Different Mercury Spectral Lines, A.R.M. Zaghloul, R.M.A Azzam

Department of Electrical and Computer Engineering: Faculty Publications

Design parameters for SiO₂- Si film-substrate single reflection retarders for several mercury spectral lines are presented. An example of an angle-of-incidence tunable retarder (AITR) capable of multiple wavelength operation (MWO) is reported Simple, approximate formulae for calculating film-substrate retarder design parameters (least film thickness d' and incidence angle) are presented.

Reply To “Comment On 'Resonance Raman Scattering And Collision-Induced Redistribution Scattering In I2’ ”, D. L. Rousseau, G. D. Patterson, P. F. Williams

P. F. (Paul Frazer) Williams Publications

We demonstrate that neither laser broadening nor inelastic collisional broadening plays a dominant role in the data of our recent experiments as has been suggested, and again we conclude that our results can only be explained by redistribution emission resulting from phase-changing processes.

Comment On “Two-Magnon Resonant Raman Scattering In Mnf2”, D. L. Rousseau, R. E. Dietz, P. F. Williams, H. J. Guggenheim

P. F. (Paul Frazer) Williams Publications

We have not been able lo reproduce the recently reported resonance enhancement of Raman scattering from magnons in MnF₂ by Amer, Chiang, and Shen. Fifteen crystals ranging from extremely pure samples to ones with high concentrations of impurities, in addition to one supplied by Amer, Chiang, and Shen, were investigated. By observing the off-resonance scattering, we conclude that if an enhancement of greater than a factor of 2 were present, it would have been seen in our resonance spectra.

Resonance Raman Scattering Of Light From A Diatomic Molecule, D. L. Rousseau, P. F. Williams

P. F. (Paul Frazer) Williams Publications

No abstract provided.

Some Comments On The Plasmon Spectrum Of Tetrathiafulvalene Tetracyano-P-Quinodimethane (Ttf- Tcnq), P. F. Williams, A. N. Bloch

P. F. (Paul Frazer) Williams Publications

Our random-phase-approximation model calculation of the high-frequency dielectric response of a quasi-one-dimensional metal is generalized to the case of n conducting strands per unit cell. For a model of the two-band system tetrathiafulvalene tetracyano-p-quinodimethane we obtain good agreement with recent experiments, and also predict an acoustic-plasmon branch, Some implications for the physics of the material are discussed.

Optimal And Suboptimal Estimation In Differential Pcm And Adaptive Predictive Coding Systems, Jerry Gibson

Department of Electrical and Computer Engineering: Faculty Publications

Both differential pulse code modulation (DPCM) and adaptive predictive coding (APC) systems have been used somewhat successfully for low date rate digital voice transmission. A DPCM system has as its goal the removal of signal redundancy prior to transmission by a linear prediction of the incoming signal with a weighted combination of past signal estimates. The error in the prediction process is then quantized and transmitted to the receiver. An identical prediction loop is used at the receiver to reinsert the redundancy, and hence, to reconstruct the speech signal. Both the quantizer and predictor may or may not be adaptive.

Resonance Raman Scattering And Collision-Induced Redistribution Scattering In I2, D. L. Rousseau, G. D. Patterson, P. F. Williams

P. F. (Paul Frazer) Williams Publications

We report the first experimental observation of broad-banded re-emission resulting from quasi-elastic collisional transfer processes. The data may be interpreted by the general theory of scattering of monochromatic light in gases. The connection between this theory and one derived for solids is discussed.

Dependence Of The Electronic Transition Moment On Internuclear Separation In Na2: A Quantum Mechanical Treatment, P. F. Williams, D. L. Rousseau

P. F. (Paul Frazer) Williams Publications

We present a quantum mechanical treatment of laser-induced atomic fluorescence from molecular sodium. It is shown that such fluorescence data may be analyzed with an ν-centroid approximation and an accurate determination of the electronic transition moment may be made.