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An atomic force microcopy study of the mechanical and electricalproperties of monolayer films of molecules with aromatic end groups

Description: The effect of intermolecular {pi}-{pi} stacking on the electrical and mechanical properties of monolayer films molecules containing aromatic groups was studied using atomic force microscopy. Two types of aromatic molecules, (4-mercaptophenyl) anthrylacetylene (MPAA) and (4-mercaptophenyl)-phenylacetylene (MPPA) were used as model systems with different {pi}-{pi} stacking strength. Monolayer films of these molecules on Au(111) surfaces exhibited conductivities differing by more than one order of magnitude, MPAA being the most conductive and MPPA the least conductive. The response to compressive loads by the AFM tip was also found to be very different for both molecules. In MPAA films distinct molecular conductivity changes are observed upon mechanical perturbation. This effect however was not observed on the MPPA film, where intermolecular {pi}-{pi} interactions are likely weaker.
Date: September 6, 2007
Creator: Fang, Liang; Park, J.Y.; Ma, H.; Jen, A.K.-Y. & Salmeron, M.
Partner: UNT Libraries Government Documents Department

Internal voltage in a conducting closed hollow cylinder with an attached end plate subjected to a direct lightning strike

Description: The interior voltage of a large metal can with thick walls struck directly by lightning was estimated using diffusion theory, aperture slot voltage theory, and experimental data. The hollow cylinder is closed at both ends. One end has a cap that is welded to the cylinder wall making a continuous electrical interface. The other end consists of a circular plate that is pressed into the cylinder wall and held under pressure with a threaded ring. From our experience with coupling measurements, this joint will be a weak link. It will allow more current to leak into the interior than from diffusion through the walls. Because the joint was designed for mechanical purposes, the electrical properties, such as continuity around the circumference, are not well controlled. Therefore, it is difficult to determine a single voltage attributed to this joint design with varying electrical characteristics. Instead, we will make a best effort of bounding the problem using both analytical calculations and data from tests of similar structures. The calculated internal cylinder voltage subjected to an extreme lightning strike from current diffusing through the wall is 19 volts. We estimate that the press-fit end plate will increase this voltage by a factor of about two to ten. The internal voltage is expected to be between 40 and 200 volts. This uncertainty can be reduced by making coupling and high-current measurements on a number of cans or by redesigning the cap to include electrical contacts. However, given that the critical components inside the cylinder are insulated to at least 3.5 kV, improving the joint design is unnecessary. The safety factor using the worst-case maximum interior voltage is 18 and is sufficient. A higher safety margin can be achieved by keeping the joint clean and under pressure.
Date: June 1, 2000
Creator: Ong, M M & Anderson, R A
Partner: UNT Libraries Government Documents Department

Failure analysis of rutile sleeves in MC3080 lightning arrestor connectors.

Description: The purpose of this SAND Report is to document efforts in the extraction and failure analyses of sleeve-style Lightning Arrestor Connectors (LACs). Several MC3080 and MC3079 LACs were recovered from the field and tested as part of the Enhanced Surveillance Campaign. A portion of these LACs failed retesting. Terry Ernest (01733), the LAC Component Engineer, provided eleven MC3080 LACs for evaluation where four of the LACs failed IR/DCW and one failed FRB requirements. The extraction of rutile sleeves from failed LACs was required to determine the source of failure. Rutile sleeves associated with connector function failures were examined for cracks, debris as well as any other anomalies which could have caused the LAC to not function properly. Sleeves that failed FRB or that experienced high FRB exhibited high symmetry, smooth surface, long-flow amicon, and slightly over-sized inside diameter. LACs that failed DCW or IR requirements had rutile sleeves that exhibited breakdown tracks.
Date: February 1, 2006
Creator: Kilgo, Alice C.; Monroe, Saundra L.; Watson, Chad Samuel & Ernest, Terry L.
Partner: UNT Libraries Government Documents Department

On the Relationship Between Microstructure and Electrical and Hydraulic Properties of Sand-Clay Mixtures

Description: A series of laboratory experiments were performed on saturated sand-clay mixtures, including electrical properties, permeability and porosity. Different mixtures and configurations of quartz sand and 0 to 10% Na-montmorillonite clay saturated with solutions of CaCl{sub 2} and deionized water were investigated. The electrical properties were dependent on clay content, fluid conductivity, and microstructure in a complex fashion. Two main regions of conduction exist: a region dominated by surface conduction and a region where the ionic strength of the saturating fluid controlled conduction. For low fluid conductivities, the sample geometry was found to greatly affect the magnitude of the surface conductance. The influence of the microstructural properties on the electrical properties was quantified by estimating formation factors, {Lambda}-parameters, and surface conductances. We suggest that high and low bounds on the expected surface and bulk conductance of natural systems can be derived from the measurements on these artificial configurations.
Date: October 25, 1999
Creator: Wildenschild, D.; Roberts, J.J. & Carlsberg, E.D.
Partner: UNT Libraries Government Documents Department

Compact X-band high power load using magnetic stainless steel

Description: We present design and experimental results of a high power X-band load. The load is formed as a disk-loaded waveguide structure using lossy, Type 430 stainless steel. The design parameters have been optimized using the recently developed mode-matching code MLEGO. The load has been designed for compactness while maintaining a band width greater than 300 MHz.
Date: May 1, 1995
Creator: Tantawi, S.G. & Vlieks, A.E.
Partner: UNT Libraries Government Documents Department

Structural and electronic properties of clean and defected Si-SiC(001) surfaces

Description: We have studied the reconstructions and electronic properties of both clean and defected Si-terminated (001) surfaces of cubic SiC, by performing -first principles computations within density functional theory. We find that the unstrained bulk exhibits a stable p(2xl) reconstruction, whereas a bulk under tensile stress shows a c(4x2) 1econstruction Furthermore our calculations indicate that ad-dimers are common defects on the Si-terminated SIC(001) surface These results permit the interpretation of recent STM and X-ray- photoemission experimental data.
Date: June 1, 1998
Creator: Galli, G.
Partner: UNT Libraries Government Documents Department

GaN Metal Oxide Semiconductor Field Effect Transistors

Description: A GaN based depletion mode metal oxide semiconductor field effect transistor (MOSFET) was demonstrated using Ga{sub 2}O{sub 3}(Gd{sub 2}O{sub 3}) as the gate dielectric. The MOS gate reverse breakdown voltage was > 35V which was significantly improved from 17V of Pt Schottky gate on the same material. A maximum extrinsic transconductance of 15 mS/mm was obtained at V{sub ds} = 30 V and device performance was limited by the contact resistance. A unity current gain cut-off frequency, f{sub {tau}}, and maximum frequency of oscillation, f{sub max} of 3.1 and 10.3 GHz, respectively, were measured at V{sub ds} = 25 V and V{sub gs} = {minus}20 V.
Date: March 2, 1999
Creator: Ren, F.; Pearton, S.J.; Abernathy, C.R.; Baca, A.; Cheng, P.; Shul, R.J. et al.
Partner: UNT Libraries Government Documents Department

High-frequency operation of 0.3 {mu}m GaAs JFETs for low-power electronic

Description: GaAs Junction Field Effect Transistors (JFETs) have attracted renewed attention for low-power, low-voltage electronics. JFETs have a significant advantage over MESFETs for low-power operation due to their higher gate barrier to current flow resulting from p/n junction gate. This paper reports recent advances in an all ion implanted self-aligned GaAs JFET with a gate length down to 0.3 {mu}m. By employing shallopw SiF implants next to the gate, dielectric sidewall spacers, and 50 keV source and drain implants, JFETs with a f{sub t} up to 49 GHz with good pinchoff and subthreshold characteristics have been realized. In addition, the JFET benefits from the use of shallow Zn or Cd implantation to form abrupt p{sup +}/n gate profiles.
Date: September 1, 1996
Creator: Zolper, J.C.; Baca, A.G.; Hietala, V.M.; Shul, R.J. & Sherwin, M.E.
Partner: UNT Libraries Government Documents Department

Effect of Substrate Composition on the Piezoelectric Response of Reactively Sputtered AlN Thin Films

Description: Deposition parameters were found to have a marked effect on piezoelectric response of reactive radio frequency (RF) sputtered AlN thin films. The authors observed peizoelectric response values ranging from {minus}3.5 to +4.2 pm/V for 1 {micro}m thick AlN films deposited onto Ti/Ru electrode stacks. An investigation of the effects of deposition parameters, in particular the nature of the Ru/AlN interface, was conducted. The lag time between deposition of adjacent thin film layers appeared to have the greatest affect on the value of the piezoelectric response. This suggests that chemical reaction occurring on the Ru thin film surface is responsible for changing an important thin film property such as dipole orientation within the overlying AlN thin film.
Date: April 21, 1999
Creator: Clem, P.G.; Dimos, D.B.; Gonzales, D.M.; Ruffner, J.A. & Tuttle, B.A.
Partner: UNT Libraries Government Documents Department

Engineering high-performance vertical cavity lasers

Description: The cw and high-speed performance of vertical cavity surface emitting laser diodes (VCSELs) are affected by both electrical and optical issues arising from the geometry and fabrication of these devices. Structures with low resistance semiconductor mirrors and Al-oxide confinement layers address these issues and have produced record performance including 50% power conversion efficiency and modulation bandwidths up to 20 GHz at small bias currents.
Date: December 31, 1996
Creator: Lear, K.L.; Hou, H.Q.; Hietala, V.M.; Choquette, K.D. & Schneider, R.P. Jr.
Partner: UNT Libraries Government Documents Department

LDRD final report on carbon nanotube composites

Description: Carbon nanotubes and their composites were examined using computational and experimental techniques in order to modify the mechanical and electrical properties of resins. Single walled nanotubes were the focus of the first year effort; however, sufficient quantities of high purity single walled nanotubes could not be obtained for mechanical property investigations. The unusually high electrical conductivity of composites loaded with <1% of multiwalled nanotubes is useful, and is the focus of continuing, externally funded, research.
Date: April 1997
Creator: Cahill, P. A. & Rand, P. B.
Partner: UNT Libraries Government Documents Department

Electrical optimization of the ICH antenna array for ITER

Description: The present design of the ITER ICH antenna array comprises two poloidal by four toroidal current elements in each of four ports.Each current element forms a resonant double loop (RDL) with power fed to a pretuned matchpoint on the strap; the matching is accomplished using slow-wave transmission lines as adjustable shorted-stub tuners on either end of the current strap. The power requirement is 12.5 MW per port over the frequency range of 40--70 MHz, with extended operation to 80 MHz desirable. The antenna design optimization process includes (1) strap shaping to minimize strap voltages and rf E-fields along B-field lines and (2) frame/Faraday shield geometry design to improve plasma coupling, wave spectrum directivity, and phase control. For the ignited plasma parameters, the optimized array design delivers full power over the ranges of 40--80 MHz in frequency and 0{degree} to 180{degree} in phase. The maximum strap voltage is 41 kV and the maximum parallel E-field is 16 kV/cm for the worst case over these ranges. The array directivity for current drive operation is calculated to be close to 80%.
Date: August 1, 1997
Creator: Ryan, P.M.; Swain, D.W.; Carter, M.D.; Taylor, D.J. & Bosia, G.
Partner: UNT Libraries Government Documents Department

Noise analysis due to strip resistance in the ATLAS SCT silicon strip module

Description: The module is made out of four 6 cm x 6 cm single sided Si microstrip detectors. Two detectors are butt glued to form a 12 cm long mechanical unit and strips of the two detectors are electrically connected to form 12 cm long strips. The butt gluing is followed by a back to back attachment. The module in this note is the R{phi} module where the electronics is oriented parallel to the strip direction and bonded directly to the strips. This module concept provides the maximum signal-to-noise ratio, particularly when the front-end electronics is placed near the middle rather than at the end. From the noise analysis, it is concluded that the worst-case {Delta}ENC (far-end injection) between end- and center-tapped modules will be 120 to 210 el. rms (9 to 15%) for a non-irradiated detector and 75 to 130 el. rms (5 to 9%) for an irradiated detector, for a metal strip resistance of 10 to 20 {Omega}/cm.
Date: August 1, 1996
Creator: Kipnis, I.
Partner: UNT Libraries Government Documents Department

Low-Dislocation-Density GaN from a Single Growth on a Textured Substrate

Description: The density of threading dislocations (TD) in GaN grown directly on flat sapphire substrates is typically greater than 10{sup 9}/cm{sup 2}. Such high dislocation densities degrade both the electronic and photonic properties of the material. The density of dislocations can be decreased by orders of magnitude using cantilever epitaxy (CE), which employs prepatterned sapphire substrates to provide reduced-dimension mesa regions for nucleation and etched trenches between them for suspended lateral growth of GaN or AlGaN. The substrate is prepatterned with narrow lines and etched to a depth that permits coalescence of laterally growing III-N nucleated on the mesa surfaces before vertical growth fills the etched trench. Low dislocation densities typical of epitaxial lateral overgrowth (ELO) are obtained in the cantilever regions and the TD density is also reduced up to 1 micrometer from the edge of the support regions.
Date: July 31, 2000
Partner: UNT Libraries Government Documents Department

Pressure as a probe of the physics of ABO{sub 3} relaxor ferroelectrics

Description: Results on a variety of mixed ABO{sub 3} oxides have revealed a pressure-induced ferroelectric-to-relaxor crossover and the continuous evolution of the energetics and dynamics of the relaxation process with increasing pressure. These common features have suggested a mechanism for the crossover phenomenon in terms of a large decrease in the correlation length for dipolar interactions with pressure--a unique property of soft mode or highly polarizable host lattices. The pressure effects as well as the interplay between pressure and dc biasing fields are illustrated for some recent results on PZN-9.5 PT,PMN and PLZT 6/65/35.
Date: February 14, 2000
Partner: UNT Libraries Government Documents Department

Investigation of Deep Levels in GaInNas

Description: This paper presents and discusses the first Deep-Level transient spectroscopy (DLTS) data obtained from measurements carried out on both Schottky barriers and homojunction devices of GaInNAs. The effect of N and In doping on the electrical properties of the GaNInAs devices, which results in structural defects and interface states, has been investigated. Moreover, the location and densities of deep levels related to the presence of N, In, and N+In are identified and correlated with the device performance. The data confirmed that the presence of N alone creates a high density of shallow hole traps related to the N atom and structural defects in the device. Doping by In, if present alone, also creates low-density deep traps (related to the In atom and structural defects) and extremely deep interface states. On the other hand, the co-presence of In and N eliminates both the interface states and levels related to structural defects. However, the device still has a high density of the shallow and deep traps that are responsible for the photocurrent loss in the GaNInAs device, together with the possible short diffusion length.
Date: November 12, 1998
Creator: Abulfotuh, F.; Balcioglu, A.; Friedman, D.; Geisz, J. & Kurtz, S.
Partner: UNT Libraries Government Documents Department

Characterization of electrical linewidth test structures patterned in (100) Silicon-on-Insulator for use as CD standards

Description: This paper describes the fabrication and measurement of the linewidths of the reference segments of cross-bridge resistors patterned in (100) Bonded and Etched Back Silicon-on-Insulator (BESOI) material. The critical dimensions (CD) of the reference segments of a selection of the cross-bridge resistor test structures were measured both electrically and by Scanning-Electron Microscopy (SEM) cross-section imaging. The reference-segment features were aligned with &lt;110&gt; directions in the BESOI surface material and had drawn linewidths ranging from 0.35 to 3.0 {micro}m. They were defined by a silicon micro-machining process which results in their sidewalls being atomically-planar and smooth and inclined at 54.737{degree} to the surface (100) plane of the substrate. This (100) implementation may usefully complement the attributes of the previously-reported vertical-sidewall one for selected reference-material applications. For example, the non-orthogonal intersection of the sidewalls and top-surface planes of the reference-segment features may alleviate difficulties encountered with atomic-force microscope measurements. In such applications it has been reported that it may be difficult to maintain probe-tip control at the sharp 90{degree} outside corner of the sidewalls and the upper surface. A second application is refining to-down image-processing algorithms and checking instrument performance. Novel aspects of the (100) SOI implementation that are reported here include the cross-bridge resistor test-structure architecture and details of its fabrication. The long-term goal is to develop a technique for the determination of the absolute dimensions of the trapezoidal cross-sections of the cross-bridge resistors' reference segments, as a prelude to developing them for dimensional reference applications. This is believed to be the first report of electrical CD measurements made on test structures of the cross-bridge resistor type that have been patterned in (100) SOI material. The electrical CD results are compared with cross-section SEM measurements made on the same features.
Date: February 29, 2000
Partner: UNT Libraries Government Documents Department

A Method to Improve Activation of Implanted Dopants in SiC

Description: Implantation of dopant ions in SiC has evolved according to the assumption that the best electrical results (i.e., carrier concentrations and mobility) is achieved by using the highest possible processing temperature. This includes implantation at &gt; 600 C followed by furnace annealing at temperatures as high as 1,750 C. Despite such aggressive and extreme processing, implantation suffers because of poor dopant activation, typically ranging between &lt; 2%--50% with p-type dopants represented in the lower portion of this range and n-types in the upper. Additionally, high-temperature processing can led to several problems including changes in the stoichiometry and topography of the surface, as well as degradation of the electrical properties of devices. A novel approach for increasing activation of implanted dopants in SiC and lowering the activation temperature will be discussed. This approach utilizes the manipulation of the ion-induced damage to enhance activation of implanted dopants. It will be shown that nearly amorphous layers containing a small amount of residual crystallinity can be recrystallized at temperatures below 900 C with little residual damage. It will be shown that recrystallization traps a high fraction of the implanted dopant residing within the amorphous phase (prior to annealing) onto substitutional sites within the SiC lattice.
Date: January 16, 2001
Creator: Holland, O.W.
Partner: UNT Libraries Government Documents Department


Description: A method for direct dc measurement of the Volta potential is presented. High intensity synchrotron x-ray beams were used to locally irradiate the atmosphere adjacent to the metal surface and produce a conducting path between a sample and a reference probe. The direct measurements of potential in the ionized air could be made at probe heights of around 1 mm compared to less than 0.1 mm for the Kelvin probe. The measurements were similar to traditional Kelvin probe measurements, but had a poorer spatial resolution. In contrast to the Kelvin probe methods, the approach described allows observation of the current as a function of impressed voltage. Methods to improve the special resolution of the technique and applications to corrosion under coating will be presented.
Date: October 22, 2000
Partner: UNT Libraries Government Documents Department

Defect structure of indium tin oxide and its relationship to conductivity

Description: Doping In{sub 2}O{sub 3} with tin results in an improved transparent conducting oxide (TCO). Although indium tin oxide (ITO) is the most frequently used commercial TCO, its defect structure is still uncertain. Previously, its defect chemistry has been inferred based on the conductivity of the material. To directly study the defect structure of ITO, the authors prepared powders under different processing environments and performed neutron powder diffraction. Structural information was obtained by performing Rietveld analysis. The results include positions of the atoms, their thermal displacements, the fractional occupancy of the defect oxygen site, and the fractional occupancies of Sn on each of the two nonequivalent cation sites, showing a strong preference for the b site. These structural results are correlated with the measured electrical properties of the same samples.
Date: May 9, 2000
Creator: Gonzalez, G. B.; Cohen, J. B.; Hwang, J.-H.; Mason, T. O.; Hodges, J. P. & Jorgensen, J. D.
Partner: UNT Libraries Government Documents Department

Dynamic electromechanical characterization of the ferroelectric ceramic PZT 95/5

Description: Shock-induced depoling of the ferroelectric PZT 95/5 has been utilized in pulsed power applications for many years. Recently, new design and certification requirements have generated a strong interest in numerically simulating the operation of pulsed power devices. Because of a scarcity of relevant experimental data obtained within the past twenty years, we have initiated an extensive experimental study of the dynamic behavior of this material in support of simulation efforts. The experiments performed to date have been limited to examining the behavior of unpoled material. Samples of PZT 95/5 have been shocked to axial stresses from 0.5 to 5.0 GPa in planar impact experiments. Impact face conditions have been recorded using PVDF stress gauges, and transmitted wave profiles have been recorded either at window interfaces or at a free surface using laser interferometry (VISAR). The results significantly extend the stresses examined in prior studies of unpoled material, and ensure that a comprehensive experimental characterization of the mechanical behavior under shock loading is available for continuing development of PZT 95/5 material models.
Date: October 1, 1997
Creator: Setchell, R.E.; Chhabildas, L.C.; Furnish, M.D.; Montgomery, S.T. & Holman, G.T.
Partner: UNT Libraries Government Documents Department

Uniformity and performance of selectively oxidized VCSEL arrays

Description: The authors report the uniformity characteristics of low threshold 1,060 nm and high power 850 nm 8 x 8 individually addressable oxide-confined VCSEL arrays. Uniformity of lasing thresholds and operating characteristics are described, as well as thermal issues for 2-dimensional laser arrays.
Date: January 1, 1998
Creator: Geib, K.M.; Choquette, K.D.; Hou, H.Q. & Hammons, B.E.
Partner: UNT Libraries Government Documents Department