Publications
162 results found
Pike WT, Standley IM, Banerdt WB, 2005, A high-sensitivity broad-band seismic sensor for shallow seismic sounding of the lunar regolith, Lunar and Planetary Sciences Conference
Kumar S, Pike WT, 2005, Technique for eliminating notching in through-wafer etching, Micromechanics Europe 2005, Goteborg, Sweden, 4 - 6 September 2005
Pike WT, Karl WJ, Kumar S, et al., 2004, Analysis of sidewall quality in through-wafer deep reactive-ion etching, 29th International Conference on Micro and Nano Engineering (MNE 2003), Publisher: ELSEVIER SCIENCE BV, Pages: 340-345, ISSN: 0167-9317
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- Citations: 35
Chassefiere E, Bertaux J L, Berthelier J J, et al., 2004, MEP (Mars Environment Package): toward a package for studying environmental conditions at the surface of Mars from future lander/rover missions, Advances in Space Research, Vol: 34, Pages: 1702-1709, ISSN: 0273-1177
Pike WT, Standley IM, Kumar S, et al., 2004, Determination of the dynamics of a micromachined lateral suspension in the scanning electron microscope, MicroMechanics Europe, Pages: 49-52
Pike WT, Standley IM, 2004, Determination of the dynamics of a micromachined lateral suspension in the scanning electron microscope, Journal of Micromechanics and Microengineering, Vol: 15, Pages: S82-S88, ISSN: 0960-1317
Anderson MS, Pike WT, 2002, A Raman-atomic force microscope for apertureless-near-field spectroscopy and optical trapping, REVIEW OF SCIENTIFIC INSTRUMENTS, Vol: 73, Pages: 1198-1203, ISSN: 0034-6748
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- Citations: 67
Gautsch S, Akiyama T, Imer R, et al., 2002, Measurement of quartz particles by means of an atomic force microscope for planetary exploration, SURFACE AND INTERFACE ANALYSIS, Vol: 33, Pages: 163-167, ISSN: 0142-2421
Akiyama T, Gautsch S, de Rooij NF, et al., 2001, Atomic force microscope for planetary applications, Solid-State Sensors and Actuators Workshop, Publisher: ELSEVIER SCIENCE SA, Pages: 321-325, ISSN: 0924-4247
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- Citations: 15
Anderson MS, Pike WT, 2001, Chemical imaging with a Raman atomic-force microscope, Bristol, Conference of the electron-microscopy-and analysis-group, University of Dundee, Dundee, Scotland, 5 - 7 September 2001, Publisher: Iop Publishing Ltd, Pages: 501-504
Pike WT, Hecht MH, Smith PH, et al., 2001, A microscopy station for Mars, Bristol, Conference of the electron-microscopy-and analysis-group, University of Dundee, Dundee, Scotland, 5 - 7 September 2001, Publisher: Iop Publishing Ltd, Pages: 163-166
Lognonné P, Giardini D, Banerdt B, et al., 2000, The NetLander very broad band seismometer, Planetary and Space Science, Vol: 48, Pages: 1289-1302, ISSN: 0032-0633
The interior of Mars is today poorly known, in contrast to the Earth interior and, to a lesser extent, to the Moon interior, for which seismic data have been used for the determination of the interior structure. This is one of the strongest facts motivating the deployment on Mars of a network of very broad band seismometers, in the framework of the 2007 CNES-NASA joint mission. These seismometers will be carried by the Netlanders, a set of 4 landers developed by a European consortium, and are expected to land in mid-2008. Despite a low mass, the seismometers will have a sensitivity comparable to the present Very Broad Band Earth sensors, i.e. better than the past Apollo Lunar seismometers. They will record the full range of seismic and gravity signals, from the expected quakes induced by the thermoelastic cooling of the lithosphere, to the possible permanent excitation of the normal modes and tidal gravity perturbations. All these seismic signals will be able to constrain the structure of Mars' mantle and its discontinuities, as well as the state and size of the Martian core, shortly after for the centennial of the discovery of the Earth core by Oldham (Quart. J. Geol. Soc. 62(1906) 456-475). © 2000 Elsevier Science Ltd. All rights reserved.
Budraa NK, Jackson HW, Barmatz M, et al., 1999, Low pressure and low temperature hermetic wafer bonding using microwave heating, Pages: 490-492
We bonded gold on silicon substrates (Au/Si) for a MEMS application by using microwave radiation in a single-mode cavity. Microwave radiation selectively heats materials; the energy is deposited in the metallic portion of the substrates in this application. This concentration of the energy forms the bonding rather quickly and with minimal heating of the substrate. The short bonding process- time allows for minimal diffusion of the Si into the metallization. Since no pressure is applied to form the bonding, mechanical stresses are minimized. The substrates bonded by our technique formed a hermetically sealed micro-cavity. Preliminary He leak-tests from these bonded samples show leak-rates on the order of 3×109 atom cc/s.
George T, Jacobsohn E, Pike WT, et al., 1995, Novel symmetry in the growth of gallium nitride on magnesium aluminate substrates, Applied Physics Letters, Vol: 68, Pages: 337-339, ISSN: 0003-6951
The growth of GaN by metalorganic chemical vapor deposition on (111) and (100) magnesium aluminate (MgAl2O4) substrates is examined using transmission electron microscopy. The results indicate that mainly wurtzite GaN is grown for both orientations. On the (111) substrate the following epitaxial relationship is observed: (0001)GaN ∥ (111)MgAl 2O4, and [112̄0]GaN ∥ [11̄0]MgAl 2O4. During the early stages of the (100) growth, four orientations of the wurtzite phase and a zinc-blende phase are formed. With increasing thickness, one of the wurtzite orientations dominates, with the epitaxial relationship being (11̄01)GaN ∥ (100)MgAl2O 4 and the [112̄0]GaN nearly parallel to [011]MgAl 2O4. This choice of growth orientation appears to be determined primarily by the nature of the interfacial bonding, with the basal plane of each of the four wurtzite GaN variants being nearly aligned along one of the four {111} planes intersecting the (100) surface of the MgAl 2O4. © 1996 American Institute of Physics.
Bell LD, Kaiser WJ, Manion SJ, et al., 1995, Measurements of local strain variation in Si<inf>1-x</inf>Ge<inf>x</inf>/Si heterostructures, Journal of Vacuum Science and Technology B: Microelectronics and Nanometer Structures, Vol: 13, Pages: 1602-1607, ISSN: 0734-211X
The energy splitting of the conduction-band minimum of Si1-xGex due to strain has been directly measured by the application of ballistic-electron-emission microscope (BEEM) spectroscopy to Ag/Si1-xGex structures. Experimental values for this conduction-band splitting agree well with calculations. For Au/Si1-xGex, however, heterogeneity in the strain of the Si1-xGex layer is introduced by deposition of the Au. This variation is attributed to species interdiffusion, which produces a rough Si1-xGex surface. Preliminary modeling indicates that the observed roughness is consistent with the strain variation measured by BEEM.
George T, Pike WT, Khan MA, et al., 1995, A microstructural comparison of the initial growth of AlN and GaN layers on basal plane sapphire and sic substrates by low pressure metalorganic chemical vapor deposition, Journal of Electronic Materials, Vol: 24, Pages: 241-247, ISSN: 0361-5235
The initial growth by low pressure metalorganic chemical vapor deposition and subsequent thermal annealing of A1N and GaN epitaxial layers on SiC and sapphire substrates is examined using high resolution transmission electron microscopy and atomic force microscopy. Growth under low pressure conditions on sapphire substrates is significantly different from that reported for conventional (atmospheric pressure) conditions. Smooth, single crystal A1N and GaN layers were deposited on sapphire in the initial low temperature (600°C) growth step. Interfacial bonding and not lattice mismatch was found to be the determin ing factor for obtaining good crystallinity for the epitaxial layers as indicated by the growth results on SiC substrates. © 1995 The Metallurgical of Society of AIME.
Bell LD, Kaiser WJ, Manion SJ, et al., 1995, Ballistic-electron-emission microscopy of strain nonuniformities in Si1-xGex/Si structures, Physical Review B, Vol: 52, Pages: 12081-12089, ISSN: 0163-1829
Ballistic-electron-emission microscopy (BEEM) is used to probe local conduction-band structure in strained Si1-xGex layers of pseudomorphic Si1-xGex/Si heterostructures. The strain variation produced by a roughened Si1-xGex surface is seen as a variation of splitting between thresholds in BEEM spectroscopy. This splitting is directly related to the strain-induced conduction-band splitting in the Si1-xGex layer, enabling BEEM to directly measure local strain variations. Elasticity calculations for a roughened Si1-xGex surface predict variations in strain that are consistent with BEEM observations. For the case of a smooth Si1-xGex surface, a uniform conduction-band splitting is observed that is in good agreement with calculations. © 1995 The American Physical Society.
Pike WT, George T, Khan MA, et al., 1994, Transmission electron microscopy of Al<inf>x</inf>Ga<inf>1-x</inf>N/SiC multilayer structures, Pages: 844-845
High resolution transmission electron microscopy was used to study the microstructure of two novel developments of wide band gap III-V nitrides: the growth of ultra-short period GaN/AlN superlattices and the incorporation of SiC layers into AlxGa1-xN structures. The superlattice samples were grown by low pressure metalorganic chemical vapor deposition using a unique switched atomic layer epitaxy procedure. GaN was grown on the basal plane sapphire substrates above a thin AlN layer. MOCVD growth of SiC on AlN on sapphire has shown poor quality as determined by structure images from the TEM. TEM analysis of SiC growth on AlN on 6-H SiC shows that initial epitaxy of 3C SiC is possible.
Gunapala SD, Bandara KMSV, Levine BF, et al., 1994, High performance InGaAs/GaAs quantum well infrared photodetectors, Applied Physics Letters, Vol: 64, Pages: 3431-3433, ISSN: 0003-6951
We have measured the optical and transport properties of In 0.2Ga0.8As/GaAs quantum well infrared photodetectors based on bound-to-bound, bound-to-quasibound, and bound-to-continuum intersubband transitions. Excellent hot electron transport and high detectivity D*=1.8×1010 cmHz/W (at λp=16.7 μm) were achieved at temperature T=40 K.
Ksendzov A, Fathauer RW, Maker PD, et al., 1994, Interferometric optical filters utilizing metal patterns on free-standing thin substrates, Pages: 39-49, ISSN: 0277-786X
A new technology for infrared optical filters is presented. We have produced a band pass filter consisting of a thin (12.4 μm) Si wafer with cross-shaped metal patterns deposited on both sides. The crosses, with 6 μm arms, have been formed by direct-write electronbeam lithography on 1000 A Al film. The filter is mounted on a 0.2 mm thick Si frame with 0.25 cm2 window, but it also can be bonded to detectors so that the filter and the detector temperature are the same. Due to the high index of refraction in Si, this filter is more tolerant to converging beams than interferometric filters made of metal meshes stretched in air that have been reported previously. When placed into an F/3 converging beam, the filter has a bandpass characteristic centered at 70 μm wavelength with width at half maximum δλ/λ = 7%. The transmission maximum is 44%. At present the band pass is limited by the non-uniformity of the available substrates. The out-of-band rejection need improving which can be achieved using additional non-interferometric filters with wider band pass made with similar technology. Another way of improving the performance is integrating the metal patterns onto the detector which will make it frequency selective. Extending the interference filter technology to shorter wavelengths is difficult due to the onset of absorption in the metal layers.
Hunt BD, Foote MC, Pike WT, et al., 1994, High-T<inf>c</inf> edge-geometry SNS weak links on silicon-on-sapphire substrates, Physica C: Superconductivity and its applications, Vol: 230, Pages: 141-152, ISSN: 0921-4534
High-quality superconductor/normal-metal/superconductor (SNS) edge-geometry weak links have been produced on silicon-on-sapphire (SOS) substrates using a new SrTiO3/"seed-layer"/cubic-zirconia (YSZ) buffer system. The seed layer is a thin YBa2Cu3O7-x (YBCO) or PrBa2Cu3O7-x (PBCO) film, which provides a template for growth of the SrTiO3. This multilayer buffer system eliminates problems with series grain-boundary weak links seen in edge junctions on single YSZ buffer layers on SOS, while the use of moderate-dielectric-constant SOS substrates should benefit high-frequency applications and enable integration with silicon circuitry. SNS weak links fabricated on SOS with PBCO and Co doped YBCO normal-metal layers exhibit current-voltage characteristics qualitatively consistent with the resistively shunted junction model, with modulating AC Josephson steps and operation to temperatures above 77 K. These are the first reported epitaxial edge-geometry SNS devices on SOS substrates. © 1994.
Hunt BD, Foote MC, Pike WT, et al., 1994, Multilayer buffer system for fabrication of high-T edge-geometry SNS weak links on silicon-on-sapphire substrates, Pages: 6-15, ISSN: 0277-786X
High frequency detector and circuit applications often require device fabrication on medium-tolow- dielectric constant substrates (ϵ<12). Silicon-on-sapphire (SOS) substrates have acceptably low dielectric constants and provide other important advantages, including the possibility of monolithic integration of silicon and superconducting circuitry. Our initial results with YBa2Cu3O7-x (YBCO) edge-geometry superconductor/normal-metal/superconductor (SNS) weak links fabricated on r-plane SOS substrates using cubic zirconia (YSZ) buffer layers revealed problems with grain boundary nucleation in the YBCO counter electrode. These results motivated development of a new multilayer buffer system consisting of an epitaxial YSZ film grown on an SOS substrate, overlayed by a thin YBCO "seed" layer, and an epitaxial SrTiO3 (STO) layer. STO - YBCO bilayers grown over the YBCO seed layer show a remarkable improvement in epitaxial quality and in YBCO electrical properties relative to similar bilayers grown directly on the YSZ buffer. In addition, SNS weak links fabricated on SOS substrates using the multilayer buffer system exhibit dramatically improved electrical characteristics compared to devices produced on YSZ buffer layers. These are the first epitaxial edgegeometry SNS weak links produced on SOS substrates.
Bell LD, Milliken AM, Manion SJ, et al., 1994, Ballistic-electron-emission microscopy of strained Si1-xGex layers, Physical Review B, Vol: 50, Pages: 8082-8085, ISSN: 0163-1829
Ballistic-electron-emission microscopy (BEEM) has been used to investigate the effects of strain on Si1-xGex alloys. Lifting of the degeneracy of the conduction-band minimum of Si1-xGex due to lattice deformation has been directly measured by application of BEEM spectroscopy to Ag/Si structures. Experimental values for this conduction-band splitting agree well with calculations. In addition, an unexpected heterogeneity in the strain of the Si1-xGex layer is introduced by deposition of Au. This effect, not observed with Ag, is attributed to species interdiffusion and has important implications for metal-semiconductor devices based on pseudomorphic Si1-xGex/Si material systems. © 1994 The American Physical Society.
Fathauer RW, George T, Jones EW, et al., 1994, Application of novel epitaxy techniques to the growth of CrSi<inf>2</inf>, Pages: 453-458, ISSN: 0272-9172
CrSi2 is of technological interest because it is a silicon-based semiconductor with a small band gap. Due to the lack of success with conventional molecular beam epitaxy of CrSi2 on Si, growth on mesotaxy-produced template layers and allotaxy have been attempted. After removal of the Si capping layer, epitaxy of additional CrSi2 on template layers formed by mesotaxy was found to be possible. However, single-crystal continuous films were not obtained, due at least in part to the presence of a network of cracks in the starting template. Allotaxy of CrSi2 was found to allow the formation of large grains of CrSi2 embedded in a single-crystal Si matrix, but coalescence of these grains into a continuous layer was not achieved.
Ksendzov A, Fathauer RW, George T, et al., 1993, Visible photoluminescence of porous Si<inf>1-x</inf>Ge<inf>x</inf> obtained by stain etching, Applied Physics Letters, Vol: 63, Pages: 200-202, ISSN: 0003-6951
We have investigated visible photoluminescence (PL) from thin porous Si1-xGex alloy layers prepared by stain etching of molecular-beam-epitaxy-grown material. Seven samples with nominal Ge fraction x varying from 0.04 to 0.41 were studied at room temperature and 80 K. Samples of bulk stain etched Si and Ge were also investigated. The composition of the porous material was determined using x-ray photoemission spectroscopy and Rutherford backscattering techniques to be considerably more Ge rich than the starting epitaxial layers. While the luminescence intensity drops significantly with the increasing Ge fraction, we observe no significant variation in the PL wavelength at room temperature. This is clearly in contradiction to the popular model based on quantum confinement in crystalline silicon which predicts that the PL energy should follow the band-gap variation of the starting material. However, our data are consistent with small active units containing only a few Si atoms that are responsible for the light emission. Such units are present in many compounds proposed in the literature as the cause of the visible PL in porous Si.
Pike WT, 1993, Measurement of lattice parameter at the nanometer scale using convergent-beam microdiffraction from a thermal emission source, Pages: 690-691, ISSN: 0424-8201
In epitaxial lattice mismatched multilayers, the study of lattice parameters and strain is important to determine the electronic behavior of these kind of structures. In this study, higher order Laue zone (holz) lines in the convergent beam microdiffraction patterns from a thermal emission TEM is utilized to measure the lattice parameters in nanometer scale. TEM with thermal emission source using condenser objective electron optics is applied to the study.
Asif Khan M, Kuznia JN, Olson DT, et al., 1993, GaN/AlN digital alloy short-period superlattices by switched atomic layer metalorganic chemical vapor deposition, Applied Physics Letters, Vol: 63, Pages: 3470-3472, ISSN: 0003-6951
In this letter we report the fabrication of GaN/AlN short-period superlattices using switched atomic layer epitaxy. Superlattice structures with GaN well thicknesses ranging from 2.6 to 20.8 Å (with AlN barrier thicknesses of 2.5, 7.5, and 15 Å) were deposited over basal plane sapphire and characterized for their structure, crystallinity, and optical properties. Cross-sectional transmission electron micrographs indicate GaN/AlN interfaces and the superlattice surfaces are atomically smooth. The structures exhibit strong room temperature photoluminescence and a sharp absorption edge indicating a high optical quality.
Barner JB, Hunt BD, Foote MC, et al., 1993, YBa<inf>2</inf>Cu<inf>3</inf>O<inf>7-δ</inf>-based, edge-geometry SNS Josephson junctions with low-resistivity PrBa<inf>2</inf>Cu<inf>3</inf>O<inf>7-δ</inf> barriers, Physica C: Superconductivity and its applications, Vol: 207, Pages: 381-390, ISSN: 0921-4534
We investigated the properties of all-high-Tc edge-geometry Josephson weak links using superconducting YBa2Cu3O7-δ (YBCO) electrodes and PrBa2Cu3O7-δ (PBCO) normal-metal layers. The fabrication of the weak links involved first ion-milling the base YBCO film using a MgO mask to form the edge and then depositing PBCO and YBCO layers in situ by pulsed-laser deposition. The optimum PBCO films had resistivities of 2 to 4 mΩ cm at room temperature and ≈30 mΩ cm at 4.2 K. Current-versus-voltage (I-V) characteristics were qualitatively consistent with the resistively-shunted-junction (RSJ) model. Strong Shapiro steps were present in the I-V characteristics of junctions under microwave irradiation and the critical current of the devices modulated with a Fraunhofer-like dependence as a function of magnetic field. The device parameters exhibited good scaling with area and PBCO thickness. The critical-current density varied exponentially with PBCO thickness, yielding a normal-metal coherence length of 9 nm for the PBCO. © 1993.
MCGIBBON AJ, BROWN LM, BLELOCH AL, et al., 1993, MICROSCOPY IN SOLID-STATE SCIENCE, MICROSCOPY RESEARCH AND TECHNIQUE, Vol: 24, Pages: 299-315, ISSN: 1059-910X
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