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Sample records for gaas monolithic surface

  1. Monolithic GaAs surface acoustic wave chemical microsensor array

    SciTech Connect

    HIETALA,VINCENT M.; CASALNUOVO,STEPHEN A.; HELLER,EDWIN J.; WENDT,JOEL R.; FRYE-MASON,GREGORY CHARLES; BACA,ALBERT G.

    2000-03-09

    A four-channel surface acoustic wave (SAW) chemical sensor array with associated RF electronics is monolithically integrated onto one GaAs IC. The sensor operates at 690 MHz from an on-chip SAW based oscillator and provides simple DC voltage outputs by using integrated phase detectors. This sensor array represents a significant advance in microsensor technology offering miniaturization, increased chemical selectivity, simplified system assembly, improved sensitivity, and inherent temperature compensation.

  2. Development of a GaAs Monolithic Surface Acoustic Wave Integrated Circuit

    SciTech Connect

    Baca, A.G.; Casalnuovo, S.C.; Drummond, T.J.; Frye, G.C.; Heller, E.J.; Hietala, V.M.; Klem, J.F.

    1999-03-08

    An oscillator technology using surface acoustic wave delay lines integrated with GaAs MESFET electronics has been developed for GaAs-based integrated microsensor applications. The oscillator consists of a two-port SAW delay line in a feedback loop with a four-stage GaAs MESFET amplifier. Oscillators with frequencies of 470, 350, and 200 MHz have been designed and fabricated. These oscillators are also promising for other RF applications.

  3. GaAs monolithic RF modules for SARSAT distress beacons

    NASA Technical Reports Server (NTRS)

    Cauley, Michael A.

    1991-01-01

    Monolithic GaAs UHF components for use in SARSAT Emergency Distress beacons are under development by Microwave Monolithics, Inc., Simi Valley, CA. The components include a bi-phase modulator, driver amplifier, and a 5 watt power amplifier.

  4. GaAs monolithic Lange and Wilkinson couplers

    NASA Astrophysics Data System (ADS)

    Waterman, R. C., Jr.; Fabian, W.; Pucel, R. A.; Tajima, Y.; Vorhaus, J. L.

    1981-02-01

    A monolithic GaAs X-band three-port Wilkinson coupler and a monolithic GaAs X-band four-port interdigitated Lange coupler are examined with reference to their design, fabrication technology, and experimental performance data. It is shown that fabrication of these couplers is compatible with present MMIC technologies. Measured loss minus fixture contributions is 0.25 dB and 0.75 dB for the Wilkinson and the Lange couplers, respectively.

  5. Surface modified aerogel monoliths

    NASA Technical Reports Server (NTRS)

    Leventis, Nicholas (Inventor); Johnston, James C. (Inventor); Kuczmarski, Maria A. (Inventor); Meador, Mary Ann B. (Inventor)

    2013-01-01

    This invention comprises reinforced aerogel monoliths such as silica aerogels having a polymer coating on its outer geometric surface boundary, and to the method of preparing said aerogel monoliths. The polymer coatings on the aerogel monoliths are derived from polymer precursors selected from the group consisting of isocyanates as a precursor, precursors of epoxies, and precursors of polyimides. The coated aerogel monoliths can be modified further by encapsulating the aerogel with the polymer precursor reinforced with fibers such as carbon or glass fibers to obtain mechanically reinforced composite encapsulated aerogel monoliths.

  6. GaAs monolithic R.F. modules for SARSAT distress beacons

    NASA Technical Reports Server (NTRS)

    Cauley, Michael A.

    1991-01-01

    Monolithic GaAs UHF components for use in SARSAT Emergency Distress beacons are under development by Microwave Monolithics, Inc., Simi Valley, CA. The components include a bi-phase modulator, driver amplifier, and a 5 watt power amplifier.

  7. Government systems and GaAs monolithic components

    NASA Astrophysics Data System (ADS)

    Sieger, K. J.

    1983-12-01

    The current state of monolithic GaAs technology and its current and future applications to government systems are reviewed, with attention given to the government investment strategy, commercial market impact, new technology, and challenges from silicon technology. Data obtained from a survey to determine the status of GaAs IC technology are presented. These contain the system type and acronym, a technical description of the system, the critical research and development needed to develop the particular IC, specific applications and functions of the IC in the system, the year of implementation, and the potential chip buyer. High volume applications, with chip counts of one million and more, are identified as phased arrays (radar and communication), expendable decoys, missile seekers, and satellite signal processors. Problem areas, future trends, and areas of uncertainty are discussed.

  8. Characterization of GaAs monolithic circuits by optical techniques

    NASA Astrophysics Data System (ADS)

    Hung, H.-L. A.; Lee, T. T.; Polak-Dingels, P.; Chauchard, E.; Webb, K.

    1989-09-01

    Optical techniques for broadband microwave signal generation and detection have been developed to characterize monolithic microwave integrated circuits (MMICs). Emphasis is on the enhancement of measurement accuracy and the identification of limitations. De-embedded complex S-parameters are derived from time-domain data obtained from both a GaAs photoconductive switch and electro-optic sampling of a Ka-band MMIC power amplifier. These parameters are directly compared with those measured from a network analyzer of the same circuit.

  9. A Ka-band GaAs monolithic phase shifter

    NASA Technical Reports Server (NTRS)

    Sokolov, V.; Geddes, J. J.; Contolatis, A.; Bauhahn, P. E.; Chao, C.

    1983-01-01

    The design and performance of a GaAs monolithic 180-degree one-bit switched line phase shifter test circuit for Ka-band operation is presented. A self-aligned gate (SAG) fabrication technique is also described that reduces resistive parasitics in the switching FET's. Over the 27.5-30 GHz band, typical measured differential insertion phase is within 10-20 deg of the ideal time delay characteristic. Over the same band, the insertion loss for the SAG phase shifter is about 2.5-3 dB per bit. The SAG fabrication technique holds promise in reducing phase shifter insertion loss to about 1.5 dB/bit for 30-GHz operation.

  10. Monolithic optical integrated control circuitry for GaAs MMIC-based phased arrays

    NASA Technical Reports Server (NTRS)

    Bhasin, K. B.; Ponchak, G. E.; Kascak, T. J.

    1985-01-01

    Gallium arsenide (GaAs) monolithic microwave integrated circuits (MMIC's) show promise in phased-array antenna applications for future space communications systems. Their efficient usage will depend on the control of amplitude and phase signals for each MMIC element in the phased array and in the low-loss radiofrequency feed. For a phased array contining several MMIC elements a complex system is required to control and feed each element. The characteristics of GaAs MMIC's for 20/30-GHz phased-array systems are discussed. The optical/MMIC interface and the desired characteristics of optical integrated circuits (OIC's) for such an interface are described. Anticipated fabrication considerations for eventual full monolithic integration of optical integrated circuits with MMIC's on a GaAs substrate are presented.

  11. Advanced digital modulation: Communication techniques and monolithic GaAs technology

    NASA Technical Reports Server (NTRS)

    Wilson, S. G.; Oliver, J. D., Jr.; Kot, R. C.; Richards, C. R.

    1983-01-01

    Communications theory and practice are merged with state-of-the-art technology in IC fabrication, especially monolithic GaAs technology, to examine the general feasibility of a number of advanced technology digital transmission systems. Satellite-channel models with (1) superior throughput, perhaps 2 Gbps; (2) attractive weight and cost; and (3) high RF power and spectrum efficiency are discussed. Transmission techniques possessing reasonably simple architectures capable of monolithic fabrication at high speeds were surveyed. This included a review of amplitude/phase shift keying (APSK) techniques and the continuous-phase-modulation (CPM) methods, of which MSK represents the simplest case.

  12. Optically controlled phased array antenna concepts using GaAs monolithic microwave integrated circuits

    NASA Technical Reports Server (NTRS)

    Kunath, R. R.; Bhasin, K. B.

    1986-01-01

    The desire for rapid beam reconfigurability and steering has led to the exploration of new techniques. Optical techniques have been suggested as potential candidates for implementing these needs. Candidates generally fall into one of two areas: those using fiber optic Beam Forming Networks (BFNs) and those using optically processed BFNs. Both techniques utilize GaAs Monolithic Microwave Integrated Circuits (MMICs) in the BFN, but the role of the MMIC for providing phase and amplitude variations is largely eliminated by some new optical processing techniques. This paper discusses these two types of optical BFN designs and provides conceptual designs of both systems.

  13. Low cost high efficiency GaAs monolithic RF module for SARSAT distress beacons

    NASA Technical Reports Server (NTRS)

    Petersen, W. C.; Siu, D. P.; Cook, H. F.

    1991-01-01

    Low cost high performance (5 Watts output) 406 MHz beacons are urgently needed to realize the maximum utilization of the Search and Rescue Satellite-Aided Tracking (SARSAT) system spearheaded in the U.S. by NASA. Although current technology can produce beacons meeting the output power requirement, power consumption is high due to the low efficiency of available transmitters. Field performance is currently unsatisfactory due to the lack of safe and reliable high density batteries capable of operation at -40 C. Low cost production is also a crucial but elusive requirement for the ultimate wide scale utilization of this system. Microwave Monolithics Incorporated (MMInc.) has proposed to make both the technical and cost goals for the SARSAT beacon attainable by developing a monolithic GaAs chip set for the RF module. This chip set consists of a high efficiency power amplifier and a bi-phase modulator. In addition to implementing the RF module in Monolithic Microwave Integrated Circuit (MMIC) form to minimize ultimate production costs, the power amplifier has a power-added efficiency nearly twice that attained with current commercial technology. A distress beacon built using this RF module chip set will be significantly smaller in size and lighter in weight due to a smaller battery requirement, since the 406 MHz signal source and the digital controller have far lower power consumption compared to the 5 watt power amplifier. All the program tasks have been successfully completed. The GaAs MMIC RF module chip set has been designed to be compatible with the present 406 MHz signal source and digital controller. A complete high performance low cost SARSAT beacon can be realized with only additional minor iteration and systems integration.

  14. Monolithic Series-Interconnected GaInAsSb/AlGaAsSb Thermophotovoltaic Devices Wafer Bonded to GaAs

    NASA Astrophysics Data System (ADS)

    Wang, C. A.; Huang, R. K.; Connors, M. K.; Shiau, D. A.; Murphy, P. G.; O'Brien, P. W.; Anderson, A. C.; Donetsky, D.; Anikeev, S.; Belenky, G.; Luryi, S.; Nichols, G.

    2004-11-01

    GaInAsSb/AlGaAsSb/GaSb epitaxial layers were wafer bonded to semi-insulating GaAs wafers for monolithic series interconnection of thermophotovoltaic (TPV) devices. SiOx/Ti/Au was used as a bonding layer to provide electrical isolation and to serve as an internal back-surface reflector (BSR). The minority-carrier lifetime in WB BSR structures is more than two times longer than that of control structures without a BSR. WB GaInAsSb/AlGaAsSb TPV cells were fabricated and monolithically interconnected in series. These cells exhibit nearly linear voltage building. At a short-circuit current density of 0.4 A/cm2, Voc of a single TPV cell is 0.2 V, compared to 0.37 and 1.8 V for 2- and 10-junction series-interconnected TPV cells, respectively.

  15. Design considerations for a monolithic, GaAs, dual-mode, QPSK/QASK, high-throughput rate transceiver. M.S. Thesis

    NASA Technical Reports Server (NTRS)

    Kot, R. A.; Oliver, J. D.; Wilson, S. G.

    1984-01-01

    A monolithic, GaAs, dual mode, quadrature amplitude shift keying and quadrature phase shift keying transceiver with one and two billion bits per second data rate is being considered to achieve a low power, small and ultra high speed communication system for satellite as well as terrestrial purposes. Recent GaAs integrated circuit achievements are surveyed and their constituent device types are evaluated. Design considerations, on an elemental level, of the entire modem are further included for monolithic realization with practical fabrication techniques. Numerous device types, with practical monolithic compatability, are used in the design of functional blocks with sufficient performances for realization of the transceiver.

  16. Monolithic integration of GaAs SAW chemical microsensor arrays and detection electronics

    SciTech Connect

    CASALNUOVO,STEPHEN A.; HIETALA,VINCENT M.; HELLER,EDWIN J.; ASON,GREGORY CHARLES; BACA,ALBERT G.

    2000-04-17

    The authors describe the integration of an array of surface acoustic wave delay line chemical sensors with the associated RF microelectronics such that the resulting device operates in a DC in/DC out mode. The microelectronics design for on-chip RF generation and detection is presented. Both hybrid and monolithic approaches are discussed. This approach improves system performance, simplifies packaging and assembly, and significantly reduces overall system size. The array design can be readily scaled to include a large number of sensors.

  17. Ka-Band GaAs FET Monolithic Power Amplifier Development

    NASA Technical Reports Server (NTRS)

    Saunier, Paul; Tserng, Hua Quen

    1997-01-01

    Over the course of this program, very extensive progress was made in Ka-band GaAs technology. At the beginning of the program, odd-shaped VPE MESFET wafers were used. A breakthrough in power and efficiency was achieved with highly doped (8 x 10(exp 17) cm(exp -3) MBE grown MESFET material. We obtained power of 112 mW with 16 dB gain and 21.6% efficiency at 34 GHz with a monolithic 50-100-250 micron amplifier. The next breakthrough came with the use of heterostructures grown by MBE (AlGaAs/InGaAs where the InGaAs is highly doped). This allowed us to achieve high power density with high efficiency. A benchmark 40% efficiency was achieved with a single-stage 100 micron MMIC at 32.5 GHz. The corresponding three-stage 50-100-250 micron amplifier achieved 180 mW with 23 dB gain and 30.3% efficiency. The next breakthrough came with 3-inch MBE grown PHEMT wafers incorporating an etch-stop layer for the gate recess (using RIE). Again, state-of-the-art performances were achieved: 40% efficiency with 235 mW output power and 20.7 dB gain. The single-stage 2 x 600 micron chip demonstrated 794 mW output power with 5 dB gain and 38.2% power-added efficiency (PAE). The Ka-band technology developed under this program has promise for extensive use: JPL demonstrated 32 GHz phased arrays with a three-stage amplifier developed under this contract. A variation of the three-stage amplifier was used successfully in a 4 x 4 phased array transmitter developed under another NASA contract.

  18. The 20 GHz GaAs monolithic power amplifier module development

    NASA Technical Reports Server (NTRS)

    1984-01-01

    The development of a 20 GHz GaAs FET monlithic power amplifier module for advanced communication applications is described. Four-way power combing of four 0.6 W amplifier modules is used as the baseline approach. For this purpose, a monolithic four-way traveling-wave power divider/combiner was developed. Over a 20 GHz bandwidth (10 to 30 GHz), an insertion loss of no more than 1.2 dB was measured for a pair of back-to-back connected divider/combiners. Isolation between output ports is better than 20 dB, and VSWRs are better than 21:1. A distributed amplifier with six 300 micron gate width FETs and gate and drain transmission line tapers has been designed, fabricated, and evaluated for use as an 0.6 W module. This amplifier has achieved state-of-the-art results of 0.5 W output power with at least 4 dB gain across the entire 2 to 21 GHz frequency range. An output power of 2 W was achieved at a measurement frequency of 18 GHz when four distributed amplifiers were power-combined using a pair of traveling-wave divider/combiners. Another approach is the direct common-source cascading of three power FET stages. An output power of up to 2W with 12 dB gain and 20% power-added efficiency has been achieved with this approach (at 17 GHz). The linear gain was 14 dB at 1 W output. The first two stages of the three-stage amplifier have achieved an output power of 1.6 W with 9 dB gain and 26% power-added efficiency at 16 GHz.

  19. Monolithic integration of optical grade GaAs on Si (001) substrates deeply patterned at a micron scale

    SciTech Connect

    Bietti, Sergio; Scaccabarozzi, Andrea; Bonera, Emiliano; Miglio, Leo; Sanguinetti, Stefano; Frigeri, Cesare; Falub, Claudiu V.; Känel, Hans von

    2013-12-23

    Dense arrays of micrometric crystals, with areal filling up to 93%, are obtained by depositing GaAs in a mask-less molecular beam epitaxy process onto Si substrates. The substrates are patterned into tall, micron sized pillars. Faceted high aspect ratio GaAs crystals are achieved by tuning the Ga adatom for short surface diffusion lengths. The crystals exhibit bulk-like optical quality due to defect termination at the sidewalls. Simultaneously, the thermal strain induced by different thermal expansion parameters of GaAs and Si is fully relieved. This opens the route to thick film applications without crack formation and wafer bowing.

  20. Atomic Structure of the Stoichiometric GaAs(114) Surface.

    PubMed

    Márquez; Kratzer; Geelhaar; Jacobi; Scheffler

    2001-01-01

    The stoichiometric GaAs(114) surface has been prepared using molecular beam epitaxy followed by annealing in ultrahigh vacuum. Based on in situ scanning tunneling microscopy measurements and first-principles electronic-structure calculations, we determine the surface reconstruction which we call alpha2(2x1). Contrary to what is expected for a high-index surface, it is surprisingly elementary. The (2x1) unit cell contains two As dimers and two rebonded Ga atoms. The surface energy is calculated as 53 meV/Å(2), which falls well within the range of low-index GaAs surface energies.

  1. Phosphine Functionalization GaAs(111)A Surfaces

    SciTech Connect

    Traub, M.; Biteen, J; Michalak, D; Webb, L; Brunschwig, B; Lewis, N

    2008-01-01

    Phosphorus-functionalized GaAs surfaces have been prepared by exposure of Cl-terminated GaAs(111)A surfaces to triethylphosphine (PEt3) or trichlorophosphine (PCl3), or by the direct functionalization of the native-oxide terminated GaAs(111)A surface with PCl3. The presence of phosphorus on each functionalized surface was confirmed by X-ray photoelectron spectroscopy. High-resolution, soft X-ray photoelectron spectroscopy was used to evaluate the As and Ga 3d regions of such surfaces. On PEt3 treated surfaces, the Ga 3d spectra exhibited a bulk Ga peak as well as peaks that were shifted to 0.35, 0.92 and 1.86 eV higher binding energy. These peaks were assigned to residual Cl-terminated Ga surface sites, surficial Ga2O and surficial Ga2O3, respectively. For PCl3-treated surfaces, the Ga 3d spectra displayed peaks ascribable to bulk Ga(As), Ga2O, and Ga2O3, as well as a peak shifted 0.30 eV to higher binding energy relative to the bulk signal. A peak corresponding to Ga(OH)3, observed on the Cl-terminated surface, was absent from all of the phosphine-functionalized surfaces. After reaction of the Cl-terminated GaAs(111)A surface with PCl3 or PEt3, the As 3d spectral region was free of As oxides and As0. Although native oxide-terminated GaAs surfaces were free of As oxides after reaction with PCl3, such surfaces contained detectable amounts of As0. Photoluminescence measurements indicted that phosphine-functionalized surfaces prepared from Cl-terminated GaAs(111)A surfaces had better electrical properties than the native-oxide capped GaAs(111)A surface, while the native-oxide covered surface treated with PCl3 showed no enhancement in PL intensity.

  2. Structure of high-index GaAs surfaces - the discovery of the stable GaAs(2511) surface

    NASA Astrophysics Data System (ADS)

    Jacobi, K.; Geelhaar, L.; Márquez, J.

    We present a brief overview of surface structures of high-index GaAs surfaces, putting emphasis on recent progress in our own laboratory. By adapting a commercial scanning tunneling microscope (STM) to our molecular beam epitaxy and ultra high vacuum analysis chamber system, we have been able to atomically resolve the GaAs( {1} {1} {3})B(8 ×1), (114)Aα2(2×1), (137), (3715), and (2511) surface structures. In cooperation with P. Kratzer and M. Scheffler from the Theory Department of the Fritz-Haber Institute we determined the structure of some of these surfaces by comparing total-energy calculations and STM image simulations with the atomically resolved STM images. We present the results for the {112}, {113}, and {114} surfaces. Then we describe what led us to proceed into the inner parts of the stereographic triangle and to discover the hitherto unknown stable GaAs(2511) surface.

  3. Wafer Bonding and Epitaxial Transfer of GaSb-based Epitaxy to GaAs for Monolithic Interconnection of Thermophotovoltaic Devices

    SciTech Connect

    C.A. Wang; D.A. Shiau; P.G. Murphy; P.W. O'brien; R.K. Huang; M.K. Connors; A.C. Anderson; D. Donetsky; S. Anikeev; G. Belenky; D.M. Depoy; G. Nichols

    2003-06-16

    GaInAsSb/AlGaAsSb/InAsSb/GaSb epitaxial layers were bonded to semi-insulating GaAs handle wafers with SiO{sub x}/Ti/Au as the adhesion layer for monolithic interconnection of thermophotovoltaic (TPV) devices. Epitaxial transfer was completed by removal of the GaSb substrate, GaSb buffer, and InAsSb etch-stop layer by selective chemical etching. The SiO{sub x}/TiAu provides not only electrical isolation, but also high reflectivity and is used as an internal back-surface reflector. Characterization of wafer-bonded epitaxy by high-resolution x-ray diffraction and time-decay photoluminescence indicates minimal residual stress and enhancement in optical quality. 0.54-eV GaInAsSb cells were fabricated and monolithically interconnected in series. A 10-junction device exhibited linear voltage building with an open-circuit voltage of 1.8 V.

  4. Surface structure of GaAs(2 5 11)

    NASA Astrophysics Data System (ADS)

    Geelhaar, L.; Temko, Y.; Márquez, J.; Kratzer, P.; Jacobi, K.

    2002-04-01

    GaAs samples with orientations vicinal to (2 5 11) within 1° were prepared by molecular beam epitaxy and analyzed in situ by scanning tunneling microscopy, low-energy electron diffraction, and reflection high-energy electron diffraction. In addition, first-principles electronic structure calculations were carried out. GaAs(2 5 11) is a stable surface whose orientation is located within the stereographic triangle. For a wide range of As-rich conditions a (1×1) reconstruction forms that is characterized by an inclined series of three As dimers and that fulfills the electron counting rule. The terrace size is limited only by the macroscopic off-orientation of the samples. The surface is perturbed by thin stripes of the nearby orientation (3 7 15). While the dangling bond densities of GaAs(2 5 11) and GaAs(3 7 15) are almost equal, GaAs(3 7 15) violates the electron counting rule. The analysis of this perturbation suggests that, in general, on semiconductor surfaces the gain in stability arising from the minimization of the number of dangling bonds is significantly greater than the gain arising from reaching a semiconducting ground state. Upon annealing of the samples in ultrahigh vacuum, a fairly rough surface structure develops whose mean orientation is different from (2 5 11).

  5. Monolithically interconnected GaAs solar cells: A new interconnection technology for high voltage solar cell output

    NASA Astrophysics Data System (ADS)

    Dinetta, L. C.; Hannon, M. H.

    1995-10-01

    Photovoltaic linear concentrator arrays can benefit from high performance solar cell technologies being developed at AstroPower. Specifically, these are the integration of thin GaAs solar cell and epitaxial lateral overgrowth technologies with the application of monolithically interconnected solar cell (MISC) techniques. This MISC array has several advantages which make it ideal for space concentrator systems. These are high system voltage, reliable low cost monolithically formed interconnections, design flexibility, costs that are independent of array voltage, and low power loss from shorts, opens, and impact damage. This concentrator solar cell will incorporate the benefits of light trapping by growing the device active layers over a low-cost, simple, PECVD deposited silicon/silicon dioxide Bragg reflector. The high voltage-low current output results in minimal 12R losses while properly designing the device allows for minimal shading and resistance losses. It is possible to obtain open circuit voltages as high as 67 volts/cm of solar cell length with existing technology. The projected power density for the high performance device is 5 kW/m for an AMO efficiency of 26% at 1 5X. Concentrator solar cell arrays are necessary to meet the power requirements of specific mission platforms and can supply high voltage power for electric propulsion systems. It is anticipated that the high efficiency, GaAs monolithically interconnected linear concentrator solar cell array will enjoy widespread application for space based solar power needs. Additional applications include remote man-portable or ultra-light unmanned air vehicle (UAV) power supplies where high power per area, high radiation hardness and a high bus voltage or low bus current are important. The monolithic approach has a number of inherent advantages, including reduced cost per interconnect and increased reliability of array connections. There is also a high potential for a large number of consumer products. Dual

  6. Monolithically interconnected GaAs solar cells: A new interconnection technology for high voltage solar cell output

    NASA Technical Reports Server (NTRS)

    Dinetta, L. C.; Hannon, M. H.

    1995-01-01

    Photovoltaic linear concentrator arrays can benefit from high performance solar cell technologies being developed at AstroPower. Specifically, these are the integration of thin GaAs solar cell and epitaxial lateral overgrowth technologies with the application of monolithically interconnected solar cell (MISC) techniques. This MISC array has several advantages which make it ideal for space concentrator systems. These are high system voltage, reliable low cost monolithically formed interconnections, design flexibility, costs that are independent of array voltage, and low power loss from shorts, opens, and impact damage. This concentrator solar cell will incorporate the benefits of light trapping by growing the device active layers over a low-cost, simple, PECVD deposited silicon/silicon dioxide Bragg reflector. The high voltage-low current output results in minimal 12R losses while properly designing the device allows for minimal shading and resistance losses. It is possible to obtain open circuit voltages as high as 67 volts/cm of solar cell length with existing technology. The projected power density for the high performance device is 5 kW/m for an AMO efficiency of 26% at 1 5X. Concentrator solar cell arrays are necessary to meet the power requirements of specific mission platforms and can supply high voltage power for electric propulsion systems. It is anticipated that the high efficiency, GaAs monolithically interconnected linear concentrator solar cell array will enjoy widespread application for space based solar power needs. Additional applications include remote man-portable or ultra-light unmanned air vehicle (UAV) power supplies where high power per area, high radiation hardness and a high bus voltage or low bus current are important. The monolithic approach has a number of inherent advantages, including reduced cost per interconnect and increased reliability of array connections. There is also a high potential for a large number of consumer products. Dual

  7. Monolithically interconnected GaAs solar cells: A new interconnection technology for high voltage solar cell output

    NASA Technical Reports Server (NTRS)

    Dinetta, L. C.; Hannon, M. H.

    1995-01-01

    Photovoltaic linear concentrator arrays can benefit from high performance solar cell technologies being developed at AstroPower. Specifically, these are the integration of thin GaAs solar cell and epitaxial lateral overgrowth technologies with the application of monolithically interconnected solar cell (MISC) techniques. This MISC array has several advantages which make it ideal for space concentrator systems. These are high system voltage, reliable low cost monolithically formed interconnections, design flexibility, costs that are independent of array voltage, and low power loss from shorts, opens, and impact damage. This concentrator solar cell will incorporate the benefits of light trapping by growing the device active layers over a low-cost, simple, PECVD deposited silicon/silicon dioxide Bragg reflector. The high voltage-low current output results in minimal 12R losses while properly designing the device allows for minimal shading and resistance losses. It is possible to obtain open circuit voltages as high as 67 volts/cm of solar cell length with existing technology. The projected power density for the high performance device is 5 kW/m for an AMO efficiency of 26% at 1 5X. Concentrator solar cell arrays are necessary to meet the power requirements of specific mission platforms and can supply high voltage power for electric propulsion systems. It is anticipated that the high efficiency, GaAs monolithically interconnected linear concentrator solar cell array will enjoy widespread application for space based solar power needs. Additional applications include remote man-portable or ultra-light unmanned air vehicle (UAV) power supplies where high power per area, high radiation hardness and a high bus voltage or low bus current are important. The monolithic approach has a number of inherent advantages, including reduced cost per interconnect and increased reliability of array connections. There is also a high potential for a large number of consumer products. Dual

  8. Passivation of GaAs Surfaces.

    DTIC Science & Technology

    1980-08-15

    hour at indicated temperatures. Each symbol indicates one of four pieces of the same starting crystal . Three of the pieces were treated four times. The...Each symbol indicates one of four pieces of the same starting crystal . Three of the pieces were treated three times ................................ 9... crystal 11 11. Luminescence intensity of GaAs treated in ammonia plasma at 575*C as a function of treatment time. Each symbol represents one of five

  9. Velocity surface measurements for ZnO films over /001/-cut GaAs

    NASA Technical Reports Server (NTRS)

    Kim, Yoonkee; Hunt, William D.; Liu, Yongsheng; Jen, Cheng-Kuei

    1994-01-01

    A potential application for a piezoelectic film deposited on a GaAs substrate is the monolithic integration of surface acoustic wave (SAW) devices with GaAs electronics. Knowledge of the SAW properties of the filmed structure is critical for the optimum design of such devices. In this article, the measurements of the velocity surface, which directly affects the SAW diffraction, on the bare and metallized ZnO/SiO2 or Si3N4/GaAs /001/-cut samples are reported using two different techniques: (1) knife-edge laser probe, (2) line-focus-beam scanning acoustic microscope. Comparisons, such as measurement accuracy and tradeoffs, between the former (dry) and the latter (wet) method are given. It is found that near the group of zone axes (110) propagation direction the autocollimating SAW property of the bare GaAs changes into a noncollimating one for the layered structure, but a reversed phenomenon exists near the group of zone axes (100) direction. The passivation layer of SiO2 or Si3N4 (less than 0.2 micrometer thick) and the metallization layer change the relative velocity but do not significantly affect the velocity surface. On the other hand, the passivation layer reduces the propagation loss by 0.5-1.3 dB/microseconds at 240 MHz depending upon the ZnO film thickness. Our SAW propagation measurements agree well with theorectical calculations. We have also obtained the anisotropy factors for samples with ZnO films of 1.6, 2.8, and 4.0 micrometer thickness. Comparisons concerning the piezoelectric coupling and acoustic loss between dc triode and rf magnetron sputtered ZnO films are provided.

  10. Multi-junction, monolithic solar cell using low-band-gap materials lattice matched to GaAs or Ge

    DOEpatents

    Olson, Jerry M.; Kurtz, Sarah R.; Friedman, Daniel J.

    2001-01-01

    A multi-junction, monolithic, photovoltaic solar cell device is provided for converting solar radiation to photocurrent and photovoltage with improved efficiency. The solar cell device comprises a plurality of semiconductor cells, i.e., active p/n junctions, connected in tandem and deposited on a substrate fabricated from GaAs or Ge. To increase efficiency, each semiconductor cell is fabricated from a crystalline material with a lattice constant substantially equivalent to the lattice constant of the substrate material. Additionally, the semiconductor cells are selected with appropriate band gaps to efficiently create photovoltage from a larger portion of the solar spectrum. In this regard, one semiconductor cell in each embodiment of the solar cell device has a band gap between that of Ge and GaAs. To achieve desired band gaps and lattice constants, the semiconductor cells may be fabricated from a number of materials including Ge, GaInP, GaAs, GaInAsP, GaInAsN, GaAsGe, BGaInAs, (GaAs)Ge, CuInSSe, CuAsSSe, and GaInAsNP. To further increase efficiency, the thickness of each semiconductor cell is controlled to match the photocurrent generated in each cell. To facilitate photocurrent flow, a plurality of tunnel junctions of low-resistivity material are included between each adjacent semiconductor cell. The conductivity or direction of photocurrent in the solar cell device may be selected by controlling the specific p-type or n-type characteristics for each active junction.

  11. Localized corrosion of GaAs surfaces and formation of porous GaAs

    SciTech Connect

    Schmuki, P.; Vitus, C.M.; Isaacs, H.S.; Fraser, J.; Graham, M.J.

    1995-12-01

    The present work deals with pitting corrosion of p- and n-type GaAs (100). Pit growth can be electrochemically initiated on both conduction types in chloride-containing solutions and leads after extended periods of time to the formation of a porous GaAs structure. In the case of p-type material, localized corrosion is only observed if a passivating film is present on the surface, otherwise -- e.g. in acidic solutions -- the material suffers from a uniform attack (electropolishing) which is independent of the anion present. In contrast, pitting corrosion of n-type material can be triggered independent of the presence of an oxide film. This is explained in terms of the different current limiting factor for the differently doped materials (oxide film in the case of the p- and a space charge layer in the case of the n-GaAs). The porous structure was characterized by SEM, EDX and AES, and consists mainly of GaAs. From scratch experiments it is clear that the pit initiation process is strongly influenced by surface defects. For n-type material, AFM investigations show that light induced roughening of the order of several hundred nm occurs under non-passivating conditions. This nm- scale roughening however does not affect the pitting process.

  12. Monolithically integrated GaAs thyristor-transistor as a hardened optically-triggered switch

    SciTech Connect

    Carson, R.F.; Hughes, R.C.; Weaver, H.T.; Brennan, T.M.; Hammons, B.E.

    1990-01-01

    Optically-triggered thyristors are hardened to high x-ray dose rates by the addition of a monolithically integrated compensating phototransistor. Tests of these devices show that sensitivity to radiation-induced switching is reduced by a factor of ten compared to conventional two-terminal thyristors (to 2 {times} 10{sup 9} Rad (Si)/sec). 3 refs., 5 figs.

  13. dc to 20 GHz monolithic GaAs FET switches based on quarter-micron gates

    NASA Astrophysics Data System (ADS)

    Dawe, Geoff; Bartle, Dylan; Spooner, Frank

    1988-08-01

    Broadband (dc to 20 GHz) high-isolation GaAs MMIC switches fabricated on ion implanted material using the standard alpha 0.25 micron gate-length process are described. They offer small-size and high-performance at low cost. It is noted that TTL compatible driver voltages with reflective or absorptive switches are available. The switches were tested both on wafer (multithrow element) and in a high-isolation channeled fixture (all others).

  14. Assessment of dynamic surface leaching of monolithic surface road materials.

    PubMed

    Paulus, Hélène; Schick, Joachim; Poirier, Jean-Eric

    2016-07-01

    Construction materials have to satisfy, among others, health and environment requirements. To check the environmental compatibility of road construction materials, release of hazardous substances into water must be assessed. Literature mostly describes the leaching behaviour of recycled aggregates for potential use in base or sub-base layers of roads. But little is known about the release of soluble substances by materials mixed with binders and compacted for intended use on road surface. In the present study, we thus performed a diffusion test with sequential renewal of water during a 64 day period according to CEN/TS 16637-2 specifications, on asphalt concretes and hydraulically bound monoliths, two common surface road materials. It is shown that release of dangerous substances is limited in these hydrodynamic conditions. It was particularly true for asphalt concrete leachates where no metallic trace element, sulphate, chloride or fluoride ion could be quantified. This is because of the low hydraulic conductivity and the low polarity of the petroleum hydrocarbon binder of these specimens. For hydraulically bound materials around 20,000 mg/m(2) of sulphate diffused from the monoliths. It is one order of magnitude higher than chloride diffusion and two orders of magnitude higher than fluoride release. No metallic trace element, except small quantities of copper in the last eluate could be quantified. No adverse effect is to be expected for human and environmental health from the leachates of these compacted surface road construction materials, because all the measured parameters were below EU (Council Directive 98/83/EC) or WHO guidelines for drinking water standards. Copyright © 2016 Elsevier Ltd. All rights reserved.

  15. Monolithic Microwave Integrated Circuits Based on GaAs Mesfet Technology

    NASA Astrophysics Data System (ADS)

    Bahl, Inder J.

    Advanced military microwave systems are demanding increased integration, reliability, radiation hardness, compact size and lower cost when produced in large volume, whereas the microwave commercial market, including wireless communications, mandates low cost circuits. Monolithic Microwave Integrated Circuit (MMIC) technology provides an economically viable approach to meeting these needs. In this paper the design considerations for several types of MMICs and their performance status are presented. Multifunction integrated circuits that advance the MMIC technology are described, including integrated microwave/digital functions and a highly integrated transceiver at C-band.

  16. ZnO Films on {001}-Cut <110>-Propagating GaAs Substrates for Surface Acoustic Wave Device Applications

    NASA Technical Reports Server (NTRS)

    Kim, Yoonkee; Hunt, William D.; Hickernell, Frederick S.; Higgins, Robert J.; Jen, Cheng-Kuei

    1995-01-01

    A potential application for piezoelectric films on GaAs substrates is the monolithic integration of surface acoustic wave (SAW) devices with GaAs electronics. Knowledge of the SAW properties of the layered structure is critical for the optimum and accurate design of such devices. The acoustic properties of ZnO films sputtered on {001}-cut <110> -propagating GaAs substrates are investigated in this article, including SAW Velocity effective piezoelectric coupling constant, propagation loss. diffraction, velocity surface, and reflectivity of shorted and open metallic gratings. The measurements of these essential SAW properties for the frequency range between 180 and 360 MHz have been performed using a knife-edge laser probe for film thicknesses over the range of 1.6-4 micron and with films or different grain sizes. The high quality of dc triode sputtered films was observed as evidenced by high K(exp 2) and low attenuation. The measurements of the velocity surface, which directly affects the SAW diffraction, on the bare and metalized ZnO on SiO2, or Si3N4 on {001}-cut GaAs samples are reported using two different techniques: 1) knife-edge laser probe, 2) line-focus-beam scanning acoustic microscope. It was found that near the <110> propagation direction, the focusing SAW property of the bare GaAs changes into a nonfocusing one for the layered structure, but a reversed phenomenon exists near the <100> direction. Furthermore, to some extent the diffraction of the substrate can be controlled with the film thickness. The reflectivity of shorted and open gratings are also analyzed and measured. Zero reflectivity is observed for a shorted grating. There is good agreement between the measured data and theoretical values.

  17. Monolithic GaAs digitizer for space-based laser pulse spreading effect

    NASA Astrophysics Data System (ADS)

    Lao, Bennig; Staples, Edward

    A 6-bit 1-GHz digitizer was designed to analyze the 1-ns pulse spreading effects in a space based altimeter. The digitizer consisted of four 4-bit flash A/D converters and a 6-bit encoder. Also, the converter utilized four 4-bit converters and a 4-to-6 bit encoder to achieve 6 bit resolution at the 1 GHz sample rate. The design was unique because it utilized only the inverters and NOR gates for the converters and encoder, hence it could be fabricated using the existing state-of-the-art GaAs processing techniques. This GHz digitizer has many commercial applications. It could be applicable to: (1) digital microwave transmission system for the telecommunication industries, (2) pulse monitoring in high kinetic chemical reactions, (3) transient signals in the medical field, and (4) microwave signals in astronomy.

  18. XPS and AFM Study of GaAs Surface Treatment

    SciTech Connect

    Contreras-Guerrero, R.; Wallace, R. M.; Aguirre-Francisco, S.; Herrera-Gomez, A.; Lopez-Lopez, M.

    2008-11-13

    Obtaining smooth and atomically clean surfaces is an important step in the preparation of a surface for device manufacturing. In this work different processes are evaluated for cleaning a GaAs surface. A good surface cleaning treatment is that which provides a high level of uniformity and controllability of the surface. Different techniques are useful as cleaning treatments depending on the growth process to be used. The goal is to remove the oxygen and carbon contaminants and then form a thin oxide film to protect the surface, which is easy to remove later with thermal desorption mechanism like molecular beam epitaxy (MBE) with minimal impact to the surface. In this study, atomic force microscopy (AFM), x-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS) were used to characterize the structure of the surface, the composition, as well as detect oxygen and carbon contaminant on the GaAs surface. This study consists in two parts. The first part the surface was subjected to different chemical treatments. The chemical solutions were: (a)H{sub 2}SO{sub 4}:H{sub 2}O{sub 2}:H{sub 2}O(4:1:100), (b) HCl: H{sub 2}O(1:3), (c)NH{sub 4}OH 29%. The treatments (a) and (b) reduced the oxygen on the surface. Treatment (c) reduces carbon contamination. In the second part we made MOS devices on the surfaces treated. They were characterized by CV and IV electrical measurements. They show frequency dispersion.

  19. ZnO films on /001/-cut (110)-propagating GaAs substrates for surface acoustic wave device applications

    NASA Technical Reports Server (NTRS)

    Hickernell, Frederick S.; Higgins, Robert J.; Jen, Cheng-Kuei; Kim, Yoonkee; Hunt, William D.

    1995-01-01

    A potential application for piezoelectric films substrates is the monolithic integration of surface acoustic wave (SAW) devices with GaAs electronics. Knowledge of the SAW properties of the layered structure is critical for the optimum and accurate design of such devices. The acoustic properties of ZnO films sputtered on /001/-cut group of (110) zone axes-propagating GaAs substrates are investigated in this article, including SAW velocity, effective piezoelectric coupling constant, propagation loss, diffraction, velocity surface, and reflectivity of shorted and open metallic gratings. The measurements of these essential SAW properties for the frequency range between 180 and 360 MHz have been performed using a knife-edge laser probe for film thicknesses over the range of 1.6-4 micron and with films of different grain sizes. The high quality of dc triode sputtered films was observed as evidenced by high K(sup 2) and low attenuation. The measurements of the velocity surface, which directly affects the SAW diffraction, on the bare and metalized ZnO on SiO2 or Si3N4 on /001/-cut GaAs samples are reported using two different techniques: (1) knife-edge laser probe, (2) line-focus-beam scanning acoustic microscope. It was found that near the group of (110) zone axes propagation direction, the focusing SAW property of the bare GaAs changes into a nonfocusing one for the layered structure, but a reversed phenomenon exists near the (100) direction. Furthermore, to some extent the diffraction of the substrate can be controlled with the film thickness. The reflectivity of shorted and open gratings are also analyzed and measured. Zero reflectivity is observed for a shorted grating. There is good agreement between the measured data and theoretical values.

  20. Electrophilic surface sites as precondition for the chemisorption of pyrrole on GaAs(001) surfaces

    SciTech Connect

    Bruhn, Thomas; Fimland, Bjørn-Ove; Vogt, Patrick

    2015-03-14

    We report how the presence of electrophilic surface sites influences the adsorption mechanism of pyrrole on GaAs(001) surfaces. For this purpose, we have investigated the adsorption behavior of pyrrole on different GaAs(001) reconstructions with different stoichiometries and thus different surface chemistries. The interfaces were characterized by x-ray photoelectron spectroscopy, scanning tunneling microscopy, and by reflectance anisotropy spectroscopy in a spectral range between 1.5 and 5 eV. On the As-rich c(4 × 4) reconstruction that exhibits only nucleophilic surface sites, pyrrole was found to physisorb on the surface without any significant modification of the structural and electronic properties of the surface. On the Ga-rich GaAs(001)-(4 × 2)/(6 × 6) reconstructions which exhibit nucleophilic as well as electrophilic surface sites, pyrrole was found to form stable covalent bonds mainly to the electrophilic (charge deficient) Ga atoms of the surface. These results clearly demonstrate that the existence of electrophilic surface sites is a crucial precondition for the chemisorption of pyrrole on GaAs(001) surfaces.

  1. Development of GaAs-Based Monolithic Surface Acoustic Wave Devices for Chemical Sensing and RF Filter Applications

    SciTech Connect

    Baca, A.G.; Casalnuovo, S.A.; Drummond, T.J.; Frye, G.C.; Heller, E.J.; Hietala, V.M.; Klem, J.F.

    1998-12-24

    Since their invention in the mid-1960's, surface acoustic wave (SAW) devices have become popular for a wide variety of applications. SAW devices represent a low-cost and compact method of achieving a variety of electronic signal processing functions at high frequencies, such as RF filters for TV or mobile wireless communications [1]. SAW devices also provide a convenient platform in chemical sensing applications, achieving extremely high sensitivity to vapor phase analytes in part-per-billion concentrations [2]. Although the SAW acoustic mode can be created on virtually any crystalline substrate, the development of SAW technology has historically focused on the use of piezoelectric materials, such as various orientations of either quartz or lithium niobate, allowing the devices to be fabricated simply and inexpensively. However, the III-V compound semiconductors, and GaAs in particular, are also piezoelectric as a result of their partially covalent bonding and support the SAW acoustic mode, allowing for the convenient fabrication of SAW devices. In addition, GaAs microelectronics has, in the past decade, matured commercially in numerous RF wireless technologies. In fact, GaAs was recognized long ago as a potential candidate for the monolithic integration of SAW devices with microelectronics, to achieve compact RF signal processing functions [3]. The details of design and fabrication of SAW devices can be found in a variety of references [1].

  2. Surface and coordination chemistry related to GaAs

    NASA Astrophysics Data System (ADS)

    Keys, Andrea

    The vapor phase structures of Al(tBU)3 and Ga(tBU)3 have been investigated by gas phase electron diffraction and consist of planar three-coordinate monomers. Salient structural parameters (ra) include: Al-C = 2.005(3) A, Ga-C = 2.034(2) A. The geometries are controlled by inter-ligand interactions. The electron diffraction structures are compared to those determined by ab initio calculations for M(tBU)3 (M = Al, Ga, In). To understand the most suitable linkages for the surface of GaAs, model compounds were synthesized by reacting Ga(tBU)3 and [tBu2Ga(mu-Cl]2 with one molar equivalent of varying ligands. The synthesized compounds include chlorides, benzenethiolate, dithiocarbamates, carboxylates, amides, benzohydroxamate, and phenylphosphonate. The Ga ⋯ Ga and Ga-ligand interatomic distances for these compounds, as well as Group 15 and 16 donor bridging ligands, are compared to the values for the surface of GaAs and cubic-GaS in order to determine their suitability as linkage groups for self-assembled monolayers. The most suitable linkages were determined to be benzenethiol and phenylphophonic acid, and these were used to grow self-assembled monolayers on {100} GaAs. Carboxylic acid was also used, to determine the success of the organometallic model compounds in predicting the suitability of ligands for surface reaction. Self-assembled monolayers were also grown on Al2O3, using carboxylic acids and phenylphosphonic acids as the surface linkages. Metallo-organic chemical vapor deposition was performed using single-source precursors ( tBU)2Ga(S2CNR2). The tert -butyl gallium bis-dialkyl-dithiocarbamate compounds, (tBu)Ga(S2CNR2)2, are formed as minor products via ligand disproportionation reactions. Gallium sulfide (GaS) thin films have been grown at 375-425°C by atmospheric pressure metal-organic chemical vapor deposition using compounds (tBu) 2Ga(S2CNMe2) and (tBu)2Ga(S 2CNEt2) as single source precursors. Polycrystalline samples of the chalcogenides InSe, In2Se3

  3. Surface photovoltage due to photo-thermo-ionization of surface states - GaAs

    NASA Technical Reports Server (NTRS)

    Morawski, A.; Slusarczuk, M. M. G.; Gatos, H. C.; Lagowski, J.

    1977-01-01

    Surface photovoltage spectroscopy was employed for studying the mechanism of subbandgap photoionization transitions from surface states in GaAs surfaces. It was found that the photoionization cross-section exhibits a maximum for a photon energy of about 0.9 eV. This finding indicates a photo-thermal mechanism of photovoltage, i.e., photo-induced transitions between surface state levels and the subsequent thermal ejection of electrons from the upper level into the conduction band.

  4. Micro structuration of gaas surface by wet etching: towards a specific surface behavior.

    PubMed

    Bienaime, Alex; Elie-Caille, Celine; Leblois, Therese

    2012-08-01

    Resonant microelectromechanical systems are promising devices for real time and highly sensitive measurements. The sensitivity of such sensors to additional mass loadings which can be increased thanks to the miniaturisation of devices is of prime importance for biological applications. The miniaturisation of structures passes through a photolithographic process and wet chemical etching. So, this paper presents new results on the anisotropic chemical etching of the gallium arsenide (GaAs) crystal used for this application, in several solutions. This paper focuses on the micro/nanostructuration of the sensing surface to increase the sensor sensitivity. Indeed, this active surface will be biofunctionalized to operate in biological liquid media in view of biomolecules detection. Several experimental conditions of etching bath composition, concentration and temperature were examined to obtain a large variety of geometrical surfaces topographies and roughness. According to the orientation dependence of the chemical etching process, the experiments were also performed on various GaAs crystal plates. The bath 1 H3PO4:9 H2O2:1 H2O appeared to be particularly adapted to the fabrication of the GaAs microstructured membrane: indeed, the bath is highly stable, anisotropic, and, as a function of temperature, it allows the production of a large variety of GaAs surface topographies.

  5. Wear performance of monolithic dental ceramics with different surface treatments.

    PubMed

    Preis, Verena; Weiser, Felix; Handel, Gerhard; Rosentritt, Martin

    2013-05-01

    To investigate the two-body wear performance of monolithic dental ceramics with different surface treatments. Standardized specimens (n = 8/ series) were fabricated from three monolithic dental ceramics (experimental translucent zirconia, experimental shaded zirconia, lithium disilicate). Four groups of each material were defined according to clinically relevant surface treatments: polished, polishedground, polished-ground-repolished, glazed. Two-body wear tests with steatite antagonists were performed in a chewing simulator. Surface roughness (R(a)) was controlled, and wear depths of specimens and antagonistic wear areas were calculated in relation to human enamel as reference. Statistical analysis of wear data was carried out using one-way ANOVA and Bonferroni multiple comparison test for post hoc analysis (α = .05). Scanning electron microscopy was applied for evaluating wear performance of ceramics and antagonists. Polished, ground, and repolished zirconia showed no wear, while glaze was abraded. Irrespective of the surface treatment, wear depth of lithium disilicate was significantly (P surfaces were smooth when opposed to polished/ground/repolished zirconia, and ploughed when opposed to glaze and lithium disilicate. Translucent and shaded experimental zirconia yielded superior wear behavior and lower antagonistic wear compared to lithium disilicate. A trend to higher ceramic and antagonistic wear was shown after grinding and glazing.

  6. Effect of nitride chemical passivation of the surface of GaAs photodiodes on their characteristics

    NASA Astrophysics Data System (ADS)

    Kontrosh, E. V.; Lebedeva, N. M.; Kalinovskiy, V. S.; Soldatenkov, F. Yu; Ulin, V. P.

    2016-11-01

    Characteristics of GaAs photodiodes have been studied before and after the chemical nitridation of their surface in hydrazine sulfide solutions, which leads to substitution of surface As atoms with N atoms to give a GaN monolayer. The resulting nitride coatings hinder the oxidation of GaAs in air and provide a decrease in the density of surface states involved in recombination processes. The device characteristics improved by nitridation are preserved during a long time.

  7. Reduction of Schottky Reverse Leakage Current Using GaAs Surface Cleaning with UVO3 Treatment

    NASA Astrophysics Data System (ADS)

    Tanimoto, Takuma; Ohbu, Isao; Ohta, Hiroshi; Takatani, Shinichiro

    1999-07-01

    A GaAs surface-cleaning method using UVO3 treatment was developed. The UVO3 treatment involves two processes: GaAs surface oxidation and oxide removal. Surface oxidation is performed by using a mercury lamp at high temperature, such as 180°C. GaAs oxide is removed by NH4OH solution dipping. Spectroscopic ellipsometry and X-ray photoelectron spectroscopy (XPS) study showed that thermally unstable As oxides exist on a non-treated surface; however, surface GaAs oxides are almost completely removed by this treatment. This cleaning method was applied in the field effect transistor (FET)-gate-formation process and, consequently, Schottky leakage current was significantly reduced.

  8. Gallium surface diffusion on GaAs (001) surfaces measured by crystallization dynamics of Ga droplets

    SciTech Connect

    Bietti, Sergio Somaschini, Claudio; Esposito, Luca; Sanguinetti, Stefano; Fedorov, Alexey

    2014-09-21

    We present accurate measurements of Ga cation surface diffusion on GaAs surfaces. The measurement method relies on atomic force microscopy measurement of the morphology of nano–disks that evolve, under group V supply, from nanoscale group III droplets, earlier deposited on the substrate surface. The dependence of the radius of such nano-droplets on crystallization conditions gives direct access to Ga diffusion length. We found an activation energy for Ga on GaAs(001) diffusion E{sub A}=1.31±0.15 eV, a diffusivity prefactor of D₀=0.53(×2.1±1) cm² s⁻¹ that we compare with the values present in literature. The obtained results permit to better understand the fundamental physics governing the motion of group III ad–atoms on III–V crystal surfaces and the fabrication of designable nanostructures.

  9. Arsenic ambient conditions preventing surface degradation of GaAs during capless annealing at high temperatures

    NASA Technical Reports Server (NTRS)

    Kang, C. H.; Kondo, K.; Lagowski, J.; Gatos, H. C.

    1987-01-01

    Changes in surface morphology and composition caused by capless annealing of GaAs were studied as a function of annealing temperature, T(GaAs), and the ambient arsenic pressure controlled by the temperature, T(As), of an arsenic source in the annealing ampul. It was established that any degradation of the GaAs surface morphology could be completely prevented, providing that T(As) was more than about 0.315T(GaAs) + 227 C. This empirical relationship is valid up to the melting point temperature of GaAs (1238 C), and it may be useful in some device-processing steps.

  10. Arsenic ambient conditions preventing surface degradation of GaAs during capless annealing at high temperatures

    NASA Technical Reports Server (NTRS)

    Kang, C. H.; Kondo, K.; Lagowski, J.; Gatos, H. C.

    1987-01-01

    Changes in surface morphology and composition caused by capless annealing of GaAs were studied as a function of annealing temperature, T(GaAs), and the ambient arsenic pressure controlled by the temperature, T(As), of an arsenic source in the annealing ampul. It was established that any degradation of the GaAs surface morphology could be completely prevented, providing that T(As) was more than about 0.315T(GaAs) + 227 C. This empirical relationship is valid up to the melting point temperature of GaAs (1238 C), and it may be useful in some device-processing steps.

  11. Cubic GaS: A Surface Passivator For GaAs

    NASA Technical Reports Server (NTRS)

    Hepp, Aloysius F.; Barron, Andrew R.; Power, Michael B.; Jenkins, Phillip P.; Macinnes, Andrew N.

    1994-01-01

    Thin films of cubic form of gallium sulfide (GaS) formed on surfaces of gallium arsenide (GaAs) substrates via metal/organic chemical vapor deposition (MOCVD). Deposited cubic GaS, crystalline lattice matched to substrate GaAs, neutralizes electrically active defects on surfaces of both n-doped and p-doped GaAs. Enabling important GaAs-based semiconducting materials to serve as substrates for metal/insulator/semiconductor (MIS) capacitors. Cubic GaS enables fabrication of ZnSe-based blue lasers and light-emitting diodes. Because GaS is optically transparent, deposited to form window layers for such optoelectronic devices as light-emitting diodes, solar optical cells, and semiconductor lasers. Its transparency makes it useful as interconnection material in optoelectronic integrated circuits. Also useful in peeled-film technology because selectively etched from GaAs.

  12. Behavior of Cu and Zn Impurities on GaAs Wafer Surfaces

    NASA Astrophysics Data System (ADS)

    Shibaya, Hiroshi

    1995-08-01

    Surface Cu and Zn contamination levels of intentionally contaminated GaAs wafers were measured by total reflection X-ray fluorescence (TXRF). Cu and Zn are both major metallic impurities on GaAs wafer surfaces, but their adsorption behaviors in an organic base solution were quite different. Surface concentration of Cu was much higher than that of Zn when concentrations of Cu and Zn in the organic base solution were the same. Cleaning effects of running deionized water rinse in an ultrasonic bath (U-RDIW) were also studied. Surface concentrations of Cu and Zn were drastically reduced by U-RDIW rinse.

  13. GaAs Surface Passivation for Device Applications.

    DTIC Science & Technology

    1982-03-01

    inter- face electrical properties as deduced by analysis of the capacitance- voltage and conductance-voltage behavior of GaAs metal-insulator...capacitance at 10 kHz. The pseudo- inversional level is substantially greater than Cin v . However, beyond -10 V, the capacitance actually drops slightly

  14. Nanoscale Footprints of Self-Running Gallium Droplets on GaAs Surface

    PubMed Central

    Wu, Jiang; Wang, Zhiming M.; Li, Alvason Z.; Benamara, Mourad; Li, Shibin; Salamo, Gregory J.

    2011-01-01

    In this work, the nanoscale footprints of self-driven liquid gallium droplet movement on a GaAs (001) surface will be presented and analyzed. The nanoscale footprints of a primary droplet trail and ordered secondary droplets along primary droplet trails are observed on the GaAs surface. A well ordered nanoterrace from the trail is left behind by a running droplet. In addition, collision events between two running droplets are investigated. The exposed fresh surface after a collision demonstrates a superior evaporation property. Based on the observation of droplet evolution at different stages as well as nanoscale footprints, a schematic diagram of droplet evolution is outlined in an attempt to understand the phenomenon of stick-slip droplet motion on the GaAs surface. The present study adds another piece of work to obtain the physical picture of a stick-slip self-driven mechanism in nanoscale, bridging nano and micro systems. PMID:21673965

  15. Nanoscale footprints of self-running gallium droplets on GaAs surface.

    PubMed

    Wu, Jiang; Wang, Zhiming M; Li, Alvason Z; Benamara, Mourad; Li, Shibin; Salamo, Gregory J

    2011-01-01

    In this work, the nanoscale footprints of self-driven liquid gallium droplet movement on a GaAs (001) surface will be presented and analyzed. The nanoscale footprints of a primary droplet trail and ordered secondary droplets along primary droplet trails are observed on the GaAs surface. A well ordered nanoterrace from the trail is left behind by a running droplet. In addition, collision events between two running droplets are investigated. The exposed fresh surface after a collision demonstrates a superior evaporation property. Based on the observation of droplet evolution at different stages as well as nanoscale footprints, a schematic diagram of droplet evolution is outlined in an attempt to understand the phenomenon of stick-slip droplet motion on the GaAs surface. The present study adds another piece of work to obtain the physical picture of a stick-slip self-driven mechanism in nanoscale, bridging nano and micro systems.

  16. Evolution of ion-induced nanoparticle arrays on GaAs surfaces

    SciTech Connect

    Kang, M.; Al-Heji, A. A.; Shende, O.; Huang, S.; Jeon, S.; Goldman, R. S.; Beskin, I.

    2014-05-05

    We have examined the evolution of irradiation-induced Ga nanoparticle (NP) arrays on GaAs surfaces. Focused-ion-beam irradiation of pre-patterned GaAs surfaces induces monotonic increases in the NP volume and aspect ratio up to a saturation ion dose, independent of NP location within the array. Beyond the saturation ion dose, the NP volume continues to increase monotonically while the NP aspect ratio decreases monotonically. In addition, the NP volumes (aspect ratios) are highest (lowest) for the corner NPs. We discuss the relative influences of bulk and surface diffusion on the evolution of Ga NP arrays.

  17. Evolution of ion-induced nanoparticle arrays on GaAs surfaces

    NASA Astrophysics Data System (ADS)

    Kang, M.; Beskin, I.; Al-Heji, A. A.; Shende, O.; Huang, S.; Jeon, S.; Goldman, R. S.

    2014-05-01

    We have examined the evolution of irradiation-induced Ga nanoparticle (NP) arrays on GaAs surfaces. Focused-ion-beam irradiation of pre-patterned GaAs surfaces induces monotonic increases in the NP volume and aspect ratio up to a saturation ion dose, independent of NP location within the array. Beyond the saturation ion dose, the NP volume continues to increase monotonically while the NP aspect ratio decreases monotonically. In addition, the NP volumes (aspect ratios) are highest (lowest) for the corner NPs. We discuss the relative influences of bulk and surface diffusion on the evolution of Ga NP arrays.

  18. Sulfur passivation of GaAs surfaces: A model for reduced surface recombination without band flattening

    NASA Astrophysics Data System (ADS)

    Spindt, C. J.; Spicer, W. E.

    1989-10-01

    It has been shown by several workers that the passivation of GaAs surfaces using sulfides results in a large reduction in the surface recombination velocity accompanied by an increase in the band bending on n-type samples. This apparently contradictory pair of results leads to the suggestion that the responsible electronic states are a midgap donor compensated by an acceptor near the valence-band maximum. We explore the consequences of such a model, particularly when the midgap state is assumed to be a double donor. In the double donor case, simple qualitative arguments indicate that the surface recombination velocity can be reduced by a factor much greater than the reduction in surface-state density. The model is consistent with observations made using a variety of experimental techniques. A correlation between the electronic states and surface chemistry is made, and the As and Ga antisite defects are discussed as candidates for the donor and acceptor states.

  19. Monolithic phononic crystals with a surface acoustic band gap from surface phonon-polariton coupling.

    PubMed

    Yudistira, D; Boes, A; Djafari-Rouhani, B; Pennec, Y; Yeo, L Y; Mitchell, A; Friend, J R

    2014-11-21

    We theoretically and experimentally demonstrate the existence of complete surface acoustic wave band gaps in surface phonon-polariton phononic crystals, in a completely monolithic structure formed from a two-dimensional honeycomb array of hexagonal shape domain-inverted inclusions in single crystal piezoelectric Z-cut lithium niobate. The band gaps appear at a frequency of about twice the Bragg band gap at the center of the Brillouin zone, formed through phonon-polariton coupling. The structure is mechanically, electromagnetically, and topographically homogeneous, without any physical alteration of the surface, offering an ideal platform for many acoustic wave applications for photonics, phononics, and microfluidics.

  20. Structural studies of sulfur passivated GaAs(001) surfaces with LEED and AFM

    NASA Astrophysics Data System (ADS)

    Wang, Xuewen; Ke, Yenjin; Milano, Steve; Tao, Nongjian; Darici, Yesim

    1997-03-01

    We present the results of auger electron spectroscopy (AES), low-energy electron diffraction (LEED) and atomic force microscopy (AFM) analysis of sulfur passivating layers on the GaAs(001) surface. The GaAs surfaces were passivated with both inorganic ((NH_4)_2S) and organic (ODT) S-based compounds. We prepared the inorganic sulfur-passivated GaAs(001) surfaces with a wet chemical treatment using (NH_4)_2S solution. This was followed by thermal annealing of the treated sample in ultra high vacuum. After ex-situ and in-situ treatments the surface resulted in a (2X1) LEED pattern. The LEED data (I-V curves) was recorded and compared with dynamical LEED calculations for different structural models for the sulfur passivated GaAs(110) surface. The results showed that sulfur passivated (2X1) surface structure is an arsenic-sulfur dimer on gallium terminated substrate. The ex-situ AFM results also showed a (2X1) structure for the inorganic passivation and a very smooth surface for the organic ODT in ethanal treated sample.

  1. Enhanced charge recombination due to surfaces and twin defects in GaAs nanostructures

    NASA Astrophysics Data System (ADS)

    Brown, Evan; Sheng, Chunyang; Shimamura, Kohei; Shimojo, Fuyuki; Nakano, Aiichiro

    2015-02-01

    Power conversion efficiency of gallium arsenide (GaAs) nanowire (NW) solar cells is severely limited by enhanced charge recombination (CR) at sidewall surfaces, but its atomistic mechanisms are not well understood. In addition, GaAs NWs usually contain a high density of twin defects that form a twin superlattice, but its effects on CR dynamics are largely unknown. Here, quantum molecular dynamics (QMD) simulations reveal the existence of an intrinsic type-II heterostructure at the (110) GaAs surface. Nonadiabatic quantum molecular dynamics (NAQMD) simulations show that the resulting staggered band alignment causes a photoexcited electron in the bulk to rapidly transfer to the surface. We have found orders-of-magnitude enhancement of the CR rate at the surface compared with the bulk value. Furthermore, QMD and NAQMD simulations show unique surface electronic states at alternating (111)A and (111)B sidewall surfaces of a twinned [111]-oriented GaAs NW, which act as effective CR centers. The calculated large surface recombination velocity quantitatively explains recent experimental observations and provides microscopic understanding of the underlying CR processes.

  2. Enhanced charge recombination due to surfaces and twin defects in GaAs nanostructures

    SciTech Connect

    Brown, Evan; Sheng, Chunyang; Nakano, Aiichiro; Shimamura, Kohei; Shimojo, Fuyuki

    2015-02-07

    Power conversion efficiency of gallium arsenide (GaAs) nanowire (NW) solar cells is severely limited by enhanced charge recombination (CR) at sidewall surfaces, but its atomistic mechanisms are not well understood. In addition, GaAs NWs usually contain a high density of twin defects that form a twin superlattice, but its effects on CR dynamics are largely unknown. Here, quantum molecular dynamics (QMD) simulations reveal the existence of an intrinsic type-II heterostructure at the (110) GaAs surface. Nonadiabatic quantum molecular dynamics (NAQMD) simulations show that the resulting staggered band alignment causes a photoexcited electron in the bulk to rapidly transfer to the surface. We have found orders-of-magnitude enhancement of the CR rate at the surface compared with the bulk value. Furthermore, QMD and NAQMD simulations show unique surface electronic states at alternating (111)A and (111)B sidewall surfaces of a twinned [111]-oriented GaAs NW, which act as effective CR centers. The calculated large surface recombination velocity quantitatively explains recent experimental observations and provides microscopic understanding of the underlying CR processes.

  3. A new structure for comparing surface passivation materials of GaAs solar cells

    NASA Technical Reports Server (NTRS)

    Desalvo, Gregory C.; Barnett, Allen M.

    1989-01-01

    The surface recombination velocity (S sub rec) for bare GaAs is typically as high as 10 to the 6th power to 10 to the 7th power cm/sec, which dramatically lowers the efficiency of GaAs solar cells. Early attempts to circumvent this problem by making an ultra thin junction (xj less than .1 micron) proved unsuccessful when compared to lowering S sub rec by surface passivation. Present day GaAs solar cells use an GaAlAs window layer to passivate the top surface. The advantages of GaAlAs in surface passivation are its high bandgap energy and lattice matching to GaAs. Although GaAlAs is successful in reducing the surface recombination velocity, it has other inherent problems of chemical instability (Al readily oxidizes) and ohmic contact formation. The search for new, more stable window layer materials requires a means to compare their surface passivation ability. Therefore, a device structure is needed to easily test the performance of different passivating candidates. Such a test device is described.

  4. Maskless micro/nanofabrication on GaAs surface by friction-induced selective etching

    PubMed Central

    2014-01-01

    In the present study, a friction-induced selective etching method was developed to produce nanostructures on GaAs surface. Without any resist mask, the nanofabrication can be achieved by scratching and post-etching in sulfuric acid solution. The effects of the applied normal load and etching period on the formation of the nanostructure were studied. Results showed that the height of the nanostructure increased with the normal load or the etching period. XPS and Raman detection demonstrated that residual compressive stress and lattice densification were probably the main reason for selective etching, which eventually led to the protrusive nanostructures from the scratched area on the GaAs surface. Through a homemade multi-probe instrument, the capability of this fabrication method was demonstrated by producing various nanostructures on the GaAs surface, such as linear array, intersecting parallel, surface mesas, and special letters. In summary, the proposed method provided a straightforward and more maneuverable micro/nanofabrication method on the GaAs surface. PMID:24495647

  5. Formation and coarsening of Ga droplets on focused-ion-beam irradiated GaAs surfaces

    SciTech Connect

    Wu, J. H.; Ye, W.; Cardozo, B. L.; Saltzman, D.; Sun, K.; Sun, H.; Mansfield, J. F.; Goldman, R. S.

    2009-10-12

    We have investigated the formation and coarsening of Ga droplets on focused-ion-beam (FIB) irradiated GaAs surfaces. To separately examine formation and coarsening, Ga droplets were fabricated by Ga{sup +} FIB irradiation of GaAs substrates with and without pre-patterned holes. We determined the droplet growth rate and size distribution as a function of FIB energy following irradiation. The data suggest a droplet formation mechanism that involves Ga precipitation from a Ga-rich layer, followed by droplet coarsening via a combination of diffusion and Ostwald ripening or coalescence via droplet migration (dynamic coalescence)

  6. Use of a corrugated surface to enhance radiation tolerance in a GaAs solar cell

    NASA Technical Reports Server (NTRS)

    Leon, Rosa P.; Piszczor, Michael F., Jr.

    1985-01-01

    The use of a corrugated surface on a GaAs solar cell and its effects on radiation resistance were studied. A compute code was developed to determine the performance of the cell for various geometric parameters. The large optical absorption coefficient of GaAs allows grooves to be only 4-5 micrometers deep. Using accepted material parameters for GaAs solar cells the theoretical performances were compared for various corrugated cells before and after minority carrier diffusion length degradation. The total power output was maximized for both n(+)/p and p(+)/n cells. Optimum values of 1.0-1.5 and 5.0 micrometers for groove and ridge widths respectively were determined.

  7. Surface science analysis of GaAs photocathodes following sustained electron beam delivery

    SciTech Connect

    Carlos Hernandez-Garcia, Fay Hannon, Marcy Stutzman, V. Shutthanandan, Z. Zhu, M. Nandasri, S. V. Kuchibhatla, S. Thevuthasan, W. P. Hess

    2012-06-01

    Degradation of the photocathode materials employed in photoinjectors represents a challenge for sustained operation of nuclear physics accelerators and high power Free Electron Lasers (FEL). Photocathode quantum efficiency (QE) degradation is due to residual gasses in the electron source vacuum system being ionized and accelerated back to the photocathode. These investigations are a first attempt to characterize the nature of the photocathode degradation, and employ multiple surface and bulk analysis techniques to investigate damage mechanisms including sputtering of the Cs-oxidant surface monolayer, other surface chemistry effects, and ion implantation. Surface and bulk analysis studies were conducted on two GaAs photocathodes, which were removed from the JLab FEL DC photoemission gun after delivering electron beam, and two control samples. The analysis techniques include Helium Ion Microscopy (HIM), Rutherford Backscattering Spectrometry (RBS), Atomic Force Microscopy (AFM) and Secondary Ion Mass Spectrometry (SIMS). In addition, two high-polarization strained superlattice GaAs photocathode samples, one removed from the Continuous Electron Beam Accelerator Facility (CEBAF) photoinjector and one unused, were also analyzed using Transmission Electron Microscopy (TEM) and SIMS. It was found that heat cleaning the FEL GaAs wafer introduces surface roughness, which seems to be reduced by prolonged use. The bulk GaAs samples retained a fairly well organized crystalline structure after delivering beam but shows evidence of Cs depletion on the surface. Within the precision of the SIMS and RBS measurements the data showed no indication of hydrogen implantation or lattice damage from ion back bombardment in the bulk GaAs wafers. In contrast, SIMS and TEM measurements of the strained superlattice photocathode show clear crystal damage in the wafer from ion back bombardment.

  8. Low energy positrons at the Ga-rich (100) surface of GaAs

    NASA Astrophysics Data System (ADS)

    Fazleev, Nail G.; Fry, John L.; Starnes, Shannon G.; Weiss, Alex H.

    2000-03-01

    We present results of theoretical studies of positron surface states and annihilation characteristics at the Ga-rich (100) surface of GaAs with different reconstructions. Calculations are based on a treatment of a positron as a single charged particle trapped in a "correlation well" in the proximity of surface atoms. Positron surface and bulk states are calculated numerically by solving the positron Schrödinger equation using the finite-difference method. The Hartree part of the positron potential is constructed taking into consideration the electronic reorganization due to interatomic bondings and surface stoichoimetry effects. Estimates of positron surface-state binding energies and work functions are provided. Computed positron surface-state characteristics and annihilation probabilities with relevant core electrons are used to analyze positron annihilation induced Auger-electron spectroscopy (PAES) spectrum from the Ga-rich GaAs (100) surface. The effect of deposition of Al on the (100) surface of GaAs on the localization of the positron surface state and on positron annihilation probabilities is also discussed.

  9. Transient Evolution of Surface Roughness on Patterned GaAs(001) during Homoepitaxial Growth

    NASA Astrophysics Data System (ADS)

    Kan, H.-C.; Shah, S.; Tadyyon-Eslami, T.; Phaneuf, R. J.

    2004-04-01

    We have investigated the length scale dependence of the transient evolution of surface roughness during homoepitaxial growth on GaAs(100), patterning the surface lithographically with an array of cylindrical pits of systematically varied sizes and spacings. Our atomic force microscopy measurements show that the amplitude of the surface corrugation has nonmonotonic behavior in both the length scale dependence and time evolution. This behavior allows us to rule out a number of existing continuum models of growth.

  10. SEMICONDUCTOR TECHNOLOGY: GaAs surface wet cleaning by a novel treatment in revolving ultrasonic atomization solution

    NASA Astrophysics Data System (ADS)

    Zaijin, Li; Liming, Hu; Ye, Wang; Ye, Yang; Hangyu, Peng; Jinlong, Zhang; Li, Qin; Yun, Liu; Lijun, Wang

    2010-03-01

    A novel process for the wet cleaning of GaAs surface is presented. It is designed for technological simplicity and minimum damage generated within the GaAs surface. It combines GaAs cleaning with three conditions consisting of (1) removal of thermodynamically unstable species and (2) surface oxide layers must be completely removed after thermal cleaning, and (3) a smooth surface must be provided. Revolving ultrasonic atomization technology is adopted in the cleaning process. At first impurity removal is achieved by organic solvents; second NH4OH:H2O2:H2O = 1:1:10 solution and HCl: H2O2:H2O = 1:1:20 solution in succession to etch a very thin GaAs layer, the goal of the step is removing metallic contaminants and forming a very thin oxidation layer on the GaAs wafer surface; NH4OH:H2O = 1:5 solution is used as the removed oxide layers in the end. The effectiveness of the process is demonstrated by the operation of the GaAs wafer. Characterization of the oxide composition was carried out by X-ray photoelectron spectroscopy. Metal-contamination and surface morphology was observed by a total reflection X-ray fluorescence spectroscopy and atomic force microscope. The research results show that the cleaned surface is without contamination or metal contamination. Also, the GaAs substrates surface is very smooth for epitaxial growth using the rotary ultrasonic atomization technology.

  11. Effects of surface passivation on twin-free GaAs nanosheets.

    PubMed

    Arab, Shermin; Chi, Chun-Yung; Shi, Teng; Wang, Yuda; Dapkus, Daniel P; Jackson, Howard E; Smith, Leigh M; Cronin, Stephen B

    2015-02-24

    Unlike nanowires, GaAs nanosheets exhibit no twin defects, stacking faults, or dislocations even when grown on lattice mismatched substrates. As such, they are excellent candidates for optoelectronic applications, including LEDs and solar cells. We report substantial enhancements in the photoluminescence efficiency and the lifetime of passivated GaAs nanosheets produced using the selected area growth (SAG) method with metal organic chemical vapor deposition (MOCVD). Measurements are performed on individual GaAs nanosheets with and without an AlGaAs passivation layer. Both steady-state photoluminescence and time-resolved photoluminescence spectroscopy are performed to study the optoelectronic performance of these nanostructures. Our results show that AlGaAs passivation of GaAs nanosheets leads to a 30- to 40-fold enhancement in the photoluminescence intensity. The photoluminescence lifetime increases from less than 30 to 300 ps with passivation, indicating an order of magnitude improvement in the minority carrier lifetime. We attribute these enhancements to the reduction of nonradiative recombination due to the compensation of surface states after passivation. The surface recombination velocity decreases from an initial value of 2.5 × 10(5) to 2.7 × 10(4) cm/s with passivation.

  12. GaAs(2 5 11): a new stable surface within the stereographic triangle.

    PubMed

    Geelhaar, L; Márquez, J; Kratzer, P; Jacobi, K

    2001-04-23

    The atomic structure of GaAs(2 5 11), a hitherto unknown stable surface, has been determined by in situ scanning tunneling microscopy and first-principles electronic structure calculations. This orientation is located within the stereographic triangle, i.e., far away from all low-index surfaces. A low-energy ( 1x1) reconstruction containing arsenic dimers forms on the surface. The analysis of the surface structure shows that, for semiconductor surfaces, the gain in stability due to minimization of the number of dangling bonds is more important than the gain from rendering a semiconducting ground state.

  13. Highly bioactive polysiloxane modified bioactive glass-poly(ethylene glycol) hybrids monoliths with controlled surface structure for bone tissue regeneration

    NASA Astrophysics Data System (ADS)

    Chen, Jing; Que, Wenxiu; Xing, Yonglei; Lei, Bo

    2015-03-01

    Crack-free monoliths with controllable surface microstructure have high bioactivities and therefore potential applications in bone tissue regeneration. In this paper, crack-free polydimethylsiloxane-modified bioactive glass-poly (ethylene glycol) (PDMS-BG-PEG) hybrids monoliths were fabricated via using a modified sol-gel process. Results show that the addition of PEG plays an important part in the formation of crack-free and gelation of the monoliths, and surface microstructures of the as-prepared hybrid monoliths were significantly influenced by the concentration and molecular weight of PEG. The samples obtained from PEG 300 had porous surface result in higher bioactivity (apatite formation) in simulated body fluid (SBF), while the samples obtained from PEG 600 had the smooth surface and inhibited the formation of apatite layer in SBF. These as-prepared hybrid monoliths can be used as a good candidate of implant and scaffold for highly efficient bone tissue regeneration.

  14. Monolithic spectrometer

    DOEpatents

    Rajic, S.; Egert, C.M.; Kahl, W.K.; Snyder, W.B. Jr.; Evans, B.M. III; Marlar, T.A.; Cunningham, J.P.

    1998-05-19

    A monolithic spectrometer is disclosed for use in spectroscopy. The spectrometer is a single body of translucent material with positioned surfaces for the transmission, reflection and spectral analysis of light rays. 6 figs.

  15. Monolithic spectrometer

    DOEpatents

    Rajic, Slobodan; Egert, Charles M.; Kahl, William K.; Snyder, Jr., William B.; Evans, III, Boyd M.; Marlar, Troy A.; Cunningham, Joseph P.

    1998-01-01

    A monolithic spectrometer is disclosed for use in spectroscopy. The spectrometer is a single body of translucent material with positioned surfaces for the transmission, reflection and spectral analysis of light rays.

  16. Periodic surface structure bifurcation induced by ultrafast laser generated point defect diffusion in GaAs

    SciTech Connect

    Abere, Michael J.; Yalisove, Steven M.; Torralva, Ben

    2016-04-11

    The formation of high spatial frequency laser induced periodic surface structures (HSFL) with period <0.3 λ in GaAs after irradiation with femtosecond laser pulses in air is studied. We have identified a point defect generation mechanism that operates in a specific range of fluences in semiconductors between the band-gap closure and ultrafast-melt thresholds that produces vacancy/interstitial pairs. Stress relaxation, via diffusing defects, forms the 350–400 nm tall and ∼90 nm wide structures through a bifurcation process of lower spatial frequency surface structures. The resulting HSFL are predominately epitaxial single crystals and retain the original GaAs stoichiometry.

  17. Twin superlattice-induced large surface recombination velocity in GaAs nanostructures

    SciTech Connect

    Sheng, Chunyang; Brown, Evan; Nakano, Aiichiro; Shimojo, Fuyuki

    2014-12-08

    Semiconductor nanowires (NWs) often contain a high density of twin defects that form a twin superlattice, but its effects on electronic properties are largely unknown. Here, nonadiabatic quantum molecular dynamics simulation shows unique surface electronic states at alternating (111)A and (111)B sidewall surfaces of a twinned [111]-oriented GaAs NW, which act as effective charge-recombination centers. The calculated large surface recombination velocity quantitatively explains recent experimental observations and provides microscopic understanding of the underlying surface-recombination processes.

  18. Micro-Reactions on Metal Contacts on Various Types of GaAs Surfaces.

    DTIC Science & Technology

    1986-02-01

    GaAs surfaces as generally employed for the manufacture of MeSFETs and their IC’s, particularly _- . - in view of device-life-time optimization...electrodes (points A(v) and (vii) of Section C-I, Award Dec.); in particular here the formation of ._ narrow, short circuiting metal filaments by field... MeSFETs has beco . -’.. a field of wide current interest particularly from the device aging point of view /9/. : - . -. . p. . Here, we describe the

  19. Surface kinetics study of metal-organic vapor phase epitaxy of GaAs1-yBiy on offcut and mesa-patterned GaAs substrates

    NASA Astrophysics Data System (ADS)

    Guan, Yingxin; Forghani, Kamran; Kim, Honghyuk; Babcock, Susan E.; Mawst, Luke J.; Kuech, Thomas F.

    2017-04-01

    The influence of the surface step termination on the metal-organic vapor phase epitaxy of GaAs1-yBiy was explored by examining the epitaxial layer growth rate, composition, and morphology characteristics on the offcut and mesa-patterned (001) GaAs substrates. Vicinal surfaces offcut to (111)B with a high density of As-terminated steps ('B-steps') increased the GaAs1-yBiy layer growth rate as well as possessed the fastest lateral growth rate on mesa-patterned substrates at a growth temperature of 420 °C, indicating that B-steps enhanced the Ga incorporation. With Bi accumulation on the surface, the Ga incorporation rate was reduced by the Bi preferential presence at B-steps blocking the Ga incorporation. Vicinal surfaces offcut to (111)A, which generated Ga-terminated steps ('A-steps') enhanced the Bi incorporation rate during growth at 380 °C. This work reveals that the surface step termination plays an important role in the growth of the metastable alloy. Appropriate choices of both the substrate surface-step structure and other growth parameters could lead to an enhanced Bi incorporation.

  20. Absorption edge determination of thick GaAs wafers using surface photovoltage spectroscopy

    NASA Astrophysics Data System (ADS)

    Sharma, T. K.; Porwal, S.; Kumar, R.; Kumar, Shailendra

    2002-04-01

    A procedure for choosing the appropriate chopping frequency (f) for the surface photovoltage spectroscopy (SPS) measurements in order to obtain the absorption related features is presented. We could obtain the absorption edge of thick n+ GaAs wafer (thickness ≈700 μm) by performing SPS measurements at f⩾1 kHz at room temperature (300 K). The similar information for semi-insulating (SI) GaAs could not be obtained due to the carrier trapping at deep levels or surface states at 300 K. However, we could obtain the absorption edge of SI-GaAs by performing SPS measurements at 395 K at f=3 kHz. Here, we demonstrate the capability of the SPS technique to measure large absorption coefficient (α) values for thick wafers by performing SPS measurements and normalizing this with the reported α value at one wavelength in the above band gap region. For comparison, we also perform quasisimultaneous SPS and transmission spectroscopy (TS) measurements. The SPS technique could provide α values up to 104cm-1 for 700-μm-thick GaAs wafers, whereas TS could only measure α values up to about 15 cm-1. An improved design of the sample holder for measuring the surface photovoltage in the chopped light geometry, which increases the signal strength by reducing the gap between the top electrode and the wafer in a controlled manner, is presented. This ensures that there is no sample damage or contamination.

  1. Grafting zwitterionic polymer onto cryogel surface enhances protein retention in steric exclusion chromatography on cryogel monolith.

    PubMed

    Tao, Shi-Peng; Zheng, Jie; Sun, Yan

    2015-04-10

    Cryogel monoliths with interconnected macropores (10-100μm) and hydrophilic surfaces can be employed as chromatography media for protein retention in steric exclusion chromatography (SXC). SXC is based on the principle that the exclusion of polyethylene glycol (PEG) on both a hydrophilic chromatography surface and a protein favors their association, leading to the protein retention on the chromatography surface. Elution of the retained protein can be achieved by reducing PEG concentration. In this work, the surface of polyacrylamide-based cryogel monolith was modified by grafting zwitterionic poly(carboxybetaine methacrylate) (pCBMA), leading the increase in the surface hydrophilicity. Observation by scanning electron microscopy revealed the presence of the grafted pCBMA chain clusters on the cryogel surface, but pCBMA grafting did not result in the changes of the physical properties of the monolith column, and the columns maintained good recyclability in SXC. The effect of the surface grafting on the SXC behavior of γ-globulin was investigated in a wide flow rate range (0.6-12cm/min). It was found that the dynamic retention capacity increased 1.4-1.8 times by the zwitterionic polymer grafting in the flow rate range of 1.5-12cm/min. The mechanism of enhanced protein retention on the zwitterionic polymer-grafted surface was proposed. The research proved that zwitterionic polymer modification was promising for the development of new materials for SXC applications.

  2. In situ Observation of Formation Process of Negative Electron Affinity Surface of GaAs by Surface Photo-Absorption

    NASA Astrophysics Data System (ADS)

    Hayase, Kazuya; Nishitani, Tomohiro; Suzuki, Katsunari; Imai, Hironobu; Hasegawa, Jun-ichi; Namba, Daiki; Meguro, Takashi

    2013-06-01

    We have used surface photo-absorption (SPA) to investigate the formation of negative electron affinity (NEA) surfaces on p-GaAs during the Yo-Yo method, under an alternating supply of Cs and O2. The SPA spectra showed that the surface during the first Cs step was different from those in the following Cs and O2 steps. This suggests that the surface structure did not change after the initial surface was formed, indicating that there could be two Cs adsorption sites on the GaAs surface, which is different from previously proposed models.

  3. Inhibition of Te surfactant effect on surface morphology of heavily Te-doped GaAs

    NASA Astrophysics Data System (ADS)

    Paquette, Bernard; Ilahi, Bouraoui; Aimez, Vincent; Arès, Richard

    2013-11-01

    The surface morphology and incorporation behavior of heavily Te-doped GaAs were studied for various growth parameters by chemical beam epitaxy (CBE). The Te precursor, DIPTe (diisopropyl telluride), acts as a volatile dopant in the growth temperature range of 475-595 °C. Electrical activation of Te is increased for lower growth temperatures. The Te surfactant effect was shown to lead to three-dimensional growth, which greatly affected the resulting surface morphology. We have shown that growth parameters can be tuned to reduce the Te surfactant effect through kinetic limitation, thus obtaining improved surface morphologies.

  4. Transient surface photoconductivity of GaAs emitter studied by terahertz pump-emission spectroscopy

    NASA Astrophysics Data System (ADS)

    Shi, Yulei; Zhou, Qing-li; Zhang, Cunlin

    2010-11-01

    The ultrafast carrier dynamics and surface photoconductivity of unbiased semi-insulating GaAs have been investigated in detail by using terahertz pump-emission technique. Through theoretical modeling based on Hertz vector potential, it is found that transient photoconductivity plays a very important role in the temporal waveform of terahertz radiation pulse. Anomalous enhancement in both terahertz radiation and transient photoconductivity is observed subsequent to the excitation of pump pulse, and our modeling gives successful analyses for the dynamics of photogenerated carriers in the GaAs. We attribute these phenomena to carrier capture in the EL2 centers. Moreover, the pump power- and temperaturedependent measurements are also performed to verify this model.

  5. Effects of ion bombardment on bulk GaAs photocathodes with different surface-cleavage planes

    NASA Astrophysics Data System (ADS)

    Liu, Wei; Zhang, Shukui; Stutzman, Marcy; Poelker, Matt

    2016-10-01

    Bulk GaAs samples with different surface cleave planes were implanted with 100 and 10 000 V hydrogen ions inside an ultrahigh vacuum test apparatus to simulate ion back-bombardment of the photocathode inside a DC high voltage photogun. The photocathode yield, or quantum efficiency, could easily be recovered following implantation with 100 V hydrogen ions but not for 10 000 V ions. Moreover, the implantation damage with 10 000 V hydrogen ions was more pronounced for GaAs photocathode samples with (100) and (111A) cleave planes, compared to the photocathode with (110) cleave plane. This result is consistent with enhanced ion channeling for the (110) cleave plane compared to the other cleave planes, with ions penetrating deeper into the photocathode material beyond the absorption depth of the laser light and beyond the region of the photocathode where the photoemitted electrons originate.

  6. Effects of ion bombardment on bulk GaAs photocathodes with different surface-cleavage planes

    DOE PAGES

    Liu, Wei; Zhang, Shukui; Stutzman, Marcy; ...

    2016-10-24

    Bulk GaAs samples with different surface cleave planes were implanted with 100 and 10 000 V hydrogen ions inside an ultrahigh vacuum test apparatus to simulate ion back-bombardment of the photocathode inside a DC high voltage photogun. The photocathode yield, or quantum efficiency, could easily be recovered following implantation with 100 V hydrogen ions but not for 10 000 V ions. Moreover, the implantation damage with 10 000 V hydrogen ions was more pronounced for GaAs photocathode samples with (100) and (111A) cleave planes, compared to the photocathode with (110) cleave plane. Lastly, this result is consistent with enhanced ionmore » channeling for the (110) cleave plane compared to the other cleave planes, with ions penetrating deeper into the photocathode material beyond the absorption depth of the laser light and beyond the region of the photocathode where the photoemitted electrons originate.« less

  7. GaP-interlayer formation on epitaxial GaAs(100) surfaces in MOVPE ambient

    NASA Astrophysics Data System (ADS)

    Döscher, Henning; Hens, Philip; Beyer, Andreas; Tapfer, Leander; Volz, Kerstin; Stolz, Wolfgang

    2017-04-01

    The challenge to embed a single monolayer of phosphorus during epitaxial gallium arsenide (GaAs) growth triggers numerous questions regarding practical preparation, effective analysis, and fundamental consideration of the resulting interlayers. Beyond better understanding of III-V heterointerface formation processes, precise interlayer incorporation may enable enhanced interface design, effective diffusion barriers, and advanced band structure engineering. We employ metalorganic vapor phase epitaxy (MOVPE) in various growth modes (continuous, with interruptions, pulsed, surface exchange) targeting the most abrupt incorporation of thinnest GaP films in the GaAs(100) matrix. The intensities of higher order interference fringes in high resolution X-ray diffraction (HR-XRD) serve as a measure of the effective GaPxAs1-x film thickness and P concentration, which is compared to compositional analysis based on scanning transmission electron microscopy (STEM). In situ reflection anisotropy spectroscopy (RAS) provided us with insights to the GaAs(100) surface configurations relevant during the P interlayer preparation.

  8. Novel anti-reflection technology for GaAs single-junction solar cells using surface patterning and Au nanoparticles.

    PubMed

    Kim, Youngjo; Lam, Nguyen Dinh; Kim, Kangho; Kim, Sangin; Rotermund, Fabian; Lim, Hanjo; Lee, Jaejin

    2012-07-01

    Single-junction GaAs solar cell structures were grown by low-pressure MOCVD on GaAs (100) substrates. Micro-rod arrays with diameters of 2 microm, 5 microm, and 10 microm were fabricated on the surfaces of the GaAs solar cells via photolithography and wet chemical etching. The patterned surfaces were coated with Au nanoparticles using an Au colloidal solution. Characteristics of the GaAs solar cells with and without the micro-rod arrays and Au nanoparticles were investigated. The short-circuit current density of the GaAs solar cell with 2 microm rod arrays and Au nanoparticles increased up to 34.9% compared to that of the reference cell without micro-rod arrays and Au nanoparticles. The conversion efficiency of the GaAs solar cell that was coated with Au nanoparticles on the patterned surface with micro-rod arrays can be improved from 14.1% to 19.9% under 1 sun AM 1.5G illumination. These results show that micro-rod arrays and Au nanoparticle coating can be applied together in surface patterning to achieve a novel cost-effective anti-reflection technology.

  9. NEA surface activation of GaAs photocathode with different gases

    NASA Astrophysics Data System (ADS)

    Guo, L.; Kuriki, M.; Iijima, H.; Uchida, K.

    2017-10-01

    The GaAs photo-cathode is a unique device which is able to generate highly polarized electron beam up to 90% and an extremely small emittance beam. The photo-electron emission is possible with IR (Infrared Red) and visible light and the quantum efficiency can be more than 20%. These unique features depend on the negative electron affinity (NEA) surface made by adsorption of Cs and O2/NF3, but this surface is easily damaged by residual gas adsorption, ion back-bombardment, etc. The exact structure of the NEA surface is not known, even there are several hypotheses. In this study, we performed the NEA activation on a cleaned GaAs surface with CO2, CO, N2, and O2 gases and compared the results to improve our understanding on the NEA surface. We found that the NEA activation with CO2 is similar to that with O2, but the maximum QE value is significantly lower than that with O2. We also found that N2 and CO gases did not contribute to NEA activation at all. By analyzing CO2 activation, we found that atomic oxygen activates the NEA surface and CO degrades the NEA surface simultaneously. We found that the NEA activation ability of atomic oxygen is almost a half of that of O2 molecule.

  10. GaAs Surface Passivation for Device Applications.

    DTIC Science & Technology

    1981-12-01

    Physics Letters 38, 167 (1981). 10. A Ga203 surface layer with the low band bending may also be pro- duced by heating the initial etched surface to... Physics of MOS Insulators, Edited by G. Lucovsky, S.T. Pantelides, and F.L. Galeener -Pergamon Press, New York, 1980) p. 202. 7. E.A. Kraut, R.W...E. Luscher , W. S. Knodle, and Y. Chai, Electronics 53, (19), 160 (1980). 2. J. P. Hobson and E. V. Kornelsen, J. Vac. Sci. Technol. 16, 701(1979). 3

  11. Regeneration of a thiolated and antibody functionalized GaAs (001) surface using wet chemical processes.

    PubMed

    Lacour, Vivien; Elie-Caille, Céline; Leblois, Thérèse; Dubowski, Jan J

    2016-03-02

    Wet chemical processes were investigated to remove alkanethiol self-assembled monolayers (SAMs) and regenerate GaAs (001) samples studied in the context of the development of reusable devices for biosensing applications. The authors focused on 16-mercaptohexadecanoic acid (MHDA) SAMs that are commonly used to produce an interface between antibodies or others proteins and metallic or semiconductor substrates. As determined by Fourier transform infrared absorption spectroscopy, among the investigated solutions of HCl, H2O2, and NH4OH, the highest efficiency in removing alkanethiol SAM from GaAs was shown by NH4OH:H2O2 (3:1 volume ratio) diluted in H2O. The authors observed that this result was related to chemical etching of GaAs that even in a weak solution of NH4OH:H2O2:H2O (3:1:100) proceeded at a rate of 130 nm/min. The surface revealed by a 2-min etching under these conditions allowed depositing successfully a new MHDA SAM with comparable quality and density to the initial coating. This work provides an important view on the perspective of the development of a family of cost-effective GaAs-based biosensors designed for repetitive detection of a variety of biomolecules immobilized with dedicated antibody architectures.

  12. A new theoretical approach to adsorption desorption behavior of Ga on GaAs surfaces

    NASA Astrophysics Data System (ADS)

    Kangawa, Y.; Ito, T.; Taguchi, A.; Shiraishi, K.; Ohachi, T.

    2001-11-01

    We propose a new theoretical approach for studying adsorption-desorption behavior of atoms on semiconductor surfaces. The new theoretical approach based on the ab initio calculations incorporates the free energy of gas phase; therefore we can calculate how adsorption and desorption depends on growth temperature and beam equivalent pressure (BEP). The versatility of the new theoretical approach was confirmed by the calculation of Ga adsorption-desorption transition temperatures and transition BEPs on the GaAs (0 0 1) -(4×2) β2 Ga-rich surface. This new approach is feasible to predict how adsorption and desorption depend on the growth conditions.

  13. Substitutional Co dopant on the GaAs(110) surface: A first principles study

    NASA Astrophysics Data System (ADS)

    Fang, Zhou; Yi, Zhijun

    2016-12-01

    Using the first principles ground state method, the electronic properties of single Co dopant replacing one Ga atom on the GaAs(110) surface are studied. Our calculated local density of states (LDOS) at Co site presents several distinct peaks above the valence band maximum (VBM), and this agrees with recent experiments. Moreover, the calculated STM images at bias voltages of 2 eV and -2 eV also agree with experiments. We discussed the origin of Co impurity induced distinct peaks, which can be characterized with the hybridization between Co d orbitals and p-like orbitals of surface As and Ga atoms.

  14. In-situ ellipsometric studies of optical and surface properties of GaAs(100) at elevated temperatures

    NASA Technical Reports Server (NTRS)

    Yao, Huade; Snyder, Paul G.

    1991-01-01

    A rotating-polarizer ellipsometer was attached to an ultrahigh vacuum (UHV) chamber. A GaAs(100) sample was introduced into the UHV chamber and heated at anumber of fixed elevated temperatures, without arsenic overpressure. In-situ spectroscopic ellipsometric (SE) measurements were taken, through a pair of low-strain quartz windows, to monitor the surface changes and measure the pseudodielectric functions at elevated temperatures. Real-time data from GaAs surface covered with native oxide showed clearly the evolution of oxide desorption at approximately 580 C. In addition, surface degradation was found before and after the oxide desorption. An oxide free and smooth GaAs surface was obtained by depositing an arsenic protective coating onto a molecular beam epitaxy grown GaAs surface. The arsenic coating was evaporated immediately prior to SE measurements. A comparison showed that our room temperature data from this GaAs surface, measured in the UHV, are in good agreement with those in the literature obtained by wet-chemical etching. The surface also remained clean and smooth at higher temperatures, so that reliable temperature-dependent dielectric functions were obtained.

  15. In-situ ellipsometric studies of optical and surface properties of GaAs(100) at elevated temperatures

    NASA Technical Reports Server (NTRS)

    Yao, Huade; Snyder, Paul G.

    1991-01-01

    A rotating-polarizer ellipsometer was attached to an ultrahigh vacuum (UHV) chamber. A GaAs(100) sample was introduced into the UHV chamber and heated at anumber of fixed elevated temperatures, without arsenic overpressure. In-situ spectroscopic ellipsometric (SE) measurements were taken, through a pair of low-strain quartz windows, to monitor the surface changes and measure the pseudodielectric functions at elevated temperatures. Real-time data from GaAs surface covered with native oxide showed clearly the evolution of oxide desorption at approximately 580 C. In addition, surface degradation was found before and after the oxide desorption. An oxide free and smooth GaAs surface was obtained by depositing an arsenic protective coating onto a molecular beam epitaxy grown GaAs surface. The arsenic coating was evaporated immediately prior to SE measurements. A comparison showed that our room temperature data from this GaAs surface, measured in the UHV, are in good agreement with those in the literature obtained by wet-chemical etching. The surface also remained clean and smooth at higher temperatures, so that reliable temperature-dependent dielectric functions were obtained.

  16. GaAs Surface Passivation for Device Applications.

    DTIC Science & Technology

    1982-07-01

    understanding Ser IV.. 20. lQ’.1 C R Brundk. Surf Soi 48. 99 tiQ󈨏,the formation of Schottky-barrier contacts. Two of the im- ’N Winograd. W E...Walkep, md Orat hide w bm"a MeeWt6 (3) For the Gatos + AsgO8 (high band bending) surface. CuJ deposition of either reactive or non-reactive metal did

  17. Optical and Surface Characteristics of Mg-Doped GaAs Nanocrystalline Thin Film Deposited by Thermionic Vacuum Arc Technique

    NASA Astrophysics Data System (ADS)

    Pat, Suat; Özen, Soner; Şenay, Volkan; Korkmaz, Şadan

    2017-01-01

    Magnesium (Mg) is the most promising p-type dopant for gallium arsenide (GaAs) semiconductor technology. Mg-doped GaAs nanocrystalline thin film has been deposited at room temperature by the thermionic vacuum arc technique, a rapid deposition method for production of doped GaAs material. The microstructure and surface and optical properties of the deposited sample were investigated by x-ray diffraction analysis, scanning electron microscopy, energy-dispersive x-ray spectroscopy, atomic force microscopy, ultraviolet-visible spectrophotometry, and interferometry. The crystalline direction of the deposited sample was determined to be (220) plane and (331) plane at 44.53° and 72.30°, respectively. The Mg-doped GaAs nanocrystalline sample showed high transmittance.

  18. Surface sum frequency generation spectroscopy on non-centrosymmetric crystal GaAs (001)

    NASA Astrophysics Data System (ADS)

    Zhang, Zhenyu; Kim, Jisun; Khoury, Rami; Saghayezhian, Mohammad; Haber, Louis H.; Plummer, E. W.

    2017-10-01

    Femtosecond broadband sum frequency generation (SFG) spectroscopy is applied to surface studies of the archetypical non-centrosymmetric semiconductor GaAs (001). Azimuthal angular dependence studies in reflection geometry under eight possible polarization configurations reveal strong surface-bulk interference owing to heterodyne amplification. The crystal symmetry and the surface quadrupole contributions need to be considered to properly interpret the resulting nonlinear spectroscopic signals. In addition, over bandgap excitation by one of the incident beams brings the semiconductor surface to a transient excited state, enabling enhanced sensitivity of broadband SFG to probe the surface electronic properties of non-centrosymmetric semiconductors. These findings suggest that this technique can be generally applied to surface studies of other non-centrosymmetric crystals.

  19. Monolithic integration of waveguide structures with surface-micromachined polysilicon actuators

    SciTech Connect

    Smith, J.H.; Carson, R.F.; Sullivan, C.T.; McClellan, G.

    1996-03-01

    The integration of optical components with polysilicon surface micromechanical actuation mechanisms show significant promise for signal switching, fiber alignment, and optical sensing applications. Monolithically integrating the manufacturing process for waveguide structures with the processing of polysilicon actuators allows actuated waveguides to take advantage of the economy of silicon manufacturing. The optical and stress properties of the oxides and nitrides considered for the waveguide design along with design, fabrication, and testing details for the polysilicon actuators are presented.

  20. Direct investigation of (sub-) surface preparation artifacts in GaAs based materials by FIB sectioning.

    PubMed

    Belz, Jürgen; Beyer, Andreas; Torunski, Torsten; Stolz, Wolfgang; Volz, Kerstin

    2016-04-01

    The introduction of preparation artifacts is almost inevitable when producing samples for (scanning) transmission electron microscopy ((S)TEM). These artifacts can be divided in extrinsic artifacts like damage processes and intrinsic artifacts caused by the deviations from the volume strain state in thin elastically strained material systems. The reduction and estimation of those effects is of great importance for the quantitative analysis of (S)TEM images. Thus, optimized ion beam preparation conditions are investigated for high quality samples. Therefore, the surface topology is investigated directly with atomic force microscopy (AFM) on the actual TEM samples. Additionally, the sectioning of those samples by a focused ion beam (FIB) is used to investigate the damage depth profile directly in the TEM. The AFM measurements show good quantitative agreement of sample height modulation due to strain relaxation to finite elements simulations. Strong indications of (sub-) surface damage by ion beams are observed. Their influence on high angle annular dark field (HAADF) imaging is estimated with focus on thickness determination by absolute intensity methods. Data consolidation of AFM and TEM measurements reveals a 3.5nm surface amorphization, negligible surface roughness on the scale of angstroms and a sub-surface damage profile in the range of up to 8.0nm in crystalline gallium arsenide (GaAs) and GaAs-based ternary alloys. A correction scheme for thickness evaluation of absolute HAADF intensities is proposed and applied for GaAs based materials.

  1. Ultrafast magneto-photocurrents in GaAs: Separation of surface and bulk contributions

    SciTech Connect

    Schmidt, Christian B. Priyadarshi, Shekhar; Bieler, Mark; Tarasenko, Sergey A.

    2015-04-06

    We induce ultrafast magneto-photocurrents in a GaAs crystal employing interband excitation with femtosecond laser pulses at room temperature and non-invasively separate surface and bulk contributions to the overall current response. The separation between the different symmetry contributions is achieved by measuring the simultaneously emitted terahertz radiation for different sample orientations. Excitation intensity and photon energy dependences of the magneto-photocurrents for linearly and circularly polarized excitations reveal an involvement of different microscopic origins, one of which is the inverse spin Hall effect. Our experiments are important for a better understanding of the complex momentum-space carrier dynamics in magnetic fields.

  2. Surface acoustic wave/silicon monolithic sensor/processor

    NASA Technical Reports Server (NTRS)

    Kowel, S. T.; Kornreich, P. G.; Nouhi, A.; Kilmer, R.; Fathimulla, M. A.; Mehter, E.

    1983-01-01

    A new technique for sputter deposition of piezoelectric zinc oxide (ZnO) is described. An argon-ion milling system was converted to sputter zinc oxide films in an oxygen atmosphere using a pure zinc oxide target. Piezoelectric films were grown on silicon dioxide and silicon dioxide overlayed with gold. The sputtered films were evaluated using surface acoustic wave measurements, X-ray diffraction, scanning electron microscopy, Auger electron spectroscopy, and resistivity measurements. The effect of the sputtering conditions on the film quality and the result of post-deposition annealing are discussed. The application of these films to the generation of surface acoustic waves is also discussed.

  3. Wrinkled Graphene Monoliths as Superabsorbing Building Blocks for Superhydrophobic and Superhydrophilic Surfaces.

    PubMed

    Lv, Li-Bing; Cui, Tian-Lu; Zhang, Bing; Wang, Hong-Hui; Li, Xin-Hao; Chen, Jie-Sheng

    2015-12-07

    Superhydrophobic and superhydrophilic surfaces are of great interest because of a large range of applications, for example, as antifogging and self-cleaning coatings, as antibiofouling paints for boats, in metal refining, and for water-oil separation. An aqueous ink based on three-dimensional graphene monoliths (Gr) can be used for constructing both superhydrophobic and superhydrophilic surfaces on arbitrary substrates with different surficial structures from the meso- to the macroscale. The surface wettability of a Gr-coated surface mainly depends on which additional layers (air for a superhydrophobic surface and water for a superhydrophilic surface) are adsorbed on the surface of the graphene sheets. Switching a Gr-coated surface between being superhydrophobic and superhydrophilic can thus be easily achieved by drying and prewetting with ethanol. The Gr-based superhydrophobic membranes or films should have great potential as efficient separators for fast and gravity-driven oil-water separation.

  4. Surface depletion and electrical transport model of AlInP-passivated GaAs nanowires

    NASA Astrophysics Data System (ADS)

    Chia, A. C. E.; Tirado, M.; Thouin, F.; Leonelli, R.; Comedi, D.; LaPierre, R. R.

    2013-10-01

    Fabrication, current-voltage characterization and analytical modeling of an AlInP-passivated GaAs nanowire (NW) ensemble device are presented. During fabrication, sonication was used as a novel and crucial step to ensure effective contacting of the NWs. Current-voltage characteristics of the passivated NW devices were fitted using an analytical surface depletion and transport model which improves upon established models by implementing a non-uniform density of GaAs surface states and including a NW diameter distribution. Scanning electron microscopy, capacitance-voltage characterization and secondary ion mass spectrometry were used to fix key parameters in the model. A 55% decrease in surface state density was achieved upon passivation, corresponding to an impressive four order of magnitude increase in the effective carrier concentration of the NWs. Moreover, the thickest NWs in the ensemble were found to dictate the device characteristics, which is a behavior that should be common to all ensemble NW devices with a distribution in radius. As final confirmation of effective passivation, time-resolved photoluminescence measurements showed a 25× improvement in carrier lifetime upon passivation. The fabrication and passivation methods can be easily implemented into future optoelectronic applications.

  5. Electronic structure around an As antisite near the (110) surface of GaAs

    NASA Astrophysics Data System (ADS)

    Iguchi, Yusuke; Fujiwara, Takeo; Hida, Akira; Maeda, Koji

    2005-03-01

    The electronic structure around a single As antisite in GaAs is investigated in bulk and near the surface both in the stable and the metastable atomic configurations. The most characteristic electronic structures of As antisite is the existence of the localized p orbitals extending from the As antisite. The major component of the highest occupied state on As antisite in the stable configuration is s -orbital connecting with neighboring As atoms with nodes whereas that in the metastable configuration is p -orbital connecting without nodes. Localized p orbitals on the surrounding As atoms around the As antisite exist in every configuration of As antisite. Such features are retained except the case of the As antisite located just in the surface layer in which the midgap level is smeared into the conduction band and no localized states exist near the top of the valence band. Scanning tunneling microscopic images of defects observed in low-temperature grown GaAs, possibly assigned as As antisite, the origin of the metastability, and the peculiarity of the defects in the surface layer are discussed.

  6. Effect of diameter and surface roughness on ultrasonic properties of GaAs nanowires

    NASA Astrophysics Data System (ADS)

    Dhawan, Punit Kumar; Wan, Meher; Verma, S. K.; Pandey, D. K.; Yadav, R. R.

    2015-02-01

    Second and third order elastic constants of GaAs Nanowires (NWs) are calculated using the many-body interaction potential model. The velocities of ultrasonic waves at different orientations of propagation with unique axis are evaluated using the second order elastic constants. The ultrasonic attenuation and thermal relaxation times of the single crystalline GaAs-NW are determined as a function of diameter and surface roughness by means of Mason theoretical approach using the thermal conductivity and higher order elastic constants. The diameter variation of ultrasonic attenuation and thermal relaxation exhibit second order polynomial function of diameter. It is also found that ultrasonic attenuation and thermal relaxation follow the exponential decay with the surface roughness for GaAs-NW due to reduction in thermal conductivity caused by dominance of surface asperities. Finally, the correlations among ultrasonic parameters, thermal conductivity, surface roughness, and diameter for GaAs-NWs are established leading towards potential applications.

  7. Monolithic Thin Film SAW (Surface Acoustic Wave) Structures.

    DTIC Science & Technology

    1984-09-01

    storage " regions. The device is simple to fabricate, requiring neither pn or Schottky diode * arrays for -ignal storage. The memory function is...and is close to the value for LiNbOj Several convolvers and diode storage correlators which exploit the banidwidth advantage of the Sezawa mode have...fLUILcti of the properties~ of the interface. Surface state storage was subscquenitly replaced by more easily controlled and repeatable diode storage

  8. Surface studies of the thermal decomposition of triethylgallium on GaAs (100)

    NASA Astrophysics Data System (ADS)

    Murrell, A. J.; Wee, A. T. S.; Fairbrother, D. H.; Singh, N. K.; Foord, J. S.; Davies, G. J.; Andrews, D. A.

    1990-10-01

    The adsorption and surface decomposition of triethylgallium (TEG) on GaAs (100) has been studied using XPS and thermal desorption techniques. TEG is found to adsorb in a molecular form on the Ga rich (4×1) surface below 150 K. As the surface temperature is raised, this molecular state dissociates to form Ga and adsorbed ethyl species. The overall cracking reaction occurs in competition with the desorption of TEG and diethylgallium (DEG). Under the conditions of our experiments the adsorbed ethyl species formed above are found to dissociate above 600 K to form mainly gas phase ethene and hydrogen with traces of ethane, resulting in the formation of a pure Ga layer within the sensitivity limits imposed by XPS.

  9. Passivation effects of polyphenylene sulphide on the surface of GaAs

    NASA Astrophysics Data System (ADS)

    Bhide, R. S.; Bhoraskar, S. V.; Rao, V. J.

    1992-08-01

    Vacuum-evaporated thin films of polyphenylene sulphide have been used as an insulating overlayer on n-GaAs(110). Sulphur present in the polymer is seen to passivate the dangling bonds of GaAs. The interface of n-GaAs/polyphenylene sulphide was studied using grazing-angle x-ray diffraction at various angles for different annealing temperatures. The electronic properties of the interface are studied using electron-beam-induced-current measurements for determining the minority-carrier diffusion length and surface recombination velocity. The x-ray-diffraction analysis indicates the formation of arsenic sulphide at the interface and is expected to reduce the dangling bond density. The treated surface shows an increase in diffusion length and reduction in the surface recombination velocity. The polymer-semiconductor interface shows stability against annealing up to a temperature of 300 °C.

  10. Structure of GaAs(001) surfaces: The role of electrostatic interactions

    SciTech Connect

    Northrup, J.E. ); Froyen, S. )

    1994-07-15

    We report first-principles total-energy calculations for the GaAs(001) surface. Our results indicate that the 2[times]4 reconstruction corresponds to the [beta]2(2[times]4) structure, which exhibits two As dimers in the top layer and a third As dimer in the third layer. This structure has a lower surface energy than the [beta](2[times]4) model, which has three As dimers in the top layer. We also find that a model recently proposed by Skala [ital et] [ital al]. [Phys. Rev. B [bold 48], 9138 (1993)] for the structure of the Ga-rich 4[times]2 phase is energetically unfavorable. From our results we conclude that electrostatic interactions between the charged building blocks of polar semiconductor surfaces play an important role in determining the equilibrium structure. We introduce a simple model for estimating these interactions.

  11. Defect metastability in surfaces: A study of EL2 defect in GaAs(110)

    SciTech Connect

    Zhang, S.B.

    1999-08-01

    Although it has been widely accepted that EL2 in GaAs is an As antisite, the identity of the metastable state of EL2thinsp(=EL2{sup {asterisk}}) has not been confirmed by experiment. Here it is suggested that cross-sectional scanning tunneling microscopy may be used to identify EL2{sup {asterisk}}. My suggestion is based on a comprehensive first-principles total energy study of surface defect metastability. It reveals rich structures of the EL2{sup {asterisk}} near the surface. The energy difference between EL2{sup {asterisk}} and EL2 can be reduced to only a tenth of that bulk due to interaction with relaxed surface atoms. {copyright} {ital 1999} {ital The American Physical Society}

  12. Modification of GaAs surface by low-current Townsend discharge

    NASA Astrophysics Data System (ADS)

    Gurevich, E. L.; Kittel, S.; Hergenröder, R.; Astrov, Yu A.; Portsel, L. M.; Lodygin, A. N.; Tolmachev, V. A.; Ankudinov, A. V.

    2010-07-01

    The influence of stationary spatially homogeneous Townsend discharge on the (1 0 0) surface of semi-insulating GaAs samples is studied. Samples exposed to both electrons and ions in a nitrogen discharge at a current density j = 60 µA cm-2 are studied by means of x-ray photoelectron spectroscopy, ellipsometry and atomic force microscopy. It is shown that an exposure to low-energy ions (<1 eV) changes the crystal structure of the semiconductor for a depth of up to 10-20 nm, although the stoichiometric composition does not change. The exposure to low-energy electrons (<10 eV) forms an oxide layer, which is 5-10 nm thick. Atomic force microscopy demonstrates that the change in the surface potential of the samples may exceed 100 mV, for both discharge polarities, while the surface roughness does not increase.

  13. Photoelectron and Auger electron diffraction studies of a sulfur-terminated GaAs(001)-(2×6) surface

    NASA Astrophysics Data System (ADS)

    Shimoda, M.; Tsukamoto, S.; Koguchi, N.

    1998-01-01

    Core-level X-ray photoelectron diffraction (XPD) and Auger electron diffraction (AED) have been applied to investigate the sulfur-terminated GaAs(001)-(2×6) surface. No forward scattering peaks were found in the XPD pattern of S 2s emission, indicating that adsorbed S atoms form a single layer on the GaAs substrate. In accordance with the zincblende structure of GaAs, the AED patterns of Ga L 3M 45M 45 and As L 3M 45M 45 emission almost coincide with each other, if one of the emissions is rotated by 90° around the [001] direction. This fact suggests that the diffraction patterns mainly reflect the structure of the bulk GaAs crystal. In order to investigate the surface structure, AED patterns in large polar angles were analyzed with single scattering cluster (SSC) calculations. The best result was obtained with a model cluster where the S-S bond length was set at 0.28 nm, 30% shorter than the corresponding length of the ideal (1×1) structure, and the adsorption height was set at 0.12-0.13 nm, 10% shorter than the ideal interlayer distance of GaAs(001) planes. These values are in good agreement with the results of STM measurements. A modulation of the inter-dimer distance was also found, suggesting the existence of missing dimers.

  14. Crystal bending by surface damaging in mosaic GaAs crystals for the LAUE project

    NASA Astrophysics Data System (ADS)

    Buffagni, E.; Bonnini, E.; Zappettini, A.; Guadalupi, G. M.; Rossi, F.; Ferrari, C.

    2013-09-01

    Curved crystals used as optical elements of a Laue lens for hard x- and gamma-ray astronomy have a larger diffraction efficiency with respect to perfect flat crystals. In this work we show how to achieve the bending of the crystals by a controlled surface damaging which introduces defects in a superficial layer of few tens micrometers in thickness undergoing a highly compressive strain. Several silicon, gallium arsenide and germanium wafer crystals have been treated. The local and mean curvature radii of each sample have been determined by means of high resolution x-ray diffraction measurements in Bragg condition at low energy (8 keV). (100) oriented silicon and (111) oriented germanium samples showed spherical curvatures, whereas (100) oriented GaAs treated samples evidenced an elliptical curvature with major axes corresponding to the <011< crystallographic directions. Curvature radii between 3 and 70 m were easily obtained in wafers with thicknesses up to 2 mm. Several 3x1x0.2 cm3 GaAs crystals (100) oriented with a radius of curvature of 40 m were prepared for the Laue Lens. Using a x-ray tube set at a distance of 20 m from the crystal for the first time the focusing of the (022) diffracted beam at a distance of 20 m was observed.

  15. Laser and voltage manipulation of bistable Si dopants in the GaAs (110) surface

    NASA Astrophysics Data System (ADS)

    Smakman, E. P.; van Bree, J.; Koenraad, P. M.

    2013-02-01

    Bistable behavior of single Si dopants in the (110) surface layer of GaAs was studied with a scanning tunneling microscope (STM). The Si atom acts as either a positively charged substitutional donor or a negatively charged interstitial. Its configuration can switch under the influence of a local biased STM tip. To independently manipulate the charge state, the sample was illuminated by a laser during STM operation. The Si atom can be reversibly switched between its positive and negative charge states by turning the laser on and off, respectively. This process occurs mostly with the photon energy tuned above the band gap of GaAs, indicating that photogenerated electron-hole pairs play an important role in the process. The occupation of the donor and interstitial configurations depends on the carrier dynamics, i.e., the possibility of the electrons to escape or to be captured. If the tip-induced band bending is large enough, it is possible for electrons to tunnel into the conduction band and the donor configuration is observed. Another escape path is created when the sample is illuminated and photogenerated holes can recombine with the bound electrons of the dopant.

  16. Generation of ammonia plasma using a helical antenna and nitridation of GaAs surface

    NASA Astrophysics Data System (ADS)

    Yasui, Kanji; Arayama, Tatsuro; Okutani, Satoshi; Akahane, Tadashi

    2003-05-01

    Using the ammonia (NH 3) plasma generated by a helical antenna surrounded by two magnetic coils, the transition of the discharge mode from low-density plasma to high-density one was observed. At the transition, the emission intensities from the H atoms and NH radicals especially increased in the optical emission spectroscopy, while the intensities of the other emission lines also increased abruptly. The nitridation of gallium arsenide (GaAs) surface was performed using the high-density NH 3 plasma, and the properties of the nitrided surface layer were compared with those nitrided by high-density N 2 plasma using the same apparatus. From the spectroscopic ellipsometry measurements, the thickness of the nitrided layer was estimated to be 16-18 nm, while that by N 2 was 3-4 nm. From the Ga 3d spectra, the contamination with oxygen in the nitridation layer by NH 3 plasma was less than that by N 2 plasma.

  17. Surface characterization of excimer laser induced deposition of W on GaAs from WF 6 and H 2

    NASA Astrophysics Data System (ADS)

    Tabbal, Malek; Izquierdo, Ricardo; Meunier, Michel; Pépin, Corinne; Yelon, Arthur

    1997-04-01

    Deposition of W thin films has been induced by a KrF excimer laser incident perpendicularly on a GaAs substrate placed in an ambient containing WF 6, H 2 and Ar. In-situ X-Ray Photoelectron Spectroscopy (XPS) shows evidence of a surface interaction between WF 6 and GaAs under laser irradiation. At 50 mJ/cm 2, fluorinated W species adsorbed on the GaAs substrate are partially dissociated by the laser beam, leading to a loss in stoichiometry and the formation of GaF 3 on the surface. The generation of stable, non-volatile, GaF 3 has been identified as a possible obstacle to the nucleation of metallic tungsten films on GaAs in CVD processes using WF 6. At 67 mJ/cm 2, the gas-substrate interaction is further enhanced, but the dissociation of WF 6 into metallic W is achieved. However, at such laser energy densities, the substrate appears to be damaged. By using H 2 as a reducing gas for WF 6, 0.2 μm thick W deposits were obtained but the process was difficult to reproduce. Two competing phenomena, the fluorination of the GaAs surface and the nucleation of the metallic W films taking place simultaneously explain the difficulty in controlling the process. The Auger profiles show limited, but noticeable, As incorporation in the films resulting from the interaction between WF 6 and GaAs under laser irradiation.

  18. Surface-morphology evolution during growth-interrupt in situ annealing on GaAs(110) epitaxial layers

    NASA Astrophysics Data System (ADS)

    Yoshita, Masahiro; Akiyama, Hidefumi; Pfeiffer, Loren N.; West, Ken W.

    2007-05-01

    Temperature and surface-coverage dependence of the evolution of surface morphology during growth-interrupt in situ annealing on GaAs epitaxial layers grown on the singular (110) cleaved edges by the cleaved-edge overgrowth method with molecular-beam epitaxy has been studied by means of atomic force microscopy. Annealing at substrate temperatures below 630 °C produced atomically flat surfaces with characteristic islands or pits, depending on the surface coverage. The atomic flatness of the surfaces is enhanced with increasing annealing temperature owing to the enhanced adatom migration. At a higher annealing temperature of about 650 °C, however, 2-monolayer-deep triangular pits with well-defined step edges due to Ga-atom desorption from the crystal appeared in the atomically flat surface. The growth-interrupt annealing temperature optimal for the formation of atomically flat GaAs(110) surfaces is therefore about 630 °C.

  19. Growth of GaAs from a free surface melt under controlled arsenic pressure in a partially confined configuration

    NASA Technical Reports Server (NTRS)

    Gatos, H. C.; Lagowski, J.; Wu, Y.

    1988-01-01

    A partially confined configuration for the growth of GaAs from melt in space was developed, consisting of a triangular prism containing the seed crystal and source material in the form of a rod. It is suggested that the configuration overcomes two obstacles in the growth of GaAs in space: total confinement in a quartz crucible and lack of arsenic pressure control. Ground tests of the configuration show that it is capable of crystal growth in space and is useful for studying the growth of GaAs from a free-surface melt on earth. The resulting chemical composition, electrical property variations, and phenomenological models to account for the results are presented.

  20. Growth of GaAs from a free surface melt under controlled arsenic pressure in a partially confined configuration

    NASA Technical Reports Server (NTRS)

    Gatos, H. C.; Lagowski, J.; Wu, Y.

    1988-01-01

    A partially confined configuration for the growth of GaAs from melt in space was developed, consisting of a triangular prism containing the seed crystal and source material in the form of a rod. It is suggested that the configuration overcomes two obstacles in the growth of GaAs in space: total confinement in a quartz crucible and lack of arsenic pressure control. Ground tests of the configuration show that it is capable of crystal growth in space and is useful for studying the growth of GaAs from a free-surface melt on earth. The resulting chemical composition, electrical property variations, and phenomenological models to account for the results are presented.

  1. Step energy and step interactions on the reconstructed GaAs(001) surface

    NASA Astrophysics Data System (ADS)

    Magri, Rita; Gupta, Sanjeev K.; Rosini, Marcello

    2014-09-01

    Using ab initio total energy calculations we have studied the relation between the step atomic configuration and its properties (step energy, donor/acceptor behavior, and step interaction) on a β2(2×4) reconstructed GaAs (001) surface. The results have been tested against the widely used elastic dipole model for the step energy and step interaction considered valid for stress-free surfaces. We have found that acceptor-behaving steps have an attractive interaction and donor-behaving steps have a repulsive interaction in contrast with the elastic dipole model which predicts always a repulsive interaction between like-oriented steps. To account for the attractive interaction we consider the electrostatic dipole interaction having the L-2 scaling with the step distance L and therefore compatible with the standard elastic model. Using a model charge distribution with localized point charges at the step based on the electron counting model we show that the electrostatic step interaction can indeed be generally attractive and of the same order of magnitude of the negative elastic dipole interaction. Our results show however that the usually employed dipole model is unable to account for the repulsive/attractive step interaction between donorlike/acceptorlike steps. Therefore, the ab initio results suggest an important electronic contribution to the step interaction, at least at the short step distances accessible to the first-principles study. Our results explain qualitatively many experimental observations and provide an explanation to the step bunching phenomenon on GaAs(001) induced by doping or by critical growth conditions as due to the stabilization of attractively interacting step structures. These ideas would lead to the development of a bottom-up surface step engineering.

  2. In-situ NAP XPS studies of dissociative water adsorption on GaAs(100) surfaces

    NASA Astrophysics Data System (ADS)

    Ptasinska, Sylwia; Zhang, Xueqiang

    2014-03-01

    In current semiconductor-based technology it is important to design and fabricate new materials in order to achieve specific well-defined properties and functionalities. Before such systems can be applied they first need to be understood, refined and controlled. Therefore, a basic knowledge about molecule/semiconductor surface interfaces is essential. In the present work dissociative water adsorption on the GaAs(100) surface is monitored using X-ray Photoelectron Spectroscopy (XPS) performed in situ under near ambient conditions. Firstly, the crystal surface is exposed to water vapor pressures ranging from UHV to 0.5 kPa. At elevated pressures an increase of oxygenation and hydroxylation of Ga surface atoms has been observed in the Ga2p XPS spectra. Moreover, intense signals obtained from molecularly adsorbed water molecules or water molecules adsorbed via hydrogen bond to surface OH groups have been also observed in the O1s spectra. Finally, the crystal surface is annealed up to 700 K at water vapor pressure of 0.01 kPa, which leads to desorption of physisorbed water molecules and further increase of surface oxidation. The research described herein was supported by the Division of Chemical Sciences, Geosciences and Biosciences, Basic Energy Sciences, Office of Science, United States Department of Energy through grant number DE-FC02-04ER15533.

  3. Molded rigid polymer monoliths as separation media for capillary electrochromatography. 1. Fine control of porous properties and surface chemistry.

    PubMed

    Peters, E C; Petro, M; Svec, F; Fréchet, J M

    1998-06-01

    Monolithic columns for capillary electrochromatography have been prepared within the confines of untreated fused-silica capillaries in a single step by a simple copolymerization of mixtures of butyl methacrylate, ethylene dimethacrylate, and 2-acrylamido-2-methyl-1-propane-sulfonic acid (AMPS) in the presence of a porogenic solvent. The use of these novel macroporous monoliths eliminates the need for frits, the difficulties encountered with packed capillaries, and capillary surface functionalization. Since the porous properties of the monolithic materials can be easily tailored through changes in the composition of the ternary porogenic solvent, the effects of both pore size and the percentage of sulfonic acid monomer on the efficiency and the electroosmotic flow velocity of the capillary columns could be studied independently over a broad range. A simple increase in the content of charged functionalities within the monolith leads to an expected acceleration of the flow velocity. However, increasing the pore size leads to a substantial deterioration of the efficiency of the separation. In contrast, monoliths with increasing levels of AMPS in which the pore size remains fixed due to adjustments in the composition of the porogenic solvent show no deterioration in efficiency while maintaining the same increase in flow velocity, thus producing a significant reduction in separation time. Additionally, measurements on monoliths with constant levels of AMPS but different pore sizes suggest that flow velocity may be affected by the flow resistance within the capillary column.

  4. Role of deep level trapping on surface photovoltage of semi-insulating GaAs

    SciTech Connect

    Liu, Q.; Ruda, H.E.; Koutzarov, I.P.; Jedral, L.; Chen, G.; Prasad, M.

    1996-12-31

    Dual beam (bias and probe) transient Surface Photovoltage (SPV) measurements were made on undoped Semi-Insulating (SI) GaAs over an extended temperature range. Above 270 K, SPV recovery transients following a bias pulse were shown to reflect near surface conductivity changes; these are in turn controlled by surface/interface state thermal emission. Owing to the absence of a strong surface electric field in this material, the emitted carriers are not immediately removed from the near surface region. The recapturing of the emitted carriers is shown to be responsible for non-exponential conductivity and reciprocal-SPV transients. This behavior is considered to be characteristic of relaxation-type semiconductors with near-surface ungated structures. Below 150 K, the photoinduced transition of EL2 from its ground to metastable state El2* was shown to change the effective electron and hole mobilities and augment the SPV signals immediately following the bias pulse. Thermally induced EL2* recovery above 120 K decreases the SPV signal from its maximum. This decay transient was analyzed and the decay rate fitted to a single exponential. An activation energy of 0.32 eV and a pre-exponential constant of 1.9 {times} 10{sup 12} s{sup {minus}1} were obtained, and attributed to the thermal recovery rate for EL2*.

  5. Nano-pits on GaAs (1 0 0) surface: Preferential sputtering and diffusion

    NASA Astrophysics Data System (ADS)

    Kumar, Tanuj; Panchal, Vandana; Kumar, Ashish; Kanjilal, D.

    2016-07-01

    Self organized nano-structure array on the surfaces of semiconductors have potential applications in photonics, magnetic devices, photovoltaics, and surface-wetting tailoring etc. Therefore, the control over their dimensions is gaining scientific interest in last couple of decades. In this work, fabrication of pits of nano-dimensions is carried out on the GaAs (1 0 0) surface using 50 keV Ar+ at normal incidence. Variation in fluence from 3 × 1017 ions/cm2 to 5 × 1018 ions/cm2 does not make a remarkable variation in the dimension of pits such as size and depth, which is confirmed by atomic force microscopy (AFM) and scanning electron microscopy (SEM). However the simultaneous dots formation is observed along with the pits at higher fluences. Average size of pits is found to be of 22 nm with depth of 1-5 nm for the used fluences. The importance of preferential sputtering of 'As' as compared to 'Ga' is estimated using energy dispersive X-ray analysis (EDX). The observed alteration in near surface composition shows the Ga enrichment of surface, which is not being much affected by variation in fluence. The growth evolution of pits and dots for the used experimental conditions is explained on the basis of ion beam induced preferential sputtering and surface diffusion.

  6. Surface chemistry of new As precursors for MOVPE and MOMBE: phenylarsine and tertiarybutylarsine on GaAs(100)

    NASA Astrophysics Data System (ADS)

    Kaul, P.; Schütze, A.; Kohl, D.; Brauers, A.; Weyers, M.

    1992-10-01

    Surface reactions of PhAs and tBAs on unoxidized and thermally oxidized GaAs(100) were studied in an UHV chamber using a differentially pumped quadrupole mass spectrometer and a molecular beam nozzle. A special sample holder allowed periodic switching between an unoxidized and an oxidized surface to observe small differences in reactivity. The following assumptions are compatible with the experimental results: Adsorption of PhAs or tBAs on GaAs(100) followed by rupture of the As-H bonds is the first step. Most of the organometallic radicals desorb from the surface, a fraction decomposes further by rupture of the As-C bond. The organic radicals react with the surface hydrogen and desorb as benzene and butane or butene, respectively. Low values of the activation energies ( ≤ 0.4 eV) for the different reaction steps suggest a diffusion of PhAs or tBAs on the surface as the rate limiting step for the overall reaction. A comparison of oxidized and unoxidized surfaces exposed to a constant gas flux of PhAs or tBAs revealed a reduced reactivity on the oxidized surface. Thermodesorption experiments with oxidized GaAs(100) surfaces showed that the desorption temperature of GA 2O decreased from 862 K without tBAs to 835 K in a tBAs flux. During this annealing process a reaction between the surface oxide and organic radicals from the tBAs decomposition seems to form a highly stable contamination layer which was observed by X-ray photoelectron spectroscopy. This contamination of the surface can be avoided by annealing in UHV without any As-species present and monitoring the Ga 2O flux from the surface with a mass spectrometer because non-stoichiometric evaporation of GaAs occurs only after desorption of the oxide.

  7. Surface patterning of GaAs under irradiation with very heavy polyatomic Au ions

    NASA Astrophysics Data System (ADS)

    Bischoff, L.; Böttger, R.; Heinig, K.-H.; Facsko, S.; Pilz, W.

    2014-08-01

    Self-organization of surface patterns on GaAs under irradiation with heavy polyatomic Au ions has been observed. The patterns depend on the ion mass, and the substrate temperature as well as the incidence angle of the ions. At room temperature, under normal incidence the surface remains flat, whereas above 200 °C nanodroplets of Ga appear after irradiation with monatomic, biatomic as well as triatomic Au ions of kinetic energies in the range of 10-30 keV per atom. In the intermediate temperature range of 100-200 °C meander- and dot-like patterns form, which are not related to Ga excess. Under oblique ion incidence up to 45° from the surface normal, at room temperature the surface remains flat for mon- and polyatomic Au ions. For bi- and triatomic ions in the range of 60° ≤ α ≤ 70° ripple patterns have been found, which become shingle-like for α ≥ 80°, whereas the surface remains flat for monatomic ions.

  8. Tip sample distance dependency of non-contact atomic force microscopy images on a GaAs(110) surface

    NASA Astrophysics Data System (ADS)

    Uehara, Nobutomo; Hosoi, Hirotaka; Sueoka, Kazuhisa; Mukasa, Koichi

    2004-02-01

    Tip-sample interactions are at the origin of atomic resolution in non-contact atomic force microscopy (NC-AFM) but also make it difficult to understand the meaning of atomic features observed as NC-AFM images. (110) surfaces of III-V semiconductors such as GaAs or InP have relaxed (1 × 1) surfaces with both anions and cations of different dangling bond states. Since these atoms are located at the surface where an atom attached to the tip apex can reach to interact with them and show significant relaxation via tip-sample interaction, NC-AFM images of the surface are expected to strongly depend upon the atomic species or the electronic state of the topmost atom at the tip apex. We have taken a number of NC-AFM images of GaAs(110) surfaces with a Si tip by means of room-temperature ultra-high vacuum NC-AFM and categorized them into two types of image which have different tip-sample distance dependencies. In comparison with a theoretical prediction of tip-surface interaction on the GaAs(110) surface, we have found that one of these images is due to a Si atom attached to the apex which reveals the tip-sample interaction with As and Ga surface atoms as individual peaks in the NC-AFM image.

  9. Nitride chemical passivation of a GaAs (100) Surface: Effect on the electrical characteristics of Au/GaAs surface-barrier structures

    SciTech Connect

    Berkovits, V. L. L'vova, T. V.; Ulin, V. P.

    2011-12-15

    The effect of chemical nitridation of GaAs substrates in a hydrazine-sulfide solution on the electrical characteristics of Au/GaAs Schottky structures has been studied. In nitridation of this kind, a solid passivating gallium nitride film with a monolayer thickness is formed on the surface of GaAs, providing almost direct contact between the semiconductor and the metal deposited on its surface. Au/GaAs structures fabricated on nitride substrates have ideality factors close to unity and are characterized by a narrow scatter of potential barrier heights. Prolonged heating of these structures at 350 Degree-Sign C does not change these parameters. The data obtained show that the nitride monolayer formed on the GaAs surface upon treatment in hydrazidesulfide solutions effectively hinders atomic migration across the metal-semiconductor phase boundary.

  10. 30 GHz monolithic balanced mixers using an ion-implanted FET-compatible 3-inch GaAs wafer process technology

    NASA Technical Reports Server (NTRS)

    Bauhahn, P.; Contolatis, A.; Sokolov, V.; Chao, C.

    1986-01-01

    An all ion-implanted Schottky barrier mixer diode which has a cutoff frequency greater than 1000 GHz has been developed. This new device is planar and FET-compatible and employs a projection lithography 3-inch wafer process. A Ka-band monolithic balanced mixer based on this device has been designed, fabricated and tested. A conversion loss of 8 dB has been measured with a LO drive of 10 dBm at 30 GHz.

  11. Piezoelectric surface acoustical phonon amplification in graphene on a GaAs substrate

    SciTech Connect

    Nunes, O. A. C.

    2014-06-21

    We study the interaction of Dirac Fermions in monolayer graphene on a GaAs substrate in an applied electric field by the combined action of the extrinsic potential of piezoelectric surface acoustical phonons of GaAs (piezoelectric acoustical (PA)) and of the intrinsic deformation potential of acoustical phonons in graphene (deformation acoustical (DA)). We find that provided the dc field exceeds a threshold value, emission of piezoelectric (PA) and deformation (DA) acoustical phonons can be obtained in a wide frequency range up to terahertz at low and high temperatures. We found that the phonon amplification rate R{sup PA,DA} scales with T{sub BG}{sup S−1} (S=PA,DA), T{sub BG}{sup S} being the Block−Gru{sup ¨}neisen temperature. In the high-T Block−Gru{sup ¨}neisen regime, extrinsic PA phonon scattering is suppressed by intrinsic DA phonon scattering, where the ratio R{sup PA}/R{sup DA} scales with ≈1/√(n), n being the carrier concentration. We found that only for carrier concentration n≤10{sup 10}cm{sup −2}, R{sup PA}/R{sup DA}>1. In the low-T Block−Gru{sup ¨}neisen regime, and for n=10{sup 10}cm{sup −2}, the ratio R{sup PA}/R{sup DA} scales with T{sub BG}{sup DA}/T{sub BG}{sup PA}≈7.5 and R{sup PA}/R{sup DA}>1. In this regime, PA phonon dominates the electron scattering and R{sup PA}/R{sup DA}<1 otherwise. This study is relevant to the exploration of the acoustic properties of graphene and to the application of graphene as an acoustical phonon amplifier and a frequency-tunable acoustical phonon device.

  12. Energetic, electronic, and magnetic properties of Mn pairs on reconstructed (001) GaAs surfaces

    NASA Astrophysics Data System (ADS)

    Birowska, Magdalena; Śliwa, Cezary; Majewski, Jacek A.

    2017-03-01

    We study energetic, magnetic, and electronic properties of diluted substitutional Mn pairs on reconstructed (001 ) GaAs surfaces. The studies are based on first-principles calculations in the framework of density functional theory. We demonstrate that the stability of the systems strongly depends on the position, orientation, and the distance between the Mn atoms constituting the pair. Independently of the considered surface reconstruction pattern, the Mn pairs with Mn atoms being the nearest neighbors (NN) on a cationic sublattice turn out to be energetically more favorable than the pairs with the larger distance between the Mn atoms. However, the preferential buildup orientation of the Mn-NN pair depends on the surface reconstruction and is parallel to either the [110 ] or the [1 1 ¯0 ] crystallographic direction. We reveal also the mechanisms of the magnetic ordering of Mn-NN pairs. The Mn-NN pairs along the [110 ] crystallographic direction exhibit always ferromagnetic alignment of Mn spins, whereas the spins in the Mn-NN pairs along the [1 1 ¯0 ] direction are mostly antiferromagnetically aligned. In the electronic structure of the systems containing Mn pairs with ferromagnetically aligned spins, we observe the valence band hole states in the neighborhood of Fermi energy. This indicates that the surface ferromagnetism in this prototype of dilute magnetic semiconductors can be explained in terms of the p -d Zener model.

  13. Droplet etched GaAs quantum dots close to surfaces and metallic interfaces

    NASA Astrophysics Data System (ADS)

    Heyn, Ch.; Zocher, M.; Pudewill, L.; Runge, H.; Küster, A.; Hansen, W.

    2017-01-01

    GaAs quantum dots (QDs) with a thin cap layer are studied as building blocks for self-aligned hybrids with a metallic nanostructure (MN). Both constituents are filled into a nanohole template that is drilled into an AlGaAs surface by self-assembled local droplet etching during molecular beam epitaxy. In a first series of samples, the interaction of a near AlGaAs surface with a single QD at varied distance is studied using microphotoluminescence (PL) spectroscopy. With decreasing distance down to 12.5 nm, surface charges cause an increase in the exciton radiative lifetime, the formation of charged excitons, and a broadening of the exciton PL peaks. The PL peak broadening is quantitatively analyzed on the basis of an analytical model assuming temporal fluctuations of the surface charge. In a second sample series, the nanoholes are filled in addition with an Au nanostructure. The optical spectra are similar to those from QDs without a metal but with a slightly stronger PL peak broadening. For a small distance of 12.5 nm clearly within the optical near-field of the MN, the QDs show a typical PL linewidth of 430 μeV that is still small enough to separate different excitonic lines.

  14. Characterization of epiready n +-GaAs (100) surfaces by SPV-transient

    NASA Astrophysics Data System (ADS)

    Sinkkonen, Juha; Novikov, Sergey; Varpula, Aapo; Haapamaa, J.

    2007-12-01

    Surface photovoltage (SPV) transient provides a non-destructive, contact-free method for characterization of semiconductor surfaces. Here we study SPV-transients of differently cleaned, heavily doped epiready GaAs wafers. After a rapid initial part the transient shows a very slow decay taking place in 100 - 1000 s time scale. Chemical NH 4OH:H IIO II:H IIO cleaning and atomic hydrogen UHV cleaning are applied. SPV-transients are measured by Kelvin probe in normal atmospheric conditions. A large signal surface trapping model is developed which includes both majority and minority carrier processes and covers the whole light on, steady state, light off sequence. Model fitting allows band bending, energy and density of surface states as well as electron and hole capture cross-sections to be extracted. The results show that the traps are electronic states in thin oxide layer covering the samples. This conclusion is based on the finding that the capture cross-sections are very small, in the range 10 -19 - 10 -26 cm2, which calls tunneling for explanation. This indicates that after cleaning the oxide layer is rapidly re-grown in laboratory atmosphere in less than 30 min. Typical band bendings are 0.6 - 0.8 eV, trap energies are slightly above the mid-gap and the density of occupied trap states is around 5×10 12 cm -2 at thermal equilibrium.

  15. Surface-barrier and polarization effects in the photoemission from GaAs(110)

    NASA Astrophysics Data System (ADS)

    Henk, J.; Schattke, W.; Cartensen, H.; Manzke, R.; Skibowski, M.

    1993-01-01

    We have developed a theory of photoemission from III-V compound semiconductors within the one-step model and discuss the effect of transition-matrix elements, final states, and the surface barrier on the energy distribution of photoelectrons. As a prototype the (110) surface of GaAs is studied, and theoretical spectra are compared with experiment in normal as well as in non-normal emission. The specific position of the interface vacuum crystal, appearing in the calculation of the transition-matrix elements, influences the shape of the spectra considerably. The energy-distribution curves strongly depend on the escape angles of the photoelectrons as well as the incidence angles of the radiation leading to significant intensity variations especially of the dangling-bond surface state. Band-mapping methods prove to be misleading, in the worst cases by an error of about 100 meV in the estimation of the valence-band energies. The corrugated surface barrier is also investigated; our analysis favors a smooth saturated image potential barrier.

  16. Chemical beam epitaxy of GaAs1-xNx using MMHy and DMHy precursors, modeled by ab initio study of GaAs(100) surfaces stability over As2, H2 and N2

    NASA Astrophysics Data System (ADS)

    Valencia, Hubert; Kangawa, Yoshihiro; Kakimoto, Koichi

    2017-06-01

    Using ab initio calculations, a simple model for GaAs1-xNx vapor-phase epitaxy on (100) surface of GaAs was created. By studying As2 and H2 molecules adsorptions and As/N atom substitutions on (100) GaAs surfaces, we obtain a relative stability diagram of all stable surfaces under varying As2, H2, and N2 conditions. We previously proved that this model could describe the vapor-phase epitaxy of GaAs1-x Nx with simple, fully decomposed, precursors. In this paper, we show that in more complex reaction conditions using monomethylhydrazine (MMHy), and dimethylhydrazine (DMHy), it is still possible to use our model to obtain an accurate description of the temperature and pressure stability domains for each surfaces, linked to chemical beam epitaxy (CBE) growth conditions. Moreover, the different N-incorporation regimes observed experimentally at different temperature can be explain and predict by our model. The use of MMHy and DMHy precursors can also be rationalized. Our model should then help to better understand the conditions needed to obtain an high quality GaAs1-xNx using vapor-phase epitaxy.

  17. GaAs nanopillar-array solar cells employing in situ surface passivation.

    PubMed

    Mariani, Giacomo; Scofield, Adam C; Hung, Chung-Hong; Huffaker, Diana L

    2013-01-01

    Arrays of III-V direct-bandgap semiconductor nanopillars represent promising photovoltaic candidates due to their inherent high optical absorption coefficients and minimized reflection arising from light trapping, efficient charge collection in the radial direction and the ability to synthesize them on low-cost platforms. However, the increased surface area results in surface states that hamper the power conversion efficiency. Here, we report the first demonstration of GaAs nanopillar-array photovoltaics employing epitaxial passivation with air mass 1.5 global power conversion efficiencies of 6.63%. High-bandgap epitaxial InGaP shells are grown in situ and cap the radial p-n junctions to alleviate surface-state effects. Under light, the photovoltaic devices exhibit open-circuit voltages of 0.44 V, short-circuit current densities of 24.3 mA cm(-2) and fill factors of 62% with high external quantum efficiencies >70% across the spectral regime of interest. A novel titanium/indium tin oxide annealed alloy is exploited as transparent ohmic anode.

  18. GaAs nanopillar-array solar cells employing in situ surface passivation

    NASA Astrophysics Data System (ADS)

    Mariani, Giacomo; Scofield, Adam C.; Hung, Chung-Hong; Huffaker, Diana L.

    2013-02-01

    Arrays of III-V direct-bandgap semiconductor nanopillars represent promising photovoltaic candidates due to their inherent high optical absorption coefficients and minimized reflection arising from light trapping, efficient charge collection in the radial direction and the ability to synthesize them on low-cost platforms. However, the increased surface area results in surface states that hamper the power conversion efficiency. Here, we report the first demonstration of GaAs nanopillar-array photovoltaics employing epitaxial passivation with air mass 1.5 global power conversion efficiencies of 6.63%. High-bandgap epitaxial InGaP shells are grown in situ and cap the radial p-n junctions to alleviate surface-state effects. Under light, the photovoltaic devices exhibit open-circuit voltages of 0.44 V, short-circuit current densities of 24.3 mA cm-2 and fill factors of 62% with high external quantum efficiencies >70% across the spectral regime of interest. A novel titanium/indium tin oxide annealed alloy is exploited as transparent ohmic anode.

  19. GaAs nanopillar-array solar cells employing in situ surface passivation

    PubMed Central

    Mariani, Giacomo; Scofield, Adam C.; Hung, Chung-Hong; Huffaker, Diana L.

    2013-01-01

    Arrays of III–V direct-bandgap semiconductor nanopillars represent promising photovoltaic candidates due to their inherent high optical absorption coefficients and minimized reflection arising from light trapping, efficient charge collection in the radial direction and the ability to synthesize them on low-cost platforms. However, the increased surface area results in surface states that hamper the power conversion efficiency. Here, we report the first demonstration of GaAs nanopillar-array photovoltaics employing epitaxial passivation with air mass 1.5 global power conversion efficiencies of 6.63%. High-bandgap epitaxial InGaP shells are grown in situ and cap the radial p–n junctions to alleviate surface-state effects. Under light, the photovoltaic devices exhibit open-circuit voltages of 0.44 V, short-circuit current densities of 24.3 mA cm−2 and fill factors of 62% with high external quantum efficiencies >70% across the spectral regime of interest. A novel titanium/indium tin oxide annealed alloy is exploited as transparent ohmic anode. PMID:23422665

  20. Optical and surface properties of the in doped GaAs layer deposition using thermionic vacuum arc method.

    PubMed

    Pat, Suat; Özen, Soner; Şenay, Volkan; Korkmaz, Şadan; Şimşek, Veli

    2016-07-01

    A broadband optical transparent InGaAs semiconductor layer production of micron thicknesses was produced in only 75 s by thermionic vacuum arc (TVA) method at the first time. The optical and surface properties of the produced layers have been investigated. InGaAs structure is using in electronics and optoelectronics devices. The main advantage of TVA method is its fast deposition rate, without any loss in the quality of the films. Doping is a very simple and fast according to common production methods. InGaAs is an alloy of indium arsenide (InAs) and gallium arsenide (GaAs). InAs with (220) crystallographic direction and GaAs with (024)/(022) crystallographic directions were detected using by XRD analysis. GaAs and InAs are in the cubic and zinc blende crystal system, respectively. According to the transmittance spectra, sample has a broadband transparency in the range of 1000-3300 nm. According to results, defined TVA method for In doping to GaAs is proper fast and friendly method. SCANNING 38:297-302, 2016. © 2015 Wiley Periodicals, Inc.

  1. Green monolithic II-VI vertical-cavity surface-emitting laser operating at room temperature

    NASA Astrophysics Data System (ADS)

    Kruse, C.; Ulrich, S. M.; Alexe, G.; Roventa, E.; Kröger, R.; Brendemühl, B.; Michler, P.; Gutowski, J.; Hommel, D.

    2004-02-01

    The realization of a monolithic all II-VI-based vertical cavity surface emitting laser (VCSEL) for the green spectral region is reported. Optically pumped lasing operation was achieved up to room temperature using a planar VCSEL structure. Taking advantage of distributed Bragg-reflectors based on MgS/Zn(Cd)Se superlattices as the low-refractive index material and ZnS0.06Se0.94 layers as the high-index material with a refractive index contrast of n = 0.6, a quality factor exceeding Q = 2000 is reached by using only 18 Bragg periods for the bottom DBR and 15 Bragg periods for the top DBR. The threshold power density is 0.32 MW/cm2 at a temperature of 10 K (emission wavelength 498.5 nm) and 1.9 MW/cm2 at room temperature (emission wavelength 502.3 nm).

  2. Optimization of VCSELs incorporating monolithic subwavelength high-refractive-index contrast surface grating mirrors

    NASA Astrophysics Data System (ADS)

    Gebski, Marcin; Marciniak, Magdalena; Dems, Maciej; Czyszanowski, Tomasz; Lott, James A.

    2017-02-01

    We present results of computer simulations of vertical cavity surface emitting lasers (VCSELs) using novel, highreflectivity monolithic high refractive-index contrast grating (MHCG) mirrors and their more advanced version, partially covered by a thin metal layer - metallic MHCG (mMHCG) mirrors. The first experimental realization of this new class of mirrors is presented and discussed. We show that the metal layer does not deteriorate the high reflectivity of an mMHCG mirror, but in contrary, is a crucial element which allows high reflectivity and additionally opens a way for a more efficient electrical pumping of a VCSEL. Comparison of results of thermal-electrical-carrier-gain self-consistent simulations of both MHCG- and mMHCG-based VCSELs is presented and discussed. It is shown that using mHCG mirror as a top mirror of a VCSEL improves electrical characteristics and greatly decreases the differential resistance of the device.

  3. Transient surface states during the CBE growth of GaAs

    NASA Astrophysics Data System (ADS)

    Farrell, T.; Hill, D.; Joyce, T. B.; Bullough, T. J.; Weightman, P.

    1997-05-01

    We report the occurrence of a transient surface state during the initial stages of CBE GaAs(0 0 1) growth. The state was detected in real-time reflectance ( R) and reflectance anisotropy spectroscopy (RAS) growth monitoring. At low growth rates, less than 1 μm/h, beam equivalent pressure (BEP) of triethylgallium (TEG) < 2.5 × 10 -5 mbar there was no change in R and the RAS signal changed from its pre-growth value under arsenic stabilisation at the growth temperature to its "during growth" value upon admission of the TEG, with the familiar monolayer oscillations. At higher TEG BEPs there was a rapid increase in R at all monitoring wavelengths, followed by a monotonic decay to its pre-growth value. This transient increase in R was accompanied by a change in the RAS signal, the magnitude and sign of which varied with wavelength. The initial increase in R is shown to be associated with the development of a metallic-like surface whereas the changes in the RAS signal are consistent with the formation of Ga dimers.

  4. Electrical and optical characterization of surface passivation in GaAs nanowires.

    PubMed

    Chang, Chia-Chi; Chi, Chun-Yung; Yao, Maoqing; Huang, Ningfeng; Chen, Chun-Chung; Theiss, Jesse; Bushmaker, Adam W; Lalumondiere, Stephen; Yeh, Ting-Wei; Povinelli, Michelle L; Zhou, Chongwu; Dapkus, P Daniel; Cronin, Stephen B

    2012-09-12

    We report a systematic study of carrier dynamics in Al(x)Ga(1-x)As-passivated GaAs nanowires. With passivation, the minority carrier diffusion length (L(diff)) increases from 30 to 180 nm, as measured by electron beam induced current (EBIC) mapping, and the photoluminescence (PL) lifetime increases from sub-60 ps to 1.3 ns. A 48-fold enhancement in the continuous-wave PL intensity is observed on the same individual nanowire with and without the Al(x)Ga(1-x)As passivation layer, indicating a significant reduction in surface recombination. These results indicate that, in passivated nanowires, the minority carrier lifetime is not limited by twin stacking faults. From the PL lifetime and minority carrier diffusion length, we estimate the surface recombination velocity (SRV) to range from 1.7 × 10(3) to 1.1 × 10(4) cm·s(-1), and the minority carrier mobility μ is estimated to lie in the range from 10.3 to 67.5 cm(2) V(-1) s(-1) for the passivated nanowires.

  5. Role of GaAs surface clearing in plasma deposition of silicon nitride films for encapsulated annealing

    NASA Technical Reports Server (NTRS)

    Valco, G. J.; Kapoor, V. J.

    1985-01-01

    The role of GaAs surface cleaning and plasma reactor cleaning prior to deposition of silicon nitride films for encapsulated annealing has been investigated. X-ray photoelectron spectroscopy was employed to determine the surface characteristics of GaAs treated with HCl, HF, and NH4OH solutions preceded by a degreasing procedure. The HCl clean left the least amount of oxygen on the surface. Fluorine contamination resulting from the CF4 plasma used to clean the reactor was found to be located at the film-substrate interface by Auger electron spectroscopy with argon-ion sputtering. A modified deposition procedure was developed to eliminate the fluorine contamination. Plasma deposition of silicon nitride encapsulating films was found to modify the I-V characteristics of Schottky diodes subsequently formed on GaAs surface. The reverse current of the diodes was slightly reduced. Substrates implanted with Si at 100 keV and a dose of 5 x 10 to the 12th/sq cm showed a peak electron concentration of 1.7 x 10 to the 17th/cu cm at a depth of 0.1-micron with 60 percent activation after encapsulation and annealing at 800 C for 7 min.

  6. Role of GaAs surface clearing in plasma deposition of silicon nitride films for encapsulated annealing

    NASA Technical Reports Server (NTRS)

    Valco, G. J.; Kapoor, V. J.

    1985-01-01

    The role of GaAs surface cleaning and plasma reactor cleaning prior to deposition of silicon nitride films for encapsulated annealing has been investigated. X-ray photoelectron spectroscopy was employed to determine the surface characteristics of GaAs treated with HCl, HF, and NH4OH solutions preceded by a degreasing procedure. The HCl clean left the least amount of oxygen on the surface. Fluorine contamination resulting from the CF4 plasma used to clean the reactor was found to be located at the film-substrate interface by Auger electron spectroscopy with argon-ion sputtering. A modified deposition procedure was developed to eliminate the fluorine contamination. Plasma deposition of silicon nitride encapsulating films was found to modify the I-V characteristics of Schottky diodes subsequently formed on GaAs surface. The reverse current of the diodes was slightly reduced. Substrates implanted with Si at 100 keV and a dose of 5 x 10 to the 12th/sq cm showed a peak electron concentration of 1.7 x 10 to the 17th/cu cm at a depth of 0.1-micron with 60 percent activation after encapsulation and annealing at 800 C for 7 min.

  7. Visualizing Donor-Acceptor-Bond Chemistry at Semiconductor Surfaces with STM: NH3 on GaAs(110)

    NASA Astrophysics Data System (ADS)

    Brown, G.; Steinshnider, J.; Weimer, M.

    1997-03-01

    We have previously used STM to examine the room-temperature chemisorption of submonolayer amounts of ammonia on GaAs(110). Atomic-resolution topographs demonstrate this reaction is non-dissociative and that bond formation occurs through the donation of lone-pair electrons from the free molecule to cation dangling bonds at the surface(G. Brown and M. Weimer, J. Vac. Sci. Technol. B 13), 1679-1683 (1995). Reaction sites on both p- and n-type substrates are uncharged so that the screening of individual donor-acceptor-bond dipoles by substrate electrons is observed. We have recently studied the interactions between adsorbed molecules through the distribution of reaction sites as a function of separation vector in the surface plane. The pair correlation function reveals a strong, short-ranged repulsion along the GaAs(110) surface chains that completely excludes bonding at adjacent cation sublattice sites, but the observed anisotropy of the pair potential is inconsistent with the expected dipole-dipole forces between adsorbates. STS indicates ammonia chemisorption significantly disrupts the GaAs(110) surface states at saturation coverages less than 0.1 ML, and that observation, together with the anisotropic short-range nature of the pair potential, suggests the predominant lateral interaction in this system is substrate mediated.

  8. A new high-efficiency GaAs solar cell structure using a heterostructure back-surface field

    NASA Technical Reports Server (NTRS)

    Gale, R. P.; Fan, J. C. C.; Turner, G. W.; Chapman, R. L.

    1984-01-01

    Shallow-homojunction GaAs solar cells are fabricated with a back-surface field (BSF) produced by a GaAs/Al(0.2)Ga(0.8)As heterostructure. These cells exhibit higher open-circuit voltages and conversion efficiencies than control cells made with a p-GaAs/p(+)-GaAs BSF. Conversion efficiencies of over 22 percent (AM1, total area) have been obtained with this new structure. The use of a higher bandgap material below the active region not only provides an enhanced BSF but will also permit the implementation of two solar-cell designs: a GaAs cell with a back-surface reflector and an AlGaAs cell that can be used as the upper cell in tandem configurations.

  9. A new high-efficiency GaAs solar cell structure using a heterostructure back-surface field

    NASA Technical Reports Server (NTRS)

    Gale, R. P.; Fan, J. C. C.; Turner, G. W.; Chapman, R. L.

    1984-01-01

    Shallow-homojunction GaAs solar cells are fabricated with a back-surface field (BSF) produced by a GaAs/Al(0.2)Ga(0.8)As heterostructure. These cells exhibit higher open-circuit voltages and conversion efficiencies than control cells made with a p-GaAs/p(+)-GaAs BSF. Conversion efficiencies of over 22 percent (AM1, total area) have been obtained with this new structure. The use of a higher bandgap material below the active region not only provides an enhanced BSF but will also permit the implementation of two solar-cell designs: a GaAs cell with a back-surface reflector and an AlGaAs cell that can be used as the upper cell in tandem configurations.

  10. Photoluminescence intensity enhancement of GaAs by vapor-deposited GaS - A rational approach to surface passivation

    NASA Technical Reports Server (NTRS)

    Jenkins, Phillip P.; Hepp, Aloysius F.; Power, Michael B.; Macinnes, Andrew N.; Barron, Andrew R.

    1993-01-01

    A two order-of-magnitude enhancement of photoluminescence intensity relative to untreated GaAs has been observed for GaAs surfaces coated with chemical vapor-deposited GaS. The increase in photoluminescence intensity can be viewed as an effective reduction in surface recombination velocity and/or band bending. The gallium cluster (/t-Bu/GaS)4 was used as a single-source precursor for the deposition of GaS thin films. The cubane core of the structurally-characterized precursor is retained in the deposited film producing a cubic phase. Furthermore, a near-epitaxial growth is observed for the GaS passivating layer. Films were characterized by transmission electron microscopy, X-ray powder diffraction, and X-ray photoelectron and Rutherford backscattering spectroscopies.

  11. Surface passivation of tellurium-doped GaAs nanowires by GaP: Effect on electrical conduction

    SciTech Connect

    Darbandi, A.; Salehzadeh, O.; Watkins, S. P.; Kuyanov, P.; LaPierre, R. R.

    2014-06-21

    We report on the surface passivation of Au-assisted Te-doped GaAs nanowires (NWs) grown by metalorganic vapor phase epitaxy. The electrical properties of individual free standing NWs were assessed using a tungsten nano-probe inside a scanning electron microscope. The diameter independent apparent resistivity of both strained and relaxed passivated NWs suggests the unpinning of the Fermi level and reduction of sidewalls surface states density. Similar current-voltage properties were observed for partially axially relaxed GaAs/GaP NWs. This indicates a negligible contribution of misfit dislocations in the charge transport properties of the NWs. Low temperature micro-photoluminescence (μ-PL) measurements were also carried out for both uncapped and passivated GaAs NWs. The improvement of the integrated (μ-PL) intensity for GaAs/GaP NWs further confirms the effect of passivation.

  12. Comparisons of GaAs, tungsten, and photoresist etch rates and GaAs surfaces using RIE with CF/sub 4/, CF/sub 4/ + N/sub 2/, and SF/sub 6/ + N/sub 2/ mixtures

    SciTech Connect

    Susa, N.

    1985-11-01

    Etch rates for GaAs, tungsten, and photoresist were compared using CF/sub 4/, CF/sub 4/ + N/sub 2/, and SF/sub 6/ + N/sub 2/ gases. Etch rate ratio between the W and photoresist can be increased by N/sub 2/ gas addition, with a negligibly low GaAs etch rate. GaAs surfaces exposed to CF/sub 4/ + N/sub 2/ or SF/sub 6/ + N/sub 2/ plasmas were characterized by means of photoluminescence (PL), Schottky contacts, secondary ion mass spectroscopy (SIMS), and Auger electron spectroscopy (AES). The PL intensity measurements and Schottky characteristics revealed that the damage to the GaAs surface was somewhat smaller than that caused by pure CF/sub 4/ gas. The AES and SIMS measurements showed that the change in Ga/As composition after reactive ion etching was negligibly small. Results of heat-treatment are also described. Curious annealing characteristics were observed in the CF/sub 4/ + N/sub 2/, suggesting the existence of GaN.

  13. The influence of surfaces on the transient terahertz conductivity and electron mobility of GaAs nanowires

    NASA Astrophysics Data System (ADS)

    Joyce, Hannah J.; Baig, Sarwat A.; Parkinson, Patrick; Davies, Christopher L.; Boland, Jessica L.; Tan, H. Hoe; Jagadish, Chennupati; Herz, Laura M.; Johnston, Michael B.

    2017-06-01

    Bare unpassivated GaAs nanowires feature relatively high electron mobilities (400-2100 cm2 V-1 s-1) and ultrashort charge carrier lifetimes (1-5 ps) at room temperature. These two properties are highly desirable for high speed optoelectronic devices, including photoreceivers, modulators and switches operating at microwave and terahertz frequencies. When engineering these GaAs nanowire-based devices, it is important to have a quantitative understanding of how the charge carrier mobility and lifetime can be tuned. Here we use optical-pump-terahertz-probe spectroscopy to quantify how mobility and lifetime depend on the nanowire surfaces and on carrier density in unpassivated GaAs nanowires. We also present two alternative frameworks for the analysis of nanowire photoconductivity: one based on plasmon resonance and the other based on Maxwell-Garnett effective medium theory with the nanowires modelled as prolate ellipsoids. We find the electron mobility decreases significantly with decreasing nanowire diameter, as charge carriers experience increased scattering at nanowire surfaces. Reducing the diameter from 50 nm to 30 nm degrades the electron mobility by up to 47%. Photoconductivity dynamics were dominated by trapping at saturable states existing at the nanowire surface, and the trapping rate was highest for the nanowires of narrowest diameter. The maximum surface recombination velocity, which occurs in the limit of all traps being empty, was calculated as 1.3  ×  106 cm s-1. We note that when selecting the optimum nanowire diameter for an ultrafast device, there is a trade-off between achieving a short lifetime and a high carrier mobility. To achieve high speed GaAs nanowire devices featuring the highest charge carrier mobilities and shortest lifetimes, we recommend operating the devices at low charge carrier densities.

  14. Relevance of GaAs(001) surface electronic structure for high frequency dispersion on n-type accumulation capacitance

    NASA Astrophysics Data System (ADS)

    Pi, T. W.; Chen, W. S.; Lin, Y. H.; Cheng, Y. T.; Wei, G. J.; Lin, K. Y.; Cheng, C.-P.; Kwo, J.; Hong, M.

    2017-01-01

    This study investigates the origin of long-puzzled high frequency dispersion on the accumulation region of capacitance-voltage characteristics in an n-type GaAs-based metal-oxide-semiconductor. Probed adatoms with a high Pauling electronegativity, Ag and Au, unexpectedly donate charge to the contacted As/Ga atoms of as-grown α2 GaAs(001)-2 × 4 surfaces. The GaAs surface atoms behave as charge acceptors, and if not properly passivated, they would trap those electrons accumulated at the oxide and semiconductor interface under a positive bias. The exemplified core-level spectra of the Al2O3/n-GaAs(001)-2 × 4 and the Al2O3/n-GaAs(001)-4 × 6 interfaces exhibit remnant of pristine surface As emission, thereby causing high frequency dispersion in the accumulation region. For the p-type GaAs, electrons under a negatively biased condition are expelled from the interface, thereby avoiding becoming trapped.

  15. Effects of surface reconstruction on the epitaxial growth of III-Sb on GaAs using interfacial misfit array

    NASA Astrophysics Data System (ADS)

    Jia, Bo Wen; Tan, Kian Hua; Loke, Wan Khai; Wicaksono, Satrio; Yoon, Soon Fatt

    2017-03-01

    The effects of pre-growth Sb reconstruction on a GaAs surface on the epitaxial growth of III-Sb (GaSb and InSb) on a (100) GaAs substrate using interfacial misfit array were investigated. All samples exhibited smooth surface with a root mean square (r.m.s.) roughness below 1.5 nm and nearly 100% relaxation. Modeling indicated that the distribution and types of misfit dislocations can be evaluated using a reciprocal space map (RSM) of the x-ray measurements. The interfacial misfit (IMF) arrays in III-Sb/GaAs samples were characterized by RSMs of high-resolution x-ray diffraction (XRD) and transmission electron microscopy (TEM). The RSM results suggest that all samples exhibited highly uniformly distributed misfit dislocations, and pre-growth (2 × 8) Sb surface reconstruction promoted the formation of 90° dislocations in an IMF array. Hall measurements of unintentionally doped GaSb and InSb layers also suggested that the highest motilities at both 77 K and 300 K were achieved at the samples grown on GaAs with pre-growth (2 × 8) Sb reconstruction.

  16. Decomposition Mechanism of Triethyl-Arsenic on a GaAs Surface for Metalorganic Molecular-Beam Epitaxy: Role of Hydrogen Radicals

    NASA Astrophysics Data System (ADS)

    Suemune, Ikuo; Hamaoka, Kazuhiko; Koui, Tomoaki; Kishimoto, Akihiro; Yamanishi, Masamichi

    1991-09-01

    Growth of GaAs in metalorganic molecular-beam epitaxy using triethyl-arsenic (TEAs) becomes possible only when TEAs is thermally precracked or when hydrogen (H) plasma is irradiated simultaneously. In this paper, it will be shown that the bottleneck in the growth of GaAs with TEAs is the quick desorption of the As-intermediate species before its decomposition to supply As to a GaAs surface. The Ga-stabilized GaAs surface after the TEAs supply is proposed to be covered with stable C2H4 species based on reflection high-energy electron diffraction and quadrupole mass spectrometric measurements. H radicals are shown to be effective in the initial stages of the decomposition process of TEAs, but once the surface is covered stably with C2H4, even the H radicals cannot enhance their desorption.

  17. Basic Study on the Radio Frequency Characteristics of the Transmission Lines Employing Periodically Perforated Ground Metal on GaAs Monolithic Microwave Integrated Circuit and Their Equivalent Ciruits

    NASA Astrophysics Data System (ADS)

    Yun, Young; Ju, Jeong-Gab; Kim, Hong Seung

    2011-01-01

    In this work, basic characteristics of transmission line employing periodically perforated ground metal (PPGM) were investigated using theoretical and experimental analysis. Concretely, bandwidth and impedance were investigated using theoretical analysis, and wavelength and effective permittivity were extracted from experimental results. In addition, insertion loss and isolation characteristics were investigated using equivalent circuit analysis. For simplification of design process, equivalent circuits for the PPGM cell were extracted, and all circuit parameters were expressed by closed-form equation. Above results indicate that the transmission line employing PPGM is a promising candidate for a development of matching and passive elements on monolithic microwave integrated circuit (MMIC) including wireless communication circuit and compound semiconducting devices such as high electron mobility transistor (HEMT), diamond field effect transistor (FET) and light emitting diode (LED).

  18. XPS investigation of ion beam induced conversion of GaAs(0 0 1) surface into GaN overlayer

    NASA Astrophysics Data System (ADS)

    Kumar, Praveen; Kumar, Mahesh; Govind; Mehta, B. R.; Shivaprasad, S. M.

    2009-10-01

    For the advance of GaN based optoelectronic devices, one of the major barriers has been the high defect density in GaN thin films, due to lattice parameter and thermal expansion incompatibility with conventional substrates. Of late, efforts are focused in fine tuning epitaxial growth and in search for a low temperature method of forming low defect GaN with zincblende structure, by a method compatible to the molecular beam epitaxy process. In principle, to grow zincblende GaN the substrate should have four-fold symmetry and thus zincblende GaN has been prepared on several substrates including Si, 3C-SiC, GaP, MgO, and on GaAs(0 0 1). The iso-structure and a common shared element make the epitaxial growth of GaN on GaAs(0 0 1) feasible and useful. In this study ion-induced conversion of GaAs(0 0 1) surface into GaN at room temperature is optimized. At the outset a Ga-rich surface is formed by Ar + ion bombardment. Nitrogen ion bombardment of the Ga-rich GaAs surface is performed by using 2-4 keV energy and fluence ranging from 3 × 10 13 ions/cm 2 to 1 × 10 18 ions/cm 2. Formation of surface GaN is manifested as chemical shift. In situ core level and true secondary electron emission spectra by X-ray photoelectron spectroscopy are monitored to observe the chemical and electronic property changes. Using XPS line shape analysis by deconvolution into chemical state, we report that 3 keV N 2+ ions and 7.2 × 10 17 ions/cm 2 are the optimal energy and fluence, respectively, for the nitridation of GaAs(0 0 1) surface at room temperature. The measurement of electron emission of the interface shows the dependence of work function to the chemical composition of the interface. Depth profile study by using Ar + ion sputtering, shows that a stoichiometric GaN of 1 nm thickness forms on the surface. This, room temperature and molecular beam epitaxy compatible, method of forming GaN temperature can serve as an excellent template for growing low defect GaN epitaxial overlayers.

  19. Characterization study of native oxides on GaAs(100) surface by XPS

    NASA Astrophysics Data System (ADS)

    Feng, Liu; Zhang, Lian-dong; Liu, Hui; Gao, Xiang; Miao, Zhuang; Cheng, Hong-chang; Wang, Long; Niu, Sen

    2013-08-01

    In order to know more about the surface state of GaAs(100) epitaxial wafer during a storage period of two years, the XPS analysis was carried out four times on the surface, respectively polished by chemical etching, stored in desiccator for half a year, one year and two years. The results indicated that even after cleaned by proper etchant solutions, the fresh surface was slightly oxidized with Ga2O3, As2O3 and organic contaminant. The epi-wafer was always exposed to air during the storage period, so more and more oxides turned out. The mixed oxide layer comprised of C-OR, COOR, Ga2O3, As2O3 and As2O5 appeared after only half a year. In the ageing process of two years, the oxide types of gallium or arsenic did not change with stable content of Ga2O3 and remarkably fluctuating relative contents of As2O3 and As2O5. Based on the intensity ratio of Ga 3d-Ga2O3 to Ga 3d-GaAs, the thickness of oxide layer was estimated. The oxide layer generated after chemical polishing was very thin, just only 0.435nm thick, and then it grew rapidly, approximately 1.822nm after one year while almost no change any more subsequently. It was indicated that after the epi-wafer was stored for one year, because of volatile As2O3 or As2O5, there remained a large amount of Ga2O3 in oxide layer, which prevented the reactions between bulk material and oxide layer with oxygen. So native oxide layer plays a role as passive film to protect epi-wafer against the environment during a long storage period.

  20. Atomic structure of InSb(001) and GaAs(001) surfaces imaged with noncontact atomic force microscopy.

    PubMed

    Kolodziej, J J; Such, B; Szymonski, M; Krok, F

    2003-06-06

    Noncontact atomic force microscopy (NC-AFM) has been used to study the c(8x2) InSb(001) and the c(8x2) GaAs(001) surfaces prepared by sputter cleaning and annealing. Atomically resolved tip-surface interaction maps display different characteristic patterns depending on the tip front atom type. It is shown that representative AFM maps can be interpreted consistently with the most recent structural model of A(III)B(V)(001) surface, as corresponding to the A(III) sublattice, to the B(V) sublattice, or to the combination of both sublattices.

  1. Attractive interaction between Mn atoms on the GaAs(110) surface observed by scanning tunneling microscopy.

    PubMed

    Taninaka, Atsushi; Yoshida, Shoji; Kanazawa, Ken; Hayaki, Eiko; Takeuchi, Osamu; Shigekawa, Hidemi

    2016-06-16

    Scanning tunneling microscopy/spectroscopy (STM/STS) was carried out to investigate the structures of Mn atoms deposited on a GaAs(110) surface at room temperature to directly observe the characteristics of interactions between Mn atoms in GaAs. Mn atoms were paired with a probability higher than the random distribution, indicating an attractive interaction between them. In fact, re-pairing of unpaired Mn atoms was observed during STS measurement. The pair initially had a new structure, which was transformed during STS measurement into one of those formed by atom manipulation at 4 K. Mn atoms in pairs and trimers were aligned in the <110> direction, which is theoretically predicted to produce a high Curie temperature.

  2. Ultra-thin flexible GaAs photovoltaics in vertical forms printed on metal surfaces without interlayer adhesives

    NASA Astrophysics Data System (ADS)

    Kim, Juho; Hwang, Jeongwoo; Song, Kwangsun; Kim, Namyun; Shin, Jae Cheol; Lee, Jongho

    2016-06-01

    Wearable flexible electronics often require sustainable power sources that are also mechanically flexible to survive the extreme bending that accompanies their general use. In general, thinner microelectronic devices are under less strain when bent. This paper describes strategies to realize ultra-thin GaAs photovoltaics through the interlayer adhesiveless transfer-printing of vertical-type devices onto metal surfaces. The vertical-type GaAs photovoltaic devices recycle reflected photons by means of bottom electrodes. Systematic studies with four different types of solar microcells indicate that the vertical-type solar microcells, at only a quarter of the thickness of similarly designed lateral-type cells, generate a level of electric power similar to that of thicker cells. The experimental results along with the theoretical analysis conducted here show that the ultra-thin vertical-type solar microcells are durable under extreme bending and thus suitable for use in the manufacturing of wearable flexible electronics.

  3. Ultra-thin flexible GaAs photovoltaics in vertical forms printed on metal surfaces without interlayer adhesives

    SciTech Connect

    Kim, Juho; Song, Kwangsun; Kim, Namyun; Lee, Jongho; Hwang, Jeongwoo; Shin, Jae Cheol

    2016-06-20

    Wearable flexible electronics often require sustainable power sources that are also mechanically flexible to survive the extreme bending that accompanies their general use. In general, thinner microelectronic devices are under less strain when bent. This paper describes strategies to realize ultra-thin GaAs photovoltaics through the interlayer adhesiveless transfer-printing of vertical-type devices onto metal surfaces. The vertical-type GaAs photovoltaic devices recycle reflected photons by means of bottom electrodes. Systematic studies with four different types of solar microcells indicate that the vertical-type solar microcells, at only a quarter of the thickness of similarly designed lateral-type cells, generate a level of electric power similar to that of thicker cells. The experimental results along with the theoretical analysis conducted here show that the ultra-thin vertical-type solar microcells are durable under extreme bending and thus suitable for use in the manufacturing of wearable flexible electronics.

  4. A Study of the Activated GaAs Surface for Application as an Electron Source in Particle Accelerators

    SciTech Connect

    Chanlek, N.; Herbert, J. D.; Jones, L. B.; Middleman, K. J.; Jones, R. M.

    2009-08-04

    The use of type III-V semiconductor materials as photocathodes has in recent years become a focus for the High Energy Physics community. Once activated to a negative electron affinity (NEA) state and illuminated by a laser, these materials can be used as a high-brightness source of both polarised and un-polarised electrons in some modern accelerators, for example, ALICE (Accelerators and Lasers in Combined Experiments) at Daresbury Laboratory. This paper will focus on the use of gallium arsenide (GaAs) as a photocathode, and detail the reconfiguration and re-commissioning of two vacuum systems that support standard surface science techniques such as ultraviolet/X-ray photoelectron spectroscopy (UPS/XPS), low energy electron diffraction (LEED) and auger electron spectroscopy (AES). The paper will present details of cleaning GaAs in order to maximise quantum efficiency and will provide evidence from XPS and LEED to demonstrate what is happening at the atomic level.

  5. The very surface states on GaAs(001) surface by means of electronic and optical techniques

    NASA Astrophysics Data System (ADS)

    Placidi, Ernesto

    2004-03-01

    Until now, Reflectance-Anisotropy Spectroscopy (RAS) in the visible has been the most used technique to quantify the anisotropy of these surfaces [1]. Low-energy electrons are believed to perturb more than photons and have not been employed to this purpose, despite their shorter penetration depth. In our presentation we show experimental results of High-Resolution Electron-Energy-Loss Spectroscopy (HREELS) applied to investigate the anisotropy of the GaAs(001)-c(4x4) and beta2(2x4) surfaces. We demonstrate the higher surface sensitivity of HREELS compared to RAS. Measurements are performed on high-quality samples grown in situ by Molecular Beam Epitaxy (MBE). The loss spectra taken in the two orthogonal surface directions have different intensities, particularly close to the fundamental gap, where surface like resonances, involving dimers, are observed. We discuss our HREELS and RAS data to identify the source of the anisotropy close to the critical point transitions where surface and bulk like excitations coexist. Our data are in very good agreement with DFT-LDA calculations for loss energies up to 3.5 eV [2]. The exposure of the reconstructed surfaces to molecular oxygen affects strongly the spectral features. [1] D.E.Aspnes, J.P.Harbison, A.A.Studna, L.T.Florez, Phys. Rev. Lett. 59 (1987) 1687; I.Kamiya, D.E.Aspnes, L.T.Florez, and J.T.Harbison, Phys. Rev. B 46 (1992) 15894. [2] A.Balzarotti, F.Arciprete, M.Fanfoni, F.Patella, E. Placidi, G.Onida, R.Del Sole, Surf. Sci. Lett. 524, L71 (2003); A.Balzarotti, E.Placidi, F.Arciprete, M.Fanfoni, F.Patella, Physical Review B, 67 115332 (2003); F.Arciprete, C. Goletti, E. Placidi, M.Fanfoni, F.Patella, P. Chiaradia, C. Hogan and A. Balzarotti, Phys. Rev. B 68 125328 (2003).

  6. Study of processes of self-catalyzed growth of gaas crystal nanowires by molecular-beam epitaxy on modified Si (111) surfaces

    SciTech Connect

    Samsonenko, Yu. B. Cirlin, G. E.; Khrebtov, A. I.; Bouravleuv, A. D.; Polyakov, N. K.; Ulin, V. P.; Dubrovskii, V. G.; Werner, P.

    2011-04-15

    The processes of growth of self-catalyzed GaAs crystal nanowires on Si (111) surfaces modified by three different methods are studied. For the technology of production of the GaAs nanowires, molecular-beam epitaxy is used. It is found that, in the range of substrate temperatures between 610 and 630 Degree-Sign C, the surface density of nanowires and their diameter sharply increases, whereas the temperature dependence of the nanowire length exhibits a maximum at 610 Degree-Sign C. An increase in the temperature to 640 Degree-Sign C suppresses the formation of nanowires. The method that provides a means for the fabrication of purely cubic GaAs nanowires is described. A theoretical justification of the formation of the cubic phase in self-catalyzed GaAs nanowires is presented.

  7. Controlling the surface chemistry and chromatographic properties of methacrylate-ester-based monolithic capillary columns via photografting.

    PubMed

    Eeltink, Sebastiaan; Hilder, Emily F; Geiser, Laurent; Svec, Frantisek; Fréchet, Jean M J; Rozing, Gerard P; Schoenmakers, Peter J; Kok, Wim Th

    2007-02-01

    Preparation of monolithic capillary columns for separations in the CEC mode using UV-initiated polymerization of the plain monolith followed by functionalization of its pore surface by photografting has been studied. The first step enabled the preparation of generic poly(butyl methacrylate-co-ethylene dimethacrylate) monoliths with optimized porous properties, controlled by the percentages of porogens 1-decanol and cyclohexanol in the polymerization mixture, irradiation time, and UV light intensity. Ionizable monomers [2-(methacryloyloxy)ethyl]trimethylammonium chloride or 2-acryloamido-2-methyl-1-propanesulfonic acid were then photografted onto the monolithic matrix, allowing us to control the direction of the EOF in CEC. Different strategies were applied to control the grafting density and, thereby, the magnitude of the EOF. To control the hydrophobic properties, two approaches were tested: (i) cografting of a mixture of the ionizable and hydrophobic monomers and (ii) sequential grafting of the ionizable and hydrophobic monomers. Cografting resulted in similar retention but higher EOF. With sequential grafting, more than 50% increase in retention factors was obtained and a slight decrease in EOF was observed due to shielding of the ionizable moieties.

  8. Synthesis of silica aerogel monoliths with controlled specific surface areas and pore sizes

    NASA Astrophysics Data System (ADS)

    Gao, Bingying; Lu, Shaoxiang; Kalulu, Mulenga; Oderinde, Olayinka; Ren, Lili

    2017-07-01

    To replace traditional preparation methods of silica aerogels, a small-molecule 1,2-epoxypropane (PO) has been introduced into the preparation process instead of using ammonia as the cross-linking agent, thus generating a lightweight, high porosity, and large surface area silica aerogel monolithic. We put forward a simple solution route for the chemical synthesis of silica aerogels, which was characterized by scanning electron microscopy (SEM), TEM, XRD, FTIR, thermogravimetric analysis (TGA) and the Brunauer-Emmett-Teller (BET) method In this paper, the effect of the amount of PO on the microstructure of silica aerogels is discussed. The BET surface areas and pore sizes of the resulting silica aerogels can be freely adjusted by changing the amount of PO, which will be helpful in promoting the development of silica aerogels to fabricate other porous materials with similar requirements. We also adopted a new organic solvent sublimation drying (OSSD) method to replace traditional expensive and dangerous drying methods such as critical point drying and freeze drying. This simple approach is easy to operate and has good repeatability, which will further facilitate actual applications of silica aerogels.

  9. Measurement of the Surface Strain Induced by Reconstructed Surfaces of GaAs (001) Using Photoreflectance and Reflectance-Difference Spectroscopies

    NASA Astrophysics Data System (ADS)

    Lastras-Martínez, L. F.; Flores-Camacho, J. M.; Lastras-Martínez, A.; Balderas-Navarro, R. E.; Cardona, M.

    2006-02-01

    We report photoreflectance-difference and reflectance-difference measurements on reconstructed GaAs (001) surfaces. From these data the linear and quadratic electro-optic coefficient spectra are determined in the important 2.8-3.4 eV spectral region. The surface strain and fields induced by the surface reconstruction are also determined. We show experimentally that between c(4×4) and (2×4) surfaces, there is an inversion of the surface electric field which we attribute to a direct piezo-electric effect related to the surface strain induced by reconstruction.

  10. Interaction of Mn with GaAs and InSb: incorporation, surface reconstruction and nano-cluster formation.

    PubMed

    Burrows, C W; Hatfield, S A; Bastiman, F; Bell, G R

    2014-10-01

    The deposition of Mn on to reconstructed InSb and GaAs surfaces, without coincident As or Sb flux, has been studied by reflection high energy electron diffraction, atomic force microscopy and scanning tunnelling microscopy. On both Ga- and As-terminated GaAs(0 0 1), (2 × n) Mn-induced reconstruction domains arise with n = 2 for the most well ordered reconstructions. On the Ga-terminated (4 × 6), the Mn-induced (2 × 2) persists up to around 0.5 ML Mn followed by Mn nano-cluster formation. For deposition on initially β2(2 × 4)-reconstructed GaAs(0 0 1), the characteristic trench structure of the reconstruction is partially preserved even beyond 1 monolayer Mn coverage. On both the β2(2 × 4) and c(4 × 4) surfaces, MnAs-like nano-clusters form alongside the reconstruction changes. In contrast, there are no new Mn-induced surface reconstructions on InSb. Instead, the Sb-terminated surfaces of InSb (0 0 1), (1 1 1)A and (1 1 1)B revert to reconstructions characteristic of clean In-rich surfaces after well defined coverages of Mn proportional to the Sb content of the starting reconstruction. These surfaces are decorated with self-assembled MnSb nanoclusters. These results are discussed in terms of basic thermodynamic quantities and the generalized electron counting rule.

  11. 3-D multilayer monolithic integration of vertical-oriented double-heterojunction GaAs based pHEMT and thermal influence on device parameters

    NASA Astrophysics Data System (ADS)

    Alim, Mohammad A.; Rezazadeh, Ali A.

    2017-06-01

    This study focuses on 3-D multilayer monolithic integration of vertical-oriented double-heterojunction AlGaAs/InGaAs/GaAs based pseudomorphic high electron mobility transistors. The effects of the presence of 3-D components above the active layer were accomplished by comparing three multilayer fabricated device of different thickness with a virgin device where the thickness of the 3-D components e.g., both metal and polyimide layer were varied. The output current, on-state gate leakage, transconductance are found to be decrease with the increase in thickness of the 3-D components and on the other hand, the on-state resistance, knee voltage and off-state gate leakage is increased. Lastly, the thermal influences on the device behaviour such as off-state and on-state gate leakage, barrier inhomogeneities at Schottky contacts, zero temperature coefficients at the transfer curve, and the threshold voltage as a function of drain bias were measured and analyzed for the both pre and post fabricated multilayer devices. These effective comparisons in terms of thickness and temperature of the both device are useful for future designs and optimizations of multilayer vertical stacked 3-D MMICs.

  12. Device and circuit modeling for a 3.5- to 6.5-GHz GaAs monolithic dual-gate FET switch module

    NASA Astrophysics Data System (ADS)

    Fu, Michael C.; Gupta, Ramesh K.

    The design approach and measured performance of a broadband (3.5- to 6.5-GHz), dual-gate field-effect transistor (DGFET) switch module with an on-chip, TTL-compatible switch control circuit are presented. This MMIC switch module is a key element in the development of a highly reliable and lightweight microwave switch matrix. A computer program was developed for modeling the equivalent circuit element values for the DGFET from physical device parameters. The program is used to predict the small-signal, three-port, S-parameters for DGFET devices. These modeled parameters are then used to design a self-biased monolithic DGFET switch module with chip dimensions of 1.5 x 2.5 mm. Measurements show that the switch module has an ON-state gain of approximately 11 dB over the 3.5- to 6.5-GHz range, with better than 50-dB ON- to-OFF isolation. The measured gain in the ON state is within 1 dB of the modeled performance over the 3.5- to 6.5-GHz band.

  13. Influence of GaAs surface termination on GaSb/GaAs quantum dot structure and band offsets

    SciTech Connect

    Zech, E. S.; Chang, A. S.; Martin, A. J.; Canniff, J. C.; Millunchick, J. M.; Lin, Y. H.; Goldman, R. S.

    2013-08-19

    We have investigated the influence of GaAs surface termination on the nanoscale structure and band offsets of GaSb/GaAs quantum dots (QDs) grown by molecular-beam epitaxy. Transmission electron microscopy reveals both coherent and semi-coherent clusters, as well as misfit dislocations, independent of surface termination. Cross-sectional scanning tunneling microscopy and spectroscopy reveal clustered GaSb QDs with type I band offsets at the GaSb/GaAs interfaces. We discuss the relative influences of strain and QD clustering on the band offsets at GaSb/GaAs interfaces.

  14. Local monitoring of atomic steps on GaAs(001) surface under oxidation, wet removal of oxides and thermal smoothing

    NASA Astrophysics Data System (ADS)

    Akhundov, I. O.; Kazantsev, D. M.; Alperovich, V. L.; Sheglov, D. V.; Kozhukhov, A. S.; Latyshev, A. V.

    2017-06-01

    The GaAs(001) step-terraced surface relief is studied under oxidation, wet oxide removal and thermal smoothing by ex situ atomic force microscopy with local monitoring of specific atomic steps using lithographic marks for surface area localization. Oxidation in the air and wet oxide removal lead to the formation of monatomic dips on terraces, while atomic steps keep their position and shape. Monitoring step mean position under thermal smoothing allows us to determine the deviation from equilibrium. The experimental smoothing kinetics is well described by Monte Carlo simulation.

  15. Design concepts of monolithic metamorphic vertical-cavity surface-emitting lasers for the 1300–1550 nm spectral range

    SciTech Connect

    Egorov, A. Yu. Karachinsky, L. Ya.; Novikov, I. I.; Babichev, A. V.; Nevedomskiy, V. N.; Bugrov, V. E.

    2015-11-15

    Possible design concepts for long-wavelength vertical-cavity surface-emitting lasers for the 1300–1550 nm spectral range on GaAs substrates are suggested. It is shown that a metamorphic GaAs–InGaAs heterostructure with a thin buffer layer providing rapid transition from the lattice constant of GaAs to that of In{sub x}Ga{sub 1–x}As with an indium fraction of x < 0.3 can be formed by molecular-beam epitaxy. Analysis by transmission electron microscopy demonstrated the effective localization of mismatch dislocations in the thin buffer layer and full suppression of their penetration into the overlying InGaAs metamorphic layer.

  16. Polymethacrylate monoliths with immobilized poly-3-mercaptopropyl methylsiloxane film for high-coverage surface functionalization by thiol-ene click reaction.

    PubMed

    Carrasco-Correa, Enrique Javier; Ramis-Ramos, Guillermo; Herrero-Martínez, José Manuel; Lämmerhofer, Michael

    2014-11-07

    In this work, new polythiol-functionalized macroporous monolithic polymethacrylate-polysiloxane composite materials are presented which can be useful substrates for highly efficient immobilization of (chiral) catalysts, chromatographic ligands, and other functional moieties by thiol-ene click reaction. Poly(glycidyl methacrylate-co-ethylene dimethacrylate) (poly(GMA-co-EDMA)) monoliths were coated with a poly-3-mercaptopropyl methylsiloxane (PMPMS) film and subsequently the polymer was covalently immobilized by formation of crosslinks via nucleophilic substitution reaction with pendent 2,3-epoxypropyl groups on the monolith surface. This monolith, though, showed similar levels of surface coverage as a reference monolith obtained by opening of the epoxide groups with sodium hydrogen sulfide. However, a 3-step functionalization by amination of the epoxy monolith, followed by its vinylation with allylglycidyl ether and subsequent thiolation by coating of a thin polythiol (PMPMS) film and crosslinking by click reaction furnished a monolith with more than 2-fold elevated thiol coverage. Its further functionalization with a clickable chiral quinine carbamate selector clearly documented the benefit of highly dense thiol surfaces for such reactions and synthesis of functional materials with proper ligand loadings. The new monoliths were chromatographically tested in capillary electrochromatography mode using N-3,5-dinitrobenzoyl-leucine as chiral probe and the capillary column with the monolith having the highest selector coverage, produced from the precursor with the most thiols on the surface, showed the largest separation factor. By performic acid oxidation the surface characteristic could be tuned and strongly altered due to a delicate balance of enantioselective and non-specific interactions.

  17. Effect of the Photoquenching of EL2 in GaAs Substrate on the Piezoelectric Photothermal and Surface Photovoltage Spectra of a GaAs Single Quantum Well Confined by GaAs/AlAs Short-Period Superlattices

    NASA Astrophysics Data System (ADS)

    Wang, Ping; Fukuyama, Atsuhiko; Akashi, Yoshito; Ikari, Tetsuo

    2008-01-01

    Two nondestructive techniques, surface photovoltage (SPV) and piezoelectric photothermal (PPT) spectroscopies, were adopted to investigate a GaAs single quantum well (SQW) confined by GaAs/AlAs short-period superlattices (SPSs) fabricated on a semi-insulating (SI) GaAs substrate, whose absorption spectra cannot be obtained easily using conventional techniques. Excitonic absorptions associated with subband transitions in a GaAs SQW and SPSs were clearly observed. We also examined how a SI-GaAs substrate affects the PPT and SPV spectra, particularly the effect of the photoquenching of the deep donor level EL2. It was found that the photoquenching of EL2 causes a significant change in the total built-in potential at the interface between the epitaxial layers and the substrate, and affected the signal intensities observed in the PPT and SPV spectra. The present experimental results have shown that a large amount of carrier leakage occurs from a GaAs SQW and SPSs to the sample surface, even in the presence of Al0.3Ga0.7As buffer layers.

  18. Smoothness and cleanliness of the GaAs (100) surface after thermal desorption of the native oxide for the synthesis of high mobility structures using molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Lee, J. J. D.; West, K. W.; Baldwin, K. W.; Pfeiffer, L. N.

    2012-10-01

    To prepare a GaAs substrate for molecular beam epitaxial (MBE) growth, the nominal ˜3 nm native oxide is typically thermally desorbed into vacuum. To test the completeness and quality of this desorption, we describe a technique, which combines MBE, thermal desorption, atomic force microscopy (AFM), reflection high-energy electron diffraction (RHEED), and secondary ion mass spectroscopy (SIMS), for detecting roughness and trace residues of contamination on (100) GaAs surfaces before MBE growth. At all desorption temperatures in the range 600-665 °C, our RHEED measurements show that the native oxide is largely desorbed within 4 min. However, the SIMS and AFM data indicate that a residue of carbon invariably remains on the GaAs (100) surface, and tenaciously resists all further attempts at its removal by thermal desorption. Since thermal desorption of the native oxide has long been the standard technique for preparing GaAs substrates for MBE growth, we suggest that MBE growth on GaAs has in general been accomplished by epitaxially growing through a partial monolayer of carbon. We believe this is the likely reason for the generally unsatisfactory quality of GaAs MBE growth after lithographic patterning on previously MBE grown structures. Our AFM data also indicate that extended native oxide desorption times or high desorption temperatures not only are ineffective at removal of the carbon residue, but are always accompanied by additional strong roughening effects on the GaAs surface morphology. Finally, we demonstrate that smoother starting surfaces for MBE growth correlate well with higher two-dimensional carrier mobilities in the resulting AlGaAs/GaAs heterostructures.

  19. Nanoripple formation on GaAs (001) surface by reverse epitaxy during ion beam sputtering at elevated temperature

    NASA Astrophysics Data System (ADS)

    Chowdhury, Debasree; Ghose, Debabrata

    2016-11-01

    Self-organized pattern formation by the process of reverse epitaxial growth has been investigated on GaAs (001) surfaces during 1 keV Ar+ bombardment at target temperature of 450 °C for a wide range of incident angles. Highly ordered ripple formation driven by diffusion instability is evidenced at near normal incidence angles. Concurrent sample rotation shows that the ripple morphology and its orientation do not depend on the incident beam direction; rather they are determined by the symmetry of the crystal face.

  20. Submilliampere continuous-wave room-temperature lasing operation of a GaAs mushroom structure surface-emitting laser

    SciTech Connect

    Yang, Y.J.; Dziura, T.G.; Wang, S.C. ); Hsin, W.; Wang, S. Electronics Research Laboratory, University of California, Berkeley, California 94720 )

    1990-05-07

    We report a GaAs mushroom structure surface-emitting laser at 900 nm with submilliampere (0.2--0.5 mA) threshold under room-temperature cw operation for the first time. The very low threshold current was achieved on devices which consisted of a 2--4 {mu}m diameter active region formed by chemical selective etching, and sandwiched between two Al{sub 0.05}Ga{sub 0.95} As/ Al{sub 0.53}Ga{sub 0.47} As distributed Bragg reflectors of very high reflectivity (98--99%) grown by metalorganic chemical vapor deposition.

  1. A theoretical study of the initial oxidation of the GaAs(001)-β2(2×4) surface

    NASA Astrophysics Data System (ADS)

    Scarrozza, M.; Pourtois, G.; Houssa, M.; Caymax, M.; Stesmans, A.; Meuris, M.; Heyns, M. M.

    2009-12-01

    The early stages of the oxidation of the GaAs(001)-β2(2×4) surface are investigated theoretically by ab initio molecular dynamics simulations. An atomistic mechanism of formation of structural defects at the interface is described. The electronic properties of the GaAs/oxide interface are computed and it is found that energy levels within the bandgap are associated with the generated interfacial structural defects. These results provide an atomistic description of the nature of the defects at the origin of the Fermi level pinning in III-V's as well as the mechanism underlying their generation.

  2. Novel Metal-Sulfur-Based Air-Stable Passivation of GaAs with Very Low Surface State Densities

    SciTech Connect

    Ashby, Carol I.H.; Baca, Albert G.; Chang, P.-C; Hafich, M.J.; Hammons, B.E.; Zavadil, Kevin R.

    1999-08-09

    A new air-stable electronic surface passivation for GaAs and other III-V compound semiconductors that employs sulfur and a suitable metal ion, e.g., Zn, and that is robust towards plasma dielectric deposition has been developed. Initial improvements in photoluminescence are twice that of S-only treatments and have been preserved for >11 months with SiO{sub x}N{sub y} dielectric encapsulation. Photoluminescence and X-ray photoelectron spectroscopies indicate that the passivation consists of two major components with one being stable for >2 years in air. This process improves heterojunction bipolar transistor current gain for both large and small area devices.

  3. Monolithic excitation and manipulation of surface plasmon polaritons on a vertical cavity surface emitting laser

    NASA Astrophysics Data System (ADS)

    Lamy, J.-M.; Justice, J.; Lévêque, G.; Corbett, B.

    2011-06-01

    We report the manipulation of surface plasmon polaritons (SPPs) on a thin Au layer integrated on top of the mirror of a vertical-cavity surface-emitting laser (VCSEL). Gratings etched into the Au layer to different depths are used to couple the light into and out of the film, and to bend the trajectory of the SPP. The result paves the way to compact integrated plasmonic devices.

  4. Laser-driven growth of silver nanoplates on p-Type GaAs substrates and their surface-enhanced raman scattering activity.

    SciTech Connect

    Sun, Y.; Pelton, M.

    2009-03-20

    Contact between aqueous solutions of silver nitrate (AgNO{sub 3}) and pristine surfaces of p-type gallium arsenide (GaAs) wafers results in essentially no reaction at room temperature and in the dark. The galvanic reactions between the GaAs wafers and AgNO{sub 3} can be triggered under illumination of laser beams with power densities higher than a critical value ({approx}15 mW/cm{sup 2} for a 630 nm laser), resulting in the growth of silver (Ag) nanoplates on the GaAs surface. The density and dimensions (including both thickness and edge length) of the resulting nanoplates can be readily tuned by controlling the growth time and laser power density. The as-grown Ag nanoplates on the substrates significantly enhance Raman signals of interesting molecules and serve as a new class of promising surface-enhanced Raman scattering substrates for sensitive chemical detection.

  5. Effective reduction of interfacial traps in Al2O3/GaAs (001) gate stacks using surface engineering and thermal annealing

    NASA Astrophysics Data System (ADS)

    Chang, Y. C.; Merckling, C.; Penaud, J.; Lu, C. Y.; Wang, W.-E.; Dekoster, J.; Meuris, M.; Caymax, M.; Heyns, M.; Kwo, J.; Hong, M.

    2010-09-01

    To effectively passivate the technologically important GaAs (001) surfaces, in situ deposition of Al2O3 was carried out with molecular beam epitaxy. The impacts of initial GaAs surface reconstruction and post-deposition annealing have been systematically investigated. The corresponding interfacial state density (Dit) were derived by applying the conductance method at 25 and 150 °C on both p-type and n-type GaAs metal-oxide-semiconductor capacitors to establish the Dit spectra in proximity of the critical midgap region. We show that significant reduction of Dit near the midgap is achieved by applying an optimized thermal annealing on samples grown on a Ga-rich (4×6) reconstructed surface.

  6. Epitaxial (100) GaAs Thin Films on Sapphire for Surface Acoustic Wave/Electronic Devices.

    DTIC Science & Technology

    1985-12-01

    demonstrated that undoped -,111> single crystal a’ gallium arsenide could be grown on 򒠰> sapphire using the metalorganic chemical vapor deposition...chip. Metalorganic chemical vapor deposition (MO-CVD) was used for all depositions during this work. Sapphire with an orientation of (01 T2 > was...as quartz. d& I SECTION 2 MO-CVD GROWTH SYSTEMS All GaAs depositions were performed in our second MO-CVD system which is also being used in a

  7. Structure of GaSb layers grown on (111) GaAs surfaces

    NASA Astrophysics Data System (ADS)

    Babkevich, A. Yu.; Cowley, R. A.; Mason, N. J.; Shields, P. A.; Stadelman, T.; Brown, S.; Mannix, D.; Paul, D.

    2004-09-01

    The structure of GaSb layers with thicknesses of 70Å, 160Å, and 1260Å grown on GaAs (111) substrates by metal-organic vapor phase epitaxy has been studied by high-resolution x-ray diffraction. The lattice mismatch between the layer and the substrate is large and most of the misfit strain is taken up by a regular network of dislocations localized at the interface between the GaSb and the GaAs. The spacing between the dislocations is about 49Å along the [1¯1¯2] direction. We observe that the layers have both the ABC … and ACB … face-centered-cubic (fcc) domains with a domain size of about 1500Å. The presence of approximately the same volume of both the domains in the overall layer suggests that the particular domain is chosen largely randomly and independent of the orientation of the substrate. In contrast, the results show that the structure of the GaAs substrate was a single fcc domain. The widths of the off-axis Bragg reflections along the [111] direction for the thinnest sample was within error the same as those for the (hhh ) Bragg reflections showing that each fcc domain penetrated through the entire layer.

  8. Ab initio model for GaAs1- x N x chemical beam epitaxy using GaAs(100) surface stability over As2, H2, and N2

    NASA Astrophysics Data System (ADS)

    Valencia, Hubert; Kangawa, Yoshihiro; Kakimoto, Koichi

    2017-06-01

    A model for the chemical beam epitaxy (CBE) of GaAs1- x N x was previously constructed on the basis of first-principles calculations of (100) surfaces of GaAs with As2 and H2 adsorptions and As/N substitution to simulate As2, H2, and N2 mixed gas conditions. We previously demonstrated that this model can be used to predict the temperature and pressure dependences of the growth behavior in metal-organic chemical vapor deposition (MOCVD). In this paper, we show that little modification is needed to transpose this model to CBE experiments. Our model allows us to predict transition temperatures at which Arrhenius regimes of N2 incorporation are changed. Additionally, an explanation of the trend of resulting regimes is given, which is based on the analysis of surface stability during growth at different temperatures.

  9. Characterization and simulation of fast neutron detectors based on surface-barrier VPE GaAs structures with polyethylene converter

    NASA Astrophysics Data System (ADS)

    Chernykh, A. V.; Chernykh, S. V.; Baryshnikov, F. M.; Didenko, S. I.; Burtebayev, N.; Britvich, G. I.; Kostin, M. Yu.; Chubenko, A. P.; Nassurlla, Marzhan; Nassurlla, Maulen; Kerimkulov, Zh.; Zholdybayev, T.; Glybin, Yu. N.; Sadykov, T. Kh.

    2016-12-01

    Fast neutron detectors with an active area of 80 mm2 based on surface-barrier VPE GaAs structures were fabricated and tested. Polyethylene with density of 0.90 g/cm3 was used as a converter layer. The recoil-proton surface-barrier sensor was fabricated on high purity VPE GaAs epilayers with a thickness of 50 μm. The neutron detection efficiency measured with a 241Am-Be source was 1.30 · 10-3 puls./neutr. for the PE converter thickness of 670 μm. The signal-to-gamma-background ratio was at the level of 50. Simulation of the detector characteristics with Geant4 toolkit has showed good correlation with the experimental data and allowed to estimate the maximal theoretical detection efficiency of the detector which is determined by the PE converter and equals to 1.37 · 10-3 puls./neutr. The difference between the measured and simulated values of the detection efficiency is due to the fact that the events with energies below 0.5 MeV were not taken into account during the measurements.

  10. Monolithic cascade-type solar cells

    NASA Technical Reports Server (NTRS)

    Yamamoto, S.; Shibukawa, A.; Yamaguchi, M.

    1985-01-01

    Solar cells consist of a semiconductor base, a bottom cell with a band-gap energy of E1, and a top cell with a band-gap energy of E2, and 0.96 E1 1.36 eV and (0.80 E + 0.77) eV E2 (0.80 E1 + 0.92) eV. A monolithic cascade-type solar cell was prepared with an n(+)-type GaAs base, a GaInAs bottom solar cell, and a GaAiInAs top solar cell. The surface of the cell is coated with a SiO antireflection film. The efficiency of the cell is 32%.

  11. Investigation of ultrafast photothermal surface expansion and diffusivity in GaAs via laser-induced dynamic gratings

    SciTech Connect

    Pennington, D.M.

    1992-04-01

    This thesis details the first direct ultrafast measurements of the dynamic thermal expansion of a surface and the temperature dependent surface thermal diffusivity using a two-color reflection transient grating technique. Studies were performed on p-type, n-type, and undoped GaAs(100) samples over a wide range of temperatures. By utilizing a 90 fs ultraviolet probe with visible excitation beams, the effects of interband saturation and carrier dynamics become negligible; thus lattice expansion due to heating and subsequent contraction caused by cooling provided the dominant influence on the probe. At room temperature a rise due to thermal expansion was observed, corresponding to a maximum net displacement of {approximately} 1 {Angstrom} at 32 ps. The diffracted signal was composed of two components, thermal expansion of the surface and heat flow away from the surface, thus allowing a determination of the rate of expansion as well as the surface thermal diffusivity, D{sub S}. By varying the fringe spacing of the grating, this technique has the potential to separate the signal contributions to the expansion of the lattice in the perpendicular and parallel directions. In the data presented here a large fringe spacing was used, thus the dominant contribution to the rising edge of the signal was expansion perpendicular to the surface. Comparison of he results with a straightforward thermal model yields good agreement over a range of temperatures (20--300{degrees}K). Values for D{sub S} in GaAs were measured and found to be in reasonable agreement with bulk values above 50{degrees}K. Below 50{degrees}K, D{sub S} were determined to be up to an order of magnitude slower than the bulk diffusivity due to increased phonon boundary scattering. The applicability and advantages of the TG technique for studying photothermal and photoacoustic phenomena are discussed.

  12. GaAs optoelectronic neuron arrays

    NASA Technical Reports Server (NTRS)

    Lin, Steven; Grot, Annette; Luo, Jiafu; Psaltis, Demetri

    1993-01-01

    A simple optoelectronic circuit integrated monolithically in GaAs to implement sigmoidal neuron responses is presented. The circuit integrates a light-emitting diode with one or two transistors and one or two photodetectors. The design considerations for building arrays with densities of up to 10,000/sq cm are discussed.

  13. Epitaxial ferromagnetic Fe{sub 3}Si on GaAs(111)A with atomically smooth surface and interface

    SciTech Connect

    Liu, Y. C.; Hung, H. Y.; Kwo, J. E-mail: raynien@phys.nthu.edu.tw; Chen, Y. W.; Lin, Y. H.; Cheng, C. K.; Hong, M. E-mail: raynien@phys.nthu.edu.tw; Tseng, S. C.; Hsu, C. H. E-mail: raynien@phys.nthu.edu.tw; Chang, M. T.; Lo, S. C.

    2015-09-21

    Single crystal ferromagnetic Fe{sub 3}Si(111) films were grown epitaxially on GaAs(111)A by molecular beam epitaxy. These hetero-structures possess extremely low surface roughness of 1.3 Å and interfacial roughness of 1.9 Å, measured by in-situ scanning tunneling microscope and X-ray reflectivity analyses, respectively, showing superior film quality, comparing to those attained on GaAs(001) in previous publications. The atomically smooth interface was revealed by the atomic-resolution Z (atomic number)-contrast scanning transmission electron microscopy (STEM) images using the correction of spherical aberration (Cs)-corrected electron probe. Excellent crystallinity and perfect lattice match were both confirmed by high resolution x-ray diffraction. Measurements of magnetic property for the Fe{sub 3}Si/GaAs(111) yielded a saturation moment of 990 emu/cm{sup 3} with a small coercive field ≤1 Oe at room temperature.

  14. Kinetics of band bending and electron affinity at GaAs(001) surface with nonequilibrium cesium overlayers

    SciTech Connect

    Zhuravlev, A. G.; Savchenko, M. L.; Paulish, A. G.; Alperovich, V. L.; Scheibler, H. E.; Jaroshevich, A. S.

    2013-12-04

    The dosage dependences of surface band bending and effective electron affinity under cesium deposition on the Ga-rich GaAs(001) surface, along with the relaxation of these electronic properties after switching off the Cs source are experimentally studied by means of modified photoreflectance spectroscopy and photoemission quantum yield spectroscopy. At small Cs coverages, below half of a monolayer, additional features in the dosage dependence and subsequent downward relaxation of the photoemission current are determined by the variations of band bending. At coverages above half of a monolayer the upward relaxation of the photocurrent is caused supposedly by the decrease of the electron affinity due to restructuring in the nonequilibrium cesium overlayer.

  15. As-pressure influence on the surface corrugation in the homoepitaxial growth of GaAs (6 3 1)A

    NASA Astrophysics Data System (ADS)

    Cruz-Hernández, E.; Shimomura, S.; López-López, M.; Vázquez-Cortes, D.; Méndez-García, V. H.

    2011-02-01

    The achievement of defect-free and highly uniform semiconductor quantum wires is a projected goal with many potential applications. In this article, we report on the homoepitaxy of GaAs on (6 3 1)A-oriented substrates grown by molecular beam epitaxy (MBE) as a function of the As 4 pressure ( PAs). By finding the optimal growth conditions that allow the minimization of intrinsic surface free energy on the substrate and the PAs value, which results in the optimal adatoms diffusion, we were able to realize the outstanding formation of a periodic array of parallel straight nano facets. An analysis of the autocorrelation function is presented, which can be used to quantitatively describe the periodic surface corrugation, and to investigate the optimal growth conditions. We review the thermodynamic and kinetic factors that contribute to the faceting process and discuss how, by reducing the kinetic influence in the growth process, we can promote homogeneous faceting on high-index substrates.

  16. Monolithic III-V and hybrid polysilicon-III-V microelectromechanical tunable vertical-cavity surface-emitting lasers

    NASA Astrophysics Data System (ADS)

    Ochoa, Edward M.; Lott, James A.; Nelson, Thomas R., Jr.; Harvey, M. C.; Raley, J. A.; Stintz, Andreas; Malloy, Kevin J.

    2003-04-01

    We report our progress on the design and fabrication of electrostatically-actuated microelectromechanical (MEM) tunable wavelength filters and vertical cavity surface-emitting lasers (VCSELs). We investigate both an all-semiconductor monolithic approach and a hybrid approach based on the combination of conventional polysilicon microelectromechanical systems (MEMS) and III-V semiconductor thin-film distributed Bragg reflector (DBR) and VCSEL structures. In the tunable hybrid structures the III-V semiconductor layers are flip-bonded onto specially designed polysilicon foundry MEMS structures and separated from their lattice-matched parent substrates by a novel post-bonding lift-off process.

  17. Capillary electrochromatography with monolithic silica column: I. Preparation of silica monoliths having surface-bound octadecyl moieties and their chromatographic characterization and applications to the separation of neutral and charged species.

    PubMed

    Allen, Darin; El Rassi, Ziad

    2003-01-01

    Monolithic silica columns with surface-bound octadecyl (C18) moieties have been prepared by a sol-gel process in 100 microm ID fused-silica capillaries for reversed-phase capillary electrochromatography of neutral and charged species. The reaction conditions for the preparation of the C18-silica monoliths were optimized for maximum surface coverage with octadecyl moieties in order to maximize retention and selectivity toward neutral and charged solutes with a sufficiently strong electroosmotic flow (> 2 mm/s) to yield rapid analysis time. Furthermore, the effect of the pore-tailoring process on the silica monoliths was performed over a wide range of treatment time with 0.010 M ammonium hydroxide solution in order to determine the optimum time and conditions that yield mesopores of narrow pore size distribution that result in high separation efficiency. Under optimum column fabrication conditions and optimum mobile phase composition and flow velocity, the average separation efficiency reached 160 000 plates/m, a value comparable to that obtained on columns packed with 3 microm C18-silica particles with the advantages of high permeability and virtually no bubble formation. The optimized monolithic C18-silica columns were evaluated for their retention properties toward neutral and charged analytes over a wide range of mobile phase compositions. A series of dimensionless retention parameters were evaluated and correlated to solute polarity and electromigration property. A dimensionless mobility modulus was introduced to describe charged solute migration and interaction behavior with the monolithic C18-silica in a counterflow regime during capillary electrochromatography (CEC )separations. The mobility moduli correlated well with the solute hydrophobic character and its charge-to-mass ratio.

  18. Accelerated colorimetric immunosensing using surface-modified porous monoliths and gold nanoparticles

    NASA Astrophysics Data System (ADS)

    Chuag, Shao-Hsuan; Chen, Guan-Hua; Chou, Hsin-Hao; Shen, Shu-Wei; Chen, Chien-Fu

    2013-08-01

    A rapid and sensitive immunoassay platform integrating polymerized monoliths and gold nanoparticles (AuNPs) has been developed. The porous monoliths are photopolymerized in situ within a silica capillary and serve as solid support for high-mass transport and high-density capture antibody immobilization to create a shorter diffusion length for antibody-antigen interactions, resulting in a rapid assay and low reagent consumption. AuNPs are modified with detection antibodies and are utilized as signals for colorimetric immunoassays without the need for enzyme, substrate and sophisticated equipment for quantitative measurements. This platform has been verified by performing a human IgG sandwich immunoassay with a detection limit of 0.1 ng ml-1. In addition, a single assay can be completed in 1 h, which is more efficient than traditional immunoassays that require several hours to complete.

  19. Quantitative comparison of terahertz emission from (100) InAs surfaces and a GaAs large-aperture photoconductive switch at high fluences.

    PubMed

    Reid, Matthew; Fedosejevs, Robert

    2005-01-01

    InAs has previously been reported to be an efficient emitter of terahertz radiation at low excitation fluences by use of femtosecond laser pulses. The scaling and saturation of terahertz emission from a (100) InAs surface as a function of excitation fluence is measured and quantitatively compared with the emission from a GaAs large-aperture photoconductive switch. We find that, although the instantaneous peak radiated terahertz field from (100) InAs exceeds the peak radiated signals from a GaAs large-aperture photoconductive switch biased at 1.6 kV/cm, the pulse duration is shorter. For the InAs source the total energy radiated is less than can be obtained from a GaAs large-aperture photoconductive switch.

  20. Effect of interaction in the Ga-As-O system on the morphology of a GaAs surface during molecular-beam epitaxy

    NASA Astrophysics Data System (ADS)

    Ageev, O. A.; Balakirev, S. V.; Solodovnik, M. S.; Eremenko, M. M.

    2016-05-01

    A thermodynamic analysis of processes of interphase interaction in the Ga-As-O system has been performed and their theoretical laws have been determined, taking into account nonlinear thermal physical properties of the compounds, the oxide film compositions, and modes of molecular-beam epitaxy of GaAs. The processes of interaction of the native oxide of GaAs with the substrate material and also with Ga and As4 from a vapor gaseous phase have been studied experimentally. The experimental results correlate with the results of the thermodynamic analysis. The laws of influence of the removal of the proper oxide on the evolution of the GaAs surface morphology under conditions of the molecular-beam epitaxy have been proposed.

  1. Coalescence of GaAs on (001) Si nano-trenches based on three-stage epitaxial lateral overgrowth

    SciTech Connect

    He, Yunrui; Wang, Jun Hu, Haiyang; Wang, Qi; Huang, Yongqing; Ren, Xiaomin

    2015-05-18

    The coalescence of selective area grown GaAs regions has been performed on patterned 1.8 μm GaAs buffer layer on Si via metal-organic chemical vapor deposition. We propose a promising method of three-stage epitaxial lateral overgrowth (ELO) to achieve uniform coalescence and flat surface. Rough surface caused by the coalescence of different growth fronts is smoothened by this method. Low root-mean-square surface roughness of 6.29 nm has been obtained on a 410-nm-thick coalesced ELO GaAs layer. Cross-sectional transmission electron microscope study shows that the coalescence of different growth fronts will induce some new dislocations. However, the coalescence-induced dislocations tend to mutually annihilate and only a small part of them reach the GaAs surface. High optical quality of the ELO GaAs layer has been confirmed by low temperature (77 K) photoluminescence measurements. This research promises a very large scale integration platform for the monolithic integration of GaAs-based device on Si.

  2. The synthesis of surface-glycosylated porous monolithic column via aqueous two-phase graft copolymerization and its application in capillary-liquid chromatography.

    PubMed

    Xiong, Xiyue; He, Haiqin; Shu, Yan; Li, Yuxin; Yang, Zihui; Chen, Yingzhuang; Ma, Ming; Chen, Bo

    2016-12-01

    A facile, flexible process was developed for the preparation of surface-glycosylated porous monolithic columns via aqueous two-phase graft copolymerization of polyethylene glycol diacrylate (PEGDA) and water-soluble dextran (dextran sulfate). The formation of poly(PEGDA) porous skeletons and surface glycosylation were achieved via a one-step process without pre-modification of the dextran. The synthesis conditions were thoroughly optimized. The optimal monolithic column exhibited a large dry state surface area (greater than 400m(2)/g), and it was evaluated as a hydrophilic liquid chromatography (HILIC) stationary phase. A typical HILIC mechanism was observed at high organic solvent content (≥65% acetonitrile). In addition, the resulting monolithic column demonstrated the potential use in analysis of complex biological sample and enviroment water. Copyright © 2016 Elsevier B.V. All rights reserved.

  3. Evaluation of modulating field of photoreflectance of surface-intrinsic-n+ type doped GaAs by using photoinduced voltage

    NASA Astrophysics Data System (ADS)

    Lee, W. Y.; Chien, J. Y.; Wang, D. P.; Huang, K. F.; Huang, T. C.

    2002-04-01

    Photoreflectance (PR) of surface-intrinsic-n+ type doped GaAs has been measured for various power densities of pump laser. The spectra exhibited many Franz-Keldysh oscillations, whereby the strength of electric field F in the undoped layer can be determined. The thus obtained Fs are subject to photovoltaic effect and are less than built-in field Fbi. In the previous work we have obtained the relation F≈Fbi-δF/2 when δF≪Fbi by using electroreflectance to simulate PR, where δF is the modulating field of the pump beam. In this work a method was devised to evaluate δF by using photoinduced voltages Vs and, hence, the relation can be verified by PR itself. The δFs obtained by Vs are also consistent with those of using imaginary part of fast Fourier transform of PR spectra.

  4. The design of a GaAs MMIC L-band voltage controlled oscillator in a surface mount package

    NASA Astrophysics Data System (ADS)

    Olsen, Alan; Ravid, Shmuel

    1991-09-01

    The design, fabrication, and performance characteristics of an L-band voltage controlled oscillator (VCO) in a surface-mount package utilizing two GaAs MMIC chips are described. The VCO generates a +15 dBm minimum output signal that is voltage tunable over an 8-10-percent bandwidth centered anywhere in the lower L-band (1-1.5 GHz). The design approach provides a frequency stability of better than + or - 4 MHz over the temperature range -54 to +85 C, a tuning sensitivity linearity of better than + or - 1 MHz, and a phase noise performance of less than -120 dBc/Hz at 100 kHz from the carrier frequency.

  5. Annealing behavior of a Cs2O/Cs2O2)/GaAs(110 surface studied by electron spectroscopy

    NASA Astrophysics Data System (ADS)

    Wu, J. X.; Li, F. Q.; Zhu, J. S.; Ji, M. R.; Ma, M. S.

    2002-09-01

    A Cs2O/Cs2O2 overlayer was prepared by simultaneous oxygen-cesium adsorption on GaAs(110) at room temperature. In situ electron spectroscopy and work function measurements have been used to study the Cs2O/Cs2O2/GaAs surface as a function of annealing temperature. The Cs2O/Cs2O2/GaAs surface exhibits metallic and has a work function value of 0.9 eV. There are Cs-O-Ga, Cs-O-As, As-O, and Ga-O bonds at the interface of Cs2O2/GaAs. Annealing facilitates the interfacial reaction and the minimum of the work function (0.7 eV) was observed after annealing at 540 K. After the decomposition of Cs2O and Cs2O2 at 620 K, the surface dominated by the Cs-O-Ga and Cs-O-As species remains negative electron affinity with a work function value of 1.1 eV. For further annealing, the fast Cs desorption is associated with the decomposition of the Cs-O-Ga and Ca-O-As bonds as well as the evaporations of As2O3 and CsAsO2, forming Ga2O3. copyright 2002 American Vacuum Society.

  6. GaAs Gigabit Monolithic Optoelectronic Transmitter.

    DTIC Science & Technology

    1983-10-01

    required for laser fabrication is the major advantage of Honeywell’s laser-in-a-well concept. The most critical processing step for the laser-in-a-well is...HEAT SINK Figure 51. Detail of the Laser/Multiplexer Chip Carrier Assembly The 14 wafers that completed the initial laser fabrication steps were sent...capabilities. It is not known if all of these char- acteristics can be achieved in a single laser or if trade-offs will be required. * The laser

  7. Monolithic Domes.

    ERIC Educational Resources Information Center

    Lanham, Carol

    2002-01-01

    Describes how the energy savings, low cost, and near-absolute protection from tornadoes provided by monolithic domes is starting to appeal to school districts for athletic and other facilities, including the Italy (Texas) Independent School District. Provides an overview of monolithic dome construction. (EV)

  8. Monolithic Millimeter Wave Oscillator

    NASA Astrophysics Data System (ADS)

    Wang, Nan-Lei

    There is an increasing interest in the millimeter -wave spectrum for use in communications and for military and scientific applications. The concept of monolithic integration aims to produce very-high-frequency circuits in a more reliable, reproducible way than conventional electronics, and also at lower cost, with smaller size and lighter weight. In this thesis, a negative resistance device is integrated monolithically with a resonator to produce an effective oscillator. This work fills the void resulting from the exclusion of the local oscillator from the monolithic millimeter-wave integrated circuit (MMMIC) receiver design. For convenience a microwave frequency model was used to design the resonator circuit. A 5 GHz hybrid oscillator was first fabricated to test the design; the necessary GaAs process technology was developed for the fabrication. Negative resistance devices and oscillator theory were studied, and a simple but practical model of the Gunn diode was devised to solve the impedance matching problem. Monolithic oscillators at the Ka band (35 GHz) were built and refined. All devices operated in CW mode. By means of an electric-field probe, the output power was coupled into a metallic waveguide for measurement purposes. The best result was 3.63 mW of power output, the highest efficiency was 0.43% and the frequency stability was better than 10-4. In the future, an IMPATT diode could replace the Gunn device to give much higher power and efficiency. A varactor-tuned circuit also suitable for large-scale integration is under study.

  9. Hypercrosslinked large surface area porous polymer monoliths for hydrophilic interaction liquid chromatography of small molecules featuring zwitterionic functionalities attached to gold nanoparticles held in layered structure.

    PubMed

    Lv, Yongqin; Lin, Zhixing; Svec, Frantisek

    2012-10-16

    A novel approach to porous polymer monoliths hypercrosslinked to obtain large surface areas and modified with zwitterionic functionalities through the attachment of gold nanoparticles in a layered architecture has been developed. The capillary columns were used for the separation of small molecules in hydrophilic interaction liquid chromatography mode. First, a monolith with a very large surface area of 430 m(2)/g was prepared by hypercrosslinking from a generic poly(4-methylstyrene-co-vinylbenzyl chloride-co-divinylbenzene) monolith via a Friedel-Crafts reaction catalyzed with iron chloride. Free radical bromination then provided this hypercrosslinked monolith with 5.7 at % Br that further reacted with cystamine under microwave irradiation, resulting in a product containing 3.8 at % sulfur. Clipping the disulfide bonds with tris(2-carboxylethyl) phosphine liberated the desired thiol groups that bind the first layer of gold nanoparticles. These immobilized nanoparticles were an intermediate ligand enabling the attachment of polyethyleneimine as a spacer followed by immobilization of the second layer of gold nanoparticles which were eventually functionalized with zwitterionic cysteine. This layered architecture, prepared using 10 nm nanoparticles, contains 17.2 wt % Au, more than twice than that found in the first layer alone. Chromatographic performance of these hydrophilic monolithic columns was demonstrated with the separation of mixtures of nucleosides and peptides in hydrophilic interaction chromatography (HILIC) mode. A column efficiency of 51,000 plates/m was achieved for retained analyte cytosine.

  10. High-k gate dielectric GaAs MOS device with LaON as interlayer and NH3-plasma surface pretreatment

    NASA Astrophysics Data System (ADS)

    Liu, Chao-Wen; Xu, Jing-Ping; Liu, Lu; Lu, Han-Han

    2015-12-01

    High-k gate dielectric HfTiON GaAs metal-oxide-semiconductor (MOS) capacitors with LaON as interfacial passivation layer (IPL) and NH3- or N2-plasma surface pretreatment are fabricated, and their interfacial and electrical properties are investigated and compared with their counterparts that have neither LaON IPL nor surface treatment. It is found that good interface quality and excellent electrical properties can be achieved for a NH3-plasma pretreated GaAs MOS device with a stacked gate dielectric of HfTiON/LaON. These improvements should be ascribed to the fact that the NH3-plasma can provide H atoms and NH radicals that can effectively remove defective Ga/As oxides. In addition, LaON IPL can further block oxygen atoms from being in-diffused, and Ga and As atoms from being out-diffused from the substrate to the high-k dielectric. This greatly suppresses the formation of Ga/As native oxides and gives rise to an excellent high-k/GaAs interface. Project supported by the National Natural Science Foundation of China (Grant Nos. 61176100 and 61274112).

  11. Half-metallicity at the Heusler alloy Co(2)Cr(0.5)Fe(0.5)Al(001) surface and its interface with GaAs(001).

    PubMed

    Zarei, Sareh; Javad Hashemifar, S; Akbarzadeh, Hadi; Hafari, Zohre

    2009-02-04

    Electronic and magnetic properties of the Heusler alloy Co(2)Cr(0.5)Fe(0.5)Al(001) surfaces and its interfaces with GaAs(001) are studied within the framework of density functional theory by using the plane-wave pseudopotential approach. The phase diagram obtained by ab initio atomistic thermodynamics shows that the CrAl surface is the most stable (001) termination of this Heusler alloy. We discuss that, at the ideal surfaces and interfaces with GaAs, half-metallicity of the alloy is lost, although the CrAl surface keeps high spin polarization. The energy band profile of the stable interface is investigated and a negative p Schottky barrier of -0.78 eV is obtained for this system.

  12. Chemotaxis for enhanced immobilization of Escherichia coli and Legionella pneumophila on biofunctionalized surfaces of GaAs.

    PubMed

    Hassen, Walid M; Sanyal, Hashimita; Hammood, Manar; Moumanis, Khalid; Frost, Eric H; Dubowski, Jan J

    2016-06-20

    The authors have investigated the effect of chemotaxis on immobilization of bacteria on the surface of biofunctionalized GaAs (001) samples. Escherichia coli K12 bacteria were employed to provide a proof-of-concept of chemotaxis-enhanced bacterial immobilization, and then, these results were confirmed using Legionella pneumophila. The recognition layer was based on a self-assembled monolayer of thiol functionalized with specific antibodies directed toward E. coli or L. pneumophila, together with the enzyme beta-galactosidase (β-gal). The authors hypothesized that this enzyme together with its substrate lactose would produce a gradient of glucose which would attract bacteria toward the biochip surface. The chemotaxis effect was monitored by comparing the number of bacteria bound to the biochip surface with and without attractant. The authors have observed that β-gal plus lactose enhanced the immobilization of bacteria on our biochips with a higher effect at low bacterial concentrations. At 100 and 10 bacteria/ml, respectively, for E. coli and L. pneumophila, the authors observed up to 11 and 8 times more bacteria bound to biochip surfaces assisted with the chemotaxis effect in comparison to biochips without chemotaxis. At 10(4) bacteria/ml, the immobilization enhancement rate did not exceed two times.

  13. Strain relaxation induced surface morphology of heterogeneous GaInNAs layers grown on GaAs substrate

    NASA Astrophysics Data System (ADS)

    Gelczuk, Ł.; Jóźwiak, G.; Moczała, M.; Dłużewski, P.; Dąbrowska-Szata, M.; Gotszalk, T. P.

    2017-07-01

    The partially-relaxed heterogeneous GaInNAs layers grown on GaAs substrate by atmospheric pressure vapor phase epitaxy (AP-MOVPE) were investigated by transmission electron microscopy (TEM) and atomic force microscopy (AFM). The planar-view TEM image shows a regular 2D network of misfit dislocations oriented in two orthogonal <1 1 0> crystallographic directions at the (0 0 1) layer interface. Moreover, the cross-sectional view TEM image reveals InAs-rich and V-shaped precipitates in the near surface region of the GaInNAs epitaxial layer. The resultant undulating surface morphology, known as a cross-hatch pattern, is formed as observed by AFM. The numerical analysis of the AFM image of the GaInNAs layer surface with the well-defined cross-hatch morphology enabled us to determine a lower bound of actual density of misfit dislocations. However, a close correspondence between the asymmetric distribution of interfacial misfit dislocations and undulating surface morphology is observed.

  14. A study of the compositional changes in chemically etched, Ar ion bombarded and reactive ion etched GaAs(100) surfaces by means of ARXPS and LEISS

    NASA Astrophysics Data System (ADS)

    Sullivan, J. L.; Yu, W.; Saied, S. O.

    1995-11-01

    The effects of chemical etching, noble gas ion bombardment and reactive ion etching on GaAs(100) surfaces was investigated by angle resolved X-ray photoelectron spectroscopy (ARXPS) and low energy ion scattering spectroscopy (LEISS). The results show that at the "as received" GaAs surface, Ga oxide is the major component, resulting in a Ga concentration slightly higher than As. Chemical cleaning by hydrochloric acid (at a HCl(conc.) to H 2O ratio of 1:1) followed by solvent washing efficiently removed the oxide layer, however, ARXPS showed that strong As enrichment occurs at the cleaned GaAs surface. Ion bombardment was carried out using 3 keV Ar ions with a beam current density of 1 μA cm -2 for a period of 50 min. XPS results show that at steady state the ion bombarded GaAs surface is depleted in As ( As/Ga ≈ 0.8 ), but ARXPS indicates an As increase at the very surface. This is further confirmed by Ne + LEISS analysis, which shows in the top layer the As concentration is increased by 50% after ion bombardment. The results indicate that bombardment induced compositional changes in this surface are due to Gibssian segregation. The results of reactive ion etching in a 200 W Freon 12 plasma for a period of 5 min at 60 mTorr, showed that this apparently low damage process also produces significant compositional changes in the surface. The report illustrates the benefits of using complementary surface analytical techniques in such studies.

  15. Monolithic silica-based capillary column with strong chiral cation-exchange type surface modification for enantioselective non-aqueous capillary electrochromatography.

    PubMed

    Preinerstorfer, Beatrix; Lubda, Dieter; Lindner, Wolfgang; Lämmerhofer, Michael

    2006-02-17

    A silica-based monolithic stationary phase prepared by the sol-gel process in a 100 microm I.D. fused-silica (FS) capillary has been modified chemically with 3-mercaptopropyl trimethoxysilane followed by immobilization of a strong cation-exchange (SCX) type chiral selector, (S)-N-(4-allyloxy-3,5-dichlorobenzoyl)-2-amino-3,3-dimethylbutane phosphonic acid, by radical addition reaction onto the reactive sulfhydryl surface. After a fine-tuning of the mobile phase composition, the enantioselective capillary column was evaluated for the separation of various chiral basic drugs by enantioselective non-aqueous capillary electrochromatography (CEC), in comparison to capillary column analogs packed with 3.5 microm silica particles having attached the same selector. The performance of the monolithic silica column was further compared to corresponding polymethacrylate-based organic polymer monoliths. The study indicated that strong counter-ions such as 2-aminobutanol or N,N,N',N'-tetramethylethylenediamine are needed, although they reduce the electroosmotic flow velocity and separation factors in comparison to less efficient counter-ions, in order to allow the elution of the oppositely charged solutes in the ion-exchange retention mode within reasonable run time and as sharp zones. In contrast, weak counter-ions such as N,N-diisopropylethylamine (Huenig base) provided stronger electroosmotic flow and much better separation factors, but relatively poor peak efficiencies. Overall, with the chemically functionalized monolithic silica column the high quality separations of packed column analogs could be approximated, with regards to both separation factors and peak performances. On the other hand, the monolithic capillary column certainly outperformed the packed column in terms of system robustness under capillary electrochromatography conditions and showed excellent column longevity. The enantioselective strong cation-exchange-type monolithic silica column performed also well in

  16. LEC GaAs for integrated circuit applications

    NASA Technical Reports Server (NTRS)

    Kirkpatrick, C. G.; Chen, R. T.; Homes, D. E.; Asbeck, P. M.; Elliott, K. R.; Fairman, R. D.; Oliver, J. D.

    1984-01-01

    Recent developments in liquid encapsulated Czochralski techniques for the growth of semiinsulating GaAs for integrated circuit applications have resulted in significant improvements in the quality and quantity of GaAs material suitable for device processing. The emergence of high performance GaAs integrated circuit technologies has accelerated the demand for high quality, large diameter semiinsulating GaAs substrates. The new device technologies, including digital integrated circuits, monolithic microwave integrated circuits and charge coupled devices have largely adopted direct ion implantation for the formation of doped layers. Ion implantation lends itself to good uniformity and reproducibility, high yield and low cost; however, this technique also places stringent demands on the quality of the semiinsulating GaAs substrates. Although significant progress was made in developing a viable planar ion implantation technology, the variability and poor quality of GaAs substrates have hindered progress in process development.

  17. High-spectral-radiance, red-emitting tapered diode lasers with monolithically integrated distributed Bragg reflector surface gratings.

    PubMed

    Feise, David; John, Wilfred; Bugge, Frank; Fiebig, Christian; Blume, Gunnar; Paschke, Katrin

    2012-10-08

    A red-emitting tapered diode laser with a monolithically integrated distributed Bragg reflector grating is presented. The device is able to emit up to 1 W of spectrally stabilized optical output power at 5°C. Depending on the period of the tenth order surface grating the emission wavelengths of these devices from the same gain material are 635 nm, 637 nm, and 639 nm. The emission is as narrow as 9 pm (FWHM) at 637.6 nm. The lateral beam quality is M(2)(1/e(2)) = 1.2. Therefore, these devices simplify techniques such as wavelength multiplexing and fiber coupling dedicating them as light sources for µ-Raman spectroscopy, absolute distance interferometry, and holographic imaging.

  18. Characterization of two MMIC GaAs switch matrices at microwave frequencies

    NASA Technical Reports Server (NTRS)

    Fujikawa, Gene

    1990-01-01

    Monolithic GaAs microwave switch matrices for use in satellite switched, time division multiple access communication systems were developed. Two monolithic GaAs MESFET switch matrices were fabricated; one for switching operation at intermediate frequencies, 3.5 to 6.0 GHz, and another for switching at radio frequencies, 17.7 to 20.2 GHz. Key switch parameters were measured for both switch matrices.

  19. Characterization of two MMIC GaAs switch matrices at microwave frequencies

    NASA Astrophysics Data System (ADS)

    Fujikawa, Gene

    Monolithic GaAs microwave switch matrices for use in satellite switched, time division multiple access communication systems were developed. Two monolithic GaAs MESFET switch matrices were fabricated; one for switching operation at intermediate frequencies, 3.5 to 6.0 GHz, and another for switching at radio frequencies, 17.7 to 20.2 GHz. Key switch parameters were measured for both switch matrices.

  20. Comparison of the reactivity of alkyl and alkyl amine precursors with native oxide GaAs(100) and InAs(100) surfaces

    NASA Astrophysics Data System (ADS)

    Henegar, A. J., , Dr.; Gougousi, T., , Prof.

    2016-12-01

    In this manuscript we compare the interaction of alkyl (trimethyl aluminum) and alkyl amine (tetrakis dimethylamino titanium) precursors during thermal atomic layer deposition with III-V native oxides. For that purpose we deposit Al2O3 and TiO2, using H2O as the oxidizer, on GaAs(100) and InAs(100) native oxide surfaces. We find that there are distinct differences in the behavior of the two films. For the Al2O3 ALD very little native oxide removal happens after the first few ALD cycles while the interaction of the alkyl amine precursor for TiO2 and the native oxides continues well after the surface has been covered with 2 nm of TiO2. This difference is traced to the superior properties of Al2O3 as a diffusion barrier. Differences are also found in the behavior of the arsenic oxides of the InAs and GaAs substrates. The arsenic oxides from the InAs surface are found to mix more efficiently in the growing dielectric film than those from the GaAs surface. This difference is attributed to lower native oxide stability as well as an initial diffusion path formation by the indium oxides.

  1. Au and Al Schottky barrier formation on GaAs (100) surfaces prepared by thermal desorption of a protective arsenic coating

    SciTech Connect

    Spindt, C.J.; Yamada, M.; Meissner, P.L.; Miyano, K.E.; Herrera, A.; Spicer, W.E. . Stanford Electronics Labs.); Arko, A.J. ); Woodall, J.M.; Pettit, G.D. . Thomas J. Watson Research Center)

    1991-01-01

    Photoelectron spectroscopy has been used as a tool to investigate the initial stages of Schottky barrier formation on GaAs (100) surfaces. This is a popular technique that has been used by many researchers in the past to measure the band bending (or shift) of the valence band and conduction band (a measure of the Schottky barrier shift), while the Fermi level remains fixed at the system ground (i.e., the ground of the spectrometer). Metal deposition on a semiconductor surface can alter the Schottky barrier at the surface and pin the Fermi level near the middle of the energy gap. Extremely clean and crystallographically perfect surfaces are required in this study. Toward this end, a method of protecting the GaAs surface was employed which consists of capping the GaAs surface with a layer of As. Upon introduction into the high vacuum system the As is thermally desorbed, revealing a pure GaAs surface. Our work was motivated by a previous study (Brillson et al) on similarly capped specimens, which suggested that metal overlayers do not pin the Schottky barrier in GaAs. Barrier heights varied by as much as 0.75 eV between Al and Au overlayers. This large energy range is a striking result in view of the fact that a considerable number of prior studies on both (110) and (100) surfaces have found that all metals will pin within a narrow (0.25 eV) range at midgap. We repeated the measurements of Brillson on the identically doped samples used in their study using two extreme range metals of Au and Al as overlayers. We found that the barrier height measurements on low doped n-type samples used in this work and in the previous work are affected by photovoltaic effects, even at room temperature. This was determined from taking spectra at a number of temperatures between 20 K and room temperature and looking for shifts. 16 refs., 7 figs.

  2. Monolithic THz Frequency Multipliers

    NASA Technical Reports Server (NTRS)

    Erickson, N. R.; Narayanan, G.; Grosslein, R. M.; Martin, S.; Mehdi, I.; Smith, P.; Coulomb, M.; DeMartinez, G.

    2001-01-01

    Frequency multipliers are required as local oscillator sources for frequencies up to 2.7 THz for FIRST and airborne applications. Multipliers at these frequencies have not previously been demonstrated, and the object of this work was to show whether such circuits are really practical. A practical circuit is one which not only performs as well as is required, but also can be replicated in a time that is feasible. As the frequency of circuits is increased, the difficulties in fabrication and assembly increase rapidly. Building all of the circuit on GaAs as a monolithic circuit is highly desirable to minimize the complexity of assembly, but at the highest frequencies, even a complete monolithic circuit is extremely small, and presents serious handling difficulty. This is compounded by the requirement for a very thin substrate. Assembly can become very difficult because of handling problems and critical placement. It is very desirable to make the chip big enough to that it can be seen without magnification, and strong enough that it may be picked up with tweezers. Machined blocks to house the chips present an additional challenge. Blocks with complex features are very expensive, and these also imply very critical assembly of the parts. It would be much better if the features in the block were as simple as possible and non-critical to the function of the chip. In particular, grounding and other electrical interfaces should be done in a manner that is highly reproducible.

  3. Evaluation of microshear bond strength of orthodontic resin cement to monolithic zirconium oxide as a function of surface conditioning method.

    PubMed

    Bavbek, Nehir Canigur; Roulet, Jean-François; Ozcan, Mutlu

    2014-10-01

    To evaluate the microshear bond strength (μSBS) of orthodontic resin cement to monolithic zirconium oxide ceramic (MZ) after different surface conditioning methods. Two types of MZ (BruxZir Solid Zirconia, n = 60; Prettau-Zirkon, n = 60) with two types of surface finish (glazed, n = 30 per group; polished, n = 30 per group) were tested after two surface conditioning methods: 1. air abrasion with 30-μm silica coated aluminum oxide (Al₂O₃) particles (CoJet), or 2. air abrasion with 50-μm Al₂O₃particles. The non-conditioned group acted as the control. A universal primer (Monobond-Plus) and an orthodontic primer (Transbond-XT Primer) were applied to all specimen surfaces. Orthodontic resin composite (Transbond-XT) was bonded using a mold and photopolymerized. The bonded specimens were subjected to μSBS testing (0.5 mm/min). Data were analyzed statistically using three-way ANOVA and the Sidac adjustment post-hoc test (α = 0.05). Failure modes were analyzed using a stereomicroscope (30X). Mean μSBS values (MPa) did not show a significant difference between the two brands of MZ (p > 0.05). In both glazed (44 ± 6.4) and polished (45.9 ± 4.8) groups, CoJet application showed the highest μSBS values (p < 0.001). The control group (34.4 ± 6) presented significantly better results compared to that of Al₂O₃(30 ± 3.8) (p < 0.05) on glazed surfaces, but it was the opposite in the polished groups (control: 20.3 ± 4.7; Al₂O₃: 33.8 ± 4.7; p < 0.001). Adhesive failure was the dominant type in all groups. Conditioning MZs with Al₂O₃and CoJet increased the percentage of mixed failure type. Air abrasion with CoJet followed by the application of universal primer improved the μSBS of orthodontic resin to both the polished and glazed monolithic zirconium oxide materials tested.

  4. Surface Chemistry and Interface Evolution during the Atomic Layer Deposition of High-k Metal Oxides on InAs(100) and GaAs(100) Surfaces

    NASA Astrophysics Data System (ADS)

    Henegar, Alex J.

    Device scaling has been key for creating faster and more powerful electronic devices. Integral circuit components like the metal-oxide semiconductor field-effect transistor (MOSFET) now rely on material deposition techniques, like atomic layer deposition (ALD), that possess atomic-scale thickness precision. At the heart of the archetypal MOSFET is a SiO2/Si interface which can be formed to near perfection. However when the thickness of the SiO 2 layer is shrunk down to a few nanometers several complications arise like unacceptably high leakage current and power consumption. Replacing Si with III-V semiconductors and SiO2 with high-k dielectric materials is appealing but comes with its own set of challenges. While SiO2 is practically defect-free, the native oxides of III-Vs are poor dielectrics. In this dissertation, the surface chemistry and interface evolution during the ALD of high-k metal oxides on Si(100), GaAs(100) and InAs(100) was studied. In particular, the surface chemistry and crystallization of TiO2 films grown on Si(100) was investigated using transmission Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and atomic force microscopy (AFM). Large, stable, and highly reactive anatase TiO2 grains were found to form during a post-deposition heat treatment after the ALD at 100 °C. The remainder of this work was focused on the evolution of the interfacial oxides during the deposition of TiO2 and Al2O3 on InAs(100) and GaAs(100) and during the deposition of Ta2O 5 on InAs(100). In summary the ALD precursor type, deposited film, and substrate had an influence in the evolution of the native oxides. Alkyl amine precursors fared better at removing the native oxides but the deposited films (TiO2 and Ta2O5) were susceptible to significant native oxide diffusion. The alkyl precursor used for the growth of Al 2O3 was relatively ineffective at removing the oxides but was

  5. Microfluidic devices and methods including porous polymer monoliths

    DOEpatents

    Hatch, Anson V.; Sommer, Gregory j.; Singh, Anup K.; Wang, Ying-Chih; Abhyankar, Vinay

    2015-12-01

    Microfluidic devices and methods including porous polymer monoliths are described. Polymerization techniques may be used to generate porous polymer monoliths having pores defined by a liquid component of a fluid mixture. The fluid mixture may contain iniferters and the resulting porous polymer monolith may include surfaces terminated with iniferter species. Capture molecules may then be grafted to the monolith pores.

  6. Microfluidic devices and methods including porous polymer monoliths

    DOEpatents

    Hatch, Anson V; Sommer, Gregory J; Singh, Anup K; Wang, Ying-Chih; Abhyankar, Vinay V

    2014-04-22

    Microfluidic devices and methods including porous polymer monoliths are described. Polymerization techniques may be used to generate porous polymer monoliths having pores defined by a liquid component of a fluid mixture. The fluid mixture may contain iniferters and the resulting porous polymer monolith may include surfaces terminated with iniferter species. Capture molecules may then be grafted to the monolith pores.

  7. Self-catalyzed GaAs nanowires on silicon by hydride vapor phase epitaxy.

    PubMed

    Dong, Zhenning; André, Yamina; Dubrovskii, Vladimir G; Bougerol, Catherine; Leroux, Christine; Ramdani, Mohammed R; Monier, Guillaume; Trassoudaine, Agnès; Castelluci, Dominique; Gil, Evelyne

    2017-03-24

    Gold-free GaAs nanowires on silicon substrates can pave the way for monolithic integration of photonic nanodevices with silicon electronic platforms. It is extensively documented that the self-catalyzed approach works well in molecular beam epitaxy but is much more difficult to implement in vapor phase epitaxies. Here, we report the first gallium-catalyzed hydride vapor phase epitaxy growth of long (more than 10 μm) GaAs nanowires on Si(111) substrates with a high integrated growth rate up to 60 μm h(-1) and pure zincblende crystal structure. The growth is achieved by combining a low temperature of 600 °C with high gaseous GaCl/As flow ratios to enable dechlorination and formation of gallium droplets. GaAs nanowires exhibit an interesting bottle-like shape with strongly tapered bases, followed by straight tops with radii as small as 5 nm. We present a model that explains the peculiar growth mechanism in which the gallium droplets nucleate and rapidly swell on the silicon surface but then are gradually consumed to reach a stationary size. Our results unravel the necessary conditions for obtaining gallium-catalyzed GaAs nanowires by vapor phase epitaxy techniques.

  8. Self-catalyzed GaAs nanowires on silicon by hydride vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    Dong, Zhenning; André, Yamina; Dubrovskii, Vladimir G.; Bougerol, Catherine; Leroux, Christine; Ramdani, Mohammed R.; Monier, Guillaume; Trassoudaine, Agnès; Castelluci, Dominique; Gil, Evelyne

    2017-03-01

    Gold-free GaAs nanowires on silicon substrates can pave the way for monolithic integration of photonic nanodevices with silicon electronic platforms. It is extensively documented that the self-catalyzed approach works well in molecular beam epitaxy but is much more difficult to implement in vapor phase epitaxies. Here, we report the first gallium-catalyzed hydride vapor phase epitaxy growth of long (more than 10 μm) GaAs nanowires on Si(111) substrates with a high integrated growth rate up to 60 μm h‑1 and pure zincblende crystal structure. The growth is achieved by combining a low temperature of 600 °C with high gaseous GaCl/As flow ratios to enable dechlorination and formation of gallium droplets. GaAs nanowires exhibit an interesting bottle-like shape with strongly tapered bases, followed by straight tops with radii as small as 5 nm. We present a model that explains the peculiar growth mechanism in which the gallium droplets nucleate and rapidly swell on the silicon surface but then are gradually consumed to reach a stationary size. Our results unravel the necessary conditions for obtaining gallium-catalyzed GaAs nanowires by vapor phase epitaxy techniques.

  9. Chemical effect of inert argon beam on nitride nanolayer formed by ion implantation into GaAs surface

    NASA Astrophysics Data System (ADS)

    Mikoushkin, V. M.

    2010-12-01

    The composition of a nitride nanolayer formed on a GaAs(100) surface by the implantation of ions with an energy of E i = 2.5 keV and the chemical state of nitrogen in this layer have been studied by the method of Auger electron spectroscopy. It is established that, in addition to GaN, a GaAsN solid solution phase is formed in the ion-implanted layer. The energies of N KVV Auger electron transitions in these phases are determined as E A (GaN) = 379.8 ± 0.2 eV and E A (GaAsN) = 382.8 ± 0.2 eV (relative to the Fermi level), which allowed the distribution of nitrogen between these phases to be evaluated as [N(GaN)] = 70% and [N(GaAsN)] = 30%. It is established that an argon ion beam produces a chemical effect on the nitride layer, which is related to a cascade mixing of the material. Under the action of the argon ion bombardment, the distribution of nitrogen in the indicated phases changes to opposite. As a result a nitride nanolayer is formed in which the narrow-bandgap semiconductor (GaAsN) predominates rather than the wide-bandgap component (GaN).

  10. Monolithic microwave integrated circuit technology for advanced space communication

    NASA Technical Reports Server (NTRS)

    Ponchak, George E.; Romanofsky, Robert R.

    1988-01-01

    Future Space Communications subsystems will utilize GaAs Monolithic Microwave Integrated Circuits (MMIC's) to reduce volume, weight, and cost and to enhance system reliability. Recent advances in GaAs MMIC technology have led to high-performance devices which show promise for insertion into these next generation systems. The status and development of a number of these devices operating from Ku through Ka band will be discussed along with anticipated potential applications.

  11. Imaging and chemical surface analysis of biomolecular functionalization of monolithically integrated on silicon Mach-Zehnder interferometric immunosensors

    NASA Astrophysics Data System (ADS)

    Gajos, Katarzyna; Angelopoulou, Michailia; Petrou, Panagiota; Awsiuk, Kamil; Kakabakos, Sotirios; Haasnoot, Willem; Bernasik, Andrzej; Rysz, Jakub; Marzec, Mateusz M.; Misiakos, Konstantinos; Raptis, Ioannis; Budkowski, Andrzej

    2016-11-01

    Time-of-flight secondary ion mass spectrometry (imaging, micro-analysis) has been employed to evaluate biofunctionalization of the sensing arm areas of Mach-Zehnder interferometers monolithically integrated on silicon chips for the immunochemical (competitive) detection of bovine κ-casein in goat milk. Biosensor surfaces are examined after: modification with (3-aminopropyl)triethoxysilane, application of multiple overlapping spots of κ-casein solutions, blocking with 100-times diluted goat milk, and reaction with monoclonal mouse anti-κ-casein antibodies in blocking solution. The areas spotted with κ-casein solutions of different concentrations are examined and optimum concentration providing homogeneous coverage is determined. Coverage of biosensor surfaces with biomolecules after each of the sequential steps employed in immunodetection is also evaluated with TOF-SIMS, supplemented by Atomic force microscopy and X-ray photoelectron spectroscopy. Uniform molecular distributions are observed on the sensing arm areas after spotting with optimum κ-casein concentration, blocking and immunoreaction. The corresponding biomolecular compositions are determined with a Principal Component Analysis that distinguished between protein amino acids and milk glycerides, as well as between amino acids characteristic for Mabs and κ-casein, respectively. Use of the optimum conditions (κ-casein concentration) for functionalization of chips with arrays of ten Mach-Zehnder interferometers provided on-chips assays with dramatically improved both intra-chip response repeatability and assay detection sensitivity.

  12. Trends in monolithic microwave integrated circuits

    NASA Astrophysics Data System (ADS)

    Sterzer, F.

    1981-11-01

    Current trends in the fabrication of monolithic microwave integrated circuits (MMICs) are reviewed. The technologies developed predominantly make use of semi-insulating GaAs substrates, GaAs FET active elements, and lumped element circuits. An increasing number of MMIC designs incorporate innovative designs, including actively matched amplifiers and mixers, analog and digital functions, SAW circuits, and increased Q with lower resistance. A new generation of hybrid integrated circuits is also being developed which is expected to compete with conventional MMICs due to the potential for significant cost reduction. MMICs are considered to have the greatest potentials in applications requiring large quantities of similar circuits, circuits using large numbers of transistors or small areas for passive elements, and novel circuits such as SAWs monolithically combined with FETs.

  13. Interface states and internal photoemission in p-type GaAs metal-oxide-semiconductor surfaces

    NASA Technical Reports Server (NTRS)

    Kashkarov, P. K.; Kazior, T. E.; Lagowski, J.; Gatos, H. C.

    1983-01-01

    An interface photodischarge study of p-type GaAs metal-oxide-semiconductor (MOS) structures revealed the presence of deep interface states and shallow donors and acceptors which were previously observed in n-type GaAs MOS through sub-band-gap photoionization transitions. For higher photon energies, internal photoemission was observed, i.e., injection of electrons to the conduction band of the oxide from either the metal (Au) or from the GaAs valence band; the threshold energies were found to be 3.25 and 3.7 + or - 0.1 eV, respectively. The measured photoemission current exhibited a thermal activation energy of about 0.06 eV, which is consistent with a hopping mechanism of electron transport in the oxide.

  14. Interface states and internal photoemission in p-type GaAs metal-oxide-semiconductor surfaces

    NASA Technical Reports Server (NTRS)

    Kashkarov, P. K.; Kazior, T. E.; Lagowski, J.; Gatos, H. C.

    1983-01-01

    An interface photodischarge study of p-type GaAs metal-oxide-semiconductor (MOS) structures revealed the presence of deep interface states and shallow donors and acceptors which were previously observed in n-type GaAs MOS through sub-band-gap photoionization transitions. For higher photon energies, internal photoemission was observed, i.e., injection of electrons to the conduction band of the oxide from either the metal (Au) or from the GaAs valence band; the threshold energies were found to be 3.25 and 3.7 + or - 0.1 eV, respectively. The measured photoemission current exhibited a thermal activation energy of about 0.06 eV, which is consistent with a hopping mechanism of electron transport in the oxide.

  15. The growth of GaAs and InAs dots on etched mesas: The effect of substrate temperature on mesa profile and surface morphology on dot distribution

    NASA Astrophysics Data System (ADS)

    Ikpi, M. E.; Atkinson, P.; Bremner, S. P.; Ritchie, D. A.

    2009-07-01

    The molecular beam epitaxy (MBE) growth of GaAs and InAs quantum dots on etched mesas has been studied using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The [0 1 1]-oriented mesas are etched into (1 0 0) GaAs substrates, exposing (5 3 3)B sidewall facets. At a substrate temperature of 610 °C a top (1 0 0) plane is seen to evolve on a ridge mesa structure. Alternatively, if the overgrowth is carried out at 630 °C no such facet is seen, and the top ridge remains unchanged during GaAs growth. By controlling the mesa shape, either ordered lines of dots can be grown or the dot density can be varied from <5×10 8 cm -2 to >1×10 11 cm -2 on the same substrate in pre-defined regions. The dot distribution observed on the mesa sidewalls and top is discussed in terms of net migration of adatoms from different facets, underlying step density, step height and surface curvature of the mesa top.

  16. Polymerisation and surface modification of methacrylate monoliths in polyimide channels and polyimide coated capillaries using 660 nm light emitting diodes.

    PubMed

    Walsh, Zarah; Levkin, Pavel A; Abele, Silvija; Scarmagnani, Silvia; Heger, Dominik; Klán, Petr; Diamond, Dermot; Paull, Brett; Svec, Frantisek; Macka, Mirek

    2011-05-20

    An investigation into the preparation of monolithic separation media utilising a cyanine dye sensitiser/triphenylbutylborate/N-methoxy-4-phenylpyridinium tetrafluoroborate initiating system activated by 660 nm light emitting diodes is reported. The work demonstrates multiple uses of red-light initiated polymerisation in the preparation of monolithic stationary phases within polyimide and polyimide coated channels and the modification of monolithic materials with molecules which absorb strongly in the UV region. This initiator complex was used to synthesise poly(butyl methacrylate-co-ethylene dimethacrylate) and poly(methyl methacrylate-co-ethylene dimethacrylate) monolithic stationary phases in polyimide coated fused silica capillaries of varying internal diameters, as well as within polyimide micro-fluidic chips. The repeatability of the preparation procedure and resultant monolithic structure was demonstrated with a batch of poly(butyl methacrylate-co-ethylene dimethacrylate) monoliths in 100 μm i.d. polyimide coated fused silica capillary, which were applied to the separation of a model protein mixture (ribonuclease A, cytochrome C, myoglobin and ovalbumin). Taking an average from 12 chromatograms originating from each batch, the maximum relative standard deviation of the retention factor (k) for the protein separations was recorded as 0.53%, the maximum variance for the selectivity factor (α) was 0.40% while the maximum relative standard deviation in peak resolution was 8.72%. All maxima were recorded for the Ribonuclease A/Cytochrome C peaks. Scanning electron microscopy confirmed the success of experiments in which poly(butyl methacrylate-co-ethylene dimethacrylate) monoliths were prepared using the same initiation approach in capillary and micro-fluidic chips, respectively. The initiating system was also applied to the photo-initiated grafting of a chromophoric monomer onto poly(butyl methacrylate-co-ethylene dimethacrylate) monoliths within poly

  17. Effect of Two Polishing Systems on Surface Roughness, Topography, and Flexural Strength of a Monolithic Lithium Disilicate Ceramic.

    PubMed

    Mohammadibassir, Mahshid; Rezvani, Mohammad Bagher; Golzari, Hossein; Moravej Salehi, Elham; Fahimi, Mohammad Amin; Kharazi Fard, Mohammad Javad

    2017-03-08

    To evaluate the effect of overglazing and two polishing procedures on flexural strength and quality and quantity of surface roughness of a monolithic lithium disilicate ceramic computer-aided design (CAD) after grinding. This in vitro study was conducted on 52 partially crystalized bar-shaped specimens (16 × 4 × 1.6 mm) of monolithic lithium disilicate ceramic. The specimens were wet polished with 600-, 800-, and 1200-grit silicon carbide papers for 15 seconds using a grinding/polishing machine at a speed of 300 rpm. Then, the specimens were crystalized and glaze-fired in one step simultaneously and randomly divided into four groups of 13: (I) Glazing group (control); (II) Grinding-glazing group, subjected to grinding with red band finishing diamond bur (46 μm) followed by glazing; (III) Grinding-D+Z group, subjected to grinding and then polishing by coarse, medium, and fine diamond rubber points (D+Z); and (IV) Grinding-OptraFine group, subjected to grinding and then polishing with a two-step diamond rubber polishing system followed by a final polishing step with an OptraFine HP brush and diamond polishing paste. The surface roughness (Ra and Rz) values (μm) were measured by a profilometer, and the mean values were compared using one-way ANOVA and Tamhane's test (post hoc comparison). One specimen of each group was evaluated under a scanning electron microscope (SEM) for surface topography. The three-point flexural strength values of the bars were measured using a universal testing machine at a 0.5 mm/min crosshead speed and recorded. The data were analyzed using one-way ANOVA and Tamhane's test (α = 0.05). Statistically significant differences were noted among the experimental groups for Ra, Rz (p < 0.0001), and flexural strength values (p < 0.009). The lowest Ra and Rz values were found in the grinding-OptraFine group (0.465 ± 0.153), which were significantly lower than those in glazing (p < 0.03) and grinding-glazing (p < 0.001) groups. The Ra and Rz

  18. An investigation of penetrant techniques for detection of machining-induced surface-breaking cracks on monolithic ceramics

    SciTech Connect

    Forster, G.A.; Ellingson, W.A.

    1996-02-01

    The purpose of this effort was to evaluate penetrant methods for their ability to detect surface-breaking cracks in monolithic ceramic materials with an emphasis on detection of cracks generated by machining. There are two basic penetrant types, visible and fluorescent. The visible penetrant method is usually augmented by powder developers and cracks detected can be seen in visible light. Cracks detected by fluorescent penetrant are visible only under ultraviolet light used with or without a developer. The developer is basically a powder that wicks up penetrant from a crack to make it more observable. Although fluorescent penetrants were recommended in the literature survey conducted early in this effort, visible penetrants and two non-standard techniques, a capillary gaseous diffusion method under development at the institute of Chemical Physics in Moscow, and the {open_quotes}statiflux{close_quotes} method which involves use of electrically charged particles, were also investigated. SiAlON ring specimens (1 in. diameter, 3/4 in. wide) which had been subjected to different thermal-shock cycles were used for these tests. The capillary gaseous diffusion method is based on ammonia; the detector is a specially impregnated paper much like litmus paper. As expected, visible dye penetrants offered no detection sensitivity for tight, surface-breaking cracks in ceramics. Although the non-standard statiflux method showed promise on high-crack-density specimens, it was ineffective on limited-crack-density specimens. The fluorescent penetrant method was superior for surface-breaking crack detection, but successful application of this procedure depends greatly on the skill of the user. Two presently available high-sensitivity fluorescent penetrants were then evaluated for detection of microcracks on Si{sub 3}N{sub 4} and SiC from different suppliers. Although 50X optical magnification may be sufficient for many applications, 200X magnification provides excellent delectability.

  19. Monolithic high voltage nonlinear transmission line fabrication process

    DOEpatents

    Cooper, G.A.

    1994-10-04

    A process for fabricating sequential inductors and varistor diodes of a monolithic, high voltage, nonlinear, transmission line in GaAs is disclosed. An epitaxially grown laminate is produced by applying a low doped active n-type GaAs layer to an n-plus type GaAs substrate. A heavily doped p-type GaAs layer is applied to the active n-type layer and a heavily doped n-type GaAs layer is applied to the p-type layer. Ohmic contacts are applied to the heavily doped n-type layer where diodes are desired. Multiple layers are then either etched away or Oxygen ion implanted to isolate individual varistor diodes. An insulator is applied between the diodes and a conductive/inductive layer is thereafter applied on top of the insulator layer to complete the process. 6 figs.

  20. Monolithic high voltage nonlinear transmission line fabrication process

    DOEpatents

    Cooper, Gregory A.

    1994-01-01

    A process for fabricating sequential inductors and varactor diodes of a monolithic, high voltage, nonlinear, transmission line in GaAs is disclosed. An epitaxially grown laminate is produced by applying a low doped active n-type GaAs layer to an n-plus type GaAs substrate. A heavily doped p-type GaAs layer is applied to the active n-type layer and a heavily doped n-type GaAs layer is applied to the p-type layer. Ohmic contacts are applied to the heavily doped n-type layer where diodes are desired. Multiple layers are then either etched away or Oxygen ion implanted to isolate individual varactor diodes. An insulator is applied between the diodes and a conductive/inductive layer is thereafter applied on top of the insulator layer to complete the process.

  1. Monolithic arrays of grating-surface-emitting diode lasers and quantum well modulators for optical communications

    NASA Technical Reports Server (NTRS)

    Carlson, N. W.; Evans, G. A.; Liew, S. K.; Kaiser, C. J.

    1990-01-01

    The electro-optic switching properties of injection-coupled coherent 2-D grating-surface-emitting laser arrays with multiple gain sections and quantum well active layers are discussed and demonstrated. Within such an array of injection-coupled grating-surface-emitting lasers, a single gain section can be operated as intra-cavity saturable loss element that can modulate the output of the entire array. Experimental results demonstrate efficient sub-nanosecond switching of high power grading-surface-emitting laser arrays by using only one gain section as an intra-cavity loss modulator.

  2. Effect of chemical surface treatments on non-native (Bi/sub 2/O/sub 3/) GaAs metal-insulator-semiconductor solar cells

    SciTech Connect

    Wang, E.Y.; Pandelisev, K.A.

    1981-07-01

    GaAs metal-insulator-semiconductor solar cells with a physically deposited Bi/sub 2/O/sub 3/ interfacial layer have been investigated. The deposition techniques used in the study were electron beam and boat thermal evaporation. The cells fabricated with interfacial layers of Bi/sub 2/O/sub 3/ showed a substantial improvement in open-circuit voltage over cells made without the physically deposited oxide layer. An etch has been used which yields an irregular ''textured'' surface. Cells employing this surface had a higher short-circuit current than those made with smooth, polished surfaces. The open-circuit voltages of these textured cells were lower than those with smooth surfaces. Calculations of the dependence of open-circuit voltage on pinhole density are in agreement with these results since a rough surface has a greater probability of pinholes.

  3. Evaluation of the minority carrier diffusion length and surface-recombination velocity in GaAs p/n solar cells

    NASA Technical Reports Server (NTRS)

    Hakimzadeh, Roshanak; Moeller, Hans J.; Bailey, Sheila

    1991-01-01

    The minority carrier diffusion length (Lp) and the surface recombination velocity (Vs) were measured as a function of distance (x) from the p-n junction in GaAs p/n concentrator solar cells. The measured Vs values were used in a theoretical expression for the normalized electron-beam-induced current. A fitting procedure was then used to fit this expression with experimental values to obtain Lp. The results show that both Vs and Lp vary with x. Lp measured in irradiated cells showed a marked reduction. These values were compared to those measured previously which did not account for Vs.

  4. Evaluation of the minority carrier diffusion length and surface-recombination velocity in GaAs p/n solar cells

    NASA Technical Reports Server (NTRS)

    Hakimzadeh, Roshanak; Moeller, Hans J.; Bailey, Sheila

    1991-01-01

    The minority carrier diffusion length (Lp) and the surface recombination velocity (Vs) were measured as a function of distance (x) from the p-n junction in GaAs p/n concentrator solar cells. The measured Vs values were used in a theoretical expression for the normalized electron-beam-induced current. A fitting procedure was then used to fit this expression with experimental values to obtain Lp. The results show that both Vs and Lp vary with x. Lp measured in irradiated cells showed a marked reduction. These values were compared to those measured previously which did not account for Vs.

  5. CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES: Transient surface photoconductivity of GaAs emitter studied by terahertz pump-emission spectroscopy

    NASA Astrophysics Data System (ADS)

    Shi, Yu-Lei; Zhou, Qing-Li; Zhang, Cun-Lin

    2009-10-01

    This paper investigates the ultrafast carrier dynamics and surface photoconductivity of unbiased semi-insulating GaAs in detail by using a terahertz pump-emission technique. Based on theoretical modelling, it finds that transient photoconductivity plays a very important role in the temporal waveform of terahertz radiation pulse. Anomalous enhancement in both terahertz radiation and transient photoconductivity is observed after the excitation of pump pulse and we attribute these phenomena to carrier capture in the EL2 centers. Moreover, the pump power- and temperature-dependent measurements are also performed to verify this trapping model.

  6. RF characterization of monolithic microwave and mm-wave ICs

    NASA Technical Reports Server (NTRS)

    Romanofsky, R. R.; Ponchak, G. E.; Shalkhauser, K. A.; Bhasin, K. B.

    1986-01-01

    A number of fixturing techniques compatible with automatic network analysis are presented. The fixtures are capable of characterizing GaAs Monolithic Microwave Integrated Circuits (MMICs) at K and Ka band. Several different transitions are used to couple the RF test port to microstrip. Fixtures which provide chip level de-embedding are included. In addition, two advanced characterization techniques are assessed.

  7. Optical detectors for GaAs MMIC integration: Technology assessment

    NASA Technical Reports Server (NTRS)

    Claspy, P. C.; Bhasin, K. B.

    1989-01-01

    Fiber optic links are being considered to transmit digital and analog signals in phased array antenna feed networks in space communications systems. The radiating elements in these arrays will be GaAs monolithic microwave integrated circuits (MMIC's) in numbers ranging from a few hundred to several thousand. If such optical interconnects are to be practical it appears essential that the associated components, including detectors, be monolithically integrated on the same chip as the microwave circuitry. The general issue of monolithic integration of microwave and optoelectronic components is addressed from the point of view of fabrication technology and compatibility. Particular attention is given to the fabrication technology of various types of GaAs optical detectors that are designed to operate at a wavelength of 830 nm.

  8. Optical detectors for GaAs MMIC integration - Technology assessment

    NASA Technical Reports Server (NTRS)

    Claspy, P. C.; Bhasin, K. B.

    1989-01-01

    Fiber optic links are being considered to transmit digital and analog signals in phased array antenna feed networks in space communications systems. The radiating elements in these arrays will be GaAs monolithic microwave integrated circuits (MMIC's) in numbers ranging from a few hundred to several thousand. If such optical interconnects are to be practical it appears essential that the associated components, including detectors, be monolithically integrated on the same chip as the microwave circuitry. The general issue of monolithic integration of microwave and optoelectronic components is addressed from the point of view of fabrication technology and compatibility. Particular attention is given to the fabrication technology of various types of GaAs optical detectors that are designed to operate at a wavelength of 830 nm.

  9. Measurements of entrance-surface vs. conventional single-ended readout of a monolithic scintillator

    PubMed Central

    Hunter, William C. J.; Li; McDougald, Wendy; Griesmer, Jerome J.; Shao, Lingxiong; Zahn, Robert; Lewellen, Tom K.; Miyaoka, Robert S.

    2012-01-01

    Availability of compact high-gain, low-noise Silicon Photomultipliers (SiPM) prompts us to examine readout sensors on the entrance surface (SES) as compared to the conventional single-ended readout with sensors on the opposing surface. We measured detector response statistics versus 3D position for these configurations using an 8×8 SiPM array on a 15-mm-thick by 32-mm-wide LYSO block. We calibrate an independently distributed multivariate-normal likelihood model and use it to generate maximum-likelihood estimates of 3D interaction position. Spatial resolution improved 14% and timing resolution improved 10% for the SES device. Bias was unaffected. Photodetection efficiency of our prototype SiPM may have limited further improvement in positioning and timing performance. In future work, we will look to utilize SiPM arrays with enhanced photodetection efficiency. PMID:23202544

  10. Measurements of entrance-surface vs. conventional single-ended readout of a monolithic scintillator.

    PubMed

    Hunter, William C J; Li; McDougald, Wendy; Griesmer, Jerome J; Shao, Lingxiong; Zahn, Robert; Lewellen, Tom K; Miyaoka, Robert S

    2011-01-01

    Availability of compact high-gain, low-noise Silicon Photomultipliers (SiPM) prompts us to examine readout sensors on the entrance surface (SES) as compared to the conventional single-ended readout with sensors on the opposing surface. We measured detector response statistics versus 3D position for these configurations using an 8×8 SiPM array on a 15-mm-thick by 32-mm-wide LYSO block. We calibrate an independently distributed multivariate-normal likelihood model and use it to generate maximum-likelihood estimates of 3D interaction position. Spatial resolution improved 14% and timing resolution improved 10% for the SES device. Bias was unaffected. Photodetection efficiency of our prototype SiPM may have limited further improvement in positioning and timing performance. In future work, we will look to utilize SiPM arrays with enhanced photodetection efficiency.

  11. Monolithic integration of vertical-cavity surface-emitting lasers with in-plane waveguides

    NASA Astrophysics Data System (ADS)

    Witzens, Jeremy; Scherer, Axel; Pickrell, Gregory; Louderback, Duane; Guilfoyle, Peter

    2005-03-01

    The ability to couple light from a vertical-cavity surface-emitting laser into a planar, on-chip waveguide creates new opportunities for achieving higher levels of integration and functionality. Here we propose to use a strong grating etched into a waveguide defined into the top layer of the epitaxially grown structure, so that epitaxial regrowth is not required. By introducing a defect mode into the cavity we were able to achieve a 40% coupling efficiency even though light is coupled through a ninety degrees bend. We also show that polarization control of the vertical-cavity surface-emitting laser is enhanced by coupling to the defect mode. Calculations were performed using the finite-difference time-domain method.

  12. Fabrication of surface gratings in GaAs and AlGaAs by electron beam lithography and chemically assisted ion beam etching

    NASA Astrophysics Data System (ADS)

    Dienelt, Jens; Otte, Karsten; Zimmer, Klaus-Peter; Pietag, F.; Bigl, Frieder

    1999-09-01

    Optical surface gratings for surface emitting semiconductor lasers require extremely smooth functional surfaces, vertical step edges, a low sidewall roughness, and a high accuracy cover a large are. We report on the fabrication of binary patterns with a period of 1300 nm in GaAs and AlGaAs by electron beam lithography and different dry etching techniques, such as IBE, CAIBE and CARIBE. In order to improve the selectivity of the etch technique as well as the sidewall roughness three different etching mask techniques were applied. For grating depths of about 150 nm the best result with respect other geometrical grating characteristics have been achieved by using the e-beam exposed and developed PMMA as a direct etching mask. Comparing the different etching techniques, CAIBE on GaAs with chlorine shows the best etching behavior. A step edge angle of 90 degrees was achieved at an energy of 200 eV and a chlorine flow of 1.25 sccm. Optical diffraction measurements reveal a high efficiency for the gratings with vertical sidewalls and a line/space ratio of approximately 1.

  13. Diffusion and interface evolution during the atomic layer deposition of TiO{sub 2} on GaAs(100) and InAs(100) surfaces

    SciTech Connect

    Ye, Liwang; Gougousi, Theodosia

    2016-01-15

    Atomic layer deposition is used to form TiO{sub 2} films from tetrakis dimethyl amino titanium and H{sub 2}O on native oxide GaAs(100) and InAs(100) surfaces. The evolution of the film/substrate interface is examined as a function of the deposition temperature (100–325 °C) using ex situ x-ray photoelectron spectroscopy. An increase in the deposition temperature up to 250 °C leads to enhancement of the native oxide removal. For depositions at 300 °C and above, interface reoxidation is observed during the initial deposition cycles but when the films are thicker than 3 nm, the surface oxides are removed steadily. Based on these observations, two distinct film growth regimes are identified; up to 250 °C, layer-by-layer dominates while at higher temperatures island growth takes over. Angle resolved x-ray photoelectron spectroscopy measurements performed on 3 nm TiO{sub 2} film deposited at 325 °C on both surfaces demonstrates a very important difference between the two substrates: for GaAs the native oxides remaining in the stack are localized at the interface, while for InAs(100), the indium oxides are mixed in the TiO{sub 2} film.

  14. Porous polymer monoliths: Preparation of sorbent materials with high-surface areas and controlled surface chemistry for high-throughput, online, solid-phase extraction of polar organic compounds

    SciTech Connect

    Xie, S.; Svec, F.; Frechet, J.M.J.

    1998-12-01

    Porous monolithic materials with high surface areas have been prepared from commercial 80% divinylbenzene. The pore properties of these materials are controlled by the type and composition of the porogenic solvent and by the percentage of cross-linking monomer (divinylbenzene) in the polymerization mixture. Surface area was found to increase with the divinylbenzene content of the monolith. Using high-grade divinylbenzene and a suitable porogenic solvent, monolithic materials with specific surface areas as high as 400 m{sup 2}/g yet still permeable to liquids at reasonable back pressure were obtained for the first time. A macroporous material with hydrodynamic properties optimized for solid-phase extraction has been designed and its permeability and adsorption ability was demonstrated by adsorbing phenols at flow velocities that exceed those of current materials by a factor of 30. A unique set of polymerization conditions had to be developed to allow the incorporation of polar 2-hydroxylethyl methacrylate into the hydrophobic nonpolar backbone of the divinylbenzene monolithic material. This improves wettability while high-flow properties are maintained and unusually high recoveries of polar compounds are allowed.

  15. Monolithic vertical-cavity surface-emitting laser with thermally tunable birefringence

    NASA Astrophysics Data System (ADS)

    Pusch, Tobias; La Tona, Eros; Lindemann, Markus; Gerhardt, Nils C.; Hofmann, Martin R.; Michalzik, Rainer

    2017-04-01

    The birefringence splitting in vertical-cavity surface-emitting lasers offers an opportunity for spintronic-based high-frequency operation. By means of coupling of the carrier spin in the active region with the photons of the laser mode, the device can be excited to oscillations in the degree of circular polarization with a frequency corresponding to the birefringence splitting. On-chip frequency tunability of those oscillations is desirable for future applications. By asymmetric current-induced heating using the elasto-optic effect, we demonstrate a reversible tuning of the birefringence splitting of 45 GHz with less than 3 dB output power penalty.

  16. Monolithic geared-mechanisms driven by a polysilicon surface-micromachined on-chip electrostatic microengine

    SciTech Connect

    Sniegowski, J.J.; Miller, S.L.; LaVigne, G.F.; Rodgers, M.S.; McWhorter, P.J.

    1996-05-01

    We have previously described a practical micromachined power source: the polysilicon, surface-micromachined, electrostatically actuated microengine. Here we report on 3 aspects of implementing the microengine. First, we discuss demonstrations of the first-generation microengine actuating geared micromechanisms including gear trains with elements having dimensions comparable to the drive gear (about 50 {mu}m) and a relatively large (1600-{mu}m-diameter) rotating optical shutter element. These configurations span expected operating extremes for the microengine and address the coupling and loading issues for very-low-aspect-ratio micromechanisms which are common to the design of surface-micromachined devices. Second, we report on a second-generation of designs that utilize improved gear teeth design, a gear speed-reduction unit, and higher force-per-unit-area electrostatic comb drives. The speed-reduction unit produces an overall angular speed reduction of 9.63 and requires dual-level compound gears. Third, we discuss a dynamics model developed to accomplish 3 objectives: drive inertial loads in a controlled fashion, minimize stress and frictional forces during operation, and determine as a function of time the forces associated with the drive gear (eg load torque on drive gear from friction).

  17. Theoretical analysis of the optical properties of GaAs(001) surfaces and the strain-dependent lattice properties of semiconductors

    NASA Astrophysics Data System (ADS)

    Eryigit, Resul

    This thesis entails two theoretical studies of the properties of semiconductors. In the first part of the thesis Weber's bond charge model is modified to study the strain dependence of phonon frequencies and elastic constants of homopolar (Si and Ge) and heteropolar (GaAs) semiconductors in quasiharmonic approximation. The dispersion in the mode Gruneisen parameters (which characterize the pressure dependence of phonon frequencies) of these materials are calculated along the high symmetry directions of the Brillouin zone. Good agreement with experimental data is found. The shifts in phonon frequencies for Ge and CaAs grown pseudomorphically on Si(001) and Si(111) are investigated and it is found that the non-hydrostatic component of the lattice mismatched created strain mainly affects the longitudinal modes. Also, some conclusions are reached about the quality of the choice of ambient force constants. The second part of the thesis focuses on ab initio calculation of the optical response of different surfaces of semiconductors of importance in optoelectronics and microelectronics. Specifically, the dielectric function anisotropy of the (001) surface of GaAs is investigated for surfaces with Ga-terminated (4 x 2)-β and (4 x 2)-/beta 2 and As-terminated (2 x 4)-β and (2 x 4)-/beta 2 reconstructions. The atomic and electronic structure of the surfaces are determined by using first principles nonlocal pseudopotentials in the density functional theory framework within the local density approximation. Surface specific electronic features of the dielectric response are specified. It is found that the exact coordinates of the surface atoms are the most important parameters that determine the agreement between calculated and experimentally available anisotropies. As part of this section of the thesis, the general issue of designing surface optical diagnostics experiments to obtain surface dielectric functions is also addressed.

  18. Characterization of large surface area polymer monoliths and their utility for rapid, selective solid phase extraction for improved sample clean up.

    PubMed

    Candish, Esme; Wirth, Hans-Jürgen; Gooley, Andrew A; Shellie, Robert A; Hilder, Emily F

    2015-09-04

    While polymer monoliths are widely described for solid phase extraction (SPE), appropriate characterization is rarely provided to unravel the links between physical characteristics and observed advantages and disadvantages. Two known approaches to fabricate large surface area polymer monoliths with a bimodal pore structure were investigated. The first incorporated a high percentage of divinyl benzene (PDVB) and the second explored hypercrosslinking of pre-formed monoliths. Adsorption of probe analytes; anisole, benzoic acid, cinnamic acid, ibuprofen and cortisone were investigated using frontal analysis and the SPE performance was compared with particulate adsorbents. Frontal analysis of anisole described maximum adsorption capacities of 164mgg(-1) and 298mgg(-1) for hypercrosslinked and PDVB adsorbents, respectively. The solvated state specific surface area was calculated to be 341 and 518m(2)g(-1) respectively. BET revealed a hypercrosslinked surface area of 817m(2)g(-1), 2.5 times greater than in the solvated state. The PDVB BET surface area was 531m(2)g(-1), similar to the solvated state. Micropores of 1nm provided the enhanced surface area for hypercrosslinked adsorbents. PDVB displayed a pore size distribution of 1-6nm. Frontal analysis demonstrated the micropores present size exclusion for the larger probes. Recovery of anisole was determined by SPE using 0.4 and 1.0mLmin(-1). Recovery for PDVB remained constant at 90%±0.103 regardless of the extraction flow rate suggesting extraction performance is independent of flow rate. A more efficient sample purification of saccharin in urine was yielded by PDVB due to selective permeation of the small pores. Copyright © 2015 Elsevier B.V. All rights reserved.

  19. Frequency dispersion reduction and bond conversion on n-type GaAs by in situ surface oxide removal and passivation

    NASA Astrophysics Data System (ADS)

    Hinkle, C. L.; Sonnet, A. M.; Vogel, E. M.; McDonnell, S.; Hughes, G. J.; Milojevic, M.; Lee, B.; Aguirre-Tostado, F. S.; Choi, K. J.; Kim, J.; Wallace, R. M.

    2007-10-01

    The method of surface preparation on n-type GaAs, even with the presence of an amorphous-Si interfacial passivation layer, is shown to be a critical step in the removal of accumulation capacitance frequency dispersion. In situ deposition and analysis techniques were used to study different surface preparations, including NH4OH, Si-flux, and atomic hydrogen exposures, as well as Si passivation depositions prior to in situ atomic layer deposition of Al2O3. As-O bonding was removed and a bond conversion process with Si deposition is observed. The accumulation capacitance frequency dispersion was removed only when a Si interlayer and a specific surface clean were combined.

  20. Towards monolithic integration of mode-locked vertical cavity surface emitting laser

    NASA Astrophysics Data System (ADS)

    Aldaz, Rafael I.

    2007-12-01

    The speed and performance of today's high end computing and communications systems have placed difficult but still feasible demands on off-chip electrical interconnects. However, future interconnect systems may need aggregate bandwidths well into the terahertz range thereby making electrical bandwidth, density, and power targets impossible to meet. Optical interconnects, and specifically compact semiconductor mode-locked lasers, could alleviate this problem by providing short pulses in time at 10s of GHz repetition rates for Optical Time Division Multiplexing (OTDM) and clock distribution applications. Furthermore, the characteristic spectral comb of frequencies of these lasers could also serve as a multi-wavelength source for Wavelength Division Multiplexing (WDM) applications. A fully integrated mode-locked Vertical Cavity Surface Emitting Laser (VCSEL) is proposed as a low-cost high-speed source for these applications. The fundamental laser platform for such a device has been developed and a continuous-wave version of these lasers has been fabricated and demonstrated excellent results. Output powers close to 60mW have been obtained with very high beam quality factor of M2 < 1.07. The mode-locked laser utilizes a passive mode-locking region provided by a semiconductor saturable absorber integrated together with the gain region. Such an aggressive integration forces the resonant beam in the cavity to have the same area on the gain and absorber sections, placing high demands on the saturation fluence and absorption coefficient for the saturable absorber. Quantum Wells (QWs), excitons in QWs and Quantum Dots (QDs) have been investigated as possible saturable absorbers for the proposed device. QDs have been found to have the lowest saturation fluence and total absorption, necessary to meet the mode-locking requirements for this configuration. The need to further understand QDs as saturable absorbers has led to the development of a theoretical model on the dynamics of

  1. Reflection Properties of Metallic Gratings on ZnO Films over GaAs Substrates

    NASA Technical Reports Server (NTRS)

    Hickernell, Fred S.; Kim, Yoonkee; Hunt, William D.

    1994-01-01

    A potential application for piezoelectric film deposited on GaAs substrates is the monolithic integration of surface acoustic wave (SAW) devices with GaAs electronics. Metallic gratings are basic elements required for the construction of such devices, and analyzing the reflectivity and the velocity change due to metallic gratings is often a critical design parameter. In this article, Datta and Hunsinger technique is extended to the case of a multilayered structure, and the developed technique is applied to analyze shorted and open gratings on ZnO films sputtered over (001)-cut (110)-propagating GaAs substrates. The analysis shows that zero reflectivity of shorted gratings can be obtained by a combination of the ZnO film and the metal thickness and the metalization ratio of the grating. Experiments are performed on shorted and an open gratings (with the center frequency of about 180 MHz) for three different metal thicknesses over ZnO films which are 0.8 and 2.6 micrometers thick. From the experiments, zero reflectivity at the resonant frequency of the grating is observed for a reasonable thickness (h/Alpha = 0.5%) of aluminum metalization. The velocity shift between the shorted and the open grating is also measured to be 0.18 MHz and 0.25 MHz for 0.8 and 1.6 micrometers respectively. The measured data show relatively good agreement with theoretical predictions.

  2. Au impact on GaAs epitaxial growth on GaAs (111)B substrates in molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Liao, Zhi-Ming; Chen, Zhi-Gang; Lu, Zhen-Yu; Xu, Hong-Yi; Guo, Ya-Nan; Sun, Wen; Zhang, Zhi; Yang, Lei; Chen, Ping-Ping; Lu, Wei; Zou, Jin

    2013-02-01

    GaAs growth behaviour under the presence of Au nanoparticles on GaAs {111}B substrate is investigated using electron microscopy. It has been found that, during annealing, enhanced Ga surface diffusion towards Au nanoparticles leads to the GaAs epitaxial growth into {113}B faceted triangular pyramids under Au nanoparticles, governed by the thermodynamic growth, while during conventional GaAs growth, growth kinetics dominates, resulting in the flatted triangular pyramids at high temperature and the epitaxial nanowires growth at relatively low temperature. This study provides an insight of Au nanoparticle impact on GaAs growth, which is critical for understanding the formation mechanisms of semiconductor nanowires.

  3. Monolithic tandem solar cell

    DOEpatents

    Wanlass, Mark W.

    1991-01-01

    A single-crystal, monolithic, tandem, photovoltaic solar cell is described which includes (a) an InP substrate having upper and lower surfaces, (b) a first photoactive subcell on the upper surface of the InP substrate, and (c) a second photoactive subcell on the first subcell. The first photoactive subcell is GaInAsP of defined composition. The second subcell is InP. The two subcells are lattice matched. The solar cell can be provided as a two-terminal device or a three-terminal device.

  4. Strain and magnetic anisotropy of as-grown and annealed Fe films on c(4x4) reconstructed GaAs (001) surface

    SciTech Connect

    Lu, J.; Meng, H. J.; Deng, J. J.; Xu, P. F.; Chen, L.; Zhao, J. H.; Jia, Q. J.

    2009-07-01

    Fe films with the different thicknesses were grown on c(4x4) reconstructed GaAs (001) surfaces at low temperature by molecular-beam epitaxy. Well-ordered bcc structural Fe epitaxial films are confirmed by x-ray diffraction patterns and high-resolution cross-sectional transmission electron microscopy images. A large lattice expansion perpendicular to the surface in Fe film is observed. In-plane uniaxial magnetic anisotropy is determined by the difference between magnetizing energy along [110] and [110] directions, and the constant of interfacial uniaxial magnetic anisotropy is calculated to be 1.02x10{sup -4} J m{sup -2}. We also find that magnetic anisotropy is not obviously influenced after in situ annealing, but in-plane strain is completely changed.

  5. Lateral interdot carrier transfer in an InAs quantum dot cluster grown on a pyramidal GaAs surface.

    PubMed

    Liang, B L; Wong, P S; Pavarelli, N; Tatebayashi, J; Ochalski, T J; Huyet, G; Huffaker, D L

    2011-02-04

    InAs quantum dot clusters (QDCs), which consist of three closely spaced QDs, are formed on nano-facets of GaAs pyramidal structures by selective-area growth using metal-organic chemical vapor deposition. Photoluminescence (PL) and time-resolved PL (TRPL) experiments, measured in the PL linewidth, peak energy and QD emission dynamics indicate lateral carrier transfer within QDCs with an interdot carrier tunneling time of 910 ps under low excitation conditions. This study demonstrates the controlled formation of laterally coupled QDCs, providing a new approach to fabricate patterned QD molecules for optical computing applications.

  6. Low-Electronegativity Overlayers and Enhanced Semiconductor Oxidation: Sm on Si(111) and GaAs(110) Surfaces.

    DTIC Science & Technology

    1986-04-15

    6 4 2 0=E F Binding Energy (eV) 81+02 hL/=13OeV Sl 2p Core --- 01 I1 0 I I 4,z eusz 6 4il0 - Bidn0nry(V I I I I I I GaAs + 02 hv=85eV AsSd Cores 1000 0 0 C 0.2 53 2 o4 6 4 2 0 -2 -4 Relative Binding Energy (eV) -... MEN

  7. Monolith electroplating process

    DOEpatents

    Agarrwal, Rajev R.

    2001-01-01

    An electroplating process for preparing a monolith metal layer over a polycrystalline base metal and the plated monolith product. A monolith layer has a variable thickness of one crystal. The process is typically carried in molten salts electrolytes, such as the halide salts under an inert atmosphere at an elevated temperature, and over deposition time periods and film thickness sufficient to sinter and recrystallize completely the nucleating metal particles into one single crystal or crystals having very large grains. In the process, a close-packed film of submicron particle (20) is formed on a suitable substrate at an elevated temperature. The temperature has the significance of annealing particles as they are formed, and substrates on which the particles can populate are desirable. As the packed bed thickens, the submicron particles develop necks (21) and as they merge into each other shrinkage (22) occurs. Then as micropores also close (23) by surface tension, metal density is reached and the film consists of unstable metal grain (24) that at high enough temperature recrystallize (25) and recrystallized grains grow into an annealed single crystal over the electroplating time span. While cadmium was used in the experimental work, other soft metals may be used.

  8. Monolithic Microwave Integrated Circuit (MMIC) technology for space communications applications

    NASA Technical Reports Server (NTRS)

    Connolly, Denis J.; Bhasin, Kul B.; Romanofsky, Robert R.

    1987-01-01

    Future communications satellites are likely to use gallium arsenide (GaAs) monolithic microwave integrated-circuit (MMIC) technology in most, if not all, communications payload subsystems. Multiple-scanning-beam antenna systems are expected to use GaAs MMIC's to increase functional capability, to reduce volume, weight, and cost, and to greatly improve system reliability. RF and IF matrix switch technology based on GaAs MMIC's is also being developed for these reasons. MMIC technology, including gigabit-rate GaAs digital integrated circuits, offers substantial advantages in power consumption and weight over silicon technologies for high-throughput, on-board baseband processor systems. For the more distant future pseudomorphic indium gallium arsenide (InGaAs) and other advanced III-V materials offer the possibility of MMIC subsystems well up into the millimeter wavelength region. All of these technology elements are in NASA's MMIC program. Their status is reviewed.

  9. Monolithic Microwave Integrated Circuit (MMIC) technology for space communications applications

    NASA Technical Reports Server (NTRS)

    Connolly, Denis J.; Bhasin, Kul B.; Romanofsky, Robert R.

    1987-01-01

    Future communications satellites are likely to use gallium arsenide (GaAs) monolithic microwave integrated-circuit (MMIC) technology in most, if not all, communications payload subsystems. Multiple-scanning-beam antenna systems are expected to use GaAs MMICs to increase functional capability, to reduce volume, weight, and cost, and to greatly improve system reliability. RF and IF matrix switch technology based on GaAs MMICs is also being developed for these reasons. MMIC technology, including gigabit-rate GaAs digital integrated circuits, offers substantial advantages in power consumption and weight over silicon technologies for high-throughput, on-board baseband processor systems. For the more distant future pseudomorphic indium gallium arsenide (InGaAs) and other advanced III-V materials offer the possibility of MMIC subsystems well up into the millimeter wavelength region. All of these technology elements are in NASA's MMIC program. Their status is reviewed.

  10. Monolithic Microwave Integrated Circuit (MMIC) technology for space communications applications

    NASA Astrophysics Data System (ADS)

    Connolly, Denis J.; Bhasin, Kul B.; Romanofsky, Robert R.

    Future communications satellites are likely to use gallium arsenide (GaAs) monolithic microwave integrated-circuit (MMIC) technology in most, if not all, communications payload subsystems. Multiple-scanning-beam antenna systems are expected to use GaAs MMICs to increase functional capability, to reduce volume, weight, and cost, and to greatly improve system reliability. RF and IF matrix switch technology based on GaAs MMICs is also being developed for these reasons. MMIC technology, including gigabit-rate GaAs digital integrated circuits, offers substantial advantages in power consumption and weight over silicon technologies for high-throughput, on-board baseband processor systems. For the more distant future pseudomorphic indium gallium arsenide (InGaAs) and other advanced III-V materials offer the possibility of MMIC subsystems well up into the millimeter wavelength region. All of these technology elements are in NASA's MMIC program. Their status is reviewed.

  11. Monolithic Microwave Integrated Circuit (MMIC) technology for space communications applications

    NASA Technical Reports Server (NTRS)

    Connolly, Denis J.; Bhasin, Kul B.; Romanofsky, Robert R.

    1987-01-01

    Future communications satellites are likely to use gallium arsenide (GaAs) monolithic microwave integrated-circuit (MMIC) technology in most, if not all, communications payload subsystems. Multiple-scanning-beam antenna systems are expected to use GaAs MMIC's to increase functional capability, to reduce volume, weight, and cost, and to greatly improve system reliability. RF and IF matrix switch technology based on GaAs MMIC's is also being developed for these reasons. MMIC technology, including gigabit-rate GaAs digital integrated circuits, offers substantial advantages in power consumption and weight over silicon technologies for high-throughput, on-board baseband processor systems. For the more distant future pseudomorphic indium gallium arsenide (InGaAs) and other advanced III-V materials offer the possibility of MMIC subsystems well up into the millimeter wavelength region. All of these technology elements are in NASA's MMIC program. Their status is reviewed.

  12. Monolithic Microwave Integrated Circuit (MMIC) technology for space communications applications

    NASA Astrophysics Data System (ADS)

    Connolly, Denis J.; Bhasin, Kul B.; Romanofsky, Robert R.

    1987-10-01

    Future communications satellites are likely to use gallium arsenide (GaAs) monolithic microwave integrated-circuit (MMIC) technology in most, if not all, communications payload subsystems. Multiple-scanning-beam antenna systems are expected to use GaAs MMIC's to increase functional capability, to reduce volume, weight, and cost, and to greatly improve system reliability. RF and IF matrix switch technology based on GaAs MMIC's is also being developed for these reasons. MMIC technology, including gigabit-rate GaAs digital integrated circuits, offers substantial advantages in power consumption and weight over silicon technologies for high-throughput, on-board baseband processor systems. For the more distant future pseudomorphic indium gallium arsenide (InGaAs) and other advanced III-V materials offer the possibility of MMIC subsystems well up into the millimeter wavelength region. All of these technology elements are in NASA's MMIC program. Their status is reviewed.

  13. Electro-optic investigation of the n-alkanethiol GaAs(001) interface: Surface phenomena and applications to photoluminescence-based biosensing

    NASA Astrophysics Data System (ADS)

    Marshall, Gregory M.

    Semiconductor surfaces coupled to molecular structures derived from organic chemistry form the basis of an emerging class of field-effect devices. In addition to molecular electronics research, these interfaces are developed for a variety of sensor applications in the electronic and optical domains. Of practical interest are self-assembled monolayers (SAMs) comprised of n-alkanethiols [HS(CH2)n], which couple to the GaAs(001) surface through S-GaAs covalent bond formation. These SAMs offer potential functionality in terms of the requisite sensor chemistry and the passivation effect such coupling is known to afford. In this thesis, the SAM-GaAs interface is investigated in the context of a photonic biosensor based on photoluminescence (PL) variation. The scope of the work is categorized into three parts: i) the structural and compositional analysis of the surface using X-ray photoelectron spectroscopy (XPS), ii) the investigation of electronic properties at the interface under equilibrium conditions using infrared (IR) spectroscopy, the Kelvin probe method, and XPS, and iii) the analysis of the electro-optic response under steady-state photonic excitation, specifically, the surface photovoltage (SPV) and PL intensity. Using a partial overlayer model of angle-resolved XPS spectra in which the component assignments are shown to be quantitatively valid, the coverage fraction of methyl-terminated SAMs is shown to exceed 90%. Notable among the findings are a low-oxide, Ga-rich surface with elemental As present in sub-monolayer quantities consistent with theoretical surface morphologies. Modal analysis of transmission IR spectra show that the SAM molecular order is sufficient to support a Beer-Lambert determination of the IR optical constants, which yields the observation of a SAM-specific absorbance enhancement. By correlation of the IR absorbance with the SAM dipole layer potential, the enhancement mechanism is attributed to the vibrational moments added by the

  14. GaAs FET microwave oscillators

    NASA Astrophysics Data System (ADS)

    Sautereau, J.-F.

    Techniques for establishing the temporal stability of functioning of GaAs FETs are presented, along with a theory of negative resistance oscillators and an analysis of noise in GaAs FETs. Conditions of stable oscillation are discussed, as are techniques for designing solid state devices. An analog microwave circuit is described and is characterized in terms of inherent nonlinearities, which allows precise determination of the period, power, and harmonic distortion for the output signal. A coefficient is defined for expressing low frequency noise in microwave terms and methods for minimizing oscillator noise are presented, based on results from experimentation in X-band and low frequency devices. A computer model is developed which includes allowances for constantly repartitioned circuitry looping impedances. The model is concluded to be useful for the design of integrated monolithic microwave circuits.

  15. Novel WSi/Au T-shaped gate GaAs metal-semiconductor field-effect-transistor fabrication process for super low-noise microwave monolithic integrated circuit amplifiers

    SciTech Connect

    Takano, H.; Hosogi, K.; Kato, T.

    1995-05-01

    A fully ion-implanted self-aligned T-shaped gate Ga As metal-semiconductor field-effect transistor (MESFET) with high frequency and extremely low-noise performance has been successfully fabricated for super low-noise microwave monolithic integrated circuit (MMIC) amplifiers. A subhalf-micrometer gate structure composed of WSi/Ti/Mo/Au is employed to reduce gate resistance effectively. This multilayer gate structure is formed by newly developed dummy SiON self-alignment technology and a photoresist planarization process. At an operating frequency of 12 GHz, a minimum noise figure of 0.87 dB with an associated gain of 10.62 dB has been obtained. Based on the novel FET process, a low-noise single-stage MMIC amplifier with an excellent low-noise figure of 1.2 dB with an associated gain of 8 dB in the 14 GHz band has been realized. This is the lowest noise figure ever reported at this frequency for low-noise MMICs based on ion-implanted self-aligned gate MESFET technology. 14 refs., 9 figs.

  16. Surface passivation and interface properties of bulk GaAs and epitaxial-GaAs/Ge using atomic layer deposited TiAlO alloy dielectric.

    PubMed

    Dalapati, G K; Chia, C K; Tan, C C; Tan, H R; Chiam, S Y; Dong, J R; Das, A; Chattopadhyay, S; Mahata, C; Maiti, C K; Chi, D Z

    2013-02-01

    High quality surface passivation on bulk-GaAs substrates and epitaxial-GaAs/Ge (epi-GaAs) layers were achieved by using atomic layer deposited (ALD) titanium aluminum oxide (TiAlO) alloy dielectric. The TiAlO alloy dielectric suppresses the formation of defective native oxide on GaAs layers. X-ray photoelectron spectroscopy (XPS) analysis shows interfacial arsenic oxide (As(x)O(y)) and elemental arsenic (As) were completely removed from the GaAs surface. Energy dispersive X-ray diffraction (EDX) analysis and secondary ion mass spectroscopy (SIMS) analysis showed that TiAlO dielectric is an effective barrier layer for reducing the out-diffusion of elemental atoms, enhancing the electrical properties of bulk-GaAs based metal-oxide-semiconductor (MOS) devices. Moreover, ALD TiAlO alloy dielectric on epi-GaAs with AlGaAs buffer layer realized smooth interface between epi-GaAs layers and TiAlO dielectric, yielding a high quality surface passivation on epi-GaAs layers, much sought-after for high-speed transistor applications on a silicon platform. Presence of a thin AlGaAs buffer layer between epi-GaAs and Ge substrates improved interface quality and gate dielectric quality through the reduction of interfacial layer formation (Ga(x)O(y)) and suppression of elemental out-diffusion (Ga and As). The AlGaAs buffer layer and TiAlO dielectric play a key role to suppress the roughening, interfacial layer formation, and impurity diffusion into the dielectric, which in turn largely enhances the electrical property of the epi-GaAs MOS devices.

  17. Clustering effects in a low coverage deposition of gold on the GaAs( 0 0 1 )-β2(2×4) surface: an STM-UHV and theoretical study

    NASA Astrophysics Data System (ADS)

    Amore Bonapasta, A.; Scavia, G.; Buda, F.

    2002-11-01

    A comparative study of gold deposition on the GaAs(0 0 1)-β2(2×4) surface based on scanning tunneling microscopy (STM)-ultra high vacuum (UHV) and Car-Parrinello calculations has been carried out. The theoretical results show that the preferential reactive sites of an isolated Au adatom on the GaAs surface drive a self-organizing process of further Au adatoms onto the surface, thus determining an Au clusterization onto the two-As-dimer cell. On the other hand, STM-UHV images reveal, for Au depositions <1 ML, a decorating effect of gold towards the GaAs(0 0 1)-β2(2×4) unit cell. In detail, gold clusters tend to cover the two-As-dimer cell without modifying the (2×4) reconstruction, in agreement with the theoretical results. Moreover, a fine comparison between the STM images of gold clusters and the theoretical results reveals that each of these clusters can be composed of four Au adatoms directly interacting with the two As dimers of the GaAs unit cell. An STM-UHV analysis of the surface for a deposition >1 ML suggests that gold clusterizes into 3D clusters rather than forming a 2D layer.

  18. ICP etching of GaAs via hole contacts

    SciTech Connect

    Shul, R.J.; Baca, A.G.; Briggs, R.D.; McClellan, G.B.; Pearton, S.J.; Constantine, C.

    1996-09-01

    Deep etching of GaAs is a critical process step required for many device applications including fabrication of through-substrate via holes for monolithic microwave integrated circuits (MMICs). Use of high-density plasmas, including inductively coupled plasmas (ICP), offers an alternative approach to etching vias as compared to more conventional parallel plate reactive ion etch systems. This paper reports ICP etching of GaAs vias at etch rates of about 5.3 {mu}m/min with via profiles ranging from highly anistropic to conical.

  19. Pre-photolithographic GaAs surface treatment for improved photoresist adhesion during wet chemical etching and improved wet etch profiles.

    SciTech Connect

    Martinez, Marino John; Clevenger, Jascinda; Austin, Franklin H., IV; Sullivan, Charles Thomas; Patrizi, Gary A.; Romero, Katherine; Timon, Robert P.; Vigil, Pablita S.; Grine, Alejandro J.

    2010-05-01

    Results of several experiments aimed at remedying photoresist adhesion failure during spray wet chemical etching of InGaP/GaAs NPN HBTs are reported. Several factors were identified that could influence adhesion and a Design of Experiment (DOE) approach was used to study the effects and interactions of selected factors. The most significant adhesion improvement identified is the incorporation of a native oxide etch immediately prior to the photoresist coat. In addition to improving adhesion, this pre-coat treatment also alters the wet etch profile of (100) GaAs so that the reaction limited etch is more isotropic compared to wafers without surface treatment; the profiles have a positive taper in both the [011] and [011] directions, but the taper angles are not identical. The altered profiles have allowed us to predictably yield fully probe-able HBTs with 5 x 5 {micro}m emitters using 5200 {angstrom} evaporated metal without planarization.

  20. Raman scattering of InAs/AlAs quantum dot superlattices grown on (001) and (311)B GaAs surfaces

    PubMed Central

    2012-01-01

    We present a comparative analysis of Raman scattering by acoustic and optical phonons in InAs/AlAs quantum dot superlattices grown on (001) and (311)B GaAs surfaces. Doublets of folded longitudinal acoustic phonons up to the fifth order were observed in the Raman spectra of (001)- and (311)B-oriented quantum dot superlattices measured in polarized scattering geometries. The energy positions of the folded acoustic phonons are well described by the elastic continuum model. Besides the acoustic phonons, the spectra display features related to confined transverse and longitudinal optical as well as interface phonons in quantum dots and spacer layers. Their frequency positions are discussed in terms of phonon confinement, elastic stress, and atomic intermixing. PMID:22916827

  1. Raman scattering of InAs/AlAs quantum dot superlattices grown on (001) and (311)B GaAs surfaces.

    PubMed

    Milekhin, Alexander; Yeryukov, Nikolay; Toropov, Alexander; Dmitriev, Dmitry; Sheremet, Evgeniya; Zahn, Dietrich Rt

    2012-08-23

    We present a comparative analysis of Raman scattering by acoustic and optical phonons in InAs/AlAs quantum dot superlattices grown on (001) and (311)B GaAs surfaces. Doublets of folded longitudinal acoustic phonons up to the fifth order were observed in the Raman spectra of (001)- and (311)B-oriented quantum dot superlattices measured in polarized scattering geometries. The energy positions of the folded acoustic phonons are well described by the elastic continuum model. Besides the acoustic phonons, the spectra display features related to confined transverse and longitudinal optical as well as interface phonons in quantum dots and spacer layers. Their frequency positions are discussed in terms of phonon confinement, elastic stress, and atomic intermixing.

  2. Combined experimental and theoretical study of fast atom diffraction on the β2(2×4) reconstructed GaAs(001) surface

    NASA Astrophysics Data System (ADS)

    Debiossac, M.; Zugarramurdi, A.; Khemliche, H.; Roncin, P.; Borisov, A. G.; Momeni, A.; Atkinson, P.; Eddrief, M.; Finocchi, F.; Etgens, V. H.

    2014-10-01

    A grazing incidence fast atom diffraction (GIFAD or FAD) setup, installed on a molecular beam epitaxy chamber, has been used to characterize the β2(2×4) reconstruction of a GaAs(001) surface at 530∘C under an As4 overpressure. Using a 400-eV 4He beam, high-resolution diffraction patterns with up to eighty well-resolved diffraction orders are observed simultaneously, providing a detailed fingerprint of the surface structure. Experimental diffraction data are in good agreement with results from quantum scattering calculations based on an ab initio projectile-surface interaction potential. Along with exact calculations, we show that a straightforward semiclassical analysis allows the features of the diffraction chart to be linked to the main characteristics of the surface reconstruction topography. Our results demonstrate that GIFAD is a technique suitable for measuring in situ the subtle details of complex surface reconstructions. We have performed measurements at very small incidence angles, where the kinetic energy of the projectile motion perpendicular to the surface can be reduced to less than 1 meV. This allowed the depth of the attractive van der Waals potential well to be estimated as -8.7 meV in very good agreement with results reported in literature.

  3. Adsorption of fullerenes Cn(n=32,36,40,44,48,60) on the GaAs(001)-c(4×4) reconstructed surface

    NASA Astrophysics Data System (ADS)

    Zhou, Chenggang; Wu, Jinping; Han, Bo; Yao, Shujuan; Cheng, Hansong

    2006-05-01

    We present first principles studies using density functional theory on adsorption of fullerene molecules Cn(n=32,36,40,44,48,60) on the c(4×4) reconstructed GaAs(001) surface. Adsorption at various surface sites coupled with numerous fullerene orientations were systematically sampled to obtain energetically most stable structures. With the orientation of a fullerene with one of the hexagons facing down the substrate, the surface trenches were identified as the sites that give the strongest adsorption. The orientational preference for C32 adsorption is an exception due to its unique stability in its electronic structure. It was found that the As atoms with a dangling bond in the second surface layer play a most critical role in determining the adsorption structure and strength, while the top layer As dimers are only capable of forming weak bonding with fullerenes, which differs significantly from adsorption of fullerenes and small unsaturated organic molecules on silicon surfaces. Strong covalent bonds between fullerenes and the substrate are formed and considerable deformation of fullerenes near the adsorption sites is observed. The calculated adsorption energy decreases as the size of fullerenes increases. The calculation yields useful physical insight into the adsorption mechanism and the physicochemical properties of the materials.

  4. The 30-GHz monolithic receive module

    NASA Technical Reports Server (NTRS)

    Bauhahn, P.; Geddes, J.; Sokolov, V.; Contolatis, T.

    1988-01-01

    The fourth year progress is described on a program to develop a 27.5 to 30 GHz GaAs monolithic receive module for spaceborne-communication antenna feed array applications, and to deliver submodules for experimental evaluation. Program goals include an overall receive module noise figure of 5 dB, a 30 dB RF to IF gain with six levels of intermediate gain control, a five bit phase shifter, and a maximum power consumption of 250 mW. Submicron gate length single and dual gate FETs are described and applied in the development of monolithic gain control amplifiers and low noise amplifiers. A two-stage monolithic gain control amplifier based on ion implanted dual gate MESFETs was designed and fabricated. The gain control amplifier has a gain of 12 dB at 29 GHz with a gain control range of over 13 dB. A two-stage monolithic low noise amplifier based on ion implanted MESFETs which provides 7 dB gain with 6.2 dB noise figure at 29 GHz was also developed. An interconnected receive module containing LNA, gain control, and phase shifter submodules was built using the LNA and gain control ICs as well as a monolithic phase shifter developed previously under this program. The design, fabrication, and evaluation of this interconnected receiver is presented. Progress in the development of an RF/IF submodule containing a unique ion implanted diode mixer diode and a broadband balanced mixer monolithic IC with on-chip IF amplifier and the initial design of circuits for the RF portion of a two submodule receiver are also discussed.

  5. Adsorption over polyacrylonitrile based carbon monoliths

    NASA Astrophysics Data System (ADS)

    Nandi, Mahasweta; Dutta, Arghya; Patra, Astam Kumar; Bhaumik, Asim; Uyama, Hiroshi

    2013-02-01

    Highly porous activated carbon monoliths have been prepared from mesoporous polyacrylonitrile (PAN) monolith as the carbon precursor. The mesoporous PAN monoliths are fabricated by a unique and facile template-free method which on carbonization gives N-doped activated carbon monoliths. The carbonization is achieved via two step thermal process which includes pretreatment in air leading to cyclization and subsequent aromatization of the PAN moieties followed by carbonization in a mixture of argon and carbon dioxide to give a layered carbon framework. Nitrogen sorption experiments carried over these carbon monoliths revealed high surface area (ca. 2500 m2g-1) for these materials with precise micropore size distribution. The activated carbons show extraordinarily high CO2 capture capacity and the uptake up to 3 bar has been found to be as high as 22.5 and 10.6 mmol/g at 273 K and 298 K, respectively.

  6. Monolithic afocal telescope

    NASA Technical Reports Server (NTRS)

    Roberts, William T. (Inventor)

    2010-01-01

    An afocal monolithic optical element formed of a shallow cylinder of optical material (glass, polymer, etc.) with fast aspheric surfaces, nominally confocal paraboloids, configured on the front and back surfaces. The front surface is substantially planar, and this lends itself to deposition of multi-layer stacks of thin dielectric and metal films to create a filter for rejecting out-of-band light. However, an aspheric section (for example, a paraboloid) can either be ground into a small area of this surface (for a Cassegrain-type telescope) or attached to the planar surface (for a Gregorian-type telescope). This aspheric section of the surface is then silvered to create the telescope's secondary mirror. The rear surface of the cylinder is figured into a steep, convex asphere (again, a paraboloid in the examples), and also made reflective to form the telescope's primary mirror. A small section of the rear surface (approximately the size of the secondary obscuration, depending on the required field of the telescope) is ground flat to provide an unpowered surface through which the collimated light beam can exit the optical element. This portion of the rear surface is made to transmit the light concentrated by the reflective surfaces, and can support the deposition of a spectral filter.

  7. GaAs Optoelectronic Integrated-Circuit Neurons

    NASA Technical Reports Server (NTRS)

    Lin, Steven H.; Kim, Jae H.; Psaltis, Demetri

    1992-01-01

    Monolithic GaAs optoelectronic integrated circuits developed for use as artificial neurons. Neural-network computer contains planar arrays of optoelectronic neurons, and variable synaptic connections between neurons effected by diffraction of light from volume hologram in photorefractive material. Basic principles of neural-network computers explained more fully in "Optoelectronic Integrated Circuits For Neural Networks" (NPO-17652). In present circuits, devices replaced by metal/semiconductor field effect transistors (MESFET's), which consume less power.

  8. GaAs Optoelectronic Integrated-Circuit Neurons

    NASA Technical Reports Server (NTRS)

    Lin, Steven H.; Kim, Jae H.; Psaltis, Demetri

    1992-01-01

    Monolithic GaAs optoelectronic integrated circuits developed for use as artificial neurons. Neural-network computer contains planar arrays of optoelectronic neurons, and variable synaptic connections between neurons effected by diffraction of light from volume hologram in photorefractive material. Basic principles of neural-network computers explained more fully in "Optoelectronic Integrated Circuits For Neural Networks" (NPO-17652). In present circuits, devices replaced by metal/semiconductor field effect transistors (MESFET's), which consume less power.

  9. Optimization of monolithic columns for microfluidic devices

    NASA Astrophysics Data System (ADS)

    Pagaduan, Jayson V.; Yang, Weichun; Woolley, Adam T.

    2011-06-01

    Monolithic columns offer advantages as solid-phase extractors because they offer high surface area that can be tailored to a specific function, fast mass transport, and ease of fabrication. Porous glycidyl methacrylate-ethylene glycol dimethacrylate monoliths were polymerized in-situ in microfluidic devices, without pre-treatment of the poly(methyl methacrylate) channel surface. Cyclohexanol, 1-dodecanol and Tween 20 were used to control the pore size of the monoliths. The epoxy groups on the monolith surface can be utilized to immobilize target-specific probes such as antibodies, aptamers, or DNA for biomarker detection. Microfluidic devices integrated with solid-phase extractors should be useful for point-of-care diagnostics in detecting specific biomarkers from complex biological fluids.

  10. Monolithic dye laser amplifier

    DOEpatents

    Kuklo, Thomas C.

    1993-01-01

    A fluid dye laser amplifier for amplifying a dye beam by pump beams has a channel structure defining a channel through which a laseable fluid flows and the dye and pump beams pass transversely to one another through a lasing region. The channel structure is formed with two pairs of mutually spaced-apart and mutually confronting glass windows, which are interlocked and make surface-contacts with one another and surround the lasing region. One of the glass window pairs passes the dye beam and the other passes the pump beams therethrough and through the lasing region. Where these glass window pieces make surface-contacts, glue is used to join the pieces together to form a monolithic structure so as to prevent the dye in the fluid passing through the channel from entering the space between the mutually contacting glass window pieces.

  11. Monolithic dye laser amplifier

    DOEpatents

    Kuklo, T.C.

    1993-03-30

    A fluid dye laser amplifier for amplifying a dye beam by pump beams has a channel structure defining a channel through which a laseable fluid flows and the dye and pump beams pass transversely to one another through a lasing region. The channel structure is formed with two pairs of mutually spaced-apart and mutually confronting glass windows, which are interlocked and make surface-contacts with one another and surround the lasing region. One of the glass window pairs passes the dye beam and the other passes the pump beams therethrough and through the lasing region. Where these glass window pieces make surface-contacts, glue is used to join the pieces together to form a monolithic structure so as to prevent the dye in the fluid passing through the channel from entering the space between the mutually contacting glass window pieces.

  12. Polymer network/carbon layer on monolith support and monolith catalytic reactor

    DOEpatents

    Nordquist, Andrew Francis; Wilhelm, Frederick Carl; Waller, Francis Joseph; Machado, Reinaldo Mario

    2003-08-26

    The present invention relates to an improved monolith catalytic reactor and a monolith support. The improvement in the support resides in a polymer network/carbon coating applied to the surface of a porous substrate and a catalytic metal, preferably a transition metal catalyst applied to the surface of the polymer network/carbon coating. The monolith support has from 100 to 800 cells per square inch and a polymer network/carbon coating with surface area of from 0.1 to 15 m.sup.2 /gram as measured by adsorption of N.sub.2 or Kr using the BET method.

  13. The impact of the surface on step-bunching and diffusion of Ga on GaAs (001) in metal-organic vapour phase epitaxy

    NASA Astrophysics Data System (ADS)

    Pristovsek, Markus; Poser, Florian; Richter, Wolfgang

    2016-07-01

    We studied diffusion by measuring step-bunching, island spacing, and the transition from step-flow growth to two-dimensional island growth of (001) GaAs in metal-organic vapour phase epitaxy and correlated them with the surface reconstruction measured by reflectance anisotropy spectroscopy. The V/III ratio had a small effect, while the square root of the growth rate was anti-proportional to the diffusion length. The thermal activation energy was about 2.3 eV on {{c}}(4× 4) terraces and 1.6 eV on (2× 4) domains at higher temperatures. Pronounced step-bunching coincided with large (4× 2) domains at the step-edges, causing smoother steps for the [11̅0] misorientation. This Ga-rich reconstruction at the step-edges is needed for the Schwoebel barrier to induce step-bunching. At higher temperatures of (2× 4) domains grow in size, the Schwoebel barrier reduces and nucleation becomes easier on this surface which reduces diffusion length and thus step-bunching.

  14. Surface activated bonding of GaAs and SiC wafers at room temperature for improved heat dissipation in high-power semiconductor lasers

    NASA Astrophysics Data System (ADS)

    Higurashi, Eiji; Okumura, Ken; Nakasuji, Kaori; Suga, Tadatomo

    2015-03-01

    Thermal management of high-power semiconductor lasers is of great importance since the output power and beam quality are affected by the temperature rise of the gain region. Thermal simulations of a vertical-external-cavity surface-emitting laser by a finite-element method showed that the solder layer between the semiconductor thin film consisting of the gain region and a heat sink has a strong influence on the thermal resistance and direct bonding is preferred to achieve effective heat dissipation. To realize thin-film semiconductor lasers directly bonded on a high-thermal-conductivity substrate, surface-activated bonding using an argon fast atom beam was applied to the bonding of gallium arsenide (GaAs) and silicon carbide (SiC) wafers. The GaAs/SiC structure was demonstrated in the wafer scale (2 in. in diameter) at room temperature. The cross-sectional transmission electron microscopy observations showed that void-free bonding interfaces were achieved.

  15. Advances in gallium arsenide monolithic microwave integrated-circuit technology for space communications systems

    NASA Technical Reports Server (NTRS)

    Bhasin, K. B.; Connolly, D. J.

    1986-01-01

    Future communications satellites are likely to use gallium arsenide (GaAs) monolithic microwave integrated-circuit (MMIC) technology in most, if not all, communications payload subsystems. Multiple-scanning-beam antenna systems are expected to use GaAs MMIC's to increase functional capability, to reduce volume, weight, and cost, and to greatly improve system reliability. RF and IF matrix switch technology based on GaAs MMIC's is also being developed for these reasons. MMIC technology, including gigabit-rate GaAs digital integrated circuits, offers substantial advantages in power consumption and weight over silicon technologies for high-throughput, on-board baseband processor systems. In this paper, current developments in GaAs MMIC technology are described, and the status and prospects of the technology are assessed.

  16. Advances in gallium arsenide monolithic microwave integrated-circuit technology for space communications systems

    NASA Astrophysics Data System (ADS)

    Bhasin, K. B.; Connolly, D. J.

    1986-10-01

    Future communications satellites are likely to use gallium arsenide (GaAs) monolithic microwave integrated-circuit (MMIC) technology in most, if not all, communications payload subsystems. Multiple-scanning-beam antenna systems are expected to use GaAs MMIC's to increase functional capability, to reduce volume, weight, and cost, and to greatly improve system reliability. RF and IF matrix switch technology based on GaAs MMIC's is also being developed for these reasons. MMIC technology, including gigabit-rate GaAs digital integrated circuits, offers substantial advantages in power consumption and weight over silicon technologies for high-throughput, on-board baseband processor systems. In this paper, current developments in GaAs MMIC technology are described, and the status and prospects of the technology are assessed.

  17. Advances in gallium arsenide monolithic microwave integrated-circuit technology for space communications systems

    NASA Technical Reports Server (NTRS)

    Bhasin, K. B.; Connolly, D. J.

    1986-01-01

    Future communications satellites are likely to use gallium arsenide (GaAs) monolithic microwave integrated-circuit (MMIC) technology in most, if not all, communications payload subsystems. Multiple-scanning-beam antenna systems are expected to use GaAs MMIC's to increase functional capability, to reduce volume, weight, and cost, and to greatly improve system reliability. RF and IF matrix switch technology based on GaAs MMIC's is also being developed for these reasons. MMIC technology, including gigabit-rate GaAs digital integrated circuits, offers substantial advantages in power consumption and weight over silicon technologies for high-throughput, on-board baseband processor systems. In this paper, current developments in GaAs MMIC technology are described, and the status and prospects of the technology are assessed.

  18. GaAs microwave devices and circuits with submicron electron-beam defined features

    NASA Technical Reports Server (NTRS)

    Wisseman, W. R.; Macksey, H. M.; Brehm, G. E.; Saunier, P.

    1983-01-01

    This paper describes the fabrication and application of GaAs FET's, both as discrete microwave devices and as the key active components in monolithic microwave integrated circuits. The performance of these devices and circuits is discussed for frequencies ranging from 3 to 25 GHz. The crucial fabrication step is the formation of the submicron gate by electron-beam lithography.

  19. GaAs microwave devices and circuits with submicron electron-beam defined features

    NASA Technical Reports Server (NTRS)

    Wisseman, W. R.; Macksey, H. M.; Brehm, G. E.; Saunier, P.

    1983-01-01

    This paper describes the fabrication and application of GaAs FET's, both as discrete microwave devices and as the key active components in monolithic microwave integrated circuits. The performance of these devices and circuits is discussed for frequencies ranging from 3 to 25 GHz. The crucial fabrication step is the formation of the submicron gate by electron-beam lithography.

  20. Material and processing issues for the monolithic integration of microelectronics with surface-micromachined polysilicon sensors and actuators

    SciTech Connect

    Smith, J.H.; Montague, S.; Sniegowski, J.J.

    1995-08-01

    The monolithic integration of micromechanical devices with their controlling electronics offers potential increases in performance as well as decreases in cost for these devices. Analog Devices has demonstrated the commercial viability of this integration by interleaving the micromechanical fabrication steps of an accelerometer with the microelectronic fabrication steps of its controlling electronics. Sandia`s Microelectronics Development Laboratory has integrated the micromechanical and microelectronic processing sequences in a segregated fashion. In this CMOS-first, micromechanics-last approach, conventional aluminum metallization is replaced by tungsten metallization to allow CMOS to withstand subsequent high-temperature processing during the micromechanical fabrication. This approach is a further development of an approach originally developed at UC Berkeley. Specifically, the issues of yield, repeatability, and uniformity of the tungsten/CMOS approach are addressed. Also, material issues related to the development of high-temperature diffusion barriers, adhesion layers, and low-stress films are discussed. Processing and material issues associated with alternative approaches to this integration such as micromechanics- first, CMOS-last or the interleaved process are also discussed.

  1. Surface-acoustic-wave study of defects in GaAs grown by molecular-beam epitaxy at 220 degree C

    SciTech Connect

    Khachaturyan, K.; Weber, E.R. Materials Science Division, Lawrence Berkeley Laboratory, Berkeley, California 94720 ); White, R.M. )

    1992-02-15

    Surface acoustic waves (SAW's) were used to study the influence of defects on the elastic properties of epitaxial films of semiconductors. The object of this study was As-rich GaAs grown by molecular-beam-epitaxy at 220 {degree}C. The SAW velocity on 0.3-wavelength-thick epilayers was 1.2% smaller than on the substrate alone. That velocity difference decreased after loss of some excess As as a result of 350 {degree}C--435 {degree}C anneals. A persistent increase as much as 0.4% of the SAW velocity at low temperatures was observed after illumination; this increase could be quenched by annealing at 120--130 K. This behavior is caused by the metastable transition of EL2-like As{sub Ga} defects and constitutes the direct experimental proof of the illumination-induced large lattice relaxation of this defect. The SAW velocity increase was correlated with the persistent bleaching of EL2-related optical absorption. The spectral dependence of rate of illumination-induced SAW velocity increase was measured.

  2. Optical techniques to feed and control GaAs MMIC modules for phased array antenna applications

    NASA Technical Reports Server (NTRS)

    Bhasin, K. B.; Anzic, G.; Kunath, R. R.; Connolly, D. J.

    1986-01-01

    A complex signal distribution system is required to feed and control GaAs monolithic microwave integrated circuits (MMICs) for phased array antenna applications above 20 GHz. Each MMIC module will require one or more RF lines, one or more bias voltage lines, and digital lines to provide a minimum of 10 bits of combined phase and gain control information. In a closely spaced array, the routing of these multiple lines presents difficult topology problems as well as a high probability of signal interference. To overcome GaAs MMIC phased array signal distribution problems optical fibers interconnected to monolithically integrated optical components with GaAs MMIC array elements are proposed as a solution. System architecture considerations using optical fibers are described. The analog and digital optical links to respectively feed and control MMIC elements are analyzed. It is concluded that a fiber optic network will reduce weight and complexity, and increase reliability and performance, but higher power will be required.

  3. Protective Skins for Aerogel Monoliths

    NASA Technical Reports Server (NTRS)

    Leventis, Nicholas; Johnston, James C.; Kuczmarski, Maria A.; Meador, Ann B.

    2007-01-01

    A method of imparting relatively hard protective outer skins to aerogel monoliths has been developed. Even more than aerogel beads, aerogel monoliths are attractive as thermal-insulation materials, but the commercial utilization of aerogel monoliths in thermal-insulation panels has been inhibited by their fragility and the consequent difficulty of handling them. Therefore, there is a need to afford sufficient protection to aerogel monoliths to facilitate handling, without compromising the attractive bulk properties (low density, high porosity, low thermal conductivity, high surface area, and low permittivity) of aerogel materials. The present method was devised to satisfy this need. The essence of the present method is to coat an aerogel monolith with an outer polymeric skin, by painting or spraying. Apparently, the reason spraying and painting were not attempted until now is that it is well known in the aerogel industry that aerogels collapse in contact with liquids. In the present method, one prevents such collapse through the proper choice of coating liquid and process conditions: In particular, one uses a viscous polymer precursor liquid and (a) carefully controls the amount of liquid applied and/or (b) causes the liquid to become cured to the desired hard polymeric layer rapidly enough that there is not sufficient time for the liquid to percolate into the aerogel bulk. The method has been demonstrated by use of isocyanates, which, upon exposure to atmospheric moisture, become cured to polyurethane/polyurea-type coats. The method has also been demonstrated by use of commercial epoxy resins. The method could also be implemented by use of a variety of other resins, including polyimide precursors (for forming high-temperature-resistant protective skins) or perfluorinated monomers (for forming coats that impart hydrophobicity and some increase in strength).

  4. Sensor Lead Wires Positioned on SiC-based Monolithic Ceramic and Fiber- reinforced Ceramic Matrix Composite Subcomponents with Flat and Curved Surfaces

    NASA Technical Reports Server (NTRS)

    Kiser, James D.; Singh, Mrityunjay; Lei, Jih-Fen; Martin, Lisa C.

    1999-01-01

    There is strong interest in the development of silicon carbide-based monolithic ceramic and composite materials and components for demanding, high-temperature applications. Thorough characterization of material properties, including high-temperature testing under simulated or actual operating conditions, is a high priority for programs involved in developing these silicon carbide- (SiC) based materials and components. Members of the Sensors and Electronics Technology Branch at the NASA Lewis Research Center are developing minimally intrusive methods of measuring the properties (such as the surface temperature, strain, and heat flux characteristics) of components and subelements that are being tested or operated in hostile, high-temperature environments. Their primary goal is to instrument the test article or operating component with durable sensors that have a minimal effect on test conditions such as the gas flow across the surface of the item and the material response (including the through-thickness conduction of heat). Therefore, the main thrust of their work has been the development of thin-film sensors (e.g., thermocouples or strain gauges) for use on various advanced material test articles, including SiC/SiC composite components. There was a need for a better method of securing sensor lead wires on SiC-based components and subelements that would be tested at temperatures to 1000 C (or higher), to enhance the durability of the overall minimally intrusive sensor system. To address this need, Lewis researchers devised an alternative approach for positioning the sensor lead wires (which are connected to the thin-film sensors) on SiC or SiC/SiC components. A reaction-forming method of joining was used to strongly bond hoop-shaped monolithic SiC and SiC/SiC composite attachments of various sizes to both flat and curved surfaces of SiC/SiC composite subelements (see the photos). This approach is based on an affordable, robust ceramic joining technology, named

  5. Investigation of Schottky Barrier on GaAs and InP Using a Multi-Disciplined Approach

    DTIC Science & Technology

    1990-10-29

    more optimum metal contacts and Schottky barriers on GaAs and for increasing productivity and reliability of monolithic as well as individual GaAs...Since this overall study was motivated by a desire to understand GaAs (as well as InP and other 3-5) interfaces on an atomic level , we recognized...properly manipulating the native defects and impurity doping near the interface. This is supported by results of studies by others as well as

  6. Monolithic exploding foil initiator

    DOEpatents

    Welle, Eric J; Vianco, Paul T; Headley, Paul S; Jarrell, Jason A; Garrity, J. Emmett; Shelton, Keegan P; Marley, Stephen K

    2012-10-23

    A monolithic exploding foil initiator (EFI) or slapper detonator and the method for making the monolithic EFI wherein the exploding bridge and the dielectric from which the flyer will be generated are integrated directly onto the header. In some embodiments, the barrel is directly integrated directly onto the header.

  7. Monolithic GaAs Dual-Gate FET Phase Shifter.

    DTIC Science & Technology

    1982-02-01

    bridge. III. PUBLICATIONS The following papers have been published since the last reporting period: 1. M. Kumar, R. J. Henna and H. C. Huang, "Broad...1981. 2. N. Kumar, R. J. Henna and H. C. Huang, "Planar Broad Band 1800 Hybrid Power Divider/Combiner Circuit," IEEE Transactions on Microwave Theory and

  8. Design of Semiconductor-Based Back Reflectors for High Voc Monolithic Multijunction Solar Cells: Preprint

    SciTech Connect

    Garcia, I.; Geisz, J.; Steiner, M.; Olson, J.; Friedman, D.; Kurtz, S.

    2012-06-01

    State-of-the-art multijunction cell designs have the potential for significant improvement before going to higher number of junctions. For example, the Voc can be substantially increased if the photon recycling taking place in the junctions is enhanced. This has already been demonstrated (by Alta Devices) for a GaAs single-junction cell. For this, the loss of re-emitted photons by absorption in the underlying layers or substrate must be minimized. Selective back surface reflectors are needed for this purpose. In this work, different architectures of semiconductor distributed Bragg reflectors (DBR) are assessed as the appropriate choice for application in monolithic multijunction solar cells. Since the photon re-emission in the photon recycling process is spatially isotropic, the effect of the incident angle on the reflectance spectrum is of central importance. In addition, the DBR structure must be designed taking into account its integration into the monolithic multijunction solar cells, concerning series resistance, growth economics, and other issues. We analyze the tradeoffs in DBR design complexity with all these requirements to determine if such a reflector is suitable to improve multijunction solar cells.

  9. Near infrared broadband emission of In0.35Ga0.65As quantum dots on high index GaAs surfaces.

    PubMed

    Wu, Jiang; Wang, Zhiming M; Dorogan, Vitaliy G; Li, Shibin; Mazur, Yuriy I; Salamo, Gregory J

    2011-04-01

    The morphology and optical properties of In(0.35)Ga(0.65)As/GaAs quantum dots (QDs) grown on (210), (311)A, (711)A, (731) and (100) substrates are investigated. QDs formed on (210) and (731) oriented substrates are grown by molecular beam epitaxy. Regular QDs are observed on (100), (311)A, and (711)A. Randomly distributed QDs and comet-shaped QDs form on (210) and (731) substrates, respectively. A high density of QDs on the order of 10(11) cm(-2) are obtained from (711)A. The optical measurement shows a spectrum linewidth (FWHM = 74.3 nm) of QDs on GaAs (210) three times wider than GaAs (100) substrate. Long exciton decay times, over 1 ns, are also measured by time-resolved photoluminescence technique for all samples. Our results demonstrate the potential for QDs on GaAs high index substrates for wideband applications.

  10. GaAs photoconductive semiconductor switch

    DOEpatents

    Loubriel, G.M.; Baca, A.G.; Zutavern, F.J.

    1998-09-08

    A high gain, optically triggered, photoconductive semiconductor switch (PCSS) implemented in GaAs as a reverse-biased pin structure with a passivation layer above the intrinsic GaAs substrate in the gap between the two electrodes of the device is disclosed. The reverse-biased configuration in combination with the addition of the passivation layer greatly reduces surface current leakage that has been a problem for prior PCSS devices and enables employment of the much less expensive and more reliable DC charging systems instead of the pulsed charging systems that needed to be used with prior PCSS devices. 5 figs.

  11. GaAs photoconductive semiconductor switch

    DOEpatents

    Loubriel, Guillermo M.; Baca, Albert G.; Zutavern, Fred J.

    1998-01-01

    A high gain, optically triggered, photoconductive semiconductor switch (PCSS) implemented in GaAs as a reverse-biased pin structure with a passivation layer above the intrinsic GaAs substrate in the gap between the two electrodes of the device. The reverse-biased configuration in combination with the addition of the passivation layer greatly reduces surface current leakage that has been a problem for prior PCSS devices and enables employment of the much less expensive and more reliable DC charging systems instead of the pulsed charging systems that needed to be used with prior PCSS devices.

  12. Green (In,Ga,Al)P-GaP light-emitting diodes grown on high-index GaAs surfaces

    SciTech Connect

    Ledentsov, N. N. Shchukin, V. A.; Lyytikäinen, J.; Okhotnikov, O.; Shernyakov, Yu. M.; Payusov, A. S.; Gordeev, N. Yu.; Maximov, M. V.; Schlichting, S.; Nippert, F.; Hoffmann, A.

    2014-11-03

    We report on green (550–560 nm) electroluminescence (EL) from (Al{sub 0.5}Ga{sub 0.5}){sub 0.5}In{sub 0.5}P-(Al{sub 0.8}Ga{sub 0.2}){sub 0.5}In{sub 0.5}P double p-i-n heterostructures with monolayer-scale GaP insertions in the cladding layers and light-emitting diodes based thereupon. The structures are grown side-by-side on high-index and (100) GaAs substrates by molecular beam epitaxy. At moderate current densities (∼500 A/cm{sup 2}), the EL intensity of the structures is comparable for all substrate orientations. Opposite to the (100)-grown strictures, the EL spectra of (211) and (311)-grown devices are shifted towards shorter wavelengths (∼550 nm at room temperature). At high current densities (>1 kA/cm{sup 2}), a much higher EL intensity is achieved for the devices grown on high-index substrates. The integrated intensity of (311)-grown structures gradually saturates at current densities above 4 kA/cm{sup 2}, whereas no saturation is revealed for (211)-grown structures up to the current densities above 14 kA/cm{sup 2}. We attribute the effect to the surface orientation-dependent engineering of the GaP band structure, which prevents the escape of the nonequilibrium electrons into the indirect conduction band minima of the p-doped (Al{sub 0.8}Ga{sub 0.2}){sub 0.5}In{sub 0.5}P cladding layers.

  13. Hydrophobic-hydrophilic monolithic dual-phase layer for two-dimensional thin-layer chromatography coupled with surface-enhanced Raman spectroscopy detection.

    PubMed

    Zheng, Binxing; Liu, Yanhua; Li, Dan; Chai, Yifeng; Lu, Feng; Xu, Jiyang

    2015-08-01

    Hydrophobic-hydrophilic monolithic dual-phase plates have been prepared by a two-step polymerization method for two-dimensional thin-layer chromatography of low-molecular-weight compounds, namely, several dyes. The thin 200 μm poly(glycidyl methacrylate-co-ethylene dimethacrylate) layers attached to microscope glass plates were prepared using a UV-initiated polymerization method within a simple glass mold. After cutting and cleaning the specific area of the layer, the reassembled mold was filled with a polymerization mixture of butyl methacrylate and ethylene dimethacrylate and subsequently irradiated with UV light. During the second polymerization process, the former layer was protected from the UV light with a UV mask. After extracting the porogens and hydrolyzing the poly(glycidyl methacrylate-co-ethylene dimethacrylate) area, these two-dimensional layers were used to separate a mixture of dyes with great difference in their polarity using reversed-phase chromatography mode within the hydrophobic layer and then hydrophilic interaction chromatography mode along the hydrophilic area. In the latter dimension only the specific spot was developed further. Detection of the separated dyes could be achieved with surface-enhanced Raman spectroscopy. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  14. Methacrylate Polymer Monoliths for Separation Applications

    PubMed Central

    Groarke, Robert J.; Brabazon, Dermot

    2016-01-01

    This review summarizes the development of methacrylate-based polymer monoliths for separation science applications. An introduction to monoliths is presented, followed by the preparation methods and characteristics specific to methacrylate monoliths. Both traditional chemical based syntheses and emerging additive manufacturing methods are presented along with an analysis of the different types of functional groups, which have been utilized with methacrylate monoliths. The role of methacrylate based porous materials in separation science in industrially important chemical and biological separations are discussed, with particular attention given to the most recent developments and challenges associated with these materials. While these monoliths have been shown to be useful for a wide variety of applications, there is still scope for exerting better control over the porous architectures and chemistries obtained from the different fabrication routes. Conclusions regarding this previous work are drawn and an outlook towards future challenges and potential developments in this vibrant research area are presented. Discussed in particular are the potential of additive manufacturing for the preparation of monolithic structures with pre-defined multi-scale porous morphologies and for the optimization of surface reactive chemistries. PMID:28773570

  15. Au impact on GaAs epitaxial growth on GaAs (111){sub B} substrates in molecular beam epitaxy

    SciTech Connect

    Liao, Zhi-Ming; Chen, Zhi-Gang; Xu, Hong-Yi; Guo, Ya-Nan; Sun, Wen; Zhang, Zhi; Yang, Lei; Lu, Zhen-Yu; Chen, Ping-Ping; Lu, Wei; Zou, Jin

    2013-02-11

    GaAs growth behaviour under the presence of Au nanoparticles on GaAs {l_brace}111{r_brace}{sub B} substrate is investigated using electron microscopy. It has been found that, during annealing, enhanced Ga surface diffusion towards Au nanoparticles leads to the GaAs epitaxial growth into {l_brace}113{r_brace}{sub B} faceted triangular pyramids under Au nanoparticles, governed by the thermodynamic growth, while during conventional GaAs growth, growth kinetics dominates, resulting in the flatted triangular pyramids at high temperature and the epitaxial nanowires growth at relatively low temperature. This study provides an insight of Au nanoparticle impact on GaAs growth, which is critical for understanding the formation mechanisms of semiconductor nanowires.

  16. Enhancement of surface plasmon resonances on the nonlinear optical properties in a GaAs quantum dot

    NASA Astrophysics Data System (ADS)

    Jiang, Xiancong; Guo, Kangxian; Liu, Guanghui; Yang, Tao; Yang, Yanlian

    2017-05-01

    In this paper, the nonlinear optical properties of a metallic nanoparticle (MNP)-semiconductor quantum dot (SQD) hybrid nanosystem with the hybrid exciton effect have been studied. Considering the influence of quantum-size effect to the dielectric function of MNP, the quantum corrected dielectric function was applied to our calculation. By using the compact-density-matrix method, the interaction between MNP and SQD has been studied theoretically. The results show that the surface plasmon resonances (SPRs) of MNP enhance indeed the nonlinear optical properties of SQD. Further more, the enhancement depends on two factors: (a) the center-to-center 7distance between MNP and SQD; (b) the radius ratio between MNP and SQD.

  17. Fabrication of poly(γ-glutamic acid) monolith by thermally induced phase separation and its application.

    PubMed

    Park, Sung-Bin; Fujimoto, Takashi; Mizohata, Eiichi; Inoue, Tsuyoshi; Sung, Moon-Hee; Uyama, Hiroshi

    2013-01-01

    Monoliths are functional porous materials with a three-dimensional continuous interconnected pore structure in a single piece. A monolith with uniform shape based on poly(γ-glutamic acid) (PGA) has been prepared via a thermally induced phase separation technique using a mixture of dimethyl sulfoxide, water, and ethanol as solvent. The morphology of the obtained monolith was observed by scanning electron microscopy and the surface area of the monolith was evaluated by the Brunauer Emmett Teller method. The effects of fabrication parameters such as the concentration and molecular mass of PGA and the solvent composition have been systematically investigated. The PGA monolith was cross-linked with hexamethylene diisocyanate to produce the water-insoluble monolith. The addition of sodium chloride to the phase separation solvent affected the properties of the cross-linked monolith. The swelling ratio of the cross-linked monolith toward aqueous solutions depended on the buffer pH as well as the monolith fabrication condition. Copper(II) ion was efficiently adsorbed on the cross-linked PGA monolith, and the obtained copper-immobilized monolith showed strong antibacterial activity for Escherichia coli. By combination of the characteristic properties of PGA (e.g., high biocompatibility and biodegradability) and the unique features of monoliths (e.g., through-pore structure, large surface area, and high porosity with small pore size), the PGA monolith possesses large potentials for various industrial applications in the biomedical, environmental, analytical, and separation fields.

  18. Tolerance of GaAs as an original substrate for HVPE growth of free standing GaN

    NASA Astrophysics Data System (ADS)

    Suzuki, Mio; Sato, T.; Suemasu, T.; Hasegawa, F.

    2004-09-01

    In order to investigate possibility of thick GaN growth on a GaAs substrate by halide vapar phase epitaxy (HVPE), GaN was grown on GaAs(111)/Ti wafer with Ti deposited by E-gun. It was found that surface treatment of the GaAs substrate by HF solution deteriorated greatly the tolerence of GaAs and that Ti can protected GaAs from erosion by NH3. By depositing Ti on GaAs(111)A surface, a millor-like GaN layer could be grown at 1000 °C for 1 hour without serious deterioration of the original GaAs substrate. By increasing the growth rate, a thick free standing GaN will be obtained with GaAs as an original substrate in near future.

  19. Preparation of GaAs photocathodes at low temperature

    SciTech Connect

    Mulhollan, G.; Clendenin, J.; Tang, H.

    1996-10-01

    The preparation of an atomically clean surface is a necessary step in the formation of negative electron affinity (NEA) GaAs. Traditional methods to this end include cleaving, heat cleaning and epitaxial growth. Cleaving has the advantage of yielding a fresh surface after each cleave, but is limited to small areas and is not suitable for specialized structures. Heat cleaning is both simple and highly successful, so it is used as a preparation method in virtually all laboratories employing a NEA source on a regular basis. Due to its high cost and complexity, epitaxial growth of GaAs with subsequent in vacuo transfer is not a practical solution for most end users of GaAs as a NEA electron source. While simple, the heating cleaning process has a number of disadvantages. Here, a variety of cleaning techniques related to preparation of an atomically clean GaAs surface without heating to 600 C are discussed and evaluated.

  20. Synthesis of Porous Carbon Monoliths Using Hard Templates

    PubMed Central

    Klepel, Olaf; Danneberg, Nina; Dräger, Matti; Erlitz, Marcel; Taubert, Michael

    2016-01-01

    The preparation of porous carbon monoliths with a defined shape via template-assisted routes is reported. Monoliths made from porous concrete and zeolite were each used as the template. The porous concrete-derived carbon monoliths exhibited high gravimetric specific surface areas up to 2000 m2·g−1. The pore system comprised macro-, meso-, and micropores. These pores were hierarchically arranged. The pore system was created by the complex interplay of the actions of both the template and the activating agent as well. On the other hand, zeolite-made template shapes allowed for the preparation of microporous carbon monoliths with a high volumetric specific surface area. This feature could be beneficial if carbon monoliths must be integrated into technical systems under space-limited conditions. PMID:28773338

  1. Micromechanical Switches on GaAs for Microwave Applications

    NASA Technical Reports Server (NTRS)

    Randall, John N.; Goldsmith, Chuck; Denniston, David; Lin, Tsen-Hwang

    1995-01-01

    In this presentation, we describe the fabrication of micro-electro-mechanical system (MEMS) devices, in particular, of low-frequency multi-element electrical switches using SiO2 cantilevers. The switches discussed are related to micromechanical membrane structures used to perform switching of optical signals on silicon substrates. These switches use a thin metal membrane which is actuated by an electrostatic potential, causing the switch to make or break contact. The advantages include: superior isolation, high power handling capabilities, high radiation hardening, very low power operations, and the ability to integrate onto GaAs monolithic microwave integrated circuit (MMIC) chips.

  2. Effect of polishing instruments and polishing regimens on surface topography and phase transformation of monolithic zirconia: An evaluation with XPS and XRD analysis.

    PubMed

    Al-Haj Husain, Nadin; Camilleri, Josette; Özcan, Mutlu

    2016-12-01

    Polishing procedures might alter monolithic zirconia (MZ) surface resulting in phase changes that can be deleterious for clinical performance and antagonist tooth wear. This study investigated the topographical features and phase transformation in MZ after polishing with different regimens simulating the clinical workflow. ​ MZ specimens (Katana Zirconia HT, Kuraray-Noritake) (12×12×1.8 mm(3)) were grinded and polished using one of the five systems assessed: BG: Silicone carbide polishers (Brownie, Greenie, Super Greenie); CG: Diamond impregnated ceramic polisher kit (Ceragloss); EV: Synthetically bonded grinder interspersed with diamond (EVE Kit); SL: Urethane coated paper with aluminium oxide grits (Soflex Finishing and Polishing System Kit) and DB: Diamond bur (8 µm). Polished specimens were initially roughened with 220 µm diamond burs (Grinding Bur-GB) (10 s, 160.000160,000 rpm) and considered for baseline measurements. Polishing regimens were performed for 10 s using a slow-speed hand piece under water-cooling except for SL, in a custom made device (750 g; 5000 and 75,000 rpm). Surface roughnesses, phase changes (XRD) were assessed, surface characterization was performed (SEM, EDS). The highest roughness was obtained with the EV system (1.11 µm) compared to those of other systems (0.13-0.4 µm) (pθ and minor peak at 34.94°2θ. While GB, CG, EV, SL and DB exhibited a peak shift to the left, BG demonstrated a right peak shift on the 2θ scale. Monoclinic phase change was not noted in any of the groups. All polishing methods, except BG, exhibited a peak shift towards the lower angles of the 2-theta scale. Since the peak shifts were in the order of fractions of an angle they are attributed to stress formation rather than a phase change in the material. Thus, all polishing systems tested may not be detrimental for the phase transformation of MZ. EV system resulted in the highest roughness and none of the polishing regimens restored the polishability to the

  3. Development of an affinity silica monolith containing human serum albumin for chiral separations.

    PubMed

    Mallik, Rangan; Hage, David S

    2008-04-14

    An affinity monolith based on silica and containing immobilized human serum albumin (HSA) was developed and evaluated in terms of its binding, efficiency and selectivity in chiral separations. The results were compared with data obtained for the same protein when used as a chiral stationary phase with HPLC-grade silica particles or a monolith based on a copolymer of glycidyl methacrylate (GMA) and ethylene dimethacrylate (EDMA). The surface coverage of HSA in the silica monolith was similar to values obtained with silica particles and a GMA/EDMA monolith. However, the higher surface area of the silica monolith gave a material that contained 1.3-2.2-times more immobilized HSA per unit volume when compared to silica particles or a GMA/EDMA monolith. The retention, efficiency and resolving power of the HSA silica monolith were evaluated using two chiral analytes: d/l-tryptophan and R/S-warfarin. The separation of R- and S-ibuprofen was also considered. The HSA silica monolith gave higher retention and higher or comparable resolution and efficiency when compared with HSA columns that contained silica particles or a GMA/EDMA monolith. The silica monolith also gave lower back pressures and separation impedances than these other materials. It was concluded that silica monoliths can be valuable alternatives to silica particles or GMA/EDMA monoliths when used with immobilized HSA as a chiral stationary phase.

  4. Air Force development of thin GaAs solar cells

    NASA Technical Reports Server (NTRS)

    Masloski, K.

    1982-01-01

    The advantages of gallium arsenide (GaAs) over silicon (Si) type solar cells are well documented. However, two major disadvantages are weight and cost. Several ideas have recently surfaced that, if successful, will diminish these disadvantages. The CLEFT peeled film technique and the galicon cell are two of the more promising approaches. Low weight, low cost, high efficiency GaAs solar cell research is summarized.

  5. A 30 GHz monolithic receive module technology assessment

    NASA Technical Reports Server (NTRS)

    Geddes, J.; Sokolov, V.; Bauhahn, P.; Contolatis, T.

    1988-01-01

    This report is a technology assessment relevant to the 30 GHz Monolithic Receive Module development. It is based on results obtained on the present NASA Contract (NAS3-23356) as well as on information gathered from literature and other industry sources. To date the on-going Honeywell program has concentrated on demonstrating the so-called interconnected receive module which consists of four monolithic chips - the low noise front-end amplifier (LNA), the five bit phase shifter (PS), the gain control amplifier (GC), and the RF to IF downconverter (RF/IF). Results on all four individual chips have been obtained and interconnection of the first three functions has been accomplished. Future work on this contract is aimed at a higher level of integration, i.e., integration of the first three functions (LNA + PS + GC) on a single GaAs chip. The report presents the status of this technology and projections of its future directions.

  6. Monolithic control components handle 27 W of RF power

    NASA Astrophysics Data System (ADS)

    Shifrin, Mitchell B.; Ayasli, Yalcin; Katzin, Peter J.

    1989-12-01

    This paper describes a general approach to overcoming the voltage limitations of the individual switch FET by effectively combining several FETs in a monolithic series configuration. The operation of this configuration is examined using, as an example, a combination of two FETs that are shunt-mounted to an RF line. The technology described is considered to be appplicable to an arbitrary number of cells in shunt or in series with the RF transmission line. It is shown that such a FET circuit allows the power-handling capability of MMIC GaAs FET switches to be increased by more than an order of magnitude.

  7. Selective oxidation of cyclohexene through gold functionalized silica monolith microreactors

    NASA Astrophysics Data System (ADS)

    Alotaibi, Mohammed T.; Taylor, Martin J.; Liu, Dan; Beaumont, Simon K.; Kyriakou, Georgios

    2016-04-01

    Two simple, reproducible methods of preparing evenly distributed Au nanoparticle containing mesoporous silica monoliths are investigated. These Au nanoparticle containing monoliths are subsequently investigated as flow reactors for the selective oxidation of cyclohexene. In the first strategy, the silica monolith was directly impregnated with Au nanoparticles during the formation of the monolith. The second approach was to pre-functionalize the monolith with thiol groups tethered within the silica mesostructure. These can act as evenly distributed anchors for the Au nanoparticles to be incorporated by flowing a Au nanoparticle solution through the thiol functionalized monolith. Both methods led to successfully achieving even distribution of Au nanoparticles along the length of the monolith as demonstrated by ICP-OES. However, the impregnation method led to strong agglomeration of the Au nanoparticles during subsequent heating steps while the thiol anchoring procedure maintained the nanoparticles in the range of 6.8 ± 1.4 nm. Both Au nanoparticle containing monoliths as well as samples with no Au incorporated were tested for the selective oxidation of cyclohexene under constant flow at 30 °C. The Au free materials were found to be catalytically inactive with Au being the minimum necessary requirement for the reaction to proceed. The impregnated Au-containing monolith was found to be less active than the thiol functionalized Au-containing material, attributable to the low metal surface area of the Au nanoparticles. The reaction on the thiol functionalized Au-containing monolith was found to depend strongly on the type of oxidant used: tert-butyl hydroperoxide (TBHP) was more active than H2O2, likely due to the thiol induced hydrophobicity in the monolith.

  8. Advanced on-chip divider for monolithic microwave VCO's

    NASA Technical Reports Server (NTRS)

    Peterson, Weddell C.

    1989-01-01

    High frequency division on a monolithic circuit is a critical technology required to significantly enhance the performance of microwave and millimeter-wave phase-locked sources. The approach used to meet this need is to apply circuit design practices which are essentially 'microwave' in nature to the basically 'digital' problem of high speed division. Following investigation of several promising circuit approaches, program phase 1 culminated in the design and layout of an 8.5 GHz (Deep Space Channel 14) divide by four circuit based on a dynamic mixing divider circuit approach. Therefore, during program phase 2, an 8.5 GHz VCO with an integral divider which provides a phase coherent 2.125 GHz reference signal for phase locking applications was fabricated and optimized. Complete phase locked operation of the monolithic GaAs devices (VCO, power splitter, and dynamic divider) was demonstrated both individually and as an integrated unit. The fully functional integrated unit in a suitable test fixture was delivered to NASA for engineering data correlation. Based on the experience gained from this 8.5 GHz super component, a monolithic GaAs millimeter-wave dynamic divider for operation with an external VCO was also designed, fabricated, and characterized. This circuit, which was also delivered to NASA, demonstrated coherent division by four at an input frequency of 24.3 GHz. The high performance monolithic microwave VCO with a coherent low frequency reference output described in this report and others based on this technology will greatly benefit advanced communications systems in both the DoD and commercial sectors. Signal processing and instrumentation systems based on phase-locking loops will also attain enhanced performance at potentially reduced cost.

  9. Catalytic Ignition and Upstream Reaction Propagation in Monolith Reactors

    NASA Technical Reports Server (NTRS)

    Struk, Peter M.; Dietrich, Daniel L.; Miller, Fletcher J.; T'ien, James S.

    2007-01-01

    Using numerical simulations, this work demonstrates a concept called back-end ignition for lighting-off and pre-heating a catalytic monolith in a power generation system. In this concept, a downstream heat source (e.g. a flame) or resistive heating in the downstream portion of the monolith initiates a localized catalytic reaction which subsequently propagates upstream and heats the entire monolith. The simulations used a transient numerical model of a single catalytic channel which characterizes the behavior of the entire monolith. The model treats both the gas and solid phases and includes detailed homogeneous and heterogeneous reactions. An important parameter in the model for back-end ignition is upstream heat conduction along the solid. The simulations used both dry and wet CO chemistry as a model fuel for the proof-of-concept calculations; the presence of water vapor can trigger homogenous reactions, provided that gas-phase temperatures are adequately high and there is sufficient fuel remaining after surface reactions. With sufficiently high inlet equivalence ratio, back-end ignition occurs using the thermophysical properties of both a ceramic and metal monolith (coated with platinum in both cases), with the heat-up times significantly faster for the metal monolith. For lower equivalence ratios, back-end ignition occurs without upstream propagation. Once light-off and propagation occur, the inlet equivalence ratio could be reduced significantly while still maintaining an ignited monolith as demonstrated by calculations using complete monolith heating.

  10. Monolithic microwave integrated circuits

    NASA Astrophysics Data System (ADS)

    Pucel, R. A.

    Monolithic microwave integrated circuits (MMICs), a new microwave technology which is expected to exert a profound influence on microwave circuit designs for future military systems as well as for the commercial and consumer markets, is discussed. The book contains an historical discussion followed by a comprehensive review presenting the current status in the field. The general topics of the volume are: design considerations, materials and processing considerations, monolithic circuit applications, and CAD, measurement, and packaging techniques. All phases of MMIC technology are covered, from design to testing.

  11. Ion Implanted Gaas Integrated Optics Fabrication Technology

    NASA Astrophysics Data System (ADS)

    Mentzer, M. A.; Hunsperger, R. G.; Bartko, J.; Zavada, J. M.; Jenkinson, H. A.

    1985-01-01

    Ion implantation of semiconductor materials is a fabrication technique that offers a number of distinct advantages for the formation of guided-wave components and microelectronic devices. Implanted damage and dopants produce optical and electronic changes that can be utilized for sensing and signal processing applications. GaAs is a very attractive material for optical fabrication since it is transparent out to the far infrared. It can be used to fabricate optical waveguides, directional couplers, EO modulators, and detectors, as well as other guided wave structures. The presence of free carriers in GaAs lowers the refractive index from that of the pure semiconductor material. This depression of the refractive index is primarily due to the negative contribution of the free carrier plasma to the dielectric constant of the semiconductor. Bombardment of n-type GaAs by protons creates damage sites near the surface of the crystal structure where free carriers are trapped. This "free carrier compensated" region in the GaAs has a higher refractive index than the bulk region. If the compensated region is sufficiently thick and has a refractive index which is sufficiently larger than that of the bulk n-type region, an optical waveguide is formed. In this paper, a description of ion implantation techniques for the fabrication of both planar and channel integrated optical structures in GaAs is presented, and is related to the selection of ion species, implant energy and fluence, and to the physical processes involved. Lithographic technology and masking techniques are discussed for achieving a particular desired implant profile. Finally, the results of a set of ion implantation experiments are presented.

  12. Photoinitiated grafting of porous polymer monoliths and thermoplastic polymers for microfluidic devices

    DOEpatents

    Frechet, Jean M. J. [Oakland, CA; Svec, Frantisek [Alameda, CA; Rohr, Thomas [Leiden, NL

    2008-10-07

    A microfluidic device preferably made of a thermoplastic polymer that includes a channel or a multiplicity of channels whose surfaces are modified by photografting. The device further includes a porous polymer monolith prepared via UV initiated polymerization within the channel, and functionalization of the pore surface of the monolith using photografting. Processes for making such surface modifications of thermoplastic polymers and porous polymer monoliths are set forth.

  13. Facile fabrication of mesoporous poly(ethylene-co-vinyl alcohol)/chitosan blend monoliths.

    PubMed

    Wang, Guowei; Xin, Yuanrong; Uyama, Hiroshi

    2015-11-05

    Poly(ethylene-co-vinyl alcohol) (EVOH)/chitosan blend monoliths were fabricated by thermally-induced phase separation method. Chitosan was successfully incorporated into the polymeric monolith by selecting EVOH as the main component of the monolith. SEM images exhibit that the chitosan was located on the inner surface of the monolith. Fourier-transform infrared analysis and elemental analysis indicate the successful blend of EVOH and chitosan. BET results show that the blend monoliths had high specific surface area and uniform mesopore structure. Good adsorption ability toward various heavy metal ions was found in the blend monoliths due to the large chelation capacity of chitosan. The blend monoliths have potential application for waste water purification or bio-related applications. Copyright © 2015 Elsevier Ltd. All rights reserved.

  14. Surface morphologies and electrical properties of molecular beam epitaxial InSb and InAs(x)Sb(1-x) grown on GaAs and InP substrates

    NASA Technical Reports Server (NTRS)

    Oh, J. E.; Chen, Y. C.; Bhattacharya, P. K.; Tsukamoto, S.

    1989-01-01

    Surface morphologies and electrical properties of molecular beam epitaxial InSb and InAs(x)Sb(1-x) grown on GaAs and InP substrates are discussed. The crystals are all n-type at 300 K and lower temperatures. The surface morphology and electrical characteristics are strongly dependent on Sb(4)/In flux ratio and substrate temperature. The highest mobilities in InSb on InP are 70,000 at 300 K and 110,000 cm(2)/V.s (n=3x10(15) cm(-3)) at 77 K. The mobilities in the alloys also increase monotonically with lowering of temperature. Good quality InAs(x)Sb(1-x) was grown directly on InP substrates by molecular beam epitaxy.

  15. GaAs MMIC: recovery from upset by x-ray pulse

    SciTech Connect

    Armendariz, M.G.; Castle, J.G. Jr.

    1986-01-01

    Tolerance for fast neutrons and total ionizing dose is a feature of GaAs microwave monolithic integrated circuits (MMIC). However, upset during an ionizing pulse is expected to occur and delayed recovery due to backgating may be a problem. The purpose of this study of an experimental MMIC design is to observe the recovery of oscillator power output following upset by a short ionizing pulse as a function of applied bias, dose per pulse and case temperature.

  16. Metal stain on monolithic zirconia restoration: A case report

    PubMed Central

    2017-01-01

    In restorative treatment using fixed dental prostheses, dentists should select appropriate restoration material among various types of dental materials. The strength, marginal fit, esthetics, wear resistance, biocompatibility, and cost are important factors in the choice of restoration materials. The present case showed a surface stain on a monolithic zirconia restoration that was due to wear between the monolithic zirconia restoration and the base metal alloy restoration. This phenomenon was confirmed by surface roughness measurement and electron probe micro-analysis. PMID:28435624

  17. Metal stain on monolithic zirconia restoration: A case report.

    PubMed

    Cha, Min-Sang; Lee, Sang-Woon; Huh, Yoon-Hyuk; Cho, Lee-Ra; Park, Chan-Jin

    2017-04-01

    In restorative treatment using fixed dental prostheses, dentists should select appropriate restoration material among various types of dental materials. The strength, marginal fit, esthetics, wear resistance, biocompatibility, and cost are important factors in the choice of restoration materials. The present case showed a surface stain on a monolithic zirconia restoration that was due to wear between the monolithic zirconia restoration and the base metal alloy restoration. This phenomenon was confirmed by surface roughness measurement and electron probe micro-analysis.

  18. High-contrast grating reflectors for 980 nm vertical-cavity surface-emitting lasers

    NASA Astrophysics Data System (ADS)

    Gebski, M.; Kuzior, O.; Wasiak, M.; Szerling, A.; Wójcik-Jedlińska, A.; Pałka, N.; Dems, M.; Xie, Y. Y.; Xu, Z. J.; Wang, Q. J.; Zhang, D. H.; Czyszanowski, T.

    2015-02-01

    This paper presents results of computer simulation of 1D monolithic high refractive index contrast grating (MHCG) reflector also called surface grating reflector (SGR). We analyzed optical properties of the GaAs reflector designed for 980 nm wavelength with respect to the grating parameters variation. We also determined the electric field patterns after reflection from the structure in several cases of parameters variation. We show that thanks to the scalability and design simplicity, proposed design is a promising candidate for simple, next generation vertical cavity surface emitting lasers emitting from ultra-violet to infrared.

  19. New Passivation Methods for GaAs

    DTIC Science & Technology

    1975-01-01

    a shutter for a short ........ t .. Tl() to cover all freely exposed elements present in the chamber with an Aluminium film which will avoid oxidation...formation of an insulating layer by suitable means on the free surface to prevent carrier injection from outside and to improve the overall dielectric...conducting layers in the coses of both GaAs and GaAQ2,s. In order to prevent mixingj up cf 5lifferent dopants, a thorough cleaning procedure was appliecd

  20. Growth of silver nanowires on GaAs wafers.

    PubMed

    Sun, Yugang

    2011-05-01

    Silver (Ag) nanowires with chemically clean surfaces have been directly grown on semi-insulating gallium arsenide (GaAs) wafers through a simple solution/solid interfacial reaction (SSIR) between the GaAs wafers themselves and aqueous solutions of silver nitrate (AgNO(3)) at room temperature. The success in synthesis of Ag nanowires mainly benefits from the low concentration of surface electrons in the semi-insulating GaAs wafers that can lead to the formation of a low-density of nuclei that facilitate their anisotropic growth into nanowires. The resulting Ag nanowires exhibit rough surfaces and reasonably good electric conductivity. These characteristics are beneficial to sensing applications based on single-nanowire surface-enhanced Raman scattering (SERS) and possible surface-adsorption-induced conductivity variation.

  1. Embedded-monolith armor

    DOEpatents

    McElfresh, Michael W.; Groves, Scott E; Moffet, Mitchell L.; Martin, Louis P.

    2016-07-19

    A lightweight armor system utilizing a face section having a multiplicity of monoliths embedded in a matrix supported on low density foam. The face section is supported with a strong stiff backing plate. The backing plate is mounted on a spall plate.

  2. A two-stage monolithic buffer amplifier for 20 GHz satellite communication

    NASA Technical Reports Server (NTRS)

    Petersen, W. C.; Gupta, A. K.

    1983-01-01

    Design, fabrication, and test results of a two-stage GaAs monolithic buffer amplifier for 20 GHz satellite communication are described in this paper. A gain of 13 + or - 0.75 dB from 17.7 to 20.2 GHz was obtained from the 1.5 x 1.5 millimeter chip, which includes all necessary bias and dc blocking circuitry.

  3. Microwave monolithic integrated circuit development for future spaceborne phased array antennas

    NASA Technical Reports Server (NTRS)

    Anzic, G.; Kascak, T. J.; Downey, A. N.; Liu, D. C.; Connolly, D. J.

    1983-01-01

    The development of fully monolithic gallium arsenide (GaAs) receive and transmit modules suitable for phased array antenna applications in the 30/20 gigahertz bands is presented. Specifications and various design approaches to achieve the design goals are described. Initial design and performance of submodules and associated active and passive components are presented. A tradeoff study summary is presented highlighting the advantages of distributed amplifier approach compared to the conventional single power source designs.

  4. Microwave monolithic integrated circuit-related metrology at the National Institute of Standards and Technology

    NASA Astrophysics Data System (ADS)

    Reeve, Gerome; Marks, Roger; Blackburn, David

    1990-12-01

    How the National Institute of Standards and Technology (NIST) interacts with the GaAs community and the Defense Advanced Research Projects Agency microwave monolithic integrated circuit (MMIC) initiative is described. The organization of a joint industry and government laboratory consortium for MMIC-related metrology research is described along with some of the initial technical developments at NIST done in support of the consortium.

  5. A two-stage monolithic buffer amplifier for 20 GHz satellite communication

    NASA Technical Reports Server (NTRS)

    Petersen, W. C.; Gupta, A. K.

    1983-01-01

    Design, fabrication, and test results of a two-stage GaAs monolithic buffer amplifier for 20 GHz satellite communication are described in this paper. A gain of 13 + or - 0.75 dB from 17.7 to 20.2 GHz was obtained from the 1.5 x 1.5 millimeter chip, which includes all necessary bias and dc blocking circuitry.

  6. Ex Situ Integration of Multifunctional Porous Polymer Monoliths into Thermoplastic Microfluidic Chips.

    PubMed

    Kendall, Eric L; Wienhold, Erik; Rahmanian, Omid D; DeVoe, Don L

    2014-10-31

    A unique method for incorporating functional porous polymer monolith elements into thermoplastic microfluidic chips is described. Monolith elements are formed in a microfabricated mold, rather than within the microchannels, and chemically functionalized off chip before insertion into solvent-softened thermoplastic microchannels during chip assembly. Because monoliths may be trimmed prior to final placement, control of their size, shape, and uniformity is greatly improved over in-situ photopolymerization methods. A characteristic trapezoidal profile facilitates rapid insertion and enables complete mechanical anchoring of the monolith periphery, eliminating the need for chemical attachment to the microchannel walls. Off-chip processing allows the parallel preparation of monoliths of differing compositions and surface chemistries in large batches. Multifunctional flow-through arrays of multiple monolith elements are demonstrated using this approach through the creation of a fluorescent immunosensor with integrated controls, and a microfluidic bubble separator comprising a combination of integrated hydrophobic and hydrophilic monolith elements.

  7. Ex Situ Integration of Multifunctional Porous Polymer Monoliths into Thermoplastic Microfluidic Chips

    PubMed Central

    Kendall, Eric L.; Wienhold, Erik; Rahmanian, Omid D.; DeVoe, Don L.

    2014-01-01

    A unique method for incorporating functional porous polymer monolith elements into thermoplastic microfluidic chips is described. Monolith elements are formed in a microfabricated mold, rather than within the microchannels, and chemically functionalized off chip before insertion into solvent-softened thermoplastic microchannels during chip assembly. Because monoliths may be trimmed prior to final placement, control of their size, shape, and uniformity is greatly improved over in-situ photopolymerization methods. A characteristic trapezoidal profile facilitates rapid insertion and enables complete mechanical anchoring of the monolith periphery, eliminating the need for chemical attachment to the microchannel walls. Off-chip processing allows the parallel preparation of monoliths of differing compositions and surface chemistries in large batches. Multifunctional flow-through arrays of multiple monolith elements are demonstrated using this approach through the creation of a fluorescent immunosensor with integrated controls, and a microfluidic bubble separator comprising a combination of integrated hydrophobic and hydrophilic monolith elements. PMID:25018587

  8. Ga nanoparticle-enhanced photoluminescence of GaAs

    SciTech Connect

    Kang, M.; Al-Heji, A. A.; Jeon, S.; Wu, J. H.; Lee, J.-E.; Saucer, T. W.; Zhao, L.; Sih, V.; Katzenstein, A. L.; Sofferman, D. L.; Goldman, R. S.

    2013-09-02

    We have examined the influence of surface Ga nanoparticles (NPs) on the enhancement of GaAs photoluminescence (PL) efficiency. We have utilized off-normal focused-ion-beam irradiation of GaAs surfaces to fabricate close-packed Ga NP arrays. The enhancement in PL efficiency is inversely proportional to the Ga NP diameter. The maximum PL enhancement occurs for the Ga NP diameter predicted to maximize the incident electromagnetic (EM) field enhancement. The PL enhancement is driven by the surface plasmon resonance (SPR)-induced enhancement of the incident EM field which overwhelms the SPR-induced suppression of the light emission.

  9. Hierarchical Porous Polystyrene Monoliths from PolyHIPE.

    PubMed

    Yang, Xinjia; Tan, Liangxiao; Xia, Lingling; Wood, Colin D; Tan, Bien

    2015-09-01

    Hierarchical porous polystyrene monoliths (HCP-PolyHIPE) are obtained by hypercrosslinking poly(styrene-divinylbenzene) monoliths prepared by polymerization of high internal phase emulsions (PolyHIPEs). The hypercrosslinking is achieved using an approach known as knitting which employs formaldehyde dimethyl acetal (FDA) as an external crosslinker. Scanning electron microscopy (SEM) confirms that the macroporous structure in the original monolith is retained during the knitting process. By increasing the amount of divinylbenzene (DVB) in PolyHIPE, the BET surface area and pore volume of the HCP-PolyHIPE decrease, while the micropore size increases. BET surface areas of 196-595 m(2) g(-1) are obtained. The presence of micropores, mesopores, and macropores is confirmed from the pore size distribution. With a hierarchical porous structure, the monoliths reveal comparable gas sorption properties and potential applications in oil spill clean-up.

  10. Acetone oxidation in a photocatalytic monolith reactor

    SciTech Connect

    Sauer, M.L.; Ollis, D.F.

    1994-09-01

    Photocatalyzed oxidation of acetone (70-400 mg/m{sup 3}) in air was carried out using near-UV illuminated TiO{sub 2} (anatase) coated on the surface of a ceramic honeycomb monolith. Considerable adsorption of acetone and water was noted on the catalyst coated monolith; these uptakes were described with a Langmuir adsorption isotherm for acetone and a modified BET adsorption isotherm for water. The acetone photocatalyzed disappearance kinetics on the TiO{sub 2} were determined with initial rate differential conversion, recycle reactor data and were analyzed using a Langmuir-Hinshel-Wood rate form coupled with a reactant mass balance including appreciable acetone monolith adsorption. The model, with parameters evaluated from initial rate data, is then shown to satisfactorily predict reactor behavior at all conversions. These kinetics and design results, together with earlier literature for photocatalytic oxidation of alkanes, 1-butanol, toluene, trichloroethylene, and odor compounds, indicate a potential for use of the photocatalytic monolith configuration for removal of all major classes of air contaminants. 14 refs., 11 figs., 1 tab.

  11. Control of size and density of self-assembled Au droplets via systematic deposition amount control on high-index GaAs type-A surfaces

    NASA Astrophysics Data System (ADS)

    Li, Ming-Yu; Sui, Mao; Kim, Eun-Soo; Lee, Jihoon

    2014-09-01

    Au droplets as a catalyst can be used to determine the size, density, and configuration of nanowires (NWs) during crystallization at the liquid-solid interface, and the growth direction, cross-sectional shape, and even the quality of the NWs can be controlled by adjusting the substrate index utilized. In this study, the control of the size and density of self-assembled Au droplets is systematically demonstrated via the deposition amount (DA) control between 2 and 12 nm on various GaAs type-A substrates: (711)A, (511)A, (411)A, and (311)A. The self-assembled Au droplets are formed owing to the much higher binding energy between Au adatoms than the energy between Au atoms and substrate atoms based on the Volmer-Weber growth mode, and even up to 12 nm DA, the three-dimensional (3D) island phase (droplets) without coalescence is observed. Within the DA range, the self-assembled Au droplets sensitively respond to the DA variation, which results in over 3 times increment in dimensions along with the corresponding change in density on the two orders of magnitude from ˜108 to ˜1010. Depending on the index utilized, the high index effect is not obvious owing to weak binding energy between GaAs substrate and Au adatoms and the wide DA range. The results are systematically analyzed using atomic force microscope (AFM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), cross-sectional line profiles, and Fourier filter transform (FFT) power spectra.

  12. Fabrication of self-assembled Au droplets by the systematic variation of the deposition amount on various type-B GaAs surfaces

    PubMed Central

    2014-01-01

    The fabrication of self-assembled Au droplets is successfully demonstrated on various GaAs (n11)B, where n is 2, 4, 5, 7, 8, and 9, by the systematic variation of the Au deposition amount (DA) from 2 to 12 nm with subsequent annealing at 550°C. Under an identical growth condition, the self-assembled Au droplets of mini to supersizes are successfully synthesized via the Volmer-Weber growth mode. Depending on the DA, an apparent evolution is clearly observed in terms of the average height (AH), lateral diameter (LD), and average density (AD). For example, compared with the mini Au droplets with a DA of 2 nm, AH of 22.5 nm, and LD of 86.5 nm, the super Au droplets with 12-nm DA show significantly increased AH of 316% and LD of 320%, reaching an AH of 71.1 nm and LD of 276.8 nm on GaAs (211)B. In addition, accompanied with the dimensional expansion, the AD of Au droplets drastically swings on 2 orders of magnitudes from 3.2 × 1010 to 4.2 × 108 cm-2. The results are systematically analyzed with respect to the atomic force microscopy (AFM) and scanning electron microscopy (SEM) images, energy-dispersive X-ray spectrometry (EDS) spectra, cross-sectional line profiles, Fourier filter transform (FFT) power spectra, and root-mean-square (RMS) roughness as well as the droplet dimension and density summary, respectively. PMID:25221460

  13. A GaAs phononic crystal with shallow noncylindrical holes.

    PubMed

    Petrus, Joseph A; Mathew, Reuble; Stotz, James A H

    2014-02-01

    A square lattice of shallow, noncylindrical holes in GaAs is shown to act as a phononic crystal (PnC) reflector. The holes are produced by wet-etching a GaAs substrate using a citric acid:H2O2 etching procedure and a photolithographed array pattern. Although nonuniform and asymmetric etch rates limit the depth and shape of the phononic crystal holes, the matrix acts as a PnC, as demonstrated by insertion loss measurements together with interferometric imaging of surface acoustic waves propagating on the GaAs surface. The measured vertical displacement induced by surface phonons compares favorably with finite-difference time-domain simulations of a PnC with rounded-square holes.

  14. Monolithic MACS micro resonators

    NASA Astrophysics Data System (ADS)

    Lehmann-Horn, J. A.; Jacquinot, J.-F.; Ginefri, J. C.; Bonhomme, C.; Sakellariou, D.

    2016-10-01

    Magic Angle Coil Spinning (MACS) aids improving the intrinsically low NMR sensitivity of heterogeneous microscopic samples. We report on the design and testing of a new type of monolithic 2D MACS resonators to overcome known limitations of conventional micro coils. The resonators' conductors were printed on dielectric substrate and tuned without utilizing lumped element capacitors. Self-resonance conditions have been computed by a hybrid FEM-MoM technique. Preliminary results reported here indicate robust mechanical stability, reduced eddy currents heating and negligible susceptibility effects. The gain in B1 /√{ P } is in agreement with the NMR sensitivity enhancement according to the principle of reciprocity. A sensitivity enhancement larger than 3 has been achieved in a monolithic micro resonator inside a standard 4 mm rotor at 500 MHz. These 2D resonators could offer higher performance micro-detection and ease of use of heterogeneous microscopic substances such as biomedical samples, microscopic specimens and thin film materials.

  15. Measurement of charge limit in a strained lattice GaAs photocathode

    SciTech Connect

    Saez, P.; Alley, R.; Aoyagi, H.

    1993-04-01

    The SLAC Linear Collider (SLC) Polarized Electron Source (PES) photocathodes have shown a charge saturation when illuminated with a high intensity laser pulse. This charge limit in the cesium-activated GaAs crystal seems to be strongly dependent on its surface condition and on the incident light wavelength. Charge limit studies with highly polarized strained lattice GaAs materials are presented.

  16. Monolithic Optoelectronic Integrated Circuit

    NASA Technical Reports Server (NTRS)

    Bhasin, Kul B.; Walters, Wayne; Gustafsen, Jerry; Bendett, Mark

    1990-01-01

    Monolithic optoelectronic integrated circuit (OEIC) receives single digitally modulated input light signal via optical fiber and converts it into 16-channel electrical output signal. Potentially useful in any system in which digital data must be transmitted serially at high rates, then decoded into and used in parallel format at destination. Applications include transmission and decoding of control signals to phase shifters in phased-array antennas and also communication of data between computers and peripheral equipment in local-area networks.

  17. Monolithic Optoelectronic Integrated Circuit

    NASA Technical Reports Server (NTRS)

    Bhasin, Kul B.; Walters, Wayne; Gustafsen, Jerry; Bendett, Mark

    1990-01-01

    Monolithic optoelectronic integrated circuit (OEIC) receives single digitally modulated input light signal via optical fiber and converts it into 16-channel electrical output signal. Potentially useful in any system in which digital data must be transmitted serially at high rates, then decoded into and used in parallel format at destination. Applications include transmission and decoding of control signals to phase shifters in phased-array antennas and also communication of data between computers and peripheral equipment in local-area networks.

  18. Sol-Gel Synthesis of Non-Silica Monolithic Materials

    PubMed Central

    Gaweł, Bartłomiej; Gaweł, Kamila; Øye, Gisle

    2010-01-01

    Monolithic materials have become very popular because of various applications, especially within chromatography and catalysis. Large surface areas and multimodal porosities are great advantages for these applications. New sol-gel preparation methods utilizing phase separation or nanocasting have opened the possibility for preparing materials of other oxides than silica. In this review, we present different synthesis methods for inorganic, non-silica monolithic materials. Some examples of application of the materials are also included.

  19. Biasable, Balanced, Fundamental Submillimeter Monolithic Membrane Mixer

    NASA Technical Reports Server (NTRS)

    Siegel, Peter; Schlecht, Erich; Mehdi, Imran; Gill, John; Velebir, James; Tsang, Raymond; Dengler, Robert; Lin, Robert

    2010-01-01

    This device is a biasable, submillimeter-wave, balanced mixer fabricated using JPL s monolithic membrane process a simplified version of planar membrane technology. The primary target application is instrumentation used for analysis of atmospheric constituents, pressure, temperature, winds, and other physical and chemical properties of the atmospheres of planets and comets. Other applications include high-sensitivity gas detection and analysis. This innovation uses a balanced configuration of two diodes allowing the radio frequency (RF) signal and local oscillator (LO) inputs to be separated. This removes the need for external diplexers that are inherently narrowband, bulky, and require mechanical tuning to change frequency. Additionally, this mixer uses DC bias-ability to improve its performance and versatility. In order to solve problems relating to circuit size, the GaAs membrane process was created. As much of the circuitry as possible is fabricated on-chip, making the circuit monolithic. The remainder of the circuitry is precision-machined into a waveguide block that holds the GaAs circuit. The most critical alignments are performed using micron-scale semiconductor technology, enabling wide bandwidth and high operating frequencies. The balanced mixer gets superior performance with less than 2 mW of LO power. This can be provided by a simple two-stage multiplier chain following an amplifier at around 90 GHz. Further, the diodes are arranged so that they can be biased. Biasing pushes the diodes closer to their switching voltage, so that less LO power is required to switch the diodes on and off. In the photo, the diodes are at the right end of the circuit. The LO comes from the waveguide at the right into a reduced-height section containing the diodes. Because the diodes are in series to the LO signal, they are both turned on and off simultaneously once per LO cycle. Conversely, the RF signal is picked up from the RF waveguide by the probe at the left, and flows

  20. High efficiency GaAs/Ge monolithic tandem solar cells

    NASA Technical Reports Server (NTRS)

    Tobin, S. P.; Vernon, S. M.; Bajgar, C.; Haven, V. E.; Geoffroy, L. M.; Sanfacon, M. M.; Lillington, D. R.; Hart, R. E., Jr.

    1988-01-01

    Two-terminal monolithic tandem cells consisting of a GaAs solar cell grown epitaxially on a Ge solar cell substrate are very attractive for space applications. Tandem cells of GaAs grown by metal-organic chemical vapor deposition on thin Ge were investigated to address both higher efficiency and reduced weight. Two materials growth issues associated with this heteroepitaxial system, autodoping of the GaAs layers by Ge and diffusion of Ga and As into the Ge substrate, were addressed. The latter appears to result in information of an unintentional p-n junction in the Ge. Early simulator measurements gave efficiencies as high as 21.7 percent for 4 cm2 GaAs/Ge cells, but recent high-altitude testing has given efficiencies of 18 percent. Sources of errors in simulator measurements of two-terminal tandem cells are discussed. A limiting efficiency of about 36 percent for the tandem cell at AMO was calculated. Ways to improve the performance of present cells, primarily by increasing the Isc and Voc of the Ge cell, are proposed.

  1. High efficiency GaAs/Ge monolithic tandem solar cells

    NASA Technical Reports Server (NTRS)

    Tobin, S. P.; Vernon, S. M.; Bajgar, C.; Haven, V. E.; Geoffroy, L. M.; Sanfacon, M. M.; Lillington, D. R.; Hart, R. E., Jr.

    1988-01-01

    Two-terminal monolithic tandem cells consisting of a GaAs solar cell grown epitaxially on a Ge solar cell substrate are very attractive for space applications. Tandem cells of GaAs grown by metal-organic chemical vapor deposition on thin Ge were investigated to address both higher efficiency and reduced weight. Two materials growth issues associated with this heteroepitaxial system, autodoping of the GaAs layers by Ge and diffusion of Ga and As into the Ge substrate, were addressed. The latter appears to result in information of an unintentional p-n junction in the Ge. Early simulator measurements gave efficiencies as high as 21.7 percent for 4 cm2 GaAs/Ge cells, but recent high-altitude testing has given efficiencies of 18 percent. Sources of errors in simulator measurements of two-terminal tandem cells are discussed. A limiting efficiency of about 36 percent for the tandem cell at AMO was calculated. Ways to improve the performance of present cells, primarily by increasing the Isc and Voc of the Ge cell, are proposed.

  2. Monolithic Continuous-Flow Bioreactors

    NASA Technical Reports Server (NTRS)

    Stephanopoulos, Gregory; Kornfield, Julia A.; Voecks, Gerald A.

    1993-01-01

    Monolithic ceramic matrices containing many small flow passages useful as continuous-flow bioreactors. Ceramic matrix containing passages made by extruding and firing suitable ceramic. Pores in matrix provide attachment medium for film of cells and allow free movement of solution. Material one not toxic to micro-organisms grown in reactor. In reactor, liquid nutrients flow over, and liquid reaction products flow from, cell culture immobilized in one set of channels while oxygen flows to, and gaseous reaction products flow from, culture in adjacent set of passages. Cells live on inner surfaces containing flowing nutrient and in pores of walls of passages. Ready access to nutrients and oxygen in channels. They generate continuous high yield characteristic of immobilized cells, without large expenditure of energy otherwise incurred if necessary to pump nutrient solution through dense biomass as in bioreactors of other types.

  3. Monolithic Continuous-Flow Bioreactors

    NASA Technical Reports Server (NTRS)

    Stephanopoulos, Gregory; Kornfield, Julia A.; Voecks, Gerald A.

    1993-01-01

    Monolithic ceramic matrices containing many small flow passages useful as continuous-flow bioreactors. Ceramic matrix containing passages made by extruding and firing suitable ceramic. Pores in matrix provide attachment medium for film of cells and allow free movement of solution. Material one not toxic to micro-organisms grown in reactor. In reactor, liquid nutrients flow over, and liquid reaction products flow from, cell culture immobilized in one set of channels while oxygen flows to, and gaseous reaction products flow from, culture in adjacent set of passages. Cells live on inner surfaces containing flowing nutrient and in pores of walls of passages. Ready access to nutrients and oxygen in channels. They generate continuous high yield characteristic of immobilized cells, without large expenditure of energy otherwise incurred if necessary to pump nutrient solution through dense biomass as in bioreactors of other types.

  4. Direct-bonded four-junction GaAs solar cells

    NASA Astrophysics Data System (ADS)

    Jingman, Shen; Lijie, Sun; Kaijian, Chen; Wei, Zhang; Xunchun, Wang

    2015-06-01

    Direct wafer bonding technology is able to integrate two smooth wafers and thus can be used in fabricating III-V multijunction solar cells with lattice mismatch. In order to monolithically interconnect between the GaInP/GaAs and InGaAsP/InGaAs subcells, the bonded GaAs/InP heterojunction must be a highly conductive ohmic junction or a tunnel junction. Three types of bonding interfaces were designed by tuning the conduction type and doping elements of GaAs and InP. The electrical properties of p-GaAs (Zn doped)/n-InP (Si doped), p-GaAs (C doped)/n-InP (Si doped) and n-GaAs (Si doped)/n-InP (Si doped) bonded heterojunctions were analyzed from the I-V characteristics. The wafer bonding process was investigated by improving the quality of the sample surface and optimizing the bonding parameters such as bonding temperature, bonding pressure, bonding time and so on. Finally, GaInP/GaAs/InGaAsP/InGaAs 4-junction solar cells have been prepared by a direct wafer bonding technique with the high efficiency of 34.14% at the AM0 condition (1 Sun). Project supported by the Shanghai Rising-Star Program (No. 14QB1402800).

  5. Anisotropically structured magnetic aerogel monoliths

    NASA Astrophysics Data System (ADS)

    Heiligtag, Florian J.; Airaghi Leccardi, Marta J. I.; Erdem, Derya; Süess, Martin J.; Niederberger, Markus

    2014-10-01

    Texturing of magnetic ceramics and composites by aligning and fixing of colloidal particles in a magnetic field is a powerful strategy to induce anisotropic chemical, physical and especially mechanical properties into bulk materials. If porosity could be introduced, anisotropically structured magnetic materials would be the perfect supports for magnetic separations in biotechnology or for magnetic field-assisted chemical reactions. Aerogels, combining high porosity with nanoscale structural features, offer an exceptionally large surface area, but they are difficult to magnetically texture. Here we present the preparation of anatase-magnetite aerogel monoliths via the assembly of preformed nanocrystallites. Different approaches are proposed to produce macroscopic bodies with gradient-like magnetic segmentation or with strongly anisotropic magnetic texture.Texturing of magnetic ceramics and composites by aligning and fixing of colloidal particles in a magnetic field is a powerful strategy to induce anisotropic chemical, physical and especially mechanical properties into bulk materials. If porosity could be introduced, anisotropically structured magnetic materials would be the perfect supports for magnetic separations in biotechnology or for magnetic field-assisted chemical reactions. Aerogels, combining high porosity with nanoscale structural features, offer an exceptionally large surface area, but they are difficult to magnetically texture. Here we present the preparation of anatase-magnetite aerogel monoliths via the assembly of preformed nanocrystallites. Different approaches are proposed to produce macroscopic bodies with gradient-like magnetic segmentation or with strongly anisotropic magnetic texture. Electronic supplementary information (ESI) available: Digital photographs of dispersions and gels with different water-to-ethanol ratios; magnetic measurements of an anatase aerogel containing 0.25 mol% Fe3O4 nanoparticles; XRD patterns of the iron oxide and

  6. Steam reforming of n-hexane on pellet and monolithic catalyst beds. A comparative study on improvements due to heat transfer

    NASA Astrophysics Data System (ADS)

    1981-10-01

    Monolithic catalysts with higher available active surface areas and better thermal conductivity than conventional pellets beds, making possible the steam reforming of fuels heavier than naphtha, were examined. Performance comparisons were made between conventional pellet beds and honeycomb monolith catalysts using n-hexane as the fuel. Metal-supported monoliths were examined. These offer higher structural stability and higher thermal conductivity than ceramic supports. Data from two metal monoliths of different nickel catalyst loadings were compared to pellets under the same operating conditions. Improved heat transfer and better conversion efficiencies were obtained with the monolith having higher catalyst loading. Surface-gas interaction was observed throughout the length of the monoliths.

  7. Steam reforming of n-hexane on pellet and monolithic catalyst beds. A comparative study on improvements due to heat transfer

    NASA Technical Reports Server (NTRS)

    1981-01-01

    Monolithic catalysts with higher available active surface areas and better thermal conductivity than conventional pellets beds, making possible the steam reforming of fuels heavier than naphtha, were examined. Performance comparisons were made between conventional pellet beds and honeycomb monolith catalysts using n-hexane as the fuel. Metal-supported monoliths were examined. These offer higher structural stability and higher thermal conductivity than ceramic supports. Data from two metal monoliths of different nickel catalyst loadings were compared to pellets under the same operating conditions. Improved heat transfer and better conversion efficiencies were obtained with the monolith having higher catalyst loading. Surface-gas interaction was observed throughout the length of the monoliths.

  8. Steam reforming of n-hexane on pellet and monolithic catalyst beds. A comparative study on improvements due to heat transfer

    NASA Technical Reports Server (NTRS)

    1981-01-01

    Monolithic catalysts with higher available active surface areas and better thermal conductivity than conventional pellets beds, making possible the steam reforming of fuels heavier than naphtha, were examined. Performance comparisons were made between conventional pellet beds and honeycomb monolith catalysts using n-hexane as the fuel. Metal-supported monoliths were examined. These offer higher structural stability and higher thermal conductivity than ceramic supports. Data from two metal monoliths of different nickel catalyst loadings were compared to pellets under the same operating conditions. Improved heat transfer and better conversion efficiencies were obtained with the monolith having higher catalyst loading. Surface-gas interaction was observed throughout the length of the monoliths.

  9. Graphitized carbon on GaAs(100) substrates

    SciTech Connect

    Simon, J.; Simmonds, P. J.; Lee, M. L.; Woodall, J. M.

    2011-02-14

    We report on the formation of graphitized carbon on GaAs(100) surfaces by molecular beam epitaxy. We grew highly carbon-doped GaAs on AlAs, which was then thermally etched in situ leaving behind carbon atoms on the surface. After thermal etching, Raman spectra revealed characteristic phonon modes for sp{sup 2}-bonded carbon, consistent with the formation of graphitic crystallites. We estimate that the graphitic crystallites are 1.5-3 nm in size and demonstrate that crystallite domain size can be increased through the use of higher etch temperatures.

  10. Electronic contribution to friction on GaAs

    SciTech Connect

    Applied Science and Technology Graduate Group, UC Berkeley; Dept. of Materials Sciences and Engineering, UC Berkeley; Salmeron, Miquel; Qi, Yabing; Park, J.Y.; Hendriksen, B.L.M.; Ogletree, D.F.; Salmeron, Miquel

    2008-04-15

    The electronic contribution to friction at semiconductor surfaces was investigated by using a Pt-coated tip with 50nm radius in an atomic force microscope sliding against an n-type GaAs(100) substrate. The GaAs surface was covered by an approximately 1 nm thick oxide layer. Charge accumulation or depletion was induced by the application of forward or reverse bias voltages. We observed a substantial increase in friction force in accumulation (forward bias) with respect to depletion (reverse bias). We propose a model based on the force exerted by the trapped charges that quantitatively explains the experimental observations of excess friction.

  11. Porous monoliths for on-line sample preparation: A review.

    PubMed

    Masini, Jorge C; Svec, Frantisek

    2017-04-29

    This review aims at presenting the state of the art concerning monolithic materials for on-line sample preparation emphasizing solid-phase extraction, matrix exchange, and analyte conversion. Emphasis was given to organic and silica-based, as well as hybrid monoliths reported in the literature mostly after 2010. The first part of this review presents materials and strategies for enrichment of inorganic species in environmental and biological samples using mostly ICP-MS detectors. In the second part we focus on organic analytes, discussing the role of surface area of the polymer monoliths and density of adsorption sites for specific interactions, including incorporation of nanoparticles, metal organic frameworks, as well as the preparation of hybrid organic-silica monoliths to increase the surface area. Incorporation of ionic liquids to increase the number of types of interaction mechanisms available for retention is also discussed. Monoliths affording molecular recognition properties achieved by including boronate moieties for cis-diol recognition, as well as antibodies and aptamers for specific molecular recognition are also reviewed. The largest number of applications of molecular recognition mechanisms was observed for molecularly imprinted polymer monoliths as a consequence of the simplicity of this approach when compared to the use of immunosorbents or aptamers. The final part examines the on-line applications of immobilized enzyme reactors used for protein digestion in proteomic analysis and for kinetic studies in drug discovery and clinical assays usually coupling the reactors to mass spectrometers.

  12. (In,Ga,Al)P–GaP laser diodes grown on high-index GaAs surfaces emitting in the green, yellow and bright red spectral range

    NASA Astrophysics Data System (ADS)

    Ledentsov, N. N.; Shchukin, V. A.; Shernyakov, Yu M.; Kulagina, M. M.; Payusov, A. S.; Gordeev, N. Yu; Maximov, M. V.; Cherkashin, N. A.

    2017-02-01

    We report on low threshold current density (<400 A cm‑2) injection lasing in (Al x Ga1–x )0.5In0.5P–GaAs-based diodes down to the green spectral range (<570 nm). The epitaxial structures are grown on high-index (611)A and (211)A GaAs substrates by metal–organic vapor phase epitaxy and contain tensile-strained GaP-enriched insertions aimed at reflection of the injected nonequilibrium electrons preventing their escape from the active region. Extended waveguide concept results in a vertical beam divergence with a full width at half maximum of 15° for (611)A substrates. The lasing at the wavelength of 569 nm is realized at 85 K. In an orange–red laser diode structure low threshold current density (190 A cm‑2) in the orange spectral range (598 nm) is realized at 85 K. The latter devices demonstrated room temperature lasing at 628 nm at ∼2 kA cm‑2 and a total power above 3 W. The red laser diodes grown on (211)A substrates demonstrated a far field characteristic for vertically multimode lasing indicating a lower optical confinement factor for the fundamental mode as compared to the devices grown on (611)A. However, as expected from previous research, the temperature stability of the threshold current and the wavelength stability were significantly higher for (211)A-grown structures.

  13. Combining thermodynamic simulations, element and surface analytics to study U(VI) retention in corroded cement monoliths upon >20 years of leaching

    NASA Astrophysics Data System (ADS)

    Bube, C.; Metz, V.; Schild, D.; Rothe, J.; Dardenne, K.; Lagos, M.; Plaschke, M.; Kienzler, B.

    Retention or release of radionuclides in a deep geological repository for radioactive wastes strongly depends on the geochemical environment and on the interaction with near-field components, e.g. waste packages and backfill materials. Deep geological disposal in rock salt is one of the concepts considered for cemented low- and intermediate-level wastes. Long-term experiments were performed to observe the evolution of full-scale cemented waste simulates (doped with (NH4)2U2O7) upon reaction with relevant salt brines, e.g. MgCl2-rich and saturated NaCl solutions, and to examine the binding mechanisms of uranium. Throughout the experiments, concentrations of major solution components, uranium and pH values were monitored regularly and compared to thermodynamic equilibrium calculations, which indicate that close-to-equilibrium conditions have been achieved after 13-14 years duration of the leaching experiments. Two of the full-scale cemented waste simulates were recovered from the solutions after 17-18 years and studied by different analytical methods to characterize the solids, especially with respect to uranium incorporation. In drill core fragments of various lateral and horizontal positions of the corroded monoliths, U-rich aggregates were detected and analyzed by means of space-resolved techniques. Raman, μ-XANES and μ-XRD analyses of several aggregates demonstrate that they consist of an amorphous diuranate-type solid. Within error, calculated U solubilities controlled by Na-diuranate (Na2U2O7·H2O) are consistent with measured U concentrations in both, the NaCl and the MgCl2-system. Since uranophane occurs also in the corroded monoliths, it is proposed that a transition towards the thermodynamic equilibrium U(VI) phase is kinetically hindered.

  14. Spatial and temporal distribution of the leaching of surface applied tracers from an irrigated monolith of a loamy vineyard soil.

    PubMed

    Bloem, E; Hermon, K M; de Rooij, G H; Stagnitti, F

    2014-01-01

    Fresh water scarcity is an increasing problem worldwide. Strategies to alleviate water scarcity include the use of low-quality water for irrigation. The risk of groundwater contamination by pollutants in this water is affected by soil heterogeneity and preferential flow. These risk factors can be assessed by measuring the spatio-temporal redistribution of uniformly applied water and solutes. We placed a soil monolith (height 29 cm) from an Australian vineyard on a 100-cell multi-compartment sampler (MCS). At this vineyard, treated wastewater is used in response to the severe shortage of water in the summer. We studied the leaching risk associated with heterogeneous or preferential flow by irrigating the soil column with 24 applications to simulate one year. We applied simulated rainfall as well as wastewater (which contained chloride) during summer while relying on rainfall only in winter. We compared the chloride leaching with the leaching of bromide, which was applied during one of the applications as a pulse. During the entire simulated year, leaching of solutes from the monolith was measured. The results indicate that the assumption of uniform flow would underestimate the risk for the fresh groundwater reserves: 25% of the solutes are transported though 6% of the soil's cross-section. The spatial distribution of drainage and solute leaching varied little during the experiment. Consequently, the mass flux density pattern of the bromide pulse was comparable to that of the repeatedly applied chloride. However, the MCS data suggested lateral 'escape' from chloride to non-mobile areas, which means in the long run, considerable quantities of these solutes can build up in areas that do not receive irrigation water.

  15. Monolithic microfluidic concentrators and mixers

    DOEpatents

    Frechet, Jean M.; Svec, Frantisek; Yu, Cong; Rohr, Thomas

    2005-05-03

    Microfluidic devices comprising porous monolithic polymer for concentration, extraction or mixing of fluids. A method for in situ preparation of monolithic polymers by in situ initiated polymerization of polymer precursors within microchannels of a microfluidic device and their use for solid phase extraction (SPE), preconcentration, concentration and mixing.

  16. Epitaxial growth of GaAs and GaN by gas source molecular beam epitaxy using organic group V compounds

    NASA Astrophysics Data System (ADS)

    Okumura, H.; Yoshida, S.; Misawa, S.; Sakuma, E.

    1992-05-01

    GaAs and GaN epilayers were grown on GaAs substrates by gas source molecular beam epitaxy technique using triethylarsine (TEAs) and diethylarsine (DEAsH) as As sources, and dimethylhydrazine (DMHy) as an N source. It was found that GaAs grows layer by layer even when organic arsine molecular sources are used. Cubic GaN was found to grow epitaxially on sufficiently nitrided surfaces of GaAs (001) substrates, in contrast with the growth of hexagonal GaN on GaAs (111) surfaces. It was also found that nitridation of GaAs surfaces does not occur when DEAsH and DMHy beams are supplied onto the GaAs substrates, simultaneously. Thus, GaN/GaAs multilayers were obtained only by intermittent supply of a DEAsH beam.

  17. The 30-GHz monolithic receive module

    NASA Technical Reports Server (NTRS)

    Sokolov, V.; Geddes, J.; Bauhahn, P.

    1983-01-01

    Key requirements for a 30 GHz GaAs monolithic receive module for spaceborne communication antenna feed array applications include an overall receive module noise figure of 5 dB, a 30 dB RF to IF gain with six levels of intermediate gain control, a five-bit phase shifter, and a maximum power consumption of 250 mW. The RF designs for each of the four submodules (low noise amplifier, some gain control, phase shifter, and RF to IF sub-module) are presented. Except for the phase shifter, high frequency, low noise FETs with sub-half micron gate lengths are employed in the submodules. For the gain control, a two stage dual gate FET amplifier is used. The phase shifter is of the passive switched line type and consists of 5-bits. It uses relatively large gate width FETs (with zero drain to source bias) as the switching elements. A 20 GHz local oscillator buffer amplifier, a FET compatible balanced mixer, and a 5-8 GHz IF amplifier constitute the RF/IF sub-module. Phase shifter fabrication using ion implantation and a self-aligned gate technique is described. Preliminary RF results obtained on such phase shifters are included.

  18. Design of monoliths through their mechanical properties.

    PubMed

    Podgornik, Aleš; Savnik, Aleš; Jančar, Janez; Krajnc, Nika Lendero

    2014-03-14

    Chromatographic monoliths have several interesting properties making them attractive supports for analytics but also for purification, especially of large biomolecules and bioassemblies. Although many of monolith features were thoroughly investigated, there is no data available to predict how monolith mechanical properties affect its chromatographic performance. In this work, we investigated the effect of porosity, pore size and chemical modification on methacrylate monolith compression modulus. While a linear correlation between pore size and compression modulus was found, the effect of porosity was highly exponential. Through these correlations it was concluded that chemical modification affects monolith porosity without changing the monolith skeleton integrity. Mathematical model to describe the change of monolith permeability as a function of monolith compression modulus was derived and successfully validated for monoliths of different geometries and pore sizes. It enables the prediction of pressure drop increase due to monolith compressibility for any monolith structural characteristics, such as geometry, porosity, pore size or mobile phase properties like viscosity or flow rate, based solely on the data of compression modulus and structural data of non-compressed monolith. Furthermore, it enables simple determination of monolith pore size at which monolith compressibility is the smallest and the most robust performance is expected. Data of monolith compression modulus in combination with developed mathematical model can therefore be used for the prediction of monolith permeability during its implementation but also to accelerate the design of novel chromatographic monoliths with desired hydrodynamic properties for particular application.

  19. Molecular beam epitaxial growth and structural characterization of ZnS on (001) GaAs

    NASA Technical Reports Server (NTRS)

    Benz, R. G., II; Huang, P. C.; Stock, S. R.; Summers, C. J.

    1988-01-01

    The effect of surface nucleation processes on the quality of ZnS layers grown on (001) GaAs substrates by molecular beam epitaxy is reported. Reflection high energy electron diffraction indicated that nucleation at high temperatures produced more planar surfaces than nucleation at low temperatures, but the crystalline quality as assessed by X-ray double crystal diffractometry is relatively independent of nucleation temperature. A critical factor in layer quality was the initial roughness of the GaAs surfaces.

  20. Structure for monolithic optical circuits

    NASA Technical Reports Server (NTRS)

    Evanchuk, Vincent L. (Inventor)

    1984-01-01

    A method for making monolithic optical circuits, with related optical devices as required or desired, on a supporting surface (10) consists of coating the supporting surface with reflecting metal or cladding resin, spreading a layer of liquid radiation sensitive plastic (12) on the surface, exposing the liquid plastic with a mask (14) to cure it in a desired pattern of light conductors (16, 18, 20), washing away the unexposed liquid plastic, and coating the conductors thus formed with reflective metal or cladding resin. The index of refraction for the cladding (22) is selected to be lower than for the conductors so that light in the conductors will be reflected by the interface with the cladding. For multiple level conductors, as where one conductor must cross over another, the process may be repeated to fabricate a bridge with columns (24, 26) of conductors to the next level, and conductor (28) between the columns. For more efficient transfer of energy over the bridge, faces at 45.degree. may be formed to reflect light up and across the bridge.

  1. Monolithic Flexure Pre-Stressed Ultrasonic Horns

    NASA Technical Reports Server (NTRS)

    Sherrit, Stewart (Inventor); Bao, Xiaoqi (Inventor); Badescu, Mircea (Inventor); Bar-Cohen, Yoseph (Inventor); Allen, Phillip Grant (Inventor)

    2015-01-01

    A monolithic ultrasonic horn where the horn, backing, and pre-stress structures are combined in a single monolithic piece is disclosed. Pre-stress is applied by external flexure structures. The provision of the external flexures has numerous advantages including the elimination of the need for a pre-stress bolt. The removal of the pre-stress bolt eliminates potential internal electric discharge points in the actuator. In addition, it reduces the chances of mechanical failure in the actuator stacks that result from the free surface in the hole of conventional ring stacks. In addition, the removal of the stress bolt and the corresponding reduction in the overall number of parts reduces the overall complexity of the resulting ultrasonic horn actuator and simplifies the ease of the design, fabrication and integration of the actuator of the present invention into other structures.

  2. Monolithic Flexure Pre-Stressed Ultrasonic Horns

    NASA Technical Reports Server (NTRS)

    Sherrit, Stewart (Inventor); Bao, Xiaoqi (Inventor); Badescu, Mircea (Inventor); Bar-Cohen, Yoseph (Inventor); Allen, Phillip Grant (Inventor)

    2016-01-01

    A monolithic ultrasonic horn where the horn, backing, and pre-stress structures are combined in a single monolithic piece is disclosed. Pre-stress is applied by external flexure structures. The provision of the external flexures has numerous advantages including the elimination of the need for a pre-stress bolt. The removal of the pre-stress bolt eliminates potential internal electric discharge points in the actuator. In addition, it reduces the chances of mechanical failure in the actuator stacks that result from the free surface in the hole of conventional ring stacks. In addition, the removal of the stress bolt and the corresponding reduction in the overall number of parts reduces the overall complexity of the resulting ultrasonic horn actuator and simplifies the ease of the design, fabrication and integration of the actuator of the present invention into other structures.

  3. A hierarchically porous cellulose monolith: A template-free fabricated, morphology-tunable, and easily functionalizable platform.

    PubMed

    Xin, Yuanrong; Xiong, Qiancheng; Bai, Qiuhong; Miyamoto, Miwa; Li, Cong; Shen, Yehua; Uyama, Hiroshi

    2017-02-10

    Recently, monoliths with continuous porous structure have received much attention for high-performance separation/adsorption matrix in biomedical and environmental fields. This study proposes a novel route to prepare cellulose monoliths with hierarchically porous structure by selecting cellulose acetate (CA) as the starting material. Thermally induced phase separation of CA solution using a mixed solvent affords a CA monolith, which is converted into the cellulose monolith by alkaline hydrolysis. Scanning electron microscopy images of the CA and cellulose monoliths reveal a continuous macropore with rough surface, and nitrogen adsorption/desorption analysis indicates the formation of a mesoporous structure. The macroporous structure could be controlled by changing the fabrication parameters. A series of reactive groups are introduced by chemical modifications on the surface of the cellulose monolith. The facile and diverse modifiability combined with its hydrophilic property make the hierarchically porous cellulose monolith a potential platform for use in separation, purification and bio-related applications.

  4. Monolithic ballasted penetrator

    DOEpatents

    Hickerson, Jr., James P.; Zanner, Frank J.; Baldwin, Michael D.; Maguire, Michael C.

    2001-01-01

    The present invention is a monolithic ballasted penetrator capable of delivering a working payload to a hardened target, such as reinforced concrete. The invention includes a ballast made from a dense heavy material insert and a monolithic case extending along an axis and consisting of a high-strength steel alloy. The case includes a nose end containing a hollow portion in which the ballast is nearly completely surrounded so that no movement of the ballast relative to the case is possible during impact with a hard target. The case is cast around the ballast, joining the two parts together. The ballast may contain concentric grooves or protrusions that improve joint strength between the case and ballast. The case further includes a second hollow portion; between the ballast and base, which has a payload fastened within this portion. The penetrator can be used to carry instrumentation to measure the geologic character of the earth, or properties of arctic ice, as they pass through it.

  5. Monolithic optical parametric oscillators

    NASA Astrophysics Data System (ADS)

    Breunig, Ingo; Beckmann, Tobias; Buse, Karsten

    2012-02-01

    Stability and footprint of optical parametric oscillators (OPOs) strongly depend on the cavity used. Monolithic OPOs tend to be most stable and compact since they do not require external mirrors that have to be aligned. The most straightforward way to get rid of the mirrors is to coat the end faces of the nonlinear crystal. Whispering gallery resonators (WGRs) are a more advanced solution since they provide ultra-high reflectivity over a wide spectral range without any coating. Furthermore, they can be fabricated out of nonlinear-optical materials like lithium niobate. Thus, they are ideally suited to serve as a monolithic OPO cavity. We present the experimental realization of optical parametric oscillators based on whispering gallery resonators. Pumped at 1 μm wavelength, they generate signal and idler fields tunable between 1.8 and 2.5 μm wavelength. We explore different schemes, how to phase match the nonlinear interaction in a WGR. In particular, we show improvements in the fabrication of quasi-phase-matching structures. They enable great flexibility for the tuning and for the choice of the pump laser.

  6. GaAs solar cells with V-grooved emitters

    NASA Technical Reports Server (NTRS)

    Bailey, S. G.; Fatemi, N.; Wilt, D. M.; Landis, G. A.; Thomas, R. D.

    1989-01-01

    A GaAs solar cell with a V-grooved front surface is described. It shows improved optical coupling and higher short-circuit current compared to planar cells. The GaAs homojunction cells, manufactured by OrganoMetallic Chemical Vapor Deposition (OMCVD), are described. The V-grooves were formed by anisotropic etching. Reflectivity measurements show significantly lower reflectance for the microgrooved cell compared to the planar structure. The short circuit current of the V-grooved solar cell is consistently higher than that of the planar controls.

  7. High efficiency thin-film GaAs solar cells

    NASA Technical Reports Server (NTRS)

    Stirn, R. J.

    1977-01-01

    Several oxidation techniques are discussed which have been found to increase the open circuit (V sub oc) of metal-GaAs Schottky barrier solar cells, the oxide chemistry, attempts to measure surface state parameters, the evolving characteristics of the solar cell as background contamination (has been decreased, but not eliminated), results of focused Nd/YAG laser beam recrystallization of Ge films evaporated onto tungsten, and studies of AMOS solar cells fabricated on sliced polycrystalline GaAs wafers. Also discussed are projected materials availability and costs for GaAs thin-film solar cells.

  8. [Preparation of a novel polymer monolith using atom transfer radical polymerization method for solid phase extraction].

    PubMed

    Shen, Ying; Qi, Li; Qiao, Juan; Mao, Lanqun; Chen, Yi

    2013-04-01

    In this study, a novel polymer monolith based solid phase extraction (SPE) material has been prepared by two-step atom transfer radical polymerization (ATRP) method. Firstly, employing ethylene glycol dimethacrylate (EDMA) as a cross-linker, a polymer monolith filled in a filter head has been in-situ prepared quickly under mild conditions. Then, the activators generated by electron transfer ATRP (ARGET ATRP) was used for the modification of poly(2-(dimethylamino)ethyl-methacrylate) (PDMAEMA) on the monolithic surface. Finally, this synthesized monolith for SPE was successfully applied in the extraction and enrichment of steroids. The results revealed that ATRP can be developed as a facile and effective method with mild reaction conditions for monolith construction and has the potential for preparing monolith in diverse devices.

  9. Comparison of monolithic silica and polymethacrylate capillary columns for LC.

    PubMed

    Moravcová, Dana; Jandera, Pavel; Urban, Jiri; Planeta, Josef

    2004-07-01

    Organic polymer monolithic capillary columns were prepared in fused-silica capillaries by radical co-polymerization of ethylene dimethacrylate and butyl methacrylate monomers with azobisisobutyronitrile as initiator of the polymerization reaction in the presence of various amounts of porogenic solvent mixtures and different concentration ratios of monomers and 1-propanol, 1,4-butanediol, and water. The chromatographic properties of the organic polymer monolithic columns were compared with those of commercial silica-based particulate and monolithic capillary and analytical HPLC columns. The tests included the determination of H-u curves, column permeabilities, pore distribution by inversed-SEC measurements, methylene and polar selectivities, and polar interactions with naphthalenesulphonic acid test samples. Organic polymer monolithic capillary columns show similar retention behaviour to chemically bonded alkyl silica columns for compounds with different polarities characterized by interaction indices, Ix, but have lower methylene selectivities and do not show polar interactions with sulphonic acids. The commercial capillary and analytical silica gel-based monolithic columns showed similar selectivities and provided symmetrical peaks, indicating no significant surface heterogeneities. To allow accurate characterization of the properties of capillary monolithic columns, the experimental data should be corrected for extra-column contributions. With 0.3 mm ID capillary columns, corrections for extra-column volume contributions are sufficient, but to obtain true information on the efficiency of 0.1 mm ID capillary columns, the experimental bandwidths should be corrected for extra-column contributions to peak broadening.

  10. Heterojunction photovoltaics using GaAs nanowires and conjugated polymers.

    PubMed

    Ren, Shenqiang; Zhao, Ni; Crawford, Samuel C; Tambe, Michael; Bulović, Vladimir; Gradecak, Silvija

    2011-02-09

    We demonstrate an organic/inorganic solar cell architecture based on a blend of poly(3-hexylthiophene) (P3HT) and narrow bandgap GaAs nanowires. The measured increase of device photocurrent with increased nanowire loading is correlated with structural ordering within the active layer that enhances charge transport. Coating the GaAs nanowires with TiO(x) shells passivates nanowire surface states and further improves the photovoltaic performance. We find that the P3HT/nanowire cells yield power conversion efficiencies of 2.36% under white LED illumination for devices containing 50 wt % of TiO(x)-coated GaAs nanowires. Our results constitute important progress for the use of nanowires in large area solution processed hybrid photovoltaic cells and provide insight into the role of structural ordering in the device performance.

  11. High efficiency thin-film GaAs solar cells

    NASA Technical Reports Server (NTRS)

    Zwerdling, S.; Wang, K. L.; Yeh, Y. C. M.

    1981-01-01

    The paper demonstrates the feasibility of producing high-efficiency GaAs solar cells with high power-to-weight ratios by organic metallic chemical vapor deposition (OM-CVD) growth of thin epi-layers on suitable substrates. An AM1 conversion efficiency of 18% (14% AM0), or 17% (13% AM0) with a 5% grid coverage is achieved for a single-crystal GaAs n(+)/p cell grown by OM-CVD on a Ge wafer. Thin GaAs epi-layers OM-CVD grown can be fabricated with good crystallographic quality using a Si-substrate on which a thin Ge epi-interlayer is first deposited by CVD from GeH4 and processed for improved surface morphology

  12. Measuring Carrier Lifetime in GaAs by Luminescence

    NASA Technical Reports Server (NTRS)

    Von Roos, O.

    1986-01-01

    Luminescence proposed as nondestructive technique for measuring Shockley-Read-Hall (SRH) recombination lifetime GaAs. Sample irradiated, and luminescence escapes through surface. Measurement requires no mechanical or electrical contact with sample. No ohmic contacts or p/n junctions needed. Sample not scrapped after tested.

  13. ZnSe Films in GaAs Solar Cells

    NASA Technical Reports Server (NTRS)

    Kachare, Ram H.

    1987-01-01

    ZnSe increases efficiency and conserves material. Two proposed uses of zinc selenide films promise to boost performance and reduce cost of gallium arsenide solar cells. Accordingly ZnSe serves as surface-passivation layer and as sacrificial layer enabling repeated use of costly GaAs substrate in fabrication.

  14. Biobased monoliths for adenovirus purification.

    PubMed

    Fernandes, Cláudia S M; Gonçalves, Bianca; Sousa, Margarida; Martins, Duarte L; Barroso, Telma; Pina, Ana Sofia; Peixoto, Cristina; Aguiar-Ricardo, Ana; Roque, A Cecília A

    2015-04-01

    Adenoviruses are important platforms for vaccine development and vectors for gene therapy, increasing the demand for high titers of purified viral preparations. Monoliths are macroporous supports regarded as ideal for the purification of macromolecular complexes, including viral particles. Although common monoliths are based on synthetic polymers as methacrylates, we explored the potential of biopolymers processed by clean technologies to produce monoliths for adenovirus purification. Such an approach enables the development of disposable and biodegradable matrices for bioprocessing. A total of 20 monoliths were produced from different biopolymers (chitosan, agarose, and dextran), employing two distinct temperatures during the freezing process (-20 °C and -80 °C). The morphological and physical properties of the structures were thoroughly characterized. The monoliths presenting higher robustness and permeability rates were further analyzed for the nonspecific binding of Adenovirus serotype 5 (Ad5) preparations. The matrices presenting lower nonspecific Ad5 binding were further functionalized with quaternary amine anion-exchange ligand glycidyltrimethylammonium chloride hydrochloride by two distinct methods, and their performance toward Ad5 purification was assessed. The monolith composed of chitosan and poly(vinyl) alcohol (50:50) prepared at -80 °C allowed 100% recovery of Ad5 particles bound to the support. This is the first report of the successful purification of adenovirus using monoliths obtained from biopolymers processed by clean technologies.

  15. X-ray photoelectron spectroscopy study of the effects of ultrapure water on GaAs

    NASA Astrophysics Data System (ADS)

    Massies, J.; Contour, J. P.

    1985-06-01

    X-ray photoelectron spectroscopy has been used to investigate the effects of de-ionized water on chemical etched GaAs surfaces. When the treatment with water is performed in static conditions (stagnant water) a Ga-rich oxide layer is formed on GaAs at the rate of 10-20 Å h-1. In contrast, when the GaAs surface is treated in dynamic conditions (running water), no oxide buildup is observed. Moreover, running water can remove the oxide film formed in static conditions, as well as oxidized layers due to air exposure. These results are discussed in the framework of cleaning prior to molecular beam epitaxy.

  16. GaAs and 3-5 compound solar cells status and prospects for use in space

    NASA Technical Reports Server (NTRS)

    Flood, D. J.; Brinker, D. J.

    1984-01-01

    Gallium arsenide solar cells equal or supass the best silicon solar cells in efficiency, radiation resistance, annealability, and in the capability to produce usable power output at elevated temperatures. NASA has been involved in a long range research and development program to capitalize on these manifold advantages, and to explore alternative III-V compounds for additional potential improvements. The current status and future prospects for research and development in this area are reviewed and the progress being made toward development of GaAs cells suitable for variety of space missions is discussed. Cell types under various stages of development include n(+)/p shallow homojunction thin film GaAs cells, x100 concentration ratio p/n and n/p GaAs small area concentrator cells, mechanically-stacked, two-junction tandem cells, and three-junction monolithic cascade cells, among various other cell types.

  17. Monolithic catalyst beds for hydrazine reactors

    NASA Technical Reports Server (NTRS)

    1973-01-01

    A monolithic catalyst bed for monopropellant hydrazine decomposition was evaluated. The program involved the evaluation of a new hydrazine catalyst concept wherein open-celled foamed materials are used as supports for the active catalysts. A high-surface-area material is deposited upon the open-celled foamed material and is then coated with an active metal to provide a spontaneous catalyst. Only a fraction of the amount of expensive active metal in currently available catalysts is needed to promote monolithic catalyst. Numerous parameters were evaluated during the program, and the importance of additional parameters became obvious only while the program was in progress. A demonstration firing (using a 2.2-Newton (N)(0.5-lbf) reactor) successfully accumulated 7,700 seconds of firing time and 16 ambient temperature starts without degradation. Based on the excellent results obtained throughout the program and the demonstrated life capability of the monolithic foam, it is recommended that additional studies be conducted to further exploit the advantages of this concept.

  18. Monolithically compatible impedance measurement

    DOEpatents

    Ericson, Milton Nance; Holcomb, David Eugene

    2002-01-01

    A monolithic sensor includes a reference channel and at least one sensing channel. Each sensing channel has an oscillator and a counter driven by the oscillator. The reference channel and the at least one sensing channel being formed integrally with a substrate and intimately nested with one another on the substrate. Thus, the oscillator and the counter have matched component values and temperature coefficients. A frequency determining component of the sensing oscillator is formed integrally with the substrate and has an impedance parameter which varies with an environmental parameter to be measured by the sensor. A gating control is responsive to an output signal generated by the reference channel, for terminating counting in the at least one sensing channel at an output count, whereby the output count is indicative of the environmental parameter, and successive ones of the output counts are indicative of changes in the environmental parameter.

  19. Monolithic microchannel heatsink

    DOEpatents

    Benett, W.J.; Beach, R.J.; Ciarlo, D.R.

    1996-08-20

    A silicon wafer has slots sawn in it that allow diode laser bars to be mounted in contact with the silicon. Microchannels are etched into the back of the wafer to provide cooling of the diode bars. To facilitate getting the channels close to the diode bars, the channels are rotated from an angle perpendicular to the diode bars which allows increased penetration between the mounted diode bars. This invention enables the fabrication of monolithic silicon microchannel heatsinks for laser diodes. The heatsinks have low thermal resistance because of the close proximity of the microchannels to the laser diode being cooled. This allows high average power operation of two-dimensional laser diode arrays that have a high density of laser diode bars and therefore high optical power density. 9 figs.

  20. Monolithic microchannel heatsink

    DOEpatents

    Benett, William J.; Beach, Raymond J.; Ciarlo, Dino R.

    1996-01-01

    A silicon wafer has slots sawn in it that allow diode laser bars to be mounted in contact with the silicon. Microchannels are etched into the back of the wafer to provide cooling of the diode bars. To facilitate getting the channels close to the diode bars, the channels are rotated from an angle perpendicular to the diode bars which allows increased penetration between the mounted diode bars. This invention enables the fabrication of monolithic silicon microchannel heatsinks for laser diodes. The heatsinks have low thermal resistance because of the close proximity of the microchannels to the laser diode being cooled. This allows high average power operation of two-dimensional laser diode arrays that have a high density of laser diode bars and therefore high optical power density.

  1. Fracture mechanics evaluation of GaAs

    NASA Technical Reports Server (NTRS)

    Chen, C. P.

    1984-01-01

    A data base of mechanical and fracture properties for GaAs was generated. The data for single crystal GaAs will be used to design reusable GaAs solar modules. Database information includes; (1) physical property characterizations; (2) fracture behavior evaluations; and (3) strength of cells determined as a function of cell processing and material parameters.

  2. A study of the vertical walls and the surface roughness GaAs after the operation in the combined plasma etching

    NASA Astrophysics Data System (ADS)

    Klimin, Viktor S.; Solodovnik, Maxim S.; Smirnov, Vladimir A.; Eskov, Andrey V.; Tominov, Roman V.; Ageev, Oleg A.

    2016-12-01

    The paper presents the experimental results of the combination of AFM lithography and plasma chemical etching the surface of the gallium arsenide samples. Results dilution and application modes for AFM lithography photoresist, also shown on the image forming modes photoresist surface. Showing results nanoprofilirovaniya surface. Results regimes plasma chemical etching. The analysis of the etching rate is etched surface roughness was studied by atomic force microscopy. Judged from the vertical deflection angle of the initial structures and photoresist obtained after etching.

  3. Influence of substrate orientation on the structural quality of GaAs nanowires in molecular beam epitaxy.

    PubMed

    Zhang, Zhi; Shi, Sui-Xing; Chen, Ping-Ping; Lu, Wei; Zou, Jin

    2015-01-26

    In this study, the effect of substrate orientation on the structural quality of Au-catalyzed epitaxial GaAs nanowires grown by a molecular beam epitaxy reactor has been investigated. It was found that the substrate orientations can be used to manipulate the nanowire catalyst composition and the catalyst surface energy and, therefore, to alter the structural quality of GaAs nanowires grown on different substrates. Defect-free wurtzite-structured GaAs nanowires grown on the GaAs (110) substrate have been achieved under our growth conditions.

  4. mm-wave passive components for monolithic circuits

    NASA Astrophysics Data System (ADS)

    Neidert, R. E.; Binari, S. C.

    1984-04-01

    One of the general problems which arise in connection with mm-wave components is related to the fact that these components are too small to be made by the techniques employed for components utilized at lower frequencies. Possibilities are now being explored regarding the design of components for a more effective use of the portion of the spectrum from 30 to 300 GHz. A description is given of some early results obtained in a research program concerned with the feasibility of quasi-TEM, microstrip components for this frequency range. The considered components are being fabricated on InP substrates, but the technology can be transferred to GaAs or Si. It is found that microstrip technology can be merged with semiconductor fabrication technology to produce mm-wave, monolithic, quasi-TEM circuitry. Attention is given to general conditions, passive components, RF resistors, transitions and transition lines, resonators, the Lange coupler, and the Wilkinson splitter.

  5. GaAs Computer Technology

    DTIC Science & Technology

    1992-01-07

    AD-A259 259 FASTC-ID FOREIGN AEROSPACE SCIENCE AND TECHNOLOGY CENTER GaAs COMPUTER TECHNOLOGY (1) by Wang Qiao-yu 93-00999 Distrir bution t,,,Nm ted...FASTC- ID(RS)T-0310-92 HUMAN TRANSLATION FASTC-ID(RS)T-0310-92 7 January 1993 GaAs COMPUTER TECHNOLOGY (1) By: Wang Qiao-yu English pages: 6 Source...SCIENCE AND DO NOT NECESSARILY REFLECT THE POSITION OR TECHNOLOGY CENiER OPINION OF THE FOREIGN AEROSPACE SCIENCE AND WPAFB, OHIO TECHNOLOGY CENTER

  6. Droplet-mediated formation of embedded GaAs nanowires in MBE GaAs1-x Bi x films

    NASA Astrophysics Data System (ADS)

    Wood, Adam W.; Collar, Kristen; Li, Jincheng; Brown, April S.; Babcock, Susan E.

    2016-03-01

    We have examined the morphology and composition of embedded nanowires that can be formed during molecular beam epitaxy of GaAs1-x Bi x using high angle annular dark field (‘Z-contrast’) imaging in an aberration-corrected scanning transmission electron microscope. Samples were grown in Ga-rich growth conditions on a stationary GaAs substrate. Ga-rich droplets are observed on the surface with lateral trails extending from the droplet in the [110] direction. Cross-sectional scanning transmission electron microscopy of the film reveals epitaxial nanowire structures of composition ˜GaAs embedded in the GaAs1-x Bi x epitaxial layers. These nanowires extend from a surface droplet to the substrate at a shallow angle of inclination (˜4°). They typically are 4 μm long and have a lens-shaped cross section with major and minor axes dimensions of 800 and 120 nm. The top surface of the nanowires exhibits a linear trace in longitudinal cross-section, across which the composition change from ˜GaAs to GaAs1-x Bi x appears abrupt. The bottom surfaces of the nanowires appear wavy and the composition change appears to be graded over ˜25 nm. The droplets have phase separated into Ga- and Bi-rich components. A qualitative model is proposed in which Bi is gettered into Ga droplets, leaving Bi depleted nanowires in the wakes of the droplets as they migrate in one direction across the surface during GaAs1-x Bi x film growth.

  7. Comparison of soil-monolith extraction techniques

    NASA Astrophysics Data System (ADS)

    Meissner, R.; Rupp, H.; Weller, U.; Vogel, H.-J.

    2009-04-01

    the soil monolith employing a rotary cutting system. This procedure should avoid structural damages and substantially reduces the necessary technical expenditure during monolith extraction. This "cutting" technology has been used successfully for different soil types (from gravel to sand to clay including contaminated sites) and for different lysimeter sizes (surface area 0.1-2 m2 and depths of 0.5-3.0 m). There is evidence in literature that lateral water and solute fluxes cannot - or only insufficient - be examined with conventional lysimeters. Lateral fluxes are of particular importance in groundwater dominated systems, as peat soils (fens or Histosols). To investigate lateral transport processes a box-shaped stainless steel lysimeter vessel (4 m long, 1 m width and 1.5 m depth) was constructed. The most challenging task of the extraction procedure was the horizontal sliding of the lysimeter vessel through the natural peat soil. At the front of the vessel a cutting tool assists in carving the soil monolith out of the peat, both vertically and at the base of the vessel. The yet unfilled vessel was inserted at the extraction site into an already prepared starting pit and aligned to a guiding system (guide tracks) adjustable in three axes. Serrated knife bars were used for cutting. A hydraulic plunger was used to support the cutting procedure. The whole horizontal extraction technology will be described and demonstrated. For the evaluation of the different extraction technologies with respect to the potential disturbance of soil structure we applied the different techniques for the same soil type (Eutric Fluvisol). At natural site conditions soil monoliths with the same size have been extracted with the "hammering", the "pressing" and the "cutting" technology. The soil structure close to the vessel wall was recorded using X-ray tomography at a resolution of some 0.1 mm. The results will be demonstrated and discussed.

  8. Monolithic microcircuit techniques and processes

    NASA Technical Reports Server (NTRS)

    Kennedy, B. W.

    1972-01-01

    Brief discussions of the techniques used to make dielectric and metal thin film depositions for monolithic circuits are presented. Silicon nitride deposition and the properties of silicon nitride films are discussed. Deposition of dichlorosilane and thermally grown silicon dioxide are reported. The deposition and thermal densification of borosilicate, aluminosilicate, and phosphosilicate glasses are discussed. Metallization for monolithic circuits and the characteristics of thin films are also included.

  9. Monolith Joint Repairs: Case Histories

    DTIC Science & Technology

    1989-08-01

    REPAIR, EVALUATION, MAINTENANCE, AND REHABILITATION RESEARCH PROGRAM TECHNICAL REPORT REMR-CS-22 MONOLITH JOINT REPAIRS: CASE HISTORVS.Z by James G ...Washington, DC 20314-1000 32307 S11. TITLE (Include Security Classification) Monolith Joint Repairs: Case Histories 12. PERSONAL AUTHOR(S) May. James G ...Research Work Unit 32307, "Tech- niques for Joint Repair and Rehabilitation," for which MAJ James G . May, CE, is the Principal Investigator. This work unit

  10. A poly(vinyl alcohol)/sodium alginate blend monolith with nanoscale porous structure.

    PubMed

    Sun, Xiaoxia; Uyama, Hiroshi

    2013-10-04

    A stimuli-responsive poly(vinyl alcohol) (PVA)/sodium alginate (SA) blend monolith with nanoscale porous (mesoporous) structure is successfully fabricated by thermally impacted non-solvent induced phase separation (TINIPS) method. The PVA/SA blend monolith with different SA contents is conveniently fabricated in an aqueous methanol without any templates. The solvent suitable for the fabrication of the present blend monolith by TINIPS is different with that of the PVA monolith. The nanostructural control of the blend monolith is readily achieved by optimizing the fabrication conditions. Brunauer Emmett Teller measurement shows that the obtained blend monolith has a large surface area. Pore size distribution plot for the blend monolith obtained by the non-local density functional theory method reveals the existence of the nanoscale porous structure. Fourier transform infrared analysis reveals the strong interactions between PVA and SA. The pH-responsive property of the blend monolith is investigated on the basis of swelling ratio in different pH solutions. The present blend monolith of biocompatible and biodegradable PVA and SA with nanoscale porous structure has large potential for applications in biomedical and environmental fields.

  11. Comparison of perfusion media and monoliths for protein and virus-like particle chromatography.

    PubMed

    Wu, Yige; Abraham, Dicky; Carta, Giorgio

    2016-05-20

    Structural and performance characteristics of perfusion chromatography media (POROS HS 20 and 50) and those of a polymethacrylate monolith (CIM SO3-1 tube monolith column) are compared for protein and virus-like particle chromatography using 1mL columns. Axial flow columns are used for POROS while the monolith has a radial flow configuration, which provides comparable operating pressures. The POROS beads contain a bimodal distribution of pore sizes, some as large as 0.5μm, which allow a small fraction of the mobile phase to flow within the particles, while the monolith contains 1-2μm flow channels. For proteins (lysozyme and IgG), the dynamic binding capacity of the POROS columns is more than twice that of the monolith at longer residence times. While the DBC of the POROS HS 50 column decreases at shorter residence times, the DBC of the POROS HS 20 column for IgG remains nearly twice that of the monolith at residence times at least as low as 0.2min as a result of intraparticle convection. Protein recoveries are comparable for all three columns. For VLPs, however, the eluted peaks are broader and recovery is lower for the monolith than for the POROS columns and is dependent on the direction of flow in the monolith, which is attributed to denser layer observed by SEM at the inlet surface of the monolith that appears to trap VLPs when loading in the normal flow direction.

  12. New Graphene Form of Nanoporous Monolith for Excellent Energy Storage.

    PubMed

    Bi, Hui; Lin, Tianquan; Xu, Feng; Tang, Yufeng; Liu, Zhanqiang; Huang, Fuqiang

    2016-01-13

    Extraordinary tubular graphene cellular material of a tetrahedrally connected covalent structure was very recently discovered as a new supermaterial with ultralight, ultrastiff, superelastic, and excellent conductive characteristics, but no high specific surface area will keep it from any next-generation energy storage applications. Herein, we prepare another new graphene monolith of mesoporous graphene-filled tubes instead of hollow tubes in the reported cellular structure. This graphene nanoporous monolith is also composed of covalently bonded carbon network possessing high specific surface area of ∼1590 m(2) g(-1) and electrical conductivity of ∼32 S cm(-1), superior to graphene aerogels and porous graphene forms self-assembled by graphene oxide. This 3D graphene monolith can support over 10 000 times its own weight, significantly superior to CNT and graphene cellular materials with a similar density. Furthermore, pseudocapacitance-active functional groups are introduced into the new nanoporous graphene monolith as an electrode material in electrochemical capacitors. Surprisingly, the electrode of 3D mesoporous graphene has a specific capacitance of 303 F g(-1) and maintains over 98% retention after 10 000 cycles, belonging to the list for the best carbon-based active materials. The macroscopic mesoporous graphene monolith suggests the great potential as an electrode for supercapacitors in energy storage areas.

  13. Ultra-Thin, Triple-Bandgap GaInP/GaAs/GaInAs Monolithic Tandem Solar Cells

    NASA Technical Reports Server (NTRS)

    Wanlass, M. W.; Ahrenkiel, S. P.; Albin, D. S.; Carapella, J. J.; Duda, A.; Emery, K.; Geisz, J. F.; Jones, K.; Kurtz, Sarah; Moriarty, T.; hide

    2007-01-01

    The performance of state-of-the-art, series-connected, lattice-matched (LM), triple-junction (TJ), III-V tandem solar cells could be improved substantially (10-12%) by replacing the Ge bottom subcell with a subcell having a bandgap of approx.1 eV. For the last several years, research has been conducted by a number of organizations to develop approx.1-eV, LM GaInAsN to provide such a subcell, but, so far, the approach has proven unsuccessful. Thus, the need for a high-performance, monolithically integrable, 1-eV subcell for TJ tandems has remained. In this paper, we present a new TJ tandem cell design that addresses the above-mentioned problem. Our approach involves inverted epitaxial growth to allow the monolithic integration of a lattice-mismatched (LMM) approx.1- eV GaInAs/GaInP double-heterostructure (DH) bottom subcell with LM GaAs (middle) and GaInP (top) upper subcells. A transparent GaInP compositionally graded layer facilitates the integration of the LM and LMM components. Handle-mounted, ultra-thin device fabrication is a natural consequence of the inverted-structure approach, which results in a number of advantages, including robustness, potential low cost, improved thermal management, incorporation of back-surface reflectors, and possible reclamation/reuse of the parent crystalline substrate for further cost reduction. Our initial work has concerned GaInP/GaAs/GaInAs tandem cells grown on GaAs substrates. In this case, the 1- eV GaInAs experiences 2.2% compressive LMM with respect to the substrate. Specially designed GaInP graded layers are used to produce 1-eV subcells with performance parameters nearly equaling those of LM devices with the same bandgap (e.g., LM, 1-eV GaInAsP grown on InP). Previously, we reported preliminary ultra-thin tandem devices (0.237 cm2) with NREL-confirmed efficiencies of 31.3% (global spectrum, one sun) (1), 29.7% (AM0 spectrum, one sun) (2), and 37.9% (low-AOD direct spectrum, 10.1 suns) (3), all at 25 C. Here, we include

  14. Molecular-beam epitaxial regrowth on oxygen-implanted GaAs substrates for device integration

    NASA Astrophysics Data System (ADS)

    Chen, C. L.; Mahoney, L. J.; Calawa, S. D.; Molvar, K. M.; Maki, P. A.; Mathews, R. H.; Sage, J. P.; Sollner, T. C. L. G.

    1999-06-01

    Device-quality layers were regrown on GaAs wafers by molecular-beam epitaxy over conductive pregrown areas and on selectively patterned high-resistivity areas formed by oxygen implantation. The regrowth over both areas resulted in comparable device-quality GaAs. The high resistivity of the oxygen-implanted area was maintained after the regrowth and no oxygen incorporation was observed in the regrown layer. The cutoff frequency of a 1.5-μm-gate metal-semiconductor field-effect transistor fabricated on the regrown layer over the high-resistivity areas is 7 GHz. This demonstration shows that planar technology can be used in epitaxial regrowth, simplifying the integration of vastly different devices into monolithic circuits.

  15. Progress toward a 30 percent-efficient, monolithic, three-junction, two-terminal concentrator solar cell for space applications

    NASA Technical Reports Server (NTRS)

    Partain, L. D.; Chung, B.-C.; Virshup, G. F.; Schultz, J. C.; Macmillan, H. F.; Ristow, M. Ladle; Kuryla, M. S.; Bertness, K. A.

    1991-01-01

    Component efficiencies of 0.2/sq cm cells at approximately 100x AMO light concentration and 80 C temperatures are not at 15.3 percent for a 1.9 eV AlGaAs top cell, 9.9 percent for a 1.4 eV GaAs middle cell under a 1.9 eV AlGaAs filter, and 2.4 percent for a bottom 1.0 eV InGaAs cell under a GaAs substrate. The goal is to continue improvement in these performance levels and to sequentially grow these devices on a single substrate to give 30 percent efficient, monolithic, two-terminal, three-junction space concentrator cells. The broad objective is a 30 percent efficient monolithic two-terminal cell that can operate under 25 to 100x AMO light concentrations and at 75 to 100 C cell temperatures. Detailed modeling predicts that this requires three junctions. Two options are being pursued, and both use a 1.9 eV AlGaAs top junction and a 1.4 eV GaAs middle junction grown by a 1 atm OMVPE on a lattice matched substrate. Option 1 uses a low-doped GaAs substrate with a lattice mismatched 1.0 eV InGaAs cell formed on the back of the substrate. Option 2 uses a Ge substrate to which the AlGaAs and GaAs top junctions are lattice matched, with a bottom 0.7 eV Ge junction formed near the substrate interface with the GaAs growth. The projected efficiency contributions are near 16, 11, and 3 percent, respectively, from the top, middle, and bottom junctions.

  16. Tandem lectin affinity chromatography monolithic columns with surface immobilised concanavalin A, wheat germ agglutinin and Ricinus communis agglutinin-I for capturing sub-glycoproteomics from breast cancer and disease-free human sera.

    PubMed

    Selvaraju, Subhashini; El Rassi, Ziad

    2012-07-01

    In this study, a liquid-phase separation platform consisting of tandem lectin affinity chromatography was introduced for the selective capturing of sub-glycoproteomics that are affected in cancers, e.g. breast cancer. The platform is comprised of three monolithic columns with surface immobilised lectins including concanavalin A (Con A), wheat germ agglutinin (WGA) and Ricinus communis agglutinin-I (RCA-I). While WGA and Con A have specificities directed towards the core portion of N-glycans on the glycoprotein surface, RCA-I specifically interacts with the non-reducing terminal moieties of the outer chain structures of N-glycans. The effects of the order in which the three lectin columns were arranged in the tandem columns format were evaluated. The most suitable order proved to be WGA → Con A → RCA-I (denoted as WCR) as far as the number of captured proteins was concerned. The WCR tandem columns allowed the capture of 113 and 112 proteins from disease-free and breast cancer sera, respectively, corresponding to 75 and 65 non-redundant proteins, respectively. Using mass spectral count ratios and Q-Q plots yielded a panel of 23 non-redundant differentially expressed proteins (i.e. a panel of 23 candidate markers), which should in principle be more representative of a pathophysiological state than a single marker candidate.

  17. A chitosan coated monolith for nucleic acid capture in a thermoplastic microfluidic chip

    PubMed Central

    Kendall, Eric L.; Wienhold, Erik; DeVoe, Don L.

    2014-01-01

    A technique for microfluidic, pH modulated DNA capture and purification using chitosan functionalized glycidyl methacrylate monoliths is presented. Highly porous polymer monoliths are formed and subsequently functionalized off-chip in a batch process before insertion into thermoplastic microchannels prior to solvent bonding, simplifying the overall fabrication process by eliminating the need for on-chip surface modifications. The monolith anchoring method allows for the use of large cross-section monoliths enabling high flowrates and high DNA capture capacity with a minimum of added design complexity. Using monolith capture elements requiring less than 1 mm2 of chip surface area, loading levels above 100 ng are demonstrated, with DNA capture and elution efficiency of 54.2% ± 14.2% achieved. PMID:25379094

  18. Preparation and photocatalytic activity of robust titania monoliths for water remediation.

    PubMed

    Nakata, Kazuya; Kagawa, Tomoya; Sakai, Munetoshi; Liu, Shanhu; Ochiai, Tsuyoshi; Sakai, Hideki; Murakami, Taketoshi; Abe, Masahiko; Fujishima, Akira

    2013-02-01

    TiO(2) monoliths were prepared, characterized, and evaluated for photocatalytic performance. The TiO(2) monoliths were found to have an interconnected void lattice and a bimodal porous structure with macropores and mesopores after calcination at 500-700 °C. Monoliths calcined at 500 °C had high specific surface area (93.1 m(2)/g) and porosity (68%), which were maintained after calcination at 700-1100 °C (51-46%). The calcined monoliths had relatively high Vickers hardness (∼104) despite their porous structure. Monoliths calcined at 500 and 700 °C exhibited high performance for methylene blue decolorization because of their high specific surface area.

  19. Atomic Geometry of GaAs(110)-p(1×1)-Al

    NASA Astrophysics Data System (ADS)

    Duke, C. B.; Paton, A.; Meyer, R. J.; Brillson, L. J.; Kahn, A.; Kanani, D.; Carelli, J.; Yeh, J. L.; Margaritondo, G.; Katnani, A. D.

    1981-02-01

    An ordered (1×1) structure is formed by evaporating approximately one-half monolayer of Al on GaAs(110) and subsequently annealing at 450°C for 30 min. Both a dynamical analysis of the low-energy electron-diffraction intensities from the resulting half-monolayer of GaAs(110)-p(1×1)-Al structure and soft-x-ray photoemission spectroscopy indicate that the Al replaces the Ga in the second atomic layer beneath the surface. The uppermost layer retains the structure of clean GaAs(110) but is relaxed 0.1 Å toward the second AlAs layer.

  20. Monolithic supports with unique geometries and enhanced mass transfer.

    SciTech Connect

    Stuecker, John Nicholas; Ferrizz, Robert Matthew; Cesarano, Joseph, III; Miller, James Edward

    2004-01-01

    The catalytic combustion of natural gas has been the topic of much research over the past decade. Interest in this technology results from a desire to decrease or eliminate the emissions of harmful nitrogen oxides (NOX) from gas turbine power plants. A low-pressure drop catalyst support, such as a ceramic monolith, is ideal for this high-temperature, high-flow application. A drawback to the traditional honeycomb monoliths under these operating conditions is poor mass transfer to the catalyst surface in the straight-through channels. 'Robocasting' is a unique process developed at Sandia National Laboratories that can be used to manufacture ceramic monoliths with alternative 3-dimensional geometries, providing tortuous pathways to increase mass transfer while maintaining low pressure drops. This report details the mass transfer effects for novel 3-dimensional robocast monoliths, traditional honeycomb-type monoliths, and ceramic foams. The mass transfer limit is experimentally determined using the probe reaction of CO oxidation over a Pt / {gamma}-Al{sub 2}O{sub 3} catalyst, and the pressure drop is measured for each monolith sample. Conversion versus temperature data is analyzed quantitatively using well-known dimensionless mass transfer parameters. The results show that, relative to the honeycomb monolith support, considerable improvement in mass transfer efficiency is observed for robocast samples synthesized using an FCC-like geometry of alternating rods. Also, there is clearly a trade-off between enhanced mass transfer and increased pressure drop, which can be optimized depending on the particular demands of a given application.

  1. Circularly polarized lasing in chiral modulated semiconductor microcavity with GaAs quantum wells

    NASA Astrophysics Data System (ADS)

    Demenev, A. A.; Kulakovskii, V. D.; Schneider, C.; Brodbeck, S.; Kamp, M.; Höfling, S.; Lobanov, S. V.; Weiss, T.; Gippius, N. A.; Tikhodeev, S. G.

    2016-10-01

    We report close to circularly polarized lasing at ℏ ω = 1.473 and 1.522 eV from an AlAs/AlGaAs Bragg microcavity, with 12 GaAs quantum wells in the active region and chirally etched upper distributed Bragg refractor under optical pump at room temperature. The advantage of using the chiral photonic crystal with a large contrast of dielectric permittivities is its giant optical activity, allowing to fabricate a very thin half-wave plate, with a thickness of the order of the emitted light wavelength, and to realize the monolithic control of circular polarization.

  2. Factorizing monolithic applications

    SciTech Connect

    Hall, J.H.; Ankeny, L.A.; Clancy, S.P.

    1998-12-31

    The Blanca project is part of the US Department of Energy`s (DOE) Accelerated Strategic Computing Initiative (ASCI), which focuses on Science-Based Stockpile Stewardship through the large-scale simulation of multi-physics, multi-dimensional problems. Blanca is the only Los Alamos National Laboratory (LANL)-based ASCI project that is written entirely in C++. Tecolote, a new framework used in developing Blanca physics codes, provides an infrastructure for gluing together any number of components; this framework is then used to create applications that encompass a wide variety of physics models, numerical solution options, and underlying data storage schemes. The advantage of this approach is that only the essential components for the given model need be activated at runtime. Tecolote has been designed for code re-use and to isolate the computer science mechanics from the physics aspects as much as possible -- allowing physics model developers to write algorithms in a style quite similar to the underlying physics equations that govern the computational physics. This paper describes the advantages of component architectures and contrasts the Tecolote framework with Microsoft`s OLE and Apple`s OpenDoc. An actual factorization of a traditional monolithic application into its basic components is also described.

  3. Growth and characterization of molecular beam epitaxial GaAs layers on porous silicon

    NASA Technical Reports Server (NTRS)

    Lin, T. L.; Liu, J. K.; Sadwick, L.; Wang, K. L.; Kao, Y. C.

    1987-01-01

    GaAs layers have been grown on porous silicon (PS) substrates with good crystallinity by molecular beam epitaxy. In spite of the surface irregularity of PS substrates, no surface morphology deterioration was observed on epitaxial GaAs overlayers. A 10-percent Rutherford backscattering spectroscopy minimum channeling yield for GaAs-on-PS layers as compared to 16 percent for GaAs-on-Si layers grown under the same condition indicates a possible improvement of crystallinity when GaAs is grown on PS. Transmission electron microscopy reveals that the dominant defects in the GaAs-on-PS layers are microtwins and stacking faults, which originate from the GaAs/PS interface. GaAs is found to penetrate into the PS layers. n-type GaAs/p-type PS heterojunction diodes were fabricated with good rectifying characteristics.

  4. Chemical beam epitaxy of GaAs films using single-source precursors

    NASA Astrophysics Data System (ADS)

    Ekerdt, J. G.; Sun, Y. M.; Jackson, M. S.; Lakhotia, V.; Pacheco, K. A.; Koschmieder, S. U.; Cowley, A. H.; Jones, R. A.

    1992-11-01

    Two types of single-source precursors were studied that contained different Ga : As stoichiometry, [Me 2Ga(μ-AS- t-Bu 2)] 2 with a 1 : 1 stoichoimetry and Ga(As>- t-Bu 2) 3 with a 1 : 3 stoichiometry. Epitaxial films were grown from Ga(As- t-Bu 2) 3 on (100) GaAs in a chemical beam epitaxy system at 750 K and 6 × 10 -5 Torr. Temperature programmed desorption (TPD) studies for [Me 2Ga(μ- As- t-Bu 2)] 2 and Ga(As- t-Bu 2) 3 have been undertaken in a surface analysis chamber to develop an understanding of how precursor structure and reaction chemistry influence film properties. tert-Butyl ligands appear to react by β-hydride elimination process to isobutene and AsH. The methyl ligands appear to desorb rather than react with surface hydride to methane.

  5. Growth and characterization of molecular beam epitaxial GaAs layers on porous silicon

    NASA Technical Reports Server (NTRS)

    Lin, T. L.; Liu, J. K.; Sadwick, L.; Wang, K. L.; Kao, Y. C.

    1987-01-01

    GaAs layers have been grown on porous silicon (PS) substrates with good crystallinity by molecular beam epitaxy. In spite of the surface irregularity of PS substrates, no surface morphology deterioration was observed on epitaxial GaAs overlayers. A 10-percent Rutherford backscattering spectroscopy minimum channeling yield for GaAs-on-PS layers as compared to 16 percent for GaAs-on-Si layers grown under the same condition indicates a possible improvement of crystallinity when GaAs is grown on PS. Transmission electron microscopy reveals that the dominant defects in the GaAs-on-PS layers are microtwins and stacking faults, which originate from the GaAs/PS interface. GaAs is found to penetrate into the PS layers. n-type GaAs/p-type PS heterojunction diodes were fabricated with good rectifying characteristics.

  6. InGaAs/InP Monolithic Interconnected Modules (MIM) for Thermophotovoltaic Applications

    NASA Technical Reports Server (NTRS)

    Wilt, David M.; Fatemi, Navid S.; Jenkins, Phillip P.; Weizer, Victor G.; Hoffman, Richard W., Jr.; Scheiman, David A.; Murray, Christopher S.; Riley, David R.

    2004-01-01

    There has been a traditional trade-off in thermophotovoltaic (TPV) energy conversion development between systems efficiency and power density. This trade-off originates from the use of front surface spectral controls such as selective emitters and various types of filters. A monolithic interconnected module (MIM) structure has been developed which allows for both high power densities and high system efficiencies. The MIM device consists of many individual indium gallium arsenide (InGaAs) devices series -connected on a single semi-insulating indium phosphide (InP) substrate. The MIMs are exposed to the entire emitter output, thereby maximizing output power density. An infrared (IR) reflector placed on the rear surface of the substrate returns the unused portion of the emitter output spectrum back to the emitter for recycling, thereby providing for high system efficiencies. Initial MIM development has focused on a 1 sq cm device consisting of eight series interconnected cells. MIM devices, produced from 0,74 eV InGAAs, have demonstrated V(sub infinity) = 3.23 volts, J(sub sc) = 70 mA/sq cm and a fill factor of 66% under flashlamp testing. Infrared (IR) reflectance measurement (less than 2 microns) of these devices indicate a reflectivity of less than 82%. MIM devices produced from 0.55 eV InGaAs have also been den=monstrated. In addition, conventional p/n InGaAs devices with record efficiencies (11.7% AM1) have been demonstrated.

  7. Surface segregation effects of erbium in GaAs growth and their implications for optical devices containing ErAs nanostructures

    SciTech Connect

    Crook, Adam M.; Nair, Hari P.; Bank, Seth R.

    2011-03-21

    We report on the integration of semimetallic ErAs nanoparticles with high optical quality GaAs-based semiconductors, grown by molecular beam epitaxy. Secondary ion mass spectrometry and photoluminescence measurements provide evidence of surface segregation and incorporation of erbium into layers grown with the erbium cell hot, despite the closed erbium source shutter. We establish the existence of a critical areal density of the surface erbium layer, below which the formation of ErAs precipitates is suppressed. Based upon these findings, we demonstrate a method for overgrowing ErAs nanoparticles with III-V layers of high optical quality, using subsurface ErAs nanoparticles as a sink to deplete the surface erbium concentration. This approach provides a path toward realizing optical devices based on plasmonic effects in an epitaxially-compatible semimetal/semiconductor system.

  8. HPLC analysis of synthetic polymers on short monolithic columns.

    PubMed

    Maksimova, Elena; Vlakh, Evgenia; Sinitsyna, Ekaterina; Tennikova, Tatiana

    2013-12-01

    Ultrashort monolithic columns (disks) were thoroughly studied as efficient stationary phases for precipitation-dissolution chromatography of synthetic polymers. Gradient elution mode was applied in all chromatographic runs. The mixtures of different flexible chain homopolymers, such as polystyrenes, poly(methyl methacrylates), and poly(tert-butylmethacrylates) were separated according to their molecular weights on both commercial poly(styrene-co-divinylbenzene) disks (12 id × 3 mm and 5 × 5 mm) and lab-made monolithic columns (4.6 id × 50 mm) filled with supports of different hydrophobicity. The experimental conditions were optimized to reach fast and highly efficient separation. It was observed that, similar to the separation of monoliths of other classes of (macro)molecules (proteins, DNA, oligonucleotides), the length of column did not affect the peak resolution. A comparison of the retention properties of the poly(styrene-co-divinylbenzene) disk-shaped monoliths with those based on poly(lauryl methacrylate-co-ethylene dimethacrylate), poly(butyl methacrylate-co-ethylene dimethacrylate), and poly(glycidyl methacrylate-co-ethylene dimethacrylate) supports demonstrated the obvious effect of surface chemistry on the resolution factor. Additionally, the results of the discussed chromatographic mode on the fast determination of the molecular weights of homopolymers used in this study were compared to those established by SEC on columns packed with sorbent beads of a similar nature to the monoliths. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  9. Edge chipping and flexural resistance of monolithic ceramics☆

    PubMed Central

    Zhang, Yu; Lee, James J.-W.; Srikanth, Ramanathan; Lawn, Brian R.

    2014-01-01

    Objective Test the hypothesis that monolithic ceramics can be developed with combined esthetics and superior fracture resistance to circumvent processing and performance drawbacks of traditional all-ceramic crowns and fixed-dental-prostheses consisting of a hard and strong core with an esthetic porcelain veneer. Specifically, to demonstrate that monolithic prostheses can be produced with a much reduced susceptibility to fracture. Methods Protocols were applied for quantifying resistance to chipping as well as resistance to flexural failure in two classes of dental ceramic, microstructurally-modified zirconias and lithium disilicate glass–ceramics. A sharp indenter was used to induce chips near the edges of flat-layer specimens, and the results compared with predictions from a critical load equation. The critical loads required to produce cementation surface failure in monolithic specimens bonded to dentin were computed from established flexural strength relations and the predictions validated with experimental data. Results Monolithic zirconias have superior chipping and flexural fracture resistance relative to their veneered counterparts. While they have superior esthetics, glass–ceramics exhibit lower strength but higher chip fracture resistance relative to porcelain-veneered zirconias. Significance The study suggests a promising future for new and improved monolithic ceramic restorations, with combined durability and acceptable esthetics. PMID:24139756

  10. Pore volume accessibility of particulate and monolithic stationary phases.

    PubMed

    Urban, Jiří

    2015-05-29

    A chromatographic characterization of pore volume accessibility for both particulate and monolithic stationary phases is presented. Size-exclusion calibration curves have been used to determine the pore volume fraction that is accessible for six alkylbenzenes and twelve polystyrene standards in tetrahydrofuran as the mobile phase. Accessible porosity has been then correlated with the size of the pores from which individual compounds are just excluded. I have determined pore volume accessibility of commercially available columns packed with fully and superficially porous particles, as well as with silica-based monolithic stationary phase. I also have investigated pore accessibility of polymer-based monolithic stationary phases. Suggested protocol is used to characterize pore formation at the early stage of the polymerization, to evaluate an extent of hypercrosslinking during modification of pore surface, and to characterize the pore accessibility of monolithic stationary phases hypercrosslinked after an early termination of polymerization reaction. Pore volume accessibility was also correlated to column efficiency of both particulate and monolithic stationary phases. Copyright © 2015 Elsevier B.V. All rights reserved.

  11. GaAs microcrystals selectively grown on silicon: Intrinsic carbon doping during chemical beam epitaxy with trimethylgallium

    NASA Astrophysics Data System (ADS)

    Molière, T.; Jaffré, A.; Alvarez, J.; Mencaraglia, D.; Connolly, J. P.; Vincent, L.; Hallais, G.; Mangelinck, D.; Descoins, M.; Bouchier, D.; Renard, C.

    2017-01-01

    The monolithic integration of III-V semiconductors on silicon and particularly of GaAs has aroused great interest since the 1980s. Potential applications are legion, ranging from photovoltaics to high mobility channel transistors. By using a novel integration method, we have shown that it is possible to achieve heteroepitaxial integration of GaAs crystals (typical size 1 μ m) on silicon without any structural defect such as antiphase domains, dislocations, or stress, usually reported for direct GaAs heteroepitaxy on silicon. However, concerning their electronic properties, conventional free carrier characterization methods are impractical due to the micrometric size of GaAs crystals. In order to evaluate the GaAs material quality for optoelectronic applications, a series of indirect analyses such as atom probe tomography, Raman spectroscopy, and micro-photoluminescence as a function of temperature were performed. These revealed a high content of partially electrically active carbon originating from the trimethylgallium used as the Ga precursor. Nevertheless, the very good homogeneity observed by this doping mechanism and the attractive properties of carbon as a dopant once controlled to a sufficient degree are a promising route to device doping.

  12. GaAs nanowire/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) hybrid solar cells.

    PubMed

    Chao, Jiun-Jie; Shiu, Shu-Chia; Hung, Shih-Che; Lin, Ching-Fuh

    2010-07-16

    In this paper, a new type of hybrid solar cell based on a heterojunction between poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and vertically aligned n-type GaAs nanowire (NW) arrays is investigated. The GaAs NW arrays are fabricated by directly performing the nano-etching of GaAs wafer with spun-on SiO(2) nanospheres as the etch mask through inductively coupled plasma reactive ion etching. The PEDOT:PSS adheres to the surface of the GaAs NW arrays to form a p-n junction. The morphology of GaAs NW arrays strongly influences the characteristics of the GaAs NW/PEDOT:PSS hybrid solar cells. The suppression of reflectance and the interpenetrating heterojunction interface of GaAs NW arrays offers great improvements in efficiency relative to a conventional planar cell. Compared to the planar GaAs/PEDOT:PSS cells, the power conversion efficiency under AM 1.5 global one sun illumination is improved from 0.29% to 5.8%.

  13. Allyl-silica Hybrid Monoliths For Chromatographic Application

    NASA Astrophysics Data System (ADS)

    Guo, Wenjuan

    Column technology continues to be the most investigated topics in the separation world, since the column is the place where the chromatographic separation happens, making it the heart of the separation system. Allyl-silica hybrid monolithic material has been exploited as support material and potential stationary phases for liquid chromatography; the stationary phase anchored to the silica surface by Si-C bond, which is more pH stable than traditional stationary phase. First, nuclear magnetic resonance spectroscopy has been used to study the sol in the synthesis of allyl-silica hybrid monoliths. Allyl-trimethoxysilane (allyl-TrMOS), dimethyldimethoxysilane (DMDMOS) and tetramethoxysilane (TMOS) have been served as co-precursors in the sol-gel synthesis of organo-silica hybrid monolithic columns for liquid chromatography (LC). 29Si nuclear magnetic resonance (NMR) and 1H NMR spectroscopy were employed to monitor reaction profiles for the acid-catalyzed hydrolysis and initial condensation reactions of the individual precursor and the hybrid system. 29Si-NMR has also been used to identify different silane species formed during the reactions. The overall hydrolysis rate has been found to follow the trend DMDMOS > allyl-TrMOS > TMOS, if each precursor is reacted individually (homo-polymerization). Precursors show different hydrolysis rate when reacted together in the hybrid system than they are reacted individually. Cross-condensation products of TMOS and DMDMOS (QD) arise about 10 minutes of initiation of the reaction. The allyl-silica monolithic columns for capillary liquid chromatography can only be prepared in capillaries with 50 im internal diameter with acceptable performance. One of the most prominent problems related to the synthesis of silica monolithic structures is the volume shrinkage. The synthesis of allylfunctionalized silica hybrid monolithic structures has been studied in an attempt to reduce the volume shrinkage during aging, drying and heat treatment

  14. Shear bond strength of indirect composite material to monolithic zirconia.

    PubMed

    Sari, Fatih; Secilmis, Asli; Simsek, Irfan; Ozsevik, Semih

    2016-08-01

    This study aimed to evaluate the effect of surface treatments on bond strength of indirect composite material (Tescera Indirect Composite System) to monolithic zirconia (inCoris TZI). Partially stabilized monolithic zirconia blocks were cut into with 2.0 mm thickness. Sintered zirconia specimens were divided into different surface treatment groups: no treatment (control), sandblasting, glaze layer & hydrofluoric acid application, and sandblasting + glaze layer & hydrofluoric acid application. The indirect composite material was applied to the surface of the monolithic zirconia specimens. Shear bond strength value of each specimen was evaluated after thermocycling. The fractured surface of each specimen was examined with a stereomicroscope and a scanning electron microscope to assess the failure types. The data were analyzed using one-way analysis of variance (ANOVA) and Tukey LSD tests (α=.05). Bond strength was significantly lower in untreated specimens than in sandblasted specimens (P<.05). No difference between the glaze layer and hydrofluoric acid application treated groups were observed. However, bond strength for these groups were significantly higher as compared with the other two groups (P<.05). Combined use of glaze layer & hydrofluoric acid application and silanization are reliable for strong and durable bonding between indirect composite material and monolithic zirconia.

  15. Shear bond strength of indirect composite material to monolithic zirconia

    PubMed Central

    2016-01-01

    PURPOSE This study aimed to evaluate the effect of surface treatments on bond strength of indirect composite material (Tescera Indirect Composite System) to monolithic zirconia (inCoris TZI). MATERIALS AND METHODS Partially stabilized monolithic zirconia blocks were cut into with 2.0 mm thickness. Sintered zirconia specimens were divided into different surface treatment groups: no treatment (control), sandblasting, glaze layer & hydrofluoric acid application, and sandblasting + glaze layer & hydrofluoric acid application. The indirect composite material was applied to the surface of the monolithic zirconia specimens. Shear bond strength value of each specimen was evaluated after thermocycling. The fractured surface of each specimen was examined with a stereomicroscope and a scanning electron microscope to assess the failure types. The data were analyzed using one-way analysis of variance (ANOVA) and Tukey LSD tests (α=.05). RESULTS Bond strength was significantly lower in untreated specimens than in sandblasted specimens (P<.05). No difference between the glaze layer and hydrofluoric acid application treated groups were observed. However, bond strength for these groups were significantly higher as compared with the other two groups (P<.05). CONCLUSION Combined use of glaze layer & hydrofluoric acid application and silanization are reliable for strong and durable bonding between indirect composite material and monolithic zirconia. PMID:27555895

  16. Monolithically integrated optical displacement sensor based on triangulation and optical beam deflection.

    PubMed

    Higurashi, E; Sawada, R; Ito, T

    1999-03-20

    A monolithically integrated optical displacement sensor based on triangulation and optical beam deflection is reported. This sensor is simple and consists of only a laser diode, a polyimide waveguide, and a split detector (a pair of photodiodes) upon a GaAs substrate. The resultant prototype device is extremely small (750 microm x 800 microm). Experiments have shown that this sensor can measure the displacement of a mirror with resolution of better than 4 nm. Additionally, we have experimentally demonstrated both axial and lateral displacement measurements when we used a cylindrical micromirror (diameter, 125 microm) as a movable external object.

  17. Microwave monolithic integrated circuit development for future spaceborne phased array antennas

    NASA Technical Reports Server (NTRS)

    Anzic, G.; Kascak, T. J.; Downey, A. N.; Liu, D. C.; Connolly, D. J.

    1984-01-01

    The development of fully monolithic gallium arsenide (GaAs) receive and transmit modules suitable for phased array antenna applications in the 30/20 gigahertz bands is presented. Specifications and various design approaches to achieve the design goals are described. Initial design and performance of submodules and associated active and passive components are presented. A tradeoff study summary is presented, highlighting the advantages of a distributed amplifier approach compared to the conventional single power source designs. Previously announced in STAR as N84-13399

  18. Molecular enhancement of ferromagnetism in GaAs /GaMnAs heterostructures

    NASA Astrophysics Data System (ADS)

    Carmeli, Itai; Bloom, Francisco; Gwinn, E. G.; Kreutz, T. C.; Scoby, Cheyne; Gossard, A. C.; Ray, S. G.; Naaman, Ron

    2006-09-01

    The authors investigate effects of chemisorption of polar organic molecules onto ferromagnetic GaAs /GaMnAs heterostructures. The chemisorbed heterostructures exhibit striking anisotropic enhancement of the magnetization, while GaAs substrates that are physisorbed with the same molecules show no change in magnetic properties. Thus the enhanced magnetism of the chemisorbed heterostructures reflects changes in spin alignment that arise from surface bonding of the organic monolayer.

  19. Oxidation of the GaAs semiconductor at the Al2O3/GaAs junction.

    PubMed

    Tuominen, Marjukka; Yasir, Muhammad; Lång, Jouko; Dahl, Johnny; Kuzmin, Mikhail; Mäkelä, Jaakko; Punkkinen, Marko; Laukkanen, Pekka; Kokko, Kalevi; Schulte, Karina; Punkkinen, Risto; Korpijärvi, Ville-Markus; Polojärvi, Ville; Guina, Mircea

    2015-03-14

    Atomic-scale understanding and processing of the oxidation of III-V compound-semiconductor surfaces are essential for developing materials for various devices (e.g., transistors, solar cells, and light emitting diodes). The oxidation-induced defect-rich phases at the interfaces of oxide/III-V junctions significantly affect the electrical performance of devices. In this study, a method to control the GaAs oxidation and interfacial defect density at the prototypical Al2O3/GaAs junction grown via atomic layer deposition (ALD) is demonstrated. Namely, pre-oxidation of GaAs(100) with an In-induced c(8 × 2) surface reconstruction, leading to a crystalline c(4 × 2)-O interface oxide before ALD of Al2O3, decreases band-gap defect density at the Al2O3/GaAs interface. Concomitantly, X-ray photoelectron spectroscopy (XPS) from these Al2O3/GaAs interfaces shows that the high oxidation state of Ga (Ga2O3 type) decreases, and the corresponding In2O3 type phase forms when employing the c(4 × 2)-O interface layer. Detailed synchrotron-radiation XPS of the counterpart c(4 × 2)-O oxide of InAs(100) has been utilized to elucidate the atomic structure of the useful c(4 × 2)-O interface layer and its oxidation process. The spectral analysis reveals that three different oxygen sites, five oxidation-induced group-III atomic sites with core-level shifts between -0.2 eV and +1.0 eV, and hardly any oxygen-induced changes at the As sites form during the oxidation. These results, discussed within the current atomic model of the c(4 × 2)-O interface, provide insight into the atomic structures of oxide/III-V interfaces and a way to control the semiconductor oxidation.

  20. Spectroscopic constants and potential energy curves of GaAs, GaAs +, and GaAs -

    NASA Astrophysics Data System (ADS)

    Balasubramanian, K.

    1990-02-01

    Twenty electronic states of GaAs, 12 electronic states of GaAs +, and 13 electronic states of GaAs - are investigated using relativistic ab initio complete active space MCSCF (CASSCF) followed by large-scale configuration interaction calculations which included up to 700 000 configurations. Potential energy curves and spectroscopic constants of all these states of three radicals are obtained. Spectroscopic constants of low-lying states of GaAs are in very good agreement with both experiment and all-electron results. Two nearly-degenerate states of 2Σ +, 2Π ( 2Σ + lower) symmetries are found as candidates for the ground state of GaAs -. The GaAs - negative ion is found to be more stable compared to the neutral GaAs ( De(GaAs -) = 3 eV). The electron affinity of GaAs is computed as 0.89 and 1.3 eV at the FOCI and SOCI levels of theory, respectively. Calculated potential energy curves of GaAs are in accord with the experimentally observed predissociation in the 3Π( III) - X3Σ- system.

  1. CBE growth of (001) GaAs: RHEED and RD studies

    NASA Astrophysics Data System (ADS)

    Samuelson, L.; Junno, B.; Paulson, G.; Fornell, J. O.; Ledebo, L.

    1992-11-01

    A novel type of epitaxial growth system has been designed and optimized for studies of surface physics and epitaxial growth during chemical beam epitaxy (CBE). The work presented here deals with the growth of GaAs on (001) oriented GaAs, and is specifically focused on detailed studies of the surface modifications appearing during exposure to triethylgallium (TEG) or tertiarybutylarsine (TBA), as well as during continuous growth. Reflection high-energy electron diffraction (RHEED) is used to characterize surface reconstructions and to monitor monolayer growth oscillations. Optical reflectance-difference (RD) is used as a very sensitive probe to track the chemical admixture and the concentration of dimers on the surface. Examples are given of direct correlations between characteristics RD features and specific surface reconstructions as determined by RHEED. The surface reconstruction phase diagram for CBE growth of (001) GaAs using TBA is presented and compared with the case for MBE growth.

  2. Preparation and evaluation of a lysine-bonded silica monolith as polar stationary phase for hydrophilic interaction pressurized capillary electrochromatography.

    PubMed

    Huang, Guihua; Lian, Qiuyan; Zeng, Wencan; Xie, Zenghong

    2008-09-01

    A silica-based monolith as polar stationary phase was described for hydrophilic interaction pressurized capillary electrochromatography (HI-pCEC). The polar monolithic column was prepared by on-column reaction of lysine with epoxy groups on a gamma-glycidoxypropyltrimethosysilane-modified silica monolith. The stationary phase yielded strong hydrophilic interaction due to the slightly polar hydroxyl groups, and the strong polar lysine ligand with amino groups and carboxylic groups contained on the surface of the monolith. In order to evaluate the hydrophilic character of lysine ligand, the chromatographic behaviors of epoxy monolith (before lysine bonded) and diol monolith (hydroxyl groups contained) were also investigated. Two groups of comparative experiment were developed in terms of the separation of typical neutral non-polar and polar compounds performed in a mobile phase of aqueous-acetonitrile solution. Results showed that the lysine monolith was much more hydrophilic than the diol monolith, which presented less hydrophobic than the epoxy monolith. For further study on its hydrophilic character, the lysine monolith was demonstrated in the HI-pCEC mode for the separations of various polar compounds such as phenols, nucleic acid bases and nucleosides.

  3. Preparation and applications of hybrid organic-inorganic monoliths: a review.

    PubMed

    Zhu, Tao; Row, Kyung Ho

    2012-06-01

    This review presents an overview of the properties of hybrid organic-inorganic monolithic materials and summarizes the recent developments in the preparation and applications of these hybrid monolithic materials. Hybrid monolithic materials with porosities, surface functionalities, and fast dynamic transport have developed rapidly, and have been used in a wide range of applications owing to the low cost, good stability, and excellent performance. Basically, these materials can be divided into two major types according to the chemical composition: hybrid silica-based monolith (HSM) and hybrid polymer-based monolith (HPM). Compared to the HPM, HSM monolith has been attracting most wide attentions, and it is commonly synthesized by the sol-gel process. The conventional preparation procedures of two type's hybrid organic-inorganic monoliths are addressed. Applications of hybrid organic-inorganic monoliths in optical devices, capillary microextraction (CME), capillary electrochromatography (CEC), high performance liquid chromatography (HPLC), and chiral separation are also reviewed. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  4. Functionalization of hybrid monolithic columns via thiol-ene click reaction for proteomics analysis.

    PubMed

    Liu, Zhongshan; Liu, Jing; Liu, Zheyi; Wang, Hongwei; Ou, Junjie; Ye, Mingliang; Zou, Hanfa

    2017-05-19

    The vinyl-functionalized hybrid monolithic columns (75 and 150μm i.d.) were prepared via sol-gel chemistry of tetramethoxysilane (TMOS) and vinyltrimethoxysilane (VTMS). The content of accessible vinyl groups was further improved after the monolithic column was post-treated with vinyldimethylethoxysilane (VDMES). The surface properties of monolithic columns were tailored via thiol-ene click reaction by using 1-octadecanethiol, sodium 3-mercapto-1-propanesulfonate and 2,2'-(ethylenedioxy)diethanethiol/vinylphosphonic acid, respectively. The preparing octadecyl-functionalized monolithic columns were adopted for proteomics analysis in cLC-MS/MS. A 37-cm-long×75-μm-i.d. monolithic column could identify 3918 unique peptides and 1067 unique proteins in the tryptic digest of proteins from HeLa cells. When a 90-cm-long×75-μm-i.d. monolithic column was used, the numbers of unique peptides and proteins were increased by 82% and 32%, respectively. Furthermore, strong cation exchange (SCX) monolithic columns (4cm in length×150μm i.d.) were also prepared and coupled with the 37-cm-long×75-μm-i.d. octadecyl-functionalized monolithic column for two-dimensional SCX-RPLC-MS/MS analysis, which could identify 17114 unique peptides and 3211 unique proteins. Copyright © 2017 Elsevier B.V. All rights reserved.

  5. Method of monolithic module assembly

    DOEpatents

    Gee, James M.; Garrett, Stephen E.; Morgan, William P.; Worobey, Walter

    1999-01-01

    Methods for "monolithic module assembly" which translate many of the advantages of monolithic module construction of thin-film PV modules to wafered c-Si PV modules. Methods employ using back-contact solar cells positioned atop electrically conductive circuit elements affixed to a planar support so that a circuit capable of generating electric power is created. The modules are encapsulated using encapsulant materials such as EVA which are commonly used in photovoltaic module manufacture. The methods of the invention allow multiple cells to be electrically connected in a single encapsulation step rather than by sequential soldering which characterizes the currently used commercial practices.

  6. Monolithical aspherical beam expanding systems

    NASA Astrophysics Data System (ADS)

    Fuchs, U.; Matthias, Sabrina

    2014-10-01

    Beam expanding is a common task, where Galileo telescopes are preferred. However researches and customers have found limitations when using these systems. A new monolithical solution which is based on the usage of only one aspherical component will be presented. It will be shown how to combine up to five monolithical beam expanding systems and to keep the beam quality at diffraction limitation. Insights will be given how aspherical beam expanding systems will help using larger incoming beams and reducing the overall length of such a system. Additionally an add-on element for divergence and wavelength adaption will be presented.

  7. Formation and properties of porous GaAs

    SciTech Connect

    Schmuki, P.; Lockwood, D.J.; Fraser, J.W.; Graham, M.J.; Isaacs, H.S.

    1996-06-01

    Porous structures on n-type GaAs (100) can be grown electrochemically in chloride-containing solutions. Crystallographic etching of the sample is a precursor stage of the attack. Polarization curves reveal the existanece of a critical onset potential for por formation (PFP). PFP is strongly dependent on the doping level of the sample and presence of surface defects. Good agreement between PFP and breakdown voltage of the space charge layer is found. Surface analysis by EDX, AES, and XPS show that the porous structure consists mainly of GaAs and that anion uptake in the structure can only observed after attackhas been initiated. Photoluminescence measurements reveal (under certain conditions) visible light emission from the porous structure.

  8. The Investigation of Intermediate Stage of Template Etching with Metal Droplets by Wetting Angle Analysis on (001) GaAs Surface.

    PubMed

    Lyamkina, A A; Dmitriev, D V; Galitsyn, Yu G; Kesler, V G; Moshchenko, S P; Toropov, A I

    2011-12-01

    In this work, we study metal droplets on a semiconductor surface that are the initial stage for both droplet epitaxy and local droplet etching. The distributions of droplet geometrical parameters such as height, radius and volume help to understand the droplet formation that strongly influences subsequent nanohole etching. To investigate the etching and intermixing processes, we offer a new method of wetting angle analysis. The aspect ratio that is defined as the ratio of the height to radius was used as an estimation of wetting angle which depends on the droplet material. The investigation of the wetting angle and the estimation of indium content revealed significant materials intermixing during the deposition time. AFM measurements reveal the presence of two droplet groups that is in agreement with nanohole investigations. To explain this observation, we consider arsenic evaporation and consequent change in the initial substrate. On the basis of our analysis, we suggest the model of droplet evolution and the formation of two droplet groups.

  9. Lectin-carbohydrate interactions on nanoporous gold monoliths.

    PubMed

    Tan, Yih Horng; Fujikawa, Kohki; Pornsuriyasak, Papapida; Alla, Allan J; Ganesh, N Vijaya; Demchenko, Alexei V; Stine, Keith J

    2013-07-01

    Monoliths of nanoporous gold (np-Au) were modified with self-assembled monolayers of octadecanethiol (C18-SH), 8-mercaptooctyl α-D-mannopyranoside (αMan-C8-SH), and 8-mercapto-3,6-dioxaoctanol (HO-PEG2-SH), and the loading was assessed using thermogravimetric analysis (TGA). Modification with mixed SAMs containing αMan-C8-SH (at a 0.20 mole fraction in the SAM forming solution) with either octanethiol or HO-PEG2-SH was also investigated. The np-Au monoliths modified with αMan-C8-SH bind the lectin Concanavalin A (Con A), and the additional mass due to bound protein was assessed using TGA analysis. A comparison of TGA traces measured before and after exposure of HO-PEG2-SH modified np-Au to Con A showed that the non-specific binding of Con A was minimal. In contrast, np-Au modified with octanethiol showed a significant mass loss due to non-specifically adsorbed Con A. A significant mass loss was also attributed to binding of Con A to bare np-Au monoliths. TGA revealed a mass loss due to the binding of Con A to np-Au monoliths modified with pure αMan-C8-SH. The use of mass losses determined by TGA to compare the binding of Con A to np-Au monoliths modified by mixed SAMs of αMan-C8-SH and either octanethiol or HO-PEG2-SH revealed that binding to mixed SAM modified surfaces is specific for the mixed SAMs with HO-PEG2-SH but shows a significant contribution from non-specific adsorption for the mixed SAMs with octanethiol. Minimal adsorption of immunoglobulin G (IgG) and peanut agglutinin (PNA) towards the mannoside modified np-Au monoliths was demonstrated. A greater mass loss was found for Con A bound onto the monolith than for either IgG or PNA, signifying that the mannose presenting SAMs in np-Au retain selectivity for Con A. TGA data also provide evidence that Con A bound to the αMan-C8-SH modified np-Au can be eluted by flowing a solution of methyl α-D-mannopyranoside through the structure. The presence of Con A proteins on the modified np-Au surface was

  10. Activation processes on GaAs photocathode by different currents of oxygen source

    NASA Astrophysics Data System (ADS)

    Miao, Zhuang; Shi, Feng; Cheng, Hongchang; Wang, Shufei; Zhang, Xiaohui; Yuan, Yuan; Chen, Chang

    2015-04-01

    In order to know the influence of activation processes on GaAs photocathodes, three GaAs samples were activated by a fixed current of cesium source and different currents of oxygen source. The current of caesium source is same during activation to ensure initial adsorption of caesium quantum is similar, which is the base to show the difference during alternation activation of caesium and oxygen. Analysed with the activation data, it is indicated that Cs-to-O current ratio of 1.07 is the optimum ratio to obtain higher sensitivity and better stability. According to double dipole model, stable and uniform double dipole layers of GaAs-O-Cs:Cs-O-Cs are formed and negative electron affinity is achieved on GaAs surface by activation with cesium and oxygen. The analytical result is just coincident with the model. Thus there is an efficient technological method to improve sensitivity and stability of GaAs photocathode.

  11. Capillary liquid chromatography using a hydrophilic/cation-exchange monolithic column with a dynamically modified cationic surfactant.

    PubMed

    Lin, Jian; Lin, Jia; Lin, Xucong; Xie, Zenghong

    2009-11-06

    A novel form of reversed-phase liquid chromatography (RPLC) by the dynamically modified hydrophilic interaction monolithic column has been described in this paper. A porous poly(SPMA-co-PETA) monolith with strong cation-exchange (SCX) was prepared and the resulting monolith showed a typical hydrophilic interaction chromatography (HILIC) mechanism at higher organic solvent content (ACN%>50%). The good selectivity for neutral, basic and acidic polar analytes was observed in the HILIC mode. In order to increase the hydrophobic interaction, the monolith with SCX was dynamically modified with a long-chain quaternary ammonium salt, cetyltrimethylammonium bromide (CTAB), which was added to the mobile phase. CTAB ions were adsorbed onto the surface of the SCX monolithic material, and the resulting hydrophobic layer was used as the stationary phase. Using the dynamically modified SCX monolithic column, neutral, basic and acidic hydrophobic analytes were well separated with the RPLC mode.

  12. On the dissolution properties of GaAs in Ga

    NASA Technical Reports Server (NTRS)

    Davidson, M. C.; Moynahan, A. H.

    1977-01-01

    The dissolution of GaAs in Ga was studied to determine the nature and cause of faceting effects. Ga was allowed to dissolve single crystalline faces under isothermal conditions. Of the crystalline planes with low number indices, only the (100) surface showed a direct correlation of dissolution sites to dislocations. The type of dissolution experienced depended on temperature, and there were three distinct types of behavior.

  13. Martensite transformations in Mn2NiGa thin films grown on GaAs substrates

    NASA Astrophysics Data System (ADS)

    Schaefer, D. M.; Neckel, I. T.; Mazzaro, I.; Graff, I. L.; Varalda, J.; Schreiner, W. H.; Mosca, D. H.

    2016-11-01

    The purpose of this work is to investigate the correlation between magnetism and crystallographic structures of Mn2NiGa thin films grown by molecular beam epitaxy on GaAs(1 1 1) and GaAs(0 0 1) surfaces. The films present themselves with thermoelastic martensitic transformations upon cooling, and heating with high-temperature leads to austenite structures exhibiting a preferable (1 1 0) texture. X-ray diffraction measurements performed as a function of temperature reveal three different types of domain variants in the films within a large interval of temperatures. The austenite structures with lattice parameters ranging from 0.574 nm to 0.601 nm undergo volume conserving structural transitions to martensite with a c/a ratio of 1.2. The coexistence of variants with different domain configurations is induced on each GaAs substrate. Although the Curie temperatures (~360 K) are similar for films grown on GaAs(1 1 1) and GaAs (0 0 1) substrates, their saturation magnetizations are respectively 18 kA m-1 and 8 kA m-1 at room temperature and exhibit quite different magnetic irreversibility behaviors. Our results indicate that a multiplicity of possible equivalent variant domains on the GaAs surfaces makes it difficult to stabilize epitaxial films on these substrates.

  14. Monolithic fiber optic sensor assembly

    SciTech Connect

    Sanders, Scott

    2015-02-10

    A remote sensor element for spectrographic measurements employs a monolithic assembly of one or two fiber optics to two optical elements separated by a supporting structure to allow the flow of gases or particulates therebetween. In a preferred embodiment, the sensor element components are fused ceramic to resist high temperatures and failure from large temperature changes.

  15. Monolithic blue upconversion fiber laser

    NASA Astrophysics Data System (ADS)

    Gaebler, Volker; Eichler, Hans J.

    2002-06-01

    We report a monolithic low threshold 482nm Tm:ZBLAN upconversion fiber laser. The laser cavity consists of a directly coated single-mode fluoride fiber. The vapor deposit coatings significantly reduce the coupling losses and are suitable to be pumped by laser diodes. The laser operation and threshold characteristics have been investigated. The output stability and beam quality was tested.

  16. In situ Fabrication of Monolithic Copper Azide

    NASA Astrophysics Data System (ADS)

    Li, Bing; Li, Mingyu; Zeng, Qingxuan; Wu, Xingyu

    2016-04-01

    Fabrication and characterization of monolithic copper azide were performed. The monolithic nanoporous copper (NPC) with interconnected pores and nanoparticles was prepared by decomposition and sintering of the ultrafine copper oxalate. The preferable monolithic NPC can be obtained through decomposition and sintering at 400°C for 30 min. Then, the available monolithic NPC was in situ reacted with the gaseous HN3 for 24 h and the monolithic NPC was transformed into monolithic copper azide. Additionally, the copper particles prepared by electrodeposition were also reacted with the gaseous HN3 under uniform conditions as a comparison. The fabricated monolithic copper azide was characterized by Fourier transform infrared (FTIR), inductively coupled plasma-optical emission spectrometry (ICP-OES), and differential scanning calorimetry (DSC).

  17. Role of sidewall diffusion in GaAs nanowire growth: A first-principles study

    NASA Astrophysics Data System (ADS)

    Pankoke, Volker; Sakong, Sung; Kratzer, Peter

    2012-08-01

    The molecular processes during the growth of GaAs nanowires in molecular beam epitaxy (MBE) are studied from first principles. For the wurtzite crystal structure of GaAs, which is formed exclusively in nanowire growth, potential energy surfaces for sidewall diffusion of Ga, As, and GaAs surface species are calculated using density functional theory. We compare materials transport on type-I and -II nanowires (with {101¯0} and {112¯0} facets of wurtzite GaAs, respectively) and discuss its role for materials supply to the growth zone at the nanowire tip. On the sidewalls of type-II nanowires, the diffusion barrier for Ga along the growth direction is particularly low, only 0.30 eV compared to 0.60 eV on type-I nanowires. For As adatoms, the corresponding diffusion barriers are 0.64 eV and 1.20 eV, respectively, and hence higher than for Ga adatoms. The GaAs molecule formed by the chemical surface reaction of Ga and As finds very stable binding sites on type-II sidewalls where it inserts itself into a chemical bond between surface atoms, triggering radial growth. In contrast, on type-I nanowires the GaAs molecule adsorbed with the As end towards the surface has a low diffusion barrier of 0.50 eV. Together with our previous finding that the gold particle at the nanowire tip is efficient in promoting dissociative adsorption of As2 molecules, we conclude that the influx of Ga adatoms from sidewall diffusion is very important to maintain stoichiometric growth of GaAs nanowires, in particular when a large V-III ratio is used in MBE.

  18. Mixed-mode reversed-phase and ion-exchange monolithic columns for micro-HPLC.

    PubMed

    Jiang, Zhengjin; Smith, Norman W; Ferguson, Paul D; Taylor, Mark R

    2008-08-01

    This paper describes the fabrication of RP/ion-exchange mixed-mode monolithic materials for capillary LC. Following deactivation of the capillary surface with 3-(trimethoxysilyl)propyl methacrylate (gamma-MAPS), monoliths were formed by copolymerisation of pentaerythritol diacrylate monostearate (PEDAS), 2-sulphoethyl methacrylate (SEMA) with/without ethylene glycol dimethacrylate (EDMA) within 100 microm id capillaries. In order to investigate the porous properties of the monoliths prepared in our laboratory, mercury intrusion porosimetry, SEM and micro-HPLC were used to measure the monolithic structures. The monolithic columns prepared without EDMA showed bad mechanical stability at high pressure, which is undesirable for micro-HPLC applications. However, it was observed that the small amount (5% w/w) of EDMA clearly improved the mechanical stability of the monoliths. In order to evaluate their application for micro-HPLC, a range of neutral, acidic and basic compounds was separated with these capillaries and satisfactory separations were obtained. In order to further investigate the separation mechanism of these monolithic columns, comparative studies were carried out on the poly(PEDAS-co-SEMA) monolithic column and two other monoliths, poly(PEDAS) and poly(PEDAS-co-2-(methacryloyloxy)ethyl-trimethylammonium methylsulphate (METAM)). As expected, different selectivities were observed for the separation of basic compounds on all three monolithic columns using the same separation conditions. The mobile phase pH also showed clear influence on the retention time of basic compounds. This could be explained by ion-exchange interaction between positively charged analytes and the negatively charged sulphate group.

  19. Monolithic Hydrogen Peroxide Catalyst Bed Development

    NASA Technical Reports Server (NTRS)

    Ponzo, J. B.

    2003-01-01

    With recent increased industry and government interest in rocket grade hydrogen peroxide as a viable propellant, significant effort has been expended to improve on earlier developments. This effort has been predominately centered in improving heterogeneous. typically catalyst beds; and homogeneous catalysts, which are typically solutions of catalytic substances. Heterogeneous catalyst beds have traditionally consisted of compressed wire screens plated with a catalytic substance, usually silver, and were used m many RCS applications (X-1, Mercury, and Centaur for example). Aerojet has devised a heterogeneous catalyst design that is monolithic (single piece), extremely compact, and has pressure drops equal to or less than traditional screen beds. The design consists of a bonded stack of very thin, photoetched metal plates, silver coated. This design leads to a high surface area per unit volume and precise flow area, resulting in high, stable, and repeatable performance. Very high throughputs have been demonstrated with 90% hydrogen peroxide. (0.60 lbm/s/sq in at 1775-175 psia) with no flooding of the catalyst bed. Bed life of over 900 seconds has also been demonstrated at throughputs of 0.60 lbm/s/sq in across varying chamber pressures. The monolithic design also exhibits good starting performance, short break-in periods, and will easily scale to various sizes.

  20. Catastrophic failure of a monolithic zirconia prosthesis.

    PubMed

    Chang, Jae-Seung; Ji, Woon; Choi, Chang-Hoon; Kim, Sunjai

    2015-02-01

    Recently, monolithic zirconia restorations have received attention as an alternative to zirconia veneered with feldspathic porcelain to eliminate chipping failures of veneer ceramics. In this clinical report, a patient with mandibular edentulism received 4 dental implants in the interforaminal area, and a screw-retained monolithic zirconia prosthesis was fabricated. The patient also received a maxillary complete removable dental prosthesis over 4 anterior roots. At the 18-month follow-up, all of the zirconia cylinders were seen to be fractured, and the contacting abutment surfaces had lost structural integrity. The damaged abutments were replaced with new abutments, and a new prosthesis was delivered with a computer-assisted design and computer-assisted manufacturing fabricated titanium framework with denture teeth and denture base resins. At the 6-month recall, the patient did not have any problems. Dental zirconia has excellent physical properties; however, care should be taken to prevent excessive stresses on the zirconia cylinders when a screw-retained zirconia restoration is planned as a definitive prosthesis.

  1. Zeolitic imidazolate framework-methacrylate composite monolith characterization by inverse gas chromatography.

    PubMed

    Yusuf, Kareem; Badjah-Hadj-Ahmed, Ahmed Yacine; Aqel, Ahmad; Aouak, Taieb; ALOthman, Zeid Abdullah

    2016-04-22

    Thermodynamic characterization of butyl methacrylate-co-ethylene dimethacrylate neat monolith and zeolitic imidazolate framework-8 incorporated with butyl methacrylate-co-ethylene dimethacrylate composite monolith were studied using inverse gas chromatography at infinite dilution under 1MPa column pressure and various column temperatures. The free energy of adsorption (ΔGA), enthalpy of adsorption (ΔHA) and entropy of adsorption (ΔSA) were determined using a series of n-alkanes. The dispersive component of surface energy (γS(D)) was estimated by Dorris-Gray and Schultz et al. The composite monolith showed a more energetic surface than the neat monolith. The acidic, KA, and basic, KD, parameters for both materials were estimated using a group of polar probes. A basic character was concluded with more basic behavior for the neat monolith. Flory-Huggins parameter, χ, was taken as a measure of miscibility between the probes with the low molecular weight and the high molecular weight monolith. Inverse gas chromatography provides a better understanding of the role of incorporated zeolitic imidazolate framework (ZIF-8) into the polymer matrix in its monolithic form. Copyright © 2016 Elsevier B.V. All rights reserved.

  2. Facile preparation of silver nanoparticles homogeneously immobilized in hierarchically monolithic silica using ethylene glycol as reductant.

    PubMed

    Yu, Huan; Zhu, Yang; Yang, Hui; Nakanishi, Kazuki; Kanamori, Kazuyoshi; Guo, Xingzhong

    2014-09-07

    A facile and "green" method was proposed to introduce Ag nanoparticles (Ag NPs) into the hierarchically monolithic silica uniformly in the presence of (3-aminopropyl)-triethoxysilane (APTES) and ethylene glycol. APTES is used to modify the monolith by incorporating amino groups onto the surface of meso-macroporous skeletons, while ethylene glycol is employed as the productive reductant. Ag NPs are homogeneously immobilized in hierarchically monolithic silica after reduction and drying at 40 °C for different duration times, and the embedded amount of Ag NPs can reach 15.44 wt% when treated once. The embedment of Ag NPs increases with the repeat treatment and the APTES amount, without uncontrollable crystalline growth. The surface areas of Ag NPs embedded in silica monoliths after heat treatment at 300 and 400 °C are higher than those before heat treatment. The modification via APTES and the embedment of Ag NPs does not spoil the morphology of monolithic silica, while changing the pore structures of the monolith. A tentative formation process and a reduction mechanism are proposed for the modification, reduction and embedment. Ag NPs embedded in monolithic silica is promising for wide applications such as catalysis and separation.

  3. Development of GaAs/Si and GaAs/Si monolithic structures for future space solar cells

    NASA Technical Reports Server (NTRS)

    Spitzer, M. B.; Vernon, S. M.; Wolfson, R. G.; Tobin, S. P.

    1984-01-01

    The results of heteroepitaxial growth of GaAs and GaAlAs directly on Si are presented, and applications to new cell structures are suggested. The novel feature is the elimination of a Ge lattice transition region. This feature not only reduces the cost of substrate preparation, but also makes possible the fabrication of high efficiency monolithic cascade structures. All films to be discussed were grown by organometallic chemical vapor deposition at atmospheric pressure. This process yielded reproducible, large-area films of GaAs, grown directly on Si, that are tightly adherent and smooth, and are characterized by a defect density of 5 x 10(6) power/sq cm. Preliminary studies indicate that GaAlAs can also be grown in this way. A number of promising applications are suggested. Certainly these substrates are ideal for low-weight GaAs space solar ells. For very high efficiency, the absence of Ge makes the technology attractive for GaAlAs/Si monolithic cascades, in which the Si substrates would first be provided with a suitable p/n junction. An evaluation of a three bandgap cascade consisting of appropriately designed GaAlAs/GaAs/Si layers is also presented.

  4. GaAs MMIC phase shifters

    NASA Astrophysics Data System (ADS)

    Lane, A. A.; Myers, F. A.

    This paper describes the design and performance of various GaAs MMIC phase shifters specifically designed for electronically scanned antennas. Phase shifting is achieved by using GaAs FETs to switch various circuits to realize the required functions. Some preliminary results on novel components and high packing density techniques leading to truly effective multifunction circuits are described.

  5. An ultra-sensitive microfluidic immunoassay using living radical polymerization and porous polymer monoliths.

    SciTech Connect

    Abhyankar, Vinay V.; Singh, Anup K.; Hatch, Anson V.

    2010-07-01

    We present a platform that combines patterned photopolymerized polymer monoliths with living radical polymerization (LRP) to develop a low cost microfluidic based immunoassay capable of sensitive (low to sub pM) and rapid (<30 minute) detection of protein in 100 {micro}L sample. The introduction of LRP functionality to the porous monolith allows one step grafting of functionalized affinity probes from the monolith surface while the composition of the hydrophilic graft chain reduces non-specific interactions and helps to significantly improve the limit of detection.

  6. GaAs solar cell development

    NASA Technical Reports Server (NTRS)

    Knechtli, R. C.; Kamath, S.; Loo, R.

    1977-01-01

    The motivation for developing GaAs solar cells is based on their superior efficiency when compared to silicon cells, their lower degradation with increasing temperature, and the expectation for better resistance to space radiation damage. The AMO efficiency of GaAs solar cells was calculated. A key consideration in the HRL technology is the production of GaAs cells of large area (greater than 4 sg cm) at a reasonable cost without sacrificing efficiency. An essential requirement for the successful fabrication of such cells is the ability to grow epitaxially a uniform layer of high quality GaAs (buffer layer) on state-of-the-art GaAs substrates, and to grow on this buffer layer the required than layer of (AlGa)As. A modified infinite melt liquid phase epitaxy (LPE) growth technique is detailed.

  7. Comparative research on activation technique for GaAs photocathodes

    NASA Astrophysics Data System (ADS)

    Chen, Liang; Qian, Yunsheng; Chang, Benkang; Chen, Xinlong; Yang, Rui

    2012-03-01

    The properties of GaAs photocathodes mainly depend on the material design and activation technique. In early researches, high-low temperature two-step activation has been proved to get more quantum efficiency than high-temperature single-step activation. But the variations of surface barriers for two activation techniques have not been well studied, thus the best activation temperature, best Cs-O ratio and best activation time for two-step activation technique have not been well found. Because the surface photovoltage spectroscopy (SPS) before activation is only in connection with the body parameters for GaAs photocathode such as electron diffusion length and the spectral response current (SRC) after activation is in connection with not only body parameters but also surface barriers, thus the surface escape probability (SEP) can be well fitted through the comparative research between SPS before activation and SEP after activation. Through deduction for the tunneling process of surface barriers by Schrödinger equation, the width and height for surface barrier I and II can be well fitted through the curves of SEP. The fitting results were well proved and analyzed by quantitative analysis of angle-dependent X-ray photoelectron spectroscopy (ADXPS) which can also study the surface chemical compositions, atomic concentration percentage and layer thickness for GaAs photocathodes. This comparative research method for fitting parameters of surface barriers through SPS before activation and SRC after activation shows a better real-time in system method for the researches of activation techniques.

  8. Testing a GaAs cathode in SRF gun

    SciTech Connect

    Wang, E.; Kewisch, J.; Ben-Zvi, I.; Burrill, A.; Rao, T.; Wu, Q.; Holmes, D.

    2011-03-28

    RF electron guns with a strained superlattice GaAs cathode are expected to generate polarized electron beams of higher brightness and lower emittance than do DC guns, due to their higher field gradient at the cathode's surface and lower cathode temperature. We plan to install a bulk GaAs:Cs in a SRF gun to evaluate the performance of both the gun and the cathode in this environment. The status of this project is: In our 1.3 GHz 1/2 cell SRF gun, the vacuum can be maintained at nearly 10{sup -12} Torr because of cryo-pumping at 2K. With conventional activation of bulk GaAs, we obtained a QE of 10% at 532 nm, with lifetime of more than 3 days in the preparation chamber and have shown that it can survive in transport from the preparation chamber to the gun. The beam line has been assembled and we are exploring the best conditions for baking the cathode under vacuum. We report here the progress of our test of the GaAs cathode in the SRF gun. Future particle accelerators, such as eRHIC and the ILC require high-brightness, high-current polarized electrons. Strained superlattice GaAs:Cs has been shown to be an efficient cathode for producing polarized electrons. Activation of GaAs with Cs,O(F) lowers the electron affinity and makes it energetically possible for all the electrons, excited into the conduction band that drift or diffuse to the emission surface, to escape into the vacuum. Presently, all operating polarized electron sources, such as the CEBAF, are DC guns. In these devices, the excellent ultra-high vacuum extends the lifetime of the cathode. However, the low field gradient on the photocathode's emission surface of the DC guns limits the beam quality. The higher accelerating gradients, possible in the RF guns, generate a far better beam. Until recently, most RF guns operated at room temperature, limiting the vacuum to {approx}10{sup -9} Torr. This destroys the GaAs's NEA surface. The SRF guns combine the excellent vacuum conditions of DC guns and the high

  9. GaAs solar cells

    NASA Technical Reports Server (NTRS)

    Conway, E. J.

    1982-01-01

    The major thrusts proposed for GaAs were increased efficiency and improved radiation damage data. Current laboratory production cells consistently achieve 16 percent AMO one-Sun efficiency. The user community wants 18-percent efficient cells as soon as possible, and such a goal is though to be achievable in 2 years with sufficient research funds. A 20-percent research cell is considered the efficiency limit with current technology, and such a cell seems realizable in approximately 4 years. Future efficiency improvements await improved substrates and materials. For still higher efficiencies, concentrator cells and multijunction cells are proposed as near-term directions.

  10. One-pot preparation of a molecularly imprinted hybrid monolithic capillary column for selective recognition and capture of lysozyme.

    PubMed

    Lin, Zian; Lin, Yao; Sun, Xiaobo; Yang, Huanghao; Zhang, Lan; Chen, Guonan

    2013-04-05

    A molecularly imprinted inorganic-organic hybrid monolithic capillary column (MIP hybrid monolith) was synthesized by one-pot process and its application in selective recognition and capture of lysozyme (Lyz) from complex biological samples was described for the first time. Due to a combination of rigid silica matrices and flexible organic hydrogels in one-pot process, stable and accessible recognition sites in the as-prepared MIP hybrid monolith could be obtained after the removal of template protein, which facilitated the rebinding of template and provided good reproducibility and lifetime of use. The morphology, permeability, and pore properties of the as-prepared MIP hybrid monolith were characterized and a uniform monolithic matrix with high surface area and large through-pores was observed. The recognition behavior of MIP and non-imprinted (NIP) hybrid monolith was evaluated by separating template protein from unfractionated protein mixture and the result indicated that the MIP hybrid monolith has much higher affinity toward the template protein than NIP hybrid monolith. High imprinted factor (IF) and separation efficiency could be obtained. In addition, the practicality of the Lyz-MIP hybrid monolith was further evaluated by selective separation of Lyz from egg white and capture of Lyz from human serum by adopting it as an in-tube solid phase microextraction (in-tube SPME), and the good results demonstrated its potential in proteome analysis.

  11. Green synthesis of mesoporous molecular sieve incorporated monoliths using room temperature ionic liquid and deep eutectic solvents.

    PubMed

    Zhang, Li-Shun; Zhao, Qing-Li; Li, Xin-Xin; Li, Xi-Xi; Huang, Yan-Ping; Liu, Zhao-Sheng

    2016-12-01

    A hybrid monolith incorporated with mesoporous molecular sieve MCM-41 of uniform pore structure and high surface area was prepared with binary green porogens in the first time. With a mixture of room temperature ionic liquids and deep eutectic solvents as porogens, MCM-41 was modified with 3-(trimethoxysilyl) propyl methacrylate (γ-MPS) and the resulting MCM-41-MPS was incorporated into poly (BMA-co-EDMA) monoliths covalently. Because of good dispersibility of MCM-41-MPS in the green solvent-based polymerization system, high permeability and homogeneity for the resultant hybrid monolithic columns was achieved. The MCM-41-MPS grafted monolith was characterized by scanning electron microscopy, energy dispersive spectrometer area scanning, transmission electron microscopy, FT-IR spectra and nitrogen adsorption tests. Chromatographic performance of MCM-41-MPS grafted monolith was characterized by separating small molecules in capillary electrochromatography, including phenol series, naphthyl substitutes, aniline series and alkyl benzenes. The maximum column efficiency of MCM-41-MPS grafted monolith reached 209,000 plates/m, which was twice higher than the corresponding MCM-41-MPS free monolith. Moreover, successful separation of non-steroidal anti-inflammatory drugs and polycyclic aromatic hydrocarbons demonstrated the capacity in broad-spectrum application of the MCM-41-MPS incorporated monolith. The results indicated that green synthesis using room temperature ionic liquid and deep eutectic solvents is an effective method to prepare molecular sieve-incorporated monolithic column. Copyright © 2016 Elsevier B.V. All rights reserved.

  12. Preparation of phenylboronate affinity rigid monolith with macromolecular porogen.

    PubMed

    Li, Xiang-Jie; Jia, Man; Zhao, Yong-Xin; Liu, Zhao-Sheng; Akber Aisa, Haji

    2016-03-18

    Boronate-affinity monolithic column was first prepared via polystyrene (PS) as porogen in this work. The monolithic polymer was synthetized using 4-vinylphenylboronic acid (4-VPBA) as functional monomer, ethylene glycol dimethacrylate (EDMA) as crosslinker monomer, and a mixture of PS solution in tetrahydrofuran, the linear macromolecular porogen, and toluene as porogen. Isoquercitrin (ISO) and hyperoside (HYP), isomer diol flavonoid glycosides, can be baseline separated on the poly(VPBA-co-EDMA) monolith. The effect of polymerization variables on the selectivity factor, e.g., the ratio of monomer to crosslinker (M/C), the amount of PS and the molecular weight of macromolecular porogen was investigated. The surface properties of the monolithic polymer were characterized by scanning electron microscopy and nitrogen adsorption. The best polymerization condition was the M/C ratio of 7:3, and the PS concentration of 40 mg/ml. The poly(VPBA-co-EDMA) polymer was also applied to extract cis-diol flavonoid glycosides from the crude extraction of cotton flower. After treated by poly(VPBA-co-EDMA) for solid phase extraction, high purity ISO and HYP (>99.96%) can be obtained with recovery of 83.7% and 78.6%, respectively.

  13. Translucency of monolithic and core zirconia after hydrothermal aging

    PubMed Central

    Fathy, Salma M.; El-Fallal, Abeer A.; El-Negoly, Salwa A.; El Bedawy, Abu Baker

    2015-01-01

    Abstract Objective: To evaluate the hydrothermal aging effect on the translucency of partially stabilized tetragonal zirconia with yttria (Y-TZP) used as monolithic or fully milled zirconia and of core type. Methods: Twenty disc-shaped specimens (1 and 10 mm) for each type of monolithic and core Y-TZP materials were milled and sintered according to the manufacturer’s instruction. The final specimens were divided into two groups according to the type of Y-TZP used. Translucency parameter (TP) was measured over white and black backgrounds with the diffuse reflectance method; X-ray diffraction (XRD) and scanning electron microscope (SEM) were used to analyze the microstructure of both Y-TZP types before and after aging. Data for TP values was statistically analyzed using Student’s t-test. Results: Monolithic Y-TZP showed the highest TP mean value (16.4 ± 0.316) before aging while core Y-TZP showed the lowest TP mean value (7.05 ± 0.261) after aging. There was a significant difference between the two Y-TZP types before and after hydrothermal aging. XRD analysis showed increases in monoclinic content in both Y-TZP surfaces after aging. Conclusion: Monolithic Y-TZP has a higher chance to low-temperature degradation than core type, which may significantly affect the esthetic appearance and translucency hence durability of translucent Y-TZP. PMID:27335897

  14. Effects of Photowashing Treatment on Gate Leakage Current of GaAs Metal-Semiconductor Field-Effect Transistors

    NASA Astrophysics Data System (ADS)

    Choi, Kyoung Jin; Moon, Jae Kyoung; Park, Min; Kim, Haechon; Lee, Jong-Lam

    2002-05-01

    Effects of photowashing treatment on gate leakage current (IGD) of a GaAs metal-semiconductor field-effect transistor were studied by observing changes in atomic composition and band bending at the surface of GaAs through X-ray photoemission spectroscopy. The photowashing treatment produces Ga2O3 on the surface of GaAs, leaving acceptor-type Ga antisites behind under the oxide. The Ga antisites played a role in reducing the maximum electric field at the drain edge of the gate, leading to the decrease of IGD. The longer photowashing time produced thicker oxide on the surface of GaAs, acting as a conducting pass for electrons, leading to the increase of IGD.

  15. Hydrophilic diol monolith for the preparation of immuno-sorbents at reduced nonspecific interactions.

    PubMed

    Gunasena, Dilani N; El Rassi, Ziad

    2011-08-01

    A polar organic polymer monolith (M1) was introduced for performing immunoaffinity chromatography (IAC) at reduced nonspecific interactions. The M1 monolith was prepared by the in situ polymerization of glyceryl methacrylate (GMM) and pentaerythritol triacrylate (PETA). Through its surface diol groups, M1 provided the functionalities to immobilize antibodies. Anti-haptoglobin antibody was used as the model antibody to study the overall behavior of the immuno monolith M1 in terms of its binding to the antigen and to evaluate its nonspecific binding with other proteins, especially the high-abundance human serum proteins. To better assess the suitability of M1 for IAC, other immuno monoliths were prepared and compared with the immuno monolith M1. Two monoliths were of the traditional ones: copolymers of (i) glycidyl methacrylate and ethylene glycol dimethacrylate (EDMA) and (ii) GMM and EDMA, referred to as M2 and M3, respectively. A fourth monolith involving the copolymerization of N-(3-aminopropyl)methacrylamide hydrochloride and EDMA (M4) was introduced to allow the site-directed immobilization of antibodies. Owing to its hydroxyl groups, the M1 exhibited negligible nonspecific hydrophobic interactions with proteins. On the other hand, M4 exhibited extensive electrostatic interactions, while the M2 and to a lesser extent M3 exhibited hydrophobic interactions.

  16. Monolith froth reactor: Development of a novel three-phase catalytic system

    SciTech Connect

    Crynes, L.L.; Cerro, R.L.; Abraham, M.A. . Dept. of Chemical Engineering)

    1995-02-01

    The monolith froth reactor, involving two-phase flow and a monolith catalyst, is developed. The flow within monolith channels, consisting of trains of gas bubbles and liquid slugs, is produced by forming a two-phase froth in a chamber immediately below the bottom of the monolith. The froth then flows upward into the monolith channels through pressure forces, which differs from previous methods since it may be carried out for a commercial-scale reactor. Because the liquid film which develops between the gas phase and the surface of the catalyst is extremely thin, two-phase flow within a monolith can provide reaction rates which are near their intrinsic values. Catalytic oxidation of aqueous phenol over copper oxide supported on [gamma]-Al[sub 2]O[sub 3] is used as a model reaction for investigating reactor performance. Generation of a froth is confirmed by visual inspection; the average bubble size is approximately that predicted by a force balance. The effect of externally controllable process variables (liquid and gas flow rates, temperature, and pressure) on the rate of phenol oxidation was investigated. Reaction rate increases with temperature or pressure increase and decreases with gas flow rate increase, achieving a maximum with respect to liquid flow rate. The activation energy calculated from the apparent reaction rate measured in the monolith froth reactor is similar to that of intrinsic value, suggesting minimal mass-transfer limitations.

  17. Clickable Periodic Mesoporous Organosilica Monolith for Highly Efficient Capillary Chromatographic Separation.

    PubMed

    Wu, Ci; Liang, Yu; Yang, Kaiguang; Min, Yi; Liang, Zhen; Zhang, Lihua; Zhang, Yukui

    2016-02-02

    A novel clickable periodic mesoporous organosilica monolith with the surface area up to 1707 m(2) g(-1) was in situ synthesized in the capillary by the one-step condensation of the organobridged-bonded alkoxysilane precursor bis(triethoxysilyl)ethylene. With Si-C bonds in the skeleton, the monolith possesses excellent chemical and mechanical stability. With vinyl groups highly loaded and homogeneously distributed throughout the structure, the monolith can be readily functionalized with functional groups by effective thiol-ene "click" chemistry reaction. Herein, with "click" modification of C18, the obtained monolith was successfully applied for capillary liquid chromatographic separation of small molecules and proteins. The column efficiency could reach 148,000 N/m, higher than most reported hybrid monoliths. Moreover, intact proteins could be separated well with good reproducibility, even after the monolithic column was exposed by basic mobile phase (pH 10.0) overnight, demonstrating the great promising of such monolith for capillary chromatographic separation.

  18. Hydrophobic polymer monoliths as novel phase separators: application in continuous liquid-liquid extraction systems.

    PubMed

    Peroni, Daniela; Vanhoutte, Dominique; Vilaplana, Francisco; Schoenmakers, Peter; de Koning, Sjaak; Janssen, Hans-Gerd

    2012-03-30

    Hydrophobic macroporous polymer monoliths are shown to be interesting materials for the construction of "selective solvent gates". With the appropriate surface chemistry and porous properties the monoliths can be made permeable only for apolar organic solvents and not for water. Different poly(butyl methacrylate-co-ethylene dimethacrylate) (BMA-EDMA) and poly(styrene-co-divinylbenzene) (PS-DVB) monoliths prepared with tailored chemistries and porosities were evaluated for this purpose. After extensive characterization, the PS-DVB monoliths were selected due to their higher hydrophobicity and their more suitable flow characteristics. BMA-EDMA monoliths are preferred for mid-polarity solvents such as ethyl acetate, for which they provide efficient separation from water. Breakthrough experiments confirmed that the pressures necessary to generate flow of organic solvents through PS-DVB monoliths were substantially lower than for water. A phase separator was constructed using the monoliths as the flow selector. This device was successfully coupled on-line with a chip-based continuous liquid-liquid-extraction (LLE) system with segmented flow. Efficient separation of different solvents was obtained across a wide range of flow rates (0.5-4.0 mL min(-1)) and aqueous-to-organic flow ratios (β=1-10). Good robustness and long life-time were also confirmed. The suitability of the device to perform simple, cheap, and reliable phase separation in a continuous LLE system prior to gas-chromatographic analysis was proven for some selected real-life applications.

  19. Polyvinyl alcohol-based hydrophilic monoliths from water-in-oil high internal phase emulsion template.

    PubMed

    Meng, Xiao; Zeng, Ni; Zhang, Jin; Jiang, Long; Dan, Yi

    2017-07-01

    Herein, we report a new approach to fabricate polyvinyl alcohol (PVA) based hydrophilic monoliths by alcoholysis of porous emulsion-templated polyvinyl acetate (PVAc). The precursory PVAc-based monolith is obtained by polymerization of a W/O high internal phase emulsion (HIPE) containing vinyl acetate as the external phase while water as the internal phase. As an alcoholysis-stable tri-functional commonomer, triallyl isocyanurate is chosen as the crosslinking agent to prevent possible collapse of the polymeric skeleton and the consequent losses in mechanical properties during the alcoholysis step. By alcoholysis of the resulting PVAc-based monolith, the PVA-based monoliths are successful prepared as confirmed by FTIR analysis. BET analysis and SEM observation confirm the formation of open-cell and highly interconnected porous structures of PVA-based monoliths with surface areas of around 16m(2)/g. Stemming from the intrinsic hydrophilicity of hydroxyl and morphology, PVA-based monoliths exhibit great enhancement in hydrophilicity with a much lower water contact angles than that of PVAc-based monoliths. Copyright © 2017 Elsevier Inc. All rights reserved.

  20. Monolithic pattern-sensitive detector

    DOEpatents

    Berger, Kurt W.

    2000-01-01

    Extreme ultraviolet light (EUV) is detected using a precisely defined reference pattern formed over a shallow junction photodiode. The reference pattern is formed in an EUV absorber preferably comprising nickel or other material having EUV- and other spectral region attenuating characteristics. An EUV-transmissive energy filter is disposed between a passivation oxide layer of the photodiode and the EUV transmissive energy filter. The device is monolithically formed to provide robustness and compactness.

  1. Monolithic Fuel Fabrication Process Development

    SciTech Connect

    C. R. Clark; N. P. Hallinan; J. F. Jue; D. D. Keiser; J. M. Wight

    2006-05-01

    The pursuit of a high uranium density research reactor fuel plate has led to monolithic fuel, which possesses the greatest possible uranium density in the fuel region. Process developments in fabrication development include friction stir welding tool geometry and cooling improvements and a reduction in the length of time required to complete the transient liquid phase bonding process. Annealing effects on the microstructures of the U-10Mo foil and friction stir welded aluminum 6061 cladding are also examined.

  2. Effects of ultrathin oxides in conducting MIS structures on GaAs

    NASA Technical Reports Server (NTRS)

    Childs, R. B.; Ruths, J. M.; Sullivan, T. E.; Fonash, S. J.

    1978-01-01

    Schottky barrier-type GaAs baseline devices (semiconductor surface etched and then immediately metalized) and GaAs conducting metal oxide-semiconductor devices are fabricated and characterized. The baseline surfaces (no purposeful oxide) are prepared by a basic or an acidic etch, while the surface for the MIS devices are prepared by oxidizing after the etch step. The metallizations used are thin-film Au, Ag, Pd, and Al. It is shown that the introduction of purposeful oxide into these Schottky barrier-type structures examined on n-type GaAs modifies the barrier formation, and that thin interfacial layers can modify barrier formation through trapping and perhaps chemical reactions. For Au- and Pd-devices, enhanced photovoltaic performance of the MIS configuration is due to increased barrier height.

  3. Thermodynamic and kinetic roughening: Monte Carlo simulation and experiment on GaAs

    NASA Astrophysics Data System (ADS)

    Kazantsev, D. M.; Akhundov, I. O.; Kozhukhov, A. S.; Alperovich, V. L.

    2017-03-01

    GaAs thermal smoothing at temperatures T ≤ 650°C in the conditions close to equilibrium yields surfaces with atomically smooth terraces separated by steps of monatomic height. At higher temperatures T ≥ 700°C, surface smoothing is changed to roughening. In the present paper, possible reasons of surface roughening at elevated temperatures are studied by means of Monte Carlo simulation and compared with the experimental results on GaAs. It is proved that the thermodynamic roughening transition, which consists in spontaneous generation of atomic steps due to decrease in the step line tension down to zero, cannot explain the experiment because it should occur at temperatures T ∼ 1800 - 2000°C, i.e. much higher than in the experiment. Kinetic instabilities caused by deviations from equilibrium towards growth or sublimation are shown to cause GaAs roughening at elevated temperatures. The microscopic mechanisms of kinetic-driven roughening are discussed.

  4. Transparent monolithic metal ion containing nanophase aerogels

    SciTech Connect

    Risen, W. M., Jr.; Hu, X.; Ji, S.; Littrell, K.

    1999-12-01

    The formation of monolithic and transparent transition metal containing aerogels has been achieved through cooperative interactions of high molecular weight functionalized carbohydrates and silica precursors, which strongly influence the kinetics of gelation. After initial gelation, subsequent modification of the ligating character of the system, coordination of the group VIII metal ions, and supercritical extraction afford the aerogels. The structures at the nanophase level have been probed by photon and electron transmission and neutron scattering techniques to help elucidate the basis for structural integrity together with the small entity sizes that permit transparency in the visible range. They also help with understanding the chemical reactivities of the metal-containing sites in these very high surface area materials. These results are discussed in connection with new reaction studies.

  5. Graphene-supported metal oxide monolith

    DOEpatents

    Worsley, Marcus A.; Baumann, Theodore F.; Biener, Juergen; Biener, Monika A.; Wang, Yinmin; Ye, Jianchao; Tylski, Elijah

    2017-01-10

    A composition comprising at least one graphene-supported metal oxide monolith, said monolith comprising a three-dimensional structure of graphene sheets crosslinked by covalent carbon bonds, wherein the graphene sheets are coated by at least one metal oxide such as iron oxide or titanium oxide. Also provided is an electrode comprising the aforementioned graphene-supported metal oxide monolith, wherein the electrode can be substantially free of any carbon-black and substantially free of any binder.

  6. Fracture Strength of Aged Monolithic and Bilayer Zirconia-Based Crowns.

    PubMed

    Lameira, Deborah Pacheco; Buarque e Silva, Wilkens Aurélio; Andrade e Silva, Frederico; De Souza, Grace M

    2015-01-01

    The purpose of this study was to evaluate the effect of design and surface finishing on fracture strength of yttria-tetragonal zirconia polycrystal (Y-TZP) crowns in monolithic (1.5 mm thickness) and bilayer (0.8 mm zirconia coping and 0.7 mm porcelain veneer) configuration after artificial aging. Bovine incisors received crown preparation and Y-TZP crowns were manufactured using CAD/CAM technique, according to the following groups (n = 10): Polished monolithic zirconia crowns (PM); Glazed monolithic zirconia crowns (GM); Bi-layer crowns (BL). Crowns were cemented with resin cement, submitted to artificial aging in a chewing simulator (2.5 million cycles/80 N/artificial saliva/37 °C), and tested for fracture strength. Two remaining crowns referring to PM and GM groups were submitted to a chemical composition analysis to measure the level of yttrium after aging. One-way ANOVA and Tukey's test (P = .05) indicated that monolithic zirconia crowns presented similar fracture strength (PM = 3476.2 N ± 791.7; GM = 3561.5 N ± 991.6), which was higher than bilayer crowns (2060.4 N ± 810.6). There was no difference in the yttrium content among the three surfaces evaluated in the monolithic crowns. Thus, monolithic zirconia crowns present higher fracture strength than bilayer veneered zirconia after artificial aging and surface finishing does not affect their fracture strength.

  7. Dopant mapping of Be δ-doped layers in GaAs tailored by counterdoping using scanning tunneling microscopy

    NASA Astrophysics Data System (ADS)

    Ebert, Ph.; Landrock, S.; Chiu, Y. P.; Breuer, U.; Dunin-Borkowski, R. E.

    2012-11-01

    The effect of counterdoping on the Be dopant distribution in delta (δ)-doped layers embedded in Si-doped and intrinsic GaAs is investigated by cross-sectional scanning tunneling microscopy. δ-doped layers in intrinsic GaAs exhibit a large spreading, whereas those surrounded by Si-doped GaAs remain spatially localized. The different spreading is explained by the Fermi-level pinning at the growth surface, which leads to an increased Ga vacancies concentration with increasing Si counterdoping. The Ga vacancies act as sinks for the diffusing Be dopant atoms, hence retarding the spreading.

  8. Modified energetics and growth kinetics on H-terminated GaAs (110)

    SciTech Connect

    Galiana, B.; Benedicto, M.; Díez-Merino, L.; Tejedor, P.; Lorbek, S.; Hlawacek, G.; Teichert, C.

    2013-10-28

    Atomic hydrogen modification of the surface energy of GaAs (110) epilayers, grown at high temperatures from molecular beams of Ga and As{sub 4}, has been investigated by friction force microscopy (FFM). The reduction of the friction force observed with longer exposures to the H beam has been correlated with the lowering of the surface energy originated by the progressive de-relaxation of the GaAs (110) surface occurring upon H chemisorption. Our results indicate that the H-terminated GaAs (110) epilayers are more stable than the As-stabilized ones, with the minimum surface energy value of 31 meV/Å{sup 2} measured for the fully hydrogenated surface. A significant reduction of the Ga diffusion length on the H-terminated surface irrespective of H coverage has been calculated from the FFM data, consistent with the layer-by-layer growth mode and the greater As incorporation coefficient determined from real-time reflection high-energy electron diffraction studies. Arsenic incorporation through direct dissociative chemisorption of single As{sub 4} molecules mediated by H on the GaAs (110) surface has been proposed as the most likely explanation for the changes in surface kinetics observed.

  9. Synthesis of high porosity, monolithic alumina aerogels

    SciTech Connect

    Poco, J F; Satcher, J H; Hrubesh, L W

    2000-09-20

    Many non-silica aerogels are notably weak and fragile in monolithic form. Particularly, few monolithic aerogels with densities less than 50kg/m3 have any significant strength. It is especially difficult to prepare uncracked monoliths of pure alumina aerogels that are robust and moisture stable. In this paper, we discuss the synthesis of strong, stable, monolithic, high porosity (>98% porous) alumina aerogels, using a two-step sol-gel process. The alumina aerogels have a polycrystalline morphology that results in enhanced physical properties. Most of the measured physical properties of the alumina aerogels are superior to those for silica aerogels for equivalent densities.

  10. Coupling reactions of trifluoroethyl iodide on GaAs(100)

    NASA Astrophysics Data System (ADS)

    Singh, N. K.; Kemp, N. T.; Paris, N.; Balan, V.

    2004-07-01

    We report on the reactions of 2-iodo-1,1,1-trifluoroethane (CF3CH2I) on gallium-rich GaAs(100)-(4×1), studied using the techniques of temperature programmed desorption and x-ray photoelectron spectroscopy. The study is to provide evidence for the formation of a higher fluorinated alkene, 1,1,4,4,4-pentafluoro-1-butene (CF2=CHCH2CF3) and alkane, 1,1,1,4,4,4-hexafluorobutane (CF3CH2CH2CF3) from the coupling reactions of covalently bonded surface alkyl (CF3CH2•) moieties. CF3CH2I adsorbs nondissociatively at 150 K. Thermal dissociation of this weakly chemisorbed state occurs below room temperature to form adsorbed CF3CH2• and I• species. The surface CF3CH2• species undergoes β-fluoride elimination to form gaseous CF2=CH2 and this represents the major pathway for the removal of CF3CH2• species from the surface. In competition with the β-fluoride elimination process the adsorbed CF3CH2• species also undergoes, recombination with surface iodine atoms to form recombinative molecular CF3CH2I, olefin insertion reaction with CF2=CH2 to form gaseous CF2=CHCH2CF3, and last self-coupling reaction to form CF3CH2CH2CF3. The adsorbed surface iodine atoms, formed by the dissociation of the molecularly chemisorbed CF3CH2I, and fluorine atoms formed during the β-fluoride elimination reaction, both form etch products (GaI, GaF, AsI, AsF, and As2) by their reactions with the surface layer Ga atoms, subsurface As atoms, and GaAs substrate. In this article we discuss the mechanisms by which these products form from the adsorbed CF3CH2• and I• species, and the role that the GaAs surface plays in the proposed reaction pathways. We compare the reactivity of the GaAs surface with transition metals in its ability to facilitate dehydrogenation and coupling reactions in adsorbed alkyl species. .

  11. Microstructure of Al contacts on GaAs

    NASA Astrophysics Data System (ADS)

    Karpov, I.; Franciosi, A.; Taylor, C.; Roberts, J.; Gladfelter, W. L.

    1997-11-01

    The microstructure of Al films deposited on GaAs(100) 2×4 surfaces through chemical vapor deposition from dimethylethylamine alane in the 100-160 °C temperature range exhibits a dominant (111) texture which is not encountered in evaporated films. Such a texture has been associated with enhanced electromigration resistance in related systems. Growth of (111)-oriented grains is observed when the deposition rate is limited by the surface reaction of the impinging precursor molecules, while at higher temperatures (160-400 °C) only the conventional texture is observed.

  12. Multiple Applications of GaAs semiconductors

    NASA Astrophysics Data System (ADS)

    Martel, Jenrené; Wonka, Willy

    2003-03-01

    The object of this discussion will be to explore the many facets of Gallium Arsenide(GaAs) semiconductors. The session will begin with a brief overview of the basic properties of semiconductors in general(band gap, doping, charge mobility etc.). It will then follow with a closer look at the properties of GaAs and how these properties could potentially translate into some very exciting applications. Furthermore, current applications of GaAs semiconductors will be dicussed and analyzed. Finally, physical limits and advantages/disadvantages of GaAs will be considered.

  13. One-pot synthesis of a new high vinyl content hybrid silica monolith dedicated to nanoliquid chromatography.

    PubMed

    Racha, El-Debs; Gay, Pauline; Dugas, Vincent; Demesmay, Claire

    2016-03-01

    A new vinyltrimethoxysilane-based hybrid silica monolith was developed and used as a reversed-phase capillary column. The synthesis of this rich vinyl hybrid macroporous monolith, by cocondensation of vinyltrimethoxysilane with tetramethoxysilane, was investigated using an unconventional (formamide, nitric acid) porogen/catalyst system. A macroporous hybrid silica monolith with 80% in mass of vinyltrimethoxysilane in the feeding silane solution was obtained and compared to a more conventional low vinyl content hybrid monolith with only of 20% vinyltrimethoxysilane. Monoliths were characterized by scanning electron microscopy, (29) Si nuclear magnetic resonance spectroscopy and N2 adsorption-desorption. About 80% of the vinyl precursor was incorporated in the final materials, leading to 15.9 and 61.5% of Si atoms bonded to vinyl groups for 20% vinyltrimethoxysilane and 80% vinyltrimethoxysilane, respectively. The 80% vinyltrimethoxysilane monolith presents a lower surface area than 20% vinyltrimethoxysilane (159 versus 551 m(2) /g), which is nevertheless compensated by a higher vinyl surface density. Chromatographic properties were evaluated in reversed-phase mode. Plots of ln(k) versus percentage of organic modifier were used to assess the reversed-phase mechanism. Its high content of organic groups leads to high retention properties. Column efficiencies of 170 000 plates/m were measured for this 80% vinyltrimethoxysilane hybrid silica monolith. Long capillary monolithic columns (90 cm) were successfully synthesized (N = 120 000).

  14. Preparation of boronate-functionalized molecularly imprinted monolithic column with polydopamine coating for glycoprotein recognition and enrichment.

    PubMed

    Lin, Zian; Wang, Juan; Tan, Xiaoqing; Sun, Lixiang; Yu, Ruifang; Yang, Huanghao; Chen, Guonan

    2013-12-06

    A novel imprinting strategy using reversible covalent complexation of glycoprotein was described for creating glycoprotein-specific recognition cavities on boronate-functionalized monolithic column. Based on it, a molecularly imprinted monolithic column was prepared by self-polymerization of dopamine (DA) on the surface of 4-vinylphenylboronic acid (VPBA)-based polymeric skeletons after reversible immobilization of horseradish peroxidase (HRP). Due to the combination of boronate affinity and surface imprinting of DA, the stable and accessible recognition sites in the as-prepared imprinted monolith could be obtained after the removal of the template, which facilitated the rebinding of the template and provided good reproducibility and lifetime of use. The recognition behaviors of proteins on the bare VPBA-based, HRP-imprinted and nonimprinted monolithic columns were evaluated in detail and the results showed that the HRP-imprinted monolith exhibited higher recognition ability toward the template than another two monolithic columns. Not only nonglycoproteins but also glycoproteins can be well separated with the HRP-imprinted monolith. In addition, the feasibility of the HRP-imprinted monolith, adopted as an in-tube solid phase microextraction (in-tube SPME), was further assessed by selective extraction and enrichment of HRP from human serum. The good results demonstrated its potential in glycoproteome analysis. Copyright © 2013 Elsevier B.V. All rights reserved.

  15. InP and GaAs characterization with variable stoichiometry obtained by molecular spray

    NASA Technical Reports Server (NTRS)

    Massies, J.; Linh, N. T.; Olivier, J.; Faulconnier, P.; Poirier, R.

    1979-01-01

    Both InP and GaAs surfaces were studied in parallel. A molecular spray technique was used to obtain two semiconductor surfaces with different superficial compositions. The structures of these surfaces were examined by electron diffraction. Electron energy loss was measured spectroscopically in order to determine surface electrical characteristics. The results are used to support conclusions relative to the role of surface composition in establishing a Schottky barrier effect in semiconductor devices.

  16. Nanoscale spatial phase modulation of GaAs growth in V-grooved trenches on Si (001) substrate

    NASA Astrophysics Data System (ADS)

    Li, Shi-Yan; Zhou, Xu-Liang; Kong, Xiang-Ting; Li, Meng-Ke; Mi, Jun-Ping; Wang, Meng-Qi; Pan, Jiao-Qing

    2016-12-01

    This letter reports the nanoscale spatial phase modulation of GaAs growth in V-grooved trenches fabricated on a Si (001) substrate by metal-organic vapor-phase epitaxy. Two hexagonal GaAs regions with high density of stacking faults parallel to Si {111} surfaces are observed. A strain-relieved and defect-free cubic phase GaAs was achieved above these highly defective regions. High-resolution transmission electron microscopy and fast Fourier transforms analysis were performed to characterize these regions of GaAs/Si interface. We also discussed the strain relaxation mechanism and phase structure modulation of GaAs selectively grown on this artificially manipulated surface. Project supported by the National Science and Technology Major Project of Science and Technology of China (Grant No. 2011ZX02708) and the National Natural Science Foundation of China (Grant No. 61504137).

  17. Highly microporous-graphene aerogel monolith of unidirectional honeycomb macro-textures

    NASA Astrophysics Data System (ADS)

    Wang, Shuwen; Wang, Zhipeng; Futamura, Ryusuke; Endo, Morinobu; Kaneko, Katsumi

    2017-04-01

    The highly microporous graphene aerogel monolith of unidirectional textures is obtained from reduction and KOH activation of colloidal graphene oxide prepared with an ice-templating route. The free-standing geometry and well-aligned textures of graphene monolith are persevered even after an intensive KOH activation at 973 K, although the frame structure is slightly disordered. The non-overestimated surface area of the KOH activated graphene monolith is 990 m2 g-1. The free-standing graphene aerogel monolith has predominant microporosity with appropriate macroporosity and a low bulk density of 8 ± 0.5 mg cm-3, being one of the lightest materials of the reported porous graphene materials.

  18. Electrically pumped continuous-wave 1.3 µm InAs/GaAs quantum dot lasers monolithically grown on on-axis Si (001) substrates.

    PubMed

    Chen, Siming; Liao, Mengya; Tang, Mingchu; Wu, Jiang; Martin, Mickael; Baron, Thierry; Seeds, Alwyn; Liu, Huiyun

    2017-03-06

    We report on the first electrically pumped continuous-wave (cw) InAs/GaAs quantum dot (QD) lasers monolithically grown on on-axis Si (001) substrates without any intermediate buffer layers. A 400 nm antiphase boundary (APB) free epitaxial GaAs film with a small root-mean-square (RMS) surface roughness of 0.86 nm was first deposited on a 300 mm standard industry-compatible on-axis Si (001) substrate by metal-organic chemical vapor deposition (MOCVD). The QD laser structure was then grown on this APB-free GaAs/Si (001) virtual substrate by molecular beam epitaxy (MBE). Room-temperature cw lasing at ~1.3 µm has been achieved with a threshold current density of 425 A/cm2 and single facet output power of 43 mW. Under pulsed operation, lasing operation up to 102 °C has been realized, with a threshold current density of 250 A/cm2 and single facet output power exceeding 130 mW at room temperature.

  19. Bismuth-induced phase control of GaAs nanowires grown by molecular beam epitaxy

    SciTech Connect

    Lu, Zhenyu; Chen, Pingping E-mail: luwei@mail.sitp.ac.cn; Shi, Suixing; Yao, Luchi; Zhou, Xiaohao; Lu, Wei E-mail: luwei@mail.sitp.ac.cn; Zhang, Zhi; Zhou, Chen; Zou, Jin

    2014-10-20

    In this work, the crystal structure of GaAs nanowires grown by molecular beam epitaxy has been tailored only by bismuth without changing the growth temperature and V/III flux ratio. The introduction of bismuth can lead to the formation of zinc-blende GaAs nanowires, while the removal of bismuth changes the structure into a 4H polytypism before it turns back to the wurtzite phase eventually. The theoretical calculation shows that it is the steadiest for bismuth to adsorb on the GaAs(111){sub B} surface compared to the liquid gold catalyst surface and the interface between the gold catalyst droplet and the nanowire, and these adsorbed bismuth could decrease the diffusion length of adsorbed Ga and hence the supersaturation of Ga in the gold catalyst droplet.

  20. The ZnSe(110) puzzle - Comparison with GaAs(110)

    NASA Technical Reports Server (NTRS)

    Duke, C. B.; Paton, A.; Kahn, A.; Tu, D.-W.

    1984-01-01

    The surface structure of monocrystalline ZnSe(110) and of 4-5-nm-thick ZnSe(110) layers epitaxially grown on GaAs(110) is investigated by means of elastic LEED and AES; the results are analyzed using the computer programs and R-factor methods of Duke et al. (1981 and 1983), presented in graphs and tables, and compared to those for GaAs(110). Significant differences are attributed to bond-length-conserving outward rotation of Se and inward rotation of Zn in the top layer, with an angle of 4 deg between the actual plane of the cation-anion chain and the truncated bulk surface. The R intensities measured for ZnSe(110) and GaAs(110) are given as Rx = 0.22 and RI = 0.21 and Rx = 0.24 and RI = 0.16, respectively.