Formation of ultrathin Ni germanides: solid-phase reaction, morphology and texture

NASA Astrophysics Data System (ADS)

van Stiphout, K.; Geenen, F. A.; De Schutter, B.; Santos, N. M.; Miranda, S. M. C.; Joly, V.; Detavernier, C.; Pereira, L. M. C.; Temst, K.; Vantomme, A.

2017-11-01

The solid-phase reaction of ultrathin (⩽10 nm) Ni films with different Ge substrates (single-crystalline (1 0 0), polycrystalline, and amorphous) was studied. As thickness goes down, thin film texture becomes a dominant factor in both the film’s phase formation and morphological evolution. As a consequence, certain metastable microstructures are epitaxially stabilized on crystalline substrates, such as the ɛ-Ni5Ge3 phase or a strained NiGe crystal structure on the single-crystalline substrates. Similarly, the destabilizing effect of axiotaxial texture on the film’s morphology becomes more pronounced as film thicknesses become smaller. These effects are contrasted by the evolution of germanide films on amorphous substrates, on which neither epitaxy nor axiotaxy can form, i.e. none of the (de)stabilizing effects of texture are observed. The crystallization of such amorphous substrates however, drives the film breakup.

Epitaxial CoSi2 on MOS devices

DOEpatents

Lim, Chong Wee; Shin, Chan Soo; Petrov, Ivan Georgiev; Greene, Joseph E.

2005-01-25

An Si.sub.x N.sub.y or SiO.sub.x N.sub.y liner is formed on a MOS device. Cobalt is then deposited and reacts to form an epitaxial CoSi.sub.2 layer underneath the liner. The CoSi.sub.2 layer may be formed through a solid phase epitaxy or reactive deposition epitaxy salicide process. In addition to high quality epitaxial CoSi.sub.2 layers, the liner formed during the invention can protect device portions during etching processes used to form device contacts. The liner can act as an etch stop layer to prevent excessive removal of the shallow trench isolation, and protect against excessive loss of the CoSi.sub.2 layer.

Selective Area Sublimation: A Simple Top-down Route for GaN-Based Nanowire Fabrication.

PubMed

Damilano, B; Vézian, S; Brault, J; Alloing, B; Massies, J

2016-03-09

Post-growth in situ partial SiNx masking of GaN-based epitaxial layers grown in a molecular beam epitaxy reactor is used to get GaN selective area sublimation (SAS) by high temperature annealing. Using this top-down approach, nanowires (NWs) with nanometer scale diameter are obtained from GaN and InxGa1-xN/GaN quantum well epitaxial structures. After GaN regrowth on InxGa1-xN/GaN NWs resulting from SAS, InxGa1-xN quantum disks (QDisks) with nanometer sizes in the three dimensions are formed. Low temperature microphotoluminescence experiments demonstrate QDisk multilines photon emission around 3 eV with individual line widths of 1-2 meV.

Metamorphic distributed Bragg reflectors for the 1440–1600 nm spectral range: Epitaxy, formation, and regrowth of mesa structures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Egorov, A. Yu., E-mail: anton@beam.ioffe.ru; Karachinsky, L. Ya.; Novikov, I. I.

It is shown that metamorphic In{sub 0.3}Ga{sub 0.7}As/In{sub 0.3}Al{sub 0.7}As distributed Bragg reflectors (DBRs) with a reflection band at 1440–1600 nm and a reflectance of no less than 0.999 can be fabricated by molecular beam epitaxy (MBE) on a GaAs substrate. It is demonstrated that mesa structures formed from metamorphic DBRs on a GaAs substrate can be regrown by MBE and microcavities can be locally formed in two separate epitaxial processes. The results obtained can find wide application in the fabrication of vertical-cavity surface-emitting lasers (VCSELs) with a buried tunnel junction.

Improvement of the Processes of Liquid-Phase Epitaxial Growth of Nanoheteroepitaxial Structures

NASA Astrophysics Data System (ADS)

Maronchuk, I. I.; Sanikovich, D. D.; Potapkov, P. V.; Vel‧chenko, A. A.

2018-05-01

We have revealed the shortcomings of equipment and technological approaches in growing nanoheteroepitaxial structures with quantum dots by liquid-phase epitaxy. We have developed and fabricated a new vertical barreltype cassette for growing quantum dots and epitaxial layers of various thicknesses in one technological process. A physico-mathematical simulation has been carried out of the processes of liquid-phase epitaxial growth of quantumdimensional structures with the use of the program product SolidWorks (FlowSimulation program). Analysis has revealed the presence of negative factors influencing the growth process of the above structures. The mathematical model has been optimized, and the equipment has been modernized without additional experiments and measurements. The flow dynamics of the process gas in the reactor at various flow rates has been investigated. A method for tuning the thermal equipment has been developed. The calculated and experimental temperature distributions in the process of growing structures with high reproducibility are in good agreement, which confirms the validity of the modernization made.

Grouped and Multistep Nanoheteroepitaxy: Toward High-Quality GaN on Quasi-Periodic Nano-Mask.

PubMed

Feng, Xiaohui; Yu, Tongjun; Wei, Yang; Ji, Cheng; Cheng, Yutian; Zong, Hua; Wang, Kun; Yang, Zhijian; Kang, Xiangning; Zhang, Guoyi; Fan, Shoushan

2016-07-20

A novel nanoheteroepitaxy method, namely, the grouped and multistep nanoheteroepitaxy (GM-NHE), is proposed to attain a high-quality gallium nitride (GaN) epilayer by metal-organic vapor phase epitaxy. This method combines the effects of sub-100 nm nucleation and multistep lateral growth by using a low-cost but unique carbon nanotube mask, which consists of nanoscale growth windows with a quasi-periodic 2D fill factor. It is found that GM-NHE can facilely reduce threading dislocation density (TDD) and modulate residual stress on foreign substrate without any regrowth. As a result, high-quality GaN epilayer is produced with homogeneously low TDD of 4.51 × 10(7) cm(-2) and 2D-modulated stress, and the performance of the subsequent 410 nm near-ultraviolet light-emitting diode is greatly boosted. In this way, with the facile fabrication of nanomask and the one-off epitaxy procedure, GaN epilayer is prominently improved with the assistance of nanotechnology, which demonstrates great application potential for high-efficiency TDD-sensitive optoelectronic and electronic devices.

Impact of recess etching and surface treatments on ohmic contacts regrown by molecular-beam epitaxy for AlGaN/GaN high electron mobility transistors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Joglekar, S.; Azize, M.; Palacios, T.

Ohmic contacts fabricated by regrowth of n{sup +} GaN are favorable alternatives to metal-stack-based alloyed contacts in GaN-based high electron mobility transistors. In this paper, the influence of reactive ion dry etching prior to regrowth on the contact resistance in AlGaN/GaN devices is discussed. We demonstrate that the dry etch conditions modify the surface band bending, dangling bond density, and the sidewall depletion width, which influences the contact resistance of regrown contacts. The impact of chemical surface treatments performed prior to regrowth is also investigated. The sensitivity of the contact resistance to the surface treatments is found to depend uponmore » the dangling bond density of the sidewall facets exposed after dry etching. A theoretical model has been developed in order to explain the observed trends.« less

Silver free III-nitride flip chip light-emitting-diode with wall plug efficiency over 70% utilizing a GaN tunnel junction

NASA Astrophysics Data System (ADS)

Yonkee, B. P.; Young, E. C.; DenBaars, S. P.; Nakamura, S.; Speck, J. S.

2016-11-01

A molecular beam epitaxy regrowth technique was demonstrated on standard industrial patterned sapphire substrate light-emitting diode (LED) epitaxial wafers emitting at 455 nm to form a GaN tunnel junction. By using an HF pretreatment on the wafers before regrowth, a voltage of 3.08 V at 20 A/cm2 was achieved on small area devices. A high extraction package was developed for comparison with flip chip devices which utilize an LED floating in silicone over a BaSO4 coated header and produced a peak external quantum efficiency (EQE) of 78%. A high reflectivity mirror was designed using a seven-layer dielectric coating backed by aluminum which has a calculated angular averaged reflectivity over 98% between 400 and 500 nm. This was utilized to fabricate a flip chip LED which had a peak EQE and wall plug efficiency of 76% and 73%, respectively. This flip chip could increase light extraction over a traditional flip chip LED due to the increased reflectivity of the dielectric based mirror.

Transmission electron microscopy study of the formation of epitaxial CoSi2/Si (111) by a room-temperature codeposition technique

NASA Technical Reports Server (NTRS)

D'Anterroches, Cecile; Yakupoglu, H. Nejat; Lin, T. L.; Fathauer, R. W.; Grunthaner, P. J.

1988-01-01

Co and Si have been codeposited on Si (111) substrates near room temperature in a stoichiometric 1:2 ratio in a molecular beam epitaxy system. Annealing of these deposits yields high-quality single-crystal CoSi2 layers. Transmission electron microscopy has been used to examine as-deposited layers and layers annealed at 300, 500, and 600 C. Single-crystal epitaxial grains of CoSi2 embedded in a matrix of amorphous Co/Si are observed in as-deposited samples, while the layer is predominantly single-crystal, inhomogeneously strained CoSi2 at 300 C. At 600 C, a homogeneously strained single-crystal layer with a high density of pinholes is observed. In contrast to other solid phase epitaxy techniques used to grow CoSi2 on Si (111), no intermediate silicide phases are observed prior to the formation of CoSi2.

Electrochemical Liquid Phase Epitaxy (ec-LPE): A New Methodology for the Synthesis of Crystalline Group IV Semiconductor Epifilms.

PubMed

Demuth, Joshua; Fahrenkrug, Eli; Ma, Luyao; Shodiya, Titilayo; Deitz, Julia I; Grassman, Tyler J; Maldonado, Stephen

2017-05-24

Deposition of epitaxial germanium (Ge) thin films on silicon (Si) wafers has been achieved over large areas with aqueous feedstock solutions using electrochemical liquid phase epitaxy (ec-LPE) at low temperatures (T ≤ 90 °C). The ec-LPE method uniquely blends the simplicity and control of traditional electrodeposition with the material quality of melt growth. A new electrochemical cell design based on the compression of a liquid metal electrode into a thin cavity that enables ec-LPE is described. The epitaxial nature, low strain character, and crystallographic defect content of the resultant solid Ge films were analyzed by electron backscatter diffraction, scanning transmission electron microscopy, high resolution X-ray diffraction, and electron channeling contrast imaging. The results here show the first step toward a manufacturing infrastructure for traditional crystalline inorganic semiconductor epifilms that does not require high temperature, gaseous precursors, or complex apparatus.

Thermoelectric Properties of Epitaxial β-FeSi2 Thin Films on Si(111) and Approach for Their Enhancement

NASA Astrophysics Data System (ADS)

Taniguchi, Tatsuhiko; Sakane, Shunya; Aoki, Shunsuke; Okuhata, Ryo; Ishibe, Takafumi; Watanabe, Kentaro; Suzuki, Takeyuki; Fujita, Takeshi; Sawano, Kentarou; Nakamura, Yoshiaki

2017-05-01

We have investigated the intrinsic thermoelectric properties of epitaxial β-FeSi2 thin films and the impact of phosphorus (P) doping. Epitaxial β-FeSi2 thin films with single phase were grown on Si(111) substrates by two different techniques in an ultrahigh-vacuum molecular beam epitaxy (MBE) system: solid-phase epitaxy (SPE), where iron silicide films formed by codeposition of Fe and Si at room temperature were recrystallized by annealing at 530°C to form epitaxial β-FeSi2 thin films on Si(111) substrates, and MBE of β-FeSi2 thin films on epitaxial β-FeSi2 templates formed on Si(111) by reactive deposition epitaxy (RDE) at 530°C (RDE + MBE). Epitaxial SPE thin films based on codeposition had a flatter surface and more abrupt β-FeSi2/Si(111) interface than epitaxial RDE + MBE thin films. We investigated the intrinsic thermoelectric properties of the epitaxial β-FeSi2 thin films on Si(111), revealing lower thermal conductivity and higher electrical conductivity compared with bulk β-FeSi2. We also investigated the impact of doping on the Seebeck coefficient of bulk and thin-film β-FeSi2. A route to enhance the thermoelectric performance of β-FeSi2 is proposed, based on (1) fabrication of thin-film structures for high electrical conductivity and low thermal conductivity, and (2) proper choice of doping for high Seebeck coefficient.

Atomic transport during solid-phase epitaxial recrystallization of amorphous germanium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Radek, M.; Bracht, H., E-mail: bracht@uni-muenster.de; Johnson, B. C.

2015-08-24

The atomic mixing of matrix atoms during solid-phase epitaxy (SPE) is studied by means of isotopically enriched germanium (Ge) multilayer structures that were amorphized by Ge ion implantation up to a depth of 1.5 μm. Recrystallization of the amorphous structure is performed at temperatures between 350 °C and 450 °C. Secondary-ion-mass-spectrometry is used to determine the concentration-depth profiles of the Ge isotope before and after SPE. An upper limit of 0.5 nm is deduced for the displacement length of the Ge matrix atoms by the SPE process. This small displacement length is consistent with theoretical models and atomistic simulations of SPE, indicating that themore » SPE mechanism consists of bond-switching with nearest-neighbours across the amorphous-crystalline (a/c) interface.« less

Subeutectic Synthesis of Epitaxial Si-NWs with Diverse Catalysts Using a Novel Si Precursor

PubMed Central

2010-01-01

The applicability of a novel silicon precursor with respect to reasonable nanowire (NW) growth rates, feasibility of epitaxial NW growth and versatility with respect to diverse catalysts was investigated. Epitaxial growth of Si-NWs was achieved using octochlorotrisilane (OCTS) as Si precursor and Au as catalyst. In contrast to the synthesis approach with SiCl4 as precursor, OCTS provides Si without the addition of H2. By optimizing the growth conditions, effective NW synthesis is shown for alternative catalysts, in particular, Cu, Ag, Ni, and Pt with the latter two being compatible to complementary metal-oxide-semiconductor technology. As for these catalysts, the growth temperatures are lower than the lowest liquid eutectic; we suggest that the catalyst particle is in the solid state during NW growth and that a solid-phase diffusion process, either in the bulk, on the surface, or both, must be responsible for NW nucleation. PMID:20843058

Height-selective etching for regrowth of self-aligned contacts using MBE

NASA Astrophysics Data System (ADS)

Burek, G. J.; Wistey, M. A.; Singisetti, U.; Nelson, A.; Thibeault, B. J.; Bank, S. R.; Rodwell, M. J. W.; Gossard, A. C.

2009-03-01

Advanced III-V transistors require unprecedented low-resistance contacts in order to simultaneously scale bandwidth, fmax and ft with the physical active region [M.J.W. Rodwell, M. Le, B. Brar, in: Proceedings of the IEEE, 96, 2008, p. 748]. Low-resistance contacts have been previously demonstrated using molecular beam epitaxy (MBE), which provides active doping above 4×10 19 cm -3 and permits in-situ metal deposition for the lowest resistances [U. Singisetti, M.A. Wistey, J.D. Zimmerman, B.J. Thibeault, M.J.W. Rodwell, A.C. Gossard, S.R. Bank, Appl. Phys. Lett., submitted]. But MBE is a blanket deposition technique, and applying MBE regrowth to deep-submicron lateral device dimensions is difficult even with advanced lithography techniques. We present a simple method for selectively etching undesired regrowth from the gate or mesa of a III-V MOSFET or laser, resulting in self-aligned source/drain contacts regardless of the device dimensions. This turns MBE into an effectively selective area growth technique.

Room-Temperature Operation of Index-Coupled Distributed-Feedback 4.75 Micron Quantum Cascade Lasers Fabricated Without Epitaxial Regrowth

NASA Technical Reports Server (NTRS)

Briggs, Ryan M.; Frez, Clifford; Forouhar, Siamak

2013-01-01

The Mars Science Laboratory (MSL) was spin-stabilized during its cruise to Mars. We discuss the effects of spin on the radiometric data and how the orbit determination team dealt with them. Additionally, we will discuss the unplanned benefits of detailed spin modeling including attitude estimation and spacecraft clock correlation.

Maskless nano-implant of 20 keV Ga+ in bulk Si(1 0 0) substrates

NASA Astrophysics Data System (ADS)

Milazzo, R. G.; D'Arrigo, G.; Mio, A. M.; Rimini, E.; Spinella, C.; Peto, L.; Nadzeyka, A.; Bauerdick, S.

2014-12-01

Multidirectional SPEG (Solid Phase Epitaxial Growth) of silicon has been investigated in micro and nanoamorphous structures generated on a crystalline substrate by a nano-sized ion beam, Gaussian shaped and with a standard deviation of about 5 nm. The 20 keV Ga+ ions were implanted at a fluence of 5 × 1014 ions cm-2 in a bulk Si(1 0 0) single crystal. Two structures were used for the implants: circular regions of 100 nm and 1 μm diameters respectively and straight lines 10 nm in width and few microns in length along (1 0 0) or (1 1 0) directions. The lateral spread of ions has been taken into account in the damage estimation. Transmission Electron Microscopy indicates that the structures are made of an amorphous core surrounded by a defective and filamentary shell. The recovery of the damaged outer regions promptly occurs during the early stages of the thermal treatment at 500-600 °C for all the structures. By prolonging annealing time, re-crystallization of the amorphous cores is achieved too by the movement of the underneath crystal-amorphous interface. The re-growth is almost defects free when the contribution of the crystalline seed below the structures is present, defective and twin mediated if it misses as in the thinnest regions of the specimen.

The Reduction of TED in Ion Implanted Silicon

NASA Astrophysics Data System (ADS)

Jain, Amitabh

2008-11-01

The leading challenge in the continued scaling of junctions made by ion implantation and annealing is the control of the undesired transient enhanced diffusion (TED) effect. Spike annealing has been used as a means to reduce this effect and has proven successful in previous nodes. The peak temperature in this process is typically 1050 °C and the time spent within 50 °C of the peak is of the order of 1.5 seconds. As technology advances along the future scaling roadmap, further reduction or elimination of the enhanced diffusion effect is necessary. We have shown that raising the peak temperature to 1175 °C or more and reduction of the anneal time at peak temperature to less than a millisecond is effective in eliminating enhanced diffusion. We show that it is possible to employ a sequence of millisecond anneal followed by spike anneal to obtain profiles that do not exhibit gradient degradation at the junction and have junction depth and sheet resistance appropriate to the needs of future technology nodes. We have implemented millisecond annealing using a carbon dioxide laser to support high-volume manufacturing of 65 nm microprocessors and system-on-chip products. We further show how the use of molecular ion implantation to produce amorphousness followed by laser annealing to produce solid phase epitaxial regrowth results in junctions that meet the shallow depth and abruptness requirements of the 32 nm node.

Metal organic chemical vapor deposition of 111-v compounds on silicon

DOEpatents

Vernon, Stanley M.

1986-01-01

Expitaxial composite comprising thin films of a Group III-V compound semiconductor such as gallium arsenide (GaAs) or gallium aluminum arsenide (GaAlAs) on single crystal silicon substrates are disclosed. Also disclosed is a process for manufacturing, by chemical deposition from the vapor phase, epitaxial composites as above described, and to semiconductor devices based on such epitaxial composites. The composites have particular utility for use in making light sensitive solid state solar cells.

Substrate-Independent Epitaxial Growth of the Metal-Organic Framework MOF-508a.

PubMed

Wilson, M; Barrientos-Palomo, S N; Stevens, P C; Mitchell, N L; Oswald, G; Nagaraja, C M; Badyal, J P S

2018-01-31

Plasmachemical deposition is a substrate-independent method for the conformal surface functionalization of solid substrates. Structurally well-defined pulsed plasma deposited poly(1-allylimidazole) layers provide surface imidazole linker groups for the directed liquid-phase epitaxial (layer-by-layer) growth of metal-organic frameworks (MOFs) at room temperature. For the case of microporous [Zn (benzene-1,4-dicarboxylate)-(4,4'-bipyridine) 0.5 ] (MOF-508), the MOF-508a polymorph containing two interpenetrating crystal lattice frameworks undergoes orientated Volmer-Weber growth and displays CO 2 gas capture behavior at atmospheric concentrations in proportion to the number of epitaxially grown MOF-508 layers.

Heterogeneous Two-Phase Pillars in Epitaxial NiFe 2 O 4 -LaFeO 3 Nanocomposites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Comes, Ryan B.; Perea, Daniel E.; Spurgeon, Steven R.

2017-07-10

Self-assembled epitaxial oxide nanocomposites have been explored for a wide range of applications, including multiferroic and magnetoelectric properties, plasmonics, and catalysis. These so-called “vertically aligned nanocomposites” form spontaneously during the deposition process when segregation into two phases is energetically favorable as compared to a solid solution. However, there has been surprisingly little work understanding the driving forces that govern the synthesis of these materials, which can include point defect energetics, surface diffusion, and interfacial energies. To explore these factors, La-Ni-Fe-O films have been synthesized by molecular beam epitaxy and it is shown that these phase segregate into spinel-perovskite nanocomposites. Usingmore » complementary scanning transmission electron microscopy and atom-probe tomography, the elemental composition of each phase is examined and found that Ni ions are exclusively found in the spinel phase. From correlative analysis, a model for the relative favorability of the Ni2+ and Ni3+ valences under the growth conditions is developed. It is shown that multidimensional characterization techniques provide previously unobserved insight into the growth process and complex driving forces for phase segregation.« less

Low Loss Substrates for Microwave Applications and Sol-Gel Processing of Superconductors

DTIC Science & Technology

1994-03-31

crystallographic axis normal to solid state technology, in the growth of ferrimagnetic garnets the substrate plane) or. better, in "epitaxial" films (i.e...hay- by liquid phase epitaxy ( LPE ). is from a melt using a para- ing their three crystallographic axes related to those of a magnetic garnet structure...yttrium barium cuprate (YBCO) films and their microwave applications have been carried out. Several promising new hosts such as Sr(All/2Tal/2)03, Sr(Al1

Epitaxial growth of VO2 by periodic annealing

NASA Astrophysics Data System (ADS)

Tashman, J. W.; Lee, J. H.; Paik, H.; Moyer, J. A.; Misra, R.; Mundy, J. A.; Spila, T.; Merz, T. A.; Schubert, J.; Muller, D. A.; Schiffer, P.; Schlom, D. G.

2014-02-01

We report the growth of ultrathin VO2 films on rutile TiO2 (001) substrates via reactive molecular-beam epitaxy. The films were formed by the cyclical deposition of amorphous vanadium and its subsequent oxidation and transformation to VO2 via solid-phase epitaxy. Significant metal-insulator transitions were observed in films as thin as 2.3 nm, where a resistance change ΔR/R of 25 was measured. Low angle annular dark field scanning transmission electron microscopy was used in conjunction with electron energy loss spectroscopy to study the film/substrate interface and revealed the vanadium to be tetravalent and the titanium interdiffusion to be limited to 1.6 nm.

Multispectral InGaAs/GaAs/AlGaAs laser arrays by MBE growth on patterned substrates

NASA Astrophysics Data System (ADS)

Kamath, K.; Bhattacharya, P.; Singh, J.

1997-05-01

Multispectral semiconductor laser arrays on single chip is demonstrated by molecular beam epitaxial (MBE) growth of {In0.2Ga0.8As}/{GaAs} quantum well lasers on GaAs (1 0 0) substrates patterned by dry etching. No regrowth is needed for simple edge emitting lasers. It was observed that the laser characteristics are not degraded by the patterned growth. The shift in the emission wavelength obtained by this method can be controlled by varying the width of the pre-patterned ridges as well as by selecting the regions with different number of vertical sidewalls on both sides. We have also shown that multispectral vertical cavity surface emitting laser (VCSEL) arrays can be made by this technique with a single regrowth.

Pure wurtzite GaP nanowires grown on zincblende GaP substrates by selective area vapor liquid solid epitaxy

NASA Astrophysics Data System (ADS)

Halder, Nripendra N.; Kelrich, Alexander; Cohen, Shimon; Ritter, Dan

2017-11-01

We report on the growth of single phase wurtzite (WZ) GaP nanowires (NWs) on GaP (111) B substrates by metal organic molecular beam epitaxy following the selective area vapor-liquid-solid (SA-VLS) approach. During the SA-VLS process, precursors are supplied directly to the NW sidewalls, and the short diffusion length of gallium (or its precursors) does not significantly limit axial growth. Transmission electron microscopy (TEM) images reveal that no stacking faults are present along a 600 nm long NW. The lattice constants of the pure WZ GaP obtained from the TEM images agree with values determined previously by x-ray diffraction from non-pure NW ensembles.

Pure wurtzite GaP nanowires grown on zincblende GaP substrates by selective area vapor liquid solid epitaxy.

PubMed

Halder, Nripendra N; Kelrich, Alexander; Cohen, Shimon; Ritter, Dan

2017-11-17

We report on the growth of single phase wurtzite (WZ) GaP nanowires (NWs) on GaP (111) B substrates by metal organic molecular beam epitaxy following the selective area vapor-liquid-solid (SA-VLS) approach. During the SA-VLS process, precursors are supplied directly to the NW sidewalls, and the short diffusion length of gallium (or its precursors) does not significantly limit axial growth. Transmission electron microscopy (TEM) images reveal that no stacking faults are present along a 600 nm long NW. The lattice constants of the pure WZ GaP obtained from the TEM images agree with values determined previously by x-ray diffraction from non-pure NW ensembles.

Initial growth processes in the epitaxy of Ge with GeH{sub 4} on oxidized Si substrates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Angermeier, D.; Kuhn, W.S.; Druihle, R.

1997-02-01

The heteroepitaxial growth of Ge on (100) Si in a horizontal, atmospheric pressure metallorganic vapor-phase epitaxy reactor is reported using germane GeH{sub 4} (0.1% in H{sub 2}). A particularly crucial parameter for germanium deposition on silicon is the time for the onset of epitaxial growth, the incubation time. The time was measured at substrate temperatures between 450 and 600{degree}C. At a substrate temperature of 450{degree}C an incubation time of 520 s was found and for the subsequent epitaxy growth rates of 50 nm/min were determined by Nomarski microscopy and electron diffraction. The existence of residual oxide in the reactor chambermore » forming an in situ SiO{sub 2} layer was evaluated by x-ray photoemission spectroscopy. To obtain a more thorough understanding of the gas- and solid-phase composition of Ge, Si, and oxygen the Gibbs energy of the system was calculated for various growth temperatures. It was concluded that SiO{sub 2} molecules are reduced by GeH{sub 4} molecules during the incubation period.« less

Growth kinetics and mass transport mechanisms of GaN columns by selective area metal organic vapor phase epitaxy

NASA Astrophysics Data System (ADS)

Wang, Xue; Hartmann, Jana; Mandl, Martin; Sadat Mohajerani, Matin; Wehmann, Hergo-H.; Strassburg, Martin; Waag, Andreas

2014-04-01

Three-dimensional GaN columns recently have attracted a lot of attention as the potential basis for core-shell light emitting diodes for future solid state lighting. In this study, the fundamental insights into growth kinetics and mass transport mechanisms of N-polar GaN columns during selective area metal organic vapor phase epitaxy on patterned SiOx/sapphire templates are systematically investigated using various pitch of apertures, growth time, and silane flow. Species impingement fluxes on the top surface of columns Jtop and on their sidewall Jsw, as well as, the diffusion flux from the substrate Jsub contribute to the growth of the GaN columns. The vertical and lateral growth rates devoted by Jtop, Jsw and Jsub are estimated quantitatively. The diffusion length of species on the SiOx mask surface λsub as well as on the sidewall surfaces of the 3D columns λsw are determined. The influences of silane on the growth kinetics are discussed. A growth model is developed for this selective area metal organic vapor phase epitaxy processing.

Growth of β-Ga2O3 Films on Sapphire by Hydride Vapor Phase Epitaxy

NASA Astrophysics Data System (ADS)

XIONG, Ze-Ning; XIU, Xiang-Qian; LI, Yue-Wen; HUA, Xue-Mei; XIE, Zi-Li; CHEN, Peng; LIU, Bin; HAN, Ping; ZHANG, Rong; ZHENG, You-Dou

2018-05-01

Not Available Supported by the National Key Research and Development Program of China under Grant No 2017YFB0404201, the Solid State Lighting and Energy-Saving Electronics Collaborative Innovation Center, PAPD, and the State Grid Shandong Electric Power Company.

Theoretical study of the composition pulling effect in InGaN metalorganic vapor-phase epitaxy growth

NASA Astrophysics Data System (ADS)

Inatomi, Yuya; Kangawa, Yoshihiro; Ito, Tomonori; Suski, Tadeusz; Kumagai, Yoshinao; Kakimoto, Koichi; Koukitu, Akinori

2017-07-01

The composition pulling effect in metalorganic vapor-phase InGaN epitaxy was theoretically investigated by thermodynamic analysis. The excess energies of biaxial-strained In x Ga1- x N were numerically calculated using empirical interatomic potentials considering different situations: (i) coherent growth on GaN(0001), (ii) coherent growth on In0.2Ga0.8N(0001), and (iii) bulk growth. Using the excess energies, the excess chemical potentials of InN and GaN alloys were computed. Our results show that compressive strain suppresses In incorporation, whereas tensile strain promotes it. Moreover, assuming chemical equilibrium, the relationship between the solid composition and the growth conditions was predicted. The results successfully reproduced the typical composition pulling effect.

Epitaxial growth and characterization of CuGa2O4 films by laser molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Wei, Hongling; Chen, Zhengwei; Wu, Zhenping; Cui, Wei; Huang, Yuanqi; Tang, Weihua

2017-11-01

Ga2O3 with a wide bandgap of ˜ 4.9 eV can crystalize in five crystalline phases. Among those phases, the most stable monoclinic β-Ga2O3 has been studied most, however, it is hard to find materials lattice matching with β-Ga2O3 to grown epitaxial thin films for optoelectronic applications. In this work, CuGa2O4 bulk were prepared by solid state reaction as target, and the films were deposited on sapphire substrates by laser molecular beam epitaxy (L-MBE) at different substrate temperatures. The influences of substrate temperature on structural and optical properties have been systematically investigated by means of X-ray diffraction, Transmission electron microscope and UV-vis absorption spectra. High quality cubic structure and [111] oriented CuGa2O4 film can be obtained at substrate temperature of 750 °C. It's also demonstrated that the CuGa2O4 film has a bandgap of ˜ 4.4 eV and a best crystal quality at 750 °C, suggesting that CuGa2O4 film is a promising candidate for applications in ultraviolet optoelectronic devices.

Si-Ge-metal ternary phase diagram calculations

NASA Technical Reports Server (NTRS)

Fleurial, J. P.; Borshchevsky, A.

1990-01-01

Solution crystal growth and doping conditions of Si-Ge alloys used for high-temperature thermoelectric generation are determined here. Liquid-phase epitaxy (LPE) has been successfully employed recently to obtain single-crystalline homogeneous layers of Si-Ge solid solutions from a liquid metal solvent. Knowledge of Si-Ge-metallic solvent ternary phase diagrams is essential for further single-crystal growth development. Consequently, a thermodynamic equilibrium model was used to calculate the phase diagrams of the Si-Ge-M systems, including solid solubilities, where M is Al, Ga, In, Sn, Pb, Sb, or Bi. Good agreement between calculated liquidus and solidus data and experimental DTA and microprobe results was obtained. The results are used to compare the suitability of the different systems for crystal growth (by LPE-type process).

Epitaxial insertion of gold silicide nanodisks during the growth of silicon nanowires.

PubMed

Um, Han-Don; Jee, Sang-Won; Park, Kwang-Tae; Jung, Jin-Young; Guo, Zhongyi; Lee, Jung-Ho

2011-07-01

Nanodisk-shaped, single-crystal gold silicide heterojunctions were inserted into silicon nanowires during vapor-liquid-solid growth using Au as a catalyst within a specific range of chlorine-to-hydrogen atomic ratio. The mechanism of nanodisk formation has been investigated by changing the source gas ratio of SiCl4 to H2. We report that an over-supply of silicon into the Au-Si liquid alloy leads to highly supersaturated solution and enhances the precipitation of Au in the silicon nanowires due to the formation of unstable phases within the liquid alloy. It is shown that the gold precipitates embedded in the silicon nanowires consisted of a metastable gold silicide. Interestingly, faceting of gold silicide was observed at the Au/Si interfaces, and silicon nanowires were epitaxially grown on the top of the nanodisk by vapor-liquid-solid growth. High resolution transmission electron microscopy confirmed that gold silicide nanodisks are epitaxially connected to the silicon nanowires in the direction of growth direction. These gold silicide nanodisks would be useful as nanosized electrical junctions for future applications in nanowire interconnections.

High gain photoconductive semiconductor switch having tailored doping profile zones

DOEpatents

Baca, Albert G.; Loubriel, Guillermo M.; Mar, Alan; Zutavern, Fred J; Hjalmarson, Harold P.; Allerman, Andrew A.; Zipperian, Thomas E.; O'Malley, Martin W.; Helgeson, Wesley D.; Denison, Gary J.; Brown, Darwin J.; Sullivan, Charles T.; Hou, Hong Q.

2001-01-01

A photoconductive semiconductor switch with tailored doping profile zones beneath and extending laterally from the electrical contacts to the device. The zones are of sufficient depth and lateral extent to isolate the contacts from damage caused by the high current filaments that are created in the device when it is turned on. The zones may be formed by etching depressions into the substrate, then conducting epitaxial regrowth in the depressions with material of the desired doping profile. They may be formed by surface epitaxy. They may also be formed by deep diffusion processes. The zones act to reduce the energy density at the contacts by suppressing collective impact ionization and formation of filaments near the contact and by reducing current intensity at the contact through enhanced current spreading within the zones.

Formation of atomically smooth epitaxial metal films on a chemically reactive interface: Mg on Si(111)

NASA Astrophysics Data System (ADS)

Özer, Mustafa M.; Weitering, Hanno H.

2013-07-01

Deposition of Mg on Si(111)7 × 7 produces an epitaxial magnesium silicide layer. Under identical annealing conditions, the thickness of this Mg2Si(111) layer increases with deposition amount, reaching a maximum of 4 monolayer (ML) and decreasing to ˜3 ML at higher Mg coverage. Excess Mg coalesces into atomically flat, crystalline Mg(0001) films. This surprising growth mode can be attributed to the accidental commensurability of the Mg(0001), Si(111), and Mg2Si(111) interlayer spacing and the concurrent minimization of in-plane Si mass transfer and domain-wall energies. The commensurability of the interlayer spacing defines a highly unique solid-phase epitaxial growth process capable of producing trilayer structures with atomically abrupt interfaces and atomically smooth surface morphologies.

Electrodeposition of Metal on GaAs Nanowires

NASA Astrophysics Data System (ADS)

Liu, Chao; Einabad, Omid; Watkins, Simon; Kavanagh, Karen

2010-10-01

Copper (Cu) electrical contacts to freestanding gallium arsenide (GaAs) nanowires have been fabricated via electrodeposition. The nanowires are zincblende (111) oriented grown epitaxially on n-type Si-doped GaAs (111)B substrates by gold-catalyzed Vapor Liquid Solid (VLS) growth in a metal organic vapour phase epitaxy (MOVPE) reactor. The epitaxial electrodeposition process, based on previous work with bulk GaAs substrates, consists of a substrate oxide pre-etch in dilute ammonium-hydroxide carried out prior to galvanostatic electrodeposition in a pure Cu sulphate aqueous electrolyte at 20-60^oC. For GaAs nanowires, we find that Cu or Fe has a preference for growth on the gold catalyst avoiding the sidewalls. After removing gold, both metals still prefer to grow only on top of the nanowire, which has the largest potential field.

Design, fabrication, and performance analysis of GaN vertical electron transistors with a buried p/n junction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yeluri, Ramya, E-mail: ramyay@ece.ucsb.edu; Lu, Jing; Keller, Stacia

2015-05-04

The Current Aperture Vertical Electron Transistor (CAVET) combines the high conductivity of the two dimensional electron gas channel at the AlGaN/GaN heterojunction with better field distribution offered by a vertical design. In this work, CAVETs with buried, conductive p-GaN layers as the current blocking layer are reported. The p-GaN layer was regrown by metalorganic chemical vapor deposition and the subsequent channel regrowth was done by ammonia molecular beam epitaxy to maintain the p-GaN conductivity. Transistors with high ON current (10.9 kA/cm{sup 2}) and low ON-resistance (0.4 mΩ cm{sup 2}) are demonstrated. Non-planar selective area regrowth is identified as the limiting factormore » to transistor breakdown, using planar and non-planar n/p/n structures. Planar n/p/n structures recorded an estimated electric field of 3.1 MV/cm, while non-planar structures showed a much lower breakdown voltage. Lowering the p-GaN regrowth temperature improved breakdown in the non-planar n/p/n structure. Combining high breakdown voltage with high current will enable GaN vertical transistors with high power densities.« less

Low-Cost Approaches to III–V Semiconductor Growth for Photovoltaic Applications

DOE PAGES

Greenaway, Ann L.; Boucher, Jason W.; Oener, Sebastian Z.; ...

2017-08-31

III–V semiconductors form the most efficient single- and multijunction photovoltaics. Metal–organic vapor-phase epitaxy, which uses toxic and pyrophoric gas-phase precursors, is the primary commercial growth method for these materials. In order for the use of highly efficient III–V-based devices to be expanded as the demand for renewable electricity grows, a lower-cost approach to the growth of these materials is needed. This Review focuses on three deposition techniques compatible with current device architectures: hydride vapor-phase epitaxy, close-spaced vapor transport, and thin-film vapor–liquid–solid growth. Here, we consider recent advances in each technique, including the available materials space, before providing an in-depth comparisonmore » of growth technology advantages and limitations and considering the impact of modifications to the method of production on the cost of the final photovoltaics.« less

Development of orientation-patterned GaP grown on foreign substrates for QPM frequency conversion devices

NASA Astrophysics Data System (ADS)

Vangala, Shivashankar; Peterson, Rita; Snure, Michael; Tassev, Vladimir

2017-02-01

Thick hydride vapor phase epitaxially grown orientation-patterned gallium phosphide (OPGaP) is a leading material for quasi-phase matching (QPM) frequency conversion in the mid- and longwave infrared (IR). This is due to its negligible two-photon absorption (2PA) in the convenient pumping range 1 - 1.7 μm, compared with the 2PA of some traditional QPM materials, such as GaAs. In this paper, we describe homo- and heteroepitaxial growth techniques aimed to produce hundreds of microns thick OPGaP on: 1) OPGaAs templates fabricated using an improved wafer-fusion process; 2) OPGaAs templates fabricated by using a molecular beam epitaxy (MBE) for sublattice polarity inversion, but one with and one without MBE regrowth after the inversion. Some of the advantages of the heteroepitaxial growth of OPGaP on OPGaAs templates include: 1) achieving good domain fidelity as a result of the significantly higher OPGaAs template quality; 2) eliminating the needs of using the poor quality commercially available GaP in the production of thick OPGaP material, and 3) suppression of the additional absorption band between 2 - 4 μm (which is due to incorporation of n-type impurities) and, in general, improvement of the IR transmittance in the entire IR region. Combining the advantages of the two most promising nonlinear materials, GaAs and GaP, will accelerate the development of high power, broadly tunable laser sources in the IR which, in addition, will be offered with higher device quality and at a reasonably lower unit cost.

Solid-state synthesis, structural and magnetic properties of CoPd films

NASA Astrophysics Data System (ADS)

Myagkov, V. G.; Bykova, L. E.; Zhigalov, V. S.; Tambasov, I. A.; Bondarenko, G. N.; Matsynin, A. A.; Rybakova, A. N.

2015-05-01

The results of the investigation of the structural and magnetic properties of CoPd films with equiatomic composition have been presented. The films have been synthesized by vacuum annealing of polycrystalline Pd/Co and epitaxial Pd/α-Co(110) and Pd/β-Co(001) bilayer samples. It has been shown that, for all samples, the annealing to 400°C does not lead to the mixing of layers and the formation of compounds. A further increase in the annealing temperature results in the formation of a disordered CoPd phase at the Pd/Co interface, which is fully completed after annealing at 650°C. The epitaxial relationships between the disordered CoPd phase and the MgO(001) substrate are determined as follows: CoPd(110)<

Growth of high-quality InGaN/GaN LED structures on (1 1 1) Si substrates with internal quantum efficiency exceeding 50%

NASA Astrophysics Data System (ADS)

Lee, JaeWon; Tak, Youngjo; Kim, Jun-Youn; Hong, Hyun-Gi; Chae, Suhee; Min, Bokki; Jeong, Hyungsu; Yoo, Jinwoo; Kim, Jong-Ryeol; Park, Youngsoo

2011-01-01

GaN-based light-emitting-diodes (LEDs) on (1 1 1) Si substrates with internal quantum efficiency (IQE) exceeding 50% have been successfully grown by metal organic vapor phase epitaxy (MOVPE). 3.5 μm thick crack-free GaN epitaxial layers were grown on the Si substrates by the re-growth method on patterned templates. Series of step-graded Al xGa 1- xN epitaxial layers were used as the buffer layers to compensate thermal tensile stresses produced during the post-growth cooling process as well as to reduce the density of threading dislocations (TDs) generated due to the lattice mismatches between III-nitride layers and the silicon substrates. The light-emitting region consisted of 1.8 μm thick n-GaN, 3 periods of InGaN/GaN superlattice, InGaN/GaN multiple quantum wells (MQWs) designed for a peak wavelength of about 455 nm, an electron blocking layer (EBL), and p-GaN. The full-widths at half-maximum (FWHM) of (0 0 0 2) and (1 0 -1 2) ω-rocking curves of the GaN epitaxial layers were 410 and 560 arcsec, respectively. Cross-sectional transmission electron microscopy (TEM) investigation revealed that the propagation of the threading dislocations was mostly limited to the interface between the last Al xGa 1- xN buffer and n-GaN layers. The density of the threading dislocations induced pits of n-GaN, as estimated by atomic force microscopy (AFM), was about 5.5×10 8 cm -2. Temperature dependent photoluminescence (PL) measurements with a relative intensity integration method were carried out to estimate the internal quantum efficiency (IQE) of the light-emitting structures grown on Si, which reached up to 55%.

Activation of boron and recrystallization in Ge preamorphization implant structure of ultra shallow junctions by microwave annealing

NASA Astrophysics Data System (ADS)

Tsai, Ming Han; Wu, Chi-Ting; Lee, Wen-His

2014-04-01

In this study, high-current and low-energy (400 eV) ion implantation and low-temperature microwave annealing were employed to achieve ultra shallow junctions. To use the characteristic of microwave annealing more effectively, two-step microwave annealing was also employed. In the first step annealing, a high-power (2400 W; ˜500 °C) microwave was used to achieve solid-state epitaxial regrowth (SPER) and enhance microwave absorption. In the second step of annealing, unlike in conventional thermal annealing, which requires a higher energy to activate the dopant, a 600 W (˜250 °C) microwave was used to achieve low sheet resistance. The device subjected to two-step microwave annealing at 2400 W for 300 s + 600 W for 600 s has the lowest Vth. It also has the lowest subthreshold swing (SS), which means that it has the highest cap ability to control sub threshold current. In these three devices, the largest Ion/Ioff ratio is 2.203 × 106, and the smallest Ion/Ioff ratio is 2.024 × 106.

Epitaxial GeSn film formed by solid phase epitaxy and its application to Yb{sub 2}O{sub 3}-gated GeSn metal-oxide-semiconductor capacitors with sub-nm equivalent oxide thickness

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Ching-Wei; Wu, Yung-Hsien; Hsieh, Ching-Heng

2014-11-17

Through the technique of solid phase epitaxy (SPE), an epitaxial Ge{sub 0.955}Sn{sub 0.045} film was formed on a Ge substrate by depositing an amorphous GeSn film followed by a rapid thermal annealing at 550 °C. A process that uses a SiO{sub 2} capping layer on the amorphous GeSn film during SPE was proposed and it prevents Sn precipitation from occurring while maintaining a smooth surface due to the reduced surface mobility of Sn atoms. The high-quality epitaxial GeSn film was observed to have single crystal structure, uniform thickness and composition, and tiny surface roughness with root mean square of 0.56 nm. Withmore » a SnO{sub x}-free surface, Yb{sub 2}O{sub 3}-gated GeSn metal-oxide-semiconductor (MOS) capacitors with equivalent oxide thickness (EOT) of 0.55 nm were developed. A small amount of traps inside the Yb{sub 2}O{sub 3} was verified by negligible hysteresis in capacitance measurement. Low leakage current of 0.4 A/cm{sup 2} at gate bias of flatband voltage (V{sub FB})-1 V suggests the high quality of the gate dielectric. In addition, the feasibility of using Yb{sub 2}O{sub 3} to well passivate GeSn surface was also evidenced by the small interface trap density (D{sub it}) of 4.02 × 10{sup 11} eV{sup −1} cm{sup −2}, which can be attributed to smooth GeSn surface and Yb{sub 2}O{sub 3} valency passivation. Both leakage current and D{sub it} performance outperform other passivation techniques at sub-nm EOT regime. The proposed epitaxial GeSn film along with Yb{sub 2}O{sub 3} dielectric paves an alternative way to enable high-performance GeSn MOS devices.« less

The 3-5 semiconductor solid solution single crystal growth. [low gravity float zone growth experiments using gallium indium antimonides and cadmium tellurides

NASA Technical Reports Server (NTRS)

Gertner, E. R.

1980-01-01

Techniques used for liquid and vapor phase epitaxy of gallium indium arsenide are described and the difficulties encountered are examined. Results show that the growth of bulk III-V solid solution single crystals in a low gravity environment will not have a major technological impact. The float zone technique in a low gravity environment is demonstrated using cadmium telluride. It is shown that this approach can result in the synthesis of a class of semiconductors that can not be grown in normal gravity because of growth problems rooted in the nature of their phase diagrams.

On the relationship between tumour growth rate and survival in non-small cell lung cancer.

PubMed

Mistry, Hitesh B

2017-01-01

A recurrent question within oncology drug development is predicting phase III outcome for a new treatment using early clinical data. One approach to tackle this problem has been to derive metrics from mathematical models that describe tumour size dynamics termed re-growth rate and time to tumour re-growth. They have shown to be strong predictors of overall survival in numerous studies but there is debate about how these metrics are derived and if they are more predictive than empirical end-points. This work explores the issues raised in using model-derived metric as predictors for survival analyses. Re-growth rate and time to tumour re-growth were calculated for three large clinical studies by forward and reverse alignment. The latter involves re-aligning patients to their time of progression. Hence, it accounts for the time taken to estimate re-growth rate and time to tumour re-growth but also assesses if these predictors correlate to survival from the time of progression. I found that neither re-growth rate nor time to tumour re-growth correlated to survival using reverse alignment. This suggests that the dynamics of tumours up until disease progression has no relationship to survival post progression. For prediction of a phase III trial I found the metrics performed no better than empirical end-points. These results highlight that care must be taken when relating dynamics of tumour imaging to survival and that bench-marking new approaches to existing ones is essential.

Surface effects of vapour-liquid-solid driven Bi surface droplets formed during molecular-beam-epitaxy of GaAsBi

PubMed Central

Steele, J. A.; Lewis, R. A.; Horvat, J.; Nancarrow, M. J. B.; Henini, M.; Fan, D.; Mazur, Y. I.; Schmidbauer, M.; Ware, M. E.; Yu, S.-Q.; Salamo, G. J.

2016-01-01

Herein we investigate a (001)-oriented GaAs1−xBix/GaAs structure possessing Bi surface droplets capable of catalysing the formation of nanostructures during Bi-rich growth, through the vapour-liquid-solid mechanism. Specifically, self-aligned “nanotracks” are found to exist trailing the Bi droplets on the sample surface. Through cross-sectional high-resolution transmission electron microscopy the nanotracks are revealed to in fact be elevated above surface by the formation of a subsurface planar nanowire, a structure initiated mid-way through the molecular-beam-epitaxy growth and embedded into the epilayer, via epitaxial overgrowth. Electron microscopy studies also yield the morphological, structural, and chemical properties of the nanostructures. Through a combination of Bi determination methods the compositional profile of the film is shown to be graded and inhomogeneous. Furthermore, the coherent and pure zincblende phase property of the film is detailed. Optical characterisation of features on the sample surface is carried out using polarised micro-Raman and micro-photoluminescence spectroscopies. The important light producing properties of the surface nanostructures are investigated through pump intensity-dependent micro-PL measurements, whereby relatively large local inhomogeneities are revealed to exist on the epitaxial surface for important optical parameters. We conclude that such surface effects must be considered when designing and fabricating optical devices based on GaAsBi alloys. PMID:27377213

Formation of (111) orientation-controlled ferroelectric orthorhombic HfO{sub 2} thin films from solid phase via annealing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mimura, Takanori; Katayama, Kiliha; Shimizu, Takao

2016-08-01

0.07YO{sub 1.5}-0.93HfO{sub 2} (YHO7) films were prepared on various substrates by pulse laser deposition at room temperature and subsequent heat treatment to enable a solid phase reaction. (111)-oriented 10 wt. % Sn-doped In{sub 2}O{sub 3}(ITO)//(111) yttria-stabilized zirconia, (111)Pt/TiO{sub x}/SiO{sub 2}/(001)Si substrates, and (111)ITO/(111)Pt/TiO{sub x}/SiO{sub 2}/(001)Si substrates were employed for film growth. In this study, X-ray diffraction measurements including θ–2θ measurements, reciprocal space mappings, and pole figure measurements were used to study the films. The film on (111)ITO//(111)yttria-stabilized zirconia was an (111)-orientated epitaxial film with ferroelectric orthorhombic phase; the film on (111)ITO/(111)Pt/TiO{sub x}/SiO{sub 2}/(001)Si was an (111)-oriented uniaxial textured film with ferroelectricmore » orthorhombic phase; and no preferred orientation was observed for the film on the (111)Pt/TiO{sub x}/SiO{sub 2}/(001)Si substrate, which does not contain ITO. Polarization–hysteresis measurements confirmed that the films on ITO covered substrates had saturated ferroelectric hysteresis loops. A remanent polarization (P{sub r}) of 9.6 and 10.8 μC/cm{sup 2} and coercive fields (E{sub c}) of 1.9 and 2.0 MV/cm were obtained for the (111)-oriented epitaxial and uniaxial textured YHO7 films, respectively. These results demonstrate that the (111)-oriented ITO bottom electrodes play a key role in controlling the orientation and ferroelectricity of the phase formation of the solid films deposited at room temperature.« less

Highly Crystalline C8-BTBT Thin-Film Transistors by Lateral Homo-Epitaxial Growth on Printed Templates.

PubMed

Janneck, Robby; Pilet, Nicolas; Bommanaboyena, Satya Prakash; Watts, Benjamin; Heremans, Paul; Genoe, Jan; Rolin, Cedric

2017-11-01

Highly crystalline thin films of organic semiconductors offer great potential for fundamental material studies as well as for realizing high-performance, low-cost flexible electronics. The fabrication of these films directly on inert substrates is typically done by meniscus-guided coating techniques. The resulting layers show morphological defects that hinder charge transport and induce large device-to-device variability. Here, a double-step method for organic semiconductor layers combining a solution-processed templating layer and a lateral homo-epitaxial growth by a thermal evaporation step is reported. The epitaxial regrowth repairs most of the morphological defects inherent to meniscus-guided coatings. The resulting film is highly crystalline and features a mobility increased by a factor of three and a relative spread in device characteristics improved by almost half an order of magnitude. This method is easily adaptable to other coating techniques and offers a route toward the fabrication of high-performance, large-area electronics based on highly crystalline thin films of organic semiconductors. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Characterization of reclaimed GaAs substrates and investigation of reuse for thin film InGaAlP LED epitaxial growth

DOE Office of Scientific and Technical Information (OSTI.GOV)

Englhard, M.; Klemp, C.; Behringer, M.

This study reports a method to reuse GaAs substrates with a batch process for thin film light emitting diode (TF-LED) production. The method is based on an epitaxial lift-off technique. With the developed reclaim process, it is possible to get an epi-ready GaAs surface without additional time-consuming and expensive grinding/polishing processes. The reclaim and regrowth process was investigated with a one layer epitaxial test structure. The GaAs surface was characterized by an atomic force microscope directly after the reclaim process. The crystal structure of the regrown In{sub 0.5}(Ga{sub 0.45}Al{sub 0.55}){sub 0.5}P (Q{sub 55}) layer was investigated by high resolution x-raymore » diffraction and scanning transmission electron microscopy. In addition, a complete TF-LED grown on reclaimed GaAs substrates was electro-optically characterized on wafer level. The crystal structure of the epitaxial layers and the performance of the TF-LED grown on reclaimed substrates are not influenced by the developed reclaim process. This process would result in reducing costs for LEDs and reducing much arsenic waste for the benefit of a green semiconductor production.« less

Lateral solid phase epitaxy of silicon and application to the fabrication of metal oxide semiconductor field-effect transistors

NASA Astrophysics Data System (ADS)

Greene, Brian Joseph

Thin film silicon on insulator fabrication is an increasingly important technology requirement for improving performance in future generation devices and circuits. One process for SOI fabrication that has recently been generating renewed interest is Lateral Solid Phase Epitaxy (LSPE) of silicon over oxide. This process involves annealing amorphous silicon that has been deposited on oxide patterned Si wafers. The (001) Si substrate forms the crystalline seed for epitaxial growth, permitting the generation of Si films that are both single crystal, and oriented to the substrate. This method is particularly attractive to fabrication that requires low temperature processing, because the Si films are deposited in the amorphous phase at temperatures near 525°C, and crystallized at temperatures near 570°C. It is also attractive for applications requiring three dimensional stacking of active silicon device layers, due to the relatively low temperatures involved. For sub-50 nm gate length MOSFET fabrication, an SOI thickness on the order of 10 nm will be required. One limitation of the LSPE process has been the need for thick films (0.5--2 mum) and/or heavy P doping (10 19--1020 cm-3) to increase the maximum achievable lateral growth distance, and therefore minimize the area on the substrate occupied by seed holes. This dissertation discusses the characterization and optimization of process conditions for large area LSPE silicon film growth, as well as efforts to adapt the traditional LSPE process to achieve ultra-thin SOI layers (Tsilicon ≤ 25 nm) while avoiding the use of heavy active doping layers. MOSFETs fabricated in these films that exhibit electron mobility comparable to the Universal Si MOS Mobility are described.

Non-Implanted Gallium-Arsenide and its Subsequent Annealing Effects.

NASA Astrophysics Data System (ADS)

Liou, Lih-Yeh

Infrared spectroscopy is used to study ion-implanted GaAs and its subsequent annealing effects. The damage in the implantation region causes a change in dielectric constant resulting in an infrared reflection spectrum which shows the interference pattern of a multilayer structure. Reflection data are fitted by values calculated from a physically realistic model by using computer codes. The first part in this work studies the solid state regrowth of amorphous GaAs made by Be implantation at -100(DEGREES)C. The regrowth temperature is around 200(DEGREES)C. The regrowth starts with a narrowing of the transition region and the transformation of the implanted layer from as-implanted amorphous (a-l) state to thermally-stablized amorphous (a-ll) state. The non-epitaxial recrystallization from both the surface and the interfacial region follows. The final regrown layer has a slightly higher refractive index than the crystalline value, indicating a high residual defect concentration. The temperature dependent regrowth velocity and the activation energy for this process are determined. The second part studies the free carrier activation in Be-implanted GaAs. Free holes are activated with prolonged annealing at 400(DEGREES)C ((TURN)50 hours) or a shorter time at higher temperature. The carrier contribution to the dielectric constant is calculated from the classical model and best fit to the reflection results show that the carrier profile can be approximated by a two half-Gaussians joined smoothly at their peaks. The peak position for the profile occurs deeper than that for the Be impurity profile measured by SIMS. The carrier distribution is speculated to be the result of the Be impurity, Ga vacancy and possible compensating defect distributions. The final part studies the free carrier removal by proton implantation in heavily doped, high carrier density, n-type GaAs. The as-implantation region is highly compensated until annealed at 550(DEGREES)C. After annealing between 300 and 400(DEGREES)C, the infrared results show a partially compensated region diffused deeply into substrate from the as-implanted region. The SIMS measurements show a well correlated hydrogen diffusion layer which suggests that the compensation defect is hydrogen related. After 500(DEGREES)C, the hydrogen diffusion layer is still observed, but the compensation layer has disappeared. The diffusion coefficient of the compensating defect and the activation energy for this process are determined. Carbon -implanted GaAs having a high carrier density substrate is also measured and compared with the H-implanted cases. (Copies available exclusively from Micrographics Department, Doheny Library, USC, Los Angeles, CA 90089 -0182.).

Room-temperature codeposition growth technique for pinhole reduction in epitaxial CoSi2 on Si (111)

NASA Technical Reports Server (NTRS)

Lin, T. L.; Fathauer, R. W.; Grunthaner, P. J.; D'Anterroches, C.

1988-01-01

A solid-phase epitaxy has been developed for the growth of CoSi2 films on Si (111) with no observable pinholes (1000/sq cm detection limit). The technique utilizes room-temperature codeposition of Co and Si in stoichiometric ratio, followed by the deposition of an amorphous Si capping layer and subsequent in situ annealing at 550-600 C. CoSi2 films grown without the Si cap are found to have pinhole densities of (1-10) x 10 to the 7th/sq cm when annealed at similar temperatures. A CF4 plasma-etching technique was used to increase the visibility of the pinholes in the silicide layer.

Spontaneous formation of GaN/AlN core-shell nanowires on sapphire by hydride vapor phase epitaxy

NASA Astrophysics Data System (ADS)

Trassoudaine, Agnès; Roche, Elissa; Bougerol, Catherine; André, Yamina; Avit, Geoffrey; Monier, Guillaume; Ramdani, Mohammed Réda; Gil, Evelyne; Castelluci, Dominique; Dubrovskii, Vladimir G.

2016-11-01

Spontaneous GaN/AlN core-shell nanowires with high crystal quality were synthesized on sapphire substrates by vapor-liquid-solid hydride vapor phase epitaxy (VLS-HVPE) without any voluntary aluminum source. Deposition of aluminum is difficult to achieve in this growth technique which uses metal-chloride gaseous precursors: the strong interaction between the AlCl gaseous molecules and the quartz reactor yields a huge parasitic nucleation on the walls of the reactor upstream the substrate. We open up an innovative method to produce GaN/AlN structures by HVPE, thanks to aluminum etching from the sapphire substrate followed by redeposition onto the sidewalls of the GaN core. The paper presents the structural characterization of GaN/AlN core-shell nanowires, speculates on the growth mechanism and discusses a model which describes this unexpected behavior.

Field-temperature phase diagrams of freestanding and substrate-constrained epitaxial Ni-Mn-Ga-Co films for magnetocaloric applications

NASA Astrophysics Data System (ADS)

Diestel, A.; Niemann, R.; Schleicher, B.; Schwabe, S.; Schultz, L.; Fähler, S.

2015-07-01

Ferroic cooling processes that rely on field-induced first-order transformations of solid materials are a promising step towards a more energy-efficient refrigeration technology. In particular, thin films are discussed for their fast heat transfer and possible applications in microsystems. Substrate-constrained films are not useful since their substrates act as a heat sink. In this article, we examine a substrate-constrained and a freestanding epitaxial film of magnetocaloric Ni-Mn-Ga-Co. We compare phase diagrams and entropy changes obtained by magnetic field and temperature scans, which differ. We observe an asymmetry of the hysteresis between heating and cooling branch, which vanishes at high magnetic fields. These effects are discussed with respect to the vector character of a magnetic field, which acts differently on the nucleation and growth processes compared to the scalar character of the temperature.

Material growth and characterization for solid state devices

NASA Technical Reports Server (NTRS)

Collis, Ward J.; Abul-Fadl, Ali; Iyer, Shanthi

1988-01-01

During the period of this research grant, the process of liquid phase electroepitaxy (LPEE) was used to grow ternary and quaternary alloy III-V semiconductor thin films. Selective area growth of InGaAs was performed on InP substrates using a patterned sputtered quartz or spin-on glass layer. The etch back and growth characteristics with respect to substrate orientation were investigated. The etch back behavior is somewhat different from wet chemical etching with respect to the sidewall profiles which are observed. LPEE was also employed to grow epitaxial layers of InGaAsP alloys on InP substrates. The behavior of Mn as an acceptor dopant was investigated with low temperature Hall coefficient and photoluminescence measurements. A metal-organic vapor phase epitaxy system was partially complete within the grant period. This atmospheric pressure system will be used to deposit III-V compound and alloy semiconductor layers in future research efforts.

All zinc-blende GaAs/(Ga,Mn)As core-shell nanowires with ferromagnetic ordering.

PubMed

Yu, Xuezhe; Wang, Hailong; Pan, Dong; Zhao, Jianhua; Misuraca, Jennifer; von Molnár, Stephan; Xiong, Peng

2013-04-10

Combining self-catalyzed vapor-liquid-solid growth of GaAs nanowires and low-temperature molecular-beam epitaxy of (Ga,Mn)As, we successfully synthesized all zinc-blende (ZB) GaAs/(Ga,Mn)As core-shell nanowires on Si(111) substrates. The ZB GaAs nanowire cores are first fabricated at high temperature by utilizing the Ga droplets as the catalyst and controlling the triple phase line nucleation, then the (Ga,Mn)As shells are epitaxially grown on the side facets of the GaAs core at low temperature. The growth window for the pure phase GaAs/(Ga,Mn)As core-shell nanowires is found to be very narrow. Both high-resolution transmission electron microscopy and scanning electron microscopy observations confirm that all-ZB GaAs/(Ga,Mn)As core-shell nanowires with smooth side surface are obtained when the Mn concentration is not more than 2% and the growth temperature is 245 °C or below. Magnetic measurements with different applied field directions provide strong evidence for ferromagnetic ordering in the all-ZB GaAs/(Ga,Mn)As nanowires. The hybrid nanowires offer an attractive platform to explore spin transport and device concepts in fully epitaxial all-semiconductor nanospintronic structures.

Thermoelectric properties of epitaxial β-FeSi2 thin films grown on Si(111) substrates with various film qualities

NASA Astrophysics Data System (ADS)

Watanabe, Kentaro; Taniguchi, Tatsuhiko; Sakane, Shunya; Aoki, Shunsuke; Suzuki, Takeyuki; Fujita, Takeshi; Nakamura, Yoshiaki

2017-05-01

Si-based epitaxial β-FeSi2 thin films are attractive as materials for on-chip thermoelectric power generators. We investigated the structure, crystallinity, and thermoelectric properties of β-FeSi2 thin films epitaxially grown on Si(111) substrates by using three different techniques: conventional reactive deposition epitaxy followed by molecular beam epitaxy (RDE+MBE), solid phase epitaxy (SPE) based on codeposition of Fe and Si presented previously, and SPE followed by MBE (SPE+MBE) presented newly by this work. Their epitaxial growth temperatures were fixed at 530 °C for comparison. RDE+MBE thin films exhibited high crystalline quality, but rough surfaces and rugged β-FeSi2/Si(111) interfaces. On the other hand, SPE thin films showed flat surfaces and abrupt β-FeSi2/Si(111) interfaces but low crystallinity. We found that SPE+MBE thin films realized crystallinity higher than SPE thin films, and also had flatter surfaces and sharper interfaces than RDE+MBE thin films. In SPE+MBE thin film growth, due to the initial SPE process with low temperature codeposition, thermal interdiffusion of Fe and Si was suppressed, resulting in the surface flatness and abrupt interface. Second high temperature MBE process improved the crystallinity. We also investigated thermoelectric properties of these β-FeSi2 thin films. Structural factors affecting the thermoelectric properties of RDE+MBE, SPE, and SPE+MBE thin films were investigated.

Nanometre-thick single-crystalline nanosheets grown at the water-air interface

NASA Astrophysics Data System (ADS)

Wang, Fei; Seo, Jung-Hun; Luo, Guangfu; Starr, Matthew B.; Li, Zhaodong; Geng, Dalong; Yin, Xin; Wang, Shaoyang; Fraser, Douglas G.; Morgan, Dane; Ma, Zhenqiang; Wang, Xudong

2016-01-01

To date, the preparation of free-standing 2D nanomaterials has been largely limited to the exfoliation of van der Waals solids. The lack of a robust mechanism for the bottom-up synthesis of 2D nanomaterials from non-layered materials has become an obstacle to further explore the physical properties and advanced applications of 2D nanomaterials. Here we demonstrate that surfactant monolayers can serve as soft templates guiding the nucleation and growth of 2D nanomaterials in large area beyond the limitation of van der Waals solids. One- to 2-nm-thick, single-crystalline free-standing ZnO nanosheets with sizes up to tens of micrometres are synthesized at the water-air interface. In this process, the packing density of surfactant monolayers adapts to the sub-phase metal ions and guides the epitaxial growth of nanosheets. It is thus named adaptive ionic layer epitaxy (AILE). The electronic properties of ZnO nanosheets and AILE of other materials are also investigated.

Electrical properties of solid-solution SrZrxTi1-xO3 grown epitaxially on Ge by molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Moghadam, Reza; Ahmadi, Kamyar; Xiao, Z.-Y.; Hong, Xia; Ngai, Joseph

The epitaxial growth of crystalline oxides on semiconductors enables new functionalities to be introduced to semiconductor devices. In particular, dielectric and ferroelectric oxides grown epitaxially on semiconductors provide a pathway to realize ultra-low power logic and memory devices. Here we present electrical characterization of solid-solution SrZrxTi1-xO3 grown epitaxially on Ge through oxide molecular beam epitaxy. SrZrxTi1-xO3 is of particular interest since the band offset with respect to the semiconductor can be tuned through Zr content x. We will present current-voltage, capacitance-voltage and piezoforce microscopy characterization of SrZrxTi1-xO3 -Ge heterojunctions. In particular, we will discuss how the electrical characteristics of SrZrxTi1-xO3 -Ge heterojunctions evolve with respect to composition, annealing and film thickness.

Wafer-Fused Orientation-Patterned GaAs

DTIC Science & Technology

2008-02-13

frequencies utilizing existing industrial foundries. 15. SUBJECT TERMS Orientation-patterned Gallium Arsenide, hydride vapor phase epitaxy, quasi-phase... Gallium Arsenide, hydride vapor phase epitaxy, quasi-phase-matching, nonlinear frequency conversion 1. INTRODUCTION Quasi-phase-matching (QPM)1...and E. Lallier, “Second harmonic generation of CO2 laser using thick quasi-phase-matched GaAs layer grown by hydride vapour phase epitaxy

Treatment of clinical solid waste using a steam autoclave as a possible alternative technology to incineration.

PubMed

Hossain, Md Sohrab; Balakrishnan, Venugopal; Rahman, Nik Norulaini Nik Ab; Sarker, Md Zaidul Islam; Kadir, Mohd Omar Ab

2012-03-01

A steam autoclave was used to sterilize bacteria in clinical solid waste in order to determine an alternative to incineration technology in clinical solid waste management. The influence of contact time (0, 5, 15, 30 and 60 min) and temperature (111 °C, 121 °C and 131 °C) at automated saturated steam pressure was investigated. Results showed that with increasing contact time and temperature, the number of surviving bacteria decreased. The optimum experimental conditions as measured by degree of inactivation of bacteria were 121 °C for 15 minutes (min) for Gram negative bacteria, 121 °C and 131 °C for 60 and 30 min for Gram positive bacteria, respectively. The re-growth of bacteria in sterilized waste was also evaluated in the present study. It was found that bacterial re-growth started two days after the inactivation. The present study recommends that the steam autoclave cannot be considered as an alternative technology to incineration in clinical solid waste management.

Treatment of Clinical Solid Waste Using a Steam Autoclave as a Possible Alternative Technology to Incineration

PubMed Central

Hossain, Md. Sohrab; Balakrishnan, Venugopal; Rahman, Nik Norulaini Nik Ab; Sarker, Md. Zaidul Islam; Kadir, Mohd Omar Ab

2012-01-01

A steam autoclave was used to sterilize bacteria in clinical solid waste in order to determine an alternative to incineration technology in clinical solid waste management. The influence of contact time (0, 5, 15, 30 and 60 min) and temperature (111 °C, 121 °C and 131 °C) at automated saturated steam pressure was investigated. Results showed that with increasing contact time and temperature, the number of surviving bacteria decreased. The optimum experimental conditions as measured by degree of inactivation of bacteria were 121 °C for 15 minutes (min) for Gram negative bacteria, 121 °C and 131 °C for 60 and 30 min for Gram positive bacteria, respectively. The re-growth of bacteria in sterilized waste was also evaluated in the present study. It was found that bacterial re-growth started two days after the inactivation. The present study recommends that the steam autoclave cannot be considered as an alternative technology to incineration in clinical solid waste management. PMID:22690168

Potential Regrowth and Recolonization of Salmonellae and Indicators in Biosolids and Biosolid-Amended Soil

PubMed Central

Zaleski, Kathleen J.; Josephson, Karen L.; Gerba, Charles P.; Pepper, Ian L.

2005-01-01

This study evaluated the potential for conversion of Class B to Class A biosolids with respect to salmonellae and fecal coliforms during solar drying in concrete lined drying beds. Anaerobically (8% solids) and aerobically (2% solids) digested Class B biosolids were pumped into field-scale drying beds, and microbial populations and environmental conditions were monitored. Numbers of fecal coliforms and salmonellae decreased as temperature and rate of desiccation increased. After 3 to 4 weeks, Class A requirements were achieved in both biosolids for the pathogens and the indicators. However, following rainfall events, significant increase in numbers was observed for both fecal coliforms and salmonellae. In laboratory studies, regrowth of fecal coliforms was observed in both biosolids and biosolid-amended soil, but the regrowth of salmonellae observed in the concrete-lined drying beds did not occur. These laboratory studies demonstrated that pathogens decreased in numbers when soil was amended with biosolids. Based on serotyping, the increased numbers of salmonellae seen in the concrete lined drying beds following rainfall events was most likely due to recolonization due to contamination from fecal matter introduced by animals and not from regrowth of salmonellae indigenous to biosolids. Overall, we conclude that the use of concrete-lined beds created a situation in which moisture added as rainfall accumulated in the beds, promoting the growth of fecal coliforms and salmonellae added from external sources. PMID:16000779

Coherent Charge Transport in Ballistic InSb Nanowire Josephson Junctions

PubMed Central

Li, S.; Kang, N.; Fan, D. X.; Wang, L. B.; Huang, Y. Q.; Caroff, P.; Xu, H. Q.

2016-01-01

Hybrid InSb nanowire-superconductor devices are promising for investigating Majorana modes and topological quantum computation in solid-state devices. An experimental realisation of ballistic, phase-coherent superconductor-nanowire hybrid devices is a necessary step towards engineering topological superconducting electronics. Here, we report on a low-temperature transport study of Josephson junction devices fabricated from InSb nanowires grown by molecular-beam epitaxy and provide a clear evidence for phase-coherent, ballistic charge transport through the nanowires in the junctions. We demonstrate that our devices show gate-tunable proximity-induced supercurrent and clear signatures of multiple Andreev reflections in the differential conductance, indicating phase-coherent transport within the junctions. We also observe periodic modulations of the critical current that can be associated with the Fabry-Pérot interference in the nanowires in the ballistic transport regime. Our work shows that the InSb nanowires grown by molecular-beam epitaxy are of excellent material quality and hybrid superconducting devices made from these nanowires are highly desirable for investigation of the novel physics in topological states of matter and for applications in topological quantum electronics. PMID:27102689

Sb-Based n- and p-Channel Heterostructure FETs for High-Speed, Low-Power Applications

DTIC Science & Technology

2008-07-01

Laboratory are presented. 2. InAlSb/InAs HEMTs The HEMT material was grown by solid-source molecu- lar beam epitaxy (MBE) on a semi-insulating (100) GaAs...and S.Y. Lin, “Strained quantum well modulation-doped InGaSb/AlGaSb struc- tures grown by molecular beam epitaxy ,” J. Electron. Mater., vol.22, no.3...where he majored in solid state physics and researched growth by molecular - beam epitaxy (MBE) of certain compound semiconductor ma- terials. Since

Hybrid tunnel junction contacts to III-nitride light-emitting diodes

NASA Astrophysics Data System (ADS)

Young, Erin C.; Yonkee, Benjamin P.; Wu, Feng; Oh, Sang Ho; DenBaars, Steven P.; Nakamura, Shuji; Speck, James S.

2016-02-01

In this work, we demonstrate highly doped GaN p-n tunnel junction (TJ) contacts on III-nitride heterostructures where the active region of the device and the top p-GaN layers were grown by metal organic chemical vapor deposition and highly doped n-GaN was grown by NH3 molecular beam epitaxy to form the TJ. The regrowth interface in these hybrid devices was found to have a high concentration of oxygen, which likely enhanced tunneling through the diode. For optimized regrowth, the best tunnel junction device had a total differential resistivity of 1.5 × 10-4 Ω cm2, including contact resistance. As a demonstration, a blue-light-emitting diode on a (20\\bar{2}\\bar{1}) GaN substrate with a hybrid tunnel junction and an n-GaN current spreading layer was fabricated and compared with a reference sample with a transparent conducting oxide (TCO) layer. The tunnel junction LED showed a lower forward operating voltage and a higher efficiency at a low current density than the TCO LED.

Phosphor-Free Apple-White LEDs with Embedded Indium-Rich Nanostructures Grown on Strain Relaxed Nano-epitaxy GaN.

PubMed

Soh, C B; Liu, W; Yong, A M; Chua, S J; Chow, S Y; Tripathy, S; Tan, R J N

2010-08-01

Phosphor-free apple-white light emitting diodes have been fabricated using a dual stacked InGaN/GaN multiple quantum wells comprising of a lower set of long wavelength emitting indium-rich nanostructures incorporated in multiple quantum wells with an upper set of cyan-green emitting multiple quantum wells. The light-emitting diodes were grown on nano-epitaxially lateral overgrown GaN template formed by regrowth of GaN over SiO(2) film patterned with an anodic aluminum oxide mask with holes of 125 nm diameter and a period of 250 nm. The growth of InGaN/GaN multiple quantum wells on these stress relaxed low defect density templates improves the internal quantum efficiency by 15% for the cyan-green multiple quantum wells. Higher emission intensity with redshift in the PL peak emission wavelength is obtained for the indium-rich nanostructures incorporated in multiple quantum wells. The quantum wells grown on the nano-epitaxially lateral overgrown GaN has a weaker piezoelectric field and hence shows a minimal peak shift with application of higher injection current. An enhancement of external quantum efficiency is achieved for the apple-white light emitting diodes grown on the nano-epitaxially lateral overgrown GaN template based on the light -output power measurement. The improvement in light extraction efficiency, η(extraction,) was found to be 34% for the cyan-green emission peak and 15% from the broad long wavelength emission with optimized lattice period.

Phosphor-Free Apple-White LEDs with Embedded Indium-Rich Nanostructures Grown on Strain Relaxed Nano-epitaxy GaN

NASA Astrophysics Data System (ADS)

Soh, C. B.; Liu, W.; Yong, A. M.; Chua, S. J.; Chow, S. Y.; Tripathy, S.; Tan, R. J. N.

2010-11-01

Phosphor-free apple-white light emitting diodes have been fabricated using a dual stacked InGaN/GaN multiple quantum wells comprising of a lower set of long wavelength emitting indium-rich nanostructures incorporated in multiple quantum wells with an upper set of cyan-green emitting multiple quantum wells. The light-emitting diodes were grown on nano-epitaxially lateral overgrown GaN template formed by regrowth of GaN over SiO2 film patterned with an anodic aluminum oxide mask with holes of 125 nm diameter and a period of 250 nm. The growth of InGaN/GaN multiple quantum wells on these stress relaxed low defect density templates improves the internal quantum efficiency by 15% for the cyan-green multiple quantum wells. Higher emission intensity with redshift in the PL peak emission wavelength is obtained for the indium-rich nanostructures incorporated in multiple quantum wells. The quantum wells grown on the nano-epitaxially lateral overgrown GaN has a weaker piezoelectric field and hence shows a minimal peak shift with application of higher injection current. An enhancement of external quantum efficiency is achieved for the apple-white light emitting diodes grown on the nano-epitaxially lateral overgrown GaN template based on the light -output power measurement. The improvement in light extraction efficiency, ηextraction, was found to be 34% for the cyan-green emission peak and 15% from the broad long wavelength emission with optimized lattice period.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Saidov, A. S., E-mail: amin@uzsci.net; Usmonov, Sh. N., E-mail: sh-usmonov@rambler.ru; Saidov, M. S.

(Si{sub 2}){sub 1−x−y}(Ge{sub 2}){sub x}(GaAs){sub y} substitutional solid solutions (0 ≤ x ≤ 0.91, 0 ≤ y ≤ 0.94) are grown by liquid-phase epitaxy from a Pb-based solution-melt on Si substrates with the (111) crystallographic orientation. The chemical composition of the epitaxial films is studied by X-rays probe microanalysis, and the distribution profile of solid solution components is determined. Spectral dependences of the photosensitivity and photoluminescence of the n-Si-p(Si{sub 2}){sub 1−x−y}(Ge{sub 2}){sub x}(GaAs){sub y} heterostructures are studied at room and liquid-nitrogen temperatures. Two maxima are found in the photoluminescence spectra of the (Si{sub 2}){sub 1−x−y}(Ge{sub 2}){sub x}(GaAs){sub y} films (0more » ≤ x ≤ 0.91, 0 ≤ y ≤ 0.94) against the background of a broad emission spectrum. The fundamental maximum with an energy of 1.45 eV is caused by the band-to-band recombination of solid solution carriers, and an additional maximum with an energy of 1.33 eV is caused by the recombination of carriers with the participation of impurity levels of the Si-Si bond (Si{sub 2} is covalently coupled with the tetrahedral lattice of the solid solution host)« less

Hyperdoping silicon with selenium: solid vs. liquid phase epitaxy

PubMed Central

Zhou, Shengqiang; Liu, Fang; Prucnal, S.; Gao, Kun; Khalid, M.; Baehtz, C.; Posselt, M.; Skorupa, W.; Helm, M.

2015-01-01

Chalcogen-hyperdoped silicon shows potential applications in silicon-based infrared photodetectors and intermediate band solar cells. Due to the low solid solubility limits of chalcogen elements in silicon, these materials were previously realized by femtosecond or nanosecond laser annealing of implanted silicon or bare silicon in certain background gases. The high energy density deposited on the silicon surface leads to a liquid phase and the fast recrystallization velocity allows trapping of chalcogen into the silicon matrix. However, this method encounters the problem of surface segregation. In this paper, we propose a solid phase processing by flash-lamp annealing in the millisecond range, which is in between the conventional rapid thermal annealing and pulsed laser annealing. Flash lamp annealed selenium-implanted silicon shows a substitutional fraction of ~ 70% with an implanted concentration up to 2.3%. The resistivity is lower and the carrier mobility is higher than those of nanosecond pulsed laser annealed samples. Our results show that flash-lamp annealing is superior to laser annealing in preventing surface segregation and in allowing scalability. PMID:25660096

Manganese-calcium intermixing facilitates heteroepitaxial growth at the (1014) calcite-water interface

DOE PAGES

Xu, Man; Riechers, Shawn L.; Ilton, Eugene S.; ...

2017-09-05

For this research, in situ atomic force microscopy (AFM) measurements were performed to probe surface precipitates that formed on the (10more » $$\\bar{1}$$4) surface of calcite (CaCO 3) single crystals following reaction with Mn2 +-bearing aqueous solutions. Three-dimensional epitaxial islands were observed to precipitate and grow on the surfaces. In situ time-sequenced measurements demonstrated that the growth rates were commensurate with those obtained for epitaxial islands formed on calcite crystals reacted with Cd2 +-bearing aqueous solutions of the same range in supersaturation with respect to the pure metal carbonate phase. This finding was unexpected as rhodochrosite (MnCO 3) and calcite display a 10% lattice mismatch, based on the area of their (10$$\\bar{1}$$4) surface unit cells, whereas the lattice mismatch is only 4% for otavite (CdCO 3) and calcite. Coatings of varying thicknesses were therefore synthesized by reacting calcite single crystals in calcite-equilibrated aqueous solutions with up to 250 μM MnCl 2. Ex situ X-ray photoelectron spectroscopy (XPS), scanning transmission electron microscopy (STEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), X-ray reflectivity (XRR), and AFM measurements of the reacted crystals demonstrated the formation of an epitaxial (Mn,Ca)CO 3 solid solution. The epitaxial solid solution had a spatially complex composition, whereby the first few nanometers were rich in Ca and the Mn content increased with distance from the original calcite surface, culminating in a topmost region of almost pure MnCO 3 for the thickest coatings. The effective lattice mismatch was therefore much smaller than the nominal mismatch thus explaining the measured growth rates. Lastly, these findings highlight the strong influence played by the substrate on the composition of surface precipitates in aqueous conditions.« less

Semiconductor Laser Diode Arrays by MOCVD (Metalorganic Chemical Vapor Deposition)

DTIC Science & Technology

1987-09-01

laser diode arrays are intended to be used as an optical pump for solid state yttrium aluminum garnet (YAG) lasers. In particular, linear uniform...corresponds to about . , 8080A. Such thin layer structures, while difficult to grow by such conventional growth methods as liquid phase epitaxy ( LPE ...lower yet than for DH lasers grown by LPE . , - Conventional self-aligned stripe laser This structure is formed by growing (on an n-type GaAs substrate

Dislocations limited electronic transport in hydride vapour phase epitaxy grown GaN templates: A word of caution for the epitaxial growers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chatterjee, Abhishek, E-mail: cabhishek@rrcat.gov.in; Khamari, Shailesh K.; Kumar, R.

2015-01-12

GaN templates grown by hydride vapour phase epitaxy (HVPE) and metal organic vapour phase epitaxy (MOVPE) techniques are compared through electronic transport measurements. Carrier concentration measured by Hall technique is about two orders larger than the values estimated by capacitance voltage method for HVPE templates. It is learnt that there exists a critical thickness of HVPE templates below which the transport properties of epitaxial layers grown on top of them are going to be severely limited by the density of charged dislocations lying at layer-substrate interface. On the contrary MOVPE grown templates are found to be free from such limitations.

Synthesis of high-oxidation Y-Ba-Cu-O phases in superoxygenated thin films

NASA Astrophysics Data System (ADS)

Zhang, H.; Gauquelin, N.; McMahon, C.; Hawthorn, D. G.; Botton, G. A.; Wei, J. Y. T.

2018-03-01

It is known that solid-state reaction in high-pressure oxygen can stabilize high-oxidation phases of Y-Ba-Cu-O superconductors in powder form. We extend this superoxygenation concept of synthesis to thin films which, due to their large surface-to-volume ratio, are more reactive thermodynamically. Epitaxial thin films of YBa2Cu3O7 -δ grown by pulsed laser deposition are annealed at up to 700 atm O2 and 900 ∘C , in conjunction with Cu enrichment by solid-state diffusion. The films show the clear formation of Y2Ba4Cu7O15 -δ and Y2Ba4Cu8O16 as well as regions of YBa2Cu5O9 -δ and YBa2Cu6O10 -δ phases, according to scanning transmission electron microscopy, x-ray diffraction, and x-ray absorption spectroscopy. Similarly annealed YBa2Cu3O7 -δ powders show no phase conversion. Our results demonstrate a route of synthesis towards discovering more complex phases of cuprates and other superconducting oxides.

Pixel switching of epitaxial Pd/YHx/CaF2 switchable mirrors

PubMed

Kerssemakers; van der Molen SJ; Koeman; Gunther; Griessen

2000-08-03

Exposure of rare-earth films to hydrogen can induce a metal-insulator transition, accompanied by pronounced optical changes. This 'switchable mirror' effect has received considerable attention from theoretical, experimental and technological points of view. Most systems use polycrystalline films, but the synthesis of yttrium-based epitaxial switchable mirrors has also been reported. The latter form an extended self-organized ridge network during initial hydrogen loading, which results in the creation of micrometre-sized triangular domains. Here we observe homogeneous and essentially independent optical switching of individual domains in epitaxial switchable mirrors during hydrogen absorption. The optical switching is accompanied by topographical changes as the domains sequentially expand and contract; the ridges block lateral hydrogen diffusion and serve as a microscopic lubricant for the domain oscillations. We observe the correlated changes in topology and optical properties using in situ atomic force and optical microscopy. Single-domain phase switching is not observed in polycrystalline films, which are optically homogeneous. The ability to generate a tunable, dense pattern of switchable pixels is of technological relevance for solid-state displays based on switchable mirrors.

Surface processes in OMVPE the frontiers

NASA Astrophysics Data System (ADS)

Stringfellow, G. B.; Shurtleff, J. K.; Lee, R. T.; Fetzer, C. M.; Jun, S. W.

2000-12-01

Surface processes have long been known to be an important part of any epitaxial growth process. These processes are closely linked to the surface structure. However, until recently, the surface structure and the surface processes were difficult to study experimentally for conventional vapor-phase epitaxy (VPE) and liquid-phase epitaxy. Recently, optical techniques such as surface photo absorption (SPA) have been developed to the point that they give useful information about the surface reconstruction in situ during organometallic vapor-phase epitaxial (OMVPE) growth. Thus, they can in many cases be used to monitor the surface processes. A powerful method for controlling the surface structure during epitaxial growth using surfactants has recently emerged. This work describes the use of the surfactants Te, a donor, and As, Sb, and Bi, elements that are isoelectronic with P, on the properties of GaInP grown by OMVPE. These surfactants are found to significantly affect the microscopic arrangement of Ga and In atoms in the bulk solid by effecting a change in the surface structure. CuPt ordering is ubiquitous in III/V semiconductor alloys. It is significant because of the dependence of bandgap energy on the degree of order. The CuPt structure is formed due to the strain induced by the formation of [ 1¯ 1 0] P dimers on the surface. Each of the surfactants studied is found to result in disordering for layers grown using conditions that would otherwise produce highly ordered GaInP. Te yields disordered material with no change in the SPA spectra. However, the step velocity is found to increased markedly. Thus, the effect appears to be kinetic. Sb causes disordering due to a replacement of [ 1¯ 1 0] P dimers on the nominally (0 0 1) surface by larger Sb dimers, which reduces the strain-induced driving force for CuPt ordering at the surface. Thus, the effect is due to surface thermodynamics. For high Sb concentrations in the vapor, a triple-period ordered structure is formed. The appearance of this phase coincides with a distinct change in the surface reconstruction as indicated by SPA spectroscopy. Modulation of the TESb flow rate during growth was used to produce an abrupt order/disorder heterostructure with a bandgap energy difference of 135 meV with no significant change in solid composition at the interface. SPA results show that addition of As during growth also reduces the degree of order by displacing some of the [ 1¯ 1 0] P dimers on the surface. In this case, significant As concentrations in the solid of a few percent are observed. Thus, As is not an effective surfactant. Addition of Bi during growth results in a change in the surface reconstruction, as indicated by SPA spectroscopy, for Bi concentrations producing disordered GaInP. Unlike Sb and As, the Bi also causes a marked increase in the step velocity coincident with the loss of order. For singular (001) substrates, island formation is suppressed by Bi, resulting in the growth of much smoother layers. Modulation of the TMBi concentration during growth has been used to produce disorder/order heterostructures. The use of isoelectronic surfactants during growth to influence the properties of a semiconducting solid is a new and exciting development in control of the OMVPE growth process. It is expected that the use of isoelectronic surfactants to determine the surface reconstruction will find application in the growth of complex device structures. It also appears likely that this will be useful for controlling other characteristics of the growth process and the properties of the resultant semiconductor materials.

Carry over effects of nutrient addition on the recovery of an invasive seaweed from the winter die-back.

PubMed

Uyà, Marc; Maggi, Elena; Mori, Giovanna; Nuccio, Caterina; Gribben, Paul E; Bulleri, Fabio

2017-05-01

Nutrient enrichment of coastal waters can enhance the invasibility and regrowth of non-native species. The invasive alga Caulerpa cylindracea has two distinct phases: a well-studied fast-growing summer phase, and a winter latent phase. To investigate the effects of nutrient enrichment on the regrowth of the seaweed after the winter resting-phase, a manipulative experiment was carried out in intertidal rockpools in the North-western Mediterranean. Nutrients were supplied under different temporal regimes: press (constant release from January to May), winter pulse (January to March) and spring pulse (March to May). Independently from the temporal characteristics of their addition, nutrients accelerated the re-growth of C. cylindracea after the winter die-back, resulting in increased percentage covers at the peak of the growing season. Nutrient addition did not influence the number and length of fronds and the biomass. Native components of the algal community did not respond to nutrient additions. Our results show that nutrient supply can favour the spread of C. cylindracea even when occurring at a time of the year at which the seaweed is not actively growing. Copyright © 2017 Elsevier Ltd. All rights reserved.

Fabrication of Ni-silicide/Si heterostructured nanowire arrays by glancing angle deposition and solid state reaction.

PubMed

Hsu, Hsun-Feng; Huang, Wan-Ru; Chen, Ting-Hsuan; Wu, Hwang-Yuan; Chen, Chun-An

2013-05-10

This work develops a method for growing Ni-silicide/Si heterostructured nanowire arrays by glancing angle Ni deposition and solid state reaction on ordered Si nanowire arrays. Samples of ordered Si nanowire arrays were fabricated by nanosphere lithography and metal-induced catalytic etching. Glancing angle Ni deposition deposited Ni only on the top of Si nanowires. When the annealing temperature was 500°C, a Ni3Si2 phase was formed at the apex of the nanowires. The phase of silicide at the Ni-silicide/Si interface depended on the diameter of the Si nanowires, such that epitaxial NiSi2 with a {111} facet was formed at the Ni-silicide/Si interface in Si nanowires with large diameter, and NiSi was formed in Si nanowires with small diameter. A mechanism that is based on flux divergence and a nucleation-limited reaction is proposed to explain this phenomenon of size-dependent phase formation.

Fabrication of Ni-silicide/Si heterostructured nanowire arrays by glancing angle deposition and solid state reaction

PubMed Central

2013-01-01

This work develops a method for growing Ni-silicide/Si heterostructured nanowire arrays by glancing angle Ni deposition and solid state reaction on ordered Si nanowire arrays. Samples of ordered Si nanowire arrays were fabricated by nanosphere lithography and metal-induced catalytic etching. Glancing angle Ni deposition deposited Ni only on the top of Si nanowires. When the annealing temperature was 500°C, a Ni3Si2 phase was formed at the apex of the nanowires. The phase of silicide at the Ni-silicide/Si interface depended on the diameter of the Si nanowires, such that epitaxial NiSi2 with a {111} facet was formed at the Ni-silicide/Si interface in Si nanowires with large diameter, and NiSi was formed in Si nanowires with small diameter. A mechanism that is based on flux divergence and a nucleation-limited reaction is proposed to explain this phenomenon of size-dependent phase formation. PMID:23663726

A comparative study of disinfection efficiency and regrowth control of microorganism in secondary wastewater effluent using UV, ozone, and ionizing irradiation process.

PubMed

Lee, O-Mi; Kim, Hyun Young; Park, Wooshin; Kim, Tae-Hun; Yu, Seungho

2015-09-15

Ionizing radiation technology was suggested as an alternative method to disinfection processes, such as chlorine, UV, and ozone. Although many studies have demonstrated the effectiveness of irradiation technology for microbial disinfection, there has been a lack of information on comparison studies of disinfection techniques and a regrowth of each treatment. In the present study, an ionizing radiation was investigated to inactivate microorganisms and to determine the critical dose to prevent the regrowth. As a result, it was observed that the disinfection efficiency using ionizing radiation was not affected by the seasonal changes of wastewater characteristics, such as temperature and turbidity. In terms of bacterial regrowth after disinfection, the ionizing radiation showed a significant resistance of regrowth, whereas, on-site UV treatment is influenced by the suspended solid, temperature, or precipitation. The electric power consumption was also compared for the economic feasibility of each technique at a given value of disinfection efficiency of 90% (1-log), showing 0.12, 36.80, and 96.53 Wh/(L/day) for ionizing radiation, ozone, and UV, respectively. The ionizing radiation requires two or three orders of magnitude lower power consumption than UV and ozone. Consequently, ionizing radiation can be applied as an effective and economical alternative technique to other conventional disinfection processes. Copyright © 2015 Elsevier B.V. All rights reserved.

Suppression of Mg propagation into subsequent layers grown by MOCVD

NASA Astrophysics Data System (ADS)

Agarwal, Anchal; Tahhan, Maher; Mates, Tom; Keller, Stacia; Mishra, Umesh

2017-01-01

Low temperature (LT) flow modulation epitaxy (FME) or "pulsed" growth was successfully used to prevent magnesium from Metalorganic Chemical Vapor Deposition (MOCVD) grown p-GaN:Mg layers riding into subsequently deposited n-type layers. Mg concentration in the subsequent layers was lowered from ˜1 × 1018 cm-3 for a medium temperature growth at 950 °C to ˜1 × 1016 cm-3 for a low temperature growth at 700 °C via FME. The slope of the Mg concentration drop in the 700 °C FME sample was 20 nm/dec—the lowest ever demonstrated by MOCVD. For growth on Mg implanted GaN layers, the drop for a medium temperature regrowth at 950 °C was ˜10 nm/dec compared to >120 nm/dec for a high temperature regrowth at 1150 °C. This drop-rate obtained at 950 °C or lower was maintained even when the growth temperature in the following layers was raised to 1150 °C. A controlled silicon doping series using LT FME was also demonstrated with the lowest and highest achieved doping levels being 5 × 1016 cm-3 and 6 × 1019 cm-3, respectively.

Polarity-inverted lateral overgrowth and selective wet-etching and regrowth (PILOSWER) of GaN.

PubMed

Jang, Dongsoo; Jue, Miyeon; Kim, Donghoi; Kim, Hwa Seob; Lee, Hyunkyu; Kim, Chinkyo

2018-03-07

On an SiO 2 -patterned c-plane sapphire substrate, GaN domains were grown with their polarity controlled in accordance with the pattern. While N-polar GaN was grown on hexagonally arranged circular openings, Ga-polar GaN was laterally overgrown on mask regions due to polarity inversion occurring at the boundary of the circular openings. After etching of N-polar GaN on the circular openings by H 3 PO 4 , this template was coated with 40-nm Si by sputtering and was slightly etched by KOH. After slight etching, a thin layer of Si left on the circular openings of sapphire,but not on GaN, was oxidized during thermal annealing and served as a dielectric mask during subsequent regrowth. Thus, the subsequent growth of GaN was made only on the existing Ga-polar GaN domains, not on the circular openings of the sapphire substrate. Transmission electron microscopy analysis revealed no sign of threading dislocations in this film. This approach may help fabricating an unholed and merged GaN film physically attached to but epitaxially separated from the SiO 2 -patterned sapphire.

Synthesis of nanostructures in nanowires using sequential catalyst reactions

DOE PAGES

Panciera, F.; Chou, Y. -C.; Reuter, M. C.; ...

2015-07-13

Nanowire growth by the vapour–liquid–solid (VLS) process enables a high level of control over nanowire composition, diameter, growth direction, branching and kinking, periodic twinning, and crystal structure. The tremendous impact of VLS-grown nanowires is due to this structural versatility, generating applications ranging from solid-state lighting and single-photon sources to thermoelectric devices. Here, we show that the morphology of these nanostructures can be further tailored by using the liquid droplets that catalyse nanowire growth as a ‘mixing bowl’, in which growth materials are sequentially supplied to nucleate new phases. Growing within the liquid, these phases adopt the shape of faceted nanocrystalsmore » that are then incorporated into the nanowires by further growth. Furthermore, we demonstrate this concept by epitaxially incorporating metal-silicide nanocrystals into Si nanowires with defect-free interfaces, and discuss how this process can be generalized to create complex nanowire-based heterostructures.« less

Synthesis of nanostructures in nanowires using sequential catalyst reactions

PubMed Central

Panciera, F.; Chou, Y.-C.; Reuter, M.C.; Zakharov, D.; Stach, E.A.; Hofmann, S.; Ross, F.M.

2016-01-01

Nanowire growth by the vapor-liquid-solid process enables a high level of control over nanowire composition, diameter, growth direction, branching and kinking, periodic twinning, and crystal structure. The tremendous impact of VLS-grown nanowires is due to this structural versatility, generating applications ranging from solid state lighting and single photon sources to thermoelectric devices. Here we show that the morphology of these nanostructures can be further tailored by using the liquid droplets that catalyze nanowire growth as a “mixing bowl”, in which growth materials are sequentially supplied to nucleate new phases. Growing within the liquid, these phases adopt the shape of faceted nanocrystals that are then incorporated into the nanowires by further growth. We demonstrate this concept by epitaxially incorporating metal silicide nanocrystals into Si nanowires with defect-free interfaces, and discuss how this process can be generalized to create complex nanowire-based heterostructures. PMID:26168344

OM-VPE growth of Mg-doped GaAs. [OrganoMetallic-Vapor Phase Epitaxy

NASA Technical Reports Server (NTRS)

Lewis, C. R.; Dietze, W. T.; Ludowise, M. J.

1982-01-01

The epitaxial growth of Mg-doped GaAs by the organometallic vapor phase epitaxial process (OM-VPE) has been achieved for the first time. The doping is controllable over a wide range of input fluxes of bis (cyclopentadienyl) magnesium, (C5H5)2Mg, the organometallic precursor to Mg.

The effect of surfactants on epitaxial growth of gallium nitride from gas phase in the Ga-HCl-NH3-H2-Ar system

NASA Astrophysics Data System (ADS)

Zhilyaev, Yu. V.; Zelenin, V. V.; Orlova, T. A.; Panteleev, V. N.; Poletaev, N. K.; Rodin, S. N.; Snytkina, S. A.

2015-05-01

We have studied epitaxial layers of gallium nitride (GaN) in a template composition grown by surfactant-mediated hydride-chloride vapor phase epitaxy. The surfactant component was provided by 5 mass % additives of antimony and indium to the source of gallium. Comparative analysis of the obtained results shows evidence of the positive influence of surfactants on the morphology of epitaxial GaN layers.

High Power Mid Wave Infrared Semiconductor Lasers

DTIC Science & Technology

2006-06-15

resonance and the gain spectrum. The devices were grown using solid source molecular beam epitaxy (MBE) in a V80 reactor. Two side polished, undoped...verify the inherent low activation energy. N-type and P-type AISb, and various compositions of InxAl 1xSb, were grown by solid-source molecular beam ...level monitoring. Advances in epitaxial growth of semiconductor materials have allowed the development of Arsenic- free optically-pumped MWIR lasers on

Inverted Al0.25Ga0.75N/GaN ultraviolet p-i-n photodiodes formed on p-GaN template layer grown by metalorganic vapor phase epitaxy

NASA Astrophysics Data System (ADS)

Chang, Kuo-Hua; Sheu, Jinn-Kong; Lee, Ming-Lun; Tu, Shang-Ju; Yang, Chih-Ciao; Kuo, Huan-Shao; Yang, J. H.; Lai, Wei-Chih

2010-07-01

Inverted Al0.25Ga0.75N/GaN ultraviolet (UV) p-i-n photodiodes (PDs) were grown by selective-area regrowth on p-GaN template. The inverted devices with low-resistivity n-type AlGaN top-contact layers exhibited a typical zero-bias peak responsivity of 66.7 mA/W at 310 nm corresponding to the external quantum efficiency of 26.6%. The typical UV-to-visible (310/400 nm) spectral rejection ratio at zero-bias was over three orders of magnitude. The differential resistance and detectivity were obtained at approximately 6.2×1012 Ω and 3.4×1013 cm Hz1/2 W-1, respectively. Compared with conventional AlGaN/GaN-based UV p-i-n PDs, the proposed device structure can potentially achieve solar-blind AlGaN/GaN-based p-i-n PDs with low-aluminum content or aluminum-free p-contact layer and reduce excessive tensile strain due to the lattice mismatch between AlGaN and GaN layers.

Transverse mode control in proton-implanted and oxide-confined VCSELs via patterned dielectric anti-phase filters

NASA Astrophysics Data System (ADS)

Kesler, Benjamin; O'Brien, Thomas; Dallesasse, John M.

2017-02-01

A novel method for controlling the transverse lasing modes in both proton implanted and oxide-confined vertical- cavity surface-emitting lasers (VCSELs) with a multi-layer, patterned, dielectric anti-phase (DAP) filter is pre- sented. Using a simple photolithographic liftoff process, dielectric layers are deposited and patterned on individual VCSELs to modify (increase or decrease) the mirror reflectivity across the emission aperture via anti-phase reflections, creating spatially-dependent threshold material gain. The shape of the dielectric pattern can be tailored to overlap with specific transverse VCSEL modes or subsets of transverse modes to either facilitate or inhibit lasing by decreasing or increasing, respectively, the threshold modal gain. A silicon dioxide (SiO2) and titanium dioxide (TiO2) anti-phase filter is used to achieve a single-fundamental-mode, continuous-wave output power greater than 4.0 mW in an oxide-confined VCSEL at a lasing wavelength of 850 nm. A filter consisting of SiO2 and TiO2 is used to facilitate injection-current-insensitive fundamental mode and lower order mode lasing in proton implanted VCSELs at a lasing wavelength of 850 nm. Higher refractive index dielectric materials such as amorphous silicon (a-Si) can be used to increase the effectiveness of the anti-phase filter on proton implanted devices by reducing the threshold modal gain of any spatially overlapping modes. This additive, non-destructive method allows for mode selection at any lasing wavelength and for any VCSEL layer structure without the need for semiconductor etching or epitaxial regrowth. It also offers the capability of designing a filter based upon available optical coating materials.

Laterally Overgrown Structures as Substrates for Lattice Mismatched Epitaxy

DTIC Science & Technology

2002-06-03

low supersaturation substrate [3]. Therefore, equilibrium growth techniques as liquid buffer with TD phase epitaxy (LPE) or vapour phase epitaxy (VPE...phase diffusion during MBE growth, so lateral over- low cost semiconductor devices. Therefore, vapour growth must rely on the surface mobility of...is replaced by graphite film not wetted For the GaAs on GaAs ELO system we attributed by the gallium melt [35]. Similarly, tungsten has been broadening

Comparison of InGaAs(100) Grown by Chemical Beam Epitaxy and Metal Organic Chemical Vapor Deposition

NASA Technical Reports Server (NTRS)

Williams, M. D.; Greene, A. L.; Daniels-Race, T.; Lum, R. M.

2000-01-01

Secondary ion mass spectrometry is used to study the effects of substrate temperature on the composition and growth rate of InGaAs/InP(100) multilayers grown by chemical beam epitaxy, metal-organic chemical vapor deposition and solid source molecular beam epitaxy. The growth kinetics of the material grown by the different techniques are analyzed and compared.

A Program of Research on Microfabrication Techniques for VLSI Magnetic Devices.

DTIC Science & Technology

1982-10-01

contribution to the implantation- induced uniaxial anisotropy field change. BACKGROUND Magnetic garnet films are grown by liquid phase epitaxy ( LPE ) on non...a single crystal, non-magnetic garnet substrate by the liquid phase epitaxy ( LPE ) method. These thin films , usually one to three microns in thickness...microscopy. Experimental Procedures Films of (SmYGdTm)3Ca0a.Fe4.6012 garnet were grown by liquid phase epitaxy ( LPE ) on gadolinium-gallium garnet (GGG

Progress with polycrystalline silicon thin-film solar cells on glass at UNSW

NASA Astrophysics Data System (ADS)

Aberle, Armin G.

2006-01-01

Polycrystalline Si (pc-Si) thin-film solar cells on glass have long been considered a very promising approach for lowering the cost of photovoltaic (PV) solar electricity. In recent years there have been dramatic advances with this PV technology, and the first commercial modules (CSG Solar) are expected to hit the marketplace in 2006. The CSG modules are based on solid-phase crystallisation of plasma-enhanced chemical vapor deposition (PECVD) -deposited amorphous Si. Independent research in the author's group at the University of New South Wales (UNSW) during recent years has led to the development of three alternative pc-Si thin-film solar cells on glass—EVA, ALICIA and ALICE. Cell thickness is generally about 2 μm. The first two cells are made by vacuum evaporation, whereas ALICE cells can be made by either vacuum evaporation or PECVD. Evaporation has the advantage of being a fast and inexpensive Si deposition method. A crucial component of ALICIA and ALICE cells is a seed layer made on glass by metal-induced crystallisation of amorphous silicon (a-Si). The absorber layer of these cells is made by either ion-assisted Si epitaxy (ALICIA) or solid-phase epitaxy of a-Si (ALICE). This paper reports on the status of these three new thin-film PV technologies. All three solar cells seem to be capable of voltages of over 500 mV and, owing to their potentially inexpensive and scalable fabrication process, have significant industrial appeal.

Surface and Thin Film Analysis during Metal Organic Vapour Phase Epitaxial Growth

NASA Astrophysics Data System (ADS)

Richter, Wolfgang

2007-06-01

In-situ analysis of epitaxial growth is the essential ingredient in order to understand the growth process, to optimize growth and last but not least to monitor or even control the epitaxial growth on a microscopic scale. In MBE (molecular beam epitaxy) in-situ analysis tools existed right from the beginning because this technique developed from Surface Science technology with all its electron based analysis tools (LEED, RHEED, PES etc). Vapour Phase Epitaxy, in contrast, remained for a long time in an empirical stage ("alchemy") because only post growth characterisations like photoluminescence, Hall effect and electrical conductivity were available. Within the last two decades, however, optical techniques were developed which provide similar capabilities as in MBE for Vapour Phase growth. I will discuss in this paper the potential of Reflectance Anisotropy Spectroscopy (RAS) and Spectroscopic Ellipsometry (SE) for the growth of thin epitaxial semiconductor layers with zincblende (GaAs etc) and wurtzite structure (GaN etc). Other techniques and materials will be also mentioned.

Trends in heteroepitaxy of III-Vs on silicon for photonic and photovoltaic applications

NASA Astrophysics Data System (ADS)

Lourdudoss, Sebastian; Junesand, Carl; Kataria, Himanshu; Metaferia, Wondwosen; Omanakuttan, Giriprasanth; Sun, Yan-Ting; Wang, Zhechao; Olsson, Fredrik

2017-02-01

We present and compare the existing methods of heteroepitaxy of III-Vs on silicon and their trends. We focus on the epitaxial lateral overgrowth (ELOG) method as a means of achieving good quality III-Vs on silicon. Initially conducted primarily by near-equilibrium epitaxial methods such as liquid phase epitaxy and hydride vapour phase epitaxy, nowadays ELOG is being carried out even by non-equilibrium methods such as metal organic vapour phase epitaxy. In the ELOG method, the intermediate defective seed and the mask layers still exist between the laterally grown purer III-V layer and silicon. In a modified ELOG method called corrugated epitaxial lateral overgrowth (CELOG) method, it is possible to obtain direct interface between the III-V layer and silicon. In this presentation we exemplify some recent results obtained by these techniques. We assess the potentials of these methods along with the other existing methods for realizing truly monolithic photonic integration on silicon and III-V/Si heterojunction solar cells.

Nanoscale Strontium Titanate Sheets and Crystals

NASA Astrophysics Data System (ADS)

Tilka, Jack Andrew

The physical properties of materials are dominated by their structure and composition. Insight into the structure of complex oxide materials has the potential to improve our understanding and eventually control of their physical properties. This PhD thesis reports the development of characterization and fabrication techniques relevant to improving the scientific understanding of complex oxide materials. The work presented here has two components. I report a way to use ideas that were originally developed in semiconductor processing to control the elastic strain state and crystallization process of the model complex oxide SrTiO3. An additional component is an important series of advances in the analysis of diffraction patterns acquired with focused x-ray nanobeams. The fabrication and characterization of nanoscale SrTiO3 has been experimentally shown to allow the introduction of elastic strain into SrTiO3. The creation of thin SrTiO3 crystals from (001)-oriented SrTiO3 bulk single crystals using focused ion beam milling techniques yields sheets with submicron thickness and arbitrary orientation within the (001) plane. Synchrotron x-ray nanodiffraction experiments show that the SrTiO 3 sheets have rocking curves with angular widths less than 0.02°. These widths are less than a factor of two larger than bulk SrTiO3, which shows that the sheets are suitable substrates for epitaxial thin film growth. A precisely selected elastic strain can be introduced into the SrTiO 3 sheets using a silicon nitride stressor layer. Synchrotron x-ray nanodiffraction studies show that the strain introduced in the SrTiO3 sheets is on the order of 10-4, matching the predictions of an elastic model. This approach to elastic strain sharing in complex oxides allows the strain to be selected within a wide and continuous range of values, an effect not achievable in heteroepitaxy on rigid substrates. An additional fabrication technique is also evaluated here based on the crystallization of SrTiO3 from initially amorphous thin films. This process is known as solid-phase epitaxy in two-dimensional samples but is just beginning to be explored in more complex geometries. I report experiments in both homoepitaxy and heteroepitaxy including measurements of crystal growth rates and the crystallographic orientations of crystals formed in this way. The lateral growth rates are consistent with previously measured vertical growth. This result indicated that previous work on vertical solid-phase epitaxy could be extended into lateral solid-phase epitaxy, which has the power to be applied to complicated non-planar geometries. The highly coherent and tightly focused x-ray beams produced by hard x-ray light sources enable the nanoscale structural characterization of materials but are accompanied by significant challenges in the interpretation of diffraction and scattering patterns. I report here a series of methods that expand the range of physical problems that can be accurately captured by coherent x-ray optical simulations. My approach has been to expand simulations methods to include arbitrary x-ray incident angles and arbitrary epitaxial heterostructures. I first applied these methods to extract the misorientation of lattice planes and the strain of individual layers of Si/SiGe heterostructures relevant to applications in quantum electronics. Further applications reported in this thesis are in probing defects created in the processing of SrTiO3 and in measuring the change in lattice parameter introduced into strained SrTiO3 sheets. The systematic interpretation of nanobeam diffraction patterns aids in the fabrication of SrTiO3 nanostructures.

Formation of co-crystals: Kinetic and thermodynamic aspects

NASA Astrophysics Data System (ADS)

Gagnière, E.; Mangin, D.; Puel, F.; Rivoire, A.; Monnier, O.; Garcia, E.; Klein, J. P.

2009-04-01

Co-crystallisation is a recent method of great interest for the pharmaceutical industry, since pharmaceutical co-crystals represent useful materials for drug products. In this study, an active pharmaceutical ingredient (carbamazepine (CBZ)) co-crystallized with a vitamin (nicotinamide (NCT)) was chosen as a model substance. This work was focused on the construction of a phase diagram for the system CBZ/NCT, split in six domains for kinetic reasons (the different solid phases which might appear during the crystallisation) and in four domains according to thermodynamic aspects (the stable final phase obtained). Although co-crystals are not ionic compounds, the supersaturation of co-crystals can be evaluated by considering the solubility product. Batch crystallisation operations were carried out in a stirred vessel equipped with an in situ video probe. This latter device was a powerful analysis tool to monitor the CBZ/NCT co-crystals and single CBZ crystals since these two crystalline phases grown in ethanol exhibited needle and platelet habits. As concerns kinetics, the different solid phases which might appear during the experiments were observed and competed against each others. In accordance with thermodynamics, the stable solid form was obtained at the end of the operation. Finally some preliminary results indicate that the nucleation of co-crystals may be favoured by the presence of CBZ crystals. Epitaxial relationships between CBZ/NCT co-crystals and CBZ crystals were suspected.

Phase transformation of molecular beam epitaxy-grown nanometer-thick Gd₂O₃ and Y₂O₃ on GaN.

PubMed

Chang, Wen-Hsin; Wu, Shao-Yun; Lee, Chih-Hsun; Lai, Te-Yang; Lee, Yi-Jun; Chang, Pen; Hsu, Chia-Hung; Huang, Tsung-Shiew; Kwo, J Raynien; Hong, Minghwei

2013-02-01

High quality nanometer-thick Gd₂O₃ and Y₂O₃ (rare-earth oxide, R₂O₃) films have been epitaxially grown on GaN (0001) substrate by molecular beam epitaxy (MBE). The R₂O₃ epi-layers exhibit remarkable thermal stability at 1100 °C, uniformity, and highly structural perfection. Structural investigation was carried out by in situ reflection high energy electron diffraction (RHEED) and ex-situ X-ray diffraction (XRD) with synchrotron radiation. In the initial stage of epitaxial growth, the R₂O₃ layers have a hexagonal phase with the epitaxial relationship of R₂O₃ (0001)(H)<1120>(H)//GaN(0001)(H)<1120>(H). With the increase in R₂O₃ film thickness, the structure of the R₂O₃ films changes from single domain hexagonal phase to monoclinic phase with six different rotational domains, following the R₂O₃ (201)(M)[020](M)//GaN(0001)(H)<1120>(H) orientational relationship. The structural details and fingerprints of hexagonal and monoclinic phase Gd₂O₃ films have also been examined by using electron energy loss spectroscopy (EELS). Approximate 3-4 nm is the critical thickness for the structural phase transition depending on the composing rare earth element.

Morphology- and orientation-controlled gallium arsenide nanowires on silicon substrates.

PubMed

Ihn, Soo-Ghang; Song, Jong-In; Kim, Tae-Wook; Leem, Dong-Seok; Lee, Takhee; Lee, Sang-Geul; Koh, Eui Kwan; Song, Kyung

2007-01-01

GaAs nanowires were epitaxially grown on Si(001) and Si(111) substrates by using Au-catalyzed vapor-liquid-solid (VLS) growth in a solid source molecular beam epitaxy system. Scanning electron microscopy analysis revealed that almost all the GaAs nanowires were grown along <111> directions on both Si substrates for growth conditions investigated. The GaAs nanowires had a very uniform diameter along the growth direction. X-ray diffraction data and transmission electron microscopy analysis revealed that the GaAs<111> nanowires had a mixed crystal structure of the hexagonal wurtzite and the cubic zinc-blende. Current-voltage characteristics of junctions formed by the epitaxially grown GaAs nanowires and the Si substrate were investigated by using a current-sensing atomic force microscopy.

Facet-controlled phase separation in supersaturated Au-Ni nanoparticles upon shape equilibration

DOE Office of Scientific and Technical Information (OSTI.GOV)

Herz, A., E-mail: andreas.herz@tu-ilmenau.de, E-mail: dong.wang@tu-ilmenau.de; Rossberg, D.; Hentschel, M.

2015-08-17

Solid-state dewetting is used to fabricate supersaturated, submicron-sized Au-Ni solid solution particles out of thin Au/Ni bilayers by means of a rapid thermal annealing technique. Phase separation in such particles is studied with respect to their equilibrium crystal (or Wulff) shape by subsequent annealing at elevated temperature. It is found that (100) faceting planes of the equilibrated particles are enriched with Ni and (111) faces with Au. Both phases are considered by quantum-mechanical calculations in combination with an error-reduction scheme that was developed to compensate for a missing exchange-correlation potential that would reliably describe both Au and Ni. The observedmore » phase configuration is then related to the minimization of strongly anisotropic elastic energies of Au- and Ni-rich phases and results in a rather unique nanoparticle composite state that is characterized by nearly uniform value of elastic response to epitaxial strains all over the faceted surface. The same conclusion is yielded also by evaluating bi-axial elastic moduli when employing interpolated experimental elastic constants. This work demonstrates a useful route for studying features of physical metallurgy at the mesoscale.« less

InN: A material with photovoltaic promise and challenges

NASA Astrophysics Data System (ADS)

Trybus, Elaissa; Namkoong, Gon; Henderson, Walter; Burnham, Shawn; Doolittle, W. Alan; Cheung, Maurice; Cartwright, Alexander

2006-03-01

The potential of InN as a photovoltaic material is described. For solar applications, several key developments such as p-type doping and solid-state rectifying junctions have yet to be demonstrated. However, the ability of InGaN materials to optimally span the solar spectrum offers a tantalizing solution for high-efficiency photovoltaics albeit in an inherently lattice mismatched material system. For this reason, the characteristics of InN grown on (1 1 1)-oriented germanium and (0 0 0 1)-plane sapphire substrates via molecular beam epitaxy for the application of InN solar cells is described. To provide an efficient sub-cell interconnect for tandem solar cells, epitaxial Al was deposited on a germanium substrate with InN grown on this epitaxial aluminum layer. Consistent with previous results, the electrical characteristics of n-InN/p-Ge, n-InN/n-Ge, and n-InN/Al/Ge were measured and showed no rectifying behavior. As evidenced by X-ray diffraction, minute amounts of unintentional oxygen incorporation during InN growth forms a secondary phase, tentatively assigned to an indium oxynitride, InON x, phase. Photoluminescence measurements of the InN/InON x show spectral peaks at ˜0.7 and ˜3.8 eV consistent with the bulk excitonic bandgap of the two materials. Photoluminescence was also found at ˜1.7 eV and shown to be related to emission from the sapphire substrates.

A semi-empirical model for the complete orientation dependence of the growth rate for vapor phase epitaxy - Chloride VPE of GaAs

NASA Technical Reports Server (NTRS)

Seidel-Salinas, L. K.; Jones, S. H.; Duva, J. M.

1992-01-01

A semi-empirical model has been developed to determine the complete crystallographic orientation dependence of the growth rate for vapor phase epitaxy (VPE). Previous researchers have been able to determine this dependence for a limited range of orientations; however, our model yields relative growth rate information for any orientation. This model for diamond and zincblende structure materials is based on experimental growth rate data, gas phase diffusion, and surface reactions. Data for GaAs chloride VPE is used to illustrate the model. The resulting growth rate polar diagrams are used in conjunction with Wulff constructions to simulate epitaxial layer shapes as grown on patterned substrates. In general, this model can be applied to a variety of materials and vapor phase epitaxy systems.

In silico carbon molecular beam epitaxial growth of graphene on the h-BN substrate: carbon source effect on van der Waals epitaxy

NASA Astrophysics Data System (ADS)

Lee, Jonghoon; Varshney, Vikas; Park, Jeongho; Farmer, Barry L.; Roy, Ajit K.

2016-05-01

Against the presumption that hexagonal boron-nitride (h-BN) should provide an ideal substrate for van der Waals (vdW) epitaxy to grow high quality graphene films, carbon molecular beam epitaxy (CMBE) techniques using solid carbon sublimation have reported relatively poor quality of the graphene. In this article, the CMBE growth of graphene on the h-BN substrate is numerically studied in order to identify the effect of the carbon source on the quality of the graphene film. The carbon molecular beam generated by the sublimation of solid carbon source materials such as graphite and glassy carbon is mostly composed of atomic carbon, carbon dimers and carbon trimers. Therefore, the graphene film growth becomes a complex process involving various deposition characteristics of a multitude of carbon entities. Based on the study of surface adsorption and film growth characteristics of these three major carbon entities comprising graphite vapour, we report that carbon trimers convey strong traits of vdW epitaxy prone to high quality graphene growth, while atomic carbon deposition is a surface-reaction limited process accompanied by strong chemisorption. The vdW epitaxial behaviour of carbon trimers is found to be substantial enough to nucleate and develop into graphene like planar films within a nanosecond of high flux growth simulation, while reactive atomic carbons tend to impair the structural integrity of the crystalline h-BN substrate upon deposition to form an amorphous interface between the substrate and the growing carbon film. The content of reactive atomic carbons in the molecular beam is suspected to be the primary cause of low quality graphene reported in the literature. A possible optimization of the molecular beam composition towards the synthesis of better quality graphene films is suggested.Against the presumption that hexagonal boron-nitride (h-BN) should provide an ideal substrate for van der Waals (vdW) epitaxy to grow high quality graphene films, carbon molecular beam epitaxy (CMBE) techniques using solid carbon sublimation have reported relatively poor quality of the graphene. In this article, the CMBE growth of graphene on the h-BN substrate is numerically studied in order to identify the effect of the carbon source on the quality of the graphene film. The carbon molecular beam generated by the sublimation of solid carbon source materials such as graphite and glassy carbon is mostly composed of atomic carbon, carbon dimers and carbon trimers. Therefore, the graphene film growth becomes a complex process involving various deposition characteristics of a multitude of carbon entities. Based on the study of surface adsorption and film growth characteristics of these three major carbon entities comprising graphite vapour, we report that carbon trimers convey strong traits of vdW epitaxy prone to high quality graphene growth, while atomic carbon deposition is a surface-reaction limited process accompanied by strong chemisorption. The vdW epitaxial behaviour of carbon trimers is found to be substantial enough to nucleate and develop into graphene like planar films within a nanosecond of high flux growth simulation, while reactive atomic carbons tend to impair the structural integrity of the crystalline h-BN substrate upon deposition to form an amorphous interface between the substrate and the growing carbon film. The content of reactive atomic carbons in the molecular beam is suspected to be the primary cause of low quality graphene reported in the literature. A possible optimization of the molecular beam composition towards the synthesis of better quality graphene films is suggested. Electronic supplementary information (ESI) available: Three movie files: 3mer-physorption.mpg and 3mer-chemisorption.mpg feature examples of the adsorption state sampling of a carbon trimer on the heated h-BN substrate as mentioned in the ``Single Molecule Adsorption Study'' section. In 3mer-film-growth.mpg, an instance of honey comb formation during the initial phase of graphene growth simulation using a carbon trimer beam is captured. An initially sp hybridized carbon atom (red colored) becomes sp2 hybridized as a result of additional covalent bonding with the impinging carbon trimer. As the bond angle around the red carbon changes from 180 degree (sp) to 120 degree (sp2), nearby carbon atoms enclose to form a hexagon structure composed of 6 carbon atoms. See DOI: 10.1039/c6nr01396a

Thin Film Synthesis of New Complex Titanates.

NASA Astrophysics Data System (ADS)

Salvador, Paul

2008-03-01

Thin film deposition methods allow for one to synthesize rationally specific compositions in targeted crystal structures. Because most of the thermodynamic and kinetic variables that control the range of materials that can be synthesized are unknown for specific compounds/processes, epitaxial stabilization and design of artificially layered crystals are driven through empirical investigations. Using examples taken primarily from the family of complex titanates, which exhibit a range of interesting physicochemical behaviors, the thermodynamic and kinetic factors that control materials design using thin film deposition are discussed. The phase competition between the pyrochlore and the (110) layered perovskite structure in the RE2Ti2O7 family (RE = rare-earth, Bi) will be explored, using pulsed laser deposition as a synthesis method. For RE = Gd, Sm, Nd, and La, the phase stability over a wide range of conditions is dictated entirely by substrate choice, indicating that the free energies of the phases are similar enough such that by controlling nucleation one controls the phase formation. In a related fashion, the growth of AETi2O5 films (AE = Ba or Sr) will be discussed with respect to the formation of single-phase films or films that phase separate into AETiO3 and TiO2. The entire Ba1-xSrxTi2O5 series was grown and will be discussed with respect to growth technique (using MBE and PLD) and/or substrate choice. In this case, rock-salt substrates, which are not expected to interact strongly with any phase in the system, allow for the formation of single-phase films. Finally, several examples will be discussed with respect to the (SrO)m(TiO2)n system, which includes the perovskite SrTiO3 and the Ruddlesden-Popper phase Sr2TiO4, grown using layer-by-layer molecular beam epitaxy. The solid phase epitaxial formation of the perovskite SrTiO3 from superlattices of rock-salt SrO and anatase TiO2 is discussed from both a kinetic and thermodynamic perspective by exploring the growth of a range of m and n values. Using similar arguments for stability, new layered intergrowths in the SrmTiO2+m family are presented and their structures are discussed.

Cleaved-edge-overgrowth nanogap electrodes.

PubMed

Luber, Sebastian M; Bichler, Max; Abstreiter, Gerhard; Tornow, Marc

2011-02-11

We present a method to fabricate multiple metal nanogap electrodes of tailored width and distance in parallel, on the cleaved plane of a GaAs/AlGaAs heterostructure. The three-dimensional patterned structures are obtained by a combination of molecular-beam-epitaxial regrowth on a crystal facet, using the cleaved-edge-overgrowth (CEO) method, and subsequent wet selective etching and metallization steps. SEM and AFM studies reveal smooth and co-planar electrodes of width and distance of the order of 10 nm. Preliminary electrical characterization indicates electrical gap insulation in the 100 MΩ range with kΩ lead resistance. We propose our methodology to realize multiple electrode geometries that would allow investigation of the electrical conductivity of complex nanoscale objects such as branched organic molecules.

All-ion-implanted planar-gate current aperture vertical Ga2O3 MOSFETs with Mg-doped blocking layer

NASA Astrophysics Data System (ADS)

Wong, Man Hoi; Goto, Ken; Morikawa, Yoji; Kuramata, Akito; Yamakoshi, Shigenobu; Murakami, Hisashi; Kumagai, Yoshinao; Higashiwaki, Masataka

2018-06-01

A vertical β-Ga2O3 metal–oxide–semiconductor field-effect transistor featuring a planar-gate architecture is presented. The device was fabricated by an all-ion-implanted process without requiring trench etching or epitaxial regrowth. A Mg-ion-implanted current blocking layer (CBL) provided electrical isolation between the source and the drain except at an aperture opening through which drain current was conducted. Successful transistor action was realized by gating a Si-ion-implanted channel above the CBL. Thermal diffusion of Mg induced a large source–drain leakage current through the CBL, which resulted in compromised off-state device characteristics as well as a reduced peak extrinsic transconductance compared with the results of simulations.

Epitaxial growth of three dimensionally structured III-V photonic crystal via hydride vapor phase epitaxy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zheng, Qiye; Kim, Honggyu; Zhang, Runyu

2015-12-14

Three-dimensional (3D) photonic crystals are one class of materials where epitaxy, and the resultant attractive electronic properties, would enable new functionalities for optoelectronic devices. Here we utilize self-assembled colloidal templates to fabricate epitaxially grown single crystal 3D mesostructured GaxIn1-xP (GaInP) semiconductor photonic crystals using hydride vapor phase epitaxy (HVPE). The epitaxial relationship between the 3D GaInP and the substrate is preserved during the growth through the complex geometry of the template as confirmed by X-ray diffraction (XRD) and high resolution transmission electron microscopy. XRD reciprocal space mapping of the 3D epitaxial layer further demonstrates the film to be nearly fullymore » relaxed with a negligible strain gradient. Fourier transform infrared spectroscopy reflection measurement indicates the optical properties of the photonic crystal which agree with finite difference time domain simulations. This work extends the scope of the very few known methods for the fabrication of epitaxial III-V 3D mesostructured materials to the well-developed HVPE technique.« less

Epitaxial growth of three dimensionally structured III-V photonic crystal via hydride vapor phase epitaxy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zheng, Qiye; Kim, Honggyu; Zhang, Runyu

2015-12-14

Three-dimensional (3D) photonic crystals are one class of materials where epitaxy, and the resultant attractive electronic properties, would enable new functionalities for optoelectronic devices. Here we utilize self-assembled colloidal templates to fabricate epitaxially grown single crystal 3D mesostructured Ga{sub x}In{sub 1−x}P (GaInP) semiconductor photonic crystals using hydride vapor phase epitaxy (HVPE). The epitaxial relationship between the 3D GaInP and the substrate is preserved during the growth through the complex geometry of the template as confirmed by X-ray diffraction (XRD) and high resolution transmission electron microscopy. XRD reciprocal space mapping of the 3D epitaxial layer further demonstrates the film to bemore » nearly fully relaxed with a negligible strain gradient. Fourier transform infrared spectroscopy reflection measurement indicates the optical properties of the photonic crystal which agree with finite difference time domain simulations. This work extends the scope of the very few known methods for the fabrication of epitaxial III-V 3D mesostructured materials to the well-developed HVPE technique.« less

Thermodynamic Control of Two-Dimensional Molecular Ionic Nanostructures on Metal Surfaces

DOE PAGES

Jeon, Seokmin; Doak, Peter W.; Sumpter, Bobby G.; ...

2016-07-26

Bulk molecular ionic solids exhibit fascinating electronic properties, including electron correlations, phase transitions and superconducting ground states. In contrast, few of these phenomena have so far been observed in low-dimensional molecular structures, including thin films, nanoparticles and molecular blends, not in the least because most of such structures have so far been composed of nearly closed-shell molecules. It is therefore desirable to develop low-dimensional molecular structures of ionic molecules toward fundamental studies and potential applications. Here we present detailed analysis of monolayer-thick structures of the canonical TTF-TCNQ (tetrathiafulvalene 7,7,8,8-tetracyanoquinodimethane) system grown on low-index gold and silver surfaces. The most distinctivemore » property of the epitaxial growth is the wide abundance of stable TTF/TCNQ ratios, in sharp contrast to the predominance of 1:1 ratio in the bulk. We propose the existence of the surface phase-diagram that controls the structures of TTF-TCNQ on the surfaces, and demonstrate phase-transitions that occur upon progressively increasing the density of TCNQ while keeping the surface coverage of TTF fixed. Based on direct observations, we propose the binding motif behind the stable phases and infer the dominant interactions that enable the existence of the rich spectrum of surface structures. Finally, we also show that the surface phase diagram will control the epitaxy beyond monolayer coverage. Multiplicity of stable surface structures, the corollary rich phase diagram and the corresponding phase-transitions present an interesting opportunity for low-dimensional molecular systems, particularly if some of the electronic properties of the bulk can be preserved or modified in the surface phases.« less

Annealed Au-assisted epitaxial growth of si nanowires: control of alignment and density.

PubMed

Park, Yi-Seul; Jung, Da Hee; Kim, Hyun Ji; Lee, Jin Seok

2015-04-14

The epitaxial growth of 1D nanostructures is of particular interest for future nanoelectronic devices such as vertical field-effect transistors because it directly influences transistor densities and 3D logic or memory architectures. Silicon nanowires (SiNWs) are a particularly important 1D nanomaterial because they possess excellent electronic and optical properties. What is more, the scalable fabrication of vertically aligned SiNW arrays presents an opportunity for improved device applications if suitable properties can be achieved through controlling the alignment and density of SiNWs, yet this is something that has not been reported in the case of SiNWs synthesized from Au films. This work therefore explores the controllable synthesis of vertically aligned SiNWs through the introduction of an annealing process prior to growth via a Au-catalyzed vapor-liquid-solid mechanism. The epitaxial growth of SiNWs was demonstrated to be achievable using SiCl4 as the Si precursor in chemical vapor deposition, whereas the alignment and density of the SiNWs could be controlled by manipulating the annealing time during the formation of Au nanoparticles (AuNPs) from Au films. During the annealing process, gold silicide was observed to form on the interface of the liquid-phase AuNPs, depending on the size of the AuNPs and the annealing time. This work therefore makes a valuable contribution to improving nanowire-based engineering by controlling its alignment and density as well as providing greater insight into the epitaxial growth of 1D nanostructures.

Buffer architecture for biaxially textured structures and method of fabricating same

DOEpatents

Norton, David P.; Park, Chan; Goyal, Amit

2004-04-06

The invention relates to an article with an improved buffer layer architecture comprising a substrate having a metal surface, and an epitaxial buffer layer on the surface of the substrate. The epitaxial buffer layer comprises at least one of the group consisting of ZrO.sub.2, HfO.sub.2, and compounds having at least one of Ca and a rare earth element stabilizing cubic phases of ZrO.sub.2 and/or HfO.sub.2. The article can also include a superconducting layer deposited on the epitaxial buffer layer. The article can also include an epitaxial capping layer between the epitaxial buffer layer and the superconducting layer. A method for preparing an epitaxial article comprises providing a substrate with a metal surface, depositing on the metal surface an epitaxial buffer layer comprising at least one material selected from the group consisting of ZrO.sub.2, HfO.sub.2, and compounds having at least one of Ca and a rare earth element stabilizing cubic phases of at least one of ZrO.sub.2 and HfO.sub.2. The epitaxial layer depositing step occurs in a vacuum with a background pressure of no more than 1.times.10.sup.-5 Torr. The method can further comprise depositing a superconducting layer on the epitaxial layer, and depositing an epitaxial capping layer between the epitaxial buffer layer and the superconducting layer.

Ultra-low temperature (≤300 °C) growth of Ge-rich SiGe by solid-liquid-coexisting annealing of a-GeSn/c-Si structures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sadoh, Taizoh, E-mail: sadoh@ed.kyushu-u.ac.jp; Chikita, Hironori; Miyao, Masanobu

2015-09-07

Ultra-low temperature (≤300 °C) growth of Ge-rich SiGe on Si substrates is strongly desired to realize advanced electronic and optical devices, which can be merged onto Si large-scale integrated circuits (LSI). To achieve this, annealing characteristics of a-GeSn/c-Si structures are investigated under wide ranges of the initial Sn concentrations (0%–26%) and annealing conditions (300–1000 °C, 1 s–48 h). Epitaxial growth triggered by SiGe mixing is observed after annealing, where the annealing temperatures necessary for epitaxial growth significantly decrease with increasing initial Sn concentration and/or annealing time. As a result, Ge-rich (∼80%) SiGe layers with Sn concentrations of ∼2% are realized by ultra-low temperature annealingmore » (300 °C, 48 h) for a sample with the initial Sn concentration of 26%. The annealing temperature (300 °C) is in the solid-liquid coexisting temperature region of the phase diagram for Ge-Sn system. From detailed analysis of crystallization characteristics and composition profiles in grown layers, it is suggested that SiGe mixing is generated by a liquid-phase reaction even at ultra-low temperatures far below the melting temperature of a-GeSn. This ultra-low-temperature growth technique of Ge-rich SiGe on Si substrates is expected to be useful to realize next-generation LSI, where various multi-functional devices are integrated on Si substrates.« less

N-MOSFETs Formed on Solid Phase Epitaxially Grown GeSn Film with Passivation by Oxygen Plasma Featuring High Mobility.

PubMed

Fang, Yung-Chin; Chen, Kuen-Yi; Hsieh, Ching-Heng; Su, Chang-Chia; Wu, Yung-Hsien

2015-12-09

Solid phase epitaxially grown GeSn was employed as the platform to assess the eligibility of direct O2 plasma treatment on GeSn surface for passivation of GeSn N-MOSFETs. It has been confirmed that O2 plasma treatment forms a GeSnO(x) film on the surface and the GeSnO(x) topped by in situ Al2O3 constitutes the gate stack of GeSn MOS devices. The capability of the surface passivation was evidenced by the low interface trap density (D(it)) of 1.62 × 10(11) cm(-2) eV(-1), which is primarily due to the formation of Ge-O and Sn-O bonds at the surface by high density/reactivity oxygen radicals that effectively suppress dangling bonds and decrease gap states. The good D(it) not only makes tiny frequency dispersion in the characterization of GeSn MOS capacitors, but results in GeSn N-MOSFETs with outstanding peak electron mobility as high as 518 cm(2)/(V s) which outperforms other devices reported in the literature due to reduced undesirable carrier scattering. In addition, the GeSn N-MOSFETs also exhibit promising characteristics in terms of acceptable subthreshold swing of 156 mV/dec and relatively large I(ON)/I(OFF) ratio more than 4 orders. Moreover, the robust reliability in terms small V(t) variation against high field stress attests the feasibility of using the O2 plasma-treated passivation to advanced GeSn technology.

Advanced Si solid phase crystallization for vertical channel in vertical NANDs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Sangsoo; Son, Yong-Hoon; Semiconductor R and D Center, Samsung Electronics Co., Ltd., Hwasung 445-701

The advanced solid phase crystallization (SPC) method using the SiGe/Si bi-layer structure is proposed to obtain high-mobility poly-Si thin-film transistors in next generation vertical NAND (VNAND) devices. During the SPC process, the top SiGe thin film acts as a selective nucleation layer to induce surface nucleation and equiaxial microstructure. Subsequently, this SiGe thin film microstructure is propagated to the underlying Si thin film by epitaxy-like growth. The initial nucleation at the SiGe surface was clearly observed by in situ transmission electron microscopy (TEM) when heating up to 600 °C. The equiaxial microstructures of both SiGe nucleation and Si channel layers weremore » shown in the crystallized bi-layer plan-view TEM measurements. Based on these experimental results, the large-grained and less-defective Si microstructure is expected to form near the channel region of each VNAND cell transistor, which may improve the electrical characteristics.« less

Strain Coupling of Conversion-type Fe 3O 4 Thin Films for Lithium Ion Batteries

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hwang, Sooyeon; Meng, Qingping; Chen, Ping-Fan

2017-05-29

Lithiation/delithiation induces significant stresses and strains into the electrodes for lithium ion batteries, which can severely degrade their cycling performance. Moreover, this electrochemically induced strain can interact with the local strain existing at solid–solid interfaces. It is not clear how this interaction affects the lithiation mechanism. The effect of this coupling on the lithiation kinetics in epitaxial Fe 3O 4 thin film on a Nb-doped SrTiO 3 substrate is investigated. In-situ and ex-situ transmission electron microscopy (TEM) results show that the lithiation is suppressed by the compressive interfacial strain. At the interface between the film and substrate, the existence ofmore » Li xFe 3O 4 rock-salt phase during lithiation consequently restrains the film from delamination. 2D phase-field simulation verifies the effect of strain. This work provides critical insights of understanding the solid–solid interfaces of conversion-type electrodes.« less

Vapor-solid-solid grown Ge nanowires at integrated circuit compatible temperature by molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Zhu, Zhongyunshen; Song, Yuxin; Zhang, Zhenpu; Sun, Hao; Han, Yi; Li, Yaoyao; Zhang, Liyao; Xue, Zhongying; Di, Zengfeng; Wang, Shumin

2017-09-01

We demonstrate Au-assisted vapor-solid-solid (VSS) growth of Ge nanowires (NWs) by molecular beam epitaxy at the substrate temperature of ˜180 °C, which is compatible with the temperature window for Si-based integrated circuit. Low temperature grown Ge NWs hold a smaller size, similar uniformity, and better fit with Au tips in diameter, in contrast to Ge NWs grown at around or above the eutectic temperature of Au-Ge alloy in the vapor-liquid-solid (VLS) growth. Six ⟨110⟩ growth orientations were observed on Ge (110) by the VSS growth at ˜180 °C, differing from only one vertical growth direction of Ge NWs by the VLS growth at a high temperature. The evolution of NWs dimension and morphology from the VLS growth to the VSS growth is qualitatively explained by analyzing the mechanism of the two growth modes.

Low symmetry phase in Pb(Zr0.52Ti0.48)O3 epitaxial thin films with enhanced ferroelectric properties

NASA Astrophysics Data System (ADS)

Yan, Li; Li, Jiefang; Cao, Hu; Viehland, D.

2006-12-01

The authors report the structural and ferroelectric properties of Pb(Zr0.52Ti0.48)O3 (PZT) epitaxial thin films grown on (001), (110), and (111) SrRuO3/SrTiO3 substrates by pulsed laser deposition. A monoclinic C (Mc) phase has been found for (101) films, whereas (001) and (111) ones were tetragonal (T ) and rhombohedral (R), respectively. The authors find that the ferroelectric polarization of the Mc phase is higher than that in either the T or R ones. These results are consistent with predictions (i) of epitaxial phase diagrams and (ii) that the enhanced ferroelectric properties of morphotropic phase boundary PZT are related to a low symmetry monoclinic phase.

The processes of formation and epitaxial alignment of SrTiO3 thin films prepared by metallo-organic decomposition

NASA Astrophysics Data System (ADS)

Braunstein, G.; Paz-Pujalt, G. R.; Mason, M. G.; Blanton, T.; Barnes, C. L.; Margevich, D.

1993-01-01

The processes of formation and crystallization of thin films of SrTiO3 prepared by the method of metallo-organic decomposition have been studied with particular emphasis on the relationship between the thermal decomposition of the metallo-organic precursors and the eventual epitaxial alignment of the crystallized films. The films are deposited by spin coating onto single-crystalline silicon and SrTiO3 substrates, pyrolyzed on a hot plate at temperatures ranging from 200 to 450 °C, and subsequently heat treated in a quartz tube furnace at temperatures ranging from 300 to 1200 °C. Heat treatment at temperatures up to 450-500 °C results in the evaporation of solvents and other organic addenda, thermal decomposition of the metallo-organic (primarily metal-carboxylates) precursors, and formation of a carbonate species. This carbonate appears to be an intermediate phase in the reaction of SrCO3 and TiO2 to form SrTiO3. Relevant to this work is the fact that the carbonate species exhibits diffraction lines, indicating the formation of grains that can serve as seeds for the nucleation and growth of randomly oriented SrTiO3 crystallites, thereby leading to a polycrystalline film. Deposition on silicon substrates indeed results in the formation of polycrystalline SrTiO3. However, when the precursor solution is deposited on single-crystalline SrTiO3 substrates, the crystallization process involves a competition between two mechanisms: the random nucleation and growth of crystallites just described, and layer-by-layer solid phase epitaxy. Epitaxial alignment on SrTiO3 substrates can be achieved when the samples are heat treated at temperatures of 1100-1200 °C or at temperatures as low as 600-650 °C when the substrate is heated to about 1100 °C before spin coating.

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.

Enhanced magnetic and thermoelectric properties in epitaxial polycrystalline SrRuO3 thin films.

PubMed

Woo, Sungmin; Lee, Sang A; Mun, Hyeona; Choi, Young Gwan; Zhung, Chan June; Shin, Soohyeon; Lacotte, Morgane; David, Adrian; Prellier, Wilfrid; Park, Tuson; Kang, Won Nam; Lee, Jong Seok; Kim, Sung Wng; Choi, Woo Seok

2018-03-01

Transition metal oxide thin films show versatile electric, magnetic, and thermal properties which can be tailored by deliberately introducing macroscopic grain boundaries via polycrystalline solids. In this study, we focus on the modification of magnetic and thermal transport properties by fabricating single- and polycrystalline epitaxial SrRuO 3 thin films using pulsed laser epitaxy. Using the epitaxial stabilization technique with an atomically flat polycrystalline SrTiO 3 substrate, an epitaxial polycrystalline SrRuO 3 thin film with the crystalline quality of each grain comparable to that of its single-crystalline counterpart is realized. In particular, alleviated compressive strain near the grain boundaries due to coalescence is evidenced structurally, which induced the enhancement of ferromagnetic ordering of the polycrystalline epitaxial thin film. The structural variations associated with the grain boundaries further reduce the thermal conductivity without deteriorating the electronic transport, and lead to an enhanced thermoelectric efficiency in the epitaxial polycrystalline thin films, compared with their single-crystalline counterpart.

Epitaxial CuInSe2 thin films grown by molecular beam epitaxy and migration enhanced epitaxy

NASA Astrophysics Data System (ADS)

Abderrafi, K.; Ribeiro-Andrade, R.; Nicoara, N.; Cerqueira, M. F.; Gonzalez Debs, M.; Limborço, H.; Salomé, P. M. P.; Gonzalez, J. C.; Briones, F.; Garcia, J. M.; Sadewasser, S.

2017-10-01

While CuInSe2 chalcopyrite materials are mainly used in their polycrystalline form to prepare thin film solar cells, epitaxial layers have been used for the characterization of defects. Typically, epitaxial layers are grown by metal-organic vapor phase epitaxy or molecular beam epitaxy (MBE). Here we present epitaxial layers grown by migration enhanced epitaxy (MEE) and compare the materials quality to MBE grown layers. CuInSe2 layers were grown on GaAs (0 0 1) substrates by co-evaporation of Cu, In, and Se using substrate temperatures of 450 °C, 530 °C, and 620 °C. The layers were characterized by high resolution X-ray diffraction (HR-XRD), high-resolution transmission electron microscopy (HRTEM), Raman spectroscopy, and atomic force microscopy (AFM). HR-XRD and HR-TEM show a better crystalline quality of the MEE grown layers, and Raman scattering measurements confirm single phase CuInSe2. AFM shows the previously observed faceting of the (0 0 1) surface into {1 1 2} facets with trenches formed along the [1 1 0] direction. The surface of MEE-grown samples appears smoother compared to MBE-grown samples, a similar trend is observed with increasing growth temperature.

Improved Boat For Liquid-Phase Epitaxy

NASA Technical Reports Server (NTRS)

Connolly, John C.

1991-01-01

Liquid-phase epitaxial (LPE) growth boat redesigned. Still fabricated from ultra-high-purity graphite, but modified to permit easy disassembly and cleaning, along with improved wiping action for more complete removal of melt to reduce carry-over of gallium. Larger substrates and more uniform composition obtained.

Phase formation and texture of thin nickel germanides on Ge(001) and Ge(111)

DOE Office of Scientific and Technical Information (OSTI.GOV)

De Schutter, B., E-mail: deschutter.bob@ugent.be; Detavernier, C.; Van Stiphout, K.

2016-04-07

We studied the solid-phase reaction between a thin Ni film and a single crystal Ge(001) or Ge(111) substrate during a ramp anneal. The phase formation sequence was determined using in situ X-ray diffraction and in situ Rutherford backscattering spectrometry (RBS), while the nature and the texture of the phases were studied using X-ray pole figures and transmission electron microscopy. The phase sequence is characterized by the formation of a single transient phase before NiGe forms as the final and stable phase. X-ray pole figures were used to unambiguously identify the transient phase as the ϵ-phase, a non-stoichiometric Ni-rich germanide withmore » a hexagonal crystal structure that can exist for Ge concentrations between 34% and 48% and which forms with a different epitaxial texture on both substrate orientations. The complementary information gained from both RBS and X-ray pole figure measurements revealed a simultaneous growth of both the ϵ-phase and NiGe over a small temperature window on both substrate orientations.« less

Phase transition and epitaxies between hydrated orthorhombic and anhydrous monoclinic uric acid crystals

NASA Astrophysics Data System (ADS)

Boistelle, R.; Rinaudo, C.

1981-05-01

Anhydrous monoclinic and hydrated orthorhombic uric acid crystals can be nucleated and grown from pure water solutions either separately or together with epitaxial relationships. When crystals of one modification exist in the solution they can act as nucleation substrate for the crystals of the other modification. In both cases the new phase grows epitaxially on the substrate; the mutual orientations are the same but the contact planes are different. In addition, the anhydrous modification grows into the hydrated one which undergoes a phase transition by a dissolution-recrystallization process. It is likely that the same processes occur in human stones made up of uric acids.

Optimization of solar cells for air mass zero operation and study of solar cells at high temperatures, phase 4

NASA Technical Reports Server (NTRS)

Hovel, H. J.; Woodall, J. M.

1980-01-01

The Pd contact to GaAs was studied using backscattering, Auger analysis, and sheet resistance measurements. Several metallurgical phases were present at low temperatures, but PdGa was the dominant phase in samples annealed at 500 C. Ti/Pd/Ag contacts appeared to have the lowest contact resistance. Etchback epitaxy (EBE) was compared to saturated melt epitaxy (SME) method of growing liquid phase epitaxial layers. The SME method resulted in a lower density of Ga microdroplets in the grown layer, although the best solar cells were made by the EBE method. Photoluminescence was developed as a tool for contactless analysis of GaAs cells. Efficiencies of over 8 percent were measured at 250 C.

Method for rapid, controllable growth and thickness, of epitaxial silicon films

DOEpatents

Wang, Qi [Littleton, CO; Stradins, Paul [Golden, CO; Teplin, Charles [Boulder, CO; Branz, Howard M [Boulder, CO

2009-10-13

A method of producing epitaxial silicon films on a c-Si wafer substrate using hot wire chemical vapor deposition by controlling the rate of silicon deposition in a temperature range that spans the transition from a monohydride to a hydrogen free silicon surface in a vacuum, to obtain phase-pure epitaxial silicon film of increased thickness is disclosed. The method includes placing a c-Si substrate in a HWCVD reactor chamber. The method also includes supplying a gas containing silicon at a sufficient rate into the reaction chamber to interact with the substrate to deposit a layer containing silicon thereon at a predefined growth rate to obtain phase-pure epitaxial silicon film of increased thickness.

Epitaxial Garnets and Hexagonal Ferrites.

DTIC Science & Technology

1982-04-20

goenv.o -,y la)ers were YIG (yttrium iron garnet ) films grown by liquid phase epitaxy w:* ( LPE ) on gadolinium gallium garnet (GGG) substrates. Magnetic...containing three epitaxial layers. In addition to the MSW work oil garnets , LPE of lithium ferrite and hexagonal fertites was studied. A substituted lead...of a stripline. The other layers are epitaxial films , generally YIG (yttrium iron garnet ) with magnetic properties adjusted by suitable modifications

White emission from non-planar InGaN/GaN MQW LEDs grown on GaN template with truncated hexagonal pyramids.

PubMed

Lee, Ming-Lun; Yeh, Yu-Hsiang; Tu, Shang-Ju; Chen, P C; Lai, Wei-Chih; Sheu, Jinn-Kong

2015-04-06

Non-planar InGaN/GaN multiple quantum well (MQW) structures are grown on a GaN template with truncated hexagonal pyramids (THPs) featuring c-plane and r-plane surfaces. The THP array is formed by the regrowth of the GaN layer on a selective-area Si-implanted GaN template. Transmission electron microscopy shows that the InGaN/GaN epitaxial layers regrown on the THPs exhibit different growth rates and indium compositions of the InGaN layer between the c-plane and r-plane surfaces. Consequently, InGaN/GaN MQW light-emitting diodes grown on the GaN THP array emit multiple wavelengths approaching near white light.

Bragg projection ptychography on niobium phase domains

NASA Astrophysics Data System (ADS)

Burdet, Nicolas; Shi, Xiaowen; Clark, Jesse N.; Huang, Xiaojing; Harder, Ross; Robinson, Ian

2017-07-01

Bragg projection ptychography (BPP) is a coherent x-ray diffraction imaging technique which combines the strengths of scanning microscopy with the phase contrast of x-ray ptychography. Here we apply it for high resolution imaging of the phase-shifted crystalline domains associated with epitaxial growth. The advantages of BPP are that the spatial extent of the sample is arbitrary, it is nondestructive, and it gives potentially diffraction limited spatial resolution. Here we demonstrate the application of BPP for revealing the domain structure caused by epitaxial misfit in a nanostructured metallic thin film. Experimental coherent diffraction data were collected from a niobium thin film, epitaxially grown on a sapphire substrate as the beam was scanned across the sample. The data were analyzed by BPP using a carefully selected combination of refinement procedures. The resulting image shows a close packed array of epitaxial domains, shifted with respect to each other due to misfit between the film and its substrate.

III-V semiconductor solid solution single crystal growth

NASA Technical Reports Server (NTRS)

Gertner, E. R.

1982-01-01

The feasibility and desirability of space growth of bulk IR semiconductor crystals for use as substrates for epitaxial IR detector material were researched. A III-V ternary compound (GaInSb) and a II-VI binary compound were considered. Vapor epitaxy and quaternary epitaxy techniques were found to be sufficient to permit the use of ground based binary III-V crystals for all major device applications. Float zoning of CdTe was found to be a potentially successful approach to obtaining high quality substrate material, but further experiments were required.

Method for forming single phase, single crystalline 2122 BCSCO superconductor thin films by liquid phase epitaxy

NASA Technical Reports Server (NTRS)

Pandey, Raghvendra K. (Inventor); Raina, Kanwal (Inventor); Solayappan, Narayanan (Inventor)

1994-01-01

A substantially single phase, single crystalline, highly epitaxial film of Bi.sub.2 CaSr.sub.2 Cu.sub.2 O.sub.8 superconductor which has a T.sub.c (zero resistance) of 83 K is provided on a lattice-matched substrate with no intergrowth. This film is produced by a Liquid Phase Epitaxy method which includes the steps of forming a dilute supercooled molten solution of a single phase superconducting mixture of oxides of Bi, Ca, Sr, and Cu having an atomic ratio of about 2:1:2:2 in a nonreactive flux such as KCl, introducing the substrate, e.g., NdGaO.sub.3, into the molten solution at 850.degree. C., cooling the solution from 850.degree. C. to 830.degree. C. to grow the film and rapidly cooling the substrate to room temperature to maintain the desired single phase, single crystalline film structure.

Template assisted strain tuning and phase stabilization in epitaxial BiFeO3 thin films

NASA Astrophysics Data System (ADS)

Saj Mohan M., M.; Ramadurai, Ranjith

2018-04-01

Strain engineering is a key to develop novel properties in functional materials. We report a strain mediated phase stabilization and epitaxial growth of bismuth ferrite(BiFeO3) thin films on LaAlO3 (LAO) substrates. The strain in the epitaxial layer is controlled by controlling the thickness of bottom electrode where the thickness of the BFO is kept constant. The thickness of La0.7Sr0.3MnO3(LSMO) template layer was optimized to grow completely strained tetragonal, tetragonal/rhombohedral mixed phase and fully relaxed rhombohedral phase of BFO layers. The results were confirmed with coupled-θ-2θ scan, and small area reciprocal space mapping. The piezoelectric d33 (˜ 45-48 pm/V) coefficient of the mixed phase was relatively larger than the strained tetragonal and relaxed rhombohedral phase for a given thickness.

Nucleation and Epitaxy-Mediated Phase Transformation of a Precursor Cadmium Carbonate Phase at the Calcite/Water Interface

DOE Office of Scientific and Technical Information (OSTI.GOV)

Riechers, Shawn L.; Rosso, Kevin M.; Kerisit, Sebastien N.

Mineral nucleation can be catalyzed by the presence of mineral substrates; however, the mechanisms of heterogeneous nucleation remain poorly understood. A combination of in situ time-sequenced measurements and nano-manipulation experiments were performed using atomic force microscopy (AFM) to probe the mechanisms of heteroepitaxial nucleation of otavite (CdCO3) on calcite (CaCO3) single crystals that exposed the (10-14) surface. Otavite and calcite are isostructural carbonates that display a 4% lattice mismatch, based on their (10-14) surface areas. AFM observations revealed a two-stage process in the nucleation of cadmium carbonate surface precipitates. As evidenced by changes in height, shape, growth behavior, and frictionmore » signal of the precipitates, a precursor phase was observed to initially form on the surface and subsequently undergo an epitaxy-mediated phase transformation to otavite, which then grew epitaxially. Nano-manipulation experiments, in which the applied force was increased progressively until precipitates were removed from the surface, showed that adhesion of the precursor phase to the substrate was distinctively weaker than that of the epitaxial phase, consistent with that of an amorphous phase. These findings demonstrate for the first time that heterogeneous mineral nucleation can follow a non-classical pathway like that found in homogenous aqueous conditions.« less

Depositing spacing layers on magnetic film with liquid phase epitaxy

NASA Technical Reports Server (NTRS)

Moody, J. W.; Shaw, R. W.; Sanfort, R. M.

1975-01-01

Liquid phase epitaxy spacing layer is compatible with systems which are hard-bubble proofed by use of second magnetic garnet film as capping layer. Composite is superior in that: circuit fabrication time is reduced; adherence is superior; visibility is better; and, good match of thermal expansion coefficients is provided.

A divalent rare earth oxide semiconductor: Yttrium monoxide

NASA Astrophysics Data System (ADS)

Kaminaga, Kenichi; Sei, Ryosuke; Hayashi, Kouichi; Happo, Naohisa; Tajiri, Hiroo; Oka, Daichi; Fukumura, Tomoteru; Hasegawa, Tetsuya

Rare earth sesquioxides like Y2O3 are known as widegap insulators with the highly stable closed shell trivalent rare earth ions. On the other hand, rare earth monoxides such as YO have been recognized as gaseous phase, and only EuO and YbO were thermodynamically stable solid-phase rock salt monoxides. In this study, solid-phase rock salt yttrium monoxide, YO, was synthesized in a form of epitaxial thin film by pulsed laser deposition method. YO possesses unusual valence of Y2+ ([Kr] 4d1) . In contrast with Y2O3, YO was narrow gap semiconductor with dark-brown color. The electrical conductivity was tunable from 10-1 to 103 Ω-1 cm-1 by introducing oxygen vacancies as electron donor. Weak antilocalization behavior was observed indicating significant spin-orbit coupling owing to 4 d electron carrier. The absorption spectral shape implies the Mott-Hubbard insulator character of YO. Rare earth monoixdes will be new platform of functional oxides. This work was supported by JST-CREST, the Japan Society for the Promotion of Science (JSPS) with Grant-in-Aid for Scientific Research on Innovative Areas (Nos. 26105002 and 26105006), and Nanotechnology Platform (Project No.12024046) of MEXT, Japan.

Ti{sub 2}AlN thin films synthesized by annealing of (Ti+Al)/AlN multilayers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cabioch, Thierry, E-mail: Thierry.cabioch@univ-poitiers.fr; Alkazaz, Malaz; Beaufort, Marie-France

2016-08-15

Highlights: • Epitaxial thin films of the MAX phase Ti{sub 2}AlN are obtained by thermal annealing. • A new metastable (Ti,Al,N) solid solution with the structure of α-T is evidenced. • The formation of the MAX phase occurs at low temperature (600 °C). - Abstract: Single-phase Ti{sub 2}AlN thin films were obtained by annealing in vacuum of (Ti + Al)/AlN multilayers deposited at room temperature by magnetron sputtering onto single-crystalline (0001) 4H-SiC and (0001) Al{sub 2}O{sub 3} substrates. In-situ X-ray diffraction experiments combined with ex-situ cross-sectional transmission electron microscopy observations reveal that interdiffusion processes occur in the multilayer at amore » temperature of ∼400 °C leading to the formation of a (Ti, Al, N) solid solution, having the hexagonal structure of α-Ti, whereas the formation of Ti{sub 2}AlN occurs at 550–600 °C. Highly oriented (0002) Ti{sub 2}AlN thin films can be obtained after an annealing at 750 °C.« less

Liquid-Phase Epitaxial Growth of ZnS, ZnSe and Their Mixed Compounds Using Te as Solvent

NASA Astrophysics Data System (ADS)

Nakamura, Hiroshi; Aoki, Masaharu

1981-01-01

Epitaxial layers of ZnS, ZnSe and their mixed compounds were grown on ZnS substrates by the liquid-phase epitaxial growth (LPE) method using Te as the solvent. The open-tube slide-boat technique was used, and a suitable starting temperature for growth was found to be 850°C for ZnS and 700-800°C for ZnSe. The ZnS epitaxial layers grown on {111}A and {111}B oriented ZnS substrates were thin (˜1 μm) and smooth, had low, uniform Te concentrations (˜0.1 at.%) and were highly luminescent. The ZnSe epitaxial layers were relatively thick (10-30 μm) and had fairly high Te concentrations (a few at.%). Various mixed compound ZnS1-xSex were also grown on ZnS substrates.

Arsine flow requirement for the flow modulation growth of high purity GaAs using adduct-grade triethylgallium

NASA Astrophysics Data System (ADS)

Pitts, B. L.; Emerson, D. T.; Shealy, J. R.

1992-10-01

Using arsine and triethylgallium with flow modulation, organometallic vapor phase epitaxy can produce high purity GaAs layers with V/III molar ratios near unity. We have estimated that under appropriate growth conditions the arsine incorporation efficiency into epitaxial GaAs can exceed 30%. The arsine flow requirement for obtaining good morphology has been identified over a range of substrate temperatures using adduct-grade triethylgallium. The process described reduces the environmental impact and life safety risk of the hydride based organometallic vapor phase epitaxial method.

Quantum well infrared photodetectors (QWIP) with selectively regrown N-GaAs plugs

NASA Astrophysics Data System (ADS)

Matsukura, Yusuke; Nishino, Hironori; Tanaka, Hitoshi; Fujii, Toshio

2001-10-01

We fabricated the GaAs/AlGaAs Quantum Well Infrared Photo detector (QWIP) focal plane array with selectively re-grown N- GaAs interconnection plugs and demonstrated its device operation, in order to establish the technology to obtain both complex device functions and device manufacturability. MBE (Molecular Beam Epitaxy) grown QWIP MQW wafers were covered with SiON and SiNx mask films to obtain selectivity of the re-growth process. N-GaAs plugs were re-grown selectively with low-pressure MOCVD (Metal-Organic Chemical Vapor Deposition) with AsH3 and Dimethylgalliumchloride as precursors, only on the bottom surfaces of the holes for the interconnection to extract the electrodes from the underlying epilayer. Cross- sectional SEM observation revealed that the feature of the re- grown N-GaAs plugs was triangular, rather than rectangular as expected. The reason for this discrepancy is not yet clear. The electrical contact between the epilayer and re-grown N- GaAs plug was 'ohmic-like,' without any trace of interfacial barrier. The Current-Voltage characteristics of the fabricated QWIP device showed no tangible leakage current between the N- GaAs plug and device structure, indicating that electrical insulation between the N-GaAs plugs and device structure was sufficient. Fabricated devices were successfully operated as a hybrid focal plane array, indicating the selective re-growth was a promising technique to realize complex QWIP based devices.

On the dielectric and optical properties of surface-anchored metal-organic frameworks: A study on epitaxially grown thin films

NASA Astrophysics Data System (ADS)

Redel, Engelbert; Wang, Zhengbang; Walheim, Stefan; Liu, Jinxuan; Gliemann, Hartmut; Wöll, Christof

2013-08-01

We determine the optical constants of two highly porous, crystalline metal-organic frameworks (MOFs). Since it is problematic to determine the optical constants for the standard powder modification of these porous solids, we instead use surface-anchored metal-organic frameworks (SURMOFs). These MOF thin films are grown using liquid phase epitaxy (LPE) on modified silicon substrates. The produced SURMOF thin films exhibit good optical properties; these porous coatings are smooth as well as crack-free, they do not scatter visible light, and they have a homogenous interference color over the entire sample. Therefore, spectroscopic ellipsometry (SE) can be used in a straightforward fashion to determine the corresponding SURMOF optical properties. After careful removal of the solvent molecules used in the fabrication process as well as the residual water adsorbed in the voids of this highly porous solid, we determine an optical constant of n = 1.39 at a wavelength of 750 nm for HKUST-1 (stands for Hong Kong University of Science and Technology-1; and was first discovered there) or [Cu3(BTC)2]. After exposing these SURMOF thin films to moisture/EtOH atmosphere, the refractive index (n) increases to n = 1.55-1.6. This dependence of the optical properties on water/EtOH adsorption demonstrates the potential of such SURMOF materials for optical sensing.

Proximity Effects of Beryllium-Doped GaN Buffer Layers on the Electronic Properties of Epitaxial AlGaN/GaN Heterostructures

DTIC Science & Technology

2010-05-17

arranged by Prof. A. Zaslavsky Keywords: Gallium nitride High electron mobility transistor Molecular beam epitaxy Homoepitaxy Doping a b s t r a c t AlGaN...GaN/Be:GaN heterostructures have been grown by rf-plasma molecular beam epitaxy on free- standing semi-insulating GaN substrates, employing...hydride vapor phase epitaxy (HVPE) grown GaN sub- strates has enabled the growth by molecular beam epitaxy (MBE) of AlGaN/GaNHEMTswith significantly

Epitaxial Garnet Investigation; Technical Report, Foreign Travel

DTIC Science & Technology

1988-10-25

Pure yttrium iron garnet (YIG) films are grown on GGG substrates by * liquid phase epitaxy ( LPE ) in production lots. In addition, one or two...epitaxial garnet films for Philips Dr. Krumme * Dr. Doormann 3-6-87 Thomson - CSF Research Center, Orsay, France Dr. J. P. Castera Dr. P. L. Meunier all...research physicists who grow, characterize, Dr. J. Y. Beguin or use epitaxial garnet films for Thomson CSF. Dr. J. L. Rolland Dr. P. Friez The

Study of structural properties of cubic InN films on GaAs(001) substrates by molecular beam epitaxy and migration enhanced epitaxy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Casallas-Moreno, Y. L.; Perez-Caro, M.; Gallardo-Hernandez, S.

InN epitaxial films with cubic phase were grown by rf-plasma-assisted molecular beam epitaxy (RF-MBE) on GaAs(001) substrates employing two methods: migration-enhanced epitaxy (MEE) and conventional MBE technique. The films were synthesized at different growth temperatures ranging from 490 to 550 Degree-Sign C, and different In beam fluxes (BEP{sub In}) ranging from 5.9 Multiplication-Sign 10{sup -7} to 9.7 Multiplication-Sign 10{sup -7} Torr. We found the optimum conditions for the nucleation of the cubic phase of the InN using a buffer composed of several thin layers, according to reflection high-energy electron diffraction (RHEED) patterns. Crystallographic analysis by high resolution X-ray diffraction (HR-XRD)more » and RHEED confirmed the growth of c-InN by the two methods. We achieved with the MEE method a higher crystal quality and higher cubic phase purity. The ratio of cubic to hexagonal components in InN films was estimated from the ratio of the integrated X-ray diffraction intensities of the cubic (002) and hexagonal (1011) planes measured by X-ray reciprocal space mapping (RSM). For MEE samples, the cubic phase of InN increases employing higher In beam fluxes and higher growth temperatures. We have obtained a cubic purity phase of 96.4% for a film grown at 510 Degree-Sign C by MEE.« less

Weakly doped InP layers prepared by liquid phase epitaxy using a modulated cooling rate

NASA Astrophysics Data System (ADS)

Krukovskyi, R.; Mykhashchuk, Y.; Kost, Y.; Krukovskyi, S.; Saldan, I.

2017-04-01

Epitaxial structures based on InP are widely used to manufacture a number of devices such as microwave transistors, light-emitting diodes, lasers and Gunn diodes. However, their temporary instability caused by heterogeneity of resistivity along the layer thickness and the influence of various external or internal factors prompts the need for the development of a new reliable technology for their preparation. Weak doping by Yb, Al and Sn together with modulation of the cooling rate applied to prepare InP epitaxial layers is suggested to be adopted within the liquid phase epitaxy (LPE) method. The experimental results confirm the optimized conditions created to get a uniform electron concentration in the active n-InP layer. A sharp profile of electron concentration in the n+-InP(substrate)/n-InP/n+-InP epitaxial structure was observed experimentally at the proposed modulated cooling rate of 0.3 °С-1.5 °С min-1. The proposed technological method can be used to control the electrical and physical properties of InP epitaxial layers to be used in Gunn diodes.

Scalable solution-phase epitaxial growth of symmetry-mismatched heterostructures on two-dimensional crystal soft template.

PubMed

Lin, Zhaoyang; Yin, Anxiang; Mao, Jun; Xia, Yi; Kempf, Nicholas; He, Qiyuan; Wang, Yiliu; Chen, Chih-Yen; Zhang, Yanliang; Ozolins, Vidvuds; Ren, Zhifeng; Huang, Yu; Duan, Xiangfeng

2016-10-01

Epitaxial heterostructures with precisely controlled composition and electronic modulation are of central importance for electronics, optoelectronics, thermoelectrics, and catalysis. In general, epitaxial material growth requires identical or nearly identical crystal structures with small misfit in lattice symmetry and parameters and is typically achieved by vapor-phase depositions in vacuum. We report a scalable solution-phase growth of symmetry-mismatched PbSe/Bi 2 Se 3 epitaxial heterostructures by using two-dimensional (2D) Bi 2 Se 3 nanoplates as soft templates. The dangling bond-free surface of 2D Bi 2 Se 3 nanoplates guides the growth of PbSe crystal without requiring a one-to-one match in the atomic structure, which exerts minimal restriction on the epitaxial layer. With a layered structure and weak van der Waals interlayer interaction, the interface layer in the 2D Bi 2 Se 3 nanoplates can deform to accommodate incoming layer, thus functioning as a soft template for symmetry-mismatched epitaxial growth of cubic PbSe crystal on rhombohedral Bi 2 Se 3 nanoplates. We show that a solution chemistry approach can be readily used for the synthesis of gram-scale PbSe/Bi 2 Se 3 epitaxial heterostructures, in which the square PbSe (001) layer forms on the trigonal/hexagonal (0001) plane of Bi 2 Se 3 nanoplates. We further show that the resulted PbSe/Bi 2 Se 3 heterostructures can be readily processed into bulk pellet with considerably suppressed thermal conductivity (0.30 W/m·K at room temperature) while retaining respectable electrical conductivity, together delivering a thermoelectric figure of merit ZT three times higher than that of the pristine Bi 2 Se 3 nanoplates at 575 K. Our study demonstrates a unique epitaxy mode enabled by the 2D nanocrystal soft template via an affordable and scalable solution chemistry approach. It opens up new opportunities for the creation of diverse epitaxial heterostructures with highly disparate structures and functions.

Scalable solution-phase epitaxial growth of symmetry-mismatched heterostructures on two-dimensional crystal soft template

PubMed Central

Lin, Zhaoyang; Yin, Anxiang; Mao, Jun; Xia, Yi; Kempf, Nicholas; He, Qiyuan; Wang, Yiliu; Chen, Chih-Yen; Zhang, Yanliang; Ozolins, Vidvuds; Ren, Zhifeng; Huang, Yu; Duan, Xiangfeng

2016-01-01

Epitaxial heterostructures with precisely controlled composition and electronic modulation are of central importance for electronics, optoelectronics, thermoelectrics, and catalysis. In general, epitaxial material growth requires identical or nearly identical crystal structures with small misfit in lattice symmetry and parameters and is typically achieved by vapor-phase depositions in vacuum. We report a scalable solution-phase growth of symmetry-mismatched PbSe/Bi2Se3 epitaxial heterostructures by using two-dimensional (2D) Bi2Se3 nanoplates as soft templates. The dangling bond–free surface of 2D Bi2Se3 nanoplates guides the growth of PbSe crystal without requiring a one-to-one match in the atomic structure, which exerts minimal restriction on the epitaxial layer. With a layered structure and weak van der Waals interlayer interaction, the interface layer in the 2D Bi2Se3 nanoplates can deform to accommodate incoming layer, thus functioning as a soft template for symmetry-mismatched epitaxial growth of cubic PbSe crystal on rhombohedral Bi2Se3 nanoplates. We show that a solution chemistry approach can be readily used for the synthesis of gram-scale PbSe/Bi2Se3 epitaxial heterostructures, in which the square PbSe (001) layer forms on the trigonal/hexagonal (0001) plane of Bi2Se3 nanoplates. We further show that the resulted PbSe/Bi2Se3 heterostructures can be readily processed into bulk pellet with considerably suppressed thermal conductivity (0.30 W/m·K at room temperature) while retaining respectable electrical conductivity, together delivering a thermoelectric figure of merit ZT three times higher than that of the pristine Bi2Se3 nanoplates at 575 K. Our study demonstrates a unique epitaxy mode enabled by the 2D nanocrystal soft template via an affordable and scalable solution chemistry approach. It opens up new opportunities for the creation of diverse epitaxial heterostructures with highly disparate structures and functions. PMID:27730211

Advanced indium phosphide based monolithic integration using quantum well intermixing and MOCVD regrowth

NASA Astrophysics Data System (ADS)

Raring, James W.

The proliferation of the internet has fueled the explosive growth of telecommunications over the past three decades. As a result, the demand for communication systems providing increased bandwidth and flexibility at lower cost continues to rise. Lightwave communication systems meet these demands. The integration of multiple optoelectronic components onto a single chip could revolutionize the photonics industry. Photonic integrated circuits (PIC) provide the potential for cost reduction, decreased loss, decreased power consumption, and drastic space savings over conventional fiber optic communication systems comprised of discrete components. For optimal performance, each component within the PIC may require a unique epitaxial layer structure, band-gap energy, and/or waveguide architecture. Conventional integration methods facilitating such flexibility are increasingly complex and often result in decreased device yield, driving fabrication costs upward. It is this trade-off between performance and device yield that has hindered the scaling of photonic circuits. This dissertation presents high-functionality PICs operating at 10 and 40 Gb/s fabricated using novel integration technologies based on a robust quantum-well-intermixing (QWI) method and metal organic chemical vapor deposition (MOCVD) regrowth. We optimize the QWI process for the integration of high-performance quantum well electroabsorption modulators (QW-EAM) with sampled-grating (SG) DBR lasers to demonstrate the first widely-tunable negative chirp 10 and 40 Gb/s EAM based transmitters. Alone, QWI does not afford the integration of high-performance semiconductor optical amplifiers (SOA) and photodetectors with the transmitters. To overcome this limitation, we have developed a novel high-flexibility integration scheme combining MOCVD regrowth with QWI to merge low optical confinement factor SOAs and 40 Gb/s uni-traveling carrier (UTC) photodiodes on the same chip as the QW-EAM based transmitters. These high-saturation power receiver structures represent the state-of-the-art technologies for even discrete components. Using the novel integration technology, we present the first widely-tunable single-chip device capable of transmit and receive functionality at 40 Gb/s. This device monolithically integrates tunable lasers, EAMs, SOAs, and photodetectors with performance that rivals optimized discrete components. The high-flexibility integration scheme requires only simple blanket regrowth steps and thus breaks the performance versus yield trade-off plaguing conventional fabrication techniques employed for high-functionality PICs.

Enhancement of the Si p-n diode NIR photoresponse by embedding β-FeSi2 nanocrystallites.

PubMed

Shevlyagin, A V; Goroshko, D L; Chusovitin, E A; Galkin, K N; Galkin, N G; Gutakovskii, A K

2015-10-05

By using solid phase epitaxy of thin Fe films and molecular beam epitaxy of Si, a p(+)-Si/p-Si/β-FeSi2 nanocrystallites/n-Si(111) diode structure was fabricated. Transmission electron microscopy data confirmed a well-defined multilayered structure with embedded nanocrystallites of two typical sizes: 3-4 and 15-20 nm, and almost coherent epitaxy of the nanocrystallites with the Si matrix. The diode at zero bias conditions exhibited a current responsivity of 1.7 mA/W, an external quantum efficiency of about 0.2%, and a specific detectivity of 1.2 × 10(9) cm × Hz(1/2)/W at a wavelength of 1300 nm at room temperature. In the avalanche mode, the responsivity reached up to 20 mA/W (2% in terms of efficiency) with a value of avalanche gain equal to 5. The data obtained indicate that embedding of β-FeSi2 nanocrystallites into the depletion region of the Si p-n junction results in expansion of the spectral sensitivity up to 1600 nm and an increase of the photoresponse by more than two orders of magnitude in comparison with a conventional Si p-n junction. Thereby, fabricated structure combines advantage of the silicon photodiode functionality and simplicity with near infrared light detection capability of β-FeSi2.

A reliable method to grow vertically-aligned silicon nanowires by a novel ramp-cooling process

NASA Astrophysics Data System (ADS)

Ho, Tzuen-Wei; Hong, Franklin Chau-Nan

2012-08-01

We have grown silicon nanowires (SiNWs) on Si (1 1 1) substrates by gold-catalyzed vapor-liquid-solid (VLS) process using tetrachlorosilane (SiCl4) in a hot-wall chemical vapor deposition reactor. Even under the optimized conditions including H2 annealing to reduce the surface native oxide, epitaxial SiNWs of 150-200 nm in diameter often grew along all four <1 1 1> family directions with one direction vertical and three others inclined to the surface. Therefore, the growth of high degree ordered SiNW arrays along [1 1 1] only was attempted on Au-coated Si (1 1 1) by a ramp-cooling process utilizing the liquid phase epitaxy (LPE) mechanism. The Au-coated Si substrate was first annealed in H2 at 650 °C to form Au-Si alloy nanoparticles, and then ramp-cooled at a controlled rate to precipitate epitaxial Si seeds on the substrate based on LPE mechanism. The substrate was further heated in SiCl4/H2 to 850 °C for the VLS growths of SiNWs on the Si seeds. Thus, almost 100% vertically-aligned SiNWs along [1 1 1] only could be reproducibly grown on Si (1 1 1), without using a template or patterning the metal catalyst. The high-density vertically-aligned SiNWs have good potentials for solar cells and nano-devices.

Systematic Study of p-type Doping and Related Defects in III-Nitrides: Pathway toward a Nitride HBT

DTIC Science & Technology

2012-11-20

InGaN growth where an intermediate regime does not exist.40 Considering GaN molecular - beam epitaxy (MBE) growth phase diagrams such as those...1009 (2007). 44 S. D. Burnham, Improved Understanding and Control of Magnesium-Doped Gallium Nitride by Plasma Assisted Molecular Beam Epitaxy , in...reported using a modified form of molecular beam epitaxy (MBE) called Metal-Modulated Epitaxy (MME).11, 12 The details of this shuttered technique

Microbial safety of air-dried and rewetted biosolids.

PubMed

Rouch, Duncan A; Mondal, Tania; Pai, Sneha; Glauche, Florian; Fleming, Vennessa A; Thurbon, Nerida; Blackbeard, Judy; Smith, Stephen R; Deighton, Margaret

2011-06-01

To assess microbial safety of treated sewage sludge (biosolids), we examined the inactivation of microbial indicators for potential bacterial, viral and protozoan pathogens. The levels of indicators were determined throughout the air-drying and storage phases of anaerobically digested sewage sludge. Samples were collected from two wastewater treatment plants (WWTPS) in Victoria, Australia. Established methods were applied for analysis of bacteria and coliphages, based on membrane filtration and layered plates, respectively. In the pan drying phase, the prevalence of Escherichia coli was reduced by >5 log10 compared with sludge entering the pan. Thus, after pan drying of 8-11 months at WWTP A and 15 months at WWTP B, the numbers of E. coli were reduced to below 10(2) cfu/g dry solids (DS). This level is acceptable for unrestricted use in agriculture in Australia (P1 treatment grade), the UK (enhanced treatment status) and the USA (Class A pathogen reduction). Coliphage numbers also decreased substantially during the air-drying phase, indicating that enteric viruses are also likely to be destroyed during this phase. Clostridium perfringens appeared to be an overly conservative indicator. Survival, but not regrowth, of E. coli or Salmonella was observed in rewetted biosolids (15-20% moisture content), after being seeded with these species, indicating a degree of safety of stored biosolids upon rewetting by rain.

Crystal phase-based epitaxial growth of hybrid noble metal nanostructures on 4H/fcc Au nanowires

NASA Astrophysics Data System (ADS)

Lu, Qipeng; Wang, An-Liang; Gong, Yue; Hao, Wei; Cheng, Hongfei; Chen, Junze; Li, Bing; Yang, Nailiang; Niu, Wenxin; Wang, Jie; Yu, Yifu; Zhang, Xiao; Chen, Ye; Fan, Zhanxi; Wu, Xue-Jun; Chen, Jinping; Luo, Jun; Li, Shuzhou; Gu, Lin; Zhang, Hua

2018-03-01

Crystal-phase engineering offers opportunities for the rational design and synthesis of noble metal nanomaterials with unusual crystal phases that normally do not exist in bulk materials. However, it remains a challenge to use these materials as seeds to construct heterometallic nanostructures with desired crystal phases and morphologies for promising applications such as catalysis. Here, we report a strategy for the synthesis of binary and ternary hybrid noble metal nanostructures. Our synthesized crystal-phase heterostructured 4H/fcc Au nanowires enable the epitaxial growth of Ru nanorods on the 4H phase and fcc-twin boundary in Au nanowires, resulting in hybrid Au-Ru nanowires. Moreover, the method can be extended to the epitaxial growth of Rh, Ru-Rh and Ru-Pt nanorods on the 4H/fcc Au nanowires to form unique hybrid nanowires. Importantly, the Au-Ru hybrid nanowires with tunable compositions exhibit excellent electrocatalytic performance towards the hydrogen evolution reaction in alkaline media.

Growth of BaSi2 continuous films on Ge(111) by molecular beam epitaxy and fabrication of p-BaSi2/n-Ge heterojunction solar cells

NASA Astrophysics Data System (ADS)

Takabe, Ryota; Yachi, Suguru; Tsukahara, Daichi; Toko, Kaoru; Suemasu, Takashi

2017-05-01

We grew BaSi2 films on Ge(111) substrates by various growth methods based on molecular beam epitaxy (MBE). First, we attempted to form BaSi2 films directly on Ge(111) by MBE without templates. We next formed BaSi2 films using BaGe2 templates as commonly used for MBE growth of BaSi2 on Si substrates. Contrary to our prediction, the lateral growth of BaSi2 was not promoted by these two methods; BaSi2 formed not into a continuous film but into islands. Although streaky patterns of reflection high-energy electron diffraction were observed inside the growth chamber, no X-ray diffraction lines of BaSi2 were observed in samples taken out from the growth chamber. Such BaSi2 islands were easily to get oxidized. We finally attempted to form a continuous BaSi2 template layer on Ge(111) by solid phase epitaxy, that is, the deposition of amorphous Ba-Si layers onto MBE-grown BaSi2 epitaxial islands, followed by post annealing. We achieved the formation of an approximately 5-nm-thick BaSi2 continuous layer by this method. Using this BaSi2 layer as a template, we succeeded in forming a-axis-oriented 520-nm-thick BaSi2 epitaxial films on Ge substrates, although (111)-oriented Si grains were included in the grown layer. We next formed a B-doped p-BaSi2(20 nm)/n-Ge(111) heterojunction solar cell. A wide-spectrum response from 400 to 2000 nm was achieved. At an external bias voltage of 1 V, the external quantum efficiency reached as high as 60%, demonstrating the great potential of BaSi2/Ge combination. However, the efficiency of a solar cell under AM1.5 illumination was quite low (0.1%). The origin of such a low efficiency was examined.

Development of lamellar structures in natural waxes - an electron diffraction investigation

NASA Astrophysics Data System (ADS)

Dorset, Douglas L.

1999-06-01

When they are recrystallized from the melt, natural plant or insect waxes tend to form solid phases with a nematic-like structure (i.e. a parallel array of polymethylene chains with little or no aggregation of the molecules into distinct layers). An electron diffraction study of carnauba wax and two types of beeswax has shown that the degree of molecular organization into lamellar structures can be enhanced by annealing in the presence of benzoic acid, which also acts as an epitaxial substrate. Nevertheless, the resultant layer structure in the annealed solid is not the same as that found for paraffin wax fractions refined from petroleum. Probably because of a small but significant fraction of a very long chain ingredient, the lamellar separation is incomplete, incorporating a number of `bridging molecules' that span the nascent lamellar interface.The same phenomenon has been described recently for a low molecular weight polyethylene.

Electroepitaxy of multicomponent systems - Ternary and quarternary compounds

NASA Technical Reports Server (NTRS)

Bryskiewicz, T.; Lagowski, J.; Gatos, H. C.

1980-01-01

A theoretical model is presented which accounts for the electroepitaxial growth kinetics and composition of multicomponent compounds in terms of mass transport in the liquid and phase diagram relationships. The mass transport in the interface is dominated by electromigration in the absence of convection and by diffusion in the presence of convection. The composition of the solid is controlled by the Peltier effect at the growth interface and by the diffusion and mobility constants of the solute components and the growth velocity (current density). Thus, for a given solution composition, the composition of the solid can be varied by varying the current density. For a given current density the composition remains constant even in the case of relatively thick epitaxial layers. All aspects of the model were found to be in good agreement with the growth and composition characteristics of Ga/x-1/Al/x/As layers.

Probing mixed tetragonal/rhombohedral-like monoclinic phases in strained bismuth ferrite films by optical second harmonic generation

NASA Astrophysics Data System (ADS)

Kumar, Amit; Denev, Sava; Zeches, Robert J.; Vlahos, Eftihia; Podraza, Nikolas J.; Melville, Alexander; Schlom, Darrell G.; Ramesh, R.; Gopalan, Venkatraman

2010-09-01

Epitaxial strain can induce the formation of morphotropic phase boundary in lead free ferroelectrics like bismuth ferrite, thereby enabling the coexistence of tetragonal and rhombohedral phases in the same film. The relative ratio of these phases is governed by the film thickness and theoretical studies suggest that there exists a monoclinic distortion of both the tetragonal as well as the rhombohedral unit cells due to imposed epitaxial strain. In this work we show that optical second harmonic generation can distinguish the tetragonal-like phase from the rhombohedral-like phase and enable detection of monoclinic distortion in only a pure tetragonal-like phase.

Epitaxial bain paths and metastable phases of tetragonal iron and manganese

NASA Astrophysics Data System (ADS)

Ma, Hong

2002-04-01

Epitaxial Bain paths and metastable states of tetragonal Fe and Mn have been studied by first-principles total-energy calculations using the full-potential linearized-augmented-plane-wave method. The main accomplishments are as follows. (1) We have performed the first ever EBP calculation of tetragonal antiferromagnetic (AF) Mn showing that when grown epitaxially on Pd(001), the AF Mn film is strained gamma-Mn, but grown on V(001) the film is strained delta-Mn, which could not be determined using the available crystallographic and elastic data because they were obtained from unstrained states. (2) We have calculated the EBP's of Fe at zero pressure in four magnetic phases, i.e., ferromagnetic (FM), nonmagnetic (NM), type-I antiferromagnetic (AF1), and type-II antiferromagnetic (AF2), which show that the AF2 is the phase of the bulk of epitaxial Fe films on Cu(001) and it is unstable for [110] and [010] shears in the (001) plane, but it can be stabilized by epitaxy on Cu(001). (3)We have unified and simplified the theory of elasticity under hydrostatic pressure p at zero temperature using the Gibbs free energy G, rather than the energy E. The minima of G, but not E, with respect to strains at the equilibrium structure give the zero temperature elastic constants; the stability of a phase at p is then determined by the same Born stability conditions used at p = 0 when applied to the elastic constants from G. The EBP's of FM Fe under hydrostatic pressure show that the bcc phase exists up to 1500 kbar. A bct phase is shown to come into existence at 1300 kbar and becomes stable at 1825 kbar and above. (4) Based on this dissertation research five papers have been published in refereed journals.

Epitaxial layers of 2122 BCSCO superconductor thin films having single crystalline structure

NASA Technical Reports Server (NTRS)

Pandey, Raghvendra K. (Inventor); Raina, Kanwal K. (Inventor); Solayappan, Narayanan (Inventor)

1995-01-01

A substantially single phase, single crystalline, highly epitaxial film of Bi.sub.2 CaSr.sub.2 Cu.sub.2 O.sub.8 superconductor which has a T.sub.c (zero resistance) of 83K is provided on a lattice-matched substrate with no intergrowth. This film is produced by a Liquid Phase Epitaxy method which includes the steps of forming a dilute supercooled molten solution of a single phase superconducting mixture of oxides of Bi, Ca, Sr, and Cu having an atomic ratio of about 2:1:2:2 in a nonreactive flux such as KCl, introducing the substrate, e.g., NdGaO.sub.3, into the molten solution at 850.degree. C., cooling the solution from 850.degree. C. to 830.degree. C. to grow the film and rapidly cooling the substrate to room temperature to maintain the desired single phase, single crystalline film structure.

Solid State Research.

DTIC Science & Technology

1982-11-22

48 Fabricated in Zone-Melting-Recrystallized Si Films on Si0 2-Coated Si Substrates V 4. MICROELECTRONICS 55 4.1 Charge-Coupled Devices: Time...OMCVD to the CLEFT (cleavage of lateral epitaxial films for transfer) process, a continuous epitaxial GaAs layer 3 Ym thick has been grown over a...complete-island-etch or local-oxidation-of-Si isolation, that were fabricated in zone-melting-recrystallized Si films on Si02-coated Si substrates. As

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.

Vertical epitaxial wire-on-wire growth of Ge/Si on Si(100) substrate.

PubMed

Shimizu, Tomohiro; Zhang, Zhang; Shingubara, Shoso; Senz, Stephan; Gösele, Ulrich

2009-04-01

Vertically aligned epitaxial Ge/Si heterostructure nanowire arrays on Si(100) substrates were prepared by a two-step chemical vapor deposition method in anodic aluminum oxide templates. n-Butylgermane vapor was employed as new safer precursor for Ge nanowire growth instead of germane. First a Si nanowire was grown by the vapor liquid solid growth mechanism using Au as catalyst and silane. The second step was the growth of Ge nanowires on top of the Si nanowires. The method presented will allow preparing epitaxially grown vertical heterostructure nanowires consisting of multiple materials on an arbitrary substrate avoiding undesired lateral growth.

A kinetic Monte Carlo simulation method of van der Waals epitaxy for atomistic nucleation-growth processes of transition metal dichalcogenides.

PubMed

Nie, Yifan; Liang, Chaoping; Cha, Pil-Ryung; Colombo, Luigi; Wallace, Robert M; Cho, Kyeongjae

2017-06-07

Controlled growth of crystalline solids is critical for device applications, and atomistic modeling methods have been developed for bulk crystalline solids. Kinetic Monte Carlo (KMC) simulation method provides detailed atomic scale processes during a solid growth over realistic time scales, but its application to the growth modeling of van der Waals (vdW) heterostructures has not yet been developed. Specifically, the growth of single-layered transition metal dichalcogenides (TMDs) is currently facing tremendous challenges, and a detailed understanding based on KMC simulations would provide critical guidance to enable controlled growth of vdW heterostructures. In this work, a KMC simulation method is developed for the growth modeling on the vdW epitaxy of TMDs. The KMC method has introduced full material parameters for TMDs in bottom-up synthesis: metal and chalcogen adsorption/desorption/diffusion on substrate and grown TMD surface, TMD stacking sequence, chalcogen/metal ratio, flake edge diffusion and vacancy diffusion. The KMC processes result in multiple kinetic behaviors associated with various growth behaviors observed in experiments. Different phenomena observed during vdW epitaxy process are analysed in terms of complex competitions among multiple kinetic processes. The KMC method is used in the investigation and prediction of growth mechanisms, which provide qualitative suggestions to guide experimental study.

Accumulation of Background Impurities in Hydride Vapor Phase Epitaxy Grown GaN Layers

NASA Astrophysics Data System (ADS)

Usikov, Alexander; Soukhoveev, Vitali; Kovalenkov, Oleg; Syrkin, Alexander; Shapovalov, Liza; Volkova, Anna; Ivantsov, Vladimir

2013-08-01

We report on accumulation of background Si and O impurities measured by secondary ion mass spectrometry (SIMS) at the sub-interfaces in undoped, Zn- and Mg-doped multi-layer GaN structures grown by hydride vapor phase epitaxy (HVPE) on sapphire substrates with growth interruptions. The impurities accumulation is attributed to reaction of ammonia with the rector quartz ware during the growth interruptions. Because of this effect, HVPE-grown GaN layers had excessive Si and O concentration on the surface that may hamper forming of ohmic contacts especially in the case of p-type layers and may complicate homo-epitaxial growth of a device structure.

High quality factor whispering gallery modes from self-assembled hexagonal GaN rods grown by metal-organic vapor phase epitaxy.

PubMed

Tessarek, C; Sarau, G; Kiometzis, M; Christiansen, S

2013-02-11

Self-assembled GaN rods were grown on sapphire by metal-organic vapor phase epitaxy using a simple two-step method that relies first on a nitridation step followed by GaN epitaxy. The mask-free rods formed without any additional catalyst. Most of the vertically aligned rods exhibit a regular hexagonal shape with sharp edges and smooth sidewall facets. Cathodo- and microphotoluminescence investigations were carried out on single GaN rods. Whispering gallery modes with quality factors greater than 4000 were measured demonstrating the high morphological and optical quality of the self-assembled GaN rods.

Optical properties of bulk gallium nitride single crystals grown by chloride-hydride vapor-phase epitaxy

NASA Astrophysics Data System (ADS)

Agyekyan, V. F.; Borisov, E. V.; Serov, A. Yu.; Filosofov, N. G.

2017-12-01

A gallium nitride crystal 5 mm in thickness was grown by chloride-hydride vapor-phase epitaxy on a sapphire substrate, from which the crystal separated during cooling. At an early stage, a three-dimensional growth mode was implemented, followed by a switch to a two-dimensional mode. Spectra of exciton reflection, exciton luminescence, and Raman scattering are studied in several regions characteristic of the sample. Analysis of these spectra and comparison with previously obtained data for thin epitaxial GaN layers with a wide range of silicon doping enabled conclusions about the quality of the crystal lattice in these characteristic regions.

Atomic layer epitaxy of hematite on indium tin oxide for application in solar energy conversion

DOEpatents

Martinson, Alex B.; Riha, Shannon; Guo, Peijun; Emery, Jonathan D.

2016-07-12

A method to provide an article of manufacture of iron oxide on indium tin oxide for solar energy conversion. An atomic layer epitaxy method is used to deposit an uncommon bixbytite-phase iron (III) oxide (.beta.-Fe.sub.2O.sub.3) which is deposited at low temperatures to provide 99% phase pure .beta.-Fe.sub.2O.sub.3 thin films on indium tin oxide. Subsequent annealing produces pure .alpha.-Fe.sub.2O.sub.3 with well-defined epitaxy via a topotactic transition. These highly crystalline films in the ultra thin film limit enable high efficiency photoelectrochemical chemical water splitting.

Single Crystal Faceplate Evaluation

DTIC Science & Technology

1993-10-25

conventional powder phosphor. The utility of garnets is amplified by the high state of the art of liquid phase epitaxy ( LPE ). Liquid phase epitaxy of...7]. Much the research at Allied-Signal, Inc. in garnet layer growth has been involved with the kinetics of crystallization of garnet from LPE melts...acceptable resolution and light output characteristics. Single crystal faceplates being evaluated are composed of yttrium aluminum garnet (YAG) with an

Low-temperature atomic layer epitaxy of AlN ultrathin films by layer-by-layer, in-situ atomic layer annealing.

PubMed

Shih, Huan-Yu; Lee, Wei-Hao; Kao, Wei-Chung; Chuang, Yung-Chuan; Lin, Ray-Ming; Lin, Hsin-Chih; Shiojiri, Makoto; Chen, Miin-Jang

2017-01-03

Low-temperature epitaxial growth of AlN ultrathin films was realized by atomic layer deposition (ALD) together with the layer-by-layer, in-situ atomic layer annealing (ALA), instead of a high growth temperature which is needed in conventional epitaxial growth techniques. By applying the ALA with the Ar plasma treatment in each ALD cycle, the AlN thin film was converted dramatically from the amorphous phase to a single-crystalline epitaxial layer, at a low deposition temperature of 300 °C. The energy transferred from plasma not only provides the crystallization energy but also enhances the migration of adatoms and the removal of ligands, which significantly improve the crystallinity of the epitaxial layer. The X-ray diffraction reveals that the full width at half-maximum of the AlN (0002) rocking curve is only 144 arcsec in the AlN ultrathin epilayer with a thickness of only a few tens of nm. The high-resolution transmission electron microscopy also indicates the high-quality single-crystal hexagonal phase of the AlN epitaxial layer on the sapphire substrate. The result opens a window for further extension of the ALD applications from amorphous thin films to the high-quality low-temperature atomic layer epitaxy, which can be exploited in a variety of fields and applications in the near future.

Low-temperature atomic layer epitaxy of AlN ultrathin films by layer-by-layer, in-situ atomic layer annealing

PubMed Central

Shih, Huan-Yu; Lee, Wei-Hao; Kao, Wei-Chung; Chuang, Yung-Chuan; Lin, Ray-Ming; Lin, Hsin-Chih; Shiojiri, Makoto; Chen, Miin-Jang

2017-01-01

Low-temperature epitaxial growth of AlN ultrathin films was realized by atomic layer deposition (ALD) together with the layer-by-layer, in-situ atomic layer annealing (ALA), instead of a high growth temperature which is needed in conventional epitaxial growth techniques. By applying the ALA with the Ar plasma treatment in each ALD cycle, the AlN thin film was converted dramatically from the amorphous phase to a single-crystalline epitaxial layer, at a low deposition temperature of 300 °C. The energy transferred from plasma not only provides the crystallization energy but also enhances the migration of adatoms and the removal of ligands, which significantly improve the crystallinity of the epitaxial layer. The X-ray diffraction reveals that the full width at half-maximum of the AlN (0002) rocking curve is only 144 arcsec in the AlN ultrathin epilayer with a thickness of only a few tens of nm. The high-resolution transmission electron microscopy also indicates the high-quality single-crystal hexagonal phase of the AlN epitaxial layer on the sapphire substrate. The result opens a window for further extension of the ALD applications from amorphous thin films to the high-quality low-temperature atomic layer epitaxy, which can be exploited in a variety of fields and applications in the near future. PMID:28045075

Epitaxial stabilization and phase instability of VO2 polymorphs

NASA Astrophysics Data System (ADS)

Lee, Shinbuhm; Ivanov, Ilia N.; Keum, Jong K.; Lee, Ho Nyung

2016-01-01

The VO2 polymorphs, i.e., VO2(A), VO2(B), VO2(M1) and VO2(R), have a wide spectrum of functionalities useful for many potential applications in information and energy technologies. However, synthesis of phase pure materials, especially in thin film forms, has been a challenging task due to the fact that the VO2 polymorphs are closely related to each other in a thermodynamic framework. Here, we report epitaxial stabilization of the VO2 polymorphs to synthesize high quality single crystalline thin films and study the phase stability of these metastable materials. We selectively deposit all the phases on various perovskite substrates with different crystallographic orientations. By investigating the phase instability, phonon modes and transport behaviours, not only do we find distinctively contrasting physical properties of the VO2 polymorphs, but that the polymorphs can be on the verge of phase transitions when heated as low as ~400 °C. Our successful epitaxy of both VO2(A) and VO2(B) phases, which are rarely studied due to the lack of phase pure materials, will open the door to the fundamental studies of VO2 polymorphs for potential applications in advanced electronic and energy devices.

Epitaxial stabilization and phase instability of VO2 polymorphs.

PubMed

Lee, Shinbuhm; Ivanov, Ilia N; Keum, Jong K; Lee, Ho Nyung

2016-01-20

The VO2 polymorphs, i.e., VO2(A), VO2(B), VO2(M1) and VO2(R), have a wide spectrum of functionalities useful for many potential applications in information and energy technologies. However, synthesis of phase pure materials, especially in thin film forms, has been a challenging task due to the fact that the VO2 polymorphs are closely related to each other in a thermodynamic framework. Here, we report epitaxial stabilization of the VO2 polymorphs to synthesize high quality single crystalline thin films and study the phase stability of these metastable materials. We selectively deposit all the phases on various perovskite substrates with different crystallographic orientations. By investigating the phase instability, phonon modes and transport behaviours, not only do we find distinctively contrasting physical properties of the VO2 polymorphs, but that the polymorphs can be on the verge of phase transitions when heated as low as ~400 °C. Our successful epitaxy of both VO2(A) and VO2(B) phases, which are rarely studied due to the lack of phase pure materials, will open the door to the fundamental studies of VO2 polymorphs for potential applications in advanced electronic and energy devices.

Epitaxial stabilization and phase instability of VO2 polymorphs

PubMed Central

Lee, Shinbuhm; Ivanov, Ilia N.; Keum, Jong K.; Lee, Ho Nyung

2016-01-01

The VO2 polymorphs, i.e., VO2(A), VO2(B), VO2(M1) and VO2(R), have a wide spectrum of functionalities useful for many potential applications in information and energy technologies. However, synthesis of phase pure materials, especially in thin film forms, has been a challenging task due to the fact that the VO2 polymorphs are closely related to each other in a thermodynamic framework. Here, we report epitaxial stabilization of the VO2 polymorphs to synthesize high quality single crystalline thin films and study the phase stability of these metastable materials. We selectively deposit all the phases on various perovskite substrates with different crystallographic orientations. By investigating the phase instability, phonon modes and transport behaviours, not only do we find distinctively contrasting physical properties of the VO2 polymorphs, but that the polymorphs can be on the verge of phase transitions when heated as low as ~400 °C. Our successful epitaxy of both VO2(A) and VO2(B) phases, which are rarely studied due to the lack of phase pure materials, will open the door to the fundamental studies of VO2 polymorphs for potential applications in advanced electronic and energy devices. PMID:26787259

Structural evolution of epitaxial SrCoO x films near topotactic phase transition

DOE PAGES

Jeen, Hyoung Jeen; Lee, Ho Nyung

2015-12-18

Control of oxygen stoichiometry in complex oxides via topotactic phase transition is an interesting avenue to not only modifying the physical properties, but utilizing in many energy technologies, such as energy storage and catalysts. However, detailed structural evolution in the close proximity of the topotactic phase transition in multivalent oxides has not been much studied. In this work, we used strontium cobaltites (SrCoO x) epitaxially grown by pulsed laser epitaxy (PLE) as a model system to study the oxidation-driven evolution of the structure, electronic, and magnetic properties. We grew coherently strained SrCoO 2.5thin films and performed post-annealing at various temperaturesmore » for topotactic conversion into the perovskite phase (SrCoO 3-δ). We clearly observed significant changes in electronic transport, magnetism, and microstructure near the critical temperature for the topotactic transformation from the brownmillerite to the perovskite phase. Furthermore, the overall crystallinity was well maintained without much structural degradation, indicating that topotactic phase control can be a useful tool to control the physical properties repeatedly via redox reactions.« less

Epitaxial growth of hybrid nanostructures

NASA Astrophysics Data System (ADS)

Tan, Chaoliang; Chen, Junze; Wu, Xue-Jun; Zhang, Hua

2018-02-01

Hybrid nanostructures are a class of materials that are typically composed of two or more different components, in which each component has at least one dimension on the nanoscale. The rational design and controlled synthesis of hybrid nanostructures are of great importance in enabling the fine tuning of their properties and functions. Epitaxial growth is a promising approach to the controlled synthesis of hybrid nanostructures with desired structures, crystal phases, exposed facets and/or interfaces. This Review provides a critical summary of the state of the art in the field of epitaxial growth of hybrid nanostructures. We discuss the historical development, architectures and compositions, epitaxy methods, characterization techniques and advantages of epitaxial hybrid nanostructures. Finally, we provide insight into future research directions in this area, which include the epitaxial growth of hybrid nanostructures from a wider range of materials, the study of the underlying mechanism and determining the role of epitaxial growth in influencing the properties and application performance of hybrid nanostructures.

Crystallization engineering as a route to epitaxial strain control

DOE Office of Scientific and Technical Information (OSTI.GOV)

Akbashev, Andrew R.; Plokhikh, Aleksandr V.; Barbash, Dmitri

2015-10-01

The controlled synthesis of epitaxial thin films offers opportunities for tuning their functional properties via enabling or suppressing strain relaxation. Examining differences in the epitaxial crystallization of amorphous oxide films, we report on an alternate, low-temperature route for strain engineering. Thin films of amorphous Bi–Fe–O were grown on (001)SrTiO{sub 3} and (001)LaAlO{sub 3} substrates via atomic layer deposition. In situ X-ray diffraction and X-ray photoelectron spectroscopy studies of the crystallization of the amorphous films into the epitaxial (001)BiFeO{sub 3} phase reveal distinct evolution profiles of crystallinity with temperature. While growth on (001)SrTiO{sub 3} results in a coherently strained film, themore » same films obtained on (001)LaAlO{sub 3} showed an unstrained, dislocation-rich interface, with an even lower temperature onset of the perovskite phase crystallization than in the case of (001)SrTiO{sub 3}. Our results demonstrate how the strain control in an epitaxial film can be accomplished via its crystallization from the amorphous state.« less

Demonstration of single crystal growth via solid-solid transformation of a glass

DOE PAGES

Savytskii, Dmytro; Knorr, Brian; Dierolf, Volkmar; ...

2016-03-18

Many advanced technologies have relied on the availability of single crystals of appropriate material such as silicon for microelectronics or superalloys for turbine blades. Similarly, many promising materials could unleash their full potential if they were available in a single crystal form. However, the current methods are unsuitable for growing single crystals of these oftentimes incongruently melting, unstable or metastable materials. Here we demonstrate a strategy to overcome this hurdle by avoiding the gaseous or liquid phase, and directly converting glass into a single crystal. Specifically, Sb 2S 3 single crystals are grown in Sb-S-I glasses as an example ofmore » this approach. In this first unambiguous demonstration of an all-solid-state glass → crystal transformation, extraneous nucleation is avoided relative to crystal growth via spatially localized laser heating and inclusion of a suitable glass former in the composition. Lastly, the ability to fabricate patterned single-crystal architecture on a glass surface is demonstrated, providing a new class of micro-structured substrate for low cost epitaxial growth, active planar devices, etc.« less

Enhancement of the Si p-n diode NIR photoresponse by embedding β-FeSi2 nanocrystallites

PubMed Central

Shevlyagin, A. V.; Goroshko, D. L.; Chusovitin, E. A.; Galkin, K. N.; Galkin, N. G.; Gutakovskii, A. K.

2015-01-01

By using solid phase epitaxy of thin Fe films and molecular beam epitaxy of Si, a p+-Si/p-Si/β-FeSi2 nanocrystallites/n-Si(111) diode structure was fabricated. Transmission electron microscopy data confirmed a well-defined multilayered structure with embedded nanocrystallites of two typical sizes: 3–4 and 15–20 nm, and almost coherent epitaxy of the nanocrystallites with the Si matrix. The diode at zero bias conditions exhibited a current responsivity of 1.7 mA/W, an external quantum efficiency of about 0.2%, and a specific detectivity of 1.2 × 109 cm × Hz1/2/W at a wavelength of 1300 nm at room temperature. In the avalanche mode, the responsivity reached up to 20 mA/W (2% in terms of efficiency) with a value of avalanche gain equal to 5. The data obtained indicate that embedding of β-FeSi2 nanocrystallites into the depletion region of the Si p-n junction results in expansion of the spectral sensitivity up to 1600 nm and an increase of the photoresponse by more than two orders of magnitude in comparison with a conventional Si p-n junction. Thereby, fabricated structure combines advantage of the silicon photodiode functionality and simplicity with near infrared light detection capability of β-FeSi2. PMID:26434582

Distribution of point defects in Si(100)/Si grown by low-temperature molecular-beam epitaxy and solid-phase epitaxy

NASA Astrophysics Data System (ADS)

Asoka-Kumar, P.; Gossmann, H.-J.; Unterwald, F. C.; Feldman, L. C.; Leung, T. C.; Au, H. L.; Talyanski, V.; Nielsen, B.; Lynn, K. G.

1993-08-01

Positron annihilation in Si is a quantitaive, depth-sensitive technique for the detection of vacancylike defects or voids. A sensitivity of 5×1015 cm-3 for voidlike defects is easily achieved. The technique has been applied to a study of point-defect distributions in thin films of Si grown by molecular-beam epitaxy. A special procedure was developed to remove the influence of the native oxide on the positron measurement. 200-nm-thick films grown at temperatures between 475 and 560 °C show no defects below the sensitivity limit and are indistinguishable from the bulk substrate. So are films grown at 220 °C, provided a 2-min high-temperature anneal to a peak temperature of >=500 °C is executed every ~=30 nm during growth. If TRTA=450 °C, part of the film contains vacancylike defects to a concentration of ~=1018 cm-3. These results correlate well with current-voltage characteristics of p-n junctions grown with different rapid thermal anneal (RTA) temperatures. Ion scattering, with a defect sensitivity of ~=1%, shows no difference between films grown with different TRTA. Recrystallization of amorphous films, deposited at room temperature and annealed in situ at 550 °C, always leaves a significant defect concentration of ~=2×1018 cm-3; those defects are reduced but still present even after a 2-h 800 °C furnace anneal.

Abrupt GaP/Si hetero-interface using bistepped Si buffer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ping Wang, Y., E-mail: yanping.wang@insa-rennes.fr; Kuyyalil, J.; Nguyen Thanh, T.

We evidence the influence of the quality of the starting Si surface on the III-V/Si interface abruptness and on the formation of defects during the growth of III-V/Si heterogeneous crystal, using high resolution transmission electron microscopy and scanning transmission electron microscopy. GaP layers were grown by molecular beam epitaxy on vicinal Si (001). The strong effect of the Si substrate chemical preparation is first demonstrated by studying structural properties of both Si homoepitaxial layer and GaP/Si heterostructure. It is then shown that choosing adequate chemical preparation conditions and subsequent III-V regrowth conditions enables the quasi-suppression of micro-twins in the epilayer.more » Finally, the abruptness of GaP/Si interface is found to be very sensitive to the Si chemical preparation and is improved by the use of a bistepped Si buffer prior to III-V overgrowth.« less

Tunable Microwave Transversal Filters.

DTIC Science & Technology

1984-05-01

magnetostatic waves MSW propagating at microwave frequency in magnetically biased, liquid phase epitaxial films of yttrium iron garnet (YIG) grown on...25 uM-thick 3 mm-wide and 15 mm-long YIG film grown by liquid phase epitaxy On a 500 uM-thick ( ) gadolinium gallium garnet (GGG) substrate was used...obtained. The delay line material was prepared by growing YIG films on one inch diameter gallium gadolinium garnet (GGG) wafers using the liquid

Chirality-Controlled Growth of Single-Wall Carbon Nanotubes Using Vapor Phase Epitaxy: Mechanistic Understanding and Scalable Production

DTIC Science & Technology

2016-09-15

controlled synthesis of single-wall carbon nanotubes. Firstly, we have successfully demonstrated a vapor-phase-epitaxy-analogous general strategy for...preselected chirality. Moreover, we carried out systematic investigations of the chirality-dependent growth kinetics and termination mechanism for the... generally believed that the diameters of the nanotubes are determined by the size of the catalytic metal particles. Unfortunately, attempts to control

Semiconductor diode laser material and devices with emission in visible region of the spectrum

NASA Technical Reports Server (NTRS)

Ladany, I.; Kressel, H.

1975-01-01

Two alloy systems, (AlGa)As and (InGa)P, were studied for their properties relevant to obtaining laser diode operation in the visible region of the spectrum. (AlGa)As was prepared by liquid-phase epitaxy (LPE) and (InGa)P was prepared both by vapor-phase epitaxy and by liquid-phase epitaxy. Various schemes for LPE growth were applied to (InGa)P, one of which was found to be capable of producing device material. All the InGaP device work was done using vapor-phase epitaxy. The most successful devices were fabricated in (AlGa)As using heterojunction structures. At room temperature, the large optical cavity design yielded devices lasing in the red (7000 A). Because of the relatively high threshold due to the basic band structure limitation in this alloy, practical laser diode operation is presently limited to about 7300 A. At liquid-nitrogen temperature, practical continuous-wave operation was obtained at a wavelength of 6500 to 6600 A, with power emission in excess of 50 mW. The lowest pulsed lasing wavelength is 6280 A. At 223 K, lasing was obtained at 6770 A, but with high threshold currents. The work dealing with CW operation at room temperature was successful with practical operation having been achieved to about 7800 A.

Gallium Nitride (GaN) High Power Electronics (FY11)

DTIC Science & Technology

2012-01-01

GaN films grown by metal-organic chemical vapor deposition (MOCVD) and ~1010 in films grown by molecular beam epitaxy (MBE) when they are deposited...inductively coupled plasma I-V current-voltage L-HVPE low doped HVPE MBE molecular beam epitaxy MOCVD metal-organic chemical vapor deposition...figure of merit HEMT high electron mobility transistor H-HVPE high doped HVPE HPE high power electronics HVPE hydride vapor phase epitaxy ICP

Effect of crystal orientation on the phase diagrams, dielectric and piezoelectric properties of epitaxial BaTiO{sub 3} thin films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Huaping, E-mail: wuhuaping@gmail.com, E-mail: hpwu@zjut.edu.cn; State Key Laboratory of Structural Analysis for Industrial Equipment, Dalian University of Technology, Dalian 116024; Ma, Xuefu

2016-01-15

The influence of crystal orientations on the phase diagrams, dielectric and piezoelectric properties of epitaxial BaTiO{sub 3} thin films has been investigated using an expanded nonlinear thermodynamic theory. The calculations reveal that crystal orientation has significant influence on the phase stability and phase transitions in the misfit strain-temperature phase diagrams. In particular, the (110) orientation leads to a lower symmetry and more complicated phase transition than the (111) orientation in BaTiO{sub 3} films. The increase of compressive strain will dramatically enhance the Curie temperature T{sub C} of (110)-oriented BaTiO{sub 3} films, which matches well with previous experimental data. The polarizationmore » components experience a great change across the boundaries of different phases at room temperature in both (110)- and (111)-oriented films, which leads to the huge dielectric and piezoelectric responses. A good agreement is found between the present thermodynamics calculation and previous first-principles calculations. Our work provides an insight into how to use crystal orientation, epitaxial strain and temperature to tune the structure and properties of ferroelectrics.« less

Epitaxial phase diagrams of SrTiO3, CaTiO3, and SrHfO3: Computational investigation including the role of antiferrodistortive and A -site displacement modes

NASA Astrophysics Data System (ADS)

Angsten, Thomas; Asta, Mark

2018-04-01

Ground-state epitaxial phase diagrams are calculated by density functional theory (DFT) for SrTiO3, CaTiO3, and SrHfO3 perovskite-based compounds, accounting for the effects of antiferrodistortive and A -site displacement modes. Biaxial strain states corresponding to epitaxial growth of (001)-oriented films are considered, with misfit strains ranging between -4 % and 4%. Ground-state structures are determined using a computational procedure in which input structures for DFT optimizations are identified as local minima in expansions of the total energy with respect to strain and soft-mode degrees of freedom. Comparison to results of previous DFT studies demonstrates the effectiveness of the computational approach in predicting ground-state phases. The calculated results show that antiferrodistortive octahedral rotations and associated A -site displacement modes act to suppress polarization and reduce the epitaxial strain energy. A projection of calculated atomic displacements in the ground-state epitaxial structures onto soft-mode eigenvectors shows that three ferroelectric and six antiferrodistortive displacement modes are dominant at all misfit strains considered, with the relative contributions from each varying systematically with the strain. Additional A -site displacement modes contribute to the atomic displacements in CaTiO3 and SrHfO3, which serve to optimize the coordination of the undersized A -site cation.

A divalent rare earth oxide semiconductor: Yttrium monoxide

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kaminaga, Kenichi; Sei, Ryosuke; Department of Chemistry, Tohoku University, Sendai 980-8578

Rare earth oxides are usually widegap insulators like Y{sub 2}O{sub 3} with closed shell trivalent rare earth ions. In this study, solid phase rock salt structure yttrium monoxide, YO, with unusual valence of Y{sup 2+} (4d{sup 1}) was synthesized in a form of epitaxial thin film by pulsed laser deposition method. YO has been recognized as gaseous phase in previous studies. In contrast with Y{sub 2}O{sub 3}, YO was dark-brown colored and narrow gap semiconductor. The tunable electrical conductivity ranging from 10{sup −1} to 10{sup 3} Ω{sup −1 }cm{sup −1} was attributed to the presence of oxygen vacancies serving as electron donor.more » Weak antilocalization behavior observed in magnetoresistance indicated significant role of spin-orbit coupling as a manifestation of 4d electron carrier.« less

Liquid phase heteroepitaxial growth on convex substrate using binary phase field crystal model

NASA Astrophysics Data System (ADS)

Lu, Yanli; Zhang, Tinghui; Chen, Zheng

2018-06-01

The liquid phase heteroepitaxial growth on convex substrate is investigated with the binary phase field crystal (PFC) model. The paper aims to focus on the transformation of the morphology of epitaxial films on convex substrate with two different radiuses of curvature (Ω) as well as influences of substrate vicinal angles on films growth. It is found that films growth experience different stages on convex substrate with different radiuses of curvature (Ω). For Ω = 512 Δx , the process of epitaxial film growth includes four stages: island coupled with layer-by-layer growth, layer-by-layer growth, island coupled with layer-by-layer growth, layer-by-layer growth. For Ω = 1024 Δx , film growth only experience islands growth and layer-by-layer growth. Also, substrate vicinal angle (π) is an important parameter for epitaxial film growth. We find the film can grow well when π = 2° for Ω = 512 Δx , while the optimized film can be obtained when π = 4° for Ω = 512 Δx .

Coexisting nanoscale inverse spinel and rock salt crystallographic phases in NiCo2O4 epitaxial thin films grown by pulsed laser deposition

NASA Astrophysics Data System (ADS)

Sharona, H.; Loukya, B.; Bhat, U.; Sahu, R.; Vishal, B.; Silwal, P.; Gupta, A.; Datta, R.

2017-12-01

The origin of alternating wavy dark-bright stripe-like contrast in strain contrast transmission electron microscopy images of NiCo2O4 (NCO) epitaxial thin films grown by pulsed laser deposition has been investigated. The nanoscale stripe-like pattern is determined to be associated with coexisting rock salt (RS) and inverse spinel crystal phases. The presence of two different phases, not addressed in previous reports, is experimentally confirmed by both electron diffraction and high resolution transmission electron microscopy imaging. First principles based calculations, together with compressive strain present in the films, support the formation of such coexisting crystallographic phases in NCO. Similar microstructural patterns and RS structure are not observed in epitaxial films of two other oxides of the spinel family, namely, NiFe2O4 and CoFe2O4. A correlation between the coexisting structures and the macroscopic physical properties of NCO is discussed.

Epitaxial Garnets and Hexagonal Ferrites.

DTIC Science & Technology

1983-12-01

operating at frequencies between 1 GHz and 25 GHz. 2. Investigate LPE growth of lithium ferrite with the objective of preparing low-loss, large area films ...and hexagonal ferrites when the series of contracts began in 1975. At that time the liquid phase epitaxy method for growth of magnetic garnet films ...principal interest in epitaxial garnets was for magnetic bubble memories. For this Uapplication the films had to be about 3pm thick with low defect density

Epitaxial Garnets and Hexagonal Ferrites.

DTIC Science & Technology

1980-02-28

shaped LPE garnet samples with 31.5um film thickness. We were informed that initial evalu- ation showed acceptably low insertion loss and that the material...frequencies above 25 GHz. c. Furnish up to eight (8) liquid phase epitaxy yttrium iron garnet films to RADC/EEA for testing and evaluation. These tasks...a "Method for Controlling Resonance Frequency of Yttrium Iron Garnet Films ." A patent, "Epitaxial Growth of M-type Hexagonal Ferrite Films on Spinel

Characterization of solar cells for space applications. Volume 14: Electrical characteristics of Hughes liquid phase epitaxy gallium arsenide solar cells as a function of intensity, temperature and irradiation

NASA Technical Reports Server (NTRS)

Anspaugh, B. E.; Downing, R. G.; Miyahira, T. F.; Weiss, R. S.

1981-01-01

Electrical characteristics of liquid phase epitaxy, P/N gallium aluminum arsenide solar cells are presented in graphical and tabular format as a function of solar illumination intensity and temperature. The solar cells were exposed to 1 MeV electron fluences of, respectively, 0, one hundred trillion, one quadrillion, and ten quadrillion e/sq cm.

Epitaxial growth of γ-InSe and α, β, and γ-In2Se3 on ε-GaSe

NASA Astrophysics Data System (ADS)

Balakrishnan, Nilanthy; Steer, Elisabeth D.; Smith, Emily F.; Kudrynskyi, Zakhar R.; Kovalyuk, Zakhar D.; Eaves, Laurence; Patanè, Amalia; Beton, Peter H.

2018-07-01

We demonstrate that γ-InSe and the α, β and γ phases of In2Se3 can be grown epitaxially on ε-GaSe substrates using a physical vapour transport method. By exploiting the temperature gradient within the tube furnace, we can grow selectively different phases of InxSey depending on the position of the substrate within the furnace. The uniform cleaved surface of ε-GaSe enables the epitaxial growth of the InxSey layers, which are aligned over large areas. The InxSey epilayers are characterised using Raman, photoluminescence, x-ray photoelectron and electron dispersive x-ray spectroscopies. Each InxSey phase and stoichiometry exhibits distinct optical and vibrational properties, providing a tuneable photoluminescence emission range from 1.3 eV to ~2 eV suitable for exploitation in electronics and optoelectronics.

Epitaxial stabilization and phase instability of VO 2 polymorphs

DOE PAGES

Lee, Shinbuhm; Ivanov, Ilia N.; Keum, Jong K.; ...

2016-01-20

The VO 2 polymorphs, i.e., VO 2(A), VO 2(B), VO 2(M1) and VO 2(R), have a wide spectrum of functionalities useful for many potential applications in information and energy technologies. However, synthesis of phase pure materials, especially in thin film forms, has been a challenging task due to the fact that the VO 2 polymorphs are closely related to each other in a thermodynamic framework. Here, we report epitaxial stabilization of the VO 2 polymorphs to synthesize high quality single crystalline thin films and study the phase stability of these metastable materials. We selectively deposit all the phases on variousmore » perovskite substrates with different crystallographic orientations. By investigating the phase instability, phonon modes and transport behaviours, not only do we find distinctively contrasting physical properties of the VO 2 polymorphs, but that the polymorphs can be on the verge of phase transitions when heated as low as ~400 °C. In conclusion, our successful epitaxy of both VO 2(A) and VO 2(B) phases, which are rarely studied due to the lack of phase pure materials, will open the door to the fundamental studies of VO 2 polymorphs for potential applications in advanced electronic and energy devices.« less

MazEF toxin-antitoxin proteins alter Escherichia coli cell morphology and infrastructure during persister formation and regrowth.

PubMed

Cho, Junho; Carr, Anita Nicole; Whitworth, Lisa; Johnson, Brent; Wilson, Kevin Scott

2017-03-01

When exposed to antibiotics, many bacteria respond by activating intracellular 'toxin' proteins, which arrest cell growth and induce formation of persister cells that survive antibiotics. After antibiotics are removed, persisters can regrow by synthesizing 'antitoxin' proteins that sequester toxin proteins. In Escherichia coli, MazE antitoxin sequesters the activity of MazF toxin, which extensively cleaves cellular RNAs. Although the functions of MazEF proteins are well characterized, there is surprisingly little known about their effects on cell structure. Here, using a combination of microscopy techniques, we visualized the effects of MazEF and three bactericidal antibiotics on E. coli cell morphology and infrastructure. When ectopically expressed in E. coli, MazF temporarily stalled cell growth and induced persister formation, but only mildly elevated DNA mutagenesis. Viewed by electron microscopy, MazF-expressing persister cells were arrested in cell growth and division. Their chromosomal DNAs were compacted into thread-like structures. Their ribosomes were excluded from their nucleoids. After exposure to ciprofloxacin, persister regrowth was activated by MazE. Cell division remained inhibited while cells became extraordinarily elongated, then divided multiple times during stationary growth phase. This extreme filamentation during persister regrowth was unique to ciprofloxacin-treated persisters, likely caused by inhibition of cell division during regrowth, and was not observed with kanamycin-treated persisters.

Room-temperature Domain-epitaxy of Copper Iodide Thin Films for Transparent CuI/ZnO Heterojunctions with High Rectification Ratios Larger than 109

NASA Astrophysics Data System (ADS)

Yang, Chang; Kneiß, Max; Schein, Friedrich-Leonhard; Lorenz, Michael; Grundmann, Marius

2016-02-01

CuI is a p-type transparent conductive semiconductor with unique optoelectronic properties, including wide band gap (3.1 eV), high hole mobility (>40 cm2 V-1 s-1 in bulk), and large room-temperature exciton binding energy (62 meV). The difficulty in epitaxy of CuI is the main obstacle for its application in advanced solid-state electronic devices. Herein, room-temperature heteroepitaxial growth of CuI on various substrates with well-defined in-plane epitaxial relations is realized by reactive sputtering technique. In such heteroepitaxial growth the formation of rotation domains is observed and hereby systematically investigated in accordance with existing theoretical study of domain-epitaxy. The controllable epitaxy of CuI thin films allows for the combination of p-type CuI with suitable n-type semiconductors with the purpose to fabricate epitaxial thin film heterojunctions. Such heterostructures have superior properties to structures without or with weakly ordered in-plane orientation. The obtained epitaxial thin film heterojunction of p-CuI(111)/n-ZnO(00.1) exhibits a high rectification up to 2 × 109 (±2 V), a 100-fold improvement compared to diodes with disordered interfaces. Also a low saturation current density down to 5 × 10-9 Acm-2 is formed. These results prove the great potential of epitaxial CuI as a promising p-type optoelectronic material.

Preparation and characterization of epitaxial Fe{sub 2-x}Ti{sub x}O{sub 3} films with various Ti concentrations (0.5

DOE Office of Scientific and Technical Information (OSTI.GOV)

Takada, Y.; Nakanishi, M.; Fujii, T.

2008-08-01

An ilmenite-hematite solid solution (Fe{sub 2-x}Ti{sub x}O{sub 3}) is one of the candidates for practical magnetic semiconductors with a high Curie temperature. We have prepared well-crystallized epitaxial Fe{sub 2-x}Ti{sub x}O{sub 3} films with a wide range of Ti concentrations--x=0.50, 0.60, 0.65, 0.76, 0.87, and 0.94--on {alpha}-Al{sub 2}O{sub 3}(001) substrates. The films are prepared by a reactive helicon plasma sputtering technique to evaporate Fe and TiO targets simultaneously under optimized oxygen pressure conditions. The structural characterizations of the films reveal that all films have a single phase of the ordered structure with R3 symmetry, where Ti-rich and Fe-rich layers are stackedmore » alternately along the c axis. All films have large ferrimagnetic moments at low temperature, and room temperature magnetization is clearly observed at x<0.7. The inverse temperature dependence of the resistivities of the films indicates their semiconducting behavior. The film resistivities decrease with decreasing Ti concentration.« less

STM studies of GeSi thin layers epitaxially grown on Si(111)

NASA Astrophysics Data System (ADS)

Motta, N.; Sgarlata, A.; De Crescenzi, M.; Derrien, J.

1996-08-01

Ge/Si alloys were prepared in UHV by solid phase epitaxy on Si(111) substrates. The alloy formation, as a function of the evaporation rate and the Ge layer thickness has been followed in situ by RHEED and scanning tunneling microscopy. The 5 × 5 surface reconstruction appeared after annealing at 450°C Ge layers (up to 10 Å thick), obtained from a low rate Knudsen cell evaporator. In this case a nearly flat and uniform layer of reconstructed alloy was observed. When using an e-gun high rate evaporator we needed to anneal the Ge layer up to 780°C to obtain a 5 × 5 reconstruction. The grown layer was not flat, with many steps and Ge clusters; at high coverages (10 Å and more) large Ge islands appeared. Moreover, we then succeeded in visualizing at atomic resolution the top of some of these Ge islands which displayed a 2 × 1 reconstruction, probably induced from the high compressive strain due to the lattice mismatch with the substrate. We suggest that this unusual behavior could be connected to the high evaporation rate, which helped the direct formation of Ge microcrystals on the Si substrate during the deposition process.

Self-Diffusion in Amorphous Silicon by Local Bond Rearrangements

NASA Astrophysics Data System (ADS)

Kirschbaum, J.; Teuber, T.; Donner, A.; Radek, M.; Bougeard, D.; Böttger, R.; Hansen, J. Lundsgaard; Larsen, A. Nylandsted; Posselt, M.; Bracht, H.

2018-06-01

Experiments on self-diffusion in amorphous silicon (Si) were performed at temperatures between 460 to 600 ° C . The amorphous structure was prepared by Si ion implantation of single crystalline Si isotope multilayers epitaxially grown on a silicon-on-insulator wafer. The Si isotope profiles before and after annealing were determined by means of secondary ion mass spectrometry. Isothermal diffusion experiments reveal that structural relaxation does not cause any significant intermixing of the isotope interfaces whereas self-diffusion is significant before the structure recrystallizes. The temperature dependence of self-diffusion is described by an Arrhenius law with an activation enthalpy Q =(2.70 ±0.11 ) eV and preexponential factor D0=(5.5-3.7+11.1)×10-2 cm2 s-1 . Remarkably, Q equals the activation enthalpy of hydrogen diffusion in amorphous Si, the migration of bond defects determining boron diffusion, and the activation enthalpy of solid phase epitaxial recrystallization reported in the literature. This close agreement provides strong evidence that self-diffusion is mediated by local bond rearrangements rather than by the migration of extended defects as suggested by Strauß et al. (Phys. Rev. Lett. 116, 025901 (2016), 10.1103/PhysRevLett.116.025901).

Interfacing epitaxial oxides to gallium nitride

NASA Astrophysics Data System (ADS)

Losego, Mark Daniel

Molecular beam epitaxy (MBE) is lauded for its ability to control thin film material structures at the atomic level. This precision of control can improve performance of microelectronic devices and cultivate the development of novel device structures. This thesis explores the utility of MBE for designing interfaces between oxide epilayers and the wide band gap semiconductor gallium nitride (GaN). The allure of wide gap semiconductor microelectronics (like GaN, 3.4 eV) is their ability to operate at higher frequencies, higher powers, and higher temperatures than current semiconductor platforms. Heterostructures between ferroelectric oxides and GaN are also of interest for studying the interaction between GaN's fixed polarization and the ferroelectric's switchable polarization. Two major obstacles to successful integration of oxides with GaN are: (1) interfacial trap states; and (2) small electronic band offsets across the oxide/nitride interface due to the semiconductor's large band gap. For this thesis, epitaxial rocksalt oxide interfacial layers (˜8 eV band gap) are investigated as possible solutions to overcoming the challenges facing oxide integration with GaN. The cubic close-packed structure of rocksalt oxides forms a suitable epitaxial interface with the hexagonal close-packed wurtzite lattice of GaN. Three rocksalt oxide compounds are investigated in this thesis: MgO, CaO, and YbO. All are found to have a (111) MO || (0001) GaN; <1 10> MO || <11 20> GaN epitaxial relationship. Development of the epilayer microstructure is dominated by the high-energy polar growth surface (drives 3D nucleation) and the interfacial symmetry, which permits the formation of twin boundaries. Using STEM, strain relief for these ionicly bonded epilayers is observed to occur through disorder within the initial monolayer of growth. All rocksalt oxides demonstrate chemical stability with GaN to >1000°C. Concurrent MBE deposition of MgO and CaO is known to form complete solid solutions. By controlling the composition of these alloys, the oxide's lattice parameter can be engineered to match GaN and reduce interfacial state density. Compositional control is a universal challenge to oxide MBE, and the MgO-CaO system (MCO) is further complicated by magnesium's high volatility and the lack of a thermodynamically stable phase. Through a detailed investigation of MgO's deposition rate and subsequent impact on MCO composition, the process space for achieving lattice-matched compositions to GaN are fully mapped. Lattice-matched compositions are demonstrated to have the narrowest off-axis rocking curve widths ever reported for an epitaxial oxide deposited directly on GaN (0.7° in φ-circle for 200 reflection). Epitaxial deposition of the ferroelectric (Ba,Sr)TiO3 by hot RF sputtering on GaN surfaces is also demonstrated. Simple MOS capacitors are fabricated from epitaxial rocksalt oxides and (Ba,Sr)TiO3 layers deposited on n-GaN substrates. Current-voltage measurements reveal that BST epilayers have 5 orders of magnitude higher current leakage than rocksalt epilayers. This higher leakage is attributed to the smaller band offset expected at this interface; modeling confirms that electronic transport occurs by Schottky emission. In contrast, current transport across the rocksalt oxide/GaN interface occurs by Frenkel-Poole emission and can be reduced with pre-deposition surface treatments. Finally, through this work, it is realized that the integration of oxides with III-nitrides requires an appreciation of many different fields of research including materials science, surface science, and electrical engineering. By recognizing the importance that each of these fields play in designing oxide/III-nitride interfaces, this thesis has the opportunity to explore other related phenomena including accessing metastable phases through MBE (ytterbium monoxide), spinodal decomposition in metastable alloys (MCO), how polar surfaces grown by MBE compensate their bound surface charge, room temperature epitaxy, and the use of surface modification to achieve selective epitaxial deposition (SeEDed growth).

High-efficiency GaAs and GaInP solar cells grown by all solid-state molecular-beam-epitaxy

PubMed Central

2011-01-01

We report the initial results of GaAs and GaInP solar cells grown by all solid-state molecular-beam-epitaxy (MBE) technique. For GaAs single-junction solar cell, with the application of AlInP as the window layer and GaInP as the back surface field layer, the photovoltaic conversion efficiency of 26% at one sun concentration and air mass 1.5 global (AM1.5G) is realized. The efficiency of 16.4% is also reached for GaInP solar cell. Our results demonstrate that the MBE-grown phosphide-contained III-V compound semiconductor solar cell can be quite comparable to the metal-organic-chemical-vapor-deposition-grown high-efficiency solar cell. PMID:22040124

Dielectric relaxation in epitaxial films of paraelectric-magnetic SrTiO3-SrMnO3 solid solution

NASA Astrophysics Data System (ADS)

Savinov, M.; Bovtun, V.; Tereshina-Chitrova, E.; Stupakov, A.; Dejneka, A.; Tyunina, M.

2018-01-01

Magneto-dielectric properties of (A2+)MnO3-type perovskites are attractive for applications and stimulate extensive studies of these materials. Here, the complex dielectric and magnetic responses are investigated as in epitaxial films of SrTi0.6Mn0.4O3, solid solution of paraelectric SrTiO3 and magnetic SrMnO3. The impedance and resonance measurements at frequencies of 10-2-1010 Hz and temperatures of 10-500 K reveal broad dielectric anomalies centered at 100-200 K, while the films are paramagnetic at all temperatures. Analysis shows polaronic electrical conductivity behind the observed behavior. Electron-phonon correlations, rather than spin-phonon correlations, are suggested to produce the apparent magneto-dielectric responses in many multiferroic manganites.

Thin film phase diagram of iron nitrides grown by molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Gölden, D.; Hildebrandt, E.; Alff, L.

2017-01-01

A low-temperature thin film phase diagram of the iron nitride system is established for the case of thin films grown by molecular beam epitaxy and nitrided by a nitrogen radical source. A fine-tuning of the nitridation conditions allows for growth of α ‧ -Fe8Nx with increasing c / a -ratio and magnetic anisotropy with increasing x until almost phase pure α ‧ -Fe8N1 thin films are obtained. A further increase of nitrogen content below the phase decomposition temperature of α ‧ -Fe8N (180 °C) leads to a mixture of several phases that is also affected by the choice of substrate material and symmetry. At higher temperatures (350 °C), phase pure γ ‧ -Fe4N is the most stable phase.

Deposition of hydrogenated silicon clusters for efficient epitaxial growth.

PubMed

Le, Ha-Linh Thi; Jardali, Fatme; Vach, Holger

2018-06-13

Epitaxial silicon thin films grown from the deposition of plasma-born hydrogenated silicon nanoparticles using plasma-enhanced chemical vapor deposition have widely been investigated due to their potential applications in photovoltaic and nanoelectronic device technologies. However, the optimal experimental conditions and the underlying growth mechanisms leading to the high-speed epitaxial growth of thin silicon films from hydrogenated silicon nanoparticles remain far from being understood. In the present work, extensive molecular dynamics simulations were performed to study the epitaxial growth of silicon thin films resulting from the deposition of plasma-born hydrogenated silicon clusters at low substrate temperatures under realistic reactor conditions. There is strong evidence that a temporary phase transition of the substrate area around the cluster impact site to the liquid state is necessary for the epitaxial growth to take place. We predict further that a non-normal incidence angle for the cluster impact significantly facilitates the epitaxial growth of thin crystalline silicon films.

Heteroepitaxial Growth of Single-Walled Carbon Nanotubes from Boron Nitride

PubMed Central

Tang, Dai-Ming; Zhang, Li-Li; Liu, Chang; Yin, Li-Chang; Hou, Peng-Xiang; Jiang, Hua; Zhu, Zhen; Li, Feng; Liu, Bilu; Kauppinen, Esko I.; Cheng, Hui-Ming

2012-01-01

The growth of single-walled carbon nanotubes (SWCNTs) with predefined structure is of great importance for both fundamental research and their practical applications. Traditionally, SWCNTs are grown from a metal catalyst with a vapor-liquid-solid mechanism, where the catalyst is in liquid state with fluctuating structures, and it is intrinsically unfavorable for the structure control of SWCNTs. Here we report the heteroepitaxial growth of SWCNTs from a platelet boron nitride nanofiber (BNNF), which is composed of stacked (002) planes and is stable at high temperatures. SWCNTs are found to grow epitaxially from the open (002) edges of the BNNFs, and the diameters of the SWCNTs are multiples of the BN (002) interplanar distance. In situ transmission electron microscopy observations coupled with first principles calculations reveal that the growth of SWCNTs from the BNNFs follows a vapor-solid-solid mechanism. Our work opens opportunities for the control over the structure of SWCNTs by hetero-crystallographic epitaxy. PMID:23240076

Prediction of Sublimation Pressures of Low Volatility Solids

NASA Astrophysics Data System (ADS)

Drake, Bruce Douglas

Sublimation pressures are required for solid-vapor phase equilibrium models in design of processes such as supercritical fluid extraction, sublimation purification and vapor epitaxy. The objective of this work is to identify and compare alternative methods for predicting sublimation pressures. A bibliography of recent sublimation data is included. Corresponding states methods based on the triple point (rather than critical point) are examined. A modified Trouton's rule is the preferred method for estimating triple point pressure in the absence of any sublimation data. Only boiling and melting temperatures are required. Typical error in log_{10} P _{rm triple} is 0.3. For lower temperature estimates, the slope of the sublimation curve is predicted by a correlation based on molar volume. Typical error is 10% of slope. Molecular dynamics methods for surface modeling are tested as estimators of vapor pressure. The time constants of the vapor and solid phases are too different to allow the vapor to come to thermal equilibrium with the solid. The method shows no advantages in prediction of sublimation pressure but provides insight into appropriate models and experimental methods for sublimation. Density-dependent augmented van der Waals equations of state based on hard-sphere distribution functions are examined. The perturbation term is almost linear and is well fit by a simple quadratic. Use of the equation provides reasonable fitting of sublimation pressures from one data point. Order-of-magnitude estimation is possible from melting temperature and solid molar volume. The inverse -12 fluid is used to develop an additional equation of state. Sublimation pressure results, including quality of pressure predictions, are similar to the hard-sphere results. Three-body (Axilrod -Teller) interactions are used to improve results.

Indium gallium nitride/gallium nitride quantum wells grown on polar and nonpolar gallium nitride substrates

NASA Astrophysics Data System (ADS)

Lai, Kun-Yu

Nonpolar (m-plane or a-plane) gallium nitride (GaN) is predicted to be a potential substrate material to improve luminous efficiencies of nitride-based quantum wells (QWs). Numerical calculations indicated that the spontaneous emission rate in a single In0.15Ga0.85N/GaN QW could be improved by ˜2.2 times if the polarization-induced internal field was avoided by epitaxial deposition on nonpolar substrates. A challenge for nonpolar GaN is the limited size (less than 10x10 mm2) of substrates, which was addressed by expansion during the regrowth by Hydride Vapor Phase Epitaxy (HVPE). Subsurface damage in GaN substrates were reduced by annealing with NH3 and N2 at 950°C for 60 minutes. It was additionally found that the variation of m-plane QWs' emission properties was significantly increased when the substrate miscut toward a-axis was increased from 0° to 0.1°. InGaN/GaN QWs were grown by Metalorganic Chemical Vapor Deposition (MOCVD) on c-plane and m-plane GaN substrates. The QWs were studied by cathodoluminescence spectroscopy with different incident electron beam probe currents (0.1 nA ˜ 1000 nA). Lower emission intensities and longer peak wavelengths from c-plane QWs were attributed to the Quantum-confined Stark Effect (QCSE). The emission intensity ratios of m-plane QWs to c-plane QWs decreased from 3.04 at 1 nA to 1.53 at 1000 nA. This was identified as the stronger screening effects of QCSE at higher current densities in c-plane QWs. To further investigate these effects in a fabricated structure, biased photoluminescence measurements were performed on m-plane InGaN/GaN QWs. The purpose was to detect the possible internal fields induced by the dot-like structure in the InGaN layer through the response of these internal fields under externally applied fields. No energy shifts of the QWs were observed, which was attributed to strong surface leakage currents.

Nanoselective area growth of GaN by metalorganic vapor phase epitaxy on 4H-SiC using epitaxial graphene as a mask

NASA Astrophysics Data System (ADS)

Puybaret, Renaud; Patriarche, Gilles; Jordan, Matthew B.; Sundaram, Suresh; El Gmili, Youssef; Salvestrini, Jean-Paul; Voss, Paul L.; de Heer, Walt A.; Berger, Claire; Ougazzaden, Abdallah

2016-03-01

We report the growth of high-quality triangular GaN nanomesas, 30-nm thick, on the C-face of 4H-SiC using nanoselective area growth (NSAG) with patterned epitaxial graphene grown on SiC as an embedded mask. NSAG alleviates the problems of defects in heteroepitaxy, and the high mobility graphene film could readily provide the back low-dissipative electrode in GaN-based optoelectronic devices. A 5-8 graphene-layer film is first grown on the C-face of 4H-SiC by confinement-controlled sublimation of silicon carbide. Graphene is then patterned and arrays of 75-nm-wide openings are etched in graphene revealing the SiC substrate. A 30-nm-thick GaN is subsequently grown by metal organic vapor phase epitaxy. GaN nanomesas grow epitaxially with perfect selectivity on SiC, in the openings patterned through graphene. The up-or-down orientation of the mesas on SiC, their triangular faceting, and cross-sectional scanning transmission electron microscopy show that they are biphasic. The core is a zinc blende monocrystal surrounded with single-crystal wurtzite. The GaN crystalline nanomesas have no threading dislocations or V-pits. This NSAG process potentially leads to integration of high-quality III-nitrides on the wafer scalable epitaxial graphene/silicon carbide platform.

Ordered arrays of multiferroic epitaxial nanostructures.

PubMed

Vrejoiu, Ionela; Morelli, Alessio; Biggemann, Daniel; Pippel, Eckhard

2011-01-01

Epitaxial heterostructures combining ferroelectric (FE) and ferromagnetic (FiM) oxides are a possible route to explore coupling mechanisms between the two independent order parameters, polarization and magnetization of the component phases. We report on the fabrication and properties of arrays of hybrid epitaxial nanostructures of FiM NiFe(2)O(4) (NFO) and FE PbZr(0.52)Ti(0.48)O(3) or PbZr(0.2)Ti(0.8)O(3), with large range order and lateral dimensions from 200 nm to 1 micron. The structures were fabricated by pulsed-laser deposition. High resolution transmission electron microscopy and high angle annular dark-field scanning transmission electron microscopy were employed to investigate the microstructure and the epitaxial growth of the structures. Room temperature ferroelectric and ferrimagnetic domains of the heterostructures were imaged by piezoresponse force microscopy (PFM) and magnetic force microscopy (MFM), respectively. PFM and MFM investigations proved that the hybrid epitaxial nanostructures show ferroelectric and magnetic order at room temperature. Dielectric effects occurring after repeated switching of the polarization in large planar capacitors, comprising ferrimagnetic NiFe2O4 dots embedded in ferroelectric PbZr0.52Ti0.48O3 matrix, were studied. These hybrid multiferroic structures with clean and well defined epitaxial interfaces hold promise for reliable investigations of magnetoelectric coupling between the ferrimagnetic / magnetostrictive and ferroelectric / piezoelectric phases.

Nanoselective area growth of GaN by metalorganic vapor phase epitaxy on 4H-SiC using epitaxial graphene as a mask

DOE Office of Scientific and Technical Information (OSTI.GOV)

Puybaret, Renaud; Jordan, Matthew B.; Voss, Paul L.

We report the growth of high-quality triangular GaN nanomesas, 30-nm thick, on the C-face of 4H-SiC using nanoselective area growth (NSAG) with patterned epitaxial graphene grown on SiC as an embedded mask. NSAG alleviates the problems of defects in heteroepitaxy, and the high mobility graphene film could readily provide the back low-dissipative electrode in GaN-based optoelectronic devices. A 5–8 graphene-layer film is first grown on the C-face of 4H-SiC by confinement-controlled sublimation of silicon carbide. Graphene is then patterned and arrays of 75-nm-wide openings are etched in graphene revealing the SiC substrate. A 30-nm-thick GaN is subsequently grown by metalmore » organic vapor phase epitaxy. GaN nanomesas grow epitaxially with perfect selectivity on SiC, in the openings patterned through graphene. The up-or-down orientation of the mesas on SiC, their triangular faceting, and cross-sectional scanning transmission electron microscopy show that they are biphasic. The core is a zinc blende monocrystal surrounded with single-crystal wurtzite. The GaN crystalline nanomesas have no threading dislocations or V-pits. This NSAG process potentially leads to integration of high-quality III-nitrides on the wafer scalable epitaxial graphene/silicon carbide platform.« less

Low-cost Engineering of Laser Rods and Slabs with Liquid Phase Epitaxy

DTIC Science & Technology

2011-09-01

SUPPLEMENTARY NOTES 14. ABSTRACT We investigated the use of a liquid phase epitaxial ( LPE ) coating to improve the performance of a rod or slab laser. A...single crystal erbium-doped yttrium aluminum garnet (Er:YAG) rod coated with undoped YAG, and an uncoated sample were procured, then compared on the...the whispering gallery modes, which otherwise would deplete the gain in ~50% of the rod volume. We also investigated LPE growth on a ceramic sample

Heteroepitaxial growth of 3-5 semiconductor compounds by metal-organic chemical vapor deposition for device applications

NASA Technical Reports Server (NTRS)

Collis, Ward J.; Abul-Fadl, Ali

1988-01-01

The purpose of this research is to design, install and operate a metal-organic chemical vapor deposition system which is to be used for the epitaxial growth of 3-5 semiconductor binary compounds, and ternary and quaternary alloys. The long-term goal is to utilize this vapor phase deposition in conjunction with existing current controlled liquid phase epitaxy facilities to perform hybrid growth sequences for fabricating integrated optoelectronic devices.

Method of varying a characteristic of an optical vertical cavity structure formed by metalorganic vapor phase epitaxy

DOEpatents

Hou, Hong Q.; Coltrin, Michael E.; Choquette, Kent D.

2001-01-01

A process for forming an array of vertical cavity optical resonant structures wherein the structures in the array have different detection or emission wavelengths. The process uses selective area growth (SAG) in conjunction with annular masks of differing dimensions to control the thickness and chemical composition of the materials in the optical cavities in conjunction with a metalorganic vapor phase epitaxy (MOVPE) process to build these arrays.

n-Type Doping of Vapor-Liquid-Solid Grown GaAs Nanowires.

PubMed

Gutsche, Christoph; Lysov, Andrey; Regolin, Ingo; Blekker, Kai; Prost, Werner; Tegude, Franz-Josef

2011-12-01

In this letter, n-type doping of GaAs nanowires grown by metal-organic vapor phase epitaxy in the vapor-liquid-solid growth mode on (111)B GaAs substrates is reported. A low growth temperature of 400°C is adjusted in order to exclude shell growth. The impact of doping precursors on the morphology of GaAs nanowires was investigated. Tetraethyl tin as doping precursor enables heavily n-type doped GaAs nanowires in a relatively small process window while no doping effect could be found for ditertiarybutylsilane. Electrical measurements carried out on single nanowires reveal an axially non-uniform doping profile. Within a number of wires from the same run, the donor concentrations ND of GaAs nanowires are found to vary from 7 × 10(17) cm(-3) to 2 × 10(18) cm(-3). The n-type conductivity is proven by the transfer characteristics of fabricated nanowire metal-insulator-semiconductor field-effect transistor devices.

Thermodynamic analysis of vapor-phase epitaxial growth of GaAsN on Ge

NASA Astrophysics Data System (ADS)

Kawano, Jun; Kangawa, Yoshihiro; Ito, Tomonori; Kakimoto, Koichi; Koukitu, Akinori

2012-03-01

In this paper, we use thermodynamic analysis to determine how the nitrogen (N) ratio in the source gases affects the solid composition of coherently grown GaAs1-xNx(x˜0.03). The source gases for Ga, As, and N are trimethylgallium ((CH3)3Ga), arsine (AsH3), and ammonia (NH3), respectively. The growth occurs on a Ge substrate, and the analysis includes the stress from the substrate-crystal lattice mismatch. Calculation results indicate that to have just a few percent N incorporation into the grown solid, the V/III ratio in the source gases should be several thousands and the input-gas partial-pressure ratio NH3/(NH3+AsH3) should exceed 0.99. We also find that the lattice mismatch stress from the Ge substrate increases the V/III source-gas ratio required for stable growth, whereas an increase in input Ga partial pressure ratio has the opposite effect.

The role of electron-electron repulsion in the problem of epitaxial graphene on a metal: Simple estimates

NASA Astrophysics Data System (ADS)

Davydov, S. Yu.

2017-08-01

For single-layer graphene placed on a metal substrate, the influence of intra- and interatomic Coulomb repulsion of electrons ( U and G, respectively) on its phase diagram is considered in the framework of an extended Hartree-Fock theory. The general solution of the problem is presented, on the basis of which special cases allowing for analytical consideration are analyzed: free and epitaxial graphene with and without regard for the energy of the electron transition between neighboring atoms of graphene. Three regions of the phase diagram are considered: spin and charge density waves (SDW and CDW, respectively) and the semimetal (SM) state uniform in the spin and charge. The main attention is paid to undoped graphene. It is shown that the allowance for the interaction with a metal substrate expands the SM existence domain. However, in all the considered cases, the boundary between the SDW and CDW states is described by the equation U = zG, where z = 3 is the number of nearest neighbors in graphene. The widening of the SM state region also results from the doping of graphene, and the effect is independent of the sign of free carriers introduced into epitaxial graphene by the substrate. According to estimates made, the only state possible in the buffer layer is the metal-type SM state, whereas, in epitaxial graphene, the CDW state is possible. The influence of temperature on the phase diagram of epitaxial graphene is discussed.

Composition and Morphology Control of Metal Dichalcogenides via Chemical Vapor Deposition for Photovoltaic and Nanoelectronic Applications

NASA Astrophysics Data System (ADS)

Samad, Leith L. J.

The body of work reviewed here encompasses a variety of metal dichalcogenides all synthesized using chemical vapor deposition (CVD) for solar and electronics applications. The first reported phase-pure CVD synthesis of iron pyrite thin films is presented with detailed structural and electrochemical analysis. The phase-pure thin film and improved crystal growth on a metallic backing material represents one of the best options for potential solar applications using iron pyrite. Large tin-sulfur-selenide solid solution plates with tunable bandgaps were also synthesized via CVD as single-crystals with a thin film geometry. Solid solution tin-sulfur-selenide plates were demonstrated to be a new material for solar cells with the first observed solar conversion efficiencies up to 3.1%. Finally, a low temperature molybdenum disulfide vertical heterostructure CVD synthesis with layered controlled growth was achieved with preferential growth enabled by Van der Waals epitaxy. Through recognition of additional reaction parameters, a fully regulated CVD synthesis enabled the controlled growth of 1-6 molybdenum disulfide monolayers for nanoelectronic applications. The improvements in synthesis and materials presented here were all enabled by the control afforded by CVD such that advances in phase purity, growth, and composition control of several metal dichalcogenides were achieved. Further work will be able to take full advantage of these advances for future solar and electronics technologies.

Reduction of degradation in vapor phase transported InP/InGaAsP mushroom stripe lasers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jung, H.; Burkhardt, E.G.; Pfister, W.

1988-10-03

The rapid degradation rate generally observed in InP/InGaAsP mushroom stripe lasers can be considerably decreased by regrowing the open sidewalls of the active stripe with low-doped InP in a second epitaxial step using the hydride vapor phase transport technique. This technique does not change the fundamental laser parameters like light-current and current-voltage characteristics. Because of this drastic reduction in degradation, the vapor phase epitaxy regrown InP/InGaAsP mushroom laser seems to be an interesting candidate for application in optical communication.

Epitaxial Growth and Cracking Mechanisms of Thermally Sprayed Ceramic Splats

NASA Astrophysics Data System (ADS)

Chen, Lin; Yang, Guan-jun

2018-02-01

In the present study, the epitaxial growth and cracking mechanisms of thermally sprayed ceramic splats were explored. We report, for the first time, the epitaxial growth of various splat/substrate combinations at low substrate temperatures (100 °C) and large lattice mismatch (- 11.26%). Our results suggest that thermal spray deposition was essentially a liquid-phase epitaxy, readily forming chemical bonding. The interface temperature was also estimated. The results convincingly demonstrated that atoms only need to diffuse and rearrange over a sufficiently short range during extremely rapid solidification. Concurrently, severe cracking occurred in the epitaxial splat/substrate systems, which indicated high tensile stress was produced during splat deposition. The origin of the tensile stress was attributed to the strong constraint of the locally heated substrate by its cold surroundings.

Depth-resolved cathodoluminescence of a homoepitaxial AlN thin film

NASA Astrophysics Data System (ADS)

Silveira, E.; Freitas, J. A.; Slack, G. A.; Schowalter, L. J.; Kneissl, M.; Treat, D. W.; Johnson, N. M.

2005-07-01

In the present work we will report on the optical properties of an AlN film homoepitaxially grown on a high-quality large bulk AlN single crystal. The latter was grown by a sublimation-recondensation technique, while the film was grown by organometallic vapor-phase epitaxy. Cathodoluminescence measurements were performed using electron beam energies between 2 and 10 keV in order to excite the sample and so to probe different sample depths, making it possible to differentiate between different features which originate in the AlN homoepitaxial film. The penetration depth has been determined through the calculation of the Bohr-Bethe maximum range of excitation using the approximation to the Everhart-Hoff expression for the energy loss within a solid.

Observation of hole accumulation in Ge/Si core/shell nanowires using off-axis electron holography.

PubMed

Li, Luying; Smith, David J; Dailey, Eric; Madras, Prashanth; Drucker, Jeff; McCartney, Martha R

2011-02-09

Hole accumulation in Ge/Si core/shell nanowires (NWs) has been observed and quantified using off-axis electron holography and other electron microscopy techniques. The epitaxial [110]-oriented Ge/Si core/shell NWs were grown on Si (111) substrates by chemical vapor deposition through the vapor-liquid-solid growth mechanism. High-angle annular-dark-field scanning transmission electron microscopy images and off-axis electron holograms were obtained from specific NWs. The excess phase shifts measured by electron holography across the NWs indicated the presence of holes inside the Ge cores. Calculations based on a simplified coaxial cylindrical model gave hole densities of (0.4 ± 0.2) /nm(3) in the core regions.

Intermetallic Compound Growth and Stress Development in Al-Cu Diffusion Couple

NASA Astrophysics Data System (ADS)

Mishler, M.; Ouvarov-Bancalero, V.; Chae, Seung H.; Nguyen, Luu; Kim, Choong-Un

2018-01-01

This paper reports experimental observations evidencing that the intermetallic compound phase interfaced with Cu in the Al-Cu diffusion couple is most likely α2-Cu3Al phase, not γ-Cu9Al4 phase as previously assumed, and that its growth to a critical thickness may result in interface failure by stress-driven fracture. These conclusions are made based on an interdiffusion study of a diffusion couple made of a thick Cu plate coated with ˜ 2- μm-thick Al thin film. The interface microstructure and lattice parameter were characterized using scanning electron microscopy and x-ray diffraction analysis. Specimens aged at temperature between 623 K (350°C) and 723 K (450°C) for various hours produced consistent results supporting the main conclusions. It is found that disordered α2-Cu3Al phase grows in a similar manner to solid-state epitaxy, probably owing to its structural similarity to the Cu lattice. The increase in the interface strain that accompanies the α2-Cu3Al phase growth ultimately leads to interface fracture proceeding from crack initiation and growth along the interface. This mechanism provides the most consistent explanation for interface failures observed in other studies.

Optical Behavior of III-TM-N Materials and Devices

DTIC Science & Technology

2008-09-26

0296 University of Florida GaN films were doped with Eu to a concentration of ~0.12 at. % during growth at 800 °C by molecular beam epitaxy , with...MAGNETIC SEMICONDUCTOR GROWTH AND CHARACTERIZATION Growth of the films presented occurred in a Varian Gen II by gas-source molecular beam epitaxy ...versus temperature for films of either undoped AlN, single phase AlMnN, or Mn4N. AlCrN films were grown by Molecular Beam Epitaxy (MBE) on c-plane

Co-crystallization of cholesterol and calcium phosphate as related to atherosclerosis

NASA Astrophysics Data System (ADS)

Hirsch, Danielle; Azoury, Reuven; Sarig, Sara

1990-09-01

Calcification of atherosclerotic plaques occurs very frequently and aggravates the disease. In biological systems, epitaxial relationships between crystal structures may be important in nucleating the deposit of a solid phase. The biologically preferred calcium phosphate species, apatite, and cholesterol crystal have structurally compatible crystallographic faces which allow epitaxial growth of one crystal upon another. The present study describes a new approach to explore, in vitro, the crystallization processes of calcium phosphate (CaP) with cholesterol (CS) and cholestanol (CN) which are related to atherosclerosis. Aqueous solutions containing calcium and phosphate ions or CaP crystals as hydroxyapatite were added into saturated ethanolic solutions of CS or CS and 10% CN. After precipitation, crystals were collected and analyzed by nuclear magnetic resonance (NMR), infra-red (IR), X-ray, scanning electron microscope (SEM-LINK), differential scanning calorimeter (DSC) and atomic absorption. The principal result is the well-formed crystals precipitation when an aqueous solution and CaP seed crystals were added to saturated solutions of CS and 10% CN. Cholesterol-cholestanol dihydrate (CC2W) crystals precipitated in the presence of CaP seeds were compared to the CC2W crystals obtained without the mineral compound. The results of this comparison indicate a special link between crystals of CaP and CC2W, and support the epitaxial relationship between the two kinds of crystals. The potential of CC2W crystals to be precipitated by CaP seed crystals prove likewise the possible significant role of the cholestanol metabolite in the process of cholesterol crystallization and calcification in the arteries.

Molecular beam epitaxy-grown wurtzite MgS thin films for solar-blind ultra-violet detection

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lai, Y. H.; He, Q. L.; Department of Physics and William Mong Institute of Nano Science and Technology, The Hong Kong University of Science and Technology, HKSAR, People's Republic of China

2013-04-29

Molecular beam epitaxy grown MgS on GaAs(111)B substrate was resulted in wurtzite phase, as demonstrated by detailed structural characterizations. Phenomenological arguments were used to account for why wurtzite phase is preferred over zincblende phase or its most stable rocksalt phase. Results of photoresponse and reflectance measurements performed on wurtzite MgS photodiodes suggest a direct bandgap at around 5.1 eV. Their response peaks at 245 nm with quantum efficiency of 9.9% and enjoys rejection of more than three orders at 320 nm and close to five orders at longer wavelengths, proving the photodiodes highly competitive in solar-blind ultraviolet detection.

Use of column V alkyls in organometallic vapor phase epitaxy (OMVPE)

NASA Technical Reports Server (NTRS)

Ludowise, M. J.; Cooper, C. B., III

1982-01-01

The use of the column V-trialkyls trimethylarsenic (TMAs) and trimethylantimony (TMSb) for the organometallic vapor phase epitaxy (OM-VPE) of III-V compound semiconductors is reviewed. A general discussion of the interaction chemistry of common Group III and Group V reactants is presented. The practical application of TMSb and TMAs for OM-VPE is demonstrated using the growth of GaSb, GaAs(1-y)Sb(y), Al(x)Ga(1-x)Sb, and Ga(1-x)In(x)As as examples.

Ultrahigh-yield growth of GaN via halogen-free vapor-phase epitaxy

NASA Astrophysics Data System (ADS)

Nakamura, Daisuke; Kimura, Taishi

2018-06-01

The material yield of Ga during GaN growth via halogen-free vapor-phase epitaxy (HF-VPE) was systematically investigated and found to be much higher than that obtained using conventional hydride VPE. This is attributed to the much lower process pressure and shorter seed-to-source distance, owing to the inherent chemical reactions and corresponding reactor design used for HF-VPE growth. Ultrahigh-yield GaN growth was demonstrated on a 4-in.-diameter sapphire seed substrate.

Growth of Y3Fe5O12/GaN layers by laser molecular-beam epitaxy and characterization of their structural and magnetic properties

NASA Astrophysics Data System (ADS)

Kaveev, A. K.; Bursian, V. E.; Gastev, S. V.; Krichevtsov, B. B.; Suturin, S. M.; Volkov, M. P.; Sokolov, N. S.

2016-12-01

Laser molecular-beam epitaxy has been employed to obtain layers of yttrium-iron garnet (YIG) Y3Fe5O12 on gallium nitride substrates. It was found that there exists a polycrystalline YIG phase without admixtures of other structural phases. A magnetic anisotropy of films of the "easy-magnetic plane" type was found. The gyromagnetic ratio and the demagnetizing field 4π M S were calculated.

Synthesis science of SrRuO3 and CaRuO3 epitaxial films with high residual resistivity ratios

NASA Astrophysics Data System (ADS)

Nair, Hari P.; Liu, Yang; Ruf, Jacob P.; Schreiber, Nathaniel J.; Shang, Shun-Li; Baek, David J.; Goodge, Berit H.; Kourkoutis, Lena F.; Liu, Zi-Kui; Shen, Kyle M.; Schlom, Darrell G.

2018-04-01

Epitaxial SrRuO3 and CaRuO3 films were grown under an excess flux of elemental ruthenium in an adsorption-controlled regime by molecular-beam epitaxy (MBE), where the excess volatile RuOx (x = 2 or 3) desorbs from the growth front leaving behind a single-phase film. By growing in this regime, we were able to achieve SrRuO3 and CaRuO3 films with residual resistivity ratios (ρ300 K/ρ4 K) of 76 and 75, respectively. A combined phase stability diagram based on the thermodynamics of MBE (TOMBE) growth, termed a TOMBE diagram, is employed to provide improved guidance for the growth of complex materials by MBE.

Graphene-Mesoporous Si Nanocomposite as a Compliant Substrate for Heteroepitaxy.

PubMed

Boucherif, Abderrahim Rahim; Boucherif, Abderraouf; Kolhatkar, Gitanjali; Ruediger, Andreas; Arès, Richard

2017-05-01

The ultimate performance of a solid state device is limited by the restricted number of crystalline substrates that are available for epitaxial growth. As a result, only a small fraction of semiconductors are usable. This study describes a novel concept for a tunable compliant substrate for epitaxy, based on a graphene-porous silicon nanocomposite, which extends the range of available lattice constants for epitaxial semiconductor alloys. The presence of graphene and its effect on the strain of the porous layer lattice parameter are discussed in detail and new remarkable properties are demonstrated. These include thermal stability up to 900 °C, lattice tuning up to 0.9 % mismatch, and compliance under stress for virtual substrate thicknesses of several micrometers. A theoretical model is proposed to define the compliant substrate design rules. These advances lay the foundation for the fabrication of a compliant substrate that could unlock the lattice constant restrictions for defect-free new epitaxial semiconductor alloys and devices. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Epitaxial growth of mixed conducting layered Ruddlesden–Popper La{sub n+1}Ni{sub n}O{sub 3n+1} (n = 1, 2 and 3) phases by pulsed laser deposition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Kuan-Ting; Soh, Yeong-Ah; Skinner, Stephen J., E-mail: s.skinner@imperial.ac.uk

2013-10-15

Graphical abstract: - Highlights: • High quality epitaxial thin films of layered Ruddlesden–Popper nickelates were prepared. • For the first time this has been achieved by the PLD process. • n = 1, 2 and 3 films were successfully deposited on SrTiO{sub 3} and NdGaO{sub 3} substrates. • c-Axis oriented films were confirmed by XRD analysis. • In-plane and out-of-plane strain effects on lattice are discussed. - Abstract: Layered Ruddlesden–Popper phases of composition La{sub n+1}Ni{sub n}O{sub 3n+1} (n = 1, 2 and 3) have been epitaxially grown on SrTiO{sub 3} (0 0 1) or NdGaO{sub 3} (1 1 0) singlemore » crystal substrates using the pulsed laser deposition technique. X-ray diffraction analyses (θ/2θ, rocking curves, and φ-scans) and atomic force microscopy confirms the high-quality growth of the series of films with low surface roughness values (less than 1 nm). In particular, epitaxial growth of the higher order phases (n = 2 and 3) of lanthanum nickelate have been demonstrated for the first time.« less

Thermodynamic considerations of the vapor phase reactions in III-nitride metal organic vapor phase epitaxy

NASA Astrophysics Data System (ADS)

Sekiguchi, Kazuki; Shirakawa, Hiroki; Chokawa, Kenta; Araidai, Masaaki; Kangawa, Yoshihiro; Kakimoto, Koichi; Shiraishi, Kenji

2017-04-01

We analyzed the metal organic vapor phase epitaxial growth mechanism of the III-nitride semiconductors GaN, AlN, and InN by first-principles calculations and thermodynamic analyses. In these analyses, we investigated the decomposition processes of the group III source gases X(CH3)3 (X = Ga, Al, In) at finite temperatures and determined whether the (CH3)2GaNH2 adduct can be formed or not. The results of our calculations show that the (CH3)2GaNH2 adduct cannot be formed in the gas phase in GaN metal organic vapor phase epitaxy (MOVPE), whereas, in AlN MOVPE, the formation of the (CH3)2AlNH2 adduct in the gas phase is exclusive. In the case of GaN MOVPE, trimethylgallium (TMG, [Ga(CH3)3]) decomposition into Ga gas on the growth surface with the assistance of H2 carrier gas, instead of the formation of the (CH3)2GaNH2 adduct, occurs almost exclusively. Moreover, in the case of InN MOVPE, the formation of the (CH3)2InNH2 adduct does not occur and it is relatively easy to produce In gas even without H2 in the carrier gas.

Observation of a system of linear loops formed by re-growing hairs on rat skin.

PubMed

Liu, Li-Yuan; Guo, Dong-Sheng; Xin, Xiu-Yu; Fang, Jin

2008-07-01

This paper details linear hair re-growth patterns observed in rats. Adult rats were shaved and observed. The first wave of hair re-growth did not distribute everywhere, but along specific craniocaudally-oriented lines. The hair-lines were 2-15 mm wide and ran from the head, through the torso to the limbs, and were symmetrical along the left and right sides of the body. The symmetric hair-lines from both sides of the body converged around the mouth, nose, and at the pubic region or ventral midline to form a system of hair-loop-lines (HLLs). The loops can be differentiated into four main patterns. The Dorsal Loop and the Lateral Dorsal Loop run along the dorsum and hindlimb. The Ventral Loop and Lateral Ventral Loop travel along the thorax, abdomen, and forelimb. These hair-lines coincide with our previously observed sympathetic-substance lines (SSLs) in the rat's skin. Histological observation indicates that rat hair follicles along the hair-lines were at anagen phase. The catecholamine histofluorescent check showed abundant sympathetic nerve fibers beneath the hair-lines. After the rats' hairs were dyed, and selected portions shaved, re-growth was only observed on the shaved portions, indicating that the linear hair growth closely correlated with the shaving. Lastly we examine the cause of the preferential re-growth and briefly discuss the purpose and physiological role of the HLL. (c) 2008 Wiley-Liss, Inc.

Liquid-phase epitaxy grown PbSnTe distributed feedback laser diodes with broad continuous single-mode tuning range

NASA Technical Reports Server (NTRS)

Hsieh, H.-H.; Fonstad, C. G.

1980-01-01

Distributed feedback (DFB) pulsed laser operation has been demonstrated in stripe geometry Pb(1-x)Sn(x)Te double-heterostructures grown by liquid-phase epitaxy. The grating structure of 0.79 micron periodicity operates in first order near 12.8 microns and was fabricated prior to the liquid-phase epitaxial growth using holographic exposure techniques. These DFB lasers had moderate thresholds, 3.6 kA/sq cm, and the output power versus current curves exhibited a sharp turn-on free of kinks. Clean, single-mode emission spectra, continuously tunable over a range in excess of 20 per cm, centered about 780 per cm (12.8 microns), and at an average rate of 1.2 per cm-K from 9 to 26 K, were observed. While weaker modes could at times be seen in the spectrum, substantially single-mode operation was obtained over the entire operating range and to over 10 times threshold.

Epitaxial VO2 thin-film-based radio-frequency switches with electrical activation

NASA Astrophysics Data System (ADS)

Lee, Jaeseong; Lee, Daesu; Cho, Sang June; Seo, Jung-Hun; Liu, Dong; Eom, Chang-Beom; Ma, Zhenqiang

2017-09-01

Vanadium dioxide (VO2) is a correlated material exhibiting a sharp insulator-to-metal phase transition (IMT) caused by temperature change and/or bias voltage. We report on the demonstration of electrically triggered radio-frequency (RF) switches based on epitaxial VO2 thin films. The highly epitaxial VO2 and SnO2 template layer was grown on a (001) TiO2 substrate by pulsed laser deposition (PLD). A resistance change of the VO2 thin films of four orders of magnitude was achieved with a relatively low threshold voltage, as low as 13 V, for an IMT phase transition. VO2 RF switches also showed high-frequency responses of insertion losses of -3 dB at the on-state and return losses of -4.3 dB at the off-state over 27 GHz. Furthermore, an intrinsic cutoff frequency of 17.4 THz was estimated for the RF switches. The study on electrical IMT dynamics revealed a phase transition time of 840 ns.

Epitaxial BiFeO3 thin films fabricated by chemical solution deposition

NASA Astrophysics Data System (ADS)

Singh, S. K.; Kim, Y. K.; Funakubo, H.; Ishiwara, H.

2006-04-01

Epitaxial BiFeO3 (BFO) thin films were fabricated on (001)-, (110)-, and (111)-oriented single-crystal SrRuO3(SRO )/SrTiO3(STO) structures by chemical solution deposition. X-ray diffraction indicates the formation of an epitaxial single-phase perovskite structure and pole figure measurement confirms the cube-on-cube epitaxial relationship of BFO ‖SRO‖STO. Chemical-solution-deposited BFO films have a rhombohedral structure with lattice parameter of 0.395nm, which is the same structure as that of a bulk single crystal. The remanent polarization of approximately 50μC/cm2 was observed in BFO (001) thin films at 80K.

Interfacial strain effects on lithium diffusion pathways in the spinel solid electrolyte Li-doped MgAl2O4

NASA Astrophysics Data System (ADS)

O'Rourke, Conn; Morgan, Benjamin J.

2018-04-01

The (Li,Al)-codoped magnesium spinel (LixMg1 -2 xAl2 +xO4 ) is a solid lithium-ion electrolyte with potential use in all-solid-state lithium-ion batteries. The spinel structure means that interfaces with spinel electrodes, such as LiyMn2O4 and Li4 +3 zTi5O12 , may be lattice matched, with potentially low interfacial resistances. Small lattice parameter differences across a lattice-matched interface are unavoidable, causing residual epitaxial strain. This strain potentially modifies lithium diffusion near the electrolyte-electrode interface, contributing to interfacial resistance. Here, we report a density functional theory study of strain effects on lithium diffusion pathways for (Li,Al)-codoped magnesium spinel, for xLi=0.25 and xLi=0.5 . We have calculated diffusion profiles for the unstrained materials, and for isotropic and biaxial tensile strains of up to 6 % , corresponding to {100 } epitaxial interfaces with LiyMn2O4 and Li4 +3 zTi5O12 . We find that isotropic tensile strain reduces lithium diffusion barriers by as much as 0.32 eV , with typical barriers reduced by ˜0.1 eV. This effect is associated with increased volumes of transitional octahedral sites, and broadly follows qualitative changes in local electrostatic potentials. For biaxial (epitaxial) strain, which more closely approximates strain at a lattice-matched electrolyte-electrode interface, changes in octahedral site volumes and in lithium diffusion barriers are much smaller than under isotropic strain. Typical barriers are reduced by only ˜0.05 eV. Individual effects, however, depend on the pathway considered and the relative strain orientation. These results predict that isotropic strain strongly affects ionic conductivities in (Li,Al)-codoped magnesium spinel electrolytes, and that tensile strain is a potential route to enhanced lithium transport. For a lattice-matched interface with candidate spinel-structured electrodes, however, epitaxial strain has a small, but complex, effect on lithium diffusion barriers.

Epitaxial thin films

DOEpatents

Hunt, Andrew Tye; Deshpande, Girish; Lin, Wen-Yi; Jan, Tzyy-Jiuan

2006-04-25

Epitatial thin films for use as buffer layers for high temperature superconductors, electrolytes in solid oxide fuel cells (SOFC), gas separation membranes or dielectric material in electronic devices, are disclosed. By using CCVD, CACVD or any other suitable deposition process, epitaxial films having pore-free, ideal grain boundaries, and dense structure can be formed. Several different types of materials are disclosed for use as buffer layers in high temperature superconductors. In addition, the use of epitaxial thin films for electrolytes and electrode formation in SOFCs results in densification for pore-free and ideal gain boundary/interface microstructure. Gas separation membranes for the production of oxygen and hydrogen are also disclosed. These semipermeable membranes are formed by high-quality, dense, gas-tight, pinhole free sub-micro scale layers of mixed-conducting oxides on porous ceramic substrates. Epitaxial thin films as dielectric material in capacitors are also taught herein. Capacitors are utilized according to their capacitance values which are dependent on their physical structure and dielectric permittivity. The epitaxial thin films of the current invention form low-loss dielectric layers with extremely high permittivity. This high permittivity allows for the formation of capacitors that can have their capacitance adjusted by applying a DC bias between their electrodes.

Applying CLIPS to control of molecular beam epitaxy processing

NASA Technical Reports Server (NTRS)

Rabeau, Arthur A.; Bensaoula, Abdelhak; Jamison, Keith D.; Horton, Charles; Ignatiev, Alex; Glover, John R.

1990-01-01

A key element of U.S. industrial competitiveness in the 1990's will be the exploitation of advanced technologies which involve low-volume, high-profit manufacturing. The demands of such manufacture limit participation to a few major entities in the U.S. and elsewhere, and offset the lower manufacturing costs of other countries which have, for example, captured much of the consumer electronics market. One such technology is thin-film epitaxy, a technology which encompasses several techniques such as Molecular Beam Epitaxy (MBE), Chemical Beam Epitaxy (CBE), and Vapor-Phase Epitaxy (VPE). Molecular Beam Epitaxy (MBE) is a technology for creating a variety of electronic and electro-optical materials. Compared to standard microelectronic production techniques (including gaseous diffusion, ion implantation, and chemical vapor deposition), MBE is much more exact, though much slower. Although newer than the standard technologies, MBE is the technology of choice for fabrication of ultraprecise materials for cutting-edge microelectronic devices and for research into the properties of new materials.

Diversity of terrestrial mammal seed dispersers along a lowland Amazon forest regrowth gradient

PubMed Central

Arévalo-Sandi, Alexander; Bobrowiec, Paulo Estefano D.; Rodriguez Chuma, Victor Juan Ulises

2018-01-01

There is increasing interest in the restoration/regeneration of degraded tropical habitats yet the potential role of natural regenerators remains unclear. We test the hypothesis that the richness and functional diversity of terrestrial mammals differs between forest regrowth stages. We quantified the richness and functional diversity of eight terrestrial mammal seed-disperser species across a forest regrowth gradient in the eastern Brazilian Amazon. We installed camera-traps in 15 sites within small-holder properties with forest regrowth stage classified into three groups, with five sites each of: late second-regrowth forest, early second-regrowth forest and abandoned pasture. Species richness and functional dispersion from the regrowth sites were compared with 15 paired forest control sites. Multi model selection showed that regrowth class was more important for explaining patterns in richness and functional diversity than other variables from three non-mutually exclusive hypotheses: hunting (distance to house, distance to river, distance to town, small holder residence), land cover (% forest cover within 50 meters, 1 kilometer and 5 kilometers) and land use (regrowth class, time since last use). Differences in functional diversity were most strongly explained by a loss of body mass. We found that diversity in regrowth sites could be similar to control sites even in some early-second regrowth areas. This finding suggests that when surrounded by large intact forest areas the richness and functional diversity close to human small-holdings can return to pre-degradation values. Yet we also found a significant reduction in richness and functional diversity in more intensely degraded pasture sites. This reduction in richness and functional diversity may limit the potential for regeneration and increase costs for ecological regeneration and restoration actions around more intense regrowth areas. PMID:29547648

Diversity of terrestrial mammal seed dispersers along a lowland Amazon forest regrowth gradient.

PubMed

Arévalo-Sandi, Alexander; Bobrowiec, Paulo Estefano D; Rodriguez Chuma, Victor Juan Ulises; Norris, Darren

2018-01-01

There is increasing interest in the restoration/regeneration of degraded tropical habitats yet the potential role of natural regenerators remains unclear. We test the hypothesis that the richness and functional diversity of terrestrial mammals differs between forest regrowth stages. We quantified the richness and functional diversity of eight terrestrial mammal seed-disperser species across a forest regrowth gradient in the eastern Brazilian Amazon. We installed camera-traps in 15 sites within small-holder properties with forest regrowth stage classified into three groups, with five sites each of: late second-regrowth forest, early second-regrowth forest and abandoned pasture. Species richness and functional dispersion from the regrowth sites were compared with 15 paired forest control sites. Multi model selection showed that regrowth class was more important for explaining patterns in richness and functional diversity than other variables from three non-mutually exclusive hypotheses: hunting (distance to house, distance to river, distance to town, small holder residence), land cover (% forest cover within 50 meters, 1 kilometer and 5 kilometers) and land use (regrowth class, time since last use). Differences in functional diversity were most strongly explained by a loss of body mass. We found that diversity in regrowth sites could be similar to control sites even in some early-second regrowth areas. This finding suggests that when surrounded by large intact forest areas the richness and functional diversity close to human small-holdings can return to pre-degradation values. Yet we also found a significant reduction in richness and functional diversity in more intensely degraded pasture sites. This reduction in richness and functional diversity may limit the potential for regeneration and increase costs for ecological regeneration and restoration actions around more intense regrowth areas.

Understanding the Growth Mechanism of GaN Epitaxial Layers on Mechanically Exfoliated Graphite

NASA Astrophysics Data System (ADS)

Li, Tianbao; Liu, Chenyang; Zhang, Zhe; Yu, Bin; Dong, Hailiang; Jia, Wei; Jia, Zhigang; Yu, Chunyan; Gan, Lin; Xu, Bingshe; Jiang, Haiwei

2018-04-01

The growth mechanism of GaN epitaxial layers on mechanically exfoliated graphite is explained in detail based on classic nucleation theory. The number of defects on the graphite surface can be increased via O-plasma treatment, leading to increased nucleation density on the graphite surface. The addition of elemental Al can effectively improve the nucleation rate, which can promote the formation of dense nucleation layers and the lateral growth of GaN epitaxial layers. The surface morphologies of the nucleation layers, annealed layers and epitaxial layers were characterized by field-emission scanning electron microscopy, where the evolution of the surface morphology coincided with a 3D-to-2D growth mechanism. High-resolution transmission electron microscopy was used to characterize the microstructure of GaN. Fast Fourier transform diffraction patterns showed that cubic phase (zinc-blend structure) GaN grains were obtained using conventional GaN nucleation layers, while the hexagonal phase (wurtzite structure) GaN films were formed using AlGaN nucleation layers. Our work opens new avenues for using highly oriented pyrolytic graphite as a substrate to fabricate transferable optoelectronic devices.

Understanding the Growth Mechanism of GaN Epitaxial Layers on Mechanically Exfoliated Graphite.

PubMed

Li, Tianbao; Liu, Chenyang; Zhang, Zhe; Yu, Bin; Dong, Hailiang; Jia, Wei; Jia, Zhigang; Yu, Chunyan; Gan, Lin; Xu, Bingshe; Jiang, Haiwei

2018-04-27

The growth mechanism of GaN epitaxial layers on mechanically exfoliated graphite is explained in detail based on classic nucleation theory. The number of defects on the graphite surface can be increased via O-plasma treatment, leading to increased nucleation density on the graphite surface. The addition of elemental Al can effectively improve the nucleation rate, which can promote the formation of dense nucleation layers and the lateral growth of GaN epitaxial layers. The surface morphologies of the nucleation layers, annealed layers and epitaxial layers were characterized by field-emission scanning electron microscopy, where the evolution of the surface morphology coincided with a 3D-to-2D growth mechanism. High-resolution transmission electron microscopy was used to characterize the microstructure of GaN. Fast Fourier transform diffraction patterns showed that cubic phase (zinc-blend structure) GaN grains were obtained using conventional GaN nucleation layers, while the hexagonal phase (wurtzite structure) GaN films were formed using AlGaN nucleation layers. Our work opens new avenues for using highly oriented pyrolytic graphite as a substrate to fabricate transferable optoelectronic devices.

Phase-separated, epitaxial composite cap layers for electronic device applications and method of making the same

DOEpatents

Aytug, Tolga [Knoxville, TN; Paranthaman, Mariappan Parans [Knoxville, TN; Polat, Ozgur [Knoxville, TN

2012-07-17

An electronic component that includes a substrate and a phase-separated layer supported on the substrate and a method of forming the same are disclosed. The phase-separated layer includes a first phase comprising lanthanum manganate (LMO) and a second phase selected from a metal oxide (MO), metal nitride (MN), a metal (Me), and combinations thereof. The phase-separated material can be an epitaxial layer and an upper surface of the phase-separated layer can include interfaces between the first phase and the second phase. The phase-separated layer can be supported on a buffer layer comprising a composition selected from the group consisting of IBAD MgO, LMO/IBAD-MgO, homoepi-IBAD MgO and LMO/homoepi-MgO. The electronic component can also include an electronically active layer supported on the phase-separated layer. The electronically active layer can be a superconducting material, a ferroelectric material, a multiferroic material, a magnetic material, a photovoltaic material, an electrical storage material, and a semiconductor material.

Metal-organic vapor-phase epitaxy-grown ultra-low density InGaAs/GaAs quantum dots exhibiting cascaded single-photon emission at 1.3 μm

DOE Office of Scientific and Technical Information (OSTI.GOV)

Paul, Matthias, E-mail: m.paul@ihfg.uni-stuttgart.de; Kettler, Jan; Zeuner, Katharina

By metal-organic vapor-phase epitaxy, we have fabricated InGaAs quantum dots on GaAs substrate with an ultra-low lateral density (<10{sup 7} cm{sup −2}). The photoluminescence emission from the quantum dots is shifted to the telecom O-band at 1.31 μm by an InGaAs strain reducing layer. In time-resolved measurements, we find fast decay times for exciton (∼600 ps) and biexciton (∼300 ps). We demonstrate triggered single-photon emission (g{sup (2)}(0)=0.08) as well as cascaded emission from the biexciton decay. Our results suggest that these quantum dots can compete with their counterparts grown by state-of-the-art molecular beam epitaxy.

Role of microstructures on the M1-M2 phase transition in epitaxial VO2 thin films

PubMed Central

Ji, Yanda; Zhang, Yin; Gao, Min; Yuan, Zhen; Xia, Yudong; Jin, Changqing; Tao, Bowan; Chen, Chonglin; Jia, Quanxi; Lin, Yuan

2014-01-01

Vanadium dioxide (VO2) with its unique sharp resistivity change at the metal-insulator transition (MIT) has been extensively considered for the near-future terahertz/infrared devices and energy harvesting systems. Controlling the epitaxial quality and microstructures of vanadium dioxide thin films and understanding the metal-insulator transition behaviors are therefore critical to novel device development. The metal-insulator transition behaviors of the epitaxial vanadium dioxide thin films deposited on Al2O3 (0001) substrates were systematically studied by characterizing the temperature dependency of both Raman spectrum and Fourier transform infrared spectroscopy. Our findings on the correlation between the nucleation dynamics of intermediate monoclinic (M2) phase with microstructures will open a new avenue for the design and integration of advanced heterostructures with controllable multifunctionalities for sensing and imaging system applications. PMID:24798056

Direct Growth of CdTe on a (211) Si Substrate with Vapor Phase Epitaxy Using a Metallic Cd Source

NASA Astrophysics Data System (ADS)

Iso, Kenji; Gokudan, Yuya; Shiraishi, Masumi; Murakami, Hisashi; Koukitu, Akinori

2017-10-01

We successfully performed epitaxial CdTe growth on a Si (211) substrate with vapor-phase epitaxy using a cost-effective metallic cadmium source as a group-II precursor. The thermodynamic data demonstrate that the combination of metallic Cd and diisopropyl-telluride (DiPTe) with a H2 carrier gas enables the growth of CdTe crystals. A CdTe single crystal with a (422) surface orientation was obtained when a growth temperature between 600°C and 650°C was employed. The surface morphology and crystalline quality were improved with increasing film thickness. The full-width at half-maximum of the x-ray rocking curves with a film thickness of 15.7 μm for the skew-symmetrical (422) and asymmetrical (111) reflection were 528 arcsec and 615 arcsec, respectively.

Antioxidant and Anti-stress Compounds Improve Regrowth of Cryopreserved Rubus Shoot Tips

USDA-ARS?s Scientific Manuscript database

Regrowth of plants after cryopreservation varies and resulting regrowth ranges from poor to excellent. Oxidative stress is a potential cause of damage in plant tissues. Antioxidants and anti-stress compounds may improve regrowth by preventing or repairing the damage. Lipoic acid (LA), glutathione (...

Modeling of Gallium Nitride Hydride Vapor Phase Epitaxy

NASA Technical Reports Server (NTRS)

Meyyappan, Meyya; Arnold, James O. (Technical Monitor)

1997-01-01

A reactor model for the hydride vapor phase epitaxy of GaN is presented. The governing flow, energy, and species conservation equations are solved in two dimensions to examine the growth characteristics as a function of process variables and reactor geometry. The growth rate varies with GaCl composition but independent of NH3 and H2 flow rates. A change in carrier gas for Ga source from H2 to N2 affects the growth rate and uniformity for a fixed reactor configuration. The model predictions are in general agreement with observed experimental behavior.

Growth of strontium ruthenate films by hybrid molecular beam epitaxy

DOE PAGES

Marshall, Patrick B.; Kim, Honggyu; Ahadi, Kaveh; ...

2017-09-01

We report on the growth of epitaxial Sr 2RuO 4 films using a hybrid molecular beam epitaxy approach in which a volatile precursor containing RuO 4 is used to supply ruthenium and oxygen. The use of the precursor overcomes a number of issues encountered in traditional molecular beam epitaxy that uses elemental metal sources. Phase-pure, epitaxial thin films of Sr 2RuO 4 are obtained. At high substrate temperatures, growth proceeds in a layer-by-layer mode with intensity oscillations observed in reflection high-energy electron diffraction. Films are of high structural quality, as documented by x-ray diffraction, atomic force microscopy, and transmission electronmore » microscopy. In conclusion, the method should be suitable for the growth of other complex oxides containing ruthenium, opening up opportunities to investigate thin films that host rich exotic ground states.« less

Epitaxial Graphene: A New Material for Electronics

NASA Astrophysics Data System (ADS)

de Heer, Walt A.

2007-10-01

Graphene multilayers are grown epitaxially on single crystal silicon carbide. This system is composed of several graphene layers of which the first layer is electron doped due to the built-in electric field and the other layers are essentially undoped. Unlike graphite the charge carriers show Dirac particle properties (i.e. an anomalous Berry's phase, weak anti-localization and square root field dependence of the Landau level energies). Epitaxial graphene shows quasi-ballistic transport and long coherence lengths; properties that may persists above cryogenic temperatures. Paradoxically, in contrast to exfoliated graphene, the quantum Hall effect is not observed in high mobility epitaxial graphene. It appears that the effect is suppressed due to absence of localized states in the bulk of the material. Epitaxial graphene can be patterned using standard lithography methods and characterized using a wide array of techniques. These favorable features indicate that interconnected room temperature ballistic devices may be feasible for low dissipation high-speed nano-electronics.

Epitaxial graphene

NASA Astrophysics Data System (ADS)

de Heer, Walt A.; Berger, Claire; Wu, Xiaosong; First, Phillip N.; Conrad, Edward H.; Li, Xuebin; Li, Tianbo; Sprinkle, Michael; Hass, Joanna; Sadowski, Marcin L.; Potemski, Marek; Martinez, Gérard

2007-07-01

Graphene multilayers are grown epitaxially on single crystal silicon carbide. This system is composed of several graphene layers of which the first layer is electron doped due to the built-in electric field and the other layers are essentially undoped. Unlike graphite the charge carriers show Dirac particle properties (i.e. an anomalous Berry's phase, weak anti-localization and square root field dependence of the Landau level energies). Epitaxial graphene shows quasi-ballistic transport and long coherence lengths; properties that may persist above cryogenic temperatures. Paradoxically, in contrast to exfoliated graphene, the quantum Hall effect is not observed in high-mobility epitaxial graphene. It appears that the effect is suppressed due to the absence of localized states in the bulk of the material. Epitaxial graphene can be patterned using standard lithography methods and characterized using a wide array of techniques. These favorable features indicate that interconnected room temperature ballistic devices may be feasible for low-dissipation high-speed nanoelectronics.

Effect of Elastic Strain Fluctuation on Atomic Layer Growth of Epitaxial Silicide in Si Nanowires by Point Contact Reactions.

PubMed

Chou, Yi-Chia; Tang, Wei; Chiou, Chien-Jyun; Chen, Kai; Minor, Andrew M; Tu, K N

2015-06-10

Effects of strain impact a range of applications involving mobility change in field-effect-transistors. We report the effect of strain fluctuation on epitaxial growth of NiSi2 in a Si nanowire via point contact and atomic layer reactions, and we discuss the thermodynamic, kinetic, and mechanical implications. The generation and relaxation of strain shown by in situ TEM is periodic and in synchronization with the atomic layer reaction. The Si lattice at the epitaxial interface is under tensile strain, which enables a high solubility of supersaturated interstitial Ni atoms for homogeneous nucleation of an epitaxial atomic layer of the disilicide phase. The tensile strain is reduced locally during the incubation period of nucleation by the dissolution of supersaturated Ni atoms in the Si lattice but the strained-Si state returns once the atomic layer epitaxial growth of NiSi2 occurs by consuming the supersaturated Ni.

Ultra High p-doping Material Research for GaN Based Light Emitters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vladimir Dmitriev

2007-06-30

The main goal of the Project is to investigate doping mechanisms in p-type GaN and AlGaN and controllably fabricate ultra high doped p-GaN materials and epitaxial structures. Highly doped p-type GaN-based materials with low electrical resistivity and abrupt doping profiles are of great importance for efficient light emitters for solid state lighting (SSL) applications. Cost-effective hydride vapor phase epitaxial (HVPE) technology was proposed to investigate and develop p-GaN materials for SSL. High p-type doping is required to improve (i) carrier injection efficiency in light emitting p-n junctions that will result in increasing of light emitting efficiency, (ii) current spreading inmore » light emitting structures that will improve external quantum efficiency, and (iii) parameters of Ohmic contacts to reduce operating voltage and tolerate higher forward currents needed for the high output power operation of light emitters. Highly doped p-type GaN layers and AlGaN/GaN heterostructures with low electrical resistivity will lead to novel device and contact metallization designs for high-power high efficiency GaN-based light emitters. Overall, highly doped p-GaN is a key element to develop light emitting devices for the DOE SSL program. The project was focused on material research for highly doped p-type GaN materials and device structures for applications in high performance light emitters for general illumination P-GaN and p-AlGaN layers and multi-layer structures were grown by HVPE and investigated in terms of surface morphology and structure, doping concentrations and profiles, optical, electrical, and structural properties. Tasks of the project were successfully accomplished. Highly doped GaN materials with p-type conductivity were fabricated. As-grown GaN layers had concentration N{sub a}-N{sub d} as high as 3 x 10{sup 19} cm{sup -3}. Mechanisms of doping were investigated and results of material studies were reported at several International conferences providing better understanding of p-type GaN formation for Solid State Lighting community. Grown p-type GaN layers were used as substrates for blue and green InGaN-based LEDs made by HVPE technology at TDI. These results proved proposed technical approach and facilitate fabrication of highly conductive p-GaN materials by low-cost HVPE technology for solid state lighting applications. TDI has started the commercialization of p-GaN epitaxial materials.« less

Formation and investigation of ultrathin layers of Co2FeSi ferromagnetic alloy synthesized on silicon covered with a CaF2 barrier layer

NASA Astrophysics Data System (ADS)

Grebenyuk, G. S.; Gomoyunova, M. V.; Pronin, I. I.; Vyalikh, D. V.; Molodtsov, S. L.

2016-03-01

Ultrathin (∼2 nm) films of Co2FeSi ferromagnetic alloy were formed on silicon by solid-phase epitaxy and studied in situ. Experiments were carried out in an ultrahigh vacuum (UHV) using substrates of Si(1 1 1) single crystals covered with a 5 nm thick CaF2 barrier layer. The elemental and phase composition as well as the magnetic properties of the synthesized films were analyzed by photoelectron spectroscopy using synchrotron radiation and by magnetic linear dichroism in photoemission of Fe 3p and Co 3p electrons. The study shows that the synthesis of the Co2FeSi ferromagnetic alloy occurs in the temperature range of 200-400 °C. At higher temperatures, the films become island-like and lose their ferromagnetic properties, as the CaF2 barrier layer is unable to prevent a mass transfer between the film and the Si substrate, which violates the stoichiometry of the alloy.

Dynamic observation on the growth behaviors in manganese silicide/silicon nanowire heterostructures.

PubMed

Hsieh, Yu-Hsun; Chiu, Chung-Hua; Huang, Chun-Wei; Chen, Jui-Yuan; Lin, Wan-Jhen; Wu, Wen-Wei

2015-02-07

Metal silicide nanowires (NWs) are very interesting materials with diverse physical properties. Among the silicides, manganese silicide nanostructures have attracted wide attention due to their several potential applications, including in microelectronics, optoelectronics, spintronics and thermoelectric devices. In this work, we exhibited the formation of pure manganese silicide and manganese silicide/silicon nanowire heterostructures through solid state reaction with line contacts between manganese pads and silicon NWs. Dynamical process and phase characterization were investigated by in situ transmission electron microscopy (in situ TEM) and spherical aberration corrected scanning transmission electron microscopy (Cs-corrected STEM), respectively. The growth dynamics of the manganese silicide phase under thermal effects were systematically studied. Additionally, Al2O3, serving as the surface oxide, altered the growth behavior of the MnSi nanowire, enhancing the silicide/Si epitaxial growth and effecting the diffusion process in the silicon nanowire as well. In addition to fundamental science, this significant study has great potential in advancing future processing techniques in nanotechnology and related applications.

Reducing the nucleation barrier in magnetocaloric Heusler alloys by nanoindentation

NASA Astrophysics Data System (ADS)

Niemann, R.; Hahn, S.; Diestel, A.; Backen, A.; Schultz, L.; Nielsch, K.; Wagner, M. F.-X.; Fähler, S.

2016-06-01

Magnetocaloric materials are promising as solid state refrigerants for more efficient and environmentally friendly cooling devices. The highest effects have been observed in materials that exhibit a first-order phase transition. These transformations proceed by nucleation and growth which lead to a hysteresis. Such irreversible processes are undesired since they heat up the material and reduce the efficiency of any cooling application. In this article, we demonstrate an approach to decrease the hysteresis by locally changing the nucleation barrier. We created artificial nucleation sites and analyzed the nucleation and growth processes in their proximity. We use Ni-Mn-Ga, a shape memory alloy that exhibits a martensitic transformation. Epitaxial films serve as a model system, but their high surface-to-volume ratio also allows for a fast heat transfer which is beneficial for a magnetocaloric regenerator geometry. Nanoindentation is used to create a well-defined defect. We quantify the austenite phase fraction in its proximity as a function of temperature which allows us to determine the influence of the defect on the transformation.

Structural phase diagram for ultra-thin epitaxial Fe 3O 4 / MgO(0 01) films: thickness and oxygen pressure dependence

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alraddadi, S.; Hines, W.; Yilmaz, T.

2016-02-19

A systematic investigation of the thickness and oxygen pressure dependence for the structural properties of ultra-thin epitaxial magnetite (Fe 3O 4) films has been carried out; for such films, the structural properties generally differ from those for the bulk when the thickness ≤10 nm. Iron oxide ultra-thin films with thicknesses varying from 3 nm to 20 nm were grown on MgO (001) substrates using molecular beam epitaxy under different oxygen pressures ranging from 1 × 10 -7 torr to 1 × 10 -5 torr. The crystallographic and electronic structures of the films were characterized using low energy electron diffraction (LEED)more » and x-ray photoemission spectroscopy (XPS), respectively. Moreover, the quality of the epitaxial Fe 3O 4 ultra-thin films was judged by magnetic measurements of the Verwey transition, along with complementary XPS spectra. We observed that under the same growth conditions the stoichiometry of ultra-thin films under 10 nm transforms from the Fe 3O 4 phase to the FeO phase. In this work, a phase diagram based on thickness and oxygen pressure has been constructed to explain the structural phase transformation. It was found that high-quality magnetite films with thicknesses ≤20 nm formed within a narrow range of oxygen pressure. An optimal and controlled growth process is a crucial requirement for the accurate study of the magnetic and electronic properties for ultra-thin Fe 3O 4 films. Furthermore, these results are significant because they may indicate a general trend in the growth of other oxide films, which has not been previously observed or considered.« less

The prevention of plaque re-growth by toothpastes and solutions containing block copolymers with and without polypeptide.

PubMed

Claydon, N C; Addy, M; Newcombe, R; Moran, J

2005-06-01

Chemicals which have a direct effect at inhibiting or reducing bacterial adherence to tooth surfaces may subsequently inhibit plaque growth and reduce gingival inflammation. This study investigated whether two anti-adherent systems could inhibit plaque re-growth in the mouth when rinsed as a solution or as a toothpaste slurry. A total of 21 subjects took part in a partially blind, seven cell cross-over study which compared the effects on plaque re-growth of a binary system containing block copolymers, a ternary system containing block copolymers and polypeptide, both used as toothpaste slurry rinses, their corresponding solution rinses, a conventional fluoride toothpaste rinse, a positive control chlorhexidine rinse and a negative water control. Following a dental prophylaxis subjects then rinsed with 10 ml of one of the test products for 1 min. twice a day over a 4-day period. Throughout each trial period the subjects were not permitted to use any other forms of oral hygiene. On the fifth day (96 h), the volunteers returned to the clinic, and plaque was assessed by (1) plaque index and (2) plaque area following disclosing with a food dye. The test phase of the trial was repeated for each agent and was followed by a 10-day "washout" period. Essentially neither of the anti-adherent systems inhibited plaque re-growth, whether administered in a toothpaste slurry or solution compared with the controls. If anything, neither of the test pastes were as effective as the marketed commercial paste (p<0.001). As expected plaque recorded following use of the chlorhexidine rinse was significantly less than that seen with any of the other rinses (p<0.001). Using this 4-day plaque re-growth model, the findings of this study failed to show any benefit in using the anti-adherent systems, either in a rinse or toothpaste, with the aim of inhibiting or reducing plaque formation.

Molecular beam epitaxy growth of niobium oxides by solid/liquid state oxygen source and lithium assisted metal-halide chemistry

NASA Astrophysics Data System (ADS)

Tellekamp, M. Brooks; Greenlee, Jordan D.; Shank, Joshua C.; Doolittle, W. Alan

2015-09-01

In order to consistently grow high quality niobium oxides and lithium niobium oxides, a novel solid/liquid state oxygen source, LiClO4, has been implemented in a molecular beam epitaxy (MBE) system. LiClO4 is shown to decompose into both molecular and atomic oxygen upon heating. This allows oxidation rates similar to that of molecular oxygen but at a reduced overall beam flux, quantified by in situ Auger analysis. LiClO4 operation is decomposition limited to less than 400 °C, and other material limitations are identified. The design of a custom near-ambient NbCl5 effusion cell is presented, which improves both short and long term stability. Films of Nb oxidation state +2, +3, and +5 are grown using these new tools, including the multi-functional sub-oxide LiNbO2.

Spectral Re-Growth Reduction for CCSDS 8-D 8-PSK TCM

NASA Technical Reports Server (NTRS)

Borah, Deva K.

2002-01-01

This report presents a study on the CCSDS recommended 8-dimensional 8 PSK Trellis Coded Modulation (TCM) scheme. The important steps of the CCSDS scheme include: conversion of serial data into parallel form, differential encoding, convolutional encoding, constellation mapping, and filtering the 8-PSK symbols using the square root raised cosine (SRRC) pulses. The last step, namely the filtering of the 8 PSK symbols using SRRC pulses, significantly affects the bandwidth of the signal. If a nonlinear power amplifier is used, the SRRC filtered signal creates spectral regrowth. The purpose of this report is to investigate a technique, called the smooth phase interpolated keying (SPIK), that can provide an alternative to SRRC filtering so that good spectral as well as power efficiencies can be obtained with the CCSDS encoder. The results of this study show that the CCSDS encoder does not affect the spectral shape of the SRRC filtered signal or the SPIK signal. When a nonlinear traveling wave tube amplifier (TWTA) is used, the spectral performance of the SRRC signal degrades significantly while the spectral performance of SPIK remains unaffected. The degrading effect of a nonlinear solid state power amplifier (SSPA) on SRRC is found to be less than that due to a nonlinear TWTA. However, in both cases, the spectral performance of the SRRC modulated signal is worse than that of the SPIK signal. The bit error rate (BER) performance of the SRRC signal in a linear amplifier environment is about 2.5 dB better than that of the SPIK signal when both the receivers use algorithms of similar complexity. In a nonlinear TWTA environment, the SRRC signal requires accurate phase tracking since the TWTA introduces additional phase distortion. This problem does not arise with SPIK signal due to its constant envelope property. When a nonlinear amplifier is used, the SRRC method loses nearly 1 dB in the bit error rate performance. The SPIK signal does not lose any performance. Thus the performance gap between SRRC and SPIK reduces. The BER performance of SPIK can be improved even further by using a more optimal receiver. A similar optimal receiver for SRRC is quite complex since the amplifier distorts the pulse shape. However, this requires further investigation and is not covered in this report.

Calculation of electron spectra and some problems in the thermodynamics of graphene layers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alisultanov, Z. Z., E-mail: zaur0102@gmail.com

The expressions for the energy spectra of monolayer, bilayer, and multilayer graphene, as well as epitaxial graphene, are derived using the quantum Green’s functions method. Analytic expressions are obtained for the densities of states of these systems. It is shown that a bandgap can appear the spectrum of an epitaxial graphene bilayer. A number of problems in the thermodynamics of electrons in free and epitaxial graphene layers are considered as applications. Analytic expressions are obtained for the chemical potential and heat capacity in the limiting cases of low and high temperatures. Quantum oscillations of heat capacity in graphene are analyzedmore » taking into account the Coulomb interaction. The Berry phase of epitaxial graphene is investigated.« less

Fifty years of HgCdTe at Texas Instruments and beyond

NASA Astrophysics Data System (ADS)

Kinch, Michael A.

2009-05-01

Work on HgCdTe began at Texas Instruments in the early 1960s, and continued through 1997 when TI's defense business was sold first to Raytheon, and subsequently in 1998 to DRS Technologies. This presentation traces the history of HgCdTe's evolution throughout this timeframe to the present day, as viewed through the eyes of the author and several of his TI contemporaries who have survived the experience. The materials technology will be traced from the early days of bulk growth by the solid state recrystalization technique, through the traveling heater method of growth, to liquid phase epitaxy from large Te-rich melts, to vapor phase growth by molecular beam epitaxy and metal organic chemical vapor deposition. The evolution of detector device architectures at TI over the years will be discussed, from the early, successful days of photoconductors and the Common Module System, through the somewhat problematic and relatively unsuccessful foray into charge coupled and charge injection devices for 2nd generation FPAs for the Javelin program, to the outstandingly successful development of the vertically integrated photodiode (VIP) and high density VIP FPA architectures for mono-color and multi-color 3rd generation systems. The versatile, and unique nature of this infrared semiconductor materials system will be highlighted by reference to current work at DRS Technologies into electron avalanche photodiodes (EAPDs), for use in active/passive IR systems, and high operating temperature (HOT) detectors, which threaten to eventually offer BLIP photon detection at uncooled operating temperatures, over the whole IR spectrum from 1 to 12um.

Deposition and dielectric characterization of strontium and tantalum-based oxide and oxynitride perovskite thin films

NASA Astrophysics Data System (ADS)

Jacq, S.; Le Paven, C.; Le Gendre, L.; Benzerga, R.; Cheviré, F.; Tessier, F.; Sharaiha, A.

2016-04-01

We have synthesized the composition x = 0.01 of the (Sr1-xLax)2(Ta1-xTix)2O7 solid solution, mixing the ferroelectric perovskite phases Sr2Ta2O7 and La2Ti2O7. Related oxide and oxynitride materials have been produced as thin films by magnetron radio frequency sputtering. Reactive sputter deposition was conducted at 750 °C under a 75 vol.% (Ar) + 25 vol.% (N2,O2) mixture. An oxygen-free plasma leads to the deposition of an oxynitride film (Sr0.99La0.01) (Ta0.99Ti0.01)O2N, characterized by a band gap Eg = 2.30 eV and a preferential (001) epitaxial growth on (001) SrTiO3 substrate. Its dielectric constant and loss tangent are respectively Epsilon' = 60 (at 1 kHz) and tanDelta = 62.5 × 10-3. In oxygen-rich conditions (vol.%N2 ≤ 15%), (110) epitaxial (Sr0.99La0.01)2(Ta0.99Ti0.01)2O7 oxides films are deposited, associated to a larger band gap value (Eg = 4.55 eV). The oxide films permittivity varies from 45 to 25 (at 1 kHz) in correlation with the decrease in crystalline orientation; measured losses are lower than 5.10-3. For 20 ≤ vol.% N2 ≤ 24.55, the films are poorly crystallized, leading to very low permittivities (minimum Epsilon' = 3). A correlation between the dielectric losses and the presence of an oxynitride phase in the samples is highlighted.

Classification of Forest Regrowth Stage using Polarimetric Decomposition and Foliage Projective Cover

NASA Astrophysics Data System (ADS)

Clewley, D.; Lucas, R.; Bunting, P.; Moghaddam, M.

2012-12-01

Within Queensland, Australia extensive clearing of vegetation for agriculture has occurred within the Brigalow Belt Bioregion (BBB), reducing forests dominated by Acacia harpophylla (brigalow) to 10 % of their former extent. Where cleared land is left abandoned or unmanaged regeneration is rapid, Regenerating vegetation represents a more efficient and cost effective method for carbon sequestration than direct planting and offers a number of benefits over plantation forest, particularly in terms of provision of habitat for native fauna. To effectively protect regenerating vegetation, maps of the distribution of forests at different stages of regeneration are required. Whilst mapping approaches have traditionally focused on optical data, the high canopy cover of brigalow regrowth in all but the very early stages limits discrimination of forests at different stages of growth. The combination of optical data, namely Landsat derived Foliage Projective Cover (FPC) and Advanced Land Observing Satellite (ALOS) Phased Array L-band Synthetic Aperture Radar (SAR) backscatter data have previously been investigated for mapping regrowth. This study therefore aimed to investigate the potential of the alpha-Entropy (α/H) decomposition (S Cloude and E Pottier, "An entropy based classification scheme for land applications of polarimetric SAR," 1997, IEEE Transactions on Geoscience and Remote Sensing, vol. 35, no. 1, pp. 68-78) applied to polarimetric ALOS PALSAR backscatter for mapping regrowth stage combined with FPC data to account for canopy variations. The study focused on the Tara Downs subregion, located in the Western Darling Downs, within the south of the BBB. PALSAR data were acquired over the study site in fully-polarimetric mode (incidence angle mid swath ~ 26 degrees). From these data α/H layers were generated and stacked with FPC data. Considering only those areas known to contain brigalow prior to clearing and with an FPC > 9 %, k-means clustering was applied, with the number of clusters set to three. The position of each cluster, within α/H space was then used to determine the appropriate regrowth stage, based on the zones defined by Cloude and Pottier (1997). The classification was compared to an existing regrowth stage classification of the area derived from time-series interpretation of aerial photography and high resolution satellite data. The overall accuracy of the classification was 47 %, with confusion attributed to the differing methods of classification in that the separation of regrowth stage based on age did not account for variation in structure, associated with differences in soil, topography and clearing history. Conversely, the proposed classification method is based on scattering properties, which vary as a function of forest structure. The approach has demonstrated the potential of α/H layers derived from PALSAR data and FPC for discriminating and mapping different stages of regrowth. A particular advantage of the technique is that regrowth stages are assigned based on scattering characteristics, placing less reliance on field data which is not always available. Further work is being undertaken to evaluate alternative supervised and rule-based approaches to classification, such that a more consistent mapping methodology can be developed.

Strain Phase Diagram of SrTiO3 Thin Films

NASA Astrophysics Data System (ADS)

He, Feizhou; Shapiro, S. M.

2005-03-01

SrTiO3 thin films were used as a model system to study the effects of strain and epitaxial constraint on structural phase transitions of oxide films. The basic phenomena revealed will apply to a variety of important structural transitions including the ferroelectric transition. Highly strained, epitaxial films of SrTiO3 were grown on different substrates. The structural phase transition temperature Tc increases from 105 K in bulk STO to 167 K for films under tensile strain and 330 K for films with compressive strain. The measured temperature-strain phase diagram is qualitatively consistent with theory [1], however the increase in Tc is much larger than predicted in all cases. The symmetry of the phases involved in the transition is different from the corresponding bulk structures largely because of epitaxial constraint, the clamping effect. Thus the shape of the STO unit cell is tetragonal at all temperatures. The possibility exists of a very unique low temperature phase with orthorhombic symmetry (Cmcm) but tetragonal unit cell shape. More generally, we have characterized at least three different manifestations of the clamping effect, showing it is much more subtle than usually recognized. This work is supported through NSF DMR-0239667, DMR-0132918, by the Research Corp, and at BNL by the US DOE DE-AC02-98CH10886. [1] N. A. Pertsev, A. K. Tagantsev and N. Setter, Phys. Rev. B61, R825 (2000).

Elemental Topological Dirac Semimetal: α -Sn on InSb(111)

DOE PAGES

Xu, Cai-Zhi; Chan, Yang-Hao; Chen, Yige; ...

2017-04-04

Three-dimensional (3D) topological Dirac semimetals (TDSs) are rare but important as a versatile platform for exploring exotic electronic properties and topological phase transitions. A quintessential feature of TDSs is 3D Dirac fermions associated with bulk electronic states near the Fermi level. We have observed such bulk Dirac cones in epitaxially grown α-Sn films on InSb(111), the first such TDS system realized in an elemental form, using angle-resolved photoemission spectroscopy. First-principles calculations confirm that epitaxial strain is key to the formation of the TDS phase. A phase diagram is established that connects the 3D TDS phase through a singular point ofmore » a zero-gap semimetal phase to a topological insulator phase. The nature of the Dirac cone crosses over from 3D to 2D as the film thickness is reduced.« less

Oriented Y-type hexagonal ferrite thin films prepared by chemical solution deposition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Buršík, J., E-mail: bursik@iic.cas.cz; Kužel, R.; Knížek, K.

2013-07-15

Thin films of Ba{sub 2}Zn{sub 2}Fe{sub 12}O{sub 22} (Y) hexaferrite were prepared through the chemical solution deposition method on SrTiO{sub 3}(1 1 1) (ST) single crystal substrates using epitaxial SrFe{sub 12}O{sub 19} (M) hexaferrite thin layer as a seed template layer. The process of crystallization was mainly investigated by means of X-ray diffraction and atomic force microscopy. A detailed inspection revealed that growth of seed layer starts through the break-up of initially continuous film into isolated grains with expressive shape anisotropy and hexagonal habit. The vital parameters of the seed layer, i.e. thickness, substrate coverage, crystallization conditions and temperature rampmore » were optimized with the aim to obtain epitaxially crystallized Y phase. X-ray diffraction Pole figure measurements and Φ scans reveal perfect parallel in-plane alignment of SrTiO{sub 3} substrate and both hexaferrite phases. - Graphical abstract: XRD pole figure and AFM patterns of Ba{sub 2}Zn{sub 2}Fe{sub 12}O{sub 22} thin film epitaxially grown on SrTiO{sub 3}(1 1 1) single crystal using seeding layer templating. - Highlights: • Single phase Y-type hexagonal ferrite thin films were prepared by CSD method. • Seed M layer breaks into isolated single crystal islands and serves as a template. • Large seed grains grow by consuming the grains within the bulk of recoated film. • We explained the observed orientation relation of epitaxial domains. • Epitaxial growth on SrTiO{sub 3}(1 1 1) with relation (0 0 1){sub M,Y}//(1 1 1){sub ST}+[1 0 0]{sub M,Y}//[2 −1 −1]{sub ST}.« less

Epitaxial Zn quantum dots coherently grown on Si(1 1 1): growth mechanism, nonlinear optical and chemical states analyses

NASA Astrophysics Data System (ADS)

Huang, Bo-Jia; Kao, Li-Chi; Brahma, Sanjaya; Jeng, Yu-En; Chiu, Shang-Jui; Ku, Ching-Shun; Lo, Kuang-Yao

2017-05-01

Oxide- and defect-free metal/semiconductor interface is important to improve Ohmic contact for the suppression of electron scattering and the avoidance of an extrinsic surface state in estimating the barrier of the Schottky contact at the nanodevice interface. This study reports the growth mechanism of Zn quantum dots coherently grown on Si(1 1 1) and the physical phenomena of the crystalline, nonlinear optics, and the chemical states of Zn quantum dots. Epitaxial Zn quantum dots were coherently formed on a non-oxide Si(1 1 1) surface through the liquid- to solid-phase transformation as a result of pattern matching between the Zn(0 0 2) and Si(1 1 1) surfaces. The growth mechanism of constrained Zn quantum dots grown through strategic magnetron radio frequency sputtering is complex. Some factors, such as substrate temperature, hydrogen gas flow, and negative DC bias, influence the configuration of epitaxial Zn quantum dots. In particular, hydrogen gas plays an important role in reducing the ZnO+ and native oxide that is bombarded by accelerated ions, thereby enhancing the Zn ion surface diffusion. The reduction reaction can be inspected by distinguishing the chemical states of ZnO/Zn quantum dots from natural oxidation or the states of Zn 3d through the analysis of x-ray absorption near the edge structure spectrum. The complex growth mechanism can be systematically understood by analyzing a noncancelled anisotropic 3 m dipole from reflective second harmonic generation and inspecting the evolution between the Zn(0 0 2) and Zn(1 1 1) peaks of the collective ZnO/Zn quantum dots in synchrotron XRD.

Optimal Design for Informative Protocols in Xenograft Tumor Growth Inhibition Experiments in Mice.

PubMed

Lestini, Giulia; Mentré, France; Magni, Paolo

2016-09-01

Tumor growth inhibition (TGI) models are increasingly used during preclinical drug development in oncology for the in vivo evaluation of antitumor effect. Tumor sizes are measured in xenografted mice, often only during and shortly after treatment, thus preventing correct identification of some TGI model parameters. Our aims were (i) to evaluate the importance of including measurements during tumor regrowth and (ii) to investigate the proportions of mice included in each arm. For these purposes, optimal design theory based on the Fisher information matrix implemented in PFIM4.0 was applied. Published xenograft experiments, involving different drugs, schedules, and cell lines, were used to help optimize experimental settings and parameters using the Simeoni TGI model. For each experiment, a two-arm design, i.e., control versus treatment, was optimized with or without the constraint of not sampling during tumor regrowth, i.e., "short" and "long" studies, respectively. In long studies, measurements could be taken up to 6 g of tumor weight, whereas in short studies the experiment was stopped 3 days after the end of treatment. Predicted relative standard errors were smaller in long studies than in corresponding short studies. Some optimal measurement times were located in the regrowth phase, highlighting the importance of continuing the experiment after the end of treatment. In the four-arm designs, the results showed that the proportions of control and treated mice can differ. To conclude, making measurements during tumor regrowth should become a general rule for informative preclinical studies in oncology, especially when a delayed drug effect is suspected.

Optimal design for informative protocols in xenograft tumor growth inhibition experiments in mice

PubMed Central

Lestini, Giulia; Mentré, France; Magni, Paolo

2016-01-01

Tumor growth inhibition (TGI) models are increasingly used during preclinical drug development in oncology for the in vivo evaluation of antitumor effect. Tumor sizes are measured in xenografted mice, often only during and shortly after treatment, thus preventing correct identification of some TGI model parameters. Our aims were i) to evaluate the importance of including measurements during tumor regrowth; ii) to investigate the proportions of mice included in each arm. For these purposes, optimal design theory based on the Fisher information matrix implemented in PFIM4.0 was applied. Published xenograft experiments, involving different drugs, schedules and cell lines, were used to help optimize experimental settings and parameters using the Simeoni TGI model. For each experiment, a two-arm design, i.e. control vs treatment, was optimized with or without the constraint of not sampling during tumor regrowth, i.e. “short” and “long” studies, respectively. In long studies, measurements could be taken up to 6 grams of tumor weight, whereas in short studies the experiment was stopped three days after the end of treatment. Predicted relative standard errors were smaller in long studies than in corresponding short studies. Some optimal measurement times were located in the regrowth phase, highlighting the importance of continuing the experiment after the end of treatment. In the four-arm designs, the results showed that the proportions of control and treated mice can differ. To conclude, making measurements during tumor regrowth should become a general rule for informative preclinical studies in oncology, especially when a delayed drug effect is suspected. PMID:27306546

Response of the RIF-1 tumor in vitro and in C3H/Km mice to x-radiation (cell survival, regrowth delay, and tumor control), chemotherapeutic agents, and activated macrophages

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brown, J.M.; Twentyman, P.R.; Zamvil, S.S.

1980-03-01

The radiation response of logarithmic growth phase and fed plateau phase RIF-1 cells in vitro was found to be characterized by D/sub 0/ values of 110 and 133 rads and extrapolation numbs of 36 and 28, respectively. The response of the tumor in vivo to X-irradiation in nonanesthetized mice showed a dependence on the tumor implantation site. In the leg muscle, the response indicated that most cells were at an intermediate level of oxygenation, whereas in the subcutaneous tissue of the flank, the response of the tumor indicated that it had a small fraction of hypoxic cells of maximum radioresistance.more » Misonidazole radiosensitized the leg-implanted tumor as measured both by cell survival and regrowth delay. The tumor was relatively insensitive to a single dose of 1,3-bis(2-chloroethyl)-1-nitrosourea, sensitive to a single dose of cis-platinum, and highly sensitive to a single dose of cyclophosphamide.« less

Crystal growth of YBCO coated conductors by TFA MOD method

NASA Astrophysics Data System (ADS)

Yoshizumi, M.; Nakanishi, T.; Matsuda, J.; Nakaoka, K.; Sutoh, Y.; Izumi, T.; Shiohara, Y.

2008-09-01

The crystal growth mechanism of TFA (trifluoroacetates)-MOD (metal organic deposition) derived YBa 2Cu 3O y has been investigated to understand the process for higher production rates of the conversion process. YBCO films were prepared by TFA-MOD on CeO 2/Gd 2Zr 2O 7/Hastelloy C276 substrates. The growth rates of YBCO derived from Y:Ba:Cu = 1:2:3 and 1:1.5:3 starting solutions were investigated by XRD and TEM analyses. YBCO growth proceeds in two steps of the epitaxial one from the substrate and solid state reaction. The overall growth rate estimated from the residual amounts of BaF 2 with time measured by XRD is proportional to a square root of P(H 2O). The trend was independent of the composition of starting solutions, however, the growth rate obtained from the 1:1.5:3 starting solutions was high as twice as that of 1:2:3, which could not be explained by the composition of BaF 2 included in the precursor films. On the other hand, the growth rate measured from the thickness of the YBCO quenched film at the same process time showed no difference between the samples of 1:2:3 and 1:1.5:3. The epitaxial growth rate of 1:1.5:3 was also the same as the overall growth rate of that, which means there was no solid state reaction to form YBCO after the epitaxial growth. The YBCO growth mechanism was found to be as follows; YBCO crystals nucleate at the surface of the substrate and epitaxially grow into the precursor by layer-by-layer by a manner with trapping unreacted particles. The amounts of YBCO and the unreacted particles trapped in the YBCO film are independent of the composition of the starting solution in this step. Unreacted particles react with each other to form YBCO and pores by solid state reaction as long as there is BaF 2 left in the film. The Ba-poor starting solution gives little BaF 2 left in the film and so the solid state reaction is completed within a short time, resulting in the fast overall growth rate.

Strain Accommodation By Facile WO6 Octahedral Distortion and Tilting During WO3 Heteroepitaxy on SrTiO3(001)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Du, Yingge; Gu, Meng; Varga, Tamas

2014-08-27

In this paper, we show that compared to other BO6 octahedra in ABO3 structured perovskite oxides, the WO6 octahedra in tungsten trioxide (WO3) can withstand a much larger degree of distortion and tilting to accommodate interfacial strain, which in turn strongly impact the nucleation, structure, and defect formation during the epitaxial growth of WO3 on SrTiO3(001). A meta-stable tetragonal phase can be stabilized by epitaxy and a thickness dependent phase transition (tetragonal to monoclinic) is observed. In contrast to misfit dislocations to accommodate the interfacial stain, the facial WO6 octahedral distortion and tilting give rise to three types of planarmore » defects that affect more than 15 monolayers from the interface. These atomically resolved, unusual interfacial defects may significantly alter the electronic, electrochromic, and mechanical properties of the epitaxial films.« less

Engineered unique elastic modes at a BaTiO 3/2x1-Ge(001) interface

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kumah, D. P.; Dogan, M.; Ngai, J. H.

Here, the strong interaction at an interface between a substrate and thin film leads to epitaxy and provides a means of inducing structural changes in the epitaxial film. These induced material phases often exhibit technologically relevant electronic, magnetic, and functional properties. The 2×1 surface of a Ge(001) substrate applies a unique type of epitaxial constraint on thin films of the perovskite oxide BaTiO 3 where a change in bonding and symmetry at the interface leads to a non-bulk-like crystal structure of the BaTiO 3. While the complex crystal structure is predicted using first-principles theory, it is further shown that themore » details of the structure are a consequence of hidden phases found in the bulk elastic response of the BaTiO 3 induced by the symmetry of forces exerted by the germanium substrate.« less

Engineered Unique Elastic Modes at a BaTiO 3 / ( 2 × 1 ) - Ge ( 001 ) Interface

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kumah, D. P.; Dogan, M.; Ngai, J. H.

The strong interaction at an interface between a substrate and thin film leads to epitaxy and provides a means of inducing structural changes in the epitaxial film. These induced material phases often exhibit technologically relevant electronic, magnetic, and functional properties. The 2×1 surface of a Ge(001) substrate applies a unique type of epitaxial constraint on thin films of the perovskite oxide BaTiO3 where a change in bonding and symmetry at the interface leads to a non-bulk-like crystal structure of the BaTiO3. While the complex crystal structure is predicted using first-principles theory, it is further shown that the details of themore » structure are a consequence of hidden phases found in the bulk elastic response of the BaTiO3 induced by the symmetry of forces exerted by the germanium substrate.« less

Engineered unique elastic modes at a BaTiO 3/2x1-Ge(001) interface

DOE PAGES

Kumah, D. P.; Dogan, M.; Ngai, J. H.; ...

2016-03-07

Here, the strong interaction at an interface between a substrate and thin film leads to epitaxy and provides a means of inducing structural changes in the epitaxial film. These induced material phases often exhibit technologically relevant electronic, magnetic, and functional properties. The 2×1 surface of a Ge(001) substrate applies a unique type of epitaxial constraint on thin films of the perovskite oxide BaTiO 3 where a change in bonding and symmetry at the interface leads to a non-bulk-like crystal structure of the BaTiO 3. While the complex crystal structure is predicted using first-principles theory, it is further shown that themore » details of the structure are a consequence of hidden phases found in the bulk elastic response of the BaTiO 3 induced by the symmetry of forces exerted by the germanium substrate.« less

Oxygen vacancies controlled multiple magnetic phases in epitaxial single crystal Co0.5(Mg0.55Zn0.45)0.5O1-v thin films

PubMed Central

Zhu, Dapeng; Cao, Qiang; Qiao, Ruimin; Zhu, Shimeng; Yang, Wanli; Xia, Weixing; Tian, Yufeng; Liu, Guolei; Yan, Shishen

2016-01-01

High quality single-crystal fcc-Cox(MgyZn1-y)1-xO1-v epitaxial thin films with high Co concentration up to x = 0.5 have been fabricated by molecular beam epitaxy. Systematic magnetic property characterization and soft X-ray absorption spectroscopy analysis indicate that the coexistence of ferromagnetic regions, superparamagnetic clusters, and non-magnetic boundaries in the as-prepared Cox(MgyZn1-y)1-xO1-v films is a consequence of the intrinsic inhomogeneous distribution of oxygen vacancies. Furthermore, the relative strength of multiple phases could be modulated by controlling the oxygen partial pressure during sample preparation. Armed with both controllable magnetic properties and tunable band-gap, Cox(MgyZn1-y)1-xO1-v films may have promising applications in future spintronics. PMID:27062992

Impurity and Defect Characterization in Epitaxial GaAs, InP and the Ternary and Quaternary Compound Semiconductors.

DTIC Science & Technology

1982-11-02

Wolfe, Phys. Rev. Lett. 27, 988 (1971). 5. H.R. Fetterman , D.M. Larsen, G.E. Stillman, P.E. Tannenwald, and J. Waldman, Phys.Rev. Lett. 26. 975(1971). 6...Kirkman, P.E. Simmonds, and R.A. Stradling, J. Phys. C., Solid State Phys. 8, 530 (1975). 18. H.R. Fetterman , J. Waldman and C.M. Wolfe, Solid State Commun

Upright and Inverted Single-Junction GaAs Solar Cells Grown by Hydride Vapor Phase Epitaxy

DOE PAGES

Simon, John; Schulte, Kevin L.; Jain, Nikhil; ...

2016-10-19

Hydride vapor phase epitaxy (HVPE) is a low-cost alternative to conventional metal-organic vapor phase epitaxy (MOVPE) growth of III-V solar cells. In this work, we show continued improvement of the performance of HVPE-grown single-junction GaAs solar cells. We show over an order of magnitude improvement in the interface recombination velocity between GaAs and GaInP layers through the elimination of growth interrupts, leading to increased short-circuit current density and open-circuit voltage compared with cells with interrupts. One-sun conversion efficiencies as high as 20.6% were achieved with this improved growth process. Solar cells grown in an inverted configuration that were removed frommore » the substrate showed nearly identical performance to on-wafer cells, demonstrating the viability of HVPE to be used together with conventional wafer reuse techniques for further cost reduction. As a result, these devices utilized multiple heterointerfaces, showing the potential of HVPE for the growth of complex and high-quality III-V devices.« less

Substrate Temperature effect on the transition characteristics of Vanadium (IV) oxide

NASA Astrophysics Data System (ADS)

Yang, Tsung-Han; Wei, Wei; Jin, Chunming; Narayan, Jay

2008-10-01

One of the semiconductor to metal transition material (SMT) is Vanadium Oxide (VO2) which has a very sharp transition temperature close to 340 K as the crystal structure changes from monoclinic phase (semiconductor) into tetragonal phase (metal phase). We have grown high-quality epitaxial vanadium oxide (VO2) films on sapphire (0001) substrates by pulsed laser deposition for oxygen pressure 10-2torr and obtained interesting results without further annealing treatments. The epitaxial growth via domain matching epitaxy, where integral multiples of planes matched across the film-substrate interface. We were able to control the transition characteristics such as the sharpness (T), amplitude (A) of SMT transition and the width of thermal hysteresis (H) by altering the substrate temperature from 300 ^oC, 400 ^oC, 500 ^oC, and 600 ^oC. We use the XRD to identify the microstructure of film and measure the optical properties of film. Finally the transition characteristics is observed by the resistance with the increase of temperature by Van Der Pauw method from 25 to 100 ^oC to measure the electrical resistivity hystersis loop during the transition temperature.

Gradual tilting of crystallographic orientation and configuration of dislocations in GaN selectively grown by vapour phase epitaxy methods

PubMed

Kuwan; Tsukamoto; Taki; Horibuchi; Oki; Kawaguchi; Shibata; Sawaki; Hiramatsu

2000-01-01

Cross-sectional transmission electron microscope (TEM) observation was performed for selectively grown gallium nitride (GaN) in order to examine the dependence of GaN microstructure on the growth conditions. The GaN films were grown by hydride vapour phase epitaxy (HVPE) or metalorganic vapour phase epitaxy (MOVPE) on GaN covered with a patterned mask. Thin foil specimens for TEM observation were prepared with focused ion beam (FIB) machining apparatus. It was demonstrated that the c-axis of GaN grown over the terrace of the mask tilts towards the centre of the terrace when the GaN is grown in a carrier gas of N2. The wider terrace results in a larger tilting angle if other growth conditions are identical. The tilting is attributed to 'horizontal dislocations' (HDs) generated during the overgrowth of GaN on the mask terrace. The HDs in HVPE-GaN have a semi-loop shape and are tangled with one another, while those in MOVPE-GaN are straight and lined up to form low-angle grain boundaries.

Strain-induced phase variation and dielectric constant enhancement of epitaxial Gd{sub 2}O{sub 3}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shekhter, P., E-mail: Pini@tx.technion.ac.il; Amouyal, Y.; Eizenberg, M.

2016-07-07

One of the approaches for realizing advanced high k insulators for metal oxide semiconductor field effect transistors based devices is the use of rare earth oxides. When these oxides are deposited as epitaxial thin films, they demonstrate dielectric properties that differ greatly from those that are known for bulk oxides. Using structural and spectroscopic techniques, as well as first-principles calculations, Gd{sub 2}O{sub 3} films deposited on Si (111) and Ge (111) were characterized. It was seen that the same 4 nm thick film, grown simultaneously on Ge and Si, presents an unstrained lattice on Ge while showing a metastable phase onmore » Si. This change from the cubic lattice to the distorted metastable phase is characterized by an increase in the dielectric constant of more than 30% and a change in band gap. The case in study shows that extreme structural changes can occur in ultra-thin epitaxial rare earth oxide films and modify their dielectric properties when the underlying substrate is altered.« less

Strain-induced modification of magnetic structure and new magnetic phases in rare-earth epitaxial films

NASA Astrophysics Data System (ADS)

Dufour, C.; Dumesnil, K.; Mangin, Ph

2006-07-01

Rare earths exhibit complex magnetic phase diagrams resulting from the competition between various contributions to the magnetic energy: exchange, anisotropy and magnetostriction. The epitaxy of a rare-earth film on a substrate induces (i) a clamping to the substrate and (ii) pseudomorphic strains. Both these effects are shown to lead to modifications of the magnetic properties in (0 0 1)Dy, (0 0 1)Tb and (1 1 0)Eu films. In Dy and Tb films, spectacular variations of the Curie temperature have been evidenced. Additionally, Tb films exhibit a new large wavelength magnetic modulation. In Eu films, one of the helical magnetic domains disappears at low temperature whereas the propagation vectors of the other helices are tilted. The link between structural and magnetic properties is underlined via magnetoelastic models. Moreover, molecular beam epitaxy permits the growth of Sm in a metastable dhcp phase. The magnetic structure of dhcp Sm has been elucidated for the first time. In this review, neutron scattering is shown to be a powerful technique to reveal the magnetic structures of rare-earth films.

Growth of epitaxial orthorhombic YO{sub 1.5}-substituted HfO{sub 2} thin film

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shimizu, Takao; Katayama, Kiliha; Kiguchi, Takanori

YO{sub 1.5}-substituted HfO{sub 2} thin films with various substitution amounts were grown on (100) YSZ substrates by the pulsed laser deposition method directly from the vapor phase. The epitaxial growth of film with different YO{sub 1.5} amounts was confirmed by the X-ray diffraction method. Wide-area reciprocal lattice mapping measurements were performed to clarify the crystal symmetry of films. The formed phases changed from low-symmetry monoclinic baddeleyite to high-symmetry tetragonal/cubic fluorite phases through an orthorhombic phase as the YO{sub 1.5} amount increased from 0 to 0.15. The additional annular bright-field scanning transmission electron microscopy indicates that the orthorhombic phase has polarmore » structure. This means that the direct growth by vapor is of polar orthorhombic HfO{sub 2}-based film. Moreover, high-temperature X-ray diffraction measurements showed that the film with a YO{sub 1.5} amount of 0.07 with orthorhombic structure at room temperature only exhibited a structural phase transition to tetragonal phase above 450 °C. This temperature is much higher than the reported maximum temperature of 200 °C to obtain ferroelectricity as well as the expected temperature for real device application. The growth of epitaxial orthorhombic HfO{sub 2}-based film helps clarify the nature of ferroelectricity in HfO{sub 2}-based films (186 words/200 words)« less

Processing of CuInSe{sub 2}-based solar cells: Characterization of deposition processes in terms of chemical reaction analyses. Phase 2 Annual Report, 6 May 1996--5 May 1997

DOE Office of Scientific and Technical Information (OSTI.GOV)

Anderson, T.

This report describes research performed by the University of Florida during Phase 2 of this subcontract. First, to study CIGS, researchers adapted a contactless, nondestructive technique previously developed for measuring photogenerated excess carrier lifetimes in SOI wafers. This dual-beam optical modulation (DBOM) technique was used to investigate the differences between three alternative methods of depositing CdS (conventional chemical-bath deposition [CBD], metal-organic chemical vapor deposition [MOCVD], and sputtering). Second, a critical assessment of the Cu-In-Se thermochemical and phase diagram data using standard CALPHAD procedures is being performed. The outcome of this research will produce useful information on equilibrium vapor compositions (requiredmore » annealing ambients, Sex fluxes from effusion cells), phase diagrams (conditions for melt-assisted growth), chemical potentials (driving forces for diffusion and chemical reactions), and consistent solution models (extents of solid solutions and extending phase diagrams). Third, an integrated facility to fabricate CIS PV devices was established that includes migration-enhanced epitaxy (MEE) for deposition of CIS, a rapid thermal processing furnace for absorber film formation, sputtering of ZnO, CBD or MOCVD of CdS, metallization, and pattern definition.« less

A transferable force field for CdS-CdSe-PbS-PbSe solid systems

NASA Astrophysics Data System (ADS)

Fan, Zhaochuan; Koster, Rik S.; Wang, Shuaiwei; Fang, Changming; Yalcin, Anil O.; Tichelaar, Frans D.; Zandbergen, Henny W.; van Huis, Marijn A.; Vlugt, Thijs J. H.

2014-12-01

A transferable force field for the PbSe-CdSe solid system using the partially charged rigid ion model has been successfully developed and was used to study the cation exchange in PbSe-CdSe heteronanocrystals [A. O. Yalcin et al., "Atomic resolution monitoring of cation exchange in CdSe-PbSe heteronanocrystals during epitaxial solid-solid-vapor growth," Nano Lett. 14, 3661-3667 (2014)]. In this work, we extend this force field by including another two important binary semiconductors, PbS and CdS, and provide detailed information on the validation of this force field. The parameterization combines Bader charge analysis, empirical fitting, and ab initio energy surface fitting. When compared with experimental data and density functional theory calculations, it is shown that a wide range of physical properties of bulk PbS, PbSe, CdS, CdSe, and their mixed phases can be accurately reproduced using this force field. The choice of functional forms and parameterization strategy is demonstrated to be rational and effective. This transferable force field can be used in various studies on II-VI and IV-VI semiconductor materials consisting of CdS, CdSe, PbS, and PbSe. Here, we demonstrate the applicability of the force field model by molecular dynamics simulations whereby transformations are initiated by cation exchange.

Control of microstructure and mechanical properties of laser solid formed Inconel 718 superalloy by electromagnetic stirring

NASA Astrophysics Data System (ADS)

Liu, Fencheng; Cheng, Hongmao; Yu, Xiaobin; Yang, Guang; Huang, Chunping; Lin, Xin; Chen, Jing

2018-02-01

The coarse columnar grains and special interface in laser solid formed (LSFed) Inconel 718 superalloy workpieces seriously affect their mechanical properties. To improve the microstructure and mechanical properties of LSFed Inconel 718 superalloy, electromagnetic stirring (EMS) was introduced to alter the solidification process of the molten pool during LSF. The results show that EMS could not completely eliminate the epitaxially growing columnar grains, however, the strong convection of liquid metals can effectively influence the solid-liquid interface growing mode. The segregation of alloying elements on the front of solid-liquid interface is inhibited and the degree of constitutional supercooling decreases correspondingly. Comparing the microstructures of samples formed under different process parameters, the size and amount of the γ+Laves eutectic phases formed in interdendritic area decrease along with the increasing magnetic field intensity, resulting in more uniformly distributed alloying elements. The residual stress distribution is proved to be more uniform, which is beneficial to the grain refinement after recrystallilzaiton. Mechanical properties testing results show an improvement of 100 MPa in tensile strength and 22% in elongation was obtained after EMS was used. The high cycle fatigue properties at room temperature was also improved from 4.09 × 104 cycles to 8.21 × 104 cycles for the as-deposited samples, and from 5.45 × 104 cycles to 12.73 × 104 cycles for the heat treated samples respectively.

Vertically aligned GaAs nanowires on graphite and few-layer graphene: generic model and epitaxial growth.

PubMed

Munshi, A Mazid; Dheeraj, Dasa L; Fauske, Vidar T; Kim, Dong-Chul; van Helvoort, Antonius T J; Fimland, Bjørn-Ove; Weman, Helge

2012-09-12

By utilizing the reduced contact area of nanowires, we show that epitaxial growth of a broad range of semiconductors on graphene can in principle be achieved. A generic atomic model is presented which describes the epitaxial growth configurations applicable to all conventional semiconductor materials. The model is experimentally verified by demonstrating the growth of vertically aligned GaAs nanowires on graphite and few-layer graphene by the self-catalyzed vapor-liquid-solid technique using molecular beam epitaxy. A two-temperature growth strategy was used to increase the nanowire density. Due to the self-catalyzed growth technique used, the nanowires were found to have a regular hexagonal cross-sectional shape, and are uniform in length and diameter. Electron microscopy studies reveal an epitaxial relationship of the grown nanowires with the underlying graphitic substrates. Two relative orientations of the nanowire side-facets were observed, which is well explained by the proposed atomic model. A prototype of a single GaAs nanowire photodetector demonstrates a high-quality material. With GaAs being a model system, as well as a very useful material for various optoelectronic applications, we anticipate this particular GaAs nanowire/graphene hybrid to be promising for flexible and low-cost solar cells.

Time scale dependent negative emission potential of forests and biomass plantations via wood burial, torrefied biomass, biochar and pyrogas condensate sequestration in soil

NASA Astrophysics Data System (ADS)

Schmidt, Hans-Peter; Kammann, Claudia; Lucht, Wolfgang; Gerten, Dieter; Foidl, Nikolaus

2017-04-01

The efficiency of Negative Emission Technologies (NET) is dependent on (1) the transformation of the biomass carbon into a form that can be sequestered, (2) the mean residence time of the sequestered carbon, (3) the regrowth and thus carbon re-accumulation of the harvested biomass, and (4) the positive or negative priming of soil carbon. These four parameters define the time scale dependent C-balance of various NET-Systems and permit a global economic and environmental evaluation. As far as geologic CO2 storage is considered to be feasible with close to zero losses and if the energy for transport, transformation and disposal is taken from the process bioenergy, conventional BE-CCS has a C sequestration potential of 50 - 70 % depending on the type of biomass and the technology used. Beside unknown risks of deep stored CO2 and high costs, regrowth of C-accumulating biomass is hampered in the long-term as not only carbon but also essential soil nutrients are mined. Under this scenario, biomass regrowth is expected to slow down and soil carbon content to decrease. These factors enlarge the time horizon until a BE-CCS system becomes carbon neutral and eventual carbon negative (when biomass regrowth exceeds the difference between the harvested biomass carbon and BE-CCS stored carbon). Thermal treatment of biomass under a low oxygen regime (torrefaction, pyrolysis, gasification) can transform up to 85% of biomass carbon into various solid and liquid forms of recalcitrant carbon that can be sequestered. Depending on the process parameters and temperature, the mean residence time of the torrefied or pyrolysed biomass can last from several decennials to centennials when applied to the soil of the biomass production site. The carbon can thus be stored at comparatively low costs within the ecosystem itself. As the thermal treatment preserves most of the biomass-accumulated nutrients (except N), natural nutrient cycles are maintained within the biomass system. Depending on the quality of the charred biomass (biochar), post thermal treatment and plant nutrient enhancement, regrowth is expected to accelerate and soil carbon content to increase. Overall, the time until such a biochar based CSS systems generates negative carbon emissions (biomass regrowth exceeds the C-loss from CSS transformation) can thus be reduced compared to BE-CCS while increasing the sustainability of the global biomass production system and fostering ecosystem services. In our presentation we will provide first assessments of various biochar-based CCS systems and compare them to conventional BE-CCS, an evaluation of their global time scale dependent C-sequestration potential and their economic frame. E.g. (1) a biochar system with pyrolysis temperatures of 750°C and without liquefying the pyrolysis gases delivers a very recalcitrant biochar but the C-efficiency is low (40%) and fostering of regrowth is only about 10-15%. A (2) biochar system with trunk burial, pyrolysis of needles, bark, twigs, and branches with organic N-enhancement, and pyrolysis gas condensation and chemical oxidation could achieve a C-efficiency of 85% to 90% and foster regrowth over a time scale of 60% by up to 50%. Future challenges of biochar classification, certification, ecotoxicology, C-leaching, carbon credits and integration into agro-forestry practices will be discussed.

Process for forming epitaxial perovskite thin film layers using halide precursors

DOEpatents

Clem, Paul G.; Rodriguez, Mark A.; Voigt, James A.; Ashley, Carol S.

2001-01-01

A process for forming an epitaxial perovskite-phase thin film on a substrate. This thin film can act as a buffer layer between a Ni substrate and a YBa.sub.2 Cu.sub.3 O.sub.7-x superconductor layer. The process utilizes alkali or alkaline metal acetates dissolved in halogenated organic acid along with titanium isopropoxide to dip or spin-coat the substrate which is then heated to about 700.degree. C. in an inert gas atmosphere to form the epitaxial film on the substrate. The YBCO superconductor can then be deposited on the layer formed by this invention.

Comparative study on the roles of anisotropic epitaxial strain and chemical doping in inducing the antiferromagnetic insulator phase in manganite films

NASA Astrophysics Data System (ADS)

Jin, Feng; Feng, Qiyuan; Guo, Zhuang; Lan, Da; Wang, Lingfei; Gao, Guanyin; Xu, Haoran; Chen, Binbin; Chen, Feng; Lu, Qingyou; Wu, Wenbin

2017-11-01

Epitaxial strain and chemical doping are two different methods that are commonly used to tune the physical properties of epitaxial perovskite oxide films, but their cooperative effects are less addressed. Here we try to tune the phase separation (PS) in (La1-xP rx) 2 /3C a1 /3Mn O3 (0 ≤x ≤0.4 , LPCMO) films via cooperatively controlling the anisotropic epitaxial strain (AES) and the Pr doping. These films are grown simultaneously on NdGa O3(110 ) ,(LaAlO3) 0.3(SrAl0.5Ta0.5O3 ) 0.7(001 ) , and NdGa O3(001 ) substrates with progressively increased in-plane AES, and probed by x-ray diffraction, magnetotransport, and magnetic force microscopy (MFM) measurements. Although it is known that for x =0 the AES can enhance the orthorhombicity of the films yielding a phase diagram with the antiferromagnetic charge-ordered insulator (AF-COI) state induced, which is quite different from the bulk one, we illustrate that the Pr doping can further drive the films towards a more robust COI state. This cooperative effect is reflected by the increasing magnetic fields needed to melt the COI phase as a function of AES and the doping level. More strikingly, by directly imaging the phase competition morphology of the LPCMO /NdGa O3(001 ) films via MFM, we find that during COI melting the PS domain structure is subject to both AES and the quenched disorder. However, in the reverse process, as the magnetic field is decreased, the COI phase reappears and the AES dominates leaving a crystalline-orientation determined self-organized microstructure. This finding suggests that the PS states and the domain configurations can be selectively controlled by the AES and/or the quenched disorder, which may shed some light on the engineering of PS domains for device fabrications.

Nanoscale self-templating for oxide epitaxy with large symmetry mismatch

DOE PAGES

Gao, Xiang; Lee, Shinbuhm; Nichols, John A.; ...

2016-12-02

Direct observations using scanning transmission electron microscopy unveil an intriguing interfacial bi-layer that enables epitaxial growth of a strain-free, monoclinic, bronze-phase VO 2(B) thin film on a perovskite SrTiO 3 (STO) substrate. For this study, we observe an ultrathin (2–3 unit cells) interlayer best described as highly strained VO 2(B) nanodomains combined with an extra (Ti,V)O 2 layer on the TiO 2 terminated STO (001) surface. By forming a fully coherent interface with the STO substrate and a semi-coherent interface with the strain-free epitaxial VO 2(B) film above, the interfacial bi-layer enables the epitaxial connection of the two materials despitemore » their large symmetry and lattice mismatch.« less

Airborne multispectral detection of regrowth cotton fields

NASA Astrophysics Data System (ADS)

Westbrook, John K.; Suh, Charles P.-C.; Yang, Chenghai; Lan, Yubin; Eyster, Ritchie S.

2015-01-01

Effective methods are needed for timely areawide detection of regrowth cotton plants because boll weevils (a quarantine pest) can feed and reproduce on these plants beyond the cotton production season. Airborne multispectral images of regrowth cotton plots were acquired on several dates after three shredding (i.e., stalk destruction) dates. Linear spectral unmixing (LSU) classification was applied to high-resolution airborne multispectral images of regrowth cotton plots to estimate the minimum detectable size and subsequent growth of plants. We found that regrowth cotton fields can be identified when the mean plant width is ˜0.2 m for an image resolution of 0.1 m. LSU estimates of canopy cover of regrowth cotton plots correlated well (r2=0.81) with the ratio of mean plant width to row spacing, a surrogate measure of plant canopy cover. The height and width of regrowth plants were both well correlated (r2=0.94) with accumulated degree-days after shredding. The results will help boll weevil eradication program managers use airborne multispectral images to detect and monitor the regrowth of cotton plants after stalk destruction, and identify fields that may require further inspection and mitigation of boll weevil infestations.

Reducing dislocations in semiconductors utilizing repeated thermal cycling during multistage epitaxial growth

DOEpatents

Fan, John C. C.; Tsaur, Bor-Yeu; Gale, Ronald P.; Davis, Frances M.

1992-02-25

Dislocation densities are reduced in growing semiconductors from the vapor phase by employing a technique of interrupting growth, cooling the layer so far deposited, and then repeating the process until a high quality active top layer is achieved. The method of interrupted growth, coupled with thermal cycling, permits dislocations to be trapped in the initial stages of epitaxial growth.

Reducing dislocations in semiconductors utilizing repeated thermal cycling during multistage epitaxial growth

DOEpatents

Fan, John C. C.; Tsaur, Bor-Yeu; Gale, Ronald P.; Davis, Frances M.

1986-12-30

Dislocation densities are reduced in growing semiconductors from the vapor phase by employing a technique of interrupting growth, cooling the layer so far deposited, and then repeating the process until a high quality active top layer is achieved. The method of interrupted growth, coupled with thermal cycling, permits dislocations to be trapped in the initial stages of epitaxial growth.

Effect of as Passivation on Vapor-Phase Epitaxial Growth of Ge on (211)Si as a Buffer Layer for CdTe Epitaxy

DTIC Science & Technology

2011-04-07

PALOSZ,5 , SUDHIR TRIVEDI,5 , PRIYALAL WIJEWARNASURIYA,3 , ISHWARA BHAT2, Brimrose Corporation of America 19 Loveton Circle Hunt Valley Loveton...Polytechnic Institute, Troy, NY 12180, USA. 5.— Brimrose Corporation of America, Sparks, MD 21152, USA. 6.—e-mail: shints@rpi.edu We report an

Epitaxial Ce and the magnetism of single-crystal Ce/Nd superlattices

NASA Astrophysics Data System (ADS)

Clegg, P. S.; Goff, J. P.; McIntyre, G. J.; Ward, R. C.; Wells, M. R.

2003-05-01

The chemical structure of epitaxial γ cerium and the chemical and magnetic structures of cerium/neodymium superlattices have been studied using x-ray and neutron diffraction techniques. The samples were grown using molecular-beam epitaxy, optimized to yield the desired Ce allotropes. The x-ray measurements show that, in the superlattices, both constituents adopt the dhcp structure and that the stacking sequence remains intact down to T˜2 K; these are the first measurements of magnetic ordering in single-crystal dhcp Ce. The magnetic structure of the superlattices with thicker Nd layers exhibit incommensurate order and ferromagnetism on separate sublattices in a similar manner to Nd under applied pressure. The sample with thickest Ce layers has a magnetic structure similar to bulk β Ce, which has commensurate transverse modulation with a propagation wave vector [1/2 0 0] and moments along the hexagonal a direction. These two types of magnetic order appear to be mutually exclusive. γ Ce is the high-temperature fcc phase of Ce, our single-phase epitaxial sample is observed to go through a new, but partial, structural transition not previously seen in the bulk material.

Ultra-Low Dark Current HgCdTe Detector in SWIR for Space Applications

NASA Astrophysics Data System (ADS)

Cervera, C.; Boulade, O.; Gravrand, O.; Lobre, C.; Guellec, F.; Sanson, E.; Ballet, P.; Santailler, J. L.; Moreau, V.; Zanatta, J. P.; Fieque, B.; Castelein, P.

2017-10-01

This paper presents recent developments at Commissariat à l'Energie atomique, Laboratoire d'Electronique et de Technologie de l'Information infrared laboratory on processing and characterization of p-on- n HgCdTe (MCT) planar infrared focal plane arrays (FPAs) in short-wave infrared (SWIR) spectral band for the astrophysics applications. These FPAs have been grown using both liquid phase epitaxy and molecular beam epitaxy on a lattice-matched CdZnTe substrate. This technology exhibits lower dark current and lower series resistance in comparison with n-on- p vacancy-doped architecture and is well adapted for low flux detection or high operating temperature. This architecture has been evaluated for space applications in long-wave infrared and very-long-wave infrared spectral bands with cut-off wavelengths from 10 μm up to 17 μm at 78 K and is now evaluated for the SWIR range. The metallurgical nature of the absorbing layer is also examined and both molecular beam epitaxy and liquid phase epitaxy have been investigated. Electro-optical characterizations have been performed on individual photodiodes from test arrays, whereas dark current investigation has been performed with a fully functional readout integrated circuit dedicated to low flux operations.

Interface morphology studies of liquid phase epitaxy grown HgCdTe films by atomic force microscopy

NASA Astrophysics Data System (ADS)

Azoulay, M.; George, M. A.; Burger, A.; Collins, W. E.; Silberman, E.

1994-04-01

In this paper we report an investigation of the morphology of the interfaces of liquid phase epitaxy (LPE) grown HgCdTe thin films on CdTe and CdZnTe substrates by atomic force microscopy (AFM) on freshly cleaved (110) crystallographic planes. An empirical observation which may be linked to lattice mismatch was indicated by an angle between the cleavage steps of the substrate to those of the film. The precipitates with size ranging from 5 nm to 20 nm were found to be most apparent near the interface.

INTERNATIONAL CONFERENCE ON SEMICONDUCTOR INJECTION LASERS SELCO-87: Two-stage liquid phase epitaxy for fabrication of buried InGaAsP/InP heterostructures

NASA Astrophysics Data System (ADS)

Procházková, O.; Novotný, J.; Šrobár, F.

1988-11-01

The technology of growth of buried heterojunction lasers emitting at 1.3 μm and some of their physical properties are described. Mesa stripes 8-μm wide were formed on heteroepitaxial wafers grown by liquid phase epitaxy at 630°C. They were buried by a second process at a lower temperature (590°C). The threshold current was about 100 mA and the temperature sensitivity was characterized by a parameter amounting to about 60 K. Single-mode lasing was observed occasionally.

Hydride vapor phase epitaxy of AlN using a high temperature hot-wall reactor

NASA Astrophysics Data System (ADS)

Baker, Troy; Mayo, Ashley; Veisi, Zeinab; Lu, Peng; Schmitt, Jason

2014-10-01

Aluminum nitride (AlN) was grown on c-plane sapphire substrates by hydride vapor phase epitaxy (HVPE). The experiments utilized a two zone inductively heated hot-wall reactor. The surface morphology, crystal quality, and growth rate were investigated as a function of growth temperature in the range of 1450-1575 °C. AlN templates grown to a thickness of 1 μm were optimized with double axis X-ray diffraction (XRD) rocking curve full width half maximums (FWHMs) of 135″ for the (002) and 513″ for the (102).

Thermoelectric La-doped SrTiO3 epitaxial layers with single-crystal quality: from nano to micrometers

NASA Astrophysics Data System (ADS)

Apreutesei, Mihai; Debord, Régis; Bouras, Mohamed; Regreny, Philippe; Botella, Claude; Benamrouche, Aziz; Carretero-Genevrier, Adrian; Gazquez, Jaume; Grenet, Geneviève; Pailhès, Stéphane; Saint-Girons, Guillaume; Bachelet, Romain

2017-12-01

High-quality thermoelectric La0.2Sr0.8TiO3 (LSTO) films, with thicknesses ranging from 20 nm to 0.7 μm, have been epitaxially grown on SrTiO3(001) substrates by enhanced solid-source oxide molecular-beam epitaxy. All films are atomically flat (with rms roughness < 0.2 nm), with low mosaicity (<0.1°), and present very low electrical resistivity (<5 × 10-4 Ω cm at room temperature), one order of magnitude lower than standard commercial Nb-doped SrTiO3 single-crystalline substrate. The conservation of transport properties within this thickness range has been confirmed by thermoelectric measurements where Seebeck coefficients of approximately -60 μV/K have been recorded for all films. These LSTO films can be integrated on Si for non-volatile memory structures or opto-microelectronic devices, functioning as transparent conductors or thermoelectric elements.

GaSb-based single-mode distributed feedback lasers for sensing (Conference Presentation)

NASA Astrophysics Data System (ADS)

Gupta, James A.; Bezinger, Andrew; Lapointe, Jean; Poitras, Daniel; Aers, Geof C.

2017-02-01

GaSb-based tunable single-mode diode lasers can enable rapid, highly-selective and highly-sensitive absorption spectroscopy systems for gas sensing. In this work, single-mode distributed feedback (DFB) laser diodes were developed for the detection of various trace gases in the 2-3.3um range, including CO2, CO, HF, H2S, H2O and CH4. The lasers were fabricated using an index-coupled grating process without epitaxial regrowth, making the process significantly less expensive than conventional DFB fabrication. The devices are based on InGaAsSb/AlGaAsSb separate confinement heterostructures grown on GaSb by molecular beam epitaxy. DFB lasers were produced using a two step etch process. Narrow ridge waveguides were first defined by optical lithography and etched into the semiconductor. Lateral gratings were then defined on both sides of the ridge using electron-beam lithography and etched to produce the index-grating. Effective index modeling was used to optimize the ridge width, etch depths and the grating pitch to ensure single-lateral-mode operation and adequate coupling strength. The effective index method was further used to simulate the DFB laser emission spectrum, based on a transfer matrix model for light transmission through the periodic structure. The fabricated lasers exhibit single-mode operation which is tunable through the absorption features of the various target gases by adjustment of the drive current. In addition to the established open-path sensing applications, these devices have great potential for optoelectronic integrated gas sensors, making use of integrated photodetectors and possibly on-chip Si photonics waveguide structures.

Role of associated defects in oxygen ion conduction and surface exchange reaction for epitaxial samaria-doped ceria thin films as catalytic coatings

DOE PAGES

Yang, Nan; Shi, Yanuo; Schweiger, Sebastian; ...

2016-05-18

Samaria-doped ceria (SDC) thin films are particularly important for energy and electronic applications such as micro-solid oxide fuel cells, electrolysers, sensors and memristors. In this paper we report a comparative study investigating ionic conductivity and surface reactions for well-grown epitaxial SDC films varying the samaria doping concentration. With increasing doping above 20 mol% of samaria, an enhancement in the defect association was observed by Raman spectroscopy. The role of such defect associates on the films` oxygen ion transport and exchange was investigated by electrochemical impedance spectroscopy and electrochemical strain microscopy (ESM). The measurements reveal that the ionic transport has amore » sharp maximum in ionic conductivity and drop in its activation energy down to 0.6 eV for 20 mol% doping. Increasing the doping concentration further up to 40 mol%, raises the activation energy substantially by a factor of two. We ascribe the sluggish transport kinetics to the "bulk" ionic-near ordering in case of the heavily doped epitaxial films. Analysis of the ESM first order reversal curve measurements indicate that these associated defects may have a beneficial role by lowering the activation of the oxygen exchange "surface" reaction for heavily doped 40 mol% of samaria. We reveal in a model experiment through a solid solution series of samaria doped ceria epitaxial films that the occurrence of associate defects in the bulk affects the surface charging state of the films to increase the exchange rates. Lastly, the implication of these findings are the design of coatings with tuned oxygen surface exchange by control of bulk associate clusters for future electro-catalytic applications.« less

Suppression of Structural Phase Transition in VO2 by Epitaxial Strain in Vicinity of Metal-insulator Transition

PubMed Central

Yang, Mengmeng; Yang, Yuanjun; Bin Hong; Wang, Liangxin; Hu, Kai; Dong, Yongqi; Xu, Han; Huang, Haoliang; Zhao, Jiangtao; Chen, Haiping; Song, Li; Ju, Huanxin; Zhu, Junfa; Bao, Jun; Li, Xiaoguang; Gu, Yueliang; Yang, Tieying; Gao, Xingyu; Luo, Zhenlin; Gao, Chen

2016-01-01

Mechanism of metal-insulator transition (MIT) in strained VO2 thin films is very complicated and incompletely understood despite three scenarios with potential explanations including electronic correlation (Mott mechanism), structural transformation (Peierls theory) and collaborative Mott-Peierls transition. Herein, we have decoupled coactions of structural and electronic phase transitions across the MIT by implementing epitaxial strain on 13-nm-thick (001)-VO2 films in comparison to thicker films. The structural evolution during MIT characterized by temperature-dependent synchrotron radiation high-resolution X-ray diffraction reciprocal space mapping and Raman spectroscopy suggested that the structural phase transition in the temperature range of vicinity of the MIT is suppressed by epitaxial strain. Furthermore, temperature-dependent Ultraviolet Photoelectron Spectroscopy (UPS) revealed the changes in electron occupancy near the Fermi energy EF of V 3d orbital, implying that the electronic transition triggers the MIT in the strained films. Thus the MIT in the bi-axially strained VO2 thin films should be only driven by electronic transition without assistance of structural phase transition. Density functional theoretical calculations further confirmed that the tetragonal phase across the MIT can be both in insulating and metallic states in the strained (001)-VO2/TiO2 thin films. This work offers a better understanding of the mechanism of MIT in the strained VO2 films. PMID:26975328

INTERNATIONAL CONFERENCE ON SEMICONDUCTOR INJECTION LASERS SELCO-87: Liquid phase epitaxial growth of GaInAsP/InP laser structures

NASA Astrophysics Data System (ADS)

Nohavica, D.; Têminová, J.; Berková, D.; Zagrádková, M.; Kortan, I.; Zelinka, I.; Walachová, I.; Malina, V.

1988-11-01

A modified single-phase liquid phase epitaxy method was developed on the basis of a novel variant of the growth boat. The method was used to grow GaInAsP/InP double heterostructures for lasers emitting at 1.3 and 1.55 μm. The main properties of wide-contact diodes (radiation power and threshold current density) were adopted as the characteristics of the quality of heterostructures characterized by different configurations of active and guiding layers. The quality of the structure was confirmed by the fabrication of laser diodes of the following types: stripe with oxide insulation, clad-ridge waveguide, and double-channel planar buried.

Aqueous solution epitaxy of CdS layers on CuInSe 2

NASA Astrophysics Data System (ADS)

Furlong, M. J.; Froment, M.; Bernard, M. C.; Cortès, R.; Tiwari, A. N.; Krejci, M.; Zogg, H.; Lincot, D.

1998-09-01

Epitaxial CdS thin films have been deposited from an aqueous ammonia solution containing cadmium ions and thiourea as precursors on single crystalline CuInSe 2 films prepared by MBE on Si(1 1 1) and GaAs(1 0 0) substrates. The structure and quality of the films were investigated by RHEED, glancing angle XRD and HRTEM in cross-section. The films are cubic on (1 0 0) substrates, and mixed cubic and hexagonal on (1 1 1) substrates due to the presence of stacking faults parallel to the substrate. The growth is under surface kinetic control with an activation energy of 85 kJ mol -1. Epitaxy improves with increasing temperature and an epitaxial transition temperature at approx. 60°C is demonstrated in the selected experimental conditions. The epitaxy is very sensitive to the preparation of the surface. Beneficial effects of in situ or ex situ chemical etching are found. Similarities between aqueous solution and vapor-phase chemical depositions are pointed out.

Epitaxy of semiconductor-superconductor nanowires

NASA Astrophysics Data System (ADS)

Krogstrup, P.; Ziino, N. L. B.; Chang, W.; Albrecht, S. M.; Madsen, M. H.; Johnson, E.; Nygård, J.; Marcus, C. M.; Jespersen, T. S.

2015-04-01

Controlling the properties of semiconductor/metal interfaces is a powerful method for designing functionality and improving the performance of electrical devices. Recently semiconductor/superconductor hybrids have appeared as an important example where the atomic scale uniformity of the interface plays a key role in determining the quality of the induced superconducting gap. Here we present epitaxial growth of semiconductor-metal core-shell nanowires by molecular beam epitaxy, a method that provides a conceptually new route to controlled electrical contacting of nanostructures and the design of devices for specialized applications such as topological and gate-controlled superconducting electronics. Our materials of choice, InAs/Al grown with epitaxially matched single-plane interfaces, and alternative semiconductor/metal combinations allowing epitaxial interface matching in nanowires are discussed. We formulate the grain growth kinetics of the metal phase in general terms of continuum parameters and bicrystal symmetries. The method realizes the ultimate limit of uniform interfaces and seems to solve the soft-gap problem in superconducting hybrid structures.

Establishment of HPC(R2A) for regrowth control in non-chlorinated distribution systems.

PubMed

Uhl, Wolfgang; Schaule, Gabriela

2004-05-01

Drinking water distributed without disinfection and without regrowth problems for many years may show bacterial regrowth when the residence time and/or temperature in the distribution system increases or when substrate and/or bacterial concentration in the treated water increases. An example of a regrowth event in a major German city is discussed. Regrowth of HPC bacteria occurred unexpectedly at the end of a very hot summer. No pathogenic or potentially pathogenic bacteria were identified. Increased residence times in the distribution system and temperatures up to 25 degrees C were identified as most probable causes and the regrowth event was successfully overcome by changing flow regimes and decreasing residence times. Standard plate counts of HPC bacteria using the spread plate technique on nutrient rich agar according to German Drinking Water Regulations (GDWR) had proven to be a very good indicator of hygienically safe drinking water and to demonstrate the effectiveness of water treatment. However, the method proved insensitive for early regrowth detection. Regrowth experiments in the lab and sampling of the distribution system during two summers showed that spread plate counts on nutrient-poor R2A agar after 7-day incubation yielded 100 to 200 times higher counts. Counts on R2A after 3-day incubation were three times less than after 7 days. As the precision of plate count methods is very poor for counts less than 10 cfu/plate, a method yielding higher counts is better suited to detect upcoming regrowth than a method yielding low counts. It is shown that for the identification of regrowth events HPC(R2A) gives a further margin of about 2 weeks for reaction before HPC(GDWR). Copyright 2003 Elsevier B.V.

Overlayer growth and electronic properties of the Bi/GaSb(110) interface

NASA Astrophysics Data System (ADS)

Gavioli, Luca; Betti, Maria Grazia; Casarini, Paolo; Mariani, Carlo

1995-06-01

The overlayer growth and electronic properties of the Bi/GaSb(110) interface and of the two-dimensional ordered (1×1)- and (1×2)-Bi layers have been investigated by complementary spectroscopic techniques (high-resolution electron-energy-loss, photoemission, and Auger spectroscopy). Bismuth forms an epitaxial monolayer, followed by island formation (Stranski-Krastanov growth mode) covering an average surface area of 40% at a nominal coverage of 4 ML. The (1×2)-symmetry stable structural phase, obtained after annealing at ~220 °C, corresponds to an average nominal Bi coverage of about 0.7 ML, suggesting an atomic geometry different from the epitaxial-continued layer structure. The disposal of Bi atoms in the (1×2) structure should build up an ``open'' layer, as the Ga-related surface exciton quenched in the (1×1) epitaxial monolayer is present in the (1×2) stable phase. The two symmetry phases are characterized by strong absorption features at 1 eV [(1×1)-Bi] and 0.54 eV [(1×2)-Bi], related to interband electronic transitions between Bi-induced electronic states. The major Bi-related occupied electronic levels, present in the valence band of the (1×1)- and (1×2)-Bi layer, have been detected by angle-integrated ultraviolet photoemission spectroscopy. Both the (1×1) and (1×2) phases show a metallic nature, with a low density of electronic states at the Fermi level. Schottky barrier heights of 0.20 and 0.14 eV are estimated for the epitaxial (1×1)- and (1×2)-symmetry stage, respectively, by analyzing the space-charge layer conditions through the study of the dopant-induced free-carrier plasmon in the GaSb substrate.

Phase transition in lead titanate thin films: a Brillouin study

NASA Astrophysics Data System (ADS)

Kuzel, P.; Dugautier, C.; Moch, P.; LeMarrec, F.; Karkut, M. G.

2002-12-01

The elastic properties of both polycrystalline and epitaxial PbTiO3 (PTO) thin films are studied using Brillouin scattering spectroscopy. The epitaxial PTO films were prepared by pulsed laser ablation on (1) a [0 0 1] single crystal of SrTiO3 (STO) doped with Nb and (2) a [0 0 1] STO buffered with a layer of YBa2Cu3O7. The polycrystalline PTO films were prepared by sol-gel on a Si substrate buffered with TiO2 and Pt layers. The data analysis takes into account the ripple and the elasto-optic contributions. The latter significantly affects the measured spectra since it gives rise to a Love mode in the p-s scattering geometry. At room temperature, the spectra of the epitaxially grown samples are interpreted using previously published elastic constants of PTO single crystals. Sol-gel samples exhibit appreciable softening of the effective elastic properties compared to PTO single crystals: this result is explained by taking into account the random orientation of the microscopic PTO grains. For both the polycrystalline and the epitaxial films we have determined that the piezoelectric terms do not contribute to the spectra. The temperature dependence of the spectra shows strong anomalies of the elastic properties near the ferroelectric phase transition. Compared to the bulk, TC is higher in the sol-gel films, while in the epitaxial films the sign of the TC shift depends on the underlying material.

Gordon Research Conference on Crystal Growth (1990)

DTIC Science & Technology

1990-04-01

Labs, MH) 14. Cox Vapor Levitation Epitaxy of Quantum Wires and Wire-like Structures Using Laterally Propagating Surface Steps. (Bellcore, Red Bank) 15...introduced many new aspects of crystal growth, including strained layer superlattices, quantum cluster growth, and vertical zone melting of GaAs...Films 2. E. Bauser Semiconductor Liquid Phase Epitaxy: Growth and Properties of Layers and Heterostructures 3. M. L. Steigerwald Growth of Quantum

Structural and kinetic studies of metal hydride hydrogen storage materials using thin film deposition and characterization techniques

NASA Astrophysics Data System (ADS)

Kelly, Stephen Thomas

Hydrogen makes an attractive energy carrier for many reasons. It is an abundant chemical fuel that can be produced from a wide variety of sources and stored for very long periods of time. When used in a fuel cell, hydrogen emits only water at the point of use, making it very attractive for mobile applications such as in an automobile. Metal hydrides are promising candidates for on-board reversible hydrogen storage in mobile applications due to their very high volumetric storage capacities---in most cases exceeding even that of liquid hydrogen. The United States Department of Energy (DOE) has set fuel system targets for an automotive hydrogen storage system, but as of yet no single material meets all the requirements. In particular, slow reaction kinetics and/or inappropriate thermodynamics plague many metal hydride hydrogen storage materials. In order to engineer a practical material that meets the DOE targets, we need a detailed understanding of the kinetic and thermodynamic properties of these materials during the phase change. In this work I employed sputter deposited thin films as a platform to study materials with highly controlled chemistry, microstructure and catalyst placement using thin film characterization techniques such as in situ x-ray diffraction (XRD) and neutron reflectivity. I observed kinetic limitations in the destabilized Mg2Si system due to the slow diffusion of the host Mg and Si atoms while forming separate MgH2 and Si phases. Conversely, I observed that the presence of Al in the Mg/Al system inhibits hydrogen diffusion while the host Mg and Al atoms interdiffuse readily, allowing the material to fall into a kinetic and/or thermodynamic trap by forming intermetallic compounds such as Mg17Al 12. By using in situ XRD to analyze epitaxial Mg films grown on (001) oriented Al2O3 substrates I observed hydride growth consistent with a model of a planar hydride layer growing into an existing metal layer. Subsequent film cycling changes the hydrogen absorption and desorption kinetics and degrades the material texture. Cycling the films to greater hydrogen loading accelerates the changes to the kinetics and material texture. In addition to in situ XRD experiments, in situ neutron reflectivity experiments on epitaxial Mg films exposed to hydrogen gas reveal details about the microstructural development of the growing hydride layer as the film absorbs and releases hydrogen. Small (10 wt%) additions of Ti to epitaxial Mg films during growth result in metastable solid solution films of Ti in Mg that deposit epitaxially on (001) Al2O3 substrates with epitaxy similar to the pure Mg films. These metastable alloy films absorb hydrogen faster than pure Mg films under identical conditions. Subsequent film cycling results in altered reaction kinetics and a transition to a different kinetic mechanism during desorption than for pure Mg films.

Epitaxial growth of iridate pyrochlore Nd 2Ir 2O 7 films

DOE PAGES

Gallagher, J. C.; Esser, B. D.; Morrow, R.; ...

2016-02-29

Epitaxial films of the pyrochlore Nd 2Ir 2O 7 have been grown on (111)-oriented yttria-stabilized zirconia (YSZ) substrates by off-axis sputtering followed by post-growth annealing. X-ray diffraction (XRD) results demonstrate phase-pure epitaxial growth of the pyrochlore films on YSZ. Scanning transmission electron microscopy (STEM) investigation of an Nd 2Ir 2O 7 film with a short post-annealing provides insight into the mechanism for crystallization of Nd 2Ir 2O 7 during the post-annealing process. STEM images reveal clear pyrochlore ordering of Nd and Ir in the films. As a result, the epitaxial relationship between the YSZ and Nd 2Ir 2O 7 ismore » observed clearly while some interfacial regions show a thin region with polycrystalline Ir nanocrystals.« less

Sharp chemical interface in epitaxial Fe{sub 3}O{sub 4} thin films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gálvez, S.; Rubio-Zuazo, J., E-mail: rubio@esrf.fr; Salas-Colera, E.

Chemically sharp interface was obtained on single phase single oriented Fe{sub 3}O{sub 4} (001) thin film (7 nm) grown on NiO (001) substrate using oxygen assisted molecular beam epitaxy. Refinement of the atomic structure, stoichiometry, and oxygen vacancies were determined by soft and hard x-ray photoelectron spectroscopy, low energy electron diffraction and synchrotron based X-ray reflectivity, and X-ray diffraction. Our results demonstrate an epitaxial growth of the magnetite layer, perfect iron stoichiometry, absence of oxygen vacancies, and the existence of an intermixing free interface. Consistent magnetic and electrical characterizations are also shown.

Epitaxial lateral overgrowth of GaAs: effect of doping on LPE growth behaviour

NASA Astrophysics Data System (ADS)

Zytkiewicz, Z. R.; Dobosz, D.; Pawlowska, M.

1999-05-01

Results of epitaxial lateral overgrowth (ELO) of GaAs on (001) GaAs substrates by liquid phase epitaxy are reported. We show that by introducing Si, Sn or Te impurities to the Ga-As solution the vertical growth rate is reduced while the lateral growth rate is significantly enhanced, which leads to a growth habit modification. Furthermore, the impurity incorporation into the growing layer is different on the upper and side surfaces of the ELO, reflecting the fundamental differences between the lateral and vertical growth modes. This phenomenon can be applied for studying the temporal development of ELO layers.

Formation of nanotwin networks during high-temperature crystallization of amorphous germanium

DOE PAGES

Sandoval, Luis; Reina, Celia; Marian, Jaime

2015-11-26

Germanium is an extremely important material used for numerous functional applications in many fields of nanotechnology. In this paper, we study the crystallization of amorphous Ge using atomistic simulations of critical nano-metric nuclei at high temperatures. We find that crystallization occurs by the recurrent transfer of atoms via a diffusive process from the amorphous phase into suitably-oriented crystalline layers. We accompany our simulations with a comprehensive thermodynamic and kinetic analysis of the growth process, which explains the energy balance and the interfacial growth velocities governing grain growth. For the <111> crystallographic orientation, we find a degenerate atomic rearrangement process, withmore » two zero-energy modes corresponding to a perfect crystalline structure and the formation of a Σ3 twin boundary. Continued growth in this direction results in the development a twin network, in contrast with all other growth orientations, where the crystal grows defect-free. This particular mechanism of crystallization from amorphous phases is also observed during solid-phase epitaxial growth of <111> semiconductor crystals, where growth is restrained to one dimension. Lastly, we calculate the equivalent X-ray diffraction pattern of the obtained nanotwin networks, providing grounds for experimental validation.« less

Formation of Nanotwin Networks during High-Temperature Crystallization of Amorphous Germanium

PubMed Central

Sandoval, Luis; Reina, Celia; Marian, Jaime

2015-01-01

Germanium is an extremely important material used for numerous functional applications in many fields of nanotechnology. In this paper, we study the crystallization of amorphous Ge using atomistic simulations of critical nano-metric nuclei at high temperatures. We find that crystallization occurs by the recurrent transfer of atoms via a diffusive process from the amorphous phase into suitably-oriented crystalline layers. We accompany our simulations with a comprehensive thermodynamic and kinetic analysis of the growth process, which explains the energy balance and the interfacial growth velocities governing grain growth. For the 〈111〉 crystallographic orientation, we find a degenerate atomic rearrangement process, with two zero-energy modes corresponding to a perfect crystalline structure and the formation of a Σ3 twin boundary. Continued growth in this direction results in the development a twin network, in contrast with all other growth orientations, where the crystal grows defect-free. This particular mechanism of crystallization from amorphous phases is also observed during solid-phase epitaxial growth of 〈111〉 semiconductor crystals, where growth is restrained to one dimension. We calculate the equivalent X-ray diffraction pattern of the obtained nanotwin networks, providing grounds for experimental validation. PMID:26607496

Molecular beam epitaxy growth and magnetic properties of Cr-Co-Ga Heusler alloy films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Feng, Wuwei, E-mail: wfeng@cugb.edu.cn; Wang, Weihua; Zhao, Chenglong

2015-11-15

We have re-investigated growth and magnetic properties of Cr{sub 2}CoGa films using molecular beam epitaxy technique. Phase separation and precipitate formation were observed experimentally again in agreement with observation of multiple phases separation in sputtered Cr{sub 2}CoGa films by M. Meinert et al. However, significant phase separation could be suppressed by proper control of growth conditions. We showed that Cr{sub 2}CoGa Heusler phase, rather than Co{sub 2}CrGa phase, constitutes the majority of the sample grown on GaAs(001) at 450 {sup o}C. The measured small spin moment of Cr{sub 2}CoGa is in agreement with predicted HM-FCF nature; however, its Curie temperaturemore » is not as high as expected from the theoretical prediction probably due to the off-stoichiometry of Cr{sub 2}CoGa and the existence of the disorders and phase separation.« less

HRTEM of microcrystalline opal in chert and porcelanite from the Monterey Formation, California

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cady, S.L.; Wenk, H.R.; Downing, K.H.

Microcrystalline opal was investigated using low-dose transmission electron microscopy (TEM) methods to identify microstructural characteristics and possible phase-transformation mechanisms that accommodate silica diagenesis. High-resolution TEM (HRTEM) revealed that microcrystalline opal in opal-CT chert (>90 wt% silica) and opal-CT porcelanite (50-90 wt% silica) from the Miocene Monterey Formation of California displays various amounts of structural disorder and coherent and incoherent lamellar intergrowths. Species of microfibrous opal identified by HRTEM in early-formed opal-CT chert include length-slow opal-C and unidimensionally disordered length-slow opal-CT ({open_quotes}lussatite{close_quotes}). These fibers often display a microstructure characterized by an aperiodic distribution of highly strained domains that separate ordered domainsmore » located at discrete positions along the direction of the fiber axes. Microfibrous opal occurs as several types of fiber-aggregation forms. TEM revealed that the siliceous matrix in later-formed opal-CT porcelanite consists of equidimensional, nanometer-size opal-CT crystallites and lussatite fibers. Pseudo-orthorhombic tridymite (PO-2) was identified by HRTEM in one sample of opal-CT porcelanite. Burial diagenesis of chert and porcelanite results in the precipitation of opal-C and the epitaxial growth of opal-C domains on opal-CT substrates. Diagenetic maturation of lussatite was identified by TEM in banded opal-CT-quartz chert to occur as a result of solid-state ordering. The primary diagenetic silica phase transformations between noncrystalline opal, microcrystalline opal, and quartz occur predominantly by a series of dissolution-precipitation reactions. However, TEM showed that in banded opal-CT-quartz chert, the epitaxial growth of quartz on microfibrous opal enhances the rate of silica diagenesis.« less

Structural and thermochemical Aspects of (III-V)IV3 Material Assembly from First Principles

NASA Astrophysics Data System (ADS)

Chizmeshya, Andrew; Kouvetakis, John

2014-03-01

Alloys with (III-V)-(IV) compositions, including Si3(AlP), Si5-2y(AlP)y, Si3Al(As1-xNx), Si5-2yAl(P1-xNx)y and Ge5-2y(InP)y and have recently been synthesized as mono-crystalline films on Si substrates, using a synthesis route specifically designed to avoid phase separation between the III-V and IV constituents. Molecular ``building blocks'' containing group-V-centered III-V-IV3 cores, formed via interactions of group-III atoms and reactive silyly/germyl hydride precursors of desired composition (e.g, P(SiH3)3 , P(GeH3)3 , etc), assemble to form stable, covalent, diamond-like materials with the inherent tetrahedral symmetry and composition of the III-V-IV3 units. The resulting systems may provide access to a broad range of new semiconductor systems with extended optoelectronic properties, provided that the required molecular sources are available, the thermodynamic processes are viable, and the resulting alloy composition can be tuned to lattice-match the growth substrate. Molecular/solid-state simulations are used to identify promising synthetic pathways and guide the epitaxial creation of new (III-V)-(IV) materials. The thermodynamics of gas phase synthesis reactions, energetic stability of the alloys, and their epitaxial/chemical compatibility with the substrate are combined to form a global figure of merit. The latter corroborates the synthesis of known systems and predicts that formation of GaPSi3/Si(100), GaAsSi3/SiGe(100), AlPGe3/Ge(100) and InAsSi3/Ge(100) may also be favorable. Supported by NSF-DMR under SusChEM award #1309090.

Growth of strained Si/relaxed SiGe heterostructures on Si(110) substrates using solid-source molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Arimoto, Keisuke; Nakazawa, Hiroki; Mitsui, Shohei; Utsuyama, Naoto; Yamanaka, Junji; Hara, Kosuke O.; Usami, Noritaka; Nakagawa, Kiyokazu

2017-11-01

A strained Si/relaxed SiGe heterostructure grown on Si(110) substrate is attractive as a platform for high-hole-mobility Si-based electronic devices. To improve the electrical property, a smoother surface is desirable. In this study, we investigated surface morphology and microstructural aspects of strained Si/relaxed SiGe/Si(110) heterostructures grown by solid-source (SS) molecular beam epitaxy (MBE). It was revealed that SSMBE provides a way to grow strained Si/relaxed SiGe heterostructures with smooth surfaces. In addition, it was found that the strain in the SiGe layer of the SSMBE-grown sample is highly anisotropic whereas that of the GSMBE-grown sample is almost biaxially relaxed. Along with the surface morphology, the symmetry in degree of strain relaxation has implications for the electrical property. Results of a calculation shows that anisotropic strain is preferable for device application since it confines holes solely in the strained Si layer where hole mobility is enhanced.

Visible-light vertical-cavity surface-emitting lasers grown by solid-source molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Saarinen, Mika J.; Xiang, Ning; Dumitrescu, Mihail M.; Vilokkinen, Ville; Melanen, Petri; Orsila, Seppo; Uusimaa, Petteri; Savolainen, Pekka; Pessa, Markus

2001-05-01

Visible vertical-cavity surface-emitting lasers (VCSELs) are potential light sources for polymer optical fibre (POF) data transmission systems. Minimum attenuation of light in standard PMMA-POFs occurs at about 650 nm. For POFs of a few tens of meters in length VCSELs at slightly longer wavelengths (670 - 690 nm) are also acceptable. So far, the visible VCSELs have been grown by metal organic chemical vapour deposition (MOCVD). They may also be grown by a novel variant of molecular beam epitaxy (MBE), a so-called all-solid-source MBE or SSMBE. In this paper, we describe growth of the first visible-light VCSELs by SSMBE and present the main results obtained. In particular, we have achieved lasing action at a sub-milliamp cw drive current for a VCSEL having the emission window of 8um in diameter, while a 10um device exhibited an external quantum efficiency of 6.65% in CW operation at room temperature. The lasing action up to temperature of 45°C has been demonstrated.

Hydride VPE: the unexpected process for the fast growth of GaAs and GaN nanowires with record aspect ratio and polytypism-free crystalline structure

NASA Astrophysics Data System (ADS)

André, Yamina; Trassoudaine, Agnès.; Avit, Geoffrey; Lekhal, Kaddour; Ramdani, Mohammed R.; Leroux, Christine; Monier, Guillaume; Varenne, Christelle; Hoggan, Philip; Castelluci, Dominique; Bougerol, Catherine; Réveret, François; Leymarie, Joël.; Petit, Elodie; Dubrovskii, Vladimir G.; Gil, Evelyne

2013-12-01

Hydride Vapor Phase Epitaxy (HVPE) makes use of chloride III-Cl and hydride V-H3 gaseous growth precursors. It is known as a near-equilibrium process, providing the widest range of growth rates from 1 to more than 100 μm/h. When it comes to metal catalyst-assisted VLS (vapor-liquid-solid) growth, the physics of HVPE growth is maintained: high dechlorination frequency, high axial growth rate of nanowires (NWs) up to 170 μm/h. The remarkable features of NWs grown by HVPE are the untapered morphology with constant diameter and the stacking fault-free crystalline phase. Record pure zinc blende cubic phase for 20 μm long GaAs NWs with radii of 10 and 5 nm is shown. The absence of wurtzite phase in GaAs NWs grown by HVPE whatever the diameter is discussed with respect to surface energetic grounds and kinetics. Ni assisted, Ni-Au assisted and catalyst-free HVPE growth of wurtzite GaN NWs is also addressed. Micro-photoluminescence spectroscopy analysis revealed GaN nanowires of great optical quality, with a FWHM of 1 meV at 10 K for the neutral donor bound exciton transition.

Effect of deep centers on the radiative characteristics of epitaxial structures in the Ga-As-P system

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ermakov, O.P.

1986-08-01

This paper studies the radiative characteristics of structures not doped with nitrogen based on AgP and GaAs /SUB 1-y/ P /SUB y/ in a wide range of compositions, containing stoichiometry and radiation defects. The structures studied were obtained by the methods of liquid-phase and gas-phase epitaxy. Zn was used as the acceptor impurity in obtaining the p-n structures. The radiation defects were introduced by irradiation with a beam of fast 2.5-MeV electrons and the radiative characteristics were studied with the help of the method of electroluminescence (EL).

Nitridation- and Buffer-Layer-Free Growth of [1100]-Oriented GaN Domains on m-Plane Sapphire Substrates by Using Hydride Vapor Phase Epitaxy

NASA Astrophysics Data System (ADS)

Seo, Yeonwoo; Lee, Sanghwa; Jue, Miyeon; Yoon, Hansub; Kim, Chinkyo

2012-12-01

Over a wide range of growth conditions, GaN domains were grown on bare m-plane sapphire substrates by using hydride vapor phase epitaxy (HVPE), and the relation between these growth conditions and three possible preferred crystallographic orientations ([1100], [1103], [1122]) of GaN domains was investigated. In contrast with the previous reports by other groups, our results revealed that preferentially [1100]-oriented GaN domains were grown without low-temperature nitridation or a buffer layer, and that the growth condition of preferentially [1100]-oriented GaN was insensitive to V/III ratio.

Controlling Surface Morphology and Circumventing Secondary Phase Formation in Non-polar m-GaN by Tuning Nitrogen Activity

NASA Astrophysics Data System (ADS)

Chang, C. W.; Wadekar, P. V.; Guo, S. S.; Cheng, Y. J.; Chou, M.; Huang, H. C.; Hsieh, W. C.; Lai, W. C.; Chen, Q. Y.; Tu, L. W.

2018-01-01

For the development of non-polar nitrides based optoelectronic devices, high-quality films with smooth surfaces, free of defects or clusters, are critical. In this work, the mechanisms governing the topography and single phase epitaxy of non-polar m-plane gallium nitride ( m-GaN) thin films are studied. The samples were grown using plasma-assisted molecular beam epitaxy on m-plane sapphire substrates. Growth of pure m-GaN thin films, concomitant with smooth surfaces is possible at low radio frequency powers and high growth temperatures as judged by the high resolution x-ray diffraction, field emission scanning electron microscopy, and atomic force microscopy measurements. Defect types and densities are quantified using transmission electron microscopy, while Raman spectroscopy was used to analyze the in-plane stress in the thin films which matches the lattice mismatch analysis. Energy dispersive spectroscopy and cathodoluminescence support a congruent growth and a dominant near band edge emission. From the analysis, a narrow growth window is discovered wherein epitaxial growth of pure m-plane GaN samples free of secondary phases with narrow rocking curves and considerable smooth surfaces are successfully demonstrated.

Two-dimensional La2/3Sr4/3MnO4 Manganite Films Probed by Epitaxial Strain and Cation Ordering

NASA Astrophysics Data System (ADS)

Nelson-Cheeseman, Brittany; Santos, Tiffany; Bhattacharya, Anand

2010-03-01

Dimensionality is known to play a central role in the properties of strongly correlated systems. Here we investigate magnetism and transport in thin films of the Ruddlesden-Popper n=1 phase, La1-xSr1+xMnO4. Within this material, the MnO6-octahedra form two-dimensional perovskite sheets separated by an extra rocksalt layer. By fabricating high quality thin films with ozone-assisted molecular beam epitaxy, we study how the effects of epitaxial strain and intentional cation ordering, known as digital synthesis, influence the properties of this 2-dimensional manganite. For example, at the same Mn^3+:Mn^4+ ratio (2:1) as its fully spin-polarized 3D manganite counterpart, this two dimensional analog at x=1/3 only displays a spin glass phase below 20K in bulk. This is believed to result from a competition between superexchange and double exchange, as well as disordered Jahn-Teller distortions. However, in our films we find weak ferromagnetic order up to much higher temperatures in addition to a low temperature spin glass phase. We will discuss how strain and cation order effect the presence of this weak ferromagnetism.

β-Ga2O3 versus ε-Ga2O3: Control of the crystal phase composition of gallium oxide thin film prepared by metal-organic chemical vapor deposition

NASA Astrophysics Data System (ADS)

Zhuo, Yi; Chen, Zimin; Tu, Wenbin; Ma, Xuejin; Pei, Yanli; Wang, Gang

2017-10-01

Gallium oxide thin films of β and ε phase were grown on c-plane sapphire using metal-organic chemical vapor deposition and the phase compositions were analyzed using X-ray diffraction. The epitaxial phase diagram was constructed as a function of the growth temperature and VI/III ratio. A low growth temperature and low VI/III ratio were beneficial for the formation of hexagonal-type ε-Ga2O3. Further structure analysis revealed that the epitaxial relationship between ε-Ga2O3 and c-plane sapphire is ε-Ga2O3 (0001) || Al2O3 (0001) and ε-Ga2O3 || Al2O3 . The structural evolution of the mixed-phase sample during film thickening was investigated. By reducing the growth rate, the film evolved from a mixed phase to the energetically favored ε phase. Based on these results, a Ga2O3 thin film with a phase-pure ε-Ga2O3 upper layer was successfully obtained.

Oxygen vacancies controlled multiple magnetic phases in epitaxial single crystal Co 0.5(Mg 0.55Zn 0.45) 0.5O 1-v thin films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhu, Dapeng; Cao, Qiang; Qiao, Ruimin

2016-04-11

High quality single-crystal fcc-Co x (Mg y Zn 1-y ) 1-x O 1-v epitaxial thin films with high Co concentration up to x = 0.5 have been fabricated by molecular beam epitaxy. Systematic magnetic property characterization and soft X-ray absorption spectroscopy analysis indicate that the coexistence of ferromagnetic regions, superparamagnetic clusters, and non-magnetic boundaries in the as-prepared Co x (Mg y Zn 1-y ) 1-x O 1-v films is a consequence of the intrinsic inhomogeneous distribution of oxygen vacancies. Furthermore, the relative strength of multiple phases could be modulated by controlling the oxygen partial pressure during sample preparation. Armed withmore » both controllable magnetic properties and tunable band-gap, Co x (Mg y Zn 1-y ) 1-x O 1-v films may have promising applications in future spintronics.« less

A novel series of isoreticular metal organic frameworks: realizing metastable structures by liquid phase epitaxy

PubMed Central

Liu, Jinxuan; Lukose, Binit; Shekhah, Osama; Arslan, Hasan Kemal; Weidler, Peter; Gliemann, Hartmut; Bräse, Stefan; Grosjean, Sylvain; Godt, Adelheid; Feng, Xinliang; Müllen, Klaus; Magdau, Ioan-Bogdan; Heine, Thomas; Wöll, Christof

2012-01-01

A novel class of metal organic frameworks (MOFs) has been synthesized from Cu-acetate and dicarboxylic acids using liquid phase epitaxy. The SURMOF-2 isoreticular series exhibits P4 symmetry, for the longest linker a channel-size of 3 × 3 nm2 is obtained, one of the largest values reported for any MOF so far. High quality, ab-initio electronic structure calculations confirm the stability of a regular packing of (Cu++)2- carboxylate paddle-wheel planes with P4 symmetry and reveal, that the SURMOF-2 structures are in fact metastable, with a fairly large activation barrier for the transition to the bulk MOF-2 structures exhibiting a lower, twofold (P2 or C2) symmetry. The theoretical calculations also allow identifying the mechanism for the low-temperature epitaxial growth process and to explain, why a synthesis of this highly interesting, new class of high-symmetry, metastable MOFs is not possible using the conventional solvothermal process. PMID:23213357

Metalorganic vapor phase epitaxial growth of red and infrared vertical-cavity surface-emitting laser diodes

NASA Astrophysics Data System (ADS)

Schneider, R. P.; Lott, J. A.; Lear, K. L.; Choquette, K. D.; Crawford, M. H.; Kilcoyne, S. P.; Figiel, J. J.

1994-12-01

Metalorganic vapor phase epitaxy (MOVPE) is used for the growth of vertical-cavity surface-emitting laser (VCSEL) diodes. MOVPE exhibits a number of important advantages over the more commonly-used molecular-beam epitaxial (MBE) techniques, including ease of continuous compositional grading and carbon doping for low-resistance p-type distributed Bragg reflectors (DBRs), higher growth rates for rapid throughput and greater versatility in choice of materials and dopants. Planar gain-guided red VCSELs based on AlGaInP/AlGaAs heterostructures lase continuous-wave at room temperature, with voltage thresholds between 2.5 and 3 V and maximum power outputs of over 0.3 mW. Top-emitting infra-red (IR) VCSELs exhibit the highest power-conversion (wall-plug) efficiencies (21%), lowest threshold voltage (1.47 V), and highest single mode power (4.4 mW from an 8 μm device) yet reported. These results establish MOVPE as a preferred growth technique for this important new family of photonic devices.

Carrier Concentration Control of GaSb/GaInAsSb System

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lazzari, J.-L.; Anda, F. de; Nieto, J.

2007-02-22

The residual carrier concentration of GaSb and GaSb-lattice matched Ga1-xInxAsySb1-y alloys (x = 0.12-0.26; y = 0.9x) grown by liquid phase epitaxy (LPE) and molecular beam epitaxy (MBE) was studied as a function of growth temperature, V/III ratio and alloy composition. Typical carrier concentrations p {approx} 2-3x1016 cm-3 were obtained for undoped GaSb grown by MBE at 480 deg. C, by LPE from Ga-rich melt at low temperature (400 deg. C), and by LPE from Sb-rich melts at {approx}600 deg. C. The native acceptor defect responsible of the high p-type residual doping in GaSb is reduced when the indium concentrationmore » is increased, and disappears for indium rich alloys (x = 0.23, 0.26). Tellurium compensation was used for controlled n-type doping in the (0.05-30)x1017 cm-3 range. A maximum of free carrier concentration was 1.5x1018 cm-3 for LPE layers, 2x1018 cm-3 for MBE layers grown at 1.0 {mu}m/h, 3.5x1018 cm-3 for MBE layers grown at 0.2 {mu}m/h. SIMS measurements showed Te concentrations of more than 1020 at/cm3, suggesting the formation of ternary GaSb1-xTex solid solution.« less

Epitaxial growth of a mono-crystalline metastable AuIn layer at the Au/InP(001) interface

NASA Astrophysics Data System (ADS)

Renda, M.; Morita, K.

1990-01-01

Thermal annealing of a gold layer deposited on the InP(001)-p(2×4) surface has been studied in-situ by means of LEED, AES and RBS techniques and by post analysis of RBS-channeling and glancing incidence X-ray diffraction. A clean LEED pattern of p(2×2) spots was observed for the specimen annealed for 10 min at 300°C. The composition ratio of Au/In in the epitaxial compound layer was found to be 49/51 by RBS and several at% of P was also detected by post sputter-AES analysis. It was also found that the epitaxial layer shows a clear channeling dip for an incident ion beam which is aligned along the <001> axis of InP substrate. The glancing incidence X-ray diffraction analysis indicates diffraction peaks from the pseudo-orthorombic phase of AuIn. From these experimental results, it is concluded that the epitaxial Au-compound layer is a mono-crystalline metastable phase of AuIn, of which every three atomic rows of Au or In in the [110] direction would be situated on every four atomic rows in the [010] direction of the In(001) face of the InP crystal.

BiFeO3 epitaxial thin films and devices: past, present and future

NASA Astrophysics Data System (ADS)

Sando, D.; Barthélémy, A.; Bibes, M.

2014-11-01

The celebrated renaissance of the multiferroics family over the past ten years has also been that of its most paradigmatic member, bismuth ferrite (BiFeO3). Known since the 1960s to be a high temperature antiferromagnet and since the 1970s to be ferroelectric, BiFeO3 only had its bulk ferroic properties clarified in the mid-2000s. It is however the fabrication of BiFeO3 thin films and their integration into epitaxial oxide heterostructures that have fully revealed its extraordinarily broad palette of functionalities. Here we review the first decade of research on BiFeO3 films, restricting ourselves to epitaxial structures. We discuss how thickness and epitaxial strain influence not only the unit cell parameters, but also the crystal structure, illustrated for instance by the discovery of the so-called T-like phase of BiFeO3. We then present its ferroelectric and piezoelectric properties and their evolution near morphotropic phase boundaries. Magnetic properties and their modification by thickness and strain effects, as well as optical parameters, are covered. Finally, we highlight various types of devices based on BiFeO3 in electronics, spintronics, and optics, and provide perspectives for the development of further multifunctional devices for information technology and energy harvesting.

Atomic Layer Deposition of Metastable β-Fe 2 O 3 via Isomorphic Epitaxy for Photoassisted Water Oxidation

DOE PAGES

Emery, Jonathan D.; Schlepütz, Christian M.; Guo, Peijun; ...

2014-12-09

Here, we report the growth and photoelectrochemical (PEC) characterization of the uncommon bibyite phase of iron(III) oxide (β-Fe 2O 3) epitaxially stabilized via atomic layer deposition on an conductive, transparent, and isomorphic template (Sn-doped In 2O 3). Furthermore, as a photoanode, unoptimized β-Fe 2O 3 ultrathin films perform similarly to their ubiquitous α-phase (hematite) counterpart, but reveal a more ideal bandgap (1.8 eV), a ~0.1 V improved photocurrent onset potential, and longer wavelength (>600 nm) spectral response. Finally, stable operation under basic water oxidation justifies further exploration of this atypical phase and motivates the investigation of other unexplored metastable phasesmore » as new PEC materials.« less

Naturally formed ultrathin V2O5 heteroepitaxial layer on VO2/sapphire(001) film

NASA Astrophysics Data System (ADS)

Littlejohn, Aaron J.; Yang, Yunbo; Lu, Zonghuan; Shin, Eunsung; Pan, KuanChang; Subramanyam, Guru; Vasilyev, Vladimir; Leedy, Kevin; Quach, Tony; Lu, Toh-Ming; Wang, Gwo-Ching

2017-10-01

Vanadium dioxide (VO2) and vanadium pentoxide (V2O5) thin films change their properties in response to external stimuli such as photons, temperature, electric field and magnetic field and have applications in electronics, optical devices, and sensors. Due to the multiple valence states of V and non-stoichiometry in thin films, it is challenging to grow epitaxial, single-phase V-oxide on a substrate, or a heterostructure of two epitaxial V-oxides. We report the formation of a heterostructure consisting of a few nm thick ultrathin V2O5 epitaxial layer on pulsed laser deposited tens of nm thick epitaxial VO2 thin films grown on single crystal Al2O3(001) substrates without post annealing of the VO2 film. The simultaneous observation of the ultrathin epitaxial V2O5 layer and VO2 epitaxial film is only possible by our unique reflection high energy electron diffraction pole figure analysis. The out-of-plane and in-plane epitaxial relationships are V2O5[100]||VO2[010]||Al2O3[001] and V2O5[03 2 bar ]||VO2[100]||Al2O3[1 1 bar 0], respectively. The existence of the V2O5 layer on the surface of the VO2 film is also supported by X-ray photoelectron spectroscopy and Raman spectroscopy.

In situ method for estimating cell survival in a solid tumor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alfieri, A.A.; Hahn, E.W.

1978-09-01

The response of the murine Meth-A fibrosarcoma to single and fractionated doses of x-irradiation, actinomycin D chemotherapy, and/or concomitant local tumor hyperthermia was assayed with the use of an in situ method for estimating cell kill within a solid tumor. The cell survival assay was based on a standard curve plotting number of inoculated viable cells with and without radiation-inactivated homologous tumor cells versus the time required for i.m. tumors to grow to 1.0 cu cm. The time for post-treatment tumors to grow to 1.0 cu cm was cross-referenced to the standard curve, and the number of surviving cells contributingmore » to tumor regrowth was estimated. The resulting surviving fraction curves closely resemble those obtained with in vitro systems.« less

Incidence of delayed hair re-growth, pruritus, and urinary retention after epidural anaesthesia in dogs.

PubMed

Kalchofner Guerrero, K S; Guerrero, T G; Schweizer-Kölliker, M; Ringer, S K; Hässig, M; Bettschart-Wolfensberger, R

2014-04-16

Delayed hair re-growth, pruritus and urinary retention are known complications after epidural anaesthesia in dogs. The aim of this study was to prospectively evaluate the effect of epidurally administered drugs on the occurrence of these complications in dogs. Ninety dogs were included in this study. Eighty client-owned dogs undergoing surgery were randomly assigned to one of three epidural treatment groups: either morphine and bupivacaine (MB), bupivacaine (B), or saline solution 0.9% (S) was administered epidurally to these patients. Ten dogs were only clipped in the lumbosacral area (C). Follow-up started 4 weeks after clipping and was performed every 4-5 weeks in cases of delayed hair re-growth or pruritus. Hair re-growth in the lumbosacral area was observed and compared to hair re-growth in the surgical field and the fentanyl patch area. Cytological analysis and a trichogram were performed if hair re-growth was delayed after 6 months. Time interval to first urination postoperatively was recorded (n = 80). Hair re-growth was delayed in 11 dogs (12.2%; B: n = 7, S: n = 2, MB: n = 1, C: n = 1) with no differences between groups. Pruritus was evident in two dogs (2.2%; MB: n = 1, S: n = 1). After 6 months, hair had started to re-grow in all but one dog (B). After 10 months the coat of this dog had re-grown. Time to first urination did not differ between groups. No direct correlation between the particular drugs injected epidurally and delayed hair re-growth, pruritus and urinary retention could be shown. Dog owners should be informed that hair re-growth after epidural anaesthesia could be markedly delayed.

Self-assembly of tin wires via phase transformation of heteroepitaxial germanium-tin on germanium substrate

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Wei; Li, Lingzi; Yeo, Yee-Chia, E-mail: yeo@ieee.org

This work demonstrates and describes for the first time an unusual strain-relaxation mechanism by the formation and self-assembly of well-ordered tin wires during the thermal annealing of epitaxial Ge{sub 0.83}Sn{sub 0.17}-on-Ge(001) substrate. Fully strained germanium-tin alloys (Ge{sub 0.83}Sn{sub 0.17}) were epitaxially grown on Ge(001) substrate by molecular beam epitaxy. The morphological and compositional evolution of Ge{sub 0.83}Sn{sub 0.17} during thermal annealing is studied by atomic force microscopy, X-ray diffraction, transmission electron microscopy. Under certain annealing conditions, the Ge{sub 0.83}Sn{sub 0.17} layer decomposes into two stable phases, and well-defined Sn wires that are preferentially oriented along two orthogonal 〈100〉 azimuths aremore » formed. The formation of the Sn wires is related to the annealing temperature and the Ge{sub 0.83}Sn{sub 0.17} thickness, and can be explained by the nucleation of a grain with Sn islands on the outer front, followed by grain boundary migration. The Sn wire formation process is found to be thermally activated, and an activation enthalpy (E{sub c}) of 0.41 eV is extracted. This thermally activated phase transformation, i.e., 2D epitaxial layer to 3D wires, occurs via a mechanism akin to “cellular precipitation.” This synthesis route of Sn wires opens new possibilities for creation of nanoscale patterns at high-throughput without the need for lithography.« less

Implications of nutrient release from iron metal for microbial regrowth in water distribution systems.

PubMed

Morton, Siyuan C; Zhang, Yan; Edwards, Marc A

2005-08-01

Control of microbial regrowth in iron pipes is a major challenge for water utilities. This work examines the inter-relationship between iron corrosion and bacterial regrowth, with a special focus on the potential of iron pipe to serve as a source of phosphorus. Under some circumstances, corroding iron and steel may serve as a source for all macronutrients necessary for bacterial regrowth including fixed carbon, fixed nitrogen and phosphorus. Conceptual models and experimental data illustrate that levels of phosphorus released from corroding iron are significant relative to that necessary to sustain high levels of biofilm bacteria. Consequently, it may not be possible to control regrowth on iron surfaces by limiting phosphorus in the bulk water.

Effects of external mechanical loading on phase diagrams and dielectric properties in epitaxial ferroelectric thin films with anisotropic in-plane misfit strains

NASA Astrophysics Data System (ADS)

Qiu, J. H.; Jiang, Q.

2007-02-01

A phenomenological Landau-Devonshine theory is used to describe the effects of external mechanical loading on equilibrium polarization states and dielectric properties in epitaxial ferroelectric thin films grown on dissimilar orthorhombic substrates which induce anisotropic misfit strains in the film plane. The calculation focuses on single-domain perovskite BaTiO3 and PbTiO3 thin films on the assumption that um1=-um2. Compared with the phase diagrams without external loading, the characteristic features of "misfit strain-misfit strain" phase diagrams at room temperature are the presence of paraelectric phase and the strain-induced ferroelectric to paraelectric phase transition. Due to the external loading, the "misfit strain-stress" and "stress-temperature" phase diagrams also have drastic changes, especially for the vanishing of paraelectric phase in "misfit strain-stress" phase map and the appearance of possible ferroelectric phases. We also investigate the dielectric properties and the tunability of both BaTiO3 and PbTiO3 thin films. We find that the external stress dependence of phase diagrams and dielectric properties largely depends on strain anisotropy as well.

Epitaxial Fe{sub 3}Pt/FePt nanocomposites on MgO and SrTiO{sub 3}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Casoli, F., E-mail: casoli@imem.cnr.it; Nasi, L.; Cabassi, R.

We have exploited the pseudomorphic growth of the magnetically soft Fe{sub 3}Pt phase on top of L1{sub 0}-FePt to obtain fully epitaxial soft/hard nanocomposites on both MgO(100) and SrTiO{sub 3}(100). The magnetic properties of this new nanocomposite system, driven by the soft/hard exchange-coupling, can be tailored by varying soft phase thickness, soft phase magnetic anisotropy and substrate. Coercivity is strongly reduced by the addition of the soft phase, a reduction which is definitely affected by the nominal composition of the soft phase and by the substrate choice; similarly is the magnetic phase diagram of the composite system. Coercive field decreasesmore » down to 21% of the hard layer value for Fe{sub 3}Pt(5 nm)/FePt(3.55 nm) nanocomposites on SrTiO{sub 3}; this maximum coercivity reduction was obtained with a nominal atomic content of Fe in the soft phase of 80%.« less

Photon Transport in One-Dimensional Incommensurately Epitaxial CsPbX 3 Arrays

DOE PAGES

Wang, Yiping; Sun, Xin; Shivanna, Ravichandran; ...

2016-11-16

One-dimensional nanoscale epitaxial arrays serve as a great model in studying fundamental physics and for emerging applications. With an increasing focus laid on the Cs-based inorganic halide perovskite out of its outstanding material stability, we have applied vapor phase epitaxy to grow well aligned horizontal CsPbX 3 (X: Cl, Br, or I or their mixed) nanowire arrays in large scale on mica substrate. The as-grown nanowire features a triangular prism morphology with typical length ranging from a few tens of micrometers to a few millimeters. Structural analysis reveals that the wire arrays follow the symmetry of mica substrate through incommensuratemore » epitaxy, paving a way for a universally applicable method to grow a broad family of halide perovskite materials. We have studied the unique photon transport in the one-dimensional structure in the all-inorganic Cs-based perovskite wires via temperature dependent and spatially resolved photoluminescence. Furthermore, epitaxy of well oriented wire arrays in halide perovskite would be a promising direction for enabling the circuit-level applications of halide perovskite in high-performance electro-optics and optoelectronics.« less

Numerical simulations of epitaxial growth process in MOVPE reactor as a tool for design of modern semiconductors for high power electronics

NASA Astrophysics Data System (ADS)

Skibinski, Jakub; Caban, Piotr; Wejrzanowski, Tomasz; Kurzydlowski, Krzysztof J.

2014-10-01

In the present study numerical simulations of epitaxial growth of gallium nitride in Metal Organic Vapor Phase Epitaxy reactor AIX-200/4RF-S is addressed. Epitaxial growth means crystal growth that progresses while inheriting the laminar structure and the orientation of substrate crystals. One of the technological problems is to obtain homogeneous growth rate over the main deposit area. Since there are many agents influencing reaction on crystal area such as temperature, pressure, gas flow or reactor geometry, it is difficult to design optimal process. According to the fact that it's impossible to determine experimentally the exact distribution of heat and mass transfer inside the reactor during crystal growth, modeling is the only solution to understand the process precisely. Numerical simulations allow to understand the epitaxial process by calculation of heat and mass transfer distribution during growth of gallium nitride. Including chemical reactions in numerical model allows to calculate the growth rate of the substrate and estimate the optimal process conditions for obtaining the most homogeneous product.

Epitaxial solar-cell fabrication, phase 2

NASA Technical Reports Server (NTRS)

Daiello, R. V.; Robinson, P. H.; Kressel, H.

1977-01-01

Dichlorosilane (SiH2Cl2) was used as the silicon source material in all of the epitaxial growths. Both n/p/p(+) and p/n/n(+) structures were studied. Correlations were made between the measured profiles and the solar cell parameters, especially cell open-circuit voltage. It was found that in order to obtain consistently high open-circuit voltage, the epitaxial techniques used to grow the surface layer must be altered to obtain very abrupt doping profiles in the vicinity of the junction. With these techniques, it was possible to grow reproducibly both p/n/n(+) and n/p/p(+) solar cell structures having open-circuit voltages in the 610- to 630-mV range, with fill-factors in excess of 0.80 and AM-1 efficiencies of about 13%. Combinations and comparisons of epitaxial and diffused surface layers were also made. Using such surface layers, we found that the blue response of epitaxial cells could be improved, resulting in AM-1 short-circuit current densities of about 30 mA/cm sq. The best cells fabricated in this manner had AM-1 efficiency of 14.1%.

Structure and strain relaxation mechanisms of ultrathin epitaxial Pr2O3 films on Si(111)

NASA Astrophysics Data System (ADS)

Schroeder, T.; Lee, T.-L.; Libralesso, L.; Joumard, I.; Zegenhagen, J.; Zaumseil, P.; Wenger, C.; Lupina, G.; Lippert, G.; Dabrowski, J.; Müssig, H.-J.

2005-04-01

The structure of ultrathin epitaxial Pr2O3 films on Si(111) was studied by synchrotron radiation-grazing incidence x-ray diffraction. The oxide film grows as hexagonal Pr2O3 phase with its (0001) plane attached to the Si(111) substrate. The hexagonal (0001) Pr2O3 plane matches the in-plane symmetry of the hexagonal Si(111) surface unit cell by aligning the ⟨101¯0⟩Pr2O3 along the ⟨112¯⟩ Si directions. The small lattice mismatch of 0.5% results in the growth of pseudomorphic oxide films of high crystalline quality with an average domain size of about 50 nm. The critical thickness tc for pseudomorphic growth amounts to 3.0±0.5nm. The relaxation of the oxide film from pseudomorphism to bulk behavior beyond tc causes the introduction of misfit dislocations, the formation of an in-plane small angle mosaicity structure, and the occurence of a phase transition towards a (111) oriented cubic Pr2O3 film structure. The observed phase transition highlights the influence of the epitaxial interface energy on the stability of Pr2O3 phases on Si(111). A mechanism is proposed which transforms the hexagonal (0001) into the cubic (111) Pr2O3 epilayer structure by rearranging the oxygen network but leaving the Pr sublattice almost unmodified.

SAPHIRA detector for infrared wavefront sensing

NASA Astrophysics Data System (ADS)

Finger, Gert; Baker, Ian; Alvarez, Domingo; Ives, Derek; Mehrgan, Leander; Meyer, Manfred; Stegmeier, Jörg; Weller, Harald J.

2014-08-01

The only way to overcome the CMOS noise barrier of near infrared sensors used for wavefront sensing and fringe tracking is the amplification of the photoelectron signal inside the infrared pixel by means of the avalanche gain. In 2007 ESO started a program at Selex to develop near infrared electron avalanche photodiode arrays (eAPD) for wavefront sensing and fringe tracking. In a first step the cutoff wavelength was reduced from 4.5 micron to 2.5 micron in order to verify that the dark current scales with the bandgap and can be reduced to less than one electron/ms, the value required for wavefront sensing. The growth technology was liquid phase epitaxy (LPE) with annular diodes based on the loophole interconnect technology. The arrays required deep cooling to 40K to achieve acceptable cosmetic performance at high APD gain. The second step was to develop a multiplexer tailored to the specific application of the GRAVITY instrument wavefront sensors and the fringe tracker. The pixel format is 320x256 pixels. The array has 32 parallel video outputs which are arranged in such a way that the full multiplex advantage is available also for small subwindows. Nondestructive readout schemes with subpixel sampling are possible. This reduces the readout noise at high APD gain well below the subelectron level at frame rates of 1 KHz. The third step was the change of the growth technology from liquid phase epitaxy to metal organic vapour phase epitaxy (MOVPE). This growth technology allows the band structure and doping to be controlled on a 0.1μm scale and provides more flexibility for the design of diode structures. The bandgap can be varied for different layers of Hg(1-x)CdxTe. It is possible to make heterojunctions and apply solid state engineering techniques. The change to MOVPE resulted in a dramatic improvement in the cosmetic quality with 99.97 % operable pixels at an operating temperature of 85K. Currently this sensor is deployed in the 4 wavefront sensors and in the fringe tracker of the VLT instrument GRAVITY. Initial results will be presented. An outlook will be given on the potential of APD technology to be employed in large format near infrared science detectors. Several of the results presented here have also been shown to a different audience at the Scientific Detector Workshop in October 2013 in Florence but this paper has been updated with new results [1].

Epitaxial growth and characterization of Si/NiSi 2/Si(111) heterostructures

NASA Astrophysics Data System (ADS)

Rizzi, Angela; Förster, A.; Lüth, H.; Slijkerman, W.

1989-04-01

Si/NiSi 2/Si(111) heterostructures are grown under UHV conditions. The well known "template" method is used to produce the epitaxial NiSi 2 interlayer. On top of the suicide, the silicon epitaxial growth is obtained by means of gas phase reaction of SiH 4 at a surface temperature of 500° C. The Si growth rate is strongly enhanced by predissociation of SiH 4 using a hot tungsten filament in the vicinity of the surface. The single steps of the growth are followed in-situ by means of AES, HREELS and LEED analysis. Ex-situ high resolution RBS analysis is also applied for characterization.

InGaN/GaN tunnel junctions for hole injection in GaN light emitting diodes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Krishnamoorthy, Sriram, E-mail: krishnamoorthy.13@osu.edu, E-mail: rajan@ece.osu.edu; Akyol, Fatih; Rajan, Siddharth, E-mail: krishnamoorthy.13@osu.edu, E-mail: rajan@ece.osu.edu

InGaN/GaN tunnel junction contacts were grown using plasma assisted molecular beam epitaxy (MBE) on top of a metal-organic chemical vapor deposition (MOCVD)-grown InGaN/GaN blue (450 nm) light emitting diode. A voltage drop of 5.3 V at 100 mA, forward resistance of 2 × 10{sup −2} Ω cm{sup 2}, and a higher light output power compared to the reference light emitting diodes (LED) with semi-transparent p-contacts were measured in the tunnel junction LED (TJLED). A forward resistance of 5 × 10{sup −4} Ω cm{sup 2} was measured in a GaN PN junction with the identical tunnel junction contact as the TJLED, grown completely by MBE. Themore » depletion region due to the impurities at the regrowth interface between the MBE tunnel junction and the MOCVD-grown LED was hence found to limit the forward resistance measured in the TJLED.« less

Tunable Solid-State Quantum Memory Using Rare-Earth-Ion-Doped Crystal, Nd(3+):GaN

DTIC Science & Technology

2017-04-01

by plasma-assisted molecular beam epitaxy in a modular Gen II reactor using liquid gallium, solid Nd, and a nitrogen plasma. The photoluminescence (PL...provide a tunable memory. To vary the applied field, we designed and grew a series of Nd-doped GaN p-i-n structures, strain- balanced superlattice...27 Fig. 23 Electric field vs. GaN well/ AlxGa(1-x)N barrier thickness for strain- balanced superlattice (SBSL) structures with

van der Waals epitaxy of SnS film on single crystal graphene buffer layer on amorphous SiO2/Si

NASA Astrophysics Data System (ADS)

Xiang, Yu; Yang, Yunbo; Guo, Fawen; Sun, Xin; Lu, Zonghuan; Mohanty, Dibyajyoti; Bhat, Ishwara; Washington, Morris; Lu, Toh-Ming; Wang, Gwo-Ching

2018-03-01

Conventional hetero-epitaxial films are typically grown on lattice and symmetry matched single crystal substrates. We demonstrated the epitaxial growth of orthorhombic SnS film (∼500 nm thick) on single crystal, monolayer graphene that was transferred on the amorphous SiO2/Si substrate. Using X-ray pole figure analysis we examined the structure, quality and epitaxy relationship of the SnS film grown on the single crystal graphene and compared it with the SnS film grown on commercial polycrystalline graphene. We showed that the SnS films grown on both single crystal and polycrystalline graphene have two sets of orientation domains. However, the crystallinity and grain size of the SnS film improve when grown on the single crystal graphene. Reflection high-energy electron diffraction measurements show that the near surface texture has more phases as compared with that of the entire film. The surface texture of a film will influence the growth and quality of film grown on top of it as well as the interface formed. Our result offers an alternative approach to grow a hetero-epitaxial film on an amorphous substrate through a single crystal graphene buffer layer. This strategy of growing high quality epitaxial thin film has potential applications in optoelectronics.

Effect of indium droplets on growth of InGaN film by molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Zheng, Xiantong; Liang, Hongwei; Wang, Ping; Sun, Xiaoxiao; Chen, Zhaoying; Wang, Tao; Sheng, Bowen; Wang, Yixin; Chen, Ling; Wang, Ding; Rong, Xin; Li, Mo; Zhang, Jian; Wang, Xinqiang

2018-01-01

Effect of indium (In) droplets on InGaN thin films grown by molecular beam epitaxy (MBE) has been investigated. The surface of InGaN covered by In droplets shows a smoother topography than that without droplets, indicating that the presence of In droplets is beneficial to the two dimensional growth. Beneath the In droplets, many ring-like structures are observed. The arrangement of these "ring" shows the movement of the In droplets during the InGaN growth. A qualitative growth model is proposed to explain the evolution of the InGaN surface morphology in In-droplet-induced-epitaxy process, giving an explanation that a local vapor-liquid-solid (VLS) system is preferentially formed at the edge of the droplets, leading to a high growth rate. Furthermore, the energy dispersive X-ray spectroscopy results reveal that the relatively higher In/Ga flux ratio in the region covered by the In droplet results in a locally higher In content.

Thermoelectric La-doped SrTiO3 epitaxial layers with single-crystal quality: from nano to micrometers

PubMed Central

Apreutesei, Mihai; Debord, Régis; Bouras, Mohamed; Regreny, Philippe; Botella, Claude; Benamrouche, Aziz; Carretero-Genevrier, Adrian; Gazquez, Jaume; Grenet, Geneviève; Pailhès, Stéphane; Saint-Girons, Guillaume; Bachelet, Romain

2017-01-01

Abstract High-quality thermoelectric La0.2Sr0.8TiO3 (LSTO) films, with thicknesses ranging from 20 nm to 0.7 μm, have been epitaxially grown on SrTiO3(001) substrates by enhanced solid-source oxide molecular-beam epitaxy. All films are atomically flat (with rms roughness < 0.2 nm), with low mosaicity (<0.1°), and present very low electrical resistivity (<5 × 10−4 Ω cm at room temperature), one order of magnitude lower than standard commercial Nb-doped SrTiO3 single-crystalline substrate. The conservation of transport properties within this thickness range has been confirmed by thermoelectric measurements where Seebeck coefficients of approximately –60 μV/K have been recorded for all films. These LSTO films can be integrated on Si for non-volatile memory structures or opto-microelectronic devices, functioning as transparent conductors or thermoelectric elements. PMID:28740558

Thermoelectric La-doped SrTiO3 epitaxial layers with single-crystal quality: from nano to micrometers.

PubMed

Apreutesei, Mihai; Debord, Régis; Bouras, Mohamed; Regreny, Philippe; Botella, Claude; Benamrouche, Aziz; Carretero-Genevrier, Adrian; Gazquez, Jaume; Grenet, Geneviève; Pailhès, Stéphane; Saint-Girons, Guillaume; Bachelet, Romain

2017-01-01

High-quality thermoelectric La 0.2 Sr 0.8 TiO 3 (LSTO) films, with thicknesses ranging from 20 nm to 0.7 μm, have been epitaxially grown on SrTiO 3 (001) substrates by enhanced solid-source oxide molecular-beam epitaxy. All films are atomically flat (with rms roughness < 0.2 nm), with low mosaicity (<0.1°), and present very low electrical resistivity (<5 × 10 -4 Ω cm at room temperature), one order of magnitude lower than standard commercial Nb-doped SrTiO 3 single-crystalline substrate. The conservation of transport properties within this thickness range has been confirmed by thermoelectric measurements where Seebeck coefficients of approximately -60 μV/K have been recorded for all films. These LSTO films can be integrated on Si for non-volatile memory structures or opto-microelectronic devices, functioning as transparent conductors or thermoelectric elements.

INTERNATIONAL CONFERENCE ON SEMICONDUCTOR INJECTION LASERS SELCO-87: High-performance 1.3-μm InGaAsP/InP heterostructures formed by two-phase liquid epitaxy

NASA Astrophysics Data System (ADS)

Novotný, J.; Procházková, O.; Šrobár, F.; Zelinka, J.

1988-11-01

A description is given of a two-phase liquid epitaxy method used to grow InGaAsP/InP heterostructures intended for injection lasers emitting in the 1.3-μm range. A study was made of heterostructures of three types: double, with an additional quaternary layer (λ approx 1.1 μm) adjoining the active layer; with two quaternary layers between the active layer and the InP confining layers. The configuration with two flanking quaternary layers was found to be the best from the point of view of the threshold current density, optical output power, and reproducibility.

Depletion-mode vertical Ga2O3 trench MOSFETs fabricated using Ga2O3 homoepitaxial films grown by halide vapor phase epitaxy

NASA Astrophysics Data System (ADS)

Sasaki, Kohei; Thieu, Quang Tu; Wakimoto, Daiki; Koishikawa, Yuki; Kuramata, Akito; Yamakoshi, Shigenobu

2017-12-01

We developed depletion-mode vertical Ga2O3 trench metal-oxide-semiconductor field-effect transistors by using n+ contact and n- drift layers. These epilayers were grown on an n+ (001) Ga2O3 single-crystal substrate by halide vapor phase epitaxy. Cu and HfO2 were used for the gate metal and dielectric film, respectively. The mesa width and gate length were approximately 2 and 1 µm, respectively. The devices showed good DC characteristics, with a specific on-resistance of 3.7 mΩ cm2 and clear current modulation. An on-off ratio of approximately 103 was obtained.

Direct observation of fatigue in epitaxially grown Pb(Zr,Ti)O3 thin films using second harmonic piezoresponse force microscopy

NASA Astrophysics Data System (ADS)

Murari, Nishit M.; Hong, Seungbum; Lee, Ho Nyung; Katiyar, Ram. S.

2011-08-01

Here, we present a direct observation of fatigue phenomena in epitaxially grown Pb(Zr0.2Ti0.8)O3 (PZT) thin films using second harmonic piezoresponse force microscopy (SH-PFM). We observed strong correlation between the SH-PFM amplitude and phase signals with the remnant piezoresponse at different switching cycles. The SH-PFM results indicate that the average fraction of switchable domains decreases globally and the phase delays of polarization switching differ locally. In addition, we found that the fatigue developed uniformly over the whole area without developing region-by-region suppression of switchable polarization as in polycrystalline PZT thin films.

Interface amorphization in hexagonal boron nitride films on sapphire substrate grown by metalorganic vapor phase epitaxy

NASA Astrophysics Data System (ADS)

Yang, Xu; Nitta, Shugo; Pristovsek, Markus; Liu, Yuhuai; Nagamatsu, Kentaro; Kushimoto, Maki; Honda, Yoshio; Amano, Hiroshi

2018-05-01

Hexagonal boron nitride (h-BN) films directly grown on c-plane sapphire substrates by pulsed-mode metalorganic vapor phase epitaxy exhibit an interlayer for growth temperatures above 1200 °C. Cross-sectional transmission electron microscopy shows that this interlayer is amorphous, while the crystalline h-BN layer above has a distinct orientational relationship with the sapphire substrate. Electron energy loss spectroscopy shows the energy-loss peaks of B and N in both the amorphous interlayer and the overlying crystalline h-BN layer, while Al and O signals are also seen in the amorphous interlayer. Thus, the interlayer forms during h-BN growth through the decomposition of the sapphire at elevated temperatures.

Reduction of threading dislocation density in SiGe epilayer on Si (0 0 1) by lateral growth liquid-phase epitaxy

NASA Astrophysics Data System (ADS)

O'Reilly, Andrew J.; Quitoriano, Nathaniel J.

2018-02-01

Si0.973Ge0.027 epilayers were grown on a Si (0 0 1) substrate by a lateral liquid-phase epitaxy (LLPE) technique. The lateral growth mechanism favoured the glide of misfit dislocations and inhibited the nucleation of new dislocations by maintaining the thickness less than the critical thicknesses for dislocation nucleation and greater than the critical thickness for glide. This promoted the formation of an array of long misfit dislocations parallel to the [1 1 0] growth direction and reduced the threading dislocation density to 103 cm-2, two orders of magnitude lower than the seed area with an isotropic misfit dislocation network.

Self-catalytic branch growth of SnO 2 nanowire junctions

NASA Astrophysics Data System (ADS)

Chen, Y. X.; Campbell, L. J.; Zhou, W. L.

2004-10-01

Multiple branched SnO2 nanowire junctions have been synthesized by thermal evaporation of SnO powder. Their nanostructures were studied by transmission electron microscopy and field emission scanning electron microcopy. It was observed that Sn nanoparticles generated from decomposition of the SnO powder acted as self-catalysts to control the SnO2 nanojunction growth. Orthorhombic SnO2 was found as a dominate phase in nanojunction growth instead of rutile structure. The branches and stems of nanojunctions were found to be an epitaxial growth by electron diffraction analysis and high-resolution electron microscopy observation. The growth directions of the branched SnO2 nanojunctions were along the orthorhombic [1 1 0] and [ 1 1 bar 0 ] . A self-catalytic vapor-liquid-solid growth mechanism is proposed to describe the growth process of the branched SnO2 nanowire junctions.

A nitride-based epitaxial surface layer formed by ammonia treatment of silicene-terminated ZrB{sub 2}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wiggers, F. B., E-mail: F.B.Wiggers@utwente.nl; Van Bui, H.; Schmitz, J.

We present a method for the formation of an epitaxial  surface layer involving B, N, and Si atoms on a ZrB{sub 2}(0001) thin film on Si(111). It has the potential to be an insulating growth template for 2D semiconductors. The chemical reaction of NH{sub 3} molecules with the silicene-terminated ZrB{sub 2}  surface was characterized by synchrotron-based, high-resolution core-level photoelectron spectroscopy and low-energy electron diffraction. In particular, the dissociative chemisorption of NH{sub 3} at 400 °C leads to surface  nitridation, and subsequent annealing up to 830 °C results in a solid phase reaction with the ZrB{sub 2} subsurface layers. In this way, amore » new nitride-based epitaxial  surface layer is formed with hexagonal symmetry and a single in-plane crystal orientation.« less

Crystallization process of a three-dimensional complex plasma

NASA Astrophysics Data System (ADS)

Steinmüller, Benjamin; Dietz, Christopher; Kretschmer, Michael; Thoma, Markus H.

2018-05-01

Characteristic timescales and length scales for phase transitions of real materials are in ranges where a direct visualization is unfeasible. Therefore, model systems can be useful. Here, the crystallization process of a three-dimensional complex plasma under gravity conditions is considered where the system ranges up to a large extent into the bulk plasma. Time-resolved measurements exhibit the process down to a single-particle level. Primary clusters, consisting of particles in the solid state, grow vertically and, secondarily, horizontally. The box-counting method shows a fractal dimension of df≈2.72 for the clusters. This value gives a hint that the formation process is a combination of local epitaxial and diffusion-limited growth. The particle density and the interparticle distance to the nearest neighbor remain constant within the clusters during crystallization. All results are in good agreement with former observations of a single-particle layer.

Water deficit and nitrogen fertility effects on NDVI of 'Tifton 85' bermudagrass during regrowth

USDA-ARS?s Scientific Manuscript database

A better understanding of how bermudagrass (Cynodon spp.) regrowth is influenced by production inputs will aid in advancing precision management in the southeast US. The objective of this two-yr study was to evaluate how irrigation and nitrogen influence bermudagrass regrowth. Normalized difference ...

A pediatric intramedullary spinal cord tumor with unusual solid-cystic and papillary features: a case report.

PubMed

Iwasaki, Takeshi; Kato, Masako; Horie, Yasushi; Kato, Shinsuke; Akatsuka, Keiichi; Watanabe, Takashi; Kuwamoto, Satoshi; Murakami, Ichiro; Hayashi, Kazuhiko

2011-12-01

Spinal cord tumors are rare in children. We report a novel case of pediatric intramedullary spinal cord tumor with unusual solid-cystic and papillary features. Clinically, the patient presented at the age of 3 years with motor deficit and urinary incontinence, and MRI demonstrated multilocular cystic lesions in the thoracic spine. Histologically the tumor consisted of solid, sheet-like components and branching papillary structures, and immunohistochemistry demonstrated positive reactivity for epithelial membrane antigen, cytokeratins (7, AE1/3, CAM5.2), E-cadherin and transthyretin, and negativity for GFAP, S-100 protein, synaptophysin and neurofilament. These histological and immunohistochemical findings appeared to be unique, and were not compatible with the features of classical ependymoma or choroid plexus papilloma. The clinical behavior, characterized by relatively rapid tumor regrowth after surgical resection and a relatively high MIB-1 labeling index, suggest that this tumor might have had moderate malignant potential. This pediatric case appears to be particularly informative with regard to the tumor biology or tumorigenesis of intramedullary spinal cord tumor with unusual solid-cystic and papillary features. © 2011 Japanese Society of Neuropathology.

Reaction mechanisms in the organometallic vapor phase epitaxial growth of GaAs

NASA Technical Reports Server (NTRS)

Larsen, C. A.; Buchan, N. I.; Stringfellow, G. B.

1988-01-01

The decomposition mechanisms of AsH3, trimethylgallium (TMGa), and mixtures of the two have been studied in an atmospheric-pressure flow system with the use of D2 to label the reaction products which are analyzed in a time-of-flight mass spectrometer. AsH3 decomposes entirely heterogeneously to give H2. TMGa decomposes by a series of gas-phase steps, involving methyl radicals and D atoms to produce CH3D, CH4, C2H6, and HD. TMGa decomposition is accelerated by the presence of AsH3. When the two are mixed, as in the organometallic vapor phase epitaxial growth of GaAs, both compounds decompose in concert to produce only CH4. A likely model is that of a Lewis acid-base adduct that forms and subsequently eliminates CH4.

Reaction mechanisms in the organometallic vapor phase epitaxial growth of GaAs

NASA Astrophysics Data System (ADS)

Larsen, C. A.; Buchan, N. I.; Stringfellow, G. B.

1988-02-01

The decomposition mechanisms of AsH3, trimethylgallium (TMGa), and mixtures of the two have been studied in an atmospheric-pressure flow system with the use of D2 to label the reaction products which are analyzed in a time-of-flight mass spectrometer. AsH3 decomposes entirely heterogeneously to give H2. TMGa decomposes by a series of gas-phase steps, involving methyl radicals and D atoms to produce CH3D, CH4, C2H6, and HD. TMGa decomposition is accelerated by the presence of AsH3. When the two are mixed, as in the organometallic vapor phase epitaxial growth of GaAs, both compounds decompose in concert to produce only CH4. A likely model is that of a Lewis acid-base adduct that forms and subsequently eliminates CH4.

Parasitic phases at the origin of magnetic moment in BiFeO3 thin films grown by low deposition rate RF sputtering

NASA Astrophysics Data System (ADS)

Mori, Thiago J. A.; Mouls, Caroline L.; Morgado, Felipe F.; Schio, Pedro; Cezar, Júlio C.

2017-09-01

A series of epitaxial BiFeO3 thin films has been grown under high partial pressure in a pure O2 atmosphere, which leads to a low deposition rate. The samples grown under these conditions have presented an evolution of the quality of the epitaxy as the deposition temperature increases, however, spurious β- Bi2O3 and supertetragonal BiFeO3 phases are present in the films grown at higher temperatures. The presence of γ- Fe2O3 is reported in one growing condition, and has been attributed to the origin of hysteretic ferromagnetic behavior. A second kind of magnetism, with higher magnetic moment and anhysteretic behaviour, is attributed to the presence of mixed phases of BiFeO3.

High-Quality GaN Epilayers Achieved by Facet-Controlled Epitaxial Lateral Overgrowth on Sputtered AlN/PSS Templates.

PubMed

He, Chenguang; Zhao, Wei; Zhang, Kang; He, Longfei; Wu, Hualong; Liu, Ningyang; Zhang, Shan; Liu, Xiaoyan; Chen, Zhitao

2017-12-13

It is widely believed that the lack of high-quality GaN wafers severely hinders the progress in GaN-based devices, especially for defect-sensitive devices. Here, low-cost AlN buffer layers were sputtered on cone-shaped patterned sapphire substrates (PSSs) to obtain high-quality GaN epilayers. Without any mask or regrowth, facet-controlled epitaxial lateral overgrowth was realized by metal-organic chemical vapor deposition. The uniform coating of the sputtered AlN buffer layer and the optimized multiple modulation guaranteed high growth selectivity and uniformity of the GaN epilayer. As a result, an extremely smooth surface was achieved with an average roughness of 0.17 nm over 3 × 3 μm 2 . It was found that the sputtered AlN buffer layer could significantly suppress dislocations on the cones. Moreover, the optimized three-dimensional growth process could effectively promote dislocation bending. Therefore, the threading dislocation density (TDD) of the GaN epilayer was reduced to 4.6 × 10 7 cm -2 , which is about an order of magnitude lower than the case of two-step GaN on the PSS. In addition, contamination and crack in the light-emitting diode fabricated on the obtained GaN were also effectively suppressed by using the sputtered AlN buffer layer. All of these advantages led to a high output power of 116 mW at 500 mA with an emission wavelength of 375 nm. This simple, yet effective growth technique is believed to have great application prospects in high-performance TDD-sensitive optoelectronic and electronic devices.

Molecular beam epitaxially grown copper indium diselenide and copper gallium diselenide films

NASA Astrophysics Data System (ADS)

Yoon, Seokhyun

2005-12-01

To eliminate the influence of grain boundaries, CuInSe2 (CIS) and CuGaSe2 (CGS) films were grown on (100) GaAs wafers. The effects of Cu to III metal ratio and dosing with Na on the growth mode and defect properties were studied at two growth temperatures. The impact of post-annealing in Se on the defect structure of CGS film was also studied. Two-dimensional simulations were used to better understand the role of grain boundary on cell performance. For growth at 360°C, the In-rich CIS films were polycrystalline, whereas the Cu-rich CIS films were epitaxial exhibiting a Stranski-Krastanov (S-K) growth mode. It is proposed that a Cu-Se secondary phase enhances the mobility of adatoms, allowing epitaxial growth to a critical thickness, at which point segregation at the nucleation sites became faster the rate of growth. Island structures, embedded in a matrix region, were oriented along the [01-1] directed edges with surface undulations apparent on the matrix surface with dominant {112} crystal planes. At the higher growth temperature of 464°C, the CIS films grew epitaxially without the need of a Cu-Se phase. Both CIS films grown at low and high temperatures were nearly relaxed. The segregation of epitaxial Cu1.5Se was also observed in the Cu-rich, Na-dosed CIS film, which is attributed to a surfactant effect of Na. At a growth temperature of 438°C, CGS films showed a S-K growth mode and nearly pseudomorphic growth. Hemispherical islands with twins were observed in the Ga-rich CGS films and epitaxial Cu1.5Se phase were identified in the top region of the island structure. From the PL analysis of Cu-rich, Na-dosed CGS film after Se-annealing, a new defect level located 20 meV above the valence band edge was identified as NaGa acceptor state. Two-dimensional simulation of the impact of grain boundaries on device performance showed that the short circuit current decreases sharply along with the other device parameters below a critical grain size due to the complete depletion. The increase of dark saturation current with decreasing grain size was predicted due to an increase in the recombination current.

Localized melt-scan strategy for site specific control of grain size and primary dendrite arm spacing in electron beam additive manufacturing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Raghavan, Narendran; Simunovic, Srdjan; Dehoff, Ryan

In addition to design geometry, surface roughness, and solid-state phase transformation, solidification microstructure plays a crucial role in controlling the performance of additively manufactured components. Crystallographic texture, primary dendrite arm spacing (PDAS), and grain size are directly correlated to local solidification conditions. We have developed a new melt-scan strategy for inducing site specific, on-demand control of solidification microstructure. We were able to induce variations in grain size (30 μm–150 μm) and PDAS (4 μm - 10 μm) in Inconel 718 parts produced by the electron beam additive manufacturing system (Arcam®). A conventional raster melt-scan resulted in a grain size ofmore » about 600 μm. The observed variations in grain size with different melt-scan strategies are rationalized using a numerical thermal and solidification model which accounts for the transient curvature of the melt pool and associated thermal gradients and liquid-solid interface velocities. The refinement in grain size at high cooling rates (>104 K/s) is also attributed to the potential heterogeneous nucleation of grains ahead of the epitaxially growing solidification front. The variation in PDAS is rationalized using a coupled numerical-theoretical model as a function of local solidification conditions (thermal gradient and liquid-solid interface velocity) of the melt pool.« less

A Kinetic Model for GaAs Growth by Hydride Vapor Phase Epitaxy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schulte, Kevin L.; Simon, John; Jain, Nikhil

2016-11-21

Precise control of the growth of III-V materials by hydride vapor phase epitaxy (HVPE) is complicated by the fact that the growth rate depends on the concentrations of nearly all inputs to the reactor and also the reaction temperature. This behavior is in contrast to metalorganic vapor phase epitaxy (MOVPE), which in common practice operates in a mass transport limited regime where growth rate and alloy composition are controlled almost exclusively by flow of the Group III precursor. In HVPE, the growth rate and alloy compositions are very sensitive to temperature and reactant concentrations, which are strong functions of themore » reactor geometry. HVPE growth, particularly the growth of large area materials and devices, will benefit from the development of a growth model that can eventually be coupled with a computational fluid dynamics (CFD) model of a specific reactor geometry. In this work, we develop a growth rate law using a Langmuir-Hinshelwood (L-H) analysis, fitting unknown parameters to growth rate data from the literature that captures the relevant kinetic and thermodynamic phenomena of the HVPE process. We compare the L-H rate law to growth rate data from our custom HVPE reactor, and develop quantitative insight into reactor performance, demonstrating the utility of the growth model.« less

Combined strain and composition-induced effects in the metal-insulator transition of epitaxial VO2 films

NASA Astrophysics Data System (ADS)

Théry, V.; Boulle, A.; Crunteanu, A.; Orlianges, J. C.

2017-12-01

The role of epitaxial strain, thermal strain, and bulk (strain-free) lattice parameters in the metal-insulator transition (MIT) and the structural phase transition (SPT) of VO2 is investigated for the case of epitaxial films grown on (001)-oriented TiO2 substrates. Temperature-resolved X-ray reciprocal space mapping has been used to determine the absolute state of strain as well as the bulk lattice parameters of VO2 at 100 °C. For the thinnest film (15 nm), the state of strain is dominated by the film/substrate lattice mismatch yielding an in-plane tensile strain which, in turn, shifts both the MIT and the SPT towards lower temperatures. Conversely, for the thickest film (100 nm), the epitaxial strain is relaxed, so that the state of strain is dominated by the VO2/TiO2 thermal expansion mismatch which is responsible for a compressive in-plane strain. In all cases, a swelling of the strain-free VO2 unit-cell is observed which indicates the presence of interfacial oxygen vacancies and/or Ti diffusion into the VO2 films. The presence of oxygen vacancies stabilizes the metallic rutile phase and counterbalances the action of thermal strain on the MIT and the SPT and degrades the electric properties for the thinnest film. For the thickest film, the resistivity ratio is 6.4 × 104.

Development of epitaxial Al xSc 1-xN for artificially structured metal/semiconductor superlattice metamaterials

DOE PAGES

Sands, Timothy D.; Stach, Eric A.; Saha, Bivas; ...

2015-02-01

Epitaxial nitride rocksalt metal/semiconductor superlattices are emerging as a novel class of artificially structured materials that have generated significant interest in recent years for their potential application in plasmonic and thermoelectric devices. Though most nitride metals are rocksalt, nitride semiconductors in general have hexagonal crystal structure. We report rocksalt aluminum scandium nitride (Al,Sc)N alloys as the semiconducting component in epitaxial rocksalt metal/semiconductor superlattices. The Al xSc 1-xN alloys when deposited directly on MgO substrates are stabilized in a homogeneous rocksalt (single) phase when x < 0.51. Employing 20 nm TiN as a seed layer on MgO substrates, the homogeneity rangemore » for stabilizing the rocksalt phase has been extended to x < 0.82 for a 120 nm film. The rocksalt Al xSc 1-xN alloys show moderate direct bandgap bowing with a bowing parameter, B = 1.41 ± 0.19 eV. The direct bandgap of metastable rocksalt AlN is extrapolated to be 4.70 ± 0.20 eV. The tunable lattice parameter, bandgap, dielectric permittivity, and electronic properties of rocksalt Al xSc 1-xN alloys enable high quality epitaxial rocksalt metal/Al xSc 1-xN superlattices with a wide range of accessible metamaterials properties.« less

Ambiguous Role of Growth-Induced Defects on the Semiconductor-to-Metal Characteristics in Epitaxial VO2/TiO2 Thin Films.

PubMed

Mihailescu, Cristian N; Symeou, Elli; Svoukis, Efthymios; Negrea, Raluca F; Ghica, Corneliu; Teodorescu, Valentin; Tanase, Liviu C; Negrila, Catalin; Giapintzakis, John

2018-04-25

Controlling the semiconductor-to-metal transition temperature in epitaxial VO 2 thin films remains an unresolved question both at the fundamental as well as the application level. Within the scope of this work, the effects of growth temperature on the structure, chemical composition, interface coherency and electrical characteristics of rutile VO 2 epitaxial thin films grown on TiO 2 substrates are investigated. It is hereby deduced that the transition temperature is lower than the bulk value of 340 K. However, it is found to approach this value as a function of increased growth temperature even though it is accompanied by a contraction along the V 4+ -V 4+ bond direction, the crystallographic c-axis lattice parameter. Additionally, it is demonstrated that films grown at low substrate temperatures exhibit a relaxed state and a strongly reduced transition temperature. It is suggested that, besides thermal and epitaxial strain, growth-induced defects may strongly affect the electronic phase transition. The results of this work reveal the difficulty in extracting the intrinsic material response to strain, when the exact contribution of all strain sources cannot be effectively determined. The findings also bear implications on the limitations in obtaining the recently predicted novel semi-Dirac point phase in VO 2 /TiO 2 multilayer structures.

Subtotal resection of vestibular schwannoma: Evaluation with Ki-67 measurement, magnetic resonance imaging, and long-term observation

PubMed Central

Iannella, Giannicola; de Vincentiis, Marco; Di Gioia, Cira; Carletti, Raffaella; Pasquariello, Benedetta; Manno, Alessandra; Angeletti, Diletta; Savastano, Ersilia; Magliulo, Giuseppe

2017-01-01

Purpose The aim of this study was to compare the postoperative clinical and radiological data of patients with vestibular schwannomas who were initially managed by near total resection (NTR) or subtotal resection (STR). The Ki-67 analysis results were compared with tumor regrowth to determine the presence of a correlation between this proliferative index and postoperative tumor regrowth. Study Design Seventeen adult patients (7 male, 10 female) were retrospectively reviewed. Nine (52.9%) and eight (47.1%) patients underwent NTR and STR, respectively. Postoperative clinical and radiological data associated with vestibular schwannoma growth were compared with the Ki-67 immunohistochemical analysis results. Results Evidence of clinically significant regrowth was observed in four (23.5%) patients. Patients who underwent NTR had a lower rate/incidence of tumor regrowth than did patients who underwent STR. Patients with a higher Ki-67 index had the highest tumor regrowth rates. Conclusions Our study indicates that assessment of the Ki-67 index may be useful for determining the probability of regrowth of vestibular schwannomas when only partial removal is accomplished. PMID:28447494

Strain-induced nanostructure of Pb(Mg1/3Nb2/3)O3-PbTiO3 on SrTiO3 epitaxial thin films with low PbTiO3 concentration

NASA Astrophysics Data System (ADS)

Kiguchi, Takanori; Fan, Cangyu; Shiraishi, Takahisa; Konno, Toyohiko J.

2017-10-01

The singularity of the structure in (1 - x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-xPT) (x = 0-50 mol %) epitaxial thin films of 100 nm thickness was investigated from the viewpoint of the localized residual strain in the nanoscale. The films were deposited on SrTiO3 (STO) (001) single-crystal substrates by chemical solution deposition (CSD) using metallo-organic decomposition (MOD) solutions. X-ray and electron diffraction patterns revealed that PMN-xPT thin films included a single phase of the perovskite-type structure with the cube-on-cube orientation relationship between PMN-xPT and STO: (001)Film ∥ (001)Sub, [100]Film ∥ [100]Sub. X-ray reciprocal space maps showed an in-plane tensile strain in all the compositional ranges considered. Unit cells in the films were strained from the rhombohedral (pseudocubic) (R) phase to a lower symmetry crystal system, the monoclinic (MB) phase. The morphotropic phase boundary (MPB) that split the R and tetragonal (T) phases was observed at x = 30-35 for bulk crystals of PMN-xPT, whereas the strain suppressed the transformation from the R phase to the T phase in the films up to x = 50. High-angle annular dark field-scanning transmission electron microscopy (HAADF-STEM) analysis and its related local strain analysis revealed that all of the films have a bilayer morphology. The nanoscale strained layer formed only above the film/substrate semi-coherent interface. The misfit dislocations generated the localized and periodic strain fields deformed the unit cells between the dislocation cores from the R to an another type of the monoclinic (MA) phase. Thus, the singular and localized residual strains in the PMN-xPT/STO (001) epitaxial thin films affect the phase stability around the MPB composition and result in the MPB shift phenomena.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gries, K. I.; Vogel, S.; Straubinger, R.

The self-assembled formation of ordered, vertically stacked rocksalt/wurtzite Mg{sub x}Zn{sub 1−x}O heterostructures by planar phase separation is shown. These heterostructures form quasi “natural” two-dimensional hetero-interfaces between the different phases upon annealing of MgO-oversaturated wurtzite Mg{sub x}Zn{sub 1−x}O layers grown by plasma-assisted molecular beam epitaxy on c-plane sapphire substrates. The optical absorption spectra show a red shift simultaneous with the appearance of a cubic phase upon annealing at temperatures between 900 °C and 1000 °C. Transmission electron microscopy reveals that these effects are caused by phase separation leading to the formation of a vertically ordered rock salt/wurtzite heterostructures. To explain these observations, wemore » suggest a phase separation epitaxy model that considers this process being initiated by the formation of a cubic (Mg,Zn)Al{sub 2}O{sub 4} spinel layer at the interface to the sapphire substrate, acting as a planar seed for the epitaxial precipitation of rock salt Mg{sub x}Zn{sub 1−x}O. The equilibrium fraction x of magnesium in the resulting wurtzite (rock salt) layers is approximately 0.15 (0.85), independent of the MgO content of the as-grown layer and determined by the annealing temperature. This model is confirmed by photoluminescence analysis of the resulting layer systems after different annealing temperatures. In addition, we show that the thermal annealing process results in a significant reduction in the density of edge- and screw-type dislocations, providing the possibility to fabricate high quality templates for quasi-homoepitaxial growth.« less

Superconducting Ga/GaSe layers grown by van der Waals epitaxy

NASA Astrophysics Data System (ADS)

Desrat, W.; Moret, M.; Briot, O.; Ngo, T.-H.; Piot, B. A.; Jabakhanji, B.; Gil, B.

2018-04-01

We report on the growth of GaSe films by molecular beam epitaxy on both (111)B GaAs and sapphire substrates. X-ray diffraction reveals the perfect crystallinity of GaSe with the c-axis normal to the substrate surface. The samples grown under Ga rich conditions possess an additional gallium film on top of the monochalcogenide layer. This metallic film shows two normal-to-superconducting transitions which are detected at T c ≈ 1.1 K and 6.0 K. They correspond likely to the β and α-phases of gallium in the form of bulk and droplets respectively. Our results demonstrate that van der Waals epitaxy can lead to future high quality hybrid superconductor/monochalcogenide heterostructures.

Microstructure and Optical Properties of Nonpolar m-Plane GaN Films Grown on m-Plane Sapphire by Hydride Vapor Phase Epitaxy

NASA Astrophysics Data System (ADS)

Wei, Tongbo; Duan, Ruifei; Wang, Junxi; Li, Jinmin; Huo, Ziqiang; Yang, Jiankun; Zeng, Yiping

2008-05-01

Thick nonpolar (1010) GaN layers were grown on m-plane sapphire substrates by hydride vapor phase epitaxy (HVPE) using magnetron sputtered ZnO buffers, while semipolar (1013) GaN layers were obtained by the conventional two-step growth method using the same substrate. The in-plane anisotropic structural characteristics and stress distribution of the epilayers were revealed by high resolution X-ray diffraction and polarized Raman scattering measurements. Atomic force microscopy (AFM) images revealed that the striated surface morphologies correlated with the basal plane stacking faults for both (1010) and (1013) GaN films. The m-plane GaN surface showed many triangular-shaped pits aligning uniformly with the tips pointing to the c-axis after etching in boiled KOH, whereas the oblique hillocks appeared on the semipolar epilayers. In addition, the dominant emission at 3.42 eV in m-plane GaN films displayed a red shift with respect to that in semipolar epilayers, maybe owing to the different strain states present in the two epitaxial layers.

Joining Chemical Pressure and Epitaxial Strain to Yield Y-doped BiFeO3 Thin Films with High Dielectric Response

PubMed Central

Scarisoreanu, N. D.; Craciun, F.; Birjega, R.; Ion, V.; Teodorescu, V. S.; Ghica, C.; Negrea, R.; Dinescu, M.

2016-01-01

BiFeO3 is one of the most promising multiferroic materials but undergoes two major drawbacks: low dielectric susceptibility and high dielectric loss. Here we report high in-plane dielectric permittivity (ε’ ∼2500) and low dielectric loss (tan δ < 0.01) obtained on Bi0.95Y0.05FeO3 films epitaxially grown on SrTiO3 (001) by pulsed laser deposition. High resolution transmission electron microscopy and geometric phase analysis evidenced nanostripe domains with alternating compressive/tensile strain and slight lattice rotations. Nanoscale mixed phase/domain ensembles are commonly found in different complex materials with giant dielectric/electromechanical (ferroelectric/ relaxors) or magnetoresistance (manganites) response. Our work brings insight into the joined role of chemical pressure and epitaxial strain on the appearance of nanoscale stripe structure which creates conditions for easy reorientation and high dielectric response, and could be of more general relevance for the field of materials science where engineered materials with huge response to external stimuli are a highly priced target. PMID:27157090

Phase formation and morphological stability of ultrathin Ni-Co-Pt silicide films formed on Si(100)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, Peng; Wu, Dongping, E-mail: dongpingwu@fudan.edu.cn; Kubart, Tomas

Ultrathin Ni, Co, and Pt films, each no more than 4 nm in thickness, as well as their various combinations are employed to investigate the competing growth of epitaxial Co{sub 1-y}Ni{sub y}Si{sub 2} films against polycrystalline Pt{sub 1-z}Ni{sub z}Si. The phase formation critically affects the morphological stability of the resulting silicide films, with the epitaxial films being superior to the polycrystalline ones. Any combination of those metals improves the morphological stability with reference to their parent individual metal silicide films. When Ni, Co, and Pt are all included, the precise initial location of Pt does little to affect the final phasemore » formation in the silicide films and the epitaxial growth of Co{sub 1-x}Ni{sub x}Si{sub 2} films is always perturbed, in accordance to thermodynamics that shows a preferential formation of Pt{sub 1-z}Ni{sub z}Si over that of Co{sub 1-y}Ni{sub y}Si{sub 2}.« less

Manganese-calcium intermixing facilitates heteroepitaxial growth at the 10 1 ¯ 4 calcite-water interface

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, Man; Riechers, Shawn L.; Ilton, Eugene S.

2017-10-01

In situ atomic force microscopy (AFM) measurements were performed to probe surface precipitates that formed on the (10-14) surface of calcite (CaCO3) single crystals following reaction with Mn2+-bearing aqueous solutions with a range of initial concentrations. Three-dimensional epitaxial islands were observed to precipitate and grow on the surfaces and in situ time-sequenced measurements demonstrated that their growth rates were commensurate with those obtained for epitaxial islands formed on calcite crystals reacted with Cd2+-bearing aqueous solutions of the same range in supersaturation with respect to the pure metal carbonate phase. This finding was unexpected as rhodochrosite (MnCO3) and calcite display amore » 10% lattice mismatch, based on the area of their (10-14) surface unit cells, whereas the lattice mismatch is only 4% for otavite (CdCO3) and calcite. Coatings of varying thicknesses were therefore synthesized by reacting calcite single crystals with calcite-equilibrated aqueous solutions with concentrations of up to 250 µM MnCl2 and analyzed to determine the composition of the surface precipitates. Ex situ X-ray photoelectron spectroscopy (XPS), scanning transmission electron microscopy (STEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), X-ray reflectivity (XRR), and AFM measurements of the reacted crystals demonstrated the formation of an epitaxial (Mn,Ca)CO3 solid solution with a spatially complex composition atop the calcite surface, whereby the first few nanometers were rich in Ca and the Mn content increased with distance from the original calcite surface, culminating in a topmost region of almost pure MnCO3 for the thickest coatings. These findings explain the measured growth rates (the effective lattice mismatch was much smaller than nominal mismatch) and highlight the strong influence played by the substrate on the composition of surface precipitates in aqueous conditions.« less

Heterotrophic bacteria in drinking water distribution system: a review.

PubMed

Chowdhury, Shakhawat

2012-10-01

The microbiological quality of drinking water in municipal water distribution systems (WDS) depends on several factors. Free residual chlorine and/or chloramines are typically used to minimize bacterial recontamination and/or regrowth in WDS. Despite such preventive measures, regrowth of heterotrophic (HPC) and opportunistic bacteria in bulk water and biofilms has yet to be controlled completely. No approach has shown complete success in eliminating biofilms or HPC bacteria from bulk water and pipe surfaces. Biofilms can provide shelter for pathogenic bacteria and protect these bacteria from disinfectants. Some HPC bacteria may be associated with aesthetic and non-life threatening diseases. Research to date has achieved important success in understanding occurrence and regrowth of bacteria in bulk water and biofilms in WDS. To achieve comprehensive understanding and to provide efficient control against bacteria regrowth, future research on bacteria regrowth dynamics and their implications is warranted. In this study, a review was performed on the literature published in this area. The findings and limitations of these papers are summarized. Occurrences of bacteria in WDS, factors affecting bacteria regrowth in bulk water and biofilms, bacteria control strategies, sources of nutrients, human health risks from bacterial exposure, modelling of bacteria regrowth and methods of bacteria sampling and detection and quantification are investigated. Advances to date are noted, and future research needs are identified. Finally, research directions are proposed to effectively control HPC and opportunistic bacteria in bulk water and biofilms in WDS.

Study of thin film growth kinetics of homoepitaxy by molecular beam epitaxy and pulsed laser deposition

NASA Astrophysics Data System (ADS)

Shin, Byungha

This thesis presents an extensive study of the growth kinetics during low temperature homoepitaxy by Molecular Beam Epitaxy (MBE) and Pulsed Laser Deposition (PLD) of our model system Ge(001). The range of the study covers from the sub-monolayer (sub-ML) regime to the later stage where film thickness amounts to a few thousand MLs; it also covers epitaxial breakdown in which epitaxial growth is no longer sustained and the growing phase becomes amorphous. First, we have conducted a systematic investigation of the phase shift of the RHEED intensity oscillations during Ge(001) homoepitaxy MBE for a wide range of diffraction conditions. We conclude that the phase shift is caused by the overlap of the specular spot and the Kikuchi features, in contrast to models involving dynamical scattering theory for the phase shift. We have studied the sub-ML growth of Ge(001) homoepitaxy by MBE at low temperatures using RHEED intensity oscillations obtained for a range of low incidence angles where the influence of the dynamical nature of electron scattering such as the Kikuchi features is minimized. We have developed a new model for RHEED specular intensity that includes the diffuse scattering off surface steps and the layer interference between terraces of different heights using the kinematic approximation. By using the model to interpret the measured RHEED intensity, we find the evolution of the coverage of the first 2--3 layers, from which we infer the ES barrier height to be 0.077 +/- 0.014 eV. Finally, using a dual MBE-PLD UHV chamber, we have conducted experiments under identical thermal, background, and surface preparation conditions to compare Ge(001) homoepitaxial growth morphology in PLD and MBE at low temperatures. To isolate the effect of kinetic energy of depositing species during PLD, we varied the average kinetic energy: ˜450 eV in PLD-HKE, ˜300 eV in PLD-LKE, and <1 eV in PLD-TH. At 150°C, we find that in PLD-LKE and in MBE the film morphology evolves in a similar fashion: initially irregularly shaped mounds form, followed by pyramidal mounds with edges of the square-base along <100> directions. The areal feature density is higher for PLD films than for MBE films grown at the same average growth rate and temperature. Furthermore, the dependence upon film thickness of roughness and feature separation differ for PLD and MBE. The thicknesses at which epitaxial breakdown occurs are ranked in the order PLD-HKE > PLD-LKE > MBE. At 100°C, PLD-LKE and MBE follow the same morphology evolution as at 150°C. The epitaxial thicknesses are ranked in the order PLD-LKE > MBE > PLD-TH; additionally, the surface is smoother in PLD-LKE than in MBE. Together, these results convincingly demonstrate that the enhancement of epitaxial growth---the reduction in roughness and the delay of epitaxial breakdown---are due to the kinetic energy of depositing species in PLD. To study the relaxation behavior, we varied the repetition rate from 5 Hz to 20 Hz in PLD-LKE at 100°C. However, we find no systematic effect on surface roughness by varying the repetition rate. This result is consistent with an investigation on the sub-ML growth regime of PLD-LKE by monitoring the intensity variations of the RHEED specular spot.

Silicon Nanosheets: Crossover between Multilayer Silicene and Diamond-like Growth Regime.

PubMed

Grazianetti, Carlo; Cinquanta, Eugenio; Tao, Li; De Padova, Paola; Quaresima, Claudio; Ottaviani, Carlo; Akinwande, Deji; Molle, Alessandro

2017-03-28

The structural and electronic properties of nanoscale Si epitaxially grown on Ag(111) can be tuned from a multilayer silicene phase, where the constitutive layers incorporate a mixed sp 2 /sp 3 bonding, to other ordinary Si phases, such as amorphous and diamond-like Si. Based on comparative scanning tunneling microscopy and Raman spectroscopy investigations, a key role in determining the nanoscale Si phase is played by the growth temperature of the epitaxial deposition on Ag(111) substrate and the presence or absence of a single-layer silicene as a seed for the successive growth. Furthermore, when integrated into a field-effect transistor device, multilayer silicene exhibits a characteristic ambipolar charge carrier transport behavior that makes it strikingly different from other conventional Si channels and suggestive of a Dirac-like character of the electronic bands of the crystal. These findings spotlight the interest in multilayer silicene as a different nanoscale Si phase for advanced nanotechnology applications such as ultrascaled nanoelectronics and nanomembranes, as well as for fundamental exploration of quantum properties.

Formation and reconstruction of Se nanoislands at the surface of thin epitaxial ZnSe layers grown on GaAs substrates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kozlovskiy, V. I.; Krivobok, V. S., E-mail: krivobok@lebedev.ru; Kuznetsov, P. I.

2016-05-15

Strained epitaxial ZnSe layers are grown on GaAs substrates by the method of vapor-phase epitaxy from metal-organic compounds. It is found that Se nanoislands with a density of 10{sup 8} to 10{sup 9} cm{sup –2} are formed at the surface of such layers. It is established that an increase in the size of Se islands and a decrease in their density take place after completion of growth. Annealing in a H{sub 2} atmosphere at a temperature higher than 260°C leads to the disappearance of Se islands and to a decrease in the surface roughness. It is shown that annealing doesmore » not lead to deterioration of the structural perfection of the epitaxial ZnSe films; rather, annealing gives rise to a decrease in the intensity of impurity–defect luminescence and to an increase in the intensity of intrinsic radiation near the bottom of the exciton band.« less

Molecular Beam Epitaxial Growth of Iron Nitrides on Zinc-Blende Gallium Nitride(001)

NASA Astrophysics Data System (ADS)

Pak, Jeongihm; Lin, Wenzhi; Chinchore, Abhijit; Wang, Kangkang; Smith, Arthur R.

2008-03-01

Iron nitrides are attractive materials for their high magnetic moments, corrosion, and oxidation resistance. We present the successful epitaxial growth of iron nitride on zinc-blende gallium nitride (c-GaN) in order to develop a novel magnetic transition metal nitride/semiconductor system. First, GaN is grown on magnesium oxide (MgO) substrates having (001) orientation using rf N2-plasma molecular beam epitaxy. Then we grow FeN at substrate temperature of ˜ 210 ^oC up to a thickness of ˜ 10.5 nm. In-situ reflection high-energy electron diffraction (RHEED) is used to monitor the surface during growth. Initial results suggest that the epitaxial relationship is FeN[001] || GaN[001] and FeN[100] || GaN[100]. Work in progress is to investigate the surface using in-situ scanning tunneling microscopy (STM) to reveal the surface structure at atomic scale, as well as to explore more Fe-rich magnetic phases.

The stability of the epitaxially introduced metastable metallic structures of thin layers and multilayers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cadeville, M.C.

Among the very large number of metallic thin films, sandwiches and multilayers which have been elaborated by epitaxy on various single crystalline substrates during the last decade, few new structures are reported. Limiting to the case of 3d metals, one finds with a great confidence bcc Cobalt, possibly bee Nickel and a non-compact hexagonal (hp) iron. Moreover structures existing at high temperature under ambient pressure are epitaxially stabilized at room temperature (RT) like fcc Cobalt, fcc Iron, fcc and bcc Manganese. The hcp iron which is stable under high pressure at RT would not be epitaxially stabilized at ambient pressuremore » conversely to first findings. The critical thickness of the metastable phase is generally limited to some monolayers in thin films, being slightly increased in sandwiches or multilayers, even if the phenomenological wetting criterion to build superlattices is not satisfied. No increased magnetic moment has been found up to now in the expanded lattices, contrary to band structure calculation predictions. 56 refs.« less

Induced Superconductivity and Engineered Josephson Tunneling Devices in Epitaxial (111)-Oriented Gold/Vanadium Heterostructures.

PubMed

Wei, Peng; Katmis, Ferhat; Chang, Cui-Zu; Moodera, Jagadeesh S

2016-04-13

We report a unique experimental approach to create topological superconductors by inducing superconductivity into epitaxial metallic thin film with strong spin-orbit coupling. Utilizing molecular beam epitaxy technique under ultrahigh vacuum conditions, we are able to achieve (111) oriented single phase of gold (Au) thin film grown on a well-oriented vanadium (V) s-wave superconductor film with clean interface. We obtained atomically smooth Au thin films with thicknesses even down to below a nanometer showing near-ideal surface quality. The as-grown V/Au bilayer heterostructure exhibits superconducting transition at around 3.9 K. Clear Josephson tunneling and Andreev reflection are observed in S-I-S tunnel junctions fabricated from the epitaxial bilayers. The barrier thickness dependent tunneling and the associated subharmonic gap structures (SGS) confirmed the induced superconductivity in Au (111), paving the way for engineering thin film heterostructures based on p-wave superconductivity and nano devices exploiting Majorana Fermions for quantum computing.

Epitaxial Ni-Mn-Ga-Co thin films on PMN-PT substrates for multicaloric applications

NASA Astrophysics Data System (ADS)

Schleicher, B.; Niemann, R.; Diestel, A.; Hühne, R.; Schultz, L.; Fähler, S.

2015-08-01

Multicaloric stacks consisting of a magnetocaloric film on a piezoelectric substrate promise improved caloric properties as the transition temperature can be controlled by both magnetic and electric fields. We present epitaxially grown magnetocaloric Ni-Mn-Ga-Co thin films on ferroelectric Pb(Mg1/3Nb2/3)0.72Ti0.28O3 substrates. Structure and microstructure of two samples, being in the austenitic and martensitic state at room temperature, are investigated by X-ray diffraction in two- and four-circle geometry and by atomic force microscopy. In addition, high temperature magnetometry was performed on the latter sample. The combination of these methods allows separating the influence of epitaxial growth and martensitic transformation. A preferential alignment of twin boundaries is observed already in the as-deposited state, which indicates the presence of prestress, without applying an electric field to the substrate. A temperature-magnetic field phase diagram is presented, which demonstrates the inverse magnetocaloric effect of the epitaxial Ni-Mn-Ga-Co film.

Constructing oxide interfaces and heterostructures by atomic layer-by-layer laser molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Lei, Qingyu; Golalikhani, Maryam; Davidson, Bruce A.; Liu, Guozhen; Schlom, Darrell G.; Qiao, Qiao; Zhu, Yimei; Chandrasena, Ravini U.; Yang, Weibing; Gray, Alexander X.; Arenholz, Elke; Farrar, Andrew K.; Tenne, Dmitri A.; Hu, Minhui; Guo, Jiandong; Singh, Rakesh K.; Xi, Xiaoxing

2017-12-01

Advancements in nanoscale engineering of oxide interfaces and heterostructures have led to discoveries of emergent phenomena and new artificial materials. Combining the strengths of reactive molecular-beam epitaxy and pulsed-laser deposition, we show here, with examples of Sr1+xTi1-xO3+δ, Ruddlesden-Popper phase Lan+1NinO3n+1 (n = 4), and LaAl1+yO3(1+0.5y)/SrTiO3 interfaces, that atomic layer-by-layer laser molecular-beam epitaxy significantly advances the state of the art in constructing oxide materials with atomic layer precision and control over stoichiometry. With atomic layer-by-layer laser molecular-beam epitaxy we have produced conducting LaAlO3/SrTiO3 interfaces at high oxygen pressures that show no evidence of oxygen vacancies, a capability not accessible by existing techniques. The carrier density of the interfacial two-dimensional electron gas thus obtained agrees quantitatively with the electronic reconstruction mechanism.

High Zn Content Single-phase RS-MgZnO Suitable for Solar-blind Frequency Applications

NASA Astrophysics Data System (ADS)

Liang, H. L.; Mei, Z. X.; Liu, Z. L.; Guo, Y.; Azarov, A. Yu.; Kuznetsov, A. Yu.; Hallen, A.; Du, X. L.

2010-11-01

Single-phase rock-salt MgZnO films with high Zn content were successfully fabricated on the templates of MgO (111)/α-sapphire (0001) by radio-frequency plasma assisted molecular beam epitaxy. The influence of growth temperature on epitaxy of MgZnO alloy films was investigated by the combined studies of crystal structures, compositions, and optical properties. It is found that the incorporation of Zn atoms into the rock-salt MgZnO films is greatly enhanced at low temperature, confirmed by in-situ reflection high-energy electron diffraction observations and ex-situ X-ray diffraction characterization. Zn fraction in the single-phase rock-salt Mg0.53Zn0.47O film was determined by Rutherford backscattering spectrometry. Optical properties of the films were investigated by transmittance spectroscopy and reflectance spectroscopy, both of which demonstrate the solar-blind band gap and its dependence on Zn content.

Influences of misfit strains on liquid phase heteroepitaxial growth

NASA Astrophysics Data System (ADS)

Lu, Yanli; Peng, Yingying; Yu, Genggeng; Chen, Zheng

2017-10-01

Influences of misfit strains with different signs on liquid phase heteroepitaxial growth are studied by binary phase field crystal model. It is amazing to find that double islands are formed because of lateral and vertical separation. The morphological evolution of epitaxial layer depends on signs of misfit strains. The maximum atomic layer thickness of double islands under negative misfit strain is larger than that of under positive misfit strain at the same evolutional time, and size differences between light and dark islands is much smaller under negative misfit strain than that of under positive misfit strain. In addition, concentration field and density field approximately have similar variational law along x direction under the same misfit strain but show opposite variational trend under misfit strains with different signs. Generally, free energy of epitaxial growth systems keeps similar variational trend under misfit strains with different signs.

Liquid-phase explosive crystallization of electron-beam-evaporated a-Si films induced by flash lamp annealing

NASA Astrophysics Data System (ADS)

Ohdaira, Keisuke; Matsumura, Hideki

2013-01-01

We succeed in the formation of micrometer-order-thick polycrystalline silicon (poly-Si) films through the flash-lamp-induced liquid-phase explosive crystallization (EC) of precursor a-Si films prepared by electron-beam (EB) evaporation. The velocity of the explosive crystallization (vEC) is estimated to be ˜14 m/s, which is close to the velocity of the liquid-phase epitaxy (LPE) of Si at a temperature around the melting point of a-Si of 1418 K. Poly-Si films formed have micrometer-order-long grains stretched along a lateral crystallization direction, and X-ray diffraction (XRD) and electron diffraction pattern measurements reveal that grains in poly-Si films tend to have a particular orientation. These features are significantly different from our previous results: the formation of poly-Si films containing randomly-oriented 10-nm-sized fine grains formed from a-Si films prepared by catalytic chemical vapor deposition (Cat-CVD) or sputtering. One possible reason for the emergence of a different EC mode in EB-evaporated a-Si films is the suppression of solid-phase nucleation (SPN) during Flash Lamp Annealing (FLA) due to tensile stress which precursor a-Si films originally hold. Poly-Si films formed from EB-evaporated a-Si films would contribute to the realization of high-efficiency thin-film poly-Si solar cells because of large and oriented grains.

Metal organic vapour-phase epitaxy growth of GaN wires on Si (111) for light-emitting diode applications

PubMed Central

2013-01-01

GaN wires are grown on a Si (111) substrate by metal organic vapour-phase epitaxy on a thin deposited AlN blanket and through a thin SiNx layer formed spontaneously at the AlN/Si interface. N-doped wires are used as templates for the growth of core-shell InGaN/GaN multiple quantum wells coated by a p-doped shell. Standing single-wire heterostructures are connected using a metallic tip and a Si substrate backside contact, and the electroluminescence at room temperature and forward bias is demonstrated at 420 nm. This result points out the feasibility of lower cost nitride-based wires for light-emitting diode applications. PMID:23391377

Highly resistive C-doped hydride vapor phase epitaxy-GaN grown on ammonothermally crystallized GaN seeds

NASA Astrophysics Data System (ADS)

Iwinska, Malgorzata; Piotrzkowski, Ryszard; Litwin-Staszewska, Elzbieta; Sochacki, Tomasz; Amilusik, Mikolaj; Fijalkowski, Michal; Lucznik, Boleslaw; Bockowski, Michal

2017-01-01

GaN crystals were grown by hydride vapor phase epitaxy (HVPE) and doped with C. The seeds were high-structural-quality ammonothermally crystallized GaN. The grown crystals were highly resistive at 296 K and of high structural quality. High-temperature Hall effect measurements revealed p-type conductivity and a deep acceptor level in the material with an activation energy of 1 eV. This is in good agreement with density functional theory calculations based on hybrid functionals as presented by the Van de Walle group. They obtained an ionization energy of 0.9 eV when C was substituted for N in GaN and acted as a deep acceptor.

Producible Alternative to CdTe for Epitaxy (PACE-2) of LWIR HgCdTe

DTIC Science & Technology

1984-01-01

esmv and .de~aty "p bisto momnberl isrepor cover the progre made toward the achievenientof device quality LWIR HgCdTe on an alternate substrte...initial phase of the research program en- titled, _Producible Alternative to CdTe for Epitaxyý(PACE-2) of LWIR HgCJie". Also described are alternate...objective of this program is the demonstration of the feasibility of PACE-2 technology through fabrication and evaluation of multi- plexed LWIR hybrid

Annual Report on Electronics Research at the University of Texas at Austin

DTIC Science & Technology

1993-02-14

Order Phase Transition in a Laser Threshold," AppI. Phys. Lett. 60 3081-3083 (22 June, 1992). 16. K. Sadra and B.G. Streetman, "’The Coupled Hole... beam epitaxy (MBE) to grow stacks of very high quality epitaxial layers. In order to achieve high reflectiviry, both the thickness and composition of...shifts in intense femtosecond laser pulses." Journal of the Optical Society of America B 9, 2032-2040 (1992). II. LIST OF CONFERENCE PROCEEDINGS

Overcoming Ehrlich-Schwöbel barrier in (1 1 1)A GaAs molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Ritzmann, Julian; Schott, Rüdiger; Gross, Katherine; Reuter, Dirk; Ludwig, Arne; Wieck, Andreas D.

2018-01-01

In this work, we first study the effect of different growth parameters on the molecular beam epitaxy (MBE) growth of GaAs layers on (1 1 1)A oriented substrates. After that we present a method for the MBE growth of atomically smooth layers by sequences of growth and annealing phases. The samples exhibit low surface roughness and good electrical properties shown by atomic force microscopy (AFM), scanning electron microscopy (SEM) and van-der-Pauw Hall measurements.

Synthesis of Multifunctional Materials

DTIC Science & Technology

2006-09-01

temperatures of 600’C and higher, whereas layers grown at lower temperature contained PbO inclusions. Growth of Pb(ZrxTi1 ..)0 3 ( PZT ) films by molecular...beam epitaxy was demonstrated for the first time. Single-crystal, single-phase PZT films were grown on (001) SrTiO3 substrates at a growth temperature...compounds of the PZT system, PbTiO 3 and PbZrO 3, and three-dimensional growth mode for PZT films of intermediate compositions. Epitaxial growth of PbO

Preface

NASA Astrophysics Data System (ADS)

Qiu, Roger; Paskova, Tania

2016-10-01

This special issue of Journal of Crystal Growth contains papers presented at the 20th American Conference on Crystal Growth and Epitaxy (ACCGE-20), the 17th Biennial Workshop on Organometallic Vapor Phase Epitaxy (OMVPE-17) and the Second 2D Electronic Materials Symposium, which were jointly held in Big Sky, Montana from August 2-7, 2015. The conference was co-chaired by Joan Redwing (Penn State, ACCGE chair), Luke Mawst (University of Wisconsin, Madison, OMVPE chair), and D. Kurt Gaskill (U.S. Naval Research Laboratory, 2D chair).

III-V Compounds and Alloys: An Update.

PubMed

Woodall, J M

1980-05-23

The III-V compounds and alloys have been studied for three decades. Until recently, these materials have been commercialized for only a few specialized optoelectronic devices and microwave devices. Advances in thin-film epitaxy techniques, such as liquid phase epitaxy and chemical vapor deposition, are now providing the ability to form good quality lattice-matched heterojunctions with III-V materials. New optoelectronic devices, such as room-temperature continuous-wave injection lasers, have already resulted. This newfound ability may also affect the field of highspeed integrated circuits.

Modeling and Optimization for Epitaxial Growth: Transport and Growth Studies

DTIC Science & Technology

1999-01-01

effect . It is expressed as the sum of these two components j i jC i jT i where jC i and jT i denote the concentration driven and thermally driven...improve manufacturing effectiveness for epitaxial growth of silicon and silicon-germanium (Si-Ge) thin films on a silicon wafer. Growth takes place in the...non-uniformity to compensate for the effects of other phenomena such as reactant depletion, gas heating and gas phase reactions, thermal diffusion of

Hair regrowth in alopecia areata patients following Stem Cell Educator therapy.

PubMed

Li, Yanjia; Yan, Baoyong; Wang, Hepeng; Li, Heng; Li, Quanhai; Zhao, Dong; Chen, Yana; Zhang, Ye; Li, Wenxia; Zhang, Jun; Wang, Shanfeng; Shen, Jie; Li, Yunxiang; Guindi, Edward; Zhao, Yong

2015-04-20

Alopecia areata (AA) is one of the most common autoimmune diseases and targets the hair follicles, with high impact on the quality of life and self-esteem of patients due to hair loss. Clinical management and outcomes are challenged by current limited immunosuppressive and immunomodulating regimens. We have developed a Stem Cell Educator therapy in which a patient's blood is circulated through a closed-loop system that separates mononuclear cells from the whole blood, allows the cells to briefly interact with adherent human cord blood-derived multipotent stem cells (CB-SC), and returns the "educated" autologous cells to the patient's circulation. In an open-label, phase 1/phase 2 study, patients (N = 9) with severe AA received one treatment with the Stem Cell Educator therapy. The median age was 20 years (median alopecic duration, 5 years). Clinical data demonstrated that patients with severe AA achieved improved hair regrowth and quality of life after receiving Stem Cell Educator therapy. Flow cytometry revealed the up-regulation of Th2 cytokines and restoration of balancing Th1/Th2/Th3 cytokine production in the peripheral blood of AA subjects. Immunohistochemistry indicated the formation of a "ring of transforming growth factor beta 1 (TGF-β1)" around the hair follicles, leading to the restoration of immune privilege of hair follicles and the protection of newly generated hair follicles against autoimmune destruction. Mechanistic studies revealed that co-culture with CB-SC may up-regulate the expression of coinhibitory molecules B and T lymphocyte attenuator (BTLA) and programmed death-1 receptor (PD-1) on CD8β(+)NKG2D(+) effector T cells and suppress their proliferation via herpesvirus entry mediator (HVEM) ligands and programmed death-1 ligand (PD-L1) on CB-SCs. Current clinical data demonstrated the safety and efficacy of the Stem Cell Educator therapy for the treatment of AA. This innovative approach produced lasting improvement in hair regrowth in subjects with moderate or severe AA. ClinicalTrials.gov, NCT01673789, 21 August 2012.

Using goats to control brush regrowth on fuelbreaks

Treesearch

Lisle R. Green; Leonard A. Newell

1982-01-01

On fuelbreaks, herbicides have been the primary tool for controlling brush regrowth. Vegetation of low volume and low growth is maintained on these wide strips as an aid to firefighting safety. Goats are a promising alternative to herbicides, and may be the best tool available for controlling brush regrowth on fuelbreaks. They eat a wider variety of plants, and more...

Cyan laser diode grown by plasma-assisted molecular beam epitaxy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Turski, H., E-mail: henryk@unipress.waw.pl; Muziol, G.; Wolny, P.

We demonstrate AlGaN-cladding-free laser diodes (LDs), operating in continuous wave (CW) mode at 482 nm grown by plasma-assisted molecular beam epitaxy (PAMBE). The maximum CW output power was 230 mW. LDs were grown on c-plane GaN substrates obtained by hydride vapor phase epitaxy. The PAMBE process was carried out in metal-rich conditions, supplying high nitrogen flux (Φ{sub N}) during quantum wells (QWs) growth. We found that high Φ{sub N} improves quality of high In content InGaN QWs. The role of nitrogen in the growth of InGaN on (0001) GaN surface as well as the influence of LDs design on threshold currentmore » density are discussed.« less

Treatment Analysis in a Cancer Stem Cell Context Using a Tumor Growth Model Based on Cellular Automata.

PubMed

Monteagudo, Ángel; Santos, José

2015-01-01

Cancer can be viewed as an emergent behavior in terms of complex system theory and artificial life, Cellular Automata (CA) being the tool most used for studying and characterizing the emergent behavior. Different approaches with CA models were used to model cancer growth. The use of the abstract model of acquired cancer hallmarks permits the direct modeling at cellular level, where a cellular automaton defines the mitotic and apoptotic behavior of cells, and allows for an analysis of different dynamics of the cellular system depending on the presence of the different hallmarks. A CA model based on the presence of hallmarks in the cells, which includes a simulation of the behavior of Cancer Stem Cells (CSC) and their implications for the resultant growth behavior of the multicellular system, was employed. This modeling of cancer growth, in the avascular phase, was employed to analyze the effect of cancer treatments in a cancer stem cell context. The model clearly explains why, after treatment against non-stem cancer cells, the regrowth capability of CSCs generates a faster regrowth of tumor behavior, and also shows that a continuous low-intensity treatment does not favor CSC proliferation and differentiation, thereby allowing an unproblematic control of future tumor regrowth. The analysis performed indicates that, contrary to the current attempts at CSC control, trying to make CSC proliferation more difficult is an important point to consider, especially in the immediate period after a standard treatment for controlling non-stem cancer cell proliferation.

Twenty years of molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Cho, A. Y.

1995-05-01

The term "molecular beam epitaxy" (MBE) was first used in one of our crystal growth papers in 1970, after having conducted extensive surface physics studies in the late 1960's of the interaction of atomic and molecular beams with solid surfaces. The unique feature of MBE is the ability to prepare single crystal layers with atomic dimensional precision. MBE sets the standard for epitaxial growth and has made possible semiconductor structures that could not be fabricated with either naturally existing materials or by other crystal growth techniques. MBE led the crystal growth technologies when it prepared the first semiconductor quantum well and superlattice structures that gave unexpected and exciting electrical and optical properties. For example, the discovery of the fractional quantized Hall effect. It brought experimental quantum physics to the classroom, and practically all major universities throughout the world are now equipped with MBE systems. The fundamental principles demonstrated by the MBE growth of III-V compound semiconductors have also been applied to the growth of group IV, II-VI, metal, and insulating materials. For manufacturing, the most important criteria are uniformity, precise control of the device structure, and reproducibility. MBE has produced more lasers (3 to 5 million per month for compact disc application) than any other crystal growth technique in the world. New directions for MBE are to incorporate in-situ, real-time monitoring capabilities so that complex structures can be precisely "engineered". In the future, as environmental concerns increase, the use of toxic arsine and phosphine may be limited. Successful use of valved cracker cells for solid arsenic and phosphorus has already produced InP based injection lasers.

Crystallographic orientation of epitaxial BaTiO3 films: The role of thermal-expansion mismatch with the substrate

NASA Astrophysics Data System (ADS)

Srikant, V.; Tarsa, E. J.; Clarke, D. R.; Speck, J. S.

1995-02-01

Expitaxial ferroelectric BaTiO3 thin films have been grown on (001) MgO and MgO-buffered (001) GaAs substrates by pulsed laser deposition to explore the effect of substrate lattice parameter. X-ray-diffraction studies showed that the BaTiO3 films on both MgO single-crystal substrates and MgO-buffered (001) GaAs substrates have a cube-on-cube epitaxy; however, for the BaTiO3 films grown on MgO the spacing of the planes parallel to the substrate was close to the c-axis dimension of the unconstrained tetragonal phase, whereas the BaTiO3 films on MgO/GaAs exhibited a spacing closer to the a-axis dimension of the unconstrained tetragonal phase. The cube-on-cube epitaxy was maintained through the heterostructures even when thin epitaxial intermediate buffer layers of SrTiO3 and La(0.5)Sr(0.5)CoO3 were used. The intermediate layers had no effect on the position of the BaTiO3 peak in theta - 2 theta scans. Together, these observations indicate that, for the materials combinations studied, it is the thermal-expansion mismatch between the film and the underlying substrate that determines the crystallographic orientation of the BaTiO3 film. Preliminary measurements indicate that the BaTiO3 films are 'weakly' ferroelectric.

Environmentally friendly method to grow wide-bandgap semiconductor aluminum nitride crystals: Elementary source vapor phase epitaxy

PubMed Central

Wu, PeiTsen; Funato, Mitsuru; Kawakami, Yoichi

2015-01-01

Aluminum nitride (AlN) has attracted increasing interest as an optoelectronic material in the deep ultraviolet spectral range due to its wide bandgap of 6.0 eV (207 nm wavelength) at room temperature. Because AlN bulk single crystals are ideal device substrates for such applications, the crystal growth of bulky AlN has been extensively studied. Two growth methods seem especially promising: hydride vapor phase epitaxy (HVPE) and sublimation. However, the former requires hazardous gases such as hydrochloric acid and ammonia, while the latter needs extremely high growth temperatures around 2000 °C. Herein we propose a novel vapor-phase-epitaxy-based growth method for AlN that does not use toxic materials; the source precursors are elementary aluminum and nitrogen gas. To prepare our AlN, we constructed a new growth apparatus, which realizes growth of AlN single crystals at a rate of ~18 μm/h at 1550 °C using argon as the source transfer via the simple reaction Al + 1/2N2 → AlN. This growth rate is comparable to that by HVPE, and the growth temperature is much lower than that in sublimation. Thus, this study opens up a novel route to achieve environmentally friendly growth of AlN. PMID:26616203

Metalorganic vapor phase epitaxy of AlN on sapphire with low etch pit density

NASA Astrophysics Data System (ADS)

Koleske, D. D.; Figiel, J. J.; Alliman, D. L.; Gunning, B. P.; Kempisty, J. M.; Creighton, J. R.; Mishima, A.; Ikenaga, K.

2017-06-01

Using metalorganic vapor phase epitaxy, methods were developed to achieve AlN films on sapphire with low etch pit density (EPD). Key to this achievement was using the same AlN growth recipe and only varying the pre-growth conditioning of the quartz-ware. After AlN growth, the quartz-ware was removed from the growth chamber and either exposed to room air or moved into the N2 purged glove box and exposed to H2O vapor. After the quartz-ware was exposed to room air or H2O, the AlN film growth was found to be more reproducible, resulting in films with (0002) and (10-12) x-ray diffraction (XRD) rocking curve linewidths of 200 and 500 arc sec, respectively, and EPDs < 100 cm-2. The EPD was found to correlate with (0002) linewidths, suggesting that the etch pits are associated with open core screw dislocations similar to GaN films. Once reproducible AlN conditions were established using the H2O pre-treatment, it was found that even small doses of trimethylaluminum (TMAl)/NH3 on the quartz-ware surfaces generated AlN films with higher EPDs. The presence of these residual TMAl/NH3-derived coatings in metalorganic vapor phase epitaxy (MOVPE) systems and their impact on the sapphire surface during heating might explain why reproducible growth of AlN on sapphire is difficult.

Substantiation of Epitaxial Growth of Diamond Crystals on the Surface of Carbide Fe3AlC0.66 Phase Nanoparticles.

PubMed

Dzevin, Ievgenij M; Mekhed, Alexander A

2017-12-01

Samples of Fe-Al-C alloys of varying composition were synthesized under high pressures and temperatures. From X-ray analysis data, only K-phase with usual for it average parameter of elemental lattice cell, a = 0.376 nm, carbide Fe 3 C and cubic diamond reflexes were present before and after cooling to the temperature of liquid nitrogen.Calculations were made of the parameters of unit cells, the enthalpy of formation of the Fe 3 AlC, Fe 3.125 Al 0.825 C 0.5 , Fe 3.5 Al 0.5 C 0.5 , Fe 3.5 Al 0.5 C, Fe 3 Al 0.66 C 0.66 , and Fe 3 AlC 0.66 unit cells and crystallographic planes were identified on which epitaxial growth of the diamond phase was possible, using density functional theory as implemented in the WIEN2k package.The possibility of epitaxial growth of diamond crystals on Fe 3 AlC 0.66 (K-phase) nanoparticles was, therefore, demonstrated. The [200] plane was established to be the most suitable plane for diamond growth, having four carbon atoms arranged in a square and a central vacancy which can be occupied by carbon during thermal-and-pressure treatment. Distances between carbon atoms in the [200] plane differ by only 5% from distances between the carbon atoms of a diamond. The electronic structure and energetic parameters of the substrate were also investigated. It was shown that the substrate with at least four intermediate layers of K-phase exhibits signs of stability such as negative enthalpy of formation and the Fermi level falling to minimum densities of states.

Plant Regrowth as a Driver of Recent Enhancement of Terrestrial CO2 Uptake

NASA Astrophysics Data System (ADS)

Kondo, Masayuki; Ichii, Kazuhito; Patra, Prabir K.; Poulter, Benjamin; Calle, Leonardo; Koven, Charles; Pugh, Thomas A. M.; Kato, Etsushi; Harper, Anna; Zaehle, Sönke; Wiltshire, Andy

2018-05-01

The increasing strength of land CO2 uptake in the 2000s has been attributed to a stimulating effect of rising atmospheric CO2 on photosynthesis (CO2 fertilization). Using terrestrial biosphere models, we show that enhanced CO2 uptake is induced not only by CO2 fertilization but also an increasing uptake by plant regrowth (accounting for 0.33 ± 0.10 Pg C/year increase of CO2 uptake in the 2000s compared with the 1960s-1990s) with its effect most pronounced in eastern North America, southern-eastern Europe, and southeastern temperate Eurasia. Our analysis indicates that ecosystems in North America and Europe have established the current productive state through regrowth since the 1960s, and those in temperate Eurasia are still in a stage from regrowth following active afforestation in the 1980s-1990s. As the strength of model representation of CO2 fertilization is still in debate, plant regrowth might have a greater potential to sequester carbon than indicated by this study.

Photoluminescence investigation of type-II GaSb/GaAs quantum dots grown by liquid phase epitaxy

NASA Astrophysics Data System (ADS)

Wang, Yang; Hu, Shuhong; Xie, Hao; Lin, Hongyu; lu, Hongbo; Wang, Chao; Sun, Yan; Dai, Ning

2018-06-01

GaSb quantum dots (QDs) with an areal density of ∼1 × 1010 cm-2 are successfully grown by the modified (rapid slider) liquid phase epitaxy technique. The morphology of the QDs has been investigated by scanning electron microscope (SEM) and atom force microscope (AFM). The power-dependence and temperature-dependence photoluminescence (PL) spectra have been studied. The bright room-temperature PL suggests a good luminescence quality of GaSb QDs/GaAs matrix system. The type-II alignment of the GaSb QDs/GaAs matrix system is verified by the blue-shift of the QDs peak with the increase of excitation power. From the temperature-dependence PL spectra, the activation energy of QDs is determined to be 111 meV.

CdZnTe substrate impurities and their effects on liquid phase epitaxy HgCdTe

NASA Astrophysics Data System (ADS)

Tower, J. P.; Tobin, S. P.; Kestigian, M.; Norton, P. W.; Bollong, A. B.; Schaake, H. F.; Ard, C. K.

1995-05-01

Impurity levels were tracked through the stages of substrate and liquid phase epitaxy (LPE) layer processing to identify sources of elements which degrade infrared photodetector performance. Chemical analysis by glow discharge mass spectrometry and Zeeman corrected graphite furnace atomic absorption effectively showed the levels of impurities introduced into CdZnTe substrate material from the raw materials and the crystal growth processes. A new purification process (in situ distillation zone refining) for raw materials was developed, resulting in improved CdZnTe substrate purity. Substrate copper contamination was found to degrade the LPE layer and device electrical properties, in the case of lightly doped HgCdTe. Anomalous HgCdTe carrier type conversion was correlated to certain CdZnTe and CdTe substrate ingots.

Indirectly pumped 3.7 THz InGaAs/InAlAs quantum-cascade lasers grown by metal-organic vapor-phase epitaxy.

PubMed

Fujita, Kazuue; Yamanishi, Masamichi; Furuta, Shinichi; Tanaka, Kazunori; Edamura, Tadataka; Kubis, Tillmann; Klimeck, Gerhard

2012-08-27

Device-performances of 3.7 THz indirect-pumping quantum-cascade lasers are demonstrated in an InGaAs/InAlAs material system grown by metal-organic vapor-phase epitaxy. The lasers show a low threshold-current-density of ~420 A/cm2 and a peak output power of ~8 mW at 7 K, no sign of parasitic currents with recourse to well-designed coupled-well injectors in the indirect pump scheme, and a maximum operating temperature of Tmax ~100 K. The observed roll-over of output intensities in current ranges below maximum currents and limitation of Tmax are discussed with a model for electron-gas heating in injectors. Possible ways toward elevation of Tmax are suggested.

Quantum dots grown in the InSb/GaSb system by liquid-phase epitaxy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Parkhomenko, Ya. A.; Dement’ev, P. A.; Moiseev, K. D., E-mail: mkd@iropt2.ioffe.rssi.ru

2016-07-15

The first results of the liquid-phase epitaxial growth of quantum dots in the InSb/GaSb system and atomic-force microscopy data on the structural characteristics of the quantum dots are reported. It is shown that the surface density, shape, and size of nanoislands depend on the deposition temperature and the chemical properties of the matrix surface. Arrays of InSb quantum dots on GaSb (001) substrates are produced in the temperature range T = 450–465°C. The average dimensions of the quantum dots correspond to a height of h = 3 nm and a base dimension of D = 30 nm; the surface densitymore » is 3 × 10{sup 9} cm{sup –2}.« less

An instrument for in situ coherent x-ray studies of metal-organic vapor phase epitaxy of III-nitrides.

PubMed

Ju, Guangxu; Highland, Matthew J; Yanguas-Gil, Angel; Thompson, Carol; Eastman, Jeffrey A; Zhou, Hua; Brennan, Sean M; Stephenson, G Brian; Fuoss, Paul H

2017-03-01

We describe an instrument that exploits the ongoing revolution in synchrotron sources, optics, and detectors to enable in situ studies of metal-organic vapor phase epitaxy (MOVPE) growth of III-nitride materials using coherent x-ray methods. The system includes high-resolution positioning of the sample and detector including full rotations, an x-ray transparent chamber wall for incident and diffracted beam access over a wide angular range, and minimal thermal sample motion, giving the sub-micron positional stability and reproducibility needed for coherent x-ray studies. The instrument enables surface x-ray photon correlation spectroscopy, microbeam diffraction, and coherent diffraction imaging of atomic-scale surface and film structure and dynamics during growth, to provide fundamental understanding of MOVPE processes.

An instrument for in situ coherent x-ray studies of metal-organic vapor phase epitaxy of III-nitrides

NASA Astrophysics Data System (ADS)

Ju, Guangxu; Highland, Matthew J.; Yanguas-Gil, Angel; Thompson, Carol; Eastman, Jeffrey A.; Zhou, Hua; Brennan, Sean M.; Stephenson, G. Brian; Fuoss, Paul H.

2017-03-01

We describe an instrument that exploits the ongoing revolution in synchrotron sources, optics, and detectors to enable in situ studies of metal-organic vapor phase epitaxy (MOVPE) growth of III-nitride materials using coherent x-ray methods. The system includes high-resolution positioning of the sample and detector including full rotations, an x-ray transparent chamber wall for incident and diffracted beam access over a wide angular range, and minimal thermal sample motion, giving the sub-micron positional stability and reproducibility needed for coherent x-ray studies. The instrument enables surface x-ray photon correlation spectroscopy, microbeam diffraction, and coherent diffraction imaging of atomic-scale surface and film structure and dynamics during growth, to provide fundamental understanding of MOVPE processes.

Gaalas/Gaas Solar Cell Process Study

NASA Technical Reports Server (NTRS)

Almgren, D. W.; Csigi, K. I.

1980-01-01

Available information on liquid phase, vapor phase (including chemical vapor deposition) and molecular beam epitaxy growth procedures that could be used to fabricate single crystal, heteroface, (AlGa) As/GaAs solar cells, for space applications is summarized. A comparison of the basic cost elements of the epitaxy growth processes shows that the current infinite melt LPE process has the lower cost per cell for an annual production rate of 10,000 cells. The metal organic chemical vapor deposition (MO-CVD) process has the potential for low cost production of solar cells but there is currently a significant uncertainty in process yield, i.e., the fraction of active material in the input gas stream that ends up in the cell. Additional work is needed to optimize and document the process parameters for the MO-CVD process.

Effect of regrowth interval and a microbial inoculant on the fermentation profile and dry matter recovery of guinea grass silages.

PubMed

Santos, E M; Pereira, O G; Garcia, R; Ferreira, C L L F; Oliveira, J S; Silva, T C

2014-07-01

The objectives of this study were to characterize and quantify the microbial populations in guinea grass (Panicum maximum Jacq. cultivar Mombasa) harvested at different regrowth intervals (35, 45, 55, and 65 d). The chemical composition and fermentation profile of silages (after 60 d) with or without the addition of a microbial inoculant were also analyzed. Before ensiling, samples of the plants were used for the isolation and identification of lactic acid bacteria (LAB) in the epiphytic microbiota. A 4 × 2 factorial arrangement of treatments (4 regrowth intervals × with/without inoculant) was used in a completely randomized design with 3 replications. Based on the morphological and biochemical characteristics and the carbohydrate fermentation profile, Lactobacillus plantarum was found to be the predominant specie of LAB in guinea grass forage. Linear increases were detected in the dry matter (DM) content and concentrations of neutral detergent fiber, acid detergent fiber, acid detergent insoluble nitrogen, and DM recovery as well as linear reductions in the concentrations of crude protein and NH3-N with regrowth interval. Additionally, linear reductions for gas and effluent losses in silages were detected with increasing regrowth interval. These results demonstrate that guinea grass plants harvested after 55 d of regrowth contain a LAB population sufficiently large to ensure good fermentation and increase the DM recovery. The use of microbial inoculant further enhanced the fermentation of guinea grass at all stages of regrowth by improving the DM recovery. Copyright © 2014 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.

Forest Edge Regrowth Typologies in Southern Sweden-Relationship to Environmental Characteristics and Implications for Management.

PubMed

Wiström, Björn; Busse Nielsen, Anders

2017-07-01

After two major storms, the Swedish Transport Administration was granted permission in 2008 to expand the railroad corridor from 10 to 20 m from the rail banks, and to clear the forest edges in the expanded area. In order to evaluate the possibilities for managers to promote and control the species composition of the woody regrowth so that a forest edge with a graded profile develops over time, this study mapped the woody regrowth and environmental variables at 78 random sites along the 610-km railroad between Stockholm and Malmö four growing seasons after the clearing was implemented. Through different clustering approaches, dominant tree species to be controlled and future building block species for management were identified. Using multivariate regression trees, the most decisive environmental variables were identified and used to develop a regrowth typology and to calculate species indicator values. Five regrowth types and ten indicator species were identified along the environmental gradients of soil moisture, soil fertility, and altitude. Six tree species dominated the regrowth across the regrowth types, but clustering showed that if these were controlled by selective thinning, lower tree and shrub species were generally present so they could form the "building blocks" for development of a graded edge. We concluded that selective thinning targeted at controlling a few dominant tree species, here named Functional Species Control, is a simple and easily implemented management concept to promote a wide range of suitable species, because it does not require field staff with specialist taxonomic knowledge.

Intralesional Osteophyte Regrowth Following Autologous Chondrocyte Implantation after Previous Treatment with Marrow Stimulation Technique.

PubMed

Demange, Marco Kawamura; Minas, Tom; von Keudell, Arvind; Sodha, Sonal; Bryant, Tim; Gomoll, Andreas H

2017-04-01

Objective Bone marrow stimulation surgeries are frequent in the treatment of cartilage lesions. Autologous chondrocyte implantation (ACI) may be performed after failed microfracture surgery. Alterations to subchondral bone as intralesional osteophytes are commonly seen after previous microfracture and removed during ACI. There have been no reports on potential recurrence. Our purpose was to evaluate the incidence of intralesional osteophyte development in 2 cohorts: existing intralesional osteophytes and without intralesional osteophytes at the time of ACI. Study Design We identified 87 patients (157 lesions) with intralesional osteophytes among a cohort of 497 ACI patients. Osteophyte regrowth was analyzed on magnetic resonance imaging and categorized as small or large (less or more than 50% of the cartilage thickness). Twenty patients (24 defects) without intralesional osteophytes at the time of ACI acted as control. Results Osteophyte regrowth was observed in 39.5% of lesions (34.4% of small osteophytes and 5.1% of large osteophytes). In subgroup analyses, regrowth was observed in 45.8% of periosteal-covered defects and in 18.9% of collagen membrane-covered defects. Large osteophyte regrowth occurred in less than 5% in either group. Periosteal defects showed a significantly higher incidence for regrowth of small osteophytes. In the control group, intralesional osteophytes developed in 16.7% of the lesions. Conclusions Even though intralesional osteophytes may regrow after removal during ACI, most of them are small. Small osteophyte regrowth occurs almost twice in periosteum-covered ACI. Large osteophytes occur only in 5% of patients. Intralesional osteophyte formation is not significantly different in preexisting intralesional osteophytes and control groups.

Intralesional Osteophyte Regrowth Following Autologous Chondrocyte Implantation after Previous Treatment with Marrow Stimulation Technique

PubMed Central

Demange, Marco Kawamura; Minas, Tom; von Keudell, Arvind; Sodha, Sonal; Bryant, Tim; Gomoll, Andreas H.

2016-01-01

Objective Bone marrow stimulation surgeries are frequent in the treatment of cartilage lesions. Autologous chondrocyte implantation (ACI) may be performed after failed microfracture surgery. Alterations to subchondral bone as intralesional osteophytes are commonly seen after previous microfracture and removed during ACI. There have been no reports on potential recurrence. Our purpose was to evaluate the incidence of intralesional osteophyte development in 2 cohorts: existing intralesional osteophytes and without intralesional osteophytes at the time of ACI. Study Design We identified 87 patients (157 lesions) with intralesional osteophytes among a cohort of 497 ACI patients. Osteophyte regrowth was analyzed on magnetic resonance imaging and categorized as small or large (less or more than 50% of the cartilage thickness). Twenty patients (24 defects) without intralesional osteophytes at the time of ACI acted as control. Results Osteophyte regrowth was observed in 39.5% of lesions (34.4% of small osteophytes and 5.1% of large osteophytes). In subgroup analyses, regrowth was observed in 45.8% of periosteal-covered defects and in 18.9% of collagen membrane–covered defects. Large osteophyte regrowth occurred in less than 5% in either group. Periosteal defects showed a significantly higher incidence for regrowth of small osteophytes. In the control group, intralesional osteophytes developed in 16.7% of the lesions. Conclusions Even though intralesional osteophytes may regrow after removal during ACI, most of them are small. Small osteophyte regrowth occurs almost twice in periosteum-covered ACI. Large osteophytes occur only in 5% of patients. Intralesional osteophyte formation is not significantly different in preexisting intralesional osteophytes and control groups. PMID:28345403

The effect of nutrient ratios on E. coli re-growth in urban streams

NASA Astrophysics Data System (ADS)

Aitkenhead-Peterson, J. A.; McCrary, K.; Gentry, T. J.; Harclerode, C. L.

2010-12-01

E. coli an indicator for fecal pathogens in aquatic systems, is one of the major impairments of streams and rivers in USA. We examined re-growth of E.coli in UV-treated wastewater effluent by spiking effluent with extract obtained from managed turf grass and ornamental tree foliage. Our original hypothesis that the increased quantity and quality of DOC would increase re-growth was rejected. Instead we found that the ratio of C:N:P of our extracts was able to explain between 64 and 89% of the variance in E. coli re-growth. The C:N:P ratio of treated sewage effluent of 0.64 was too low to produce re-growth which commenced at C:N:P ratio’s of around 3.7 at 24 hrs and > 5.8 at 12 hrs. As precipitation or irrigation water interacts with the landscape vegetation of urban golf courses, athletic fields, parks and homeowner gardens in urban watersheds prior to running off to streams and rivers its solution C:N:P ratio may be conducive to E. coli re-growth in those watersheds with wastewater treatment plant point source discharge. To test this theory further we examined E. coli and stream C:N:P ratio in four watersheds downstream of wastewater treatment plants. Here we found that stream C:N:P ratio explained 98% of the variance in E. coli. Interestingly this phenomenon only occurs in streams downstream of waste water treatment plants suggesting that revival of E. coli in sewage effluent is possible if watershed conditions are conducive to their re-growth.

Heteroepitaxial Cu 2O thin film solar cell on metallic substrates

DOE PAGES

Wee, Sung Hun; Huang, Po-Shun; Lee, Jung-Kun; ...

2015-11-06

Heteroepitaxial, single-crystal-like Cu 2O films on inexpensive, flexible, metallic substrates can potentially be used as absorber layers for fabrication of low-cost, high-performance, non-toxic, earth-abundant solar cells. Here, we report epitaxial growth of Cu 2O films on low cost, flexible, textured metallic substrates. Cu 2O films were deposited on the metallic templates via pulsed laser deposition under various processing conditions to study the influence of processing parameters on the structural and electronic properties of the films. It is found that pure, epitaxial Cu 2O phase without any trace of CuO phase is only formed in a limited deposition window of P(Omore » 2) - temperature. The (00l) single-oriented, highly textured, Cu 2O films deposited under optimum P(O 2) - temperature conditions exhibit excellent electronic properties with carrier mobility in the range of 40-60 cm 2 V -1 s -1 and carrier concentration over 10 16 cm -3. The power conversion efficiency of 1.65% is demonstrated from a proof-of-concept Cu 2O solar cell based on epitaxial Cu 2O film prepared on the textured metal substrate.« less

Fabrication of selective-area growth InGaN LED by mixed-source hydride vapor-phase epitaxy

NASA Astrophysics Data System (ADS)

Bae, Sung Geun; Jeon, Injun; Jeon, Hunsoo; Kim, Kyoung Hwa; Yang, Min; Yi, Sam Nyung; Lee, Jae Hak; Ahn, Hyung Soo; Yu, Young Moon; Sawaki, Nobuhiko; Kim, Suck-Whan

2018-01-01

We prepared InGaN light-emitting diodes (LEDs) with the active layers grown from a mixed source of Ga-In-N materials on an n-type GaN substrate by a selective-area growth method and three fabrication steps: photolithography, epitaxial layer growth, and metallization. The preparation followed a previously developed experimental process using apparatus for mixed-source hydride vapor-phase epitaxy (HVPE), which consisted of a multi-graphite boat, for insulating against the high temperature and to control the growth rate of epilayers, filled with the mixed source on the inside and a radio-frequency (RF) heating coil for heating to a high temperature (T > 900 °C) and for easy control of temperature outside the source zone. Two types of LEDs were prepared, with In compositions of 11.0 and 6.0% in the InGaN active layer, and room-temperature electroluminescence measurements exhibited a main peak corresponding to the In composition at either 420 or 390 nm. The consecutive growth of InGaN LEDs by the mixed-source HVPE method provides a technique for the production of LEDs with a wide range of In compositions in the active layer.

Liquid phase epitaxy of binary III–V nanocrystals in thin Si layers triggered by ion implantation and flash lamp annealing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wutzler, Rene, E-mail: r.wutzler@hzdr.de; Rebohle, Lars; Prucnal, Slawomir

2015-05-07

The integration of III–V compound semiconductors in Si is a crucial step towards faster and smaller devices in future technologies. In this work, we investigate the formation process of III–V compound semiconductor nanocrystals, namely, GaAs, GaSb, and InP, by ion implantation and sub-second flash lamp annealing in a SiO{sub 2}/Si/SiO{sub 2} layer stack on Si grown by plasma-enhanced chemical vapor deposition. Raman spectroscopy, Rutherford Backscattering spectrometry, and transmission electron microscopy were performed to identify the structural and optical properties of these structures. Raman spectra of the nanocomposites show typical phonon modes of the compound semiconductors. The formation process of themore » III–V compounds is found to be based on liquid phase epitaxy, and the model is extended to the case of an amorphous matrix without an epitaxial template from a Si substrate. It is shown that the particular segregation and diffusion coefficients of the implanted group-III and group-V ions in molten Si significantly determine the final appearance of the nanostructure and thus their suitability for potential applications.« less

Heteroepitaxial Cu2O thin film solar cell on metallic substrates

PubMed Central

Wee, Sung Hun; Huang, Po-Shun; Lee, Jung-Kun; Goyal, Amit

2015-01-01

Heteroepitaxial, single-crystal-like Cu2O films on inexpensive, flexible, metallic substrates can potentially be used as absorber layers for fabrication of low-cost, high-performance, non-toxic, earth-abundant solar cells. Here, we report epitaxial growth of Cu2O films on low cost, flexible, textured metallic substrates. Cu2O films were deposited on the metallic templates via pulsed laser deposition under various processing conditions to study the influence of processing parameters on the structural and electronic properties of the films. It is found that pure, epitaxial Cu2O phase without any trace of CuO phase is only formed in a limited deposition window of P(O2) - temperature. The (00l) single-oriented, highly textured, Cu2O films deposited under optimum P(O2) - temperature conditions exhibit excellent electronic properties with carrier mobility in the range of 40–60 cm2 V−1 s−1 and carrier concentration over 1016 cm−3. The power conversion efficiency of 1.65% is demonstrated from a proof-of-concept Cu2O solar cell based on epitaxial Cu2O film prepared on the textured metal substrate. PMID:26541499

Modulation of magnetic interaction in Bismuth ferrite through strain and spin cycloid engineering

NASA Astrophysics Data System (ADS)

Yadav, Rama Shanker; Reshi, Hilal Ahmad; Pillai, Shreeja; Rana, D. S.; Shelke, Vilas

2016-12-01

Bismuth ferrite, a widely studied room temperature multiferroic, provides new horizons of multifunctional behavior in phase transited bulk and thin film forms. Bismuth ferrite thin films were deposited on lattice mismatched LaAlO3 substrate using pulsed laser deposition technique. X-ray diffraction confirmed nearly tetragonal (T-type) phase of thin film involving role of substrate induced strain. The film thickness of 56 nm was determined by X-ray reflectivity measurement. The perfect coherence and epitaxial nature of T- type film was observed through reciprocal space mapping. The room temperature Raman measurement of T-type bismuth ferrite thin film also verified phase transition with appearance of only few modes. In parallel, concomitant La and Al substituted Bi1-xLaxFe0.95Al0.05O3 (x = 0.1, 0.2, 0.3) bulk samples were synthesized using solid state reaction method. A structural phase transition into orthorhombic (Pnma) phase at x = 0.3 was observed. The structural distortion at x = 0.1, 0.2 and phase transition at x = 0.3 substituted samples were also confirmed by changes in Raman active modes. The remnant magnetization moment of 0.199 emu/gm and 0.28 emu/gm were observed for x = 0.2 and 0.3 bulk sample respectively. The T-type bismuth ferrite thin film also showed high remnant magnetization of around 20emu/cc. The parallelism in magnetic behavior between T-type thin film and concomitant La and Al substituted bulk samples is indication of modulation, frustration and break in continuity of spiral spin cycloid.

Study of process technology for GaAlAs/GaAs heteroface solar cells

NASA Technical Reports Server (NTRS)

Conway, E. J.; Walker, G. H.; Byvik, C. E.; Almgren, D. W.

1980-01-01

Two processes were considered: the infinite melt process and the finite melt process. The only technique that is developed to the point that 10,000 cells could be produced in one year is the infinite melt liquid phase epitaxy process. The lowest cost per cell was achieved with the advanced metal organic chemical vapor deposition process. Molecular beam epitaxy was limited by the slow growth rate. The lowest cost, an 18 percent efficient cell at air mass zero, was approximately $70 per watt.

High-efficiency solar cells fabricated from direct-current magnetron sputtered n-indium tin oxide onto p-InP grown by atmospheric pressure metalorganic vapor phase epitaxy

NASA Technical Reports Server (NTRS)

Li, X.; Wanlass, M. W.; Gessert, T. A.; Emery, K. A.; Coutts, T. J.

1989-01-01

An attempt is made to improve device efficiencies by depositing indium tin oxide onto epitaxially grown p-InP on p(+)-InP substrates. This leads to a reduction in the device series resistance, high-quality reproducible surfaces, and an improvement in the transport properties of the base layer. Moreover, many of the facets associated with badly characterized bulk liquid encapsulated Czochralski substrates used in previous investigations are removed in this way.

Epitaxial growth and photoluminescence of hexagonal CdS 1- xSe x alloy films

NASA Astrophysics Data System (ADS)

Grün, M.; Gerlach, H.; Breitkopf, Th.; Hetterich, M.; Reznitsky, A.; Kalt, H.; Klingshirn, C.

1995-01-01

CdSSe ternary alloy films were grown on GaAs(111) by hot-wall beam epitaxy. The hexagonal crystal phase is obtained. The composition varies from 0 to 40% selenium. Luminescence spectroscopy at low temperatures shows a dominant effect by alloy disorder. Localization of carriers, for example, is still observed at a pulsed optical excitation density of 6 mJ/cm 2. The overall quality of the CdSSe films is sufficient to use them as buffer layers for the growth of hexagonal superlattices.

Mechanical properties of metal-organic frameworks: An indentation study on epitaxial thin films

NASA Astrophysics Data System (ADS)

Bundschuh, S.; Kraft, O.; Arslan, H. K.; Gliemann, H.; Weidler, P. G.; Wöll, C.

2012-09-01

We have determined the hardness and Young's modulus of a highly porous metal-organic framework (MOF) using a standard nanoindentation technique. Despite the very low density of these films, 1.22 g cm-3, Young's modulus reaches values of almost 10 GPa for HKUST-1, demonstrating that this porous coordination polymer is substantially stiffer than normal polymers. This progress in characterizing mechanical properties of MOFs has been made possible by the use of high quality, oriented thin films grown using liquid phase epitaxy on modified Au substrates.

Native oxides formation and surface wettability of epitaxial III-V materials: The case of InP and GaAs

NASA Astrophysics Data System (ADS)

Gocalinska, A.; Rubini, S.; Pelucchi, E.

2016-10-01

The time dependent transition from hydrophobic to hydrophilic states of the metalorganic vapour phase epitaxy (MOVPE) grown InP, GaAs and InAs is systematically documented by contact angle measurements. Natural oxides forming on the surfaces of air-exposed materials, as well as the results of some typical wet chemical process to remove those oxides, were studied by X-ray photoemission spectroscopy (XPS), revealing, surprisingly, a fundamental lack of strong correlations between the surface oxide composition and the reported systematic changes in hydrophobicity.

Phase degradation in BxGa1-xN films grown at low temperature by metalorganic vapor phase epitaxy

NASA Astrophysics Data System (ADS)

Gunning, Brendan P.; Moseley, Michael W.; Koleske, Daniel D.; Allerman, Andrew A.; Lee, Stephen R.

2017-04-01

Using metalorganic vapor phase epitaxy, a comprehensive study of BxGa1-xN growth on GaN and AlN templates is described. BGaN growth at high-temperature and high-pressure results in rough surfaces and poor boron incorporation efficiency, while growth at low-temperature and low-pressure (750-900 °C and 20 Torr) using nitrogen carrier gas results in improved surface morphology and boron incorporation up to 7.4% as determined by nuclear reaction analysis. However, further structural analysis by transmission electron microscopy and x-ray pole figures points to severe degradation of the high boron composition films, into a twinned cubic structure with a high density of stacking faults and little or no room temperature photoluminescence emission. Films with <1% triethylboron (TEB) flow show more intense, narrower x-ray diffraction peaks, near-band-edge photoluminescence emission at 362 nm, and primarily wurtzite-phase structure in the x-ray pole figures. For films with >1% TEB flow, the crystal structure becomes dominated by the cubic phase. Only when the TEB flow is zero (pure GaN), does the cubic phase entirely disappear from the x-ray pole figure, suggesting that under these growth conditions even very low boron compositions lead to mixed crystalline phases.

High Growth Rate Metal-Organic Molecular Beam Epitaxy for the Fabrication of GaAs Space Solar Cells

NASA Technical Reports Server (NTRS)

Freundlich, A.; Newman, F.; Monier, C.; Street, S.; Dargan, P.; Levy, M.

2005-01-01

In this work it is shown that high quality GaAs photovoltaic devices can be produced by Molecular Beam Epitaxy (MBE) with growth rates comparable to metal-organic chemical vapor deposition (MOCVD) through the subsitution of group III solid sources by metal-organic compounds. The influence the III/V flux-ratio and growth temperatures in maintaining a two dimensional layer by layer growth mode and achieving high growth rates with low residual background impurities is investigated. Finally subsequent to the study of the optimization of n- and p doping of such high growth rate epilayers, results from a preliminary attempt in the fabrication of GaAs photovoltaic devices such as tunnel diodes and solar cells using the proposed high growth rate approach are reported.

Dynamics of ultrathin metal films on amorphous substrates under fast thermal processing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Favazza, Christopher; Kalyanaraman, Ramki; Sureshkumar, Radhakrishna

A mathematical model is developed to analyze the growth/decay rate of surface perturbations of an ultrathin metal film on an amorphous substrate (SiO{sub 2}). The formulation combines the approach of Mullins [W. W. Mullins, J. Appl. Phys. 30, 77 (1959)] for bulk surfaces, in which curvature-driven mass transport and surface deformation can occur by surface/volume diffusion and evaporation-condensation processes, with that of Spencer et al. [B. J. Spencer, P. W. Voorhees, and S. H. Davis, Phys. Rev. Lett. 67, 26 (1991)] to describe solid-state transport in thin films under epitaxial strain. Modifications of the Mullins model to account for thin-filmmore » boundary conditions result in qualitatively different dispersion relationships especially in the limit as kh{sub o}<<1, where k is the wavenumber of the perturbation and h{sub o} is the unperturbed film height. The model is applied to study the relative rate of solid-state mass transport as compared to that of liquid phase dewetting in a thin film subjected to a fast thermal pulse. Specifically, we have recently shown that multiple cycles of nanosecond (ns) pulsed laser melting and resolidification of ultrathin metal films on amorphous substrates can lead to the formation of various types of spatially ordered nanostructures [J. Trice, D. Thomas, C. Favazza, R. Sureshkumar, and R. Kalyanaraman, Phys. Rev. B 75, 235439 (2007)]. The pattern formation has been attributed to the dewetting of the thin film by a hydrodynamic instability. In such experiments the film is in the solid state during a substantial fraction of each thermal cycle. However, results of a linear stability analysis based on the aforementioned model suggest that solid-state mass transport has a negligible effect on morphological changes of the surface. Further, a qualitative analysis of the effect of thermoelastic stress, induced by the rapid temperature changes in the film-substrate bilayer, suggests that stress relaxation does not appreciably contribute to surface deformation. Hence, surface deformation caused by liquid phase instabilities is rapidly quenched-in during the cooling phase. This deformed state is further evolved by subsequent laser pulses. These results have implications to developing accurate computer simulations of thin-film dewetting by energetic beams aimed at the manufacturing of optically active nanoscale materials for applications including information processing, optical devices, and solar energy harvesting.« less

Dynamics of ultrathin metal films on amorphous substrates under fast thermal processing

NASA Astrophysics Data System (ADS)

Favazza, Christopher; Kalyanaraman, Ramki; Sureshkumar, Radhakrishna

2007-11-01

A mathematical model is developed to analyze the growth/decay rate of surface perturbations of an ultrathin metal film on an amorphous substrate (SiO2). The formulation combines the approach of Mullins [W. W. Mullins, J. Appl. Phys. 30, 77 (1959)] for bulk surfaces, in which curvature-driven mass transport and surface deformation can occur by surface/volume diffusion and evaporation-condensation processes, with that of Spencer etal . [B. J. Spencer, P. W. Voorhees, and S. H. Davis, Phys. Rev. Lett. 67, 26 (1991)] to describe solid-state transport in thin films under epitaxial strain. Modifications of the Mullins model to account for thin-film boundary conditions result in qualitatively different dispersion relationships especially in the limit as kho≪1, where k is the wavenumber of the perturbation and ho is the unperturbed film height. The model is applied to study the relative rate of solid-state mass transport as compared to that of liquid phase dewetting in a thin film subjected to a fast thermal pulse. Specifically, we have recently shown that multiple cycles of nanosecond (ns) pulsed laser melting and resolidification of ultrathin metal films on amorphous substrates can lead to the formation of various types of spatially ordered nanostructures [J. Trice, D. Thomas, C. Favazza, R. Sureshkumar, and R. Kalyanaraman, Phys. Rev. B 75, 235439 (2007)]. The pattern formation has been attributed to the dewetting of the thin film by a hydrodynamic instability. In such experiments the film is in the solid state during a substantial fraction of each thermal cycle. However, results of a linear stability analysis based on the aforementioned model suggest that solid-state mass transport has a negligible effect on morphological changes of the surface. Further, a qualitative analysis of the effect of thermoelastic stress, induced by the rapid temperature changes in the film-substrate bilayer, suggests that stress relaxation does not appreciably contribute to surface deformation. Hence, surface deformation caused by liquid phase instabilities is rapidly quenched-in during the cooling phase. This deformed state is further evolved by subsequent laser pulses. These results have implications to developing accurate computer simulations of thin-film dewetting by energetic beams aimed at the manufacturing of optically active nanoscale materials for applications including information processing, optical devices, and solar energy harvesting.

Solid state photomultiplier for astronomy, phase 2

NASA Technical Reports Server (NTRS)

Besser, P. J.; Hays, K. M.; Laviolette, R. A.

1989-01-01

Epitaxial layers with varying donor concentration profiles were grown on silicon substrate wafers using chemical vapor deposition (CVD) techniques, and solid state photomultiplier (SSPM) devices were fabricated from the wafers. Representative detectors were tested in a low background photon flux, low temperature environment to determine the device characteristics for comparison to NASA goals for astronomical applications. The SSPM temperatures varied between 6 and 11 K with background fluxes in the range from less than 5 x 10 to the 6th power to 10 to the 13th power photons/square cm per second at wavelengths of 3.2 and 20 cm. Measured parameters included quantum efficiency, dark count rate and bias current. Temperature for optimal performance is 10 K, the highest ever obtained for SSPMs. The devices exhibit a combination of the lowest dark current and highest quantum efficiency yet achieved. Experimental data were reduced, analyzed and used to generate recommendations for future studies. The background and present status of the microscopic theory of SSPM operation were reviewed and summarized. Present emphasis is on modeling of the avalanche process which is the basis for SSPM operation. Approaches to the solution of the Boltzmann transport equation are described and the treatment of electron scattering mechanisms is presented. The microscopic single-electron transport theory is ready to be implemented for large-scale computations.

Growth Twinning and Generation of High-Frequency Surface Nanostructures in Ultrafast Laser-Induced Transient Melting and Resolidification.

PubMed

Sedao, Xxx; Shugaev, Maxim V; Wu, Chengping; Douillard, Thierry; Esnouf, Claude; Maurice, Claire; Reynaud, Stéphanie; Pigeon, Florent; Garrelie, Florence; Zhigilei, Leonid V; Colombier, Jean-Philippe

2016-07-26

The structural changes generated in surface regions of single crystal Ni targets by femtosecond laser irradiation are investigated experimentally and computationally for laser fluences that, in the multipulse irradiation regime, produce sub-100 nm high spatial frequency surface structures. Detailed experimental characterization of the irradiated targets combining electron back scattered diffraction analysis with high-resolution transmission electron microscopy reveals the presence of multiple nanoscale twinned domains in the irradiated surface regions of single crystal targets with (111) surface orientation. Atomistic- and continuum-level simulations performed for experimental irradiation conditions reproduce the generation of twinned domains and establish the conditions leading to the formation of growth twin boundaries in the course of the fast transient melting and epitaxial regrowth of the surface regions of the irradiated targets. The observation of growth twins in the irradiated Ni(111) targets provides strong evidence of the role of surface melting and resolidification in the formation of high spatial frequency surface structures. This also suggests that the formation of twinned domains can be used as a sensitive measure of the levels of liquid undercooling achieved in short pulse laser processing of metals.

Growth and Characterization of (211)B Cadmium Telluride Buffer Layer Grown by Metal-organic Vapor Phase Epitaxy on Nanopatterned Silicon for Mercury Cadmium Telluride Based Infrared Detector Applications

NASA Astrophysics Data System (ADS)

Shintri, Shashidhar S.

Mercury cadmium telluride (MCT or Hg1-xCdxTe) grown by molecular beam epitaxy (MBE) is presently the material of choice for fabricating infrared (IR) detectors used in night vision based military applications. The focus of MCT epitaxy has gradually shifted since the last decade to using Si as the starting substrate since it offers several advantages. But the ˜19 % lattice mismatch between MCT and Si generates lots of crystal defects some of which degrade the performance of MCT devices. Hence thick CdTe films are used as buffer layers on Si to accommodate the defects. However, growth of high quality single crystal CdTe on Si is challenging and to date, the best MBE CdTe/Si reportedly has defects in the mid-105 cm -2 range. There is a critical need to reduce the defect levels by at least another order of magnitude, which is the main motivation behind the present work. The use of alternate growth technique called metal-organic vapor phase epitaxy (MOVPE) offers some advantages over MBE and in this work MOVPE has been employed to grow the various epitaxial films. In the first part of this work, conditions for obtaining high quality (211)B CdTe epitaxy on (211)Si were achieved, which also involved studying the effect of having additional intermediate buffer layers such as Ge and ZnTe and incorporation of in-situ thermal cyclic annealing (TCA) to reduce the dislocation density. A critical problem of Si cross-contamination due to 'memory effect' of different reactant species was minimized by introducing tertiarybutylArsine (TBAs) which resulted in As-passivation of (211)Si. The best 8-10 µm thick CdTe films on blanket (non-patterned) Si had dislocations around 3×105 cm-2, which are the best reported by MOVPE till date and comparable to the highest quality films available by MBE. In the second part of the work, nanopatterned (211)Si was used to study the effect of patterning on the crystal quality of epitaxial CdTe. In one such study, patterning of ˜20 nm holes in SiO2/Ge/(211)Si was achieved by block co-polymer (BCP) lithography. Conditions for selective CdTe epitaxy was achieved and results showed different defect propagation mechanism at the patterned interface compared to the films grown on blanket Si. In another study, patterning of ˜360 nm holes in SiO2/(211)Si was done by molecular transfer lithography (MxL). Conditions for selective Ge and CdTe epitaxy were achieved which was the most challenging part of this work. Thin CdTe films were characterized to check the effect of nanopatterning. Certain results invariably showed that CdTe grown on nanopatterned substrates demonstrated promise of defect reduction and blocking close to the growth interface. But presently, nanopatterning also offers some serious challenges such as uniformity of patterns and substrate cleaning prior to growth for successful implementation of epitaxy on very large areas. Such factors resulted in degradation of overall crystal quality and will be discussed in this work. This is the first successful demonstration of selective (211)B CdTe epitaxy on Si by MOVPE using some of the relatively novel and promising nanopatterning techniques.

Advanced deposition model for thermal activated chemical vapor deposition

NASA Astrophysics Data System (ADS)

Cai, Dang

Thermal Activated Chemical Vapor Deposition (TACVD) is defined as the formation of a stable solid product on a heated substrate surface from chemical reactions and/or dissociation of gaseous reactants in an activated environment. It has become an essential process for producing solid film, bulk material, coating, fibers, powders and monolithic components. Global market of CVD products has reached multi billions dollars for each year. In the recent years CVD process has been extensively used to manufacture semiconductors and other electronic components such as polysilicon, AlN and GaN. Extensive research effort has been directed to improve deposition quality and throughput. To obtain fast and high quality deposition, operational conditions such as temperature, pressure, fluid velocity and species concentration and geometry conditions such as source-substrate distance need to be well controlled in a CVD system. This thesis will focus on design of CVD processes through understanding the transport and reaction phenomena in the growth reactor. Since the in situ monitor is almost impossible for CVD reactor, many industrial resources have been expended to determine the optimum design by semi-empirical methods and trial-and-error procedures. This approach has allowed the achievement of improvements in the deposition sequence, but begins to show its limitations, as this method cannot always fulfill the more and more stringent specifications of the industry. To resolve this problem, numerical simulation is widely used in studying the growth techniques. The difficulty of numerical simulation of TACVD crystal growth process lies in the simulation of gas phase and surface reactions, especially the latter one, due to the fact that very limited kinetic information is available in the open literature. In this thesis, an advanced deposition model was developed to study the multi-component fluid flow, homogeneous gas phase reactions inside the reactor chamber, heterogeneous surface reactions on the substrate surface, conductive, convective, inductive and radiative heat transfer, species transport and thereto-elastic stress distributions. Gas phase and surface reactions are studied thermodynamically and kinetically. Based on experimental results, detailed reaction mechanisms are proposed and the deposition rates are predicted. The deposition model proposed could be used for other experiments with similar operating conditions. Four different growth systems are presented in this thesis to discuss comprehensive transport phenomena in crystal growth from vapor. The first is the polysilicon bulk growth by modified Siemens technique in which a silicon tube is used as the starting material. The research effort has been focused on system design, geometric and operating parameters optimization, and heterogeneous and homogeneous silane pyrolysis analysis. The second is the GaN thin film growth by iodine vapor phase epitaxy technique. Heat and mass transport is studied analytically and numerically. Gas phase and surface reactions are analyzed thermodynamically and kinetically. Quasi-equilibrium and kinetic deposition models are developed to predict the growth rate. The third one is the AlN thin film growth by halide vapor phase epitaxy technique. The effects of gas phase and surface reactions on the crystal growth rate and deposition uniformity are studied. The last one is the AlN sublimation growth system. The research effort has been focused on the effect of thermal environment evolution on the crystal growth process. The thermoelastic stress formed in the as-grown AlN crystal is also calculated.

Strain tuning of electronic structure in Bi 4Ti 3O 12-LaCoO 3 epitaxial thin films

DOE PAGES

Choi, Woo Seok; Lee, Ho Nyung

2015-05-08

In this study, we investigated the crystal and electronic structures of ferroelectric Bi 4Ti 3O 12 single-crystalline thin films site-specifically substituted with LaCoO 3 (LCO). The epitaxial films were grown by pulsed laser epitaxy on NdGaO 3 and SrTiO 3 substrates to vary the degree of strain. With increasing the LCO substitution, we observed a systematic increase in the c-axis lattice constant of the Aurivillius phase related with the modification of pseudo-orthorhombic unit cells. These compositional and structural changes resulted in a systematic decrease in the band gap, i.e., the optical transition energy between the oxygen 2p and transition-metal 3dmore » states, based on a spectroscopic ellipsometry study. In particular, the Co 3d state seems to largely overlap with the Ti t 2g state, decreasing the band gap. Interestingly, the applied tensile strain facilitates the band-gap narrowing, demonstrating that epitaxial strain is a useful tool to tune the electronic structure of ferroelectric transition-metal oxides.« less

Characterization of structural defects in SnSe2 thin films grown by molecular beam epitaxy on GaAs (111)B substrates

NASA Astrophysics Data System (ADS)

Tracy, Brian D.; Li, Xiang; Liu, Xinyu; Furdyna, Jacek; Dobrowolska, Margaret; Smith, David J.

2016-11-01

Tin selenide thin films have been grown by molecular beam epitaxy on GaAs (111)B substrates at a growth temperature of 150 °C, and a microstructural study has been carried out, primarily using the technique of transmission electron microscopy. The Se:Sn flux ratio during growth was systematically varied and found to have a strong impact on the resultant crystal structure and quality. Low flux ratios (Se:Sn=3:1) led to defective films consisting primarily of SnSe, whereas high flux ratios (Se:Sn>10:1) gave higher quality, single-phase SnSe2. The structure of the monoselenide films was found to be consistent with the Space Group Pnma with the epitaxial growth relationship of [011]SnSe// [ 1 1 bar 0 ] GaAs, while the diselenide films were consistent with the Space Group P 3 bar m1 , and had the epitaxial growth relationship [ 2 1 bar 1 bar 0 ]SnSe2// [ 1 1 bar 0 ] GaAs.

Thermal stability of MBE-grown epitaxial MoSe2 and WSe2 thin films

NASA Astrophysics Data System (ADS)

Chang, Young Jun; Choy, Byoung Ki; Phark, Soo-Hyon; Kim, Minu

Layered transition metal dichalcogenides (TMDs) draw much attention, because of its unique optical properties and band structures depending on the layer thicknesses. However, MBE growth of epitaxial films demands information about thermal stability of stoichiometry and related electronic structure for high temperature range. We grow epitaxial MoSe2 and WSe2 ultrathin films by using molecular beam epitaxy (MBE). We characterize stoichiometry of films grown at various growth temperature by using various methods, XPS, EDX, and TOF-MEIS. We further test high temperature stability of electronic structure for those films by utilizing in-situ ellipsometry attached to UHV chamber. We discuss threshold temperatures up to 700~1000oC, at which electronic phases changes from semiconductor to metal due to selenium deficiency. This information can be useful for potential application of TMDs for fabrication of Van der Waals multilayers and related devices. This research was supported by Nano.Material Technology Development Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT and Future Planning. (2009-0082580), NRF-2014R1A1A1002868.

Interface engineering in epitaxial growth of layered oxides via a conducting layer insertion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yun, Yu; Meng, Dechao; Wang, Jianlin

2015-07-06

There is a long-standing challenge in the fabrication of layered oxide epitaxial films due to their thermodynamic phase-instability and the large stacking layer number. Recently, the demand for high-quality thin films is strongly pushed by their promising room-temperature multiferroic properties. Here, we find that by inserting a conducting and lattice matched LaNiO{sub 3} buffer layer, high quality m = 5 Bi{sub 6}FeCoTi{sub 3}O{sub 18} epitaxial films can be fabricated using the laser molecular beam epitaxy, in which the atomic-scale sharp interface between the film and the metallic buffer layer explains the enhanced quality. The magnetic and ferroelectric properties of the high qualitymore » Bi{sub 6}FeCoTi{sub 3}O{sub 18} films are studied. This study demonstrates that insertion of the conducting layer is a powerful method in achieving high quality layered oxide thin films, which opens the door to further understand the underline physics and to develop new devices.« less

Epitaxial Ni-Mn-Ga-Co thin films on PMN-PT substrates for multicaloric applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schleicher, B., E-mail: b.schleicher@ifw-dresden.de; Niemann, R.; Schultz, L.

2015-08-07

Multicaloric stacks consisting of a magnetocaloric film on a piezoelectric substrate promise improved caloric properties as the transition temperature can be controlled by both magnetic and electric fields. We present epitaxially grown magnetocaloric Ni-Mn-Ga-Co thin films on ferroelectric Pb(Mg{sub 1/3}Nb{sub 2/3}){sub 0.72}Ti{sub 0.28}O{sub 3} substrates. Structure and microstructure of two samples, being in the austenitic and martensitic state at room temperature, are investigated by X-ray diffraction in two- and four-circle geometry and by atomic force microscopy. In addition, high temperature magnetometry was performed on the latter sample. The combination of these methods allows separating the influence of epitaxial growth andmore » martensitic transformation. A preferential alignment of twin boundaries is observed already in the as-deposited state, which indicates the presence of prestress, without applying an electric field to the substrate. A temperature-magnetic field phase diagram is presented, which demonstrates the inverse magnetocaloric effect of the epitaxial Ni-Mn-Ga-Co film.« less

Epitaxial growth of GaN/AlN/InAlN heterostructures for HEMTs in horizontal MOCVD reactors with different designs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tsatsulnikov, A. F., E-mail: andrew@beam.ioffe.ru; Lundin, W. V.; Sakharov, A. V.

2016-09-15

The epitaxial growth of InAlN layers and GaN/AlN/InAlN heterostructures for HEMTs in growth systems with horizontal reactors of the sizes 1 × 2', 3 × 2', and 6 × 2' is investigated. Studies of the structural properties of the grown InAlN layers and electrophysical parameters of the GaN/AlN/InAlN heterostructures show that the optimal quality of epitaxial growth is attained upon a compromise between the growth conditions for InGaN and AlGaN. A comparison of the epitaxial growth in different reactors shows that optimal conditions are realized in small-scale reactors which make possible the suppression of parasitic reactions in the gas phase.more » In addition, the size of the reactor should be sufficient to provide highly homogeneous heterostructure parameters over area for the subsequent fabrication of devices. The optimal compositions and thicknesses of the InAlN layer for attaining the highest conductance in GaN/AlN/InAlN transistor heterostructures.« less

Epitaxially Grown Films of Standing and Lying Pentacene Molecules on Cu(110) Surfaces

PubMed Central

2011-01-01

Here, it is shown that pentacene thin films (30 nm) with distinctively different crystallographic structures and molecular orientations can be grown under essentially identical growth conditions in UHV on clean Cu(110) surfaces. By X-ray diffraction, we show that the epitaxially oriented pentacene films crystallize either in the “thin film” phase with standing molecules or in the “single crystal” structure with molecules lying with their long axes parallel to the substrate. The morphology of the samples observed by atomic force microscopy shows an epitaxial alignment of pentacene crystallites, which corroborates the molecular orientation observed by X-ray diffraction pole figures. Low energy electron diffraction measurements reveal that these dissimilar growth behaviors are induced by subtle differences in the monolayer structures formed by slightly different preparation procedures. PMID:21479111

Cancer: a profit-driven biosystem?

PubMed

Deisboeck, Thomas S

2008-08-01

The argument is made that solid malignant tumors behave as profit-driven biological systems in that they expand their nutrient-uptaking surface to increase energetic revenue, at a comparably low metabolic cost. Within this conceptual framework, cancer cell migration is a critical mechanism as it maximizes systemic surface expansion while minimizing diffusion distance. Treating these tumor systems with adjuvant anti-proliferative regimen only should increase the energetic net gain of the viable cancer cells left behind, hence would facilitate tumor recurrence. Therapeutic attempts to better control tumor (re)growth should therefore aim primarily at containing its surface expansion, thus reducing its energetic revenue, or increasing its metabolic costs or better yet, both.

Cancer: A profit-driven biosystem ?

PubMed Central

Deisboeck, Thomas S.

2008-01-01

The argument is made that solid malignant tumors behave as profit-driven biological systems in that they expand their nutrient-uptaking surface to increase energetic revenue, at a comparably low metabolic cost. Within this conceptual framework, cancer cell migration is a critical mechanism as it maximizes systemic surface expansion while minimizing diffusion distance. Treating these tumor systems with adjuvant anti-proliferative regimen only should increase the energetic net gain of the viable cancer cells left behind, hence would facilitate tumor recurrence. Therapeutic attempts to better control tumor (re)growth should therefore aim primarily at containing its surface expansion, thus reducing its energetic revenue, or increasing its metabolic costs or better yet, both. PMID:18420354

Magnetic phase change in Mn-doped ZnSnAs2 thin films depending on Mn concentration

NASA Astrophysics Data System (ADS)

Uchitomi, Naotaka; Hidaka, Shiro; Saito, Shin; Asubar, Joel T.; Toyota, Hideyuki

2018-04-01

The relationship between Mn concentration and Curie temperature (TC) is studied for Mn-doped ZnSnAs2 ferromagnetic semiconductors, epitaxially grown on InP substrates by molecular beam epitaxy. In the ferromagnetic phase, Mn distributions in a (Zn,Mn,Sn)As2 thin film with 7.2 cation percent (cat. %) Mn are investigated using three-dimensional atom probe tomography. The results indicate an inhomogeneous distribution which spreads to a relatively high Mn concentration of 9.0 at. % (at. %). In the paramagnetic phase, it is found that the paramagnetic to ferromagnetic transition takes place sharply with a TC of 334 K when the Mn doping concentration increases to about 4 cat. % Mn, which corresponds to a magnetic percolation threshold for ferromagnetism in (Zn,Mn,Sn)As2. An effective Curie temperature ⟨TC⟩ is considered to bridge the Curie temperatures obtained experimentally to those calculated theoretically in inhomogeneous magnetic semiconductors. The behavior of magnetism in Mn-doped ZnSnAs2 can be explained by three different phases within the present framework.

Self-assembled GaInNAs/GaAsN quantum dot lasers: solid source molecular beam epitaxy growth and high-temperature operation

PubMed Central

Liu, CY; Sun, ZZ; Yew, KC

2006-01-01

Self-assembled GaInNAs quantum dots (QDs) were grown on GaAs (001) substrate using solid-source molecular-beam epitaxy (SSMBE) equipped with a radio-frequency nitrogen plasma source. The GaInNAs QD growth characteristics were extensively investigated using atomic-force microscopy (AFM), photoluminescence (PL), and transmission electron microscopy (TEM) measurements. Self-assembled GaInNAs/GaAsN single layer QD lasers grown using SSMBE have been fabricated and characterized. The laser worked under continuous wave (CW) operation at room temperature (RT) with emission wavelength of 1175.86 nm. Temperature-dependent measurements have been carried out on the GaInNAs QD lasers. The lowest obtained threshold current density in this work is ∼1.05 kA/cm2from a GaInNAs QD laser (50 × 1,700 µm2) at 10 °C. High-temperature operation up to 65 °C was demonstrated from an unbonded GaInNAs QD laser (50 × 1,060 µm2), with high characteristic temperature of 79.4 K in the temperature range of 10–60 °C.

Epitaxial structure and electronic property of β-Ga2O3 films grown on MgO (100) substrates by pulsed-laser deposition

NASA Astrophysics Data System (ADS)

Wakabayashi, Ryo; Yoshimatsu, Kohei; Hattori, Mai; Ohtomo, Akira

2017-10-01

We investigated heteroepitaxial growth of Si-doped Ga2O3 films on MgO (100) substrates by pulsed-laser deposition as a function of growth temperature (Tg) to find a strong correlation between the structural and electronic properties. The films were found to contain cubic γ-phase and monoclinic β-phase, the latter of which indicated rotational twin domains when grown at higher Tg. The formation of the metastable γ-phase and twin-domain structure in the stable β-phase are discussed in terms of the in-plane epitaxial relationships with a square MgO lattice, while crystallinity of the β-phase degraded monotonically with decreasing Tg. The room-temperature conductivity indicated a maximum at the middle of Tg, where the β-Ga2O3 layer was relatively highly crystalline and free from the twin-domain structure. Moreover, both crystallinity and conductivity of β-Ga2O3 films on the MgO substrates were found superior to those on α-Al2O3 (0001) substrates. A ratio of the conductivity, attained to the highest quantity on each substrate, was almost three orders of magnitude.

Layer-by-layer epitaxial growth of defect-engineered strontium cobaltites

DOE PAGES

Andersen, Tassie K.; Cook, Seyoung; Wan, Gang; ...

2018-01-18

Here, control over structure and composition of (ABO 3) perovskite oxides offers exciting opportunities since these materials possess unique, tunable properties. Perovskite oxides with cobalt B-site cations are particularly promising, as the range of the cation’s stable oxidation states leads to many possible structural frameworks. Here, we report growth of strontium cobalt oxide thin films by molecular beam epitaxy, and conditions necessary to stabilize different defect concentration phases. In situ X-ray scattering is used to monitor structural evolution during growth, while in situ X-ray absorption near-edge spectroscopy is used to probe oxidation state and measure changes to oxygen vacancy concentrationmore » as a function of film thickness. Experimental results are compared to kinetically-limited thermodynamic predictions, in particular, solute trapping, with semi-quantitative agreement. Agreement between observations of dependence of cobaltite phase on oxidation activity and deposition rate, and predictions indicates that a combined experimental/theoretical approach is key to understanding phase behavior in the strontium cobalt oxide system.« less

Layer-by-layer epitaxial growth of defect-engineered strontium cobaltites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Andersen, Tassie K.; Cook, Seyoung; Wan, Gang

Here, control over structure and composition of (ABO 3) perovskite oxides offers exciting opportunities since these materials possess unique, tunable properties. Perovskite oxides with cobalt B-site cations are particularly promising, as the range of the cation’s stable oxidation states leads to many possible structural frameworks. Here, we report growth of strontium cobalt oxide thin films by molecular beam epitaxy, and conditions necessary to stabilize different defect concentration phases. In situ X-ray scattering is used to monitor structural evolution during growth, while in situ X-ray absorption near-edge spectroscopy is used to probe oxidation state and measure changes to oxygen vacancy concentrationmore » as a function of film thickness. Experimental results are compared to kinetically-limited thermodynamic predictions, in particular, solute trapping, with semi-quantitative agreement. Agreement between observations of dependence of cobaltite phase on oxidation activity and deposition rate, and predictions indicates that a combined experimental/theoretical approach is key to understanding phase behavior in the strontium cobalt oxide system.« less

Layer-by-Layer Epitaxial Growth of Defect-Engineered Strontium Cobaltites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Andersen, Tassie K.; Cook, Seyoung; Wan, Gang

Control over structure and composition of (ABO(3)) perovskite oxides offers exciting opportunities since these materials possess unique, tunable properties. Perovskite oxides with cobalt B-site cations are particularly promising, as the range of the cations stable oxidation states leads to many possible structural frameworks. Here, we report growth of strontium cobalt oxide thin films by molecular beam epitaxy, and conditions necessary to stabilize different defect concentration phases. In situ X-ray scattering is used to monitor structural evolution during growth, while in situ X-ray absorption near-edge spectroscopy is used to probe oxidation state and measure changes to oxygen vacancy concentration as amore » function of film thickness. Experimental results are compared to kinetically limited thermodynamic predictions, in particular, solute trapping, with semiquantitative agreement. Agreement between observations of dependence of cobaltite phase on oxidation activity and deposition rate, and predictions indicates that a combined experimental/theoretical approach is key to understanding phase behavior in the strontium cobalt oxide system.« less

Investigation of the growth of garnet films by liquid phase epitaxy

NASA Technical Reports Server (NTRS)

Moody, J. W.; Shaw, R. W.; Sandfort, R. M.

1974-01-01

Liquid phase expitaxy was investigated to determine its applicability to fabricating magnetic rare earth garnet films for spacecraft data recording systems. Two mixed garnet systems were investigated in detail: (1) Gd-Y and (2) Eu-Yb-Y. All films were deposited on Gd3Ga5012 substrates. The uniaxial anisotropy of the Gd-Y garnets is primarily stress-induced. These garnets are characterized by high-domain wall mobility, low coercivity and modest anisotropy. Characteristic length was found to be relatively sensitive to temperature. The Eu-Yb-Y garnets exhibit acceptable mobilities, good temperature stability and reasonable quality factors. The uniaxial anisotropy of these garnets is primarily growth-induced. The system is well suited for compositional "tailoring" to optimize specific desirable properties. Liquid phase epitaxy can be used to deposit Gd3Ga5012 spacing layers on magnetic garnet films and this arrangement possesses certain advantages over more conventional magnetic filmspacing layer combinations. However, it cannot be used if the magnetic film is to be ion implanted.

Effect of levofloxacin, erythromycin or rifampicin pretreatment on growth of Legionella pneumophila in human monocytes.

PubMed

Smith, R P; Baltch, A L; Franke, M; Hioe, W; Ritz, W; Michelsen, P

1997-11-01

Opsonophagocytic killing of some bacteria (Staphylococcus aureus, Pseudomonas aeruginosa) by phagocytes is enhanced by previous brief exposure of the organism to antibiotics. We studied the regrowth of Legionella pneumophila previously pretreated with levofloxacin, erythromycin and/or rifampicin in human monocytes. The MIC for the L. pneumophila isolate of levofloxacin, erythromycin and rifampicin was 0.03, 0.5 and 0.001 mg/L, respectively. Growth of L. pneumophila from buffered charcoal yeast extract (BCYE) agar for 24 h was subcultured into BYE broth containing from 0 to 4x MIC of levofloxacin, erythromycin or rifampicin. After incubation at 35 degrees C in 5% CO2 for 18 h, the organisms were washed and opsonized with 20% heat inactivated pooled normal human serum. Thereafter, L. pneumophila was exposed to human monocytes (5:1 ratio) previously adhered to wells in tissue culture plates containing RPMI and 10% fetal calf serum. After 0, 24, 48 and 72 h of incubation, quantitative cultures of lysed human monocytes were done on BCYE agar. Our results indicate effective inhibition on L. pneumophila at 0 h regardless of the antibiotic (levofloxacin, rifampicin or erythromycin) or their concentrations (1x, 2x or 4x MIC). At 24, 48 and 72 h, recovery and regrowth of L. pneumophila were both antibiotic- and concentration-dependent. In comparison with controls (no antibiotic pretreatment), peak regrowth of L. pneumophila pretreated with either 1x MIC of levofloxacin or erythromycin was delayed (48 versus 24 h) and reduced (30% of control peak regrowth). Regrowth of L. pneumophila pretreated with 1x MIC of rifampicin continued beyond 72 h. Pretreatment with levofloxacin at 4x MIC caused the greatest degree of growth inhibition (2 log10). In contrast, at 72 h, regrowth of organisms pretreated with 4x MIC of erythromycin or rifampicin was less than peak control (P < 0.01) but greater than that seen with levofloxacin (P < 0.01). The rate and degree of regrowth of L. pneumophila pretreated with combinations of levofloxacin or erythromycin with rifampicin, or levofloxacin with erythromycin (all at 1x MIC) was similar to that seen with single drugs. Thus, significant delay and reduction of regrowth in this phagocytic system occurred with levofloxacin only. Prolonged exposure of the organism at 4x MIC levofloxacin concentrations was effective in suppressing regrowth of pretreated L. pneumophila in human monocytes.

Vitamins C and E improve regrowth and reduce lipid peroxidation of blackberry shoot tips following cryopreservation.

PubMed

Uchendu, Esther E; Leonard, Scott W; Traber, Maret G; Reed, Barbara M

2010-01-01

Oxidative processes involved in cryopreservation protocols may be responsible for the reduced viability of tissues after liquid nitrogen exposure. Antioxidants that counteract these reactions should improve recovery. This study focused on oxidative lipid injury and the effects of exogenous vitamin E (tocopherol, Vit E) and vitamin C (ascorbic acid, Vit C) treatments on regrowth at four critical steps of the plant vitrification solution number 2 (PVS2) vitrification cryopreservation technique; pretreatment, loading, rinsing, and regrowth. Initial experiments showed that Vit E at 11-15 mM significantly increased regrowth (P < 0.001) when added at any of the four steps. There was significantly more malondialdehyde (MDA), a lipid peroxidation product, at each of the steps than in fresh untreated shoot tips. Vit E uptake was assayed at each step and showed significantly more alpha- and gamma-tocopherols in treated shoots than those without Vit E. Vit E added at each step significantly reduced MDA formation and improved shoot regrowth. Vit C (0.14-0.58 mM) also significantly improved regrowth of shoot tips at each step compared to the controls. Regrowth medium with high iron concentrations and Vit C decreased recovery. However, in iron-free medium, Vit C significantly improved recovery. Treatments with Vit E (11 mM) and Vit C (0.14 mM) combined were not significantly better than Vit C alone. We recommend adding Vit C (0.28 mM) to the pretreatment medium, the loading solution or the rinse solution in the PVS2 vitrification protocol. This is the first report of the application of vitamins for improving cryopreservation of plant tissues by minimizing oxidative damage.

Intake and digestion of wethers fed with dwarf elephant grass hay with or without the inclusion of peanut hay.

PubMed

Schnaider, Maria Alice; Ribeiro-Filho, Henrique Mendonça Nunes; Vilmar Kozloski, Gilberto; Reiter, Tatiana; Dall Orsoletta, Aline Cristina; Dallabrida, Ademar Luiz

2014-08-01

The aim of this study was to evaluate the effect of the inclusion of peanut (Arachis pintoi cv. Amarillo) hay in diets based on dwarf elephant grass (DEG, Pennisetum purpureum Schum cv. Kurumi) hay of different regrowth ages on forage intake and digestibility in wether lambs. The experimental treatments consisted of DEG hay with an interval of regrowth of 30 or 45 days offered as the only feed or in mixture with peanut hay (300 g/kg of total dry matter (DM)), which were tested in eight Texel × Suffolk crossbred wethers in a replicated 4 × 4 Latin square experiment. Both organic matter (OM) and digestible OM intakes were higher (P < 0.05) in animals receiving the legume forage. Total apparent OM digestibility was higher (P < 0.05) at an increased grass regrowth age. Ruminal OM digestibility increased (P < 0.05) with legume inclusion and at a higher grass regrowth age. The nitrogen (N) intake was higher (P < 0.05) in legume treatments and lower (P < 0.05) as the grass regrowth age increased, but retention of N was not affected by treatments. Duodenal flow of both, non-ammonia N and microbial N, were not affected by legume inclusion and were lower (P < 0.05) as grass regrowth age increased. The efficiency of rumen microbial protein synthesis (ERMPS) was negatively affected (P < 0.05) by legume inclusion and was lower (P < 0.05) as the grass regrowth age increased. Supplementation of dwarf elephant grass hay cut at the vegetative stage with peanut legume hay improves nutritional supply to wethers due to an increase in the forage intake.

LONG-TERM CONSERVATION OF PROTOCORMS OF Brassavola nodosa (L) LIND. (ORCHIDACEAE): EFFECT OF ABA AND A RANGE OF CRYOCONSERVATION TECHNIQUES.

PubMed

Mata-Rosas, M; Lastre-Puertos, E

2015-01-01

Populations of Brassavola nodosa have been severely affected by habitat destruction and illegal collecting, and as with the majority of orchid species, it is critical to take action to guarantee their continued survival. The present study aimed to establish protocols for the long-term conservation of protocorms of species. Four different cryogenic techniques were compared: encapsulation-dehydration (ED), encapsulation-vitrification (EV), encapsulation-dehydration-vitrification (EDV) and vitrification. Preculture of protocorms with ABA was a critical factor in obtaining high percentages of regrowth. With vitrification, 100% regrowth was achieved in five treatments, mainly when protocorms were dehydrated with PVS2 for 120 min. 100% regrowth was also obtained with EDV, where the protocorms were precultured with ABA 5 mg/l for 3 days and incubated with PVS2 for 60 min. With the ED, regrowth of 72% was achieved with the preculture of protocorms with ABA 5 mg/l for the three times of incubation used (3, 6 and 9 days). In the case of EV, 92% regrowth, was recorded when protocorms were precultured for 9 days with ABA 3 mg/l and incubated with PVS2 for 90 min. Although regrowth of protocorms was obtained with all the techniques used, the vitrification technique is preferred since it requires less labour and is less costly.

Thin film seeds for melt processing textured superconductors for practical applications

DOEpatents

Veal, Boyd W.; Paulikas, Arvydas; Balachandran, Uthamalingam; Zhong, Wei

1999-01-01

A method of fabricating bulk superconducting material such as RBa.sub.2 Cu.sub.3 O.sub.7-.delta. where R is La or Y comprising depositing a thin epitaxially oriented film of Nd or Sm (123) on an oxide substrate. The powder oxides of RBa.sub.2 Cu.sub.3 O.sub.7-.delta. or oxides and/or carbonates of R and Ba and Cu present in mole ratios to form RBa.sub.2 Cu.sub.3 O.sub.7-.delta., where R is Y or La are heated, in physical contact with the thin film of Nd or Sm (123) on the oxide substrate to a temperature sufficient to form a liquid phase in the oxide or carbonate mixture while maintaining the thin film solid to grow a large single domain 123 superconducting material. Then the material is cooled. The thin film is between 200 .ANG. and 2000 .ANG.. A construction prepared by the method is also disclosed.

Thin film seeds for melt processing textured superconductors for practical applications

DOEpatents

Veal, B.W.; Paulikas, A.; Balachandran, U.; Zhong, W.

1999-02-09

A method of fabricating bulk superconducting material such as RBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} where R is La or Y comprising depositing a thin epitaxially oriented film of Nd or Sm (123) on an oxide substrate is disclosed. The powder oxides of RBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} or oxides and/or carbonates of R and Ba and Cu present in mole ratios to form RBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}}, where R is Y or La are heated, in physical contact with the thin film of Nd or Sm (123) on the oxide substrate to a temperature sufficient to form a liquid phase in the oxide or carbonate mixture while maintaining the thin film solid to grow a large single domain 123 superconducting material. Then the material is cooled. The thin film is between 200 {angstrom} and 2000 {angstrom}. A construction prepared by the method is also disclosed.

1.55 µm InAs/GaAs Quantum Dots and High Repetition Rate Quantum Dot SESAM Mode-locked Laser

NASA Astrophysics Data System (ADS)

Zhang, Z. Y.; Oehler, A. E. H.; Resan, B.; Kurmulis, S.; Zhou, K. J.; Wang, Q.; Mangold, M.; Süedmeyer, T.; Keller, U.; Weingarten, K. J.; Hogg, R. A.

2012-06-01

High pulse repetition rate (>=10 GHz) diode-pumped solid-state lasers, modelocked using semiconductor saturable absorber mirrors (SESAMs) are emerging as an enabling technology for high data rate coherent communication systems owing to their low noise and pulse-to-pulse optical phase-coherence. Quantum dot (QD) based SESAMs offer potential advantages to such laser systems in terms of reduced saturation fluence, broader bandwidth, and wavelength flexibility. Here, we describe the development of an epitaxial process for the realization of high optical quality 1.55 µm In(Ga)As QDs on GaAs substrates, their incorporation into a SESAM, and the realization of the first 10 GHz repetition rate QD-SESAM modelocked laser at 1.55 µm, exhibiting ~2 ps pulse width from an Er-doped glass oscillator (ERGO). With a high areal dot density and strong light emission, this QD structure is a very promising candidate for many other applications, such as laser diodes, optical amplifiers, non-linear and photonic crystal based devices.

Fast solid-phase synthesis of large-area few-layer 1T'-MoTe2 films

NASA Astrophysics Data System (ADS)

Xie, Sheng; Chen, Lin; Zhang, Tian-Bao; Nie, Xin-Ran; Zhu, Hao; Ding, Shi-Jin; Sun, Qing-Qing; Zhang, David Wei

2017-06-01

In this study, we report on a novel approach to produce ∼12 nm thick few-layer monoclinic 1T'-MoTe2 films. The deposition method comprised sputtering of Mo, molecular beam epitaxy of Te, and rapid thermal processing to effect tellurization of the Mo into 1T'-MoTe2. The heating rate and annealing time are the critical factors. 30 °C s-1 heating rate and 2 min annealing at 470 °C were adopted in this work. X-ray photoelectron spectroscopy confirmed the formation of stoichiometric 1T'-MoTe2 films, while X-ray diffraction confirmed the monoclinic polymorph. Raman spectroscopy confirmed spatial uniformity over the sample size of 1 cm × 1.5 cm. Our fast synthesis approach to realize high-quality 1T'-MoTe2 paves the way towards the large-scale application of 1T'-MoTe2 in high-performance nanoelectronics and optoelectronics.

Formation and photoluminescence of GaAs1-xNx dilute nitride achieved by N-implantation and flash lamp annealing

NASA Astrophysics Data System (ADS)

Gao, Kun; Prucnal, S.; Skorupa, W.; Helm, M.; Zhou, Shengqiang

2014-07-01

In this paper, we present the fabrication of dilute nitride semiconductor GaAs1-xNx by nitrogen-ion-implantation and flash lamp annealing (FLA). N was implanted into the GaAs wafers with atomic concentration of about ximp1 = 0.38% and ximp2 = 0.76%. The GaAs1-xNx layer is regrown on GaAs during FLA treatment in a solid phase epitaxy process. Room temperature near band-edge photoluminescence (PL) has been observed from the FLA treated GaAs1-xNx samples. According to the redshift of the near band-edge PL peak, up to 80% and 44% of the implanted N atoms have been incorporated into the lattice by FLA for ximp1 = 0.38% and ximp2 = 0.76%, respectively. Our investigation shows that ion implantation followed by ultrashort flash lamp treatment, which allows for large scale production, exhibits a promising prospect on bandgap engineering of GaAs based semiconductors.

Strain-free bulk-like GaN grown by hydride-vapor-phase-epitaxy on two-step epitaxial lateral overgrown GaN template

NASA Astrophysics Data System (ADS)

Gogova, D.; Kasic, A.; Larsson, H.; Hemmingsson, C.; Monemar, B.; Tuomisto, F.; Saarinen, K.; Dobos, L.; Pécz, B.; Gibart, P.; Beaumont, B.

2004-07-01

Crack-free bulk-like GaN with high crystalline quality has been obtained by hydride-vapor-phase-epitaxy (HVPE) growth on a two-step epitaxial lateral overgrown GaN template on sapphire. During the cooling down stage, the as-grown 270-μm-thick GaN layer was self-separated from the sapphire substrate. Plan-view transmission electron microscopy images show the dislocation density of the free-standing HVPE-GaN to be ˜2.5×107 cm-2 on the Ga-polar face. A low Ga vacancy related defect concentration of about 8×1015 cm-3 is extracted from positron annihilation spectroscopy data. The residual stress and the crystalline quality of the material are studied by two complementary techniques. Low-temperature photoluminescence spectra show the main neutral donor bound exciton line to be composed of a doublet structure at 3.4715 (3.4712) eV and 3.4721 (3.4718) eV for the Ga- (N-) polar face with the higher-energy component dominating. These line positions suggest virtually strain-free material on both surfaces with high crystalline quality as indicated by the small full width at half maximum values of the donor bound exciton lines. The E1(TO) phonon mode position measured at 558.52 cm-1 (Ga face) by infrared spectroscopic ellipsometry confirms the small residual stress in the material, which is hence well suited to act as a lattice-constant and thermal-expansion-coefficient matched substrate for further homoepitaxy, as needed for high-quality III-nitride device applications.

S6 Kinase Inhibits Intrinsic Axon Regeneration Capacity via AMP Kinase in Caenorhabditis elegans

PubMed Central

Hubert, Thomas; Wu, Zilu; Chisholm, Andrew D.

2014-01-01

The ability of axons to regrow after injury is determined by the complex interplay of intrinsic growth programs and external cues. In Caenorhabditis elegans mechanosensory neuron, axons exhibit robust regenerative regrowth following laser axotomy. By surveying conserved metabolic signaling pathways, we have identified the ribosomal S6 kinase RSKS-1 as a new cell-autonomous inhibitor of axon regeneration. RSKS-1 is not required for axonal development but inhibits axon regrowth after injury in multiple neuron types. Loss of function in rsks-1 results in more rapid growth cone formation after injury and accelerates subsequent axon extension. The enhanced regrowth of rsks-1 mutants is partly dependent on the DLK-1 MAPK cascade. An essential output of RSKS-1 in axon regrowth is the metabolic sensor AMP kinase, AAK-2. We further show that the antidiabetic drug phenformin, which activates AMP kinase, can promote axon regrowth. Our data reveal a new function for an S6 kinase acting through an AMP kinase in regenerative growth of injured axons. PMID:24431434

Encapsulation of nodal cuttings and shoot tips for storage and exchange of cassava germplasm.

PubMed

Danso, K E; Ford-Lloyd, B V

2003-04-01

We report the encapsulation of in vitro-derived nodal cuttings or shoot tips of cassava in 3% calcium alginate for storage and germplasm exchange purposes. Shoot regrowth was not significantly affected by the concentration of sucrose in the alginate matrix while root formation was. In contrast, increasing the sucrose concentration in the calcium chloride polymerisation medium significantly reduced regrowth from encapsulated nodal cuttings of accession TME 60444. Supplementing the alginate matrix with increased concentrations of 6-benzylaminopurine and alpha-naphthaleneacetic acid enhanced complete plant regrowth within 2 weeks. Furthermore, plant regrowth by encapsulated nodal cuttings and shoot tips was significantly affected by the duration of the storage period as shoot recovery decreased from almost 100% to 73.3% for encapsulated nodal cuttings and 94.4% to 60% for shoot tips after 28 days of storage. The high frequency of plant regrowth from alginate-coated micropropagules coupled with high viability percentage after 28 days of storage is highly encouraging for the exchange of cassava genetic resources. Such encapsulated micropropagules could be used as an alternative to synthetic seeds derived from somatic embryos.

The {alpha}-particle excited scintillation response of the liquid phase epitaxy grown LuAG:Ce thin films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Prusa, P.; Cechak, T.; Mares, J. A.

2008-01-28

Liquid phase epitaxy grown Lu{sub 3}Al{sub 5}O{sub 12}:Ce (LuAG:Ce) 20 {mu}m thick films and plate cut from the bulk Czochralski-grown LuAG:Ce crystal were prepared for comparison of photoelectron yield (PhY) and PhY dependence on shaping time (0.5-10 {mu}s). {sup 241}Am ({alpha} particles) was used for excitation. At the 0.5 {mu}s shaping time, the best film shows comparable PhY with the bulk sample. PhY of bulk material increases noticeably more with shaping time than that of the films. Energy resolution of films is better. Influence of Pb{sup 2+} contamination in the films (from the flux) and antisite Lu{sub Al} defect inmore » bulk material is discussed.« less

Approach to high quality GaN lateral nanowires and planar cavities fabricated by focused ion beam and metal-organic vapor phase epitaxy.

PubMed

Pozina, Galia; Gubaydullin, Azat R; Mitrofanov, Maxim I; Kaliteevski, Mikhail A; Levitskii, Iaroslav V; Voznyuk, Gleb V; Tatarinov, Evgeniy E; Evtikhiev, Vadim P; Rodin, Sergey N; Kaliteevskiy, Vasily N; Chechurin, Leonid S

2018-05-08

We have developed a method to fabricate GaN planar nanowires and cavities by combination of Focused Ion Beam (FIB) patterning of the substrate followed by Metal Organic Vapor Phase Epitaxy (MOVPE). The method includes depositing a silicon nitride mask on a sapphire substrate, etching of the trenches in the mask by FIB with a diameter of 40 nm with subsequent MOVPE growth of GaN within trenches. It was observed that the growth rate of GaN is substantially increased due to enhanced bulk diffusion of the growth precursor therefore the model for analysis of the growth rate was developed. The GaN strips fabricated by this method demonstrate effective luminescence properties. The structures demonstrate enhancement of spontaneous emission via formation of Fabry-Perot modes.

Phase-field simulations of GaN growth by selective area epitaxy on complex mask geometries

DOE PAGES

Aagesen, Larry K.; Coltrin, Michael Elliott; Han, Jung; ...

2015-05-15

Three-dimensional phase-field simulations of GaN growth by selective area epitaxy were performed. Furthermore, this model includes a crystallographic-orientation-dependent deposition rate and arbitrarily complex mask geometries. The orientation-dependent deposition rate can be determined from experimental measurements of the relative growth rates of low-index crystallographic facets. Growth on various complex mask geometries was simulated on both c-plane and a-plane template layers. Agreement was observed between simulations and experiment, including complex phenomena occurring at the intersections between facets. The sources of the discrepancies between simulated and experimental morphologies were also investigated. We found that the model provides a route to optimize masks andmore » processing conditions during materials synthesis for solar cells, light-emitting diodes, and other electronic and opto-electronic applications.« less

Elimination of macrostep-induced current flow nonuniformity in vertical GaN PN diode using carbon-free drift layer grown by hydride vapor phase epitaxy

NASA Astrophysics Data System (ADS)

Fujikura, Hajime; Hayashi, Kentaro; Horikiri, Fumimasa; Narita, Yoshinobu; Konno, Taichiro; Yoshida, Takehiro; Ohta, Hiroshi; Mishima, Tomoyoshi

2018-04-01

In vertical GaN PN diodes (PNDs) grown entirely by metal–organic chemical vapor deposition (MOCVD), large current nonuniformity was observed. This nonuniformity was induced by macrosteps on the GaN surface through modulation of carbon incorporation into the n-GaN crystal. It was eliminated in a hybrid PND consisting of a carbon-free n-GaN layer grown by hydride vapor phase epitaxy (HVPE) and an MOCVD-regrown p-GaN layer. The hybrid PND showed a fairly low on-resistance (2 mΩ cm2) and high breakdown voltage (2 kV) even without a field plate electrode. These results clearly indicated the strong advantages of the HVPE-grown drift layer for improving power device performance, uniformity, and yield.

Deep-level transient spectroscopy studies of Ni- and Zn-diffused vapor-phase-epitaxy n-GaAs

NASA Technical Reports Server (NTRS)

Partin, D. L.; Chen, J. W.; Milnes, A. G.; Vassamillet, L. F.

1979-01-01

The paper presents deep-level transient spectroscopy studies of Ni- and Zn-diffused vapor-phase epitaxy n-GaAs. Nickel diffused into VPE n-GaAs reduces the hole diffusion length L sub p from 4.3 to 1.1 microns. Deep-level transient spectroscopy was used to identify energy levels in Ni-diffused GaAs; the as-grown VPE GaAs contains traces of these levels and an electron trap. Ni diffusion reduces the concentration of this level by an amount that matches the increase in concentration of each of the two Ni-related levels. A technique for measuring minority-carrier capture cross sections was developed, which indicates that L sub p in Ni-diffused VPE n-GaAs is controlled by the E sub c - 0.39 eV defect level.

Thermodynamic analysis of trimethylgallium decomposition during GaN metal organic vapor phase epitaxy

NASA Astrophysics Data System (ADS)

Sekiguchi, Kazuki; Shirakawa, Hiroki; Chokawa, Kenta; Araidai, Masaaki; Kangawa, Yoshihiro; Kakimoto, Koichi; Shiraishi, Kenji

2018-04-01

We analyzed the decomposition of Ga(CH3)3 (TMG) during the metal organic vapor phase epitaxy (MOVPE) of GaN on the basis of first-principles calculations and thermodynamic analysis. We performed activation energy calculations of TMG decomposition and determined the main reaction processes of TMG during GaN MOVPE. We found that TMG reacts with the H2 carrier gas and that (CH3)2GaH is generated after the desorption of the methyl group. Next, (CH3)2GaH decomposes into (CH3)GaH2 and this decomposes into GaH3. Finally, GaH3 becomes GaH. In the MOVPE growth of GaN, TMG decomposes into GaH by the successive desorption of its methyl groups. The results presented here concur with recent high-resolution mass spectroscopy results.

Effect of AlInGaN barrier layers with various TMGa flows on optoelectronic characteristics of near UV light-emitting diodes grown by atmospheric pressure metalorganic vapor phase epitaxy

NASA Astrophysics Data System (ADS)

Fu, Yi-Keng; Lu, Yu-Hsuan; Jiang, Ren-Hao; Chen, Bo-Chun; Fang, Yen-Hsiang; Xuan, Rong; Su, Yan-Kuin; Lin, Chia-Feng; Chen, Jebb-Fang

2011-08-01

Near ultraviolet light-emitting diodes (LEDs) with quaternary AlInGaN quantum barriers (QBs) are grown by atmospheric pressure metalorganic vapor phase epitaxy. The indium mole fraction of AlInGaN QB could be enhanced as we increased the TMG flow rate. Both the wavelength shift in EL spectra and forward voltage at 20 mA current injection were reduced by using AlInGaN QB. Under 100 mA current injection, the LED output power with Al 0.089In 0.035Ga 0.876N QB can be enhanced by 15.9%, compared to LED with GaN QB. It should be attributed to a reduction of lattice mismatch induced polarization mismatch in the active layer.

New PbSnTe heterojunction laser diode structures with improved performance

NASA Technical Reports Server (NTRS)

Fonstad, C. G.; Kasemset, D.; Hsieh, H. H.; Rotter, S.

1980-01-01

Several recent advances in the state-of-the-art of lead tin telluride double heterojunction laser diodes are summarized. Continuous Wave operation to 120 K and pulsed operation to 166 K with single, lowest order transverse mode emission to in excess of four times threshold at 80 K were achieved in buried stripe lasers fabricated by liquid phase epitaxy in the lattice-matched system, lead-tin telluride-lead telluride selenide. At the same time, liquid phase epitaxy was used to produce PbSnTe distributed feedback lasers with much broader continuous single mode tuning ranges than are available from Fabry-Perot lasers. The physics and philosophy behind these advances is as important as the structures and performance of the specific devices embodying the advances, particularly since structures are continually being evolved and the performance continues to be improved.

An instrument for in situ coherent x-ray studies of metal-organic vapor phase epitaxy of III-nitrides

DOE PAGES

Ju, Guangxu; Highland, Matthew J.; Yanguas-Gil, Angel; ...

2017-03-21

Here, we describe an instrument that exploits the ongoing revolution in synchrotron sources, optics, and detectors to enable in situ studies of metal-organic vapor phase epitaxy (MOVPE) growth of III-nitride materials using coherent x-ray methods. The system includes high-resolution positioning of the sample and detector including full rotations, an x-ray transparent chamber wall for incident and diffracted beam access over a wide angular range, and minimal thermal sample motion, giving the sub-micron positional stability and reproducibility needed for coherent x-ray studies. The instrument enables surface x-ray photon correlation spectroscopy, microbeam diffraction, and coherent diffraction imaging of atomic-scale surface and filmmore » structure and dynamics during growth, to provide fundamental understanding of MOVPE processes.« less