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Sample records for selected energy epitaxial

  1. Effects of contamination on selective epitaxial growth

    NASA Astrophysics Data System (ADS)

    MacDonald, Brian J.; Paton, Eric; Adem, Ercan; En, Bill

    2004-06-01

    As MOSFET dimensions scale down in size, it has become increasingly difficult to maintain high drive current while suppressing the off-state leakage current. One method of avoiding short-channel effects is to scale the source/drain (S/D) junction depths proportionally with the gate length. Unfortunately, this increases the S/D resistance, which slows the circuit. To keep the S/D junction shallow without affecting the S/D resistance, a raised S/D (RSD) structure is required. Integrating RSD can be difficult. Selective epitaxial growth (SEG) is the process used to incorporate RSD. This process requires a relatively clean surface to initiate the growth. Insertion of SEG earlier in the process flow facilitates selective epitaxial growth. Insertion of SEG later in the process flow results in higher levels of contamination at the interface of the Si substrate and the RSD structure. In this paper, we identify some mechanisms that determine the quality of the selective epitaxial film. Results indicate that Si defects are not a dominant mechanism in SEG film quality. Instead, results suggest that higher levels of contamination increased the surface roughness of the epitaxial film. PMOS regions were found to have higher levels of contamination and rougher epitaxial films than NMOS regions. Hydrogen bake as high as 900 °C was required to lower the surface contamination and provide excellent epitaxial morphology. Unfortunately, this high temperature causes enhanced dopant diffusion and deactivation of the device. Previous work [H. van Meer, K. De Meyer, Symposium on VLSI Technology Digest of Technical Papers, 2002, p. 170.] identified an alternative integration that provides excellent quality selective epitaxy, without dopant diffusion and deactivation.

  2. Low energy dislocation structures in epitaxy

    NASA Technical Reports Server (NTRS)

    Van Der Merwe, Jan H.; Woltersdorf, J.; Jesser, W. A.

    1986-01-01

    The principle of minimum energy was applied to epitaxial interfaces to show the interrelationship beteen misfit, overgrowth thickness and misfit dislocation spacing. The low energy dislocation configurations were presented for selected interfacial geometries. A review of the interfacial energy calculations was made and a critical assessment of the agreement between theory and experiment was presented. Modes of misfit accommodation were presented with emphasis on the distinction between kinetic effects and equilibrium conditions. Two-dimensional and three-dimensional overgrowths were treated together with interdiffusion-modified interfaces, and several models of interfacial structure were treated including the classical and the current models. The paper is concluded by indicating areas of needed investigation into interfacial structure.

  3. Selective epitaxy using the gild process

    DOEpatents

    Weiner, Kurt H.

    1992-01-01

    The present invention comprises a method of selective epitaxy on a semiconductor substrate. The present invention provides a method of selectively forming high quality, thin GeSi layers in a silicon circuit, and a method for fabricating smaller semiconductor chips with a greater yield (more error free chips) at a lower cost. The method comprises forming an upper layer over a substrate, and depositing a reflectivity mask which is then removed over selected sections. Using a laser to melt the unmasked sections of the upper layer, the semiconductor material in the upper layer is heated and diffused into the substrate semiconductor material. By varying the amount of laser radiation, the epitaxial layer is formed to a controlled depth which may be very thin. When cooled, a single crystal epitaxial layer is formed over the patterned substrate. The present invention provides the ability to selectively grow layers of mixed semiconductors over patterned substrates such as a layer of Ge.sub.x Si.sub.1-x grown over silicon. Such a process may be used to manufacture small transistors that have a narrow base, heavy doping, and high gain. The narrowness allows a faster transistor, and the heavy doping reduces the resistance of the narrow layer. The process does not require high temperature annealing; therefore materials such as aluminum can be used. Furthermore, the process may be used to fabricate diodes that have a high reverse breakdown voltage and a low reverse leakage current.

  4. Nanoscale selective area epitaxy for optoelectronic devices

    NASA Astrophysics Data System (ADS)

    Elarde, V. C.; Coleman, J. J.

    Self-assembled quantum dots have been heavily researched in recent years because of the potential applications to quantum electronic and optoelectronic devices they present. The non-uniformity and random ordering resulting from the self-assembly processes, however, are detrimental to potential applications, prohibiting the type of engineering control necessary for complex systems. The work presented in this document has sought to overcome the limitations of self-assembly by combining selective area epitaxy via MOCVD with high-resolution electron beam lithography to achieve lateral control over semiconductor structures at the nanometer scale. Two different structures are presented. The first is patterned quantum dots which improve on the uniformity and order of similar self-assembled quantum dots. The second is an entirely novel structure, the nanopore active layer, which demonstrates the potential for this process to extend beyond the constraints of self-assembly. Experimental and theoretical results for both structures are presented.

  5. Chiral habit selection on nanostructured epitaxial quartz films.

    PubMed

    Carretero-Genevrier, Adrián; Gich, Martí; Picas, Laura; Sanchez, Clément; Rodriguez-Carvajal, Juan

    2015-01-01

    Understanding the crystallization of enantiomorphically pure systems can be relevant to diverse fields such as the study of the origins of life or the purification of racemates. Here we report on polycrystalline epitaxial thin films of quartz on Si substrates displaying two distinct types of chiral habits that never coexist in the same film. We combine Atomic Force Microscopy (AFM) analysis and computer-assisted crystallographic calculations to make a detailed study of these habits of quartz. By estimating the surface energies of the observed crystallites we argue that the films are enantiomorphically pure and we briefly outline a possible mechanism to explain the habit and chiral selection in this system.

  6. Computational Approach for Epitaxial Polymorph Stabilization through Substrate Selection

    SciTech Connect

    Ding, Hong; Dwaraknath, Shyam S.; Garten, Lauren; Ndione, Paul; Ginley, David; Persson, Kristin A.

    2016-05-25

    With the ultimate goal of finding new polymorphs through targeted synthesis conditions and techniques, we outline a computational framework to select optimal substrates for epitaxial growth using first principle calculations of formation energies, elastic strain energy, and topological information. To demonstrate the approach, we study the stabilization of metastable VO2 compounds which provides a rich chemical and structural polymorph space. We find that common polymorph statistics, lattice matching, and energy above hull considerations recommends homostructural growth on TiO2 substrates, where the VO2 brookite phase would be preferentially grown on the a-c TiO2 brookite plane while the columbite and anatase structures favor the a-b plane on the respective TiO2 phases. Overall, we find that a model which incorporates a geometric unit cell area matching between the substrate and the target film as well as the resulting strain energy density of the film provide qualitative agreement with experimental observations for the heterostructural growth of known VO2 polymorphs: rutile, A and B phases. The minimal interfacial geometry matching and estimated strain energy criteria provide several suggestions for substrates and substrate-film orientations for the heterostructural growth of the hitherto hypothetical anatase, brookite, and columbite polymorphs. These criteria serve as a preliminary guidance for the experimental efforts stabilizing new materials and/or polymorphs through epitaxy. The current screening algorithm is being integrated within the Materials Project online framework and data and hence publicly available.

  7. Computational Approach for Epitaxial Polymorph Stabilization through Substrate Selection

    DOE PAGES

    Ding, Hong; Dwaraknath, Shyam S.; Garten, Lauren; ...

    2016-05-04

    With the ultimate goal of finding new polymorphs through targeted synthesis conditions and techniques, we outline a computational framework to select optimal substrates for epitaxial growth using first principle calculations of formation energies, elastic strain energy, and topological information. To demonstrate the approach, we study the stabilization of metastable VO 2 compounds which provides a rich chemical and structural polymorph space. Here, we find that common polymorph statistics, lattice matching, and energy above hull considerations recommends homostructural growth on TiO 2 substrates, where the VO 2 brookite phase would be preferentially grown on the a-c TiO 2 brookite plane whilemore » the columbite and anatase structures favor the a-b plane on the respective TiO 2 phases. Overall, we find that a model which incorporates a geometric unit cell area matching between the substrate and the target film as well as the resulting strain energy density of the film provide qualitative agreement with experimental observations for the heterostructural growth of known VO 2 polymorphs: rutile, A and B phases. The minimal interfacial geometry matching and estimated strain energy criteria provide several suggestions for substrates and substrate-film orientations for the heterostructural growth of the hitherto hypothetical anatase, brookite, and columbite polymorphs. Our criteria serve as a preliminary guidance for the experimental efforts stabilizing new materials and/or polymorphs through epitaxy. The current screening algorithm is being integrated within the Materials Project online framework and data and hence publicly available.« less

  8. Computational Approach for Epitaxial Polymorph Stabilization through Substrate Selection

    SciTech Connect

    Ding, Hong; Dwaraknath, Shyam S.; Garten, Lauren; Ndione, Paul; Ginley, David; Persson, Kristin A.

    2016-05-04

    With the ultimate goal of finding new polymorphs through targeted synthesis conditions and techniques, we outline a computational framework to select optimal substrates for epitaxial growth using first principle calculations of formation energies, elastic strain energy, and topological information. To demonstrate the approach, we study the stabilization of metastable VO 2 compounds which provides a rich chemical and structural polymorph space. Here, we find that common polymorph statistics, lattice matching, and energy above hull considerations recommends homostructural growth on TiO 2 substrates, where the VO 2 brookite phase would be preferentially grown on the a-c TiO 2 brookite plane while the columbite and anatase structures favor the a-b plane on the respective TiO 2 phases. Overall, we find that a model which incorporates a geometric unit cell area matching between the substrate and the target film as well as the resulting strain energy density of the film provide qualitative agreement with experimental observations for the heterostructural growth of known VO 2 polymorphs: rutile, A and B phases. The minimal interfacial geometry matching and estimated strain energy criteria provide several suggestions for substrates and substrate-film orientations for the heterostructural growth of the hitherto hypothetical anatase, brookite, and columbite polymorphs. Our criteria serve as a preliminary guidance for the experimental efforts stabilizing new materials and/or polymorphs through epitaxy. The current screening algorithm is being integrated within the Materials Project online framework and data and hence publicly available.

  9. Anisotropy of selective epitaxy in nanoscale-patterned growth: GaAs nanowires selectively grown on a SiO2-patterned (001) substrate by molecular-beam epitaxy

    NASA Astrophysics Data System (ADS)

    Lee, S. C.; Dawson, L. R.; Brueck, S. R. J.; Jiang, Y.-B.

    2005-12-01

    Anisotropic selective epitaxy in nanoscale-patterned growth (NPG) by molecular-beam epitaxy is investigated on a 355nm period two-dimensional array of circular holes fabricated in a 30-nm-thick SiO2 film on a GaAs(001) substrate. The hole diameter ranged from 70to150nm. The small hole diameter and the very thin masking layer stimulated lateral growth over the SiO2 surface at an early stage of selective epitaxy on this patterned substrate. Lateral overgrowth associated with selective epitaxy, however, did not proceed isotropically along the circular boundary between the open substrate surface and the SiO2 mask. There was preferential growth direction parallel to ⟨111⟩B. This anisotropy in the selective epitaxy resulted in the formation of a nanoscale, nontapered, straight-wire-type epitaxial layer (GaAs nanowires), which had a length of up to 1.8μm for a nominal 200nm deposition. Every GaAs nanowire had a hexagonal prismatic shape directed along ⟨111⟩B and was surrounded by six (110) sidewalls. The anisotropy of selective epitaxy and faceting in NPG were affected by the profile of the SiO2 mask and are interpreted using a minimization of the total surface energy for equilibrium crystal shape.

  10. Selective epitaxial growth of graphene on SiC

    NASA Astrophysics Data System (ADS)

    Camara, N.; Rius, G.; Huntzinger, J.-R.; Tiberj, A.; Mestres, N.; Godignon, P.; Camassel, J.

    2008-09-01

    We present a method of selective epitaxial growth of few layers graphene (FLG) on a "prepatterned" silicon carbide (SiC) substrate. The methods involves, successively, the sputtering of a thin aluminium nitride (AlN) layer on top of a monocrystalline SiC substrate and, then, patterning it with e-beam lithography and wet etching. The sublimation of few atomic layers of Si from the SiC substrate occurs only through the selectively etched AlN layer. The presence of the Raman G-band at ˜1582cm-1 in the AlN-free areas is used to validate the concept. It gives absolute evidence of selective FLG growth.

  11. Selective epitaxial growth of graphene on SiC

    SciTech Connect

    Camara, N.; Rius, G.; Godignon, P.; Huntzinger, J.-R.; Tiberj, A.; Camassel, J.

    2008-09-22

    We present a method of selective epitaxial growth of few layers graphene (FLG) on a ''prepatterned'' silicon carbide (SiC) substrate. The methods involves, successively, the sputtering of a thin aluminium nitride (AlN) layer on top of a monocrystalline SiC substrate and, then, patterning it with e-beam lithography and wet etching. The sublimation of few atomic layers of Si from the SiC substrate occurs only through the selectively etched AlN layer. The presence of the Raman G-band at {approx}1582 cm{sup -1} in the AlN-free areas is used to validate the concept. It gives absolute evidence of selective FLG growth.

  12. Integrated optoelectronic devices by selective-area epitaxy

    NASA Astrophysics Data System (ADS)

    Jones, A. M.; Coleman, James J.

    1997-01-01

    The development of a simulation model for selective-area epitaxy and the fabrication of semiconductor lasers monolithically integrated with electroabsorption modulators by this technique are presented. Diffusion equations and boundary conditions from selective-area MOCVD theory are applied in a computational model to predict column III reactant concentrations, and self-consistent solutions for reaction parameters are found using the finite element method. Data are presented to demonstrate accurate predictions of the thickness and composition of selectively grown ternary InGaAs quantum wells. This model was utilized to design the selective growth mask for Fabry-Perot lasers integrated with intracavity electroabsorption modulators. These devices, with modulator lengths of 290, 620, and 1020 micrometer, exhibit cw threshold currents of 9, 7.5, and 7.5 mA, respectively. Also, extinction ratios of 16.5, 19.5, and 20.5 dB, respectively, are measured at a modulator reverse bias of 2 V. Distributed Bragg reflector lasers with monolithically integrated external cavity modulators are also fabricated, and the selective-area MOCVD simulation was employed to design the growth mask dimensions and the location of the gratings. Cw threshold currents of 10.5 mA, slope efficiencies of 0.21 W/A, and extinction ratios of 18 dB at a modulator reverse bias of 1.0 V are achieved for these devices.

  13. Selective Area Epitaxial Growth of Silicon by the A.C. Technique

    NASA Astrophysics Data System (ADS)

    Wang, Qing Sheng

    Four major areas are covered in this dissertation: (1) Thermodynamic analyses for blanket and selective area deposition of silicon and TiN; (2) Kinetic and hydrodynamic considerations in CVD processes; (3) The hot wall low pressure epitaxial system design and description; and (4) Experimental results of selective area growth of epitaxial silicon. The thermodynamic analyses and calculations for the blanket and selective area deposition of silicon and TiN by the alternating cyclic, A.C., reduction technique were carried out using a computer free energy minimization program, SOLGASMIX, coupled with a first principles analysis as an integrity check. The A.C. technique was shown to be thermodynamically feasible for a global reaction chemistry in which an embedded disproportionation chemistry for removing spurious nuclei could be cyclically activated in a simple fashion. A generalized study of some kinetic and hydrodynamic concepts for chemical vapor transport system provided insights into the design of an A.C. chemical vapor deposition process, and provided sufficient information for designing and testing an experimental low pressure CVD system, and optimizing the experimental conditions. The experimental system design and installation were intended to provide a unique hot wall LPCVD epitaxial system, which is equipped with an internally designed vacuum load-lock, an automatic wafer loading mechanism, a water -cooling system, a complete gas panel, and a hydrogen pulsing mechanism for carrying out the A.C. process. Extensive experiments were conducted on selective area silicon epitaxial growth over a range of the available parameter space, using "standard" non-A.C. deposition process and comparing it with A.C. processes. It was found that substrate topology, substrate pre-treatment, including ion implantation, as well as various system and experimental conditions influenced, to varying degrees, the tendency for spurious nucleation to occur in masked areas where

  14. Tuning a strain-induced orbital selective Mott transition in epitaxial VO2

    NASA Astrophysics Data System (ADS)

    Mukherjee, Shantanu; Quackenbush, N. F.; Paik, H.; Schlueter, C.; Lee, T.-L.; Schlom, D. G.; Piper, L. F. J.; Lee, Wei-Cheng

    2016-06-01

    We present evidence of strain-induced modulation of electron correlation effects and increased orbital anisotropy in the rutile phase of epitaxial VO2/TiO2 films from hard x-ray photoelectron spectroscopy and soft V L-edge x-ray absorption spectroscopy, respectively. By using the U(1) slave spin formalism, we further argue that the observed anisotropic correlation effects can be understood by a model of orbital selective Mott transition at a filling that is noninteger but close to the half filling. Because the overlaps of wave functions between d orbitals are modified by the strain, orbital-dependent renormalizations of the bandwidths and the onsite energy occur. These renormalizations generally result in different occupation numbers in different orbitals. We find that if the system has a noninteger filling number near the half filling such as for VO2, certain orbitals could reach an occupation number closer to half filling under the strain, resulting in a strong reduction in the quasiparticle weight Zα of that orbital. Our work demonstrates that such an orbital selective Mott transition, defined as the case with Zα=0 in some but not all orbitals, could be accessed by epitaxial-strain engineering of correlated electron systems.

  15. Integrated DFB-DBR laser modulator grown by selective area metalorganic vapor phase epitaxy growth technique

    NASA Astrophysics Data System (ADS)

    Tanbun-Ek, T.; Chen, Y. K.; Grenko, J. A.; Byrne, E. K.; Johnson, J. E.; Logan, R. A.; Tate, A.; Sergent, A. M.; Wecht, K. W.; Sciortine, P. F.; Chu, S. N. G.

    1994-12-01

    A device quality of selective epitaxy growth of InGaAsP/InP multiple quantum well (MQW) structure using low-pressure metalorganic vapor phase epitaxy (MOVPE) technique is described. The technique is applied to a monolithically integrated electroabsorption modulator with distributed feedback (DFB) and distributed Bragg reflector (DBR) lasers. Superior device characteristics such as efficient modulation, low threshold current and high efficiency operation of the integrated devices are obtained.

  16. The role of Energy Deposition in the Epitaxial Layer in Triggering SEGR in Power MOSFETs

    NASA Technical Reports Server (NTRS)

    Selva, L.; Swift, G.; Taylor, W.; Edmonds, L.

    1999-01-01

    In these SEGR experiments, three identical-oxide MOSFET types were irradiated with six ions of significantly different ranges. Results show the prime importance of the total energy deposited in the epitaxial layer.

  17. The role of Energy Deposition in the Epitaxial Layer in Triggering SEGR in Power MOSFETs

    NASA Technical Reports Server (NTRS)

    Selva, L.; Swift, G.; Taylor, W.; Edmonds, L.

    1999-01-01

    In these SEGR experiments, three identical-oxide MOSFET types were irradiated with six ions of significantly different ranges. Results show the prime importance of the total energy deposited in the epitaxial layer.

  18. An experimental study on the quality and selectivity of silicon epitaxial growth using disilane and chlorine

    NASA Astrophysics Data System (ADS)

    O'Neil, Patricia Ann

    With CMOS device technologies continuing to rapidly mature, the design and fabrication of novel device structures is presently being researched within the scientific community. Such novel structures, however, often require the development of unique silicon growth methods. The development of a robust selective silicon epitaxial growth process is therefore of much interest to the scientific community. Within this dissertation, the development and optimization of a selective silicon epitaxy process utilizing disilane and chlorine in a novel ultrahigh vacuum rapid thermal chemical vapor deposition reactor has been accomplished. The growth, epitaxial quality, and selectivity with respect to silicon dioxide has been studied as a function of various process parameters, system contamination levels, and pre-epitaxy substrate conditions. In regard to the basic process parameters (temperature, pressure, and chlorine to silicon ratio), maximizing the growth temperature while minimizing the chlorine to silicon ratio has been shown to increase the quality of epitaxial films resulting in bulk generation lifetimes of approximately 250 mus. However, reducing the amount of chlorine will limit the degee of selectivity to insulator surfaces and increased temperatures can enhance unwanted diffusion of previously formed junctions. Therefore, a balance between the various process parameters has been recommended. In addition to examining standard operating conditions, the influence of contamination introduced via the process source gases or background ambient has been investigated. Source gases without purification have been shown to degrade both the selectivity and epitaxial quality. Background oxygen levels, however, have demonstrated little effect on the chlorinated growth process until elevated to extremely high partial pressures (≥ 1 × 10sp{-4} Torr). Therefore, the removal of oxygen down to ultrahigh vacuum pressures is not necessary for the successful growth of the developed

  19. Selective growth of GaAs by organometallic vapor phase epitaxy at atmospheric pressure

    NASA Astrophysics Data System (ADS)

    Azoulay, R.; Dugrand, L.

    1991-01-01

    Complete selective epitaxy of GaAs by organometallic vapor phase epitaxy at atmospheric pressure was achieved by using TMG, AsH3, and AsCl3 as starting gases. Selectivity was observed at growth temperatures ranging from 650 to 750 °C. The blocking of polycrystal deposition on the mask, Si3N4, or W, is attributed to the adsorption of HCl on the mask, thus preventing the nucleation of GaAs. On the openings, the growth rate may be adjusted by controlling the TMG/AsCl3 ratio. When TMG/AsCl3<1, no growth occurs, but etching is observed.

  20. Kinetic-energy induced smoothening and delay of epitaxial breakdown in pulsed-laser deposition

    SciTech Connect

    Shin, Byungha; Aziz, Michael J.

    2007-08-15

    We have isolated the effect of kinetic energy of depositing species from the effect of flux pulsing during pulsed-laser deposition (PLD) on surface morphology evolution of Ge(001) homoepitaxy at low temperature (100 deg. C). Using a dual molecular beam epitaxy (MBE) PLD chamber, we compare morphology evolution from three different growth methods under identical experimental conditions except for the differing nature of the depositing flux: (a) PLD with average kinetic energy 300 eV (PLD-KE); (b) PLD with suppressed kinetic energy comparable to thermal evaporation energy (PLD-TH); and (c) MBE. The thicknesses at which epitaxial breakdown occurs are ranked in the order PLD-KE>MBE>PLD-TH; additionally, the surface is smoother in PLD-KE than in MBE. The surface roughness of the films grown by PLD-TH cannot be compared due to the early epitaxial breakdown. These results demonstrate convincingly that kinetic energy is more important than flux pulsing in the enhancement of epitaxial growth, i.e., the reduction in roughness and the delay of epitaxial breakdown.

  1. The impact of substrate selection for the controlled growth of graphene by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Schumann, T.; Lopes, J. M. J.; Wofford, J. M.; Oliveira, M. H.; Dubslaff, M.; Hanke, M.; Jahn, U.; Geelhaar, L.; Riechert, H.

    2015-09-01

    We examine how substrate selection impacts the resulting film properties in graphene growth by molecular beam epitaxy (MBE). Graphene growth on metallic as well as dielectric templates was investigated. We find that MBE offers control over the number of atomic graphene layers regardless of the substrate used. High structural quality could be achieved for graphene prepared on Ni (111) films which were epitaxially grown on MgO (111). For growth either on Al2O3 (0001) or on (6√3×6√3)R30°-reconstructed SiC (0001) surfaces, graphene with a higher density of defects is obtained. Interestingly, despite their defective nature, the layers possess a well defined epitaxial relation to the underlying substrate. These results demonstrate the feasibility of MBE as a technique for realizing the scalable synthesis of this two-dimensional crystal on a variety of substrates.

  2. Selective molecular beam epitaxy of germanium on oxide-covered silicon

    NASA Astrophysics Data System (ADS)

    Li, Qiming

    This study demonstrates that Ge can be selectively grown on Si through openings in SiO2 nanotemplates by molecular beam epitaxy without applying selectivity-control agents. The SiO2 nanotemplates are created either by interferometric lithography or by "touchdown" process. The "touchdown" process takes advantage of the unique interaction between Ge and an ultra-thin layer of chemical SiO2. Due to the high concentration of OH groups in the chemical oxide layer, Ge readily diffuses through the oxide, segregates at the SiO2/Si interface, and creates dense nanoscale windows in the chemical oxide. Ge then selectively grows in the windows and coalesces into a high-quality relaxed Ge epilayer over the remaining SiO2. The high-quality and relaxation are attributed to three mechanisms: (1) the strain at the junction pad decays below the critical limit within 2 nm due to the nanoscale heterojunction; (2) the remaining SiO2 serves as artificially introduced 60° dislocations; and (3) the intermixing between Ge and Si at the heterojunction reduces the effective lattice mismatch. To understand the surface phenomena governing the selectivity, we further experimentally measure the desorption activation energy (Edes = 42 +/- 3 kJ/mol) of Ge on SiO2 surface. The low Edes gives rise to a high Ge desorption flux from the SiO2 surface and a low diffusion barrier ( Edif ˜ 13 kJ/mol), which in turn leads to a long characteristic diffusion length. Based on these findings, we further demonstrate that hexagonally packed, single-crystal Ge rings can be grown at the contact region between self-assembled SiO2 spheres and chemical oxide covered Si substrates. These SiO2 spheres provide a surface diffusion path, which guides the Ge adspecies to the substrate. The Ge adspecies on SiO2 spheres undergo surface diffusion as well as desorption, and a fraction of Ge adspecies aggregate at the sphere/substrate contact region to form epitaxial rings by "touchdown" through the chemical SiO2.

  3. Exposing high-energy surfaces by rapid-anneal solid phase epitaxy

    NASA Astrophysics Data System (ADS)

    Wang, Y.; Song, Y.; Peng, R.; Herklotz, A.; Chisholm, M. F.; Wu, Z. L.; Ward, T. Z.; Weitering, H. H.; Snijders, P. C.

    2017-08-01

    The functional design of transition metal oxide heterostructures depends critically on the growth of atomically flat epitaxial thin films. Often, improved functionality is expected for heterostructures and surfaces with orientations that do not have the lowest surface free energy. For example, crystal faces with a high surface free energy, such as rutile (001) planes, frequently exhibit higher catalytic activities but are correspondingly harder to synthesize due to faceting transitions. Here we propose a broadly applicable rapid-anneal solid phase epitaxial synthesis approach for the creation of nanometer thin, high surface free energy oxide heterostructures that are atomically flat. We demonstrate its efficacy by synthesizing atomically flat epitaxial RuO2(001) and TiO2(001) model systems. The former have a superior oxygen evolution activity, quantified by their lower onset potential and higher current density, relative to that of more common RuO2(110) films.

  4. Low thermal budget surface preparation for selective silicon epitaxy

    NASA Astrophysics Data System (ADS)

    Celik, Salih Muhsin

    In this dissertation, a low thermal budget surface preparation method which combines an ex situ dilute HF dip with an in situ anneal in vacuum has been investigated. After a 10-second anneal at 750sp° C, oxygen and chlorine levels at the epitaxy/substrate interface are reduced below the secondary ion mass spectroscopy (SIMS) detection levels and carbon level at the interface is decreased significantly. It is determined that silicon-dioxide patterns on silicon surface does not cause an adverse effect on the in-situ clean efficiency. In-situ cleaning with and without chlorinated background were compared and no adverse effects of chlorine were observed for the ranges of chlorine flows used. A correlation between the defect density in the eptaxial layers and the interfacial carbon dose has been observed. The surface roughness measurements showed that annealing in vacuum did not cause any roughening on the wafer surface. NMOS transistors were fabricated on silicon epitaxial layers with different surface treatments and no significant variations in the electrical characteristics were observed. In situ cleaning is studied in ambients with different partial pressures of nitrogen and oxygen backgrounds. Oxygen was removed from Si(100) by a 800sp° C/10s anneal for nitrogen partial pressures in the cleaning ambient up to 1× 10sp{-6} Torr. When the oxygen partial pressure in the ambient is sufficiently high (1× 10sp{-6} Torr), oxide removal was not complete after in situ cleaning (800sp° C/20s). There was no observable increase in the surface roughness for samples annealed in oxygen partial pressure up to 1× 10sp{-5} Torr. Hydrogen passivation was removed from the substrates and the surfaces were exposed to vacuum at room temperature for times varying from 10 to 10000 seconds. After 10000 seconds of wait time in vacuum, the oxygen coverage was less than 2% of a monolayer. The carbon contamination on the surface was instantaneous and no additional carbon accumulation on

  5. Selective-area growth of heavily n–doped GaAs nanostubs on Si(001) by molecular beam epitaxy

    SciTech Connect

    Chang, Yoon Jung Woo, Jason C. S.; Simmonds, Paul J.

    2016-04-18

    Using an aspect ratio trapping technique, we demonstrate molecular beam epitaxy of GaAs nanostubs on Si(001) substrates. Nanoholes in a SiO{sub 2} mask act as a template for GaAs-on-Si selective-area growth (SAG) of nanostubs 120 nm tall and ≤100 nm in diameter. We investigate the influence of growth parameters including substrate temperature and growth rate on SAG. Optimizing these parameters results in complete selectivity with GaAs growth only on the exposed Si(001). Due to the confined-geometry, strain and defects in the GaAs nanostubs are restricted in lateral dimensions, and surface energy is further minimized. We assess the electrical properties of the selectively grown GaAs nanostubs by fabricating heterogeneous p{sup +}–Si/n{sup +}–GaAs p–n diodes.

  6. Selective-area growth of heavily n-doped GaAs nanostubs on Si(001) by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Chang, Yoon Jung; Simmonds, Paul J.; Beekley, Brett; Goorsky, Mark S.; Woo, Jason C. S.

    2016-04-01

    Using an aspect ratio trapping technique, we demonstrate molecular beam epitaxy of GaAs nanostubs on Si(001) substrates. Nanoholes in a SiO2 mask act as a template for GaAs-on-Si selective-area growth (SAG) of nanostubs 120 nm tall and ≤100 nm in diameter. We investigate the influence of growth parameters including substrate temperature and growth rate on SAG. Optimizing these parameters results in complete selectivity with GaAs growth only on the exposed Si(001). Due to the confined-geometry, strain and defects in the GaAs nanostubs are restricted in lateral dimensions, and surface energy is further minimized. We assess the electrical properties of the selectively grown GaAs nanostubs by fabricating heterogeneous p+-Si/n+-GaAs p-n diodes.

  7. Fermi energy tuning with light to control doping profiles during epitaxy

    SciTech Connect

    Sanders, C. E.; Beaton, D. A.; Reedy, R. C.; Alberi, K.

    2015-05-04

    The influence of light stimulation and photogenerated carriers on the process of dopant surface segregation during growth is studied in molecular beam epitaxially grown Si-doped GaAs structures. The magnitude of surface segregation decreases under illumination by above-bandgap photons, wherein splitting of the quasi Fermi levels reduces the band bending at the growth surface and raises the formation energy of compensating defects that can enhance atomic diffusion. We further show that light-stimulated epitaxy can be used as a practical approach to diminish dopant carry-forward in device structures and improve the performance of inverted modulation-doped quantum wells.

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

    SciTech Connect

    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.

  9. Highly selective covalent organic functionalization of epitaxial graphene

    NASA Astrophysics Data System (ADS)

    Bueno, Rebeca A.; Martínez, José I.; Luccas, Roberto F.; Del Árbol, Nerea Ruiz; Munuera, Carmen; Palacio, Irene; Palomares, Francisco J.; Lauwaet, Koen; Thakur, Sangeeta; Baranowski, Jacek M.; Strupinski, Wlodek; López, María F.; Mompean, Federico; García-Hernández, Mar; Martín-Gago, José A.

    2017-05-01

    Graphene functionalization with organics is expected to be an important step for the development of graphene-based materials with tailored electronic properties. However, its high chemical inertness makes difficult a controlled and selective covalent functionalization, and most of the works performed up to the date report electrostatic molecular adsorption or unruly functionalization. We show hereafter a mechanism for promoting highly specific covalent bonding of any amino-terminated molecule and a description of the operating processes. We show, by different experimental techniques and theoretical methods, that the excess of charge at carbon dangling-bonds formed on single-atomic vacancies at the graphene surface induces enhanced reactivity towards a selective oxidation of the amino group and subsequent integration of the nitrogen within the graphene network. Remarkably, functionalized surfaces retain the electronic properties of pristine graphene. This study opens the door for development of graphene-based interfaces, as nano-bio-hybrid composites, fabrication of dielectrics, plasmonics or spintronics.

  10. Highly selective covalent organic functionalization of epitaxial graphene.

    PubMed

    Bueno, Rebeca A; Martínez, José I; Luccas, Roberto F; Del Árbol, Nerea Ruiz; Munuera, Carmen; Palacio, Irene; Palomares, Francisco J; Lauwaet, Koen; Thakur, Sangeeta; Baranowski, Jacek M; Strupinski, Wlodek; López, María F; Mompean, Federico; García-Hernández, Mar; Martín-Gago, José A

    2017-05-08

    Graphene functionalization with organics is expected to be an important step for the development of graphene-based materials with tailored electronic properties. However, its high chemical inertness makes difficult a controlled and selective covalent functionalization, and most of the works performed up to the date report electrostatic molecular adsorption or unruly functionalization. We show hereafter a mechanism for promoting highly specific covalent bonding of any amino-terminated molecule and a description of the operating processes. We show, by different experimental techniques and theoretical methods, that the excess of charge at carbon dangling-bonds formed on single-atomic vacancies at the graphene surface induces enhanced reactivity towards a selective oxidation of the amino group and subsequent integration of the nitrogen within the graphene network. Remarkably, functionalized surfaces retain the electronic properties of pristine graphene. This study opens the door for development of graphene-based interfaces, as nano-bio-hybrid composites, fabrication of dielectrics, plasmonics or spintronics.

  11. Polarity-Induced Selective Area Epitaxy of GaN Nanowires.

    PubMed

    de Souza Schiaber, Ziani; Calabrese, Gabriele; Kong, Xiang; Trampert, Achim; Jenichen, Bernd; Dias da Silva, José Humberto; Geelhaar, Lutz; Brandt, Oliver; Fernández-Garrido, Sergio

    2017-01-11

    We present a conceptually novel approach to achieve selective area epitaxy of GaN nanowires. The approach is based on the fact that these nanostructures do not form in plasma-assisted molecular beam epitaxy on structurally and chemically uniform cation-polar substrates. By in situ depositing and nitridating Si on a Ga-polar GaN film, we locally reverse the polarity to induce the selective area epitaxy of N-polar GaN nanowires. We show that the nanowire number density can be controlled over several orders of magnitude by varying the amount of predeposited Si. Using this growth approach, we demonstrate the synthesis of single-crystalline and uncoalesced nanowires with diameters as small as 20 nm. The achievement of nanowire number densities low enough to prevent the shadowing of the nanowire sidewalls from the impinging fluxes paves the way for the realization of homogeneous core-shell heterostructures without the need of using ex situ prepatterned substrates.

  12. Surface stability and the selection rules of substrate orientation for optimal growth of epitaxial II-VI semiconductors

    SciTech Connect

    Yin, Wan-Jian; Yang, Ji-Hui; Zaunbrecher, Katherine; Gessert, Tim; Barnes, Teresa; Wei, Su-Huai; Yan, Yanfa

    2015-10-05

    The surface structures of ionic zinc-blende CdTe (001), (110), (111), and (211) surfaces are systematically studied by first-principles density functional calculations. Based on the surface structures and surface energies, we identify the detrimental twinning appearing in molecular beam epitaxy (MBE) growth of II-VI compounds as the (111) lamellar twin boundaries. To avoid the appearance of twinning in MBE growth, we propose the following selection rules for choosing optimal substrate orientations: (1) the surface should be nonpolar so that there is no large surface reconstructions that could act as a nucleation center and promote the formation of twins; (2) the surface structure should have low symmetry so that there are no multiple equivalent directions for growth. These straightforward rules, in consistent with experimental observations, provide guidelines for selecting proper substrates for high-quality MBE growth of II-VI compounds.

  13. III-V Nanowire Array Growth by Selective Area Epitaxy

    SciTech Connect

    Chu, Hyung-Joon; Stewart, Lawrence; Yeh, Tingwei; Dapkus, P. Daniel

    2011-12-23

    III-V semiconductor nanowires are unique material phase due to their high aspect ratio, large surface area, and strong quantum confinement. This affords the opportunity to control charge transport and optical properties for electrical and photonic applications. Nanoscale selective area metalorganic chemical vapor deposition growth (NS-SAG) is a promising technique to maximize control of nanowire diameter and position, which are essential for device application. In this work, InP and GaAs nanowire arrays are grown by NS-SAG. We observe enhanced sidewall growth and array uniformity disorder in high growth rate condition. Disorder in surface morphology and array uniformity of InP nanowire array is explained by enhanced growth on the sidewall and stacking faults. We also find that AsH{sub 3} decomposition on the sidewall affects the growth behavior of GaAs nanowire arrays.

  14. Epitaxial Growth of Oriented Metalloporphyrin Network Thin Film for Improved Selectivity of Volatile Organic Compounds.

    PubMed

    Li, De-Jing; Gu, Zhi-Gang; Vohra, Ismail; Kang, Yao; Zhu, Yong-Sheng; Zhang, Jian

    2017-03-03

    This study reports an oriented and homogenous cobalt-metalloporphyrin network (PIZA-1) thin film prepared by liquid phase epitaxial (LPE) method. The thickness of the obtained thin films can be well controlled, and their photocurrent properties can also be tuned by LPE cycles or the introduction of conductive guest molecules (tetracyanoquinodimethane and C60 ) into the PIZA-1 pores. The study of quartz crystal microbalance adsorption confirms that the PIZA-1 thin film with [110]-orientation presents much higher selectivity of benzene over toluene and p-xylene than that of the PIZA-1 powder with mixed orientations. These results reveal that the selective adsorption of volatile organic compounds highly depends on the growth orientations of porphyrin-based metal-organic framework thin films. Furthermore, the work will provide a new perspective for developing important semiconductive sensing materials with improved selectivity of guest compounds.

  15. Selecting windows for energy efficiency

    SciTech Connect

    1997-05-01

    New window technologies have increased energy benefits and comfort, and have provided more practical options for consumers. This selection guide will help homeowners, architects, and builders take advantage of the expanding window market. The guide contains three sections: an explanation of energy-related window characteristics, a discussion of window energy performance ratings, and a convenient checklist for window selection.

  16. Process for selectively patterning epitaxial film growth on a semiconductor substrate

    DOEpatents

    Sheldon, Peter; Hayes, Russell E.

    1986-01-01

    A process is disclosed for selectively patterning epitaxial film growth on a semiconductor substrate. The process includes forming a masking member on the surface of the substrate, the masking member having at least two layers including a first layer disposed on the substrate and the second layer covering the first layer. A window is then opened in a selected portion of the second layer by removing that portion to expose the first layer thereunder. The first layer is then subjected to an etchant introduced through the window to dissolve a sufficient amount of the first layer to expose the substrate surface directly beneath the window, the first layer being adapted to preferentially dissolve at a substantially greater rate than the second layer so as to create an overhanging ledge portion with the second layer by undercutting the edges thereof adjacent to the window. The epitaxial film is then deposited on the exposed substrate surface directly beneath the window. Finally, an etchant is introduced through the window to dissolve the remainder of the first layer so as to lift-off the second layer and materials deposited thereon to fully expose the balance of the substrate surface.

  17. Process for selectively patterning epitaxial film growth on a semiconductor substrate

    DOEpatents

    Sheldon, P.; Hayes, R.E.

    1984-12-04

    Disclosed is a process for selectively patterning epitaxial film growth on a semiconductor substrate. The process includes forming a masking member on the surface of the substrate, the masking member having at least two layers including a first layer disposed on the substrate and the second layer covering the first layer. A window is then opened in a selected portion of the second layer by removing that portion to expose the first layer thereunder. The first layer is then subjected to an etchant introduced through the window to dissolve the first layer a sufficient amount to expose the substrate surface directly beneath the window, the first layer being adapted to preferentially dissolve at a substantially greater rate than the second layer so as to create an overhanging ledge portion with the second layer by undercutting the edges thereof adjacent the window. The epitaxial film is then deposited on the exposed substrate surface directly beneath the window. Finally, an etchant is introduced through the window to dissolve the remainder of the first layer so as to lift-off the second layer and materials deposited thereon to fully expose the balance of the substrate surface.

  18. Evolution of GaAs nanowire geometry in selective area epitaxy

    NASA Astrophysics Data System (ADS)

    Bassett, Kevin P.; Mohseni, Parsian K.; Li, Xiuling

    2015-03-01

    Nanowires (NWs) grown via selective area epitaxy (SAE) show great promise for applications in next generation electronic and photonic devices, yet the design of NW-based devices can be complicated due to the complex kinetics involved in the growth process. The presence of the patterned selective area mask, as well as the changing geometry of the NWs themselves during growth, leads to non-linear growth rates which can vary significantly based on location in the mask and the NW size. Here, we present a systematic study of the evolution of GaAs NW geometry during growth as a function of NW size and pitch. We highlight a breakdown of NW uniformity at extended growth times, which is accelerated for NW arrays with larger separations. This work is intended to outline potential fundamental growth challenges in achieving desired III-V NW array patterns and uniformity via SAE.

  19. Monolithically integrated multi-wavelength MQW-DBR laser diodes fabricated by selective metalorganic vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    Sasaki, Tatsuya; Yamaguchi, Masayuki; Kitamura, Mitsuhiro

    1994-12-01

    Selective metalorganic vapor phase epitaxy (MOVPE) was used to grow InGaAsP/InP layers for fabricating multi-wavelength laser diodes. Multiple quantum well (MQW) active and passive waveguides were simultaneously grown by one step selective growth. The selectively grown layer thickness increases with the mask stripe width. This growth enhancement can be used to control the lasing wavelength of distributed Bragg reflector (DBR) laser diodes, because the effective refractive index of the MQW passive waveguide at the DBR region can be controlled by the mask stripe width. This simple technique was used to fabricate multi-wavelength MQW-DBR laser diodes. In the selective growth, the MQW structure was grown under 150 Torr to obtain large bandgap energy shift for the MQW passive waveguides compared to the active waveguide, which was effective for wide wavelength tuning range. On the contrary, a bulk InGaAsP guide layer was grown under 35 Torr to prevent too much composition shift and maintain high crystalline quality of the MQW passive waveguide. For 10 consecutive laser diodes, a wavelength span of over 20 nm with accurate wavelength control was achieved.

  20. Selective epitaxial growth of Ge1-xSnx on Si by using metal-organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Washizu, Tomoya; Ike, Shinichi; Inuzuka, Yuki; Takeuchi, Wakana; Nakatsuka, Osamu; Zaima, Shigeaki

    2017-06-01

    Selective epitaxial growth of Ge and Ge1-xSnx layers on Si substrates was performed by using metal-organic chemical vapor deposition (MOCVD) with precursors of tertiary-butyl-germane (t-BGe) and tri-butyl-vinyl-tin (TBVSn). We investigated the effects of growth temperature and total pressure during growth on the selectivity and the crystallinity of the Ge and Ge1-xSnx epitaxial layers. Under low total pressure growth conditions, the dominant mechanism of the selective growth of Ge epitaxial layers is the desorption of the Ge precursors. At a high total pressure case, it is needed to control the surface migration of precursors to realize the selectivity because the desorption of Ge precursors was suppressed. The selectivity of Ge growth was improved by diffusion of the Ge precursors on the SiO2 surfaces when patterned substrates were used at a high total pressure. The selective epitaxial growth of Ge1-xSnx layer was also realized using MOCVD. We found that the Sn precursors less likely to desorb from the SiO2 surfaces than the Ge precursors.

  1. Evolution of (001) and (111) facets for selective epitaxial growth inside submicron trenches

    SciTech Connect

    Jiang, S. Heyns, M.; Merckling, C.; Guo, W.; Waldron, N.; Caymax, M.; Vandervorst, W.; Seefeldt, M.

    2014-01-14

    The evolution of (001) and (111) facets for the epitaxial growth inside submicron trenches is systematically studied in this report. The analysis with the method of “Lagrange multiplier” indicates the equilibrium crystal shape. In the case of non-equilibrium without external fluxes, we employed the “weighted mean curvature” method to mathematically model the inter-facet migration rate for two extreme kinetic cases: “surface diffusion limited” and “surface attachment/detachment limited.” Coupled with external supply of atoms, the self-limited behavior of facet size is theoretically predicted. Moreover, we find that the self-limited stable facet size in trenches of different widths has a specific relationship determined by the surface energy ratio, kinetic rate ratio, and isolated growth rate difference. The two limited cases could be discriminated according to the mathematical fitting of one exponent in this relationship based on the stable facet size in trenches of different widths.

  2. Selective epitaxial silicon growth in the 650-1100 °C range in a reduced pressure chemical vapor deposition reactor using dichlorosilane

    NASA Astrophysics Data System (ADS)

    Regolini, J. L.; Bensahel, D.; Scheid, E.; Mercier, J.

    1989-02-01

    Selective epitaxial silicon layers have been grown in a reduced pressure (<2 Torr) reactor in the 650-1100 °C temperature range using only dichlorosilane (DCS) gas diluted in hydrogen. The growth rate plotted in Arrhenius coordinates (log G vs 1/T) shows an activation energy of 59 kcal/mol in the 650-800 °C range. A comparison is made between the DCS system and our previous results concerning the SiH4/HCl/H2 system.

  3. Usage of antimony segregation for selective doping of Si in molecular beam epitaxy

    SciTech Connect

    Yurasov, D. V.; Drozdov, M. N.; Murel, A. V.; Shaleev, M. V.; Novikov, A. V.; Zakharov, N. D.

    2011-06-01

    An original approach to selective doping of Si by antimony (Sb) in molecular beam epitaxy (MBE) is proposed and verified experimentally. This approach is based on controllable utilization of the effect of Sb segregation. In particular, the sharp dependence of Sb segregation on growth temperature in the range of 300-550 deg. C is exploited. The growth temperature variations between the kinetically limited and maximum segregation regimes are suggested to be utilized in order to obtain selectively doped structures with abrupt doping profiles. It is demonstrated that the proposed technique allows formation of selectively doped Si:Sb layers, including delta ({delta}-)doped layers in which Sb concentrations can be varied from 5 x 10{sup 15} to 10{sup 20} cm{sup -3}. The obtained doped structures are shown to have a high crystalline quality and the short-term growth interruptions, which are needed to change the substrate temperature, do not lead to any significant accumulation of background impurities in grown samples. Realization of the proposed approach requires neither too low (<300 deg. C), nor too high (>600 deg. C) growth temperatures or any special equipment for the MBE machines.

  4. Energy: An annotated selected bibliography

    NASA Technical Reports Server (NTRS)

    Blow, S. J. (Compiler); Peacock, R. W. (Compiler); Sholy, J. J. (Compiler)

    1979-01-01

    This updated bibliography contains approximately 7,000 selected references on energy and energy related topics from bibliographic and other data sources from June 1977. Under each subject heading the entries are arranged by the date, with the latest works first. Geothermal, solar, wind, and ocean/water power sources are included. Magnetohydrodynamics and electrohydrodynamics, electric power engineering, automotive power plants, and energy storage are also covered.

  5. Modulation of Pb chemical state of epitaxial lead zirconate titanate thin films under high energy irradiation

    NASA Astrophysics Data System (ADS)

    Barala, Surendra Singh; Roul, Basanta; Banerjee, Nirupam; Kumar, Mahesh

    2016-09-01

    The chemical states of epitaxial PbZrxTi1-xO3 films were investigated by an X-ray photoelectron spectroscopy as a function of the gamma-ray doses. An anomalous behaviour was observed in Pb4f states, and a core level of Pb4f shifts towards a higher binding energy at 50 kGy and towards a lower binding energy at 200 kGy. The behaviour can be explained by a radiation induced reduction of PbO to metallic Pb. The metal-insulator-metal electrodes were fabricated by lithography, and the current-voltage characteristics were measured. A negative differential resistance (NDR) was observed in the leakage currents at room temperature. A higher current and disappearance of NDR characteristics were found in the 200 kGy irradiated samples, which further confirms the presence of metallic Pb.

  6. Big-data reflection high energy electron diffraction analysis for understanding epitaxial film growth processes.

    PubMed

    Vasudevan, Rama K; Tselev, Alexander; Baddorf, Arthur P; Kalinin, Sergei V

    2014-10-28

    Reflection high energy electron diffraction (RHEED) has by now become a standard tool for in situ monitoring of film growth by pulsed laser deposition and molecular beam epitaxy. Yet despite the widespread adoption and wealth of information in RHEED images, most applications are limited to observing intensity oscillations of the specular spot, and much additional information on growth is discarded. With ease of data acquisition and increased computation speeds, statistical methods to rapidly mine the data set are now feasible. Here, we develop such an approach to the analysis of the fundamental growth processes through multivariate statistical analysis of a RHEED image sequence. This approach is illustrated for growth of La(x)Ca(1-x)MnO(3) films grown on etched (001) SrTiO(3) substrates, but is universal. The multivariate methods including principal component analysis and k-means clustering provide insight into the relevant behaviors, the timing and nature of a disordered to ordered growth change, and highlight statistically significant patterns. Fourier analysis yields the harmonic components of the signal and allows separation of the relevant components and baselines, isolating the asymmetric nature of the step density function and the transmission spots from the imperfect layer-by-layer (LBL) growth. These studies show the promise of big data approaches to obtaining more insight into film properties during and after epitaxial film growth. Furthermore, these studies open the pathway to use forward prediction methods to potentially allow significantly more control over growth process and hence final film quality.

  7. Segregation of Sb in Ge epitaxial layers and its usage for the selective doping of Ge-based structures

    SciTech Connect

    Antonov, A. V.; Drozdov, M. N.; Novikov, A. V. Yurasov, D. V.

    2015-11-15

    The segregation of Sb in Ge epitaxial layers grown by the method of molecular beam epitaxy on Ge (001) substrates is investigated. For a growth temperature range of 180–325°C, the temperature dependence is determined for the segregation ratio of Sb in Ge, which shows a sharp increase (by more than three orders of magnitude) with increasing temperature. The strong dependence of the segregation properties of Sb on the growth temperature makes it possible to adapt a method based on the controlled use of segregation developed previously for the doping of Si structures for the selective doping of Ge structures with a donor impurity. Using this method selectively doped Ge:Sb structures, in which the bulk impurity concentration varies by an order of magnitude at distances of 3–5 nm, are obtained.

  8. Facet-selective nucleation and conformal epitaxy of Ge shells on Si nanowires

    SciTech Connect

    Nguyen, Binh -Minh; Swartzentruber, Brian; Ro, Yun Goo; Dayeh, Shadi A.

    2015-10-08

    Knowledge of nanoscale heteroepitaxy is continually evolving as advances in material synthesis reveal new mechanisms that have not been theoretically predicted and are different than what is known about planar structures. In addition to a wide range of potential applications, core/shell nanowire structures offer a useful template to investigate heteroepitaxy at the atomistic scale. We show that the growth of a Ge shell on a Si core can be tuned from the theoretically predicted island growth mode to a conformal, crystalline, and smooth shell by careful adjustment of growth parameters in a narrow growth window that has not been explored before. In the latter growth mode, Ge adatoms preferentially nucleate islands on the {113} facets of the Si core, which outgrow over the {220} facets. Islands on the low-energy {111} facets appear to have a nucleation delay compared to the {113} islands; however, they eventually coalesce to form a crystalline conformal shell. As a result, synthesis of epitaxial and conformal Si/Ge/Si core/multishell structures enables us to fabricate unique cylindrical ring nanowire field-effect transistors, which we demonstrate to have steeper on/off characteristics than conventional core/shell nanowire transistors.

  9. Facet-selective nucleation and conformal epitaxy of Ge shells on Si nanowires

    DOE PAGES

    Nguyen, Binh -Minh; Swartzentruber, Brian; Ro, Yun Goo; ...

    2015-10-08

    Knowledge of nanoscale heteroepitaxy is continually evolving as advances in material synthesis reveal new mechanisms that have not been theoretically predicted and are different than what is known about planar structures. In addition to a wide range of potential applications, core/shell nanowire structures offer a useful template to investigate heteroepitaxy at the atomistic scale. We show that the growth of a Ge shell on a Si core can be tuned from the theoretically predicted island growth mode to a conformal, crystalline, and smooth shell by careful adjustment of growth parameters in a narrow growth window that has not been exploredmore » before. In the latter growth mode, Ge adatoms preferentially nucleate islands on the {113} facets of the Si core, which outgrow over the {220} facets. Islands on the low-energy {111} facets appear to have a nucleation delay compared to the {113} islands; however, they eventually coalesce to form a crystalline conformal shell. As a result, synthesis of epitaxial and conformal Si/Ge/Si core/multishell structures enables us to fabricate unique cylindrical ring nanowire field-effect transistors, which we demonstrate to have steeper on/off characteristics than conventional core/shell nanowire transistors.« less

  10. Numerical approximations for the molecular beam epitaxial growth model based on the invariant energy quadratization method

    NASA Astrophysics Data System (ADS)

    Yang, Xiaofeng; Zhao, Jia; Wang, Qi

    2017-03-01

    The Molecular Beam Epitaxial model is derived from the variation of a free energy, that consists of either a fourth order Ginzburg-Landau double well potential or a nonlinear logarithmic potential in terms of the gradient of a height function. One challenge in solving the MBE model numerically is how to develop proper temporal discretization for the nonlinear terms in order to preserve energy stability at the time-discrete level. In this paper, we resolve this issue by developing a first and second order time-stepping scheme based on the "Invariant Energy Quadratization" (IEQ) method. The novelty is that all nonlinear terms are treated semi-explicitly, and the resulted semi-discrete equations form a linear system at each time step. Moreover, the linear operator is symmetric positive definite and thus can be solved efficiently. We then prove that all proposed schemes are unconditionally energy stable. The semi-discrete schemes are further discretized in space using finite difference methods and implemented on GPUs for high-performance computing. Various 2D and 3D numerical examples are presented to demonstrate stability and accuracy of the proposed schemes.

  11. 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.

  12. Application of Silicon Selective Epitaxial Growth and Chemo-Mechanical Polishing to Bipolar and Soi Mosfet Devices.

    NASA Astrophysics Data System (ADS)

    Nguyen, Cuong Tan

    1994-01-01

    Polished Epitaxy, or the combination of silicon Selective Epitaxial Growth and Chemo-Mechanical Polishing, provides new flexibility in process and device design, including optimized isolation, planar active-area definition, low-capacitance contacts, and SOI thin films. In this work, Polished Epitaxy has been developed with particular effort on overcoming junction leakage problems widely reported in devices fabricated in similar processes. It was found that in addition to careful surface preparation and defect control in the selective epitaxy process, issues such as sidewall orientation, junction passivation, crystal annealing, and surface damage removal were equally important and needed to be addressed. Coupled with the proper processing steps, Polished Epitaxy was able to deliver material of comparable quality to bulk silicon, suitable for device applications. By growing epitaxy laterally over an oxide step followed by polishing, a pedestal structure was created in which a thin film of single-crystal silicon was formed over oxide. Serving as the extrinsic base contact to a T-Pedestal bipolar transistor device, this pedestal helped minimize the parasitic extrinsic-base-collector overlap capacitance. The cut-off frequency (f_ {T}) in a device with a 1.0-mu m wide emitter stripe was found to improve from 17GHz to 22GHz when the contact overlap was reduced from a more conventional, larger size of 1.0 mu m to 0.2 mum. It is expected that the high-frequency performance of this structure can still be improved further in an optimized process with reduced emitter and collector resistances. The same pedestal structure was applied to a Pedestal -SOI (Silicon-On-Insulator) MOSFET device concept. At one extreme, a conventional bulk MOSFET structure is obtained when the pedestal is not utilized; quasi-SOI occurs when the drain and part of the channel overlap with the pedestal over buried oxide; at the other extreme, complete-SOI behavior results when source, channel, and drain

  13. Chiral-Selective Growth of Single-Walled Carbon Nanotubes on Lattice-Mismatched Epitaxial Cobalt Nanoparticles

    PubMed Central

    He, Maoshuai; Jiang, Hua; Liu, Bilu; Fedotov, Pavel V.; Chernov, Alexander I.; Obraztsova, Elena D.; Cavalca, Filippo; Wagner, Jakob B.; Hansen, Thomas W.; Anoshkin, Ilya V.; Obraztsova, Ekaterina A.; Belkin, Alexey V.; Sairanen, Emma; Nasibulin, Albert G.; Lehtonen, Juha; Kauppinen, Esko I.

    2013-01-01

    Controlling chirality in growth of single-walled carbon nanotubes (SWNTs) is important for exploiting their practical applications. For long it has been conceptually conceived that the structural control of SWNTs is potentially achievable by fabricating nanoparticle catalysts with proper structures on crystalline substrates via epitaxial growth techniques. Here, we have accomplished epitaxial formation of monometallic Co nanoparticles with well-defined crystal structure, and its use as a catalyst in the selective growth of SWNTs. Dynamics of Co nanoparticles formation and SWNT growth inside an atomic-resolution environmental transmission electron microscope at a low CO pressure was recorded. We achieved highly preferential growth of semiconducting SWNTs (~90%) with an exceptionally large population of (6, 5) tubes (53%) in an ambient CO atmosphere. Particularly, we also demonstrated high enrichment in (7, 6) and (9, 4) at a low growth temperature. These findings open new perspectives both for structural control of SWNTs and for elucidating the growth mechanisms. PMID:23492872

  14. Growth of InGaAs nanowires on Ge(111) by selective-area metal-organic vapor-phase epitaxy

    NASA Astrophysics Data System (ADS)

    Yoshida, Akinobu; Tomioka, Katsuhiro; Ishizaka, Fumiya; Motohisa, Junichi

    2017-04-01

    We report the growth of InGaAs nanowires (NWs) on Ge(111) substrates using selective-area metal-organic vapor-phase epitaxy (SA-MOVPE) for novel InGaAs/Ge hybrid complementary metal-oxide-semiconductor (CMOS) applications. Ge(111) substrates with periodic arrays of mask opening were prepared, and InGaAs was selectively grown on the opening region of Ge(111). A uniform array of InGaAs NWs with a diameter around 100 nm was successfully grown using appropriate preparation of the initial surfaces with an AsH3 thermal treatment and flow-rate modulation epitaxy (FME). We found that optimizing partial pressure of AsH3 and the number of FME cycles improved the yield of vertical InGaAs NWs. Line-scan profile analysis of energy dispersive X-ray (EDX) spectrometry showed that the In composition in the InGaAs NW was almost constant from the bottom to the top. Transmission electron microscope (TEM) analysis revealed that the interface between InGaAs NW and Ge had misfit dislocations, but their distance was longer than that expected from the difference in their lattice constants.

  15. Energy: An annotated selected bibliography

    NASA Technical Reports Server (NTRS)

    Blow, S. J. (Compiler); Peacock, R. W. (Compiler); Sholy, J. J. (Compiler)

    1979-01-01

    This updated bibliography contains approximately 7,000 selected references on energy and energy related topics from bibliographic and other data sources from June 1977. Under each subject heading the entries are arranged by the data, with the latest works first. Subject headings include: resources supply/demand, and forecasting; policy, legislation, and regulation; environment; consumption, conservation, and economics; analysis, systems, and modeling, and information sources and documentation. Fossil fuels, hydrogen and other fuels, liquid/solid wastes and biomass, waste heat utilization, and nuclear power sources are also included.

  16. Continuous-wave lasing in colloidal quantum dot solids enabled by facet-selective epitaxy

    NASA Astrophysics Data System (ADS)

    Fan, Fengjia; Voznyy, Oleksandr; Sabatini, Randy P.; Bicanic, Kristopher T.; Adachi, Michael M.; McBride, James R.; Reid, Kemar R.; Park, Young-Shin; Li, Xiyan; Jain, Ankit; Quintero-Bermudez, Rafael; Saravanapavanantham, Mayuran; Liu, Min; Korkusinski, Marek; Hawrylak, Pawel; Klimov, Victor I.; Rosenthal, Sandra J.; Hoogland, Sjoerd; Sargent, Edward H.

    2017-03-01

    Colloidal quantum dots (CQDs) feature a low degeneracy of electronic states at the band edges compared with the corresponding bulk material, as well as a narrow emission linewidth. Unfortunately for potential laser applications, this degeneracy is incompletely lifted in the valence band, spreading the hole population among several states at room temperature. This leads to increased optical gain thresholds, demanding high photoexcitation levels to achieve population inversion (more electrons in excited states than in ground states—the condition for optical gain). This, in turn, increases Auger recombination losses, limiting the gain lifetime to sub-nanoseconds and preventing steady laser action. State degeneracy also broadens the photoluminescence linewidth at the single-particle level. Here we demonstrate a way to decrease the band-edge degeneracy and single-dot photoluminescence linewidth in CQDs by means of uniform biaxial strain. We have developed a synthetic strategy that we term facet-selective epitaxy: we first switch off, and then switch on, shell growth on the (0001) facet of wurtzite CdSe cores, producing asymmetric compressive shells that create built-in biaxial strain, while still maintaining excellent surface passivation (preventing defect formation, which otherwise would cause non-radiative recombination losses). Our synthesis spreads the excitonic fine structure uniformly and sufficiently broadly that it prevents valence-band-edge states from being thermally depopulated. We thereby reduce the optical gain threshold and demonstrate continuous-wave lasing from CQD solids, expanding the library of solution-processed materials that may be capable of continuous-wave lasing. The individual CQDs exhibit an ultra-narrow single-dot linewidth, and we successfully propagate this into the ensemble of CQDs.

  17. Low-energy electron diffraction investigation of epitaxial growth: Pt and Pd on Pd(100)

    SciTech Connect

    Flynn-Sanders, D.

    1990-09-21

    We investigate the epitaxial growth of Pt and Pd and Pd(100) via spot profile analysis using conventional low-energy electron diffraction (LEED). We resolve a central-spike and diffuse component in the spot profiles, reflecting the layer-occupations and pair-correlations, respectively. Kinetic limitations inhibit layer-by-layer growth at low temperatures. Our data suggest diffusion switches on at ca. 150 K for Pt and ca. 170 K for Pd indicating activation barriers to surface diffusion of ca. 10 and ca. 13 kcal/mol, respectively. To clarify the role of diffusion in determining the resulting film morphology, we develop a growth model that incorporates the adsorption-site requirement and predicts intensity oscillations. We present a new procedure to experimentally determine out-of-phase scattering conditions. At these energies, ring-structure is evident in the profiles during Pd growth between ca. 200 and 400 K. We report ring intensity oscillations as a function of coverage, which demonstrate the filling of individual layers.

  18. Why do dislocations assemble into interfaces in epitaxy as well as in crystal plasticity? To minimize free energy

    NASA Astrophysics Data System (ADS)

    Kuhlmann-Wilsdorf, D.

    2002-08-01

    Dislocations commonly form planar arrays that minimize the free interfacial energy between relatively mismatched crystal volumes. In epitaxy and phase transformations, the causative misfit is that between differences in lattice structure and/or orientations of different phases. In deformed homogeneous crystalline materials, the planar dislocation arrays are grain and mosaic block boundaries that accommodate relative misorientations within the same crystal structure. Thus, overwhelmingly, planar dislocation arrays have a basically common origin, namely minimization of interfacial energies. Consequently, they are all subject to the low-energy dislocation structures (LEDS) hypothesis. While the specific applications of the underlying general theory are well advanced in terms of epitaxy, phase, and grain boundaries, in connection with plastic deformation that very basis is widely overlooked, if not denied. The present article aims to (a) document the fact that, while being formed, dislocation structures due to plastic deformation are in thermodynamical equilibrium, (b) firmly establish the outlined connection between planar dislocation arrays of all types, and, thereby, (c) establish the kinship between epitaxy and plastic deformation of crystalline materials.

  19. Photoelectrochemistry of III-V epitaxial layers and nanowires for solar energy conversion

    NASA Astrophysics Data System (ADS)

    Parameshwaran, Vijay; Enck, Ryan; Chung, Roy; Kelley, Stephen; Sampath, Anand; Reed, Meredith; Xu, Xiaoqing; Clemens, Bruce

    2017-05-01

    III-V materials, which exhibit high absorption coefficients and charge carrier mobility, are ideal templates for solar energy conversion applications. This work describes the photoelectrochemistry research in several IIIV/electrolyte junctions as an enabler for device design for solar chemical reactions. By designing lattice-matched epitaxial growth of InGaP and GaP on GaAs and Si, respectively, extended depletion region electrodes achieve photovoltages which provide an additional boost to the underlying substrate photovoltage. The InGaP/GaAs and GaP/Si electrodes drive hydrogen evolution currents under aqueous conditions. By using nanowires of InN and InP under carefully controlled growth conditions, current and capacitance measurements are obtained to reveal the nature of the nanowire-electrolyte interface and how light is translated into photocurrent for InP and a photovoltage in InN. The materials system is expanded into the III-V nitride semiconductors, in which it is shown that varying the morphology of GaN on silicon yields insights to how the interface and light conversion is modulated as a basis for future designs. Current extensions of this work address growth and tuning of the III-V nitride electrodes with doping and polarization engineering for efficient coupling to solar-driven chemical reactions, and rapid-throughput methods for III-V nanomaterials synthesis in this materials space.

  20. Chemical order and selection of the mechanism for strain relaxation in epitaxial FePd(Pt) thin layers

    SciTech Connect

    Halley, D.; Marty, A.; Bayle-Guillemaud, P.; Attane, J.P.; Samson, Y.

    2004-11-01

    We observed that the relaxation mechanism of the epitaxial strain is dramatically dependent on the chemical ordering within the L1{sub 0} structure in FePd(Pt) thin films. In disordered or weakly ordered layers, the relaxation takes place though perfect (1/2)[101] dislocations, whereas well-ordered films relax through the partial 1/6[112] Shockley dislocations, piled-up within microtwins, with a huge impact on both the morphology and the magnetic properties of the film. We show that the antiphase boundary energy is the key factor preventing the propagation of perfect dislocations in ordered alloys.

  1. Selective area epitaxy of monolithic white-light InGaN/GaN quantum well microstripes with dual color emission

    SciTech Connect

    Li, Yuejing; Tong, Yuying; Yang, Guofeng Yao, Chujun; Sun, Rui; Cai, Lesheng; Xu, Guiting; Wang, Jin; Zhang, Qing; Ye, Xuanchao; Wu, Mengting; Wen, Zhiqin

    2015-09-15

    Monolithic color synthesis is demonstrated using InGaN/GaN multiple quantum wells (QWs) grown on GaN microstripes formed by selective area epitaxy on SiO{sub 2} mask patterns. The striped microfacet structure is composed of (0001) and (11-22) planes, attributed to favorable surface polarity and surface energy. InGaN/GaN QWs on different microfacets contain spatially inhomogeneous compositions owing to the diffusion of adatoms among the facets. This unique property allows the microfacet QWs to emit blue light from the (11-22) plane and yellow light from the top (0001) plane, the mixing of which leads to the perception of white light emission.

  2. Dislocation reduction via selective-area growth of InN accompanied by lateral growth by rf-plasma-assisted molecular-beam epitaxy

    SciTech Connect

    Kamimura, Jumpei; Kishino, Katsumi; Kikuchi, Akihiko

    2010-10-04

    We investigated the selective-area growth (SAG) of InN by rf-plasma-assisted molecular-beam epitaxy using molybdenum (Mo)-mask-patterned sapphire (0001) substrates, which resulted in the formation of regularly arranged N-polar InN microcrystals. Transmission electron microscopy observation confirmed that the laterally grown side areas were nearly dislocation-free, although many threading dislocations (10{sup 9}-10{sup 10} cm{sup -2}) were generated at the InN/sapphire interface and propagated into the center of the InN microcrystals along the crystal c-axis. The laterally grown InN microcrystals exhibited narrow near-IR emission spectra with a peak photon energy of 0.627 eV and a linewidth of 39 meV at room temperature.

  3. Imaging pulsed laser deposition growth of homo-epitaxial SrTiO3 by low-energy electron microscopy

    NASA Astrophysics Data System (ADS)

    van der Torren, A. J. H.; van der Molen, S. J.; Aarts, J.

    2016-12-01

    By combining low-energy electron microscopy with in situ pulsed laser deposition we have developed a new technique for film growth analysis, making use of both diffraction and real-space information. Working at the growth temperature, we can use: the intensity and profile variations of the specular beam to follow the coverage in a layer-by-layer fashion; real-space microscopy to follow e.g. atomic steps at the surface; and electron reflectivity to probe the unoccupied band structure of the grown material. Here, we demonstrate our methodology for homo-epitaxial growth of SrTiO3. Interestingly, the same combination of techniques will also be applicable to hetero-epitaxial oxide growth, largely extending the scope of research possibilities.

  4. Shadowing and mask opening effects during selective-area vapor-liquid-solid growth of InP nanowires by metalorganic molecular beam epitaxy.

    PubMed

    Kelrich, A; Calahorra, Y; Greenberg, Y; Gavrilov, A; Cohen, S; Ritter, D

    2013-11-29

    Indium phosphide nanowires were grown by metalorganic molecular beam epitaxy using the selective-area vapor-liquid-solid method. We show experimentally and theoretically that the size of the annular opening around the nanowire has a major impact on nanowire growth rate. In addition, we observed a considerable reduction of the growth rate in dense two-dimensional arrays, in agreement with a calculation of the shadowing of the scattered precursors. Due to the impact of these effects on growth, they should be considered during selective-area vapor-liquid-solid nanowire epitaxy.

  5. Design and characterization of integrated photonic devices fabricated using selective-area epitaxy and distributed Bragg reflector surface gratings

    NASA Astrophysics Data System (ADS)

    Lammert, Robert Morand

    Two of the main challenges involved with the fabrication of integrated photonic devices are the control of the in-plane band gap and the formation of integrable high-Q cavities. In-plane bandgap control is required to fabricate emitters, passive waveguides, detectors, and modulators all on a single wafer and all optimized for operation at a particular wavelength. The formation of integrable high-Q cavities is needed to integrate the laser source. Selective-area epitaxy (SAE) is a powerful technique which enables the tailoring of the in-plane band gap energy to fabricate numerous optimized photonic devices on a single wafer. In this dissertation, a three-step SAE process in the InGaAs-GaAs-AlGaAs material system is investigated. This process produced discrete Fabry-Perot lasers with threshold currents as low as 2.65 mA for an uncoated device and 0.97 mA for a coated device. Several integrated photonic devices that utilize the in-plane bandgap control of this SAE process are also investigated. These devices include lasers with nonabsorbing mirrors, dual-channel wavelength division multiplexing sources with integrated coupler, lasers with integrated photodiodes, lasers with integrated intracavity modulators, and lasers with integrated external cavity modulators. The second challenge involved with the fabricating of integrated photonic devices is the formation of integrable high-Q cavities. The optical feedback in most laser diodes is provided by cleaved facets. Unfortunately, cleaved facets are not an option when designing integrated photonic devices. However, optical feedback can be provided in integrated photonic devices using distributed Bragg reflectors (DBRs). In this dissertation, ridge-waveguide DBR lasers with first-order surface gratings are investigated. These lasers exhibit low thresholds (6 mA), high slope efficiencies (0.46 W/A), and single-frequency operation with narrow linewidths (<25 kHz). By varying the period of the first-order DBR grating, a wide

  6. Selective Epitaxy of InP on Si and Rectification in Graphene/InP/Si Hybrid Structure.

    PubMed

    Niu, Gang; Capellini, Giovanni; Hatami, Fariba; Di Bartolomeo, Antonio; Niermann, Tore; Hussein, Emad Hameed; Schubert, Markus Andreas; Krause, Hans-Michael; Zaumseil, Peter; Skibitzki, Oliver; Lupina, Grzegorz; Masselink, William Ted; Lehmann, Michael; Xie, Ya-Hong; Schroeder, Thomas

    2016-10-12

    The epitaxial integration of highly heterogeneous material systems with silicon (Si) is a central topic in (opto-)electronics owing to device applications. InP could open new avenues for the realization of novel devices such as high-mobility transistors in next-generation CMOS or efficient lasers in Si photonics circuitry. However, the InP/Si heteroepitaxy is highly challenging due to the lattice (∼8%), thermal expansion mismatch (∼84%), and the different lattice symmetries. Here, we demonstrate the growth of InP nanocrystals showing high structural quality and excellent optoelectronic properties on Si. Our CMOS-compatible innovative approach exploits the selective epitaxy of InP nanocrystals on Si nanometric seeds obtained by the opening of lattice-arranged Si nanotips embedded in a SiO2 matrix. A graphene/InP/Si-tip heterostructure was realized on obtained materials, revealing rectifying behavior and promising photodetection. This work presents a significant advance toward the monolithic integration of graphene/III-V based hybrid devices onto the mainstream Si technology platform.

  7. Template-assisted selective epitaxy of III–V nanoscale devices for co-planar heterogeneous integration with Si

    SciTech Connect

    Schmid, H. Borg, M.; Moselund, K.; Cutaia, D.; Riel, H.; Gignac, L.; Breslin, C. M.; Bruley, J.

    2015-06-08

    III–V nanoscale devices were monolithically integrated on silicon-on-insulator (SOI) substrates by template-assisted selective epitaxy (TASE) using metal organic chemical vapor deposition. Single crystal III–V (InAs, InGaAs, GaAs) nanostructures, such as nanowires, nanostructures containing constrictions, and cross junctions, as well as 3D stacked nanowires were directly obtained by epitaxial filling of lithographically defined oxide templates. The benefit of TASE is exemplified by the straightforward fabrication of nanoscale Hall structures as well as multiple gate field effect transistors (MuG-FETs) grown co-planar to the SOI layer. Hall measurements on InAs nanowire cross junctions revealed an electron mobility of 5400 cm{sup 2}/V s, while the alongside fabricated InAs MuG-FETs with ten 55 nm wide, 23 nm thick, and 390 nm long channels exhibit an on current of 660 μA/μm and a peak transconductance of 1.0 mS/μm at V{sub DS} = 0.5 V. These results demonstrate TASE as a promising fabrication approach for heterogeneous material integration on Si.

  8. 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.

  9. Highly manufacturable silicon vertical diode switches for new memories using selective epitaxial growth with batch-type equipment

    NASA Astrophysics Data System (ADS)

    Lee, K. S.; Han, J. J.; Kim, B. H.; Lim, H. J.; Nam, S. W.; Kang, H. K.; Chung, C. H.; Jeong, H. S.; Park, H. H.; Jeong, H. W.; Kim, K. R.; Choi, B. D.

    2011-05-01

    Practical selectivity window of selective epitaxial growth (SEG) using a H2/SiH4/Cl2 cyclic chemical vapor deposition (CVD) system has been investigated with the batch-type vertical furnace equipment, replacing a conventional single-wafer H2/dichlorosilane/HCl CVD system. The process temperature was less than 700 °C, which is suitable for a low thermal budget process applicable to next-generation memories including vertical pn-diode switches. Selectivity loss is quantified by an in-line inspection tool to determine the practical number of selectivity losses. The H2/SiH4/Cl2 cyclic CVD system provides an excellent capacity of 40 wafers per batch. Selectivity loss, which is one of the most crucial features in the SEG process for the diode application, is controlled with both the amount of SiH4 and Cl2 and the period of gas supply, and the practical number of selectivity loss is confirmed to be less than 100 in 200 mm wafers. Without high temperature annealing in hydrogen ambient, low temperature cyclic SEG in the batch reactor ensures the clean interface and improved crystalline quality of SEG-Si, as well as high throughput.

  10. Selective epitaxial growth of zinc blende-derivative on wurtzite-derivative: the case of polytypic Cu2CdSn(S1-xSex)4 nanocrystals

    NASA Astrophysics Data System (ADS)

    Wu, Liang; Fan, Feng-Jia; Gong, Ming; Ge, Jin; Yu, Shu-Hong

    2014-02-01

    Polytypic nanocrystals with zinc blende (ZB) cores and wurtzite (WZ) arms, such as tetrapod and octopod nanocrystals, have been widely reported. However, polytypic nanocrystals with WZ cores and ZB arms or ends have been rarely reported. Here, we report a facile, solution-based approach to the synthesis of polytypic Cu2CdSn(S1-xSex)4 (CCTSSe) nanocrystals with ZB-derivative selectively engineered on (000+/-2)WZ facets of WZ-derived cores. Accordingly, two typical morphologies, i.e., bullet-like nanocrystals with a WZ-derivative core and one ZB-derivative end, and rugby ball-like nanocrystals with a WZ-derivative core and two ZB-derivative ends, can be selectively prepared. The epitaxial growth mechanism is confirmed by the time-dependent experiments. The ratio of rugby ball-like and bullet-like polytypic CCTSSe nanocrystals can be tuned through changing the amount of Cd precursor to adjust the reactivity difference between (0002)WZ and (000-2)WZ facets. These unique polytypic CCTSSe nanocrystals may find applications in energetic semiconducting materials for energy conversion in the future.Polytypic nanocrystals with zinc blende (ZB) cores and wurtzite (WZ) arms, such as tetrapod and octopod nanocrystals, have been widely reported. However, polytypic nanocrystals with WZ cores and ZB arms or ends have been rarely reported. Here, we report a facile, solution-based approach to the synthesis of polytypic Cu2CdSn(S1-xSex)4 (CCTSSe) nanocrystals with ZB-derivative selectively engineered on (000+/-2)WZ facets of WZ-derived cores. Accordingly, two typical morphologies, i.e., bullet-like nanocrystals with a WZ-derivative core and one ZB-derivative end, and rugby ball-like nanocrystals with a WZ-derivative core and two ZB-derivative ends, can be selectively prepared. The epitaxial growth mechanism is confirmed by the time-dependent experiments. The ratio of rugby ball-like and bullet-like polytypic CCTSSe nanocrystals can be tuned through changing the amount of Cd precursor

  11. Selective epitaxial growth techniques to integrate high-quality germanium on silicon

    NASA Astrophysics Data System (ADS)

    Leonhardt, Darin

    2011-12-01

    High-quality Ge-on-Si heterostructures have been actively pursued for many advanced applications, including near-infrared photodetectors, high-mobility field effect transistors, and virtual substrates for integrating III-V multijunction solar cells. However, growing epitaxial Ge on Si poses many engineering challenges, ranging from lattice mismatch, to thermal expansion coefficient mismatch, to non-planar morphological evolution. The lattice mismatch between Ge and Si often leads to a high density of threading dislocations. These dislocations, if not reduced, propagate through the subsequently grown GaAs layer, deteriorating its quality. To overcome these engineering challenges, we have developed three different approaches based on molecular beam epitaxy to significantly reduce, manage, or eliminate the defects in Ge films grown on Si. The first approach involves the nucleation of Ge islands within nanoscale windows in a thin layer of chemically grown SiO2 and successive island coalescence over the SiO2 to form a continuous film. Nanoscale contact areas between Ge and Si effectively relieve the lattice mismatch stress between Ge/Si so that dislocations do not nucleate. We observe that annealing the nucleated islands prior to full coalescence also leads to Ge films that are free of defects, along with significant improvement in GaAs integrated on Ge. The second approach involves trapping dislocations in Ge between high aspect ratio walls of SiO2. Defects form during coalescence of Ge from adjacent channels and at the corners of the SiO2 walls due to stress resulting from differences in thermal expansion coefficients of Ge, Si, and SiO2. The third approach involves filling etch pits, which reveal dislocations, with SiO2 and subsequent Ge growth over SiO2. The filling prevents dislocations in the lower Ge layer from propagating into the upper Ge layer. The third method reduces the defect density from 2.8 x 108 cm-2 to 9.1 x 10 6 cm-2, and is proven to be the most

  12. Energy: An Annotated Bibliography of Selected Energy Education Materials.

    ERIC Educational Resources Information Center

    Massachusetts Audubon Society, Lincoln. Hatheway Environmental Education Inst.

    This is an annotated bibliography of selected energy education materials. These materials were selected according to the following criteria: (1) Usability in an instructional atmosphere; (2) Relevancy to issues on energy use in the environment; (3) Accuracy and current relevancy of energy facts and trends; (4) Attractiveness of format including…

  13. In situ mask designed for selective growth of InAs quantum dots in narrow regions developed for molecular beam epitaxy system

    NASA Astrophysics Data System (ADS)

    Ohkouchi, Shunsuke; Nakamura, Yusui; Ikeda, Naoki; Sugimoto, Yoshimasa; Asakawa, Kiyoshi

    2007-07-01

    We have developed an in situ mask that enables the selective formation of molecular beam epitaxially grown layers in narrow regions. This mask can be fitted to a sample holder and removed in an ultrahigh-vacuum environment; thus, device structures can be fabricated without exposing the sample surfaces to air. Moreover, this mask enables the observation of reflection high-energy electron diffraction during growth with the mask positioned on the sample holder and provides for the formation of marker layers for ensuring alignment in the processes following the selective growth. To explore the effectiveness of the proposed in situ mask, we used it to grow quantum dot (QD) structures in narrow regions and verified the perfect selectivity of the QD growth. The grown QDs exhibited high optical quality with a photoluminescence peak at approximately 1.30μm and a linewidth of 30meV at room temperature. The proposed technique can be applied for the integration of microstructures into optoelectronic functional devices.

  14. All-epitaxial, lithographically defined, current- and mode-confined vertical-cavity surface-emitting laser based on selective interfacial fermi-level pinning

    SciTech Connect

    Ahn, J.; Lu, D.; Deppe, D.G.

    2005-01-10

    An approach is presented to fabricate a current- and mode-confined vertical-cavity surface-emitting laser that is all-epitaxial and lithographically defined. The device uses selective Fermi level pinning to self-align the electrical injection to a mode-confining intracavity phase-shifting mesa.

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

    PubMed

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

    2017-09-08

    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. © 2017 IOP Publishing Ltd.

  16. Phase-field simulations of GaN growth by selective area epitaxy on complex mask geometries

    SciTech Connect

    Aagesen, Larry K.; Coltrin, Michael Elliott; Han, Jung; Thornton, Katsuyo

    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 and processing conditions during materials synthesis for solar cells, light-emitting diodes, and other electronic and opto-electronic applications.

  17. Phase-field simulations of GaN growth by selective area epitaxy from complex mask geometries

    SciTech Connect

    Aagesen, Larry K.; Thornton, Katsuyo; Coltrin, Michael E.; Han, Jung

    2015-05-21

    Three-dimensional phase-field simulations of GaN growth by selective area epitaxy were performed. The 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. The model provides a route to optimize masks and processing conditions during materials synthesis for solar cells, light-emitting diodes, and other electronic and opto-electronic applications.

  18. 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

  19. A review of III–V planar nanowire arrays: selective lateral VLS epitaxy and 3D transistors

    NASA Astrophysics Data System (ADS)

    Zhang, Chen; Miao, Xin; Chabak, Kelson D.; Li, Xiuling

    2017-10-01

    Nanowires have long been regarded as a promising architecture for beyond Si CMOS logic, future III–V RF electronics, next generation optoelectronic applications, as well as heterogeneous integration. The inherent 3D structure also enables new device concepts that are otherwise not accessible with conventional technology. Nanowires grown using bottom-up epitaxial methods such as metalorganic chemical vapor deposition are free of ion-induced damage, which is especially critical for III–V because of the irreversibility of such damage, and can be scaled to dimensions smaller than lithographically defined. The challenges for nanowire based devices have been the controllability and compatibility with Si CMOS manufacturing. The discovery of parallel arrays of planar III–V nanowire growth mode provides an in-plane nanowire configuration that is perfectly compatible with existing planar processing technology for industry. The selective lateral epitaxy nature guided by the metal nanoparticles via the vapor–liquid–solid (VLS) mechanism opens up a new paradigm of crystal growth and consequently enabled in situ lateral and radial junctions. In this article, we review the planar nanowire based transistor development, particularly, planar III-As compound semiconductor based transistors enabled by this bottom-up self-assembled selective lateral VLS mechanism. We first review the characteristics and mechanism of planar nanowire growth, then focus on the growth, fabrication, and DC and RF performance of metal-semiconductor field-effect transistors, metal-oxide semiconductor field-effect transistors, and high electron mobility transistors (HEMTs), before providing our perspective on future development.

  20. Low-temperature epitaxial growth of β-SiC by multiple-energy ion implantation

    NASA Astrophysics Data System (ADS)

    Zhang, Z. J.; Naramoto, H.; Miyashita, A.; Stritzker, B.; Lindner, J. K. N.

    1998-11-01

    A cubic silicon carbide (β-SiC) buried layer was synthesized in Si(111) using a combination of multienergy carbon ion implantation at room temperature and post-thermal annealing. The crystal structure and the crystalline quality of the β-SiC layer was identified by x-ray diffraction in the θ-2θ mode and was examined by pole figure measurement of x-ray diffraction. Interestingly, by using the multienergy implantation technique, the β-SiC buried layer showed epitaxial growth at annealing temperatures as low as 400 °C. At an annealing temperature of 800 °C, the x-ray pole figures show that the β-SiC buried layer has a near-perfect epitaxial relationship with the silicon substrate.

  1. Magnetism of epitaxial Tb films on W(110) studied by spin-polarized low-energy electron microscopy

    NASA Astrophysics Data System (ADS)

    Prieto, J. E.; Chen, Gong; Schmid, A. K.; de la Figuera, J.

    2016-11-01

    Thin epitaxial films of Tb metal were grown on a clean W(110) substrate in ultrahigh vacuum and studied in situ by low-energy electron microscopy. Annealed films present magnetic contrast in spin-polarized low-energy electron microscopy. The energy dependence of the electron reflectivity was determined and a maximum value of its spin asymmetry of about 1% was measured. The magnetization direction of the Tb films is in-plane. Upon raising the temperature, no change in the domain distribution is observed, while the asymmetry in the electron reflectivity decreases when approaching the critical temperature, following a power law ˜(1-T /TC) β with a critical exponent β of 0.39.

  2. Highly oriented diamond (111) films synthesized by pulse bias-enhanced nucleation and epitaxial grain selection on a 3C-SiC/Si (111) substrate

    NASA Astrophysics Data System (ADS)

    Suto, Takeru; Yaita, Junya; Iwasaki, Takayuki; Hatano, Mutsuko

    2017-02-01

    We report the synthesis of highly oriented diamond (HOD) (111) films on 3C-SiC/Si (111) substrates. Bias-enhanced nucleation (BEN) is a key process for the heteroepitaxial growth of HOD films. Conventional long nucleation periods have been found to lead to a polycrystalline diamond film on the 3C-SiC (111) surface. Here, we propose a method that combines brief BEN (<30 s), called pulse BEN, and epitaxial grain selection by oxidative etching. Smaller diamond nuclei with a higher spatial density on the substrate were formed by pulse BEN with a pulse duration of <30 s. We found that precisely controlling the pulse duration is important for obtaining a nucleation density that is sufficiently high to obtain the HOD films. By adding oxygen gas to the subsequent growth process, non-epitaxial nuclei were removed and epitaxial diamond grains selectively remained. There was no notable difference in the relative growth rate of [111] to [100] with and without oxygen, and the orientation improvement was observed on both the (100) and (111) substrates. This suggests that the mechanism of oxidative removal was not evolutionary selective growth, but etching of the non-epitaxial interfaces between the nuclei and the (111) substrate. Finally, the HOD (111) films covering the entire 3C-SiC surface were synthesized, and they exhibited distinct diffraction spots, indicating the formation of the oriented diamond.

  3. Selective area growth of In(Ga)N/GaN nanocolumns by molecular beam epitaxy on GaN-buffered Si(111): from ultraviolet to infrared emission.

    PubMed

    Albert, S; Bengoechea-Encabo, A; Sánchez-García, M A; Kong, X; Trampert, A; Calleja, E

    2013-05-03

    Selective area growth of In(Ga)N/GaN nanocolumns was performed on GaN-buffered Si(111) substrates by plasma-assisted molecular beam epitaxy. Undoped and Si-doped GaN buffer layers were first grown on Si(111) substrates, showing photoluminescence excitonic emission without traces of other low energy contributions, in particular, the yellow band. The GaN buffer surface roughness (between 10 and 14 nm, the rms value in a 10 × 10 μm(2) area) was low enough to allow the fabrication of a thin (7 nm thick) well defined Ti nanohole mask, for the selective area growth. Ordered In(Ga)N/GaN nanocolumns emitting from the ultraviolet (3.2 eV) to the infrared (0.78 eV) were obtained. The morphology and the emission efficiency of the In(Ga)N/GaN nanocolumns emitting at a given wavelength could be substantially improved by tuning the In/Ga and total III/N ratios. An estimated internal quantum efficiency of 36% was derived from photoluminescence data for green emitting nanocolumns.

  4. Impact of P/In flux ratio and epilayer thickness on faceting for nanoscale selective area growth of InP by molecular beam epitaxy.

    PubMed

    Fahed, M; Desplanque, L; Coinon, C; Troadec, D; Wallart, X

    2015-07-24

    The impact of the P/In flux ratio and the deposited thickness on the faceting of InP nanostructures selectively grown by molecular beam epitaxy (MBE) is reported. Homoepitaxial growth of InP is performed inside 200 nm wide stripe openings oriented either along a [110] or [1-10] azimuth in a 10 nm thick SiO2 film deposited on an InP(001) substrate. When varying the P/In flux ratio, no major shape differences are observed for [1-10]-oriented apertures. On the other hand, the InP nanostructure cross sections strongly evolve for [110]-oriented apertures for which (111)B facets are more prominent and (001) ones shrink for large P/In flux ratio values. These results show that the growth conditions allow tailoring the nanocrystal shape. They are discussed in the framework of the equilibrium crystal shape model using existing theoretical calculations of the surface energies of different low-index InP surfaces as a function of the phosphorus chemical potential, directly related to the P/In ratio. Experimental observations strongly suggest that the relative (111)A surface energy is probably smaller than the calculated value. We also discuss the evolution of the nanostructure shape with the InP-deposited thickness.

  5. Origin of the low-energy emission band in epitaxially grown para-sexiphenyl nanocrystallites

    NASA Astrophysics Data System (ADS)

    Kadashchuk, A.; Schols, S.; Heremans, P.; Skryshevski, Yu.; Piryatinski, Yu.; Beinik, I.; Teichert, C.; Hernandez-Sosa, G.; Sitter, H.; Andreev, A.; Frank, P.; Winkler, A.

    2009-02-01

    A comparative study of steady-state and time-resolved photoluminescence of para-sexiphenyl (PSP) films grown by organic molecular beam epitaxy (OMBE) and hot wall epitaxy (HWE) under comparable conditions is presented. Using different template substrates [mica(001) and KCl(001) surfaces] as well as different OMBE growth conditions has enabled us to vary greatly the morphology of the PSP crystallites while keeping their chemical structure virtually untouched. We prove that the broad redshifted emission band has a structure-related origin rather than being due to monomolecular oxidative defects. We conclude that the growth conditions and type of template substrate impacts substantially on the film morphology (measured by atomic force microscopy) and emission properties of the PSP films. The relative intensity of the defect emission band observed in the delayed spectra was found to correlate with the structural quality of PSP crystallites. In particular, the defect emission has been found to be drastically suppressed when (i) a KCl template substrate was used instead of mica in HWE-grown films, and (ii) in the OMBE-grown films dominated by growth mounds composed of upright standing molecules as opposed to the films consisting of crystallites formed by molecules lying parallel to the substrate.

  6. Origin of the low-energy emission band in epitaxially grown para-sexiphenyl nanocrystallites

    SciTech Connect

    Kadashchuk, A.; Schols, S.; Heremans, P.; Skryshevski, Yu.; Piryatinski, Yu.; Beinik, I.; Teichert, C.; Hernandez-Sosa, G.; Sitter, H.; Andreev, A.; Frank, P.; Winkler, A.

    2009-02-28

    A comparative study of steady-state and time-resolved photoluminescence of para-sexiphenyl (PSP) films grown by organic molecular beam epitaxy (OMBE) and hot wall epitaxy (HWE) under comparable conditions is presented. Using different template substrates [mica(001) and KCl(001) surfaces] as well as different OMBE growth conditions has enabled us to vary greatly the morphology of the PSP crystallites while keeping their chemical structure virtually untouched. We prove that the broad redshifted emission band has a structure-related origin rather than being due to monomolecular oxidative defects. We conclude that the growth conditions and type of template substrate impacts substantially on the film morphology (measured by atomic force microscopy) and emission properties of the PSP films. The relative intensity of the defect emission band observed in the delayed spectra was found to correlate with the structural quality of PSP crystallites. In particular, the defect emission has been found to be drastically suppressed when (i) a KCl template substrate was used instead of mica in HWE-grown films, and (ii) in the OMBE-grown films dominated by growth mounds composed of upright standing molecules as opposed to the films consisting of crystallites formed by molecules lying parallel to the substrate.

  7. Mushroom-free selective epitaxial growth of Si, SiGe and SiGe:B raised sources and drains

    NASA Astrophysics Data System (ADS)

    Hartmann, J. M.; Benevent, V.; Barnes, J. P.; Veillerot, M.; Lafond, D.; Damlencourt, J. F.; Morvan, S.; Prévitali, B.; Andrieu, F.; Loubet, N.; Dutartre, D.

    2013-05-01

    We have evaluated various Cyclic Selective Epitaxial Growth/Etch (CSEGE) processes in order to grow "mushroom-free" Si and SiGe:B Raised Sources and Drains (RSDs) on each side of ultra-short gate length Extra-Thin Silicon-On-Insulator (ET-SOI) transistors. The 750 °C, 20 Torr Si CSEGE process we have developed (5 chlorinated growth steps with four HCl etch steps in-between) yielded excellent crystalline quality, typically 18 nm thick Si RSDs. Growth was conformal along the Si3N4 sidewall spacers, without any poly-Si mushrooms on top of unprotected gates. We have then evaluated on blanket 300 mm Si(001) wafers the feasibility of a 650 °C, 20 Torr SiGe:B CSEGE process (5 chlorinated growth steps with four HCl etch steps in-between, as for Si). As expected, the deposited thickness decreased as the total HCl etch time increased. This came hands in hands with unforeseen (i) decrease of the mean Ge concentration (from 30% down to 26%) and (ii) increase of the substitutional B concentration (from 2 × 1020 cm-3 up to 3 × 1020 cm-3). They were due to fluctuations of the Ge concentration and of the atomic B concentration [B] in such layers (drop of the Ge% and increase of [B] at etch step locations). Such blanket layers were a bit rougher than layers grown using a single epitaxy step, but nevertheless of excellent crystalline quality. Transposition of our CSEGE process on patterned ET-SOI wafers did not yield the expected results. HCl etch steps indeed helped in partly or totally removing the poly-SiGe:B mushrooms on top of the gates. This was however at the expense of the crystalline quality and 2D nature of the ˜45 nm thick Si0.7Ge0.3:B recessed sources and drains selectively grown on each side of the imperfectly protected poly-Si gates. The only solution we have so far identified that yields a lesser amount of mushrooms while preserving the quality of the S/D is to increase the HCl flow during growth steps.

  8. On the phase shift of reflection high energy electron diffraction intensity oscillations during Ge(001) homoepitaxy by molecular beam epitaxy

    SciTech Connect

    Shin Byungha; Leonard, John P.; McCamy, James W.; Aziz, Michael J.

    2007-03-15

    The authors have conducted a systematic investigation of the phase shift of the reflection high energy electron diffraction (RHEED) intensity oscillations during homoepitaxy of Ge(001) by molecular beam epitaxy for a wide range of diffraction conditions. Their results show that for small incidence angles with a beam azimuth several degrees away from the <110> crystallographic symmetry direction, the phase is independent of incidence angle; however, it starts to shift once the incidence angle is high enough that the (004) Kikuchi line appears in the RHEED pattern. Moreover, under some conditions they observe the oscillations from only the Kikuchi feature and not from the specular spot, and the oscillatory behavior of the Kikuchi feature is almost out of phase with that of the specular spot. They 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. They discuss necessary conditions for avoiding interference.

  9. Hanle precession in the presence of energy-dependent coupling between localized states and an epitaxial graphene spin channel

    NASA Astrophysics Data System (ADS)

    van den Berg, J. J.; Kaverzin, A.; van Wees, B. J.

    2016-12-01

    Hanle spin precession measurements are a common method to extract the spin transport properties of graphene. In epitaxial graphene on silicon carbide, these measurements show unexpected behavior, due to presumed localized states in the carbon buffer layer that is present between the channel and the substrate. As a consequence, the Hanle curve narrows in its magnetic field dependence and can show an unconventional shape, which has been experimentally observed and modeled in previous studies. Here, we extend the previously developed model by assuming that the localized states are charge traps, that have a power-law distribution of trapping times. Our simulations show that the energy dependence of these trapping times can be extracted from the temperature evolution of the Hanle curve, which was previously observed in experiments. Our extended model gives better insight into what processes play a role when a spin channel is coupled to localized states and their relation to the experimental observations.

  10. Low-energy electron diffraction and photoemission study of epitaxial films of Cu on Ag l brace 001 r brace

    SciTech Connect

    Li, H.; Tian, D.; Quinn, J.; Li, Y.S.; Jona, F. ); Marcus, P.M. )

    1991-03-15

    The epitaxy of Cu on Ag{l brace}001{r brace} is studied by qualitative and quantitative low-energy electron diffraction (LEED) and by angle-resolved photoemission. LEED indicates that ultrathin (two- to three-atomic-layer) films have a limited amount of long-range order, and the ordered component has interlayer spacings of 1.45{plus minus}0.06 A, which compares well with the theoretically determined cubic lattice constant 2.87{plus minus}0.06 A of a metastable body-centered-cubic (bcc) modification of Cu. Thicker (10- to 12-layer) films have almost no long-range order, and photoemission indicates that regions of bcc and fcc Cu coexist amid large amounts of defects.

  11. Surface Reaction Kinetics of InP and InAs Metalorganic Vapor Phase Epitaxy Analyzed by Selective Area Growth Technique

    NASA Astrophysics Data System (ADS)

    Wang, Yunpeng; Song, Haizheng; Sugiyama, Masakazu; Nakano, Yoshiaki; Shimogaki, Yukihiro

    2008-10-01

    The surface kinetic information of metalorganic vapor phase epitaxy (MOVPE) is difficult to obtain, because growth rate is normally limited by diffusional mass-transfer rate. In this study, by using a selective area growth (SAG) technique, the surface kinetics has been successfully clarified for InP and InAs growth. The temperature dependence of surface reaction rate constant (ks) was examined, and it revealed that for both compounds ks continuously increases with activation energies of 20.1 kJ/mol for InP and 15.0 kJ/mol for InAs. The sticking probability of indium species, converted from ks, was in the range of 0.54-0.79. This is two or three times that of gallium species during GaAs MOVPE. For indium-related binary compounds, the ks of InP is always larger than that of InAs. This kinetic information suggests that group V elements have a significant effect on the ks of III-V binary compounds. These preliminary results show that indium species have quite different reactivities in phosphorus and arsenic sites, which could be fundamental for the kinetic analysis of ternary and quaternary compounds, such as InAsP and InGaAsP.

  12. Energy Bandgap and Edge States in an Epitaxially Grown Graphene/h-BN Heterostructure

    PubMed Central

    Hwang, Beomyong; Hwang, Jeongwoon; Yoon, Jong Keon; Lim, Sungjun; Kim, Sungmin; Lee, Minjun; Kwon, Jeong Hoon; Baek, Hongwoo; Sung, Dongchul; Kim, Gunn; Hong, Suklyun; Ihm, Jisoon; Stroscio, Joseph A.; Kuk, Young

    2016-01-01

    Securing a semiconducting bandgap is essential for applying graphene layers in switching devices. Theoretical studies have suggested a created bulk bandgap in a graphene layer by introducing an asymmetry between the A and B sub-lattice sites. A recent transport measurement demonstrated the presence of a bandgap in a graphene layer where the asymmetry was introduced by placing a graphene layer on a hexagonal boron nitride (h-BN) substrate. Similar bandgap has been observed in graphene layers on metal substrates by local probe measurements; however, this phenomenon has not been observed in graphene layers on a near-insulating substrate. Here, we present bulk bandgap-like features in a graphene layer epitaxially grown on an h-BN substrate using scanning tunneling spectroscopy. We observed edge states at zigzag edges, edge resonances at armchair edges, and bandgap-like features in the bulk. PMID:27503427

  13. Position-controlled III-V compound semiconductor nanowire solar cells by selective-area metal-organic vapor phase epitaxy.

    PubMed

    Fukui, Takashi; Yoshimura, Masatoshi; Nakai, Eiji; Tomioka, Katsuhiro

    2012-01-01

    We demonstrate position-controlled III-V semiconductor nanowires (NWs) by using selective-area metal-organic vapor phase epitaxy and their application to solar cells. Efficiency of 4.23% is achieved for InP core-shell NW solar cells. We form a 'flexible NW array' without a substrate, which has the advantage of saving natural resources over conventional thin film photovoltaic devices. Four junction NW solar cells with over 50% efficiency are proposed and discussed.

  14. Selective-area growth of GaN microrods on strain-induced templates by hydride vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    Lekhal, Kaddour; Bae, Si-Young; Lee, Ho-Jun; Mitsunari, Tadashi; Tamura, Akira; Deki, Manato; Honda, Yoshio; Amano, Hiroshi

    2016-05-01

    In this paper, we discuss the influence of parameters such as type of carrier gas and NH3/HCl flow ratio on the growth of vertical GaN microstructures by selective-area growth (SAG) hydride vapor phase epitaxy (HVPE). On various strain-induced templates such as GaN/sapphire, GaN/Si, and AlN/Si, regular arrays of Ga-polar GaN microrods were properly achieved by adjusting the growth parameters. The photoluminescence and micro-Raman measurements reveal not only the crystal quality of the GaN microrods but also strain distribution. These results will give insight into the control of the morphology of GaN microrods in terms of the strain induced from templates in SAG-HVPE. The precisely controlled arrays of GaN microrods can be used for next-generation light-emitting diodes (LEDs) by realizing InGaN/GaN multi-quantum wells (MQWs) with a radial structure.

  15. Largely enhanced energy density in epitaxial SmCo5/Fe/SmCo5 exchange spring trilayers

    NASA Astrophysics Data System (ADS)

    Sawatzki, S.; Heller, R.; Mickel, Ch.; Seifert, M.; Schultz, L.; Neu, V.

    2011-06-01

    In order to enhance the energy density (BH)max as a key property for permanent magnet applications, exchanged-coupled trilayers of SmCo5/Fe/SmCo5 with fixed SmCo5 layer thicknesses (25 nm) and varying soft magnetic Fe film thickness have been epitaxially grown by pulsed laser deposition on Cr buffered MgO(110) substrates. The effect of the increasing soft layer thickness on the reversal mechanism and improved remanence due to the higher Fe-volume fraction was investigated by vibrating sample magnetometry in external fields up to 9 T. As the energy density strongly depends on the volume of the samples, emphasis is put on multilayer architecture investigation and reliable thickness determination. Concerning the latter all applied analysis methods as energy dispersive x-ray analysis, Rutherford backscattering spectroscopy and transmission electron microscopy confirm energy densities with maximum values of 312 kJ/m3 (39 MGOe) for a soft layer thickness of 12.6 nm.

  16. Pattern dependency in selective epitaxy of B-doped SiGe layers for advanced metal oxide semiconductor field effect transistors

    NASA Astrophysics Data System (ADS)

    Hâllstedt, J.; Kolahdouz, M.; Ghandi, R.; Radamson, H. H.; Wise, R.

    2008-03-01

    This study presents investigations about the physical mechanisms, origin, and methods to control the pattern dependency in selective epitaxial growth of Si1-xGex (x=0.14-0.32) layers. It is shown with a comprehensive experimental study that the local Si coverage of individual chips on patterned wafers is the main parameter for the layer profile in the epitaxial growth. This was explained by the gas depletion of the growth species in the low velocity boundary layer over the wafer. The gas depletion radius around each oxide opening was in the centimeter range which is related to the boundary layer thickness. The results from these experiments were applied to grow Si0.75Ge0.25 layers with B concentration of 4×1020cm-3 selectively for elevated source and drains in fully depleted ultrathin body silicon on insulator p metal oxide semiconductor field effect transistor (p-MOSFET) devices. The epitaxy control was maintained over a wide range of device sizes by optimized process parameters in combination with a wafer pattern design consisting of dummy features causing a uniform gas depletion over the chips on the wafer.

  17. Energy dissipation channels affecting photoluminescence from resonantly excited Er3+ ions doped in epitaxial ZnO host films

    NASA Astrophysics Data System (ADS)

    Akazawa, Housei; Shinojima, Hiroyuki

    2015-04-01

    We identified prerequisite conditions to obtain intense photoluminescence at 1.54 μm from Er3+ ions doped in ZnO host crystals. The epitaxial ZnO:Er films were grown on sapphire C-plane substrates by sputtering, and Er3+ ions were resonantly excited at a wavelength of 532 nm between energy levels of 4I15/2 and 2H11/2. There is a threshold deposition temperature between 500 and 550 °C, above which epitaxial ZnO films become free of miss-oriented domains. In this case, Er3+ ions are outside ZnO crystallites, having the same c-axis lattice parameters as those of undoped ZnO crystals. The improved crystallinity was correlated with enhanced emissions peaking at 1538 nm. Further elevating the deposition temperature up to 650 °C generated cracks in ZnO crystals to relax the lattice mismatch strains, and the emission intensities from cracked regions were three times as large as those from smooth regions. These results can be consistently explained if we assume that emission-active Er3+ ions are those existing at grain boundaries and bonded to single-crystalline ZnO crystallites. In contrast, ZnO:Er films deposited on a ZnO buffer layer exhibited very weak emissions because of their degraded crystallinity when most Er3+ ions were accommodated into ZnO crystals. Optimizing the degree of oxidization of ZnO crystals is another important factor because reduced films suffer from non-radiative decay of excited states. The optimum Er content to obtain intense emissions was between 2 and 4 at. %. When 4 at. % was exceeded, the emission intensity was severely attenuated because of concentration quenching as well as the degradation in crystallinity. Precipitation of Er2O3 crystals was clearly observed at 22 at. % for films deposited above 650 °C. Minimizing the number of defects and impurities in ZnO crystals prevents energy dissipation, thus exclusively utilizing the excitation energy to emissions from Er3+ ions.

  18. Epitaxial growth of CZT(S,Se) on silicon

    DOEpatents

    Bojarczuk, Nestor A.; Gershon, Talia S.; Guha, Supratik; Shin, Byungha; Zhu, Yu

    2016-03-15

    Techniques for epitaxial growth of CZT(S,Se) materials on Si are provided. In one aspect, a method of forming an epitaxial kesterite material is provided which includes the steps of: selecting a Si substrate based on a crystallographic orientation of the Si substrate; forming an epitaxial oxide interlayer on the Si substrate to enhance wettability of the epitaxial kesterite material on the Si substrate, wherein the epitaxial oxide interlayer is formed from a material that is lattice-matched to Si; and forming the epitaxial kesterite material on a side of the epitaxial oxide interlayer opposite the Si substrate, wherein the epitaxial kesterite material includes Cu, Zn, Sn, and at least one of S and Se, and wherein a crystallographic orientation of the epitaxial kesterite material is based on the crystallographic orientation of the Si substrate. A method of forming an epitaxial kesterite-based photovoltaic device and an epitaxial kesterite-based device are also provided.

  19. Thermodynamic guiding principles in selective synthesis of strontium iridate Ruddlesden-Popper epitaxial Films

    DOE PAGES

    Nishio, Kazunori; Hwang, Harold Y.; Hikita, Yasuyuki

    2016-03-10

    We demonstrate the selective fabrication of Ruddlesden-Popper (RP) type SrIrO3, Sr3Ir2O7, and Sr2IrO4 epitaxialthin films from a single SrIrO3 target using pulsed laser deposition(PLD). We identified that the growth conditions stabilizing each phase directly map onto the phase diagram expected from thermodynamic equilibria. This approach allows precise cation stoichiometry control as evidenced by the stabilization of single phase Sr3Ir2O7 for the first time, overcoming the close thermodynamic stability between neighboring RP phases. Furthermore, despite the non-equilibrium nature of PLD, these results highlight the importance of thermodynamic guiding principles to strategically synthesize the targeted phase in complex oxide thin films.

  20. Azimuthal reflection high-energy electron diffraction study of MnAs growth on GaAs(001) by molecular beam epitaxy

    SciTech Connect

    Satapathy, Dillip K.; Jenichen, Bernd; Ploog, Klaus H.; Braun, Wolfgang

    2011-07-15

    Azimuthal reflection high-energy electron diffraction (ARHEED) and in situ grazing incidence synchrotron x-ray diffraction techniques are employed to investigate the growth, epitaxial orientation, and interfacial structure of MnAs layers grown on GaAs(001) by molecular beam epitaxy (MBE). We demonstrate the power and reliability of ARHEED scans as a routine tool in characterizing the formation of epitaxial films. The ARHEED scans clearly reveal the formation of the rectangular MnAs unit cell during growth on GaAs(001) for a MnAs layer thickness of 2.1 {+-} 0.2 monolayers with a tensile strain along the MnAs[1120] direction. A periodic coincidence site lattice, which is known to form along the MnAs [0001] direction to release the strain due to the huge lattice mismatch ({approx}30%) also produces periodic satellites of the diffraction spots in the ARHEED scan. The formation of different epitaxial orientations of MnAs during MBE growth can be directly observed using ARHEED scans. ARHEED is demonstrated to have a resolution similar to synchrotron x-ray diffraction with a double crystal monochromator, yielding full width at half maximum values of reflections as small as 0.005 reciprocal lattice units.

  1. Low temperature selective epitaxy of in situ doped silicon and applications in nanoscale CMOS

    NASA Astrophysics Data System (ADS)

    Ban, Ibrahim

    Continuous scaling of the Complementary Metal-Oxide-Semiconductor (CMOS) devices places stringent requirements on conventional doping technologies such as ion implantation. To keep the short channel effects under control while obtaining acceptable device characteristics, super-retrograde channel profiles and ultra-shallow source-drain junctions will be required in the sub 0.1 mum regime. In this study, in-situ doped selective silicon films grown at 800°C in an Ultra-High Vacuum Rapid Thermal Chemical Vapor Deposition (UHV-RTCVD) reactor were investigated to form highly non-uniform doping profiles for channel engineering as well as ultra-shallow p+-n junctions. In-situ boron incorporation in the low-to-heavy doping range (10 16 cm--3-1019 cm--3 ) was studied and modeled with respect to silicon growth rate, diborane (B2H6), chlorine (Cl2), and hydrogen partial pressures. Multi-layer ultra-thin (100 A-500 A) in-situ boron doped films were characterized. Effects of interface contamination (oxygen and carbon), which takes place during multi-layer growth with temperature switching, on impurity (boron, carbon, and oxygen) diffusion were investigated. Using this process, very short channel lightly-doped (Leff = 0.12 mum) and moderately-doped (Leff = 0.25 mum) NMOSFETs were fabricated with respectable device characteristics. The investigations were then extended to phosphorus incorporation using phosphine (PH3) as a source gas. In the second part of our work, a heavily boron-doped silicon deposition process was developed. Growth kinetics, surface morphology, selectivity, and out-diffusion behavior were studied. We demonstrated ultra-shallow (Xj ≤ 400 A) p+-n junctions by diffusion from these films with a high interface concentration (2 x 1020 cm--3 ) achieving the lowest sheet resistance values (Rs ≤ 50 O/Sq.) reported by any technique to date. We also demonstrated, for the first time, Zero-Depth p+-n junctions using as-deposited unannealed heavily-boron-doped silicon

  2. Renewable energy recovery through selected industrial wastes

    NASA Astrophysics Data System (ADS)

    Zhang, Pengchong

    Typically, industrial waste treatment costs a large amount of capital, and creates environmental concerns as well. A sound alternative for treating these industrial wastes is anaerobic digestion. This technique reduces environmental pollution, and recovers renewable energy from the organic fraction of those selected industrial wastes, mostly in the form of biogas (methane). By applying anaerobic technique, selected industrial wastes could be converted from cash negative materials into economic energy feed stocks. In this study, three kinds of industrial wastes (paper mill wastes, brown grease, and corn-ethanol thin stillage) were selected, their performance in the anaerobic digestion system was studied and their applicability was investigated as well. A pilot-scale system, including anaerobic section (homogenization, pre-digestion, and anaerobic digestion) and aerobic section (activated sludge) was applied to the selected waste streams. The investigation of selected waste streams was in a gradually progressive order. For paper mill effluents, since those effluents contain a large amount of recalcitrant or toxic compounds, the anaerobic-aerobic system was used to check its treatability, including organic removal efficiency, substrate utilization rate, and methane yield. The results showed the selected effluents were anaerobically treatable. For brown grease, as it is already well known as a treatable substrate, a high rate anaerobic digester were applied to check the economic effect of this substrate, including methane yield and substrate utilization rate. These data from pilot-scale experiment have the potential to be applied to full-scale plant. For thin stillage, anaerobic digestion system has been incorporated to the traditional ethanol making process as a gate-to-gate process. The performance of anaerobic digester was applied to the gate-to-gate life-cycle analysis to estimate the energy saving and industrial cost saving in a typical ethanol plant.

  3. Large-scale self-assembled epitaxial growth of highly-ordered three-dimensional micro/nano single-crystalline PbSe pyramid arrays by selective chemical bath deposition

    NASA Astrophysics Data System (ADS)

    Qiu, Jijun; Weng, Binbin; Li, Lin; Li, Xiaomin; Shi, Zhisheng

    2015-05-01

    Highly ordered three-dimensional micro- and nano- PbSe pyramid arrays were synthesized by using selective epitaxial self-assembled chemical bath deposition method. Each pyramid consists of a very sharp (111) tip with six smooth equivalent {100} facets. Every (100) facet forms an angle of about 54.7° with respect to the (111) facet. The structural features including pyramidal size and period could be precisely tailored by pre-patterned Au mask and etching time. Pyramids are self-assembled on the confined positions by the dual functions of one-dimensional and two-dimensional oriented attachment mechanisms along [110] directions on the (111) surface, following the Gibbs-Curie-Wulff minimum energy principle. This method could effectively create large, bottom-up 3D pyramidal surface patterns in a cost-effective and time-saving manner, which has potential applications in infrared photoconductors, solar cells and light emitting enhancement for display, etc.

  4. Copper Oxide Substrates and Epitaxial Copper Oxide/Zinc Oxide Thin Film Heterostructures for Solar Energy Conversion

    NASA Astrophysics Data System (ADS)

    Darvish, Davis Solomon

    Future fossil fuel scarcity and environmental degradation have demonstrated the need for renewable, low-carbon sources of energy to power an increasingly industrialized world. Solar energy with its infinite supply makes it an extraordinary resource that should not go unused. However with current materials, adoption is limited by cost and so a paradigm shift must occur to get everyone on the same page embracing solar technology. Cuprous Oxide (Cu2O) is a promising earth abundant material that can be a great alternative to traditional thin-film photovoltaic materials like CIGS, CdTe, etc. We have prepared Cu 2O bulk substrates by the thermal oxidation of copper foils as well Cu2O thin films deposited via plasma-assisted Molecular Beam Epitaxy. From preliminary Hall measurements it was determined that Cu2O would need to be doped extrinsically. This was further confirmed by simulations of ZnO/Cu2O heterojunctions. A cyclic interdependence between, defect concentration, minority carrier lifetime, film thickness, and carrier concentration manifests itself a primary reason for why efficiencies greater than 4% has yet to be realized. Our growth methodology for our thin-film heterostructures allow precise control of the number of defects that incorporate into our film during both equilibrium and nonequilibrium growth. We also report process flow/device design/fabrication techniques in order to create a device. A typical device without any optimizations exhibited open-circuit voltages Voc, values in excess 500mV; nearly 18% greater than previous solid state devices.

  5. Strain in epitaxial Bi2Se3 grown on GaN and graphene substrates: A reflection high-energy electron diffraction study

    NASA Astrophysics Data System (ADS)

    Li, Bin; Guo, Xin; Ho, Wingkin; Xie, Maohai

    2015-08-01

    Topological insulator (TI) has been one of the focus research themes in condensed matter physics in recent years. Due to the relatively large energy bandgap, Bi2Se3 has been identified as one of the most promising three-dimensional TIs with application potentials. Epitaxial Bi2Se3 by molecular-beam epitaxy has been reported by many groups using different substrates. A common feature is that Bi2Se3 grows readily along the c-axis direction irrespective of the type and condition of the substrate. Because of the weak van deer Waals interaction between Bi2Se3 quintuple layers, the grown films are reported to be strain-free, taking the lattice constant of the bulk crystal. At the very initial stage of Bi2Se3 deposition, however, strain may still exist depending on the substrate. Strain may bring some drastic effects to the properties of the TIs and so achieving strained TIs can be of great fundamental interests as well as practical relevance. In this work, we employ reflection high-energy electron diffraction to follow the lattice constant evolution of Bi2Se3 during initial stage depositions on GaN and graphene, two very different substrates. We reveal that epitaxial Bi2Se3 is tensile strained on GaN but strain-free on graphene. Strain relaxation on GaN is gradual.

  6. Study of growth rate and composition variations in metalorganic vapour phase selective area epitaxy at atmospheric pressure and application to the growth of strained layer DBR lasers

    NASA Astrophysics Data System (ADS)

    Silvestre, L.; Ougazzaden, A.; Delprat, D.; Ramdane, A.; Daguet, C.; Patriarche, G.

    1997-01-01

    In selective area epitaxy (SAE), a lateral variation of thickness accompanied by a variation of composition occurs because of the presence of dielectric masks on the substrate surface. To take advantage of these behaviours for monolithic integration of electronic devices, a good control of growth rate and composition is necessary. For this aim, different bulk materials InP, InGaAs and InGaAsP have been systematically investigated as a function of the geometry of dielectric masks specially designed for this work. All growths were performed by metalorganic vapour phase epitaxy (MOVPE) at atmospheric pressure. An estimation of growth rate enhancement and composition variation between the open regions in dielectric masks and the unmasked region has been established, allowing the choice of specific mask geometry for each application. Following this study, a strained multiple quantum well (MQW) structure for a distributed Bragg reflector (DBR) laser has been selectively grown. The standard buried ridge structure (BRS) processed presents good characteristics (8 mA threshold current) and we obtained a 7 nm tuning range with a ridge structure, which constitutes the best value reported with SAE.

  7. Selective-area growth of GaN nanowires on SiO{sub 2}-masked Si (111) substrates by molecular beam epitaxy

    SciTech Connect

    Kruse, J. E.; Doundoulakis, G.; Lymperakis, L.; Eftychis, S.; Georgakilas, A.; Adikimenakis, A.; Tsagaraki, K.; Androulidaki, M.; Konstantinidis, G.; Olziersky, A.; Dimitrakis, P.; Ioannou-Sougleridis, V.; Normand, P.; Koukoula, T.; Kehagias, Th.; Komninou, Ph.

    2016-06-14

    We analyze a method to selectively grow straight, vertical gallium nitride nanowires by plasma-assisted molecular beam epitaxy (MBE) at sites specified by a silicon oxide mask, which is thermally grown on silicon (111) substrates and patterned by electron-beam lithography and reactive-ion etching. The investigated method requires only one single molecular beam epitaxy MBE growth process, i.e., the SiO{sub 2} mask is formed on silicon instead of on a previously grown GaN or AlN buffer layer. We present a systematic and analytical study involving various mask patterns, characterization by scanning electron microscopy, transmission electron microscopy, and photoluminescence spectroscopy, as well as numerical simulations, to evaluate how the dimensions (window diameter and spacing) of the mask affect the distribution of the nanowires, their morphology, and alignment, as well as their photonic properties. Capabilities and limitations for this method of selective-area growth of nanowires have been identified. A window diameter less than 50 nm and a window spacing larger than 500 nm can provide single nanowire nucleation in nearly all mask windows. The results are consistent with a Ga diffusion length on the silicon dioxide surface in the order of approximately 1 μm.

  8. Selective area growth of Bernal bilayer epitaxial graphene on 4H-SiC (0001) substrate by electron-beam irradiation

    NASA Astrophysics Data System (ADS)

    Dharmaraj, P.; Jeganathan, K.; Parthiban, S.; Kwon, J. Y.; Gautam, S.; Chae, K. H.; Asokan, K.

    2014-11-01

    We report selective area growth of large area homogeneous Bernal stacked bilayer epitaxial graphene (BLEG) on 4H-SiC (0001) substrate by electron-beam irradiation. Sublimation of Si occurs by energetic electron irradiations on SiC surface via breaking of Si-C bonds in the localized region, which allows the selective growth of graphene. Raman measurements ensure the formation of homogeneous BLEG with weak compressive strain of -0.08%. The carrier mobility of large area BLEG is ˜5100 cm2 V-1 s-1 with a sheet carrier density of 2.2 × 1013 cm-2. Current-voltage measurements reveal that BLEG on 4H-SiC forms a Schottky junction with an operation at mA level. Our study reveals that the barrier height at the Schottky junction is low (˜0.58 eV) due to the Fermi-level pinning above the Dirac point.

  9. Modeling of {311} facets using a lattice kinetic Monte Carlo three-dimensional model for selective epitaxial growth of silicon

    NASA Astrophysics Data System (ADS)

    Martin-Bragado, Ignacio; Moroz, Victor

    2011-04-01

    Using lattice kinetic Monte Carlo, we provide a quantitative physically based atomistic model for the selective grown of Si-based materials, and explain {311} facet formation while remaining computationally efficient. Descriptions of the local atomistic configurations critical for the developing of {100}, {110}, {111}, and {311} facets are given. The model also introduces (a) three different microscopic growth rates for local {100} planes, needed to properly simulate the formation of perfect {100} terraces in miscut substrates and (b) a break-up energy to account for bonding during {311} facet formation. The model has been verified against experimental results.

  10. The influence of selective chemical doping on clean, low-carrier density SiC epitaxial graphene

    NASA Astrophysics Data System (ADS)

    Chuang, Chiashain; Yang, Yanfei; Huang, Lung-I.; Liang, Chi-Te; Elmquist, Randolph E.; National Institute of of Standards; Technology Collaboration; National Taiwan University, Department of Physics Collaboration

    2015-03-01

    The charge-transfer effect of ambient air on magneto-transport in polymer-free SiC graphene was investigated. Interestingly, adsorption of atmospheric gas molecules on clean epitaxial graphene can reduce the carrier density to near charge neutrality, allowing observation of highly precise v = 2 quantum Hall plateaus. The atmospheric adsorbates were reproducibly removed and pure gases (N2, O2, CO2, H2O) were used to form new individual adsorbates on SiC graphene. Our experimental results (τt/τq ~ 2) support the theoretical predictions for the ratio of transport relaxation time τt to quantum lifetime τq in clean graphene. The analysis of Shubnikov-de Haas oscillations at intermediate doping levels indicates that the carrier scattering is reduced by water and oxygen so as to increase both the classical and quantum mobility. This study points to the key dopant gases in ambient air and also paves the way towards extremely precise quantized Hall resistance standards in epitaxial graphene systems with carrier density tuned by exposure to highly pure gases and vacuum annealing treatment. National Institute of Standard and Technology.

  11. Financial arrangement selection for energy management projects

    NASA Astrophysics Data System (ADS)

    Woodroof, Eric Aubrey

    Scope and method of study. The purpose of this study was to develop a model (E-FUND) to help facility managers select financial arrangements for energy management projects (EMPs). The model was developed with the help of a panel of expert financiers. The panel also helped develop a list of key objectives critical to the decision process. The E-FUND model was tested by a population of facility managers in four case studies. Findings and conclusions. The results may indicate that having a high economic benefit (from an EMP) is not overwhelmingly important, when compared to other qualitative objectives. The results may also indicate that the true lease and performance contract may be the most applicable financial arrangements for EMPs.

  12. Epitaxial silicon growth for solar cells

    NASA Technical Reports Server (NTRS)

    Daiello, R. V.; Robinson, P. H.; Richman, D.

    1979-01-01

    The epitaxial procedures, solar cell fabrication, and evaluation techniques are described. The development of baseline epitaxial solar cell structures grown on high quality conventional silicon substrates is discussed. Diagnostic layers and solar cells grown on four potentially low cost silicon substrates are considered. The crystallographic properties of such layers and the performance of epitaxially grown solar cells fabricated on these materials are described. An advanced epitaxial reactor, the rotary disc, is described along with the results of growing solar cell structures of the baseline type on low cost substrates. The add on cost for the epitaxial process is assessed and the economic advantages of the epitaxial process as they relate to silicon substrate selection are examined.

  13. Strain in epitaxial Bi{sub 2}Se{sub 3} grown on GaN and graphene substrates: A reflection high-energy electron diffraction study

    SciTech Connect

    Li, Bin; Guo, Xin; Ho, Wingkin; Xie, Maohai

    2015-08-24

    Topological insulator (TI) has been one of the focus research themes in condensed matter physics in recent years. Due to the relatively large energy bandgap, Bi{sub 2}Se{sub 3} has been identified as one of the most promising three-dimensional TIs with application potentials. Epitaxial Bi{sub 2}Se{sub 3} by molecular-beam epitaxy has been reported by many groups using different substrates. A common feature is that Bi{sub 2}Se{sub 3} grows readily along the c-axis direction irrespective of the type and condition of the substrate. Because of the weak van der Waals interaction between Bi{sub 2}Se{sub 3} quintuple layers, the grown films are reported to be strain-free, taking the lattice constant of the bulk crystal. At the very initial stage of Bi{sub 2}Se{sub 3} deposition, however, strain may still exist depending on the substrate. Strain may bring some drastic effects to the properties of the TIs and so achieving strained TIs can be of great fundamental interests as well as practical relevance. In this work, we employ reflection high-energy electron diffraction to follow the lattice constant evolution of Bi{sub 2}Se{sub 3} during initial stage depositions on GaN and graphene, two very different substrates. We reveal that epitaxial Bi{sub 2}Se{sub 3} is tensile strained on GaN but strain-free on graphene. Strain relaxation on GaN is gradual.

  14. Vacancies in epitaxial graphene

    SciTech Connect

    Davydov, S. Yu.

    2015-08-15

    The coherent-potential method is used to consider the problem of the influence of a finite concentration of randomly arranged vacancies on the density of states of epitaxial graphene. To describe the density of states of the substrate, simple models (the Anderson model, Haldane-Anderson model, and parabolic model) are used. The electronic spectrum of free single-sheet graphene is considered in the low-energy approximation. Charge transfer in the graphene-substrate system is discussed. It is shown that, in all cases, the density of states of epitaxial graphene decreases proportionally to the vacancy concentration. At the same time, the average charge transferred from graphene to the substrate increases.

  15. Energy use in selected metal casting facilities - 2003

    SciTech Connect

    Eppich, Robert E.

    2004-05-01

    This report represents an energy benchmark for various metal casting processes. It describes process flows and energy use by fuel type and processes for selected casting operations. It also provides recommendations for improving energy efficiency in casting.

  16. Enhanced light extraction of InGaN LEDs with photonic crystals grown on p-GaN using selective-area epitaxy and nanospherical-lens photolithography

    NASA Astrophysics Data System (ADS)

    Linghui, Zhao; Tongbo, Wei; Junxi, Wang; Qingfeng, Yan; Yiping, Zeng; Jinmin, Li

    2013-10-01

    We report a new method for the fabrication of two-dimensional photonic crystal (PhC) hole arrays to improve the light extraction of GaN-based light-emitting diodes (LEDs). The PhC structures were realized using nanospherical-lens photolithography and the selective-area epitaxy method, which ensured the electrical properties of the LEDs through leaving the p-GaN damage-free. At a current of 350 mA, the light output power of LEDs with PhC hole arrays of 450 nm and 600 nm in diameter with the same lattice period of 900 nm were enhanced by 49.3% and 72.2%, respectively, compared to LEDs without a PhC. Furthermore, the LEDs with PhC hole structures showed an obviously smaller divergent angle compared with conventional LEDs, which is consistent with the results of finite-difference time-domain simulation.

  17. Assessment of Selected Energy Efficiency Policies

    EIA Publications

    2005-01-01

    This report responds to a request from Senator Byron L. Dorgan, asking the Energy Information Administration (EIA) to undertake a quantitative analysis of a variety of energy efficiency policies using assumptions provided by the Alliance to Save Energy (ASE).

  18. Role of strain relaxation in exciton resonance energies of ZnO epitaxial layers grown on SiC substrates

    NASA Astrophysics Data System (ADS)

    Almamun Ashrafi, Abm

    2004-03-01

    The wide bandgap ZnO semiconductor is currently the subject of interest for the study of physics as well as investigations in response to the industrial demand for applications in optoelectronics devices. The most exciting physical properties of ZnO are the largest exciton binding energy of 60 meV and this can be tuned up to 120 meV by controlling the ZnO active layers1. Towards these goals, a great deal of efforts has been made on ZnO layers grown mostly on Al2O3 substrates. It is noted that the lattice mismatch in ZnO/Al2O3 is 18structural defects, and higher residual carrier concentration. To overcome these basic but unavoidable problems for crystalline quality, nearly-matched SiC substrate may play a role including reproducible p-type conductivity in ZnO layers2. Considering the ZnO lattice constant, the estimated lattice mismatch between the ZnO and SiC is to be 5may explore the ZnO epitaxy with the superior crystalline as well as optical properties towards the study of quantum physics in nanoscale level where strain governs the local atomic mechanisms in principle. Recently, we have reported the superior ZnO crystalline quality grown on SiC substrates compared to the ZnO/Al2O3 samples by MOCVD3. In progress to these results, strain relaxation effects in exciton resonance energies of ZnO layers have been addressed in this letter. The surface morphology of ZnO layers grown on SiC exhibited hexagons geometry for the VI/II falux raio of 4 by reflecting the +c ZnO surface. From these layers, therefore, free exciton (FX) emission was appeared with A and B bands to the corresponding energies of 3.377 and 3.390 eV4. With the increase of temperature, however, the FXs emission showed the quenching of excitons energy as well as intensity which may be a subject of overlapping the A and donor-bound (D0X) excitons4. The deduced activation energies of A and D0X exciton emissions suggested a consistency with an inclusion of exciton-defect binding energy in optical bands. The

  19. Low-thermal surface preparation, HCl etch and Si/SiGe selective epitaxy on (1 1 0) silicon surfaces

    NASA Astrophysics Data System (ADS)

    Destefanis, V.; Hartmann, J. M.; Hopstaken, M.; Delaye, V.; Bensahel, D.

    2008-10-01

    We have first investigated the influence of the in situ H2 bake temperature (between 750 °C and 850 °C) on (1 0 0) and (1 1 0) fullsheet surface preparations (after 'HF-last' wet cleaning). A strong increase of the (1 1 0) surface roughness occurred when baking between 750 and 775 °C, with high C and O contamination peaks at the Si substrate/Si overlayer interface. A high H2 bake temperature (>=800 °C) is thus mandatory for both (1 0 0) and (1 1 0) Si surfaces. We have also studied the 750 °C-950 °C, high HCl partial pressure etch of blanket Si wafers. HCl etch rates are roughly four times higher on (1 1 0) than on (1 0 0). Etch rate activation energies are however quite close to each other (57 kcal mol-1 on (1 0 0) ⇔ 59 kcal mol-1 on (1 0 0)), suggesting similar etch-limiting mechanisms. We have then investigated the low-temperature growth of high Ge content (10-37%) SiGe layers on blanket Si wafers with dichlorosilane + germane chemistry (selective versus SiO2 on patterned wafers). The SiGe growth rate on (1 1 0) bows downwards from linearity and then saturates when increasing the germane mass flow. In contrast, it almost linearly increases on (1 0 0) surfaces, reaching values more than three times higher than on (1 1 0). A parabolic relationship between experimental Ge concentrations and the F(GeH4)/F(SiH2Cl2) mass-flow ratio has been evidenced on (1 0 0). In contrast, a linear relationship links the (1 1 0) Ge concentration to the F(GeH4)/F(SiH2Cl2) mass-flow ratio. Finally, 63 and 65 kcal mol-1 activation energies are associated with the fullsheet Si growth rate increase with the inverse absolute temperature on (1 0 0) and (1 1 0) (dichlorosilane chemistry). The GR(1 1 0)/GR(1 0 0) Si growth rate ratio, ≈0.74, is close to the dangling bond surface density (DBSD) ratio (DBSD(1 1 0)/DBSD(1 0 0) ≈ 0.71). Such growth rate discrepancies are thus justified by these DBSD differences. Results obtained on fullsheet wafers have been used to selectively grow

  20. Selective epitaxial growth of zinc blende-derivative on wurtzite-derivative: the case of polytypic Cu2CdSn(S(1-x)Se(x))4 nanocrystals.

    PubMed

    Wu, Liang; Fan, Feng-Jia; Gong, Ming; Ge, Jin; Yu, Shu-Hong

    2014-03-21

    Polytypic nanocrystals with zinc blende (ZB) cores and wurtzite (WZ) arms, such as tetrapod and octopod nanocrystals, have been widely reported. However, polytypic nanocrystals with WZ cores and ZB arms or ends have been rarely reported. Here, we report a facile, solution-based approach to the synthesis of polytypic Cu2CdSn(S1-xSex)4 (CCTSSe) nanocrystals with ZB-derivative selectively engineered on (000±2)WZ facets of WZ-derived cores. Accordingly, two typical morphologies, i.e., bullet-like nanocrystals with a WZ-derivative core and one ZB-derivative end, and rugby ball-like nanocrystals with a WZ-derivative core and two ZB-derivative ends, can be selectively prepared. The epitaxial growth mechanism is confirmed by the time-dependent experiments. The ratio of rugby ball-like and bullet-like polytypic CCTSSe nanocrystals can be tuned through changing the amount of Cd precursor to adjust the reactivity difference between (0002)WZ and (000-2)WZ facets. These unique polytypic CCTSSe nanocrystals may find applications in energetic semiconducting materials for energy conversion in the future.

  1. Selective area epitaxy of ultra-high density InGaN quantum dots by diblock copolymer lithography

    PubMed Central

    2011-01-01

    Highly uniform InGaN-based quantum dots (QDs) grown on a nanopatterned dielectric layer defined by self-assembled diblock copolymer were performed by metal-organic chemical vapor deposition. The cylindrical-shaped nanopatterns were created on SiNx layers deposited on a GaN template, which provided the nanopatterning for the epitaxy of ultra-high density QD with uniform size and distribution. Scanning electron microscopy and atomic force microscopy measurements were conducted to investigate the QDs morphology. The InGaN/GaN QDs with density up to 8 × 1010 cm-2 are realized, which represents ultra-high dot density for highly uniform and well-controlled, nitride-based QDs, with QD diameter of approximately 22-25 nm. The photoluminescence (PL) studies indicated the importance of NH3 annealing and GaN spacer layer growth for improving the PL intensity of the SiNx-treated GaN surface, to achieve high optical-quality QDs applicable for photonics devices. PMID:21711862

  2. Antimony segregation in Ge and formation of n-type selectively doped Ge films in molecular beam epitaxy

    SciTech Connect

    Yurasov, D. V. Antonov, A. V.; Drozdov, M. N.; Schmagin, V. B.; Novikov, A. V.; Spirin, K. E.

    2015-10-14

    Antimony segregation in Ge(001) films grown by molecular beam epitaxy was studied. A quantitative dependence of the Sb segregation ratio in Ge on growth temperature was revealed experimentally and modeled theoretically taking into account both the terrace-mediated and step-edge-mediated segregation mechanisms. A nearly 5-orders-of-magnitude increase in the Sb segregation ratio in a relatively small temperature range of 180–350 °C was obtained, which allowed to form Ge:Sb doped layers with abrupt boundaries and high crystalline quality using the temperature switching method that was proposed earlier for Si-based structures. This technique was employed for fabrication of different kinds of n-type Ge structures which can be useful for practical applications like heavily doped n{sup +}-Ge films or δ-doped layers. Estimation of the doping profiles sharpness yielded the values of 2–5 nm per decade for the concentration gradient at the leading edge and 2–3 nm for the full-width-half-maximum of the Ge:Sb δ-layers. Electrical characterization of grown Ge:Sb structures revealed nearly full electrical activation of Sb atoms and the two-dimensional nature of charge carrier transport in δ-layers.

  3. Tailoring the optical property by a three-dimensional epitaxial heterostructure: a case of ZnO/SnO2.

    PubMed

    Kuang, Qin; Jiang, Zhi-Yuan; Xie, Zhao-Xiong; Lin, Shui-Chao; Lin, Zhi-Wei; Xie, Su-Yuan; Huang, Rong-Bin; Zheng, Lan-Sun

    2005-08-24

    Epitaxial growth, as a best strategy to attain a heterostructure with a well-defined and clean interface, usually takes place on a planar substrate. In this paper, using a ZnO/SnO2 core-shell heterostructure as an example, we demonstrate the possibility of establishing a three-dimensional epitaxial interface between two materials with different crystal systems for the first time and show possible tailoring optical properties by building the heteroepitaxial crystal interface. The characterization results of element mapping, high-resolution transmission electron microscopy, and selected area electric diffraction reveal that the as-prepared ZnO/SnO2 heterostructure has a tetrapod-like ZnO core and a SnO2 shell with 15-30 nm, and their special epitaxial relation is (010)SnO2//(010)ZnO and [100]SnO2//[0001]ZnO. Such three-dimensional epitaxy between the ZnO core and SnO2 shell is quite different from the usual planar epitaxy or three-dimensional epitaxy between materials having the same crystal structure. A rational model of such complicated epitaxy has been proposed through investigating the certain structural comparability between the wurtzite ZnO and rutile SnO2 crystals. The as-prepared T-ZnO/SnO2 epitaxial heterostructure exhibits unique luminescence properties in contrast with individual tetrapod ZnO and SnO2 nanostructures, in which the epitaxial interface induces new luminescence properties. This result may inspire great interest in exploring other complicated epitaxy systems and their potential applications in laser, gas sensor, solar energy conversion, photo catalysis, and nanodevices in the future.

  4. Research and Energy Efficiency: Selected Success Stories

    DOE R&D Accomplishments Database

    Garland, P. W.; Garland, R. W.

    1997-06-26

    Energy use and energy technology play critical roles in the U.S. economy and modern society. The Department of Energy (DOE) conducts civilian energy research and development (R&D) programs for the purpose of identifying promising technologies that promote energy security, energy efficiency, and renewable energy use. DOE-sponsored research ranges from basic investigation of phenomena all the way through development of applied technology in partnership with industry. DOE`s research programs are conducted in support of national strategic energy objectives, however austere financial times have dictated that R&D programs be measured in terms of cost vs. benefit. In some cases it is difficult to measure the return on investment for the basic "curiosity-driven" research, however many applied technology development programs have resulted in measurable commercial successes. The DOE has published summaries of their most successful applied technology energy R&D programs. In this paper, we will discuss five examples from the Building Technologies area of the DOE Energy Efficiency program. Each story will describe the technology, discuss the level of federal funding, and discuss the returns in terms of energy savings, cost savings, or national economic impacts.

  5. Research and energy efficiency: Selected success stories

    SciTech Connect

    Garland, P.W.; Garland, R.W.

    1997-06-26

    Energy use and energy technology play critical roles in the U.S. economy and modern society. The Department of Energy (DOE) conducts civilian energy research and development (R&D) programs for the purpose of identifying promising technologies that promote energy security, energy efficiency, and renewable energy use. DOE-sponsored research ranges from basic investigation of phenomena all the way through development of applied technology in partnership with industry. DOE`s research programs are conducted in support of national strategic energy objectives, however austere financial times have dictated that R&D programs be measured in terms of cost vs. benefit. In some cases it is difficult to measure the return on investment for the basic {open_quotes}curiosity-driven{close_quotes} research, however many applied technology development programs have resulted in measurable commercial successes. The DOE has published summaries of their most successful applied technology energy R&D programs. In this paper, we will discuss five examples from the Building Technologies area of the DOE Energy Efficiency program. Each story will describe the technology, discuss the level of federal funding, and discuss the returns in terms of energy savings, cost savings, or national economic impacts.

  6. Cassava as an energy source: a selected bibliography

    SciTech Connect

    Sherman, C.

    1980-01-01

    This selected bibliography includes 250 articles on cassava as a potential energy source. Factors included are things which influence cassava growth; such as weeding, fertilizer, diseases and genetic selection, as well as the conversion of cassava to ethanol. (DP)

  7. Energy-Efficient Electric Motor Selection Handbook

    SciTech Connect

    McCoy, Gilbert A.; Litman, Todd; Douglass, John G.

    1990-10-01

    Substantial reductions in energy and operational costs can be achieved through the use of energy-efficient electric motors. A handbook was compiled to help industry identify opportunities for cost-effective application of these motors. It covers the economic and operational factors to be considered when motor purchase decisions are being made. Its audience includes plant managers, plant engineers, and others interested in energy management or preventative maintenance programs.

  8. Selective Plasmon-Exciton Coupling in Nonradiative Energy Transfer: Donor-Selective versus Acceptor-Selective

    NASA Astrophysics Data System (ADS)

    Hernandez-Martinez, Pedro Ludwig; Ozel, Tuncay; Mutlugun, Evren; Akin, Onur; Nizamoglu, Sedat; Ozel, Ilkem Ozge; Zhang, Qing; Xiong, Qihua; Demir, Hilmi Volkan

    2014-03-01

    We report selectively plasmon-mediated nonradiative energy transfer between quantum dot (QD) emitters interacting with each other via Förster-type resonance energy transfer (FRET) under controlled plasmon coupling either to only the donor QDs or to only the acceptor QDs. The comparative results of theoretical modelling of the donor- and acceptor selective plasmon-exciton coupling of nonradiative energy transfer is presented. Here, we demonstrate the ability to enable/disable the coupled plasmon-exciton formation distinctly at the donor site or at the acceptor site of our choice. In the case of donor-selective plasmon-exciton coupling, we observed a substantial shortening in the donor QD lifetime from 1.33 to 0.29 ns as a result of plasmon-coupling to the donors and the FRET-assisted exciton transfer from the donors to the acceptors. This enhances the acceptor emission by a factor of 1.93. In the complementary case, we observed a 2.70-fold emission enhancement in the acceptor QDs as a result of the combined effects of the acceptor plasmon coupling and the FRET-assisted exciton feeding. Our theoretical results are in good agreement with the systematic experimental characterization. Bilkent University.

  9. A benchmark of co-flow and cyclic deposition/etch approaches for the selective epitaxial growth of tensile-strained Si:P

    NASA Astrophysics Data System (ADS)

    Hartmann, J. M.; Veillerot, M.; Prévitali, B.

    2017-10-01

    We have compared co-flow and cyclic deposition/etch processes for the selective epitaxial growth of Si:P layers. High growth rates, relatively low resistivities and significant amounts of tensile strain (up to 10 nm min-1, 0.55 mOhm cm and a strain equivalent to 1.06% of substitutional C in Si:C layers) were obtained at 700 °C, 760 Torr with a co-flow approach and a SiH2Cl2 + PH3 + HCl chemistry. This approach was successfully used to thicken the sources and drains regions of n-type fin-shaped Field Effect Transistors. Meanwhile, the (Si2H6 + PH3/HCl + GeH4) CDE process evaluated yielded at 600 °C, 80 Torr even lower resistivities (0.4 mOhm cm, typically), at the cost however of the tensile strain which was lost due to (i) the incorporation of Ge atoms (1.5%, typically) into the lattice during the selective etch steps and (ii) a reduction by a factor of two of the P atomic concentration in CDE layers compared to that in layers grown in a single step (5 × 1020 cm-3 compared to 1021 cm-3).

  10. Experimental determination of electron-hole pair creation energy in 4H-SiC epitaxial layer: An absolute calibration approach

    SciTech Connect

    Chaudhuri, Sandeep K.; Zavalla, Kelvin J.; Mandal, Krishna C.

    2013-01-21

    Electron-hole pair creation energy ({epsilon}) has been determined from alpha spectroscopy using 4H-SiC epitaxial layer Schottky detectors and a pulser calibration technique. We report an experimentally obtained {epsilon} value of 7.28 eV in 4H-SiC. The obtained {epsilon} value and theoretical models were used to calculate a Fano factor of 0.128 for 5.48 MeV alpha particles. The contributions of different factors to the ultimate alpha peak broadening in pulse-height spectra were determined using the calculated {epsilon} value and Monte-Carlo simulations. The determined {epsilon} value was verified using a drift-diffusion model of variation of charge collection efficiency with applied bias.

  11. Thickness measurement of semiconductor thin films by energy dispersive X-ray fluorescence benchtop instrumentation: Application to GaN epilayers grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Queralt, I.; Ibañez, J.; Marguí, E.; Pujol, J.

    2010-07-01

    The importance of thin films in modern high technology products, such as semiconductors, requires fast and non-destructive analysis. A methodology to determine the thickness of single layers with benchtop energy dispersive X-ray fluorescence (EDXRF) instrumentation is described and tested following analytical validation criteria. The experimental work was carried out on gallium nitride thin films epitaxially grown on sapphire substrate. The results of samples with layers in the range from 400 to 1000 nm exhibit a good correlation with the layer thickness determined by optical reflectance. Spectral data obtained using thin layered samples indicate the possibility to precisely evaluate layer thickness from 5 nm, with a low relative standard deviation (RSD < 2%) of the results. In view of the limits of optical reflectance for very thin layer determination, EDXRF analysis offers the potential for the thickness determination of such kind of samples.

  12. Epitaxial Growth of Mo Single Crystal on Sapphire by H2 Reduction of MoO3 and Characterization by Reflection High-Energy Electron Diffraction

    NASA Astrophysics Data System (ADS)

    Igarashi, Osamu

    1995-05-01

    Mo depositions on sapphire ( Al2O3) were effected by H2 reduction of MoO3, and the crystallinity of the films was characterized by reflection high-energy electron diffraction (RHEED). In the case of growth on the (1\\=102) Al2O3 substrates, single-crystal epitaxial growth of (001) Mo was realized. On (0001) Al2O3, single-crystal Mo was not obtained; Mo deposited on (0001) Al2O3 was composed of three sets of (110)-oriented crystallites. To obtain Debye-Scherrer ring-free Mo films whose RHEED patterns did not include arcs, growth temperatures of 890 and 920° C were required in growths on (1\\=102) and (0001) Al2O3 substrates, respectively.

  13. CoSi2 growth on Si(001) by reactive deposition epitaxy: Effects of high-flux, low-energy ion irradiation

    NASA Astrophysics Data System (ADS)

    Lim, C. W.; Greene, J. E.; Petrov, I.

    2006-07-01

    CoSi2 layers, <40nm thick, were grown on Si(001) by reactive deposition epitaxy (RDE) in which Co was deposited at 700°C by magnetically unbalanced ultrahigh vacuum magnetron sputtering. X-ray diffraction pole figures and transmission electron microscopy (TEM) reveal that the layers, which exhibit a cube-on-cube epitaxial relationship with the substrate, (001)CoSi2‖(001)Si and [100]CoSi2‖[100]Si, contain fourfold symmetric {111} twinned domains oriented such that {221}CoSi2‖(001)Si and ⟨110⟩CoSi2‖[110]Si. We demonstrate that high-flux low-energy (EAr+=9.6eV) Ar+ ion irradiation during deposition dramatically increases the area fraction fu of untwinned regions from 0.17 in films grown under standard magnetically balanced conditions in which the ratio JAr+/JCo of the incident Ar+ to Co fluxes is 1.4 to 0.72 with JAr+/JCo=13.3. TEM analyses show that the early stages of RDE CoSi2(001) film growth proceed via the Volmer-Weber mode with independent nucleation of both untwinned and twinned islands. Increasing JAr+/JCo results in larger values of both the number density and area of untwinned with respect to twinned islands. The intense Ar+ ion bombardment creates additional low-energy adsorption sites that favor the nucleation of untwinned islands while collisionally enhancing Co surface mobilities which, in turn, increases the probability of itinerant Co adatoms reaching these sites.

  14. Morphology and Electrical Characterization of Reduced Epitaxial Graphene Oxide

    NASA Astrophysics Data System (ADS)

    Hu, Yike; Wu, Xiaosong; Sprinkle, Michael; Madiomanana, Nerasoa; Ruan, Ming; Berger, Claire; de Heer, Walter

    2009-03-01

    We present results for on-chip oxidation of epitaxial graphene and sequential reduction of the insulating graphene oxide layers. In our previous work , we have used the Hummer's method to oxidize epitaxial graphene and used electron beam exposure and heat treatment to reduce the epitaxial graphene oxide (EGO) band gap by changing the degree of oxidation. Here we further explore various oxidation and reduction methods on epitaxial graphene. EGO is characterized by atomic force microscopy, low-energy electron diffraction, ellipsometry, and Raman Spectrometry. Mobility measurements of patterned structures are presented where epitaxial graphene layers pads are seamlessly connected to EGO ribbons.

  15. Enhanced energy density with a wide thermal stability in epitaxial Pb0.92La0.08Zr0.52Ti0.48O3 thin films

    NASA Astrophysics Data System (ADS)

    Hu, Guangliang; Ma, Chunrui; Wei, Wei; Sun, Zixiong; Lu, Lu; Mi, Shao-Bo; Liu, Ming; Ma, Beihai; Wu, Judy; Jia, Chun-lin

    2016-11-01

    High-quality epitaxial Pb0.92La0.08Zr0.52Ti0.48O3 (PLZT) films of thickness of ˜880 nm were fabricated using pulsed laser deposition on (001) Nb doped SrTiO3 (Nb:STO) substrates. Besides a confirmation of the epitaxial relationship [100]PLZT//[100]Nb:STO and (001)PLZT//(001)Nb:STO using X-ray diffraction, a transmission electron microscopy study has revealed a columnar structure across the film thickness. The recoverable energy density (Wrec) of the epitaxial PLZT thin film capacitors increases linearly with the applied electric field and the best value of ˜31 J/cm3 observed at 2.27 MV/cm is considerably higher by 41% than that of the polycrystalline PLZT film of a comparable thickness. In addition to the high Wrec value, an excellent thermal stability as illustrated in a negligible temperature dependence of the Wrec in the temperature range from room temperature to 180 °C is achieved. The enhanced Wrec and the thermal stability are attributed to the reduced defects and grain boundaries in epitaxial PLZT thin films, making them promising for energy storage applications that require both high energy density, power density, and wide operation temperatures.

  16. Correlating low-energy electron microscopy and micro-Raman imaging of epitaxial graphene on SiC

    NASA Astrophysics Data System (ADS)

    Cheng, Guangjun; Calizo, Irene; Meade, Patrick; He, Guowei; Real, M. A.; Elmquist, R. E.; Feenstra, R. M.; Hight Walker, A. R.

    2013-03-01

    Several techniques exist for determining the number of graphene layers grown on SiC such as low-energy electron microscopy (LEEM) and Raman spectroscopy. The method which is arguably the most definitive for SiC-grown graphene isLEEM. Low-energy (0 - 10 eV) electrons interfere with the graphene layers, yielding minima in the electron reflectivity vs. energy curve that can be used to determine the layer number.1 LEEM also provides the means of collecting selected-area diffraction on ?m-size surface regions (micro-LEED), giving access to further useful structural information. While Raman spectroscopy is also commonly used to determine graphene layer number on SiC substrates; such measurements have no definitive calibration for large-area graphene on SiC, unlike the case of exfoliated graphene on SiO2. In this talk, results of correlated LEEM/micro-Raman imaging of large-area, mono and multilayer graphene samples are presented. These initial findings show that LEEM can show the contrast between terrace regions and step edges at particular areas of monolayer-graphene surfaces. Micro-Raman imaging of these same locations show Raman shifts in the G' (2D) band. The influence of heterogeneities on electrical behavior of graphene will be discussed. Comparative studies of multilayer graphene are in progress, and will also be reported. 1. H. Hibino, et al., Phys. Rev. B 77, 075413 (2008). 2. L. I. Johansson, et al., Phys. Rev. B 84, 125405 (2011).

  17. Wind Energy Developments: Incentives In Selected Countries

    EIA Publications

    1999-01-01

    This paper discusses developments in wind energy for the countries with significant wind capacity. After a brief overview of world capacity, it examines development trends, beginning with the United States - the number one country in wind electric generation capacity until 1997.

  18. Growth kinetics in position-controlled and catalyst-free InAs nanowire arrays on Si(111) grown by selective area molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Hertenberger, S.; Rudolph, D.; Bichler, M.; Finley, J. J.; Abstreiter, G.; Koblmüller, G.

    2010-12-01

    We investigated the interwire distance dependence on the growth kinetics of vertical, high-yield InAs nanowire arrays on Si(111) grown by catalyst-free selective area molecular beam epitaxy (MBE). Utilizing lithographically defined SiO2 nanomasks on Si(111) with regular hole patterns, catalyst-free and site-selective growth of vertically (111)-oriented InAs nanowires was achieved with very high yields of ˜90 percent. Interestingly, the yield of vertically ordered nanowires was independent of the interwire distance and the initial growth stages. Significant size variation in the nanowires was found to depend critically on the interwire distance and growth time. Two growth regimes were identified—(i) a competitive growth regime with shorter and thinner nanowires for narrow interwire distances and (ii) a diffusion-limited growth regime for wider distances, providing good estimates for the surface diffusion lengths. Surprisingly, despite these size-dependent effects the nanowire geometries remained unaltered with uniform, almost nontapered morphologies even over large variation in nanowire density (˜mid-106-109 cm-2 range). X-ray diffraction further confirmed the vertical (111) directionality with low crystal tilt by rocking curve widths (ω scans) as low as ˜0.6°. These findings demonstrate the capability to precisely tailor the position and size of well-oriented III-V semiconductor nanowires through noncatalytic MBE selective area growth and provide an important step toward fully integrated, uniform vertical III-V nanowire array-on-Si devices.

  19. Tailoring the morphology and luminescence of GaN/InGaN core-shell nanowires using bottom-up selective-area epitaxy

    NASA Astrophysics Data System (ADS)

    Nami, Mohsen; Eller, Rhett F.; Okur, Serdal; Rishinaramangalam, Ashwin K.; Liu, Sheng; Brener, Igal; Feezell, Daniel F.

    2017-01-01

    Controlled bottom-up selective-area epitaxy (SAE) is used to tailor the morphology and photoluminescence properties of GaN/InGaN core-shell nanowire arrays. The nanowires are grown on c-plane sapphire substrates using pulsed-mode metal organic chemical vapor deposition. By varying the dielectric mask configuration and growth conditions, we achieve GaN nanowire cores with diameters ranging from 80 to 700 nm that exhibit various degrees of polar, semipolar, and nonpolar faceting. A single InGaN quantum well (QW) and GaN barrier shell is also grown on the GaN nanowire cores and micro-photoluminescence is obtained and analyzed for a variety of nanowire dimensions, array pitch spacings, and aperture diameters. By increasing the nanowire pitch spacing on the same growth wafer, the emission wavelength redshifts from 440 to 520 nm, while increasing the aperture diameter results in a ˜35 nm blueshift. The thickness of one QW/barrier period as a function of pitch and aperture diameter is inferred using scanning electron microscopy, with larger pitches showing significantly thicker QWs. Significant increases in indium composition were predicted for larger pitches and smaller aperture diameters. The results are interpreted in terms of local growth conditions and adatom capture radius around the nanowires. This work provides significant insight into the effects of mask configuration and growth conditions on the nanowire properties and is applicable to the engineering of monolithic multi-color nanowire LEDs on a single chip.

  20. Influence of the carrier Gas, trimethylgallium flow, and growth time on the character of the selective epitaxy of GaN

    SciTech Connect

    Rozhavskaya, M. M. Lundin, V. V.; Zavarin, E. E.; Troshkov, S. I.; Brunkov, P. N.; Tsatsulnikov, A. F.

    2013-03-15

    The influence of the carrier gas, trimethylgallium flow, and growth time on the character of the selective epitaxy of GaN in stripe windows oriented along the crystallographic direction Left-Pointing-Angle-Bracket 11-bar00 Right-Pointing-Angle-Bracket GaN for various widths of the mask between the stripes is studied. It is shown that the addition of nitrogen in the reactor atmosphere leads to changes in the form of the stripes in the case of wide (40 {mu}m) mask from a rectangular form restricted by a {l_brace}1 1-bar20{r_brace} lateral face to a trapezoidal form restricted by a {l_brace}1 1-bar22{r_brace} lateral face. It is also shown that during growth in the nitrogen-hydrogen mixture, the gallium flow starts to considerably affect the form of the growing stripes. It is shown that the process is significantly unstable, which leads to a noticeable variation in the form type as the transverse section of the stripe increases.

  1. Tailoring the morphology and luminescence of GaN/InGaN core-shell nanowires using bottom-up selective-area epitaxy.

    PubMed

    Nami, Mohsen; Eller, Rhett F; Okur, Serdal; Rishinaramangalam, Ashwin K; Liu, Sheng; Brener, Igal; Feezell, Daniel F

    2017-01-13

    Controlled bottom-up selective-area epitaxy (SAE) is used to tailor the morphology and photoluminescence properties of GaN/InGaN core-shell nanowire arrays. The nanowires are grown on c-plane sapphire substrates using pulsed-mode metal organic chemical vapor deposition. By varying the dielectric mask configuration and growth conditions, we achieve GaN nanowire cores with diameters ranging from 80 to 700 nm that exhibit various degrees of polar, semipolar, and nonpolar faceting. A single InGaN quantum well (QW) and GaN barrier shell is also grown on the GaN nanowire cores and micro-photoluminescence is obtained and analyzed for a variety of nanowire dimensions, array pitch spacings, and aperture diameters. By increasing the nanowire pitch spacing on the same growth wafer, the emission wavelength redshifts from 440 to 520 nm, while increasing the aperture diameter results in a ∼35 nm blueshift. The thickness of one QW/barrier period as a function of pitch and aperture diameter is inferred using scanning electron microscopy, with larger pitches showing significantly thicker QWs. Significant increases in indium composition were predicted for larger pitches and smaller aperture diameters. The results are interpreted in terms of local growth conditions and adatom capture radius around the nanowires. This work provides significant insight into the effects of mask configuration and growth conditions on the nanowire properties and is applicable to the engineering of monolithic multi-color nanowire LEDs on a single chip.

  2. Widely tunable alloy composition and crystal structure in catalyst-free InGaAs nanowire arrays grown by selective area molecular beam epitaxy

    SciTech Connect

    Treu, J. E-mail: Gregor.Koblmueller@wsi.tum.de; Speckbacher, M.; Saller, K.; Morkötter, S.; Xu, X.; Riedl, H.; Abstreiter, G.; Finley, J. J.; Koblmüller, G. E-mail: Gregor.Koblmueller@wsi.tum.de; Döblinger, M.

    2016-02-01

    We delineate the optimized growth parameter space for high-uniformity catalyst-free InGaAs nanowire (NW) arrays on Si over nearly the entire alloy compositional range using selective area molecular beam epitaxy. Under the required high group-V fluxes and V/III ratios, the respective growth windows shift to higher growth temperatures as the Ga-content x(Ga) is tuned from In-rich to Ga-rich InGaAs NWs. Using correlated x-ray diffraction, transmission electron microscopy, and micro-photoluminescence spectroscopy, we identify structural defects to govern luminescence linewidths in In-rich (x(Ga) < 0.4) and Ga-rich (x(Ga) > 0.6) NWs, whereas limitations at intermediate Ga-content (0.4 < x(Ga) < 0.6) are mainly due to compositional inhomogeneities. Most remarkably, the catalyst-free InGaAs NWs exhibit a characteristic transition in crystal structure from wurtzite to zincblende (ZB) dominated phase near x(Ga) ∼ 0.4 that is further reflected in a cross-over from blue-shifted to red-shifted photoluminescence emission relative to the band edge emission of the bulk ZB InGaAs phase.

  3. Energy-selective neutron radiography and tomography at FRM.

    PubMed

    Kardjilov, Nikolay; Schillinger, Burkhard; Steichele, Erich

    2004-10-01

    At the reactor FRM at Technical University of Munich energy-selective neutron radiography and tomography experiments were performed. For an energy separation of the neutrons from the primary beam a mechanical velocity selector was used. The radiography images show a different contrast of the investigated elements for neutron energies below and above their Bragg-cutoff energy. A comparison between the standard and energy-selective neutron tomography is presented. In spite of a reduction of the neutron intensity due to the velocity selector technique a realistic experimental time in order of some hours for the tomography experiment was achieved.

  4. Selected Energy Management Options for Small Business and Local Government.

    ERIC Educational Resources Information Center

    Wert, Jonathan M.; Worthington, Barry K.

    This document is a checklist of 257 energy management options for small business and local government. The energy management options are categorized under: (1) Energy management strategies; (2) Buildings; (3) Lighting; (4) Water; (5) Waste operations; (6) Equipment; (7) Transportation; and (8) Food preparation. To select options for…

  5. Theoretical minimum energies to produce steel for selected conditions

    SciTech Connect

    Fruehan, R. J.; Fortini, O.; Paxton, H. W.; Brindle, R.

    2000-03-01

    An ITP study has determined the theoretical minimum energy requirements for producing steel from ore, scrap, and direct reduced iron. Dr. Richard Fruehan's report, Theoretical Minimum Energies to Produce Steel for Selected Conditions, provides insight into the potential energy savings (and associated reductions in carbon dioxide emissions) for ironmaking, steelmaking, and rolling processes (PDF 459 KB).

  6. Energy equivalents for selected pavement materials: Their production and placement

    NASA Astrophysics Data System (ADS)

    Lane, K. R.

    1981-03-01

    Energy requirements for selected pavement surfaces are discussed. Energy requirements for hot-mixed bituminous recycling and portland cement concrete recycling projects are presented along with conventional pavement methods. Energy requirements for conventional thin surface treatments are also discussed. Environmental analyses involving both air and noise quality measurement are included for various recycling and conventional paving options.

  7. Orientational ordering of solution derived epitaxial Gd-doped ceria nanowires induced by nanoscratching

    NASA Astrophysics Data System (ADS)

    Zabaleta, Jone; Mestres, Narcis; Abellán, Patricia; Gibert, Marta; Sandiumenge, Felip; Puig, Teresa; Obradors, Xavier

    2010-01-01

    When one-dimensional nanostructures are epitaxially grown on a substrate a key goal is to control the nanowire's position and orientation. Nanoscratching of single crystalline (001)- LaAlO3 substrates is demonstrated to be extraordinarily effective in directing the self-assembly of Ce0.9Gd0.1O2-y epitaxial nanowires grown by chemical solution deposition. The local anisotropic elastic strain field imposed by the indentation lines is responsible for the breaking of the pre-existing orientation energy degeneracy and selects the nanowires' orientation parallel to the lines to an extent that can reach 100%.

  8. Energy Use in Transportation. Selected References

    DTIC Science & Technology

    1980-08-01

    Bernhard J. Abrahamson, ed. Boulder, Colo., Westview Press, 1978. xviii, 151 p. (HE9502.U52R63) HQ Papers presented at the 10th Institute, June 26-29...TOOLS TO MEET THE NATIONAL OBJECTIVE. Sarah J. LaBelle, ed. Summary of meeting, Argonne National Laboratory, Feb. 12, 1976. Argonne, 111., 1976...into the air. 407. Bernard, Martin Joseph and Sarah LaBelle. ENERGY CONSERVATION IN URBAN TRANSIT SYSTEMS. Chicago, uegional Transportation

  9. Ion mass and energy selective hyperthermal ion-beam assisted deposition setup

    NASA Astrophysics Data System (ADS)

    Gerlach, J. W.; Schumacher, P.; Mensing, M.; Rauschenbach, S.; Cermak, I.; Rauschenbach, B.

    2017-06-01

    For the synthesis of high-quality thin films, ion-beam assisted deposition (IBAD) is a frequently used technique providing precise control over several substantial film properties. IBAD typically relies on the use of a broad-beam ion source. Such ion sources suffer from the limitation that they deliver a blend of ions with different ion masses, each of them possessing a certain distribution of kinetic energy. In this paper, a compact experimental setup is presented that enables the separate control of ion mass and ion kinetic energy in the region of hyperthermal energies (few 1 eV - few 100 eV). This ion energy region is of increasing interest not only for ion-assisted film growth but also for the wide field of preparative mass spectrometry. The setup consists of a constricted glow-discharge plasma beam source and a tailor-made, compact quadrupole system equipped with entry and exit ion optics. It is demonstrated that the separation of monoatomic and polyatomic nitrogen ions (N+ and N2+) is accomplished. For both ion species, the kinetic energy is shown to be selectable in the region of hyperthermal energies. At the sample position, ion current densities are found to be in the order of 1 μA/cm2 and the full width at half maximum of the ion beam profile is in the order of 10 mm. Thus, the requirements for homogeneous deposition processes in sufficiently short periods of time are fulfilled. Finally, employing the described setup, for the first time in practice epitaxial GaN films were deposited. This opens up the opportunity to fundamentally study the influence of the simultaneous irradiation with hyperthermal ions on the thin film growth in IBAD processes and to increase the flexibility of the technique.

  10. Transactions of the Chinese Solar Energy Society (Selected Articles),

    DTIC Science & Technology

    1983-08-04

    iDAld- 870 TRANSACTIONS OF THE CHINESE SOLAR ENERGY SOCIETY i/i ’A1 (SELECTED ARTICLES)<U) FOREIGN TECHNOLOGY DIV I WRIGHT-PRTTERSON RF8 OH 7 SUN ET...34 . -.-. - - - - , " ’ ’-. . .. .. ...- " . ’ " FTD-ID(RS)T-1067-83 10 00 FOREIGN TECHNOLOGY DIVISION TRANSACTIONS OF THE CHINESE SOLAR ENERGY SOCIETY (Selected Articles...l067-83 4 August 1983 MICROFICHE NR: FTD-83-C-000960 TRANSACTIONS OF THE CHINESE SOLAR ENERGY SOCIETYI(Selected Articles) English pages: 16 Source: Acta

  11. Misfit dislocations in epitaxy

    NASA Astrophysics Data System (ADS)

    van der Merwe, Jan H.

    2002-08-01

    This article on epitaxy highlights the following: the definition and some historical milestones; the introduction by Frenkel and Kontorowa (FK) of a truncated Fourier series to model the periodic interaction at crystalline interfaces; the invention by Frank and van der Merwe (FvdM)—using the FK model—of (interfacial) misfit dislocations as an important mechanism in accommodating misfit at epilayer-substrate interfaces; the generalization of the FvdM theory to multilayers; the application of the parabolic model by Jesser and van der Merwe to describe, for growing multilayers and superlattices, the impact of Fourier coefficients in the realization of epitaxial orientations and the stability of modes of misfit accommodation; the involvement of intralayer interaction in the latter—all features that impact on the attainment of perfection in crystallinity of thin films, a property that is so vital in the fabrication of useful uniformly thick epilayers (uniformity being another technological requirement), which also depends on misfit accommodation through the interfacial energy that function strongly in the criterion for growth modes, proposed by Bauer; and the ingenious application of the Volterra model by Matthews and others to describe misfit accommodation by dislocations in growing epilayers.

  12. Selection of promising sites for magma energy experiments

    SciTech Connect

    Carson, C.C.

    1985-01-01

    The Long Valley and Coso Hot Springs areas of California have been identified as the most promising sites for conducting a magma energy extraction experiment. These two locations were selected from among the potential sites on the basis of several factors that are critical to the success of the proposed long-term energy extraction experiment. These factors include the likelihood of the existence of shallow magma targets as well as several other drilling, energy extraction and programmatic considerations. As the magma energy extraction program continues, these sites will be analyzed in detail so that one can be selected as the site for the planned magma experiment.

  13. Energy dissipation channels affecting photoluminescence from resonantly excited Er{sup 3+} ions doped in epitaxial ZnO host films

    SciTech Connect

    Akazawa, Housei; Shinojima, Hiroyuki

    2015-04-21

    We identified prerequisite conditions to obtain intense photoluminescence at 1.54 μm from Er{sup 3+} ions doped in ZnO host crystals. The epitaxial ZnO:Er films were grown on sapphire C-plane substrates by sputtering, and Er{sup 3+} ions were resonantly excited at a wavelength of 532 nm between energy levels of {sup 4}I{sub 15/2} and {sup 2}H{sub 11/2}. There is a threshold deposition temperature between 500 and 550 °C, above which epitaxial ZnO films become free of miss-oriented domains. In this case, Er{sup 3+} ions are outside ZnO crystallites, having the same c-axis lattice parameters as those of undoped ZnO crystals. The improved crystallinity was correlated with enhanced emissions peaking at 1538 nm. Further elevating the deposition temperature up to 650 °C generated cracks in ZnO crystals to relax the lattice mismatch strains, and the emission intensities from cracked regions were three times as large as those from smooth regions. These results can be consistently explained if we assume that emission-active Er{sup 3+} ions are those existing at grain boundaries and bonded to single-crystalline ZnO crystallites. In contrast, ZnO:Er films deposited on a ZnO buffer layer exhibited very weak emissions because of their degraded crystallinity when most Er{sup 3+} ions were accommodated into ZnO crystals. Optimizing the degree of oxidization of ZnO crystals is another important factor because reduced films suffer from non-radiative decay of excited states. The optimum Er content to obtain intense emissions was between 2 and 4 at. %. When 4 at. % was exceeded, the emission intensity was severely attenuated because of concentration quenching as well as the degradation in crystallinity. Precipitation of Er{sub 2}O{sub 3} crystals was clearly observed at 22 at. % for films deposited above 650 °C. Minimizing the number of defects and impurities in ZnO crystals prevents energy dissipation, thus exclusively utilizing the excitation energy to emissions from

  14. Effects of high-flux low-energy ion bombardment on the low-temperature growth morphology of TiN(001) epitaxial layers

    SciTech Connect

    Karr, Brian W.; Cahill, David G.; Petrov, I.; Greene, J. E.

    2000-06-15

    Ultrahigh vacuum scanning tunneling microscopy (STM) is used to characterize the surface morphology of TiN(001) epitaxial layers grown by dc reactive magnetron sputtering at growth temperatures of T{sub s}=650 and T{sub s}=750 degree sign C. An auxiliary anode is used to bias the N{sub 2} plasma and produce a large flux of low-energy N{sub 2}{sup +} ions that bombard the film surface during growth: the ratio of the N{sub 2}{sup +} flux to the Ti growth flux is {approx_equal}25. At ion energies E{sub i} near the threshold for the production of bulk defects (E{sub i}=43 eV and T{sub s}=650 degree sign C), ion bombardment decreases the amplitude of the roughness, decreases the average distance between growth mounds, and reduces the sharpness of grooves between growth mounds. The critical island radius for second layer nucleation R{sub c} is approximately 12 and 17 nm at growth temperatures of 650 and 750 degree sign C respectively; at 650 degree sign C, R{sub c} is reduced to (approx =)10 nm by ion bombardment. (c) 2000 The American Physical Society.

  15. Screening and selection of lignocellulosic crops for energy

    SciTech Connect

    Turhollow, A.F.; Cushman, J.H.; Elmore, J.L.; Johnston, J.W.

    1985-01-01

    The Department of Energy's Herbaceous Energy Crops Program at Oak Ridge National Laboratory is beginning its research on lignocellulosic energy crops with five studies in the Southeast and Midwest/Lakes regions. Early objectives for these studies include selecting species that show promise on marginal croplands typical of the regions, determining productivity rates under various levels of management, defining cost-effective and environmentally sound production systems for each region, and identifying the most promising means of reducing costs. 2 tabs.

  16. Energy and daylight performance of angular selective glazings

    SciTech Connect

    Sullivan, R.; Beltran,; Lee, E.S.; Rubin, M.; Selkowitz, S.E.

    1998-11-01

    This paper presents the results of a study investigating the energy and daylight performance of anisotropic angular selective glazings. The DOE-2.1E energy simulation program was used to determine the annual cooling, lighting and total electricity use, and peak electric demand. RADIANCE, a lighting simulation program, was used to determine daylight illuminance levels and distribution. We simulated a prototypical commercial office building module located in Blythe, California. We chose three hypothetical conventional windows for comparison: a single-pane tinted window, a double-pane low-E window, and a double-pane spectrally selective window. Daylighting controls were used. No interior shades were modeled in order to isolate the energy effects of the angular selective glazing. Our results show that the energy performance of the prototype angular selective windows is about the same as conventional windows for a 9.14 m (30 ft) deep south-facing perimeter zone with a large-area window in the hot, sunny climate of Blythe. It is theoretically possible to tune the angular selectivity of the glazing to achieve annual cooling energy reductions of 18%, total electricity use reductions of 15%, and peak electric demand reductions of 11% when compared to a conventional glazing with the same solar-optical properties at normal incidence. Angular selective glazings can provide more uniformly distributed daylight, particularly in the area next to the window, which will result in a more visually comfortable work environment.

  17. Modeling and characterization of double resonant tunneling diodes for application as energy selective contacts in hot carrier solar cells

    NASA Astrophysics Data System (ADS)

    Jehl, Zacharie; Suchet, Daniel; Julian, Anatole; Bernard, Cyril; Miyashita, Naoya; Gibelli, Francois; Okada, Yoshitaka; Guillemolles, Jean-Francois

    2017-02-01

    Double resonant tunneling barriers are considered for an application as energy selective contacts in hot carrier solar cells. Experimental symmetric and asymmetric double resonant tunneling barriers are realized by molecular beam epitaxy and characterized by temperature dependent current-voltage measurements. The negative differential resistance signal is enhanced for asymmetric heterostructures, and remains unchanged between low- and room-temperatures. Within Tsu-Esaki description of the tunnel current, this observation can be explained by the voltage dependence of the tunnel transmission amplitude, which presents a resonance under finite bias for asymmetric structures. This effect is notably discussed with respect to series resistance. Different parameters related to the electronic transmission of the structure and the influence of these parameters on the current voltage characteristic are investigated, bringing insights on critical processes to optimize in double resonant tunneling barriers applied to hot carrier solar cells.

  18. Probing optical band gaps at the nanoscale in NiFe₂O₄ and CoFe₂O₄ epitaxial films by high resolution electron energy loss spectroscopy

    SciTech Connect

    Dileep, K.; Loukya, B.; Datta, R.; Pachauri, N.; Gupta, A.

    2014-09-14

    Nanoscale optical band gap variations in epitaxial thin films of two different spinel ferrites, i.e., NiFe₂O₄ (NFO) and CoFe₂O₄ (CFO), have been investigated by spatially resolved high resolution electron energy loss spectroscopy. Experimentally, both NFO and CFO show indirect/direct band gaps around 1.52 eV/2.74 and 2.3 eV, and 1.3 eV/2.31 eV, respectively, for the ideal inverse spinel configuration with considerable standard deviation in the band gap values for CFO due to various levels of deviation from the ideal inverse spinel structure. Direct probing of the regions in both the systems with tetrahedral A site cation vacancy, which is distinct from the ideal inverse spinel configuration, shows significantly smaller band gap values. The experimental results are supported by the density functional theory based modified Becke-Johnson exchange correlation potential calculated band gap values for the different cation configurations.

  19. Investigation of Sn surface segregation during GeSn epitaxial growth by Auger electron spectroscopy and energy dispersive x-ray spectroscopy

    SciTech Connect

    Tsukamoto, Takahiro; Suda, Yoshiyuki; Hirose, Nobumitsu; Kasamatsu, Akifumi; Mimura, Takashi; Matsui, Toshiaki

    2015-02-02

    The mechanism of Sn surface segregation during the epitaxial growth of GeSn on Si (001) substrates was investigated by Auger electron spectroscopy and energy dispersive X-ray spectroscopy. Sn surface segregation depends on the growth temperature and Sn content of GeSn layers. During Sn surface segregation, Sn-rich nanoparticles form and move on the surface during the deposition, which results in a rough surface owing to facet formation. The Sn-rich nanoparticles moving on the surface during the deposition absorb Sn from the periphery and yield a lower Sn content, not on the surface but within the layer, because the Sn surface segregation and the GeSn deposition occur simultaneously. Sn surface segregation can occur at a lower temperature during the deposition compared with that during postannealing. This suggests that the Sn surface segregation during the deposition is strongly promoted by the migration of deposited Ge and Sn adatoms on the surface originating from the thermal effect of substrate temperature, which also suggests that limiting the migration of deposited Ge and Sn adatoms can reduce the Sn surface segregation and improve the crystallinity of GeSn layers.

  20. Epitaxial BaTiO3(100) films on Pt(100): a low-energy electron diffraction, scanning tunneling microscopy, and x-ray photoelectron spectroscopy study.

    PubMed

    Förster, Stefan; Huth, Michael; Schindler, Karl-Michael; Widdra, Wolf

    2011-09-14

    The growth of epitaxial ultrathin BaTiO(3) films on a Pt(100) substrate has been studied by scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), and x-ray photoelectron spectroscopy (XPS). The films have been prepared by radio-frequency-assisted magnetron sputter deposition at room temperature and develop a long-range order upon annealing at 900 K in O(2). By adjusting the Ar and O(2) partial pressures of the sputter gas, the stoichiometry was tuned to match that of a BaTiO(3)(100) single crystal as determined by XPS. STM reveals the growth of continuous BaTiO(3) films with unit cell high islands on top. With LEED already for monolayer thicknesses, the formation of a BaTiO(3)(100)-(1 × 1) structure has been observed. Films of 2-3 unit cell thickness show a brilliant (1 × 1) LEED pattern for which an extended set of LEED I-V data has been acquired. At temperatures above 1050 K the BaTiO(3) thin film starts to decay by formation of vacancy islands. In addition (4 × 4) and (3 × 3) surface reconstructions develop upon prolonged heating.

  1. Measure Guideline: Energy-Efficient Window Performance and Selection

    SciTech Connect

    Carmody, J.; Haglund, K.

    2012-11-01

    This document provides guidelines for the selection of energy-efficient windows in new and existing residential construction in all US climate zones. It includes information on window products, their attributes and performance. It provides cost/benefit information on window energy savings as well as information on non-energy benefits such as thermal comfort and reduced HVAC demands. The document also provides information on energy impacts of design decisions such as window orientation, total glazing area and shading devices and conditions. Information on resources for proper window installation is included as well. This document is for builders, homeowners, designers and anyone making decisions about selecting energy efficient window. It is intended to complement other Building America information and efforts.

  2. Developing a framework for energy technology portfolio selection

    NASA Astrophysics Data System (ADS)

    Davoudpour, Hamid; Ashrafi, Maryam

    2012-11-01

    Today, the increased consumption of energy in world, in addition to the risk of quick exhaustion of fossil resources, has forced industrial firms and organizations to utilize energy technology portfolio management tools viewed both as a process of diversification of energy sources and optimal use of available energy sources. Furthermore, the rapid development of technologies, their increasing complexity and variety, and market dynamics have made the task of technology portfolio selection difficult. Considering high level of competitiveness, organizations need to strategically allocate their limited resources to the best subset of possible candidates. This paper presents the results of developing a mathematical model for energy technology portfolio selection at a R&D center maximizing support of the organization's strategy and values. The model balances the cost and benefit of the entire portfolio.

  3. Improved crystalline properties of laser molecular beam epitaxy grown SrTiO{sub 3} by rutile TiO{sub 2} layer on hexagonal GaN

    SciTech Connect

    Luo, W. B.; Zhu, J.; Chen, H.; Wang, X. P.; Zhang, Y.; Li, Y. R.

    2009-11-15

    Epitaxial SrTiO{sub 3} films were fabricated by laser molecular beam epitaxy on bare and TiO{sub 2} buffered GaN(0002), respectively. The whole deposition processes were in situ monitored by reflection high energy electron diffraction (RHEED). X-ray diffraction (XRD) was carried out to study the growth orientation and crystalline quality of STO films. The interfacial characters and epitaxial relationships were also investigated by high revolution transition electron microscope and selected area electron diffraction (SAED). According to the RHEED observation, the lowest epitaxy temperature of STO on TiO{sub 2} buffered GaN was decreased compared with the direct deposited one. The epitaxial relationship was (111)[110]STO//(0002)[1120]GaN in both cases as confirmed by RHEED, XRD, and SAED. The full width at half maximum of omega-scan and PHI-scan of STO on TiO{sub 2} buffered GaN was reduced compared with that deposited on bare GaN, indicating that epitaxial quality of STO film is improved by inserting TiO{sub 2} layer. In summary, the lattice mismatch was reduced by inserting rutile TiO{sub 2}. As a result, the crystalline temperature was reduced and enhanced epitaxial quality of STO thin film was obtained.

  4. Measure Guideline. Energy-Efficient Window Performance and Selection

    SciTech Connect

    Carmody, John; Haglund, Kerry

    2012-11-01

    This document provides guidelines for the selection of energy-efficient windows in new and existing residential construction in all U.S. climate zones. It includes information on window products, their attributes and performance. It provides cost/benefit information on window energy savings as well as information on non-energy benefits such as thermal comfort and reduced HVAC demands. The report also provides information on energy impacts of design decisions such as window orientation, total glazing area and shading devices and conditions. Information on resources for proper window installation is included as well.

  5. Model selection as a science driver for dark energy surveys

    NASA Astrophysics Data System (ADS)

    Mukherjee, Pia; Parkinson, David; Corasaniti, Pier Stefano; Liddle, Andrew R.; Kunz, Martin

    2006-07-01

    A key science goal of upcoming dark energy surveys is to seek time-evolution of the dark energy. This problem is one of model selection, where the aim is to differentiate between cosmological models with different numbers of parameters. However, the power of these surveys is traditionally assessed by estimating their ability to constrain parameters, which is a different statistical problem. In this paper, we use Bayesian model selection techniques, specifically forecasting of the Bayes factors, to compare the abilities of different proposed surveys in discovering dark energy evolution. We consider six experiments - supernova luminosity measurements by the Supernova Legacy Survey, SNAP, JEDI and ALPACA, and baryon acoustic oscillation measurements by WFMOS and JEDI - and use Bayes factor plots to compare their statistical constraining power. The concept of Bayes factor forecasting has much broader applicability than dark energy surveys.

  6. Development of anion-selective membranes. [for energy storage

    NASA Technical Reports Server (NTRS)

    Lacey, R. E.; Cowsar, D. R.

    1975-01-01

    Methods were studied of preparing anion-exchange membranes that would have low resistance, high selectivity, and physical and chemical stability when used in acidic media in a redox energy storage system. Of the twelve systems selected for study, only the system that was based on crosslinked poly-4-vinylpyridinium chloride produced physically strong membranes when equilibrated in l M HCl. The resistivity of the best membrane was 12 ohm-cm, and the transference number for chloride ions was 0.81.

  7. Supply of and demand for selected energy related mineral commodities

    USGS Publications Warehouse

    Sibley, Scott F.

    2010-01-01

    In this report, subjects discussed include components of mineral supply, production, and consumption data, and information on selected mineral commodities in which the Energy Critical Elements Study Group has an interest, and U.S. Geological Survey (USGS) recycling studies, with some results of these studies.

  8. Method of forming silicon structures with selectable optical characteristics

    NASA Technical Reports Server (NTRS)

    Fathauer, Robert W. (Inventor); Schowalter, Leo (Inventor)

    1993-01-01

    Silicon and metal are coevaporated onto a silicon substrate in a molecular beam epitaxy system with a larger than stoichiometric amount of silicon so as to epitaxially grow particles of metal silicide embedded in a matrix of single crystal epitaxially grown silicon. The particles interact with incident photons by resonant optical absorption at the surface plasmon resonance frequency. Controlling the substrate temperature and deposition rate and time allows the aspect ratio of the particles to be tailored to desired wavelength photons and polarizations. The plasmon energy may decay as excited charge carriers or phonons, either of which can be monitored to indicate the amount of incident radiation at the selected frequency and polarization.

  9. 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

  10. Temperature-gradient epitaxy under in situ growth mode diagnostics by scanning reflection high-energy electron diffraction

    NASA Astrophysics Data System (ADS)

    Koida, T.; Komiyama, D.; Koinuma, H.; Ohtani, M.; Lippmaa, M.; Kawasaki, M.

    2002-01-01

    We have developed a parallel film growth method on a temperature-gradient substrate to quickly control and optimize the film growth mode. A continuous-wave neodymium-doped yttrium-aluminum-garnet laser heating was used to achieve a stable temperature gradient covering a 300 °C range of temperatures over a distance of 11 mm. The growth mode was determined by time-resolved scanning reflection high-energy electron diffraction. Transition from layer-by-layer to step-flow growth by the deposition temperature was observed during La0.5Sr0.5MnO3 film growth on a single SrTiO3 substrate, proving a powerful tool not only for investigating the growth dynamics but also for seeking the optimized deposition conditions in one run of experiment.

  11. Energy-loss magnetic chiral dichroism study of epitaxial MnAs film on GaAs(001)

    SciTech Connect

    Fu, X.; Warot-Fonrose, B.; Arras, R.; Serin, V.; Demaille, D.; Eddrief, M.; Etgens, V.

    2015-08-10

    The room-temperature ferromagnetic behavior of MnAs/GaAs(001) thin film has been locally explored by Transmission Electron Microscope (TEM). We first differentiated hexagonal α-MnAs and quasi-hexagonal β-MnAs which are very similar in atomic structure by electron diffraction. Local magnetic moment information of the identified α-MnAs was extracted from manganese-L{sub 2,3} edges using Energy-loss Magnetic Circular Dichroism technique and the ratio of orbital to spin magnetic moment was measured. In this experiment, atomic structure identification, chemical analysis, and magnetic moment measurement were simultaneously achieved at high spatial resolution in TEM, thus providing a potential method for in-situ study of local properties of multiphase magnetic materials.

  12. Monitoring non-pseudomorphic epitaxial growth of spinel/perovskite oxide heterostructures by reflection high-energy electron diffraction

    SciTech Connect

    Schütz, P.; Pfaff, F.; Scheiderer, P.; Sing, M.; Claessen, R.

    2015-02-09

    Pulsed laser deposition of spinel γ-Al{sub 2}O{sub 3} thin films on bulk perovskite SrTiO{sub 3} is monitored by high-pressure reflection high-energy electron diffraction (RHEED). The heteroepitaxial combination of two materials with different crystal structures is found to be inherently accompanied by a strong intensity modulation of bulk diffraction patterns from inelastically scattered electrons, which impedes the observation of RHEED intensity oscillations. Avoiding such electron surface-wave resonance enhancement by de-tuning the RHEED geometry allows for the separate observation of the surface-diffracted specular RHEED signal and thus the real-time monitoring of sub-unit cell two-dimensional layer-by-layer growth. Since these challenges are essentially rooted in the difference between film and substrate crystal structure, our findings are of relevance for the growth of any heterostructure combining oxides with different crystal symmetry and may thus facilitate the search for novel oxide heterointerfaces.

  13. The growth of epitaxial iron oxides on platinum (111) as studied by X-ray photoelectron diffraction, scanning tunneling microscopy, and low energy electron diffraction

    SciTech Connect

    Kim, Yong -Joo

    1995-05-01

    Three complementary surface structure probes, x-ray photoelectron diffraction (XPD), scanning tunneling microscopy (STM), and low-energy electron diffraction (LEED) have been combined in a single instrument. This experimental system has been utilized to study the structure and growth mechanisms of iron oxide films on Pt(111); these films were formed by first depositing a single overlayer of Fe with a certain coverage in monolayers (ML`s), and then thermally oxidizing it in an oxygen atmosphere. For films up to ~1 ML in thickness, a bilayer of Fe and O similar to those in FeO(111) is found to form. In agreement with prior studies, STM and LEED show this to be an incommensurate oxide film forming a lateral superlattice with short- and long-range periodicities of ~3.1 Å and ~26.0 Å. XPD in addition shows a topmost oxygen layer to be relaxed inward by -0.6 Å compared to bulk FeO(111), and these are new structural conclusions. The oxygen stacking in the FeO(111) bilayer is dominated by one of two possible binding sites. For thicker iron oxide films from 1.25 ML to 3.0 ML, the growth mode is essentially Stranski-Krastanov: iron oxide islands form on top of the FeO(111) bilayer mentioned above. For iron oxide films of 3.0 ML thickness, x-ray photoelectron spectroscopy (XPS) yields an Fe 2p3/2 binding energy and an Fe:O stoichiometry consistent with the presence of Fe3O4. Our XPD data further prove this overlayer to be Fe3O4(111)-magnetite in two almost equally populated domains with a 180° rotation between them. The structural parameters for this Fe3O4 overlayer generally agree with those of a previous LEED study, except that we find a significant difference in the first Fe-O interplanar spacing. This work demonstrates the considerable benefits to be derived by using this set of complementary surface structure probes in such epitaxial growth studies.

  14. Steric and electronic interactions between source gas and substrate surface during the Al-CVD/Al selective epitaxy process as investigated by quantum chemical calculations

    NASA Astrophysics Data System (ADS)

    Vetrivel, R.; Yamauchi, R.; Yamano, H.; Kubo, M.; Miyamoto, A.; Ohta, T.

    1994-12-01

    We have performed quantum chemical calculations by semiempirical MNDO and by density functional theory (DFT) to rationalize the selection of an Al source gas for the selective Al-CVD/Al process. The electronic properties of Al(CH 3) nH 3-n, ( n = 0 to 3) and their adsorption complexes over representative aluminum metal clusters were calculated. Initially, the interaction of Al source gases with a representative Al metal was studied by both MNDO and DFT methods and the results were found to be qualitatively comparable. Further detailed calculations were performed by MNDO to understand the interaction of Al(CH 3) nH 3-n with larger cluster models of Al substrate as well as insulator silica surface. The results of the calculations indicate that the interaction energy between the substrate and the source are controlled by both steric and electronic factors. The steric factor favors the interaction of unsubstituted hydride, namely aluminum trihydride and the electronic factor favors the interaction of maximum substituted aluminum organic, namely trimethyl aluminum with the substrates. However, dimethyl aluminum hydride has the most favorable interaction energy with the Al metal, since it has the right combination of steric and electronic factors. The interaction energy of DMAH with chlorided silica surface is more favorable than the untreated silica surface.

  15. Epitaxial Graphene Quantum Electronics

    DTIC Science & Technology

    2014-05-19

    ferromagnetism with spintronics potential. * We have achieved the highest operational frequency in graphene transistors. Epitaxial graphene; quantum transport...important discovery with implications for spintronics . * We have found that ballistic transport most likely involves non-conventional charge carriers

  16. Thermophotovoltaic energy conversion using photonic bandgap selective emitters

    DOEpatents

    Gee, James M.; Lin, Shawn-Yu; Fleming, James G.; Moreno, James B.

    2003-06-24

    A method for thermophotovoltaic generation of electricity comprises heating a metallic photonic crystal to provide selective emission of radiation that is matched to the peak spectral response of a photovoltaic cell that converts the radiation to electricity. The use of a refractory metal, such as tungsten, for the photonic crystal enables high temperature operation for high radiant flux and high dielectric contrast for a full 3D photonic bandgap, preferable for efficient thermophotovoltaic energy conversion.

  17. EFFECT OF ENERGY DRINKS ON SELECTED FINE MOTOR TASKS.

    PubMed

    Jacobson, B H; Hughes, P P; Conchola, E C; Hester, G M; Woolsey, C L

    2015-08-01

    This study assessed the effect of energy shots on selected fine motor tasks. The participants were college-age male (n=19; M age=20.5 yr., SD=0.7) and female (n=21; M age=21.1 yr., SD=0.7) volunteers who were assessed on hand steadiness, choice reaction time, rotary pursuit, and simple reaction time. The energy shots group scored significantly poorer on the hand steadiness tests and significantly better on choice reaction time and simple reaction time tests. The enhanced reaction time and disruption in hand steadiness afforded by energy shots would not be apparent in many gross motor activities, but it is possible that reaction time improvement could be beneficial in sports that require quick, reflexive movements. However, the potential adverse psychological and physiological effects warrant discretionary use of such products.

  18. Materials selection guidelines for geothermal energy utilization systems

    SciTech Connect

    Ellis, P.F. II; Conover, M.F.

    1981-01-01

    This manual includes geothermal fluid chemistry, corrosion test data, and materials operating experience. Systems using geothermal energy in El Salvador, Iceland, Italy, Japan, Mexico, New Zealand, and the United States are described. The manual provides materials selection guidelines for surface equipment of future geothermal energy systems. The key chemical species that are significant in determining corrosiveness of geothermal fluids are identified. The utilization modes of geothermal energy are defined as well as the various physical fluid parameters that affect corrosiveness. Both detailed and summarized results of materials performance tests and applicable operating experiences from forty sites throughout the world are presented. The application of various non-metal materials in geothermal environments are discussed. Included in appendices are: corrosion behavior of specific alloy classes in geothermal fluids, corrosion in seawater desalination plants, worldwide geothermal power production, DOE-sponsored utilization projects, plant availability, relative costs of alloys, and composition of alloys. (MHR)

  19. An affine transformation description of epitaxial heterostructures

    NASA Astrophysics Data System (ADS)

    Dakshinamurthy, S.; Rajan, K.

    1991-07-01

    The matching at the interface between the substrate and the film in an epitaxial deposit has been analyzed and explained very well in the literature for the various fcc-bcc metallic systems by the use of the energy minimization criteria such as invariant line criterion, the O-lattice approach etc. Though many orientation relationships have been reported for other crystal structures and non-metals, very little effort has been made to explain these relationships. Here, we attempt to rationalize the orientation relationships that we have obtained and which others have reported for epitaxial suicides using the above mentioned criteria.

  20. Resonance Energy Transfer in Upconversion Nanoplatforms for Selective Biodetection.

    PubMed

    Su, Qianqian; Feng, Wei; Yang, Dongpeng; Li, Fuyou

    2017-01-17

    Resonance energy transfer (RET) describes the process that energy is transferred from an excited donor to an acceptor molecule, leading to a reduction in the fluorescence emission intensity of the donor and an increase in that of the acceptor. By this technique, measurements with the good sensitivity can be made about distance within 1 to 10 nm under physiological conditions. For this reason, the RET technique has been widely used in polymer science, biochemistry, and structural biology. Recently, a number of RET systems incorporated with nanoparticles, such as quantum dots, gold nanoparticles, and upconversion nanoparticles, have been developed. These nanocrystals retain their optical superiority and can act as either a donor or a quencher, thereby enhancing the performance of RET systems and providing more opportunities in excitation wavelength selection. Notably, lanthanide-doped upconversion nanophosphors (UCNPs) have attracted considerable attention due to their inherent advantages of large anti-Stoke shifts, long luminescence lifetimes, and absence of autofluorescence under low energy near-infrared (NIR) light excitation. These nanoparticles are promising for the biodetection of various types of analytes. Undoubtedly, the developments of those applications usually rely on resonance energy transfer, which could be regarded as a flexible technology to mediate energy transfer from upconversion phosphor to acceptor for the design of luminescent functional nanoplatforms. Currently, researchers have developed many RET-based upconversion nanosystems (RET-UCNP) that respond to specific changes in the biological environments. Specifically, small organic molecules, biological molecules, metal-organic complexes, or inorganic nanoparticles were carefully selected and bound to the surface of upconversion nanoparticles for the preparation of RET-UCNP nanosystems. Benefiting from the advantage and versatility offered by this technology, the research of RET

  1. Predictions of Ligand Selectivity from Absolute Binding Free Energy Calculations

    PubMed Central

    2016-01-01

    Binding selectivity is a requirement for the development of a safe drug, and it is a critical property for chemical probes used in preclinical target validation. Engineering selectivity adds considerable complexity to the rational design of new drugs, as it involves the optimization of multiple binding affinities. Computationally, the prediction of binding selectivity is a challenge, and generally applicable methodologies are still not available to the computational and medicinal chemistry communities. Absolute binding free energy calculations based on alchemical pathways provide a rigorous framework for affinity predictions and could thus offer a general approach to the problem. We evaluated the performance of free energy calculations based on molecular dynamics for the prediction of selectivity by estimating the affinity profile of three bromodomain inhibitors across multiple bromodomain families, and by comparing the results to isothermal titration calorimetry data. Two case studies were considered. In the first one, the affinities of two similar ligands for seven bromodomains were calculated and returned excellent agreement with experiment (mean unsigned error of 0.81 kcal/mol and Pearson correlation of 0.75). In this test case, we also show how the preferred binding orientation of a ligand for different proteins can be estimated via free energy calculations. In the second case, the affinities of a broad-spectrum inhibitor for 22 bromodomains were calculated and returned a more modest accuracy (mean unsigned error of 1.76 kcal/mol and Pearson correlation of 0.48); however, the reparametrization of a sulfonamide moiety improved the agreement with experiment. PMID:28009512

  2. Module energy rating candidate reference days: Criteria and selection process

    NASA Astrophysics Data System (ADS)

    Myers, Daryl R.

    1999-03-01

    Presently the performance of flat-plate photovoltaic (PV) modules is based upon module power, open circuit voltage, short-circuit current, or peak power voltage and current with respect to fixed environmental conditions such as Standard Reporting Conditions, (SRC) or nominal operating cell temperature. These reporting conditions represent ideal conditions under which PV module performance (e.g., between manufacturers or technologies) may be compared. They result in overly optimistic expectations of performance by PV industry customers. A recommended practice for PV module energy-rating methodologies to relate PV module performance to real world conditions is under development. The methodologies will provide system designers and PV customers with an energy rating representative of real world conditions. The rating methodology reports energy production under 5 selected types of days representative of possible operational environments. The development and application of qualitative and quantitative criteria for identifying and selecting these representative days from the 30-year U.S. National Solar Radiation Data Base is described.

  3. 7 CFR 4280.193 - Selecting energy audit and renewable energy development assistance grant applications for award.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 7 Agriculture 15 2012-01-01 2012-01-01 false Selecting energy audit and renewable energy development assistance grant applications for award. 4280.193 Section 4280.193 Agriculture Regulations of the... Renewable Energy Development Assistance Grants § 4280.193 Selecting energy audit and renewable...

  4. 7 CFR 4280.193 - Selecting energy audit and renewable energy development assistance grant applications for award.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 7 Agriculture 15 2014-01-01 2014-01-01 false Selecting energy audit and renewable energy development assistance grant applications for award. 4280.193 Section 4280.193 Agriculture Regulations of the... Renewable Energy Development Assistance Grants § 4280.193 Selecting energy audit and renewable...

  5. 7 CFR 4280.193 - Selecting energy audit and renewable energy development assistance grant applications for award.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 7 Agriculture 15 2013-01-01 2013-01-01 false Selecting energy audit and renewable energy development assistance grant applications for award. 4280.193 Section 4280.193 Agriculture Regulations of the... Renewable Energy Development Assistance Grants § 4280.193 Selecting energy audit and renewable...

  6. Energy band alignment of atomic layer deposited HfO{sub 2} oxide film on epitaxial (100)Ge, (110)Ge, and (111)Ge layers

    SciTech Connect

    Hudait, Mantu K.; Zhu Yan

    2013-03-21

    Crystallographically oriented epitaxial Ge layers were grown on (100), (110), and (111)A GaAs substrates by in situ growth process using two separate molecular beam epitaxy chambers. The band alignment properties of atomic layer hafnium oxide (HfO{sub 2}) film deposited on crystallographically oriented epitaxial Ge were investigated using x-ray photoelectron spectroscopy (XPS). Valence band offset, {Delta}E{sub v} values of HfO{sub 2} relative to (100)Ge, (110)Ge, and (111)Ge orientations were 2.8 eV, 2.28 eV, and 2.5 eV, respectively. Using XPS data, variation in valence band offset, {Delta}E{sub V}(100)Ge>{Delta}E{sub V}(111)Ge>{Delta}E{sub V}(110)Ge, was obtained related to Ge orientation. Also, the conduction band offset, {Delta}E{sub c} relation, {Delta}E{sub c}(110)Ge>{Delta}E{sub c}(111)Ge>{Delta}E{sub c}(100)Ge related to Ge orientations was obtained using the measured bandgap of HfO{sub 2} on each orientation and with the Ge bandgap of 0.67 eV. These band offset parameters for carrier confinement would offer an important guidance to design Ge-based p- and n-channel metal-oxide field-effect transistor for low-power application.

  7. Greater sage-grouse winter habitat selection and energy development

    SciTech Connect

    Doherty, K.E.; Naugle, D.E.; Walker, B.L.; Graham, J.M.

    2008-01-15

    Recent energy development has resulted in rapid and large-scale changes to western shrub-steppe ecosystems without a complete understanding of its potential impacts on wildlife populations. We modeled winter habitat use by female greater sage-grouse (Centrocercus urophasianus) in the Powder River Basin (PRB) of Wyoming and Montana, USA, to 1) identify landscape features that influenced sage-grouse habitat selection, 2) assess the scale at which selection occurred, 3) spatially depict winter habitat quality in a Geographic Information System, and 4) assess the effect of coal-bed natural gas (CBNG) development on winter habitat selection. We developed a model of winter habitat selection based on 435 aerial relocations of 200 radiomarked female sage-grouse obtained during the winters of 2005 and 2006. Percent sagebrush (Artemisia spp.) cover on the landscape was an important predictor of use by sage-grouse in winter. Sage-grouse were 1.3 times more likely to occupy sagebrush habitats that lacked CBNG wells within a 4-km{sup 2} area, compared to those that had the maximum density of 12.3 wells per 4 km{sup 2} allowed on federal lands. We validated the model with 74 locations from 74 radiomarked individuals obtained during the winters of 2004 and 2007. This winter habitat model based on vegetation, topography, and CBNG avoidance was highly predictive (validation R{sup 2} = 0.984). Our spatially explicit model can be used to identify areas that provide the best remaining habitat for wintering sage-grouse in the PRB to mitigate impacts of energy development.

  8. Epitaxial Garnets and Hexagonal Ferrites.

    DTIC Science & Technology

    1983-12-01

    Ferrites Lithium Ferrite Magnetostatic Wave Garnets Epitaxy Yttrium Iron Garnet Liquid Phase Epitaxy Hexagonal Ferrite Microwave Signal Processing...epitaxial ferrit ( materials for use in microwave and millirreter-wave signal processing devices. The major emphasis has been on multiple layer...overall objective of this research is to develop epitaxial single crystal ferrite films suitable for microwave and millimeter-wave signal processing at

  9. Dimensionality and noise in energy selective x-ray imaging

    PubMed Central

    Alvarez, Robert E.

    2013-01-01

    Purpose: To develop and test a method to quantify the effect of dimensionality on the noise in energy selective x-ray imaging. Methods: The Cramèr-Rao lower bound (CRLB), a universal lower limit of the covariance of any unbiased estimator, is used to quantify the noise. It is shown that increasing dimensionality always increases, or at best leaves the same, the variance. An analytic formula for the increase in variance in an energy selective x-ray system is derived. The formula is used to gain insight into the dependence of the increase in variance on the properties of the additional basis functions, the measurement noise covariance, and the source spectrum. The formula is also used with computer simulations to quantify the dependence of the additional variance on these factors. Simulated images of an object with three materials are used to demonstrate the trade-off of increased information with dimensionality and noise. The images are computed from energy selective data with a maximum likelihood estimator. Results: The increase in variance depends most importantly on the dimension and on the properties of the additional basis functions. With the attenuation coefficients of cortical bone, soft tissue, and adipose tissue as the basis functions, the increase in variance of the bone component from two to three dimensions is 1.4 × 103. With the soft tissue component, it is 2.7 × 104. If the attenuation coefficient of a high atomic number contrast agent is used as the third basis function, there is only a slight increase in the variance from two to three basis functions, 1.03 and 7.4 for the bone and soft tissue components, respectively. The changes in spectrum shape with beam hardening also have a substantial effect. They increase the variance by a factor of approximately 200 for the bone component and 220 for the soft tissue component as the soft tissue object thickness increases from 1 to 30 cm. Decreasing the energy resolution of the detectors increases the

  10. Effects of selective lattice deformation on YbBa2Cu4O8 and YBa2Cu3O7 epitaxial films

    NASA Astrophysics Data System (ADS)

    Mito, M.; Matsui, H.; Imakyurei, T.; Deguchi, H.; Horide, T.; Matsumoto, K.; Ichinose, A.; Yoshida, Y.

    2014-03-01

    Alternating current magnetic measurements of YbBa2Cu4O8 (Yb-124) and YBa2Cu3O7 (Y-123) epitaxial films were performed under hydrostatic pressure (HP). Here, the strain under HP results in uniaxial strain along the c-axis, in addition to the biaxial strain due to mismatching with the substrate. This uniaxial effect on Yb-124 film brings about a prominent increase in the superconducting transition temperature (Tc) against the initial strain. However, a nearly optimal Y-123 film hardly exhibits an initial change in Tc, and even an underdoped one only exhibits an increase in Tc, that is, one-third as much as that in the Yb-124 film. Effective carrier doping by the use of effective out-of-plane contraction prominently appears in the 124-structure rather than in the 123-structure.

  11. Observation of selective plasmon-exciton coupling in nonradiative energy transfer: donor-selective versus acceptor-selective plexcitons.

    PubMed

    Ozel, Tuncay; Hernandez-Martinez, Pedro Ludwig; Mutlugun, Evren; Akin, Onur; Nizamoglu, Sedat; Ozel, Ilkem Ozge; Zhang, Qing; Xiong, Qihua; Demir, Hilmi Volkan

    2013-07-10

    We report selectively plasmon-mediated nonradiative energy transfer between quantum dot (QD) emitters interacting with each other via Förster-type resonance energy transfer (FRET) under controlled plasmon coupling either to only the donor QDs (i.e., donor-selective) or to only the acceptor QDs (i.e., acceptor-selective). Using layer-by-layer assembled colloidal QD nanocrystal solids with metal nanoparticles integrated at carefully designed spacing, we demonstrate the ability to enable/disable the coupled plasmon-exciton (plexciton) formation distinctly at the donor (exciton departing) site or at the acceptor (exciton feeding) site of our choice, while not hindering the donor exciton-acceptor exciton interaction but refraining from simultaneous coupling to both sites of the donor and the acceptor in the FRET process. In the case of donor-selective plexciton, we observed a substantial shortening in the donor QD lifetime from 1.33 to 0.29 ns as a result of plasmon-coupling to the donors and the FRET-assisted exciton transfer from the donors to the acceptors, both of which shorten the donor lifetime. This consequently enhanced the acceptor emission by a factor of 1.93. On the other hand, in the complementary case of acceptor-selective plexciton we observed a 2.70-fold emission enhancement in the acceptor QDs, larger than the acceptor emission enhancement of the donor-selective plexciton, as a result of the combined effects of the acceptor plasmon coupling and the FRET-assisted exciton feeding. Here we present the comparative results of theoretical modeling of the donor- and acceptor-selective plexcitons of nonradiative energy transfer developed here for the first time, which are in excellent agreement with the systematic experimental characterization. Such an ability to modify and control energy transfer through mastering plexcitons is of fundamental importance, opening up new applications for quantum dot embedded plexciton devices along with the development of new

  12. InGaAs heterostructure formation in catalyst-free GaAs nanopillars by selective-area metal-organic vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    Shapiro, J. N.; Lin, A.; Wong, P. S.; Scofield, A. C.; Tu, C.; Senanayake, P. N.; Mariani, G.; Liang, B. L.; Huffaker, D. L.

    2010-12-01

    We investigate axial GaAs/InGaAs/GaAs heterostructures embedded in GaAs nanopillars via catalyst-free selective-area metal-organic chemical vapor deposition. Structural characterization by transmission electron microscopy with energy dispersive x-ray spectroscopy (EDS) indicates formation of axial InxGa1-xAs (x˜0.20) inserts with thicknesses from 36 to 220 nm with ±10% variation and graded Ga:In transitions controlled by In segregation. Using the heterointerfaces as markers, the vertical growth rate is determined to increase linearly during growth. Photoluminescence from 77 to 290 K and EDS suggest the presence of strain in the shortest inserts. This capability to control the formation of axial nanopillar heterostructures is crucial for optimized device integration.

  13. Energy efficiency of substance and energy recovery of selected waste fractions.

    PubMed

    Fricke, Klaus; Bahr, Tobias; Bidlingmaier, Werner; Springer, Christian

    2011-04-01

    In order to reduce the ecological impact of resource exploitation, the EU calls for sustainable options to increase the efficiency and productivity of the utilization of natural resources. This target can only be achieved by considering resource recovery from waste comprehensively. However, waste management measures have to be investigated critically and all aspects of substance-related recycling and energy recovery have to be carefully balanced. This article compares recovery methods for selected waste fractions with regard to their energy efficiency. Whether material recycling or energy recovery is the most energy efficient solution, is a question of particular relevance with regard to the following waste fractions: paper and cardboard, plastics and biowaste and also indirectly metals. For the described material categories material recycling has advantages compared to energy recovery. In accordance with the improved energy efficiency of substance opposed to energy recovery, substance-related recycling causes lower emissions of green house gases. For the fractions paper and cardboard, plastics, biowaste and metals it becomes apparent, that intensification of the separate collection systems in combination with a more intensive use of sorting technologies can increase the extent of material recycling. Collection and sorting systems must be coordinated. The objective of the overall system must be to achieve an optimum of the highest possible recovery rates in combination with a high quality of recyclables. The energy efficiency of substance related recycling of biowaste can be increased by intensifying the use of anaerobic technologies. In order to increase the energy efficiency of the overall system, the energy efficiencies of energy recovery plants must be increased so that the waste unsuitable for substance recycling is recycled or treated with the highest possible energy yield.

  14. Energy efficiency of substance and energy recovery of selected waste fractions

    SciTech Connect

    Fricke, Klaus; Bahr, Tobias; Bidlingmaier, Werner; Springer, Christian

    2011-04-15

    In order to reduce the ecological impact of resource exploitation, the EU calls for sustainable options to increase the efficiency and productivity of the utilization of natural resources. This target can only be achieved by considering resource recovery from waste comprehensively. However, waste management measures have to be investigated critically and all aspects of substance-related recycling and energy recovery have to be carefully balanced. This article compares recovery methods for selected waste fractions with regard to their energy efficiency. Whether material recycling or energy recovery is the most energy efficient solution, is a question of particular relevance with regard to the following waste fractions: paper and cardboard, plastics and biowaste and also indirectly metals. For the described material categories material recycling has advantages compared to energy recovery. In accordance with the improved energy efficiency of substance opposed to energy recovery, substance-related recycling causes lower emissions of green house gases. For the fractions paper and cardboard, plastics, biowaste and metals it becomes apparent, that intensification of the separate collection systems in combination with a more intensive use of sorting technologies can increase the extent of material recycling. Collection and sorting systems must be coordinated. The objective of the overall system must be to achieve an optimum of the highest possible recovery rates in combination with a high quality of recyclables. The energy efficiency of substance related recycling of biowaste can be increased by intensifying the use of anaerobic technologies. In order to increase the energy efficiency of the overall system, the energy efficiencies of energy recovery plants must be increased so that the waste unsuitable for substance recycling is recycled or treated with the highest possible energy yield.

  15. Epitaxial stabilization and phase instability of VO2 polymorphs

    DOE PAGES

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

    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. Bymore » 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. In conclusion, 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.« less

  16. 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

  17. White light generation by resonant nonradiative energy transfer from epitaxial InGaN/GaN quantum wells to colloidal CdSe/ZnS core/shell quantum dots

    NASA Astrophysics Data System (ADS)

    Nizamoglu, Sedat; Sari, Emre; Baek, Jong-Hyeob; Lee, In-Hwan; Demir, Hilmi Volkan

    2008-12-01

    We propose and demonstrate white-light-generating nonradiative energy transfer (ET) from epitaxial quantum wells (QWs) to colloidal quantum dots (QDs) in their close proximity. This proof-of-concept hybrid color-converting system consists of chemically synthesized red-emitting CdSe/ZnS core/shell heteronanocrystals intimately integrated on epitaxially grown cyan-emitting InGaN/GaN QWs. The white light is generated by the collective luminescence of QWs and QDs, for which the dot emission is further increased by 63% with nonradiative ET, setting the operating point in the white region of CIE chromaticity diagram. Using cyan emission at 490 nm from the QWs and red emission at 650 nm from the nanocrystal (NC) luminophors, we obtain warm white light generation with a correlated color temperature of Tc = 3135 K and tristimulus coordinates of (x,y) = (0.42, 0.39) in the white region. By analyzing the time-resolved radiative decay of these NC emitters in our hybrid system with a 16 ps time resolution, the luminescence kinetics reveals a fast ET with a rate of (2 ns)-1 using a multiexponential fit with χ 2 = 1.0171.

  18. Electronic structure of few-layer epitaxial graphene on Ru(0001).

    PubMed

    Sutter, P; Hybertsen, M S; Sadowski, J T; Sutter, E

    2009-07-01

    The electronic structure of epitaxial monolayer, bilayer, and trilayer graphene on Ru(0001) was determined by selected-area angle-resolved photoelectron spectroscopy (micro-ARPES). Micro-ARPES band maps provide evidence for a strong electronic coupling between monolayer graphene and the adjacent metal, which causes the complete disruption of the graphene pi-bands near the Fermi energy. However, the perturbation by the metal decreases rapidly with the addition of further graphene sheets, and already an epitaxial graphene bilayer on Ru recovers the characteristic Dirac cones of isolated monolayer graphene. A graphene trilayer on Ru behaves like free-standing bilayer graphene. Density-functional theory based calculations show that this decoupling is due to the efficient passivation of metal d-states by the interfacial graphene layer.

  19. Unusual catalyst-free epitaxial growth of silicon nanowires by thermal evaporation

    NASA Astrophysics Data System (ADS)

    Qin, Y.; Zhang, X. N.; Zheng, K.; Li, H.; Han, X. D.; Zhang, Z.

    2008-08-01

    We report a catalyst-free epitaxial growth of silicon nanowires on polyhedral facets of mother Si nanoparticles by thermal evaporation process. Single silicon nanowires and octopuslike silicon nanowires (OSNWs) were synthesized under different temperatures. The OSNWs have several directions including ⟨112⟩, ⟨110⟩, and the unusual directions of ⟨100⟩ and ⟨111⟩. A catalyst-free temperature-dependent epitaxial growth model was suggested. Using the Wulff theory and first principle calculations, these growth directions can be explained by the preferential selection of temperature-dependent surface energies. It thus revealed an important but simple growth model in which the growth directions could be delicately controlled through only determining temperature and substrate orientation.

  20. Implications of light energy on food quality and packaging selection.

    PubMed

    Duncan, Susan E; Chang, Hao-Hsun

    2012-01-01

    Light energy in the ultraviolet and visible light regions plays a critical role in overall food quality, leading to various degradation and oxidation reactions. Food degradation and oxidation result in the destruction of nutrients and bioactive compounds, the formation of off odors and flavors, the loss of food color, and the formation of toxic substances. Food compounds are sensitive to various light wavelengths. Understanding the effect that specific light wavelengths have on food compounds will allow the development of novel food packaging materials that block the most damaging light wavelengths to photostability of specific food compounds. Future research should focus more specifically on the effect of specific light wavelengths on the quality of specific food products, as there is limited published information on this particular topic. This information also can be directly related to the selection of food packaging materials to retain both high quality and visual clarity of food products exposed to light.

  1. Electrochemical Atomic Layer Epitaxy

    NASA Astrophysics Data System (ADS)

    Gregory, Brian Wayne

    1992-01-01

    Presented here are initial investigations into an electrochemical method whereby thin films of compound semiconductors are produced by epitaxial growth of the constituent elements. This method is the electrochemical analogue of atomic layer epitaxy (ALE) (a vacuum-based technique which relies on sequential formation of atomic layers of the constituent elements) and has been termed "Electrochemical atomic layer epitaxy" (ECALE). These preliminary studies are centered on the formation of CdTe, though in principle they could be extended to a number of other compound semiconductors. A background introduction on topics relevant to epitaxial growth in electrochemical systems will be presented. Predictions of underpotential behavior in the CdTe system will be made using potential -pH (Pourbaix) diagrams. Development of the method will proceed from our initial studies of Cd and Te underpotential deposition (UPD) on a number of metallic substrates, followed by results demonstrating the ECALE formation of two monolayers of CdTe on polycrystalline and single crystal gold substrates. The final chapter will present current attempts to design and construct an automated, computer-controlled thin-layer electrochemical flow cell, which is to be used for the deposition of thicker layers (up to 1 mu m) of compound semiconductors.

  2. 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.

  3. Metformin selectively targets redox control of complex I energy transduction.

    PubMed

    Cameron, Amy R; Logie, Lisa; Patel, Kashyap; Erhardt, Stefan; Bacon, Sandra; Middleton, Paul; Harthill, Jean; Forteath, Calum; Coats, Josh T; Kerr, Calum; Curry, Heather; Stewart, Derek; Sakamoto, Kei; Repiščák, Peter; Paterson, Martin J; Hassinen, Ilmo; McDougall, Gordon; Rena, Graham

    2017-08-26

    Many guanide-containing drugs are antihyperglycaemic but most exhibit toxicity, to the extent that only the biguanide metformin has enjoyed sustained clinical use. Here, we have isolated unique mitochondrial redox control properties of metformin that are likely to account for this difference. In primary hepatocytes and H4IIE hepatoma cells we found that antihyperglycaemic diguanides DG5-DG10 and the biguanide phenformin were up to 1000-fold more potent than metformin on cell signalling responses, gluconeogenic promoter expression and hepatocyte glucose production. Each drug inhibited cellular oxygen consumption similarly but there were marked differences in other respects. All diguanides and phenformin but not metformin inhibited NADH oxidation in submitochondrial particles, indicative of complex I inhibition, which also corresponded closely with dehydrogenase activity in living cells measured by WST-1. Consistent with these findings, in isolated mitochondria, DG8 but not metformin caused the NADH/NAD(+) couple to become more reduced over time and mitochondrial deterioration ensued, suggesting direct inhibition of complex I and mitochondrial toxicity of DG8. In contrast, metformin exerted a selective oxidation of the mitochondrial NADH/NAD(+) couple, without triggering mitochondrial deterioration. Together, our results suggest that metformin suppresses energy transduction by selectively inducing a state in complex I where redox and proton transfer domains are no longer efficiently coupled. Copyright © 2017 The Authors. Published by Elsevier B.V. All rights reserved.

  4. Applications of Optimal Building Energy System Selection and Operation

    SciTech Connect

    Marnay, Chris; Stadler, Michael; Siddiqui, Afzal; DeForest, Nicholas; Donadee, Jon; Bhattacharya, Prajesh; Lai, Judy

    2011-04-01

    Berkeley Lab has been developing the Distributed Energy Resources Customer Adoption Model (DER-CAM) for several years. Given load curves for energy services requirements in a building microgrid (u grid), fuel costs and other economic inputs, and a menu of available technologies, DER-CAM finds the optimum equipment fleet and its optimum operating schedule using a mixed integer linear programming approach. This capability is being applied using a software as a service (SaaS) model. Optimisation problems are set up on a Berkeley Lab server and clients can execute their jobs as needed, typically daily. The evolution of this approach is demonstrated by description of three ongoing projects. The first is a public access web site focused on solar photovoltaic generation and battery viability at large commercial and industrial customer sites. The second is a building CO2 emissions reduction operations problem for a University of California, Davis student dining hall for which potential investments are also considered. And the third, is both a battery selection problem and a rolling operating schedule problem for a large County Jail. Together these examples show that optimization of building u grid design and operation can be effectively achieved using SaaS.

  5. A review of selected energy-related data sets

    SciTech Connect

    Nicholls, A.K.; Elliott, D.B.; Jones, M.L.; Hannifan, J.M.; Degroat, K.J.; Eichner, M.J.; King, J.E.

    1992-09-01

    DOE`s Office of Planning and Assessment (OPA) performs crosscutting technical, policy, and environmental assessments of energy technologies and markets. To support these efforts, OPA is in the process of creating a data base management system (DBMS) that will include relevant data compiled from other sources. One of the first steps is a review of selected data sets that may be considered for inclusion in the DBMS. The review covered data sets in five categories: buildings-specific data, industry-specific data, transportation-specific data, utilities-specific data, and crosscutting/general data. Reviewed data sets covered a broad array of energy efficiency, renewable, and/or benchmark technologies. Most data sets reviewed in this report are sponsored by Federal government entities and major industry organizations. Additional data sets reviewed are sponsored by the states of California and New York and regional entities in the Pacific Northwest. Prior to full review, candidate data sets were screened for their utility to OPA. Screening criteria included requirements that a data set be particularly applicable to OPA`s data needs, documented, current, and obtainable. To fully implement its DBMS, OPA will need to expand the review to other data sources, and must carefully consider the implications of differing assumptions and methodologies when comparing data.

  6. A review of selected energy-related data sets

    SciTech Connect

    Nicholls, A.K.; Elliott, D.B.; Jones, M.L. ); Hannifan, J.M.; Degroat, K.J.; Eichner, M.J.; King, J.E. )

    1992-09-01

    DOE's Office of Planning and Assessment (OPA) performs crosscutting technical, policy, and environmental assessments of energy technologies and markets. To support these efforts, OPA is in the process of creating a data base management system (DBMS) that will include relevant data compiled from other sources. One of the first steps is a review of selected data sets that may be considered for inclusion in the DBMS. The review covered data sets in five categories: buildings-specific data, industry-specific data, transportation-specific data, utilities-specific data, and crosscutting/general data. Reviewed data sets covered a broad array of energy efficiency, renewable, and/or benchmark technologies. Most data sets reviewed in this report are sponsored by Federal government entities and major industry organizations. Additional data sets reviewed are sponsored by the states of California and New York and regional entities in the Pacific Northwest. Prior to full review, candidate data sets were screened for their utility to OPA. Screening criteria included requirements that a data set be particularly applicable to OPA's data needs, documented, current, and obtainable. To fully implement its DBMS, OPA will need to expand the review to other data sources, and must carefully consider the implications of differing assumptions and methodologies when comparing data.

  7. Proton Acceleration: New Developments in Energy Increase, Focusing and Energy Selection

    SciTech Connect

    D'Humieres, Emmanuel; Fuchs, Julien; Antici, Patrizio; Audebert, Patrick; Brambrink, Erik; Romagnani, Lorenzo; Borghesi, Marco; Cecchetti, Carlo Alberto; Kaluza, Malte; Schreiber, Joerg; Lefebvre, Erik; Malka, Victor; Manclossi, Mauro; Meyroneinc, Samuel; Mora, Patrick; Pepin, Henri; Pipahl, Ariane; Toncian, Toma; Willi, Oswald; Sentoku, Yasuhiko

    2006-11-27

    In the last few years, intense research has been conducted on laser-accelerated ion sources and their applications. These sources have exceptional properties, i.e. high brightness and high spectral cut-oft high directionality and laminarity, short burst duration. These proton sources open new opportunities for ion beam generation and control, and could stimulate development of compact ion accelerators for many applications. We have studied the variations of the proton acceleration characteristic time with target and laser parameters. We used these variations to correct one of the model recently developed to predict maximum energies of laser-accelerated protons for low energy, short duration laser pulses. We have also developed an ultra-fast laser-triggered micro-lens that allows tunable control of the beam divergence as well as energy selection, therefore solving two of the major problems that these proton beams were facing. We used PIC simulations to explain the focusing and energy selection mechanisms, and to study the symmetry of the expanding plasma inside the cylinder.

  8. Low temperature laser molecular beam epitaxy and characterization of AlGaN epitaxial layers

    NASA Astrophysics Data System (ADS)

    Tyagi, Prashant; Ch., Ramesh; Kushvaha, S. S.; Kumar, M. Senthil

    2017-05-01

    We have grown AlGaN (0001) epitaxial layers on sapphire (0001) by using laser molecular beam epitaxy (LMBE) technique. The growth was carried out using laser ablation of AlxGa1-x liquid metal alloy under r.f. nitrogen plasma ambient. Before epilayer growth, the sapphire nitradation was performed at 700 °C using r.f nitrogen plasma followed by AlGaN layer growth. The in-situ reflection high energy electron diffraction (RHEED) was employed to monitor the substrate nitridation and AlGaN epitaxial growth. High resolution x-ray diffraction showed wurtzite hexagonal growth of AlGaN layer along c-axis. An absorption bandgap of 3.97 eV is obtained for the grown AlGaN layer indicating an Al composition of more than 20 %. Using ellipsometry, a refractive index (n) value of about 2.19 is obtained in the visible region.

  9. 2D vibrational properties of epitaxial silicene on Ag(111)

    NASA Astrophysics Data System (ADS)

    Solonenko, Dmytro; Gordan, Ovidiu D.; Le Lay, Guy; Sahin, Hasan; Cahangirov, Seymur; Zahn, Dietrich R. T.; Vogt, Patrick

    2017-03-01

    The two-dimensional silicon allotrope, silicene, could spur the development of new and original concepts in Si-based nanotechnology. Up to now silicene can only be epitaxially synthesized on a supporting substrate such as Ag(111). Even though the structural and electronic properties of these epitaxial silicene layers have been intensively studied, very little is known about its vibrational characteristics. Here, we present a detailed study of epitaxial silicene on Ag(111) using in situ Raman spectroscopy, which is one of the most extensively employed experimental techniques to characterize 2D materials, such as graphene, transition metal dichalcogenides, and black phosphorous. The vibrational fingerprint of epitaxial silicene, in contrast to all previous interpretations, is characterized by three distinct phonon modes with A and E symmetries. Both, energies and symmetries of theses modes are confirmed by ab initio theory calculations. The temperature dependent spectral evolution of these modes demonstrates unique thermal properties of epitaxial silicene and a significant electron-phonon coupling. These results unambiguously support the purely two-dimensional character of epitaxial silicene up to about 300 °C, whereupon a 2D-to-3D phase transition takes place. The detailed fingerprint of epitaxial silicene will allow us to identify it in different environments or to study its modifications.

  10. 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.

  11. Near-Infrared Photoluminescence Enhancement in Ge/CdS and Ge/ZnS Core/Shell Nanocrystals: Utilizing IV/II-VI Semiconductor Epitaxy

    SciTech Connect

    Guo, Yijun; Rowland, Clare E; Schaller, Richard D; Vela, Javier

    2014-08-26

    Ge nanocrystals have a large Bohr radius and a small, size-tunable band gap that may engender direct character via strain or doping. Colloidal Ge nanocrystals are particularly interesting in the development of near-infrared materials for applications in bioimaging, telecommunications and energy conversion. Epitaxial growth of a passivating shell is a common strategy employed in the synthesis of highly luminescent II–VI, III–V and IV–VI semiconductor quantum dots. Here, we use relatively unexplored IV/II–VI epitaxy as a way to enhance the photoluminescence and improve the optical stability of colloidal Ge nanocrystals. Selected on the basis of their relatively small lattice mismatch compared with crystalline Ge, we explore the growth of epitaxial CdS and ZnS shells using the successive ion layer adsorption and reaction method. Powder X-ray diffraction and electron microscopy techniques, including energy dispersive X-ray spectroscopy and selected area electron diffraction, clearly show the controllable growth of as many as 20 epitaxial monolayers of CdS atop Ge cores. In contrast, Ge etching and/or replacement by ZnS result in relatively small Ge/ZnS nanocrystals. The presence of an epitaxial II–VI shell greatly enhances the near-infrared photoluminescence and improves the photoluminescence stability of Ge. Ge/II–VI nanocrystals are reproducibly 1–3 orders of magnitude brighter than the brightest Ge cores. Ge/4.9CdS core/shells show the highest photoluminescence quantum yield and longest radiative recombination lifetime. Thiol ligand exchange easily results in near-infrared active, water-soluble Ge/II–VI nanocrystals. We expect this synthetic IV/II–VI epitaxial approach will lead to further studies into the optoelectronic behavior and practical applications of Si and Ge-based nanomaterials.

  12. Selection effects on GRB spectral-energy correlations

    SciTech Connect

    Nava, Lara; Ghirlanda, Giancarlo; Ghisellini, Gabriele

    2009-05-25

    Instrumental selection effects can act upon the estimates of the peak energy E{sub peak}{sup obs}, the fluence F and the peak flux P of GRBs. If this were the case, then the correlations involving the corresponding rest frame quantities (i.e. E{sub peak}, E{sub obs} and the peak luminosity L{sub iso}) would be questioned. We estimated, as a function of E{sub peak}{sup obs}, the minimum peak flux necessary to trigger a GRB and the minimum fluence a burst must have to determine the value of E{sub peak}{sup obs} by considering different instruments (BATSE, Swift, BeppoSAX). We find that the latter dominates over the former. We then study the E{sub peak}{sup obs}-fluence (and flux) correlation in the observer plane. GRBs with redshift show well defined E{sub peak}{sup obs}-F and E{sub peak}{sup obs}-P correlations: in this planes the selection effects are present, but do not determine the found correlations. This is not true for Swift GRBs with redshift, for which the spectral analysis threshold does affect their distribution in the observer planes. Extending the sample to GRBs without z, we still find a significant E{sub peak}{sup obs}-F correlation, although with a larger scatter than that defined by GRBs with redshift. We find that 6% are outliers of the Amati correlation. The E{sub peak}{sup obs}-P correlation of GRBs with or without redshift is the same and no outlier is found among bursts without redshift.

  13. Selection of herbaceous energy crops for the western corn belt

    SciTech Connect

    Anderson, I.C.; Buxton, D.R.; Hallam, J.A.

    1994-05-01

    The ultimate economic feasibility of biomass depends on its cost of production and on the cost of competing fuels. The purpose of this research project is to evaluate the production costs of several combinations of species and management systems for producing herbaceous biomass for energy use in Iowa. Herbaceous biomass production systems have costs similar to other crop production systems, such as corn, soybean, and forages. Thus, the factors influencing the costs of producing dedicated biomass energy crops include technological factors such as the cultivation system, species, treatments, soil type, and site and economic factors such as input prices and use of fixed resources. In order to investigate how these production alternatives are influenced by soil resources, and climate conditions, two locations in Iowa, Ames and Chariton, with different soil types and slightly different weather patterns were selected for both the agronomic and economic analyses. Nine crops in thirteen cropping systems were grown at the two sites for five years, from 1988 to 1992. Some of the systems had multiple cropping or interplanting, using combinations of cool-season species and warm-season species, in order to meet multiple objectives of maximum biomass, minimal soil loss, reduced nitrogen fertilization or diminished pesticide inputs. Six of the systems use continuous monocropping of herbaceous crops with an emphasis on production. The seven other systems consist of similar crops, but with crop rotation and soil conservation considerations. While the erosion and other off-site effects of these systems is an important consideration in their overall evaluation, this report will concentrate on direct production costs only.

  14. Germanium epitaxy on silicon

    PubMed Central

    Ye, Hui; Yu, Jinzhong

    2014-01-01

    With the rapid development of on-chip optical interconnects and optical computing in the past decade, silicon-based integrated devices for monolithic and hybrid optoelectronic integration have attracted wide attention. Due to its narrow pseudo-direct gap behavior and compatibility with Si technology, epitaxial Ge-on-Si has become a significant material for optoelectronic device applications. In this paper, we describe recent research progress on heteroepitaxy of Ge flat films and self-assembled Ge quantum dots on Si. For film growth, methods of strain modification and lattice mismatch relief are summarized, while for dot growth, key process parameters and their effects on the dot density, dot morphology and dot position are reviewed. The results indicate that epitaxial Ge-on-Si materials will play a bigger role in silicon photonics. PMID:27877657

  15. Germanium epitaxy on silicon.

    PubMed

    Ye, Hui; Yu, Jinzhong

    2014-04-01

    With the rapid development of on-chip optical interconnects and optical computing in the past decade, silicon-based integrated devices for monolithic and hybrid optoelectronic integration have attracted wide attention. Due to its narrow pseudo-direct gap behavior and compatibility with Si technology, epitaxial Ge-on-Si has become a significant material for optoelectronic device applications. In this paper, we describe recent research progress on heteroepitaxy of Ge flat films and self-assembled Ge quantum dots on Si. For film growth, methods of strain modification and lattice mismatch relief are summarized, while for dot growth, key process parameters and their effects on the dot density, dot morphology and dot position are reviewed. The results indicate that epitaxial Ge-on-Si materials will play a bigger role in silicon photonics.

  16. Germanium epitaxy on silicon

    NASA Astrophysics Data System (ADS)

    Ye, Hui; Yu, Jinzhong

    2014-04-01

    With the rapid development of on-chip optical interconnects and optical computing in the past decade, silicon-based integrated devices for monolithic and hybrid optoelectronic integration have attracted wide attention. Due to its narrow pseudo-direct gap behavior and compatibility with Si technology, epitaxial Ge-on-Si has become a significant material for optoelectronic device applications. In this paper, we describe recent research progress on heteroepitaxy of Ge flat films and self-assembled Ge quantum dots on Si. For film growth, methods of strain modification and lattice mismatch relief are summarized, while for dot growth, key process parameters and their effects on the dot density, dot morphology and dot position are reviewed. The results indicate that epitaxial Ge-on-Si materials will play a bigger role in silicon photonics.

  17. Selection rules in low energy string effective lagrangians

    NASA Astrophysics Data System (ADS)

    Dolan, L.; Lau, S.

    1992-01-01

    Selection rules which restrict elementary particle interactions are derived as the low-energy limit of superstring theory. A general mechanism is demonstrated, in four-dimensional string tree-amplitudes, whereby the supersymmetric trilinear Yukawa-like couplings in the effective lagrangian which violate lepton number vanish, terms which otherwise occur naturally in supersymmetric versions of the standard model. Explicit expressions for the vertex operators, and all cubic bosonic couplings involving the Yang-Mills gauge bosons and the graviton, together with the scalar and anti-symmetric tensor components of gravity are given. There are no √2 α' corrections to the three-point string tree-amplitudes, a result which eliminates any higher derivative trilinear couplings among these fields in the effective action. In this four-dimensional string theory, expressions are derived for the gravitational coupling constant κ and the Yang-Mills coupling constant gYM in terms of the two string parameters: the universal Regge slope parameter which is the origin of the length scale √2 α', and the dimensionless string coupling constant g. We find κ = {1}/{2}g√2α' and g YM = g .

  18. Growth of strontium ruthenate films by hybrid molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

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

    2017-09-01

    We report on the growth of epitaxial Sr2RuO4 films using a hybrid molecular beam epitaxy approach in which a volatile precursor containing RuO4 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 Sr2RuO4 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 electron microscopy. 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.

  19. Epitaxial thinning process

    NASA Technical Reports Server (NTRS)

    Siegel, C. M. (Inventor)

    1984-01-01

    A method is described for thinning an epitaxial layer of a wafer that is to be used in producing diodes having a specified breakdown voltage and which also facilitates the thinning process. Current is passed through the epitaxial layer, by connecting a current source between the substrate of the wafer and an electrolyte in which the wafer is immersed. When the wafer is initially immersed, the voltage across the wafer initially drops and then rises at a steep rate. When light is applied to the wafer the voltage drops, and when the light is interrupted the voltage rises again. These changes in voltage, each indicate the breakdown voltage of a Schottky diode that could be prepared from the wafer at that time. The epitaxial layer is thinned by continuing to apply current through the wafer while it is immersed and light is applied, to form an oxide film and when the oxide film is thick the wafer can then be cleaned of oxide and the testing and thinning continued. Uninterrupted thinning can be achieved by first forming an oxide film, and then using an electrolyte that dissolves the oxide about as fast as it is being formed, to limit the thickness of the oxide layer.

  20. The growth of pinhole-free epitaxial DySi2-x films on atomically clean Si(111)

    NASA Astrophysics Data System (ADS)

    Shen, G. H.; Chen, J. C.; Lou, C. H.; Cheng, S. L.; Chen, L. J.

    1998-10-01

    The growth of pinhole-free epitaxial DySi2-x films on atomically clean Si(111) has been achieved by depositing a 2-nm-thick Dy layer onto Si(111) with a 1.5-nm-thick capping amorphous Si (a-Si) layer at room temperature followed by annealing at 700 °C in ultrahigh vacuum. The thickness of the a-Si was selected to be such that the consumption of Si atoms from the substrate is minimized by taking into account the formation of an amorphous interlayer at the Dy/Si(111) interface. Based on our experimental findings, a new mechanism for the formation of pinhole is proposed. The Stranski-Krastanov growth behavior of epitaxial DySi2-x on Si(111) by solid phase epitaxy leads to the apparently random formation of a high density of recessed regions at the initial stage of silicidation. Polycrystalline DySi2-x was found to be present at the areas inside and epitaxial DySi2-x outside the recessed regions. Large numbers of Si atoms from the substrate can therefore diffuse through the recessed regions. As a result, the depth and size of the recessed regions increase with annealing time. Finally, the DySi2-x thin layer inside the recessed regions with higher interface energy is thermally unstable and breaks apart to form pinholes.

  1. Net energy analysis - powerful tool for selecting elective power options

    SciTech Connect

    Baron, S.

    1995-12-01

    A number of net energy analysis studies have been conducted in recent years for electric power production from coal, oil and uranium fuels; synthetic fuels from coal and oil shale; and heat and electric power from solar energy. This technique is an excellent indicator of investment costs, environmental impact and potential economic competitiveness of alternative electric power systems for energy planners from the Eastern European countries considering future options. Energy conservation is also important to energy planners and the net energy analysis technique is an excellent accounting system on the extent of energy resource conservation. The author proposes to discuss the technique and to present the results of his studies and others in the field. The information supplied to the attendees will serve as a powerful tool to the energy planners considering their electric power options in the future.

  2. Time gating for energy selection and scatter rejection: High-energy pulsed neutron imaging at LANSCE

    NASA Astrophysics Data System (ADS)

    Swift, Alicia; Schirato, Richard; McKigney, Edward; Hunter, James; Temple, Brian

    2015-09-01

    The Los Alamos Neutron Science Center (LANSCE) is a linear accelerator in Los Alamos, New Mexico that accelerates a proton beam to 800 MeV, which then produces spallation neutron beams. Flight path FP15R uses a tungsten target to generate neutrons of energy ranging from several hundred keV to ~600 MeV. The beam structure has micropulses of sub-ns width and period of 1.784 ns, and macropulses of 625 μs width and frequency of either 50 Hz or 100 Hz. This corresponds to 347 micropulses per macropulse, or 1.74 x 104 micropulses per second when operating at 50 Hz. Using a very fast, cooled ICCD camera (Princeton Instruments PI-Max 4), gated images of various objects were obtained on FP15R in January 2015. Objects imaged included blocks of lead and borated polyethylene; a tungsten sphere; and a tungsten, polyethylene, and steel cylinder. Images were obtained in 36 min or less, with some in as little as 6 min. This is novel because the gate widths (some as narrow as 10 ns) were selected to reject scatter and other signal not of interest (e.g. the gamma flash that precedes the neutron pulse), which has not been demonstrated at energies above 14 MeV. This proof-of-principle experiment shows that time gating is possible above 14MeV and is useful for selecting neutron energy and reducing scatter, thus forming clearer images. Future work (simulation and experimental) is being undertaken to improve camera shielding and system design and to precisely determine optical properties of the imaging system.

  3. Morphology evolution and emission properties of InGaN/GaN multiple quantum wells grown on GaN microfacets using crossover stripe patterns by selective area epitaxy

    NASA Astrophysics Data System (ADS)

    Wu, Zhenlong; Chen, Peng; Yang, Guofeng; Xu, Zhou; Xu, Feng; Jiang, Fulong; Zhang, Rong; Zheng, Youdou

    2015-03-01

    We investigate the morphological evolution of selective area epitaxy (SAE) GaN microfacets structures on crossover stripe patterns as a function of temperature, and the emission properties of semipolar InGaN/GaN multiple quantum wells (MQWs) grown on these microstructures with semipolar facets are also studied. The shapes of inner rings gradually change from nearly rectangular to hexagonal when the GaN growth temperature elevates, as a result of growth rates and surface stability varies with elevated temperatures. Three types of semipolar facets ({1 1 -2 2}, {2 1 -3 3} and {1 -1 0 1} facets) can be identified on the inner rings of these structures, which are verified by the emission properties of semipolar InGaN/GaN MQWs. The emission wavelengths of MQWs on these semipolar facets are ordered as {1 -1 0 1} > {2 1 -3 3} > {1 1 -2 2}, which is attributed to variations of growth rate and indium incorporation on different planes during InGaN growth. Furthermore, the indium composition of MQWs changes with the morphological evolution.

  4. Energy metabolism, fuel selection and body weight regulation.

    PubMed

    Galgani, J; Ravussin, E

    2008-12-01

    Energy homeostasis is critical for the survival of species. Therefore, multiple and complex mechanisms have evolved to regulate energy intake and expenditure to maintain body weight. For weight maintenance, not only does energy intake have to match energy expenditure, but also macronutrient intake must balance macronutrient oxidation. However, this equilibrium seems to be particularly difficult to achieve in individuals with low fat oxidation, low energy expenditure, low sympathetic activity or low levels of spontaneous physical activity, as in addition to excess energy intake, all of these factors explain the tendency of some people to gain weight. Additionally, large variability in weight change is observed when energy surplus is imposed experimentally or spontaneously. Clearly, the data suggest a strong genetic influence on body weight regulation implying a normal physiology in an 'obesogenic' environment. In this study, we also review evidence that carbohydrate balance may represent the potential signal that regulates energy homeostasis by impacting energy intake and body weight. Because of the small storage capacity for carbohydrate and its importance for metabolism in many tissues and organs, carbohydrate balance must be maintained at a given level. This drive for balance may in turn cause increased energy intake when consuming a diet high in fat and low in carbohydrate. If sustained over time, such an increase in energy intake cannot be detected by available methods, but may cause meaningful increases in body weight. The concept of metabolic flexibility and its impact on body weight regulation is also presented.

  5. Energy metabolism, fuel selection and body weight regulation

    PubMed Central

    Galgani, J; Ravussin, E

    2010-01-01

    Energy homeostasis is critical for the survival of species. Therefore, multiple and complex mechanisms have evolved to regulate energy intake and expenditure to maintain body weight. For weight maintenance, not only does energy intake have to match energy expenditure, but also macronutrient intake must balance macronutrient oxidation. However, this equilibrium seems to be particularly difficult to achieve in individuals with low fat oxidation, low energy expenditure, low sympathetic activity or low levels of spontaneous physical activity, as in addition to excess energy intake, all of these factors explain the tendency of some people to gain weight. Additionally, large variability in weight change is observed when energy surplus is imposed experimentally or spontaneously. Clearly, the data suggest a strong genetic influence on body weight regulation implying a normal physiology in an ‘obesogenic’ environment. In this study, we also review evidence that carbohydrate balance may represent the potential signal that regulates energy homeostasis by impacting energy intake and body weight. Because of the small storage capacity for carbohydrate and its importance for metabolism in many tissues and organs, carbohydrate balance must be maintained at a given level. This drive for balance may in turn cause increased energy intake when consuming a diet high in fat and low in carbohydrate. If sustained over time, such an increase in energy intake cannot be detected by available methods, but may cause meaningful increases in body weight. The concept of metabolic flexibility and its impact on body weight regulation is also presented. PMID:19136979

  6. Island morphologies in epitaxial growth.

    NASA Astrophysics Data System (ADS)

    Hessinger, Uwe; Leskovar, M.; Rumaner, Lee; Ohuchi, Fumio; Olmstead, Marjorie A.; Ueno, Keiji; Koma, Atsushi

    1996-03-01

    Growth of epitaxial films commonly occurs through the coalescence of individual islands. The morphology of islands has therefore a key importance for the film qualities desired. A uniform layer-by-layer growth of the film is achieved when islands in the first layer coalesce to form a uniform layer before a second layer nucleates; a non-uniform multi-layer growth results from multiple layers successively nucleating on top of each other before the first layer coalesces. We developed a kinetic model based on an analytic solution of the diffusion equation between nucleation events to calculate the evolving island morphology during growth. The morphologies depend on deposition rate, substrate temperature, and activation energies for surface diffusion on the substrate and deposited material. By applying this theory to atomic force microscopy data of GaSe multi-layer islands, we extract a value for the activation energy for Ga diffusion across steps of GaSe. Supported by NSF Grant No. ECS-9209652, DOE Grant No. DE-FG06-94ER45516, and the Japanese New Energy Development Organization.

  7. Molecular Beam Epitaxy of

    NASA Astrophysics Data System (ADS)

    Hsieh, Kuan Hsiung

    Ga(,0.48)In(,0.52)As recently emerges as a promising material for high speed applications. It also has a direct bandgap with gap energy suitable for optical applications. It is the purpose of this thesis to grow high quality Ga(,0.47)In(,0.53)As, lattice-matched Al(,0.48)In(,0.52)As and heterojunction structures by molecular beam epitaxy technique for applications in the areas of modulation-doped high mobility devices and internal photoemission Schottky diodes for infrared detection. Single crystal Al metal deposition on GaInAs by MBE is also studied for its electrical properties. Mobility enhancement has been demonstrated in modulation-doped structures at low temperatures. Very high mobilities were obtained: 10,900 cm('2)/Vs at room temperature, 55,500 cm('2)/Vs at 77K and 70,200 cm('2)/Vs at 10K with corresponding two-dimensional electron gas densities greater than 1 x 10('12) l/cm('2). The quality of Ga(,0.47)In(,0.53)As and the parallel conduction in this material are the limiting factors in its mobility. A new ohmic contact phenomenon has been observed in the MBE single crystal Al metal on Ga(,0.47)In(,0.53)AS samples. Its contact resistivity is measured to be as small as 1 x 10('-6) (OMEGA)-cm('2). The Fermi-level pinning near the conduction band edge might be caused by the interface defects. A planar doping technique has been employed to enhance the built-in barrier height to a value of about 0.5 eV in the single crystal Al on n-p('+)-n-Ga(,0.47)In(,0.52)As structures. This novel quasi-Schottky diode also shows a forward ideal factor of 1.03. As for optical detectors, four kinds of diodes were made for internal photoemission studies: Au Schottky on Ga(,0.47)In(,0.53)As in the wavelength range of 1.9 (mu)m to 2.5 (mu)m, Au Schottky on Al(,0.48)In(,0.52)As in 1.1 (mu)m to 2.0 (mu)m range, single crystal Al on (Al(,0.8)Ga(,0.2))(,0.48)In(,0.52)As with improved quantum yields and lastly a Ga(,0.47)In(,0.53)As/Al(,0.48)In(,0.52)As heterojunction with a measured

  8. Epitaxial europium oxide on Ni(100) with single-crystal quality

    SciTech Connect

    Foerster, Daniel F.; Klinkhammer, Juergen; Busse, Carsten; Altendorf, Simone G.; Michely, Thomas; Hu Zhiwei; Chin Yiying; Tjeng, L. H.; Coraux, Johann; Bourgault, Daniel

    2011-01-15

    High quality epitaxy of EuO on Ni(100) is developed in an in situ scanning tunneling microscopy (STM) and low-energy electron diffraction (LEED) study. A careful selection of the initial growth parameters is decisive to obtain a surface oxide suitable for the subsequent epitaxy of single phase EuO(100). After the creation of a three layer thick coalesced oxide film for the subsequent growth a distillation technique is applied. Appropriate annealing of films with up to 100 nm thickness generates sufficient conductivity for STM and electron spectroscopies. Oxygen vacancies are directly imaged by STM. They are of decisive importance for the metal-to-insulator transition around the temperature of the ferromagnetic-to-paramagnetic transition. A fast relaxation of the initial biaxial strain observed by LEED leaves little hope for an increase of the Curie temperature through epitaxial compression. Ex situ x-ray adsorption spectroscopy and magneto-optical Kerr effect microscopy measurements of thicker films are consistent with the stoichiometric single phase EuO with bulk properties.

  9. Theoretical Minimum Energies to Produce Steel for Selected Conditions

    SciTech Connect

    Fruehan, R.J.; Fortini, O.; Paxton, H.W.; Brindle, R.

    2000-05-01

    The energy used to produce liquid steel in today's integrated and electric arc furnace (EAF) facilities is significantly higher than the theoretical minimum energy requirements. This study presents the absolute minimum energy required to produce steel from ore and mixtures of scrap and scrap alternatives. Additional cases in which the assumptions are changed to more closely approximate actual operating conditions are also analyzed. The results, summarized in Table E-1, should give insight into the theoretical and practical potentials for reducing steelmaking energy requirements. The energy values have also been converted to carbon dioxide (CO{sub 2}) emissions in order to indicate the potential for reduction in emissions of this greenhouse gas (Table E-2). The study showed that increasing scrap melting has the largest impact on energy consumption. However, scrap should be viewed as having ''invested'' energy since at one time it was produced by reducing ore. Increasing scrap melting in the BOF mayor may not decrease energy if the ''invested'' energy in scrap is considered.

  10. A Data Envelopment Analysis Model for Renewable Energy Technology Selection

    USDA-ARS?s Scientific Manuscript database

    Public and media interest in alternative energy sources, such as renewable fuels, has rapidly increased in recent years due to higher prices for oil and natural gas. However, the current body of research providing comparative decision making models that either rank these alternative energy sources a...

  11. Selected Energy Conservation Options for Homeowners: Options, Expenses and Payoffs.

    ERIC Educational Resources Information Center

    Lengyel, Dorothy L.; And Others

    This publication is a check list for homeowners and renters to help them reduce energy costs. The list consists of 126 energy conservation options. These options range from "change clothes instead of adjusting thermostat" and "air conditioners turned off when not home" to "use sink stopper" and "weatherstripping…

  12. Selected Energy Education Activities for Pennsylvania Middle School Grades. Draft.

    ERIC Educational Resources Information Center

    Hack, Nancy; And Others

    These activities are intended to help increase awareness and understanding of the energy situation and to encourage students to become energy conservationists. The document is divided into sections according to discipline area. A final section is devoted to interdisciplinary activities involving several discipline areas integrated with the energy…

  13. Summary of selected compressed air energy storage studies

    SciTech Connect

    Allen, R.D.; Doherty, T.J.; Kannberg, L.D.

    1985-01-01

    A descriptive summarily of research and development in compressed air energy storage technology is presented. Research funded primarily by the Department of Energy is described. Results of studies by other groups and experience at the Huntorf plant in West Germany are included. Feasibility studies performed by General Electric are summarized. The feasibility of air storage in dissolved salt cavities is also demonstrated. (BCS)

  14. Nanocluster dynamics in fast rate epitaxy under mesoplasma condition

    NASA Astrophysics Data System (ADS)

    Chen, L. W.; Shibuta, Y.; Kambara, M.; Yoshida, T.

    2013-03-01

    The dynamics of Si nano-clusters during epitaxial growth has been investigated with molecular dynamics simulation using the Tersoff potential. Several nm sized Si cluster formed during rapid cooling was found to deform instantaneously upon impingement on a Si(1 0 0) substrate at the same time with the spontaneous ordering of the atomic structure to that of the substrate. Due to the increased fraction of high-energy atoms at the surface, smaller clusters (˜1 nm) are favorable for such a deformation even at lower temperatures. This is the advantage of loosely-bound cluster as growth precursor to attain epitaxy with reduced impact energies.

  15. Magnetic Nanostructures by Adaptive Twinning in Strained Epitaxial Films

    NASA Astrophysics Data System (ADS)

    Kauffmann-Weiss, Sandra; Gruner, Markus E.; Backen, Anja; Schultz, Ludwig; Entel, Peter; Fähler, Sebastian

    2011-11-01

    We exploit the intrinsic structural instability of the Fe70Pd30 magnetic shape memory alloy to obtain functional epitaxial films exhibiting a self-organized nanostructure. We demonstrate that coherent epitaxial straining by 54% is possible. The combination of thin film experiments and large-scale first-principles calculations enables us to establish a lattice relaxation mechanism, which is not expected for stable materials. We identify a low twin boundary energy compared to a high elastic energy as key prerequisite for the adaptive nanotwinning. Our approach is versatile as it allows to control both, nanostructure and intrinsic properties for ferromagnetic, ferroelastic, and ferroelectric materials.

  16. Research Update: Enhancement of figure of merit for energy-harvesters based on free-standing epitaxial Pb(Zr0.52Ti0.48)0.99Nb0.01O3 thin-film cantilevers

    NASA Astrophysics Data System (ADS)

    Nguyen, Minh D.; Houwman, Evert; Dekkers, Matthijn; Schlom, Darrell; Rijnders, Guus

    2017-07-01

    All-oxide free-standing cantilevers were fabricated with epitaxial (001)-oriented Pb(Zr0.52Ti0.48)O3 (PZT) and Pb(Zr0.52Ti0.48)0.99Nb0.01O3 (PNZT) as piezoelectric layers and SrRuO3 electrodes. The ferroelectric and piezoelectric hysteresis loops were measured. From the zero-bias values, the figure-of-merits (FOMs) for piezoelectric energy harvesting systems were calculated. For the PNZT cantilever, an extremely large value FOM = 55 GPa was obtained. This very high value is due to the large shifts of the hysteresis loops such that the zero-bias piezoelectric coefficient e31f is maximum and the zero-bias dielectric constant is strongly reduced compared to the value in the undoped PZT device. The results show that by engineering the self-bias field the energy-harvesting properties of piezoelectric systems can be increased significantly.

  17. Energy resources in southern Africa: a select bibliography

    SciTech Connect

    Cavan, A.

    1981-01-01

    The aims, progress, and possibilities involved in Southern Africa's energy development are the subject of this 473-item bibliography. The primary items of information described in this document are relatively recent (1975-81), originate from both indigenous and international sources, and are mostly in English, although a few are in French and Portuguese. The presented information focuses on the African continent, the Southern African region, and the nations of Angola, Botswana, Lesotho, Malawi, Mozambique, Namibia, Swaziland, South Africa, Tanzania, Zambia, and Zimbabwe. The energy source topics include alcohol, coal, gas, oil, solar, uranium, water, wind, and wood; as well as a general energy-development category.

  18. Analysis of interface formation mechanism in GaN double-polarity selective-area growth by metalorganic vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    Kuze, Kenta; Osumi, Noriyuki; Fujita, Yohei; Inoue, Yoku; Nakano, Takayuki

    2016-05-01

    The fabrication of quasi-phase-matching (QPM) crystals by selective-area growth on the two asymmetrically polar surfaces of GaN is examined. We attempted the fabrication of GaN-QPM crystals by one-time growth using a carbon mask. For GaN double-polarity selective-area growth (DP-SAG), we investigated the effect of varied nitriding times of the Al2O3 templates patterned with the carbon mask. We optimized the nitriding conditions for the DP-SAG process, and evaluated the substrate fabricated by the optimized DP-SAG process. In addition, we examined the interface formation mechanism of DP-GaN fabricated by GaN DP-SAG process. We determined that it is possible to fabricate DP-GaN with a sharp interface by optimizing the growth conditions.

  19. Growth of pseudomorphic structures through organic epitaxy

    SciTech Connect

    Kaviyil, Sreejith Embekkat; Sassella, Adele; Borghesi, Alessandro; Campione, Marcello; Su Genbo; He Youping; Chen Chenjia

    2012-12-14

    The control of molecular orientation in thin solid film phases of organic semiconductors is a basic factor for the exploitation of their physical properties for optoelectronic devices. We compare structural and optical properties of thin films of the organic semiconductor {alpha}-quarterthiophene grown by molecular beam epitaxy on different organic substrates. We show how epitactic interactions, characteristic of the surface of organic crystals, can drive the orientation of the crystalline overlayer and the selection of specific polymorphs and new pseudomorphic phases. We identify a key role in this phenomenon played by the marked groove-like corrugations present in some organic crystal surfaces. Since different polymorphs possess rather different performance in terms of, e.g., charge carrier mobility, this strategy is demonstrated to allow for the growth of oriented phases with enhanced physical properties, while keeping the substrate at room temperature. These results provide useful guidelines for the design of technological substrates for organic epitaxy and they substantiate the adoption of an organic epitaxy approach for the fabrication of optoelectronic devices based on thin films of organic semiconductors.

  20. Spectrally Selective Surface Coatings for Energy Efficiency and Solar Applications.

    ERIC Educational Resources Information Center

    Granqvist, C. G.

    1984-01-01

    Outlines how the radiative properties of a surface can be tailored so as to be favorable for efficient utilization of energy. The radiative properties of concern are transmittance, reflectance, absorptance, and emittance. (JN)

  1. Energy Saving Glass Lamination via Selective Radio Frequency Heating

    SciTech Connect

    Shawn M. Allan; Patricia M. Strickland; Holly S. Shulman

    2009-11-11

    Ceralink Inc. developed FastFuse™, a rapid, new, energy saving process for lamination of glass and composites using radio frequency (RF) heating technology. The Inventions and Innovations program supported the technical and commercial research and development needed to elevate the innovation from bench scale to a self-supporting technology with significant potential for growth. The attached report provides an overview of the technical and commerical progress achieved for FastFuse™ during the course of the project. FastFuse™ has the potential to revolutionize the laminate manufacturing industries by replacing energy intensive, multi-step processes with an energy efficient, single-step process that allows higher throughput. FastFuse™ transmits RF energy directly into the interlayer to generate heat, eliminating the need to directly heat glass layers and the surrounding enclosures, such as autoclaves or vacuum systems. FastFuse™ offers lower start-up and energy costs (up to 90% or more reduction in energy costs), and faster cycles times (less than 5 minutes). FastFuse™ is compatible with EVA, TPU, and PVB interlayers, and has been demonstrated for glass, plastics, and multi-material structures such as photovoltaics and transparent armor.

  2. Energy/Environment/Economy. An Annotated Bibliography of Selected U.S. Government Publications Concerning United States Energy Policy, Supplement.

    ERIC Educational Resources Information Center

    ENVIRO/INFO, Green Bay, WI.

    This annotated bibliography supplements ED 077 704. It provides a selective listing of 93 U.S. Federal Government publications germane to the energy crisis and its attendant environmental and economic implications. Primary emphasis is placed upon documents presenting energy policy issues which have emerged, plus statistical reportage which…

  3. Energy/Environment/Economy. An Annotated Bibliography of Selected U.S. Government Publications Concerning United States Energy Policy, Supplement.

    ERIC Educational Resources Information Center

    ENVIRO/INFO, Green Bay, WI.

    This annotated bibliography supplements ED 077 704. It provides a selective listing of 93 U.S. Federal Government publications germane to the energy crisis and its attendant environmental and economic implications. Primary emphasis is placed upon documents presenting energy policy issues which have emerged, plus statistical reportage which…

  4. Dissociation of energy-selected 1,1-dimethylhydrazine ions.

    PubMed

    Gengeliczki, Zsolt; Borkar, Sampada N; Sztáray, Bálint

    2010-05-27

    The unimolecular dissociation of 1,1-dimethylhydrazine ions was studied by threshold photoelectron photoion coincidence spectroscopy (TPEPICO). Time-of-flight distributions and breakdown curves were recorded in the photon energy range of 9.5-10.4 eV. The 0 K appearance energies of the fragment ions were extracted by modeling the experimental data with rigid activated complex (RAC-) RRKM theory. It was found that the data could be well-reproduced with a single TS for each dissociation channel if two different H-loss channels were assumed, one corresponding to a C-H and the other to a N-H bond dissociation. Once the appearance energies were established, heats of formation of the fragment ions could be derived. The heat of formation of the neutral molecule was computed by applying composite ab initio methods (G3, CBS-APNO, W1U) on a series of isodesmic reactions between methyl hydrazines and methyl amines.

  5. Energy Saving Glass Lamination via Selective Radio-Frequency Heating

    SciTech Connect

    Shulman, Holly S.; Allan, Shawn M.

    2009-11-11

    This Inventions and Innovations program supported the technical and commercial research and development needed to elevate Ceralink's energy saving process for flat glass lamination from bench scale to a self-supporting technology with significant potential for growth. Radio-frequency heating was any un-explored option for laminating glass prior to this program. With significant commercial success through time and energy savings in the wood, paper, and plastics industries, RF heating was found to have significant promise for the energy intensive glass lamination industry. A major technical goal of the program was to demonstrate RF lamination across a wide range of laminate sizes and materials. This was successfully accomplished, dispelling many skeptics' concerns about the abilities of the technology. Ceralink laminated panels up to 2 ft x 3 ft, with four sets processed simultaneously, in a 3 minute cycle. All major categories of interlayer materials were found to work with RF lamination. In addition to laminating glass, other materials including photovoltaic silicon solar cells, light emitting diodes, metallized glass, plastics (acrylic and polycarbonate), and ceramics (alumina) were found compatible with the RF process. This opens up a wide range of commercial opportunities beyond the initially targeted automotive industry. The dramatic energy savings reported for RF lamination at the bench scale were found to be maintained through the scale up of the process. Even at 2 ft x 3 ft panel sizes, energy savings are estimated to be at least 90% compared to autoclaving or vacuum lamination. With targeted promotion through conference presentations, press releases and internet presence, RF lamination has gained significant attention, drawing large audiences at American Ceramic Society meetings. The commercialization success of the project includes the establishment of a revenue-generating business model for providing process development and demonstrations for potential RF

  6. Pattern-dependent anisotropic stress evaluation in SiGe epitaxially grown on a Si substrate with selective Ar+ ion implantation using oil-immersion Raman spectroscopy

    NASA Astrophysics Data System (ADS)

    Yamamoto, Shotaro; Kosemura, Daisuke; Takeuchi, Kazuma; Ishihara, Seiya; Sawano, Kentarou; Nohira, Hiroshi; Ogura, Atsushi

    2017-05-01

    Biaxial stress states in SiGe stripes on Si substrates fabricated by a novel selective Ar+ ion implantation technique were evaluated by oil-immersion Raman spectroscopy. The oil-immersion technique is appropriate for the measurement of strain induced in nanostructure devices, because it has a higher spatial resolution than conventional Raman spectroscopy and can evaluate anisotropic stress states owing to the excitation of multiple optical phonon modes. Results indicate that quasi-uniaxial stress states exist in SiGe layers in unimplanted Si areas, which depends on the stripe-width ratio of implanted and unimplanted areas, and that quasi-uniaxial stress states are successfully induced in SiGe by the present technique, which can be considered as the channel materials of high-performance transistors.

  7. Selecting herbaceous energy crops for the southeast and midwest/lake states

    SciTech Connect

    Cushman, J.H.; Turhollow, A.F.

    1990-01-01

    This paper summarizes an approach to crop selection and development that has evolved through the five years of species screening and selection in the US Department of Energy's Herbaceous Energy Crops Program. The first phase of this program was designed to identify a number of species for development as energy crops for the Southeast and Midwest/Lake States, specifically as feedstocks for the biochemical and thermochemical conversion processes for alcohol fuels now under development. 14 refs., 1 tab.

  8. Energy values for whole trees and crowns of selected species.

    Treesearch

    James O. Howard

    1988-01-01

    Energy values, BTU's (British thermal units) per ovendry pound, were determined for whole-tree and crown materials from western hemlock (Tsuga heterophylla (Raf.) Sarg.), coast Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco var. menziesii), and western redcedar (Thuja plicata Donn ex D. Don)....

  9. Analyses of Selected Provisions of Proposed Energy Legislation: 2003

    EIA Publications

    2003-01-01

    This study responds to a July 31, 2003 request from Senator Byron L. Dorgan. The study is based primarily on analyses the Energy Information Administration has previously done for studies requested by Congress. It includes analysis of the Renewable Portfolio Standard, Renewable Fuels Standard, production in the Alaskan National Wildlife Refuge, the construction of an Alaskan Natural Gas pipeline, and various tax provisions.

  10. Energy coupling in Saccharomyces cerevisiae: selected opportunities for metabolic engineering.

    PubMed

    de Kok, Stefan; Kozak, Barbara U; Pronk, Jack T; van Maris, Antonius J A

    2012-06-01

    Free-energy (ATP) conservation during product formation is crucial for the maximum product yield that can be obtained, but often overlooked in metabolic engineering strategies. Product pathways that do not yield ATP or even demand input of free energy (ATP) require an additional pathway to supply the ATP needed for product formation, cellular maintenance, and/or growth. On the other hand, product pathways with a high ATP yield may result in excess biomass formation at the expense of the product yield. This mini-review discusses the importance of the ATP yield for product formation and presents several opportunities for engineering free-energy (ATP) conservation, with a focus on sugar-based product formation by Saccharomyces cerevisiae. These engineering opportunities are not limited to the metabolic flexibility within S. cerevisiae itself, but also expression of heterologous reactions will be taken into account. As such, the diversity in microbial sugar uptake and phosphorylation mechanisms, carboxylation reactions, product export, and the flexibility of oxidative phosphorylation via the respiratory chain and H(+) -ATP synthase can be used to increase or decrease free-energy (ATP) conservation. For product pathways with a negative, zero or too high ATP yield, analysis and metabolic engineering of the ATP yield of product formation will provide a promising strategy to increase the product yield and simplify process conditions. © 2012 Federation of European Microbiological Societies. Published by Blackwell Publishing Ltd. All rights reserved.

  11. Determinants of Household Use of Selected Energy Star Appliances

    EIA Publications

    2016-01-01

    The main objective of this paper is to test a series of hypotheses regarding the influences of household characteristics (such as education, age, sex, race, income, and size of household), building characteristics (such as age, ownership, and type), and electricity prices on the use of ENERGY STAR appliances.

  12. Energy Savings in School Buildings: A Selected Checklist.

    ERIC Educational Resources Information Center

    Wismer, Don, Comp.

    The 43 references in this booklet emphasize practical, rather than theoretical, information. They were chosen on that basis from two computer-retrievable data bases maintained by the U.S. Department of Energy. The citations, for the most part, are arranged by source and include industry pamphlets, journal articles, and state and consultant…

  13. The Energy-Wise Homebuyer: A Guide to Selecting an Energy-Efficient Home.

    ERIC Educational Resources Information Center

    Hogarth, Peter T.; And Others

    Presented is a guide for purchasers of new or used homes who wish to make informed comparisons of energy costs. Included are 12 energy features to look for, detailed energy checklists, and charts for calculating energy expenses. Among the considerations discussed are heating systems, insulation, thermostats, caulking and weatherstripping, and…

  14. Method for making an aluminum or copper substrate panel for selective absorption of solar energy

    NASA Technical Reports Server (NTRS)

    Roberts, M. L.; Sharpe, M. H.; Krupnick, A. C. (Inventor)

    1978-01-01

    A panel is described for selectively absorbing solar energy comprising an aluminum substrate. A zinc layer was covered by a layer of nickel and an outer layer of solar energy absorbing nickel oxide or a copper substrate with a nickel layer. A layer of solar energy absorbing nickel oxide distal from the copper substrate was included. A method for making these panels is disclosed.

  15. On-site energy consumption and selected emissions at softwood sawmills in the southwestern United States

    Treesearch

    Dan Loeffler; Nathaniel Anderson; Todd A. Morgan; Colin B. Sorenson

    2016-01-01

    Presently there is a lack of information describing US southwestern energy consumption and emissions generated from the sawmilling industry. This article uses a mail survey of softwood sawmills in the states of Arizona, Colorado, and New Mexico to develop a profile of on-site energy consumption and selected emissions for the industry. Energy consumption is...

  16. Epitaxial BaTiO{sub 3}(100) films on Pt(100): A low-energy electron diffraction, scanning tunneling microscopy, and x-ray photoelectron spectroscopy study

    SciTech Connect

    Foerster, Stefan; Huth, Michael; Schindler, Karl-Michael; Widdra, Wolf

    2011-09-14

    The growth of epitaxial ultrathin BaTiO{sub 3} films on a Pt(100) substrate has been studied by scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), and x-ray photoelectron spectroscopy (XPS). The films have been prepared by radio-frequency-assisted magnetron sputter deposition at room temperature and develop a long-range order upon annealing at 900 K in O{sub 2}. By adjusting the Ar and O{sub 2} partial pressures of the sputter gas, the stoichiometry was tuned to match that of a BaTiO{sub 3}(100) single crystal as determined by XPS. STM reveals the growth of continuous BaTiO{sub 3} films with unit cell high islands on top. With LEED already for monolayer thicknesses, the formation of a BaTiO{sub 3}(100)-(1 x 1) structure has been observed. Films of 2-3 unit cell thickness show a brilliant (1 x 1) LEED pattern for which an extended set of LEED I-V data has been acquired. At temperatures above 1050 K the BaTiO{sub 3} thin film starts to decay by formation of vacancy islands. In addition (4 x 4) and (3 x 3) surface reconstructions develop upon prolonged heating.

  17. Apparatus for generating coherent infrared energy of selected wavelength

    DOEpatents

    Stevens, C.G.

    A tunable source of coherent infrared energy includes a heat pipe having an intermediate region at which cesium is heated to vaporizing temperature and end regions at which the vapor is condensed and returned to the intermediate region for reheating and recirculation. Optical pumping light is directed along the axis of the heat pipe through a first end window to stimulate emission of coherent infrared energy which is transmitted out through an opposite end window. A porous walled tubulation extends along the axis of the heat pipe and defines a region in which cesium vapor is further heated to a temperature sufficient to dissociate cesium dimers which would decrease efficiency by absorbing pump light. Efficient generation of any desired infrared wavelength is realized by varying the wavelength of the pump light.

  18. Apparatus for generating coherent infrared energy of selected wavelength

    DOEpatents

    Stevens, Charles G.

    1985-01-01

    A tunable source (11) of coherent infrared energy includes a heat pipe (12) having an intermediate region (24) at which cesium (22) is heated to vaporizing temperature and end regions (27, 28) at which the vapor is condensed and returned to the intermediate region (24) for reheating and recirculation. Optical pumping light (43) is directed along the axis of the heat pipe (12) through a first end window (17) to stimulate emission of coherent infrared energy which is transmitted out through an opposite end window (18). A porous walled tubulation (44) extends along the axis of the heat pipe (12) and defines a region (46) in which cesium vapor is further heated to a temperature sufficient to dissociate cesium dimers which would decrease efficiency by absorbing pump light (43). Efficient generation of any desired infrared wavelength is realized by varying the wavelength of the pump light (43).

  19. Selective chemical detection by energy modulation of sensors

    DOEpatents

    Stetter, J.R.; Otagawa, T.

    1985-05-20

    A portable instrument for use in the field in detecting, identifying, and quantifying a component of a sampled fluid includes a sensor which chemically reacts with the component of interest or a derivative thereof, an electrical heating filament for heating the sample before it is applied to the sensor, and modulating means for continuously varying the temperature of the filament (and hence the reaction rate) between two values sufficient to produce the chemical reaction. In response to this thermal modulation, the sensor produces a modulated output signal, the modulation of which is a function of the activation energy of the chemical reaction, which activation energy is specific to the particular component of interest and its concentration. Microprocessor means compares the modulated output signal with standard responses for a plurality of components to identify and quantify the particular component of interest. 4 figs.

  20. Laser-synthesized epitaxial graphene.

    PubMed

    Lee, Sangwon; Toney, Michael F; Ko, Wonhee; Randel, Jason C; Jung, Hee Joon; Munakata, Ko; Lu, Jesse; Geballe, Theodore H; Beasley, Malcolm R; Sinclair, Robert; Manoharan, Hari C; Salleo, Alberto

    2010-12-28

    Owing to its unique electronic properties, graphene has recently attracted wide attention in both the condensed matter physics and microelectronic device communities. Despite intense interest in this material, an industrially scalable graphene synthesis process remains elusive. Here, we demonstrate a high-throughput, low-temperature, spatially controlled and scalable epitaxial graphene (EG) synthesis technique based on laser-induced surface decomposition of the Si-rich face of a SiC single-crystal. We confirm the formation of EG on SiC as a result of excimer laser irradiation by using reflection high-energy electron diffraction (RHEED), Raman spectroscopy, synchrotron-based X-ray diffraction, transmission electron microscopy (TEM), and scanning tunneling microscopy (STM). Laser fluence controls the thickness of the graphene film down to a single monolayer. Laser-synthesized graphene does not display some of the structural characteristics observed in EG grown by conventional thermal decomposition on SiC (0001), such as Bernal stacking and surface reconstruction of the underlying SiC surface.

  1. Selected Papers on Low-Energy Antiprotons and Possible Applications

    SciTech Connect

    Noble, Robert

    1998-09-19

    The only realistic means by which to create a facility at Fermilab to produce large amounts of low energy antiprotons is to use resources which already exist. There is simply too little money and manpower at this point in time to generate new accelerators on a time scale before the turn of the century. Therefore, innovation is required to modify existing equipment to provide the services required by experimenters.

  2. Transportation Energy Conservation Data Book: A Selected Bibliography. Edition 3,

    DTIC Science & Technology

    1978-11-01

    Implications International Operations of the U.S. for Energy "ase - Some Economic Considerations Supplemental Dir Carriers, Calendar 1963 - Fiscal 1975...Sociotechnical Systems TITL; Local Service Carriers Passengers ADDRESS; 2101 Constitution Avenue #I, Washington. Enplanementsi Fiscal Yeta 1976 and 1975 DC...Constitution ATe. I, Washington, DC 20910 $5.00 for Traneportatio Research Record 561 97 ង 3> > TITLES The United states Budet in Brief - Fiscal ethyl

  3. Selective chemical detection by energy modulation of sensors

    DOEpatents

    Stetter, J.R.; Otagawa, T.

    1991-09-10

    A portable instrument for use in the field in detecting, identifying, and quantifying a component of a sampled fluid includes a sensor which chemically reacts with the component of interest or a derivative thereof, an electrical heating filament for heating the sample before it is applied to the sensor, and modulator for continuously varying the temperature of the filament (and hence the reaction rate) between two values sufficient to produce the chemical reaction. In response to this thermal modulation, the sensor produces a modulated output signal, the modulation of which is a function of the activation energy of the chemical reaction, which activation energy is specific to the particular component of interest and its concentration. Microprocessor which compares the modulated output signal with standard responses for a plurality of components to identify and quantify the particular component of interest. In particular, the concentration of the component of interest is proportional to the amplitude of the modulated output signal, while the identifying activation output energy of the chemical interaction indicative of that component is proportional to a normalized parameter equal to the peak-to-peak amplitude divided by the height of the upper peaks above a base line signal level. 5 figures.

  4. Selective chemical detection by energy modulation of sensors

    DOEpatents

    Stetter, Joseph R.; Otagawa, Takaaki

    1991-01-01

    A portable instrument for use in the field in detecting, identifying, and quantifying a component of a sampled fluid includes a sensor which chemically reacts with the component of interest or a derivative thereof, an electrical heating filament for heating the sample before it is applied to the sensor, and modulator for continuously varying the temperature of the filament (and hence the reaction rate) between two values sufficient to produce the chemical reaction. In response to this thermal modulation, the sensor produces a modulated output signal, the modulation of which is a function of the activation energy of the chemical reaction, which activation energy is specific to the particular component of interest and its concentration. Microprocessor which compares the modulated output signal with standard responses for a plurality of components to identify and quantify the particular component of interest. In particular, the concentration of the component of interest is proportional to the amplitude of the modulated output signal, while the identifying activation output energy of the chemical interaction indicative of that component is proportional to a normalized parameter equal to the peak-to-peak amplitude divided by the height of the upper peaks above a base line signal level.

  5. Increasing the energy yield of mechanochemical transformations: selected case studies.

    PubMed

    Politov, Anatoly; Golyazimova, Olga

    2014-01-01

    The products of mechanical treatment are surface atoms or molecules, substances with a crystal structure different from their initial one (another polymorph, amorphous), point or linear defects, radicals and new chemical substances. It is often assumed, that to increase the yield of the products of a mechanical treatment, it is necessary to increase the treatment time and the mechanical power input. In view of the low energy yield of many mechanochemical transformations, this leads to high power consumption and contamination of the matter under treatment with the wear products of the material of a mill or reactor, in which the mechanical treatment is carried out. As a result, the technological attractiveness of mechanochemical processes is reduced, so that many mechanochemical transformations that have been discovered recently do not reach the stage of commercialization. In the present paper we describe different examples of increasing successfully the energy yield of mechanochemical processes, by a factor of several times to several orders of magnitude, for inorganic and organic substances. An increase in the energy yield of mechanochemical transformations opens new possibilities for their practical usage. In particular, the methods of preliminary treatment and the modes of conducting enzymatic processes that may find application in the production of second-generation biofuels are discussed using lignocellulose materials as examples.

  6. Population dynamics in epitaxial Er{sub 2}O{sub 3} thin films grown on Si(111)

    SciTech Connect

    Tawara, T.; Omi, H.; Hozumi, T.; Kaji, R.; Adachi, S.; Gotoh, H.; Sogawa, T.

    2013-06-17

    We grow single crystal erbium-oxide (Er{sub 2}O{sub 3}) epitaxially on a Si (111) substrate by using molecular beam epitaxy and investigate the population dynamics in Er{sup 3+} ions for the coherent manipulation of the population in Er{sub 2}O{sub 3}. Sharp and discrete Stark energy levels of the {sup 4}I{sub 13/2} manifold as small as 200 {mu}eV are observed with inhomogeneous broadening caused by the uniform crystal field of the epitaxial Er{sub 2}O{sub 3}. We also experimentally determine the time constant of the resonant population transfer between spatially distant Er{sup 3+}-ion sites, which is limited to the manipulation time of the population in the Er{sub 2}O{sub 3} crystals. Using selective excitation of the Stark level in the {sup 4}I{sub 13/2} manifold, we obtain the energy transfer times between spatially distant Er{sup 3+} ions, and they are about 2 {mu}s between sites whose crystallographic symmetry is different and 10 {mu}s between sites whose symmetry is the same.

  7. Epitaxial Silicon Doped With Antimony

    NASA Technical Reports Server (NTRS)

    Huffman, James E.; Halleck, Bradley L.

    1996-01-01

    High-purity epitaxial silicon doped with antimony made by chemical vapor deposition, using antimony pentachloride (SbCI5) as source of dopant and SiH4, SiCI2H2, or another conventional source of silicon. High purity achieved in layers of arbitrary thickness. Epitaxial silicon doped with antimony needed to fabricate impurity-band-conduction photodetectors operating at wavelengths from 2.5 to 40 micrometers.

  8. Epitaxial Silicon Doped With Antimony

    NASA Technical Reports Server (NTRS)

    Huffman, James E.; Halleck, Bradley L.

    1996-01-01

    High-purity epitaxial silicon doped with antimony made by chemical vapor deposition, using antimony pentachloride (SbCI5) as source of dopant and SiH4, SiCI2H2, or another conventional source of silicon. High purity achieved in layers of arbitrary thickness. Epitaxial silicon doped with antimony needed to fabricate impurity-band-conduction photodetectors operating at wavelengths from 2.5 to 40 micrometers.

  9. Tandem filters using frequency selective surfaces for enhanced conversion efficiency in a thermophotovoltaic energy conversion system

    DOEpatents

    Dziendziel, Randolph J.; DePoy, David Moore; Baldasaro, Paul Francis

    2007-01-23

    This invention relates to the field of thermophotovoltaic (TPV) direct energy conversion. In particular, TPV systems use filters to minimize parasitic absorption of below bandgap energy. This invention constitutes a novel combination of front surface filters to increase TPV conversion efficiency by reflecting useless below bandgap energy while transmitting a very high percentage of the useful above bandgap energy. In particular, a frequency selective surface is used in combination with an interference filter. The frequency selective surface provides high transmission of above bandgap energy and high reflection of long wavelength below bandgap energy. The interference filter maintains high transmission of above bandgap energy and provides high reflection of short wavelength below bandgap energy and a sharp transition from high transmission to high reflection.

  10. Tandem filters using frequency selective surfaces for enhanced conversion efficiency in a thermophotovoltaic energy conversion system

    DOEpatents

    Dziendziel, Randolph J.; Baldasaro, Paul F.; DePoy, David M.

    2010-09-07

    This invention relates to the field of thermophotovoltaic (TPV) direct energy conversion. In particular, TPV systems use filters to minimize parasitic absorption of below bandgap energy. This invention constitutes a novel combination of front surface filters to increase TPV conversion efficiency by reflecting useless below bandgap energy while transmitting a very high percentage of the useful above bandgap energy. In particular, a frequency selective surface is used in combination with an interference filter. The frequency selective surface provides high transmission of above bandgap energy and high reflection of long wavelength below bandgap energy. The interference filter maintains high transmission of above bandgap energy and provides high reflection of short wavelength below bandgap energy and a sharp transition from high transmission to high reflection.

  11. Large area epitaxial germanane for electronic devices

    NASA Astrophysics Data System (ADS)

    Amamou, Walid; Odenthal, Patrick M.; Bushong, Elizabeth J.; O'Hara, Dante J.; Luo, Yunqiu Kelly; van Baren, Jeremiah; Pinchuk, Igor; Wu, Yi; Ahmed, Adam S.; Katoch, Jyoti; Bockrath, Marc W.; Tom, Harry W. K.; Goldberger, Joshua E.; Kawakami, Roland K.

    2015-09-01

    We report the synthesis and transfer of epitaxial germanane (GeH) onto arbitrary substrates by electrochemical delamination and investigate its optoelectronic properties. GeH films with thickness ranging from 1 to 600 nm (2-1000 layers) and areas up to ˜1 cm2 have been reliably transferred and characterized by photoluminescence, x-ray diffraction, and energy-dispersive x-ray spectroscopy. Wavelength dependent photoconductivity measurements on few-layer GeH exhibit an absorption edge and provide a sensitive characterization tool for ultrathin germanane materials. The transfer process also enables the possibility of integrating germanane into vertically stacked heterostructures.

  12. Environmental, operational, and economic aspects of thirteen selected energy technologies

    NASA Astrophysics Data System (ADS)

    Hoffman, L.; Noren, S. E.; Holt, E. C., Jr.

    1980-09-01

    The environmental operational and economic aspects of thirteen current and developing technologies are examined as applied to the generation of electric power, steam generation, and the conversion of fossil energy into alternative forms. The following technologies are addressed: (1) Conventional Boiler; (2) Diesel Engine; (3) Fluidized Bed Combustion; (4) Combined Cycle Systems; (5) Low/Medium Btu Gasification; (6) Chemically Active Fluid Bed; (7) Indirect Coal Liquefaction; (8) High Btu Gasification; (9) Surface Shale Oil Processing; (10) In situ Shale Oil Processing; (11) Direct Coal Liquefaction; (12) Fuel Cells; and (13) Magnetohydrodynamics.

  13. Multicriteria Decision Analysis of Material Selection of High Energy Performance Residential Building

    NASA Astrophysics Data System (ADS)

    Čuláková, Monika; Vilčeková, Silvia; Katunská, Jana; Krídlová Burdová, Eva

    2013-11-01

    In world with limited amount of energy sources and with serious environmental pollution, interest in comparing the environmental embodied impacts of buildings using different structure systems and alternative building materials will be increased. This paper shows the significance of life cycle energy and carbon perspective and the material selection in reducing energy consumption and emissions production in the built environment. The study evaluates embodied environmental impacts of nearly zero energy residential structures. The environmental assessment uses framework of LCA within boundary: cradle to gate. Designed alternative scenarios of material compositions are also assessed in terms of energy effectiveness through selected thermal-physical parameters. This study uses multi-criteria decision analysis for making clearer selection between alternative scenarios. The results of MCDA show that alternative E from materials on nature plant base (wood, straw bales, massive wood panel) present possible way to sustainable perspective of nearly zero energy houses in Slovak republic

  14. Observation of core-level binding energy shifts between (100) surface and bulk atoms of epitaxial CuInSe{sub 2}

    SciTech Connect

    Nelson, A.J.; Berry, G.; Rockett, A.

    1997-04-01

    Core-level and valence band photoemission from semiconductors has been shown to exhibit binding energy differences between surface atoms and bulk atoms, thus allowing one to unambiguously distinguish between the two atomic positions. Quite clearly, surface atoms experience a potential different from the bulk due to the lower coordination number - a characteristic feature of any surface is the incomplete atomic coordination. Theoretical accounts of this phenomena are well documented in the literature for III-V and II-VI semiconductors. However, surface state energies corresponding to the equilibrium geometry of (100) and (111) surfaces of Cu-based ternary chalcopyrite semiconductors have not been calculated or experimental determined. These compounds are generating great interest for optoelectronic and photovoltaic applications, and are an isoelectronic analog of the II-VI binary compound semiconductors. Surface core-level binding energy shifts depend on the surface cohesive energies, and surface cohesive energies are related to surface structure. For ternary compound semiconductor surfaces, such as CuInSe{sub 2}, one has the possibility of variations in surface stoichiometry. Applying standard thermodynamical calculations which consider the number of individual surface atoms and their respective chemical potentials should allow one to qualitatively determine the magnitude of surface core-level shifts and, consequently, surface state energies.

  15. Thermodynamic and Kinetic Aspects of III/V Epitaxy

    DTIC Science & Technology

    1992-05-22

    a applications electroniques et optiques University of Utah Dept. of Materials Science & Engineering Salt Lake City, UT 84112 May 22, 1992... microscopic strain energy. The kinetic aspects of epitaxy are by far the most complex and, consequently, the least understood. We are beginning to understand

  16. Seed layer technique for high quality epitaxial manganite films.

    PubMed

    Graziosi, P; Gambardella, A; Calbucci, M; O'Shea, K; MacLaren, D A; Riminucci, A; Bergenti, I; Fugattini, S; Prezioso, M; Homonnay, N; Schmidt, G; Pullini, D; Busquets-Mataix, D; Dediu, V

    2016-08-01

    We introduce an innovative approach to the simultaneous control of growth mode and magnetotransport properties of manganite thin films, based on an easy-to-implement film/substrate interface engineering. The deposition of a manganite seed layer and the optimization of the substrate temperature allows a persistent bi-dimensional epitaxy and robust ferromagnetic properties at the same time. Structural measurements confirm that in such interface-engineered films, the optimal properties are related to improved epitaxy. A new growth scenario is envisaged, compatible with a shift from heteroepitaxy towards pseudo-homoepitaxy. Relevant growth parameters such as formation energy, roughening temperature, strain profile and chemical states are derived.

  17. Seed layer technique for high quality epitaxial manganite films

    NASA Astrophysics Data System (ADS)

    Graziosi, P.; Gambardella, A.; Calbucci, M.; O'Shea, K.; MacLaren, D. A.; Riminucci, A.; Bergenti, I.; Fugattini, S.; Prezioso, M.; Homonnay, N.; Schmidt, G.; Pullini, D.; Busquets-Mataix, D.; Dediu, V.

    2016-08-01

    We introduce an innovative approach to the simultaneous control of growth mode and magnetotransport properties of manganite thin films, based on an easy-to-implement film/substrate interface engineering. The deposition of a manganite seed layer and the optimization of the substrate temperature allows a persistent bi-dimensional epitaxy and robust ferromagnetic properties at the same time. Structural measurements confirm that in such interface-engineered films, the optimal properties are related to improved epitaxy. A new growth scenario is envisaged, compatible with a shift from heteroepitaxy towards pseudo-homoepitaxy. Relevant growth parameters such as formation energy, roughening temperature, strain profile and chemical states are derived.

  18. Seed layer technique for high quality epitaxial manganite films

    PubMed Central

    Graziosi, P.; Gambardella, A.; Calbucci, M.; O’Shea, K.; MacLaren, D. A.; Bergenti, I.; Homonnay, N.; Schmidt, G.; Pullini, D.; Busquets-Mataix, D.; Dediu, V.

    2016-01-01

    We introduce an innovative approach to the simultaneous control of growth mode and magnetotransport properties of manganite thin films, based on an easy-to-implement film/substrate interface engineering. The deposition of a manganite seed layer and the optimization of the substrate temperature allows a persistent bi-dimensional epitaxy and robust ferromagnetic properties at the same time. Structural measurements confirm that in such interface-engineered films, the optimal properties are related to improved epitaxy. A new growth scenario is envisaged, compatible with a shift from heteroepitaxy towards pseudo-homoepitaxy. Relevant growth parameters such as formation energy, roughening temperature, strain profile and chemical states are derived. PMID:27648371

  19. DOE (Department of Energy) Epidemiologic Research Program: Selected bibliography

    SciTech Connect

    Not Available

    1991-01-01

    The objective of the Department of Energy (DOE) Epidemiologic Research Program is to determine the human health effects resulting from the generation and use of energy, and from the operation of DOE facilities. The program has been divided into seven general areas of activity: the Radiation Effects Research Foundation (RERF) which supports studies of survivors of the atomic weapons in Hiroshima and Nagasaki, mortality and morbidity studies of DOE workers, studies on internally deposited alpha emitters, medical/histologic studies, studies on the genetic aspects of radiation damage, community health surveillance studies, and the development of computational techniques and of databases to make the results as widely useful as possible. Excluding the extensive literature from the RERF, the program has produced 380 publications in scientific journals, contributing significantly to improving the understanding of the health effects of ionizing radiation exposure. In addition, a large number of public presentations were made and are documented elsewhere in published proceedings or in books. The purpose of this bibliograhpy is to present a guide to the research results obtained by scientists supported by the program. The bibliography, which includes doctoral theses, is classified by national laboratory and by year. Multi-authored studies are indicated only once, according to the main supporting laboratory.

  20. Manipulation of Dirac cones in intercalated epitaxial graphene

    DOE PAGES

    Kim, Minsung; Tringides, Michael C.; Hershberger, Matthew T.; ...

    2017-07-12

    Graphene is an intriguing material in view of its unique Dirac quasi-particles, and the manipulation of its electronic structure is important in material design and applications. Here, we theoretically investigate the electronic band structure of epitaxial graphene on SiC with intercalation of rare earth metal ions (e.g., Yb and Dy) using first-principles calculations. We can use the intercalation to control the coupling of the constituent components (buffer layer, graphene, and substrate), resulting in strong modification of the graphene band structure. We also demonstrate that the metal-intercalated epitaxial graphene has tunable band structures by controlling the energies of Dirac cones asmore » well as the linear and quadratic band dispersion depending on the intercalation layer and density. Thus, the metal intercalation is a viable method to manipulate the electronic band structure of the epitaxial graphene, which can enhance the functional utility and controllability of the material.« less

  1. Electric circuit model for strained-layer epitaxy

    NASA Astrophysics Data System (ADS)

    Kujofsa, Tedi; Ayers, John E.

    2016-11-01

    For the design and analysis of a strained-layer semiconductor device structure, the equilibrium strain profile may be determined numerically by energy minimization but this method is computationally intense and non-intuitive. Here we present an electric circuit model approach for the equilibrium analysis of an epitaxial stack, in which each sublayer may be represented by an analogous configuration involving a current source, a resistor, a voltage source, and an ideal diode. The resulting node voltages in the analogous electric circuit correspond to the equilibrium strains in the original epitaxial structure. This new approach enables analysis using widely accessible circuit simulators, and an intuitive understanding of electric circuits may be translated to the relaxation of strained-layer structures. In this paper, we describe the mathematical foundation of the electrical circuit model and demonstrate its application to epitaxial layers of Si1-x Ge x grown on a Si (001) substrate.

  2. Epitaxial Atomic Layer Deposition of Sn-Doped Indium Oxide

    SciTech Connect

    Emery, Jonathan D.; Schlepütz, Christian M.; Guo, Peijun; Chang, Robert P. H.; Martinson, Alex B. F.

    2016-02-03

    Coherently strained, epitaxial Sn-doped In2O3 (ITO) thin films were fabricated at temperatures as low as 250 degrees C using atomic layer deposition (ALD) on (001)-, (011)-, and (111)-oriented single-crystal Y-stabilized ZrO2 (YSZ) substrates. Resultant films possess cube-on-cube epitaxial relationships with the underlying YSZ substrates and are smooth, highly conductive, and optically transparent. This epitaxial ALD approach is favorable compared to many conventional growth techniques as it is a large-scale synthesis method that does not necessitate the use of high temperatures or ultrahigh vacuum. These films may prove valuable as a conductive growth template in areas where high-quality crystalline thin film substrates are important, such as solar energy materials, light-emitting diodes, or wide bandgap semiconductors. Furthermore, we discuss the applicability of this ALD system as an excellent model system for the study of ALD surface chemistry, nucleation, and film growth.

  3. Energy-selective filtration of dental x-ray beams

    SciTech Connect

    Gelskey, D.E.; Baker, C.G.

    1981-11-01

    Samarium is known for its ability to filter simultaneously low- and high-energy x-ray photons from an x-ray beam that are not useful in producing a diagnostic radiograph. This study was undertaken to determine the optimum thickness of samarium required to minimize patient exposure and exposure time. The results indicate that use of a filter thickness of 0.16 mm. minimized patient radiation exposure and permitted the use of an exposure time sufficiently short to minimize motion unsharpness. The incorporation of a 0.16 mm. samarium filter in the x-ray beam reduced exposure by about 40 percent as compared to a 2.5 mm. aluminum filter; the exposure time must be increased approximately twice to obtain optical densities equivalent to those produced with aluminum filtration.

  4. Catalog of selected heavy duty transport energy management models

    NASA Technical Reports Server (NTRS)

    Colello, R. G.; Boghani, A. B.; Gardella, N. C.; Gott, P. G.; Lee, W. D.; Pollak, E. C.; Teagan, W. P.; Thomas, R. G.; Snyder, C. M.; Wilson, R. P., Jr.

    1983-01-01

    A catalog of energy management models for heavy duty transport systems powered by diesel engines is presented. The catalog results from a literature survey, supplemented by telephone interviews and mailed questionnaires to discover the major computer models currently used in the transportation industry in the following categories: heavy duty transport systems, which consist of highway (vehicle simulation), marine (ship simulation), rail (locomotive simulation), and pipeline (pumping station simulation); and heavy duty diesel engines, which involve models that match the intake/exhaust system to the engine, fuel efficiency, emissions, combustion chamber shape, fuel injection system, heat transfer, intake/exhaust system, operating performance, and waste heat utilization devices, i.e., turbocharger, bottoming cycle.

  5. Methods of preparing flexible photovoltaic devices using epitaxial liftoff, and preserving the integrity of growth substrates used in epitaxial growth

    DOEpatents

    Forrest, Stephen R; Zimmerman, Jeramy; Lee, Kyusang; Shiu, Kuen-Ting

    2015-01-06

    There is disclosed methods of making photosensitive devices, such as flexible photovoltaic (PV) devices, through the use of epitaxial liftoff. Also described herein are methods of preparing flexible PV devices comprising a structure having a growth substrate, wherein the selective etching of protective layers yields a smooth growth substrate that us suitable for reuse.

  6. Methods of preparing flexible photovoltaic devices using epitaxial liftoff, and preserving the integrity of growth substrates used in epitaxial growth

    DOEpatents

    Forrest, Stephen R; Zimmerman, Jeramy; Lee, Kyusang; Shiu, Kuen-Ting

    2013-02-19

    There is disclosed methods of making photosensitive devices, such as flexible photovoltaic (PV) devices, through the use of epitaxial liftoff. Also described herein are methods of preparing flexible PV devices comprising a structure having a growth substrate, wherein the selective etching of protective layers yields a smooth growth substrate that us suitable for reuse.

  7. Influence of the cluster orientation on the epitaxy: deposition of Co nanoclusters on Cu(001) surfaces.

    PubMed

    Jiménez-Sáez, J C; Ettaoussi, M S; Pérez-Martín, A M C; Kerkeb, M L; Jiménez-Rodríguez, J J

    2010-02-01

    Deposition at low energy of 147-atom icosahedral Co nanoclusters on Cu(001) substrates is studied by molecular-dynamics simulations. Atomic interactions were mimicked by a many-body potential based on the tight-binding second-moment approximation. Clusters were rotated by using the two first Euler angles, in the so-called "x-convention," and subsequently, they were deposited on the substrate. The dependence of the degree of epitaxy on these angles has been obtained. Epitaxy is also related to the initial number of (001)-oriented atoms, especially for extreme values of this latter quantity. A better epitaxial matching is connected with a larger spreading index. The explanation of the epitaxial behavior of the supported clusters resides mainly in the dynamical interaction between grains during approximately the first 40 ps. Whenever the newly-formed (001)-oriented grain competes against a large number of grains after the collision, a very low epitaxial matching is obtained.

  8. Structure and magnetism of epitaxial rare-earth-transition-metal films

    SciTech Connect

    Fullerton, E.E.; Sowers, C.H.; Pearson, J.P.; Bader, S.D.

    1996-10-01

    Growth of epitaxial transition-metal superlattices; has proven essential in elucidating the role of crystal orientation and structure on magnetic properties such as giant magnetoresistance, interlayer coupling, and magnetic surface anisotropies. Extending these studies to the growth of epitaxial rare earth-transition metal (RE-TM) films and superlattices promises to play an equally important role in exploring and optimizing the properties of hard magnets. For instance, Skomski and Coey predict that a giant energy product (120 MG Oe) is possible in multilayer structures consisting of aligned hard-magnet layers exchanged coupled with soft-phase layers with high magnetization. Epitaxy provides one route to synthesizing such exchange-hardened magnets on controlled length scales. Epitaxial growth also allows the magnetic properties to be tailored by controlling the crystal orientation and the anisotropies of the magnetic layers and holds the possibility of stabilizing metastable phases. This paper describes the epitaxy and magnetic properties for several alloys.

  9. A novel fast-neutron detector concept for energy-selective imaging and imaging spectroscopy

    SciTech Connect

    Cortesi, M.; Prasser, H.-M.; Dangendorf, V.; Zboray, R.

    2014-07-15

    We present and discuss the operational principle of a new fast-neutron detector concept suitable for either energy-selective imaging or for imaging spectroscopy. The detector is comprised of a series of energy-selective stacks of converter foils immersed in a noble-gas based mixture, coupled to a position-sensitive charge readout. Each foil in the various stacks is made of two layers of different thicknesses, fastened together: a hydrogen-rich (plastic) layer for neutron-to-proton conversion, and a hydrogen-free coating to selectively stop/absorb the recoil protons below a certain energy cut-off. The neutron-induced recoil protons, that escape the converter foils, release ionization electrons in the gas gaps between consecutive foils. The electrons are then drifted towards and localized by a position-sensitive charge amplification and readout stage. Comparison of the images detected by stacks with different energy cut-offs allows energy-selective imaging. Neutron energy spectrometry is realized by analyzing the responses of a sufficient large number of stacks of different energy response and unfolding techniques. In this paper, we present the results of computer simulation studies and discuss the expected performance of the new detector concept. Potential applications in various fields are also briefly discussed, in particularly, the application of energy-selective fast-neutron imaging for nuclear safeguards application, with the aim of determining the plutonium content in Mixed Oxide (MOX) fuels.

  10. A novel fast-neutron detector concept for energy-selective imaging and imaging spectroscopy.

    PubMed

    Cortesi, M; Dangendorf, V; Zboray, R; Prasser, H-M

    2014-07-01

    We present and discuss the operational principle of a new fast-neutron detector concept suitable for either energy-selective imaging or for imaging spectroscopy. The detector is comprised of a series of energy-selective stacks of converter foils immersed in a noble-gas based mixture, coupled to a position-sensitive charge readout. Each foil in the various stacks is made of two layers of different thicknesses, fastened together: a hydrogen-rich (plastic) layer for neutron-to-proton conversion, and a hydrogen-free coating to selectively stop/absorb the recoil protons below a certain energy cut-off. The neutron-induced recoil protons, that escape the converter foils, release ionization electrons in the gas gaps between consecutive foils. The electrons are then drifted towards and localized by a position-sensitive charge amplification and readout stage. Comparison of the images detected by stacks with different energy cut-offs allows energy-selective imaging. Neutron energy spectrometry is realized by analyzing the responses of a sufficient large number of stacks of different energy response and unfolding techniques. In this paper, we present the results of computer simulation studies and discuss the expected performance of the new detector concept. Potential applications in various fields are also briefly discussed, in particularly, the application of energy-selective fast-neutron imaging for nuclear safeguards application, with the aim of determining the plutonium content in Mixed Oxide (MOX) fuels.

  11. A novel fast-neutron detector concept for energy-selective imaging and imaging spectroscopy

    NASA Astrophysics Data System (ADS)

    Cortesi, M.; Dangendorf, V.; Zboray, R.; Prasser, H.-M.

    2014-07-01

    We present and discuss the operational principle of a new fast-neutron detector concept suitable for either energy-selective imaging or for imaging spectroscopy. The detector is comprised of a series of energy-selective stacks of converter foils immersed in a noble-gas based mixture, coupled to a position-sensitive charge readout. Each foil in the various stacks is made of two layers of different thicknesses, fastened together: a hydrogen-rich (plastic) layer for neutron-to-proton conversion, and a hydrogen-free coating to selectively stop/absorb the recoil protons below a certain energy cut-off. The neutron-induced recoil protons, that escape the converter foils, release ionization electrons in the gas gaps between consecutive foils. The electrons are then drifted towards and localized by a position-sensitive charge amplification and readout stage. Comparison of the images detected by stacks with different energy cut-offs allows energy-selective imaging. Neutron energy spectrometry is realized by analyzing the responses of a sufficient large number of stacks of different energy response and unfolding techniques. In this paper, we present the results of computer simulation studies and discuss the expected performance of the new detector concept. Potential applications in various fields are also briefly discussed, in particularly, the application of energy-selective fast-neutron imaging for nuclear safeguards application, with the aim of determining the plutonium content in Mixed Oxide (MOX) fuels.

  12. Continuum model of surface roughening and epitaxial breakdown during low-temperature Ge(001) molecular beam epitaxy

    SciTech Connect

    Bratland, K. A.; Spila, T.; Cahill, D. G.; Greene, J. E.; Desjardins, P.

    2011-03-15

    Numerical simulations based on a discrete model describing step edge motion are used to compute the surface morphological evolution of Ge(001) layers deposited by low-temperature (T{sub s} = 45-230 deg. C) molecular beam epitaxy and to probe the relationship between surface roughening and the onset of epitaxial breakdown - the abrupt growth mode transition from epitaxial to amorphous - at temperature-dependent critical film thicknesses h{sub 1}(T{sub s}). Computed surface widths w and in-plane coherence lengths d as a function of layer thickness h exhibit good agreement with experimental values. Inspired by experimental results indicating that epitaxial breakdown is initiated at facetted interisland trenches as the surface roughness reaches a T{sub s}-independent overall aspect ratio, we show that simulated data for w/d = 0.03 correspond to thicknesses h{sub 1{proportional_to}} exp (-E{sub 1}/kT{sub s}) with E{sub 1} = 0.63 eV, a value equal to the Ge adatom diffusion activation energy on Ge(001). Simulated h{sub 1} values agree well with experimental data. Above a critical growth temperature of 170 deg. C, computed w/d values saturate at large film thicknesses, never reaching the critical aspect ratio w/d = 0.03. Thus, the model also predicts that epitaxial breakdown does not occur for T{sub s} > 170 deg. C as observed experimentally.

  13. Fully planar method for creating adjacent ``self-isolating'' silicon-on-insulator and epitaxial layers by epitaxial lateral overgrowth

    NASA Astrophysics Data System (ADS)

    Glenn, J. L., Jr.; Neudeck, G. W.; Subramanian, C. K.; Denton, J. P.

    1992-01-01

    A novel and simple process is demonstrated for creating isolated silicon-on-insulator (SOI) tubs adjacent to selective epitaxial substrate layers. The process results in a fully planar wafer surface which is uniquely suited for mixed bipolar/complementary metal-oxide-semiconductor device fabrication. Low-temperature epitaxial lateral overgrowth (ELO) using SiH2Cl2/HCl/H2 is carried out in a reduced-pressure chemical vapor deposition reactor to create SOI islands in thermally grown SiO2 valleys. SOI islands and epitaxial seed regions are ``self-isolated'' by chemical-mechanical planarization. The as-grown ELO is single-crystal material with well-defined facets. Planarized SOI and epilayer regions have planar, featureless surfaces. Defect etching for the nonoptimized SOI layers indicates about 5×104 stacking faults/cm2.

  14. Carbon-Water-Energy Relations for Selected River Basins

    NASA Technical Reports Server (NTRS)

    Choudhury, B. J.

    1998-01-01

    A biophysical process-based model was run using satellite, assimilated and ancillary data for four years (1987-1990) to calculate components of total evaporation (transpiration, interception, soil and snow evaporation), net radiation, absorbed photosynthetically active radiation and net primary productivity over the global land surface. Satellite observations provided fractional vegetation cover, solar and photosynthetically active radiation incident of the surface, surface albedo, fractional cloud cover, air temperature and vapor pressure. The friction velocity and surface air pressure are obtained from a four dimensional data assimilation results, while precipitation is either only surface observations or a blended product of surface and satellite observations. All surface and satellite data are monthly mean values; precipitation has been disaggregated into daily values. All biophysical parameters of the model are prescribed according to published records. From these global land surface calculations results for river basins are derived using digital templates of basin boundaries. Comparisons with field observations (micrometeorologic, catchment water balance, biomass production) and atmospheric water budget analysis for monthly evaporation from six river basins have been done to assess errors in the calculations. Comparisons are also made with previous estimates of zonal variations of evaporation and net primary productivity. Efficiencies of transpiration, total evaporation and radiation use, and evaporative fraction for selected river basins will be presented.

  15. Guided-wave approaches to spectrally selective energy absorption

    NASA Technical Reports Server (NTRS)

    Stegeman, G. I.; Burke, J. J.

    1987-01-01

    Results of experiments designed to demonstrate spectrally selective absorption in dielectric waveguides on semiconductor substrates are reported. These experiments were conducted with three waveguides formed by sputtering films of PSK2 glass onto silicon-oxide layers grown on silicon substrates. The three waveguide samples were studied at 633 and 532 nm. The samples differed only in the thickness of the silicon-oxide layer, specifically 256 nm, 506 nm, and 740 nm. Agreement between theoretical predictions and measurements of propagation constants (mode angles) of the six or seven modes supported by these samples was excellent. However, the loss measurements were inconclusive because of high scattering losses in the structures fabricated (in excess of 10 dB/cm). Theoretical calculations indicated that the power distribution among all the modes supported by these structures will reach its steady state value after a propagation length of only 1 mm. Accordingly, the measured loss rates were found to be almost independent of which mode was initially excited. The excellent agreement between theory and experiment leads to the conclusion that low loss waveguides confirm the predicted loss rates.

  16. Selective coatings for solar-to-thermal energy converters

    NASA Astrophysics Data System (ADS)

    Gukhman, G. A.; Koltun, M. M.

    1984-02-01

    A selective coating proposed for flat plate solar collectors consists of a thick Al2O3 layer with embedded metal particles and on it an infrared reflecting layer of electrically conducting vitreous ceramic material (PbO or In2O3). Both layers are deposited electromatically on collectors made of aluminum or an aluminum alloy. A double layer of 2 to 3 micron thick chromium on 9 to 10 micron thick nickel is effective in preventing oxidation on copper surfaces. Specimens of such coatings were tested in a laboratory humidity chamber and are now tested under the climatic conditions in the Crimea, 750,000 Wh/sq m of solar radiation at a mean-weekly intensity of 700 W/sq m having been accumulated in nine months. The ratio of heat absorbint to total surface area is or = 0.9 and emissivity is or = 0.2 were not degraded by holding in a furnace at 500 C for 50 h. The feasibility of producing multilayer coatings of this type was established on the basis of computer calculations for various combinations of collector material and protective interlayers.

  17. Carbon-Water-Energy Relations for Selected River Basins

    NASA Technical Reports Server (NTRS)

    Choudhury, B. J.

    1998-01-01

    A biophysical process-based model was run using satellite, assimilated and ancillary data for four years (1987-1990) to calculate components of total evaporation (transpiration, interception, soil and snow evaporation), net radiation, absorbed photosynthetically active radiation and net primary productivity over the global land surface. Satellite observations provided fractional vegetation cover, solar and photosynthetically active radiation incident of the surface, surface albedo, fractional cloud cover, air temperature and vapor pressure. The friction velocity and surface air pressure are obtained from a four dimensional data assimilation results, while precipitation is either only surface observations or a blended product of surface and satellite observations. All surface and satellite data are monthly mean values; precipitation has been disaggregated into daily values. All biophysical parameters of the model are prescribed according to published records. From these global land surface calculations results for river basins are derived using digital templates of basin boundaries. Comparisons with field observations (micrometeorologic, catchment water balance, biomass production) and atmospheric water budget analysis for monthly evaporation from six river basins have been done to assess errors in the calculations. Comparisons are also made with previous estimates of zonal variations of evaporation and net primary productivity. Efficiencies of transpiration, total evaporation and radiation use, and evaporative fraction for selected river basins will be presented.

  18. Selected computer system controls at the Energy Information Administration

    SciTech Connect

    Not Available

    1991-09-01

    The purpose of our review of the Energy Information Administration's (EIA) computer system was to evaluate disk and tape information storage and the adequacy of internal controls in the operating system programs. We used a set of computer-assisted audit techniques called CAATS, developed by the US Department of Transportation, Office of Inspector General, in performing the review at the EIA Forrestal Computer Facility. Improved procedures are needed to assure more efficient use of disk space. By transferring data sets from disk to tape, deleting invalid data, releasing unused reserve space and blocking data efficiently, disk space with an estimated value of $1.1 million a year could be recovered for current use. Also, procedures governing the maximum times for storage of information on tapes should be enforced to help ensure that data is not lost. In addition, improved internal controls are needed over granting users system-wide privileges and over authorized program library names to prevent unauthorized access to the system and possible destruction or manipulation of data. Automated Data Processing (ADP) Services Staff officials indicated that software maintenance was not current, due to contractual difficulties with the operating contractor for the Forrestal Facility. Our review confirmed that improvements were needed to help prevent malfunctions of the operating system, which could cause performance degradations, system failures, or loss of either system or user data. Management generally concurred with the recommendations in the report.

  19. Erosive wear of selected materials for fossil energy applications

    SciTech Connect

    Adler, Thomas A.; Rawers, James C.; Tylczak, Joseph H.; Hawk, Jeffrey A.

    2001-01-01

    A number of materials have been evaluated to determine their erosion resistance for fossil energy applications. This is part of a larger program to study wear and corrosion at Albany Research Center. This paper will present the results for some of these materials, including FeAl, FeAl cermets, WC-Co cemented carbides, Si3N4-MoSi2, Si3N4, Stellite 6B, white cast irons and 440C steel. Trends in erosion rates due to material properties and erosive conditions will be presented. FeAl cermets performed well compared to the WC-Co cemented carbides. The interparticle spacing of the WC-Co cemented carbides correlated with the erosion rate. The erosion rate of the WC-Co cemented carbides decreased as the interparticle spacing decreased. It is important to realize that erosion resistance is not an intrinsic material property, but is a system response. A change in the wear environment can significantly alter the relative rankings of materials with respect to their wear rate. For example, at relatively low velocities, the carbides in the white cast irons are more erosion resistant than the matrix, while at higher velocities the matrix is more erosion resistant.

  20. Theory of Energy-Assisted Epitaxy; Theory of Ordered Semiconductor Alloys; In1-xTIxSb as a Long-Wave Infrared Material

    DTIC Science & Technology

    1993-10-01

    COSM , = COOVI is also required to ensure that U is zero under any infinitesimal rigid rotation. In light of these properties, the energy density can...Vegard (1921) law a = (1 - x)aAC + xaBc. Figure 5 shows an example of the results for the bond lengths in GaI _.,InAs deduced by Mikkelsen and Boyce

  1. Select Results from the Energy Assessor Experiment in the 2012 Commercial Buildings Energy Consumption Survey

    EIA Publications

    2015-01-01

    As part of an effort to make EIA’s energy consumption surveys as accurate and efficient as possible, EIA invited the National Research Council (NRC) to review the Commercial Buildings Energy Consumption Survey (CBECS) data-gathering process and make recommendations for improvements. The NRC suggested sending professional energy assessors to some sites and comparing the data obtained from the survey to the data collected by the assessors. Results from the energy assessment data collection have largely confirmed the quality of data gathered by CBECS interviewers.

  2. Submonolayer epitaxy with impurities

    NASA Astrophysics Data System (ADS)

    Kotrla, Miroslav; Krug, Joachim; Smilauer, Pavel

    2000-03-01

    The effect of impurities on epitaxial growth in the submonolayer regime is studied using kinetic Monte Carlo simulations of a two-species solid-on-solid growth model. Both species are mobile, and attractive interactions among adatoms and between adatoms and impurities are incorporated. Impurities can be codeposited with the growing material or predeposited prior to growth. The activated exchange of impurities and adatoms is identified as the key kinetic process in the formation a growth morphology in which the impurities decorate the island edges. The dependence of the island density N on flux F and coverage θ is studied in detail. The impurities strongly increase the island density without appreciably changing the exponent \\chi in the power law relation N ~ F^\\chi, apart from a saturation of the flux dependence at large F and small θ. Within the present model, even completely decorated island edges do not provide efficient barriers to the attachment of adatoms, and therefore the mechanism for the increase of \\chi proposed by D. Kandel [Phys. Rev. Lett. 78, 499 (1997)] is not operative. A simple analytic theory taking into account only the dependence of the adatom diffusion constant on impurity coverage is shown to provide semi-quantitative agreement with many features observed in the simulations.

  3. High spin spectroscopy near the N=Z line: Channel selection and excitation energy systematics

    SciTech Connect

    Svensson, C.E.; Cameron, J.A.; Flibotte, S.

    1996-12-31

    The total {gamma}-ray and charged-particle energies emitted in fusion-evaporation reactions leading to N=Z compound systems in the A = 50-70 mass region have been measured with the 8{pi} {gamma}-ray spectrometer and the miniball charged-particle detector array. A new method of channel selection has been developed which combines particle identification with these total energy measurements and greatly improves upon the selectivity possible with particle detection alone. In addition, the event by event measurement of total {gamma}-ray energies using the BGO ball of the 8{pi} spectrometer has allowed a determination of excitation energies following particle evaporation for a large number of channels in several different reactions. The new channel selection procedure and excitation energy systematics are illustrated with data from the reaction of {sup 24}Mg on {sup 40}Ca at E{sub lab} = 80MeV.

  4. Energy Saving Glass Lamination via Selective Radio Frequency Heating

    SciTech Connect

    Allan, Shawn M.

    2012-02-27

    This project focused on advancing radio-frequency (RF) lamination technology closer to commercial implementation, in order to reduce the energy intensity of glass lamination by up to 90%. Lamination comprises a wide range of products including autoglass, architectural safety and innovative design glass, transparent armor (e.g. bullet proof glass), smart glass, mirrors, and encapsulation of photovoltaics. Lamination is also the fastest growing segment of glass manufacturing, with photovoltaics, architectural needs, and an anticipated transition to laminated side windows in vehicles. The state-of-the-art for glass lamination is to use autoclaves, which apply heat and uniform gas pressure to bond the laminates over the course of 1 to 18 hours. Laminates consist of layers of glass or other materials bonded with vinyl or urethane interlayers. In autoclaving, significant heat energy is lost heating the chamber, pressurized air, glass racks, and the glass. In RF lamination, the heat is generated directly in the vinyl interlayer, causing it to heat and melt quickly, in just 1 to 10 minutes, without significantly heating the glass or the equipment. The main purpose of this project was to provide evidence that low energy, rapid RF lamination quality met the same standards as conventionally autoclaved windows. The development of concepts for laminating curved glass with RF lamination was a major goal. Other primary goals included developing a stronger understanding of the lamination product markets described above, and to refine the potential benefits of commercial implementation. The scope of the project was to complete implementation concept studies in preparation for continuation into advanced development, pilot studies, and commercial implementation. The project consisted of 6 main tasks. The first dealt with lamination with poly-vinyl butyral (PVB) interlayers, which prior work had shown difficulties in achieving good quality laminates, working with Pilkington North

  5. Energy Saving Glass Lamination via Selective Radio Frequency Heating

    SciTech Connect

    Allan, Shawn M; Baranova, Inessa; Poley, Joseph; Reis, Henrique

    2012-02-27

    This project focused on advancing radio-frequency (RF) lamination technology closer to commercial implementation, in order to reduce the energy intensity of glass lamination by up to 90%. Lamination comprises a wide range of products including autoglass, architectural safety and innovative design glass, transparent armor (e.g. bullet proof glass), smart glass, mirrors, and encapsulation of photovoltaics. Lamination is also the fastest growing segment of glass manufacturing, with photovoltaics, architectural needs, and an anticipated transition to laminated side windows in vehicles. The state-of-the-art for glass lamination is to use autoclaves, which apply heat and uniform gas pressure to bond the laminates over the course of 1 to 18 hours. Laminates consist of layers of glass or other materials bonded with vinyl or urethane interlayers. In autoclaving, significant heat energy is lost heating the chamber, pressurized air, glass racks, and the glass. In RF lamination, the heat is generated directly in the vinyl interlayer, causing it to heat and melt quickly, in just 1 to 10 minutes, without significantly heating the glass or the equipment. The main purpose of this project was to provide evidence that low energy, rapid RF lamination quality met the same standards as conventionally autoclaved windows. The development of concepts for laminating curved glass with RF lamination was a major goal. Other primary goals included developing a stronger understanding of the lamination product markets described above, and to refine the potential benefits of commercial implementation. The scope of the project was to complete implementation concept studies in preparation for continuation into advanced development, pilot studies, and commercial implementation. The project consisted of 6 main tasks. The first dealt with lamination with poly-vinyl butyral (PVB) interlayers, which prior work had shown difficulties in achieving good quality laminates, working with Pilkington North

  6. Method of epitaxially depositing cadmium sulfide

    NASA Technical Reports Server (NTRS)

    Hawrylo, Frank Z. (Inventor)

    1980-01-01

    A single crystal layer of either cadmium sulfide or an alloy of cadmium sulfide and indium phosphide is epitaxially deposited on a substrate of cadmium sulfide by liquid phase epitaxy using indium as the solvent.

  7. Energy Opinions of Southern, Northern and Academically Prepared Energy Students in Selected Secondary Schools.

    ERIC Educational Resources Information Center

    Karst, Ralph R.

    1985-01-01

    Examines the effects of sex, grade level, region, and academic preparation of secondary school students on energy opinions. Assesses the responses of students on energy items related to the government, cars, and conservation. Results reveal significant regional and sex differences. (ML)

  8. Energy Opinions of Southern, Northern and Academically Prepared Energy Students in Selected Secondary Schools.

    ERIC Educational Resources Information Center

    Karst, Ralph R.

    1985-01-01

    Examines the effects of sex, grade level, region, and academic preparation of secondary school students on energy opinions. Assesses the responses of students on energy items related to the government, cars, and conservation. Results reveal significant regional and sex differences. (ML)

  9. Quantitative low-energy electron-diffraction study of the epitaxy of Fe on Ag l brace 001 r brace : Questions about the growth mode

    SciTech Connect

    Li, H.; Li, Y.S.; Quinn, J.; Tian, D. ); Sokolov, J. ); Jona, F. ); Marcus, P.M. )

    1990-11-15

    We point out contradictions among several reports relating to the mode of growth of Fe on Ag{l brace}001{r brace}, particularly between the studies done by reflection-high-energy electron diffraction (RHEED) and those done by low-energy electron diffraction (LEED). We describe qualitative LEED observations that agree with those of other workers. These observations, as well as quantitative analyses reported herein, indicate that on the samples used in all LEED experiments reported to date, the growth of Fe on Ag{l brace}001{r brace} was neither layer by layer nor of Stranski-Krastanov type. These results are inconsistent with the conclusions drawn by others from RHEED intensity oscillations. We also establish quantitatively that the structure of thicker (10--30 layers) films of Fe on Ag{l brace}001{r brace} is either the stable bcc structure of {alpha}-Fe or a slight body-centered-tetragonal distortion thereof.

  10. Selected bibliography: cost and energy savings of conservation and renewable energy technologies

    SciTech Connect

    1980-05-01

    This bibliography is a compilation of reports on the cost and energy savings of conservation and renewable energy applications throughout the United States. It is part of an overall effort to inform utilities of technological developments in conservation and renewable energy technologies and so aid utilities in their planning process to determine the most effective and economic combination of capital investments to meet customer needs. Department of Energy assessments of the applications, current costs and cost goals for the various technologies included in this bibliography are presented. These assessments are based on analyses performed by or for the respective DOE Program Offices. The results are sensitive to a number of variables and assumptions; however, the estimates presented are considered representative. These assessments are presented, followed by some conclusions regarding the potential role of the conservation and renewable energy alternative. The approach used to classify the bibliographic citations and abstracts is outlined.

  11. Epitaxial integration of nanowires in microsystems by local micrometer-scale vapor-phase epitaxy.

    PubMed

    Mølhave, Kristian; Wacaser, Brent A; Petersen, Dirch Hjorth; Wagner, Jakob B; Samuelson, Lars; Bøggild, Peter

    2008-10-01

    Free-standing epitaxially grown nanowires provide a controlled growth system and an optimal interface to the underlying substrate for advanced optical, electrical, and mechanical nanowire device connections. Nanowires can be grown by vapor-phase epitaxy (VPE) methods such as chemical vapor deposition (CVD) or metal organic VPE (MOVPE). However, VPE of semiconducting nanowires is not compatible with several microfabrication processes due to the high synthesis temperatures and issues such as cross-contamination interfering with the intended microsystem or the VPE process. By selectively heating a small microfabricated heater, growth of nanowires can be achieved locally without heating the entire microsystem, thereby reducing the compatibility problems. The first demonstration of epitaxial growth of silicon nanowires by this method is presented and shows that the microsystem can be used for rapid optimization of VPE conditions. The important issue of the cross-contamination of other parts of the microsystem caused by the local growth of nanowires is also investigated by growth of GaN near previously grown silicon nanowires. The design of the cantilever heaters makes it possible to study the grown nanowires with a transmission electron microscope without sample preparation.

  12. Energy Conservation: A Workshop for Selected Eastern U.S. Industrial Arts Teacher Educators.

    ERIC Educational Resources Information Center

    Wenig, Robert E., Ed.

    This set of 25 instructional modules was produced by a group of industrial arts teacher educators, local teachers, and supervisors from eastern United States. Topic areas of these modules include: societal implications of the energy situation; awareness of energy terms, supply, and use; assessment of conventional and selected renewable alternative…

  13. Linking habitat selection to fitness-related traits in herbivores: the role of the energy landscape

    Treesearch

    Ryan A. Long; R. T. Bowyer; Warren P. Porter; Paul Mathewson; Kevin L. Monteith; Scott L. Findholt; Brian L. Dick; John G. Kie

    2016-01-01

    Animals may partially overcome environmental constraints on fitness by behaviorally adjusting their exposure to costs and supplies of energy. Few studies, however, have linked spatiotemporal variation in the energy landscape to behaviorally mediated measures of performance that ostensibly influence individual fitness. We hypothesized that strength of selection by North...

  14. Epitaxial technology for low cost solar cells

    NASA Technical Reports Server (NTRS)

    Kressel, H.; Raccah, P. M.

    1975-01-01

    Epitaxial solar cell structures on low cost silicon substrates are compared to direct diffusion substrates. Dislocation density in the epitaxial layers is found to be significantly lower than that of the substrate material. The saturation current density of diodes epitaxially formed on the substrate is commonly 2 to 3 orders of magnitude lower than for diodes formed by direct diffusion. Solar cells made epitaxially are substantially better than those made by direct diffusion into similar material.

  15. Fluorination of epitaxial oxides: Creating ferrite and nickelate oxyfluoride films

    NASA Astrophysics Data System (ADS)

    May, Steven; Moon, Eun; Xie, Yujun; Keavney, David; Goebel, Justin; Laird, Eric; Li, Christopher

    2013-03-01

    In ABO3 perovskites, the physical properties are directly coupled to the nominal valence state of the B-site cation. In epitaxial thin films, the dominant strategy to control B-site valence is through the selection of a di- or trivalent cation on the A-site. However, this approach is limited, particularly when electron doping on the B-site is desired. Here we report a simple method for realizing oxyfluoride films, where the substitution of F for O is expected to reduce the B-site valence, providing a new means to tune electronic, optical and magnetic properties in thin films. Fluorination is achieved by spin coating an oxygen deficient film with poly(vinylidene fluoride). The film/polymer bilayer is then annealed, promoting the diffusion of F into the film. We have used this method to synthesize SrFeO3-δFδ and LaNiO3-δFδ (δ ? 0.5) films, as confirmed by x-ray photoemission spectroscopy and x-ray absorption spectroscopy. This work is supported by the U. S. Army Research Office under grant number W911NF-12-1-0132. Work at the Advanced Photon Source is supported by the U.S. Department of Energy (DOE), Office of Basic Energy Sciences under contract DE-AC02-06CH11357.

  16. Molecular beam epitaxial growth of tin oxide semiconductors

    NASA Astrophysics Data System (ADS)

    Medina, Gabriel A.

    In an effort to develop a method to utilize SnO in transparent electronic and optoelectronic applications, the molecular beam epitaxy method was used to grow a thin film SnO sample. Five samples were grown and studied using various conventional techniques. X-ray diffraction and Raman spectroscopy was used to identify the composition of the samples. The quality and thickness of the samples was studied using Scanning Electron Microscopy. This data was used to determine which samples were successful growths of SnO and how the growth conditions of each may have affected the outcomes. From the compiled data, single phase SnO was identified and selected for further study of it electrical properties. Previous studies have not been able to accurately identify the band gap energy of SnO due to its instability as an oxide. A bandgap energy of 2.56 eV was determined by photoluminescence analysis. This is consistent with reported estimates of between 2.5 to 3 eV for SnO.

  17. Dual-energy X-ray photon counting using an LSO-MPPC spectrometer and an energy-selecting device

    NASA Astrophysics Data System (ADS)

    Sato, Eiichi; Oda, Yasuyuki; Yamaguchi, Satoshi; Hagiwara, Osahiko; Matsukiyo, Hiroshi; Watanabe, Manabu; Kusachi, Shinya

    2015-08-01

    Dual-energy photon counting was performed using an energy-selecting device (ESD) and a detector, consisting of a Lu2(SiO4)O [LSO)] crystal and a multipixel photon counter (MPPC). The ESD is used to determine a low-energychannel range for CT and consists of two comparators and a microcomputer (MC). The two threshold channels in proportion to energies are determined using low and high-energy comparators, respectively. The MC in the ESD produces a single logical pulse when only a logical pulse from the low-energy comparator is input to the MC. To determine the high-energy-channel range for CT, logical pulses from the high-energy comparator are input to the MC outside the ESD. Logical pulses from the two MCs are input to frequency-voltage converters (FVCs) to convert count rates into voltages. The output voltages from the two FVCs are sent to a personal computer through an analog-digital converter to reconstruct tomograms. Dual-energy computed tomography was accomplished at a tube voltage of 70 kV and a maximum count rate of 14.3 kilocounts per second, and two-different-energy tomograms were obtained simultaneously.

  18. Aluminium or copper substrate panel for selective absorption of solar energy

    NASA Technical Reports Server (NTRS)

    Roberts, M. L.; Sharpe, M. H.; Krupnick, A. C. (Inventor)

    1979-01-01

    A method for making panels which selectively absorb solar energy is disclosed. The panels are comprised of an aluminum substrate, a layer of zinc thereon, a layer of nickel over the zinc layer and an outer layer of solar energy absorbing nickel oxide or a copper substrate with a layer of nickel thereon and a layer of solar energy absorbing nickel oxide distal from the copper substrate.

  19. Interfacial phases in epitaxial growth of Y{sub 2}O{sub 3} on MgO studied via combining electron energy-loss spectroscopy and real-space self-consistent full multiple scattering calculations

    SciTech Connect

    Pailloux, F.; Jublot, M.; Gaboriaud, R.J.; Jaouen, M.; Paumier, F.; Imhoff, D.

    2005-09-15

    Electron energy loss spectroscopy (EELS), high resolution transmission electron microscopy (HRTEM), and electron diffraction were used to investigate Y{sub 2}O{sub 3} thin films epitaxially grown on (001) MgO substrate. In the vicinity of the film/substrate interface, HRTEM experiments evidenced the presence of grains with various crystallographic structures most of them crystallizing in the well-known Ia3 cubic phase. Some other grains, nanometric in size, and only observed in the vicinity of the film/substrate interface, have a different and unknown crystallographic structure. EELS spectra have been acquired close to the Y{sub 2}O{sub 3}/MgO interface, to get a better knowledge of the phases nucleated close to the substrate surface. Spectra exhibiting different fine structures have been recorded and compared to multiple scattering calculations. The Ia3 phase has been detected as constituting the main component of the Y{sub 2}O{sub 3} thin film in agreement with previous observations. It is found that calculations performed in a real space self-consistent full multiple scattering scheme (SC-FMS) and experiments are in pretty good agreement even for small cluster sizes. The second family of spectra has also been compared to calculations performed for monoclinic C2/m yttrium oxide, with a little success. Another approach considering a local oxygen neighboring close to a distorted rock-salt-like structure led to a good match between experimental and calculated spectra. Our results emphasize how powerful is the combination of spectroscopic measurements at nanometer scale, as feasible with EELS and modern microscopes, with ab initio calculations for structure determination at such small scale lengths.

  20. Natural selection reduces energy metabolism in the garden snail, helix aspersa (cornu aspersum).

    PubMed

    Artacho, Paulina; Nespolo, Roberto F

    2009-04-01

    Phenotypic selection is widely recognized as the primary cause of adaptive evolution in natural populations, a fact that has been documented frequently over the last few decades, mainly in morphological and life-history traits. The energetic definition of fitness predicts that natural selection will maximize the residual energy available for growth and reproduction, suggesting that energy metabolism could be a target of selection. To address this problem, we chose the garden snail, Helix aspersa (Cornu aspersum). We performed a seminatural experiment for measuring phenotypic selection on standard metabolic rate (SMR), the minimum cost of maintenance in ectotherm organisms. To discount selection on correlated traits, we included two additional whole-organism performance traits (mean speed and maximum force of dislodgement). We found a combination of linear (negative directional selection, beta=-0.106 +/- 0.06; P= 0.001) and quadratic (stabilizing selection, gamma=-0.012 +/- 0.033; P= 0.061) selection on SMR. Correlational selection was not significant for any possible pair of traits. This suggests that individuals with average-to-reduced SMRs were promoted by selection. To the best of our knowledge, this is the first study showing significant directional selection on the obligatory cost of maintenance in an animal, providing support for the energetic definition of fitness.

  1. Quantification of correlational selection on thermal physiology, thermoregulatory behavior, and energy metabolism in lizards.

    PubMed

    Artacho, Paulina; Saravia, Julia; Ferrandière, Beatriz Decencière; Perret, Samuel; Le Galliard, Jean-François

    2015-09-01

    Phenotypic selection is widely accepted as the primary cause of adaptive evolution in natural populations, but selection on complex functional properties linking physiology, behavior, and morphology has been rarely quantified. In ectotherms, correlational selection on thermal physiology, thermoregulatory behavior, and energy metabolism is of special interest because of their potential coadaptation. We quantified phenotypic selection on thermal sensitivity of locomotor performance (sprint speed), thermal preferences, and resting metabolic rate in captive populations of an ectothermic vertebrate, the common lizard, Zootoca vivipara. No correlational selection between thermal sensitivity of performance, thermoregulatory behavior, and energy metabolism was found. A combination of high body mass and resting metabolic rate was positively correlated with survival and negatively correlated with fecundity. Thus, different mechanisms underlie selection on metabolism in lizards with small body mass than in lizards with high body mass. In addition, lizards that selected the near average preferred body temperature grew faster that their congeners. This is one of the few studies that quantifies significant correlational selection on a proxy of energy expenditure and stabilizing selection on thermoregulatory behavior.

  2. Quantification of correlational selection on thermal physiology, thermoregulatory behavior, and energy metabolism in lizards

    PubMed Central

    Artacho, Paulina; Saravia, Julia; Ferrandière, Beatriz Decencière; Perret, Samuel; Le Galliard, Jean-François

    2015-01-01

    Phenotypic selection is widely accepted as the primary cause of adaptive evolution in natural populations, but selection on complex functional properties linking physiology, behavior, and morphology has been rarely quantified. In ectotherms, correlational selection on thermal physiology, thermoregulatory behavior, and energy metabolism is of special interest because of their potential coadaptation. We quantified phenotypic selection on thermal sensitivity of locomotor performance (sprint speed), thermal preferences, and resting metabolic rate in captive populations of an ectothermic vertebrate, the common lizard, Zootoca vivipara. No correlational selection between thermal sensitivity of performance, thermoregulatory behavior, and energy metabolism was found. A combination of high body mass and resting metabolic rate was positively correlated with survival and negatively correlated with fecundity. Thus, different mechanisms underlie selection on metabolism in lizards with small body mass than in lizards with high body mass. In addition, lizards that selected the near average preferred body temperature grew faster that their congeners. This is one of the few studies that quantifies significant correlational selection on a proxy of energy expenditure and stabilizing selection on thermoregulatory behavior. PMID:26380689

  3. Versatile Large-Area Custom-Feature van der Waals Epitaxy of Topological Insulators.

    PubMed

    Trivedi, Tanuj; Roy, Anupam; Movva, Hema C P; Walker, Emily S; Bank, Seth R; Neikirk, Dean P; Banerjee, Sanjay K

    2017-07-25

    As the focus of applied research in topological insulators (TI) evolves, the need to synthesize large-area TI films for practical device applications takes center stage. However, constructing scalable and adaptable processes for high-quality TI compounds remains a challenge. To this end, a versatile van der Waals epitaxy (vdWE) process for custom-feature bismuth telluro-sulfide TI growth and fabrication is presented, achieved through selective-area fluorination and modification of surface free-energy on mica. The TI features grow epitaxially in large single-crystal trigonal domains, exhibiting armchair or zigzag crystalline edges highly oriented with the underlying mica lattice and only two preferred domain orientations mirrored at 180°. As-grown feature thickness dependence on lateral dimensions and denuded zones at boundaries are observed, as explained by a semiempirical two-species surface migration model with robust estimates of growth parameters and elucidating the role of selective-area surface modification. Topological surface states contribute up to 60% of device conductance at room temperature, indicating excellent electronic quality. High-yield microfabrication and the adaptable vdWE growth mechanism with readily alterable precursor and substrate combinations lend the process versatility to realize crystalline TI synthesis in arbitrary shapes and arrays suitable for facile integration with processes ranging from rapid prototyping to scalable manufacturing.

  4. Epitaxial stabilization and phase instability of VO2 polymorphs

    SciTech Connect

    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. In conclusion, 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.

  5. Unusual role of epilayer–substrate interactions in determining orientational relations in van der Waals epitaxy

    PubMed Central

    Liu, Lei; Siegel, David A.; Chen, Wei; Liu, Peizhi; Guo, Junjie; Duscher, Gerd; Zhao, Chong; Wang, Hao; Wang, Wenlong; Bai, Xuedong; McCarty, Kevin F.; Zhang, Zhenyu; Gu, Gong

    2014-01-01

    Using selected-area low-energy electron diffraction analysis, we showed strict orientational alignment of monolayer hexagonal boron nitride (h-BN) crystallites with Cu(100) surface lattices of Cu foil substrates during atmospheric pressure chemical vapor deposition. In sharp contrast, the graphene–Cu(100) system is well-known to assume a wide range of rotations despite graphene’s crystallographic similarity to h-BN. Our density functional theory calculations uncovered the origin of this surprising difference: The crystallite orientation is determined during nucleation by interactions between the cluster’s edges and the substrate. Unlike the weaker B– and N–Cu interactions, strong C–Cu interactions rearrange surface Cu atoms, resulting in the aligned geometry not being a distinct minimum in total energy. The discovery made in this specific case runs counter to the conventional wisdom that strong epilayer–substrate interactions enhance orientational alignment in epitaxy and sheds light on the factors that determine orientational relation in van der Waals epitaxy of 2D materials. PMID:25385622

  6. Epitaxial growth of large-gap quantum spin Hall insulator on semiconductor surface

    PubMed Central

    Zhou, Miao; Ming, Wenmei; Liu, Zheng; Wang, Zhengfei; Li, Ping; Liu, Feng

    2014-01-01

    Formation of topological quantum phase on a conventional semiconductor surface is of both scientific and technological interest. Here, we demonstrate epitaxial growth of 2D topological insulator, i.e., quantum spin Hall state, on Si(111) surface with a large energy gap, based on first-principles calculations. We show that the Si(111) surface functionalized with one-third monolayer of halogen atoms [Si(111)-3×3-X (X = Cl, Br, I)] exhibiting a trigonal superstructure provides an ideal template for epitaxial growth of heavy metals, such as Bi, which self-assemble into a hexagonal lattice with high kinetic and thermodynamic stability. Most remarkably, the Bi overlayer is atomically bonded to but electronically decoupled from the underlying Si substrate, exhibiting isolated quantum spin Hall state with an energy gap as large as ∼0.8 eV. This surprising phenomenon originates from an intriguing substrate-orbital-filtering effect, which critically selects the orbital composition around the Fermi level, leading to different topological phases. In particular, the substrate-orbital-filtering effect converts the otherwise topologically trivial freestanding Bi lattice into a nontrivial phase; and the reverse is true for Au lattice. The underlying physical mechanism is generally applicable, opening a new and exciting avenue for exploration of large-gap topological surface/interface states. PMID:25246584

  7. Thermoreversible, epitaxial fcc<-->bcc transitions in block copolymer solutions.

    PubMed

    Bang, Joona; Lodge, Timothy P; Wang, Xiaohui; Brinker, Kristin L; Burghardt, Wesley R

    2002-11-18

    Uncharged block copolymer micelles display thermoreversible transitions between close-packed and bcc lattices for a range of concentration, solvent selectivity, and copolymer composition. Using small-angle x-ray scattering on shear-oriented solutions, highly aligned fcc crystals are seen to transform epitaxially to bcc crystals, with fcc/bcc orientational relationships that are well established in martensitic transformations in metals. The transition is driven by decreasing solvent selectivity with increasing temperature, inducing solvent penetration of the micellar core.

  8. Gradient bounds for a thin film epitaxy equation

    NASA Astrophysics Data System (ADS)

    Li, Dong; Qiao, Zhonghua; Tang, Tao

    2017-02-01

    We consider a gradient flow modeling the epitaxial growth of thin films with slope selection. The surface height profile satisfies a nonlinear diffusion equation with biharmonic dissipation. We establish optimal local and global wellposedness for initial data with critical regularity. To understand the mechanism of slope selection and the dependence on the dissipation coefficient, we exhibit several lower and upper bounds for the gradient of the solution in physical dimensions d ≤ 3.

  9. Tuning the terahertz low-energy charge dynamics by simultaneous effect of epitaxial and anisotropic strain in PrNi O3 thin films

    NASA Astrophysics Data System (ADS)

    Phanindra, V. Eswara; Das, Sarmistha; Kumar, K. Santhosh; Agarwal, Piyush; Rana, Rakesh; Rana, D. S.

    2017-02-01

    The interplay of charge, spin, and lattice correlations strongly influence the insulator-metal (I-M) transition and magnetic ordering in rare earth nickelates. In this context, we explored the low-energy charge dynamics in structurally modulated PrNi O3 (PNO) thin films to unravel the complexity of ground state across I-M transition using terahertz (THz) spectroscopy. The THz optical constants of compressive film on LaAl O3 (100) substrate and the tensile films on NdGa O3 (100), (001), (110), and (111) substrates with varying orthorhombic distortion exhibit remarkably distinct features as a function of frequency and temperature. The THz conductivity of compressive film sans any I-M transition follows the Drude model. In contrast, the tensile strained films exhibit non-Drude THz conductivity, a giant positive dielectric permittivity, and negative imaginary conductivity, all of which can be explained by the Drude-Smith model. This rich variety of low-energy dynamics manifests as a function of temperature, strain, and crystal orientation. Such distinct THz spectral features, as induced by a subtle variation in strain while crossing over from tensile to compressive strain and with varying degree of orthorhombicity coupled with oxygen vacancies, reveal a novel facet of structure-property relationship of PNO.

  10. Daily energy intake, energy expenditure and activity patterns of selected Malaysian sportsmen.

    PubMed

    Ismail, M N; Wannudri, W; Zawiah, H

    1995-09-01

    Seventeen members of the national sepaktakraw squad undergoing centralised training participated in a comprehensive study to determine their daily food intake, activity patterns and energy requirements. Food intake was recorded as a mean of 3-days weighed food intake and the nutrient contents were calculated using a local food composition table. The energy cost of standardised activities was determined by indirect calorimetry while time and motion study was used to estimate the daily energy expenditure of each subject. The mean daily energy intake was 2784±373 kcal (11.6±1.6 MJ) while the mean daily energy expenditure was 3004±298 kcal (12.6±1.2 MJ), with a negative energy balance of 220 kcal ((0.9 MJ). Intake of other nutrients were adequate when compared with the Malaysian RDA, with the exception of niacin. The results of the activity pattern study indicated that the subjects spent about 80% of the day doing light activities while 20% of the day was devoted to their training programme comprising of moderate to heavy activities. This data set represents the first of its kind in Malaysia and should provide impetus for further research in this area which would help establish dietary guidelines for Malaysian sportsmen.

  11. Growth of EuO/Si and EuO/SrO/Si heteroepitaxial structures by molecular-beam epitaxy

    SciTech Connect

    Teterin, P. E. Averyanov, D. V.; Sadofyev, Yu. G. Parfenov, O. E.; Likhachev, I. A.; Storchak, V. G.

    2015-01-15

    Epitaxial EuO thin films with thickness up to 60 nm have been grown by molecular beam epitaxy both on SrO sublayers and directly on Si (001) substrates. Crystal structure has been controlled in situ by reflection high energy electron diffraction. Ex situ studies by X-ray diffraction and Rutherford backscattering have confirmed high crystalline quality of the films.

  12. Laser Induced Surface Chemical Epitaxy

    DTIC Science & Technology

    1990-03-01

    Laser-Induced Surface Chemical Epitaxy ( LSCE ). The essential features of LSCE as applied to CdTe epitaxy involve: coadsorption of DMCd and DMTe on a GaAs...DIAGRAM OF THE LSCE PROCESS UHV environment 1M substra1e 9 /X Adsorbed thin film produced CH 3 -Cd-GH 3 CH 3 -Te-CH, by molecular beam source hv ’ CH...with Anneal W/// substraIe %/"/,’ Figure 1.1. Schematic of the LSCE process. (1-2) t I 2. EXPERIMENTAL APPROACH 2.1 Experimental Apparatus The

  13. Current and future industrial energy service characterizations. Volume III. Energy data on 15 selected states' manufacturing subsector

    SciTech Connect

    Krawiec, F.; Thomas, T.; Jackson, F.; Limaye, D.R.; Isser, S.; Karnofsky, K.; Davis, T.D.

    1980-11-01

    An examination is made of the current and future energy demands, and uses, and cost to characterize typical applications and resulting services in the US and industrial sectors of 15 selected states. Volume III presents tables containing data on selected states' manufacturing subsector energy consumption, functional uses, and cost in 1974 and 1976. Alabama, California, Illinois, Indiana, Louisiana, Michigan, Missouri, New Jersey, New York, Ohio, Oregon, Pennsylvania, Texas, West Virginia, and Wisconsin were chosen as having the greatest potential for replacing conventional fuel with solar energy. Basic data on the quantities, cost, and types of fuel and electric energy purchased by industr for heat and power were obtained from the 1974 and 1976 Annual Survey of Manufacturers. The specific indutrial energy servic cracteristics developed for each selected state include. 1974 and 1976 manufacturing subsector fuels and electricity consumption by 2-, 3-, and 4-digit SIC and primary fuel (quantity and relative share); 1974 and 1976 manufacturing subsector fuel consumption by 2-, 3-, and 4-digit SIC and primary fuel (quantity and relative share); 1974 and 1976 manufacturing subsector average cost of purchsed fuels and electricity per million Btu by 2-, 3-, and 4-digit SIC and primary fuel (in 1976 dollars); 1974 and 1976 manufacturing subsector fuels and electric energy intensity by 2-, 3-, and 4-digit SIC and primary fuel (in 1976 dollars); manufacturing subsector average annual growth rates of (1) fuels and electricity consumption, (2) fuels and electric energy intensity, and (3) average cost of purchased fuels and electricity (1974 to 1976). Data are compiled on purchased fuels, distillate fuel oil, residual ful oil, coal, coal, and breeze, and natural gas. (MCW)

  14. Epitaxial gallium oxide on a SiC/Si substrate

    NASA Astrophysics Data System (ADS)

    Kukushkin, S. A.; Nikolaev, V. I.; Osipov, A. V.; Osipova, E. V.; Pechnikov, A. I.; Feoktistov, N. A.

    2016-09-01

    Well-textured gallium oxide β-Ga2O3 layers with a thickness of 1 μm and a close to epitaxial layer structure were grown by the method of chloride vapor phase epitaxy on Si(111) wafers with a nano-SiC buffer layer. In order to improve the growth, a high-quality silicon carbide buffer layer 100 nm thick was preliminarily synthesized by the substitution of atoms on the silicon surface. The β-Ga2O3 films were thoroughly investigated using reflection high-energy electron diffraction, ellipsometry, X-ray diffraction, scanning electron microscopy, and micro-Raman spectroscopy. The investigations revealed that the films are textured with a close to epitaxial structure and consist of a pure β-phase Ga2O3 with the (overline 2 01) orientation. The dependence of the dielectric constant of epitaxial β-Ga2O3 on the photon energy ranging from 0.7 to 6.5 eV in the isotropic approximation was measured.

  15. Temperature dependence of the energy gap of zinc-blende CdSe and Cd1 - xZnxSe epitaxial layers

    NASA Astrophysics Data System (ADS)

    Lunz, U.; Kuhn, J.; Goschenhofer, F.; Schüssler, U.; Einfeldt, S.; Becker, C. R.; Landwehr, G.

    1996-12-01

    The temperature dependence of the energy gap of zinc-blende CdSe and Cd1-xZnxSe has been determined over the entire range of composition from optical transmission and reflection measurements at temperatures between 5 and 300 K. The experimental results can be expressed by the following modified empirical Varshni formula, whose parameters are functions of the composition x: Eg(x,T)=Eg(x,0)-β(x)T2/[T+γ(x)]. Eg(x,0) exhibits a nonlinear dependence on composition, according to Eg=Eg(0,0)(1-x)+Eg(1,0)x-ax(1-x). The parameters β(x) and γ(x) can be expressed by β(x)=β(0)(1-x)+β(1)x+bx(1-x) and γ(x)=γ(0)(1-x)+γ(1)x.

  16. Asymmetric shape transitions of epitaxial quantum dots

    NASA Astrophysics Data System (ADS)

    Wei, Chaozhen; Spencer, Brian J.

    2016-06-01

    We construct a two-dimensional continuum model to describe the energetics of shape transitions in fully faceted epitaxial quantum dots (strained islands) via minimization of elastic energy and surface energy at fixed volume. The elastic energy of the island is based on a third-order approximation, enabling us to consider shape transitions between pyramids, domes, multifaceted domes and asymmetric intermediate states. The energetics of the shape transitions are determined by numerically calculating the facet lengths that minimize the energy of a given island type of prescribed island volume. By comparing the energy of different island types with the same volume and analysing the energy surface as a function of the island shape parameters, we determine the bifurcation diagram of equilibrium solutions and their stability, as well as the lowest barrier transition pathway for the island shape as a function of increasing volume. The main result is that the shape transition from pyramid to dome to multifaceted dome occurs through sequential nucleation of facets and involves asymmetric metastable transition shapes. We also explicitly determine the effect of corner energy (facet edge energy) on shape transitions and interpret the results in terms of the relative stability of asymmetric island shapes as observed in experiment.

  17. Line-on-Line Coincidence: A New Type of Epitaxy Found in Organic-Organic Heterolayers

    NASA Astrophysics Data System (ADS)

    Mannsfeld, Stefan C.; Leo, Karl; Fritz, Torsten

    2005-02-01

    We propose a new type of epitaxy, line-on-line coincidence (LOL), which explains the ordering in the organic-organic heterolayer system PTCDA on HBC on graphite. LOL epitaxy is similar to point-on-line coincidence (POL) in the sense that all overlayer molecules lie on parallel, equally spaced lines. The key difference to POL is that these lines are not restricted to primitive lattice lines of the substrate lattice. Potential energy calculations demonstrate that this new type of epitaxy is indeed characterized by a minimum in the overlayer-substrate interaction potential.

  18. Epitaxy on Substrates with Hexagonal Lattice Symmetry.

    NASA Astrophysics Data System (ADS)

    Braun, Max Willi Hermann

    A general description of epitaxy between thin films and substrates of general symmetry was developed from a model with rigid substrate and overgrowth and extended to include strain of the overgrowth. The overgrowth-substrate interaction was described by Fourier series, usually truncated, defined on the reciprocal lattice of the interface surfaces of the crystals. Energy considerations lead directly to a criterion that epitaxial configurations occur when a pair of surface reciprocal lattice vectors of the substrate and overgrowth coincide, equivalent to atomic row matching. This is analogous to the von Laue criterion and Bragg equations of diffraction theory, with a geometrical realization related to the Ewald construction. When generalized, misfit strain, the spacing, line sense and Burgers vectors of misfit dislocations and misfit verniers are obtained from the reciprocal lattices of crystals with any symmetry and misfit. The most general structures can be described with convenient unit cells by using structure factors. Homogeneous misfit strain, the interfacial atom positions after local relaxation and misfit and elastic (harmonic approximation) strain energies were obtained by direct minimization of the total interfacial energy of a large (1105 atoms), but finite, system. The local relaxation was calculated with a Finite Element formulation. Systems with fcc {111 } or bcc{ 110} overgrowths on fcc {111} or hcp{0001} substrates were studied with respect to substrate symmetry, overgrowth size and anisotropy of the overgrowth elastic constants. Configurations such as Kurdjumov-Sachs (KS), Nishiyama-Wassermann (NW) and a pseudomorphic phase (2DC) were explained, while several other higher order configurations were predicted. The inherent difference in nature between the KS and NW and their relationship to the 2DC were emphasized. Deviations from the ideal orientation of KS linked to anisotropy for systems undergoing misfit strain were discovered. Deviations were also

  19. Optical Properties of Epitaxially Grown Silver Films

    NASA Astrophysics Data System (ADS)

    Wu, Yanwen; Zhang, Chendong; Zhang, Matt; Shih, Chih-Kang; Li, Xiaoqin

    2013-03-01

    One major obstacle in the advancing field of plasmonics is the loss in metals. A sizable contribution of this loss comes from grain boundaries and surface roughness introduced during thin film growth using conventional deposition methods. A novel epitaxial growth technique is used to produce silver (Ag) thin films free of such flaws. We investigate the optical properties-namely the dielectric optical constants-of these new epitaxial films in the bulk region and in the ultrathin film limit where quantum mechanical behaviors emerge due to energy quantization in the growth direction. The values for the dielectric optical constants are extracted from the spectral ellipsometry (SE) measurements over a wide range of optical frequencies. By using an adequate model of the sample structure and initial values of the fitting parameters (i.e. the real and imaginary parts of the optical constants), we can extract these measured values for the new Ag films. We have confirmed that in the bulk region, the optical constants converge with the well-known Johnson and Christy measurements. In the ultrathin film limit, however, we observed significant changes near the D-band transition likely due to a quantum well-like density of states. Equal contribution. Also affiliated with Department of Physics, The University of South Carolina, Columbia, SC 29208

  20. Molecular Beam Epitaxy,

    DTIC Science & Technology

    1981-07-30

    between the two types. In the former case, molecules can grow directly either at positions of low potential energy on the surface of substrate of...molecules ave re-evaporated fi, a the surface arid carried away by the vacum systc::,. Withln the r’ nje Let;. the onset of deposition and the constant... energy electron diffrac- tion, high energy electro diffraction and Aug.er spectrometers should be installed as surface analysis instruments. The present

  1. Final report on implementation of energy conservation practices training in selected public housing developments

    SciTech Connect

    Not Available

    1991-10-01

    This report on the implementation of energy conservation practices training in selected public housing developments represents an initiative of the Research and Education Division, Office of Minority Economic Impact, US Department of Energy. The Office of Minority Economic Impact (MI) was created by Congress in 1979, within the US Department of Energy, to afford the Secretary advice on the effect policies, regulations and other actions of DOE respecting minority participation in energy programs. The Director of MI is responsible for the conduct of ongoing research into the effects, including socio-economic and environmental, of national energy programs, policies, and regulations of the Department of minorities. Public housing in the United States is dominated by minorities, public housing is a large consumer of residential energy. Consequently, this project is a logical merging of these two factors and an attempt to somehow influence energy savings through improving public housing residents' energy-consumption practices. This final report attempts to capture the results of this current demonstration, and incorporate the historical basis for today's results by renewing the efforts that preceded the implementation of energy conservation practices training in selected public housing developments.

  2. Final report on implementation of energy conservation practices training in selected public housing developments

    SciTech Connect

    Not Available

    1991-10-01

    This report on the implementation of energy conservation practices training in selected public housing developments represents an initiative of the Research and Education Division, Office of Minority Economic Impact, US Department of Energy. The Office of Minority Economic Impact (MI) was created by Congress in 1979, within the US Department of Energy, to afford the Secretary advice on the effect policies, regulations and other actions of DOE respecting minority participation in energy programs. The Director of MI is responsible for the conduct of ongoing research into the effects, including socio-economic and environmental, of national energy programs, policies, and regulations of the Department of minorities. Public housing in the United States is dominated by minorities, public housing is a large consumer of residential energy. Consequently, this project is a logical merging of these two factors and an attempt to somehow influence energy savings through improving public housing residents` energy-consumption practices. This final report attempts to capture the results of this current demonstration, and incorporate the historical basis for today`s results by renewing the efforts that preceded the implementation of energy conservation practices training in selected public housing developments.

  3. Expected Satiety: Application to Weight Management and Understanding Energy Selection in Humans.

    PubMed

    Forde, Ciarán G; Almiron-Roig, Eva; Brunstrom, Jeffrey M

    2015-03-01

    Recent advances in the approaches used to quantify expectations of satiation and satiety have led to a better understanding of how humans select and consume food, and the associated links to energy intake regulation. When compared calorie for calorie some foods are expected to deliver several times more satiety than others, and multiple studies have demonstrated that people are able to discriminate between similar foods reliably and with considerable sensitivity. These findings have implications for the control of meal size and the design of foods that can be used to lower the energy density of diets. These methods and findings are discussed in terms of their implications for weight management. The current paper also highlights why expected satiety may also play an important role beyond energy selection, in moderating appetite sensations after a meal has been consumed, through memory for recent eating and the selection of foods across future meals.

  4. Selecting representative climate stations for use in a building energy model

    SciTech Connect

    Hadley, D.L.

    1993-11-01

    An energy impacts model is being refined to support ongoing development of major energy conservation standards for US commercial buildings. When completed, the model will be used to evaluate potential impacts (energy savings and associated costs) of implementing the proposed standards. To work as intended, the model must contain a set of climate stations to represent the wide range of climatic conditions that occur across the United States. Researchers developed a procedure that employs a user-selectable climate database (1) to objectively identify, using a clustering technique, a unique set of climate zones for a specified geographical area, and (2) to specify the single most representative station for each climate zone. The process provides a more objective, technically sound basis for selecting climate zones and stations, thereby minimizing researcher bias. The procedure and its application to US energy conservation standards development activities are described in this paper.

  5. Transport and energy selection of laser generated protons for postacceleration with a compact linac

    NASA Astrophysics Data System (ADS)

    Sinigardi, Stefano; Turchetti, Giorgio; Londrillo, Pasquale; Rossi, Francesco; Giove, Dario; De Martinis, Carlo; Sumini, Marco

    2013-03-01

    Laser accelerated proton beams have a considerable potential for various applications including oncological therapy. However, the most consolidated target normal sheath acceleration regime based on irradiation of solid targets provides an exponential energy spectrum with a significant divergence. The low count number at the cutoff energy seriously limits at present its possible use. One realistic scenario for the near future is offered by hybrid schemes. The use of transport lines for collimation and energy selection has been considered. We present here a scheme based on a high field pulsed solenoid and collimators which allows one to select a beam suitable for injection at 30 MeV into a compact linac in order to double its energy while preserving a significant intensity. The results are based on a fully 3D simulation starting from laser acceleration.

  6. Integrated environmental and safety assessment of selected mechanical energy storage systems

    NASA Astrophysics Data System (ADS)

    1982-01-01

    The environmental, safety, and social impacts of two mechanical storage systems, underground pumped hydro (UPH) and compressed air energy storage (CAES) are similar to those of existing peaking power plants. These impacts, with engineering factors, form a methodology for selecting sites for these two systems. Application of this methodology to a hypothetical case indicates that, although design alternatives which mitigate adverse environmental impacts are recommended, site selection effectively limits the environmental effect of CAES or UPH plants. Public perception of CAES and UPH energy storage facilities should generally be positive, provided that those affected are informed and allowed to participate in the siting process.

  7. Linking habitat selection to fitness-related traits in herbivores: the role of the energy landscape.

    PubMed

    Long, Ryan A; Bowyer, R T; Porter, Warren P; Mathewson, Paul; Monteith, Kevin L; Findholt, Scott L; Dick, Brian L; Kie, John G

    2016-07-01

    Animals may partially overcome environmental constraints on fitness by behaviorally adjusting their exposure to costs and supplies of energy. Few studies, however, have linked spatiotemporal variation in the energy landscape to behaviorally mediated measures of performance that ostensibly influence individual fitness. We hypothesized that strength of selection by North American elk (Cervus elaphus) for areas that reduced costs of thermoregulation and activity, and increased access to high-quality forage, would influence four energetically mediated traits related to fitness: birth mass of young, nutritional condition of adult females at the onset of winter, change in nutritional condition of females between spring and winter, and neonatal survival. We used a biophysical model to map spatiotemporally explicit costs of thermoregulation and activity experienced by elk in a heterogeneous landscape. We then combined model predictions with data on forage characteristics, animal locations, nutritional condition, and mass and survival of young to evaluate behaviorally mediated effects of the energy landscape on fitness-related traits. During spring, when high-quality forage was abundant, female elk that consistently selected low-cost areas before parturition gave birth to larger young than less-selective individuals, and birth mass had a strong, positive influence on probability of survival. As forage quality declined during autumn, however, lactating females that consistently selected the highest quality forage available accrued more fat and entered winter in better condition than less-selective individuals. Results of our study highlight the importance of understanding the dynamic nature of energy landscapes experienced by free-ranging animals.

  8. First Attempts on Energy-selective Neutron Imaging at IBR-2

    NASA Astrophysics Data System (ADS)

    Lukin, E. V.; Kozlenko, D. P.; Kichanov, S. E.; Rutkauskas, A. V.; Bokuchava, G. D.; Savenko, B. N.

    A new neutron imaging facility has been started at the IBR-2 high flux pulsed reactor. It isattractive not only for traditional neutron imaging applications but in particular also for thedevelopment of modern energy-selective techniques using a time-of-flight methods.A short overview of the first obtained results of theenergy-selected experiments by means of time-of-flight methods realised on neutron radiography and tomography station on high-flux pulsed reactor IBR-2 are presented.

  9. Free energy calculation provides insight into the action mechanism of selective PARP-1 inhibitor.

    PubMed

    Cao, Ran

    2016-04-01

    Selective poly (ADP-ribose) polymerase (PARP)-1 inhibitor represents promising therapy against cancers with a good balance between efficacy and safety. Owing to the conserved structure between PARP-1 and PARP-2, most of the clinical and experimental drugs show equivalent inhibition against both targets. Most recently, it's disclosed a highly selective PARP-1 inhibitor (NMS-P118) with promising pharmacokinetic properties. Herein, we combined molecular simulation with free energy calculation to gain insights into the selective mechanism of NMS-P118. Our results suggest the reduction of binding affinity for PARP-2 is attributed to the unfavorable conformational change of protein, which is accompanied by a significant energy penalty. Alanine-scanning mutagenesis study further reveals the important role for a tyrosine residue of donor loop (Tyr889(PARP-1) and Tyr455(PARP-2)) in contributing to the ligand selectivity. Retrospective structural analysis indicates the ligand-induced movement of Tyr455(PARP-2) disrupts the intra-molecule hydrogen bonding network, which partially accounts for the "high-energy" protein conformation in the presence of NMS-P118. Interestingly, such effect isn't observed in other non-selective PARP inhibitors including BMN673 and A861695, which validates the computational prediction. Our work provides energetic insight into the subtle variations in the crystal structures and could facilitate rational design of new selective PARP inhibitor.

  10. Ultrathin and Ion-Selective Janus Membranes for High-Performance Osmotic Energy Conversion.

    PubMed

    Zhang, Zhen; Sui, Xin; Li, Pei; Xie, Ganhua; Kong, Xiang-Yu; Xiao, Kai; Gao, Longcheng; Wen, Liping; Jiang, Lei

    2017-07-05

    The osmotic energy existing in fluids is recognized as a promising "blue" energy source that can help solve the global issues of energy shortage and environmental pollution. Recently, nanofluidic channels have shown great potential for capturing this worldwide energy because of their novel transport properties contributed by nanoconfinement. However, with respect to membrane-scale porous systems, high resistance and undesirable ion selectivity remain bottlenecks, impeding their applications. The development of thinner, low-resistance membranes, meanwhile promoting their ion selectivity, is a necessity. Here, we engineered ultrathin and ion-selective Janus membranes prepared via the phase separation of two block copolymers, which enable osmotic energy conversion with power densities of approximately 2.04 W/m(2) by mixing natural seawater and river water. Both experiments and continuum simulation help us to understand the mechanism for how membrane thickness and channel structure dominate the ion transport process and overall device performance, which can serve as a general guiding principle for the future design of nanochannel membranes for high-energy concentration cells.

  11. Merriam's kangaroo rats (Dipodomys merriami) voluntarily select temperatures that conserve energy rather than water.

    PubMed

    Banta, Marilyn R

    2003-01-01

    Desert endotherms such as Merriam's kangaroo rat (Dipodomys merriami) use both behavioral and physiological means to conserve energy and water. The energy and water needs of kangaroo rats are affected by their thermal environment. Animals that choose temperatures within their thermoneutral zone (TNZ) minimize energy expenditure but may impair water balance because the ratio of water loss to water gain is high. At temperatures below the TNZ, water balance may be improved because animals generate more oxidative water and reduce evaporative water loss; however, they must also increase energy expenditure to maintain a normal body temperature. Hence, it is not possible for kangaroo rats to choose thermal environments that simultaneously minimize energy expenditure and increase water conservation. I used a thermal gradient to test whether water stress, energy stress, simultaneous water and energy stress, or no water/energy stress affected the thermal environment selected by D. merriami. During the night (i.e., active phase), animals in all four treatments chose temperatures near the bottom of their TNZ. During the day (i.e., inactive phase), animals in all four treatments settled at temperatures near the top of their TNZ. Thus, kangaroo rats chose thermal environments that minimized energy requirements, not water requirements. Because kangaroo rats have evolved high water use efficiency, energy conservation may be more important than water conservation to the fitness of extant kangaroo rats.

  12. Polydomain structures in ferroelectric and ferroelastic epitaxial films

    NASA Astrophysics Data System (ADS)

    Roytburd, Alexander L.; Ouyang, Jun; Artemev, Andrei

    2017-04-01

    A review of theoretical models, phase field modeling and experimental studies of domain structures in epitaxial films is presented. The thermodynamic theory of such domain structures is presented within the macroscopic thermo-mechanical framework. The theory allows for the evaluation of the main parameters of the domain structure using the energy minimization approach applied to the energy of elastic interactions. For homophase (polytwin) films, the thermodynamic theory provides a quantitative tool that can be used to estimate domain fractions in the film and the type of domain structure architecture. For heterophase films, the theory describes (a) the conditions under which two-phase structures can be obtained in epitaxial films, and (b) the phase and domain fractions in these films. The thermodynamic theory can also be used to describe the extrinsic contributions from domain structures to the functional properties of epitaxial ferroelectric films. The review of phase field modeling demonstrates that computational results reproduce the predictions of the thermodynamic theory. It is also shown that the phase field modeling that utilizes the energy minimization procedure for elastic and interfacial energies can be used to predict domain morphology for the films with two-phase structures produced either by phase transformation or through the co-deposition of immiscible phases. The experimental data presented in the review validate predictions of the thermodynamic model and the results of phase field modeling.

  13. Selective detection of mitochondrial malfunction in situ by energy transfer spectroscopy

    NASA Astrophysics Data System (ADS)

    Schneckenburger, Herbert; Gschwend, Michael H.; Sailer, Reinhard; Strauss, Wolfgang S. L.; Schoch, Lars; Schuh, Alexander; Stock, Karl; Steiner, Rudolf W.; Zipfl, Peter

    1999-01-01

    To establish optical in situ detection of mitochondrial malfunction, non-radiative energy transfer from the coenzyme NADH to the mitochondrial marker rhodamine 123 (R123) was examined. Dual excitation of R123 via energy transfer from excited NADH molecules as well as by direct absorption of light results in two fluorescence signals whose ratio is a measure of mitochondrial NADH. These signals are detected simultaneously using a time-gated (nanosecond) technique for energy transfer measurements and a frequency selective technique for direct excitation and fluorescence monitoring of R123. Optical and electronic components of the experimental setup are described and compared with a previously established microscopic system.

  14. Efficient Interlayer Relaxation and Transition of Excitons in Epitaxial and Non-epitaxial MoS2/WS2 Heterostructures

    SciTech Connect

    Yu, Yifei; Hu, Shi; Su, Liqin; Huang, Lujun; Liu, Yi; Jin, Zhenghe; Puretzky, Alexander A.; Geohegan, David B.; Kim, Ki Wook; Zhang, Yong; Cao, Linyou

    2014-12-03

    Semiconductor heterostructurs provide a powerful platform for the engineering of excitons. Here we report on the excitonic properties of two-dimensional (2D) heterostructures that consist of monolayer MoS2 and WS2 stacked epitaxially or non-epitaxially in the vertical direction. We find similarly efficient interlayer relaxation and transition of excitons in both the epitaxial and non-epitaxial heterostructures. This is manifested by a two orders of magnitude decrease in the photoluminescence and an extra absorption peak at low energy region of both heterostructures. The MoS2/WS2 heterostructures show weak interlayer coupling and essentially act as an atomic-scale heterojunction with the intrinsic band structures of the two monolayers largely preserved. They are particularly promising for the applications that request efficient dissociation of excitons and strong light absorption, including photovoltaics, solar fuels, photodetectors, and optical modulators. Our results also indicate that 2D heterostructures promise to provide capabilities to engineer excitons from the atomic level without concerns of interfacial imperfection.

  15. Efficient Interlayer Relaxation and Transition of Excitons in Epitaxial and Non-epitaxial MoS2/WS2 Heterostructures

    DOE PAGES

    Yu, Yifei; Hu, Shi; Su, Liqin; ...

    2014-12-03

    Semiconductor heterostructurs provide a powerful platform for the engineering of excitons. Here we report on the excitonic properties of two-dimensional (2D) heterostructures that consist of monolayer MoS2 and WS2 stacked epitaxially or non-epitaxially in the vertical direction. We find similarly efficient interlayer relaxation and transition of excitons in both the epitaxial and non-epitaxial heterostructures. This is manifested by a two orders of magnitude decrease in the photoluminescence and an extra absorption peak at low energy region of both heterostructures. The MoS2/WS2 heterostructures show weak interlayer coupling and essentially act as an atomic-scale heterojunction with the intrinsic band structures of themore » two monolayers largely preserved. They are particularly promising for the applications that request efficient dissociation of excitons and strong light absorption, including photovoltaics, solar fuels, photodetectors, and optical modulators. Our results also indicate that 2D heterostructures promise to provide capabilities to engineer excitons from the atomic level without concerns of interfacial imperfection.« less

  16. Friction boosted by spontaneous epitaxial rotations

    NASA Astrophysics Data System (ADS)

    Mandelli, Davide; Vanossi, Andrea; Manini, Nicola; Tosatti, Erio

    2015-03-01

    It is well known in surface science that incommensurate adsorbed monolayers undergo a spontaneous, energy-lowering epitaxial rotation from aligned to misaligned relative to a periodic substrate. We show first of all that a model 2D colloidal monolayer in an optical lattice, of recent importance as a frictional model, also develops in full equilibrium a small rotation angle, easy to detect in the Moiré pattern. The colloidal monolayer misalignment is then shown by extensive sliding simulations to increase the dynamic friction by a considerable factor over the aligned case. More generally, this example suggests that spontaneous rotations are rather ubiquitous and should not be ignored in all tribological phenomena between mismatched lattices. This work was mainly supported by the ERC Advanced Grant No. 320796-MODPHYSFRICT, and partly by SINERGIA contract CRSII2 136287, by PRIN/COFIN Contract 2010LLKJBX 004, by COST Action MP1303.

  17. Infrared Rugates by Molecular Beam Epitaxy

    NASA Technical Reports Server (NTRS)

    Rona, M.

    1993-01-01

    Rugates are optical structures that have a sinusoidal index of refraction (harmonic gradient-index field). As their discrete high/ low index filter counterparts, they can be used as narrow rejection band filters. However, since rugates do not have abrupt interfaces, they tend to have a smaller absorption, hence deliver a higher in band reflectivity. The absence of sharp interfaces makes rugates even more desirable for high-energy narrow band reflectors. In this application, the lack of a sharp interface at the maximum internal standing wave electric field results in higher breakdown strengths. Our method involves fabricating rugates, with molecular beam epitaxy, on GaAs wafers as an Al(x)Ga(1-x)As single-crystal film.

  18. Selected Resource Materials for Developing Energy Conservation Programs in the Small Business/Commercial Sector.

    ERIC Educational Resources Information Center

    Lengyel, Dorothy L.; And Others

    This annotated bibliography is a selected listing of references for use by small business managers in the development of energy conservation programs. The references are listed under the agency through which they are available. The agency listings are alphabetized and include complete mailing addresses. There are 35 agency listings, many of which…

  19. Selective Energy Feasibility Study -- Richmond College, City University of New York

    ERIC Educational Resources Information Center

    Consulting Engineer, 1974

    1974-01-01

    A study of the presently available data on magnitude, duration, and coincidence of electrical demands determined that onsite electrical power generation in the form of a selective energy system should be incorporated within the central utilities plant projected for the Richmond College Campus of the City University of New York (CUNY). (Author/MLF)

  20. Selected Resource Materials for Developing Energy Conservation Programs in the Small Business/Commercial Sector.

    ERIC Educational Resources Information Center

    Lengyel, Dorothy L.; And Others

    This annotated bibliography is a selected listing of references for use by small business managers in the development of energy conservation programs. The references are listed under the agency through which they are available. The agency listings are alphabetized and include complete mailing addresses. There are 35 agency listings, many of which…

  1. Selective Energy Feasibility Study -- Richmond College, City University of New York

    ERIC Educational Resources Information Center

    Consulting Engineer, 1974

    1974-01-01

    A study of the presently available data on magnitude, duration, and coincidence of electrical demands determined that onsite electrical power generation in the form of a selective energy system should be incorporated within the central utilities plant projected for the Richmond College Campus of the City University of New York (CUNY). (Author/MLF)

  2. Evaluation and Selection of Renewable Energy Technologies for Highway Maintenance Facilities

    NASA Astrophysics Data System (ADS)

    Andrews, Taylor

    The interest in renewable energy has been increasing in recent years as attempts to reduce energy costs as well the consumption of fossil fuels are becoming more common. Companies and organizations are recognizing the increasing reliance on limited fossil fuels' resources, and as competition and costs for these resources grow, alternative solutions are becoming more appealing. Many federally run buildings and associations also have the added pressure of meeting the mandates of federal energy policies that dictate specific savings or reductions. Federal highway maintenance facilities run by the Department of Transportation fall into this category. To help meet energy saving goals, an investigation into potential renewable energy technologies was completed for the Ohio Department of Transportation. This research examined several types of renewable energy technologies and the major factors that affect their performance and evaluated their potential for implementation at highway maintenance facilities. Facilities energy usage data were provided, and a facility survey and site visits were completed to enhance the evaluation of technologies and the suitability for specific projects. Findings and technology recommendations were presented in the form of selection matrices, which were designed to help make selections in future projects. The benefits of utilization of other tools such as analysis software and life cycle assessments were also highlighted. These selection tools were designed to be helpful guides when beginning the pursuit of a renewable energy technology for highway maintenance facilities, and can be applied to other similar building types and projects. This document further discusses the research strategies and findings as well as the recommendations that were made to the personnel overseeing Ohio's highway maintenance facilities.

  3. Angular selective window systems: Assessment of technical potential for energy savings

    DOE PAGES

    Fernandes, Luis L.; Lee, Eleanor S.; McNeil, Andrew; ...

    2014-10-16

    Static angular selective shading systems block direct sunlight and admit daylight within a specific range of incident solar angles. The objective of this study is to quantify their potential to reduce energy use and peak demand in commercial buildings using state-of-the art whole-building computer simulation software that allows accurate modeling of the behavior of optically-complex fenestration systems such as angular selective systems. Three commercial systems were evaluated: a micro-perforated screen, a tubular shading structure, and an expanded metal mesh. This evaluation was performed through computer simulation for multiple climates (Chicago, Illinois and Houston, Texas), window-to-wall ratios (0.15-0.60), building codes (ASHRAEmore » 90.1-2004 and 2010) and lighting control configurations (with and without). The modeling of the optical complexity of the systems took advantage of the development of state-of-the-art versions of the EnergyPlus, Radiance and Window simulation tools. Results show significant reductions in perimeter zone energy use; the best system reached 28% and 47% savings, respectively without and with daylighting controls (ASHRAE 90.1-2004, south facade, Chicago,WWR=0.45). As a result, angular selectivity and thermal conductance of the angle-selective layer, as well as spectral selectivity of low-emissivity coatings, were identified as factors with significant impact on performance.« less

  4. Angular selective window systems: Assessment of technical potential for energy savings

    SciTech Connect

    Fernandes, Luis L.; Lee, Eleanor S.; McNeil, Andrew; Jonsson, Jacob C.; Nouidui, Thierry; Pang, Xiufeng; Hoffmann, Sabine

    2014-10-16

    Static angular selective shading systems block direct sunlight and admit daylight within a specific range of incident solar angles. The objective of this study is to quantify their potential to reduce energy use and peak demand in commercial buildings using state-of-the art whole-building computer simulation software that allows accurate modeling of the behavior of optically-complex fenestration systems such as angular selective systems. Three commercial systems were evaluated: a micro-perforated screen, a tubular shading structure, and an expanded metal mesh. This evaluation was performed through computer simulation for multiple climates (Chicago, Illinois and Houston, Texas), window-to-wall ratios (0.15-0.60), building codes (ASHRAE 90.1-2004 and 2010) and lighting control configurations (with and without). The modeling of the optical complexity of the systems took advantage of the development of state-of-the-art versions of the EnergyPlus, Radiance and Window simulation tools. Results show significant reductions in perimeter zone energy use; the best system reached 28% and 47% savings, respectively without and with daylighting controls (ASHRAE 90.1-2004, south facade, Chicago,WWR=0.45). As a result, angular selectivity and thermal conductance of the angle-selective layer, as well as spectral selectivity of low-emissivity coatings, were identified as factors with significant impact on performance.

  5. Optimal energy window selection of a CZT-based small-animal SPECT for quantitative accuracy

    NASA Astrophysics Data System (ADS)

    Park, Su-Jin; Yu, A. Ram; Choi, Yun Young; Kim, Kyeong Min; Kim, Hee-Joung

    2015-05-01

    Cadmium zinc telluride (CZT)-based small-animal single-photon emission computed tomography (SPECT) has desirable characteristics such as superior energy resolution, but data acquisition for SPECT imaging has been widely performed with a conventional energy window. The aim of this study was to determine the optimal energy window settings for technetium-99 m (99mTc) and thallium-201 (201Tl), the most commonly used isotopes in SPECT imaging, using CZT-based small-animal SPECT for quantitative accuracy. We experimentally investigated quantitative measurements with respect to primary count rate, contrast-to-noise ratio (CNR), and scatter fraction (SF) within various energy window settings using Triumph X-SPECT. The two ways of energy window settings were considered: an on-peak window and an off-peak window. In the on-peak window setting, energy centers were set on the photopeaks. In the off-peak window setting, the ratios of energy differences between the photopeak from the lower- and higher-threshold varied from 4:6 to 3:7. In addition, the energy-window width for 99mTc varied from 5% to 20%, and that for 201Tl varied from 10% to 30%. The results of this study enabled us to determine the optimal energy windows for each isotope in terms of primary count rate, CNR, and SF. We selected the optimal energy window that increases the primary count rate and CNR while decreasing SF. For 99mTc SPECT imaging, the energy window of 138-145 keV with a 5% width and off-peak ratio of 3:7 was determined to be the optimal energy window. For 201Tl SPECT imaging, the energy window of 64-85 keV with a 30% width and off-peak ratio of 3:7 was selected as the optimal energy window. Our results demonstrated that the proper energy window should be carefully chosen based on quantitative measurements in order to take advantage of desirable characteristics of CZT-based small-animal SPECT. These results provided valuable reference information for the establishment of new protocol for CZT

  6. Influence of Energy Input on Degradation Behavior of Plastic Components Manufactured by Selective Laser Melting

    NASA Astrophysics Data System (ADS)

    Drummer, Dietmar; Wudy, Katrin; Drexler, Maximilian

    Additive manufacturing techniques, such as selective laser melting of plastics, generate components directly from a CAD data set without using a specific mold. High building chamber temperatures in combination with long building times lead to physical and chemical degradation of the surrounding powder and the manufactured component in the case of selective laser melting of polyamide 12 (PA12). Thus the following investigations show the influence of energy densities on mechanical properties as well as on the aging behavior of the manufactured components. Therefore several building processes with varying energy densities will be conducted. Aged polymer components were analyzed with physical, thermo analytical and mechanical methods with regards to their process relevant material properties. Considered material properties for example are phase transition temperatures, melting viscosity or molecular weight. The basic understanding of the influence of energy input on material properties will lead to new process strategies with minimized polymer degradation.

  7. On the density of states of disordered epitaxial graphene

    SciTech Connect

    Davydov, S. Yu.

    2015-05-15

    The study is concerned with two types of disordered epitaxial graphene: (i) graphene with randomly located carbon vacancies and (ii) structurally amorphous graphene. The former type is considered in the coherent potential approximation, and for the latter type, a model of the density of states is proposed. The effects of two types of substrates, specifically, metal and semiconductor substrates are taken into account. The specific features of the density of states of epitaxial graphene at the Dirac point and the edges of the continuous spectrum are analyzed. It is shown that vacancies in epitaxial graphene formed on the metal substrate bring about logarithmic nulling of the density of states of graphene at the Dirac point and the edges of the continuous spectrum. If the Dirac point corresponds to the middle of the band gap of the semiconductor substrate, the linear trend of the density of states to zero in the vicinity of the Dirac point in defect-free graphene transforms into a logarithmic decrease in the presence of vacancies. In both cases, the graphene-substrate interaction is assumed to be weak (quasi-free graphene). In the study of amorphous epitaxial graphene, a simple model of free amorphous graphene is proposed as the initial model, in which account is taken of the nonzero density of states at the Dirac point, and then the interaction of the graphene sheet with the substrate is taken into consideration. It is shown that, near the Dirac point, the quadratic behavior of the density of states of free amorphous graphene transforms into a linear dependence for amorphous epitaxial graphene. In the study, the density of states of free graphene corresponds to the low-energy approximation of the electron spectrum.

  8. Characterizing China's energy consumption with selective economic factors and energy-resource endowment: a spatial econometric approach

    NASA Astrophysics Data System (ADS)

    Jiang, Lei; Ji, Minhe; Bai, Ling

    2014-09-01

    Coupled with intricate regional interactions, the provincial disparity of energy-resource endowment and other economic conditions in China have created spatially complex energy consumption patterns that require analyses beyond the traditional ones. To distill the spatial effect out of the resource and economic factors on China's energy consumption, this study recast the traditional econometric model in a spatial context. Several analytic steps were taken to reveal different aspects of the issue. Per capita energy consumption (AVEC) at the provincial level was first mapped to reveal spatial clusters of high energy consumption being located in either well developed or energy resourceful regions. This visual spatial autocorrelation pattern of AVEC was quantitatively tested to confirm its existence among Chinese provinces. A Moran scatterplot was employed to further display a relatively centralized trend occurring in those provinces that had parallel AVEC, revealing a spatial structure with attraction among high-high or low-low regions and repellency among high-low or low-high regions. By a comparison between the ordinary least square (OLS) model and its spatial econometric counterparts, a spatial error model (SEM) was selected to analyze the impact of major economic determinants on AVEC. While the analytic results revealed a significant positive correlation between AVEC and economic development, other determinants showed some intricate influential patterns. The provinces endowed with rich energy reserves were inclined to consume much more energy than those otherwise, whereas changing the economic structure by increasing the proportion of secondary and tertiary industries also tended to consume more energy. Both situations seem to underpin the fact that these provinces were largely trapped in the economies that were supported by technologies of low energy efficiency during the period, while other parts of the country were rapidly modernized by adopting advanced

  9. Characterizing China's energy consumption with selective economic factors and energy-resource endowment: a spatial econometric approach

    NASA Astrophysics Data System (ADS)

    Jiang, Lei; Ji, Minhe; Bai, Ling

    2015-06-01

    Coupled with intricate regional interactions, the provincial disparity of energy-resource endowment and other economic conditions in China have created spatially complex energy consumption patterns that require analyses beyond the traditional ones. To distill the spatial effect out of the resource and economic factors on China's energy consumption, this study recast the traditional econometric model in a spatial context. Several analytic steps were taken to reveal different aspects of the issue. Per capita energy consumption (AVEC) at the provincial level was first mapped to reveal spatial clusters of high energy consumption being located in either well developed or energy resourceful regions. This visual spatial autocorrelation pattern of AVEC was quantitatively tested to confirm its existence among Chinese provinces. A Moran scatterplot was employed to further display a relatively centralized trend occurring in those provinces that had parallel AVEC, revealing a spatial structure with attraction among high-high or low-low regions and repellency among high-low or low-high regions. By a comparison between the ordinary least square (OLS) model and its spatial econometric counterparts, a spatial error model (SEM) was selected to analyze the impact of major economic determinants on AVEC. While the analytic results revealed a significant positive correlation between AVEC and economic development, other determinants showed some intricate influential patterns. The provinces endowed with rich energy reserves were inclined to consume much more energy than those otherwise, whereas changing the economic structure by increasing the proportion of secondary and tertiary industries also tended to consume more energy. Both situations seem to underpin the fact that these provinces were largely trapped in the economies that were supported by technologies of low energy efficiency during the period, while other parts of the country were rapidly modernized by adopting advanced

  10. Chemical Vapor Deposition Epitaxy an Patternless and Patterned Substrates.

    ERIC Educational Resources Information Center

    Takoudis, Christos G.

    1990-01-01

    Discusses chemical vapor deposition epitaxy on patternless and patterned substrates for an electronic materials processing course. Describes the processs types and features of epitaxy. Presents some potential problems of epitaxy. Lists 38 references. (YP)

  11. Structural and electronic properties of molecular beam epitaxially grown Ni1+xTiSn films

    NASA Astrophysics Data System (ADS)

    Rice, A. D.; Kawasaki, J. K.; Verma, N.; Pennachio, D. J.; Schultz, B. D.; Palmstrøm, C. J.

    2017-06-01

    This paper demonstrates the molecular beam epitaxial growth of metallic full-Heusler Ni2TiSn precipitates within semiconducting NiTiSn host matrix, and discusses the structural and chemical stability of this biphasic epitaxial composite and its influence on the electronic properties. Structural properties of the epitaxial films were characterized by in-situ reflection high-energy electron diffraction and ex-situ by X-ray diffraction and transmission electron microscopy. The results indicate the presence of a secondary phase with full Heusler ordering within half-Heusler host matrix. Both the parent half-Heusler and the secondary full-Heusler phases in the epitaxial films are strained from their bulk lattice parameters. Electronic properties show an increase in resistivity at low Ni excess.

  12. Epitaxial Garnets and Hexagonal Ferrites.

    DTIC Science & Technology

    1982-04-20

    Iron Garnet Liquid Phase Epitaxy Hexagonal Ferrite microwave Signal Processing Millimeter-Wave 20. ABSTRACT (Continue ani revee arde if necoeermy and...le.’uIfy by block rns.) e objective of this research is to develop new and improved epitauial ferrite materials for use in microwave and millimeter... ferrite films suitable for microwave and millimeter-wave signal processing at frequencies above 1 GHz. The specific tasks are: a. Analyze and develop

  13. Recent developments in droplet epitaxy

    SciTech Connect

    Mano, Takaaki; Jo, Masafumi; Kuroda, Takashi; Abbarchi, Marco; Noda, Takeshi; Sakoda, Kazuaki

    2014-05-15

    The droplet epitaxy allows for self-assembly of lattice-matched GaAs quantum dots (QDs) with high quality and high uniformity. In this article, we show our efforts to realize the GaAs QDs with excellent optical properties. After the optimization of the several growth processes, we achieved current-injection lasing in the GaAs QDs. In addition, formation of further advanced nanostructure is presented.

  14. Fuzzy C-Means Clustering and Energy Efficient Cluster Head Selection for Cooperative Sensor Network.

    PubMed

    Bhatti, Dost Muhammad Saqib; Saeed, Nasir; Nam, Haewoon

    2016-09-09

    We propose a novel cluster based cooperative spectrum sensing algorithm to save the wastage of energy, in which clusters are formed using fuzzy c-means (FCM) clustering and a cluster head (CH) is selected based on a sensor's location within each cluster, its location with respect to fusion center (FC), its signal-to-noise ratio (SNR) and its residual energy. The sensing information of a single sensor is not reliable enough due to shadowing and fading. To overcome these issues, cooperative spectrum sensing schemes were proposed to take advantage of spatial diversity. For cooperative spectrum sensing, all sensors sense the spectrum and report the sensed energy to FC for the final decision. However, it increases the energy consumption of the network when a large number of sensors need to cooperate; in addition to that, the efficiency of the network is also reduced. The proposed algorithm makes the cluster and selects the CHs such that very little amount of network energy is consumed and the highest efficiency of the network is achieved. Using the proposed algorithm maximum probability of detection under an imperfect channel is accomplished with minimum energy consumption as compared to conventional clustering schemes.

  15. Fuzzy C-Means Clustering and Energy Efficient Cluster Head Selection for Cooperative Sensor Network

    PubMed Central

    Bhatti, Dost Muhammad Saqib; Saeed, Nasir; Nam, Haewoon

    2016-01-01

    We propose a novel cluster based cooperative spectrum sensing algorithm to save the wastage of energy, in which clusters are formed using fuzzy c-means (FCM) clustering and a cluster head (CH) is selected based on a sensor’s location within each cluster, its location with respect to fusion center (FC), its signal-to-noise ratio (SNR) and its residual energy. The sensing information of a single sensor is not reliable enough due to shadowing and fading. To overcome these issues, cooperative spectrum sensing schemes were proposed to take advantage of spatial diversity. For cooperative spectrum sensing, all sensors sense the spectrum and report the sensed energy to FC for the final decision. However, it increases the energy consumption of the network when a large number of sensors need to cooperate; in addition to that, the efficiency of the network is also reduced. The proposed algorithm makes the cluster and selects the CHs such that very little amount of network energy is consumed and the highest efficiency of the network is achieved. Using the proposed algorithm maximum probability of detection under an imperfect channel is accomplished with minimum energy consumption as compared to conventional clustering schemes. PMID:27618061

  16. Energy and traffic light labelling have no impact on parent and child fast food selection.

    PubMed

    Dodds, Pennie; Wolfenden, Luke; Chapman, Kathy; Wellard, Lyndal; Hughes, Clare; Wiggers, John

    2013-10-25

    Labelling of food from fast food restaurants at point-of-purchase has been suggested as one strategy to reduce population energy consumption and contribute to reductions in obesity prevalence. The aim of this study was to examine the effects of energy and single traffic light labelling systems on the energy content of child and adult intended food purchases. The study employed a randomised controlled trial design. English speaking parents of children aged between three and 12 years were recruited from an existing research cohort. Participants were mailed one of three hypothetical fast food menus. Menus differed in their labelling technique- either energy labels, single traffic light labels, or a no-label control. Participants then completed a telephone survey which assessed intended food purchases for both adult and child. The primary trial outcome was total energy of intended food purchase. A total of 329 participants completed the follow-up telephone interview. Eighty-two percent of the energy labelling group and 96% of the single traffic light labelling group reported noticing labelling information on their menu. There were no significant differences in total energy of intended purchases of parents, or intended purchases made by parents for children, between the menu labelling groups, or between menu labelling groups by socio-demographic subgroups. This study provided no evidence to suggest that energy labelling or single traffic light labelling alone were effective in reducing the energy of fast food items selected from hypothetical fast food menus for purchase. Additional complementary public health initiatives promoting the consumption of healthier foods identified by labelling, and which target other key drivers of menu item selection in this setting may be required. Copyright © 2013. Published by Elsevier Ltd.

  17. Epitaxial complex oxide tunnel barriers

    NASA Astrophysics Data System (ADS)

    Son, Junwoo; Moetakef, Pouya; Cagnon, Joël; Stemmer, Susanne

    2009-03-01

    Tunnel junctions with complex oxide thin film barriers are of interest for studies of the critical thickness of ferroelectricity, of phonon modes in ultrathin films and of traps by inelastic tunneling spectroscopy. We show that high-quality epitaxial SrTiO3 and BaTiO3 tunnel barriers can be grown on Pt bottom electrodes. Coherent, epitaxial Pt films with roughness of less than a unit cell were grown on (001) SrTiO3 to serve as bottom electrodes for epitaxial SrTiO3 and BaTiO3 tunnel barriers. All interfaces were atomically abrupt as confirmed by atomic resolution Z-contrast imaging. The IV characteristics were non-linear, demonstrating good insulating properties. For the SrTiO3 barriers and voltage sweeps up to ± 0.5 V, the measured tunnel current was independent of the sweep direction. At low biases, dynamic conductance curves showed a symmetrical parabolic shape around the origin in both resistance states. At high bias, deviation from the ideal tunnel behavior was observed. A large increase of the tunnel conductance occurred above a minimum positive bias. A dramatic decrease of tunnel conductance occurred for a large negative bias, indicating bipolar switching. We show the contributions to the resistive switching. Phonon modes and traps are determined using inelastic tunneling spectroscopy with both paraelectric and ferroelectric tunnel barriers.

  18. The Controller Synthesis of Metastable Oxides Utilizing Epitaxy and Epitaxial Stabilization

    SciTech Connect

    Schlom, Darrell

    2003-12-02

    Molecular beam epitaxy (MBE) has achieved unparalleled control in the integration of semiconductors at the nanometer. These advances were made through the use of epitaxy, epitaxial stabilization, and a combination of composition-control techniques including adsorption-controlled growth and RHEED-based composition control that we have developed, understood, and utilized for the growth of oxides. Also key was extensive characterization (utilizing RHEED, four-circle x-ray diffraction, AFM, TEM, and electrical characterization techniques) in order to study growth modes, optimize growth conditions, and probe the structural, dielectric, and ferroelectric properties of the materials grown. The materials that we have successfully engineered include titanates (PbTiO3, Bi4Ti3O12), tantalates (SrBi2Ta2O9), and niobates (SrBi2Nb2O9); layered combinations of these perovskite-related materials (Bi4Ti3O12-SrTiO3 and Bi4Ti3O12-PbTiO3 Aurivillius phases and metastable PbTiO3/SrTiO3 and BaTiO3/SrTiO3 superlattices), and new metastable phases (Srn+1TinO3n+1 Ruddlesden-Popper phases). The films were grown by reactive MBE and pulsed laser deposition (PLD). Many of these materials are either new or have been synthesized with the highest perfection ever reported. The controlled synthesis of such layered oxide heterostructures offers great potential for tailoring the superconducting, ferroelectric, and dielectric properties of these materials. These properties are important for energy technologies.

  19. Comparative analyisis of energy consumption of selected buildings on morehead state university's main campus

    NASA Astrophysics Data System (ADS)

    Brandt, Ronald E.

    Currently there is a need for energy efficiency on the main campus of Morehead State University main campus. Evidence shows that there is room for improvement in order to lower the usage and cost efficiency at MSU. The purpose of this study is to propose, that Net Zero technology should be implemented towards the main campus of Morehead State University in the near future. The goal is to come up with a study of comparing selected current traditional buildings with the LEED buildings (Wellness Recreational Center and CHER building). To form this analysis will be applied using SPC software on Energy usage for year by year trends from 2012. In conclusion, Net-Zero construction has steadily increased since then, with the number of completed buildings more than doubling since 2008, according to the latest study. Thanks to advances in structural insulation, energy-efficient appliances, this will help the MSU campus in the near future. As for energy efficiency, to make sure we have plenty of energy in the future, it's up to all of us to use energy wisely. We must all conserve energy and use it efficiently. It's also up to those who will create the new energy technologies of the future..

  20. Near optimal energy selective x-ray imaging system performance with simple detectors

    SciTech Connect

    Alvarez, Robert E.

    2010-02-15

    Purpose: This article describes a method to achieve near optimal performance with low energy resolution detectors. Tapiovaara and Wagner [Phys. Med. Biol. 30, 519-529 (1985)] showed that an energy selective x-ray system using a broad spectrum source can produce images with a larger signal to noise ratio (SNR) than conventional systems using energy integrating or photon counting detectors. They showed that there is an upper limit to the SNR and that it can be achieved by measuring full spectrum information and then using an optimal energy dependent weighting. Methods: A performance measure is derived by applying statistical detection theory to an abstract vector space of the line integrals of the basis set coefficients of the two function approximation to the x-ray attenuation coefficient. The approach produces optimal results that utilize all the available energy dependent data. The method can be used with any energy selective detector and is applied not only to detectors using pulse height analysis (PHA) but also to a detector that simultaneously measures the total photon number and integrated energy, as discussed by Roessl et al. [Med. Phys. 34, 959-966 (2007)]. A generalization of this detector that improves the performance is introduced. A method is described to compute images with the optimal SNR using projections in a ''whitened'' vector space transformed so the noise is uncorrelated and has unit variance in both coordinates. Material canceled images with optimal SNR can also be computed by projections in this space. Results: The performance measure is validated by showing that it provides the Tapiovaara-Wagner optimal results for a detector with full energy information and also a conventional detector. The performance with different types of detectors is compared to the ideal SNR as a function of x-ray tube voltage and subject thickness. A detector that combines two bin PHA with a simultaneous measurement of integrated photon energy provides near ideal

  1. Features of impurity photoconductivity in Si:Er/Si epitaxial diodes

    SciTech Connect

    Antonov, A. V.; Kudryavtsev, K. E. Shengurov, D. V.; Shmagin, V. B.; Krasilnik, Z. F.

    2013-11-15

    The photocurrent spectra of Si:Er/Si epitaxial diode structures are studied. It is shown that the nature of the sub-band-gap photoresponse is determined by the epitaxial growth temperature of the Si:Er layer and is not related to the composition of erbium emission centers. It is found that the absorption of light with photon energies lower than the energy-gap of silicon is determined by impurity-defect complexes that appear during the growth of the epitaxial layer and form a quasi-continuous spectrum of states in the energy gap of silicon. It is assumed that these impurity centers are not related to optically active erbium centers and are not involved in excitation-energy transfer to the rare-earth impurity.

  2. Analysis Of Spectrally Selective Liquid Absorption Filters For Hybrid Solar Energy Conversion

    NASA Astrophysics Data System (ADS)

    Chendo, M. A. C.; Osborn, D. E.; Swenson, Rick

    1985-12-01

    Various techniques have been proposed to convert solar energy to both electric power and heat in hybrid systems. Many of these approaches are designed to utilize spectral selectivity to improve the overall conversion efficiency. Examples include spectrally selective beamsplitters and arrangements of long-wave or short-wave-pass glass filters that divide the spectrum so that photon energies are roughly matched to the energies corresponding to the solar-cell bandgaps or to efficient photothermal convertors. This paper describes the analysis of liquid optical filters that have high transmittance in the visible spectrum and high absorptance in the infrared. These qualities make it possible to capture that portion of the spectrum useful to a quantum convertor, such as a photovoltaic cell, while channeling the "excess heat" of the photons with energies below the bandgap to a thermal convertor, thereby enhancing the overall conversion efficiency of the system. The preliminary studies show that spectral responses of the tested solutions (salts in water) are primarily influenced by the cation component of the salt solution. By changing the solutions and concentrations, a variety of spectrally selective filters can be tailored to match system requirements.

  3. Three-dimensional lattice matching of epitaxially embedded nanoparticles

    NASA Astrophysics Data System (ADS)

    May, Brelon J.; Anderson, Peter M.; Myers, Roberto C.

    2017-02-01

    For a given degree of in-plane lattice mismatch between a two-dimensional (2D) epitaxial layer and a substrate (εIP*), there is a critical thickness above which interfacial defects form to relax the elastic strain energy. Here, we extend the 2D lattice-matching conditions to three-dimensions in order to predict the critical size beyond which epitaxially encased nanoparticles, characterized by both εIP* and out-of-plane lattice mismatch (εOP*), relax by dislocation formation. The critical particle length (Lc) at which defect formation proceeds is determined by balancing the reduction in elastic energy associated with dislocation introduction with the corresponding increase in defect energy. Our results, which use a modified Eshelby inclusion technique for an embedded, arbitrarily-faceted nanoparticle, provide new insight to the nanoepitaxy of low dimensional structures, especially quantum dots and nanoprecipitates. By engineering εIP* and εOP*, the predicted Lc for nanoparticles can be increased to well beyond the case of encapsulation in a homogenous matrix. For the case of truncated pyramidal shaped InAs, Lc 10.8 nm when fully embedded in GaAs (εIP* = εOP* = - 0.072); 16.4 nm when the particle is grown on GaAs, but capped with InSb (εIP* = - 0.072 and εOP* =+0.065); and a maximum of 18.4 nm if capped with an alloy corresponding to εOP* =+0.037. The effect, which we term "3D Poisson-stabilization" provides a means to increase the epitaxial strain tolerance in epitaxial heterostructures by tailoring εOP*.

  4. Tunneling Spectroscopy Studies of Epitaxial Graphene on Silicon Carbide(0001) and Its Interfaces

    NASA Astrophysics Data System (ADS)

    Sandin, Andreas Axel Tomas

    graphene. STS, STM along with DFT calculations are used to determine the interface location of Sodium, SiC-bufferlayer or bufferlayer-graphene intercalation. In this thesis, STM, and STS are used to study the interactions of paramagnetic FePc molecules with epitaxial graphene. The molecules, FePc, is found to interact with the graphene substrate where STM images show substrate induced orientation of FePc densely packed square lattice structure. At sub-monolayer coverages, FePc form a molecular gas at room temperature suggesting a low diffusion barrier on the graphene lattice. The substrate interaction is probed by STS and show an abnormally low LUMO energy that suggest strong electronic coupling between graphene and FePc. DFT calculations support the experimental observations and predict a spin-dependent molecule-graphene hybridization close to the Fermi energy in unoccupied states. For majority spins, DFT demonstrates the Dirac cone splits and a delocalized hybrid state is found in the band gap. For minority spin the Dirac cone is intact with energy of Dirac point empty. In addition, a novel method of improving UHV graphene growth on SiC(0001) is presented. During growth the SiC surface is exposed to atomic hydrogen which allows selective etching of Si over Carbon. This result in more uniform non-thermal formation of the buffer layer with many fewer defects and thus leads to nearly pit-free and defect-free thermal graphene layers.

  5. Application configuration selection for energy-efficient execution on multicore systems

    DOE PAGES

    Wang, Shinan; Luo, Bing; Shi, Weisong; ...

    2015-09-21

    Balanced performance and energy consumption are incorporated in the design of modern computer systems. Several runtime factors, such as concurrency levels, thread mapping strategies, and dynamic voltage and frequency scaling (DVFS) should be considered in order to achieve optimal energy efficiency fora workload. Selecting appropriate run-time factors, however, is one of the most challenging tasks because the run-time factors are architecture-specific and workload-specific. And while most existing works concentrate on either static analysis of the workload or run-time prediction results, we present a hybrid two-step method that utilizes concurrency levels and DVFS settings to achieve the energy efficiency configuration formore » a worldoad. The experimental results based on a Xeon E5620 server with NPB and PARSEC benchmark suites show that the model is able to predict the energy efficient configuration accurately. On average, an additional 10% EDP (Energy Delay Product) saving is obtained by using run-time DVFS for the entire system. An off-line optimal solution is used to compare with the proposed scheme. Finally, the experimental results show that the average extra EDP saved by the optimal solution is within 5% on selective parallel benchmarks.« less

  6. Application configuration selection for energy-efficient execution on multicore systems

    SciTech Connect

    Wang, Shinan; Luo, Bing; Shi, Weisong; Tiwari, Devesh

    2015-09-21

    Balanced performance and energy consumption are incorporated in the design of modern computer systems. Several runtime factors, such as concurrency levels, thread mapping strategies, and dynamic voltage and frequency scaling (DVFS) should be considered in order to achieve optimal energy efficiency fora workload. Selecting appropriate run-time factors, however, is one of the most challenging tasks because the run-time factors are architecture-specific and workload-specific. And while most existing works concentrate on either static analysis of the workload or run-time prediction results, we present a hybrid two-step method that utilizes concurrency levels and DVFS settings to achieve the energy efficiency configuration for a worldoad. The experimental results based on a Xeon E5620 server with NPB and PARSEC benchmark suites show that the model is able to predict the energy efficient configuration accurately. On average, an additional 10% EDP (Energy Delay Product) saving is obtained by using run-time DVFS for the entire system. An off-line optimal solution is used to compare with the proposed scheme. Finally, the experimental results show that the average extra EDP saved by the optimal solution is within 5% on selective parallel benchmarks.

  7. Ultrafast laser-driven microlens to focus and energy-select mega-electron volt protons.

    PubMed

    Toncian, Toma; Borghesi, Marco; Fuchs, Julien; d'Humières, Emmanuel; Antici, Patrizio; Audebert, Patrick; Brambrink, Erik; Cecchetti, Carlo Alberto; Pipahl, Ariane; Romagnani, Lorenzo; Willi, Oswald

    2006-04-21

    We present a technique for simultaneous focusing and energy selection of high-current, mega-electron volt proton beams with the use of radial, transient electric fields (10(7) to 10(10) volts per meter) triggered on the inner walls of a hollow microcylinder by an intense subpicosecond laser pulse. Because of the transient nature of the focusing fields, the proposed method allows selection of a desired range out of the spectrum of the polyenergetic proton beam. This technique addresses current drawbacks of laser-accelerated proton beams, such as their broad spectrum and divergence at the source.

  8. Frequency-sweeping: A new technique for energy-selective transport

    SciTech Connect

    Mynick, H.E.; Pomphrey, N.

    1994-02-01

    A new method is described for inducing energy-selective transport by `sweeping` the frequency of applied low-n magnetic perturbations. The mechanism, formally analogous to the `rising buckets` concept in accelerator physics, can move particles with a selected velocity in a nondiffusive fashion from one specified radius to another. The technique is considered principally as a means for removal of Helium ash. Other likely applications are as a method for burn control, profile control, as a diagnostic, and perhaps as a nonstochastic means of effecting the direct coupling of alpha power recently discussed by Fisch and Rax.

  9. The LILIA experiment: Energy selection and post-acceleration of laser generated protons

    NASA Astrophysics Data System (ADS)

    Turchetti, Giorgio; Sinigardi, Stefano; Londrillo, Pasquale; Rossi, Francesco; Sumini, Marco; Giove, Dario; De Martinis, Carlo

    2012-12-01

    The LILIA experiment is planned at the SPARCLAB facility of the Frascati INFN laboratories. We have simulated the laser acceleration of protons, the transport and energy selection with collimators and a pulsed solenoid and the post-acceleration with a compact high field linac. For the highest achievable intensity corresponding to a = 30 over 108 protons at 30 MeV with a 3% spread are selected, and at least107 protons are post-accelerated up to 60 MeV. If a 10 Hz repetition rated can be achieved the delivered dose would be suitable for the treatment of small superficial tumors.

  10. Energy and matter-efficient size-selective growth of thin quantum wires in a plasma

    SciTech Connect

    Ostrikov, K.; Mehdipour, H.

    2011-01-17

    It is shown that plasmas can minimize the adverse Gibbs-Thompson effect in thin quantum wire growth. The model of Si nanowire nucleation includes the unprecedented combination of the plasma sheath, ion- and radical-induced species creation and heating effects on the surface and within an Au catalyst nanoparticle. Compared to neutral gas thermal processes, much thinner, size-selective wires can nucleate at the same temperature and pressure while much lower energy and matter budget is needed to grow same-size wires. This explains the experimental observations and may lead to energy- and matter-efficient synthesis of a broader range of one-dimensional quantum structures.

  11. Selection of substrate orientation and phosphorus flux to achieve p-type carbon doping of Ga{sub 0.5}In{sub 0.5}P by molecular beam epitaxy

    SciTech Connect

    Friedman, D.J.; Kibbler, A.E.; Reedy, R.

    1997-08-01

    We show that the p-type doping of Ga{sub 0.5}In{sub 0.5}P grown by solid-source molecular beam epitaxy using CBr{sub 4} as a carbon source is very strongly dependent upon the phosphorus flux and upon the substrate misorientation from (100). High densities of A-type steps and low phosphorus flux favor the incorporated carbon acting as a p-type dopant. We demonstrate that with the substrate orientation and phosphorus flux chosen to satisfy these two criteria, doping of C:Ga{sub 0.5}In{sub 0.5}P into the mid-10{sup 18}holes/cm{sup 3} range can be achieved for the as-grown material. {copyright} {ital 1997 American Institute of Physics.}

  12. STM Properties and Manipulation of Epitaxial Graphene

    NASA Astrophysics Data System (ADS)

    Thibado, Paul

    2014-03-01

    Epitaxial graphene grown on SiC has been identified as one of the most likely avenues to graphene-based electronics. Understanding how morphology affects electronic properties is therefore important. In our work, epitaxial graphene was grown on the polar and non-polar a-, m-, and r-crystallographic oriented surfaces of SiC, and was investigated using scanning tunneling microscopy (STM). Bunched nano-ridges ten times smaller than previously recorded were observed throughout the surface. A new STM technique called electrostatic-manipulation scanning tunneling microscopy (EM-STM) was performed to modify the morphology of the nano-ridges. By modeling the electrostatics involved in the EM-STM measurement, we estimate that a force of 5 nN and energy of 10 eV was required to alter the local interfacial bonding. At the atomic scale, STM images of Moire patterns reveal low-angle, twisted bi-layer graphene, grain boundaries, and an apparent lattice constant dilation. We will show that this dilation is due to the STM tip electrostatically dragging the graphene surface. Collaborators: P. Xu, D. Qi, M.L. Ackerman, S.D. Barber, J.K. Schoelz, and J. Thompson, Department of Physics, University of Arkansas, Fayetteville, AR, 72701, USA; V.D. Wheelr, R.L. Myers-Ward, C.R. Eddy, Jr., and D.K. Gaskill, U.S. Naval Research Laboratory, Washington, DC 20375, USA; and L.O. Nyakiti, Texas A&M University. Department of Physics, University of Arkansas, Fayetteville, AR, 72701, USA.

  13. Considerations of dietary sodium/potassium/energy ratios of selected foods.

    PubMed

    Arbeit, M L; Nicklas, T A; Berenson, G S

    1992-04-01

    Various electrolytes and energy intakes have been shown to contribute to the risk of hypertension and other cardiovascular diseases. Further, dietary sodium (Na) and potassium (K) balance are important in both nonpharmacologic and pharmacologic management of various cardiovascular states. Emphasis is also given to weight reduction and electrolyte balance. As an aid to food selection to enhance K intake and decrease Na intake, we have categorized foods according to their electrolyte density as related to caloric content. More than 100 individual food items were assigned to one of four categories. Ratios of individual Na, K, and energy content were calculated, based on USDA-generated food nutrient values. Category 1 includes foods that are low in Na, high in K and low in energy: fresh or frozen vegetable sources with vitamins A and C. Category 2 contains foods low in Na relative to high K and high energy: most fruit, starchy vegetables, nuts, milk and meat products, and chocolate. Category 3 includes foods high in Na that are also high in K in relation to low energy: vegetables (canned, frozen in butter sauce or au gratin), most cheeses, cured or frozen meats. Category 4 contains foods high in Na and low in K relative to high energy: bread, rice, luncheon meats, commercial cookies and pastries, and fast food entrees. Commercial cereals could be differentiated by the guidelines, with bran cereals in Category 1, shredded wheat products in Category 2, fruit-containing cereals in Category 3, and presweetened or instant cereals in Category 4. Identification of the ratio of Na and K to content of foods, compared with relative energy ratio, is useful in selecting foods that will help meet specific dietary criteria for management of essential hypertension and other cardiovascular-renal states, both in the adult and pediatric populations.

  14. Epitaxy of MgO magnetic tunnel barriers on epitaxial graphene.

    PubMed

    Godel, Florian; Pichonat, Emmanuelle; Vignaud, Dominique; Majjad, Hicham; Metten, Dominik; Henry, Yves; Berciaud, Stéphane; Dayen, Jean-Francois; Halley, David

    2013-11-29

    Epitaxial growth of electrodes and tunnel barriers on graphene is one of the main technological bottlenecks for graphene spintronics. In this paper, we demonstrate that MgO(111) epitaxial tunnel barriers, one of the prime candidates for spintronic application, can be grown by molecular beam epitaxy on epitaxial graphene on SiC(0001). Ferromagnetic metals (Fe, Co, Fe20Ni80) were epitaxially grown on top of the MgO barrier, thus leading to monocrystalline electrodes on graphene. Structural and magnetic characterizations were performed on these ferromagnetic metals after annealing and dewetting: they form clusters with a 100 nm typical lateral width, which are mostly magnetic monodomains in the case of Fe. This epitaxial stack opens the way to graphene spintronic devices taking benefits from a coherent tunnelling current through the epitaxial MgO/graphene stack.

  15. Epitaxial Nanoflag Photonics: Semiconductor Nanoemitters Grown with Their Nanoantennas.

    PubMed

    Sorias, Ofir; Kelrich, Alexander; Gladstone, Ran; Ritter, Dan; Orenstein, Meir

    2017-09-06

    Semiconductor nanostructures are desirable for electronics, photonics, quantum circuitry, and energy conversion applications as well as for fundamental science. In photonics, optical nanoantennas mediate the large size difference between photons and semiconductor nanoemitters or detectors and hence are instrumental for exhibiting high efficiency. In this work we present epitaxially grown InP nanoflags as optically active nanostructures encapsulating the desired characteristics of a photonic emitter and an efficient epitaxial nanoantenna. We experimentally characterize the polarized and directional emission of the nanoflag-antenna and show the control of these properties by means of structure, dimensions, and constituents. We analyze field enhancement and light extraction by the semiconductor nanoflag antenna, which yield comparable values to enhancement factors of metallic plasmonic antennas. We incorporated quantum emitters within the nanoflag structure and characterized their emission properties. Merging of active nanoemitters with nanoantennas at a single growth process enables a new class of devices to be used in nanophotonics applications.

  16. Epitaxial growth of VO{sub 2} by periodic annealing

    SciTech Connect

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

    2014-02-10

    We report the growth of ultrathin VO{sub 2} films on rutile TiO{sub 2} (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 VO{sub 2} 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.

  17. Energy-selective neutron imaging for morphological and phase analysis of iron-nickel meteorites.

    PubMed

    Peetermans, S; Grazzi, F; Salvemini, F; Lehmann, E H; Caporali, S; Pratesi, G

    2013-09-21

    We propose energy-selective neutron imaging as a new and non-destructive method to investigate rare metallic meteorites. It is based on attenuation of a neutron beam of limited spectral distribution in a sample depending on the elemental composition and crystalline structure. Radiography and tomography allow obtaining the presence, morphology and orientation information in the bulk of mineral inclusions, oxide crust and crystalline structure. Its usage in classification and meteor formation studies would be of great value.

  18. High efficiency thermal to electric energy conversion using selective emitters and spectrally tuned solar cells

    NASA Technical Reports Server (NTRS)

    Chubb, Donald L.; Flood, Dennis J.; Lowe, Roland A.

    1992-01-01

    Thermophotovoltaic (TPV) systems are attractive possibilities for direct thermal-to-electric energy conversion, but have typically required the use of black body radiators operating at high temperatures. Recent advances in both the understanding and performance of solid rare-earth oxide selective emitters make possible the use of TPV at temperatures as low as 1500 K. Depending on the nature of parasitic losses, overall thermal-to-electric conversion efficiencies greater than 20 percent are feasible.

  19. Identity Recognition Algorithm Using Improved Gabor Feature Selection of Gait Energy Image

    NASA Astrophysics Data System (ADS)

    Chao, LIANG; Ling-yao, JIA; Dong-cheng, SHI

    2017-01-01

    This paper describes an effective gait recognition approach based on Gabor features of gait energy image. In this paper, the kernel Fisher analysis combined with kernel matrix is proposed to select dominant features. The nearest neighbor classifier based on whitened cosine distance is used to discriminate different gait patterns. The approach proposed is tested on the CASIA and USF gait databases. The results show that our approach outperforms other state of gait recognition approaches in terms of recognition accuracy and robustness.

  20. Eating frequency and energy regulation in free-living adults consuming self-selected diets.

    PubMed

    McCrory, Megan A; Howarth, Nancy C; Roberts, Susan B; Huang, Terry T-K

    2011-01-01

    The relative importance of eating frequency to weight control is poorly understood. This review examines the evidence to date on the role of eating frequency in weight control in free-living adults. The majority of cross-sectional studies in free-living adults show an inverse relationship between eating frequency and adiposity; however, this is likely an artifact produced by the underreporting of eating frequency concurrent with underreporting of energy intake. When implausible energy intake reporting (which is mostly underreporting) is taken into account, the association between eating frequency and adiposity becomes positive. In studies in which eating frequency is prescribed and food intake is mostly self-selected, there is either no effect or a minor positive effect of eating frequency on energy intake. Most of those studies have been short-term and lack the necessary dietary biomarkers to validate reported energy intakes and eating frequencies. In conclusion, there is some suggestion from cross-sectional studies in which energy intake underreporting is taken into account and from experimental studies to date that greater eating frequency may promote positive energy balance. However, experimental studies of longer-term duration that include objective dietary biomarkers are necessary before firm conclusions about the relative importance of eating frequency in weight control can be made.

  1. Spectrally-selective all-inorganic scattering luminophores for solar energy-harvesting clear glass windows.

    PubMed

    Alghamedi, Ramzy; Vasiliev, Mikhail; Nur-E-Alam, Mohammad; Alameh, Kamal

    2014-10-16

    All-inorganic visibly-transparent energy-harvesting clear laminated glass windows are the most practical solution to boosting building-integrated photovoltaics (BIPV) energy outputs significantly while reducing cooling- and heating-related energy consumption in buildings. By incorporating luminophore materials into lamination interlayers and using spectrally-selective thin-film coatings in conjunction with CuInSe2 solar cells, most of the visible solar radiation can be transmitted through the glass window with minimum attenuation while ultraviolet (UV) radiation is down-converted and routed together with a significant part of infrared radiation to the edges for collection by solar cells. Experimental results demonstrate a 10 cm × 10 cm vertically-placed energy-harvesting clear glass panel of transparency exceeding 60%, invisible solar energy attenuation greater than 90% and electrical power output near 30 Wp/m(2) mainly generated by infrared (IR) and UV radiations. These results open the way for the realization of large-area visibly-transparent energy-harvesting clear glass windows for BIPV systems.

  2. Spectrally-selective all-inorganic scattering luminophores for solar energy-harvesting clear glass windows

    PubMed Central

    Alghamedi, Ramzy; Vasiliev, Mikhail; Nur-E-Alam, Mohammad; Alameh, Kamal

    2014-01-01

    All-inorganic visibly-transparent energy-harvesting clear laminated glass windows are the most practical solution to boosting building-integrated photovoltaics (BIPV) energy outputs significantly while reducing cooling- and heating-related energy consumption in buildings. By incorporating luminophore materials into lamination interlayers and using spectrally-selective thin-film coatings in conjunction with CuInSe2 solar cells, most of the visible solar radiation can be transmitted through the glass window with minimum attenuation while ultraviolet (UV) radiation is down-converted and routed together with a significant part of infrared radiation to the edges for collection by solar cells. Experimental results demonstrate a 10 cm × 10 cm vertically-placed energy-harvesting clear glass panel of transparency exceeding 60%, invisible solar energy attenuation greater than 90% and electrical power output near 30 Wp/m2 mainly generated by infrared (IR) and UV radiations. These results open the way for the realization of large-area visibly-transparent energy-harvesting clear glass windows for BIPV systems. PMID:25321890

  3. Spectrally-selective all-inorganic scattering luminophores for solar energy-harvesting clear glass windows

    NASA Astrophysics Data System (ADS)

    Alghamedi, Ramzy; Vasiliev, Mikhail; Nur-E-Alam, Mohammad; Alameh, Kamal

    2014-10-01

    All-inorganic visibly-transparent energy-harvesting clear laminated glass windows are the most practical solution to boosting building-integrated photovoltaics (BIPV) energy outputs significantly while reducing cooling- and heating-related energy consumption in buildings. By incorporating luminophore materials into lamination interlayers and using spectrally-selective thin-film coatings in conjunction with CuInSe2 solar cells, most of the visible solar radiation can be transmitted through the glass window with minimum attenuation while ultraviolet (UV) radiation is down-converted and routed together with a significant part of infrared radiation to the edges for collection by solar cells. Experimental results demonstrate a 10 cm × 10 cm vertically-placed energy-harvesting clear glass panel of transparency exceeding 60%, invisible solar energy attenuation greater than 90% and electrical power output near 30 Wp/m2 mainly generated by infrared (IR) and UV radiations. These results open the way for the realization of large-area visibly-transparent energy-harvesting clear glass windows for BIPV systems.

  4. Design of selective emitting media within a cylindrical tube for conversion of wasted heat energy to electrical energy

    NASA Astrophysics Data System (ADS)

    Starvaggi, P.; Hoffman, M.; Clemons, C. B.; Young, G. W.

    2011-01-01

    Thermophotovoltaic (TPV) energy conversion is the conversion of heat energy to electrical energy via light. This manuscript focuses on the geometric design of emitting material within an exhaust tube to convert wasted heat energy to light, and achieve an optimal amount of irradiance at the PV diode cells. Due to the large value of the absorption coefficient for the selectively emitting erbia-doped nanofibers under discussion, the diffusion approximation to the equation of radiation transfer is used. This approximate equation is solved for emission from hot-spot sources within the emitting material. Several geometric distributions of the emitting material are considered. Within an axisymmetric geometry all erbia-doped nanofibers, all quartz wool, and mixtures of disk-shaped or cylindrical shell shaped distributions of nanofibers and wool are investigated. Within a polar geometry all erbia-doped nanofibers, all quartz wool, and mixtures of spoke-shaped or cylindrical shell shaped distributions are investigated. In both geometries the mixture distributions consist of alternating thin layers of emitting and non-emitting material. Homogenization techniques are applied to these distributions to define expressions for the effective absorption and scattering coefficients for these spatially distributed emitting structures. The effective expressions are input into the diffusion approximation that is solved for the spectral irradiance. The net radiation obtained from these emitting structures is examined to optimize the geometry of the TPV material to maximize emission with use of minimal TPV material. Results show that disk-shaped bands or spokes allow for maximum irradiation in the radial direction toward the diode collectors. A large volume fraction of erbia-doped nanofibers is optimal when hot spots are close to the diodes. Smaller volume fractions work better when hot spots are away from the diodes due to reabsorption of emitted light by the emitting material.

  5. Epitaxial Growth of Aluminum on Silicon Substrates by Metalorganic Molecular Beam Epitaxy using Dimethyl-Ethylamine Alane

    NASA Astrophysics Data System (ADS)

    Neo, Yoichiro; Otoda, Toshihiro; Sagae, Katumi; Mimura, Hidenori; Yokoo, Kuniyoshi

    1998-05-01

    In this paper, the growth process of aluminum on a silicon substrate by metalorganic molecular beam epitaxy using dimethyl-ethylamine alane has been described. The crystallographic orientation of the aluminum grains strongly depends on the substrate temperature. The epitaxial single crystalline (111) Al grains grow on a (111) Si substrate at a substrate temperature between 450 and 500°C. The bi-crystalline (110) Al grains grow on a (100) Si substrate at the substrate temperature between 350 and 450°C. For a (100) Si substrate, the orientation of Al is related to the reconstruction of the Si substrate. Furthermore, the selective growth of Al into 1.5-µm-diameter via-holes is shown to be possible.

  6. Report on HVAC option selections for a relocatable classroom energy and indoor environmental quality field study

    SciTech Connect

    Apte, Michael G.; Delp, Woody W.; Diamond, Richard C.; Hodgson, Alfred T.; Kumar, Satish; Rainer, Leo I.; Shendell, Derek G.; Sullivan, Doug P.; Fisk, William J.

    2001-10-11

    It is commonly assumed that efforts to simultaneously develop energy efficient building technologies and to improve indoor environmental quality (IEQ) are unfeasible. The primary reason for this is that IEQ improvements often require additional ventilation that is costly from an energy standpoint. It is currently thought that health and productivity in work and learning environments requires adequate, if not superior, IEQ. Despite common assumptions, opportunities do exist to design building systems that provide improvements in both energy efficiency and IEQ. This report outlines the selection of a heating, ventilation, and air conditioning (HVAC) system to be used in demonstrating such an opportunity in a field study using relocatable school classrooms. Standard classrooms use a common wall mounted heat pump HVAC system. After reviewing alternative systems, a wall-mounting indirect/direct evaporative cooling system with an integral hydronic gas heating is selected. The anticipated advantages of this system include continuous ventilation of 100 percent outside air at or above minimum standards, projected cooling energy reductions of about 70 percent, inexpensive gas heating, improved airborne particle filtration, and reduced peak load electricity use. Potential disadvantages include restricted climate regions and possible increases in indoor relative humidity levels under some conditions.

  7. Selection for high and low oxygen consumption-induced differences in maintenance energy requirements of mice.

    PubMed

    Darhan, Hongyu; Kikusato, Motoi; Toyomizu, Masaaki; Roh, Sang-Gun; Katoh, Kazuo; Sato, Masahiro; Suzuki, Keiichi

    2017-07-01

    Maintenance energy requirements (MER) of mice selected for high (H) or low (L) oxygen consumption (OC) were compared. Forty-four mice from H and L OC lines were weaned at 3 weeks and divided into four experimental groups: group A were sacrificed at 4 weeks; group B were fed ad libitum, and groups C and D were fed 2.8 and 2.4 g/day, respectively, from 4 to 8 weeks of age. Groups B-D were sacrificed at 8 weeks. Chemical components were estimated for all groups. MER was estimated using a model that partitioned metabolizable energy intake into that used for maintenance, and protein and fat deposition. The feed conversion ratio for the B group was significantly higher in the H than in the L line. Feed intake for metabolic energy content per metabolic body size was significantly also higher in the H line, whereas accumulated energy content per metabolic body size was significantly higher in the L line. MER of the H line was greater than that of the L line (P < 0.10). These results suggest that selection for H or L OC produced differences in chemical components, feed efficiency, and MER between the H and L lines. © 2016 Japanese Society of Animal Science.

  8. Selection of energy optimized pump concepts for multi core and multi mode erbium doped fiber amplifiers.

    PubMed

    Krummrich, Peter M; Akhtari, Simon

    2014-12-01

    The selection of an appropriate pump concept has a major impact on amplifier cost and power consumption. The energy efficiency of different pump concepts is compared for multi core and multi mode active fibers. In preamplifier stages, pump power density requirements derived from full C-band low noise WDM operation result in superior energy efficiency of direct pumping of individual cores in a multi core fiber with single mode pump lasers compared to cladding pumping with uncooled multi mode lasers. Even better energy efficiency is achieved by direct pumping of the core in multi mode active fibers. Complexity of pump signal combiners for direct pumping of multi core fibers can be reduced by deploying integrated components.

  9. Molecular beam epitaxial growth mechanism of ZnSe epilayers on (100) GaAs as determined by reflection high-energy electron diffraction, transmission electron microscopy and X-ray diffraction

    NASA Astrophysics Data System (ADS)

    Landwehr, G.; Wagg, A.; Heinke, H.; Behr, T.; Hommel, D.; Ruppert, P.

    1994-04-01

    The properties of the molecular beam epitaxial ZnSe epilayers deposited directly on a GaAs substrate are compared to those grown on a GaAs buffer layer. The superior quality of the latter is confirmed by RHEED, TEM and X-ray diffraction. Based on RHEED oscillation studies, a model explaining the dependence of the ZnSe growth rate on Zn and Se fluxes and the substrate temperature is developed taking into account physi- and chemisorbed states. For partially relaxed epilayers, the correlation between the relaxation state and the crystalline mosaicity, as found by high resolution X-ray diffraction, is discussed.

  10. Epitaxial growth of europium monoxide on diamond

    SciTech Connect

    Melville, A.; Heeg, T.; Mairoser, T.; Schmehl, A.; Fischer, M.; Gsell, S.; Schreck, M.; Awschalom, D. D.; Holländer, B.; Schubert, J.; Schlom, D. G.

    2013-11-25

    We report the epitaxial integration of phase-pure EuO on both single-crystal diamond and on epitaxial diamond films grown on silicon utilizing reactive molecular-beam epitaxy. The epitaxial orientation relationship is (001) EuO ‖ (001) diamond and [110] EuO ‖[100] diamond. The EuO layer is nominally unstrained and ferromagnetic with a transition temperature of 68 ± 2 K and a saturation magnetization of 5.5 ± 0.1 Bohr magnetons per europium ion on the single-crystal diamond, and a transition temperature of 67 ± 2 K and a saturation magnetization of 2.1 ± 0.1 Bohr magnetons per europium ion on the epitaxial diamond film.

  11. Molecular-Beam-Epitaxy Program

    NASA Technical Reports Server (NTRS)

    Sparks, Patricia D.

    1988-01-01

    Molecular Beam Epitaxy (MBE) computer program developed to aid in design of single- and double-junction cascade cells made of silicon. Cascade cell has efficiency 1 or 2 percent higher than single cell, with twice the open-circuit voltage. Input parameters include doping density, diffusion lengths, thicknesses of regions, solar spectrum, absorption coefficients of silicon (data included for 101 wavelengths), and surface recombination velocities. Results include maximum power, short-circuit current, and open-circuit voltage. Program written in FORTRAN IV.

  12. Fabrication of GaN nanowire arrays by confined epitaxy

    NASA Astrophysics Data System (ADS)

    Wang, Xin; Sun, Xinyu; Fairchild, Michael; Hersee, Stephen D.

    2006-12-01

    The authors report the fabrication of GaN nanowire arrays inside a thick SiNx, selective growth mask that was patterned by interferometric lithography and dry etching. The GaN nanowires are molded by the apertures in the selective growth mask and the growth is epitaxial with respect to the underlying GaN layer. The precise location and diameter of each nanowire in the array are controlled by the growth mask patterning, and the resulting array has a long-range order that is compatible with photonic crystal applications. This process uses conventional metal organic precursors and does not require any additional metal catalysts.

  13. In-situ height engineering of InGaAs/GaAs quantum dots by chemical beam epitaxy

    NASA Astrophysics Data System (ADS)

    Zribi, Jihene; Morris, Denis; Ilahi, Bouraoui; Aldhubaib, Amal; Aimez, Vincent; Ares, Richard

    2016-07-01

    This work reports on a chemical beam epitaxy growth study of InGaAs/GaAs quantum dots (QDs) engineered using an in-situ indium-flush technique. The emission energy of these structures has been selectively tuned over 225 meV by varying the dot height from 7 to 2 nm. A blueshift of the photoluminescence (PL) emission peak and a decrease of the intersublevel spacing energy are observed when the dot height is reduced. Numerical investigations of the influence of dot structural parameters on their electronic structure have been carried out by solving the single-particle one-band effective mass Schrödinger equation in cylindrical coordinates, for lens-shaped QDs. The correlation between numerical calculations and PL results is used to better describe the influence of the In-flush technique on both the dot height and the dot composition.

  14. Parallel cascade selection molecular dynamics for efficient conformational sampling and free energy calculation of proteins

    NASA Astrophysics Data System (ADS)

    Kitao, Akio; Harada, Ryuhei; Nishihara, Yasutaka; Tran, Duy Phuoc

    2016-12-01

    Parallel Cascade Selection Molecular Dynamics (PaCS-MD) was proposed as an efficient conformational sampling method to investigate conformational transition pathway of proteins. In PaCS-MD, cycles of (i) selection of initial structures for multiple independent MD simulations and (ii) conformational sampling by independent MD simulations are repeated until the convergence of the sampling. The selection is conducted so that protein conformation gradually approaches a target. The selection of snapshots is a key to enhance conformational changes by increasing the probability of rare event occurrence. Since the procedure of PaCS-MD is simple, no modification of MD programs is required; the selections of initial structures and the restart of the next cycle in the MD simulations can be handled with relatively simple scripts with straightforward implementation. Trajectories generated by PaCS-MD were further analyzed by the Markov state model (MSM), which enables calculation of free energy landscape. The combination of PaCS-MD and MSM is reported in this work.

  15. Development of a carbonaceous selective absorber for solar thermal energy collection and process for its formation

    NASA Astrophysics Data System (ADS)

    Garrison, John D.

    1989-02-01

    The main goal of the US Department of Energy supported part of this project is to develop information about controlling the complicated chemical processes involved in the formation of a carbonaceous selective absorber and learn what equipment will allow production of this absorber commercially. The work necessary to accomplish this goal is not yet complete. Formation of the carbonaceous selective absorber in the conveyor oven tried so far has been unsatisfactory, because the proper conditions for applying the carbonaceous coating in each conveyor oven fabricated, either have been difficult to obtain, or have been difficult to maintain over an extended period of time. A new conveyor oven is nearing completion which is expected to allow formation of the carbonaceous selective absorber on absorber tubes in a continuous operation over many days without the necessity of cleaning the conveyor oven or changing the thickness of the electroplated nickel catalyst to compensate for changes in the coating environment in the oven. Work under this project concerned with forming and sealing glass panels to test ideas on evacuated glass solar collector designs and production have been generally quite satisfactory. Delays in completion of the selective absorber work, has caused postponement of the fabrication of a small prototype evacuated glass solar collector panel. Preliminary cost estimates of the selective absorber and solar collector panel indicate that this collector system should be lower in cost than evacuated solar collectors now on the market.

  16. Modeling of a water vapor selective membrane unit to increase the energy efficiency of humidity harvesting

    NASA Astrophysics Data System (ADS)

    Bergmair, D.; Metz, S. J.; de Lange, H. C.; van Steenhoven, A. A.

    2012-11-01

    Air humidity is a promising source of clean and safe drinking water. However, in conventional systems a lot of energy is wasted on the production of cold air, rather than the condensation of water vapor. This study examines the possibility of using a hollow fiber membrane module to make this process more energy efficient, by separating the vapor from other gases, prior to the cooling process with the help of selective membranes. The water vapor concentration within a fiber has been modeled using a random walker approach, and the membrane permeability has been implemented as a re-bounce probability for simulation particles interacting with the membrane. Considering the additional work requirement for driving a feed flow through the membrane section and the computed water vapor permeation it could be shown that the energy demand per unit water is lowest for slow flow speeds and favors short and thin fibers. The total energy requirement was estimated to be less than half of the conventional one. Comparison with other CFD simulations and a real life module has shown a good level of agreement, indicating that a membrane section could improve the energy efficiency of humidity harvesting significantly.

  17. Refrigeration Playbook: Natural Refrigerants; Selecting and Designing Energy-Efficient Commercial Refrigeration Systems That Use Low Global Warming Potential Refrigerants

    SciTech Connect

    Nelson, Caleb; Reis, Chuck; Nelson, Eric; Armer, James; Arthur, Rob; Heath, Richard; Rono, James; Hirsch, Adam; Doebber, Ian

    2015-03-01

    This report provides guidance for selecting and designing energy efficient commercial refrigeration systems using low global warming potential refrigerants. Refrigeration systems are generally the largest energy end use in a supermarket type building, often accounting for more than half of a building's energy consumption.

  18. Characteristics of the Telescope for High Energy Gamma-ray Astronomy Selected for Definition Studies on the Gamma Ray Observatory

    NASA Technical Reports Server (NTRS)

    Hughes, E. B.; Hofstadter, R.; Johansson, A.; Rolfe, J.; Bertsch, D. L.; Cruickshank, W. J.; Ehrmann, C. H.; Fichtel, C. E.; Hartman, R. C.; Kniffen, D. A.

    1979-01-01

    The high energy gamma-ray selected for definition studies on the Gamma Ray Observatory provides a substantial improvement in observational capability over earlier instruments. It will have about 20 times more sensitivity, cover a much broader energy range, have considerably better energy resolution and provide a significantly improved angular resolution. The design and performance are described.

  19. Characteristics of the telescope for high energy gamma-ray astronomy selected for definition studies on the Gamma Ray Observatory

    NASA Technical Reports Server (NTRS)

    Hughes, E. B.; Hofstadter, R.; Rolfe, J.; Johansson, A.; Bertsch, D. L.; Cruickshank, W. J.; Ehrmann, C. H.; Fichtel, C. E.; Hartman, R. C.; Kniffen, D. A.

    1980-01-01

    The high energy gamma-ray telescope selected for definition studies on the Gamma Ray Observatory provides a substantial improvement in observational capability over earlier instruments. It will have about 20 times more sensitivity, cover a much broader energy range, have considerably better energy resolution and provide a significantly improved angular resolution. The design and performance are described.

  20. Characterization of defects and evaluation of material quality of low temperature epitaxial growth

    NASA Astrophysics Data System (ADS)

    Das, Hrishikesh

    A novel process for low-temperature (LT) epitaxial growth of silicon carbide (SiC) by replacing the growth precursor propane with chloro-methane was recently developed at Mississippi State University. However, only limited information was available about the defects and impurity incorporation in the various types of epitaxial layers produced by this new method like blanket epitaxial layers, selectively grown epitaxial mesas, and highly doped epitaxial layers, prior to their comprehensive characterization in this work. Molten potassium hydroxide (KOH) etching, mechanical polishing and a variety of other characterizing techniques were used to delineate and identify the defects both in the epilayer and substrates. Under optimum growth conditions, the concentration of defects in the epitaxial layers was found to be less than that in the substrate, which established the good quality of the LT growth process. Defect concentrations, on selectively grown epitaxial layers, strongly depended on the crystallographic orientation of the mesa sidewall. The addition of HCl to the growth process, aimed at increasing the growth rate, caused a significant concentration of triangular defects (TDs) to be formed in the epitaxial layers. The TDs were traced down to the substrate by a combination of repeated polishing and molten KOH etching steps. The TDs were found not to originate from any substrate defects. Their origin was traced to polycrystalline silicon islands which form on the surface during growth and subsequently get evaporated away, which had made it impossible to detect them and suspect their influence on the TD generation prior to this work. The TDs were found to include single or multiple stacking faults bound by partial dislocations and, in some cases, inclusions of other SiC polytypes. Gradual degradation of the epitaxial morphology was found in heavily aluminum doped p+ layers, with an increase in the level of doping, followed by much steeper degradation when

  1. Semiconductor-based Multilayer Selective Solar Absorber for Unconcentrated Solar Thermal Energy Conversion.

    PubMed

    Thomas, Nathan H; Chen, Zhen; Fan, Shanhui; Minnich, Austin J

    2017-07-13

    Solar thermal energy conversion has attracted substantial renewed interest due to its applications in industrial heating, air conditioning, and electricity generation. Achieving stagnation temperatures exceeding 200 °C, pertinent to these technologies, with unconcentrated sunlight requires spectrally selective absorbers with exceptionally low emissivity in the thermal wavelength range and high visible absorptivity for the solar spectrum. In this Communication, we report a semiconductor-based multilayer selective absorber that exploits the sharp drop in optical absorption at the bandgap energy to achieve a measured absorptance of 76% at solar wavelengths and a low emittance of approximately 5% at thermal wavelengths. In field tests, we obtain a peak temperature of 225 °C, comparable to that achieved with state-of-the-art selective surfaces. With straightforward optimization to improve solar absorption, our work shows the potential for unconcentrated solar thermal systems to reach stagnation temperatures exceeding 300 °C, thereby eliminating the need for solar concentrators for mid-temperature solar applications such as supplying process heat.

  2. Semiconductor-based Multilayer Selective Solar Absorber for Unconcentrated Solar Thermal Energy Conversion

    DOE PAGES

    Thomas, Nathan H.; Chen, Zhen; Fan, Shanhui; ...

    2017-07-13

    Solar thermal energy conversion has attracted substantial renewed interest due to its applications in industrial heating, air conditioning, and electricity generation. Achieving stagnation temperatures exceeding 200 °C, pertinent to these technologies, with unconcentrated sunlight requires spectrally selective absorbers with exceptionally low emissivity in the thermal wavelength range and high visible absorptivity for the solar spectrum. In this Communication, we then report a semiconductor-based multilayer selective absorber that exploits the sharp drop in optical absorption at the bandgap energy to achieve a measured absorptance of 76% at solar wavelengths and a low emittance of approximately 5% at thermal wavelengths. In fieldmore » tests, we obtain a peak temperature of 225 °C, comparable to that achieved with state-of-the-art selective surfaces. Furthemore, with straightforward optimization to improve solar absorption, our work shows the potential for unconcentrated solar thermal systems to reach stagnation temperatures exceeding 300 °C, thereby eliminating the need for solar concentrators for mid-temperature solar applications such as supplying process heat« less

  3. Mechanism of sensitization of MDR cancer cells by Pluronic block copolymers: Selective energy depletion

    PubMed Central

    Batrakova, E V; Li, S; Elmquist, W F; Miller, D W; Alakhov, V Y; Kabanov, A V

    2001-01-01

    This paper, for the first time, demonstrates that exposure of cells to the poly(ethylene oxide)-poly(propylene oxide) block copolymer, Pluronic P85, results in a substantial decrease in ATP levels selectively in MDR cells. Cells expressing high levels of functional P-glycoprotein (MCF-7/ADR, KBv; LLC-MDR1; Caco-2, bovine brain microvessel endothelial cells [BBMECs]) are highly responsive to Pluronic treatment, while cells with low levels of P-glycoprotein expression (MCF-7, KB, LLC-PK1, human umbilical vein endothelial cells [HUVECs] C2C12 myoblasts) are much less responsive to such treatment. Cytotoxicity studies suggest that Pluronic acts as a chemosensitizer and potentiates cytotoxic effects of doxorubicin in MDR cells. The ability of Pluronic to inhibit P-glycoprotein and sensitize MDR cells appears to be a result of ATP depletion. Because many mechanisms of drug resistance are energy dependent, a successful strategy for treating MDR cancer could be based on selective energy depletion in MDR cells. Therefore, the finding of the energy-depleting effects of Pluronic P85, in combination with its sensitization effects is of considerable theoretical and practical significance. © 2001 Cancer Research Campaign http://www.bjcancer.com PMID:11747344

  4. Potential-energy surfaces of local excited states from subsystem- and selective Kohn-Sham-TDDFT

    NASA Astrophysics Data System (ADS)

    Kovyrshin, Arseny; Neugebauer, Johannes

    2011-11-01

    Calculating excited-state potential-energy surfaces for systems with a large number of close-lying excited states requires the identification of the relevant electronic transitions for several geometric structures. Time-dependent density functional theory (TDDFT) is very efficient in such calculations, but the assignment of local excited states of the active molecule can be difficult. We compare the results of the frozen-density embedding (FDE) method with those of standard Kohn-Sham density-functional theory (KS-DFT) and simpler QM/MM-type methods. The FDE results are found to be more accurate for the geometry dependence of excitation energies than classical models. We also discuss how selective iterative diagonalization schemes can be exploited to directly target specific excitations for different structures. Problems due to strongly interacting orbital transitions and possible solutions are discussed. Finally, we apply FDE and the selective KS-TDDFT to investigate the potential energy surface of a high-lying π → π∗ excitation in a pyridine molecule approaching a silver cluster.

  5. Performance of solenoids versus quadrupoles in focusing and energy selection of laser accelerated protons

    NASA Astrophysics Data System (ADS)

    Hofmann, Ingo

    2013-04-01

    Using laser accelerated protons or ions for various applications—for example in particle therapy or short-pulse radiographic diagnostics—requires an effective method of focusing and energy selection. We derive an analytical scaling for the performance of a solenoid compared with a doublet/triplet as function of the energy, which is confirmed by TRACEWIN simulations. Generally speaking, the two approaches are equivalent in focusing capability, if parameters are such that the solenoid length approximately equals its diameter. The scaling also shows that this is usually not the case above a few MeV; consequently, a solenoid needs to be pulsed or superconducting, whereas the quadrupoles can remain conventional. It is also important that the transmission of the triplet is found only 25% lower than that of the equivalent solenoid. Both systems are equally suitable for energy selection based on their chromatic effect as is shown using an initial distribution following the RPA simulation model by Yan et al. [Phys. Rev. Lett. 103, 135001 (2009PRLTAO0031-900710.1103/PhysRevLett.103.135001].

  6. Agile Blocker and Clock Jitter Tolerant Low-Power Frequency Selective Receiver with Energy Harvesting Capability.

    PubMed

    Hasan, Abul; Helaoui, Mohamed; Ghannouchi, Fadhel M

    2017-08-29

    In this article, a novel tunable, blocker and clock jitter tolerant, low power, quadrature phase shift frequency selective (QPS-FS) receiver with energy harvesting capability is proposed. The receiver's design embraces and integrates (i) the baseband to radio frequency (RF) impedance translation concept to improve selectivity over that of conventional homodyne receiver topologies and (ii) broadband quadrature phase shift circuitry in the RF path to remove an active multi-phase clock generation circuit in passive mixer (PM) receivers. The use of a single local oscillator clock signal with a passive clock division network improves the receiver's robustness against clock jitter and reduces the source clock frequency by a factor of N, compared to PM receivers using N switches (N≥4). As a consequence, the frequency coverage of the QPS-FS receiver is improved by a factor of N, given a clock source of maximum frequency; and, the power consumption of the whole receiver system can eventually be reduced. The tunable QPS-FS receiver separates the wanted RF band signal from the unwanted blockers/interferers. The desired RF signal is frequency down-converted to baseband, while the undesired blocker/interferer signals are reflected by the receiver, collected and could be energy recycled using an auxiliary energy harvesting device.

  7. Compliant substrate epitaxy: Au on MoS2

    NASA Astrophysics Data System (ADS)

    Zhou, Yuzhi; Kiriya, Daisuke; Haller, E. E.; Ager, Joel W.; Javey, Ali; Chrzan, D. C.

    2016-02-01

    A theory for the epitaxial growth of Au on MoS2 is developed and analyzed. The theory combines continuum linear elasticity theory with density functional theory to analyze epitaxial growth in this system. It is demonstrated that if one accounts for interfacial energies and strains, the presence of misfit dislocations, and the compliance of the MoS2 substrate, the experimentally observed growth orientation is favored despite the fact that it represents a larger elastic mismatch than two competing structures. The stability of the experimentally preferred orientation is attributed to the formation of a large number of strong Au-S bonds, and it is noted that this strong bond may serve as a means to exfoliate and transfer large single layers sheets of MoS2, as well as to engineer strain within single layers of MoS2. The potential for using a van der Waals-bonded layered material as a compliant substrate for applications in 2D electronic devices and epitaxial thin film growth is discussed.

  8. Hydride vapor phase epitaxy of aluminum nitride

    NASA Astrophysics Data System (ADS)

    Kamber, Derrick Shane

    AlN is a promising substrate material for AlGaN-based UV optoelectronic devices and high-power, high-frequency electronic devices. Since large-area bulk AlN crystals are not readily available, one approach to prepare AlN substrates is to heteroepitaxially deposit thick (e.g., 10-300+ mum) AlN layers by hydride vapor phase epitaxy. Initial efforts focused on growing AlN layers on sapphire substrates with growth rates up to 75 mum/hr. The resulting layers were colorless, smooth, and specular. Subsurface cracking, attributed to the plastic relief of tensile strain from island coalescence, was observed but did not adversely affect the surface morphology of the AlN layers. The surfaces possessed rms roughnesses as low as 0.316 nm over 5 x 5 mum2 sampling areas, but hexagonal hillock formation was observed for thick films grown at high growth rates. TEM revealed that the threading dislocation (TD) density of the films was 2 x 109 cm-2. The high TD densities for direct growth of AlN films on foreign substrates motivated the development of lateral epitaxial overgrowth approaches for defect reduction. Growth of AlN layers on patterned SiC substrates produced coalesced AlN films possessing TD densities below 8.3 x 106 cm -2 in the laterally grown wing regions, as compared to 1.8 x 109 cm-2 in the seed regions. These films, however, cracked on cooldown due to the difference in thermal expansion coefficients for AlN and SiC. To avoid this cracking, AlN layers were grown on patterned sapphire substrates. Although the films were able to be coalesced and contained few or no cracks, the TDs in these films were not confined to the seed regions. This produced a relatively uniform distribution of TDs over the surfaces of the films, with only a modest reduction in the TD density of 1 x 10 8 cm-2. Selective area growth of AlN was also pursued using Si3N4, SiO2, and Ti masks. Growth selectivity and film coalescence was observed for films grown on each masking material, but none of the

  9. Epitaxial Halide Perovskite Lateral Double Heterostructure.

    PubMed

    Wang, Yiping; Chen, Zhizhong; Deschler, Felix; Sun, Xin; Lu, Toh-Ming; Wertz, Esther A; Hu, Jia-Mian; Shi, Jian

    2017-03-28

    Epitaxial III-V semiconductor heterostructures are key components in modern microelectronics, electro-optics, and optoelectronics. With superior semiconducting properties, halide perovskite materials are rising as promising candidates for coherent heterostructure devices. In this report, spinodal decomposition is proposed and experimentally implemented to produce epitaxial double heterostructures in halide perovskite system. Pristine epitaxial mixed halide perovskites rods and films were synthesized via van der Waals epitaxy by chemical vapor deposition method. At room temperature, photon was applied as a knob to regulate the kinetics of spinodal decomposition and classic coarsening. By this approach, halide perovskite double heterostructures were created carrying epitaxial interfaces and outstanding optical properties. Reduced Fröhlich electron-phonon coupling was discovered in coherent halide double heterostructure, which is hypothetically attributed to the classic phonon confinement effect widely existing in III-V double heterostructures. As a proof-of-concept, our results suggest that halide perovskite-based epitaxial heterostructures may be promising for high-performance and low-cost optoelectronics, electro-optics, and microelectronics. Thus, ultimately, for practical device applications, it may be worthy to pursue these heterostructures via conventional vapor phase epitaxy approaches widely practised in III-V field.

  10. The influence of mitigation on sage-grouse habitat selection within an energy development field.

    PubMed

    Fedy, Bradley C; Kirol, Christopher P; Sutphin, Andrew L; Maechtle, Thomas L

    2015-01-01

    Growing global energy demands ensure the continued growth of energy development. Energy development in wildlife areas can significantly impact wildlife populations. Efforts to mitigate development impacts to wildlife are on-going, but the effectiveness of such efforts is seldom monitored or assessed. Greater sage-grouse (Centrocercus urophasianus) are sensitive to energy development and likely serve as an effective umbrella species for other sagebrush-steppe obligate wildlife. We assessed the response of birds within an energy development area before and after the implementation of mitigation action. Additionally, we quantified changes in habitat distribution and abundance in pre- and post-mitigation landscapes. Sage-grouse avoidance of energy development at large spatial scales is well documented. We limited our research to directly within an energy development field in order to assess the influence of mitigation in close proximity to energy infrastructure. We used nest-location data (n = 488) within an energy development field to develop habitat selection models using logistic regression on data from 4 years of research prior to mitigation and for 4 years following the implementation of extensive mitigation efforts (e.g., decreased activity, buried powerlines). The post-mitigation habitat selection models indicated less avoidance of wells (well density β = 0.18 ± 0.08) than the pre-mitigation models (well density β = -0.09 ± 0.11). However, birds still avoided areas of high well density and nests were not found in areas with greater than 4 wells per km2 and the majority of nests (63%) were located in areas with ≤ 1 well per km2. Several other model coefficients differed between the two time periods and indicated stronger selection for sagebrush (pre-mitigation β = 0.30 ± 0.09; post-mitigation β = 0.82 ± 0.08) and less avoidance of rugged terrain (pre-mitigation β = -0.35 ± 0.12; post-mitigation β = -0.05 ± 0.09). Mitigation efforts implemented may

  11. The Influence of Mitigation on Sage-Grouse Habitat Selection within an Energy Development Field

    PubMed Central

    Fedy, Bradley C.; Kirol, Christopher P.; Sutphin, Andrew L.; Maechtle, Thomas L.

    2015-01-01

    Growing global energy demands ensure the continued growth of energy development. Energy development in wildlife areas can significantly impact wildlife populations. Efforts to mitigate development impacts to wildlife are on-going, but the effectiveness of such efforts is seldom monitored or assessed. Greater sage-grouse (Centrocercus urophasianus) are sensitive to energy development and likely serve as an effective umbrella species for other sagebrush-steppe obligate wildlife. We assessed the response of birds within an energy development area before and after the implementation of mitigation action. Additionally, we quantified changes in habitat distribution and abundance in pre- and post-mitigation landscapes. Sage-grouse avoidance of energy development at large spatial scales is well documented. We limited our research to directly within an energy development field in order to assess the influence of mitigation in close proximity to energy infrastructure. We used nest-location data (n = 488) within an energy development field to develop habitat selection models using logistic regression on data from 4 years of research prior to mitigation and for 4 years following the implementation of extensive mitigation efforts (e.g., decreased activity, buried powerlines). The post-mitigation habitat selection models indicated less avoidance of wells (well density β = 0.18 ± 0.08) than the pre-mitigation models (well density β = -0.09 ± 0.11). However, birds still avoided areas of high well density and nests were not found in areas with greater than 4 wells per km2 and the majority of nests (63%) were located in areas with ≤ 1 well per km2. Several other model coefficients differed between the two time periods and indicated stronger selection for sagebrush (pre-mitigation β = 0.30 ± 0.09; post-mitigation β = 0.82 ± 0.08) and less avoidance of rugged terrain (pre-mitigation β = -0.35 ± 0.12; post-mitigation β = -0.05 ± 0.09). Mitigation efforts implemented may

  12. Signal to noise ratio of energy selective x-ray photon counting systems with pileup.

    PubMed

    Alvarez, Robert E

    2014-11-01

    To derive fundamental limits on the effect of pulse pileup and quantum noise in photon counting detectors on the signal to noise ratio (SNR) and noise variance of energy selective x-ray imaging systems. An idealized model of the response of counting detectors to pulse pileup is used. The model assumes a nonparalyzable response and delta function pulse shape. The model is used to derive analytical formulas for the noise and energy spectrum of the recorded photons with pulse pileup. These formulas are first verified with a Monte Carlo simulation. They are then used with a method introduced in a previous paper [R. E. Alvarez, "Near optimal energy selective x-ray imaging system performance with simple detectors," Med. Phys. 37, 822-841 (2010)] to compare the signal to noise ratio with pileup to the ideal SNR with perfect energy resolution. Detectors studied include photon counting detectors with pulse height analysis (PHA), detectors that simultaneously measure the number of photons and the integrated energy (NQ detector), and conventional energy integrating and photon counting detectors. The increase in the A-vector variance with dead time is also computed and compared to the Monte Carlo results. A formula for the covariance of the NQ detector is developed. The validity of the constant covariance approximation to the Cramèr-Rao lower bound (CRLB) for larger counts is tested. The SNR becomes smaller than the conventional energy integrating detector (Q) SNR for 0.52, 0.65, and 0.78 expected number photons per dead time for counting (N), two, and four bin PHA detectors, respectively. The NQ detector SNR is always larger than the N and Q SNR but only marginally so for larger dead times. Its noise variance increases by a factor of approximately 3 and 5 for the A1 and A2 components as the dead time parameter increases from 0 to 0.8 photons per dead time. With four bin PHA data, the increase in variance is approximately 2 and 4 times. The constant covariance approximation

  13. Energy and Raw Materials in the Selection of Technologies for Iron and Steel

    NASA Astrophysics Data System (ADS)

    Fortini, Otavio Macedo

    2016-09-01

    This paper discusses the selection of metal extraction technologies according to the regional availability of energy resources. The most important energy sources in iron and steel production are determined from a review of current technologies to inform possible future scenarios of capacity replacement or expansion according to geography. Alternative technologies are not discussed, considering that actual investment in capacity is most often dominated by high degrees of risk aversion. As such, only technologies proven at a reasonable scale are included in the selection matrix. Scenarios of capacity choice are defined in terms of actions from external agents, those which are not directly involved in the industry but have the capacity to regulate actions by metal producing players. Two extreme scenarios corresponding to closed and open economies are used to set bounds for future expectations. Among steelmaking processes under fully open trade conditions, it is found that EAF steelmaking with charge pre-heat should be the technology of choice in all regions of the world except for South America and Europe, where Integrated Steel Mills have a cost advantage. In fully closed exchange scenarios, Integrated Steel Mills would be the prevalent technology in South America, Sub-Saharan Africa, India, and the former USSR, EAF with scrap pre-heating prevailing in all other regions. On the other hand, HYL-ZR would be the iron making technology of choice in all regions under full exchange scenarios. Under fully closed exchange conditions, Mini-Blast Furnaces, COREX, and HYL-ZR would find regional applications. Increases in raw materials and energy costs of 38 pct in steelmaking and 63 pct in ironmaking are found in going from fully open to fully closed exchange regimes. It is also found that Southeast Asia is the most suitable region for deploying new steelmaking capacity, while Australia and Russia are the best selection for new iron making capacity.

  14. Inherent surface roughening as a limiting factor in epitaxial cluster deposition

    NASA Astrophysics Data System (ADS)

    Meinander, K.; Nordlund, K.; Keinonen, J.

    2005-01-01

    Deposition of nanoclusters at thermal energies will result in an onset of roughening of the deposited surface. In order to grow epitaxial films using cluster deposition at soft landing conditions, the effect of this inherent surface roughness on the alignment of deposited clusters must be investigated. Using molecular dynamics computer simulations we have determined the maximum size of Cu clusters that will align epitaxially, upon deposition at thermal energies, on rough (1 0 0) Cu substrates with temperatures ranging from 0 K to 750 K. We have also shown that the likelihood of epitaxial alignment for the resulting structures is dependent on the point of impact of a cluster relative to previously deposited clusters.

  15. The comparison and selection of programming languages for high energy physics applications

    SciTech Connect

    White, B.

    1991-06-01

    This paper discusses the issues surrounding the comparison and selection of a programming language to be used in high energy physics software applications. The evaluation method used was specifically devised to address the issues of particular importance to high energy physics (HEP) applications, not just the technical features of the languages considered. The method assumes a knowledge of the requirements of current HEP applications, the data-processing environments expected to support these applications and relevant non-technical issues. The languages evaluated were Ada, C, FORTRAN 77, FORTRAN 99 (formerly 8X), Pascal and PL/1. Particular emphasis is placed upon the past, present and anticipated future role of FORTRAN in HEP software applications. Upon examination of the technical and practical issues, conclusions are reached and some recommendations are made regarding the role of FORTRAN and other programming languages in the current and future development of HEP software. 54 refs.

  16. Characterization of selected application of biomass energy technologies and a solar district heating and cooling system

    NASA Astrophysics Data System (ADS)

    1980-09-01

    An assessment is made of four applications of biomass and solar energy conversion technologies. The first is an energy self-sufficient farm that provides all of its space heating and hot water needs by burning wood obtained by selective timber cutting on the farm acreage. The heating system is a commerical boiler furnace. A Purox gasification system is described which uses wood feedstock with a capacity of 850 dry tons/day. This system requires 2,000 farms, each with 30 acres of wooded land having a sustainable capacity of 5 dry tons/day per acre. The efficiency of silviculture plantations is then addressed in regard to different conversion strategies. Finally, a solar heat and cooling system designed for a one story school building is assessed. Land and materials requirements, climatology, and economic factors are discussed.

  17. Internal energy selection in vacuum ultraviolet photoionization of ethanol and ethanol dimers.

    PubMed

    Bodi, Andras

    2013-10-14

    Internal energy selected ethanol monomer and ethanol dimer ions were prepared by threshold photoionization of a supersonic molecular beam seeded with ethanol. The dissociative photoionization processes of the monomer, the lowest-energy CH3-loss channel of the dimer, and the fragmentation of larger clusters were found to be disjunct from the ionization onset to about 12 eV, which made it possible to determine the 0 K appearance energy of C-C bond breaking in the H-donor unit of the ethanol dimer cation as 9.719 ± 0.004 eV. This reaction energy is used together with ab initio calculations in a thermochemical cycle to determine the binding energy change from the neutral ethanol dimer to a protonated ethanol-formaldehyde adduct. The cycle also shows general agreement between experiment, theory, and previously published enthalpies of formation. The role of the initial ionization site, or rather the initial photoion state, is also discussed based on the dimer breakdown diagram and excited state calculations. There is no evidence for isolated state behavior, and the ethanol dimer dissociative photoionization processes appear to be governed by statistical theory and the ground electronic state of the ion. In the monomer breakdown diagram, the smoothly changing branching ratio between H and CH3 loss is at odds with rate theory predictions, and shows that none of the currently employed few-parameter rate models, appropriate for experimental rate curve fitting, yields a correct description for this process in the experimental energy range.

  18. The characterization and assessment of selected solar thermal energy systems for residential and process heat applications

    NASA Astrophysics Data System (ADS)

    Hyde, J. C.

    1980-09-01

    Results of studies of seven solar thermal energy applications are presented. Five of these are residential applications: space heating--active liquid, space heating--active air, domestic hot water--active, space heating--passive, and space heating and cooling--active liquid. Denver, Colorado, was selected as a representative location for each of the above applications. The remaining two applications produce industrial process heat: a flat plate collector system producing 50 C - 100 C hot water for a commercial laundry in Indianapolis, Indiana; and a concentrating collector system that could produce 100 C - 300 C process heat adequate to the needs of a pulp mill in Madison, Wisconsin.

  19. [Selective excitation spectra and energy level structure of Dy3+:ThO2 crystal].

    PubMed

    Yin, M; Krupa, J C

    2001-08-01

    Dy3+:ThO2 crystal was grown by the flux technique for the first time. The emission spectra, excitation spectra and fluorescence decay curves were measured and discussed. By using emission spectra obtained under selective dye laser excitation at 12 K, together with the crystal-field theory, the site symmetry of Dy3+ ions in ThO2 was determined as C3 nu and its energy level structure was tabulated. The lifetime of radiative level 4F9/2 was also determined as 0.40 ms.

  20. Selection and Evaluation of Priority Domains in Global Energy Internet Standard Development Based on Technology Foresight

    NASA Astrophysics Data System (ADS)

    Jin, Yang; Ciwei, Gao; Jing, Zhang; Min, Sun; Jie, Yu

    2017-05-01

    The selection and evaluation of priority domains in Global Energy Internet standard development will help to break through limits of national investment, thus priority will be given to standardizing technical areas with highest urgency and feasibility. Therefore, in this paper, the process of Delphi survey based on technology foresight is put forward, the evaluation index system of priority domains is established, and the index calculation method is determined. Afterwards, statistical method is used to evaluate the alternative domains. Finally the top four priority domains are determined as follows: Interconnected Network Planning and Simulation Analysis, Interconnected Network Safety Control and Protection, Intelligent Power Transmission and Transformation, and Internet of Things.

  1. Surface energy-mediated construction of anisotropic semiconductor wires with selective crystallographic polarity

    NASA Astrophysics Data System (ADS)

    Sohn, Jung Inn; Hong, Woong-Ki; Lee, Sunghoon; Lee, Sanghyo; Ku, Jiyeon; Park, Young Jun; Hong, Jinpyo; Hwang, Sungwoo; Park, Kyung Ho; Warner, Jamie H.; Cha, Seungnam; Kim, Jong Min

    2014-07-01

    ZnO is a wide band-gap semiconductor with piezoelectric properties suitable for opto-electronics, sensors, and as an electrode material. Controlling the shape and crystallography of any semiconducting nanomaterial is a key step towards extending their use in applications. Whilst anisotropic ZnO wires have been routinely fabricated, precise control over the specific surface facets and tailoring of polar and non-polar growth directions still requires significant refinement. Manipulating the surface energy of crystal facets is a generic approach for the rational design and growth of one-dimensional (1D) building blocks. Although the surface energy is one basic factor for governing crystal nucleation and growth of anisotropic 1D structures, structural control based on surface energy minimization has not been yet demonstrated. Here, we report an electronic configuration scheme to rationally modulate surface electrostatic energies for crystallographic-selective growth of ZnO wires. The facets and orientations of ZnO wires are transformed between hexagonal and rectangular/diamond cross-sections with polar and non-polar growth directions, exhibiting different optical and piezoelectrical properties. Our novel synthetic route for ZnO wire fabrication provides new opportunities for future opto-electronics, piezoelectronics, and electronics, with new topological properties.

  2. Surface energy-mediated construction of anisotropic semiconductor wires with selective crystallographic polarity

    PubMed Central

    Sohn, Jung Inn; Hong, Woong-Ki; Lee, Sunghoon; Lee, Sanghyo; Ku, JiYeon; Park, Young Jun; Hong, Jinpyo; Hwang, Sungwoo; Park, Kyung Ho; Warner, Jamie H.; Cha, SeungNam; Kim, Jong Min

    2014-01-01

    ZnO is a wide band-gap semiconductor with piezoelectric properties suitable for opto-electronics, sensors, and as an electrode material. Controlling the shape and crystallography of any semiconducting nanomaterial is a key step towards extending their use in applications. Whilst anisotropic ZnO wires have been routinely fabricated, precise control over the specific surface facets and tailoring of polar and non-polar growth directions still requires significant refinement. Manipulating the surface energy of crystal facets is a generic approach for the rational design and growth of one-dimensional (1D) building blocks1234. Although the surface energy is one basic factor for governing crystal nucleation and growth of anisotropic 1D structures, structural control based on surface energy minimization has not been yet demonstrated56789. Here, we report an electronic configuration scheme to rationally modulate surface electrostatic energies for crystallographic-selective growth of ZnO wires. The facets and orientations of ZnO wires are transformed between hexagonal and rectangular/diamond cross-sections with polar and non-polar growth directions, exhibiting different optical and piezoelectrical properties. Our novel synthetic route for ZnO wire fabrication provides new opportunities for future opto-electronics, piezoelectronics, and electronics, with new topological properties. PMID:25017476

  3. Surface energy-mediated construction of anisotropic semiconductor wires with selective crystallographic polarity.

    PubMed

    Sohn, Jung Inn; Hong, Woong-Ki; Lee, Sunghoon; Lee, Sanghyo; Ku, JiYeon; Park, Young Jun; Hong, Jinpyo; Hwang, Sungwoo; Park, Kyung Ho; Warner, Jamie H; Cha, SeungNam; Kim, Jong Min

    2014-07-14

    ZnO is a wide band-gap semiconductor with piezoelectric properties suitable for opto-electronics, sensors, and as an electrode material. Controlling the shape and crystallography of any semiconducting nanomaterial is a key step towards extending their use in applications. Whilst anisotropic ZnO wires have been routinely fabricated, precise control over the specific surface facets and tailoring of polar and non-polar growth directions still requires significant refinement. Manipulating the surface energy of crystal facets is a generic approach for the rational design and growth of one-dimensional (1D) building blocks. Although the surface energy is one basic factor for governing crystal nucleation and growth of anisotropic 1D structures, structural control based on surface energy minimization has not been yet demonstrated. Here, we report an electronic configuration scheme to rationally modulate surface electrostatic energies for crystallographic-selective growth of ZnO wires. The facets and orientations of ZnO wires are transformed between hexagonal and rectangular/diamond cross-sections with polar and non-polar growth directions, exhibiting different optical and piezoelectrical properties. Our novel synthetic route for ZnO wire fabrication provides new opportunities for future opto-electronics, piezoelectronics, and electronics, with new topological properties.

  4. Electroless epitaxial etching for semiconductor applications

    DOEpatents

    McCarthy, Anthony M.

    2002-01-01

    A method for fabricating thin-film single-crystal silicon on insulator substrates using electroless etching for achieving efficient etch stopping on epitaxial silicon substrates. Microelectric circuits and devices are prepared on epitaxial silicon wafers in a standard fabrication facility. The wafers are bonded to a holding substrate. The silicon bulk is removed using electroless etching leaving the circuit contained within the epitaxial layer remaining on the holding substrate. A photolithographic operation is then performed to define streets and wire bond pad areas for electrical access to the circuit.

  5. Epitaxial silicon devices for dosimetry applications

    SciTech Connect

    Bruzzi, M.; Bucciolini, M.; Casati, M.; Menichelli, D.; Talamonti, C.; Piemonte, C.; Svensson, B. G.

    2007-04-23

    A straightforward improvement of the efficiency and long term stability of silicon dosimeters has been obtained with a n{sup +}-p junction surrounded by a guard-ring structure implanted on an epitaxial p-type Si layer grown on a Czochralski substrate. The sensitivity of devices made on 50-{mu}m-thick epitaxial Si degrades by only 7% after an irradiation with 6 MeV electrons up to 1.5 kGy, and shows no significant further decay up to 10 kGy. These results prove the enhanced radiation tolerance and stability of epitaxial diodes as compared to present state-of-the-art Si devices.

  6. Ion implanted epitaxially grown ZnSe

    NASA Technical Reports Server (NTRS)

    1974-01-01

    The epitaxial growth of ZnSe on (100) Ge using the close-spaced transport process is described. Substrate temperature of 575 C and source temperatures of 675 C yield 10 micron, single crystal layers in 10 hours. The Ge substrates provides a nonreplenishable chemical transport agent and the epitaxial layer thickness is limited to approximately 10 microns. Grown epitaxial layers show excellent photoluminescence structure at 77 K. Grown layers exhibit high resistivity, and annealing in Zn vapor at 575 C reduces the resistivity to 10-100 ohms-cm. Zinc vapor annealing quenches the visible photoluminescence.

  7. Large-Area Dry Transfer of Single-Crystalline Epitaxial Bismuth Thin Films.

    PubMed

    Walker, Emily S; Na, Seung Ryul; Jung, Daehwan; March, Stephen D; Kim, Joon-Seok; Trivedi, Tanuj; Li, Wei; Tao, Li; Lee, Minjoo L; Liechti, Kenneth M; Akinwande, Deji; Bank, Seth R

    2016-11-09

    We report the first direct dry transfer of a single-crystalline thin film grown by molecular beam epitaxy. A double cantilever beam fracture technique was used to transfer epitaxial bismuth thin films grown on silicon (111) to silicon strips coated with epoxy. The transferred bismuth films retained electrical, optical, and structural properties comparable to the as-grown epitaxial films. Additionally, we isolated the bismuth thin films on freestanding flexible cured-epoxy post-transfer. The adhesion energy at the bismuth/silicon interface was measured to be ∼1 J/m(2), comparable to that of exfoliated and wet transferred graphene. This low adhesion energy and ease of transfer is unexpected for an epitaxially grown film and may enable the study of bismuth's unique electronic and spintronic properties on arbitrary substrates. Moreover, this method suggests a route to integrate other group-V epitaxial films (i.e., phosphorus) with arbitrary substrates, as well as potentially to isolate bismuthene, the atomic thin-film limit of bismuth.

  8. High throughput vacuum chemical epitaxy

    NASA Astrophysics Data System (ADS)

    Fraas, L. M.; Malocsay, E.; Sundaram, V.; Baird, R. W.; Mao, B. Y.; Lee, G. Y.

    1990-10-01

    We have developed a vacuum chemical epitaxy (VCE) reactor which avoids the use of arsine and allows multiple wafers to be coated at one time. Our vacuum chemical epitaxy reactor closely resembles a molecular beam epitaxy system in that wafers are loaded into a stainless steel vacuum chamber through a load chamber. Also as in MBE, arsenic vapors are supplied as reactant by heating solid arsenic sources thereby avoiding the use of arsine. However, in our VCE reactor, a large number of wafers are coated at one time in a vacuum system by the substitution of Group III alkyl sources for the elemental metal sources traditionally used in MBE. Higher wafer throughput results because in VCE, the metal-alkyl sources for Ga, Al, and dopants can be mixed at room temperature and distributed uniformly though a large area injector to multiple substrates as a homogeneous array of mixed element molecular beams. The VCE reactor that we have built and that we shall describe here uniformly deposits films on 7 inch diameter substrate platters. Each platter contains seven two inch or three 3 inch diameter wafers. The load chamber contains up to nine platters. The vacuum chamber is equipped with two VCE growth zones and two arsenic ovens, one per growth zone. Finally, each oven has a 1 kg arsenic capacity. As of this writing, mirror smooth GaAs films have been grown at up to 4 μm/h growth rate on multiple wafers with good thickness uniformity. The background doping is p-type with a typical hole concentration and mobility of 1 × 10 16/cm 3 and 350 cm 2/V·s. This background doping level is low enough for the fabrication of MESFETs, solar cells, and photocathodes as well as other types of devices. We have fabricated MESFET devices using VCE-grown epi wafers with peak extrinsic transconductance as high as 210 mS/mm for a threshold voltage of - 3 V and a 0.6 μm gate length. We have also recently grown AlGaAs epi layers with up to 80% aluminum using TEAl as the aluminum alkyl source. The Al

  9. Study of zinc oxide epitaxial film growth and UV photodetectors

    NASA Astrophysics Data System (ADS)

    Nahhas, Ahmed Mohammed

    ZnO is a versatile material, and has been extensively studied for various applications such as varistors, transducers, transparent conducting electrodes, sensors, and catalysts. While polycrystalline ZnO is commonly used in these conventional applications, there has been a growing interest in obtaining single-crystalline ZnO films on various substrates. ZnO is a II-VI wide bandgap semiconductor with a relatively large exciton binding energy, and holds a potential for light emitting/detecting or nonlinear optical devices in the UV range. ZnO is isomorphic to wurtzite GaN with good lattice match, and therefore there has been a great deal of interest in using ZnO as a buffer layer or a substrate in growing high quality GaN films (or vice versa ZnO growth on GaN). In this study, we have investigated epitaxial growth of ZnO films on sapphire and silicon substrates. High quality epitaxial ZnO films were grown on sapphire (0001) single crystal substrates using a rf magnetron sputtering technique. X-ray diffraction analysis shows that the ZnO films are of a monocrystalline wurtzite structure with their epitaxial relationship of ZnO[0001]//sapphire[0001] along the growth direction and ZnO[112&barbelow;0]//sapphire[11&barbelow;00] along the in-plane direction. ZnO on Si also offers an interesting opportunity that the various functional properties of ZnO can be combined with the advanced Si electronics on the same substrate. Direct growth of epitaxial ZnO on Si, however, is known to be an extremely difficult task due to the oxidation problem during the nucleation stage of a ZnO growth process. We have overcome this problem by introducing an epitaxial GaN buffer layer, and have successfully grown epitaxial ZnO films on Si(111) substrates. X-ray diffraction analysis confirms an epitaxial relationship of ZnO[0001]//GaN[0001]//Si[111] along the growth direction and ZnO[112&barbelow;0]//GaN[112&barbelow;0]//Si[11&barbelow;0] along the in-plane direction. As an application of the

  10. 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.

  11. Resonant tunneling diodes as energy-selective contacts used in hot-carrier solar cells

    NASA Astrophysics Data System (ADS)

    Takeda, Yasuhiko; Ichiki, Akihisa; Kusano, Yuya; Sugimoto, Noriaki; Motohiro, Tomoyoshi

    2015-09-01

    Among the four features unique to hot-carrier solar cells (HC-SCs): (i) carrier thermalization time and (ii) carrier equilibration time in the absorber, (iii) energy-selection width and (iv) conductance of the energy-selective contacts (ESCs), requisites of (i)-(iii) for high conversion efficiency have been clarified. We have tackled the remaining issues related to (iv) in the present study. The detailed balance model of HC-SC operation has been improved to involve a finite value of the ESC conductance to find the required values, which in turn has been revealed to be feasible using resonant tunneling diodes (RTDs) consisting of semiconductor quantum dots (QDs) and quantum wells (QWs) by means of a formulation to calculate the conductance of the QD- and QW-RTDs derived using the rigorous solutions of the effective-mass Hamiltonians. Thus, all of the four requisites unique to HC-SCs to achieve high conversion efficiency have been elucidated, and the two requisites related to the ESCs can be fulfilled using the QD- and QW-RTDs.

  12. Hepatic mitogen-activated protein kinase phosphatase 1 selectively regulates glucose metabolism and energy homeostasis.

    PubMed

    Lawan, Ahmed; Zhang, Lei; Gatzke, Florian; Min, Kisuk; Jurczak, Michael J; Al-Mutairi, Mashael; Richter, Patric; Camporez, Joao Paulo G; Couvillon, Anthony; Pesta, Dominik; Roth Flach, Rachel J; Shulman, Gerald I; Bennett, Anton M

    2015-01-01

    The liver plays a critical role in glucose metabolism and communicates with peripheral tissues to maintain energy homeostasis. Obesity and insulin resistance are highly associated with nonalcoholic fatty liver disease (NAFLD). However, the precise molecular details of NAFLD remain incomplete. The p38 mitogen-activated protein kinase (MAPK) and c-Jun NH2-terminal kinase (JNK) regulate liver metabolism. However, the physiological contribution of MAPK phosphatase 1 (MKP-1) as a nuclear antagonist of both p38 MAPK and JNK in the liver is unknown. Here we show that hepatic MKP-1 becomes overexpressed following high-fat feeding. Liver-specific deletion of MKP-1 enhances gluconeogenesis and causes hepatic insulin resistance in chow-fed mice while selectively conferring protection from hepatosteatosis upon high-fat feeding. Further, hepatic MKP-1 regulates both interleukin-6 (IL-6) and fibroblast growth factor 21 (FGF21). Mice lacking hepatic MKP-1 exhibit reduced circulating IL-6 and FGF21 levels that were associated with impaired skeletal muscle mitochondrial oxidation and susceptibility to diet-induced obesity. Hence, hepatic MKP-1 serves as a selective regulator of MAPK-dependent signals that contributes to the maintenance of glucose homeostasis and peripheral tissue energy balance. These results also demonstrate that hepatic MKP-1 overexpression in obesity is causally linked to the promotion of hepatosteatosis. Copyright © 2015, American Society for Microbiology. All Rights Reserved.

  13. Hepatic Mitogen-Activated Protein Kinase Phosphatase 1 Selectively Regulates Glucose Metabolism and Energy Homeostasis

    PubMed Central

    Lawan, Ahmed; Zhang, Lei; Gatzke, Florian; Min, Kisuk; Jurczak, Michael J.; Al-Mutairi, Mashael; Richter, Patric; Camporez, Joao Paulo G.; Couvillon, Anthony; Pesta, Dominik; Roth Flach, Rachel J.; Shulman, Gerald I.

    2014-01-01

    The liver plays a critical role in glucose metabolism and communicates with peripheral tissues to maintain energy homeostasis. Obesity and insulin resistance are highly associated with nonalcoholic fatty liver disease (NAFLD). However, the precise molecular details of NAFLD remain incomplete. The p38 mitogen-activated protein kinase (MAPK) and c-Jun NH2-terminal kinase (JNK) regulate liver metabolism. However, the physiological contribution of MAPK phosphatase 1 (MKP-1) as a nuclear antagonist of both p38 MAPK and JNK in the liver is unknown. Here we show that hepatic MKP-1 becomes overexpressed following high-fat feeding. Liver-specific deletion of MKP-1 enhances gluconeogenesis and causes hepatic insulin resistance in chow-fed mice while selectively conferring protection from hepatosteatosis upon high-fat feeding. Further, hepatic MKP-1 regulates both interleukin-6 (IL-6) and fibroblast growth factor 21 (FGF21). Mice lacking hepatic MKP-1 exhibit reduced circulating IL-6 and FGF21 levels that were associated with impaired skeletal muscle mitochondrial oxidation and susceptibility to diet-induced obesity. Hence, hepatic MKP-1 serves as a selective regulator of MAPK-dependent signals that contributes to the maintenance of glucose homeostasis and peripheral tissue energy balance. These results also demonstrate that hepatic MKP-1 overexpression in obesity is causally linked to the promotion of hepatosteatosis. PMID:25312648

  14. Resonant tunneling diodes as energy-selective contacts used in hot-carrier solar cells

    SciTech Connect

    Takeda, Yasuhiko Sugimoto, Noriaki; Ichiki, Akihisa; Kusano, Yuya; Motohiro, Tomoyoshi

    2015-09-28

    Among the four features unique to hot-carrier solar cells (HC-SCs): (i) carrier thermalization time and (ii) carrier equilibration time in the absorber, (iii) energy-selection width and (iv) conductance of the energy-selective contacts (ESCs), requisites of (i)-(iii) for high conversion efficiency have been clarified. We have tackled the remaining issues related to (iv) in the present study. The detailed balance model of HC-SC operation has been improved to involve a finite value of the ESC conductance to find the required values, which in turn has been revealed to be feasible using resonant tunneling diodes (RTDs) consisting of semiconductor quantum dots (QDs) and quantum wells (QWs) by means of a formulation to calculate the conductance of the QD- and QW-RTDs derived using the rigorous solutions of the effective-mass Hamiltonians. Thus, all of the four requisites unique to HC-SCs to achieve high conversion efficiency have been elucidated, and the two requisites related to the ESCs can be fulfilled using the QD- and QW-RTDs.

  15. Decision-making model for the selection of appropriate energy technologies in the Caribbean Basin

    SciTech Connect

    Carpenter, K.H.

    1987-01-01

    This research addressed four main objectives: (1) appropriate technology was investigated in terms of its characteristics and/or criteria: (2) a process-oriented decision-making model was developed which encompassed the selected appropriate technology criteria; (3) test instruments were designed and tested that would determine the social/cultural acceptability of an alternative energy system; and (4) the decision-making model was modified to reflect the results of the instrument application. The test sites selected for the testing of the instruments were a group of islands in the Commonwealth of the Bahamas known as the Abacos. Conclusions of the research were that: (1) perceived need for electricity among the less-developed island was the same as on the more highly developed islands; (2) electricity usage did not vary among the islands; (3) there were no social, cultural, or technological barriers that would preclude the introduction of an alternative energy system; (4) reliability of the data collected on an underdeveloped island was as reliable as the data collected on a more highly developed island, and (5) current criteria of appropriate technology are those identified in UNESCO publication 61 and identified as the criteria to be used in the assessment of technologies for developing countries.

  16. Selected configuration interaction with truncation energy error and application to the Ne atom.

    PubMed

    Bunge, Carlos F

    2006-07-07

    Selected configuration interaction (SCI) for atomic and molecular electronic structure calculations is reformulated in a general framework encompassing all CI methods. The linked cluster expansion is used as an intermediate device to approximate CI coefficients B(K) of disconnected configurations (those that can be expressed as products of combinations of singly and doubly excited ones) in terms of CI coefficients of lower-excited configurations where each K is a linear combination of configuration-state-functions (CSFs) over all degenerate elements of K. Disconnected configurations up to sextuply excited ones are selected by Brown's energy formula, Delta E(K) = (E-H(KK))B(K)2/(1-B(K)2), with B(K) determined from coefficients of singly and doubly excited configurations. The truncation energy error from disconnected configurations, Delta E(dis), is approximated by the sum of Delta E(K)s of all discarded Ks. The remaining (connected) configurations are selected by thresholds based on natural orbital concepts. Given a model CI space M, a usual upper bound E(S) is computed by CI in a selected space S, and E(M) = E(S) + Delta E(dis) + delta E, where delta E is a residual error which can be calculated by well-defined sensitivity analyses. An SCI calculation on Ne ground state featuring 1077 orbitals is presented. Convergence to within near spectroscopic accuracy (0.5 cm(-1)) is achieved in a model space M of 1.4 x 10(9) CSFs (1.1 x 10(12) determinants) containing up to quadruply excited CSFs. Accurate energy contributions of quintuples and sextuples in a model space of 6.5 x 10(12) CSFs are obtained. The impact of SCI on various orbital methods is discussed. Since Delta E(dis) can readily be calculated for very large basis sets without the need of a CI calculation, it can be used to estimate the orbital basis incompleteness error. A method for precise and efficient evaluation of E(S) is taken up in a companion paper.

  17. Optical and electrical properties of high-quality Ti2O3 epitaxial film grown on sapphire substrate

    NASA Astrophysics Data System (ADS)

    Fan, Haibo; Wang, Mingzi; Yang, Zhou; Ren, Xianpei; Yin, Mingli; Liu, Shengzhong

    2016-11-01

    Epitaxial film of Ti2O3 with high crystalline quality was grown on Al2O3 substrate by pulsed laser deposition process using a powder-pressed TiO2 target in active O2 flow. X-ray diffraction clearly reveals the (0006) crystalline Ti2O3 orientation and its (10overline{1} 0)_{{{{Ti}}_{ 2} {{O}}_{ 3} }} ||(10overline{1} 0)_{{sapphire}} in-plane epitaxial relationship with the substrate. Scanning electron microscopy images show that the film grew uniformly on the substrate with a Volmer-Weber mode. High-resolution transmission electron microscopy and selected area electron diffraction further confirm the high crystalline quality of the film. Transmittance spectrum shows that the Ti2O3 film is highly transparent in 400-800 nm with the optical band gap estimated to be 3.53 eV by Tauc plot. The temperature-dependent Hall effect measurement indicates that the Ti2O3 film appears to be n-type semiconductor with carrier concentration, mobility, and resistivity showing typical temperature-dependent behavior. The donor ionization energy was estimated to be 83.6 meV by linear relationship of conductivity versus temperature.

  18. Epitaxial growth of single crystal films

    NASA Technical Reports Server (NTRS)

    Lind, M. D.

    1980-01-01

    An experiment in gallium arsenide liquid phase epitaxy was performed successfully on the SPAR 6 flight October 17, 1979. The design, fabrication, and testing of the experimental apparatus, and the performance and results of the experiment are discussed.

  19. Epitaxial growth of silicon for layer transfer

    DOEpatents

    Teplin, Charles; Branz, Howard M

    2015-03-24

    Methods of preparing a thin crystalline silicon film for transfer and devices utilizing a transferred crystalline silicon film are disclosed. The methods include preparing a silicon growth substrate which has an interface defining substance associated with an exterior surface. The methods further include depositing an epitaxial layer of silicon on the silicon growth substrate at the surface and separating the epitaxial layer from the substrate substantially along the plane or other surface defined by the interface defining substance. The epitaxial layer may be utilized as a thin film of crystalline silicon in any type of semiconductor device which requires a crystalline silicon layer. In use, the epitaxial transfer layer may be associated with a secondary substrate.

  20. Amorphous/epitaxial superlattice for thermoelectric application

    NASA Astrophysics Data System (ADS)

    Ishida, Akihiro; Thao, Hoang Thi Xuan; Shibata, Mamoru; Nakashima, Seisuke; Tatsuoka, Hirokazu; Yamamoto, Hidenari; Kinoshita, Yohei; Ishikiriyama, Mamoru; Nakamura, Yoshiaki

    2016-08-01

    An amorphous/epitaxial superlattice system is proposed for application to thermoelectric devices, and the superlattice based on a PbGeTeS system was prepared by the alternate deposition of PbS and GeTe using a hot wall epitaxy technique. The structure was analyzed by high-resolution transmission electron microscopy (HRTEM) and X-ray analysis, and it was found that the superlattice consists of an epitaxial PbTe-based layer and a GeS-based amorphous layer by the reconstruction of the constituents. A reduction in thermal conductivity due to the amorphous/epitaxial system was confirmed by a 2ω method. Electrical and thermoelectric properties were measured for the samples.

  1. Assessing risk to birds from industrial wind energy development via paired resource selection models.

    PubMed

    Miller, Tricia A; Brooks, Robert P; Lanzone, Michael; Brandes, David; Cooper, Jeff; O'Malley, Kieran; Maisonneuve, Charles; Tremblay, Junior; Duerr, Adam; Katzner, Todd

    2014-06-01

    When wildlife habitat overlaps with industrial development animals may be harmed. Because wildlife and people select resources to maximize biological fitness and economic return, respectively, we estimated risk, the probability of eagles encountering and being affected by turbines, by overlaying models of resource selection for each entity. This conceptual framework can be applied across multiple spatial scales to understand and mitigate impacts of industry on wildlife. We estimated risk to Golden Eagles (Aquila chrysaetos) from wind energy development in 3 topographically distinct regions of the central Appalachian Mountains of Pennsylvania (United States) based on models of resource selection of wind facilities (n = 43) and of northbound migrating eagles (n = 30). Risk to eagles from wind energy was greatest in the Ridge and Valley region; all 24 eagles that passed through that region used the highest risk landscapes at least once during low altitude flight. In contrast, only half of the birds that entered the Allegheny Plateau region used highest risk landscapes and none did in the Allegheny Mountains. Likewise, in the Allegheny Mountains, the majority of wind turbines (56%) were situated in poor eagle habitat; thus, risk to eagles is lower there than in the Ridge and Valley, where only 1% of turbines are in poor eagle habitat. Risk within individual facilities was extremely variable; on average, facilities had 11% (SD 23; range = 0-100%) of turbines in highest risk landscapes and 26% (SD 30; range = 0-85%) of turbines in the lowest risk landscapes. Our results provide a mechanism for relocating high-risk turbines, and they show the feasibility of this novel and highly adaptable framework for managing risk of harm to wildlife from industrial development. © 2014 Society for Conservation Biology.

  2. Selective cerebral perfusion: real-time evidence of brain oxygen and energy metabolism preservation.

    PubMed

    Salazar, Jorge D; Coleman, Ryan D; Griffith, Stephen; McNeil, Jeffrey D; Steigelman, Megan; Young, Haven; Hensler, Bart; Dixon, Patricia; Calhoon, John; Serrano, Faridis; DiGeronimo, Robert

    2009-07-01

    Deep hypothermic circulatory arrest (DHCA) is commonly used for complex cardiac operations in children, often with selective cerebral perfusion (SCP). Little data exist concerning the real-time effects of DHCA with or without SCP on cerebral metabolism. Our objective was to better define these effects, focusing on brain oxygenation and energy metabolism. Piglets undergoing cardiopulmonary bypass were assigned to either 60 minutes of DHCA at 18 degrees C (n = 9) or DHCA with SCP at 18 degrees C (n = 8), using pH-stat management. SCP was administered at 10 mL/kg/min. A cerebral microdialysis catheter was implanted into the cortex for monitoring of cellular ischemia and energy stores. Cerebral oxygen tension and intracranial pressure also were monitored. After DHCA with or without SCP, animals were recovered for 4 hours off cardiopulmonary bypass. With SCP, brain oxygen tension was preserved in contrast to DHCA alone (p < 0.01). Deep hypothermic circulatory arrest was associated with marked elevations of lactate (p < 0.01), glycerol (p < 0.01), and the lactate to pyruvate ratio (p < 0.001), as well as profound depletion of the energy substrates glucose (p < 0.001) and pyruvate (p < 0.001). These changes persisted well into recovery. With SCP, no significant cerebral microdialysis changes were observed. A strong correlation was demonstrated between cerebral oxygen levels and cerebral microdialysis markers (p < 0.001). Selective cerebral perfusion preserves cerebral oxygenation and attenuates derangements in cerebral metabolism associated with DHCA. Cerebral microdialysis provides real-time metabolic feedback that correlates with changes in brain tissue oxygenation. This model enables further study and refinement of strategies aiming to limit brain injury in children requiring complex cardiac operations.

  3. Kinetic selection vs. free energy of DNA base pairing in control of polymerase fidelity.

    PubMed

    Oertell, Keriann; Harcourt, Emily M; Mohsen, Michael G; Petruska, John; Kool, Eric T; Goodman, Myron F

    2016-04-19

    What is the free energy source enabling high-fidelity DNA polymerases (pols) to favor incorporation of correct over incorrect base pairs by 10(3)- to 10(4)-fold, corresponding to free energy differences of ΔΔGinc∼ 5.5-7 kcal/mol? Standard ΔΔG° values (∼0.3 kcal/mol) calculated from melting temperature measurements comparing matched vs. mismatched base pairs at duplex DNA termini are far too low to explain pol accuracy. Earlier analyses suggested that pol active-site steric constraints can amplify DNA free energy differences at the transition state (kinetic selection). A recent paper [Olson et al. (2013)J Am Chem Soc135:1205-1208] used Vent pol to catalyze incorporations in the presence of inorganic pyrophosphate intended to equilibrate forward (polymerization) and backward (pyrophosphorolysis) reactions. A steady-state leveling off of incorporation profiles at long reaction times was interpreted as reaching equilibrium between polymerization and pyrophosphorolysis, yielding apparent ΔG° = -RTlnKeq, indicating ΔΔG° of 3.5-7 kcal/mol, sufficient to account for pol accuracy without need of kinetic selection. Here we perform experiments to measure and account for pyrophosphorolysis explicitly. We show that forward and reverse reactions attain steady states far from equilibrium for wrong incorporations such as G opposite T. Therefore,[Formula: see text]values obtained from such steady-state evaluations ofKeqare not dependent on DNA properties alone, but depend largely on constraints imposed on right and wrong substrates in the polymerase active site.

  4. A Study of Quasar Selection in the Supernova Fields of the Dark Energy Survey

    NASA Astrophysics Data System (ADS)

    Tie, S. S.; Martini, P.; Mudd, D.; Ostrovski, F.; Reed, S. L.; Lidman, C.; Kochanek, C.; Davis, T. M.; Sharp, R.; Uddin, S.; King, A.; Wester, W.; Tucker, B. E.; Tucker, D. L.; Buckley-Geer, E.; Carollo, D.; Childress, M.; Glazebrook, K.; Hinton, S. R.; Lewis, G.; Macaulay, E.; O'Neill, C. R.; Abbott, T. M. C.; Abdalla, F. B.; Annis, J.; Benoit-Lévy, A.; Bertin, E.; Brooks, D.; Carnero Rosell, A.; Carrasco Kind, M.; Carretero, J.; Cunha, C. E.; da Costa, L. N.; DePoy, D. L.; Desai, S.; Doel, P.; Eifler, T. F.; Evrard, A. E.; Finley, D. A.; Flaugher, B.; Fosalba, P.; Frieman, J.; García-Bellido, J.; Gaztanaga, E.; Gerdes, D. W.; Goldstein, D. A.; Gruen, D.; Gruendl, R. A.; Gutierrez, G.; Honscheid, K.; James, D. J.; Kuehn, K.; Kuropatkin, N.; Lima, M.; Maia, M. A. G.; Marshall, J. L.; Menanteau, F.; Miller, C. J.; Miquel, R.; Nichol, R. C.; Nord, B.; Ogando, R.; Plazas, A. A.; Romer, A. K.; Sanchez, E.; Santiago, B.; Scarpine, V.; Schubnell, M.; Sevilla-Noarbe, I.; Smith, R. C.; Soares-Santos, M.; Sobreira, F.; Suchyta, E.; Swanson, M. E. C.; Tarle, G.; Thomas, D.; Walker, A. R.; DES Collaboration

    2017-03-01

    We present a study of quasar selection using the supernova fields of the Dark Energy Survey (DES). We used a quasar catalog from an overlapping portion of the SDSS Stripe 82 region to quantify the completeness and efficiency of selection methods involving color, probabilistic modeling, variability, and combinations of color/probabilistic modeling with variability. In all cases, we considered only objects that appear as point sources in the DES images. We examine color selection methods based on the Wide-field Infrared Survey Explorer (WISE) mid-IR W1-W2 color, a mixture of WISE and DES colors (g - i and i-W1), and a mixture of Vista Hemisphere Survey and DES colors (g - i and i - K). For probabilistic quasar selection, we used XDQSO, an algorithm that employs an empirical multi-wavelength flux model of quasars to assign quasar probabilities. Our variability selection uses the multi-band χ 2-probability that sources are constant in the DES Year 1 griz-band light curves. The completeness and efficiency are calculated relative to an underlying sample of point sources that are detected in the required selection bands and pass our data quality and photometric error cuts. We conduct our analyses at two magnitude limits, i < 19.8 mag and i < 22 mag. For the subset of sources with W1 and W2 detections, the W1-W2 color or XDQSOz method combined with variability gives the highest completenesses of >85% for both i-band magnitude limits and efficiencies of >80% to the bright limit and >60% to the faint limit; however, the giW1 and giW1+variability methods give the highest quasar surface densities. The XDQSOz method and combinations of W1W2/giW1/XDQSOz with variability are among the better selection methods when both high completeness and high efficiency are desired. We also present the OzDES Quasar Catalog of 1263 spectroscopically confirmed quasars from three years of OzDES observation in the 30 deg2 of the DES supernova fields. The catalog includes quasars with redshifts up

  5. Chemical beam epitaxy for high efficiency photovoltaic devices

    NASA Technical Reports Server (NTRS)

    Bensaoula, A.; Freundlich, A.; Vilela, M. F.; Medelci, N.; Renaud, P.

    1994-01-01

    InP-based multijunction tandem solar cells show great promise for the conversion efficiency (eta) and high radiation resistance. InP and its related ternary and quanternary compound semiconductors such as InGaAs and InGaAsP offer desirable combinations for energy bandgap values which are very suitable for multijunction tandem solar cell applications. The monolithically integrated InP/In(0.53)Ga(0.47)As tandem solar cells are expected to reach efficiencies above 30 percent. Wanlass, et.al., have reported AMO efficiencies as high as 20.1% for two terminal cells fabricated using atmospheric-pressure metalorganic vapor phase epitaxy (APMOVPE). The main limitations in their technique are first related to the degradation of the intercell ohmic contact (IOC), in this case the In(0.53)Ga(0.47)As tunnel junction during the growth of the top InP subcell structure, and second to the current matching, often limited by the In(0.53)Ga(0.47)As bottom subcell. Chemical beam epitaxy (CBE) has been shown to allow the growth of high quality materials with reproducible complex compositional and doping profiles. The main advantage of CBE compared to metalorganic chemical vapor deposition (MOCVD), the most popular technique for InP-based photovoltaic device fabrication, is the ability to grow high purity epilayers at much lower temperatures (450 C - 530 C). In a recent report it was shown that cost-wise CBE is a breakthrough technology for photovoltaic (PV) solar energy progress in the energy conversion efficiency of InP-based solar cells fabricated using chemical beam epitaxy. This communication summarizes our recent results on PV devices and demonstrates the strength of this new technology.

  6. Silicon Holder For Molecular-Beam Epitaxy

    NASA Technical Reports Server (NTRS)

    Hoenk, Michael E.; Grunthaner, Paula J.; Grunthaner, Frank J.

    1993-01-01

    Simple assembly of silicon wafers holds silicon-based charge-coupled device (CCD) during postprocessing in which silicon deposited by molecular-beam epitaxy. Attains temperatures similar to CCD, so hotspots suppressed. Coefficients of thermal expansion of holder and CCD equal, so thermal stresses caused by differential thermal expansion and contraction do not develop. Holder readily fabricated, by standard silicon processing techniques, to accommodate various CCD geometries. Silicon does not contaminate CCD or molecular-beam-epitaxy vacuum chamber.

  7. Epitaxial Deposition Of Germanium Doped With Gallium

    NASA Technical Reports Server (NTRS)

    Huffman, James E.

    1994-01-01

    Epitaxial layers of germanium doped with gallium made by chemical vapor deposition. Method involves combination of techniques and materials used in chemical vapor deposition with GeH4 or GeCl4 as source of germanium and GaCl3 as source of gallium. Resulting epitaxial layers of germanium doped with gallium expected to be highly pure, with high crystalline quality. High-quality material useful in infrared sensors.

  8. Epitaxial Deposition Of Germanium Doped With Gallium

    NASA Technical Reports Server (NTRS)

    Huffman, James E.

    1994-01-01

    Epitaxial layers of germanium doped with gallium made by chemical vapor deposition. Method involves combination of techniques and materials used in chemical vapor deposition with GeH4 or GeCl4 as source of germanium and GaCl3 as source of gallium. Resulting epitaxial layers of germanium doped with gallium expected to be highly pure, with high crystalline quality. High-quality material useful in infrared sensors.

  9. Predicting and mapping potential Whooping Crane stopover habitat to guide site selection for wind energy projects.

    PubMed

    Belaire, J Amy; Kreakie, Betty J; Keitt, Timothy; Minor, Emily

    2014-04-01

    Migratory stopover habitats are often not part of planning for conservation or new development projects. We identified potential stopover habitats within an avian migratory flyway and demonstrated how this information can guide the site-selection process for new development. We used the random forests modeling approach to map the distribution of predicted stopover habitat for the Whooping Crane (Grus americana), an endangered species whose migratory flyway overlaps with an area where wind energy development is expected to become increasingly important. We then used this information to identify areas for potential wind power development in a U.S. state within the flyway (Nebraska) that minimize conflicts between Whooping Crane stopover habitat and the development of clean, renewable energy sources. Up to 54% of our study area was predicted to be unsuitable as Whooping Crane stopover habitat and could be considered relatively low risk for conflicts between Whooping Cranes and wind energy development. We suggest that this type of analysis be incorporated into the habitat conservation planning process in areas where incidental take permits are being considered for Whooping Cranes or other species of concern. Field surveys should always be conducted prior to construction to verify model predictions and understand baseline conditions. © 2013 Society for Conservation Biology.

  10. Characterization and assessment of selected solar thermal energy systems for residential and process heat applications

    SciTech Connect

    D'Alessio, Gregory J.; Blaustein, Robert P.

    1980-09-01

    The results of studies of seven solar thermal energy applications are presented. Five of these are residential applications: space heating-active liquid, space heating-active air, domestic hot water-active, space heating-passive, and space heating and cooling- active liquid. Denver, Colorado, was selected as a representative location for each of the above applications. The remaining two applications produce industrial process heat: a flat-plate collector system producing 50/sup 0/C to 100/sup 0/C hot water for a commercial laundry in Indianapolis, Indiana; and a concentrating collector system that could produce 100/sup 0/C to 300/sup 0/C process heat adequate to the needs of a pulp mill in Madison, Wisconsin. For each application, a representative system model and preliminary designs of major system elements were established. Then the following data were generated: annual useful energy produced, type and weight of the basic component materials, environmental residuals generated during system operation, and land and water requirements. These data were generalized for other TASE study purposes by expressing them as quantities per 10/sup 15/ Btu of useful energy. The system characteristics are discussed and the environmental impacts are evaluated. To allow the reader to estimate system performance at other geographic locations than those studied, insolation and other pertinent data are provided.

  11. Energy-aware Gateway Selection for increasing the lifetime of Wireless Body Area Sensor Networks.

    PubMed

    Bayilmis, Cuneyt; Younis, Mohamed

    2012-06-01

    A Wireless Body Area Sensor Network (WBASN) is composed of a set of sensor nodes, placed on, near or within a human body. WBASNs opt to continuously monitor the health conditions of individuals under medical risk, e.g., elders and chronically ill people, without keeping them in a hospital or restraining their motion. A WBASN needs to stay connected to local or wide area networks using wireless technologies in order to send sensor readings to a medical center. The WBASN nodes are implanted within the human body and would thus have limited energy supply. Since the mission of the WBASN is very critical, increasing the lifetime of nodes is essential in order to maintain both practicality and effectiveness. This paper presents a new Gateway Selection Algorithm (GSA) that factors in the use of energy harvesting technologies and dynamically picks the most suitable WBASN node that serves as a gateway to other wireless networks. The goal of GSA is to balance the load among the nodes by adaptively changing the gateway node in WBASN depending on the energy reserve of nodes. Computer modeling and simulations of the proposed GSA are carried out using OPNET. The simulation results demonstrate the effectiveness of the proposed GSA approach.

  12. Large-area, laterally-grown epitaxial semiconductor layers

    DOEpatents

    Han, Jung; Song, Jie; Chen, Danti

    2017-07-18

    Structures and methods for confined lateral-guided growth of a large-area semiconductor layer on an insulating layer are described. The semiconductor layer may be formed by heteroepitaxial growth from a selective growth area in a vertically-confined, lateral-growth guiding structure. Lateral-growth guiding structures may be formed in arrays over a region of a substrate, so as to cover a majority of the substrate region with laterally-grown epitaxial semiconductor tiles. Quality regions of low-defect, stress-free GaN may be grown on silicon.

  13. 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.

  14. Formation of Sm suicides on Si(111): composition and epitaxy

    NASA Astrophysics Data System (ADS)

    Wigren, C.; Andersen, J. N.; Nyholm, R.; Karlsson, U. O.

    1993-08-01

    The formation of Sm silicides on Si(111) by means of solid phase epitaxy has been studied with low energy electron diffraction, Auger electron spectroscopy and photoelectron spectroscopy of the Sm 4f level and Si 2p level. A limited reaction is found to occur already at room temperature whereas at higher temperatures a strongly intermixed Sm/Si layer showing some long range order is formed. The Sm atoms of this intermixed phase are found to be completely trivalent in accordance with expectations. The intermixed layer consists of two silicides with different compositions, one of them being SmSi 2- x, the other being tentatively ascribed to SmSi.

  15. Delayed Shutters For Dual-Beam Molecular Epitaxy

    NASA Technical Reports Server (NTRS)

    Grunthaner, Frank J.; Liu, John L.; Hancock, Bruce

    1989-01-01

    System of shutters for dual-molecular-beam epitaxy apparatus delays start of one beam with respect to another. Used in pulsed-beam equipment for deposition of low-dislocation layers of InAs on GaAs substrates, system delays application of arsenic beam with respect to indium beam to assure proper stoichiometric proportions on newly forming InAs surface. Reflectance high-energy electron diffraction (RHEED) instrument used to monitor condition of evolving surface of deposit. RHEED signal used to time pulsing of molecular beams in way that minimizes density of defects and holds lattice constant of InAs to that of GaAs substrate.

  16. Delayed Shutters For Dual-Beam Molecular Epitaxy

    NASA Technical Reports Server (NTRS)

    Grunthaner, Frank J.; Liu, John L.; Hancock, Bruce

    1989-01-01

    System of shutters for dual-molecular-beam epitaxy apparatus delays start of one beam with respect to another. Used in pulsed-beam equipment for deposition of low-dislocation layers of InAs on GaAs substrates, system delays application of arsenic beam with respect to indium beam to assure proper stoichiometric proportions on newly forming InAs surface. Reflectance high-energy electron diffraction (RHEED) instrument used to monitor condition of evolving surface of deposit. RHEED signal used to time pulsing of molecular beams in way that minimizes density of defects and holds lattice constant of InAs to that of GaAs substrate.

  17. Overall Energy Considerations for Algae Species Comparison and Selection in Algae-to-Fuels Processes

    SciTech Connect

    Link, D.; Kail, B.; Curtis, W.; Tuerk,A.

    2011-01-01

    The controlled growth of microalgae as a feedstock for alternative transportation fuel continues to receive much attention. Microalgae have the characteristics of rapid growth rate, high oil (lipid) content, and ability to be grown in unconventional scenarios. Algae have also been touted as beneficial for CO{sub 2} reuse, as algae can be grown using CO{sub 2} emissions from fossil-based energy generation. Moreover, algae does not compete in the food chain, lessening the 'food versus fuel' debate. Most often, it is assumed that either rapid production rate or high oii content should be the primary factor in algae selection for algae-to-fuels production systems. However, many important characteristics of algae growth and lipid production must be considered for species selection, growth condition, and scale-up. Under light limited, high density, photoautotrophic conditions, the inherent growth rate of an organism does not affect biomass productivity, carbon fixation rate, and energy fixation rate. However, the oil productivity is organism dependent, due to physiological differences in how the organisms allocate captured photons for growth and oil production and due to the differing conditions under which organisms accumulate oils. Therefore, many different factors must be considered when assessing the overall energy efficiency of fuel production for a given algae species. Two species, Chlorella vulgaris and Botryococcus braunii, are popular choices when discussing algae-to-fuels systems. Chlorella is a very robust species, often outcompeting other species in mixed-culture systems, and produces a lipid that is composed primarily of free fatty acids and glycerides. Botryococcus is regarded as a slower growing species, and the lipid that it produces is characterized by high hydrocarbon content, primarily C28-C34 botryococcenes. The difference in growth rates is often considered to be an advantage oiChlorella. However, the total energy captured by each algal species in

  18. Microbial catabolic activities are naturally selected by metabolic energy harvest rate

    PubMed Central

    González-Cabaleiro, Rebeca; Ofiţeru, Irina D; Lema, Juan M; Rodríguez, Jorge

    2015-01-01

    The fundamental trade-off between yield and rate of energy harvest per unit of substrate has been largely discussed as a main characteristic for microbial established cooperation or competition. In this study, this point is addressed by developing a generalized model that simulates competition between existing and not experimentally reported microbial catabolic activities defined only based on well-known biochemical pathways. No specific microbial physiological adaptations are considered, growth yield is calculated coupled to catabolism energetics and a common maximum biomass-specific catabolism rate (expressed as electron transfer rate) is assumed for all microbial groups. Under this approach, successful microbial metabolisms are predicted in line with experimental observations under the hypothesis of maximum energy harvest rate. Two microbial ecosystems, typically found in wastewater treatment plants, are simulated, namely: (i) the anaerobic fermentation of glucose and (ii) the oxidation and reduction of nitrogen under aerobic autotrophic (nitrification) and anoxic heterotrophic and autotrophic (denitrification) conditions. The experimentally observed cross feeding in glucose fermentation, through multiple intermediate fermentation pathways, towards ultimately methane and carbon dioxide is predicted. Analogously, two-stage nitrification (by ammonium and nitrite oxidizers) is predicted as prevailing over nitrification in one stage. Conversely, denitrification is predicted in one stage (by denitrifiers) as well as anammox (anaerobic ammonium oxidation). The model results suggest that these observations are a direct consequence of the different energy yields per electron transferred at the different steps of the pathways. Overall, our results theoretically support the hypothesis that successful microbial catabolic activities are selected by an overall maximum energy harvest rate. PMID:26161636

  19. Microbial catabolic activities are naturally selected by metabolic energy harvest rate.

    PubMed

    González-Cabaleiro, Rebeca; Ofiţeru, Irina D; Lema, Juan M; Rodríguez, Jorge

    2015-12-01

    The fundamental trade-off between yield and rate of energy harvest per unit of substrate has been largely discussed as a main characteristic for microbial established cooperation or competition. In this study, this point is addressed by developing a generalized model that simulates competition between existing and not experimentally reported microbial catabolic activities defined only based on well-known biochemical pathways. No specific microbial physiological adaptations are considered, growth yield is calculated coupled to catabolism energetics and a common maximum biomass-specific catabolism rate (expressed as electron transfer rate) is assumed for all microbial groups. Under this approach, successful microbial metabolisms are predicted in line with experimental observations under the hypothesis of maximum energy harvest rate. Two microbial ecosystems, typically found in wastewater treatment plants, are simulated, namely: (i) the anaerobic fermentation of glucose and (ii) the oxidation and reduction of nitrogen under aerobic autotrophic (nitrification) and anoxic heterotrophic and autotrophic (denitrification) conditions. The experimentally observed cross feeding in glucose fermentation, through multiple intermediate fermentation pathways, towards ultimately methane and carbon dioxide is predicted. Analogously, two-stage nitrification (by ammonium and nitrite oxidizers) is predicted as prevailing over nitrification in one stage. Conversely, denitrification is predicted in one stage (by denitrifiers) as well as anammox (anaerobic ammonium oxidation). The model results suggest that these observations are a direct consequence of the different energy yields per electron transferred at the different steps of the pathways. Overall, our results theoretically support the hypothesis that successful microbial catabolic activities are selected by an overall maximum energy harvest rate.

  20. Mn-assisted molecular-beam epitaxy growth (Ga,Mn)As nanowires

    NASA Astrophysics Data System (ADS)

    Reznik, R. R.; Samsonenko, Yu B.; Khrebtov, A. I.; Bouravleuv, A. D.; Werner, P.; Cirlin, G. E.

    2016-11-01

    Arrays of (Ga,Mn)As crystal nanowires on a GaAs (100) substrate were obtained using molecular-beam epitaxy at the substrate temperature 485°C. From the high energy electron diffraction patterns, the crystallographic phase of the nanowires is detected to be cubic which is supporting by ex situ microscopy study.

  1. Interfacial reactions in epitaxial Al/Ti[sub 1[minus][ital x

    SciTech Connect

    Petrov, I.; Mojab, E.; Adibi, F.; Greene, J.E. ); Hultman, L.; Sundgren, J. )

    1993-01-01

    Transmission electron microscopy (TEM), cross-sectional TEM, scanning TEM with energy dispersive x-ray analysis, and Auger electron spectroscopy were used to investigate the nature of rate-controlling interfacial reactions in epitaxial Al/Ti[sub 1[minus][ital x

  2. Perpendicularly magnetized τ-MnAl (001) thin films epitaxied on GaAs

    NASA Astrophysics Data System (ADS)

    Nie, S. H.; Zhu, L. J.; Lu, J.; Pan, D.; Wang, H. L.; Yu, X. Z.; Xiao, J. X.; Zhao, J. H.

    2013-04-01

    Perpendicularly magnetized τ-MnAl films have been epitaxied on GaAs (001) by molecular-beam epitaxy. Crystalline quality and magnetic properties of the samples were strongly dependent on growth temperature. The highest coercivity of 10.7 kOe, saturation magnetization of 361.4 emu/cm3, perpendicular magnetic anisotropy constant of 13.65 Merg/cm3, and magnetic energy product of 4.44 MGOe were achieved. These tunable magnetic properties make MnAl films valuable as excellent and cost-effective alternative for not only high density perpendicular magnetic recording storage and spintronics devices but also permanent magnets.

  3. Sharp chemical interface in epitaxial Fe{sub 3}O{sub 4} thin films

    SciTech Connect

    Gálvez, S.; Rubio-Zuazo, J. Salas-Colera, E.; Muñoz-Noval, A.; Castro, G. R.

    2014-12-15

    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.

  4. Cyclotron resonance in epitaxial Bi1-xSbx films grown by molecular-beam epitaxy

    NASA Astrophysics Data System (ADS)

    Heremans, J.; Partin, D. L.; Thrush, C. M.; Karczewski, G.; Richardson, M. S.; Furdyna, J. K.

    1993-10-01

    The far-infrared magnetotransmission of thin films of semiconducting and semimetallic Bi1-xSbx alloys grown by molecular-beam epitaxy has been measured at fixed photon energies between 2.5 and 21.4 meV in magnetic fields up to 6 T, at T=1.8 K. The samples, grown on BaF2 substrates with composition 0<=x<=22.5%, were monocrystalline, with the trigonal axis perpendicular to the surface plane. The measurements were carried out in Faraday and Voigt geometries, with the magnetic field oriented parallel to binary, bisectrix, and trigonal axes of the films. Cyclotron-resonance lines of both electrons and holes were observed. From them, we establish the composition dependence of the effective-mass tensor, of the direct L-point band gap, and of the energy overlap in the semimetallic samples. We conclude that all band-structure parameters are the same in the films as in bulk Bi1-xSbx alloys, except for the energy overlap, which is increased by 16 meV independently of composition, possibly because of the strain induced by the substrate.

  5. Suppression of planar defects in the molecular beam epitaxy of GaAs/ErAs/GaAs heterostructures

    SciTech Connect

    Crook, Adam M.; Nair, Hari P.; Ferrer, Domingo A.; Bank, Seth R.

    2011-08-15

    We present a growth method that overcomes the mismatch in rotational symmetry of ErAs and conventional III-V semiconductors, allowing for epitaxially integrated semimetal/semiconductor heterostructures. Transmission electron microscopy and reflection high-energy electron diffraction reveal defect-free overgrowth of ErAs layers, consisting of >2x the total amount of ErAs that can be embedded with conventional layer-by-layer growth methods. We utilize epitaxial ErAs nanoparticles, overgrown with GaAs, as a seed to grow full films of ErAs. Growth proceeds by diffusion of erbium atoms through the GaAs spacer, which remains registered to the underlying substrate, preventing planar defect formation during subsequent GaAs growth. This growth method is promising for metal/semiconductor heterostructures that serve as embedded Ohmic contacts to epitaxial layers and epitaxially integrated active plasmonic devices.

  6. Ultrathin IBAD MgO films for epitaxial growth on amorphous substrates and sub-50 nm membranes

    DOE PAGES

    Wang, Siming; Antonakos, C.; Bordel, C.; ...

    2016-11-07

    Here, a fabrication process has been developed for high energy ion beam assisted deposition (IBAD) biaxial texturing of ultrathin (~1 nm) MgO films, using a high ion-to-atom ratio and post-deposition annealing instead of a homoepitaxial MgO layer. These films serve as the seed layer for epitaxial growth of materials on amorphous substrates such as electron/X-ray transparent membranes or nanocalorimetry devices. Stress measurements and atomic force microscopy of the MgO films reveal decreased stress and surface roughness, while X-ray diffraction of epitaxial overlayers demonstrates the improved crystal quality of films grown epitaxially on IBAD MgO. The process simplifies the synthesis ofmore » IBAD MgO, fundamentally solves the “wrinkle” issue induced by the homoepitaxial layer on sub-50 nm membranes, and enables studies of epitaxial materials in electron/X-ray transmission and nanocalorimetry.« less

  7. Van der Waals Epitaxy of Ultrathin Halide Perovkistes

    NASA Astrophysics Data System (ADS)

    Wang, Yiping; Shi, Yunfeng; Shi, Jian

    We present our understanding, with CH3NH3PbX3 as a model system, on the 2D van der Waals growth and kinetics of 3D parent materials. We show the successful synthesis of ultrathin (sub-10 nm), large scale (a few tens of μm) single crystalline 2D perovskite thin films on layered mica substrate by van der Waals (VDW) epitaxy. Classical nucleation and growth model explaining conventional epitaxy has been modified to interpret the unique 2D results under VDW mechanism. The generalization of our model shows that a 3D crystal with low cohesive energy tends to favor the 2D growth while the one with strong cohesive energy has less kinetic window. With Monte Carlo simulations, we show that the fractal 2D morphology in perovskite precisely manifests the kinetic competition between VDW diffusivity and thermodynamic driving force, a unique phenomenon to VDW growth, suggesting a fundamental limit on the morphology stability of the 2D form of a 3D material. On the other hand, our single crystal thin film growth results and subsequent cryogenic study in the iodide perovskite provide a perfect resource for the exploration of its complex optical and electronic properties and unveiling the origins of its popularity in the energy conversion field.

  8. Advances in modeling semiconductor epitaxy: Contributions of growth orientation and surface reconstruction to InN metalorganic vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    Kusaba, Akira; Kangawa, Yoshihiro; Kempisty, Pawel; Shiraishi, Kenji; Kakimoto, Koichi; Koukitu, Akinori

    2016-12-01

    We propose a newly improved thermodynamic analysis method that incorporates surface energies. The new theoretical approach enables us to investigate the effects of the growth orientation and surface reconstruction. The obtained knowledge would be indispensable for examining the preferred growth conditions in terms of the contribution of the surface state. We applied the theoretical approach to study the growth processes of InN(0001) and (000\\bar{1}) by metalorganic vapor phase epitaxy. Calculation results reproduced the difference in optimum growth temperature. That is, we successfully developed a new theoretical approach that can predict growth processes on various growth surfaces.

  9. Signal to noise ratio of energy selective x-ray photon counting systems with pileup

    PubMed Central

    Alvarez, Robert E.

    2014-01-01

    Purpose: To derive fundamental limits on the effect of pulse pileup and quantum noise in photon counting detectors on the signal to noise ratio (SNR) and noise variance of energy selective x-ray imaging systems. Methods: An idealized model of the response of counting detectors to pulse pileup is used. The model assumes a nonparalyzable response and delta function pulse shape. The model is used to derive analytical formulas for the noise and energy spectrum of the recorded photons with pulse pileup. These formulas are first verified with a Monte Carlo simulation. They are then used with a method introduced in a previous paper [R. E. Alvarez, “Near optimal energy selective x-ray imaging system performance with simple detectors,” Med. Phys. 37, 822–841 (2010)] to compare the signal to noise ratio with pileup to the ideal SNR with perfect energy resolution. Detectors studied include photon counting detectors with pulse height analysis (PHA), detectors that simultaneously measure the number of photons and the integrated energy (NQ detector), and conventional energy integrating and photon counting detectors. The increase in the A-vector variance with dead time is also computed and compared to the Monte Carlo results. A formula for the covariance of the NQ detector is developed. The validity of the constant covariance approximation to the Cramèr–Rao lower bound (CRLB) for larger counts is tested. Results: The SNR becomes smaller than the conventional energy integrating detector (Q) SNR for 0.52, 0.65, and 0.78 expected number photons per dead time for counting (N), two, and four bin PHA detectors, respectively. The NQ detector SNR is always larger than the N and Q SNR but only marginally so for larger dead times. Its noise variance increases by a factor of approximately 3 and 5 for the A1 and A2 components as the dead time parameter increases from 0 to 0.8 photons per dead time. With four bin PHA data, the increase in variance is approximately 2 and 4 times. The

  10. Low temperature growth of crystalline magnesium oxide on hexagonal silicon carbide (0001) by molecular beam epitaxy

    SciTech Connect

    Goodrich, T. L.; Parisi, J.; Cai, Z.; Ziemer, K. S.

    2007-01-22

    Magnesium oxide (111) was grown epitaxially on hexagonal silicon carbide (6H-SiC) (0001) substrates at low temperatures by molecular beam epitaxy and a remote oxygen plasma source. The films were characterized by reflection high-energy electron diffraction, Auger electron spectroscopy, x-ray photoelectron spectroscopy, and atomic force microscopy. Crystal structure, morphology, and growth rate of the magnesium oxide (MgO) films were found to be dependent on the magnesium flux, indicating a magnesium adsorption controlled growth mechanism. The single crystalline MgO thin films had an epitaxial relationship where MgO (111) parallel 6H-SiC (0001) and were stable in both air and 10{sup -9} Torr up to 1023 K.

  11. Temperature dependence of band gap in MoSe2 grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Choi, Byoung Ki; Kim, Minu; Jung, Kwang-Hwan; Kim, Jwasoon; Yu, Kyu-Sang; Chang, Young Jun

    2017-08-01

    We report on a temperature-dependent band gap property of epitaxial MoSe2 ultrathin films. We prepare uniform MoSe2 films epitaxially grown on graphenized SiC substrates with controlled thicknesses by molecular beam epitaxy. Spectroscopic ellipsometry measurements upon heating sample in ultra-high vacuum showed temperature-dependent optical spectra between room temperature to 850 °C. We observed a gradual energy shift of optical band gap depending on the measurement temperature for different film thicknesses. Fitting with the vibronic model of Huang and Rhys indicates that the constant thermal expansion accounts for the steady decrease of band gap. We also directly probe both optical and stoichiometric changes across the decomposition temperature, which should be useful for developing high-temperature electronic devices and fabrication process with the similar metal chalcogenide films.

  12. Epitaxial strain-engineered self-assembly of magnetic nanostructures in FeRh thin films

    NASA Astrophysics Data System (ADS)

    Witte, Ralf; Kruk, Robert; Molinari, Alan; Wang, Di; Schlabach, Sabine; Brand, Richard A.; Provenzano, Virgil; Hahn, Horst

    2017-01-01

    In this paper we introduce an innovative bottom-up approach for engineering self-assembled magnetic nanostructures using epitaxial strain-induced twinning and phase separation. X-ray diffraction, 57Fe Mössbauer spectroscopy, scanning tunneling microscopy, and transmission electron microscopy show that epitaxial films of a near-equiatomic FeRh alloy respond to the applied epitaxial strain by laterally splitting into two structural phases on the nanometer length scale. Most importantly, these two structural phases differ with respect to their magnetic properties, one being paramagnetic and the other ferromagnetic, thus leading to the formation of a patterned magnetic nanostructure. It is argued that the phase separation directly results from the different strain-dependence of the total energy of the two competing phases. This straightforward relation directly enables further tailoring and optimization of the nanostructures’ properties.

  13. Growth of epitaxial iron nitride ultrathin film on zinc-blende gallium nitride

    SciTech Connect

    Pak, J.; Lin, W.; Wang, K.; Chinchore, A.; Shi, M.; Ingram, D. C.; Smith, A. R.; Sun, K.; Lucy, J. M.; Hauser, A. J.; Yang, F. Y.

    2010-07-15

    The authors report the growth of iron nitride on zinc-blende gallium nitride using molecular beam epitaxy. First, zinc-blende GaN is grown on a magnesium oxide substrate having (001) orientation; second, an ultrathin layer of FeN is grown on top of the GaN layer. In situ reflection high-energy electron diffraction is used to monitor the surface during growth, and a well-defined epitaxial relationship is observed. Cross-sectional transmission electron microscopy is used to reveal the epitaxial continuity at the gallium nitride-iron nitride interface. Surface morphology of the iron nitride, similar to yet different from that of the GaN substrate, can be described as plateau valley. The FeN chemical stoichiometry is probed using both bulk and surface sensitive methods, and the magnetic properties of the sample are revealed.

  14. Decoupling of epitaxial graphene via gold intercalation probed by dispersive Raman spectroscopy

    SciTech Connect

    Pillai, P. B. E-mail: m.desouza@sheffield.ac.uk; DeSouza, M. E-mail: m.desouza@sheffield.ac.uk; Narula, R.; Reich, S.; Wong, L. Y.; Batten, T.; Pokorny, J.

    2015-05-14

    Signatures of a superlattice structure composed of a quasi periodic arrangement of atomic gold clusters below an epitaxied graphene (EG) layer are examined using dispersive Raman spectroscopy. The gold-graphene system exhibits a laser excitation energy dependant red shift of the 2D mode as compared to pristine epitaxial graphene. The phonon dispersions in both the systems are mapped using the experimentally observed Raman signatures and a third-nearest neighbour tight binding electronic band structure model. Our results reveal that the observed excitation dependent Raman red shift in gold EG primarily arise from the modifications of the phonon dispersion in gold-graphene and shows that the extent of decoupling of graphene from the underlying SiC substrate can be monitored from the dispersive nature of the Raman 2D modes. The intercalated gold atoms restore the phonon band structure of epitaxial graphene towards free standing graphene.

  15. Exploring the optimal performances of irreversible single resonance energy selective electron refrigerators

    NASA Astrophysics Data System (ADS)

    Zhou, Junle; Chen, Lingen; Ding, Zemin; Sun, Fengrui

    2016-05-01

    Applying finite-time thermodynamics (FTT) and electronic transport theory, the optimal performances of irreversible single resonance energy selective electron (ESE) refrigerator are analyzed. The effects of heat leakage between two electron reservoirs on optimal performances are discussed. The influences of system operating parameters on cooling load, coefficient of performance (COP), figure of merit and ecological function are demonstrated using numerical examples. Comparative performance analyses among different objective functions show that performance characteristics at maximum ecological function and maximum figure of merit are of great practical significance. Combining the two optimization objectives of maximum ecological function and maximum figure of merit together, more specific optimal ranges of cooling load and COP are obtained. The results can provide some advices to the design of practical electronic machine systems.

  16. Experimental measurement of binding energy, selectivity, and allostery using fluctuation theorems.

    PubMed

    Camunas-Soler, Joan; Alemany, Anna; Ritort, Felix

    2017-01-27

    Thermodynamic bulk measurements of binding reactions rely on the validity of the law of mass action and the assumption of a dilute solution. Yet, important biological systems such as allosteric ligand-receptor binding, macromolecular crowding, or misfolded molecules may not follow these assumptions and may require a particular reaction model. Here we introduce a fluctuation theorem for ligand binding and an experimental approach using single-molecule force spectroscopy to determine binding energies, selectivity, and allostery of nucleic acids and peptides in a model-independent fashion. A similar approach could be used for proteins. This work extends the use of fluctuation theorems beyond unimolecular folding reactions, bridging the thermodynamics of small systems and the basic laws of chemical equilibrium.

  17. The Demand for Scientific and Technical Manpower in Selected Energy-Related Industries, 1970-85: A Methodology Applied to a Selected Scenario of Energy Output. A Summary.

    ERIC Educational Resources Information Center

    Gutmanis, Ivars; And Others

    The primary purpose of the study was to develop and apply a methodology for estimating the need for scientists and engineers by specialty in energy and energy-related industries. The projections methodology was based on the Case 1 estimates by the National Petroleum Council of the results of "maximum efforts" to develop domestic fuel sources by…

  18. Construction of Direction Selectivity through Local Energy Computations in Primary Visual Cortex

    PubMed Central

    Lochmann, Timm; Blanche, Timothy J.; Butts, Daniel A.

    2013-01-01

    Despite detailed knowledge about the anatomy and physiology of neurons in primary visual cortex (V1), the large numbers of inputs onto a given V1 neuron make it difficult to relate them to the neuron’s functional properties. For example, models of direction selectivity (DS), such as the Energy Model, can successfully describe the computation of phase-invariant DS at a conceptual level, while leaving it unclear how such computations are implemented by cortical circuits. Here, we use statistical modeling to derive a description of DS computation for both simple and complex cells, based on physiologically plausible operations on their inputs. We present a new method that infers the selectivity of a neuron’s inputs using extracellular recordings in macaque in the context of random bar stimuli and natural movies in cat. Our results suggest that DS is initially constructed in V1 simple cells through summation and thresholding of non-DS inputs with appropriate spatiotemporal relationships. However, this de novo construction of DS is rare, and a majority of DS simple cells, and all complex cells, appear to receive both excitatory and suppressive inputs that are already DS. For complex cells, these numerous DS inputs typically span a fraction of their overall receptive fields and have similar spatiotemporal tuning but different phase and spatial positions, suggesting an elaboration to the Energy Model that incorporates spatially localized computation. Furthermore, we demonstrate how these computations might be constructed from biologically realizable components, and describe a statistical model consistent with the feed-forward framework suggested by Hubel and Wiesel. PMID:23554913

  19. Thermodynamic theory of epitaxial alloys: first-principles mixed-basis cluster expansion of (In, Ga)N alloy film.

    PubMed

    Liu, Jefferson Zhe; Zunger, Alex

    2009-07-22

    Epitaxial growth of semiconductor alloys onto a fixed substrate has become the method of choice to make high quality crystals. In the coherent epitaxial growth, the lattice mismatch between the alloy film and the substrate induces a particular form of strain, adding a strain energy term into the free energy of the alloy system. Such epitaxial strain energy can alter the thermodynamics of the alloy, leading to a different phase diagram and different atomic microstructures. In this paper, we present a general-purpose mixed-basis cluster expansion method to describe the thermodynamics of an epitaxial alloy, where the formation energy of a structure is expressed in terms of pair and many-body interactions. With a finite number of first-principles calculation inputs, our method can predict the energies of various atomic structures with an accuracy comparable to that of first-principles calculations themselves. Epitaxial (In, Ga)N zinc-blende alloy grown on GaN(001) substrate is taken as an example to demonstrate the details of the method. Two (210) superlattice structures, (InN)(2)/(GaN)(2) (at x = 0.50) and (InN)(4)/(GaN)(1) (at x = 0.80), are identified as the ground state structures, in contrast to the phase-separation behavior of the bulk alloy.

  20. Microstructure of Co/X (X=Cu,Ag,Au) epitaxial thin films grown on Al{sub 2}O{sub 3}(0001) substrates

    SciTech Connect

    Ohtake, Mitsuru; Akita, Yuta; Futamoto, Masaaki; Kirino, Fumiyoshi

    2007-05-01

    Epitaxial thin films of Co/X (X=Cu,Ag,Au) were prepared on Al{sub 2}O{sub 3}(0001) substrates at substrate temperatures of 100 and 300 degree sign C by UHV molecular beam epitaxy. A complicated microstructure was realized for the epitaxial thin films. In-situ reflection high-energy electron diffraction observation has shown that X atoms of the buffer layer segregated to the surface during Co layer deposition, and it yielded a unique epitaxial granular structure. The structure consists of small Co grains buried in the X buffer layer, where both the magnetic small Co grains and the nonmagnetic X layer are epitaxially grown on the single crystal substrate. The structure varied depending on the X element and the substrate temperature. The crystal structure of Co grains is influenced by the buffer layer material and determined to be hcp and fcc structures for the buffer layer materials of Au and Cu, respectively.