Nanodopant-Induced Band Modulation in AgPbmSbTe2+m-Type Nanocomposites

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

Zhang, Yi; Ke, Xuezhi; Chen, Changfeng

2011-01-01

We elucidate the fundamental physics of nanoscale dopants in narrow band-gap thermoelectric nanocomposites XPbmYTe2+m (X=Ag,Na; Y=Sb,Bi) using first-principles calculations. Our re- sults unveil distinct band-structure modulations, most notably a sizable band-gap widening driven by nanodopant-induced lattice strain and a band split-off at the conduction band minimum caused by the spin-orbit interaction of the dopant Sb or Bi atoms. Boltzmann transport calculations demon- strate that these band modulations have significant but competing effects on high-temperature elec- tron transport behavior. These results offer insights for understanding recent experimental findings and suggest principles for optimizing thermoelectric properties of narrow band-gap semiconductors.

Diode-Laser Pumped Far-Infrared Local Oscillator Based on Semiconductor Quantum Wells

NASA Technical Reports Server (NTRS)

Kolokolov, K.; Li, J.; Ning, C. Z.; Larrabee, D. C.; Tang, J.; Khodaparast, G.; Kono, J.; Sasa, S.; Inoue, M.; Biegel, Bryan A. (Technical Monitor)

2002-01-01

The contents include: 1) Tetrahertz Field: A Technology Gap; 2) Existing THZ Sources and Shortcomings; 3) Applications of A THZ Laser; 4) Previous Optical Pumped LW Generations; 5) Optically Pumped Sb based Intersubband Generation Whys; 6) InGaAs/InP/AlAsSb QWs; 7) Raman Enhanced Optical Gain; 8) Pump Intensity Dependence of THZ Gain; 9) Pump-Probe Interaction Induced Raman Shift; 10) THZ Laser Gain in InGaAs/InP/AlAsSb QWs; 11) Diode-Laser Pumped Difference Frequency Generation (InGaAs/InP/AlAsSb QWs); 12) 6.1 Angstrom Semiconductor Quantum Wells; 13) InAs/GaSb/AlSb Nanostructures; 14) InAs/AlSb Double QWs: DFG Scheme; 15) Sb-Based Triple QWs: Laser Scheme; and 16) Exciton State Pumped THZ Generation. This paper is presented in viewgraph form.

A comparative TCAD assessment of III-V channel materials for future high speed and low power logic applications

NASA Astrophysics Data System (ADS)

Gomes, U. P.; Takhar, K.; Ranjan, K.; Rathi, S.; Biswas, D.

2015-02-01

In this work, by means physics based drift-diffusion simulations, three different narrow band gap semiconductors; InAs, InSb and In0.53Ga0.47As, and their associated heterostructures have been studied for future high speed and low power logic applications. It is observed that In0.53Ga0.47As has higher immunity towards short channel effects with low DIBL and sub-threshold slope than InSb and InAs. Also it is observed that for the same device geometry InSb has the highest drive current and lower intrinsic delay but its ION/IOFF figure of merit is deteriorated due to excess leakage current.

Advanced thermoelectric materials with enhanced crystal lattice structure and methods of preparation

NASA Technical Reports Server (NTRS)

Fleurial, Jean-Pierre (Inventor); Caillat, Thierry F. (Inventor); Borshchevsky, Alexander (Inventor)

1998-01-01

New skutterudite phases including Ru.sub.0.5 Pd.sub.0.5 Sb.sub.3, RuSb.sub.2 Te, and FeSb.sub.2 Te, have been prepared having desirable thermoelectric properties. In addition, a novel thermoelectric device has been prepared using skutterudite phase Fe.sub.0.5 Ni.sub.0.5 Sb.sub.3. The skutterudite-type crystal lattice structure of these semiconductor compounds and their enhanced thermoelectric properties results in semiconductor materials which may be used in the fabrication of thermoelectric elements to substantially improve the efficiency of the resulting thermoelectric device. Semiconductor materials having the desired skutterudite-type crystal lattice structure may be prepared in accordance with the present invention by using powder metallurgy techniques. Measurements of electrical and thermal transport properties of selected semiconductor materials prepared in accordance with the present invention, demonstrated high Hall mobilities and good Seebeck coefficients. These materials have low thermal conductivity and relatively low electrical resistivity, and are good candidates for low temperature thermoelectric applications.

Metal-Semiconductor Nanocomposites for High Efficiency Thermoelectric Power Generation

DTIC Science & Technology

2013-12-07

standard III–V compound semiconductor processing techniques with terbium- doped InGaAs of high terbium concentration, Journal of Vacuum Science...even lower the required temperature for strong covalent bonding. We performed the oxide bonding for this substrate transfer task (see Figure 16 for...appropriate controls for assessing ErSb:InGaSb and other nanocomposites of p-type III-V compound semiconductors and their alloys. UCSC group calculated

Electric measurement and magnetic control of spin transport in InSb-based lateral spin devices

NASA Astrophysics Data System (ADS)

Viglin, N. A.; Ustinov, V. V.; Demokritov, S. O.; Shorikov, A. O.; Bebenin, N. G.; Tsvelikhovskaya, V. M.; Pavlov, T. N.; Patrakov, E. I.

2017-12-01

Electric injection and detection of spin-polarized electrons in InSb semiconductors have been realized in nonlocal experimental geometry using an InSb-based "lateral spin valve." The valve of the InSb /MgO /C o0.9F e0.1 composition has semiconductor/insulator/ferromagnet nanoheterojunctions in which the thickness of the InSb layer considerably exceeded the spin diffusion length of conduction electrons. The spin direction in spin diffusion current has been manipulated by a magnetic field under the Hanle effect conditions. The spin polarization of the electron gas has been registered using ferromagnetic C o0.9F e0.1 probes by measuring electrical potentials arising in the probes in accordance with the Johnson-Silsbee concept of the spin-charge coupling. The developed theory is valid at any degree of degeneracy of electron gas in a semiconductor. The spin relaxation time and spin diffusion length of conduction electrons in InSb have been determined, and the electron-spin polarization in InSb has been evaluated for electrons injected from C o0.9F e0.1 through an MgO tunnel barrier.

Ultrathin body GaSb-on-insulator p-channel metal-oxide-semiconductor field-effect transistors on Si fabricated by direct wafer bonding

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

Yokoyama, Masafumi, E-mail: yokoyama@mosfet.t.u-tokyo.ac.jp; Takenaka, Mitsuru; Takagi, Shinichi

2015-02-16

We have realized ultrathin body GaSb-on-insulator (GaSb-OI) on Si wafers by direct wafer bonding technology using atomic-layer deposition (ALD) Al{sub 2}O{sub 3} and have demonstrated GaSb-OI p-channel metal-oxide-semiconductor field-effect transistors (p-MOSFETs) on Si. A 23-nm-thick GaSb-OI p-MOSFET exhibits the peak effective mobility of ∼76 cm{sup 2}/V s. We have found that the effective hole mobility of the thin-body GaSb-OI p-MOSFETs decreases with a decrease in the GaSb-OI thickness or with an increase in Al{sub 2}O{sub 3} ALD temperature. The InAs passivation of GaSb-OI MOS interfaces can enhance the peak effective mobility up to 159 cm{sup 2}/V s for GaSb-OI p-MOSFETs with themore » 20-nm-thick GaSb layer.« less

Electrical characteristics and thermal stability of HfO{sub 2} metal-oxide-semiconductor capacitors fabricated on clean reconstructed GaSb surfaces

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

Miyata, Noriyuki, E-mail: nori.miyata@aist.go.jp; Mori, Takahiro; Yasuda, Tetsuji

2014-06-09

HfO{sub 2}/GaSb interfaces fabricated by high-vacuum HfO{sub 2} deposition on clean reconstructed GaSb surfaces were examined to explore a thermally stable GaSb metal-oxide-semiconductor structure with low interface-state density (D{sub it}). Interface Sb-O bonds were electrically and thermally unstable, and post-metallization annealing at temperatures higher than 200 °C was required to stabilize the HfO{sub 2}/GaSb interfaces. However, the annealing led to large D{sub it} in the upper-half band gap. We propose that the decomposition products that are associated with elemental Sb atoms act as interface states, since a clear correlation between the D{sub it} and the Sb coverage on the initial GaSbmore » surfaces was observed.« less

The section TiInSe/sub 2/-TiSbSe/sub 2/ of the system Ti-In-Sb-Se

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

Guseinov, G.D.; Chapanova, L.M.; Mal'sagov, A.U.

1985-09-01

The ternary compounds A /SUP I/ B /SUP III/ C/sub 2/ /SUP VI/ (A /SUP I/ is univalent Ti; B /SUP III/ is Ga or In; and C /SUP VI/ is S, Se or Te) form a class of semiconductors with a large number of different gap widths. The compounds crystallize in the chalcopyrite structure. Solid solutions based on these compounds, which permit varying smoothly the gap width and other physical parameters over wide limits, are of great interest. The authors synthesized the compounds TiInSe/sub 2/ and TiSbSe/sub 2/ from the starting materials Ti-000, In-000, Sb-000 and Se-OSCh-17-4 by directmore » fusion of the components, taken in a stoichiometric ratio, in quartz ampules evacuated to 1.3 X 10/sup -3/ Pa and sealed.« less

Growth of InxGa1−xSb alloy semiconductor at the International Space Station (ISS) and comparison with terrestrial experiments

PubMed Central

Inatomi, Y; Sakata, K; Arivanandhan, M; Rajesh, G; Nirmal Kumar, V; Koyama, T; Momose, Y; Ozawa, T; Okano, Y; Hayakawa, Y

2015-01-01

Background: InxGa1−xSb is an important material that has tunable properties in the infrared (IR) region and is suitable for IR-device applications. Since the quality of crystals relies on growth conditions, the growth process of alloy semiconductors can be examined better under microgravity (μG) conditions where convection is suppressed. Aims: To investigate the dissolution and growth process of InxGa1−xSb alloy semiconductors via a sandwiched structure of GaSb(seed)/InSb/GaSb(feed) under normal and μG conditions. Methods: InxGa1−xSb crystals were grown at the International Space Station (ISS) under μG conditions, and a similar experiment was conducted under terrestrial conditions (1G) using the vertical gradient freezing (VGF) method. The grown crystals were cut along the growth direction and its growth properties were studied. The indium composition and growth rate of grown crystals were calculated. Results: The shape of the growth interface was nearly flat under μG, whereas under 1G, it was highly concave with the initial seed interface being nearly flat and having facets at the peripheries. The quality of the μG crystals was better than that of the 1G samples, as the etch pit density was low in the μG sample. The growth rate was higher under μG compared with 1G. Moreover, the growth started at the peripheries under 1G, whereas it started throughout the seed interface under μG. Conclusions: Kinetics played a dominant role under 1G. The suppressed convection under μG affected the dissolution and growth process of the InxGa1−xSb alloy semiconductor. PMID:28725715

Growth of In x Ga1-x Sb alloy semiconductor at the International Space Station (ISS) and comparison with terrestrial experiments.

PubMed

Inatomi, Y; Sakata, K; Arivanandhan, M; Rajesh, G; Nirmal Kumar, V; Koyama, T; Momose, Y; Ozawa, T; Okano, Y; Hayakawa, Y

2015-01-01

In x Ga 1- x Sb is an important material that has tunable properties in the infrared (IR) region and is suitable for IR-device applications. Since the quality of crystals relies on growth conditions, the growth process of alloy semiconductors can be examined better under microgravity (μG) conditions where convection is suppressed. To investigate the dissolution and growth process of In x Ga 1- x Sb alloy semiconductors via a sandwiched structure of GaSb(seed)/InSb/GaSb(feed) under normal and μG conditions. In x Ga 1- x Sb crystals were grown at the International Space Station (ISS) under μG conditions, and a similar experiment was conducted under terrestrial conditions (1G) using the vertical gradient freezing (VGF) method. The grown crystals were cut along the growth direction and its growth properties were studied. The indium composition and growth rate of grown crystals were calculated. The shape of the growth interface was nearly flat under μG, whereas under 1G, it was highly concave with the initial seed interface being nearly flat and having facets at the peripheries. The quality of the μG crystals was better than that of the 1G samples, as the etch pit density was low in the μG sample. The growth rate was higher under μG compared with 1G. Moreover, the growth started at the peripheries under 1G, whereas it started throughout the seed interface under μG. Kinetics played a dominant role under 1G. The suppressed convection under μG affected the dissolution and growth process of the In x Ga 1- x Sb alloy semiconductor.

Planar Nernst effect and Mott relation in (In,Fe)Sb ferromagnetic semiconductor

NASA Astrophysics Data System (ADS)

Bui, Cong Tinh; Garcia, Christina A. C.; Tu, Nguyen Thanh; Tanaka, Masaaki; Hai, Pham Nam

2018-05-01

Transverse magneto-thermoelectric effects were studied in an (In,Fe)Sb ferromagnetic semiconductor thin film under an in-plane magnetic field. We find that the thermal voltage is governed by the planar Nernst effect. We show that the magnetic field intensity dependence, magnetic field direction dependence, and temperature dependence of the transverse Seebeck coefficient can be explained by assuming a Mott relation between the in-plane magneto-transport and magneto-thermoelectric phenomena in (In,Fe)Sb.

Non-metal spintronics: study of spin-dependent transport in InSb- and InAs-based nanopatterned heterostructures

NASA Astrophysics Data System (ADS)

Heremans, J. J.; Chen, Hong; Peters, J. A.; Goel, N.; Chung, S. J.; Santos, M. B.; van Roy, W.; Borghs, G.

2006-03-01

Spin-orbit interaction in semiconductor heterostructures can lead to various spin-dependent electronic transport effects without the presence of magnetic materials. Mesoscopic samples were fabricated on InSb/InAlSb and InAs/AlGaSb two-dimensional electron systems, where spin-orbit interaction is strong. In mesoscopic devices, the effects of spin-orbit interaction are not averaged out over the geometry, and lead to observable electronic properties. We experimentally demonstrate spin-split ballistic transport and the creation of fully spin-polarized electron beams using spin-dependent reflection geometries and transverse magnetic focusing geometries. Spin-dependent transport properties in the semiconductor materials are also investigated using antidot lattices. Spin-orbit interaction effects in high-mobility semiconductor devices may be utilized toward the design of novel spintronics implementations. We acknowledge NSF DMR-0094055 (JJH), DMR-0080054, DMR-0209371 (MBS).

Strain-compensated infrared photodetector and photodetector array

DOEpatents

Kim, Jin K; Hawkins, Samuel D; Klem, John F; Cich, Michael J

2013-05-28

A photodetector is disclosed for the detection of infrared light with a long cutoff wavelength in the range of about 4.5-10 microns. The photodetector, which can be formed on a semiconductor substrate as an nBn device, has a light absorbing region which includes InAsSb light-absorbing layers and tensile-strained layers interspersed between the InAsSb light-absorbing layers. The tensile-strained layers can be formed from GaAs, InAs, InGaAs or a combination of these III-V compound semiconductor materials. A barrier layer in the photodetector can be formed from AlAsSb or AlGaAsSb; and a contact layer in the photodetector can be formed from InAs, GaSb or InAsSb. The photodetector is useful as an individual device, or to form a focal plane array.

Skutterudite Compounds For Power Semiconductor Devices

NASA Technical Reports Server (NTRS)

Fleurial, Jean-Pierre; Caillat, Thierry; Borshchevsky, Alexander; Vandersande, Jan

1996-01-01

New semiconducting materials with p-type carrier mobility values much higher than state-of-art semiconductors discovered. Nine compounds, antimonides CoSb(sub3), RhSb(sub3), IrSb(sub3), arsenides CoAs(sub3), RhAs(sub3), IrAs(sub3), and phosphides CoP(sub3), RhP(sub3) and IrP(sub3), exhibit same skutterudite crystallographic structure and form solid solutions of general composition Co(1-x-y)RH(x)Ir(y)P(1-w-z)As(w)Sb(z). Materials exhibit high hole mobilities, high doping levels, and high electronic figures of merit. Some compositions show great potential for application to thermoelectric devices.

Majorana zero modes in superconductor-semiconductor heterostructures

NASA Astrophysics Data System (ADS)

Lutchyn, R. M.; Bakkers, E. P. A. M.; Kouwenhoven, L. P.; Krogstrup, P.; Marcus, C. M.; Oreg, Y.

2018-05-01

Realizing topological superconductivity and Majorana zero modes in the laboratory is a major goal in condensed-matter physics. In this Review, we survey the current status of this rapidly developing field, focusing on proposals for the realization of topological superconductivity in semiconductor-superconductor heterostructures. We examine materials science progress in growing InAs and InSb semiconductor nanowires and characterizing these systems. We then discuss the observation of robust signatures of Majorana zero modes in recent experiments, paying particular attention to zero-bias tunnelling conduction measurements and Coulomb blockade experiments. We also outline several next-generation experiments probing exotic properties of Majorana zero modes, including fusion rules and non-Abelian exchange statistics. Finally, we discuss prospects for implementing Majorana-based topological quantum computation.

Impact of process temperature on GaSb metal-oxide-semiconductor interface properties fabricated by ex-situ process

NASA Astrophysics Data System (ADS)

Yokoyama, Masafumi; Asakura, Yuji; Yokoyama, Haruki; Takenaka, Mitsuru; Takagi, Shinichi

2014-06-01

We have studied the impact of process temperature on interface properties of GaSb metal-oxide-semiconductor (MOS) structures fabricated by an ex-situ atomic-layer-deposition (ALD) process. We have found that the ALD temperature strongly affects the Al2O3/GaSb MOS interface properties. The Al2O3/GaSb MOS interfaces fabricated at the low ALD temperature of 150 °C have the minimum interface-trap density (Dit) of ˜4.5 × 1013 cm-2 eV-1. We have also found that the post-metalization annealing at temperature higher than 200 °C degrades the Al2O3/GaSb MOS interface properties. The low-temperature process is preferable in fabricating GaSb MOS interfaces in the ex-situ ALD process to avoid the high-temperature-induced degradations.

A new quaternary semiconductor compound (Ba2Sb4GeS10): Ab initio study

NASA Astrophysics Data System (ADS)

Ozisik, Havva Bogaz; Ozisik, Haci; Deligoz, Engin

2017-03-01

The newly synthesised Ba2Sb4GeS10 compound is notable because of the interesting features of the quaternary Sb-containing materials. The first principle method has been used to determine the physical properties of this compound. In particular, the electronic structure has been analysed using both conventional GGA-PBE and HSE06 functional. The values of the band gap for PBE and HSE06 calculations were 1.324 and 1.84 eV, respectively. The calculated elastic constants were used to predict polycrystalline mechanical properties. The estimated Vickers hardness (2.7 GPa) values show that Ba2Sb4GeS10 is soft matter. Moreover, the vibrational properties of the compound have been studied. The calculation of the elastic constants and phonon dispersion curves indicates that the Ba2Sb4GeS10 compound is stable both mechanically and dynamically. Furthermore, the minimum thermal conductivity and optical properties, such as dielectric functions and energy loss function, have also been discussed in detail in this paper.

Tunable multifunctional topological insulators in ternary Heusler and related compounds

NASA Astrophysics Data System (ADS)

Felser, Claudia

2011-03-01

Recently the quantum spin Hall effect was theoretically predicted and experimentally realized in quantum wells based on the binary semiconductor HgTe. The quantum spin Hall state and topological insulators are new states of quantum matter interesting for both fundamental condensed-matter physics and material science. Many Heusler compounds with C1b structure are ternary semiconductors that are structurally and electronically related to the binary semiconductors. The diversity of Heusler materials opens wide possibilities for tuning the bandgap and setting the desired band inversion by choosing compounds with appropriate hybridization strength (by the lattice parameter) and magnitude of spin--orbit coupling (by the atomic charge). Based on first-principle calculations we demonstrate that around 50 Heusler compounds show band inversion similar to that of HgTe. The topological state in these zero-gap semiconductors can be created by applying strain or by designing an appropriate quantumwell structure, similar to the case of HgTe. Many of these ternary zero-gap semiconductors (LnAuPb, LnPdBi, LnPtSb and LnPtBi) contain the rare-earth element Ln, which can realize additional properties ranging from superconductivity (for example LaPtBi) to magnetism (for example GdPtBi) and heavy fermion behaviour (for example YbPtBi). These properties can open new research directions in realizing the quantized anomalous Hall effect and topological superconductors. Heusler compounds are similar to a stuffed diamond, correspondingly, it should be possible to find the ``high Z'' equivalent of graphene in a graphite-like structure with 18 valence electrons and with inverted bands. Indeed the ternary compounds, such as LiAuSe and KHgSb with a honeycomb structure of their Au-Se and Hg-Sb layers feature band inversion very similar to HgTe which is a strong precondition for existence of the topological surface states. These materials have a gap at the Fermi energy and are therefore candidates for 3D-topological insulators. Additionally they are centro-symmetric, therefore, it is possible to determine the parity of their wave functions, and hence, their topological character. Surprisingly, the compound KHgSb with the strong SOC is topologically trivial, whereas LiAuSe is found to be a topological non-trivial insulator.

Analytical model of threshold voltage degradation due to localized charges in gate material engineered Schottky barrier cylindrical GAA MOSFETs

NASA Astrophysics Data System (ADS)

Kumar, Manoj; Haldar, Subhasis; Gupta, Mridula; Gupta, R. S.

2016-10-01

The threshold voltage degradation due to the hot carrier induced localized charges (LC) is a major reliability concern for nanoscale Schottky barrier (SB) cylindrical gate all around (GAA) metal-oxide-semiconductor field-effect transistors (MOSFETs). The degradation physics of gate material engineered (GME)-SB-GAA MOSFETs due to LC is still unexplored. An explicit threshold voltage degradation model for GME-SB-GAA-MOSFETs with the incorporation of localized charges (N it) is developed. To accurately model the threshold voltage the minimum channel carrier density has been taken into account. The model renders how +/- LC affects the device subthreshold performance. One-dimensional (1D) Poisson’s and 2D Laplace equations have been solved for two different regions (fresh and damaged) with two different gate metal work-functions. LCs are considered at the drain side with low gate metal work-function as N it is more vulnerable towards the drain. For the reduction of carrier mobility degradation, a lightly doped channel has been considered. The proposed model also includes the effect of barrier height lowering at the metal-semiconductor interface. The developed model results have been verified using numerical simulation data obtained by the ATLAS-3D device simulator and excellent agreement is observed between analytical and simulation results.

Structural and electronic properties of the V-V compounds isoelectronic to GaN and isostructural to gray arsenic

NASA Astrophysics Data System (ADS)

Yang, Zhao; Han, Dan; Chen, Guohong; Chen, Shiyou

2018-03-01

The III-V binary compound semiconductors such as GaN, GaP, InN and InP have extensive applications in various optoelectronic, microwave and power-electronic devices. Using first-principles calculation, we systematically studied the structural and electronic properties of the V-V binary compounds (BiN, BiP, SbN and SbP) that are isoelectronic to GaN, GaP, InN and InP if Bi and Sb are in the +3 valence state. Interestingly, we found that the ground-state structures of BiP, SbN and SbP have the R-3m symmetry and are isostructural to the layered structure of gray arsenic, whereas BiN prefers a different ground-state structure with the C2 symmetry. Electronic structure calculations showed that the bulk BiN is a narrow bandgap semiconductor for its bandgap is about 0.2 eV. In contrast, BiP, SbN and SbP are metallic. The layered ground-state structure of the V-V binary compounds motivates us to study the electronic properties of their few-layer structures. As the structure becomes monolayer, their bandgaps increase significantly and are all in the range from about 1 eV to 1.7 eV, which are comparative to the bandgap of the monolayer gray arsenic. The monolayer BiP, SbN and SbP have indirect bandgaps, and they show a semiconductor-metal transition as the number of layers increase. Interestingly, the monolayer BiP has the largest splitting (350 meV) of the CBM valley, and thus may have potential application in novel spintronics and valleytronics devices.

Electrical properties and transport mechanisms in phase change memory thin films of quasi-binary-line GeTe–Sb{sub 2}Te{sub 3} chalcogenide semiconductors

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

Sherchenkov, A. A.; Kozyukhin, S. A., E-mail: sergkoz@igic.ras.ru; Lazarenko, P. I.

The temperature dependences of the resistivity and current–voltage (I–V) characteristics of phase change memory thin films based on quasi-binary-line GeTe–Sb{sub 2}Te{sub 3} chalcogenide semiconductors Ge{sub 2}Sb{sub 2}Te{sub 5}, GeSb{sub 2}Te{sub 5}, and GeSb{sub 4}Te{sub 7} are investigated. The effect of composition variation along the quasibinary line on the electrical properties and transport mechanisms of the thin films is studied. The existence of three ranges with different I–V characteristics is established. The position and concentration of energy levels controlling carrier transport are estimated. The results obtained show that the electrical properties of the thin films can significantly change during a shiftmore » along the quasi-binary line GeTe–Sb{sub 2}Te{sub 3}, which is important for targeted optimization of the phase change memory technology.« less

Impact of process temperature on GaSb metal-oxide-semiconductor interface properties fabricated by ex-situ process

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

Yokoyama, Masafumi, E-mail: yokoyama@mosfet.t.u-tokyo.ac.jp; Takenaka, Mitsuru; Takagi, Shinichi

We have studied the impact of process temperature on interface properties of GaSb metal-oxide-semiconductor (MOS) structures fabricated by an ex-situ atomic-layer-deposition (ALD) process. We have found that the ALD temperature strongly affects the Al{sub 2}O{sub 3}/GaSb MOS interface properties. The Al{sub 2}O{sub 3}/GaSb MOS interfaces fabricated at the low ALD temperature of 150 °C have the minimum interface-trap density (D{sub it}) of ∼4.5 × 10{sup 13 }cm{sup −2} eV{sup −1}. We have also found that the post-metalization annealing at temperature higher than 200 °C degrades the Al{sub 2}O{sub 3}/GaSb MOS interface properties. The low-temperature process is preferable in fabricating GaSb MOS interfaces in the ex-situmore » ALD process to avoid the high-temperature-induced degradations.« less

Operation of the GaSb p-channel metal-oxide-semiconductor field-effect transistors fabricated on (111)A surfaces

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

Nishi, K., E-mail: nishi@mosfet.t.u-tokyo.ac.jp; Takenaka, M.; Takagi, S.

2014-12-08

We demonstrate the operation of GaSb p-channel metal-oxide-semiconductor field-effect transistors (p-MOSFETs) on (111)A surfaces with Al{sub 2}O{sub 3} gate dielectrics formed by atomic-layer deposition at 150 °C. The p-MOSFETs on (111)A surfaces exhibit higher drain current and lower subthreshold swing than those on (100) surfaces. We find that the interface-state density (D{sub it}) values at the Al{sub 2}O{sub 3}/GaSb MOS interfaces on the (111)A surfaces are lower than those on the (100) surfaces, which can lead to performance enhancement of the GaSb p-MOSFETs on (111)A surfaces. The mobility of the GaSb p-MOSFETs on (111)A surfaces is 80% higher than that onmore » (100) surfaces.« less

Hg-Based Epitaxial Materials for Topological Insulators

DTIC Science & Technology

2014-07-01

Research Laboratory for investigation of properties. 15. SUBJECT TERMS EOARD, topological insulator , diluted magnetic ...topological superconductors and spintronics to quantum computation (e.g. see C.L.Kane and J.E.Moore "Topological Insulators " Physics World (2011) 24...tetradymite semiconductors Bi2Te3, Bi2Se3, and Sb2Te3 which form magnetically ordered insulators when doped with transition metal elements Cr or Fe (Rui Yu et

Photoconductivity in the chalcohalide semiconductor, SbSeI: a new candidate for hard radiation detection.

PubMed

Wibowo, Arief C; Malliakas, Christos D; Liu, Zhifu; Peters, John A; Sebastian, Maria; Chung, Duck Young; Wessels, Bruce W; Kanatzidis, Mercouri G

2013-06-17

We investigated an antimony chalcohalide compound, SbSeI, as a potential semiconductor material for X-ray and γ-ray detection. SbSeI has a wide band gap of 1.70 eV with a density of 5.80 g/cm(3), and it crystallizes in the orthorhombic Pnma space group with a one-dimensional chain structure comprised of infinite zigzag chains of dimers [Sb2Se4I8]n running along the crystallographic b axis. In this study, we investigate conditions for vertical Bridgman crystal growth using combinations of the peak temperature and temperature gradients as well as translation rate set in a three-zone furnace. SbSeI samples grown at 495 °C peak temperature and 19 °C/cm temperature gradient with 2.5 mm/h translation rate produced a single phase of columnar needlelike crystals aligned along the translational direction of the growth. The ingot sample exhibited an n-type semiconductor with resistivity of ∼10(8) Ω·cm. Photoconductivity measurements on these specimens allowed us to determine mobility-lifetime (μτ) products for electron and hole carriers that were found to be of similar order of magnitude (∼10(-4) cm(2)/V). Further, the SbSeI ingot with well-aligned, one-dimensional columnar needlelike crystals shows an appreciable response of Ag Kα X-ray.

Features of conductivity mechanisms in heavily doped compensated V{sub 1–x}Ti{sub x}FeSb Semiconductor

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

Romaka, V. A., E-mail: vromaka@polynet.lviv.ua; Rogl, P.; Romaka, V. V.

2016-07-15

The crystal and electronic structure and also the energy and kinetic properties of n-VFeSb semiconductor heavily doped with the Ti acceptor impurity are investigated in the temperature and Ti concentration ranges of T = 4.2–400 K and N{sub A}{sup Ti} ≈ 9.5 × 10{sup 19}–3.6 × 10{sup 21} cm{sup –3} (x = 0.005–0.20), respectively. The complex mechanism of the generation of acceptor and donor structural defects is established. It is demonstrated that the presence of vacancies at Sb atomic sites in n-VFeSb gives rise to donor structural defects (“a priori doping”). Substitution of the Ti dopant for V in VFeSbmore » leads simultaneously to the generation of acceptortype structural defects, a decrease in the number of donor defects, and their removal in the concentration range of 0 ≤ x ≤ 0.03 via the occupation of vacancies by Sb atoms, and the generation of donor defects due to the occurrence of vacancies and an increase in their number. The result obtained underlies the technique for fabricating new n-VFeSb-based thermoelectric materials. The results are discussed in the context of the Shklovsky–Efros model for a heavily doped compensated semiconductor.« less

Disordered Zinc in Zn4Sb3 with Phonon-Glass and Electron-Crystal Thermoelectric Properties

NASA Technical Reports Server (NTRS)

Snyder, G. Jeffrey; Christensen, Mogens; Nishibori, Eiji; Caillat, Thierry; Brummerstedt Iversen, Bo

2004-01-01

By converting waste heat into electricity, thermoelectric generators could be an important part of the solution to today's energy challenges. The compound Zn4Sb3 is one of the most efficient thermoelectric materials known. Its high efficiency results from an extraordinarily low thermal conductivity in conjunction with the electronic structure of a heavily doped semiconductor. Previous structural studies have been unable to explain this unusual combination of properties. Here, we show through a comprehensive structural analysis using single-crystal X-ray and powder-synchrotron-radiation diffraction methods, that both the electronic and thermal properties of Zn4Sb3 can be understood in terms of unique structural features that have been previously overlooked. The identification of Sb3- ions and Sb-2(4-) dimers reveals that Zn4Sb3 is a valence semiconductor with the ideal stoichiometry Zn13Sb10. In addition, the structure contains significant disorder, with zinc atoms distributed over multiple positions. The discovery of glass-like interstitial sites uncovers a highly effective mechanism for reducing thermal conductivity. Thus Zn4Sb3 is in many ways an ideal 'phonon glass, electron crystal' thermoelectric material.

Low-temperature magnetotransport of the narrow-gap semiconductor FeSb2

NASA Astrophysics Data System (ADS)

Takahashi, H.; Okazaki, R.; Yasui, Y.; Terasaki, I.

2011-11-01

We present a study of the magnetoresistance and Hall effect in the narrow-gap semiconductor FeSb2 at low temperatures. Both the electrical and Hall resistivities show unusual magnetic field dependence in the low-temperature range where a large Seebeck coefficient was observed. By applying a two-carrier model, we find that the carrier concentration decreases from 1 down to 10-4 ppm/unit cell and the mobility increases from 2000 to 28 000 cm2/Vs with decreasing temperature from 30 down to 4 K. At lower temperatures, the magnetoresistive behavior drastically changes and a negative magnetoresistance is observed at 3 K. These low-temperature behaviors are reminiscent of the low-temperature magnetotransport observed in doped semiconductors such as As-doped Ge, which is well described by a weak-localization picture. We argue a detailed electronic structure in FeSb2 inferred from our observations.

Faceting, composition and crystal phase evolution in III-V antimonide nanowire heterostructures revealed by combining microscopy techniques.

PubMed

Xu, Tao; Dick, Kimberly A; Plissard, Sébastien; Nguyen, Thanh Hai; Makoudi, Younes; Berthe, Maxime; Nys, Jean-Philippe; Wallart, Xavier; Grandidier, Bruno; Caroff, Philippe

2012-03-09

III-V antimonide nanowires are among the most interesting semiconductors for transport physics, nanoelectronics and long-wavelength optoelectronic devices due to their optimal material properties. In order to investigate their complex crystal structure evolution, faceting and composition, we report a combined scanning electron microscopy (SEM), transmission electron microscopy (TEM), and scanning tunneling microscopy (STM) study of gold-nucleated ternary InAs/InAs(1-x)Sb(x) nanowire heterostructures grown by molecular beam epitaxy. SEM showed the general morphology and faceting, TEM revealed the internal crystal structure and ternary compositions, while STM was successfully applied to characterize the oxide-free nanowire sidewalls, in terms of nanofaceting morphology, atomic structure and surface composition. The complementary use of these techniques allows for correlation of the morphological and structural properties of the nanowires with the amount of Sb incorporated during growth. The addition of even a minute amount of Sb to InAs changes the crystal structure from perfect wurtzite to perfect zinc blende, via intermediate stacking fault and pseudo-periodic twinning regimes. Moreover, the addition of Sb during the axial growth of InAs/InAs(1-x)Sb(x) heterostructure nanowires causes a significant conformal lateral overgrowth on both segments, leading to the spontaneous formation of a core-shell structure, with an Sb-rich shell.

Effect of p–d hybridization, structural distortion and cation electronegativity on electronic properties of ZnSnX{sub 2} (X=P, As, Sb) chalcopyrite semiconductors

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

Mishra, S.; Ganguli, B., E-mail: biplabg@nitrkl.ac.in

2013-04-15

Significant effects of p–d hybridization, structural distortion and cation-electro-negativity are found on band gap in ZnSnX{sub 2} (X=P, As, Sb). Our study suggests these compounds to be direct band gap semiconductors with band gaps of 1.23, 0.68 and 0.19 eV respectively. Lattice constants, tetragonal distortion (η), anion displacement, bond lengths and bulk moduli are calculated by Density Functional Theory based on Tight binding Linear Muffin-Tin orbital method. Our result of structural properties is in good agreement with the available experimental and other theoretical results. Calculated band gaps also agree well with the experimental works within LDA limitation. Unlike other semiconductorsmore » in the group II–IV–V{sub 2}, there is a reduction in the band gap of 0.22, 0.20 and 0.24 eV respectively in ZnSnX{sub 2} (X=P, As, Sb) due to p–d hybridization. Structural distortion decreases band gap by 0.20, 0.12 and 0.10 eV respectively. We find that cation electronegativity effect is responsible for increasing the band gap relative to their binary analogs GaInP{sub 2}, InGaAs{sub 2} and GaInSb{sub 2} respectively and increment are 0.13, 0.04 and 0.13 eV respectively. - Graphical abstract: One unit cell of ZnSnX{sub 2} (X=P, As, Sb) chalcopyrite semiconductor. Semiconductors ZnSnX{sub 2} (X=P, As, Sb) are found to be direct band gap semiconductors with band gaps 1.23, 0.68 and 0.19 eV respectively. The quantitative estimate of effects of p–d hybridization, structural distortion and cation electronegativity shows band gaps change significantly due to these effects. Highlights: ► ZnSnX{sub 2} (X=P, As, Sb) are direct band gap semiconductors. ► These have band gaps of 1.23 eV, 0.68 eV and 0.19 eV respectively. ► The band gap reduction due to p–d hybridization is 13.41%, 18.51% and 40% respectively. ► Band gap reduction due to structural distortion is 12.12%, 11.11% and 16.66% respectively. ► Band gap increases 8.38%, 3.70% and 21.31% respectively due to cation electronegativity.« less

Anomalous Temperature Dependence in Metal-Black Phosphorus Contact.

PubMed

Li, Xuefei; Grassi, Roberto; Li, Sichao; Li, Tiaoyang; Xiong, Xiong; Low, Tony; Wu, Yanqing

2018-01-10

Metal-semiconductor contact has been the performance limiting problem for electronic devices and also dictates the scaling potential for future generation devices based on novel channel materials. Two-dimensional semiconductors beyond graphene, particularly few layer black phosphorus, have attracted much attention due to their exceptional electronic properties such as anisotropy and high mobility. However, due to its ultrathin body nature, few layer black phosphorus-metal contact behaves differently than conventional Schottky barrier (SB) junctions, and the mechanisms of its carrier transport across such a barrier remain elusive. In this work, we examine the transport characteristic of metal-black phosphorus contact under varying temperature. We elucidated the origin of apparent negative SB heights extracted from classical thermionic emission model and also the phenomenon of metal-insulator transition observed in the current-temperature transistor characteristic. In essence, we found that the SB height can be modulated by the back-gate voltage, which beyond a certain critical point becomes so low that the injected carrier can no longer be described by the conventional thermionic emission theory. The transition from transport dominated by a Maxwell-Boltzmann distribution for the high energy tail states, to that of a Fermi distribution by low energy Fermi sea electrons, is the physical origin of the observed metal-insulator transition. We identified two distinctive tunneling limited transport regimes in the contact: vertical and longitudinal tunneling.

Recent Vertical External Cavity Surface Emitting Lasers (VECSELs) Developments for Sensor Applications (POSTPRINT)

DTIC Science & Technology

2013-02-01

edge-emitting strained InxGa1−xSb/AlyGa1−ySb quantum well struc- tures using solid-source molecular beam epitaxy (MBE) with varying barrier heights...intersubband quantum wells. The most common high-power edge-emitting semiconductor lasers suffter from poor beam quality, due primarily to the linewidth...reduces the power scalability of semiconductor lasers. In vertical cavity surface emitting lasers ( VCSELs ), light propagates parallel to the growth

Mechanochemical synthesis and physico-chemical investigations of new materials for gas sensors

NASA Astrophysics Data System (ADS)

Shubenkova, E. G.

2018-01-01

Solid solutions of the InSb-ZnTe semiconductor system containing up to 20 mol.% of ZnTe were synthesized for the first time. The role of mechanochemical treatment in the process of obtaining solid solutions of this system is shown. Solid solutions in the InSb-ZnTe system have been identified by Raman spectroscopy, and the optical properties of its components have been studied. On the basis of an analysis of the anti-stokes spectral radiation distribution the solid solutions formation was identified both on the dependence of the spectral distribution maximum’s shift on the composition of the InSb1-x-ZnTex system, and by estimating the radiation intensity of the initial binary semiconductors at frequencies corresponding to the LO- and TO- vibrations of the binary compounds crystal lattice. The values of the band gap for InSb, (InSb)0.95(ZnTe)0.05 and (InSb)0.9(ZnTe)0.1 were calculated, their values were 0.22 eV, 0.30 eV and 0.38 eV, respectively.

High quality HfO{sub 2}/p-GaSb(001) metal-oxide-semiconductor capacitors with 0.8 nm equivalent oxide thickness

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

Barth, Michael; Datta, Suman, E-mail: sdatta@engr.psu.edu; Bruce Rayner, G.

2014-12-01

We investigate in-situ cleaning of GaSb surfaces and its effect on the electrical performance of p-type GaSb metal-oxide-semiconductor capacitor (MOSCAP) using a remote hydrogen plasma. Ultrathin HfO{sub 2} films grown by atomic layer deposition were used as a high permittivity gate dielectric. Compared to conventional ex-situ chemical cleaning methods, the in-situ GaSb surface treatment resulted in a drastic improvement in the impedance characteristics of the MOSCAPs, directly evidencing a much lower interface trap density and enhanced Fermi level movement efficiency. We demonstrate that by using a combination of ex-situ and in-situ surface cleaning steps, aggressively scaled HfO{sub 2}/p-GaSb MOSCAP structuresmore » with a low equivalent oxide thickness of 0.8 nm and efficient gate modulation of the surface potential are achieved, allowing to push the Fermi level far away from the valence band edge high up into the band gap of GaSb.« less

Drastic effect of the Mn-substitution in the strongly correlated semiconductor FeSb2.

NASA Astrophysics Data System (ADS)

Kassem, Mohamed A.; Tabata, Yoshikazu; Waki, Takeshi; Nakamura, Hiroyuki

2017-06-01

We report the effects of Mn substitution, corresponding to hole doping, on the electronic properties of the narrow gap semiconductor, FeSb2, using single crystals of Fe1- x Mn x Sb2 grown by the Sb flux method. The orthorhombic Pnnm structure was confirmed by powder X-ray diffraction (XRD) for the pure and Mn-substituted samples. Their crystal structure parameters were refined using the Rietveld method. The chemical composition was investigated by wavelength-dispersive X-ray spectroscopy (WDX). The solubility limit of Mn in FeSb2 is x max ˜ 0.05 and the lattice constants change monotonically with increasing the actual Mn concentration. A drastic change from semiconducting to metallic electronic transports was found at very low Mn concentration at x ˜ 0.01. Our experimental results and analysis indicate that the substitution of a small amount of Mn changes drastically the electronic state in FeSb2 as well as the Co-substitution does: closing of the narrow gap and emergence of the density of states (DOS) at the Fermi level.

Electron-Spin Filters Based on the Rashba Effect

NASA Technical Reports Server (NTRS)

Ting, David Z.-Y.; Cartoixa, Xavier; McGill, Thomas C.; Moon, Jeong S.; Chow, David H.; Schulman, Joel N.; Smith, Darryl L.

2004-01-01

Semiconductor electron-spin filters of a proposed type would be based on the Rashba effect, which is described briefly below. Electron-spin filters more precisely, sources of spin-polarized electron currents have been sought for research on, and development of, the emerging technological discipline of spintronics (spin-based electronics). There have been a number of successful demonstrations of injection of spin-polarized electrons from diluted magnetic semiconductors and from ferromagnetic metals into nonmagnetic semiconductors. In contrast, a device according to the proposal would be made from nonmagnetic semiconductor materials and would function without an applied magnetic field. The Rashba effect, named after one of its discoverers, is an energy splitting, of what would otherwise be degenerate quantum states, caused by a spin-orbit interaction in conjunction with a structural-inversion asymmetry in the presence of interfacial electric fields in a semiconductor heterostructure. The magnitude of the energy split is proportional to the electron wave number. The present proposal evolved from recent theoretical studies that suggested the possibility of devices in which electron energy states would be split by the Rashba effect and spin-polarized currents would be extracted by resonant quantum-mechanical tunneling. Accordingly, a device according to the proposal would be denoted an asymmetric resonant interband tunneling diode [a-RITD]. An a-RITD could be implemented in a variety of forms, the form favored in the proposal being a double-barrier heterostructure containing an asymmetric quantum well. It is envisioned that a-RITDs would be designed and fabricated in the InAs/GaSb/AlSb material system for several reasons: Heterostructures in this material system are strong candidates for pronounced Rashba spin splitting because InAs and GaSb exhibit large spin-orbit interactions and because both InAs and GaSb would be available for the construction of highly asymmetric quantum wells. This mate-rial system affords a variety of energy-band alignments that can be exploited to obtain resonant tunneling and other desired effects. The no-common-atom InAs/GaSb and InAs/AlSb interfaces would present opportunities for engineering interface potentials for optimizing Rashba spin splitting.

Fermi Level Unpinning of GaSb (100) using Plasma Enhanced Atomic Layer Deposition of Al2O3

DTIC Science & Technology

2010-01-01

of high-/GaSb semiconductor interface. GaSb has a highly reactive surface and on exposure to air it will form a native oxide layer composed of Ga2O3 ...and Sb2O3 2GaSb+3O2→ Ga2O3 +Sb2O3. The Sb2O3 can fur- ther react with the GaSb surface forming elemental Sb and Ga2O3 Sb2O3+2GaSb→ Ga2O3 +4Sb.5,6...rights_and_permissions mentioned before, Sb2O3 reacts with GaSb forming Ga2O3 and elemental Sb.6 The kinetics of this reaction is enhanced at higher temperatures200 °C.14

Use of layer strains in strained-layer superlattices to make devices for operation in new wavelength ranges, E. G. , InAsSb at 8 to 12. mu. m. [InAs/sub 1-x/Sb/sub x/

DOEpatents

Osbourn, G.C.

1983-10-06

An intrinsic semiconductor electro-optical device comprises a p-n junction intrinsically responsive, when cooled, to electromagnetic radiation in the wavelength range of 8 to 12 ..mu..m. This radiation responsive p-n junction comprises a strained-layer superlattice (SLS) of alternating layers of two different III-V semiconductors. The lattice constants of the two semiconductors are mismatched, whereby a total strain is imposed on each pair of alternating semiconductor layers in the SLS structure, the proportion of the total strain which acts on each layer of the pair being proportional to the ratio of the layer thicknesses of each layer in the pair.

First-Principles Calculations of Structural, Electronic and Optical Properties of Ternary Semiconductor Alloys ZAs x Sb1- x ( Z = B, Al, Ga, In)

NASA Astrophysics Data System (ADS)

Bounab, S.; Bentabet, A.; Bouhadda, Y.; Belgoumri, Gh.; Fenineche, N.

2017-08-01

We have investigated the structural and electronic properties of the BAs x Sb 1- x , AlAs x Sb 1- x , GaAs x Sb 1- x and InAs x Sb 1- x semiconductor alloys using first-principles calculations under the virtual crystal approximation within both the density functional perturbation theory and the pseudopotential approach. In addition the optical properties have been calculated by using empirical methods. The ground state properties such as lattice constants, both bulk modulus and derivative of bulk modulus, energy gap, refractive index and optical dielectric constant have been calculated and discussed. The obtained results are in reasonable agreement with numerous experimental and theoretical data. The compositional dependence of the lattice constant, bulk modulus, energy gap and effective mass of electrons for ternary alloys show deviations from Vegard's law where our results are in agreement with the available data in the literature.

Thermal conductivity switch: Optimal semiconductor/metal melting transition

NASA Astrophysics Data System (ADS)

Kim, Kwangnam; Kaviany, Massoud

2016-10-01

Scrutinizing distinct solid/liquid (s /l ) and solid/solid (s /s ) phase transitions (passive transitions) for large change in bulk (and homogenous) thermal conductivity, we find the s /l semiconductor/metal (S/M) transition produces the largest dimensionless thermal conductivity switch (TCS) figure of merit ZTCS (change in thermal conductivity divided by smaller conductivity). At melting temperature, the solid phonon and liquid molecular thermal conductivities are comparable and generally small, so the TCS requires localized electron solid and delocalized electron liquid states. For cyclic phase reversibility, the congruent phase transition (no change in composition) is as important as the thermal transport. We identify X Sb and X As (X =Al , Cd, Ga, In, Zn) and describe atomic-structural metrics for large ZTCS, then show the superiority of S/M phonon- to electron-dominated transport melting transition. We use existing experimental results and theoretical and ab initio calculations of the related properties for both phases (including the Kubo-Greenwood and Bridgman formulations of liquid conductivities). The 5 p orbital of Sb contributes to the semiconductor behavior in the solid-phase band gap and upon disorder and bond-length changes in the liquid phase this changes to metallic, creating the large contrast in thermal conductivity. The charge density distribution, electronic localization function, and electron density of states are used to mark this S/M transition. For optimal TCS, we examine the elemental selection from the transition, basic, and semimetals and semiconductor groups. For CdSb, addition of residual Ag suppresses the bipolar conductivity and its ZTCS is over 7, and for Zn3Sb2 it is expected to be over 14, based on the structure and transport properties of the better-known β -Zn4Sb3 . This is the highest ZTCS identified. In addition to the metallic melting, the high ZTCS is due to the electron-poor nature of II-V semiconductors, leading to the significantly low phonon conductivity.

Electronic Properties, Screening, and Efficient Carrier Transport in NaSbS 2

DOE PAGES

Sun, Jifeng; Singh, David J.

2017-02-13

NaSbS 2 is a semiconductor that was recently shown to have remarkable efficacy as a solar absorber indicating efficient charge collection even in material containing defects. We report first-principles calculations of properties that show (1) an indirect gap only slightly smaller than the direct gap, which may impede the recombination of photoexcited carriers, (2) highly anisotropic electronic and optical properties reflecting a layered crystal structure, (3) a pushed-up valence-band maximum due to repulsion from the Sb 5s states, and (4) cross-gap hybridization between the S p—derived valence bands and the Sb 5p states. This latter feature leads to enhanced Bornmore » effective charges that can provide local screening and, therefore, defect tolerance. Finally, these features are discussed in relation to the performance of the compound as a semiconductor with efficient charge collection.« less

Strain Engineering of Epitaxially Transferred, Ultrathin Layers of III-V Semiconductor on Insulator

DTIC Science & Technology

2011-01-01

The structure of the source wafer is shown schematically in Fig. 2a, with both InAs and AlGaSb layers coherently strained to the GaSb 001...is due to the surface plasmon-LO phonon FIG. 2. Color online a The structure of GaSb /AlGaSb/InAs source wafer with an assumed strain state for...insulator layers obtained from an epitaxial transfer process is studied. The as-grown InAs epilayer 10–20 nm thick on the GaSb /AlGaSb source wafer has the

Development of an electronic device quality aluminum antimonide (AlSb) semiconductor for solar cell applications

DOEpatents

Sherohman, John W; Yee, Jick Hong; Combs, III, Arthur W

2014-11-11

Electronic device quality Aluminum Antimonide (AlSb)-based single crystals produced by controlled atmospheric annealing are utilized in various configurations for solar cell applications. Like that of a GaAs-based solar cell devices, the AlSb-based solar cell devices as disclosed herein provides direct conversion of solar energy to electrical power.

Indium antimonide quantum well structures for electronic device applications

NASA Astrophysics Data System (ADS)

Edirisooriya, Madhavie

The electron effective mass is smaller in InSb than in any other III-V semiconductor. Since the electron mobility depends inversely on the effective mass, InSb-based devices are attractive for field effect transistors, magnetic field sensors, ballistic transport devices, and other applications where the performance depends on a high mobility or a long mean free path. In addition, electrons in InSb have a large g-factor and strong spin orbit coupling, which makes them well suited for certain spin transport devices. The first n-channel InSb high electron mobility transistor (HEMT) was produced in 2005 with a power-delay product superior to HEMTs with a channel made from any other III-V semiconductor. The high electron mobility in the InSb quantum-well channel increases the switching speed and lowers the required supply voltage. This dissertation focuses on several materials challenges that can further increase the appeal of InSb quantum wells for transistors and other electronic device applications. First, the electron mobility in InSb quantum wells, which is the highest for any semiconductor quantum well, can be further increased by reducing scattering by crystal defects. InSb-based heteroepitaxy is usually performed on semi-insulating GaAs (001) substrates due to the lack of a lattice matched semi-insulating substrate. The 14.6% mismatch between the lattice parameters of GaAs and InSb results in the formation of structural defects such as threading dislocations and microtwins which degrade the electrical and optical properties of InSb-based devices. Chapter 1 reviews the methods and procedures for growing InSb-based heterostructures by molecular beam epitaxy. Chapters 2 and 3 introduce techniques for minimizing the crystalline defects in InSb-based structures grown on GaAs substrates. Chapter 2 discusses a method of reducing threading dislocations by incorporating AlyIn1-ySb interlayers in an AlxIn1-xSb buffer layer and the reduction of microtwin defects by growth on GaAs substrates that are oriented 2° away from the [011] direction. Chapter 3 discusses designing InSb QW layer structures that are strain balanced. By applying these defect-reducing techniques, the electron mobility in InSb quantum wells at room temperature was significantly increased. For complementary logic technology, p-channel transistors with high mobility are equally as important as n-channel transistors. However, achieving a high hole mobility in III-V semiconductors is challenging. A controlled introduction of strain in the quantum-well material is an effective technique for enhancing the hole mobility beyond its value in bulk material. The strain reduces the hole effective mass by splitting the heavy hole and light hole valence bands. Chapter 4 discusses a successful attempt to realize p-type InSb quantum well structures. The biaxial strain applied via a relaxed metamorphic buffer resulted in a significantly higher room-temperature hole mobility and a record high low-temperature hole mobility. To demonstrate the usefulness of high mobility in a device structure, magnetoresistive devices were fabricated from remotely doped InSb QWs. Such devices have numerous practical applications such as position and speed sensors and as read heads in magnetic storage systems. In a magnetoresistive device composed of a series of shorted Hall bars, the magnetoresistance is proportional to the electron mobility squared for small magnetic fields. Hence, the high electron mobility in InSb QWs makes them highly preferable for geometrical magnetoresistors. Chapter 5 reports the fabrication and characterization of InSb quantum-well magnetoresistors. The excellent transport properties of the InSb QWs resulted in high room-temperature sensitivity to applied magnetic fields. Finally, Chapter 6 provides the conclusions obtained during this research effort, and makes suggestions for future work.

Intermediate type excitons in Schottky barriers of A3B6 layer semiconductors and UV photodetectors

NASA Astrophysics Data System (ADS)

Alekperov, O. Z.; Guseinov, N. M.; Nadjafov, A. I.

2006-09-01

Photoelectric and photovoltaic spectra of Schottky barrier (SB) structures of InSe, GaSe and GaS layered semiconductors (LS) are investigated at quantum energies from the band edge excitons of corresponding materials up to 6.5eV. Spectral dependences of photoconductivity (PC) of photo resistors and barrier structures are strongly different at the quantum energies corresponding to the intermediate type excitons (ITE) observed in these semiconductors. It was suggested that high UV photoconductivity of A3B6 LS is due to existence of high mobility light carriers in the depth of the band structure. It is shown that SB of semitransparent Au-InSe is high sensitive photo detector in UV region of spectra.

Van der Waals metal-semiconductor junction: Weak Fermi level pinning enables effective tuning of Schottky barrier

PubMed Central

Liu, Yuanyue; Stradins, Paul; Wei, Su-Huai

2016-01-01

Two-dimensional (2D) semiconductors have shown great potential for electronic and optoelectronic applications. However, their development is limited by a large Schottky barrier (SB) at the metal-semiconductor junction (MSJ), which is difficult to tune by using conventional metals because of the effect of strong Fermi level pinning (FLP). We show that this problem can be overcome by using 2D metals, which are bounded with 2D semiconductors through van der Waals (vdW) interactions. This success relies on a weak FLP at the vdW MSJ, which is attributed to the suppression of metal-induced gap states. Consequently, the SB becomes tunable and can vanish with proper 2D metals (for example, H-NbS2). This work not only offers new insights into the fundamental properties of heterojunctions but also uncovers the great potential of 2D metals for device applications. PMID:27152360

Van der Waals metal-semiconductor junction: Weak Fermi level pinning enables effective tuning of Schottky barrier

DOE PAGES

Liu, Yuanyue; Stradins, Paul; Wei, Su -Huai

2016-04-22

Two-dimensional (2D) semiconductors have shown great potential for electronic and optoelectronic applications. However, their development is limited by a large Schottky barrier (SB) at the metal-semiconductor junction (MSJ), which is difficult to tune by using conventional metals because of the effect of strong Fermi level pinning (FLP). We show that this problem can be overcome by using 2D metals, which are bounded with 2D semiconductors through van der Waals (vdW) interactions. This success relies on a weak FLP at the vdW MSJ, which is attributed to the suppression of metal-induced gap states. Consequently, the SB becomes tunable and can vanishmore » with proper 2D metals (for example, H-NbS2). This work not only offers new insights into the fundamental properties of heterojunctions but also uncovers the great potential of 2D metals for device applications.« less

Semiconductor crystal growth in crossed electric and magnetic fields: Center Director's Discretionary Fund

NASA Technical Reports Server (NTRS)

Mazuruk, K.; Volz, M. P.

1996-01-01

A unique growth cell was designed in which crossed electric and magnetic fields could be separately or simultaneously applied during semiconductor crystal growth. A thermocouple was inserted into an InSb melt inside the growth cell to examine the temperature response of the fluid to applied electromagnetic fields. A static magnetic field suppressed time-dependent convection when a destabilizing thermal field was applied. The simultaneous application of electric and magnetic fields resulted in forced convection in the melt. The InSb ingots grown in the cell were polycrystalline. An InGaSb crystal, 0.5 cm in diameter and 23-cm long, was grown without electromagnetic fields applied. The axial composition results indicated that complete mixing in the melt occurred for this large aspect ratio.

Crystal Growth and Characterization of the Narrow-Band-Gap Semiconductors OsPn 2 (Pn = P, As, Sb)

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

Bugaris, Daniel E.; Malliakas, Christos D.; Shoemaker, Daniel P.

2014-09-15

Using metal fluxes, crystals of the binary osmium dipnictides OsPn(2) (Pn = P, As, Sb) have been grown for the first time. Single-crystal X-ray diffraction confirms that these compounds crystallize in the marcasite structure type with orthorhombic space group Pnnm. The structure is a three-dimensional framework of corner- and edge-sharing OsPn(6) octahedra, as well as [Pn(2)(-4)] anions. Raman spectroscopy shows the presence of PP single bonds, consistent with the presence of [Pn(2)(-4)] anions and formally Os4+ cations. Optical-band-gap and high-temperature electrical resistivity measurements indicate that these materials are narrow-band-gap semiconductors. The experimentally determined Seebeck coefficients reveal that nominally undoped OsP2more » and OsSb2 are n-type semiconductors, whereas OsAs2 is p-type. Electronic band structure using density functional theory calculations shows that these compounds are indirect narrow-band-gap semiconductors. The bonding p orbitals associated with the Pn(2) dimer are below the Fermi energy, and the corresponding antibonding states are above, consistent with a PnPn single bond. Thermopower calculations using Boltzmann transport theory and constant relaxation time approximation show that these materials are potentially good thermoelectrics, in agreement with experiment.« less

Syntheses and characterization of one-dimensional alkali metal antimony(III) thiostannates(IV), A{sub 2}Sb{sub 2}Sn{sub 3}S{sub 10} (A=K, Rb, Cs)

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

Yohannan, Jinu P.; Vidyasagar, Kanamaluru, E-mail: kvsagar@iitm.ac.in

2015-01-15

Three new isostructural quaternary antimony(III) thiostannates(IV), A{sub 2}Sb{sub 2}Sn{sub 3}S{sub 10} (A=K, Rb, Cs) have been synthesized by using alkali metal thiosulfate flux and structurally characterized by X-ray diffraction. Their structures contain A{sup +} ions around the [Sb{sub 2}Sn{sub 3}S{sub 10}]{sup 2−} chains, which are built from SbS{sub 3} pyramids, SnS{sub 6} octahedra and SnS{sub 4} tetrahedra. Raman and Mössbauer spectroscopic measurements corroborate the oxidation states and coordination environments of Sb(III) and Sn(IV). All three compounds are wide band gap semiconductors. Potassium compound undergoes partial exchange with strontium, cadmium and lead ions. - Graphical abstract: Syntheses, crystal structure, spectroscopic andmore » partial ion-exchange studies of new one-dimensional alkali metal antimony(III) thiostannates(IV), A{sub 2}Sb{sub 2}Sn{sub 3}S{sub 10} (A=K, Rb, Cs) are described. - Highlights: • Syntheses of new alkali metal antimony(III) thiostannates(IV), A{sub 2}Sb{sub 2}Sn{sub 3}S{sub 10} (A=K, Rb, Cs). • Wide band gap semiconductors with one-dimensional structure. • Topotactic partial exchange of K{sup +} ions of K{sub 2}Sb{sub 2}Sn{sub 3}S{sub 10} with Sr{sup 2+}, Cd{sup 2+} and Pb{sup 2+} ions.« less

Quasiparticle semiconductor band structures including spin-orbit interactions.

PubMed

Malone, Brad D; Cohen, Marvin L

2013-03-13

We present first-principles calculations of the quasiparticle band structure of the group IV materials Si and Ge and the group III-V compound semiconductors AlP, AlAs, AlSb, InP, InAs, InSb, GaP, GaAs and GaSb. Calculations are performed using the plane wave pseudopotential method and the 'one-shot' GW method, i.e. G(0)W(0). Quasiparticle band structures, augmented with the effects of spin-orbit, are obtained via a Wannier interpolation of the obtained quasiparticle energies and calculated spin-orbit matrix. Our calculations explicitly treat the shallow semicore states of In and Ga, which are known to be important in the description of the electronic properties, as valence states in the quasiparticle calculation. Our calculated quasiparticle energies, combining both the ab initio evaluation of the electron self-energy and the vector part of the pseudopotential representing the spin-orbit effects, are in generally very good agreement with experimental values. These calculations illustrate the predictive power of the methodology as applied to group IV and III-V semiconductors.

Quantum-Dot Laser for Wavelengths of 1.8 to 2.3 micron

NASA Technical Reports Server (NTRS)

Qiu, Yueming

2006-01-01

The figure depicts a proposed semiconductor laser, based on In(As)Sb quantum dots on a (001) InP substrate, that would operate in the wavelength range between 1.8 and 2.3 m. InSb and InAsSb are the smallest-bandgap conventional III-V semiconductor materials, and the present proposal is an attempt to exploit the small bandgaps by using InSb and InAsSb nanostructures as midinfrared emitters. The most closely related prior III-V semiconductor lasers are based, variously, on strained InGaAs quantum wells and InAs quantum dots on InP substrates. The emission wavelengths of these prior devices are limited to about 2.1 m because of critical quantum-well thickness limitations for these lattice mismatched material systems. The major obstacle to realizing the proposed laser is the difficulty of fabricating InSb quantum dots in sufficient density on an InP substrate. This difficulty arises partly because of the weakness of the bond between In and Sb and partly because of the high temperature needed to crack metalorganic precursor compounds during the vapor-phase epitaxy used to grow quantum dots: The mobility of the weakly bound In at the high growth temperature is so high that In adatoms migrate easily on the growth surface, resulting in the formation of large InSb islands at a density, usually less than 5 x 10(exp 9) cm(exp -2), that is too low for laser operation. The mobility of the In adatoms could be reduced by introducing As atoms to the growth surface because the In-As bond is about 30 percent stronger than is the In-Sb bond. The fabrication of the proposed laser would include a recently demonstrated process that involves the use of alternative supplies of precursors to separate group-III and group-V species to establish local non-equilibrium process conditions, so that In(As)Sb quantum dots assemble themselves on a (001) InP substrate at a density as high as 4 x 10(exp 10) cm(exp -2). Room-temperature photoluminescence spectra of quantum dots formed by this process indicate that they emit at wavelengths from 1.7 to 2.3 microns.

Plasma Reflection in Multigrain Layers of Narrow-Bandgap Semiconductors

NASA Astrophysics Data System (ADS)

Zhukov, N. D.; Shishkin, M. I.; Rokakh, A. G.

2018-04-01

Qualitatively similar spectral characteristics of plasma-resonance reflection in the region of 15-25 μm were obtained for layers of electrodeposited submicron particles of InSb, InAs, and GaAs and plates of these semiconductors ground with M1-grade diamond powder. The most narrow-bandgap semiconductor InSb (intrinsic absorption edge ˜7 μm) is characterized by an absorption band at 2.1-2.3 μm, which is interpreted in terms of the model of optical excitation of electrons coupled by the Coulomb interaction. The spectra of a multigrain layer of chemically deposited PbS nanoparticles (50-70 nm) exhibited absorption maxima at 7, 10, and 17 μm, which can be explained by electron transitions obeying the energy-quantization rules for quantum dots.

Determination of atomic vacancies in InAs/GaSb strained-layer superlattices by atomic strain

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

Kim, Honggyu; Meng, Yifei; Kwon, Ji-Hwan

Determining vacancy in complex crystals or nanostructures represents an outstanding crystallographic problem that has a large impact on technology, especially for semiconductors, where vacancies introduce defect levels and modify the electronic structure. However, vacancy is hard to locate and its structure is difficult to probe experimentally. Reported here are atomic vacancies in the InAs/GaSb strained-layer superlattice (SLS) determined by atomic-resolution strain mapping at picometre precision. It is shown that cation and anion vacancies in the InAs/GaSb SLS give rise to local lattice relaxations, especially the nearest atoms, which can be detected using a statistical method and confirmed by simulation. Themore » ability to map vacancy defect-induced strain and identify its location represents significant progress in the study of vacancy defects in compound semiconductors.« less

Determination of atomic vacancies in InAs/GaSb strained-layer superlattices by atomic strain

DOE PAGES

Kim, Honggyu; Meng, Yifei; Kwon, Ji-Hwan; ...

2018-01-01

Determining vacancy in complex crystals or nanostructures represents an outstanding crystallographic problem that has a large impact on technology, especially for semiconductors, where vacancies introduce defect levels and modify the electronic structure. However, vacancy is hard to locate and its structure is difficult to probe experimentally. Reported here are atomic vacancies in the InAs/GaSb strained-layer superlattice (SLS) determined by atomic-resolution strain mapping at picometre precision. It is shown that cation and anion vacancies in the InAs/GaSb SLS give rise to local lattice relaxations, especially the nearest atoms, which can be detected using a statistical method and confirmed by simulation. Themore » ability to map vacancy defect-induced strain and identify its location represents significant progress in the study of vacancy defects in compound semiconductors.« less

Semiconductor Eutectic Solar Cell.

DTIC Science & Technology

1986-12-01

growth of the eutectics was conducted in a three-zone furnace ( SATEC Systems, Inc.). Figure 4 is the temperature-regulation circuit. The main power...34Electromagnetic Properties of Eutectic Composites (A Critical Review)", Met. Trans. 2, 1513 (1971). 6. B. Paul and H. Weiss, "Anisotropic InSb-NiSb Es an

Pseudopotential calculations of AlSb under pressure

NASA Astrophysics Data System (ADS)

Algarni, H.; Al-Hagan, O. A.; Bouarissa, N.; Khan, M. A.; Alhuwaymel, T. F.

2018-02-01

The dependence on hydrostatic pressure of the electronic and optical properties of zinc-blende AlSb semiconducting material in the pressure range of 0-20 kbar has been reported using a pseudopotential approach. At zero pressure, our findings showed that the electron and heavy hole effective masses are 0.11 and 0.38 m0, respectively. Moreover, our results yielded values of 3.3289 and 11.08 for refractive index and high frequency dielectric constant, respectively. These results are found to be in good accord with experiment. Upon compression, all physical parameters of interest showed a monotonic behavior. The pressure-induced energy shifts for the optical transition related to band-gaps indicated that AlSb remains an indirect (D-X) band-gap semiconductor at pressures from 0 to 20 kbar. The trend in all features of interest versus pressure has been presented and discussed. It is found that the lattice parameter is reduced from 0.61355 to 0.60705 nm when pressure is raised from 0 to 20 kbar. The present investigation may be useful for mid-infrared lasers applications, detectors and communication devices.

High performance thermoelectric materials and methods of preparation

NASA Technical Reports Server (NTRS)

Fleurial, Jean-Pierre (Inventor); Caillat, Thierry F. (Inventor); Borshchevsky, Alexander (Inventor)

1997-01-01

Transition metals (T) of Group VIII (Co, Rh and Ir) have been prepared as semiconductor alloys with Sb having the general formula TSb.sub.3. The skutterudite-type crystal lattice structure of these semiconductor alloys and their enhanced thermoelectric properties results in semiconductor materials which may be used in the fabrication of thermoelectric elements to substantially improve the efficiency of the resulting thermoelectric device. Semiconductor alloys having the desired skutterudite-type crystal lattice structure may be prepared in accordance with the present invention by using vertical gradient freeze techniques, liquid-solid phase sintering techniques, low temperature powder sintering and/or hot-pressing. Measurements of electrical and thermal transport properties of selected semiconductor materials prepared in accordance with the present invention, demonstrated high Hall mobilities (up to 8000 cm.sup.2.V.sup.-1.s.sup.-1), good Seebeck coefficients (up to 400 .mu.VK.sup.-1 between 300.degree. C. and 700.degree. C.), and low thermal conductivities (as low as 15 mW/cmK). Optimizing the transport properties of semiconductor materials prepared from elemental mixtures Co, Rh, Ir and Sb resulted in a two fold increase in the thermoelectric figure of merit (ZT) at temperatures as high as 400.degree. C. for thermoelectric elements fabricated from such semiconductor materials.

Bandgap Tuning of GaAs/GaAsSb Core-Shell Nanowires Grown by Molecular Beam Epitaxy

DTIC Science & Technology

2015-09-21

SECURITY CLASSIFICATION OF: Semiconductor nanowires have been identified as a viable technology for next-generation infrared (IR) photodetectors with... nanowires , by varying the Sb content using Ga-assisted molecular beam epitaxy. An increase in Sb content leads to strain accumulation in shell...manifesting in rough surface morphology, multifaceted growths, curved nanowires , and deterioration in the 1. REPORT DATE (DD-MM-YYYY) 4. TITLE AND SUBTITLE

The new Zintl phases Eu{sub 21}Cd{sub 4}Sb{sub 18} and Eu{sub 21}Mn{sub 4}Sb{sub 18}

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

Wang, Yi; Darone, Gregory M.; Bobev, Svilen, E-mail: bobev@udel.edu

Crystals of two new Zintl compounds, Eu{sub 21}Mn{sub 4}Sb{sub 18} and Eu{sub 21}Cd{sub 4}Sb{sub 18} have been synthesized using the molten metal flux method, and their structures have been established by single-crystal X-ray diffraction. Both compounds are isotypic and crystallize in the monoclinic space group C2/m (No. 12, Z=4). The structures are based on edge- and corner-shared MnSb{sub 4} or CdSb{sub 4} tetrahedra, which make octameric [Mn{sub 8}Sb{sub 22}] or [Cd{sub 8}Sb{sub 22}] polyanions. Homoatomic Sb–Sb bonds are present in both structures. The Eu atoms take the role of Eu{sup 2+}cations with seven unpaired 4f electrons, as suggested by themore » temperature-dependent magnetization measurements. The magnetic susceptibilities of Eu{sub 21}Mn{sub 4}Sb{sub 18} and Eu{sub 21}Cd{sub 4}Sb{sub 18} indicate that both phases order anti-ferromagnetically with Néel temperatures of ca. 7 K and ca. 10 K, respectively. The unpaired 3d electrons of the Mn atoms in Eu{sub 21}Mn{sub 4}Sb{sub 18} do contribute to the magnetic response, however, the bulk magnetization measurements do not provide evidence for long-range ordering of the Mn spins down to 5 K. Electrical resistivity measurements suggest that both compounds are narrow band gap semiconductors. - Graphical abstract: Eu{sub 21}Mn{sub 4}Sb{sub 18} and Eu{sub 21}Cd{sub 4}Sb{sub 18} have complex monoclinic structures, based on MnSb{sub 4} and CdSb{sub 4} tetrahedra, both edge- and corner-shared. A perspective of the crystal structure is shown, as viewed along the b axis. Display Omitted - Highlights: • Eu{sub 21}Mn{sub 4}Sb{sub 18} and Eu{sub 21}Cd{sub 4}Sb{sub 18} are novel compounds in the respective ternary phase diagrams. • For both structures, the Zintl-Klemm rules are followed, and both are small gap semiconductors. • Eu{sub 21}Mn{sub 4}Sb{sub 18} and Eu{sub 21}Cd{sub 4}Sb{sub 18} are air-stable Zintl phases and could be new thermoelectric materials.« less

The fabrication of carbon nanotube field-effect transistors with semiconductors as the source and drain contact materials.

PubMed

Xiao, Z; Camino, F E

2009-04-01

Sb(2)Te(3) and Bi(2)Te(2)Se semiconductor materials were used as the source and drain contact materials in the fabrication of carbon nanotube field-effect transistors (CNTFETs). Ultra-purified single-walled carbon nanotubes (SWCNTs) were ultrasonically dispersed in N-methyl pyrrolidone solvent. Dielectrophoresis was used to deposit and align SWCNTs for fabrication of CNTFETs. The Sb(2)Te(3)- and Bi(2)Te(2)Se-based CNTFETs demonstrate p-type metal-oxide-silicon-like I-V curves with high on/off drain-source current ratio at large drain-source voltages and good saturation of drain-source current with increasing drain-source voltage. The fabrication process developed is novel and has general meaning, and could be used for the fabrication of SWCNT-based integrated devices and systems with semiconductor contact materials.

A Study of Electron and Phonon Dynamics by Broadband Two-Dimensional THz Time-Domain Spectroscopy

NASA Astrophysics Data System (ADS)

Fu, Zhengping

Terahertz (THz) wave interacts with semiconductors in many ways, such as resonant excitation of lattice vibration, intraband transition and polaron formation. Different from the optical waves, THz wave has lower photon energy (1 THz = 4.14 meV) and is suitable for studying dynamics of low-energy excitations. Recently the studies of the interaction of THz wave and semiconductors have been extending from the linear regime to the nonlinear regime, owing to the advance of the high-intensity THz generation and detection methods. Two-dimensional (2D) spectroscopy, as a useful tool to unravel the nonlinearity of materials, has been well developed in nuclear magnetic resonance and infrared region. However, the counterpart in THz region has not been well developed and was only demonstrated at frequency around 20 THz due to the lack of intense broadband THz sources. Using laser-induced plasma as the THz source, we developed collinear broadband 2D THz time-domain spectroscopy covering from 0.5 THz to 20 THz. Broadband intense THz pulses emitted from laser-induced plasma provide access to a variety of nonlinear properties of materials. Ultrafast optical and THz pulses make it possible to resolve the transient change of the material properties with temporal resolution of tens of femtoseconds. This thesis focuses on the linear and nonlinear interaction of the THz wave with semiconductors. Since a great many physical processes, including vibrational motion of lattice and plasma oscillation, has resonant frequency in the THz range, rich physics can be studies in our experiment. The thesis starts from the linear interaction of the THz wave with semiconductors. In the narrow band gap semiconductor InSb, the plasma absorption edge, Restrahlen band and dispersion of polaritons are observed. The nonlinear response of InSb in high THz field is verified in the frequency-resolved THz Z-scan experiment. The third harmonic generations due to the anharmonicity of plasma oscillation and the second order signal due to the plasma-phonon interaction are observed in 2D THz transmission spectra. In this thesis, the coherent phonons excited by THz pulses are experimentally demonstrated for the first time in both GaAs and InSb. The resonant excitation using THz pulses enables the coherent control of the lattice motion via direct interaction of atoms and electromagnetic wave, without inducing electronic transition as reported in the optical excitation of coherent phonons. The classic model is used to explain both excitation and detection mechanisms. An increase of the damping rate of the coherent lattice motion due to higher carrier density is observed in our experiment. Transient reflectivity change of GaAs induced by THz pulses is studied in 2D THz-pump/optical-probe configuration. Using the perturbative analysis of nonlinear electrooptic effect, we conclude that the nonlinear response of GaAs to two phase-locked THz pulses is mainly caused by the nonlinearity of the electronic response.

Semiconductor Alloy Theory.

DTIC Science & Technology

1986-01-14

0.15 0.352 GaPAs) 3.5 191 0.10 0.11 0.307 In(As,SbJ 6.8 635 0.52 0.79 0.840 Ga(As,Sb) 7.6 924 0.53 0.94 0.844 AI(As,Sb) 8.1 1030 0.56 0.78 0.810 - ln(PSb...to prov ide good estimiates, of the mixing enthalpies *T, /T 2 is plotted against bi8 ) alone, the FPT points are fl of pseudobinaryN alloys. The

Electro-optical SLS devices for operating at new wavelength ranges

DOEpatents

Osbourn, Gordon C.

1986-01-01

An intrinsic semiconductor electro-optical device includes a p-n junction intrinsically responsive, when cooled, to electromagnetic radiation in the wavelength range of 8-12 um. The junction consists of a strained-layer superlattice of alternating layers of two different III-V semiconductors having mismatched lattice constants when in bulk form. A first set of layers is either InAs.sub.1-x Sb.sub.x (where x is aobut 0.5 to 0.7) or In.sub.1-x Ga.sub.x As.sub.1-y Sb.sub.y (where x and y are chosen such that the bulk bandgap of the resulting layer is about the same as the minimum bandgap in the In.sub.1-x Ga.sub.x As.sub.1-y Sb.sub.y family). The second set of layers has a lattice constant larger than the lattice constant of the layers in the first set.

Excitations and magnetization density distribution in the dilute ferromagnetic semiconductor Yb 14 MnSb 11

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

Stone, M. B.; Garlea, V. O.; Gillon, B.

2017-01-23

One rare example of a Kondo lattice compound with ferromagnetic dominated RKKY interactions is Ybmore » $$_{14}$$MnSb$$_{11}$$. As a ferromagnetic semiconductor with $$T_c \\approx 53$$~K, it is also a potential compound for exploration of spintronic devices. This material is furthermore one of the most efficient high temperature thermoelectrics. We describe measurements which answer remaining questions regarding the energy scales of the exchange interactions, the valence and the magnetization density distribution in this system. We also find that the system consists of RKKY exchange coupled Mn$$^{2+}$$ sites with nearest and next nearest exchange interactions dominating the magnetic spectrum with no significant magnetization density localized on other atomic sites. The extended spread of a negative magnetization around each of the Mn ions supports a Kondo screening cloud scenario for Yb$$_{14}$$MnSb$$_{11}$$.« less

Structural phase transition, electronic structure and optical properties of half Heusler alloys LiBeZ (Z = As, Sb)

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

Amudhavalli, A.; Rajeswarapalanichamy, R., E-mail: rajeswarapalanichamy@gmail.com

2016-05-23

Ab initio calculations are performed to investigate the structural stability, electronic structure, mechanical properties and optical properties of half Heusler alloys (LiBeAs and LiBeSb) for three different phases of zinc blende crystal structure. Among the considered phases, α- phase is found to be the most stable phase for these alloys at normal pressure. A pressure induced structural phase transition from α-phase to β- phase is observed for LiBeAs. The electronic structure reveals that these alloys are semiconductors. The optical properties confirm that these alloys are semiconductor in nature.

Growth and characterization of vertical cavity structures on InP with GaAsSb/AlAsSb Bragg mirrors for 1.55 μm emission

NASA Astrophysics Data System (ADS)

Genty, Frédéric; Almuneau, Guilhem; Chusseau, Laurent; Wilk, Arnaud; Gaillard, Serge; Boissier, Guilhem; Grech, Pierre; Jacquet, Joel

1999-05-01

With the aim of fabricating vertical cavity semiconductor lasers (VCSEL), the molecular beam epitaxy growth of GaAsSb using two different element-V precursor sets has been first evaluated. Alloy compositions as well as ease of achieving lattice-matching are compared with both (As 2-Sb 4) or (As 2-Sb 2). Change in the growth mode process that depends on the precursor couple is presumed to influence strongly As and Sb incorporation rates thereby causing difficulties in reaching lattice-matching with Sb 4. The above study has allowed the fabrication of a fully doped 3 λ/2 monolithic Sb-based VCSEL on InP. The main devices performing at 77 K are a 200 nm wide stopband centered at 1.5 μm and a clear cavity resonance at 1.53 μm from which electroluminescence has been observed.

Suppression of compensating native defect formation during semiconductor processing via excess carriers

NASA Astrophysics Data System (ADS)

Alberi, K.; Scarpulla, M. A.

2016-06-01

In many semiconductors, compensating defects set doping limits, decrease carrier mobility, and reduce minority carrier lifetime thus limiting their utility in devices. Native defects are often responsible. Suppressing the concentrations of compensating defects during processing close to thermal equilibrium is difficult because formation enthalpies are lowered as the Fermi level moves towards the majority band edge. Excess carriers, introduced for example by photogeneration, modify the formation enthalpy of semiconductor defects and thus can be harnessed during crystal growth or annealing to suppress defect populations. Herein we develop a rigorous and general model for defect formation in the presence of steady-state excess carrier concentrations by combining the standard quasi-chemical formalism with a detailed-balance description that is applicable for any defect state in the bandgap. Considering the quasi-Fermi levels as chemical potentials, we demonstrate that increasing the minority carrier concentration increases the formation enthalpy for typical compensating centers, thus suppressing their formation. This effect is illustrated for the specific example of GaSb. While our treatment is generalized for excess carrier injection or generation in semiconductors by any means, we provide a set of guidelines for applying the concept in photoassisted physical vapor deposition.

Suppression of compensating native defect formation during semiconductor processing via excess carriers

DOE PAGES

Alberi, Kirstin; Scarpulla, M. A.

2016-06-21

In many semiconductors, compensating defects set doping limits, decrease carrier mobility, and reduce minority carrier lifetime thus limiting their utility in devices. Native defects are often responsible. Suppressing the concentrations of compensating defects during processing close to thermal equilibrium is difficult because formation enthalpies are lowered as the Fermi level moves towards the majority band edge. Excess carriers, introduced for example by photogeneration, modify the formation enthalpy of semiconductor defects and thus can be harnessed during crystal growth or annealing to suppress defect populations. Herein we develop a rigorous and general model for defect formation in the presence of steady-statemore » excess carrier concentrations by combining the standard quasi-chemical formalism with a detailed-balance description that is applicable for any defect state in the bandgap. Considering the quasi-Fermi levels as chemical potentials, we demonstrate that increasing the minority carrier concentration increases the formation enthalpy for typical compensating centers, thus suppressing their formation. Furthermore, this effect is illustrated for the specific example of GaSb. While our treatment is generalized for excess carrier injection or generation in semiconductors by any means, we provide a set of guidelines for applying the concept in photoassisted physical vapor deposition.« less

Passivation of GaSb using molecular beam epitaxy Y{sub 2}O{sub 3} to achieve low interfacial trap density and high-performance self-aligned inversion-channel p-metal-oxide-semiconductor field-effect-transistors

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

Chu, R. L.; Chiang, T. H.; Hsueh, W. J.

2014-11-03

Molecular beam epitaxy deposited rare-earth oxide of Y{sub 2}O{sub 3} has effectively passivated GaSb, leading to low interfacial trap densities of (1–4) × 10{sup 12 }cm{sup −2} eV{sup −1} across the energy bandgap of GaSb. A high saturation drain current density of 130 μA/μm, a peak transconductance of 90 μS/μm, a low subthreshold slope of 147 mV/decade, and a peak field-effect hole mobility of 200 cm{sup 2}/V-s were obtained in 1 μm-gate-length self-aligned inversion-channel GaSb p-Metal-Oxide-Semiconductor Field-Effect-Transistors (MOSFETs). In this work, high-κ/GaSb interfacial properties were better in samples with a high substrate temperature of 200 °C than in those with high κ's deposited at room temperature, in terms of themore » interfacial electrical properties, particularly, the reduction of interfacial trap densities near the conduction band and the MOSFET device performance.« less

Effects of Ge and Sn substitution on the metal-semiconductor transition and thermoelectric properties of Cu12Sb4S13 tetrahedrite.

PubMed

Kosaka, Yasufumi; Suekuni, Koichiro; Hashikuni, Katsuaki; Bouyrie, Yohan; Ohta, Michihiro; Takabatake, Toshiro

2017-03-29

The synthetic tetrahedrites Cu 12-y Tr y Sb 4 S 13 (Tr: Mn, Fe, Co, Ni, Zn) have been extensively studied due to interest in metal-semiconductor transition as well as in superior thermoelectric performance. We have prepared Ge- and Sn-bearing tetrahedrites, Cu 12-x M x Sb 4 S 13 (M = Ge, Sn; x ≤ 0.6), and investigated the effects of the substitutions on the phase transition and the thermoelectric properties. The substitutions of Ge and Sn for Cu suppress the metal-semiconductor transition and increase the electrical resistivity ρ and the positive thermopower S. This finding suggests that the phase transition is prevented by electron doping into the unoccupied states of the valence band. The variations of ρ, S, and magnetic susceptibility for the present systems correspond well with those for the system with Tr = Zn 2+ , confirming the tetravalent states for Ge and Sn. The substitution of M 4+ for Cu 1+ decreases the power factor S 2 /ρ but enhances the dimensionless thermoelectric figure of merit ZT, due to reductions in both the charge carrier contribution and lattice contribution to the thermal conductivity. As a result, ZT has a maximum value of ∼0.65 at 665 K for x = 0.3-0.5 in Cu 12-x M x Sb 4 S 13 with M = Ge and Sn.

Nonlinear THz absorption and cyclotron resonance in InSb

NASA Astrophysics Data System (ADS)

Heffernan, Kate; Yu, Shukai; Talbayev, Diyar

The emergence of coherent high-field terahertz (THz) sources in the past decade has allowed the exploration of nonlinear light-matter interaction at THz frequencies. Nonlinear THz response of free electrons in semiconductors has received a great deal of attention. Such nonlinear phenomena as saturable absorption and self-phase modulation have been reported. InSb is a narrow-gap (bandgap 0.17 eV) semiconductor with a very low electron effective mass and high electron mobility. Previous high-field THz work on InSb reported the observation of ultrafast electron cascades via impact ionization. We study the transmission of an intense THz electric field pulse by an InSb wafer at different incident THz amplitudes and 10 K temperature. Contrary to previous reports, we observe an increased transmission at higher THz field. Our observation appears similar to the saturable THz absorption reported in other semiconductors. Along with the increased absorption, we observe a strong modulation of the THz phase at high incident fields, most likely due to the self-phase modulation of the THz pulse. We also study the dependence of the cyclotron resonance on the incident THz field amplitude. The cyclotron resonance exhibits a lower strength and frequency at the higher incident THz field. The work at Tulane was supported by the Louisiana Board of Regents through the Board of Regents Support Fund Contract No. LEQSF(2012-15)-RD-A-23 and through the Pilot Funding for New Research (PFund) Contract No. LEQSF-EPS(2014)-PFUND-378.

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

NASA Technical Reports Server (NTRS)

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

1982-01-01

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

Investigation of Electrical and Optical Properties of Bulk III-V Ternary Semiconductors

DTIC Science & Technology

2009-03-01

metalorganic vapour phase epitaxial grown (MOVPE) InxGa1-xSb with indium mole fractions less than 0.06. [28] They observed that GaSb and InxGa1-xSb had...Treideris, A. Krotkus, and K. Grigoras, “Picosecond GaAs and InGaAs photoconductive switches obtained by low-temperature metal-organic chemical vapour ...Time Dependent Annealing Study of Silicon Implanted Aluminum Gallium Nitride,” Master’s Thesis, Air Force Institute of Technology (AU), Wright

Optical properties of InAsBi and optimal designs of lattice-matched and strain-balanced III-V semiconductor superlattices

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

Webster, P. T., E-mail: preston.t.webster@asu.edu; Riordan, N. A.; Gogineni, C.

The optical properties of bulk InAs{sub 0.936}Bi{sub 0.064} grown by molecular beam epitaxy on a (100)-oriented GaSb substrate are measured using spectroscopic ellipsometry. The index of refraction and absorption coefficient are measured over photon energies ranging from 44 meV to 4.4 eV and are used to identify the room temperature bandgap energy of bulk InAs{sub 0.936}Bi{sub 0.064} as 60.6 meV. The bandgap of InAsBi is expressed as a function of Bi mole fraction using the band anticrossing model and a characteristic coupling strength of 1.529 eV between the Bi impurity state and the InAs valence band. These results are programmed into a software toolmore » that calculates the miniband structure of semiconductor superlattices and identifies optimal designs in terms of maximizing the electron-hole wavefunction overlap as a function of transition energy. These functionalities are demonstrated by mapping the design spaces of lattice-matched GaSb/InAs{sub 0.911}Sb{sub 0.089} and GaSb/InAs{sub 0.932}Bi{sub 0.068} and strain-balanced InAs/InAsSb, InAs/GaInSb, and InAs/InAsBi superlattices on GaSb. The absorption properties of each of these material systems are directly compared by relating the wavefunction overlap square to the absorption coefficient of each optimized design. Optimal design criteria are provided for key detector wavelengths for each superlattice system. The optimal design mid-wave infrared InAs/InAsSb superlattice is grown using molecular beam epitaxy, and its optical properties are evaluated using spectroscopic ellipsometry and photoluminescence spectroscopy.« less

Antimonide-Based Compound Semiconductors for Low-Power Electronics

DTIC Science & Technology

2013-01-01

A, Madan HS, Kirk AP, Zhao DA, Mourey DA, Hudait MK, et al. Fermi level unpinning of GaSb (100) using plasma enhanced atomic layer deposition of...et al. Atomic layer deposition of Al2O3 on GaSb using in situ hydrogen plasma exposure. Appl Phys Lett. 2012;101: 231601. [18] Ali A, Madan H

Nanoscopic diffusion studies on III-V compound semiconductor structures: Experiment and theory

NASA Astrophysics Data System (ADS)

Gonzalez Debs, Mariam

The electronic structure of multilayer semiconductor heterostructures is affected by the detailed compositional profiles throughout the structure and at critical interfaces. The extent of interdiffusion across these interfaces places limits on both the processing time and temperatures for many applications based on the resultant compositional profile and associated electronic structure. Atomic and phenomenological methods were used in this work through the combination of experiment and theory to understand the nanoscopic mechanisms in complex heterostructures. Two principal studies were conducted. Tin diffusion in GaAs was studied by fitting complex experimental diffusion profiles to a phenomenological model which involved the diffusion of substitutional and interstitial dopant atoms. A methodology was developed combining both the atomistic model and the use of key features within these experimentally-obtained diffusion profiles to determine meaningful values of the transport and defect reaction rate parameters. Interdiffusion across AlSb/GaSb multi-quantum well interfaces was also studied. The chemical diffusion coefficient characterizing the AlSb/GaSb diffusion couple was quantitatively determined by fitting the observed photoluminescence (PL) peak shifts to the solution of the Schrodinger equation using a potential derived from the solution of the diffusion equation to quantify the interband transition energy shifts. First-principles calculations implementing Density Functional Theory were performed to study the thermochemistry of point defects as a function of local environment, allowing a direct comparison of interfacial and bulk diffusion phenomena within these nanoscopic structures. Significant differences were observed in the Ga and Al vacancy formation energies at the AlSb/GaSb interface when compared to bulk AlSb and GaSb with the largest change found for Al vacancies. The AlSb/GaSb structures were further studied using positron annihilation spectroscopy (PAS) to investigate the role of vacancies in the interdiffusion of Al and Ga in the superlattices. The PL and PAS experimental techniques together with the phenomenological and atomistic modeling allowed for the determination of the underlying mass transport mechanisms at the nanoscale.

Spin-orbit coupling effects in indium antimonide quantum well structures

NASA Astrophysics Data System (ADS)

Dedigama, Aruna Ruwan

Indium antimonide (InSb) is a narrow band gap material which has the smallest electron effective mass (0.014m0) and the largest electron Lande g-facture (-51) of all the III-V semiconductors. Spin-orbit effects of III-V semiconductor heterostructures arise from two different inversion asymmetries namely bulk inversion asymmetry (BIA) and structural inversion asymmetry (SIA). BIA is due to the zinc-blende nature of this material which leads to the Dresselhaus spin splitting consisting of both linear and cubic in-plane wave vector terms. As its name implies SIA arises due to the asymmetry of the quantum well structure, this leads to the Rashba spin splitting term which is linear in wave vector. Although InSb has theoretically predicted large Dresselhaus (760 eVA3) and Rashba (523 eA 2) coefficients there has been relatively little experimental investigation of spin-orbit coefficients. Spin-orbit coefficients can be extracted from the beating patterns of Shubnikov--de Haas oscillations (SdH), for material like InSb it is hard to use this method due to the existence of large electron Lande g-facture. Therefore it is essential to use a low field magnetotransport technique such as weak antilocalization to extract spin-orbit parameters for InSb. The main focus of this thesis is to experimentally determine the spin-orbit parameters for both symmetrically and asymmetrically doped InSb/InxAl 1-xSb heterostructures. During this study attempts have been made to tune the Rashba spin-orbit coupling coefficient by using a back gate to change the carrier density of the samples. Dominant phase breaking mechanisms for InSb/InxAl1-xSb heterostructures have been identified by analyzing the temperature dependence of the phase breaking field from weak antilocalization measurements. Finally the strong spin-orbit effects on InSb/InxAl1-xSb heterostructures have been demonstrated with ballistic spin focusing devices.

Optically efficient InAsSb nanowires for silicon-based mid-wavelength infrared optoelectronics.

PubMed

Zhuang, Q D; Alradhi, H; Jin, Z M; Chen, X R; Shao, J; Chen, X; Sanchez, Ana M; Cao, Y C; Liu, J Y; Yates, P; Durose, K; Jin, C J

2017-03-10

InAsSb nanowires (NWs) with a high Sb content have potential in the fabrication of advanced silicon-based optoelectronics such as infrared photondetectors/emitters and highly sensitive phototransistors, as well as in the generation of renewable electricity. However, producing optically efficient InAsSb NWs with a high Sb content remains a challenge, and optical emission is limited to 4.0 μm due to the quality of the nanowires. Here, we report, for the first time, the success of high-quality and optically efficient InAsSb NWs enabling silicon-based optoelectronics operating in entirely mid-wavelength infrared. Pure zinc-blende InAsSb NWs were realized with efficient photoluminescence emission. We obtained room-temperature photoluminescence emission in InAs NWs and successfully extended the emission wavelength in InAsSb NWs to 5.1 μm. The realization of this optically efficient InAsSb NW material paves the way to realizing next-generation devices, combining advances in III-V semiconductors and silicon.

Preparation and Thermoelectric Properties of IR(sub x)Co(sub 1-x)Sb(sub 2) Alloys

NASA Technical Reports Server (NTRS)

Caillat, Thierry

1995-01-01

The preparation and characterization of the binary arsenopyrite compounds CoSb2 and IrSb2 and IrxCo1-xSb2 alloys is reported. Single crystals of CoSb2 were grown by the vertical gradient freeze technique from solution rich in antimony. Polycrystalline samples of IrSb2 and IrxCo1-xSb2 alloys were prepared by hot-pressing of prereacted elemental powders. Samples were investigated by X-ray diffractometry, microprobe analysis and density measurements. It was found that a range of solid solution exist in the system IrxCo1-xSb2 for 0.1

Interfacial characterization and electrical properties of Ni–GaSb contacts

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

Lin, Kun-Lin, E-mail: kllin@narlabs.org.tw; Chen, Szu-Hung, E-mail: shchen168@narlabs.org.tw

2014-10-06

The microstructural characterization of Ni–GaSb junctions in samples annealed at 300 °C, 350 °C, and 400 °C in a N{sub 2} atmosphere was elucidated using transmission electron microscopy in conjunction with energy-dispersive spectrometry, nanobeam electron diffraction, and grazing-incident X-ray diffraction. Only the NiSb(Ga) phase is formed at the interface of Ni/GaSb when the annealing temperature is below 350 °C. However, three phases—NiSb, Ni{sub 2}Ga{sub 3}, and NiSb(Ga)—are formed simultaneously at the interface between Ni/GaSb when the annealing temperature is increased to 400 °C, which causes a significant increase in the sheet resistance of the Ni–GaSb alloy. These results indicate that the annealing temperature of themore » Ni/GaSb structure should be maintained below 350 °C for the formation of low-resistance metal Ni/GaSb contacts in GaSb-based p-type metal-oxide-semiconductor field-effect transistors.« less

Formation of III–V ternary solid solutions on GaAs and GaSb plates via solid-phase substitution reactions

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

Vasil’ev, V. I.; Gagis, G. S., E-mail: galina.gagis@gmail.com; Kuchinskii, V. I.

2015-07-15

Processes are considered in which ultrathin layers of III–V ternary solid solutions are formed via the delivery of Group-V element vapors to GaAs and GaSb semiconductor plates, with solid-phase substitution reactions occurring in the surface layers of these plates. This method can form defect-free GaAs{sup 1–x}P{sup x}, GaAs{sup x}Sb{sup 1–x}, and GaP{sup x}Sb{sup 1–x} layers with thicknesses of 10–20 nm and a content x of the embedded components of up to 0.04.

Nonreciprocal reflection-beam isolators for far-infrared use

NASA Technical Reports Server (NTRS)

Kanda, M.; May, W. G.

1973-01-01

Magnetoplasma reflection-beam isolators for submillimeter-wave use are discussed in theory and experiment. The basic device uses the Kerr transverse magnetooptic effect (plane of polarization of the EM wave in the plane of incidence, which is perpendicular to a dc magnetic field) in InSb near room temperature. When the semiconductor slab is covered with a thin dielectric layer acting as a matching transformer, improved performance is predicted and observed at 337 microns, and very efficient isolator performance is predicted for 118 microns. Physical arguments are presented to explain the nonreciprocal phenomenon and lead to better device design.

Modeling direct interband tunneling. I. Bulk semiconductors

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

Pan, Andrew, E-mail: pandrew@ucla.edu; Chui, Chi On; California NanoSystems Institute, University of California, Los Angeles, Los Angeles, California 90095

Interband tunneling is frequently studied using the semiclassical Kane model, despite uncertainty about its validity. Revisiting the physical basis of this formula, we find that it neglects coupling to other bands and underestimates transverse tunneling. As a result, significant errors can arise at low and high fields for small and large gap materials, respectively. We derive a simple multiband tunneling model to correct these defects analytically without arbitrary parameters. Through extensive comparison with band structure and quantum transport calculations for bulk InGaAs, InAs, and InSb, we probe the accuracy of the Kane and multiband formulas and establish the superiority ofmore » the latter. We also show that the nonlocal average electric field should be used when applying either of these models to nonuniform potentials. Our findings are important for efficient analysis and simulation of bulk semiconductor devices involving tunneling.« less

Compact, High Power, Multi-Spectral Mid-Infrared Semiconductor Laser Package

NASA Astrophysics Data System (ADS)

Guo, Bujin; Hwang, Wen-Yen; Lin, Chich-Hsiang

2001-10-01

Through a vertically integrated effort involving atomic level material engineering, advanced device processing development, state-of-the-art optomechanical packaging, and thermal management, Applied Optoelectronics, Inc. (AOI), University of Houston (U H), and Physical Science, Inc. (PSI) have made progress in both Sb-based type-II semiconductor material and in P-based type-I laser device development. We have achieved record performance on inP based quantum cascade continuous wave (CW) laser (with more than 5 mW CW power at 210 K). Grating-coupled external-cavity quantum cascade lasers were studied for temperatures from 20 to 230 K. A tuning range of 88 nm has been obtained at 80 K. The technology can be made commercially available and represents a significant milestone with regard to the Dual Use Science and Technology (DUST) intention of fostering dual use commercial technology for defense need. AOI is the first commercial company to ship products of this licensed technology.

Optoelectronic properties of candidate photovoltaic Cu 2PbSiS 4, Ag 2PbGeS 4 and KAg 2SbS 4 semiconductors

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

Nhalil, Hariharan; Han, Dan; Du, Mao-Hua

High temperature synthesis and optical band gaps are reported for three candidate photovoltaic earth-abundant Cu 2PbSiS 4, Ag 2PbGeS 4 and KAg 2SbS 4 semiconductors. The reported synthesis method is found to be more advantageous for KAg 2SbS 4 compared to the literature reported synthesis utilizing supercritical ammonia as a reaction medium, which produces a mixture of chalcogenide products. Based on optical diffuse reflectance data, Cu 2PbSiS 4, Ag 2PbGeS 4 and KAg 2SbS 4 have band gaps in the 1.6–1.8 eV range, and are shown to be stable in ambient air for a period of 6 weeks, making themmore » attractive candidates for solar cell applications. Density functional theory (DFT) calculations indicate indirect band gaps for Cu 2PbSiS 4 and KAg 2SbS 4, and a nearly direct band gap for Ag 2PbGeS 4 with the calculated difference between indirect and direct gaps of only 30 meV. The p-type semiconducting behavior of Cu 2PbSiS 4, Ag 2PbGeS 4 is also verified by the transport measurments. The 3D connectivity of the polyanionic networks in these compounds results in dispersive valence and conduction bands, which is especially noticeable for KAg 2SbS 4. This fact is in part attributed to the presence of formally pentavalent SbV in this compound leading to empty Sb 5s orbitals in the conduction band. Finally, we discuss the potential of Cu 2PbSiS 4, Ag 2PbGeS 4 and KAg 2SbS 4 for photovoltaic applications based on synthesis, stability, band gap and electronic structure considerations.« less

Optoelectronic properties of candidate photovoltaic Cu 2PbSiS 4, Ag 2PbGeS 4 and KAg 2SbS 4 semiconductors

DOE PAGES

Nhalil, Hariharan; Han, Dan; Du, Mao-Hua; ...

2018-03-01

High temperature synthesis and optical band gaps are reported for three candidate photovoltaic earth-abundant Cu 2PbSiS 4, Ag 2PbGeS 4 and KAg 2SbS 4 semiconductors. The reported synthesis method is found to be more advantageous for KAg 2SbS 4 compared to the literature reported synthesis utilizing supercritical ammonia as a reaction medium, which produces a mixture of chalcogenide products. Based on optical diffuse reflectance data, Cu 2PbSiS 4, Ag 2PbGeS 4 and KAg 2SbS 4 have band gaps in the 1.6–1.8 eV range, and are shown to be stable in ambient air for a period of 6 weeks, making themmore » attractive candidates for solar cell applications. Density functional theory (DFT) calculations indicate indirect band gaps for Cu 2PbSiS 4 and KAg 2SbS 4, and a nearly direct band gap for Ag 2PbGeS 4 with the calculated difference between indirect and direct gaps of only 30 meV. The p-type semiconducting behavior of Cu 2PbSiS 4, Ag 2PbGeS 4 is also verified by the transport measurments. The 3D connectivity of the polyanionic networks in these compounds results in dispersive valence and conduction bands, which is especially noticeable for KAg 2SbS 4. This fact is in part attributed to the presence of formally pentavalent SbV in this compound leading to empty Sb 5s orbitals in the conduction band. Finally, we discuss the potential of Cu 2PbSiS 4, Ag 2PbGeS 4 and KAg 2SbS 4 for photovoltaic applications based on synthesis, stability, band gap and electronic structure considerations.« less

Using the Semiconductors Materials of InSb-ZnTe System in Sensors for Gas Control

NASA Astrophysics Data System (ADS)

Shubenkova, E. G.

2017-04-01

The samples of thin film semiconductor compounds InSb, ZnTe and solid solutions based on them were obtained by vapor deposition of components on a dielectric substrate in a vacuum, followed by annealing and their surface properties in CO, O2 and NH3 gas atmospheres were investigated. Identification of the samples was carried out by X-ray diffraction techniques. In the temperature range 253 ÷ 403 K and a pressure range of 1÷12 Pa the gas adsorption was measured by piezoelectric microbalance technique. In order to establish the basic regularities of processes flowing on samples surface in addition to the electrophisical were used Infrared and Raman spectroscopic measurements. The resulting addiction “surface property - composition” is extreme and have allowed to determine solid solution InSb0,95-ZnTe0,05 as the most sensitive to the presence of ammonia, selective and this sample exhibits a negligible oxidation of surface.

A hard oxide semiconductor with a direct and narrow bandgap and switchable p-n electrical conduction.

PubMed

Ovsyannikov, Sergey V; Karkin, Alexander E; Morozova, Natalia V; Shchennikov, Vladimir V; Bykova, Elena; Abakumov, Artem M; Tsirlin, Alexander A; Glazyrin, Konstantin V; Dubrovinsky, Leonid

2014-12-23

An oxide semiconductor (perovskite-type Mn2 O3 ) is reported which has a narrow and direct bandgap of 0.45 eV and a high Vickers hardness of 15 GPa. All the known materials with similar electronic band structures (e.g., InSb, PbTe, PbSe, PbS, and InAs) play crucial roles in the semiconductor industry. The perovskite-type Mn2 O3 described is much stronger than the above semiconductors and may find useful applications in different semiconductor devices, e.g., in IR detectors. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Diamagnetic excitons and exciton magnetopolaritons in semiconductors

NASA Astrophysics Data System (ADS)

Seisyan, R. P.

2012-05-01

Interband magneto-absorption in semiconductors is reviewed in the light of the diamagnetic exciton (DE) concept. Beginning with a proof of the exciton nature of oscillating-magnetoabsorption (the DE discovery), development of the DE concept is discussed, including definition of observation conditions, quasi-cubic approximation for hexagonal crystals, quantum-well effects in artificial structures, and comprehension of an important role of the DE polariton. The successful use of the concept application to a broad range of substances is reviewed, namely quasi-Landau magnetic spectroscopy of the ‘Rydberg’ exciton states in cubic semiconductors such as InP and GaAs and in hexagonal ones such as CdSe, the proof of exciton participation in the formation of optical spectra in narrow-gap semiconductors such as InSb, InAs, and, especially, PbTe, observation of DE spectra in semiconductor solid solutions like InGaAs. The most fundamental findings of the DE spectroscopy for various quantum systems are brought together, including the ‘Coulomb-well’ effect, fine structure of discrete oscillatory states in the InGaAs/GaAs multiple quantum wells, the magneto-optical observation of above-barrier exciton. Prospects of the DE physics in ultrahigh magnetic field are discussed, including technological creation of controllable low-dimensional objects with extreme oscillator strengths, formation of magneto-quantum exciton polymer, and even modelling of the hydrogen behaviour in the atmosphere of a neutron star.

Semiconductor tunnel junction with enhancement layer

DOEpatents

Klem, John F.; Zolper, John C.

1997-01-01

The incorporation of a pseudomorphic GaAsSb layer in a runnel diode structure affords a new degree of freedom in designing runnel junctions for p-n junction device interconnects. Previously only doping levels could be varied to control the tunneling properties. This invention uses the valence band alignment band of the GaAsSb with respect to the surrounding materials to greatly relax the doping requirements for tunneling.

Small Scale Burner Review

DTIC Science & Technology

2009-07-01

dopants in the semiconductor components of the devices (5). Venkatasubramanian (46) reviewed some state- of-the-art TE materials such as quantum-dot...conversion efficiency of a GaSb micro TPV system incorporating broadband silicon carbide (SiC) and selective emitted materials ( cobalt [Co]/nickel...carbon CFD computational fluid dynamics Co cobalt CO carbon monoxide CO2 carbon dioxide Cu copper GaSb gallium antimonide InGaAs indium gallium

Modeling the thermal conductivities of the zinc antimonides ZnSb and Zn4Sb3

NASA Astrophysics Data System (ADS)

Bjerg, Lasse; Iversen, Bo B.; Madsen, Georg K. H.

2014-01-01

ZnSb and Zn4Sb3 are interesting as thermoelectric materials because of their low cost and low thermal conductivity. We introduce a model of the lattice thermal conductivity which is independent of fitting parameters and takes the full phonon dispersions into account. The model is found to give thermal conductivities with the correct relative magnitudes and in reasonable quantitative agreement with experiment for a number of semiconductor structures. The thermal conductivities of the zinc antimonides are reviewed and the relatively large effect of nanostructuring on the zinc antimonides is rationalized in terms of the mean free paths of the heat carrying phonons. The very low thermal conductivity of Zn4Sb3 is found to be intrinsic to the structure. However, the low-lying optical modes are observed in both Zn-Sb structures and involve both Zn and Sb vibrations, thereby strongly questioning dumbbell rattling. A mechanism for the very low thermal conductivity observed in Zn4Sb3 is identified. The large Grüneisen parameter of this compound is traced to the Sb atoms which coordinate only Zn atoms.

Entirely relaxed lattice-mismatched GaSb/GaAs/Si(001) heterostructure grown via metalorganic chemical vapor deposition

NASA Astrophysics Data System (ADS)

Ha, Minh Thien Huu; Hoang Huynh, Sa; Binh Do, Huy; Nguyen, Tuan Anh; Luc, Quang Ho; Lee, Ching Ting; Chang, Edward Yi

2018-05-01

A GaSb epilayer is grown on a GaAs/Si(001) epitaxial substrate via metalorganic chemical vapor deposition. High-resolution transmission electron microscopy micrographs and high-resolution X-ray reciprocal space mapping indicate an entirely relaxed interfacial misfit (IMF) array GaSb epilayer. The valence-band offset and conduction-band offset of the Al2O3/GaSb/GaAs/Si structure are estimated to be 2.39 and 3.65 eV, respectively. The fabricated Al2O3/p-GaSb/GaAs/Si MOS capacitors exhibited good capacitance–voltage characteristics with a small accumulation frequency dispersion of approximately 1.05% per decade. These results imply that the GaSb epilayer grown on the GaAs/Si platform in the IMF mode can be used for future complementary metal–oxide semiconductor applications.

High Temperature Electronic and Thermal Transport Properties of EuGa2- x In x Sb2

NASA Astrophysics Data System (ADS)

Chanakian, Sevan; Weber, Rochelle; Aydemir, Umut; Ormeci, Alim; Fleurial, Jean-Pierre; Bux, Sabah; Snyder, G. Jeffrey

2017-08-01

The Zintl phase EuGa2Sb2 was synthesized via ball milling followed by hot pressing. The crystal structure of EuGa2Sb2 is comprised of a 3-D network of polyanionic [Ga2Sb2]2- tunnels filled with Eu cations that provide charge balance (Eu2+[Ga2Sb2]2-). Here we report the temperature-dependent resistivity, Hall Effect, Seebeck coefficient and thermal conductivity for EuGa2- x In x Sb2 ( x = 0, 0.05, 0.1) from 300 K to 775 K. Experimental results demonstrate that the material is a p-type semiconductor. However, a small band gap (˜0.1 eV) prevents EuGa2Sb2 from having high zT at higher temperatures. Isoelectronic substitution of In on the Ga site leads to point defect scattering of holes and phonons, thus reducing thermal conductivity and resulting in a slight improvement in zT.

Localization of the interband transitions in the bulk of the Brillouin zone of III–V compound crystals

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

Sobolev, V. V., E-mail: sobolev@uni.udm.ru; Perevoshchikov, D. A.

2016-05-15

The localization of the transitions in the bulk of the Brillouin zone that form the main structures in the spectra of the imaginary part of the permittivity in the range up to ~7 eV for III–V semiconductors (AlSb, GaSb, InSb, and InAs) is determined using electron density functional theory. It is established that intense transitions occur not only in the vicinity of the high-symmetry axes of the Brillouin zone, but also in some specific large volumes of the irreducible part of the Brillouin zone.

Narrow band gap amorphous silicon semiconductors

DOEpatents

Madan, A.; Mahan, A.H.

1985-01-10

Disclosed is a narrow band gap amorphous silicon semiconductor comprising an alloy of amorphous silicon and a band gap narrowing element selected from the group consisting of Sn, Ge, and Pb, with an electron donor dopant selected from the group consisting of P, As, Sb, Bi and N. The process for producing the narrow band gap amorphous silicon semiconductor comprises the steps of forming an alloy comprising amorphous silicon and at least one of the aforesaid band gap narrowing elements in amount sufficient to narrow the band gap of the silicon semiconductor alloy below that of amorphous silicon, and also utilizing sufficient amounts of the aforesaid electron donor dopant to maintain the amorphous silicon alloy as an n-type semiconductor.

Influence of Asymmetric Contact Form on Contact Resistance and Schottky Barrier, and Corresponding Applications of Diode.

PubMed

Zhao, Yudan; Xiao, Xiaoyang; Huo, Yujia; Wang, Yingcheng; Zhang, Tianfu; Jiang, Kaili; Wang, Jiaping; Fan, Shoushan; Li, Qunqing

2017-06-07

We have fabricated carbon nanotube and MoS 2 field-effect transistors with asymmetric contact forms of source-drain electrodes, from which we found the current directionality of the devices and different contact resistances under the two current directions. By designing various structures, we can conclude that the asymmetric electrical performance was caused by the difference in the effective Schottky barrier height (Φ SB ) caused by the different contact forms. A detailed temperature-dependent study was used to extract and compare the Φ SB for both contact forms of CNT and MoS 2 devices; we found that the Φ SB for the metal-on-semiconductor form was much lower than that of the semiconductor-on-metal form and is suitable for all p-type, n-type, or ambipolar semiconductors. This conclusion is meaningful with respect to the design and application of nanomaterial electronic devices. Additionally, using the difference in barrier height caused by the contact forms, we have also proposed and fabricated Schottky barrier diodes with a current ratio up to 10 4 ; rectifying circuits consisting of these diodes were able to work in a wide frequency range. This design avoided the use of complex chemical doping or heterojunction methods to achieve fundamental diodes that are relatively simple and use only a single material; these may be suitable for future application in nanoelectronic radio frequency or integrated circuits.

Semiconductor tunnel junction with enhancement layer

DOEpatents

Klem, J.F.; Zolper, J.C.

1997-10-21

The incorporation of a pseudomorphic GaAsSb layer in a runnel diode structure affords a new degree of freedom in designing runnel junctions for p-n junction device interconnects. Previously only doping levels could be varied to control the tunneling properties. This invention uses the valence band alignment band of the GaAsSb with respect to the surrounding materials to greatly relax the doping requirements for tunneling. 5 figs.

Simulations of Resonant Intraband and Interband Tunneling Spin Filters

NASA Technical Reports Server (NTRS)

Ting, David; Cartoixa-Soler, Xavier; McGill, T. C.; Smith, Darryl L.; Schulman, Joel N.

2001-01-01

This viewgraph presentation reviews resonant intraband and interband tunneling spin filters It explores the possibility of building a zero-magnetic-field spin polarizer using nonmagnetic III-V semiconductor heterostructures. It reviews the extensive simulations of quantum transport in asymmetric InAs/GaSb/AlSb resonant tunneling structures with Rashba spin splitting and proposes a. new device concept: side-gated asymmetric Resonant Interband Tunneling Diode (a-RITD).

A New Method for Growth and Analysis of Next-generation Infrared (IR) Detector Materials

DTIC Science & Technology

2009-03-01

N) into the group V sites of the semiconductor lattice. Until recently the highest concentration of nitrogen reported in GaSb1– xNx was 1.75% (2...Adams, A. R.; Andreev, A.; Murdin, B. N.; O’Reilly, E. P.; Pidgeon, C. R. InSb1− xNx Growth and Devices. Solid-State Electronics 47 2003, 3, 387–394

Complex doping of group 13 elements In and Ga in caged skutterudite CoSb 3

DOE PAGES

Xi, Lili; Qiu, Yting; Zheng, Shang; ...

2014-12-12

The complex doping behavior of Ga and In in CoSb 3 has been investigated using ab initio total-energy calculations and thermodynamics. The formation energies of void filling, Sb substitution and complex dual-site occupancy defects with different charge states, and their dependence on chemical potentials of species, were studied. Results show that Ga predominantly forms dual-site 2Ga VF–Ga Sb defects and substitutes for Sb only at very high Fermi levels or electron concentrations. In, on the other hand, can play multiple roles in skutterudites, including filling in the crystalline voids, substituting for Sb atoms or forming dual-site occupancy, among which themore » fully charge-compensated dual-site defects (2In VF–In Sb and 4In VF–2In Sb) are dominant. The equilibrium concentration ratio of impurities at void-filling sites to those at Sb-substitution sites for Ga-doped CoSb 3 is very close to be 2:1, while this value markedly deviates from 2:1 for In-doped CoSb 3. Furthermore, the 2:1 ratio of Ga doping in CoSb 3 leads to low electron concentration (~2 × 10 19 cm –3) and makes the doped system a semiconductor.« less

Non-equilibrium Green's function calculation of AlGaAs-well-based and GaSb-based terahertz quantum cascade laser structures

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

Yasuda, H., E-mail: yasuda@nict.go.jp; Hosako, I.

2015-03-16

We investigate the performance of terahertz quantum cascade lasers (THz-QCLs) based on Al{sub x}Ga{sub 1−x}As/Al{sub y}Ga{sub 1−y}As and GaSb/AlGaSb material systems to realize higher-temperature operation. Calculations with the non-equilibrium Green's function method reveal that the AlGaAs-well-based THz-QCLs do not show improved performance, mainly because of alloy scattering in the ternary compound semiconductor. The GaSb-based THz-QCLs offer clear advantages over GaAs-based THz-QCLs. Weaker longitudinal optical phonon–electron interaction in GaSb produces higher peaks in the spectral functions of the lasing levels, which enables more electrons to be accumulated in the upper lasing level.

Prediction of weak and strong topological insulators in layered semiconductors.

NASA Astrophysics Data System (ADS)

Felser, Claudia

2013-03-01

We investigate a new class of ternary materials such as LiAuSe and KHgSb with a honeycomb structure in Au-Se and Hg-Sb layers. We demonstrate the band inversion in these materials similar to HgTe, which is a strong precondition for existence of the topological surface states. In contrast with graphene, these materials exhibit strong spin-orbit coupling and a small direct band gap at the point. Since these materials are centrosymmetric, it is straightforward to determine the parity of their wave functions, and hence their topological character. Surprisingly, the compound with strong spin-orbit coupling (KHgSb) is trivial, whereas LiAuSe is found to be a topological insulator. However KHgSb is a weak topological insulators in case of an odd number of layers in the primitive unit cell. Here, the single-layered KHgSb shows a large bulk energy gap of 0.24 eV. Its side surface hosts metallic surface states, forming two anisotropic Dirac cones. Although the stacking of even-layered structures leads to trivial insulators, the structures can host a quantum spin Hall layer with a large bulk gap, if an additional single layer exists as a stacking fault in the crystal. The reported honeycomb compounds can serve as prototypes to aid in the finding of new weak topological insulators in layered small-gap semiconductors. In collaboration with Binghai Yan, Lukas Müchler, Hai-Jun Zhang, Shou-Cheng Zhang and Jürgen Kübler.

SbSI Nanosensors: from Gel to Single Nanowire Devices

NASA Astrophysics Data System (ADS)

Mistewicz, Krystian; Nowak, Marian; Paszkiewicz, Regina; Guiseppi-Elie, Anthony

2017-02-01

The gas-sensing properties of antimony sulfoiodide (SbSI) nanosensors have been tested for humidity and carbon dioxide in nitrogen. The presented low-power SbSI nanosensors have operated at relatively low temperature and have not required heating system for recovery. Functionality of sonochemically prepared SbSI nanosensors made of xerogel as well as single nanowires has been compared. In the latter case, small amount of SbSI nanowires has been aligned in electric field and bonded ultrasonically to Au microelectrodes. The current and photocurrent responses of SbSI nanosensors have been investigated as function of relative humidity. Mechanism of light-induced desorption of H2O from SbSI nanowires' surface has been discussed. SbSI nanosensors have been tested for concentrations from 51 to 106 ppm of CO2 in N2, exhibiting a low detection limit of 40(31) ppm. The current response sensitivity has shown a tendency to decrease with increasing CO2 concentration. The experimental results have been explained taking into account proton-transfer process and Grotthuss' chain reaction, as well as electronic theory of adsorption and catalysis on semiconductors.

Trap density of GeNx/Ge interface fabricated by electron-cyclotron-resonance plasma nitridation

NASA Astrophysics Data System (ADS)

Fukuda, Yukio; Otani, Yohei; Toyota, Hiroshi; Ono, Toshiro

2011-07-01

We have investigated GeNx/Ge interface properties using Si3N4(7 nm)/GeNx(2 nm)/Ge metal-insulator-semiconductor structures fabricated by the plasma nitridation of Ge substrates using an electron-cyclotron-resonance-generated nitrogen plasma. The interface trap density (Dit) measured by the conductance method is found to be distributed symmetrically in the Ge band gap with a minimum Dit value lower than 3 × 1011 cm-2eV-1 near the midgap. This result may lead to the development of processes for the fabrication of p- and n-Ge Schottky-barrier (SB) source/drain metal-insulator-semiconductor field-effect transistors using chemically and thermally robust GeNx dielectrics as interlayers for SB source/drain contacts and high-κ gate dielectrics.

New two-dimensional V-V binary compounds with a honeycomb-like structure: a first-principles study

NASA Astrophysics Data System (ADS)

Xiao, Wen-Zhi; Xiao, Gang; Rong, Qing-Yan; Wang, Ling-Ling

2018-03-01

We systematically search for the stable structures of two-dimensional (2D) V-V binary compounds with honeycomb-like structure by using the first-principles calculation. We identify 26 stable structures out of 54 2D V-V compounds based on various assessments of stabilities: total energy, thermodynamics, and mechanics. Among them, 12 2D V-V compounds are previously unrecognized structures. For each class V-V isomer, the most stable structures are found to be β-AsP, β-SbAs, α-BiAs, α-BiSb, α 2-SbP, and α 2-BiP. For all isomers of the AsP, they are always stable, and hence PAs monolayer is most likely to be prepared experimentally. All the stable structures are semiconductors with bandgaps ranging from 0.06 eV to 2.52 eV at the Heyd-Scuseria-Ernzerhof level. Therefore, they are potential materials for versatile semiconductor devices. Our findings provide a new clue to facilitate the design of 2D materials for potential applications.

Anisotropic magnetic properties of the ferromagnetic semiconductor CrSbSe3

NASA Astrophysics Data System (ADS)

Kong, Tai; Stolze, Karoline; Ni, Danrui; Kushwaha, Satya K.; Cava, Robert J.

2018-01-01

Single crystals of CrSbSe3, a structurally pseudo-one-dimensional ferromagnetic semiconductor, were grown using a high-temperature solution growth technique and were characterized by x-ray diffraction, anisotropic temperature- and field-dependent magnetization, temperature-dependent resistivity, and optical absorption measurements. A band gap of 0.7 eV was determined from both resistivity and optical measurements. At high temperatures, CrSbSe3 is paramagnetic and isotropic, with a Curie-Weiss temperature of ˜145 K and an effective moment of ˜4.1 μB /Cr. A ferromagnetic transition occurs at Tc=71 K. The a axis, perpendicular to the chains in the structure, is the magnetic easy axis, while the chain axis direction, along b , is the hard axis. Magnetic isotherms measured around Tc do not follow the behavior predicted by simple mean-field critical exponents for a second-order phase transition. A tentative set of critical exponents is estimated based on a modified Arrott plot analysis, giving β ˜0.25 , γ ˜1.38 , and δ ˜6.6 .

First-Principles Study on the Ferromagnetism and Curie Temperature of Mn-Doped AlX and InX (X=N, P, As, and Sb)

NASA Astrophysics Data System (ADS)

Sato, Kazunori; Dederichs, Peter H.; Katayama-Yoshida, Hiroshi

2007-02-01

We investigate the electronic structure and magnetic properties of AlN-, AlP-, AlAs-, AlSb-, InN-, InP-, InAs-, and InSb-based dilute magnetic semiconductors (DMS) with Mn impurities from first-principles. The electronic structure of DMS is calculated by using the Korringa-Kohn-Rostoker coherent potential approximation (KKR-CPA) method in connection with the local density approximation (LDA) and the LDA+U method. Describing the magnetic properties by a classical Heisenberg model, effective exchange interactions are calculated by applying magnetic force theorem for two impurities embedded in the CPA medium. With the calculated exchange interactions, TC is estimated by using the mean field approximation, the random phase approximation and the Monte Carlo simulation. It is found that the p-d exchange model [Dietl et al.: Science 287 (2000) 1019] is adequate for a limited class of DMS and insufficient to describe the ferromagnetism in wide gap semiconductor based DMS such as (Ga,Mn)N and the presently investigated (Al,Mn)N and (In,Mn)N.

Terahertz transmission properties of a triadic-Cantor-set photonic crystal containing a semiconductor

NASA Astrophysics Data System (ADS)

King, Tzu-Chyang; Liu, Chi-Chung; Huang, Chih-Hsi; Wu, Chien-Jang

2016-08-01

Terahertz transmission properties of a stage 3 triadic-Cantor-set photonic crystal (S3 TCS PC) containing a semiconductor of n-InSb are theoretically investigated. With the resonant frequency in the permittivity function of n-InSb, transmission responses can be classified as three regions. In the two regions with frequencies well above and below the resonant frequency, the permittivity functions are nearly a positive constant and n-InSb is dielectric-like. For these two regions, transmittance response of S3 TCS PC at a given number of periods Np reveals that, within a photonic band gap, there are two groups of defect modes with numbers of Np and Np-1, respectively. Defect modes are shown to be blue-shifted as the angle of incidence increases for both TE and TM waves. Additionally, adjusting the layer thickness enables us to control mode positions for the group of (Np-1)-mode, but the one with Np-mode is not able to be controlled. In a region of 5.1-6.2 THz, where the loss is large, there also are many transmission modes.

Ultraviolet and visible range plasmonics in the topological insulator Bi1.5Sb0.5Te1.8Se1.2

NASA Astrophysics Data System (ADS)

Ou, Jun-Yu; So, Jin-Kyu; Adamo, Giorgio; Sulaev, Azat; Wang, Lan; Zheludev, Nikolay I.

2014-10-01

The development of metamaterials, data processing circuits and sensors for the visible and ultraviolet parts of the spectrum is hampered by the lack of low-loss media supporting plasmonic excitations. This has driven the intense search for plasmonic materials beyond noble metals. Here we show that the semiconductor Bi1.5Sb0.5Te1.8Se1.2, also known as a topological insulator, is also a good plasmonic material in the blue-ultraviolet range, in addition to the already-investigated terahertz frequency range. Metamaterials fabricated from Bi1.5Sb0.5Te1.8Se1.2 show plasmonic resonances from 350 to 550 nm, while surface gratings exhibit cathodoluminescent peaks from 230 to 1,050 nm. The observed plasmonic response is attributed to the combination of bulk charge carriers from interband transitions and surface charge carriers of the topological insulator. The importance of our result is in the identification of new mechanisms of negative permittivity in semiconductors where visible range plasmonics can be directly integrated with electronics.

First principles calculations of electronic structure and magnetic properties of Cr-based magnetic semiconductors Al{sub 1-x}Cr{sub x}X (X=N, P, As, Sb)

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

Saeed, Y., E-mail: yasir_saeed54321@yahoo.co; Shaukat, A., E-mail: schaukat@gmail.co; Nazir, S., E-mail: nazirsafdar@gmail.co

2010-01-15

First principles calculations based on the density functional theory (DFT) within the local spin density approximation are performed to investigate the electronic structure and magnetic properties of Cr-based zinc blende diluted magnetic semiconductors Al{sub 1-x}Cr{sub x}X (X=N, P, As, Sb) for 0<=x<=0.50.The behaviour of magnetic moment of Al{sub 1-x}Cr{sub x}X at each Cr site as well as the change in the band gap value due to spin down electrons has been studied by increasing the concentration of Cr atom and through changing X from N to Sb. Furthermore, the role of p-d hybridization is analyzed in the electronic band structuremore » and exchange splitting of d-dominated bands. The interaction strength is stronger in Al{sub 1-x}Cr{sub x}N and becomes weaker in Al{sub 1-x}Cr{sub x}Sb. The band gap due to the spin down electrons decreases with the increased concentration of Cr in Al{sub 1-x}Cr{sub x}X, and as one moves down along the isoelectronic series in the group V from N to Sb. Our calculations also verify the half-metallic ferromagnetic character in Cr doped AlX. - Graphical abstract: The prototype structures of Cr doped AlX (X=N, P, As, Sb) compounds: (A) zinc blende AlP for x=0, (B) Cr{sub 1}Al{sub 7}P{sub 8} for x=0.125, (C) Cr{sub 1}Al{sub 3}P{sub 4} for x=0.25, (D) Cr{sub 1}Al{sub 1}P{sub 2} for x=0.5.« less

Diluted magnetic semiconductors with narrow band gaps

NASA Astrophysics Data System (ADS)

Gu, Bo; Maekawa, Sadamichi

2016-10-01

We propose a method to realize diluted magnetic semiconductors (DMSs) with p - and n -type carriers by choosing host semiconductors with a narrow band gap. By employing a combination of the density function theory and quantum Monte Carlo simulation, we demonstrate such semiconductors using Mn-doped BaZn2As2 , which has a band gap of 0.2 eV. In addition, we found a nontoxic DMS Mn-doped BaZn2Sb2 , of which the Curie temperature Tc is predicted to be higher than that of Mn-doped BaZn2As2 , the Tc of which was up to 230 K in a recent experiment.

Facile synthesis of hybrid nanorods with the Sb2Se3/AgSbSe2 heterojunction structure for high performance photodetectors.

PubMed

Chen, Shuo; Qiao, Xvsheng; Wang, Fengxia; Luo, Qun; Zhang, Xianghua; Wan, Xia; Xu, Yang; Fan, Xianping

2016-01-28

An effective colloidal process involving the hot-injection method is developed to synthesize uniform single-crystalline Sb2Se3 nanorods in high yields. The photoconductive characteristics of the as-synthesized Sb2Se3 nanorods are investigated by developing a film-based photodetector and this device displays a remarkable response to visible light with an "ON/OFF" ratio as high as 50 (with an incident light density of 12.05 mW cm(-2)), short response/recovery times and long-term durability. To overcome the challenge of the intrinsic low electrical conductivity of Sb2Se3, hybrid nanorods with the Sb2Se3/AgSbSe2 heterojunction structure having a type-II band alignment are firstly prepared. The electric current of the photodetector based on the Sb2Se3/AgSbSe2 hybrid nanorod film has been significantly increased both in the dark and under light illumination. The responsivity of the photodetector based on the Sb2Se3/AgSbSe2 hybrid nanorod film is about 4.2 times as much as that of the photodetector based on the Sb2Se3 nanorod film. This improvement can be considered as an important step to promote Sb2Se3 based semiconductors for applications in high performance photodetectors.

Mo(3)Sb(7-x)Te(x) for Thermoelectric Power Generation

NASA Technical Reports Server (NTRS)

Snyder, G. Jeffrey; Gascoin, Frank S.; Rasmussen, Julia

2009-01-01

Compounds having compositions of Mo(3)Sb(7-x)Te(x) (where x = 1.5 or 1.6) have been investigated as candidate thermoelectric materials. These compounds are members of a class of semiconductors that includes previously known thermoelectric materials. All of these compounds have complex crystalline and electronic structures. Through selection of chemical compositions and processing conditions, it may be possible to alter the structures to enhance or optimize thermoelectric properties.

Rashba effect in single-layer antimony telluroiodide SbTeI

DOE PAGES

Zhuang, Houlong L.; Cooper, Valentino R.; Xu, Haixuan; ...

2015-09-04

Exploring spin-orbit coupling (SOC) in single-layer materials is important for potential spintronics applications. In this paper, using first-principles calculations, we show that single-layer antimony telluroiodide SbTeI behaves as a two-dimensional semiconductor exhibiting a G 0W 0 band gap of 1.82 eV. More importantly, we observe the Rashba spin splitting in the SOC band structure of single-layer SbTeI with a sizable Rashba coupling parameter of 1.39 eV Å, which is significantly larger than that of a number of two-dimensional systems including surfaces and interfaces. The low formation energy and real phonon modes of single-layer SbTeI imply that it is stable. Finally,more » our study suggests that single-layer SbTeI is a candidate single-layer material for applications in spintronics devices.« less

Engineering hybrid epitaxial InAsSb/Al nanowires for stronger topological protection

NASA Astrophysics Data System (ADS)

Sestoft, Joachim E.; Kanne, Thomas; Gejl, Aske Nørskov; von Soosten, Merlin; Yodh, Jeremy S.; Sherman, Daniel; Tarasinski, Brian; Wimmer, Michael; Johnson, Erik; Deng, Mingtang; Nygârd, Jesper; Jespersen, Thomas Sand; Marcus, Charles M.; Krogstrup, Peter

2018-04-01

The combination of strong spin-orbit coupling, large g factors, and the coupling to a superconductor can be used to create a topologically protected state in a semiconductor nanowire. Here we report on growth and characterization of hybrid epitaxial InAsSb/Al nanowires, with varying composition and crystal structure. We find the strongest spin-orbit interaction at intermediate compositions in zinc-blende InAs1 -xSbx nanowires, exceeding that of both InAs and InSb materials, confirming recent theoretical studies. We show that the epitaxial InAsSb/Al interface allows for a hard induced superconducting gap and 2 e transport in Coulomb charging experiments, similarly to experiments on InAs/Al and InSb/Al materials, and find measurements consistent with topological phase transitions at low magnetic fields due to large effective g factors. Finally we present a method to grow pure wurtzite InAsSb nanowires which are predicted to exhibit even stronger spin-orbit coupling than the zinc-blende structure.

Thickness dependent band gap of Bi{sub 2-x}Sb{sub x}Te{sub 3} (x = 0, 0.05, 0.1) thin films

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

Patel, M. M.; Soni, P. H., E-mail: phsoni-msu@yahoo.com; Desai, C. F.

2016-05-23

Thin films of Bi{sub 2}Te{sub 3}(Sb) were prepared on alkali halide crystal substrates. Sb content and the film thickness were varied. Bi{sub 2}Te{sub 3} is a narrow gap semiconductor. Bi-Sb is a continuous solid solution of substitutional type and Sb therefore was used to test its effect on the band gap. The film thickness variation was also taken up. The infra-red absorption spectra were used in the wave number range 400 cm{sup −1} to 4000 cm{sup −1}. The band gap obtained from the absorption data was found to increase with decreasing thickness since the thickness range used was from 30more » nm to 170 nm. This is a range corresponding to nanostructures and hence quantum size effect was observed as expected. The band gap also exhibited Sb content dependence. The detail results are have been reported and explained.« less

Highly mismatched GaN1-x Sb x alloys: synthesis, structure and electronic properties

NASA Astrophysics Data System (ADS)

Yu, K. M.; Sarney, W. L.; Novikov, S. V.; Segercrantz, N.; Ting, M.; Shaw, M.; Svensson, S. P.; Martin, R. W.; Walukiewicz, W.; Foxon, C. T.

2016-08-01

Highly mismatched alloys (HMAs) is a class of semiconductor alloys whose constituents are distinctly different in terms of size, ionicity and/or electronegativity. Electronic properties of the alloys deviate significantly from an interpolation scheme based on small deviations from the virtual crystal approximation. Most of the HMAs were only studied in a dilute composition limit. Recent advances in understanding of the semiconductor synthesis processes allowed growth of thin films of HMAs under non-equilibrium conditions. Thus reducing the growth temperature allowed synthesis of group III-N-V HMAs over almost the entire composition range. This paper focuses on the GaN x Sb1-x HMA which has been suggested as a potential material for solar water dissociation devices. Here we review our recent work on the synthesis, structural and optical characterization of GaN1-x Sb x HMA. Theoretical modeling studies on its electronic structure based on the band anticrossing (BAC) model are also reviewed. In particular we discuss the effects of growth temperature, Ga flux and Sb flux on the incorporation of Sb, film microstructure and optical properties of the alloys. Results obtained from two separate MBE growths are directly compared. Our work demonstrates that a large range of direct bandgap energies from 3.4 eV to below 1.0 eV can be achieved for this alloy grown at low temperature. We show that the electronic band structure of GaN1-x Sb x HMA over the entire composition range is well described by a modified BAC model which includes the dependence of the host matrix band edges as well as the BAC model coupling parameters on composition. We emphasize that the modified BAC model of the electronic band structure developed for the full composition of GaN x Sb1-x is general and is applicable to any HMA.

Dielectric relaxation studies in Se{sub 90}Cd{sub 8}Sb{sub 2} glassy alloy

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

Shukla, Nitesh; Rao, Vandita; Dwivedi, D. K.

2016-05-06

Se{sub 90}Cd{sub 8}Sb{sub 2} chalcogenide semiconducting alloy was prepared by melt quench technique. The prepared glassy alloy has been characterized by techniques such as scanning electron microscopy (SEM) and energy dispersive X-ray (EDAX).Dielectric properties of Se{sub 90}Cd{sub 8}Sb{sub 2} chalcogenide semiconductor have been studied using impedance spectroscopic technique in the frequency range 5×10{sup 2}Hz - 1×10{sup 5}Hz and in temperature range 303-318K. It is found that dielectric constant ε′ and dielectric loss factor ε″ are dependent on frequency and temperature.

Epitaxial growth of GaSb on V-grooved Si (001) substrates with an ultrathin GaAs stress relaxing layer

NASA Astrophysics Data System (ADS)

Li, Qiang; Lai, Billy; Lau, Kei May

2017-10-01

We report epitaxial growth of GaSb nano-ridge structures and planar thin films on V-groove patterned Si (001) substrates by leveraging the aspect ratio trapping technique. GaSb was deposited on {111} Si facets of the V-shaped trenches using metal-organic chemical vapor deposition with a 7 nm GaAs growth initiation layer. Transmission electron microscopy analysis reveals the critical role of the GaAs layer in providing a U-shaped surface for subsequent GaSb epitaxy. A network of misfit dislocations was uncovered at the GaSb/GaAs hetero-interface. We studied the evolution of the lattice relaxation as the growth progresses from closely pitched GaSb ridges to coalesced thin films using x-ray diffraction. The omega rocking curve full-width-at-half-maximum of the resultant GaSb thin film is among the lowest values reported by molecular beam epitaxy, substantiating the effectiveness of the defect necking mechanism. These results thus present promising opportunities for the heterogeneous integration of devices based on 6.1 Å family compound semiconductors.

Discovery of highly spin-polarized conducting surface states in the strong spin-orbit coupling semiconductor Sb2Se3

NASA Astrophysics Data System (ADS)

Das, Shekhar; Sirohi, Anshu; Kumar Gupta, Gaurav; Kamboj, Suman; Vasdev, Aastha; Gayen, Sirshendu; Guptasarma, Prasenjit; Das, Tanmoy; Sheet, Goutam

2018-06-01

Majority of the A2B3 -type chalcogenide systems with strong spin-orbit coupling (SOC), such as Bi2Se3,Bi2Te3 , and Sb2Te3 , etc., are topological insulators. One important exception is Sb2Se3 where a topological nontrivial phase was argued to be possible under ambient conditions, but such a phase could be detected to exist only under pressure. In this paper, we show that Sb2Se3 like Bi2Se3 displays a generation of highly spin-polarized current under mesoscopic superconducting point contacts as measured by point-contact Andreev reflection spectroscopy. In addition, we observe a large negative and anisotropic magnetoresistance of the mesoscopic metallic point contacts formed on Sb2Se3 . Our band-structure calculations confirm the trivial nature of Sb2Se3 crystals and reveal two trivial surface states one of which shows large spin splitting due to Rashba-type SOC. The observed high spin polarization and related phenomena in Sb2Se3 can be attributed to this spin splitting.

Excitons in coupled type-II double quantum wells under electric and magnetic fields: InAs/AlSb/GaSb

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

Lyo, S. K., E-mail: sklyo@uci.edu; Pan, W.

2015-11-21

We calculate the wave functions and the energy levels of an exciton in double quantum wells under electric (F) and magnetic (B) fields along the growth axis. The result is employed to study the energy levels, the binding energy, and the boundary on the F–B plane of the phase between the indirect exciton ground state and the semiconductor ground state for several typical structures of the type-II quasi-two-dimensional quantum wells such as InAs/AlSb/GaSb. The inter-well inter-band radiative transition rates are calculated for exciton creation and recombination. We find that the rates are modulated over several orders of magnitude by themore » electric and magnetic fields.« less

Tuning Rashba spin-orbit coupling in homogeneous semiconductor nanowires

NASA Astrophysics Data System (ADS)

Wójcik, Paweł; Bertoni, Andrea; Goldoni, Guido

2018-04-01

We use k .p theory to estimate the Rashba spin-orbit coupling (SOC) in large semiconductor nanowires. We specifically investigate GaAs- and InSb-based devices with different gate configurations to control symmetry and localization of the electron charge density. We explore gate-controlled SOC for wires of different size and doping, and we show that in high carrier density SOC has a nonlinear electric field susceptibility, due to large reshaping of the quantum states. We analyze recent experiments with InSb nanowires in light of our calculations. Good agreement is found with the SOC coefficients reported in Phys. Rev. B 91, 201413(R) (2015), 10.1103/PhysRevB.91.201413, but not with the much larger values reported in Nat. Commun. 8, 478 (2017), 10.1038/s41467-017-00315-y. We discuss possible origins of this discrepancy.

High Power Mid Wave Infrared Semiconductor Lasers

DTIC Science & Technology

2006-06-15

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

Quaternary laser devices: history and state of the art

NASA Astrophysics Data System (ADS)

Eliseev, Petr G.

1993-05-01

Quaternary alloys of semiconductor compounds are suitable materials for wide-spectrum optoelectronic applications. The most important property of these efficient luminescent materials is the opportunity to fit the lattice parameter in some range to a given value corresponding to another crystalline material. This leads to the method to construct defect-free and stress-free heterojunctions, which was used for the preparation of a number of laser and LED devices. Quaternaries of InGaAsP, InGaSbAs, InSbAsP, PbSnTeSe, and other alloys were introduced into practical usage particularly in diode laser devices. The alloy InGaAsP appears to be one of the most widely used in optoelectronic applications at present as it covers ranges near 1.3 and 1.55 micrometers wavelengths of fiber-optic communication. For the spectral range near 2 micrometers the alloy InGaSbAs seems to be most attractive, and cw-operating diode lasers at room temperature were demonstrated at 2.0 - 2.4 micrometers . The alloy PbSnTeSe was used to obtain a longest wave of diode laser emission 46 micrometers . Quaternaries played an important role in the development of the semiconductor optoelectronics during the last two decades.

Formation of the InAs-, InSb-, GaAs-, and GaSb-polished surface

NASA Astrophysics Data System (ADS)

Levchenko, Iryna; Tomashyk, Vasyl; Stratiychuk, Iryna; Malanych, Galyna; Korchovyi, Andrii; Kryvyi, Serhii; Kolomys, Oleksandr

2018-04-01

The features of the InAs, InSb, GaAs, and GaSb ultra-smooth surface have been investigated using chemical-mechanical polishing with the (NH4)2Cr2O7-HBr-CH2(OH)CH2(OH)-etching solutions. The etching rate of the semiconductors has been measured as a function of the solution saturation by organic solvent (ethylene glycol). It was found that mechanical effect significantly increases the etching rate from 1.5 to 57 µm/min, and the increase of the organic solvent concentration promotes the decrease of the damaged layer-removing rate. According to AFM, RS, HRXRD results, the treatment with the (NH4)2Cr2O7-HBr-ethylene glycol solutions produces the clean surface of the nanosize level (R a < 0.5 nm).

Infrared light sources with semimetal electron injection

DOEpatents

Kurtz, Steven R.; Biefeld, Robert M.; Allerman, Andrew A.

1999-01-01

An infrared light source is disclosed that comprises a layered semiconductor active region having a semimetal region and at least one quantum-well layer. The semimetal region, formed at an interface between a GaAsSb or GalnSb layer and an InAsSb layer, provides electrons and holes to the quantum-well layer to generate infrared light at a predetermined wavelength in the range of 2-6 .mu.m. Embodiments of the invention can be formed as electrically-activated light-emitting diodes (LEDs) or lasers, and as optically-pumped lasers. Since the active region is unipolar, multiple active regions can be stacked to form a broadband or multiple-wavelength infrared light source.

Surface phase stability and surfactant behavior of InAsSb alloy surfaces.

NASA Astrophysics Data System (ADS)

Anderson, Evan M.; Lundquist, Adam M.; Pearson, Chris; Millunchick, Joanna M.

InAsSb has the narrowest bandgap of any of the conventional III-V semiconductors: low enough for long wavelength infrared applications. Such devices are sensitive to point defects, which can be detrimental to performance. To control these defects, all aspects of synthesis must be considered, especially the atomic bonding at the surface. We use an ab initio statistical mechanics approach that combines density functional theory with a cluster expansion formalism to determine the stable surface reconstructions of Sb (As) on InAs (InSb) substrates. The surface phase diagram of Sb on InAs is dominated by Sb-dimer termination α2(2x4) and β2(2x4) and c(4x4). Smaller regions of mixed Sb-As dimers appear for high Sb chemical potentials and intermediate As chemical potential. We propose that InAsSb films could be grown on (2x4), which maintain bulk-like stoichiometry, to eliminate the formation of typically observed n-type defects. Scanning tunneling microscopy and reflection high energy electron diffraction confirm the calculated phase diagram. Based on these calculations, we propose a new mechanism for the surfactant behavior of Sb in these materials. We gratefully acknowledge Chakrapani Varanasi and the support of the Department of Defense, Army Research Office via the Grant Number W911NF-12-1-0338.

Direct measurement of the effective infrared dielectric response of a highly doped semiconductor metamaterial.

PubMed

Al Mohtar, Abeer; Kazan, Michel; Taliercio, Thierry; Cerutti, Laurent; Blaize, Sylvain; Bruyant, Aurélien

2017-03-24

We have investigated the effective dielectric response of a subwavelength grating made of highly doped semiconductors (HDS) excited in reflection, using numerical simulations and spectroscopic measurement. The studied system can exhibit strong localized surface resonances and has, therefore, a great potential for surface-enhanced infrared absorption (SEIRA) spectroscopy application. It consists of a highly doped InAsSb grating deposited on lattice-matched GaSb. The numerical analysis demonstrated that the resonance frequencies can be inferred from the dielectric function of an equivalent homogeneous slab by accounting for the complex reflectivity of the composite layer. Fourier transform infrared reflectivity (FTIR) measurements, analyzed with the Kramers-Kronig conversion technique, were used to deduce the effective response in reflection of the investigated system. From the knowledge of this phenomenological dielectric function, transversal and longitudinal energy-loss functions were extracted and attributed to transverse and longitudinal resonance modes frequencies.

Electronic and total energy properties of ternary and quaternary semiconductor compounds, alloys and superlattices

NASA Technical Reports Server (NTRS)

Lambrecht, Walter R. L.

1992-01-01

This proposal was mainly concerned with the theoretical study of semiconductor compounds, alloys, and superlattices of interest for photovoltaic applications. In the last year (1991) a study was devoted to metal/graphite bonding in relation to use of graphite fiber reinforcement of Cu for high thermal conductivity applications. The main research topics addressed during the full period of the grant are briefly described: studies of the In-Ga-As ternary system; band-offsets at common anion and InAs/GaSb/AlSb heterojunctions; alloy theory (cluster variation method); and Cu/graphite bonding. Most of the work was described more extensively in previous yearly reports and renewal applications and in publications. The last topic is described more fully in a separate report attached. A list of publications resulting directly from this grant or from other grants but related to this work and of conference presentations is given at the end.

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

Seña, N.; Dussan, A.; Mesa, F.

We have carried out first-principles spin polarized calculations to obtain comprehensive information regarding the structural, magnetic, and electronic properties of the Mn-doped GaSb compound with dopant concentrations: x = 0.062, 0.083, 0.125, 0.25, and 0.50. The plane-wave pseudopotential method was used in order to calculate total energies and electronic structures. It was found that the Mn{sub Ga} substitution is the most stable configuration with a formation energy of ∼1.60 eV/Mn-atom. The calculated density of states shows that the half-metallic ferromagnetism is energetically stable for all dopant concentrations with a total magnetization of about 4.0 μ{sub B}/Mn-atom. The results indicate that the magnetic ground statemore » originates from the strong hybridization between Mn-d and Sb-p states, which agree with previous studies on Mn-doped wide gap semiconductors. This study gives new clues to the fabrication of diluted magnetic semiconductors.« less

Electronic and total energy properties of ternary and quaternary semiconductor compounds, alloys and superlattices

NASA Astrophysics Data System (ADS)

Lambrecht, Walter R. L.

1992-08-01

This proposal was mainly concerned with the theoretical study of semiconductor compounds, alloys, and superlattices of interest for photovoltaic applications. In the last year (1991) a study was devoted to metal/graphite bonding in relation to use of graphite fiber reinforcement of Cu for high thermal conductivity applications. The main research topics addressed during the full period of the grant are briefly described: studies of the In-Ga-As ternary system; band-offsets at common anion and InAs/GaSb/AlSb heterojunctions; alloy theory (cluster variation method); and Cu/graphite bonding. Most of the work was described more extensively in previous yearly reports and renewal applications and in publications. The last topic is described more fully in a separate report attached. A list of publications resulting directly from this grant or from other grants but related to this work and of conference presentations is given at the end.

High levels of antimony in dust from e-waste recycling in southeastern China.

PubMed

Bi, Xiangyang; Li, Zhonggen; Zhuang, Xiaochun; Han, Zhixuan; Yang, Wenlin

2011-11-01

Environmental contamination due to uncontrolled e-waste recycling is an emerging global issue. Antimony (Sb) is a toxic element used in semiconductor components and flame retardants for circuit board within electronic equipment. When e-waste is recycled, Sb is released and contaminates the surrounding environment; however, few studies have characterized the extent of this problem. In this study, we investigated Sb and arsenic (As) distributions in indoor dust from 13 e-waste recycling villages in Guiyu, Guangdong Province, southeastern China. Results revealed significantly elevated concentrations of Sb (6.1-232 mg/kg) in dust within all villages, which were 3.9-147 times higher than those from the non e-waste sites, indicating e-waste recycling was an important source of Sb pollution. On the contrary, As concentrations (5.4-17.7 mg/kg) in e-waste dusts were similar to reference values from the control sites. Therefore, dusts emitted from e-waste recycling may be characterized by high Sb/As ratios, which may help identify the contamination due to the e-waste recycling activities. Copyright © 2011 Elsevier B.V. All rights reserved.

Interfacial structure, bonding and composition of InAs and GaSb thin films determined using coherent Bragg rod analysis.

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

Cionca, C.; Walko, D. A.; Yacoby, Y.

2007-01-01

We have used Bragg rod x-ray diffraction combined with a direct method of phase retrieval to extract atomic resolution electron-density maps of a complementary series of heteroepitaxial III-V semiconductor samples. From the three-dimensional electron-density maps we derive the monolayer spacings, the chemical compositions, and the characteristics of the bonding for all atomic planes in the film and across the film-substrate interface. InAs films grown on GaSb(001) under two different As conditions (using dimer or tetramer forms) both showed conformal roughness and mixed GaAs/InSb interfacial bonding character. The As tetramer conditions favored InSb bonding at the interface while, in the casemore » of the dimer, the percentages corresponding to GaAs and InSb bonding were equal within the experimental error. The GaSb film grown on InAs(001) displayed significant In and As interdiffusion and had a relatively large fraction of GaAs-like bonds at the interface.« less

Thermoelectric Properties of Cu-doped Bi2-xSbxTe3 Prepared by Encapsulated Melting and Hot Pressing

NASA Astrophysics Data System (ADS)

Jung, Woo-Jin; Kim, Il-Ho

2018-03-01

P-type Bi2-xSbxTe3:Cum (x = 1.5-1.7 and m = 0.002-0.003) solid solutions were synthesized using encapsulated melting and were consolidated using hot pressing. The effects of Sb substitution and Cu doping on the charge transport and thermoelectric properties were examined. The lattice constants decreased with increasing Sb and Cu contents. As the amount of Sb substitution and Cu doping was increased, the electrical conductivity increased, and the Seebeck coefficient decreased owing to the increase in the carrier concentration. All specimens exhibited degenerate semiconductor characteristics and positive Hall and Seebeck coefficients, indicating p-type conduction. The increased Sb substitution caused a shift in the onset temperature of the intrinsic transition and bipolar conduction to higher temperatures. The electronic thermal conductivity increased with increasing Sb and Cu contents owing to the increase in the carrier concentration, while the lattice thermal conductivity slightly decreased due to alloy scattering. A maximum figure of merit, ZTmax = 1.25, was achieved at 373 K for Bi0.4Sb1.6Te3:Cu0.003.

Cross-section imaging and p-type doping assessment of ZnO/ZnO:Sb core-shell nanowires by scanning capacitance microscopy and scanning spreading resistance microscopy

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

Wang, Lin, E-mail: lin.wang@insa-lyon.fr; Brémond, Georges; Sallet, Vincent

2016-08-29

ZnO/ZnO:Sb core-shell structured nanowires (NWs) were grown by the metal organic chemical vapor deposition method where the shell was doped with antimony (Sb) in an attempt to achieve ZnO p-type conduction. To directly investigate the Sb doping effect in ZnO, scanning capacitance microscopy (SCM) and scanning spreading resistance microscopy (SSRM) were performed on the NWs' cross-sections mapping their two dimensional (2D) local electrical properties. Although no direct p-type inversion in ZnO was revealed, a lower net electron concentration was pointed out for the Sb-doped ZnO shell layer with respect to the non-intentionally doped ZnO core, indicating an evident compensating effectmore » as a result of the Sb incorporation, which can be ascribed to the formation of Sb-related acceptors. The results demonstrate SCM/SSRM investigation being a direct and effective approach for characterizing radial semiconductor one-dimensional (1D) structures and, particularly, for the doping study on the ZnO nanomaterial towards its p-type realization.« less

Room temperature-synthesized vertically aligned InSb nanowires: electrical transport and field emission characteristics

PubMed Central

2013-01-01

Vertically aligned single-crystal InSb nanowires were synthesized via the electrochemical method at room temperature. The characteristics of Fourier transform infrared spectrum revealed that in the syntheses of InSb nanowires, energy bandgap shifts towards the short wavelength with the occurrence of an electron accumulation layer. The current–voltage curve, based on the metal–semiconductor–metal model, showed a high electron carrier concentration of 2.0 × 1017 cm−3 and a high electron mobility of 446.42 cm2 V−1 s−1. Additionally, the high carrier concentration of the InSb semiconductor with the surface accumulation layer induced a downward band bending effect that reduces the electron tunneling barrier. Consequently, the InSb nanowires exhibit significant field emission properties with an extremely low turn-on field of 1.84 V μm−1 and an estimative threshold field of 3.36 V μm−1. PMID:23399075

Band Structure Engineering and Thermoelectric Properties of Charge-Compensated Filled Skutterudites

PubMed Central

Shi, Xiaoya; Yang, Jiong; Wu, Lijun; Salvador, James R.; Zhang, Cheng; Villaire, William L.; Haddad, Daad; Yang, Jihui; Zhu, Yimei; Li, Qiang

2015-01-01

Thermoelectric properties of semiconductors are intimately related to their electronic band structure, which can be engineered via chemical doping. Dopant Ga in the cage-structured skutterudite Co4Sb12 substitutes Sb sites while occupying the void sites. Combining quantitative scanning transmission electron microscopy and first-principles calculations, we show that Ga dual-site occupancy breaks the symmetry of the Sb-Sb network, splits the deep triply-degenerate conduction bands, and drives them downward to the band edge. The charge-compensating nature of the dual occupancy Ga increases overall filling fraction limit. By imparting this unique band structure feature, and judiciously doping the materials by increasing the Yb content, we promote the Fermi level to a point where carriers are in energetic proximity to these features. Increased participation of these heavier bands in electronic transport leads to increased thermopower and effective mass. Further, the localized distortion from Ga/Sb substitution enhances the phonon scattering to reduce the thermal conductivity effectively. PMID:26456013

Band structure engineering and thermoelectric properties of charge-compensated filled skutterudites

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

Shi, Xiaoya; Yang, Jiong; Wu, Lijun

2015-10-12

Thermoelectric properties of semiconductors are intimately related to their electronic band structure, which can be engineered via chemical doping. Dopant Ga in the cage-structured skutterudite Co 4Sb 12 substitutes Sb sites while occupying the void sites. Combining quantitative scanning transmission electron microscopy and first-principles calculations, we show that Ga dual-site occupancy breaks the symmetry of the Sb-Sb network, splits the deep triply-degenerate conduction bands, and drives them downward to the band edge. The charge-compensating nature of the dual occupancy Ga increases overall filling fraction limit. By imparting this unique band structure feature, and judiciously doping the materials by increasing themore » Yb content, we promote the Fermi level to a point where carriers are in energetic proximity to these features. Increased participation of these heavier bands in electronic transport leads to increased thermopower and effective mass. Further, the localized distortion from Ga/Sb substitution enhances the phonon scattering to reduce the thermal conductivity effectively.« less

Band Structure Engineering and Thermoelectric Properties of Charge-Compensated Filled Skutterudites

NASA Astrophysics Data System (ADS)

Shi, Xiaoya; Yang, Jiong; Wu, Lijun; Salvador, James R.; Zhang, Cheng; Villaire, William L.; Haddad, Daad; Yang, Jihui; Zhu, Yimei; Li, Qiang

2015-10-01

Thermoelectric properties of semiconductors are intimately related to their electronic band structure, which can be engineered via chemical doping. Dopant Ga in the cage-structured skutterudite Co4Sb12 substitutes Sb sites while occupying the void sites. Combining quantitative scanning transmission electron microscopy and first-principles calculations, we show that Ga dual-site occupancy breaks the symmetry of the Sb-Sb network, splits the deep triply-degenerate conduction bands, and drives them downward to the band edge. The charge-compensating nature of the dual occupancy Ga increases overall filling fraction limit. By imparting this unique band structure feature, and judiciously doping the materials by increasing the Yb content, we promote the Fermi level to a point where carriers are in energetic proximity to these features. Increased participation of these heavier bands in electronic transport leads to increased thermopower and effective mass. Further, the localized distortion from Ga/Sb substitution enhances the phonon scattering to reduce the thermal conductivity effectively.

Terahertz plasmon-induced transparency based on asymmetric dual-disk resonators coupled to a semiconductor InSb waveguide and its biosensor application

NASA Astrophysics Data System (ADS)

Shahamat, Yadollah; Vahedi, Mohammad

2017-06-01

An ultracompact double eight-shaped plasmonic structure for the realization of plasmon-induced transparency (PIT) in the terahertz (THz) region has been studied. The device consists of a semiconductor-insulator-semiconductor bus waveguide coupled to the dual-disk resonators. Indium antimonide is employed to excite SPP in the THz region. The transmission characteristics of the proposed device are simulated numerically by the finite-difference time-domain method. In addition, a theoretical analysis based on the coupled-mode theory for transmission features is presented and compared with the numerical results. Results are in good agreement. Also, the dependence of PIT frequency characteristics on the radius of the outer disk is discussed in detail. In addition, by removing one of the outer disk resonators, double-PIT peaks can be observed in the transmission spectrum, and the physical mechanism of the appeared peaks is investigated. Finally, an application of the proposed structure for distinguishing different states of DNA molecules is discussed. Results show that the maximum sensitivity with 654 GHz/RIU-1 could be obtained for a single PIT structure. The frequency shifts equal to 37 and 99 GHz could be observed for the denatured and the hybridized DNA states, respectively.

Synthesis, crystal structures, and physical properties of the new Zintl phases A{sub 21}Zn{sub 4}Pn{sub 18} (A=Ca, Eu; Pn=As, Sb)—Versatile arrangements of [ZnPn{sub 4}] tetrahedra

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

Suen, Nian-Tzu; Wang, Yi; Bobev, Svilen, E-mail: bobev@udel.edu

Four new Zintl phases, Ca{sub 21}Zn{sub 4}As{sub 18}, Ca{sub 21}Zn{sub 4}Sb{sub 18}, Eu{sub 21}Zn{sub 4}As{sub 18} and Eu{sub 21}Zn{sub 4}Sb{sub 18} have been synthesized by metal flux reactions. Their structures have been established from single-crystal X-ray diffraction. Despite the similar chemical makeup and the identical formulae, the structures of the four compounds are not the same—Ca{sub 21}Zn{sub 4}As{sub 18}, Ca{sub 21}Zn{sub 4}Sb{sub 18} and Eu{sub 21}Zn{sub 4}As{sub 18} crystallize in the monoclinic space group C2/m (No. 12, Z=4) with the β-Ca{sub 21}Mn{sub 4}Sb{sub 18} structure type, while Eu{sub 21}Zn{sub 4}Sb{sub 18} adopts the Ba{sub 21}Cd{sub 4}Sb{sub 18} structure type withmore » the orthorhombic space group Cmce (No. 64, Z=8). Both structures are based on ZnAs{sub 4} or ZnSb{sub 4} tetrahedra, linked in slightly different ways, and Ca{sup 2+} and Eu{sup 2+} cations that fill the space between them. The structural relationships between the title compounds and other known ternary phases with intricate structures are discussed. Electrical resistivity measurement on single-crystalline Eu{sub 21}Zn{sub 4}Sb{sub 18} suggests an intrinsic semiconductor behavior with a band gap of ca. 0.2 eV. The temperature dependent DC magnetization measurement on the same material indicates Curie–Weiss paramagnetism in the high-temperature regime, and a spontaneous antiferromagnetic ordering below 8 K. The calculated effective moments of Eu confirm the divalent Eu{sup 2+} ground state, as expected from the Zintl–Klemm concept. - Graphical abstract: The four new Zintl phases—Ca{sub 21}Zn{sub 4}As{sub 18}, Ca{sub 21}Zn{sub 4}Sb{sub 18}, Eu{sub 21}Zn{sub 4}As{sub 18}, and Eu{sub 21}Zn{sub 4}Sb{sub 18}—crystallize in two structure types, showing the versatility in the arrangements of ZnAs{sub 4} and ZnSb{sub 4} tetrahedra. - Highlights: • Ca{sub 21}Zn{sub 4}As{sub 18}, Ca{sub 21}Zn{sub 4}Sb{sub 18}, Eu{sub 21}Zn{sub 4}As{sub 18}, and Eu{sub 21}Zn{sub 4}Sb{sub 18} are new compounds in the respective ternary phase diagrams. • They form with structure types, showing the versatility in the arrangements of ZnAs{sub 4} and ZnSb{sub 4} tetrahedra. • For both structures, the valence electron count follows the Zintl–Klemm rules.« less

Hole-dominated transport in InSb nanowires grown on high-quality InSb films

NASA Astrophysics Data System (ADS)

Algarni, Zaina; George, David; Singh, Abhay; Lin, Yuankun; Philipose, U.

2016-12-01

We have developed an effective strategy for synthesizing p-type indium antimonide (InSb) nanowires on a thin film of InSb grown on glass substrate. The InSb films were grown by a chemical reaction between S b 2 S 3 and I n and were characterized by structural, compositional, and optical studies. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) studies reveal that the surface of the substrate is covered with a polycrystalline InSb film comprised of sub-micron sized InSb islands. Energy dispersive X-ray (EDX) results show that the film is stoichiometric InSb. The optical constants of the InSb film, characterized using a variable-angle spectroscopic ellipsometer (VASE) shows a maximum value for refractive index at 3.7 near 1.8 eV, and the extinction coefficient (k) shows a maximum value 3.3 near 4.1 eV. InSb nanowires were subsequently grown on the InSb film with 20 nm sized Au nanoparticles functioning as the metal catalyst initiating nanowire growth. The InSb nanowires with diameters in the range of 40-60 nm exhibit good crystallinity and were found to be rich in Sb. High concentrations of anions in binary semiconductors are known to introduce acceptor levels within the band gap. This un-intentional doping of the InSb nanowire resulting in hole-dominated transport in the nanowires is demonstrated by the fabrication of a p-channel nanowire field effect transistor. The hole concentration and field effect mobility are estimated to be ≈1.3 × 1017 cm-3 and 1000 cm2 V-1 s-1, respectively, at room temperature, values that are particularly attractive for the technological implications of utilizing p-InSb nanowires in CMOS electronics.

A comprehensive study of g-factors, elastic, structural and electronic properties of III-V semiconductors using hybrid-density functional theory

NASA Astrophysics Data System (ADS)

Bastos, Carlos M. O.; Sabino, Fernando P.; Sipahi, Guilherme M.; Da Silva, Juarez L. F.

2018-02-01

Despite the large number of theoretical III-V semiconductor studies reported every year, our atomistic understanding is still limited. The limitations of the theoretical approaches to yield accurate structural and electronic properties on an equal footing, is due to the unphysical self-interaction problem that mainly affects the band gap and spin-orbit splitting (SOC) in semiconductors and, in particular, III-V systems with similar magnitude of the band gap and SOC. In this work, we report a consistent study of the structural and electronic properties of the III-V semiconductors by using the screening hybrid-density functional theory framework, by fitting the α parameters for 12 different III-V compounds, namely, AlN, AlP, AlAs, AlSb, GaN, GaP, GaAs, GaSb, InN, InP, InAs, and InSb, to minimize the deviation between the theoretical and experimental values of the band gap and SOC. Structural relaxation effects were also included. Except for AlP, whose α = 0.127, we obtained α values that ranged from 0.209 to 0.343, which deviate by less than 0.1 from the universal value of 0.25. Our results for the lattice parameter and elastic constants indicate that the fitting of α does not affect those structural parameters when compared with the HSE06 functional, where α = 0.25. Our analysis of the band structure based on the k ṡ p method shows that the effective masses are in agreement with the experimental values, which can be attributed to the simultaneous fitting of the band gap and SOC. Also, we estimate the values of g-factors, extracted directly from the band structure, which are close to experimental results, which indicate that the obtained band structure produced a realistic set of k ṡ p parameters.

Core-Level Photoemission Investigations of the CADMIUM-TELLURIDE(100) and INDIUM-ANTIMONY(100) Surface and Interfacial Structures.

NASA Astrophysics Data System (ADS)

John, Peter James

1988-12-01

Photoemission techniques, utilizing a synchrotron light source, were used to analyze the clean (100) surfaces of the zinc-blende semiconductor materials CdTe and InSb. Several interfacial systems involving the surfaces of these materials were also studied, including the CdTe(100)-Ag interface, the CdTe(100)-Sb system, and the InSb(100)-Sn interface. High -energy electron diffraction was also employed to acquire information about of surface structure. A one-domain (2x1) structure was observed for the CdTe(100) surface. Analysis of photoemission spectra of the Cd 4d core level for this surface structure revealed two components resulting from Cd surface atoms. The total intensity of these components accounts for a full monolayer of Cd atoms on the surface. A structural model is discussed commensurate with these results. Photoemission spectra of the Cd and Te 4d core levels indicate that Ag or Sb deposited on the CdTe(100)-(2x1) surface at room temperature do not bound strongly to the surface Cd atoms. The room temperature growth characteristics for these two elements on the CdTe(100)-(2x1) are discussed. The growth at elevated substrate temperatures was also studied for Sb deposition. The InSb(100) surface differed from the CdTe(100) surface. Using molecular beam epitaxy, several structures could be generated for the InSb(100) surface, including a c(8x2), a c(4x4), an asymmetric (1x3), a symmetric (1x3), and a (1x1). Analysis of photoemission intensities and line shapes indicates that the c(4x4) surface is terminated with 1{3 over 4} monolayers of Sb atoms. The c(8x2) surface is found to be terminated with {3over 4} monolayer of In atoms. Structural models for both of these surfaces are proposed based upon the photoemission results and upon models of the similar GaAs(100) structures. The room temperature growth characteristics of grey Sn on the InSb(100)-c(4x4) and InSb(100)-c(8x2) surfaces were studied with photoemission. The discontinuity in the valence band maximum for this semiconductor heterojunction system is measured to be 0.40 eV, independent of the starting surface structure and stoichiometry. This result is reconciled with theoretical predictions for heterostructure behavior.

GaSb thermophotovoltaic cells grown on GaAs by molecular beam epitaxy using interfacial misfit arrays

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

Juang, Bor-Chau, E-mail: bcjuang@ucla.edu; Laghumavarapu, Ramesh B.; Foggo, Brandon J.

There exists a long-term need for foreign substrates on which to grow GaSb-based optoelectronic devices. We address this need by using interfacial misfit arrays to grow GaSb-based thermophotovoltaic cells directly on GaAs (001) substrates and demonstrate promising performance. We compare these cells to control devices grown on GaSb substrates to assess device properties and material quality. The room temperature dark current densities show similar characteristics for both cells on GaAs and on GaSb. Under solar simulation the cells on GaAs exhibit an open-circuit voltage of 0.121 V and a short-circuit current density of 15.5 mA/cm{sup 2}. In addition, the cells on GaAsmore » substrates maintain 10% difference in spectral response to those of the control cells over a large range of wavelengths. While the cells on GaSb substrates in general offer better performance than the cells on GaAs substrates, the cost-savings and scalability offered by GaAs substrates could potentially outweigh the reduction in performance. By further optimizing GaSb buffer growth on GaAs substrates, Sb-based compound semiconductors grown on GaAs substrates with similar performance to devices grown directly on GaSb substrates could be realized.« less

Theoretical Prediction of an Antimony-Silicon Monolayer (penta-Sb2Si): Band Gap Engineering by Strain Effect

NASA Astrophysics Data System (ADS)

Morshedi, Hosein; Naseri, Mosayeb; Hantehzadeh, Mohammad Reza; Elahi, Seyed Mohammad

2018-04-01

In this paper, using a first principles calculation, a two-dimensional structure of silicon-antimony named penta-Sb2Si is predicted. The structural, kinetic, and thermal stabilities of the predicted monolayer are confirmed by the cohesive energy calculation, phonon dispersion analysis, and first principles molecular dynamic simulation, respectively. The electronic properties investigation shows that the pentagonal Sb2Si monolayer is a semiconductor with an indirect band gap of about 1.53 eV (2.1 eV) from GGA-PBE (PBE0 hybrid functional) calculations which can be effectively engineered by employing external biaxial compressive and tensile strain. Furthermore, the optical characteristics calculation indicates that the predicted monolayer has considerable optical absorption and reflectivity in the ultraviolet region. The results suggest that a Sb2Si monolayer has very good potential applications in new nano-optoelectronic devices.

Thermoelectric properties of Nb3SbxTe7-x compounds

NASA Technical Reports Server (NTRS)

Snyder, J.; Wang, S.; Caillat, T.

2002-01-01

Niobium antimony telluride, Nb3Sbx,Te7-x, was synthesized and tested for thermoelectric properties in the Thermoelectrics group at the Jet Propulsion Laboratory. The forty atoms per unit cell of Nb3Sb2Te5 and its varied mixture of atoms yield acomplicated structure, suggesting that Nb3Sb2Te5 and related compounds may exhibit low thermal conductivity and hence a higher ZT value. Nb3SbxTe7-x, compounds were synthesized and subsequently analyzed for their Seebeck voltage, heat conduction, and electrical resistivity. Results indicate that Nb3Sb2Te5 is a heavily doped semiconductor whose thermoelectric properties are compromised by compensating n-type and p-type carriers. Attempts to dope in favor of either carrier by varying the Sb:Te ratio yielded samples containing secondary metallic phases that dominated the transport properties of the resulting compounds.

Chalcogenide glass-ceramic with self-organized heterojunctions: application to photovoltaic solar cells

NASA Astrophysics Data System (ADS)

Zhang, Xianghua; Korolkov, Ilia; Fan, Bo; Cathelinaud, Michel; Ma, Hongli; Adam, Jean-Luc; Merdrignac, Odile; Calvez, Laurent; Lhermite, Hervé; Brizoual, Laurent Le; Pasquinelli, Marcel; Simon, Jean-Jacques

2018-03-01

In this work, we present for the first time the concept of chalcogenide glass-ceramic for photovoltaic applications with the GeSe2-Sb2Se3-CuI system. It has been demonstrated that thin films, deposited with the sputtering technique, are amorphous and can be crystallized with appropriate heat treatment. The thin film glass-ceramic behaves as a p-type semiconductor, even if it contains p-type Cu2GeSe3 and n-type Sb2Se3. The conductivity of Sb2Se3 has been greatly improved by appropriate iodine doping. The first photovoltaic solar cells based on the association of iodine-doped Sb2Se3 and the glass-ceramic thin films give a short-circuit current density JSC of 10 mA/cm2 and an open-circuit voltage VOC of 255 mV, with a power conversion efficiency of about 0.9%.

Behavior of GaSb (100) and InSb (100) surfaces in the presence of H2O2 in acidic and basic cleaning solutions

NASA Astrophysics Data System (ADS)

Seo, Dongwan; Na, Jihoon; Lee, Seunghyo; Lim, Sangwoo

2017-03-01

Gallium antimonide (GaSb) and indium antimonide (InSb) have attracted strong attention as new channel materials for transistors due to their excellent electrical properties and lattice matches with various group III-V compound semiconductors. In this study, the surface behavior of GaSb (100) and InSb (100) was investigated and compared in hydrochloric acid/hydrogen peroxide mixture (HPM) and ammonium hydroxide/hydrogen peroxide mixture (APM) solutions. In the acidic HPM solution, surface oxidation was greater and the etching rates of the GaSb and InSb surfaces increased when the solution is concentrated, which indicates that H2O2 plays a key role in the surface oxidation of GaSb and InSb in acidic HPM solution. However, the GaSb and InSb surfaces were hardly oxidized in basic APM solution in the presence of H2O2 because gallium and indium are in the thermodynamically stable forms of H2GaO3- and InO2-, respectively. When the APM solution was diluted, however, the Ga on the GaSb surface was oxidized by H2O, increasing the etching rate. However, the effect of dilution of the APM solution on the oxidation of the InSb surface was minimal; thus, the InSb surface was less oxidized than the GaSb surface and the change in the etching rate of InSb with dilution of the APM solution was not significant. Additionally, the oxidation behavior of gallium and indium was more sensitive to the composition of the HPM and APM solutions than that of antimony. Therefore, the surface properties and etching characteristics of GaSb and InSb in HPM and APM solutions are mainly dependent on the behavior of the group III elements rather than the group V elements.

First-principles calculations of nitrogen-doped antimony triselenide: A prospective material for solar cells and infrared optoelectronic devices

NASA Astrophysics Data System (ADS)

Sajid-ur-Rehman; Butt, Faheem K.; Li, Chuanbo; Ul Haq, Bakhtiar; Tariq, Zeeshan; Aleem, F.

2018-06-01

This study is focused on calculation of the electronic structure and optical properties of non-metal doped Sb2Se3 using the first-principles method. One and two N atoms are introduced to Sb and Se sites in a Sb2Se3 crystal. When one and two N atoms are introduced into the Sb2Se3 lattice at Sb sites, the electronic structure shows that the doping significantly modifies the bandgap of Sb2Se3 from 1.11 eV to 0.787 and 0.685 eV, respectively. When N atoms are introduced to Se sites, the material shows a metallic behavior. The static dielectric constants ɛ1(0) for Sb16Se24, Sb15N1Se24, Sb14N2Se24, Sb16Se23N1, and Sb16Se22N2 are 14.84, 15.54, 15.02, 18.9, and 39.29, respectively. The calculated values of the refractive index n(0) for Sb16Se24, Sb15N1Se24, Sb14N2Se24, Sb16Se23N1, and Sb16Se22N2 are 3.83, 3.92, 3.86, 4.33, and 6.21, respectively. The optical absorbance and optical conductivity curves of the crystal for N-doping at Sb sites show a significant redshift towards the short-wave infrared spectral region as compared to N-doping at Se sites. The modulation of the static refractive index and static dielectric constant is mainly dependent on the doping level. The optical properties and bandgap narrowing effect suggest that the N-doped Sb2Se3is a promising new semiconductor and can be a replacement for GaSb due to its very similar bandgap and low cost.

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES: Switching Characteristics of Phase Change Memory Cell Integrated with Metal-Oxide Semiconductor Field Effect Transistor

NASA Astrophysics Data System (ADS)

Xu, Cheng; Liu, Bo; Chen, Yi-Feng; Liang, Shuang; Song, Zhi-Tang; Feng, Song-Lin; Wan, Xu-Dong; Yang, Zuo-Ya; Xie, Joseph; Chen, Bomy

2008-05-01

A Ge2Sb2Te5 based phase change memory device cell integrated with metal-oxide semiconductor field effect transistor (MOSFET) is fabricated using standard 0. 18 μm complementary metal-oxide semiconductor process technology. It shows steady switching characteristics in the dc current-voltage measurement. The phase changing phenomenon from crystalline state to amorphous state with a voltage pulse altitude of 2.0 V and pulse width of 50 ns is also obtained. These results show the feasibility of integrating phase change memory cell with MOSFET.

Thermodynamic properties of semiconductor compounds studied based on Debye-Waller factors

NASA Astrophysics Data System (ADS)

Van Hung, Nguyen; Toan, Nguyen Cong; Ba Duc, Nguyen; Vuong, Dinh Quoc

2015-08-01

Thermodynamic properties of semiconductor compounds have been studied based on Debye-Waller factors (DWFs) described by the mean square displacement (MSD) which has close relation with the mean square relative displacement (MSRD). Their analytical expressions have been derived based on the statistical moment method (SMM) and the empirical many-body Stillinger-Weber potentials. Numerical results for the MSDs of GaAs, GaP, InP, InSb, which have zinc-blende structure, are found to be in reasonable agreement with experiment and other theories. This paper shows that an elements value for MSD is dependent on the binary semiconductor compound within which it resides.

Study on electrical properties of metal/GaSb junctions using metal-GaSb alloys

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

Nishi, Koichi, E-mail: nishi@mosfet.t.u-tokyo.ac.jp; Yokoyama, Masafumi; Kim, Sanghyeon

2014-01-21

We study the metal-GaSb alloy formation, the structural properties and the electrical characteristics of the metal-alloy/GaSb diodes by employing metal materials such as Ni, Pd, Co, Ti, Al, and Ta, in order to clarify metals suitable for GaSb p-channel metal-oxide-semiconductor field-effect transistors (pMOSFETs) as metal-GaSb alloy source/drain (S/D). It is found that Ni, Pd, Co, and Ti can form alloy with GaSb by rapid thermal annealing at 250, 250, 350, and 450 °C, respectively. The Ni-GaSb and Pd-GaSb alloy formation temperature of 250 °C is lower than the conventional dopant activation annealing for ion implantation, which enable us to lower the processmore » temperature. The alloy layers show lower sheet resistance (R{sub Sheet}) than that of p{sup +}-GaSb layer formed by ion implantation and activation annealing. We also study the electrical characteristics of the metal-alloy/GaSb junctions. The alloy/n-GaSb contact has large Schottky barrier height (ϕ{sub B}) for electrons, ∼0.6 eV, and low ϕ{sub B} for holes, ∼0.2 eV, which enable us to realize high on/off ratio in pMOSFETs. We have found that the Ni-GaSb/GaSb Schottky junction shows the best electrical characteristics with ideal factor (n) of 1.1 and on-current/off-current ratio (I{sub on}/I{sub off}) of ∼10{sup 4} among the metal-GaSb alloy/GaSb junctions evaluated in the present study. These electrical properties are also superior to those of a p{sup +}-n diode fabricated by Be ion implantation with activation annealing at 350 °C. As a result, the Ni-GaSb alloy can be regarded as one of the best materials to realize metal S/D in GaSb pMOSFETs.« less

Semiconducting Ba 3Sn 3Sb 4 and Metallic Ba 7–xSn 11Sb 15–y ( x = 0.4, y = 0.6) Zintl Phases

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

Chen, Haijie; Narayan, Awadhesh; Stoumpos, Constantinos C.

In this paper, we report the discovery of two ternary Zintl phases Ba 3Sn 3Sb 4 and Ba 7-xSn 11Sb 15-y, (x = 0.4, y = 0.6). Ba 3Sn 3Sb 4 adopts the monoclinic space group P2 1/c with a = 14.669(3) Å, b = 6.9649(14) Å, c = 13.629(3) Å, and β = 104.98(3)°. It features a unique corrugated two-dimensional (2D) structure consisting of [Sn 3Sb 4] 6- layers extending along the ab plane with Ba 2+ atoms sandwiched between them. The non-stoichiometric Ba 6.6Sn 11Sb 14.4 has a complex one-dimensional (1D) structure adopting the orthorhombic space group Pnma,more » with unit cell parameters a = 37.964(8) Å, b = 4.4090(9) Å and c = 24.682(5) Å. It consists of large double Sn-Sb ribbons separated by Ba 2+ atoms. Ba3Sn3Sb4 is an n-type semiconductor which has a narrow energy gap of ~0.18 eV and a room temperature carrier concentration of ~4.2 × 10 18 cm -3. Lastly, Ba 6.6Sn 11Sb 14.4 is determined to be a metal with electrons being the dominant carriers.« less

Semiconducting Ba 3Sn 3Sb 4 and Metallic Ba 7–xSn 11Sb 15–y ( x = 0.4, y = 0.6) Zintl Phases

DOE PAGES

Chen, Haijie; Narayan, Awadhesh; Stoumpos, Constantinos C.; ...

2017-11-08

In this paper, we report the discovery of two ternary Zintl phases Ba 3Sn 3Sb 4 and Ba 7-xSn 11Sb 15-y, (x = 0.4, y = 0.6). Ba 3Sn 3Sb 4 adopts the monoclinic space group P2 1/c with a = 14.669(3) Å, b = 6.9649(14) Å, c = 13.629(3) Å, and β = 104.98(3)°. It features a unique corrugated two-dimensional (2D) structure consisting of [Sn 3Sb 4] 6- layers extending along the ab plane with Ba 2+ atoms sandwiched between them. The non-stoichiometric Ba 6.6Sn 11Sb 14.4 has a complex one-dimensional (1D) structure adopting the orthorhombic space group Pnma,more » with unit cell parameters a = 37.964(8) Å, b = 4.4090(9) Å and c = 24.682(5) Å. It consists of large double Sn-Sb ribbons separated by Ba 2+ atoms. Ba3Sn3Sb4 is an n-type semiconductor which has a narrow energy gap of ~0.18 eV and a room temperature carrier concentration of ~4.2 × 10 18 cm -3. Lastly, Ba 6.6Sn 11Sb 14.4 is determined to be a metal with electrons being the dominant carriers.« less

Collaborative Research and Development (CR&D). Delivery Order 0051: Atomic Scale Transmission Electron Microscope Image Modeling and Application to Semiconductor Heterointerface Characterization

DTIC Science & Technology

2008-01-01

information if it does not display a currently valid OMB control number. PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. 1. REPORT DATE (DD...microscopy ( AEM ), to characterize a variety of III-V semiconductor thin films. The materials investigated include superlattices based on the InAs- GaSb...technique. TEM observations were performed using a Philips-CM 200 FEG transmission electron microscope equipped with a field emission gun, operated at an

Enhancing Hole Mobility in III-V Semiconductors

DTIC Science & Technology

2012-05-21

acteristics of the digital superlattice (n¼1,0, andþ 1) that was used in the metamorphic buffer. The GaSb channel peak gets buried in the n¼ 0...materials have been used for a variety of analog and high frequency applications driven by the high electron mobilities in III-V materials. On the other...hand, the hole mobility in III-V materials has always lagged compared to group-IV semiconductors such as germanium. In this paper, we explore the use

INTERNATIONAL CONFERENCE ON SEMICONDUCTOR INJECTION LASERS SELCO-87: Injection lasers based on the AlGaAsSb system emitting at 1.6 μm

NASA Astrophysics Data System (ADS)

Virro, A. L.; Eliseev, P. G.; Lyuk, P. A.; Fridental, Ya K.; Khaller, Yu E.

1988-11-01

An experimental dependence of the threshold current density jth on the thickness of the active region was used to find the reduced threshold current density for AlGaAsSb (λ = 1.59μm, T = 295K) lasers: this density was 8 kA·cm-2·μm-1. The minimum threshold current was jth = 1.8 kA/cm2. Wide-contact lasers exhibited cw operation down to 175 K.

Study of the solid-state amorphization of (GaSb){sub 1-x}Ge{sub x} semiconductors by real-time neutron diffraction and electron microscopy

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

Fedotov, V. K., E-mail: fedotov@issp.ac.ru; Ponyatovsky, E. G.

2011-12-15

The spontaneous amorphization of high-pressure quenched phases of the GaSb-Ge system has been studied by neutron diffraction while slowly heating the phases at atmospheric pressure. The sequence of changes in the structural parameters of the initial crystalline phase and the final amorphous phase is established. The behavior of the phases and the correlation in the structural features of the phase transitions and anomalous thermal effects exhibit signs of the inhomogeneous model of solid-state amorphization.

Long wavelength, high gain InAsSb strained-layer superlattice photoconductive detectors

DOEpatents

Biefeld, Robert M.; Dawson, L. Ralph; Fritz, Ian J.; Kurtz, Steven R.; Zipperian, Thomas E.

1991-01-01

A high gain photoconductive device for 8 to 12 .mu.m wavelength radiation including an active semiconductor region extending from a substrate to an exposed face, the region comprising a strained-layer superlattice of alternating layers of two different InAs.sub.1-x Sb.sub.x compounds having x>0.75. A pair of spaced electrodes are provided on the exposed face, and changes in 8 to 12 .mu.m radiation on the exposed face cause a large photoconductive gain between the spaced electrodes.

Excited-state thermionic emission in III-antimonides: Low emittance ultrafast photocathodes

NASA Astrophysics Data System (ADS)

Berger, Joel A.; Rickman, B. L.; Li, T.; Nicholls, A. W.; Andreas Schroeder, W.

2012-11-01

The normalized rms transverse emittance of an electron source is shown to be proportional to √m* , where m* is the effective mass of the state from which the electron is emitted, by direct observation of the transverse momentum distribution for excited-state thermionic emission from two III-V semiconductor photocathodes, GaSb and InSb, together with a control experiment employing two-photon emission from gold. Simulations of the experiment using an extended analytical Gaussian model of electron pulse propagation are in close agreement with the data.

Lower lattice thermal conductivity in SbAs than As or Sb monolayers: a first-principles study.

PubMed

Guo, San-Dong; Liu, Jiang-Tao

2017-12-06

Phonon transport in group-VA element (As, Sb and Bi) monolayer semiconductors has been widely investigated in theory, and, of them, monolayer Sb (antimonene) has recently been synthesized. In this work, phonon transport in monolayer SbAs is investigated with a combination of first-principles calculations and the linearized phonon Boltzmann equation. It is found that the lattice thermal conductivity of monolayer SbAs is lower than those of both monolayer As and Sb, and the corresponding sheet thermal conductance is 28.8 W K -1 at room temperature. To understand the lower lattice thermal conductivity in monolayer SbAs than those in monolayer As and Sb, the group velocities and phonon lifetimes of monolayer As, SbAs and Sb are calculated. The calculated results show that the group velocities of monolayer SbAs are between those of monolayer As and Sb, but that the phonon lifetimes of SbAs are smaller than those of both monolayer As and Sb. Hence, the low lattice thermal conductivity in monolayer SbAs is attributed to very small phonon lifetimes. Unexpectedly, the ZA branch has very little contribution to the total thermal conductivity, only 2.4%, which is obviously different from those of monolayer As and Sb with very large contributions. This can be explained by very small phonon lifetimes for the ZA branch of monolayer SbAs. The lower lattice thermal conductivity of monolayer SbAs compared to that of monolayer As or Sb can be understood by the alloying of As (Sb) with Sb (As), which should introduce phonon point defect scattering. We also consider the isotope and size effects on the lattice thermal conductivity. It is found that isotope scattering produces a neglectful effect, and the lattice thermal conductivity with a characteristic length smaller than 30 nm can reach a decrease of about 47%. These results may offer perspectives on tuning the lattice thermal conductivity by the mixture of multiple elements for applications of thermal management and thermoelectricity, and motivate further experimental efforts to synthesize monolayer SbAs.

Semiconductor apparatus utilizing gradient freeze and liquid-solid techniques

NASA Technical Reports Server (NTRS)

Fleurial, Jean-Pierre (Inventor); Caillat, Thierry F. (Inventor); Borshchevsky, Alexander (Inventor)

1998-01-01

Transition metals of Group VIII (Co, Rh and Ir) have been prepared as semiconductor compounds with the general formula TSb.sub.3. The skutterudite-type crystal lattice structure of these semiconductor compounds and their enhanced thermoelectric properties results in semiconductor materials which may be used in the fabrication of thermoelectric elements to substantially improve the efficiency of the resulting thermoelectric device. Semiconductor materials having the desired skutterudite-type crystal lattice structure may be prepared in accordance with the present invention by using vertical gradient freezing techniques and/or liquid phase sintering techniques. Measurements of electrical and thermal transport properties of selected semiconductor materials prepared in accordance with the present invention, demonstrated high Hall mobilities (up to 1200 cm.sup.2.V.sup.-1.s.sup.-1) and good Seebeck coefficients (up to 150 .mu.VK.sup.-1 between 300.degree. C. and 700.degree. C.). Optimizing the transport properties of semiconductor materials prepared from elemental mixtures Co, Rh, Ir and Sb resulted in a substantial increase in the thermoelectric figure of merit (ZT) at temperatures as high as 400.degree. C. for thermoelectric elements fabricated from such semiconductor materials.

Improved half-metallic gap of zincblende half-metal superlattices with the Tran-Blaha modified Becke-Johnson density functional

NASA Astrophysics Data System (ADS)

Guo, San-Dong

2016-08-01

Binary transition-metal pnictides and chalcogenides half-metallic ferromagnetic materials with zincblende structure, being compatible with current semiconductor technology, can be used to make high-performance spintronic devices. Here, we investigate electronic structures and magnetic properties of composite structure ((CrX)2 /(YX)2 (X=As, Sb; Se, Te and Y=Ga; Zn) superlattices) of zincblende half-metallic ferromagnetism and semiconductor by using Tran and Blaha's modified Becke and Johnson (mBJ) exchange potential. Calculated results show that they all are half-metallic ferromagnets with both generalized gradient approximation (GGA) and mBJ, and the total magnetic moment per formula unit follows a Slater-Pauling-like "rule of 8". The key half-metallic gaps by using mBJ are enhanced with respect to GGA results, which is because mBJ makes the occupied minority-spin p-bands move toward lower energy, but toward higher energy for empty minority-spin Cr-d bands. When the spin-orbit coupling (SOC) is included, the spin polarization deviates from 100%, and a most reduced polarization of 98.3% for (CrSb)2 /(GaSb)2, which indicates that SOC has small effects, of the order of 1%, in the considered four kinds of superlattice.

High-pressure phase transition and elastic behavior of aluminum compound semiconductors

NASA Astrophysics Data System (ADS)

Singh, R. K.; Singh, Sadhna

1992-01-01

A three-body-force-potential approach, developed earlier [Phys. Rev. B 39, 671 (1989)] for III-V compound semiconductors, has been extended to describe the high-pressure phase transition and elastic behavior of the remaining members (AlAs, AlSb, and AlP) of this family. We have obtained a reasonably better agreement between our theoretical (10.2, 6.6, and 18.0 GPa) and experimental (12.0, 8.3, and 14.0-17.0 GPa) results on the phase-transition pressures, respectively, in Al compounds (AlAs, AlSb, and AlP) than those obtained by Chelikowsky (31.0, 10.2, and 45.0 GPa) and by Zhang and Cohen (7.6, 5.6, and 9.3 GPa). The volume collapses and transition heats are also in good agreement with their experimental results available only in AlSb and they are comparable to those obtained by earlier workers. The variations of the second-order elastic constants with pressure have shown systematic trends in all Al compounds similar to those observed in other compounds of zinc-blende structure. The present approach has also succeeded in predicting the relative stability and satisfying the Born stability criterion. The slight disagreements have been ascribed to the exclusion of covalency effects.

Preparation and Thermoelectric Properties of the Skutterudite-Related Phase Ru(0.5)Pd(0.5)Sb3

NASA Technical Reports Server (NTRS)

Caillat, T.; Kulleck, J.; Borshchevsky, A.; Fleurial, J.-P.

1996-01-01

A new skutterudite phase Ru(0.5)Pd(0.5)Sb3 was prepared. This new phase adds to a large number of already known materials with the skutterudite structure which have shown good potential for thermoelectric applications. Single phase, polycrystalline samples were prepared and characterized by x-ray analysis, electron probe microanalysis, density, sound velocity, thermal-expansion coefficient, and differential thermal analysis measurements. Ru(0.5)Pd(0.5)Sb3 has a cubic lattice, space group Im3 (T(sup 5, sub h)), with a = 9.298 A and decomposes at about 920 K. The Seebeck coefficient, the electrical resistivity, the Hall effect, and the thermal conductivity were measured on hot-pressed samples over a wide range of temperatures. Preliminary results show that Ru(0.5)Pd(0.5)Sb3 behaves as a heavily doped semiconductor with an estimated band gap of about 0.6 eV. The lattice thermal conductivity of Ru(0.5)Pd(0.5)Sb3 is substantially lower than that of the binary isostructural compounds CoSb3 and IrSb3. The unusually low thermal conductivity might be explained by additional hole and charge transfer phonon scattering in this material. The potential of this material for thermoelectric applications is discussed.

Influence of Composition on the Thermoelectric Properties of Bi1- x Sb x Thin Films

NASA Astrophysics Data System (ADS)

Rogacheva, E. I.; Nashchekina, O. N.; Orlova, D. S.; Doroshenko, A. N.; Dresselhaus, M. S.

2017-07-01

Bi1- x Sb x solid solutions have attracted much attention as promising thermoelectric (TE) materials for cooling devices at temperatures below ˜200 K and as unique model materials for solid-state science because of a high sensitivity of their band structure to changes in composition, temperature, pressure, etc. Earlier, we revealed a non-monotonic behavior of the concentration dependences of TE properties for polycrystalline Bi1- x Sb x solid solutions and attributed these anomalies to percolation effects in the solid solution, transition to a gapless state, and to a semimetal-semiconductor transition. The goal of the present work is to find out whether the non-monotonic behavior of the concentration dependences of TE properties is observed in the thin film state as well. The objects of the study are Bi1- x Sb x thin films with thicknesses in the range d = 250-300 nm prepared by thermal evaporation of Bi1- x Sb x crystals ( x = 0-0.09) onto mica substrates. It was shown that the anomalies in the dependence of the TE properties on Bi1- x Sb x crystal composition are reproduced in thin films.

ThE SYnthesis of R z Fe4- x Co x Sb12 (R: Yb, La, Ce) skutterudites and their thermoelectric properties

NASA Astrophysics Data System (ADS)

Park, Kwan-Ho; Lee, Soonil; Seo, Won-Seon; Shin, Dong-Kil; Kim, Il-Ho

2014-03-01

Rare-earth-filled skutterudites R z Fe4- x Co x Sb12 (R: Yb, La, Ce) were prepared, and their transport and thermoelectric properties were examined. All specimens showed p-type conduction and exhibited a degenerate semiconductor behavior. R0.9Fe3CoSb12 had lower electrical conductivities and higher Seebeck coefficients than RFe4Sb12, which meant that Co led to charge compensation through electron donations. All specimens had positive Hall coefficients, and their carrier concentrations were decreased by charge compensation with increasing Co substitution. The thermal conductivities of R0.9Fe3CoSb12 were lower than those of RFe4Sb12 due to the decreased carrier concentration, as well as the lattice scattering induced by the substitution of Co for Fe. Yb-filled and La-filled skutterudites showed enhanced thermoelectric figures of merit through charge compensation with Co, but Ce-filled skutterudites did not. Yb2˜3+ and La3+ ions required charge compensation to stabilize their skutterudite phases, but Ce3˜4+ ions did not.

Composition dependence of band alignments in GaxIn1-xAsySb1-y heterojunctions lattice matched to GaSb and InAs

NASA Astrophysics Data System (ADS)

Shim, Kyurhee

2013-11-01

A theoretical model utilizing a universal tight binding method and a correlated function expansion technique is presented to calculate the valence band maximum (VBM) and the conduction band minimum (CBM) of the binary (GaAs, InAS, GaSb, and InSb) and quaternary alloy GaxIn1-xAsySb1-y systems. By organizing the relative positions of the VBM and CBM between semiconductors, the band alignments and band types in the heterojunctions are determined. A straddling (type-I) band alignment in InAs/GaAs, InSb/GaAs, and GaSb/InSb, staggered (type-II) band alignment in GaSb/GaAs, and broken (type-III) band alignment in InSb/InAs and InAs/GaSb are found respectively. In addition, the compositional variations of VBM, CBM, valence band offset, conduction band offset, and band type for the alloy GaxIn1-xAsySb1-y lattice matched on GaSb and InAs are obtained as increasing the composition x. A pronounced upward bowing for the VBM and a very slight upward bowing (almost linear) for CBM are found, respectively. By controlling the compositions (x, y), band type transitions occur. The GaxIn1-xAsySb1-y heterojunctions lattice matched to GaSb changes their band types from type-III at x ˜0→ to type-II at x = 0.07, and → to type-I at x = 0.38. In contrast, the GaxIn1-xAsySb1-y heterojunctions lattice matched to InAs changes their band types from type-II x ˜0→ to type-III at x = 0.32. Reasonable agreement is obtained between our theoretical results and existing experimental data.

Comparison of accelerometer-measured sedentary behavior, and light- and moderate-to-vigorous-intensity physical activity in white- and blue-collar workers in a Japanese manufacturing plant.

PubMed

Fukushima, Noritoshi; Kitabayashi, Makiko; Kikuchi, Hiroyuki; Sasai, Hiroyuki; Oka, Koichiro; Nakata, Yoshio; Tanaka, Shigeho; Inoue, Shigeru

2018-05-25

The times spent in sedentary behavior (SB) and moderate-to-vigorous physical activity (MVPA) are independently associated with health outcomes; however, objective data on physical activity levels including SB among different occupations is limited. We compared accelerometer-measured times spent in SB, light-intensity physical activity (LPA), and MVPA, and the patterns associated with prolonged bouts of SB between white- and blue-collar workers. The study population consisted of 102 full-time plant workers (54 white-collar and 48 blue-collar) who wore a triaxial accelerometer during waking hours for 5 working days. Accelerometer-measured activity levels were categorized as SB (≤1.5 metabolic equivalents (METs)), LPA (1.6-2.9 METs), and MVPA (≥3.0 METs). A sedentary bout was defined as consecutive minutes during which the accelerometer registered less than ≤1.5 METs. Accelerometer variables were compared between white- and blue-collar workers through analysis of covariance. During working hours, white-collar workers spent significantly more time in SB and less time in LPA than blue-collar workers (SB: 6.4 h vs. 4.8 h, 73% vs. 55% of total work time; LPA: 1.9 h vs. 3.5 h, 22% vs. 40% of total work time, p<.001), whereas the MVPA time was similar between the groups. White-collar workers spent significantly more SB time in prolonged sedentary bouts (≥30 min) compared to blue-collar workers. During leisure time, the SB, LPA, and MVPA times were similar between the groups. White-collar workers have significantly longer SB times than blue-collar workers during work hours, and do not compensate for their excess SB during work by reducing SB during leisure time.

Preface: phys. stat. sol. (a) 202/7

NASA Astrophysics Data System (ADS)

Pollak, Fred H.; Misiewicz, Jan; Sitarek, Piotr

2005-05-01

We have recently observed a growing interest in using the powerful technique of optical modulation spectroscopy. These applications are related mostly to the characterization of low dimensional semiconductor structures and devices based on them.The International Workshop on Modulation Spectroscopy of Semiconductor Structures (MS3) at the beginning of July 2004 gathered in Wrocaw (in the southwest part of Poland) almost 40 participants, half of them from abroad. The 8 invited and 16 contributed talks were presented by the leaders of research teams from the USA, Japan, Taiwan, Canada, Germany, France, the Netherlands, Sweden, Ireland, Russia, Lithuania and Poland. Part of the MS3 workshop was held at the Laboratory of Advanced Optical Spectroscopy, Institute of Physics, Wrocaw University of Technology, where discussions on technical matter of the modulation spectroscopy were carried out in a relaxing atmosphere over a cup of coffee.The topics of the MS3 workshop included: advantages of photoreflectance, electroreflectance, contactless electroreflectance, thermoreflectance, differential reflectance and wavelength-modulated surface photovoltage spectroscopy. The applications of the above methods to investigate transistor, diode and laser structures including VCSELs, low dimensional structures of both wings of the spectrum, i.e. wide band gap materials like GaN, AlGaN, ZnO and low band gap materials such as GaInN(Sb)As, InAs, InSb, and FeSi2 were demonstrated.It is our great pleasure to publish the most interesting of the MS3 workshop presentations in this issue of physica status solidi (a).The organizers acknowledge Wrocaw University of Technology, the Center of Exellence CEPHONA from the Institute of Electron Technology in Warsaw and the Polish Committee for Scientific Research for financial support of the workshop.

Modulational instability of helicon waves in a magnetoactive semiconductor n-InSb

NASA Astrophysics Data System (ADS)

Salimullah, M.; Ferdous, T.

1984-03-01

In this paper the modulational instabilithy of a beam of high amplitude helicon wave in a magnetoactive piezoelectric semiconductor is studied. The nonlinear response of electrons in the semiconductor plasma has been found by following the fluid model of homogeneous plasmas. The low frequency nonlinearity has been taken through the ponderomotive force on electrons, whereas the nonlinearity in the scattered helicon waves arises through the nonlinear current densities of electrons. For typical plasma parameters in n-type indium antimonide and for a considerable power density (approximately 20 kW/sq cm) of the incident helicon beam, the growth rate of the modulational instability is quite high (approximately 10 to the 7th rad/s).

Plasmonic-Electronic Transduction

DTIC Science & Technology

2012-01-31

including metal silicides (Pt-, Pd-, Ni-, W- silicides ), semimetals (Sb, Bi, graphite), doped-semiconductors (Si, CuInSe), and conducting polymers... silicides and doped silicon,” J. W. Cleary, R. E. Peale, D. J. Shelton, G. D. Boreman, C. W. Smith, M. Ishigami, R. Soref, A. Drehman, W.R. Buchwald

Circularly polarized electroluminescence of light-emitting InGaAs/GaAs (III, Mn)V diodes on the basis of structures with a tunneling barrier

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

Malysheva, E. I., E-mail: malysheva@phys.unn.ru; Dorokhin, M. V.; Ved’, M. V.

2015-11-15

The comparative investigation of circularly polarized electroluminescence in Zener diodes based on InGaAs/n-GaAs/n{sup +}-GaAs/GaMnAs and InGaAs/n-GaAs/n{sup +}-GaAs/GaMnSb is carried out. It is established that the circularly polarized electroluminescence is associated with the spin injection of electrons from a ferromagnetic semiconductor layer. The luminescence parameters are determined by the properties of these layers. It is shown that the ferromagnetic properties of the GaMnSb layer allow us to obtain circularly polarized emission at room temperature from InGaAs/n-GaAs/n{sup +}-GaAs/GaMnSb heterostructures.

First-Principles Study of Structural, Electronic, Optical, and Thermal Properties of BeSiSb2 and MgSiSb2

NASA Astrophysics Data System (ADS)

Benlamari, S.; Boukhtouta, M.; Taïri, L.; Meradji, H.; Amirouche, L.; Ghemid, S.

2018-03-01

Structural, electronic, optical, and thermal properties of ternary II-IV-V2 (BeSiSb2 and MgSiSb2) chalcopyrite semiconductors have been calculated using the full-potential linearized augmented plane wave scheme␣in the generalized gradient approximation. The optimized equilibrium structural parameters ( a, c, and u) are in good agreement with theoretical results obtained using other methods. The band structure and density of states reveal that BeSiSb2 has an indirect (Γ-Z) bandgap of about 0.61 eV, whereas MgSiSb2 has a direct (Γ-Γ) bandgap of 0.80 eV. The dielectric function, refractive index, and extinction coefficient were calculated to investigate the optical properties, revealing that BeSiSb2 and MgSiSb2 present very weak birefringence. The temperature dependence of the volume, bulk modulus, Debye temperature, and heat capacities ( C v and C p) was predicted using the quasiharmonic Debye model at different pressures. Significant differences in properties are observed at high pressure and high temperature. We predict that, at 300 K and 0 GPa, the heat capacity at constant volume C v, heat capacity at constant pressure C P, Debye temperature θ D, and Grüneisen parameter γ will be about 94.91 J/mol K, 98.52 J/mol K, 301.30 K, and 2.11 for BeSiSb2 and about 96.08 J/mol K, 100.47 J/mol K, 261.38 K, and 2.20 for MgSiSb2, respectively.

Synthesis and characterization of Fe-Ti-Sb intermetallic compounds: Discovery of a new Slater-Pauling phase

NASA Astrophysics Data System (ADS)

Naghibolashrafi, N.; Keshavarz, S.; Hegde, Vinay I.; Gupta, A.; Butler, W. H.; Romero, J.; Munira, K.; LeClair, P.; Mazumdar, D.; Ma, J.; Ghosh, A. W.; Wolverton, C.

2016-03-01

Compounds of Fe, Ti, and Sb were prepared using arc melting and vacuum annealing. Fe2TiSb , expected to be a full Heusler compound crystallizing in the L 21 structure, was shown by XRD and SEM analyses to be composed of weakly magnetic grains of nominal composition Fe1.5TiSb with iron-rich precipitates in the grain boundaries. FeTiSb, a composition consistent with the formation of a half-Heusler compound, also decomposed into Fe1.5TiSb grains with Ti-Sb rich precipitates and was weakly magnetic. The dominant Fe1.5TiSb phase appears to crystallize in a defective L 21 -like structure with iron vacancies. Based on this finding, a first-principles DFT-based binary cluster expansion of Fe and vacancies on the Fe sublattice of the L 21 structure was performed. Using the cluster expansion, we computationally scanned >103 configurations and predict a novel, stable, nonmagnetic semiconductor phase to be the zero-temperature ground state. This new structure is an ordered arrangement of Fe and vacancies, belonging to the space group R 3 m , with composition Fe1.5TiSb , i.e., between the full- and half-Heusler compositions. This phase can be visualized as alternate layers of L 21 phase Fe2TiSb and C 1b phase FeTiSb, with layering along the [111] direction of the original cubic phases. Our experimental results on annealed samples support this predicted ground-state composition, but further work is required to confirm that the R 3 m structure is the ground state.

Characterization of basic physical properties of Sb 2Se 3 and its relevance for photovoltaics

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

Chen, Chao; Bobela, David C.; Yang, Ye

Antimony selenide (Sb 2Se 3) is a promising absorber material for thin film photovoltaics because of its attractive material, optical and electrical properties. In recent years, the power conversion efficiency (PCE) of Sb 2Se 3 thin film solar cells has gradually enhanced to 5.6%. In this article, we systematically studied the basic physical properties of Sb 2Se 3 such as dielectric constant, anisotropic mobility, carrier lifetime, diffusion length, defect depth, defect density and optical band tail states. Here, we believe such a comprehensive characterization of the basic physical properties of Sb 2Se 3 lays a solid foundation for further optimizationmore » of solar device performance.« less

Characterization of basic physical properties of Sb 2Se 3 and its relevance for photovoltaics

DOE PAGES

Chen, Chao; Bobela, David C.; Yang, Ye; ...

2017-03-17

Antimony selenide (Sb 2Se 3) is a promising absorber material for thin film photovoltaics because of its attractive material, optical and electrical properties. In recent years, the power conversion efficiency (PCE) of Sb 2Se 3 thin film solar cells has gradually enhanced to 5.6%. In this article, we systematically studied the basic physical properties of Sb 2Se 3 such as dielectric constant, anisotropic mobility, carrier lifetime, diffusion length, defect depth, defect density and optical band tail states. Here, we believe such a comprehensive characterization of the basic physical properties of Sb 2Se 3 lays a solid foundation for further optimizationmore » of solar device performance.« less

Microwave properties of n-type InSb in a magnetic field between 4 and 300 K.

NASA Technical Reports Server (NTRS)

Eldumiati, I. I.; Haddad, G. I.

1973-01-01

A two-band conduction model is used to determine the properties of shallow-type impurity semiconductors in the presence of microwave and dc magnetic fields as a function of temperature. Measurements using cavity perturbation techniques are employed to determine the properties of n-type InSb and theoretical and experimental results between 4 and 300 K are compared. The hot-electron effect was found to be insignificant between 77 and 300 K, and the scattering mechanisms are dominated by acoustic and polar modes over the same temperature range.-

Mode-locked Tm,Ho:KLu(WO(4))(2) laser at 2060 nm using InGaSb-based SESAMs.

PubMed

Aleksandrov, Veselin; Gluth, Alexander; Petrov, Valentin; Buchvarov, Ivan; Steinmeyer, Günter; Paajaste, Jonna; Suomalainen, Soile; Härkönen, Antti; Guina, Mircea; Mateos, Xavier; Díaz, Francesc; Griebner, Uwe

2015-02-23

Passive mode-locking of a Tm,Ho:KLu(WO(4))(2) laser operating at 2060 nm using different designs of InGaAsSb quantum-well based semiconductor saturable absorber mirrors (SESAMs) is demonstrated. The self-starting mode-locked laser delivers pulse durations between 4 and 8 ps at a repetition rate of 93 MHz with maximum average output power of 155 mW. Mode-locking performance of a Tm,Ho:KLu(WO(4))(2) laser is compared for usage of a SESAM to a single-walled carbon nanotube saturable absorber.

Sub-kHz Linewidth GaSb Semiconductor Diode Lasers Operating Near 2 Micrometers

NASA Technical Reports Server (NTRS)

Bagheri, Mahmood; Briggs, Ryan M.; Frez, Clifford; Ksendzov, Alexander; Forouhar, Siamak

2012-01-01

We report on the phase noise properties of DFB lasers operating near 2.0 microns. Measured noise spectra indicate intrinsic laser linewidths below 1 kHz. An effective linewidth of less than 200 kHz for 5 ms measurement times is estimated.

Electronic Properties of III-V Semiconductor Interfaces.

DTIC Science & Technology

1980-11-30

ONG . REPORT NUMBER S.B CONTRACT 0R GRANT NUMSERa) S. PERFORMING ORGANIZATION NAMIE AND ADDRESS 10. PROGRAM EL.EMIENT. PROJECT. TASK AREA G WORK UNIT...Fred Nedoluha, Dave Collins, Larry Mainers, Derek Lile, and Carl Zeisse. And several of the samples studied were supplied by industrial colleagues

Decoherence of spin states induced by Rashba coupling for an electron confined to a semiconductor quantum dot in the presence of a magnetic field

NASA Astrophysics Data System (ADS)

Poszwa, A.

2018-05-01

We investigate quantum decoherence of spin states caused by Rashba spin-orbit (SO) coupling for an electron confined to a planar quantum dot (QD) in the presence of a magnetic field (B). The Schrödinger equation has been solved in a frame of second-order perturbation theory. The relationship between the von Neumann (vN) entropy and the spin polarization is obtained. The relation is explicitly demonstrated for the InSb semiconductor QD.

III-V semiconductor solid solution single crystal growth

NASA Technical Reports Server (NTRS)

Gertner, E. R.

1982-01-01

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

Strong Reduction of Thermal Conductivity and Enhanced Thermoelectric Properties in CoSbS1-xSex Paracostibite

PubMed Central

Chmielowski, Radoslaw; Bhattacharya, Sandip; Jacob, Stéphane; Péré, Daniel; Jacob, Alain; Moriya, Kenzo; Delatouche, Bruno; Roussel, Pascal; Madsen, Georg; Dennler, Gilles

2017-01-01

In order to reduce the thermal conductivity of CoSbS, a newly developed thermoelectric semiconductor, we have aimed at intentionally induce atomic disorder in its structure. This endeavor was guided by Density Functional Theory(DFT) calculations which indicated that substituting sulfur with selenium might be easily achievable experimentally because of the low formation energy of this point defect. Thereby, CoSbS1−xSex compounds having 0 ≤ x ≤ 1 have been synthesized by solid state reaction. Besides the expected semiconducting paracostibite phase, we have observed the appearance of a semimetallic costibite phase, never reported experimentally before. This cross-fertilized theoretical and experimental approach allowed us to reduce by 50% the thermal conductivity of paracostibite and therefore reach a maximum zT of 0.62 at 730 K. This makes this entirely new CoSbS1−xSex alloy very attractive for further optimizations and potential usage in thermoelectric applications. PMID:28425457

Strong Reduction of Thermal Conductivity and Enhanced Thermoelectric Properties in CoSbS1-xSex Paracostibite

NASA Astrophysics Data System (ADS)

Chmielowski, Radoslaw; Bhattacharya, Sandip; Jacob, Stéphane; Péré, Daniel; Jacob, Alain; Moriya, Kenzo; Delatouche, Bruno; Roussel, Pascal; Madsen, Georg; Dennler, Gilles

2017-04-01

In order to reduce the thermal conductivity of CoSbS, a newly developed thermoelectric semiconductor, we have aimed at intentionally induce atomic disorder in its structure. This endeavor was guided by Density Functional Theory(DFT) calculations which indicated that substituting sulfur with selenium might be easily achievable experimentally because of the low formation energy of this point defect. Thereby, CoSbS1-xSex compounds having 0 ≤ x ≤ 1 have been synthesized by solid state reaction. Besides the expected semiconducting paracostibite phase, we have observed the appearance of a semimetallic costibite phase, never reported experimentally before. This cross-fertilized theoretical and experimental approach allowed us to reduce by 50% the thermal conductivity of paracostibite and therefore reach a maximum zT of 0.62 at 730 K. This makes this entirely new CoSbS1-xSex alloy very attractive for further optimizations and potential usage in thermoelectric applications.

Isotemporal Substitution of Sedentary Behavior and Physical Activity on Function.

PubMed

Lerma, Nicholas L; Cho, Chi C; Swartz, Ann M; Miller, Nora E; Keenan, Kevin G; Strath, Scott J

2018-04-01

The amount of time spent in sedentary behaviors (SB) progressively increases with age, while reducing time spent in light-intensity physical activity (LPA) and moderate- to vigorous-intensity physical activity (MVPA). These trajectories in PA and SB are linked to accelerated reductions in physical functioning. This study aimed to examine the association of substituting SB time with LPA and MVPA on physical function in older adults. Ninety-one older adults (mean age, 70.7 ± 10.2 yr) wore a hip-mounted accelerometer to measure SB, LPA, and MVPA time. Measures of physical function included a 400-m walk test (400W), the usual gait speed (UGS), the five times sit-to-stand (5xSTS) test, and the short physical performance battery (SPPB). Isotemporal substitution regression modeling was performed to assess the relationship of replacing the amount of time spent in one activity for another. Replacing 30 min·d of SB with LPA was associated with a significant improvement in 400W (P = 0.0497), whereas MVPA resulted in a significant improvement (P < 0.01) in 400W, UGS, 5xSTS, and SPPB. Replacing 60 min·d of SB with 10 min·d of MVPA and 50 min·d of LPA was associated with significant improvements in the 400W, UGS, and 5xSTS (P < 0.05). Meanwhile, as little as 5 min·d of MVPA and 55 min·d of LPA were linked to a 78% increased odds of scoring with good function in the SPPB (P = 0.0247). Replacing SB with LPA was linked to a significant improvement in the 400W, but not the other brief functional measures. Mixed doses of LPA and MVPA may add flexibility to interventions targeting reductions of SB in older adults for clinically relevant improvements in physical function.

Synthesis and Thermoelectric Properties of Partially Double-Filled (Ce1- z Pr z ) y Fe4- x Co x Sb12 Skutterudites

NASA Astrophysics Data System (ADS)

Cha, Ye-Eun; Shin, Dong-Kil; Kim, Il-Ho

2018-06-01

Partially double-filled p-type (Ce1- z Pr z ) y Fe4- x Co x Sb12 ( z = 0.25, 0.75; y = 0.8; x = 0, 0.5, 1.0) skutterudites were synthesized by encapsulated melting and consolidated by hot pressing. The microstructure, phase, charge transport characteristics, and thermoelectric properties of the hot-pressed specimens were analyzed. Detailed measurements indicated that the skutterudite phase was successfully synthesized, but a small amount of a secondary phase (FeSb2) was also identified. However, the amount of the FeSb2 phase decreased with an increase in the Co substitution. Unlike for the filled Ce1- z Pr z Fe4- x Co x Sb12 skutterudites with y = 1, the (Ce,Pr)Sb2 phases were not formed by partial filling with Ce/Pr. The electrical conductivity decreased with increasing temperature, similar to the behavior shown by degenerate semiconductors. The Hall coefficient and the Seebeck coefficients were positive, indicating that all specimens exhibited p-type characteristics. The electrical conductivity and the electronic thermal conductivity decreased with increasing Pr filling and Co substitution because of the decreased carrier concentration caused by charge compensation. A maximum dimensionless figure of merit, ZTmax = 0.84, was obtained at 623 K for (Ce0.75Pr0.25)0.8Fe3CoSb12.

A study of doping influences on transmission of large-diameter gallium antimonide substrates for long-wave (LWIR) to very long wavelength (VLWIR) infra-red applications

NASA Astrophysics Data System (ADS)

Martinez, Rebecca; Tybjerg, Marius; Smith, Brian; Mowbray, Andrew; Furlong, Mark J.

2015-06-01

Gallium antimonide (GaSb) is an important Group III-V compound semiconductor for infra-red (IR) photodetectors used in sensing and imaging applications. Operating in the mid (3-5 μm) to long wavelength region (8-12 μm) of the IR spectrum, the application of GaSb detectors is extensive, encompassing military, industrial, medical and environmental uses. A significant developing technology for GaSb based detectors are those effective in the very long wavelength (VLWIR) infra-red region (13 μm and beyond) which are advantageous in space and stealth based applications which necessitate high operating temperatures. In this study different doping levels of GaSb are considered and the IR transmission spectra examined by Fourier Transform IR analysis. GaSb n-type doped material consistent in delivering long to very long wavelength transmission is demonstrated which is preferable to p-type material which requires backside thinning for IR transmission. Czochralski (Cz) grown GaSb wafers are assessed for electrical quality and uniformity results, on Hall mobility, resistivity and carrier level reported. Results of this work will establish the carrier concentration that ultimately results in high transparency substrates. In summary enhancements in IR transmission will be shown to be achieved in GaSb bulk crystals by tellurium (Te) compensation.

Semiconductor/dielectric interface engineering and characterization

NASA Astrophysics Data System (ADS)

Lucero, Antonio T.

The focus of this dissertation is the application and characterization of several, novel interface passivation techniques for III-V semiconductors, and the development of an in-situ electrical characterization. Two different interface passivation techniques were evaluated. The first is interface nitridation using a nitrogen radical plasma source. The nitrogen radical plasma generator is a unique system which is capable of producing a large flux of N-radicals free of energetic ions. This was applied to Si and the surface was studied using x-ray photoelectron spectroscopy (XPS). Ultra-thin nitride layers could be formed from 200-400° C. Metal-oxide-semiconductor capacitors (MOSCAPs) were fabricated using this passivation technique. Interface nitridation was able to reduce leakage current and improve the equivalent oxide thickness of the devices. The second passivation technique studied is the atomic layer deposition (ALD) diethylzinc (DEZ)/water treatment of sulfur treated InGaAs and GaSb. On InGaAs this passivation technique is able to chemically reduce higher oxidation states on the surface, and the process results in the deposition of a ZnS/ZnO interface passivation layer, as determined by XPS. Capacitance-voltage (C-V) measurements of MOSCAPs made on p-InGaAs reveal a large reduction in accumulation dispersion and a reduction in the density of interfacial traps. The same technique was applied to GaSb and the process was studied in an in-situ half-cycle XPS experiment. DEZ/H2O is able to remove all Sb-S from the surface, forming a stable ZnS passivation layer. This passivation layer is resistant to further reoxidation during dielectric deposition. The final part of this dissertation is the design and construction of an ultra-high vacuum cluster tool for in-situ electrical characterization. The system consists of three deposition chambers coupled to an electrical probe station. With this setup, devices can be processed and subsequently electrically characterized without exposing the sample to air. This is the first time that such a system has been reported. A special air-gap C-V probe will allow top gated measurements to be made, allowing semiconductor-dielectric interfaces to be studied during device processing.

Trap and transfer. two-step hole injection across the Sb2S3/CuSCN interface in solid-state solar cells.

PubMed

Christians, Jeffrey A; Kamat, Prashant V

2013-09-24

In solid-state semiconductor-sensitized solar cells, commonly known as extremely thin absorber (ETA) or solid-state quantum-dot-sensitized solar cells (QDSCs), transfer of photogenerated holes from the absorber species to the p-type hole conductor plays a critical role in the charge separation process. Using Sb2S3 (absorber) and CuSCN (hole conductor), we have constructed ETA solar cells exhibiting a power conversion efficiency of 3.3%. The hole transfer from excited Sb2S3 into CuSCN, which limits the overall power conversion efficiency of these solar cells, is now independently studied using transient absorption spectroscopy. In the Sb2S3 absorber layer, photogenerated holes are rapidly localized on the sulfur atoms of the crystal lattice, forming a sulfide radical (S(-•)) species. This trapped hole is transferred from the Sb2S3 absorber to the CuSCN hole conductor with an exponential time constant of 1680 ps. This process was monitored through the spectroscopic signal seen for the S(-•) species in Sb2S3, providing direct evidence for the hole transfer dynamics in ETA solar cells. Elucidation of the hole transfer mechanism from Sb2S3 to CuSCN represents a significant step toward understanding charge separation in Sb2S3 solar cells and provides insight into the design of new architectures for higher efficiency devices.

Sedentary and Physical Activity Habits of Obese Adolescents

ERIC Educational Resources Information Center

Starkoff, Brooke E.; Petosa, Rick L.; Balk, Elizabeth K.; Eneli, Ihuoma U.; Bonny, Andrea E.; Hoffman, Robert P.; Devor, Steven T.

2014-01-01

Background: The independent association between sedentary behavior (SB) and physical activity (PA) is such that, regardless of accumulated PA, high amounts of SB are detrimental to health, even in adolescents. Purpose: Our aim was to profile activity patterns in free-living environments and to measure levels of SB and light (LT) and moderate (MOD)…

Strain-balanced type-II superlattices for efficient multi-junction solar cells.

PubMed

Gonzalo, A; Utrilla, A D; Reyes, D F; Braza, V; Llorens, J M; Fuertes Marrón, D; Alén, B; Ben, T; González, D; Guzman, A; Hierro, A; Ulloa, J M

2017-06-21

Multi-junction solar cells made by assembling semiconductor materials with different bandgap energies have hold the record conversion efficiencies for many years and are currently approaching 50%. Theoretical efficiency limits make use of optimum designs with the right lattice constant-bandgap energy combination, which requires a 1.0-1.15 eV material lattice-matched to GaAs/Ge. Nevertheless, the lack of suitable semiconductor materials is hindering the achievement of the predicted efficiencies, since the only candidates were up to now complex quaternary and quinary alloys with inherent epitaxial growth problems that degrade carrier dynamics. Here we show how the use of strain-balanced GaAsSb/GaAsN superlattices might solve this problem. We demonstrate that the spatial separation of Sb and N atoms avoids the ubiquitous growth problems and improves crystal quality. Moreover, these new structures allow for additional control of the effective bandgap through the period thickness and provide a type-II band alignment with long carrier lifetimes. All this leads to a strong enhancement of the external quantum efficiency under photovoltaic conditions with respect to bulk layers of equivalent thickness. Our results show that GaAsSb/GaAsN superlattices with short periods are the ideal (pseudo)material to be integrated in new GaAs/Ge-based multi-junction solar cells that could approach the theoretical efficiency limit.

Electronic structure modeling of InAs/GaSb superlattices with hybrid density functional theory

NASA Astrophysics Data System (ADS)

Garwood, T.; Modine, N. A.; Krishna, S.

2017-03-01

The application of first-principles calculations holds promise for greatly improving our understanding of semiconductor superlattices. Developing a procedure to accurately predict band gaps using hybrid density functional theory lays the groundwork for future studies investigating more nuanced properties of these structures. Our approach allows a priori prediction of the properties of SLS structures using only the band gaps of the constituent materials. Furthermore, it should enable direct investigation of the effects of interface structure, e.g., intermixing or ordering at the interface, on SLS properties. In this paper, we present band gap data for various InAs/GaSb type-II superlattice structures calculated using the generalized Kohn-Sham formulation of density functional theory. A PBE0-type hybrid functional was used, and the portion of the exact exchange was tuned to fit the band gaps of the binary compounds InAs and GaSb with the best agreement to bulk experimental values obtained with 18% of the exact exchange. The heterostructures considered in this study are 6 monolayer (ML) InAs/6 ML GaSb, 8 ML InAs/8 ML GaSb and 10 ML InAs/10 ML GaSb with deviations from the experimental band gaps ranging from 3% to 11%.

Electronic structure modeling of InAs/GaSb superlattices with hybrid density functional theory

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

Garwood, Tristan; Modine, Normand A.; Krishna, S.

2016-12-18

The application of first-principles calculations holds promise for greatly improving our understanding of semiconductor superlattices. By developing a procedure to accurately predict band gaps using hybrid density functional theory, it lays the groundwork for future studies investigating more nuanced properties of these structures. Our approach allows a priori prediction of the properties of SLS structures using only the band gaps of the constituent materials. Furthermore, it should enable direct investigation of the effects of interface structure, e.g., intermixing or ordering at the interface, on SLS properties. In this paper, we present band gap data for various InAs/GaSb type-II superlattice structuresmore » calculated using the generalized Kohn-Sham formulation of density functional theory. A PBE0-type hybrid functional was used, and the portion of the exact exchange was tuned to fit the band gaps of the binary compounds InAs and GaSb with the best agreement to bulk experimental values obtained with 18% of the exact exchange. The heterostructures considered in this study are 6 monolayer (ML) InAs/6 ML GaSb, 8 ML InAs/8 ML GaSb and 10 ML InAs/10 ML GaSb with deviations from the experimental band gaps ranging from 3% to 11%.« less

Solid Solutions Formation: Improving the Thermoelectric Properties of Skutterudites

NASA Technical Reports Server (NTRS)

Borshchevsky, A.; Caillat, T.; Fleurial, J. P.

1996-01-01

Materials with skutterudite structure have been known for a long time. Some of them are semiconductors. A typical skutterudite is CoSb(sub 3) and its thermoelectric properties were partially studied in the 1960's. Recently, it has been discovered that many skutterudite compounds are thermoelectrics with promising future.

Microscopic Modeling of Intersubband Optical Processes in Type II Semiconductor Quantum Wells: Linear Absorption

NASA Technical Reports Server (NTRS)

Li, Jian-Zhong; Kolokolov, Kanstantin I.; Ning, Cun-Zheng

2003-01-01

Linear absorption spectra arising from intersubband transitions in semiconductor quantum well heterostructures are analyzed using quantum kinetic theory by treating correlations to the first order within Hartree-Fock approximation. The resulting intersubband semiconductor Bloch equations take into account extrinsic dephasing contributions, carrier-longitudinal optical phonon interaction and carrier-interface roughness interaction which is considered with Ando s theory. As input for resonance lineshape calculation, a spurious-states-free 8-band kp Hamiltonian is used, in conjunction with the envelop function approximation, to compute self-consistently the energy subband structure of electrons in type II InAs/AlSb single quantum well structures. We demonstrate the interplay of nonparabolicity and many-body effects in the mid-infrared frequency range for such heterostructures.

Primary research efforts on exploring the commercial possibilities of thin film growth and materials purification in space

NASA Technical Reports Server (NTRS)

1989-01-01

The progress made on research programs in the 1987 to 1988 year is reported. The research is aimed at producing thin film semiconductors and superconductor materials in space. Sophisticated vacuum chambers and equipment were attained for the epitaxial thin film growth of semiconductors, metals and superconductors. In order to grow the best possible epitaxial films at the lowest possible temperatures on earth, materials are being isoelectronically doped during growth. It was found that isoelectrically doped film shows the highest mobility in comparison with films grown at optimal temperatures. Success was also attained in growing epitaxial films of InSb on sapphire which show promise for infrared sensitive devices in the III-V semiconductor system.

Development of sputtered CuSbS2 thin films grown by sequential deposition of binary sulfides

NASA Astrophysics Data System (ADS)

Medina-Montes, M. I.; Vieyra-Brito, O.; Mathews, N. R.; Mathew, X.

2018-05-01

In this work, CuSbS2 thin films were developed by annealing binary precursors deposited sequentially by rf magnetron sputtering. The recrystallization process was optimized and the films were extensively characterized using a number of tools such as XRD, Raman, SEM, energy dispersive x-ray spectroscopy, atomic force microscopy, Hall, UV–vis spectroscopy, Ellipsometry, Seebeck, and photoresponse. The influence of annealing temperature on the structure, morphology, elemental composition, optical and electrical properties are reported. Annealing below 350 °C resulted in famatinite (Cu3SbS4) and chalcostibite (CuSbS2) ternaries as well as binary phases. Phase-pure chalcostibite was obtained in the range of 350 °C–375 °C. At 400 °C, although CuSbS2 was predominant, tetrahedrite phase (Cu12Sb4S13) appeared as an additional phase. The elemental composition of the films was slightly sulfur deficient, and the atomic percentages of Cu, Sb and S showed a dependence on annealing temperature. The material properties of the phase-pure CuSbS2 thin films are: optical band gap in the range of 1.5–1.62 eV, absorption coefficient close to 105 cm‑1, atomic ratios of Cu/Sb ∼1 and (Cu + Sb)/S ∼1.2, crystal size 18.3–24.5 nm and grain size 50–300 nm. The films were photo-sensitive, showed p-type semiconductor behavior. Electrical resistivity, carrier density and hole mobility were 94–459 Ω cm, 1.6–7.0 × 1015 cm‑3 and 8.4–9.5 cm2 V‑1 s respectively.

Bulk growth and surface characterization of epitaxy ready cadmium zinc telluride substrates for use in IR imaging applications

NASA Astrophysics Data System (ADS)

Flint, J. P.; Martinez, B.; Betz, T. E. M.; Mackenzie, J.; Kumar, F. J.; Burgess, L.

2017-02-01

Cadmium Zinc Telluride (Cd1-xZnxTe or CZT) is a compound semiconductor substrate material that has been used for infrared detector (IR) applications for many years. CZT is a perfect substrate for the epitaxial growth of Mercury Cadmium Telluride (Hg1-xCdxTe or MCT) epitaxial layers and remains the material of choice for many high performance IR detectors and focal plane arrays that are used to detect across wide IR spectral bands. Critical to the fabrication of high performance MCT IR detectors is a high quality starting CZT substrate, this being a key determinant of epitaxial layer crystallinity, defectivity and ultimately device electro-optical performance. In this work we report on a new source of substrates suitable for IR detector applications, grown using the Travelling Heater Method (THM). This proven method of crystal growth has been used to manufacture high quality IR specification CZT substrates where industry requirements for IR transmission, dislocations, tellurium precipitates and copper impurity levels have been met. Results will be presented for the chemo-mechanical (CMP) polishing of CZT substrates using production tool sets that are identical to those that are used to produce epitaxy-ready surface finishes on related IR compound semiconductor materials such as GaSb and InSb. We will also discuss the requirements to scale CZT substrate manufacture and how with a new III-V like approach to both CZT crystal growth and substrate polishing, we can move towards a more standardized product and one that can ultimately deliver a standard round CZT substrate, as is the case for competing IR materials such as GaSb, InSb and InP.

Metallization for Yb14MnSb11-Based Thermoelectric Materials

NASA Technical Reports Server (NTRS)

Firdosy, Samad; Li, Billy Chun-Yip; Ravi, Vilupanur; Sakamoto, Jeffrey; Caillat, Thierry; Ewell, Richard C.; Brandon, Erik J.

2011-01-01

Thermoelectric materials provide a means for converting heat into electrical power using a fully solid-state device. Power-generating devices (which include individual couples as well as multicouple modules) require the use of ntype and p-type thermoelectric materials, typically comprising highly doped narrow band-gap semiconductors which are connected to a heat collector and electrodes. To achieve greater device efficiency and greater specific power will require using new thermoelectric materials, in more complex combinations. One such material is the p-type compound semiconductor Yb14MnSb11 (YMS), which has been demonstrated to have one of the highest ZT values at 1,000 C, the desired operational temperature of many space-based radioisotope thermoelectric generators (RTGs). Despite the favorable attributes of the bulk YMS material, it must ultimately be incorporated into a power-generating device using a suitable joining technology. Typically, processes such as diffusion bonding and/or brazing are used to join thermoelectric materials to the heat collector and electrodes, with the goal of providing a stable, ohmic contact with high thermal conductivity at the required operating temperature. Since YMS is an inorganic compound featuring chemical bonds with a mixture of covalent and ionic character, simple metallurgical diffusion bonding is difficult to implement. Furthermore, the Sb within YMS readily reacts with most metals to form antimonide compounds with a wide range of stoichiometries. Although choosing metals that react to form high-melting-point antimonides could be employed to form a stable reaction bond, it is difficult to limit the reactivity of Sb in YMS such that the electrode is not completely consumed at an operating temperature of 1,000 C. Previous attempts to form suitable metallization layers resulted in poor bonding, complete consumption of the metallization layer or fracture within the YMS thermoelement (or leg).

Effect of Retraining Approach-Avoidance Tendencies on an Exercise Task: A Randomized Controlled Trial.

PubMed

Cheval, Boris; Sarrazin, Philippe; Pelletier, Luc; Friese, Malte

2016-12-01

Promoting regular physical activity (PA) and lessening sedentary behaviors (SB) constitute a public health priority. Recent evidence suggests that PA and SB are not only related to reflective processes (eg, behavioral intentions), but also to impulsive approach-avoidance tendencies (IAAT). This study aims to test the effect of a computerized IAAT intervention on an exercise task. Participants (N = 115) were randomly assigned to 1 of 3 experimental conditions, in which they were either trained to approach PA and avoid SB (ApPA-AvSB condition), to approach SB and avoid PA (ApSB-AvPA condition), or to approach and avoid PA and SB equally often (active control condition). The main outcome variable was the time spent carrying out a moderate intensity exercise task. IAAT toward PA decreased in the ApSB-AvPA condition, tended to increase in the ApPA-AvSB condition, and remained stable in the control condition. Most importantly, the ApPA-AvSB manipulation led to more time spent exercising than the ApSB-AvPA condition. Sensitivity analyses excluding individuals who were highly physically active further revealed that participants in the ApPA-AvSB condition spent more time exercising than participants in the control condition. These findings provide preliminary evidence that a single intervention session can successfully change impulsive approach tendencies toward PA and can increase the time devoted to an exercise task, especially among individuals who need to be more physically active. Potential implications for health behavior theories and behavior change interventions are outlined.

Optical characteristics of p-type GaAs-based semiconductors towards applications in photoemission infrared detectors

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

Lao, Y. F.; Perera, A. G. U., E-mail: uperera@gsu.edu; Center for Nano-Optics

2016-03-14

Free-carrier effects in a p-type semiconductor including the intra-valence-band and inter-valence-band optical transitions are primarily responsible for its optical characteristics in infrared. Attention has been paid to the inter-valence-band transitions for the development of internal photoemission (IPE) mid-wave infrared (MWIR) photodetectors. The hole transition from the heavy-hole (HH) band to the spin-orbit split-off (SO) band has demonstrated potential applications for 3–5 μm detection without the need of cooling. However, the forbidden SO-HH transition at the Γ point (corresponding to a transition energy Δ{sub 0}, which is the split-off gap between the HH and SO bands) creates a sharp drop around 3.6 μmmore » in the spectral response of p-type GaAs/AlGaAs detectors. Here, we report a study on the optical characteristics of p-type GaAs-based semiconductors, including compressively strained InGaAs and GaAsSb, and a dilute magnetic semiconductor, GaMnAs. A model-independent fitting algorithm was used to derive the dielectric function from experimental reflection and transmission spectra. Results show that distinct absorption dip at Δ{sub 0} is observable in p-type InGaAs and GaAsSb, while GaMnAs displays enhanced absorption without degradation around Δ{sub 0}. This implies the promise of using GaMnAs to develop MWIR IPE detectors. Discussions on the optical characteristics correlating with the valence-band structure and free-hole effects are presented.« less

Objectively measured sedentary behavior and moderate-to-vigorous physical activity on the health-related quality of life in US adults: The National Health and Nutrition Examination Survey 2003-2006.

PubMed

Kim, Junghoon; Im, Jeong-Soo; Choi, Yoon-Hyeong

2017-05-01

Health-related quality of life (HRQOL) represents an individual's perception of physical, mental, and social well-being and is a strong predictor of health status. Few studies have examined associations of sedentary behavior (SB) and moderate-to-vigorous physical activity (MVPA) with HRQOL in the general population. This study aimed to determine combined associations of objectively measured SB and MVPA on the risk of poor HRQOL in the general US population, after controlling for potential confounding factors. We analyzed data from 5359 adults from the National Health and Nutrition Examination Survey 2003-2006. HRQOL was measured using a HRQOL-4 consisting of four questions focused on the self-perception of general health, physical health, mental health, and activity limitation. We dichotomized each HRQOL-4 component as good versus poor and defined poor overall HRQOL when participants had any poor HRQOL components. SB and MVPA were measured using an accelerometer. Survey logistic models were examined to estimate the odds ratio (OR) and 95% confidence interval (CI) for poor HRQOL by SB and MVPA as tertiles. When examined as a combination of SB and MVPA, a substantial decrease in the risk of poor overall HRQOL was found in individuals with low SB/high MVPA [OR 0.69 (95% CI 0.51-0.94) and moderate SB/high MVPA (OR 0.56 (95% CI 0.40-0.78)], but no significant decrease was found in individuals with high SB/high MVPA (vs. high SB/low MVPA). Our findings suggest that both increasing MVPA and reducing time spent in SB may be useful strategies to improve HRQOL.

Joint effect of physical activity and sedentary behaviour on cardiovascular risk factors in Chilean adults.

PubMed

Cristi-Montero, Carlos; Steell, Lewis; Petermann, Fanny; Garrido-Méndez, Alex; Díaz-Martínez, Ximena; Salas-Bravo, Carlos; Ramirez-Campillo, Rodrigo; Alvarez, Cristian; Rodriguez, Fernando; Aguilar-Farias, Nicolas; Martinez, Maria A; Leiva, Ana M; Poblete-Valderrama, Felipe; Willis, Naomi D; Celis-Morales, Carlos A

2017-10-17

To investigate the associations between combined categories of moderate-to-vigorous physical activity (MVPA) and sedentary behaviour (SB) with markers of adiposity and cardiovascular risk in adults. Overall, 5040 participants (mean age 46.4 years and 59.3% women) from the cross-sectional Chilean National Health Survey 2009-2010 were included in this study. MVPA and SB were measured using the Global Physical Activity questionnaire. Four categories were computed using MVPA- and SB-specific cut-offs ('High-SB & Active', 'Low-SB & Active', 'High-SB & Inactive' and 'Low-SB & Inactive'). Compared to the reference group ('High-SB & Inactive'), those in 'High-SB & Active' and 'Low-SB & Active' were less likely to have an obese BMI (OR: 0.67 [0.54; 0.85], P = 0.0001 and 0.74 [0.59; 0.92] P = 0.0007, respectively) and less likely to have metabolic syndrome (OR: 0.63 [0.49; 0.82], P < 0.0001 and 0.72 [0.57; 0.91], P = 0.007), central obesity (OR: 0.79 [0.65; 0.96], P = 0.016 and 0.71 [0.59; 0.84], P < 0.0001), diabetes (OR: 0.45 [0.35; 0.59], P < 0.0001 and 0.44 [0.34; 0.56], P < 0.0001) and hypertension (OR: 0.52 [0.43; 0.63], P < 0.0001 and 0.60 [0.50; 0.72], P < 0.0001), respectively. Being physically active and spending less time in SBs was associated with lower adiposity and improvements in cardiovascular risk factors. © The Author 2017. Published by Oxford University Press on behalf of Faculty of Public Health. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com

Ballistic superconductivity in semiconductor nanowires.

PubMed

Zhang, Hao; Gül, Önder; Conesa-Boj, Sonia; Nowak, Michał P; Wimmer, Michael; Zuo, Kun; Mourik, Vincent; de Vries, Folkert K; van Veen, Jasper; de Moor, Michiel W A; Bommer, Jouri D S; van Woerkom, David J; Car, Diana; Plissard, Sébastien R; Bakkers, Erik P A M; Quintero-Pérez, Marina; Cassidy, Maja C; Koelling, Sebastian; Goswami, Srijit; Watanabe, Kenji; Taniguchi, Takashi; Kouwenhoven, Leo P

2017-07-06

Semiconductor nanowires have opened new research avenues in quantum transport owing to their confined geometry and electrostatic tunability. They have offered an exceptional testbed for superconductivity, leading to the realization of hybrid systems combining the macroscopic quantum properties of superconductors with the possibility to control charges down to a single electron. These advances brought semiconductor nanowires to the forefront of efforts to realize topological superconductivity and Majorana modes. A prime challenge to benefit from the topological properties of Majoranas is to reduce the disorder in hybrid nanowire devices. Here we show ballistic superconductivity in InSb semiconductor nanowires. Our structural and chemical analyses demonstrate a high-quality interface between the nanowire and a NbTiN superconductor that enables ballistic transport. This is manifested by a quantized conductance for normal carriers, a strongly enhanced conductance for Andreev-reflecting carriers, and an induced hard gap with a significantly reduced density of states. These results pave the way for disorder-free Majorana devices.

Dewetting and Segregation of Zn-Doped InSb in Microgravity Experiments

NASA Technical Reports Server (NTRS)

Ostrogorsky, A. G.; Marin, C.; Duffar, T.; Volz, M.

2009-01-01

In directional solidification, dewetting is characterized by the lack of contact between the crystal and the crucible walls, due to the existence of a liquid meniscus at the level of the solid-liquid interface. This creates a gap of a few tens of micrometers between the crystal and the crucible. One of the immediate consequences of this phenomenon is the dramatic improvement of the quality of the crystal. This improvement is partly due to the modification of the solid-liquid interface curvature and partly to the absence of sticking and spurious nucleation at the crystal-crucible interface. Dewetting has been, commonly observed during the growth of semiconductors in crucibles under microgravity conditions where it appears to be very stable: the gap between the crystal and the crucible remains constant along several centimetres of growth. The physical models of the phenomenon are well established and they predict that dewetting should not occur in microgravity, if sufficient static pressure is imposed on the melt, pushing it towards the crucible. We present the results of InSb(Zn) solidification experiments conducted at the International Space Station (ISS) where, in spite of a spring exerting a pressure on the liquid, partial dewetting did occur. This surprising result is discussed in terms of force exerted .by the spring on the liquid and of possibility that the spring did not work properly. Furthermore, it appears that the segregation of the Zn was not affected by the occurrence of the dewetting. The data suggest that there was no significant interference of convection with segregation of Zn in InSb.

Single InAs/GaSb nanowire low-power CMOS inverter.

PubMed

Dey, Anil W; Svensson, Johannes; Borg, B Mattias; Ek, Martin; Wernersson, Lars-Erik

2012-11-14

III-V semiconductors have so far predominately been employed for n-type transistors in high-frequency applications. This development is based on the advantageous transport properties and the large variety of heterostructure combinations in the family of III-V semiconductors. In contrast, reports on p-type devices with high hole mobility suitable for complementary metal-oxide-semiconductor (CMOS) circuits for low-power operation are scarce. In addition, the difficulty to integrate both n- and p-type devices on the same substrate without the use of complex buffer layers has hampered the development of III-V based digital logic. Here, inverters fabricated from single n-InAs/p-GaSb heterostructure nanowires are demonstrated in a simple processing scheme. Using undoped segments and aggressively scaled high-κ dielectric, enhancement mode operation suitable for digital logic is obtained for both types of transistors. State-of-the-art on- and off-state characteristics are obtained and the individual long-channel n- and p-type transistors exhibit minimum subthreshold swings of SS = 98 mV/dec and SS = 400 mV/dec, respectively, at V(ds) = 0.5 V. Inverter characteristics display a full signal swing and maximum gain of 10.5 with a small device-to-device variability. Complete inversion is measured at low frequencies although large parasitic capacitances deform the waveform at higher frequencies.

High performance p-type thermoelectric materials and methods of preparation

NASA Technical Reports Server (NTRS)

Caillat, Thierry (Inventor); Borshchevsky, Alexander (Inventor); Fleurial, Jean-Pierre (Inventor)

2005-01-01

The present invention is embodied in high performance p-type thermoelectric materials having enhanced thermoelectric properties and the methods of preparing such materials. In one aspect of the invention, p-type semiconductors of formula Zn4-xAxSb3-yBy wherein 0?x?4, A is a transition metal, B is a pnicogen, and 0?y?3 are formed for use in manufacturing thermoelectric devices with substantially enhanced operating characteristics and improved efficiency. Two methods of preparing p-type Zn4Sb3 and related alloys of the present invention include a crystal growth method and a powder metallurgy method.

Investigation of the properties of Sb doping on tin oxide SNO2 materials for technological applications

NASA Astrophysics Data System (ADS)

Hachoun, Z.; Ouerdane, A.; Bouslama, M.; Ghaffour, M.; Abdellaoui, A.; Caudano, Y.; benamara, A. Ali

2016-04-01

The conductivities of the oxide SnO2 is dependent on the nature of the surrounding gas. This property stems from the adsorption or desorption on the surface of oxide grains. These phenomena are usually accompanied by electronic transfer between the adsorbed molecule and the semiconductor material, changing its conductivity. Tin oxidation and Sb doping were realized without and with heating process. The XPS technique and the TEM microscopy showed the synthesized nanocrystals. Simulated Monte Carlo program Casino is used for a scanning its profile. The surface characteristics are highlighted in the aim to be used as spatial gas sensors.

Adolescents' Physical Activity and Sedentary Behavior: A Pathway in Reducing Overweight and Obesity. The PRALIMAP 2-Year Cluster Randomized Controlled Trial.

PubMed

Omorou, Abdou Y; Langlois, Johanne; Lecomte, Edith; Vuillemin, Anne; Briançon, Serge

2015-05-01

explaining why and how overweight prevention programs were effective was a real need; especially the potential role of physical activity (PA) and sedentary behavior (SB) should be highlighted. This study aimed to evaluate the 2-year effectiveness of a screening and care strategy in adolescents' weight reduction with regards to PA and SB change. 1745 adolescents aged 15.1 years from PRALIMAP trial was included (n = 840 for screening and care group and n = 905 for control group). PA and SB time (international physical activity questionnaire: IPAQ), body mass index (BMI), and BMI z-score were assessed at inclusion and after 2-year intervention. Hierarchical mixed models were applied. Compared with the control group, screening and care strategy was associated with an increase in global PA (58 min/week), a moderate PA (43 min/week), the adherence to the French PA guidelines (OR = 1.3), and a decrease in SB (-198 min/week). The 2-year weight change decreased when adjusted for PA and SB suggesting that the effect of screening and care strategy was partly mediated by PA and SB. Screening and care intervention seemed to be effective in increasing PA and decreasing SB. The induced PA and SB modifications contributed to the observed weight change.

Multifunctional semiconductor micro-Hall devices for magnetic, electric, and photo-detection

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

Gilbertson, A. M.; Cohen, L. F.; Sadeghi, Hatef

2015-12-07

We report the real-space voltage response of InSb/AlInSb micro-Hall devices to local photo-excitation, electric, and magnetic fields at room temperature using scanning probe microscopy. We show that the ultrafast generation of localised photocarriers results in conductance perturbations analogous to those produced by local electric fields. Experimental results are in good agreement with tight-binding transport calculations in the diffusive regime. The magnetic, photo, and charge sensitivity of a 2 μm wide probe are evaluated at a 10 μA bias current in the Johnson noise limit (valid at measurement frequencies > 10 kHz) to be, respectively, 500 nT/√Hz; 20 pW/√Hz (λ = 635 nm) comparable to commercial photoconductive detectors;more » and 0.05 e/√Hz comparable to that of single electron transistors. These results demonstrate the remarkably versatile sensing attributes of simple semiconductor micro-Hall devices that can be applied to a host of imaging and sensing applications.« less

Quantum cascade lasers grown on silicon.

PubMed

Nguyen-Van, Hoang; Baranov, Alexei N; Loghmari, Zeineb; Cerutti, Laurent; Rodriguez, Jean-Baptiste; Tournet, Julie; Narcy, Gregoire; Boissier, Guilhem; Patriarche, Gilles; Bahriz, Michael; Tournié, Eric; Teissier, Roland

2018-05-08

Technological platforms offering efficient integration of III-V semiconductor lasers with silicon electronics are eagerly awaited by industry. The availability of optoelectronic circuits combining III-V light sources with Si-based photonic and electronic components in a single chip will enable, in particular, the development of ultra-compact spectroscopic systems for mass scale applications. The first circuits of such type were fabricated using heterogeneous integration of semiconductor lasers by bonding the III-V chips onto silicon substrates. Direct epitaxial growth of interband III-V laser diodes on silicon substrates has also been reported, whereas intersubband emitters grown on Si have not yet been demonstrated. We report the first quantum cascade lasers (QCLs) directly grown on a silicon substrate. These InAs/AlSb QCLs grown on Si exhibit high performances, comparable with those of the devices fabricated on their native InAs substrate. The lasers emit near 11 µm, the longest emission wavelength of any laser integrated on Si. Given the wavelength range reachable with InAs/AlSb QCLs, these results open the way to the development of a wide variety of integrated sensors.

Ion beam nanopatterning of III-V semiconductors: Consistency of experimental and simulation trends within a chemistry-driven theory

DOE PAGES

El-Atwani, O.; Norris, S. A.; Ludwig, K.; ...

2015-12-16

In this study, several proposed mechanisms and theoretical models exist concerning nanostructure evolution on III-V semiconductors (particularly GaSb) via ion beam irradiation. However, making quantitative contact between experiment on the one hand and model-parameter dependent predictions from different theories on the other is usually difficult. In this study, we take a different approach and provide an experimental investigation with a range of targets (GaSb, GaAs, GaP) and ion species (Ne, Ar, Kr, Xe) to determine new parametric trends regarding nanostructure evolution. Concurrently, atomistic simulations using binary collision approximation over the same ion/target combinations were performed to determine parametric trends onmore » several quantities related to existing model. A comparison of experimental and numerical trends reveals that the two are broadly consistent under the assumption that instabilities are driven by chemical instability based on phase separation. Furthermore, the atomistic simulations and a survey of material thermodynamic properties suggest that a plausible microscopic mechanism for this process is an ion-enhanced mobility associated with energy deposition by collision cascades.« less

Growth, strain relaxation properties and high-κ dielectric integration of mixed-anion GaAs{sub 1-y}Sb{sub y} metamorphic materials

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

Zhu, Y.; Clavel, M.; Goley, P.

Mixed-anion, GaAs{sub 1-y}Sb{sub y} metamorphic materials with a wide range of antimony (Sb) compositions extending from 15% to 62%, were grown by solid source molecular beam epitaxy (MBE) on GaAs substrates. The impact of different growth parameters on the Sb composition in GaAs{sub 1-y}Sb{sub y} materials was systemically investigated. The Sb composition was well-controlled by carefully optimizing the As/Ga ratio, the Sb/Ga ratio, and the substrate temperature during the MBE growth process. High-resolution x-ray diffraction demonstrated a quasi-complete strain relaxation within each composition of GaAs{sub 1-y}Sb{sub y}. Atomic force microscopy exhibited smooth surface morphologies across the wide range of Sbmore » compositions in the GaAs{sub 1-y}Sb{sub y} structures. Selected high-κ dielectric materials, Al{sub 2}O{sub 3}, HfO{sub 2}, and Ta{sub 2}O{sub 5} were deposited using atomic layer deposition on the GaAs{sub 0.38}Sb{sub 0.62} material, and their respective band alignment properties were investigated by x-ray photoelectron spectroscopy (XPS). Detailed XPS analysis revealed a valence band offset of >2 eV for all three dielectric materials on GaAs{sub 0.38}Sb{sub 0.62}, indicating the potential of utilizing these dielectrics on GaAs{sub 0.38}Sb{sub 0.62} for p-type metal-oxide-semiconductor (MOS) applications. Moreover, both Al{sub 2}O{sub 3} and HfO{sub 2} showed a conduction band offset of >2 eV on GaAs{sub 0.38}Sb{sub 0.62}, suggesting these two dielectrics can also be used for n-type MOS applications. The well-controlled Sb composition in several GaAs{sub 1-y}Sb{sub y} material systems and the detailed band alignment analysis of multiple high-κ dielectric materials on a fixed Sb composition, GaAs{sub 0.38}Sb{sub 0.62}, provides a pathway to utilize GaAs{sub 1-y}Sb{sub y} materials in future microelectronic and optoelectronic applications.« less

Yb5Ga2Sb6: a mixed valent and narrow-band gap material in the RE5M2X6 family.

PubMed

Subbarao, Udumula; Sarkar, Sumanta; Gudelli, Vijay Kumar; Kanchana, V; Vaitheeswaran, G; Peter, Sebastian C

2013-12-02

A new compound Yb5Ga2Sb6 was synthesized by the metal flux technique as well as high frequency induction heating. Yb5Ga2Sb6 crystallizes in the orthorhombic space group Pbam (no. 55), in the Ba5Al2Bi6 structure type, with a unit cell of a = 7.2769(2) Å, b = 22.9102(5) Å, c = 4.3984(14) Å, and Z = 2. Yb5Ga2Sb6 has an anisotropic structure with infinite anionic double chains (Ga2Sb6)(10-) cross-linked by Yb(2+) and Yb(3+) ions. Each single chain is made of corner-sharing GaSb4 tetrahedra. Two such chains are bridged by Sb2 groups to form double chains of 1/∞ [Ga2Sb6(10-)]. The compound satisfies the classical Zintl-Klemm concept and is a narrow band gap semiconductor with an energy gap of around 0.36 eV calculated from the electrical resistivity data corroborating with the experimental absorption studies in the IR region (0.3 eV). Magnetic measurements suggest Yb atoms in Yb5Ga2Sb6 exist in the mixed valent state. Temperature dependent magnetic susceptibility data follows the Curie-Weiss behavior above 100 K and no magnetic ordering was observed down to 2 K. Experiments are accompanied by all electron full-potential linear augmented plane wave (FP-LAPW) calculations based on density functional theory to calculate the electronic structure and density of states. The calculated band structure shows a weak overlap of valence band and conduction band resulting in a pseudo gap in the density of states revealing semimetallic character.

Optic phonons and anisotropic thermal conductivity in hexagonal Ge 2Sb 2Te 5

DOE PAGES

Mukhopadhyay, Saikat; Lindsay, Lucas R.; Singh, David

2016-11-16

The lattice thermal conductivity ($κ$) of hexagonal Ge 2Sb 2Tesub>5 (h-GST) is studied via direct first-principles calculations. We find significant intrinsic anisotropy of ( $κ$ a/$κ$ c~2) of $κ$ in bulk h-GST along different transport directions. The dominant contribution to$κ$ is from optic phonons, ~75%. This is extremely unusual as the acoustic phonon modes carry most of the heat in typical semiconductors and insulators with small unit cells. Very recently, Lee et. al. observed anisotropic in GST thin films and attributed this to thermal resistance of amorphous regions near grain boundaries. However, our results suggest an additional strong intrinsic anisotropymore » for the pure hexagonal phase. This derives from bonding anisotropy along different crystal directions, specifically from weak interlayer coupling, which gives anisotropic phonon dispersions. The phonon spectrum of h-GST has very dispersive optic branches with higher group velocities along the a-axis as compared to flat optic bands along the c-axis. The importance of optic mode contributions for the thermal conductivity in low-$κ$ h-GST is unusual, and development of fundamental physical understanding of these contributions may be critical to better understanding of thermal conduction in other complex layered materials.« less

FAST TRACK COMMUNICATION: Evaluation of the In concentration of an InxGa1-xSb alloy layer in cross-sectional HRTEM images of III-V semiconductor superlattices

NASA Astrophysics Data System (ADS)

Quan, Maohua; Guo, Fengyun; Li, Meicheng; Zhao, Liancheng

2010-08-01

Atomic-scale positional resolved lattice spacing measurement is used to study the In concentration of the alloy layer in InAs/InxGa1-xSb superlattices by the molecular beam epitaxy techniques. The unstrained lattice distance d along three directions, [0 0 1], [1 1 0] and [1 1 1], was measured and the average lattice constant was calculated. The experimental lattice constants of InAs layers are almost equal to the theoretical ones. We have found that the average lattice constant of In0.25Ga0.75Sb alloy layers is in good agreement with previously reported Vegard's values, being slightly larger. The results indicate that the In concentration of x = 0.18 has a larger deviation compared with the designed values.

The Effects of Excess Co on the Phase Composition and Thermoelectric Properties of Half-Heusler NbCoSb.

PubMed

Huang, Lihong; Wang, Junchen; Chen, Xi; He, Ran; Shuai, Jing; Zhang, Jianjun; Zhang, Qinyong; Ren, Zhifeng

2018-05-11

NbCoSb with nominal 19 valence electrons, and is supposed to be metallic, has recently been reported to also exhibit the thermoelectric properties of a heavily doped n-type semiconductor. In this study, we prepared Co-rich NbCo 1+ x Sb samples ( x = 0, 0.2, 0.3, 0.4, 0.5), and their phase compositions, microstructures and thermoelectric properties were investigated. The Seebeck coefficient increased a great deal with increasing x , due to decreasing carrier concentration, and the total thermal conductivity reduced mainly because of declining κ e . Finally, a peak thermoelectric figure of merit, ZT , was about 0.46 for NbCo 1.3 Sb at 973 K. This enhancement was mainly attributed to the reduction of electric thermal conductivity and the increase of Seebeck coefficient. The excess Co had effects on the carrier concentration, deformation potential E def and DOS effective mass m * . Adding an excessive amount of Co leads to a very high E def , which was detrimental for transport characteristics.

Spin Decoherence in III-V Quantum Wells and Superlattices

NASA Astrophysics Data System (ADS)

Lau, Wayne H.; Flatté, Michael E.

2001-03-01

Electron spin decoherence in zincblende type quantum wells (QW) and superlattices (SL) near room temperature is dominated by the precessional D'yakonov-Perel' (DP) mechanism. The effective precession is a direct result of the spin splitting of the conduction band due to bulk inversion asymmetry (BIA) of the constituent zincblende semiconductors and also to any native interface asymmetry (NIA) of the heterointerfaces. The effect of BIA is dominant in common atom (CA) systems such as GaAs/AlGaAs QWs. However, in no common atom (NCA) systems such as InAs/GaSb, the interface bonds are different in character from those in the bulk and are asymmetrically oriented (giving rise to NIA). To accurately describe the DP spin relaxation mechanism we employ a nonperturbative nanostructure model based on a fourteen-bulk-band basis, including both BIA and NIA. Quantitative agreement between these calculations and measurements is found for GaAs/AlGaAs, InGaAs/InP, and GaSb/AlSb QW's, as well as for an InAs/GaSb SL.

Optimizing the Carrier Density and Thermoelectric Properties of Sb2Te3 Films by Using the Growth Temperature

NASA Astrophysics Data System (ADS)

Thiet, Duong Van; Quang, Nguyen Van; Hai, Nguyen Thi Minh; Huong, Nguyen Thi; Cho, Sunglae; Tuan, Duong Anh; Dung, Dang Duc; Tam, Tran Van

2018-04-01

In this work, we report on the structural and thermoelectric properties of Sb2Te3 films deposited on GaSb(111) substrates by using molecular beam epitaxy. The effects of the growth temperature on the microstructure and thermoelectric properties of the films were investigated. The results show that Sb2Te3 films grow on GaSb(111) along (00l) axis normal to the substrate and have a hexagonal structure with a layer-by-layer growth mode in growth temperature range from 200 to 250 °C while at 175 and 300 °C, the films show an island growth mode. Te and Sb2Te3 phases coexist at a growth temperature of 175 °C. The films exhibit a metallic behavior for growth temperatures below 250 °C and a semiconductor behavior at 300 °C. By changing growth temperature, we were able to vary the carrier density from 9.96×1018 to 4.55×1019 cm -3. At room temperature, the Seebeck coefficients are 110, 146, and 138 μV/K for growth temperatures of 175, 200 and 250 °C, respectively, and a large value of the power factor 61.67 μW/cm-K2 is achieved for the film grown at 250 °C.

Combined Effects of Time Spent in Physical Activity, Sedentary Behaviors and Sleep on Obesity and Cardio-Metabolic Health Markers: A Novel Compositional Data Analysis Approach

PubMed Central

Chastin, Sebastien F. M.; Palarea-Albaladejo, Javier; Dontje, Manon L.; Skelton, Dawn A.

2015-01-01

The associations between time spent in sleep, sedentary behaviors (SB) and physical activity with health are usually studied without taking into account that time is finite during the day, so time spent in each of these behaviors are codependent. Therefore, little is known about the combined effect of time spent in sleep, SB and physical activity, that together constitute a composite whole, on obesity and cardio-metabolic health markers. Cross-sectional analysis of NHANES 2005–6 cycle on N = 1937 adults, was undertaken using a compositional analysis paradigm, which accounts for this intrinsic codependence. Time spent in SB, light intensity (LIPA) and moderate to vigorous activity (MVPA) was determined from accelerometry and combined with self-reported sleep time to obtain the 24 hour time budget composition. The distribution of time spent in sleep, SB, LIPA and MVPA is significantly associated with BMI, waist circumference, triglycerides, plasma glucose, plasma insulin (all p<0.001), and systolic (p<0.001) and diastolic blood pressure (p<0.003), but not HDL or LDL. Within the composition, the strongest positive effect is found for the proportion of time spent in MVPA. Strikingly, the effects of MVPA replacing another behavior and of MVPA being displaced by another behavior are asymmetric. For example, re-allocating 10 minutes of SB to MVPA was associated with a lower waist circumference by 0.001% but if 10 minutes of MVPA is displaced by SB this was associated with a 0.84% higher waist circumference. The proportion of time spent in LIPA and SB were detrimentally associated with obesity and cardiovascular disease markers, but the association with SB was stronger. For diabetes risk markers, replacing SB with LIPA was associated with more favorable outcomes. Time spent in MVPA is an important target for intervention and preventing transfer of time from LIPA to SB might lessen the negative effects of physical inactivity. PMID:26461112

Study of Structural, Optical and Electrical Properties of InAs/InAsSb Superlattices Using Multiple Characterization Techniques

NASA Astrophysics Data System (ADS)

Shen, Xiaomeng

InAs/InAsSb type-II superlattices (T2SLs) can be considered as potential alternatives for conventional HgCdTe photodetectors due to improved uniformity, lower manufacturing costs with larger substrates, and possibly better device performance. This dissertation presents a comprehensive study on the structural, optical and electrical properties of InAs/InAsSb T2SLs grown by Molecular Beam Epitaxy. The effects of different growth conditions on the structural quality were thoroughly investigated. Lattice-matched condition was successfully achieved and material of exceptional quality was demonstrated. After growth optimization had been achieved, structural defects could hardly be detected, so different characterization techniques, including etch-pit-density (EPD) measurements, cathodoluminescence (CL) imaging and X-ray topography (XRT), were explored, in attempting to gain better knowledge of the sparsely distributed defects. EPD revealed the distribution of dislocation-associated pits across the wafer. Unfortunately, the lack of contrast in images obtained by CL imaging and XRT indicated their inability to provide any quantitative information about defect density in these InAs/InAsSb T2SLs. The nBn photodetectors based on mid-wave infrared (MWIR) and long-wave infrared (LWIR) InAs/InAsSb T2SLs were fabricated. The significant difference in Ga composition in the barrier layer coupled with different dark current behavior, suggested the possibility of different types of band alignment between the barrier layers and the absorbers. A positive charge density of 1.8 x 1017/cm3 in the barrier of MWIR nBn photodetector, as determined by electron holography, confirmed the presence of a potential well in its valence band, thus identifying type-II alignment. In contrast, the LWIR nBn photodetector was shown to have type-I alignment because no sign of positive charge was detected in its barrier. Capacitance-voltage measurements were performed to investigate the temperature dependence of carrier densities in a metal-oxide-semiconductor (MOS) structure based on MWIR InAs/InAsSb T2SLs, and a nBn structure based on LWIR InAs/InAsSb T2SLs. No carrier freeze-out was observed in either sample, indicating very shallow donor levels. The decrease in carrier density when temperature increased was attributed to the increased density of holes that had been thermally excited from localized states near the oxide/semiconductor interface in the MOS sample. No deep-level traps were revealed in deep-level transient spectroscopy temperature scans.

Thin-film preparation and characterization of Cs 3Sb 2I 9: A lead-free layered perovskite semiconductor

DOE PAGES

Saparov, Bayrammurad; Hong, Feng; Sun, Jon -Paul; ...

2015-07-09

In this study, computational, thin-film deposition and characterization approaches have been used to examine the ternary halide semiconductor Cs 3Sb 2I 9. Cs 3Sb 2I 9 has two known structural modifications, the 0-D dimer form (space group P6 3/mmc, No. 194) and the 2-D layered form (Pmore » $$\\bar{3}$$ m1, No. 164), which can be prepared via solution and solid state or gas phase reactions, respectively. Our computational investigations suggest that the layered form, which is a one-third Sb-deficient derivative of the ubiquitous perovskite structure, is a potential candidate for high-band-gap photovoltaic (PV) applications. In this work, we describe details of a two-step deposition approach that enables the preparation of large grain (>1 µm) and continuous thin films of the lead-free layered perovskite derivative Cs 3Sb 2I 9. Depending on the deposition conditions, films that are c-axis oriented or randomly oriented can be obtained. The fabricated thin films show enhanced stability under ambient air, compared to methylammonium lead (II) iodide perovskite films stored under similar conditions, and an optical band gap value of 2.05 eV. Photoelectron spectroscopy study yields an ionization energy of 5.6 eV, with the valence band maximum approximately 0.85 eV below the Fermi level, indicating near-intrinsic, weakly p-type character. Density Functional Theory (DFT) analysis points to a nearly direct band gap for this material (less than 0.02 eV difference between the direct and indirect band gaps) and a similar high-level of absorption compared to CH 3NH 3PbI 3. The photoluminescence peak intensity of Cs 3Sb 2I 9 is substantially suppressed compared to that of CH 3NH 3PbI 3, likely reflecting the presence of deep level defects that result in non-radiative recombination in the film, with computational results pointing to I i, IS b, and V I as being likely candidates. A key further finding from this study is that, despite a distinctly layered structure, the electronic transport anisotropy is less pronounced due to the high ionicity of the I atoms and the strong anti-bonding interactions between the Sb s lone pair states and I p states, which leads to a moderately dispersive valence band.« less

Probing the band structure and local electronic properties of low-dimensional semiconductor structures

NASA Astrophysics Data System (ADS)

Walrath, Jenna Cherie

Low-dimensional semiconductor structures are important for a wide variety of applications, and recent advances in nanoscale fabrication are paving the way for increasingly precise nano-engineering of a wide range of materials. It is therefore essential that the physics of materials at the nanoscale are thoroughly understood to unleash the full potential of nanotechnology, requiring the development of increasingly sophisticated instrumentation and modeling. Of particular interest is the relationship between the local density of states (LDOS) of low-dimensional structures and the band structure and local electronic properties. This dissertation presents the investigation of the band structure, LDOS, and local electronic properties of nanostructures ranging from zero-dimensional (0D) quantum dots (QDs) to two-dimensional (2D) thin films, synthesizing computational and experimental approaches including Poisson-Schrodinger band structure calculations, scanning tunneling microscopy (STM), scanning tunneling spectroscopy (STS), and scanning thermoelectric microscopy (SThEM). A method is presented for quantifying the local Seebeck coefficient (S) with SThEM, using a quasi-3D conversion matrix approach to directly convert temperature gradient-induced voltages S. For a GaAs p-n junction, the resulting S-profile is consistent with that computed using the free carrier concentration profile. This combined computational-experimental approach is expected to enable nanoscale measurements of S across a wide variety of heterostructure interfaces. The local carrier concentration, n, is profiled across epitaxial InAs/GaAs QDs, where SThEM is used to profile the temperature gradient-induced voltage, which is converted to a profile of the local S and finally to an n profile. The S profile is converted to a conduction band-edge profile and compared with Poisson-Schrodinger band-edge simulations. The combined computational-experimental approach suggests a reduced n in the QD center in comparison to that of the 2D alloy layer. The surface composition and band structure of ordered horizontal Sb2Te3 nanowires induced by femtosecond laser irradiation of a thin film are investigated, revealing a band gap modulation between buried Sb2Te3 nanowires and the surrounding insulating material. Finally, STM and STS are used to investigate the band structure of BiSbTe alloys at room temperature, revealing both the Fermi level and Dirac point located inside the bulk bandgap, indicating bulk-like insulating behavior with accessible surface states.

Schoolyard Characteristics, Physical Activity, and Sedentary Behavior: Combining GPS and Accelerometry

ERIC Educational Resources Information Center

Van Kann, Dave H. H.; de Vries, Sanne I.; Schipperijn, Jasper; de Vries, Nanne K.; Jansen, Maria W. J.; Kremers, Stef P. J.

2016-01-01

Background: Physical activity (PA) is decreasing among children, while sedentary behavior (SB) is increasing. Schoolyards seem suitable settings to influence children's PA behavior. This study investigated the associations between schoolyard characteristics and moderate-to-vigorous physical activity (MVPA) and SB of children aged 8-11 years at…

Direct Band Gap Gallium Antimony Phosphide (GaSbxP1−x) Alloys

PubMed Central

Russell, H. B.; Andriotis, A. N.; Menon, M.; Jasinski, J. B.; Martinez-Garcia, A.; Sunkara, M. K.

2016-01-01

Here, we report direct band gap transition for Gallium Phosphide (GaP) when alloyed with just 1–2 at% antimony (Sb) utilizing both density functional theory based computations and experiments. First principles density functional theory calculations of GaSbxP1−x alloys in a 216 atom supercell configuration indicate that an indirect to direct band gap transition occurs at x = 0.0092 or higher Sb incorporation into GaSbxP1−x. Furthermore, these calculations indicate band edge straddling of the hydrogen evolution and oxygen evolution reactions for compositions ranging from x = 0.0092 Sb up to at least x = 0.065 Sb making it a candidate for use in a Schottky type photoelectrochemical water splitting device. GaSbxP1−x nanowires were synthesized by reactive transport utilizing a microwave plasma discharge with average compositions ranging from x = 0.06 to x = 0.12 Sb and direct band gaps between 2.21 eV and 1.33 eV. Photoelectrochemical experiments show that the material is photoactive with p-type conductivity. This study brings attention to a relatively uninvestigated, tunable band gap semiconductor system with tremendous potential in many fields. PMID:26860470

Doping-Induced Interband Gain in InAs/AlSb Quantum Wells

NASA Technical Reports Server (NTRS)

Kolokolov, K. I.; Ning, C. Z.

2005-01-01

A paper describes a computational study of effects of doping in a quantum well (QW) comprising a 10-nm-thick layer of InAs sandwiched between two 21-nm-thick AlSb layers. Heretofore, InAs/AlSb QWs have not been useful as interband gain devices because they have type-II energy-band-edge alignment, which causes spatial separation of electrons and holes, thereby leading to weak interband dipole matrix elements. In the doping schemes studied, an interior sublayer of each AlSb layer was doped at various total areal densities up to 5 X 10(exp 12) / square cm. It was found that (1) proper doping converts the InAs layer from a barrier to a well for holes, thereby converting the heterostructure from type II to type I; (2) the resultant dipole matrix elements and interband gains are comparable to those of typical type-I heterostructures; and (3) dipole moments and optical gain increase with the doping level. Optical gains in the transverse magnetic mode can be almost ten times those of other semiconductor material systems in devices used to generate medium-wavelength infrared (MWIR) radiation. Hence, doped InAs/AlSb QWs could be the basis of an alternative material system for devices to generate MWIR radiation.

Using the 18-Electron Rule To Understand the Nominal 19-Electron Half-Heusler NbCoSb with Nb Vacancies

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

Zeier, Wolfgang G.; Anand, Shashwat; Huang, Lihong

The 18-electron rule is a widely used criterion in the search for new half-Heusler thermoelectric materials. However, several 19-electron compounds such as NbCoSb have been found to be stable and exhibit thermoelectric properties rivaling state-of-the art materials. Using synchrotron X-ray diffraction and density functional theory calculations, we show that samples with nominal (19-electron) composition NbCoSb actually contain a half-Heusler phase with composition Nb0.84CoSb. The large amount of stable Nb vacancies reduces the overall electron count, which brings the stoichiometry of the compound close to an 18-electron count, and stabilizes the material. Excess electrons beyond 18 electrons provide heavy doping neededmore » to make these good thermoelectric materials. This work demonstrates that considering possible defect chemistry and allowing small variation of electron counting leads to extra degrees of freedom for tailoring thermoelectric properties and exploring new compounds. Here we discuss the 18-electron rule as a guide to find defect-free half-Heusler semiconductors. Other electron counts such as 19-electron NbCoSb can also be expected to be stable as n-type metals, perhaps with cation vacancy defects to reduce the electron count.« less

A review of the assessment and prevalence of sedentarism in older adults, its physiology/health impact and non-exercise mobility counter-measures.

PubMed

Wullems, Jorgen A; Verschueren, Sabine M P; Degens, Hans; Morse, Christopher I; Onambélé, Gladys L

2016-06-01

This literature review focuses on aspects of sedentary behaviour (SB) in elderly. Since it has been identified as a distinct health risk, independent of physical activity, SB is a significant issue. This is particularly true for an ageing population as evidence shows that older adults (aged ≥65 years) are the most sedentary age group (on average 8.5-9.6 h daily sitting time). Accurate SB assessment is important for understanding this habitual behaviour and its impact. However, SB measurement is challenging, regardless of the method used. Although negative associations of SB in elderly have been reported for several health outcomes, evidence is inconclusive, apart from the evidence on the adverse SB effect on the all-cause mortality rate. Generally, strategies have been proposed to counteract SB, of which breaking prolonged sedentary bouts with at least light-intensity physical activity seems to be the most promising. Overall, further research in elderly is required to increase the evidence and to either support or refute the current findings. Moreover, further research will help to develop informed SB guidelines for an optimal strategy to counteract SB and its health effects in older adults.

High performance P-type thermoelectric materials and methods of preparation

NASA Technical Reports Server (NTRS)

Caillat, Thierry (Inventor); Borshchevsky, Alexander (Inventor); Fleurial, Jean-Pierre (Inventor)

2002-01-01

The present invention is embodied in high performance p-type thermoelectric materials having enhanced thermoelectric properties and the methods of preparing such materials. In one aspect of the invention, p-type semiconductors of formula Zn.sub.4-x A.sub.x Sb.sub.3-y B.sub.y wherein 0.ltoreq.x.ltoreq.4, A is a transition metal, B is a pnicogen, and 0.ltoreq.y.ltoreq.3 are formed for use in manufacturing thermoelectric devices with substantially enhanced operating characteristics and improved efficiency. Two methods of preparing p-type Zn.sub.4 Sb.sub.3 and related alloys of the present invention include a crystal growth method and a powder metallurgy method.

Mediated Effects of Perceived Competence on Youth Physical Activity and Sedentary Behavior.

PubMed

Bai, Yang; Chen, Senlin; Vazou, Spyridoula; Welk, Gregory J; Schaben, Jodee

2015-01-01

This study evaluates whether physical activity (PA) and sedentary behavior (SB) are influenced by a common mediating relationship. A total of 1,552 participants in 3rd to 12th grade completed an online survey that included assessments of PA at school (PAS), PA at home (PAH), and SB as well as a battery of psychosocial variables (i.e., attraction to PA and perceived competence). Perceived competence had a direct positive effect on PA and a negative effect on SB. These associations were consistently (but partially) mediated by attraction to PA; however, the indirect effect (IE) of perceived competence was stronger for PAH (IE = .27, p < .05) than for PAS (IE = .07, p < .05), or SB (IE = .13, p < .05). This study revealed some direct effects and IEs of perceived competence on PAS, PAH, and SB through attraction to PA as the mediator. PA and SB may be influenced by some common underlying psychosocial mediators.

Experimental phase diagram of zero-bias conductance peaks in superconductor/semiconductor nanowire devices

PubMed Central

Chen, Jun; Yu, Peng; Stenger, John; Hocevar, Moïra; Car, Diana; Plissard, Sébastien R.; Bakkers, Erik P. A. M.; Stanescu, Tudor D.; Frolov, Sergey M.

2017-01-01

Topological superconductivity is an exotic state of matter characterized by spinless p-wave Cooper pairing of electrons and by Majorana zero modes at the edges. The first signature of topological superconductivity is a robust zero-bias peak in tunneling conductance. We perform tunneling experiments on semiconductor nanowires (InSb) coupled to superconductors (NbTiN) and establish the zero-bias peak phase in the space of gate voltage and external magnetic field. Our findings are consistent with calculations for a finite-length topological nanowire and provide means for Majorana manipulation as required for braiding and topological quantum bits. PMID:28913432

Formation and evolution of ripples on ion-irradiated semiconductor surfaces

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

Kang, M.; Wu, J. H.; Ye, W.

We have examined the formation and evolution of ripples on focused-ion-beam (FIB) irradiated compound semiconductor surfaces. Using initially normal-incidence Ga{sup +} FIB irradiation of InSb, we tuned the local beam incidence angle (θ{sub eff}) by varying the pitch and/or dwell time. For single-pass FIB irradiation, increasing θ{sub eff} induces morphological evolution from pits and islands to ripples to featureless surfaces. Multiple-pass FIB irradiation of the rippled surfaces at a fixed θ{sub eff} leads to island formation on the ripple crests, followed by nanorod (NR) growth. This ripple-NR transition provides an alternative approach for achieving dense arrays of NRs.

Self-assembling of impurity clusters in AlN:(Ga, BV, CV), (BV, CV = P, As; P, Sb; As, Sb)

NASA Astrophysics Data System (ADS)

Elyukhin, V. A.

2015-11-01

The self-assembling conditions of arrays of tetrahedral impurity clusters of two types in zinc blende AlN:(Ga, BV, CV), (BV, CV = P, As; P, Sb; As, Sb) are represented. Doping with one cation and two anion isoelectronic impurities transforms AlN into AlN-rich GaxAl1-xBVyCVzN1-y-z alloy of GaBV, GaCV, GaN, AlBV, AlCV and AlN. The cause of self-assembling is the preference of GaBV, GaCV and AlN bonding over that of GaN, AlBV, AlCV. The conditions are considered from 0 °C to 1000 °C in the dilute and ultra dilute limits for the cation and anion impurities, correspondingly. The temperature ranges between the cluster occurrence and self-assembling completion when the same anion impurities are in clusters are very small. 1P4Ga and 1As4Ga cluster occurrence temperatures are equal, correspondingly, to 797 °C and 736 °C at Ga content 2% and P and As contents 0.01%. 1P4Ga and 1Sb4Ga cluster occurrence temperatures are equal, correspondingly, to 976 °C and 736 °C at the same impurity contents. The cluster densities in AlN:(Ga, As, Sb) are close to those in AlN:(Ga, P, Sb). The results demonstrate that studied semiconductors are promising materials to produce arrays of identical ∼1 nm low band gap objects of two types embedded in the wide band gap matrix.

Thermoelectric properties, Shubnikov-de Haas effect and mobility of charge carriers in bismuth antimony tellurides and selenides and nanocomposite based on these materials

NASA Astrophysics Data System (ADS)

Kulbachinskii, V. A.; Kytin, V. G.; Kudryashov, A. A.; Lunin, R. A.; Banerjee, A.

2017-04-01

We describe here the study of the Shubnikov-de Haas effect and thermoelectric properties of p-(Bi0.5Sb0.5)2Te3 single crystals doped with Ga, n-Bi2-xTlxSe3 and p-Sb2-xTlxTe3. Using Fourier spectra of the oscillations we calculated the mobility of charge carriers and its variation upon doping. We found that Ga has a donor effect in p-(Bi0.5Sb0.5)2Te3, Tl is an acceptor in n-Bi2-xTlxSe3 and increases the mobility of electrons, while in p-Sb2-xTlxTe3, Tl is a donor and decreases the mobility of holes. We consider the evolution of the defectiveness of crystals that leads to the observed effects. We also synthesized and investigated nanocomposites of solid solutions Sb2Te3-xSex (0 < x < 1). When Se concentration increases in Sb2Te3-xSex, the concentration of holes decreases. At the same time the Seebeck coefficient decreases. This is not typical for semiconductors but correlates with the earlier data. A theoretical model was developed to calculate simultaneously the dependences of the Seebeck coefficient, Hall coefficient and conductivity on the selenium concentration x. Calculations showed that for a simultaneous quantitative description of the thermoelectric and galvanomagnetic data it is necessary to take into consideration both the evolution of the band structure of Sb2Te3-xSex and partial localization of holes.

High-efficiency photovoltaic cells

DOEpatents

Yang, H.T.; Zehr, S.W.

1982-06-21

High efficiency solar converters comprised of a two cell, non-lattice matched, monolithic stacked semiconductor configuration using optimum pairs of cells having bandgaps in the range 1.6 to 1.7 eV and 0.95 to 1.1 eV, and a method of fabrication thereof, are disclosed. The high band gap subcells are fabricated using metal organic chemical vapor deposition (MOCVD), liquid phase epitaxy (LPE) or molecular beam epitaxy (MBE) to produce the required AlGaAs layers of optimized composition, thickness and doping to produce high performance, heteroface homojunction devices. The low bandgap subcells are similarly fabricated from AlGa(As)Sb compositions by LPE, MBE or MOCVD. These subcells are then coupled to form a monolithic structure by an appropriate bonding technique which also forms the required transparent intercell ohmic contact (IOC) between the two subcells. Improved ohmic contacts to the high bandgap semiconductor structure can be formed by vacuum evaporating to suitable metal or semiconductor materials which react during laser annealing to form a low bandgap semiconductor which provides a low contact resistance structure.

Ballistic superconductivity in semiconductor nanowires

PubMed Central

Zhang, Hao; Gül, Önder; Conesa-Boj, Sonia; Nowak, Michał P.; Wimmer, Michael; Zuo, Kun; Mourik, Vincent; de Vries, Folkert K.; van Veen, Jasper; de Moor, Michiel W. A.; Bommer, Jouri D. S.; van Woerkom, David J.; Car, Diana; Plissard, Sébastien R; Bakkers, Erik P.A.M.; Quintero-Pérez, Marina; Cassidy, Maja C.; Koelling, Sebastian; Goswami, Srijit; Watanabe, Kenji; Taniguchi, Takashi; Kouwenhoven, Leo P.

2017-01-01

Semiconductor nanowires have opened new research avenues in quantum transport owing to their confined geometry and electrostatic tunability. They have offered an exceptional testbed for superconductivity, leading to the realization of hybrid systems combining the macroscopic quantum properties of superconductors with the possibility to control charges down to a single electron. These advances brought semiconductor nanowires to the forefront of efforts to realize topological superconductivity and Majorana modes. A prime challenge to benefit from the topological properties of Majoranas is to reduce the disorder in hybrid nanowire devices. Here we show ballistic superconductivity in InSb semiconductor nanowires. Our structural and chemical analyses demonstrate a high-quality interface between the nanowire and a NbTiN superconductor that enables ballistic transport. This is manifested by a quantized conductance for normal carriers, a strongly enhanced conductance for Andreev-reflecting carriers, and an induced hard gap with a significantly reduced density of states. These results pave the way for disorder-free Majorana devices. PMID:28681843

Entropy-driven loss of gas-phase Group 5 species from GOLD/3-5 compound semiconductor systems

NASA Astrophysics Data System (ADS)

Pugh, J. H.; Williams, R. S.

1986-02-01

Temperature dependent chemical interactions between Au and nine 3-5 compound semiconductors (3=A1, Ga, In and V=P, As, Sb) have been calculated using bulk thermodynamic properties. Enthalpic considerations alone are insufficient to predict metal/compound-semiconductor reactivities. The entropy of vaporization of the group 5 elements is shown to be an extremely important driving force for chemical reactions involving the 3-5's, since it enables several endothermic reactions to occur spontaneously under certain temperature and pressure conditions. Plots of either Gibb's free energies of reaction or equilibrium vapor pressure of the group 5 element versus temperature are used to predict critical reaction temperatures for each of the systems studied. These plots agree extremely well with previous experimental observations of thin film reactions of Au on GaAs.

Physical activity: from epidemiological evidence to individualized patient management.

PubMed

Charansonney, Olivier Luc; Vanhees, Luc; Cohen-Solal, Alain

2014-01-01

Physical activity (PA), physical fitness (PF), and even a few sedentary behaviors (SB) are strongly and independently linked to improved survival rate. However, key questions remain: what are the physiological interrelationships between SB, PA, and PF? How should we differently emphasize promoting PA, increasing PF with exercise, and decreasing SB among other prevention measures? What are the interrelationships of both PA and SB levels with drug treatment efficacy? To address these questions we developed an integrated patient-centric model combining physiology with epidemiological evidence to characterize the individual risk attached to PA level, PF, and SB. Epidemiological data were collected by extensive literature review. Nine meta-analyses, 198 cohort studies (3.8 million people), and 13 controlled trials were reviewed. 1. A high level of SB induces chronic stress and increases the risk of both chronic disease and mortality. 2. Vigorous PA increases PF and physiological reserve, thereby improving survival rate. This effect is not mediated by improved traditional risk factors. The risk for most individuals is a mix of high SB, low to mild PA, and low to mild PF. This model can improve the individualized prescription of PA modalities. Furthermore, the benefit of treatments such as statins or beta-blockers can be cancelled out if a decrease in PA or an increase in SB is induced by drug related side effects. To improve patient management both types of therapeutic interventions and dose should be carefully chosen for each individual in order to maintain/increase PA level while decreasing SB. Copyright © 2013 Elsevier Ireland Ltd. All rights reserved.

Impacts of active school design on school-time sedentary behavior and physical activity: A pilot natural experiment.

PubMed

Brittin, Jeri; Frerichs, Leah; Sirard, John R; Wells, Nancy M; Myers, Beth M; Garcia, Jeanette; Sorensen, Dina; Trowbridge, Matthew J; Huang, Terry

2017-01-01

Children spend a significant portion of their days in sedentary behavior (SB) and on average fail to engage in adequate physical activity (PA). The school built environment may influence SB and PA, but research is limited. This natural experiment evaluated whether an elementary school designed to promote movement impacted students' school-time SB and PA. Accelerometers measured SB and PA at pre and post time-points in an intervention group who moved to the new school (n = 21) and in a comparison group experiencing no school environmental change (n = 20). Difference-in-difference (DD) analysis examined SB and PA outcomes in these groups. Measures were also collected post-intervention from an independent, grade-matched group of students in the new school (n = 21). As expected, maturational increases in SB were observed. However, DD analysis estimated that the intervention attenuated increase in SB by 81.2 ± 11.4 minutes/day (p<0.001), controlling for time in moderate to vigorous physical activity (MVPA). The intervention was also estimated to increase daily number of breaks from SB by 23.4 ± 2.6 (p < .001) and to increase light physical activity (LPA) by 67.7 ± 10.7 minutes/day (p<0.001). However, the intervention decreased MVPA by 10.3 ± 2.3 minutes/day (p<0.001). Results of grade-matched independent samples analysis were similar, with students in the new vs. old school spending 90.5 ± 16.1 fewer minutes/day in SB, taking 21.1 ± 2.7 more breaks from SB (p<0.001), and spending 64.5 ± 14.8 more minutes in LPA (p<0.001), controlling for time in MVPA. Students in the new school spent 13.1 ± 2.7 fewer minutes in MVPA (p<0.001) than their counterparts in the old school. This pilot study found that active school design had beneficial effects on SB and LPA, but not on MVPA. Mixed results point to a need for active classroom design strategies to mitigate SB, and quick access from classrooms to areas permissive of high-intensity activities to promote MVPA. Integrating active design with programs/policies to promote PA may yield greatest impact on PA of all intensities.

Impacts of active school design on school-time sedentary behavior and physical activity: A pilot natural experiment

PubMed Central

Frerichs, Leah; Sirard, John R.; Wells, Nancy M.; Myers, Beth M.; Garcia, Jeanette; Sorensen, Dina; Trowbridge, Matthew J.; Huang, Terry

2017-01-01

Background Children spend a significant portion of their days in sedentary behavior (SB) and on average fail to engage in adequate physical activity (PA). The school built environment may influence SB and PA, but research is limited. This natural experiment evaluated whether an elementary school designed to promote movement impacted students’ school-time SB and PA. Methods Accelerometers measured SB and PA at pre and post time-points in an intervention group who moved to the new school (n = 21) and in a comparison group experiencing no school environmental change (n = 20). Difference-in-difference (DD) analysis examined SB and PA outcomes in these groups. Measures were also collected post-intervention from an independent, grade-matched group of students in the new school (n = 21). Results As expected, maturational increases in SB were observed. However, DD analysis estimated that the intervention attenuated increase in SB by 81.2 ± 11.4 minutes/day (p<0.001), controlling for time in moderate to vigorous physical activity (MVPA). The intervention was also estimated to increase daily number of breaks from SB by 23.4 ± 2.6 (p < .001) and to increase light physical activity (LPA) by 67.7 ± 10.7 minutes/day (p<0.001). However, the intervention decreased MVPA by 10.3 ± 2.3 minutes/day (p<0.001). Results of grade-matched independent samples analysis were similar, with students in the new vs. old school spending 90.5 ± 16.1 fewer minutes/day in SB, taking 21.1 ± 2.7 more breaks from SB (p<0.001), and spending 64.5 ± 14.8 more minutes in LPA (p<0.001), controlling for time in MVPA. Students in the new school spent 13.1 ± 2.7 fewer minutes in MVPA (p<0.001) than their counterparts in the old school. Conclusions This pilot study found that active school design had beneficial effects on SB and LPA, but not on MVPA. Mixed results point to a need for active classroom design strategies to mitigate SB, and quick access from classrooms to areas permissive of high-intensity activities to promote MVPA. Integrating active design with programs/policies to promote PA may yield greatest impact on PA of all intensities. PMID:29216300

Engineering half-Heusler thermoelectric materials using Zintl chemistry

NASA Astrophysics Data System (ADS)

Zeier, Wolfgang G.; Schmitt, Jennifer; Hautier, Geoffroy; Aydemir, Umut; Gibbs, Zachary M.; Felser, Claudia; Snyder, G. Jeffrey

2016-06-01

Half-Heusler compounds based on XNiSn and XCoSb (X = Ti, Zr or Hf) have rapidly become important thermoelectric materials for converting waste heat into electricity. In this Review, we provide an overview on the electronic properties of half-Heusler compounds in an attempt to understand their basic structural chemistry and physical properties, and to guide their further development. Half-Heusler compounds can exhibit semiconducting transport behaviour even though they are described as ‘intermetallic’ compounds. Therefore, it is most useful to consider these systems as rigid-band semiconductors within the framework of Zintl (or valence-precise) compounds. These considerations aid our understanding of their properties, such as the bandgap and low hole mobility because of interstitial Ni defects in XNiSn. Understanding the structural and bonding characteristics, including the presence of defects, will help to develop different strategies to improve and design better half-Heusler thermoelectric materials.

Synthesis, Structure, Te Alloying, and Physical Properties of CuSbS 2

DOE PAGES

Hobbis, Dean; Wei, Kaya; Wang, Hsin; ...

2017-10-30

Materials with very low thermal conductivities continue to be of interest for a variety of applications. In this paper, we synthesized CuSbS 2 employing a mechanical alloying technique in order to investigate its physical properties. The trigonal pyramid arrangement of the S atoms around the Sb atoms allows for lone-pair electron formation that results in very low thermal conductivity. Finally, in addition to thermal properties, the structural, electrical, and optical properties, as well as compositional stability measurements, are also discussed. CuSbS 1.8Te 0.2 was similarly synthesized and characterized in order to compare its structural and transport properties with that ofmore » CuSbS 2, in addition to investigating the effect of Te alloying on these properties.« less

Synthesis, Structure, Te Alloying, and Physical Properties of CuSbS 2

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

Hobbis, Dean; Wei, Kaya; Wang, Hsin

Materials with very low thermal conductivities continue to be of interest for a variety of applications. In this paper, we synthesized CuSbS 2 employing a mechanical alloying technique in order to investigate its physical properties. The trigonal pyramid arrangement of the S atoms around the Sb atoms allows for lone-pair electron formation that results in very low thermal conductivity. Finally, in addition to thermal properties, the structural, electrical, and optical properties, as well as compositional stability measurements, are also discussed. CuSbS 1.8Te 0.2 was similarly synthesized and characterized in order to compare its structural and transport properties with that ofmore » CuSbS 2, in addition to investigating the effect of Te alloying on these properties.« less

The recent and prospective developments of cooled IR FPAs for double application at Electron NRI

NASA Astrophysics Data System (ADS)

Arutunov, V. A.; Vasilyev, I. S.; Ivanov, V. G.; Prokofyev, A. E.

2003-09-01

The recent and prospective developments of monolithic silicon IR-Schottky-barrier staring focal plane arrays (IR SB FPAs), photodetector assembly, and digital thermal imaging cameras (TICs) at Electron National Research Institute (Electron NRI) are considered. Basic parameters for IR SB FPAs with 256x256 and 512x512 pixels, and TICs based on these arrays are presented. The problems emerged while proceeding from the developments of IR SB FPAs for the wavelength range from 3 μm to 5 μm to the developments of those ones for xLWIR range are indicated (an abrupt increase in the level of background architecture). Possibility for further improvement in basic parameters of IR SB FPAs are discussed (a decrease in threshold signal power down to 0.5-1.0"1013 W/element with an increase in quantum efficiency, a decrease in output noise and proceeding to Schottky barriers of degenerated semiconductor/silicon heterojunction, and implementation of these array parameters in photodetector assembly with improved thermal background shielding taking into consideration an optical structure of TIC for concrete application). It is concluded that relative simplicity of the technology and expected low cost of monolithic silicon IR SB FPAs with basic parameters compared with hybrid IR FPAs for the wavelength ranges from 3 μm to 5 μm and from 8 μm to 12 μm maintain large monolithic IR SB FPAs as a basis for developments of double application digital TICs in the Russian Federation.

The descriptive epidemiology of total physical activity, muscle-strengthening exercises and sedentary behaviour among Australian adults--results from the National Nutrition and Physical Activity Survey.

PubMed

Bennie, Jason A; Pedisic, Zeljko; van Uffelen, Jannique G Z; Gale, Joanne; Banting, Lauren K; Vergeer, Ineke; Stamatakis, Emmanuel; Bauman, Adrian E; Biddle, Stuart J H

2016-01-25

The current Australia's Physical Activity and Sedentary Behaviour Guidelines recommend that adults engage in regular moderate-to-vigorous-intensity physical activity (MVPA) and strength training (ST), and minimise time spent in sedentary behaviours (SB). However, evidence about the specific individual and concurrent distribution of these behaviours in Australia is scarce. Therefore, the aim of this study was to determine the prevalence and sociodemographic correlates of MVPA, ST and SB in a national-representative sample of Australian adults. Data were collected using face-to-face interviews, as part of the National Nutrition and Physical Activity Survey 2011-12. The population-weighted proportions meeting the MVPA (≥ 150 min/week), ST (≥ 2 sessions/week) and combined MVPA-ST guidelines, and proportions classified as having 'low levels of SB' (< 480 min/day) were calculated, and their associations with selected sociodemographic and health-related variables were assessed using multiple logistic regression analyses. This was also done for those at potentially 'high-risk', defined as insufficient MVPA-ST and 'high-sedentary' behaviour. Out of 9345 participants (response rate = 77.0 %), aged 18-85 years, 52.6 % (95 % CI: 51.2 %-54.0 %), 18.6 % (95 % CI: 17.5 %-19.7 %) and 15.0 % (95 % CI: 13.9 %-16.1 %) met the MVPA, ST and combined MVPA-ST guidelines, respectively. Female gender, older age, low/medium education, poorer self-rated health, being classified as underweight or obese, and being a current smoker were independently associated with lower odds of meeting the MVPA, ST and combined MVPA-ST guidelines. A total of 78.9 % (95 % CI: 77.9 %-80.0 %) were classified as having low levels of SB. Females, older adults and those with lower education were more likely to report lower levels of SB, whilst those with poor self-rated health and obese individuals were less likely to report lower levels of SB (i.e. SB = ≥ 480 min/day). A total of 8.9 % (95 % CI: 8.1 %-9.6 %) were categorised as individuals at potentially 'high-risk'. Those with poorer self-rated health, obese individuals, those aged 25-44, and current smokers were more likely to be in the 'high risk' group. The large majority of Australian adults do not meet the full physical activity guidelines and/or report excessive SB. Our results call for public health interventions to reduce physical inactivity and SB in Australia, particularly among the subgroups at the highest risk of these unhealthy behaviours.

Associations of physical activity and sedentary behavior with academic skills--a follow-up study among primary school children.

PubMed

Haapala, Eero A; Poikkeus, Anna-Maija; Kukkonen-Harjula, Katriina; Tompuri, Tuomo; Lintu, Niina; Väistö, Juuso; Leppänen, Paavo H T; Laaksonen, David E; Lindi, Virpi; Lakka, Timo A

2014-01-01

There are no prospective studies that would have compared the relationships of different types of physical activity (PA) and sedentary behavior (SB) with academic skills among children. We therefore investigated the associations of different types of PA and SB with reading and arithmetic skills in a follow-up study among children. The participants were 186 children (107 boys, 79 girls, 6-8 yr) who were followed-up in Grades 1-3. PA and SB were assessed using a questionnaire in Grade 1. Reading fluency, reading comprehension and arithmetic skills were assessed using standardized tests at the end of Grades 1-3. Among all children more recess PA and more time spent in SB related to academic skills were associated with a better reading fluency across Grades 1-3. In boys, higher levels of total PA, physically active school transportation and more time spent in SB related to academic skills were associated with a better reading fluency across the Grades 1-3. Among girls, higher levels of total PA were related to worse arithmetic skills across Grades 1-3. Moreover, total PA was directly associated with reading fluency and arithmetic skills in Grades 1-3 among girls whose parents had a university degree, whereas these relationships were inverse in girls of less educated parents. Total PA, physically active school transportation and SB related to academic skills may be beneficial for the development of reading skills in boys, whereas factors that are independent of PA or SB may be more important for academic skills in girls. ClinicalTrials.gov: NCT01803776.

Quaternary Narrow-Band Semiconductors (HgTe)x(InSb)1-X for Far-Infrared Detectors.

DTIC Science & Technology

1986-08-31

A. L. Petrov, and G. A. Kuzmina . Sov. Phys. Semicond., 13, 480 (1979). 34. A. V. Voitsekhovskii and V. P. Drobyazko. Inorg. Materials, 3, 1976 (1967...801, 807 (1973); Izv. VUZ Fiz. USSR, 16, 76, 82 (1973). 37. A. L. Petrov and G. A. Kuzmina . Sov. Phys. Semicond., 14, . 604 (1980). 38. G. I

Thermoelectric Properties of Complex Zintl Phases

NASA Astrophysics Data System (ADS)

Snyder, G. Jeffrey

2008-03-01

Complex Zintl phases make ideal thermoelectric materials because they can exhibit the necessary ``electron-crystal, phonon-glass'' properties required for high thermoelectric efficiency. Complex crystal structures can lead to high thermoelectric figure of merit (zT) by having extraordinarily low lattice thermal conductivity. A recent example is the discovery that Yb14MnSb11, a complex Zintl compound, has twice the zT as the SiGe based material currently in use at NASA. The high temperature (300K - 1300K) electronic properties of Yb14MnSb11 can be understood using models for heavily doped semiconductors. The free hole concentration, confirmed by Hall effect measurements, is set by the electron counting rules of Zintl and the valence of the transition metal (Mn^+2). Substitution of nonmagnetic Zn^+2 for the magnetic Mn^+2 reduces the spin-disorder scattering and leads to increased zT (10%). The reduction of spin-disorder scattering is consistent with the picture of Yb14MnSb11 as an underscreened Kondo lattice as derived from low temperature measurements. The hole concentration can be reduced by the substitution of Al^+3 for Mn^+2, which leads to an increase in the Seebeck coefficient and electrical resistivity consistent with models for degenerate semiconductors. This leads to further improvements (about 25%) in zT and a reduction in the temperature where the zT peaks. The peak in zT is due to the onset of minority carrier conduction and can be correlated with reduction in Seebeck coefficient, increase in electrical conductivity and increase in thermal conductivity due to bipolar thermal conduction.

Uncooled EuSbTe3 photodetector highly sensitive from ultraviolet to terahertz frequencies

NASA Astrophysics Data System (ADS)

Niu, Ying Y.; Wu, Dong; Su, Yu Q.; Zhu, Hai; Wang, Biao; Wang, Ying X.; Zhao, Zi R.; Zheng, Ping; Niu, Jia S.; Zhou, Hui B.; Wei, Jian; Wang, Nan L.

2018-01-01

Light probe from Uv to THz is critical in photoelectronics and has great applications ranging from imaging, communication to medicine (Woodward et al 2002 Phys. Med. Biol. 47 3853-63 Pospischil et al 2013 Nat. Photon. 7 892-6 Martyniuk and Rogalski 2003 Prog. Quantum Electron. 27 59-210). However, the room temperature ultrabroadband photodetection across visible down to far-infrared is still challenging. The challenging arises mainly from the lack of suitable photoactive materials. Because that conventional semiconductors, such as silicon, have their photosensitive properties cut off by the bandgap and are transparent to spectrum at long-wavelength infrared side (Ciupa and Rogalski 1997 Opto-Electron. Rev. 5 257-66 Tonouchi 2007 Nat. Photon. 1 97-105 Sizov and Rogalski 2010 Prog. Quantum Electron. 34 278-347 Kinch 2000 J. Electron. Mater. 29 809-17). Comparatively, the dielectrics with very narrow band-gap but maintain the semiconductor-like electrical conduction would have priorities for ultrabroadband photodetection. Here we report on EuSbTe3 is highly sensitive from ultraviolet directly to terahertz (THz) at room temperature. High photoresponsivities 1-8 A W-1 reached in our prototype EuSbTe3 detectors with low noise equivalent power (NEP) recorded, for instances ~150 pW · Hz-1/2 (at λ  =  532 nm) and ~0.6 nW · Hz-1/2 (at λ  =  118.8 µm) respectively. Our results demonstrate a promising system with direct photosensitivity extending well into THz regime at room temperature, shed new light on exploring more sophisticated multi-band photoelectronics.

Ab Initio Prediction of the Structural, Electronic, Elastic, and Thermoelectric Properties of Half-Heusler Ternary Compounds TiIrX (X = As and Sb)

NASA Astrophysics Data System (ADS)

Chibani, S.; Arbouche, O.; Zemouli, M.; Amara, K.; Benallou, Y.; Azzaz, Y.; Belgoumène, B.; Bentayeb, A.; Ameri, M.

2018-01-01

The structural, electronic, elastic, and thermoelectric properties of TiIrX (X = As and Sb) half-Heusler compounds with 18 valence electrons were studied using density functional theory. The generalized gradient approximation of Perdew-Burke and Ernzerhof used for calculation of the structural parameters and elastic properties of TiIrAs and TiIrSb denotes that the computed lattice constants were in excellent agreement with the available experimental data and previous theoretical works. Furthermore, the calculated elastic constants for both compounds satisfy the Born criteria indicating their mechanical stabilities. The modified Becke-Johnson potential (TB-mBJ) was used to provide a better description of the electronic structures, which indicate that both compounds are narrow-gap semiconductors. Additionally, the investigations of thermoelectric performance were carried out using the results of ab initio band-structure calculations and the semi-classical Boltzmann theory within the constant relaxation time approximations. The predicted values of the figure of merit ZT e are close to unity at room temperature. This reveals that TiIrAs and TiIrSb compounds are excellent candidates for practical applications in the thermoelectric devices.

The growth of InAs{sub 1-x}Sb{sub x}/InAs strained-layer superlattices by metal-organic chemical vapor deposition

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

Biefeld, R.M.; Baucom, K.C.; Kurtz, S.R.

1993-06-01

InAs{sub 1-x}Sb{sub x}/InAs strained-layer superlattice (SLS) semiconductors and thick epitaxial layers of InAs{sub 1-x}Sb{sub x} were grown under a variety of conditions by metal-organic chemical vapor deposition on InAs substrates. The III/V ratio was varied from 0.026 to 1.0 over a temperature range of 475--525C, at pressures of 200 to 660 torr and growth rates of 0.75 to 3.0 {mu}m/hour. The composition of the ternary can be predicted from the input gas molar flow rates using a thermodynamic model. At lower temperatures, the thermodynamic model must be modified to take account of the incomplete decomposition of arsine and trimethylantimony. Thesemore » layers were characterized by optical microscopy, SIMS, and x-ray diffraction. The optical properties of these SLS`s were determined by infrared photoluminescence and absorption measurements. The PL peak energies of the alloys` and the SLS`s are consistently lower than the previously reported values for the bandgap of InAs{sub 1-x}Sb{sub x} alloys.« less

Crystallization kinetics of the phase change material GeSb 6Te measured with dynamic transmission electron microscopy

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

Winseck, M. M.; Cheng, H. -Y.; Campbell, G. H.

2016-03-30

GeSb 6Te is a chalcogenide-based phase change material that has shown great ptoential for use in solid-state memory devices. The crystallization kinetics of amorphous thin films of GeSb 6Te during laser crystallization were followed with dynamic transmission electron microscopy, a photo-emission electron microscopy technique with nanosecond-scale time resolution. Nine-frame movies of crystal growth were taken during laser crystallization. The nucleation rate is observed to be very low and the growth rates are very high, up to 10.8 m s –1 for amorphous as-deposited films and significantly higher for an amorphous film subject to sub-threshold laser annealing before crystallization. The measuredmore » growth rates exceed any directly measured growth rate of a phase change material. Here, the crystallization is reminiscent of explosive crystallization of elemental semiconductors both in the magnitude of the growth rate and in the resulting crystalline microstructures.« less

Brush head composition, wear profile, and cleaning efficacy: an assessment of three electric brush heads using in vitro methods.

PubMed

Kaiser, Eva; Meyners, Michael; Markgraf, Dirk; Stoerkel, Ulrich; von Koppenfels, Roxana; Adam, Ralf; Soukup, Martin; Wehrbein, Heinrich; Erbe, Christina

2014-01-01

The objective of this research was to evaluate a current store brand (SB) brush head for composition/physical characteristics, Wear Index (WI), and cleaning efficacy versus the previous SB brush head refill design (SB control) and the Oral-B Precision Clean brush head (positive control, PC). This research consisted of three parts: 1) Analytical analysis using Fourier Transform Infrared (FT-IR) spectrometry to evaluate the chemical composition of the current SB brush head bristles relative to the SB control. In addition, physical parameters such as bristle count and diameter were determined. 2) Wear Index (WI) investigation to determine the Wear Index scores of in vitro-aged brush heads at four weeks (one month) and 13 weeks (three months) by a trained investigator. To "age" the brush heads, a robot system was used as a new alternative in vitro method to simulate aging by consumer use. 3) Robot testing to determine the cleaning performance of in vitro-aged brush heads, comparing one month-aged current SB brush heads with the SB control (one and three months-aged) and the PC brush heads (three months-aged) in a standardized fashion. 1) FT-IR analysis revealed that the chemical composition of the current and control SB refill brush heads is identical. In terms of physical parameters, the current SB brush head has 12% more bristles and a slightly oval brush head compared to the round brush head of the SB control. 2) Wear Index analysis showed there was no difference in the one month-aged current SB brush head versus the one month-aged SB control (1.67 vs. 1.50, p = 0.65) or versus the three months-aged PC brush head (1.67 vs. 1.50, p = 0.65). The one month-aged current SB brush head demonstrated statistically significantly less wear than the three months-aged SB control (1.67 vs. 2.67, p = 0.01). 3) Analysis of cleaning efficacy shows that the one month-aged current SB brush head had improved cleaning performance over the one month-aged SB control brush head (p < 0.05), despite no statistically significant difference in wear. Both the one month-aged current and control SB brush heads showed statistically significantly lower cleaning performance compared to the three months-aged PC brush heads (p < 0.01). While the current SB brush head showed improved cleaning over the SB control, it demonstrated significantly lower durability and cleaning in comparison to the PC brush head. Dental professionals should be aware of these differences, both in durability and in cleaning performance, when recommending brush heads to their patients.

Correlating microbial community profiles with geochemical conditions in a watershed heavily contaminated by an antimony tailing pond.

PubMed

Xiao, Enzong; Krumins, Valdis; Tang, Song; Xiao, Tangfu; Ning, Zengping; Lan, Xiaolong; Sun, Weimin

2016-08-01

Mining activities have introduced various pollutants to surrounding aquatic and terrestrial environments, causing adverse impacts to the environment. Indigenous microbial communities are responsible for the biogeochemical cycling of pollutants in diverse environments, indicating the potential for bioremediation of such pollutants. Antimony (Sb) has been extensively mined in China and Sb contamination in mining areas has been frequently encountered. To date, however, the microbial composition and structure in response to Sb contamination has remained overlooked. Sb and As frequently co-occur in sulfide-rich ores, and co-contamination of Sb and As is observed in some mining areas. We characterized, for the first time, the microbial community profiles and their responses to Sb and As pollution from a watershed heavily contaminated by Sb tailing pond in Southwest China. The indigenous microbial communities were profiled by high-throughput sequencing from 16 sediment samples (535,390 valid reads). The comprehensive geochemical data (specifically, physical-chemical properties and different Sb and As extraction fractions) were obtained from river water and sediments at different depths as well. Canonical correspondence analysis (CCA) demonstrated that a suite of in situ geochemical and physical factors significantly structured the overall microbial community compositions. Further, we found significant correlations between individual phylotypes (bacterial genera) and the geochemical fractions of Sb and As by Spearman rank correlation. A number of taxonomic groups were positively correlated with the Sb and As extractable fractions and various Sb and As species in sediment, suggesting potential roles of these phylotypes in Sb biogeochemical cycling. Copyright © 2016 Elsevier Ltd. All rights reserved.

Characterization of GaSb/InAs type II infrared detectors at very long wavelengths: carrier scattering at defect clusters

NASA Astrophysics Data System (ADS)

Kitchin, M. R.; Jaros, M.

2003-06-01

We report a systematic study into carrier scattering by isovalent defects within GaSb/InAs superlattices. The heterostructure system which we investigate has attracted recent interest as the active region of a photodetector for very long wavelength infrared (VLWIR) (⩾12 μm) radiation. To achieve our objective, we employed models of the electronic band structure and scattering cross-section. We considered isolated, substitutional defects at each atom site throughout the unit cell in turn and found that the scattering magnitude generally follows the carrier envelope function, being greatest where the overlap of charge with the defect is highest. We scrutinized the contribution of lattice relaxation around defects to the overall scattering, by comparing calculations where this effect was, in turn, included and excluded. We identified some anomalous contributions of relaxation to both qualitative and quantitative features of the cross-section. Physical mechanisms to explain these effects must be arrived at in order to attain satisfactory characterization of these materials, highlighting the need for both microscopic models and further research. Additional modelling of islands of such defects indicated that the cross-section is proportional to the square of the number of constituent atoms, for both carrier types (holes and electrons) and each defect type. This article demonstrates important links between key growth issues and the dynamical properties of these novel semiconductor devices.

Physical activity and sedentary behavior in metabolically healthy obese young women

USDA-ARS?s Scientific Manuscript database

Studies of physical activity (PA) and sedentary behavior (SB) in metabolically healthy obese (MHO) have been limited to postmenopausal white women. We sought to determine whether PA and SB differ between MHO and metabolically abnormal obese (MAO), in young black and white women....

MOCVD of HfO2 and ZrO2 high-k gate dielectrics for InAlN/AlN/GaN MOS-HEMTs

NASA Astrophysics Data System (ADS)

Abermann, S.; Pozzovivo, G.; Kuzmik, J.; Strasser, G.; Pogany, D.; Carlin, J.-F.; Grandjean, N.; Bertagnolli, E.

2007-12-01

We apply metal organic chemical vapour deposition (MOCVD) of HfO2 and of ZrO2 from β-diketonate precursors to grow high-k gate dielectrics for InAlN/AlN/GaN metal oxide semiconductor (MOS)-high electron mobility transistors (HEMTs). High-k oxides of about 12 nm-14 nm are deposited for the MOS-HEMTs incorporating Ni/Au gates, whereas as a reference, Ni-contact-based 'conventional' Schottky-barrier (SB)-HEMTs are processed. The processed dielectrics decrease the gate current leakage of the HEMTs by about four orders of magnitude if compared with the SB-gated HEMTs and show superior device characteristics in terms of IDS and breakdown.

SEMICONDUCTOR MATERIALS: Chemical etching of a GaSb crystal incorporated with Mn grown by the Bridgman method under microgravity conditions

NASA Astrophysics Data System (ADS)

Xiaofeng, Chen; Nuofu, Chen; Jinliang, Wu; Xiulan, Zhang; Chunlin, Chai; Yude, Yu

2009-08-01

A GaSb crystal incorporated with Mn has been grown by the Bridgman method on the Polizon facility onboard the FOTON-M3 spacecraft. Structural defects and growth striations have been successfully revealed by the chemical etching method. By calculating various parameters of the convection, the striation patterns can be explained, and the critical value of the Taylor number, which characterizes the convective condition of the rotating magnetic field induced azimuthal flow, was shown. The stresses generated during crystal growth can be reflected by the observations of etch pit distribution and other structural defects. Suggestions for improving the space experiment to improve the quality of the crystal are given.

The effects of gamma irradiation on electrical characteristics of Zn/ZnO/n-Si/Au-Sb structure

NASA Astrophysics Data System (ADS)

Salari, M. Abdolahpour; Güzeldir, B.; Saǧlam, M.

2018-02-01

In this research, we have investigated the electrical characteristics of Zn/ZnO/n-Si/Au-Sb structure before and after 60Co gamma (γ)-ray source irradiation with the total dose range of 0-500 kGy at room temperature. Electrical measurements of this structure have been performed using current-voltage (I-V) and capacitance-voltage (C-V) techniques. Experimental results show that the values of the ideality factor obtained from I-V measurements increased and the values of the barrier height obtained from reverse-bias C-V measurements decreased after gamma-irradiation. The results show that the main effect of the radiation is the generation of laterally inhomogeneous defects near the semiconductor surface.

The Photocatalytic Application of Semiconductor Stibnite Nanostructure Synthesized via a Simple Microwave-Assisted Approach in Propylene Glycol for Degradation of Dye Pollutants and its Optical Property

NASA Astrophysics Data System (ADS)

Saksornchai, Eksuree; Kavinchan, Jutarat; Thongtem, Somchai; Thongtem, Titipun

2017-11-01

Stibnite (Sb2S3) semiconducting material was successfully synthesized by a rapid and facile microwave route using antimony chloride (SbCl3) and sodiumthiosulfate (Na2S2O3) dissolved in propylene glycol (PG) containing different hydroxyethyl cellulose (HEC) masses. The phase identification, morphology, and elemental composition of products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), field- emission scanning electron microscopy (FE-SEM), energy dispersive X-ray (EDX) spectroscopy, and Fourier transform infrared spectroscopy (FTIR). The results revealed the orthorhombic phase of Sb2S3 single crystal-forming sheaf-like nanostructure, and a possible formation mechanism was proposed and discussed. Its direct band gap calculated from UV-visible absorption is 1.60 eV. In this research, the photocatalytic activities of Sb2S3 nanostructure were investigated through the degradation of methyl orange (MO) and methylene blue (MB) under visible light irradiation. The as-obtained 0.30 g HEC-added solution (0.3 HEC-Sb2S3) photocatalyst exhibited better photocatalytic activity than the other products, which degraded 91% of MO within 300 min and 90% of MB within 240 min under the Xe-lamp irradiation. The first-order plot was fitted with this experiment which the rate constant ( k) of 0.3 HEC-Sb2S3 for MO and MB degradation are 0.0085 and 0.0098 min-1, respectively. Therefore, the new experience with a novel and simple synthetic procedure of Sb2S3 photocatalyst that exhibits the characteristics of a highly effective photocatalyst under visible light irradiation was discovered.

Associations of Physical Activity and Sedentary Behavior with Academic Skills – A Follow-Up Study among Primary School Children

PubMed Central

Haapala, Eero A.; Poikkeus, Anna-Maija; Kukkonen-Harjula, Katriina; Tompuri, Tuomo; Lintu, Niina; Väistö, Juuso; Leppänen, Paavo H. T.; Laaksonen, David E.; Lindi, Virpi; Lakka, Timo A.

2014-01-01

Background There are no prospective studies that would have compared the relationships of different types of physical activity (PA) and sedentary behavior (SB) with academic skills among children. We therefore investigated the associations of different types of PA and SB with reading and arithmetic skills in a follow-up study among children. Methods The participants were 186 children (107 boys, 79 girls, 6–8 yr) who were followed-up in Grades 1–3. PA and SB were assessed using a questionnaire in Grade 1. Reading fluency, reading comprehension and arithmetic skills were assessed using standardized tests at the end of Grades 1–3. Results Among all children more recess PA and more time spent in SB related to academic skills were associated with a better reading fluency across Grades 1–3. In boys, higher levels of total PA, physically active school transportation and more time spent in SB related to academic skills were associated with a better reading fluency across the Grades 1–3. Among girls, higher levels of total PA were related to worse arithmetic skills across Grades 1–3. Moreover, total PA was directly associated with reading fluency and arithmetic skills in Grades 1–3 among girls whose parents had a university degree, whereas these relationships were inverse in girls of less educated parents. Conclusions Total PA, physically active school transportation and SB related to academic skills may be beneficial for the development of reading skills in boys, whereas factors that are independent of PA or SB may be more important for academic skills in girls. Trial Registration ClinicalTrials.gov: NCT01803776 PMID:25207813

III-V/II-VI Hybrid Quantum Well Mid-Infrared Lasers

DTIC Science & Technology

2005-01-25

semiconductor lasers are of great importance for many applications such as laser diode spectroscopy , pollution monitoring, low-loss optical communication...great importance for many applications such as laser diode spectroscopy, pollutant monitoring, low-losses longwavelength optical communication...InAsSb/CdMgSe laser structure 1.2. Characterization of the laser structures and interface quality (STM, EPFM etc) 1.3. Study of spontaneous and

Multicolor (UV-IR) Photodetectors Based on Lattice-Matched 6.1 A II/VI and III/V Semiconductors

DTIC Science & Technology

2015-08-27

photodiodes with different cutoff wavelengths connected in series with tunnel diodes between adjacent photodiodes. The LEDs optically bias the inactive...perfectly conductive n-CdTe/p-InSb tunnel junction. 15. SUBJECT TERMS optical biasing; multi-junction photodetectors; triple-junction solar cell...during this project, including initial demonstrations of optical addressing, tunnel junction studies and multicolor device characterization

Characterizing the context of sedentary lifestyles in a representative sample of adults: a cross-sectional study from the physical activity measurement study project.

PubMed

Kim, Youngwon; Welk, Gregory J

2015-12-09

Research has clearly demonstrated that excess time spent on sedentary behavior (SB) increases health risks in the population. However, the lack of information on the context of SB in the population prevents a detailed understanding of sedentary lifestyles. The purpose of this study was to characterize the context of SB in a representative sample of adults and to examine differences across various socio-demographic indicators. A diverse sample of 1442 adults (ages 20-71 year) completed an interviewer-administered 24-h activity recall to provide detailed information about the time, type and location of the previous day's activities. All reported activities were matched with MET scores from the Compendium of Physical Activity but only SB (i.e., METS < 1.5) were extracted for the present analyses. The reported SB were broadly distributed across 5 primary location categories (Work: 27.5%, Community: 24.8%, Home/Indoor: 20.5%, Home/Outdoor: 15.8%, and Transportation: 11.3%). Patterns of SB allocations varied considerably across different socio-demographic indicators indicating the extreme variability in SB in the population. The findings provide unique insights about the context of SB at the population level, and can serve as a guide for developing intervention/policy studies to reduce sedentary time and minimize disparities in SB.

Electrical and optical characterization of n-InAsSb/n-GaSb heterojunctions

NASA Astrophysics Data System (ADS)

Lackner, D.; Martine, M.; Cherng, Y. T.; Steger, M.; Walukiewicz, W.; Thewalt, M. L. W.; Mooney, P. M.; Watkins, S. P.

2010-01-01

We report the electrical properties of n-InAsSb/n-GaSb heterojunctions as a function of the GaSb doping concentration. Because of the staggered type II band alignment, strong electron accumulation occurs on the InAsSb side. For low GaSb doping, depletion occurs on the GaSb side resulting in a Schottky-like junction as previously reported. As the GaSb doping increases, the built-in voltage as well as depletion width decreases as shown using self-consistent simulations. For GaSb doping levels above 5×1017 cm-3, the junction loses its rectifying properties due to tunneling. Under zero and reverse bias voltage, the photoresponse of these diodes is solely due to the photovoltaic effect in the GaSb depletion region. For forward bias voltages >400 mV, we also observed a photoconductive response from the InAsSb layer. The proposed physical mechanism is quite different from the one suggested in a recent paper.

Preparation and Thermoelectric Properties of Semiconcucting Zn(sub 4) Sb(sub 3)

NASA Technical Reports Server (NTRS)

Caillat, T.; Fleurial, J. P.; Barshchevsky, A.

1996-01-01

Hot-pressed samples fothe semiconducting compound Beta - Zn(sub 4) Sb(sub 3) were prepared and characterized by x-ray and microprobe analysis. Some physical properties of Beta - Zn(sub 4) Sb(sub 3) were determined and its thermoelectric properties measured between room temperature and 650K.

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

McCall, Kyle M.; Stoumpos, Constantinos C.; Kostina, Svetlana S.

The optical and electronic properties of Bridgman grown single crystals of the wide-bandgap semiconducting defect halide perovskites A3M2I9 (A = Cs, Rb; M = Bi, Sb) have been investigated. Intense Raman scattering was observed at room temperature for each compound, indicating high polarizability and strong electron–phonon coupling. Both low-temperature and room-temperature photoluminescence (PL) were measured for each compound. Cs3Sb2I9 and Rb3Sb2I9 have broad PL emission bands between 1.75 and 2.05 eV with peaks at 1.96 and 1.92 eV, respectively. The Cs3Bi2I9 PL spectra showed broad emission consisting of several overlapping bands in the 1.65–2.2 eV range. Evidence of strong electron–phononmore » coupling comparable to that of the alkali halides was observed in phonon broadening of the PL emission. Effective phonon energies obtained from temperature-dependent PL measurements were in agreement with the Raman peak energies. A model is proposed whereby electron–phonon interactions in Cs3Sb2I9, Rb3Sb2I9, and Cs3Bi2I9 induce small polarons, resulting in trapping of excitons by the lattice. The recombination of these self-trapped excitons is responsible for the broad PL emission. Rb3Bi2I9, Rb3Sb2I9, and Cs3Bi2I9 exhibit high resistivity and photoconductivity response under laser photoexcitation, indicating that these compounds possess potential as semiconductor hard radiation detector materials.« less

Motivators and Barriers to Reducing Sedentary Behavior Among Overweight and Obese Older Adults.

PubMed

Greenwood-Hickman, Mikael Anne; Renz, Anne; Rosenberg, Dori E

2016-08-01

To explore individual, social, environmental, and program-related motivators, barriers, and impacts of sedentary behavior (SB) reduction among a group of overweight and obese older adults aged 60 and older. Semistructured interviews were conducted with 24 participants following a SB reduction intervention. Transcripts from these interviews were iteratively coded by a team, and key themes were defined and refined guided by the social-ecological framework. Motivators included the desire to improve health, newly acquired awareness of SB, the ease of incorporating SB reduction into current lifestyle, an adaptable environment, and the use of reminders. Barriers included existing health conditions, enjoyment of sedentary activities, unadaptable environments, fatigue, and difficulty understanding SB reduction as distinct from physical activity (PA). Participants reported impacts on physical and mental health and changes in awareness, exercise, and daily activity. Although in many ways motivators and barriers to reducing SB are similar to those of PA, SB interventions have special considerations and may ultimately be easier for some individuals to incorporate into their lifestyle. © The Author 2015. Published by Oxford University Press on behalf of The Gerontological Society of America. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

The Development of III-V Semiconductor MOSFETs for Future CMOS Applications

NASA Astrophysics Data System (ADS)

Greene, Andrew M.

Alternative channel materials with superior transport properties over conventional strained silicon are required for supply voltage scaling in low power complementary metal-oxide-semiconductor (CMOS) integrated circuits. Group III-V compound semiconductor systems offer a potential solution due to their high carrier mobility, low carrier effective mass and large injection velocity. The enhancement in transistor drive current at a lower overdrive voltage allows for the scaling of supply voltage while maintaining high switching performance. This thesis focuses on overcoming several material and processing challenges associated with III-V semiconductor development including a low thermal processing budget, high interface trap state density (Dit), low resistance source/drain contacts and growth on lattice mismatched substrates. Non-planar In0.53Ga0.47As FinFETs were developed using both "gate-first" and "gate-last" fabrication methods for n-channel MOSFETs. Electron beam lithography and anisotropic plasma etching processes were optimized to create highly scaled fins with near vertical sidewalls. Plasma damage was removed using a wet etch process and improvements in gate efficiency were characterized on MOS capacitor structures. A two-step, selective removal of the pre-grown n+ contact layer was developed for "gate-last" recess etching. The final In0.53Ga 0.47As FinFET devices demonstrated an ION = 70 mA/mm, I ON/IOFF ratio = 15,700 and sub-threshold swing = 210 mV/dec. Bulk GaSb and strained In0.36Ga0.64Sb quantum well (QW) heterostructures were developed for p-channel MOSFETs. Dit was reduced to 2 - 3 x 1012 cm-2eV-1 using an InAs surface layer, (NH4)2S passivation and atomic layer deposition (ALD) of Al2O3. A self-aligned "gate-first" In0.36Ga0.64Sb MOSFET fabrication process was invented using a "T-shaped" electron beam resist patterning stack and intermetallic source/drain contacts. Ni contacts annealed at 300°C demonstrated an ION = 166 mA/mm, ION/IOFF ratio = 1,500 and sub-threshold swing = 340 mV/dec. Split C-V measurements were used to extract an effective channel mobility of muh* = 300 cm2/Vs at Ns = 2 x 1012 cm -2. "Gate-last" MOSFETs grown with an epitaxial p + contact layer were fabricated using selective gate-recess etching techniques. A parasitic "n-channel" limited ION/I OFF ratio and sub-threshold swing, most likely due to effects from the InAs surface layer.

The practice of problem-based investigative teaching reform in semiconductor physics course

NASA Astrophysics Data System (ADS)

Chen, Aiping; Wu, Gaojian; Gu, Dawei; Jiang, Hongying; Wang, Lei

2017-08-01

Semiconductor physics is an important basic course for the students of the majors of applied physics, optoelectronics, and microelectronics. The authors have been carrying out investigative-teaching reform in semiconductor physics teaching. Firstly, the teaching content was re-structured based on scientific problems. Secondly, the students were placed in groups to discuss different scientific problems and to present a few short science-reports. Thirdly, micro-lesson videos were produced for the students to study and analyze before or after class. With comparative analysis, we find out that the semiconductor-physics curriculum content was greatly enriched. In addition, the students' learning motivation and scientific thinking ability increased, and their innovation ability was improved. Overall, the teaching quality of the semiconductor physics course could be significantly improved.

Quantum oscillations and coherent interlayer transport in a new topological Dirac semimetal candidate YbMnSb2

NASA Astrophysics Data System (ADS)

Wang, Yi-Yan; Xu, Sheng; Sun, Lin-Lin; Xia, Tian-Long

2018-02-01

Dirac semimetals, which host Dirac fermions and represent a new state of quantum matter, have been studied intensively in condensed-matter physics. The exploration of new materials with topological states is important in both physics and materials science. We report the synthesis and the transport properties of high-quality single crystals of YbMnSb2. YbMnSb2 is a new compound with metallic behavior. Quantum oscillations, including Shubnikov-de Haas (SdH) oscillation and de Haas-van Alphen-type oscillation, have been observed at low temperature and high magnetic field. Small effective masses and nontrivial Berry phase are extracted from the analyses of quantum oscillations, which provide the transport evidence for the possible existence of Dirac fermions in YbMnSb2. The measurements of angular-dependent interlayer magnetoresistance indicate that the interlayer transport is coherent. The Fermi surface of YbMnSb2 possesses a quasi-two-dimensional characteristic as determined by the angular dependence of SdH oscillation frequency. These findings suggest that YbMnSb2 is a new candidate of topological Dirac semimetals.

Classes of Physical Activity and Sedentary Behavior in 5th Grade Children

PubMed Central

Dowda, Marsha; Dishman, Rod K; Pate, Russell R.

2016-01-01

Objectives To identify classes of physical activity (PA) and sedentary behaviors (SB) in 5th grade children, associated factors, and trajectories of change into 7th grade. Methods This study included n=495 children (221 boys, 274 girls) who participated in the Transitions and Activity Changes in Kids (TRACK) Study. PA was assessed objectively and via self-report. Children, parents, and school administrators completed surveys to assess related factors. Latent class analysis, growth modeling, and adjusted multinomial logistic regression procedures were used to classify children based on self-reported PA and SB and examine associated factors. Results Three classes of behavior were identified: Class 1: Low PA/Low SB, Class 2: Moderate PA/High SB, and Class 3: High PA/High SB (boys) or Class 3: High PA (girls). Class 3 children had higher levels of self-efficacy (boys), and enjoyment, parental support, and physical activity equipment at home (girls). Class 2 boys and Class 3 girls did not experience decline in PA (accelerometer) over time. Conclusions Self-efficacy (boys) and home environment (girls) may play a role in shaping patterns of PA in children. Findings may help to inform future interventions to encourage children to meet national PA guidelines. PMID:27103414

Level and potential social-ecological factors associated with physical inactivity and sedentary behavior among Moroccan school-age adolescents: a cross-sectional study.

PubMed

El-Ammari, Abdelghaffar; El Kazdouh, Hicham; Bouftini, Siham; El Fakir, Samira; El Achhab, Youness

2017-05-18

Creating a successful intervention that supports an active lifestyle and prevents sedentary one requires a better understanding of the factors associated with physical inactivity (PI) and sedentary behavior (SB). However, these factors have not been assessed among Moroccan adolescents. This study aimed to determine prevalence of PI and SB and to explore their potential social-ecological associated factors in school-age adolescents. In this cross-sectional study, 764 students (age range, 14-19 years) were enrolled from six schools in Taza city, Morocco. The Global School-based Student Health Survey was used to collect data about variables. We used bivariate and multivariate analyses to assess relations between dependent and independent variables. Overall, the prevalence of PI was 79.5% and SB was 36.5%. Among girls, these rates were higher (87.0 and 39.1%, respectively) than rates shown in boys (70.9 and 33.6%, respectively). In the multivariate logistic regression analysis, PI was associated with the following variables: illiterate father, hunger, suicidal ideation, inadequate vegetable consumption, and absence from physical education classes. Age, inadequate vegetable consumption, and absenteeism were associated with SB. The prevalence of PI and SB is high, especially among girls. Thus, there is an urgent need to implement appropriate interventions to reduce PI and SB levels in secondary school-age adolescents and the associated factors identified can be useful.

Fine genetic mapping of spot blotch resistance gene Sb3 in wheat (Triticum aestivum).

PubMed

Lu, Ping; Liang, Yong; Li, Delin; Wang, Zhengzhong; Li, Wenbin; Wang, Guoxin; Wang, Yong; Zhou, Shenghui; Wu, Qiuhong; Xie, Jingzhong; Zhang, Deyun; Chen, Yongxing; Li, Miaomiao; Zhang, Yan; Sun, Qixin; Han, Chenggui; Liu, Zhiyong

2016-03-01

Spot blotch disease resistance gene Sb3 was mapped to a 0.15 centimorgan (cM) genetic interval spanning a 602 kb physical genomic region on chromosome 3BS. Wheat spot blotch disease, caused by B. sorokiniana, is a devastating disease that can cause severe yield losses. Although inoculum levels can be reduced by planting disease-free seed, treatment of plants with fungicides and crop rotation, genetic resistance is likely to be a robust, economical and environmentally friendly tool in the control of spot blotch. The winter wheat line 621-7-1 confers immune resistance against B. sorokiniana. Genetic analysis indicates that the spot blotch resistance of 621-7-1 is controlled by a single dominant gene, provisionally designated Sb3. Bulked segregant analysis (BSA) and simple sequence repeat (SSR) mapping showed that Sb3 is located on chromosome arm 3BS linked with markers Xbarc133 and Xbarc147. Seven and twelve new polymorphic markers were developed from the Chinese Spring 3BS shotgun survey sequence contigs and 3BS reference sequences, respectively. Finally, Sb3 was mapped in a 0.15 cM genetic interval spanning a 602 kb physical genomic region of Chinese Spring chromosome 3BS. The genetic and physical maps of Sb3 provide a framework for map-based cloning and marker-assisted selection (MAS) of the spot blotch resistance.

Helicons, magnetoplasma edge, and faraday rotation in solid state plasmas at microwave frequencies.

PubMed

Furdyna, J K

1967-04-01

The effect of magnetic field on propagation of electromagnetic waves through free carrier plasmas in semiconductors is discussed. The Faraday configuration and the parameter ranges omega(c),omega(p) > omega and omega(c) > tau(-1) are specifically considered. Dispersion of helicon waves, propagation near the magnetoplasma edge (omega(p)(2) = omegaomega(c)), and the Faraday rotation are developed in terms of the one-electron Drude theory. Microwave transmission measurements at 35 Gc/s on n-type InSb are presented. Experiments near the magnetoplasma edge yield the value of the static dielectric constant of the InSb lattice K(l) = 19.3 +/- 0.8. Faraday rotation, observed beyond the edge, is found to be extremely large. Some practical possibilities for this effect are considered.

High precision AlGaAsSb ridge-waveguide etching by in situ reflectance monitored ICP-RIE

NASA Astrophysics Data System (ADS)

Tran, N. T.; Breivik, Magnus; Patra, S. K.; Fimland, Bjørn-Ove

2014-05-01

GaSb-based semiconductor diode lasers are promising candidates for light sources working in the mid-infrared wavelength region of 2-5 μm. Using edge emitting lasers with ridge-waveguide structure, light emission with good beam quality can be achieved. Fabrication of the ridge waveguide requires precise etch stop control for optimal laser performance. Simulation results are presented that show the effect of increased confinement in the waveguide when the etch depth is well-defined. In situ reflectance monitoring with a 675 nm-wavelength laser was used to determine the etch stop with high accuracy. Based on the simulations of laser reflectance from a proposed sample, the etching process can be controlled to provide an endpoint depth precision within +/- 10 nm.

Highly scaled equivalent oxide thickness of 0.66 nm for TiN/HfO2/GaSb MOS capacitors by using plasma-enhanced atomic layer deposition

NASA Astrophysics Data System (ADS)

Tsai, Ming-Li; Wang, Shin-Yuan; Chien, Chao-Hsin

2017-08-01

Through in situ hydrogen plasma treatment (HPT) and plasma-enhanced atomic-layer-deposited TiN (PEALD-TiN) layer capping, we successfully fabricated TiN/HfO2/GaSb metal-oxide-semiconductor capacitors with an ultrathin equivalent oxide thickness of 0.66 nm and a low density of states of approximately 2 × 1012 cm-2 eV-1 near the valence band edge. After in situ HPT, a native oxide-free surface was obtained through efficient etching. Moreover, the use of the in situ PEALD-TiN layer precluded high-κ dielectric damage that would have been caused by conventional sputtering, thereby yielding a superior high-κ dielectric and low gate leakage current.

Novel Chalcogenide Materials for X-ray and Gamma-ray Detection

DTIC Science & Technology

2016-05-01

53 Novel Chalcogenide Materials for x-ray and y-ray Detection Distribution Statement A. Approved for public release; distribution is unlimited. 0...TITLE AND SUBTITLE Sa. CONTRACT NUMBER Novel Chalcogenide Materials for x-ray and y-ray Detection Sb. GRANT NUMBER HDTRA 1-09-1-0044 Sc. PROGRAM...heavy atom chalcogenide family of semiconductors for room temperature gamma radiation detection . Its goal was to accelerate nuclear detector material

Electrical Characterization of GaSb Based Semiconductors for 2-4 micrometers Diode Laser Applications

DTIC Science & Technology

1996-06-01

to experience the dynamics of working with Jim Scofield whose knowledge seemed complementary to my own, providing an excellent sounding board to dig...111-2 Theoretical Aspects of Deep Level Energies and Capture Cross S ectio n s...111-37 Table 111-3. Summary of the theoretical estimates and experimental measurements of the valence band offset at the AlAs-GaAs heterointerface

Fabrication of Smart Chemical Sensors Based on Transition-Doped-Semiconductor Nanostructure Materials with µ-Chips

PubMed Central

Rahman, Mohammed M.; Khan, Sher Bahadar; Asiri, Abdullah M.

2014-01-01

Transition metal doped semiconductor nanostructure materials (Sb2O3 doped ZnO microflowers, MFs) are deposited onto tiny µ-chip (surface area, ∼0.02217 cm2) to fabricate a smart chemical sensor for toxic ethanol in phosphate buffer solution (0.1 M PBS). The fabricated chemi-sensor is also exhibited higher sensitivity, large-dynamic concentration ranges, long-term stability, and improved electrochemical performances towards ethanol. The calibration plot is linear (r2 = 0.9989) over the large ethanol concentration ranges (0.17 mM to 0.85 M). The sensitivity and detection limit is ∼5.845 µAcm−2mM−1 and ∼0.11±0.02 mM (signal-to-noise ratio, at a SNR of 3) respectively. Here, doped MFs are prepared by a wet-chemical process using reducing agents in alkaline medium, which characterized by UV/vis., FT-IR, Raman, X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction (XRD), and field-emission scanning electron microscopy (FE-SEM) etc. The fabricated ethanol chemical sensor using Sb2O3-ZnO MFs is simple, reliable, low-sample volume (<70.0 µL), easy of integration, high sensitivity, and excellent stability for the fabrication of efficient I–V sensors on μ-chips. PMID:24454785

Fabrication of smart chemical sensors based on transition-doped-semiconductor nanostructure materials with µ-chips.

PubMed

Rahman, Mohammed M; Khan, Sher Bahadar; Asiri, Abdullah M

2014-01-01

Transition metal doped semiconductor nanostructure materials (Sb2O3 doped ZnO microflowers, MFs) are deposited onto tiny µ-chip (surface area, ∼0.02217 cm(2)) to fabricate a smart chemical sensor for toxic ethanol in phosphate buffer solution (0.1 M PBS). The fabricated chemi-sensor is also exhibited higher sensitivity, large-dynamic concentration ranges, long-term stability, and improved electrochemical performances towards ethanol. The calibration plot is linear (r(2) = 0.9989) over the large ethanol concentration ranges (0.17 mM to 0.85 M). The sensitivity and detection limit is ∼5.845 µAcm(-2)mM(-1) and ∼0.11±0.02 mM (signal-to-noise ratio, at a SNR of 3) respectively. Here, doped MFs are prepared by a wet-chemical process using reducing agents in alkaline medium, which characterized by UV/vis., FT-IR, Raman, X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction (XRD), and field-emission scanning electron microscopy (FE-SEM) etc. The fabricated ethanol chemical sensor using Sb2O3-ZnO MFs is simple, reliable, low-sample volume (<70.0 µL), easy of integration, high sensitivity, and excellent stability for the fabrication of efficient I-V sensors on μ-chips.

Thermally controlled growth of surface nanostructures on ion-modified AIII-BV semiconductor crystals

NASA Astrophysics Data System (ADS)

Trynkiewicz, Elzbieta; Jany, Benedykt R.; Wrana, Dominik; Krok, Franciszek

2018-01-01

The primary motivation for our systematic study is to provide a comprehensive overview of the role of sample temperature on the pattern evolution of several AIII-BV semiconductor crystal (001) surfaces (i.e., InSb, InP, InAs, GaSb) in terms of their response to low-energy Ar+ ion irradiation conditions. The surface morphology and the chemical diversity of such ion-modified binary materials has been characterized by means of scanning electron microscopy (SEM). In general, all surface textures following ion irradiation exhibit transitional behavior from small islands, via vertically oriented 3D nanostructures, to smoothened surface when the sample temperature is increased. This result reinforces our conviction that the mass redistribution of adatoms along the surface plays a vital role during the formation and growth process of surface nanostructures. We would like to emphasize that this paper addresses in detail for the first time the topic of the growth kinetics of the nanostructures with regard to thermal surface diffusion, while simultaneously offering some possible approaches to supplementing previous studies and therein gaining a new insight into this complex issue. The experimental results are discussed with reference to models of the pillars growth, abutting on preferential sputtering, the self-sustained etch masking effect and the redeposition process recently proposed to elucidate the observed nanostructuring mechanism.

Identifying Au-based Te alloys for optical data storage

NASA Astrophysics Data System (ADS)

Wamwangi, D.; Detemple, R.; Woeltgens, H.-W.; Wuttig, M.; Zhang, X.

2004-06-01

Au18Sb23Te59 and Au19In26Te55 have been investigated to determine their suitability as phase change recording alloys. Recrystallization experiments identify Au18Sb23Te59 as a suitable phase change material with a recrystallization time of 110 ns and high optical contrast. Coupled to the high optical contrast is a considerable density increase of 4% upon crystallization which allows phase change recording for the Au18Sb23Te59 alloy. On the other hand no recrystallization has been observed optically for Au19In26Te55 due to its low optical contrast of less than 1%. This is related to a lower density contrast of 2%. The crystallization for the Au18Sb23Te59 and Au19In26Te55 alloys observed from temperature-dependent sheet resistance measurements have yielded transition temperatures of 113 and 175 °C, and activation barriers of 1.61±0.01 eV and 2.42±0.02 eV, respectively. We report a cubic structure (a=2.99±0.002 Å) for the Au18Sb23Te59 alloy and a chalcopyrite structure (a=6.50±0.018 Å and 12.27±0.025 Å) for the Au19In26Te55 material. These results confirm that suitable phase change alloys possess cubic structures rather than the chalcopyrite structure typical for sp3 bonded semiconductors.

Intrinsic Topological Insulator Bi1.5Sb0.5Te3-xSex Thin Crystals

NASA Astrophysics Data System (ADS)

Wang, Wei; Li, Li; Zou, Wenqin; He, Liang; Song, Fengqi; Zhang, Rong; Wu, Xiaoshan; Zhang, Fengming

2015-01-01

The quaternary topological insulator (Bi,Sb)2(Te,Se)3 has demonstrated topological surface states with an insulating bulk. Scientists have identified an optimized composition of Bi1.5Sb0.5Te1.7Se1.3 with the highest resistivity reported. But the physics that drive to this composition remains unclear. Here we report the crystal structure and the magneto-transport properties of Bi1.5Sb0.5Te3-xSex (BSTS) series. A correlation between the structure and the physical properties has been revealed. We found out that within the rhombohedral structure, the composition with most Te substituting Se has the highest resistivity. On the other hand, segregation of other composition phases will introduce much higher bulk concentration.

David Adler Lectureship Award Talk: III-V Semiconductor Nanowires on Silicon for Future Devices

NASA Astrophysics Data System (ADS)

Riel, Heike

Bottom-up grown nanowires are very attractive materials for direct integration of III-V semiconductors on silicon thus opening up new possibilities for the design and fabrication of nanoscale devices for electronic, optoelectronic as well as quantum information applications. Template-Assisted Selective Epitaxy (TASE) allows the well-defined and monolithic integration of complex III-V nanostructures and devices on silicon. Achieving atomically abrupt heterointerfaces, high crystal quality and control of dimension down to 1D nanowires enabled the demonstration of FETs and tunnel devices based on In(Ga)As and GaSb. Furthermore, the strong influence of strain on nanowires as well as results on quantum transport studies of InAs nanowires with well-defined geometry will be presented.

Spectroscopy of materials for terahertz photonics

NASA Astrophysics Data System (ADS)

Postava, K.; Chochol, J.; Mičica, M.; Vanwolleghem, M.; Kolejak, P.; Halagačka, L.; Cada, M.; Pištora, J.; Lampin, J.-F.

2016-12-01

In this paper we apply the terahertz time-domain spectroscopy (THz-TDS) to obtain optical function spectra in the range from 0.06 to 3 THz. Polarization sensitivity is obtained using azimuth-controlled wire-grid polarizers. We demonstrate general methods on characterization of plasmonic semiconductors. Detail characterization of optical and magneto-optical material properties is also motivated by a need of optical isolator in THz spectral range. The technique is applied to III-V semiconductors. The typical material is a single crystal undoped InSb having the plasma frequency in the range of interest. With appropriate magnetic field (in our case 0.4 T) we observed coupling of plasma and cyclotron behavior of free electrons with gigantic magneto-optic effect in the THz spectral range.

Effects of Cu and Ag as ternary and quaternary additions on some physical properties of SnSb7 bearing alloy

NASA Astrophysics Data System (ADS)

El-Bediwi, A. B.

2004-02-01

The structure, electrical resistivity, and elastic modulus of SnSb7 and SnSb7X (X = Cu , Ag, or Cu and Ag) rapidly solidified alloys have been investigated using X-ray diffractometer, double bridge, and dynamic resonance techniques. Copper and silver additions to SnSb result in the formation of a eutectic matrix containing embedded crystals (intermetallic phases) of SnCu, SnAg, and SnSb. The hard crystals SnCu, SnAg, and SnSb increase the overall hardness and wear resistance of SnSb bearing alloys. Addition of copper and silver improves internal friction, electrical conductivity, and elastic modulus values of SnSb rapidly solidified bearing alloys. The internal friction, elastic modulus, and electrical resistivity values are relatively sensitive to the composition of the intermediate phases in the matrix. The SbSb(7)Cu(2)g(2) has better properties (lowest internal friction, cost, adequate elastic modulus, and electrical resistivity) for bearing alloys as compared to cast iron and bronzes.

Materials growth and characterization of thermoelectric and resistive switching devices

NASA Astrophysics Data System (ADS)

Norris, Kate J.

In the 74 years since diode rectifier based radar technology helped the allied forces win WWII, semiconductors have transformed the world we live in. From our smart phones to semiconductor-based energy conversion, semiconductors touch every aspect of our lives. With this thesis I hope to expand human knowledge of semiconductor thermoelectric devices and resistive switching devices through experimentation with materials growth and subsequent materials characterization. Metal organic chemical vapor deposition (MOCVD) was the primary method of materials growth utilized in these studies. Additionally, plasma enhanced chemical vapor deposition (PECVD), atomic layer deposition (ALD),ion beam sputter deposition, reactive sputter deposition and electron-beam (e-beam) evaporation were also used in this research for device fabrication. Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), and Electron energy loss spectroscopy (EELS) were the primary characterization methods utilized for this research. Additional device and materials characterization techniques employed include: current-voltage measurements, thermoelectric measurements, x-ray diffraction (XRD), reflection absorption infra-red spectroscopy (RAIRS), atomic force microscopy (AFM), photoluminescence (PL), and raman spectroscopy. As society has become more aware of its impact on the planet and its limited resources, there has been a push toward developing technologies to sustainably produce the energy we need. Thermoelectric devices convert heat directly into electricity. Thermoelectric devices have the potential to save huge amounts of energy that we currently waste as heat, if we can make them cost-effective. Semiconducting thin films and nanowires appear to be promising avenues of research to attain this goal. Specifically, in this work we will explore the use of ErSb thin films as well as Si and InP nanowire networks for thermoelectric applications. First we will discuss the growth of erbium monoantimonide (ErSb) thin films with thermal conductivities close to or slightly smaller than the alloy limit of the two ternary alloy hosts. Second we consider an ex-situ monitoring technique based on glancing-angle infrared-absorption used to determine small amounts of erbium antimonide (ErSb) deposited on an indium antimonide (InSb) layer, a concept for thermoelectric devices to scatter phonons. Thirdly we begin our discussion of nanowires with the selective area growth (SAG) of single crystalline indium phosphide (InP) nanopillars on an array of template segments composed of a stack of gold and amorphous silicon. Our approach enables flexible and scalable nanofabrication using industrially proven tools and a wide range of semiconductors on various non-semiconductor substrates. Then we examine the use of graphene to promote the growth of nanowire networks on flexible copper foil leading to the testing of nanowire network devices for thermoelectric applications and the concept of multi-stage devices. We present the ability to tailor current-voltage characteristics to fit a desired application of thermoelectric devices by using nanowire networks as building blocks that can be stacked vertically or laterally. Furthermore, in the study of our flexible nanowire network multi-stage devices, we discovered the presence of nonlinear current-voltage characteristics and discuss how this feature could be utilized to increase efficiency for thermoelectric devices. This work indicates that with sufficient volume and optimized doping, flexible nanowire networks could be a low cost semiconductor solution to our wasted heat challenge. Resistive switching devices are two terminal electrical resistance switches that retain a state of internal resistance based on the history of applied voltage and current. The occurrence of reversible resistance switching has been widely studied in a variety of material systems for applications including nonvolatile memory, logic circuits, and neuromorphic computing. To this end we next we studied devices in each resistance state of a TaOx switch, which has previously shown high endurance and desirable switching behavior, to better understand the system in nanoscale devices. Finally, we will discuss a self-aligned NbO2 nano-cap demonstrated atop a TaO2.2 switching layer. The goal of this device is to create a nanoscale RRAM and selector device in a single stack. These results indicate that ternary resistive switching devices may be a beneficial method of combining behaviors of different material systems and that with proper engineering a self-aligned selector is possible.

Double exposure technique for 45nm node and beyond

NASA Astrophysics Data System (ADS)

Hsu, Stephen; Park, Jungchul; Van Den Broeke, Douglas; Chen, J. Fung

2005-11-01

The technical challenges in using F2 lithography for the 45nm node, along with the insurmountable difficulties in EUV lithography, has driven the semiconductor chipmaker into the low k1 lithography era under the pressure of ever decreasing feature sizes. Extending lithography towards lower k1 puts heavy demand on the resolution enhancement technique (RET), exposure tool, and the need for litho friendly design. Hyper numerical aperture (NA) exposure tools, immersion, and double exposure techniques (DET's) are the promising methods to extend lithography manufacturing to the 45nm node at k1 factors below 0.3. Scattering bars (SB's) have become an integral part of the lithography process as chipmakers move to production at ever lower k1 factors. To achieve better critical dimension (CD) control, polarization is applied to enhance the image contrast in the preferential imaging orientation, which increases the risk of SB printability. The optimum SB width is approximately (0.20 ~ 0.25)*(λ/NA). When the SB width becomes less than the exposure wavelength on the 4X mask, Kirchhoff's scalar theory under predicts the SB intensity. The optical weighting factor of the SB increases (Figure 1b) and the SB's become more susceptible to printing. Meanwhile, under hyper NA conditions, the effectiveness of "subresolution" SB's is significantly diminished. A full-sized scattering bars (FSB) scheme becomes necessary. Double exposure methods, such as using ternary 6% attenuated PSM (attPSM) for DDL, are good imaging solutions that can reach and likely go beyond the 45nm node. Today DDL, using binary chrome masks, is capable of printing 65 nm device patterns. In this work, we investigate the use of DET with 6% attPSM masks to target 45nm node device. The SB scalability and printability issues can be taken cared of by using "mutual trimming", i.e., with the combined energy from the two exposures. In this study, we share our findings of using DET to pattern a 45nm node device design with polarization and immersion. We also explore other double patterning methods which in addition to having two exposures, incorporates double coat/developing/etch processing to break the 0.25 k1 barrier.

Superconducting proximity effect in MBE grown Nb-InAs junctions

NASA Astrophysics Data System (ADS)

Kan, Carolyn; Xue, Chi; Law, Stephanie; Eckstein, James

2013-03-01

Several proposals for the realization of Majorana fermions rely on excellent quality proximity coupling between a superconductor and a high-mobility semiconductor. We examine the long-range proximity coupling between MBE-grown InAs and in situ grown superconducting overlayers by fabricating transport devices, and investigate the effect of substrate choice and growth conditions on the quality of the MBE InAs. GaAs is commonly available as a high quality insulating substrate. Overcoming its lattice mismatch with InAs using GaSb and AlSb layers results in locally smooth terraced surfaces, but global spiral dislocation structures also appear and have a negative impact on the InAs mobility. Growing InAs on homoepitaxial GaSb results in improved morphology and increases the mean free path. We compare the proximity effect in devices made both ways. This material is based upon work supported by the U.S. Department of Energy, Division of Materials Sciences under Award No. DE-FG02 07ER46453, through the Frederick Seitz Materials Research Laboratory at the University of Illinois at Urbana-Champaign.

Electronic and Thermoelectric Properties of Ternary Chalcohalide Semiconductors: First Principles Study

NASA Astrophysics Data System (ADS)

Khan, Wilayat; Hussain, Sajjad; Minar, Jan; Azam, Sikander

2018-02-01

Ternary chalcohalides have been widely utilized for different device applications. The thermoelectric properties of SbSI, SbSeI and SbSBr have been investigated by theoretical simulations, and the findings have been performed using BoltzTraP code, based on semi-classical Boltzmann transport theory. In this study, we simulated the electronic structures using the Englo-Vosko generalized gradient approximation employed in the WIEN2k program. From the electronic band structures, we found a combination of light and heavy bands around the Fermi level in the valence band, which strongly affect the effective masses of the carriers. The entire thermoelectric parameters, like the electrical, the electronic part of the thermal conductivities, the Seebeck coefficient and the power factor have been analysed as functions of temperature and chemical potential. The correlation between the effective masses and the thermoelectric properties is also included in the discussion because the effective mass reveals the mobility of the carriers which in turn affect the thermoelectric properties. The substitution of sulfur reveals high electrical conductivity and a smaller Seebeck coefficient based on effective mass leads to the increase in the power factor.

Material Engineering for Phase Change Memory

NASA Astrophysics Data System (ADS)

Cabrera, David M.

As semiconductor devices continue to scale downward, and portable consumer electronics become more prevalent there is a need to develop memory technology that will scale with devices and use less energy, while maintaining performance. One of the leading prototypical memories that is being investigated is phase change memory. Phase change memory (PCM) is a non-volatile memory composed of 1 transistor and 1 resistor. The resistive structure includes a memory material alloy which can change between amorphous and crystalline states repeatedly using current/voltage pulses of different lengths and magnitudes. The most widely studied PCM materials are chalcogenides - Germanium-Antimony-Tellerium (GST) with Ge2Sb2Te3 and Germanium-Tellerium (GeTe) being some of the most popular stochiometries. As these cells are scaled downward, the current/voltage needed to switch these materials becomes comparable to the voltage needed to sense the cell's state. The International Roadmap for Semiconductors aims to raise the threshold field of these devices from 66.6 V/mum to be at least 375 V/mum for the year 2024. These cells are also prone to resistance drift between states, leading to bit corruption and memory loss. Phase change material properties are known to influence PCM device performance such as crystallization temperature having an effect on data retention and litetime, while resistivity values in the amorphous and crystalline phases have an effect on the current/voltage needed to write/erase the cell. Addition of dopants is also known to modify the phase change material parameters. The materials G2S2T5, GeTe, with dopants - nitrogen, silicon, titanium, and aluminum oxide and undoped Gallium-Antimonide (GaSb) are studied for these desired characteristics. Thin films of these compositions are deposited via physical vapor deposition at IBM Watson Research Center. Crystallization temperatures are investigated using time resolved x-ray diffraction at Brookhaven National Laboratory. Subsequently, these are incorporated into PCM cells with structure designed as shown in Fig.1. A photolithographic lift-off process is developed to realize these devices. Electrical parameters such as the voltage needed to switch the device between memory states, the difference in resistance between these memory states, and the amount of time to switch are studied using HP4145 equipped with a pulsed generator. The results show that incorporating aluminum oxide dopant into G2S2T 5 raises its threshold field from 60 V/mum to 96 V/mum, while for GeTe, nitrogen doping raises its threshold field from 143 V/mum to 248 V/mum. It is found that GaSb at comparable volume devices has a threshold field of 130 V/mum. It was also observed that nitrogen and silicon doping made G 2S2T5 more resistant to drift, raising time to drift from 2 to 16.6 minutes while titanium and aluminum oxide doping made GeTe drift time rise from 3 to 20 minutes. It was also found that shrinking the cell area in GaSb from 1 mum2 to 0.5 mum2 lengthened drift time from 45s to over 24 hours. The PCM process developed in this study is extended to GeTe/Sb2 Te3 multilayers called the superlattice (SL) structure that opens opportunities for future work. Recent studies have shown that the superlattice structure exhibits low switching energies, therefore has potential for low power operation.

No Evidence of Reciprocal Associations between Daily Sleep and Physical Activity.

PubMed

Mitchell, Jonathan A; Godbole, Suneeta; Moran, Kevin; Murray, Kate; James, Peter; Laden, Francine; Hipp, J Aaron; Kerr, Jacqueline; Glanz, Karen

2016-10-01

This study aimed to determine whether physical activity patterns are associated with sleep later at night and if nighttime sleep is associated with physical activity patterns the next day among adult women. Women (N = 353) living throughout the United States wore a wrist and a hip accelerometer for 7 d. Total sleep time (TST, hours per night) and sleep efficiency (SE, %) were estimated from the wrist accelerometer, and moderate to vigorous physical activity (MVPA, >1040 counts per minute, h·d) and sedentary behavior (SB, <100 counts per minute, h·d) were estimated from the hip accelerometer. Mixed-effects models adjusted for age, race, body mass index, education, employment, marital status, health status, and hip accelerometer wear time were used to analyze the data. Follow-up analyses using quantile regression were used to investigate associations among women with below average TST and MVPA and above average SB. The average age of our sample was 55.5 yr (SD = 10.2 yr). The majority of participants were White (79%) and married (72%), and half were employed full time (49%). The participants spent on average 8.9 and 1.1 h·d in SB and MVPA, respectively, and 6.8 h per night asleep. No associations were observed between MVPA and SB with nighttime TST or SE. There were no associations between nighttime TST and SE with MVPA or SB the next day. The findings were the same in the quantile regression analyses. In free-living adult women, accelerometry-estimated nighttime sleep and physical activity patterns were not associated with one another. On the basis of our observational study involving a sample of adult women, higher physical activity will not necessarily improve sleep at night on a day-to-day basis (and vice versa).

Ultra-low input power long-wavelength GaSb type-I laser diodes at 2.7-3.0 μm

NASA Astrophysics Data System (ADS)

Vizbaras, Augustinas; Greibus, Mindaugas; Dvinelis, Edgaras; Trinkūnas, Augustinas; Kovalenkovas, Deividas; Šimonytė, Ieva; Vizbaras, Kristijonas

2014-02-01

Mid-infrared spectral region (2-4 μm) is gaining significant attention recently due to the presence of numerous enabling applications in the field of gas sensing, medical, environmental and defense applications. Major requirement for these applications is the availability of laser sources in this spectral window. Type-I GaSb-based laser diodes are ideal candidates for these applications being compact, electrically pumped, power efficient and able to operate at room temperature in continuous-wave. Moreover, due to the nature of type-I transition; these devices have a characteristic low operation voltage, typically below 1 V, resulting in low power consumption, and high-temperature of operation. In this work, we present recent progress of 2.7 μm - 3.0 μm wavelength single-spatial mode GaSb type-I laser diode development at Brolis Semiconductors. Experimental device structures were grown by solid-source multi-wafer MBE, consisting of an active region with 2 compressively strained (~1.3 %-1.5 %) GaInAsSb quantum wells with GaSb barriers for 2.7 μm devices and quinternary AlGaInAsSb barriers for 3.0 μm devices. Epi-wafers were processed into a narrow-ridge (2-4 μm) devices and mounted p-side up on CuW heatsink. Devices exhibited very low CW threshold powers of < 100 mW, and single spatial mode (TE00) operation with room-temperature output powers up to 40 mW in CW mode. Operating voltage was as low as 1.2 V at 1.2 A. As-cleaved devices worked CW up to 50 deg C.

Physical Education Classes, Physical Activity, and Sedentary Behavior in Children.

PubMed

Silva, Diego Augusto Santos; Chaput, Jean-Philippe; Katzmarzyk, Peter T; Fogelholm, Mikael; Hu, Gang; Maher, Carol; Olds, Timothy; Onywera, Vincent; Sarmiento, Olga L; Standage, Martyn; Tudor-Locke, Catrine; Tremblay, Mark S

2018-05-01

This study aimed to examine the associations between participation frequency in physical education (PE) classes and objective measures of physical activity (PA) and sedentary behavior (SB) in children from 12 countries at different levels of development. This multinational, cross-sectional study included 5874 children 9-11 yr old from sites in Australia, Brazil, Canada, China, Colombia, Finland, India, Kenya, Portugal, South Africa, the United Kingdom, and the United States. PA and SB were monitored for seven consecutive days using a waist-worn accelerometer. PA and SB data were presented for weekdays (times in and out of school) and weekend days. Participation frequency in PE classes was determined by questionnaire. Multilevel modeling analyses stratified by sex were used. Overall, 24.8% of children self-reported participation in PE classes ≥3 times per week (25.3% in high-income countries [HIC] and 24.3% in low- and middle-income countries [LMIC]). After adjusting for age, sex, parental education, and body mass index z-score, results showed that children from low- and middle-income countries who took PE classes one to two times per week were more likely to present better indicators of PA and shorter time in SB in and out of school. In HIC, boys that participated in PE classes were more likely to meet the moderate-to-vigorous PA recommendations and to present better indicators of PA (in school) and shorter time in SB in and out of school. For girls in HIC, attending PE classes increased the likelihood of spending more time in moderate-to-vigorous PA, especially if they attended ≥3 times per week. Attending PE classes is associated with a higher level of PA and a lower level of SB in and out of school during weekdays in children from countries at various levels of development.

Growth and Electronic Structure of Heusler Compounds for Use in Electron Spin Based Devices

NASA Astrophysics Data System (ADS)

Patel, Sahil Jaykumar

Spintronic devices, where information is carried by the quantum spin state of the electron instead of purely its charge, have gained considerable interest for their use in future computing technologies. For optimal performance, a pure spin current, where all electrons have aligned spins, must be generated and transmitted across many interfaces and through many types of materials. While conventional spin sources have historically been elemental ferromagnets, like Fe or Co, these materials pro duce only partially spin polarized currents. To increase the spin polarization of the current, materials like half-metallic ferromagnets, where there is a gap in the minority spin density of states around the Fermi level, or topological insulators, where the current transport is dominated by spin-locked surface states, show promise. A class of materials called Heusler compounds, with electronic structures that range from normal metals, to half metallic ferromagnets, semiconductors, superconductors and even topological insulators, interfaces well with existing device technologies, and through the use of molecular beam epitaxy (MBE) high quality heterostructures and films can be grown. This dissertation examines the electronic structure of surfaces and interfaces of both topological insulator (PtLuSb-- and PtLuBi--) and half-metallic ferromagnet (Co2MnSi-- and Co2FeSi--) III-V semiconductor heterostructures. PtLuSb and PtLuBi growth by MBE was demonstrated on Alx In1--xSb (001) ternaries. PtLuSb (001) surfaces were observed to reconstruct with either (1x3) or c(2x2) unit cells depending on Sb overpressure and substrate temperature. viii The electronic structure of these films was studied by scanning tunneling microscopy/spectroscopy (STM/STS) and photoemission spectroscopy. STS measurements as well as angle resolved photoemission spectropscopy (ARPES) suggest that PtLuSb has a zero-gap or semimetallic band structure. Additionally, the observation of linearly dispersing surface states, with an approximate crossing point 240meV above the Fermi level, suggests that PtLuSb (001) films are topologically non-trivial. PtLuBi films also display a Fermi level position approximately 500meV below the valence band maximum. Co2MnSi and Co2FeSi were also grown by MBE on GaAs (001) for use as spin injectors into GaAs lateral spin valve devices. By the growth of the quaternary alloy Co2FexMn1-- xSi and varying x, electron doping of the full Heusler compound was demonstrated by observation of a crossover from a majority spin polarization of Co2MnSi to a minority spin polarization in Co2FeSi. Co2MnSi films were studied as a function of the nucleation sequence, using either Co-- or MnSi-- initiated films on c(4x4) GaAs. Studies using x-ray photoemission spectroscopy (XPS), STM/STS, and transmission electron microscopy (TEM) suggest that the bulk of the Co2MnSi films and the interfacial structure between Co 2MnSi and GaAs is not modified by the nucleation sequence, but a change in spin transport characteristics suggests a modification of semiconductor band structure at the Co2MnSi/GaAs interface due to diffusion of Mn leading to compensation of the Schottky barrier contact. Diffusion of Mn into the GaAs was confirmed by secondary ion mass spectrometry (SIMS) measurements. The proposed mechanism for the modified spin transport characteristics for MnSi initiated films is that additional diffusion of Mn into the GaAs, widens the Schottky barrier contact region. These studies suggest that the ideal initiation sequence for Co2MnSi/GaAs (001) lateral spin valve devices is achieved by deposition of Co first.

Objectively Measured Patterns of Activities of Different Intensity Categories and Steps Taken Among Working Adults in a Multi-ethnic Asian Population.

PubMed

Müller-Riemenschneider, Falk; Ng, Sheryl Hui Xian; Koh, David; Chu, Anne Hin Yee

2016-06-01

To objectively assess sedentary behavior (SB), light- and moderate-to-vigorous intensity physical activity (MVPA), and steps among Singaporean office-based workers across days of the week. A convenience sample of office-based employees of a public University was recruited. Time spent for SB, light-, and MVPA using different validated accelerometry counts per minute (CPM), and step count were determined. Depending on applied CPM for SB (less than 100, less than 150 and less than 200 CPM), 107 working adults spent between 69.2% and 76.4% of their daily wakeful time in SB. Time spent in SB and MVPA were higher on weekdays than weekends. The hourly analysis highlights patterns of greater SB during usual working hours on weekdays but not on weekends. SB at work contributes greatly toward total daily sitting time. Low PA levels and high SB levels were found on weekends.

Mediated Effects of Perceived Competence on Youth Physical Activity and Sedentary Behavior

ERIC Educational Resources Information Center

Bai, Yang; Chen, Senlin; Vazou, Spyridoula; Welk, Gregory J.; Schaben, Jodee

2015-01-01

Purpose: This study evaluates whether physical activity (PA) and sedentary behavior (SB) are influenced by a common mediating relationship. Method: A total of 1,552 participants in 3rd to 12th grade completed an online survey that included assessments of PA at school (PAS), PA at home (PAH), and SB as well as a battery of psychosocial variables…

Concurrent Associations of Physical Activity and Screen-Based Sedentary Behavior on Obesity Among US Adolescents: A Latent Class Analysis.

PubMed

Kim, Youngdeok; Barreira, Tiago V; Kang, Minsoo

2016-01-01

Independent associations of physical activity (PA) and sedentary behavior (SB) with obesity are well documented. However, little is known about the combined associations of these behaviors with obesity in adolescents. The present study examines the prevalence of concurrent levels of PA and SB, and their associations with obesity among US adolescents. Data from a total of 12 081 adolescents who participated in the Youth Risk Behaviors Survey during 2012-2013 were analyzed. A latent class analysis was performed to identify latent subgroups with varying combined levels of subjectively measured PA and screen-based SB. Follow-up analysis examined the changes in the likelihood of being obese as determined by the Center for Disease Control and Prevention Growth Chart between latent subgroups. Four latent subgroups with varying combined levels of PA and SB were identified across gender. The likelihood of being obese was significantly greater for the subgroups featuring either or both Low PA or High SB when compared with High PA/Low SB across genders (odds ratio [OR] ranges, 2.1-2.7 for males and 9.6-23.5 for females). Low PA/High SB showed the greater likelihood of being obese compared to subgroups featuring either or both High PA and Low SB (OR ranges, 2.2-23.5) for female adolescents only. The findings imply that promoting sufficient levels of PA while reducing SB should be encouraged in order to reduce obesity risk among adolescents, particularly for males. The risk of obesity for female adolescents can be reduced by engaging in either high levels of PA or low levels of SB.

Local bonding structure of tellurium and antimony in the phase change chalcogenides germanium-antimony-tellurium: A nuclear magnetic resonance study

NASA Astrophysics Data System (ADS)

Bobela, David C.

Recent technological applications of some chalcogenide materials, compounds containing a group VI atom, have prompted studies of the local atomic structure of the amorphous phase. In the case of Ge2Sb2Te 5, metastability in the local bonding structure is responsible for its usefulness as a phase-change memory material. There is no consensus on the exact phase-change mechanism, which is partly due to the inadequacy of standard scattering techniques to probe the structure of the amorphous phase. Nuclear magnetic resonance methods, on the other hand, are well suited to study local structural order even in the absence of a periodic lattice. In this technique, structural information is encoded as an oscillating voltage caused by the nuclear spin. For the tellurium isotope, 125Te (spin = 1/2 in the ground state), the dominant interaction comes from the core and valence electrons that carry angular momentum. This interaction is helpful in identifying Te sites of different local coordination since the number of neighboring atoms should markedly change the local electronic structure. The antimony isotope 125Sb has a spin = 5/2 in the ground state and possesses an asymmetric nuclear charge. This quadrupole moment will interact with an electric field gradient at the nuclear site, which is provided by an asymmetric electron cloud surrounding the nucleus. The frequency-space spectra will reflect the strength of the interaction as well as the symmetry of the local electronic environment. This work investigates the nuclear magnetic resonance spectrum of 125Te and 125Sb in the crystalline and amorphous forms of several GexSbyTe 1-x-y compounds where 0 < (x, y) < 1. Results from the crystalline phase 125Te data show a trend in the spectral position that can be related to the tellurium bonded to three and six neighbors. In the amorphous phase, the same trend is observed, and the nuclear magnetic resonance fingerprint of two-fold and three-fold coordinated tellurium is obtained. It is concluded, based upon this comparison that the Te atoms see a dramatically different bonding environment depending on which phase the lattice has. The 125Sb data for the crystalline phase indicate electric field gradients that are consistent with similarly bonded quadrupolar nuclei, such as Sb atoms in crystalline Sb or five-fold coordinated Sb in crystalline MnSb. The NMR data exemplify the consequences of combinatorial disorder on the spectra via the absence of certain line-shape features. In the amorphous phase, the electric field gradients are approximately seven times larger, and the fingerprints of both highly-symmetric and asymmetric antimony sites emerge. Details of field gradient, i.e. the magnitude and symmetry, are remarkably similar to those found in Sb containing compounds where the Sb sites are three-fold pyramidal, such as in crystalline Sb2X3 where X = O, S, or Se. The observations from the NMR data provide a critical litmus test for recent structural models of the amorphous phase. In particular, the amorphous phase data provides clear evidence that the Te atoms are two-fold and three-fold coordinated while the Sb atoms are most likely bonded in three-fold pyramidal configurations. These observations imply a structural model of the amorphous phase that agrees best with a models based upon the "8 minus n", or "8-n" rule for chemical bonding in amorphous semiconductors. Thus, the lattice of these compounds is arranged such that the constituent elements have enough bonds, on average, to satisfy their valence requirement. The implications of the NMR data on theoretical modeling data are immediate. Theoretical models of these systems must possess some aspect of the "8-n" mentality. With this idea as a foundation for physically realistic representations of the amorphous phase, the origin of the phase-change mechanism may be unraveled, which will ultimately speed the process of compositional optimization of phase-change materials.

An ultrahigh vacuum, low-energy ion-assisted deposition system for III-V semiconductor film growth

NASA Astrophysics Data System (ADS)

Rohde, S.; Barnett, S. A.; Choi, C.-H.

1989-06-01

A novel ion-assisted deposition system is described in which the substrate and growing film can be bombarded with high current densities (greater than 1 mA/sq cm) of very low energy (10-200 eV) ions. The system design philosophy is similar to that used in III-V semiconductor molecular-beam epitaxy systems: the chamber is an all-metal ultrahigh vacuum system with liquid-nitrogen-cooled shrouds, Knudsen-cell evaporation sources, a sample insertion load-lock, and a 30-kV reflection high-energy electron diffraction system. III-V semiconductor film growth is achieved using evaporated group-V fluxes and group-III elemental fluxes sputtered from high-purity targets using ions extracted from a triode glow discharge. Using an In target and an As effusion cell, InAs deposition rates R of 2 microns/h have been obtained. Epitaxial growth of InAs was observed on both GaSb(100) and Si(100) substrates.

Analytical study of acoustically perturbed Brillouin active magnetized semiconductor plasma

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

Shukla, Arun, E-mail: arunshuklaujn@gmail.com; Jat, K. L.

2015-07-31

An analytical study of acoustically perturbed Brillouin active magnetized semiconductor plasma has been reported. In the present analytical investigation, the lattice displacement, acousto-optical polarization, susceptibility, acousto-optical gain constant arising due to the induced nonlinear current density and acousto-optical process are deduced in an acoustically perturbed Brillouin active magnetized semiconductor plasma using the hydrodynamical model of plasma and coupled mode scheme. The influence of wave number and magnetic field has been explored. The analysis has been applied to centrosymmetric crystal. Numerical estimates are made for n-type InSb crystal duly irradiated by a frequency doubled 10.6 µm CO{sub 2} laser. It is foundmore » that lattice displacement, susceptibility and acousto-optical gain increase linearly with incident wave number and applied dc magnetic field, while decrease with scattering angle. The gain also increases with electric amplitude of incident laser beam. Results are found to be well in agreement with available literature.« less

Narrowing of band gap at source/drain contact scheme of nanoscale InAs-nMOS

NASA Astrophysics Data System (ADS)

Mohamed, A. H.; Oxland, R.; Aldegunde, M.; Hepplestone, S. P.; Sushko, P. V.; Kalna, K.

2018-04-01

A multi-scale simulation study of Ni/InAs nano-scale contact aimed for the sub-14 nm technology is carried out to understand material and transport properties at a metal-semiconductor interface. The deposited Ni metal contact on an 11 nm thick InAs channel forms an 8.5 nm thick InAs leaving a 2.5 nm thick InAs channel on a p-type doped (1 × 1016 cm-3) AlAs0.47Sb0.53 buffer. The density functional theory (DFT) calculations reveal a band gap narrowing in the InAs at the metal-semiconductor interface. The one-dimensional (1D) self-consistent Poisson-Schrödinger transport simulations using real-space material parameters extracted from the DFT calculations at the metal-semiconductor interface, exhibiting band gap narrowing, give a specific sheet resistance of Rsh = 90.9 Ω/sq which is in a good agreement with an experimental value of 97 Ω/sq.

New Fluoride-arsenide Diluted Magnetic Semiconductor (Ba,K)F(Zn,Mn)As with Independent Spin and Charge Doping

NASA Astrophysics Data System (ADS)

Chen, Bijuan; Deng, Zheng; Li, Wenmin; Gao, Moran; Liu, Qingqing; Gu, C. Z.; Hu, F. X.; Shen, B. G.; Frandsen, Benjamin; Cheung, Sky; Lian, Liu; Uemura, Yasutomo J.; Ding, Cui; Guo, Shengli; Ning, Fanlong; Munsie, Timothy J. S.; Wilson, Murray Neff; Cai, Yipeng; Luke, Graeme; Guguchia, Zurab; Yonezawa, Shingo; Li, Zhi; Jin, Changqing

2016-11-01

We report the discovery of a new fluoride-arsenide bulk diluted magnetic semiconductor (Ba,K)F(Zn,Mn)As with the tetragonal ZrCuSiAs-type structure which is identical to that of the “1111” iron-based superconductors. The joint hole doping via (Ba,K) substitution & spin doping via (Zn,Mn) substitution results in ferromagnetic order with Curie temperature up to 30 K and demonstrates that the ferromagnetic interactions between the localized spins are mediated by the carriers. Muon spin relaxation measurements confirm the intrinsic nature of the long range magnetic order in the entire volume in the ferromagnetic phase. This is the first time that a diluted magnetic semiconductor with decoupled spin and charge doping is achieved in a fluoride compound. Comparing to the isostructure oxide counterpart of LaOZnSb, the fluoride DMS (Ba,K)F(Zn,Mn)As shows much improved semiconductive behavior that would be benefit for further application developments.

Dog ownership and health-related physical activity among Japanese adults.

PubMed

Oka, Koichiro; Shibata, Ai

2009-07-01

Dog ownership appears to have associated health benefits as a result of increased physical activity through dog walking. This study examined the association between dog ownership and health-related physical activity among Japanese adults. Male and female respondents to an Internet-based cross-sectional survey were divided into the following groups: dog owner (DOG), nondog pet owner (NDOG), and nonpet owner (NPOG). Moderate and vigorous physical activity amount (MVPA), walking amount (Walking), and sedentary behavior time (SB) were estimated from the International Physical Activity Questionnaire. Analyses of covariance and logistic regression analysis were used. The differences in MVPA, Walking, and SB were statistically significant among the three groups. DOG had a significantly greater amount of MVPA than NDOG and NPOG. DOG also had a significantly greater amount of Walking and less SB time than NPOG, and DOG was 1.5 times more likely to meet the physical activity recommendation than NDOG and NPOG. The dog owners had higher physical activity levels than owners of other kinds of pets and those without any pets, suggesting that dogs may play a major role in promoting physical activity. However, only 30% of the dog owners met the recommended criteria for physical activity.

32nd International Conference on the Physics of Semiconductors

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

Chelikowsky, James

The International Conference on the Physics of Semiconductors (ICPS) continues a series of biennial conferences that began in the 1950's. ICPS is the premier meeting for reporting all aspects of semiconductor physics including electronic, structural, optical, magnetic and transport properties with an emphasis on new materials and their applications. The meeting will reflect the state of art in the semiconductor physics field and will serve as a forum where scholars, researchers, and specialists can interact to discuss future research directions and technological advancements. The conference typically draws 1,000 international physicists, scientists, and students. This is one of the largest sciencemore » meetings on semiconductors and related materials to be held in the United States.« less

Uncooled infrared photon detection concepts and devices

NASA Astrophysics Data System (ADS)

Piyankarage, Viraj Vishwakantha Jayaweera

This work describes infrared (IR) photon detector techniques based on novel semiconductor device concepts and detector designs. The aim of the investigation was to examine alternative IR detection concepts with a view to resolve some of the issues of existing IR detectors such as operating temperature and response range. Systems were fabricated to demonstrate the following IR detection concepts and determine detector parameters: (i) Near-infrared (NIR) detection based on dye-sensitization of nanostructured semiconductors, (ii) Displacement currents in semiconductor quantum dots (QDs) embedded dielectric media, (iii) Split-off band transitions in GaAs/AlGaAs heterojunction interfacial workfunction internal photoemission (HEIWIP) detectors. A far-infrared detector based on GaSb homojunction interfacial workfunction internal photoemission (HIWIP) structure is also discussed. Device concepts, detector structures, and experimental results discussed in the text are summarized below. Dye-sensitized (DS) detector structures consisting of n-TiO 2/Dye/p-CuSCN heterostructures with several IR-sensitive dyes showed response peaks at 808, 812, 858, 866, 876, and 1056 nm at room temperature. The peak specific-detectivity (D*) was 9.5x1010 cm Hz-1/2 W-1 at 812 nm at room temperature. Radiation induced carrier generation alters the electronic polarizability of QDs provided the quenching of excitation is suppressed by separation of the QDs. A device constructed to illustrate this concept by embedding PbS QDs in paraffin wax showed a peak D* of 3x108 cm Hz 1/2 W-1 at ˜540 nm at ambient temperature. A typical HEIWIP/HIWIP detector structures consist of single (or multiple) period(s) of doped emitter(s) and undoped barrier(s) which are sandwiched between two highly doped contact layers. A p-GaAs/AlGaAs HEIWIP structure showed enhanced absorption in NIR range due to heavy/light-hole band to split-off band transitions and leading to the development of GaAs based uncooled sensors for IR detection in the 2--5 microm wavelength range with a peak D* of 6.8x105 cm Hz1/2 W-1. A HIWIP detector based on p-GaSb/GaSb showed a free carrier response threshold wavelength at 97 microm (˜3 THz) with a peak D* of 5.7x1011 cm Hz1/2 W-1 at 36 microm and 4.9 K. In this detector, a bolometric type response in the 97--200 microm (3--1.5 THz) range was also observed. INDEX WORDS: Infrared detectors, Photon detection, NIR detectors, THz detectors, Uncooled detectors, Dye-sensitized, IR dye, Quantum dot, Split-off band, GaSb, GaAs, AlGaAs, TiO2, CuSCN, PbS, Homojunction, Heterojunction, Workfunction, Photoemission, Displacement currents, 1/f noise.

Combinations of physical activity, sedentary behaviour and sleep: relationships with health indicators in school-aged children and youth.

PubMed

Saunders, Travis John; Gray, Casey Ellen; Poitras, Veronica Joan; Chaput, Jean-Philippe; Janssen, Ian; Katzmarzyk, Peter T; Olds, Timothy; Connor Gorber, Sarah; Kho, Michelle E; Sampson, Margaret; Tremblay, Mark S; Carson, Valerie

2016-06-01

The purpose of this systematic review was to determine how combinations of physical activity (PA), sedentary behaviour (SB), and sleep were associated with important health indicators in children and youth aged 5-17 years. Online databases (MEDLINE, EMBASE, SPORTdiscus, CINAHL, and PsycINFO) were searched for relevant studies examining the relationship between time spent engaging in different combinations of PA, SB, and sleep with the following health indicators: adiposity, cardiometabolic biomarkers, physical fitness, emotional regulation/psychological distress, behavioural conduct/pro-social behaviour, cognition, quality of life/well-being, injuries, bone density, motor skill development, and self-esteem. PA had to be objectively measured, while sleep and SB could be objectively or subjectively measured. The quality of research evidence and risk of bias for each health indicator and for each individual study was assessed using the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) framework. A total of 13 cross-sectional studies and a single prospective cohort study reporting data from 36 560 individual participants met the inclusion criteria. Children and youth with a combination of high PA/high sleep/low SB had more desirable measures of adiposity and cardiometabolic health compared with those with a combination of low PA/low sleep/high SB. Health benefits were also observed for those with a combination of high PA/high sleep (cardiometabolic health and adiposity) or high PA/low SB (cardiometabolic health, adiposity and fitness), compared with low PA/low sleep or low PA/high SB. Of the 3 movement behaviours, PA (especially moderate- to vigorous-intensity PA) was most consistently associated with desirable health indicators. Given the lack of randomized trials, the overall quality of the available evidence was low.

Association of physiological and psychological health outcomes with physical activity and sedentary behavior in adults with type 2 diabetes

PubMed Central

Garcia, Jeanette M; Cox, Daniel; Rice, David J

2017-01-01

Purpose To examine the association between change in moderate-to-vigorous physical activity (MVPA) and sedentary behavior (SB) over a 6-month period with physiological and psychological factors in adults with type 2 diabetes (T2D). Methods Participants included 26 middle-aged (mean age=56.1±10.8 years; 42% women), overweight/obese (mean body mass index (BMI) =37.22±8.78 kg/m2) adults who had been diagnosed with T2D within the past 5 years (mean HbA1c=7.81%). Participants underwent a physical examination, blood tests, and psychological questionnaires, including a self-report questionnaire that assessed the consumption of high glycemic and low glycemic load foods. Participants wore an Actigraph accelerometer for 7 days to assess MVPA and SB. All measures were collected at baseline and at the 6-month follow-up. Spearman rank correlations and regression models were conducted to examine the relationship between activity variables, and the association of activity measures with health outcomes at the 6-month follow-up. Results Decreases in duration of SB bouts and increases in MVPA were associated with decreased levels of HbA1c (p<0.05). Over 50% of the variance in HbA1c levels could be attributed to changes in MVPA and SB. Conclusions MVPA and SB were independently associated with diabetes-related health outcomes. Results suggest that emphasis should be placed on increasing MVPA while decreasing SB, particularly duration of SB bouts. This suggests that even small changes in daily behavior may contribute to improvement in diabetes-related health outcomes. PMID:28405340

Association of physiological and psychological health outcomes with physical activity and sedentary behavior in adults with type 2 diabetes.

PubMed

Garcia, Jeanette M; Cox, Daniel; Rice, David J

2017-01-01

To examine the association between change in moderate-to-vigorous physical activity (MVPA) and sedentary behavior (SB) over a 6-month period with physiological and psychological factors in adults with type 2 diabetes (T2D). Participants included 26 middle-aged (mean age=56.1±10.8 years; 42% women), overweight/obese (mean body mass index (BMI) =37.22±8.78 kg/m 2 ) adults who had been diagnosed with T2D within the past 5 years (mean HbA1c=7.81%). Participants underwent a physical examination, blood tests, and psychological questionnaires, including a self-report questionnaire that assessed the consumption of high glycemic and low glycemic load foods. Participants wore an Actigraph accelerometer for 7 days to assess MVPA and SB. All measures were collected at baseline and at the 6-month follow-up. Spearman rank correlations and regression models were conducted to examine the relationship between activity variables, and the association of activity measures with health outcomes at the 6-month follow-up. Decreases in duration of SB bouts and increases in MVPA were associated with decreased levels of HbA1c (p<0.05). Over 50% of the variance in HbA1c levels could be attributed to changes in MVPA and SB. MVPA and SB were independently associated with diabetes-related health outcomes. Results suggest that emphasis should be placed on increasing MVPA while decreasing SB, particularly duration of SB bouts. This suggests that even small changes in daily behavior may contribute to improvement in diabetes-related health outcomes.

The Effect of Changes in Physical Activity on Sedentary Behavior: Results From a Randomized Lifestyle Intervention Trial.

PubMed

Siddique, Juned; de Chavez, Peter John; Craft, Lynette L; Freedson, Patty; Spring, Bonnie

2017-07-01

To investigate whether changes in physical activity (PA) have an impact on sedentary behavior (SB) during a lifestyle intervention. Study design was a randomized trial. Participants (n = 204) were individuals with low PA and high sedentary leisure screen time from the Chicago area. Participants were randomized to either increase PA (iPA) or decrease sedentary leisure (dSED). The intervention consisted of decision support, coaching, and financial incentives. For iPA participants, the goal was at least 60 min/d of self-reported moderate-tovigorous-intensity PA (MVPA). For dSED participants the goal was less than 90 min/d of sedentary leisure screen time. Daily accelerometer-based measures of SB and bout-corrected MVPA were obtained. Linear mixed-effects models were fit to estimate the effect of the intervention on MVPA and total SB and to estimate the effect of daily changes in MVPA on daily SB. The iPA participants increased their bout-corrected MVPA by 14 min/d (p < .001) and decreased their total SB by 18 min/d (p < .001). The dSED participants did not significantly change their PA or their total SB. On days when participants exercised, each 10-minute bout of MVPA was associated with a 6-minute decrease in SB on the same day (p < .001). In an intervention study designed to increase MVPA, participants who increase their time spent exercising will obtain much of this time by reducing their SB.

Physical activity intensities in youth: the effect of month of assessment.

PubMed

Silva, Pedro; Seabra, André; Saint-Maurice, Pedro; Soares-Miranda, Luisa; Mota, Jorge

2013-01-01

There is clear evidence that environmental factors play an important role regarding physical activity (PA) and sedentary behaviour (SB) in youth. This short report highlights seasonal differences in the amount and intensities of PA and SB, in Portuguese youth. Three hundred and eighty-seven participants (aged 14.7 ± 1.9 years), 220 girls, used the Actigraph GT1M accelerometer for 7 days (15-second epochs), between January and June in 2008. PA and SB differences were assessed using an ANCOVA. Boys had significantly higher values of PA, with the exception of Light intensity. Girls were significantly more sedentary. PA intensities and SB changed significantly according to gender and month of assessment. SB (Gender F = 16.32, p < 0.001; Month F = 2.95, p < 0.013), Light PA (Gender F = 9.30, p = 0.002; Month F = 8.37, p < 0.001; Gender*Month F = 2.24, p = 0.050), Moderate PA (Gender F = 40.04, p < 0.001), Vigorous PA (Gender F = 32.89, p < 0.001; Month F = 2.56, p = 0.027). Both genders increased PA from winter to summer months and SB decreased. Seasonality in PA intensities and SB suggest that interventions to promote PA and decrease SB must be tailored to take into consideration the month of the year they are going to be implemented and also gender characteristics.

Physical inactivity, but not sedentary behavior or energy intake, is associated with higher fat mass in Latina and African American girls.

PubMed

McClain, Arianna D; Hsu, Ya-Wen; Belcher, Britni R; Nguyen-Rodriguez, Selena; Weigensberg, Marc; Spruijt-Metz, Donna

2011-01-01

Minority girls are disproportionately affected by overweight and obesity. The independent effects of physical activity (PA), sedentary behavior (SB), and diet are not well understood. This study examined the individual influences of PA, SB and diet on fat mass in Latina and African American (AA) girls, aged 8-11. Baseline data from a longitudinal cohort study in minority girls is presented. Multiple linear regression analysis assessed the effects of PA, SB, and energy intake on fat mass, adjusting for lean mass, age, Tanner stage and ethnicity. Participants were 53 Latina and AA girls (77% Latina; M age=9.8 +/- .9; M(BMI%)=80.8 +/- 23.1). Moderate-to-vigorous physical activity (MVPA) by accelerometry (beta= -.13, P<.01) and lean mass (beta=.69, P<.001) were associated with fat mass (Model R2=.63; P<.0001). MVPA by 3-day-physical-activity-recall (beta=-.04, P=.01) and lean mass (beta=.75, P<.001) were associated with fat mass (Model R2=.61; P<.0001). SB and energy intake were not associated with fat mass in any model. Using both objective and subjective measures of PA, MVPA, but not SB or diet, was associated with higher fat mass in Latina and AA girls, independent of lean mass, age, Tanner stage, and ethnicity. Prospective studies are needed to clarify the differential impact of diet and activity levels on adiposity in this population.

Intersubband polaritons at λ ˜ 2 μm in the InAs/AlSb system

NASA Astrophysics Data System (ADS)

Laffaille, P.; Manceau, J.-M.; Laurent, T.; Bousseksou, A.; Le Gratiet, L.; Teissier, R.; Baranov, A. N.; Colombelli, R.

2018-05-01

We demonstrate intersubband polaritons at very short wavelengths, down to λ ˜ 2 μm, using a mature semiconductor material system InAs/AlSb and a metal-insulator-metal resonator architecture. The demonstration is given for intersubband transitions centered at 350 meV (λ = 3.54 μm) and 525 meV (λ = 2.36 μm). The polaritonic dispersions are measured at room-temperature and minimum splittings (Rabi splitting) of ≈50 meV are observed. We also quantitatively show that non-parabolicity effects limit the Rabi energy that can be obtained and must be crucially taken into account to correctly model these devices. Intersubband polaritons operating in the short-wave infrared region could enable the use of extremely effective pump laser sources in the quest for an intersubband polariton laser.

Heterostructures with diffused interfaces: Luminescent technique for ascertainment of band alignment type

NASA Astrophysics Data System (ADS)

Abramkin, D. S.; Gutakovskii, A. K.; Shamirzaev, T. S.

2018-03-01

The experimental ascertainment of band alignment type for semiconductor heterostructures with diffused interfaces is discussed. A method based on the analysis of the spectral shift of photoluminescence (PL) band with excitation density (Pex) that takes into account state filling and band bending effects on the PL band shift is developed. It is shown that the shift of PL band maximum position is proportional to ℏωmax ˜ (Ue + Uh).ln(Pex) + b.Pex1/3, where Ue (Uh) are electron (hole) Urbach energy tail, and parameter b characterizes the effect of band bending or is equal to zero for heterostructures with type-II or type-I band alignment, respectively. The method was approved with InAs/AlAs, GaAs/AlAs, GaSb/AlAs, and AlSb/AlAs heterostructures containing quantum wells.

Probing atomic-scale friction on reconstructed surfaces of single-crystal semiconductors

NASA Astrophysics Data System (ADS)

Goryl, M.; Budzioch, J.; Krok, F.; Wojtaszek, M.; Kolmer, M.; Walczak, L.; Konior, J.; Gnecco, E.; Szymonski, M.

2012-02-01

Friction force microscopy (FFM) investigations have been performed on reconstructed (001) surfaces of InSb and Ge in an ultrahigh vacuum. On the c(8×2) reconstruction of InSb(001) atomic resolution is achieved under superlubric conditions, and the features observed in the lateral force images are precisely reproduced by numerical simulations, taking into account possible decorations of the probing tip. On the simultaneously acquired (1×3) reconstruction a significant disorder of the surface atoms is observed. If the loading force increases, friction becomes much larger on this reconstruction compared to the c(8×2) one. In FFM images acquired on the Ge(001)(2×1) characteristic substructures are resolved within the unit cells. In such a case, a strong dependence of the friction pattern on the scan direction is observed.

Imaging Atomic-Scale Clustering in III–V Semiconductor Alloys

DOE PAGES

Hirst, Louise C.; Kotulak, Nicole A.; Tomasulo, Stephanie; ...

2017-03-13

Quaternary alloys are essential for the development of high-performance optoelectronic devices. However, immiscibility of the constituent elements can make these materials vulnerable to phase segregation, which degrades the optical and electrical properties of the solid. High-efficiency III–V photovoltaic cells are particularly sensitive to this degradation. InAlAsSb lattice matched to InP is a promising candidate material for high-bandgap subcells of a multijunction photovoltaic device. However, previous studies of this material have identified characteristic signatures of compositional variation, including anomalous low-energy photoluminescence. In this paper, atomic-scale clustering is observed in InAlAsSb via quantitative scanning transmission electron microscopy. Finally, image quantification of atomicmore » column intensity ratios enables the comparison with simulated images, confirming the presence of nonrandom compositional variation in this multispecies alloy.« less

Effect of temperature on terahertz photonic and omnidirectional band gaps in one-dimensional quasi-periodic photonic crystals composed of semiconductor InSb.

PubMed

Singh, Bipin K; Pandey, Praveen C

2016-07-20

Engineering of thermally tunable terahertz photonic and omnidirectional bandgaps has been demonstrated theoretically in one-dimensional quasi-periodic photonic crystals (PCs) containing semiconductor and dielectric materials. The considered quasi-periodic structures are taken in the form of Fibonacci, Thue-Morse, and double periodic sequences. We have shown that the photonic and omnidirectional bandgaps in the quasi-periodic structures with semiconductor constituents are strongly depend on the temperature, thickness of the constituted semiconductor and dielectric material layers, and generations of the quasi-periodic sequences. It has been found that the number of photonic bandgaps increases with layer thickness and generation of the quasi-periodic sequences. Omnidirectional bandgaps in the structures have also been obtained. Results show that the bandwidths of photonic and omnidirectional bandgaps are tunable by changing the temperature and lattice parameters of the structures. The generation of quasi-periodic sequences can also change the properties of photonic and omnidirectional bandgaps remarkably. The frequency range of the photonic and omnidirectional bandgaps can be tuned by the change of temperature and layer thickness of the considered quasi-periodic structures. This work will be useful to design tunable terahertz PC devices.

Development of III-V p-MOSFETs with high-kappa gate stack for future CMOS applications

NASA Astrophysics Data System (ADS)

Nagaiah, Padmaja

As the semiconductor industry approaches the limits of traditional silicon CMOS scaling, non-silicon materials and new device architectures are gradually being introduced to improve Si integrated circuit performance and continue transistor scaling. Recently, the replacement of SiO2 with a high-k material (HfO2) as gate dielectric has essentially removed one of the biggest advantages of Si as channel material. As a result, alternate high mobility materials are being considered to replace Si in the channel to achieve higher drive currents and switching speeds. III-V materials in particular have become of great interest as channel materials, owing to their superior electron transport properties. However, there are several critical challenges that need to be addressed before III-V based CMOS can replace Si CMOS technology. Some of these challenges include development of a high quality, thermally stable gate dielectric/III-V interface, and improvement in III-V p-channel hole mobility to complement the n-channel mobility, low source/drain resistance and integration onto Si substrate. In this thesis, we would be addressing the first two issues i.e. the development high performance III-V p-channels and obtaining high quality III-V/high-k interface. We start with using the device architecture of the already established InGaAs n-channels as a baseline to understand the effect of remote scattering from the high-k oxide and oxide/semiconductor interface on channel transport properties such as electron mobility and channel electron concentration. Temperature dependent Hall electron mobility measurements were performed to separate various scattering induced mobility limiting factors. Dependence of channel mobility on proximity of the channel to the oxide interface, oxide thickness, annealing conditions are discussed. The results from this work will be used in the design of the p-channel MOSFETs. Following this, InxGa1-xAs (x>0.53) is chosen as channel material for developing p-channel MOSFETs. Band engineering, strain induced valence band splitting and quantum confinement is used to improve channel hole mobility. Experimental results on the Hall hole mobility is presented for InxGa1-xAs channels with varying In content, thickness of the quantum well and temperature. Then, high mobility InxGa 1-xAs heterostructure thus obtained are integrated with in-situ deposited high-k gate oxide required for high performance p-MOSFET and discuss the challenges associated with the gated structure and draw conclusions on this material system. Antimonide based channel materials such as GaSb and InxGa 1-xSb are explored for III-V based p-MOSFETs in last two chapters. Options for Sb based strained QW channels to obtain maximum hole mobility by varying the strain, channel and barrier material, thickness of the layers etc. is discussed followed by the growth of these Sb channels on GaAs and InP substrates using molecular beam epitaxy. The physical properties of the structures such as the heterostructure quality, alloy content and surface roughness are examined via TEM, XRD and AFM. Following this, electrical measurement results on Hall hole mobility is presented. The effect of strain, alloy content, temperature and thickness on channel mobility and concentration is reported. Development of GaSb n- and p-MOS capacitor structures with in-situ deposited HfO2 gate oxide dielectric using in-situ deposited amorphous Si (a-Si) interface passivation layer (IPL) to improve the interface quality of high-k oxide and (In)GaSb surface is presented. In-situ deposited gate oxides such as Al2O3 and combination oxide of Al 2O3 and HfO2 with and without the a-Si IPL are also explored as alternate gate dielectrics. Subsequently, MOS capacitor structures using buried InGaSb QWs are demonstrated. Development of an inversion type bulk GaSb with implanted source-drain contacts and in-situ deposited gate oxide HfO2 gate oxide is discussed. The merits of biaxial compressive strain is demonstrated on strained surface and buried channel In0.36 Ga0.64Sb QW MOSFETs with thin top barrier and in-situ deposited a-Si IPL and high-k HfO2 as well as combination Al 2O3+HfO2 gate stacks and ex-situ atomic layer deposited (ALD) combination gate oxide and with thin 2 nm InAs surface passivation layer is presented. Finally, summary of the salient results from the different chapters is provided with recommendations for future research.

Validation and Comparison of Accelerometers Worn on the Hip, Thigh, and Wrists for Measuring Physical Activity and Sedentary Behavior.

PubMed

Montoye, Alexander H K; Pivarnik, James M; Mudd, Lanay M; Biswas, Subir; Pfeiffer, Karin A

2016-01-01

Recent evidence suggests that physical activity (PA) and sedentary behavior (SB) exert independent effects on health. Therefore, measurement methods that can accurately assess both constructs are needed. To compare the accuracy of accelerometers placed on the hip, thigh, and wrists, coupled with machine learning models, for measurement of PA intensity category (SB, light-intensity PA [LPA], and moderate- to vigorous-intensity PA [MVPA]) and breaks in SB. Forty young adults (21 female; age 22.0 ± 4.2 years) participated in a 90-minute semi-structured protocol, performing 13 activities (three sedentary, 10 non-sedentary) for 3-10 minutes each. Participants chose activity order, duration, and intensity. Direct observation (DO) was used as a criterion measure of PA intensity category, and transitions from SB to a non-sedentary activity were breaks in SB. Participants wore four accelerometers (right hip, right thigh, and both wrists), and a machine learning model was created for each accelerometer to predict PA intensity category. Sensitivity and specificity for PA intensity category classification were calculated and compared across accelerometers using repeated measures analysis of variance, and the number of breaks in SB was compared using repeated measures analysis of variance. Sensitivity and specificity values for the thigh-worn accelerometer were higher than for wrist- or hip-worn accelerometers, > 99% for all PA intensity categories. Sensitivity and specificity for the hip-worn accelerometer were 87-95% and 93-97%. The left wrist-worn accelerometer had sensitivities and specificities of > 97% for SB and LPA and 91-95% for MVPA, whereas the right wrist-worn accelerometer had sensitivities and specificities of 93-99% for SB and LPA but 67-84% for MVPA. The thigh-worn accelerometer had high accuracy for breaks in SB; all other accelerometers overestimated breaks in SB. Coupled with machine learning modeling, the thigh-worn accelerometer should be considered when objectively assessing PA and SB.

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

NASA Astrophysics Data System (ADS)

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

2017-02-01

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

Long-wavelength room-temperature luminescence from InAs/GaAs quantum dots with an optimized GaAsSbN capping layer

PubMed Central

2014-01-01

An extensive study on molecular beam epitaxy growth conditions of quaternary GaAsSbN as a capping layer (CL) for InAs/GaAs quantum dots (QD) was carried out. In particular, CL thickness, growth temperature, and growth rate were optimized. Problems related to the simultaneous presence of Sb and N, responsible for a significant degradation of photoluminescence (PL), are thereby solved allowing the achievement of room-temperature (RT) emission. A particularly strong improvement on the PL is obtained when the growth rate of the CL is increased. This is likely due to an improvement in the structural quality of the quaternary alloy that resulted from reduced strain and composition inhomogeneities. Nevertheless, a significant reduction of Sb and N incorporation was found when the growth rate was increased. Indeed, the incorporation of N is intrinsically limited to a maximum value of approximately 1.6% when the growth rate is at 2.0 ML s−1. Therefore, achieving RT emission and extending it somewhat beyond 1.3 μm were possible by means of a compromise among the growth conditions. This opens the possibility of exploiting the versatility on band structure engineering offered by this QD-CL structure in devices working at RT. PACS 81.15.Hi (molecular beam epitaxy); 78.55.Cr (III-V semiconductors); 73.21.La (quantum dots) PMID:24438542

Direct wafer bonding of highly conductive GaSb/GaInAs and GaSb/GaInP heterojunctions prepared by argon-beam surface activation

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

Predan, Felix, E-mail: felix.predan@ise.fraunhofer.de; Reinwand, Dirk; Cariou, Romain

The authors present a low-temperature wafer bonding process for the formation of electrically conductive n-GaSb/n-Ga{sub 0.79}In{sub 0.21}As and n-GaSb/n-Ga{sub 0.32}In{sub 0.68}P heterojunctions. The surfaces are deoxidized by sputter-etching with an argon-beam and bonded in ultrahigh vacuum. The sputtering behavior was investigated for each material, revealing a distinct selective sputtering characteristic for Ga{sub 0.32}In{sub 0.68}P. According to these findings, the settings for the bonding process were chosen. The mechanical and electrical properties of the wafer bonds were studied. Fully bonded 2 in. wafer pairs were found for both material combinations exhibiting high bond energies, which are comparable to the binding energiesmore » in the semiconductors. Furthermore, bond resistances below 5 mΩ cm{sup 2} could be reached, which are in the range of the lowest resistances that have been reported for wafer bonded heterojunctions. This speaks, together with the high bond energies, for a high amount of covalent bonds at the interfaces. These promising bond characteristics make the integration of antimonides with arsenides or phosphides by wafer bonding attractive for various optoelectronic applications such as multijunction solar cells.« less

Interband magneto-spectroscopy in InSb square and parabolic quantum wells

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

Kasturiarachchi, T.; Edirisooriya, M.; Mishima, T. D.

We measure the magneto-optical absorption due to intersubband optical transitions between conduction and valence subband Landau levels in InSb square and parabolic quantum wells. InSb has the narrowest band gap (0.24 eV at low temperature) of the III–V semiconductors leading to a small effective mass (0.014 m{sub 0}) and a large g–factor (−51). As a result, the Landau level spacing is large at relatively small magnetic fields (<8 T), and one can observe spin-splitting of the Landau levels. We examine two structures: (i) a multiple-square-well structure and (ii) a structure containing multiple parabolic wells. The energies and intensities of the strongest featuresmore » are well explained by a modified Pidgeon-Brown model based on an 8-band k•p model that explicitly incorporates pseudomorphic strain. The strain is essential for obtaining agreement between theory and experiment. While modeling the square well is relatively straight-forward, the parabolic well consists of 43 different layers of various thickness to approximate a parabolic potential. Agreement between theory and experiment for the parabolic well validates the applicability of the model to complicated structures, which demonstrates the robustness of our model and confirms its relevance for developing electronic and spintronic devices that seek to exploit the properties of the InSb band structure.« less

Off-stoichiometric silver antimony telluride: An experimental study of transport properties with intrinsic and extrinsic doping

DOE PAGES

Nielsen, Michele D.; Jaworski, Christopher M.; Heremans, Joseph P.

2015-03-20

AgSbTe 2 is a thermoelectric semiconductor with an intrinsically low thermal conductivity and a valence band structure that is favorable to obtaining a high thermoelectric figure of merit zT. It also has a very small energy gap Eg ~ 7.6 ± 3 meV. As this gap is less than the thermal excitation energy at room temperature, near-intrinsic AgSbTe 2 is a two carrier system having both holes (concentration p) and electrons ( n). Good thermoelectric performance requires heavy p-type doping ( p > > n). This can be achieved with native defects or with extrinsic doping, e.g. with transition metalmore » element. The use of defect doping is complicated by the fact that many of the ternary Ag-Sb-Te and pseudo-binary Sb 2Te 3-Ag 2Te phase diagrams are contradictory. This paper determines the compositional region most favorable to creating a single phase material. Through a combination of intrinsic and extrinsic doping, values of zT > 1 are achieved, though not on single-phased material. In addition, we show that thermal conductivity is not affected by defects, further demonstrating that the low lattice thermal conductivity of I-V-VI 2 materials is due to an intrinsic mechanism, insensitive to changes in defect structure.« less

Social and physical environmental correlates of adults' weekend sitting time and moderating effects of retirement status and physical health.

PubMed

Van Holle, Veerle; McNaughton, Sarah A; Teychenne, Megan; Timperio, Anna; Van Dyck, Delfien; De Bourdeaudhuij, Ilse; Salmon, Jo

2014-09-19

Emerging research suggests that prolonged sedentary behaviour (SB) is detrimental to health. Changes in SB patterns are likely to occur during particular life stages, for example at retirement age (55-65-year-old). Evidence on socio-ecological SB correlates is scarce and inconsistent in this age group. Moreover, the influence of socio-ecological correlates may vary depending on health and retirement status. This study examined social and environment correlates of overall weekend day sitting among adults at or approaching retirement age, and moderating effects of perceived physical health and retirement status. Baseline data from the Wellbeing, Eating and Exercise for a Long Life study in 2839 Australian adults (55-65-year-old) were analysed. Participants self-reported proximal social factors, neighbourhood social and physical environment, physical health and retirement status. MLwiN multilevel regression analyses were conducted. In the multivariable model, only social support from friends/colleagues to discourage sitting (B = -0.891; p = 0.036) was associated with overall weekend day sitting. No moderation of retirement status, nor physical health were found in the multivariable results. Results from this study suggest the importance of social factors in relation to weekend day sitting among 55-65-year-old adults. Health promotion initiatives in this age group should pay special attention to enhancing social interaction opportunities. Moreover, findings suggest that SB-specific correlates may need to be examined in future research.

Insulator Charging in RF MEMS Capacitive Switches

DTIC Science & Technology

2005-06-01

and Simulations,” Journal of Microelectromechanical Systems, 8: 208-217 (June 1999). 5. Neaman , Donald. Semiconductor Physics & Devices. Boston...227-230 (2001). 5. Sze, S.M. Semiconductor Devices: Physics and Technology. New York: Wiley, 1985. 6. Neaman , Donald A. Semiconductor Physics...Radiation Response of Hafnium-Silicate Capacitors,” IEEE Transactions on Nuclear Science, 49: 3191-3196 (December 2002). 3. Neaman , D.A

Template directed fabrication and characterization of one-dimensional nanostructures for nanoelectronics

NASA Astrophysics Data System (ADS)

Khan, Muhammad Ibrahim

Limitation of near future scaling down of conventional silicon technology stimulated the quest for alternative technologies in nanometer-scale materials and devices in recent years. Since the discovery of carbon nanotubes, there has been great interest in the synthesis and characterization of other one-dimensional materials. Nanorods, wires, belts, and tubes make up one particular class of anisotropic nanomaterials, which are considered quasi one-dimensional structures. Nanowires are promising materials for many novel applications, ranging from chemical and biological sensors to optical and electronic devices. This is not only because of their unique geometry, but also because they possess many unique physical properties, including electrical, magnetic, optical, as well as mechanical properties. In this dissertation, we describe the synthesis, structure and properties of nanowires of various inorganic materials fabricated simply by filling up pores or via in a template by means of electrochemical deposition (ECD). The architecture of the porous template defines the wire shape, direction and size. Because of the extreme aspect ratios of these 3D porous membranes, most physical and chemical vapor deposition techniques are ill suited for this template-directed growth technique and template directed fabrication is found to be superior in terms of low cost, high throughput, high volume, and ease of production. Also multicomponent nanowires can be grown simply by switching the solution composition or in some cases even in the same solution by switching the deposition potential. The nanowires can be released from the template matrix by chemical dissolution of the template. Based on the successful fabrication of elemental and multicomponent nanowires we have designed and fabricated InSb nanowire based field effect transistor (FET) devices on Si substrate. InSb is well known for its direct narrow band gap (0.18 eV at 300 K) with a very high electron mobility (8x10 4 cm2 V-1 s-1 at 300 K), electron velocity, and ballistic length (up to 0.7 mum at 300 K) of any known semiconductor. We demonstrated InSb nanowire devices at different diameter range from 30nm to 200nm using template directed technique which promises smaller feature sizes and an alternate, more economical path to atomic-scale computing structures than top-down lithography.

Incorporation Kinetics in Mixed Anion Compound Semiconductor Alloys

DTIC Science & Technology

2013-01-01

been studied . 5-8 but few reports attempting to systematically determine the Sb/As incorporation as a function of growth parameters exist other...droplets are not expected to form. In this case , the surface is always covered in either the anion or segregant such that s + a =1. The rate of...values were determined in two different ways. In the first case we started by measuring the growth rates with RHEED oscillations under excess group

Experimental and Theoretical Study of the Temperature Performance of Type-II Quantum Well Lasers

DTIC Science & Technology

2007-05-31

performance of type-II Interband Cascade (IC) GaSb-based semiconductor lasers has been developed. The method includes comparing the temperature-concentration... dependence at the laser threshold with steady-state carrier heating characteristics. The number of cascades in prototype type-II IC lasers has been...Monroy, and R.L.Tober, "Wavelength Tuning of Interband Cascade Laser Based on the Stark Effect", in “Future Trends in Microelectronics” ed. by

Next generation DIRCM for 2.1-2.3 micron wavelength based on direct-diode GaSb technology

NASA Astrophysics Data System (ADS)

Dvinelis, Edgaras; Naujokaitė, Greta; Greibus, Mindaugas; Trinkūnas, Augustinas; Vizbaras, Kristijonas; Vizbaras, Augustinas

2018-02-01

Continuous advances in low-cost MANPAD heat-seeking missile technology over the past 50 years remains the number one hostile threat to airborne platforms globally responsible for over 60 % of casualties. Laser based directional countermeasure (DIRCM) technology have been deployed to counter the threat. Ideally, a laser based DIRCM system must involve a number of lasers emitting at different spectral bands mimicking the spectral signature of the airborne platform. Up to now, near and mid infrared spectral bands have been covered with semiconductor laser technology and only SWIR band remained with bulky fiber laser technology. Recent technology developments on direct-diode GaSb laser technology at Brolis Semiconductors offer a replacement for the fiber laser source leading to significant improvements by few orders of magnitude in weight, footprint, efficiency and cost. We demonstrate that with careful engineering, several multimode emitters can be combined to provide a directional laser beam with radiant intensity from 10 kW/sr to 60 kW/sr in an ultra-compact hermetic package with weight < 30 g and overall efficiency of 15 % in the 2.1- 2.3 micron spectral band offering 150 times improvement in efficiency and reduction in footprint. We will discuss present results, challenges and future developments for such next-generation integrated direct diode DIRCM modules for SWIR band.

Method of physical vapor deposition of metal oxides on semiconductors

DOEpatents

Norton, David P.

2001-01-01

A process for growing a metal oxide thin film upon a semiconductor surface with a physical vapor deposition technique in a high-vacuum environment and a structure formed with the process involves the steps of heating the semiconductor surface and introducing hydrogen gas into the high-vacuum environment to develop conditions at the semiconductor surface which are favorable for growing the desired metal oxide upon the semiconductor surface yet is unfavorable for the formation of any native oxides upon the semiconductor. More specifically, the temperature of the semiconductor surface and the ratio of hydrogen partial pressure to water pressure within the vacuum environment are high enough to render the formation of native oxides on the semiconductor surface thermodynamically unstable yet are not so high that the formation of the desired metal oxide on the semiconductor surface is thermodynamically unstable. Having established these conditions, constituent atoms of the metal oxide to be deposited upon the semiconductor surface are directed toward the surface of the semiconductor by a physical vapor deposition technique so that the atoms come to rest upon the semiconductor surface as a thin film of metal oxide with no native oxide at the semiconductor surface/thin film interface. An example of a structure formed by this method includes an epitaxial thin film of (001)-oriented CeO.sub.2 overlying a substrate of (001) Ge.

A National Survey of Physical Activity and Sedentary Behavior of Chinese City Children and Youth Using Accelerometers

ERIC Educational Resources Information Center

Wang, Chao; Chen, Peijie; Zhuang, Jie

2013-01-01

Purpose: The purpose of this study was to objectively assess levels of physical activity (PA) and sedentary behavior (SB) of Chinese city children and youth aged 9 to 17 years old using accelerometers and to examine their differences by gender, age, grade, and weight status. Method: The PA and SB of 2,163 students in 4th grade through 11th grade…

Does duration of physical activity bouts matter for adiposity and metabolic syndrome? A cross-sectional study of older British men.

PubMed

Jefferis, Barbara J; Parsons, Tessa J; Sartini, Claudio; Ash, Sarah; Lennon, Lucy T; Wannamethee, S Goya; Lee, I-Min; Whincup, Peter H

2016-03-15

Older adults have low physical activity(PA) and high sedentary behaviour(SB) levels. We investigate how total volume and specific patterns of moderate to vigorous PA(MVPA), light PA(LPA) and SB are related to adiposity and metabolic syndrome (MS). Then, with reference to physical activity guidelines which encourage MVPA in bouts > =10 min and avoiding "long" sedentary bouts, we investigate whether accumulating PA and SB in bouts of different defined durations are differently associated with these outcomes. Cross-sectional study of men (71-91 years) recruited in UK primary care centres. Nurses made physical measures (weight, height, bio-impedance, blood pressure) and took fasting blood samples. 1528/3137 (49%) surviving men had ≥3 valid days (≥600 min) accelerometer data. 450 men with pre-existing chronic disease were excluded. 1009/1078 (93.6%) had complete covariate data. Men (n = 1009, mean age 78.5(SD 4.7) years) spent 612(SD 83), 202(SD 64) and 42(SD 33) minutes in SB, LIPA and MVPA respectively. Each additional 30 min/day of SB and MVPA were associated with 0.32 (95% CI 0.23, 0.40)Kg/m(2) higher Body Mass Index (BMI) and -0.72(-0.93, -0.51) lower BMI Kg/m(2) respectively. Patterns for waist circumference (WC), fat mass index (FMI), fasting insulin and MS were similar. MVPA in bouts lasting <10 min or ≥10 min duration were not associated differently with outcomes. In models adjusted for total MVPA, each minute accumulated in SB bouts lasting 1-15 min was associated with lower BMI -0.012 kg/m(2), WC -0.029 cm, and OR 0.989 for MS (all p < 0.05), and coefficients for LPA bouts 1-9 min were very similar in separate models adjusted for total MVPA. Minutes accumulated in SB bouts 1-15 min and LPA bouts 1-9 min were correlated, r = 0.62. Objectively measured MVPA, LPA and SB were all associated with lower adiposity and metabolic risk. The beneficial associations of LPA are encouraging for older adults for whom initiating MVPA and maintaining bouts lasting ≥10 min may be particularly challenging. Findings that short bouts of LPA (1-9 min) and SB (1-15 min), but that all MVPA, not just MVPA accumulated in bouts ≥10 min were associated with lower adiposity and better metabolic health could help refine older adult PA guidelines.

Crystal growth and characterization of bulk Sb2Te3 topological insulator

NASA Astrophysics Data System (ADS)

Sultana, Rabia; Gurjar, Ganesh; Patnaik, S.; Awana, V. P. S.

2018-04-01

The Sb2Te3 crystals are grown using the conventional self flux method via solid state reaction route, by melting constituent elements (Sb and Te) at high temperature (850 °C), followed by slow cooling (2 °C/h). As grown Sb2Te3 crystals are analysed for various physical properties by x-ray diffraction (XRD), Raman Spectroscopy, Scanning Electron Microscopy (SEM) coupled with Energy Dispersive x-ray Spectroscopy (EDAX) and electrical measurements under magnetic field (6 Tesla) down to low temperature (2.5 K). The XRD pattern revealed the growth of synthesized Sb2Te3 sample along (00l) plane, whereas the SEM along with EDAX measurements displayed the layered structure with near stoichiometric composition, without foreign contamination. The Raman scattering studies displayed known ({{{{A}}}1{{g}}}1, {{{{E}}}{{g}}}2 and {{{{A}}}1{{g}}}2) vibrational modes for the studied Sb2Te3. The temperature dependent electrical resistivity measurements illustrated the metallic nature of the as grown Sb2Te3 single crystal. Further, the magneto—transport studies represented linear positive magneto-resistance (MR) reaching up to 80% at 2.5 K under an applied field of 6 Tesla. The weak anti localization (WAL) related low field (±2 Tesla) magneto-conductance at low temperatures (2.5 K and 20 K) has been analysed and discussed using the Hikami—Larkin—Nagaoka (HLN) model. Summarily, the short letter reports an easy and versatile method for crystal growth of bulk Sb2Te3 topological insulator (TI) and its brief physical property characterization.

Reliability and Validity of 2 Self-Report Measures to Assess Sedentary Behavior in Older Adults.

PubMed

Gennuso, Keith P; Matthews, Charles E; Colbert, Lisa H

2015-05-01

The purpose of this study was to examine the reliability and validity of 2 currently available physical activity surveys for assessing time spent in sedentary behavior (SB) in older adults. Fifty-eight adults (≥65 years) completed the Yale Physical Activity Survey for Older Adults (YPAS) and Community Health Activities Model Program for Seniors (CHAMPS) before and after a 10-day period during which they wore an ActiGraph accelerometer (ACC). Intraclass correlation coefficients (ICC) examined test-retest reliability. Overall percent agreement and a kappa statistic examined YPAS validity. Lin's concordance correlation, Pearson correlation, and Bland-Altman analysis examined CHAMPS validity. Both surveys had moderate test-retest reliability (ICC: YPAS = 0.59 (P < .001), CHAMPS = 0.64 (P < .001)) and significantly underestimated SB time. Agreement between YPAS and ACC was low (κ = -0.0003); however, there was a linear increase (P < .01) in ACC-derived SB time across YPAS response categories. There was poor agreement between ACC-derived SB and CHAMPS (Lin's r = .005; 95% CI, -0.010 to 0.020), and no linear trend across CHAMPS quartiles (P = .53). Neither of the surveys should be used as the sole measure of SB in a study; though the YPAS has the ability to rank individuals, providing it with some merit for use in correlational SB research.

Photoelectroconversion by Semiconductors: A Physical Chemistry Experiment.

ERIC Educational Resources Information Center

Fan, Qinbai; And Others

1995-01-01

Presents an experiment designed to give students some experience with photochemistry, electrochemistry, and basic theories about semiconductors. Uses a liquid-junction solar cell and illustrates some fundamental physical and chemical principles related to light and electricity interconversion as well as the properties of semiconductors. (JRH)

Buried homojunction in CdS/Sb2Se3 thin film photovoltaics generated by interfacial diffusion

NASA Astrophysics Data System (ADS)

Zhou, Ying; Li, Yang; Luo, Jiajun; Li, Dengbing; Liu, Xinsheng; Chen, Chao; Song, Huaibing; Ma, Jingyuan; Xue, Ding-Jiang; Yang, Bo; Tang, Jiang

2017-07-01

Antimony selenide (Sb2Se3) emerges as a very promising non-toxic absorber material for thin film photovoltaics, and most of the devices, either in the superstrate or substrate configuration, employed CdS as the buffer layer. Due to the peculiar one-dimensional crystal structure of Sb2Se3, severe interfacial diffusion would be expected. In this letter, the interfacial diffusion in CdS/Sb2Se3 photovoltaics was carefully characterized from a combined material and device physics characterization. The results indicated that a buried homojunction located deep inside the Sb2Se3 absorber layer due to Cd diffusion, instead of the apparent CdS/Sb2Se3 heterojunction, dictated charge separation and device performance in Sb2Se3 thin film solar cells. Cd diffusion converted p-type Sb2Se3 into n-type by introducing a donor level with an activation energy of 0.22 eV. Our studies deepen the understanding of Sb2Se3 photovoltaics and shed light on their further performance optimization.

Classification Accuracy of a Wearable Activity Tracker for Assessing Sedentary Behavior and Physical Activity in 3-5-Year-Old Children.

PubMed

Byun, Wonwoo; Lee, Jung-Min; Kim, Youngwon; Brusseau, Timothy A

2018-03-26

This study examined the accuracy of the Fitbit activity tracker (FF) for quantifying sedentary behavior (SB) and varying intensities of physical activity (PA) in 3-5-year-old children. Twenty-eight healthy preschool-aged children (Girls: 46%, Mean age: 4.8 ± 1.0 years) wore the FF and were directly observed while performing a set of various unstructured and structured free-living activities from sedentary to vigorous intensity. The classification accuracy of the FF for measuring SB, light PA (LPA), moderate-to-vigorous PA (MVPA), and total PA (TPA) was examined calculating Pearson correlation coefficients (r), mean absolute percent error (MAPE), Cohen's kappa ( k ), sensitivity (Se), specificity (Sp), and area under the receiver operating curve (ROC-AUC). The classification accuracies of the FF (ROC-AUC) were 0.92, 0.63, 0.77 and 0.92 for SB, LPA, MVPA and TPA, respectively. Similarly, values of kappa, Se, Sp and percentage of correct classification were consistently high for SB and TPA, but low for LPA and MVPA. The FF demonstrated excellent classification accuracy for assessing SB and TPA, but lower accuracy for classifying LPA and MVPA. Our findings suggest that the FF should be considered as a valid instrument for assessing time spent sedentary and overall physical activity in preschool-aged children.

Mothers’ perceptions of the UK physical activity and sedentary behaviour guidelines for the early years (Start Active, Stay Active): a qualitative study

PubMed Central

Bentley, Georgina F; Jago, Russell; Turner, Katrina M

2015-01-01

Objectives Higher levels of physical activity (PA) during early childhood have been associated with improved health outcomes, whereas sedentary behaviour (SB) has been associated with poorer health outcomes in children. In 2011, the UK produced guidelines for PA and SB in children under 5 years. Mothers have been identified as key influences in young children's PA and SB. The aim of this study was to use in-depth interviews with mothers of preschool children to examine attitudes to the guidance. Design Qualitative study using one-to-one, semistructured interviews; Data were analysed thematically using a framework approach. Setting Mothers were recruited from preschools, nurseries, and mother and toddler groups located in four areas of varying socioeconomic status within Bristol, UK. Participants 24 mothers who were considered the main or joint carer for a preschool child who was at least 2 years of age but had not yet started formal schooling. Results Mothers are not aware of the UK PA and SB guidelines for the early years. They believe that their child achieves the guideline targets for PA and SB and therefore, they do not believe these quidelines are relevant to them. Mothers feel that an increase in PA and reduction in SB (especially screen-viewing) would cause stress for mothers. Mothers found defining and quantifying PA and SB in their preschool child problematic. Conclusions As mothers do not identify with the need to increase PA or reduce SB in their child, awareness of the guidelines alone is unlikely to initiate behaviour change. Information on how mothers can make a more accurate assessment of their preschool child's PA and SB levels, and information about the benefits of increased PA and reduced SB should be provided alongside the guideline targets. Clear messages need to be developed that reframe the guidelines into pragmatic and usable targets. PMID:26351186

Quench hardening of Sb0.2 Bi1.8Te3, Bi2Te2.8Se0.2 and Sn0.2 Bi1.8Te3 single crystals

NASA Astrophysics Data System (ADS)

Soni, P. H.

2018-02-01

The V2-VI3 intermetallics are narrow band gap semiconductors and well known for their thermoelectric properties. They therefore offer a convenient route to tune band gap for manipulating thermoelectric parameters. The V group element Sb can be fruitfully used to substitute Bi in various proportions thus forming a psuedobinary solid solution. The electronic in general and the thermoelectric properties in particular of this psuedobinary have been amply reported. However there are no reports found on mechanical properties. I have used Sb0.2 Bi1.8Te3, Bi2Te2.8Se0.2 and Sn0.2 Bi1.8Te3single crystals grown using Bridgman technique for the quenching treatment followed by hardness testing. Vickers hardness tests were conducted on the cleavage planes of the crystals quenched from various high temperatures and the quench hardenening coefficient values have been determined. The hardness tests were carried out at various applied loads also to explore load dependence of the measured hardness. The results are reported in the paper.

Room-temperature spin-orbit torque in NiMnSb

NASA Astrophysics Data System (ADS)

Ciccarelli, C.; Anderson, L.; Tshitoyan, V.; Ferguson, A. J.; Gerhard, F.; Gould, C.; Molenkamp, L. W.; Gayles, J.; Železný, J.; Šmejkal, L.; Yuan, Z.; Sinova, J.; Freimuth, F.; Jungwirth, T.

2016-09-01

Materials that crystallize in diamond-related lattices, with Si and GaAs as their prime examples, are at the foundation of modern electronics. Simultaneously, inversion asymmetries in their crystal structure and relativistic spin-orbit coupling led to discoveries of non-equilibrium spin-polarization phenomena that are now extensively explored as an electrical means for manipulating magnetic moments in a variety of spintronic structures. Current research of these relativistic spin-orbit torques focuses primarily on magnetic transition-metal multilayers. The low-temperature diluted magnetic semiconductor (Ga, Mn)As, in which spin-orbit torques were initially discovered, has so far remained the only example showing the phenomenon among bulk non-centrosymmetric ferromagnets. Here we present a general framework, based on the complete set of crystallographic point groups, for identifying the potential presence and symmetry of spin-orbit torques in non-centrosymmetric crystals. Among the candidate room-temperature ferromagnets we chose to use NiMnSb, which is a member of the broad family of magnetic Heusler compounds. By performing all-electrical ferromagnetic resonance measurements in single-crystal epilayers of NiMnSb we detect room-temperature spin-orbit torques generated by effective fields of the expected symmetry and of a magnitude consistent with our ab initio calculations.

A model-based approach for the scattering-bar printing avoidance

NASA Astrophysics Data System (ADS)

Du, Yaojun; Li, Liang; Zhang, Jingjing; Shao, Feng; Zuniga, Christian; Deng, Yunfei

2018-03-01

As the technology node for the semiconductor manufacturing approaches advanced nodes, the scattering-bars (SBs) are more crucial than ever to ensure a good on-wafer printability of the line space pattern and hole pattern. The main pattern with small pitches requires a very narrow PV (process variation) band. A delicate SB addition scheme is thus needed to maintain a sufficient PW (process window) for the semi-iso- and iso-patterns. In general, the wider, longer, and closer to main feature SBs will be more effective in enhancing the printability; on the other hand, they are also more likely to be printed on the wafer; resulting in undesired defects transferable to subsequent processes. In this work, we have developed a model based approach for the scattering-bar printing avoidance (SPA). A specially designed optical model was tuned based on a broad range of test patterns which contain a variation of CDs and SB placements showing printing and non-printing scattering bars. A printing threshold is then obtained to check the extra-printings of SBs. The accuracy of this threshold is verified by pre-designed test patterns. The printing threshold associated with our novel SPA model allows us to set up a proper SB rule.

The relationship between the electronic structure and thermoelectric properties of Zintl compounds M2Zn5As4 (M = K, Rb).

PubMed

Yang, Gui; Yang, Jueming; Yan, Yuli; Wang, Yuanxu

2014-03-28

The electronic structure and the thermoelectric properties of M2Zn5As4 (M = K, Rb) are studied by the first principles and the semiclassical BoltzTraP theory. It is determined that they are semiconductors with an indirect band gap of about 1 eV, which is much larger than that of Ca5Al2Sb6 (0.50 eV). The calculated electronic localization function indicates that they are typical Zintl bonding compounds. The combination of heavy and light bands near the valence band maximum may improve their thermoelectric performance. Rb2Zn5As4 exhibits relatively large Seebeck coefficients, high electrical conductivities, and the large "maximum" thermoelectric figures of merit (ZeT). Compared with Ca5Al2Sb6, the highest ZeT of Rb2Zn5As4 appears at relatively low carrier concentration. For Rb2Zn4As5, the p-type doping may achieve a higher thermoelectric performance than n-type doping. The thermoelectric properties of Rb2Zn5As4 are possibly superior to those of Ca5Al2Sb6.

Correlation between structural and thermodynamic properties of some selenium based phase-change materials

NASA Astrophysics Data System (ADS)

Chandel, Namrata; Mehta, Neeraj

2018-04-01

In this study, we prepared novel selenium rich multi-component glasses by incorporating In, Cd and Sb as foreign elements in an Sn containing Sesbnd Te system in order to study their metal-induced effects on the thermal properties of the parent ternary glass. In particular, we determined the thermodynamic parameters of Se80Te18Sn2 and Se80Te8Sn2M10 (M = Cd, In, Sb) glassy semiconductors in a non-isothermal environment using the differential scanning calorimetry. Calorimetric measurements were obtained in the glass transition regions for Se80Te18Sn2 and Se80Te8Sn2M10 (M = Cd, In, Sb) glasses to determine their thermodynamic parameters such as the specific heat, enthalpy, and entropy during glass transition. We analyzed the variation in the specific heat before and after the heat capacity jump in these alloys. The metal-induced effects of foreign elements on the thermodynamic properties of the parent glass were also investigated in terms of the influence of the elemental specific heat of the added elemental metal as well as the thermal stability and glass-forming ability of the glasses.

Interplay between strain, quantum confinement, and ferromagnetism in strained ferromagnetic semiconductor (In,Fe)As thin films

NASA Astrophysics Data System (ADS)

Sasaki, Daisuke; Anh, Le Duc; Nam Hai, Pham; Tanaka, Masaaki

2014-04-01

We systematically investigated the influence of strain on the electronic structure and ferromagnetism of (In,Fe)As thin films. It is found that while the shift of the critical point energies of compressive-strained (In,Fe)As layers grown on (In1-y,Gay)As (y = 0.05, 0.1) buffer layers can be explained by the hydrostatic deformation effect (HDE) alone, those of tensile-strained (In,Fe)As layers grown on (Ga1-z,Alz)Sb (z = 0, 0.5, 1) buffer layers can be explained by the combination of HDE and the quantum confinement effect (QCE). The Curie temperature TC of the (In,Fe)As layers strongly depends on the strain, and shows a maximum for the (In,Fe)As layer grown on a GaSb buffer layer. The strain dependence of TC can be explained by the s-d exchange mechanism taking into account HDE and QCE.

Single-Mode Near-Infrared Lasing in a GaAsSb-Based Nanowire Superlattice at Room Temperature

NASA Astrophysics Data System (ADS)

Ren, Dingding; Ahtapodov, Lyubomir; Nilsen, Julie S.; Yang, Jianfeng; Gustafsson, Anders; Huh, Junghwan; Conibeer, Gavin J.; van Helvoort, Antonius T. J.; Fimland, Bjørn-Ove; Weman, Helge

2018-04-01

Semiconductor nanowire lasers can produce guided coherent light emission with miniaturized geometry, bringing about new possibility for a variety of applications including nanophotonic circuits, optical sensing, and on-chip and chip-to-chip optical communications. Here, we report on the realization of single-mode room-temperature lasing from 890 nm to 990 nm utilizing a novel design of single nanowires with GaAsSb-based multiple superlattices as gain medium under optical pumping. The wavelength tunability with comprehensively enhanced lasing performance is shown to result from the unique nanowire structure with efficient gain materials, which delivers a lasing quality factor as high as 1250, a reduced lasing threshold ~ 6 kW cm-2 and a high characteristic temperature ~ 129 K. These results present a major advancement for the design and synthesis of nanowire laser structures, which can pave the way towards future nanoscale integrated optoelectronic systems with stunning performance.

Performance analysis of gate all around GaAsP/AlGaSb CP-TFET

NASA Astrophysics Data System (ADS)

Lemtur, Alemienla; Sharma, Dheeraj; Suman, Priyanka; Patel, Jyoti; Yadav, Dharmendra Singh; Sharma, Neeraj

2018-05-01

Illustration of importance of gate all around (GAA) structure and hetero-junction formed by III-V semiconductor compounds has been analysed through GaAsP/AlGaSb CP-TFET (charge plasma tunnel field effect transistor). Charge plasma concept has been incorporated here to make this device more immune towards random dopant fluctuations (RDF). A high driving current of 1.28 ×10-5 A/μm and transconductance (gm) of 96.4 μS at supply voltages VGS = 1V and VDS = 0.5V is achieved. Further, implications of employing this device in analog/RF circuits have been supported with simulated results showing a high cut-off frequency of 34.5 THz and device efficiency of 3.45 MV-1. Apart from this, an insight of the linearity performances has also been included. Simultaneously, all the results are compared with a conventional gate all around charge plasma TFET.

Transparent ambipolar organic thin film transistors based on multilayer transparent source-drain electrodes

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

Zhang, Nan; Hu, Yongsheng, E-mail: huyongsheng@ciomp.ac.cn, E-mail: liuxy@ciomp.ac.cn; Lin, Jie

A fabrication method for transparent ambipolar organic thin film transistors with transparent Sb{sub 2}O{sub 3}/Ag/Sb{sub 2}O{sub 3} (SAS) source and drain electrodes has been developed. A pentacene/N,N′-ditridecylperylene-3,4,9,10-tetracarboxylic di-imide (PTCDI-C13) bilayer heterojunction is used as the active semiconductor. The electrodes are deposited by room temperature electron beam evaporation. The devices are fabricated without damaging the active layers. The SAS electrodes have high transmittance (82.5%) and low sheet resistance (8 Ω/sq). High performance devices with hole and electron mobilities of 0.3 cm{sup 2}/V s and 0.027 cm{sup 2}/V s, respectively, and average visible range transmittance of 72% were obtained. These transistors have potential for transparent logicmore » integrated circuit applications.« less

Controlled nanopatterning & modifications of materials by energetic ions

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

Sinha, O. P.

Compound semiconductors (InP, InAs and GaSb) has been exposed to energetic 3 keV Ar{sup +} ions for a varying fluence range of 10{sup 13} ions/cm{sup 2} to 10{sup 18} ions/cm{sup 2} at room temperature. Morphological modifications of the irradiated surfaces have been investigated by Scanning Tunneling Microscopy (STM) in UHV conditions. It is observed that InP and GaSb have fluence dependent nanopattering e.g. nanoneedle, aligned nanodots, superimposed nanodots ripple like structures while InAs has little fluence dependent behaviour indicating materials dependent growth of features on irradiated surfaces. Moreover, surface roughness and wavelength of the features are also depending on themore » materials and fluences. The RMS surface roughness has been found to be increased rapidly in the early stage of irradiation followed by slower escalate rate and later tends to saturate indicating influence of the nonlinear processes.« less

Effect of Sb on physical properties and microstructures of laser nano/amorphous-composite film

NASA Astrophysics Data System (ADS)

Li, Jia-Ning; Gong, Shui-Li; Sun, Mei; Shan, Fei-Hu; Wang, Xi-Chang; Jiang, Shuai

2013-11-01

A nano/amorphous-composite film was fabricated by laser cladding (LC) of the Co-Ti-B4C-Sb mixed powders on a TA15 alloy. Such film mainly consisted of Ti-Al, Co-Ti, Co-Sb intermetallics, TiC, TiB2, TiB, and the amorphous phases. Experimental results indicated that the crystal systems of TiB2 (hexagonal)/TiC (cubic) and Sb (rhombohedral) played important role on the formation of such film. Due to the mismatch of these crystals systems and mutual immiscibility of the metallic components, Sb was not incorporated in TiB2/TiC, but formed separate nuclei during the film growth. Thus, the growth of TiB2/TiC was stopped by the Sb nucleus in such LC molten pool, so as to form the nanoscale particles.

Regional differences of physical activity and sedentary behaviour in Swiss children are not explained by socio-demographics or the built environment.

PubMed

Bringolf-Isler, Bettina; Mäder, Urs; Dössegger, Alain; Hofmann, Heidi; Puder, Jardena J; Braun-Fahrländer, Charlotte; Kriemler, Susi

2015-03-01

We evaluated whether regional differences in physical activity (PA) and sedentary behaviour (SB) existed along language boundaries within Switzerland and whether potential differences would be explained by socio-demographics or environmental characteristics. We combined data of 611 children aged 4 to 7 years from four regional studies. PA and SB were assessed by accelerometers. Information about the socio-demographic background was obtained by questionnaires. Objective neighbourhood attributes could be linked to home addresses. Multivariate regression models were used to test associations between PA and SB and socio-demographic characteristics and neighbourhood attributes. Children from the German compared to the French-speaking region were more physically active and less sedentary (by 10-15 %, p < 0.01). Although German-speaking children lived in a more favourable environment and a higher socioeconomic neighbourhood (differences p < 0.001), these characteristics did not explain the differences in PA behaviour between French and German speaking. Factors related to the language region, which might be culturally rooted were among the strongest correlates of PA and SB among Swiss children, independent of individual, social and environmental factors.

Free Surface Properties of III-V Compound Semiconductor Surfaces.

DTIC Science & Technology

1980-06-01

selvage. Most important is the fact that atomic displacements also occur up to two layers into the substrate in the IaSb (ll0) selvage, presumably because of...result is that the interaction is of a disordering nature. 1 2,1 3 We took LEED measurements for a very large range of exposure to molecular oxygen (103...which the Al replaces the Ga. Arguments in favor of this reaction are given by measured photoemission peak shifts: 1 8󈧗 the Ga 3-d core level shifts

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

Gadzhaliev, M. M.; Daunov, M. I.; Musaev, A. M., E-mail: akhmed-musaev@yandex.ru

The pressure dependence of permittivity χ of direct gap ZnO, CdTe, InSb, InAs, CdSnAs{sub 2}, and CdGeAs{sub 2} semiconductors in the hydrostatic pressure range from zero to 1 GPa is determined from the results of quantitative analysis of the pressure dependences of resistivity ρ(P) and Hall constant R{sub H}(P). It is found that the dielectric constant decreases upon an increase in pressure so that coefficient (dχ/d{sub P})/χ increases with (dE{sub g}/dP)/E{sub g}.

Bibliography of Soviet Laser Developments, Number 48 July-August 1980.

DTIC Science & Technology

1981-07-01

equilibrium and thermodvnamic properties of alloys of erbium with tellurium in the solid state. Moskovskiv Cli. Vestnik. Khimiva, no. 4, 1980, 339-344. 3...processes in a gamma laser. Sb 12, 147-163. (RZhF, 7/80, 7DI140) 292. Vysotskiy, V.I., and R.N. Kuz’min (51,2). Focusing and channeling of neutrons and...metal-nitride- oxide - semiconductor structure and a laser CRT. KE, no. 7, 1980, 1585-1588. 55 359. Soroka, S.1., and S.I. Ratnikov (0). Hologram

INAS hole-immobilized doping superlattice long-wave-infrared detector

NASA Technical Reports Server (NTRS)

Maserjian, Joseph (Inventor)

1992-01-01

An approach to long-wave-infrared (LWIR) technology is discussed. The approach is based on molecular beam epitaxy (MBE) growth of hole immobilized doping superlattices in narrow band gap 3-5 semiconductors, specifically, InAs and InSb. Such superlattices are incorporated into detector structures suitable for focal plane arrays. An LWIR detector that has high detectivity performance to wavelengths of about 16 microns at operating temperatures of 65K, where long-duration space refrigeration is plausible, is presented.

InxGa1-xSb Channel p-Metal-Oxide-Semiconductor Field Effect Transistors: Effect of Strain and Heterostructure Design

DTIC Science & Technology

2011-07-06

biaxial compressive strain is known to split the light- and heavy-hole bands, reducing the interband scattering and causing the light hole band to move up...and heterostructure design are presented. In Section V, we use temperature- dependent measurements and pulsed I-V measurements to analyze the results...minimal in our devices. The temperature dependence of hole mobility was stud- ied for both the surface and buried channel devices, as plot- ted in Fig

Coherent acoustic phonons in nanostructures

NASA Astrophysics Data System (ADS)

Dekorsy, T.; Taubert, R.; Hudert, F.; Bartels, A.; Habenicht, A.; Merkt, F.; Leiderer, P.; Köhler, K.; Schmitz, J.; Wagner, J.

2008-02-01

Phonons are considered as a most important origin of scattering and dissipation for electronic coherence in nanostructures. The generation of coherent acoustic phonons with femtosecond laser pulses opens the possibility to control phonon dynamics in amplitude and phase. We demonstrate a new experimental technique based on two synchronized femtosecond lasers with GHz repetition rate to study the dynamics of coherently generated acoustic phonons in semiconductor heterostructures with high sensitivity. High-speed synchronous optical sampling (ASOPS) enables to scan a time-delay of 1 ns with 100 fs time resolution with a frequency in the kHz range without a moving part in the set-up. We investigate the dynamics of coherent zone-folded acoustic phonons in semiconductor superlattices (GaAs/AlAs and GaSb/InAs) and of coherent vibration of metallic nanostructures of non-spherical shape using ASOPS.

Prediction of weak topological insulators in layered semiconductors.

PubMed

Yan, Binghai; Müchler, Lukas; Felser, Claudia

2012-09-14

We report the discovery of weak topological insulators by ab initio calculations in a honeycomb lattice. We propose a structure with an odd number of layers in the primitive unit cell as a prerequisite for forming weak topological insulators. Here, the single-layered KHgSb is the most suitable candidate for its large bulk energy gap of 0.24 eV. Its side surface hosts metallic surface states, forming two anisotropic Dirac cones. Although the stacking of even-layered structures leads to trivial insulators, the structures can host a quantum spin Hall layer with a large bulk gap, if an additional single layer exists as a stacking fault in the crystal. The reported honeycomb compounds can serve as prototypes to aid in the finding of new weak topological insulators in layered small-gap semiconductors.

Subwavelength InSb-based Slot wavguides for THz transport: concept and practical implementations.

PubMed

Ma, Youqiao; Zhou, Jun; Pištora, Jaromír; Eldlio, Mohamed; Nguyen-Huu, Nghia; Maeda, Hiroshi; Wu, Qiang; Cada, Michael

2016-12-07

Seeking better surface plasmon polariton (SPP) waveguides is of critical importance to construct the frequency-agile terahertz (THz) front-end circuits. We propose and investigate here a new class of semiconductor-based slot plasmonic waveguides for subwavelength THz transport. Optimizations of the key geometrical parameters demonstrate its better guiding properties for simultaneous realization of long propagation lengths (up to several millimeters) and ultra-tight mode confinement (~λ 2 /530) in the THz spectral range. The feasibility of the waveguide for compact THz components is also studied to lay the foundations for its practical implementations. Importantly, the waveguide is compatible with the current complementary metal-oxide-semiconductor (CMOS) fabrication technique. We believe the proposed waveguide configuration could offer a potential for developing a CMOS plasmonic platform and can be designed into various components for future integrated THz circuits (ITCs).

Physical activity ameliorates the association between sedentary behavior and cardiometabolic risk among inpatients with schizophrenia: A comparison versus controls using accelerometry.

PubMed

Stubbs, Brendon; Chen, Li-Jung; Chung, Ming-Shun; Ku, Po-Wen

2017-04-01

A lack of clarity exists regarding the relationship between objectively measured physical activity (PA) and sedentary behavior (SB) and cardiometabolic outcomes in people with schizophrenia. We conducted a large study investigating the independent relationships of PA and SB among inpatients with schizophrenia versus healthy controls (HCs). A cross sectional study including 199 inpatients with schizophrenia (mean age 44.0years, mean illness duration 23.8years) versus 60 age/sex/body mass index matched HCs. Participants wore accelerometers for 7days to capture SB and daily steps. Cardiometabolic outcomes included blood pressure, fasting blood glucose (FBG), triglycerides, high-density lipoprotein cholesterol (HDL-C) and waist circumference (WC). Multivariate regression analyses adjusting for multiple confounders were undertaken. Compared to HCs, patients engaged in more sedentary behavior and less daily steps versus HCs (p<0.001). Patients with higher levels of SB (n=89) had increased fasting glucose compared to patients with low levels of SB (105.2 vs. 96.3mg/dl, p<0.05). In the multivariate analysis, sedentary behavior was associated with higher FBG (β = .146, p=.041) but this was ameliorated when daily steps were inserted in to the model (β = .141, p=.059). In the final model, higher daily steps were associated with more favorable HDL-C (β=-.226, p=.004), independent of SB and other confounders. Our data suggest that higher than while sedentary behavior is related to worse fasting glucose, this relationship is attenuated when PA is taken into account. Physical activity is also associated with favorable HDL-C. Interventions targeting replacing sedentary behavior with PA may improve metabolic risk. Copyright © 2017 Elsevier Inc. All rights reserved.

Physical Activity and Sedentary Behavior Patterns Before and During Pregnancy in a Multi-ethnic Sample of Asian Women in Singapore.

PubMed

Padmapriya, N; Shen, Liang; Soh, Shu-E; Shen, Zhe; Kwek, Kenneth; Godfrey, Keith M; Gluckman, Peter D; Chong, Yap-Seng; Saw, Seang-Mei; Müller-Riemenschneider, Falk

2015-11-01

To describe physical activity (PA) and sedentary behavior (SB) patterns before and during pregnancy among Chinese, Malay and Indian women. In addition, to investigate determinants of change in PA and SB during pregnancy. The Growing Up in Singapore Towards healthy Outcomes cohort recruited first trimester pregnant women. PA and SB (sitting time and television time) before and during pregnancy were assessed as a part of an interview questionnaire at weeks 26-28 gestational clinic visit. Total energy expenditure (TEE) on PA and time in SB were calculated. Determinants of change in PA and SB were investigated using multiple logistic regression analysis. PA and SB questions were answered by 94 % (n = 1171) of total recruited subjects. A significant reduction in TEE was observed from before to during pregnancy [median 1746.0-1039.5 metabolic equivalent task (MET) min/week, p < 0.001]. The proportion of women insufficiently active (<600 MET-min/week) increased from 19.0 to 34.1 % (p <0.001). Similarly, sitting time (median 56.0-63.0 h/week, p < 0.001) and television time (mean 16.1-16.7 h/week, p = 0.01) increased. Women with higher household income, lower level of perceived health, nausea/vomiting during pregnancy and higher level of pre-pregnancy PA were more likely to reduce PA. Women with children were less likely to reduce PA. Women reporting nausea/vomiting and lower level of pre-pregnancy sitting time were more likely to increase sitting time. Participants substantially reduced PA and increased SB by 26-28 weeks of pregnancy. Further research is needed to better understand determinants of change in PA and SB and develop effective health promotion strategies.

Charge Transport and Thermoelectric Properties of (Nd1- z Yb z ) y Fe4- x Co x Sb12 Skutterudites

NASA Astrophysics Data System (ADS)

Shin, Dong-Kil; Jang, Kyung-Wook; Choi, Soon-Mok; Lee, Soonil; Seo, Won-Seon; Kim, Il-Ho

2018-06-01

Partially double-filled (Nd1- z Yb z ) y Fe4- x Co x Sb12 ( z = 0.25, 0.75, y = 0.8, and x = 0, 0.5, 1.0) skutterudites were prepared by encapsulated melting, annealing, and hot pressing, and the effects of Nd/Yb partial double filling and Co charge compensation on the microstructure, charge transport, and thermoelectric properties were investigated. All the specimens were transformed to the skutterudite phase together with a few secondary phases such as FeSb2, but FeSb2 formation was suppressed on increasing Co content. Nd and Yb were successfully double-filled in the voids of the skutterudite lattice and Co was well substituted at Fe sites, as indicated by changes in the lattice constant with Nd/Yb filling and Fe/Co substitution. All the specimens showed p-type conduction and exhibited degenerate semiconductor characteristics at temperatures from 323 K to 823 K, and the charge transport properties depended on the filling ratio of Nd and Yb because of the difference between the valencies of Nd and Yb. The electrical conductivity decreased and the Seebeck coefficient increased owing to a decrease in the carrier concentration with increasing Co content. The lattice thermal conductivity decreased because phonon scattering was enhanced by Nd and Yb partial double filling, but partially double-filled specimens did not exhibit a further significant reduction in the lattice thermal conductivity compared with the completely double-filled specimens. A maximum ZT of 0.83 was obtained for (Nd0.75Yb0.25)0.8Fe3CoSb12 at 723 K.

Infrared emitting device and method

DOEpatents

Kurtz, S.R.; Biefeld, R.M.; Dawson, L.R.; Howard, A.J.; Baucom, K.C.

1997-04-29

The infrared emitting device comprises a III-V compound semiconductor substrate upon which are grown a quantum-well active region having a plurality of quantum-well layers formed of a ternary alloy comprising InAsSb sandwiched between barrier layers formed of a ternary alloy having a smaller lattice constant and a larger energy bandgap than the quantum-well layers. The quantum-well layers are preferably compressively strained to increase the threshold energy for Auger recombination; and a method is provided for determining the preferred thickness for the quantum-well layers. Embodiments of the present invention are described having at least one cladding layer to increase the optical and carrier confinement in the active region, and to provide for waveguiding of the light generated within the active region. Examples have been set forth showing embodiments of the present invention as surface- and edge-emitting light emitting diodes (LEDs), an optically-pumped semiconductor laser, and an electrically-injected semiconductor diode laser. The light emission from each of the infrared emitting devices of the present invention is in the midwave infrared region of the spectrum from about 2 to 6 microns. 8 figs.

Inactive lifestyles and sedentary behavior in persons with chronic aneurysmal subarachnoid hemorrhage: evidence from accelerometer-based activity monitoring.

PubMed

Harmsen, Wouter J; Ribbers, Gerard M; Heijenbrok-Kal, Majanka H; Bussmann, Johannes B J; Sneekes, Emiel M; Khajeh, Ladbon; van Kooten, Fop; Neggers, Sebastian J C M M; van den Berg-Emons, Rita J

2017-11-23

Aneurysmal subarachnoid hemorrhage (a-SAH) is a potential life-threatening stroke. Because survivors may be at increased risk for inactive and sedentary lifestyles, this study evaluates physical activity (PA) and sedentary behavior (SB) in the chronic phase after a-SAH. PA and SB were objectively measured at six months post a-SAH with an accelerometer-based activity monitor, with the aim to cover three consecutive weekdays. Total time spent in PA (comprising walking, cycling, running and non-cyclic movement) and SB (comprising sitting and lying) was determined. Also, in-depth analyses were performed to determine the accumulation and distribution of PA and SB throughout the day. Binary time series were created to determine the mean bout length and the fragmentation index. Measures of PA and SB in persons with a-SAH were compared to those in sex- and age-matched healthy controls. The 51 participants comprised 33 persons with a-SAH and 18 controls. None of the participants had signs of paresis or spasticity. Persons with a-SAH spent 105 min/24 h being physically active, which was 35 min/24 h less than healthy controls (p = 0.005). For PA, compared with healthy controls, the mean bout length was shorter in those with a-SAH (12.0 vs. 13.5 s, p = 0.006) and the fragmentation index was higher (0.053 vs. 0.041, p < 0.001). Total sedentary time during waking hours showed no significant difference between groups (514 min vs. 474 min, p = 0.291). For SB, the mean bout length was longer in persons with a-SAH (122.3 vs. 80.5 s, p = 0.024), whereas there was no difference in fragmentation index between groups (0.0032 vs 0.0036, p = 0.396). Persons with a-SAH are less physically active, they break PA time into shorter periods, and SB periods last longer compared to healthy controls. Since inactive lifestyles and prolonged uninterrupted periods of SB are independent risk factors for poor cardiovascular health, interventions seem necessary and should target both PA and SB. Dutch registry number: NTR 2085.

In Situ Growth of Metal Sulfide Nanocrystals in Poly(3-hexylthiophene): [6,6]-Phenyl C61-Butyric Acid Methyl Ester Films for Inverted Hybrid Solar Cells with Enhanced Photocurrent.

PubMed

Yang, Chunyan; Sun, Yingying; Li, Xinjie; Li, Cheng; Tong, Junfeng; Li, Jianfeng; Zhang, Peng; Xia, Yangjun

2018-06-20

It has been reported that the performance of bulk heterojunction organic solar cells can be improved by incorporation of nano-heterostructures of metals, semiconductors, and dielectric materials in the active layer. In this manuscript, CdS or Sb 2 S 3 nanocrystals were in situ generated inside the poly(3-hexylthiophene): [6,6]-phenyl C61-butyric acid (P3HT:PC 61 BM) system by randomly mixing P3HT and PC 61 BM in the presence of cadmium or antimony xanthate precursor. Hybrid solar cells (HSCs) with the configurations of tin-doped indium oxide substrate (ITO)/CdS interface layer/P3HT:PC 61 BM: x wt.% CdS/MoO 3 /Ag and ITO/CdS interface layer /P3HT:PC 61 BM: x wt.% Sb 2 S 3 /MoO 3 /Ag were fabricated. Hybrid active layers (P3HT:PC 61 BM: x wt.% CdS or P3HT:PC 61 BM: x wt.% Sb 2 S 3 ) were formed completely by thermally annealing the film resulting in the decomposition of the cadmium or antimony xanthate precursor to CdS or Sb 2 S 3 nanocrystals, respectively. The effects of x wt.% CdS (or Sb 2 S 3 ) nanocrystals on the performance of the HSCs were studied. From UV-Vis absorption, hole mobilities, and surface morphological characterizations, it has been proved that incorporation of 3 wt.% CdS (or Sb 2 S 3 ) nanocrystals in the active layer of P3HT:PC 61 BM-based solar cells improved the optical absorption, the hole mobility, and surface roughness in comparison with P3HT:PC 61 BM-based solar cells, thus resulting in the improved power conversion efficiencies (PCEs) of the devices.

Investigation of the transport properties and compositions of the Ca{sub 2}RE{sub 7}Pn{sub 5}O{sub 5} series (RE=Pr, Sm, Gd, Dy; Pn=Sb, Bi)

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

Forbes, Scott; Yuan, Fang; Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044

The Ca{sub 2}RE{sub 7}Pn{sub 5}O{sub 5} phases (RE=Pr, Sm, Gd, Dy; Pn=Sb, Bi) were successfully prepared from high temperature reactions at 1225–1300 °C. These phases maintain the same structure types as the parent RE{sub 9}Pn{sub 5}O{sub 5} phases, except for a Ca/RE mixing. The study and preparation of these phases was motivated by the desire to shift the metallic type properties of the parent RE{sub 9}Pn{sub 5}O{sub 5} phases to a level more suitable for thermoelectric applications. Electrical resistivity measurements performed on pure, bulk samples indicated all phases to be narrow band gap semiconductors or semimetals, supporting the charge balancedmore » electron count of the Ca{sub 2}RE{sub 7}Pn{sub 5}O{sub 5} composition. Unfortunately, all samples are too electrically resistive for any potential usage as thermoelectrics. Electronic band structure calculations performed on idealized RE{sub 9}Pn{sub 5}O{sub 5} structures revealed the presence of a pseudogap at the Fermi level, which is consistent with the observed electrical resistivity and Seebeck coefficient behavior. - Graphical abstract: Ca substitution in RE{sub 9}Pn{sub 5}O{sub 5} leads to charge-balanced Ca{sub 2}RE{sub 7}Pn{sub 5}O{sub 5} phases with semiconducting or semimetallic properties. - Highlights: • The RE{sub 9}Pn{sub 5}O{sub 5} structure may be stabilized with calcium substitution in the form of Ca{sub 2}RE{sub 7}Pn{sub 5}O{sub 5}. • The Ca{sub 2}RE{sub 7}Pn{sub 5}O{sub 5} phases maintain the parent P 4/n structure, albeit with Ca/RE mixing. • The Ca{sub 2}RE{sub 7}Sb{sub 5}O{sub 5} phases behave as semiconductors while Ca{sub 2}RE{sub 7}Bi{sub 5}O{sub 5} are semimetals with electron-electron correlations. • Electronic structure calculations yield a semimetal-like density of states for both Ca{sub 2}RE{sub 7}Sb{sub 5}O{sub 5} and Ca{sub 2}RE{sub 7}Bi{sub 5}O{sub 5}.« less

Synthesis and Characteristics of HgCdSe for IR Detection

DTIC Science & Technology

2014-03-11

Photoelectron Spectroscopy Study of Oxide Removal Using Atomic Hydrogen for Large-Area II–VI Material Growth, Journal of Electronic Materials...Workshop on the Physics and Chemistry of II-VI Materials, Chicago IL (October 1-3, 2013) “Use of Atomic Hydrogen to Prepare GaSb(211)B and GaSb(100...Workshop on the Physics and Chemistry of II-VI Materials, Chicago IL (October, 2011) "Xray photoelectron spectroscopy study of oxide removal using

Development and validation of a new self-report instrument for measuring sedentary behaviors and light-intensity physical activity in adults.

PubMed

Barwais, Faisal Awad; Cuddihy, Thomas F; Washington, Tracy; Tomson, L Michaud; Brymer, Eric

2014-08-01

Low levels of physical activity and high levels of sedentary behavior (SB) are major public health concerns. This study was designed to develop and validate the 7-day Sedentary (S) and Light Intensity Physical Activity (LIPA) Log (7-day SLIPA Log), a self-report measure of specific daily behaviors. To develop the log, 62 specific SB and LIPA behaviors were chosen from the Compendium of Physical Activities. Face-to-face interviews were conducted with 32 sedentary volunteers to identify domains and behaviors of SB and LIPA. To validate the log, a further 22 sedentary adults were recruited to wear the GT3x for 7 consecutive days and nights. Pearson correlations (r) between the 7-day SLIPA Log and GT3x were significant for sedentary (r = .86, P < .001), for LIPA (r = .80, P < .001). Lying and sitting postures were positively correlated with GT3x output (r = .60 and r = .64, P < .001, respectively). No significant correlation was found for standing posture (r = .14, P = .53).The kappa values between the 7-day SLIPA Log and GT3x variables ranged from 0.09 to 0.61, indicating poor to good agreement. The 7-day SLIPA Log is a valid self-report measure of SB and LIPA in specific behavioral domains.

Inter-band optoelectronic properties in quantum dot structure of low band gap III-V semiconductors

NASA Astrophysics Data System (ADS)

Dey, Anup; Maiti, Biswajit; Chanda Sarkar, Debasree

2014-04-01

A generalized theory is developed to study inter-band optical absorption coefficient (IOAC) and material gain (MG) in quantum dot structures of narrow gap III-V compound semiconductor considering the wave-vector (k→) dependence of the optical transition matrix element. The band structures of these low band gap semiconducting materials with sufficiently separated split-off valance band are frequently described by the three energy band model of Kane. This has been adopted for analysis of the IOAC and MG taking InAs, InSb, Hg1-xCdxTe, and In1-xGaxAsyP1-y lattice matched to InP, as example of III-V compound semiconductors, having varied split-off energy band compared to their bulk band gap energy. It has been found that magnitude of the IOAC for quantum dots increases with increasing incident photon energy and the lines of absorption are more closely spaced in the three band model of Kane than those with parabolic energy band approximations reflecting the direct the influence of energy band parameters. The results show a significant deviation to the MG spectrum of narrow-gap materials having band nonparabolicity compared to the parabolic band model approximations. The results reflect the important role of valence band split-off energies in these narrow gap semiconductors.

Optoelectronic Devices and Materials

NASA Astrophysics Data System (ADS)

Sweeney, Stephen; Adams, Alfred

Unlike the majority of electronic devices, which are silicon based, optoelectronic devices are predominantly made using III-V semiconductor compounds such as GaAs, InP, GaN and GaSb and their alloys due to their direct band gap. Understanding the properties of these materials has been of vital importance in the development of optoelectronic devices. Since the first demonstration of a semiconductor laser in the early 1960s, optoelectronic devices have been produced in their millions, pervading our everyday lives in communications, computing, entertainment, lighting and medicine. It is perhaps their use in optical-fibre communications that has had the greatest impact on humankind, enabling high-quality and inexpensive voice and data transmission across the globe. Optical communications spawned a number of developments in optoelectronics, leading to devices such as vertical-cavity surface-emitting lasers, semiconductor optical amplifiers, optical modulators and avalanche photodiodes. In this chapter we discuss the underlying theory of operation of the most important optoelectronic devices. The influence of carrier-photon interactions is discussed in the context of producing efficient emitters and detectors. Finally we discuss how the semiconductor band structure can be manipulated to enhance device properties using quantum confinement and strain effects, and how the addition of dilute amounts of elements such as nitrogen is having a profound effect on the next generation of optoelectronic devices.

Quantum effects on compressional Alfven waves in compensated semiconductors

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

Amin, M. R.

2015-03-15

Amplitude modulation of a compressional Alfven wave in compensated electron-hole semiconductor plasmas is considered in the quantum magnetohydrodynamic regime in this paper. The important ingredients of this study are the inclusion of the particle degeneracy pressure, exchange-correlation potential, and the quantum diffraction effects via the Bohm potential in the momentum balance equations of the charge carriers. A modified nonlinear Schrödinger equation is derived for the evolution of the slowly varying amplitude of the compressional Alfven wave by employing the standard reductive perturbation technique. Typical values of the parameters for GaAs, GaSb, and GaN semiconductors are considered in analyzing the linearmore » and nonlinear dispersions of the compressional Alfven wave. Detailed analysis of the modulation instability in the long-wavelength regime is presented. For typical parameter ranges of the semiconductor plasmas and at the long-wavelength regime, it is found that the wave is modulationally unstable above a certain critical wavenumber. Effects of the exchange-correlation potential and the Bohm potential in the wave dynamics are also studied. It is found that the effect of the Bohm potential may be neglected in comparison with the effect of the exchange-correlation potential in the linear and nonlinear dispersions of the compressional Alfven wave.« less

Reliability and Validity of Two Self-report Measures to Assess Sedentary Behavior in Older Adults

PubMed Central

Gennuso, Keith P.; Matthews, Charles E.; Colbert, Lisa H.

2015-01-01

Background The purpose of this study was to examine the reliability and validity of two currently available physical activity surveys for assessing time spent in sedentary behavior (SB) in older adults. Methods Fifty-eight adults (≥65 years) completed the Yale Physical Activity Survey for Older Adults (YPAS) and Community Health Activities Model Program for Seniors (CHAMPS) before and after a 10-day period during which they wore an ActiGraph accelerometer (ACC). Intraclass correlation coefficients (ICC) examined test-retest reliability. Overall percent agreement and a kappa statistic examined YPAS validity. Lin’s concordance correlation, Pearson correlation, and Bland-Altman analysis examined CHAMPS validity. Results Both surveys had moderate test-retest reliability (ICC: YPAS=0.59 (P<0.001), CHAMPS=0.64 (P<0.001)) and significantly underestimated SB time. Agreement between YPAS and ACC was low (κ=−0.0003); however, there was a linear increase (P< 0.01) in ACC-derived SB time across YPAS response categories. There was poor agreement between ACC-derived SB and CHAMPS (Lin’s r=0.005; 95% CI, −0.010 to 0.020), and no linear trend across CHAMPS quartiles (p=0.53). Conclusions Neither of the surveys should be used as the sole measure of SB in a study; though the YPAS has the ability to rank individuals, providing it with some merit for use in correlational SB research. PMID:25110344

Theoretical investigations of electrical transport properties in CoSb3 skutterudites under hydrostatic loadings

DOE PAGES

Hu, Chongze; Ni, Peter; Zhan, Li; ...

2018-01-30

We report that CoSb 3-based skutterudites have been a benchmark mid-temperature thermoelectric material under intensive experimental and theoretical studies for decades. Doping and filling, to the first order, alter the crystal lattice constant of CoSb 3 in the context of “chemical pressure.” In this work, we employed ab initio density functional theory in conjunction with semiclassical Boltzmann transport theory to investigate the mechanical properties and especially how hydrostatic loadings, i.e., “physical pressure,” impact the electronic band structure, Seebeck coefficient, and power factor of pristine CoSb 3. It is found that hydrostatic pressure enlarges the band gap, suppresses the density ofmore » states (DOS) near the valence band edge, and fosters the band convergence between the valley bands and the conduction band minimum (CBM). By contrast, hydrostatic tensile reduces the band gap, increases the DOS near the valence band edge, and diminishes the valley bands near the CBM. Therefore, applying hydrostatic pressure provides an alternative avenue for achieving band convergence to improve thermoelectric properties of N-type CoSb 3, which is further supported by our carrier concentration studies. Lastly, these results provide valuable insight into the further improvement of thermoelectric performance of CoSb 3-based skutterudites via a synergy of physical and chemical pressures.« less

Electrical Transport Properties of Single-Crystalline β-Zn4Sb3 Prepared Through the Zn-Sn Mixed-Flux Method

NASA Astrophysics Data System (ADS)

Liu, Hongxia; Deng, Shuping; Shen, Lanxian; Wang, Jinsong; Feng, Cheng; Deng, Shukang

2017-03-01

β-Zn4Sb3 is a promising p-type thermoelectric material for utilization in moderate temperatures. This study prepares a group of single-crystalline β-Zn4Sb3 samples using the Zn-Sn mixed-flux method based on the stoichiometric ratios of Zn4+ x Sb3Sn y . The effect of Zn-to-Sn proportion in the flux on the structure and electrical transport properties is investigated. All samples are strip-shaped single crystals of different sizes. The actual Zn content of the present samples is improved (>3.9) compared with that of the samples prepared through the Sn flux method. Larger lattice parameters are also obtained. The carrier concentration of all the samples is in the order of over 1019 cm-3. With increasing Sn rate in the flux, this carrier concentration decreases, whereas mobility is significantly enhanced. The electrical conductivity and Seebeck coefficients of all the samples exhibit a behavior that of a degenerate semiconductor transport. Electrical conductivity initially increases and then decreases as the Sn ratio in the flux increases. The electrical conductivity of the x: y = 5:1 sample reaches 6.45 × 104 S m-1 at 300 K. Benefitting from the electrical conductivity and Seebeck coefficient, the flux proportion of the x: y = 7:1 sample finally achieves the highest power factor value of 1.4 × 10-3 W m-1 K-2 at 598 K.

Insights on the Synthesis, Crystal and Electronic Structures, and Optical and Thermoelectric Properties of Sr1- xSb xHfSe3 Orthorhombic Perovskite.

PubMed

Moroz, Nicholas A; Bauer, Christopher; Williams, Logan; Olvera, Alan; Casamento, Joseph; Page, Alexander A; Bailey, Trevor P; Weiland, Ashley; Stoyko, Stanislav S; Kioupakis, Emmanouil; Uher, Ctirad; Aitken, Jennifer A; Poudeu, Pierre F P

2018-06-18

Single-phase polycrystalline powders of Sr 1- x Sb x HfSe 3 ( x = 0, 0.005, 0.01), a new member of the chalcogenide perovskites, were synthesized using a combination of high temperature solid-state reaction and mechanical alloying approaches. Structural analysis using single-crystal as well as powder X-ray diffraction revealed that the synthesized materials are isostructural with SrZrSe 3 , crystallizing in the orthorhombic space group Pnma (#62) with lattice parameters a = 8.901(2) Å; b = 3.943(1) Å; c = 14.480(3) Å; and Z = 4 for the x = 0 composition. Thermal conductivity data of SrHfSe 3 revealed low values ranging from 0.9 to 1.3 W m -1 K -1 from 300 to 700 K, which is further lowered to 0.77 W m -1 K -1 by doping with 1 mol % Sb for Sr. Electronic property measurements indicate that the compound is quite insulating with an electrical conductivity of 2.9 S/cm at 873 K, which was improved to 6.7 S/cm by 0.5 mol % Sb doping. Thermopower data revealed that SrHfSe 3 is a p-type semiconductor with thermopower values reaching a maximum of 287 μV/K at 873 K for the 1.0 mol % Sb sample. The optical band gap of Sr 1- x Sb x HfSe 3 samples, as determined by density functional theory calculations and the diffuse reflectance method, is ∼1.00 eV and increases with Sb concentration to 1.15 eV. Careful analysis of the partial densities of states (PDOS) indicates that the band gap in SrHfSe 3 is essentially determined by the Se-4p and Hf-5d orbitals with little to no contribution from Sr atoms. Typically, band edges of p- and d-character are a good indication of potentially strong absorption coefficient due to the high density of states of the localized p and d orbitals. This points to potential application of SrHfSe 3 as absorbing layer in photovoltaic devices.

Effect of MultiSubstitution on the Thermoelectric Performance of the Ca11-xYbxSb10-yGez (0 ≤ x ≤ 9; 0 ≤ y ≤ 3; 0 ≤ z ≤ 3) System: Experimental and Theoretical Studies.

PubMed

Nam, Gnu; Choi, Woongjin; Lee, Junsu; Lim, Seong-Ji; Jo, Hongil; Ok, Kang Min; Ahn, Kyunghan; You, Tae-Soo

2017-06-19

The Zintl phase solid-solution Ca 11-x Yb x Sb 10-y Ge z (0 ≤ x ≤ 9; 0 ≤ y ≤ 3; 0 ≤ z ≤ 3) system with the cationic/anionic multisubstitution has been synthesized by molten Sn metal flux and arc-melting methods. The crystal structure of the nine title compounds were characterized by both powder and single-crystal X-ray diffractions and adopted the Ho 11 Ge 10 -type structure with the tetragonal space group I4/mmm (Z = 4, Pearson Code tI84). The overall isotypic structure of the nine title compounds can be illustrated as an assembly of three different types of cationic polyhedra sharing faces with their neighboring polyhedra and the three-dimensional cage-shaped anionic frameworks consisting of the dumbbell-shaped Sb 2 units and the square-shaped Sb 4 or (Sb/Ge) 4 units. During the multisubstitution trials, interestingly, we observed a metal-to-semiconductor transition as the Ca and Ge contents increased in the title system from Yb 11 Sb 10 to Ca 9 Yb 2 Sb 7 Ge 3 (nominal compositions) on the basis of a series of thermoelectric property measurements. This phenomenon can be elucidated by the suppression of a bipolar conduction of holes and electrons via an extra hole-carrier doping. The tight-binding linear muffin-tin orbital calculations using four hypothetical structural models nicely proved that the size of a pseudogap and the magnitude of the density of states at the Fermi level are significantly influenced by substituting elements as well as their atomic sites in a unit cell. The observed particular cationic/anionic site preferences, the historically known abnormalities of atomic displacement parameters, and the occupation deficiencies of particular atomic sites are further rationalized by the QVAL value criterion on the basis of the theoretical calculations. The results of SEM, EDS, and TGA analyses are also provided.

Physical activity, sedentary behaviour, and socioeconomic status among Finnish girls and boys aged 6-8 years.

PubMed

Lampinen, Eeva-Kaarina; Eloranta, Aino-Maija; Haapala, Eero A; Lindi, Virpi; Väistö, Juuso; Lintu, Niina; Karjalainen, Panu; Kukkonen-Harjula, Katriina; Laaksonen, David; Lakka, Timo A

2017-05-01

We studied differences in physical activity (PA), sedentary behaviour (SB), and the types of PA and SB between Finnish girls and boys and children from different socioeconomic backgrounds (SES). We assessed PA, SB, parental education, and household income using detailed questionnaires in a representative population sample of 486 children (238 girls, 248 boys) aged 6-8 years. Girls spent on average 1.7 h/day and boys 2.0 h/day in total PA (p = 0.002). Altogether 66% of girls and 54% of boys had less than 2 h of total PA per day (p = 0.012). Girls had lower levels of unsupervised PA (45 vs. 54 min/day, p = 0.001), supervised PA (1.5 vs. 1.9 h/week, p = 0.009), and PA during school recess (1.8 vs. 1.9 h/week, p = 0.032) than boys. Girls had higher levels of total SB (3.8 vs. 3.4 h/day, p = 0.015) but lower levels of screen-based SB (1.5 vs. 1.9 h/day, p < 0.001) than boys. Lower parental education and household income were associated with lower levels of supervised PA in girls (p = 0.011 and p = 0.008, respectively) and in boys (p = 0.006 and p = 0.003, respectively). Lower parental education and household income were also related to higher levels of screen-based SB in boys (p = 0.005 and p < 0.001, respectively) but not in girls. Girls have lower levels of total, unsupervised, and supervised PA, PA during recess, and screen-based SB but higher levels of total SB than boys. Lower parental education and household income are associated with lower levels of supervised PA in both genders and higher levels of screen-based SB in boys.

Physical Activity is Associated with Higher Sleep Efficiency in the General Population: The CoLaus Study.

PubMed

Gubelmann, Cédric; Heinzer, Raphael; Haba-Rubio, José; Vollenweider, Peter; Marques-Vidal, Pedro

2018-03-30

To evaluate the association of objective physical activity (PA) and sedentary behaviour (SB) with sleep duration and quality. Cross-sectional study including 2649 adults (53.5% women, 45-86 years) from the general population. Proportions of time spent in PA and SB were measured using 14-day accelerometry. Low PA and high SB status were defined as the lowest and highest tertile of each behaviour. 'Inactive', 'Weekend warrior' and 'Regularly active' weekly patterns were also defined. Sleep parameters were derived from the accelerometer and validated questionnaires. High PA, relative to low PA, was associated with higher sleep efficiency [76.6 vs. 73.8%, p<0.01] and lower likelihood of evening chronotype [relative-risk ratio (RR) and 95%CI: 0.71 (0.52; 0.97)]. Similar associations were found for low SB relative to high SB. 'Weekend warriors', relative to 'Inactives', had higher sleep efficiency [76.4 vs. 73.9%, p<0.01] and lower likelihood of evening chronotype [RR: 0.63 (0.43; 0.93)]. 'Regularly actives', relative to 'Inactives', had higher sleep efficiency [76.7 vs. 73.9%, p<0.01] and tended to have less frequently an evening chronotype [RR: 0.75 (0.54; 1.04), p=0.09]. No associations were found for PA and SB with sleep duration, daytime sleepiness, insomnia, and risk of sleep apnea (after adjustment for body mass index). High PA and low SB individuals, even if they do not sleep longer, have higher sleep efficiency and have less frequently an evening chronotype.

The Physics of Semiconductors

NASA Astrophysics Data System (ADS)

Brennan, Kevin F.

1999-02-01

Modern fabrication techniques have made it possible to produce semiconductor devices whose dimensions are so small that quantum mechanical effects dominate their behavior. This book describes the key elements of quantum mechanics, statistical mechanics, and solid-state physics that are necessary in understanding these modern semiconductor devices. The author begins with a review of elementary quantum mechanics, and then describes more advanced topics, such as multiple quantum wells. He then disusses equilibrium and nonequilibrium statistical mechanics. Following this introduction, he provides a thorough treatment of solid-state physics, covering electron motion in periodic potentials, electron-phonon interaction, and recombination processes. The final four chapters deal exclusively with real devices, such as semiconductor lasers, photodiodes, flat panel displays, and MOSFETs. The book contains many homework exercises and is suitable as a textbook for electrical engineering, materials science, or physics students taking courses in solid-state device physics. It will also be a valuable reference for practicing engineers in optoelectronics and related areas.

The Structural, Photocatalytic Property Characterization and Enhanced Photocatalytic Activities of Novel Photocatalysts Bi2GaSbO7 and Bi2InSbO7 during Visible Light Irradiation

PubMed Central

Luan, Jingfei; Shen, Yue; Li, Yanyan; Paz, Yaron

2016-01-01

In order to develop original and efficient visible light response photocatalysts for degrading organic pollutants in wastewater, new photocatalysts Bi2GaSbO7 and Bi2InSbO7 were firstly synthesized by a solid-state reaction method and their chemical, physical and structural properties were characterized. Bi2GaSbO7 and Bi2InSbO7 were crystallized with a pyrochlore-type structure and the lattice parameter of Bi2GaSbO7 or Bi2InSbO7 was 10.356497 Å or 10.666031 Å. The band gap of Bi2GaSbO7 or Bi2InSbO7 was estimated to be 2.59 eV or 2.54 eV. Compared with nitrogen doped TiO2, Bi2GaSbO7 and Bi2InSbO7, both showed excellent photocatalytic activities for degrading methylene blue during visible light irradiation due to their narrower band gaps and higher crystallization perfection. Bi2GaSbO7 showed higher catalytic activity compared with Bi2InSbO7. The photocatalytic degradation of methylene blue followed by the first-order reaction kinetics and the first-order rate constant was 0.01470 min−1, 0.00967 min−1 or 0.00259 min−1 with Bi2GaSbO7, Bi2InSbO7 or nitrogen doped TiO2 as a catalyst. The evolution of CO2 and the removal of total organic carbon were successfully measured and these results indicated continuous mineralization of methylene blue during the photocatalytic process. The possible degradation scheme and pathway of methylene blue was also analyzed. Bi2GaSbO7 and Bi2InSbO7 photocatalysts both had great potential to purify textile industry wastewater. PMID:28773922

Modeling of THz Lasers Based on Intersubband Transitions in Semiconductor Quantum Wells

NASA Technical Reports Server (NTRS)

Liu, Ansheng; Woo, Alex C. (Technical Monitor)

1999-01-01

In semiconductor quantum well structures, the intersubband energy separation can be adjusted to the terahertz (THz) frequency range by changing the well width and material combinations. The electronic and optical properties of these nanostructures can also be controlled by an applied dc electric field. These unique features lead to a large frequency tunability of the quantum well devices. In the on-going project of modeling of the THz lasers, we investigate the possibility of using optical pumping to generate THz radiation based on intersubband transitions in semiconductor quantum wells. We choose the optical pumping because in the electric current injection it is difficult to realize population inversion in the THz frequency range due to the small intersubband separation (4-40 meV). We considered both small conduction band offset (GaAs/AlGaAs) and large band offset (InGaAs/AlAsSb) quantum well structures. For GaAs/AlGaAs quantum wells, mid-infrared C02 lasers are used as pumping sources. For InGaAs/AlAsSb quantum wells, the resonant intersubband transitions can be excited by the near-infrared diode lasers. For three- and four-subband quantum wells, we solve the pumpfield-induced nonequilibrium distribution function for each subband of the quantum well system from a set of rate equations that include both intrasubband and intersubband relaxation processes. Taking into account the coherent interactions between pump and THz (signal) waves, we calculate the optical gain for the THz field. The gain arising from population inversion and stimulated Raman processes is calculated in a unified manner. A graph shows the calculated THz gain spectra for three-subband GaAs/AlGaAs quantum wells. We see that the coherent pump and signal wave interactions contribute significantly to the gain. The pump intensity dependence of the THz gain is also studied. The calculated results are shown. Because of the optical Stark effect and pump-induced population redistribution, the maximum THz gain saturates at larger pump intensities.

Monte Carlo model for the analysis and development of III-V Tunnel-FETs and Impact Ionization-MOSFETs

NASA Astrophysics Data System (ADS)

Talbo, V.; Mateos, J.; González, T.; Lechaux, Y.; Wichmann, N.; Bollaert, S.; Vasallo, B. G.

2015-10-01

Impact-ionization metal-oxide-semiconductor FETs (I-MOSFETs) are in competition with tunnel FETs (TFETs) in order to achieve the best behaviour for low power logic circuits. Concretely, III-V I-MOSFETs are being explored as promising devices due to the proper reliability, since the impact ionization events happen away from the gate oxide, and the high cutoff frequency, due to high electron mobility. To facilitate the design process from the physical point of view, a Monte Carlo (MC) model which includes both impact ionization and band-to-band tunnel is presented. Two ungated InGaAs and InAlAs/InGaAs 100 nm PIN diodes have been simulated. In both devices, the tunnel processes are more frequent than impact ionizations, so that they are found to be appropriate for TFET structures and not for I- MOSFETs. According to our simulations, other narrow bandgap candidates for the III-V heterostructure, such as InAs or GaSb, and/or PININ structures must be considered for a correct I-MOSFET design.

Electrical Characterization of Critical Phase Change Conditions in Nanoscale Ge2Sb2Te5 Pillars

NASA Astrophysics Data System (ADS)

Ozatay, Ozhan; Stipe, Barry; Katine, Jordan; Terris, Bruce

2008-03-01

Following the original work of Ovshinsky on disordered semiconductors that exhibit ovonic threshold switching (OTS) there has been substantial interest in the electronic reversible switching properties of chalcogenides^1. The current induced phase transitions between polycrystalline and amorphous states in these materials offer orders of magnitude changes in the conductance which makes them an ideal candidate for non-volatile data storage applications. In this work we investigate the scaling of critical programming conditions required to observe such transitions between highly resistive (disordered) and highly conductive (ordered) states by constructing a resistance map with various pulse widths and amplitudes under different cooling conditions (as a function of pulse trailing edge). We study the evolution of critical phase change conditions as a function of contact size (50nm-1μm) and shape (circle-square-rectangle). We compare the resulting switching behaviour with the predictions of a finite-element model of the electro-thermal physics to analyze the nature of the switching dynamics at the nanoscale. ^1 S-H. Lee, Y. Jung, R. Agarwal, Nature Nanotechnology; doi:10:1038/nnano.2007.291

Magnetosonic solitons in semiconductor plasmas in the presence of quantum tunneling and exchange correlation effects

NASA Astrophysics Data System (ADS)

Hussain, S.; Mahmood, S.

2018-01-01

Low frequency magnetosonic wave excitations are investigated in semiconductor hole-electron plasmas. The quantum mechanical effects such as Fermi pressure, quantum tunneling, and exchange-correlation of holes and electrons in the presence of the magnetic field are considered. The two fluid quantum magnetohydrodynamic model is used to study magnetosonic wave dynamics, while electric and magnetic fields are coupled via Maxwell equations. The dispersion relation of the magnetosonic wave in electron-hole semiconductor plasma propagating in the perpendicular direction of the magnetic field is obtained, and its dispersion effects are discussed. The Korteweg-de Vries equation (KdV) for magnetosonic solitons is derived by employing the reductive perturbation method. For numerical analysis, the plasma parameters are taken from the semiconductors such as GaAs, GaSb, GaN, and InP already existing in the literature. It is found that the phase velocity of the magnetosonic wave is increased with the inclusion of exchange-correlation force in the model. The soliton dip structures of the magnetosonic wave in GaN semiconductor plasma are obtained, which satisfy the quantum plasma conditions for electron and hole fluids. The magnetosonic soliton dip structures move with speed less than the magnetosonic wave phase speed in the lab frame. The effects of exchange-correlation force in the model and variations of magnetic field intensity and electron/hole density on the magnetosonic wave dip structures are also investigated numerically for illustration.

Patterns of physical activity, sedentary behavior, and diet in U.S. adolescents.

PubMed

Iannotti, Ronald J; Wang, Jing

2013-08-01

To identify patterns in adolescents' obesogenic behaviors and their relations to physical and psychological health. A nationally representative sample of 9,174 U.S. adolescents ages 11 to 16 years was surveyed on physical activity (PA), screen-based sedentary behavior (SB), frequency of consumption of healthy and unhealthy food items, weight status, weight control behavior, depression, physical symptoms, body dissatisfaction, overall health, and life satisfaction. Latent class analysis was used to identify patterns of PA, SB, and diet. A model with three latent classes best fit the data: Class 1 with high PA and high fruit and vegetable intake and low SB and intake of sweets, soft drinks, chips, and fries; Class 2 with high SB and high intake of sweets, soft drinks, chips, and fries; and Class 3 with low PA, low fruit and vegetable intake, and low intake of sweets, chips, and fries. Membership in the three classes was related to age, gender, race/ethnicity, and socioeconomic status. In addition, members of Class 1 (26.5%) were more likely to be of normal weight status and to fare well on most of the other health indices; of Class 2 (26.4%) were less likely to be trying to lose weight but scored poorly on the mental health indices; and of Class 3 (47.2%) were less likely to be underweight and reported greater body dissatisfaction. Three prevalent patterns of adolescent obesogenic behaviors were identified and these patterns related to weight status, depression, and other indicators of physical and psychological health. Published by Elsevier Inc.

Optical orientation in ferromagnet/semiconductor hybrids

NASA Astrophysics Data System (ADS)

Korenev, V. L.

2008-11-01

The physics of optical pumping of semiconductor electrons in ferromagnet/semiconductor hybrids is discussed. Optically oriented semiconductor electrons detect the magnetic state of a ferromagnetic film. In turn, the ferromagnetism of the hybrid can be controlled optically with the help of a semiconductor. Spin-spin interactions near the ferromagnet/semiconductor interface play a crucial role in the optical readout and the manipulation of ferromagnetism.

Electrolysis of a molten semiconductor

PubMed Central

Yin, Huayi; Chung, Brice; Sadoway, Donald R.

2016-01-01

Metals cannot be extracted by electrolysis of transition-metal sulfides because as liquids they are semiconductors, which exhibit high levels of electronic conduction and metal dissolution. Herein by introduction of a distinct secondary electrolyte, we reveal a high-throughput electro-desulfurization process that directly converts semiconducting molten stibnite (Sb2S3) into pure (99.9%) liquid antimony and sulfur vapour. At the bottom of the cell liquid antimony pools beneath cathodically polarized molten stibnite. At the top of the cell sulfur issues from a carbon anode immersed in an immiscible secondary molten salt electrolyte disposed above molten stibnite, thereby blocking electronic shorting across the cell. As opposed to conventional extraction practices, direct sulfide electrolysis completely avoids generation of problematic fugitive emissions (CO2, CO and SO2), significantly reduces energy consumption, increases productivity in a single-step process (lower capital and operating costs) and is broadly applicable to a host of electronically conductive transition-metal chalcogenides. PMID:27553525

Tunability of temperature dependent THz photonic band gaps in 1-D photonic crystals composed of graded index materials and semiconductor InSb

NASA Astrophysics Data System (ADS)

Singh, Bipin K.; Pandey, Praveen C.; Rastogi, Vipul

2018-05-01

Tunable temperature dependent terahertz photonic band gaps (PBGs) in one-dimensional (1-D) photonic crystal composed of alternating layers of graded index and semiconductor materials are demonstrated. Results show the influence of temperature, geometrical parameters, grading profile and material damping factor on the PBGs. Number of PBG increases with increasing the layer thickness and their bandwidth can be tuned with external temperature and grading parameters. Lower order band gap is more sensitive to the temperature which shows increasing trend with temperature, and higher order PBGs can also be tuned by controlling the external temperature. Band edges of PBGs are shifted toward higher frequency side with increasing the temperature. Results show that the operational frequencies of PBGs are unaffected when loss involved. This work enables to design tunable Temperature dependent terahertz photonic devices such as reflectors, sensors and filters etc.

Electrolysis of a molten semiconductor.

PubMed

Yin, Huayi; Chung, Brice; Sadoway, Donald R

2016-08-24

Metals cannot be extracted by electrolysis of transition-metal sulfides because as liquids they are semiconductors, which exhibit high levels of electronic conduction and metal dissolution. Herein by introduction of a distinct secondary electrolyte, we reveal a high-throughput electro-desulfurization process that directly converts semiconducting molten stibnite (Sb2S3) into pure (99.9%) liquid antimony and sulfur vapour. At the bottom of the cell liquid antimony pools beneath cathodically polarized molten stibnite. At the top of the cell sulfur issues from a carbon anode immersed in an immiscible secondary molten salt electrolyte disposed above molten stibnite, thereby blocking electronic shorting across the cell. As opposed to conventional extraction practices, direct sulfide electrolysis completely avoids generation of problematic fugitive emissions (CO2, CO and SO2), significantly reduces energy consumption, increases productivity in a single-step process (lower capital and operating costs) and is broadly applicable to a host of electronically conductive transition-metal chalcogenides.

Electrolysis of a molten semiconductor

NASA Astrophysics Data System (ADS)

Yin, Huayi; Chung, Brice; Sadoway, Donald R.

2016-08-01

Metals cannot be extracted by electrolysis of transition-metal sulfides because as liquids they are semiconductors, which exhibit high levels of electronic conduction and metal dissolution. Herein by introduction of a distinct secondary electrolyte, we reveal a high-throughput electro-desulfurization process that directly converts semiconducting molten stibnite (Sb2S3) into pure (99.9%) liquid antimony and sulfur vapour. At the bottom of the cell liquid antimony pools beneath cathodically polarized molten stibnite. At the top of the cell sulfur issues from a carbon anode immersed in an immiscible secondary molten salt electrolyte disposed above molten stibnite, thereby blocking electronic shorting across the cell. As opposed to conventional extraction practices, direct sulfide electrolysis completely avoids generation of problematic fugitive emissions (CO2, CO and SO2), significantly reduces energy consumption, increases productivity in a single-step process (lower capital and operating costs) and is broadly applicable to a host of electronically conductive transition-metal chalcogenides.

Spin-splitting calculation for zincblende semiconductors using an atomic bond-orbital model.

PubMed

Kao, Hsiu-Fen; Lo, Ikai; Chiang, Jih-Chen; Chen, Chun-Nan; Wang, Wan-Tsang; Hsu, Yu-Chi; Ren, Chung-Yuan; Lee, Meng-En; Wu, Chieh-Lung; Gau, Ming-Hong

2012-10-17

We develop a 16-band atomic bond-orbital model (16ABOM) to compute the spin splitting induced by bulk inversion asymmetry in zincblende materials. This model is derived from the linear combination of atomic-orbital (LCAO) scheme such that the characteristics of the real atomic orbitals can be preserved to calculate the spin splitting. The Hamiltonian of 16ABOM is based on a similarity transformation performed on the nearest-neighbor LCAO Hamiltonian with a second-order Taylor expansion k at the Γ point. The spin-splitting energies in bulk zincblende semiconductors, GaAs and InSb, are calculated, and the results agree with the LCAO and first-principles calculations. However, we find that the spin-orbit coupling between bonding and antibonding p-like states, evaluated by the 16ABOM, dominates the spin splitting of the lowest conduction bands in the zincblende materials.

Retrieving the Quantitative Chemical Information at Nanoscale from Scanning Electron Microscope Energy Dispersive X-ray Measurements by Machine Learning

NASA Astrophysics Data System (ADS)

Jany, B. R.; Janas, A.; Krok, F.

2017-11-01

The quantitative composition of metal alloy nanowires on InSb(001) semiconductor surface and gold nanostructures on germanium surface is determined by blind source separation (BSS) machine learning (ML) method using non negative matrix factorization (NMF) from energy dispersive X-ray spectroscopy (EDX) spectrum image maps measured in a scanning electron microscope (SEM). The BSS method blindly decomposes the collected EDX spectrum image into three source components, which correspond directly to the X-ray signals coming from the supported metal nanostructures, bulk semiconductor signal and carbon background. The recovered quantitative composition is validated by detailed Monte Carlo simulations and is confirmed by separate cross-sectional TEM EDX measurements of the nanostructures. This shows that SEM EDX measurements together with machine learning blind source separation processing could be successfully used for the nanostructures quantitative chemical composition determination.

Investigation of the abnormal Zn diffusion phenomenon in III-V compound semiconductors induced by the surface self-diffusion of matrix atoms

NASA Astrophysics Data System (ADS)

Tang, Liangliang; Xu, Chang; Liu, Zhuming

2017-01-01

Zn diffusion in III-V compound semiconductorsare commonly processed under group V-atoms rich conditions because the vapor pressure of group V-atoms is relatively high. In this paper, we found that group V-atoms in the diffusion sources would not change the shaped of Zn profiles, while the Zn diffusion would change dramatically undergroup III-atoms rich conditions. The Zn diffusions were investigated in typical III-V semiconductors: GaAs, GaSb and InAs. We found that under group V-atoms rich or pure Zn conditions, the double-hump Zn profiles would be formed in all materials except InAs. While under group III-atoms rich conditions, single-hump Zn profiles would be formed in all materials. Detailed diffusion models were established to explain the Zn diffusion process; the surface self-diffusion of matrix atoms is the origin of the abnormal Zn diffusion phenomenon.

Objectively Measured Sedentary Behavior, Obesity, and Psychological Well-Being: A Cross-Sectional Study of Japanese Schoolchildren.

PubMed

Ishii, Kaori; Shibata, Ai; Adachi, Minoru; Mano, Yoshiyuki; Oka, Koichiro

2017-04-01

Sedentary behaviors (SB) are associated with health indicators; however, there are currently very few studies that have examined these associations, especially in conjunction with psychological factors, in children. The current study examined the independent relationship between objectively assessed SB, and indicators of obesity and psychological well-being, among Japanese children. A total of 967 elementary-school children completed a cross-sectional survey. SB was measured with accelerometers for 7 consecutive days. Psychological well-being data (eg, anxiety and behavior problems) were collected via a self-report questionnaire. To determine the relationship of SB with degree of obesity and psychological well-being, linear regression analyses were conducted to relate the indicators of obesity and psychological well-being on SB, adjusted by gender, grade, percentage of moderate-to-vigorous physical activity per day, duration spent wearing the accelerometer, and degree of obesity. SB was significantly related to behavioral/emotional problems (β = .280, P = .010, R 2 = .015). There was a statistically significant relationship between SB and anxiety (β = .206, P = .059, R 2 = .007). No significant association with degree of obesity was found. Excess SB relates higher levels of behavioral/emotional problems and anxiety. These results can inspire the development of interventions that promote well-being and enhance psychological health, by focusing on SB in Japanese children.

Physical activity and sedentary behavior in preschoolers: a longitudinal assessment of trajectories and determinants.

PubMed

Schmutz, Einat A; Haile, Sarah R; Leeger-Aschmann, Claudia S; Kakebeeke, Tanja H; Zysset, Annina E; Messerli-Bürgy, Nadine; Stülb, Kerstin; Arhab, Amar; Meyer, Andrea H; Munsch, Simone; Puder, Jardena J; Jenni, Oskar G; Kriemler, Susi

2018-04-04

Despite physical activity (PA) being recognized as a critically important factor for good physical and mental health already early in life and throughout the life course, prospective data on activity behavior during the preschool years remains scarce. This study examined trajectories and determinants of levels and change in total PA (TPA), moderate-to-vigorous PA (MVPA) and sedentary behavior (SB) in a representative sample of Swiss preschoolers. Data were drawn from the Swiss Preschoolers' Health Study (SPLASHY), a multi-site prospective cohort study including 555 children (53% boys) aged 2-to-6 years at baseline. A follow-up was conducted after 12 months. Activity behavior was measured using accelerometers. Information on 35 potential determinants from different socio-ecological domains was either directly measured or parent-reported. Trajectories of TPA, MVPA and SB over time were described for boys and girls. Linear mixed models were used to investigate factors that predicted levels and change in TPA, MVPA and SB. All children were sufficiently physically active according to published recommendations for preschoolers. Trajectory profiles revealed a marked increase in TPA and MVPA in boys and girls whereas SB remained fairly stable over time. Mixed modeling demonstrated that variables most relevant to determining PA levels were sex, age and activity temperament (all positively associated). Together with gross motor skills, birth weight, family structure (only for TPA) and season (only for MVPA), these factors accounted for 26 and 32% of total variance explained in TPA and MVPA, respectively. Activity temperament emerged as the strongest determinant of SB (negative association) and explained with sex, season and family structure 20% of total variance in SB. The presence of older siblings was the only factor that predicted change in PA over time. In this healthy physically active cohort of preschoolers, non-modifiable individual-level factors had the greatest influence on PA. The limited success of this and previous studies to identify modifiable determinants and the finding that most preschoolers were sufficiently active suggest that future attempts should provide insights into how preschoolers' activity levels can be maintained and fostered to prevent subsequent harmful declines attributable, amongst others, to educational transitions. Thus, good-quality longitudinal studies are needed. Current Controlled Trials ISRCTN41045021 (date of registration: 21.03.14).

Prevalence of sedentary behavior and its correlates among primary and secondary school students

PubMed Central

Ferreira, Rodrigo Wiltgen; Rombaldi, Airton José; Ricardo, Luiza Isnardi Cardoso; Hallal, Pedro Curi; Azevedo, Mario Renato

2016-01-01

Abstract Objective: To determine the students’ exposure to four different sedentary behavior (SB) indicators and their associations with gender, grade, age, economic status and physical activity level. Methods: A cross-sectional study was conducted in 2013. The SB was collected using the HELENA instrument, composed by screen time questions (TV, video games and internet) and sitting activities on school opposite shift. The cut point of ≥2h/day was used to categorize the outcome. The Poisson regression was used for associations between the outcome and the independent variables (95% significance level), controlling for confounding variables and the possible design effect. Results: The sample was composed by 8661 students. The overall prevalence of SB was 69.2% (CI95% 68.1–70.2) on weekdays, and 79.6% (CI95% 78.7–80.5) on weekends. Females were more associated with the outcome, except to electronic games. Advanced grades students were more involved in sitting tasks when compared to the early grades. Older students were more likely to surf on net for ≥2h/day. Higher economic level students were more likely to engage in video games and internet. Active individuals were less likely to engage in SB on weekdays. Conclusions: The prevalence of SB was high, mainly on weekends. The associations with sex, age, grade and physical activity level should be considered into elaboration of more efficient interventions on SB control. PMID:26826878

A study on the temperature dependence of the threshold switching characteristics of Ge2Sb2Te5

NASA Astrophysics Data System (ADS)

Lee, Suyoun; Jeong, Doo Seok; Jeong, Jeung-hyun; Zhe, Wu; Park, Young-Wook; Ahn, Hyung-Woo; Cheong, Byung-ki

2010-01-01

We investigated the temperature dependence of the threshold switching characteristics of a memory-type chalcogenide material, Ge2Sb2Te5. We found that the threshold voltage (Vth) decreased linearly with temperature, implying the existence of a critical conductivity of Ge2Sb2Te5 for its threshold switching. In addition, we investigated the effect of bias voltage and temperature on the delay time (tdel) of the threshold switching of Ge2Sb2Te5 and described the measured relationship by an analytic expression which we derived based on a physical model where thermally activated hopping is a dominant transport mechanism in the material.

High potential thermoelectric figure of merit in ternary La 3Cu 3X 4 (X = P, As, Sb and Bi) compounds

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

Pandey, Tribhuwan; Parker, David S.

Here, we investigate the thermoelectric properties of the relatively unexplored rare-earth ternary compounds La 3Cu 3X 4 (X= Bi, Sb, As, and P) using first principles electronic structure and Boltzmann transport calculations. These compounds, of which the La 3Cu 3Sb 4 and La 3Cu 3Bi 4 compounds have previously been synthesized, are all predicted to semiconductors and present a wide range of band gaps varying from 0.23 eV (for the Bi compound) to 0.87 eV (for the P compound). We further find a mixture of light and heavy bands, which results in a high thermoelectric power factor. In addition wemore » find that at high temperatures of 1000 K these compounds exhibit lattice thermal conductivity less than 1 W/m-K. The combination of low thermal conductivity and good transport properties results in a predicted ZT as high as ~1.5 for both La 3Cu 3P 4 and La 3Cu 3As 4, under high p-type doping. This predicted high performance makes these compounds promising candidates for high performance thermoelectric performance and thus merits further experimental investigation.« less

Metal colloids and semiconductor quantum dots: Linear and nonlinear optical properties

NASA Technical Reports Server (NTRS)

Henderson, D. O.; My, R.; Tung, Y.; Ueda, A.; Zhu, J.; Collins, W. E.; Hall, Christopher

1995-01-01

One aspect of this project involves a collaborative effort with the Solid State Division of ORNL. The thrust behind this research is to develop ion implantion for synthesizing novel materials (quantum dots wires and wells, and metal colloids) for applications in all optical switching devices, up conversion, and the synthesis of novel refractory materials. In general the host material is typically a glass such as optical grade silica. The ions of interest are Au, Ag, Cd, Se, In, P, Sb, Ga and As. An emphasis is placed on host guest interactions between the matrix and the implanted ion and how the matrix effects and implantation parameters can be used to obtain designer level optical devices tailored for specific applications. The specific materials of interest are: CdSe, CdTe, InAs, GaAs, InP, GaP, InSb, GaSb and InGaAs. A second aspect of this research program involves using porous glass (25-200 A) for fabricating materials of finite size. In this part of the program, we are particularly interested in characterizing the thermodynamic and optical properties of these non-composite materials. We also address how phase diagram of the confined material is altered by the interfacial properties between the confined material and the pore wall.

High Field Magnetic Circular Dichroism in Ferromagnetic InMnSb and InMnAs

NASA Astrophysics Data System (ADS)

Meeker, M. A.; Magill, B. A.; Khodaparast, G. A.; Saha, D.; Stanton, C. J.; McGill, S.; Wessels, B. W.

An understanding of the fundamental interactions in narrow gap ferromagnetic semiconductors such as InMnAs and InMnSb has been developed primarily from static magnetization and electrical transport measurements. In this study, to provide a better understanding of the coupling of the Mn impurities to the conduction and valence bands through the sp-d exchange interactions, we have performed magnetic circular dichroism measurements (MCD) on MOVPE grown InMnAs and InMnSb. In our samples, the Mn content varies from 2% to 10.7% and all the samples have Curie temperatures above 300 K. The samples were photo-excited using a Quartz Tungsten Halogen lamp with energies ranging between 0.92-1.45 eV, and in magnetic fields up to 31 T. The temperatures ranged from 15-190 K. Comparison of the observed MCD with theoretical calculations provides a direct method to probe the band structure including the temperature dependence of the spin-orbit split-off bandgap and g-factors, as well as a means to estimate the sp-d coupling constants. Supported by the AFOSR through grant FA9550-14-1-0376, NSF-Career Award DMR-0846834 , NSF-DMR-60035274 , NSF-DMR-1305666, NSF MRI program (DMR-1229217).

High potential thermoelectric figure of merit in ternary La 3Cu 3X 4 (X = P, As, Sb and Bi) compounds

DOE PAGES

Pandey, Tribhuwan; Parker, David S.

2017-10-27

Here, we investigate the thermoelectric properties of the relatively unexplored rare-earth ternary compounds La 3Cu 3X 4 (X= Bi, Sb, As, and P) using first principles electronic structure and Boltzmann transport calculations. These compounds, of which the La 3Cu 3Sb 4 and La 3Cu 3Bi 4 compounds have previously been synthesized, are all predicted to semiconductors and present a wide range of band gaps varying from 0.23 eV (for the Bi compound) to 0.87 eV (for the P compound). We further find a mixture of light and heavy bands, which results in a high thermoelectric power factor. In addition wemore » find that at high temperatures of 1000 K these compounds exhibit lattice thermal conductivity less than 1 W/m-K. The combination of low thermal conductivity and good transport properties results in a predicted ZT as high as ~1.5 for both La 3Cu 3P 4 and La 3Cu 3As 4, under high p-type doping. This predicted high performance makes these compounds promising candidates for high performance thermoelectric performance and thus merits further experimental investigation.« less

Theoretical investigation of the structural stabilities, optoelectronic properties and thermodynamic characteristics of GaPxSb1-x ternary alloys

NASA Astrophysics Data System (ADS)

Oumelaz, F.; Nemiri, O.; Boumaza, A.; Ghemid, S.; Meradji, H.; Bin Omran, S.; El Haj Hassan, F.; Rai, D. P.; Khenata, R.

2018-06-01

In this theoretical study, we have investigated the structural, phase transition, electronic, thermodynamic and optical properties of GaPxSb1-x ternary alloys. Our calculations are performed with the WIEN2k code based on density functional theory using the full-potential linearized augmented plane wave method. For the electron exchange-correlation potential, a generalized gradient approximation within Wu-Cohen scheme is considered. The recently developed Tran-Blaha modified Becke-Johnson potential has also been used to improve the underestimated band gap. The structural properties, including the lattice constants, the bulk moduli and their pressure derivatives are in very good agreement with the available experimental data and theoretical results. Several structural phase transitions were studied here to establish the stable structure and to predict the phase transition under hydrostatic pressure. The computed transition pressure (Pt) of the material of our interest from the zinc blende (B3) to the rock salt (B1) phase has been determined and found to agree well with the experimental and theoretical data. The calculated band structure shows that GaSb binary compound and the ternary alloys are direct band gap semiconductors. Optical parameters such as the dielectric constants and the refractive indices are calculated and analyzed. The thermodynamic results are also interpreted and analyzed.

Prominent metallic surface conduction and the singular magnetic response of topological Dirac fermion in three-dimensional topological insulator Bi1.5Sb0.5Te1.7Se1.3.

PubMed

Dutta, Prithwish; Pariari, Arnab; Mandal, Prabhat

2017-07-07

We report semiconductor to metal-like crossover in the temperature dependence of resistivity (ρ) due to the switching of charge transport from bulk to surface channel in three-dimensional topological insulator Bi 1.5 Sb 0.5 Te 1.7 Se 1.3 . Unlike earlier studies, a much sharper drop in ρ(T) is observed below the crossover temperature due to the dominant surface conduction. Remarkably, the resistivity of the conducting surface channel follows a rarely observable T 2 dependence at low temperature, as predicted theoretically for a two-dimensional Fermi liquid system. The field dependence of magnetization shows a cusp-like paramagnetic peak in the susceptibility (χ) at zero field over the diamagnetic background. The peak is found to be robust against temperature and χ decays linearly with the field from its zero-field value. This unique behavior of the χ is associated with the spin-momentum locked topological surface state in Bi 1.5 Sb 0.5 Te 1.7 Se 1.3 . The reconstruction of the surface state with time is clearly reflected through the reduction of the peak height with the age of the sample.

Growth of InSb and InI Crystals on Earth and in Microgravity

NASA Technical Reports Server (NTRS)

Ostrogorsky, A. G.; Churilov, A.; Volz, M. P.; Riabov, V.; Van den Berg, L.

2015-01-01

During the past 40 years, dozens of semiconductor crystal growth experiments have been conducted in space laboratories. The subsequent analysis of the space-grown crystals revealed (i) that weak convection existed in virtually all melt-growth experiments, (ii) de-wetting significantly reduced the level of stress-induced defects, and (iii) particularly encouraging results were obtained in vapor-growth experiments. In 2002, following a decade of ground based research in growing doped Ge and GaSb crystals, a series of crystal growth experiments was performed at the ISS, within the SUBSA (Solidification Using a Baffle in Sealed Ampoules) investigation. Te- and Zn-doped InSb crystals were grown from the melt. The specially designed furnace provided a side-view of the melt and precise seeding measurement of the growth rate. At present, under sponsorship of CASIS (Center for the Advancement of Science in Space, www.iss-casis.org), we are conducting ground-based experiments with indium mono-iodide (InI) in preparation for the "SUBSA II" ISS investigation, planned for 2017. The experiments include: i) Horizontal Bridgman (HB) growth and ii) Vapor Transport (VT) growth. Finite element modeling will also be conducted, to optimize the design of the flight ampoules, for vapor and melt growth.

Cognitive and Motivational Factors Associated with Sedentary Behavior: A Systematic Review

PubMed Central

Rollo, Scott; Gaston, Anca; Prapavessis, Harry

2016-01-01

Excessive time spent in sedentary behavior (SB) is associated with numerous health risks. These associations remain even after controlling for moderate-to-vigorous physical activity (PA) and body mass index, indicating that efforts to promote leisure time physical activity alone are insufficient. Cognitive and motivation variables represent potentially modifiable factors and have the potential of furthering our understanding of sedentary behavior. Hence, a systematic review was conducted to synthesize and critique the literature on the relationship between cognitive and motivational factors and sedentary behaviors. In April 2016, four electronic databases (Psych info, Pub Med, SPORTDiscus, Web of Science) were searched and a total of 4866 titles and abstracts were reviewed. After meeting inclusion criteria, study characteristics were extracted and the methodological quality of each study was assessed according to the Downs and Black Checklist. PRISMA guidelines for reporting of systematic reviews were followed. Twenty-five studies (16 cross-sectional, 8 longitudinal and one examining two populations and employing both a cross-sectional and prospective design) assessed 23 different cognitive and motivational factors. Seventeen studies were theory-based and 8 did not employ a theoretical model. Results showed that among SB-related cognitions, risk factors for greater sedentary time included having a more positive attitude towards SB, perceiving greater social support/norms for SB, reporting greater SB habits, having greater intentions to be sedentary, and having higher intrinsic, introjected, and external motivation towards SB. Protective factors associated with lower sedentary time included having greater feelings of self-efficacy/control over SB and greater intentions to reduce SB. Among PA-related cognitions, protective factors for lower SB included a more positive attitude towards PA, having greater social support/norms for PA, greater self-efficacy/control for PA, higher PA intentions, and higher intrinsic and identified motivation towards PA. In addition, feeling more supported and empowered in general was related with lower levels of SB. The average methodological quality score for included studies was 69% (SD = 9.15%; range 35–80%). In conclusion, a number of cognitive and motivational factors were identified that were associated with sedentarism. These findings have come from reasonably high quality studies. To further extend our understanding of the relation between cognitive and motivational factors and SB, more longitudinal, theory-driven studies examining cognitions and motivation from a sedentary perspective are required. PMID:29546206

Experiments on Quantum Hall Topological Phases in Ultra Low Temperatures

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

Du, Rui-Rui

2015-02-14

This project is to cool electrons in semiconductors to extremely low temperatures and to study new states of matter formed by low-dimensional electrons (or holes). At such low temperatures (and with an intense magnetic field), electronic behavior differs completely from ordinary ones observed at room temperatures or regular low temperature. Studies of electrons at such low temperatures would open the door for fundamental discoveries in condensed matter physics. Present studies have been focused on topological phases in the fractional quantum Hall effect in GaAs/AlGaAs semiconductor heterostructures, and the newly discovered (by this group) quantum spin Hall effect in InAs/GaSb materials.more » This project consists of the following components: 1) Development of efficient sample cooling techniques and electron thermometry: Our goal is to reach 1 mK electron temperature and reasonable determination of electron temperature; 2) Experiments at ultra-low temperatures: Our goal is to understand the energy scale of competing quantum phases, by measuring the temperature-dependence of transport features. Focus will be placed on such issues as the energy gap of the 5/2 state, and those of 12/5 (and possible 13/5); resistive signature of instability near 1/2 at ultra-low temperatures; 3) Measurement of the 5/2 gaps in the limit of small or large Zeeman energies: Our goal is to gain physics insight of 5/2 state at limiting experimental parameters, especially those properties concerning the spin polarization; 4) Experiments on tuning the electron-electron interaction in a screened quantum Hall system: Our goal is to gain understanding of the formation of paired fractional quantum Hall state as the interaction pseudo-potential is being modified by a nearby screening electron layer; 5) Experiments on the quantized helical edge states under a strong magnetic field and ultralow temperatures: our goal is to investigate both the bulk and edge states in a quantum spin Hall insulator under time-reversal symmetry-broken conditions.« less

10-year cumulative and bidirectional associations of domain-specific physical activity and sedentary behaviour with health-related quality of life in French adults: Results from the SU.VI.MAX studies.

PubMed

Omorou, Abdou Y; Vuillemin, Anne; Menai, Medhi; Latarche, Clotilde; Kesse-Guyot, Emmanuelle; Galan, Pilar; Hercberg, Serge; Oppert, Jean-Michel; Briançon, Serge

2016-07-01

The directionality of the associations of domain-specific physical activity (PA) and sedentary behaviour (SB) with health-related quality of life (HRQoL) in adults remain insufficiently known. This study investigated the longitudinal associations of 10-year cumulative levels of PA and SB with HRQoL and the reverse associations. A sample of 2093 (47.8% men) participants from a cohort of French adult (SU.VI.MAX) was included. Data were collected at 3 time points (1998, 2001 and 2007) using the Modifiable Activity Questionnaire (MAQ) for PA (leisure-time and occupational) and SB (screen-viewing, reading and total sitting time) and the DUKE Health Profile for HRQoL. The cumulative level (from 0 to 3) referred to the number of time points where a high PA level, high SB or good HRQoL was reported. Regression models examined the 10-year cumulative level of PA, SB as predictors of HRQoL and reverse associations. The 10-year cumulative level of high PA, both leisure-time and occupational, predicted a higher HRQoL while the 10-year cumulative level of high screen-viewing time and high total sitting time was associated with lower HRQoL. For the reverse association, cumulative level of good HRQoL predicted more leisure-time PA, less screen-viewing time and less total sitting time but was not related to occupational PA. Relationships between PA, SB and HRQoL are complex and should not be oversimplified in one or the other direction. Taking into account domain-specific PA and SB in health promotion programs appears of prime importance to design interventions aiming at improving HRQoL. Copyright © 2016 Elsevier Inc. All rights reserved.

Physical Activity and Pediatric Obesity: A Quantile Regression Analysis

PubMed Central

Mitchell, Jonathan A.; Dowda, Marsha; Pate, Russell R.; Kordas, Katarzyna; Froberg, Karsten; Sardinha, Luís B.; Kolle, Elin; Page, Angela

2016-01-01

Purpose We aimed to determine if moderate-to-vigorous physical activity (MVPA) and sedentary behavior (SB) were independently associated with body mass index (BMI) and waist circumference (WC) in children and adolescents. Methods Data from the International Children’s Accelerometry Database (ICAD) were used to address our objectives (N=11,115; 6-18y; 51% female). We calculated age and gender specific body mass index (BMI) and waist circumference (WC) Z-scores and used accelerometry to estimate MVPA and total SB. Self-reported television viewing was used as a measure of leisure time SB. Quantile regression was used to analyze the data. Results MVPA and total SB were associated with lower and higher BMI and WC Z-scores, respectively. These associations were strongest at the higher percentiles of the Z-score distributions. After including MVPA and total SB in the same model the MVPA associations remained, but the SB associations were no longer present. For example, each additional hour per day of MVPA was not associated with BMI Z-score at the 10th percentile (b=-0.02, P=0.170), but was associated with lower BMI Z-score at the 50th (b=-0.19, P<0.001) and 90th percentiles (b=-0.41, P<0.001). More television viewing was associated with higher BMI and WC and the associations were strongest at the higher percentiles of the Z-score distributions, with adjustment for MVPA and total SB. Conclusions Our observation of stronger associations at the higher percentiles indicate that increasing MVPA and decreasing television viewing at the population-level could shift the upper tails of the BMI and WC frequency distributions to lower values, thereby lowering the number of children and adolescents classified as obese. PMID:27755284

Clean Intermittent Catheterization in the School Setting

ERIC Educational Resources Information Center

Katrancha, Elizabeth D.

2008-01-01

Spina bifida (SB) is a neural tube defect that causes many physical and mental disabilities. Bowel and bladder incontinence is the disability seen most often in these students that requires the school nurse's attention. Clean intermittent catheterization (CIC) provides the student with SB a vehicle to reach a satisfactory level of continence,…

Ba-filled Ni–Sb–Sn based skutterudites with anomalously high lattice thermal conductivity

DOE PAGES

Paschinger, W.; Rogl, Gerda; Grytsiv, A.; ...

2016-06-21

Here, in this study, novel filled skutterudites Ba yNi 4Sb 12-xSn x (y max = 0.93) have been prepared by arc melting followed by annealing at 250, 350 and 450°C up to 30 days in vacuum-sealed quartz vials. Extension of the homogeneity region, solidus temperatures and structural investigations were performed for the skutterudite phase in the ternary Ni–Sn–Sb and in the quaternary Ba–Ni–Sb–Sn systems. Phase equilibria in the Ni–Sn–Sb system at 450°C were established by means of Electron Probe Microanalysis (EPMA) and X-ray Powder Diffraction (XPD). With rather small cages Ni 4(Sb,Sn) 12, the Ba–Ni–Sn–Sb skutterudite system is perfectly suitedmore » to study the influence of filler atoms on the phonon thermal conductivity. Single-phase samples with the composition Ni 4Sb 8.2Sn 3.8, Ba 0.42Ni 4Sb 8.2Sn 3.8 and Ba 0.92Ni 4Sb 6.7Sn 5.3 were used to measure their physical properties, i.e. temperature dependent electrical resistivity, Seebeck coefficient and thermal conductivity. The resistivity data demonstrate a crossover from metallic to semiconducting behaviour. The corresponding gap width was extracted from the maxima in the Seebeck coefficient data as a function of temperature. Single crystal X-ray structure analyses at 100, 200 and 300 K revealed the thermal expansion coefficients as well as Einstein and Debye temperatures for Ba 0.73Ni 4Sb 8.1Sn 3.9 and Ba 0.95Ni 4Sb 6.1Sn 5.9. These data were in accordance with the Debye temperatures obtained from the specific heat (4.4 K < T < 140 K) and Mössbauer spectroscopy (10 K < T < 290 K). Rather small atom displacement parameters for the Ba filler atoms indicate a severe reduction in the “rattling behaviour” consistent with the high levels of lattice thermal conductivity. The elastic moduli, collected from Resonant Ultrasonic Spectroscopy ranged from 100 GPa for Ni 4Sb 8.2Sn 3.8 to 116 GPa for Ba 0.92Ni 4Sb 6.7Sn 5.3. The thermal expansion coefficients were 11.8 × 10 -6 K -1 for Ni 4Sb 8.2Sn 3.8 and 13.8 × 10 -6 K -1 for Ba 0.92Ni 4Sb 6.7Sn 5.3. The room temperature Vickers hardness values vary within the range from 2.6 GPa to 4.7 GPa. Lastly, severe plastic deformation via high-pressure torsion was used to introduce nanostructuring; however, the physical properties before and after HPT showed no significant effect on the materials thermoelectric behaviour.« less

Studies of Nano-structured Se77Sb23- x Ge x Thin Films Prepared by Physical Vapor Condensation Technique

NASA Astrophysics Data System (ADS)

Alvi, M. A.

2017-02-01

Bulk Se77Sb23- x Ge x material with x = 4 and 12 was prepared by employing a melt quench technique. Its amorphous as well as glassy nature was confirmed by x-ray diffraction analysis and nonisothermal differential scanning calorimetry measurements. The physical vapor condensation technique was applied to prepare nanostructured thin films of Se77Sb23- x Ge x material. The surface morphology of the films was examined using field-emission scanning electron microscopy, revealing average particle size between 20 nm and 50 nm. Systematic investigation of optical absorption data indicated that the optical transition was indirect in nature. The dark conductivity (dc conductivity) of nano-structured Se77Sb23- x Ge x thin films was also investigated at temperatures from 313 K to 463 K, revealing that it tended to increase with increasing temperature. Analyses of our experimental data also indicate that the conduction is due to thermally supported tunneling of charge carriers in confined states close to the band edges. The calculated values of activation energy agree well with the optical bandgap.

Comparison of Summer and Winter Objectively Measured Physical Activity and Sedentary Behavior in Older Adults: Age, Gene/Environment Susceptibility Reykjavik Study.

PubMed

Arnardottir, Nanna Yr; Oskarsdottir, Nina Dora; Brychta, Robert J; Koster, Annemarie; van Domelen, Dane R; Caserotti, Paolo; Eiriksdottir, Gudny; Sverrisdottir, Johanna E; Johannsson, Erlingur; Launer, Lenore J; Gudnason, Vilmundur; Harris, Tamara B; Chen, Kong Y; Sveinsson, Thorarinn

2017-10-21

In Iceland, there is a large variation in daylight between summer and winter. The aim of the study was to identify how this large variation influences physical activity (PA) and sedentary behavior (SB). Free living PA was measured by a waist-worn accelerometer for one week during waking hours in 138 community-dwelling older adults (61.1% women, 80.3 ± 4.9 years) during summer and winter months. In general, SB occupied about 75% of the registered wear-time and was highly correlated with age (β = 0.36). Although the differences were small, more time was spent during the summer in all PA categories, except for the moderate-to-vigorous PA (MVPA), and SB was reduced. More lifestyle PA (LSPA) was accumulated in ≥5-min bouts during summer than winter, especially among highly active participants. This information could be important for policy makers and health professionals working with older adults. Accounting for seasonal difference is necessary in analyzing SB and PA data.

Optical characterization of semiconductor materials by using FTIR-PAS

NASA Astrophysics Data System (ADS)

Arévalo, Fabiola; Saavedra, Renato; Paulraj, M.

2008-11-01

In this paper we discuss the procedures for photoacoustic measurements for semiconducting materials, including bulk samples like Gallium Antimonide (GaSb). The optical absorption at photon energies near the band gap was measured at room temperature using Fourier Transform Infrared Photoacoustic spectroscopy (FTIR-PAS). Measurements were performed using a NEXUS 670 FTIR-spectrometer (from Thermo Nicolet) with a MTEC model 300 PA cell (MTEC Photoacoustics, Inc.). Optical properties of the studied samples were determined from their room temperature PA spectra and band gaps were calculated directly from absorption spectra

Thermal Conductivity and Large Isotope Effect in GaN from First Principles

DTIC Science & Technology

2012-08-28

August 2012) We present atomistic first principles results for the lattice thermal conductivity of GaN and compare them to those for GaP, GaAs, and GaSb ...weak scattering results from stiff atomic bonds and the large Ga to N mass ratio, which give phonons high frequencies and also a pronounced energy gap...66.70.f, 63.20.kg, 71.15.m Introduction.—Gallium nitride (GaN) is a wide band gap semiconductor and a promising candidate for use in opto- electronic

Low-Cost Lattice Matching Zn(Se)Te/Si Composite Substrates for HgCdSe and Type-2 Superlattices

DTIC Science & Technology

2013-09-01

far from optimized. In similar fashion, we studied the impact of Zn/Te flux ratio during ZnTe growth. In this case , three ZnTe(100) layers were...6.1 Å, such as HgCdSe and GaSb-based type-II strained-layer superlattices. In this report, we present our findings on the systematic studies of...versus lattice parameter for several semiconductor material systems. We conducted systematic studies on the MBE growth of ZnTe on Si in both (211) and

Mid-infrared two photon absorption sensitivity of commercial detectors

NASA Astrophysics Data System (ADS)

Boiko, D. L.; Antonov, A. V.; Kuritsyn, D. I.; Yablonskiy, A. N.; Sergeev, S. M.; Orlova, E. E.; Vaks, V. V.

2017-10-01

We report on broad-band two-photon absorption (TPA) in several commercially available MIR inter-band bulk semiconductor photodetectors with the spectral cutoff in the range of 4.5-6 μm. The highest TPA responsivity of 2 × 10-5 A.mm2/W2 is measured for a nitrogen-cooled InSb photovoltaic detector. Its performance as a two-photon detector is validated by measuring the second-order interferometric autocorrelation function of a multimode quantum cascade laser emitting at the wavelength of 8 μm.

InAs/GaSb type-II superlattice infrared detectors: Future prospect

NASA Astrophysics Data System (ADS)

Rogalski, A.; Martyniuk, P.; Kopytko, M.

2017-09-01

Investigations of antimonide-based materials began at about the same time as HgCdTe ternary alloys—in the 1950s, and the apparent rapid success of their technology, especially low-dimensional solids, depends on the previous five decades of III-V materials and device research. However, the sophisticated physics associated with the antimonide-based bandgap engineering concept started at the beginning of 1990s gave a new impact and interest in development of infrared detector structures within academic and national laboratories. The development of InAs/GaSb type-II superlattices (T2SLs) results from two primary motivations: the perceived challenges of reproducibly fabricating high-operability HgCdTe focal plane arrays (FPAs) at reasonable cost and the theoretical predictions of lower Auger recombination for type T2SL detectors compared with HgCdTe. Second motivation—lower Auger recombination should be translated into a fundamental advantage for T2SL over HgCdTe in terms of lower dark current and/or higher operating temperature, provided other parameters such as Shockley-Read-Hall (SRH) lifetime are equal. InAs/GaSb T2SL photodetectors offer similar performance to HgCdTe at an equivalent cut-off wavelength, but with a sizeable penalty in operating temperature, due to the inherent difference in SRH lifetimes. It is predicted that since the future infrared (IR) systems will be based on the room temperature operation of depletion-current limited arrays with pixel densities that are fully consistent with background- and diffraction-limited performance due to the system optics, the material system with long SRH lifetime will be required. Since T2SLs are very much resisted in attempts to improve its SRH lifetime, currently the only material that meets this requirement is HgCdTe. Due to less ionic chemical bonding, III-V semiconductors are more robust than their II-VI counterparts. As a result, III-V-based FPAs excel in operability, spatial uniformity, temporal stability, scalability, producibility, and affordability—the so-called "ibility" advantages.

Post-hospitalization course and predictive signs of suicidal behavior of suicidal patients admitted to a psychiatric hospital: a 2-year prospective follow-up study.

PubMed

Hayashi, Naoki; Igarashi, Miyabi; Imai, Atsushi; Yoshizawa, Yuka; Utsumi, Kaori; Ishikawa, Yoichi; Tokunaga, Taro; Ishimoto, Kayo; Harima, Hirohiko; Tatebayashi, Yoshitaka; Kumagai, Naoki; Nozu, Makoto; Ishii, Hidetoki; Okazaki, Yuji

2012-10-31

Suicidal patients admitted to a psychiatric hospital are considered to be at risk of suicidal behavior (SB) and suicide. The present study aimed to seek predictors of SB recurrence of the high-risk patients by examining their post-hospitalization course. The design was 2-year prospective follow-up study of patients consecutively admitted with SB to a psychiatric center in Tokyo. The DSM-IV diagnoses and SB-related features of subjects were determined in structured interviews. Subsequently, the subjects underwent a series of follow-up assessments at 6-month intervals. The assessment included inquiries into SB recurrence, its accompanying suicidal intent (SI) and SF-8 health survey. Analyses of serial change over time in the follow-up data and Cox proportional hazards regression analyses of SB recurrence were performed. 106 patients participated in this study. The dropout rate during the follow-up was 9%. Within 2 years, incidences of SB as a whole, SB with certain SI (suicide attempt) and suicide were 67% (95% CI 58 - 75%), 38% (95% CI 29 - 47%) and 6% (95% CI 3 - 12%), respectively. Younger age, number of lifetime SBs and maltreatment in the developmental period were predictive of SB as a whole, and younger age and hopelessness prior to index admission were predictive of suicide attempt. Regarding diagnostic variables, anxiety disorders and personality disorders appeared to have predictive value for SB. Additionally, poor physical health assessed during the follow-up was indicated as a possible short-term predictor of SB recurrence. This study demonstrated a high incidence of SB and suicide and possible predictors of SB recurrence in the post-hospitalization period of psychiatric suicidal patients. Specialized interventions should be developed to reduce the suicide risk of this patient population.

GaSb solar cells grown on GaAs via interfacial misfit arrays for use in the III-Sb multi-junction cell

NASA Astrophysics Data System (ADS)

Nelson, George T.; Juang, Bor-Chau; Slocum, Michael A.; Bittner, Zachary S.; Laghumavarapu, Ramesh B.; Huffaker, Diana L.; Hubbard, Seth M.

2017-12-01

Growth of GaSb with low threading dislocation density directly on GaAs may be possible with the strategic strain relaxation of interfacial misfit arrays. This creates an opportunity for a multi-junction solar cell with access to a wide range of well-developed direct bandgap materials. Multi-junction cells with a single layer of GaSb/GaAs interfacial misfit arrays could achieve higher efficiency than state-of-the-art inverted metamorphic multi-junction cells while forgoing the need for costly compositionally graded buffer layers. To develop this technology, GaSb single junction cells were grown via molecular beam epitaxy on both GaSb and GaAs substrates to compare homoepitaxial and heteroepitaxial GaSb device results. The GaSb-on-GaSb cell had an AM1.5g efficiency of 5.5% and a 44-sun AM1.5d efficiency of 8.9%. The GaSb-on-GaAs cell was 1.0% efficient under AM1.5g and 4.5% at 44 suns. The lower performance of the heteroepitaxial cell was due to low minority carrier Shockley-Read-Hall lifetimes and bulk shunting caused by defects related to the mismatched growth. A physics-based device simulator was used to create an inverted triple-junction GaInP/GaAs/GaSb model. The model predicted that, with current GaSb-on-GaAs material quality, the not-current-matched, proof-of-concept cell would provide 0.5% absolute efficiency gain over a tandem GaInP/GaAs cell at 1 sun and 2.5% gain at 44 suns, indicating that the effectiveness of the GaSb junction was a function of concentration.

Is the time right for quantitative public health guidelines on sitting? A narrative review of sedentary behaviour research paradigms and findings.

PubMed

Stamatakis, Emmanuel; Ekelund, Ulf; Ding, Ding; Hamer, Mark; Bauman, Adrian E; Lee, I-Min

2018-06-10

Sedentary behaviour (SB) has been proposed as an 'independent' risk factor for chronic disease risk, attracting much research and media attention. Many countries have included generic, non-quantitative reductions in SB in their public health guidelines and calls for quantitative SB targets are increasing. The aim of this narrative review is to critically evaluate key evidence areas relating to the development of guidance on sitting for adults. We carried out a non-systematic narrative evidence synthesis across seven key areas: (1) definition of SB, (2) independence of sitting from physical activity, (3) use of television viewing as a proxy of sitting, (4) interpretation of SB evidence, (5) evidence on 'sedentary breaks', (6) evidence on objectively measured sedentary SB and mortality and (7) dose response of sitting and mortality/cardiovascular disease. Despite research progress, we still know little about the independent detrimental health effects of sitting, and the possibility that sitting is mostly the inverse of physical activity remains. Unresolved issues include an unclear definition, inconsistencies between mechanistic and epidemiological studies, over-reliance on surrogate outcomes, a very weak epidemiological evidence base to support the inclusion of 'sedentary breaks' in guidelines, reliance on self-reported sitting measures, and misinterpretation of data whereby methodologically inconsistent associations are claimed to be strong evidence. In conclusion, public health guidance requires a consistent evidence base but this is lacking for SB. The development of quantitative SB guidance, using an underdeveloped evidence base, is premature; any further recommendations for sedentary behaviour require development of the evidence base and refinement of the research paradigms used in the field. © Article author(s) (or their employer(s) unless otherwise stated in the text of the article) 2018. All rights reserved. No commercial use is permitted unless otherwise expressly granted.

Longitudinal Physical Activity, Body Composition, and Physical Fitness in Preschoolers.

PubMed

Leppänen, Marja H; Henriksson, Pontus; Delisle Nyström, Christine; Henriksson, Hanna; Ortega, Francisco B; Pomeroy, Jeremy; Ruiz, Jonatan R; Cadenas-Sanchez, Cristina; Löf, Marie

2017-10-01

This study aimed to investigate longitudinal associations of objectively measured physical activity (PA) and sedentary behavior (SB) with body composition and physical fitness at a 12-month follow-up in healthy Swedish 4-yr-old children. The data from the population-based MINISTOP trial were collected between 2014 and 2016, and this study included the 138 children who were in the control group. PA and SB were assessed using the wrist-worn ActiGraph (wGT3x-BT) accelerometer during seven 24-h periods and, subsequently, defined as SB, light-intensity PA, moderate-intensity PA, vigorous-intensity PA (VPA), and moderate-to-vigorous PA (MVPA). Body composition was measured using air-displacement plethysmography and physical fitness (cardiorespiratory fitness, lower and upper muscular strength as well as motor fitness) by the PREFIT fitness battery. Linear regression and isotemporal substitution models were applied. Greater VPA and MVPA at the age of 4.5 yr were associated with higher fat-free mass index (FFMI) at 5.5 yr (P < 0.001 and P = 0.044, respectively). Furthermore, greater VPA and MVPA at the age of 4.5 yr were associated with higher scores for cardiorespiratory fitness, lower body muscular strength, and motor fitness at 12-month follow-up (P = 0.001 to P = 0.031). Substituting 5 min·d of SB, light-intensity PA, or moderate-intensity PA for VPA at the age of 4.5 yr were associated with higher FFMI, and with greater upper and lower muscular strength at 12-month follow-up (P < 0.001 to P = 0.046). Higher VPA and MVPA at the age of 4.5 yr were significantly associated with higher FFMI and better physical fitness at 12-month follow-up. Our results indicate that promoting high-intensity PA at young ages may have long-term beneficial effects on childhood body composition and physical fitness, in particular muscular strength.

Demonstrating antiphase domain boundary-free GaAs buffer layer on zero off-cut Si (0 0 1) substrate for interfacial misfit dislocation GaSb film by metalorganic chemical vapor deposition

NASA Astrophysics Data System (ADS)

Ha, Minh Thien Huu; Hoang Huynh, Sa; Binh Do, Huy; Nguyen, Tuan Anh; Luc, Quang Ho; Chang, Edward Yi

2017-08-01

High quality 40 nm GaSb thin film was grown on the zero off-cut Si (0 0 1)-oriented substrate using metalorganic chemical vapor deposition with the temperature-graded GaAs buffer layer. The growth time of the GaAs nucleation layer, which was deposited at a low temperature of 490 °C, is systematically investigated in this paper. Cross-sections of the high resolution transmission electron microscopy images indicate that the GaAs compound formed 3D-islands first before to quasi-2D islands, and finally formed uniform GaAs layer. The optimum thickness of the 490 °C-GaAs layer was found to be 10 nm to suppress the formation of antiphase domain boundaries (APDs). The thin GaAs nucleation layer had a root-mean-square surface roughness of 0.483 nm. This allows the continued high temperature GaAs buffer layer to be achieved with low threading dislocation density of around 7.1  ×  106 cm-2 and almost invisible APDs. Finally, a fully relaxed GaSb film was grown on the top of the GaAs/Si heterostructure using interfacial misfit dislocation growth mode. These results indicate that the GaSb epitaxial layer can be grown on Si substrate with GaAs buffer layer for future p-channel metal-oxide-semiconductor field effect transistors (MOSFETs) applications.

InAs/GaSb type-II superlattices versus HgCdTe ternary alloys: future prospect

NASA Astrophysics Data System (ADS)

Rogalski, A.

2017-10-01

InAs/GaSb T2SL photodetectors offer similar performance to HgCdTe at an equivalent cutoff wavelength, but with a sizeable penalty in operating temperature, due to the inherent difference in Shockley-Read lifetimes. It is predicted that since the future IR systems will be based on the room temperature operation of depletion-current limited arrays with pixel densities that are fully consistent with background- and diffraction-limited performance due to the system optics, the material system with long Shockley-Read lifetime will be required. Since T2SLs are much resisted in attempts to improve its SR lifetime, currently the only material that meets this requirement is HgCdTe. Due to less ionic chemical bonding, III-V semiconductors are more robust than their II-VI counterparts. As a result, III-V-based FPAs excel in operability, spatial uniformity, temporal stability, scalability, producibility, and affordability - the so-called "ibility" advantages.

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

El-Atwani, O.; Norris, S. A.; Ludwig, K.

In this study, several proposed mechanisms and theoretical models exist concerning nanostructure evolution on III-V semiconductors (particularly GaSb) via ion beam irradiation. However, making quantitative contact between experiment on the one hand and model-parameter dependent predictions from different theories on the other is usually difficult. In this study, we take a different approach and provide an experimental investigation with a range of targets (GaSb, GaAs, GaP) and ion species (Ne, Ar, Kr, Xe) to determine new parametric trends regarding nanostructure evolution. Concurrently, atomistic simulations using binary collision approximation over the same ion/target combinations were performed to determine parametric trends onmore » several quantities related to existing model. A comparison of experimental and numerical trends reveals that the two are broadly consistent under the assumption that instabilities are driven by chemical instability based on phase separation. Furthermore, the atomistic simulations and a survey of material thermodynamic properties suggest that a plausible microscopic mechanism for this process is an ion-enhanced mobility associated with energy deposition by collision cascades.« less

Robust fully-compensated ferrimagnetism and semiconductivity in inverse Heusler compounds: Ti2VZ (Z = P, As, Sb, Bi)

NASA Astrophysics Data System (ADS)

Zhang, Y. J.; Liu, Z. H.; Liu, G. D.; Ma, X. Q.; Cheng, Z. X.

2018-03-01

Compensated ferrimagnets, due to their zero net magnetization and potential for large spin-polarization, have been attracting more and more attention in the field of spintronics. We demonstrate potential candidate materials among the inverse Heusler compounds Ti2VZ (Z = P, As, Sb, Bi) by first principles calculations. It is found that these compounds with 18 valence electrons per unit cell have zero net magnetic moment with compensated sublattice magnetization, as anticipated by a variant of Slater-Pauling rule of Mt = NV - 18, where Mt is the total spin magnetic moment per formula unit and NV is the number of valence electrons per formula unit, and show semiconducting behavior in both spin channels with a moderate exchange splitting, as with ordinary ferromagnetic semiconductors. Furthermore, the fully compensated ferrimagnetism and semiconductivity are rather robust over a wide range of lattice contraction and expansion. Due to the above distinct advantages, these compounds will be promising candidates for spintronic applications.

New group-V elemental bilayers: A tunable structure model with four-, six-, and eight-atom rings

NASA Astrophysics Data System (ADS)

Kong, Xiangru; Li, Linyang; Leenaerts, Ortwin; Liu, Xiong-Jun; Peeters, François M.

2017-07-01

Two-dimensional group-V elemental materials have attracted widespread attention due to their nonzero band gap while displaying high electron mobility. Using first-principles calculations, we propose a series of new elemental bilayers with group-V elements (Bi, Sb, As). Our study reveals the dynamical stability of four-, six-, and eight-atom ring structures, demonstrating their possible coexistence in such bilayer systems. The proposed structures for Sb and As are large-gap semiconductors that are potentially interesting for applications in future nanodevices. The Bi structures have nontrivial topological properties with a direct nontrivial band gap. The nontrivial gap is shown to arise from a band inversion at the Brillouin zone center due to the strong intrinsic spin-orbit coupling in Bi atoms. Moreover, we demonstrate the possibility of tuning the properties of these materials by enhancing the ratio of six-atom rings to four- and eight-atom rings, which results in wider nontrivial band gaps and lower formation energies.

Investigations of Cyclotron Resonance in InSb and PbTe: Intraband Transitions between Landau Levels

NASA Astrophysics Data System (ADS)

Burstein, Elias

2005-06-01

We describe the investigations of cyclotron resonance, and its formulation in terms of intraband transitions between Landau levels, that were carried out at the Naval Research Laboratory and the University of Pennsylvania in the 1950's and 1960's. Measurements were carried out as a function of magnetic field at fixed wavelength in the infrared in both the Faraday and Voigt configurations on an intrinsic sample of InSb sample for which ωP << ωC, and on doped n-type samples for which ωP is comparable to ωC. Azbel'-Kaner cyclotron resonance, which is also observed in the Voigt configuration, was investigated at microwave frequencies in degenerate p-type PbTe where the cyclotron orbit of the carriers is comparable to the skin depth. The results showed that AK-CR is a particularly effective tool for determining the effective mass of carriers in semiconductors at microwave frequencies when ωP cannot be made smaller than ωC.

Superconductivity in the Narrow Gap Semiconductor RbBi 11/3Te 6

DOE PAGES

Malliakas, Christos D.; Chung, Duck Young; Claus, Helmut; ...

2016-10-16

Superconductivity was discovered in the layered compound RbBi 11/3Te 6, featuring Bi vacancies and a narrow band gap of 0.25(2) eV at room temperature. In addition, a sharp superconducting transition at similar to 3.2 K was observed in polycrystalline ingots. The superconducting volume fraction of oriented single crystals is almost 100%, confirming bulk superconductivity. Systematic Se and Sb substitutions in RbBi 11/3-ySb ySe xTe 6-x, revealed a dependence of the superconducting transition on composition that can increase the T c up to similar to 10%. The RbBi 11/3Te 6 system is the first member of the new homologous series Rb[Bimore » 2n+11/3Te 3n+6] with infinite Bi 2Te 3-like layers. Lastly, the large degree of chemical tunability of the electronic structure of the homology via doping and/or substitution gives rise to a new family of superconductors.« less

Validity and responsiveness of the Global Physical Activity Questionnaire (GPAQ) in assessing physical activity during pregnancy

PubMed Central

Micklesfield, Lisa K.; van Poppel, Mireille N. M.; Norris, Shane A.; Sattler, Matteo C.; Dietz, Pavel

2017-01-01

The physiological and biomechanical changes that occur during pregnancy make accurate measurement of physical activity (PA) a challenge during this unique period. The Global Physical Activity Questionnaire (GPAQ) has been used extensively in low-to-middle income countries, but has never been validated in a pregnant population. In this longitudinal study, 95 pregnant women (mean age: 29.5±5.7 years; BMI: 26.9±5.0 kg/m2) completed the GPAQ and were asked to wear an accelerometer for 7 days at two time points during pregnancy (14–18 and 29–33 weeks gestation). There was a significant difference between accelerometry and GPAQ when measuring moderate-to-vigorous physical activity (MVPA) at 29–33 weeks gestation (16.6 vs 21.4 min/day; p = 0.02) as well as sedentary behaviour (SB) at both 14–18 weeks (457.0 vs 300 min/day; p < 0.01) and 29–33 weeks gestation (431.5 vs 300 min/day; p < 0.01). There was poor agreement between the GPAQ and accelerometry for both PA and SB at both time points (ICC: -0.05–0.08). Bland Altman plots indicated that the GPAQ overestimates PA by 14.8 min/day at 14–18 weeks and by 15.8 min/day at 29–33 weeks gestation. It underestimates SB by 127.5 min/day at 14–18 weeks and by 89.2 min/day at 29–33 weeks gestation. When compared to accelerometry, the GPAQ shows poor agreement and appears to overestimate PA and underestimate SB during pregnancy. PMID:28552977

Dual passivation of intrinsic defects at the compound semiconductor/oxide interface using an oxidant and a reductant.

PubMed

Kent, Tyler; Chagarov, Evgeniy; Edmonds, Mary; Droopad, Ravi; Kummel, Andrew C

2015-05-26

Studies have shown that metal oxide semiconductor field-effect transistors fabricated utilizing compound semiconductors as the channel are limited in their electrical performance. This is attributed to imperfections at the semiconductor/oxide interface which cause electronic trap states, resulting in inefficient modulation of the Fermi level. The physical origin of these states is still debated mainly because of the difficulty in assigning a particular electronic state to a specific physical defect. To gain insight into the exact source of the electronic trap states, density functional theory was employed to model the intrinsic physical defects on the InGaAs (2 × 4) surface and to model the effective passivation of these defects by utilizing both an oxidant and a reductant to eliminate metallic bonds and dangling-bond-induced strain at the interface. Scanning tunneling microscopy and spectroscopy were employed to experimentally determine the physical and electronic defects and to verify the effectiveness of dual passivation with an oxidant and a reductant. While subsurface chemisorption of oxidants on compound semiconductor substrates can be detrimental, it has been shown theoretically and experimentally that oxidants are critical to removing metallic defects at oxide/compound semiconductor interfaces present in nanoscale channels, oxides, and other nanostructures.

Phase mismatched optical parametric generation in semiconductor magnetoplasma

NASA Astrophysics Data System (ADS)

Dubey, Swati; Ghosh, S.; Jain, Kamal

2017-05-01

Optical parametric generation involves the interaction of pump, signal, and idler waves satisfying law of conservation of energy. Phase mismatch parameter plays important role for the spatial distribution of the field along the medium. In this paper instead of exactly matching wave vector, a small mismatch is admitted with a degree of phase velocity mismatch between these waves. Hence the medium must possess certain finite coherence length. This wave mixing process is well explained by coupled mode theory and one dimensional hydrodynamic model. Based on this scheme, expressions for threshold pump field and transmitted intensity have been derived. It is observed that the threshold pump intensity and transmitted intensity can be manipulated by varying doping concentration and magnetic field under phase mismatched condition. A compound semiconductor crystal of n-InSb is assumed to be shined at 77 K by a 10.6μm CO2 laser with photon energy well below band gap energy of the crystal, so that only free charge carrier influence the optical properties of the medium for the I.R. parametric generation in a semiconductor plasma medium. Favorable parameters were explored to incite the said process keeping in mind the cost effectiveness and conversion efficiency of the process.

Intracavity double diode structures with GaInP barrier layers for thermophotonic cooling

NASA Astrophysics Data System (ADS)

Tiira, Jonna; Radevici, Ivan; Haggren, Tuomas; Hakkarainen, Teemu; Kivisaari, Pyry; Lyytikäinen, Jari; Aho, Arto; Tukiainen, Antti; Guina, Mircea; Oksanen, Jani

2017-02-01

Optical cooling of semiconductors has recently been demonstrated both for optically pumped CdS nanobelts and for electrically injected GaInAsSb LEDs at very low powers. To enable cooling at larger power and to understand and overcome the main obstacles in optical cooling of conventional semiconductor structures, we study thermophotonic (TPX) heat transport in cavity coupled light emitters. Our structures consist of a double heterojunction (DHJ) LED with a GaAs active layer and a corresponding DHJ or a p-n-homojunction photodiode, enclosed within a single semiconductor cavity to eliminate the light extraction challenges. Our presently studied double diode structures (DDS) use GaInP barriers around the GaAs active layer instead of the AlGaAs barriers used in our previous structures. We characterize our updated double diode structures by four point probe IV- measurements and measure how the material modifications affect the recombination parameters and coupling quantum efficiencies in the structures. The coupling quantum efficiency of the new devices with InGaP barrier layers is found to be approximately 10 % larger than for the structures with AlGaAs barriers at the point of maximum efficiency.

Field induced gap infrared detector

NASA Technical Reports Server (NTRS)

Elliott, C. Thomas (Inventor)

1990-01-01

A tunable infrared detector which employs a vanishing band gap semimetal material provided with an induced band gap by a magnetic field to allow intrinsic semiconductor type infrared detection capabilities is disclosed. The semimetal material may thus operate as a semiconductor type detector with a wavelength sensitivity corresponding to the induced band gap in a preferred embodiment of a diode structure. Preferred semimetal materials include Hg(1-x)Cd(x)Te, x is less than 0.15, HgCdSe, BiSb, alpha-Sn, HgMgTe, HgMnTe, HgZnTe, HgMnSe, HgMgSe, and HgZnSe. The magnetic field induces a band gap in the semimetal material proportional to the strength of the magnetic field allowing tunable detection cutoff wavelengths. For an applied magnetic field from 5 to 10 tesla, the wavelength detection cutoff will be in the range of 20 to 50 micrometers for Hg(1-x)Cd(x)Te alloys with x about 0.15. A similar approach may also be employed to generate infrared energy in a desired band gap and then operating the structure in a light emitting diode or semiconductor laser type of configuration.

Liquid phase epitaxy of binary III–V nanocrystals in thin Si layers triggered by ion implantation and flash lamp annealing

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

Wutzler, Rene, E-mail: r.wutzler@hzdr.de; Rebohle, Lars; Prucnal, Slawomir

2015-05-07

The integration of III–V compound semiconductors in Si is a crucial step towards faster and smaller devices in future technologies. In this work, we investigate the formation process of III–V compound semiconductor nanocrystals, namely, GaAs, GaSb, and InP, by ion implantation and sub-second flash lamp annealing in a SiO{sub 2}/Si/SiO{sub 2} layer stack on Si grown by plasma-enhanced chemical vapor deposition. Raman spectroscopy, Rutherford Backscattering spectrometry, and transmission electron microscopy were performed to identify the structural and optical properties of these structures. Raman spectra of the nanocomposites show typical phonon modes of the compound semiconductors. The formation process of themore » III–V compounds is found to be based on liquid phase epitaxy, and the model is extended to the case of an amorphous matrix without an epitaxial template from a Si substrate. It is shown that the particular segregation and diffusion coefficients of the implanted group-III and group-V ions in molten Si significantly determine the final appearance of the nanostructure and thus their suitability for potential applications.« less

Transforming common III-V/II-VI insulating building blocks into topological heterostructure via the intrinsic electric polarization

NASA Astrophysics Data System (ADS)

Zunger, Alex; Zhang, Xiuwen; Abdalla, Leonardo; Liu, Qihang

Currently known topological insulators (TIs) are limited to narrow gap compounds incorporating heavy elements, thus severely limiting the material pool available for such applications. We show how a heterovalent superlattice made of common semiconductor building blocks can transform its non-TI components into a topological heterostructure. The heterovalent nature of such interfaces sets up, in the absence of interfacial atomic exchange, a natural internal electric field that along with the quantum confinement leads to band inversion, transforming these semiconductors into a topological phase while also forming a giant Rashba spin splitting. We demonstrate this paradigm of designing TIs from ordinary semiconductors via first-principle calculations on III-V/II-VI superlattice InSb/CdTe. We illustrate the relationship between the interfacial stability and the topological transition, finding a ``window of opportunity'' where both conditions can be optimized. This work illustrates the general principles of co-evaluation of TI functionality with thermodynamic stability as a route of identifying realistic combination of common insulators that could produce topological heterostructures. This work was supported by Basic Energy Science, MSE division (Grant DE-FG02-13ER46959).

Infrared emitting device and method

DOEpatents

Kurtz, Steven R.; Biefeld, Robert M.; Dawson, L. Ralph; Howard, Arnold J.; Baucom, Kevin C.

1997-01-01

An infrared emitting device and method. The infrared emitting device comprises a III-V compound semiconductor substrate upon which are grown a quantum-well active region having a plurality of quantum-well layers formed of a ternary alloy comprising InAsSb sandwiched between barrier layers formed of a ternary alloy having a smaller lattice constant and a larger energy bandgap than the quantum-well layers. The quantum-well layers are preferably compressively strained to increase the threshold energy for Auger recombination; and a method is provided for determining the preferred thickness for the quantum-well layers. Embodiments of the present invention are described having at least one cladding layer to increase the optical and carrier confinement in the active region, and to provide for waveguiding of the light generated within the active region. Examples have been set forth showing embodiments of the present invention as surface- and edge-emitting light emitting diodes (LEDs), an optically-pumped semiconductor laser, and an electrically-injected semiconductor diode laser. The light emission from each of the infrared emitting devices of the present invention is in the midwave infrared region of the spectrum from about 2 to 6 microns.

[Risk Factors Associated With School Bullying in Local Authority Schools in Four Municipalities of Valle del Cauca, Colombia. Year 2009].

PubMed

Hernández Carrillo, Mauricio; Gutiérrez Martínez, María Isabel

2013-09-01

To determine the association between family and social relationships and School Bullying (SB) among peers in public education institutions in four municipalities of the department of Valle del Cauca, Colombia, during 2009. A case-control study matched by sex and educational institution was carried out. The study population came from a secondary database provided by the Departof Health Secretaryhealth, which consisted of data gathered in a survey of schoolchildren enrolled in grades 6 to 11. The CISNEROS scale and the Family APGAR test were applied to measure outcome and exposure variables. A conditional logistic regression model was obtained to explain SB. It was found that schoolchildren living with a family where verbal and physical violence prevails, as well as in a hostile neighborhood, are more vulnerable to SB. The probability of being an SB victim is explained by: family dysfunction (OR=2.67; 95%CI, 1.05-6.82), verbal aggression at home (OR=2.81; 95%CI, 1.45-5.46), physical punishing parents (OR=2.53; 95%CI, 1.12-5.75), and neighbors who are physically aggressive to each other (OR=1.87; 95% CI, 1.00-3.56). The study confirmed that reported by Lopez, who suggested that victimization and school rejection in adolescence is related to factors outside the classroom, such as the quality of communication between parents and children. As regards family influence in the SB, Bowes indicates that a positive family atmosphere is significantly associated with the resilience of school victimization. Furthermore, being physically punished by parents generates low self-esteem in the schoolchild that leads to lack of self-protective attitudes to the attacks that occur within the school. Copyright © 2013 Asociación Colombiana de Psiquiatría. Publicado por Elsevier España. All rights reserved.

Association of change in brain structure to objectively measured physical activity and sedentary behavior in older adults: Age, Gene/Environment Susceptibility-Reykjavik Study.

PubMed

Arnardottir, Nanna Yr; Koster, Annemarie; Domelen, Dane R Van; Brychta, Robert J; Caserotti, Paolo; Eiriksdottir, Gudny; Sverrisdottir, Johanna E; Sigurdsson, Sigurdur; Johannsson, Erlingur; Chen, Kong Y; Gudnason, Vilmundur; Harris, Tamara B; Launer, Lenore J; Sveinsson, Thorarinn

2016-01-01

Many studies have examined the hypothesis that greater participation in physical activity (PA) is associated with less brain atrophy. Here we examine, in a sub-sample (n=352, mean age 79.1 years) of the Age, Gene/Environment Susceptibility-Reykjavik Study cohort, the association of the baseline and 5-year change in magnetic resonance imaging (MRI)-derived volumes of gray matter (GM) and white matter (WM) to active and sedentary behavior (SB) measured at the end of the 5-year period by a hip-worn accelerometer for seven consecutive days. More GM (β=0.11; p=0.044) and WM (β=0.11; p=0.030) at baseline was associated with more total physical activity (TPA). Also, when adjusting for baseline values, the 5-year change in GM (β=0.14; p=0.0037) and WM (β=0.11; p=0.030) was associated with TPA. The 5-year change in WM was associated with SB (β=-0.11; p=0.0007). These data suggest that objectively measured PA and SB late in life are associated with current and prior cross-sectional measures of brain atrophy, and that change over time is associated with PA and SB in expected directions. Copyright © 2015 Elsevier B.V. All rights reserved.

Use of global positioning system for physical activity research in youth: ESPAÇOS Adolescentes, Brazil.

PubMed

Alberico, Claudia Oliveira; Schipperijn, Jasper; Reis, Rodrigo S

2017-10-01

The built environment is an important factor associated with physical activity and sedentary behavior (SB) during adolescence. This study presents the methods for objective assessment of context-specific moderate to vigorous physical activity (MVPA) and SB, as well as describes results from the first project using such methodology in adolescents from a developing country. An initial sample of 381 adolescents was recruited from 32 census tracts in Curitiba, Brazil (2013); 80 had their homes geocoded and wore accelerometer and GPS devices for seven days. Four domains were defined as important contexts: home, school, transport and leisure. The majority of participants (n=80) were boys (46; 57.5%), with a normal BMI (52; 65.0%) and a mean age (SD) of 14.5 (5.5) years. Adolescents spent most of their time at home, engaging in SB. Overall, the largest proportion of MVPA was while in transport (17.1% of time spent in this context) and SB while in leisure (188.6min per day). Participants engaged in MVPA for a median of 28.7 (IQR 18.2-43.2) and 17.9 (IQR 9.2-32.1) minutes during week and weekend days, respectively. Participants spent most of their day in the leisure and home domains. The use of Geographic Information System (GIS), Global Positioning System (GPS) and accelerometer data allowed objective identification of the amount of time spent in MVPA and SB in four different domains. Though the combination of objective measures is still an emerging methodology, this is a promising and feasible approach to understanding interactions between people and their environments in developing countries. Copyright © 2017 Elsevier Inc. All rights reserved.

Android Adiposity and Lack of Moderate and Vigorous Physical Activity Are Associated With Insulin Resistance and Diabetes in Aging Adults.

PubMed

Peterson, Mark D; Al Snih, Soham; Serra-Rexach, José A; Burant, Charles

2015-08-01

Physical inactivity and excess adiposity are thought to be interdependent "lifestyle" factors and thus, many older adults are at exaggerated risk for preventable diseases. The purposes of this study were to determine the degree of discordance between body mass index (BMI) and adiposity among adults older than 50 years, and to determine the extent to which direct measures of adiposity, and objectively measured sedentary behavior (SB) and physical activity (PA) are associated with insulin resistance (IR) or diabetes. A population representative sample of 2,816 individuals, aged 50-85 years, was included from the combined 2003-2006 National Health and Nutrition Examination Survey (NHANES) datasets. BMI, percent body fat (%BF) and android adiposity as determined by dual energy x-ray absorptiometry, objectively measured SB and PA, established markers of cardiometabolic risk, IR, and type 2 diabetes were analyzed. Approximately 50% of the men and 64% of the women who were normal weight according to BMI had excessive %BF. Adults with the least SB and greatest moderate and vigorous PA exhibited the healthiest cardiometabolic profiles, whereas adults with the greatest SB and lowest activity had highest risk. Greater android adiposity stores were robustly associated with IR or diabetes in all adults, independent of SB and activity. Among men, less moderate-to-vigorous PA was associated with IR or diabetes; whereas among women, less lifestyle moderate activity was associated with IR or diabetes. Android adiposity and low moderate and vigorous PA are the strongest predictors of IR or diabetes among aging adults. © The Author 2015. Published by Oxford University Press on behalf of The Gerontological Society of America. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

Growth and characterization of AlInAsSb layers lattice-matched to GaSb

NASA Astrophysics Data System (ADS)

Tournet, J.; Rouillard, Y.; Tournié, E.

2017-11-01

We report on the growth by solid-source MBE of random-alloy AlxIn1-xAsySb1-y layers lattice-matched to (0 0 1)-GaSb substrates, with xAl ∈ [0.25; 0.75]. The samples quality and morphology were characterized by X-ray diffraction, Nomarski microscopy and atomic force microscopy. Layers grown at 400 °C demonstrated smooth surfaces and no sign of phase decomposition. Samples with xAl ≤ 0.60 demonstrated photoluminescence (PL) at 300 K whereas samples with higher Al content only demonstrated PL at low temperature. Samples grown at 430 °C, in contrast, exhibited PL at low temperature only, whatever their composition. Inferred bandgap energies corroborate the estimation of a non-null quaternary bowing parameter made by Donati, Kaspi and Malloy in Journal of Applied Physics 94 (2003) 5814. Upon annealing, the PL peak energies increased, getting even closer to the theoretical values. These results are in agreement with recently published results on digital AlInAsSb alloys. Our work, which reports the first evidence for PL emission from random-alloy AlInAsSb layers lattice-matched to GaSb, opens the way to their use in optoelectronic devices.

Associations between objectively-measured sedentary behaviour and physical activity with bone mineral density in adults and older adults, the NHANES study.

PubMed

Chastin, S F M; Mandrichenko, O; Helbostadt, J L; Skelton, D A

2014-07-01

Lack of physical activity (PA) is an important modifiable risk factor for bone mineral density (BMD). Time spent in sedentary behaviour (SB), or time spent in non-exercising seated and reclining postures, has recently emerged as a new public health risk, independent of the amount of time someone spends being active. As national surveys report that adults spend on average 8h per day being sedentary, rising to 10h a day in older age, it has been hypothesised that a repeated exposure to sitting in modern daily life, whether it is for travelling, working or leisure, might have a deleterious effect on bone health in a way that mirrors the results of studies into the effect of lengthy periods of bed-rest. The aim of this study was to investigate for the first time a) how time spent in SB is associated with bone mineral density (BMD), b) whether this association changes depending on the amount of time spent engaging in different intensity levels of PA, and c) if the pattern of accumulation of SB and long uninterrupted periods of SB are associated with BMD. The 2005/2006 National Health and Nutrition Examination Survey (NHANES), is a cross-sectional study of a representative sample of the US population that is conducted biannually by the National Centers for Disease Control. PA and SB were assessed objectively over 7 days using an Actigraph accelerometer and BMD was measured via dual-energy X-ray absorptiometry. In this study, data are presented on four regions of the femur (femoral neck, trochanter, inter trochanter and total femur) and total spine (L1-L4). The associations between BMD, SB and PA levels were examined using multiple linear regressions stratified by gender. In addition, the association between the pattern of accumulation of SB (quantified as frequency and duration of SB) and BMD was also investigated. All models were adjusted for known risk factors associated with BMD. In total, data for 2117 individuals, aged 23-90+years (males N=1158), were available to analyse SB and femur BMD and 1942 individuals (males N=1053) for analysis of SB and spine BMD. There was no evidence of an association between SB time and hip or spinal BMD in men. For men, time spent doing moderate to vigorous activity (MVPA) and vigorous activity (VIG) was associated with higher total femur and the other hip sub-region BMD. The regression coefficient was BMVPA=0.306 (95% CI: 0.021-0.591)g/cm2 for each 10 minute increment in daily MVPA. For VIG, the regression coefficient is BVIG=0.320 (95% CI: 0.058-0.583) but this cannot be interpreted linearly as time spent in vigorous activity was square root transformed. In women, SB was negatively associated with total femur BMD and all sub-regions but not MVPA nor VIG. The regression coefficient for total femur BMD was BSB = -0.159 (95% CI: -0.241-0.076)g/cm2 for each 10 minute increment spent being sedentary each day. In addition, the duration of SB bouts was deleteriously associated with BMD for the total femur and of other hip sub-regions, but the number of bouts of SB did not have a significant effect. These associations were found to be independent of the amount of MVPA and VIG that women engage in. No associations were found between SB or PA and spinal BMD for either men or women. These results provide the first evidence that repeated exposure to sitting (SB), measured objectively in daily life, is deleteriously associated with BMD of the total femur and of all hip sub-regions in women, independent of the amount of time women engage in moderate and vigorous activity. This suggests that SB might be a risk factor for bone health in women independent of whether they engage in physical activity. In addition, the duration of SB bouts, rather than their frequency, appears to be deleteriously associated with BMD of the total femur and of all hip sub-regions. Future research should investigate the effect on bone health of interventions which set out to reduce SB and the duration of SB bouts in comparison, and as adjunct, to the promotion of PA. For men, SB is not significantly associated with BMD of the femur or spine and the results appear to confirm that moderate and vigorous activity has a protective effect. Copyright © 2014 Elsevier Inc. All rights reserved.

Seasonal variation in physical activity, sedentary behaviour and sleep in a sample of UK adults.

PubMed

O'Connell, Sophie E; Griffiths, Paula L; Clemes, Stacy A

2014-01-01

Physical activity (PA), sedentary behaviour (SB), sleep and diet have all been associated with increased risk for chronic disease. Seasonality is often overlooked as a determinant of these behaviours in adults. Currently, no study has simultaneously monitored these behaviours in UK adults to assess seasonal variation. The present study investigated whether PA, SB, sleep and diet differed over season in UK adults. Forty-six adults (72% female; age = 41.7 ± 14.4 years, BMI = 24.9 ± 4.4 kg/m(2)) completed four 7-day monitoring periods; one during each season of the year. The ActiGraph GT1M was used to monitor PA and SB. Daily sleep diaries monitored time spent in bed (TIB) and total sleep time (TST). The European Prospective Investigation of Cancer (EPIC) food frequency questionnaire (FFQ) assessed diet. Repeated measures ANOVAs were used to identify seasonal differences in behaviours. Light-intensity PA was significantly higher in summer and spring (p < 0.001). SB and TIB were significantly higher in winter (p < 0.01). There were no seasonal variations detected in moderate-vigorous PA, TST or diet (p > 0.05). Findings support the concept that health promotion campaigns need to encourage year-round participation in light intensity PA, whilst limiting SB, particularly during the winter months.

Classroom-Based Physical Activity and Sedentary Behavior Interventions in Adolescents: A Systematic Review and Meta-Analysis.

PubMed

McMichan, Lauren; Gibson, Ann-Marie; Rowe, David A

2018-05-01

It is reported that 81% of adolescents are insufficiently active. Schools play a pivotal role in promoting physical activity (PA) and reducing sedentary behavior (SB). The aim of this systematic review and meta-analysis was to evaluate classroom-based PA and SB interventions in adolescents. A search strategy was developed using the Population Intervention Comparison Outcome Study (PICOS) design framework. Articles were screened using strict inclusion criteria. Study quality was assessed using the Effective Public Health Practice Project quality assessment tool ( http://www.ephpp.ca/tools.html ). Outcome data for preintervention and postintervention were extracted, and effect sizes were calculated using Cohen's d. The strategy yielded 7574 potentially relevant articles. Nine studies were included for review. Study quality was rated as strong for 1 study, moderate for 5 studies, and weak for 3 studies. Five studies were included for meta-analyses, which suggested that the classroom-based interventions had a nonsignificant effect on PA (P = .55, d = 0.05) and a small, nonsignificant effect on SB (P = .16, d = -0.11). Only 9 relevant studies were found, and the effectiveness of the classroom-based PA and SB interventions varied. Based on limited empirical studies, there is not enough evidence to determine the most effective classroom-based methodology to increase PA and SB.

Environmental and personal correlates of physical activity and sedentary behavior in African American women: An ecological momentary assessment study.

PubMed

Zenk, Shannon N; Horoi, Irina; Jones, Kelly K; Finnegan, Lorna; Corte, Colleen; Riley, Barth; Wilbur, JoEllen

2017-04-01

The authors of this study examined within-person associations of environmental factors (weather, built and social environmental barriers) and personal factors (daily hassles, affect) with moderate-to-vigorous physical activity (MVPA) and sedentary behavior (SB) in African American women aged 25-64 years living in metropolitan Chicago (n = 97). In 2012-13, for seven days, women wore an accelerometer and were signaled five times per day to complete a survey covering environmental and personal factors on a study-provided smartphone. Day-level measures of each were derived, and mixed regression models were used to test associations. Poor weather was associated with a 27.3% reduction in daily MVPA. Associations between built and social environmental barriers and daily MVPA or SB were generally not statistically significant. Negative affect at the first daily signal was associated with a 38.6% decrease in subsequent daily MVPA and a 33.2-minute increase in subsequent daily SB. Each one-minute increase in MVPA during the day was associated with a 2.2% higher likelihood of positive affect at the end of the day. SB during the day was associated with lower subsequent positive affect. Real-time interventions that address overcoming poor weather and negative affect may help African American women increase MVPA and/or decrease SB.

Understanding children's sedentary behaviour: a qualitative study of the family home environment.

PubMed

Granich, Joanna; Rosenberg, Michael; Knuiman, Matthew; Timperio, Anna

2010-04-01

Electronic media (EM) (television, electronic games and computer) use has been associated with overweight and obesity among children. Little is known about the time spent in sedentary behaviour (SB) among children within the family context. The aim of this study was to explore how the family home environment may influence children's electronic-based SB. Focus groups and family interviews were conducted with 11- to 12-year old children (n = 54) and their parents (n = 38) using a semi-structured discussion guide. Transcripts were analysed using a thematic content approach. A brief self-completed questionnaire was also used to measure leisure behaviour and electronic devices at home. Children incorporated both sedentary and physical activities into their weekly routine. Factors influencing children's EM use included parent and sibling modelling and reinforcement, personal cognitions, the physical home environment and household EM use rules and restrictions. Participants were not concerned about the excessive time children spent with EM. This under-recognition emerged as a personal influencing factor and was viewed as a major barrier to modifying children's electronic-based SB. Efforts to reduce SB in children should focus on the influencing factors that reciprocally interact within the family home. An emphasis on increasing awareness about the risks associated with spending excessive time in screen-based activities should be a priority when developing intervention strategies aimed at modifying the time children spend in SB.

Family satisfaction, pain, and quality-of-life in emerging adults with spina bifida: a longitudinal analysis.

PubMed

Bellin, Melissa H; Dicianno, Brad E; Osteen, Philip; Dosa, Nienke; Aparicio, Elizabeth; Braun, Patricia; Zabel, T Andrew

2013-08-01

This study uses the Life Course Model for Spina Bifida (SB) to advance knowledge of factors associated with change in quality-of-life (QOL) among emerging adults with SB. Forty-eight participants (mean [SD], 22.04 [2.16] yrs) completed self-report questionnaires at two time points, 15 mos apart. Four QOL domains (physical health, psychological, social relationships, and environment) were measured using the World Health Organization QOL-BREF version. SB clinical data were collected via chart reviews. Paired t tests and reliable change indices evaluated group- and individual-level QOL change, respectively. Multiple regression analyses tested the contributions of the Life Course variables in explaining change in QOL over time. No significant group-level differences in the QOL domains were found between time 1 and time 2, but there was substantial individual variation in QOL over time. SB severity was related to a decline only in psychological QOL (B = -0.68, P = 0.02). Increased pain was associated with reduced physical health (B = -0.29, P = 0.049) and psychological (B = -0.29, P = 0.03) QOL at time 2, whereas greater family satisfaction was related to improved QOL in several domains. Clinicians should be aware of the negative impact of pain and the protective influence of family satisfaction on QOL in emerging adults with SB.

Rocksalt nitride metal/semiconductor superlattices: A new class of artificially structured materials

NASA Astrophysics Data System (ADS)

Saha, Bivas; Shakouri, Ali; Sands, Timothy D.

2018-06-01

Artificially structured materials in the form of superlattice heterostructures enable the search for exotic new physics and novel device functionalities, and serve as tools to push the fundamentals of scientific and engineering knowledge. Semiconductor heterostructures are the most celebrated and widely studied artificially structured materials, having led to the development of quantum well lasers, quantum cascade lasers, measurements of the fractional quantum Hall effect, and numerous other scientific concepts and practical device technologies. However, combining metals with semiconductors at the atomic scale to develop metal/semiconductor superlattices and heterostructures has remained a profoundly difficult scientific and engineering challenge. Though the potential applications of metal/semiconductor heterostructures could range from energy conversion to photonic computing to high-temperature electronics, materials challenges primarily had severely limited progress in this pursuit until very recently. In this article, we detail the progress that has taken place over the last decade to overcome the materials engineering challenges to grow high quality epitaxial, nominally single crystalline metal/semiconductor superlattices based on transition metal nitrides (TMN). The epitaxial rocksalt TiN/(Al,Sc)N metamaterials are the first pseudomorphic metal/semiconductor superlattices to the best of our knowledge, and their physical properties promise a new era in superlattice physics and device engineering.

Quantum spin Hall effect and topological phase transition in InN x Bi y Sb1-x-y /InSb quantum wells

NASA Astrophysics Data System (ADS)

Song, Zhigang; Bose, Sumanta; Fan, Weijun; Zhang, Dao Hua; Zhang, Yan Yang; Shen Li, Shu

2017-07-01

Quantum spin Hall (QSH) effect, a fundamentally new quantum state of matter and topological phase transitions are characteristics of a kind of electronic material, popularly referred to as topological insulators (TIs). TIs are similar to ordinary insulator in terms of their bulk bandgap, but have gapless conducting edge-states that are topologically protected. These edge-states are facilitated by the time-reversal symmetry and they are robust against nonmagnetic impurity scattering. Recently, the quest for new materials exhibiting non-trivial topological state of matter has been of great research interest, as TIs find applications in new electronics and spintronics and quantum-computing devices. Here, we propose and demonstrate as a proof-of-concept that QSH effect and topological phase transitions can be realized in {{InN}}x{{Bi}}y{{Sb}}1-x-y/InSb semiconductor quantum wells (QWs). The simultaneous incorporation of nitrogen and bismuth in InSb is instrumental in lowering the bandgap, while inducing opposite kinds of strain to attain a near-lattice-matching conducive for lattice growth. Phase diagram for bandgap shows that as we increase the QW thickness, at a critical thickness, the electronic bandstructure switches from a normal to an inverted type. We confirm that such transition are topological phase transitions between a traditional insulator and a TI exhibiting QSH effect—by demonstrating the topologically protected edge-states using the bandstructure, edge-localized distribution of the wavefunctions and edge-state spin-momentum locking phenomenon, presence of non-zero conductance in spite of the Fermi energy lying in the bandgap window, crossover points of Landau levels in the zero-mode indicating topological band inversion in the absence of any magnetic field and presence of large Rashba spin-splitting, which is essential for spin-manipulation in TIs.

Residual Gas Effects on Detached Solidification in Microgravity

NASA Technical Reports Server (NTRS)

Wilcox, William R.; Regel, Liya L.; Ramakrishnan; Kota, Arun; Anand, Gaurav

2004-01-01

Our long term goal has been to make detached solidification reproducible, which requires a full understanding of the mechanisms underlying it. Our Moving Meniscus Model of steady-state detachment predicts that it depends strongly on the surface tension of the melt and the advancing contact angle with the ampoule wall. Thus, the objective of the current project was to determine the influence of residual gases on the surface tension and contact angle of molten semiconductors on typical ampoule materials. Our focus was on the influence of oxygen on indium antimonide on clean silica ("quartz"). The research was performed by three chemical engineering graduate students, the third of whom will complete his research in the summer of 2005. Originally, we had planned to use a sealed silica cell containing a zirconia electrochemical element to control the oxygen partial pressure. However, zirconia requires an operating temperature above the 530 C melting point of InSb and is difficult to form a gas-tight seal with silica. Thus, we decided instead to flow an oxygen-containing gas through the cell. A special apparatus was designed, built and perfected. A piece of InSb was placed on a horizontal silica plate in a quartz cell. High purity argon, helium or hydrogen-containing gas is passed continuously through the cell while the oxygen concentration in the effluent gas is measured. The shape of the resulting drop was used to determine contact angle and surface tension of Ga-doped and high purity InSb. Oxygen appeared to decrease the contact angle, and definitely did not increase it. The following section gives the background for the research. Section 2 summarizes the results obtained on Ga-doped InSb with relatively high oxygen concentrations. Section 3 describes recent improvements made to the apparatus and methods of analysis. Section 4 gives recent results for high-purity InSb at low oxygen concentrations. Final results will be obtained only this summer (2005). Each section has its own references.

Sedentary behaviour in rheumatoid arthritis: definition, measurement and implications for health.

PubMed

Fenton, Sally A M; Veldhuijzen van Zanten, Jet J C S; Duda, Joan L; Metsios, George S; Kitas, George D

2018-02-01

RA is a chronic autoimmune disease characterized by high grade-inflammation, and associated with elevated cardiovascular risk, rheumatoid-cachexia and functional impairment. Sedentary behaviour (SB) is linked to heightened inflammation, and is highly pervasive in RA, likely as a result of compromised physical function and persistent fatigue. This high sedentarity may exacerbate the inflammatory process in RA, and hold relevance for disease-related outcomes. The aim of this narrative review is to provide an overview of the definition, measurement and health relevance of SB in the context of RA. Contradictions are highlighted with regard to the manner in which SB is operationalized, and the significance of SB for disease outcomes in RA is outlined. The advantages and disadvantages of SB measurement approaches are also discussed. Against this background, we summarize studies that have reported SB and its health correlates in RA, and propose directions for future research. © The Author 2017. Published by Oxford University Press on behalf of the British Society for Rheumatology. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Energetics of the Semiconductor-Electrolyte Interface.

ERIC Educational Resources Information Center

Turner, John A.

1983-01-01

The use of semiconductors as electrodes for electrochemistry requires an understanding of both solid-state physics and electrochemistry, since phenomena associated with both disciplines are seen in semiconductor/electrolyte systems. The interfacial energetics of these systems are discussed. (JN)

Organic semiconductor crystals.

PubMed

Wang, Chengliang; Dong, Huanli; Jiang, Lang; Hu, Wenping

2018-01-22

Organic semiconductors have attracted a lot of attention since the discovery of highly doped conductive polymers, due to the potential application in field-effect transistors (OFETs), light-emitting diodes (OLEDs) and photovoltaic cells (OPVs). Single crystals of organic semiconductors are particularly intriguing because they are free of grain boundaries and have long-range periodic order as well as minimal traps and defects. Hence, organic semiconductor crystals provide a powerful tool for revealing the intrinsic properties, examining the structure-property relationships, demonstrating the important factors for high performance devices and uncovering fundamental physics in organic semiconductors. This review provides a comprehensive overview of the molecular packing, morphology and charge transport features of organic semiconductor crystals, the control of crystallization for achieving high quality crystals and the device physics in the three main applications. We hope that this comprehensive summary can give a clear picture of the state-of-art status and guide future work in this area.

Theoretical study of charge and spin-resolved quantum transport in III-V semiconductor nanostructures

NASA Astrophysics Data System (ADS)

Botha, Andre Erasmus

2003-07-01

This thesis is a theoretical investigation into the spin-resolved transport properties of III-V semiconductor quantum wells. Based on a modified 8 x 8 k · p matrix Hamiltonian, a theory is developed to study the recombination rate in type-II semi metallic quantum wells. The non-parabolicity of the energy band structure and its anisotropy is included via the interband matrix elements and the addition of an anisotropic crystal field potential (parameterized by delta). The effects of externally applied electric and magnetic fields are incorporated into the theory. The electric field is incorporated using a WKB-type approximation. In order to study the anisotropy, the magnetic field is incorporated so that it can be applied at an arbitrary angle theta, with respect to the crystallographic direction c[001]. The case of oblique tunneling (k|| ≠ 0), is also considered. Several interesting results, from calculations of the transmission coefficient, recombination rate, and electron-spin polarization, are presented and discussed for both n-type and p-type single and double quantum wells made from clean InAs and GaSb. For example, in the case of a 150 A wide GaSb/InAs/GaSb quantum well, with B = 4 T, and theta = pi/8, the two maxima in the electron-spin polarization, from the ground and first excited resonant states, are found to be approximately 75%, and 35%, respectively. As theta is varied, a maximum polarization is achieved for a given magnetic field, and this maximum depends on the value of the anisotropy parameter, delta. By using a more sophisticated 14 x 14 band k · p formalism, which explicitly takes into account the coupling between higher bands ( Gc15-Gu 15,Gc1-G u15 , and Gc1-Gc15 ), a theory is developed for the total zero-field spin-splitting and resulting electron-spin polarization in symmetric and asymmetric type-II quantum wells. This theory includes the non-parabolicity, non sphericity, and anisotropy of the energy band structure. The anisotropy in the band structure is introduced via the addition of an anisotropic crystal potential. In the case of an asymmetric GaSb/InAs/GaSb quantum well, it is predicted that the two contributions to the total spin-splitting will be roughly of equal importance. It is also shown that the polarization maxima and minima, for a given resonance state, may not be equal in magnitude. If the resonant state lies close to the forbidden energy gap, the transmission peaks for spin-up and spin-down are skewed. This feature may have potential applications in the design of spintronic filtering and switching devices, in which it is desirable to filter unpolarized electrons (with respect to energy and spin) in order to produce highly polarized, adjustable low-energy beams.

Editorial

NASA Astrophysics Data System (ADS)

Bruzzi, Mara; Cartiglia, Nicolo; Pace, Emanuele; Talamonti, Cinzia

2015-10-01

The 10th edition of the International Conference on Radiation Effects on Semiconductor Materials, Detectors and Devices (RESMDD) was held in Florence, at Dipartimento di Fisica ed Astronomia on October 8-10, 2014. It has been aimed at discussing frontier research activities in several application fields as nuclear and particle physics, astrophysics, medical and solid-state physics. Main topics discussed in this conference concern performance of heavily irradiated silicon detectors, developments required for the luminosity upgrade of the Large Hadron Collider (HL-LHC), ultra-fast silicon detectors design and manufacturing, high-band gap semiconductor detectors, novel semiconductor-based devices for medical applications, radiation damage issues in semiconductors and related radiation-hardening technologies.

Post-hospitalization course and predictive signs of suicidal behavior of suicidal patients admitted to a psychiatric hospital: a 2-year prospective follow-up study

PubMed Central

2012-01-01

Background Suicidal patients admitted to a psychiatric hospital are considered to be at risk of suicidal behavior (SB) and suicide. The present study aimed to seek predictors of SB recurrence of the high-risk patients by examining their post-hospitalization course. Method The design was 2-year prospective follow-up study of patients consecutively admitted with SB to a psychiatric center in Tokyo. The DSM-IV diagnoses and SB-related features of subjects were determined in structured interviews. Subsequently, the subjects underwent a series of follow-up assessments at 6-month intervals. The assessment included inquiries into SB recurrence, its accompanying suicidal intent (SI) and SF-8 health survey. Analyses of serial change over time in the follow-up data and Cox proportional hazards regression analyses of SB recurrence were performed. Results 106 patients participated in this study. The dropout rate during the follow-up was 9%. Within 2 years, incidences of SB as a whole, SB with certain SI (suicide attempt) and suicide were 67% (95% CI 58 - 75%), 38% (95% CI 29 - 47%) and 6% (95% CI 3 - 12%), respectively. Younger age, number of lifetime SBs and maltreatment in the developmental period were predictive of SB as a whole, and younger age and hopelessness prior to index admission were predictive of suicide attempt. Regarding diagnostic variables, anxiety disorders and personality disorders appeared to have predictive value for SB. Additionally, poor physical health assessed during the follow-up was indicated as a possible short-term predictor of SB recurrence. Conclusions This study demonstrated a high incidence of SB and suicide and possible predictors of SB recurrence in the post-hospitalization period of psychiatric suicidal patients. Specialized interventions should be developed to reduce the suicide risk of this patient population. PMID:23114285

Thermoelectric Properties of Cu-doped Bi0.4Sb1.6Te3 Prepared by Hot Extrusion

NASA Astrophysics Data System (ADS)

Jung, Woo-Jin; Kim, Il-Ho

2018-06-01

Cu0.003Bi0.4Sb1.6Te3 alloys were prepared by using encapsulated melting and hot extrusion (HE). The hot-extruded specimens had the relative average density of 98%. The ( 00l) planes were preferentially oriented parallel to the extrusion direction, but the specimens showed low crystallographic anisotropy with low orientation factors. The specimens were hot-extruded at 698 K, and they showed excellent mechanical properties with a Vickers hardness of 76 Hv and a bending strength of 59 MPa. However, as the HE temperature increased, the mechanical properties degraded due to grain growth. The hot-extruded specimens showed positive Seebeck coefficients, indicating that the specimens have p-type conduction. These specimens exhibited negative temperature dependences of electrical conductivity, and thus behaved as degenerate semiconductors. The Seebeck coefficient reached the maximum value at 373 K and then decreased with increasing temperature due to intrinsic conduction. Cu-doped specimens exhibited high power factors due to relatively higher electrical conductivities and Seebeck coefficients than those of undoped specimens. A thermal conductivity of 1.00 Wm-1 K-1 was obtained at 373 K for Cu0.003Bi0.4Sb1.6Te3 hot-extruded at 723 K. A maximum dimensionless figure of merit, ZT max = 1.05, and an average dimensionless figure of merit, ZT ave = 0.98, were achieved at 373 K.

Performance of Ge-Sb-Bi-Te-B Recording Media for Phase-Change Optical Disks

NASA Astrophysics Data System (ADS)

Lee, Chain-Ming; Yen, Wen-Shin; Liu, Ren-Haur; Chin, Tsung-Shune

2001-09-01

We investigated the physical properties of GeSbBiTeB materials and examined the feasibility for phase change recording. The studied compositions were Ge4Sb0.5Bi0.5Te5 and Ge2Sb1.5Bi0.5Te5 with B doping. The coexistence of Bi and B atoms into both Ge4SbTe5 and Ge2Sb2Te5 lattice maintains single fcc structure without phase separation. The Bi substitution shows benefits in decreasing crystallization temperature and activation energy, however the reflectivity is slightly reduced. 3 With small amount addition of boron about 1 at.%, the reflectivity can be increased. 2 Conventional 4-layer structure of digital versatile disk-random access memory (DVD-RAM) 2.6 GB format was used to prepare the disks for dynamic characterization and overwrite cyclability evaluations. The disk with Ge4Sb0.5Bi0.5Te5(B) recording layer shows large noise fluctuation and low overwrite erase ratio, suggesting that the crystallization speed is still insufficient. While the disk with Ge2Sb1.5Bi0.5Te5(B) recording layer shows lower writing and erasing powers, stable noise level and high overwrite erase ratio, indicating the capability for DVD-RAM applications. The effect of B doping was verified to enhance the signal amplitude and modulation.

International Conference on Narrow Gap Semiconductors Held in Southampton, England on 19-23 July 1992. Abstracts Booklet

DTIC Science & Technology

1992-07-01

materials. The calculatedelectronic band structure of Ga,.,lnSb/lnAs superlattices is qualitatively distinct from that of conventional LWIR materials...have grown MCT layers on (I I I)B CdTe and CdZnTe for LWIR applications with uniformity in thickness within 1.5% (largest difference from the mean...at 300K over the same area. For undoped n-type LWIR layers mobilities in the range of 7-10xI04 cm 2/volt.sec and carrier concentrations of 5-10x10 14

Passive mode locking of an in-band-pumped Ho:YLiF4 laser at 2.06 μm.

PubMed

Coluccelli, Nicola; Lagatsky, Alexander; Di Lieto, Alberto; Tonelli, Mauro; Galzerano, Gianluca; Sibbett, Wilson; Laporta, Paolo

2011-08-15

We demonstrate the passive mode-locking operation of an in-band-pumped Ho:YLiF(4) laser at 2.06 μm using a semiconductor saturable absorber mirror based on InGaAsSb quantum wells. A transform-limited pulse train with minimum duration of 1.1 ps and average power of 0.58 W has been obtained at a repetition frequency of 122 MHz. A maximum output power of 1.7 W has been generated with a corresponding pulse duration of 1.9 ps. © 2011 Optical Society of America

Femtosecond (191 fs) NaY(WO4)2 Tm,Ho-codoped laser at 2060 nm.

PubMed

Lagatsky, A A; Han, X; Serrano, M D; Cascales, C; Zaldo, C; Calvez, S; Dawson, M D; Gupta, J A; Brown, C T A; Sibbett, W

2010-09-15

We report, for the first time to our knowledge, femtosecond-pulse operation of a Tm,Ho:NaY(WO(4))(2) laser at around 2060 nm. Transform-limited 191 fs pulses are produced with an average output power of 82 mW at a 144 MHz pulse repetition frequency. Maximum output power of up to 155 mW is generated with a corresponding pulse duration of 258 fs. An ion-implanted InGaAsSb quantum-well-based semiconductor saturable absorber mirror is used for passive mode-locking maintenance.

Physical activity and sedentary behavior in people with major depressive disorder: A systematic review and meta-analysis.

PubMed

Schuch, Felipe; Vancampfort, Davy; Firth, Joseph; Rosenbaum, Simon; Ward, Philip; Reichert, Thaís; Bagatini, Natália Carvalho; Bgeginski, Roberta; Stubbs, Brendon

2017-03-01

Low levels of physical activity (PA) and sedentary behavior (SB) are independent risk factors for cardiovascular disease and premature mortality in people with major depressive disorder (MDD). Investigate levels of PA and SB and their predictors in people with MDD. Electronic databases were searched from inception till 04/2016 for articles measuring PA and SB with a self-report questionnaire (SRQ) or objective measure (e.g. accelerometer) in people with MDD. Random-effects meta-analyses and meta-regression analyses were conducted. Twenty-four eligible studies were identified including 2901 people with MDD (78.4% female, mean age=54 years; range: 21-77 years). People with MDD spent 126.0min (95%CI=91.9-160.1) per day engaging in all types of PA and spent 8.5hours (95%CI=7.51-9.62) during their waking day being sedentary. Compared to controls, people with MDD spent less time in total PA (SMD=-0.25, 95%CI=-0.03 to 0.15) and moderate to vigorous PA (SMD=-0.30, 95%CI=-0.40 to 0.21) and engaged in higher levels of SB (SMD=0.09, 95%CI=0.01-0.18). The proportion of people with MDD not meeting the recommended PA guidelines was 67.8% (n=13 studies), which was higher in studies relying on objective versus self-report measures (85.7% v 62.1%, p=0.04). People with MDD were more likely than controls to not meeting the recommended PA guidelines (OR = 1.50, 95%CI = 1.10–2.10). Heterogeneity was evident in most analyses. Adults with MDD engage in low levels of PA and high levels of SB. PA and SB are independent predictors of mortality, therefore, future lifestyle interventions targeting both the prevention of SB and adoption and maintenance of PA are warranted. Copyright © 2016 Elsevier B.V. All rights reserved.

Operant Conditioning: A Tool for Special Physical Educators in the 1980s.

ERIC Educational Resources Information Center

Dunn, John M.; French, Ron

1982-01-01

The usefulness of operant conditioning for the special physical educator in managing behavior problems is pointed out, and steps to follow in applying operant conditioning techniques are outlined. (SB)

Optical gain tuning within IR region in type-II In0.5Ga0.5As0.8P0.2/GaAs0.5Sb0.5 nano-scale heterostructure under external uniaxial strain

NASA Astrophysics Data System (ADS)

Singh, A. K.; Rathi, Amit; Riyaj, Md.; Bhardwaj, Garima; Alvi, P. A.

2017-11-01

Quaternary and ternary alloy semiconductors offer an extra degree of flexibility in terms of bandgap tuning. Modifications in the wave functions and alterations in optical transitions in quaternary and ternary QW (quantum well) heterostructures due to external uniaxial strain provide valuable insights on the characteristics of the heterostructure. This paper reports the optical gain in strained InGaAsP/GaAsSb type-II QW heterostructure (well width = 20 Å) under external uniaxial strain at room temperature (300 K). The entire heterostructure is supposed to be grown on InP substrate pseudomorphically. Band structure, wave functions, energy dispersion and momentum matrix elements of the heterostructure have been computed. 6 × 6 diagonalised k → ·p → Hamiltonian matrix of the system is evaluated and Luttinger-Kohn model has been applied for the band structure and wavefunction calculations. TE mode optical gain spectrum in the QW-heterostructure under uniaxial strain along [110] is calculated. Optical gain of the heterostructure as a function of 2D carrier density and temperature variation is investigated. The variation of the peak optical gain as a function of As and Sb fractions in InGaAsP as a barrier and GaAsSb as a well respectively is exhibited. For a charge carrier injection of 5 ×1012 /cm2 , the TE optical gain is 3952 cm-1 at room temperature under no external uniaxial strain. Significant increase in TE mode optical gain is observed under high external uniaxial strain (1, 5 and 10 GPa) along [110] within IR (Infrared region) region.

Interface and facet control during Czochralski growth of (111) InSb crystals for cost reduction and yield improvement of IR focal plane array substrates

NASA Astrophysics Data System (ADS)

Gray, Nathan W.; Perez-Rubio, Victor; Bolke, Joseph G.; Alexander, W. B.

2014-10-01

Focal plane arrays (FPAs) made on InSb wafers are the key cost-driving component in IR imaging systems. The electronic and crystallographic properties of the wafer directly determine the imaging device performance. The "facet effect" describes the non-uniform electronic properties of crystals resulting from anisotropic dopant segregation during bulk growth. When the segregation coefficient of dopant impurities changes notably across the melt/solid interface of a growing crystal the result is non-uniform electronic properties across wafers made from these crystals. The effect is more pronounced in InSb crystals grown on the (111) axis compared with other orientations and crystal systems. FPA devices made on these wafers suffer costly yield hits due to inconsistent device response and performance. Historically, InSb crystal growers have grown approximately 9-19 degree off-axis from the (111) to avoid the facet effect and produced wafers with improved uniformity of electronic properties. It has been shown by researchers in the 1960s that control of the facet effect can produce uniform small diameter crystals. In this paper, we share results employing a process that controls the facet effect when growing large diameter crystals from which 4, 5, and 6" wafers can be manufactured. The process change resulted in an increase in wafers yielded per crystal by several times, all with high crystal quality and uniform electronic properties. Since the crystals are grown on the (111) axis, manufacturing (111) oriented wafers is straightforward with standard semiconductor equipment and processes common to the high-volume silicon wafer industry. These benefits result in significant manufacturing cost savings and increased value to our customers.

Development and Production of Array Barrier Detectors at SCD

NASA Astrophysics Data System (ADS)

Klipstein, P. C.; Avnon, E.; Benny, Y.; Berkowicz, E.; Cohen, Y.; Dobromislin, R.; Fraenkel, R.; Gershon, G.; Glozman, A.; Hojman, E.; Ilan, E.; Karni, Y.; Klin, O.; Kodriano, Y.; Krasovitsky, L.; Langof, L.; Lukomsky, I.; Nevo, I.; Nitzani, M.; Pivnik, I.; Rappaport, N.; Rosenberg, O.; Shtrichman, I.; Shkedy, L.; Snapi, N.; Talmor, R.; Tessler, R.; Weiss, E.; Tuito, A.

2017-09-01

XB n or XB p barrier detectors exhibit diffusion-limited dark currents comparable with mercury cadmium telluride Rule-07 and high quantum efficiencies. In 2011, SemiConductor Devices (SCD) introduced "HOT Pelican D", a 640 × 512/15- μm pitch InAsSb/AlSbAs XB n mid-wave infrared (MWIR) detector with a 4.2- μm cut-off and an operating temperature of ˜150 K. Its low power (˜3 W), high pixel operability (>99.5%) and long mean time to failure make HOT Pelican D a highly reliable integrated detector-cooler product with a low size, weight and power. More recently, "HOT Hercules" was launched with a 1280 × 1024/15- μm format and similar advantages. A 3-megapixel, 10- μm pitch version ("HOT Blackbird") is currently completing development. For long-wave infrared applications, SCD's 640 × 512/15- μm pitch "Pelican-D LW" XB p type II superlattice (T2SL) detector has a ˜9.3- μm cut-off wavelength. The detector contains InAs/GaSb and InAs/AlSb T2SLs, and is fabricated into focal plane array (FPA) detectors using standard production processes including hybridization to a digital silicon read-out integrated circuit (ROIC), glue underfill and substrate thinning. The ROIC has been designed so that the complete detector closely follows the interfaces of SCD's MWIR Pelican-D detector family. The Pelican-D LW FPA has a quantum efficiency of ˜50%, and operates at 77 K with a pixel operability of >99% and noise equivalent temperature difference of 13 mK at 30 Hz and F/2.7.

Sex-specific genetic effects in physical activity: results from a quantitative genetic analysis.

PubMed

Diego, Vincent P; de Chaves, Raquel Nichele; Blangero, John; de Souza, Michele Caroline; Santos, Daniel; Gomes, Thayse Natacha; dos Santos, Fernanda Karina; Garganta, Rui; Katzmarzyk, Peter T; Maia, José A R

2015-08-01

The objective of this study is to present a model to estimate sex-specific genetic effects on physical activity (PA) levels and sedentary behaviour (SB) using three generation families. The sample consisted of 100 families covering three generations from Portugal. PA and SB were assessed via the International Physical Activity Questionnaire short form (IPAQ-SF). Sex-specific effects were assessed by genotype-by-sex interaction (GSI) models and sex-specific heritabilities. GSI effects and heterogeneity were tested in the residual environmental variance. SPSS 17 and SOLAR v. 4.1 were used in all computations. The genetic component for PA and SB domains varied from low to moderate (11% to 46%), when analyzing both genders combined. We found GSI effects for vigorous PA (p = 0.02) and time spent watching television (WT) (p < 0.001) that showed significantly higher additive genetic variance estimates in males. The heterogeneity in the residual environmental variance was significant for moderate PA (p = 0.02), vigorous PA (p = 0.006) and total PA (p = 0.001). Sex-specific heritability estimates were significantly higher in males only for WT, with a male-to-female difference in heritability of 42.5 (95% confidence interval: 6.4, 70.4). Low to moderate genetic effects on PA and SB traits were found. Results from the GSI model show that there are sex-specific effects in two phenotypes, VPA and WT with a stronger genetic influence in males.

Band alignment measurements at heterojunction interfaces in layered thin film solar cells & thermoelectrics

NASA Astrophysics Data System (ADS)

Fang, Fang

2011-12-01

Public awareness of the increasing energy crisis and the related serious environmental concerns has led to a significantly growing demand for alternative clean and renewable energy resources. Thin film are widely applied in multiple renewable energy devices owing to the reduced amount of raw materials and increase flexibility of choosing from low-cost candidates, which translates directly into reduced capital cost. This is a key driving force to make renewable technology competitive in the energy market. This thesis is focused on the measurement of energy level alignments at interfaces of thin film structures for renewable energy applications. There are two primary foci: II -VI semiconductor ZnSe/ZnTe thin film solar cells and Bi2Te3/Sb2Te3 thin film structures for thermoelectric applications. In both cases, the electronic structure and energy band alignment at interfaces usually controls the carrier transport behavior and determines the quality of the device. High-resolution photoemission spectroscopy (lab-based XPS & synchrotron-based UPS) was used to investigate the chemical and electronic properties of epitaxial Bi2Te3 and Sb2Te3 thin films, in order to validate the anticipated band alignment at interfaces in Bi 2Te3/Sb2Te3 superlattices as one favoring electron-transmission. A simple, thorough two-step treatment of a chemical etching in dilute hydrochloric acid solution and a subsequent annealing at ˜150°C under ultra-high vacuum environment is established to remove the surface oxides completely. It is an essential step to ensure the measurements on electronic states are acquired on stoichimetric, oxide-free clean surface of Bi 2Te3 and Sb2Te3 films. The direct measurement of valence band offsets (VBO) at a real Sb 2Te3/Bi2Te3 interface is designed based on the Kraut model; a special stacking film structure is prepared intentionally: sufficiently thin Sb2Te3 film on top of Bi2Te 3 that photoelectrons from both of them are collected simultaneously. From a combination of core levels and valence band ultraviolet photoemission spectra of the bulk materials as well as the heterojunction (Sb2Te 3/Bi2Te3), the VBO at p-type Sb2Te 3 and n-type Bi2Te3 is determined as 0.04 +/- 0.10 eV. Such a small energy offset is within the same magnitude of the thermal energy of kT, at room temperature. The motivation for the II-VI ZnTe-based thin film solar cell derives from the need to identify and overcome performance-limiting properties related to the processing of film deposition using close space sublimation (CSS). Chemical and electronic properties of the CSS grown ZnTe/ZnSe films were studied in x-ray diffraction, scanning electron microscopy and photoemission spectroscopy. Specifically, Se oxide was observed on the ZnSe surface, the removal of this oxide generated apparent offsets in the valence band and hence the alignment at the heterojunction energy diagram. Processing steps to mitigate oxidation yielded the best cells. Film structure was studied on the dependence of growth time; physical film damage is found during the initial stages when depositing ZnTe on a grown ZnSe film. Preliminary studies of films grown by evaporation and their characterizations are presented at last. In this thesis, a better understanding of the electronic structure at interfaces is built in two different thin film devices, and the resulting band energy diagram of the corresponding devices offered effective feedback in materials and device.The problem of energy equilibrium in the human body has received a great deal.

Changes in microstructure and physical properties of skutterudites after severe plastic deformation.

PubMed

Rogl, Gerda; Grytsiv, Andriy; Bursik, Jiri; Horky, Jelena; Anbalagan, Ramakrishnan; Bauer, Ernst; Mallik, Ramesh Chandra; Rogl, Peter; Zehetbauer, Michael

2015-02-07

The best p-type skutterudites with ZT > 1.1 so far are didymium (DD) filled, Fe/Co substituted, Sb-based skutterudites. DD0.68Fe3CoSb12 was prepared using an annealing-reacting-melting-quenching technique followed by ball milling and hot pressing. After severe plastic deformation via high-pressure torsion (HPT), no phase changes but particular structural variations were achieved, leading to modified transport properties with higher ZT values. Although after measurement-induced heating some of the HPT induced defects were annealed out, a still attractive ZT-value was preserved. In this paper we focus on explanations for these changes via TEM investigations, Raman spectroscopy and texture measurements. The grain sizes and dislocation densities, evaluated from TEM images, showed that (i) the majority of cracks generated during high-pressure torsion are healed during annealing, leaving only small pores, that (ii) the grains have grown, and that (iii) the dislocation density is decreased. While Raman spectra indicate that after HPT processing and annealing the vibration modes related to the shorter Sb-Sb bonds in the Sb4 rings are more affected than those related to the longer Sb-Sb bonds, almost no visible changes were observed in the pole intensity and/or orientation.

Optical and Electrical Characterization of Single Semiconductor Nanowires

NASA Astrophysics Data System (ADS)

Wickramasuriya, Nadeeka Thejanie

Strain distribution in the core and the shell of a semiconductor nanowire (NW) and its effect on band structures including carrier recombination dynamics of individual Wurtzite (WZ) In1- xGxAs/InP and Zincblende (ZB) GaAs1-xSbx/InP strained core-shell NWs are investigated using room temperature Raman scattering and transient Rayleigh scattering (TRS) optical spectroscopy techniques. In addition, the electrical transport properties of individual ZB InP NWs are explored using gate-dependent current-voltage (I-V) measurements. Micro-Raman scattering from individual In1-xGaxAs NWs show InAs like TO and GaAs like TO modes with frequencies which are consistent with the 35% Ga concentration determined from the growth parameters. Calculations showed that the In0.65Ga0.35As core is under compressive strain of 0.26% while the InP shell is in tensile strain of 0.42% in In 0.65Ga0.35As/InP NWs. TRS measurements of single NWs show clear evidence for a strong band resonance in the WZ In0.65Ga 0.35As NW at 0.819 eV which is estimated to be a 186 meV blue-shift with respect to bulk ZB In0.65Ga0.35As. Furthermore, both Raman scattering and TRS measurements are on excellent agreement with the band gap shift of In0.65Ga0.35As/InP core-shell NWs with respect to the core only NW by 46 48 meV which experimentally confirmed the InP shell induced compression of the core. The time decays of the resonance are observed to be long ( 125 ps) for core-shell NWs while it is short ( 31 ps) for core only NWs consistent with a larger nonradiative recombination rate. Optical phonon modes of GaAs1-xSbx are observed to be red-shifted with increasing Antimony fraction in GaAs1-xSb x NWs which can be expected in an alloy with increasing concentration of a heavier atom in the lattice. Using TRS measurements, the GaAs0.71 Sb0.29 band gap for the coreshell NW is observed to be reduced by 0.04 eV with respect to the core only NW because of the tensile strain in the core. Raman experiments show a blue-shift of the InP phonons and a redshift of the GaAs1-xSbx phonons in individual GaAs 0.71Sb0.29/InP NWs, which is consistent with the tensile core strain inferred from TRS results. The recombination life times in GaAs 0.71Sb0.29, GaAs0.71Sb0.29/InP NWs are found to be 31 ps and 127 ps respectively reflecting the effectiveness of the InP shell surface passivation. Individual InP NW field effect transistors are fabricated using photolithography to investigate the electrical transport properties of InP NWs. Gate-dependent I-V plots showed that the InP NWs are n-type and displayed typical non-Ohmic behavior due to the contact resistance between NW and metal electrodes. Carrier mobility determined for the InP NWs is as high as 655 cm2/(V.s) for the carrier density of 4.08 x 1017 cm-3 which is comparable to n-type InP thin film materials with similar carrier densities and thus demonstrates the high quality of the NWs. An equivalent circuit model of the metal-semiconductor-metal structure is used to extract the carrier density and mobility of the NW as 1.00 x 1017 cm -3 and 511 cm2/(V.s), This model makes it possible to determine the barrier heights of the NW device while providing a good agreement with the experimental results.

Phonon induced magnetism in ionic materials

NASA Astrophysics Data System (ADS)

Restrepo, Oscar D.; Antolin, Nikolas; Jin, Hyungyu; Heremans, Joseph P.; Windl, Wolfgang

2014-03-01

Thermoelectric phenomena in magnetic materials create exciting possibilities in future spin caloritronic devices by manipulating spin information using heat. An accurate understanding of the spin-lattice interactions, i.e. the coupling between magnetic excitations (magnons) and lattice vibrations (phonons), holds the key to unraveling their underlying physics. We report ab initio frozen-phonon calculations of CsI that result in non-zero magnetization when the degeneracy between spin-up and spin-down electronic density of states is lifted for certain phonon displacement patterns. For those, the magnetization as a function of atomic displacement shows a sharp resonance due to the electronic states on the displaced Cs atoms, while the electrons on indium form a continuous background magnetization. We relate this resonance to the generation of a two-level system in the spin-polarized Cs partial density of states as a function of displacement, which we propose to be described by a simple resonant-susceptibility model. Current work extends these investigations to semiconductors such as InSb. ODR and WW are supported by the Center for Emergent Materials, an NSF MRSEC at OSU (Grant DMR-0820414).HJ and JPH are supported by AFOSR MURI Cryogenic Peltier Cooling, Contract #FA9550-10-1-0533.

From lattice Hamiltonians to tunable band structures by lithographic design

NASA Astrophysics Data System (ADS)

Tadjine, Athmane; Allan, Guy; Delerue, Christophe

2016-08-01

Recently, new materials exhibiting exotic band structures characterized by Dirac cones, nontrivial flat bands, and band crossing points have been proposed on the basis of effective two-dimensional lattice Hamiltonians. Here, we show using atomistic tight-binding calculations that these theoretical predictions could be experimentally realized in the conduction band of superlattices nanolithographed in III-V and II-VI semiconductor ultrathin films. The lithographed patterns consist of periodic lattices of etched cylindrical holes that form potential barriers for the electrons in the quantum well. In the case of honeycomb lattices, the conduction minibands of the resulting artificial graphene host several Dirac cones and nontrivial flat bands. Similar features, but organized in different ways, in energy or in k -space are found in kagome, distorted honeycomb, and Lieb superlattices. Dirac cones extending over tens of meV could be obtained in superlattices with reasonable sizes of the lithographic patterns, for instance in InAs/AlSb heterostructures. Bilayer artificial graphene could be also realized by lithography of a double quantum-well heterostructure. These new materials should be interesting for the experimental exploration of Dirac-based quantum systems, for both fundamental and applied physics.

KIDS OUT! Protocol of a brief school-based intervention to promote physical activity and to reduce screen time in a sub-cohort of Finnish eighth graders.

PubMed

Jussila, Anne-Mari; Vasankari, Tommi; Paronen, Olavi; Sievänen, Harri; Tokola, Kari; Vähä-Ypyä, Henri; Broberg, Anna; Aittasalo, Minna

2015-07-10

Adolescents' physical activity (PA) is decreasing and sedentary behavior (SB) increasing alarmingly. Insufficient PA and excessive SB are both related to various health risks indicating that interventions to promote adolescents' PA and to reduce their SB are needed. Schools have a great potential to reach most adolescents, and in Finland health education (HE) as stand-alone subject provides an excellent platform for health promotion. This paper describes the protocol and evaluation (RE-AIM) of an intervention developed for three HE lessons to increase PA and reduce SB during leisure among 8(th) graders. All city-owned secondary schools in Tampere (n = 14) were invited to the study and were randomized in pairs to intervention (n = 7) and comparison group (n = 7). A specific content on PA and SB based on Health Action Process Approach model was integrated into routinely scheduled three HE lessons with the help of educational material: SoftGIS-questionnaire followed by feedback views on adolescents' current PA and SB, FeetEnergy-homework leaflet for adolescents, FeetEnergy-video in YouTube, FeetEnergy-poster for classroom and FeetEnergy-leaflet for parents. In the comparison group standard HE lessons were held. The primary indicators of Effectiveness are changes in PA and SB and in their psychosocial factors as well as in parental interference with PA and SB. The measurement points are baseline, 4 weeks after the intervention and 7 months from baseline, the last indicating also the measurement point for individual level Maintenance. The measures are accelerometers, 7-day activity diaries and questionnaires. The evaluation of Reach, Adoption and Implementation is based on the data collected during the intervention. Maintenance at organizational level is assessed two years after the intervention with a questionnaire to the HE teachers. The intervention was implemented in 2012 and the last measurements to assess organizational Maintenance were conducted in the end of 2014. A detailed description of the protocol and evaluation is provided to enable replication and better understanding of the findings, which will be reported in 2015. The findings will add our current knowledge about the feasibility and effectiveness of integrating simple structured elements into the HE lessons to increase PA and reduce SB in adolescents. NCT01633918 (June 27th, 2012).

Electrolysis of a molten semiconductor

DOE PAGES

Yin, Huayi; Chung, Brice; Sadoway, Donald R.

2016-08-24

Metals cannot be extracted by electrolysis of transition-metal sulfides because as liquids they are semiconductors, which exhibit high levels of electronic conduction and metal dissolution. Herein by introduction of a distinct secondary electrolyte, we reveal a high-throughput electro-desulfurization process that directly converts semiconducting molten stibnite (Sb 2S 3) into pure (99.9%) liquid antimony and sulfur vapour. At the bottom of the cell liquid antimony pools beneath cathodically polarized molten stibnite. At the top of the cell sulfur issues from a carbon anode immersed in an immiscible secondary molten salt electrolyte disposed above molten stibnite, thereby blocking electronic shorting across themore » cell. In conclusion, as opposed to conventional extraction practices, direct sulfide electrolysis completely avoids generation of problematic fugitive emissions (CO 2, CO and SO 2), significantly reduces energy consumption, increases productivity in a single-step process (lower capital and operating costs) and is broadly applicable to a host of electronically conductive transition-metal chalcogenides.« less