Application of positron annihilation lifetime technique to the study of deep level transients in semiconductors

NASA Astrophysics Data System (ADS)

Deng, A. H.; Shan, Y. Y.; Fung, S.; Beling, C. D.

2002-03-01

Unlike its conventional applications in lattice defect characterization, positron annihilation lifetime technique was applied to study temperature-dependent deep level transients in semiconductors. Defect levels in the band gap can be determined as they are determined by conventional deep level transient spectroscopy (DLTS) studies. The promising advantage of this application of positron annihilation over the conventional DLTS is that it could further extract extra microstructure information of deep-level defects, such as whether a deep level defect is vacancy related or not. A demonstration of EL2 defect level transient study in GaAs was shown and the EL2 level of 0.82±0.02 eV was obtained by a standard Arrhenius analysis, similar to that in conventional DLTS studies.

Impact of strain on electronic defects in (Mg,Zn)O thin films

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

Schmidt, Florian, E-mail: fschmidt@physik.uni-leipzig.de; Müller, Stefan; Wenckstern, Holger von

2014-09-14

We have investigated the impact of strain on the incorporation and the properties of extended and point defects in (Mg,Zn)O thin films by means of photoluminescence, X-ray diffraction, deep-level transient spectroscopy (DLTS), and deep-level optical spectroscopy. The recombination line Y₂, previously detected in ZnO thin films grown on an Al-doped ZnO buffer layer and attributed to tensile strain, was exclusively found in (Mg,Zn)O samples being under tensile strain and is absent in relaxed or compressively strained thin films. Furthermore a structural defect E3´ can be detected via DLTS measurements and is only incorporated in tensile strained samples. Finally it ismore » shown that the omnipresent deep-level E3 in ZnO can only be optically recharged in relaxed ZnO samples.« less

Deep levels in as-grown and electron-irradiated n-type GaN studied by deep level transient spectroscopy and minority carrier transient spectroscopy

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

Duc, Tran Thien; School of Engineering Physics, Hanoi University of Science and Technology, 1 Dai Co Viet Road, Hanoi; Pozina, Galia

2016-03-07

Development of high performance GaN-based devices is strongly dependent on the possibility to control and understand defects in material. Important information about deep level defects is obtained by deep level transient spectroscopy and minority carrier transient spectroscopy on as-grown and electron irradiated n-type bulk GaN with low threading dislocation density produced by halide vapor phase epitaxy. One hole trap labelled H1 (E{sub V} + 0.34 eV) has been detected on as-grown GaN sample. After 2 MeV electron irradiation, the concentration of H1 increases and at fluences higher than 5 × 10{sup 14 }cm{sup −2}, a second hole trap labelled H2 is observed. Simultaneously, the concentration of twomore » electron traps, labelled T1 (E{sub C} – 0.12 eV) and T2 (E{sub C} – 0.23 eV), increases. By studying the increase of the defect concentration versus electron irradiation fluence, the introduction rate of T1 and T2 using 2 MeV- electrons was determined to be 7 × 10{sup −3 }cm{sup −1} and 0.9 cm{sup −1}, respectively. Due to the low introduction rate of T1, it is suggested that the defect is associated with a complex. The high introduction rate of trap H1 and T2 suggests that the defects are associated with primary intrinsic defects or complexes. Some deep levels previously observed in irradiated GaN layers with higher threading dislocation densities are not detected in present investigation. It is therefore suggested that the absent traps may be related to primary defects segregated around dislocations.« less

Bond-center hydrogen in dilute Si1-xGex alloys: Laplace deep-level transient spectroscopy

NASA Astrophysics Data System (ADS)

Bonde Nielsen, K.; Dobaczewski, L.; Peaker, A. R.; Abrosimov, N. V.

2003-07-01

We apply Laplace deep-level transient spectroscopy in situ after low-temperature proton implantation into dilute Si1-xGex alloys and identify the deep donor state of hydrogen occupying a strained Si-Si bond-center site next to Ge. The activation energy of the electron emission from the donor is ˜158 meV when extrapolated to zero electrical field. We construct a configuration diagram of the Ge-strained site from formation and annealing data and deduce that alloying with ˜1% Ge does not significantly influence the low-temperature migration of hydrogen as compared to elemental Si. We observe two bond-center-type carbon-hydrogen centers and conclude that carbon impurities act as much stronger traps for hydrogen than the alloy Ge atoms.

High-accuracy deep-UV Ramsey-comb spectroscopy in krypton

NASA Astrophysics Data System (ADS)

Galtier, Sandrine; Altmann, Robert K.; Dreissen, Laura S.; Eikema, Kjeld S. E.

2017-01-01

In this paper, we present a detailed account of the first precision Ramsey-comb spectroscopy in the deep UV. We excite krypton in an atomic beam using pairs of frequency-comb laser pulses that have been amplified to the millijoule level and upconverted through frequency doubling in BBO crystals. The resulting phase-coherent deep-UV pulses at 212.55 nm are used in the Ramsey-comb method to excite the two-photon 4p^6 → 4p^5 5p [1/2 ]_0 transition. For the {}^{84}Kr isotope, we find a transition frequency of 2829833101679(103) kHz. The fractional accuracy of 3.7 × 10^{-11} is 34 times better than previous measurements, and also the isotope shifts are measured with improved accuracy. This demonstration shows the potential of Ramsey-comb excitation for precision spectroscopy at short wavelengths.

Deep levels in as-grown and Si-implanted In(0.2)Ga(0.8)As-GaAs strained-layer superlattice optical guiding structures

NASA Technical Reports Server (NTRS)

Dhar, S.; Das, U.; Bhattacharya, P. K.

1986-01-01

Trap levels in about 2-micron In(0.2)Ga(0.8)As(94 A)/GaAs(25 A) strained-layer superlattices, suitable for optical waveguides, have been identified and characterized by deep-level transient spectroscopy and optical deep-level transient spectroscopy measurements. Several dominant electron and hole traps with concentrations of approximately 10 to the 14th/cu cm, and thermal ionization energies Delta-E(T) varying from 0.20 to 0.75 eV have been detected. Except for a 0.20-eV electron trap, which might be present in the In(0.2)Ga(0.8)As well regions, all the other traps have characteristics similar to those identified in molecular-beam epitaxial GaAs. Of these, a 0.42-eV hole trap is believed to originate from Cu impurities, and the others are probably related to native defects. Upon Si implantation and halogen lamp annealing, new deep centers are created. These are electron traps with Delta-E(T) = 0.81 eV and hole traps with Delta-E(T) = 0.46 eV. Traps occurring at room temperature may present limitations for optical devices.

Deep level transient spectroscopic investigation of phosphorus-doped silicon by self-assembled molecular monolayers.

PubMed

Gao, Xuejiao; Guan, Bin; Mesli, Abdelmadjid; Chen, Kaixiang; Dan, Yaping

2018-01-09

It is known that self-assembled molecular monolayer doping technique has the advantages of forming ultra-shallow junctions and introducing minimal defects in semiconductors. In this paper, we report however the formation of carbon-related defects in the molecular monolayer-doped silicon as detected by deep-level transient spectroscopy and low-temperature Hall measurements. The molecular monolayer doping process is performed by modifying silicon substrate with phosphorus-containing molecules and annealing at high temperature. The subsequent rapid thermal annealing drives phosphorus dopants along with carbon contaminants into the silicon substrate, resulting in a dramatic decrease of sheet resistance for the intrinsic silicon substrate. Low-temperature Hall measurements and secondary ion mass spectrometry indicate that phosphorus is the only electrically active dopant after the molecular monolayer doping. However, during this process, at least 20% of the phosphorus dopants are electrically deactivated. The deep-level transient spectroscopy shows that carbon-related defects are responsible for such deactivation.

Quenched-in defects in flashlamp-annealed silicon

NASA Technical Reports Server (NTRS)

Borenstein, J. T.; Jones, J. T.; Corbett, J. W.; Oehrlein, G. S.; Kleinhenz, R. L.

1986-01-01

Deep levels introduced in boron-doped silicon by heat-pulse annealing with a tungsten-halogen flashlamp are investigated using deep-level transient spectroscopy. Two majority-carrier trapping levels in the band gap, at Ev + 0.32 eV and at Ev + 0.45 eV, are observed. These results are compared to those obtained by furnace-quenching and laser-annealing studies. Both the position in the gap and the annealing kinetics of the hole trap at Ev + 0.45 eV suggest that this center is due to an interstitial iron impurity in the lattice. The deep levels are not consistently observed in all flashlamp-annealed Si crystals utilized.

Processing-Induced Electrically Active Defects in Black Silicon Nanowire Devices.

PubMed

Carapezzi, Stefania; Castaldini, Antonio; Mancarella, Fulvio; Poggi, Antonella; Cavallini, Anna

2016-04-27

Silicon nanowires (Si NWs) are widely investigated nowadays for implementation in advanced energy conversion and storage devices, as well as many other possible applications. Black silicon (BSi)-NWs are dry etched NWs that merge the advantages related to low-dimensionality with the special industrial appeal connected to deep reactive ion etching (RIE). In fact, RIE is a well established technique in microelectronics manufacturing. However, RIE processing could affect the electrical properties of BSi-NWs by introducing deep states into their forbidden gap. This work applies deep level transient spectroscopy (DLTS) to identify electrically active deep levels and the associated defects in dry etched Si NW arrays. Besides, the successful fitting of DLTS spectra of BSi-NWs-based Schottky barrier diodes is an experimental confirmation that the same theoretical framework of dynamic electronic behavior of deep levels applies in bulk as well as in low dimensional structures like NWs, when quantum confinement conditions do not occur. This has been validated for deep levels associated with simple pointlike defects as well as for deep levels associated with defects with richer structures, whose dynamic electronic behavior implies a more complex picture.

Identification of the spatial location of deep trap states in AlGaN/GaN heterostructures by surface photovoltage spectroscopy

NASA Astrophysics Data System (ADS)

Jana, Dipankar; Porwal, S.; Sharma, T. K.

2017-12-01

Spatial and spectral origin of deep level defects in molecular beam epitaxy grown AlGaN/GaN heterostructures are investigated by using surface photovoltage spectroscopy (SPS) and pump-probe SPS techniques. A deep trap center ∼1 eV above the valence band is observed in SPS measurements which is correlated with the yellow luminescence feature in GaN. Capture of electrons and holes is resolved by performing temperature dependent SPS and pump-probe SPS measurements. It is found that the deep trap states are distributed throughout the sample while their dominance in SPS spectra depends on the density, occupation probability of deep trap states and the background electron density of GaN channel layer. Dynamics of deep trap states associated with GaN channel layer is investigated by performing frequency dependent photoluminescence (PL) and SPS measurements. A time constant of few millisecond is estimated for the deep defects which might limit the dynamic performance of AlGaN/GaN based devices.

Structure of the Global Nanoscience and Nanotechnology Research Literature

DTIC Science & Technology

2006-01-01

Transistors, Nature, 424 (6949): 654-657, 2003. Joannopoulos, JD, Meade, RD, Winn, JN, Photonic Crystals: Molding the Flow of Light, Princeton...1.27 Force Microscopy 40 0.10 0.00 Electron Spectroscopy 40 0.10 0.00 Rutherford backscattering spectrometry 38 0.10 0.00 flow cytometry 36 0.09...Backscattering Spectroscopy/Spectrometry • Flow Cytometry • Spectrophotometry (UV-Visible) • Deep Level Transient Spectroscopy • Inductively

The effects of illumination on deep levels observed in as-grown and low-energy electron irradiated high-purity semi-insulating 4H-SiC

NASA Astrophysics Data System (ADS)

Alfieri, G.; Knoll, L.; Kranz, L.; Sundaramoorthy, V.

2018-05-01

High-purity semi-insulating 4H-SiC can find a variety of applications, ranging from power electronics to quantum computing applications. However, data on the electronic properties of deep levels in this material are scarce. For this reason, we present a deep level transient spectroscopy study on HPSI 4H-SiC substrates, both as-grown and irradiated with low-energy electrons (to displace only C-atoms). Our investigation reveals the presence of four deep levels with activation energies in the 0.4-0.9 eV range. The concentrations of three of these levels increase by at least one order of magnitude after irradiation. Furthermore, we analyzed the behavior of these traps under sub- and above-band gap illumination. The nature of the traps is discussed in the light of the present data and results reported in the literature.

Capacitance Techniques | Photovoltaic Research | NREL

Science.gov Websites

transient spectroscopy generated graph showing six defect levels; DLTS signal (Y-axis) versus Temperature (X -axis). DLTS characterizes defect levels to assist in identification of impurities and potential levels of interface states (or both) that often exist between the surfaces of dissimilar materials. Deep

Cryogenic Laser Calorimetry for Impurity Analysis

NASA Technical Reports Server (NTRS)

Swimm, R. T.

1985-01-01

The results of a one-year effort to determine the applicability of laser-calorimetric spectroscopy to the study of deep-level impurities in silicon are presented. Critical considerations for impurity analysis by laser-calorimetric spectroscopy are discussed, the design and performance of a cryogenic laser calorimeter is described, and measurements of background absorption in high-purity silicon are presented.

Electrical characterisation of SiGe heterojunction bipolar transistors and Si pseudo-HBTS

NASA Astrophysics Data System (ADS)

De Barros, O.; Le Tron, B.; Woods, R. C.; Giroult-Matlakowski, G.; Vincent, G.; Brémond, G.

1996-08-01

This paper reports an electrical characterisation of the emitter-base junction of Si pseudo-HBTs and SiGe HBTs fabricated in a CMOS compatible single polysilicon self-aligned process. From the reverse characteristics it appears that the definition of the emitter-base junction by plasma etching induces peripheral defects that increase the base current of the transistors. Deep level transient spectroscopy measurements show a deep level in the case of SiGe base, whose spatial origin is not fully determinate up to now.

Defects with deep levels in a semiconductor structure of a photoelectric converter of solar energy with an antireflection film of porous silicon

NASA Astrophysics Data System (ADS)

Tregulov, V. V.; Litvinov, V. G.; Ermachikhin, A. V.

2017-11-01

Defects in a semiconductor structure of a photoelectric converter of solar energy based on a p-n junction with an antireflection film of porous silicon on the front surface have been studied by current deeplevel transient spectroscopy. An explanation of the influence of thickness of a porous-silicon film formed by electrochemical etching on the character of transformation of defects with deep levels and efficiency of solarenergy conversion is proposed.

Minority Carrier Electron Traps in CZTSSe Solar Cells Characterized by DLTS and DLOS

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

Kheraj, V.; Lund, E. A.; Caruso, A. E.

2016-11-21

We report observations of minority carrier interactions with deep levels in 6-8% efficient Cu2ZnSn(S, Se)4 (CZTSSe) devices using conventional and minority deep level transient spectroscopy (DLTS) and deep level optical spectroscopy (DLOS). Directly observing defect interactions with minority carriers is critical to understanding the recombination impact of deep levels. In devices with Cu2ZnSn(S, Se)4 nanoparticle ink absorber layers we identify a mid-gap state capturing and emitting minority electrons. It is 590+/-50 meV from the conduction band mobility edge, has a concentration near 1015/cm3, and has an apparent electron capture cross section ~10-14 cm2. We conclude that, while energetically positioned nearly-ideallymore » to be a recombination center, these defects instead act as electron traps because of a smaller hole cross-section. In CZTSe devices produced using coevaporation, we used minority carrier DLTS on traditional samples as well as ones with transparent Ohmic back contacts. These experiments demonstrate methods for unambiguously probing minority carrier/defect interactions in solar cells in order to establish direct links between defect energy level observations and minority carrier lifetimes. Furthermore, we demonstrate the use of steady-state device simulation to aid in the interpretation of DLTS results e.g. to put bounds on the complimentary carrier cross section even in the absence its direct measurement. This combined experimental and theoretical approach establishes rigorous bounds on the impact on carrier lifetime and Voc of defects observed with DLTS as opposed to, for example, assuming that all deep states act as strong recombination centers.« less

HgCdTe Surface and Defect Study Program.

DTIC Science & Technology

1984-07-01

double layer heterojunction (DLHJ) devices. There are however many complications on this once we consider implanted junctions, LWIR devices or even the...It is not possible from this measurement to discriminate between real interface states and charge nonuniformities . Admittance spectroscopy (discussed...earlier) and deep level transient spectroscopy (DLTS) are not usually affected by these nonuniformities due to their observation of a speci- fic

Iron and intrinsic deep level states in Ga2O3

NASA Astrophysics Data System (ADS)

Ingebrigtsen, M. E.; Varley, J. B.; Kuznetsov, A. Yu.; Svensson, B. G.; Alfieri, G.; Mihaila, A.; Badstübner, U.; Vines, L.

2018-01-01

Using a combination of deep level transient spectroscopy, secondary ion mass spectrometry, proton irradiation, and hybrid functional calculations, we identify two similar deep levels that are associated with Fe impurities and intrinsic defects in bulk crystals and molecular beam epitaxy and hydride vapor phase epitaxi-grown epilayers of β-Ga2O3. First, our results indicate that FeGa, and not an intrinsic defect, acts as the deep acceptor responsible for the often dominating E2 level at ˜0.78 eV below the conduction band minimum. Second, by provoking additional intrinsic defect generation via proton irradiation, we identified the emergence of a new level, labeled as E2*, having the ionization energy very close to that of E2, but exhibiting an order of magnitude larger capture cross section. Importantly, the properties of E2* are found to be consistent with its intrinsic origin. As such, contradictory opinions of a long standing literature debate on either extrinsic or intrinsic origin of the deep acceptor in question converge accounting for possible contributions from E2 and E2* in different experimental conditions.

Impact of the silicon substrate resistivity and growth condition on the deep levels in Ni-Au/AlN/Si MIS Capacitors

NASA Astrophysics Data System (ADS)

Wang, Chong; Simoen, Eddy; Zhao, Ming; Li, Wei

2017-10-01

Deep levels formed under different growth conditions of a 200 nm AlN buffer layer on B-doped Czochralski Si(111) substrates with different resistivity were investigated by deep-level transient spectroscopy (DLTS) on metal-insulator-semiconductor capacitors. Growth-temperature-dependent Al diffusion in the Si substrate was derived from the free carrier density obtained by capacitance-voltage measurement on samples grown on p- substrates. The DLTS spectra revealed a high concentration of point and extended defects in the p- and p+ silicon substrates, respectively. This indicated a difference in the electrically active defects in the silicon substrate close to the AlN/Si interface, depending on the B doping concentration.

Traps in AlGaN /GaN/SiC heterostructures studied by deep level transient spectroscopy

NASA Astrophysics Data System (ADS)

Fang, Z.-Q.; Look, D. C.; Kim, D. H.; Adesida, I.

2005-10-01

AlGaN /GaN/SiC Schottky barrier diodes (SBDs), with and without Si3N4 passivation, have been characterized by temperature-dependent current-voltage and capacitance-voltage measurements, and deep level transient spectroscopy (DLTS). A dominant trap A1, with activation energy of 1.0 eV and apparent capture cross section of 2×10-12cm2, has been observed in both unpassivated and passivated SBDs. Based on the well-known logarithmic dependence of DLTS peak height with filling pulse width for a line-defect related trap, A1, which is commonly observed in thin GaN layers grown by various techniques, is believed to be associated with threading dislocations. At high temperatures, the DLTS signal sometimes becomes negative, likely due to an artificial surface-state effect.

Donors, Acceptors, and Traps in AlGaN and AlGaN/GaN Epitaxial Layers

DTIC Science & Technology

2006-07-31

the background. 3.3 Positron annihilation spectroscopy (PAS): acceptor-type defects Positrons injected into defect-free GaN are annihilated by electrons...electron concentration n, and the average Ga-vacancy VGa concentration deduced from positron annihilation spectroscopy . 0.09 3.47 3.46 - 3.45 •ŗ.47225...of this paper, are often investigated by deep level transient spectroscopy (DLTS), and the usual analysis of DLTS data is based on the assumption that

Deep-level transient spectroscopy of Pd-H complexes in silicon

NASA Astrophysics Data System (ADS)

Sachse, J.-U.; Weber, J.; Lemke, H.

2000-01-01

The interaction of atomic hydrogen with substitutional palladium impurities is studied in n- and p-type Si by deep-level transient spectroscopy. After wet-chemical etching, we determine seven different electrically active and at least one passive palladium hydrogen complex. The levels belong to Pd complexes with different number of hydrogen atoms. The PdH1 complex exhibits one level E(200) at EC-0.43 eV. PdH2 has two levels E(60) at EC-0.10 eV and H(280) at EV+0.55 eV. Four levels are assigned to the PdH3 complex E(160) at EC-0.29 eV, H(140) at EV+0.23 eV, H(55) at EV+0.08 eV, and H(45) at EV+0.07 eV. An electrically passive complex is associated with a PdH4 complex. There is great similarity with the correspondent complexes in Pt-doped Si. Annealing above 650 K destroys all hydrogen related complexes and restores the original substitutional Pd concentration.

Identification of oxygen-related midgap level in GaAs

NASA Technical Reports Server (NTRS)

Lagowski, J.; Lin, D. G.; Gatos, H. C.; Aoyama, T.

1984-01-01

An oxygen-related deep level ELO was identified in GaAs employing Bridgman-grown crystals with controlled oxygen doping. The activation energy of ELO is almost the same as that of the dominant midgap level: EL2. This fact impedes the identification of ELO by standard deep level transient spectroscopy. However, it was found that the electron capture cross section of ELO is about four times greater than that of EL2. This characteristic served as the basis for the separation and quantitative investigation of ELO employing detailed capacitance transient measurements in conjunction with reference measurements on crystals grown without oxygen doping and containing only EL2.

Semiconductor technology program. Progress briefs

NASA Technical Reports Server (NTRS)

Bullis, W. M.

1980-01-01

Measurement technology for semiconductor materials, process control, and devices is reviewed. Activities include: optical linewidth and thermal resistance measurements; device modeling; dopant density profiles; resonance ionization spectroscopy; and deep level measurements. Standardized oxide charge terminology is also described.

Optical transitions of the silicon vacancy in 6H-SiC studied by positron annihilation spectroscopy

NASA Astrophysics Data System (ADS)

Arpiainen, S.; Saarinen, K.; Hautojärvi, P.; Henry, L.; Barthe, M.-F.; Corbel, C.

2002-08-01

Positron annihilation spectroscopy has been applied to identify Si and C vacancies as irradiation-induced defects in 6H-SiC. Si vacancies are shown to have ionization levels at EC-0.6 eV and EC-1.1 eV below the conduction-band edge EC by detecting changes of positron trapping under monochromatic illumination. These levels are attributed to (2-/1-) and (1-/0) ionizations of the isolated Si vacancy. In as-grown n-type 6H-SiC, a native defect complex involving VSi is shown to have an ionization level slightly closer to conduction band at roughly EC-0.3 eV. These results are used further to present microscopic interpretations to effects seen in optical-absorption spectra and to electrical levels observed previously by deep-level transient spectroscopy.

Deep levels in H-irradiated GaAs1-xNx (x < 0.01) grown by molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Shafi, M.; Mari, R. H.; Khatab, A.; Henini, M.; Polimeni, A.; Capizzi, M.; Hopkinson, M.

2011-12-01

Dilute nitride GaAs1-xNx layers have been grown by molecular beam epitaxy with nitrogen concentration ranging from 0.2% to 0.8%. These samples have been studied before and after hydrogen irradiation by using standard deep level transient spectroscopy (DLTS) and high resolution Laplace DLTS techniques. The activation energy, capture cross section and density of the electron traps have been estimated and compared with results obtained in N-free as-grown and H-irradiated bulk GaAs.

Crystal growth of device quality GaAs in space

NASA Technical Reports Server (NTRS)

Gatos, H. C.; Lagowski, J.

1980-01-01

The apparatus and techniques used in effort to determine the relationships between crystal growth and electronic properties are described with emphasis on electroepitaxy and melt-grown gallium aresenide crystal. Applications of deep level transient spectroscopy, derivative photocapitance spectroscopy, and SEM-cathodoluminescene in characterizing wide bandgap semiconductors; determining photoionization in MOS, Schottky barriers, and p-n junctions; and for identifying inhomogeneities are examined, as well as the compensation of indium phosphide.

Electrical characterization and comparison of CIGS solar cells made with different structures and fabrication techniques

DOE PAGES

Garris, Rebekah L.; Johnston, Steven; Li, Jian V.; ...

2017-08-31

In a previous study, we reported on Cu(In,Ga)Se2-based (CIGS) solar cell samples collected from different research laboratories and industrial companies with the purpose of understanding the range of CIGS materials that can lead to high-quality and high-efficiency solar panels. Here, we report on electrical measurements of those same samples. Electron-beam induced current and time-resolved photoluminescence (TRPL) gave insights about the collection probability and the lifetime of carriers generated in each absorber. Capacitance and drive-level capacitance profiling revealed nonuniformity in carrier-density profiles. Admittance spectroscopy revealed small activation energies (= 0.03 eV) indicative of the inversion strength, larger activation energies (> 0.1more » eV) reflective of thermal activation of absorber conductivity and a deeper defect level. Deep-level transient spectroscopy (DLTS) probed deep hole-trapping defects and showed that all samples in this study had a majority-carrier defect with activation energy between 0.3 eV and 0.9 eV. Optical-DLTS revealed deep electron-trapping defects in several of the CIGS samples. This work focused on revealing similarities and differences between high-quality CIGS solar cells made with various structures and fabrication techniques.« less

Electrical characterization and comparison of CIGS solar cells made with different structures and fabrication techniques

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

Garris, Rebekah L.; Johnston, Steven; Li, Jian V.

In a previous study, we reported on Cu(In,Ga)Se2-based (CIGS) solar cell samples collected from different research laboratories and industrial companies with the purpose of understanding the range of CIGS materials that can lead to high-quality and high-efficiency solar panels. Here, we report on electrical measurements of those same samples. Electron-beam induced current and time-resolved photoluminescence (TRPL) gave insights about the collection probability and the lifetime of carriers generated in each absorber. Capacitance and drive-level capacitance profiling revealed nonuniformity in carrier-density profiles. Admittance spectroscopy revealed small activation energies (= 0.03 eV) indicative of the inversion strength, larger activation energies (> 0.1more » eV) reflective of thermal activation of absorber conductivity and a deeper defect level. Deep-level transient spectroscopy (DLTS) probed deep hole-trapping defects and showed that all samples in this study had a majority-carrier defect with activation energy between 0.3 eV and 0.9 eV. Optical-DLTS revealed deep electron-trapping defects in several of the CIGS samples. This work focused on revealing similarities and differences between high-quality CIGS solar cells made with various structures and fabrication techniques.« less

Subgap time of flight: A spectroscopic study of deep levels in semi-insulating CdTe:Cl

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

Pousset, J.; Farella, I.; Cola, A., E-mail: adriano.cola@le.imm.cnr.it

2016-03-14

We report on a study of deep levels in semi-insulating CdTe:Cl by means of a time-of-flight spectral approach. By varying the wavelength of a pulsed optical source within the CdTe energy gap, transitions to/from localized levels generate free carriers which are analysed through the induced photocurrent transients. Both acceptor-like centers, related to the A-center, and a midgap level, 0.725 eV from the valence band, have been detected. The midgap level is close to the Fermi level and is possibly a recombination center responsible for the compensation mechanism. When the irradiance is varied, either linear or quadratic dependence of the electron andmore » hole collected charge are observed, depending on the dominant optical transitions. The analysis discloses the potentiality of such a novel approach exploitable in the field of photorefractive materials as well as for deep levels spectroscopy.« less

Deep level defects in Ge-doped (010) β-Ga2O3 layers grown by plasma-assisted molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Farzana, Esmat; Ahmadi, Elaheh; Speck, James S.; Arehart, Aaron R.; Ringel, Steven A.

2018-04-01

Deep level defects were characterized in Ge-doped (010) β-Ga2O3 layers grown by plasma-assisted molecular beam epitaxy (PAMBE) using deep level optical spectroscopy (DLOS) and deep level transient (thermal) spectroscopy (DLTS) applied to Ni/β-Ga2O3:Ge (010) Schottky diodes that displayed Schottky barrier heights of 1.50 eV. DLOS revealed states at EC - 2.00 eV, EC - 3.25 eV, and EC - 4.37 eV with concentrations on the order of 1016 cm-3, and a lower concentration level at EC - 1.27 eV. In contrast to these states within the middle and lower parts of the bandgap probed by DLOS, DLTS measurements revealed much lower concentrations of states within the upper bandgap region at EC - 0.1 - 0.2 eV and EC - 0.98 eV. There was no evidence of the commonly observed trap state at ˜EC - 0.82 eV that has been reported to dominate the DLTS spectrum in substrate materials synthesized by melt-based growth methods such as edge defined film fed growth (EFG) and Czochralski methods [Zhang et al., Appl. Phys. Lett. 108, 052105 (2016) and Irmscher et al., J. Appl. Phys. 110, 063720 (2011)]. This strong sensitivity of defect incorporation on crystal growth method and conditions is unsurprising, which for PAMBE-grown β-Ga2O3:Ge manifests as a relatively "clean" upper part of the bandgap. However, the states at ˜EC - 0.98 eV, EC - 2.00 eV, and EC - 4.37 eV are reminiscent of similar findings from these earlier results on EFG-grown materials, suggesting that possible common sources might also be present irrespective of growth method.

Surface photovoltage spectroscopy applied to gallium arsenide surfaces

NASA Technical Reports Server (NTRS)

Bynik, C. E.

1975-01-01

The experimental and theoretical basis for surface photovoltage spectroscopy is outlined. Results of this technique applied to gallium arsenide surfaces, are reviewed and discussed. The results suggest that in gallium arsenide the surface voltage may be due to deep bulk impurity acceptor states that are pinned at the Fermi level at the surface. Establishment of the validity of this model will indicate the direction to proceed to increase the efficiency of gallium arsenide solar cells.

Low-temperature anneal of the divacancy in p-type silicon: A transformation from V2 to VxOy complexes?

NASA Astrophysics Data System (ADS)

Trauwaert, M.-A.; Vanhellemont, J.; Maes, H. E.; Van Bavel, A.-M.; Langouche, G.; Clauws, P.

1995-05-01

Deep level transient spectroscopy of electron irradiated p-type silicon reveals a defect level at Ev+0.19 eV, which during anneal treatments at 200 °C gradually transforms into a band with Ev+0.24 eV. Both energy levels however, are reported in literature to be the donor level of the divacancy. In the present study it is proposed that during the low-temperature anneal the divacancy interacts with oxygen, forming a V2O complex. During heat treatments at temperatures in the range between 250 and 450 °C a further shift of the deep level to higher energy positions is observed which might be related with other vacancy-oxygen complexes.

Inversion of Qubit Energy Levels in Qubit-Oscillator Circuits in the Deep-Strong-Coupling Regime.

PubMed

Yoshihara, F; Fuse, T; Ao, Z; Ashhab, S; Kakuyanagi, K; Saito, S; Aoki, T; Koshino, K; Semba, K

2018-05-04

We report on experimentally measured light shifts of superconducting flux qubits deep-strongly coupled to LC oscillators, where the coupling constants are comparable to the qubit and oscillator resonance frequencies. By using two-tone spectroscopy, the energies of the six lowest levels of each circuit are determined. We find huge Lamb shifts that exceed 90% of the bare qubit frequencies and inversions of the qubits' ground and excited states when there are a finite number of photons in the oscillator. Our experimental results agree with theoretical predictions based on the quantum Rabi model.

Inversion of Qubit Energy Levels in Qubit-Oscillator Circuits in the Deep-Strong-Coupling Regime

NASA Astrophysics Data System (ADS)

Yoshihara, F.; Fuse, T.; Ao, Z.; Ashhab, S.; Kakuyanagi, K.; Saito, S.; Aoki, T.; Koshino, K.; Semba, K.

2018-05-01

We report on experimentally measured light shifts of superconducting flux qubits deep-strongly coupled to L C oscillators, where the coupling constants are comparable to the qubit and oscillator resonance frequencies. By using two-tone spectroscopy, the energies of the six lowest levels of each circuit are determined. We find huge Lamb shifts that exceed 90% of the bare qubit frequencies and inversions of the qubits' ground and excited states when there are a finite number of photons in the oscillator. Our experimental results agree with theoretical predictions based on the quantum Rabi model.

Proton irradiation effects on deep level states in Mg-doped p-type GaN grown by ammonia-based molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Zhang, Z.; Arehart, A. R.; Kyle, E. C. H.; Chen, J.; Zhang, E. X.; Fleetwood, D. M.; Schrimpf, R. D.; Speck, J. S.; Ringel, S. A.

2015-01-01

The impact of proton irradiation on the deep level states throughout the Mg-doped p-type GaN bandgap is investigated using deep level transient and optical spectroscopies. Exposure to 1.8 MeV protons of 1 × 1013 cm-2 and 3 × 1013 cm-2 fluences not only introduces a trap with an EV + 1.02 eV activation energy but also brings monotonic increases in concentration for as-grown deep states at EV + 0.48 eV, EV + 2.42 eV, EV + 3.00 eV, and EV + 3.28 eV. The non-uniform sensitivities for individual states suggest different physical sources and/or defect generation mechanisms. Comparing with prior theoretical calculations reveals that several traps are consistent with associations to nitrogen vacancy, nitrogen interstitial, and gallium vacancy origins, and thus are likely generated through displacing nitrogen and gallium atoms from the crystal lattice in proton irradiation environment.

A first-principles study of carbon-related energy levels in GaN. I. Complexes formed by substitutional/interstitial carbons and gallium/nitrogen vacancies

NASA Astrophysics Data System (ADS)

Matsubara, Masahiko; Bellotti, Enrico

2017-05-01

Various forms of carbon based complexes in GaN are studied with first-principles calculations employing Heyd-Scuseria-Ernzerhof hybrid functionals within the framework of the density functional theory. We consider carbon complexes made of the combinations of single impurities, i.e., CN-CGa, CI-CN , and CI-CGa , where CN, CGa , and CI denote C substituting nitrogen, C substituting gallium, and interstitial C, respectively, and of neighboring gallium/nitrogen vacancies ( VGa / VN ), i.e., CN-VGa and CGa-VN . Formation energies are computed for all these configurations with different charge states after full geometry optimizations. From our calculated formation energies, thermodynamic transition levels are evaluated, which are related to the thermal activation energies observed in experimental techniques such as deep level transient spectroscopy. Furthermore, the lattice relaxation energies (Franck-Condon shift) are computed to obtain optical activation energies, which are observed in experimental techniques such as deep level optical spectroscopy. We compare our calculated values of activation energies with the energies of experimentally observed C-related trap levels and identify the physical origins of these traps, which were unknown before.

Electrical characterisation of defects in wide bandgap semiconductors

NASA Astrophysics Data System (ADS)

Elsherif, Osama S.

Defects usually have a very large influence on the semiconductor material properties and hence on fabricated electronic devices. The nature and properties of defects in semiconducting materials can be investigated by applying electrical characterization techniques such as thermal admittance spectroscopy (TAS), deep level transient spectroscopy (DLTS) and high resolution Laplace-DLTS measurements. This dissertation presents the electrical characterisation of two different wide bandgap semiconducting materials (polycrystalline diamond and GaN) which have both recently attracted a great deal of attention because of their potential applications in the fields of power electronics and optoelectronics. Raman spectroscopy, I-V and C-V measurements were carried out as supporting experiments for the above investigations. The first part of this work focuses on studying the effect of B concentration on the electronic states in polycrystalline diamond thin films grown on silicon by the hot filament chemical vapour deposition method. A combination of high-resolution LDLTS and direct-capture cross-section measurements was used to investigate whether the deep electronic states present in the layers originated from point or extended defects. There was good agreement between data on deep electronic levels obtained from DLTS and TAS experiments. A number of hole traps have been detected; the majority of these levels show an unusual dependence of the DLTS signal on the fill pulse duration which is interpreted as possibly the levels are part of extended defects within the grain boundaries. In contrast, a defect level found in a more highly doped film, with an activation energy of -0.37 eV, exhibited behaviour characteristic of an isolated point defect, which we attribute to B-related centres in the bulk diamond, away from the dislocations. The second part of this thesis presents electrical measurements carried out at temperatures up to 450 K in order to study the electronic states associated with Mg in Mg-doped GaN films grown on sapphire by metalorganic vapour phase epitaxy, and to determine how these are affected by the threading dislocation density (TDD). Two different buffer layer schemes between the film and the sapphire substrate were used, giving rise to different TDDs in the GaN. Admittance spectroscopy of the films finds a single impurity-related acceptor level. It is observed in theses experiments that admittance spectroscopy detects no traps that can be attributed to extended defects, despite the fact that the dislocations are well-known to be active recombination centres. This unexpected finding is discussed in detail.

Electrical characterisation of defects in wide bandgap semiconductors

NASA Astrophysics Data System (ADS)

Elsherif, Osama S.

Defects usually have a very large influence on the semiconductor material properties and hence on fabricated electronic devices. The nature and properties of defects in semiconducting materials can be investigated by applying electrical characterization techniques such as thermal admittance spectroscopy (TAS), deep level transient spectroscopy (DLTS) and high resolution Laplace-DLTS measurements. This dissertation presents the electrical characterisation of two different wide bandgap semiconducting materials (polycrystalline diamond and GaN) which have both recently attracted a great deal of attention because of their potential applications in the fields of power electronics and optoelectronics. Raman spectroscopy, I-V and C-V measurements were carried out as supporting experiments for the above investigations.The first part of this work focuses on studying the effect of B concentration on the electronic states in polycrystalline diamond thin films grown on silicon by the hot filament chemical vapour deposition method. A combination of high-resolution LDLTS and direct-capture cross-section measurements was used to investigate whether the deep electronic states present in the layers originated from point or extended defects. There was good agreement between data on deep electronic levels obtained from DLTS and TAS experiments. A number of hole traps have been detected; the majority of these levels show an unusual dependence of the DLTS signal on the fill pulse duration which is interpreted as possibly the levels are part of extended defects within the grain boundaries. In contrast, a defect level found in a more highly doped film, with an activation energy of -0.37 eV, exhibited behaviour characteristic of an isolated point defect, which we attribute to B-related centres in the bulk diamond, away from the dislocations.The second part of this thesis presents electrical measurements carried out at temperatures up to 450 K in order to study the electronic states associated with Mg in Mg-doped GaN films grown on sapphire by metalorganic vapour phase epitaxy, and to determine how these are affected by the threading dislocation density (TDD). Two different buffer layer schemes between the film and the sapphire substrate were used, giving rise to different TDDs in the GaN. Admittance spectroscopy of the films finds a single impurity-related acceptor level. It is observed in theses experiments that admittance spectroscopy detects no traps that can be attributed to extended defects, despite the fact that the dislocations are well-known to be active recombination centres. This unexpected finding is discussed in detail.

Influence of surface pre-treatment on the electronic levels in silicon MaWCE nanowires.

PubMed

Venturi, Giulia; Castaldini, Antonio; Schleusener, Alexander; Sivakov, Vladimir; Cavallini, Anna

2015-05-15

Deep level transient spectroscopy (DLTS) was performed on n-doped silicon nanowires grown by metal-assisted wet chemical etching (MaWCE) with gold as the catalyst in order to investigate the energetic scheme inside the bandgap. To observe the possible dependence of the level scheme on the processing temperature, DLTS measurements were performed on the nanowires grown on a non-treated Au/Si surface and on a thermally pre-treated Au/Si surface. A noticeable modification of the configuration of the energy levels was observed, induced by the annealing process. Based on our results on these MaWCE nanowires and on literature data about deep levels in bulk silicon, some hypotheses were advanced regarding the identification of the defects responsible of the energy levels revealed.

Energy Levels of Defects Created in Silicon Supersaturated with Transition Metals

NASA Astrophysics Data System (ADS)

García, H.; Castán, H.; Dueñas, S.; García-Hemme, E.; García-Hernansaz, R.; Montero, D.; González-Díaz, G.

2018-03-01

Intermediate-band semiconductors have attracted much attention for use in silicon-based solar cells and infrared detectors. In this work, n-Si substrates have been implanted with very high doses (1013 cm-2 and 1014 cm-2) of vanadium, which gives rise to a supersaturated layer inside the semiconductor. However, the Mott limit was not exceeded. The energy levels created in the supersaturated silicon were studied in detail by means of thermal admittance spectroscopy. We found a single deep center at energy near E C - 200 meV. This value agrees with one of the levels found for vanadium in silicon. The capture cross-section values of the deep levels were also calculated, and we found a relationship between the capture cross-section and the energy position of the deep levels which follows the Meyer-Neldel rule. This process usually appears in processes involving multiple excitations. The Meyer-Neldel energy values agree with those previously obtained for silicon supersaturated with titanium and for silicon contaminated with iron.

Deep Ultraviolet Laser Diode for UV-Resonance Enhanced Raman Identification of Biological Agents

DTIC Science & Technology

2007-03-31

Advanced Research Projects Agency (DOD) ( Controlling DARPA Office) ARPA Order Q51 1/00 Issued by U.S. Army Aviation and Missile Command Under Contract No...documented in a wide range of books, research papers and monographs well described in McCreery14. Raman spectroscopy offers a non -contact method of...magnitude non -linear increase in intensity. High levels of chemical specificity can be obtained using Raman spectroscopy without sample preparation, contact

Anomalous photoluminescence in InP1−xBix

PubMed Central

Wu, Xiaoyan; Chen, Xiren; Pan, Wenwu; Wang, Peng; Zhang, Liyao; Li, Yaoyao; Wang, Hailong; Wang, Kai; Shao, Jun; Wang, Shumin

2016-01-01

Low temperature photoluminescence (PL) from InP1−xBix thin films with Bi concentrations in the 0–2.49% range reveals anomalous spectral features with strong and very broad (linewidth of 700 nm) PL signals compared to other bismide alloys. Multiple transitions are observed and their energy levels are found much smaller than the band-gap measured from absorption measurements. These transitions are related to deep levels confirmed by deep level transient spectroscopy, which effectively trap free holes and enhance radiative recombination. The broad luminescence feature is beneficial for making super-luminescence diodes, which can theoretically enhance spatial resolution beyond 1 μm in optical coherent tomography (OCT). PMID:27291823

Spectroscopic Chemical Analysis Methods and Apparatus

NASA Technical Reports Server (NTRS)

Hug, William F. (Inventor); Lane, Arthur L. (Inventor); Bhartia, Rohit (Inventor); Reid, Ray D. (Inventor)

2017-01-01

Spectroscopic chemical analysis methods and apparatus are disclosed which employ deep ultraviolet (e.g. in the 200 nm to 300 nm spectral range) electron beam pumped wide bandgap semiconductor lasers, incoherent wide bandgap semiconductor light emitting devices, and hollow cathode metal ion lasers to perform non-contact, non-invasive detection of unknown chemical analytes. These deep ultraviolet sources enable dramatic size, weight and power consumption reductions of chemical analysis instruments. In some embodiments, Raman spectroscopic detection methods and apparatus use ultra-narrow-band angle tuning filters, acousto-optic tuning filters, and temperature tuned filters to enable ultra-miniature analyzers for chemical identification. In some embodiments Raman analysis is conducted along with photoluminescence spectroscopy (i.e. fluorescence and/or phosphorescence spectroscopy) to provide high levels of sensitivity and specificity in the same instrument.

Spectroscopic Chemical Analysis Methods and Apparatus

NASA Technical Reports Server (NTRS)

Hug, William F. (Inventor); Lane, Arthur L. (Inventor); Reid, Ray D. (Inventor); Bhartia, Rohit (Inventor)

2018-01-01

Spectroscopic chemical analysis methods and apparatus are disclosed which employ deep ultraviolet (e.g. in the 200 nm to 300 nm spectral range) electron beam pumped wide bandgap semiconductor lasers, incoherent wide bandgap semiconductor light emitting devices, and hollow cathode metal ion lasers to perform non-contact, non-invasive detection of unknown chemical analytes. These deep ultraviolet sources enable dramatic size, weight and power consumption reductions of chemical analysis instruments. In some embodiments, Raman spectroscopic detection methods and apparatus use ultra-narrow-band angle tuning filters, acousto-optic tuning filters, and temperature tuned filters to enable ultra-miniature analyzers for chemical identification. In some embodiments Raman analysis is conducted along with photoluminescence spectroscopy (i.e. fluorescence and/or phosphorescence spectroscopy) to provide high levels of sensitivity and specificity in the same instrument.

Reduced thalamic N-acetylaspartate in idiopathic normal pressure hydrocephalus: a controlled 1H-magnetic resonance spectroscopy study of frontal deep white matter and the thalamus using absolute quantification.

PubMed

Lundin, F; Tisell, A; Dahlqvist Leinhard, O; Tullberg, M; Wikkelsö, C; Lundberg, P; Leijon, G

2011-07-01

Patients with idiopathic normal pressure hydrocephalus (INPH) frequently have a reduction in cerebral blood flow in the subcortical frontal lobe/basal ganglia/thalamic areas. With magnetic resonance spectroscopy, the metabolism in the brain can be examined. The aim of this study was to investigate if there was a compromised metabolism in the thalamus and in the subcortical frontal areas in INPH patients. This was done by measuring total creatine, myo-inositol, total choline, N-acetylaspartate (NAA), total N-acetylaspartate (tNA), glutamate and lactate levels. A comparison was made with healthy individuals (HI). 16 patients (nine males, seven females, mean age 74 years, range 49-83) diagnosed as INPH and 15 HI (nine males, six females, mean age 74 years, range 62-89) were examined. (1)H magnetic resonance spectroscopy (1.5 T, point-resolved spectroscopy, echo time/relaxation time 30/3000 ms, volume of interest 2.5-3 ml) was performed in frontal deep white matter and in the thalamus. Absolute quantification with internal water as a reference was used. INPH patients had lower NAA (p=0.02) and lower tNA (p=0.05) concentrations in the thalamus compared with HI. NAA and tNA in the frontal deep white matter did not differ between patients and HI. The absolute metabolic concentrations of total creatine, myo-inositol total choline, tNA, lactate and Cr ratios in frontal deep white matter and in the thalamus were similar in INPH patients and HI. Reduced thalamic NAA and tNA in INPH patients suggest a compromised metabolic neuronal function in these regions. Thus, the thalamus might have an important role in the pathogenesis of INPH.

Injection deep level transient spectroscopy: An improved method for measuring capture rates of hot carriers in semiconductors

DOE PAGES

Fleming, R. M.; Seager, C. H.; Lang, D. V.; ...

2015-07-02

In this study, an improved method for measuring the cross sections for carrier trapping at defects in semiconductors is described. This method, a variation of deep level transient spectroscopy(DLTS) used with bipolar transistors, is applied to hot carrier trapping at vacancy-oxygen, carbon-oxygen, and three charge states of divacancy centers (V 2) in n- and p-type silicon. Unlike standard DLTS, we fill traps by injecting carriers into the depletion region of a bipolar transistor diode using a pulse of forward bias current applied to the adjacent diode. We show that this technique is capable of accurately measuring a wide range ofmore » capture cross sections at varying electric fields due to the control of the carrier density it provides. Because this technique can be applied to a variety of carrier energy distributions, it should be valuable in modeling the effect of radiation-induced generation-recombination currents in bipolar devices.« less

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

Danno, Katsunori; Kimoto, Tsunenobu

The authors have investigated deep levels in as-grown and electron-irradiated p-type 4H-SiC epilayers by deep level transient spectroscopy. In as-grown epilayers, the D center and four deep levels are observed. In p-type 4H-SiC, reactive ion etching followed by thermal treatment (at 1150 degree sign C) induces the HK0 (E{sub V}+0.79 eV) and HK2 (E{sub V}+0.84 eV) centers. By the electron irradiation, two deep levels at 0.98 eV (EP1) and 1.44 eV (EP2) are observed in all the samples irradiated at 116-400 keV, while two additional deep levels (EP3 and EP4) are observed only in the samples irradiated at 400 keV.more » After annealing at 950 degree sign C, these centers are annealed out, and the HK4 (E{sub V}+1.44 eV) concentration is increased. By the electron irradiation at more than 160 keV followed by annealing at 950 degree sign C, three deep levels are always observed at 0.30 eV (UK1), 0.58 eV (UK2), and 1.44 eV (HK4). These centers may be defect complexes including carbon displacement-related defects. All the centers except for the D center are reduced to below the detection limit (1-3x10{sup 11} cm{sup -3}) by annealing at 1550 degree sign C for 30 min.« less

Metastable defect response in CZTSSe from admittance spectroscopy

DOE PAGES

Koeper, Mark J.; Hages, Charles J.; Li, Jian V.; ...

2017-10-02

Admittance spectroscopy is a useful tool used to study defects in semiconductor materials. However, metastable defect responses in non-ideal semiconductors can greatly impact the measurement and therefore the interpretation of results. Here, admittance spectroscopy was performed on Cu2ZnSn(S,Se) 4 where metastable defect response is illustrated due to the trapping of injected carriers into a deep defect state. To investigate the metastable response, admittance measurements were performed under electrically and optically relaxed conditions in comparison to a device following a low level carrier-injection pretreatment. The relaxed measurement demonstrates a single capacitance signature while two capacitance signatures are observed for the devicemore » measured following carrier-injection. The deeper level signature, typically reported for kesterites, is activated by charge trapping following carrier injection. Both signatures are attributed to bulk level defects. The significant metastable response observed on kesterites due to charge trapping obscures accurate interpretation of defect levels from admittance spectroscopy and indicates that great care must be taken when performing and interpreting this measurement on non-ideal devices.« less

Thermally stimulated capacitance in gamma irradiated epitaxial 4H-SiC Schottky barrier diodes

NASA Astrophysics Data System (ADS)

Vigneshwara Raja, P.; Narasimha Murty, N. V. L.

2018-04-01

Deep level defects in 4H-SiC Schottky barrier diodes (SBDs) fabricated on n-type epitaxial 4H-SiC have been identified by thermally stimulated capacitance (TSCAP) spectroscopy prior to and after 60Co-gamma irradiation. The TSCAP measurements on the non-irradiated SBDs reveal two electron traps at Ec-0.63 eV (˜250 K) and Ec-1.13 eV (˜525 K), whereas only one trap at Ec-0.63 eV is identified by conventional thermally stimulated current (TSC) measurements. Hence, TSCAP spectroscopy is more effective in identifying deep level defects in epitaxial 4 H-SiC SBDs as compared to the TSC spectroscopy. Upon exposure to 60Co-gamma rays up to a dose of 100 Mrad, significant changes in the concentration of the traps at Ec-0.63 eV, Ec-1.13 eV, and one new trap at Ec-0.89 eV (˜420 K) are observed. The electrical characteristics of the SBDs are considerably changed after gamma irradiation. The dominant mechanisms responsible for the irradiation induced changes in the SBD electrical characteristics are analyzed by incorporating the trap signatures in the commercial Silvaco® TCAD device simulator. The extracted trap parameters of the irradiated SBDs may be helpful in predicting the survival of 4H-SiC SBD detectors at higher irradiation levels.

Formation of copper precipitates in silicon

NASA Astrophysics Data System (ADS)

Flink, Christoph; Feick, Henning; McHugo, Scott A.; Mohammed, Amna; Seifert, Winfried; Hieslmair, Henry; Heiser, Thomas; Istratov, Andrei A.; Weber, Eicke R.

1999-12-01

The formation of copper precipitates in silicon was studied after high-temperature intentional contamination of p- and n-type FZ and Cz-grown silicon and quench to room temperature. With the Transient Ion Drift (TID) technique on p-type silicon a critical Fermi level position at EC-0.2 eV was found. Only if the Fermi level position, which is determined by the concentrations of the acceptors and the copper donors, surpasses this critical value precipitation takes place. If the Fermi level is below this level the supersaturated interstitial copper diffuses out. An electrostatic precipitation model is introduced that correlates the observed precipitation behavior with the electrical activity of the copper precipitates as detected with Deep Level Transient Spectroscopy (DLTS) on n-type and with Minority Carrier Transient Spectroscopy (MCTS) on p-type silicon.

Electronic properties of deep-level defects in proton irradiated AlGaAs-GaAs solar cells

NASA Technical Reports Server (NTRS)

Li, S. S.

1981-01-01

Deep level transient spectroscopy and capacitance voltage techniques as well as analysis of the forward current voltage (I-V) characteristics and SEM-EIC data were carried out for proton irradiated GaAs solar cells over a wide range of proton energies and proton fluences. Defect and recombination parameters such as defect energy levels and density, carrier capture cross sections and lifetimes as well as diffusion lengths in the undoped n-GaAs LPE layers were determined. Good correlation between these defect parameters and solar cell performance parameters was obtained for GaAs solar cells irradiated by 200 and 290 KeV protons. It was found that 200 to 290 KeV protons will produce the most defects and damages to the GaAs solar cell structure used. The influence of the low temperature (200 to 400 C) periodic thermal annealing on the deep level defects and the performance of the 200 KeV proton irradiated cells is discussed.

Cell performance and defect behavior in proton-irradiated lithium-counterdoped n(+)p silicon solar cells

NASA Technical Reports Server (NTRS)

Weinberg, I.; Stupica, J. W.; Swartz, C. K.; Goradia, C.

1986-01-01

Lithium-counterdoped n(+)p silicon solar cells were irradiated by 10-MeV protons, and their performance was determined as a function of fluence. It was found that the cell with the highest lithium concentration exhibited the higher radiation resistance. Deep-level transient spectroscopy studies of deep-level defects were used to identify two lithium-related defects. Defect energy levels obtained after the present 10-MeV irradiations were found to be markedly different than those observed after previous 1-MeV electron irradiations. However, the present DLTS data are consistent with previous suggestion by Weinberg et al. (1984) of a lithium-oxygen interaction which tends to inhibit formation of an interstitial boron-oxygen defect.

Investigation of defect properties in Cu(In,Ga)Se 2 solar cells by deep-level transient spectroscopy

NASA Astrophysics Data System (ADS)

Kerr, L. L.; Li, Sheng S.; Johnston, S. W.; Anderson, T. J.; Crisalle, O. D.; Kim, W. K.; Abushama, J.; Noufi, R. N.

2004-09-01

The performance of the chalcopyrite material Cu(In,Ga)Se 2 (CIGS) used as an absorber layer in thin-film photovoltaic devices is significantly affected by the presence of native defects. The deep-level transient spectroscopy (DLTS) technique is used in this work to characterize the defect properties, yielding relevant information about the defect types, their capture cross-sections, and energy levels and densities in the CIGS cells. Three solar cells developed using different absorber growth technologies were analyzed using DLTS, capacitance-voltage ( C- V), and capacitance-temperature ( C- T) techniques. It was found that CIS cells grown at the University of Florida exhibits a middle-gap defect level that may relate to the cell's low fill factor and open-circuit voltage values observed. A high efficiency ( ηc>18%) CIGS cell produced by the National Renewable Energy Laboratory (NREL) was found to contain three minority-carrier (electron) traps and a 13% CIGS cell produced by the Energy Photovoltaics Inc. (EPV) exhibited one majority (hole) trap. The approach followed using the DLTS technique serves as a paradigm for revealing the presence of significant defect levels in absorber materials, and may be used to support the identification of remedial processing operations.

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

King, M. P.; Kaplar, R. J.; Dickerson, J. R.

Electrical performance and characterization of deep levels in vertical GaN P-i-N diodes grown on low threading dislocation density (~10 4 –10 6 cm –2) bulk GaN substrates are investigated. The lightly doped n drift region of these devices is observed to be highly compensated by several prominent deep levels detected using deep level optical spectroscopy at E c-2.13, 2.92, and 3.2 eV. A combination of steady-state photocapacitance and lighted capacitance-voltage profiling indicates the concentrations of these deep levels to be N t = 3 × 10 12, 2 × 10 15, and 5 × 10 14 cm –3, respectively. Themore » E c-2.92 eV level is observed to be the primary compensating defect in as-grown n-type metal-organic chemical vapor deposition GaN, indicating this level acts as a limiting factor for achieving controllably low doping. The device blocking voltage should increase if compensating defects reduce the free carrier concentration of the n drift region. Understanding the incorporation of as-grown and native defects in thick n-GaN is essential for enabling large V BD in the next-generation wide-bandgap power semiconductor devices. Furthermore, controlling the as-grown defects induced by epitaxial growth conditions is critical to achieve blocking voltage capability above 5 kV.« less

Deep level defects in dilute GaAsBi alloys grown under intense UV illumination

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

Mooney, P. M.; Tarun, Marianne; Beaton, D. A.

2016-07-21

Dilute GaAs1-xBix alloys exhibiting narrow band edge photoluminescence (PL) were recently grown by molecular beam epitaxy (MBE) with the growth surface illuminated by intense UV radiation. To investigate whether the improved optical quality of these films results from a reduction in the concentration of deep level defects, p+/n and n+/p junction diodes were fabricated on both the illuminated and dark areas of several samples. Deep Level Transient Spectroscopy (DLTS) measurements show that the illuminated and dark areas of both the n- and p-type GaAs1-xBix epi-layers have similar concentrations of near mid-gap electron and hole traps, in the 1015 cm-3 range.more » Thus the improved PL spectra cannot be explained by a reduction in non-radiative recombination at deep level defects. We note that carrier freeze-out above 35 K is significantly reduced in the illuminated areas of the p-type GaAs1-xBix layers compared to the dark areas, allowing the first DLTS measurements of defect energy levels close to the valence band edge. These defect levels may account for differences in the PL spectra from the illuminated and dark areas of un-doped layers with a similar Bi fraction.« less

Nonvolatile memories using deep traps formed in HfO2 by Nb ion implantation

NASA Astrophysics Data System (ADS)

Choul Kim, Min; Oh Kim, Chang; Taek Oh, Houng; Choi, Suk-Ho; Belay, K.; Elliman, R. G.; Russo, S. P.

2011-03-01

We report nonvolatile memories (NVMs) based on deep-energy trap levels formed in HfO2 by metal ion implantation. A comparison of Nb- and Ta-implanted samples shows that suitable charge-trapping centers are formed in Nb-implanted samples, but not in Ta-implanted samples. This is consistent with density-functional theory calculations which predict that only Nb will form deep-energy levels in the bandgap of HfO2. Photocurrent spectroscopy exhibits characteristics consistent with one of the trap levels predicted in these calculations. Nb-implanted samples showing memory windows in capacitance-voltage (V) curves always exhibit current (I) peaks in I-V curves, indicating that NVM effects result from deep traps in HfO2. In contrast, Ta-implanted samples show dielectric breakdowns during the I-V sweeps between 5 and 11 V, consistent with the fact that no trap levels are present. For a sample implanted with a fluence of 1013 Nb cm-2, the charge losses after 104 s are ˜9.8 and ˜25.5% at room temperature (RT) and 85°C, respectively, and the expected charge loss after 10 years is ˜34% at RT, very promising for commercial NVMs.

Compensation and persistent photocapacitance in homoepitaxial Sn-doped β-Ga2O3

NASA Astrophysics Data System (ADS)

Polyakov, A. Y.; Smirnov, N. B.; Shchemerov, I. V.; Gogova, D.; Tarelkin, S. A.; Pearton, S. J.

2018-03-01

The electrical properties of epitaxial β-Ga2O3 doped with Sn (1016-9 × 1018 cm-3) and grown by metalorganic chemical vapor deposition on semi-insulating β-Ga2O3 substrates are reported. Shallow donors attributable to Sn were observed only in a narrow region near the film/substrate interface and with a much lower concentration than the total Sn density. For heavily Sn doped films (Sn concentration, 9 × 1018 cm-3), the electrical properties in the top portion of the layer were determined by deep centers with a level at Ec-0.21 eV not described previously. In more lightly doped layers, the Ec-0.21 eV centers and deeper traps at Ec-0.8 eV were present, with the latter pinning the Fermi level. Low temperature photocapacitance and capacitance voltage measurements of illuminated samples indicated the presence of high densities (1017-1018 cm-3) of deep acceptors with an optical ionization threshold of 2.3 eV. Optical deep level transient spectroscopy (ODLTS) and photoinduced current transient spectroscopy (PICTS) detected electron traps at Ec-0.8 eV and Ec-1.1 eV. For lightly doped layers, the compensation of film conductivity was mostly provided by the Ec-2.3 eV acceptors. For heavily Sn doped films, deep acceptor centers possibly related to Ga vacancies were significant. The photocapacitance and the photocurrent caused by illumination at low temperatures were persistent, with an optical threshold of 1.9 eV and vanished only at temperatures of ˜400 K. The capture barrier for electrons causing the persistent photocapacitance effect was estimated from ODLTS and PICTS to be 0.25-0.35 eV.

Effect of impurities and processing on silicon solar cells. Volume 1: Characterization methods for impurities in silicon and impurity effects data base

NASA Technical Reports Server (NTRS)

Hopkins, R. H.; Davis, J. R.; Rohatgi, A.; Campbell, R. B.; Blais, P. D.; Rai-Choudhury, P.; Stapleton, R. E.; Mollenkopf, H. C.; Mccormick, J. R.

1980-01-01

Two major topics are treated: methods to measure and evaluate impurity effects in silicon and comprehensive tabulations of data derived during the study. Discussions of deep level spectroscopy, detailed dark I-V measurements, recombination lifetime determination, scanned laser photo-response, conventional solar cell I-V techniques, and descriptions of silicon chemical analysis are presented and discussed. The tabulated data include lists of impurity segregation coefficients, ingot impurity analyses and estimated concentrations, typical deep level impurity spectra, photoconductive and open circuit decay lifetimes for individual metal-doped ingots, and a complete tabulation of the cell I-V characteristics of nearly 200 ingots.

Electroluminescence and other diagnostic techniques for the study of hot-electron effects in compound semiconductor devices

NASA Astrophysics Data System (ADS)

Zanoni, Enrico; Meneghesso, Gaudenzio; Menozzi, Roberto

2000-03-01

Hot electron in III-V FETs can be indirectly monitored by measuring the current coming out from the gate when the device is biased at high electric fields. This negative current is due to the collection of holes generated by impact ionization in the gate-to drain region. Electroluminescence represents a powerful tool in order to characterize not only hot electrons but also material properties. By using spatially resolved emission microscopy it is possible to show that the light due to cold electron/hole recombination is emitted between the gate and the source (low electric field region), while the contribution due to hot electrons is emitted between the gate and the drain (high electric field region). Deep-traps created in the device by hot carriers can be analysed by means of drain current deep level transient spectroscopy and by transconductance frequency dispersion. Cathodoluminescence, optical beam induced current, X-ray spectroscopy, electron energy loss spectroscopy in combination with a transmission electron microscopy are powerful tools in order to identify and localize surface modification following hot-electron stress tests.

Identification of the primary compensating defect level responsible for determining blocking voltage of vertical GaN power diodes

DOE PAGES

King, M. P.; Kaplar, R. J.; Dickerson, J. R.; ...

2016-10-31

Electrical performance and characterization of deep levels in vertical GaN P-i-N diodes grown on low threading dislocation density (~10 4 –10 6 cm –2) bulk GaN substrates are investigated. The lightly doped n drift region of these devices is observed to be highly compensated by several prominent deep levels detected using deep level optical spectroscopy at E c-2.13, 2.92, and 3.2 eV. A combination of steady-state photocapacitance and lighted capacitance-voltage profiling indicates the concentrations of these deep levels to be N t = 3 × 10 12, 2 × 10 15, and 5 × 10 14 cm –3, respectively. Themore » E c-2.92 eV level is observed to be the primary compensating defect in as-grown n-type metal-organic chemical vapor deposition GaN, indicating this level acts as a limiting factor for achieving controllably low doping. The device blocking voltage should increase if compensating defects reduce the free carrier concentration of the n drift region. Understanding the incorporation of as-grown and native defects in thick n-GaN is essential for enabling large V BD in the next-generation wide-bandgap power semiconductor devices. Furthermore, controlling the as-grown defects induced by epitaxial growth conditions is critical to achieve blocking voltage capability above 5 kV.« less

Recombination activity of light-activated copper defects in p-type silicon studied by injection- and temperature-dependent lifetime spectroscopy

NASA Astrophysics Data System (ADS)

Inglese, Alessandro; Lindroos, Jeanette; Vahlman, Henri; Savin, Hele

2016-09-01

The presence of copper contamination is known to cause strong light-induced degradation (Cu-LID) in silicon. In this paper, we parametrize the recombination activity of light-activated copper defects in terms of Shockley—Read—Hall recombination statistics through injection- and temperature dependent lifetime spectroscopy (TDLS) performed on deliberately contaminated float zone silicon wafers. We obtain an accurate fit of the experimental data via two non-interacting energy levels, i.e., a deep recombination center featuring an energy level at Ec-Et=0.48 -0.62 eV with a moderate donor-like capture asymmetry ( k =1.7 -2.6 ) and an additional shallow energy state located at Ec-Et=0.1 -0.2 eV , which mostly affects the carrier lifetime only at high-injection conditions. Besides confirming these defect parameters, TDLS measurements also indicate a power-law temperature dependence of the capture cross sections associated with the deep energy state. Eventually, we compare these results with the available literature data, and we find that the formation of copper precipitates is the probable root cause behind Cu-LID.

Deep level transient spectroscopy signatures of majority traps in GaN p-n diodes grown by metal-organic vapor-phase epitaxy technique on GaN substrates

NASA Astrophysics Data System (ADS)

PŁaczek-Popko, E.; Trzmiel, J.; Zielony, E.; Grzanka, S.; Czernecki, R.; Suski, T.

2009-12-01

In this study, we present the results of investigation on p-n GaN diodes by means of deep level transient spectroscopy (DLTS) within the temperature range of 77-350 K. Si-doped GaN layers were grown by metal-organic vapor-phase epitaxy technique (MOVPE) on the free-standing GaN substrates. Subsequently Mg-doped GaN layers were grown. To perform DLTS measurements Ni/Au contacts to p-type material and Ti/Au contacts to n-type material were processed. DLTS signal spectra revealed the presence of two majority traps of activation energies obtained from Arrhenius plots equal to E1=0.22 eV and E2=0.65 eV. In present work we show that the trap E1 is linked with the extended defects whereas the trap E2 is the point defect related. Its capture cross section is thermally activated with energy barrier for capture equal to 0.2 eV.

Optical signatures of deep level defects in Ga2O3

NASA Astrophysics Data System (ADS)

Gao, Hantian; Muralidharan, Shreyas; Pronin, Nicholas; Karim, Md Rezaul; White, Susan M.; Asel, Thaddeus; Foster, Geoffrey; Krishnamoorthy, Sriram; Rajan, Siddharth; Cao, Lei R.; Higashiwaki, Masataka; von Wenckstern, Holger; Grundmann, Marius; Zhao, Hongping; Look, David C.; Brillson, Leonard J.

2018-06-01

We used depth-resolved cathodoluminescence spectroscopy and surface photovoltage spectroscopy to measure the effects of near-surface plasma processing and neutron irradiation on native point defects in β-Ga2O3. The near-surface sensitivity and depth resolution of these optical techniques enabled us to identify spectral changes associated with removing or creating these defects, leading to identification of one oxygen vacancy-related and two gallium vacancy-related energy levels in the β-Ga2O3 bandgap. The combined near-surface detection and processing of Ga2O3 suggests an avenue for identifying the physical nature and reducing the density of native point defects in this and other semiconductors.

Effect of antimony on the deep-level traps in GaInNAsSb thin films

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

Islam, Muhammad Monirul, E-mail: islam.monir.ke@u.tsukuba.ac.jp; Miyashita, Naoya; Ahsan, Nazmul

2014-09-15

Admittance spectroscopy has been performed to investigate the effect of antimony (Sb) on GaInNAs material in relation to the deep-level defects in this material. Two electron traps, E1 and E2 at an energy level 0.12 and 0.41 eV below the conduction band (E{sub C}), respectively, were found in undoped GaInNAs. Bias-voltage dependent admittance confirmed that E1 is an interface-type defect being spatially localized at the GaInNAs/GaAs interface, while E2 is a bulk-type defect located around mid-gap of GaInNAs layer. Introduction of Sb improved the material quality which was evident from the reduction of both the interface and bulk-type defects.

Probing carbon impurities in hexagonal boron nitride epilayers

NASA Astrophysics Data System (ADS)

Uddin, M. R.; Li, J.; Lin, J. Y.; Jiang, H. X.

2017-05-01

Carbon doped hexagonal boron nitride epilayers have been grown by metal organic chemical vapor deposition. Photocurrent excitation spectroscopy has been utilized to probe the energy levels associated with carbon impurities in hexagonal boron nitride (h-BN). The observed transition peaks in photocurrent excitation spectra correspond well to the energy positions of the bandgap, substitutional donors (CB, carbon impurities occupying boron sites), and substitutional acceptors (CN, carbon impurities occupying nitrogen sites). From the observed transition peak positions, the derived energy level of CB donors in h-BN is ED ˜ 0.45 eV, which agrees well with the value deduced from the temperature dependent electrical resistivity. The present study further confirms that the room temperature bandgap of h-BN is about 6.42-6.45 eV, and the CN deep acceptors have an energy level of about 2.2-2.3 eV. The results also infer that carbon doping introduces both shallow donors (CB) and deep acceptors (CN) via self-compensation, and the energy level of carbon donors appears to be too deep to enable carbon as a viable candidate as an n-type dopant in h-BN epilayers.

Hemodynamic measurements in deep brain tissues of humans by near-infrared time-resolved spectroscopy

NASA Astrophysics Data System (ADS)

Suzuki, Hiroaki; Oda, Motoki; Yamaki, Etsuko; Suzuki, Toshihiko; Yamashita, Daisuke; Yoshimoto, Kenji; Homma, Shu; Yamashita, Yutaka

2014-03-01

Using near-infrared time-resolved spectroscopy (TRS), we measured the human head in transmittance mode to obtain the optical properties, tissue oxygenation, and hemodynamics of deep brain tissues in 50 healthy adult volunteers. The right ear canal was irradiated with 3-wavelengths of pulsed light (760, 795, and 835nm), and the photons passing through the human head were collected at the left ear canal. Optical signals with sufficient intensity could be obtained from 46 of the 50 volunteers. By analyzing the temporal profiles based on the photon diffusion theory, we successfully obtained absorption coefficients for each wavelength. The levels of oxygenated hemoglobin (HbO2), deoxygenated hemoglobin (Hb), total hemoglobin (tHb), and tissue oxygen saturation (SO2) were then determined by referring to the hemoglobin spectroscopic data. Compared with the SO2 values for the forehead measurements in reflectance mode, the SO2 values of the transmittance measurements of the human head were approximately 10% lower, and tHb values of the transmittance measurements were always lower than those of the forehead reflectance measurements. Moreover, the level of hemoglobin and the SO2 were strongly correlated between the human head measurements in transmittance mode and the forehead measurements in the reflectance mode, respectively. These results demonstrated a potential application of this TRS system in examining deep brain tissues of humans.

Defect levels of semi-insulating CdMnTe:In crystals

NASA Astrophysics Data System (ADS)

Kim, K. H.; Bolotinikov, A. E.; Camarda, G. S.; Hossain, A.; Gul, R.; Yang, G.; Cui, Y.; Prochazka, J.; Franc, J.; Hong, J.; James, R. B.

2011-06-01

Using photoluminescence (PL) and current deep-level transient spectroscopy (I-DLTS), we investigated the electronic defects of indium-doped detector-grade CdMnTe:In (CMT:In) crystals grown by the vertical Bridgman method. We similarly analyzed CdZnTe:In (CZT:In) and undoped CdMnTe (CMT) crystals grown under the amount of same level of excess Te and/or indium doping level to detail the fundamental properties of the electronic defect structure more readily. Extended defects, existing in all the samples, were revealed by synchrotron white beam x-ray diffraction topography and scanning electron microscopy. The electronic structure of CMT is very similar to that of CZT, with shallow traps, A-centers, Cd vacancies, deep levels, and Te antisites. The 1.1-eV deep level, revealed by PL in earlier studies of CZT and CdTe, were attributed to dislocation-induced defects. In our I-DLTS measurements, the 1.1-eV traps showed different activation energies with applied bias voltage and an exponential dependence on the trap-filling time, which are typical characteristics of dislocation-induced defects. We propose a new defect-trap model for indium-doped CMT crystals.

TOPICAL REVIEW: The shallow-to-deep instability of hydrogen and muonium in II VI and III V semiconductors

NASA Astrophysics Data System (ADS)

Cox, S. F. J.

2003-11-01

The structure and electrical activity of monatomic hydrogen defect centres are inferred from the spectroscopy and charge-state transitions of muonium, the light pseudo-isotope of hydrogen. Introductions are given to all these topics. Special attention is paid to the shallow-donor behaviour recently established in a number of II VI compounds and one III nitride. This contrasts with trapped-atom states suggestive of an acceptor function in other members of the II VI family as well as with the deep-level amphoteric behaviour which has long been known in the elemental group-IV semiconductors and certain III V compounds. The systematics of this remarkable shallow-to-deep instability are examined in terms of simple chemical considerations, as well as current theoretical and computational models. The muonium data appear to confirm predictions that the switch from shallow to deep behaviour is governed primarily by the depth of the conduction-band minimum below the vacuum continuum. The threshold electron affinity is around 3.5 eV, which compares favourably with computational estimates of a so-called pinning level for hydrogen (+/-) charge-state transitions of between -3 and -4.5 eV. A purely ionic model gives some intuitive understanding of this behaviour as well as the invariance of the threshold. Another current description applies equally to covalent materials and relates the threshold to the origin of the electrochemical scale. At the present level of approximation, zero-point energy corrections to the transition levels are small, so that muonium data should provide a reliable guide to the behaviour of hydrogen. Muonium spectroscopy proves to be more sensitive to the (0/+) donor level than to the (+/-) pinning level but, as a tool which does not rely on favourable hydrogen solubility, it looks set to test further predictions of these models in a large number of other materials, notably oxides. Certain candidate thin-film insulators and high-permittivity gate dielectrics appear to be uncomfortably close to conditions in which hydrogen impurity may cause electronic conduction.

Origin of dislocation luminescence centers and their reorganization in p-type silicon crystal subjected to plastic deformation and high temperature annealing.

PubMed

Pavlyk, Bohdan; Kushlyk, Markiyan; Slobodzyan, Dmytro

2017-12-01

Changes of the defect structure of silicon p-type crystal surface layer under the influence of plastic deformation and high temperature annealing in oxygen atmosphere were investigated by deep-level capacitance-modulation spectroscopy (DLCMS) and IR spectroscopy of molecules and atom vibrational levels. Special role of dislocations in the surface layer of silicon during the formation of its energy spectrum and rebuilding the defective structure was established. It is shown that the concentration of linear defects (N ≥ 10 4  cm -2 ) enriches surface layer with electrically active complexes (dislocation-oxygen, dislocation-vacancy, and dislocation-interstitial atoms of silicon) which are an effective radiative recombination centers.

Dual-wavelength excited photoluminescence spectroscopy of deep-level hole traps in Ga(In)NP

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

Dagnelund, D.; Huang, Y. Q.; Buyanova, I. A.

2015-01-07

By employing photoluminescence (PL) spectroscopy under dual-wavelength optical excitation, we uncover the presence of deep-level hole traps in Ga(In)NP alloys grown by molecular beam epitaxy (MBE). The energy level positions of the traps are determined to be at 0.56 eV and 0.78 eV above the top of the valance band. We show that photo-excitation of the holes from the traps, by a secondary light source with a photon energy below the bandgap energy, can lead to a strong enhancement (up to 25%) of the PL emissions from the alloys under a primary optical excitation above the bandgap energy. We further demonstrate thatmore » the same hole traps can be found in various MBE-grown Ga(In)NP alloys, regardless of their growth temperatures, chemical compositions, and strain. The extent of the PL enhancement induced by the hole de-trapping is shown to vary between different alloys, however, likely reflecting their different trap concentrations. The absence of theses traps in the GaNP alloy grown by vapor phase epitaxy suggests that their incorporation could be associated with a contaminant accompanied by the N plasma source employed in the MBE growth, possibly a Cu impurity.« less

A compensating point defect in carbon-doped GaN substrates studied with electron paramagnetic resonance spectroscopy

NASA Astrophysics Data System (ADS)

Willoughby, W. R.; Zvanut, M. E.; Paudel, Subash; Iwinska, M.; Sochacki, T.; Bockowski, M.

2018-04-01

Electron paramagnetic resonance (EPR) spectroscopy was used to investigate a type of point defect present in 1019 cm-3 carbon-doped GaN substrates grown by hydride vapor phase epitaxy. A broad, isotropic resonance at g ˜ 1.987 was observed at 3.5 K, and the EPR intensity increased with illumination at energies greater than 2.75 eV and decreased with photon energies greater than 0.95 eV. The latter is consistent with a deep level of 0.95 eV above the valence band maximum and implies that the associated defect likely participates in donor compensation. The ionization energy for this defect is close to the predicted value for the (-/0) transition level of CN and transition levels associated with Ga vacancies such as VGa and VGa-ON-2H.

The effects of lithium counterdoping on radiation damage and annealing in n(+)p silicon solar cells

NASA Technical Reports Server (NTRS)

Weinberg, I.; Brandhorst, H. W., Jr.; Mehta, S.; Swartz, C. K.

1984-01-01

Boron-doped silicon n(+)p solar cells were counterdoped with lithium by ion implantation and the resultant n(+)p cells irradiated by 1 MeV electrons. Performance parameters were determined as a function of fluence and a deep level transient spectroscopy (DLTS) study was conducted. The lithium counterdoped cells exhibited significantly increased radiation resistance when compared to boron doped control cells. Isochronal annealing studies of cell performance indicate that significant annealing occurs at 100 C. Isochronal annealing of the deep level defects showed a correlation between a single defect at E sub v + 0.43 eV and the annealing behavior of short circuit current in the counterdoped cells. The annealing behavior was controlled by dissociation and recombination of this defect. The DLTS studies showed that counterdoping with lithium eliminated three deep level defects and resulted in three new defects. The increased radiation resistance of the counterdoped cells is due to the interaction of lithium with oxygen, single vacancies and divacancies. The lithium-oxygen interaction is the most effective in contributing to the increased radiation resistance.

Joint Services Electronics Program.

DTIC Science & Technology

1987-12-31

and annealing, using deep level transient spectroscopy (DLTS), and the effects of co-implantation on 4l the activation of amphoteric dopants and...theriithe study of optical quantum effects with emphasis on nonlinear optical phenomena. For example, a significant accomplishment write-up describes...Millimeter-Wave Array Components Tatsuo Itoh A number of novel solid state devices such as metal semiconductor field effect transistors (MESFET

Characterization of iron in silicon by low-temperature photoluminescence and deep-level transient spectroscopy

NASA Astrophysics Data System (ADS)

Nakamura, Minoru; Murakami, Susumu; Udono, Haruhiko

2018-03-01

We investigate the relationship between the intensity of band-edge (BDE) photoluminescence (PL) from 10 to 70 K and the concentration of iron diffused in boron-doped p-type silicon. Because of the nonradiative recombination activity of the interstitial iron-boron complex (FeiB center), the BDE-PL intensity at each temperature varies distinctively and systematically with the iron concentration, which means that this method has the potential to make the accurate measurements of a wide range of interstitial iron concentrations in silicon. The iron precipitates formed in the bulk and/or at the surface are found to exert much weaker recombination activity for excess carriers than FeiB center by exploiting both PL and deep-level transient spectroscopy (DLTS) measurements. The unexpected enhancement in BDE-PL intensity from iron-diffused silicon between 20 and 50 K is attributed to the passivation of the Si-oxide/Si interface by iron. For the samples diffused with trace amounts of iron, the iron concentration within 20 μm of the surface is significantly greater than that in the bulk, as measured by DLTS. This result is tentatively attributed to the affinity of iron with the Si-oxide.

Investigation of structural, morphological, luminescent and thermal properties of combusted aluminium-based iron oxide

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

Shinde, S.S.; Rajpure, K.Y., E-mail: rajpure@yahoo.co

Nanocomposites of aluminium integrated hematite {alpha}-Fe{sub 2}O{sub 3} are synthesized by combustion route using aqueous solutions of AR grade ferric trichloride and aluminium nitrate as precursors. The influence of aluminium incorporation on to the morphology, XPS, photoluminescence and thermal properties has been investigated. The FESEM and AFM micrographs depict that the samples are compact and have homogeneously distributed grains of varying sizes ({approx}20-60 nm). Chemical composition and valence states of constituent elements in hematite are analyzed by XPS. In room temperature photoluminescence (PL) study, we observed strong violet emission around 436 nm without any deep-level emission and a small PLmore » FWHM indicating that the concentrations of defects are responsible for deep-level emissions. The specific heat and thermal conductivity study shows the phonon conduction behavior is dominant. We studied interparticle interactions using complex impedance spectroscopy. We report a new potential candidate for its possible applications in optoelectronics and magnetic devices. -- Graphical abstract: Frequency and temperature dependent interparticle interactions like grains, grain boundary effects using complex impedance spectroscopy of pure and 10 at% Al:Fe{sub 2}O{sub 3} have been studied. Display Omitted« less

Defect States in InP/InGaAs/InP Heterostructures by Current-Voltage Characteristics and Deep Level Transient Spectroscopy.

PubMed

Vu, Thi Kim Oanh; Lee, Kyoung Su; Lee, Sang Jun; Kim, Eun Kyu

2018-09-01

We studied defect states in In0.53Ga0.47As/InP heterojunctions with interface control by group V atoms during metalorganic chemical vapor (MOCVD) deposition. From deep level transient spectroscopy (DLTS) measurements, two defects with activation energies of 0.28 eV (E1) and 0.15 eV (E2) below the conduction band edge, were observed. The defect density of E1 for In0.53Ga0.47As/InP heterojunctions with an addition of As and P atoms was about 1.5 times higher than that of the heterojunction added P atom only. From the temperature dependence of current- voltage characteristics, the thermal activation energies of In0.53Ga0.47As/InP of heterojunctions were estimated to be 0.27 and 0.25 eV, respectively. It appeared that the reverse light current for In0.53Ga0.47As/InP heterojunction added P atom increased only by illumination of a 940 nm-LED light source. These results imply that only the P addition at the interface can enhance the quality of InGaAs/InP heterojunction.

Electrical characterization of deep levels created by bombarding nitrogen-doped 4H-SiC with alpha-particle irradiation

NASA Astrophysics Data System (ADS)

Omotoso, Ezekiel; Meyer, Walter E.; Auret, F. Danie; Paradzah, Alexander T.; Legodi, Matshisa J.

2016-03-01

Deep-level transient spectroscopy (DLTS) and Laplace-DLTS were used to investigate the effect of alpha-particle irradiation on the electrical properties of nitrogen-doped 4H-SiC. The samples were bombarded with alpha-particles at room temperature (300 K) using an americium-241 (241Am) radionuclide source. DLTS revealed the presence of four deep levels in the as-grown samples, E0.09, E0.11, E0.16 and E0.65. After irradiation with a fluence of 4.1 × 1010 alpha-particles-cm-2, DLTS measurements indicated the presence of two new deep levels, E0.39 and E0.62 with energy levels, EC - 0.39 eV and EC - 0.62 eV, with an apparent capture cross sections of 2 × 10-16 and 2 × 10-14 cm2, respectively. Furthermore, irradiation with fluence of 8.9 × 1010 alpha-particles-cm-2 resulted in the disappearance of shallow defects due to a lowering of the Fermi level. These defects re-appeared after annealing at 300 °C for 20 min. Defects, E0.39 and E0.42 with close emission rates were attributed to silicon or carbon vacancy and could only be separated by using high resolution Laplace-DLTS. The DLTS peaks at EC - (0.55-0.70) eV (known as Z1/Z2) were attributed to an isolated carbon vacancy (VC).

Identification of nitrogen- and host-related deep-level traps in n-type GaNAs and their evolution upon annealing

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

Gelczuk, Ł., E-mail: lukasz.gelczuk@pwr.edu.pl; Kudrawiec, R., E-mail: robert.kudrawiec@pwr.edu.pl; Henini, M.

2014-07-07

Deep level traps in as-grown and annealed n-GaNAs layers (doped with Si) of various nitrogen concentrations (N=0.2%, 0.4%, 0.8%, and 1.2%) were investigated by deep level transient spectroscopy. In addition, optical properties of GaNAs layers were studied by photoluminescence and contactless electroreflectance. The identification of N- and host-related traps has been performed on the basis of band gap diagram [Kudrawiec, Appl. Phys. Lett. 101, 082109 (2012)], which assumes that the activation energy of electron traps of the same microscopic nature decreases with the rise of nitrogen concentration in accordance with the N-related shift of the conduction band towards trap levels.more » The application of this diagram has allowed to investigate the evolution of donor traps in GaNAs upon annealing. In general, it was observed that the concentration of N- and host-related traps decreases after annealing and PL improves very significantly. However, it was also observed that some traps are generated due to annealing. It explains why the annealing conditions have to be carefully optimized for this material system.« less

Spectroscopic chemical analysis methods and apparatus

NASA Technical Reports Server (NTRS)

Hug, William F. (Inventor); Reid, Ray D. (Inventor); Bhartia, Rohit (Inventor)

2013-01-01

Spectroscopic chemical analysis methods and apparatus are disclosed which employ deep ultraviolet (e.g. in the 200 nm to 300 nm spectral range) electron beam pumped wide bandgap semiconductor lasers, incoherent wide bandgap semiconductor light emitting devices, and hollow cathode metal ion lasers to perform non-contact, non-invasive detection of unknown chemical analytes. These deep ultraviolet sources enable dramatic size, weight and power consumption reductions of chemical analysis instruments. Chemical analysis instruments employed in some embodiments include capillary and gel plane electrophoresis, capillary electrochromatography, high performance liquid chromatography, flow cytometry, flow cells for liquids and aerosols, and surface detection instruments. In some embodiments, Raman spectroscopic detection methods and apparatus use ultra-narrow-band angle tuning filters, acousto-optic tuning filters, and temperature tuned filters to enable ultra-miniature analyzers for chemical identification. In some embodiments Raman analysis is conducted along with photoluminescence spectroscopy (i.e. fluorescence and/or phosphorescence spectroscopy) to provide high levels of sensitivity and specificity in the same instrument.

Fibrillation mechanism of a model intrinsically disordered protein revealed by 2D correlation deep UV resonance Raman spectroscopy.

PubMed

Sikirzhytski, Vitali; Topilina, Natalya I; Takor, Gaius A; Higashiya, Seiichiro; Welch, John T; Uversky, Vladimir N; Lednev, Igor K

2012-05-14

Understanding of numerous biological functions of intrinsically disordered proteins (IDPs) is of significant interest to modern life science research. A large variety of serious debilitating diseases are associated with the malfunction of IDPs including neurodegenerative disorders and systemic amyloidosis. Here we report on the molecular mechanism of amyloid fibrillation of a model IDP (YE8) using 2D correlation deep UV resonance Raman spectroscopy. YE8 is a genetically engineered polypeptide, which is completely unordered at neutral pH yet exhibits all properties of a fibrillogenic protein at low pH. The very first step of the fibrillation process involves structural rearrangements of YE8 at the global structure level without the detectable appearance of secondary structural elements. The formation of β-sheet species follows the global structural changes and proceeds via the simultaneous formation of turns and β-strands. The kinetic mechanism revealed is an important new contribution to understanding of the general fibrillation mechanism proposed for IDP.

Defect-Reduction Mechanism for Improving Radiative Efficiency in InGaN/GaN Light-Emitting Diodes using InGaN Underlayers

DOE PAGES

Armstrong, Andrew M.; Bryant, Benjamin N.; Crawford, Mary H.; ...

2015-04-01

The influence of a dilute In xGa 1-xN (x~0.03) underlayer (UL) grown below a single In 0.16Ga 0.84N quantum well (SQW), within a light-emitting diode(LED), on the radiative efficiency and deep level defect properties was studied using differential carrier lifetime (DCL) measurements and deep level optical spectroscopy (DLOS). DCL measurements found that inclusion of the UL significantly improved LED radiative efficiency. At low current densities, the non-radiative recombination rate of the LED with an UL was found to be 3.9 times lower than theLED without an UL, while the radiative recombination rates were nearly identical. This, then, suggests that themore » improved radiative efficiency resulted from reduced non-radiative defect concentration within the SQW. DLOS measurement found the same type of defects in the InGaN SQWs with and without ULs. However, lighted capacitance-voltage measurements of the LEDs revealed a 3.4 times reduction in a SQW-related near-mid-gap defect state for the LED with an UL. Furthermore, quantitative agreement in the reduction of both the non-radiative recombination rate (3.9×) and deep level density (3.4×) upon insertion of an UL corroborates deep level defect reduction as the mechanism for improved LED efficiency.« less

A simple model of proton damage in GaAs solar cells

NASA Technical Reports Server (NTRS)

Wilson, J. W.; Walker, G. H.; Outlaw, R. A.

1982-01-01

A simple proton damage model for GaAs solar cells is derived and compared to experimental values of change in short circuit currents. The recombination cross section associated with the defects was determined from the experimental comparison to be approximately 1.2 x 10 to the -13th power sq cm in fair agreement with values determined from the deep level transient spectroscopy technique.

Radiation damage and defect behavior in proton irradiated lithium-counterdoped n+p silicon solar cells

NASA Technical Reports Server (NTRS)

Stupica, John; Goradia, Chandra; Swartz, Clifford K.; Weinberg, Irving

1987-01-01

Two lithium-counterdoped n+p silicon solar cells with different lithium concentrations were irradiated by 10-MeV protons. Cell performance was measured as a function of fluence, and it was found that the cell with the highest concentration of lithium had the highest radiation resistance. Deep level transient spectroscopy which showed two deep level defects that were lithium related. Relating the defect energy levels obtained from this study with those from earlier work using 1-MeV electron irradiation shows no correlation of the defect energy levels. There is one marked similarity: the absence of the boron-interstitial-oxygen-interstitial defect. This consistency strengthens the belief that lithium interacts with oxygen to prevent the formation of the boron interstitial-oxygen interstitial defect. The results indicate that, in general, addition of lithium in small amounts to the p-base of a boron doped silicon solar cell such that the base remains p-type, tends to increase the radiation resistance of the cell.

Near band edge emission characteristics of sputtered nano-crystalline ZnO films

NASA Astrophysics Data System (ADS)

Kunj, Saurabh; Sreenivas, K.

2016-05-01

Sputtered zinc oxide (ZnO) thin films deposited on unheated glass substrate under different sputtering gas mixtures (Ar+O2) have been investigated using X-ray diffraction and photo luminescence spectroscopy. Earlier reported studies on ZnO films prepared by different techniques exhibit either a sharp/broad near band edge (NBE) emission peak depending on the crystalline quality of the film. In the present study zinc oxide films, grown on unheated substrates, are seen to possess a preferred (002) orientation with a microstructure consisting of clustered nano-sized crystallites. The splitting in the near band edge emission (NBE) into three characteristic peaks is attributed to quantum confinement effect, and is observed specifically under an excitation of 270 nm. Deep level emission (DLE) in the range 400 to 700 nm is not observed indicating absence of deep level radiative defects.

Electric Propulsion Induced Secondary Mass Spectroscopy

NASA Technical Reports Server (NTRS)

Amini, Rashied; Landis, Geoffrey

2012-01-01

A document highlights a means to complement remote spectroscopy while also providing in situ surface samples without a landed system. Historically, most compositional analysis of small body surfaces has been done remotely by analyzing reflection or nuclear spectra. However, neither provides direct measurement that can unambiguously constrain the global surface composition and most importantly, the nature of trace composition and second-phase impurities. Recently, missions such as Deep Space 1 and Dawn have utilized electric propulsion (EP) accelerated, high-energy collimated beam of Xe+ ions to propel deep space missions to their target bodies. The energies of the Xe+ are sufficient to cause sputtering interactions, which eject material from the top microns of a targeted surface. Using a mass spectrometer, the sputtered material can be determined. The sputtering properties of EP exhaust can be used to determine detailed surface composition of atmosphereless bodies by electric propulsion induced secondary mass spectroscopy (EPI-SMS). EPI-SMS operation has three high-level requirements: EP system, mass spectrometer, and altitude of about 10 km. Approximately 1 keV Xe+ has been studied and proven to generate high sputtering yields in metallic substrates. Using these yields, first-order calculations predict that EPI-SMS will yield high signal-to-noise at altitudes greater than 10 km with both electrostatic and Hall thrusters.

Characterization of Thallium Bromide (TlBr) for Room Temperature Radiation Detectors

NASA Astrophysics Data System (ADS)

Smith, Holland McTyeire

Thallium bromide (TlBr) has emerged as a remarkably well-suited material for room temperature radiation detection. The unique combination of high-Z elements, high density, suitable band gap, and excellent electrical transport properties present in TlBr have brought device performance up to par with CdZnTe (CZT), the current market-leading room temperature radiation detector material. TlBr research is at an earlier stage than that of CZT, giving hope that the material will see even further improvement in electronic properties. Improving a resistive semiconductor material requires knowledge of deep levels present in the material and the effects of these deep levels on transport properties. Very few deep level studies have been conducted on TlBr, and none with the depth required to generate useful growth suggestions. In this dissertation, deep levels in nominally undoped and doped TlBr samples are studied with electrical and optical methods. Photo-Induced Conductivity Transient Spectroscopy (PICTS) is used to discover many deep levels in TlBr electrically. These levels are compared to sub-band gap optical transitions originating from defects observed in emission spectra. The results of this research indicate that the origin of resistivity in TlBr is likely due to deep level defects pinning the Fermi level at least ˜0.7 eV from either the conduction or valence band edge. The effect of dopants and deep levels on transport in TlBr is assessed with microwave photoconductivity decay analysis. It is found that Pb-, Se-, and O-doping decreases carrier lifetime in TlBr, whereas C-doping does not. TlBr exhibits weak ionic conductivity at room temperature, which both negatively affects the leakage current of detectors and leads to device degradation over time. Researchers are actively looking for ways to reduce or eliminate the ionic conductivity, but are faced with an intriguing challenge of materials engineering: is it possible to mitigate the ionic conduction of TlBr without harming the excellent electronic transport properties? Doping TlBr in order to control the ionic conductivity has been proposed and shown to be effective in reducing dark ionic current, but the electronic effects of the dopants has not been previously studied in detail. In this dissertation, the electronic effects of dopants introduced for ionic reasons are evaluated.

Defect study in ZnO related structures—A multi-spectroscopic approach

NASA Astrophysics Data System (ADS)

Ling, C. C.; Cheung, C. K.; Gu, Q. L.; Dai, X. M.; Xu, S. J.; Zhu, C. Y.; Luo, J. M.; Zhu, C. Y.; Tam, K. H.; Djurišić, A. B.; Beling, C. D.; Fung, S.; Lu, L. W.; Brauer, G.; Anwand, W.; Skorupa, W.; Ong, H. C.

2008-10-01

ZnO has attracted a great deal of attention in recent years because of its potential applications for fabricating optoelectronic devices. Using a multi-spectroscopic approach including positron annihilation spectroscopy (PAS), deep level transient spectroscopy (DLTS), photoluminescence (PL) and X-ray photoelectron spectroscopy (XPS), we have studied the two observed phenomena from ZnO related structures. They namely included the H 2O 2 pre-treatment induced ohmic to rectifying contact conversion on Au/ n-ZnO contact and the p-type doping by nitrogen ion implantation. The aim of the studies was to offering comprehensive views as to how the defects influenced the structures electrical and optical properties of the structures. It was also shown that PAS measurement using the monoenergetic positron beam could offer valuable information of vacancy type defects in the vertical ZnO nanorod array structure.

Deep levels due to hydrogen in ZnO single crystals

NASA Astrophysics Data System (ADS)

Parmar, Narendra; Weber, Marc; Lynn, Kelvin

2009-05-01

Hydrogen impurities and oxygen vacancies are involved in the ˜0.7 eV shift of the optical absorption edge of ZnO. Deuterium causes a smaller shift. Titanium metal is used to bind hydrogen as it diffuses out of ZnO. Positron annihilation spectroscopy coupled with other techniques point to the presence of oxygen vacancies. Removing hydrogen followed by annealing in oxygen reduces the carrier concentration.

A deep-level transient spectroscopy study of gamma-ray irradiation on the passivation properties of silicon nitride layer on silicon

NASA Astrophysics Data System (ADS)

Dong, Peng; Yu, Xuegong; Ma, Yao; Xie, Meng; Li, Yun; Huang, Chunlai; Li, Mo; Dai, Gang; Zhang, Jian

2017-08-01

Plasma-enhanced chemical vapor deposited silicon nitride (SiNx) films are extensively used as passivation material in the solar cell industry. Such SiNx passivation layers are the most sensitive part to gamma-ray irradiation in solar cells. In this work, deep-level transient spectroscopy has been applied to analyse the influence of gamma-ray irradiation on the passivation properties of SiNx layer on silicon. It is shown that the effective carrier lifetime decreases with the irradiation dose. At the same time, the interface state density is significantly increased after irradiation, and its energy distribution is broadened and shifts deeper with respect to the conduction band edge, which makes the interface states becoming more efficient recombination centers for carriers. Besides, C-V characteristics show a progressive negative shift with increasing dose, indicating the generation of effective positive charges in SiNx films. Such positive charges are beneficial for shielding holes from the n-type silicon substrates, i. e. the field-effect passivation. However, based on the reduced carrier lifetime after irradiation, it can be inferred that the irradiation induced interface defects play a dominant role over the trapped positive charges, and therefore lead to the degradation of passivation properties of SiNx on silicon.

Cobalt related defect levels in silicon analyzed by temperature- and injection-dependent lifetime spectroscopy

NASA Astrophysics Data System (ADS)

Diez, S.; Rein, S.; Roth, T.; Glunz, S. W.

2007-02-01

Temperature- and injection-dependent lifetime spectroscopy (TIDLS) as a method to characterize point defects in silicon with several energy levels is demonstrated. An intentionally cobalt-contaminated p-type wafer was investigated by means of lifetime measurements performed at different temperatures up to 151°C. Two defect energy levels were required to model the lifetime curves on basis of the Shockley-Read-Hall statistics. The detailed analysis is based on the determination of the recently introduced defect parameter solution surface (DPSS) in order to extract the underlying defect parameters. A unique solution has been found for a deep defect level located in the upper band gap half with an energy depth of EC-Et=0.38±0.01eV, with a corresponding ratio of capture cross sections k =σn/σp=0.16 within the interval of uncertainty of 0.06-0.69. Additionally, a deep donor level in the lower band gap half known from the literature could be assigned to a second energy level within the DPSS analysis at Et-EV=0.41±0.02eV with a corresponding ratio of capture cross sections k =σn/σp=16±3. An investigation of the temperature dependence of the capture cross section for electrons suggests that the underlying recombination process of the defect in the lower band gap half is driven by a two stage cascade capture with an activation energy of ΔE =52±2meV. These results show that TIDLS in combination with DPSS analysis is a powerful method to characterize even multiple defect levels that are affecting carrier recombination lifetime in parallel.

Defect properties of InGaAsN layers grown as sub-monolayer digital alloys by molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Baranov, Artem I.; Gudovskikh, Alexander S.; Kudryashov, Dmitry A.; Lazarenko, Alexandra A.; Morozov, Ivan A.; Mozharov, Alexey M.; Nikitina, Ekaterina V.; Pirogov, Evgeny V.; Sobolev, Maxim S.; Zelentsov, Kirill S.; Egorov, Anton Yu.; Darga, Arouna; Le Gall, Sylvain; Kleider, Jean-Paul

2018-04-01

The defect properties of InGaAsN dilute nitrides grown as sub-monolayer digital alloys (SDAs) by molecular beam epitaxy for photovoltaic application were studied by space charge capacitance spectroscopy. Alloys of i-InGaAsN (Eg = 1.03 eV) were lattice-matched grown on GaAs wafers as a superlattice of InAs/GaAsN with one monolayer of InAs (<0.5 nm) between wide GaAsN (7-12 nm) layers as active layers in single-junction solar cells. Low p-type background doping was demonstrated at room temperature in samples with InGaAsN layers 900 nm and 1200 nm thick (less 1 × 1015 cm-3). According to admittance spectroscopy and deep-level transient spectroscopy measurements, the SDA approach leads to defect-free growth up to a thickness of 900 nm. An increase in thickness to 1200 nm leads to the formation of non-radiative recombination centers with an activation energy of 0.5 eV (NT = 8.4 × 1014 cm-3) and a shallow defect level at 0.20 eV. The last one leads to the appearance of additional doping, but its concentration is low (NT = 5 × 1014 cm-3) so it does not affect the photoelectric properties. However, further increase in thickness to 1600 nm, leads to significant growth of its concentration to (3-5) × 1015 cm-3, while the concentration of deep levels becomes 1.3 × 1015 cm-3. Therefore, additional free charge carriers appearing due to ionization of the shallow level change the band diagram from p-i-n to p-n junction at room temperature. It leads to a drop of the external quantum efficiency due to the effect of pulling electric field decrease in the p-n junction and an increased number of non-radiative recombination centers that negatively impact lifetimes in InGaAsN.

Radiation damage annealing mechanisms and possible low temperature annealing in silicon solar cells

NASA Technical Reports Server (NTRS)

Weinberg, I.; Swartz, C. K.

1980-01-01

Deep level transient spectroscopy and the Shockley-Read-Hall recombination theory are used to identify the defect responsible for reverse annealing in 2 ohm-cm n+/p silicon solar cells. This defect, with energy level at Ev + 0.30 eV, has been tentatively identified as a boron-oxygen-vacancy complex. It has been also determined by calculation that the removal of this defect could result in significant annealing at temperatures as low as 200 C for 2 ohm-cm and lower resistivity cells.

Measurement of Venous Blood Flow in the Lower Limbs: Prevention of Deep Vein Thrombosis during Prolonged Sitting

DTIC Science & Technology

2004-06-01

Abstract. The venous blood flow during stretching and deep breathing in the sitting posture was examined in the present study. First, an...increase in the venous return. Therefore, we suggest that stretching and deep breathing can be used sometimes as preventive measures for deep vein...thrombosis during prolonged sitting. Keywords. Venous blood flow, Near infrared spectroscopy, Deep vein thrombosis. 1. Introduction It has been

Influence of annealing atmosphere on formation of electrically-active defects in rutile TiO2

NASA Astrophysics Data System (ADS)

Zimmermann, C.; Bonkerud, J.; Herklotz, F.; Sky, T. N.; Hupfer, A.; Monakhov, E.; Svensson, B. G.; Vines, L.

2018-04-01

Electronic states in the upper part of the bandgap of reduced and/or hydrogenated n-type rutile TiO2 single crystals have been studied by means of thermal admittance and deep-level transient spectroscopy measurements. The studies were performed at sample temperatures between 28 and 300 K. The results reveal limited charge carrier freeze-out even at 28 K and evidence the existence of dominant shallow donors with ionization energies below 25 meV. Interstitial atomic hydrogen is considered to be a major contributor to these shallow donors, substantiated by infrared absorption measurements. Three defect energy levels with positions of about 70 meV, 95 meV, and 120 meV below the conduction band edge occur in all the studied samples, irrespective of the sample production batch and the post-growth heat treatment used. The origin of these levels is discussed in terms of electron polarons, intrinsic point defects, and/or common residual impurities, where especially interstitial titanium atoms, oxygen vacancies, and complexes involving Al atoms appear as likely candidates. In contrast, no common deep-level defect, exhibiting a charge state transition in the 200-700 meV range below the conduction band edge, is found in different samples. This may possibly indicate a strong influence on deep-level defects by the post-growth heat treatments employed.

Radiation damage and defect behavior in ion-implanted, lithium counterdoped silicon solar cells

NASA Technical Reports Server (NTRS)

Weinberg, I.; Mehta, S.; Swartz, C. K.

1984-01-01

Boron doped silicon n+p solar cells were counterdoped with lithium by ion implantation and the resuitant n+p cells irradiated by 1 MeV electrons. The function of fluence and a Deep Level Transient Spectroscopy (DLTS) was studied to correlate defect behavior with cell performance. It was found that the lithium counterdoped cells exhibited significantly increased radiation resistance when compared to boron doped control cells. It is concluded that the annealing behavior is controlled by dissociation and recombination of defects. The DLTS studies show that counterdoping with lithium eliminates at least three deep level defects and results in three new defects. It is speculated that the increased radiation resistance of the counterdoped cells is due primarily to the interaction of lithium with oxygen, single vacanies and divacancies and that the lithium-oxygen interaction is the most effective in contributing to the increased radiation resistance.

Radiation damage and defect behavior in ion-implanted, lithium counterdoped silicon solar cells

NASA Technical Reports Server (NTRS)

Weinberg, I.; Mehta, S.; Swartz, C. K.

1984-01-01

Boron doped silicon n+p solar cells were counterdoped with lithium by ion implanation and the resultant n+p cells irradiated by 1 MeV electrons. The function of fluence and a Deep Level Transient Spectroscopy (DLTS) was studied to correlate defect behavior with cell performance. It was found that the lithium counterdoped cells exhibited significantly increased radiation resistance when compared to boron doped control cells. It is concluded that the annealing behavior is controlled by dissociation and recombination of defects. The DLTS studies show that counterdoping with lithium eliminates at least three deep level defects and results in three new defects. It is speculated that the increased radiation resistance of the counterdoped cells is due primarily to the interaction of lithium with oxygen, single vacancies and divacancies and that the lithium-oxygen interaction is the most effective in contributing to the increased radiation resistance.

Defects and annealing studies in 1-Me electron irradiated (AlGa)As-GaAs solar cells

NASA Technical Reports Server (NTRS)

Li, S. S.; Wang, W. L.; Loo, R. Y.; Rahilly, W. P.

1982-01-01

The deep-level defects and recombination mechanisms in the one-MeV electron irradiated (AlGa)As-GaAs solar cells under various irradiation and annealing conditions are discussed. Deep-level transient spectroscopy (DLTS) and capacitance-voltage (CV) techniques were used to determine the defect and recombination parameters such as energy levels and defect density, carrier capture cross sections and lifetimes for both electron and hole traps as well as hole diffusion lengths in these electron irradiated GaAs solar cells. GaAs solar cells used in this study were prepared by the infinite solution melt liquid phase epitaxial (LPE) technique at Hughes Research Lab., with (Al0.9Ga0.1)-As window layer, Be-diffused p-GaAs layer on Sn-doped n-GaAs or undoped n-GaAs active layer grown on n(+)-GaAs substrate. Mesa structure with area of 5.86x1000 sq cm was fabricated. Three different irradiation and annealing experiments were performed on these solar cells.

Collaborative Research and Development (CR&D). Task Order 0036: Physical and Chemical Processes of Operating Electronic Devices

DTIC Science & Technology

2006-09-01

actually seen. A. Hierro , … S. A. Ringel et al., Phys. Stat. Sol (b) 228, 937 (2001). Ohio State U. Use DLTS and DLOS (Deep Level Optical Spectroscopy...to threading dislocations. Also see A. Hierro et al., APL 76, 3064 (2000), where traps at EC-ET=0.58-0.62, 1.35, 2.57-2.64, 3.22eV are seen in GaN

The MIND PALACE: A Multi-Spectral Imaging and Spectroscopy Database for Planetary Science

NASA Astrophysics Data System (ADS)

Eshelman, E.; Doloboff, I.; Hara, E. K.; Uckert, K.; Sapers, H. M.; Abbey, W.; Beegle, L. W.; Bhartia, R.

2017-12-01

The Multi-Instrument Database (MIND) is the web-based home to a well-characterized set of analytical data collected by a suite of deep-UV fluorescence/Raman instruments built at the Jet Propulsion Laboratory (JPL). Samples derive from a growing body of planetary surface analogs, mineral and microbial standards, meteorites, spacecraft materials, and other astrobiologically relevant materials. In addition to deep-UV spectroscopy, datasets stored in MIND are obtained from a variety of analytical techniques obtained over multiple spatial and spectral scales including electron microscopy, optical microscopy, infrared spectroscopy, X-ray fluorescence, and direct fluorescence imaging. Multivariate statistical analysis techniques, primarily Principal Component Analysis (PCA), are used to guide interpretation of these large multi-analytical spectral datasets. Spatial co-referencing of integrated spectral/visual maps is performed using QGIS (geographic information system software). Georeferencing techniques transform individual instrument data maps into a layered co-registered data cube for analysis across spectral and spatial scales. The body of data in MIND is intended to serve as a permanent, reliable, and expanding database of deep-UV spectroscopy datasets generated by this unique suite of JPL-based instruments on samples of broad planetary science interest.

Characterisation of signal enhancements achieved when utilizing a photon diode in deep Raman spectroscopy of tissue

PubMed Central

Vardaki, Martha Z.; Matousek, Pavel; Stone, Nicholas

2016-01-01

We characterise the performance of a beam enhancing element (‘photon diode’) for use in deep Raman spectroscopy (DRS) of biological tissues. The optical component enhances the number of laser photons coupled into a tissue sample by returning escaping photons back into it at the illumination zone. The method is compatible with transmission Raman spectroscopy, a deep Raman spectroscopy concept, and its implementation leads to considerable enhancement of detected Raman photon rates. In the past, the enhancement concept was demonstrated with a variety of samples (pharmaceutical tablets, tissue, etc) but it was not systematically characterized with biological tissues. In this study, we investigate the enhancing properties of the photon diode in the transmission Raman geometry as a function of: a) the depth and b) the optical properties of tissue samples. Liquid tissue phantoms were employed to facilitate systematic variation of optical properties. These were chosen to mimic optical properties of human tissues, including breast and prostate. The obtained results evidence that a photon diode can enhance Raman signals of tissues by a maximum of × 2.4, although it can also decrease the signals created towards the back of samples that exhibit high scattering or absorption properties. PMID:27375932

Electronic effects of Se and Pb dopants in TlBr

NASA Astrophysics Data System (ADS)

Smith, Holland M.; Phillips, David J.; Sharp, Ian D.; Beeman, Jeffrey W.; Chrzan, Daryl C.; Haegel, Nancy M.; Haller, Eugene E.; Ciampi, Guido; Kim, Hadong; Shah, Kanai S.

2012-05-01

Deep levels in Se- and Pb-doped bulk TlBr detectors were characterized with photo-induced conductivity transient spectroscopy (PICTS) and cathodoluminescence (CL). Se-doped TlBr revealed two traps with energies of 0.35 and 0.45 eV in PICTS spectra. The Pb-doped material revealed three levels with energies of 0.11, 0.45, and 0.75 eV. CL measurements in both materials correlate with optical transitions involving some of the identified levels. The ambipolar carrier lifetimes of Se-doped and Pb-doped TlBr were measured with microwave reflectivity transients and found to be significantly lower than the lifetime of undoped TlBr.

Deep level transient spectroscopic analysis of p/n junction implanted with boron in n-type silicon substrate

NASA Astrophysics Data System (ADS)

Wakimoto, Hiroki; Nakazawa, Haruo; Matsumoto, Takashi; Nabetani, Yoichi

2018-04-01

For P-i-N diodes implanted and activated with boron ions into a highly-resistive n-type Si substrate, it is found that there is a large difference in the leakage current between relatively low temperature furnace annealing (FA) and high temperature laser annealing (LA) for activation of the p-layer. Since electron trap levels in the n-type Si substrate is supposed to be affected, we report on Deep Level Transient Spectroscopy (DLTS) measurement results investigating what kinds of trap levels are formed. As a result, three kinds of electron trap levels are confirmed in the region of 1-4 μm from the p-n junction. Each DLTS peak intensity of the LA sample is smaller than that of the FA sample. In particular, with respect to the trap level which is the closest to the silicon band gap center most affecting the reverse leakage current, it was not detected in LA. It is considered that the electron trap levels are decreased due to the thermal energy of LA. On the other hand, four kinds of trap levels are confirmed in the region of 38-44 μm from the p-n junction and the DLTS peak intensities of FA and LA are almost the same, considering that the thermal energy of LA has not reached this area. The large difference between the reverse leakage current of FA and LA is considered to be affected by the deep trap level estimated to be the interstitial boron.

Effect of precursor solutions stirring on deep level defects concentration and spatial distribution in low temperature aqueous chemical synthesis of zinc oxide nanorods

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

Alnoor, Hatim, E-mail: hatim.alnoor@liu.se; Chey, Chan Oeurn; Pozina, Galia

Hexagonal c-axis oriented zinc oxide (ZnO) nanorods (NRs) with 120-300 nm diameters are synthesized via the low temperature aqueous chemical route at 80 °C on silver-coated glass substrates. The influence of varying the precursor solutions stirring durations on the concentration and spatial distributions of deep level defects in ZnO NRs is investigated. Room temperature micro-photoluminesnce (μ-PL) spectra were collected for all samples. Cathodoluminescence (CL) spectra of the as-synthesized NRs reveal a significant change in the intensity ratio of the near band edge emission (NBE) to the deep-level emission (DLE) peaks with increasing stirring durations. This is attributed to the variation inmore » the concentration of the oxygen-deficiency with increasing stirring durations as suggested from the X-ray photoelectron spectroscopy analysis. Spatially resolved CL spectra taken along individual NRs revealed that stirring the precursor solutions for relatively short duration (1-3 h), which likely induced high super saturation under thermodynamic equilibrium during the synthesis process, is observed to favor the formation of point defects moving towards the tip of the NRs. In contrary, stirring for longer duration (5-15 h) will induce low super saturation favoring the formation of point defects located at the bottom of the NRs. These findings demonstrate that it is possible to control the concentration and spatial distribution of deep level defects in ZnO NRs by varying the stirring durations of the precursor solutions.« less

Carbon-hydrogen defects with a neighboring oxygen atom in n-type Si

NASA Astrophysics Data System (ADS)

Gwozdz, K.; Stübner, R.; Kolkovsky, Vl.; Weber, J.

2017-07-01

We report on the electrical activation of neutral carbon-oxygen complexes in Si by wet-chemical etching at room temperature. Two deep levels, E65 and E75, are observed by deep level transient spectroscopy in n-type Czochralski Si. The activation enthalpies of E65 and E75 are obtained as EC-0.11 eV (E65) and EC-0.13 eV (E75). The electric field dependence of their emission rates relates both levels to single acceptor states. From the analysis of the depth profiles, we conclude that the levels belong to two different defects, which contain only one hydrogen atom. A configuration is proposed, where the CH1BC defect, with hydrogen in the bond-centered position between neighboring C and Si atoms, is disturbed by interstitial oxygen in the second nearest neighbor position to substitutional carbon. The significant reduction of the CH1BC concentration in samples with high oxygen concentrations limits the use of this defect for the determination of low concentrations of substitutional carbon in Si samples.

Energy levels distribution in supersaturated silicon with titanium for photovoltaic applications

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

Pérez, E., E-mail: eduper@ele.uva.es; Castán, H.; García, H.

2015-01-12

In the attempt to form an intermediate band in the bandgap of silicon substrates to give it the capability to absorb infrared radiation, we studied the deep levels in supersaturated silicon with titanium. The technique used to characterize the energy levels was the thermal admittance spectroscopy. Our experimental results showed that in samples with titanium concentration just under Mott limit there was a relationship among the activation energy value and the capture cross section value. This relationship obeys to the well known Meyer-Neldel rule, which typically appears in processes involving multiple excitations, like carrier capture/emission in deep levels, and itmore » is generally observed in disordered systems. The obtained characteristic Meyer-Neldel parameters were Tmn = 176 K and kTmn = 15 meV. The energy value could be associated to the typical energy of the phonons in the substrate. The almost perfect adjust of all experimental data to the same straight line provides further evidence of the validity of the Meyer Neldel rule, and may contribute to obtain a deeper insight on the ultimate meaning of this phenomenon.« less

Compact, multi-exposure speckle contrast optical spectroscopy (SCOS) device for measuring deep tissue blood flow

PubMed Central

Dragojević, Tanja; Hollmann, Joseph L.; Tamborini, Davide; Portaluppi, Davide; Buttafava, Mauro; Culver, Joseph P.; Villa, Federica; Durduran, Turgut

2017-01-01

Speckle contrast optical spectroscopy (SCOS) measures absolute blood flow in deep tissue, by taking advantage of multi-distance (previously reported in the literature) or multi-exposure (reported here) approach. This method promises to use inexpensive detectors to obtain good signal-to-noise ratio, but it has not yet been implemented in a suitable manner for a mass production. Here we present a new, compact, low power consumption, 32 by 2 single photon avalanche diode (SPAD) array that has no readout noise, low dead time and has high sensitivity in low light conditions, such as in vivo measurements. To demonstrate the capability to measure blood flow in deep tissue, healthy volunteers were measured, showing no significant differences from the diffuse correlation spectroscopy. In the future, this array can be miniaturized to a low-cost, robust, battery operated wireless device paving the way for measuring blood flow in a wide-range of applications from sport injury recovery and training to, on-field concussion detection to wearables. PMID:29359106

Effects of Iron Contamination and Hydrogen Passivation on the Electrical Properties of Oxygen Precipitates in CZ-Si

NASA Astrophysics Data System (ADS)

Li, Jiyang; Song, Lihui; Yu, Xuegong; Yang, Deren

2018-04-01

Oxygen precipitates (OPs) are unavoidably formed in Czochralski silicon (CZ-Si) containing relatively high concentrations of oxygen. The recombination behavior of such defects is also vital for bulk devices like solar cells as they can reduce the minority carrier lifetime and degrade the cell performance. In our experiments, the characteristics of oxygen precipitation in n-type CZ-Si are systematically investigated by means of Fourier transform infrared spectroscopy (FTIR), deep level transient spectroscopy (DLTS) and electron beam induced current (EBIC). It is found that the iron contamination in n-type CZ-Si can strongly influence the OPs generation and their electrical properties, whereas the hydrogen passivation can effectively reduce the recombination activity of OPs.

Influence of deposition conditions on electrical and mechanical properties of Sm2O3-doped CeO2 thin films prepared by EB-PVD (+IBAD) methods. Part 1: Effective relative permittivity

NASA Astrophysics Data System (ADS)

Hartmanová, Mária; Nádaždy, Vojtech; Kundracik, František; Mansilla, Catina

2013-03-01

Study is devoted to the effective relative permittivity ɛr of CeO2 + x. Sm2O3 thin films prepared by electron-beam physical vapour deposition and ionic beam-assisted deposition methods; ɛr was investigated by three independent ways from the bulk parallel capacitance Cp, impedance capacitance Cimp, and accumulation capacitance Cacc in dependence on the deposition conditions (deposition temperature, dopant amount x and Ar+ ion bombardment during the film deposition) used. Investigations were performed using impedance spectroscopy, capacitance-voltage and current-voltage characteristics as well as deep level transient spectroscopy. Results obtained are described and discussed.

Electrical conductivity of In2O3 and Ga2O3 after low temperature ion irradiation; implications for instrinsic defect formation and charge neutrality level.

PubMed

Vines, L; Bhoodoo, C; von Wenckstern, H; Grundmann, M

2017-12-13

The evolution of sheet resistance of n-type In 2 O 3 and Ga 2 O 3 exposed to bombardment with MeV 12 C and 28 Si ions at 35 K is studied in situ. While the sheet resistance of Ga 2 O 3 increased by more than eight orders of magnitude as a result of ion irradiation, In 2 O 3 showed a more complex defect evolution and became more conductive when irradiated at the highest doses. Heating up to room temperature reduced the sheet resistivity somewhat, but Ga 2 O 3 remained highly resistive, while In 2 O 3 showed a lower resistance than as deposited samples. Thermal admittance spectroscopy and deep level transient spectroscopy did not reveal new defect levels for irradiation up to [Formula: see text] cm -2 . A model where larger defect complexes preferentially produce donor like defects in In 2 O 3 is proposed, and may reveal a microscopic view of a charge neutrality level within the conduction band, as previously proposed.

Electrical conductivity of In2O3 and Ga2O3 after low temperature ion irradiation; implications for instrinsic defect formation and charge neutrality level

NASA Astrophysics Data System (ADS)

Vines, L.; Bhoodoo, C.; von Wenckstern, H.; Grundmann, M.

2018-01-01

The evolution of sheet resistance of n-type In2O3 and Ga2O3 exposed to bombardment with MeV 12C and 28Si ions at 35 K is studied in situ. While the sheet resistance of Ga2O3 increased by more than eight orders of magnitude as a result of ion irradiation, In2O3 showed a more complex defect evolution and became more conductive when irradiated at the highest doses. Heating up to room temperature reduced the sheet resistivity somewhat, but Ga2O3 remained highly resistive, while In2O3 showed a lower resistance than as deposited samples. Thermal admittance spectroscopy and deep level transient spectroscopy did not reveal new defect levels for irradiation up to 2 × 1012 cm-2. A model where larger defect complexes preferentially produce donor like defects in In2O3 is proposed, and may reveal a microscopic view of a charge neutrality level within the conduction band, as previously proposed.

Deep Raman spectroscopy for the non-invasive standoff detection of concealed chemical threat agents.

PubMed

Izake, Emad L; Cletus, Biju; Olds, William; Sundarajoo, Shankaran; Fredericks, Peter M; Jaatinen, Esa

2012-05-30

Deep Raman spectroscopy has been utilized for the standoff detection of concealed chemical threat agents from a distance of 15 m under real life background illumination conditions. By using combined time and space resolved measurements, various explosive precursors hidden in opaque plastic containers were identified non-invasively. Our results confirm that combined time and space resolved Raman spectroscopy leads to higher selectivity towards the sub-layer over the surface layer as well as enhanced rejection of fluorescence from the container surface when compared to standoff spatially offset Raman spectroscopy. Raman spectra that have minimal interference from the packaging material and good signal-to-noise ratio were acquired within 5 s of measurement time. A new combined time and space resolved Raman spectrometer has been designed with nanosecond laser excitation and gated detection, making it of lower cost and complexity than picosecond-based laboratory systems. Copyright © 2012 Elsevier B.V. All rights reserved.

Possible origin of photoconductivity in La0.7Ca0.3MnO3

NASA Astrophysics Data System (ADS)

Sagdeo, P. R.; Choudhary, R. J.; Phase, D. M.

2010-01-01

The effect of photon energy on the density of states near Fermi level of pulsed laser deposited La0.7Ca0.3MnO3 thin film has been studied to investigate the possible origin of change in the conductivity of these manganites upon photon exposure. For this purpose the photoelectron spectroscopy measurements were carried out using CSR beamline (BL-2) on Indus-1 synchrotron radiation source. The valance band spectra were measured at room temperature with photon energy ranging from 40 to 60 eV. We could see huge change in the density of states near Fermi level and this change is observed to be highest at 56 eV which is due to the resonance between Mn 3p to Mn 3d level. Our results suggest that the probability of electron transfer from deep Mn 3p level to Mn 3d-eg level is higher than that of Mn 3d-t2g level. It appears that this transfer of electron from deep Mn level to Mn 3d-eg level not only modifies the density of state near Fermi level but also changes the mobility of electrons by modifying the electron lattice coupling due to presence of Mn+3 Jahn-Teller ion.

DLTS analysis of radiation-induced defects in one-MeV electron irradiated germanium and Alsub0.17Gasub0.83As solar cells

NASA Technical Reports Server (NTRS)

Li, S. B.; Choi, C. G.; Loo, R. Y.

1985-01-01

The radiation-induced deep-level defects in one-MeV electron-irradiated germanium and AlxGal-xAs solar cell materials using the deep-level transient spectroscopy (DLTS) and C-V techniques were investigated. Defect and recombination parameters such as defect density and energy levels, capture cross sections and lifetimes for both electron and hole traps were determined. The germanium and AlGaAs p/n junction cells were irradiated by one-MeV electrons. The DLTS, I-V, and C-V measurements were performed on these cells. The results are summarized as follows: (1) for the irradiated germanium samples, the dominant electron trap was due to the E sub - 0.24 eV level with density around 4x10 to the 14th power 1/cu cm, independent of electron fluence, its origin is attributed to the vacancy-donor complex defect formed during the electron irradiation; (2) in the one-MeV electron irradiated Al0.17Ga0.83 as sample, two dominant electron traps with energies of Ec-0.19 and -0.29 eV were observed, the density for both electron traps remained nearly constant, independent of electron fluence. It is shown that one-MeV electron irradiation creates very few or no new deep-level traps in both the germanium and AlxGa1-xAs cells, and are suitable for fabricating the radiation-hard high efficiency multijunction solar cells for space applications.

Development of Raman spectral markers to assess metastatic bone in breast cancer

PubMed Central

Ding, Hao; Nyman, Jeffry S.; Sterling, Julie A.; Perrien, Daniel S.; Mahadevan-Jansen, Anita; Bi, Xiaohong

2014-01-01

Abstract. Bone is the most common site for breast cancer metastases. One of the major complications of bone metastasis is pathological bone fracture caused by chronic bone loss and degeneration. Current guidelines for the prediction of pathological fracture mainly rely on radiographs or computed tomography, which are limited in their ability to predict fracture risk. The present study explored the feasibility of using Raman spectroscopy to estimate pathological fracture risk by characterizing the alterations in the compositional properties of metastatic bones. Tibiae with evident bone destruction were investigated using Raman spectroscopy. The carbonation level calculated by the ratio of carbonate/phosphate ν1 significantly increased in the tumor-bearing bone at all the sampling regions at the proximal metaphysis and diaphysis, while tumor-induced elevation in mineralization and crystallinity was more pronounced in the metaphysis. Furthermore, the increased carbonation level is positively correlated to bone lesion size, indicating that this parameter could serve as a unique spectral marker for tumor progression and bone loss. With the promising advances in the development of spatially offset Raman spectroscopy for deep tissue measurement, this spectral marker can potentially be used for future noninvasive evaluation of metastatic bone and prediction of pathological fracture risk. PMID:24933683

Development of Raman spectral markers to assess metastatic bone in breast cancer

NASA Astrophysics Data System (ADS)

Ding, Hao; Nyman, Jeffry S.; Sterling, Julie A.; Perrien, Daniel S.; Mahadevan-Jansen, Anita; Bi, Xiaohong

2014-11-01

Bone is the most common site for breast cancer metastases. One of the major complications of bone metastasis is pathological bone fracture caused by chronic bone loss and degeneration. Current guidelines for the prediction of pathological fracture mainly rely on radiographs or computed tomography, which are limited in their ability to predict fracture risk. The present study explored the feasibility of using Raman spectroscopy to estimate pathological fracture risk by characterizing the alterations in the compositional properties of metastatic bones. Tibiae with evident bone destruction were investigated using Raman spectroscopy. The carbonation level calculated by the ratio of carbonate/phosphate ν1 significantly increased in the tumor-bearing bone at all the sampling regions at the proximal metaphysis and diaphysis, while tumor-induced elevation in mineralization and crystallinity was more pronounced in the metaphysis. Furthermore, the increased carbonation level is positively correlated to bone lesion size, indicating that this parameter could serve as a unique spectral marker for tumor progression and bone loss. With the promising advances in the development of spatially offset Raman spectroscopy for deep tissue measurement, this spectral marker can potentially be used for future noninvasive evaluation of metastatic bone and prediction of pathological fracture risk.

Persistent photocurrent and deep level traps in PLD-grown In-Ga-Zn-O thin films studied by thermally stimulated current spectroscopy

NASA Astrophysics Data System (ADS)

Wang, Buguo; Anders, Jason; Leedy, Kevin; Schuette, Michael; Look, David

2018-02-01

InGaZnO (IGZO) is a promising semiconductor material for thin-film transistors (TFTs) used in DC and RF switching applications, especially since it can be grown at low temperatures on a wide variety of substrates. Enhancement-mode TFTs based on IGZO thin films grown by pulsed laser deposition (PLD) have been recently fabricated and these transistors show excellent performance; however, compositional variations and defects can adversely affect film quality, especially in regard to electrical properties. In this study, we use thermally stimulated current (TSC) spectroscopy to characterize the electrical properties and the deep traps in PLD-grown IGZO thin films. It was found that the as-grown sample has a DC activation energy of 0.62 eV, and two major traps with activation energies at 0.16-0.26 eV and at 0.90 eV. However, a strong persistent photocurrent (PPC) sometimes exists in the as-grown sample, so we carry out post-growth annealing in an attempt to mitigate the effect. It was found that annealing in argon increases the conduction, produces more PPC and also makes more traps observable. Annealing in air makes the film more resistive, and removes PPC and all traps but one. This work demonstrates that current-based trap emission, such as that associated with the TSC, can effectively reveal electronic defects in highlyresistive semiconductor materials, especially those are not amenable to capacitance-based techniques, such as deeplevel transient spectroscopy (DLTS).

Electrical and Optical Studies of Deep Levels in Nominally Undoped Thallium Bromide

NASA Astrophysics Data System (ADS)

Smith, Holland M.; Haegel, Nancy M.; Phillips, David J.; Cirignano, Leonard; Ciampi, Guido; Kim, Hadong; Chrzan, Daryl C.; Haller, Eugene E.

2014-02-01

Photo-induced conductivity transient spectroscopy (PICTS) and cathodoluminescence (CL) measurements were performed on nominally undoped detector grade samples of TlBr. In PICTS measurements, nine traps were detected in the temperature range 80-250 K using four-gate analysis. Five of the traps are tentatively identified as electron traps, and four as hole traps. CL measurements yielded two broad peaks common to all samples and most likely associated with defects. Correlations between the optically and electrically detected deep levels are considered. Above 250 K, the photoconductivity transients measured in the PICTS experiments exhibited anomalous transient behavior, indicated by non-monotonic slope variations as a function of time. The origin of the transients is under further investigation, but their presence precludes the accurate determination of trap parameters in TlBr above 250 K with traditional PICTS analysis. Their discovery was made possible by the use of a PICTS system that records whole photoconductivity transients, as opposed to reduced and processed signals.

Surface acceptor states in MBE-grown CdTe layers

NASA Astrophysics Data System (ADS)

Wichrowska, Karolina; Wosinski, Tadeusz; Tkaczyk, Zbigniew; Kolkovsky, Valery; Karczewski, Grzegorz

2018-04-01

A deep-level hole trap associated with surface defect states has been revealed with deep-level transient spectroscopy investigations of metal-semiconductor junctions fabricated on nitrogen doped p-type CdTe layers grown by the molecular-beam epitaxy technique. The trap displayed the hole-emission activation energy of 0.33 eV and the logarithmic capture kinetics indicating its relation to extended defect states at the metal-semiconductor interface. Strong electric-field-induced enhancement of the thermal emission rate of holes from the trap has been attributed to the phonon-assisted tunneling effect from defect states involving very large lattice relaxation around the defect and metastability of its occupied state. Passivation with ammonium sulfide of the CdTe surface, prior to metallization, results in a significant decrease in the trap density. It also results in a distinct reduction in the width of the surface-acceptor-state-induced hysteresis loops in the capacitance vs. voltage characteristics of the metal-semiconductor junctions.

Influence of electron irradiation on hydrothermally grown zinc oxide single crystals

NASA Astrophysics Data System (ADS)

Lu, L. W.; So, C. K.; Zhu, C. Y.; Gu, Q. L.; Li, C. J.; Fung, S.; Brauer, G.; Anwand, W.; Skorupa, W.; Ling, C. C.

2008-09-01

The resistivity of hydrothermally grown ZnO single crystals increased from ~103 Ω cm to ~106 Ω cm after 1.8 MeV electron irradiation with a fluence of ~1016 cm-2, and to ~109 Ω cm as the fluence increased to ~1018 cm-2. Defects in samples were studied by thermally stimulated current (TSC) spectroscopy and positron lifetime spectroscopy (PLS). After the electron irradiation with a fluence of 1018 cm-2, the normalized TSC signal increased by a factor of ~100. A Zn vacancy was also introduced by the electron irradiation, though with a concentration lower than expected. After annealing in air at 400 °C, the resistivity and the deep traps concentrations recovered to the levels of the as-grown sample, and the Zn vacancy was removed.

Hydrogen-bearing iron peroxide and its implications to the deep Earth

NASA Astrophysics Data System (ADS)

Liu, J.; Hu, Q.; Kim, D. Y.; Wu, Z.; Wang, W.; Alp, E. E.; Yang, L.; Xiao, Y.; Meng, Y.; Chow, P.; Greenberg, E.; Prakapenka, V. B.; Mao, H. K.; Mao, W. L.

2017-12-01

Hydrous materials subducted into the deep mantle may play a significant role in the geophysical and geochemical processes of the lower mantle through geological time, but their roles have not become clear yet in the region. Hydrogen-bearing iron peroxide (FeO2Hx) was recently discovered to form through dehydrogenation of goethite (e.g., FeOOH) and the reaction between hematite (Fe2O3) and water under deep lower mantle conditions. We conducted synchrotron Mössbauer, X-ray absorption, and X-ray emission spectroscopy measurements to investigate the electronic spin and valence states of iron in hydrogen-bearing iron peroxide (FeO2Hx) in-situ at high pressures. Combined with theoretical calculations and other high-pressure experiments (i.e., nuclear resonant inelastic x-ray scattering spectroscopy and X-ray diffraction coupled with laser-heated diamond-anvil cell techniques), we find that the intriguing properties of FeO2Hx could shed light on the origin of a number of the observed geochemical and geophysical anomalies in the deep Earth.

Electrical characterisation of deep level defects in Be-doped AlGaAs grown on (100) and (311)A GaAs substrates by MBE

PubMed Central

2011-01-01

The growth of high mobility two-dimensional hole gases (2DHGs) using GaAs-GaAlAs heterostructures has been the subject of many investigations. However, despite many efforts hole mobilities in Be-doped structures grown on (100) GaAs substrate remained considerably lower than those obtained by growing on (311)A oriented surface using silicon as p-type dopant. In this study we will report on the properties of hole traps in a set of p-type Be-doped Al0.29Ga0.71As samples grown by molecular beam epitaxy on (100) and (311)A GaAs substrates using deep level transient spectroscopy (DLTS) technique. In addition, the effect of the level of Be-doping concentration on the hole deep traps is investigated. It was observed that with increasing the Be-doping concentration from 1 × 1016 to 1 × 1017 cm-3 the number of detected electrically active defects decreases for samples grown on (311)A substrate, whereas, it increases for (100) orientated samples. The DLTS measurements also reveal that the activation energies of traps detected in (311)A are lower than those in (100). From these findings it is expected that mobilities of 2DHGs in Be-doped GaAs-GaAlAs devices grown on (311)A should be higher than those on (100). PMID:21711687

Algorithm for removing scalp signals from functional near-infrared spectroscopy signals in real time using multidistance optodes.

PubMed

Kiguchi, Masashi; Funane, Tsukasa

2014-11-01

A real-time algorithm for removing scalp-blood signals from functional near-infrared spectroscopy signals is proposed. Scalp and deep signals have different dependencies on the source-detector distance. These signals were separated using this characteristic. The algorithm was validated through an experiment using a dynamic phantom in which shallow and deep absorptions were independently changed. The algorithm for measurement of oxygenated and deoxygenated hemoglobins using two wavelengths was explicitly obtained. This algorithm is potentially useful for real-time systems, e.g., brain-computer interfaces and neuro-feedback systems.

The Excitation of High Spin States with Quasielastic and Deep Inelastic Reactions.

NASA Astrophysics Data System (ADS)

Knott, Clinton Neal

1988-12-01

The feasibility of populating high spin states using reactions induced by a 220 MeV ^{22 }Ne beam on a ^{170} Er target was studied. The experiment was carried out using a multidetector array for high resolution gamma-ray spectroscopy, a 14 element sum multiplicity spectrometer and six DeltaE-E particle telescopes. Detailed information was obtained concerning the reaction mechanisms associated with various reaction channels. Deep inelastic collisions are shown to be a promising tool for high spin spectroscopy in regions of the chart of nuclides which are not accessible by other reactions.

Population of high spin states by quasi-elastic and deep inelastic collisions

NASA Astrophysics Data System (ADS)

Takai, H.; Knott, C. N.; Winchell, D. F.; Saladin, J. X.; Kaplan, M. S.; de Faro, L.; Aryaeinejad, R.; Blue, R. A.; Ronningen, R. M.; Morrissey, D. J.; Lee, I. Y.; Dietzsch, O.

1988-09-01

The feasibility of populating high spin states using reactions induced by a 10 MeV/nucleon 22Ne beam on 170Er was studied. The experiment was carried out using a multidetector array for high resolution γ-ray spectroscopy, a 14 element sum-multiplicity spectrometer and six ΔE-E telescopes. Detailed information was obtained concerning the reaction mechanisms associated with various reaction channels. Deep inelastic collisions are shown to be a promising tool for high spin spectroscopy in regions of the chart of nuclides which are not accessible by other reactions.

Validation of a high-power, time-resolved, near-infrared spectroscopy system for measurement of superficial and deep muscle deoxygenation during exercise.

PubMed

Koga, Shunsaku; Barstow, Thomas J; Okushima, Dai; Rossiter, Harry B; Kondo, Narihiko; Ohmae, Etsuko; Poole, David C

2015-06-01

Near-infrared assessment of skeletal muscle is restricted to superficial tissues due to power limitations of spectroscopic systems. We reasoned that understanding of muscle deoxygenation may be improved by simultaneously interrogating deeper tissues. To achieve this, we modified a high-power (∼8 mW), time-resolved, near-infrared spectroscopy system to increase depth penetration. Precision was first validated using a homogenous optical phantom over a range of inter-optode spacings (OS). Coefficients of variation from 10 measurements were minimal (0.5-1.9%) for absorption (μa), reduced scattering, simulated total hemoglobin, and simulated O2 saturation. Second, a dual-layer phantom was constructed to assess depth sensitivity, and the thickness of the superficial layer was varied. With a superficial layer thickness of 1, 2, 3, and 4 cm (μa = 0.149 cm(-1)), the proportional contribution of the deep layer (μa = 0.250 cm(-1)) to total μa was 80.1, 26.9, 3.7, and 0.0%, respectively (at 6-cm OS), validating penetration to ∼3 cm. Implementation of an additional superficial phantom to simulate adipose tissue further reduced depth sensitivity. Finally, superficial and deep muscle spectroscopy was performed in six participants during heavy-intensity cycle exercise. Compared with the superficial rectus femoris, peak deoxygenation of the deep rectus femoris (including the superficial intermedius in some) was not significantly different (deoxyhemoglobin and deoxymyoglobin concentration: 81.3 ± 20.8 vs. 78.3 ± 13.6 μM, P > 0.05), but deoxygenation kinetics were significantly slower (mean response time: 37 ± 10 vs. 65 ± 9 s, P ≤ 0.05). These data validate a high-power, time-resolved, near-infrared spectroscopy system with large OS for measuring the deoxygenation of deep tissues and reveal temporal and spatial disparities in muscle deoxygenation responses to exercise. Copyright © 2015 the American Physiological Society.

Carrier removal and defect behavior in p-type InP

NASA Technical Reports Server (NTRS)

Weinberg, I.; Swartz, C. K.; Drevinsky, P. J.

1992-01-01

A simple expression, obtained from the rate equation for defect production, was used to relate carrier removal to defect production and hole trapping rates in p-type InP after irradiation by 1-MeV electrons. Specific contributions to carrier removal from defect levels H3, H4, and H5 were determined from combined deep-level transient spectroscopy (DLTS) and measured carrier concentrations. An additional contribution was attributed to one or more defects not observed by the present DLTS measurements. The high trapping rate observed for H5 suggests that this defect, if present in relatively high concentration, could be dominant in p-type InP.

A detailed analysis of the energy levels configuration existing in the band gap of supersaturated silicon with titanium for photovoltaic applications

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

Pérez, E.; Dueñas, S.; Castán, H.

2015-12-28

The energy levels created in supersaturated n-type silicon substrates with titanium implantation in the attempt to create an intermediate band in their band-gap are studied in detail. Two titanium ion implantation doses (10{sup 13 }cm{sup -2} and 10{sup 14 }cm{sup -2}) are studied in this work by conductance transient technique and admittance spectroscopy. Conductance transients have been measured at temperatures of around 100 K. The particular shape of these transients is due to the formation of energy barriers in the conduction band, as a consequence of the band-gap narrowing induced by the high titanium concentration. Moreover, stationary admittance spectroscopy results suggest the existencemore » of different energy level configuration, depending on the local titanium concentration. A continuum energy level band is formed when titanium concentration is over the Mott limit. On the other hand, when titanium concentration is lower than the Mott limit, but much higher than the donor impurity density, a quasi-continuum energy level distribution appears. Finally, a single deep center appears for low titanium concentration. At the n-type substrate, the experimental results obtained by means of thermal admittance spectroscopy at high reverse bias reveal the presence of single levels located at around E{sub c}-425 and E{sub c}-275 meV for implantation doses of 10{sup 13 }cm{sup −2} and 10{sup 14 }cm{sup −2}, respectively. At low reverse bias voltage, quasi-continuously distributed energy levels between the minimum of the conduction bands, E{sub c} and E{sub c}-450 meV, are obtained for both doses. Conductance transients detected at low temperatures reveal that the high impurity concentration induces a band gap narrowing which leads to the formation of a barrier in the conduction band. Besides, the relationship between the activation energy and the capture cross section values of all the energy levels fits very well to the Meyer-Neldel rule. As it is known, the Meyer-Neldel rule typically appears in processes involving multiple excitations, like carrier capture and emission in deep levels, and it is generally observed in disordered systems. The obtained Meyer-Neldel energy value, 15.19 meV, is very close to the value obtained in multicrystalline silicon samples contaminated with iron (13.65 meV), meaning that this energy value could be associated to the phonons energy in this kind of substrates.« less

Donor and double-donor transitions of the carbon vacancy related EH{sub 6∕7} deep level in 4H-SiC

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

Booker, I. D., E-mail: ianbo@ifm.liu.se; Janzén, E., E-mail: erija@ifm.liu.se; Son, N. T.

Using medium- and high-resolution multi-spectra fitting of deep level transient spectroscopy (DLTS), minority carrier transient spectroscopy (MCTS), optical O-DLTS and optical-electrical (OE)-MCTS measurements, we show that the EH{sub 6∕7} deep level in 4H-SiC is composed of two strongly overlapping, two electron emission processes with thermal activation energies of 1.49 eV and 1.58 eV for EH{sub 6} and 1.48 eV and 1.66 eV for EH{sub 7}. The electron emission peaks of EH{sub 7} completely overlap while the emission peaks of EH{sub 6} occur offset at slightly different temperatures in the spectra. OE-MCTS measurements of the hole capture cross section σ{sub p0}(T) in p-type samples revealmore » a trap-Auger process, whereby hole capture into the defect occupied by two electrons leads to a recombination event and the ejection of the second electron into the conduction band. Values of the hole and electron capture cross sections σ{sub n}(T) and σ{sub p}(T) differ strongly due to the donor like nature of the deep levels and while all σ{sub n}(T) have a negative temperature dependence, the σ{sub p}(T) appear to be temperature independent. Average values at the DLTS measurement temperature (∼600 K) are σ{sub n2+}(T) ≈ 1 × 10{sup −14} cm{sup 2}, σ{sub n+}(T) ≈ 1 × 10{sup −14} cm{sup 2}, and σ{sub p0}(T) ≈ 9 × 10{sup −18} cm{sup 2} for EH{sub 6} and σ{sub n2+}(T) ≈ 2 × 10{sup −14} cm{sup 2}, σ{sub n+}(T) ≈ 2 × 10{sup −14} cm{sup 2}, σ{sub p0}(T) ≈ 1 × 10{sup −20} cm{sup 2} for EH{sub 7}. Since EH{sub 7} has already been identified as a donor transition of the carbon vacancy, we propose that the EH{sub 6∕7} center in total represents the overlapping first and second donor transitions of the carbon vacancy defects on both inequivalent lattice sites.« less

New applications of laser-induced breakdown and stand-off Raman spectroscopy

NASA Astrophysics Data System (ADS)

Snyder, Marion Lawrence

Two novel spectroscopic applications, with the common theme of remote spectroscopy are described. In one application, laser-induced breakdown spectroscopy (LIBS) is investigated for deep ocean measurements of hydrothermal vent chemistry. This technique is demonstrated for the first time for solution measurements at pressures corresponding to those found at hydrothermal vent sites, at ocean depths of one to three kilometers. In the other application, Raman spectroscopy is investigated for stand-off detection of high explosive (HE) materials. We demonstrate several HE materials in silica can be measured at 50-meter range under ambient light conditions, a new record for this application. Chapters one through three of this dissertation contain published and recently submitted articles describing LIBS for in situ multi-elemental detection in high-pressure aqueous environments such as the deep ocean. Initial work shows the potential of single-pulse LIBS (SP-LIBS) to measure dissolved elements (e.g., Na, Ca, Li, K, and Mn) at the part-per-million level in aqueous solutions at pressures exceeding 276 bar. Dual-pulse LIBS (DP-LIBS) of high-pressure aqueous solutions is also presented. We show significant DP-LIBS enhancements are achieved through excitation of a vapor bubble formed by laser-induced breakdown of the solution with a previous laser pulse, thereby increasing the sensitivity of LIBS and allowing additional elements to be measured. Preliminary findings show that increasing solution pressure has a detrimental effect on DP-LIBS emission intensities, such that little if any DP-LIBS emission was observed above approximately 100 bar. Recent results suggest a direct relationship exists between the size of the bubble and the resulting DP-LIBS emission, and that reduction in bubble size and lifetime at elevated pressure lead to the decreased DP-LIBS emission. Chapter four contains published work examining the potential of stand-off Raman spectroscopy for remote HE detection. A small, transportable, telescope-based standoff Raman system is demonstrated for detection of HE materials, including RDX, TNT, and PETN, and simulants at distances up to 50 meters in ambient light conditions. Possible detection limits on the hundreds of parts-per-million level and detection ranges of hundreds of meters are suggested. Merits of pulsed laser excitation sources and intensified charge-coupled devices (ICCD) for detection are discussed.

Comparison of gain degradation and deep level transient spectroscopy in pnp Si bipolar junction transistors irradiated with different ion species

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

Aguirre, B. A.; Bielejec, E.; Fleming, R. M.

Here, we studied the effect of light ion and heavy ion irradiations on pnp Si BJTs. A mismatch in DLTS deep peak amplitude for devices with same final gain but irradiated with different ion species was observed. Also, different ions cause different gain degradation when the DLTS spectra are matched. Pre-dosed ion-irradiated samples show that ion induced ionization does not account for the differences in DLTS peak height but isochronal annealing studies suggest that light ions produce more VP defects than heavy ions to compensate for the lack of clusters that heavy ions produce. The creation of defect clusters bymore » heavy ions is evident by the higher content of E4 and V* 2 defects compared to light ions.« less

Comparison of gain degradation and deep level transient spectroscopy in pnp Si bipolar junction transistors irradiated with different ion species

DOE PAGES

Aguirre, B. A.; Bielejec, E.; Fleming, R. M.; ...

2016-12-09

Here, we studied the effect of light ion and heavy ion irradiations on pnp Si BJTs. A mismatch in DLTS deep peak amplitude for devices with same final gain but irradiated with different ion species was observed. Also, different ions cause different gain degradation when the DLTS spectra are matched. Pre-dosed ion-irradiated samples show that ion induced ionization does not account for the differences in DLTS peak height but isochronal annealing studies suggest that light ions produce more VP defects than heavy ions to compensate for the lack of clusters that heavy ions produce. The creation of defect clusters bymore » heavy ions is evident by the higher content of E4 and V* 2 defects compared to light ions.« less

A SHERLOC Study: Detection of Organics in Simulated Martian Soil using Deep UV Raman Spectroscopy

NASA Astrophysics Data System (ADS)

Abbey, W.; Bhartia, R.; Carrier, B. L.; Doloboff, I.; Hara, E. K.; Beegle, L. W.

2017-12-01

The SHERLOC investigation is a vital part of NASA's 2020 Mars payload [1]. It utilizes deep UV Raman and fluorescence spectroscopy to enable non-contact, non-destructive detection and characterization of in situ organics and minerals in the Martian surface and near subsurface. Raman spectroscopy using deep UV excitation wavelengths (<250 nm) offers the benefit of spectra obtained in a largely fluorescence-free region, while taking advantage of signal enhancing resonance effects for key classes of organic compounds [2,3]. To further demonstrate SHERLOC's capabilities, we interrogated 3 sample sets using a bench-top version of SHERLOC, utilizing a 248.6 nm hollow cathode laser. Sample sets included: (1) a well characterized Martian soil simulant (MMS) [4] containing 0.04 wt% (400 ppm) condensed carbon; (2) a suite of organic standards and astrobiologically relevant mineral standards; and (3) the MMS spiked with a selection of these standards, at a concentration of 1 wt%, in order to investigate 'real world' matrix effects. We were able to resolve all standards examined at the 1 wt% level. Some organic compounds, such as aromatic hydrocarbons, had especially strong signals, due to resonance effects, even when present in trace amounts. Phenanthrene, for example, was also examined at a concentration of 0.1 wt%, and even at this level it still had a very strong signal-to-noise ratio. Also, it should be noted that this technique requires very low fluence on the sample ( 60 J/cm2), minimizing degradation of organics and allowing their detection in the presence of strong oxidizers without fear of combustion due to heating [5,6]. In this study, perchlorate at 1 wt% was successfully detected in the presence of organic compounds native to the MMS; this concentration is comparable to the amount of perchlorate suspected to be present in Mars soil [6,7]. This work expands on data previously reported in Abbey et al., 2017 [8]. References: [1] Beegle et al., 2015 IEEE Aerospace Conf., 2015; [2] Asher, Anal. Chem. 65 (4), 1993; [3] Bhartia et al., Appl. Spectrosc. 62 (10), 2008; [4] Peters et al., Icarus 197, 2008; [5] Navarro-Gonzalez et al., J. Geophys. Res. 115, 2010; [6] Glavin et al., J. Geophys. Res. 118, 2013; [7] Hecht et al., Science 325, 2009; [8] Abbey et al., Icarus 290, 2017.

NATO Advanced Research Workshop: Optics of Biological Particles. Held in Novosibirsk, Russia on 3-6 Oct 2005

DTIC Science & Technology

2005-01-01

acterization of health relevant bacteria should be critically discussed, and experimentally further evidenced. References [1] D. Naumann, « Infrared spectroscopy ...application of conventional meth- ods for characterizing protein conformational transformations. Raman spectroscopy has been proven to be an efficient...appli- cation of deep ultraviolet res- onance Raman spectroscopy for structural characteriza- tion of a protein at all stages of fibrillation process

Status of miniature integrated UV resonance fluorescence and Raman sensors for detection and identification of biochemical warfare agents

NASA Astrophysics Data System (ADS)

Hug, William F.; Bhartia, Rohit; Taspin, Alexandre; Lane, Arthur; Conrad, Pamela; Sijapati, Kripa; Reid, Ray D.

2005-11-01

Laser induced native fluorescence (LINF) is the most sensitive method of detection of biological material including microorganisms, virus', and cellular residues. LINF is also a sensitive method of detection for many non-biological materials as well. The specificity with which these materials can be classified depends on the excitation wavelength and the number and location of observation wavelengths. Higher levels of specificity can be obtained using Raman spectroscopy but a much lower levels of sensitivity. Raman spectroscopy has traditionally been employed in the IR to avoid fluorescence. Fluorescence rarely occurs at wavelength below about 270nm. Therefore, when excitation occurs at a wavelength below 250nm, no fluorescence background occurs within the Raman fingerprint region for biological materials. When excitation occurs within electronic resonance bands of the biological target materials, Raman signal enhancement over one million typically occurs. Raman sensitivity within several hundred times fluorescence are possible in the deep UV where most biological materials have strong absorption. Since the Raman and fluorescence emissions occur at different wavelength, both spectra can be observed simultaneously, thereby providing a sensor with unique sensitivity and specificity capability. We will present data on our integrated, deep ultraviolet, LINF/Raman instruments that are being developed for several applications including life detection on Mars as well as biochemical warfare agents on Earth. We will demonstrate the ability to discriminate organic materials based on LINF alone. Together with UV resonance Raman, higher levels of specificity will be demonstrated. In addition, these instruments are being developed as on-line chemical sensors for industrial and municipal waste streams and product quality applications.

Detection of resting state functional connectivity using partial correlation analysis: A study using multi-distance and whole-head probe near-infrared spectroscopy.

PubMed

Sakakibara, Eisuke; Homae, Fumitaka; Kawasaki, Shingo; Nishimura, Yukika; Takizawa, Ryu; Koike, Shinsuke; Kinoshita, Akihide; Sakurada, Hanako; Yamagishi, Mika; Nishimura, Fumichika; Yoshikawa, Akane; Inai, Aya; Nishioka, Masaki; Eriguchi, Yosuke; Matsuoka, Jun; Satomura, Yoshihiro; Okada, Naohiro; Kakiuchi, Chihiro; Araki, Tsuyoshi; Kan, Chiemi; Umeda, Maki; Shimazu, Akihito; Uga, Minako; Dan, Ippeita; Hashimoto, Hideki; Kawakami, Norito; Kasai, Kiyoto

2016-11-15

Multichannel near-infrared spectroscopy (NIRS) is a functional neuroimaging modality that enables easy-to-use and noninvasive measurement of changes in blood oxygenation levels. We developed a clinically-applicable method for estimating resting state functional connectivity (RSFC) with NIRS using a partial correlation analysis to reduce the influence of extraneural components. Using a multi-distance probe arrangement NIRS, we measured resting state brain activity for 8min in 17 healthy participants. Independent component analysis was used to extract shallow and deep signals from the original NIRS data. Pearson's correlation calculated from original signals was significantly higher than that calculated from deep signals, while partial correlation calculated from original signals was comparable to that calculated from deep (cerebral-tissue) signals alone. To further test the validity of our method, we also measured 8min of resting state brain activity using a whole-head NIRS arrangement consisting of 17 cortical regions in 80 healthy participants. Significant RSFC between neighboring, interhemispheric homologous, and some distant ipsilateral brain region pairs was revealed. Additionally, females exhibited higher RSFC between interhemispheric occipital region-pairs, in addition to higher connectivity between some ipsilateral pairs in the left hemisphere, when compared to males. The combined results of the two component experiments indicate that partial correlation analysis is effective in reducing the influence of extracerebral signals, and that NIRS is able to detect well-described resting state networks and sex-related differences in RSFC. Copyright © 2016 Elsevier Inc. All rights reserved.

Resistivity dependence on Zn concentration in semi-insulating (Cd,Zn)Te

NASA Astrophysics Data System (ADS)

Fiederle, Michael; Fauler, Alex; Babentsov, Vladimir N.; Franc, Jan; Benz, Klaus Werner

2003-01-01

The resistivity dependence on Zn concentration had been investigated in semi-insulating (Cd,Zn)Te crystals grown by the vertical Bridgman method. A coorelation between the zinc concentration and the resistivity distribution could be found. The obtained resistivity was in the interval of 2 ×109-1010 Ω cm as expected from the model of compensation. The main deep compensating levels detected by Photo Induced Current Transient Spectroscopy (PICTS) were at 0.64 +/- 0.02 eV and close the middle of the band gap at 0.80 +/- 0.02 eV.

Semiconductor technology program. Progress briefs

NASA Technical Reports Server (NTRS)

Bullis, W. M. (Editor)

1979-01-01

The current status of NBS work on measurement technology for semiconductor materials, process control, and devices is reported. Results of both in-house and contract research are covered. Highlighted activities include modeling of diffusion processes, analysis of model spreading resistance data, and studies of resonance ionization spectroscopy, resistivity-dopant density relationships in p-type silicon, deep level measurements, photoresist sensitometry, random fault measurements, power MOSFET thermal characteristics, power transistor switching characteristics, and gross leak testing. New and selected on-going projects are described. Compilations of recent publications and publications in press are included.

Deep radio imaging of the UKIDSS Ultra Deep Survey field : the nature of the faint radio population, and the star-formation history of the Universe

NASA Astrophysics Data System (ADS)

Arumugam, Vinodiran

2013-08-01

Breast cancer remains a significant cause of morbidity and mortality. Assessment of the axillary lymph nodes is part of the staging of the disease. Advances in surgical management of breast cancer have seen a move towards intra-operative lymph node assessment that facilitates an immediate axillary clearance if it is indicated. Raman spectroscopy, a technique based on the inelastic scattering of light, has previously been shown to be capable of differentiating between normal and malignant tissue. These results, based on the biochemical composition of the tissue, potentially allow for this technique to be utilised in this clinical context. The aim of this study was to evaluate the facility of Raman spectroscopy to both assess axillary lymph node tissue within the theatre setting and to achieve results that were comparable to other intra-operative techniques within a clinically relevant time frame. Initial experiments demonstrated that these aims were feasible within the context of both the theatre environment and current surgical techniques. A laboratory based feasibility study involving 17 patients and 38 lymph node samples achieved sensivities and specificities of >90% in unsupervised testing. 339 lymph node samples from 66 patients were subsequently assessed within the theatre environment. Chemometric analysis of this data demonstrated sensitivities of up to 94% and specificities of up to 99% in unsupervised testing. The best results were achieved when comparing negative nodes from N0 patients and nodes containing macrometastases. Spectral analysis revealed increased levels of lipid in the negative nodes and increased DNA and protein levels in the positive nodes. Further studies highlighted the reproducibility of these results using different equipment, users and time from excision. This study uses Raman spectroscopy for the first time in an operating theatre and demonstrates that the results obtained, in real-time, are comparable, if not superior, to current intra-operative techniques of lymph nodes assessment.

Deep centers in AlGaN-based light emitting diode structures

NASA Astrophysics Data System (ADS)

Polyakov, A. Y.; Smirnov, N. B.; Govorkov, A. V.; Mil'vidskii, M. G.; Usikov, A. S.; Pushnyi, B. V.; Lundin, W. V.

1999-10-01

Deep traps were studied in GaN homojunction and AlGaN/GaN heterojunction light emitting diode (LED) p-i-n structures by means of deep levels transient spectroscopy (DLTS), admittance and electroluminescence (EL) spectra measurements. It is shown that, in homojunction LED structures, the EL spectra comes from recombination involving Mg acceptors in-diffusing into the active i-layer. This Mg in-diffusion is strongly suppressed in heterostructures with the upper p-type layer containing about 5% of Al. As a result the main peak in the EL spectra of heterostructures is shifted toward higher energy compared to homojunctions. Joint doping of the i-layer with Zn and Si allows to shift the main EL peak to longer wavelength. The dominant electron traps observed in the studied LED structures had ionization energies of 0.55 and 0.85 eV. The dominant hole traps had apparent ionization energies of 0.85 and 0.4 eV. The latter traps were shown to be metastable and it is argued that they could be at least in part responsible for the persistent photoconductivity observed in p-GaN.

Hyperspectral depth-profiling with deep Raman spectroscopy for detecting chemicals in building materials.

PubMed

Cho, Youngho; Song, Si Won; Sung, Jiha; Jeong, Young-Su; Park, Chan Ryang; Kim, Hyung Min

2017-09-25

Toxic chemicals inside building materials have long-term harmful effects on human bodies. To prevent secondary damage caused by the evaporation of latent chemicals, it is necessary to detect the chemicals inside building materials at an early stage. Deep Raman spectroscopy is a potential candidate for on-site detection because it can provide molecular information about subsurface components. However, it is very difficult to spectrally distinguish the Raman signal of the internal chemicals from the background signal of the surrounding materials and to acquire the geometric information of chemicals. In this study, we developed hyperspectral wide-depth spatially offset Raman spectroscopy coupled with a data processing algorithm to identify toxic chemicals, such as chemical warfare agent (CWA) simulants in building materials. Furthermore, the spatial distribution of the chemicals and the thickness of the building material were also measured from one-dimensional (1D) spectral variation.

Multi-Object Spectroscopy with MUSE

NASA Astrophysics Data System (ADS)

Kelz, A.; Kamann, S.; Urrutia, T.; Weilbacher, P.; Bacon, R.

2016-10-01

Since 2014, MUSE, the Multi-Unit Spectroscopic Explorer, is in operation at the ESO-VLT. It combines a superb spatial sampling with a large wavelength coverage. By design, MUSE is an integral-field instrument, but its field-of-view and large multiplex make it a powerful tool for multi-object spectroscopy too. Every data-cube consists of 90,000 image-sliced spectra and 3700 monochromatic images. In autumn 2014, the observing programs with MUSE have commenced, with targets ranging from distant galaxies in the Hubble Deep Field to local stellar populations, star formation regions and globular clusters. This paper provides a brief summary of the key features of the MUSE instrument and its complex data reduction software. Some selected examples are given, how multi-object spectroscopy for hundreds of continuum and emission-line objects can be obtained in wide, deep and crowded fields with MUSE, without the classical need for any target pre-selection.

Characterization of deep level defects and thermally stimulated depolarization phenomena in La-doped TlInS{sub 2} layered semiconductor

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

Seyidov, MirHasan Yu., E-mail: smirhasan@gyte.edu.tr; Suleymanov, Rauf A.; Mikailzade, Faik A.

2015-06-14

Lanthanum-doped high quality TlInS{sub 2} (TlInS{sub 2}:La) ferroelectric-semiconductor was characterized by photo-induced current transient spectroscopy (PICTS). Different impurity centers are resolved and identified. Analyses of the experimental data were performed in order to determine the characteristic parameters of the extrinsic and intrinsic defects. The energies and capturing cross section of deep traps were obtained by using the heating rate method. The observed changes in the Thermally Stimulated Depolarization Currents (TSDC) near the phase transition points in TlInS{sub 2}:La ferroelectric-semiconductor are interpreted as a result of self-polarization of the crystal due to the internal electric field caused by charged defects. Themore » TSDC spectra show the depolarization peaks, which are attributed to defects of dipolar origin. These peaks provide important information on the defect structure and localized energy states in TlInS{sub 2}:La. Thermal treatments of TlInS{sub 2}:La under an external electric field, which was applied at different temperatures, allowed us to identify a peak in TSDC which was originated from La-dopant. It was established that deep energy level trap BTE43, which are active at low temperature (T ≤ 156 K) and have activation energy 0.29 eV and the capture cross section 2.2 × 10{sup −14} cm{sup 2}, corresponds to the La dopant. According to the PICTS results, the deep level trap center B5 is activated in the temperature region of incommensurate (IC) phases of TlInS{sub 2}:La, having the giant static dielectric constant due to the structural disorders. From the PICTS simulation results for B5, native deep level trap having an activation energy of 0.3 eV and the capture cross section of 1.8 × 10{sup −16} cm{sup 2} were established. A substantial amount of residual space charges is trapped by the deep level localized energy states of B5 in IC-phase. While the external electric field is applied, permanent dipoles, which are originated from the charged B5 deep level defects, are aligned in the direction of the applied electric field and the equilibrium polarization can be reached in a relatively short time. When the polarization field is maintained, while cooling the temperature of sample to a sufficiently low degrees, the relaxation times of the aligned dipoles drastically increases. Practically, frozen internal electric field or electrets states remain inside the TlInS{sub 2}:La when the applied bias field is switched off. The influence of deep level defects on TSDC spectra of TlInS{sub 2}:La has been revealed for the first time.« less

In situ Detection of Microbial Life in the Deep Biosphere in Igneous Ocean Crust.

PubMed

Salas, Everett C; Bhartia, Rohit; Anderson, Louise; Hug, William F; Reid, Ray D; Iturrino, Gerardo; Edwards, Katrina J

2015-01-01

The deep biosphere is a major frontier to science. Recent studies have shown the presence and activity of cells in deep marine sediments and in the continental deep biosphere. Volcanic lavas in the deep ocean subsurface, through which substantial fluid flow occurs, present another potentially massive deep biosphere. We present results from the deployment of a novel in situ logging tool designed to detect microbial life harbored in a deep, native, borehole environment within igneous oceanic crust, using deep ultraviolet native fluorescence spectroscopy. Results demonstrate the predominance of microbial-like signatures within the borehole environment, with densities in the range of 10(5) cells/mL. Based on transport and flux models, we estimate that such a concentration of microbial cells could not be supported by transport through the crust, suggesting in situ growth of these communities.

Two different carbon-hydrogen complexes in silicon with closely spaced energy levels

NASA Astrophysics Data System (ADS)

Stübner, R.; Kolkovsky, Vl.; Weber, J.

2015-08-01

An acceptor and a single donor state of carbon-hydrogen defects (CHA and CHB) are observed by Laplace deep level transient spectroscopy at 90 K. CHA appears directly after hydrogenation by wet chemical etching or hydrogen plasma treatment, whereas CHB can be observed only after a successive annealing under reverse bias at about 320 K. The activation enthalpies of these states are 0.16 eV for CHA and 0.14 eV for CHB. Our results reconcile previous controversial experimental results. We attribute CHA to the configuration where substitutional carbon binds a hydrogen atom on a bond centered position between carbon and the neighboring silicon and CHB to another carbon-hydrogen defect.

Effect of alpha-particle irradiation on the electrical properties of n-type Ge

NASA Astrophysics Data System (ADS)

Roro, K. T.; Janse van Rensburg, P. J.; Auret, F. D.; Coelho, S.

2009-12-01

Deep-level transient spectroscopy was used to investigate the effect of alpha particle irradiation on the electrical properties of n-type Ge. The samples were irradiated with alpha particles at room temperature using an americium-241 (Am-241) radionuclide source. The main defects introduced were found to be electron traps with energy levels at EC-0.38, EC-0.21, EC-0.20, EC-0.15, and EC-0.10 eV, respectively. The main defects in alpha particle irradiation are similar to those introduced by MeV electron irradiation, where the main defect is the E-center. A quadratic increase in concentration as a function of dose is observed.

MIS capacitor studies on silicon carbide single crystals

NASA Technical Reports Server (NTRS)

Kopanski, J. J.

1990-01-01

Cubic SIC metal-insulator-semiconductor (MIS) capacitors with thermally grown or chemical-vapor-deposited (CVD) insulators were characterized by capacitance-voltage (C-V), conductance-voltage (G-V), and current-voltage (I-V) measurements. The purpose of these measurements was to determine the four charge densities commonly present in an MIS capacitor (oxide fixed charge, N(f); interface trap level density, D(it); oxide trapped charge, N(ot); and mobile ionic charge, N(m)) and to determine the stability of the device properties with electric-field stress and temperature. The section headings in the report include the following: Capacitance-voltage and conductance-voltage measurements; Current-voltage measurements; Deep-level transient spectroscopy; and Conclusions (Electrical characteristics of SiC MIS capacitors).

Impacts of Carrier Transport and Deep Level Defects on Delayed Cathodoluminescence in Droop-Mitigating InGaN/GaN LEDs

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

Zhao, Zhibo; Singh, Akshay; Chesin, Jordan

Prevalent droop mitigation strategies in InGaN-based LEDs require structural and/or compositional changes in the active region but are accompanied by a detrimental reduction in external quantum efficiency (EQE) due to increased Shockley-Read-Hall recombination. Understanding the optoelectronic impacts of structural modifications in InGaN/GaN quantum wells (QW) remains critical for emerging high-power LEDs. In this work, we use a combination of electron microscopy tools along with standard electrical characterization to investigate a wide range of low-droop InGaN/GaN QW designs. We find that chip-scale EQE is uncorrelated with extended well-width fluctuations observed in scanning transmission electron microscopy. Further, we observe delayed cathodoluminescence (CL)more » response from designs in which calculated band profiles suggest facile carrier escape from individual QWs. Samples with the slowest CL responses also exhibit the lowest EQEs and highest QW defect densities in deep level optical spectroscopy. We propose a model in which the electron beam (i) passivates deep level defect states and (ii) drives charge carrier accumulation and subsequent reduction of the built-in field across the multi-QW active region, resulting in delayed radiative recombination. Finally, we correlate CL rise dynamics with capacitance-voltage measurements and show that certain early-time components of the CL dynamics reflect the open circuit carrier population within one or more QWs.« less

The influence of thermal annealing on the characteristics of Au/Ni Schottky contacts on n-type 4 H-SiC

NASA Astrophysics Data System (ADS)

Omotoso, E.; Auret, F. D.; Igumbor, E.; Tunhuma, S. M.; Danga, H. T.; Ngoepe, P. N. M.; Taleatu, B. A.; Meyer, W. E.

2018-05-01

The effects of isochronal annealing on the electrical, morphological and structural characteristics of Au/Ni/4 H-SiC Schottky barrier diodes (SBDs) have been studied. Current-voltage ( I- V), capacitance-voltage ( C- V), deep-level transient spectroscopy, scanning electron microscope (SEM) and X-ray diffraction measurements were employed to study the thermal effect on the characteristics of the SBDs. Prior to thermal annealing of Schottky contacts, the I- V measurements results confirmed the good rectification behaviour with ideality factor of 1.06, Schottky barrier height of 1.20 eV and series resistance of 7 Ω. The rectification properties after annealing was maintained up to an annealing temperature of 500 °C, but deviated slightly above 500 °C. The uncompensated ionized donor concentration decreased with annealing temperature, which could be attributed to out-diffusion of the 4 H-SiC into the Au/Ni contacts and decrease in bonding due to formation of nickel silicides. We observed the presence of four deep-level defects with energies 0.09, 0.11, 0.16 and 0.65 eV below the conduction band before and after the isochronal annealing up to 600 °C. The conclusion drawn was that annealing did not affect the number of deep-level defects present in Au/Ni/4 H-SiC contacts. The variations in electrical properties of the devices were attributed to the phase transformations and interfacial reactions that occurred after isochronal annealing.

Deep UV Raman spectroscopy for planetary exploration: The search for in situ organics

NASA Astrophysics Data System (ADS)

Abbey, William J.; Bhartia, Rohit; Beegle, Luther W.; DeFlores, Lauren; Paez, Veronica; Sijapati, Kripa; Sijapati, Shakher; Williford, Kenneth; Tuite, Michael; Hug, William; Reid, Ray

2017-07-01

Raman spectroscopy has emerged as a powerful, non-contact, non-destructive technique for detection and characterization of in situ organic compounds. Excitation using deep UV wavelengths (< 250 nm), in particular, offers the benefits of spectra obtained in a largely fluorescence-free region while taking advantage of signal enhancing resonance Raman effects for key classes of organic compounds, such as the aromatics. In order to demonstrate the utility of this technique for planetary exploration and astrobiological applications, we interrogated three sets of samples using a custom built Raman instrument equipped with a deep UV (248.6 nm) excitation source. The sample sets included: (1) the Mojave Mars Simulant, a well characterized basaltic sample used as an analog for Martian regolith, in which we detected ∼0.04 wt% of condensed carbon; (2) a suite of organic (aromatic hydrocarbons, carboxylic acids, and amino acids) and astrobiologically relevant inorganic (sulfates, carbonates, phosphates, nitrates and perchlorate) standards, many of which have not had deep UV Raman spectra in the solid phase previously reported in the literature; and (3) Mojave Mars Simulant spiked with a representative selection of these standards, at a concentration of 1 wt%, in order to investigate natural 'real world' matrix effects. We were able to resolve all of the standards tested at this concentration. Some compounds, such as the aromatic hydrocarbons, have especially strong signals due to resonance effects even when present in trace amounts. Phenanthrene, one of the aromatic hydrocarbons, was also examined at a concentration of 0.1 wt% and even at this level was found to have a strong signal-to-noise ratio. It should be noted that the instrument utilized in this study was designed to approximate the operation of a 'fieldable' spectrometer in order to test astrobiological applications both here on Earth as well as for current and future planetary missions. It is the foundation of SHERLOC, an arm mounted instrument recently selected by NASA to fly on the next rover mission to Mars in 2020.

Spectroscopic chemical analysis methods and apparatus

NASA Technical Reports Server (NTRS)

Hug, William F. (Inventor); Reid, Ray D. (Inventor)

2009-01-01

Spectroscopic chemical analysis methods and apparatus are disclosed which employ deep ultraviolet (e.g. in the 200 nm to 300 nm spectral range) electron beam pumped wide bandgap semiconductor lasers, incoherent wide bandgap semiconductor light emitting devices, and hollow cathode metal ion lasers to perform non-contact, non-invasive detection of unknown chemical analytes. These deep ultraviolet sources enable dramatic size, weight and power consumption reductions of chemical analysis instruments. Chemical analysis instruments employed in some embodiments include capillary and gel plane electrophoresis, capillary electrochromatography, high performance liquid chromatography, flow cytometry, flow cells for liquids and aerosols, and surface detection instruments. In some embodiments, Raman spectroscopic detection methods and apparatus use ultra-narrow-band angle tuning filters, acousto-optic tuning filters, and temperature tuned filters to enable ultra-miniature analyzers for chemical identification. In some embodiments Raman analysis is conducted simultaneously with native fluorescence spectroscopy to provide high levels of sensitivity and specificity in the same instrument.

Spectroscopic chemical analysis methods and apparatus

NASA Technical Reports Server (NTRS)

Reid, Ray D. (Inventor); Hug, William F. (Inventor)

2010-01-01

Spectroscopic chemical analysis methods and apparatus are disclosed which employ deep ultraviolet (e.g. in the 200 nm to 300 nm spectral range) electron beam pumped wide bandgap semiconductor lasers, incoherent wide bandgap semiconductor light emitting devices, and hollow cathode metal ion lasers to perform non-contact, non-invasive detection of unknown chemical analytes. These deep ultraviolet sources enable dramatic size, weight and power consumption reductions of chemical analysis instruments. Chemical analysis instruments employed in some embodiments include capillary and gel plane electrophoresis, capillary electrochromatography, high performance liquid chromatography, flow cytometry, flow cells for liquids and aerosols, and surface detection instruments. In some embodiments, Raman spectroscopic detection methods and apparatus use ultra-narrow-band angle tuning filters, acousto-optic tuning filters, and temperature tuned filters to enable ultra-miniature analyzers for chemical identification. In some embodiments Raman analysis is conducted simultaneously with native fluorescence spectroscopy to provide high levels of sensitivity and specificity in the same instrument.

Deep-level traps in lightly Si-doped n-GaN on free-standing m-oriented GaN substrates

NASA Astrophysics Data System (ADS)

Yamada, H.; Chonan, H.; Takahashi, T.; Yamada, T.; Shimizu, M.

2018-04-01

In this study, we investigated the deep-level traps in Si-doped GaN epitaxial layers by metal-organic chemical vapor deposition on c-oriented and m-oriented free-standing GaN substrates. The c-oriented and m-oriented epitaxial layers, grown at a temperature of 1000 °C and V/III ratio of 1000, contained carbon atomic concentrations of 1.7×1016 and 4.0×1015 cm-3, respectively. A hole trap was observed at about 0.89 eV above the valence band maximum by minority carrier transient spectroscopy. The trap concentrations in the c-oriented and m-oriented GaN epitaxial layers were consistent with the carbon atomic concentrations from secondary ion mass spectroscopy and the yellow luminescence intensity at 2.21 eV from photoluminescence. The trap concentrations in the m-oriented GaN epitaxial layers were lower than those in the c-oriented GaN. Two electron traps, 0.24 and 0.61 eV below the conduction band (EC) minimum, were observed in the c-oriented GaN epitaxial layer. In contrast, the m-oriented GaN epitaxial layer was free from the electron trap at EC - 0.24 eV, and the trap concentration at EC - 0.61 eV in the m-oriented GaN epitaxial layer was lower than that in the c-oriented GaN epitaxial layer. The m-oriented GaN epitaxial layer exhibited fewer hole and electron traps compared to the c-oriented GaN epitaxial layers.

Hamacanthins A and B, new antifungal bis indole alkaloids from the deep-water marine sponge, Hamacantha sp.

PubMed

Gunasekera, S P; McCarthy, P J; Kelly-Borges, M

1994-10-01

Hamacanthin A [1] and hamacanthin B [2] are two bioactive dihydropyrazinonediylbis(indole) alkaloids isolated from a new species of deep-water marine sponge, Hamacantha sp. The hamacanthins are growth inhibitors of Candida albicans and Cryptococcus neoformans. Isolation and structure elucidation of 1 and 2 by nmr spectroscopy are described.

Ophirapstanol trisulfate, a new biologically active steroid sulfate from the deep water marine sponge Topsentia ophiraphidites.

PubMed

Gunasekera, S P; Sennett, S H; Kelly-Borges, M; Bryant, R W

1994-12-01

Ophirapstanol trisulfate [1], a new steroid trisulfate related to sokotrasterol trisulfate was isolated from a deep water marine sponge Topsentia ophiraphidites. Compound 1 exhibited significant inhibition in the guanosine diphosphate/G-protein RAS exchange assay. The structure elucidation of 1 and ophirapstanol [2] by nmr spectroscopy is described.

In situ Detection of Microbial Life in the Deep Biosphere in Igneous Ocean Crust

PubMed Central

Salas, Everett C.; Bhartia, Rohit; Anderson, Louise; Hug, William F.; Reid, Ray D.; Iturrino, Gerardo; Edwards, Katrina J.

2015-01-01

The deep biosphere is a major frontier to science. Recent studies have shown the presence and activity of cells in deep marine sediments and in the continental deep biosphere. Volcanic lavas in the deep ocean subsurface, through which substantial fluid flow occurs, present another potentially massive deep biosphere. We present results from the deployment of a novel in situ logging tool designed to detect microbial life harbored in a deep, native, borehole environment within igneous oceanic crust, using deep ultraviolet native fluorescence spectroscopy. Results demonstrate the predominance of microbial-like signatures within the borehole environment, with densities in the range of 105 cells/mL. Based on transport and flux models, we estimate that such a concentration of microbial cells could not be supported by transport through the crust, suggesting in situ growth of these communities. PMID:26617595

Lifetime degradation of n-type Czochralski silicon after hydrogenation

NASA Astrophysics Data System (ADS)

Vaqueiro-Contreras, M.; Markevich, V. P.; Mullins, J.; Halsall, M. P.; Murin, L. I.; Falster, R.; Binns, J.; Coutinho, J.; Peaker, A. R.

2018-04-01

Hydrogen plays an important role in the passivation of interface states in silicon-based metal-oxide semiconductor technologies and passivation of surface and interface states in solar silicon. We have shown recently [Vaqueiro-Contreras et al., Phys. Status Solidi RRL 11, 1700133 (2017)] that hydrogenation of n-type silicon slices containing relatively large concentrations of carbon and oxygen impurity atoms {[Cs] ≥ 1 × 1016 cm-3 and [Oi] ≥ 1017 cm-3} can produce a family of C-O-H defects, which act as powerful recombination centres reducing the minority carrier lifetime. In this work, evidence of the silicon's lifetime deterioration after hydrogen injection from SiNx coating, which is widely used in solar cell manufacturing, has been obtained from microwave photoconductance decay measurements. We have characterised the hydrogenation induced deep level defects in n-type Czochralski-grown Si samples through a series of deep level transient spectroscopy (DLTS), minority carrier transient spectroscopy (MCTS), and high-resolution Laplace DLTS/MCTS measurements. It has been found that along with the hydrogen-related hole traps, H1 and H2, in the lower half of the gap reported by us previously, hydrogenation gives rise to two electron traps, E1 and E2, in the upper half of the gap. The activation energies for electron emission from the E1 and E2 trap levels have been determined as 0.12, and 0.14 eV, respectively. We argue that the E1/H1 and E2/H2 pairs of electron/hole traps are related to two energy levels of two complexes, each incorporating carbon, oxygen, and hydrogen atoms. Our results show that the detrimental effect of the C-O-H defects on the minority carrier lifetime in n-type Si:O + C materials can be very significant, and the carbon concentration in Czochralski-grown silicon is a key parameter in the formation of the recombination centers.

Identification of dopant-induced point defects and their effect on the performance of CZT detectors (Conference Presentation)

NASA Astrophysics Data System (ADS)

Gul, Rubi; Bolotnikov, Aleksey E.; Camarda, Giuseppe S.; Cui, Yonggang; Didic, Václav; Egarievwe, Stephen U.; Hossain, Anwar; Roy, Utpal N.; Yang, Ge; James, Ralph B.

2016-09-01

In our prior research we investigated room-temperature radiation detectors (CZT, CMT, CdMgTe, CTS, among other compound semiconductors) for point defects related to different dopants and impurities. In this talk we will report on our most recent research on newly grown CZT crystals doped with In, In+Al, In+Ni, and In+Sn. The main focus will be on the study of dopant-induced point defects using deep-level current transient spectroscopy (i-DLTS). In addition the performance, ? product, gamma-ray spectral response and internal electric field of the detectors were measured and correlated with the dopant-induced point defects and their concentrations. Characterization of the detectors was carried out using i-DLTS for the point defects, Pockels effect for the internal electric-field distribution, and γ-ray spectroscopy for the spectral properties.

New developments in laser-based photoemission spectroscopy and its scientific applications: a key issues review

NASA Astrophysics Data System (ADS)

Zhou, Xingjiang; He, Shaolong; Liu, Guodong; Zhao, Lin; Yu, Li; Zhang, Wentao

2018-06-01

The significant progress in angle-resolved photoemission spectroscopy (ARPES) in last three decades has elevated it from a traditional band mapping tool to a precise probe of many-body interactions and dynamics of quasiparticles in complex quantum systems. The recent developments of deep ultraviolet (DUV, including ultraviolet and vacuum ultraviolet) laser-based ARPES have further pushed this technique to a new level. In this paper, we review some latest developments in DUV laser-based photoemission systems, including the super-high energy and momentum resolution ARPES, the spin-resolved ARPES, the time-of-flight ARPES, and the time-resolved ARPES. We also highlight some scientific applications in the study of electronic structure in unconventional superconductors and topological materials using these state-of-the-art DUV laser-based ARPES. Finally we provide our perspectives on the future directions in the development of laser-based photoemission systems.

Inferring deep-brain activity from cortical activity using functional near-infrared spectroscopy

PubMed Central

Liu, Ning; Cui, Xu; Bryant, Daniel M.; Glover, Gary H.; Reiss, Allan L.

2015-01-01

Functional near-infrared spectroscopy (fNIRS) is an increasingly popular technology for studying brain function because it is non-invasive, non-irradiating and relatively inexpensive. Further, fNIRS potentially allows measurement of hemodynamic activity with high temporal resolution (milliseconds) and in naturalistic settings. However, in comparison with other imaging modalities, namely fMRI, fNIRS has a significant drawback: limited sensitivity to hemodynamic changes in deep-brain regions. To overcome this limitation, we developed a computational method to infer deep-brain activity using fNIRS measurements of cortical activity. Using simultaneous fNIRS and fMRI, we measured brain activity in 17 participants as they completed three cognitive tasks. A support vector regression (SVR) learning algorithm was used to predict activity in twelve deep-brain regions using information from surface fNIRS measurements. We compared these predictions against actual fMRI-measured activity using Pearson’s correlation to quantify prediction performance. To provide a benchmark for comparison, we also used fMRI measurements of cortical activity to infer deep-brain activity. When using fMRI-measured activity from the entire cortex, we were able to predict deep-brain activity in the fusiform cortex with an average correlation coefficient of 0.80 and in all deep-brain regions with an average correlation coefficient of 0.67. The top 15% of predictions using fNIRS signal achieved an accuracy of 0.7. To our knowledge, this study is the first to investigate the feasibility of using cortical activity to infer deep-brain activity. This new method has the potential to extend fNIRS applications in cognitive and clinical neuroscience research. PMID:25798327

High-Resolution Integrated Optical System

NASA Astrophysics Data System (ADS)

Prakapenka, V. B.; Goncharov, A. F.; Holtgrewe, N.; Greenberg, E.

2017-12-01

Raman and optical spectroscopy in-situ at extreme high pressure and temperature conditions relevant to the planets' deep interior is a versatile tool for characterization of wide range of properties of minerals essential for understanding the structure, composition, and evolution of terrestrial and giant planets. Optical methods, greatly complementing X-ray diffraction and spectroscopy techniques, become crucial when dealing with light elements. Study of vibrational and optical properties of minerals and volatiles, was a topic of many research efforts in past decades. A great deal of information on the materials properties under extreme pressure and temperature has been acquired including that related to structural phase changes, electronic transitions, and chemical transformations. These provide an important insight into physical and chemical states of planetary interiors (e.g. nature of deep reservoirs) and their dynamics including heat and mass transport (e.g. deep carbon cycle). Optical and vibrational spectroscopy can be also very instrumental for elucidating the nature of the materials molten states such as those related to the Earth's volatiles (CO2, CH4, H2O), aqueous fluids and silicate melts, planetary ices (H2O, CH4, NH3), noble gases, and H2. The optical spectroscopy study performed concomitantly with X-ray diffraction and spectroscopy measurements at the GSECARS beamlines on the same sample and at the same P-T conditions would greatly enhance the quality of this research and, moreover, will provide unique new information on chemical state of matter. The advanced high-resolution user-friendly integrated optical system is currently under construction and expected to be completed by 2018. In our conceptual design we have implemented Raman spectroscopy with five excitation wavelengths (266, 473, 532, 660, 946 nm), confocal imaging, double sided IR laser heating combined with high temperature Raman (including coherent anti-Stokes Raman scattering) and transient (based on a bright supercontinuum light source) spectroscopies in a wide spectral range (200-1600 nm). Details and future combination of this innovative system with high-resolution synchrotron micro-diffraction at GSECARS for full characterization of materials in-situ at extreme conditions will be discussed.

The Metal Abundances across Cosmic Time (MACT) Survey. I. Optical Spectroscopy in the Subaru Deep Field

NASA Astrophysics Data System (ADS)

Ly, Chun; Malhotra, Sangeeta; Malkan, Matthew A.; Rigby, Jane R.; Kashikawa, Nobunari; de los Reyes, Mithi A.; Rhoads, James E.

2016-09-01

Deep rest-frame optical spectroscopy is critical for characterizing and understanding the physical conditions and properties of the ionized gas in galaxies. Here, we present a new spectroscopic survey called “Metal Abundances across Cosmic Time” or { M }{ A }{ C }{ T }, which will obtain rest-frame optical spectra for ˜3000 emission-line galaxies. This paper describes the optical spectroscopy that has been conducted with MMT/Hectospec and Keck/DEIMOS for ≈1900 z = 0.1-1 emission-line galaxies selected from our narrowband and intermediate-band imaging in the Subaru Deep Field. In addition, we present a sample of 164 galaxies for which we have measured the weak [O III]λ4363 line (66 with at least 3σ detections and 98 with significant upper limits). This nebular emission line determines the gas-phase metallicity by measuring the electron temperature of the ionized gas. This paper presents the optical spectra, emission-line measurements, interstellar properties (e.g., metallicity, gas density), and stellar properties (e.g., star formation rates, stellar mass). Paper II of the { M }{ A }{ C }{ T } survey (Ly et al.) presents the first results on the stellar mass-gas metallicity relation at z ≲ 1 using the sample with [O III]λ4363 measurements.

Electrical conductivity of In₂O₃ and Ga₂O₃ after low temperature ion irradiation; implications for instrinsic defect formation and charge neutrality level.

PubMed

Vines, Lasse; Bhoodoo, Chidanand; von Wenckstern, Holger; Grundmann, Marius

2017-11-29

The evolution of sheet resistance of n-type In2O3 and Ga2O3 exposed to bombardment with MeV 12C and 28Si ions at 35 K is studied in situ. While the sheet resistance of Ga2O3 increased by more than 8 orders of magnitude as a result of ion irradiation, In2O3 showed a more complex defect evolution and became more conductive when irradiated at the highest doses. Heating up to room temperature reduced the sheet resistivity somewhat, but Ga2O3 remained highly resistive, while In2O3 showed a lower resistance than as deposited samples. Thermal admittance spectroscopy and deep level transient spectroscopy did not reveal new defect levels for irradiation up to 2 1012 cm2. A model where larger defect complexes preferentially produce donor like defects in In2O3 is proposed, and may reveal a microscopic view of a charge neutrality level within the conduction band, as previously proposed. © 2017 IOP Publishing Ltd.

Delayed avalanche breakdown of high-voltage silicon diodes: Various structures exhibit different picosecond-range switching behavior

NASA Astrophysics Data System (ADS)

Brylevskiy, Viktor; Smirnova, Irina; Gutkin, Andrej; Brunkov, Pavel; Rodin, Pavel; Grekhov, Igor

2017-11-01

We present a comparative study of silicon high-voltage diodes exhibiting the effect of delayed superfast impact-ionization breakdown. The effect manifests itself in a sustainable picosecond-range transient from the blocking to the conducting state and occurs when a steep voltage ramp is applied to the p+-n-n+ diode in the reverse direction. Nine groups of diodes with graded and abrupt pn-junctions have been specially fabricated for this study by different techniques from different Si substrates. Additionally, in two groups of these structures, the lifetime of nonequilibrium carriers was intentionally reduced by electron irradiation. All diodes have identical geometrical parameters and similar stationary breakdown voltages. Our experimental setup allows measuring both device voltage and current during the kilovolt switching with time resolution better than 50 ps. Although all devices are capable of forming a front with kilovolt amplitude and 100 ps risetime in the in-series load, the structures with graded pn-junctions have anomalously large residual voltage. The Deep Level Transient Spectroscopy study of all diode structures has been performed in order to evaluate the effect of deep centers on device performance. It was found that the presence of deep-level electron traps negatively correlates with parameters of superfast switching, whereas a large concentration of recombination centers created by electron irradiation has virtually no influence on switching characteristics.

Investigation of deep-level defects in Cu(In,Ga)Se2 thin films by two-wavelength excitation photo-capacitance spectroscopy

NASA Astrophysics Data System (ADS)

Hu, Xiaobo; Gupta, Amit; Sakurai, Takeaki; Yamada, Akimasa; Ishizuka, Shogo; Niki, Shigeru; Akimoto, Katsuhiro

2013-10-01

The properties of the defect level located 0.8 eV above the valence band in Cu(In1-x,Gax)Se2 thin films were investigated by a photo-capacitance method using a monochromatic probe light with an energy of 0.7 to 1.8 eV. In addition to the probe light, laser light with a wavelength of 1.55 μm, corresponding to 0.8 eV, was also used to study the saturation effect of the defect level at 0.8 eV. A suppression of electron-hole recombination due to saturation of the defect level was observed at room temperature while no saturation effect was observed at 140 K. The results suggest that the defect level at 0.8 eV acts as a recombination center at least at room temperature.

Characterisation of Cs ion implanted GaN by DLTS

NASA Astrophysics Data System (ADS)

Ngoepe, P. N. M.; Meyer, W. E.; Auret, F. D.; Omotoso, E.; Hlatshwayo, T. T.; Diale, M.

2018-04-01

Deep level transient spectroscopy (DLTS) was used to characterise Cs implanted GaN grown by hydride vapour phase epitaxy (HVPE). This implantation was done at room temperature using energy of 360 keV to a fluence of 10-11 cm-2. A defect with activation energy of 0.19 eV below the conduction band and an apparent capture cross section of 1.1 × 10-15 cm2 was induced. This defect has previously been observed after rare earth element (Eu, Er and Pr) implantation. It has also been reported after electron, proton and He ion implantation.

Increased radiation resistance in lithium-counterdoped silicon solar cells

NASA Technical Reports Server (NTRS)

Weinberg, I.; Swartz, C. K.; Mehta, S.

1984-01-01

Lithium-counterdoped n(+)p silicon solar cells are found to exhibit significantly increased radiation resistance to 1-MeV electron irradiation when compared to boron-doped n(+)p silicon solar cells. In addition to improved radiation resistance, considerable damage recovery by annealing is observed in the counterdoped cells at T less than or equal to 100 C. Deep level transient spectroscopy measurements are used to identify the defect whose removal results in the low-temperature aneal. It is suggested that the increased radiation resistance of the counterdoped cells is primarily due to interaction of the lithium with interstitial oxygen.

Electronic and transformation properties of a metastable defect introduced in epitaxially grown boron-doped p-type Si by alpha particle irradiation

NASA Astrophysics Data System (ADS)

Mamor, M.; Auret, F. D.; Goodman, S. A.; Meyer, W. E.; Myburg, G.

1998-06-01

Titanium (Ti) Schottky barrier diodes on epitaxially grown boron-doped p-type Si films with a free carrier density of 6-8×1016cm-3 were irradiated with alpha particles at room temperature using an americium-241 (Am-241) radio nuclide. We report the electronic and transformation characteristics of an α-particle irradiation-induced defect Hα2 in epitaxially grown p-Si with metastable properties. The energy level and apparent capture cross section, as determined by deep-level transient spectroscopy, are Ev+0.43 eV and 1.4×10-15 cm2, respectively. This defect can be removed and re-introduced using a conventional bias-on/off cooling technique.

Noncontact diffuse correlation spectroscopy for noninvasive deep tissue blood flow measurement

NASA Astrophysics Data System (ADS)

Lin, Yu; He, Lian; Shang, Yu; Yu, Guoqiang

2012-01-01

A noncontact diffuse correlation spectroscopy (DCS) probe has been developed using two separated optical paths for the source and detector. This unique design avoids the interference between the source and detector and allows large source-detector separations for deep tissue blood flow measurements. The noncontact probe has been calibrated against a contact probe in a tissue-like phantom solution and human muscle tissues; flow changes concurrently measured by the two probes are highly correlated in both phantom (R2=0.89, p<10-5) and real-tissue (R2=0.77, p<10-5, n=9) tests. The noncontact DCS holds promise for measuring blood flow in vulnerable (e.g., pressure ulcer) and soft (e.g., breast) tissues without distorting tissue hemodynamic properties.

Voxel-based measurement sensitivity of spatially resolved near-infrared spectroscopy in layered tissues

NASA Astrophysics Data System (ADS)

Niwayama, Masatsugu

2018-03-01

We quantitatively investigated the measurement sensitivity of spatially resolved spectroscopy (SRS) across six tissue models: cerebral tissue, a small animal brain, the forehead of a fetus, an adult brain, forearm muscle, and thigh muscle. The optical path length in the voxel of the model was analyzed using Monte Carlo simulations. It was found that the measurement sensitivity can be represented as the product of the change in the absorption coefficient and the difference in optical path length in two states with different source-detector distances. The results clarified the sensitivity ratio between the surface layer and the deep layer at each source-detector distance for each model and identified changes in the deep measurement area when one of the detectors was close to the light source. A comparison was made with the results from continuous-wave spectroscopy. The study also identified measurement challenges that arise when the surface layer is inhomogeneous. Findings on the measurement sensitivity of SRS at each voxel and in each layer can support the correct interpretation of measured values when near-infrared oximetry or functional near-infrared spectroscopy is used to investigate different tissue structures.

Fiber-based tissue identification for electrode placement in deep brain stimulation neurosurgery (Conference Presentation)

NASA Astrophysics Data System (ADS)

DePaoli, Damon T.; Lapointe, Nicolas; Goetz, Laurent; Parent, Martin; Prudhomme, Michel; Cantin, Léo.; Galstian, Tigran; Messaddeq, Younès.; Côté, Daniel C.

2016-03-01

Deep brain stimulation's effectiveness relies on the ability of the stimulating electrode to be properly placed within a specific target area of the brain. Optical guidance techniques that can increase the accuracy of the procedure, without causing any additional harm, are therefore of great interest. We have designed a cheap optical fiber-based device that is small enough to be placed within commercially available DBS stimulating electrodes' hollow cores and that is capable of sensing biological information from the surrounding tissue, using low power white light. With this probe we have shown the ability to distinguish white and grey matter as well as blood vessels, in vitro, in human brain samples and in vivo, in rats. We have also repeated the in vitro procedure with the probe inserted in a DBS stimulating electrode and found the results were in good agreement. We are currently validating a second fiber optic device, with micro-optical components, that will result in label free, molecular level sensing capabilities, using CARS spectroscopy. The final objective will be to use this data in real time, during deep brain stimulation neurosurgery, to increase the safety and accuracy of the procedure.

Native hole trap in bulk GaAs and its association with the double-charge state of the arsenic antisite defect

NASA Technical Reports Server (NTRS)

Lagowski, J.; Lin, D. G.; Chen, T.-P.; Skowronski, M.; Gatos, H. C.

1985-01-01

A dominant hole trap has been identified in p-type bulk GaAs employing deep level transient and photocapacitance spectroscopies. The trap is present at a concentration up to about 4 x 10 to the 16th per cu cm, and it has two charge states with energies 0.54 + or - 0.02 and 0.77 + or - 0.02 eV above the top of the valence band (at 77 K). From the upper level the trap can be photoexcited to a persistent metastable state just as the dominant midgap level, EL2. Impurity analysis and the photoionization characteristics rule out association of the trap with impurities Fe, Cu, or Mn. Taking into consideration theoretical results, it appears most likely that the two charge states of the trap are the single and double donor levels of the arsenic antisite As(Ga) defect.

INTERNATIONAL CONFERENCE ON SEMICONDUCTOR INJECTION LASERS SELCO-87: Degradation phenomena in laser diodes

NASA Astrophysics Data System (ADS)

Beister, G.; Krispin, P.; Maege, J.; Richter, G.; Weber, H.; Rechenberg, I.

1988-11-01

Accelerated tests on GaAlAs/GaAs double heterostructure laser diodes showed, in agreement with earlier results on light-emitting diodes, that ageing appeared in three distinct forms: initial and slow degradation stages, both obeying a logarithmic time dependence, and a superimposed "gradation" (enhancement of the output power). Measurements made by the method of deep level transient spectroscopy during the accelerated tests on these lasers, operated as light-emitting diodes, revealed the appearance right from the beginning of B levels attributed to the antisite GaAs defects. The B levels appeared again in diodes tested in the lasing mode. In the case of a group of 21 laser diodes the mean time-to-failure was 9000 h at 70°C for 5 mW (in accordance with the Weibull statistics of degradation rates).

Investigation of low leakage current radiation detectors on n-type 4H-SiC epitaxial layers

NASA Astrophysics Data System (ADS)

Nguyen, Khai V.; Chaudhuri, Sandeep K.; Mandal, Krishna C.

2014-09-01

The surface leakage current of high-resolution 4H-SiC epitaxial layer Schottky barrier detectors has been improved significantly after surface passivations of 4H-SiC epitaxial layers. Thin (nanometer range) layers of silicon dioxide (SiO2) and silicon nitride (Si3N4) were deposited on 4H-SiC epitaxial layers using plasma enhanced chemical vapor deposition (PECVD) on 20 μm thick n-type 4H-SiC epitaxial layers followed by the fabrication of large area (~12 mm2) Schottky barrier radiation detectors. The fabricated detectors have been characterized through current-voltage (I-V), capacitance-voltage (C-V), and alpha pulse height spectroscopy measurements; the results were compared with that of detectors fabricated without surface passivations. Improved energy resolution of ~ 0.4% for 5486 keV alpha particles was observed after passivation, and it was found that the performance of these detectors were limited by the presence of macroscopic and microscopic crystal defects affecting the charge transport properties adversely. Capacitance mode deep level transient studies (DLTS) revealed the presence of a titanium impurity related shallow level defects (Ec-0.19 eV), and two deep level defects identified as Z1/2 and Ci1 located at Ec-0.62 and ~ Ec-1.40 eV respectively.

A Nth-order linear algorithm for extracting diffuse correlation spectroscopy blood flow indices in heterogeneous tissues.

PubMed

Shang, Yu; Yu, Guoqiang

2014-09-29

Conventional semi-infinite analytical solutions of correlation diffusion equation may lead to errors when calculating blood flow index (BFI) from diffuse correlation spectroscopy (DCS) measurements in tissues with irregular geometries. Very recently, we created an algorithm integrating a N th-order linear model of autocorrelation function with the Monte Carlo simulation of photon migrations in homogenous tissues with arbitrary geometries for extraction of BFI (i.e., αD B ). The purpose of this study is to extend the capability of the N th-order linear algorithm for extracting BFI in heterogeneous tissues with arbitrary geometries. The previous linear algorithm was modified to extract BFIs in different types of tissues simultaneously through utilizing DCS data at multiple source-detector separations. We compared the proposed linear algorithm with the semi-infinite homogenous solution in a computer model of adult head with heterogeneous tissue layers of scalp, skull, cerebrospinal fluid, and brain. To test the capability of the linear algorithm for extracting relative changes of cerebral blood flow (rCBF) in deep brain, we assigned ten levels of αD B in the brain layer with a step decrement of 10% while maintaining αD B values constant in other layers. Simulation results demonstrate the accuracy (errors < 3%) of high-order ( N  ≥ 5) linear algorithm in extracting BFIs in different tissue layers and rCBF in deep brain. By contrast, the semi-infinite homogenous solution resulted in substantial errors in rCBF (34.5% ≤ errors ≤ 60.2%) and BFIs in different layers. The N th-order linear model simplifies data analysis, thus allowing for online data processing and displaying. Future study will test this linear algorithm in heterogeneous tissues with different levels of blood flow variations and noises.

Deep learning for hybrid EEG-fNIRS brain-computer interface: application to motor imagery classification.

PubMed

Chiarelli, Antonio Maria; Croce, Pierpaolo; Merla, Arcangelo; Zappasodi, Filippo

2018-06-01

Brain-computer interface (BCI) refers to procedures that link the central nervous system to a device. BCI was historically performed using electroencephalography (EEG). In the last years, encouraging results were obtained by combining EEG with other neuroimaging technologies, such as functional near infrared spectroscopy (fNIRS). A crucial step of BCI is brain state classification from recorded signal features. Deep artificial neural networks (DNNs) recently reached unprecedented complex classification outcomes. These performances were achieved through increased computational power, efficient learning algorithms, valuable activation functions, and restricted or back-fed neurons connections. By expecting significant overall BCI performances, we investigated the capabilities of combining EEG and fNIRS recordings with state-of-the-art deep learning procedures. We performed a guided left and right hand motor imagery task on 15 subjects with a fixed classification response time of 1 s and overall experiment length of 10 min. Left versus right classification accuracy of a DNN in the multi-modal recording modality was estimated and it was compared to standalone EEG and fNIRS and other classifiers. At a group level we obtained significant increase in performance when considering multi-modal recordings and DNN classifier with synergistic effect. BCI performances can be significantly improved by employing multi-modal recordings that provide electrical and hemodynamic brain activity information, in combination with advanced non-linear deep learning classification procedures.

Deep learning for hybrid EEG-fNIRS brain–computer interface: application to motor imagery classification

NASA Astrophysics Data System (ADS)

Chiarelli, Antonio Maria; Croce, Pierpaolo; Merla, Arcangelo; Zappasodi, Filippo

2018-06-01

Objective. Brain–computer interface (BCI) refers to procedures that link the central nervous system to a device. BCI was historically performed using electroencephalography (EEG). In the last years, encouraging results were obtained by combining EEG with other neuroimaging technologies, such as functional near infrared spectroscopy (fNIRS). A crucial step of BCI is brain state classification from recorded signal features. Deep artificial neural networks (DNNs) recently reached unprecedented complex classification outcomes. These performances were achieved through increased computational power, efficient learning algorithms, valuable activation functions, and restricted or back-fed neurons connections. By expecting significant overall BCI performances, we investigated the capabilities of combining EEG and fNIRS recordings with state-of-the-art deep learning procedures. Approach. We performed a guided left and right hand motor imagery task on 15 subjects with a fixed classification response time of 1 s and overall experiment length of 10 min. Left versus right classification accuracy of a DNN in the multi-modal recording modality was estimated and it was compared to standalone EEG and fNIRS and other classifiers. Main results. At a group level we obtained significant increase in performance when considering multi-modal recordings and DNN classifier with synergistic effect. Significance. BCI performances can be significantly improved by employing multi-modal recordings that provide electrical and hemodynamic brain activity information, in combination with advanced non-linear deep learning classification procedures.

The geometry of organophosphonates: Fourier-transform microwave spectroscopy and ab initio study of diethyl methylphosphonate, diethyl ethylphosphonate, and diisopropyl methylphosphonate

NASA Astrophysics Data System (ADS)

DaBell, Ryan S.; Suenram, Richard D.; Lavrich, Richard J.; Lochner, J. Michael; Ellzy, Michael W.; Sumpter, Kenneth; Jensen, James O.; Samuels, Alan C.

2004-12-01

The rotational spectra of diethyl methylphosphonate (DEMP), diethyl ethylphosphonate (DEEP), and diisopropyl methylphosphonate (DIMP) in supersonic expansions have been acquired using Fourier-transform microwave spectroscopy. Spectroscopic constants have been determined for five distinct conformers of the three molecules. Experimental data have been compared to ab initio calculations performed for each species. For both DEMP and DEEP, the calculations indicate the presence of several low-energy conformers (i.e., ⩽˜400 cm -1 above the ground state) may be present at room temperature (300 K) for both DEMP and DEEP. When entrained in a supersonic expansion, the rotational temperatures of the samples are much colder (˜2 K); nonetheless, spectra from three conformers of DEEP are still observed experimentally, whereas only one conformer of DEMP is observed. In contrast, only a single low-energy conformer of DIMP is predicted by theory, and is present in the molecular beam. The relative abundance of low-energy conformers of DEMP and DEEP is attributed to the flexibility of the ethoxy groups within each molecule. The presence of multiple DEEP conformers in the supersonic beam indicates a more complex potential energy surface for this molecule that is directly related to conformational shifts of the PCH 2CH 3 group. Conversely, the absence of low-energy conformers of DIMP is attributed to steric hindrance between isopropoxy groups in the molecule. The internal rotation barrier for the PCH 3 group in DEMP and DIMP is compared to that found in DMMP and several phosphonate-based chemical weapon agents.

Direct Absorption Spectroscopy with Electro-Optic Frequency Combs

NASA Astrophysics Data System (ADS)

Fleisher, Adam J.; Long, David A.; Plusquellic, David F.; Hodges, Joseph T.

2017-06-01

The application of electro-optic frequency combs to direct absorption spectroscopy has increased research interest in high-agility, modulator-based comb generation. This talk will review common architectures for electro-optic frequency comb generators as well as describe common self-heterodyne and multi-heterodyne (i.e., dual-comb) detection approaches. In order to achieve a sufficient signal-to-noise ratio on the recorded interferogram while allowing for manageable data volumes, broadband electro-optic frequency combs require deep coherent averaging, preferably in real-time. Applications such as cavity-enhanced spectroscopy, precision atomic and molecular spectroscopy, as well as time-resolved spectroscopy will be introduced. D.A. Long et al., Opt. Lett. 39, 2688 (2014) A.J. Fleisher et al., Opt. Express 24, 10424 (2016)

Improved sensing using simultaneous deep-UV Raman and fluorescence detection-II

NASA Astrophysics Data System (ADS)

Hug, W. F.; Bhartia, R.; Sijapati, K.; Beegle, L. W.; Reid, R. D.

2014-05-01

Photon Systems in collaboration with JPL is continuing development of a new technology robot-mounted or hand-held sensor for reagentless, short-range, standoff detection and identification of trace levels chemical, biological, and explosive (CBE) materials on surfaces. This deep ultraviolet CBE sensor is the result of Army STTR and DTRA programs. The evolving 10 to 15 lb, 20 W, sensor can discriminate CBE from background clutter materials using a fusion of deep UV excited resonance Raman (RR) and laser induced native fluorescence (LINF) emissions collected is less than 1 ms. RR is a method that provides information about molecular bonds, while LINF spectroscopy is a much more sensitive method that provides information regarding the electronic configuration of target molecules. Standoff excitation of suspicious packages, vehicles, persons, and other objects that may contain hazardous materials is accomplished using excitation in the deep UV where there are four main advantages compared to near-UV, visible or near-IR counterparts. 1) Excited between 220 and 250 nm, Raman emission occur within a fluorescence-free region of the spectrum, eliminating obscuration of weak Raman signals by fluorescence from target or surrounding materials. 2) Because Raman and fluorescence occupy separate spectral regions, detection can be done simultaneously, providing an orthogonal set of information to improve both sensitivity and lower false alarm rates. 3) Rayleigh law and resonance effects increase Raman signal strength and sensitivity of detection. 4) Penetration depth into target in the deep UV is short, providing spatial/spectral separation of a target material from its background or substrate. 5) Detection in the deep UV eliminates ambient light background and enable daylight detection.

Deep Soil Carbon in the Critical Zone: Amount and Nature of Carbon in Weathered Bedrock, and its Implication for Soil Carbon Inventory

NASA Astrophysics Data System (ADS)

Moreland, K. C.; Tian, Z.; Berhe, A. A.; O'Geen, A. T.

2017-12-01

Globally, soils store more carbon (C) than the vegetation and the atmosphere combined. Up to 60-80% of the C stored in soils is found in below 30cm soil depth, but there is little data on C storage in weathered bedrock or saprolite. Deep soil organic matter (SOM) can be a mixture of new and old SOM; that is rendered relatively stable due to burial, aggregation, its disconnection from decomposers, and chemical association that organic matter forms with soil minerals. The limited data available on deep SOM dynamics suggests that stock, distribution, and composition of deep SOM are strongly correlated to climate. The overall objective of this research is to investigate how climate regulates OM storage, composition, stability, and stabilization mechanisms. Expecting that the amount of OM stored in deep soil and the stability are a function of soil thickness and availability of weathering products (i.e. reactive minerals), the stock and stability of deep SOM is expected to follow a similar relationship with climate, as does the intensity of weathering. This research is conducted in the NSF funded Southern Sierra Critical Zone Observatories that is located along a climosequence, the western slopes of the Sierra Naevada Mountains of California. Here we will present results derived from characterization of soils and weathered bedrock using elemental and stable isotope elemental analysis, and Fourier Transformed Infrared Spectroscopy to determine OM concentration and functional group level composition of bulk SOM. Our findings show that adding in subsoil and weathered bedrock C stocks increases estimates of soil C stock by 1/3rd to 2/3rd.

[Case of interval form of carbon monoxide poisoning without increased carboxyhemoglobin level diagnosed by characteristic MR spectroscopy findings].

PubMed

Kamisawa, Tomoko; Ikawa, Masamichi; Hamano, Tadanori; Nagata, Miwako; Kimura, Hirohiko; Yoneda, Makoto

2014-01-01

A 67-year-old man living alone was admitted for acute disturbance of consciousness during winter. He presented with semicoma, a decorticate posture, and exaggerated tendon reflexes of the limbs, but brainstem reflexes were intact. The carboxyhemoglobin (COHb) level was normal in arterial blood gas on admission, and protein in cerebrospinal fluid was increased without pleocytosis. Brain MRI showed diffuse T2 high intensities in the deep white matter bilaterally without a contrast effect and abnormal T1 intensity in the pallidum. (1)H-MR spectroscopy (MRS) of the white matter lesion demonstrated findings suggesting demyelination as an increased choline peak, enhanced anaerobic metabolism as increased lactate and lipids peaks, and reduced neurons as a decreased N-acetylaspartate peak, which corresponded to delayed encephalopathy due to the interval form of carbon monoxide (CO) poisoning. The possibility of CO exposure due to coal briquette use 2 weeks before the symptomatic onset was indicated by his family, so he was diagnosed with CO poisoning. His consciousness slightly improved with corticosteroid therapy and repetitive hyperbaric oxygen therapy, but brain MRI and MRS findings did not improve. Characteristic MRS findings of leukoencephalopathy are helpful for diagnosing the interval form of CO poisoning in the case of a normal COHb level.

Charge Trapping Properties of Ge Nanocrystals Grown via Solid-State Dewetting

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

Johnston, Steven; Jadli, I.; Aouassa, M.

2018-05-04

In the present work, we report on the charge trapping properties of Germanium Nanocrystals (Ge NCs) self assembled on SiO2 thin layer for promising applications in next-generation non volatile memory by the means of Deep Level Transient Spectroscopy (DLTS) and high frequency C-V method. The Ge NCs were grown via dewetting phenomenon at solid state by Ultra-High Vacuum (UHV) annealing and passivated with silicon before SiO2 capping. The role of the surface passivation is to reduce the electrical defect density at the Ge NCs-SiO2 interface. The presence of the Ge NCs in the oxide of the MOS capacitors strongly affectsmore » the C-V characteristics and increases the accumulation capacitance, causes a negative flat band voltage (VFB) shift. The DLTS has been used to study the individual Ge NCs as a single point deep level defect in the oxide. DLTS reveals two main features: the first electron traps around 255 K could correspond to dangling bonds at the Si/SiO2 interface and the second, at high-temperature (>300 K) response, could be originated from minority carrier generation in Ge NCs.« less

Dopant incorporation in Al0.9Ga0.1As0.06Sb0.94 grown by molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Patra, Saroj Kumar; Tran, Thanh-Nam; Vines, Lasse; Kolevatov, Ilia; Monakhov, Edouard; Fimland, Bjørn-Ove

2017-04-01

Incorporation of beryllium (Be) and tellurium (Te) dopants in epitaxially grown Al0.9Ga0.1As0.06Sb0.94 layers was investigated. Carrier concentrations and mobilities of the doped layers were obtained from room temperature Hall effect measurements, and dopant densities from secondary ion mass spectrometry depth profiling. An undoped Al0.3Ga0.7As cap layer and side wall passivation were used to reduce oxidation and improve accuracy in Hall effect measurements. The measurements on Be-doped samples revealed high doping efficiency and the carrier concentration varied linearly with dopant density up to the highest Be dopant density of 2.9 × 1019 cm-3, whereas for Te doped samples the doping efficiency was in general low and the carrier concentration saturated for Te-dopant densities above 8.0 × 1018 cm-3. The low doping efficiency in Te-doped Al0.9Ga0.1As0.06Sb0.94 layer was studied by deep-level transient spectroscopy, revealing existence of deep trap levels and related DX-centers which explains the low doping efficiency.

Investigation of buffer traps in AlGaN/GaN-on-Si devices by thermally stimulated current spectroscopy and back-gating measurement

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

Yang, Shu; Zhou, Chunhua; Jiang, Qimeng

2014-01-06

Thermally stimulated current (TSC) spectroscopy and high-voltage back-gating measurement are utilized to study GaN buffer traps specific to AlGaN/GaN lateral heterojunction structures grown on a low-resistivity Si substrate. Three dominating deep-level traps in GaN buffer with activation energies of ΔE{sub T1} ∼ 0.54 eV, ΔE{sub T2} ∼ 0.65 eV, and ΔE{sub T3} ∼ 0.75 eV are extracted from TSC spectroscopy in a vertical GaN-on-Si structure. High back-gate bias applied to the Si substrate could influence the drain current in an AlGaN/GaN-on-Si high-electron-mobility transistor in a way that cannot be explained with a simple field-effect model. By correlating the trap states identified in TSC with the back-gating measurement results, itmore » is proposed that the ionization/deionization of both donor and acceptor traps are responsible for the generation of buffer space charges, which impose additional modulation to the 2DEG channel.« less

Au/n-ZnO rectifying contact fabricated with hydrogen peroxide pretreatment

NASA Astrophysics Data System (ADS)

Gu, Q. L.; Cheung, C. K.; Ling, C. C.; Ng, A. M. C.; Djurišić, A. B.; Lu, L. W.; Chen, X. D.; Fung, S.; Beling, C. D.; Ong, H. C.

2008-05-01

Au contacts were deposited on n-type ZnO single crystals with and without hydrogen peroxide pretreatment for the ZnO substrate. The Au/ZnO contacts fabricated on substrates without H2O2 pretreatment were Ohmic and those with H2O2 pretreatment were rectifying. With an aim of fabricating a good quality Schottky contact, the rectifying property of the Au/ZnO contact was systemically investigated by varying the treatment temperature and duration. The best performing Schottky contact was found to have an ideality factor of 1.15 and a leakage current of ˜10-7 A cm-2. A multispectroscopic study, including scanning electron microscopy, positron annihilation spectroscopy, deep level transient spectroscopy, x-ray photoelectron spectroscopy, and photoluminescence, showed that the H2O2 treatment removed the OH impurity and created Zn-vacancy related defects hence decreasing the conductivity of the ZnO surface layer, a condition favorable for forming good Schottky contact. However, the H2O2 treatment also resulted in a deterioration of the surface morphology, leading to an increase in the Schottky contact ideality factor and leakage current in the case of nonoptimal treatment time and temperature.

Point defect induced degradation of electrical properties of Ga2O3 by 10 MeV proton damage

NASA Astrophysics Data System (ADS)

Polyakov, A. Y.; Smirnov, N. B.; Shchemerov, I. V.; Yakimov, E. B.; Yang, Jiancheng; Ren, F.; Yang, Gwangseok; Kim, Jihyun; Kuramata, A.; Pearton, S. J.

2018-01-01

Deep electron and hole traps in 10 MeV proton irradiated high-quality β-Ga2O3 films grown by Hydride Vapor Phase Epitaxy (HVPE) on bulk β-Ga2O3 substrates were measured by deep level transient spectroscopy with electrical and optical injection, capacitance-voltage profiling in the dark and under monochromatic irradiation, and also electron beam induced current. Proton irradiation caused the diffusion length of charge carriers to decrease from 350-380 μm in unirradiated samples to 190 μm for a fluence of 1014 cm-2, and this was correlated with an increase in density of hole traps with optical ionization threshold energy near 2.3 eV. These defects most likely determine the recombination lifetime in HVPE β-Ga2O3 epilayers. Electron traps at Ec-0.75 eV and Ec-1.2 eV present in as-grown samples increase in the concentration after irradiation and suggest that these centers involve native point defects.

Sodium doping in ZnO crystals

NASA Astrophysics Data System (ADS)

Parmar, N. S.; Lynn, K. G.

2015-01-01

ZnO bulk single crystals were doped with sodium by thermal diffusion. Positron annihilations spectroscopy confirms the filling of zinc vacancies, to >6 μm deep in the bulk. Secondary-ion mass spectrometry measurement shows the diffusion of sodium up to 8 μm with concentration (1-3.5) × 1017 cm-3. Broad photoluminescence excitation peak at 3.1 eV, with onset appearance at 3.15 eV in Na:ZnO, is attributed to an electronic transition from a NaZn level at ˜(220-270) meV to the conduction band. Resistivity in Na doped ZnO crystals increases up to (4-5) orders of magnitude at room temperature.

Hole defects in molecular beam epitaxially grown p-GaAs introduced by alpha irradiation

NASA Astrophysics Data System (ADS)

Goodman, S. A.; Auret, F. D.; Meyer, W. E.

1994-01-01

Epitaxial aluminum Schottky barrier diodes on molecular beam epitaxially grown p-GaAs with a free carrier density of 2×1016 cm-3 were irradiated with alpha particles at room temperature using an americium-241 (Am-241) radio nuclide. For the first time, the radiation induced hole defects are characterized using conventional deep level transient spectroscopy (DLTS). The introduction rates and DLTS ``signatures'' of three prominent radiation induced defects Hα1, Hα4, and Hα5, situated 0.08, 0.20, and 0.30 eV above the valence band, respectively, are calculated and compared to those of similar defects introduced during electron irradiation.

Thermal stability of deep level defects induced by high energy proton irradiation in n-type GaN

NASA Astrophysics Data System (ADS)

Zhang, Z.; Farzana, E.; Sun, W. Y.; Chen, J.; Zhang, E. X.; Fleetwood, D. M.; Schrimpf, R. D.; McSkimming, B.; Kyle, E. C. H.; Speck, J. S.; Arehart, A. R.; Ringel, S. A.

2015-10-01

The impact of annealing of proton irradiation-induced defects in n-type GaN devices has been systematically investigated using deep level transient and optical spectroscopies. Moderate temperature annealing (>200-250 °C) causes significant reduction in the concentration of nearly all irradiation-induced traps. While the decreased concentration of previously identified N and Ga vacancy related levels at EC - 0.13 eV, 0.16 eV, and 2.50 eV generally followed a first-order reaction model with activation energies matching theoretical values for NI and VGa diffusion, irradiation-induced traps at EC - 0.72 eV, 1.25 eV, and 3.28 eV all decrease in concentration in a gradual manner, suggesting a more complex reduction mechanism. Slight increases in concentration are observed for the N-vacancy related levels at EC - 0.20 eV and 0.25 eV, which may be due to the reconfiguration of other N-vacancy related defects. Finally, the observed reduction in concentrations of the states at EC - 1.25 and EC - 3.28 eV as a function of annealing temperature closely tracks the detailed recovery behavior of the background carrier concentration as a function of annealing temperature. As a result, it is suggested that these two levels are likely to be responsible for the underlying carrier compensation effect that causes the observation of carrier removal in proton-irradiated n-GaN.

Greater contribution of cerebral than extracerebral hemodynamics to near-infrared spectroscopy signals for functional activation and resting-state connectivity in infants.

PubMed

Funane, Tsukasa; Homae, Fumitaka; Watanabe, Hama; Kiguchi, Masashi; Taga, Gentaro

2014-10-01

While near-infrared spectroscopy (NIRS) has been increasingly applied to neuroimaging and functional connectivity studies in infants, it has not been quantitatively examined as to what extent the deep tissue (such as cerebral tissue) as opposed to shallow tissue (such as scalp), contributes to NIRS signals measured in infants. A method for separating the effects of deep- and shallow-tissue layers was applied to data of nine sleeping three-month-old infants who had been exposed to 3-s speech sounds or silence (i.e., resting state) and whose hemodynamic changes over their bilateral temporal cortices had been measured by using an NIRS system with multiple source-detector (S-D) distances. The deep-layer contribution was found to be large during resting [67% at S-D 20 mm, 78% at S-D 30 mm for oxygenated hemoglobin (oxy-Hb)] as well as during the speech condition (72% at S-D 20 mm, 82% at S-D 30 mm for oxy-Hb). A left-right connectivity analysis showed that correlation coefficients between left and right channels did not differ between original- and deep-layer signals under no-stimulus conditions and that of original- and deep-layer signals were larger than those of the shallow layer. These results suggest that NIRS signals obtained in infants with appropriate S-D distances largely reflected cerebral hemodynamic changes.

Greater contribution of cerebral than extracerebral hemodynamics to near-infrared spectroscopy signals for functional activation and resting-state connectivity in infants

PubMed Central

Funane, Tsukasa; Homae, Fumitaka; Watanabe, Hama; Kiguchi, Masashi; Taga, Gentaro

2014-01-01

Abstract. While near-infrared spectroscopy (NIRS) has been increasingly applied to neuroimaging and functional connectivity studies in infants, it has not been quantitatively examined as to what extent the deep tissue (such as cerebral tissue) as opposed to shallow tissue (such as scalp), contributes to NIRS signals measured in infants. A method for separating the effects of deep- and shallow-tissue layers was applied to data of nine sleeping three-month-old infants who had been exposed to 3-s speech sounds or silence (i.e., resting state) and whose hemodynamic changes over their bilateral temporal cortices had been measured by using an NIRS system with multiple source-detector (S-D) distances. The deep-layer contribution was found to be large during resting [67% at S-D 20 mm, 78% at S-D 30 mm for oxygenated hemoglobin (oxy-Hb)] as well as during the speech condition (72% at S-D 20 mm, 82% at S-D 30 mm for oxy-Hb). A left-right connectivity analysis showed that correlation coefficients between left and right channels did not differ between original- and deep-layer signals under no-stimulus conditions and that of original- and deep-layer signals were larger than those of the shallow layer. These results suggest that NIRS signals obtained in infants with appropriate S-D distances largely reflected cerebral hemodynamic changes. PMID:26157977

The Chandra Deepest Fields in the Infrared: Making the Connection between Normal Galaxies and AGN

NASA Astrophysics Data System (ADS)

Grogin, N. A.; Ferguson, H. C.; Dickinson, M. E.; Giavalisco, M.; Mobasher, B.; Padovani, P.; Williams, R. E.; Chary, R.; Gilli, R.; Heckman, T. M.; Stern, D.; Winge, C.

2001-12-01

Within each of the two Chandra Deepest Fields (CDFs), there are ~10'x15' regions targeted for non-proprietary, deep SIRTF 3.6--24μ m imaging as part of the Great Observatories Origins Deep Survey (GOODS) Legacy program. In advance of the SIRTF observations, the GOODS team has recently begun obtaining non-proprietary, deep ground-based optical and near-IR imaging and spectroscopy over these regions, which contain virtually all of the current ≈1 Msec CXO coverage in the CDF North and much of the ≈1 Msec coverage in the CDF South. In particular, the planned depth of the near-IR imaging (JAB ~ 25.3; HAB ~ 24.8; KAB ~ 24.4) combined with the deep Chandra data can allow us to trace the evolutionary connection between normal galaxies, starbursts, and AGN out to z ~ 1 and beyond. We describe our CDF Archival program, which is integrating these GOODS-supporting observations together with the CDF archival data and other publicly-available datasets in these regions to create a multi-wavelength deep imaging and spectroscpic database available to the entire community. We highlight progress toward near-term science goals of this program, including: (a) pushing constraints on the redshift distribution and spectral-energy distributions of the faintest X-ray sources to the deepest possible levels via photometric redshifts; and (b) better characterizing the heavily-obscured and the high-redshift populations via both a near-IR search for optically-undetected CDF X-ray sources and also X-ray stacking analyses on the CXO-undetected EROs in these fields.

Kerr-gated picosecond Raman spectroscopy and Raman photon migration of equine bone tissue with 400-nm excitation

NASA Astrophysics Data System (ADS)

Morris, Michael D.; Goodship, Allen E.; Draper, Edward R. C.; Matousek, Pavel; Towrie, Michael; Parker, Anthony W.

2004-07-01

We show that Raman spectroscopy with visible lasers, even in the deep blue is possible with time-gated Raman spectroscopy. A 4 picosec time gate allows efficient fluorescence rejection, up to 1000X, and provides almost background-free Raman spectra with low incident laser power. The technology enables spectroscopy with better than 10X higher scattering efficiency than is possible with the NIR (785 nm and 830 nm) lasers that are conventionally used. Raman photon migration is shown to allow depth penetration. We show for the first time that Kerr-gated Raman spectra of bone tissue with blue laser excitation enables both fluorescence rejection and depth penetration.

Electronic defects in the halide antiperovskite semiconductor Hg3Se2I2

NASA Astrophysics Data System (ADS)

Kim, Joon-Il; Peters, John A.; He, Yihui; Liu, Zhifu; Das, Sanjib; Kontsevoi, Oleg Y.; Kanatzidis, Mercouri G.; Wessels, Bruce W.

2017-10-01

Halide perovskites have emerged as a potential photoconducting material for photovoltaics and hard radiation detection. We investigate the nature of charge transport in the semi-insulating chalcohalide Hg3Se2I2 compound using the temperature dependence of dark current, thermally stimulated current (TSC) spectroscopy, and photoconductivity measurements as well as first-principles density functional theory (DFT) calculations. Dark conductivity measurements and TSC spectroscopy indicate the presence of multiple shallow and deep level traps that have relatively low concentrations of the order of 1013-1015c m-3 and capture cross sections of ˜10-16c m2 . A distinct persistent photoconductivity is observed at both low temperatures (<170 K ) and high temperatures (>230 K), with major implications for room-temperature compound semiconductor radiation detection. From preliminary DFT calculations, the origin of the traps is attributed to intrinsic vacancy defects (VHg, VSe, and VI) and interstitials (Seint) or other extrinsic impurities. The results point the way for future improvements in crystal quality and detector performance.

Blood flow measurement of human skeletal muscle during various exercise intensity using diffuse correlation spectroscopy (DCS)

NASA Astrophysics Data System (ADS)

Murakami, Yuya; Ono, Yumie; Ichinose, Masashi

2017-02-01

We studied blood flow dynamics of active skeletal muscle using diffuse correlation spectroscopy (DCS), an emerging optical modality that is suitable for noninvasive quantification of microcirculation level in deep tissue. Seven healthy subjects conducted 0.5 Hz dynamic handgrip exercise for 3 minutes at intensities of 10, 20, 30, and 50 % of maximal voluntary contraction (MVC). DCS could detect the time-dependent increase of the blood flow response of the forearm muscle for continuous exercises, and the increase ratios of the mean blood flow through the exercise periods showed good correlation with the exercise intensities. We also compared blood flow responses detected from DCS with two different photon sampling rates and found that an appropriate photon sampling rates should be selected to follow the wide-ranged increase in the muscle blood flow with dynamic exercise. Our results demonstrate the possibility for utilizing DCS in a field of sports medicine to noninvasively evaluate the dynamics of blood flow in the active muscles.

Pentacene Schottky diodes studied by impedance spectroscopy: Doping properties and trap response

NASA Astrophysics Data System (ADS)

Pahner, Paul; Kleemann, Hans; Burtone, Lorenzo; Tietze, Max L.; Fischer, Janine; Leo, Karl; Lüssem, Björn

2013-11-01

We study doping properties and charge carrier trap distributions in pentacene Schottky diodes doped by the fluorinated fullerene derivate C60F36 and 2,2'-(perdiylidene)dimalononitrile (F6-TCNNQ) upon small signal excitation. We show that the charge carrier depletion zones present in these Schottky diodes are tunable by the applied bias and temperature. Mott-Schottky evaluations yield reduced doping efficiencies and dopant activation energies between 19 and 54 meV. In the low-frequency regime, we resolve additional capacitive contributions from inherent charge carrier traps. A Gaussian distributed trap center 0.6 eV above the hole transport level with a density in the range of 1016 cm-3 depending on the material purity is found to be an intrinsic feature of the pentacene matrix. Upon doping, the deep Gaussian trap center saturates in density and broad exponentially tailing trap distributions arise. Subsequent ultraviolet photoelectron spectroscopy measurements are conducted to inspect for energetic broadening due to doping.

Electrically active defects in p-type silicon after alpha-particle irradiation

NASA Astrophysics Data System (ADS)

Danga, Helga T.; Auret, F. Danie; Tunhuma, Shandirai M.; Omotoso, Ezekiel; Igumbor, Emmanuel; Meyer, Walter E.

2018-04-01

In this work, we investigated the defects introduced when boron (B) doped silicon (Si) was irradiated by making use of a 5.4 MeV americium (Am) 241 foil radioactive source with a fluence rate of 7×106 cm-2 s-1 at room temperature. Deep level transient spectroscopy (DLTS) and Laplace-DLTS measurements were used to investigate the electronic properties of the introduced defects. After exposure at a fluence of 5.1×1010 cm-2, the energy levels of the hole traps measured were: H(0.10), H(0.16), H(0.33) and H(0.52) The defect level H(0.10) was tri-vacancy related. H(0.33) was identified as the interstitial carbon (Ci) related defect which was a result of radiation induced damage. H(0.52) was a B-related defect. Explicit deductions about the origin of H(0.16) have not yet been achieved.

Cerebral Oximetry During Infant Cardiac Surgery: Evaluation of and Relationship to Early Postoperative Outcome

PubMed Central

Kussman, Barry D.; Wypij, David; DiNardo, James A.; Newburger, Jane W.; Mayer, John E.; del Nido, Pedro J.; Bacha, Emile A.; Pigula, Frank; McGrath, Ellen; Laussen, Peter C.

2009-01-01

Background We examined changes in cerebral oxygen saturation during infant heart surgery and its relationship to anatomic diagnosis and early outcome Methods Regional cerebral oxygen saturation (rSO2) was measured by near-infrared spectroscopy in 104 infants undergoing biventricular repair without aortic arch obstruction as part of a randomized trial of hemodilution to a hematocrit of 25% versus 35%. Results Prior to cardiopulmonary bypass (CPB), infants with tetralogy of Fallot had higher rSO2 values compared to those with D-transposition of the great arteries (D-TGA) or ventricular septal defect (P < 0.001). During CPB cooling, low flow and at the termination of CPB, D-TGA subjects had the highest rSO2 values (P < 0.001). There were no significant associations between intraoperative rSO2 and early postoperative outcomes after adjustment for diagnosis. In 39 D-TGA subjects with ≥5 minutes of deep hypothermic circulatory arrest, there was no correlation between the rSO2 (91 ± 6%) or hematocrit (29.2 ± 5.5%) at the onset of arrest and the rate of decline in rSO2 during arrest. Conclusions Intraoperative rSO2 varies according to anatomic diagnosis but accounts for very little of the variance in early outcome. As measured by frontal near-infrared spectroscopy, higher levels of hematocrit and current perfusion techniques appear to provide an adequate oxygen reservoir prior to relatively short periods of deep hypothermic circulatory arrest. PMID:19299774

A new cytotoxic sterol methoxymethyl ether from a deep water marine sponge Scleritoderma sp. cf. paccardi.

PubMed

Gunasekera, S P; Kelly-Borges, M; Longley, R E

1996-02-01

24(R)-Methyl-5 alpha-cholest-7-enyl 3 beta-methoxymethyl ether (1), a new sterol ether, has been isolated from a deep-water marine sponge Scleritoderma sp. cf. paccardi. Compound 1 exhibited in vitro cytotoxicity against the cultured murine P-388 tumor cell line with an IC50 of 2.3 micrograms/mL. The isolation and structure elucidation of 1 by NMR spectroscopy is described.

Through the Looking GLASS: A JWST Exploration of Galaxy Formation and Evolution from Cosmic Dawn to Present Day

NASA Astrophysics Data System (ADS)

Treu, Tommaso; Abramson, L.; Bradac, M.; Brammer, G.; Fontana, A.; Henry, A.; Hoag, A.; Huang, K.; Mason, C.; Morishita, T.; Pentericci, L.; Wang, X.

2017-11-01

We propose a carefully designed set of observations of the lensing cluster Abell 2744 to study intrinsically faint magnified galaxies from the epoch of reionization to redshift of 1, demonstrating and characterizing complementary spectroscopic modes with NIRSPEC and NIRISS. The observations are designed to address the questions: 1) when did reionization happen and what were the sources of reionizing photons? 2) How do baryons cycle in and out of galaxies? This dataset with deep spectroscopy on the cluster and deep multiband NIRCAM imaging in parallel will enable a wealth of investigations and will thus be of interest to a broad section of the astronomical community. The dataset will illustrate the power and challenges of: 1) combining rest frame UV and optical NIRSPEC spectroscopy for galaxies at the epoch of reionization, 2) obtaining spatially resolved emission line maps with NIRISS, 3) combining NIRISS and NIRSPEC spectroscopy. Building on our extensive experience with HST slitless spectroscopy and imaging in clusters of galaxies as part of the GLASS, WISP, SURFSUP, and ASTRODEEP projects, we will provide the following science-enabling products to the community: 1)quantitative comparison of spatially resolved (NIRISS) and spectrally resolved (NIRSPEC) spectroscopy, 2) Object based interactive exploration tools for multi-instrument datasets, 3) Interface for easy forced extractionof slitless spectra based on coordinates, 4) UV-optical spectroscopic templates of highredshift galaxies, 5) NIRCAM parallel catalogs and a list of 26 z>=9 dropouts for spectroscopic follow-up in Cycle-2.

Review—hexagonal boron nitride epilayers: Growth, optical properties and device applications

DOE PAGES

Jiang, H. X.; Lin, Jing Yu

2016-09-07

This paper provides a brief overview on recent advances made in authors’ laboratory in epitaxial growth and optical studies of hexagonal boron nitride (h-BN) epilayers and heterostructures. Photoluminescence spectroscopy has been employed to probe the optical properties of h-BN. It was observed that the near band edge emission of h-BN is unusually high and is more than two orders of magnitude higher than that of high quality AlN epilayers. It was shown that the unique quasi-2D nature induced by the layered structure of h-BN results in high optical absorption and emission. The impurity related and near band-edge transitions in h-BNmore » epilayers were probed for materials synthesized under varying ammonia flow rates. Our results have identified that the most dominant impurities and deep level defects in h-BN epilayers are related to nitrogen vacancies. By growing h-BN under high ammonia flow rates, nitrogen vacancy related defects can be eliminated and epilayers exhibiting pure free exciton emission have been obtained. Deep UV and thermal neutron detectors based on h-BN epilayers were shown to possess unique features. Lastly, it is our belief that h-BN will lead to many potential applications from deep UV emitters and detectors, radiation detectors, to novel 2D photonic and electronic devices.« less

Review—hexagonal boron nitride epilayers: Growth, optical properties and device applications

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

Jiang, H. X.; Lin, Jing Yu

This paper provides a brief overview on recent advances made in authors’ laboratory in epitaxial growth and optical studies of hexagonal boron nitride (h-BN) epilayers and heterostructures. Photoluminescence spectroscopy has been employed to probe the optical properties of h-BN. It was observed that the near band edge emission of h-BN is unusually high and is more than two orders of magnitude higher than that of high quality AlN epilayers. It was shown that the unique quasi-2D nature induced by the layered structure of h-BN results in high optical absorption and emission. The impurity related and near band-edge transitions in h-BNmore » epilayers were probed for materials synthesized under varying ammonia flow rates. Our results have identified that the most dominant impurities and deep level defects in h-BN epilayers are related to nitrogen vacancies. By growing h-BN under high ammonia flow rates, nitrogen vacancy related defects can be eliminated and epilayers exhibiting pure free exciton emission have been obtained. Deep UV and thermal neutron detectors based on h-BN epilayers were shown to possess unique features. Lastly, it is our belief that h-BN will lead to many potential applications from deep UV emitters and detectors, radiation detectors, to novel 2D photonic and electronic devices.« less

Single and double acceptor-levels of a carbon-hydrogen defect in n-type silicon

NASA Astrophysics Data System (ADS)

Stübner, R.; Scheffler, L.; Kolkovsky, Vl.; Weber, J.

2016-05-01

In the present study, we discuss the origin of two dominant deep levels (E42 and E262) observed in n-type Si, which is subjected to hydrogenation by wet chemical etching or a dc H-plasma treatment. Their activation enthalpies determined from Laplace deep level transient spectroscopy measurements are EC-0.06 eV (E42) and EC-0.51 eV (E262). The similar annealing behavior and identical depth profiles of E42 and E262 correlate them with two different charge states of the same defect. E262 is attributed to a single acceptor state due to the absence of the Poole-Frenkel effect and the lack of a capture barrier for electrons. The emission rate of E42 shows a characteristic enhancement with the electric field, which is consistent with the assignment to a double acceptor state. In samples with different carbon and hydrogen content, the depth profiles of E262 can be explained by a defect with one H-atom and one C-atom. From a comparison with earlier calculations [Andersen et al., Phys. Rev. B 66, 235205 (2002)], we attribute E42 to the double acceptor and E262 to the single acceptor state of the CH1AB configuration, where one H atom is directly bound to carbon in the anti-bonding position.

Single and double acceptor-levels of a carbon-hydrogen defect in n-type silicon

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

Stübner, R.; Scheffler, L.; Kolkovsky, Vl., E-mail: kolkov@ifpan.edu.pl

In the present study, we discuss the origin of two dominant deep levels (E42 and E262) observed in n-type Si, which is subjected to hydrogenation by wet chemical etching or a dc H-plasma treatment. Their activation enthalpies determined from Laplace deep level transient spectroscopy measurements are E{sub C}-0.06 eV (E42) and E{sub C}-0.51 eV (E262). The similar annealing behavior and identical depth profiles of E42 and E262 correlate them with two different charge states of the same defect. E262 is attributed to a single acceptor state due to the absence of the Poole-Frenkel effect and the lack of a capture barrier formore » electrons. The emission rate of E42 shows a characteristic enhancement with the electric field, which is consistent with the assignment to a double acceptor state. In samples with different carbon and hydrogen content, the depth profiles of E262 can be explained by a defect with one H-atom and one C-atom. From a comparison with earlier calculations [Andersen et al., Phys. Rev. B 66, 235205 (2002)], we attribute E42 to the double acceptor and E262 to the single acceptor state of the CH{sub 1AB} configuration, where one H atom is directly bound to carbon in the anti-bonding position.« less

Noninvasive deep Raman detection with 2D correlation analysis

NASA Astrophysics Data System (ADS)

Kim, Hyung Min; Park, Hyo Sun; Cho, Youngho; Jin, Seung Min; Lee, Kang Taek; Jung, Young Mee; Suh, Yung Doug

2014-07-01

The detection of poisonous chemicals enclosed in daily necessaries is prerequisite essential for homeland security with the increasing threat of terrorism. For the detection of toxic chemicals, we combined a sensitive deep Raman spectroscopic method with 2D correlation analysis. We obtained the Raman spectra from concealed chemicals employing spatially offset Raman spectroscopy in which incident line-shaped light experiences multiple scatterings before being delivered to inner component and yielding deep Raman signal. Furthermore, we restored the pure Raman spectrum of each component using 2D correlation spectroscopic analysis with chemical inspection. Using this method, we could elucidate subsurface component under thick powder and packed contents in a bottle.

Double negatively charged carbon vacancy at the h- and k-sites in 4H-SiC: Combined Laplace-DLTS and DFT study

NASA Astrophysics Data System (ADS)

Capan, Ivana; Brodar, Tomislav; Pastuović, Željko; Siegele, Rainer; Ohshima, Takeshi; Sato, Shin-ichiro; Makino, Takahiro; Snoj, Luka; Radulović, Vladimir; Coutinho, José; Torres, Vitor J. B.; Demmouche, Kamel

2018-04-01

We present results from combined Laplace-Deep Level Transient Spectroscopy (Laplace-DLTS) and density functional theory studies of the carbon vacancy (VC) in n-type 4H-SiC. Using Laplace-DLTS, we were able to distinguish two previously unresolved sub-lattice-inequivalent emissions, causing the broad Z1/2 peak at 290 K that is commonly observed by conventional DLTS in n-type 4H-SiC. This peak has two components with activation energies for electron emission of 0.58 eV and 0.65 eV. We compared these results with the acceptor levels of VC obtained by means of hybrid density functional supercell calculations. The calculations support the assignment of the Z1/2 signal to a superposition of emission peaks from double negatively charged VC defects. Taking into account the measured and calculated energy levels, the calculated relative stability of VC in hexagonal (h) and cubic (k) lattice sites, as well as the observed relative amplitude of the Laplace-DLTS peaks, we assign Z1 and Z2 to VC(h) and VC(k), respectively. We also present the preliminary results of DLTS and Laplace-DLTS measurements on deep level defects (ET1 and ET2) introduced by fast neutron irradiation and He ion implantation in 4H-SiC. The origin of ET1 and ET2 is still unclear.

Simultaneous signal reconstruction from both superficial and deep tissue for fNIRS using depth-selective filtering method

NASA Astrophysics Data System (ADS)

Fujii, M.

2017-07-01

Two variations of a depth-selective back-projection filter for functional near-infrared spectroscopy (fNIRS) systems are introduced. The filter comprises a depth-selective algorithm that uses inverse problems applied to an optically diffusive multilayer medium. In this study, simultaneous signal reconstruction of both superficial and deep tissue from fNIRS experiments of the human forehead using a prototype of a CW-NIRS system is demonstrated.

Deep Eutectic Solvent Synthesis of LiMnPO4/C Nanorods as a Cathode Material for Lithium Ion Batteries

PubMed Central

Wu, Zhi; Huang, Rong-Rong; Yu, Hang; Xie, Yong-Chun; Lv, Xiao-Yan; Su, Jing; Long, Yun-Fei; Wen, Yan-Xuan

2017-01-01

Olivine-type LiMnPO4/C nanorods were successfully synthesized in a chloride/ethylene glycol-based deep eutectic solvent (DES) at 130 °C for 4 h under atmospheric pressure. As-synthesized samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR) and electrochemical tests. The prepared LiMnPO4/C nanorods were coated with a thin carbon layer (approximately 3 nm thick) on the surface and had a length of 100–150 nm and a diameter of 40–55 nm. The prepared rod-like LiMnPO4/C delivered a discharge capacity of 128 mAh·g−1 with a capacity retention ratio of approximately 93% after 100 cycles at 1 C. Even at 5 C, it still had a discharge capacity of 106 mAh·g−1, thus exhibiting good rate performance and cycle stability. These results demonstrate that the chloride/ethylene glycol-based deep eutectic solvents (DES) can act as a new crystal-face inhibitor to adjust the oriented growth and morphology of LiMnPO4. Furthermore, deep eutectic solvents provide a new approach in which to control the size and morphology of the particles, which has a wide application in the synthesis of electrode materials with special morphology. PMID:28772493

Deep learning approaches for detection and removal of ghosting artifacts in MR spectroscopy.

PubMed

Kyathanahally, Sreenath P; Döring, André; Kreis, Roland

2018-09-01

To make use of deep learning (DL) methods to detect and remove ghosting artifacts in clinical magnetic resonance spectra of human brain. Deep learning algorithms, including fully connected neural networks, deep-convolutional neural networks, and stacked what-where auto encoders, were implemented to detect and correct MR spectra containing spurious echo ghost signals. The DL methods were trained on a huge database of simulated spectra with and without ghosting artifacts that represent complex variations of ghost-ridden spectra, transformed to time-frequency spectrograms. The trained model was tested on simulated and in vivo spectra. The preliminary results for ghost detection are very promising, reaching almost 100% accuracy, and the DL ghost removal methods show potential in simulated and in vivo spectra, but need further refinement and quantitative testing. Ghosting artifacts in spectroscopy are problematic, as they superimpose with metabolites and lead to inaccurate quantification. Detection and removal of ghosting artifacts using traditional machine learning approaches with feature extraction/selection is difficult, as ghosts appear at different frequencies. Here, we show that DL methods perform extremely well for ghost detection if the spectra are treated as images in the form of time-frequency representations. Further optimization for in vivo spectra will hopefully confirm their "ghostbusting" capacity. Magn Reson Med 80:851-863, 2018. © 2018 International Society for Magnetic Resonance in Medicine. © 2018 International Society for Magnetic Resonance in Medicine.

Deep Eutectic Solvent Synthesis of LiMnPO₄/C Nanorods as a Cathode Material for Lithium Ion Batteries.

PubMed

Wu, Zhi; Huang, Rong-Rong; Yu, Hang; Xie, Yong-Chun; Lv, Xiao-Yan; Su, Jing; Long, Yun-Fei; Wen, Yan-Xuan

2017-02-06

Olivine-type LiMnPO₄/C nanorods were successfully synthesized in a chloride/ethylene glycol-based deep eutectic solvent (DES) at 130 °C for 4 h under atmospheric pressure. As-synthesized samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR) and electrochemical tests. The prepared LiMnPO₄/C nanorods were coated with a thin carbon layer (approximately 3 nm thick) on the surface and had a length of 100-150 nm and a diameter of 40-55 nm. The prepared rod-like LiMnPO₄/C delivered a discharge capacity of 128 mAh·g -1 with a capacity retention ratio of approximately 93% after 100 cycles at 1 C. Even at 5 C, it still had a discharge capacity of 106 mAh·g -1 , thus exhibiting good rate performance and cycle stability. These results demonstrate that the chloride/ethylene glycol-based deep eutectic solvents (DES) can act as a new crystal-face inhibitor to adjust the oriented growth and morphology of LiMnPO₄. Furthermore, deep eutectic solvents provide a new approach in which to control the size and morphology of the particles, which has a wide application in the synthesis of electrode materials with special morphology.

Essay

NASA Astrophysics Data System (ADS)

Xu, Shuping

2018-05-01

Professor Yukihiro Ozaki has made great impacts in the spectroscopy communities all over the world. Throughout his career, he has established strong collaborations and communications with scientists from Asian countries, which solidified his grand academic stature in the field of molecular spectroscopy. In the past years, he has been pushing forward the development of spectroscopy in many Asian countries, particularly to China. Since his first trip to China in 1994, he has visited China almost 40 times. Under his continuous efforts during these years, deep and long-term collaborations with several universities and research institutes in China were established. Prof. Ozaki was endowed with honorary professorships in numerous institutes and universities in China including Jilin University and Changchun Institute of Applied Chemistry, Chinese Academy of Sciences. He has been a visiting professor of many Chinese universities including Shanghai JiaoTong University, Hunan University, Central South University, Peking University, East China Normal University, and Beijing University of Chemical Technology. Great friendships have been established between him and his Chinese colleagues as a result of mutual respect and common scientific interests. Prof. Ozaki is an expert in various facets of spectroscopy including two-dimensional correlation spectroscopy, polymer material science, deep-UV and near infrared spectroscopy, chemometrics, and surface-enhanced Raman spectroscopy. Over the past decades, Prof. Ozaki has contributed greatly to training the Chinese youth scientists: 11 doctoral students, 16 post-doctoral researchers and 9 guest-professors and 17 visiting scholars from China have been studied/worked in his research group. He is not only a historical witness for the development of molecular spectroscopy in China, but also a creator. He has served on the editorial board of several Chinese journals such as the Journal of Light Scattering, Spectroscopy and Spectral Analysis, Journal of Near Infrared and Millimeter Waves, etc. He has coauthored more than 200 publications with Chinese researchers. Owing to his great contributions to the spectroscopy research of China, Prof. Ozaki has been awarded Changbai Mountain Friendship Award, the highest honor from Jilin Province, China in 2010 and China Friendship Award on Molecular Spectroscopy, from the Chinese Optical Society in 2016. Prof. Ozaki is a trustworthy and respected mentor, as well as a meritorious friend for Chinese spectroscopic scientists. His outstanding contributions to the field of spectroscopy in China is already a shining hallmark to Prof. Ozaki's career and will be remembered by all who follow.

Main chemical species and molecular structure of deep eutectic solvent studied by experiments with DFT calculation: a case of choline chloride and magnesium chloride hexahydrate.

PubMed

Zhang, Chao; Jia, Yongzhong; Jing, Yan; Wang, Huaiyou; Hong, Kai

2014-08-01

The infrared spectrum of deep eutectic solvent of choline chloride and magnesium chloride hexahydrate was measured by the FTIR spectroscopy and analyzed with the aid of DFT calculations. The main chemical species and molecular structure in deep eutectic solvent of [MgClm(H2O)6-m]2-m and [ChxCly]x+y complexes were mainly identified and the active ion of magnesium complex during the electrochemical process was obtained. The mechanism of the electrochemical process of deep eutectic solvent of choline chloride and magnesium chloride hexahydrate was well explained by combination theoretical calculations and experimental. Besides, based on our results we proposed a new system for the dehydration study of magnesium chloride hexahydrate.

Electronic properties of the Cu2ZnSn(Se,S)4 absorber layer in solar cells as revealed by admittance spectroscopy and related methods

NASA Astrophysics Data System (ADS)

Gunawan, Oki; Gokmen, Tayfun; Warren, Charles W.; Cohen, J. David; Todorov, Teodor K.; Barkhouse, D. Aaron R.; Bag, Santanu; Tang, Jiang; Shin, Byungha; Mitzi, David B.

2012-06-01

Admittance spectra and drive-level-capacitance profiles of several high performance Cu2ZnSn(Se,S)4 (CZTSSe) solar cells with bandgap ˜1.0-1.5 eV are reported. In contrast to the case for Cu(In,Ga)(S,Se)2, the CZTSSe capacitance spectra exhibit a dielectric freeze out to the geometric capacitance plateau at moderately low frequencies and intermediate temperatures (120-200 K). These spectra reveal important information regarding the bulk properties of the CZTSSe films, such as the dielectric constant and a dominant acceptor with energy level of 0.13-0.2 eV depending on the bandgap. This deep acceptor leads to a carrier freeze out effect that quenches the CZTSSe fill factor and efficiency at low temperatures.

Silicon materials task of the low cost solar array project, phase 2

NASA Technical Reports Server (NTRS)

Hopkins, R. H.; Davis, J. R., Jr.; Blais, P. D.; Rohatgi, A.; Rai-Choudhury, P.; Hanes, M. H.; Mccormick, J. R.

1977-01-01

The object of phase 2 of this program is to investigate and define the effects of various processes, contaminants and process-contaminant interactions in the performance of terrestrial solar cells. The major effort this quarter was in the areas of crystal growth and thermal processing, comparison of impurity effects in low and high resistivity silicon, modeling the behavior of p-type ingots containing Mo, and C and, quantitative analysis of bulk lifetime and junction degradation effects in contaminated solar cells. The performance of solar cells fabricated on silicon web crystals grown from melts containing about 10 to the 18th power/cu cm of Cr, Mn, Fe, Ni, Ti, and V, respectively were measured. Deep level spectroscopy of metal-contaminated ingots was employed to determine the level and density of recombination centers due to Ti, V, Ni, and Cr.

Two different carbon-hydrogen complexes in silicon with closely spaced energy levels

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

Stübner, R., E-mail: ronald.stuebner@physik.tu-dresden.de, E-mail: kolkov@ifpan.edu.pl; Kolkovsky, Vl., E-mail: ronald.stuebner@physik.tu-dresden.de, E-mail: kolkov@ifpan.edu.pl; Weber, J.

An acceptor and a single donor state of carbon-hydrogen defects (CH{sub A} and CH{sub B}) are observed by Laplace deep level transient spectroscopy at 90 K. CH{sub A} appears directly after hydrogenation by wet chemical etching or hydrogen plasma treatment, whereas CH{sub B} can be observed only after a successive annealing under reverse bias at about 320 K. The activation enthalpies of these states are 0.16 eV for CH{sub A} and 0.14 eV for CH{sub B}. Our results reconcile previous controversial experimental results. We attribute CH{sub A} to the configuration where substitutional carbon binds a hydrogen atom on a bond centered position between carbonmore » and the neighboring silicon and CH{sub B} to another carbon-hydrogen defect.« less

Pressure-Induced Dissolution and Reentrant Formation of Condensed, Liquid-Liquid Phase-Separated Elastomeric α-Elastin.

PubMed

Cinar, Hasan; Cinar, Süleyman; Chan, Hue Sun; Winter, Roland

2018-05-08

We investigated the combined effects of temperature and pressure on liquid-liquid phase separation (LLPS) phenomena of α-elastin up to the multi-kbar regime. FT-IR spectroscopy, CD, UV/Vis absorption, phase-contrast light and fluorescence microscopy techniques were employed to reveal structural changes and mesoscopic phase states of the system. A novel pressure-induced reentrant LLPS was observed in the intermediate temperature range. A molecular-level picture, in particular on the role of hydrophobic interactions, hydration, and void volume in controlling LLPS phenomena is presented. The potential role of the LLPS phenomena in the development of early cellular compartmentalization is discussed, which might have started in the deep sea, where pressures up to the kbar level are encountered. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Effect of combined platinum and electron on the temperature dependence of forward voltage in fast recovery diode

NASA Astrophysics Data System (ADS)

Jia, Yun-Peng; Zhao, Bao; Yang, Fei; Wu, Yu; Zhou, Xuan; Li, Zhe; Tan, Jian

2015-12-01

The temperature dependences of forward voltage drop (VF) of the fast recovery diodes (FRDs) are remarkably influenced by different lifetime controlled treatments. In this paper the results of an experimental study are presented, which are the lifetime controls of platinum treatment, electron irradiation treatment, and the combined treatment of the above ones. Based on deep level transient spectroscopy (DLTS) measurements, a new level E6 (EC-0.376 eV) is found in the combined lifetime treated (CLT) sample, which is different from the levels of the individual platinum and electron irradiation ones. Comparing the tested VF results of CLT samples with the others, the level E6 is responsible for the degradation of temperature dependence of the forward voltage drop in the FRD. Project supported by the Doctoral Fund of Ministry of Education of China (Grant No. 20111103120016) and the State Grid Corporation of China Program of Science and Technology, China (Grant No. 5455DW140003).

Radiation tolerance of boron doped dendritic web silicon solar cells

NASA Technical Reports Server (NTRS)

Rohatgi, A.

1980-01-01

The potential of dendritic web silicon for giving radiation hard solar cells is compared with the float zone silicon material. Solar cells with n(+)-p-P(+) structure and approximately 15% (AMl) efficiency were subjected to 1 MeV electron irradiation. Radiation tolerance of web cell efficiency was found to be at least as good as that of the float zone silicon cell. A study of the annealing behavior of radiation-induced defects via deep level transient spectroscopy revealed that E sub v + 0.31 eV defect, attributed to boron-oxygen-vacancy complex, is responsible for the reverse annealing of the irradiated cells in the temperature range of 150 to 350 C.

Zinc vacancy and oxygen interstitial in ZnO revealed by sequential annealing and electron irradiation

NASA Astrophysics Data System (ADS)

Knutsen, K. E.; Galeckas, A.; Zubiaga, A.; Tuomisto, F.; Farlow, G. C.; Svensson, B. G.; Kuznetsov, A. Yu.

2012-09-01

By combining results from positron annihilation and photoluminescence spectroscopy with data from Hall effect measurements, the characteristic deep level emission centered at ˜1.75 eV and exhibiting an activation energy of thermal quenching of 11.5 meV is associated with the zinc vacancy. Further, a strong indication that oxygen interstitials act as a dominating acceptor is derived from the analysis of charge carrier losses induced by electron irradiation with variable energy below and above the threshold for Zn-atom displacement. We also demonstrate that the commonly observed green emission is related to an extrinsic acceptorlike impurity, which may be readily passivated by oxygen vacancies.

Functionalization of graphene using deep eutectic solvents

NASA Astrophysics Data System (ADS)

Hayyan, Maan; Abo-Hamad, Ali; AlSaadi, Mohammed AbdulHakim; Hashim, Mohd Ali

2015-08-01

Deep eutectic solvents (DESs) have received attention in various applications because of their distinctive properties. In this work, DESs were used as functionalizing agents for graphene due to their potential to introduce new functional groups and cause other surface modifications. Eighteen different types of ammonium- and phosphonium-salt-based DESs were prepared and characterized by FTIR. The graphene was characterized by FTIR, STA, Raman spectroscopy, XRD, SEM, and TEM. Additional experiments were performed to study the dispersion behavior of the functionalized graphene in different solvents. The DESs exhibited both reduction and functionalization effects on DES-treated graphene. Dispersion stability was investigated and then characterized by UV-vis spectroscopy and zeta potential. DES-modified graphene can be used in many applications, such as drug delivery, wastewater treatment, catalysts, composite materials, nanofluids, and biosensors. To the best of our knowledge, this is the first investigation on the use of DESs for graphene functionalization.

Functionalization of graphene using deep eutectic solvents.

PubMed

Hayyan, Maan; Abo-Hamad, Ali; AlSaadi, Mohammed AbdulHakim; Hashim, Mohd Ali

2015-12-01

Deep eutectic solvents (DESs) have received attention in various applications because of their distinctive properties. In this work, DESs were used as functionalizing agents for graphene due to their potential to introduce new functional groups and cause other surface modifications. Eighteen different types of ammonium- and phosphonium-salt-based DESs were prepared and characterized by FTIR. The graphene was characterized by FTIR, STA, Raman spectroscopy, XRD, SEM, and TEM. Additional experiments were performed to study the dispersion behavior of the functionalized graphene in different solvents. The DESs exhibited both reduction and functionalization effects on DES-treated graphene. Dispersion stability was investigated and then characterized by UV-vis spectroscopy and zeta potential. DES-modified graphene can be used in many applications, such as drug delivery, wastewater treatment, catalysts, composite materials, nanofluids, and biosensors. To the best of our knowledge, this is the first investigation on the use of DESs for graphene functionalization.

Functionalization of CNTs surface with phosphonuim based deep eutectic solvents for arsenic removal from water

NASA Astrophysics Data System (ADS)

AlOmar, Mohamed Khalid; Alsaadi, Mohammed Abdulhakim; Hayyan, Maan; Akib, Shatirah; Hashim, Mohd Ali

2016-12-01

Herein, we present the use of deep eutectic solvent (DES) as functionalization agents for carbon nanotubes (CNTs) to form novel adsorbents for removal of arsenic ions (As3+) from water. Two DESs systems were prepared using methyltriphenylphosphonium bromide (MTPB) and benzyltriphenylphosphonium chloride (BTPC) as salts, in conjugation with glycerol (Gly) as a hydrogen bond donor. The resulting novel adsorbents were characterized using thermogravimetric analysis (TGA), Zeta potential, Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy, XRD, EDX, FESEM, and BET surface area. Optimization studies were carried out utilizing RSM-CCD experimental design to estimate the optimum removal conditions for each adsorbent. The adsorption experimental data of both adsorbents were found to fit well with pseudo-second-order kinetics model, as well as with Langmuir and Freundlich adsorption isotherm models. The maximum adsorption capacity of a MTPB-DES-functionalized CNTs adsorbent was 23.4 mg/g.

Improved Fast, Deep Record Length, Time-Resolved Visible Spectroscopy of Plasmas Using Fiber Grids

NASA Astrophysics Data System (ADS)

Brockington, S.; Case, A.; Cruz, E.; Williams, A.; Witherspoon, F. D.; Horton, R.; Klauser, R.; Hwang, D.

2017-10-01

HyperV Technologies is developing a fiber-coupled, deep record-length, low-light camera head for performing high time resolution spectroscopy on visible emission from plasma events. By coupling the output of a spectrometer to an imaging fiber bundle connected to a bank of amplified silicon photomultipliers, time-resolved spectroscopic imagers of 100 to 1,000 pixels can be constructed. A second generation prototype 32-pixel spectroscopic imager employing this technique was constructed and successfully tested at the University of California at Davis Compact Toroid Injection Experiment (CTIX). Pixel performance of 10 Megaframes/sec with record lengths of up to 256,000 frames ( 25.6 milliseconds) were achieved. Pixel resolution was 12 bits. Pixel pitch can be refined by using grids of 100 μm to 1000 μm diameter fibers. Experimental results will be discussed, along with future plans for this diagnostic. Work supported by USDOE SBIR Grant DE-SC0013801.

Time-resolved Spectroscopy of RS CVn Binaries and dMe Flare Stars

NASA Astrophysics Data System (ADS)

Brown, Alexander

One of the most striking feature of the first two years of EUVE spectroscopy is the frequent occurrence of largescale coronal variability, in the form of stellar flares and slower changes in activity level due to rotational modulation and evolution of active regions. We propose EUVE observations of a set of RS CVn and dMe star binaries, most with short (< 2 days) periods, to investigate the coronal conditions and physical processes associated with this variability. EUVE flare outbursts have mostly been long duration events lasting many satellite orbits and been readily studied using time-resolved spectroscopy. Our targets are the dMe binaries YY Gem, CC Eri and Gliese 2123, and the RS CVn systems EI Eri, AR Psc, and TY Pyx. YY Gem and TY Pyx are eclipsing systems and Deep Survey photometry will be used to investigate the size of the coronal emitting regions. Situated 73 arcmin from YY Gem is Castor (Alpha Gem) another X-ray source that can be observed (and spatially resolved) simultaneously. We shall use the DS lightcurve to guide our time resolved spectral analysis. Changes in the coronal emission measure as a function of temperature and possibly changes in coronal density will be used to constrain magnetic loop models.

(+/-)-Gelliusines A and B, two diastereomeric brominated tris-indole alkaloids from a deep water new caledonian marine sponge (Gellius or Orina sp.).

PubMed

Bifulco, G; Bruno, I; Minale, L; Riccio, R; Calignano, A; Debitus, C

1994-09-01

Two new diastereomeric brominated tris-indole alkaloids occurring as enantiomeric pairs, (+/-)-gelliusines A [1] and B [2], have been isolated from a deep water New Caledonian sponge (Gellius or Orina sp.), whose crude extract exhibited cytotoxicity against KB cells. Their structures were elucidated by spectroscopic methods including one- and two-dimensional nmr spectroscopy. The major compound, (+/-) gelliusine A [1], which showed very weak cytotoxicity, proved to be active at the serotonin receptor.

The interrelationship of microstructure and hardness of human coronal dentin using reference point indentation technique and micro-Raman spectroscopy.

PubMed

Seyedmahmoud, Rasoul; McGuire, Jacob D; Wang, Yong; Thiagarajan, Ganesh; Walker, Mary P

2017-10-01

The aim of this paper is to determine the interrelationship between the microstructure - in terms of chemical composition and crystallinity - to the microhardness of coronal dentin. Dentin microhardness was tested by a novel reference point indenter and compared to the traditional Knoop hardness method. Micro-Raman spectroscopy was used to determine the chemical composition and crystallinity of dentin. From the occlusal groove to the border of the coronal pulp chamber, dentin hardness decreased from superficial dentin (SD) to deep dentin (DD). Mineral/organic matrix ratios (phosphate/CH and phosphate/amide I) also decreased from SD to DD; however, this change was significant (P<0.05) in the phosphate/amide I ratio only. The phosphate/carbonate ratio decreased significantly by varying position from SD to DD. The degree of the crystallinity, as measured by the full width at half maximum (FWHM) of the peak at 960cm -1 , decreased significantly going from superficial to deep dentin. For the first time, the interrelationship between the microstructure and the mechanical properties of coronal dentin was determined by using the novel reference point indentation technique and micro-Raman spectroscopy. We hypothesize that the decrease in hardness from superficial to deep dentin can potentially be explained by decreased mineral content and increased carbonate content, which is also associated with decreased crystallinity. Collectively, there is a positive association between dentin hardness and mineral content and a negative association between dentin hardness and carbonate content. Copyright © 2017 The Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Demonstration of miniaturized 20mW CW 280nm and 266nm solid-state UV laser sources

NASA Astrophysics Data System (ADS)

Landru, Nicolas; Georges, Thierry; Beaurepaire, Julien; Le Guen, Bruno; Le Bail, Guy

2015-02-01

Visible 561 nm and 532 nm laser emissions from 14-mm long DPSS monolithic cavities are frequency converted to deep UV 280 nm and 266 nm in 16-mm long monolithic external cavities. Wavelength conversion is fully insensitive to mechanical vibrations and the whole UV laser sources fit in a miniaturized housing. More than 20 mW deep UV laser emission is demonstrated with high power stability, low noise and good beam quality. Aging tests are in progress but long lifetimes are expected thanks to the cavity design. Protein detection and deep UV resonant Raman spectroscopy are applications that could benefit from these laser sources.

Study of barrier height and trap centers of Au/n-Hg{sub 3}In{sub 2}Te{sub 6} Schottky contacts by current-voltage (I-V) characteristics and deep level transient spectroscopy

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

Li, Yapeng; Fu, Li, E-mail: fuli@nwpu.edu.cn; Sun, Jie

2015-02-28

The temperature-dependent electrical characteristics of the Au/n-Hg{sub 3}In{sub 2}Te{sub 6} Schottky contact have been studied at the temperature range of 140 K–315 K. Based on the thermionic emission theory, the ideality factor and Schottky barrier height were calculated to decrease and increase from 3.18 to 1.88 and 0.39 eV to 0.5 eV, respectively, when the temperature rose from 140 K to 315 K. This behavior was interpreted by the lateral inhomogeneities of Schottky barrier height at the interface of Au/n-Hg{sub 3}In{sub 2}Te{sub 6} contact, which was shown by the plot of zero-bias barrier heights Φ{sub bo} versus q/2kT. Meanwhile, it was found that the Schottky barriermore » height with a Gaussian distribution was 0.67 eV and the standard deviation σ{sub 0} was about 0.092 eV, indicating that the uneven distribution of barrier height at the interface region. In addition, the mean value of Φ{sup ¯}{sub b0} and modified Richardson constant was determined to be 0.723 eV and 62.8 A/cm{sup 2}K{sup 2} from the slope and intercept of the ln(I{sub o}/T{sup 2}) – (qσ{sub 0}{sup 2}/2k{sup 2}T{sup 2}) versus q/kT plot, respectively. Finally, two electron trap centers were observed at the interface of Au/n-Hg{sub 3}In{sub 2}Te{sub 6} Schottky contact by means of deep level transient spectroscopy.« less

The Great Observatories Origins Deep Survey (GOODS): Overview and Status

NASA Astrophysics Data System (ADS)

Hook, R. N.; GOODS Team

2002-12-01

GOODS is a very large project to gather deep imaging data and spectroscopic followup of two fields, the Hubble Deep Field North (HDF-N) and the Chandra Deep Field South (CDF-S), with both space and ground-based instruments to create an extensive multiwavelength public data set for community research on the distant Universe. GOODS includes a SIRTF Legacy Program (PI: Mark Dickinson) and a Hubble Treasury Program of ACS imaging (PI: Mauro Giavalisco). The ACS imaging was also optimized for the detection of high-z supernovae which are being followed up by a further target of opportunity Hubble GO Program (PI: Adam Riess). The bulk of the CDF-S ground-based data presently available comes from an ESO Large Programme (PI: Catherine Cesarsky) which includes both deep imaging and multi-object followup spectroscopy. This is currently complemented in the South by additional CTIO imaging. Currently available HDF-N ground-based data forming part of GOODS includes NOAO imaging. Although the SIRTF part of the survey will not begin until later in the year the ACS imaging is well advanced and there is also a huge body of complementary ground-based imaging and some follow-up spectroscopy which is already publicly available. We summarize the current status of GOODS and give an overview of the data products currently available and present the timescales for the future. Many early science results from the survey are presented in other GOODS papers at this meeting. Support for the HST GOODS program presented here and in companion abstracts was provided by NASA thorugh grant number GO-9425 from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555.

Gamma radiation effects on polydimethylsiloxane rubber foams under different radiation conditions

NASA Astrophysics Data System (ADS)

Sui, H. L.; Liu, X. Y.; Zhong, F. C.; Li, X. Y.; Wang, L.; Ju, X.

2013-07-01

Polydimethylsiloxane rubber foams were irradiated by gamma ray under different radiation conditions designed by orthogonal design method. Compression set measurement, infrared attenuated total reflectance spectroscopy (ATR) and X-ray induced photoelectron spectroscopy (XPS) were used. Three aging factors' influence effects on the mechanical property and chemical structure were studied. It was found that among the three factors and the chosen levels, both properties were affected most by radiation dose, while radiation dose rate had no obvious influence on both properties. The stiffening of the rubber foams was caused by cross-linking reactions in the Si-CH3. At the same radiation dose, the rigidity of the foams irradiated in air was lower than that in nitrogen. When polydimethylsiloxane was irradiated at a high dose in sealed nitrogen atmosphere, carbon element distribution would be changed. Hydrocarbons produced by gamma ray in the sealed tube would make the carbon content in the skin-deep higher than that in the middle, which indicated that polydimethylsiloxane rubber foams storing in a sealed atmosphere filled with enough hydrocarbons should be helpful to extend the service life.

Effect of low-oxygen-concentration layer on iron gettering capability of carbon-cluster ion-implanted Si wafer for CMOS image sensors

NASA Astrophysics Data System (ADS)

Onaka-Masada, Ayumi; Nakai, Toshiro; Okuyama, Ryosuke; Okuda, Hidehiko; Kadono, Takeshi; Hirose, Ryo; Koga, Yoshihiro; Kurita, Kazunari; Sueoka, Koji

2018-02-01

The effect of oxygen (O) concentration on the Fe gettering capability in a carbon-cluster (C3H5) ion-implanted region was investigated by comparing a Czochralski (CZ)-grown silicon substrate and an epitaxial growth layer. A high Fe gettering efficiency in a carbon-cluster ion-implanted epitaxial growth layer, which has a low oxygen region, was observed by deep-level transient spectroscopy (DLTS) and secondary ion mass spectroscopy (SIMS). It was demonstrated that the amount of gettered Fe in the epitaxial growth layer is approximately two times higher than that in the CZ-grown silicon substrate. Furthermore, by measuring the cathodeluminescence, the number of intrinsic point defects induced by carbon-cluster ion implantation was found to differ between the CZ-grown silicon substrate and the epitaxial growth layer. It is suggested that Fe gettering by carbon-cluster ion implantation comes through point defect clusters, and that O in the carbon-cluster ion-implanted region affects the formation of gettering sinks for Fe.

Contributions from gallium vacancies and carbon-related defects to the ``yellow luminescence'' in GaN

NASA Astrophysics Data System (ADS)

Armitage, R.; Hong, William; Yang, Qing; Feick, H.; Gebauer, J.; Weber, E. R.; Hautakangas, S.; Saarinen, K.

2003-05-01

Carbon-doped GaN layers grown by molecular-beam epitaxy are studied with photoluminescence and positron annihilation spectroscopy. Semi-insulating layers doped with >1018 cm-3 carbon show a strong luminescence band centered at ˜2.2 eV (yellow luminescence). The absolute intensity of the 2.2 eV band is compared with the gallium vacancy concentration determined by positron annihilation spectroscopy. The results indicate that a high concentration of gallium vacancies is not necessary for yellow luminescence and that there is in fact a causal relationship between carbon and the 2.2 eV band. Markedly different deep-level ionization energies are found for the high-temperature quenching of the 2.2 eV photoluminescence in carbon-doped and reference samples. We propose that while the model of Neugebauer and Van de Walle [Appl. Phys. Lett. 69, 503 (1996)] applies for GaN of low carbon concentration, a different yellow luminescence mechanism is involved when the interstitial carbon concentration is comparable to or exceeds the gallium vacancy concentration.

Radiation damage annealing mechanisms and possible low temperature annealing in silicon solar cells

NASA Technical Reports Server (NTRS)

Weinberg, I.; Swartz, C. K.

1980-01-01

The defect responsible for reverse annealing in 2 ohm/cm n(+)/p silicon solar cells was identified. This defect, with energy level at e sub v + 0.30 eV was tentatively identified as a boron oxygen-vacancy complex. Results indicate that its removal could result in significant annealing for 2 ohm/cm and lower resistivity cells at temperatures as low as 200 C. These results were obtained by use of an expression derived from the Shockley-Read-Hall recombination theory which relates measured diffusion length ratios to relative defect concentrations and electron capture cross sections. The relative defect concentrations and one of the required capture cross sections are obtained from Deep Level Transient Spectroscopy. Four additional capture cross sections are obtained using diffusion length data and data from temperature dependent lifetime studied. These calculated results are in reasonable agreement with experimental data.

In Vivo Noninvasive Analysis of Human Forearm Muscle Function and Fatigue: Applications to EVA Operations and Training Maneuvers

NASA Technical Reports Server (NTRS)

Fotedar, L. K.; Marshburn, T.; Quast, M. J.; Feeback, D. L.

1999-01-01

Forearm muscle fatigue is one of the major limiting factors affecting endurance during performance of deep-space extravehicular activity (EVA) by crew members. Magnetic resonance (MR) provides in vivo noninvasive analysis of tissue level metabolism and fluid exchange dynamics in exercised forearm muscles through the monitoring of proton magnetic resonance imaging (MRI) and phosphorus magnetic resonance spectroscopy (P-31-MRS) parameter variations. Using a space glove box and EVA simulation protocols, we conducted a preliminary MRS/MRI study in a small group of human test subjects during submaximal exercise and recovery and following exhaustive exercise. In assessing simulated EVA-related muscle fatigue and function, this pilot study revealed substantial changes in the MR image longitudinal relaxation times (T2) as an indicator of specific muscle activation and proton flux as well as changes in spectral phosphocreatine-to-phosphate (PCr/Pi) levels as a function of tissue bioenergetic potential.

Hydrogen passivation of titanium impurities in silicon: Effect of doping conditions

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

Santos, P.; Coutinho, J., E-mail: jose.coutinho@ua.pt; Torres, V. J. B.

2014-07-21

While the contamination of solar silicon by fast diffusing transition metals can be now limited through gettering, much attention has been drawn to the slow diffusing species, especially the early 3d and 4d elements. To some extent, hydrogen passivation has been successful in healing many deep centers, including transition metals in Si. Recent deep-level transient spectroscopy (DLTS) measurements concerning hydrogen passivation of Ti revealed the existence of at least four electrical levels related to Ti{sub i}H{sub n} in the upper-half of the gap. These findings challenge the existing models regarding both the current level assignment as well as the structure/speciesmore » involved in the defects. We revisit this problem by means of density functional calculations and find that progressive hydrogenation of interstitial Ti is thermodynamically stable in intrinsic and n-doped Si. Full passivation may not be possible to attain in p-type Si as Ti{sub i}H{sub 3} and Ti{sub i}H{sub 4} are metastable against dissociation and release of bond-centered protons. All DLTS electron traps are assigned, namely, E40′ to Ti{sub i}H(-/0), E170′ to Ti{sub i}H{sub 3}(0/+), E(270) to Ti{sub i}H{sub 2}(0/+), and E170 to Ti{sub i}H(0/+) transitions. Ti{sub i}H{sub 4} is confirmed to be electrically inert.« less

Wideband laser locking to an atomic reference with modulation transfer spectroscopy.

PubMed

Negnevitsky, V; Turner, L D

2013-02-11

We demonstrate that conventional modulated spectroscopy apparatus, used for laser frequency stabilization in many atomic physics laboratories, can be enhanced to provide a wideband lock delivering deep suppression of frequency noise across the acoustic range. Using an acousto-optic modulator driven with an agile oscillator, we show that wideband frequency modulation of the pump laser in modulation transfer spectroscopy produces the unique single lock-point spectrum previously demonstrated with electro-optic phase modulation. We achieve a laser lock with 100 kHz feedback bandwidth, limited by our laser control electronics. This bandwidth is sufficient to reduce frequency noise by 30 dB across the acoustic range and narrows the imputed linewidth by a factor of five.

Cell and defect behavior in lithium-counterdoped solar cells

NASA Technical Reports Server (NTRS)

Weinberg, I.; Mehta, S.; Swartz, C. K.

1984-01-01

Some n(+)/p cells in which lithium is introduced as a counterdopant, by ion-implantation, into the cell's boron-doped p-region were studied. To determine if the cells radiation resistance could be significantly improved by lithium counterdoping. Defect behavior was related to cell performance using deep level transient spectroscopy. Results indicate a significantly increased radiation resistance for the lithium counterdoped cells when compared to the boron doped 1 ohm-cm control cell. The increased radiation resistance of the lithium counterdoped cells is due to the complexing of lithium with divacancies and boron. It is speculated that complexing with oxygen and single vacancies also contributes to the increased radiation resistance. Counterdoping silicon with lithium results in a different set of defects.

Point defects in CdTe xSe 1-x crystals grown from a Te-rich solution for applications in detecting radiation

DOE PAGES

Gul, R.; Roy, U. N.; Bolotnikov, A. E.; ...

2015-04-15

We investigated cadmium telluride selenide (CdTeSe) crystals, newly grown by the Traveling Heater Method (THM), for the presence and abundance of point defects. Deep Level Transient spectroscopy (I-DLTS) was used to determine the energies of the traps, their capture cross sections, and densities. The bias across the detectors was varied from (1–30) V. Four types of point defects were identified, ranging from 10 meV to 0.35 eV. Two dominant traps at energies of 0.18 eV and 0.14 eV were studied in depth. Cd vacancies are found at lower concentrations than other point defects present in the material.

Effect of gamma-ray irradiation on the device process-induced defects in 4H-SiC epilayers

NASA Astrophysics Data System (ADS)

Miyazaki, T.; Makino, T.; Takeyama, A.; Onoda, S.; Ohshima, T.; Tanaka, Y.; Kandori, M.; Yoshie, T.; Hijikata, Y.

2016-11-01

We investigated the gamma-ray irradiation effect on 4H-SiC device process-induced defects by photoluminescence (PL) imaging and deep level transient spectroscopy (DLTS). We found that basal plane dislocations (BPDs) that were present before the irradiation were eliminated by gamma-ray irradiation of 1 MGy. The reduction mechanism of BPD was discussed in terms of BPD-threading edge dislocation (TED) transformation and shrinkage of stacking faults. In addition, the entire PL image was gradually darkened with increasing absorbed dose, which is presumably due to the point defects generated by gamma-ray irradiation. We obtained DLTS peaks that could be assigned to complex defects, termed RD series, and found that the peaks increased with absorbed dose.

Effect of Ion Sputtering on Interface Chemistry and Electrical Properties of an Gaas (100) Schottky Contacts

NASA Technical Reports Server (NTRS)

Wang, Y. X.; Holloway, P. H.

1984-01-01

Auger and electron photoelectron spectroscopy were used to measure the extent of As depletion during 1 keV to 5 keV argon sputtering of GaAs surfaces. This depletion was correlated with a general decrease in the barrier height of the rectifying Au contact deposited in situ. However, nondestructive angle resolved XPS measurements showed As was depleted at the outer surface more by 1 keV than 3 keV argon. These effects are explained based on a combined work effective work function model and creation of a donor like surface damage layer. The donor layer was correlated with As depletion by sputtering. Deep level trap formation and annealing of sputtering effects were studied.

Copper interstitial recombination centers in Cu3N

NASA Astrophysics Data System (ADS)

Yee, Ye Sheng; Inoue, Hisashi; Hultqvist, Adam; Hanifi, David; Salleo, Alberto; Magyari-Köpe, Blanka; Nishi, Yoshio; Bent, Stacey F.; Clemens, Bruce M.

2018-06-01

We present a comprehensive study of the earth-abundant semiconductor Cu3N as a potential solar energy conversion material, using density functional theory and experimental methods. Density functional theory indicates that among the dominant intrinsic point defects, copper vacancies VCu have shallow defect levels while copper interstitials Cui behave as deep potential wells in the conduction band, which mediate Shockley-Read-Hall recombination. The existence of Cui defects has been experimentally verified using photothermal deflection spectroscopy. A Cu3N /ZnS heterojunction diode with good current-voltage rectification behavior has been demonstrated experimentally, but no photocurrent is generated under illumination. The absence of photocurrent can be explained by a large concentration of Cui recombination centers capturing electrons in p -type Cu3N .

All-photonic drying and sintering process via flash white light combined with deep-UV and near-infrared irradiation for highly conductive copper nano-ink

PubMed Central

Hwang, Hyun-Jun; Oh, Kyung-Hwan; Kim, Hak-Sung

2016-01-01

We developed an ultra-high speed photonic sintering method involving flash white light (FWL) combined with near infrared (NIR) and deep UV light irradiation to produce highly conductive copper nano-ink film. Flash white light irradiation energy and the power of NIR/deep UV were optimized to obtain high conductivity Cu films. Several microscopic and spectroscopic characterization techniques such as scanning electron microscopy (SEM), a x-ray diffraction (XRD), and Fourier-transform infrared (FT-IR) spectroscopy were employed to characterize the Cu nano-films. Optimally sintered Cu nano-ink films produced using a deep UV-assisted flash white light sintering technique had the lowest resistivity (7.62 μΩ·cm), which was only 4.5-fold higher than that of bulk Cu film (1.68 μΩ•cm). PMID:26806215

All-photonic drying and sintering process via flash white light combined with deep-UV and near-infrared irradiation for highly conductive copper nano-ink.

PubMed

Hwang, Hyun-Jun; Oh, Kyung-Hwan; Kim, Hak-Sung

2016-01-25

We developed an ultra-high speed photonic sintering method involving flash white light (FWL) combined with near infrared (NIR) and deep UV light irradiation to produce highly conductive copper nano-ink film. Flash white light irradiation energy and the power of NIR/deep UV were optimized to obtain high conductivity Cu films. Several microscopic and spectroscopic characterization techniques such as scanning electron microscopy (SEM), a x-ray diffraction (XRD), and Fourier-transform infrared (FT-IR) spectroscopy were employed to characterize the Cu nano-films. Optimally sintered Cu nano-ink films produced using a deep UV-assisted flash white light sintering technique had the lowest resistivity (7.62 μΩ·cm), which was only 4.5-fold higher than that of bulk Cu film (1.68 μΩ•cm).

WFIRST: Science from Deep Field Surveys

NASA Astrophysics Data System (ADS)

Koekemoer, Anton M.; Foley, Ryan; WFIRST Deep Field Working Group

2018-06-01

WFIRST will enable deep field imaging across much larger areas than those previously obtained with Hubble, opening up completely new areas of parameter space for extragalactic deep fields including cosmology, supernova and galaxy evolution science. The instantaneous field of view of the Wide Field Instrument (WFI) is about 0.3 square degrees, which would for example yield an Ultra Deep Field (UDF) reaching similar depths at visible and near-infrared wavelengths to that obtained with Hubble, over an area about 100-200 times larger, for a comparable investment in time. Moreover, wider fields on scales of 10-20 square degrees could achieve depths comparable to large HST surveys at medium depths such as GOODS and CANDELS, and would enable multi-epoch supernova science that could be matched in area to LSST Deep Drilling fields or other large survey areas. Such fields may benefit from being placed on locations in the sky that have ancillary multi-band imaging or spectroscopy from other facilities, from the ground or in space. The WFIRST Deep Fields Working Group has been examining the science considerations for various types of deep fields that may be obtained with WFIRST, and present here a summary of the various properties of different locations in the sky that may be considered for future deep fields with WFIRST.

WFIRST: Science from Deep Field Surveys

NASA Astrophysics Data System (ADS)

Koekemoer, Anton; Foley, Ryan; WFIRST Deep Field Working Group

2018-01-01

WFIRST will enable deep field imaging across much larger areas than those previously obtained with Hubble, opening up completely new areas of parameter space for extragalactic deep fields including cosmology, supernova and galaxy evolution science. The instantaneous field of view of the Wide Field Instrument (WFI) is about 0.3 square degrees, which would for example yield an Ultra Deep Field (UDF) reaching similar depths at visible and near-infrared wavelengths to that obtained with Hubble, over an area about 100-200 times larger, for a comparable investment in time. Moreover, wider fields on scales of 10-20 square degrees could achieve depths comparable to large HST surveys at medium depths such as GOODS and CANDELS, and would enable multi-epoch supernova science that could be matched in area to LSST Deep Drilling fields or other large survey areas. Such fields may benefit from being placed on locations in the sky that have ancillary multi-band imaging or spectroscopy from other facilities, from the ground or in space. The WFIRST Deep Fields Working Group has been examining the science considerations for various types of deep fields that may be obtained with WFIRST, and present here a summary of the various properties of different locations in the sky that may be considered for future deep fields with WFIRST.

The trap states in lightly Mg-doped GaN grown by MOVPE on a freestanding GaN substrate

NASA Astrophysics Data System (ADS)

Narita, Tetsuo; Tokuda, Yutaka; Kogiso, Tatsuya; Tomita, Kazuyoshi; Kachi, Tetsu

2018-04-01

We investigated traps in lightly Mg-doped (2 × 1017 cm-3) p-GaN fabricated by metalorganic vapor phase epitaxy (MOVPE) on a freestanding GaN substrate and the subsequent post-growth annealing, using deep level transient spectroscopy. We identified four hole traps with energy levels of EV + 0.46, 0.88, 1.0, and 1.3 eV and one electron trap at EC - 0.57 eV in a p-type GaN layer uniformly doped with magnesium (Mg). The Arrhenius plot of hole traps with the highest concentration (˜3 × 1016 cm-3) located at EV + 0.88 eV corresponded to those of hole traps ascribed to carbon on nitrogen sites in n-type GaN samples grown by MOVPE. In fact, the range of the hole trap concentrations at EV + 0.88 eV was close to the carbon concentration detected by secondary ion mass spectroscopy. Moreover, the electron trap at EC - 0.57 eV was also identical to the dominant electron traps commonly observed in n-type GaN. Together, these results suggest that the trap states in the lightly Mg-doped GaN grown by MOVPE show a strong similarity to those in n-type GaN, which can be explained by the Fermi level close to the conduction band minimum in pristine MOVPE grown samples due to existing residual donors and Mg-hydrogen complexes.

Defect related electrical and optical properties of AlN bulk crystals grown by physical vapor transport

NASA Astrophysics Data System (ADS)

Irmscher, Klaus

AlN crystallizes thermodynamically stable in the wurtzite structure and possesses a direct band gap of about 6 eV. It is the ideal substrate for the epitaxial growth of Al-rich AlxGa1-xN films that enable deep ultraviolet (UV) emitters. Appropriate AlN bulk crystals can be grown by physical vapor transport (PVT). Besides high structural perfection, such substrate crystals should be highly UV transparent and ideally, electrically conductive. It is well known that point defects like impurities and intrinsic defects may introduce electronic energy levels within the bandgap, which lead to additional optical absorption or electrical compensation. Among the impurities, which may be incorporated into the AlN crystals during PVT growth at well above 2000 ° C, oxygen, carbon, and silicon play the major role. Based on our own experimental data as well as on experimental and theoretical results reported in literature, we discuss energy levels, charge states and possible negative-U behavior of these impurities and of vacancy-type defects. In particular, we develop a model that explains the absorption behavior of the crystals in dependence on the Fermi level that can be controlled by the growth conditions, including intentional doping. Further, we pay attention on spectroscopic investigations giving direct evidence for the chemical nature and atomic arrangement of the involved point defects. As examples local vibrational mode (LVM) spectroscopy of carbon related defects and recent reports of electron paramagnetic resonance (EPR) spectroscopy are discussed.

Novel x-ray silicon detector for 2D imaging and high-resolution spectroscopy

NASA Astrophysics Data System (ADS)

Castoldi, Andrea; Gatti, Emilio; Guazzoni, Chiara; Longoni, Antonio; Rehak, Pavel; Strueder, Lothar

1999-10-01

A novel x-ray silicon detector for 2D imaging has been recently proposed. The detector, called Controlled-Drift Detector, is operated in integrate-readout mode. Its basic feature is the fast transport of the integrated charge to the output electrode by means of a uniform drift field. The drift time of the charge packet identifies the pixel of incidence. A new architecture to implement the Controlled- Drift Detector concept will be presented. The potential wells for the integration of the signal charge are obtained by means of a suitable pattern of deep n-implants and deep p-implants. During the readout mode the signal electrons are transferred in the drift channel that flanks each column of potential wells where they drift towards the collecting electrode at constant velocity. The first experimental measurements demonstrate the successful integration, transfer and drift of the signal electrons. The low output capacitance of the readout electrode together with the on- chip front-end electronics allows high resolution spectroscopy of the detected photons.

Screening and investigation of triplex DNA binders from Stephania tetrandra S. Moore by a combination of peak area-fading UHPLC with orbitrap MS and optical spectroscopies.

PubMed

Yang, Hongmei; Wang, Yihan; Yu, Wenjing; Shi, Lei; Wang, Hongfeng; Su, Rui; Chen, Changbao; Liu, Shuying

2018-05-15

The identification and screening of triplex DNA binders are important because these compounds, in many cases, are potential anticancer agents as well as promising drug candidates. Therefore, the ability to screen for these compounds in a high-throughput mode could dramatically improve the drug screening process. A method involving a combination of 96-well plate format and peak area-fading ultra high performance liquid chromatography coupled with Orbitrap mass spectrometry was employed for screening bioactive compounds binding to the triplex DNA from the extracts of Stephania tetrandra S. Moore. Two compounds were screened out and identified as fangchinoline and tetrandrine, based on the comparison of retention time and MS 2 data with those of standards. The binding mechanisms of fangchinoline and tetrandrine at the molecular level were explored using MS 2 , fluorescence spectroscopy, ultraviolet-visible spectroscopy, and circular dichroism. Collision-induced dissociation experiments showed that the complexes with fangchinoline and tetrandrine were dissociated by ligand elimination. According to these measurements, an intercalating binding is the most appropriate binding mode of these two alkaloids to the triplex DNA. The current work provides not only deep insight into alkaloid-triplex DNA complexes but also useful guidelines for the design of efficient anticancer agents. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.

4H-SiC p i n diodes grown by sublimation epitaxy in vacuum (SEV) and their application as microwave diodes

NASA Astrophysics Data System (ADS)

Camara, N.; Zekentes, K.; Zelenin, V. V.; Abramov, P. L.; Kirillov, A. V.; Romanov, L. P.; Boltovets, N. S.; Krivutsa, V. A.; Thuaire, A.; Bano, E.; Tsoi, E.; Lebedev, A. A.

2008-02-01

Sublimation epitaxy under vacuum (SEV) was investigated as a method for growing 4H-SiC epitaxial structures for p-i-n diode fabrication. The SEV-grown 4H-SiC material was investigated with scanning electron microscopy (SEM), atomic force microscopy (AFM), x-ray diffraction, photo-luminescence spectroscopy (PL), cathodo-luminescence (CL) spectroscopy, photocurrent method for carrier diffusion length determination, electro-luminescence microscopy (EL), deep level transient spectroscopy (DLTS), C-V profiling and Hall-effect measurements. When possible, the same investigation techniques were used in parallel with similar layers grown by chemical vapour deposition (CVD) epitaxy and the physical properties of the two kind of epitaxied layers were compared. p-i-n diodes were fabricated in parallel on SEV and CVD-grown layers and showed close electrical performances in dc mode in term of capacitance, resistance and transient time switching, despite the lower mobility and the diffusion length of the SEV-grown layers. X-band microwave switches based on the SEV-grown p-i-n diodes have been demonstrated with insertion loss lower than 4 dB and an isolation higher than 17 dB. These single-pole single-throw (SPST) switches were able to handle a pulsed power up to 1800 W in isolation mode, similar to the value obtained with switches incorporating diodes with CVD-grown layers.

Study of GaAs-oxide interface by transient capacitance spectroscopy - Discrete energy interface states

NASA Technical Reports Server (NTRS)

Kamieniecki, E.; Kazior, T. E.; Lagowski, J.; Gatos, H. C.

1980-01-01

Interface states and bulk GaAs energy levels were simultaneously investigated in GaAs MOS structures prepared by anodic oxidation. These two types of energy levels were successfully distinguished by carrying out a comparative analysis of deep level transient capacitance spectra of the MOS structures and MS structures prepared on the same samples of epitaxially grown GaAs. The identification and study of the interface states and bulk levels was also performed by investigating the transient capacitance spectra as a function of the filling pulse magnitude. It was found that in the GaAs-anodic oxide interface there are states present with a discrete energy rather than with a continuous energy distribution. The value of the capture cross section of the interface states was found to be 10 to the 14th to 10 to the 15th/sq cm, which is more accurate than the extremely large values of 10 to the -8th to 10 to the -9th/sq cm reported on the basis of conductance measurements.

Thermal quenching effect of an infrared deep level in Mg-doped p-type GaN films

NASA Astrophysics Data System (ADS)

Kim, Keunjoo; Chung, Sang Jo

2002-03-01

The thermal quenching of an infrared deep level of 1.2-1.5 eV has been investigated on Mg-doped p-type GaN films, using one- and two-step annealing processes and photocurrent measurements. The deep level appeared in the one-step annealing process at a relatively high temperature of 900 °C, but disappeared in the two-step annealing process with a low-temperature step and a subsequent high-temperature step. The persistent photocurrent was residual in the sample including the deep level, while it was terminated in the sample without the deep level. This indicates that the deep level is a neutral hole center located above a quasi-Fermi level, estimated with an energy of EpF=0.1-0.15 eV above the valence band at a hole carrier concentration of 2.0-2.5×1017/cm3.

Growth and characterization of β-Ga2O3 thin films by molecular beam epitaxy for deep-UV photodetectors

NASA Astrophysics Data System (ADS)

Ghose, Susmita; Rahman, Shafiqur; Hong, Liang; Rojas-Ramirez, Juan Salvador; Jin, Hanbyul; Park, Kibog; Klie, Robert; Droopad, Ravi

2017-09-01

The growth of high quality epitaxial beta-gallium oxide (β-Ga2O3) using a compound source by molecular beam epitaxy has been demonstrated on c-plane sapphire (Al2O3) substrates. The compound source provides oxidized gallium molecules in addition to oxygen when heated from an iridium crucible in a high temperature effusion cell enabling a lower heat of formation for the growth of Ga2O3, resulting in a more efficient growth process. This source also enabled the growth of crystalline β-Ga2O3 without the need for additional oxygen. The influence of the substrate temperatures on the crystal structure and quality, chemical bonding, surface morphology, and optical properties has been systematically evaluated by x-ray diffraction, scanning transmission electron microscopy, x-ray photoelectron spectroscopy, atomic force microscopy, spectroscopic ellipsometry, and UV-vis spectroscopy. Under optimized growth conditions, all films exhibited pure (" separators="|2 ¯01 ) oriented β-Ga2O3 thin films with six-fold rotational symmetry when grown on a sapphire substrate. The thin films demonstrated significant absorption in the deep-ultraviolet (UV) region with an optical bandgap around 5.0 eV and a refractive index of 1.9. A deep-UV photodetector fabricated on the high quality β-Ga2O3 thin film exhibits high resistance and small dark current (4.25 nA) with expected photoresponse for 254 nm UV light irradiation suggesting that the material grown using the compound source is a potential candidate for deep-ultraviolet photodetectors.

VizieR Online Data Catalog: VANDELS High-Redshift Galaxy Evolution (McLure+, 2017)

NASA Astrophysics Data System (ADS)

McLure, R.; Pentericci, L.; Vandels Team

2017-11-01

This is the first data release (DR1) of the VANDELS survey, an ESO public spectroscopy survey targeting the high-redshift Universe. The VANDELS survey uses the VIMOS spectrograph on ESO's VLT to obtain ultra-deep, medium resolution, optical spectra of galaxies within the UKIDSS Ultra Deep Survey (UDS) and Chandra Deep Field South (CDFS) survey fields (0.2 sq. degree total area). Using robust photometric redshift pre-selection, VANDELS is targeting ~2100 galaxies in the redshift interval 1.0=3. In addition, VANDELS is targeting a substantial number of passive galaxies in the redshift interval 1.0

Early postoperative changes in cerebral oxygen metabolism following neonatal cardiac surgery: Effects of surgical duration

PubMed Central

Buckley, Erin M.; Lynch, Jennifer M.; Goff, Donna A.; Schwab, Peter J.; Baker, Wesley B.; Durduran, Turgut; Busch, David R.; Nicolson, Susan C.; Montenegro, Lisa M.; Naim, Maryam Y.; Xiao, Rui; Spray, Thomas L.; Yodh, A. G.; Gaynor, J. William; Licht, Daniel J.

2013-01-01

Objective The early postoperative period following neonatal cardiac surgery is a time of increased risk for brain injury, yet the mechanisms underlying this risk are unknown. To understand these risks more completely, we quantified changes in postoperative cerebral metabolic rate of oxygen (CMRO2), oxygen extraction fraction (OEF), and cerebral blood flow (CBF) compared with preoperative levels by using noninvasive optical modalities. Methods Diffuse optical spectroscopy and diffuse correlation spectroscopy were used concurrently to derive cerebral blood flow and oxygen utilization postoperatively for 12 hours. Relative changes in CMRO2, OEF, and CBF were quantified with reference to preoperative data. A mixed-effect model was used to investigate the influence of total support time and deep hypothermic circulatory arrest duration on relative changes in CMRO2, OEF, and CBF. Results Relative changes in CMRO2, OEF, and CBF were assessed in 36 patients, 21 with single-ventricle defects and 15 with 2-ventricle defects. Among patients with single-ventricle lesions, deep hypothermic circulatory arrest duration did not affect relative changes in CMRO2, CBF, or OEF (P > .05). Among 2-ventricle patients, total support time was not a significant predictor of relative changes in CMRO2 or CBF (P > .05), although longer total support time was associated significantly with greater increases in relative change of postoperative OEF (P = .008). Conclusions Noninvasive diffuse optical techniques were used to quantify postoperative relative changes in CMRO2, CBF, and OEF for the first time in this observational pilot study. Pilot data suggest that surgical duration does not account for observed variability in the relative change in CMRO2, and that more comprehensive clinical studies using the new technology are feasible and warranted to elucidate these issues further. PMID:23111021

Study of calcification formation and disease diagnostics utilising advanced vibrational spectroscopy

NASA Astrophysics Data System (ADS)

Kerssens, Marleen Maartje

The accurate and safe diagnosis of breast cancer is a significant societal issue, with annual disease incidence of 48,000 women and around 370 men in the UK. Early diagnosis of the disease allows more conservative treatments and better patient outcomes. Microcalcifications in breast tissue are an important indicator for breast cancers, and often the only sign of their presence. Several studies have suggested that the type of calcification formed may act as a marker for malignancy and its presence may be of biological significance. In this work, breast calcifications are studied with FTIR, synchrotron FTIR, ATR FTIR, and Raman mapping to explore their disease specific composition. From a comparison between vibrational spectroscopy and routine staining procedures it becomes clear that calcium builds up prior to calcification formation. Raman and FTIR indicate the same size for calcifications and are in agreement with routine staining techniques. From the synchrotron FTIR measurements it can be proven that amide is present in the centre of the calcifications and the intensity of the bands depends on the pathology. Special attention is paid to the type of carbonate substitution in the calcifications relating to different pathology grades. In contrast to mammography, Raman spectroscopy has the capability to distinguish calcifications based on their chemical composition. The ultimate goal is to turn the acquired knowledge from the mapping studies into a clinical tool based on deep Raman spectroscopy. Deep Raman techniques have a considerable potential to reduce large numbers of normal biopsies, reduce the time delay between screening and diagnosis and therefore diminish patient anxiety. In order to achieve this, a deep Raman system is designed and after evaluation of its performance tested on buried calcification standards in porcine soft tissue and human mammary tissue. It is shown that, when the calcification is probed through tissue, the strong 960 cm-1 phosphate band can be used as a pseudo marker for carbonate substitution which is related to the pathology of the surrounding tissue. Furthermore, the first study in which human breast calcifications are measured in bulk tissue with a thickness of several millimetres to centimetres is presented. To date, measurements have been performed at 41 specimens with a thickness up to 25 mm. Measurements could be performed through skin and blue dye. The proposed deep Raman technique is promising for probing of calcifications through tissue but will need refinement before being adopted in hospitals.

Anomalously deep polarization in SrTiO3 (001) interfaced with an epitaxial ultrathin manganite film

DOE PAGES

Wang, Zhen; Tao, Jing; Yu, Liping; ...

2016-10-17

Using atomically-resolved imaging and spectroscopy, we reveal a remarkably deep polarization in non-ferroelectric SrTiO 3 near its interface with an ultrathin nonmetallic film of La 2/3Sr 1/3MnO 3. Electron holography shows an electric field near the interface in SrTiO 3, yielding a surprising spontaneous polarization density of ~ 21 μC/cm 2. Combining the experimental results with first principles calculations, we propose that the observed deep polarization is induced by the electric field originating from oxygen vacancies that extend beyond a dozen unit-cells from the interface, thus providing important evidence of the role of defects in the emergent interface properties ofmore » transition metal oxides.« less

[Terahertz Spectroscopic Identification with Deep Belief Network].

PubMed

Ma, Shuai; Shen, Tao; Wang, Rui-qi; Lai, Hua; Yu, Zheng-tao

2015-12-01

Feature extraction and classification are the key issues of terahertz spectroscopy identification. Because many materials have no apparent absorption peaks in the terahertz band, it is difficult to extract theirs terahertz spectroscopy feature and identify. To this end, a novel of identify terahertz spectroscopy approach with Deep Belief Network (DBN) was studied in this paper, which combines the advantages of DBN and K-Nearest Neighbors (KNN) classifier. Firstly, cubic spline interpolation and S-G filter were used to normalize the eight kinds of substances (ATP, Acetylcholine Bromide, Bifenthrin, Buprofezin, Carbazole, Bleomycin, Buckminster and Cylotriphosphazene) terahertz transmission spectra in the range of 0.9-6 THz. Secondly, the DBN model was built by two restricted Boltzmann machine (RBM) and then trained layer by layer using unsupervised approach. Instead of using handmade features, the DBN was employed to learn suitable features automatically with raw input data. Finally, a KNN classifier was applied to identify the terahertz spectrum. Experimental results show that using the feature learned by DBN can identify the terahertz spectrum of different substances with the recognition rate of over 90%, which demonstrates that the proposed method can automatically extract the effective features of terahertz spectrum. Furthermore, this KNN classifier was compared with others (BP neural network, SOM neural network and RBF neural network). Comparisons showed that the recognition rate of KNN classifier is better than the other three classifiers. Using the approach that automatic extract terahertz spectrum features by DBN can greatly reduce the workload of feature extraction. This proposed method shows a promising future in the application of identifying the mass terahertz spectroscopy.

MUSE deep-fields: the Ly α luminosity function in the Hubble Deep Field-South at 2.91 < z < 6.64

NASA Astrophysics Data System (ADS)

Drake, Alyssa B.; Guiderdoni, Bruno; Blaizot, Jérémy; Wisotzki, Lutz; Herenz, Edmund Christian; Garel, Thibault; Richard, Johan; Bacon, Roland; Bina, David; Cantalupo, Sebastiano; Contini, Thierry; den Brok, Mark; Hashimoto, Takuya; Marino, Raffaella Anna; Pelló, Roser; Schaye, Joop; Schmidt, Kasper B.

2017-10-01

We present the first estimate of the Ly α luminosity function using blind spectroscopy from the Multi Unit Spectroscopic Explorer, MUSE, in the Hubble Deep Field-South. Using automatic source-detection software, we assemble a homogeneously detected sample of 59 Ly α emitters covering a flux range of -18.0 < log10 (F) < -16.3 (erg s-1 cm-2), corresponding to luminosities of 41.4 < log10 (L) < 42.8 (erg s-1). As recent studies have shown, Ly α fluxes can be underestimated by a factor of 2 or more via traditional methods, and so we undertake a careful assessment of each object's Ly α flux using a curve-of-growth analysis to account for extended emission. We describe our self-consistent method for determining the completeness of the sample, and present an estimate of the global Ly α luminosity function between redshifts 2.91 < z < 6.64 using the 1/Vmax estimator. We find that the luminosity function is higher than many number densities reported in the literature by a factor of 2-3, although our result is consistent at the 1σ level with most of these studies. Our observed luminosity function is also in good agreement with predictions from semi-analytic models, and shows no evidence for strong evolution between the high- and low-redshift halves of the data. We demonstrate that one's approach to Ly α flux estimation does alter the observed luminosity function, and caution that accurate flux assessments will be crucial in measurements of the faint-end slope. This is a pilot study for the Ly α luminosity function in the MUSE deep-fields, to be built on with data from the Hubble Ultra Deep Field that will increase the size of our sample by almost a factor of 10.

Sulfate Reduction and Sulfide Biomineralization By Deep-Sea Hydrothermal Vent Microorganisms

NASA Astrophysics Data System (ADS)

Picard, A.; Gartman, A.; Clarke, D. R.; Girguis, P. R.

2014-12-01

Deep-sea hydrothermal vents are characterized by steep temperature and chemical gradients and moderate pressures. At these sites, mesophilic sulfate-reducing bacteria thrive, however their significance for the formation of sulfide minerals is unknown. In this study we investigated sulfate reduction and sulfide biomineralization by the deep-sea bacterium Desulfovibrio hydrothermalis isolated from a deep-sea vent chimney at the Grandbonum vent site (13°N, East Pacific Rise, 2600 m water depth) [1]. Sulfate reduction rates were determined as a function of pressure and temperature. Biomineralization of sulfide minerals in the presence of various metal concentrations was characterized using light and electron microscopy and optical spectroscopy. We seek to better understand the significance of biological sulfate reduction in deep-sea hydrothermal environments, to characterize the steps in sulfide mineral nucleation and growth, and identify the interactions between cells and minerals. [1] D. Alazard, S. Dukan, A. Urios, F. Verhe, N. Bouabida, F. Morel, P. Thomas, J.L. Garcia and B. Ollivier, Desulfovibrio hydrothermalis sp. nov., a novel sulfate-reducing bacterium isolated from hydrothermal vents, Int. J. Syst. Evol. Microbiol., 53 (2003) 173-178.

Deep ultraviolet semiconductor light sources for sensing and security

NASA Astrophysics Data System (ADS)

Shatalov, Max; Bilenko, Yuri; Yang, Jinwei; Gaska, Remis

2009-09-01

III-Nitride based deep ultraviolet (DUV) light emitting diodes (LEDs) rapidly penetrate into sensing market owing to several advantages over traditional UV sources (i.e. mercury, xenon and deuterium lamps). Small size, a wide choice of peak emission wavelengths, lower power consumption and reduced cost offer flexibility to system integrators. Short emission wavelength offer advantages for gas detection and optical sensing systems based on UV induced fluorescence. Large modulation bandwidth for these devices makes them attractive for frequency-domain spectroscopy. We will review present status of DUV LED technology and discuss recent advances in short wavelength emitters and high power LED lamps.

VizieR Online Data Catalog: NGC 1068 deep millimeter spectroscopy observations (Qiu+, 2018)

NASA Astrophysics Data System (ADS)

Qiu, J.; Wang, J.; Shi, Y.; Zhang, J.; Fang, M.; Li, F.

2018-05-01

We present the results of 1-3mm molecular line survey towards NGC1068. We show the final averaged spectra after eliminating bad scans and subtracting baselines of order 0 to the individual spectra. Y-axis is in antenna temperature scale. (3 data files).

Decadal trends in deep ocean salinity and regional effects on steric sea level

NASA Astrophysics Data System (ADS)

Purkey, S. G.; Llovel, W.

2017-12-01

We present deep (below 2000 m) and abyssal (below 4000 m) global ocean salinity trends from the 1990s through the 2010s and assess the role of deep salinity in local and global sea level budgets. Deep salinity trends are assessed using all deep basins with available full-depth, high-quality hydrographic section data that have been occupied two or more times since the 1980s through either the World Ocean Circulation Experiment (WOCE) Hydrographic Program or the Global Ship-Based Hydrographic Investigations Program (GO-SHIP). All salinity data is calibrated to standard seawater and any intercruise offsets applied. While the global mean deep halosteric contribution to sea level rise is close to zero (-0.017 +/- 0.023 mm/yr below 4000 m), there is a large regional variability with the southern deep basins becoming fresher and northern deep basins becoming more saline. This meridional gradient in the deep salinity trend reflects different mechanisms driving the deep salinity variability. The deep Southern Ocean is freshening owing to a recent increased flux of freshwater to the deep ocean. Outside of the Southern Ocean, the deep salinity and temperature changes are tied to isopycnal heave associated with a falling of deep isopycnals in recent decades. Therefore, regions of the ocean with a deep salinity minimum are experiencing both a halosteric contraction with a thermosteric expansion. While the thermosteric expansion is larger in most cases, in some regions the halosteric compensates for as much as 50% of the deep thermal expansion, making a significant contribution to local sea level rise budgets.

A comparison of point defects in Cd1-xZnxTe1-ySey crystals grown by Bridgman and traveling heater methods

NASA Astrophysics Data System (ADS)

Gul, R.; Roy, U. N.; Camarda, G. S.; Hossain, A.; Yang, G.; Vanier, P.; Lordi, V.; Varley, J.; James, R. B.

2017-03-01

In this paper, the properties of point defects in Cd1-xZnxTe1-ySey (CZTS) radiation detectors are characterized using deep-level transient spectroscopy and compared between materials grown using two different methods, the Bridgman method and the traveling heater method. The nature of the traps was analyzed in terms of their capture cross-sections and trap concentrations, as well as their effects on the measured charge-carrier trapping and de-trapping times, and then compared for the two growth techniques. The results revealed that Se addition to CdZnTe can reduce the VCd- concentration. In Travelling Heater Method (THM) and Bridgman Method (BM) grown CZTS detectors, besides a few similarities in the shallow and medium energy traps, there were major differences in the deep traps. It was observed that the excess-Te and lower growth-temperature conditions in THM-grown CZTS led to a complete compensation of VCd- and two additional traps (attributed to Tei- and TeCd++ appearing at around Ev + 0.26 eV and Ec - 0.78 eV, respectively). The 1.1-eV deep trap related to large Te secondary phases was a dominant trap in the BM-grown CZTS crystals. In addition to i-DLTS data, the effects of point defects induced due to different processing techniques on the detector's resistivity, spectral response to gammas, and μτ product were determined.

Copper interstitial recombination centers in Cu 3 N

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

Yee, Ye Sheng; Inoue, Hisashi; Hultqvist, Adam

We present a comprehensive study of the earth-abundant semiconductor Cu 3N as a potential solar energy conversion material, using density functional theory and experimental methods. Density functional theory indicates that among the dominant intrinsic point defects, copper vacancies V Cu have shallow defect levels while copper interstitials Cu i behave as deep potential wells in the conduction band which mediate Shockley-Read-Hall recombination. The existence of Cu i defects has been experimentally verified using photothermal deflection spectroscopy. A Cu 3N/ZnS heterojunction diode with good current-voltage rectification behavior has been demonstrated experimentally, but no photocurrent is generated under illumination. Finally, the absencemore » of photocurrent can be explained by a large concentration of Cu i recombination centers capturing electrons in p-type Cu 3N.« less

Magnetic Resonance Techniques Applied to the Diagnosis and Treatment of Parkinson’s Disease

PubMed Central

de Celis Alonso, Benito; Hidalgo-Tobón, Silvia S.; Menéndez-González, Manuel; Salas-Pacheco, José; Arias-Carrión, Oscar

2015-01-01

Parkinson’s disease (PD) affects at least 10 million people worldwide. It is a neurodegenerative disease, which is currently diagnosed by neurological examination. No neuroimaging investigation or blood biomarker is available to aid diagnosis and prognosis. Most effort toward diagnosis using magnetic resonance (MR) has been focused on the use of structural/anatomical neuroimaging and diffusion tensor imaging (DTI). However, deep brain stimulation, a current strategy for treating PD, is guided by MR imaging (MRI). For clinical prognosis, diagnosis, and follow-up investigations, blood oxygen level-dependent MRI, DTI, spectroscopy, and transcranial magnetic stimulation have been used. These techniques represent the state of the art in the last 5 years. Here, we focus on MR techniques for the diagnosis and treatment of Parkinson’s disease. PMID:26191037

Defect and field-enhancement characterization through electron-beam-induced current analysis

NASA Astrophysics Data System (ADS)

Umezawa, Hitoshi; Gima, Hiroki; Driche, Khaled; Kato, Yukako; Yoshitake, Tsuyoshi; Mokuno, Yoshiaki; Gheeraert, Etienne

2017-05-01

To investigate the effects of defects and field enhancement in diamond power devices, a biased Schottky barrier diode was characterized by electron-beam-induced current (EBIC) analysis. The nonuniform distribution of the electrical field was revealed by bright spots on the laterally expanded depletion layer of the EBIC intensity map when the applied electrical field exceeded 0.95 MV/cm. The nonuniformity is partly due to a structural effect: the roughness at the edge of the Schottky electrode, induced by lithography and lift-off processes. A second family of spots was shown to increase the leakage current of the device. The time constant associated with this second spot family was 0.98 ms, which is three orders of magnitude shorter than that for defects previously characterized by deep-level transient spectroscopy.

Effect of electron injection on defect reactions in irradiated silicon containing boron, carbon, and oxygen

NASA Astrophysics Data System (ADS)

Makarenko, L. F.; Lastovskii, S. B.; Yakushevich, H. S.; Moll, M.; Pintilie, I.

2018-04-01

Comparative studies employing Deep Level Transient Spectroscopy and C-V measurements have been performed on recombination-enhanced reactions between defects of interstitial type in boron doped silicon diodes irradiated with alpha-particles. It has been shown that self-interstitial related defects which are immobile even at room temperatures can be activated by very low forward currents at liquid nitrogen temperatures. Their activation is accompanied by the appearance of interstitial carbon atoms. It has been found that at rather high forward current densities which enhance BiOi complex disappearance, a retardation of Ci annealing takes place. Contrary to conventional thermal annealing of the interstitial boron-interstitial oxygen complex, the use of forward current injection helps to recover an essential part of charge carriers removed due to irradiation.

Electrically Active Defects In Solar Cells Based On Amorphous Silicon/Crystalline Silicon Heterojunction After Irradiation By Heavy Xe Ions

NASA Astrophysics Data System (ADS)

Harmatha, Ladislav; Mikolášek, Miroslav; Stuchlíková, L'ubica; Kósa, Arpád; Žiška, Milan; Hrubčín, Ladislav; Skuratov, Vladimir A.

2015-11-01

The contribution is focused on the diagnostics of structures with a heterojunction between amorphous and crystalline silicon prepared by HIT (Heterojunction with an Intrinsic Thin layer) technology. The samples were irradiated by Xe ions with energy 167 MeV and doses from 5 × 108 cm-2 to 5 × 1010 cm-2. Radiation defects induced in the bulk of Si and at the hydrogenated amorphous silicon and crystalline silicon (a-Si:H/c-Si) interface were identified by Deep Level Transient Spectroscopy (DLTS). Radiation induced A-centre traps, boron vacancy traps and different types of divacancies with a high value of activation energy were observed. With an increased fluence of heavy ions the nature and density of the radiation induced defects was changed.

Copper interstitial recombination centers in Cu 3 N

DOE PAGES

Yee, Ye Sheng; Inoue, Hisashi; Hultqvist, Adam; ...

2018-06-04

We present a comprehensive study of the earth-abundant semiconductor Cu 3N as a potential solar energy conversion material, using density functional theory and experimental methods. Density functional theory indicates that among the dominant intrinsic point defects, copper vacancies V Cu have shallow defect levels while copper interstitials Cu i behave as deep potential wells in the conduction band which mediate Shockley-Read-Hall recombination. The existence of Cu i defects has been experimentally verified using photothermal deflection spectroscopy. A Cu 3N/ZnS heterojunction diode with good current-voltage rectification behavior has been demonstrated experimentally, but no photocurrent is generated under illumination. Finally, the absencemore » of photocurrent can be explained by a large concentration of Cu i recombination centers capturing electrons in p-type Cu 3N.« less

VizieR Online Data Catalog: CANDELS z~2 galaxy properties (Trump+, 2014)

NASA Astrophysics Data System (ADS)

Trump, J. R.; Barro, G.; Juneau, S.; Weiner, B. J.; Luo, B.; Brammer, G. B.; Bell, E. F.; Brandt, W. N.; Dekel, A.; Guo, Y.; Hopkins, P. F.; Koo, D. C.; Kocevski, D. D.; McIntosh, D. H.; Momcheva, I.; Faber, S. M.; Ferguson, H. C.; Grogin, N. A.; Kartaltepe, J.; Koekemoer, A. M.; Lotz, J.; Maseda, M.; Mozena, M.; Nandra, K.; Rosario, D. J.; Zeimann, G. R.

2017-04-01

We select a sample of 44 clumpy galaxies from the Great Observatories Origins Deep Survey South (GOODS-S; Giavalisco et al. 2004ApJ...600L..93G) region of CANDELS. For comparison, we also construct mass-matched samples of 41 smooth (non-clumpy) and 35 intermediate galaxies. All galaxies have H<24 (to ensure reliable classification of clumpiness) and have [O III] detected at the 3σ level (for reliable AGN line ratio diagnostics) in the redshift range 1.3

Improved memory characteristics by NH3-nitrided GdO as charge storage layer for nonvolatile memory applications

NASA Astrophysics Data System (ADS)

Liu, L.; Xu, J. P.; Ji, F.; Chen, J. X.; Lai, P. T.

2012-07-01

Charge-trapping memory capacitor with nitrided gadolinium oxide (GdO) as charge storage layer (CSL) is fabricated, and the influence of post-deposition annealing in NH3 on its memory characteristics is investigated. Transmission electron microscopy, x-ray photoelectron spectroscopy, and x-ray diffraction are used to analyze the cross-section and interface quality, composition, and crystallinity of the stack gate dielectric, respectively. It is found that nitrogen incorporation can improve the memory window and achieve a good trade-off among the memory properties due to NH3-annealing-induced reasonable distribution profile of a large quantity of deep-level bulk traps created in the nitrided GdO film and reduction of shallow traps near the CSL/SiO2 interface.

Artificial Intelligence in planetary spectroscopy

NASA Astrophysics Data System (ADS)

Waldmann, Ingo

2017-10-01

The field of exoplanetary spectroscopy is as fast moving as it is new. Analysing currently available observations of exoplanetary atmospheres often invoke large and correlated parameter spaces that can be difficult to map or constrain. This is true for both: the data analysis of observations as well as the theoretical modelling of their atmospheres.Issues of low signal-to-noise data and large, non-linear parameter spaces are nothing new and commonly found in many fields of engineering and the physical sciences. Recent years have seen vast improvements in statistical data analysis and machine learning that have revolutionised fields as diverse as telecommunication, pattern recognition, medical physics and cosmology.In many aspects, data mining and non-linearity challenges encountered in other data intensive fields are directly transferable to the field of extrasolar planets. In this conference, I will discuss how deep neural networks can be designed to facilitate solving said issues both in exoplanet atmospheres as well as for atmospheres in our own solar system. I will present a deep belief network, RobERt (Robotic Exoplanet Recognition), able to learn to recognise exoplanetary spectra and provide artificial intelligences to state-of-the-art atmospheric retrieval algorithms. Furthermore, I will present a new deep convolutional network that is able to map planetary surface compositions using hyper-spectral imaging and demonstrate its uses on Cassini-VIMS data of Saturn.

Investigation of a combined platinum and electron lifetime control treatment for silicon

NASA Astrophysics Data System (ADS)

Jia, Yunpeng; Cui, Zhihang; Yang, Fei; Zhao, Bao; Zou, Shikai; Liang, Yongsheng

2017-02-01

In silicon, the effect of Combined Lifetime Treatment (CLT) involving platinum diffusion and subsequent electron irradiation is different from the separate treatments of platinum diffusion and electron irradiation, even the treatment of electron irradiation followed by platinum diffusion. In this paper, we investigated the experimental behavior of different kinds of lifetime treated samples. We found that the reverse leakage current (Irr) increases with the increasing platinum diffusion temperature or electron irradiation dose in the separate treatments. Conversely, Irr of the CLT samples decreased with rising platinum diffusion temperature at the same dose of subsequent electron irradiation. By deep-level transient spectroscopy (DLTS), a new energy level E7 (Ec -0.376 eV) was found in our CLT samples. The new level E7 suppresses the dominance of the deeper level E8 (Ec -0.476 eV), which is caused by electron irradiation directly and results in Irr's increase. The formation of the level E7 comes from the complex defect-combined effect between platinum atoms and silicon vacancies, and it affects device's characteristics finally. These research will be helpful to the development of platinum-diffused devices used in intense electron irradiation environments.

Post-growth annealing induced change of conductivity in As-doped ZnO grown by radio frequency magnetron sputtering

NASA Astrophysics Data System (ADS)

To, C. K.; Yang, B.; Su, S. C.; Ling, C. C.; Beling, C. D.; Fung, S.

2011-12-01

Arsenic-doped ZnO films were fabricated by radio frequency magnetron sputtering method at a relatively low substrate temperature of 200 °C. Post-growth annealing in air was carried out up to a temperature of 1000 °C. The samples were characterized by Hall measurement, positron annihilation spectroscopy (PAS), secondary ion mass spectroscopy (SIMS), and cathodoluminescence (CL). The as-grown sample was of n-type and it converted to p-type material after the 400 °C annealing. The resulting hole concentration was found to increase with annealing temperature and reached a maximum of 6 × 1017 cm-3 at the annealing temperature of 600 °C. The origin of the p-type conductivity was consistent with the AsZn(VZn)2 shallow acceptor model. Further increasing the annealing temperature would decrease the hole concentration of the samples finally converted the sample back to n-type. With evidence, it was suggested that the removal of the p-type conductivity was due to the dissociation of the AsZn(VZn)2 acceptor and the creation of the deep level defect giving rise to the green luminescence.

Multiscale characterization of partially demineralized superficial and deep dentin surfaces.

PubMed

Pelin, Irina M; Trunfio-Sfarghiu, Ana-Maria; Farge, Pierre; Piednoir, Agnes; Pirat, Christophe; Ramos, Stella M M

2013-08-01

The objective of this study was to address the following question: 'Which properties are modified in partially demineralized surfaces, compared with non-demineralized dentin surfaces, following orthophosphoric acid-etching as performed in clinical procedures?'. For this purpose, the complementary techniques atomic force microscopy/spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and contact angle measurements were used to provide a multiscale characterization of the dentin substrate undergoing the acidic preconditioning designed to enhance wetting. Special attention was given to the influence of the etching pretreatment on the nanomechanical properties at different levels of dentin surfaces, in both dry and hydrated conditions. The four-sided pyramid model (extended Hertz contact model) proved to be accurate for calculating the apparent Young's modulus, offering new information on the elasticity of dentin. The modulus value notably decreased following etching and surface hydration. This study underlines that after the acid etching pretreatment the contribution of the nanomechanical, morphological, and physicochemical modifications has a strong influence on the dentin adhesion properties and thus plays a significant role in the coupling of the adhesive-resin composite build-up material at the dentin surface. © 2013 Eur J Oral Sci.

Genetic engineering combined with deep UV resonance Raman spectroscopy for structural characterization of amyloid-like fibrils.

PubMed

Sikirzhytski, Vitali; Topilina, Natalya I; Higashiya, Seiichiro; Welch, John T; Lednev, Igor K

2008-05-07

Elucidating the structure of the cross-beta core in large amyloid fibrils is a challenging problem in modern structural biology. For the first time, a set of de novo polypeptides was genetically engineered to form amyloid-like fibrils with similar morphology and yet different strand length. Differential ultraviolet Raman spectroscopy allowed for separation of the spectroscopic signatures of the highly ordered beta-sheet strands and turns of the fibril core. The relationship between Raman frequencies and Ramachandran dihedral angles of the polypeptide backbone indicates the nature of the beta-sheet and turn structural elements.

Preparation, characterization and optoelectronic properties of nanodiamonds doped zinc oxide nanomaterials by a ball milling technique

NASA Astrophysics Data System (ADS)

Ullah, Hameed; Sohail, Muhammad; Malik, Uzma; Ali, Naveed; Bangash, Masroor Ahmad; Nawaz, Mohsan

2016-07-01

Zinc oxide (ZnO) is one of the very important metal oxides (MOs) for applications in optoelectronic devices which work in the blue and UV regions. However, to meet the challenges of obtaining ZnO nanomaterials suitable for practical applications, various modifications in physico-chemical properties are highly desirable. One of the ways adopted for altering the properties is to synthesize composite(s) of ZnO with various reinforcements. Here we report on the tuning of optoelectronic properties of ZnO upon doping by nanodiamonds (NDs) using the ball milling technique. A varying weight percent (wt.%) of NDs were ball milled for 2 h with ZnO nanoparticles prepared by a simple precipitation method. The effects of different parameters, the calcination temperature of ZnO, wt.% of NDs and mechanical milling upon the optoelectronic properties of the resulting ZnO-NDs nanocomposites have been investigated. The ZnO-NDs nanocomposites were characterized by IR spectroscopy, powder x-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDX). The UV-vis spectroscopy revealed the alteration in the bandgap energy (Eg ) of ZnO as a function of the calcination temperature of ZnO, changing the concentration of NDs, and mechanical milling of the resulting nanocomposites. The photoluminescence (PL) spectroscopy showed a decrease in the deep level emission (DLE) peaks and an increase in near-band-edge transition peaks as a result of the increasing concentration of NDs. The decrease in DLE and increase in band to band transition peaks were due to the strong interaction between the NDs and the Zn+; consequently, the Zn+ concentration decreased on the interstitial sites.

The deep levels in InGaAlP epilayers grown by metalorganic chemical vapor deposition using tertiarybutylphosphine

NASA Astrophysics Data System (ADS)

Izumiya, T.; Ishikawa, H.; Mashita, M.

1994-12-01

InGaAlP epilayers and double-hetero structure light emitting diodes (LEDs) were grown by metalorganic chemical vapor deposition (MOCVD) using tertiarybutylphosphine (TBP). The photoluminescence (PL) intensities were low compared with the epilayer grown using PH 3, and depended markedly on the TBP synthesis lots. Deep levels, were studied and two oxygen related levels were observed in the epilayers with small PL intensities. An intimate relation between the deep levels and the photoluminescence (PL) intensity has been found. A larger TBP flow rate reduced the deep level concentrations and improved the PL intensity.

Geological Carbon Sequestration: A New Approach for Near-Surface Assurance Monitoring

PubMed Central

Wielopolski, Lucian

2011-01-01

There are two distinct objectives in monitoring geological carbon sequestration (GCS): Deep monitoring of the reservoir’s integrity and plume movement and near-surface monitoring (NSM) to ensure public health and the safety of the environment. However, the minimum detection limits of the current instrumentation for NSM is too high for detecting weak signals that are embedded in the background levels of the natural variations, and the data obtained represents point measurements in space and time. A new approach for NSM, based on gamma-ray spectroscopy induced by inelastic neutron scatterings (INS), offers novel and unique characteristics providing the following: (1) High sensitivity with a reducible error of measurement and detection limits, and, (2) temporal- and spatial-integration of carbon in soil that results from underground CO2 seepage. Preliminary field results validated this approach showing carbon suppression of 14% in the first year and 7% in the second year. In addition the temporal behavior of the error propagation is presented and it is shown that for a signal at the level of the minimum detection level the error asymptotically approaches 47%. PMID:21556180

Deep-red to near-infrared fluorescent dyes: Synthesis, photophysical properties, and application in cell imaging

NASA Astrophysics Data System (ADS)

Li, Qi; Liu, Weimin; Wu, Jiasheng; Zhou, Bingjiang; Niu, Guangle; Zhang, Hongyan; Ge, Jiechao; Wang, Pengfei

2016-07-01

More and more attention has been paid to the design of new fluorescent imaging agents with good photostability and water solubility, especially those with emissions in the deep-red and near-infrared regions. In this work, we designed and synthesized four novel fluorescent dyes with deep-red or NIR fluorescence by hybridizing coumarin and pyronin moieties based on our previous work. Introduction of carboxylic acid in the dyes not only imparted the dyes with water solubility but also provided a versatile sensing platform for designing the fluorescent probes and sensors of biomolecules. The photophysical properties of these new dyes were investigated through absorption and fluorescence spectroscopy. Cell imaging experiments showed that esterification products could selectively stain lysosomes with good photostability, thereby indicating that they could be useful in the development of fluorescent probes for bioimaging.

Isolated oxygen defects in 3C- and 4H-SiC: A theoretical study

NASA Astrophysics Data System (ADS)

Gali, A.; Heringer, D.; Deák, P.; Hajnal, Z.; Frauenheim, Th.; Devaty, R. P.; Choyke, W. J.

2002-09-01

Ab initio calculations in the local-density approximation have been carried out in SiC to determine the possible configurations of the isolated oxygen impurity. Equilibrium geometry and occupation levels were calculated. Substitutional oxygen in 3C-SiC is a relatively shallow effective mass like double donor on the carbon site (OC) and a hyperdeep double donor on the Si site (OSi). In 4H-SiC OC is still a double donor but with a more localized electron state. In 3C-SiC OC is substantially more stable under any condition than OSi or interstitial oxygen (Oi). In 4H-SiC OC is also the most stable one except for heavy n-type doping. We propose that OC is at the core of the electrically active oxygen-related defect family found by deep level transient spectroscopy in 4H-SiC. The consequences of the site preference of oxygen on the SiC/SiO2 interface are discussed.

Charge carriers' trapping states in pentacene films studied by modulated photocurrent

NASA Astrophysics Data System (ADS)

Gorgolis, S.; Giannopoulou, A.; Kounavis, P.

2013-03-01

The modulated photocurrent (MPC) technique is employed to study the charge carriers' trapping states of pentacene films. The characteristics of the experimental MPC spectra were found to be compatible with trapping-detrapping process of holes in gap states in which their occupancy can be modified by the bias illumination. A demarcation energy level separating empty from partially occupied traps was deduced from the MPC spectra, which can be used to monitor bias-light induced changes in the quasi Fermi level. An exponential trap distribution from structural disorder and a deep metastable gaussian trap distribution from adsorbed environmental impurities were extracted by means of the MPC spectroscopy. An attempt to escape frequency of the order of 1010s-1 was deduced for the gap sates. The derived trap distributions agree with those found before by means of other techniques. The present results indicate that the MPC technique can be used as a valuable tool for pentacene films characterization since it can be also applied to field effect samples.

Impurities in silicon solar cells

NASA Technical Reports Server (NTRS)

Hopkins, R. H.

1985-01-01

Metallic impurities, both singly and in combinations, affect the performance of silicon solar cells. Czochralski silicon web crystals were grown with controlled additions of secondary impurities. The primary electrical dopants were boron and phosphorus. The silicon test ingots were grown under controlled and carefully monitored conditions from high-purity charge and dopant material to minimize unintentional contamination. Following growth, each crystal was characterized by chemical, microstructural, electrical, and solar cell tests to provide a detailed and internally consistent description of the relationships between silicon impurity concentration and solar cell performance. Deep-level spectroscopy measurements were used to measure impurity concentrations at levels below the detectability of other techniques and to study thermally-induced changes in impurity activity. For the majority of contaminants, impurity-induced performance loss is due to a reduction of the base diffusion length. From these observations, a semi-empirical model which predicts cell performance as a function of metal impurity concentration was formulated. The model was then used successfully to predict the behavior of solar cells bearing as many as 11 different impurities.

Electrical and structural characterizations of crystallized Al{sub 2}O{sub 3}/GaN interfaces formed by in situ metalorganic chemical vapor deposition

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

Liu, X., E-mail: xliu@ece.ucsb.edu; Yeluri, R.; Kim, J.

2016-01-07

Al{sub 2}O{sub 3} films were grown in situ by metalorganic chemical vapor deposition at 900 °C on GaN of both Ga- and N-face polarities. High-resolution transmission electron microscopy revealed that the Al{sub 2}O{sub 3} films were crystalline and primarily γ-phase. The Al{sub 2}O{sub 3}/Ga-GaN and Al{sub 2}O{sub 3}/N-GaN interfaces were both atomically sharp, and the latter further exhibited a biatomic step feature. The corresponding current-voltage (J-V) characteristics were measured on a metal-Al{sub 2}O{sub 3}-semiconductor capacitor (MOSCAP) structure. The leakage current was very high when the Al{sub 2}O{sub 3} thickness was comparable with the size of the crystalline defects, but was suppressedmore » to the order of 1 × 10{sup −8} A/cm{sup 2} with larger Al{sub 2}O{sub 3} thicknesses. The interface states densities (D{sub it}) were measured on the same MOSCAPs by using combined ultraviolet (UV)-assisted capacitance-voltage (C-V), constant capacitance deep level transient spectroscopy (CC-DLTS), and constant capacitance deep level optical spectroscopy (CC-DLOS) techniques. The average D{sub it} measured by CC-DLTS and CC-DLOS were 6.6 × 10{sup 12} and 8.8 × 10{sup 12} cm{sup −2} eV{sup −1} for Al{sub 2}O{sub 3}/Ga-GaN and 8.6 × 10{sup 12} and 8.6 × 10{sup 12 }cm{sup −2} eV{sup −1} for Al{sub 2}O{sub 3}/N-GaN, respectively. The possible origins of the positive (negative) polarization compensation charges in Al{sub 2}O{sub 3}/Ga-GaN (Al{sub 2}O{sub 3}/N-GaN), including the filling of interface states and the existence of structure defects and impurities in the Al{sub 2}O{sub 3} layer, were discussed in accordance with the experimental results and relevant studies in the literature.« less

Ferrocene Derivatives Included in a Water-Soluble Cavitand: Are They Electroinactive?

PubMed Central

Podkoscielny, Dagmara; Hooley, Richard J.; Rebek, Julius; Kaifer, Angel E.

2009-01-01

The formation in aqueous solution of kinetically stable inclusion complexes between a deep-cavity cavitand and several redox active ferrocene derivatives was demonstrated using 1H NMR spectroscopy. The electrochemical kinetics of the inclusion complexes was strongly attenuated as compared to that observed with the free guests. PMID:18537255

Noninvasive diagnosis and therapeutic effect evaluation of deep vein thrombosis in clinics by near-infrared spectroscopy

NASA Astrophysics Data System (ADS)

Li, Ting; Sun, Yunlong; Chen, Xiao; Zhao, Yue; Ren, Rongrong

2015-01-01

Deep vein thrombosis (DVT) has become a severe disease with a rising incidence rate. The conventional diagnosis relies on complicated imaging modalities that may also involve invasive contrast agent injection and ionizing procedures (e.g., venography). Noninvasive near-infrared spectroscopy (NIRS) methods have been explored which required the DVT patients to follow some exercise protocols. Here, we attempt to use portable NIRS under patients' natural state for DVT diagnosis. Nine DVT patients and seven healthy subjects participated in NIRS measurements of concentration of oxy- and deoxy-hemoglobins (Δ[HbO2] and Δ[Hb]) relative to data on a tissue mimicking phantom at six particular sites of calves. It was found that Δ[HbO2] is significantly lower in DVT patients than healthy ones, whereas Δ[Hb] is distinctly higher. Moreover, after thrombolytic therapy, both Δ[HbO2] and Δ[Hb] in DVT calves assume a gradual convergence to the curves of healthy ones. This reveals the potential of NIRS for the noninvasive, continuous, and straightforward monitoring/therapeutic effect evaluation of DVT in clinics with appropriate bedside monitoring capability.

Differential Epitope Mapping by STD NMR Spectroscopy To Reveal the Nature of Protein-Ligand Contacts.

PubMed

Monaco, Serena; Tailford, Louise E; Juge, Nathalie; Angulo, Jesus

2017-11-27

Saturation transfer difference (STD) NMR spectroscopy is extensively used to obtain epitope maps of ligands binding to protein receptors, thereby revealing structural details of the interaction, which is key to direct lead optimization efforts in drug discovery. However, it does not give information about the nature of the amino acids surrounding the ligand in the binding pocket. Herein, we report the development of the novel method differential epitope mapping by STD NMR (DEEP-STD NMR) for identifying the type of protein residues contacting the ligand. The method produces differential epitope maps through 1) differential frequency STD NMR and/or 2) differential solvent (D 2 O/H 2 O) STD NMR experiments. The two approaches provide different complementary information on the binding pocket. We demonstrate that DEEP-STD NMR can be used to readily obtain pharmacophore information on the protein. Furthermore, if the 3D structure of the protein is known, this information also helps in orienting the ligand in the binding pocket. © 2017 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

Sungsanpin, a lasso peptide from a deep-sea streptomycete.

PubMed

Um, Soohyun; Kim, Young-Joo; Kwon, Hyuknam; Wen, He; Kim, Seong-Hwan; Kwon, Hak Cheol; Park, Sunghyouk; Shin, Jongheon; Oh, Dong-Chan

2013-05-24

Sungsanpin (1), a new 15-amino-acid peptide, was discovered from a Streptomyces species isolated from deep-sea sediment collected off Jeju Island, Korea. The planar structure of 1 was determined by 1D and 2D NMR spectroscopy, mass spectrometry, and UV spectroscopy. The absolute configurations of the stereocenters in this compound were assigned by derivatizations of the hydrolysate of 1 with Marfey's reagents and 2,3,4,6-tetra-O-acetyl-β-d-glucopyranosyl isothiocyanate, followed by LC-MS analysis. Careful analysis of the ROESY NMR spectrum and three-dimensional structure calculations revealed that sungsanpin possesses the features of a lasso peptide: eight amino acids (-Gly(1)-Phe-Gly-Ser-Lys-Pro-Ile-Asp(8)-) that form a cyclic peptide and seven amino acids (-Ser(9)-Phe-Gly-Leu-Ser-Trp-Leu(15)) that form a tail that loops through the ring. Sungsanpin is thus the first example of a lasso peptide isolated from a marine-derived microorganism. Sungsanpin displayed inhibitory activity in a cell invasion assay with the human lung cancer cell line A549.

A Poor Relationship Between Sea Level and Deep-Water Sand Delivery

NASA Astrophysics Data System (ADS)

Harris, Ashley D.; Baumgardner, Sarah E.; Sun, Tao; Granjeon, Didier

2018-08-01

The most commonly cited control on delivery of sand to deep water is the rate of relative sea-level fall. The rapid rate of accommodation loss on the shelf causes sedimentation to shift basinward. Field and experimental numerical modeling studies have shown that deep-water sand delivery can occur during any stage of relative sea level position and across a large range of values of rate of relative sea-level change. However, these studies did not investigate the impact of sediment transport efficiency on the relationship between rate of relative sea-level change and deep-water sand delivery rate. We explore this relationship using a deterministic nonlinear diffusion-based numerical stratigraphic forward model. We vary across three orders of magnitude the diffusion coefficient value for marine settings, which controls sediment transport efficiency. We find that the rate of relative sea-level change can explain no more than 1% of the variability in deep-water sand delivery rates, regardless of sediment transport efficiency. Model results show a better correlation with relative sea level, with up to 55% of the variability in deep water sand delivery rates explained. The results presented here are consistent with studies of natural settings which suggest stochastic processes such as avulsion and slope failure, and interactions among such processes, may explain the remaining variance. Relative sea level is a better predictor of deep-water sand delivery than rate of relative sea-level change because it is the sea-level fall itself which promotes sand delivery, not the rate of the fall. We conclude that the poor relationship between sea level and sand delivery is not an artifact of the modeling parameters but is instead due to the inadequacy of relative sea level and the rate of relative sea-level change to fully describe the dimensional space in which depositional systems reside. Subsequently, sea level itself is unable to account for the interaction of multiple processes that contribute to sand delivery to deep water.

An electron trap related to phosphorus deficiency in high-purity InP grown by metalorganic chemical vapor deposition

NASA Astrophysics Data System (ADS)

Yamamoto, Norio; Uwai, Kunihiko; Takahei, Kenichiro

1989-04-01

Deep levels in high-purity InP crystal grown by metalorganic chemical vapor deposition (MOCVD) have been measured by deep level transient spectroscopy. While no electron traps are observed in the samples grown at 600 °C with a [PH3]/[In(C2H5)3] of 170, three electron traps with activation energies of 0.80, 0.44, and 0.24 eV were observed in the samples grown at 500 °C with the same [PH3]/[In(C2H5)3]. The 0.44-eV trap, whose capture cross section is 1.5×10-18 cm2, observed at a low [PH3]/[In(C2H5)3] shows a decrease in concentration as [PH3]/[In(C2H5)3] is increased, and becomes less than 5×1012 cm-3 at a [PH3]/[In(C2H5)3] of more than 170. The comparison of annealing behavior of this trap in MOCVD InP and that in liquid-encapsulated Czochralski InP suggests that the 0.44-eV trap is related to a complex formed from residual impurities and native defects related to a phosphorus deficiency such as phosphorus vacancies or indium interstitials. This trap is found to show configurational bistability similar to that observed for the trap in an Fe-doped InP, MFe center.

Yrast excitations of neutron-rich nuclei around doubly magic Tin-132

NASA Astrophysics Data System (ADS)

Bhattacharyya, Pallab Kumar

Investigation of the yrast structures of neutron-rich nuclei around the double closed shell nucleus 132Sn is important in the understanding of simple two-body nucleon-nucleon interactions in that region. However conventional fusion-evaporation methods do not populate these nuclei and β-decay studies are useful only in studying low spin states. The spectroscopy of these nuclei from thick target γ-γ coincidence measurements of deep inelastic heavy ion collisions as well as from fission fragment γ-ray studies using large multidetector arrays are presented in this thesis. Analyses of data from the 124Sn + 665 MeV 136Xe and 130Te + 272 MeV 64Ni deep inelastic experiments identified new yrast isomers in the N = 80 nuclei 134Xe and 136Ba which de- excite by γ-ray cascades concluding with their known 4+/to2+ and 2+/to0+ transitions. The isomeric decay characteristics are presented and discussed in light of the systematic features in N = 80 isotones. By analyzing fission product γ-ray data measured at Eurogam II using a 248Cm source, yrast level structures of the two-, three- and four-proton N = 82 isotones 134Te, 135I and 136Xe were developed, and the proton-proton interactions from the two-body nucleus 134Te were used in interpreting 135I and 136Xe levels using shell model calculations. From the same data the yrast states in the N = 83 isotones 134Sb, 135Te, 136I and 137Xe were explored, and key proton-neutron interactions were extracted from the 134Sb level spectrum which were used in interpreting the levels of the other N = 83 isotones. Similarly yrast states in previously unexplored N = 81 isotones 132Sb and 133Te were also identified and interpreted with shell model calculations; the 132Sb level spectrum yielded important proton-neutron hole interactions. Neutron core-excited states at higher energies were also identified in most of these nuclei. For establishing isotopic assignments of unknown cascades, the γgamma cross coincidences between heavy and light fission partners were vital. Overall, both deep inelastic and fission product studies have contributed to the exploration of an otherwise inaccessible region of the nuclidic chart. This opens up a new horizon in studying the structure of these important neutron-rich nuclei.

Broadband stimulated Raman spectroscopy in the deep ultraviolet region

NASA Astrophysics Data System (ADS)

Kuramochi, Hikaru; Fujisawa, Tomotsumi; Takeuchi, Satoshi; Tahara, Tahei

2017-09-01

We report broadband stimulated Raman measurements in the deep ultraviolet (DUV) region, which enables selective probing of the aromatic amino acid residues inside proteins through the resonance enhancement. We combine the narrowband DUV Raman pump pulse (<10 cm-1) at wavelengths as short as 240 nm and the broadband DUV probe pulse (>1000 cm-1) to realize stimulated Raman measurements covering a >1500 cm-1 spectral window. The stimulated Raman measurements for neat solvents, tryptophan, tyrosine, and glucose oxidase are performed using 240- and 290-nm Raman pump, highlighting the high potential of the DUV stimulated Raman probe for femtosecond time-resolved study of proteins.

Deep-levels in gallium arsenide for device applications

NASA Astrophysics Data System (ADS)

McManis, Joseph Edward

Defects in semiconductors have been studied for over 40 years as a diagnostic of the quality of crystal growth. In this thesis, we investigate GaAs deep-levels specifically intended for devices. This thesis summarizes our efforts to characterize the near-infrared photoluminescence from deep-levels, study optical transitions via absorption, and fabricate and characterize deep-level light-emitting diodes (LEDs). This thesis also describes the first tunnel diodes which explicitly make use of GaAs deep-levels. Photoluminescence measurements of GaAs deep-levels showed a broad peak around a wavelength extending from 1.0--1.7 mum, which includes important wavelengths for fiber-optic communications (1.3--1.55 mum). Transmission measurements show the new result that very little of the radiative emission is self-absorbed. We measured the deep-level photoluminescence at several temperatures. We are also the first to report the internal quantum efficiency associated with the deep-level transitions. We have fabricated LEDs that, utilize the optical transitions of GaAs deep-levels. The electroluminescence spectra showed a broad peak from 1.0--1.7 mum at low currents, but the spectrum exhibited a blue-shift as the current was increased. To improve device performance, we designed an AlGaAs layer into the structure of the LEDs. The AlGaAs barrier layer acts as a resistive barrier so that the holes in the p-GaAs layer are swept away from underneath the gold p-contact. The AlGaAs layer also reduces the blue-shift by acting as a potential barrier so that only higher-energy holes are injected. We found that the LEDs with AlGaAs were brighter at long wavelengths, which was a significant improvement. Photoluminescence measurements show that the spectral blue-shift is not due to sample heating. We have developed a new physical model to explain the blue-shift: it is caused by Coloumb charging of the deep-centers. We have achieved the first tunnel diodes with which specifically utilize deep-levels in low-temperature-grown (LTG) GaAs. Our devices show the largest ever peak current density in a GaAs tunnel diode at room temperature. Our devices also show significant room-temperature peak-to-valley current ratios. The shape of the current-voltage characteristic and the properties of the optical emission enable us to determine the peak and valley transport mechanisms.

Online UV-visible spectroscopy and multivariate curve resolution as powerful tool for model-free investigation of laccase-catalysed oxidation.

PubMed

Kandelbauer, A; Kessler, W; Kessler, R W

2008-03-01

The laccase-catalysed transformation of indigo carmine (IC) with and without a redox active mediator was studied using online UV-visible spectroscopy. Deconvolution of the mixture spectra obtained during the reaction was performed on a model-free basis using multivariate curve resolution (MCR). Thereby, the time courses of educts, products, and reaction intermediates involved in the transformation were reconstructed without prior mechanistic assumptions. Furthermore, the spectral signature of a reactive intermediate which could not have been detected by a classical hard-modelling approach was extracted from the chemometric analysis. The findings suggest that the combined use of UV-visible spectroscopy and MCR may lead to unexpectedly deep mechanistic evidence otherwise buried in the experimental data. Thus, although rather an unspecific method, UV-visible spectroscopy can prove useful in the monitoring of chemical reactions when combined with MCR. This offers a wide range of chemists a cheap and readily available, highly sensitive tool for chemical reaction online monitoring.

Growth control and design principles of self-assembled quantum dot multiple layer structures for photodetector applications

NASA Astrophysics Data System (ADS)

Asano, Tetsuya

Self-assembled quantum dots (SAQDs) formed by lattice-mismatch strain-driven epitaxy are currently the most advanced nanostructure-based platform for high performance optoelectronic applications such as lasers and photodetectors. While the QD lasers have realized the best performance in terms of threshold current and temperature stability, the performance of QD photodetectors (QDIPs) has not surpassed that of quantum well (QW) photodetectors. This is because the requirement of maximal photon absorption for photodetectors poses the challenge of forming an appropriately-doped large number of uniform multiple SAQD (MQD) layers with acceptable structural defect (dislocation etc.) density. This dissertation addresses this challenge and, through a combination of innovative approach to control of defects in MQD growth and judicious placement of SAQDs in a resonant cavity, shows that SAQD based quantum dot infrared photodetectors (QDIPs) can be made competitive with their quantum well counterparts. Specifically, the following major elements were accomplished: (i) the molecular beam epitaxy (MBE) growth of dislocation-free and uniform InAs/InAlGaAs/GaAs MQD strained structures up to 20-period, (ii) temperature-dependent photo- and dark-current based analysis of the electron density distribution inside the MQD structures for various doping schemes, (iii) deep level transient spectroscopy based identification of growth procedure dependent deleterious deep traps in SAQD structures and their reduction, and (iv) the use of an appropriately designed resonant cavity (RC) and judicious placement of the SAQD layers for maximal enhancement of photon absorption to realize over an order of magnitude enhancement in QDIP detectivity. The lattermost demonstration indicates that implementation of the growth approach and resonant cavity strategy developed here while utilizing the currently demonstrated MIR and LWIR QDIPs with detectivities > 10 10 cmHz1/2/W at ˜ 77 K will enable RC-QDIP with detectivites > 1011 cmHz1/2/W that become competitive with other photodetector technologies in the mid IR (3 -- 5 mum) and long wavelength IR (8 -- 12 mum) ranges with the added advantage of materials stability and normal incidence sensitivity. Extended defect-free and size-uniform MQD structures of shallow InAs on GaAs (001) SAQDs capped with In0.15Ga0.85As strain relief layers and separated by GaAs spacer layer were grown up to 20 periods employing a judicious combination of MBE and migration enhanced epitaxy (MEE) techniques and examined by detailed transmission electron microscopy studies to reveal the absence of detectable extended defects (dislocation density < ˜ 107 /cm2). Photoluminescence studies revealed high optical quality. As our focus was on mid-infrared detectors, the MQD structures were grown in n (GaAs) -- i (MQD) -- n (GaAs) structures providing electron occupancy in at least the quantum confined ground energy states of the SAQDs and thus photodetection based upon transitions to electron excited states. Bias and temperature-dependent dark and photocurrent measurements were carried out for a variety of doping profiles and the electron density spatial distribution was determined from the resulting band bending profiles. It is revealed that almost no free electrons are present in the middle SAQD layers in the 10-period and 20-period n--i--n QDIP structures, indicating the existence of a high density (˜1015/cm3) of negative charges which can be attributed to electrons trapped in deep levels. To examine the nature of these deep traps, samples suitable for deep level transient spectroscopy measurement were synthesized and examined. These studies, carried out for the first time for SAQDs, revealed that the deep traps are dominantly present in the GaAs overgrowth layers grown at 500°C by MBE. For structures involving GaAs overgrowths using MEE at temperatures as low as 350°C, the deep trap density in the GaAs overgrowth layer was found to be significantly reduced by factor of ˜ 20. Thus, employing MEE growth for GaAs spacer layers in n--i(20-period MQD)-- n QDIP structures, electrons could be provided to all the SAQDs owing to the significantly reduced deep trap density. Finally, for enhancement of the incident photon absorption, we designed and fabricated asymmetric Fabry-Perot resonant cavity-enhanced QDIPs. For effective enhancement, SAQDs with a narrow photoresponse in the 3 -- 5 mum infrared regime were realized utilizing [(AlAs)1(GaAs)4]4 short-period superlattices as the confining barrier layers. Incorporating such SAQDs in RC-QDIPs, we successfully demonstrated ˜ 10 times enhancement of the QDIP detectivity. As stated above, this makes RC-QDIPs containing QDIPs with the currently demonstrated detectivities of ˜ 1010 cmHz 1/2/W at ˜ 77 K competitive with other IR photodetector technologies.

Effect of pressure-assisted thermal annealing on the optical properties of ZnO thin films.

PubMed

Berger, Danielle; Kubaski, Evaldo Toniolo; Sequinel, Thiago; da Silva, Renata Martins; Tebcherani, Sergio Mazurek; Varela, José Arana

2013-01-01

ZnO thin films were prepared by the polymeric precursor method. The films were deposited on silicon substrates using the spin-coating technique, and were annealed at 330 °C for 32 h under pressure-assisted thermal annealing and under ambient pressure. Their structural and optical properties were characterized, and the phases formed were identified by X-ray diffraction. No secondary phase was detected. The ZnO thin films were also characterized by field-emission scanning electron microscopy, Fourier transform infrared spectroscopy, photoluminescence and ultraviolet emission intensity measurements. The effect of pressure on these thin films modifies the active defects that cause the recombination of deep level states located inside the band gap that emit yellow-green (575 nm) and orange (645 nm) photoluminescence. Copyright © 2012 John Wiley & Sons, Ltd.

A narrow-band injection-seeded pulsed titanium:sapphire oscillator-amplifier system with on-line chirp analysis for high-resolution spectroscopy.

PubMed

Hannemann, S; van Duijn, E-J; Ubachs, W

2007-10-01

A narrow-band tunable injection-seeded pulsed titanium:sapphire laser system has been developed for application in high-resolution spectroscopic studies at the fundamental wavelengths in the near infrared as well as in the ultraviolet, deep ultraviolet, and extreme ultraviolet after upconversion. Special focus is on the quantitative assessment of the frequency characteristics of the oscillator-amplifier system on a pulse-to-pulse basis. Frequency offsets between continuous-wave seed light and the pulsed output are measured as well as linear chirps attributed mainly to mode pulling effects in the oscillator cavity. Operational conditions of the laser are found in which these offset and chirp effects are minimal. Absolute frequency calibration at the megahertz level of accuracy is demonstrated on various atomic and molecular resonance lines.

Application Of Optical Processing For Growth Of Silicon Dioxide

DOEpatents

Sopori, Bhushan L.

1997-06-17

A process for producing a silicon dioxide film on a surface of a silicon substrate. The process comprises illuminating a silicon substrate in a substantially pure oxygen atmosphere with a broad spectrum of visible and infrared light at an optical power density of from about 3 watts/cm.sup.2 to about 6 watts/cm.sup.2 for a time period sufficient to produce a silicon dioxide film on the surface of the silicon substrate. An optimum optical power density is about 4 watts/cm.sup.2 for growth of a 100.ANG.-300.ANG. film at a resultant temperature of about 400.degree. C. Deep level transient spectroscopy analysis detects no measurable impurities introduced into the silicon substrate during silicon oxide production and shows the interface state density at the SiO.sub.2 /Si interface to be very low.

Development of high-efficiency solar cells on silicon web

NASA Technical Reports Server (NTRS)

Meier, D. L.

1986-01-01

Achievement of higher efficiency cells by directing efforts toward identifying carrier loss mechanisms; design of cell structures; and development of processing techniques are described. Use of techniques such as deep-level transient spectroscopy (DLTS), laser-beam-induced current (LBIC), and transmission electron microscopy (TEM) indicated that dislocations in web material rather than twin planes were primarily responsible for limiting diffusion lengths in the web. Lifetimes and cell efficiencies can be improved from 19 to 120 microns, and 8 to 10.3% (no AR), respectively, by implanting hydrogen at 1500 eV and a beam current density of 2.0 mA/sq cm. Some of the processing improvements included use of a double-layer AR coating (ZnS and MgF2) and an addition of an aluminum back surface reflectors. Cells of more than 16% efficiency were achieved.

Dark energy and the inhomogeneous universe

NASA Astrophysics Data System (ADS)

Bull, Philip J.

2013-08-01

The accurate and safe diagnosis of breast cancer is a significant societal issue, with annual disease incidence of 48,000 women and around 370 men in the UK. Early diagnosis of the disease allows more conservative treatments and better patient outcomes. Microcalcifications in breast tissue are an important indicator for breast cancers, and often the only sign of their presence. Several studies have suggested that the type of calcification formed may act as a marker for malignancy and its presence may be of biological significance. In this work, breast calcifications are studied with FTIR, synchrotron FTIR, ATR FTIR, and Raman mapping to explore their disease specific composition. From a comparison between vibrational spectroscopy and routine staining procedures it becomes clear that calcium builds up prior to calcification formation. Raman and FTIR indicate the same size for calcifications and are in agreement with routine staining techniques. From the synchrotron FTIR measurements it can be proven that amide is present in the centre of the calcifications and the intensity of the bands depends on the pathology. Special attention is paid to the type of carbonate substitution in the calcifications relating to different pathology grades. In contrast to mammography, Raman spectroscopy has the capability to distinguish calcifications based on their chemical composition. The ultimate goal is to turn the acquired knowledge from the mapping studies into a clinical tool based on deep Raman spectroscopy. Deep Raman techniques have a considerable potential to reduce large numbers of normal biopsies, reduce the time delay between screening and diagnosis and therefore diminish patient anxiety. In order to achieve this, a deep Raman system is designed and after evaluation of its performance tested on buried calcification standards in porcine soft tissue and human mammary tissue. It is shown that, when the calcification is probed through tissue, the strong 960 cm-1 phosphate band can be used as a pseudo marker for carbonate substitution which is related to the pathology of the surrounding tissue. Furthermore, the first study in which human breast calcifications are measured in bulk tissue with a thickness of several millimetres to centimetres is presented. To date, measurements have been performed at 41 specimens with a thickness up to 25 mm. Measurements could be performed through skin and blue dye. The proposed deep Raman technique is promising for probing of calcifications through tissue but will need refinement before being adopted in hospitals.

Sea-level and deep-sea-temperature variability over the past 5.3 million years.

PubMed

Rohling, E J; Foster, G L; Grant, K M; Marino, G; Roberts, A P; Tamisiea, M E; Williams, F

2014-04-24

Ice volume (and hence sea level) and deep-sea temperature are key measures of global climate change. Sea level has been documented using several independent methods over the past 0.5 million years (Myr). Older periods, however, lack such independent validation; all existing records are related to deep-sea oxygen isotope (δ(18)O) data that are influenced by processes unrelated to sea level. For deep-sea temperature, only one continuous high-resolution (Mg/Ca-based) record exists, with related sea-level estimates, spanning the past 1.5 Myr. Here we present a novel sea-level reconstruction, with associated estimates of deep-sea temperature, which independently validates the previous 0-1.5 Myr reconstruction and extends it back to 5.3 Myr ago. We find that deep-sea temperature and sea level generally decreased through time, but distinctly out of synchrony, which is remarkable given the importance of ice-albedo feedbacks on the radiative forcing of climate. In particular, we observe a large temporal offset during the onset of Plio-Pleistocene ice ages, between a marked cooling step at 2.73 Myr ago and the first major glaciation at 2.15 Myr ago. Last, we tentatively infer that ice sheets may have grown largest during glacials with more modest reductions in deep-sea temperature.

Arduino Due based tool to facilitate in vivo two-photon excitation microscopy.

PubMed

Artoni, Pietro; Landi, Silvia; Sato, Sebastian Sulis; Luin, Stefano; Ratto, Gian Michele

2016-04-01

Two-photon excitation spectroscopy is a powerful technique for the characterization of the optical properties of genetically encoded and synthetic fluorescent molecules. Excitation spectroscopy requires tuning the wavelength of the Ti:sapphire laser while carefully monitoring the delivered power. To assist laser tuning and the control of delivered power, we developed an Arduino Due based tool for the automatic acquisition of high quality spectra. This tool is portable, fast, affordable and precise. It allowed studying the impact of scattering and of blood absorption on two-photon excitation light. In this way, we determined the wavelength-dependent deformation of excitation spectra occurring in deep tissues in vivo.

Picocyanobacteria and deep-ocean fluorescent dissolved organic matter share similar optical properties

NASA Astrophysics Data System (ADS)

Zhao, Zhao; Gonsior, Michael; Luek, Jenna; Timko, Stephen; Ianiri, Hope; Hertkorn, Norbert; Schmitt-Kopplin, Philippe; Fang, Xiaoting; Zeng, Qinglu; Jiao, Nianzhi; Chen, Feng

2017-05-01

Marine chromophoric dissolved organic matter (CDOM) and its related fluorescent components (FDOM), which are widely distributed but highly photobleached in the surface ocean, are critical in regulating light attenuation in the ocean. However, the origins of marine FDOM are still under investigation. Here we show that cultured picocyanobacteria, Synechococcus and Prochlorococcus, release FDOM that closely match the typical fluorescent signals found in oceanic environments. Picocyanobacterial FDOM also shows comparable apparent fluorescent quantum yields and undergoes similar photo-degradation behaviour when compared with deep-ocean FDOM, further strengthening the similarity between them. Ultrahigh-resolution mass spectrometry (MS) and nuclear magnetic resonance spectroscopy reveal abundant nitrogen-containing compounds in Synechococcus DOM, which may originate from degradation products of the fluorescent phycobilin pigments. Given the importance of picocyanobacteria in the global carbon cycle, our results indicate that picocyanobacteria are likely to be important sources of marine autochthonous FDOM, which may accumulate in the deep ocean.

Picocyanobacteria and deep-ocean fluorescent dissolved organic matter share similar optical properties

PubMed Central

Zhao, Zhao; Gonsior, Michael; Luek, Jenna; Timko, Stephen; Ianiri, Hope; Hertkorn, Norbert; Schmitt-Kopplin, Philippe; Fang, Xiaoting; Zeng, Qinglu; Jiao, Nianzhi; Chen, Feng

2017-01-01

Marine chromophoric dissolved organic matter (CDOM) and its related fluorescent components (FDOM), which are widely distributed but highly photobleached in the surface ocean, are critical in regulating light attenuation in the ocean. However, the origins of marine FDOM are still under investigation. Here we show that cultured picocyanobacteria, Synechococcus and Prochlorococcus, release FDOM that closely match the typical fluorescent signals found in oceanic environments. Picocyanobacterial FDOM also shows comparable apparent fluorescent quantum yields and undergoes similar photo-degradation behaviour when compared with deep-ocean FDOM, further strengthening the similarity between them. Ultrahigh-resolution mass spectrometry (MS) and nuclear magnetic resonance spectroscopy reveal abundant nitrogen-containing compounds in Synechococcus DOM, which may originate from degradation products of the fluorescent phycobilin pigments. Given the importance of picocyanobacteria in the global carbon cycle, our results indicate that picocyanobacteria are likely to be important sources of marine autochthonous FDOM, which may accumulate in the deep ocean. PMID:28513605

Phonon-assisted changes in charge states of deep level defects in germanium

NASA Astrophysics Data System (ADS)

Markevich, A. V.; Litvinov, V. V.; Emtsev, V. V.; Markevich, V. P.; Peaker, A. R.

2006-04-01

Electronic processes associated with changes in the charge states of the vacancy-oxygen center (VO or A center) and vacancy-group-V-impurity atom (P, As, Sb or Bi) pairs (E centers) in irradiated germanium crystals have been studied using deep level transient spectroscopy (DLTS), high-resolution Laplace DLTS and Hall effect measurements. It is found that the electron emission and capture processes related to transitions between the doubly and the singly negatively charged states of the A center and the E centers in Ge are phonon-assisted, i.e., they are accompanied by significant vibrations and re-arrangements of atoms in the vicinity of the defects. Manifestations of the phonon involvements are: (i) temperature-dependent electron capture cross-sections which are well described in the frame of the multi-phonon-assisted capture model; (ii) large changes in entropy related to the ionization of the defects and, associated with these, temperature-dependent positions of energy levels; and (iii) electron emission via phonon-assisted tunneling upon the application of electric field. These effects have been considered in detail for the vacancy-oxygen and the vacancy-donor complexes. On the basis of a combined analysis of the electronic processes a configuration-coordinate diagram of the acceptor states of the A and E centers is plotted. It is found that changes in the entropy of ionization and the energy for electron emission for these traps follow the empirical Meyer-Neldel rule. A model based on multi-phonon-assisted carrier emission from defects is adapted for the explanation of the origin of this rule for the case of electronic processes in Ge.

The Rapid Detection of Single Bacterial Cells by Deep UV Micro Raman Spectroscopy.

DTIC Science & Technology

1992-04-01

Saltzman and C.T. Gregg, Appl. Environ. Microbiol. 44, 1081 (1982). 14. D.’. Mc Greggor, W.K. Grace and G.C. Salzman, in "Rapid Methods and...was used by Dr. Marcus Peter of the Dana -Farber Cancer Institute. During that period he came to our laboratories weekly to study GTP- binding

A Comparison of Point Defects in Cd 1-xZn xTe 1-ySe y Crystals Grown by Bridgman and Traveling Heater Methods

DOE PAGES

Gul, R.; Roy, U. N.; Camarda, G. S.; ...

2017-03-28

In this study, the properties of point defects in Cd 1–xZn xTe 1–ySe y (CZTS) radiation detectors are characterized using deep-level transient spectroscopy and compared between materials grown using two different methods, the Bridgman method and the traveling heater method. The nature of the traps was analyzed in terms of their capture cross-sections and trap concentrations, as well as their effects on the measured charge-carrier trapping and de-trapping times, and then compared for the two growth techniques. The results revealed that Se addition to CdZnTe can reduce the V Cd – concentration. In Travelling Heater Method (THM) and Bridgman Methodmore » (BM) grown CZTS detectors, besides a few similarities in the shallow and medium energy traps, there were major differences in the deep traps. It was observed that the excess-Te and lower growth-temperature conditions in THM-grown CZTS led to a complete compensation of V Cd – and two additional traps (attributed to Te i – and Te Cd ++ appearing at around E v + 0.26 eV and E c – 0.78 eV, respectively). The 1.1-eV deep trap related to large Te secondary phases was a dominant trap in the BM-grown CZTS crystals. In addition to i-DLTS data, the effects of point defects induced due to different processing techniques on the detector's resistivity, spectral response to gammas, and μτ product were determined.« less

A Comparison of Point Defects in Cd 1-xZn xTe 1-ySe y Crystals Grown by Bridgman and Traveling Heater Methods

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

Gul, R.; Roy, U. N.; Camarda, G. S.

In this study, the properties of point defects in Cd 1–xZn xTe 1–ySe y (CZTS) radiation detectors are characterized using deep-level transient spectroscopy and compared between materials grown using two different methods, the Bridgman method and the traveling heater method. The nature of the traps was analyzed in terms of their capture cross-sections and trap concentrations, as well as their effects on the measured charge-carrier trapping and de-trapping times, and then compared for the two growth techniques. The results revealed that Se addition to CdZnTe can reduce the V Cd – concentration. In Travelling Heater Method (THM) and Bridgman Methodmore » (BM) grown CZTS detectors, besides a few similarities in the shallow and medium energy traps, there were major differences in the deep traps. It was observed that the excess-Te and lower growth-temperature conditions in THM-grown CZTS led to a complete compensation of V Cd – and two additional traps (attributed to Te i – and Te Cd ++ appearing at around E v + 0.26 eV and E c – 0.78 eV, respectively). The 1.1-eV deep trap related to large Te secondary phases was a dominant trap in the BM-grown CZTS crystals. In addition to i-DLTS data, the effects of point defects induced due to different processing techniques on the detector's resistivity, spectral response to gammas, and μτ product were determined.« less

Deep Learning and Developmental Learning: Emergence of Fine-to-Coarse Conceptual Categories at Layers of Deep Belief Network.

PubMed

Sadeghi, Zahra

2016-09-01

In this paper, I investigate conceptual categories derived from developmental processing in a deep neural network. The similarity matrices of deep representation at each layer of neural network are computed and compared with their raw representation. While the clusters generated by raw representation stand at the basic level of abstraction, conceptual categories obtained from deep representation shows a bottom-up transition procedure. Results demonstrate a developmental course of learning from specific to general level of abstraction through learned layers of representations in a deep belief network. © The Author(s) 2016.

Analysis of Deep and Shallow Traps in Semi-Insulating CdZnTe

DOE PAGES

Kim, Kihyun; Yoon, Yongsu; James, Ralph B.

2018-03-13

Trap levels which are deep or shallow play an important role in the electrical and the optical properties of a semiconductor; thus, a trap level analysis is very important in most semiconductor devices. Deep-level defects in CdZnTe are essential in Fermi level pinning at the middle of the bandgap and are responsible for incomplete charge collection and polarization effects. However, a deep level analysis in semi-insulating CdZnTe (CZT) is very difficult. Theoretical capacitance calculation for a metal/insulator/CZT (MIS) device with deep-level defects exhibits inflection points when the donor/acceptor level crosses the Fermi level in the surface-charge layer (SCL). Three CZTmore » samples with different resistivities, 2 × 10 4 (n-type), 2 × 10 6 (p-type), and 2 × 10 10 (p-type) Ω·cm, were used in fabricating the MIS devices. These devices showed several peaks in their capacitance measurements due to upward/downward band bending that depend on the surface potential. In conclusion, theoretical and experimental capacitance measurements were in agreement, except in the fully compensated case.« less

Analysis of Deep and Shallow Traps in Semi-Insulating CdZnTe

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

Kim, Kihyun; Yoon, Yongsu; James, Ralph B.

Trap levels which are deep or shallow play an important role in the electrical and the optical properties of a semiconductor; thus, a trap level analysis is very important in most semiconductor devices. Deep-level defects in CdZnTe are essential in Fermi level pinning at the middle of the bandgap and are responsible for incomplete charge collection and polarization effects. However, a deep level analysis in semi-insulating CdZnTe (CZT) is very difficult. Theoretical capacitance calculation for a metal/insulator/CZT (MIS) device with deep-level defects exhibits inflection points when the donor/acceptor level crosses the Fermi level in the surface-charge layer (SCL). Three CZTmore » samples with different resistivities, 2 × 10 4 (n-type), 2 × 10 6 (p-type), and 2 × 10 10 (p-type) Ω·cm, were used in fabricating the MIS devices. These devices showed several peaks in their capacitance measurements due to upward/downward band bending that depend on the surface potential. In conclusion, theoretical and experimental capacitance measurements were in agreement, except in the fully compensated case.« less

Unraveling the mechanism of ultraviolet-induced optical gating in Zn1-x Mg x O nanocrystal solid solution field effect transistors

NASA Astrophysics Data System (ADS)

Kim, Youngjun; Cho, Seongeun; Park, Byoungnam

2018-03-01

We report ultraviolet (UV)-induced optical gating in a Zn1-x Mg x O nanocrystal solid solution (NCSS) field effect transistor (FET) through a systematic study in which UV-induced charge transport properties are probed as a function of Mg composition. Change in the electrical properties of Zn1-x Mg x O NCSS associated with electronic traps is investigated by field effect-modulated current-voltage characteristic curves in the dark and under illumination. Under UV illumination, significant threshold voltage shift to a more negative value in an n-channel Zn1-x Mg x O NCSS FET is observed. Importantly, as the Mg composition increases, the effect of UV illumination on the threshold voltage shift is alleviated. We found that threshold voltage shift as a function of Mg composition in the dark and under illumination is due to difference in the deep trap density in the Zn1-x Mg x O NCSS. This is supported by Mg composition dependent photoluminescence intensity in the visible range and reduced FET mobility with Mg addition. The presence of the deep traps and the corresponding trap energy levels in the Zn1-x Mg x O NCSS are ensured by photoelectron spectroscopy in air.

Theory of Semiconducting Superlattices and Microstructures

DTIC Science & Technology

1992-03-01

theory elucidated the various factors affecting deep levels, sets forth the conditions for obtaining shallow-deep transitions, and predicts that Si (a...theory elucidates the various factors affecting deep levels, sets forth the conditions for obtaining shallow-deep transitions, and predicts that Si (a...ondenotes the anion vacancy, which can be thought any quantitative theoretical factor are theof as originating from Column-O of the Period strengths of

Laser techniques for spectroscopy of core-excited atomic levels

NASA Technical Reports Server (NTRS)

Harris, S. E.; Young, J. F.; Falcone, R. W.; Rothenberg, J. E.; Willison, J. R.

1982-01-01

We discuss three techniques which allow the use of tunable lasers for high resolution and picosecond time scale spectroscopy of core-excited atomic levels. These are: anti-Stokes absorption spectroscopy, laser induced emission from metastable levels, and laser designation of selected core-excited levels.

[Application of in situ cryogenic Raman spectroscopy to analysis of fluid inclusions in reservoirs].

PubMed

Chen, Yong; Lin, Cheng-yan; Yu, Wen-quan; Zheng, Jie; Wang, Ai-guo

2010-01-01

Identification of salts is a principal problem for analysis of fluid inclusions in reservoirs. The fluid inclusions from deep natural gas reservoirs in Minfeng sub-sag were analyzed by in situ cryogenic Raman spectroscopy. The type of fluid inclusions was identified by Raman spectroscopy at room temperature. The Raman spectra show that the inclusions contain methane-bearing brine aqueous liquids. The fluid inclusions were analyzed at -180 degrees C by in situ cryogenic Raman spectroscopy. The spectra show that inclusions contain three salts, namely NaCl2, CaCl2 and MgCl2. Sodium chloride is most salt component, coexisting with small calcium chloride and little magnesium chloride. The origin of fluids in inclusions was explained by analysis of the process of sedimentation and diagenesis. The mechanism of diagenesis in reservoirs was also given in this paper. The results of this study indicate that in situ cryogenic Raman spectroscopy is an available method to get the composition of fluid inclusions in reservoirs. Based on the analysis of fluid inclusions in reservoirs by in situ cryogenic Raman spectroscopy with combination of the history of sedimentation and diagenesis, the authors can give important evidence for the type and mechanism of diagenesis in reservoirs.

Comparative evaluation of differential laser-induced perturbation spectroscopy as a technique to discriminate emerging skin pathology

NASA Astrophysics Data System (ADS)

Kozikowski, Raymond T.; Smith, Sarah E.; Lee, Jennifer A.; Castleman, William L.; Sorg, Brian S.; Hahn, David W.

2012-06-01

Fluorescence spectroscopy has been widely investigated as a technique for identifying pathological tissue; however, unrelated subject-to-subject variations in spectra complicate data analysis and interpretation. We describe and evaluate a new biosensing technique, differential laser-induced perturbation spectroscopy (DLIPS), based on deep ultraviolet (UV) photochemical perturbation in combination with difference spectroscopy. This technique combines sequential fluorescence probing (pre- and post-perturbation) with sub-ablative UV perturbation and difference spectroscopy to provide a new spectral dimension, facilitating two improvements over fluorescence spectroscopy. First, the differential technique eliminates significant variations in absolute fluorescence response within subject populations. Second, UV perturbations alter the extracellular matrix (ECM), directly coupling the DLIPS response to the biological structure. Improved biosensing with DLIPS is demonstrated in vivo in a murine model of chemically induced skin lesion development. Component loading analysis of the data indicates that the DLIPS technique couples to structural proteins in the ECM. Analysis of variance shows that DLIPS has a significant response to emerging pathology as opposed to other population differences. An optimal likelihood ratio classifier for the DLIPS dataset shows that this technique holds promise for improved diagnosis of epithelial pathology. Results further indicate that DLIPS may improve diagnosis of tissue by augmenting fluorescence spectra (i.e. orthogonal sensing).

IBS-like Symptoms in Patients with Ulcerative Colitis in Deep Remission Are Associated with Increased Levels of Serum Cytokines and Poor Psychological Well-being.

PubMed

Jonefjäll, Börje; Öhman, Lena; Simrén, Magnus; Strid, Hans

2016-11-01

Gastrointestinal symptoms (GI) compatible with irritable bowel syndrome (IBS) are common in patients with ulcerative colitis (UC) in remission. The causes of these symptoms remain to be clarified. Our aim was to investigate prevalence and factors associated with IBS-like symptoms in patients with UC in deep remission. We included 298 patients with UC and used Mayo score, sigmoidoscopy, and fecal calprotectin to define deep remission versus active disease. Presence of IBS-like symptoms according to the Rome III criteria, severity of GI, extraintestinal and psychological symptoms, stress levels, and quality of life were measured with validated questionnaires. Serum cytokines and high-sensitive C-reactive peptide were determined. The criteria for deep remission was fulfilled by 132 patients (44%) and 24 of these fulfilled the Rome III criteria for IBS (18%). Patients with UC in deep remission with IBS-like symptoms had comparable levels of GI symptoms, non-GI somatic symptoms, and quality of life as patients with active UC. The patients with UC in deep remission with IBS-like symptoms had similar levels of fecal calprotectin as patients in deep remission without IBS-like symptoms (18 versus 31 μg/g, P = 0.11), but higher levels of serum cytokines (interleukin [IL]-1β, IL-6, IL-13, IL-10 and IL-8, P < 0.05) and higher levels of anxiety (P < 0.001), depression (P = 0.02) and perceived stress (P = 0.03). IBS-like symptoms in patients with UC in deep remission are common, but not as prevalent as previously reported. Poor psychological well-being and increased serum cytokine levels, but not colonic low-grade inflammation, were associated with IBS-like symptoms.

Levels-of-processing effects on a task of olfactory naming.

PubMed

Royet, Jean-Pierre; Koenig, Olivier; Paugam-Moisy, Helene; Puzenat, Didier; Chasse, Jean-Luc

2004-02-01

The effects of odor processing were investigated at various analytical levels, from simple sensory analysis to deep or semantic analysis, on a subsequent task of odor naming. Students (106 women, 23.6 +/- 5.5 yr. old; 65 men, 25.1 +/- 7.1 yr. old) were tested. The experimental procedure included two successive sessions, a first session to characterize a set of 30 odors with criteria that used various depths of processing and a second session to name the odors as quickly as possible. Four processing conditions rated the odors using descriptors before naming the odor. The control condition did not rate the odors before naming. The processing conditions were based on lower-level olfactory judgments (superficial processing), higher-level olfactory-gustatory-somesthetic judgments (deep processing), and higher-level nonolfactory judgments (Deep-Control processing, with subjects rating odors with auditory and visual descriptors). One experimental condition successively grouped lower- and higher-level olfactory judgments (Superficial-Deep processing). A naming index which depended on response accuracy and the subjects' response time were calculated. Odor naming was modified for 18 out of 30 odorants as a function of the level of processing required. For 94.5% of significant variations, the scores for odor naming were higher following those tasks for which it was hypothesized that the necessary olfactory processing was carried out at a deeper level. Performance in the naming task was progressively improved as follows: no rating of odors, then superficial, deep-control, deep, and superficial-deep processings. These data show that the deepest olfactory encoding was later associated with progressively higher performance in naming.

The origins of near band-edge transitions in hexagonal boron nitride epilayers

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

Du, X. Z.; Li, J.; Lin, J. Y.

2016-02-01

Photoluminescence spectroscopy has been employed to probe the near band-edge transitions in hexagonal BN (h-BN) epilayers synthesized under varying ammonia flow rates. The results suggest that the quasi-donor-acceptor pair emission line at 5.3 eV is due to the transition between the nitrogen vacancy and a deep acceptor, whereas the 5.5 eV emission line is due to the recombination of an exciton bound to a deep acceptor formed by carbon impurity occupying the nitrogen site. By growing h-BN under high ammonia flow rates, nitrogen vacancy related peaks can be eliminated and epilayers exhibiting pure free exciton emission have been obtained.

A critical review on the carrier dynamics in 2D layered materials investigated using THz spectroscopy

NASA Astrophysics Data System (ADS)

Lu, Junpeng; Liu, Hongwei

2018-01-01

Accurately illustrating the photocarrier dynamics and photoelectrical properties of two dimensional (2D) materials is crucial in the development of 2D material-based optoelectronic devices. Considering this requirement, terahertz (THz) spectroscopy has emerged as a befitting characterization tool to provide deep insights into the carrier dynamics and measurements of the electrical/photoelectrical conductivity of 2D materials. THz spectroscopic measurements would provide information of transient behaviors of carriers with high accuracy in a nondestructive and noncontact manner. In this article, we present a comprehensive review on recent research efforts on investigations of 2D materials of graphene and transition metal dichalcogenides (TMDs) using THz spectroscopy. A brief introduction of THz time-domain spectroscopy (THz-TDS) and optical pump-THz probe spectroscopy (OPTP) is provided. The characterization of the electron transport of graphene at equilibrium state and transient behavior at non-equilibrium state is reviewed. We also review the characterizations of TMDs including MoS2 and WSe2. Finally, we conclude the recent reports and give a prospect on how THz characterizations would guide the design and optimization of 2D material-based optoelectronic devices.

Raman Spectroscopy: an essential tool for future IODP expeditions

NASA Astrophysics Data System (ADS)

Andò, Sergio; Garzanti, Eduardo; Kulhanek, Denise K.

2016-04-01

The scientific drilling of oceanic sedimentary sequences plays a fundamental part in provenance studies, paleoclimate recostructions, and source-to-sink investigations (e.g., France-Lanord et al., 2015; Pandey et al., 2015). When studying oceanic deposits, Raman spectroscopy can and does represent an essential flexible tool for the multidisciplinary approach necessary to integrate the insight provided by different disciplines. This new user-friendly technique opens up an innovative avenue to study in real time the composition of detrital mineral grains of any origin, complementing traditional methods of provenance analysis (e.g., sedimentary petrography, heavy minerals; Andò and Garzanti, 2014). Raman spectra can readily reveal the chemistry of foraminiferal tests, nannofossils and other biogenic debris for the study of ecosystem evolution and paleoclimate, or the Ca/Mg ratio in biogenic or terrigenous carbonates for geological or marine biological applications and oil exploration (Borromeo et al., 2015). For the study of pelagic or turbiditic muds, which represent the bulk of the deep-marine sedimentary record, Raman spectroscopy allows us to identify silt-sized grains down to the size of a few microns with the same precision level required in quantitative provenance analysis of sand-sized sediments (Andò et al., 2011). Silt and siltstone also represent a very conspicuous part of the stratigraphic record onshore and usually preserve original mineralogical assemblages better than more permeable interbedded sand and sandstone (Blatt, 1985). Raman spectra can be obtained on sample volumes of only a few cubic microns by a confocal micro-Raman coupled with a standard polarizing light microscope using a 50× objective. The size of this apparatus can be easily placed onboard an IODP vessel to provide crucial information and quickly solve identification problems for the benefit of a wide range of scientists during future expeditions. Cited references Andò, S., Vignola, P., Garzanti, E., 2011. Raman counting: a new method to determine provenance of silt. Rend. Fis. Acc. Lincei, 22: 327-347. Andò, S., Garzanti, E., 2014. Raman spectroscopy in heavy-mineral studies. Geological Society, London, Special Publications, 386 (1), 395-412. Blatt, H., (1985). Provenance studies and mudrocks. Journal of Sedimentary Research, 55 (1), 69-75. Borromeo, L., Zimmermann, U., Andò, S., Coletti, G., Bersani, D., Basso, D., Gentile, P., Garzanti, E., 2015. Raman Spectroscopy as a tool for magnesium estimation in Mg-calcite. Periodico di Mineralogia , ECMS, 35-36. France-Lanord, C., Spiess, V., Klaus, A., and the Expedition 354 Scientists, 2015. IODP, Exp. 354, Preliminary Report: Bengal Fan, Neogene and late Paleogene record of Himalayan orogeny and climate: a transect across the Middle Bengal Fan. Pandey, D.K., Clift, P.D., Kulhanek, D.K. and the Expedition 355 Scientists, 2015. IODP, Exp. 355, Preliminary Report: Arabian Sea Monsoon, Deep sea drilling in the Arabian Sea: constraining tectonic-monsoon interactions in South Asia.

Detection of Explosives Using Differential Laser-Induced Perturbation Spectroscopy with a Raman-based Probe.

PubMed

Oztekin, Erman K; Burton, Dallas J; Hahn, David W

2016-04-01

Explosives detection is carried out with a novel spectral analysis technique referred to as differential laser-induced perturbation spectroscopy (DLIPS) on thin films of TNT, RDX, HMX, and PETN. The utility of Raman spectroscopy for detection of explosives is enhanced by inducing deep ultraviolet laser perturbation on molecular structures in combination with a differential Raman sensing scheme. Principal components analysis (PCA) is used to quantify the DLIPS method as benchmarked against a traditional Raman scattering probe, and the related photo-induced effects on the molecular structure of the targeted explosives are discussed in detail. Finally, unique detection is observed with TNT samples deposited on commonly available background substrates of nylon and polyester. Overall, the data support DLIPS as a noninvasive method that is promising for screening explosives in real-world environments and backgrounds. © The Author(s) 2016.

Deep Restricted Kernel Machines Using Conjugate Feature Duality.

PubMed

Suykens, Johan A K

2017-08-01

The aim of this letter is to propose a theory of deep restricted kernel machines offering new foundations for deep learning with kernel machines. From the viewpoint of deep learning, it is partially related to restricted Boltzmann machines, which are characterized by visible and hidden units in a bipartite graph without hidden-to-hidden connections and deep learning extensions as deep belief networks and deep Boltzmann machines. From the viewpoint of kernel machines, it includes least squares support vector machines for classification and regression, kernel principal component analysis (PCA), matrix singular value decomposition, and Parzen-type models. A key element is to first characterize these kernel machines in terms of so-called conjugate feature duality, yielding a representation with visible and hidden units. It is shown how this is related to the energy form in restricted Boltzmann machines, with continuous variables in a nonprobabilistic setting. In this new framework of so-called restricted kernel machine (RKM) representations, the dual variables correspond to hidden features. Deep RKM are obtained by coupling the RKMs. The method is illustrated for deep RKM, consisting of three levels with a least squares support vector machine regression level and two kernel PCA levels. In its primal form also deep feedforward neural networks can be trained within this framework.

Sub-100 nm gold nanohole-enhanced Raman scattering on flexible PDMS sheets.

PubMed

Lee, Seunghyun; Ongko, Andry; Kim, Ho Young; Yim, Sang-Gu; Jeon, Geumhye; Jeong, Hee Jin; Lee, Seungwoo; Kwak, Minseok; Yang, Seung Yun

2016-08-05

Surface-enhanced Raman spectroscopy (SERS) is a highly sensitive vibrational spectroscopy technique enabling detection of multiple analytes at the molecular level in a nondestructive and rapid manner. In this work, we introduce a new approach to fabricate deep subwavelength-scaled (sub-100 nm) metallic nanohole arrays (quasi-3D metallic nanoholes) on flexible and highly efficient SERS substrates. Target structures have been fabricated using a two-step process consisting of (i) direct pattern transfer of spin-coated polymer films onto polydimethylsiloxane (PDMS) substrates by plasma etching with transferred anodic aluminum oxide masks, and (ii) producing SERS-active substrates by functionalization of the etched polymeric films followed by Au deposition. Such an all-dry, top-down lithographic approach enables on-demand patterning of SERS-active metallic nanoholes with high structural fidelity even onto flexible and stretchable substrates, thus making possible multiple sensing modes in a versatile fashion. For example, metallic nanoholes on flexible PDMS substrates are highly amenable to their integration with curved glass sticks, which can be used in optical fiber-integrated SERS systems. Au surfaces immobilized by probe DNA molecules show a selective enhancement of Raman scattering with Cy5-labeled complementary DNA (as compared to flat Au surfaces), demonstrating the potential of using the quasi-3D Au nanohole arrays for bio-sensing applications.

Sub-100 nm gold nanohole-enhanced Raman scattering on flexible PDMS sheets

NASA Astrophysics Data System (ADS)

Lee, Seunghyun; Ongko, Andry; Kim, Ho Young; Yim, Sang-Gu; Jeon, Geumhye; Jeong, Hee Jin; Lee, Seungwoo; Kwak, Minseok; Yang, Seung Yun

2016-08-01

Surface-enhanced Raman spectroscopy (SERS) is a highly sensitive vibrational spectroscopy technique enabling detection of multiple analytes at the molecular level in a nondestructive and rapid manner. In this work, we introduce a new approach to fabricate deep subwavelength-scaled (sub-100 nm) metallic nanohole arrays (quasi-3D metallic nanoholes) on flexible and highly efficient SERS substrates. Target structures have been fabricated using a two-step process consisting of (i) direct pattern transfer of spin-coated polymer films onto polydimethylsiloxane (PDMS) substrates by plasma etching with transferred anodic aluminum oxide masks, and (ii) producing SERS-active substrates by functionalization of the etched polymeric films followed by Au deposition. Such an all-dry, top-down lithographic approach enables on-demand patterning of SERS-active metallic nanoholes with high structural fidelity even onto flexible and stretchable substrates, thus making possible multiple sensing modes in a versatile fashion. For example, metallic nanoholes on flexible PDMS substrates are highly amenable to their integration with curved glass sticks, which can be used in optical fiber-integrated SERS systems. Au surfaces immobilized by probe DNA molecules show a selective enhancement of Raman scattering with Cy5-labeled complementary DNA (as compared to flat Au surfaces), demonstrating the potential of using the quasi-3D Au nanohole arrays for bio-sensing applications.

Superconductivity across Lifshitz transition and anomalous insulating state in surface K-dosed (Li0.8Fe0.2OH)FeSe.

PubMed

Ren, Mingqiang; Yan, Yajun; Niu, Xiaohai; Tao, Ran; Hu, Die; Peng, Rui; Xie, Binping; Zhao, Jun; Zhang, Tong; Feng, Dong-Lai

2017-07-01

In iron-based superconductors, understanding the relation between superconductivity and electronic structure upon doping is crucial for exploring the pairing mechanism. Recently, it was found that, in iron selenide (FeSe), enhanced superconductivity ( T c of more than 40 K) can be achieved via electron doping, with the Fermi surface only comprising M-centered electron pockets. By using surface K dosing, scanning tunneling microscopy/spectroscopy, and angle-resolved photoemission spectroscopy, we studied the electronic structure and superconductivity of (Li 0.8 Fe 0.2 OH)FeSe in the deep electron-doped regime. We find that a Γ-centered electron band, which originally lies above the Fermi level ( E F ), can be continuously tuned to cross E F and contribute a new electron pocket at Γ. When this Lifshitz transition occurs, the superconductivity in the M-centered electron pocket is slightly suppressed, and a possible superconducting gap with a small size (up to ~5 meV) and a dome-like doping dependence is observed on the new Γ electron pocket. Upon further K dosing, the system eventually evolves into an insulating state. Our findings provide new clues to understand superconductivity versus Fermi surface topology and the correlation effect in FeSe-based superconductors.

Large-area silicon sheet task

NASA Technical Reports Server (NTRS)

Morrison, A. D.

1982-01-01

A set of computer models was used to define a growth system configuration that was then built and used to grow web with lower thermally generated stress. Aspects of research in the edge-defined film-fed growth (EFG) method of making Si ribbon are reported. A technique was developed to determine base resistivity and carrier lifetime in semicrystalline wafers. Automated growth of 150 kg of 15 cm-dia ingot material per crucible is reviewed. Scanning transmisson electron microscopy (STEM) and microprobe investigations of processed EFG ribbon are reported. The chemical composition of the large precipitates was studied. The structural arrangement and the electrical activity of distentions or close to the central twin plane in processed material were studied. The electrical and structural properties of grain boundaries in silicon are discussed. Temperature-dependence measurements of zero-bias conductance, a photoconductivity technique, and deep-level transient spectroscopy (DLTS) were developed. A grooving and staining technique, secondary ion mass spectroscopy, and EBIC measurements in scanning electron microscopy were used to study enhanced diffusion of phosphorus at grain boundaries in polycrystaline silicon. The fundamental mechanisms of abrasion and wear and the deformation of Si by a diamond in various fluid environments are described. The efficiency of solar cells made from EFG ribbon and Semix Inc. material is reported.

Superconductivity across Lifshitz transition and anomalous insulating state in surface K–dosed (Li0.8Fe0.2OH)FeSe

PubMed Central

Ren, Mingqiang; Yan, Yajun; Niu, Xiaohai; Tao, Ran; Hu, Die; Peng, Rui; Xie, Binping; Zhao, Jun; Zhang, Tong; Feng, Dong-Lai

2017-01-01

In iron-based superconductors, understanding the relation between superconductivity and electronic structure upon doping is crucial for exploring the pairing mechanism. Recently, it was found that, in iron selenide (FeSe), enhanced superconductivity (Tc of more than 40 K) can be achieved via electron doping, with the Fermi surface only comprising M-centered electron pockets. By using surface K dosing, scanning tunneling microscopy/spectroscopy, and angle-resolved photoemission spectroscopy, we studied the electronic structure and superconductivity of (Li0.8Fe0.2OH)FeSe in the deep electron-doped regime. We find that a Γ-centered electron band, which originally lies above the Fermi level (EF), can be continuously tuned to cross EF and contribute a new electron pocket at Γ. When this Lifshitz transition occurs, the superconductivity in the M-centered electron pocket is slightly suppressed, and a possible superconducting gap with a small size (up to ~5 meV) and a dome-like doping dependence is observed on the new Γ electron pocket. Upon further K dosing, the system eventually evolves into an insulating state. Our findings provide new clues to understand superconductivity versus Fermi surface topology and the correlation effect in FeSe-based superconductors. PMID:28740865

Infiltrated Zinc Oxide in Poly(methyl methacrylate): An Atomic Cycle Growth Study

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

Ocola, Leonidas E.; Connolly, Aine; Gosztola, David J.

We have investigated the growth of zinc oxide in a polymer matrix by sequential infiltration synthesis (SiS). The atomic cycle-by-cycle self-terminating reaction growth investigation was done using photoluminescence (PL), Raman, and X-ray photoemission spectroscopy (XPS). Results show clear differences between Zn atom configurations at the initial stages of growth. Mono Zn atoms (O-Zn and O-Zn-O) exhibit pure UV emission with little evidence of deep level oxygen vacancy states (VO). Dimer Zn atoms (O-Zn-O-Zn and O-Zn-O-Zn-O) show strong UV and visible PL emission from VO states 20 times greater than that from the mono Zn atom configuration. After three precursor cycles,more » the PL emission intensity drops significantly exhibiting first evidence of crystal formation as observed with Raman spectroscopy via the presence of longitudinal optical phonons. We also report a first confirmation of energy transfer between polymer and ZnO where the polymer absorbs light at 241 nm and emits at 360 nm, which coincides with the ZnO UV emission peak. Our work shows that ZnO dimers are unique ZnO configurations with high PL intensity, unique O1s oxidation states, and sub-10 ps absorption and decay, which are interesting properties for novel quantum material applications.« less

Infection

DTIC Science & Technology

2010-09-01

promote host tissue attachment and prevent sepsis represent new areas of scientific inquiry. Novel Ways to Detect Infection Swabs, needle aspiration, deep...chromosome, the bacteria emits light at 486-nm wavelength during normal bacteria respiration, and the amount of photons emitted is determined by the amount of...within 5 hours.3 Bacterial or fungal DNA is amplified by polymerase chain reaction and introduced into a mass spectroscopy by electrospray ionization

Fast, deep record length, time-resolved visible spectroscopy of plasmas using fiber grids

NASA Astrophysics Data System (ADS)

Brockington, Samuel; Case, Andrew; Cruz, Edward; Witherspoon, F. Douglas; Horton, Robert; Klauser, Ruth; Hwang, D. Q.

2016-10-01

HyperV Technologies is developing a fiber-coupled, deep-record-length, low-light camera head for performing high time resolution spectroscopy on visible emission from plasma events. New solid-state Silicon Photo-Multiplier (SiPM) chips are capable of single photon event detection and high speed data acquisition. By coupling the output of a spectrometer to an imaging fiber bundle connected to a bank of amplified SiPMs, time-resolved spectroscopic imagers of 100 to 1,000 pixels can be constructed. Target pixel performance is 10 Megaframes/sec with record lengths of up to 256,000 frames yielding 25.6 milliseconds of record at10 Megasamples/sec resolution. Pixel resolutions of 8 to 12 bits are pos- sible. Pixel pitch can be refined by using grids of 100 μm to 1000 μm diameter fibers. A prototype 32-pixel spectroscopic imager employing this technique was constructed and successfully tested at the University of California at Davis Compact Toroid Injection Experiment (CTIX) as a full demonstration of the concept. Experimental results will be dis-cussed, along with future plans for the Phase 2 project, and potential applications to plasma experiments . Work supported by USDOE SBIR Grant DE-SC0013801.

The Compton-thick AGN fraction from the deepest X-ray spectroscopy in the CDF-S

NASA Astrophysics Data System (ADS)

Corral, A.; Georgantopoulos, I.; Akylas, A.; Ranalli, P.

2017-10-01

Highly obscured AGN, especially Compton-thick (CT) AGN, likely play a key role in the galaxy-AGN co-evolution scenario. They would comprise the early stages of AGN activity, preceding the AGN-feedback/star-formation quenching phase, during which most of both the SMBH and galaxy growth take place. However, the actual CT fraction among the AGN population is still largely unconstrained. The most reliable way of confirming the obscured nature of an AGN by X-ray spectroscopy, but very deep observations are needed to extend local analyses to larger distances. We will present the X-ray spectral analysis of the deepest X-ray data obtained to date, the almost 7Ms observation of the Chandra Deep Field South. The unprecedented depth of this survey allow us to carry out reliable spectral analyses down to a flux limit of 10^{-16} erg cm^{-2} s^{-1} in the hard 2-8 keV band. Besides the new deeper X-ray data, our approach also includes the implementation of Bayesian inference in the determination of the CT fraction. Our results favor X-ray background synthesis models which postulate a moderate fraction (25%) of CT objects among the obscured AGN population.

The FLARE mission: deep and wide-field 1-5um imaging and spectroscopy for the early universe: a proposal for M5 cosmic vision call

NASA Astrophysics Data System (ADS)

Burgarella, D.; Levacher, P.; Vives, S.; Dohlen, K.; Pascal, S.

2016-07-01

FLARE (First Light And Reionization Explorer) is a space mission that will be submitted to ESA (M5 call). Its primary goal (~80% of lifetime) is to identify and study the universe before the end of the reionization at z > 6. A secondary objective (~20% of lifetime) is to survey star formation in the Milky Way. FLARE's strategy optimizes the science return: imaging and spectroscopic integral-field observations will be carried out simultaneously on two parallel focal planes and over very wide instantaneous fields of view. FLARE will help addressing two of ESA's Cosmic Vision themes: a) << How did the universe originate and what is it made of? » and b) « What are the conditions for planet formation and the emergence of life? >> and more specifically, << From gas and dust to stars and planets >>. FLARE will provide to the ESA community a leading position to statistically study the early universe after JWST's deep but pin-hole surveys. Moreover, the instrumental development of wide-field imaging and wide-field integral-field spectroscopy in space will be a major breakthrough after making them available on ground-based telescopes.

Aqueous alteration of VHTR fuels particles under simulated geological conditions

NASA Astrophysics Data System (ADS)

Ait Chaou, Abdelouahed; Abdelouas, Abdesselam; Karakurt, Gökhan; Grambow, Bernd

2014-05-01

Very High Temperature Reactor (VHTR) fuels consist of the bistructural-isotropic (BISO) or tristructural-isotropic (TRISO)-coated particles embedded in a graphite matrix. Management of the spent fuel generated during VHTR operation would most likely be through deep geological disposal. In this framework we investigated the alteration of BISO (with pyrolytic carbon) and TRISO (with SiC) particles under geological conditions simulated by temperatures of 50 and 90 °C and in the presence of synthetic groundwater. Solid state (scanning electron microscopy (SEM), micro-Raman spectroscopy, electron probe microanalyses (EPMA) and X-ray photoelectron spectroscopy (XPS)) and solution analyses (ICP-MS, ionique chromatography (IC)) showed oxidation of both pyrolytic carbon and SiC at 90 °C. Under air this led to the formation of SiO2 and a clay-like Mg-silicate, while under reducing conditions (H2/N2 atmosphere) SiC and pyrolytic carbon were highly stable after a few months of alteration. At 50 °C, in the presence and absence of air, the alteration of the coatings was minor. In conclusion, due to their high stability in reducing conditions, HTR fuel disposal in reducing deep geological environments may constitute a viable solution for their long-term management.

Ultraviolet refractometry using field-based light scattering spectroscopy

PubMed Central

Fu, Dan; Choi, Wonshik; Sung, Yongjin; Oh, Seungeun; Yaqoob, Zahid; Park, YongKeun; Dasari, Ramachandra R.; Feld, Michael S.

2010-01-01

Accurate refractive index measurement in the deep ultraviolet (UV) range is important for the separate quantification of biomolecules such as proteins and DNA in biology. This task is demanding and has not been fully exploited so far. Here we report a new method of measuring refractive index using field-based light scattering spectroscopy, which is applicable to any wavelength range and suitable for both solutions and homogenous objects with well-defined shape such as microspheres. The angular scattering distribution of single microspheres immersed in homogeneous media is measured over the wavelength range 260 to 315 nm using quantitative phase microscopy. By least square fitting the observed scattering distribution with Mie scattering theory, the refractive index of either the sphere or the immersion medium can be determined provided that one is known a priori. Using this method, we have measured the refractive index dispersion of SiO2 spheres and bovine serum albumin (BSA) solutions in the deep UV region. Specific refractive index increments of BSA are also extracted. Typical accuracy of the present refractive index technique is ≤0.003. The precision of refractive index measurements is ≤0.002 and that of specific refractive index increment determination is ≤0.01 mL/g. PMID:20372622

Quantitative methods for structural characterization of proteins based on deep UV resonance Raman spectroscopy.

PubMed

Shashilov, Victor A; Sikirzhytski, Vitali; Popova, Ludmila A; Lednev, Igor K

2010-09-01

Here we report on novel quantitative approaches for protein structural characterization using deep UV resonance Raman (DUVRR) spectroscopy. Specifically, we propose a new method combining hydrogen-deuterium (HD) exchange and Bayesian source separation for extracting the DUVRR signatures of various structural elements of aggregated proteins including the cross-beta core and unordered parts of amyloid fibrils. The proposed method is demonstrated using the set of DUVRR spectra of hen egg white lysozyme acquired at various stages of HD exchange. Prior information about the concentration matrix and the spectral features of the individual components was incorporated into the Bayesian equation to eliminate the ill-conditioning of the problem caused by 100% correlation of the concentration profiles of protonated and deuterated species. Secondary structure fractions obtained by partial least squares (PLS) and least squares support vector machines (LS-SVMs) were used as the initial guess for the Bayessian source separation. Advantages of the PLS and LS-SVMs methods over the classical least squares calibration (CLSC) are discussed and illustrated using the DUVRR data of the prion protein in its native and aggregated forms. Copyright (c) 2010 Elsevier Inc. All rights reserved.

In situ fabrication of electrochemically grown mesoporous metallic thin films by anodic dissolution in deep eutectic solvents.

PubMed

Renjith, Anu; Roy, Arun; Lakshminarayanan, V

2014-07-15

We describe here a simple electrodeposition process of forming thin films of noble metallic nanoparticles such as Au, Ag and Pd in deep eutectic solvents (DES). The method consists of anodic dissolution of the corresponding metal in DES followed by the deposition on the cathodic surface. The anodic dissolution process in DES overcomes the problems associated with copious hydrogen and oxygen evolution on the electrode surface when carried out in aqueous medium. The proposed method utilizes the inherent abilities of DES to act as a reducing medium while simultaneously stabilizing the nanoparticles that are formed. The mesoporous metal films were characterized by SEM, XRD and electrochemical techniques. Potential applications of these substrates in surface enhanced Raman spectroscopy and electrocatalysis have been investigated. A large enhancement of Raman signal of analyte was achieved on the mesoporous silver substrate after removing all the stabilizer molecules from the surface by calcination. The highly porous texture of the electrodeposited film provides superior electro catalytic performance for hydrogen evolution reaction (HER). The mechanisms of HER on the fabricated substrates were studied by Tafel analysis and electrochemical impedance spectroscopy (EIS). Copyright © 2014 Elsevier Inc. All rights reserved.

Ultrafast exciton dynamics in cadmium selenide nanocrystals determined by femtosecond fluorescence upconversion spectroscopy

NASA Astrophysics Data System (ADS)

Underwood, David Frederick

Femtosecond fluorescence upconversion spectroscopy is a technique that allows the unambiguous determination of the excited state dynamics of an analyte. Combining this method with the use of tunable laser excitation, the exciton dynamics in semiconducting nanocrystals (NC's) of cadmium selenide (CdSe) have been determined, devoid of the complications arising from more common spectroscopic methods such as pump-probe. The results of this investigation were used to construct a model to fully describe the three-level system comprising of the valence and conduction bands and surface states, which have been calculated by others to lie mid-gap in energy. Smaller NC's showed faster decay components due to increased interaction between the exciton and surface states. The deep trap emission, which has never before been measured by ultrafast fluorescence techniques, shows a rapid rise time (˜2 ps), which is attributed to surface selenium dangling bonds relaxing to the valence band and radiatively combining with the photo-generated hole. The band edge fluorescence decays as the deep trap emission grows in, inherently coupling the two processes. An experiment which measured the dependence of the excitation energy showed that increased energy imparted to the NC's resulted in increased rise times, yielding the timescales for exciton relaxation through the valence and conduction band states to the lowest emitting state. Surface-oxidized and normally-passivated NC's display the same decay dynamics in time but differ in relative amplitude; the latter point agrees with steady-state measurements. The rotational anisotrophy of the NC's was measured and agrees with previous pump-probe data. Upconversion on the red and blue sides of the static fluorescence spectrum showed no discernable differences, which is either and inherent limitation of the experimental apparatus, or the possibility that lower-lying triplet states are populated on a timescale below the instrument resolution.

Changes in VEGF and nitric oxide after deep dermal injury in the female, red Duroc pig-further similarities between female, Duroc scar and human hypertrophic scar.

PubMed

Zhu, Kathy Q; Engrav, Loren H; Armendariz, Rebecca; Muangman, Pornprom; Klein, Matthew B; Carrougher, Gretchen J; Deubner, Heike; Gibran, Nicole S

2005-02-01

Despite decades of research, our understanding of human hypertrophic scar is limited. A reliable animal model could significantly increase our understanding. We previously confirmed similarities between scarring in the female, red, Duroc pig and human hypertrophic scarring. The purpose of this study was to: (1) measure vascular endothelial growth factor (VEGF) and nitric oxide (NO) levels in wounds on the female Duroc; and (2) to compare the NO levels to those reported for human hypertrophic scar. Shallow and deep wounds were created on four female Durocs. VEGF levels were measured using ELISA and NO levels with the Griess reagent. VEGF and NO levels were increased in deep wounds at 10 days when compared to shallow wounds (p < 0.05). At 15 weeks, VEGF and NO levels had returned to the level of shallow wounds. At 21 weeks, VEGF and NO levels had declined below baseline levels in deep wounds and the NO levels were significantly lower (p < 0.01). We found that VEGF and NO exhibit two distinctly different temporal patterns in shallow and deep wounds on the female Durocs. Furthermore, NO is decreased in female, Duroc scar as it is in human, hypertrophic scar further validating the usefulness of the model.

A physical model for the reverse leakage current in (In,Ga)N/GaN light-emitting diodes based on nanowires

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

Musolino, M.; Treeck, D. van, E-mail: treeck@pdi-berlin.de; Tahraoui, A.

2016-01-28

We investigated the origin of the high reverse leakage current in light emitting diodes (LEDs) based on (In,Ga)N/GaN nanowire (NW) ensembles grown by molecular beam epitaxy on Si substrates. To this end, capacitance deep level transient spectroscopy (DLTS) and temperature-dependent current-voltage (I-V) measurements were performed on a fully processed NW-LED. The DLTS measurements reveal the presence of two distinct electron traps with high concentrations in the depletion region of the p-i-n junction. These band gap states are located at energies of 570 ± 20 and 840 ± 30 meV below the conduction band minimum. The physical origin of these deep level states is discussed. Themore » temperature-dependent I-V characteristics, acquired between 83 and 403 K, show that different conduction mechanisms cause the observed leakage current. On the basis of all these results, we developed a quantitative physical model for charge transport in the reverse bias regime. By taking into account the mutual interaction of variable range hopping and electron emission from Coulombic trap states, with the latter being described by phonon-assisted tunnelling and the Poole-Frenkel effect, we can model the experimental I-V curves in the entire range of temperatures with a consistent set of parameters. Our model should be applicable to planar GaN-based LEDs as well. Furthermore, possible approaches to decrease the leakage current in NW-LEDs are proposed.« less

Arduino Due based tool to facilitate in vivo two-photon excitation microscopy

PubMed Central

Artoni, Pietro; Landi, Silvia; Sato, Sebastian Sulis; Luin, Stefano; Ratto, Gian Michele

2016-01-01

Two-photon excitation spectroscopy is a powerful technique for the characterization of the optical properties of genetically encoded and synthetic fluorescent molecules. Excitation spectroscopy requires tuning the wavelength of the Ti:sapphire laser while carefully monitoring the delivered power. To assist laser tuning and the control of delivered power, we developed an Arduino Due based tool for the automatic acquisition of high quality spectra. This tool is portable, fast, affordable and precise. It allowed studying the impact of scattering and of blood absorption on two-photon excitation light. In this way, we determined the wavelength-dependent deformation of excitation spectra occurring in deep tissues in vivo. PMID:27446677

Application of optical processing for growth of silicon dioxide

DOEpatents

Sopori, B.L.

1997-06-17

A process for producing a silicon dioxide film on a surface of a silicon substrate is disclosed. The process comprises illuminating a silicon substrate in a substantially pure oxygen atmosphere with a broad spectrum of visible and infrared light at an optical power density of from about 3 watts/cm{sup 2} to about 6 watts/cm{sup 2} for a time period sufficient to produce a silicon dioxide film on the surface of the silicon substrate. An optimum optical power density is about 4 watts/cm{sup 2} for growth of a 100{angstrom}-300{angstrom} film at a resultant temperature of about 400 C. Deep level transient spectroscopy analysis detects no measurable impurities introduced into the silicon substrate during silicon oxide production and shows the interface state density at the SiO{sub 2}/Si interface to be very low. 1 fig.

Intrinsic defect oriented visible region absorption in zinc oxide films

NASA Astrophysics Data System (ADS)

Rakhesh, V.; Shankar, Balakrishnan

2018-05-01

Zinc Oxide films were deposited on the glass substrate using vacuum arc sputtering technology. Films were prepared in oxygen ambience for 10mA and 15 mA deposition current separately. The UV-Visible spectroscopy of the samples showed that both samples possess sharp absorption near 3.5eV which is the characteristic band gap absorption energy of ZnO films. The absorption coefficient were calculated for the samples and the (αℎϑ)2 vs energy plot is drawn. The plot suggested that in addition to the sharp band edge absorption, the sample prepared at 10mA deposition current showed sharp absorption edge near 1.51eV and that at 15 mA showed absorption edge near 1.47eV. This refers to the presence of an intrinsic defect level which is likely to be deep in the band gap.

Nitrided SrTiO3 as charge-trapping layer for nonvolatile memory applications

NASA Astrophysics Data System (ADS)

Huang, X. D.; Lai, P. T.; Liu, L.; Xu, J. P.

2011-06-01

Charge-trapping characteristics of SrTiO3 with and without nitrogen incorporation were investigated based on Al/Al2O3/SrTiO3/SiO2/Si (MONOS) capacitors. A Ti-silicate interlayer at the SrTiO3/SiO2 interface was confirmed by x-ray photoelectron spectroscopy and transmission electron microscopy. Compared with the MONOS capacitor with SrTiO3 as charge-trapping layer (CTL), the one with nitrided SrTiO3 showed a larger memory window (8.4 V at ±10 V sweeping voltage), higher P/E speeds (1.8 V at 1 ms +8 V) and better retention properties (charge loss of 38% after 104 s), due to the nitrided SrTiO3 film exhibiting higher dielectric constant, higher deep-level traps induced by nitrogen incorporation, and suppressed formation of Ti silicate between the CTL and SiO2 by nitrogen passivation.

Study of GaN nanorods converted from β-Ga2O3

NASA Astrophysics Data System (ADS)

Li, Yuewen; Xiong, Zening; Zhang, Dongdong; Xiu, Xiangqian; Liu, Duo; Wang, Shuang; Hua, Xuemei; Xie, Zili; Tao, Tao; Liu, Bin; Chen, Peng; Zhang, Rong; Zheng, Youdou

2018-05-01

We report here high-quality β-Ga2O3 nanorods (NRs) grown on sapphire substrates by hydrothermal method. Ammoniating the β-Ga2O3 NRs results in strain-free wurtzite gallium nitride (GaN) NRs. It was shown by XRD and Raman spectroscopy that β-Ga2O3 was partially converted to GaN/β-Ga2O3 at 1000 °C and then completely converted to GaN NRs at 1050 °C, as confirmed by high-resolution transmission electron microscopy (HRTEM). There is no band-edge emission of β-Ga2O3 in the cathodoluminescence spectrum, and only a deep-level broad emission observed at 3.68-3.73 eV. The band edge emission (3.39 eV) of GaN NRs converted from β-Ga2O3 can also be observed.

230 s room-temperature storage time and 1.14 eV hole localization energy in In{sub 0.5}Ga{sub 0.5}As quantum dots on a GaAs interlayer in GaP with an AlP barrier

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

Bonato, Leo, E-mail: leo.bonato@tu-berlin.de; Sala, Elisa M.; Stracke, Gernot

2015-01-26

A GaP n{sup +}p-diode containing In{sub 0.5}Ga{sub 0.5}As quantum dots (QDs) and an AlP barrier is characterized electrically, together with two reference samples: a simple n{sup +}p-diode and an n{sup +}p-diode with AlP barrier. Localization energy, capture cross-section, and storage time for holes in the QDs are determined using deep-level transient spectroscopy. The localization energy is 1.14(±0.04) eV, yielding a storage time at room temperature of 230(±60) s, which marks an improvement of 2 orders of magnitude compared to the former record value in QDs. Alternative material systems are proposed for still higher localization energies and longer storage times.

Origin and enhancement of the 1.3 μm luminescence from GaAs treated by ion-implantation and flash lamp annealing

NASA Astrophysics Data System (ADS)

Gao, Kun; Prucnal, S.; Skorupa, W.; Helm, M.; Zhou, Shengqiang

2013-09-01

GaAs and GaAs based materials have outstanding optoelectronic properties and are widely used as light emitting media in devices. Many approaches have been applied to GaAs to generate luminescence at 0.88, 1.30, and 1.55 μm which are transmission windows of optical fibers. In this paper, we present the photoluminescence at 1.30 μm from deep level defects in GaAs treated by ion-implantation and flash lamp annealing (FLA). Such emission, which exhibits superior temperature stability, can be obtained from FLA treated virgin GaAs as well as doped GaAs. Indium-doping in GaAs can greatly enhance the luminescence. By photoluminescence, Raman measurements, and positron annihilation spectroscopy, we conclude that the origin of the 1.30 μm emission is from transitions between the VAs-donor and X-acceptor pairs.

EBIC spectroscopy - A new approach to microscale characterization of deep levels in semi-insulating GaAs

NASA Technical Reports Server (NTRS)

Li, C.-J.; Sun, Q.; Lagowski, J.; Gatos, H. C.

1985-01-01

The microscale characterization of electronic defects in (SI) GaAs has been a challenging issue in connection with materials problems encountered in GaAs IC technology. The main obstacle which limits the applicability of high resolution electron beam methods such as Electron Beam-Induced Current (EBIC) and cathodoluminescence (CL) is the low concentration of free carriers in semiinsulating (SI) GaAs. The present paper provides a new photo-EBIC characterization approach which combines the spectroscopic advantages of optical methods with the high spatial resolution and scanning capability of EBIC. A scanning electron microscope modified for electronic characterization studies is shown schematically. The instrument can operate in the standard SEM mode, in the EBIC modes (including photo-EBIC and thermally stimulated EBIC /TS-EBIC/), and in the cathodo-luminescence (CL) and scanning modes. Attention is given to the use of CL, Photo-EBIC, and TS-EBIC techniques.

Electrostatic thin film chemical and biological sensor

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

Prelas, Mark A.; Ghosh, Tushar K.; Tompson, Jr., Robert V.

A chemical and biological agent sensor includes an electrostatic thin film supported by a substrate. The film includes an electrostatic charged surface to attract predetermined biological and chemical agents of interest. A charge collector associated with said electrostatic thin film collects charge associated with surface defects in the electrostatic film induced by the predetermined biological and chemical agents of interest. A preferred sensing system includes a charge based deep level transient spectroscopy system to read out charges from the film and match responses to data sets regarding the agents of interest. A method for sensing biological and chemical agents includesmore » providing a thin sensing film having a predetermined electrostatic charge. The film is exposed to an environment suspected of containing the biological and chemical agents. Quantum surface effects on the film are measured. Biological and/or chemical agents can be detected, identified and quantified based on the measured quantum surface effects.« less

Vertical wind shear characteristics that promote supercell-to-MCS transitions

NASA Astrophysics Data System (ADS)

Peters, J. M.

2017-12-01

What causes supercells to transition into MCSs in some situations, but not others? To explore this question, I first examined observed environmental characteristics of supercell events when MCSs formed, and compared them to the analogous environmental characteristics of supercell events when MCSs did not form. During events when MCS growth occurred, 0-1 km (low-level) vertical wind shear was stronger and 0-10 km (deep-layer) vertical wind shear was weaker than the wind shear during events when MCS growth did not occur. Next, I used idealized simulations of supercell thunderstorms to understand the connections between low-level and deep-layer shear and MCS growth. Compared to simulations with strong deep-layer shear, the simulations with weak deep-layer shear had rain in the storm's forward-flank downdraft (FFD) that fell closer to the updraft, fell through storm-moistened air and evaporated less, and produced a more intense FFD. Compared to simulations with weak low-level shear, the simulations with stronger low-level shear showed enhanced northward low-level hydrometeor transport into the FFD. Environments with strong low-level shear and weak deep-layer shear therefore conspired to produce a storm with a more intense FFD cold pool, when compared to environments with weak low-level shear and/or strong deep-layer shear. This strong FFD periodically disrupted the supercells' mesocyclones, and favorably interacted with westerly wind shear to produce widespread linear convection initiation, which drove MCS growth. These results suggest that increasing low-level wind shear after dark - while commonly assumed to enhance tornado potential - may in fact drive MCS growth and reduce tornado potential, unless it is combined with sufficiently strong deep layer shear.

Using Deep UV Raman Spectroscopy to Identify In Situ Microbial Activity

NASA Astrophysics Data System (ADS)

Sapers, H. M.; Wanger, G.; Amend, J.; Orphan, V. J.; Bhartia, R.

2017-12-01

Microbial communities living in close association with lithic substrates play a critical role in biogeochemical cycles. Understanding the interactions between microorganisms and their abiotic substrates requires knowledge of microbial activity. Identifying active cells adhered to complex environmental substrates, especially in low biomass systems, remains a challenge. Stable isotope probing (SIP) provides a means to trace microbial activity in environmental systems. Active members of the community take up labeled substrates and incorporate the labels into biomolecules that can be detected through downstream analyses. Here we show for the first time that Deep UV (248 nm) Raman spectroscopy can differentiate microbial cells labeled with stable isotopes. Previous studies have used Raman spectroscopy with a 532 nm source to identify active bacterial cells by measuring a Raman shift between peaks corresponding to amino acids incorporating 13C compared to controls. However, excitation at 532 nm precludes detection on complex substrates due to high autofluorescence of native minerals. Excitation in the DUV range offers non-destructive imaging on mineral surfaces - retaining critical contextual information. We prepared cultures of E. coli grown in 50 atom% 13C glucose spotted onto Al wafers to test the ability of DUV Raman spectroscopy to differentiate labeled and unlabeled cells. For the first time, we are able to demonstrate a distinct and repeatable shift between cells grown in labeled media and unlabeled media when imaged on Al wafers with DUV Raman spectroscopy. The Raman spectra are dominated by the characteristic Raman bands of guanine. The dominant marker peak for guanine attributed to N7-C8 and C8-N9 ring stretching and C8-H in-plane bending, is visible at 1480 cm-1 in the unlabeled cells and is blue-shifted by 20 wavenumbers to 1461 cm-1 in the labeled cells. The ability of DUV Raman to effectively identify regions containing cells that have incorporated isotopic labels will allow in situ detection of metabolically-targeted active community members on complex natural substrates providing a crucial link between microbial activity and environmental context.

Deep Levels of Processing Elicit a Distinctiveness Heuristic: Evidence from the Criterial Recollection Task

ERIC Educational Resources Information Center

Gallo, David A.; Meadow, Nathaniel G.; Johnson, Elizabeth L.; Foster, Katherine T.

2008-01-01

Thinking about the meaning of studied words (deep processing) enhances memory on typical recognition tests, relative to focusing on perceptual features (shallow processing). One explanation for this levels-of-processing effect is that deep processing leads to the encoding of more distinctive representations (i.e., more unique semantic or…

Diffusivity of the double negatively charged mono-vacancy in silicon

NASA Astrophysics Data System (ADS)

Bhoodoo, Chidanand; Vines, Lasse; Monakhov, Edouard; Svensson, Bengt Gunnar

2017-05-01

Lightly-doped silicon (Si) samples of n-type conductivity have been irradiated with 2.0 MeV {{\\text{H}}+} ions at a temperature of 30 K and characterized in situ by deep level transient spectroscopy (DLTS) measurements using an on-line setup. Migration of the Si mono-vacancy in its double negative charge state (V 2-) starts to occur at temperatures above  ˜70 K and is monitored via trapping of V 2- by interstitial oxygen impurity atoms ({{\\text{O}}i} ), leading to the growth of the prominent vacancy-oxygen (V\\text{O} ) center. The V\\text{O} center gives rise to an acceptor level located at  ˜0.17 eV below the conduction band edge (E c ) and is readily detected by DLTS measurements. Post-irradiation isothermal anneals at temperatures in the range of 70 to 90 K reveal first-order kinetics for the reaction {{V}2-}+{{\\text{O}}i}\\to V\\text{O} ≤ft(+ 2{{e}-}\\right) in both Czochralski-grown and Float-zone samples subjected to low fluences of {{\\text{H}}+} ions, i.e. the irradiation-induced V concentration is dilute (≤slant 1013 cm-3). On the basis of these kinetics data and the content of {{\\text{O}}i} , the diffusivity of V 2- can be determined quantitatively and is found to exhibit an activation energy for migration of  ˜0.18 eV with a pre-exponential factor of  ˜4× {{10}-3} cm2 s-1. The latter value evidences a simple jump process without any entropy effects for the motion of V 2-. No deep level in the bandgap to be associated with V 2- is observed but the results suggest that the level is situated deeper than  ˜0.19 eV below E c , corroborating results reported previously in the literature.

Electron emission from deep level defects EL2 and EL6 in semi-insulating GaAs observed by positron drift velocity transient measurements

NASA Astrophysics Data System (ADS)

Tsia, J. M.; Ling, C. C.; Beling, C. D.; Fung, S.

2002-09-01

A plus-or-minus100 V square wave applied to a Au/semi-insulating SI-GaAs interface was used to bring about electron emission from and capture into deep level defects in the region adjacent to the interface. The electric field transient resulting from deep level emission was studied by monitoring the positron drift velocity in the region. A deep level transient spectrum was obtained by computing the trap emission rate as a function of temperature and two peaks corresponding to EL2 (Ea=0.81plus-or-minus0.15 eV) and EL6 (Ea=0.30plus-or-minus0.12 eV) have been identified.

Temperature-Dependent Photoluminescence Imaging and Characterization of a Multi-Crystalline Silicon Solar Cell Defect Area

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

Johnston, S.; Yan, F.; Li, J.

2011-01-01

Photoluminescence (PL) imaging is used to detect areas in multi-crystalline silicon that appear dark in band-to-band imaging due to high recombination. Steady-state PL intensity can be correlated to effective minority-carrier lifetime, and its temperature dependence can provide additional lifetime-limiting defect information. An area of high defect density has been laser cut from a multi-crystalline silicon solar cell. Both band-to-band and defect-band PL imaging have been collected as a function of temperature from {approx}85 to 350 K. Band-to-band luminescence is collected by an InGaAs camera using a 1200-nm short-pass filter, while defect band luminescence is collected using a 1350-nm long passmore » filter. The defect band luminescence is characterized by cathodoluminescence. Small pieces from adjacent areas within the same wafer are measured by deep-level transient spectroscopy (DLTS). DLTS detects a minority-carrier electron trap level with an activation energy of 0.45 eV on the sample that contained defects as seen by imaging.« less

Temperature-Dependent Photoluminescence Imaging and Characterization of a Multi-Crystalline Silicon Solar Cell Defect Area: Preprint

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

Johnston, S.; Yan, F.; Li, J.

2011-07-01

Photoluminescence (PL) imaging is used to detect areas in multi-crystalline silicon that appear dark in band-to-band imaging due to high recombination. Steady-state PL intensity can be correlated to effective minority-carrier lifetime, and its temperature dependence can provide additional lifetime-limiting defect information. An area of high defect density has been laser cut from a multi-crystalline silicon solar cell. Both band-to-band and defect-band PL imaging have been collected as a function of temperature from ~85 to 350 K. Band-to-band luminescence is collected by an InGaAs camera using a 1200-nm short-pass filter, while defect band luminescence is collected using a 1350-nm long passmore » filter. The defect band luminescence is characterized by cathodo-luminescence. Small pieces from adjacent areas within the same wafer are measured by deep-level transient spectroscopy (DLTS). DLTS detects a minority-carrier electron trap level with an activation energy of 0.45 eV on the sample that contained defects as seen by imaging.« less

DLTS and in situ C-V analysis of trap parameters in swift 50 MeV Li3+ ion-irradiated Ni/SiO2/Si MOS capacitors

NASA Astrophysics Data System (ADS)

Shashank, N.; Singh, Vikram; Gupta, Sanjeev K.; Madhu, K. V.; Akhtar, J.; Damle, R.

2011-04-01

Ni/SiO2/Si MOS structures were fabricated on n-type Si wafers and were irradiated with 50 MeV Li3+ ions with fluences ranging from 1×1010 to 1×1012 ions/cm2. High frequency C-V characteristics are studied in situ to estimate the build-up of fixed and oxide charges. The nature of the charge build-up with ion fluence is analyzed. Defect levels in bulk Si and its properties such as activation energy, capture cross-section, trap concentration and carrier lifetimes are studied using deep-level transient spectroscopy. Electron traps with energies ranging from 0.069 to 0.523 eV are observed in Li ion-irradiated devices. The dependence of series resistance, substrate doping and accumulation capacitance on Li ion fluence are clearly explained. The study of dielectric properties (tan δ and quality factor) confirms the degradation of the oxide layer to a greater extent due to ion irradiation.

Evidence for room-temperature in-diffusion of nickel into silicon

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

Yarykin, Nikolai, E-mail: nay@iptm.ru; Weber, Jörg

2016-09-05

Interstitial nickel in crystalline Si is shown to be a fast diffuser at room temperature. In this study, Ni is incorporated in Si by wet chemical etching in nickel-contaminated alkaline solutions. Nickel in-diffusion is observed by means of detecting the electrically active NiVO defect, which is formed due to Ni capture to the vacancy–oxygen complex in electron-irradiated Si. The depth profiles of the NiVO concentration measured by the deep-level transient spectroscopy technique extend to ∼15 μm in the samples doped with Ni at 35 °C for 30 min. This allows us to get a lower estimate for the nickel diffusivity at this temperaturemore » as 10{sup −9} cm{sup 2}/s. The activation energy for electron emission from the NiVO level and the apparent capture cross section are equal to 371 meV and 3 × 10{sup −15} cm{sup 2}, respectively. The NiVO complex dissociates at 300 °C reestablishing the initial concentration of the VO centers.« less

Band alignment of atomic layer deposited MgO/Zn0.8Al0.2O heterointerface determined by charge corrected X-ray photoelectron spectroscopy

NASA Astrophysics Data System (ADS)

Yan, Baojun; Liu, Shulin; Yang, Yuzhen; Heng, Yuekun

2016-05-01

Pure magnesium (MgO) and zinc oxide doped with aluminum oxide (Zn0.8Al0.2O) were prepared via atomic layer deposition. We have studied the structure and band gap of bulk Zn0.8Al0.2O material by X-ray diffractometer (XRD) and Tauc method, and the band offsets and alignment of atomic layer deposited MgO/Zn0.8Al0.2O heterointerface were investigated systematically using X-ray photoelectron spectroscopy (XPS) in this study. Different methodologies, such as neutralizing electron gun, the use of C 1s peak recalibration and zero charging method, were applied to recover the actual position of the core levels in insulator materials which were easily influenced by differential charging phenomena. Schematic band alignment diagram, valence band offset (ΔEV) and conduction band offset (ΔEC) for the interface of the MgO/Zn0.8Al0.2O heterostructure have been constructed. An accurate value of ΔEV = 0.72 ± 0.11 eV was obtained from various combinations of core levels of heterojunction with varied MgO thickness. Given the experimental band gaps of 7.83 eV for MgO and 5.29 eV for Zn0.8Al0.2O, a type-II heterojunction with a ΔEC of 3.26 ± 0.11 eV was found. Band offsets and alignment studies of these heterojunctions are important for gaining deep consideration to the design of various optoelectronic devices based on such heterointerface.

Synthesis of ZnSe and ZnSe:Cu quantum dots by a room temperature photochemical (UV-assisted) approach using Na2 SeO3 as Se source and investigating optical properties.

PubMed

Khafajeh, R; Molaei, M; Karimipour, M

2017-06-01

In this study, ZnSe and ZnSe:Cu quantum dots (QDs) were synthesized using Na 2 SeO 3 as the Se source by a rapid and room temperature photochemical (UV-assisted) approach. Thioglycolic acid (TGA) was employed as the capping agent and UV illumination activated the chemical reactions. Synthesized QDs were successfully characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), photoluminescence (PL) and UV-visible (UV-vis) spectroscopy, Fourier transform-infrared (FT-IR), and energy dispersive X-ray spectroscopy (EDX). XRD analysis demonstrated the cubic zinc blend phase QDs. TEM images indicated that round-shaped particles were formed, most of which had a diameter of about 4 nm. The band gap of the ZnSe QDs was higher than that for ZnSe in bulk. PL spectra indicated an emission with three peaks related to the excitonic, surface trap states and deep level (DL) states. The band gap and QD emission were tunable only by UV illumination time during synthesis. ZnSe:Cu showed green emission due to transition of electrons from the Conduction band (CB) or surface trap states to the 2 T 2 acceptor levels of Cu 2 + . The emission was increased by increasing the Cu 2 + ion concentration, such that the optimal value of PL intensity was obtained for the nominal mole ratio of Cu:Zn 1.5%. Copyright © 2016 John Wiley & Sons, Ltd.

Toward noninvasive detection and monitoring of malaria with broadband diffuse optical spectroscopy

NASA Astrophysics Data System (ADS)

Campbell, Chris; Tromberg, Bruce J.; O'Sullivan, Thomas D.

2018-02-01

Despite numerous advances, malaria continues to kill nearly half a million people globally every year. New analytical methods and diagnostics are critical to understanding how treatments under development affect the lifecycle of malaria parasites. A biomarker that has been gaining interest is the "malaria pigment" hemozoin. This byproduct of hemoglobin digestion by the parasite has a unique spectral signature but is difficult to differentiate from hemoglobin and other tissue chromophores. Hemozoin can be detected in blood samples, but only utilizing approaches that require specialized training and facilities. Diffuse optical spectroscopy (DOS) is a noninvasive sensing technique that is sensitive to near-infrared absorption and scattering and capable of probing centimeter-deep volumes of tissue in vivo. DOS is relatively low-cost, does not require specialized training and thus potentially suitable for use in low-resource settings. In this work, we assess the potential of DOS to detect and quantify the presence of hemozoin noninvasively and at physiologically relevant levels. We suspended synthetic hemozoin in Intralipid-based tissue-simulating phantoms in order to mimic malaria infection in multiply-scattering tissue. Using a fiber probe that combines frequency-domain and continuous-wave broadband DOS (650-1000 nm), we detected hemozoin concentrations below 250 ng/ml, which corresponds to parasitemia sensitivities comparable to modern rapid diagnostic tests. We used the experimental variability to simulate and estimate the sensitivity of DOS to hemozoin in tissue that includes hemoglobin, water, and lipid under various tissue oxygen saturation levels. The results indicate that with increased precision, it may be possible to detect Hz noninvasively with DOS.

DeepMirTar: a deep-learning approach for predicting human miRNA targets.

PubMed

Wen, Ming; Cong, Peisheng; Zhang, Zhimin; Lu, Hongmei; Li, Tonghua

2018-06-01

MicroRNAs (miRNAs) are small noncoding RNAs that function in RNA silencing and post-transcriptional regulation of gene expression by targeting messenger RNAs (mRNAs). Because the underlying mechanisms associated with miRNA binding to mRNA are not fully understood, a major challenge of miRNA studies involves the identification of miRNA-target sites on mRNA. In silico prediction of miRNA-target sites can expedite costly and time-consuming experimental work by providing the most promising miRNA-target-site candidates. In this study, we reported the design and implementation of DeepMirTar, a deep-learning-based approach for accurately predicting human miRNA targets at the site level. The predicted miRNA-target sites are those having canonical or non-canonical seed, and features, including high-level expert-designed, low-level expert-designed, and raw-data-level, were used to represent the miRNA-target site. Comparison with other state-of-the-art machine-learning methods and existing miRNA-target-prediction tools indicated that DeepMirTar improved overall predictive performance. DeepMirTar is freely available at https://github.com/Bjoux2/DeepMirTar_SdA. lith@tongji.edu.cn, hongmeilu@csu.edu.cn. Supplementary data are available at Bioinformatics online.

The Grism Lens-Amplified Survey from Space (GLASS). III. A Census of Lyα Emission at z ≳ 7 from HST Spectroscopy

NASA Astrophysics Data System (ADS)

Schmidt, K. B.; Treu, T.; Bradač, M.; Vulcani, B.; Huang, K.-H.; Hoag, A.; Maseda, M.; Guaita, L.; Pentericci, L.; Brammer, G. B.; Dijkstra, M.; Dressler, A.; Fontana, A.; Henry, A. L.; Jones, T. A.; Mason, C.; Trenti, M.; Wang, X.

2016-02-01

We present a census of Lyα emission at z≳ 7, utilizing deep near-infrared Hubble Space Telescope grism spectroscopy from the first six completed clusters of the Grism Lens-Amplified Survey from Space (GLASS). In 24/159 photometrically selected galaxies we detect emission lines consistent with Lyα in the GLASS spectra. Based on the distribution of signal-to-noise ratios and on simulations, we expect the completeness and the purity of the sample to be 40%-100% and 60%-90%, respectively. For the objects without detected emission lines we show that the observed (not corrected for lensing magnification) 1σ flux limits reach 5 × 10-18 erg s-1 cm-2 per position angle over the full wavelength range of GLASS (0.8-1.7 μm). Based on the conditional probability of Lyα emission measured from the ground at z˜ 7, we would have expected 12-18 Lyα emitters. This is consistent with the number of detections, within the uncertainties, confirming the drop in Lyα emission with respect to z˜ 6. Deeper follow-up spectroscopy, here exemplified by Keck spectroscopy, is necessary to improve our estimates of completeness and purity and to confirm individual candidates as true Lyα emitters. These candidates include a promising source at z = 8.1. The spatial extent of Lyα in a deep stack of the most convincing Lyα emitters with < z> = 7.2 is consistent with that of the rest-frame UV continuum. Extended Lyα emission, if present, has a surface brightness below our detection limit, consistent with the properties of lower-redshift comparison samples. From the stack we estimate upper limits on rest-frame UV emission line ratios and find {f}{{C}{{IV}}}/{f}{Lyα }≲ 0.32 and {f}{{C}{{III}}]}/{f}{Lyα }≲ 0.23, in good agreement with other values published in the literature.

Deep-convection events foster carbonate ion reduction in deep coral reefs

NASA Astrophysics Data System (ADS)

Perez, Fiz F.; Fontela, Marcos; Garcia-Ibañez, Maribel I.; Lherminier, Pascale; Zunino, Patricia; de la Paz, Mercedes; Padín, Xose A.; Alonso-Pérez, Fernando; Velo, Anton; Guallart, Elisa F.; Mercier, Herle

2017-04-01

Since millennial times, water mass circulation and deep-convection events have been transforming warm upper waters at high latitudes into cold and well-oxygenated deep waters. These processes have filled the deep North Atlantic Ocean with waters moderately saturated in calcium carbonate, thus promoting the growth of stony corals, which are hotspots of biodiversity. During the Anthropocene, the meridional circulation has been conveying cumulative amounts of more acidified waters with lower calcium carbonate saturation levels due to the incorporation of anthropogenic carbon dioxide, with very harsh conditions for deep cold-water corals projected by 2100. We evaluate the diminution of calcium carbonate saturation levels (aragonite form) due to the increase in anthropogenic carbon dioxide during the last two decades (2002-2016). We observe a strong decrease in the aragonite saturation levels concomitant with the reduction in the volume transport of aragonite-saturated waters. We estimate a 30-35% reduction in the transport of ion carbonate excess over the saturation levels with respect to the natural carbon cycle for the period 2002-2016. This reduction is associated with an increase in the downward transport of hydrogen ions. We also observe a heaving of the aragonite saturation horizons during the last 25 years, which is estimated at 6 m year-1 for the deep waters and 12-14 m year-1 for the intermediated waters. The harsh winters of 2015 and 2016 have fostered the fast addition of more acidified water into the lower layers of the North Atlantic through deep-convection events. In the future scenario of 2oC warming, the anthropogenic carbon dioxide in the water column would be double than today and the associated transport of hydrogen ions towards the bottom water would reduce the aragonite saturation levels to 60-80% with respect to preindustrial levels. This reduction in the aragonite saturation levels would suppose a strong diminution of the North Atlantic habitats where stony corals will be able to inhabit.

Simultaneous measurement of temperature, stress, and electric field in GaN HEMTs with micro-Raman spectroscopy.

PubMed

Bagnall, Kevin R; Moore, Elizabeth A; Badescu, Stefan C; Zhang, Lenan; Wang, Evelyn N

2017-11-01

As semiconductor devices based on silicon reach their intrinsic material limits, compound semiconductors, such as gallium nitride (GaN), are gaining increasing interest for high performance, solid-state transistor applications. Unfortunately, higher voltage, current, and/or power levels in GaN high electron mobility transistors (HEMTs) often result in elevated device temperatures, degraded performance, and shorter lifetimes. Although micro-Raman spectroscopy has become one of the most popular techniques for measuring localized temperature rise in GaN HEMTs for reliability assessment, decoupling the effects of temperature, mechanical stress, and electric field on the optical phonon frequencies measured by micro-Raman spectroscopy is challenging. In this work, we demonstrate the simultaneous measurement of temperature rise, inverse piezoelectric stress, thermoelastic stress, and vertical electric field via micro-Raman spectroscopy from the shifts of the E 2 (high), A 1 longitudinal optical (LO), and E 2 (low) optical phonon frequencies in wurtzite GaN. We also validate experimentally that the pinched OFF state as the unpowered reference accurately measures the temperature rise by removing the effect of the vertical electric field on the Raman spectrum and that the vertical electric field is approximately the same whether the channel is open or closed. Our experimental results are in good quantitative agreement with a 3D electro-thermo-mechanical model of the HEMT we tested and indicate that the GaN buffer acts as a semi-insulating, p-type material due to the presence of deep acceptors in the lower half of the bandgap. This implementation of micro-Raman spectroscopy offers an exciting opportunity to simultaneously probe thermal, mechanical, and electrical phenomena in semiconductor devices under bias, providing unique insight into the complex physics that describes device behavior and reliability. Although GaN HEMTs have been specifically used in this study to demonstrate its viability, this technique is applicable to any solid-state material with a suitable Raman response and will likely enable new measurement capabilities in a wide variety of scientific and engineering applications.

Simultaneous measurement of temperature, stress, and electric field in GaN HEMTs with micro-Raman spectroscopy

NASA Astrophysics Data System (ADS)

Bagnall, Kevin R.; Moore, Elizabeth A.; Badescu, Stefan C.; Zhang, Lenan; Wang, Evelyn N.

2017-11-01

As semiconductor devices based on silicon reach their intrinsic material limits, compound semiconductors, such as gallium nitride (GaN), are gaining increasing interest for high performance, solid-state transistor applications. Unfortunately, higher voltage, current, and/or power levels in GaN high electron mobility transistors (HEMTs) often result in elevated device temperatures, degraded performance, and shorter lifetimes. Although micro-Raman spectroscopy has become one of the most popular techniques for measuring localized temperature rise in GaN HEMTs for reliability assessment, decoupling the effects of temperature, mechanical stress, and electric field on the optical phonon frequencies measured by micro-Raman spectroscopy is challenging. In this work, we demonstrate the simultaneous measurement of temperature rise, inverse piezoelectric stress, thermoelastic stress, and vertical electric field via micro-Raman spectroscopy from the shifts of the E2 (high), A1 longitudinal optical (LO), and E2 (low) optical phonon frequencies in wurtzite GaN. We also validate experimentally that the pinched OFF state as the unpowered reference accurately measures the temperature rise by removing the effect of the vertical electric field on the Raman spectrum and that the vertical electric field is approximately the same whether the channel is open or closed. Our experimental results are in good quantitative agreement with a 3D electro-thermo-mechanical model of the HEMT we tested and indicate that the GaN buffer acts as a semi-insulating, p-type material due to the presence of deep acceptors in the lower half of the bandgap. This implementation of micro-Raman spectroscopy offers an exciting opportunity to simultaneously probe thermal, mechanical, and electrical phenomena in semiconductor devices under bias, providing unique insight into the complex physics that describes device behavior and reliability. Although GaN HEMTs have been specifically used in this study to demonstrate its viability, this technique is applicable to any solid-state material with a suitable Raman response and will likely enable new measurement capabilities in a wide variety of scientific and engineering applications.

Raman technology for future planetary missions

NASA Astrophysics Data System (ADS)

Thiele, Hans; Hofer, Stefan; Stuffler, Timo; Glier, Markus; Popp, Jürgen; Sqalli, Omar; Wuttig, Andreas; Riesenberg, Rainer

2017-11-01

Scientific experiments on mineral and biological samples with Raman excitation below 300nm show a wealth of scientific information. The fluorescence, which typically decreases signal quality in the visual or near infrared wavelength regime can be avoided with deep ultraviolet excitation. This wavelength regime is therefore regarded as highly attractive for a compact high performance Raman spectrometer for in-situ planetary research. Main objective of the MIRAS II breadboard activity presented here (MIRAS: Mineral Investigation with Raman Spectroscopy) is to evaluate, design and build a compact fiber coupled deep-UV Raman system breadboard. Additionally, the Raman system is combined with an innovative scanning microscope system to allow effective auto-focusing and autonomous orientation on the sample surface for high precise positioning or high resolution Raman mapping.

In situ Raman and synchrotron X-ray diffraction study on crystallization of Choline chloride/Urea deep eutectic solvent under high pressure

NASA Astrophysics Data System (ADS)

Yuan, Chaosheng; Chu, Kunkun; Li, Haining; Su, Lei; Yang, Kun; Wang, Yongqiang; Li, Xiaodong

2016-09-01

Pressure-induced crystallization of Choline chloride/Urea (ChCl/Urea) deep eutectic solvent (DES) has been investigated by in-situ Raman spectroscopy and synchrotron X-ray diffraction. The results indicated that high pressure crystals appeared at around 2.6 GPa, and the crystalline structure was different from that formed at ambient pressure. Upon increasing the pressure, the Nsbnd H stretching modes of Urea underwent dramatic change after liquid-solid transition. It appears that high pressures may enhance the hydrogen bonds formed between ChCl and Urea. P versus T phase diagram of ChCl/Urea DES was constructed, and the crystallization mechanism of ChCl/Urea DES was discussed in view of hydrogen bonds.

Tulongicin, an Antibacterial Tri-Indole Alkaloid from a Deep-Water Topsentia sp. Sponge.

PubMed

Liu, Hong-Bing; Lauro, Gianluigi; O'Connor, Robert D; Lohith, Katheryn; Kelly, Michelle; Colin, Patrick; Bifulco, Giuseppe; Bewley, Carole A

2017-09-22

Antibacterial-guided fractionation of an extract of a deep-water Topsentia sp. marine sponge led to the isolation of two new indole alkaloids, tulongicin A (1) and dihydrospongotine C (2), along with two known analogues, spongotine C (3) and dibromodeoxytopsentin (4). Their planar structures were determined by NMR spectroscopy. Their absolute configurations were determined through a combination of experimental and computational analyses. Tulongicin (1) is the first natural product to contain a di(6-Br-1H-indol-3-yl)methyl group linked to an imidazole core. The coexistence of tri-indole 1 and bis-indole alcohol 2 suggests a possible route to 1. All of the compounds showed strong antimicrobial activity against Staphylococcus aureus.

Synthesis of gold nanoflowers using deep eutectic solvent with high surface enhanced Raman scattering properties

NASA Astrophysics Data System (ADS)

Aghakhani Mahyari, Farzaneh; Tohidi, Maryam; Safavi, Afsaneh

2016-09-01

A facile, seed-less and one-pot method was developed for synthesis of gold nanoflowers with multiple tips through reduction of HAuCl4 with deep eutectic solvent at room temperature. This solvent is eco-friendly, low-cost, non-toxic and biodegradable and can act as both reducing and shape-controlling agent. In this protocol, highly branched and stable gold nanoflowers were obtained without using any capping agent. The obtained products were characterized by different techniques including, field emission scanning electron microscopy, transmission electron microscopy, x-ray diffraction and UV-vis spectroscopy. The as-prepared gold nanoflowers exhibit efficient surface-enhanced Raman scattering (SERS) properties which can be used as excellent substrates for SERS.

Solar Cell Fabrication Studies Pertinent to Developing Countries.

NASA Astrophysics Data System (ADS)

Prah, Joseph Henry

That there is a need in the world today, and in the Third World in particular, for developing renewable energy sources is a proposition without question. Toward that end, the harnessing of solar energy has attracted much attention recently. In this thesis, we have addressed the question of Photovoltaics among the many approaches to the problem as being of poignant relevance in the Third World. Based on our studies, which involved the physics of solar cells, various solar cell configurations, the materials for their fabrication and their fabrication sequences, we arrived at the conclusion that silicon homojunction solar cells are best suited to the present needs and environment of, and suitable for development in the Third World, though Cadmium Sulphide-Cuprous Sulphide solar cell could be considered as a viable future candidate. Attendant with the adoption of photovoltaics as electric energy supply, is the problem of technology transfer and development. Towards that goal, we carried out in the laboratory, the fabrication of solar cells using very simple fabrication sequences and materials to demonstrate that tolerable efficiencies are achievable by their use. The view is also presented that for a thriving and viable solar cell industry in the Third World, the sine qua non is an integrated national policies involving all facets of solar cell manufacture and application, namely, material processing and fabrication, basic research, and development and socio -economic acceptance of solar cell appliances. To demonstrate how basic research could benefit solar cell fabrication, we undertook a number of experiments, such as varying our fabrication sequences and materials, finding their radiation tolerance, and carrying out Deep Level Transient Spectroscopy (DLTS) studies, in an attempt to understand some of the fabrication and environmental factors which limit solar cell performance. We thus found that subjecting wafers to preheat treatments does not improve solar cell performance, but rather reduces solar cell radiation tolerance. Also P-type substrate solar cells were found to be more radiation resistant than N-type substrate solar cells. The Deep Level Transient Spectroscopy results showed that carbon and oxygen, as one would expect, are chief contaminants of the silicon wafers that we used in the fabrication of our solar cells. . . . (Author's abstract exceeds stipulated maximum length. Discontinued here with permission of author.) UMI.

Reductive precipitation of neptunium on iron surfaces under anaerobic conditions

NASA Astrophysics Data System (ADS)

Yang, H.; Cui, D.; Grolimund, D.; Rondinella, V. V.; Brütsch, R.; Amme, M.; Kutahyali, C.; Wiss, A. T.; Puranen, A.; Spahiu, K.

2017-12-01

Reductive precipitation of the radiotoxic nuclide 237Np from nuclear waste on the surface of iron canister material at simulated deep repository conditions was investigated. Pristine polished as well as pre-corroded iron specimens were interacted in a deoxygenated solution containing 10-100 μM Np(V), with 10 mM NaCl and 2 mM NaHCO3 as background electrolytes. The reactivity of each of the two different systems was investigated by analyzing the temporal evolution of the Np concentration in the reservoir. It was observed that pre-oxidized iron specimen with a 40 μm Fe3O4 corrosion layer are considerably more reactive regarding the reduction and immobilization of aqueous Np(V) as compared to pristine polished Fe(0) surfaces. 237Np immobilized by the reactive iron surfaces was characterized by scanning electron microscopy as well as synchrotron-based micro-X-ray fluorescence and X-ray absorption spectroscopy. At the end of experiments, a 5-8 μm thick Np-rich layer was observed to be formed ontop of the Fe3O4 corrosion layer on the iron specimen. The findings from this work are significant in the context of performance assessments of deep geologic repositories using iron as high level radioactive waste (HLW) canister material and are of relevance regarding removing pollutants from contaminated soil or groundwater aquifer systems.

Brain proton magnetic resonance spectroscopy for hepatic encephalopathy

NASA Astrophysics Data System (ADS)

Ong, Chin-Sing; McConnell, James R.; Chu, Wei-Kom

1993-08-01

Liver failure can induce gradations of encephalopathy from mild to stupor to deep coma. The objective of this study is to investigate and quantify the variation of biochemical compounds in the brain in patients with liver failure and encephalopathy, through the use of water- suppressed, localized in-vivo Proton Magnetic Resonance Spectroscopy (HMRS). The spectral parameters of the compounds quantitated are: N-Acetyl Aspartate (NAA) to Creatine (Cr) ratio, Choline (Cho) to Creatine ratio, Inositol (Ins) to Creatine ratio and Glutamine-Glutamate Amino Acid (AA) to Creatine ratio. The study group consisted of twelve patients with proven advanced chronic liver failure and symptoms of encephalopathy. Comparison has been done with results obtained from five normal subjects without any evidence of encephalopathy or liver diseases.

Electrical properties of metal/Al2O3/In0.53Ga0.47As capacitors grown on InP

NASA Astrophysics Data System (ADS)

Ferrandis, Philippe; Billaud, Mathilde; Duvernay, Julien; Martin, Mickael; Arnoult, Alexandre; Grampeix, Helen; Cassé, Mikael; Boutry, Hervé; Baron, Thierry; Vinet, Maud; Reimbold, Gilles

2018-04-01

To overcome the Fermi-level pinning in III-V metal-oxide-semiconductor capacitors, attention is usually focused on the choice of dielectric and surface chemical treatments prior to oxide deposition. In this work, we examined the influence of the III-V material surface cleaning and the semiconductor growth technique on the electrical properties of metal/Al2O3/In0.53Ga0.47As capacitors grown on InP(100) substrates. By means of the capacitance-voltage measurements, we demonstrated that samples do not have the same total oxide charge density depending on the cleaning solution used [(NH4)2S or NH4OH] prior to oxide deposition. The determination of the interface trap density revealed that a Fermi-level pinning occurs for samples grown by metalorganic chemical vapor deposition but not for similar samples grown by molecular beam epitaxy. Deep level transient spectroscopy analysis explained the Fermi-level pinning by an additional signal for samples grown by metalorganic chemical vapor deposition, attributed to the tunneling effect of carriers trapped in oxide toward interface states. This work emphasizes that the choice of appropriate oxide and cleaning treatment is not enough to prevent a Fermi-level pinning in III-V metal-oxide-semiconductor capacitors. The semiconductor growth technique needs to be taken into account because it impacts the trapping properties of the oxide.

Processes governing transient responses of the deep ocean buoyancy budget to a doubling of CO2

NASA Astrophysics Data System (ADS)

Palter, J. B.; Griffies, S. M.; Hunter Samuels, B. L.; Galbraith, E. D.; Gnanadesikan, A.

2012-12-01

Recent observational analyses suggest there is a temporal trend and high-frequency variability in deep ocean buoyancy in the last twenty years, a phenomenon reproduced even in low-mixing models. Here we use an earth system model (GFDL's ESM2M) to evaluate physical processes that influence buoyancy (and thus steric sea level) budget of the deep ocean in quasi-steady state and under a doubling of CO2. A new suite of model diagnostics allows us to quantitatively assess every process that influences the buoyancy budget and its temporal evolution, revealing surprising dynamics governing both the equilibrium budget and its transient response to climate change. The results suggest that the temporal evolution of the deep ocean contribution to sea level rise is due to a diversity of processes at high latitudes, whose net effect is then advected in the Eulerian mean flow to mid and low latitudes. In the Southern Ocean, a slowdown in convection and spin up of the residual mean advection are approximately equal players in the deep steric sea level rise. In the North Atlantic, the region of greatest deep steric sea level variability in our simulations, a decrease in mixing of cold, dense waters from the marginal seas and a reduction in open ocean convection causes an accumulation of buoyancy in the deep subpolar gyre, which is then advected equatorward.

On the challenges of using field spectroscopy to measure the impact of soil type on leaf traits

NASA Astrophysics Data System (ADS)

Nunes, Matheus H.; Davey, Matthew P.; Coomes, David A.

2017-07-01

Understanding the causes of variation in functional plant traits is a central issue in ecology, particularly in the context of global change. Spectroscopy is increasingly used for rapid and non-destructive estimation of foliar traits, but few studies have evaluated its accuracy when assessing phenotypic variation in multiple traits. Working with 24 chemical and physical leaf traits of six European tree species growing on strongly contrasting soil types (i.e. deep alluvium versus nearby shallow chalk), we asked (i) whether variability in leaf traits is greater between tree species or soil type, and (ii) whether field spectroscopy is effective at predicting intraspecific variation in leaf traits as well as interspecific differences. Analysis of variance showed that interspecific differences in traits were generally much stronger than intraspecific differences related to soil type, accounting for 25 % versus 5 % of total trait variation, respectively. Structural traits, phenolic defences and pigments were barely affected by soil type. In contrast, foliar concentrations of rock-derived nutrients did vary: P and K concentrations were lower on chalk than alluvial soils, while Ca, Mg, B, Mn and Zn concentrations were all higher, consistent with the findings of previous ecological studies. Foliar traits were predicted from 400 to 2500 nm reflectance spectra collected by field spectroscopy using partial least square regression, a method that is commonly employed in chemometrics. Pigments were best modelled using reflectance data from the visible region (400-700 nm), while all other traits were best modelled using reflectance data from the shortwave infrared region (1100-2500 nm). Spectroscopy delivered accurate predictions of species-level variation in traits. However, it was ineffective at detecting intraspecific variation in rock-derived nutrients (with the notable exception of P). The explanation for this failure is that rock-derived elements do not have absorption features in the 400-2500 nm region, and their estimation is indirect, relying on elemental concentrations covarying with structural traits that do have absorption features in that spectral region (constellation effects). Since the structural traits did not vary with soil type, it was impossible for our regression models to predict intraspecific variation in rock-derived nutrients via constellation effects. This study demonstrates the value of spectroscopy for rapid, non-destructive estimation of foliar traits across species, but highlights problems with predicting intraspecific variation indirectly. We discuss the implications of these findings for mapping functional traits by airborne imaging spectroscopy.

Antitumour polyether macrolides: four new halichondrins from the New Zealand deep-water marine sponge Lissodendoryx sp.

PubMed

Hickford, Sarah J H; Blunt, John W; Munro, Murray H G

2009-03-15

The isolation is reported of four new variants of the halichondrin B skeleton, very minor potently bioactive components from the Poecilosclerid sponge Lissodendoryx sp. These compounds were isolated in microgram quantities only from a collection of 1tonne of sponge. The structural elucidations relied heavily on the use of capillary NMR spectroscopy and the application of an HSQC-DEPT overlay technique.

Non-invasive Assessment of Cerebral Blood Flow and Oxygen Metabolism in Neonates during Hypothermic Cardiopulmonary Bypass: Feasibility and Clinical Implications

PubMed Central

Ferradal, Silvina L.; Yuki, Koichi; Vyas, Rutvi; Ha, Christopher G.; Yi, Francesca; Stopp, Christian; Wypij, David; Cheng, Henry H.; Newburger, Jane W.; Kaza, Aditya K.; Franceschini, Maria A.; Kussman, Barry D.; Grant, P. Ellen

2017-01-01

The neonatal brain is extremely vulnerable to injury during periods of hypoxia and/or ischemia. Risk of brain injury is increased during neonatal cardiac surgery, where pre-existing hemodynamic instability and metabolic abnormalities are combined with long periods of low cerebral blood flow and/or circulatory arrest. Our understanding of events associated with cerebral hypoxia-ischemia during cardiopulmonary bypass (CPB) remains limited, largely due to inadequate tools to quantify cerebral oxygen delivery and consumption non-invasively and in real-time. This pilot study aims to evaluate cerebral blood flow (CBF) and oxygen metabolism (CMRO2) intraoperatively in neonates by combining two novel non-invasive optical techniques: frequency-domain near-infrared spectroscopy (FD-NIRS) and diffuse correlation spectroscopy (DCS). CBF and CMRO2 were quantified before, during and after deep hypothermic cardiopulmonary bypass (CPB) in nine neonates. Our results show significantly decreased CBF and CMRO2 during hypothermic CPB. More interestingly, a change of coupling between both variables is observed during deep hypothermic CPB in all subjects. Our results are consistent with previous studies using invasive techniques, supporting the concept of FD-NIRS/DCS as a promising technology to monitor cerebral physiology in neonates providing the potential for individual optimization of surgical management. PMID:28276534

Non-invasive Assessment of Cerebral Blood Flow and Oxygen Metabolism in Neonates during Hypothermic Cardiopulmonary Bypass: Feasibility and Clinical Implications.

PubMed

Ferradal, Silvina L; Yuki, Koichi; Vyas, Rutvi; Ha, Christopher G; Yi, Francesca; Stopp, Christian; Wypij, David; Cheng, Henry H; Newburger, Jane W; Kaza, Aditya K; Franceschini, Maria A; Kussman, Barry D; Grant, P Ellen

2017-03-09

The neonatal brain is extremely vulnerable to injury during periods of hypoxia and/or ischemia. Risk of brain injury is increased during neonatal cardiac surgery, where pre-existing hemodynamic instability and metabolic abnormalities are combined with long periods of low cerebral blood flow and/or circulatory arrest. Our understanding of events associated with cerebral hypoxia-ischemia during cardiopulmonary bypass (CPB) remains limited, largely due to inadequate tools to quantify cerebral oxygen delivery and consumption non-invasively and in real-time. This pilot study aims to evaluate cerebral blood flow (CBF) and oxygen metabolism (CMRO 2 ) intraoperatively in neonates by combining two novel non-invasive optical techniques: frequency-domain near-infrared spectroscopy (FD-NIRS) and diffuse correlation spectroscopy (DCS). CBF and CMRO 2 were quantified before, during and after deep hypothermic cardiopulmonary bypass (CPB) in nine neonates. Our results show significantly decreased CBF and CMRO 2 during hypothermic CPB. More interestingly, a change of coupling between both variables is observed during deep hypothermic CPB in all subjects. Our results are consistent with previous studies using invasive techniques, supporting the concept of FD-NIRS/DCS as a promising technology to monitor cerebral physiology in neonates providing the potential for individual optimization of surgical management.

Thin teflon-like films for MEMS: Film properties and reliability studies

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

Smith, B.K.; LaVigne, G.; Sniegowski, J.J.

1998-07-01

This work presents film properties and initial reliability studies for thin Teflon-like films applied to a unique test vehicle, the Sandia-designed and fabricated microengine. Results on microengines coated with the film show a factor of three improvement in their lifetime and an order of magnitude reduction in the coefficient of friction when compared to uncoated samples. Coefficients Of Friction (COF) of 0.07 for the Teflon-like film and 1.0 for uncoated samples are extracted from models which match the measured behavior of working microengines. These films, deposited form a plasma source, exhibit the ability to penetrate into very narrow, deep channelsmore » common to many MEMS devices. For as-deposited film, both the refractive index at 1.4 and the contact angle with water at 108{degree} show the film to be very similar to bulk Teflon PTFE. Film stability as a function of temperature has been examined using Fourier Transformation Infrared (FTIR) spectroscopy. The film structure as observed by the fluorine-carbon (F-C) peak is stable up to 200 C, but starts decomposing above 250 C. Film composition has been examined using X-ray photoelectron spectroscopy (XPS) and is quite different for directly exposed surfaces compared with deep, narrow channels where the deposition process is diffusion limited.« less

DENIS J081730.0-615520: AN OVERLOOKED MID-T DWARF IN THE SOLAR NEIGHBORHOOD

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

Artigau, Etienne; Lafreniere, David; Doyon, Rene

2010-07-20

Recent wide-field near-infrared surveys have uncovered a large number of cool brown dwarfs (BDs), extending the temperature sequence down to less than 500 K and constraining the faint end of the luminosity function (LF). One interesting implication of the derived LF is that the BD census in the immediate (<10 pc) solar neighborhood is still largely incomplete, and some bright (J < 16) BDs remain to be identified in existing surveys. These objects are especially interesting as they are the ones that can be studied in most detail, especially with techniques that require large fluxes (e.g., time-variability, polarimetry, and high-resolutionmore » spectroscopy) that cannot realistically be applied to objects uncovered by deep surveys. By cross-matching the DEep Near-Infrared Survey of the Southern sky (DENIS) and the Two Micron All Sky Survey point-source catalogs, we have identified an overlooked BD-DENIS J081730.0-615520-that is the brightest field mid-T dwarf in the sky (J = 13.6). We present astrometry and spectroscopy follow-up observations of this BD. Our data indicate a spectral type T6 and a distance-from parallax measurement-of 4.9 {+-} 0.3 pc, placing this mid-T dwarf among the three closest isolated BDs to the Sun.« less

UV Raman detection of 2,4-DNT in contact with sand particles

NASA Astrophysics Data System (ADS)

Blanco, Alejandro; Pacheco-Londoño, Leonardo C.; Peña-Quevedo, Alvaro J.; Hernández-Rivera, Samuel P.

2006-05-01

Deep Ultra Violet Raman Spectroscopy (DUV-RS) is an emerging tool for vibrational spectroscopy analysis and can be used in Point Detection mode to detect explosive components of landmines and Improvised Explosive Devices (IED). Interactions of explosives with different substrates can be measured by using quantitative vibrational signal shift information of scattered Raman light associated with these interactions. In this research, grounds were laid for detection of explosives using UV-Raman Spectroscopy equipped with 244 nm laser excitation line from a 488 nm frequency doubled Coherent FreD laser. In other experiments, samples of 2,4-DNT were allowed to interact with Ottawa Sand and were studied using DUV-RS. Characteristic vibrational signals of energetic compounds were analyzed in the ranges: 400-1200 cm -1, 1200-1800 cm -1, and 2800-3500 cm -1. In addition these Raman spectra were compared with dispersive spectra that were acquired using Raman Microscopy equipped with 514.5 nm (VIS) 785 nm (NIR) and 1064 nm (NIR) excitation lasers.

In situ dynamic tracking of heterogeneous nanocatalytic processes by shell-isolated nanoparticle-enhanced Raman spectroscopy

PubMed Central

Zhang, Hua; Wang, Chen; Sun, Han-Lei; Fu, Gang; Chen, Shu; Zhang, Yue-Jiao; Chen, Bing-Hui; Anema, Jason R.; Yang, Zhi-Lin; Li, Jian-Feng; Tian, Zhong-Qun

2017-01-01

Surface molecular information acquired in situ from a catalytic process can greatly promote the rational design of highly efficient catalysts by revealing structure-activity relationships and reaction mechanisms. Raman spectroscopy can provide this rich structural information, but normal Raman is not sensitive enough to detect trace active species adsorbed on the surface of catalysts. Here we develop a general method for in situ monitoring of heterogeneous catalytic processes through shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) satellite nanocomposites (Au-core silica-shell nanocatalyst-satellite structures), which are stable and have extremely high surface Raman sensitivity. By combining operando SHINERS with density functional theory calculations, we identify the working mechanisms for CO oxidation over PtFe and Pd nanocatalysts, which are typical low- and high-temperature catalysts, respectively. Active species, such as surface oxides, superoxide/peroxide species and Pd–C/Pt–C bonds are directly observed during the reactions. We demonstrate that in situ SHINERS can provide a deep understanding of the fundamental concepts of catalysis. PMID:28537269

Gemini Observations of Galaxies in Rich Early Environments (GOGREEN) I: survey description

NASA Astrophysics Data System (ADS)

Balogh, Michael L.; Gilbank, David G.; Muzzin, Adam; Rudnick, Gregory; Cooper, Michael C.; Lidman, Chris; Biviano, Andrea; Demarco, Ricardo; McGee, Sean L.; Nantais, Julie B.; Noble, Allison; Old, Lyndsay; Wilson, Gillian; Yee, Howard K. C.; Bellhouse, Callum; Cerulo, Pierluigi; Chan, Jeffrey; Pintos-Castro, Irene; Simpson, Rane; van der Burg, Remco F. J.; Zaritsky, Dennis; Ziparo, Felicia; Alonso, María Victoria; Bower, Richard G.; De Lucia, Gabriella; Finoguenov, Alexis; Lambas, Diego Garcia; Muriel, Hernan; Parker, Laura C.; Rettura, Alessandro; Valotto, Carlos; Wetzel, Andrew

2017-10-01

We describe a new Large Program in progress on the Gemini North and South telescopes: Gemini Observations of Galaxies in Rich Early Environments (GOGREEN). This is an imaging and deep spectroscopic survey of 21 galaxy systems at 1 < z < 1.5, selected to span a factor >10 in halo mass. The scientific objectives include measuring the role of environment in the evolution of low-mass galaxies, and measuring the dynamics and stellar contents of their host haloes. The targets are selected from the SpARCS, SPT, COSMOS, and SXDS surveys, to be the evolutionary counterparts of today's clusters and groups. The new red-sensitive Hamamatsu detectors on GMOS, coupled with the nod-and-shuffle sky subtraction, allow simultaneous wavelength coverage over λ ˜ 0.6-1.05 μm, and this enables a homogeneous and statistically complete redshift survey of galaxies of all types. The spectroscopic sample targets galaxies with AB magnitudes z΄ < 24.25 and [3.6] μm < 22.5, and is therefore statistically complete for stellar masses M* ≳ 1010.3 M⊙, for all galaxy types and over the entire redshift range. Deep, multiwavelength imaging has been acquired over larger fields for most systems, spanning u through K, in addition to deep IRAC imaging at 3.6 μm. The spectroscopy is ˜50 per cent complete as of semester 17A, and we anticipate a final sample of ˜500 new cluster members. Combined with existing spectroscopy on the brighter galaxies from GCLASS, SPT, and other sources, GOGREEN will be a large legacy cluster and field galaxy sample at this redshift that spectroscopically covers a wide range in stellar mass, halo mass, and clustercentric radius.

The Hubble Deep UV Legacy Survey (HDUV)

NASA Astrophysics Data System (ADS)

Montes, Mireia; Oesch, Pascal

2015-08-01

Deep HST imaging has shown that the overall star formation density and UV light density at z>3 is dominated by faint, blue galaxies. Remarkably, very little is known about the equivalent galaxy population at lower redshifts. Understanding how these galaxies evolve across the epoch of peak cosmic star-formation is key to a complete picture of galaxy evolution. Here, we present a new HST WFC3/UVIS program, the Hubble Deep UV (HDUV) legacy survey. The HDUV is a 132 orbit program to obtain deep imaging in two filters (F275W and F336W) over the two CANDELS Deep fields. We will cover ~100 arcmin2 sampling the rest-frame far-UV at z>~0.5, this will provide a unique legacy dataset with exquisite HST multi-wavelength imaging as well as ancillary HST grism NIR spectroscopy for a detailed study of faint, star-forming galaxies at z~0.5-2. The HDUV will enable a wealth of research by the community, which includes tracing the evolution of the FUV luminosity function over the peak of the star formation rate density from z~3 down to z~0.5, measuring the physical properties of sub-L* galaxies, and characterizing resolved stellar populations to decipher the build-up of the Hubble sequence from sub-galactic clumps. This poster provides an overview of the HDUV survey and presents the reduced data products and catalogs which will be released to the community, reaching down to 27.5-28.0 mag at 5 sigma. By directly sampling the rest-frame far-UV at z>~0.5, this will provide a unique legacy dataset with exquisite HST multi-wavelength imaging as well as ancillary HST grism NIR spectroscopy for a detailed study of faint, star-forming galaxies at z~0.5-2. The HDUV will enable a wealth of research by the community, which includes tracing the evolution of the FUV luminosity function over the peak of the star formation rate density from z~3 down to z~0.5, measuring the physical properties of sub-L* galaxies, and characterizing resolved stellar populations to decipher the build-up of the Hubble sequence from sub-galactic clumps. This poster provides an overview of the HDUV survey and presents reduced data products and catalogs which will be released to the community.

Cerebral oximetry during infant cardiac surgery: evaluation and relationship to early postoperative outcome.

PubMed

Kussman, Barry D; Wypij, David; DiNardo, James A; Newburger, Jane W; Mayer, John E; del Nido, Pedro J; Bacha, Emile A; Pigula, Frank; McGrath, Ellen; Laussen, Peter C

2009-04-01

We examined changes in cerebral oxygen saturation during infant heart surgery and its relationship to anatomic diagnosis and early outcome. Regional cerebral oxygen saturation (rSO(2)) was measured by near-infrared spectroscopy in 104 infants undergoing biventricular repair without aortic arch obstruction as part of a randomized trial of hemodilution to a hematocrit of 25% vs 35%. Before cardiopulmonary bypass (CPB), infants with tetralogy of Fallot had higher rSO(2) values compared to those with D-transposition of the great arteries (D-TGA) or ventricular septal defect (P < 0.001). During CPB cooling, low flow, and at the termination of CPB, D-TGA subjects had the highest rSO(2) values (P < 0.001). There were no significant associations between intraoperative rSO(2) and early postoperative outcomes after adjustment for diagnosis. In 39 D-TGA subjects with > or =5 min of deep hypothermic circulatory arrest (DHCA), there was no correlation between the rSO(2) (91% +/- 6%) or hematocrit (29.2% +/- 5.5%) at the onset of arrest and the rate of decline in rSO(2) during arrest. Intraoperative rSO(2) varies according to anatomic diagnosis but accounts for very little of the variance in early outcome. As measured by frontal near-infrared spectroscopy, higher levels of hematocrit and current perfusion techniques appear to provide an adequate oxygen reservoir prior to relatively short periods of DHCA.

Micro- to nanostructure and geochemistry of extant crinoidal echinoderm skeletons.

PubMed

Gorzelak, P; Stolarski, J; Mazur, M; Meibom, A

2013-01-01

This paper reports the results of micro- to nanostructural and geochemical analyses of calcitic skeletons from extant deep-sea stalked crinoids. Fine-scale (SEM, FESEM, AFM) observations show that the crinoid skeleton is composed of carbonate nanograins, about 20-100 nm in diameter, which are partly separated by what appears to be a few nm thick organic layers. Sub-micrometre-scale geochemical mapping of crinoid ossicles using a NanoSIMS ion microprobe, combined with synchrotron high-spatial-resolution X-ray micro-fluorescence (μ-XRF) maps and X-ray absorption near-edge structure spectroscopy (XANES) show that high Mg concentration in the central region of the stereom bars correlates with the distribution of S-sulphate, which is often associated with sulphated polysaccharides in biocarbonates. These data are consistent with biomineralization models suggesting a close association between organic components (including sulphated polysaccharides) and Mg ions. Additionally, geochemical analyses (NanoSIMS, energy dispersive spectroscopy) reveal that significant variations in Mg occur at many levels: within a single stereom trabecula, within a single ossicle and within a skeleton of a single animal. Together, these data suggest that physiological factors play an important role in controlling Mg content in crinoid skeletons and that great care should be taken when using their skeletons to reconstruct, for example, palaeotemperatures and Mg/Ca palaeo-variations of the ocean. © 2012 Blackwell Publishing Ltd.

Partially Ionized Beam Deposition of Silicon-Dioxide and Aluminum Thin Films - Defects Generation.

NASA Astrophysics Data System (ADS)

Wong, Justin Wai-Chow

1987-09-01

Detect formation in SiO_2 and Al thin films and interfaces were studied using a partially ionized beam (PIB) deposition technique. The evaporated species (the deposition material) were partially ionized to give an ion/atom ratio of <=q0.1% and the substrate was biased at 0-5kV during the deposition. The results suggest that due to the ion bombardment, stoichiometric SiO_2 films can be deposited at a low substrate temperature (~300 ^circC) and low oxygen pressure (<=q10^{-4} Torr). Such deposition cannot be achieved using conventional evaporation-deposition techniques. However, traps and mobile ions were observed in the oxide and local melt-down was observed when a sufficiently high electric field was applied to the film. For the PIB Al deposition on the Si substrate, stable Al/Si Schottky contact was formed when the substrate bias was <=q1kV. For a substrate bias of 2.5kV, the capacitance of the Al/Si interface increased dramatically. A model of self-ion implantation with a p-n junction created by the Al^+ ion implantation was proposed and tested to explain the increase of the interface capacitance. Several deep level states at the Al/Si interface were observed using Deep Level Transient Spectroscopy (DLTS) technique when the film was deposited at a bias of 3kV. The PIB Al films deposited on the Si substrate showed unusually strong electromigration resistance under high current density operation. This phenomenon was explained by the highly oriented microstructure of the Al films created by the self-ion bombardment during deposition. These findings show that PIB has potential applications in a number of areas, including low temperature thin film deposition, and epitaxial growth of thin films in the microelectronics thin film industry.

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

Shang, Yu; Yu, Guoqiang, E-mail: guoqiang.yu@uky.edu

Conventional semi-infinite analytical solutions of correlation diffusion equation may lead to errors when calculating blood flow index (BFI) from diffuse correlation spectroscopy (DCS) measurements in tissues with irregular geometries. Very recently, we created an algorithm integrating a Nth-order linear model of autocorrelation function with the Monte Carlo simulation of photon migrations in homogenous tissues with arbitrary geometries for extraction of BFI (i.e., αD{sub B}). The purpose of this study is to extend the capability of the Nth-order linear algorithm for extracting BFI in heterogeneous tissues with arbitrary geometries. The previous linear algorithm was modified to extract BFIs in different typesmore » of tissues simultaneously through utilizing DCS data at multiple source-detector separations. We compared the proposed linear algorithm with the semi-infinite homogenous solution in a computer model of adult head with heterogeneous tissue layers of scalp, skull, cerebrospinal fluid, and brain. To test the capability of the linear algorithm for extracting relative changes of cerebral blood flow (rCBF) in deep brain, we assigned ten levels of αD{sub B} in the brain layer with a step decrement of 10% while maintaining αD{sub B} values constant in other layers. Simulation results demonstrate the accuracy (errors < 3%) of high-order (N ≥ 5) linear algorithm in extracting BFIs in different tissue layers and rCBF in deep brain. By contrast, the semi-infinite homogenous solution resulted in substantial errors in rCBF (34.5% ≤ errors ≤ 60.2%) and BFIs in different layers. The Nth-order linear model simplifies data analysis, thus allowing for online data processing and displaying. Future study will test this linear algorithm in heterogeneous tissues with different levels of blood flow variations and noises.« less

The Grism Lens-amplified Survey from Space (GLASS). IV. Mass Reconstruction of the Lensing Cluster Abell 2744 from Frontier Field Imaging and GLASS Spectroscopy

NASA Astrophysics Data System (ADS)

Wang, X.; Hoag, A.; Huang, K.-H.; Treu, T.; Bradač, M.; Schmidt, K. B.; Brammer, G. B.; Vulcani, B.; Jones, T. A.; Ryan, R. E., Jr.; Amorín, R.; Castellano, M.; Fontana, A.; Merlin, E.; Trenti, M.

2015-09-01

We present a strong and weak lensing reconstruction of the massive cluster Abell 2744, the first cluster for which deep Hubble Frontier Fields (HFF) images and spectroscopy from the Grism Lens-Amplified Survey from Space (GLASS) are available. By performing a targeted search for emission lines in multiply imaged sources using the GLASS spectra, we obtain five high-confidence spectroscopic redshifts and two tentative ones. We confirm one strongly lensed system by detecting the same emission lines in all three multiple images. We also search for additional line emitters blindly and use the full GLASS spectroscopic catalog to test reliability of photometric redshifts for faint line emitters. We see a reasonable agreement between our photometric and spectroscopic redshift measurements, when including nebular emission in photometric redshift estimations. We introduce a stringent procedure to identify only secure multiple image sets based on colors, morphology, and spectroscopy. By combining 7 multiple image systems with secure spectroscopic redshifts (at 5 distinct redshift planes) with 18 multiple image systems with secure photometric redshifts, we reconstruct the gravitational potential of the cluster pixellated on an adaptive grid, using a total of 72 images. The resulting mass map is compared with a stellar mass map obtained from the deep Spitzer Frontier Fields data to study the relative distribution of stars and dark matter in the cluster. We find that the stellar to total mass ratio varies substantially across the cluster field, suggesting that stars do not trace exactly the total mass in this interacting system. The maps of convergence, shear, and magnification are made available in the standard HFF format.

THE GRISM LENS-AMPLIFIED SURVEY FROM SPACE (GLASS). IV. MASS RECONSTRUCTION OF THE LENSING CLUSTER ABELL 2744 FROM FRONTIER FIELD IMAGING AND GLASS SPECTROSCOPY

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

Wang, X.; Schmidt, K. B.; Jones, T. A.

2015-09-20

We present a strong and weak lensing reconstruction of the massive cluster Abell 2744, the first cluster for which deep Hubble Frontier Fields (HFF) images and spectroscopy from the Grism Lens-Amplified Survey from Space (GLASS) are available. By performing a targeted search for emission lines in multiply imaged sources using the GLASS spectra, we obtain five high-confidence spectroscopic redshifts and two tentative ones. We confirm one strongly lensed system by detecting the same emission lines in all three multiple images. We also search for additional line emitters blindly and use the full GLASS spectroscopic catalog to test reliability of photometricmore » redshifts for faint line emitters. We see a reasonable agreement between our photometric and spectroscopic redshift measurements, when including nebular emission in photometric redshift estimations. We introduce a stringent procedure to identify only secure multiple image sets based on colors, morphology, and spectroscopy. By combining 7 multiple image systems with secure spectroscopic redshifts (at 5 distinct redshift planes) with 18 multiple image systems with secure photometric redshifts, we reconstruct the gravitational potential of the cluster pixellated on an adaptive grid, using a total of 72 images. The resulting mass map is compared with a stellar mass map obtained from the deep Spitzer Frontier Fields data to study the relative distribution of stars and dark matter in the cluster. We find that the stellar to total mass ratio varies substantially across the cluster field, suggesting that stars do not trace exactly the total mass in this interacting system. The maps of convergence, shear, and magnification are made available in the standard HFF format.« less

Integrated Mg/TiO2-ionic liquid system for deep desulfurization

NASA Astrophysics Data System (ADS)

Yin, Yee Cia; Kait, Chong Fai; Fatimah, Hayyiratul; Wilfred, Cecilia

2014-10-01

A series of Mg/TiO2 photocatalysts were prepared using wet impregnation method followed by calcination at 300, 400 and 500°C for 1 h. The photocatalysts were characterized using Thermal Gravimetric Analysis, Fourier-Transform Infrared Spectroscopy, X-Ray Diffraction, and Field Emission Scanning Electron Microscopy. The performance for deep desulfurization was investigated using model oil with 100 ppm sulfur (in the form of dibenzothiophene). The integrated system involves photocatalytic oxidation followed by ionic liquid-extraction processes. The best performing photocatalyst was 0.25wt% Mg loaded on titania calcined at 400°C (0.25Mg400), giving 98.5% conversion of dibenzothiophene to dibenzothiophene sulfone. The highest extraction efficiency of 97.8% was displayed by 1,2-diethylimidazolium diethylphosphate. The overall total sulfur removal was 96.3%.

The endpoint detection technique for deep submicrometer plasma etching

NASA Astrophysics Data System (ADS)

Wang, Wei; Du, Zhi-yun; Zeng, Yong; Lan, Zhong-went

2009-07-01

The availability of reliable optical sensor technology provides opportunities to better characterize and control plasma etching processes in real time, they could play a important role in endpoint detection, fault diagnostics and processes feedback control and so on. The optical emission spectroscopy (OES) method becomes deficient in the case of deep submicrometer gate etching. In the newly developed high density inductively coupled plasma (HD-ICP) etching system, Interferometry endpoint (IEP) is introduced to get the EPD. The IEP fringe count algorithm is investigated to predict the end point, and then its signal is used to control etching rate and to call end point with OES signal in over etching (OE) processes step. The experiment results show that IEP together with OES provide extra process control margin for advanced device with thinner gate oxide.

The effect of SF6 addition in a Cl2/Ar inductively coupled plasma for deep titanium etching

NASA Astrophysics Data System (ADS)

Laudrel, E.; Tillocher, T.; Meric, Y.; Lefaucheux, P.; Boutaud, B.; Dussart, R.

2018-05-01

Titanium is a material of interest for the biomedical field and more particularly for body implantable devices. Titanium deep etching by plasma was carried out in an inductively coupled plasma with a chlorine-based chemistry for the fabrication of titanium-based microdevices. Bulk titanium etch rate was first studied in Cl2/Ar plasma mixture versus the source power and the self-bias voltage. The plasma was characterized by Langmuir probe and by optical emission spectroscopy. The addition of SF6 in the plasma mixture was investigated. Titanium etch rate was optimized and reached a value of 2.4 µm · min-1. The nickel hard mask selectivity was also enhanced. The etched titanium surface roughness was reduced significantly.

Fully reflective deep ultraviolet to near infrared spectrometer and entrance optics for resonance Raman spectroscopy

NASA Astrophysics Data System (ADS)

Schulz, B.; Bäckström, J.; Budelmann, D.; Maeser, R.; Rübhausen, M.; Klein, M. V.; Schoeffel, E.; Mihill, A.; Yoon, S.

2005-07-01

We present the design and performance of a new triple-grating deep ultraviolet to near-infrared spectrometer. The system is fully achromatic due to the use of reflective optics. The minimization of image aberrations by using on- and off- axis parabolic mirrors as well as elliptical mirrors yields a strong stray light rejection with high resolution over a wavelength range between 165 and 1000nm. The Raman signal is collected with a reflective entrance objective with a numerical aperture of 0.5, featuring a Cassegrain-type design. Resonance Raman studies on semiconductors and on correlated compounds, such as LaMnO3, highlight the performance of this instrument, and show diverse resonance effects between 1.96 and 5.4eV.

[Progress in Raman spectroscopic measurement of methane hydrate].

PubMed

Xu, Feng; Zhu, Li-hua; Wu, Qiang; Xu, Long-jun

2009-09-01

Complex thermodynamics and kinetics problems are involved in the methane hydrate formation and decomposition, and these problems are crucial to understanding the mechanisms of hydrate formation and hydrate decomposition. However, it was difficult to accurately obtain such information due to the difficulty of measurement since methane hydrate is only stable under low temperature and high pressure condition, and until recent years, methane hydrate has been measured in situ using Raman spectroscopy. Raman spectroscopy, a non-destructive and non-invasive technique, is used to study vibrational modes of molecules. Studies of methane hydrate using Raman spectroscopy have been developed over the last decade. The Raman spectra of CH4 in vapor phase and in hydrate phase are presented in this paper. The progress in the research on methane hydrate formation thermodynamics, formation kinetics, decomposition kinetics and decomposition mechanism based on Raman spectroscopic measurements in the laboratory and deep sea are reviewed. Formation thermodynamic studies, including in situ observation of formation condition of methane hydrate, analysis of structure, and determination of hydrate cage occupancy and hydration numbers by using Raman spectroscopy, are emphasized. In the aspect of formation kinetics, research on variation in hydrate cage amount and methane concentration in water during the growth of hydrate using Raman spectroscopy is also introduced. For the methane hydrate decomposition, the investigation associated with decomposition mechanism, the mutative law of cage occupancy ratio and the formulation of decomposition rate in porous media are described. The important aspects for future hydrate research based on Raman spectroscopy are discussed.

Hepatic gene expression profiling of 5'-AMP-induced hypometabolism in mice.

PubMed

Zhao, Zhaoyang; Miki, Takao; Van Oort-Jansen, Anita; Matsumoto, Tomoko; Loose, David S; Lee, Cheng Chi

2011-04-12

There is currently much interest in clinical applications of therapeutic hypothermia. Hypothermia can be a consequence of hypometabolism. We have recently established a procedure for the induction of a reversible deep hypometabolic state in mice using 5'-adenosine monophosphate (5'-AMP) in conjunction with moderate ambient temperature. The current study aims at investigating the impact of this technology at the gene expression level in a major metabolic organ, the liver. Our findings reveal that expression levels of the majority of genes in liver are not significantly altered by deep hypometabolism. However, among those affected by hypometabolism, more genes are differentially upregulated than downregulated both in a deep hypometabolic state and in the early arousal state. These altered gene expression levels during 5'-AMP induced hypometabolism are largely restored to normal levels within 2 days of the treatment. Our data also suggest that temporal control of circadian genes is largely stalled during deep hypometabolism.

Paleozoic oil/gas shale reservoirs in southern Tunisia: An overview

NASA Astrophysics Data System (ADS)

Soua, Mohamed

2014-12-01

During these last years, considerable attention has been given to unconventional oil and gas shale in northern Africa where the most productive Paleozoic basins are located (e.g. Berkine, Illizi, Kufra, Murzuk, Tindouf, Ahnet, Oued Mya, Mouydir, etc.). In most petroleum systems, which characterize these basins, the Silurian played the main role in hydrocarbon generation with two main 'hot' shale levels distributed in different locations (basins) and their deposition was restricted to the Rhuddanian (Lllandovery: early Silurian) and the Ludlow-Pridoli (late Silurian). A third major hot shale level had been identified in the Frasnian (Upper Devonian). Southern Tunisia is characterized by three main Paleozoic sedimentary basins, which are from North to South, the southern Chotts, Jeffara and Berkine Basin. They are separated by a major roughly E-W trending lower Paleozoic structural high, which encompass the Mehrez-Oued Hamous uplift to the West (Algeria) and the Nefusa uplift to the East (Libya), passing by the Touggourt-Talemzane-PGA-Bou Namcha (TTPB) structure close to southern Tunisia. The forementioned major source rocks in southern Tunisia are defined by hot shales with elevated Gamma ray values often exceeding 1400 API (in Hayatt-1 well), deposited in deep water environments during short lived (c. 2 Ma) periods of anoxia. In the course of this review, thickness, distribution and maturity maps have been established for each hot shale level using data for more than 70 wells located in both Tunisia and Algeria. Mineralogical modeling was achieved using Spectral Gamma Ray data (U, Th, K), SopectroLith logs (to acquire data for Fe, Si and Ti) and Elemental Capture Spectroscopy (ECS). The latter technique provided data for quartz, pyrite, carbonate, clay and Sulfur. In addition to this, the Gamma Ray (GR), Neutron Porosity (ΦN), deep Resistivity (Rt) and Bulk Density (ρb) logs were used to model bulk mineralogy and lithology. Biostratigraphic and complete geochemical review has been undertaken from published papers and unpublished internal reports to better assess these important source intervals.

A Wide Band Gap Polymer with a Deep Highest Occupied Molecular Orbital Level Enables 14.2% Efficiency in Polymer Solar Cells.

PubMed

Li, Sunsun; Ye, Long; Zhao, Wenchao; Yan, Hongping; Yang, Bei; Liu, Delong; Li, Wanning; Ade, Harald; Hou, Jianhui

2018-05-21

To simultaneously achieve low photon energy loss ( E loss ) and broad spectral response, the molecular design of the wide band gap (WBG) donor polymer with a deep HOMO level is of critical importance in fullerene-free polymer solar cells (PSCs). Herein, we developed a new benzodithiophene unit, i.e., DTBDT-EF, and conducted systematic investigations on a WBG DTBDT-EF-based donor polymer, namely, PDTB-EF-T. Due to the synergistic electron-withdrawing effect of the fluorine atom and ester group, PDTB-EF-T exhibits a higher oxidation potential, i.e., a deeper HOMO level (ca. -5.5 eV) than most well-known donor polymers. Hence, a high open-circuit voltage of 0.90 V was obtained when paired with a fluorinated small molecule acceptor (IT-4F), corresponding to a low E loss of 0.62 eV. Furthermore, side-chain engineering demonstrated that subtle side-chain modulation of the ester greatly influences the aggregation effects and molecular packing of polymer PDTB-EF-T. With the benefits of the stronger interchain π-π interaction, the improved ordering structure, and thus the highest hole mobility, the most symmetric charge transport and reduced recombination are achieved for the linear decyl-substituted PDTB-EF-T (P2)-based PSCs, leading to the highest short-circuit current density and fill factor (FF). Due to the high Flory-Huggins interaction parameter (χ), surface-directed phase separation occurs in the P2:IT-4F blend, which is supported by X-ray photoemission spectroscopy results and cross-sectional transmission electron microscope images. By taking advantage of the vertical phase distribution of the P2:IT-4F blend, a high power conversion efficiency (PCE) of 14.2% with an outstanding FF of 0.76 was recorded for inverted devices. These results demonstrate the great potential of the DTBDT-EF unit for future organic photovoltaic applications.

The Effects of Test Anxiety on Learning at Superficial and Deep Levels of Processing.

ERIC Educational Resources Information Center

Weinstein, Claire E.; And Others

1982-01-01

Using a deep-level processing strategy, low test-anxious college students performed significantly better than high test-anxious students in learning a paired-associate word list. Using a superficial-level processing strategy resulted in no significant difference in performance. A cognitive-attentional theory and test anxiety mechanisms are…

Optoacoustic Spectroscopy.

DTIC Science & Technology

1984-06-15

cosmic ray muons or neutrinos) in deep oceans. To cause acoustic generation, the incident beam can be pulsed, or modulated at close to 50% duty...the case in most OA studies) or in other spectral regions from RF to X- rays ; it can also be a particle beam of electron, proton, muon , neutrino, 0. etc...discovered by A. G. Bell in 1880, who observed that audible sound is produced when chopped sunlight is absorbed at a surface . Although the OA effect

Reconciliation of late Quaternary sea levels derived from coral terraces at Huon Peninsula with deep sea oxygen isotope records

NASA Astrophysics Data System (ADS)

Chappell, John; Omura, Akio; Esat, Tezer; McCulloch, Malcolm; Pandolfi, John; Ota, Yoko; Pillans, Brad

1996-06-01

A major discrepancy between the Late Quaternary sea level changes derived from raised coral reef terraces at the Huon Peninsula in Papua New Guinea and from oxygen isotopes in deep sea cores is resolved. The two methods agree closely from 120 ka to 80 ka and from 20 ka to 0 ka (ka = 1000 yr before present), but between 70 and 30 ka the isotopic sea levels are 20-40 m lower than the Huon Peninsula sea levels derived in earlier studies. New, high precision U-series age measurements and revised stratigraphic data for Huon Peninsula terraces aged between 30 and 70 ka now give similar sea levels to those based on deep sea oxygen isotope data planktonic and benthic δ 18O data. Using the sea level and deep sea isotopic data, oxygen isotope ratios are calculated for the northern continental ice sheets through the last glacial cycle and are consistent with results from Greenland ice cores. The record of ice volume changes through the last glacial cycle now appears to be reasonably complete.

A deep learning framework for financial time series using stacked autoencoders and long-short term memory.

PubMed

Bao, Wei; Yue, Jun; Rao, Yulei

2017-01-01

The application of deep learning approaches to finance has received a great deal of attention from both investors and researchers. This study presents a novel deep learning framework where wavelet transforms (WT), stacked autoencoders (SAEs) and long-short term memory (LSTM) are combined for stock price forecasting. The SAEs for hierarchically extracted deep features is introduced into stock price forecasting for the first time. The deep learning framework comprises three stages. First, the stock price time series is decomposed by WT to eliminate noise. Second, SAEs is applied to generate deep high-level features for predicting the stock price. Third, high-level denoising features are fed into LSTM to forecast the next day's closing price. Six market indices and their corresponding index futures are chosen to examine the performance of the proposed model. Results show that the proposed model outperforms other similar models in both predictive accuracy and profitability performance.

Growth of bulk ZnO crystals by self-selecting CVT method

NASA Astrophysics Data System (ADS)

Fan, Long; Jiang, Tao; Xiao, TingTing; Chen, Jie; Peng, Liping; Wang, Xuemin; Yan, Dawei; Wu, Weidong

2018-05-01

Bulk ZnO crystals were grown by self-selecting CVT method using carbon as the transport agent. The crystal growth process took place on the top of the polycrystalline source material, and deep-red colored ZnO crystals of several millimeters were obtained. The as-grown crystals were characterized by X-ray diffraction (XRD), Energy Dispersive Spectrometer (EDS), Raman scattering (RS) spectroscopy, visible-near infrared (VIS-NIR) spectrophotometer and room temperature photoluminescence (PL) spectroscopy. XRD results indicate good crystallinity of the ZnO crystal. The EDS analysis shows that the crystal has a stoichiometry ratio Zn: O = 52: 48. The results suggest the existence of native defects of oxygen vacancies (OV) in the as-grown ZnO samples, which is caused by the stoichiometry shift to Zn-rich.

Speckle contrast optical spectroscopy, a non-invasive, diffuse optical method for measuring microvascular blood flow in tissue

PubMed Central

Valdes, Claudia P.; Varma, Hari M.; Kristoffersen, Anna K.; Dragojevic, Tanja; Culver, Joseph P.; Durduran, Turgut

2014-01-01

We introduce a new, non-invasive, diffuse optical technique, speckle contrast optical spectroscopy (SCOS), for probing deep tissue blood flow using the statistical properties of laser speckle contrast and the photon diffusion model for a point source. The feasibility of the method is tested using liquid phantoms which demonstrate that SCOS is capable of measuring the dynamic properties of turbid media non-invasively. We further present an in vivo measurement in a human forearm muscle using SCOS in two modalities: one with the dependence of the speckle contrast on the source-detector separation and another on the exposure time. In doing so, we also introduce crucial corrections to the speckle contrast that account for the variance of the shot and sensor dark noises. PMID:25136500

Characterisation of a novel transmission Raman spectroscopy platform for non-invasive detection of breast micro-calcifications

NASA Astrophysics Data System (ADS)

Ghita, Adrian; Matousek, Pavel; Stone, Nick

2018-02-01

Our work focuses on the development of a medical Raman spectroscopy based platform to non-invasively detect and determine in-vivo molecular information deep inside biological tissues by monitoring the chemical composition of breast calcifications. The ultimate goal is to replace a needle biopsy which typically follows the detection of an abnormality in mammographic images. Here we report the non-invasive detection of calcium oxalate monohydrate in tissue through 40 mm of phantom tissues using our recently developed advanced Raman instrument complementing our previous detection of calcium hydroxyapatite through this thickness of tissue. The ability to detect these two key types of calcifications opens avenues for the development of non-invasive in-vivo breast cancer diagnostic tool in the future.

Band Transport and Trapping in Didodecyl[1]benzothieno[3,2-b][1]benzothiophene Probed by Terahertz Spectroscopy.

PubMed

Arend, Thomas R; Wimmer, Andreas; Schweicher, Guillaume; Chattopadhyay, Basab; Geerts, Yves H; Kersting, Roland

2017-11-02

Terahertz electromodulation spectroscopy provides insight into the material-inherent transport properties of charge carriers in organic semiconductors. Experiments on didodecyl[1]benzothieno[3,2-b][1]benzothiophene (C 12 -BTBT-C 12 ) devices yield for holes an intraband mobility of 9 cm 2 V -1 s -1 . The short duration of the THz pulses advances the understanding of the hole transport on the molecular scale. The efficient screening of Coulomb potentials leads to a collective response of the hole gas to external fields, which can be well described by the Drude model. Bias stress of the devices generates deep traps that capture mobile holes. Although the resulting polarization across the device hinders the injection of mobile holes, the hole mobilities are not affected.

Melting of iron determined by X-ray absorption spectroscopy to 100 GPa

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

Aquilanti, Giuliana; Trapananti, Angela; Karandikar, Amol

2015-09-14

There is a long-standing controversy over the melting curve of Fe at high pressure as determined from static laser heated diamond anvil cell and dynamic compression studies. X-ray absorption spectroscopy measurements are used here as a criterion to detect melting under pressure. Confronted with a diversity of obtained melting curves, this technique, used at such pressure and temperature conditions, is eligible to be at the forefront to probe Earth's deep interior. Furthermore, the experiment reported here holds promise for addressing important issues related to the structure and phase diagram of compressed melts, such as the existence of structural complexity (polyamorphism)more » in the liquid phase or the extent of icosahedral ordering whose investigation has been limited until now to ambient conditions.« less

Deep-level dominated electrical characteristics of Au contacts on beta-SiC

NASA Technical Reports Server (NTRS)

Das, K.; Kong, H. S.; Petit, J. B.; Bumgarner, J. W.; Davis, R. F.; Matus, L. G.

1990-01-01

Electrical characteristics of Au contacts on beta-SiC films, grown epitaxially on both nominal and off-axis (100) silicon substrates, are reported. An analysis of the logarithmic I-V plots of the Au/beta-SiC diodes revealed information pertaining to the deep states present in the materials. It was found that while the beta-SiC films grown on nominally (100) oriented substrates show the presence of two deep levels located between 0.26 and 0.38 eV below the conduction bandedge, the beta-SiC films deposited on off-axis substrates have only one deep level, located about 0.49 eV below the conduction bandedge for the 2-deg off (100) substrates and 0.57 eV for the 4-deg off (100) substrates. The presence of the shallower deep states in the beta-SiC films grown on nominal (100) substrates is attributed to the electrical activity of antiphase domain boundaries.

A High-Resolution Multitechniques Approach to Characterize Bio-Organo-Mineral Associations Within Rock Samples: Tracking Biological vs Abiotic Processes? Towards a Better Understanding of the Deep Carbon Cycle.

NASA Astrophysics Data System (ADS)

Pisapia, C.

2015-12-01

Among all elements, carbon plays one of the major roles for the sustainability of life on Earth. Past considerations of the carbon cycle have mainly focused on surface processes occurring at the atmosphere, oceans and shallow crustal environments. By contrast, little is known about the Deep Carbon cycle whereas both geochemical and biological processes may induce organic carbon production and/or consumption at depth. Indeed, the nowadays-recognized capability of geochemical processes such as serpentinization to generate abiotic organic compounds as well as the existence of a potentially important intraterrestrial life raises questions about the limit of biotic/abiotic carbon on Earth's deep interior and how it impacts global biogeochemical cycles. It is then mandatory to increase our knowledge on the nature and extent of carbon reservoirs along with their sources, sinks and fluxes in the subsurface. This implies to be able to finely characterize organomineral associations within crustal rocks although it might be hampered by the scarceness and heterogeneous micrometric spatial distribution of organic molecules in natural rocks. We then developed an in situ analytical strategy based on the combination of high-resolution techniques to track organic molecules at the pore level in natural rocks and to determine their biological or abiotic origin. We associated classical high-resolution techniques and synchrotron-based imaging techniques in order to characterize their nature and localization (SEM/TEM, coupled CLSM/Raman spectroscopy, Tof-SIMS) along with their 3D-distribution relatively to mineral phases (S-FTIR, S-DeepUV, XANES, Biphoton microscopy). The effectiveness of this approach to shed light on the speciation and nature of carbon in subsurface environments will be illustrated through the study of (i) subsurface ecosystems and abiotic organic carbon within ultramafic rocks of the oceanic lithosphere as putative analogs for the nature and functioning of primitive ecosystems on Earth and of (ii) ecosystems inhabiting Archean craton and potentially playing a role in punk-rock karstification processes and rocks weathering.

Ionization processes in a local analogue of distant clumpy galaxies: VLT MUSE IFU spectroscopy and FORS deep images of the TDG NGC 5291N

NASA Astrophysics Data System (ADS)

Fensch, J.; Duc, P.-A.; Weilbacher, P. M.; Boquien, M.; Zackrisson, E.

2016-01-01

Context. We present Integral Field Unit (IFU) observations with MUSE and deep imaging with FORS of a dwarf galaxy recently formed within the giant collisional HI ring surrounding NGC 5291. This Tidal Dwarf Galaxy (TDG) -like object has the characteristics of typical z = 1-2 gas-rich spiral galaxies: a high gas fraction, a rather turbulent clumpy interstellar medium, the absence of an old stellar population, and a moderate metallicity and star formation efficiency. Aims: The MUSE spectra allow us to determine the physical conditions within the various complex substructures revealed by the deep optical images and to scrutinize the ionization processes at play in this specific medium at unprecedented spatial resolution. Methods: Starburst age, extinction, and metallicity maps of the TDG and the surrounding regions were determined using the strong emission lines Hβ, [OIII], [OI], [NII], Hα, and [SII] combined with empirical diagnostics. Different ionization mechanisms were distinguished using BPT-like diagrams and shock plus photoionization models. Results: In general, the physical conditions within the star-forming regions are homogeneous, in particular with a uniform half-solar oxygen abundance. On small scales, the derived extinction map shows narrow dust lanes. Regions with atypically strong [OI] emission line immediately surround the TDG. The [OI]/ Hα ratio cannot be easily accounted for by the photoionization by young stars or shock models. At greater distances from the main star-foming clumps, a faint diffuse blue continuum emission is observed, both with the deep FORS images and the MUSE data. It does not have a clear counterpart in the UV regime probed by GALEX. A stacked spectrum towards this region does not exhibit any emission line, excluding faint levels of star formation, or stellar absorption lines that might have revealed the presence of old stars. Several hypotheses are discussed for the origin of these intriguing features. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile: ESO MUSE programme 60.A-9320(A) and FORS programme 382.B-0213(A).

Electronic characterization of defects in narrow gap semiconductors

NASA Technical Reports Server (NTRS)

Patterson, James D.

1994-01-01

We use a Green's function technique to calculate the position of deep defects in narrow gap semiconductors. We consider substitutional (including antisite), vacancy, and interstitial (self and foreign) deep defects. We also use perturbation theory to look at the effect of nonparabolic bands on shallow defect energies and find nonparabolicity can increase the binding by 10 percent or so. We consider mercury cadmium telluride (MCT), mercury zinc telluride (MZT), and mercury zinc selenide (MZS). For substitutional and interstitial defects we look at the situation with and without relaxation. For substitutional impurities in MCT, MZT, and MZS, we consider x (the concentration of Cd or Zn) in the range 0.1 less than x less than 0.3 and also consider appropriate x so E(sub g) = 0.1 eV for each of the three compounds. We consider several cation site s-like deep levels and anion site p-like levels. For E(sub g) = 0.1 eV, we also consider the effects of relaxation. Similar comments apply to the interstitial deep levels whereas no relaxation is considered for the ideal vacancy model. Relaxation effects can be greater for the interstitial than the substitutional cases. Specific results are given in figures and tables and comparison to experiment is made in a limited number of cases. We find, for example, that I, Se, S, Rn, and N are possible cation site, s-like deep levels in MCT and Zn and Mg are for anion site, p-like levels (both levels for substitutional cases). The corresponding cation and anion site levels for interstitial deep defects are (Au, Ag, Hg, Cd, Cu, Zn) and (N, Ar, O, F). For the substitutional cases we have some examples of relaxation moving the levels into the band gap, whereas for the interstitial case we have examples where relaxation moves it out of the band gap. Future work involves calculating the effects of charge state interaction and seeing the effect of relaxation on vacancy levels.

Investigation of microstructure, electrical and photoluminescence behaviour of Ni-doped Zn0.96Mn0.04O nanoparticles: Effect of Ni concentration

NASA Astrophysics Data System (ADS)

Rajakarthikeyan, R. K.; Muthukumaran, S.

2017-07-01

ZnO, Zn0.96Mn0.04O and Ni-doped Zn0.96Mn0.04O nanoparticles with different Ni concentrations (0%, 2% and 4%) have been synthesized successfully by sol-gel method. The effects of Ni doping on the structural and optical properties were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-visible spectroscopy, Fourier transform infrared (FTIR) spectroscopy and photoluminescence (PL) spectroscopy. The XRD pattern confirmed the existence of single phase wurtzite-like hexagonal structure throughout the Ni concentrations without any additional phases. The substitution of Ni created the lattice distortion due to the disparity of ionic radius between Zn and Ni which reduced the crystallite size. The microscopic images showed that the size of ZnO nanoparticles reduced by Ni-doping while the shape remains almost spherical/hexagonal type. The electrical conductivity found to be maximum at Ni = 2% due to the availability of more charge carriers generated by Ni. The decrease of electrical conductivity at higher doping (Ni = 4%) is due to the fact that the generation of more defects. The enhanced band gap from 3.73 eV (Ni = 0%) to 3.79 eV (Ni = 4%) by the addition of Ni explained by Burstein-Moss effect. The change in infra-red (IR) intensity and full width at half maximum (FWHM) corresponding to the frequency around defect states were caused by the difference in the bond lengths that occurs when Ni ion replaces Zn ion. The observed blue band emission from 474 nm to 481 nm is due to a radiative transition of an electron from the deep donar level of Zni to an acceptor level of neutral VZn and the origin of green band may be due to oxygen vacancies and intrinsic defects. The tuning of the band gap and the visible emission bands by Ni doping concluded that Ni-doped Zn0.96Mn0.04O is suitable for various nano-photo-electronics applications.

Deep Learning as an Individual, Conditional, and Contextual Influence on First-Year Student Outcomes

ERIC Educational Resources Information Center

Reason, Robert D.; Cox, Bradley E.; McIntosh, Kadian; Terenzini, Patrick T.

2010-01-01

For years, educators have drawn a distinction between deep cognitive processing and surface-level cognitive processing, with the former resulting in greater learning. In recent years, researchers at NSSE have created DEEP Learning scales, which consist of items related to students' experiences which are believed to encourage deep processing. In…

L-proline-based deep eutectic solvents (DESs) for deep catalytic oxidative desulfurization (ODS) of diesel.

PubMed

Hao, Lingwan; Wang, Meiri; Shan, Wenjuan; Deng, Changliang; Ren, Wanzhong; Shi, Zhouzhou; Lü, Hongying

2017-10-05

A series of L-proline-based DESs was prepared through an atom economic reaction between L-proline (L-Pro) and four different kinds of organic acids. The DESs were characterized by Fourier transform infrared spectroscopy (FT-IR), H nuclear magnetic resonance ( 1 HNMR), cyclic voltammogram (CV) and the Hammett method. The synthesized DESs were used for the oxidative desulfurization and the L-Pro/p-toluenesultonic acid (L-Pro/p-TsOH) system shows the highest catalytic activity that the removal of dibenzothiophene (DBT) reached 99% at 60°C in 2h, which may involve the dual activation of the L-Pro/p-TsOH. The acidity of four different L-proline-based DESs was measured and the results show that it could not simply conclude that the correlation between the acidity of DESs and desulfurization capability was positive or negative. The electrochemical measurements evidences and recycling experiment indicate a good stability performance of L-Pro/p-TsOH in desulfurization. This work will provide a novel and potential method for the deep oxidation desulfurization. Copyright © 2017 Elsevier B.V. All rights reserved.

Femtosecond ablation applied to deep-drilling of hard metals

NASA Astrophysics Data System (ADS)

Bruneau, Sebastien; Hermann, Joerg; Dumitru, Gabriel; Sentis, Marc L.

2004-09-01

Mechanisms responsible for the limitation of the aspect ratio obtained by deep drilling of hard metals are investigated in the present work. Cemented carbide targets have been irradiated with laser pulses of 100 fs duration and 100 μJ maximum energy delivered by a Ti:sapphire laser system. The experiments are carried out in different gas environments (vacuum, air, helium up to atmospheric pressure) with incident laser fluences ranging from 1 to 20 Jcm-2. During deep drilling, the laser-induced ablation plume is characterized by means of in-situ plasma diagnostics. Fast imaging is used to observe the expansion behavior of the plasma plume whereas time- and space-resolved emission spectroscopy is employed to analyze the plasma composition. After irradiation, the laser-produced craters were examined by optical microscopy. A correlation between the ablation plume characteristics and the morphological changes of the mciro-holes is established. The results indicate that nanoclusters, that present a significant part of the ablated material, are responsbile for the alteration of the crater shape in the high laser fluence regime.

Quantitative evaluation of deep and shallow tissue layers' contribution to fNIRS signal using multi-distance optodes and independent component analysis.

PubMed

Funane, Tsukasa; Atsumori, Hirokazu; Katura, Takusige; Obata, Akiko N; Sato, Hiroki; Tanikawa, Yukari; Okada, Eiji; Kiguchi, Masashi

2014-01-15

To quantify the effect of absorption changes in the deep tissue (cerebral) and shallow tissue (scalp, skin) layers on functional near-infrared spectroscopy (fNIRS) signals, a method using multi-distance (MD) optodes and independent component analysis (ICA), referred to as the MD-ICA method, is proposed. In previous studies, when the signal from the shallow tissue layer (shallow signal) needs to be eliminated, it was often assumed that the shallow signal had no correlation with the signal from the deep tissue layer (deep signal). In this study, no relationship between the waveforms of deep and shallow signals is assumed, and instead, it is assumed that both signals are linear combinations of multiple signal sources, which allows the inclusion of a "shared component" (such as systemic signals) that is contained in both layers. The method also assumes that the partial optical path length of the shallow layer does not change, whereas that of the deep layer linearly increases along with the increase of the source-detector (S-D) distance. Deep- and shallow-layer contribution ratios of each independent component (IC) are calculated using the dependence of the weight of each IC on the S-D distance. Reconstruction of deep- and shallow-layer signals are performed by the sum of ICs weighted by the deep and shallow contribution ratio. Experimental validation of the principle of this technique was conducted using a dynamic phantom with two absorbing layers. Results showed that our method is effective for evaluating deep-layer contributions even if there are high correlations between deep and shallow signals. Next, we applied the method to fNIRS signals obtained on a human head with 5-, 15-, and 30-mm S-D distances during a verbal fluency task, a verbal working memory task (prefrontal area), a finger tapping task (motor area), and a tetrametric visual checker-board task (occipital area) and then estimated the deep-layer contribution ratio. To evaluate the signal separation performance of our method, we used the correlation coefficients of a laser-Doppler flowmetry (LDF) signal and a nearest 5-mm S-D distance channel signal with the shallow signal. We demonstrated that the shallow signals have a higher temporal correlation with the LDF signals and with the 5-mm S-D distance channel than the deep signals. These results show the MD-ICA method can discriminate between deep and shallow signals. Copyright © 2013 Elsevier Inc. All rights reserved.

Deep-breathing exercises reduce atelectasis and improve pulmonary function after coronary artery bypass surgery.

PubMed

Westerdahl, Elisabeth; Lindmark, Birgitta; Eriksson, Tomas; Friberg, Orjan; Hedenstierna, Göran; Tenling, Arne

2005-11-01

To investigate the effects of deep-breathing exercises on pulmonary function, atelectasis, and arterial blood gas levels after coronary artery bypass graft (CABG) surgery. In a prospective, randomized trial, patients performing deep-breathing exercises (n = 48) were compared to a control group (n = 42) who performed no breathing exercises postoperatively. Patient management was similar in the groups in terms of assessment, positioning, and mobility. The patients in the deep-breathing group were instructed to perform breathing exercises hourly during daytime for the first 4 postoperative days. The exercises consisted of 30 slow, deep breaths performed with a positive expiratory pressure blow-bottle device (+ 10 cm H(2)O). Spirometric measurements, spiral CT (three transverse levels), arterial blood gas analysis, and scoring of subjective experience of the breathing exercises were performed on the fourth postoperative day. Atelectasis was only half the size in the deep-breathing group compared to the control group, amounting to 2.6 +/- 2.2% vs 4.7 +/- 5.7% (p = 0.045) at the basal level and 0.1 +/- 0.2% vs 0.3 +/- 0.5% (mean +/- SD) [p = 0.01] at the apical level. Compared to the control subjects, the patients in the deep-breathing group had a significantly smaller reduction in FVC (to 71 +/- 12%, vs 64 +/- 13% of the preoperative values; p = 0.01) and FEV(1) (to 71 +/- 11%, vs 65 +/- 13% of the preoperative values; p = 0.01). Arterial oxygen tension, carbon dioxide tension, fever, or length of ICU or hospital stay did not differ between the groups. In the deep-breathing group, 72% of the patients experienced a subjective benefit from the exercises. Patients performing deep-breathing exercises after CABG surgery had significantly smaller atelectatic areas and better pulmonary function on the fourth postoperative day compared to a control group performing no exercises.

The effects of deep level traps on the electrical properties of semi-insulating CdZnTe

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

Zha, Gangqiang; Yang, Jian; Xu, Lingyan

2014-01-28

Deep level traps have considerable effects on the electrical properties and radiation detection performance of high resistivity CdZnTe. A deep-trap model for high resistivity CdZnTe was proposed in this paper. The high resistivity mechanism and the electrical properties were analyzed based on this model. High resistivity CdZnTe with high trap ionization energy E{sub t} can withstand high bias voltages. The leakage current is dependent on both the deep traps and the shallow impurities. The performance of a CdZnTe radiation detector will deteriorate at low temperatures, and the way in which sub-bandgap light excitation could improve the low temperature performance canmore » be explained using the deep trap model.« less

A dominant electron trap in molecular beam epitaxial InAlN lattice-matched to GaN

NASA Astrophysics Data System (ADS)

Pandey, Ayush; Bhattacharya, Aniruddha; Cheng, Shaobo; Botton, Gianluigi A.; Mi, Zetian; Bhattacharya, Pallab

2018-04-01

Deep levels in lattice-matched undoped and Si-doped InAlN/GaN grown by plasma-assisted molecular beam epitaxy have been identified and characterized by capacitance and photocapacitance measurements. From x-ray diffraction, reflectance measurements, electron energy loss spectroscopy and high-resolution transmission electron microscopy it is evident that the material has two distinct phases with different compositions. These correspond to In compositions of 18.1% and 25.8%, with corresponding bandgaps of 4.6 eV and 4.1 eV, respectively. The lower bandgap material is present as columnar microstructures in the form of quantum wires. A dominant electron trap with an activation energy of 0.293  ±  0.01 eV, a small capture cross-section of (1.54  ±  0.25)  ×  10-18 cm2, and density increasing linearly with Si doping density is identified in all the samples. The characteristics of the electron trap and variation of diode capacitance are discussed in the context of carrier dynamics involving the dominant trap level and the quantum wires.

Modification of electron states in CdTe absorber due to a buffer layer in CdTe/CdS solar cells

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

Fedorenko, Y. G., E-mail: y.fedorenko@liverpool.ac.uk; Major, J. D.; Pressman, A.

2015-10-28

By application of the ac admittance spectroscopy method, the defect state energy distributions were determined in CdTe incorporated in thin film solar cell structures concluded on ZnO, ZnSe, and ZnS buffer layers. Together with the Mott-Schottky analysis, the results revealed a strong modification of the defect density of states and the concentration of the uncompensated acceptors as influenced by the choice of the buffer layer. In the solar cells formed on ZnSe and ZnS, the Fermi level and the energy position of the dominant deep trap levels were observed to shift closer to the midgap of CdTe, suggesting the mid-gapmore » states may act as recombination centers and impact the open-circuit voltage and the fill factor of the solar cells. For the deeper states, the broadening parameter was observed to increase, indicating fluctuations of the charge on a microscopic scale. Such changes can be attributed to the grain-boundary strain and the modification of the charge trapped at the grain-boundary interface states in polycrystalline CdTe.« less

Design rules for charge-transport efficient host materials for phosphorescent organic light-emitting diodes.

PubMed

May, Falk; Al-Helwi, Mustapha; Baumeier, Björn; Kowalsky, Wolfgang; Fuchs, Evelyn; Lennartz, Christian; Andrienko, Denis

2012-08-22

The use of blue phosphorescent emitters in organic light-emitting diodes (OLEDs) imposes demanding requirements on a host material. Among these are large triplet energies, the alignment of levels with respect to the emitter, the ability to form and sustain amorphous order, material processability, and an adequate charge carrier mobility. A possible design strategy is to choose a π-conjugated core with a high triplet level and to fulfill the other requirements by using suitable substituents. Bulky substituents, however, induce large spatial separations between conjugated cores, can substantially reduce intermolecular electronic couplings, and decrease the charge mobility of the host. In this work we analyze charge transport in amorphous 2,8-bis(triphenylsilyl)dibenzofuran, an electron-transporting material synthesized to serve as a host in deep-blue OLEDs. We show that mesomeric effects delocalize the frontier orbitals over the substituents recovering strong electronic couplings and lowering reorganization energies, especially for electrons, while keeping energetic disorder small. Admittance spectroscopy measurements reveal that the material has indeed a high electron mobility and a small Poole-Frenkel slope, supporting our conclusions. By linking electronic structure, molecular packing, and mobility, we provide a pathway to the rational design of hosts with high charge mobilities.

Group III Acceptors with Shallow and Deep Levels in Silicon Carbide: ESR and ENDOR Studies

NASA Astrophysics Data System (ADS)

Il'in, I. V.; Uspenskaya, Yu. A.; Kramushchenko, D. D.; Muzafarova, M. V.; Soltamov, V. A.; Mokhov, E. N.; Baranov, P. G.

2018-04-01

Results of investigations of Group III acceptors (B, Al, and Ga) in crystals of silicon carbide using the most informative electron spin resonance and electron nuclear double resonance methods are presented. Structural models of the acceptors with shallow and deep levels are considered. In addition to the data obtained earlier, studies using high-frequency magnetic resonance were obtained, which allowed revealing orthorhombic deviations from the axial symmetry for the deep acceptors; theoretical analysis explains experimentally found shifts of g factors for the deep acceptors arising due to the orthorhombic deviations, which appear probably due to the Jahn-Teller effect.

Sub-cycle light transients for attosecond, X-ray, four-dimensional imaging

NASA Astrophysics Data System (ADS)

Fattahi, Hanieh

2016-10-01

This paper reviews the revolutionary development of ultra-short, multi-TW laser pulse generation made possible by current laser technology. The design of the unified laser architecture discussed in this paper, based on the synthesis of ultrabroadband optical parametric chirped-pulse amplifiers, promises to provide powerful light transients with electromagnetic forces engineerable on the electron time scale. By coherent combination of multiple amplifiers operating in different wavelength ranges, pulses with wavelength spectra extending from less than 1 ?m to more than 10 ?m, with sub-cycle duration at unprecedented peak and average power levels can be generated. It is shown theoretically that these light transients enable the efficient generation of attosecond X-ray pulses with photon flux sufficient to image, for the first time, picometre-attosecond trajectories of electrons, by means of X-ray diffraction and record the electron dynamics by attosecond spectroscopy. The proposed system leads to a tool with sub-atomic spatio-temporal resolution for studying different processes deep inside matter.

One-step synthesis of magnetic chitosan polymer composite films

NASA Astrophysics Data System (ADS)

Cesano, Federico; Fenoglio, Gaia; Carlos, Luciano; Nisticò, Roberto

2015-08-01

In this study, a magnetic iron oxide-chitosan composite film is synthesized by one-step method and thoroughly investigated in order to better understand its inorganic/organic properties. A deep physico-chemical characterization of the magnetic films has been performed. In particular, the material composition was evaluated by means of XRD and ATR-FTIR spectroscopy, whereas the thermal stability and the subsequent inorganic phase transitions involving iron oxide species were followed by TGA analyses carried out at different experimental conditions (i.e. inert and oxidative atmosphere). The magnetic properties of the films were tested at the bulk and at the surface level, performing respectively magnetization hysteresis curve and magnetic force microscopy (MFM) surface mapping. Results indicate that the synthesized material can be prepared through a very simple synthetic procedure and suggests that it can be successfully applied for instance to environmental applications, such as the adsorption of contaminants from solid and liquid media thanks to its pronounced magnetic properties, which favour its recover.

Applications of XPS in the characterization of Battery materials

DOE PAGES

Shutthanandan, Vaithiyalingam; Nandasiri, Manjula; Zheng, Jianming; ...

2018-05-26

In this study, technological development requires reliable power sources where energy storage devices are emerging as a critical component. Wide range of energy storage devices, Redox-flow batteries (RFB), Lithium ion based batteries (LIB), and Lithium-sulfur (LSB) batteries are being developed for various applications ranging from grid-scale level storage to mobile electronics. Material complexities associated with these energy storage devices with unique electrochemistry are formidable challenge which needs to be address for transformative progress in this field. X-ray photoelectron spectroscopy (XPS) - a powerful surface analysis tool - has been widely used to study these energy storage materials because of itsmore » ability to identify, quantify and image the chemical distribution of redox active species. However, accessing the deeply buried solid-electrolyte interfaces (which dictates the performance of energy storage devices) has been a challenge in XPS usage. Herein we report our recent efforts to utilize the XPS to gain deep insight about these interfaces under realistic conditions with varying electrochemistry involving RFB, LIB and LSB.« less

Applications of XPS in the characterization of Battery materials

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

Shutthanandan, Vaithiyalingam; Nandasiri, Manjula; Zheng, Jianming

In this study, technological development requires reliable power sources where energy storage devices are emerging as a critical component. Wide range of energy storage devices, Redox-flow batteries (RFB), Lithium ion based batteries (LIB), and Lithium-sulfur (LSB) batteries are being developed for various applications ranging from grid-scale level storage to mobile electronics. Material complexities associated with these energy storage devices with unique electrochemistry are formidable challenge which needs to be address for transformative progress in this field. X-ray photoelectron spectroscopy (XPS) - a powerful surface analysis tool - has been widely used to study these energy storage materials because of itsmore » ability to identify, quantify and image the chemical distribution of redox active species. However, accessing the deeply buried solid-electrolyte interfaces (which dictates the performance of energy storage devices) has been a challenge in XPS usage. Herein we report our recent efforts to utilize the XPS to gain deep insight about these interfaces under realistic conditions with varying electrochemistry involving RFB, LIB and LSB.« less

Potential approaches to the spectroscopic characterization of high performance polymers exposed to energetic protons and heavy ions

NASA Technical Reports Server (NTRS)

Suleman, Naushadalli K.

1991-01-01

A potential limitation to human activity on the lunar surface or in deep space is the exposure of the crew to unacceptably high levels of penetrating space radiations. The radiations of most concerns for such missions are high-energy protons emitted during solar flares, and galactic cosmic rays which are high-energy ions ranging from protons to iron. The development of materials for effective shielding from energetic space radiations will clearly require a greater understanding of the underlying mechanisms of radiation-induced damage in bulk materials. This can be accomplished in part by the detailed spectroscopic characterization of bulk materials that were exposed to simulated space radiations. An experimental data base thus created can then be used in conjunction with existing radiation transport codes in the design and fabrication of effective radiation shielding materials. Electron Paramagnetic Resonance Spectroscopy was proven very useful in elucidating radiation effects in polymers (high performance polymers are often an important components of structural composites).

Space radiation effects in InP solar cells

NASA Astrophysics Data System (ADS)

Walters, R. J.; Messenger, S. R.; Summers, G. P.; Burke, E. A.; Keavney, C. J.

1991-12-01

InP solar cells and mesa diodes grown by metalorganic chemical vapor deposition (MOCVD) were irradiated with electrons and protons at room temperature. The radiation-induced defects (RIDs) were characterized by deep level transient spectroscopy (DLTS), and the degradation of the solar cell performance was determined through I-V measurements. The nonionizing energy loss (NIEL) of electrons and protons in InP was calculated as a function of energy from 1 to 200 MeV and compared to the measured defect introduction rates. A linear dependence was evident. InP solar cells showed significantly more radiation resistance than c-Si or GaAs/Ge cells under 1 MeV electron irradiation. Using the calculated InP damage rates and measured damage factors, the performance of InP solar cells as a function of orbital altitude and time in orbit was predicted and compared with the performance of c-Si solar cells in the same environment. In all cases, the InP cells showed highly superior radiation resistance.

Evidence for carrier localization in the pseudogap state of cuprate superconductors from coherent quench experiments

PubMed Central

Madan, I.; Kurosawa, T.; Toda, Y.; Oda, M.; Mertelj, T.; Mihailovic, D.

2015-01-01

A ‘pseudogap' was introduced by Mott to describe a state of matter that has a minimum in the density of states at the Fermi level, deep enough for states to become localized. It can arise either from Coulomb repulsion between electrons, and/or incipient charge or spin order. Here we employ ultrafast spectroscopy to study dynamical properties of the normal to pseudogap state transition in the prototype high-temperature superconductor Bi2Sr2CaCu2O8+δ. We perform a systematic temperature and doping dependence study of the pseudogap photodestruction and recovery in coherent quench experiments, revealing marked absence of critical behaviour of the elementary excitations, which implies an absence of collective electronic ordering beyond a few coherence lengths on short timescales. The data imply ultrafast carrier localization into a textured polaronic state arising from a competing Coulomb interaction and lattice strain, enhanced by a Fermi surface instability. PMID:25891310

High performance SONOS flash memory with in-situ silicon nanocrystals embedded in silicon nitride charge trapping layer

NASA Astrophysics Data System (ADS)

Lim, Jae-Gab; Yang, Seung-Dong; Yun, Ho-Jin; Jung, Jun-Kyo; Park, Jung-Hyun; Lim, Chan; Cho, Gyu-seok; Park, Seong-gye; Huh, Chul; Lee, Hi-Deok; Lee, Ga-Won

2018-02-01

In this paper, SONOS-type flash memory device with highly improved charge-trapping efficiency is suggested by using silicon nanocrystals (Si-NCs) embedded in silicon nitride (SiNX) charge trapping layer. The Si-NCs were in-situ grown by PECVD without additional post annealing process. The fabricated device shows high program/erase speed and retention property which is suitable for multi-level cell (MLC) application. Excellent performance and reliability for MLC are demonstrated with large memory window of ∼8.5 V and superior retention characteristics of 7% charge loss for 10 years. High resolution transmission electron microscopy image confirms the Si-NC formation and the size is around 1-2 nm which can be verified again in X-ray photoelectron spectroscopy (XPS) where pure Si bonds increase. Besides, XPS analysis implies that more nitrogen atoms make stable bonds at the regular lattice point. Photoluminescence spectra results also illustrate that Si-NCs formation in SiNx is an effective method to form deep trap states.

Solar cells and modules from dentritic web silicon

NASA Technical Reports Server (NTRS)

Campbell, R. B.; Rohatgi, A.; Seman, E. J.; Davis, J. R.; Rai-Choudhury, P.; Gallagher, B. D.

1980-01-01

Some of the noteworthy features of the processes developed in the fabrication of solar cell modules are the handling of long lengths of web, the use of cost effective dip coating of photoresist and antireflection coatings, selective electroplating of the grid pattern and ultrasonic bonding of the cell interconnect. Data on the cells is obtained by means of dark I-V analysis and deep level transient spectroscopy. A histogram of over 100 dentritic web solar cells fabricated in a number of runs using different web crystals shows an average efficiency of over 13%, with some efficiencies running above 15%. Lower cell efficiency is generally associated with low minority carrier time due to recombination centers sometimes present in the bulk silicon. A cost analysis of the process sequence using a 25 MW production line indicates a selling price of $0.75/peak watt in 1986. It is concluded that the efficiency of dentritic web cells approaches that of float zone silicon cells, reduced somewhat by the lower bulk lifetime of the former.

Effect of Rare Earth Elements (Er, Ho) on Semi-Metallic Materials (ScN) in an Applied Electric Field

NASA Technical Reports Server (NTRS)

Kim, Hyunjung; Park, Yeonjoon; King, Glen C.; Lee, Kunik; Choi, Sang H.

2012-01-01

The development of materials and fabrication technology for field-controlled spectrally active optics is essential for applications such as membrane optics, filters for LIDARs, windows for sensors, telescopes, spectroscopes, cameras and flat-panel displays. The dopants of rare earth elements, in a host of optical systems, create a number of absorption and emission band structures and can easily be incorporated into many high quality crystalline and amorphous hosts. In wide band-gap semiconductors like ScN, the existing deep levels can capture or emit the mobile charges, and can be ionized with the loss or capture of the carriers which are the fundamental basis of concept for smart optic materials. The band gap shrinkage or splitting with dopants supports the possibility of this concept. In the present work, a semi-metallic material (ScN) was doped with rare earth elements (Er, Ho) and tested under an applied electric field to characterize spectral and refractive index shifts by either Stark or Zeeman Effect. These effects can be verified using the UV-Vis spectroscopy, the Hall Effect measurement and the ellipsometric spectroscopy. The optical band gaps of ScN doped with Er and doped with Ho were experimentally estimated as 2.33eV and 2.24eV ( 0.2eV) respectively. This is less than that of undoped ScN (2.5 0.2eV). The red-shifted absorption onset is a direct evidence for the decrease of band gap energy (Eg), and the broadening of valence band states is attributable to the doping cases. A decrease in refractive index with an applied field was observed as a small shift in absorption coefficient using a variable angle spectroscopic ellipsometer. In the presence of an electric field, mobile carriers are redistributed within the space charge region (SCR) to produce this electro-refractive effect. The shift in refractive index is also affected by the density and location of deep potential wells within the SCR. In addition, the microstructure change was observed by a TEM analysis. These results give an insight for future applications for the field-controlled spectrally active material systems.

Transient Fluorescence Spectroscopy and laser induced fluorescence lifetimes of terbium doped dipicolinic acid

NASA Astrophysics Data System (ADS)

Makoui, Anali

We have investigated the use of deep UV laser induced fluorescence for the sensitive detection and spectroscopic lifetime studies of terbium doped dipicolinic acid (DPA-Tb) and used this to study the optical characteristics of DPA which is a chemical surrounding most bacterial spores. Background absorption spectra, fluorescence spectra, and Excitation Emission Matrix (EEM) spectra were made of the DPA-Tb complex, using both fixed 266 nm wavelength and tunable (220 nm--280 nm) UV laser excitations. Of importance, the fluorescence lifetimes of the four main fluorescence peaks (488 nm, 543 nm, 581 nm, and 618 nm) of the DPA-Tb complex have been measured for the first time to our knowledge. The lifetimes of all the fluorescing lines have been measured as a function of DPA-Tb concentration, solvent pH, and solvent composition, including that for the weakest fluorescing line of DPA-Tb at 618 nm. In addition, a new spectroscopic lifetime measurement technique, which we call "Transient Fluorescence Spectroscopy", was developed. In this technique, a weak, quasi-CW, amplitude modulated UV laser (8.5 kHz) was used to measure the lifetimes of the fluorescence lines, and yields insight into energy transfer and excitation lifetimes within the system. This technique is especially useful when a high power laser is not either available or not suitable. In the latter case, this would be when a high power pulsed deep-UV laser could produce bleaching or destruction of the biological specimen. In addition, this technique simulated the excitation and fluorescence emission of the DPA-Tb using a 4-level energy model, and solved the dynamic transient rate equations to predict the temporal behavior of the DPA-Tb emitted fluorescence. Excellent agreement between the experiments and the simulation were found. This technique has the potential to provide a more accurate value for the fluorescence lifetime values. In addition, with the use of asymmetric excitation waveforms, the dynamic transient rate equation analysis may allow for detailed studies of selected transfer mechanisms in a wide range of other spectroscopic applications including rare-earth solid-state lasing materials and biological samples.

Terrestrial source to deep-sea sink sediment budgets at high and low sea levels: Insights from tectonically active Southern California

USGS Publications Warehouse

Covault, J.A.; Romans, B.W.; Graham, S.A.; Fildani, A.; Hilley, G.E.

2011-01-01

Sediment routing from terrestrial source areas to the deep sea influences landscapes and seascapes and supply and filling of sedimentary basins. However, a comprehensive assessment of land-to-deep-sea sediment budgets over millennia with significant climate change is lacking. We provide source to sink sediment budgets using cosmogenic radionuclide-derived terrestrial denudation rates and submarine-fan deposition rates through sea-level fluctuations since oxygen isotope stage 3 (younger than 40 ka) in tectonically active, spatially restricted sediment-routing systems of Southern California. We show that source-area denudation and deep-sea deposition are balanced during a period of generally falling and low sea level (40-13 ka), but that deep-sea deposition exceeds terrestrial denudation during the subsequent period of rising and high sea level (younger than 13 ka). This additional supply of sediment is likely owed to enhanced dispersal of sediment across the shelf caused by seacliff erosion during postglacial shoreline transgression and initiation of submarine mass wasting. During periods of both low and high sea level, land and deep-sea sediment fluxes do not show orders of magnitude imbalances that might be expected in the wake of major sea-level changes. Thus, sediment-routing processes in a globally significant class of small, tectonically active systems might be fundamentally different from those of larger systems that drain entire orogens, in which sediment storage in coastal plains and wide continental shelves can exceed millions of years. Furthermore, in such small systems, depositional changes offshore can reflect onshore changes when viewed over time scales of several thousand years to more than 10 k.y. ?? 2011 Geological Society of America.

Towards label-free and site-specific probing of the local pH in proteins: pH-dependent deep UV Raman spectra of histidine and tyrosine

NASA Astrophysics Data System (ADS)

Bröermann, Andreas; Steinhoff, Heinz-Jürgen; Schlücker, Sebastian

2014-09-01

The site-specific pH is an experimental probe for assessing models of structural folding and function of a protein as well as protein-protein and protein-ligand interactions. It can be determined by various techniques such as NMR, FT-IR, fluorescence and EPR spectroscopy. The latter require the use of external labels, i.e., employ pH-dependent dyes and spin labels, respectively. In this contribution, we outline an approach to a label-free and site-specific method for determining the local pH using deep ultraviolet resonance Raman (UVRR) spectroscopic fingerprints of the aromatic amino acids histidine and tyrosine in combination with a robust algorithm that determines the pH value using three UVRR reference spectra and without prior knowledge of the pKa.

The Deep-Sea Polyextremophile Halobacteroides lacunaris TB21 Rough-Type LPS: Structure and Inhibitory Activity towards Toxic LPS

PubMed Central

Di Lorenzo, Flaviana; Palmigiano, Angelo; Paciello, Ida; Pallach, Mateusz; Garozzo, Domenico; Bernardini, Maria-Lina; La Cono, Violetta; Yakimov, Michail M.; Molinaro, Antonio; Silipo, Alba

2017-01-01

The structural characterization of the lipopolysaccharide (LPS) from extremophiles has important implications in several biomedical and therapeutic applications. The polyextremophile Gram-negative bacterium Halobacteroides lacunaris TB21, isolated from one of the most extreme habitats on our planet, the deep-sea hypersaline anoxic basin Thetis, represents a fascinating microorganism to investigate in terms of its LPS component. Here we report the elucidation of the full structure of the R-type LPS isolated from H. lacunaris TB21 that was attained through a multi-technique approach comprising chemical analyses, NMR spectroscopy, and Matrix-Assisted Laser Desorption Ionization (MALDI) mass spectrometry. Furthermore, cellular immunology studies were executed on the pure R-LPS revealing a very interesting effect on human innate immunity as an inhibitor of the toxic Escherichia coli LPS. PMID:28653982

Eremophilane Sesquiterpenes from a Deep Marine-Derived Fungus, Aspergillus sp. SCSIOW2, Cultivated in the Presence of Epigenetic Modifying Agents.

PubMed

Wang, Liyan; Li, Mengjie; Tang, Jianqiang; Li, Xiaofan

2016-04-18

Chemical epigenetic manipulation was applied to a deep marine-derived fungus, Aspergillus sp. SCSIOW2, resulting in significant changes of the secondary metabolites. Three new eremophilane-type sesquiterpenes, dihydrobipolaroxin B (2), dihydrobipolaroxin C (3), and dihydrobipolaroxin D (4), along with one known analogue, dihydrobipolaroxin (1), were isolated from the culture treated with a combination of histone deacetylase inhibitor (suberohydroxamic acid) and DNA methyltransferase inhibitor (5-azacytidine). 1-4 were not produced in the untreated cultures. 2 and 3 might be artificial because 1 could form 2 and 3 spontaneously in water by intracellular acetalization reaction. The absolute configurations of 1 and 2 were assigned based on ECD spectroscopy combined with time-dependent density functional theory calculations. All four compounds exhibited moderate nitric oxide inhibitory activities without cytotoxic effects.

Spatial Statistics of Deep-Water Ambient Noise; Dispersion Relations for Sound Waves and Shear Waves

DTIC Science & Technology

2015-09-30

propagation in very fine-grained sediments (silt and clay ). OBJECTIVES 1) The scientific objective of the deep-water ambient noise research is to...forces in silts and clays and the role they play in controlling wave speeds and attenuations. On a 2 quantum mechanical level, these forces are... clays . APPROACH 1) Deep-water ambient noise Three deep-diving, autonomous instrument platforms, known as Deep Sound I, II, & III, have been

Levels-Of-Processing Effect on Word Recognition in Schizophrenia

PubMed Central

Ragland, J. Daniel; Moelter, Stephen T.; McGrath, Claire; Hill, S. Kristian; Gur, Raquel E.; Bilker, Warren B.; Siegel, Steven J.; Gur, Ruben C.

2015-01-01

Background Individuals with schizophrenia have difficulty organizing words semantically to facilitate encoding. This is commonly attributed to organizational rather than semantic processing limitations. By requiring participants to classify and encode words on either a shallow (e.g., uppercase/lowercase) or deep level (e.g., concrete/abstract), the levels-of-processing paradigm eliminates the need to generate organizational strategies. Methods This paradigm was administered to 30 patients with schizophrenia and 30 healthy comparison subjects to test whether providing a strategy would improve patient performance. Results Word classification during shallow and deep encoding was slower and less accurate in patients. Patients also responded slowly during recognition testing and maintained a more conservative response bias following deep encoding; however, both groups showed a robust levels-of-processing effect on recognition accuracy, with unimpaired patient performance following both shallow and deep encoding. Conclusions This normal levels-of-processing effect in the patient sample suggests that semantic processing is sufficiently intact for patients to benefit from organizational cues. Memory remediation efforts may therefore be most successful if they focus on teaching patients to form organizational strategies during initial encoding. PMID:14643082

Levels-of-processing effect on word recognition in schizophrenia.

PubMed

Ragland, J Daniel; Moelter, Stephen T; McGrath, Claire; Hill, S Kristian; Gur, Raquel E; Bilker, Warren B; Siegel, Steven J; Gur, Ruben C

2003-12-01

Individuals with schizophrenia have difficulty organizing words semantically to facilitate encoding. This is commonly attributed to organizational rather than semantic processing limitations. By requiring participants to classify and encode words on either a shallow (e.g., uppercase/lowercase) or deep level (e.g., concrete/abstract), the levels-of-processing paradigm eliminates the need to generate organizational strategies. This paradigm was administered to 30 patients with schizophrenia and 30 healthy comparison subjects to test whether providing a strategy would improve patient performance. Word classification during shallow and deep encoding was slower and less accurate in patients. Patients also responded slowly during recognition testing and maintained a more conservative response bias following deep encoding; however, both groups showed a robust levels-of-processing effect on recognition accuracy, with unimpaired patient performance following both shallow and deep encoding. This normal levels-of-processing effect in the patient sample suggests that semantic processing is sufficiently intact for patients to benefit from organizational cues. Memory remediation efforts may therefore be most successful if they focus on teaching patients to form organizational strategies during initial encoding.

Hepatic gene expression profiling of 5′-AMP-induced hypometabolism in mice

PubMed Central

Miki, Takao; Van Oort-Jansen, Anita; Matsumoto, Tomoko; Loose, David S.; Lee, Cheng Chi

2011-01-01

There is currently much interest in clinical applications of therapeutic hypothermia. Hypothermia can be a consequence of hypometabolism. We have recently established a procedure for the induction of a reversible deep hypometabolic state in mice using 5′-adenosine monophosphate (5′-AMP) in conjunction with moderate ambient temperature. The current study aims at investigating the impact of this technology at the gene expression level in a major metabolic organ, the liver. Our findings reveal that expression levels of the majority of genes in liver are not significantly altered by deep hypometabolism. However, among those affected by hypometabolism, more genes are differentially upregulated than downregulated both in a deep hypometabolic state and in the early arousal state. These altered gene expression levels during 5′-AMP induced hypometabolism are largely restored to normal levels within 2 days of the treatment. Our data also suggest that temporal control of circadian genes is largely stalled during deep hypometabolism. PMID:21224422

Electronic characterization of defects in narrow gap semiconductors

NASA Technical Reports Server (NTRS)

Patterson, James D.

1993-01-01

The study of point defects in semiconductors has a long and honorable history. In particular, the detailed understanding of shallow defects in common semiconductors traces back to the classic work of Kohn and Luttinger. However, the study of defects in narrow gap semiconductors represents a much less clear story. Here, both shallow defects (caused by long range potentials) and deep defects (from short range potentials) are far from being completely understood. In this study, all results are calculational and our focus is on the chemical trend of deep levels in narrow gap semiconductors. We study substitutional (including antisite), interstitial and ideal vacancy defects. For substitutional and interstitial impurities, the efects of relaxation are included. For materials like Hg(1-x)Cd(x)Te, we study how the deep levels vary with x, of particular interest is what substitutional and interstitial atoms yield energy levels in the gap i.e. actually produce deep ionized levels. Also, since the main technique utilized is Green's functions, we include some summary of that method.

Dual-Band Optical Bench for Terahertz Radiometer for Outer Planet Atmospheres (TROPA)

NASA Technical Reports Server (NTRS)

Schlecht, Erich; Jamnejad, Vahraz

2012-01-01

We have developed a wide-band dual frequency spectrometer for use in deep space planetary atmospheric spectroscopy. The instrument uses a dual-band architecture, both to be able to observe spectral lines from a wide range of atmospheric species, and to allow a higher precision retrieval of temperature/pressure/partial pressure and wind profiles. This dual-band approach requires a new design for the optical bench to couple both frequencies into their respective receivers.

Deep millimeter spectroscopy observations toward NGC 1068

NASA Astrophysics Data System (ADS)

Qiu, Jianjie; Wang, Junzhi; Shi, Yong; Zhang, Jiangshui; Fang, Min; Li, Fei

2018-05-01

Aims: We aim for a better understanding of gas properties in the circum-nuclear disk (CND) region of the nearby gas-rich Seyfert 2 galaxy NGC 1068. We focus on line identification and the basic physical parameters estimation of molecular gas in the CND region. Methods: We used the IRAM 30 m telescope to conduct deep millimeter spectroscopy observations toward the center of NGC 1068. Results: Thirty-two lines were detected in this galaxy, 15 lines of wich were detected for the first time. With a sensitivity better by about a factor of 4 than observations in the literature for this source at 3 mm band, we detected several weak lines for the first time in this source, such as lines from CH3CCH, CH3OCH3, and HC18O+. Column densities of these molecules were estimated based on line emissions. Some marginal detections in the literature, such as HN13C (1-0), were confirmed. CH3OCH3 was detected for the first time in external galaxies. Lines from several carbon chain molecules and shock-related molecules were also detected in this source. The reduced spectrum (FITS file) is only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/613/A3

Monitoring brain temperature by time-resolved near-infrared spectroscopy: pilot study

NASA Astrophysics Data System (ADS)

Bakhsheshi, Mohammad Fazel; Diop, Mamadou; St. Lawrence, Keith; Lee, Ting-Yim

2014-05-01

Mild hypothermia (HT) is an effective neuroprotective strategy for a variety of acute brain injuries. However, the wide clinical adaptation of HT has been hampered by the lack of a reliable noninvasive method for measuring brain temperature, since core measurements have been shown to not always reflect brain temperature. The goal of this work was to develop a noninvasive optical technique for measuring brain temperature that exploits both the temperature dependency of water absorption and the high concentration of water in brain (80%-90%). Specifically, we demonstrate the potential of time-resolved near-infrared spectroscopy (TR-NIRS) to measure temperature in tissue-mimicking phantoms (in vitro) and deep brain tissue (in vivo) during heating and cooling, respectively. For deep brain tissue temperature monitoring, experiments were conducted on newborn piglets wherein hypothermia was induced by gradual whole body cooling. Brain temperature was concomitantly measured by TR-NIRS and a thermocouple probe implanted in the brain. Our proposed TR-NIRS method was able to measure the temperature of tissue-mimicking phantoms and brain tissues with a correlation of 0.82 and 0.66 to temperature measured with a thermometer, respectively. The mean difference between the TR-NIRS and thermometer measurements was 0.15°C±1.1°C for the in vitro experiments and 0.5°C±1.6°C for the in vivo measurements.

Investigation of hydrogen interaction with defects in zirconia

NASA Astrophysics Data System (ADS)

Melikhova, O.; Kuriplach, J.; Čížek, J.; Procházka, I.; Brauer, G.; Anwand, W.

2010-04-01

Defect studies of a ZrO2 + 9 mol. % Y2O3 single crystal were performed in this work using a high resolution positron lifetime spectroscopy combined with slow positron implantation spectroscopy. In order to elucidate the nature of positron trapping sites observed experimentally, the structural relaxations of several types of vacancy-like defects in zirconia were performed and positron characteristics for them were calculated. Relaxed atomic configurations of studied defects were obtained by means of ab initio pseudopotential method within the supercell approach. Theoretical calculations indicated that neither oxygen vacancies nor their neutral complexes with substitute yttrium atoms are capable of positron trapping. On the other hand, zirconium vacancies are deep positron traps and are most probably responsible for the saturated positron trapping observed in yttria stabilized zirconia single crystals. However, the calculated positron lifetime for zirconium vacancy is apparently longer than the experimental value corresponding to a single-component spectrum measured for the cubic ZrO2 + 9 mol. % Y2O3 single crystal. It was demonstrated that this effect can be explained by hydrogen trapped in zirconium vacancies. On the basis of structure relaxations, we found that zirconium vacancy - hydrogen complexes represent deep positron traps with the calculated lifetime close to the experimental one. In zirconium vacancy - hydrogen complexes the hydrogen atom forms an O-H bond with one of the nearest neighbour oxygen atoms. The calculated bond length is close to 1 Å.

Sleuthing the Dynamo: the Final Frontier

NASA Astrophysics Data System (ADS)

Ayres, Thomas

1996-07-01

Innovative technologies are opening new windows into the Sun;from its hidden interior to the far reaches of its turbulentouter envelope: rare-earth detectors for solar neutrinos; theGONG project for helioseismology; SOHO for high-resolutionXUV spectroscopy, and YOHKOH for coronal X-ray imaging. Atthe same time, a fleet of space observatories--ROSAT, EUVE,ASCA, and HST itself--are providing unprecedented views ofthe vacuum-UV and X-ray emissions of stars in our Galacticneighborhood. These seemingly unrelated developments are infact deeply connected. A central issue of solar-stellarphysics is the nature and origin of magnetic activity: thelink between the interior dynamics of a late-type star and theviolent state of its outermost coronal layers. As solarphysicists are unlocking the secrets of the hydromagneticDynamo deep inside the Sun, we and others have beendocumenting the early evolution of the Dynamo and itsassociated external gas-dynamic activity. In particular, wehave obtained HST/FOS spectra of ten young solar-type starsin three nearby open clusters--the Hyades, Pleiades, andAlpha Persei--ranging in age from 50 Myr to 600 Myr. We havesupplemented the HST spectroscopy with deep ROSAT pointings, and ground-based studies. Here, we will continue the HSTside of our project by obtaining FUV spectra of two AlphaPerseids from our original program (but not yet observed),and high-S/N follow-up measurements of the hyperactive PleiadH II 314.

Vena cava filters and thrombolytic therapeutic monitoring based on functional near-infrared spectroscopy for deep vein thrombosis

NASA Astrophysics Data System (ADS)

Pan, Boan; Liu, Weichao; Fang, Xiang; Zhao, Ke; Li, Ting

2018-02-01

Deep vein thrombosis (DVT), happening in inpatients usually and especially with the postoperative population, is a serious disease characterized by an increased incidence. The venography is the golden standard to diagnose DVT. However, it involves invasive contrast agent injection and give patients physical and mental pressure. Functional nearinfrared spectroscopy (fNIRS) has been reported recently to diagnose DVT. Thrombolytic therapy activates the dissolution system with an exogenous activator that dissolves coronary thrombosis. The vena cava filter is a medical filter used for the treatment of thrombosis and the prevention of pulmonary embolism. Here we attempt to use portable NIRS for the DVT monitoring in the whole process of vena cava filter implantation and thrombolytic treatment, and contrast the patients of untreated, vena cava filter implantation and thrombolytic treatment. 19 DVT patients and 12 normal subjects were recruited. Thereinto, 7 patients have taken vena cava filter implantation, and 6 patients have taken the thrombolytic treatment. It was found that deoxyhemoglobins (Δ[Hb]) fluctuates and even increases in DVT. After vena cava filter implantation, Δ[Hb] increases first, then decreases. However, it emerges the rising trend and converge to the curves of normal subjects in thrombolytic treatment. The oxyhemoglobins (Δ[HbO2]) emerges opposite trend in most paradigms. The findings reveal the potential of fNIRS for monitoring DVT and therapeutic effect evaluation of thrombolysis and vena cava filters.

Antecedent reactivation by surface and deep anaphora in Norwegian

PubMed Central

HESTVIK, ARILD; NORDBY, HELGE; KARLSEN, GEIR

2005-01-01

Anaphora are expressions in language that depend on other linguistic entities for their full meaning. They can furthermore be divided into two types according to the level of representation where they find their antecedents: Surface anaphora, which resolve their reference at the sentence representation level, and deep anaphora, which resolve their reference at the non-grammatical level of discourse representation. The linguistic theory of these two anaphor types, and recent findings about processing differences at these two levels, combine to predict that surface anaphora should show fast and immediate reactivation of their antecedents, whereas deep anaphora should have a slower time course of antecedent reaccess. These predictions were confirmed with two lexical decision task experiments with Norwegian stimuli. PMID:15842413

Direct Quantification of Solute Diffusivity in Agarose and Articular Cartilage Using Correlation Spectroscopy.

PubMed

Shoga, Janty S; Graham, Brian T; Wang, Liyun; Price, Christopher

2017-10-01

Articular cartilage is an avascular tissue; diffusive transport is critical for its homeostasis. While numerous techniques have been used to quantify diffusivity within porous, hydrated tissues and tissue engineered constructs, these techniques have suffered from issues regarding invasiveness and spatial resolution. In the present study, we implemented and compared two separate correlation spectroscopy techniques, fluorescence correlation spectroscopy (FCS) and raster image correlation spectroscopy (RICS), for the direct, and minimally-invasive quantification of fluorescent solute diffusion in agarose and articular cartilage. Specifically, we quantified the diffusional properties of fluorescein and Alexa Fluor 488-conjugated dextrans (3k and 10k) in aqueous solutions, agarose gels of varying concentration (i.e. 1, 3, 5%), and in different zones of juvenile bovine articular cartilage explants (i.e. superficial, middle, and deep). In agarose, properties of solute diffusion obtained via FCS and RICS were inversely related to molecule size, gel concentration, and applied strain. In cartilage, the diffusional properties of solutes were similarly dependent upon solute size, cartilage zone, and compressive strain; findings that agree with work utilizing other quantification techniques. In conclusion, this study established the utility of FCS and RICS as simple and minimally invasive techniques for quantifying microscale solute diffusivity within agarose constructs and articular cartilage explants.

Deep learning decision fusion for the classification of urban remote sensing data

NASA Astrophysics Data System (ADS)

Abdi, Ghasem; Samadzadegan, Farhad; Reinartz, Peter

2018-01-01

Multisensor data fusion is one of the most common and popular remote sensing data classification topics by considering a robust and complete description about the objects of interest. Furthermore, deep feature extraction has recently attracted significant interest and has become a hot research topic in the geoscience and remote sensing research community. A deep learning decision fusion approach is presented to perform multisensor urban remote sensing data classification. After deep features are extracted by utilizing joint spectral-spatial information, a soft-decision made classifier is applied to train high-level feature representations and to fine-tune the deep learning framework. Next, a decision-level fusion classifies objects of interest by the joint use of sensors. Finally, a context-aware object-based postprocessing is used to enhance the classification results. A series of comparative experiments are conducted on the widely used dataset of 2014 IEEE GRSS data fusion contest. The obtained results illustrate the considerable advantages of the proposed deep learning decision fusion over the traditional classifiers.

A deep learning framework for financial time series using stacked autoencoders and long-short term memory

PubMed Central

Bao, Wei; Rao, Yulei

2017-01-01

The application of deep learning approaches to finance has received a great deal of attention from both investors and researchers. This study presents a novel deep learning framework where wavelet transforms (WT), stacked autoencoders (SAEs) and long-short term memory (LSTM) are combined for stock price forecasting. The SAEs for hierarchically extracted deep features is introduced into stock price forecasting for the first time. The deep learning framework comprises three stages. First, the stock price time series is decomposed by WT to eliminate noise. Second, SAEs is applied to generate deep high-level features for predicting the stock price. Third, high-level denoising features are fed into LSTM to forecast the next day’s closing price. Six market indices and their corresponding index futures are chosen to examine the performance of the proposed model. Results show that the proposed model outperforms other similar models in both predictive accuracy and profitability performance. PMID:28708865

A New Method for Reconstructing Sea-Level and Deep-Sea-Temperature Variability over the Past 5.3 Million Years

NASA Astrophysics Data System (ADS)

Rohling, E. J.

2014-12-01

Ice volume (and hence sea level) and deep-sea temperature are key measures of global climate change. Sea level has been documented using several independent methods over the past 0.5 million years (Myr). Older periods, however, lack such independent validation; all existing records are related to deep-sea oxygen isotope (d18O) data that are influenced by processes unrelated to sea level. For deep-sea temperature, only one continuous high-resolution (Mg/Ca-based) record exists, with related sea-level estimates, spanning the past 1.5 Myr. We have recently presented a novel sea-level reconstruction, with associated estimates of deep-sea temperature, which independently validates the previous 0-1.5 Myr reconstruction and extends it back to 5.3 Myr ago. A serious of caveats applies to this new method, especially in older times of its application, as is always the case with new methods. Independent validation exercises are needed to elucidate where consistency exists, and where solutions drift away from each other. A key observation from our new method is that a large temporal offset existed during the onset of Plio-Pleistocene ice ages, between a marked cooling step at 2.73 Myr ago and the first major glaciation at 2.15 Myr ago. This observation relies on relative changes within the dataset, which are more robust than absolute values. I will discuss our method and its main caveats and avenues for improvement.

Dual nature of acceptors in GaN and ZnO: The curious case of the shallow MgGa deep state

NASA Astrophysics Data System (ADS)

Lany, Stephan; Zunger, Alex

2010-04-01

Employing a Koopmans corrected density functional method, we find that the metal-site acceptors Mg, Be, and Zn in GaN and Li in ZnO bind holes in deep levels that are largely localized at single anion ligand atoms. In addition to this deep ground state (DGS), we observe an effective-masslike delocalized state that can exist as a short lived shallow transient state (STS). The Mg dopant in GaN represents the unique case where the ionization energy of the localized deep level exceeds only slightly that of the shallow effective-mass acceptor, which explains why Mg works so exceptionally well as an acceptor dopant.

Deep Reconditioning Testing for near Earth Orbits

NASA Technical Reports Server (NTRS)

Betz, F. E.; Barnes, W. L.

1984-01-01

The problems and benefits of deep reconditioning to near Earth orbit missions with high cycle life and shallow discharge depth requirements is discussed. A simple battery level approach to deep reconditioning of nickel cadmium batteries in near Earth orbit is considered. A test plan was developed to perform deep reconditioning in direct comparison with an alternative trickle charge approach. The results demonstrate that the deep reconditioning procedure described for near Earth orbit application is inferior to the alternative of trickle charging.

[Рroblems of ensuring the safety of deep-fried fast food products].

PubMed

Simakova, I V; Perkel, R L; Kutkina, M N; Volovey, A G

There are no doubts that fast-food restaurants, where deep-frying is actively used, are now very popular in Russia. This article focuses on the problems of deep-fried food safety. During deep-frying a considerable amount of fat penetrates the food. That is why the safety of deep-fried food depends on the fat safety and quality, on the level of fat absorption, and on the intensity of oxidative changes of fat during storage. This article contains the results of the research, which demonstrate that in order to insure the safety of fast-food products it is necessary to introduce into normative and technical documents the following standards: peroxide value, acid value, content of oxidation products insoluble in petroleum ether, and content of epoxides in fat phase and to food mass. According to the current norms on content of oxidation products in deep-frying fat and allowed level of fat absorption by a food product equal to 20%, the recommended level of oxidation products insoluble in petroleum ether for French fries is not higher than 0.2% to the food mass. As a temporary measure we can recommend the level of epoxides not higher than 5 mmol/kg to the food mass. It is important to control the content of trans-isomers in deepfrying fat, it must be not higher than 2% of fatty acid mass. In order to lower fat absorption during French fries production it is recommended to use halffinished products of high readiness, and to air fry.

Complications of Moderate Sedation Versus Deep Sedation/General Anesthesia for Adolescent Patients Undergoing Third Molar Extraction.

PubMed

Inverso, Gino; Dodson, Thomas B; Gonzalez, Martin L; Chuang, Sung-Kiang

2016-03-01

To examine the complications resulting from moderate sedation versus deep sedation/general anesthesia for adolescent patients undergoing third molar extraction and determine whether any differences in complication risks exist between the 2 levels of sedation. We performed a prospective study of the Oral and Maxillofacial Surgery Outcomes System from January 2001 to December 2010. The primary predictor variable was the level of sedation, divided into 2 groups: moderate sedation versus deep sedation/general anesthesia. The primary outcome was the incidence of adverse complications resulting from the sedation level. Differences in the cohort characteristics were analyzed using the independent samples t test, χ(2) test, and analysis of variance, as appropriate. Multivariable logistic regression was used to measure the effect the level of sedation had on the adverse complication rate. Patients in the moderate sedation group had a complication rate of 0.5%, and patients in the deep sedation/general anesthesia group had a complication rate of 0.9%. Compared with moderate sedation, deep sedation/general anesthesia did not pose a significantly increased risk of adverse anesthesia complications (adjusted odds ratio 1.63, 95% confidence interval 0.95 to 2.81; P = .077). The results of our study have shown that the risk of adverse anesthesia complications is not increased when choosing between moderate and deep sedation/general anesthesia for adolescent patients undergoing third molar extraction. Copyright © 2016 American Association of Oral and Maxillofacial Surgeons. Published by Elsevier Inc. All rights reserved.

Synthesizing and Characterizing Graphene via Raman Spectroscopy: An Upper-Level Undergraduate Experiment That Exposes Students to Raman Spectroscopy and a 2D Nanomaterial

ERIC Educational Resources Information Center

Parobek, David; Shenoy, Ganesh; Zhou, Feng; Peng, Zhenbo; Ward, Michelle; Liu, Haitao

2016-01-01

In this upper-level undergraduate experiment, students utilize micro-Raman spectroscopy to characterize graphene prepared by mechanical exfoliation and chemical vapor deposition (CVD). The mechanically exfoliated samples are prepared by the students while CVD graphene can be purchased or obtained through outside sources. Owing to the intense Raman…

Evolution of Defect Structures and Deep Subgap States during Annealing of Amorphous In-Ga-Zn Oxide for Thin-Film Transistors

NASA Astrophysics Data System (ADS)

Jia, Junjun; Suko, Ayaka; Shigesato, Yuzo; Okajima, Toshihiro; Inoue, Keiko; Hosomi, Hiroyuki

2018-01-01

We investigate the evolution behavior of defect structures and the subgap states in In-Ga-Zn oxide (IGZO) films with increasing postannealing temperature by means of extended x-ray absorption fine-structure (EXAFS) measurements, positron annihilation lifetime spectroscopy (PALS), and cathodoluminescence (CL) spectroscopy, aiming to understand the relationship between defect structures and subgap states. EXAFS measurements reveal the varied oxygen coordination numbers around cations during postannealing and confirm two types of point defects, namely, excess oxygen around Ga atoms and oxygen deficiency around In and/or Zn atoms. PALS suggests the existence of cation-vacancy (VM )-related clusters with neutral or negative charge in both amorphous and polycrystalline IGZO films. CL spectra show a main emission band at approximately 1.85 eV for IGZO films, and a distinct shoulder located at about 2.15 eV for IGZO films postannealed above 600 °C . These two emission bands are assigned to a recombination between the electrons in the conduction band and/or in the shallow donor levels near the conduction band and the acceptors trapped above the valence-band maximum. The shallow donors are attributed to the oxygen deficiency, and the acceptors are thought to possibly arise from the excess oxygen or the VM-related clusters. These results open up an alternative route for understanding the device instability of amorphous IGZO-based thin-film transistors, especially the presence of the neutral or negatively charged VM-related clusters in amorphous IGZO films.

Laplace deep level transient spectroscopy: Embodiment and evolution

NASA Astrophysics Data System (ADS)

Peaker, A. R.; Markevich, V. P.; Hawkins, I. D.; Hamilton, B.; Bonde Nielsen, K.; Gościński, K.

2012-08-01

This paper is to commemorate the work of Leszek Dobaczewski who devoted much of his life to the development and application of high resolution DLTS. Under good experimental conditions Laplace DLTS provides an order of magnitude higher energy resolution than conventional DLTS techniques. This has had a profound effect on electrical defect spectroscopy enabling the effect of external probes, such as uniaxial stress, and internal perturbations, such as the proximity of atoms isovalent with the host, to be quantified in terms of electronic behaviour. Laplace DLTS provides a synergy with other techniques that was difficult or impossible to achieve previously. In this paper we present an overview of the development of LDLTS and illustrate some of its uses by describing its application in a number of key areas of defect research. Leszek Dobaczewski was born on 25th December 1954. He received his education in Warsaw taking his PhD in 1986 with Jerzy Langer at the Institute of Physics on “Recombination Processes at defects with the large lattice relaxation”. He held a research position at the institute in Warsaw until he came to Manchester in 1990 and thereafter alternated between Manchester and Warsaw. He worked primarily on the development and application of high resolution DLTS. He was awarded the degree of DSc in 1994 for his work on DX centres and held an appointment as full professor in Warsaw with Visiting Professor posts at Manchester and Aarhus. Professor Leszek Dobaczewski died in April 2010.

Dual-modal cancer detection based on optical pH sensing and Raman spectroscopy

NASA Astrophysics Data System (ADS)

Kim, Soogeun; Lee, Seung Ho; Min, Sun Young; Byun, Kyung Min; Lee, Soo Yeol

2017-10-01

A dual-modal approach using Raman spectroscopy and optical pH sensing was investigated to discriminate between normal and cancerous tissues. Raman spectroscopy has demonstrated the potential for in vivo cancer detection. However, Raman spectroscopy has suffered from strong fluorescence background of biological samples and subtle spectral differences between normal and disease tissues. To overcome those issues, pH sensing is adopted to Raman spectroscopy as a dual-modal approach. Based on the fact that the pH level in cancerous tissues is lower than that in normal tissues due to insufficient vasculature formation, the dual-modal approach combining the chemical information of Raman spectrum and the metabolic information of pH level can improve the specificity of cancer diagnosis. From human breast tissue samples, Raman spectra and pH levels are measured using fiber-optic-based Raman and pH probes, respectively. The pH sensing is based on the dependence of pH level on optical transmission spectrum. Multivariate statistical analysis is performed to evaluate the classification capability of the dual-modal method. The analytical results show that the dual-modal method based on Raman spectroscopy and optical pH sensing can improve the performance of cancer classification.

Theoretical Explanation for Success of Deep-Level-Learning Study Tours

ERIC Educational Resources Information Center

Bergsteiner, Harald; Avery, Gayle C.

2008-01-01

Study tours can help internationalize curricula and prepare students for global workplaces. We examine benefits of tours providing deep-level learning experiences rather than industrial tourism using five main theoretical frameworks to highlight the diverse learning benefits associated with intensive study tours in particular. Relevant theoretical…

Apache Clinical Text and Knowledge Extraction System (cTAKES) | Informatics Technology for Cancer Research (ITCR)

Cancer.gov

The tool extracts deep phenotypic information from the clinical narrative at the document-, episode-, and patient-level. The final output is FHIR compliant patient-level phenotypic summary which can be consumed by research warehouses or the DeepPhe native visualization tool.

Unfolding the atmospheric and deep internal flows on Jupiter and Saturn using the Juno and Cassini gravity measurements

NASA Astrophysics Data System (ADS)

Galanti, Eli; Kaspi, Yohai

2016-10-01

In light of the first orbits of Juno at Jupiter, we discuss the Juno gravity experiment and possible initial results. Relating the flow on Jupiter and Saturn to perturbations in their density field is key to the analysis of the gravity measurements expected from both the Juno (Jupiter) and Cassini (Saturn) spacecraft during 2016-17. Both missions will provide latitude-dependent gravity fields, which in principle could be inverted to calculate the vertical structure of the observed cloud-level zonal flow on these planets. Current observations for the flow on these planets exists only at the cloud-level (0.1-1 bar). The observed cloud-level wind might be confined to the upper layers, or be a manifestation of deep cylindrical flows. Moreover, it is possible that in the case where the observed wind is superficial, there exists deep interior flow that is completely decoupled from the observed atmospheric flow.In this talk, we present a new adjoint based inverse model for inversion of the gravity measurements into flow fields. The model is constructed to be as general as possible, allowing for both cloud-level wind extending inward, and a decoupled deep flow that is constructed to produce cylindrical structures with variable width and magnitude, or can even be set to be completely general. The deep flow is also set to decay when approaching the upper levels so it has no manifestation there. The two sources of flow are then combined to a total flow field that is related to the density anomalies and gravity moments via a dynamical model. Given the measured gravitational moments from Jupiter and Saturn, the dynamical model, together with the adjoint inverse model are used for optimizing the control parameters and by this unfolding the deep and surface flows. Several scenarios are examined, including cases in which the surface wind and the deep flow have comparable effects on the gravity field, cases in which the deep flow is dominating over the surface wind, and an extreme case where the deep flow can have an unconstrained pattern. The method enables also the calculation of the uncertainties associated with each solution. We discuss the physical limitations to the method in view of the measurement uncertainties.

A record of deep-ocean dissolved O2 from the oxidation state of iron in submarine basalts.

PubMed

Stolper, Daniel A; Keller, C Brenhin

2018-01-18

The oxygenation of the deep ocean in the geological past has been associated with a rise in the partial pressure of atmospheric molecular oxygen (O 2 ) to near-present levels and the emergence of modern marine biogeochemical cycles. It has also been linked to the origination and diversification of early animals. It is generally thought that the deep ocean was largely anoxic from about 2,500 to 800 million years ago, with estimates of the occurrence of deep-ocean oxygenation and the linked increase in the partial pressure of atmospheric oxygen to levels sufficient for this oxygenation ranging from about 800 to 400 million years ago. Deep-ocean dissolved oxygen concentrations over this interval are typically estimated using geochemical signatures preserved in ancient continental shelf or slope sediments, which only indirectly reflect the geochemical state of the deep ocean. Here we present a record that more directly reflects deep-ocean oxygen concentrations, based on the ratio of Fe 3+ to total Fe in hydrothermally altered basalts formed in ocean basins. Our data allow for quantitative estimates of deep-ocean dissolved oxygen concentrations from 3.5 billion years ago to 14 million years ago and suggest that deep-ocean oxygenation occurred in the Phanerozoic (541 million years ago to the present) and potentially not until the late Palaeozoic (less than 420 million years ago).

A record of deep-ocean dissolved O2 from the oxidation state of iron in submarine basalts

NASA Astrophysics Data System (ADS)

Stolper, Daniel A.; Keller, C. Brenhin

2018-01-01

The oxygenation of the deep ocean in the geological past has been associated with a rise in the partial pressure of atmospheric molecular oxygen (O2) to near-present levels and the emergence of modern marine biogeochemical cycles. It has also been linked to the origination and diversification of early animals. It is generally thought that the deep ocean was largely anoxic from about 2,500 to 800 million years ago, with estimates of the occurrence of deep-ocean oxygenation and the linked increase in the partial pressure of atmospheric oxygen to levels sufficient for this oxygenation ranging from about 800 to 400 million years ago. Deep-ocean dissolved oxygen concentrations over this interval are typically estimated using geochemical signatures preserved in ancient continental shelf or slope sediments, which only indirectly reflect the geochemical state of the deep ocean. Here we present a record that more directly reflects deep-ocean oxygen concentrations, based on the ratio of Fe3+ to total Fe in hydrothermally altered basalts formed in ocean basins. Our data allow for quantitative estimates of deep-ocean dissolved oxygen concentrations from 3.5 billion years ago to 14 million years ago and suggest that deep-ocean oxygenation occurred in the Phanerozoic (541 million years ago to the present) and potentially not until the late Palaeozoic (less than 420 million years ago).

De novo peptide sequencing by deep learning

PubMed Central

Tran, Ngoc Hieu; Zhang, Xianglilan; Xin, Lei; Shan, Baozhen; Li, Ming

2017-01-01

De novo peptide sequencing from tandem MS data is the key technology in proteomics for the characterization of proteins, especially for new sequences, such as mAbs. In this study, we propose a deep neural network model, DeepNovo, for de novo peptide sequencing. DeepNovo architecture combines recent advances in convolutional neural networks and recurrent neural networks to learn features of tandem mass spectra, fragment ions, and sequence patterns of peptides. The networks are further integrated with local dynamic programming to solve the complex optimization task of de novo sequencing. We evaluated the method on a wide variety of species and found that DeepNovo considerably outperformed state of the art methods, achieving 7.7–22.9% higher accuracy at the amino acid level and 38.1–64.0% higher accuracy at the peptide level. We further used DeepNovo to automatically reconstruct the complete sequences of antibody light and heavy chains of mouse, achieving 97.5–100% coverage and 97.2–99.5% accuracy, without assisting databases. Moreover, DeepNovo is retrainable to adapt to any sources of data and provides a complete end-to-end training and prediction solution to the de novo sequencing problem. Not only does our study extend the deep learning revolution to a new field, but it also shows an innovative approach in solving optimization problems by using deep learning and dynamic programming. PMID:28720701

HD-MTL: Hierarchical Deep Multi-Task Learning for Large-Scale Visual Recognition.

PubMed

Fan, Jianping; Zhao, Tianyi; Kuang, Zhenzhong; Zheng, Yu; Zhang, Ji; Yu, Jun; Peng, Jinye

2017-02-09

In this paper, a hierarchical deep multi-task learning (HD-MTL) algorithm is developed to support large-scale visual recognition (e.g., recognizing thousands or even tens of thousands of atomic object classes automatically). First, multiple sets of multi-level deep features are extracted from different layers of deep convolutional neural networks (deep CNNs), and they are used to achieve more effective accomplishment of the coarseto- fine tasks for hierarchical visual recognition. A visual tree is then learned by assigning the visually-similar atomic object classes with similar learning complexities into the same group, which can provide a good environment for determining the interrelated learning tasks automatically. By leveraging the inter-task relatedness (inter-class similarities) to learn more discriminative group-specific deep representations, our deep multi-task learning algorithm can train more discriminative node classifiers for distinguishing the visually-similar atomic object classes effectively. Our hierarchical deep multi-task learning (HD-MTL) algorithm can integrate two discriminative regularization terms to control the inter-level error propagation effectively, and it can provide an end-to-end approach for jointly learning more representative deep CNNs (for image representation) and more discriminative tree classifier (for large-scale visual recognition) and updating them simultaneously. Our incremental deep learning algorithms can effectively adapt both the deep CNNs and the tree classifier to the new training images and the new object classes. Our experimental results have demonstrated that our HD-MTL algorithm can achieve very competitive results on improving the accuracy rates for large-scale visual recognition.

Model United Nations and Deep Learning: Theoretical and Professional Learning

ERIC Educational Resources Information Center

Engel, Susan; Pallas, Josh; Lambert, Sarah

2017-01-01

This article demonstrates that the purposeful subject design, incorporating a Model United Nations (MUN), facilitated deep learning and professional skills attainment in the field of International Relations. Deep learning was promoted in subject design by linking learning objectives to Anderson and Krathwohl's (2001) four levels of knowledge or…

The relationship between the deep-level structure in crust and brewing of strong earthquakes in Xingtai area

NASA Astrophysics Data System (ADS)

Xiao, Lan-Xi; Zhu, Yuan-Qing; Zhang, Shao-Quan; Liu, Xu; Guo, Yu

1999-11-01

In this paper, crust medium is treated as Maxwell medium, and crust model includes hard inclusion, soft inclusion, deep-level fault. The stress concentration and its evolution with time are obtained by using three-dimensional finite element method and differential method. The conclusions are draw as follows: (1) The average stress concentration and maximum shear stress concentration caused by non-heterogeneous of crust are very high in hard inclusion and around the deep fault. With the time passing by, the concentration of average stress in the model gradually trends to uniform. At the same time, the concentration of maximum shear stress in hard inclusion increases gradually. This character is favorable to transfer shear strain energy from soft inclusion to hard inclusion. (2) When the upper mantle beneath the inclusion upheave at a certain velocity of 1 cm/a, the changes of average stress concentration with time become complex, and the boundary of the hard and soft inclusion become unconspicuous, but the maximum shear stress concentration increases much more in the hard inclusion with time at a higher velocity. This feature make for transformation of energy from the soft inclusion to the hard inclusion. (3) The changes of average stress concentration and maximum shear stress concentration with time around the deep-level fault result in further accumulation of maximum shear stress concentration and finally cause the deep-level fault instable and accelerated creep along fault direction. (4) The changes of vertical displacement on the surface of the model, which is caused by the accelerated creep of the deep-level fault, is similar to that of the observation data before Xingtai strong earthquake.

Raman spectroscopy of saliva as a perspective method for periodontitis diagnostics Raman spectroscopy of saliva

NASA Astrophysics Data System (ADS)

Gonchukov, S.; Sukhinina, A.; Bakhmutov, D.; Minaeva, S.

2012-01-01

In view of its potential for biological tissues analyses at a molecular level, Raman spectroscopy in optical range has been the object of biomedical research for the last years. The main aim of this work is the development of Raman spectroscopy for organic content identifying and determination of biomarkers of saliva at a molecular level for periodontitis diagnostics. Four spectral regions were determined: 1155 and 1525 cm-1, 1033 and 1611 cm-1, which can be used as biomarkers of this widespread disease.

The Hubble Deep UV Legacy Survey (HDUV): Survey Overview and First Results

NASA Astrophysics Data System (ADS)

Oesch, Pascal; Montes, Mireia; HDUV Survey Team

2015-08-01

Deep HST imaging has shown that the overall star formation density and UV light density at z>3 is dominated by faint, blue galaxies. Remarkably, very little is known about the equivalent galaxy population at lower redshifts. Understanding how these galaxies evolve across the epoch of peak cosmic star-formation is key to a complete picture of galaxy evolution. Here, we present a new HST WFC3/UVIS program, the Hubble Deep UV (HDUV) legacy survey. The HDUV is a 132 orbit program to obtain deep imaging in two filters (F275W and F336W) over the two CANDELS Deep fields. We will cover ~100 arcmin2, reaching down to 27.5-28.0 mag at 5 sigma. By directly sampling the rest-frame far-UV at z>~0.5, this will provide a unique legacy dataset with exquisite HST multi-wavelength imaging as well as ancillary HST grism NIR spectroscopy for a detailed study of faint, star-forming galaxies at z~0.5-2. The HDUV will enable a wealth of research by the community, which includes tracing the evolution of the FUV luminosity function over the peak of the star formation rate density from z~3 down to z~0.5, measuring the physical properties of sub-L* galaxies, and characterizing resolved stellar populations to decipher the build-up of the Hubble sequence from sub-galactic clumps. This poster provides an overview of the HDUV survey and presents the reduced data products and catalogs which will be released to the community.

Subduction zone forearc serpentinites as incubators for deep microbial life

NASA Astrophysics Data System (ADS)

Plümper, Oliver; King, Helen E.; Geisler, Thorsten; Liu, Yang; Pabst, Sonja; Savov, Ivan P.; Rost, Detlef; Zack, Thomas

2017-04-01

Serpentinization-fueled systems in the cool, hydrated forearc mantle of subduction zones may provide an environment that supports deep chemolithoautotrophic life. Here, we examine serpentinite clasts expelled from mud volcanoes above the Izu-Bonin-Mariana subduction zone forearc (Pacific Ocean) that contain complex organic matter and nanosized Ni-Fe alloys. Using time-of-flight secondary ion mass spectrometry and Raman spectroscopy, we determined that the organic matter consists of a mixture of aliphatic and aromatic compounds and functional groups such as amides. Although an abiotic or subduction slab-derived fluid origin cannot be excluded, the similarities between the molecular signatures identified in the clasts and those of bacteria-derived biopolymers from other serpentinizing systems hint at the possibility of deep microbial life within the forearc. To test this hypothesis, we coupled the currently known temperature limit for life, 122 °C, with a heat conduction model that predicts a potential depth limit for life within the forearc at ˜10,000 m below the seafloor. This is deeper than the 122 °C isotherm in known oceanic serpentinizing regions and an order of magnitude deeper than the downhole temperature at the serpentinized Atlantis Massif oceanic core complex, Mid-Atlantic Ridge. We suggest that the organic-rich serpentinites may be indicators for microbial life deep within or below the mud volcano. Thus, the hydrated forearc mantle may represent one of Earth’s largest hidden microbial ecosystems. These types of protected ecosystems may have allowed the deep biosphere to thrive, despite violent phases during Earth’s history such as the late heavy bombardment and global mass extinctions.

Subduction zone forearc serpentinites as incubators for deep microbial life.

PubMed

Plümper, Oliver; King, Helen E; Geisler, Thorsten; Liu, Yang; Pabst, Sonja; Savov, Ivan P; Rost, Detlef; Zack, Thomas

2017-04-25

Serpentinization-fueled systems in the cool, hydrated forearc mantle of subduction zones may provide an environment that supports deep chemolithoautotrophic life. Here, we examine serpentinite clasts expelled from mud volcanoes above the Izu-Bonin-Mariana subduction zone forearc (Pacific Ocean) that contain complex organic matter and nanosized Ni-Fe alloys. Using time-of-flight secondary ion mass spectrometry and Raman spectroscopy, we determined that the organic matter consists of a mixture of aliphatic and aromatic compounds and functional groups such as amides. Although an abiotic or subduction slab-derived fluid origin cannot be excluded, the similarities between the molecular signatures identified in the clasts and those of bacteria-derived biopolymers from other serpentinizing systems hint at the possibility of deep microbial life within the forearc. To test this hypothesis, we coupled the currently known temperature limit for life, 122 °C, with a heat conduction model that predicts a potential depth limit for life within the forearc at ∼10,000 m below the seafloor. This is deeper than the 122 °C isotherm in known oceanic serpentinizing regions and an order of magnitude deeper than the downhole temperature at the serpentinized Atlantis Massif oceanic core complex, Mid-Atlantic Ridge. We suggest that the organic-rich serpentinites may be indicators for microbial life deep within or below the mud volcano. Thus, the hydrated forearc mantle may represent one of Earth's largest hidden microbial ecosystems. These types of protected ecosystems may have allowed the deep biosphere to thrive, despite violent phases during Earth's history such as the late heavy bombardment and global mass extinctions.

Subduction zone forearc serpentinites as incubators for deep microbial life

PubMed Central

Plümper, Oliver; Geisler, Thorsten; Liu, Yang; Pabst, Sonja; Savov, Ivan P.; Rost, Detlef; Zack, Thomas

2017-01-01

Serpentinization-fueled systems in the cool, hydrated forearc mantle of subduction zones may provide an environment that supports deep chemolithoautotrophic life. Here, we examine serpentinite clasts expelled from mud volcanoes above the Izu–Bonin–Mariana subduction zone forearc (Pacific Ocean) that contain complex organic matter and nanosized Ni–Fe alloys. Using time-of-flight secondary ion mass spectrometry and Raman spectroscopy, we determined that the organic matter consists of a mixture of aliphatic and aromatic compounds and functional groups such as amides. Although an abiotic or subduction slab-derived fluid origin cannot be excluded, the similarities between the molecular signatures identified in the clasts and those of bacteria-derived biopolymers from other serpentinizing systems hint at the possibility of deep microbial life within the forearc. To test this hypothesis, we coupled the currently known temperature limit for life, 122 °C, with a heat conduction model that predicts a potential depth limit for life within the forearc at ∼10,000 m below the seafloor. This is deeper than the 122 °C isotherm in known oceanic serpentinizing regions and an order of magnitude deeper than the downhole temperature at the serpentinized Atlantis Massif oceanic core complex, Mid-Atlantic Ridge. We suggest that the organic-rich serpentinites may be indicators for microbial life deep within or below the mud volcano. Thus, the hydrated forearc mantle may represent one of Earth’s largest hidden microbial ecosystems. These types of protected ecosystems may have allowed the deep biosphere to thrive, despite violent phases during Earth’s history such as the late heavy bombardment and global mass extinctions. PMID:28396389

Mode identification from spectroscopy of gravity-mode pulsators

NASA Astrophysics Data System (ADS)

Pollard, K. R.; Brunsden, E.; Cottrell, P. L.; Davie, M.; Greenwood, A.; Wright, D. J.; De Cat, P.

2014-02-01

The gravity modes present in γ Doradus stars probe the deep stellar interiors and are thus of particular interest in asteroseismology. For the MUSICIAN programme at the University of Canterbury, we obtain extensive high-resolution echelle spectra of γ Dor stars from the Mt John University Observatory in New Zealand. We analyze these to obtain the pulsational frequencies and identify these with the multiple pulsational modes excited in the star. A summary of recent results from our spectroscopic mode-identification programme is given.