Surface photovoltage studies of p-type AlGaN layers after reactive-ion etching

Science.gov (United States)

McNamara, J. D.; Phumisithikul, K. L.; Baski, A. A.; Marini, J.; Shahedipour-Sandvik, F.; Das, S.; Reshchikov, M. A.

2016-10-01

The surface photovoltage (SPV) technique was used to study the surface and electrical properties of Mg-doped, p-type AlxGa1-xN (0.06 GaN:Mg thin films and from the predictions of a thermionic model for the SPV behavior. In particular, the SPV of the p-AlGaN:Mg layers exhibited slower-than-expected transients under ultraviolet illumination and delayed restoration to the initial dark value. The slow transients and delayed restorations can be attributed to a defective surface region which interferes with normal thermionic processes. The top 45 nm of the p-AlGaN:Mg layer was etched using a reactive-ion etch which caused the SPV behavior to be substantially different. From this study, it can be concluded that a defective, near-surface region is inhibiting the change in positive surface charge by allowing tunneling or hopping conductivity of holes from the bulk to the surface, or by the trapping of electrons traveling to the surface by a high concentration of defects in the near-surface region. Etching removes the defective layer and reveals a region of presumably higher quality, as evidenced by substantial changes in the SPV behavior.

Studies of surface states in zinc oxide nanopowders

Science.gov (United States)

Peters, Raul Mugabe

The surface of ZnO semiconductor nanosystems is a key performance-defining factor in numerous applications. In this work we present experimental results for the surface defect-related properties of ZnO nanoscale systems. Surface photovoltage spectroscopy was used to determine the defect level energies within the band gap, the conduction vs. valence band nature of the defect-related transitions, and to probe key dynamic parameters of the surface on a number of commercially available ZnO nanopowders. In our experimental setup, surface photovoltage characterization is conducted in high vacuum in tandem with in situ oxygen remote plasma treatments. Surface photovoltage investigations of the as-received and plasma-processed samples revealed a number of common spectral features related to surface states. Furthermore, we observed significant plasma-induced changes in the surface defect properties. Ex situ positron annihilation and photoluminescence measurements were performed on the studied samples and correlated with surface photovoltage results. The average positron lifetimes were found to be substantially longer than in a bulk single crystalline sample, which is consistent with the model of grains with defect-rich surface and subsurface layers. Compression of the powders into pellets yielded reduction of the average positron lifetimes. Surface photovoltage, positron annihilation, and photoluminescence spectra consistently showed sample-to-sample differences due to the variation in the overall quality of the nanopowders, which partially obscures observation of the scaling effects. However, the results demonstrated that our approach is efficient in detecting specific surface states in nanoscale ZnO specimens and in elucidating their nature.

Photovoltage method for the research of CdS and ZnO nanoparticles and hybrid MEH-PPV/nanoparticle structures

Czech Academy of Sciences Publication Activity Database

Toušková, J.; Toušek, J.; Rohovec, Jan; Růžička, A.; Polonskyi, O.; Urbánek, P.; Kuřitka, I.

2014-01-01

Roč. 16, č. 3 (2014), Art. 2314 ISSN 1388-0764 Institutional support: RVO:67985831 Keywords : CdS * energy conversion * MEH-PPV * nanoparticles * photovoltage spectra * transmission electron microscopy * ZnO Subject RIV: DD - Geochemistry Impact factor: 2.184, year: 2014

Large photovoltages generated by plant photosystem I crystals

Energy Technology Data Exchange (ETDEWEB)

Toporik, Hila; Carmeli, Chanoch; Nelson, Nathan [Department of Biochemistry and Molecular Biology, Faculty of Life Sciences, Tel Aviv University, Tel Aviv 69978 (Israel); Carmeli, Itai [School of Chemistry, Faculty of Exact Sciences, Tel Aviv University, Tel Aviv 69978 (Israel); Volotsenko, Irina; Molotskii, Michel; Rosenwaks, Yossi [Department of Physical Electronics, Faculty of Engineering, Tel Aviv University, Tel Aviv 69978 (Israel)

2012-06-12

Micrometer-thick plant photosystem I crystals made of up to 1000 layers of serially arranged protein complexes generate unprecedented high photovoltages when placed on a conducting solid surface and measured using Kelvin probe force microscopy. The successive layers form serially photoinduced dipoles in the crystal that give rise to electric fields as large as 100 kV cm{sup -1}. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Comparative study of Cu(In,Ga)Se{sub 2}/CdS and Cu(In,Ga)Se{sub 2}/In{sub 2}S{sub 3} systems by surface photovoltage techniques

Energy Technology Data Exchange (ETDEWEB)

Dittrich, Th., E-mail: dittrich@helmholtz-berlin.de [Helmholtz-Zentrum Berlin für Materialien und Energie, Hahn-Meitner-Platz 1, D-14109 Berlin (Germany); Gonzáles, A.; Rada, T. [Helmholtz-Zentrum Berlin für Materialien und Energie, Hahn-Meitner-Platz 1, D-14109 Berlin (Germany); Departamento de Física, Universidad del Norte, km 5 Via Pto Colombia, Barranquilla (Colombia); Rissom, T.; Zillner, E. [Helmholtz-Zentrum Berlin für Materialien und Energie, Hahn-Meitner-Platz 1, D-14109 Berlin (Germany); Sadewasser, S. [Helmholtz-Zentrum Berlin für Materialien und Energie, Hahn-Meitner-Platz 1, D-14109 Berlin (Germany); International Iberian Nanotechnology Laboratory, Avda. Mestre José Veiga s/n, 4715-330 Braga (Portugal); Lux-Steiner, M. [Helmholtz-Zentrum Berlin für Materialien und Energie, Hahn-Meitner-Platz 1, D-14109 Berlin (Germany)

2013-05-01

Cu(In,Ga)Se{sub 2} absorbers were investigated by surface photovoltage (SPV) in the Kelvin probe and fixed capacitor arrangements before and after deposition of CdS or In{sub 2}S{sub 3} buffer layers as well as before and after deposition of ZnO window layers. Effects such as passivation of surface states, partial electron transfer from ZnO into In{sub 2}S{sub 3}, decrease of the ideality factor after deposition of ZnO and slow electron transfer through In{sub 2}S{sub 3} were demonstrated. The results show that SPV measurements open opportunities for dedicated studies of charge separation at hetero-junctions between ordered and disordered semiconductors. - Highlights: ► Surface photovoltage on chalcopyrite/buffer layer at different stages of formation ► Comparison of CdS and In{sub 2}S{sub 3} buffer layers ► Information about surface passivation, surface defects, ideality factor, transport.

Conditioning of Si-interfaces by wet-chemical oxidation: Electronic interface properties study by surface photovoltage measurements

Energy Technology Data Exchange (ETDEWEB)

Angermann, Heike, E-mail: angermann@helmholtz-berlin.de

2014-09-01

Highlights: • Determination of electronic interface properties by contact-less surface photovoltage (SPV) technique. • Systematic correlations of substrate morphology and surface electronic properties. • Optimization of surface pre-treatment for flat, saw damage etched, and textured Si solar cell substrates. • Ultra-thin passivating Si oxide layers with low densities of rechargeable states by wet-chemical oxidation and subsequent annealing. • Environmentally acceptable processes, utilizing hot water, diluted HCl, or ozone low cost alternative to current approaches with concentrated chemicals. • The effect of optimized wet-chemical pre-treatments can be preserved during subsequent layer deposition. - Abstract: The field-modulated surface photovoltage (SPV) method, a very surface sensitive technique, was utilized to determine electronic interface properties on wet-chemically oxidized and etched silicon (Si) interfaces. The influence of preparation-induced surface micro-roughness and un-stoichiometric oxides on the resulting the surface charge, energetic distribution D{sub it}(E), and density D{sub it,min} of rechargeable states was studied by simultaneous, spectroscopic ellipsometry (SE) measurements on polished Si(111) and Si(100) substrates. Based on previous findings and new research, a study of conventional and newly developed wet-chemical oxidation methods was established, correlating the interactions between involved oxidizing and etching solutions and the initial substrate morphology to the final surface conditioning. It is shown, which sequences of wet-chemical oxidation and oxide removal, have to be combined in order to achieve atomically smooth, hydrogen terminated surfaces, as well as ultra-thin oxide layers with low densities of rechargeable states on flat, saw damage etched, and textured Si substrates, as commonly applied in silicon device and solar cell manufacturing. These conventional strategies for wet-chemical pre-treatment are mainly

Conditioning of Si-interfaces by wet-chemical oxidation: Electronic interface properties study by surface photovoltage measurements

International Nuclear Information System (INIS)

Angermann, Heike

2014-01-01

Highlights: • Determination of electronic interface properties by contact-less surface photovoltage (SPV) technique. • Systematic correlations of substrate morphology and surface electronic properties. • Optimization of surface pre-treatment for flat, saw damage etched, and textured Si solar cell substrates. • Ultra-thin passivating Si oxide layers with low densities of rechargeable states by wet-chemical oxidation and subsequent annealing. • Environmentally acceptable processes, utilizing hot water, diluted HCl, or ozone low cost alternative to current approaches with concentrated chemicals. • The effect of optimized wet-chemical pre-treatments can be preserved during subsequent layer deposition. - Abstract: The field-modulated surface photovoltage (SPV) method, a very surface sensitive technique, was utilized to determine electronic interface properties on wet-chemically oxidized and etched silicon (Si) interfaces. The influence of preparation-induced surface micro-roughness and un-stoichiometric oxides on the resulting the surface charge, energetic distribution D it (E), and density D it,min of rechargeable states was studied by simultaneous, spectroscopic ellipsometry (SE) measurements on polished Si(111) and Si(100) substrates. Based on previous findings and new research, a study of conventional and newly developed wet-chemical oxidation methods was established, correlating the interactions between involved oxidizing and etching solutions and the initial substrate morphology to the final surface conditioning. It is shown, which sequences of wet-chemical oxidation and oxide removal, have to be combined in order to achieve atomically smooth, hydrogen terminated surfaces, as well as ultra-thin oxide layers with low densities of rechargeable states on flat, saw damage etched, and textured Si substrates, as commonly applied in silicon device and solar cell manufacturing. These conventional strategies for wet-chemical pre-treatment are mainly based on

Hall Effect and transient surface photovoltage (SPV study of Cu3BiS3 thin films

Directory of Open Access Journals (Sweden)

F. Mesa

2014-03-01

Full Text Available Here, we present the electrical properties of the compound Cu3BiS3 deposited by co-evaporation. This new compound may have the properties necessary to be used as an absorbent layer in solar cells. The samples were characterized by Hall effect and transient surface photovoltage (SPV measurements. Using Hall effect measurements, we found that the concentration of n charge carriers is in the order of 1016 cm-3 irrespective of the Cu/Bi mass ratio. We also found that the mobility of this compound (μ in the order of 4 cm2 V-1s-1 varies according to the transport mechanisms that govern it and are dependent on temperature. Based on the SPV, we found a high density of surface defects, which can be passivated by superimposing a buffer layer over the Cu3BiS3 compound.

Correlation between processing conditions of Cu2ZnSn(SxSe1-x)4 and modulated surface photovoltage

Science.gov (United States)

Lin, X. Z.; Dittrich, Th.; Fengler, S.; Lux-Steiner, M. Ch.; Ennaoui, A.

2013-04-01

Cu2ZnSn(SxSe1-x)4 (CZTSSe) layers deposited from multi-component nanoparticle inks were characterized by modulated surface photovoltage (SPV) spectroscopy to investigate the effect of annealing conditions. The SPV signals increased strongly with decreasing sulfur content. Band gaps were obtained in terms of SPV onset energy. A diffusion length of above 1 μm was estimated for photo-generated electrons at x = 0.28. The band gap increased with increasing x showing an anomaly in the range of 0.5 < x < 1. The results suggested that an excess of selenium is required for the formation of a photo-active phase reliable for efficient Cu2ZnSn(SxSe1-x)4-based solar cells.

Interaction of light with the ZnO surface: Photon induced oxygen “breathing,” oxygen vacancies, persistent photoconductivity, and persistent photovoltage

International Nuclear Information System (INIS)

Gurwitz, Ron; Cohen, Rotem; Shalish, Ilan

2014-01-01

ZnO surfaces adsorb oxygen in the dark and emit CO 2 when exposed to white light, reminiscent of the lungs of living creatures. We find that this exchange of oxygen with the ambient affects the integrity of the ZnO surface. Thus, it forms a basis for several interesting surface phenomena in ZnO, such as photoconductivity, photovoltage, and gas sensing, and has a role in ZnO electrical conduction. Using x-ray photoelectron spectroscopy on ZnO nanowires, we observed a decomposition of ZnO under white light and formation of oxygen-depleted surface, which explains photoconductivity by the electron donation of oxygen vacancies. Our findings suggest that the observed decomposition of the ZnO lattice may only take place due to photon-induced reduction of ZnO by carbon containing molecules (or carbo-photonic reduction), possibly from the ambient gas, accounting in a consistent way for both the reduced demands on the energy required for decomposition and for the observed emission of lattice oxygen in the form of CO 2 . The formation of oxygen-vacancy rich surface is suggested to induce surface delta doping, causing accumulation of electrons at the surface, which accounts for both the increase in conductivity and the flattening of the energy bands. Using surface photovoltage spectroscopy in ultra high vacuum, we monitored changes in the deep level spectrum. We observe a wide optical transition from a deep acceptor to the conduction band, which energy position coincides with the position of the so called “green luminescence” in ZnO. This green transition disappears with the formation of surface oxygen vacancies. Since the oxygen vacancies are donors, while the green transition involves surface acceptors, the results suggest that the initial emission of oxygen originates at the defect sites of the latter, thereby eliminating each other. This suggests that the green transition originates at surface Zn vacancy acceptors. Removing an oxygen atom from a Zn vacancy completes

Interaction of light with the ZnO surface: Photon induced oxygen “breathing,” oxygen vacancies, persistent photoconductivity, and persistent photovoltage

Energy Technology Data Exchange (ETDEWEB)

Gurwitz, Ron; Cohen, Rotem; Shalish, Ilan, E-mail: shalish@ee.bgu.ac.il [Ben Gurion University, Beer Sheva 84105 (Israel)

2014-01-21

ZnO surfaces adsorb oxygen in the dark and emit CO{sub 2} when exposed to white light, reminiscent of the lungs of living creatures. We find that this exchange of oxygen with the ambient affects the integrity of the ZnO surface. Thus, it forms a basis for several interesting surface phenomena in ZnO, such as photoconductivity, photovoltage, and gas sensing, and has a role in ZnO electrical conduction. Using x-ray photoelectron spectroscopy on ZnO nanowires, we observed a decomposition of ZnO under white light and formation of oxygen-depleted surface, which explains photoconductivity by the electron donation of oxygen vacancies. Our findings suggest that the observed decomposition of the ZnO lattice may only take place due to photon-induced reduction of ZnO by carbon containing molecules (or carbo-photonic reduction), possibly from the ambient gas, accounting in a consistent way for both the reduced demands on the energy required for decomposition and for the observed emission of lattice oxygen in the form of CO{sub 2}. The formation of oxygen-vacancy rich surface is suggested to induce surface delta doping, causing accumulation of electrons at the surface, which accounts for both the increase in conductivity and the flattening of the energy bands. Using surface photovoltage spectroscopy in ultra high vacuum, we monitored changes in the deep level spectrum. We observe a wide optical transition from a deep acceptor to the conduction band, which energy position coincides with the position of the so called “green luminescence” in ZnO. This green transition disappears with the formation of surface oxygen vacancies. Since the oxygen vacancies are donors, while the green transition involves surface acceptors, the results suggest that the initial emission of oxygen originates at the defect sites of the latter, thereby eliminating each other. This suggests that the green transition originates at surface Zn vacancy acceptors. Removing an oxygen atom from a Zn vacancy

Tuning the photovoltage of dye-sensitized solar cells based on electrodeposited ZnO

Energy Technology Data Exchange (ETDEWEB)

Oekermann, Torsten [Institute of Physical Chemistry and Electrochemistry, Leibniz Universitaet Hannover, Callinstrasse 3- 3A, 30167 Hannover (Germany); Peter, Laurence [Department of Chemistry, University of Bath, Bath BA2 7AY (United Kingdom); Yoshida, Tsukasa [Graduate School of Engineering, Gifu University, Yanagido 1-1, Gifu 501-1193 (Japan)

2007-07-01

Nanoporous, fully crystalline ZnO films can be prepared by cathodic electrodeposition from aqueous solutions of Zn salts under the influence of structure-directing agents such as surfactants. Dye-sensitized solar cells (DSSC) based on such films have emerged as a possible alternative for nanocrystalline TiO2-based DSSC due to the very high porosity and good electron transport properties of the films. In this study, we have investigated the influence of the sensitizer dye molecules on the photovoltage of the ZnO-based DSSC. Impedance measurements show that the adsorbed dye molecules lead to a shift of the flatband potential of the ZnO. Electron pushing or withdrawing effects of the dye molecules and protonation or deprotonation of the ZnO surface are discussed as possible explanations. The shifts in the flatband potential partly explain the differences in the photovoltages caused by different dyes, however, differences in the electron injection efficiency and the blocking of electron back reaction by the dye molecules have to be taken into account, too, for a complete description.

The molecular nature of photovoltage losses in organic solar cells

KAUST Repository

Schlenker, Cody W.

2011-01-01

Since the inception of heterojunction organic photovoltaic research the organic/organic interface has been thought to play a crucial role in determining the magnitude of the open-circuit voltage. Yet, the task of defining the molecular properties dictating the photovoltage delivered by these devices, that employ mixed or neat layers of different organic molecules to convert incident photons to electricity, is still an active area of research. This will likely be a key step in designing the new materials required for improving future device efficiencies. With the intent to underscore the importance of considering both thermodynamic and kinetic factors, this article highlights recent progress in elucidating molecular characteristics dictating photovoltage losses in heterojunction organic photovoltaics. © The Royal Society of Chemistry.

The molecular nature of photovoltage losses in organic solar cells

KAUST Repository

Schlenker, Cody W.; Thompson, Mark E.

2011-01-01

dictating the photovoltage delivered by these devices, that employ mixed or neat layers of different organic molecules to convert incident photons to electricity, is still an active area of research. This will likely be a key step in designing the new

Overcoming the Photovoltage Plateau in Large Bandgap Perovskite Photovoltaics.

Science.gov (United States)

Rajagopal, Adharsh; Stoddard, Ryan J; Jo, Sae Byeok; Hillhouse, Hugh W; Jen, Alex K-Y

2018-05-09

Development of large bandgap (1.80-1.85 eV E g ) perovskite is crucial for perovskite-perovskite tandem solar cells. However, the performance of 1.80-1.85 eV E g perovskite solar cells (PVKSCs) are significantly lagging their counterparts in the 1.60-1.75 eV E g range. This is because the photovoltage ( V oc ) does not proportionally increase with E g due to lower optoelectronic quality of conventional (MA,FA,Cs)Pb(I,Br) 3 and results in a photovoltage plateau ( V oc limited to 80% of the theoretical limit for ∼1.8 eV E g ). Here, we incorporate phenylethylammonium (PEA) in a mixed-halide perovskite composition to solve the inherent material-level challenges in 1.80-1.85 eV E g perovskites. The amount of PEA incorporation governs the topography and optoelectronic properties of resultant films. Detailed structural and spectroscopic characterization reveal the characteristic trends in crystalline size, orientation, and charge carrier recombination dynamics and rationalize the origin of improved material quality with higher luminescence. With careful interface optimization, the improved material characteristics were translated to devices and V oc values of 1.30-1.35 V were achieved, which correspond to 85-87% of the theoretical limit. Using an optimal amount of PEA incorporation to balance the increase in V oc and the decrease in charge collection, a highest power conversion efficiency of 12.2% was realized. Our results clearly overcome the photovoltage plateau in the 1.80-1.85 eV E g range and represent the highest V oc achieved for mixed-halide PVKSCs. This study provides widely translatable insights, an important breakthrough, and a promising platform for next-generation perovskite tandems.

Raman Spectra from Pesticides on the Surface of Fruits

International Nuclear Information System (INIS)

Zhang, P X; Zhou Xiaofang; Cheng, Andrew Y S; Fang Yan

2006-01-01

Raman spectra of several vegetables and fruits were studied by micro-Raman spectrometer (514.5 nm) and Near-infrared Fourier Transform Raman spectrometer (FTRaman). It is shown that at 514.5 nm excitation, most of the spectra are from that of carotene with some very strong fluorescence in some cases. While at 1064 nm wavelength excitation, the spectra from the different samples demonstrate different characteristic Raman spectra without fluorescence. We discuss the spectroscopic difference by the two excitation wavelengths, and the application of Raman spectra for detection of pesticides left on the surface of vegetables and fruits. Raman spectra of fruits and pesticides were successfully recorded, and using the FT-Raman spectra the pesticides left on the surface of the fruits can be detected conveniently

Database for Simulation of Electron Spectra for Surface Analysis (SESSA)Database for Simulation of Electron Spectra for Surface Analysis (SESSA)

Science.gov (United States)

SRD 100 Database for Simulation of Electron Spectra for Surface Analysis (SESSA)Database for Simulation of Electron Spectra for Surface Analysis (SESSA) (PC database for purchase)   This database has been designed to facilitate quantitative interpretation of Auger-electron and X-ray photoelectron spectra and to improve the accuracy of quantitation in routine analysis. The database contains all physical data needed to perform quantitative interpretation of an electron spectrum for a thin-film specimen of given composition. A simulation module provides an estimate of peak intensities as well as the energy and angular distributions of the emitted electron flux.

A family of uranyl-aromatic dicarboxylate (pht-, ipa-, tpa-) framework hybrid materials: photoluminescence, surface photovoltage and dye adsorption.

Science.gov (United States)

Gao, Xue; Wang, Che; Shi, Zhong-Feng; Song, Jian; Bai, Feng-Ying; Wang, Ji-Xiao; Xing, Yong-Heng

2015-07-07

Four uranyl complexes [(UO2)(pht)H2O]·H2O (pht = phthalic acid) (1), (UO2)2(Hipa)4(H2O)2 (Hipa = isophthalic acid) (2), (UO2)(tpa)(DMF)2 (tpa = terephthalic acid) (3) and (UO2)(box)2 (box = benzoic acid) (4) were synthesized by the reaction of UO2(CH3COO)2·2H2O as the metal source and phthalic acid, isophthalic acid, terephthalic acid or benzoic acid as the ligand. They were characterized by elemental analyses, IR, UV-Vis, XRD, single crystal X-ray diffraction analysis and thermal gravimetric analysis. The structural analysis reveals that complex 1 exhibits a one-dimensional chain structure constructed by the building unit [(UO2)2(pht)4(H2O)2] and further extends the chain into a 2D supramolecular architecture by hydrogen bonding interactions. Complex 2 is a discrete [(UO2)2(Hipa)4(H2O)2] structure, and by the hydrogen bonding interaction, forms a 3D supramolecular structure. In complexes 3 and 4, adjacent uranyl polyhedra form a 1D chain through bridging terephthalic acid and benzoic acid, respectively. In order to extend their functional properties, their photoluminescence, surface photovoltage and dye adsorption properties have been studied.

Spectrally dependent photovoltages in Schottky photodiode based on (100) B-doped diamond

Science.gov (United States)

Čermák, Jan; Koide, Yasuo; Takeuchi, Daisuke; Rezek, Bohuslav

2014-02-01

Spectrally and spatially resolved photovoltages were measured by Kelvin probe force microscopy (KPFM) on a Schottky photo-diode made of a 4 nm thin tungsten-carbide (WC) layer on a 500 nm oxygen-terminated boron-doped diamond epitaxial layer (O-BDD) that was grown on a Ib (100) diamond substrate. The diode was grounded by the sideways ohmic contact (Ti/WC), and the semitransparent Schottky contact was let unconnected. The electrical potentials across the device were measured in dark (only 650 nm LED of KPFM being on), under broad-band white light (halogen lamp), UV (365 nm diode), and deep ultraviolet (deuterium lamp) illumination. Illumination induced shift of the electrical potential remains within 210 mV. We propose that the photovoltage actually corresponds to a shift of Fermi level inside the BDD channel and thereby explains orders of magnitude changes in photocurrent.

DETERMINING REFLECTANCE SPECTRA OF SURFACES AND CLOUDS ON EXOPLANETS

Energy Technology Data Exchange (ETDEWEB)

Cowan, Nicolas B.; Strait, Talia E., E-mail: n-cowan@northwestern.edu [Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA), Northwestern University, 2131 Tech Dr., IL 60208 (United States)

2013-03-01

Planned missions will spatially resolve temperate terrestrial planets from their host star. Although reflected light from such a planet encodes information about its surface, it has not been shown how to establish surface characteristics of a planet without assuming known surfaces to begin with. We present a reanalysis of disk-integrated, time-resolved, multiband photometry of Earth obtained by the Deep Impact spacecraft as part of the EPOXI Mission of Opportunity. We extract reflectance spectra of clouds, ocean, and land without a priori knowledge of the numbers or colors of these surfaces. We show that the inverse problem of extracting surface spectra from such data is a novel and extreme instance of spectral unmixing, a well-studied problem in remote sensing. Principal component analysis is used to determine an appropriate number of model surfaces with which to interpret the data. Shrink-wrapping a simplex to the color excursions of the planet yields a conservative estimate of the planet's endmember spectra. The resulting surface maps are unphysical, however, requiring negative or larger-than-unity surface coverage at certain locations. Our ''rotational unmixing'' supersedes the endmember analysis by simultaneously solving for the surface spectra and their geographical distributions on the planet, under the assumption of diffuse reflection and known viewing geometry. We use a Markov Chain Monte Carlo to determine best-fit parameters and their uncertainties. The resulting albedo spectra are similar to clouds, ocean, and land seen through a Rayleigh-scattering atmosphere. This study suggests that future direct-imaging efforts could identify and map unknown surfaces and clouds on exoplanets.

Spectrally dependent photovoltages in Schottky photodiode based on (100) B-doped diamond

International Nuclear Information System (INIS)

Čermák, Jan; Rezek, Bohuslav; Koide, Yasuo; Takeuchi, Daisuke

2014-01-01

Spectrally and spatially resolved photovoltages were measured by Kelvin probe force microscopy (KPFM) on a Schottky photo-diode made of a 4 nm thin tungsten-carbide (WC) layer on a 500 nm oxygen-terminated boron-doped diamond epitaxial layer (O-BDD) that was grown on a Ib (100) diamond substrate. The diode was grounded by the sideways ohmic contact (Ti/WC), and the semitransparent Schottky contact was let unconnected. The electrical potentials across the device were measured in dark (only 650 nm LED of KPFM being on), under broad-band white light (halogen lamp), UV (365 nm diode), and deep ultraviolet (deuterium lamp) illumination. Illumination induced shift of the electrical potential remains within 210 mV. We propose that the photovoltage actually corresponds to a shift of Fermi level inside the BDD channel and thereby explains orders of magnitude changes in photocurrent

Spectrally dependent photovoltages in Schottky photodiode based on (100) B-doped diamond

Energy Technology Data Exchange (ETDEWEB)

Čermák, Jan, E-mail: cermakj@fzu.cz; Rezek, Bohuslav [Institute of Physics, Academy of Sciences of the Czech Republic, Cukrovarnická 10, 16200 Prague 6 (Czech Republic); Koide, Yasuo [Sensor Materials Center, National Institute for Material Science (NIMS), 1-1 Namiki, Tsukuba 305-0044 (Japan); Takeuchi, Daisuke [Energy Technology Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Umezono, Tsukuba 305-8568 (Japan)

2014-02-07

Spectrally and spatially resolved photovoltages were measured by Kelvin probe force microscopy (KPFM) on a Schottky photo-diode made of a 4 nm thin tungsten-carbide (WC) layer on a 500 nm oxygen-terminated boron-doped diamond epitaxial layer (O-BDD) that was grown on a Ib (100) diamond substrate. The diode was grounded by the sideways ohmic contact (Ti/WC), and the semitransparent Schottky contact was let unconnected. The electrical potentials across the device were measured in dark (only 650 nm LED of KPFM being on), under broad-band white light (halogen lamp), UV (365 nm diode), and deep ultraviolet (deuterium lamp) illumination. Illumination induced shift of the electrical potential remains within 210 mV. We propose that the photovoltage actually corresponds to a shift of Fermi level inside the BDD channel and thereby explains orders of magnitude changes in photocurrent.

Surface spectra of Weyl semimetals through self-adjoint extensions

Science.gov (United States)

Seradjeh, Babak; Vennettilli, Michael

2018-02-01

We apply the method of self-adjoint extensions of Hermitian operators to the low-energy, continuum Hamiltonians of Weyl semimetals in bounded geometries and derive the spectrum of the surface states on the boundary. This allows for the full characterization of boundary conditions and the surface spectra on surfaces both normal to the Weyl node separation as well as parallel to it. We show that the boundary conditions for quadratic bulk dispersions are, in general, specified by a U (2 ) matrix relating the wave function and its derivatives normal to the surface. We give a general procedure to obtain the surface spectra from these boundary conditions and derive them in specific cases of bulk dispersion. We consider the role of global symmetries in the boundary conditions and their effect on the surface spectrum. We point out several interesting features of the surface spectra for different choices of boundary conditions, such as a Mexican-hat shaped dispersion on the surface normal to Weyl node separation. We find that the existence of bound states, Fermi arcs, and the shape of their dispersion, depend on the choice of boundary conditions. This illustrates the importance of the physics at and near the boundaries in the general statement of bulk-boundary correspondence.

Photovoltage versus microprobe sheet resistance measurements on ultrashallow structures

DEFF Research Database (Denmark)

Clarysse, T.; Moussa, A.; Parmentier, B.

2010-01-01

on ultrashallow (sub-50-nm) chemical-vapor-deposited layers [T. Clarysse , Mater. Res. Soc. Symp. Proc. 912, 197 (2006)], especially in the presence of medium/highly doped underlying layers (representative for well/halo implants). Here the authors examine more closely the sheet resistance anomalies which have...... recently been observed between junction photovoltage (JPV) based tools and a micrometer-resolution four-point probe (M4PP) tool on a variety of difficult, state-of-the-art sub-32-nm complementary metal-oxide semiconductor structures (low energy and cluster implants, with/without halo, flash- and laser...

Photocurrent and photovoltage induced in a 2DEG under intense, pulsed THz radiation

International Nuclear Information System (INIS)

Lewis, R.A.; Xu, W.; Pellemans, H.P.M.; Langerak, C.J.G.M.

1999-01-01

Full text: Intense THz radiation emitted by FELIX (Free Electron Laser for Infrared eXperiments) induces both photovoltage and photocurrent signals in a high-mobility (μ = 2 x 10 6 cm 2 /V s), low-density (n e = 2 x 10 11 cm -2 ) GaAs/AlGaAs-based 2DEG. Within the ∼5 μs FELIX macropulse, there is a rapid response in the longitudinal voltage of a Hall-bar sample, reproducible between pulses. A large response continues well after the pulse; this long-time-scale behaviour varies between pulses if the current exceeds a critical value (which decreases with radiation intensity and magnetic field). Within the macropulse, the photovoltage varies with magnetic field, saturating at low field (<100 mT). The photocurrent shows a rapid, non-resonant response, evident at integral filling factors in both longitudinal and transverse data, and a slower, cyclotron resonant response, peaking at ∼390 μs after the FELIX pulse. No anisotropy in the resistivity under polarised radiation was found

A climatology of visible surface reflectance spectra

International Nuclear Information System (INIS)

Zoogman, Peter; Liu, Xiong; Chance, Kelly; Sun, Qingsong; Schaaf, Crystal; Mahr, Tobias; Wagner, Thomas

2016-01-01

We present a high spectral resolution climatology of visible surface reflectance as a function of wavelength for use in satellite measurements of ozone and other atmospheric species. The Tropospheric Emissions: Monitoring of Pollution (TEMPO) instrument is planned to measure backscattered solar radiation in the 290–740 nm range, including the ultraviolet and visible Chappuis ozone bands. Observation in the weak Chappuis band takes advantage of the relative transparency of the atmosphere in the visible to achieve sensitivity to near-surface ozone. However, due to the weakness of the ozone absorption features this measurement is more sensitive to errors in visible surface reflectance, which is highly variable. We utilize reflectance measurements of individual plant, man-made, and other surface types to calculate the primary modes of variability of visible surface reflectance at a high spectral resolution, comparable to that of TEMPO (0.6 nm). Using the Moderate-resolution Imaging Spectroradiometer (MODIS) Bidirection Reflectance Distribution Function (BRDF)/albedo product and our derived primary modes we construct a high spatial resolution climatology of wavelength-dependent surface reflectance over all viewing scenes and geometries. The Global Ozone Monitoring Experiment–2 (GOME-2) Lambertian Equivalent Reflectance (LER) product provides complementary information over water and snow scenes. Preliminary results using this approach in multispectral ultraviolet+visible ozone retrievals from the GOME-2 instrument show significant improvement to the fitting residuals over vegetated scenes. - Highlights: • Our goals was visible surface reflectance for satellite trace gas measurements. • Captured the range of surface reflectance spectra through EOF analysis. • Used satellite surface reflectance products for each given scene to anchor EOFs. • Generated a climatology of time/geometry dependent surface reflectance spectra. • Demonstrated potential to

Computer simulation of RBS spectra from samples with surface roughness

Energy Technology Data Exchange (ETDEWEB)

Malinský, P., E-mail: malinsky@ujf.cas.cz [Nuclear Physics Institute of the Academy of Sciences of the Czech Republic, v. v. i., 250 68 Rez (Czech Republic); Department of Physics, Faculty of Science, J. E. Purkinje University, Ceske mladeze 8, 400 96 Usti nad Labem (Czech Republic); Hnatowicz, V., E-mail: hnatowicz@ujf.cas.cz [Nuclear Physics Institute of the Academy of Sciences of the Czech Republic, v. v. i., 250 68 Rez (Czech Republic); Macková, A., E-mail: mackova@ujf.cas.cz [Nuclear Physics Institute of the Academy of Sciences of the Czech Republic, v. v. i., 250 68 Rez (Czech Republic); Department of Physics, Faculty of Science, J. E. Purkinje University, Ceske mladeze 8, 400 96 Usti nad Labem (Czech Republic)

2016-03-15

A fast code for the simulation of common RBS spectra including surface roughness effects has been written and tested on virtual samples comprising either a rough layer deposited on a smooth substrate or smooth layer deposited on a rough substrate and simulated at different geometries. The sample surface or interface relief has been described by a polyline and the simulated RBS spectrum has been obtained as the sum of many particular spectra from randomly chosen particle trajectories. The code includes several procedures generating virtual samples with random and regular (periodical) roughness. The shape of the RBS spectra has been found to change strongly with increasing sample roughness and an increasing angle of the incoming ion beam.

Titan's surface spectra at the Huygens landing site and Shangri-La

Science.gov (United States)

Rannou, P.; Toledo, D.; Lavvas, P.; D'Aversa, E.; Moriconi, M. L.; Adriani, A.; Le Mouélic, S.; Sotin, C.; Brown, R.

2016-05-01

Titan is an icy satellite of Saturn with a dense atmosphere and covered by a global photochemical organic haze. Ground based observations and the Huygens descent probe allowed to retrieve the main spectral signature of the water ice (Griffith, C.A. et al. [2003]. Science 300(5619), 628-630; Coustenis, A. et al. [2005]. Icarus 177, 89-105) at the surface, possibly covered by a layer of sedimented organic material (Tomasko, M.G. et al. [2005]. Nature 438(7069), 765-778). However, the spectrum of the surface is not yet understood. In this study, we find that the surface reflectivity at the Huygens Landing Site (HLS) is well modeled by a layer of water ice grains overlaid by a moist layer of weakly compacted photochemical aggregated aerosols. Moist soils have spectra shifted toward short wavelengths relatively to spectra of dry soils. Cassini observations of Shangri-La region from orbit also show a very dark surface with a reflectivity peak shifted toward short wavelengths in respect to the reflectivity peak of bright surfaces, revealing a dichotomy between terrains based to their spectra in visible.

The research on the surface photovoltaic properties of porphyrin affected by nano-TiO2

International Nuclear Information System (INIS)

Li Ziheng; Wang Dejun; Shi Yingyan; Wang Ping; Wang Xingqiao

2005-01-01

The degeneration of energy level of α, β, γ, δ-tetrahydroxylphenylporphyrin (THPP) and red shift of the photovoltage peaks of THPP are observed as the size of nano-TiO 2 decreasing using surface photovoltage (SPV) technique, while that of α, β, γ, δ-tetraphenylporphyrin (TPP) have little change. The reason for that is the existence of hydroxyls of THPP, which interact with the surface of nano-TiO 2 . This difference was also demonstrated by IR spectrum

Surface wave statistics and spectra for Valiathura coastlines, SW coast of India

Digital Repository Service at National Institute of Oceanography (India)

Asharaf, T.T.M.; Nair, R.P.; Sanjana, M.C.; Muraleedharan, G.; Kurup, P.G.

Sciences Vol. 30, March , 2001, pp 9-17 Surface wave statistics and spectra for Valiathura coastline, SW coast of India T T Mohamed Asharaf National Institute of Oceanography, Regional Centre, Cochin, 682 014, India and Ratish P Nair, M.... 2D), the prominent direction was MOHAMED ASHARAF et al. : WAVE STATISTICS AND SPECTRA 11 Fig. 2Direction surface plots of January-June INDIAN J. MAR. SCI., VOL 30, MARCH 2001 12 Fig. 2  (Contd) ... Direction surface...

Explanation of the surface peak in charge integrated LEIS spectra

CERN Document Server

Draxler, M; Taglauer, E; Schmid, K; Gruber, R; Ermolov, S N; Bauer, P

2003-01-01

Low energy ion scattering is very surface sensitive if scattered ions are analyzed. By time-of-flight (TOF) techniques, also neutral and charge integrated spectra (ions plus neutrals) can be obtained, which yield information about deeper layers. In the literature, the observation of a more or less pronounced surface peak was reported for charge integrated spectra, the intensity of the surface peak being higher at low energies and for heavy projectiles. Aiming at a more profound physical understanding of this surface peak, we performed TOF-experiments and computer simulations for He projectiles and a copper target. Experiments were done in the range 1-9 keV for a scattering angle of 129 deg. . The simulation was performed using the MARLOWE code for the given experimental parameters and a polycrystalline target. At low energies, a pronounced surface peak was observed, which fades away at higher energies. This peak is quantitatively reproduced by the simulation, and corresponds to scattering from approx 2 atomic...

Electronic transitions and band offsets in C60:SubPc and C60:MgPc on MoO3 studied by modulated surface photovoltage spectroscopy

International Nuclear Information System (INIS)

Fengler, S.; Dittrich, Th.; Rusu, M.

2015-01-01

Electronic transitions at interfaces between MoO 3 layers and organic layers of C 60 , SubPc, MgPc, and nano-composite layers of SubPc:C 60 and MgPc:C 60 have been studied by modulated surface photovoltage (SPV) spectroscopy. For all systems, time dependent and modulated SPV signals pointed to dissociation of excitons at the MoO 3 /organic layer interfaces with a separation of holes towards MoO 3 . The highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gaps (E HL ) of C 60 , SubPc, and MgPc and the effective E HL of SubPc:C 60 and MgPc:C 60 were measured. The offsets between the LUMO (ΔE L ) or HOMO (ΔE H ) bands were obtained with high precision and amounted to 0.33 or 0.73 eV for SubPc:C 60 , respectively, and to −0.33 or 0.67 eV for MgPc:C 60 , respectively. Exponential tails below E HL and most pronounced sub-bandgap transitions were characterized and ascribed to disorder and transitions from HOMO bands to unoccupied defect states

Controlled synthesis of TiO2-B nanowires and nanoparticles for dye-sensitized solar cells

International Nuclear Information System (INIS)

Qi Lihong; Liu Yongjun; Li Chunyan

2010-01-01

Controllable synthesis of the TiO 2 -B nanowires (NWs) and nanoparticles (NPs) had been achieved via a facile hydrothermal route, respectively, only by tuning the solution volume. The dye-sensitized solar cells prototypes had been fabricated using TiO 2 -B NW and NP electrodes, respectively. The TiO 2 -B NP cells had higher photocurrent and photoelectrical conversion efficiency than the TiO 2 -B NW cells though the latter exhibited larger photovoltage compared to the former. The key factors such as the photogenerated electron injection drive force, surface defects and the interfacial charge transfer, which determined the photoelectrical properties, had been systematically researched with the surface photovoltage spectra (SPS) and the electrochemical impedance spectra (EIS). The SPS proved that there was larger photoelectron injection drive force in TiO 2 -B NP photoelectrode than that in NW photoelectrode. And the electrochemical impedance spectra (EIS) revealed that TiO 2 -B NP cells had faster interface charge transfer compared to TiO 2 -B NW cells. Both proved that NP cells had the higher photocurrents.

Surface and bulk 4f-photoemission spectra of CeIn3 and CeSn3

International Nuclear Information System (INIS)

Kim, H.; Tjernberg, O.; Chiaia, G.; Kumigashira, H.; Takahashi, T.; Duo, L.; Sakai, O.; Kasaya, M.; Lindau, I.

1997-01-01

Resonant photoemission spectroscopy was performed on CeIn 3 and CeSn 3 at the 4d-4f and 3d-4f core thresholds. Using the different surface sensitivity between the two photon energies, surface and bulk 4f-photoemission spectra were derived for both compounds. With the noncrossing approximation of the Anderson impurity model, the 4d-4f resonant spectra together with the surface and bulk spectra were self-consistently analyzed to obtain the microscopic parameters such as the 4f-electron energy and the hybridization strength with conduction electrons. The result shows a substantial difference in these parameters between the surface and the bulk, indicating that it is important to take into account the surface effect in analyzing photoemission spectra of Ce compounds. It is also found that the 4f surface core-level shift is different between CeIn 3 and CeSn 3 . copyright 1997 The American Physical Society

Angle-sensitive and fast photovoltage of silver nanocluster embeded ZnO thin films induced by 1.064-μm pulsed laser

International Nuclear Information System (INIS)

Song-Qing, Zhao; Li-Min, Yang; Wen-Wei, Liu; Kun, Zhao; Yue-Liang, Zhou; Qing-Li, Zhou

2010-01-01

Silver nanocluster embedded ZnO composite thin film was observed to have an angle-sensitive and fast photovoltaic effect in the angle range from −90° to 90°, its peak value and the polarity varied regularly with the angle of incidence of the 1.064-μm pulsed Nd:YAG laser radiation onto the ZnO surface. Meanwhile, for each photovoltaic signal, its rising time reached ∼2 ns with an open-circuit photovoltage of ∼2 ns full width at half-maximum. This angle-sensitive fast photovoltaic effect is expected to put this composite film a candidate for angle-sensitive and fast photodetector. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

Quantification of aluminium-27 NMR spectra of high-surface-area oxides

International Nuclear Information System (INIS)

Pearson, R.M.; Schramm, C.M.

1990-01-01

This paper discusses the quantitation of 27 Al NMR spectra. It is showns that the so called 'invisible' aluminium atoms seen by recent workers are completely consistent with known continuous wave NMR studies of the 27 Al NMR spectra of high surface area aluminium oxides. The use of pulsed NMR techniques further complicate the quantitative measurement of 27 Al NMR spectra, especially when high resolution NMR spectrometers are used for this purpose. Methods are described which allow both the estimation of aluminium not seen by continuous wave techniques and the amounts of the NMR spectra lost in pulsed work. (author). 24 refs.; 6 figs.; 1 tab

Reflectance variability of surface coatings reveals characteristic eigenvalue spectra

Science.gov (United States)

Medina, José M.; Díaz, José A.; Barros, Rui

2012-10-01

We have examined the trial-to-trial variability of the reflectance spectra of surface coatings containing effect pigments. Principal component analysis of reflectances was done at each detection angle separately. A method for classification of principal components is applied based on the eigenvalue spectra. It was found that the eigenvalue spectra follow characteristic power laws and depend on the detection angle. Three different subsets of principal components were examined to separate the relevant spectral features related to the pigments from other noise sources. Reconstruction of the reflectance spectra by taking only the first subset indicated that reflectance variability was higher at near-specular reflection, suggesting a correlation with the trial-to-trial deposition of effect pigments. Reconstruction by using the second subset indicates that variability was higher at short wavelengths. Finally, reconstruction by using only the third subset indicates that reflectance variability was not totally random as a function of the wavelength. The methods employed can be useful in the evaluation of color variability in industrial paint application processes.

Trajectory resolved analysis of LEIS energy spectra: Neutralization and surface structure

International Nuclear Information System (INIS)

Beikler, Robert; Taglauer, Edmund

2001-01-01

For a quantitative evaluation of low-energy ion scattering (LEIS) data with respect to surface composition and structure a detailed analysis of the energy spectra is required. This includes the identification of multiple scattering processes and the determination of ion survival probabilities. We analyzed scattered ion energy spectra by using the computer code MARLOWE for which we developed a new analysis routine that allows to record energy distributions in dependence of the number of projectile-target atom collisions, in dependence of the distance of closest approach, or in dependence of the scattering crystalline layer. This procedure also permits the determination of ion survival probabilities by applying simple collision-dependent neutralization models. Experimental energy spectra for various projectile (He + , Ne + , Na + ) and target (transition metals, oxides) combinations are well reproduced and quantitative results for ion survival probabilities are obtained. These are largely in agreement with results obtained for bimetallic crystal surfaces obtained in a different way. Such MARLOWE calculations are also useful for the identification of structure relevant processes. This is shown exemplarily for the reconstructed Au(1 1 0) surface including a possibility to determine the (1x2)→(1x1) transition temperature

Ion implanters contamination on wafer surface analyzed by ToF-SIMS and SPV analytical techniques

International Nuclear Information System (INIS)

Ricciari, R.; Bertini, M.; Ferlito, E.P.; Pizzo, G.; Anastasi, G.; Mello, D.; Franco, G.

2007-01-01

In ULSI processes, metallic contamination controls are very important issues. For the ion implantation process it is known that several sources of contaminations still need to be controlled: metals from sputtering of the apertures or wafer holders, Na + contaminations from filament impurities and messy maintenance procedure. ToF-SIMS is one of the most promising candidates to perform in-line surface analysis due to its high sensitivity. It is very common to use surface photo-voltage (SPV) techniques to control ion implanter equipments but this kind of analysis is an indirect measure for metallic contamination. The aim of this work is to study the possibility to use ToF-SIMS instead of SPV for in line equipment contamination monitoring. For this reason a comparison between SPV and ToF-SIMS data occurred. Good correlation between the data is shown; moreover ToF-SIMS spectra give detailed information about the other contaminations present on the wafer surface

Diagnostic x-ray spectra measurements using a silicon surface barrier detector

International Nuclear Information System (INIS)

Pani, R.; Laitano, R.F.

1987-01-01

A silicon surface barrier detector having a low efficiency for x-ray is used to analyse diagnostic x-ray spectra. This characteristic is advantageous in overcoming experimental problems caused by high fluence rates typical of diagnostic x-ray beams. The pulse height distribution obtained with silicon surface barrier detectors is very different from the true photon spectra because of the presence of escaped Compton photons and the fact that detection efficiency falls abruptly when photon energy increases. A detailed analysis of the spurious effects involved in detection is made by a Monte Carlo method. A stripping procedure is described for implementation on a personal computer. The validity of this method is tested by comparison with experimental results obtained with a Ge detector. The spectra obtained with the Si detector are in fairly good agreement with the analogous spectra measured with a Ge detector. The advantages of using Si as opposed to Ge detectors in x-ray spectrometry are: its simplicity of use, its greater economy for use in routine diagnostic x-ray spectroscopy and the possibility that the stripping procedure can be implemented on a personal computer. (author)

Laser induced photocurrent and photovoltage transient measurements of dye-sensitized solar cells based on TiO_2 nanosheets and TiO_2 nanoparticles

International Nuclear Information System (INIS)

Ghaithan, Hamid M.; Qaid, Saif M.H.; Hezam, Mahmoud; Labis, Joselito P.; Alduraibi, Mohammad; Bedja, Idriss M.; Aldwayyan, Abdullah S.

2016-01-01

Dye-sensitized solar cells (DSSCs) based on TiO_2 nanoparticles and TiO_2 nanosheets with exposed {001} facets are investigated using laser-induced photovoltage and photocurrent transient decay (LIPVCD) measurements. We adopted a simplified version of LIPVCD technique, in which a single illumination light source and a laboratory oscilloscope could be conveniently used for the measurements. Although the {001} surface of TiO_2 nanosheets allowed a noticeably slower recombination with the electrolyte, this was counterpoised by a slower electron transport probably due to its planar morphology, resulting in a shorter diffusion length in TiO_2 nanosheets. The nanosheet morphology also resulted in less surface area and therefore reduced short circuit current density in the fabricated devices. Our work highlights the fact that the morphological parameters of TiO_2 nanosheets finally resulting after electrode film deposition is of no less importance than the reported efficient dye adsorption and slow electron recombination at the surface of individual nanosheets.

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

Science.gov (United States)

Marshall, Gregory M.

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

Stair-Step Particle Flux Spectra on the Lunar Surface: Evidence for Nonmonotonic Potentials?

Science.gov (United States)

Collier, Michael R.; Newheart, Anastasia; Poppe, Andrew R.; Hills, H. Kent; Farrell, William M.

2016-01-01

We present examples of unusual "stair-step" differential flux spectra observed by the Apollo 14 Suprathermal Ion Detector Experiment on the lunar dayside surface in Earth's magnetotail. These spectra exhibit a relatively constant differential flux below some cutoff energy and then drop off precipitously, by about an order of magnitude or more, at higher energies. We propose that these spectra result from photoions accelerated on the lunar dayside by nonmonotonic potentials (i.e.,potentials that do not decay to zero monotonically) and present a model for the expected differential flux. The energy of the cutoff and the magnitude of the differential flux are related to the properties of the local space environment and are consistent with the observed flux spectra. If this interpretation is correct, these surface-based ion observations provide a unique perspective that both complements and enhances the conclusions obtained by remote-sensing orbiter observations on the Moon's exospheric and electrostatic properties.

Reduction of Fermi level pinning and recombination at polycrystalline CdTe surfaces by laser irradiation

Energy Technology Data Exchange (ETDEWEB)

Simonds, Brian J. [Electrical and Computer Engineering, University of Utah, Salt Lake City, Utah 84112 (United States); Kheraj, Vipul [Electrical and Computer Engineering, University of Utah, Salt Lake City, Utah 84112 (United States); Department of Applied Physics, S. V. National Institute of Technology, Surat 395 007 (India); Palekis, Vasilios; Ferekides, Christos [Electrical Engineering, University of South Florida, Tampa, Florida 33620 (United States); Scarpulla, Michael A., E-mail: scarpulla@eng.utah.edu [Electrical and Computer Engineering, University of Utah, Salt Lake City, Utah 84112 (United States); Materials Science and Engineering, University of Utah, Salt Lake City, Utah 84112 (United States)

2015-06-14

Laser processing of polycrystalline CdTe is a promising approach that could potentially increase module manufacturing throughput while reducing capital expenditure costs. For these benefits to be realized, the basic effects of laser irradiation on CdTe must be ascertained. In this study, we utilize surface photovoltage spectroscopy (SPS) to investigate the changes to the electronic properties of the surface of polycrystalline CdTe solar cell stacks induced by continuous-wave laser annealing. The experimental data explained within a model consisting of two space charge regions, one at the CdTe/air interface and one at the CdTe/CdS junction, are used to interpret our SPS results. The frequency dependence and phase spectra of the SPS signal are also discussed. To support the SPS findings, low-temperature spectrally-resolved photoluminescence and time-resolved photoluminescence were also measured. The data show that a modest laser treatment of 250 W/cm{sup 2} with a dwell time of 20 s is sufficient to reduce the effects of Fermi level pinning at the surface due to surface defects.

Enhancement of the photocatalytic activity of TiO2 nanoparticles by surface-capping DBS groups

International Nuclear Information System (INIS)

Wang Baiqi; Jing Liqiang; Qu Yichun; Li Shudan; Jiang Baojiang; Yang Libin; Xin Baifu; Fu Honggang

2006-01-01

TiO 2 nanoparticles capped with sodium dodecylbenzenesulfonate (DBS) are synthesized by a sol-hydrothermal process using tetrabutyl titanate and DBS as raw materials. The effects of surface-capping DBS on the surface photovoltage spectroscopy (SPS), photoluminescence (PL) and photocatalytic performance of TiO 2 nanoparticles are principally investigated together with their relationships. The results show that the surface of TiO 2 nanoparticles can be well capped by DBS groups while the pH value and added DBS amount are controlled at 5.0 and 2% of TiO 2 mass weight, respectively, and the linkage between DBS groups and TiO 2 surfaces is mainly by means of quasi-sulphonate bond. The intensities of SPS and PL spectra of TiO 2 obviously decrease after DBS-capping, while the activity can greatly increase during the photocatalytic degradation of Rhodamine B (RhB) solution, which are mainly attributed to the electron-withdrawing character of the DBS groups. Moreover, the enhancement of photocatalytic activity of DBS-capped TiO 2 is also related to the increase in the capability for adsorbing RhB

Band engineering in core/shell ZnTe/CdSe for photovoltage and efficiency enhancement in exciplex quantum dot sensitized solar cells.

Science.gov (United States)

Jiao, Shuang; Shen, Qing; Mora-Seró, Iván; Wang, Jin; Pan, Zhenxiao; Zhao, Ke; Kuga, Yuki; Zhong, Xinhua; Bisquert, Juan

2015-01-27

Even though previously reported CdTe/CdSe type-II core/shell QD sensitizers possess intrinsic superior optoelectronic properties (such as wide absorption range, fast charge separation, and slow charge recombination) in serving as light absorbers, the efficiency of the resultant solar cell is still limited by the relatively low photovoltage. To further enhance photovoltage and cell efficiency accordingly, ZnTe/CdSe type-II core/shell QDs with much larger conduction band (CB) offset in comparison with that of CdTe/CdSe (1.22 eV vs 0.27 eV) are adopted as sensitizers in the construction of quantum dot sensitized solar cells (QDSCs). The augment of band offset produces an increase of the charge accumulation across the QD/TiO2 interface under illumination and induces stronger dipole effects, therefore bringing forward an upward shift of the TiO2 CB edge after sensitization and resulting in enhancement of the photovoltage of the resultant cell devices. The variation of relative chemical capacitance, Cμ, between ZnTe/CdSe and reference CdTe/CdSe cells extracted from impedance spectroscopy (IS) characterization under dark and illumination conditions clearly demonstrates that, under light irradiation conditions, the sensitization of ZnTe/CdSe QDs upshifts the CB edge of TiO2 by the level of ∼ 50 mV related to that in the reference cell and results in the enhancement of V(oc) of the corresponding cell devices. In addition, charge extraction measurements have also confirmed the photovoltage enhancement in the ZnTe/CdSe cell related to reference CdTe/CdSe cell. Furthermore, transient grating (TG) measurements have revealed a faster electron injection rate for the ZnTe/CdSe-based QDSCs in comparison with the CdSe cells. The resultant ZnTe/CdSe QD-based QDSCs exhibit a champion power conversion efficiency of 7.17% and a certified efficiency of 6.82% under AM 1.5 G full one sun illumination, which is, as far as we know, one of the highest efficiencies for liquid-junction QDSCs.

On hole spectra at YBa2Cu3O7 surfaces

International Nuclear Information System (INIS)

Calandra, C.; Manghi, F.; Minerva, T.

1989-01-01

The author present a theoretical study of the modification of the one-hole spectra induced by the surface in YBa 2 Cu 3 O 7 . Basal plane surface terminated either with Ba or CuO planes are considered. Correlation effects are included by using a Hubbard model Hamiltonian and by calculating the self-energy in the low density approximation. The results indicate that both the main bands and the satellites are sensitive to the choice of the surface

VNIR Reflectance and MIR Emissivity Spectra of Ordinary Chondrite Meteorites Under Simulated Asteroid Surface Conditions

Science.gov (United States)

Gemma, M.; Shirley, K.; Glotch, T. D.; Ebel, D. S. S.

2017-12-01

Recent missions have revealed much about the nature of many Near-Earth asteroids, including the NEAR-Shoemaker target 433 Eros and Hayabusa target 25142 Itokawa. Both asteroids appear to have mineralogy consistent with ordinary chondrite meteorites. Laboratory spectral analysis of well-constrained meteorite samples can be employed as a reference tool to characterize and constrain data from current and future asteroid studies. A sample set of ordinary chondrite meteorites was chosen from the collection at the American Museum of Natural History. Six meteorites, spanning groups H, L, and LL, were prepared at four different size fractions (25-63 μm, 63-90 μm, 90-125 μm, 125-250 μm) in an attempt to mimic regolith known to exist on asteroids such as 433 Eros and 25142 Itokawa. At the Center for Planetary Exploration at Stony Brook University, spectra of the ordinary chondrite material were measured under simulated asteroid surface conditions ( 10-6 mbar, 150 K chamber temperature, low intensity illumination). The samples were used in two experiments: one measuring visible and near-infrared (VNIR) reflectance spectra at a series of temperatures, and the other measuring mid-infrared (MIR) emissivity spectra. The emissivity measurements require accurate simulation of the thermal environment within asteroid regolith, achieved by inducing a thermal gradient within the sample that results in a surface brightness temperature around 323 K (similar to the surface of 25142 Itokawa). Mid-IR emissivity spectra were collected for each sample at a surface temperature of 323 K, and reflectance spectra were collected in increments of 10 K, over the range 283 K to 373 K. Preliminary VNIR spectra show spreads similar to those seen in Hinrichs and Lucey (2002). Preliminary MIR emissivity spectra suggest that under asteroid surface conditions, the position of the Christiansen feature shifts to shorter wavelengths and emissivity is lower in the Reststrahlen bands when compared to

A novel research approach on the dynamic properties of photogenerated charge carriers at Ag{sub 2}S quantum-dots-sensitized TiO{sub 2} films by a frequency-modulated surface photovoltage technology

Energy Technology Data Exchange (ETDEWEB)

Zhang, Yu; Zhang, Wei [Liaoning Key Laboratory for Green Synthesis and Preparative Chemistry of Advanced Materials, College of Chemistry, Liaoning University, Shenyang 110036 (China); Xie, Tengfeng; Wang, Dejun [College of Chemistry, Jilin University, Changchun 130012 (China); Song, Xi-Ming, E-mail: songlab@lnu.edu.cn [Liaoning Key Laboratory for Green Synthesis and Preparative Chemistry of Advanced Materials, College of Chemistry, Liaoning University, Shenyang 110036 (China)

2013-09-01

Graphical abstract: The changed SPV with chopping frequencies indicate the separation speeds of photogenerated charge carriers in different films. - Highlights: • Ag{sub 2}S-sensitized TiO{sub 2} films show good photoelectric responses in visible-light region. • Frequency-modulated SPV give dynamic information and evidence of Ag{sub 2}S QDSSCs’ performance. • Frequency-modulated SPV can supply complementary information in the study of Ag{sub 2}S ODSSCs. - Abstract: Ag{sub 2}S quantum-dots-sensitized TiO{sub 2} films with different amount of Ag{sub 2}S were fabricated by a successive ionic layer adsorption and reaction (SILAR) method. The separation and transport of photogenerated charge carriers at different spectral regions were studied by the frequency-modulated surface photovoltage technology. Some novel dynamic information of photogenerated charge carriers in a wide spectral range is found. The results indicate that the rate and direction of separation (diffusion) for photogenerated charge carriers are closely related to the performance of quantum-dots-sensitized solar cells (QDSSCs) based on the Ag{sub 2}S/TiO{sub 2} nano-structure.

Observations of discrete energy loss effects in spectra of positrons reflected from solid surfaces

International Nuclear Information System (INIS)

Dale, J.M.; Hulett, L.D.; Pendyala, S.

1980-01-01

Surfaces of tungsten and silicon have been bombarded with monoenergetic beams of positrons and electrons. Spectra of reflected particles show energy loss tails with discrete peaks at kinetic energies about 15 eV lower than that of the elastic peaks. In the higher energy loss range for tungsten, positron spectra show fine structure that is not apparent in the electron spectra. This suggests that the positrons are losing energy through mechanisms different from that of the electrons

Scaling of turbulence spectra measured in strong shear flow near the Earth’s surface

Science.gov (United States)

Mikkelsen, T.; Larsen, S. E.; Jørgensen, H. E.; Astrup, P.; Larsén, X. G.

2017-12-01

Within the lowest kilometer of the Earth’s atmosphere, in the so-called atmospheric boundary layer, winds are often gusty and turbulent. Nearest to the ground, the turbulence is predominately generated by mechanical wall-bounded wind shear, whereas at higher altitudes turbulent mixing of heat and moisture also play a role. The variance (square of the standard deviation) of the fluctuation around the mean wind speed is a measure of the kinetic energy content of the turbulence. This kinetic energy can be resolved into the spectral distributions, or spectra, as functions of eddy size, wavenumber, or frequency. Spectra are derived from Fourier transforms of wind records as functions of space or time corresponding to wavenumber and frequency spectra, respectively. Atmospheric spectra often exhibit different subranges that can be distinguished and scaled by the physical parameters responsible for: (1) their generation; (2) the cascade of energy across the spectrum from large- to small-scale; and (3) the eventual decay of turbulence into heat owing to viscosity effects on the Kolmogorov microscale, in which the eddy size is only a fraction of a millimeter. This paper addresses atmospheric turbulence spectra in the lowest part of the atmospheric boundary layer—the so-called surface layer—where the wind shear is strong owing to the nonslip condition at the ground. Theoretical results dating back to Tchen’s early work in 1953 ‘on the spectrum of energy in turbulent shear flow’ led Tchen to predict a shear production subrange with a distinct inverse-linear power law for turbulence in a strongly sheared high-Reynolds number wall-bounded flow, as is encountered in the lowest sheared part of the atmospheric boundary layer, also known as the eddy surface layer. This paper presents observations of spectra measured in a meteorological mast at Høvsøre, Denmark, that support Tchen’s prediction of a shear production subrange following a distinct power law of degree -1

Persistent photovoltage in methylammonium lead iodide perovskite solar cells

Directory of Open Access Journals (Sweden)

A. Baumann

2014-08-01

Full Text Available We herein perform open circuit voltage decay (OCVD measurements on methylammonium lead iodide (CH3NH3PbI3 perovskite solar cells to increase the understanding of the charge carrier recombination dynamics in this emerging technology. Optically pulsed OCVD measurements are conducted on CH3NH3PbI3 solar cells and compared to results from another type of thin-film photovoltaics, namely, the two reference polymer–fullerene bulk heterojunction solar cell devices based on P3HT:PC60BM and PTB7:PC70BM blends. We observe two very different time domains of the voltage transient in the perovskite solar cell with a first drop on a short time scale that is similar to the decay in the studied organic solar cells. However, 65%–70% of the maximum photovoltage persists on much longer timescales in the perovskite solar cell than in the organic devices. In addition, we find that the recombination dynamics in all time regimes are dependent on the starting illumination intensity, which is also not observed in the organic devices. We then discuss the potential origins of these unique behaviors.

Modeling and interpretation of electrical impedance spectra of dye solar cells operated under open-circuit conditions

International Nuclear Information System (INIS)

Kern, R.; Sastrawan, R.; Ferber, J.; Stangl, R.; Luther, J.

2002-01-01

Electrical impedance spectroscopy (EIS) was applied in order to investigate electrochemical nanocrystalline TiO 2 dye solar cells (DSC). Typically, three characteristic frequency peaks were observed in the spectra. These frequency peaks could be explained by variations of cell parameters and by comparison with intensity-modulated photovoltage spectroscopy (IMVS). It was shown that the low-frequency peak (in the mHz range) corresponds to the Nernstian diffusion within the electrolyte, while the middle-frequency peak (in the 10-100 Hz range) reflects the properties of the photoinjected electrons within the TiO 2 . The high-frequency peak (in the kHz range) corresponds to the charge-transfer at the platinum counter electrode. For a detailed analysis of the spectra, a model was developed which allows the evaluation of EIS spectra, measured under bias illumination and under open-circuit conditions. The influence of cell parameters such as the TiO 2 layer thickness, cell thickness, charge-transfer resistance of the platinum counter electrode, and the lifetime of the photoinjected electrons, on the impedance spectra was studied both experimentally and theoretically. Finally, it is shown that EIS is a measurement method suited well for the investigation of the long-term stability of DSC, as changes of the inner cell parameters can be revealed

Surface passivation and carrier selectivity of the thermal-atomic-layer-deposited TiO₂ on crystalline silicon

DEFF Research Database (Denmark)

Plakhotnyuk, Maksym; Schüler, Nadine; Shkondin, Evgeniy

2017-01-01

Here, we demonstrate the use of an ultrathin TiO2 film as a passivating carrier-selective contact for silicon photovoltaics. The effective lifetime, surface recombination velocity, and diode quality dependence on TiO2 deposition temperature with and without a thin tunneling oxide interlayer (SiO2...... heterojunction with optimized photovoltage, interface quality, and electron extraction to maximize the photovoltage of TiO2–Si heterojunction photovoltaic cells are formulated. Diode behaviour was analysed with the help of experimental, analytical, and simulation methods. It is predicted that TiO2 with a high...

Comparison of Surface-enhanced Raman Scattering Spectra of Two Kinds of Silver Nanoplate Films

Institute of Scientific and Technical Information of China (English)

TAO Jin-long; TANG Bin; XU Shu-ping; PAN Ling-yun; XU Wei-qing

2012-01-01

Surface-enhanced Raman scattering(SERS) spectra of different silver nanoplate self-assembled films at different excitation wavelengths were fairly compared.Shape conversion from silver nanoprisms to nanodisks on slides was in situ carried out.The SERS spectra of 4-mercaptopyridine(4-MPY) on these anisotropic silver nanoparticle self-assembled films present that strong enhancement appeared when the excitation line and the surface plasmon resonance(SPR) band of silver substrate overlapped.In this model,the influence of the crystal planes of silver nanoplates on SERS enhancement could be ignored because the basal planes were nearly unchanged in two kinds of silver nanoplate self-assembled films.

Quantifying the effect of anode surface roughness on diagnostic x-ray spectra using Monte Carlo simulation

Energy Technology Data Exchange (ETDEWEB)

Mehranian, A.; Ay, M. R.; Alam, N. Riyahi; Zaidi, H. [Department of Medical Physics and Biomedical Engineering, Tehran University of Medical Sciences, P.O. Box 14155-6447, Tehran (Iran, Islamic Republic of) and Research Center for Science and Technology in Medicine, Tehran University of Medical Sciences, P.O. Box 14185-615, Tehran (Iran, Islamic Republic of); Department of Medical Physics and Biomedical Engineering, Tehran University of Medical Sciences, P.O. Box 14155-6447, Tehran (Iran, Islamic Republic of); Research Center for Science and Technology in Medicine, Tehran University of Medical Sciences, P.O. Box 14185-615, Tehran (Iran, Islamic Republic of) and Research Institute for Nuclear Medicine, Tehran University of Medical Sciences, P.O. Box 14155-6447, Tehran (Iran, Islamic Republic of); Department of Medical Physics and Biomedical Engineering, Tehran University of Medical Sciences, P.O. Box 14155-6447, Tehran (Iran, Islamic Republic of); Division of Nuclear Medicine, Geneva University Hospital, CH-1211 Geneva (Switzerland) and Geneva Neuroscience Center, Geneva University, CH-1205 Geneva (Switzerland)

2010-02-15

Purpose: The accurate prediction of x-ray spectra under typical conditions encountered in clinical x-ray examination procedures and the assessment of factors influencing them has been a long-standing goal of the diagnostic radiology and medical physics communities. In this work, the influence of anode surface roughness on diagnostic x-ray spectra is evaluated using MCNP4C-based Monte Carlo simulations. Methods: An image-based modeling method was used to create realistic models from surface-cracked anodes. An in-house computer program was written to model the geometric pattern of cracks and irregularities from digital images of focal track surface in order to define the modeled anodes into MCNP input file. To consider average roughness and mean crack depth into the models, the surface of anodes was characterized by scanning electron microscopy and surface profilometry. It was found that the average roughness (R{sub a}) in the most aged tube studied is about 50 {mu}m. The correctness of MCNP4C in simulating diagnostic x-ray spectra was thoroughly verified by calling its Gaussian energy broadening card and comparing the simulated spectra with experimentally measured ones. The assessment of anode roughness involved the comparison of simulated spectra in deteriorated anodes with those simulated in perfectly plain anodes considered as reference. From these comparisons, the variations in output intensity, half value layer (HVL), heel effect, and patient dose were studied. Results: An intensity loss of 4.5% and 16.8% was predicted for anodes aged by 5 and 50 {mu}m deep cracks (50 kVp, 6 deg. target angle, and 2.5 mm Al total filtration). The variations in HVL were not significant as the spectra were not hardened by more than 2.5%; however, the trend for this variation was to increase with roughness. By deploying several point detector tallies along the anode-cathode direction and averaging exposure over them, it was found that for a 6 deg. anode, roughened by 50 {mu}m deep

Implant Monitoring Measurements On Ultra Shallow Implants Before And After Anneal Using Photomodulated Reflection And Junction Photovoltage Measurement Techniques

Science.gov (United States)

Tallian, M.; Pap, A.; Mocsar, K.; Somogyi, A.; Nadudvari, Gy.; Kosztka, D.; Pavelka, T.

2011-01-01

Ultra shallow junctions are becoming widely used in the micro- and nanoelectronic devices, and novel measurement methods are needed to monitor the manufacturing processes. Photomodulated Reflection measurements before anneal and Junction Photovoltage-based sheet resistance measurements after anneal are non-contact, nondestructive techniques suitable for characterizing both the implantation and the annealing process. Tests verify that these methods are consistent with each other and by using them together, defects originating in the implantation and anneal steps can be separated.

Mathematical analysis of the Photovoltage Decay (PVD) method for minority carrier lifetime measurements

Science.gov (United States)

Vonroos, O. H.

1982-01-01

When the diffusion length of minority carriers becomes comparable with or larger than the thickness of a p-n junction solar cell, the characteristic decay of the photon-generated voltage results from a mixture of contributions with different time constants. The minority carrier recombination lifetime tau and the time constant l(2)/D, where l is essentially the thickness of the cell and D the minority carrier diffusion length, determine the signal as a function of time. It is shown that for ordinary solar cells (n(+)-p junctions), particularly when the diffusion length L of the minority carriers is larger than the cell thickness l, the excess carrier density decays according to exp (-t/tau-pi(2)Dt/4l(2)), tau being the lifetime. Therefore, tau can be readily determined by the photovoltage decay method once D and L are known.

Novel surface anisotropy term in the FMR spectra of amorphous microwires

International Nuclear Information System (INIS)

Gutowski, M.W.; Zuberek, R.; Zhukov, A.

2004-01-01

Some recent publications on ferromagnetic resonance in amorphous wires mention presumably a new kind of anisotropy, called there circumferential anisotropy, as an explanation of various observed spectral features. In this paper, we argue that there is no special reason to speak of the new kind of anisotropy, since the observed spectra can be well described in terms of more traditional uniaxial and surface anisotropies alone

Photoassisted Kelvin probe force microscopy at GaN surfaces: The role of polarity

Science.gov (United States)

Wei, J. D.; Li, S. F.; Atamuratov, A.; Wehmann, H.-H.; Waag, A.

2010-10-01

The behavior of GaN surfaces during photoassisted Kelvin probe force microscopy is demonstrated to be strongly dependant on surface polarity. The surface photovoltage of GaN surfaces illuminated with above-band gap light is analyzed as a function of time and light intensity. Distinct differences between Ga-polar and N-polar surfaces could be identified, attributed to photoinduced chemisorption of oxygen during illumination. These differences can be used for a contactless, nondestructive, and easy-performable analysis of the polarity of GaN surfaces.

Photo-electrochemical solar cells with a SnO/sub 2/-liquid junction sensitized with highly concentrated dyes

Energy Technology Data Exchange (ETDEWEB)

Shimura, Michiko; Shakushiro, Kiyoaki; Shimura, Yukio

1986-09-01

The sensitization of a SnO/sub 2/-liquid junction cell with highly concentrated dyes was investigated. The dyes used were Crystal Violet, Methyl Violet B, Malachite Green, Pararosaniline, and Rhodamine B. Anomalous or positive photovoltages were obtained in the system when Fe(CN)/sub 6//sup 3 -/ was added. The performance of the photovoltaic cells showed an open-circuit photovoltage, Vsub(oc), of 175 mV, a short-circuit photocurrent, Isub(sc), of 12 ..mu..A, and a fill factor of 0.42. The action spectra resembled the absorption spectra of the aggregated dyes. A D-D mechanism is introduced to explain the anomaly of the photovoltage of the SnO/sub 2/ electrode sensitized with the dyes. This behaviour is relevant to the practical usage of such photo-electrochemical cells and merits further investigation.

Program for the surface muon spectra calculation

International Nuclear Information System (INIS)

Arkatov, Yu.M.; Voloshchuk, V.I.; Zolenko, V.A.; Prokhorets, I.M.; Soldatov, S.A.

1987-01-01

Program for the ''surface'' muon spectrum calculation is described. The algorithm is based on simulation of coordinates of π-meson birth point and direction of its escape from meson-forming target (MFT) according to angular distribution with the use of Monte Carlo method. Ionization losses of π-(μ)-mesons in the target are taken into account in the program. Calculation of ''surface'' muon spectrum is performed in the range of electron energies from 150 MeV up to 1000 MeV. Spectra of π-mesons are calculated with account of ionization losses in the target and without it. Distributions over lengths of π-meson paths in MFT and contribution of separate sections of the target to pion flux at the outlet of meson channel are calculated as well. Meson-forming target for calculation can be made of any material. The program provides for the use of the MFT itself in the form of photon converter or photon converter is located in front of the target. The program is composed of 13 subprograms; 2 of them represent generators of pseudorandom numbers, distributed uniformly in the range from 0 up to 1, and numbers with Gauss distribution. Example of calculation for copper target of 3 cm length, electron beam current-1 μA, energy-300 MeV is presented

How to calculate linear absorption spectra with lifetime broadening using fewest switches surface hopping trajectories: A simple generalization of ground-state Kubo theory

International Nuclear Information System (INIS)

Petit, Andrew S.; Subotnik, Joseph E.

2014-01-01

In this paper, we develop a surface hopping approach for calculating linear absorption spectra using ensembles of classical trajectories propagated on both the ground and excited potential energy surfaces. We demonstrate that our method allows the dipole-dipole correlation function to be determined exactly for the model problem of two shifted, uncoupled harmonic potentials with the same harmonic frequency. For systems where nonadiabatic dynamics and electronic relaxation are present, preliminary results show that our method produces spectra in better agreement with the results of exact quantum dynamics calculations than spectra obtained using the standard ground-state Kubo formalism. As such, our proposed surface hopping approach should find immediate use for modeling condensed phase spectra, especially for expensive calculations using ab initio potential energy surfaces

Opto-electro-modulated transient photovoltage and photocurrent system for investigation of charge transport and recombination in solar cells.

Science.gov (United States)

Shi, Jiangjian; Li, Dongmei; Luo, Yanhong; Wu, Huijue; Meng, Qingbo

2016-12-01

An opto-electro-modulated transient photovoltage/photocurrent system has been developed to probe microscopic charge processes of a solar cell in its adjustable operating conditions. The reliability of this system is carefully determined by electric circuit simulations and experimental measurements. Using this system, the charge transport, recombination and storage properties of a conventional multicrystalline silicon solar cell under different steady-state bias voltages, and light illumination intensities are investigated. This system has also been applied to study the influence of the hole transport material layer on charge extraction and the microscopic charge processes behind the widely considered photoelectric hysteresis in perovskite solar cells.

A Generalized Approach to Model the Spectra and Radiation Dose Rate of Solar Particle Events on the Surface of Mars

Science.gov (United States)

Guo, Jingnan; Zeitlin, Cary; Wimmer-Schweingruber, Robert F.; McDole, Thoren; Kühl, Patrick; Appel, Jan C.; Matthiä, Daniel; Krauss, Johannes; Köhler, Jan

2018-01-01

For future human missions to Mars, it is important to study the surface radiation environment during extreme and elevated conditions. In the long term, it is mainly galactic cosmic rays (GCRs) modulated by solar activity that contribute to the radiation on the surface of Mars, but intense solar energetic particle (SEP) events may induce acute health effects. Such events may enhance the radiation level significantly and should be detected as immediately as possible to prevent severe damage to humans and equipment. However, the energetic particle environment on the Martian surface is significantly different from that in deep space due to the influence of the Martian atmosphere. Depending on the intensity and shape of the original solar particle spectra, as well as particle types, the surface spectra may induce entirely different radiation effects. In order to give immediate and accurate alerts while avoiding unnecessary ones, it is important to model and well understand the atmospheric effect on the incoming SEPs, including both protons and helium ions. In this paper, we have developed a generalized approach to quickly model the surface response of any given incoming proton/helium ion spectra and have applied it to a set of historical large solar events, thus providing insights into the possible variety of surface radiation environments that may be induced during SEP events. Based on the statistical study of more than 30 significant solar events, we have obtained an empirical model for estimating the surface dose rate directly from the intensities of a power-law SEP spectra.

Effect of surface states on the electrochemical behaviour of single crystal n-ZnSe photoelectrode

International Nuclear Information System (INIS)

El-Dessouki, M.S.

1987-10-01

Surface Photovoltage Spectroscopy (SPS) technique has been used to detect the surface states of ZnSe (110) surfaces. Aqueous electrolyte/ZnSe junction has been electrochemically investigated in dark and under illumination. The effect of surface states on the kinetics of charge transfer through the semiconductor-electrolyte (S/E) junction has been discussed. The low leakage and photocurrents measured by the application of DC bias were referred to the blocking nature of S/E interface, in which the localized and induced surface states play an important role. (author). 19 refs, 4 figs

Thermal Infrared Spectra of Microcrystalline Sedimentary Phases: Effects of Natural Surface Roughness on Spectral Feature Shape

Science.gov (United States)

Hardgrove, C.; Rogers, A. D.

2012-03-01

Thermal infrared spectral features of common microcrystalline phases (chert, alabaster, micrite) are presented. Spectra are sensitive to mineralogy and micron-scale (~1-25 µm) surface roughness. Roughness is on the scale of the average crystal size.

Scikit-spectra: Explorative Spectroscopy in Python

Directory of Open Access Journals (Sweden)

Adam Hughes

2015-06-01

Full Text Available Scikit-spectra is an intuitive framework for explorative spectroscopy in Python. Scikit-spectra leverages the Pandas library for powerful data processing to provide datastructures and an API designed for spectroscopy. Utilizing the new IPython Notebook widget system, scikit-spectra is headed towards a GUI when you want it, API when you need it approach to spectral analysis. As an application, analysis is presented of the surface-plasmon resonance shift in a solution of gold nanoparticles induced by proteins binding to the gold’s surface. Please refer to the scikit-spectra website for full documentation and support: http://hugadams.github.io/scikit-spectra/

Local secondary-electron emission spectra of graphite and gold surfaces obtained using the Scanning Probe Energy Loss Spectrometer (SPELS)

International Nuclear Information System (INIS)

Lawton, J J; Pulisciano, A; Palmer, R E

2009-01-01

Secondary-electron emission (SEE) spectra have been obtained with the Scanning Probe Energy Loss Spectrometer at a tip-sample distance of only 50 nm. Such short working distances are required for the best theoretical spatial resolution (<10 nm). The SEE spectra of graphite, obtained as a function of tip bias voltage, are shown to correspond to unoccupied states in the electronic band structure. The SEE spectra of thin gold films demonstrate the capability of identifying (carbonaceous) surface contamination with this technique.

Local secondary-electron emission spectra of graphite and gold surfaces obtained using the Scanning Probe Energy Loss Spectrometer (SPELS)

Energy Technology Data Exchange (ETDEWEB)

Lawton, J J; Pulisciano, A; Palmer, R E, E-mail: R.E.Palmer@bham.ac.u [Nanoscale Physics Research Laboratory, School of Physics and Astronomy, University of Birmingham, Birmingham B15 2TT (United Kingdom)

2009-11-25

Secondary-electron emission (SEE) spectra have been obtained with the Scanning Probe Energy Loss Spectrometer at a tip-sample distance of only 50 nm. Such short working distances are required for the best theoretical spatial resolution (<10 nm). The SEE spectra of graphite, obtained as a function of tip bias voltage, are shown to correspond to unoccupied states in the electronic band structure. The SEE spectra of thin gold films demonstrate the capability of identifying (carbonaceous) surface contamination with this technique.

Gigantic 2D laser-induced photovoltaic effect in magnetically doped topological insulators for surface zero-bias spin-polarized current generation

Science.gov (United States)

Shikin, A. M.; Voroshin, V. Yu; Rybkin, A. G.; Kokh, K. A.; Tereshchenko, O. E.; Ishida, Y.; Kimura, A.

2018-01-01

A new kind of 2D photovoltaic effect (PVE) with the generation of anomalously large surface photovoltage up to 210 meV in magnetically doped topological insulators (TIs) has been studied by the laser time-resolved pump-probe angle-resolved photoelectron spectroscopy. The PVE has maximal efficiency for TIs with high occupation of the upper Dirac cone (DC) states and the Dirac point located inside the fundamental energy gap. For TIs with low occupation of the upper DC states and the Dirac point located inside the valence band the generated surface photovoltage is significantly reduced. We have shown that the observed giant PVE is related to the laser-generated electron-hole asymmetry followed by accumulation of the photoexcited electrons at the surface. It is accompanied by the 2D relaxation process with the generation of zero-bias spin-polarized currents flowing along the topological surface states (TSSs) outside the laser beam spot. As a result, the spin-polarized current generates an effective in-plane magnetic field that is experimentally confirmed by the k II-shift of the DC relative to the bottom non-spin-polarized conduction band states. The realized 2D PVE can be considered as a source for the generation of zero-bias surface spin-polarized currents and the laser-induced local surface magnetization developed in such kind 2D TSS materials.

First Derivative UV Spectra of Surface Water as a Monitor of Chlorination in Drinking Water Treatment

Directory of Open Access Journals (Sweden)

V. Zitko

2001-01-01

Full Text Available Many countries require the presence of free chlorine at about 0.1 mg/l in their drinking water supplies. For various reasons, such as cast-iron pipes or long residence times in the distribution system, free chlorine may decrease below detection limits. In such cases it is important to know whether or not the water was chlorinated or if nonchlorinated water entered the system by accident. Changes in UV spectra of natural organic matter in lakewater were used to assess qualitatively the degree of chlorination in the treatment to produce drinking water. The changes were more obvious in the first derivative spectra. In lakewater, the derivative spectra have a maximum at about 280 nm. This maximum shifts to longer wavelengths by up to 10 nm, decreases, and eventually disappears with an increasing dose of chlorine. The water treatment system was monitored by this technique for over 1 year and changes in the UV spectra of water samples were compared with experimental samples treated with known amounts of chlorine. The changes of the UV spectra with the concentration of added chlorine are presented. On several occasions, water, which received very little or no chlorination, may have entered the drinking water system. The results show that first derivative spectra are potentially a tool to determine, in the absence of residual chlorine, whether or not surface water was chlorinated during the treatment to produce potable water.

Extracting Optical Fiber Background from Surface-Enhanced Raman Spectroscopy Spectra Based on Bi-Objective Optimization Modeling.

Science.gov (United States)

Huang, Jie; Shi, Tielin; Tang, Zirong; Zhu, Wei; Liao, Guanglan; Li, Xiaoping; Gong, Bo; Zhou, Tengyuan

2017-08-01

We propose a bi-objective optimization model for extracting optical fiber background from the measured surface-enhanced Raman spectroscopy (SERS) spectrum of the target sample in the application of fiber optic SERS. The model is built using curve fitting to resolve the SERS spectrum into several individual bands, and simultaneously matching some resolved bands with the measured background spectrum. The Pearson correlation coefficient is selected as the similarity index and its maximum value is pursued during the spectral matching process. An algorithm is proposed, programmed, and demonstrated successfully in extracting optical fiber background or fluorescence background from the measured SERS spectra of rhodamine 6G (R6G) and crystal violet (CV). The proposed model not only can be applied to remove optical fiber background or fluorescence background for SERS spectra, but also can be transferred to conventional Raman spectra recorded using fiber optic instrumentation.

Scaling of turbulence spectra measured in strong shear flow near the Earth’s surface

DEFF Research Database (Denmark)

Mikkelsen, Torben Krogh; Larsen, Søren Ejling; Ejsing Jørgensen, Hans

2017-01-01

Within the lowest kilometer of the Earth's atmosphere, in the so-called atmospheric boundary layer, winds are often gusty and turbulent. Nearest to the ground, the turbulence is predominately generated by mechanical wall-bounded wind shear, whereas at higher altitudes turbulent mixing of heat...... subrange with a distinct inverse-linear power law for turbulence in a strongly sheared high-Reynolds number wall-bounded flow, as is encountered in the lowest sheared part of the atmospheric boundary layer, also known as the eddy surface layer. This paper presents observations of spectra measured...... and moisture also play a role. The variance (square of the standard deviation) of the fluctuation around the mean wind speed is a measure of the kinetic energy content of the turbulence. This kinetic energy can be resolved into the spectral distributions, or spectra, as functions of eddy size, wavenumber...

Redshift of A 1(longitudinal optical) mode for GaN crystals under strong electric field

Science.gov (United States)

Gu, Hong; Wu, Kaijie; Zheng, Shunan; Shi, Lin; Zhang, Min; Liu, Zhenghui; Liu, Xinke; Wang, Jianfeng; Zhou, Taofei; Xu, Ke

2018-01-01

We investigated the property of GaN crystals under a strong electric field. The Raman spectra of GaN were measured using an ultraviolet laser, and a remarkable redshift of the A 1(LO) mode was observed. The role of the surface depletion layer was discussed, and the interrelation between the electric field and phonons was revealed. First-principles calculations indicated that, in particular, the phonons that vibrate along the [0001] direction are strongly influenced by the electric field. This effect was confirmed by a surface photovoltage experiment. The results revealed the origin of the redshift and presented the phonon property of GaN under a strong electric field.

Artificial intelligence analysis of paraspinal power spectra.

Science.gov (United States)

Oliver, C W; Atsma, W J

1996-10-01

OBJECTIVE: As an aid to discrimination of sufferers with back pain an artificial intelligence neural network was constructed to differentiate paraspinal power spectra. DESIGN: Clinical investigation using surface electromyography. METHOD: The surface electromyogram power spectra from 60 subjects, 33 non-back-pain sufferers and 27 chronic back pain sufferers were used to construct a back propagation neural network that was then tested. Subjects were placed on a test frame in 30 degrees of lumbar forward flexion. An isometric load of two-thirds maximum voluntary contraction was held constant for 30 s whilst surface electromyograms were recorded at the level of the L(4-5). Paraspinal power spectra were calculated and loaded into the input layer of a three-layer back propagation network. The neural network classified the spectra into normal or back pain type. RESULTS: The back propagation neural was shown to have satisfactory convergence with a specificity of 79% and a sensitivity of 80%. CONCLUSIONS: Artificial intelligence neural networks appear to be a useful method of differentiating paraspinal power spectra in back-pain sufferers.

Surface states and spectra

International Nuclear Information System (INIS)

Jaksic, V.; Last, Y.; California Inst. of Tech., Pasadena, CA

2001-01-01

Let Z + d+1 =Z d x Z + , let H 0 be the discrete Laplacian on the Hilbert space l 2 (Z + d+1 ) with a Dirichlet boundary condition, and let V be a potential supported on the boundary ∂Z + d+1 . We introduce the notions of surface states and surface spectrum of the operator H=H 0 +V and explore their properties. Our main result is that if the potential V is random and if the disorder is either large or small enough, then in dimension two H has no surface spectrum on σ(H 0 ) with probability one. To prove this result we combine Aizenman-Molchanov theory with techniques of scattering theory. (orig.)

Measurement of Near-Surface Salinity, Temperature and Directional Wave Spectra using a Novel Wave-Following, Lagrangian Surface Contact Buoy

Science.gov (United States)

Boyle, J. P.

2016-02-01

Results from a surface contact drifter buoy which measures near-surface conductivity ( 10 cm depth), sea state characteristics and near-surface water temperature ( 2 cm depth) are described. This light (righting. It has a small above-surface profile and low windage, resulting in near-Lagrangian drift characteristics. It is autonomous, with low power requirements and solar panel battery recharging. Onboard sensors include an inductive toroidal conductivity probe for salinity measurement, a nine-degrees-of-freedom motion package for derivation of directional wave spectra and a thermocouple for water temperature measurement. Data retrieval for expendable, ocean-going operation uses an onboard Argos transmitter. Scientific results as well as data processing algorithms are presented from laboratory and field experiments which support qualification of buoy platform measurements. These include sensor calibration experiments, longer-term dock-side biofouling experiments during 2013-2014 and a series of short-duration ocean deployments in the Gulf Stream in 2014. In addition, a treatment method will be described which appears to minimize the effects of biofouling on the inductive conductivity probe when in coastal surface waters. Due to its low cost and ease of deployment, scores, perhaps hundreds of these novel instruments could be deployed from ships or aircraft during process studies or to provide surface validation for satellite-based measurements, particularly in high precipitation regions.

Improving interpretation of infrared spectra for OM characterization by subtraction of spectra from incinerated samples

Science.gov (United States)

Ellerbrock, Ruth H.; Gerke, Horst H.; Leue, Martin

2017-04-01

Non-destructive methods such as diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) have been applied to characterize organic matter (OM) at intact structural surfaces among others. However, it is often difficult to distinguish effects of organic components on DRIFT signal intensities from those of mineral components. The objective of this study was to re-evaluate DRIFT spectra from intact earthworm burrow walls and coated cracks to improve the interpretation of C-H and C=O bands. We compared DRIFT and transmission Fourier transform infrared (FTIR) spectra of entire samples that were from the same pedogenetic soil horizon, but different in mineral composition and texture (i.e., glacial till versus loess). Spectra of incinerated samples were subtracted from the original spectra. Transmission FTIR and DRIFT spectra were almost identical for entire soil samples. However, the DRIFT spectra were affected by the bulk mode bands (i.e., wavenumbers 2000 to 1700 cm-1) that affected spectral resolution and reproducibility. The ratios between C-H and C=O band intensities as indicator for OM quality obtained with DRIFT were smaller than those obtained from transmission FTIR. A spectral subtraction procedure was found to reduce effects of mineral absorption bands on DRIFT spectra allowing an improved interpretation. DRIFT spectroscopy as a non-destructive method for analyzing OM composition at intact surfaces in structured soils could be calibrated with information obtained with the more detailed transmission FTIR and complementary methods.

Resonance Raman spectra of organic molecules absorbed on inorganic semiconducting surfaces: Contribution from both localized intramolecular excitation and intermolecular charge transfer excitation

International Nuclear Information System (INIS)

Ye, ChuanXiang; Zhao, Yi; Liang, WanZhen

2015-01-01

The time-dependent correlation function approach for the calculations of absorption and resonance Raman spectra (RRS) of organic molecules absorbed on semiconductor surfaces [Y. Zhao and W. Z. Liang, J. Chem. Phys. 135, 044108 (2011)] is extended to include the contribution of the intermolecular charge transfer (CT) excitation from the absorbers to the semiconducting nanoparticles. The results demonstrate that the bidirectionally interfacial CT significantly modifies the spectral line shapes. Although the intermolecular CT excitation makes the absorption spectra red shift slightly, it essentially changes the relative intensities of mode-specific RRS and causes the oscillation behavior of surface enhanced Raman spectra with respect to interfacial electronic couplings. Furthermore, the constructive and destructive interferences of RRS from the localized molecular excitation and CT excitation are observed with respect to the electronic coupling and the bottom position of conductor band. The interferences are determined by both excitation pathways and bidirectionally interfacial CT

Photon- and electron-induced surface voltage in electron spectroscopies on ZnSe(0 0 1)

International Nuclear Information System (INIS)

Cantoni, M.; Bertacco, R.; Brambilla, A.; Ciccacci, F.

2009-01-01

The surface band bending in ZnSe(0 0 1), as a function of the temperature, is investigated both in the valence band (by photoemission) and in the conduction band (by inverse photoemission and absorbed current spectroscopies). Two different mechanisms are invoked for interpreting the experimental data: the band bending due to surface states, and the surface voltage induced by the incident beam. While the latter is well known in photoemission (surface photovoltage), we demonstrate the existence of a similar effect in inverse photoemission and absorbed current spectroscopies, induced by the incident electrons instead of photons. These results point to the importance of considering the surface voltage effect even in electron-in techniques for a correct evaluation of the band bending.

Photoelectrochemical Complexes of Fucoxanthin-Chlorophyll Protein for Bio-Photovoltaic Conversion with a High Open-Circuit Photovoltage.

Science.gov (United States)

Zhang, Tianning; Liu, Cheng; Dong, Wenjing; Wang, Wenda; Sun, Yan; Chen, Xin; Yang, Chunhong; Dai, Ning

2017-12-05

Open-circuit photovoltage (V oc ) is among the critical parameters for achieving an efficient light-to-charge conversion in existing solar photovoltaic devices. Natural photosynthesis exploits light-harvesting chlorophyll (Chl) protein complexes to transfer sunlight energy efficiently. We describe the exploitation of photosynthetic fucoxanthin-chlorophyll protein (FCP) complexes for realizing photoelectrochemical cells with a high V oc . An antenna-dependent photocurrent response and a V oc up to 0.72 V are observed and demonstrated in the bio-photovoltaic devices fabricated with photosynthetic FCP complexes and TiO 2 nanostructures. Such high V oc is determined by fucoxanthin in FCP complexes, and is rarely found in photoelectrochemical cells with other natural light-harvesting antenna. We think that the FCP-based bio-photovoltaic conversion will provide an opportunity to fabricate environmental benign photoelectrochemical cells with high V oc , and also help improve the understanding of the essential physics behind the light-to-charge conversion in photosynthetic complexes. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Enhancing the Photovoltage of Ni/ n-Si Photoanode for Water Oxidation through a Rapid Thermal Process.

Science.gov (United States)

Li, Shengyang; She, Guangwei; Chen, Cheng; Zhang, Shaoyang; Mu, Lixuan; Guo, Xiangxin; Shi, Wensheng

2018-03-14

The Ni in the Ni/ n-Si photoanode can not only protect Si from corrosion, but also catalyze the water oxidation reaction. However, the high density of interface states at the Ni/ n-Si interface could pin the Fermi level of silicon, which will lower the Schottky barrier height of the Ni/ n-Si. As a result, a low photovoltage and consequent high onset potential of Ni/ n-Si photoanode for water oxidation were generated. In this study, the interfacial states of the Ni/ n-Si photoanodes were efficiently diminished through a rapid thermal process (RTP). Calculated from the Mott-Schottky plots, the Schottky barrier height of Ni/ n-Si was increased from 0.58 to 0.78 eV after RTP. Under the illumination of 100 mW cm -2 of the Xe lamp, the onset potential of the Ni/ n-Si photoanode for water oxidation was negatively shifted for 150 mV after RTP. Besides, the RTP-treated Ni/ n-Si photoanode exhibited a high stability during the PEC water oxidation of 8 h in 1 M KOH solution.

Channeling effect in electronic spectra produced by grazing impact of fast protons on insulator surfaces

Energy Technology Data Exchange (ETDEWEB)

Archubi, C D; Gravielle, M S, E-mail: archubi@iafe.uba.a, E-mail: msilvia@iafe.uba.a [Instituto de Astronomia y Fisica del Espacio, Casilla de Correo 67, Sucursal 28, 1428, Buenos Aires (Argentina)

2009-11-01

Electron emission due to grazing scattering of fast protons from LiF and KCl surfaces is studied under axial incidence conditions. The differential emission probability is calculated within a distorted-wave formalism, taking into account axial channeled trajectories. For different emission angles, electronic spectra for proton incidence along the two principal crystal axes ([100] and [110]) are compared with those corresponding to an impact velocity in a random direction, finding effects associated with the channeling conditions.

Fabrication and charge/energy-transfer study of 4,7-bis(4-triphenylamino)benzo- 2,1,3-thiadiazole/CuPc composite films

International Nuclear Information System (INIS)

Zhu Yuanyuan; Wei Xiao; Xue Minzhao; Zhang Qing; Sheng Qiaorong; Liu Yangang; Gu Shuangxi

2010-01-01

Composite films of 4,7-bis(4-triphenylamino)benzo-2,1,3-thiadiazole (TBT) and copper phthalocyanine (CuPc) are fabricated via protonation-coelectrophoretic deposition from nitromethane solutions of TBT/CuPc mixture in the presence of trifluoroacetic acid as a protonation reagent. A nanospheres-nanowires interpenetrating network structure is obtained when the molar percentage of TBT is 70%. Furthermore, the existence of TBT makes α-phased CuPc be partly transformed into the β-phase, and simultaneously, CuPc disorganizes the TBT unit cells. The blue shift on the absorption edge of TBT and the significant fluorescence quenching in the composite films indicate energy/charge transfer and donor-acceptor (D-A) heterojunction formation. Then these results are proved from another point of view: the mutual overlap of absorption and emission spectra of TBT and CuPc lead to a bidirectional Foerster resonance energy transfer at the interface; the molecular energy levels calculated from the results of cyclic voltammetry theoretically determine that there exist a D-A heterojunction and charge transfer from TBT to CuPc. Finally, from the investigation of the field-induced surface photovoltage spectra, it can be concluded that this charge transfer results in efficient dissociation of the photoinduced excitons in the composite films, followed by the generation of a strong photovoltage response.

Fabrication and charge/energy-transfer study of 4,7-bis(4-triphenylamino)benzo- 2,1,3-thiadiazole/CuPc composite films

Energy Technology Data Exchange (ETDEWEB)

Zhu Yuanyuan; Wei Xiao; Xue Minzhao; Zhang Qing; Sheng Qiaorong; Liu Yangang [School of Chemistry and Chemical Engineering, Shanghai Jiao Tong University, Shanghai 200240 (China); Gu Shuangxi, E-mail: mzxue@sjtu.edu.c [Department of Chemistry, Fudan University, Shanghai 200433 (China)

2010-12-15

Composite films of 4,7-bis(4-triphenylamino)benzo-2,1,3-thiadiazole (TBT) and copper phthalocyanine (CuPc) are fabricated via protonation-coelectrophoretic deposition from nitromethane solutions of TBT/CuPc mixture in the presence of trifluoroacetic acid as a protonation reagent. A nanospheres-nanowires interpenetrating network structure is obtained when the molar percentage of TBT is 70%. Furthermore, the existence of TBT makes {alpha}-phased CuPc be partly transformed into the {beta}-phase, and simultaneously, CuPc disorganizes the TBT unit cells. The blue shift on the absorption edge of TBT and the significant fluorescence quenching in the composite films indicate energy/charge transfer and donor-acceptor (D-A) heterojunction formation. Then these results are proved from another point of view: the mutual overlap of absorption and emission spectra of TBT and CuPc lead to a bidirectional Foerster resonance energy transfer at the interface; the molecular energy levels calculated from the results of cyclic voltammetry theoretically determine that there exist a D-A heterojunction and charge transfer from TBT to CuPc. Finally, from the investigation of the field-induced surface photovoltage spectra, it can be concluded that this charge transfer results in efficient dissociation of the photoinduced excitons in the composite films, followed by the generation of a strong photovoltage response.

Rapid, nondestructive estimation of surface polymer layer thickness using attenuated total reflection fourier transform infrared (ATR FT-IR) spectroscopy and synthetic spectra derived from optical principles.

Science.gov (United States)

Weinstock, B André; Guiney, Linda M; Loose, Christopher

2012-11-01

We have developed a rapid, nondestructive analytical method that estimates the thickness of a surface polymer layer with high precision but unknown accuracy using a single attenuated total reflection Fourier transform infrared (ATR FT-IR) measurement. Because the method is rapid, nondestructive, and requires no sample preparation, it is ideal as a process analytical technique. Prior to implementation, the ATR FT-IR spectrum of the substrate layer pure component and the ATR FT-IR and real refractive index spectra of the surface layer pure component must be known. From these three input spectra a synthetic mid-infrared spectral matrix of surface layers 0 nm to 10,000 nm thick on substrate is created de novo. A minimum statistical distance match between a process sample's ATR FT-IR spectrum and the synthetic spectral matrix provides the thickness of that sample. We show that this method can be used to successfully estimate the thickness of polysulfobetaine surface modification, a hydrated polymeric surface layer covalently bonded onto a polyetherurethane substrate. A database of 1850 sample spectra was examined. Spectrochemical matrix-effect unknowns, such as the nonuniform and molecularly novel polysulfobetaine-polyetherurethane interface, were found to be minimal. A partial least squares regression analysis of the database spectra versus their thicknesses as calculated by the method described yielded an estimate of precision of ±52 nm.

Pattern recognition in spectra

International Nuclear Information System (INIS)

Gebran, M; Paletou, F

2017-01-01

We present a new automated procedure that simultaneously derives the effective temperature T eff , surface gravity log g , metallicity [ Fe/H ], and equatorial projected rotational velocity v e sin i for stars. The procedure is inspired by the well-known PCA-based inversion of spectropolarimetric full-Stokes solar data, which was used both for Zeeman and Hanle effects. The efficiency and accuracy of this procedure have been proven for FGK, A, and late type dwarf stars of K and M spectral types. Learning databases are generated from the Elodie stellar spectra library using observed spectra for which fundamental parameters were already evaluated or with synthetic data. The synthetic spectra are calculated using ATLAS9 model atmospheres. This technique helped us to detect many peculiar stars such as Am, Ap, HgMn, SiEuCr and binaries. This fast and efficient technique could be used every time a pattern recognition is needed. One important application is the understanding of the physical properties of planetary surfaces by comparing aboard instrument data to synthetic ones. (paper)

Spectra of resonance surface photoionization

Energy Technology Data Exchange (ETDEWEB)

Antsiferov, V.V.; Smirnov, G.I.; Telegin, G.G. [Budker Nuclear Physics Institute, Novosibirsk (Russian Federation)

1995-09-01

The theory of nonactivated electron transfer between atoms interacting reasonantly with coherent radiation and a metal surface is developed. The spectral resonances in photoabsorption and surface photoionization are found to be related to nonlinear interference effects in the interaction between discrete atomic levels and the continuum formed by the quasi-continuous electron spectrum of a normal metal. The asymmetry in the resonance surface photoionization spectrum is shown to have a shape typical of the Fano autoionization resonances. 18 refs.

Effects of Oriented Surface Dipole on Photoconversion Efficiency in an Alkane/Lipid-Hybrid-Bilayer-Based Photovoltaic Model System

KAUST Repository

Liu, Lixia

2013-06-21

When a phospholipid monolayer containing a zinc-coordinated porphyrin species formed atop a self-assembled monolayer of heptadecafluoro-1-decanethiol (CF3(CF2)7(CH2)2SH) is subjected to photoelectrochemical current generation, a significant modulation effect is observed. Compared with devices that contain similar photoactive lipid monolayers but formed on 1-dodecanethiol SAMs, these fluorinated hybrid bilayers produce a >60 % increase in cathodic currents and a similar decrease in anodic currents. Photovoltages recorded from these hybrid bilayers are found to vary in the same fashion. The modulation of photovoltaic responses in these hybrid-bilayer-based devices is explained by the opposite surface dipoles associated with the thiols employed in this study, which in one case (fluorothiol) increase and in another (alkanethiol) decrease the work function of the underlying gold substrates. A similar trend of photovoltage/photocurrent modulation is also observed if fullerene is used as the photoagent in these devices. Our results reveal the intricacy of orientated surface dipole in influencing the photovoltaic processes, and its subtle interplay with other factors related to the photoagents, such as their location and orientation within the organic matrix. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Effects of Oriented Surface Dipole on Photoconversion Efficiency in an Alkane/Lipid-Hybrid-Bilayer-Based Photovoltaic Model System

KAUST Repository

Liu, Lixia; Xie, Hong; Bostic, Heidi E.; Jin, Limei; Best, Michael D.; Zhang, X. Peter; Zhan, Wei

2013-01-01

When a phospholipid monolayer containing a zinc-coordinated porphyrin species formed atop a self-assembled monolayer of heptadecafluoro-1-decanethiol (CF3(CF2)7(CH2)2SH) is subjected to photoelectrochemical current generation, a significant modulation effect is observed. Compared with devices that contain similar photoactive lipid monolayers but formed on 1-dodecanethiol SAMs, these fluorinated hybrid bilayers produce a >60 % increase in cathodic currents and a similar decrease in anodic currents. Photovoltages recorded from these hybrid bilayers are found to vary in the same fashion. The modulation of photovoltaic responses in these hybrid-bilayer-based devices is explained by the opposite surface dipoles associated with the thiols employed in this study, which in one case (fluorothiol) increase and in another (alkanethiol) decrease the work function of the underlying gold substrates. A similar trend of photovoltage/photocurrent modulation is also observed if fullerene is used as the photoagent in these devices. Our results reveal the intricacy of orientated surface dipole in influencing the photovoltaic processes, and its subtle interplay with other factors related to the photoagents, such as their location and orientation within the organic matrix. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Correlation of tunneling spectra with surface nano-morphology and doping in thin YBa2Cu3O7-delta films

OpenAIRE

Sharoni, A.; Koren, G.; Millo, O.

2001-01-01

Tunneling spectra measured on thin epitaxial YBa2Cu3O7-delta films are found to exhibit strong spatial variations, showing U and V-shaped gaps as well as zero bias conductance peaks typical of a d-wave superconductor. A full correspondence is found between the tunneling spectra and the surface morphology down to a level of a unit-cell step. Splitting of the zero bias conductance peak is seen in optimally-doped and overdoped films, but not in the underdoped ones, suggesting that there is no tr...

Photoelectric properties of ZnO/Ag2S heterostructure and its photoelectric ethanol sensing characteristics

International Nuclear Information System (INIS)

Zhang Yu; Liu Bingkun; Wang Dejun; Lin Yanhong; Xie Tengfeng; Zhai Jiali

2012-01-01

Highlights: ► The ZnO/Ag 2 S heterostructure shows good photoelectric properties under visible-light irradiation. ► Transient photovoltage results reveal the separation process of photo-generated charges and give further evidence of interfacial effects. ► Photoelectric ethanol sensing characteristics have been found for the ZnO/Ag 2 S heterostructure at room temperature. - Abstract: The photoelectric properties of ZnO microspheres, ZnO/Ag 2 S heterogeneous microspheres and Ag 2 S hollow microspheres were investigated systematically by surface photovoltage, transient photovoltage and surface photocurrent techniques. The ZnO/Ag 2 S heterostructure shows superior photoelectric properties in visible-light region compared with pure Ag 2 S. Transient photovoltage results reveal the separation processes of photo-generated charge carriers in the samples. The photoelectric ethanol sensing property induced by visible light for the ZnO/Ag 2 S heterostructure has been found, which should be valuable for the practical application of semiconductor gas sensors at room temperature.

Sn-L3 EDGE and Fe K edge XANES spectra of the surface layer of ancient Chinese black mirror Heiqigu

International Nuclear Information System (INIS)

Gaowei Mengjia; Liu Yuzhen; Chu Wangsheng; Wu Ziyu; Wang Changsui

2009-01-01

The Chinese ancient black mirror known as Heiqigu was studied by x-ray-absorption near-edge structure spectroscopy and results were reported. The Sn-L 3 edge and Fe K edge spectra further confirmed the Schottky-type defect model in the Heiqigu surface system. And it was suggested that the surface layer of the mirror was a combined structure of oxidation of Sn(IV) and Sn(II). (authors)

Photosensitive heterostructures made of sulfonamide zinc phthalocyanine and organic semiconductor

Czech Academy of Sciences Publication Activity Database

Lutsyk, P.; Vertsimakha, Ya.; Nešpůrek, Stanislav; Pomaz, I.

2011-01-01

Roč. 535, - (2011), s. 18-29 ISSN 1542-1406 Institutional research plan: CEZ:AV0Z40500505 Keywords : heterostructure * reversal of sign in photovoltage spectra * sulphonamide-substituted phthalocyanine Subject RIV: CD - Macromolecular Chemistry Impact factor: 0.580, year: 2011

Distribution of iron and titanium on the lunar surface from lunar prospector gamma ray spectra

International Nuclear Information System (INIS)

Prettyman, T.H.; Feldman, W.C.; Lawrence, David J.; Elphic, R.C.; Gasnault, O.M.; Maurice, S.; Moore, K.R.; Binder, A.B.

2001-01-01

Gamma ray pulse height spectra acquired by the Lunar Prospector (LP) Gamma-Ray Spectrometer (GRS) contain information on the abundance of major elements in the lunar surface, including O, Si, Ti, Al, Fe, Mg, Ca, K, and Th. With the exception of Th and K, prompt gamma rays produced by cosmic ray interactions with surface materials are used to determine elemental abundance. Most of these gamma rays are produced by inelastic scattering of fast neutrons and by neutron capture. The production of neutron-induced gamma rays reaches a maximum deep below the surface (e.g. ∼140 g/cm 2 for inelastic scattering and ∼50 g/cm 2 for capture). Consequently, gamma rays sense the bulk composition of lunar materials, in contrast to optical methods (e.g. Clementine Spectral Reflectance (CSR)), which only sample the top few microns. Because most of the gamma rays are produced deep beneath the surface, few escape unscattered and the continuum of scattered gamma rays dominates the spectrum. In addition, due to the resolution of the spectrometer, there are few well-isolated peaks and peak fitting algorithms must be used to deconvolve the spectrum in order to determine the contribution of individual elements.

Chemometric evaluation of temperature-dependent surface-enhanced Raman spectra of riboflavin: What is the best multivariate approach to describe the effect of temperature?

Science.gov (United States)

Kokaislová, Alžběta; Kalhousová, Milena; Gráfová, Michaela; Matějka, Pavel

2014-10-01

Riboflavin is an essential nutrient involved in energetic metabolism. It is used as a pharmacologically active substance in treatment of several diseases. From analytical point of view, riboflavin can be used as an active part of sensors for substances with affinity to riboflavin molecules. In biological environment, metal substrates coated with riboflavin are exposed to temperatures that are different from room temperature. Hence, it is important to describe the influence of temperature on adsorbed molecules of riboflavin, especially on orientation of molecules towards the metal surface and on stability of adsorbed molecular layer. Surface-enhanced Raman scattering (SERS) spectroscopy is a useful tool for investigation of architecture of molecular layers adsorbed on metal surfaces because the spectral features in SERS spectra change with varying orientation of molecules towards the metal surface, as well as with changes in mutual interactions among adsorbed molecules. In this study, riboflavin was adsorbed on electrochemically prepared massive silver substrates that were exposed to temperature changes according to four different temperature programs. Raman spectra measured at different temperatures were compared considering positions of spectral bands, their intensities, bandwidths and variability of all these parameters. It was found out that increase of substrate temperature up to 50 °C does not lead to any observable decomposition of riboflavin molecules, but the changes of band intensity ratios within individual spectra are apparent. To distinguish sources of variability beside changes in band intensities and widths, Principal Component Analysis (PCA) was applied. Discriminant Analysis (DA) was used to explore if the SERS spectra can be separated according to temperature. The results of Partial Least Squares (PLS) regression demonstrate the possibility to predict the sample temperature using SERS spectral features. Results of all performed experiments and

Effects of terraces, surface steps and 'over-specular' reflection due to inelastic energy losses on angular scattering spectra for glancing incidence scattering

CERN Document Server

Danailov, D; O'Connor, D J

2002-01-01

Recent experiments and our molecular-dynamics simulations indicate that the main signal of the angular scattering spectra of glancing incidence scattering are not affected by the thermal motion of surface atoms and can be explained by our row-model with averaged cylindrical potentials. At the ICACS-18 Conference [Nucl. Instr. and Meth. B 164-165 (2000) 583] we reported good agreement between experimental and calculated multimodal azimuthal angular scattering spectra for the glancing scattering of 10 and 15 keV [Nucl. Instr. and Meth. B 180 (2001) 265, Appl. Surf. Sci. 171 (2001) 113] He sup 0 beam along the [1 0 0] direction on the Fe(1 0 0) face. Our simulations also predicted that in contrast to the 2D angular scattering distribution, the 1D azimuthal angular distribution of scattered particles is very sensitive to the interaction potential used. Here, we report more detailed calculations incorporating the influence of terraces and surface steps on surface channeling, which show a reduction of the angular s...

Tailoring surface plasmon resonance and dipole cavity plasmon modes of scattering cross section spectra on the single solid-gold/gold-shell nanorod

International Nuclear Information System (INIS)

Chou Chau, Yuan-Fong; Lim, Chee Ming; Kumara, N. T. R. N.; Yoong, Voo Nyuk; Lee, Chuanyo; Huang, Hung Ji; Lin, Chun-Ting; Chiang, Hai-Pang

2016-01-01

Tunable surface plasmon resonance (SPR) and dipole cavity plasmon modes of the scattering cross section (SCS) spectra on the single solid-gold/gold-shell nanorod have been numerically investigated by using the finite element method. Various effects, such as the influence of SCS spectra under x- and y-polarizations on the surface of the single solid-gold/gold-shell nanorod, are discussed in detail. With the single gold-shell nanorod, one can independently tune the relative SCS spectrum width by controlling the rod length and rod diameter, and the surface scattering by varying the shell thickness and polarization direction, as well as the dipole peak energy. These behaviors are consistent with the properties of localized SPRs and offer a way to optically control and produce selected emission wavelengths from the single solid-gold/gold-shell nanorod. The electric field and magnetic distributions provide us a qualitative idea of the geometrical properties of the single solid-gold/gold-shell nanorod on plasmon resonance.

Contributions of conduction band offset to the enhanced separation efficiency of photoinduced charges for SrTiO3/Bi2O3 heterojunction semiconductor

International Nuclear Information System (INIS)

Zhang, Zhenlong; Zhu, Jichun; Li, Shengjun; Mao, Yanli

2014-01-01

SrTiO 3 /Bi 2 O 3 heterojunction semiconductor was prepared and characterized by X-ray diffraction, UV–vis absorption spectrum, and scanning electron microscope, surface photovoltage spectroscopy, and photoluminescence spectroscopy. The surface photovoltage spectra indicate that the separation efficiency of photoinduced charges for SrTiO 3 /Bi 2 O 3 was enhanced compared with that of SrTiO 3 or Bi 2 O 3 . The energy band diagram of SrTiO 3 /Bi 2 O 3 heterojunction was directly determined with X-ray photoelectron spectroscopy, and the conduction band offset between SrTiO 3 and Bi 2 O 3 was quantified to be 0.28±0.03 eV. The photoluminescence spectra display that the recombination rate of photoinduced carriers for SrTiO 3 /Bi 2 O 3 decreases compared with that of SrTiO 3 or Bi 2 O 3 , which is mainly due to the energy levels matching between them. Therefore the enhanced separation efficiency of photoinduced charges is resulting from the energy difference between the conduction band edges of SrTiO 3 and Bi 2 O 3 . -- Graphical abstract: Enhanced separation efficiency for SrTiO 3 /Bi 2 O 3 is resulting from the energy difference between the conduction band edges. Highlights: ●Heterojunction semiconductor of SrTiO 3 /Bi 2 O 3 was prepared. ●SrTiO 3 /Bi 2 O 3 presents enhanced separation efficiency. ●Conduction band offset between SrTiO 3 and Bi 2 O 3 is quantified. ●Recombination rate of SrTiO 3 /Bi 2 O 3 decreases compared with single phases

Proposed Site-Specific Response Spectra for Surabaya-Madura Bridge

Directory of Open Access Journals (Sweden)

Dyah Kusumastuti

2008-01-01

Full Text Available This paper presents a site-specific seismic hazard study to determine the recommended seismic design criteria for Suramadu Bridge. The study is performed using probabilistic seismic hazard approach to determine maximum acceleration and response spectra at bedrock and followed by local site effect analysis to determine maximum acceleration and response spectra at ground surface. The probabilistic seismic hazard analysis (PSHA is carried out using 3-dimension (3-D seismic source models (fault source model. Two hazard levels are analysed to represent 150 and 3,300 years return period of ground motion around site location. The local site effect analysis is performed using 1-dimension (1-D shear wave propagation theory to obtain peak ground acceleration and response spectra at ground surface. Finally, the site-specific surface response spectra with 5 percent damping are developed based on the mean plus one standard deviation concept from the result of local site effect analysis.

Coupling of Nanocrystalline Anatase TiO2 to Porous Nanosized LaFeO3 for Efficient Visible-Light Photocatalytic Degradation of Pollutants

Directory of Open Access Journals (Sweden)

Muhammad Humayun

2016-01-01

Full Text Available In this work we have successfully fabricated nanocrystalline anatase TiO2/perovskite-type porous nanosized LaFeO3 (T/P-LFO nanocomposites using a simple wet chemical method. It is clearly demonstrated by means of atmosphere-controlled steady-state surface photovoltage spectroscopy (SPS responses, photoluminescence spectra, and fluorescence spectra related to the formed OH− radical amount that the photogenerated charge carriers in the resultant T/P-LFO nanocomposites with a proper mole ratio percentage of TiO2 display much higher separation in comparison to the P-LFO alone. This is highly responsible for the improved visible-light activities of T/P-LFO nanocomposites for photocatalytic degradation of gas-phase acetaldehyde and liquid-phase phenol. This work will provide a feasible route to synthesize visible-light responsive nano-photocatalysts for efficient solar energy utilization.

Inverse modelling of Köhler theory – Part 1: A response surface analysis of CCN spectra with respect to surface-active organic species

Directory of Open Access Journals (Sweden)

S. Lowe

2016-09-01

Full Text Available In this study a novel framework for inverse modelling of cloud condensation nuclei (CCN spectra is developed using Köhler theory. The framework is established by using model-generated synthetic measurements as calibration data for a parametric sensitivity analysis. Assessment of the relative importance of aerosol physicochemical parameters, while accounting for bulk–surface partitioning of surface-active organic species, is carried out over a range of atmospherically relevant supersaturations. By introducing an objective function that provides a scalar metric for diagnosing the deviation of modelled CCN concentrations from synthetic observations, objective function response surfaces are presented as a function of model input parameters. Crucially, for the chosen calibration data, aerosol–CCN spectrum closure is confirmed as a well-posed inverse modelling exercise for a subset of the parameters explored herein. The response surface analysis indicates that the appointment of appropriate calibration data is particularly important. To perform an inverse aerosol–CCN closure analysis and constrain parametric uncertainties, it is shown that a high-resolution CCN spectrum definition of the calibration data is required where single-valued definitions may be expected to fail. Using Köhler theory to model CCN concentrations requires knowledge of many physicochemical parameters, some of which are difficult to measure in situ on the scale of interest and introduce a considerable amount of parametric uncertainty to model predictions. For all partitioning schemes and environments modelled, model output showed significant sensitivity to perturbations in aerosol log-normal parameters describing the accumulation mode, surface tension, organic : inorganic mass ratio, insoluble fraction, and solution ideality. Many response surfaces pertaining to these parameters contain well-defined minima and are therefore good candidates for calibration using a Monte

An algorithm for hyperspectral remote sensing of aerosols: 2. Information content analysis for aerosol parameters and principal components of surface spectra

Science.gov (United States)

Hou, Weizhen; Wang, Jun; Xu, Xiaoguang; Reid, Jeffrey S.

2017-05-01

This paper describes the second part of a series of investigation to develop algorithms for simultaneous retrieval of aerosol parameters and surface reflectance from the future hyperspectral and geostationary satellite sensors such as Tropospheric Emissions: Monitoring of POllution (TEMPO). The information content in these hyperspectral measurements is analyzed for 6 principal components (PCs) of surface spectra and a total of 14 aerosol parameters that describe the columnar aerosol volume Vtotal, fine-mode aerosol volume fraction, and the size distribution and wavelength-dependent index of refraction in both coarse and fine mode aerosols. Forward simulations of atmospheric radiative transfer are conducted for 5 surface types (green vegetation, bare soil, rangeland, concrete and mixed surface case) and a wide range of aerosol mixtures. It is shown that the PCs of surface spectra in the atmospheric window channel could be derived from the top-of-the-atmosphere reflectance in the conditions of low aerosol optical depth (AOD ≤ 0.2 at 550 nm), with a relative error of 1%. With degree freedom for signal analysis and the sequential forward selection method, the common bands for different aerosol mixture types and surface types can be selected for aerosol retrieval. The first 20% of our selected bands accounts for more than 90% of information content for aerosols, and only 4 PCs are needed to reconstruct surface reflectance. However, the information content in these common bands from each TEMPO individual observation is insufficient for the simultaneous retrieval of surface's PC weight coefficients and multiple aerosol parameters (other than Vtotal). In contrast, with multiple observations for the same location from TEMPO in multiple consecutive days, 1-3 additional aerosol parameters could be retrieved. Consequently, a self-adjustable aerosol retrieval algorithm to account for surface types, AOD conditions, and multiple-consecutive observations is recommended to derive

3D spectrum imaging of multi-wall carbon nanotube coupled π-surface modes utilising electron energy-loss spectra acquired using a STEM/Enfina system

International Nuclear Information System (INIS)

Seepujak, A.; Bangert, U.; Gutierrez-Sosa, A.; Harvey, A.J.; Blank, V.D.; Kulnitskiy, B.A.; Batov, D.V.

2005-01-01

Numerous studies have utilised electron energy-loss (EEL) spectra acquired in the plasmon (2-10 eV) regime in order to probe delocalised π-electronic states of multi-wall carbon nanotubes (MWCNTs). Interpretation of electron energy loss (EEL) spectra of MWCNTs in the 2-10 eV regime. Carbon (accepted for publication); Blank et al. J. Appl. Phys. 91 (2002) 1657). In the present contribution, EEL spectra were acquired from a 2D raster defined on a bottle-shaped MWCNT, using a Gatan UHV Enfina system attached to a dedicated scanning transmission electron microscope (STEM). The technique utilised to isolate and sequentially filter each of the volume and surface resonances is described in detail. Utilising a scale for the intensity of a filtered mode enables one to 'see' the distribution of each resonance in the raster. This enables striking 3D resonance-filtered spectrum images (SIs) of π-collective modes to be observed. Red-shift of the lower energy split π-surface resonance provides explicit evidence of π-surface mode coupling predicted for thin graphitic films (Lucas et al. Phys. Rev. B 49 (1994) 2888). Resonance-filtered SIs are also compared to non-filtered SIs with suppressed surface contributions, acquired utilising a displaced collector aperture. The present filtering technique is seen to isolate surface contributions more effectively, and without the significant loss of statistics, associated with the displaced collector aperture mode. Isolation of collective modes utilising 3D resonance-filtered spectrum imaging, demonstrates a valuable method for 'pinpointing' the location of discrete modes in irregularly shaped nanostructures

Good abundances from bad spectra - I. Techniques

Science.gov (United States)

Jones, J. Bryn; Gilmore, Gerard; Wyse, Rosemary F. G.

1996-01-01

Stellar spectra derived from multiple-object fibre-fed spectroscopic radial-velocity surveys, of the type feasible with, among other examples, AUTOFIB, 2dF, HYDRA, NESSIE, and the Sloan survey, differ significantly from those traditionally used for determination of stellar abundances. The spectra tend to be of moderate resolution (around 1A) and signal-to-noise ratio (around 10-20 per resolution element), and cannot usually have reliable continuum shapes determined over wavelength ranges in excess of a few tens of Angstroms. None the less, with care and a calibration of stellar effective temperature from photometry, independent of the spectroscopy, reliable iron abundances can be derived. We have developed techniques to extract true iron abundances and surface gravities from low-signal-to-noise ratio, intermediate-resolution spectra of G-type stars in the 4000-5000A wavelength region. Spectroscopic indices sensitive to iron abundance and gravity are defined from a set of narrow (few-several A wide) wavelength intervals. The indices are calibrated theoretically using synthetic spectra. Given adequate data and a photometrically determined effective temperature, one can derive estimates of the stellar iron abundance and surface gravity. We have also defined a single abundance indicator for the analysis of very low-signal-to-noise ratio spectra; with the further assumption of a value for the stellar surface gravity, this is able to provide useful iron abundance information from spectra having signal-to-noise ratios as low as 10 (1-A elements). The theoretical basis and calibration using synthetic spectra are described in this paper. The empirical calibration of these techniques by application to observational data is described in a separate paper (Jones, Wyse & Gilmore). The technique provides precise iron abundances, with zero-point correct to ~0.1 dex, and is reliable, with typical uncertainties being <~0.2 dex. A derivation of the in situ thick disc metallicity

Absorption spectra for collinear (nonreactive) H3: Comparison between quantal and classical calculations

International Nuclear Information System (INIS)

Engel, V.; Bacic, Z.; Schinke, R.; Shapiro, M.

1985-01-01

Absorption spectra for the collinear (nonreactive) H+H 2 →H/sup number-sign/ 3 →H+H 2 are calculated quantum mechanically, using the Siegbahn--Liu--Truhlar--Horowitz (SLTH) ab initio potential and a model H( 3 surface as the ground and excited H 3 surface, respectively. They are compared to classical spectra previously computed by Mayne, Poirier, and Polanyi using the same potential energy surfaces [J. Chem. Phys. 80, 4025 (1984)]. The spectra are calculated at several collision energies and for both H+H 2 (v = 0) and H+H 2 (v = 1). The quantal and classical spectra are shown to agree with respect to basic features and trends. Nevertheless, the two sets of spectra differ considerably in their overall appearance because of some purely quantum aspects of the H+H 2 system

Dye-Sensitized Solar Cells Based on Bi4Ti3O12

Directory of Open Access Journals (Sweden)

Zeng Chen

2011-01-01

Full Text Available Bismuth titanate (Bi4Ti3O12 particles were synthesized by hydrothermal treatment and nanoporous thin films were prepared on conducting glass substrates. The structures and morphologies of the samples were examined with X-ray diffraction and scanning electron microscope (SEM. Significant absorbance spectra emerged in visible region which indicated the efficient sensitization of Bi4Ti3O12 with N3 dye. Surface photovoltaic properties of the samples were investigated by surface photovoltage. The results further indicate that N3 can extend the photovoltaic response range of Bi4Ti3O12 nanoparticles to the visible region, which shows potential application in dye-sensitized solar cell. As a working electrode in dye-sensitized solar cells (DSSCs, the overall efficiency reached 0.48% after TiO2 modification.

Hydrothermal synthesis and photoelectric properties of BiVO4 with different morphologies: An efficient visible-light photocatalyst

International Nuclear Information System (INIS)

Fan Haimei; Wang Dejun; Wang Lingling; Li Haiyan; Wang Ping; Jiang Tengfei; Xie Tengfeng

2011-01-01

Different morphologies of monoclinic BiVO 4 with smaller size were hydrothermal synthesized by simply adjusting the amount of surfactant (polyvinyl pyrrolidone PVP K30) added. The detailed field emission scanning electron microscope (FESEM) analysis revealed that the amount of PVP added could significantly affect the morphology and size of BiVO 4 . Their photocatalytic activities were evaluated by the decolorization of methylene blue (MB) aqueous solution under visible-light irradiation (λ > 400 nm), and the as-prepared sample with well-assembled flower-like morphology showed a much higher photocatalytic activity due to larger specific surface area and higher separation efficiency of photo-induced carriers. The relationship between the behavior of photo-induced carriers and photocatalytic activity was studied using the surface photovoltage spectroscopy (SPS) and corresponding phase spectra.

The effect of nonlocal dielectric response on the surface-enhanced Raman and fluorescence spectra of molecular systems

Science.gov (United States)

Wei, Yong; Pei, Huan; Li, Li; Zhu, Yanying

2018-06-01

We present a theoretical study on the influence of the nonlocal dielectric response on surface-enhanced resonant Raman scattering (SERRS) and fluorescence (SEF) spectra of a model molecule confined in the center of a Ag nanoparticle (NP) dimer. In the simulations, the nonlocal dielectric response caused by the electron–hole pair generation in Ag NPs was computed with the d-parameter theory, and the scattering spectra of a model molecule representing the commonly used fluorescent dye rhodamine 6G (R6G) were obtained by density-matrix calculations. The influence of the separation between Ag NP dimers on the damping rate and scattering spectra with and without the nonlocal response were systematically analyzed. The results show that the nonlocal dielectric response is very sensitive to the gap distance of the NP dimers, and it undergoes much faster decay with the increase of the separation than the radiative and energy transfer rates. The Raman and fluorescence peaks as simulated with the nonlocal dielectric response are relative weaker than that without the nonlocal effect for smaller NP separations because the extra decay rates of the nonlocal effect could reduce both the population of the excited state and the interband coherence between the ground and excited states. Our result also indicates that the nonlocal effect is more prominent on the SEF process than the SERRS process.

Preparation and photoelectric properties of p-CaFe2O4/n-WO3 composites

International Nuclear Information System (INIS)

Wan, Ruiqin; Jia, Caihong; Zhang, Weifeng

2012-01-01

Highlights: ► Surface photovoltage spectroscopy investigation on p-CaFe 2 O 4 /n-WO 3 composites. ► The photovoltaic response is enhanced in p-CaFe 2 O 4 /n-WO 3 composites. ► The multielectron process and high rate of carrier migration in WO 3 . - Abstract: Composites of p-CaFe 2 O 4 /n-WO 3 are prepared via a sol–gel technique. Their structures and optical properties are characterized with X-ray diffraction, scanning electron microscopy and UV–vis absorption spectroscopy. The photoelectric characteristics are investigated by surface photovoltage spectroscopy combined with electric field induced surface photovoltage spectroscopy. The results indicate that CaFe 2 O 4 can well form a p–n type composite with WO 3 , and the intensity and spectral region of surface photovoltaic response for the composites are strongly dependent on the molar ratio of two components. The enhancement in photoelectric properties and the effective separation of photogenerated carriers could be attributed to the energy level matching between the two components, multielectron process and the high migration rate in WO 3 .

Photoinduced surface voltage mapping study for large perovskite single crystals

Energy Technology Data Exchange (ETDEWEB)

Liu, Xiaojing; Liu, Yucheng; Gao, Fei; Yang, Zhou [Key Laboratory of Applied Surface and Colloid Chemistry, National Ministry of Education, Shaanxi Engineering Laboratory for Advanced Energy Technology, School of Materials Science and Engineering, Shaanxi Normal University, Xi' an 710062 (China); Liu, Shengzhong, E-mail: liusz@snnu.edu.cn [Key Laboratory of Applied Surface and Colloid Chemistry, National Ministry of Education, Shaanxi Engineering Laboratory for Advanced Energy Technology, School of Materials Science and Engineering, Shaanxi Normal University, Xi' an 710062 (China); Dalian Institute of Chemical Physics, iChEM, Dalian National Laboratory for Clean Energy, Chinese Academy of Sciences, Dalian 116023 (China)

2016-05-02

Using a series of illumination sources, including white light (tungsten-halogen lamp), 445-nm, 532-nm, 635-nm, and 730-nm lasers, the surface photovoltage (SPV) images were mapped for centimeter-sized CH{sub 3}NH{sub 3}PbX{sub 3} (X = Cl, Br, I) perovskite single crystals using Kelvin probe force microscopy. The significant SPV signals were observed to be wavelength-dependent. We attribute the appreciable SPV to the built-in electric field in the space charge region. This study shines light into the understanding of photoinduced charge generation and separation processes at nanoscale to help advance the development of perovskite solar cells, optoelectronics, laser, photodetector, and light-emitting diode (LED).

Spectra investigation on surface characteristics of graphene oxide nanosheets treated with tartaric, malic and oxalic acids.

Science.gov (United States)

Teng, Xiyao; Yan, Manqing; Bi, Hong

2014-01-24

The surface characteristics of graphene oxide nanosheets (GO) treated respectively with tartaric acid, malic acid and oxalic acid, have been investigated by mainly using optical spectroscopic methods including Fourier transform infrared spectroscopy (FT-IR), Ultraviolet-visible (UV-Vis) absorption and Raman spectroscopy. Additionally, the electrochemical property of the products has also been studied. The data revealed that oxygen-containing groups such as OH, COOH and CO on the GO surface have been almost removed and thus reduced graphene oxide nanosheets (RGN) were obtained. Interestingly, the number of sp(2) domains of RGN increases as treated by tartaric acidspectra result of the tendency of surface conjugated degree alteration. We claim that the difference in both SH and IC among these acids is the main reason for the diverse surface characteristics as well as the improved Cs of the RGN. Copyright © 2013 Elsevier B.V. All rights reserved.

Velocity Spectra in the Unstable Planetary Boundary Layer

DEFF Research Database (Denmark)

Højstrup, Jørgen

1982-01-01

Models for velocity spectra of all three components in the lower half of the unstable PBL are presented. The model spectra are written as a sum of two parts, nS(n) = A(fi, z/zi)w*2 + B(f, z/zi)u*02, a mixed layer part with a stability dependence, and a surface layer part without stability...

Highly Efficient Perovskite-Perovskite Tandem Solar Cells Reaching 80% of the Theoretical Limit in Photovoltage.

Science.gov (United States)

Rajagopal, Adharsh; Yang, Zhibin; Jo, Sae Byeok; Braly, Ian L; Liang, Po-Wei; Hillhouse, Hugh W; Jen, Alex K-Y

2017-09-01

Organic-inorganic hybrid perovskite multijunction solar cells have immense potential to realize power conversion efficiencies (PCEs) beyond the Shockley-Queisser limit of single-junction solar cells; however, they are limited by large nonideal photovoltage loss (V oc,loss ) in small- and large-bandgap subcells. Here, an integrated approach is utilized to improve the V oc of subcells with optimized bandgaps and fabricate perovskite-perovskite tandem solar cells with small V oc,loss . A fullerene variant, Indene-C 60 bis-adduct, is used to achieve optimized interfacial contact in a small-bandgap (≈1.2 eV) subcell, which facilitates higher quasi-Fermi level splitting, reduces nonradiative recombination, alleviates hysteresis instabilities, and improves V oc to 0.84 V. Compositional engineering of large-bandgap (≈1.8 eV) perovskite is employed to realize a subcell with a transparent top electrode and photostabilized V oc of 1.22 V. The resultant monolithic perovskite-perovskite tandem solar cell shows a high V oc of 1.98 V (approaching 80% of the theoretical limit) and a stabilized PCE of 18.5%. The significantly minimized nonideal V oc,loss is better than state-of-the-art silicon-perovskite tandem solar cells, which highlights the prospects of using perovskite-perovskite tandems for solar-energy generation. It also unlocks opportunities for solar water splitting using hybrid perovskites with solar-to-hydrogen efficiencies beyond 15%. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Scaling properties of velocity and temperature spectra above the surface friction layer in a convective atmospheric boundary layer

Directory of Open Access Journals (Sweden)

K. G. McNaughton

2007-06-01

Full Text Available We report velocity and temperature spectra measured at nine levels from 1.42 meters up to 25.7 m over a smooth playa in Western Utah. Data are from highly convective conditions when the magnitude of the Obukhov length (our proxy for the depth of the surface friction layer was less than 2 m. Our results are somewhat similar to the results reported from the Minnesota experiment of Kaimal et al. (1976, but show significant differences in detail. Our velocity spectra show no evidence of buoyant production of kinetic energy at at the scale of the thermal structures. We interpret our velocity spectra to be the result of outer eddies interacting with the ground, not "local free convection".

We observe that velocity spectra represent the spectral distribution of the kinetic energy of the turbulence, so we use energy scales based on total turbulence energy in the convective boundary layer (CBL to collapse our spectra. For the horizontal velocity spectra this scale is (z_i ε_o^2/3, where z_i is inversion height and ε_o is the dissipation rate in the bulk CBL. This scale functionally replaces the Deardorff convective velocity scale. Vertical motions are blocked by the ground, so the outer eddies most effective in creating vertical motions come from the inertial subrange of the outer turbulence. We deduce that the appropriate scale for the peak region of the vertical velocity spectra is (z ε_o^2/3 where z is height above ground. Deviations from perfect spectral collapse under these scalings at large and small wavenumbers are explained in terms of the energy transport and the eddy structures of the flow.

We find that the peaks of the temperature spectra collapse when wavenumbers are scaled using (z^1/2 z_i^1/2. That is, the lengths of the thermal structures depend on both the lengths of the

Investigation of the optical properties of InAs/InGaAs/GaAs quantum dot in quantum well multilayer structures for infrared photodetectors

KAUST Repository

Ivanov, Ts

2012-03-29

A detailed study of InAs/InGaAs quantum dots in quantum well (DWELL) structures grown on GaAs substrates for infrared photodetectors was performed using surface photovoltage (SPV) spectroscopy. Three types of samples were investigated: as-grown, and annealed with dielectric coating SiO 2 or SiN. The annealing resulted in intermixing of the material components. The amplitude and phase SPV spectra were measured at room temperature under various experimental conditions. The comparison of the SPV with the photoluminescence (PL) spectra allows one to conclude that the spectral features are due to optical transitions in the DWELL structure. The blueshift observed of these features in the intermixed samples implies that the energy levels responsible for the transitions change correspondingly due to the intermixing process. The interface band-bending in the samples and the mechanisms of the carrier dynamics were determined by a comparative analysis of the SPV amplitude and phase spectra, using our vector model for representation of the SPV signal. © Published under licence by IOP Publishing Ltd.

Investigation of the optical properties of InAs/InGaAs/GaAs quantum dot in quantum well multilayer structures for infrared photodetectors

KAUST Repository

Ivanov, Ts; Borissov, K.; David, J P R; Donchev, V.; Germanova, K.; Hongpinyo, V.; Ooi, Boon S.; Tellaleva, Ts; Vines, P.

2012-01-01

A detailed study of InAs/InGaAs quantum dots in quantum well (DWELL) structures grown on GaAs substrates for infrared photodetectors was performed using surface photovoltage (SPV) spectroscopy. Three types of samples were investigated: as-grown, and annealed with dielectric coating SiO 2 or SiN. The annealing resulted in intermixing of the material components. The amplitude and phase SPV spectra were measured at room temperature under various experimental conditions. The comparison of the SPV with the photoluminescence (PL) spectra allows one to conclude that the spectral features are due to optical transitions in the DWELL structure. The blueshift observed of these features in the intermixed samples implies that the energy levels responsible for the transitions change correspondingly due to the intermixing process. The interface band-bending in the samples and the mechanisms of the carrier dynamics were determined by a comparative analysis of the SPV amplitude and phase spectra, using our vector model for representation of the SPV signal. © Published under licence by IOP Publishing Ltd.

Correlation of tunneling spectra with surface nanomorphology and doping in thin YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} films

Energy Technology Data Exchange (ETDEWEB)

Sharoni, A.; Millo, O. [Hebrew Univ., Jerusalem (Israel). Racah Inst. of Physics; Koren, G. [Technion-Israel Inst. of Tech., Haifa (Israel). Dept. of Physics

2001-06-01

Tunneling spectra measured on thin epitaxial YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} films are found to exhibit strong spatial variations, showing U- and V-shaped gaps as well as zero-bias conductance peaks typical of a d-wave superconductor. A full correspondence is found between the tunneling spectra and the surface morphology down to a level of a unit-cell step. Splitting of the zero-bias conductance peak is seen in optimally-doped and overdoped films, but not in the underdoped ones, suggesting that there is no transition to a state of broken time-reversal symmetry in the underdoped regime. (orig.)

Resonance Raman and surface-enhanced resonance Raman spectra of LH2 antenna complex from Rhodobacter sphaeroides and Ectothiorhodospira sp. excited in the Qx and Qy transitions.

Science.gov (United States)

Chumanov, G; Picorel, R; Ortiz de Zarate, I; Cotton, T M; Seibert, M

2000-05-01

Well-resolved vibrational spectra of LH2 complex isolated from two photosynthetic bacteria, Rhodobacter sphaeroides and Ectothiorhodospira sp., were obtained using surface-enhanced resonance Raman scattering (SERRS) exciting into the Qx and the Qy transitions of bacteriochlorophyll a. High-quality SERRS spectra in the Qy region were accessible because the strong fluorescence background was quenched near the roughened Ag surface. A comparison of the spectra obtained with 590 nm and 752 nm excitation in the mid- and low-frequency regions revealed spectral differences between the two LH2 complexes as well as between the LH2 complexes and isolated bacteriochlorophyll a. Because peripheral modes of pigments contribute mainly to the low-frequency spectral region, frequencies and intensities of many vibrational bands in this region are affected by interactions with the protein. The results demonstrate that the microenvironment surrounding the pigments within the two LH2 complexes is somewhat different, despite the fact that the complexes exhibit similar electronic absorption spectra. These differences are most probably due to specific pigment-pigment and pigment-protein interactions within the LH2 complexes, and the approach might be useful for addressing subtle static and dynamic structural variances between pigment-protein complexes from different sources or in complexes altered chemically or genetically.

[Micro-Raman and fluorescence spectra of several agrochemicals].

Science.gov (United States)

Xiao, Yi-lin; Zhang, Peng-xiang; Qian, Xiao-fan

2004-05-01

Raman and fluorescence spectra from several agrochemicals were measured, which are sold for the use in vegetables, fruits and grains. Characteristic vibration Raman peaks from some of the agrochemicals were recorded, hence the spectra can be used for their identification. Other marketed agrochemicals demonstrated strong fluorescence under 514.5 nm excitation. It was found that the fluorescence spectra of the agrochemicals are very different. According to these results one can detect the trace amount of agrochemicals left on the surface of fruits, vegetables and grains in situ and conveniently.

Geal: A general program for the analysis of alpha spectra

International Nuclear Information System (INIS)

Garcia-Torano, E.; Acena Barrenechea, M.L.

1978-01-01

A computing program for analysis and representation of alpha spectra obtained with surface barrier detectors is described. Several methods for fitting spectra are studied. A monoenergetic line or a doublet previously fitted has been used as a standard for the analyses of all kind of spectra. Some examples of application as well as a list of the program are shown. The program has been written in Fortran V language. (author)

Principal spectra describing magnetooptic permittivity tensor in cubic crystals

Energy Technology Data Exchange (ETDEWEB)

Hamrlová, Jana [Nanotechnology Centre, VSB – Technical University of Ostrava, listopadu 15, Ostrava, 708 33 Czech Republic (Czech Republic); IT4Innovations Centre, VSB – Technical University of Ostrava, listopadu 15, Ostrava, 708 33 Czech Republic (Czech Republic); Legut, Dominik [IT4Innovations Centre, VSB – Technical University of Ostrava, listopadu 15, Ostrava, 708 33 Czech Republic (Czech Republic); Veis, Martin [Faculty of Mathematics and Physics, Charles University, Ke Karlovu 3, Prague, 121 16 Czech Republic (Czech Republic); Pištora, Jaromír [Nanotechnology Centre, VSB – Technical University of Ostrava, listopadu 15, Ostrava, 708 33 Czech Republic (Czech Republic); Hamrle, Jaroslav, E-mail: jaroslav.hamrle@vsb.cz [IT4Innovations Centre, VSB – Technical University of Ostrava, listopadu 15, Ostrava, 708 33 Czech Republic (Czech Republic); Faculty of Mathematics and Physics, Charles University, Ke Karlovu 3, Prague, 121 16 Czech Republic (Czech Republic); Department of Physics, VSB – Technical University of Ostrava, 17. listopadu 15, Ostrava, 708 33 Czech Republic (Czech Republic)

2016-12-15

We provide unified phenomenological description of magnetooptic effects being linear and quadratic in magnetization. The description is based on few principal spectra, describing elements of permittivity tensor up to the second order in magnetization. Each permittivity tensor element for any magnetization direction and any sample surface orientation is simply determined by weighted summation of the principal spectra, where weights are given by crystallographic and magnetization orientations. The number of principal spectra depends on the symmetry of the crystal. In cubic crystals owning point symmetry we need only four principal spectra. Here, the principal spectra are expressed by ab initio calculations for bcc Fe, fcc Co and fcc Ni in optical range as well as in hard and soft x-ray energy range, i.e. at the 2p- and 3p-edges. We also express principal spectra analytically using modified Kubo formula.

Estimates of Uncertainties in Analysis of Positron Lifetime Spectra for Metals

DEFF Research Database (Denmark)

Eldrup, Morten Mostgaard; Huang, Y. M.; McKee, B. T. A.

1978-01-01

by excluding the peak regions of the spectra from the analysis. The influence of using incorrect source-surface components in the analysis may on the other hand be reduced by including the peak regions of the spectra. A main conclusion of the work is that extreme caution should be exercised to avoid......The effects of uncertainties and errors in various constraints used in the analysis of multi-component life-time spectra of positrons annihilating in metals containing defects have been investigated in detail using computer simulated decay spectra and subsequent analysis. It is found...... that the errors in the fitted values of the main components lifetimes and intensities introduced from incorrect values of the instrumental resolution function and of the source-surface components can easily exceed the statistical uncertainties. The effect of an incorrect resolution function may be reduced...

Electronic Raman spectra in iron-based superconductors with two-orbital model

International Nuclear Information System (INIS)

Lu Hongyan; Wang Da; Chen San; Wang Wei; Gong Pifeng

2011-01-01

Electronic Raman spectra were calculated in orbital space in a microscopic theory. Both Raman spectra and spectra weight were presented. Raman spectra for the gap symmetries are different from each other. The results can help decide the gap symmetry by comparing with experiments. Electronic Raman spectra in iron-based superconductors with two-orbital model is discussed. In the orbital space, some possible pairing symmetries of the gap are selected. To further discriminate them, electronic Raman spectra and spectra weight at Fermi surface (FS) which helps understand the Raman spectra are calculated in each case. From the low energy threshold, the number of Raman peaks, and the low frequency power law behavior, we can judge whether it is full gap or nodal gap, and even one gap or multi-gaps. The results provide useful predictions for comparison with experiments.

Global Learning Spectral Archive- A new Way to deal with Unknown Urban Spectra -

Science.gov (United States)

Jilge, M.; Heiden, U.; Habermeyer, M.; Jürgens, C.

2015-12-01

Rapid urbanization processes and the need of identifying urban materials demand urban planners and the remote sensing community since years. Urban planners cannot overcome the issue of up-to-date information of urban materials due to time-intensive fieldwork. Hyperspectral remote sensing can facilitate this issue by interpreting spectral signals to provide information of occurring materials. However, the complexity of urban areas and the occurrence of diverse urban materials vary due to regional and cultural aspects as well as the size of a city, which makes identification of surface materials a challenging analysis task. For the various surface material identification approaches, spectral libraries containing pure material spectra are commonly used, which are derived from field, laboratory or the hyperspectral image itself. One of the requirements for successful image analysis is that all spectrally different surface materials are represented by the library. Currently, a universal library, applicable in every urban area worldwide and taking each spectral variability into account, is and will not be existent. In this study, the issue of unknown surface material spectra and the demand of an urban site-specific spectral library is tackled by the development of a learning spectral archive tool. Starting with an incomplete library of labelled image spectra from several German cities, surface materials of pure image pixels will be identified in a hyperspectral image based on a similarity measure (e.g. SID-SAM). Additionally, unknown image spectra of urban objects are identified based on an object- and spectral-based-rule set. The detected unknown surface material spectra are entered with additional metadata, such as regional occurrence into the existing spectral library and thus, are reusable for further studies. Our approach is suitable for pure surface material detection of urban hyperspectral images that is globally applicable by taking incompleteness into account

Temperature dependent analysis of three classes of fluorescence spectra from p-6P nanofiber films

DEFF Research Database (Denmark)

Balzer, F.; Pogantsch, Alexander; Rubahn, Horst-Günter

2009-01-01

devices, given that the spectra are reproducible for varying surface temperatures. A detailed investigation as a function of surface temperature variation from 300 to 30 K reveals three classes of spectra: (a) spectra with well resolved excitonic peaks, which shift 35meV to the blue with decreasing...... temperature, (b) similar spectra with an additional intermediate broadening around 150 K, and (c) excitonic spectra similar to (b), but with a green defect emission band. Quantitative fitting of type (a) spectra results in an  exciton–phonon coupling factor of 80 ± 10meV and an average phonon temperature of Θ...... = 670 ± 70 K. The Huang–Rhys factor decreases linearly from 1.2 at 300 K to 1.0 at 30 K. Fitting of type (b) spectra reveals that the apparent intermediate temperature broadening is due to additional fluorescence peaks, the relative importance of which increasing with decreasing temperature....

Simultaneous in-bore rail and insulator spectra from a railgun plasma armature

International Nuclear Information System (INIS)

Keefer, D.; Sedghinasah, A.; Crawford, R.

1991-01-01

This paper reports on absolute spectral radiance measurements obtained simultaneously at the rail and insulator surface of the UTSI 1 cm square-bore railgun. The emission spectra were obtained through the use of quartz optical fibers which penetrated both the rail and the insulator walls. The spectral characteristics of the rail and insulator emission are quite similar but differ significantly in magnitude. A detailed plasma radiation model was used to analyze these spectra. In order to obtain reasonable agreement between the model predictions and the experimental spectra, it was necessary to assume that these existed a broadband absorbing layer at the insulator surface. This result suggests a new physical model of the plasma armature in which insulator ablation leads to significant 3-dimensional flow and affects the shape of the current emission pattern on the rail surfaces

Estimates of uncertainties in analysis of positron lifetime spectra for metals

International Nuclear Information System (INIS)

Eldrup, M.; Huang, Y.M.; McKee, B.T.A.

1978-01-01

The effects of uncertainties and errors in various constraints used in the analysis of multi-component life-time spectra of positrons annihilating in metals containing defects have been investigated in detail using computer simulated decay spectra and subsequent analysis. It is found that the errors in the fitted values of the main component lifetimes and intensities introduced from incorrect values of the instrumental resolution function and off the source-surface components can easily exceed the statistic uncertainties. The effect of an incorrect resolution function may be reduced by excluding the peak regions of the spectra from the analysis. The influence of using incorrect source-surface components in the analysis may on the other hand be reduced by including the peak regions of the spectra. A main conclusion of the work is that extreme caution should be exercised to avoid introducing large errors through the constraints used in the analysis of experimental lifetime data. (orig.) [de

A catalogue of photon spectra inside water or lung phantoms

International Nuclear Information System (INIS)

Petoussi, N.; Zankl, M.; Panzer, W.; Drexler, G.

1991-01-01

This catalogue contains a large amount of photon spectra inside a cubic (30 cm side) and a cuboid (40x20x40 cm 3 ) water or lung phantom, calculated using the Monte Carlo program KASTENSPEC. The beams considered here are mainly those relevant to X-ray diagnosis, nuclear medicine and some other applications. The spectra are shown in tabular form for 10, 20 or 50 keV steps for different depths between the entrance surface and the exit surface and for one or two off-axis distances. The alteration of the spectrum with depth, field size and phantom size is discussed. (orig.)

Visible and Near-IR Reflectance Spectra of Smectite Acquired Under Dry Conditions for Interpretation of Martian Surface Mineralogy

Science.gov (United States)

Morris, Richard V.; Achilles, Cherie N; Archer, Paul D.; Graff, Trevor G.; Agresti, David G.; Ming, Douglas W; Golden, Dadi C.; Mertzman, Stanley A.

2011-01-01

Visible and near-IR (VNIR) spectra from the MEx OMEGA and the MRO CRISM hyper-spectral imaging instruments have spectral features associated with the H2O molecule and M OH functional groups (M = Mg, Fe, Al, and Si). Mineralogical assignments of martian spectral features are made on the basis of laboratory VNIR spectra, which were often acquired under ambient (humid) conditions. Smectites like nontronite, saponite, and montmorillionite have interlayer H2O that is exchangeable with their environment, and we have acquired smectite reflectance spectra under dry environmental conditions for interpretation of martian surface mineralogy. We also obtained chemical, Moessbauer (MB), powder X-ray diffraction (XRD), and thermogravimetric (TG) data to understand variations in spectral properties. VNIR spectra were recorded in humid lab air at 25-35C, in a dynamic dry N2 atmosphere (50-150 ppmv H2O) after exposing the smectite samples (5 nontronites, 3 montmorillionites, and 1 saponite) to that atmosphere for up to approximately l000 hr each at 25-35C, approximately 105C, and approximately 215C, and after re-exposure to humid lab air. Heating at 105C and 215C for approximately 1000 hr is taken as a surrogate for geologic time scales at lower temperatures. Upon exposure to dry N2, the position and intensity of spectral features associated with M-OH were relatively insensitive to the dry environment, and the spectral features associated with H2O (e.g., approximately 1.90 micrometers) decreased in intensity and are sometimes not detectable by the end of the 215C heating step. The position and intensity of H2O spectral features recovered upon re-exposure to lab air. XRD data show interlayer collapse for the nontronites and Namontmorillionites, with the interlayer remaining collapsed for the latter after re-exposure to lab air. The interlayer did not collapse for the saponite and Ca-montmorillionite. TG data show that the concentration of H2O derived from structural OH was invariant

Synthesis of Zn-doped TiO{sub 2} microspheres with enhanced photovoltaic performance and application for dye-sensitized solar cells

Energy Technology Data Exchange (ETDEWEB)

Zhang Yu [State Key Laboratory of Theoretical and Computational Chemistry, College of Chemistry, Jilin University, Changchun 130023 (China); Wang Lingling [State Key Laboratory of Theoretical and Computational Chemistry, College of Chemistry, Jilin University, Changchun 130023 (China); State Key Laboratory of Supramolecular Structure and Materials, College of Chemistry, Jilin University, Changchun 130012 (China); Liu Bingkun; Zhai Jiali; Fan Haimei; Wang Dejun; Lin Yanhong [State Key Laboratory of Theoretical and Computational Chemistry, College of Chemistry, Jilin University, Changchun 130023 (China); Xie Tengfeng, E-mail: xietf@jlu.edu.cn [State Key Laboratory of Theoretical and Computational Chemistry, College of Chemistry, Jilin University, Changchun 130023 (China)

2011-07-15

Highlights: > Near-monodisperse Zn-doped TiO{sub 2} microspheres have been synthesized. > The photovoltaic properties of the samples were examined by SPS, FISPS and TPV measurements. > Surface photovoltage results revealed Zn doping can promote charge transfer in TiO{sub 2} film electrode. - Abstract: Zn-doped TiO{sub 2} microspheres have been synthesized by introducing a trace amount of zinc nitrate hexahydrate to the reaction system. Scanning electron microscope (SEM), field-emission scanning electron microscope (FESEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) have been utilized to characterize the samples. Both surface photovoltage spectroscopy (SPS) technique based on lock-in amplifier and transient photovoltage (TPV) measurement reveal that the slight doping of Zn can promote the separation of photo-generated charges as well as restrain the recombination due to the strong interface built-in electric field and the decreasing of surface trap states. The photovoltaic parameters of dye-sensitized solar cells (DSSCs) based on Zn-doped TiO{sub 2} are significantly better, compared to that of a cell based on undoped TiO{sub 2}. The relation between the performance of DSSCs and their photovoltaic properties is also discussed.

Preparation and photoelectric properties of p-CaFe{sub 2}O{sub 4}/n-WO{sub 3} composites

Energy Technology Data Exchange (ETDEWEB)

Wan, Ruiqin; Jia, Caihong [Key Laboratory of Photovoltaic Materials of Henan Province and School of Physics and Electronics, Henan University, Kaifeng 475004 (China); Zhang, Weifeng, E-mail: wfzhang@henu.edu.cn [Key Laboratory of Photovoltaic Materials of Henan Province and School of Physics and Electronics, Henan University, Kaifeng 475004 (China)

2012-12-15

Highlights: Black-Right-Pointing-Pointer Surface photovoltage spectroscopy investigation on p-CaFe{sub 2}O{sub 4}/n-WO{sub 3} composites. Black-Right-Pointing-Pointer The photovoltaic response is enhanced in p-CaFe{sub 2}O{sub 4}/n-WO{sub 3} composites. Black-Right-Pointing-Pointer The multielectron process and high rate of carrier migration in WO{sub 3}. - Abstract: Composites of p-CaFe{sub 2}O{sub 4}/n-WO{sub 3} are prepared via a sol-gel technique. Their structures and optical properties are characterized with X-ray diffraction, scanning electron microscopy and UV-vis absorption spectroscopy. The photoelectric characteristics are investigated by surface photovoltage spectroscopy combined with electric field induced surface photovoltage spectroscopy. The results indicate that CaFe{sub 2}O{sub 4} can well form a p-n type composite with WO{sub 3}, and the intensity and spectral region of surface photovoltaic response for the composites are strongly dependent on the molar ratio of two components. The enhancement in photoelectric properties and the effective separation of photogenerated carriers could be attributed to the energy level matching between the two components, multielectron process and the high migration rate in WO{sub 3}.

Deconvolution of Thermal Emissivity Spectra of Mercury to their Endmember Counterparts measured in Simulated Mercury Surface Conditions

Science.gov (United States)

Varatharajan, I.; D'Amore, M.; Maturilli, A.; Helbert, J.; Hiesinger, H.

2017-12-01

The Mercury Radiometer and Thermal Imaging Spectrometer (MERTIS) payload of ESA/JAXA Bepicolombo mission to Mercury will map the thermal emissivity at wavelength range of 7-14 μm and spatial resolution of 500 m/pixel [1]. Mercury was also imaged at the same wavelength range using the Boston University's Mid-Infrared Spectrometer and Imager (MIRSI) mounted on the NASA Infrared Telescope Facility (IRTF) on Mauna Kea, Hawaii with the minimum spatial coverage of 400-600km/spectra which blends all rocks, minerals, and soil types [2]. Therefore, the study [2] used quantitative deconvolution algorithm developed by [3] for spectral unmixing of this composite thermal emissivity spectrum from telescope to their respective areal fractions of endmember spectra; however, the thermal emissivity of endmembers used in [2] is the inverted reflectance measurements (Kirchhoff's law) of various samples measured at room temperature and pressure. Over a decade, the Planetary Spectroscopy Laboratory (PSL) at the Institute of Planetary Research (PF) at the German Aerospace Center (DLR) facilitates the thermal emissivity measurements under controlled and simulated surface conditions of Mercury by taking emissivity measurements at varying temperatures from 100-500°C under vacuum conditions supporting MERTIS payload. The measured thermal emissivity endmember spectral library therefore includes major silicates such as bytownite, anorthoclase, synthetic glass, olivine, enstatite, nepheline basanite, rocks like komatiite, tektite, Johnson Space Center lunar simulant (1A), and synthetic powdered sulfides which includes MgS, FeS, CaS, CrS, TiS, NaS, and MnS. Using such specialized endmember spectral library created under Mercury's conditions significantly increases the accuracy of the deconvolution model results. In this study, we revisited the available telescope spectra and redeveloped the algorithm by [3] by only choosing the endmember spectral library created at PSL for unbiased model

Beta spectra. II-Positron spectra

International Nuclear Information System (INIS)

Grau, A.; Garcia-Torano, E.

1981-01-01

Using the Fermi theory of beta decay, the beta spectra for 30 positron emitters have been computed, introducing a correction factor for unique forbidden transitions. The spectra are ploted vs. energy, once normalised, and tabulated with the related Fermi functions. The average and median energies are calculated. (author)

Optical characterization of bulk Zn1-xBexTe crystals

International Nuclear Information System (INIS)

Shih, Y C; Huang, Y S; Firszt, F; Legowski, S; Meczynska, H; Tiong, K K

2008-01-01

This paper presents an optical characterization of three bulk sphalerite Zn 1-x Be x Te crystals grown by the modified high pressure Bridgman method. The study was conducted in the near-band-edge interband transition regime using low temperature photoluminescence (PL), temperature-dependent contactless electroreflectance (CER) and/or photoreflectance (PR) in the temperature range of 15-400 K, and surface photovoltage spectroscopy (SPS) at room temperature. PL spectra at low temperatures of the samples investigated consist of an excitonic line, a band due to recombination of free electrons with holes located at shallow acceptors and a broad band related to recombination through deeper level defects. The band-edge excitonic transitions have been observed in the CER/PR spectra. The fundamental transition energies E 0 are determined via lineshape fits to the CER/PR spectra. The values of E 0 at room temperature obtained from CER/PR spectra correspond well to that determined from SPS measurements, and the Be contents x of the samples are determined using a linear equation which describes the room temperature band gap dependence on composition for the Zn 1-x Be x Te alloy system. The parameters describing the temperature dependence of the band-edge excitonic transition energies are evaluated and discussed

BETA SPECTRA. I. Negatrons spectra

International Nuclear Information System (INIS)

Grau Malonda, A.; Garcia-Torano, E.

1978-01-01

Using the Fermi theory of beta decay, the beta spectra for 62 negatrons emitters have been computed introducing a correction factor for unique forbidden transitions. These spectra are plotted vs. energy, once normal i sed, and tabulated with the related Fermi functions. The average and median energies are calculated. (Author)

Intramolecular charge separation in spirobifluorene-based donor–acceptor compounds adsorbed on Au and indium tin oxide electrodes

International Nuclear Information System (INIS)

Heredia, Daniel; Otero, Luis; Gervaldo, Miguel; Fungo, Fernando; Dittrich, Thomas; Lin, Chih-Yen; Chi, Liang-Chen; Fang, Fu-Chuan; Wong, Ken-Tsung

2013-01-01

Surface photovoltage (SPV) measurements were performed with a Kelvin-probe in spirobifluorene-based donor (diphenylamine)–acceptor (dicyano or cyanoacrylic acid moieties) compounds adsorbed from highly diluted solutions onto Au and indium tin oxide electrode surfaces. Strong intramolecular charge separation (negative SPV signals up to more than 0.1 V) due to directed molecule adsorption was observed only for spirobifluorene donor–acceptor compounds with carboxylic acid moiety. SPV signals and onset energies of electronic transitions depended on ambience conditions. - Highlights: ► Fluorene donor–acceptor derivatives were adsorbed at Au and indium tin oxide. ► Surface photovoltage measurements were performed with a Kelvin-probe. ► Strong intra-molecular charge separation was observed. ► SPV signals depended on ambience conditions

Computer enhancement of ESR spectra of magnetite nanoparticles

Energy Technology Data Exchange (ETDEWEB)

Dobosz, B.; Krzyminiewski, R. [Medical Physics Division, Faculty of Physics, Adam Mickiewicz University, Umultowska 85, 61-614 Poznan (Poland); Koralewski, M. [Optics Laboratory, Faculty of Physics, Adam Mickiewicz University, Umultowska 85, 61-614 Poznan (Poland); Hałupka-Bryl, M. [Medical Physics Division, Faculty of Physics, Adam Mickiewicz University, Umultowska 85, 61-614 Poznan (Poland); The PhD Program in Nanoscience and Nanotechnology, The Nanobiomedical Centre, Umultowska 85, 61-614 Poznan (Poland)

2016-06-01

We present ESR measurements of non-interacting magnetic nanoparticle systems. Temperature and orientational dependence of ESR spectra were measured for Fe{sub 3}O{sub 4} nanoparticle coated by dextran or oleic acid, frozen in different magnetic field. Several parameters describing magnetic properties such as g-factor, line width, the anisotropy constant were calculated and discussed. The ESR spectra of investigated nanoparticles were also subjected to Computer Resolution Enhancement Method (CREM). This procedure allows to separate a narrow line on the background of the broad line, which presence in this type of materials was recognized in the recent literature and have been further discussed in the paper. CREM is a valuable tool for monitoring of changes on the surface of magnetic core of nanoparticles. - Highlights: • CREM – a new tool for monitoring of changes on the surface of magnetic core of nanoparticles. • CREM allows to separate a narrow line on the background of the broad line. • Temperature and orientational dependence of ESR spectra of Fe{sub 3}O{sub 4} nanoparticles were measured. • Parameters describing magnetic properties were calculated and discussed.

X-ray absorption spectra and emission spectra of plasmas

International Nuclear Information System (INIS)

Peng Yonglun; Yang Li; Wang Minsheng; Li Jiaming

2002-01-01

The author reports a theoretical method to calculate the resolved absorption spectra and emission spectra (optically thin) of hot dense plasmas. Due to its fully relativistic treatment incorporated with the quantum defect theory, it calculates the absorption spectra and emission spectra for single element or multi-element plasmas with little computational efforts. The calculated absorption spectra of LTE gold plasmas agree well with the experimental ones. It also calculates the optical thin emission spectra of LTE gold plasmas, which is helpful to diagnose the plasmas of relevant ICF plasmas. It can also provide the relevant parameters such as population density of various ionic stages, precise radiative properties for ICF studies

Photogenerated carriers transport behaviors in L-cysteine capped ZnSe core-shell quantum dots

Science.gov (United States)

Shan, Qingsong; Li, Kuiying; Xue, Zhenjie; Lin, Yingying; Yin, Hua; Zhu, Ruiping

2016-02-01

The photoexcited carrier transport behavior of zinc selenide (ZnSe) quantum dots (QDs) with core-shell structure is studied because of their unique photoelectronic characteristics. The surface photovoltaic (SPV) properties of self-assembled ZnSe/ZnS/L-Cys core-shell QDs were probed via electric field induced surface photovoltage and transient photovoltage (TPV) measurements supplemented by Fourier transform infrared, laser Raman, absorption, and photoluminescence spectroscopies. The ZnSe QDs displayed p-type SPV characteristics with a broader stronger SPV response over the whole ultraviolet-to-near-infrared range compared with those of other core-shell QDs in the same group. The relationship between the SPV phase value of the QDs and external bias was revealed in their SPV phase spectrum. The wide transient photovoltage response region from 3.3 × 10-8 to 2 × 10-3 s was closely related to the long diffusion distance of photoexcited free charge carriers in the interfacial space-charge region of the QDs. The strong SPV response corresponding to the ZnSe core mainly originated from an obvious quantum tunneling effect in the QDs.

Analysis of serum from type II diabetes mellitus and diabetic complication using surface-enhanced Raman spectra (SERS)

Science.gov (United States)

Han, H. W.; Yan, X. L.; Dong, R. X.; Ban, G.; Li, K.

2009-03-01

In this paper, we show surface-enhanced Raman spectra (SERS) of serums from type II diabetes mellitus and diabetic complication (coronary disease, glaucoma and cerebral infarction), and analyze the SERS through the multivariate statistical methods of principal component analysis (PCA). In particular, we find that there exist many adenines in these serums, which maybe come from DNA (RNA) damage. The relative intensity of the band at 725±2 cm-1 assigned to adenine is higher for patients than for the healthy volunteers; therefore, it can be used as an important ‘fingerprint’ in order to diagnose these diseases. It is also shown that serums from type II diabetes mellitus group, diabetic complication group and healthy volunteers group can be discriminated by PCA.

Dynamics and fluctuation spectra of electrostatic resistive interchange turbulence

International Nuclear Information System (INIS)

Sydora, R.D.; Leboeuf, J.N.; An, Z.G.; Diamond, P.H.; Lee, G.S.; Hahm, T.S.

1985-11-01

The saturation mechanism for density and potential fluctuation spectra which evolve from linearly unstable electrostatic resistive interchange modes, are investigated using particle simulations. Detailed comparisons of the nonlinear evolution, saturation levels and resultant spectra between two- and three-dimensional sheared magnetic field configurations are made. Significant differences appear. The single rational surface, quasilinear-dominated evolution, fluctuation spectrum is adequately described using a density convection model. For the multiple rational surface case, the potential fluctuations are adequately represented by a balance between the nonlinearly modified source (curvature drive) and linear sink (parallel resistive field line diffusion). An accurate description of the density spectrum requires a mode coupling theory based on the two-point density correlation evolution equation. 24 refs., 15 figs

Conformation and orientation effects in the x-ray photoelectron spectra of organic polymers

International Nuclear Information System (INIS)

Beamson, G.

2001-01-01

Conformation and orientation effects in the XPS spectra of organic polymers are small but can be observed with modem high performance equipment. This paper discusses some of the experimental factors that should be considered when attempting to detect such effects, and describes several recent studies which illustrate the subtle phenomena that can now be observed. Conformation effects, revealed by melting semicrystalline polymer samples in the analysis chamber of an XPS spectrometer, are reported for the valence band and C 1s spectra of nylon 12 and poly(ethylene adipate), and for the valence band spectrum of poly(ethylene succinate). For nylon 12 the changes in the C 2s region of the valence band spectrum are interpreted in terms of disordering of the planar zig-zag conformation of the (CH 2 ) 11 segments of the polymer chain. Pendant group surface orientation effects, detected by angle resolved XPS (with emission angles as low as 5 deg. relative to the sample surface), are reported for poly(2-chloroethyl methacrylate) (PCEMA), poly(lauryl methacrylate) (PLMA) and poly(2-hydroxyethyl methacrylate) (PHEMA). For PCEMA and PLMA the uppermost surfaces are enriched with -CH 2 CH 2 Cl and -(CH 2 ) 11 CH 3 pendant groups respectively, whereas for PHEMA the data suggest relatively few -CH 2 CH 2 OH pendant groups at the surface. The C 1s and Cl 2p spectra of PCEMA reveal surface core level binding energy shifts of - +0.2 eV, and the Cl L 23 M 23 M 23 spectrum a surface Auger kinetic energy shift of ∼ -0.6. The C 1s spectra of PLMA and PHEMA also reveal surface core level shifts and for PLMA this is interpreted in terms of a disordered and open arrangement of the -(CH 2 ) 11 CH 3 pendant groups at the polymer surface. (author)

Many-body effects on the x-ray spectra of metals

International Nuclear Information System (INIS)

Satpathy, S.S.

1982-01-01

The effects of band structure, of a solid surface, of temperature, and of disorder on the many-electron x-ray spectra of metals are evaluated in a change-of-mean-field approximation using a one-dimensional nearest-neighbor tight-binding model of a metal. The x-ray spectral shapes are determined by both the band structure and the final-state interactions. The effect of the band being non-free-electron-like is not felt at the x-ray threshold, but away from it such effects are noticeable. When the core hole is created at the surface, the spectra at the edge exhibit a Nozieres-de Dominicis-type singularity with the appropriate surface phase-shifts. At energies away from the edge, the one-particle effects are prominent with the x-ray emission and absorption spectra closely reflecting the local one-electron density of states. The recoil spectrum of a Fermi sea at a non-zero temperature has less asymmetry than the zero-temperature case. It was found that at ordinary temperatures the reduction of the asymmetry due to the thermal distribution of one-electron states is not very significant. Finally, using a one-dimensional Anderson model, the effect of lattice disorder on the x-ray absorption spectra is studied for the first time. There are two effects: (1) the strong infrared divergence peak is gradually quenched as disorder is increased, and (2) the threshold is broadened because the threshold energies for absorption at different sites in the crystal depend on the varying local lattice environment. It is proposed that the x-ray spectra may be useful as a tool for studying the degree of electron localization in disordered many-electron systems

Enhancing Efficiency of Perovskite Solar Cells via Surface Passivation with Graphene Oxide Interlayer.

Science.gov (United States)

Li, Hao; Tao, Leiming; Huang, Feihong; Sun, Qiang; Zhao, Xiaojuan; Han, Junbo; Shen, Yan; Wang, Mingkui

2017-11-08

Perovskite solar cells have been demonstrated as promising low-cost and highly efficient next-generation solar cells. Enhancing V OC by minimization the interfacial recombination kinetics can further improve device performance. In this work, we for the first time reported on surface passivation of perovskite layers with chemical modified graphene oxides, which act as efficient interlayer to reduce interfacial recombination and enhance hole extraction as well. Our modeling points out that the passivation effect mainly comes from the interaction between functional group (4-fluorophenyl) and under-coordinated Pb ions. The resulting perovskite solar cells achieved high efficient power conversion efficiency of 18.75% with enhanced high open circuit V OC of 1.11 V. Ultrafast spectroscopy, photovoltage/photocurrent transient decay, and electronic impedance spectroscopy characterizations reveal the effective passivation effect and the energy loss mechanism. This work sheds light on the importance of interfacial engineering on the surface of perovskite layers and provides possible ways to improve device efficiency.

Constrained energy minimization applied to apparent reflectance and single-scattering albedo spectra: a comparison

Science.gov (United States)

Resmini, Ronald G.; Graver, William R.; Kappus, Mary E.; Anderson, Mark E.

1996-11-01

Constrained energy minimization (CEM) has been applied to the mapping of the quantitative areal distribution of the mineral alunite in an approximately 1.8 km2 area of the Cuprite mining district, Nevada. CEM is a powerful technique for rapid quantitative mineral mapping which requires only the spectrum of the mineral to be mapped. A priori knowledge of background spectral signatures is not required. Our investigation applies CEM to calibrated radiance data converted to apparent reflectance (AR) and to single scattering albedo (SSA) spectra. The radiance data were acquired by the 210 channel, 0.4 micrometers to 2.5 micrometers airborne Hyperspectral Digital Imagery Collection Experiment sensor. CEM applied to AR spectra assumes linear mixing of the spectra of the materials exposed at the surface. This assumption is likely invalid as surface materials, which are often mixtures of particulates of different substances, are more properly modeled as intimate mixtures and thus spectral mixing analyses must take account of nonlinear effects. One technique for approximating nonlinear mixing requires the conversion of AR spectra to SSA spectra. The results of CEM applied to SSA spectra are compared to those of CEM applied to AR spectra. The occurrence of alunite is similar though not identical to mineral maps produced with both the SSA and AR spectra. Alunite is slightly more widespread based on processing with the SSA spectra. Further, fractional abundances derived from the SSA spectra are, in general, higher than those derived from AR spectra. Implications for the interpretation of quantitative mineral mapping with hyperspectral remote sensing data are discussed.

Electron spectroscopy of nanodiamond surface states

Energy Technology Data Exchange (ETDEWEB)

Belobrov, P.I.; Bursill, L.A.; Maslakov, K.I.; Dementjev, A.P

2003-06-15

Electronic states of nanodiamond (ND) were investigated by PEELS, XPS and CKVV Auger spectra. Parallel electron energy loss spectra (PEELS) show that the electrons inside of ND particles are sp{sup 3} hybridized but there is a surface layer containing distinct hybridized states. The CKVV Auger spectra imply that the HOMO of the ND surface has a shift of 2.5 eV from natural diamond levels of {sigma}{sub p} up to the Fermi level. Hydrogen (H) treatment of natural diamond surface produces a chemical state indistinguishable from that of ND surfaces using CKVV. The ND electronic structure forms {sigma}{sub s}{sup 1}{sigma}{sub p}{sup 2}{pi}{sup 1} surface states without overlapping of {pi}-levels. Surface electronic states, including surface plasmons, as well as phonon-related electronic states of the ND surface are also interesting and may also be important for field emission mechanisms from the nanostructured diamond surface.

Sputtered indium-tin oxide/cadmium telluride junctions and cadmium telluride surfaces

International Nuclear Information System (INIS)

Courreges, F.G.; Fahrenbruch, A.L.; Bube, R.H.

1980-01-01

The properties of indium-tin oxide (ITO)/CdTe junction solar cells prepared by rf sputtering of ITO on P-doped CdTe single-crystal substrates have been investigated through measurements of the electrical and photovoltaic properties of ITO/CdTe and In/CdTe junctions, and of electron beam induced currents (EBIC) in ITO/CdTe junctions. In addition, surface properties of CdTe related to the sputtering process were investigated as a function of sputter etching and thermal oxidation using the techniques of surface photovoltage and photoluminescence. ITO/CdTe cells prepared by this sputtering method consist of an n + -ITO/n-CdTe/p-CdTe buried homojunction with about a 1-μm-thick n-type CdTe layer formed by heating of the surface of the CdTe during sputtering. Solar efficiencies up to 8% have been observed with V/sub 0c/=0.82 V and J/sub s/c=14.5 mA/cm 2 . The chief degradation mechanism involves a decrease in V/sub 0c/ with a transformation of the buried homojunction structure to an actual ITO/CdTe heterojunction

The characterization of tungsten disulfide single crystals doped with gold

International Nuclear Information System (INIS)

Dumcenco, D.O.; Huang, Y.S.; Tiong, K.K.; Liang, C.H.; Chen, C.H.

2007-01-01

Single crystals of WS 2 doped with gold (WS 2 :Au) have been grown by the chemical vapour transport method using iodine as a transporting agent. Hall measurements indicate that the samples are p-type in nature. The doping effect of the materials are characterized by conductivity, surface photovoltage and piezo reflectance measurements. The higher conductivity respect to that of the undoped one suggests that more charge carriers are available for conduction in the doped compound. The surface photovoltage spectrum reveals an impurity level located below the A exciton. The direct band-edge excitonic transition energies for WS 2 :Au show redshifts and the broadening parameters of the excitonic transition features increase due to impurity scattering. (authors)

Probing hot-electron effects in wide area plasmonic surfaces using X-ray photoelectron spectroscopy

Energy Technology Data Exchange (ETDEWEB)

Ayas, Sencer; Cupallari, Andi; Dana, Aykutlu, E-mail: aykutlu@unam.bilkent.edu.tr [UNAM Institute of Materials Science and Nanotechnology, Bilkent University, 06800 Ankara (Turkey)

2014-12-01

Plasmon enhanced hot carrier formation in metallic nanostructures increasingly attracts attention due to potential applications in photodetection, photocatalysis, and solar energy conversion. Here, hot-electron effects in nanoscale metal-insulator-metal (MIM) structures are investigated using a non-contact X-ray photoelectron spectroscopy based technique using continuous wave X-ray and laser excitations. The effects are observed through shifts of the binding energy of the top metal layer upon excitation with lasers of 445, 532, and 650 nm wavelength. The shifts are polarization dependent for plasmonic MIM grating structures fabricated by electron beam lithography. Wide area plasmonic MIM surfaces fabricated using a lithography free route by the dewetting of evaporated Ag on HfO{sub 2} exhibit polarization independent optical absorption and surface photovoltage. Using a simple model and making several assumptions about the magnitude of the photoemission current, the responsivity and external quantum efficiency of wide area plasmonic MIM surfaces are estimated as 500 nA/W and 11 × 10{sup −6} for 445 nm illumination.

Observing the Spectra of MEarth and TRAPPIST Planets with JWST

Science.gov (United States)

Morley, Caroline; Kreidberg, Laura; Rustamkulov, Zafar; Robinson, Tyler D.; Fortney, Jonathan J.

2017-10-01

During the past two years, nine planets close to Earth in radius have been discovered around nearby M dwarfs cooler than 3300 K. These planets include the 7 planets in the TRAPPIST-1 system and two planets discovered by the MEarth survey, GJ 1132b and LHS 1140b (Dittmann et al. 2017; Berta-Thompson et al. 2015; Gillon et al. 2017). These planets are the smallest planets discovered to date that will be amenable to atmospheric characterization with JWST. They span equilibrium temperatures from ˜130 K to >500 K, and radii from 0.7 to 1.43 Earth radii. Some of these planets orbit as distances potentially amenable to surface liquid water, though the actual surface temperatures will depend strongly on the albedo of the planet and the thickness and composition of its atmosphere. The stars they orbit also vary in activity levels, from the quiet LHS 1140b host star to the more active TRAPPIST-1 host star. This set of planets will form the testbed for our first chance to study the diversity of atmospheres around Earth-sized planets. Here, we will present model spectra of these 9 planets, varying the composition and the surface pressure of the atmosphere. We base our elemental compositions on three outcomes of planetary atmosphere evolution in our own solar system: Earth, Titan, and Venus. We calculate the molecular compositions in chemical equilibrium. We present both thermal emission spectra and transmission spectra for each of these objects, and make predictions for the observability of these spectra with different instrument modes with JWST.

VIRTIS on Venus Express thermal emission spectra near 1μm

Science.gov (United States)

Mueller, Nils; Tsang, Constantine; Helbert, Joern; Smrekar, Suzanne; Piccioni, Giuseppe; Drossart, Pierre

2016-10-01

Thermal emission from the surface of Venus is observable through narrow spectral windows close to 1μm. Surface temperature is strongly constrained by surface elevation, due to the thick and dense atmosphere. The data from Visible and InfraRed Thermal Imaging Spectrometer VIRTIS on Venus Express together with altimetry constrain surface emissivity. In VIRTIS observations at 1.02μm, strongly deformed highland plateaus (tesserae) appear to have a lower emissivity consistent with continental crust, an interpretation that implies existence of an early ocean. Comparison between the Magellan stereo digital elevation model (DEM) and altimetry shows that the altimetry height error in rough tesserae greatly exceeds the formal error. In the one tesserae outlier covered by altimetry, DEM, and VIRTIS, the height error could account for the observed emissivity variation. The radiances observed at 1.10 and 1.18μm have a different response to topography, mostly due to spectrally varying absorption in the overlying atmospheric column. Thus if the tesserae have the same emissivity as volcanic plains, its spectrum should be the same as that of plains of the correct surface elevation. In order to investigate this statistically, we create a database of all long exposure duration VIRTIS spectra in the range of 1 - 1.4μm. The spectra are corrected for the ubiquitous straylight from the dayside, based on analysis of spectra showing deep space. Because the 1.10 and 1.18μm peaks are narrow compared to the variation of instrument spectral registration, we fit each spectrum with a synthetic spectrum from an atmospheric radiative transfer model, using wavelength offset and bandwidths as parameters in addition to atmospheric variables. This dataset of ~28 million thermal emission spectra spans a wide range of southern latitudes and night local times, and thus may be useful for studies beyond the question of surface emissivity. A portion of this research was conducted at the Jet Propulsion

INTRIGOSS: A new Library of High Resolution Synthetic Spectra

Science.gov (United States)

Franchini, Mariagrazia; Morossi, Carlo; Di Marcancantonio, Paolo; Chavez, Miguel; GES-Builders

2018-01-01

INTRIGOSS (INaf Trieste Grid Of Synthetic Spectra) is a new High Resolution (HiRes) synthetic spectral library designed for studying F, G, and K stars. The library is based on atmosphere models computed with specified individual element abundances via ATLAS12 code. Normalized SPectra (NSP) and surface Flux SPectra (FSP), in the 4800-5400 Å wavelength range, were computed by means of the SPECTRUM code. The synthetic spectra are computed with an atomic and bi-atomic molecular line list including "bona fide" Predicted Lines (PLs) built by tuning loggf to reproduce very high SNR Solar spectrum and the UVES-U580 spectra of five cool giants extracted from the Gaia-ESO survey (GES). The astrophysical gf-values were then assessed by using more than 2000 stars with homogenous and accurate atmosphere parameters and detailed chemical composition from GES. The validity and greater accuracy of INTRIGOSS NSPs and FSPs with respect to other available spectral libraries is discussed. INTRIGOSS will be available on the web and will be a valuable tool for both stellar atmospheric parameters and stellar population studies.

Library search with regular reflectance IR spectra

International Nuclear Information System (INIS)

Staat, H.; Korte, E.H.; Lampen, P.

1989-01-01

Characterisation in situ for coatings and other surface layers is generally favourable, but a prerequisite for precious items such as art objects. In infrared spectroscopy only reflection techniques are applicable here. However for attenuated total reflection (ATR) it is difficult to obtain the necessary optical contact of the crystal with the sample, when the latter is not perfectly plane or flexible. The measurement of diffuse reflectance demands a scattering sample and usually the reflectance is very poor. Therefore in most cases one is left with regular reflectance. Such spectra consist of dispersion-like feature instead of bands impeding their interpretation in the way the analyst is used to. Furthermore for computer search in common spectral libraries compiled from transmittance or absorbance spectra a transformation of the reflectance spectra is needed. The correct conversion is based on the Kramers-Kronig transformation. This somewhat time - consuming procedure can be speeded up by using appropriate approximations. A coarser conversion may be obtained from the first derivative of the reflectance spectrum which resembles the second derivative of a transmittance spectrum. The resulting distorted spectra can still be used successfully for the search in peak table libraries. Experiences with both transformations are presented. (author)

Graphene assisted effective hole-extraction on In2O3:H/CH3NH3PbI3 interface: Studied by modulated surface spectroscopy

Science.gov (United States)

Vinoth Kumar, Sri Hari Bharath; Muydinov, Ruslan; Kol'tsova, Tat‘yana; Erfurt, Darja; Steigert, Alexander; Tolochko, Oleg; Szyszka, Bernd

2018-01-01

Charge separation in CH3NH3PbI3 (MAPbI3) films deposited on a hydrogen doped indium oxide (In2O3:H) photoelectrode was investigated by modulated surface photovoltage (SPV) spectroscopy in a fixed capacitor arrangement. It was found that In2O3:H reproducibly extracts photogenerated-holes from MAPbI3 films. The oxygen-plasma treatment of the In2O3:H surface is suggested to be a reason for this phenomenon. Introducing graphene interlayer increased charge separation nearly 6 times as compared to that on the In2O3:H/MAPbI3 interface. Furthermore, it is confirmed by SPV spectroscopy that the defects of the MAPbI3 interface are passivated by graphene.

Ambient pressure photoemission spectroscopy of metal surfaces

Energy Technology Data Exchange (ETDEWEB)

Baikie, Iain D., E-mail: iain@kptechnology.ltd.uk; Grain, Angela C.; Sutherland, James; Law, Jamie

2014-12-30

Highlights: • Ambient pressure photoemission spectroscopy of metals. • Rastered photon energy scan overcomes inelastic scattering. • Relationship between photoemission threshold and contact potential difference. - Abstract: We describe a novel photoemission technique utilizing a traditional Kelvin probe as a detector of electrons/atmospheric ions ejected from metallic surfaces (Au, Ag, Cu, Fe, Ni, Ti, Zn, Al) illuminated by a deep ultra-violet (DUV) source under ambient pressure. To surmount the limitation of electron scattering in air the incident photon energy is rastered rather than applying a variable retarding electric field as is used with UPS. This arrangement can be applied in several operational modes: using the DUV source to determine the photoemission threshold (Φ) with 30–50 meV resolution and also the Kelvin probe, under dark conditions, to measure contact potential difference (CPD) between the Kelvin probe tip and the metallic sample with an accuracy of 1–3 meV. We have studied the relationship between the photoelectric threshold and CPD of metal surfaces cleaned in ambient conditions. Inclusion of a second spectroscopic visible source was used to confirm a semiconducting oxide, possibly Cu{sub 2}O, via surface photovoltage measurements with the KP. This dual detection system can be easily extended to controlled gas conditions, relative humidity control and sample heating/cooling.

Application of NASVD method in the CE1-GRS spectra analysis

International Nuclear Information System (INIS)

Yang Jia; Ge Liangquan; Xiong Shengqing

2010-01-01

From the spectral shape features of the Chang'e-1 gamma-ray spectrometer (CE1-GRS) spectra data of level 3, it is difficult to identify elemental composition of the lunar surface. The paper proposes using Noise Adjusted Singular Value Decomposition (NASVD) method to qualitative analysis of CE1-GRS spectra. The result shows that a number of possible elements such as U, Th, K, Fe, Ti, Si, O, Al, Mg and Ca are qualitatively determined by this method.On the other hand, for each measured spectrum, the absolute value of the amplitude corresponding to the first spectral component indicates the total activity of its corresponding lunar surface region's radioactivity. (authors)

Synthesis of LaVO4/TiO2 heterojunction nanotubes by sol-gel coupled with hydrothermal method for photocatalytic air purification.

Science.gov (United States)

Zou, Xuejun; Li, Xinyong; Zhao, Qidong; Liu, Shaomin

2012-10-01

With the aim of improving the effective utilization of visible light, the LaVO(4)/TiO(2) heterojunction nanotubes were fabricated by sol-gel coupled with hydrothermal method. The photocatalytic ability was demonstrated through catalytic removal of gaseous toluene species. The nanotube samples were characterized by scanning electron microscope (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), surface photovoltage (SPV), Raman spectra and N(2) adsorption-desorption measurements. The characterization results showed that the samples with high specific surface areas were of typical nanotubular morphology, which would lead to the high separation and transfer efficiency of photo induced electron-hole pairs. The as-prepared nanotubes exhibited high photocatalytic activity in decomposing toluene species under visible light irradiation with fine photochemical stability. The enhanced photocatalytic performance of LaVO(4)/TiO(2) nanotubes might be attributed to the matching band potentials, the interconnected heterojunction of LaVO(4) versus TiO(2), and the large specific surface areas of nanotubes. Copyright © 2012 Elsevier Inc. All rights reserved.

[Study on Square Super-Lattice Pattern with Surface Discharge in Dielectric Barrier Discharge by Optical Emission Spectra].

Science.gov (United States)

Niu, Xue-jiao; Dong, Li-fang; Liu, Ying; Wang, Qian; Feng, Jian-yu

2016-02-01

Square super-lattice pattern with surface discharge consisting of central spots and dim spots is firstly observed in the mixture of argon and air by using a dielectric barrier discharge device with water electrodes. By observing the image, it is found that the central spot is located at the centriod of its surrounding four dim spots. The short-exposure image recorded by a high speed video camera shows that the dim spot results from the surface discharges (SDs). The brightness of the central spot and is quite different from that of the dim spot, which indicates that the plasma states of the central spot and the dim spot may be differentiated. The optical emission spectrum method is used to further study the several plasma parameters of the central spot and the dim spot in different argon content. The emission spectra of the N₂ second positive band (C³IIu --> B³ IIg) are measured, from which the molecule vibration temperatures of the central spot and the dim spot are calculated respectively. The broadening of spectral line 696.57 nm (2P₂-->1S₅) is used to study the electron densities of the central spot and the dim spot. It is found that the molecule vibration temperature and electron density of the dim spot are higher than those of the central spot in the same argon content The molecule vibration temperature and electron density of the central spot and the dim spot increase with the argon content increasing from 90% to 99.9%. The surface discharge induced by the volume discharge (VD) has the determinative effect on the formation of the dim spot The experimental results above play an important role in studying the formation mechanism of surface discharg&of square super-lattice pattern with surface discharge. In addition, the studies exert an influence on the application of surface discharge and volume discharge in different fields.

The structure of BPS spectra

Science.gov (United States)

Longhi, Pietro

computing generating functions of 2d-4d BPS spectra, based on the topological data of an ideal triangulation of the Riemann surface defining the theory. We provide a set of building blocks and corresponding rules, from which the 2d-4d spectra of a vast class of theories can be algorithmically recovered. Finally, we present previously unpublished exact results on the BPS spectrum of the SU(2) N = 2* theory, and briefly comment on its wall crossing.

Photogenerated carriers transport behaviors in L-cysteine capped ZnSe core-shell quantum dots

Energy Technology Data Exchange (ETDEWEB)

Shan, Qingsong; Li, Kuiying, E-mail: kuiyingli@ysu.edu.cn; Lin, Yingying; Yin, Hua; Zhu, Ruiping [State Key Laboratory of Metastable Materials Manufacture Technology and Science, Yanshan University, Qinhuangdao 066004 (China); Xue, Zhenjie [Beijing National Laboratory for Molecular Sciences, Key Laboratory of Analytical Chemistry for Living Biosystems, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190 (China)

2016-02-07

The photoexcited carrier transport behavior of zinc selenide (ZnSe) quantum dots (QDs) with core–shell structure is studied because of their unique photoelectronic characteristics. The surface photovoltaic (SPV) properties of self-assembled ZnSe/ZnS/L-Cys core–shell QDs were probed via electric field induced surface photovoltage and transient photovoltage (TPV) measurements supplemented by Fourier transform infrared, laser Raman, absorption, and photoluminescence spectroscopies. The ZnSe QDs displayed p-type SPV characteristics with a broader stronger SPV response over the whole ultraviolet-to-near-infrared range compared with those of other core–shell QDs in the same group. The relationship between the SPV phase value of the QDs and external bias was revealed in their SPV phase spectrum. The wide transient photovoltage response region from 3.3 × 10{sup −8} to 2 × 10{sup −3} s was closely related to the long diffusion distance of photoexcited free charge carriers in the interfacial space–charge region of the QDs. The strong SPV response corresponding to the ZnSe core mainly originated from an obvious quantum tunneling effect in the QDs.

Analysis of polymer surfaces and thin-film coatings with Raman and surface enhanced Raman scattering

International Nuclear Information System (INIS)

McAnally, Gerard David

2001-01-01

This thesis investigates the potential of surface-enhanced Raman scattering (SERS) for the analysis and characterisation of polymer surfaces. The Raman and SERS spectra from a PET film are presented. The SERS spectra from the related polyester PBT and from the monomer DMT are identical to PET, showing that only the aromatic signals are enhanced. Evidence from other compounds is presented to show that loss of the carbonyl stretch (1725 cm -1 ) from the spectra is due to a chemical interaction between the silver and surface carbonyl groups. The interaction of other polymer functional groups with silver is discussed. A comparison of Raman and SERS spectra collected from three faces of a single crystal shows the SERS spectra are depolarised. AFM images of the silver films used to obtain SERS are presented. They consist of regular islands of silver, fused together to form a complete film. The stability and reproducibility and of these surfaces is assessed. Band assignments for the SERS spectrum of PET are presented. A new band in the spectrum (1131 cm -1 ) is assigned to a complex vibration using a density functional calculation. Depth profiling through a polymer film on to the silver layer showed the SERS signals arise from the silver surface only. The profiles show the effects of refraction on the beam, and the adverse affect on the depth resolution. Silver films were used to obtain SERS spectra from a 40 nm thin-film coating on PET, without interference from the PET layer. The use of an azo dye probe as a marker to detect the coating is described. Finally, a novel method for the synthesis of a SERS-active vinyl-benzotriazole monomer is reported. The monomer was incorporated into a thin-film coating and the SERS spectrum obtained from the polymer. (author)

Chloride ion-dependent surface-enhanced Raman scattering study of biotin on the silver surface

International Nuclear Information System (INIS)

Liu Fangfang; Gu Huaimin; Yuan Xiaojuan; Dong Xiao; Lin Yue

2011-01-01

In the present paper, the surface enhanced Raman scattering (SERS) technique was employed to study the SERS spectra of biotin molecules formed on the silver surface. The adsorption geometries of biotin molecules on the silver surface were analyzed based on the SERS data. It can be found that most vibration modes show a Raman shift in silver sol after the addition of sodium chloride solution. In addition, The Raman signals of biotin become weaker and weaker with the increase of the concentration of sodium chloride. This may be due to that the interaction between chloride ions and silver particles is stronger than the interaction between biotin molecules and silver particles. When the concentration of sodium chloride in silver colloid is higher than 0.05mol/L, superfluous chloride ions may form an absorption layer so that biotin can not be adsorbed on silver surface directly. The changes in intensity and profile shape in the SERS spectra suggest different adsorption behavior and surface-coverage of biotin on silver surface. The SERS spectra of biotin suggest that the contribution of the charge transfer mechanism to SERS may be dominant.

Effect of particle surface area on ice active site densities retrieved from droplet freezing spectra

Directory of Open Access Journals (Sweden)

H. Beydoun

2016-10-01

Full Text Available Heterogeneous ice nucleation remains one of the outstanding problems in cloud physics and atmospheric science. Experimental challenges in properly simulating particle-induced freezing processes under atmospherically relevant conditions have largely contributed to the absence of a well-established parameterization of immersion freezing properties. Here, we formulate an ice active, surface-site-based stochastic model of heterogeneous freezing with the unique feature of invoking a continuum assumption on the ice nucleating activity (contact angle of an aerosol particle's surface that requires no assumptions about the size or number of active sites. The result is a particle-specific property g that defines a distribution of local ice nucleation rates. Upon integration, this yields a full freezing probability function for an ice nucleating particle. Current cold plate droplet freezing measurements provide a valuable and inexpensive resource for studying the freezing properties of many atmospheric aerosol systems. We apply our g framework to explain the observed dependence of the freezing temperature of droplets in a cold plate on the concentration of the particle species investigated. Normalizing to the total particle mass or surface area present to derive the commonly used ice nuclei active surface (INAS density (ns often cannot account for the effects of particle concentration, yet concentration is typically varied to span a wider measurable freezing temperature range. A method based on determining what is denoted an ice nucleating species' specific critical surface area is presented and explains the concentration dependence as a result of increasing the variability in ice nucleating active sites between droplets. By applying this method to experimental droplet freezing data from four different systems, we demonstrate its ability to interpret immersion freezing temperature spectra of droplets containing variable particle concentrations. It is shown

Exciton spectra of mixed LiH1-xDx crystals

International Nuclear Information System (INIS)

Plekhanov, V.G.

1989-01-01

The results of low-tempertaure experimental investigation of exciton spectra of pure surface of mixed crystals LiH 1-x d x forming the continuous series of a solved solution are presented. The long-wave reflection spectra is formed, as in pure crystals, by excitons of a large radius. The developed structure of spectra of exciton luminiscence consisting mainly of LO-lines, testifies to the intraband Frelich mechanism of free exciton scattering by LO-phonos, playing the considerable role in renormalization of the exciton Rydberg and the energy of interband transitions. Increase of the concentration of deuterium in mixed crystals causes a short-wave shift in the reflection spectrum and luminescence and continuous decrease of LO-phonon energy together with the increase of Rydberg exciton

Analysis of the experimental positron lifetime spectra by neural networks

International Nuclear Information System (INIS)

Avdic, S.; Chakarova, R.; Pazsit, I.

2003-01-01

This paper deals with the analysis of experimental positron lifetime spectra in polymer materials by using various algorithms of neural networks. A method based on the use of artificial neural networks for unfolding the mean lifetime and intensity of the spectral components of simulated positron lifetime spectra was previously suggested and tested on simulated data [Pazsit et al., Applied Surface Science, 149 (1998), 97]. In this work, the applicability of the method to the analysis of experimental positron spectra has been verified in the case of spectra from polymer materials with three components. It has been demonstrated that the backpropagation neural network can determine the spectral parameters with a high accuracy and perform the decomposition of lifetimes which differ by 10% or more. The backpropagation network has not been suitable for the identification of both the parameters and the number of spectral components. Therefore, a separate artificial neural network module has been designed to solve the classification problem. Module types based on self-organizing map and learning vector quantization algorithms have been tested. The learning vector quantization algorithm was found to have better performance and reliability. A complete artificial neural network analysis tool of positron lifetime spectra has been constructed to include a spectra classification module and parameter evaluation modules for spectra with a different number of components. In this way, both flexibility and high resolution can be achieved. (author)

Determination of the optical absorption spectra of thin layers from their photoacoustic spectra

Science.gov (United States)

Bychto, Leszek; Maliński, Mirosław; Patryn, Aleksy; Tivanov, Mikhail; Gremenok, Valery

2018-05-01

This paper presents a new method for computations of the optical absorption coefficient spectra from the normalized photoacoustic amplitude spectra of thin semiconductor samples deposited on the optically transparent and thermally thick substrates. This method was tested on CuIn(Te0.7Se0.3)2 thin films. From the normalized photoacoustic amplitude spectra, the optical absorption coefficient spectra were computed with the new formula as also with the numerical iterative method. From these spectra, the value of the energy gap of the thin film material and the type of the optical transitions were determined. From the experimental optical transmission spectra, the optical absorption coefficient spectra were computed too, and compared with the optical absorption coefficient spectra obtained from photoacoustic spectra.

A symmetry based study of positron annihilation spectra

International Nuclear Information System (INIS)

Adam, G.; Adam, S.; Inst. of Physics and Nuclear Engineering, Bucharest

1995-01-01

The authors describe a method for off-line analysis of spectra measured by two-dimensional angular correlation of annihilation radiation (2D-ACAR) positron spectroscopy. The method takes into account, at all its stages, two salient data features: the piecewise constant discretization of the 2D physical momentum distribution into square pixels, performed by the setup, and the occurrence of a characteristic 2D projected symmetry of the positron-electron pair momentum distribution. Several validating criteria are derived which secure significantly increased reliability of the output. The method is tested on 2D-ACAR spectra measured on (R)Ba 2 Cu 3 O 7-δ (R123; R = Y, Dy) single crystals. It resolves ridge Fermi surfaces (FS) up to 3rd Umklapp components on both kinds of R123 spectra. Moreover, on a c-axis-projected Y123 spectrum, measured at 300 K, it resolves a small but clear signature of the pillbox FS at the S point of the first Brillouin zone as well

Calculation of ground vibration spectra from heavy military vehicles

Science.gov (United States)

Krylov, V. V.; Pickup, S.; McNuff, J.

2010-07-01

The demand for reliable autonomous systems capable to detect and identify heavy military vehicles becomes an important issue for UN peacekeeping forces in the current delicate political climate. A promising method of detection and identification is the one using the information extracted from ground vibration spectra generated by heavy military vehicles, often termed as their seismic signatures. This paper presents the results of the theoretical investigation of ground vibration spectra generated by heavy military vehicles, such as tanks and armed personnel carriers. A simple quarter car model is considered to identify the resulting dynamic forces applied from a vehicle to the ground. Then the obtained analytical expressions for vehicle dynamic forces are used for calculations of generated ground vibrations, predominantly Rayleigh surface waves, using Green's function method. A comparison of the obtained theoretical results with the published experimental data shows that analytical techniques based on the simplified quarter car vehicle model are capable of producing ground vibration spectra of heavy military vehicles that reproduce basic properties of experimental spectra.

Electromagnetic excitation of phonons at C(001) surfaces

International Nuclear Information System (INIS)

Perez-Sanchez, F L; Perez-Rodriguez, F

2009-01-01

The photon-phonon coupling at C(001)-(2 x 1) surfaces and its manifestation in far-infrared reflectance anisotropy spectra (FIR-RAS) are theoretically investigated. We solve the coupled system of equations for the electromagnetic field and lattice vibrations, described within the adiabatic bond charge model (ABCM), with the method of expansion into bulk phonon and photon modes. The calculated FIR-RAS exhibit resonances associated with zone-center surface phonons in good agreement with available HREELS experiments and predictions of vibrational modes for diamond (001)-(2 x 1) surfaces from ABCM and ab initio calculations. Interestingly, the reflectance anisotropy spectra for a C(001)-(2 x 1) surface turn out to be qualitatively different from the spectra for a Si(001)-(2 x 1) surface, reported previously.

Electromagnetic excitation of phonons at C(001) surfaces

Energy Technology Data Exchange (ETDEWEB)

Perez-Sanchez, F L [Escuela de Ciencias, Universidad Autonoma ' Benito Juarez' de Oaxaca, Avenida Universidad S/N, Ex-Hacienda de Cinco Senores, Ciudad Universitaria, Oaxaca de Juarez, Oaxaca, 68120 (Mexico); Perez-Rodriguez, F, E-mail: fperez@sirio.ifuap.buap.m [Instituto de Fisica, Benemerita Universidad Autonoma de Puebla, Apartado Post. J-48, Puebla 72570 (Mexico)

2009-09-02

The photon-phonon coupling at C(001)-(2 x 1) surfaces and its manifestation in far-infrared reflectance anisotropy spectra (FIR-RAS) are theoretically investigated. We solve the coupled system of equations for the electromagnetic field and lattice vibrations, described within the adiabatic bond charge model (ABCM), with the method of expansion into bulk phonon and photon modes. The calculated FIR-RAS exhibit resonances associated with zone-center surface phonons in good agreement with available HREELS experiments and predictions of vibrational modes for diamond (001)-(2 x 1) surfaces from ABCM and ab initio calculations. Interestingly, the reflectance anisotropy spectra for a C(001)-(2 x 1) surface turn out to be qualitatively different from the spectra for a Si(001)-(2 x 1) surface, reported previously.

High-Efficiency Dye-Sensitized Solar Cell with Three-Dimensional Photoanode

KAUST Repository

Tétreault, Nicolas

2011-11-09

Herein, we present a straightforward bottom-up synthesis of a high electron mobility and highly light scattering macroporous photoanode for dye-sensitized solar cells. The dense three-dimensional Al/ZnO, SnO2, or TiO 2 host integrates a conformal passivation thin film to reduce recombination and a large surface-area mesoporous anatase guest for high dye loading. This novel photoanode is designed to improve the charge extraction resulting in higher fill factor and photovoltage for DSCs. An increase in photovoltage of up to 110 mV over state-of-the-art DSC is demonstrated. © 2011 American Chemical Society.

High-Efficiency Dye-Sensitized Solar Cell with Three-Dimensional Photoanode

KAUST Repository

Té treault, Nicolas; Arsenault, É ric; Heiniger, Leo-Philipp; Soheilnia, Navid; Brillet, Jé ré mie; Moehl, Thomas; Zakeeruddin, Shaik; Ozin, Geoffrey A.; Grä tzel, Michael

2011-01-01

Herein, we present a straightforward bottom-up synthesis of a high electron mobility and highly light scattering macroporous photoanode for dye-sensitized solar cells. The dense three-dimensional Al/ZnO, SnO2, or TiO 2 host integrates a conformal passivation thin film to reduce recombination and a large surface-area mesoporous anatase guest for high dye loading. This novel photoanode is designed to improve the charge extraction resulting in higher fill factor and photovoltage for DSCs. An increase in photovoltage of up to 110 mV over state-of-the-art DSC is demonstrated. © 2011 American Chemical Society.

Interpretation of the Near-IR Spectra of the Kuiper Belt Object

Science.gov (United States)

Eluszkiewicz, Janusz; Cady-Pereira, Karen; Brown, Michael E.; Stansberry, John A.

2007-01-01

Visible and near-IR observations of the Kuiper Belt Object (136472) 2005 FY(9) have indicated the presence of unusually long (1 cm or more) optical path lengths in a layer of methane ice. Using microphysical and radiative transfer modeling, we show that even at the frigid temperatures in the outer reaches of the solar system, a slab of low porosity methane ice can indeed form by pressureless sintering of micron-sized grains, and it can qualitatively reproduce the salient features of the measured spectra. A good semiquantitative match with the near-IR spectra can be obtained with a realistic slab model, provided the spectra are scaled to a visible albedo of 0.6, at the low end of the values currently estimated from Spitzer thermal measurements. Consistent with previous modeling studies, matching spectra scaled to higher albedos requires the incorporation of strong backscattering effects. The albedo may become better constrained through an iterative application of the slab model to the analysis of the thermal measurements from Spitzer and the visible/near-IR reflectance spectra. The slab interpretation offers two falsifiable predictions (1) Absence of an opposition surge, which is commonly attributed to the fluffiness of the optical surface. This prediction is best testable with a spacecraft, as Earth-based observations at true opposition will not be possible until early next century. (2) Unlikelihood of the simultaneous occurrence of very long spectroscopic path lengths in both methane and nitrogen ice on the surface of any Kuiper Belt Object, as the more volatile nitrogen would hinder densification in methane ice.

Interatomic scattering in energy dependent photoelectron spectra of Ar clusters

Energy Technology Data Exchange (ETDEWEB)

Patanen, M.; Benkoula, S.; Nicolas, C.; Goel, A. [Synchrotron SOLEIL, L’Orme des Merisiers, Saint-Aubin, BP 48, 91192 Gif-sur-Yvette Cedex (France); Antonsson, E. [Synchrotron SOLEIL, L’Orme des Merisiers, Saint-Aubin, BP 48, 91192 Gif-sur-Yvette Cedex (France); Physikalische und Theoretische Chemie Institut für Chemie und Biochemie, Fachbereich Biologie, Chemie, Pharmazie, Freie Universität Berlin, Takustrasse 3, 14195 Berlin (Germany); Neville, J. J. [Synchrotron SOLEIL, L’Orme des Merisiers, Saint-Aubin, BP 48, 91192 Gif-sur-Yvette Cedex (France); Department of Chemistry, University of New Brunswick, Fredericton, New Brunswick E3B 6E2 (Canada); Miron, C., E-mail: Catalin.Miron@synchrotron-soleil.fr [Synchrotron SOLEIL, L’Orme des Merisiers, Saint-Aubin, BP 48, 91192 Gif-sur-Yvette Cedex (France); Extreme Light Infrastructure - Nuclear Physics (ELI-NP), ‘Horia Hulubei’ National Institute for Physics and Nuclear Engineering, 30 Reactorului Street, RO-077125 Măgurele, Jud. Ilfov (Romania)

2015-09-28

Soft X-ray photoelectron spectra of Ar 2p levels of atomic argon and argon clusters are recorded over an extended range of photon energies. The Ar 2p intensity ratios between atomic argon and clusters’ surface and bulk components reveal oscillations similar to photoelectron extended X-ray absorption fine structure signal (PEXAFS). We demonstrate here that this technique allows us to analyze separately the PEXAFS signals from surface and bulk sites of free-standing, neutral clusters, revealing a bond contraction at the surface.

Spectra of electrons emitted as a result of the sticking and annihilation of low energy positrons to the surfaces of graphene and highly oriented pyrolytic graphite (HOPG)

Science.gov (United States)

Chrysler, M.; Chirayath, V.; McDonald, A.; Lim, Z.; Shastry, K.; Gladen, R.; Fairchild, A.; Koymen, A.; Weiss, A.

Positron annihilation induced Auger electron spectroscopy (PAES) was used to study the positron induced low energy electron spectra from HOPG and a sample composed of 6-8 layers of graphene grown on polycrystalline copper. A low energy (~2eV) beam of positrons was used to implant positrons into a surface localized state on the graphene and HOPG samples. Measurements of the energy spectra of the positron induced electrons obtained using a TOF spectrometer indicate the presence of an annihilation induced KLL C Auger peak (at ~263 eV) along with a narrow low energy secondary peak due to an Auger mediated positron sticking (AMPS) process. A broad spectral feature was also observed below ~15 eV which we believe may be due to a VVV C Auger transition not previously observed. The energy dependence of the integrated intensity of the AMPS peak was measured for a series of incident positron kinetic energies ranging from ~1.5 eV up to 11 eV from which the binding energy of the surface localized positron state on graphene and HOPG was estimated. The implication of our results regarding the applicability of AMPS and PAES to the study of graphene surfaces and interfaces will be discussed. This work was supported by NSF Grant No. DMR 1508719 and DMR 1338130.

Measurements of the neutral particle spectra on Mars by MSL/RAD from 2015-11-15 to 2016-01-15

Science.gov (United States)

Guo, Jingnan; Zeitlin, Cary; Wimmer-Schweingruber, Robert; Hassler, Donald M.; Köhler, Jan; Ehresmann, Bent; Böttcher, Stephan; Böhm, Eckart; Brinza, David E.

2017-08-01

The Radiation Assessment Detector (RAD), onboard the Mars Science Laboratory (MSL) rover Curiosity, has been measuring the energetic charged and neutral particles and the radiation dose rate on the surface of Mars since the landing of the rover in August 2012. In contrast to charged particles, neutral particles (neutrons and γ-rays) are measured indirectly: the energy deposition spectra produced by neutral particles are complex convolutions of the incident particle spectra with the detector response functions. An inversion technique has been developed and applied to jointly unfold the deposited energy spectra measured in two scintillators of different types (CsI for high γ detection efficiency, and plastic for neutrons) to obtain the neutron and γ-ray spectra. This result is important for determining the biological impact of the Martian surface radiation contributed by neutrons, which interact with materials differently from the charged particles. These first in-situ measurements on Mars provide (1) an important reference for assessing the radiation-associated health risks for future manned missions to the red planet and (2) an experimental input for validating the particle transport codes used to model the radiation environments within spacecraft or on the surface of planets. Here we present neutral particle spectra as well as the corresponding dose and dose equivalent rates derived from RAD measurement during a period (November 15, 2015 to January 15, 2016) for which the surface particle spectra have been simulated via different transport models.

Satellite Atmospheric Sounder IRFS-2 1. Analysis of Outgoing Radiation Spectra Measurements

Science.gov (United States)

Polyakov, A. V.; Timofeyev, Yu. M.; Virolainen, Ya. A.; Uspensky, A. B.; Zavelevich, F. S.; Golovin, Yu. M.; Kozlov, D. A.; Rublev, A. N.; Kukharsky, A. V.

2017-12-01

The outgoing radiation spectra measured by the IRFS-2 spectrometer onboard Meteor-M no. 2 satellite have been analyzed. Some statistical parameters of more than 106 spectra measured in spring in 2015 have been calculated. The radiation brightness temperature varied from ˜300 K (surface temperature) up to ˜210 K (tropopause temperature). The quite high variability of the longwave measured radiation has been demonstrated. The signal-to-noise ratio distinctively decreases in the shortwave region (higher than 1300 cm-1). Intercomparisons of IR sounders IRFS-2 with IASI and CrIS spectra showed that the discrepancies in the average spectra and their variability do not exceed measurement errors in the spectral region 660-1300 cm-1. A comparison of specially chosen pairs of the simultaneously measured spectra showed that the differences between IRFS-2 and European instruments in the region of the 15-μm CO2 band and the transparency windows 8-12 μm are less than 1 mW/(m2 sr cm-1) and no more than the differences between the two IASI instruments (-A and -B). The differences between measured and simulated spectra are less than 1 mW/(m2 sr cm-1) in the mean part of CO2 band. However, starting from 720 cm-1, values appear that reach 2-4 mW/(m2 sr cm-1). This is caused by the absence of precise information about the surface temperature. Further investigations into the possible reasons for the observed disagreements are required in order to improve both the method of initial processing and the radiative model of the atmosphere.

Novel optical probe for quantum Hall system

Indian Academy of Sciences (India)

to explore Landau levels of a two-dimensional electron gas (2DEG) in modulation doped ... Keywords. Surface photovoltage spectroscopy; quantum Hall effect; Landau levels; edge states. ... An optical fibre carries light from tunable diode laser.

Ion surface collisions on surfaces relevant for fusion devices

International Nuclear Information System (INIS)

Rasul, B.; Endstrasser, N.; Zappa, F.; Grill, V.; Scheier, P.; Mark, T.

2006-01-01

Full text: One of the great challenges of fusion research is the compatibility of reactor grade plasmas with plasma facing materials coating the inner walls of a fusion reactor. The question of which surface coating should be used is of particular interest for the design of ITER. The impact of energetic plasma particles leads to sputtering of wall material into the plasma. A possible solution for the coating of plasma facing walls would be the use of special carbon surfaces. Investigations of these various surfaces have been started at BESTOF ion-surface collision apparatus. Experiment beam of singly charged molecular ions of hydrocarbon molecules, i.e. C 2 H + 4 , is generated in a Nier-type electron impact ionization source at an electron energy of about 70 eV. In the first double focusing mass spectrometer the ions are mass and energy analyzed and afterwards refocused onto a surface. The secondary reaction products are monitored using a Time Of Flight mass spectrometer. The secondary ion mass spectra are recorded as a function of the collision energy for different projectile ions and different surfaces. A comparison of these spectra show for example distinct changes in the survival probability of the same projectile ion C 2 H + 4 for different surfaces. (author)

Surface-enhanced Raman spectrum of Gly-Gly adsorbed on the silver colloidal surface

Science.gov (United States)

Xiaojuan, Yuan; Huaimin, Gu; Jiwei, Wu

2010-08-01

Raman and SERS spectra of homodipeptide Gly-Gly and Gly were recorded and compared in this paper, and band assignment for the functional groups contained in these molecules was analyzed in detail. Time-dependent and pH-dependent SERS spectra of Gly-Gly molecule adsorbed on nano-colloidal silver surface were also studied. The time-dependent SERS spectra of Gly-Gly are characterized by the increase in intensity of bands primarily representing the vibrational signatures emanating from the amino and amide moiety of Gly-Gly molecule. It is found that the adsorption style of Gly-Gly on the silver colloid changes as time goes on; at 5 min after adding the sample to the silver colloid, Gly-Gly adsorbs on silver surface firstly through the carboxylate, amino and amide groups, and then the carboxylate group is far away from the silver surface at 10 min to 3 days. The SERS variation of Gly-Gly with the change of pH suggests that the adsorption style is pH-dependent, the different adsorption behavior of the Gly-Gly occurs on silver surface at different pH values.

Surface modification of porous nanocrystalline TiO2 films for dye-sensitized solar cell application by various gas plasmas

International Nuclear Information System (INIS)

Kim, Youngsoo; Yoon, Chang-Ho; Kim, Kang-Jin; Lee, Yeonhee

2007-01-01

Titanium dioxide (TiO 2 ) film for dye-sensitized solar cells (DSSCs) has surface defects such as oxygen vacancies created during the annealing process. The authors used a plasma treatment technique to reduce defects on TiO 2 surfaces. They investigated the influence of different gas plasma treatments of TiO 2 film on the photoelectric performance of DSSC. Short-circuit photocurrent density (J sc ), open-circuit photovoltage (V oc ), and the amount of adsorbed dye for DSSCs were measured. As a result, the solar-to-electricity conversion efficiencies of the O 2 - and N 2 -treated cells increased by 15%-20% compared to untreated cells. On the other hand, solar energy conversion efficiency of CF 4 -plasma treated cells decreased drastically. The increased amount of adsorbed dye on the TiO 2 film was measured by time-of-flight secondary ion mass spectrometry. TiO 2 surfaces modified by plasma treatment were characterized using analytical instruments such as x-ray photoelectron spectroscopy and near-edge x-ray absorption fine structure

The effect of quadrupole force to the spectra of nuclei in the f7/2 shell

International Nuclear Information System (INIS)

Zhang Qingying

1992-01-01

The effect of quadrupole force on the spectra of nuclei in the f 7/2 shell is tested. The nuclear spectra are calculated by using the surface delta interaction plus quadrupole interaction and the modified surface delta interaction respectively. The results calculated with the former are much better than those with the latter, the role of the isospin modified term in the modified surface delta interaction can be substituted by the quadrupole interaction term. It is also shown that the effect of quadrupole interaction in the f 7/2 shell is important although the quadrupole deformations of nuclei in this region are not large

Towards modelling the vibrational signatures of functionalized surfaces: carboxylic acids on H-Si(111) surfaces

Science.gov (United States)

Giresse Tetsassi Feugmo, Conrard; Champagne, Benoît; Caudano, Yves; Cecchet, Francesca; Chabal, Yves J.; Liégeois, Vincent

2012-03-01

In this work, we investigate the adsorption process of two carboxylic acids (stearic and undecylenic) on a H-Si(111) surface via the calculation of structural and energy changes as well as the simulation of their IR and Raman spectra. The two molecules adsorb differently at the surface since the stearic acid simply physisorbs while the undecylenic acid undergoes a chemical reaction with the hydrogen atoms of the surface. This difference is observed in the change of geometry during the adsorption. Indeed, the chemisorption of the undecylenic acid has a bigger impact on the structure than the physisorption of the stearic acid. Consistently, the former is also characterized by a larger value of adsorption energy and a smaller value of the tilting angle with respect to the normal plane. For both the IR and Raman signatures, the spectra of both molecules adsorbed at the surface are in a first approximation the superposition of the spectra of the Si cluster and of the carboxylic acid considered individually. The main deviation from this simple observation is the peak of the stretching Si-H (ν(Si-H)) mode, which is split into two peaks upon adsorption. As expected, the splitting is bigger for the chemisorption than the physisorption. The modes corresponding to atomic displacements close to the adsorption site display a frequency upshift by a dozen wavenumbers. One can also see the disappearance of the peaks associated with the C=C double bond when the undecylenic acid chemisorbs at the surface. The Raman and IR spectra are complementary and one can observe here that the most active Raman modes are generally IR inactive. Two exceptions to this are the two ν(Si-H) modes which are active in both spectroscopies. Finally, we compare our simulated spectra with some experimental measurements and we find an overall good agreement.

Towards modelling the vibrational signatures of functionalized surfaces: carboxylic acids on H-Si(111) surfaces

International Nuclear Information System (INIS)

Tetsassi Feugmo, Conrard Giresse; Champagne, Benoît; Liégeois, Vincent; Caudano, Yves; Cecchet, Francesca; Chabal, Yves J

2012-01-01

In this work, we investigate the adsorption process of two carboxylic acids (stearic and undecylenic) on a H-Si(111) surface via the calculation of structural and energy changes as well as the simulation of their IR and Raman spectra. The two molecules adsorb differently at the surface since the stearic acid simply physisorbs while the undecylenic acid undergoes a chemical reaction with the hydrogen atoms of the surface. This difference is observed in the change of geometry during the adsorption. Indeed, the chemisorption of the undecylenic acid has a bigger impact on the structure than the physisorption of the stearic acid. Consistently, the former is also characterized by a larger value of adsorption energy and a smaller value of the tilting angle with respect to the normal plane. For both the IR and Raman signatures, the spectra of both molecules adsorbed at the surface are in a first approximation the superposition of the spectra of the Si cluster and of the carboxylic acid considered individually. The main deviation from this simple observation is the peak of the stretching Si-H (ν(Si-H)) mode, which is split into two peaks upon adsorption. As expected, the splitting is bigger for the chemisorption than the physisorption. The modes corresponding to atomic displacements close to the adsorption site display a frequency upshift by a dozen wavenumbers. One can also see the disappearance of the peaks associated with the C=C double bond when the undecylenic acid chemisorbs at the surface. The Raman and IR spectra are complementary and one can observe here that the most active Raman modes are generally IR inactive. Two exceptions to this are the two ν(Si-H) modes which are active in both spectroscopies. Finally, we compare our simulated spectra with some experimental measurements and we find an overall good agreement. (paper)

ON THE EMERGENT SPECTRA OF HOT PROTOPLANET COLLISION AFTERGLOWS

International Nuclear Information System (INIS)

Miller-Ricci, Eliza; Meyer, Michael R.; Seager, Sara; Elkins-Tanton, Linda

2009-01-01

We explore the appearance of terrestrial planets in formation by studying the emergent spectra of hot molten protoplanets during their collisional formation. While such collisions are rare, the surfaces of these bodies may remain hot at temperatures of 1000-3000 K for up to millions of years during the epoch of their formation (of duration 10-100 Myr). These objects are luminous enough in the thermal infrared to be observable with current and next-generation optical/IR telescopes, provided that the atmosphere of the forming planet permits astronomers to observe brightness temperatures approaching that of the molten surface. Detectability of a collisional afterglow depends on properties of the planet's atmosphere-primarily on the mass of the atmosphere. A planet with a thin atmosphere is more readily detected, because there is little atmosphere to obscure the hot surface. Paradoxically, a more massive atmosphere prevents one from easily seeing the hot surface, but also keeps the planet hot for a longer time. In terms of planetary mass, more massive planets are also easier to detect than smaller ones because of their larger emitting surface areas-up to a factor of 10 in brightness between 1 and 10 M + planets. We present preliminary calculations assuming a range of protoplanet masses (1-10 M + ), surface pressures (1-1000 bar), and atmospheric compositions, for molten planets with surface temperatures ranging from 1000 to 1800 K, in order to explore the diversity of emergent spectra that are detectable. While current 8 to 10 m class ground-based telescopes may detect hot protoplanets at wide orbital separations beyond 30 AU (if they exist), we will likely have to wait for next-generation extremely large telescopes or improved diffraction suppression techniques to find terrestrial planets in formation within several AU of their host stars.

Effect of Shear Applied During a Pharmaceutical Process on Near Infrared Spectra.

Science.gov (United States)

Hernández, Eduardo; Pawar, Pallavi; Rodriguez, Sandra; Lysenko, Sergiy; Muzzio, Fernando J; Romañach, Rodolfo J

2016-03-01

This study describes changes observed in the near-infrared (NIR) diffuse reflectance (DR) spectra of pharmaceutical tablets after these tablets were subjected to different levels of strain (exposure to shear) during the mixing process. Powder shearing is important in the mixing of powders that are cohesive. Shear stress is created in a system by moving one surface over another causing displacements in the direction of the moving surface and is part of the mixing dynamics of particulates in many industries including the pharmaceutical industry. In continuous mixing, shear strain is developed within the process when powder particles are in constant movement and can affect the quality attributes of the final product such as dissolution. These changes in the NIR spectra could affect results obtained from NIR calibration models. The aim of the study was to understand changes in the NIR diffuse reflectance spectra that can be associated with different levels of strain developed during blend shearing of laboratory samples. Shear was applied using a Couette cell and tablets were produced using a tablet press emulator. Tablets with different shear levels were measured using NIR spectroscopy in the diffuse reflectance mode. The NIR spectra were baseline corrected to maintain the scattering effect associated with the physical properties of the tablet surface. Principal component analysis was used to establish the principal sources of variation within the samples. The angular dependence of elastic light scattering shows that the shear treatment reduces the size of particles and produces their uniform and highly isotropic distribution. Tablet compaction further reduces the diffuse component of scattering due to realignment of particles. © The Author(s) 2016.

Coupling molecular catalysts with nanostructured surfaces for efficient solar fuel production

Science.gov (United States)

Jin, Tong

photosensitizers. In Chapter 3, effective coupling of the macrocyclic Co(III) complex with titanium dioxide (TiO¬2) nanoparticles was achieved by two deposition methods. The synthesized hybrid photocatalysts were thoroughly characterized with a variety of techniques. Upon UV light irradiation, photoexcited electrons in TiO2 nanoparticles were transferred to the surface Co(III) catalyst for CO2 reduction. Production of carbon monoxide (CO) from CO2 was confirmed by isotope labeling combined with infrared spectroscopy. Deposition of the Co(III) catalyst through Ti-O-Co linkages was essential for the photo-induced electron transfer and CO2-reduction activity using the hybrid photocatalysts. In Chapter 4, molecular Re(I) and Co(II) catalysts were coupled with silicon-based photoelectrodes, including a silicon nanowire (SiNW) photoelectrode, to achieve photoelectrochemical CO2 reduction. Photovoltages between 300-600 mV were obtained using the molecular catalysts on the silicon photoelectrodes. SiNWs exhibited enhanced properties, including significantly higher photovoltages than a planar silicon photoelectrode, the ability to protect one of the molecular catalysts from photo-induced decomposition, and excellent selectivity towards CO production in CO2 reduction. Recent theoretical and experimental work have demonstrated low-energy, binuclear pathways for CO2-to-CO conversion using several molecular catalysts. In such binuclear pathways, two metal centers work cooperatively to achieve two-electron CO2 reduction. Chapter 5 describes our effort to promote the binuclear pathway by grafting the molecular Co(III) catalyst onto silica surfaces. Different linking strategies were attempted to achieve this goal by planting the surface Co(III) sites in close proximity.

Effects of annealing conditions on the photoelectrochemical properties of dye-sensitized solar cells made with ZnO nanoparticles

Energy Technology Data Exchange (ETDEWEB)

Lu, Lanlan; Li, Renjie; Fan, Ke [College of Chemistry and Molecular Science, Wuhan University, Wuhan 430072 (China); Peng, Tianyou [College of Chemistry and Molecular Science, Wuhan University, Wuhan 430072 (China); State Key Laboratory of Rare Earth Materials Chemistry and Applications, Peking University, Beijing 100871 (China)

2010-05-15

Dye-sensitized solar cells (DSSCs) were fabricated by using porous ZnO electrodes derived from home-made ZnO nanoparticles. Electrochemical impedance spectra and open-circuit photovoltage decay curves measurements were performed to investigate the photoelectrochemical characteristics of ZnO films annealed at different temperatures. The experimental results indicate that the effects of the bulk traps and the surface states within the ZnO films on the recombination processes of the photoinjected electrons in DSSCs depend on the annealing temperature. The DSSC based on the ZnO electrode annealed at 400 C exhibits an optimal energy conversion efficiency of 3.92% under the illumination of one sun simulated sunlight because the farthest decrease in the effects of both bulk traps and surface states at this film can maintain a lower charge recombination probability. This result indicates that the ZnO film electrode has promising application in the field of DSSCs, and the optimization of porous film fabrication condition is efficient for the improvement of ZnO-based DSSC's performances. (author)

Covalently attached multilayer assemblies of diazo-resins and binuclear cobalt phthalocyanines

International Nuclear Information System (INIS)

Li Xiaofang; Zhao Shuang; Yang Min; Sun Changqing; Guo, Liping

2005-01-01

By using the ionic self-assembly technique, ordered multilayer thin films composed of diazo-resin (DAR) as polycation and water-soluble binuclear cobalt phthalocyaninehexasulfonate (Bi-CoPc) as polyanion were alternately fabricated on quartz, CaF 2 and glassy carbon electrodes (GCEs). Upon ultraviolet irradiation, the adjacent interface of the multilayer films reacted to form a covalently cross-linking structure. The obtained thin films were characterized by ultraviolet (UV)-vis, Fourier transform infrared spectrometer (FTIR), X-ray diffraction (XRD), atomic force microscope (AFM), surface photovoltage spectra (SPS), and cyclic voltammetry. The results show that the uniform, highly stable and ordered multilayer thin films were formed. The linkage nature between the adjacent interface of the multilayer films converts from ionic to covalent, and, as a result, the stability of the multilayer thin films dramatically improved. The multilayer thin films on GCEs also exhibited excellent electrochemical behavior

Covalently attached multilayer assemblies of diazo-resins and binuclear cobalt phthalocyanines

Energy Technology Data Exchange (ETDEWEB)

Li Xiaofang [Key Lab of Supramolecular Structure and Materials, College of Chemistry, Jilin University, Changchun 130023 (China); Zhao Shuang [Key Lab of Supramolecular Structure and Materials, College of Chemistry, Jilin University, Changchun 130023 (China); Yang Min [Key Lab of Supramolecular Structure and Materials, College of Chemistry, Jilin University, Changchun 130023 (China); Sun Changqing [Key Lab of Supramolecular Structure and Materials, College of Chemistry, Jilin University, Changchun 130023 (China)]. E-mail: sunchq@mail.jlu.edu.cn; Guo, Liping [Department of Chemistry, Northeast Normal University, Changchun 130024 (China)

2005-05-01

By using the ionic self-assembly technique, ordered multilayer thin films composed of diazo-resin (DAR) as polycation and water-soluble binuclear cobalt phthalocyaninehexasulfonate (Bi-CoPc) as polyanion were alternately fabricated on quartz, CaF{sub 2} and glassy carbon electrodes (GCEs). Upon ultraviolet irradiation, the adjacent interface of the multilayer films reacted to form a covalently cross-linking structure. The obtained thin films were characterized by ultraviolet (UV)-vis, Fourier transform infrared spectrometer (FTIR), X-ray diffraction (XRD), atomic force microscope (AFM), surface photovoltage spectra (SPS), and cyclic voltammetry. The results show that the uniform, highly stable and ordered multilayer thin films were formed. The linkage nature between the adjacent interface of the multilayer films converts from ionic to covalent, and, as a result, the stability of the multilayer thin films dramatically improved. The multilayer thin films on GCEs also exhibited excellent electrochemical behavior.

Modulation spectroscopy study of the effects of growth interruptions on the interfaces of GaAsSb/GaAs multiple quantum wells

International Nuclear Information System (INIS)

Hsu, H P; Sitarek, P; Huang, Y S; Liu, P W; Lin, J M; Lin, H H; Tiong, K K

2006-01-01

The effects of growth interruption times combined with Sb exposure of GaAsSb/GaAs multiple quantum wells (MQWs) have been investigated by using phototransmittance (PT), contactless electroreflectance (CER) and wavelength modulated surface photovoltage spectroscopy (WMSPS). The features originated from different portions of the samples, including interband transitions of MQWs, interfaces and GaAs, are observed and identified through a detailed comparison of the obtained spectra and theoretical calculation. A red-shift of the interband transitions and a broader lineshape of the fundamental transition are observed from samples grown under Sb exposure compared to the reference sample grown without interruption. The results can be interpreted in terms of both increases in Sb content and mixing of Sb in the GaAs interface layers. An additional feature has been observed below the GaAs region in the samples with Sb treatment. The probable origin of this additional feature is discussed

[The NIR spectra based variety discrimination for single soybean seed].

Science.gov (United States)

Zhu, Da-Zhou; Wang, Kun; Zhou, Guang-Hua; Hou, Rui-Feng; Wang, Cheng

2010-12-01

With the development of soybean producing and processing, the quality breeding becomes more and more important for soybean breeders. Traditional sampling detection methods for soybean quality need to destroy the seed, and does not satisfy the requirement of earlier generation materials sieving for breeding. Near infrared (NIR) spectroscopy has been widely used for soybean quality detection. However, all these applications were referred to mass samples, and they were not suitable for little or single seed detection in breeding procedure. In the present study, the acousto--optic tunable filter (AOTF) NIR spectroscopy was used to measure the single soybean seed. Two varieties of soybean were measured, which contained 60 KENJIANDOU43 seeds and 60 ZHONGHUANG13 seeds. The results showed that NIR spectra combined with soft independent modeling of class analogy (SIMCA) could accurately discriminate the soybean varieties. The classification accuracy for KENJIANDOU43 seeds and ZHONGHUANG13 was 100%. The spectra of single soybean seed were measured at different positions, and it showed that the seed shape has significant influence on the measurement of spectra, therefore, the key point for single seed measurement was how to accurately acquire the spectra and keep their representativeness. The spectra for soybeans with glossy surface had high repeatability, while the spectra of seeds with external defects had significant difference for several measurements. For the fast sieving of earlier generation materials in breeding, one could firstly eliminate the seeds with external defects, then apply NIR spectra for internal quality detection, and in this way the influence of seed shape and external defects could be reduced.

Raman spectra of thiolated arsenicals with biological importance.

Science.gov (United States)

Yang, Mingwei; Sun, Yuzhen; Zhang, Xiaobin; McCord, Bruce; McGoron, Anthony J; Mebel, Alexander; Cai, Yong

2018-03-01

Surface enhanced Raman scattering (SERS) has great potential as an alternative tool for arsenic speciation in biological matrices. SERS measurements have advantages over other techniques due to its ability to maintain the integrity of arsenic species and its minimal requirements for sample preparation. Up to now, very few Raman spectra of arsenic compounds have been reported. This is particularly true for thiolated arsenicals, which have recently been found to be widely present in humans. The lack of data for Raman spectra in arsenic speciation hampers the development of new tools using SERS. Herein, we report the results of a study combining the analysis of experimental Raman spectra with that obtained from density functional calculations for some important arsenic metabolites. The results were obtained with a hybrid functional B3LYP approach using different basis sets to calculate Raman spectra of the selected arsenicals. By comparing experimental and calculated spectra of dimethylarsinic acid (DMA V ), the basis set 6-311++G** was found to provide computational efficiency and precision in vibrational frequency prediction. The Raman frequencies for the rest of organoarsenicals were studied using this basis set, including monomethylarsonous acid (MMA III ), dimethylarsinous acid (DMA III ), dimethylmonothioarinic acid (DMMTA V ), dimethyldithioarsinic acid (DMDTA V ), S-(Dimethylarsenic) cysteine (DMA III (Cys)) and dimethylarsinous glutathione (DMA III GS). The results were compared with fingerprint Raman frequencies from As─O, As─C, and As─S obtained under different chemical environments. These fingerprint vibrational frequencies should prove useful in future measurements of different species of arsenic using SERS. Copyright © 2017 Elsevier B.V. All rights reserved.

Junction formation of CuInSe2 with CdS: A comparative study of 'dry' and 'wet' interfaces

International Nuclear Information System (INIS)

Hunger, R.; Lebedev, M.V.; Sakurai, K.; Schulmeyer, T.; Mayer, Th.; Klein, A.; Niki, S.; Jaegermann, W.

2007-01-01

The junction formation of polycrystalline CuInSe 2 absorbers (CIS) with thermally evaporated CdS was investigated by high-resolution synchrotron X-ray photoelectron spectroscopy. The chemistry and electronics of the interfaces of Cd partial electrolyte treated CIS ('wet' processed) and clean, decapped CIS ('dry' processed) were compared. A valence band offset of 0.96(10) eV was determined in both cases. The Cd(Se,OH) surface layer induced by the wet Cd partial electrolyte process does not significantly modify the band alignment at the CIS/CdS heterointerface from the 'dry', vacuum-processed CIS/CdS interface. During the stepwise interface formation the energy converting capability of the CIS/CdS heterojunction was assessed by in situ surface photovoltage measurements at room temperature. The evolution of the surface photovoltage significantly differs for the 'wet' and the 'dry' interfaces and is discussed in relation to the function in solar cell devices

Surface States and Effective Surface Area on Photoluminescent P-Type Porous Silicon

Science.gov (United States)

Weisz, S. Z.; Porras, A. Ramirez; Resto, O.; Goldstein, Y.; Many, A.; Savir, E.

1997-01-01

The present study is motivated by the possibility of utilizing porous silicon for spectral sensors. Pulse measurements on the porous-Si/electrolyte system are employed to determine the surface effective area and the surface-state density at various stages of the anodization process used to produce the porous material. Such measurements were combined with studies of the photoluminescence spectra. These spectra were found to shift progressively to the blue as a function of anodization time. The luminescence intensity increases initially with anodization time, reaches a maximum and then decreases with further anodization. The surface state density, on the other hand, increases with anodization time from an initial value of about 2 x 10(exp 12)/sq cm surface to about 1013 sq cm for the anodized surface. This value is attained already after -2 min anodization and upon further anodization remains fairly constant. In parallel, the effective surface area increases by a factor of 10-30. This behavior is markedly different from the one observed previously for n-type porous Si.

The dynamic method for time-of-flight measurement of thermal neutron spectra from pulsed sources

International Nuclear Information System (INIS)

Pepyolyshev, Yu.N.; Chuklyaev, S.V.; Tulaev, A.B.; Bobrakov, V.F.

1995-01-01

A time-of-flight method for measurement of thermal neutron spectra in pulsed neutron sources with an efficiency more than 10 5 times higher than the standard method is described. The main problems associated with the electric current technique for time-of-flight spectra measurement are examined. The methodical errors, problems of special neutron detector design and other questions are discussed. Some experimental results for spectra from the surfaces of water and solid methane moderators obtained at the IBR-2 pulsed reactor (Dubna, Russia) are presented. (orig.)

Optimisation of electronic interface properties of a-Si:H/c-Si hetero-junction solar cells by wet-chemical surface pre-treatment

Energy Technology Data Exchange (ETDEWEB)

Angermann, H. [Hahn-Meitner-Institut, Abt. Siliziumphotovoltaik, Kekulestrasse 5, D-12489 Berlin (Germany)], E-mail: angermann@hmi.de; Korte, L.; Rappich, J.; Conrad, E.; Sieber, I.; Schmidt, M. [Hahn-Meitner-Institut, Abt. Siliziumphotovoltaik, Kekulestrasse 5, D-12489 Berlin (Germany); Huebener, K.; Hauschild, J. [Freie Universitaet Berlin, FB Physik, Arnimallee 14, 14195 Berlin (Germany)

2008-08-30

The relation between structural imperfections at structured silicon surfaces, energetic distribution of interface state densities, recombination loss at a-Si:H/c-Si interfaces and solar cell characteristics have been intensively investigated using non-destructive, surface sensitive techniques, surface photovoltage (SPV) and photoluminescence (PL) measurements, atomic force microscopy (AFM) and electron microscopy (SEM). Sequences of wet-chemical oxidation and etching steps were optimised with respect to the etching behaviour of Si(111) pyramids. Special wet-chemical smoothing and oxide removal procedures for structured substrates were developed, in order to reduce the preparation-induced surface micro-roughness and density of electronically active defects. H-termination and passivation by wet-chemical oxides were used to inhibit surface contamination and native oxidation during the technological process. We achieved significantly lower micro-roughness, densities of surface states D{sub it}(E) and recombination loss at a-Si:H/c-Si interfaces on wafers with randomly distributed pyramids, compared to conventional pre-treatments. For amorphous-crystalline hetero-junction solar cells (ZnO/a-Si:H/c-Si/BSF/Al), the c-Si surface becomes part of the a-Si:H/c-Si interface, whose recombination activity determines cell performance. With textured substrates, the smoothening procedure results in a significant increase of short circuit current, fill factor and efficiency.

Optimisation of electronic interface properties of a-Si:H/c-Si hetero-junction solar cells by wet-chemical surface pre-treatment

International Nuclear Information System (INIS)

Angermann, H.; Korte, L.; Rappich, J.; Conrad, E.; Sieber, I.; Schmidt, M.; Huebener, K.; Hauschild, J.

2008-01-01

The relation between structural imperfections at structured silicon surfaces, energetic distribution of interface state densities, recombination loss at a-Si:H/c-Si interfaces and solar cell characteristics have been intensively investigated using non-destructive, surface sensitive techniques, surface photovoltage (SPV) and photoluminescence (PL) measurements, atomic force microscopy (AFM) and electron microscopy (SEM). Sequences of wet-chemical oxidation and etching steps were optimised with respect to the etching behaviour of Si(111) pyramids. Special wet-chemical smoothing and oxide removal procedures for structured substrates were developed, in order to reduce the preparation-induced surface micro-roughness and density of electronically active defects. H-termination and passivation by wet-chemical oxides were used to inhibit surface contamination and native oxidation during the technological process. We achieved significantly lower micro-roughness, densities of surface states D it (E) and recombination loss at a-Si:H/c-Si interfaces on wafers with randomly distributed pyramids, compared to conventional pre-treatments. For amorphous-crystalline hetero-junction solar cells (ZnO/a-Si:H/c-Si/BSF/Al), the c-Si surface becomes part of the a-Si:H/c-Si interface, whose recombination activity determines cell performance. With textured substrates, the smoothening procedure results in a significant increase of short circuit current, fill factor and efficiency

Exploration of faint absorption bands in the reflectance spectra of the asteroids by method of optimal smoothing: Vestoids

Science.gov (United States)

Shestopalov, D. I.; McFadden, L. A.; Golubeva, L. F.

2007-04-01

An optimization method of smoothing noisy spectra was developed to investigate faint absorption bands in the visual spectral region of reflectance spectra of asteroids and the compositional information derived from their analysis. The smoothing algorithm is called "optimal" because the algorithm determines the best running box size to separate weak absorption bands from the noise. The method is tested for its sensitivity to identifying false features in the smoothed spectrum, and its correctness of forecasting real absorption bands was tested with artificial spectra simulating asteroid reflectance spectra. After validating the method we optimally smoothed 22 vestoid spectra from SMASS1 [Xu, Sh., Binzel, R.P., Burbine, T.H., Bus, S.J., 1995. Icarus 115, 1-35]. We show that the resulting bands are not telluric features. Interpretation of the absorption bands in the asteroid spectra was based on the spectral properties of both terrestrial and meteorite pyroxenes. The bands located near 480, 505, 530, and 550 nm we assigned to spin-forbidden crystal field bands of ferrous iron, whereas the bands near 570, 600, and 650 nm are attributed to the crystal field bands of trivalent chromium and/or ferric iron in low-calcium pyroxenes on the asteroids' surface. While not measured by microprobe analysis, Fe 3+ site occupancy can be measured with Mössbauer spectroscopy, and is seen in trace amounts in pyroxenes. We believe that trace amounts of Fe 3+ on vestoid surfaces may be due to oxidation from impacts by icy bodies. If that is the case, they should be ubiquitous in the asteroid belt wherever pyroxene absorptions are found. Pyroxene composition of four asteroids of our set is determined from the band position of absorptions at 505 and 1000 nm, implying that there can be orthopyroxenes in all range of ferruginosity on the vestoid surfaces. For the present we cannot unambiguously interpret of the faint absorption bands that are seen in the spectra of 4005 Dyagilev, 4038

Utilizing Raman Spectroscopy and Surface-Enhanced Raman Spectroscopy to investigate healthy and cancerous colon samples

International Nuclear Information System (INIS)

Barzegar, A.; Rezaei, H.; Malekfar, R.

2012-01-01

In this study, spontaneous Raman scattering and surface-enhanced Raman scattering, Surface-Enhanced Raman Spectroscopy spectra have been investigated. The samples which were kept in the formalin solution selected from the human's healthy and cancerous colon tissues. The Surface-Enhanced Raman Spectroscopy spectra were collected by adding colloidal solution contained silver nanoparticles to the top of the samples. The recorded spectra were compared for the spontaneous Raman spectra of healthy and cancerous colon samples. The spontaneous and surface enhanced Raman scattering data were also collected and compared for both healthy and damaged samples.

Polarity analysis of GaN nanorods by photo-assisted Kelvin probe force microscopy

Energy Technology Data Exchange (ETDEWEB)

Wei, Jiandong; Neumann, Richard; Wang, Xue; Li, Shunfeng; Fuendling, Soenke; Merzsch, Stephan; Al-Suleiman, Mohamed A.M.; Soekmen, Uensal; Wehmann, Hergo-H.; Waag, Andreas [Institut fuer Halbleitertechnik, TU Braunschweig (Germany)

2011-07-15

Polarity dependence (N-polar (000-1) and Ga-polar (0001)) of surface photovoltage of epitaxially grown, vertically aligned GaN nanorods has been investigated by photo-assisted Kelvin probe force microscopy (KPFM). Commercial GaN substrates with known polarities are taken as reference samples. The polarity of GaN substrates can be well distinguished by the change in surface photovoltage upon UV illumination in air ambient. These different behaviors of Ga- and N-polar surfaces are attributed to the polarity-related surface-bound charges and photochemical reactivity. GaN nanorods were grown on patterned SiO{sub 2}/sapphire templates by metal-organic vapor phase epitaxy (MOVPE). In order to analyze the bottom surface of the grown GaN nanorods, a technique known from high power electronics and joining techniques is applied to remove the substrate. The top and bottom surfaces of the GaN nanorods are identified to be N-polar and Ga-polar according to the KPFM results, respectively. Our experiments demonstrate that KPFM is a simple and suitable method capable to identify the polarity of GaN nanorods. (copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

RESEARCH OF THE ENTRANCE ANGLE EFFECT ON THE REFLECTANCE SPECTRA OF THE STAINLESS STEEL SURFACE OXIDIZED BY PULSED LASER RADIATION

Directory of Open Access Journals (Sweden)

V. P. Veiko

2016-05-01

Full Text Available Subject of Research.Oxide films on the metal surfaces can be obtained both by surface-uniform infrared heating and local laser treatment e.g. by sequence of nanosecond laser pulses. Due to interference in created films the coloration of treated area is observed. The present work shows the results of spectrophotometric measurements for various light entrance angles in the range of 10-60°. Method. AISI 304 stainless steel plates were oxidized by two methods: in muffle furnace FM - 10 (Т= 500-600° С, t = 5-7 min. and at line-by-line scanning by sequence of nanosecond laser pulses (λ = 1.06 μm, τ =100 ns, r = 25 μm,q=2.91∙107 W/cm2, Nx = 30, Ny = 1. Surface research in optical resolution was realized by Carl Zeiss Axio Imager A1M. Reflectance spectra were obtained with spectrophotometer Lambda Perkin 1050 with integrating sphere at different fixed light incidence angles. Topographic features were detected by scanning probe microscopy investigation with NanoEducator equipment. Main Results. The quantitative surface geometry characteristics of AISI 304 stainless steel patterns treated by different methods are obtained. It was found that the increase of light entrance angle has no influence on the form of reflection coefficient dependence from a wavelength, but a blue-shift occurs especially for the case of laser treatment. This difference can be caused by surface topology formed by laser heating and variety of oxide film thickness. This effect results in more significant change in observed sample color for laser treatment then for infrared heating. Practical Relevance. The results obtained in the present work can be used to implement a new element of product protection against forgery with the product marking.

0.7–2.5 μ m Spectra of Hilda Asteroids

International Nuclear Information System (INIS)

Wong, Ian; Brown, Michael E.; Emery, Joshua P.

2017-01-01

The Hilda asteroids are primitive bodies in resonance with Jupiter whose origin and physical properties are not well understood. Current models posit that these asteroids formed in the outer solar system and were scattered along with the Jupiter Trojans into their present-day positions during a chaotic episode of dynamical restructuring. In order to explore the surface composition of these enigmatic objects in comparison with an analogous study of Trojans, we present new near-infrared spectra (0.7–2.5 μ m) of 25 Hilda asteroids. No discernible absorption features are apparent in the data. Synthesizing the bimodalities in optical color and infrared reflectivity reported in previous studies, we classify 26 of the 28 Hildas in our spectral sample into the so-called less-red and red sub-populations and find that the two sub-populations have distinct average spectral shapes. Combining our results with visible spectra, we find that Trojans and Hildas possess similar overall spectral shapes, suggesting that the two minor body populations share a common progenitor population. A more detailed examination reveals that while the red Trojans and Hildas have nearly identical spectra, less-red Hildas are systematically bluer in the visible and redder in the near-infrared than less-red Trojans, indicating a putative broad, shallow absorption feature between 0.5 and 1.0  μ m. We argue that the less-red and red objects found in both Hildas and Trojans represent two distinct surface chemistries and attribute the small discrepancy between less-red Hildas and Trojans to the difference in surface temperatures between the two regions.

0.7–2.5 μ m Spectra of Hilda Asteroids

Energy Technology Data Exchange (ETDEWEB)

Wong, Ian; Brown, Michael E. [Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125 (United States); Emery, Joshua P., E-mail: iwong@caltech.edu [Earth and Planetary Science Department and Planetary Geosciences Institute, University of Tennessee, Knoxville, TN 37996 (United States)

2017-09-01

The Hilda asteroids are primitive bodies in resonance with Jupiter whose origin and physical properties are not well understood. Current models posit that these asteroids formed in the outer solar system and were scattered along with the Jupiter Trojans into their present-day positions during a chaotic episode of dynamical restructuring. In order to explore the surface composition of these enigmatic objects in comparison with an analogous study of Trojans, we present new near-infrared spectra (0.7–2.5 μ m) of 25 Hilda asteroids. No discernible absorption features are apparent in the data. Synthesizing the bimodalities in optical color and infrared reflectivity reported in previous studies, we classify 26 of the 28 Hildas in our spectral sample into the so-called less-red and red sub-populations and find that the two sub-populations have distinct average spectral shapes. Combining our results with visible spectra, we find that Trojans and Hildas possess similar overall spectral shapes, suggesting that the two minor body populations share a common progenitor population. A more detailed examination reveals that while the red Trojans and Hildas have nearly identical spectra, less-red Hildas are systematically bluer in the visible and redder in the near-infrared than less-red Trojans, indicating a putative broad, shallow absorption feature between 0.5 and 1.0  μ m. We argue that the less-red and red objects found in both Hildas and Trojans represent two distinct surface chemistries and attribute the small discrepancy between less-red Hildas and Trojans to the difference in surface temperatures between the two regions.

Detection of Pb-LIII edge XANES spectra of urban atmospheric particles combined with simple acid extraction

International Nuclear Information System (INIS)

Funasaka, K.; Tojo, T.; Katahira, K.; Shinya, M.; Miyazaki, T.; Kamiura, T.; Yamamoto, O.; Moriwaki, H.; Tanida, H.; Takaoka, M.

2008-01-01

Pb-LIII edge XANES spectra of atmospheric particles are directly obtained by fluorescent XAFS spectroscopy using a 19-element solid state detector (SSD). Particulate sample was collected on a quartz fiber filter using a high-volume air sampler, and the filter was cut into small pieces (25 x 25 mm). Then, surface layer of the filter piece was scaled and accumulated in order to enhance the particle density per filter unit. Use of 10 pieces of the surface layer enables the measurement of Pb-LIII edge XANES spectra on beamline BL01B1 at SPring-8, Hyogo, Japan. The shape of the Pb-LIII edge XANES spectra of the particulate sample is similar to the shapes of the spectra for PbS, PbCO 3 , PbSO 4 and/or PbCl 2 . Additionally, the filter sample is also divided into water-soluble, 0.1 M HCl-extractable, and residual fractions of Pb compounds by a simple acid extraction procedure. We discuss the possibility of Pb speciation in the particulate samples with combination of highly sensitive XANES spectroscopy and simple acid extraction

A Spectral Library of Emissivity Spectra for MERTIS on BepiColombo

Science.gov (United States)

Maturilli, A.; Helbert, J.; Varatharajan, I.; D'Amore, M.; Hiesinger, H.

2018-05-01

At PSL we measured emissivity spectra in vacuum for a suite of Mercury surface analogues for temperatures from 100°C to >400°C. The spectral library is completed by reflectance on samples fresh and post-heating (0.2 to 200 µm spectral range).

Visible and Near-IR Reflectance Spectra for Smectite, Sulfate And Perchlorate under Dry Conditions for Interpretation of Martian Surface Mineralogy

Science.gov (United States)

Morris, R.V.; Ming, W.; Golden, D.C.; Arvidson, R.E.; Wiseman, S.M.; Lichtenberg, K.A.; Cull, S.; Graff, T.G.

2009-01-01

Visible and near-IR (VNIR) spectral data for the martian surface obtained from orbit by the MRO-CRISM and OMEGA instruments are interpreted as having spectral signatures of H2O/OH-bearing phases, including smectites and other phyllosilicates, sulfates, and high-SiO2 phases [e.g., 1-4]. Interpretations of martian spectral signatures are based on and constrained by spectra that are obtained in the laboratory on samples with known mineralogical compositions and other physicochemical characteristics under, as appropriate, Mars-like environmental conditions (e.g., temperature, pressure, and humidity). With respect to environmental conditions, differences in the absolute concentration of atmospheric H2O can effect the hydration state and therefore the spectra signatures of smectite phyllosilicates (solvation H2O) and certain sulfates (hydration H2O) [e.g., 5-7]. We report VNIR spectral data acquired under humid (laboratory air) and dry (dry N2 gas) environments for two natural smectites (nontronite API-33A and saponite SapCa-1) to characterize the effect of solvation H2O on spectral properties. We also report spectral data for the thermal dehydration products of (1) melanterite (FeSO4.7H2O) in both air and dry N2 gas and (2) Mg-perchlorate (Mg(ClO4)2.6H2O) in dry N2 environments. Spectral measurements for samples dehydrated in dry N2 were made without exposing them to humid laboratory air.

Adsorption geometry and core excitation spectra of three phenylpropene isomers on Cu(111)

International Nuclear Information System (INIS)

Kolczewski, C.; Williams, F. J.; Cropley, R. L.; Vaughan, O. P. H.; Urquhart, A. J.; Tikhov, M. S.; Lambert, R. M.; Hermann, K.

2006-01-01

Theoretical C 1s near edge x-ray absorption fine structure (NEXAFS) spectra for the C 9 H 10 isomers trans-methylstyrene, α-methylstyrene, and allylbenzene in gas phase and adsorbed at Cu(111) surfaces have been obtained from density functional theory calculations where adsorbate geometries were determined by corresponding total energy optimizations. The three species show characteristic differences in widths and peak shapes of the lowest C 1s→π* transitions which are explained by different coupling of the π-electron system of the C 6 ring with that of the side chain in the molecules as well as by the existence of nonequivalent carbon centers. The adsorbed molecules bind only weakly with the substrate which makes the use of theoretical NEXAFS spectra of the oriented free molecules meaningful for an interpretation of experimental angle-resolved NEXAFS spectra of the adsorbate systems obtained in this work. However, a detailed quantitative account of relative peak intensities requires theoretical angle-resolved NEXAFS spectra of the complete adsorbate systems which have been evaluated within the surface cluster approach. The comparison with experiment yields almost perfect agreement and confirms the reliability of the calculated equilibrium geometries of the adsorbates. This can help to explain observed differences in the catalytic epoxidation of the three molecules on Cu(111) based on purely geometric considerations

Multi-year ozone concentration and its spectra in Shanghai, China

Energy Technology Data Exchange (ETDEWEB)

Geng, Fuhai; Mao, Xiaoqin [Shanghai Meteorological Bureau, Shanghai (China); Shanghai Key Laboratory of Meteorology and Health, Shanghai (China); Zhou, Mingyu, E-mail: mingyuzhou34@163.com [National Marine Environmental Forecasts Center, State Oceanic Administration, Beijing (China); Zhong, Shiyuan [Department of Geography, Michigan State University, East Lansing, MI (United States); Lenschow, Donald [National Center for Atmospheric Research, Boulder, CO (United States)

2015-07-15

The periodic properties of surface ozone variation were studied at five stations with different environmental conditions in Shanghai based on multi-year observations of ozone concentration and UV radiation using spectral decomposition methods. The spectra of surface ozone have distinct peaks at semi-diurnal, diurnal, intraseasonal, semiannual, annual, and quasi-biennial periods. The spectra for the frequency band larger than the semi-diurnal follow a − 5/3 power law at all the stations. The diurnal peak values for all stations in different years are similar to each other, while the semi-diurnal peak values are somewhat different among the stations. The peak value of semi-diurnal cycle at the station Dongtan (ecological environment area) is smaller than that at the other stations. The monthly mean of surface ozone has a significant seasonal variation with a maximum in May, a secondary maximum in fall, a lower value in summer (July and August), and a minimum in December or January. However the seasonal variation of UV radiation monthly mean shows a relatively higher value in summer (July and August), and for other months it is closely related to the ozone monthly mean. These secondary peaks of the ozone monthly mean in fall might be caused by the UV radiation coming back to its relevant value after falling off during the Asia summer monsoon; it was not related to biomass burning. The intraseasonal cycling of ozone might be related to the MJO (Madden–Julian Oscillation). Further studies are needed to understand the relationship between the local ozone intraseasonal variation and the MJO. The quasi-biennial variation of ozone in Shanghai might be a local reflection of climate change and could be associated with ENSO (El-Nino Southern Oscillation). Further studies will be needed to understand the relationship of the quasi-biennial variation of ozone to ENSO. - Highlights: • The spectral decomposition methods are used. • The spectra of surface ozone have multi

Multi-year ozone concentration and its spectra in Shanghai, China

International Nuclear Information System (INIS)

Geng, Fuhai; Mao, Xiaoqin; Zhou, Mingyu; Zhong, Shiyuan; Lenschow, Donald

2015-01-01

The periodic properties of surface ozone variation were studied at five stations with different environmental conditions in Shanghai based on multi-year observations of ozone concentration and UV radiation using spectral decomposition methods. The spectra of surface ozone have distinct peaks at semi-diurnal, diurnal, intraseasonal, semiannual, annual, and quasi-biennial periods. The spectra for the frequency band larger than the semi-diurnal follow a − 5/3 power law at all the stations. The diurnal peak values for all stations in different years are similar to each other, while the semi-diurnal peak values are somewhat different among the stations. The peak value of semi-diurnal cycle at the station Dongtan (ecological environment area) is smaller than that at the other stations. The monthly mean of surface ozone has a significant seasonal variation with a maximum in May, a secondary maximum in fall, a lower value in summer (July and August), and a minimum in December or January. However the seasonal variation of UV radiation monthly mean shows a relatively higher value in summer (July and August), and for other months it is closely related to the ozone monthly mean. These secondary peaks of the ozone monthly mean in fall might be caused by the UV radiation coming back to its relevant value after falling off during the Asia summer monsoon; it was not related to biomass burning. The intraseasonal cycling of ozone might be related to the MJO (Madden–Julian Oscillation). Further studies are needed to understand the relationship between the local ozone intraseasonal variation and the MJO. The quasi-biennial variation of ozone in Shanghai might be a local reflection of climate change and could be associated with ENSO (El-Nino Southern Oscillation). Further studies will be needed to understand the relationship of the quasi-biennial variation of ozone to ENSO. - Highlights: • The spectral decomposition methods are used. • The spectra of surface ozone have multi

The high-frequency ESR spectra of the syntetic diamond and nanodiamonds type Ib at low temperature

International Nuclear Information System (INIS)

Khatsko, E.; Kobets, M.; Dergachev, K.; Kulbickas, A.; Rasteniene, L.; Vaisnoras, R.

2013-01-01

The ESR absorption spectra of nonirradiated and irradiated (by electrons with an energy of 2 MeV) bulk diamond and nanodiamond powder of type Ib have been studied at a wide range of frequencies (70-20 GHz) and temperature (4.2-0 K) by ESR method. It is shown, that in the ESR spectrum of bulk diamond absorption lines of ion nickel catalyst Ni +a nd a paramagnetic single center of the nitrogen N 0 is observed. Absorption lines of the paramagnetic centers with dangling bonds on the nanodiamond surface (surface defects) in the ESR spectra are obtained.

Spectroscopic observations of the Moon at the lunar surface

Science.gov (United States)

Wu, Yunzhao; Hapke, Bruce

2018-02-01

The Moon's reflectance spectrum records many of its important properties. However, prior to Chang'E-3 (CE-3), no spectra had previously been measured on the lunar surface. Here we show the in situ reflectance spectra of the Moon acquired on the lunar surface by the Visible-Near Infrared Spectrometer (VNIS) onboard the CE-3 rover. The VNIS detected thermal radiation from the lunar regolith, though with much shorter wavelength range than typical thermal radiometer. The measured temperatures are higher than expected from theoretical model, indicating low thermal inertia of the lunar soil and the effects of grain facet on soil temperature in submillimeter scale. The in situ spectra also reveal that 1) brightness changes visible from orbit are related to the reduction in maturity due to the removal of the fine and weathered particles by the lander's rocket exhaust, not the smoothing of the surface and 2) the spectra of the uppermost soil detected by remote sensing exhibit substantial differences with that immediately beneath, which has important implications for the remote compositional analysis. The reflectance spectra measured by VNIS not only reveal the thermal, compositional, and space-weathering properties of the Moon but also provide a means for the calibration of optical instruments that view the surface remotely.

Surface enhanced raman spectroscopy on chip

DEFF Research Database (Denmark)

Hübner, Jörg; Anhøj, Thomas Aarøe; Zauner, Dan

2007-01-01

In this paper we report low resolution surface enhanced Raman spectra (SERS) conducted with a chip based spectrometer. The flat field spectrometer presented here is fabricated in SU-8 on silicon, showing a resolution of around 3 nm and a free spectral range of around 100 nm. The output facet...... is projected onto a CCD element and visualized by a computer. To enhance the otherwise rather weak Raman signal, a nanosurface is prepared and a sample solutions is impregnated on this surface. The surface enhanced Raman signal is picked up using a Raman probe and coupled into the spectrometer via an optical...... fiber. The obtained spectra show that chip based spectrometer together with the SERS active surface can be used as Raman sensor....

The atmospheric parameters of FGK stars using wavelet analysis of CORALIE spectra

Science.gov (United States)

Gill, S.; Maxted, P. F. L.; Smalley, B.

2018-05-01

Context. Atmospheric properties of F-, G- and K-type stars can be measured by spectral model fitting or with the analysis of equivalent width (EW) measurements. These methods require data with good signal-to-noise ratios (S/Ns) and reliable continuum normalisation. This is particularly challenging for the spectra we have obtained with the CORALIE échelle spectrograph for FGK stars with transiting M-dwarf companions. The spectra tend to have low S/Ns, which makes it difficult to analyse them using existing methods. Aims: Our aim is to create a reliable automated spectral analysis routine to determine Teff, [Fe/H], V sini from the CORALIE spectra of FGK stars. Methods: We use wavelet decomposition to distinguish between noise, continuum trends, and stellar spectral features in the CORALIE spectra. A subset of wavelet coefficients from the target spectrum are compared to those from a grid of models in a Bayesian framework to determine the posterior probability distributions of the atmospheric parameters. Results: By testing our method using synthetic spectra we found that our method converges on the best fitting atmospheric parameters. We test the wavelet method on 20 FGK exoplanet host stars for which higher-quality data have been independently analysed using EW measurements. We find that we can determine Teff to a precision of 85 K, [Fe/H] to a precision of 0.06 dex and V sini to a precision of 1.35 km s-1 for stars with V sini ≥ 5 km s-1. We find an offset in metallicity ≈- 0.18 dex relative to the EW fitting method. We can determine log g to a precision of 0.13 dex but find systematic trends with Teff. Measurements of log g are only reliable enough to confirm dwarf-like surface gravity (log g ≈ 4.5). Conclusions: The wavelet method can be used to determine Teff, [Fe/H], and V sini for FGK stars from CORALIE échelle spectra. Measurements of log g are unreliable but can confirm dwarf-like surface gravity. We find that our method is self consistent, and

The Dynamic Method for Time-of-Flight Measurement of Thermal Neutron Spectra from Pulsed Sources

International Nuclear Information System (INIS)

Pepelyshev, Yu.N.; Tulaev, A.B.; Bobrakov, V.F.

1994-01-01

The time-of-flight method for a measurement of thermal neutron spectra in the pulsed neutron sources with high efficiency of neutron registration, more than 10 5 times higher in comparison with traditional one, is described. The main problems connected with the electric current technique for time-of-flight spectra measurement are examined. The methodical errors, problems of a special neutron detector design and other questions are discussed. Some experimental results, spectra from surfaces of the water and solid methane moderators, obtained in the pulsed reactor IBR-2 (Dubna, Russia) are presented. 4 refs., 5 figs

Analysis of spatial and temporal spectra of liquid film surface in annular gas-liquid flow

Science.gov (United States)

Alekseenko, Sergey; Cherdantsev, Andrey; Heinz, Oksana; Kharlamov, Sergey; Markovich, Dmitriy

2013-09-01

Wavy structure of liquid film in annular gas-liquid flow without liquid entrainment consists of fast long-living primary waves and slow short-living secondary waves. In present paper, results of spectral analysis of this wavy structure are presented. Application of high-speed LIF technique allowed us to perform such analysis in both spatial and temporal domains. Power spectra in both domains are characterized by one-humped shape with long exponential tail. Influence of gas velocity, liquid Reynolds number, liquid viscosity and pipe diameter on frequency of the waves is investigated. When gravity effect is much lesser than the shear stress, similarity of power spectra at different gas velocities is observed. Using combination of spectral analysis and identification of characteristic lines of primary waves, frequency of generation of secondary waves by primary waves is measured.

Spectra of Graphs

NARCIS (Netherlands)

Brouwer, A.E.; Haemers, W.H.

2012-01-01

This book gives an elementary treatment of the basic material about graph spectra, both for ordinary, and Laplace and Seidel spectra. The text progresses systematically, by covering standard topics before presenting some new material on trees, strongly regular graphs, two-graphs, association

Physical aspects of electron emission spectra shape for ferroelectrics-electrets

International Nuclear Information System (INIS)

Kolesnikov, V.V.; Kozakov, A.T.

2002-01-01

One introduces a theoretical approach establishing a link between the peculiarities of spectrum of electron emission from ferroelectrics-electrets and the behavior of potential at a specimen surface. From these points of view one analyzes physical nature of the key peculiarities in the experimental spectra. One points out strong effect of electret charge relaxation on their shape due to bifurcation (branching) of peculiarities in a spectrum. A complex shape of spectrum of electron emission from ferroelectrics-electrets results from peculiarities of distribution of electrical field and polarization along their surface [ru

The effect of radiation-thermal treatment on the physicochemical properties of the Ni-Mo/Al2O3 hydrotreatment catalyst. II. UV-Vis diffuse reflectance spectra of surface compounds after irradiation

International Nuclear Information System (INIS)

Solovetskii, Yu.I.; Miroshinichenko, I.I.; Lunin, V.V.

1993-01-01

Radiation-thermal damage of the surface and the active metal phases of hydrodesulfurization Ni-Mo/Al 2 O 3 catalysts by a fast electron beam of up to 2.0 MeV energy was studied. UV-Vis diffuse reflectance spectra of the industrial and model coked systems after radiation-thermal treatment were measured. 14 refs., 2 figs

Multifunctional MgO Layer in Perovskite Solar Cells.

Science.gov (United States)

Guo, Xudong; Dong, Haopeng; Li, Wenzhe; Li, Nan; Wang, Liduo

2015-06-08

A multifunctional magnesium oxide (MgO) layer was successfully introduced into perovskite solar cells (PSCs) to enhance their performance. MgO was coated onto the surface of mesoporous TiO(2) by the decomposition of magnesium acetate and, therefore, could block contact between the perovskite and TiO(2). X-ray photoelectron spectroscopy and infrared spectroscopy showed that the amount of H(2)O/hydroxyl absorbed on the TiO(2) decreased after MgO modification. The UV/Vis absorption spectra of the perovskite with MgO modification revealed an enhanced photoelectric performance compared with that of unmodified perovskite after UV illumination. In addition to the photocurrent, the photovoltage and fill factor also showed an enhancement after modification, which resulted in an increase in the overall efficiency of the cell from 9.6 to 13.9 %. Electrochemical impedance spectroscopy (EIS) confirmed that MgO acts as an insulating layer to reduce charge recombination. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Surface composition of Mercury from reflectance spectrophotometry

Science.gov (United States)

Vilas, Faith

1988-01-01

The controversies surrounding the existing spectra of Mercury are discussed together with the various implications for interpretations of Mercury's surface composition. Special attention is given to the basic procedure used for reducing reflectance spectrophotometry data, the factors that must be accounted for in the reduction of these data, and the methodology for defining the portion of the surface contributing the greatest amount of light to an individual spectrum. The application of these methodologies to Mercury's spectra is presented.

Raman spectra of zinc phthalocyanine monolayers absorbed on glassy carbon and gold electrodes by application of a confocal Raman microspectrometer

NARCIS (Netherlands)

Palys-Staron, B.J.; Palys, B.J.; Puppels, G.J.; Puppels, G.J.; van den Ham, D.M.W.; van den Ham, D.M.W.; Feil, D.; Feil, D.

1992-01-01

Raman spectra of zinc phthalocyanine monolayers, adsorbed on gold and on glassy carbon surfaces (electrodes), are presented. These spectra have been recorded with the electrodes inside and outside an electrochemical cell filled with an aqueous electrolyte. A confocal Raman microspectrometer was

Manifestation of surface phonons in far infrared reflectivity of diamond-type semiconductors

Energy Technology Data Exchange (ETDEWEB)

Perez-Sanchez, F.L.; Perez-Rodriguez, F. [Instituto de Fisica, Universidad Autonoma de Puebla, Apdo. Post. J-48, Puebla, Pue. 72570 (Mexico)

2004-11-01

The coupling of surface phonons with light at (001) surfaces of diamond-structure crystals and its manifestation in far-infrared anisotropy spectra are theoretically studied. We apply the adiabatic bond charge model to describe short-range mechanical interactions together with long-range Coulomb forces and radiation fields, and we solve the corresponding system of coupled equations for the electromagnetic field and the lattice vibrations. We calculate far-infrared normal reflectance spectra of (001) surfaces of semi-infinite diamond-type crystals. In particular, we analyse reflectance spectra for the Si(001) (2 x 1) surface, which exhibit a resonance structure associated with the excitation of surface phonon modes. (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Preparation of Semiconducting Materials in the Laboratory, Part 3: The One-Penny Photovoltaic Cell

Science.gov (United States)

Ibanez, Jorge G.; Finck-Pastrana, Adolfo; Mugica-Barrera, Alejandra; Balderas-Hernandez, Patricia; Ibarguengoitia-Cervantes, Martha E.; Garcia-Pintor, Elizabeth; Hartasanchez-Frenk, Jose Miguel; Bonilla-Jaurez, Cesar E.; Maldonado-Cordero, Casandra; Struck-Garza, Adelwart; Suberbie-Rocha, Felipe

2011-01-01

Copper(I) oxide photoresponsive layers are prepared on copper surfaces (e.g., U.S. pre-1982 pennies) by simple thermal, chemical, and electrochemical procedures. An easily measurable photovoltage (up to 100 mV) is obtained in each case under visible light illumination. (Contains 2 figures.)

Charge transfer from TiO2 into adsorbed benzene diazonium compounds

Science.gov (United States)

Merson, A.; Dittrich, Th.; Zidon, Y.; Rappich, J.; Shapira, Yoram

2004-08-01

Electron transfer from sol-gel-prepared TiO2 into adsorbed benzene diazonium compounds has been investigated using cyclic voltammetry, x-ray photoelectron spectroscopy, contact potential difference, and surface photovoltage spectroscopy. The results show that the potential of maximum electron transfer depends strongly on the dipole moment of the benzene compound. Two reactive surface sites at which electron transfer occurs have been identified.

Multivariate analysis of TOF-SIMS spectra of monolayers on scribed silicon.

Science.gov (United States)

Yang, Li; Lua, Yit-Yian; Jiang, Guilin; Tyler, Bonnie J; Linford, Matthew R

2005-07-15

Static time-of-flight secondary ion mass spectrometry (TOF-SIMS) was performed on monolayers on scribed silicon (Si(scr)) derived from 1-alkenes, 1-alkynes, 1-holoalkanes, aldehydes, and acid chlorides. To rapidly determine the variation in the data without introducing user bias, a multivariate analysis was performed. First, principal components analysis (PCA) was done on data obtained from silicon scribed with homologous series of aldehydes and acid chlorides. For this study, the positive ion spectra, the negative ion spectra, and the concatentated (linked) positive and negative ion spectra were preprocessed by normalization, mean centering, and autoscaling. The mean centered data consistently showed the best correlations between the scores on PC1 and the number of carbon atoms in the adsorbate. These correlations were not as strong for the normalized and autoscaled data. After reviewing these methods, it was concluded that mean centering is the best preprocessing method for TOF-SIMS spectra of monolayers on Si(scr). A PCA analysis of all of the positive ion spectra revealed a good correlation between the number of carbon atoms in all of the adsorbates and the scores on PC1. PCA of all of the negative ion spectra and the concatenated positive and negative ion spectra showed a correlation based on the number of carbon atoms in the adsorbate and the class of the adsorbate. These results imply that the positive ion spectra are most sensitive to monolayer thickness, while the negative ion spectra are sensitive to the nature of the substrate-monolayer interface and the monolayer thickness. Loadings show an inverse relationship between (inorganic) fragments that are expected from the substrate and (organic) fragments expected from the monolayer. Multivariate peak intensity ratios were derived. It is also suggested that PCA can be used to detect outlier surfaces. Partial least squares showed a strong correlation between the number of carbon atoms in the adsorbate and the

Atomic beams probe surface vibrations

International Nuclear Information System (INIS)

Robinson, A.L.

1982-01-01

In the last two years, surface scientist have begun trying to obtain the vibrational frequencies of surface atoms in both insulating and metallic crystals from beams of helium atoms. It is the inelastic scattering that researchers use to probe surface vibrations. Inelastic atomic beam scattering has only been used to obtain vibrational frequency spectra from clean surfaces. Several experiments using helium beams are cited. (SC)

Surface-enhanced Raman scattering spectra revealing the inter-cultivar differences for Chinese ornamental Flos Chrysanthemum: a new promising method for plant taxonomy

Directory of Open Access Journals (Sweden)

Heng Zhang

2017-10-01

Full Text Available Abstract Background Flos Chrysanthemi, as a part of Chinese culture for a long history, is valuable for not only environmental decoration but also the medicine and food additive. Due to their voluminously various breeds and extensive distributions worldwide, it is burdensome to make recognition and classification among numerous cultivars with conventional methods which still rest on the level of morphologic observation and description. As a fingerprint spectrum for parsing molecular information, surface-enhanced Raman scattering (SERS could be a suitable candidate technique to characterize and distinguish the inter-cultivar differences at molecular level. Results SERS spectra were used to analyze the inter-cultivar differences among 26 cultivars of Chinese ornamental Flos Chrysanthemum. The characteristic peaks distribution patterns were abstracted from SERS spectra and varied from cultivars to cultivars. For the bands distributed in the pattern map, the similarities in general showed their commonality while in the finer scales, the deviations and especially the particular bands owned by few cultivars revealed their individualities. Since the Raman peaks could characterize specific chemical components, those diversity of patterns could indicate the inter-cultivar differences at the chemical level in fact. Conclusion In this paper, SERS technique is feasible for distinguishing the inter-cultivar differences among Flos Chrysanthemum. The Raman spectral library was built with SERS characteristic peak distribution patterns. A new method was proposed for Flos Chrysanthemum recognition and taxonomy.

Sensitivity Analysis of X-ray Spectra from Scanning Electron Microscopes

Energy Technology Data Exchange (ETDEWEB)

Miller, Thomas Martin [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Patton, Bruce W. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Weber, Charles F. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Bekar, Kursat B. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

2014-10-01

The primary goal of this project is to evaluate x-ray spectra generated within a scanning electron microscope (SEM) to determine elemental composition of small samples. This will be accomplished by performing Monte Carlo simulations of the electron and photon interactions in the sample and in the x-ray detector. The elemental inventories will be determined by an inverse process that progressively reduces the difference between the measured and simulated x-ray spectra by iteratively adjusting composition and geometric variables in the computational model. The intended benefit of this work will be to develop a method to perform quantitative analysis on substandard samples (heterogeneous phases, rough surfaces, small sizes, etc.) without involving standard elemental samples or empirical matrix corrections (i.e., true standardless quantitative analysis).

α-spectra hyperfine structure resolution by silicon planar detectors

International Nuclear Information System (INIS)

Eremin, V.K.; Verbitskaya, E.M.; Strokan, N.B.; Sukhanov, V.L.; Malyarenko, A.M.

1986-01-01

The lines with 13 keV step from the main one is α-spectra of nuclei with an odd number of nucleons take place. Silicon planar detectors n-Si with the operation surface of 10 mm 2 are developed for resolution of this hyperfine structure. The mechanism of losses in detectors for short-range-path particles is analyzed. The results of measurements from detectors with 10 keV resolution are presented

Simulation of electron energy loss spectra of nanomaterials with linear-scaling density functional theory

International Nuclear Information System (INIS)

Tait, E W; Payne, M C; Ratcliff, L E; Haynes, P D; Hine, N D M

2016-01-01

Experimental techniques for electron energy loss spectroscopy (EELS) combine high energy resolution with high spatial resolution. They are therefore powerful tools for investigating the local electronic structure of complex systems such as nanostructures, interfaces and even individual defects. Interpretation of experimental electron energy loss spectra is often challenging and can require theoretical modelling of candidate structures, which themselves may be large and complex, beyond the capabilities of traditional cubic-scaling density functional theory. In this work, we present functionality to compute electron energy loss spectra within the onetep linear-scaling density functional theory code. We first demonstrate that simulated spectra agree with those computed using conventional plane wave pseudopotential methods to a high degree of precision. The ability of onetep to tackle large problems is then exploited to investigate convergence of spectra with respect to supercell size. Finally, we apply the novel functionality to a study of the electron energy loss spectra of defects on the (1 0 1) surface of an anatase slab and determine concentrations of defects which might be experimentally detectable. (paper)

Optical properties of tungsten disulfide single crystals doped with gold

International Nuclear Information System (INIS)

Dumcenco, D.O.; Hsu, H.P.; Huang, Y.S.; Liang, C.H.; Tiong, K.K.; Du, C.H.

2008-01-01

Single crystals of WS 2 doped with gold have been grown by the chemical vapour transport method using iodine as a transporting agent. X-ray diffraction (XRD) pattern analysis revealed presence of mixed three-layer rhombohedral (3R) and two-layer hexagonal (2H) polytypes for the doped crystals while the undoped one shows only 2H form. Hall measurements indicate that the samples are p-type in nature. The doping effects of the materials are characterized by surface photovoltage (SPV), photoconductivity (PC) and piezoreflectance (PzR) measurements. Room temperature SPV and PC spectra reveal a feature located at ∼60 meV below the A exciton and has been tentatively assigned to be an impurity level caused by Au dopant. Excitonic transition energies of the A, B, d and C excitons detected in PzR spectra show red shift due to the presence of a small amount of Au and the broadening parameters of the excitonic transition features increase due to impurity scattering. The values of the parameters that describe the electron (exciton)-phonon interaction of excitonic transitions of A-B are about two times larger than that of d-C excitonic pairs. The possible assignments of the different origins of A-B and d-C excitonic pairs have been discussed

Facile synthesis of bismuth oxyhalide nanosheet films with distinct conduction type and photo-induced charge carrier behavior

Science.gov (United States)

Jia, Huimin; He, Weiwei; Zhang, Beibei; Yao, Lei; Yang, Xiaokai; Zheng, Zhi

2018-05-01

A modified successive ionic layer adsorption and reaction (SILAR) method was developed to fabricate 2D ordered BiOX (X = CI, Br, I) nanosheet array films on FTO substrates at room temperature. The formation of BiOX films were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), UV-vis absorption spectroscopy, and X-ray photoelectron spectroscopy (XPS). The semiconductor surface states determine the type of semiconductor. Although BiOCI, BiOBr and BiOI belong to the bismuth oxyhalide semiconductor family and possess similar crystal and electronic structures, they show different conductivity types due to their respective surface states. Mott-Schottky curve results demonstrate that the BiOCl and BiOI nanosheet arrays display n-type semiconductor properties, while the BiOBr films exhibit p-type semiconductor properties. Assisted by surface photovoltage (SPV) and transient photovoltage (TPV) techniques, the photoinduced charge transfer dynamics on the surface/interface of the BiOX/FTO nanosheet films were systematically and comparatively investigated. As revealed by the results, both the separation and transfer dynamics of the photo-induced carrier are influenced by film thickness.

The effect of work function changes on secondary ion energy spectra

International Nuclear Information System (INIS)

Wittmaack, K.

1983-01-01

The effect of work function changes on experimental secondary ion energy spectra is discussed. In agreement with theory the measured ion intensities frequently exhibit an exponential work function dependence. However, the predicted velocity dependence is only observed at fairly high secondary ion energies. In the absence of a velocity dependence of the degree of ionization measured shifts of energy spectra reflect work function changes directly. Various instrumental problems are shown to aggravate a detailed comparison between experiment and theory. Significant artefacts must be expected if the extraction field is of the order of or less than the lateral field induced by a work function difference between the bombarded spot and the surrounding sample surface. (Auth.)

Charged particle discrimination with silicon surface barrier detectors

International Nuclear Information System (INIS)

Coote, G.E.; Pithie, J.; Vickridge, I.C.

1996-01-01

The application for materials analysis of nuclear reactions that give rise to charged particles is a powerful surface analytical and concentration depth profiling technique. Spectra of charged particles, with energies in the range 0.1 to 15 MeV, emitted from materials irradiated with beams of light nuclei such as deuterons are measured with silicon surface barrier detectors. The spectra from multi-elemental materials typically encountered in materials research are usually composed of an overlapping superposition of proton, alpha, and other charged particle spectra. Interpretation of such complex spectra would be simplified if a means were available to electronically discriminate between the detector response to the different kinds of charged particle. We have investigated two methods of discriminating between different types of charged particles. The fast charge pulses from a surface barrier detector have different shapes, depending on the spatial distribution of energy deposition of the incident particle. Fast digitisation of the pulses, followed by digital signal processing provides one avenue for discrimination. A second approach is to use a thin transmission detector in front of a thick detector as a detector telescope. For a given incident energy, different types of charged particles will lose different amounts of energy in the thin detector, providing an alternative means of discrimination. We show that both approaches can provide significant simplification in the interpretation of charged particle spectra in practical situations, and suggest that silicon surface barrier detectors having graded electronic properties could provide improved discrimination compared to the current generation of detectors having homogeneous electronic properties. (author).12 refs., 2 tabs., 28 figs

Accounting for nanometer-thick adventitious carbon contamination in X-ray absorption spectra of carbon-based materials.

Science.gov (United States)

Mangolini, Filippo; McClimon, J Brandon; Rose, Franck; Carpick, Robert W

2014-12-16

Near-edge X-ray absorption fine structure (NEXAFS) spectroscopy is a powerful technique for characterizing the composition and bonding state of nanoscale materials and the top few nanometers of bulk and thin film specimens. When coupled with imaging methods like photoemission electron microscopy, it enables chemical imaging of materials with nanometer-scale lateral spatial resolution. However, analysis of NEXAFS spectra is often performed under the assumption of structural and compositional homogeneity within the nanometer-scale depth probed by this technique. This assumption can introduce large errors when analyzing the vast majority of solid surfaces due to the presence of complex surface and near-surface structures such as oxides and contamination layers. An analytical methodology is presented for removing the contribution of these nanoscale overlayers from NEXAFS spectra of two-layered systems to provide a corrected photoabsorption spectrum of the substrate. This method relies on the subtraction of the NEXAFS spectrum of the overlayer adsorbed on a reference surface from the spectrum of the two-layer system under investigation, where the thickness of the overlayer is independently determined by X-ray photoelectron spectroscopy (XPS). This approach is applied to NEXAFS data acquired for one of the most challenging cases: air-exposed hard carbon-based materials with adventitious carbon contamination from ambient exposure. The contribution of the adventitious carbon was removed from the as-acquired spectra of ultrananocrystalline diamond (UNCD) and hydrogenated amorphous carbon (a-C:H) to determine the intrinsic photoabsorption NEXAFS spectra of these materials. The method alters the calculated fraction of sp(2)-hybridized carbon from 5 to 20% and reveals that the adventitious contamination can be described as a layer containing carbon and oxygen ([O]/[C] = 0.11 ± 0.02) with a thickness of 0.6 ± 0.2 nm and a fraction of sp(2)-bonded carbon of 0.19 ± 0.03. This

High reduction of interfacial charge recombination in colloidal quantum dot solar cells by metal oxide surface passivation.

Science.gov (United States)

Chang, Jin; Kuga, Yuki; Mora-Seró, Iván; Toyoda, Taro; Ogomi, Yuhei; Hayase, Shuzi; Bisquert, Juan; Shen, Qing

2015-03-12

Bulk heterojunction (BHJ) solar cells based on colloidal QDs and metal oxide nanowires (NWs) possess unique and outstanding advantages in enhancing light harvesting and charge collection in comparison to planar architectures. However, the high surface area of the NW structure often brings about a large amount of recombination (especially interfacial recombination) and limits the open-circuit voltage in BHJ solar cells. This problem is solved here by passivating the surface of the metal oxide component in PbS colloidal quantum dot solar cells (CQDSCs). By coating thin TiO2 layers onto ZnO-NW surfaces, the open-circuit voltage and power conversion efficiency have been improved by over 40% in PbS CQDSCs. Characterization by transient photovoltage decay and impedance spectroscopy indicated that the interfacial recombination was significantly reduced by the surface passivation strategy. An efficiency as high as 6.13% was achieved through the passivation approach and optimization for the length of the ZnO-NW arrays (device active area: 16 mm2). All solar cells were tested in air, and exhibited excellent air storage stability (without any performance decline over more than 130 days). This work highlights the significance of metal oxide passivation in achieving high performance BHJ solar cells. The charge recombination mechanism uncovered in this work could shed light on the further improvement of PbS CQDSCs and/or other types of solar cells.

Influence of probe pressure on diffuse reflectance spectra of human skin measured in vivo

Science.gov (United States)

Popov, Alexey P.; Bykov, Alexander V.; Meglinski, Igor V.

2017-11-01

Mechanical pressure superficially applied on the human skin surface by a fiber-optic probe influences the spatial distribution of blood within the cutaneous tissues. Upon gradual load of weight on the probe, a stepwise increase in the skin reflectance spectra is observed. The decrease in the load follows the similar inverse staircase-like tendency. The observed stepwise reflectance spectra changes are due to, respectively, sequential extrusion of blood from the topical cutaneous vascular beds and their filling afterward. The obtained results are confirmed by Monte Carlo modeling. This implies that pressure-induced influence during the human skin diffuse reflectance spectra measurements in vivo should be taken into consideration, in particular, in the rapidly developing area of wearable gadgets for real-time monitoring of various human body parameters.

Transmission Spectra of HgTe-Based Quantum Wells and Films in the Far-Infrared Range

Science.gov (United States)

Savchenko, M. L.; Vasil'ev, N. N.; Yaroshevich, A. S.; Kozlov, D. A.; Kvon, Z. D.; Mikhailov, N. N.; Dvoretskii, S. A.

2018-04-01

Strained 80-nm-thick HgTe films belong to a new class of materials referred to as three-dimensional topological insulators (i.e., they have a bulk band gap and spin-nondegenerate surface states). Though there are a number of studies devoted to analysis of the properties of surface states using both transport and magnetooptical techniques in the THz range, the information about direct optical transitions between bulk and surface bands in these systems has not been reported. This study is devoted to the analysis of transmission and reflection spectra of HgTe films of different thicknesses in the far-infrared range recorded in a wide temperature range in order to detect the above interband transitions. A peculiarity at 15 meV, which is sensitive to a change in the temperature, is observed in spectra of both types. Detailed analysis of the data obtained revealed that this feature is related to absorption by HgTe optical phonons, while the interband optical transitions are suppressed.

Curved Radio Spectra of Weak Cluster Shocks

Science.gov (United States)

Kang, Hyesung; Ryu, Dongsu

2015-08-01

In order to understand certain observed features of arc-like giant radio relics such as the rareness, uniform surface brightness, and curved integrated spectra, we explore a diffusive shock acceleration (DSA) model for radio relics in which a spherical shock impinges on a magnetized cloud containing fossil relativistic electrons. Toward this end, we perform DSA simulations of spherical shocks with the parameters relevant for the Sausage radio relic in cluster CIZA J2242.8+5301, and calculate the ensuing radio synchrotron emission from re-accelerated electrons. Three types of fossil electron populations are considered: a delta-function like population with the shock injection momentum, a power-law distribution, and a power law with an exponential cutoff. The surface brightness profile of the radio-emitting postshock region and the volume-integrated radio spectrum are calculated and compared with observations. We find that the observed width of the Sausage relic can be explained reasonably well by shocks with speed {u}{{s}}˜ 3× {10}3 {km} {{{s}}}-1 and sonic Mach number {M}{{s}}˜ 3. These shocks produce curved radio spectra that steepen gradually over (0.1-10){ν }{br} with a break frequency {ν }{br}˜ 1 GHz if the duration of electron acceleration is ˜60-80 Myr. However, the abrupt increase in the spectral index above ˜1.5 GHz observed in the Sausage relic seems to indicate that additional physical processes, other than radiative losses, operate for electrons with {γ }{{e}}≳ {10}4.

Field verification of ADCP surface gravity wave elevation spectra

NARCIS (Netherlands)

Hoitink, A.J.F.; Peters, H.C.; Schroevers, M.

2007-01-01

Acoustic Doppler current profilers (ADCPs) can measure orbital velocities induced by surface gravity waves, yet the ADCP estimates of these velocities are subject to a relatively high noise level. The present paper introduces a linear filtration technique to significantly reduce the influence of

Neutron and photon spectra in LINACs

International Nuclear Information System (INIS)

Vega-Carrillo, H.R.; Martínez-Ovalle, S.A.; Lallena, A.M.; Mercado, G.A.; Benites-Rengifo, J.L.

2012-01-01

A Monte Carlo calculation, using the MCNPX code, was carried out in order to estimate the photon and neutron spectra in two locations of two linacs operating at 15 and 18 MV. Detailed models of both linac heads were used in the calculations. Spectra were estimated below the flattening filter and at the isocenter. Neutron spectra show two components due to evaporation and knock-on neutrons. Lethargy spectra under the filter were compared to the spectra calculated from the function quoted by Tosi et al. that describes reasonably well neutron spectra beyond 1 MeV, though tends to underestimate the energy region between 10 –6 and 1 MeV. Neutron and the Bremsstrahlung spectra show the same features regardless of the linac voltage. - Highlights: ► With MCNPX code realistic models of two LINACs were built. ► Photon and neutron spectra below the flattening filter and at the isocenter were calculated. ► Neutron spectrum at the flattening filter was compared against the Tosi et al. source-term model. ► Tosi et al. model underestimates the neutron contribution below 1 MeV. ► Photon spectra look alike to those published in literature.

Surface vibrational spectroscopy (EELS)

International Nuclear Information System (INIS)

Okuyama, Hiroshi

2006-01-01

Adsorbed states of hydrogen on metal surfaces have been studied by means of electron energy loss spectroscopy (EELS). In this article, typical spectra and analysis as well as recent development are introduced. (author)

Surface-electronic-state effects in electron emission from the Be(0001) surface

International Nuclear Information System (INIS)

Archubi, C. D.; Gravielle, M. S.; Silkin, V. M.

2011-01-01

We study the electron emission produced by swift protons impinging grazingly on a Be(0001) surface. The process is described within a collisional formalism using the band-structure-based (BSB) approximation to represent the electron-surface interaction. The BSB model provides an accurate description of the electronic band structure of the solid and the surface-induced potential. Within this approach we derive both bulk and surface electronic states, with these latter characterized by a strong localization at the crystal surface. We found that such surface electronic states play an important role in double-differential energy- and angle-resolved electron emission probabilities, producing noticeable structures in the electron emission spectra.

Surface-electronic-state effects in electron emission from the Be(0001) surface

Energy Technology Data Exchange (ETDEWEB)

Archubi, C. D. [Instituto de Astronomia y Fisica del Espacio, casilla de correo 67, sucursal 28, C1428EGA, Buenos Aires (Argentina); Gravielle, M. S. [Instituto de Astronomia y Fisica del Espacio, casilla de correo 67, sucursal 28, C1428EGA, Buenos Aires (Argentina); Departamento de Fisica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires (Argentina); Silkin, V. M. [Donostia International Physics Center, E-20018 San Sebastian (Spain); Departamento de Fisica de Materiales, Facultad de Ciencias Quimicas, Universidad del Pais Vasco, Apartado 1072, E-20080 San Sebastian (Spain); IKERBASQUE, Basque Foundation for Science, E-48011 Bilbao (Spain)

2011-07-15

We study the electron emission produced by swift protons impinging grazingly on a Be(0001) surface. The process is described within a collisional formalism using the band-structure-based (BSB) approximation to represent the electron-surface interaction. The BSB model provides an accurate description of the electronic band structure of the solid and the surface-induced potential. Within this approach we derive both bulk and surface electronic states, with these latter characterized by a strong localization at the crystal surface. We found that such surface electronic states play an important role in double-differential energy- and angle-resolved electron emission probabilities, producing noticeable structures in the electron emission spectra.

A high resolution photoemission study of surface core-level shifts in clean and oxygen-covered Ir(2 1 0) surfaces

Energy Technology Data Exchange (ETDEWEB)

Gladys, M.J.; Ermanoski, I.; Jackson, G.; Quinton, J.S.; Rowe, J.E.; Madey, T.E. E-mail: madey@physics.rutgers.edu

2004-04-01

High resolution soft X-ray photoemission electron spectroscopy (SXPS), using synchrotron radiation, is employed to investigate 4f core-level features of four differently-prepared Ir(2 1 0) surfaces: clean planar, oxygen-covered planar, oxygen-induced faceted, and clean faceted surfaces. Surface and bulk peak identifications are supported by measurements at different photon energies (thus probing different electron escape depths) and variable emission angles. Iridium 4f{sub 7/2} photoemission spectra are fitted with Doniach-Sunjic lineshapes. The surface components are identified with core levels positioned at lower binding energies than the bulk components, in contrast to previous reports of binding energy inversion on Ir(1 0 0) (1x1) and (5x1) surfaces. For clean planar Ir(2 1 0) three surface Ir 4f{sub 7/2} features are observed with core-level shifts of -765, -529, and -281 meV, with respect to the bulk; these are associated with the first, second and third layers of atoms, respectively, for atomically rough Ir(2 1 0). Adsorption of oxygen onto the planar Ir(2 1 0) surface is found to cause a suppression and shift of the surface features to higher binding energies. Annealing at T{>=}600 K in oxygen produces a faceted surface as verified by low energy electron diffraction (LEED). A comparison of planar and faceted oxygen-covered surfaces reveals minor differences in the normal emission SXPS spectra, while grazing emission spectra exhibit differences. The SXPS spectrum of the clean, faceted Ir(2 1 0) exhibits small differences in comparison to the clean planar case, with surface features having binding energy shifts of -710, -450, and -230 meV.

Solar Energetic Particle Spectra

Science.gov (United States)

Ryan, J. M.; Boezio, M.; Bravar, U.; Bruno, A.; Christian, E. R.; de Nolfo, G. A.; Martucci, M.; Mergè, M.; Munini, R.; Ricci, M.; Sparvoli, R.; Stochaj, S.

2017-12-01

We report updated event-integrated spectra from several SEP events measured with PAMELA. The measurements were made from 2006 to 2014 in the energy range starting at 80 MeV and extending well above the neutron monitor threshold. The PAMELA instrument is in a high inclination, low Earth orbit and has access to SEPs when at high latitudes. Spectra have been assembled from these high-latitude measurements. The field of view of PAMELA is small and during the high-latitude passes it scans a wide range of asymptotic directions as the spacecraft orbits. Correcting for data gaps, solid angle effects and improved background corrections, we have compiled event-integrated intensity spectra for twenty-eight SEP events. Where statistics permit, the spectra exhibit power law shapes in energy with a high-energy exponential roll over. The events analyzed include two genuine ground level enhancements (GLE). In those cases the roll-over energy lies above the neutron monitor threshold ( 1 GV) while the others are lower. We see no qualitative difference between the spectra of GLE vs. non-GLE events, i.e., all roll over in an exponential fashion with rapidly decreasing intensity at high energies.

Analytical Model of Doppler Spectra of Light Backscattered from Rotating Convex Bodies of Revolution in the Global Cartesian Coordinate System

International Nuclear Information System (INIS)

Yan-Jun, Gong; Zhen-Sen, Wu; Jia-Ji, Wu

2009-01-01

We present an analytical model of Doppler spectra in backscattering from arbitrary rough convex bodies of revolution rotating around their axes in the global Cartesian coordinate system. This analytical model is applied to analyse Doppler spectra in backscatter from two cones and two cylinders, as well as two ellipsoids of revolution. We numerically analyse the influences of attitude and geometry size of objects on Doppler spectra. The analytical model can give contribution of the surface roughness, attitude and geometry size of convex bodies of revolution to Doppler spectra and may contribute to laser Doppler velocimetry as well as ladar applications

Response spectra in alluvial soils

International Nuclear Information System (INIS)

Chandrasekharan, A.R.; Paul, D.K.

1975-01-01

For aseismic design of structures, the ground motion data is assumed either in the form of ground acceleration as a function of time or indirectly in the form of response spectra. Though the response spectra approach has limitations like not being applicable for nonlinear problems, it is usually used for structures like nuclear power plants. Fifty accelerograms recorded at alluvial sites have been processed. Since different empirical formulas relating acceleration with magnitude and distance give a wide scatter of values, peak ground acceleration alone cannot be the parameter as is assumed by a number of authors. The spectra corresponding to 5% damping have been normalised with respect to three parameters, namely, peak ground acceleration, peak ground velocity and a nondimensional quantity ad/v 2 . Envelopee of maxima and minima as well as average response spectra has been obtained. A comparison with the USAEC spectra has been made. A relation between ground acceleration, ground velocity and ad/v 2 has been obtained which would nearly give the same magnification of the response. A design response spectra for alluvial soils has been recommended. (author)

Rotational Spectral Unmixing of Exoplanets: Degeneracies between Surface Colors and Geography

Energy Technology Data Exchange (ETDEWEB)

Fujii, Yuka [NASA Goddard Institute for Space Studies, New York, NY 10025 (United States); Lustig-Yaeger, Jacob [Astronomy Department, University of Washington, Box 951580, Seattle, WA 98195 (United States); Cowan, Nicolas B., E-mail: yuka.fujii.ebihara@gmail.com [Department of Earth and Planetary Sciences, McGill University, Montreal, Quebec, H3A 0E8 (Canada)

2017-11-01

Unmixing the disk-integrated spectra of exoplanets provides hints about heterogeneous surfaces that we cannot directly resolve in the foreseeable future. It is particularly important for terrestrial planets with diverse surface compositions like Earth. Although previous work on unmixing the spectra of Earth from disk-integrated multi-band light curves appeared successful, we point out a mathematical degeneracy between the surface colors and their spatial distributions. Nevertheless, useful constraints on the spectral shape of individual surface types may be obtained from the premise that albedo is everywhere between 0 and 1. We demonstrate the degeneracy and the possible constraints using both mock data based on a toy model of Earth, as well as real observations of Earth. Despite the severe degeneracy, we are still able to recover an approximate albedo spectrum for an ocean. In general, we find that surfaces are easier to identify when they cover a large fraction of the planet and when their spectra approach zero or unity in certain bands.

Rotational Spectral Unmixing of Exoplanets: Degeneracies Between Surface Colors and Geography

Science.gov (United States)

Fujii, Yuka; Lustig-Yaeger, Jacob; Cowan, Nicolas B.

2017-01-01

Unmixing the disk-integrated spectra of exoplanets provides hints about heterogeneous surfaces that we cannot directly resolve in the foreseeable future. It is particularly important for terrestrial planets with diverse surface compositions like Earth. Although previous work on unmixing the spectra of Earth from disk-integrated multi-band light curves appeared successful, we point out a mathematical degeneracy between the surface colors and their spatial distributions. Nevertheless, useful constraints on the spectral shape of individual surface types may be obtained from the premise that albedo is everywhere between 0 and 1. We demonstrate the degeneracy and the possible constraints using both mock data based on a toy model of Earth, as well as real observations of Earth. Despite the severe degeneracy, we are still able to recover an approximate albedo spectrum for an ocean. In general, we find that surfaces are easier to identify when they cover a large fraction of the planet and when their spectra approach zero or unity in certain bands.

Effect of surface structure on catalytic reactions: A sum frequency generation surface vibrational spectroscopy study

International Nuclear Information System (INIS)

McCrea, Keith R.

2001-01-01

In the results discussed above, it is clear that Sum Frequency Generation (SFG) is a unique tool that allows the detection of vibrational spectra of adsorbed molecules present on single crystal surfaces under catalytic reaction conditions. Not only is it possible to detect active surface intermediates, it is also possible to detect spectator species which are not responsible for the measured turnover rates. By correlating high-pressure SFG spectra under reaction conditions and gas chromatography (GC) kinetic data, it is possible to determine which species are important under reaction intermediates. Because of the flexibility of this technique for studying surface intermediates, it is possible to determine how the structures of single crystal surfaces affect the observed rates of catalytic reactions. As an example of a structure insensitive reaction, ethylene hydrogenation was explored on both Pt(111) and Pt(100). The rates were determined to be essentially the same. It was observed that both ethylidyne and di-(sigma) bonded ethylene were present on the surface under reaction conditions on both crystals, although in different concentrations. This result shows that these two species are not responsible for the measured turnover rate, as it would be expected that one of the two crystals would be more active than the other, since the concentration of the surface intermediate would be different on the two crystals. The most likely active intermediates are weakly adsorbed molecules such as(pi)-bonded ethylene and ethyl. These species are not easily detected because their concentration lies at the detection limit of SFG. The SFG spectra and GC data essentially show that ethylene hydrogenation is structure insensitive for Pt(111) and Pt(100). SFG has proven to be a unique and excellent technique for studying adsorbed species on single crystal surfaces under high-pressure catalytic reactions. Coupled with kinetic data obtained from gas chromatography measurements, it can

Quantitative analysis of Moessbauer backscatter spectra from multilayer films

International Nuclear Information System (INIS)

Bainbridge, J.

1975-01-01

The quantitative interpretation of Moessbauer backscatter spectra with particular reference to internal conversion electrons has been treated assuming that electron attenuation in a surface film can be satisfactorily described by a simple exponential law. The theory of Krakowski and Miller has been extended to include multi-layer samples, and a relation between the Moessbauer spectrum area and an individual layer thickness derived. As an example, numerical results are obtained for a duplex oxide film grown on pure iron. (Auth.)

Ab initio potential energy surface, electric-dipole moment, polarizability tensor, and theoretical rovibrational spectra in the electronic ground state of {sup 14}NH{sub 3}{sup +}

Energy Technology Data Exchange (ETDEWEB)

Yurchenko, Sergei N. [Technische Universitaet Dresden, Institut fuer Physikalische Chemie und Elektrochemie, D-01062 Dresden (Germany); Thiel, Walter [Max-Planck-Institut fuer Kohlenforschung, Kaiser-Wilhelm-Platz 1, D-45470 Muelheim an der Ruhr (Germany); Carvajal, Miguel [Departamento de Fisica Aplicada, Facultad de Ciencias Experimentales, Avenida de las Fuerzas Armadas s/n, Universidad de Huelva, E-21071 Huelva (Spain); Jensen, Per [Theoretische Chemie, Bergische Universitaet, D-42097 Wuppertal (Germany)], E-mail: jensen@uni-wuppertal.de

2008-05-04

We report the calculation of a six-dimensional CCSD(T)/aug-cc-pVQZ potential energy surface for the electronic ground state of NH{sub 3}{sup +} together with the corresponding CCSD(T)/aug-cc-pVTZ dipole moment and polarizability surface of {sup 14}NH{sub 3}{sup +}. These electronic properties have been computed on a large grid of molecular geometries. A number of newly calculated band centers are presented along with the associated electric-dipole transition moments. We further report the first calculation of vibrational matrix elements of the polarizability tensor components for {sup 14}NH{sub 3}{sup +}; these matrix elements determine the intensities of Raman transitions. In addition, the rovibrational absorption spectra of the {nu}{sub 2}, {nu}{sub 3}, {nu}{sub 4}, 2{nu}{sub 2}-{nu}{sub 2}, and {nu}{sub 2}+{nu}{sub 3}-{nu}{sub 2} bands have been simulated.

The Effects of Spherical Surface and Laser Polarization on the Photodetachment Cross Section of H−

International Nuclear Information System (INIS)

Haneef Muhammad; Arif Suneela; Akbar Jehan; Shamim Aneela; Shah Nasrullah; Zahir Muhammad; Ullah Hameed

2013-01-01

We report the combined effects of laser polarization and curvature of the spherical surface on the detached electron spectra from H − . The Theoretical imaging method is used as a tool of investigation. The photodetachment cross sections for various polarization angles, radii of curvatures and inter ion surface distances are displayed. The analysis of the spectra reveals that the laser polarization angle θ L , curvature of the surface r c and inter ion surface distance d strongly affect oscillations in the spectra. Therefore, a fine control on the laser polarization and that of curvature in the surface can be used to control oscillations in the photodetachment of negative ions. (atomic and molecular physics)

BETA SPECTRA. I. Negatrons spectra; ESPECTROS BETA. I. Espectros simples de negatrones

Energy Technology Data Exchange (ETDEWEB)

Grau Malonda, A; Garcia-Torano, E

1978-07-01

Using the Fermi theory of beta decay, the beta spectra for 62 negatrons emitters have been computed introducing a correction factor for unique forbidden transitions. These spectra are plotted vs. energy, once normal i sed, and tabulated with the related Fermi functions. The average and median energies are calculated. (Author)

Side-by-side comparison of Raman spectra of anchored and suspended carbon nanomaterials

International Nuclear Information System (INIS)

Sidorov, Anton N; Pabba, Santosh; Cohn, Robert W; Sumanasekera, G U; Hewaparakrama, Kapila P

2008-01-01

Raman spectra of ordered carbon nanomaterials are quite sensitive to surface perturbations, including trace residues, structural defects and residual stress. This is demonstrated by a series of experiments with carbon nanotubes and graphene. Their spectra change due to subtle changes in preparation and attachment to the substrate and to each other. Differences are most clearly seen by forming a material into an air bridge and probing it in the air gap and at the anchor points. A monolayer graphene sheet, shows a larger disorder band at the anchor points than in the air gap. However, a bundle or rope of parallel-aligned single-wall nanotubes shows a larger disorder band in the gap than at the anchor points. For the graphene sheet the substrate surface deforms the graphene, leading to increases in the disorder band. For the rope, the close proximity of the nanotubes to each other appears to produce a larger stress than the rope resting on the substrate

Design spectra development considering short time histories

International Nuclear Information System (INIS)

Weiner, E.O.

1983-01-01

The need for generation of seismic acceleration histories to prescribed response spectra arises several ways in structural dynamics. For example, one way of obtaining floor spectra is to generate a history from a foundation spectra and then solve for the floor motion from which a floor spectrum can be obtained. Two separate programs, MODQKE and MDOF, were written to provide a capability of obtaining equipment spectra from design spectra. MODQKE generates or modifies acceleration histories to conform with design spectra pertaining to, say, a foundation. MDOF is a simple linear modal superposition program that solves for equipment support histories using the design spectra conforming histories as input. Equipment spectra, then, are obtained from the support histories using MODQKE

Angle resolved electron spectroscopy of spontaneous ionization processes occurring in doubly charged ion-surface collisions at grazing incidence

International Nuclear Information System (INIS)

Wouters, P.A.A.F.; Emmichoven, P.A.Z. van; Niehaus, A.

1989-01-01

The experimental setup used to measure electron spectra at well defined detection angles for grazing incidence doubly charged ion-surface collisions at keV-energies is described. Electron spectra are reported for the rare gas ions colliding with a Cu(110)-surface. The spectra are analyzed in terms of various spontaneous ionization processes using a newly developed model. It is found that double capture followed by atomic auto-ionization on the incoming trajectory and Auger-capture processes in which the first and second hole in the doubly charged projectiles are successively filled are the main processes contributing to the electron spectra. From a comparison of model calculations with measured spectra it is concluded that the metal electrons cannot adapt adiabatically to the sudden changes of the charge state of the projectile in front of the surface. A parameter characterizing the partly diabatic behavior is determined. The variation of spectra upon adsorption of a monolayer of oxygen on the surface is reported and discussed. (author)

Spectral sensitization of TiO2 by new hemicyanine dyes in dye solar cell yielding enhanced photovoltage: Probing chain length effect on performance

International Nuclear Information System (INIS)

Fadadu, Kishan B.; Soni, Saurabh S.

2013-01-01

Graphical abstract: New hemicyanine dyes based on indolenine moiety were utilized as light harvesting materials in dye sensitized solar cell. Chain lengths of the molecules were varied in order to study its effect of chain length on the performance of DSSC. Electron transfer kinetic of the solar cell was studied and it was found that the chain length changes the electron transfer kinetic. We have achieved remarkable photovoltage and overall performance of DSSC. Highlights: ► New hemicyanine dyes based on indolenine moiety were utilized as light harvesting materials in dye sensitized solar cell. ► Chain lengths of the molecules were varied in order to study its effect of chain length on the performance of DSSC. ► Electron transfer kinetic of the solar cell was studied and it was found that the chain length changes the electron transfer kinetic. -- Abstract: New hemicyanine dyes having indole nucleus with different alkyl chain length were synthesized and characterized using 1 H NMR and mass spectroscopy. These dyes were used to sensitize the TiO 2 film in dye sensitized solar cell. Nanocrystalline dye solar cells were fabricated and characterized using various electrochemical techniques. It has been found that the alkyl chain length present in the dye molecules greatly affects the overall performance of dye solar cell. Molecules having longer alkyl chain are having better sensitizers which enhance V oc to significant extent. Chain length dependent performance was further investigated using Tafel polarization and impedance method. Hemicyanine dye having hexyl chain has outperformed by attaining 2.9% solar to electricity conversion efficiency

Contrastive Analysis of the Raman Spectra of Polychlorinated Benzene: Hexachlorobenzene and Benzene

Directory of Open Access Journals (Sweden)

Zhengjun Zhang

2011-12-01

Full Text Available Detection of persistent pollutants such as polychlorinated benzene in environment in trace amounts is challenging, but important. It is more difficult to distinguish homologues and isomers of organic pollutantd when present in trace amounts because of their similar physical and chemical properties. In this work we simulate the Raman spectra of hexachlorobenzene and benzene, and figure out the vibration mode of each main peak. The effect on the Raman spectrum of changing substituents from H to Cl is analyzed to reveal the relations between the Raman spectra of homologues and isomers of polychlorinated benzene, which should be helpful for distinguishing one kind of polychlorinated benzene from its homologues and isomers by surface enhanced Raman scattering.

Synoptic Mid-IR Spectra ToO Novae

Science.gov (United States)

Helton, L. Andrew; Woodward, Chick; Evans, Nye; Geballe, Tom; Spitzer Nova Team

2007-02-01

Stars are the engines of energy production and chemical evolution in our Universe, depositing radiative and mechanical energy into their environments and enriching the ambient ISM with elements synthesized in their interiors and dust grains condensed in their atmospheres. Classical novae (CN) contribute to this cycle of chemical enrichment through explosive nucleosynthesis and the violent ejection of material dredged from the white dwarf progenitor and mixed with the accreted surface layers. We propose to obtain mid-IR spectra of a new galactic CN in outburst to investigate aspects of the CN phenomenon including the in situ formation and mineralogy of nova dust and the elemental abundances resulting from thermonuclear runaway. Synoptic, high S/N Michelle spectra permit: 1) determination of the grain size distribution and mineral composition of nova dust; 2) estimation of chemical abundances of nova ejecta from coronal and other emission line spectroscopy; and 3) measurement of the density and masses of the ejecta. This Gemini `Target of Opportunity' initiative (trigger K=5- 8 mag, assuming adequate PWFS guide stars exist) complements our extensive Spitzer, Chandra, Swift, XMM-Newton CN DDT/ToO programs.

Generate floor response spectra, Part 2: Response spectra for equipment-structure resonance

International Nuclear Information System (INIS)

Li, Bo; Jiang, Wei; Xie, Wei-Chau; Pandey, Mahesh D.

2015-01-01

Highlights: • The concept of tRS is proposed to deal with tuning of equipment and structures. • Established statistical approaches for estimating tRS corresponding to given GRS. • Derived a new modal combination rule from the theory of random vibration. • Developed efficient and accurate direct method for generating floor response spectra. - Abstract: When generating floor response spectra (FRS) using the direct spectra-to-spectra method developed in the companion paper, probability distribution of t-response spectrum (tRS), which deals with equipment-structure resonance or tuning, corresponding to a specified ground response spectrum (GRS) is required. In this paper, simulation results using a large number of horizontal and vertical ground motions are employed to establish statistical relationships between tRS and GRS. It is observed that the influence of site conditions on horizontal statistical relationships is negligible, whereas the effect of site conditions on vertical statistical relationships cannot be ignored. Considering the influence of site conditions, horizontal statistical relationship suitable for all site conditions and vertical statistical relationships suitable for hard sites and soft sites, respectively, are established. The horizontal and vertical statistical relationships are suitable to estimate tRS for design spectra in USNRC R.G. 1.60 and NUREG/CR-0098, Uniform Hazard Spectra (UHS) in Western North America (WNA), or any GRS falling inside the valid coverage of the statistical relationship. For UHS with significant high frequency spectral accelerations, such as UHS in Central and Eastern North America (CENA), an amplification ratio method is proposed to estimate tRS. Numerical examples demonstrate that the statistical relationships and the amplification ratio method are acceptable to estimate tRS for given GRS and to generate FRS using the direct method in different practical situations.

Generate floor response spectra, Part 2: Response spectra for equipment-structure resonance

Energy Technology Data Exchange (ETDEWEB)

Li, Bo, E-mail: b68li@uwaterloo.ca; Jiang, Wei, E-mail: w46jiang@uwaterloo.ca; Xie, Wei-Chau, E-mail: xie@uwaterloo.ca; Pandey, Mahesh D., E-mail: mdpandey@uwaterloo.ca

2015-11-15

Highlights: • The concept of tRS is proposed to deal with tuning of equipment and structures. • Established statistical approaches for estimating tRS corresponding to given GRS. • Derived a new modal combination rule from the theory of random vibration. • Developed efficient and accurate direct method for generating floor response spectra. - Abstract: When generating floor response spectra (FRS) using the direct spectra-to-spectra method developed in the companion paper, probability distribution of t-response spectrum (tRS), which deals with equipment-structure resonance or tuning, corresponding to a specified ground response spectrum (GRS) is required. In this paper, simulation results using a large number of horizontal and vertical ground motions are employed to establish statistical relationships between tRS and GRS. It is observed that the influence of site conditions on horizontal statistical relationships is negligible, whereas the effect of site conditions on vertical statistical relationships cannot be ignored. Considering the influence of site conditions, horizontal statistical relationship suitable for all site conditions and vertical statistical relationships suitable for hard sites and soft sites, respectively, are established. The horizontal and vertical statistical relationships are suitable to estimate tRS for design spectra in USNRC R.G. 1.60 and NUREG/CR-0098, Uniform Hazard Spectra (UHS) in Western North America (WNA), or any GRS falling inside the valid coverage of the statistical relationship. For UHS with significant high frequency spectral accelerations, such as UHS in Central and Eastern North America (CENA), an amplification ratio method is proposed to estimate tRS. Numerical examples demonstrate that the statistical relationships and the amplification ratio method are acceptable to estimate tRS for given GRS and to generate FRS using the direct method in different practical situations.

StarNet: An application of deep learning in the analysis of stellar spectra

Science.gov (United States)

Kielty, Collin; Bialek, Spencer; Fabbro, Sebastien; Venn, Kim; O'Briain, Teaghan; Jahandar, Farbod; Monty, Stephanie

2018-06-01

In an era when spectroscopic surveys are capable of collecting spectra for hundreds of thousands of stars, fast and efficient analysis methods are required to maximize scientific impact. These surveys provide a homogeneous database of stellar spectra that are ideal for machine learning applications. In this poster, we present StarNet: a convolutional neural network model applied to the analysis of both SDSS-III APOGEE DR13 and synthetic stellar spectra. When trained on synthetic spectra alone, the calculated stellar parameters (temperature, surface gravity, and metallicity) are of excellent precision and accuracy for both APOGEE data and synthetic data, over a wide range of signal-to-noise ratios. While StarNet was developed using the APOGEE observed spectra and corresponding ASSeT synthetic grid, we suggest that this technique is applicable to other spectral resolutions, spectral surveys, and wavelength regimes. As a demonstration of this, we present a StarNet model trained on lower resolution, R=6000, IR synthetic spectra, describing the spectra delivered by Gemini/NIFS and the forthcoming Gemini/GIRMOS instrument (PI Sivanandam, UToronto). Preliminary results suggest that the stellar parameters determined from this low resolution StarNet model are comparable in precision to the high-resolution APOGEE results. The success of StarNet at lower resolution can be attributed to (1) a large training set of synthetic spectra (N ~200,000) with a priori stellar labels, and (2) the use of the entire spectrum in the solution rather than a few weighted windows, which are common methods in other spectral analysis tools (e.g. FERRE or The Cannon). Remaining challenges in our StarNet applications include rectification, continuum normalization, and wavelength coverage. Solutions to these problems could be used to guide decisions made in the development of future spectrographs, spectroscopic surveys, and data reduction pipelines, such as for the future MSE.

Directional uv photoemission from (100) and (110) molybdenum surfaces

DEFF Research Database (Denmark)

Cinti, R. C.; Khoury, E. Al; Chakraverty, B. K.

1976-01-01

A study of the (100) and (110) molybdenum surfaces by directional photoemission spectroscopy is presented. Energy distribution spectra formed by photoelectrons emitted normal to the surfaces have been measured for photon energies between 10.2 and 21.2 eV. The results are discussed in terms of cal......-transition and surface-emission processes. Two extra structures are interpreted in terms of surface states or resonances: on the (100) surface, 0.5 eV below EF; on the (110) surface, 4.5 eV below EF in the s-d hybridization gap....... of calculated band structure within the framework of the K∥-conservation assumption. A good agreement is found between the main features of the experimental spectra and the emission expected from the band structure along the corresponding symmetry line in the Brillouin zone, assuming essentially direct...

Spectra of alkali atoms

International Nuclear Information System (INIS)

Santoso, Budi; Arumbinang, Haryono.

1981-01-01

Emission spectra of alkali atoms has been determined by using spectrometer at the ultraviolet to infra red waves range. The spectra emission can be obtained by absorption spectrophotometric analysis. Comparative evaluations between experimental data and data handbook obtained by spark method were also presented. (author tr.)

SERS spectra of pyridine adsorbed on nickel film prepared by magnetron sputtering

Science.gov (United States)

Li, Daoyong; Ouyang, Yu; Chen, Li; Cao, Weiran; Shi, Shaohua

2011-02-01

As a repeating well and cheaper enhancement substrate, the nickel film was fabricated with magnetron sputtering coating instrument. Surface enhanced Raman spectra (SERS) of pyridine adsorbed on this nickel film are compared with the experimental values of gaseous pyridine, the theoretical value of pyridine solution listed in other literatures and our method is better than electro-chemical etching electrode method for large scale preparation. The enhancement factor of the nickel film is calculated and the result indicates that magnetron sputtering coating technology is feasible for obtaining good SERS active surface.

Reconstruction of neutron spectra through neural networks

International Nuclear Information System (INIS)

Vega C, H.R.; Hernandez D, V.M.; Manzanares A, E.

2003-01-01

A neural network has been used to reconstruct the neutron spectra starting from the counting rates of the detectors of the Bonner sphere spectrophotometric system. A group of 56 neutron spectra was selected to calculate the counting rates that would produce in a Bonner sphere system, with these data and the spectra it was trained the neural network. To prove the performance of the net, 12 spectra were used, 6 were taken of the group used for the training, 3 were obtained of mathematical functions and those other 3 correspond to real spectra. When comparing the original spectra of those reconstructed by the net we find that our net has a poor performance when reconstructing monoenergetic spectra, this attributes it to those characteristic of the spectra used for the training of the neural network, however for the other groups of spectra the results of the net are appropriate with the prospective ones. (Author)

Radiative capture of slow electrons by tungsten surface

International Nuclear Information System (INIS)

Artamonov, O.M.; Belkina, G.M.; Samarin, S.N.; Yakovlev, I.I.

1987-01-01

Isochromatic spectra of radiation capture of slow electrons by the surface of mono- and polycrystal tungsten recorded on 322 and 405 nm wave lengths are presented. The effect of oxygen adsorption on isochromates of the (110) face of tungsten monocrystal is investigated. The obtained isochromatic spectra are compared with energy band structure of tungsten. Based on the analysis of the obtained experimental results it is assumed that optical transition to the final state at the energy of 7.3 eV relatively to Fermi level is conditioned by surface states of the tungsten face (110)

Exciton diffusion length in some thermocleavable polythiophenes by the surface photovoltage method

DEFF Research Database (Denmark)

Tousek, J.; Touskova, J.; Remes, Z.

2012-01-01

property is that P3MHOCT can serve as a precursor which, after thermal annealing, converts into more rigid and insoluble P3CT and further thermal treatment produces native unsubstituted PT. Ellipsometric measurement yielded data on the thickness of the spin coated layers; absorption coefficients were...... be ascribed to the increase of the crystalline fraction. The highest diffusion length was found in P3CT polymer but its large resistivity represents a disadvantage in application in solar cells. Taking into account just these parameters, relatively low resistivity together with quite high diffusion length (13...

The influence of magnetic field geometry on magnetars X-ray spectra

International Nuclear Information System (INIS)

Viganò, D; Pons, J A; Miralles, J A; Parkins, N; Zane, S; Turolla, R

2012-01-01

Nowadays, the analysis of the X-ray spectra of magnetically powered neutron stars or magnetars is one of the most valuable tools to gain insight into the physical processes occurring in their interiors and magnetospheres. In particular, the magnetospheric plasma leaves a strong imprint on the observed X-ray spectrum by means of Compton up-scattering of the thermal radiation coming from the star surface. Motivated by the increased quality of the observational data, much theoretical work has been devoted to develop Monte Carlo (MC) codes that incorporate the effects of resonant Compton scattering (RCS) in the modeling of radiative transfer of photons through the magnetosphere. The two key ingredients in this simulations are the kinetic plasma properties and the magnetic field (MF) configuration. The MF geometry is expected to be complex, but up to now only mathematically simple solutions (self-similar solutions) have been employed. In this work, we discuss the effects of new, more realistic, MF geometries on synthetic spectra. We use new force-free solutions [14] in a previously developed MC code [9] to assess the influence of MF geometry on the emerging spectra. Our main result is that the shape of the final spectrum is mostly sensitive to uncertain parameters of the magnetospheric plasma, but the MF geometry plays an important role on the angle-dependence of the spectra.

Sophisticated visualization algorithms for analysis of multidimensional experimental nuclear spectra

International Nuclear Information System (INIS)

Morhac, M.; Kliman, J.; Matousek, V.; Turzo, I.

2004-01-01

This paper describes graphical models of visualization of 2-, 3-, 4-dimensional scalar data used in nuclear data acquisition, processing and visualization system developed at the Institute of Physics, Slovak Academy of Sciences. It focuses on presentation of nuclear spectra (histograms). However it can be successfully applied for visualization of arrays of other data types. In the paper we present conventional as well as new developed surface and volume rendering visualization techniques used (Authors)

cap alpha. -spectra hyperfine structure resolution by silicon planar detectors

Energy Technology Data Exchange (ETDEWEB)

Eremin, V K; Verbitskaya, E M; Strokan, N B; Sukhanov, V L; Malyarenko, A M

1986-10-01

The lines with 13 keV step from the main one is ..cap alpha..-spectra of nuclei with an odd number of nucleons take place. Silicon planar detectors n-Si with the operation surface of 10 mm/sup 2/ are developed for resolution of this hyperfine structure. The mechanism of losses in detectors for short-range-path particles is analyzed. The results of measurements from detectors with 10 keV resolution are presented.

An RGB approach to extraordinary spectra

Science.gov (United States)

Grusche, Sascha; Theilmann, Florian

2015-09-01

After Newton had explained a series of ordinary spectra and Goethe had pointed out its complementary counterpart, Nussbaumer discovered a series of extraordinary spectra which are geometrically identical and colourwise analogous to Newton’s and Goethe’s spectra. To understand the geometry and colours of extraordinary spectra, the wavelength composition is explored with filters and spectroscopic setups. Visualized in a dispersion diagram, the wavelength composition is interpreted in terms of additive colour mixing. Finally, all spectra are simulated as the superposition of red, green, and blue images that are shifted apart. This RGB approach makes it easy to understand the complex relationship between wavelengths and colours.

Electron spectroscopic study of electronic and morphological modifications of the WSe2 surface induced by Rb adsorption

International Nuclear Information System (INIS)

Buck, Jens

2010-01-01

The rubidium-covered surface of the semiconducting transition metal dichalcogenide tungsten diselenide (WSe 2 ) is examined using photoelectron spectroscopy (PES) and photoemission electron microscopy (PEEM). Adsorbed Rb is known to induce a variety of effects in this system concerning electronic, structural, and mechanical properties. In this work, the surface potential created by charge transfer upon Rb deposition is examined in thermal equilibrium (band bending) and stationary non-equilibrium (surface photovoltage (SPV) effect), which is induced by the absorption of light. It is shown that combined measurements and numerical simulations of the SPV effect as a function of the photon flux can be exploited for the estimation of many material parameters of the system, especially of the unoccupied adsorbate state. Issues of extending a conventional photoelectron spectrometer setup by a secondary light source will be discussed in the context of simulations and calibration measurements. The customization of an existing theoretical model of the SPV effect for the WSe 2 : Rb system is introduced, and a comprehensive validation of the obtained predictions is given in the context of experimental data. In addition, the self-organized formation of Rb domains at room temperature was examined by application of spatially resolved XPS spectroscopy using the PEEM setup at the end station of beamline UE49/PGMa at the BESSY II synchrotron facility. From the obtained results, the arrangement of Rb in surface lattices can be concluded. Furthermore, an X-Ray absorption study of self-organized nanostructure networks, aiming at the chemical characterization, is presented. Based on the interpretation of the examined structures as tension-induced cracks, a statistical approach to analyzing large-scale features was pursued. First accordance with the predictions made by a primitive, mechanical model of crack creation developed here gives gives some evidence for the validity of the proposed

Operator functions and localization of spectra

CERN Document Server

Gil’, Michael I

2003-01-01

"Operator Functions and Localization of Spectra" is the first book that presents a systematic exposition of bounds for the spectra of various linear nonself-adjoint operators in a Hilbert space, having discrete and continuous spectra. In particular bounds for the spectra of integral, differential and integro-differential operators, as well as finite and infinite matrices are established. The volume also presents a systematic exposition of estimates for norms of operator-valued functions and their applications.

Absorption spectra of localized surface plasmon resonance observed in an inline/picoliter spectrometer cell fabricated by a near ultraviolet femtosecond laser

Science.gov (United States)

Shiraishi, Masahiko; Nishiyama, Michiko; Watanabe, Kazuhiro; Kubodera, Shoichi

2018-03-01

Absorption spectra based on localized surface plasmon resonance (LSPR) were obtained with an inline/picoliter spectrometer cell. The spectrometer cell was fabricated into an optical glass fiber by focusing a near UV (NUV) femtosecond laser pulses at a wavelength of 400 nm with an energy of 30 μJ. The laser beam was focused from two directions opposite to each other to fabricate a through-hole spectrometer cell. A diameter of the cell was approximately 3 μm, and the length was approximately 62.5 μm, which was nearly equal to the core diameter of the optical fiber. Liquid solution of gold nanoparticles (GNPs) with a diameter of 5-10 nm was injected into the spectrometer cell with its volume of 0.4 pL. The absorption peak centered at 518 nm was observed. An increase of absorption associated with the increase of the number of nanoparticles was in agreement with the numerical calculation based on the Lambert-Beer law.

An experimental method for making spectral emittance and surface temperature measurements of opaque surfaces

International Nuclear Information System (INIS)

Moore, Travis J.; Jones, Matthew R.; Tree, Dale R.; Daniel Maynes, R.; Baxter, Larry L.

2011-01-01

An experimental procedure has been developed to make spectral emittance and temperature measurements. The spectral emittance of an object is calculated using measurements of the spectral emissive power and of the surface temperature of the object obtained using a Fourier transform infrared (FTIR) spectrometer. A calibration procedure is described in detail which accounts for the temperature dependence of the detector. The methods used to extract the spectral emissive power and surface temperature from measured infrared spectra were validated using a blackbody radiator at known temperatures. The average error in the measured spectral emittance was 2.1% and the average difference between the temperature inferred from the recorded spectra and the temperature indicated on the blackbody radiator was 1.2%. The method was used to measure the spectral emittance of oxidized copper at various temperatures.

Engaging students in astronomy and spectroscopy through Project SPECTRA!

Science.gov (United States)

Wood, E. L.

2011-12-01

Computer simulations for minds-on learning with "Project Spectra!" How do we gain information about the Sun? How do we know Mars has CO2 or that Enceladus has H2O geysers? How do we use light in astronomy? These concepts are something students and educators struggle with because they are abstract. Using simulations and computer interactives (games) where students experience and manipulate the information makes concepts accessible. Visualizing lessons with multi-media solidifies understanding and retention of knowledge and is completely unlike its paper-and-pencil counterpart. Visualizations also enable teachers to forgo purchasing expensive laboratory equipment. "Project Spectra!" is a science and engineering program that uses computer-based Flash interactives to expose students to astronomical spectroscopy and actual data in a way that is not possible with traditional in-class activities. To engage students in "Project Spectra!", students are given a mission, which connects them with the research at hand. Missions range from exploring remote planetary atmospheres and surfaces, experimenting with the Sun using different filters, or analyzing the soil of a remote planet. Additionally, students have an opportunity to learn about NASA missions, view movies, and see images connected with their mission, which is something that is not practical to do during a typical paper-and-pencil activity. Since students can choose what to watch and explore, the interactives accommodate a broad range of learning styles. Students can go back and forth through the interactives if they've missed a concept or wish to view something again. In the end, students are asked critical thinking questions and conduct web-based research. These interactives complement in-class Project SPECTRA! activities exploring applications of the electromagnetic spectrum.

Observed and theoretical spectra in the 10-100 A interval. [of solar spectra

Science.gov (United States)

Brown, W. A.; Bruner, M. E.; Acton, L. W.

1988-01-01

The soft X-ray spectra recorded in two sounding-rocket flights in 1982 and 1985 are compared with predicted spectra. The processed densitometer trace of the full spectrum is presented, together with the new spectrum from the 1985 experiment. The intensities of the lines are then compared with predictions.

Remote compositional analysis of lunar olivine-rich lithologies with Moon Mineralogy Mapper (M3) spectra

Science.gov (United States)

Isaacson, P.J.; Pieters, C.M.; Besse, S.; Clark, R.N.; Head, J.W.; Klima, R.L.; Mustard, J.F.; Petro, N.E.; Staid, M.I.; Sunshine, J.M.; Taylor, L.A.; Thaisen, K.G.; Tompkins, S.

2011-01-01

A systematic approach for deconvolving remotely sensed lunar olivine-rich visible to near-infrared (VNIR) reflectance spectra with the Modified Gaussian Model (MGM) is evaluated with Chandrayaan-1 Moon Mineralogy Mapper (M 3) spectra. Whereas earlier studies of laboratory reflectance spectra focused only on complications due to chromite inclusions in lunar olivines, we develop a systematic approach for addressing (through continuum removal) the prominent continuum slopes common to remotely sensed reflectance spectra of planetary surfaces. We have validated our continuum removal on a suite of laboratory reflectance spectra. Suites of olivine-dominated reflectance spectra from a small crater near Mare Moscoviense, the Copernicus central peak, Aristarchus, and the crater Marius in the Marius Hills were analyzed. Spectral diversity was detected in visual evaluation of the spectra and was quantified using the MGM. The MGM-derived band positions are used to estimate the olivine's composition in a relative sense. Spectra of olivines from Moscoviense exhibit diversity in their absorption features, and this diversity suggests some variation in olivine Fe/Mg content. Olivines from Copernicus are observed to be spectrally homogeneous and thus are predicted to be more compositionally homogeneous than those at Moscoviense but are of broadly similar composition to the Moscoviense olivines. Olivines from Aristarchus and Marius exhibit clear spectral differences from those at Moscoviense and Copernicus but also exhibit features that suggest contributions from other phases. If the various precautions discussed here are weighed carefully, the methods presented here can be used to make general predictions of absolute olivine composition (Fe/Mg content). Copyright ?? 2011 by the American Geophysical Union.

Surface Plasmons and Surface Enhanced Raman Spectra of Aggregated and Alloyed Gold-Silver Nanoparticles

Directory of Open Access Journals (Sweden)

Y. Fleger

2009-01-01

Full Text Available Effects of size, morphology, and composition of gold and silver nanoparticles on surface plasmon resonance (SPR and surface enhanced Raman spectroscopy (SERS are studied with the purpose of optimizing SERS substrates. Various gold and silver films made by evaporation and subsequent annealing give different morphologies and compositions of nanoparticles and thus different position of the SPR peak. SERS measurements of 4-mercaptobenzoic acid obtained from these films reveal that the proximity of the SPR peak to the exciting laser wavelength is not the only factor leading to the highest Raman enhancement. Silver nanoparticles evaporated on top of larger gold nanoparticles show higher SERS than gold-silver alloyed nanoparticles, in spite of the fact that the SPR peak of alloyed nanoparticles is narrower and closer to the excitation wavelength. The highest Raman enhancement was obtained for substrates with a two-peak particle size distribution for excitation wavelengths close to the SPR.

Simulation of attenuated total reflection infrared absorbance spectra: applications to automotive clear coat forensic analysis.

Science.gov (United States)

Lavine, Barry K; Fasasi, Ayuba; Mirjankar, Nikhil; Nishikida, Koichi; Campbell, Jay

2014-01-01

Attenuated total reflection (ATR) is a widely used sampling technique in infrared (IR) spectroscopy because minimal sample preparation is required. Since the penetration depth of the ATR analysis beam is quite shallow, the outer layers of a laminate or multilayered paint sample can be preferentially analyzed with the entire sample intact. For this reason, forensic laboratories are taking advantage of ATR to collect IR spectra of automotive paint systems that may consist of three or more layers. However, the IR spectrum of a paint sample obtained by ATR will exhibit distortions, e.g., band broadening and lower relative intensities at higher wavenumbers, compared with its transmission counterpart. This hinders library searching because most library spectra are measured in transmission mode. Furthermore, the angle of incidence for the internal reflection element, the refractive index of the clear coat, and surface contamination due to inorganic contaminants can profoundly influence the quality of the ATR spectrum obtained for automotive paints. A correction algorithm to allow ATR spectra to be searched using IR transmission spectra of the paint data query (PDQ) automotive database is presented. The proposed correction algorithm to convert transmission spectra from the PDQ library to ATR spectra is able to address distortion issues such as the relative intensities and broadening of the bands, and the introduction of wavelength shifts at lower frequencies, which prevent library searching of ATR spectra using archived IR transmission data.

Fast forward modeling of Titan’s infrared spectra to invert VIMS/CASSINI hyperspectral images

Science.gov (United States)

Rodriguez, S.; Le Mouélic, S.; Rannou, P.; Combe, J.; Le Corre, L.; Griffith, C. A.; Tobie, G.; Barnes, J. W.; Sotin, C.; Brown, R. H.; Baines, K. H.; Buratti, B. J.; Clark, R. N.

2009-12-01

The surface of Titan, the largest icy moon of Saturn, is veiled by a very thick and hazy atmosphere. The Visual and Infrared Mapping Spectrometer onboard the Cassini spacecraft, in orbit around Saturn since July 2004, has been conducting an intensive survey of Titan with the objective of understanding the complex nature and interaction of the atmosphere and surface of this mysterious moon. Retrieving and separating contributions from the surface and the atmosphere in Titan’s infrared spectra requires accurate radiative transfer modeling, which is often very demanding of computer resources. As Cassini has gathered hitherto millions of spectra of Titan and will continue to observe it until at least 2010, we report here on the development of a new rapid, simple and versatile radiative transfer model specially designed to process VIMS datacubes. Currently, our model accounts for gas absorption, haze scattering and surface reflectance and can be implemented in an inversion scheme. First results of forward modeling provide spectral shapes that are consistent with VIMS measurements, as well as surface and aerosol properties in the range of validity for Titan. Further inversion tests will be carried on VIMS hyperspectral images for the estimate of spatial coherence of the results, accuracy of the surface reflectance within the atmospheric windows, and potential needs for improved input data and modeling. This work was partly performed at the Jet Propulsion Laboratory, California Institute of Technology, under contract to the National Aeronautics and Space Administration. Calibrated VIMS data appear courtesy of the VIMS team. We thank the CNES French agency for its financial support.

Cosensitization process effect of D-A-π-A featured dyes on photovoltaic performances

Directory of Open Access Journals (Sweden)

Bo Liu

2016-04-01

Full Text Available Cosensitization based on two or multiple dyes as “dye cocktails” can hit the target on compensating and broadening light-harvesting region. Two indoline D-A-π-A motif sensitizers (WS-2 and WS-39 that possess similar light response area but distinctly reversed feature in photovoltaic performance are selected as the specific cosensitization couple. That is, WS-2 shows quite high photocurrent but low photovoltage, and WS-39 gives relatively low photocurrent but quite high photovoltage. Due to the obvious “barrel effect”, both dyes show medium PCE around 8.50%. In contrast with the previous cosensitization strategy mostly focused on the compensation of light response region, herein we perform different cosensitization sequence, for taking insight into the balance of photocurrent and photovoltage, and achieving the synergistic improvement in power conversion efficiency (PCE. Electronic impedance spectra (EIS indicate that exploiting dye WS-39 with high VOC value as the primary sensitizer can repress the charge recombination more effectively, resulting in superior VOC rather than using dye WS-2 with high JSC as the primary sensitizer. As a consequence, a high PCE value of 9.48% is obtained with the delicate cosensitization using WS-39 as primary dye and WS-2 as accessory dye, which is higher than the corresponding devices sensitized by each individual dye (around 8.48–8.67%. It provides an effective optimizing strategy of cosensitization how to combine the individual dye advantages for developing highly efficient solar cells. Keywords: Indoline dye, Cosensitization, Adsorption sequence, Charge recombination, Photovoltaic performances

Electron spectroscopic study of electronic and morphological modifications of the WSe{sub 2} surface induced by Rb adsorption

Energy Technology Data Exchange (ETDEWEB)

Buck, Jens

2010-07-20

The rubidium-covered surface of the semiconducting transition metal dichalcogenide tungsten diselenide (WSe{sub 2}) is examined using photoelectron spectroscopy (PES) and photoemission electron microscopy (PEEM). Adsorbed Rb is known to induce a variety of effects in this system concerning electronic, structural, and mechanical properties. In this work, the surface potential created by charge transfer upon Rb deposition is examined in thermal equilibrium (band bending) and stationary non-equilibrium (surface photovoltage (SPV) effect), which is induced by the absorption of light. It is shown that combined measurements and numerical simulations of the SPV effect as a function of the photon flux can be exploited for the estimation of many material parameters of the system, especially of the unoccupied adsorbate state. Issues of extending a conventional photoelectron spectrometer setup by a secondary light source will be discussed in the context of simulations and calibration measurements. The customization of an existing theoretical model of the SPV effect for the WSe{sub 2}: Rb system is introduced, and a comprehensive validation of the obtained predictions is given in the context of experimental data. In addition, the self-organized formation of Rb domains at room temperature was examined by application of spatially resolved XPS spectroscopy using the PEEM setup at the end station of beamline UE49/PGMa at the BESSY II synchrotron facility. From the obtained results, the arrangement of Rb in surface lattices can be concluded. Furthermore, an X-Ray absorption study of self-organized nanostructure networks, aiming at the chemical characterization, is presented. Based on the interpretation of the examined structures as tension-induced cracks, a statistical approach to analyzing large-scale features was pursued. First accordance with the predictions made by a primitive, mechanical model of crack creation developed here gives gives some evidence for the validity of the

The short range effective interaction and the spectra of calcium isotopes in (f-p) space

International Nuclear Information System (INIS)

Qing-ying, Z.; Shen-wu, L.; Jian-xin, W.

1986-01-01

In this work, the authors use a new type of extremely short range interaction, the double delta interaction (DDI) to calculate the low-lying spectra of calcium isotopes /sup 41/Ca through /sup 48/Ca. The configuration space (f-p) includes configurations ( f/sub 7/2//sup n/ ) and ( f/sub 7/2//sup n-1/2p/sub 3/2/). The calculated energies are compared with experimental data for 75 levels. For comparison, they also use usual modified surface delta interaction (MSDI) to calculate the same spectra aforementioned. It is clear that the results calculated with DDI are better than with MSDI. Therefore, in the short-range effective interaction the addition of body delta force to the modified surface delta force may improve the agreement with experiment. The authors believe that the conclusion will not be changed if one enlarges the shell model space

Design energy spectra for Turkey

OpenAIRE

López Almansa, Francisco; Yazgan, Ahmet Utku; Benavent Climent, Amadeo

2012-01-01

This work proposes design energy spectra in terms of velocity, derived through linear dynamic analyses on Turkish registers and intended for regions with design peak acceleration 0.3 g or higher. In the long and mid period ranges the analyses are linear, taking profit of the rather insensitivity of the spectra to the structural parameters other than the fundamental period; in the short period range, the spectra are more sensitive to the structural parameters and nonlinear analyses would be re...

Pramana – Journal of Physics | Indian Academy of Sciences

Indian Academy of Sciences (India)

Abstract. Surface photovoltage (SPV) spectroscopy has been used for the first time to explore Landau levels of a two-dimensional electron gas (2DEG) in modulation doped InP/InGaAs/InP QW in the quantum Hall regime. The technique gives spectroscopically distinct signals from the bulk Landau levels and the edge states.

Surface topography and morphology characterization of PIII irradiated silicon surface

International Nuclear Information System (INIS)

Sharma, Satinder K.; Barthwal, Sumit

2008-01-01

The effect of plasma immersion ion implantation (PIII) treatment on silicon surfaces was investigated by micro-Raman and atomic force microscopy (AFM) technique. The surface damage was given by the implantation of carbon, nitrogen, oxygen and argon ions using an inductively coupled plasma (ICP) source at low pressure. AFM studies show that surface topography of the PIII treated silicon wafers depend on the physical and chemical nature of the implanted species. Micro-Raman spectra indicate that the significant reduction of intensity of Raman peak after PIII treatment. Plasma immersion ion implantation is a non-line-of-sight ion implantation method, which allows 3D treatment of materials. Therefore, PIII based surface modification and plasma immersion ion deposition (PIID) coatings are applied in a wide range of situations.

An Empirical Template Library of Stellar Spectra for a Wide Range of Spectral Classes, Luminosity Classes, and Metallicities Using SDSS BOSS Spectra

Energy Technology Data Exchange (ETDEWEB)

Kesseli, Aurora Y.; West, Andrew A.; Veyette, Mark; Harrison, Brandon; Feldman, Dan [Boston University Astronomy Department, 725 Commonwealth Ave., Boston, MA 02215 (United States); Bochanski, John J., E-mail: aurorak@bu.edu [Rider University, 2083 Lawrenceville Rd., Lawrence Township, NJ 08648 (United States)

2017-06-01

We present a library of empirical stellar spectra created using spectra from the Sloan Digital Sky Survey’s Baryon Oscillation Spectroscopic Survey. The templates cover spectral types O5 through L3, are binned by metallicity from −2.0 dex through +1.0 dex, and are separated into main-sequence (dwarf) stars and giant stars. With recently developed M dwarf metallicity indicators, we are able to extend the metallicity bins down through the spectral subtype M8, making this the first empirical library with this degree of temperature and metallicity coverage. The wavelength coverage for the templates is from 3650 to 10200 Å at a resolution of better than R  ∼ 2000. Using the templates, we identify trends in color space with metallicity and surface gravity, which will be useful for analyzing large data sets from upcoming missions like the Large Synoptic Survey Telescope. Along with the templates, we are releasing a code for automatically (and/or visually) identifying the spectral type and metallicity of a star.

(90377) SEDNA: INVESTIGATION OF SURFACE COMPOSITIONAL VARIATION

International Nuclear Information System (INIS)

Barucci, M. A.; De Bergh, C.; Merlin, F.; Morea Dalle Ore, C.; Cruikshank, D.; Alvarez-Candal, A.; Dumas, C.

2010-01-01

The dwarf planet (90377) Sedna is one of the most remote solar system objects accessible to investigations. To better constrain its surface composition and to investigate the possible heterogeneity of the surface of Sedna, several observations have been carried out at ESO-VLT with the powerful spectrometer SINFONI observing simultaneously the H and K bands. The analyzed spectra (obtained in 2005, 2007, and 2008) show a non-uniform spectral signature, particularly in the K band. Spectral modeling using the Shkuratov radiative transfer code for surface scattering has been performed using the various sets of data, including previous observations at visible wavelengths and photometry at 3.6 and 4.5 μm by the Spitzer Space Telescope. The visible and near-infrared spectra can be modeled with organic materials (triton and titan tholin), serpentine, and H 2 O ice in fairly significant amounts, and CH 4 , N 2 , and C 2 H 6 in varying trace amounts. One of the spectra obtained in 2005 October shows a different signature in the K band and is best modeled with CH 3 OH in place of CH 4 , with reduced amounts of serpentine and with the addition of olivine. The compositional surface heterogeneity can give input on the past history as well clues to the origin of this peculiar, distant object.

Direct visual evidence of end-on adsorption geometry of pyridine on silver surface investigated by surface enhanced Raman scattering and density functional theory calculations.

Science.gov (United States)

Bhunia, Snehasis; Forster, Stefan; Vyas, Nidhi; Schmitt, Hans-Christian; Ojha, Animesh K

2015-12-05

Fourier transform Raman (FT-Raman) spectra of neat pyridine (Py) and surface enhanced Raman scattering (SERS) spectra of Py with silver nanoparticles (AgNPs) solution at different molar concentrations (X=1.5M, 1.0M, 0.50 M, 0.25 M, and 0.125 M) were recorded using 1064 nm excitation wavelength. The intensity of Raman bands at ∼1003 (ν11) and ∼1035 (ν21) cm(-1) of Py is enhanced in the SERS spectra. Two new Raman bands were observed at ∼1009 (ν12) and ∼1038 (ν22) cm(-1) in the SERS spectra. These bands correspond to the ring breathing vibrations of Py molecules adsorbed at the AgNPs surface. The value of intensity ratios (I12/I11) and (I21/I22) is increased with dilution and attains a maximum value at X=0.5M and upon further dilution (0.25 and 0.125 M) it drops gradually. The theoretically calculated Raman spectra were found to be in good agreement with experimentally observed Raman spectra. Both, experimental and theoretical investigations have confirmed that the Py interacts with AgNPs via the end-on geometry. Copyright © 2015 Elsevier B.V. All rights reserved.

Correlation Functions and Power Spectra

DEFF Research Database (Denmark)

Larsen, Jan

2006-01-01

The present lecture note is a supplement to the textbook Digital Signal Processing by J. Proakis and D.G. Manolakis used in the IMM/DTU course 02451 Digital Signal Processing and provides an extended discussion of correlation functions and power spectra. The definitions of correlation functions...... and spectra for discrete-time and continuous-time (analog) signals are pretty similar. Consequently, we confine the discussion mainly to real discrete-time signals. The Appendix contains detailed definitions and properties of correlation functions and spectra for analog as well as discrete-time signals....... It is possible to define correlation functions and associated spectra for aperiodic, periodic and random signals although the interpretation is different. Moreover, we will discuss correlation functions when mixing these basic signal types. In addition, the note include several examples for the purpose...

Spectroscopic XPEEM of highly conductive SI-doped GaN wires

Energy Technology Data Exchange (ETDEWEB)

Renault, O., E-mail: olivier.renault@cea.fr [Univ. Grenoble Alpes, F-38000 Grenoble (France); CEA, LETI, MINATEC Campus, F-38054 Grenoble (France); Morin, J. [Univ. Grenoble Alpes, F-38000 Grenoble (France); CEA, LETI, MINATEC Campus, F-38054 Grenoble (France); Tchoulfian, P. [Univ. Grenoble Alpes, F-38000 Grenoble (France); CEA, LETI, MINATEC Campus, F-38054 Grenoble (France); CNRS, Inst. NEEL, F-38042 Grenoble (France); Chevalier, N. [Univ. Grenoble Alpes, F-38000 Grenoble (France); CEA, LETI, MINATEC Campus, F-38054 Grenoble (France); Feyer, V. [Peter Grünberg Institute (PGI-6) and JARA-FIT, Research Center Jülich, D-52425 Jülich (Germany); Pernot, J. [Univ. Grenoble Alpes, F-38000 Grenoble (France); CNRS, Inst. NEEL, F-38042 Grenoble (France); Institut Universitaire de France, F-75005 Paris (France); Schneider, C.M. [Peter Grünberg Institute (PGI-6) and JARA-FIT, Research Center Jülich, D-52425 Jülich (Germany)

2015-12-15

Using soft X-ray photoelectron emission microscopy (XPEEM), complemented by scanning Auger microscopy (SAM) and scanning capacitance microscopy, we have quantitatively studied the incorporation of silicon and band bending at the surface (m-facet) of an individual, highly conductive Si-doped GaN micro-wires (Tchoulfian et al., Applied Physics Letters 102 (12), 2013). Electrically active n-dopants Si atoms in Ga interstitial sites are detected as nitride bonding states in the high-resolution Si2p core level spectra, and represent only a small fraction (<10%) of the overall Si surface concentration measured by SAM. The derived carrier concentration of 2×10{sup 21} at cm{sup −3} is in reasonable agreement with electrical measurements. A consistent surface band bending of ~1 eV is directly evidenced by surface photo-voltage measurements. Such an approach combining different surface-sensitive microscopies is of interest for studying other heavily doped semiconducting wires. - Highlights: • XPEEM analysis of state-of-the-art, heavily doped GaN wires with insights on the issue of the origin of the increased conductivity. • Combined microscopic approach with Scanning Auger microscopy and X-ray Photoeletron Emission Microscopy, to quantity the electrically active Si-dopants in GaN. • The determined concentration is found in reasonable agreement with the one derived from bulk electrical measurements. • The proposed method is of interest for studying the electronics and chemistry of doping in other heavily doped semiconducting wires.

Multifunctional uranyl hybrid materials: structural diversities as a function of pH, luminescence with potential nitrobenzene sensing, and photoelectric behavior as p-type semiconductors.

Science.gov (United States)

Song, Jian; Gao, Xue; Wang, Zhi-Nan; Li, Cheng-Ren; Xu, Qi; Bai, Feng-Ying; Shi, Zhong-Feng; Xing, Yong-Heng

2015-09-21

A series of uranyl-organic frameworks (UOFs), {[(UO2)2(H2TTHA)(H2O)]·4,4'-bipy·2H2O}n (1), {[(UO2)3(TTHA)(H2O)3]}n (2), and {[(UO2)5(TTHA) (HTTHA)(H2O)3]·H3O}n (3), have been obtained by the hydrothermal reaction of uranyl acetate with a flexible hexapodal ligand (1,3,5-triazine-2,4,6-triamine hexaacetic acid, H6TTHA). These compounds exhibited three distinct 3D self-assembly architectures as a function of pH by single-crystal structural analysis, although the used ligand was the same in each reaction. Surprisingly, all of the coordination modes of the H6TTHA ligand in this work are first discovered. Furthermore, the photoluminescent results showed that these compounds displayed high-sensitivity luminescent sensing functions for nitrobenzene. Additionally, the surface photovoltage spectroscopy and electric-field-induced surface photovoltage spectroscopy showed that compounds 1-3 could behave as p-type semiconductors.

Interrelating meteorite and asteroid spectra at UV-Vis-NIR wavelengths using novel multiple-scattering methods

Science.gov (United States)

Martikainen, Julia; Penttilä, Antti; Gritsevich, Maria; Muinonen, Karri

2017-10-01

Asteroids have remained mostly the same for the past 4.5 billion years, and provide us information on the origin, evolution and current state of the Solar System. Asteroids and meteorites can be linked by matching their respective reflectance spectra. This is difficult, because spectral features depend strongly on the surface properties, and meteorite surfaces are free of regolith dust present in asteroids. Furthermore, asteroid surfaces experience space weathering which affects their spectral features.We present a novel simulation framework for assessing the spectral properties of meteorites and asteroids and matching their reflectance spectra. The simulations are carried out by utilizing a light-scattering code that takes inhomogeneous waves into account and simulates light scattering by Gaussian-random-sphere particles large compared to the wavelength of the incident light. The code uses incoherent input and computes phase matrices by utilizing incoherent scattering matrices. Reflectance spectra are modeled by combining olivine, pyroxene, and iron, the most common materials that dominate the spectral features of asteroids and meteorites. Space weathering is taken into account by adding nanoiron into the modeled asteroid spectrum. The complex refractive indices needed for the simulations are obtained from existing databases, or derived using an optimization that utilizes our ray-optics code and the measured spectrum of the material.We demonstrate our approach by applying it to the reflectance spectrum of (4) Vesta and the reflectance spectrum of the Johnstown meteorite measured with the University of Helsinki integrating-sphere UV-Vis-NIR spectrometer.Acknowledgments. The research is funded by the ERC Advanced Grant No. 320773 (SAEMPL).

Quasi-classical approaches to vibronic spectra revisited

Science.gov (United States)

Karsten, Sven; Ivanov, Sergei D.; Bokarev, Sergey I.; Kühn, Oliver

2018-03-01

The framework to approach quasi-classical dynamics in the electronic ground state is well established and is based on the Kubo-transformed time correlation function (TCF), being the most classical-like quantum TCF. Here we discuss whether the choice of the Kubo-transformed TCF as a starting point for simulating vibronic spectra is as unambiguous as it is for vibrational ones. Employing imaginary-time path integral techniques in combination with the interaction representation allowed us to formulate a method for simulating vibronic spectra in the adiabatic regime that takes nuclear quantum effects and dynamics on multiple potential energy surfaces into account. Further, a generalized quantum TCF is proposed that contains many well-established TCFs, including the Kubo one, as particular cases. Importantly, it also provides a framework to construct new quantum TCFs. Applying the developed methodology to the generalized TCF leads to a plethora of simulation protocols, which are based on the well-known TCFs as well as on new ones. Their performance is investigated on 1D anharmonic model systems at finite temperatures. It is shown that the protocols based on the new TCFs may lead to superior results with respect to those based on the common ones. The strategies to find the optimal approach are discussed.

Stellar parametrization from Gaia RVS spectra

Science.gov (United States)

Recio-Blanco, A.; de Laverny, P.; Allende Prieto, C.; Fustes, D.; Manteiga, M.; Arcay, B.; Bijaoui, A.; Dafonte, C.; Ordenovic, C.; Ordoñez Blanco, D.

2016-01-01

Context. Among the myriad of data collected by the ESA Gaia satellite, about 150 million spectra will be delivered by the Radial Velocity Spectrometer (RVS) for stars as faint as GRVS~ 16. A specific stellar parametrization will be performed on most of these RVS spectra, I.e. those with enough high signal-to-noise ratio (S/N), which should correspond to single stars that have a magnitude in the RVS band brighter than ~14.5. Some individual chemical abundances will also be estimated for the brightest targets. Aims: We describe the different parametrization codes that have been specifically developed or adapted for RVS spectra within the GSP-Spec working group of the analysis consortium. The tested codes are based on optimisation (FERRE and GAUGUIN), projection (MATISSE), or pattern-recognition methods (Artificial Neural Networks). We present and discuss each of their expected performances in the recovered stellar atmospheric parameters (effective temperature, surface gravity, overall metallicity) for B- to K-type stars. The performances for determining of [α/Fe] ratios are also presented for cool stars. Methods: Each code has been homogeneously tested with a large grid of RVS simulated synthetic spectra of BAFGK-spectral types (dwarfs and giants), with metallicities varying from 10-2.5 to 10+ 0.5 the solar metallicity, and taking variations of ±0.4 dex in the composition of the α-elements into consideration. The tests were performed for S/N ranging from ten to 350. Results: For all the stellar types we considered, stars brighter than GRVS~ 12.5 are very efficiently parametrized by the GSP-Spec pipeline, including reliable estimations of [α/Fe]. Typical internal errors for FGK metal-rich and metal-intermediate stars are around 40 K in Teff, 0.10 dex in log(g), 0.04 dex in [M/H], and 0.03 dex in [α/Fe] at GRVS = 10.3. They degrade to 155 K in Teff, 0.15 dex in log(g), 0.10 dex in [M/H], and 0.1 dex in [α/Fe] at GRVS~ 12. Similar accuracies in Teff and [M/H] are

Surface-enhanced vibrational spectroscopy of B vitamins: what is the effect of SERS-active metals used?

Science.gov (United States)

Kokaislová, A; Matějka, P

2012-05-01

Surface-enhanced Raman scattering (SERS) spectroscopy and surface-enhanced infrared absorption (SEIRA) spectroscopy are analytical tools suitable for the detection of small amounts of various analytes adsorbed on metal surfaces. During recent years, these two spectroscopic methods have become increasingly important in the investigation of adsorption of biomolecules and pharmaceuticals on nanostructured metal surfaces. In this work, the adsorption of B-group vitamins pyridoxine, nicotinic acid, folic acid and riboflavin at electrochemically prepared gold and silver substrates was investigated using Fourier transform SERS spectroscopy at an excitation wavelength of 1,064 nm. Gold and silver substrates were prepared by cathodic reduction on massive platinum targets. In the case of gold substrates, oxidation-reduction cycles were applied to increase the enhancement factor of the gold surface. The SERS spectra of riboflavin, nicotinic acid, folic acid and pyridoxine adsorbed on silver substrates differ significantly from SERS spectra of these B-group vitamins adsorbed on gold substrates. The analysis of near-infrared-excited SERS spectra reveals that each of B-group vitamin investigated interacts with the gold surface via a different mechanism of adsorption to that with the silver surface. In the case of riboflavin adsorbed on silver substrate, the interpretation of surface-enhanced infrared absorption (SEIRA) spectra was also helpful in investigation of the adsorption mechanism.

Oxide/water interfaces: how the surface chemistry modifies interfacial water properties

International Nuclear Information System (INIS)

Gaigeot, Marie-Pierre; Sprik, Michiel; Sulpizi, Marialore

2012-01-01

The organization of water at the interface with silica and alumina oxides is analysed using density functional theory-based molecular dynamics simulation (DFT-MD). The interfacial hydrogen bonding is investigated in detail and related to the chemistry of the oxide surfaces by computing the surface charge density and acidity. We find that water molecules hydrogen-bonded to the surface have different orientations depending on the strength of the hydrogen bonds and use this observation to explain the features in the surface vibrational spectra measured by sum frequency generation spectroscopy. In particular, ‘ice-like’ and ‘liquid-like’ features in these spectra are interpreted as the result of hydrogen bonds of different strengths between surface silanols/aluminols and water. (paper)

TRANSMISSION SPECTRA OF THREE-DIMENSIONAL HOT JUPITER MODEL ATMOSPHERES

International Nuclear Information System (INIS)

Fortney, J. J.; Shabram, M.; Showman, A. P.; Lian, Y.; Lewis, N. K.; Freedman, R. S.; Marley, M. S.

2010-01-01

We compute models of the transmission spectra of planets HD 209458b, HD 189733b, and generic hot Jupiters. We examine the effects of temperature, surface gravity, and metallicity for the generic planets as a guide to understanding transmission spectra in general. We find that carbon dioxide absorption at 4.4 and 15 μm is prominent at high metallicity, and is a clear metallicity indicator. For HD 209458b and HD 189733b, we compute spectra for both one-dimensional and three-dimensional model atmospheres and examine the differences between them. The differences are usually small, but can be large if atmospheric temperatures are near important chemical abundance boundaries. The calculations for the three-dimensional atmospheres, and their comparison with data, serve as constraints on these dynamical models that complement the secondary eclipse and light curve data sets. For HD 209458b, even if TiO and VO gases are abundant on the dayside, their abundances can be considerably reduced on the cooler planetary limb. However, given the predicted limb temperatures and TiO abundances, the model's optical opacity is too high. For HD 189733b we find a good match with some infrared data sets and constrain the altitude of a postulated haze layer. For this planet, substantial differences can exist between the transmission spectra of the leading and trailing hemispheres, which are an excellent probe of carbon chemistry. In thermochemical equilibrium, the cooler leading hemisphere is methane-dominated, and the hotter trailing hemisphere is CO-dominated, but these differences may be eliminated by non-equilibrium chemistry due to vertical mixing. It may be possible to constrain the carbon chemistry of this planet, and its spatial variation, with James Webb Space Telescope.

Dynamical and Radiative Properties of X-Ray Pulsar Accretion Columns: Phase-averaged Spectra

Energy Technology Data Exchange (ETDEWEB)

West, Brent F. [Department of Electrical and Computer Engineering, United States Naval Academy, Annapolis, MD (United States); Wolfram, Kenneth D. [Naval Research Laboratory (retired), Washington, DC (United States); Becker, Peter A., E-mail: bwest@usna.edu, E-mail: kswolfram@gmail.com, E-mail: pbecker@gmu.edu [Department of Physics and Astronomy, George Mason University, Fairfax, VA (United States)

2017-02-01

The availability of the unprecedented spectral resolution provided by modern X-ray observatories is opening up new areas for study involving the coupled formation of the continuum emission and the cyclotron absorption features in accretion-powered X-ray pulsar spectra. Previous research focusing on the dynamics and the associated formation of the observed spectra has largely been confined to the single-fluid model, in which the super-Eddington luminosity inside the column decelerates the flow to rest at the stellar surface, while the dynamical effect of gas pressure is ignored. In a companion paper, we have presented a detailed analysis of the hydrodynamic and thermodynamic structure of the accretion column obtained using a new self-consistent model that includes the effects of both gas and radiation pressures. In this paper, we explore the formation of the associated X-ray spectra using a rigorous photon transport equation that is consistent with the hydrodynamic and thermodynamic structure of the column. We use the new model to obtain phase-averaged spectra and partially occulted spectra for Her X-1, Cen X-3, and LMC X-4. We also use the new model to constrain the emission geometry, and compare the resulting parameters with those obtained using previously published models. Our model sheds new light on the structure of the column, the relationship between the ionized gas and the photons, the competition between diffusive and advective transport, and the magnitude of the energy-averaged cyclotron scattering cross-section.

Energy-resolved attosecond interferometric photoemission from Ag(111) and Au(111) surfaces

Science.gov (United States)

Ambrosio, M. J.; Thumm, U.

2018-04-01

Photoelectron emission from solid surfaces induced by attosecond pulse trains into the electric field of delayed phase-coherent infrared (IR) pulses allows the surface-specific observation of energy-resolved electronic phase accumulations and photoemission delays. We quantum-mechanically modeled interferometric photoemission spectra from the (111) surfaces of Au and Ag, including background contributions from secondary electrons and direct emission by the IR pulse, and adjusted parameters of our model to energy-resolved photoelectron spectra recently measured at a synchrotron light source by Roth et al. [J. Electron Spectrosc. 224, 84 (2018), 10.1016/j.elspec.2017.05.008]. Our calculated spectra and photoelectron phase shifts are in fair agreement with the experimental data of Locher et al. [Optica 2, 405 (2015), 10.1364/OPTICA.2.000405]. Our model's not reproducing the measured energy-dependent oscillations of the Ag(111) photoemission phases may be interpreted as evidence for subtle band-structure effects on the final-state photoelectron-surface interaction not accounted for in our simulation.

Validity of abundances derived from spaxel spectra of the MaNGA survey

Science.gov (United States)

Pilyugin, L. S.; Grebel, E. K.; Zinchenko, I. A.; Nefedyev, Y. A.; Shulga, V. M.; Wei, H.; Berczik, P. P.

2018-05-01

We measured the emission lines in the spaxel spectra of Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) galaxies in order to determine the abundance distributions therein. It has been suggested that the strength of the low-ionization lines, R2, N2, and S2, may be increased (relative to Balmer lines) in (some) spaxel spectra of the MaNGA survey due to a contribution of the radiation of the diffuse ionized gas. Consequently, the abundances derived from the spaxel spectra through strong-line methods may suffer from large errors. We examined this expectation by comparing the behaviour of the line intensities and the abundances estimated through different calibrations for slit spectra of H II regions in nearby galaxies, for fibre spectra from the Sloan Digital Sky Survey, and for spaxel spectra of the MaNGA survey. We found that the S2 strength is increased significantly in the fibre and spaxel spectra. The mean enhancement changes with metallicity and can be as large as a factor of 2. The mean distortion of R2 and N2 is less than a factor of 1.3. This suggests that Kaufmann et al.'s (2003, MNRAS, 346, 1055) demarcation line between active galactic nuclei and H II regions in the Baldwin, Phillips, & Terlevich (BPT, 1981, PASP, 93, 5) diagram is a useful criterion to reject spectra with significantly distorted strengths of the N2 and R2 lines. We find that the three-dimensional R calibration, which uses the N2 and R2 lines, produces reliable abundances in the MaNGA galaxies. The one-dimensional N2 calibration produces either reliable or wrong abundances depending on whether excitation and N/O abundance ratio in the target region (spaxel) are close to or differ from those parameters in the calibrating points located close to the calibration relation. We then determined abundance distributions within the optical radii in the discs of 47 MaNGA galaxies. The optical radii of the galaxies were estimated from the surface brightness profiles constructed based on the

Determination of fast neutrons energy spectra by Monte-Carlo Method

International Nuclear Information System (INIS)

Chetaine, A.

1986-01-01

Two computation codes based on the Monte-Carlo method are established for studying the spectrometry of neutrons with 14 Mev as initial energy. The spectra are determined, on one hand, around a neutron generator Ti-T target and, on the other hand, in a big paraffin cylinder. One code allows to determine the spectrum of neutrons irradiating the sample at various distances from the Ti-T target versus accelerator parameters: high voltage, atomic or molecular nature of deuterons beam, target thickness and materials surrounding the target. The other code determines neutron spectra at various positions inside and outside the 30 x 30 cm paraffin cylinder. The validity of the procedure used in these codes is verified by determining the spectrum of neutrons crossing a big surface, using the procedure in question and using direct simulation method. The biasing procedure used in the two codes permits to have results with good statistics from a reduced number of drawings. 70 figs.; 62 refs.; 1 tab. (author)

Two-dimensional spectra of electron collisions with acrylonitrile and methacrylonitrile reveal nuclear dynamics

Energy Technology Data Exchange (ETDEWEB)

Regeta, K., E-mail: khrystyna.regeta@unifr.ch; Allan, M., E-mail: michael.allan@unifr.ch [Department of Chemistry, University of Fribourg, Chemin du Musée 9, CH-1700 Fribourg (Switzerland)

2015-05-14

Detailed experimental information on the motion of a nuclear packet on a complex (resonant) anion potential surface is obtained by measuring 2-dimensional (2D) electron energy loss spectra. The cross section is plotted as a function of incident electron energy, which determines which resonant anion state is populated, i.e., along which normal coordinate the wave packet is launched, and of the electron energy loss, which reveals into which final states each specific resonant state decays. The 2D spectra are presented for acrylonitrile and methacrylonitrile, at the incident energy range 0.095-1.0 eV, where the incoming electron is temporarily captured in the lowest π{sup ∗} orbital. The 2D spectra reveal selectivity patterns with respect to which vibrations are excited in the attachment and de-excited in the detachment. Further insight is gained by recording 1D spectra measured along horizontal, vertical, and diagonal cuts of the 2D spectrum. The methyl group in methacrylonitrile increases the resonance width 7 times. This converts the sharp resonances of acrylonitrile into boomerang structures but preserves the essence of the selectivity patterns. Selectivity of vibrational excitation by higher-lying shape resonances up to 8 eV is also reported.

An investigation of the mass spectra of secondary ions ejected from the single crystal surface of semiconductors

International Nuclear Information System (INIS)

Koval', A.G.; Mel'nikov, V.N.; Enukov, Yu.V.

1976-01-01

The mass spectra of secondary positive and negative ions, ejected by an Ar + ion beam from the (100) face of an epitaxial film of the semiconductor Alsub(x)Gasub(1-x)As were investigated. There are many various secondary ions in the mass spectrum under investigation. They may be divided into four groups according to their origins. Mass spectra of secondary positive and negative secondary ions differ much, either in their composition or the intensities of homogeneous ions. The I(T) dependences (I=the current of corresponding secondary ions, T=target temperature) were obtained for secondary and negative ions taken from groups differing by their origin. The I(T) dependences were obtained at several oxygen pressures in a chamber. For the ions with 'superficial' origin a strong dependence of their current on target temperature is observed. Oxygen pressure increase leads to substantial change of the I(T)curves. (Auth.)

Surface transport properties of Fe-based superconductors: The influence of degradation and inhomogeneity

Energy Technology Data Exchange (ETDEWEB)

Plecenik, T.; Gregor, M.; Sobota, R.; Truchly, M.; Satrapinskyy, L.; Kus, P.; Plecenik, A. [Department of Experimental Physics, FMPI, Comenius University, 842 48 Bratislava (Slovakia); Kurth, F.; Holzapfel, B.; Iida, K. [Institute for Metallic Materials, IFW Dresden, P. O. Box 270116, D-01171 Dresden (Germany)

2013-07-29

Surface properties of Co-doped BaFe{sub 2}As{sub 2} epitaxial superconducting thin films were inspected by X-ray photoelectron spectroscopy, scanning spreading resistance microscopy (SSRM), and point contact spectroscopy (PCS). It has been shown that surface of Fe-based superconductors degrades rapidly if being exposed to air, what results in suppression of gap-like structure on PCS spectra. Moreover, SSRM measurements revealed inhomogeneous surface conductivity, what is consistent with strong dependence of PCS spectra on contact position. Presented results suggest that fresh surface and small probing area should be assured for surface sensitive measurements like PCS to obtain intrinsic properties of Fe-based superconductors.

Different spectra with the same neutron source

International Nuclear Information System (INIS)

Vega C, H. R.; Ortiz R, J. M.; Hernandez D, V. M.; Martinez B, M. R.; Hernandez A, B.; Ortiz H, A. A.; Mercado, G. A.

2010-01-01

Using as source term the spectrum of a 239 Pu-Be source several neutron spectra have been calculated using Monte Carlo methods. The source term was located in the centre of spherical moderators made of light water, heavy water and polyethylene of different diameters. Also a 239 Pu-Be source was used to measure its neutron spectrum, bare and moderated by water. The neutron spectra were measured at 100 cm with a Bonner spheres spectrometer. Monte Carlo calculations were used to calculate the neutron spectra of bare and water-moderated spectra that were compared with those measured with the spectrometer. Resulting spectra are similar to those found in power plants with PWR, BWR and Candu nuclear reactors. Beside the spectra the dosimetric features were determined. Using moderators and a single neutron source can be produced neutron spectra alike those found in workplaces, this neutron fields can be utilized to calibrate neutron dosimeters and area monitors. (Author)

Deconvolution of Positrons' Lifetime spectra

International Nuclear Information System (INIS)

Calderin Hidalgo, L.; Ortega Villafuerte, Y.

1996-01-01

In this paper, we explain the iterative method previously develop for the deconvolution of Doppler broadening spectra using the mathematical optimization theory. Also, we start the adaptation and application of this method to the deconvolution of positrons' lifetime annihilation spectra

Time-space distribution of laser-induced plasma parameters and its influence on emission spectra of the laser plumes

International Nuclear Information System (INIS)

Ershov-Pavlov, E.A.; Katsalap, K.Yu.; Stepanov, K.L.; Stankevich, Yu.A.

2008-01-01

A physical model is developed accounting for dynamics and radiation of plasma plumes induced by nanosecond laser pulses on surface of solid samples. The model has been applied to simulate emission spectra of the laser erosion plasma at the elemental analysis of metals using single- and double-pulse excitation modes. Dynamics of the sample heating and expansion of the erosion products are accounted for by the thermal conductivity and gas dynamic equations, respectively, supposing axial symmetry. Using the resulting time-space distributions of the plasma parameters, emission spectra of the laser plumes are evaluated by solving the radiation transfer equation. Particle concentration in consecutive ionization stages is described by the Saha equation in the Debye approximation. The population of excited levels is determined according to Boltzmann distribution. Local characteristics determining spectral emission and absorption coefficients are obtained point-by-point along an observation line. Voigt spectral line profiles are considered with main broadening mechanisms taken into account. The plasma dynamics and plume emission spectra have been studied experimentally and by the model. A Q-switched Nd:YAG laser at 1064 nm wavelength has been used to irradiate Al sample with the pulses of 15 ns and 50 mJ duration and energy, respectively. It has resulted in maximum power density of 0.8 MW/cm 2 on the sample surface. The laser plume emission spectra have been recorded at a side-on observation. Problems of the spectra contrast and of the elemental analysis efficiency are considered relying on a comparative study of the measurement and simulation results at the both excitation modes

Specific behavior of the p-aminothiophenol--silver sol system in their Ultra-Violet-Visible (UV-Visible) and Surface Enhanced Raman (SERS) spectra.

Science.gov (United States)

Firkala, Tamás; Tálas, Emília; Mihály, Judith; Imre, Tímea; Kristyán, Sándor

2013-11-15

The UV-Visible and Surface Enhanced Raman Spectroscopy (SERS) behavior of silver sol (a typical SERS agent) were studied in the presence of different bifunctional thiols such as p-aminothiophenol, p-mercaptobenzoic acid, p-nitrothiophenol, p-aminothiophenol hydrochloride, and 2-mercaptoethylamine hydrochloride in diluted aqueous solution. Our results confirm that the p-aminothiophenol induced aggregation of citrate stabilized silver colloid originates from its electrostatic nature, as well as the azo-bridge formation cannot be the reason of the observed time dependent UV-Visible spectra. Based on our parallel SERS and electrospray ionization mass spectrometry measurements, we have concluded that certain amount of oxidized form of the probe molecule has to be present for the so-called b2-mode enhancement in the SERS spectrum of p-aminothiophenol. Our findings seem to support the idea that the azo-bridge formation is responsible for the b2-mode enhancement in the SERS spectrum of p-aminothiophenol. Copyright © 2013 Elsevier Inc. All rights reserved.

The physical basis for estimating wave-energy spectra with the radar ocean-wave spectrometer

Science.gov (United States)

Jackson, Frederick C.

1987-01-01

The derivation of the reflectivity modulation spectrum of the sea surface for near-nadir-viewing microwave radars using geometrical optics is described. The equations required for the derivation are presented. The derived reflectivity modulation spectrum provides data on the physical basis of the radar ocean-wave spectrometer measurements of ocean-wave directional spectra.

Advanced LWIR hyperspectral sensor for on-the-move proximal detection of liquid/solid contaminants on surfaces

Science.gov (United States)

Giblin, Jay P.; Dixon, John; Dupuis, Julia R.; Cosofret, Bogdan R.; Marinelli, William J.

2017-05-01

Sensor technologies capable of detecting low vapor pressure liquid surface contaminants, as well as solids, in a noncontact fashion while on-the-move continues to be an important need for the U.S. Army. In this paper, we discuss the development of a long-wave infrared (LWIR, 8-10.5 μm) spatial heterodyne spectrometer coupled with an LWIR illuminator and an automated detection algorithm for detection of surface contaminants from a moving vehicle. The system is designed to detect surface contaminants by repetitively collecting LWIR reflectance spectra of the ground. Detection and identification of surface contaminants is based on spectral correlation of the measured LWIR ground reflectance spectra with high fidelity library spectra and the system's cumulative binary detection response from the sampled ground. We present the concepts of the detection algorithm through a discussion of the system signal model. In addition, we present reflectance spectra of surfaces contaminated with a liquid CWA simulant, triethyl phosphate (TEP), and a solid simulant, acetaminophen acquired while the sensor was stationary and on-the-move. Surfaces included CARC painted steel, asphalt, concrete, and sand. The data collected was analyzed to determine the probability of detecting 800 μm diameter contaminant particles at a 0.5 g/m2 areal density with the SHSCAD traversing a surface.

Comparison between simplified load spectra in accordance with Germanische Lloyd guidelines, and load spectra derived from time domain simulations

Energy Technology Data Exchange (ETDEWEB)

Rees, M [Aerodyn Energiesysteme gmbH, Rendsburg (Germany)

1996-09-01

The Germanische Lloyd guideline allows calculations of load spectra in two fundamentally different ways. In the case of the so-called `simplified load spectra` the maximum amplitude of fluctuation of a load component is formed as {+-}75% of the average value of the purely aerodynamic loads of this component at rated wind conditions, together with an overlay of mass-related loads. The second method allowed in the GL guideline is the calculation of load spectra from simulation results in the time domain. For a number of average wind speeds the time-dependent characteristics of the load components are calculated taking account of the natural spatial turbulence of the wind. These are converted into load spectra using the rainflow method. In a parametric study the load spectra are calculated according to both methods and compared. The calculations are performed for turbines with rated powers of 100 kW to 2000 kW, with two and three blades, and also for stall-controlled and pitch-controlled turbines. The calculated load spectra are compared with each by means of 1 P fatigue equivalent load spectra. The influence of individual parameters is presented, as is the validity of the simplified load spectra. (au)

Prediction of UV spectra and UV-radiation damage in actual plasma etching processes using on-wafer monitoring technique

International Nuclear Information System (INIS)

Jinnai, Butsurin; Fukuda, Seiichi; Ohtake, Hiroto; Samukawa, Seiji

2010-01-01

UV radiation during plasma processing affects the surface of materials. Nevertheless, the interaction of UV photons with surface is not clearly understood because of the difficulty in monitoring photons during plasma processing. For this purpose, we have previously proposed an on-wafer monitoring technique for UV photons. For this study, using the combination of this on-wafer monitoring technique and a neural network, we established a relationship between the data obtained from the on-wafer monitoring technique and UV spectra. Also, we obtained absolute intensities of UV radiation by calibrating arbitrary units of UV intensity with a 126 nm excimer lamp. As a result, UV spectra and their absolute intensities could be predicted with the on-wafer monitoring. Furthermore, we developed a prediction system with the on-wafer monitoring technique to simulate UV-radiation damage in dielectric films during plasma etching. UV-induced damage in SiOC films was predicted in this study. Our prediction results of damage in SiOC films shows that UV spectra and their absolute intensities are the key cause of damage in SiOC films. In addition, UV-radiation damage in SiOC films strongly depends on the geometry of the etching structure. The on-wafer monitoring technique should be useful in understanding the interaction of UV radiation with surface and in optimizing plasma processing by controlling UV radiation.

Fitting the curve in Excel® : Systematic curve fitting of laboratory and remotely sensed planetary spectra

NARCIS (Netherlands)

McCraig, M.A.; Osinski, G.R.; Cloutis, E.A.; Flemming, R.L.; Izawa, M.R.M.; Reddy, V.; Fieber-Beyer, S.K.; Pompilio, L.; van der Meer, F.D.; Berger, J.A.; Bramble, M.S.; Applin, D.M.

2017-01-01

Spectroscopy in planetary science often provides the only information regarding the compositional and mineralogical make up of planetary surfaces. The methods employed when curve fitting and modelling spectra can be confusing and difficult to visualize and comprehend. Researchers who are new to

Structure of high-resolution NMR spectra

CERN Document Server

Corio, PL

2012-01-01

Structure of High-Resolution NMR Spectra provides the principles, theories, and mathematical and physical concepts of high-resolution nuclear magnetic resonance spectra.The book presents the elementary theory of magnetic resonance; the quantum mechanical theory of angular momentum; the general theory of steady state spectra; and multiple quantum transitions, double resonance and spin echo experiments.Physicists, chemists, and researchers will find the book a valuable reference text.

FSFE: Fake Spectra Flux Extractor

Science.gov (United States)

Bird, Simeon

2017-10-01

The fake spectra flux extractor generates simulated quasar absorption spectra from a particle or adaptive mesh-based hydrodynamic simulation. It is implemented as a python module. It can produce both hydrogen and metal line spectra, if the simulation includes metals. The cloudy table for metal ionization fractions is included. Unlike earlier spectral generation codes, it produces absorption from each particle close to the sight-line individually, rather than first producing an average density in each spectral pixel, thus substantially preserving more of the small-scale velocity structure of the gas. The code supports both Gadget (ascl:0003.001) and AREPO.

Distortions in frequency spectra of signals associated with sampling-pulse shapes

International Nuclear Information System (INIS)

Njau, E.C.

1983-04-01

A method developed earlier by the author [IC/82/44; IC/82/45] is used to investigate distortions introduced into frequency spectra of signals by the shapes of the sampling pulses involved. Conditions are established under which the use of trapezoid or exponentially-edged pulses to digitize signals can make the frequency spectra of the resultant data samples devoid of the main features of the signals. This observation does not, however, apply in any way to cosinusoidally-edged pulses or to pulses with cosine-squared edges. Since parts of the Earth's surface and atmosphere receive direct solar energy in discrete samples (i.e. only from sunrise to sunset) we have extended the technique and attempted to develop a theory that explains the observed solar terrestrial relationships. A very good agreement is obtained between the theory and previous long-term and short-term observations. (author)

Excitonic surface polaritons in luminescence from ZnTe crystals

International Nuclear Information System (INIS)

Brodin, M.S.; Bandura, V.M.; Matsko, M.G.

1984-01-01

The form and structure of reflection and exciton-polariton luminescence spectra of ZnTe crystals are studied in the region of the ground (n = 1) exciton state. The longitudinal-transverse splitting magnitude ΔE/sub LT/ is determined from the shape of the reflection spectra. A detected doublet structure of an emission band from the lower polariton branch is associated with the k-linear term. The evolution of bulk and surface polariton luminescence spectra versus temperature and wavelength of the exciting light is investigated. (author)

Excitonic surface polaritons in luminescence from ZnTe crystals

Energy Technology Data Exchange (ETDEWEB)

Brodin, M.S.; Bandura, V.M.; Matsko, M.G. (AN Ukrainskoj SSR, Kiev. Inst. Fiziki)

1984-10-01

The form and structure of reflection and exciton-polariton luminescence spectra of ZnTe crystals are studied in the region of the ground (n = 1) exciton state. The longitudinal-transverse splitting magnitude ..delta..E/sub LT/ is determined from the shape of the reflection spectra. A detected doublet structure of an emission band from the lower polariton branch is associated with the k-linear term. The evolution of bulk and surface polariton luminescence spectra versus temperature and wavelength of the exciting light is investigated.

Characteristics of meter-scale surface electrical discharge propagating along water surface at atmospheric pressure

International Nuclear Information System (INIS)

Hoffer, Petr; Sugiyama, Yuki; Hosseini, S Hamid R; Akiyama, Hidenori; Lukes, Petr; Akiyama, Masahiro

2016-01-01

This paper reports physical characteristics of water surface discharges. Discharges were produced by metal needle-to-water surface geometry, with the needle electrode driven by 47 kV (FWHM) positive voltage pulses of 2 µ s duration. Propagation of discharges along the water surface was confined between glass plates with 2 mm separation. This allowed generation of highly reproducible 634 mm-long plasma filaments. Experiments were performed using different atmospheres: air, N 2 , and O 2 , each at atmospheric pressure. Time- and spatially-resolved spectroscopic measurements revealed that early spectra of discharges in air and nitrogen atmospheres were dominated by N 2 2nd positive system. N 2 radiation disappeared after approx. 150 ns, replaced by emissions from atomic hydrogen. Spectra of discharges in O 2 atmosphere were dominated by emissions from atomic oxygen. Time- and spatially-resolved emission spectra were used to determine temperatures in plasma. Atomic hydrogen emissions showed excitation temperature of discharges in air to be about 2  ×  10 4 K. Electron number densities determined by Stark broadening of the hydrogen H β line reached a maximum value of ∼10 18 cm −3 just after plasma initiation. Electron number densities and temperatures depended only slightly on distance from needle electrode, indicating formation of high conductivity leader channels. Direct observation of discharges by high speed camera showed that the average leader head propagation speed was 412 km · s −1 , which is substantially higher value than that observed in experiments with shorter streamers driven by lower voltages. (paper)

On the interpretation of total current spectroscopy (TCS) spectra from MoS2 crystals

International Nuclear Information System (INIS)

Mohamed, M.H.; Moeller, P.J.

1981-01-01

Total Current Spectroscopy (TCS) spectra from MoS 2 (0001) face for three different angles of incidence of the primary beam with respect to the c-axis as well as TCS spectrum from an edge surface cut perpendicularly to the (001) face of a molybdenite crystal are given. Energy positions of the TCS structure are found to be independent of the variations in the angle of incidence of the primary beam and also of the change of crystal face. From this it is concluded that the fine structure in the TCS spectra from molybdenite crystal for the primary energies studied is due to electron-electron scattering and not to Bragg interference effects. (author)

Variation of Raman spectra of CdSe/ZnS quantum dots at the bioconjugation

Energy Technology Data Exchange (ETDEWEB)

Macotela, L.G.V.; Douda, J. [UPIITA - Instituto Politecnico Nacional, Mexico (Mexico); Torchynska, T.V. [ESFM - Instituto Politecnico Nacional, Mexico (Mexico); Sierra, R.P. [CINVESTAV del IPN, Mexico (Mexico)

2010-04-15

This paper presents the results of comparative analysis of Raman scattering spectra of CdSe/ZnS QDs covered by polymer with and without bio-conjugation to the mouse anti PSA (Prostate-Specific Antigen) antibodies (mab). Commercial CdSe/ZnS QDs used in the study are characterized by the color emission with the maximum at 565 nm (2.19 eV) at 300 K. Raman scattering spectra measured at room temperature demonstrate two groups of peaks: (i) related to the Si substrate at 230-460, 522, 610, 670, 940-1040 cm{sup -1} and (2) to polymer on the QD surface in the spectral range 1268-3310 cm{sup -1}. It is revealed that the QD bio-conjugation to the anti PSA mab is accompanied by the variation dramatically in the intensity of Raman lines of both types. The explanation of Raman peak stimulation in bio-conjugated QDs has been proposed on the base of surface enhanced Raman scattering (SERS) effect (copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Core-level spectra and binding energies of transition metal nitrides by non-destructive x-ray photoelectron spectroscopy through capping layers

Energy Technology Data Exchange (ETDEWEB)

Greczynski, G., E-mail: grzgr@ifm.liu.se [Thin Film Physics Division, Department of Physics (IFM), Linköping University, SE-581 83 Linköping (Sweden); Primetzhofer, D. [Department of Physics and Astronomy, The Ångström Laboratory, Uppsala University, P.O. Box 516, SE-751 20 Uppsala (Sweden); Lu, J.; Hultman, L. [Thin Film Physics Division, Department of Physics (IFM), Linköping University, SE-581 83 Linköping (Sweden)

2017-02-28

Highlights: • First non-destructive measurements of XPS core level binding energies for group IVb-VIb transition metal nitrides are presented. • All films are grown under the same conditions and analyzed in the same instrument, providing a useful reference for future XPS studies. • Extracted core level BE values are more reliable than those obtained from sputter-cleaned N-deficient surfaces. • Comparison to Ar+-etched surfaces reveals that even mild etching conditions result in the formation of a nitrogen-deficient surface layer. • The N/metal concentration ratios from capped samples are found to be 25-90% higher than those from the corresponding ion-etched surfaces. - Abstract: We present the first measurements of x-ray photoelectron spectroscopy (XPS) core level binding energies (BE:s) for the widely-applicable group IVb-VIb polycrystalline transition metal nitrides (TMN’s) TiN, VN, CrN, ZrN, NbN, MoN, HfN, TaN, and WN as well as AlN and SiN, which are common components in the TMN-based alloy systems. Nitride thin film samples were grown at 400 °C by reactive dc magnetron sputtering from elemental targets in Ar/N{sub 2} atmosphere. For XPS measurements, layers are either (i) Ar{sup +} ion-etched to remove surface oxides resulting from the air exposure during sample transfer from the growth chamber into the XPS system, or (ii) in situ capped with a few nm thick Cr or W overlayers in the deposition system prior to air-exposure and loading into the XPS instrument. Film elemental composition and phase content is thoroughly characterized with time-of-flight elastic recoil detection analysis (ToF-E ERDA), Rutherford backscattering spectrometry (RBS), and x-ray diffraction. High energy resolution core level XPS spectra acquired with monochromatic Al Kα radiation on the ISO-calibrated instrument reveal that even mild etching conditions result in the formation of a nitrogen-deficient surface layer that substantially affects the extracted binding energy

Core-level spectra and binding energies of transition metal nitrides by non-destructive x-ray photoelectron spectroscopy through capping layers

International Nuclear Information System (INIS)

Greczynski, G.; Primetzhofer, D.; Lu, J.; Hultman, L.

2017-01-01

Highlights: • First non-destructive measurements of XPS core level binding energies for group IVb-VIb transition metal nitrides are presented. • All films are grown under the same conditions and analyzed in the same instrument, providing a useful reference for future XPS studies. • Extracted core level BE values are more reliable than those obtained from sputter-cleaned N-deficient surfaces. • Comparison to Ar+-etched surfaces reveals that even mild etching conditions result in the formation of a nitrogen-deficient surface layer. • The N/metal concentration ratios from capped samples are found to be 25-90% higher than those from the corresponding ion-etched surfaces. - Abstract: We present the first measurements of x-ray photoelectron spectroscopy (XPS) core level binding energies (BE:s) for the widely-applicable group IVb-VIb polycrystalline transition metal nitrides (TMN’s) TiN, VN, CrN, ZrN, NbN, MoN, HfN, TaN, and WN as well as AlN and SiN, which are common components in the TMN-based alloy systems. Nitride thin film samples were grown at 400 °C by reactive dc magnetron sputtering from elemental targets in Ar/N 2 atmosphere. For XPS measurements, layers are either (i) Ar + ion-etched to remove surface oxides resulting from the air exposure during sample transfer from the growth chamber into the XPS system, or (ii) in situ capped with a few nm thick Cr or W overlayers in the deposition system prior to air-exposure and loading into the XPS instrument. Film elemental composition and phase content is thoroughly characterized with time-of-flight elastic recoil detection analysis (ToF-E ERDA), Rutherford backscattering spectrometry (RBS), and x-ray diffraction. High energy resolution core level XPS spectra acquired with monochromatic Al Kα radiation on the ISO-calibrated instrument reveal that even mild etching conditions result in the formation of a nitrogen-deficient surface layer that substantially affects the extracted binding energy values. These

Experimental study of surface plasmon-phonon polaritons in GaAs-based microstructures

Science.gov (United States)

Galimov, A. I.; Shalygin, V. A.; Moldavskaya, M. D.; Panevin, V. Yu; Melentyev, G. A.; Artemyev, A. A.; Firsov, D. A.; Vorobjev, L. E.; Klimko, G. V.; Usikova, A. A.; Komissarova, T. A.; Sedova, I. V.; Ivanov, S. V.

2018-03-01

Optical properties of a heavily-doped GaAs epitaxial layer with a regular grating at its surface have been experimentally investigated in the terahertz spectral range. Reflectivity spectra for the layer with a profiled surface drastically differ from those for the as-grown epilayer with a planar surface. For s-polarized radiation, this difference is totally caused by the electromagnetic wave diffraction at the grating. For p-polarized radiation, additional resonant dips arise due to excitation of surface plasmon-phonon polaritons. Terahertz radiation emission under significant electron heating in an applied pulsed electric field has also been studied. Polarization measurements revealed pronounced peaks related to surface plasmon-phonon polariton resonances of the first and second order in the emission spectra.

Thermal Infrared Spectra of a Suite of Forsterite Samples and Ab-initio Modelling of theirs Spectra

Science.gov (United States)

Maturilli, A.; Stangarone, C.; Helbert, J.; Tribaudino, M.; Prencipe, M.

2017-12-01

Forsterite is the dominating component in olivine, a major constituent in ultrafemic rocks, as well as planetary bodies. Messenger X-ray spectrometer has shown that Mg-rich silicate minerals, such as enstatite and forsterite, dominate Mercury's surface (Weider et al 2012). A careful and detailed acquaintance with the forsterite spectral features and their dependence wrt environmental conditions on Mercury is needed to interpret the remote sensing data from previous and forthcoming missions. We propose an experimental vs calculation approach to reproduce and describe the spectral features of forsterite. TIR emissivity measurements are performed by the Planetary Spectroscopy Laboratory (PSL) of DLR. PSL offers the unique capability to measure the emissivity of samples at temperature up to 1000K under vacuum conditions. TIR emissivity and reflectance measurements are performed on 11 olivine samples having a different composition within the forsterite-fayalite series. When available, the sample has been measured in 2 different grain sizes (chameleon-like effects of Mercury surface already observed (Helbert et al. 2013), this study wants to point out the main spectral features due to the composition and temperature. Our results are used to create a theoretical background to interpret the high temperature infrared emissivity spectra from MERTIS onboard the ESA BepiColombo mission to Mercury (Helbert et al. 2010).

Surface investigations using monolayer-resolvable high-resolution Rutherford backscattering spectroscopy

International Nuclear Information System (INIS)

Kimura, Kenji; Ohtsuka, Hisashi; Ohshima, Kazuomi; Mannami, Michi-hiko

1994-01-01

Energy spectra of scattered 0.5 MeV He ions from a clean (001) surface of SnTe are measured with a 90 sector magnetic spectrometer (ΔE/E ∼ 0.1%). The ions scattered from successive atomic layers can be resolved in the energy spectra. Inelastic energy losses and charge state distributions of 0.5 MeV He ions scattered from the topmost atomic layer of the SnTe(001) are measured. A position-dependent stopping power at the surface is proposed from the observed energy losses. The observed charge state distribution shows the importance of the charge-exchange processes with valence electrons in the tail of the electron distribution at the surface. (orig.)

Design spectra development considering short time histories

International Nuclear Information System (INIS)

Weiner, E.O.

1983-01-01

Two separate programs, MODQKE and MDOF, were written to provide a capability of obtaining equipment spectra from design spectra. MODQKE generates or modifies acceleration histories to conform with design spectra pertaining to, say, a foundation. MDOF is a simple linear modal superposition program that solves for equipment support histories using the design spectra conforming histories as input. Equipment spectra, then, are obtained from the support histories using MODQKE. MODQKE was written to modify or provide new histories with special attention paid to short seismic records. A technique from the open literature was borrowed to generate an initial history that approximates a given response spectrum. Further refinement is done with smoothing cycles in which several correction signals are added to the history in a way that produces a least squares fit between actual and prescribed spectra. Provision is made for history shaping, a baseline correction, and final scaling. MODQKE performance has been demonstrated with seven examples having zero to ten percent damping ratios, and 2.5 seconds to 20 seconds durations and a variety of target spectra. The examples show the program is inexpensive to use. MDOF is a simple modal superposition program. It has no eigensolver, and the user supplies mode shapes, frequencies, and participation factors as input. Floor spectra can be generated from design spectra by using a history from MODQKE that conforms to the design spectrum as input to MDOF. Floor motions from MDOF can be fed back to MODQKE without modification to obtain the floor spectra. A simple example is given to show how equipment mass effects can be incorporated into the MDOF solution. Any transient solution capability can be used to replace MDOF. For example, a direct transient approach may be desirable if both the equipment and floor structures are to be included in the model with different damping fractions. (orig./HP)

Statistical properties of Fermi GBM GRBs' spectra

Science.gov (United States)

Rácz, István I.; Balázs, Lajos G.; Horvath, Istvan; Tóth, L. Viktor; Bagoly, Zsolt

2018-03-01

Statistical studies of gamma-ray burst (GRB) spectra may result in important information on the physics of GRBs. The Fermi GBM catalogue contains GRB parameters (peak energy, spectral indices, and intensity) estimated fitting the gamma-ray spectral energy distribution of the total emission (fluence, flnc), and during the time of the peak flux (pflx). Using contingency tables, we studied the relationship of the models best-fitting pflx and flnc time intervals. Our analysis revealed an ordering of the spectra into a power law - Comptonized - smoothly broken power law - Band series. This result was further supported by a correspondence analysis of the pflx and flnc spectra categorical variables. We performed a linear discriminant analysis (LDA) to find a relationship between categorical (spectral) and model independent physical data. LDA resulted in highly significant physical differences among the spectral types, that is more pronounced in the case of the pflx spectra, than for the flnc spectra. We interpreted this difference as caused by the temporal variation of the spectrum during the outburst. This spectral variability is confirmed by the differences in the low-energy spectral index and peak energy, between the pflx and flnc spectra. We found that the synchrotron radiation is significant in GBM spectra. The mean low-energy spectral index is close to the canonical value of α = -2/3 during the peak flux. However, α is ˜ -0.9 for the spectra of the fluences. We interpret this difference as showing that the effect of cooling is important only for the fluence spectra.

Shaping surface of palladium nanospheres through the control of reaction parameters

International Nuclear Information System (INIS)

Wang Lianmeng; Tan Enzhong; Guo Lin; Wang Lihua; Han Xiaodong

2011-01-01

Solid, cracked, and flower-shaped surfaces of palladium nanospheres with high yields and good uniformity were successfully prepared by a wet chemical method. On the basis of the experimental data, the same size of palladium nanosphere with different surface morphologies can be regulated only by changing the amount of ammonium hydroxide and reductant in one experimental system. The as-prepared products were studied by transmission electron microscopy (TEM), scanning electron microscopy (SEM) and x-ray diffraction (XRD). In addition, surface-enhanced Raman scattering (SERS) spectra on the as-prepared different surface of palladium nanospheres exhibit high activity towards p-aminothiophenol (PATP) detection, and the result further reveals that the predominance of the a1 vibration mode in the SERS spectra via an electromagnetic (EM) mechanism is significant.

Raman spectra of lithium compounds

Science.gov (United States)

Gorelik, V. S.; Bi, Dongxue; Voinov, Y. P.; Vodchits, A. I.; Gorshunov, B. P.; Yurasov, N. I.; Yurasova, I. I.

2017-11-01

The paper is devoted to the results of investigating the spontaneous Raman scattering spectra in the lithium compounds crystals in a wide spectral range by the fibre-optic spectroscopy method. We also present the stimulated Raman scattering spectra in the lithium hydroxide and lithium deuteride crystals obtained with the use of powerful laser source. The symmetry properties of the lithium hydroxide, lithium hydroxide monohydrate and lithium deuteride crystals optical modes were analyzed by means of the irreducible representations of the point symmetry groups. We have established the selection rules in the Raman and infrared absorption spectra of LiOH, LiOH·H2O and LiD crystals.

Photon and photoneutron spectra produced in radiotherapy Linacs

International Nuclear Information System (INIS)

Vega C, H. R.; Martinez O, S. A.; Benites R, J. L.; Lallena, A. M.

2011-10-01

A Monte Carlo calculation, using the MCNPX code, was carried out in order to estimate the photon and neutron spectra in two locations of two linacs operating at 15 and 18 MV. Detailed models of both linac heads were used in the calculations. Spectra were estimated below the flattening filter and at the isocenter. Neutron spectra show two components due to evaporation and knock-on neutrons. Lethargy spectra under the filter were compared to the spectra calculated from the function quoted by Tosi et al. that describes reasonably well neutron spectra beyond 1 MeV, though tends to underestimate the energy region between 10 -6 and 1 MeV. Neutron and Bremsstrahlung spectra show the same features regardless of the linac voltage. The amount of photons and neutrons produced by the 15 MV linac is smaller than that found for the 18 MV linac. As expected, Bremsstrahlung spectra ends according to the voltage used to accelerate the electrons. (Author)

Photon and photoneutron spectra produced in radiotherapy Linacs

Energy Technology Data Exchange (ETDEWEB)

Vega C, H. R. [Universidad Autonoma de Zacatecas, Unidad Academica de Estudios Nucleares, Calle Cipres No. 10, Fracc. La Penuela, 98068 Zacatecas (Mexico); Martinez O, S. A. [Universidad Pedagogica y Tecnologica de Colombia, Grupo de Fisica Nuclear Aplicada y Simulacion, Av. Central del Norte Km. 1, Via Paipa Tunja, Boyaca (Colombia); Benites R, J. L. [Universidad Autonoma de Nayarit, Postgrado CBAP, Carretera Tepic Compostela Km. 9, Xalisco, Nayarit (Mexico); Lallena, A. M., E-mail: fermineutron@yahoo.com [Universida de Granada, Departamento de Fisica Atomica, Molecular y Nuclear, E-18071 Granada (Spain)

2011-10-15

A Monte Carlo calculation, using the MCNPX code, was carried out in order to estimate the photon and neutron spectra in two locations of two linacs operating at 15 and 18 MV. Detailed models of both linac heads were used in the calculations. Spectra were estimated below the flattening filter and at the isocenter. Neutron spectra show two components due to evaporation and knock-on neutrons. Lethargy spectra under the filter were compared to the spectra calculated from the function quoted by Tosi et al. that describes reasonably well neutron spectra beyond 1 MeV, though tends to underestimate the energy region between 10{sup -6} and 1 MeV. Neutron and Bremsstrahlung spectra show the same features regardless of the linac voltage. The amount of photons and neutrons produced by the 15 MV linac is smaller than that found for the 18 MV linac. As expected, Bremsstrahlung spectra ends according to the voltage used to accelerate the electrons. (Author)

Theoretical study on photon-phonon coupling at (001)-(2 x 1) surfaces of Ge and {alpha}-Sn

Energy Technology Data Exchange (ETDEWEB)

Perez-Sanchez, F.L. [Escuela de Ciencias, Universidad Autonoma ' ' Benito Juarez' ' de Oaxaca, Av. Universidad S/N, Ex-Hacienda de Cinco Senores, Ciudad Universitaria, Oaxaca de Juarez, Oax., 68120 (Mexico); Perez-Rodriguez, F. [Instituto de Fisica, Benemerita Universidad Autonoma de Puebla, Apdo. Post. J-48, Puebla, Pue. 72570 (Mexico)

2011-06-15

We present a study of the far-infrared reflectance anisotropy spectra for (001) surfaces of Ge and {alpha}-Sn in the (2 x 1) asymmetric dimer geometry, which exhibit a resonance structure associated with the excitation of surface phonon modes. We have employed a theoretical formalism, based on the adiabatic bond-charge model (ABCM), for computing the far-infrared reflectance anisotropy spectra. In comparison with previous theoretical results for silicon and diamond surfaces, the resonance structure in the reflectance anisotropy spectrum for Ge(001)-(2 x 1) turns out to be similar to that observed in the spectrum for the Si(001)-(2 x 1) surface, whereas the spectrum for {alpha}-Sn(001)-(2 x 1) surface is noticeably different from the others. We have established a trend of far-infrared reflectance anisotropy spectra for IV(001) surfaces: the weaker dimer strength, the stronger resonances of low-frequency surface phonons. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Interaction of the wood surface with metal ions. Part 3: The effects of light on chromium impregnated wood surface

International Nuclear Information System (INIS)

Stipta, J.; Németh, K.; Molnárné Hamvas, L.

2004-01-01

UV-light changes of untreated and chromium impregnated wood surface were investigated by absorption spectrophotometric methods. The properties of indifferent silicagel and celulose layers were to the behaviour of poplar and black locust surface. Chromic-ion-impregnation had no significant effect on the absorption spectra of these layers. On the other hand, hexavalent chromium was reduced and UV-light caused irreversible wood degradation. Surface treatment caused considerable modification in black locust

AUTOMATED UNSUPERVISED CLASSIFICATION OF THE SLOAN DIGITAL SKY SURVEY STELLAR SPECTRA USING k-MEANS CLUSTERING

Energy Technology Data Exchange (ETDEWEB)

Sanchez Almeida, J.; Allende Prieto, C., E-mail: jos@iac.es, E-mail: callende@iac.es [Instituto de Astrofisica de Canarias, E-38205 La Laguna, Tenerife (Spain)

2013-01-20

Large spectroscopic surveys require automated methods of analysis. This paper explores the use of k-means clustering as a tool for automated unsupervised classification of massive stellar spectral catalogs. The classification criteria are defined by the data and the algorithm, with no prior physical framework. We work with a representative set of stellar spectra associated with the Sloan Digital Sky Survey (SDSS) SEGUE and SEGUE-2 programs, which consists of 173,390 spectra from 3800 to 9200 A sampled on 3849 wavelengths. We classify the original spectra as well as the spectra with the continuum removed. The second set only contains spectral lines, and it is less dependent on uncertainties of the flux calibration. The classification of the spectra with continuum renders 16 major classes. Roughly speaking, stars are split according to their colors, with enough finesse to distinguish dwarfs from giants of the same effective temperature, but with difficulties to separate stars with different metallicities. There are classes corresponding to particular MK types, intrinsically blue stars, dust-reddened, stellar systems, and also classes collecting faulty spectra. Overall, there is no one-to-one correspondence between the classes we derive and the MK types. The classification of spectra without continuum renders 13 classes, the color separation is not so sharp, but it distinguishes stars of the same effective temperature and different metallicities. Some classes thus obtained present a fairly small range of physical parameters (200 K in effective temperature, 0.25 dex in surface gravity, and 0.35 dex in metallicity), so that the classification can be used to estimate the main physical parameters of some stars at a minimum computational cost. We also analyze the outliers of the classification. Most of them turn out to be failures of the reduction pipeline, but there are also high redshift QSOs, multiple stellar systems, dust-reddened stars, galaxies, and, finally, odd

Two-dimensional sum-frequency generation (2D SFG) reveals structure and dynamics of a surface-bound peptide

Science.gov (United States)

Laaser, Jennifer E.; Skoff, David R.; Ho, Jia-Jung; Joo, Yongho; Serrano, Arnaldo L.; Steinkruger, Jay D.; Gopalan, Padma; Gellman, Samuel H.; Zanni, Martin T.

2014-01-01

Surface-bound polypeptides and proteins are increasingly used to functionalize inorganic interfaces such as electrodes, but their structural characterization is exceedingly difficult with standard technologies. In this paper, we report the first two-dimensional sum-frequency generation (2D SFG) spectra of a peptide monolayer, which is collected by adding a mid-IR pulse shaper to a standard femtosecond SFG spectrometer. On a gold surface, standard FTIR spectroscopy is inconclusive about the peptide structure because of solvation-induced frequency shifts, but the 2D lineshapes, anharmonic shifts, and lifetimes obtained from 2D SFG reveal that the peptide is largely α-helical and upright. Random coil residues are also observed, which do not themselves appear in SFG spectra due to their isotropic structural distribution, but which still absorb infrared light and so can be detected by cross-peaks in 2D SFG spectra. We discuss these results in the context of peptide design. Because of the similar way in which the spectra are collected, these 2D SFG spectra can be directly compared to 2D IR spectra, thereby enabling structural interpretations of surface-bound peptides and biomolecules based on the well-studied structure/2D IR spectra relationships established from soluble proteins. PMID:24372101

Surface-enhanced Raman Spectroscopy of Ethephone Adsorbed on Silver Surface

International Nuclear Information System (INIS)

Lee, Chul Jae; Kim, Hee Jin; Karim, Mohammad Rezaul; Lee, Mu Sang

2006-01-01

We investigated the Surface-enhanced Raman Spectroscopy (SERS) spectrum of ethephone (2- chloroethylphosphonic acid). We observed significant signals in the ordinary Raman spectrum for solid-state ethephone as well as when it was adsorbed on a colloidal silver surface, strong vibrational signals were obtained at a very low concentration. The SERS spectra were obtained by silver colloids that were prepared by the γ - irradiation method. The influence of pH and the influence of anion (Cl - , Br - , I - ) on the adsorption orientation were investigated. Two different adsorption mechanisms were deduced, depending on the experimental conditions. The chlorine atom or the chlorine and two oxygen atoms were adsorbed on the colloidal silver surface. Among halide ions, Br - and I - were more strongly adsorbed on the colloidal silver surfaces. As a result, the adsorption of ethephone was less effective due to their steric hinderance

Hierarchical FeTiO3-TiO2 hollow spheres for efficient simulated sunlight-driven water oxidation.

Science.gov (United States)

Han, Taoran; Chen, Yajie; Tian, Guohui; Wang, Jian-Qiang; Ren, Zhiyu; Zhou, Wei; Fu, Honggang

2015-10-14

Oxygen generation is the key step for the photocatalytic overall water splitting and considered to be kinetically more challenging than hydrogen generation. Here, an effective water oxidation catalyst of hierarchical FeTiO3-TiO2 hollow spheres are prepared via a two-step sequential solvothermal processes and followed by thermal treatment. The existence of an effective heterointerface and built-in electric field in the surface space charge region in FeTiO3-TiO2 hollow spheres plays a positive role in promoting the separation of photoinduced electron-hole pairs. Surface photovoltage, transient-state photovoltage, fluorescence and electrochemical characterization are used to investigate the transfer process of photoinduced charge carriers. The photogenerated charge carriers in the hierarchical FeTiO3-TiO2 hollow spheres with a proper molar ratio display much higher separation efficiency and longer lifetime than those in the FeTiO3 alone. Moreover, it is suggested that the hierarchical porous hollow structure can contribute to the enhancement of light utilization, surface active sites and material transportation through the framework walls. This specific synergy significantly contributes to the remarkable improvement of the photocatalytic water oxidation activity of the hierarchical FeTiO3-TiO2 hollow spheres under simulated sunlight (AM1.5).

PCA: Principal Component Analysis for spectra modeling

Science.gov (United States)

Hurley, Peter D.; Oliver, Seb; Farrah, Duncan; Wang, Lingyu; Efstathiou, Andreas

2012-07-01

The mid-infrared spectra of ultraluminous infrared galaxies (ULIRGs) contain a variety of spectral features that can be used as diagnostics to characterize the spectra. However, such diagnostics are biased by our prior prejudices on the origin of the features. Moreover, by using only part of the spectrum they do not utilize the full information content of the spectra. Blind statistical techniques such as principal component analysis (PCA) consider the whole spectrum, find correlated features and separate them out into distinct components. This code, written in IDL, classifies principal components of IRS spectra to define a new classification scheme using 5D Gaussian mixtures modelling. The five PCs and average spectra for the four classifications to classify objects are made available with the code.

Resonant Ni and Fe KLL Auger spectra photoexcited from NiFe alloys

International Nuclear Information System (INIS)

Koever, L.; Cserny, I.; Berenyi, Z.; Egri, S.; Novak, M.

2005-01-01

Complete text of publication follows. KLL Auger spectra of 3d transition metal atoms in solid environment, measured using high energy resolution, give an insight into the details of the local electronic structure surrounding the particular atoms emitting the signal Auger electrons. Fine tuning the energy of the exciting monochromatic photons across the K-absorption edge, features characteristic to resonant phenomena can be identified in the spectra. The shapes of the resonantly photoexcited KLL Auger spectra induced from 3d transition metals and alloys are well interpreted by the single step model of the Auger process, based on the resonant scattering theory. The peak shapes are strongly influenced by the 4p partial density of unoccupied electronic states around the excited atom. High energy resolution studies of KLL Auger spectra of 3d transition metals using laboratory X-ray sources, however, request very demanding experiments and yield spectra of limited statistical quality making the evaluation of the fine details in the spectra difficult. The Tunable High Energy XPS (THE- XPS) instrument at BW2 offers optimum photon x and energy resolution for spectroscopy of deep core Auger transitions. For the present measurements high purity polycrystalline Ni and Fe sheets as well as NiFe alloy samples of different compositions (Ni 80 Fe 20 , Ni 50 Fe 50 , Ni 20 Fe 80 ) were used. The surfaces of the samples were cleaned by in-situ argon ion sputtering. The measurements of the Ni and Fe KL 23 L 23 Auger spectra of the metal and alloy samples were performed with the THE-XPS instrument using high electron energy resolution (0.2 eV). In Fig.1, the measured Fe KL 23 L 23 spectrum, photoexcited at the Fe K absorption edge from Fe metal, is compared with the respective spectrum excited from a Ni 50 Fe 50 alloy. A significant broadening of the 1 D 2 peak and an enhancement of the spectral intensity at the low energy loss part of this peak observed in the alloy sample, while the

QUALITATIVE INTERPRETATION OF GALAXY SPECTRA

Energy Technology Data Exchange (ETDEWEB)

Sanchez Almeida, J.; Morales-Luis, A. B. [Instituto de Astrofisica de Canarias, E-38205 La Laguna, Tenerife (Spain); Terlevich, R.; Terlevich, E. [Instituto Nacional de Astrofisica, Optica y Electronica, Tonantzintla, Puebla (Mexico); Cid Fernandes, R., E-mail: jos@iac.es, E-mail: abml@iac.es, E-mail: rjt@ast.cam.ac.uk, E-mail: eterlevi@inaoep.mx, E-mail: cid@astro.ufsc.br [Departamento de Fisica-CFM, Universidade Federal de Santa Catarina, P.O. Box 476, 88040-900 Florianopolis, SC (Brazil)

2012-09-10

We describe a simple step-by-step guide to qualitative interpretation of galaxy spectra. Rather than an alternative to existing automated tools, it is put forward as an instrument for quick-look analysis and for gaining physical insight when interpreting the outputs provided by automated tools. Though the recipe is for general application, it was developed for understanding the nature of the Automatic Spectroscopic K-means-based (ASK) template spectra. They resulted from the classification of all the galaxy spectra in the Sloan Digital Sky Survey data release 7, thus being a comprehensive representation of the galaxy spectra in the local universe. Using the recipe, we give a description of the properties of the gas and the stars that characterize the ASK classes, from those corresponding to passively evolving galaxies, to H II galaxies undergoing a galaxy-wide starburst. The qualitative analysis is found to be in excellent agreement with quantitative analyses of the same spectra. We compare the mean ages of the stellar populations with those inferred using the code STARLIGHT. We also examine the estimated gas-phase metallicity with the metallicities obtained using electron-temperature-based methods. A number of byproducts follow from the analysis. There is a tight correlation between the age of the stellar population and the metallicity of the gas, which is stronger than the correlations between galaxy mass and stellar age, and galaxy mass and gas metallicity. The galaxy spectra are known to follow a one-dimensional sequence, and we identify the luminosity-weighted mean stellar age as the affine parameter that describes the sequence. All ASK classes happen to have a significant fraction of old stars, although spectrum-wise they are outshined by the youngest populations. Old stars are metal-rich or metal-poor depending on whether they reside in passive galaxies or in star-forming galaxies.

A comparison of telescopic and Phobos-2 ISM spectra of Mars in the short-wave near-infrared (0.76-1.02 microns)

Science.gov (United States)

Bell, James F., III; Mustard, John F.

1993-01-01

Recent analyses of near-IR (0.76-3.16 microns) Mars surface reflectance spectra obtained by the Phobos-2 ISM instrument during early 1989 have revealed the presence of substantial variability in surface spectral properties. Strong absorption features seen in the 0.85-1.05 micron region are up to 10-15 percent deep relative to the local continuum and have been interpreted as evidence of Fe(2+) and Fe(3+) bearing minerals (pyroxenes and iron oxides, respectively). Though these observed band depths are comparable to those seen in laboratory reflectance spectra, they are up to three times larger than most previously reported band depths for Mars spectra at these wavelengths. Six regions of variable albedo and geologic setting were identified where ISM and 1988 opposition telescopic coverage either overlapped physically or sampled the same surface geologic unit. The areal sizes and positions of the regions measured telescopically were compiled by Bell et al. ISM pixels falling within these spots were averaged to produce a spatially convolved spectrum that simulates what would have been seen telescopically. To facilitate comparisons of absorption band positions and relative strengths, the convolved ISM data and the 1988 telescopic spectra were scaled to unity at 0.81 microns and are presented. The data have also been convolved to equivalent band pass normalized reflectances in the region of spectral overlap. A scatter diagram of telescopic vs. ISM reflectances is shown. The results from the investigation are discussed.

Optical absorption spectra of Ag-11 isomers

DEFF Research Database (Denmark)

Martinez, Jose Ignacio; Fernandez, E. M.

2009-01-01

The optical absorption spectra of the three most; stable structural isomers of the Ag-11 cluster were calculated using the time-dependent, density functional theory within the Casida formalism. The slightly different, spectra, of the isomers may permit the identification of the ground-stale confi......The optical absorption spectra of the three most; stable structural isomers of the Ag-11 cluster were calculated using the time-dependent, density functional theory within the Casida formalism. The slightly different, spectra, of the isomers may permit the identification of the ground...

Complementary views on electron spectra: From fluctuation diagnostics to real-space correlations

Science.gov (United States)

Gunnarsson, O.; Merino, J.; Schäfer, T.; Sangiovanni, G.; Rohringer, G.; Toschi, A.

2018-03-01

We study the relation between the microscopic properties of a many-body system and the electron spectra, experimentally accessible by photoemission. In a recent paper [O. Gunnarsson et al., Phys. Rev. Lett. 114, 236402 (2015), 10.1103/PhysRevLett.114.236402], we introduced the "fluctuation diagnostics" approach to extract the dominant wave-vector-dependent bosonic fluctuations from the electronic self-energy. Here, we first reformulate the theory in terms of fermionic modes to render its connection with resonance valence bond (RVB) fluctuations more transparent. Second, by using a large-U expansion, where U is the Coulomb interaction, we relate the fluctuations to real-space correlations. Therefore, it becomes possible to study how electron spectra are related to charge, spin, superconductivity, and RVB-like real-space correlations, broadening the analysis of an earlier work [J. Merino and O. Gunnarsson, Phys. Rev. B 89, 245130 (2014), 10.1103/PhysRevB.89.245130]. This formalism is applied to the pseudogap physics of the two-dimensional Hubbard model, studied in the dynamical cluster approximation. We perform calculations for embedded clusters with up to 32 sites, having three inequivalent K points at the Fermi surface. We find that as U is increased, correlation functions gradually attain values consistent with an RVB state. This first happens for correlation functions involving the antinodal point and gradually spreads to the nodal point along the Fermi surface. Simultaneously, a pseudogap opens up along the Fermi surface. We relate this to a crossover from a Kondo-type state to an RVB-like localized cluster state and to the presence of RVB and spin fluctuations. These changes are caused by a strong momentum dependence in the cluster bath couplings along the Fermi surface. We also show, from a more algorithmic perspective, how the time-consuming calculations in fluctuation diagnostics can be drastically simplified.

Retrieval of vertical concentration profiles from OSIRIS UV-visible limb spectra

International Nuclear Information System (INIS)

Strong, K.; Joseph, B.M.; Dosanjh, R.; McDade, I.C.; McLinden, C.A.; McConnell, J.C.; Stegman, J.; Murtagh, D.P.; Llewellyn, E.J.

2002-01-01

The OSIRIS instrument, launched on the Odin satellite in February 2001, includes an optical spectrograph that will record UV-visible spectra of sunlight scattered from the limb over a range of tangent heights. These spectra will be used to retrieve vertical profiles of ozone, NO 2 , OC1O, BrO, NO 3 , O 2 , and aerosols, for the investigation of both stratospheric and mesospheric processes, particularly those related to ozone chemistry. In this work, the retrieval of vertical profiles of trace-gas concentrations from OSIRIS limb-radiance spectra is described. A forward model has been developed to simulate these spectra, and it consists of a single-scattering radiative-transfer model with partial spherical geometry, trace-gas absorption, Mic scattering by stratospheric aerosols, a Lambertian surface contribution, and OSIRIS instrument response and noise. Number-density profiles have been retrieved by using optimal estimation (OE) to combine an a priori profile with the information from sets of synthetic 'measurements'. For ozone, OE has been applied both to limb radiances at one or more discrete wavelengths and to effective-column abundances retrieved over a broad spectral range using differential optical absorption spectroscopy (DOAS). The results suggest that, between 15 and 35 km, ozone number densities can be retrieved to 10% accuracy or better on 1 and 2 km grids and to 5% on a 5 km grid. The combined DOAS-OE approach has also been used to retrieve NO 2 number densities, yielding 13% accuracy or better for altitudes from 18 to 36 km (in a 2 km grid. Differential optical absorption spectroscopy - optimal estimation retrievals of BrO and OC1O reproduce the true profiles above 15 km in the noise-free case, but the quality of the retrievals is highly sensitive to noise on the simulated OSIRIS spectra because of the weak absorption of these two gases. The development of inversion methods for the retrieval of trace-gas concentrations from OSIRIS spectra is continuing

Vibronic spectra of Gd3+ in metaphosphate glasses: Comparison with Raman and infrared spectra

International Nuclear Information System (INIS)

Hall, D.W.; Brawer, S.A.; Weber, M.J.

1982-01-01

Vibronic sidebands associated with the 6 P/sub 7/2/→ 8 S/sub 7/2/ transition of Gd 3+ -doped metaphosphate glasses are observed using line-narrowed fluorescence techniques. Glasses having metal cations of different mass and charge (La,Al,Mg,Ba) are examined. Vibronic spectra, which probe vibrations about the rare-earth element site, are compared with polarized Raman scattering data and the infrared dielectric constant obtained from near-normal reflectance measurements. Results indicate that in metaphosphate glasses vibronic selection rules are similar to HV (vertical height) Raman selection rules. The wavelengths and relative intensities of peaks in the high-frequency portion of the vibronic spectra change with respect to corresponding peaks in the Raman spectra when the mass and/or charge of Gd 3+ differs significantly from that of the metal cation

Photoelectrochemical characterization of the role of organic sensitizers adsorbed on nanostructured ZnO

Energy Technology Data Exchange (ETDEWEB)

Hastall, Andreas; Loewenstein, Thomas; Schlettwein, Derck [Institut fuer Angewandte Physik, Justus-Liebig-Universitaet Giessen, Heinrich-Buff-Ring 16, D-35392 Giessen (Germany)

2008-07-01

Porous sensitized ZnO is a promising material for application as electrode in dye-sensitized solar cells (DSSC) to utilize the intense absorption of organic sensitizers in the visible spectral range. Electrochemical deposition of ZnO from aqueous solutions is a low temperature process (<150 C) which allows the use of various substrates. The process can be performed at low energy input and cost and is therefore promising short pay-back times and high net energy gains. The role of the adsorbed sensitizer dye and resulting charge carrier generation, collection, but also recombination in the interface of ZnO/sensitizer/electrolyte of DSSC were analyzed in detail by transient photocurrent measurements, intensity modulated photocurrent and photovoltage spectroscopy (IMPS/IMVS), photovoltage decay and charge-extraction. Results are discussed for different sensitizers adsorbed to the ZnO surface and for ZnO prepared on various substrates and optimized in structure and morphology.

Variation of boundary-layer wind spectra with height

DEFF Research Database (Denmark)

Larsén, Xiaoli Guo; Petersen, Erik L.; Larsen, Søren Ejling

2018-01-01

This study revisits the height dependence of the wind speed power spectrum from the synoptic scale to the spectral gap. Measurements from cup anemometers and sonics at heights of 15 m to 244 m are used. The measurements are from one land site, one coastal land‐based site and three offshore sites...... the atmospheric tide. The second finding regards the height dependence of the general spectrum. We describe the dependence through a so‐called effective roughness, which is calculated from wind spectra and represents the energy removal at different frequencies, and thus surface conditions in the footprint areas....... The generalizable spectral properties of winds presented herein may prove useful for validating numerical models....

Quantitative analysis of satellite structures in XPS spectra of gold and silver

Energy Technology Data Exchange (ETDEWEB)

Pauly, N., E-mail: nipauly@ulb.ac.be [Université libre de Bruxelles, Service de Métrologie Nucléaire (CP 165/84), 50 av. F. D. Roosevelt, B-1050 Brussels (Belgium); Yubero, F. [Instituto de Ciencia de Materiales de Sevilla, Univ. Sevilla – CSIC, av. Américo Vespucio 49, E-41092 Sevilla (Spain); Tougaard, S. [Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, DK-5230 Odense M (Denmark)

2016-10-15

Highlights: • Accurate determination of the energy loss functions for Au and Ag. • Calculation of effective inelastic electron scattering cross sections for Au and Ag. • Convolution of these cross sections with varying model primary spectra F(E). • Variation of F(E) until a good agreement with experimental XPS spectra is reached. • Quantitative determination of Au 4f and Ag 3d characteristics. - Abstract: Identification of specific chemical states and local electronic environments at surfaces by X-ray photoelectron spectroscopy (XPS) is often difficult because it is not straightforward to quantitatively interpret the shape and intensity of shake-up structures that originate from the photoexcitation process. Indeed the shape and intensity of measured XPS structures are strongly affected by both extrinsic excitations due to electron transport out of the surface and intrinsic excitations induced by the sudden creation of the static core hole. These processes must be taken into account to quantitatively extract, from experimental XPS, the primary excitation spectrum of the considered transition which includes all effects that are part of the initial photo-excitation process, i.e. lifetime broadening, spin–orbit coupling, and multiplet splitting. It was previously shown [N. Pauly, S. Tougaard, F. Yubero, Surf. Sci. 620 (2014) 17] that both extrinsic and intrinsic excitations could be included in an effective energy-differential inelastic electron scattering cross section for XPS which is then convoluted with the primary excitation spectrum to model the full XPS spectrum. This method can thus be applied to determine the primary excitation spectrum from any XPS spectrum. We use this approach in the present paper to determine the Au 4f and Ag 3d photoemission spectra from pure metals. We observe that characteristic energy loss features of the XPS spectra are not only due to photoelectron energy losses. We thus prove the existence of a double shake-up process

Wavelet data analysis of micro-Raman spectra for follow-up monitoring in oral pathologies

Science.gov (United States)

Camerlingo, C.; Zenone, F.; Perna, G.; Capozzi, V.; Cirillo, N.; Gaeta, G. M.; Lepore, M.

2008-02-01

A wavelet multi-component decomposition algorithm has been used for data analysis of micro-Raman spectra from human biological samples. In particular, measurements have been performed on some samples of oral tissue and blood serum from patients affected by pemphigus vulgaris at different stages. Pemphigus is a chronic, autoimmune, blistering disease of the skin and mucous membranes with a potentially fatal outcome. The disease is characterized histologically by intradermal blisters and immunopathologically by the finding of tissue bound and circulating immunoglobulin G (IgG) antibody directed against the cell surface of keratinocytes. More than 150 spectra were measured by means of a Raman confocal microspectrometer apparatus using the 632.8 nm line of a He-Ne laser source. A discrete wavelet transform decomposition method has been applied to the recorded Raman spectra in order to overcome related to low-level signals and the presence of noise and background components due to light scattering and fluorescence. The results indicate that appropriate data processing can contribute to enlarge the medical applications of micro-Raman spectroscopy.

Proposal and Evaluation of Subordinate Standard Solar Irradiance Spectra for Applications in Solar Energy Systems

Energy Technology Data Exchange (ETDEWEB)

Habte, Aron M [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Jessen, Wilko [German Aerospace Center (DLR); Wilbert, Stefan [German Aerospace Center (DLR); Gueymard, Christian A. [Solar Consulting Services; Polo, Jesus [CIEMAT; Bian, Zeqiang [China Meteorological Administration; Driesse, Anton [Photovoltaic Performance Labs; Marzo, Aitor [University of Antofagasta; Armstrong, Peter [Masdar Institute of Science & Technology; Vignola, Frank [University of Oregon; Ramirez, Lourdes [CIEMAT

2018-04-01

Reference solar irradiance spectra are needed to specify key parameters of solar technologies such as photovoltaic cell efficiency, in a comparable way. The IEC 60904-3 and ASTM G173 standards present such spectra for Direct Normal Irradiance (DNI) and Global Tilted Irradiance (GTI) on a 37 degrees tilted sun-facing surface for one set of clear-sky conditions with an air mass of 1.5 and low aerosol content. The IEC/G173 standard spectra are the widely accepted references for these purposes. Hence, the authors support the future replacement of the outdated ISO 9845 spectra with the IEC spectra within the ongoing update of this ISO standard. The use of a single reference spectrum per component of irradiance is important for clarity when comparing and rating solar devices such as PV cells. However, at some locations the average spectra can differ strongly from those defined in the IEC/G173 standards due to widely different atmospheric conditions and collector tilt angles. Therefore, additional subordinate standard spectra for other atmospheric conditions and tilt angles are of interest for a rough comparison of product performance under representative field conditions, in addition to using the main standard spectrum for product certification under standard test conditions. This simplifies the product selection for solar power systems when a fully-detailed performance analysis is not feasible (e.g. small installations). Also, the effort for a detailed yield analyses can be reduced by decreasing the number of initial product options. After appropriate testing, this contribution suggests a number of additional spectra related to eight sets of atmospheric conditions and tilt angles that are currently considered within ASTM and ISO working groups. The additional spectra, called subordinate standard spectra, are motivated by significant spectral mismatches compared to the IEC/G173 spectra (up to 6.5%, for PV at 37 degrees tilt and 10-15% for CPV). These mismatches

Formation of a silicon terminated (100) diamond surface

International Nuclear Information System (INIS)

Schenk, Alex; Sear, Michael; Pakes, Chris; Tadich, Anton; O'Donnell, Kane M.; Ley, Lothar; Stacey, Alastair

2015-01-01

We report the preparation of an ordered silicon terminated diamond (100) surface with a two domain 3 × 1 reconstruction as determined by low energy electron diffraction. Based on the dimensions of the surface unit cell and on chemical information provided by core level photoemission spectra, a model for the structure is proposed. The termination should provide a homogeneous, nuclear, and electron spin-free surface for the development of future near-surface diamond quantum device architectures

Surface-induced dissociation and chemical reactions of C2D4(+) on stainless steel, carbon (HOPG), and two different diamond surfaces.

Science.gov (United States)

Feketeová, Linda; Zabka, Jan; Zappa, Fabio; Grill, Verena; Scheier, Paul; Märk, Tilmann D; Herman, Zdenek

2009-06-01

Surface-induced interactions of the projectile ion C(2)D(4)(+) with room-temperature (hydrocarbon covered) stainless steel, carbon highly oriented pyrolytic graphite (HOPG), and two different types of diamond surfaces (O-terminated and H-terminated) were investigated over the range of incident energies from a few eV up to 50 eV. The relative abundance of the product ions in dependence on the incident energy of the projectile ion [collision-energy resolved mass spectra, (CERMS) curves] was determined. The product ion mass spectra contained ions resulting from direct dissociation of the projectile ions, from chemical reactions with the hydrocarbons on the surface, and (to a small extent) from sputtering of the surface material. Sputtering of the surface layer by low-energy Ar(+) ions (5-400 eV) indicated the presence of hydrocarbons on all studied surfaces. The CERMS curves of the product ions were analyzed to obtain both CERMS curves for the products of direct surface-induced dissociation of the projectile ion and CERMS curves of products of surface reactions. From the former, the fraction of energy converted in the surface collision into the internal excitation of the projectile ion was estimated as 10% of the incident energy. The internal energy of the surface-excited projectile ions was very similar for all studied surfaces. The H-terminated room-temperature diamond surface differed from the other surfaces only in the fraction of product ions formed in H-atom transfer surface reactions (45% of all product ions formed versus 70% on the other surfaces).

Estimating Eulerian spectra from pairs of drifters

Science.gov (United States)

LaCasce, Joe

2017-04-01

GPS-tracked surface drifters offer the possibility of sampling energetic variations at the ocean surface on scales of only 10s of meters, much less than that resolved by satellite. Here we investigate whether velocity differences between pairs of drifters can be used to estimate kinetic energy spectra. Theoretical relations between the spectrum and the second-order longitudinal structure function for 2D non-divergent flow are derived. The structure function is a natural statistic for particle pairs and is easily calculated. However it integrates contributions across wavenumber, and this tends to obscure the spectral dependencies when turbulent inertial ranges are of finite extent. Nevertheless, the transform from spectrum to structure function is robust, as illustrated with Eulerian data collected from aircraft. The inverse transform, from structure function to spectrum, is much less robust, yielding poor results in particular at large wavenumbers. This occurs because the transform involves a filter function which magnifies contributions from large pair separations, which tend to be noisy. Fitting the structure function to a polynomial improves the spectral estimate, but not sufficiently to distinguish correct inertial range dependencies. Thus with Lagrangian data, it is appears preferable to focus on structure functions, despite their shortcomings.

EMS mutant spectra generated by multi-parameter flow cytometry

Energy Technology Data Exchange (ETDEWEB)

Keysar, Stephen B. [Cell and Molecular Biology Graduate Program, Colorado State University, Fort Collins, CO (United States); Fox, Michael H., E-mail: michael.fox@colostate.edu [Cell and Molecular Biology Graduate Program, Colorado State University, Fort Collins, CO (United States); Department of Environmental and Radiological Health Sciences, Colorado State University, Fort Collins, CO (United States)

2009-12-01

The CHO A{sub L} cell line contains a single copy of human chromosome 11 that encodes several cell surface proteins including glycosyl phosphatidylinositol (GPI) linked CD59 and CD90, as well as CD98, CD44 and CD151 which are not GPI-linked. The flow cytometry mutation assay (FCMA) measures mutations of the CD59 gene by the absence of fluorescence when stained with antibodies against the CD59 cell surface protein. We have measured simultaneous mutations in CD59, CD44, CD90, CD98 and CD151 to generate a mutant spectrum for ionizing radiation. After treatment with ethyl methanesulfonate (EMS) many cells have an intermediate level of CD59 staining. Single cells were sorted from CD59{sup -} regions with varying levels of fluorescence and the resulting clonal populations had a stable phenotype for CD59 expression. Mutant spectra were generated by flow cytometry using the isolated clones and nearly all clones were mutated in CD59 only. Interestingly, about 60% of the CD59 negative clones were actually GPI mutants determined by staining with the GPI specific fluorescently labeled bacterial toxin aerolysin (FLAER). The GPI negative cells are most likely caused by mutations in the X-linked pigA gene important in GPI biosynthesis. Small mutations of pigA and CD59 were expected for the alkylating agent EMS and the resulting spectra are significantly different than the large deletions found when analyzing radiation mutants. After analyzing the CD59{sup -} clonal populations we have adjusted the FCMA mutant regions from 1% to 10% of the mean of the CD59 positive peak to include the majority of CD59 mutants.

Theoretical studies of surface enhanced hyper-Raman spectroscopy: The chemical enhancement mechanism

Science.gov (United States)

Valley, Nicholas; Jensen, Lasse; Autschbach, Jochen; Schatz, George C.

2010-08-01

Hyper-Raman spectra for pyridine and pyridine on the surface of a tetrahedral 20 silver atom cluster are calculated using static hyperpolarizability derivatives obtained from time dependent density functional theory. The stability of the results with respect to choice of exchange-correlation functional and basis set is verified by comparison with experiment and with Raman spectra calculated for the same systems using the same methods. Calculated Raman spectra were found to match well with experiment and previous theoretical calculations. The calculated normal and surface enhanced hyper-Raman spectra closely match experimental results. The chemical enhancement factors for hyper-Raman are generally larger than for Raman (102-104 versus 101-102). Integrated hyper-Raman chemical enhancement factors are presented for a set of substituted pyridines. A two-state model is developed to predict these chemical enhancement factors and this was found to work well for the majority of the molecules considered, providing a rationalization for the difference between hyper-Raman and Raman enhancement factors.

General Notes on Processes and Their Spectra

Directory of Open Access Journals (Sweden)

Gustav Cepciansky

2012-01-01

Full Text Available The frequency spectrum performs one of the main characteristics of a process. The aim of the paper is to show the coherence between the process and its own spectrum and how the behaviour and properties of a process itself can be deduced from its spectrum. Processes are categorized and general principles of their spectra calculation and recognition are given. The main stress is put on power spectra of electric and optic signals, as they also perform a kind of processes. These spectra can be directly measured, observed and examined by means of spectral analyzers and they are very important characteristics which can not be omitted at transmission techniques in telecommunication technologies. Further, the paper also deals with non electric processes, mainly with processes and spectra at mass servicing and how these spectra can be utilised in praxis.

Computer simulation of RBS spectra from samples with surface roughness

Czech Academy of Sciences Publication Activity Database

Malinský, Petr; Hnatowicz, Vladimír; Macková, Anna

2016-01-01

Roč. 371, MAR (2016), s. 101-105 ISSN 0168-583X. [22nd International conference on Ion Beam Analysis (IBA). Opatija, 14.06.2015-19.06.2015] R&D Projects: GA MŠk(CZ) LM2011019; GA ČR GA15-01602S Institutional support: RVO:61389005 Keywords : computer simulation * Rutherford backscattering * surface roughness Subject RIV: BG - Nuclear, Atomic and Molecular Physics, Colliders Impact factor: 1.109, year: 2016

THE Be STAR SPECTRA (BeSS) DATABASE

International Nuclear Information System (INIS)

Neiner, C.; De Batz, B.; Cochard, F.; Floquet, M.; Mekkas, A.; Desnoux, V.

2011-01-01

Be stars vary on many timescales, from hours to decades. A long time base of observations to analyze certain phenomena in these stars is therefore necessary. Collecting all existing and future Be star spectra into one database has thus emerged as an important tool for the Be star community. Moreover, for statistical studies, it is useful to have centralized information on all known Be stars via an up-to-date catalog. These two goals are what the Be Star Spectra (BeSS, http://basebe.obspm.fr) database proposes to achieve. The database contains an as-complete-as-possible catalog of known Be stars with stellar parameters, as well as spectra of Be stars from all origins (any wavelength, any epoch, any resolution, etc.). It currently contains over 54,000 spectra of more than 600 different Be stars among the ∼2000 Be stars in the catalog. A user can access and query this database to retrieve information on Be stars or spectra. Registered members can also upload spectra to enrich the database. Spectra obtained by professional as well as amateur astronomers are individually validated in terms of format and science before being included in BeSS. In this paper, we present the database itself as well as examples of the use of BeSS data in terms of statistics and the study of individual stars.

IRAS low-resolution spectra of galaxies

International Nuclear Information System (INIS)

Cohen, M.; Volk, K.

1989-01-01

The spectra of external galaxies are selected and extracted from the IRAS LRS database. Twenty-one objects present viable spectra. One is a peculiar star-forming E-S0 galaxy. The remainder are all starburst or H II region galaxies. Their average spectrum demonstrates the importance of the PAH emission bands in the 8-23-micron region and reinforces the conclusion reached from ground-based spectra, that there is a strong correlation between the PAH bands and the starburst or H II region character of a galaxy. 32 refs

Efficient H2 production over Au/graphene/TiO2 induced by surface plasmon resonance of Au and band-gap excitation of TiO2

International Nuclear Information System (INIS)

Liu, Yang; Yu, Hongtao; Wang, Hua; Chen, Shuo; Quan, Xie

2014-01-01

Highlights: • Both surface plasmon resonance and band-gap excitation were used for H 2 production. • Au/Gr/TiO 2 composite photocatalyst was synthesized. • Au/Gr/TiO 2 exhibited enhancement of light absorption and charge separation. • H 2 production rate of Au/Gr/TiO 2 was about 2 times as high as that of Au/TiO 2 . - Abstract: H 2 production over Au/Gr/TiO 2 composite photocatalyst induced by surface plasmon resonance of Au and band-gap excitation of TiO 2 using graphene (Gr) as an electron acceptor has been investigated. Electron paramagnetic resonance study indicated that, in this composite, Gr collected electrons not only from Au with surface plasmon resonance but also from TiO 2 with band-gap excitation. Surface photovoltage and UV–vis absorption measurements revealed that compared with Au/TiO 2 , Au/Gr/TiO 2 displayed more effective photogenerated charge separation and higher optical absorption. Benefiting from these advantages, the H 2 production rate of Au/Gr/TiO 2 composite with Gr content of 1.0 wt% and Au content of 2.0 wt% was about 2 times as high as that of Au/TiO 2 . This work represents an important step toward the efficient application of both surface plasmon resonance and band-gap excitation on the way to converting solar light into chemical energy

Peakr: simulating solid-state NMR spectra of proteins

International Nuclear Information System (INIS)

Schneider, Robert; Odronitz, Florian; Hammesfahr, Bjorn; Hellkamp, Marcel; Kollmar, Martin

2013-01-01

When analyzing solid-state nuclear magnetic resonance (NMR) spectra of proteins, assignment of resonances to nuclei and derivation of restraints for 3D structure calculations are challenging and time-consuming processes. Simulated spectra that have been calculated based on, for example, chemical shift predictions and structural models can be of considerable help. Existing solutions are typically limited in the type of experiment they can consider and difficult to adapt to different settings. Here, we present Peakr, a software to simulate solid-state NMR spectra of proteins. It can generate simulated spectra based on numerous common types of internuclear correlations relevant for assignment and structure elucidation, can compare simulated and experimental spectra and produces lists and visualizations useful for analyzing measured spectra. Compared with other solutions, it is fast, versatile and user friendly. (authors)

Optical manifestation of magnetoexcitons in near-surface quantum wells

Energy Technology Data Exchange (ETDEWEB)

Flores-Desirena, B.; Perez-Rodriguez, F

2003-05-15

The optical response of excitons in quantum wells, close to the sample boundary and under the action of a strong magnetic field perpendicular to their plane, is investigated theoretically. Solving the system of coupled equations for the coherent electron-hole interband amplitude and the electromagnetic field, reflectivity spectra for such nanostructures are calculated. The effect of the interaction of magnetoexcitons with the sample surface on the resonance structure of reflectivity spectra is analyzed. These optical spectra are also affected by the phase change of the electromagnetic wave as it propagates in the cap layer, overlying the quantum well.

Parity violation constraints using cosmic microwave background polarization spectra from 2006 and 2007 observations by the QUaD polarimeter.

Science.gov (United States)

Wu, E Y S; Ade, P; Bock, J; Bowden, M; Brown, M L; Cahill, G; Castro, P G; Church, S; Culverhouse, T; Friedman, R B; Ganga, K; Gear, W K; Gupta, S; Hinderks, J; Kovac, J; Lange, A E; Leitch, E; Melhuish, S J; Memari, Y; Murphy, J A; Orlando, A; Piccirillo, L; Pryke, C; Rajguru, N; Rusholme, B; Schwarz, R; O'Sullivan, C; Taylor, A N; Thompson, K L; Turner, A H; Zemcov, M

2009-04-24

We constrain parity-violating interactions to the surface of last scattering using spectra from the QUaD experiment's second and third seasons of observations by searching for a possible systematic rotation of the polarization directions of cosmic microwave background photons. We measure the rotation angle due to such a possible "cosmological birefringence" to be 0.55 degrees +/-0.82 degrees (random) +/-0.5 degrees (systematic) using QUaD's 100 and 150 GHz temperature-curl and gradient-curl spectra over the spectra over the multipole range 200

Qualitative and quantitative validation of the SINBAD code on complex HPGe gamma-ray spectra

Energy Technology Data Exchange (ETDEWEB)

Rohee, E.; Coulon, R.; Normand, S.; Carrel, F. [CEA, LIST, Laboratoire Capteurs et Architectures electroniques, F-91191 Gif-sur-Yvette, (France); Dautremer, T.; Barat, E.; Montagu, T. [CEA, LIST, Laboratoire Modelisation, Simulation et Systemes, F-91191 Gif-sur-Yvette, (France); Jammes, C. [CEA/DEN/SPEx/LDCI, Centre de Cadarache, F-13109 Saint-Paul-lez-Durance, (France)

2015-07-01

Radionuclides identification and quantification is a serious concern for many applications as safety or security of nuclear power plant or fuel cycle facility, CBRN risk identification, environmental radioprotection and waste measurements. High resolution gamma-ray spectrometry based on HPGe detectors is a performing solution for all these topics. During last decades, a great number of software has been developed to improve gamma spectra analysis. However, some difficulties remain in the analysis when photoelectric peaks are folded together with a high ratio between theirs amplitudes, when the Compton background is much larger compared to the signal of a single peak and when spectra are composed of a great number of peaks. This study deals with the comparison between conventional methods in radionuclides identification and quantification and the code called SINBAD ('Spectrometrie par Inference Non parametrique Bayesienne Deconvolutive'). For many years, SINBAD has been developed by CEA LIST for unfolding complex spectra from HPGe detectors. Contrary to conventional methods using fitting procedures, SINBAD uses a probabilistic approach with Bayesian inference to describe spectrum data. This conventional fitting method founded for example in Genie 2000 is compared with the nonparametric SINBAD approach regarding some key figures of merit as the peak centroid evaluation (identification) and peak surface evaluation (quantification). Unfriendly cases are studied for nuclides detection with closed gamma-rays energies and high photoelectric peak intensity differences. Tests are performed with spectra from the International Atomic Energy Agency (IAEA) for gamma spectra analysis software benchmark and with spectra acquired at the laboratory. Results show that SINBAD and Genie 2000 performances are quite similar with sometimes best results for SINBAD with the important difference that to achieve same performances the nonparametric method is user-friendly compared

Analysis of the electrodeposition and surface chemistry of CdTe, CdSe, and CdS thin films through substrate-overlayer surface-enhanced Raman spectroscopy.

Science.gov (United States)

Gu, Junsi; Fahrenkrug, Eli; Maldonado, Stephen

2014-09-02

The substrate-overlayer approach has been used to acquire surface enhanced Raman spectra (SERS) during and after electrochemical atomic layer deposition (ECALD) of CdSe, CdTe, and CdS thin films. The collected data suggest that SERS measurements performed with off-resonance (i.e. far from the surface plasmonic wavelength of the underlying SERS substrate) laser excitation do not introduce perturbations to the ECALD processes. Spectra acquired in this way afford rapid insight on the quality of the semiconductor film during the course of an ECALD process. For example, SERS data are used to highlight ECALD conditions that yield crystalline CdSe and CdS films. In contrast, SERS measurements with short wavelength laser excitation show evidence of photoelectrochemical effects that were not germane to the intended ECALD process. Using the semiconductor films prepared by ECALD, the substrate-overlayer SERS approach also affords analysis of semiconductor surface adsorbates. Specifically, Raman spectra of benzenethiol adsorbed onto CdSe, CdTe, and CdS films are detailed. Spectral shifts in the vibronic features of adsorbate bonding suggest subtle differences in substrate-adsorbate interactions, highlighting the sensitivity of this methodology.

JADSPE, Multi-Channel Gamma Spectra Unfolding Program

International Nuclear Information System (INIS)

Rikovska, J.; Stejskalova, E.

2005-01-01

1 - Description of program or function: JADSPE is a package of eight programs to process multi-channel gamma-ray spectra. The programs can be used to: - locate automatically spectral peaks and calculate their positions, areas, and full widths at half maximum (FWHM); - plot the spectra on a CALCOMP plotter, TEKTRONIX terminal or a line printer; - add or subtract several spectra with the possibility of adjusting either their start and end channels or the maxima of the chosen corresponding peaks. The JADSPE package comprises the following programs: - SPECTF: automatic location of peaks and calculation of their positions, areas and FWHMS. The standard deviations of peak parameters are also determined, and each evaluated region is plotted on the line printer. - SPECT1: The areas and FWHMs are calculated for peaks whose positions are known beforehand. The standard deviations of calculated parameters are also determined, and each evaluated region is plotted on the line printer. - PLOCHA: The peak net area is calculated by summing the channel contents in specified regions and by subtracting a linear background. - GRAPH: Spectrum plotting on the line printer. - PLTNEW: Spectrum plotting on CALCOMP plotter or on TEKTRONIX terminal. - SUMDIF: The channel contents of several gamma-ray spectra are added or subtracted. - SSPFP: The channel contents of several gamma-ray spectra are added with adjustment of the maxima of specified peaks. - SOUCET: The channel contents of several gamma-ray spectra are added with the adjustment of start and end channels of the spectra. 2 - Method of solution: Non-linear least-square fit. 3 - Restrictions on the complexity of the problem: The full energy peaks are approximated by a symmetrical Gaussian function and the underlying background is approximated by a first-order polynomial. A fixed spectrum length of 4096 channels is assumed. Maxima of: - number of peaks in one multiplet: 9; - number of peaks identified by the automatic search procedure

Core-level spectra and molecular deformation in adsorption: V-shaped pentacene on Al(001)

Science.gov (United States)

Lin, He; Brivio, Gian Paolo; Floreano, Luca; Fratesi, Guido

2015-01-01

Summary By first-principle simulations we study the effects of molecular deformation on the electronic and spectroscopic properties as it occurs for pentacene adsorbed on the most stable site of Al(001). The rationale for the particular V-shaped deformed structure is discussed and understood. The molecule–surface bond is made evident by mapping the charge redistribution. Upon X-ray photoelectron spectroscopy (XPS) from the molecule, the bond with the surface is destabilized by the electron density rearrangement to screen the core hole. This destabilization depends on the ionized carbon atom, inducing a narrowing of the XPS spectrum with respect to the molecules adsorbed hypothetically undistorted, in full agreement to experiments. When looking instead at the near-edge X-ray absorption fine structure (NEXAFS) spectra, individual contributions from the non-equivalent C atoms provide evidence of the molecular orbital filling, hybridization, and interchange induced by distortion. The alteration of the C–C bond lengths due to the V-shaped bending decreases by a factor of two the azimuthal dichroism of NEXAFS spectra, i.e., the energy splitting of the sigma resonances measured along the two in-plane molecular axes. PMID:26734516

Core-level spectra and molecular deformation in adsorption: V-shaped pentacene on Al(001

Directory of Open Access Journals (Sweden)

Anu Baby

2015-11-01

Full Text Available By first-principle simulations we study the effects of molecular deformation on the electronic and spectroscopic properties as it occurs for pentacene adsorbed on the most stable site of Al(001. The rationale for the particular V-shaped deformed structure is discussed and understood. The molecule–surface bond is made evident by mapping the charge redistribution. Upon X-ray photoelectron spectroscopy (XPS from the molecule, the bond with the surface is destabilized by the electron density rearrangement to screen the core hole. This destabilization depends on the ionized carbon atom, inducing a narrowing of the XPS spectrum with respect to the molecules adsorbed hypothetically undistorted, in full agreement to experiments. When looking instead at the near-edge X-ray absorption fine structure (NEXAFS spectra, individual contributions from the non-equivalent C atoms provide evidence of the molecular orbital filling, hybridization, and interchange induced by distortion. The alteration of the C–C bond lengths due to the V-shaped bending decreases by a factor of two the azimuthal dichroism of NEXAFS spectra, i.e., the energy splitting of the sigma resonances measured along the two in-plane molecular axes.

Magnetic signature of surface defects at nanodiamonds

Energy Technology Data Exchange (ETDEWEB)

Vollmers, Nora Jenny; Gerstmann, Uwe; Schmidt, Wolf Gero [Theoretische Physik, Universitaet Paderborn (Germany)

2011-07-01

The n-type doping of diamond has been a long-standing issue, which recently gained attention in the context of nanodiamonds. Attempts of doping with nitrogen failed to result in the Electron paramagnetic Resonance (EPR) fingerprints expected from bulk material. Instead, the nanodiamond signals show a much larger deviation from the free-electron g-value and are believed to be related to intrinsic, carbon inherited defects. However, the absence of the bulk-like EPR spectra does not mean that nitrogen is not incorporated at all. The N atoms could be built in predominantly at or at least close to the surfaces yielding EPR spectra, very different from those measured in the bulk. In this work, we elucidate the situation by investigating the magnetic signature of paramagnetic defects in the nanodiamonds. We use the gauge-including projector augmented plane wave (GI-PAW) approach to calculate the hyperfine splittings and the elements of the electronic g-tensor. Taking the C(100) surface as a first model system, a possible contribution of nitrogen is discussed by comparing EPR parameters for different N incorporation depths: Incorporated directly at the surface, N gives rise to surface states similar to intrinsic carbon dangling bond-like states. Otherwise N is able to introduce surface conductivity as demonstrated by calculated effective mass tensors.

EFFECTS OF FORSTERITE GRAIN SHAPE ON INFRARED SPECTRA

International Nuclear Information System (INIS)

Koike, C.; Imai, Y.; Chihara, H.; Murata, K.; Tsuchiyama, A.; Suto, H.; Tachibana, S.; Ohara, S.

2010-01-01

The Infrared Space Observatory (ISO) detected several sharp infrared features around young stars, comets, and evolved stars. These sharp features were identified as Mg-rich crystalline silicates of forsterite and enstatite by comparison with spectra from laboratory data. However, certain infrared emission bands in the observed spectra cannot be identified because they appear at slightly shorter wavelengths than the peaks in forsterite laboratory spectra, where the shapes of forsterite particles are irregular. To solve this problem, we measured infrared spectra of forsterite grains of various shapes (irregular, plate-like with no sharp edges, elliptical, cauliflower, and spherical) in the infrared spectral region between 5 and 100 μm. The spectra depend on particle shape. The spectra of the 11, 19, 23, and 33 μm bands, in particular, are extremely sensitive to particle shape, whereas some peaks such as the 11.9, 49, and 69 μm bands remained almost unchanged despite different particle shapes. This becomes most evident from the spectra of near-spherical particles produced by annealing an originally amorphous silicate sample at temperature from 600 to 1150 deg. C. The spectra of these samples differ strongly from those of other ones, showing peaks at much shorter wavelengths. At a higher annealing temperature of 1200 deg. C, the particle shapes changed drastically from spherical to irregular and the spectra became similar to those of forsterite particles with irregular shapes. Based on ISO data and other observational data, the spectra of outflow sources and disk sources may correspond to differences in forsterite shape, and further some unidentified peaks, such as those at 32.8 or 32.5 μm, may be due to spherical or spherical-like forsterite.

Resonance Raman Optical Activity and Surface Enhanced Resonance Raman Optical Activity analysis of Cytochrome C

DEFF Research Database (Denmark)

Johannessen, Christian; Abdali, Salim; White, Peter C.

2007-01-01

High quality Resonance Raman (RR) and resonance Raman Optical Activity (ROA) spectra of cytochrome c were obtained in order to perform full assignment of spectral features of the resonance ROA spectrum. The resonance ROA spectrum of cytochrome c revealed a distinct spectral signature pattern due...... to resonance enhanced skeletal porphyrin vibrations, more pronounced than any contribution from the protein back-bone. Combining the intrinsic resonance enhancement of cytochrome c with surface plasmon enhancement by colloidal silver particles, the Surface Enhanced Resonance Raman Scattering (SERRS) and Chiral...... Enhanced Raman Spectroscopy (ChERS) spectra of the protein were successfully obtained at very low concentration (as low as 1 µM). The assignment of spectral features was based on the information obtained from the RR and resonance ROA spectra. Excellent agreement between RR and SERRS spectra is reported...

Measurement of neutron spectra through composed material block bombarded with D-T neutrons

Energy Technology Data Exchange (ETDEWEB)

Zhu, T.H. [Institute of Nuclear Physics and Chemistry, China Academy of Engineering Physics, P.O. BOX 919-213, Mian yang 621900 (China)], E-mail: zhutonghua@yahoo.com.cn; Liu, R.; Lu, X.X.; Jiang, L.; Wen, Z.W.; Wang, M.; Lin, J.F. [Institute of Nuclear Physics and Chemistry, China Academy of Engineering Physics, P.O. BOX 919-213, Mian yang 621900 (China)

2009-12-15

A 2-dimensional composed material assembly made of the iron and hydric block has been established. The neutron spectra from the assembly bombarded with 14-MeV neutrons at neutron generator have been obtained using the proton recoil technique with a stillbene detector. The detector positions were selected at the 60 deg., 120 deg., 180 deg. on the surface of the iron spherical shell. The background neutron spectra consisted of background and room return radiation were subtracted with combination of methods of experimental shielding and MCNP calculation. The uncertainty of results was 6.3-7.4%. The experiment results were analyzed and simulated by MCNP code and two data library. The difference is integral neutron flux (background neutron subtracted) of measured results greater than calculations with maximum of 21.2% in the range of 1-16 MeV.

Infrared spectral reflectances of asteroid surfaces

Science.gov (United States)

Larson, H. P.; Veeder, G. J.

1979-01-01

This review compares the types of compositional information produced by three complementary techniques used in infrared observations of asteroid surfaces: broadband JHKL photometry, narrow band photometry, and multiplex spectroscopy. The high information content of these infrared observations permits definitive interpretations of asteroid surface compositions in terms of the major meteoritic minerals (olivine, pyroxene, plagioclase feldspar, hydrous silicates, and metallic Ni-Fe). These studies emphasize the individuality of asteroid surface compositions, the inadequacy of simple comparisons with spectra of meteorites, and the need to coordinate spectral measurements of all types to optimize diagnostic capabilities.

Infrared spectra of phosphate sorbed on iron hydroxide gel and the sorption products

International Nuclear Information System (INIS)

Nanzyo, M.

1986-01-01

Infrared absorption spectra of phosphate sorbed on iron hydroxide gel were obtained by applying the differential diffuse reflectance method. Absorption bands due to P-O stretching vibration were observed at 1,110 and 1,010 cm -1 at pH 12.3. With decreasing pH, these absorption bands gradually shifted to 1,100 and 1,020 cm -1 at pH 4.9. At pH 2.3, they became a broad single absorption band at 1,060 cm -1 . At pH 11 or above, the difference in the Na + adsorption between phosphated iron hydroxide gel and iron hydroxide gel was almost equal to the amount of phosphate sorption. This finding shows that phosphate was retained on the iron hydroxide gel surface as a bidentate ligand at a high pH. It was concluded that at a high pH phosphate was sorbed on iron hydroxide gel as a binuclear surface complex similar to that on goethite; the change in spectra for P-O stretching vibration with decreasing pH value was mainly caused by an increase in the fraction of amorphous iron phosphate; at pH 2.3, the phosphate sorption product consisted of amorphous iron phosphate. (author)

Composite Spectra Paper 1: HR 6902

Indian Academy of Sciences (India)

tribpo

spectra; in many cases we have used the maximum width permitted by the optics of ... 10 mЕ, corresponding to 1 µm the plate, are the norm. ..... an inequality ..... on the spectra of HR 6902, we have thought it appropriate to weight the four ...

Surface modification and electrochemical properties of activated carbons for supercapacitor electrodes

Science.gov (United States)

Yang, Dan; Qiu, Wenmei; Xu, Jingcai; Han, Yanbing; Jin, Hongxiao; Jin, Dingfeng; Peng, Xiaoling; Hong, Bo; Li, Ji; Ge, Hongliang; Wang, Xinqing

2015-12-01

Modifications with different acids (HNO3, H2SO4, HCl and HF, respectively) were introduced to treat the activated carbons (ACs) surface. The microstructures and surface chemical properties were discussed by X-ray diffraction (XRD), thermogravimetric analysis (TGA), ASAP, Raman spectra and Fourier transform infrared (FTIR) spectra. The ACs electrode-based supercapacitors were assembled with 6 mol ṡ L-1 KOH electrolyte. The electrochemical properties were studied by galvanostatic charge-discharge and cyclic voltammetry. The results indicated that although the BET surface area of modified ACs decreased, the functional groups were introduced and the ash contents were reduced on the surface of ACs, receiving larger specific capacitance to initial AC. The specific capacitance of ACs modified with HCl, H2SO4, HF and HNO3 increased by 31.4%, 23%, 21% and 11.6%, respectively.

Crystallinity, Surface Morphology, and Photoelectrochemical Effects in Conical InP and InN Nanowires Grown on Silicon.

Science.gov (United States)

Parameshwaran, Vijay; Xu, Xiaoqing; Clemens, Bruce

2016-08-24

The growth conditions of two types of indium-based III-V nanowires, InP and InN, are tailored such that instead of yielding conventional wire-type morphologies, single-crystal conical structures are formed with an enlarged diameter either near the base or near the tip. By using indium droplets as a growth catalyst, combined with an excess indium supply during growth, "ice cream cone" type structures are formed with a nanowire "cone" and an indium-based "ice cream" droplet on top for both InP and InN. Surface polycrystallinity and annihilation of the catalyst tip of the conical InP nanowires are observed when the indium supply is turned off during the growth process. This growth design technique is extended to create single-crystal InN nanowires with the same morphology. Conical InN nanowires with an enlarged base are obtained through the use of an excess combined Au-In growth catalyst. Electrochemical studies of the InP nanowires on silicon demonstrate a reduction photocurrent as a proof of photovolatic behavior and provide insight as to how the observed surface polycrystallinity and the resulting interface affect these device-level properties. Additionally, a photovoltage is induced in both types of conical InN nanowires on silicon, which is not replicated in epitaxial InN thin films.

The Martian surface radiation environment – a comparison of models and MSL/RAD measurements

Directory of Open Access Journals (Sweden)

Matthiä Daniel

2016-01-01

Full Text Available Context: The Radiation Assessment Detector (RAD on the Mars Science Laboratory (MSL has been measuring the radiation environment on the surface of Mars since August 6th 2012. MSL-RAD is the first instrument to provide detailed information about charged and neutral particle spectra and dose rates on the Martian surface, and one of the primary objectives of the RAD investigation is to help improve and validate current radiation transport models. Aims: Applying different numerical transport models with boundary conditions derived from the MSL-RAD environment the goal of this work was to both provide predictions for the particle spectra and the radiation exposure on the Martian surface complementing the RAD sensitive range and, at the same time, validate the results with the experimental data, where applicable. Such validated models can be used to predict dose rates for future manned missions as well as for performing shield optimization studies. Methods: Several particle transport models (GEANT4, PHITS, HZETRN/OLTARIS were used to predict the particle flux and the corresponding radiation environment caused by galactic cosmic radiation on Mars. From the calculated particle spectra the dose rates on the surface are estimated. Results: Calculations of particle spectra and dose rates induced by galactic cosmic radiation on the Martian surface are presented. Although good agreement is found in many cases for the different transport codes, GEANT4, PHITS, and HZETRN/OLTARIS, some models still show large, sometimes order of magnitude discrepancies in certain particle spectra. We have found that RAD data is helping to make better choices of input parameters and physical models. Elements of these validated models can be applied to more detailed studies on how the radiation environment is influenced by solar modulation, Martian atmosphere and soil, and changes due to the Martian seasonal pressure cycle. By extending the range of the calculated particle

Climatology of tropospheric vertical velocity spectra

Science.gov (United States)

Ecklund, W. L.; Gage, K. S.; Balsley, B. B.; Carter, D. A.

1986-01-01

Vertical velocity power spectra obtained from Poker Flat, Alaska; Platteville, Colorado; Rhone Delta, France; and Ponape, East Caroline Islands using 50-MHz clear-air radars with vertical beams are given. The spectra were obtained by analyzing the quietest periods from the one-minute-resolution time series for each site. The lengths of available vertical records ranged from as long as 6 months at Poker Flat to about 1 month at Platteville. The quiet-time vertical velocity spectra are shown. Spectral period ranging from 2 minutes to 4 hours is shown on the abscissa and power spectral density is given on the ordinate. The Brunt-Vaisala (B-V) periods (determined from nearby sounding balloons) are indicated. All spectra (except the one from Platteville) exhibit a peak at periods slightly longer than the B-V period, are flat at longer periods, and fall rapidly at periods less than the B-V period. This behavior is expected for a spectrum of internal waves and is very similar to what is observed in the ocean (Eriksen, 1978). The spectral amplitudes vary by only a factor of 2 or 3 about the mean, and show that under quiet conditions vertical velocity spectra from the troposphere are very similar at widely different locations.

Path spectra derived from inversion of source and site spectra for earthquakes in Southern California

Science.gov (United States)

Klimasewski, A.; Sahakian, V. J.; Baltay, A.; Boatwright, J.; Fletcher, J. B.; Baker, L. M.

2017-12-01

A large source of epistemic uncertainty in Ground Motion Prediction Equations (GMPEs) is derived from the path term, currently represented as a simple geometric spreading and intrinsic attenuation term. Including additional physical relationships between the path properties and predicted ground motions would produce more accurate and precise, region-specific GMPEs by reclassifying some of the random, aleatory uncertainty as epistemic. This study focuses on regions of Southern California, using data from the Anza network and Southern California Seismic network to create a catalog of events magnitude 2.5 and larger from 1998 to 2016. The catalog encompasses regions of varying geology and therefore varying path and site attenuation. Within this catalog of events, we investigate several collections of event region-to-station pairs, each of which share similar origin locations and stations so that all events have similar paths. Compared with a simple regional GMPE, these paths consistently have high or low residuals. By working with events that have the same path, we can isolate source and site effects, and focus on the remaining residual as path effects. We decompose the recordings into source and site spectra for each unique event and site in our greater Southern California regional database using the inversion method of Andrews (1986). This model represents each natural log record spectra as the sum of its natural log event and site spectra, while constraining each record to a reference site or Brune source spectrum. We estimate a regional, path-specific anelastic attenuation (Q) and site attenuation (t*) from the inversion site spectra and corner frequency from the inversion event spectra. We then compute the residuals between the observed record data, and the inversion model prediction (event*site spectra). This residual is representative of path effects, likely anelastic attenuation along the path that varies from the regional median attenuation. We examine the

Spectrophotometric evaluation of surface morphology dependent catalytic activity of biosynthesized silver and gold nanoparticles using UV–vis spectra: A comparative kinetic study

Energy Technology Data Exchange (ETDEWEB)

Ankamwar, Balaprasad, E-mail: bankamwar@yahoo.com [Bio-inspired Materials Research Laboratory, Department of Chemistry, Savitribai Phule Pune University, Ganeshkhind, Pune 411007 (India); Kamble, Vaishali; Sur, Ujjal Kumar [Bio-inspired Materials Research Laboratory, Department of Chemistry, Savitribai Phule Pune University, Ganeshkhind, Pune 411007 (India); Santra, Chittaranjan [Department of Chemistry, Netaji Nagar Day College, Regent Park, Kolkata 700092 (India)

2016-03-15

Graphical abstract: - Highlights: • The biosynthesized silver nanoparticles were stable for 6 months and used as effective SERS active substrate. • They are effective catalyst in the chemical reduction of 4-nitrophenol to 4-aminophenol. • Comparative catalytic efficiency of both silver and gold nanoparticles was studied spectrophotometrically. • Our results demonstrate surface morphology dependent catalytic activity of both nanoparticles. - Abstract: The development of eco-friendly and cost-effective synthetic protocol for the preparation of nanomaterials, especially metal nanoparticles is an emerging area of research in nanotechnology. These metal nanoparticles, especially silver can play a crucial role in various catalytic reactions. The biosynthesized silver nanoparticles described here was very stable up to 6 months and can be further exploited as an effective catalyst in the chemical reduction of 4-nitrophenol to 4-aminophenol. The silver nanoparticles were utilized as an efficient surface-enhanced Raman scattering (SERS) active substrate using Rhodamine 6G as Raman probe molecule. We have also carried out systematic comparative studies on the catalytic efficiency of both silver and gold nanoparticles using UV–vis spectra to monitor the above reaction spectrophotometrically. We find that the reaction follows pseudo-first order kinetics and the catalytic activity can be explained by a simple model based on Langmuir–Hinshelwood mechanism for heterogeneous catalysis. We also find that silver nanoparticles are more efficient as a catalyst compare to gold nanoparticles in the reduction of 4-nitrophenol to 4-aminophenol, which can be explained by the morphology of the nanoparticles as determined by transmission electron microscopy.

Spectrophotometric evaluation of surface morphology dependent catalytic activity of biosynthesized silver and gold nanoparticles using UV–vis spectra: A comparative kinetic study

International Nuclear Information System (INIS)

Ankamwar, Balaprasad; Kamble, Vaishali; Sur, Ujjal Kumar; Santra, Chittaranjan

2016-01-01

Graphical abstract: - Highlights: • The biosynthesized silver nanoparticles were stable for 6 months and used as effective SERS active substrate. • They are effective catalyst in the chemical reduction of 4-nitrophenol to 4-aminophenol. • Comparative catalytic efficiency of both silver and gold nanoparticles was studied spectrophotometrically. • Our results demonstrate surface morphology dependent catalytic activity of both nanoparticles. - Abstract: The development of eco-friendly and cost-effective synthetic protocol for the preparation of nanomaterials, especially metal nanoparticles is an emerging area of research in nanotechnology. These metal nanoparticles, especially silver can play a crucial role in various catalytic reactions. The biosynthesized silver nanoparticles described here was very stable up to 6 months and can be further exploited as an effective catalyst in the chemical reduction of 4-nitrophenol to 4-aminophenol. The silver nanoparticles were utilized as an efficient surface-enhanced Raman scattering (SERS) active substrate using Rhodamine 6G as Raman probe molecule. We have also carried out systematic comparative studies on the catalytic efficiency of both silver and gold nanoparticles using UV–vis spectra to monitor the above reaction spectrophotometrically. We find that the reaction follows pseudo-first order kinetics and the catalytic activity can be explained by a simple model based on Langmuir–Hinshelwood mechanism for heterogeneous catalysis. We also find that silver nanoparticles are more efficient as a catalyst compare to gold nanoparticles in the reduction of 4-nitrophenol to 4-aminophenol, which can be explained by the morphology of the nanoparticles as determined by transmission electron microscopy.

Multifractal spectra in shear flows

Science.gov (United States)

Keefe, L. R.; Deane, Anil E.

1989-01-01

Numerical simulations of three-dimensional homogeneous shear flow and fully developed channel flow, are used to calculate the associated multifractal spectra of the energy dissipation field. Only weak parameterization of the results with the nondimensional shear is found, and this only if the flow has reached its asymptotic development state. Multifractal spectra of these flows coincide with those from experiments only at the range alpha less than 1.

Characterization of Silicon Nanocrystal Surfaces by Multidimensional Solid-State NMR Spectroscopy

International Nuclear Information System (INIS)

Hanrahan, Michael P.; Fought, Ellie L.; Windus, Theresa L.; Wheeler, Lance M.; Anderson, Nicholas C.

2017-01-01

The chemical and photophysical properties of silicon nanocrystals (Si NCs) are strongly dependent on the chemical composition and structure of their surfaces. Here we use fast magic angle spinning (MAS) and proton detection to enable the rapid acquisition of dipolar and scalar 2D 1 H– 29 Si heteronuclear correlation (HETCOR) solid-state NMR spectra and reveal a molecular picture of hydride-terminated and alkyl-functionalized surfaces of Si NCs produced in a nonthermal plasma. 2D 1 H– 29 Si HETCOR and dipolar 2D 1 H– 1 H multiple-quantum correlation spectra illustrate that resonances from surface mono-, di-, and trihydride groups cannot be resolved, contrary to previous literature assignments. Instead the 2D NMR spectra illustrate that there is large distribution of 1 H and 29 Si chemical shifts for the surface hydride species in both the as-synthesized and functionalized Si NCs. However, proton-detected 1 H– 29 Si refocused INEPT experiments can be used to unambiguously differentiate NMR signals from the different surface hydrides. Varying the 29 Si evolution time in refocused INEPT experiments and fitting the oscillation of the NMR signals allows for the relative populations of the different surface hydrides to be estimated. This analysis confirms that monohydride species are the predominant surface species on the as-synthesized Si NCs. A reduction in the populations of the di- and trihydrides is observed upon functionalization with alkyl groups, consistent with our previous hypothesis that the trihydride, or silyl (*SiH 3 ), group is primarily responsible for initiating surface functionalization reactions. Density functional theory (DFT) calculations were used to obtain quantum chemical structural models of the Si NC surface and reproduce the observed 1 H and 29 Si chemical shifts. Furthermore, the approaches outlined here will be useful to obtain a more detailed picture of surface structures for Si NCs and other hydride-passivated nanomaterials.

Laboratory simulations of the Vis-NIR spectra of comet 67P using sub-μm sized cosmochemical analogues

Science.gov (United States)

Rousseau, B.; Érard, S.; Beck, P.; Quirico, É.; Schmitt, B.; Brissaud, O.; Montes-Hernandez, G.; Capaccioni, F.; Filacchione, G.; Bockelée-Morvan, D.; Leyrat, C.; Ciarniello, M.; Raponi, A.; Kappel, D.; Arnold, G.; Moroz, L. V.; Palomba, E.; Tosi, F.; Virtis Team

2018-05-01

Laboratory spectral measurements of relevant analogue materials were performed in the framework of the Rosetta mission in order to explain the surface spectral properties of comet 67P. Fine powders of coal, iron sulphides, silicates and their mixtures were prepared and their spectra measured in the Vis-IR range. These spectra are compared to a reference spectrum of 67P nucleus obtained with the VIRTIS/Rosetta instrument up to 2.7 μm, excluding the organics band centred at 3.2 μm. The species used are known to be chemical analogues for cometary materials which could be present at the surface of 67P. Grain sizes of the powders range from tens of nanometres to hundreds of micrometres. Some of the mixtures studied here actually reach the very low reflectance level observed by VIRTIS on 67P. The best match is provided by a mixture of sub-micron coal, pyrrhotite, and silicates. Grain sizes are in agreement with the sizes of the dust particles detected by the GIADA, MIDAS and COSIMA instruments on board Rosetta. The coal used in the experiment is responsible for the spectral slope in the visible and infrared ranges. Pyrrhotite, which is strongly absorbing, is responsible for the low albedo observed in the NIR. The darkest components dominate the spectra, especially within intimate mixtures. Depending on sample preparation, pyrrhotite can coat the coal and silicate aggregates. Such coating effects can affect the spectra as much as particle size. In contrast, silicates seem to play a minor role.

Photon scattering and interaction analysis of interfacial corrosion and catalysis. Technical progress report, 1 February 1982-31 August 1982

International Nuclear Information System (INIS)

Furtak, T.E.

1982-01-01

Photon spectroscopic techniques are being developed as tools with which to study fundamental and applied problems associated with the composition, structure, and evolution of the metal-electrolyte interface. The main research is built around surface enhanced Raman scattering with differential reflectance and photo-voltage spectroscopy as supplementary techniques. All of these techniques are used in situ while the sample is exposed to the electrochemical environment of interest

Correlation versus surface effects in photoemission of quasi-1D organic conductors

DEFF Research Database (Denmark)

Claessen, R.; Schwingenschlogl, U.; Sing, M.

2002-01-01

The absence of spectral weight at the Fermi level in photoemission spectra of quasi-1D organic conductors has been interpreted as possible evidence for an unusual many-body state. We demonstrate that great care must be exercised to draw this conclusion exclusively on the basis of a pseudogap....... A detailed surface characterization of the charge transfer salts (TMTSF)(2)PFt(6) and TTF-TCNQ shows that signatures of electronic correlations in the valence band spectra are strongly affected by surface effects and may even be completely obscured....

Surface tension of liquid Al-Cu binary alloys.

OpenAIRE

Schmitz, Julianna; Brillo, Jürgen; Egry, Ivan; Schmid-Fetzer, Rainer

2009-01-01

Surface tension data of liquid Al–Cu binary alloys have been measured contactlessly using the technique of electromagnetic levitation. A digital CMOS-camera (400 fps) recorded image sequences of the oscillating liquid sample and surface tensions were determined from analysis of the frequency spectra. Measurements were performed for samples covering the entire range of composition and precise data were obtained in a broad temperature range. It was found that the surface tensions can ...

Experimental phase diagram for random laser spectra

International Nuclear Information System (INIS)

El-Dardiry, Ramy G S; Mooiweer, Ronald; Lagendijk, Ad

2012-01-01

We systematically study the presence of narrow spectral features in a wide variety of random laser samples. Less gain or stronger scattering are shown to lead to a crossover from spiky to smooth spectra. A decomposition of random laser spectra into a set of Lorentzians provides unprecedented detail in the analysis of random laser spectra. We suggest an interpretation in terms of mode competition that enables an understanding of the observed experimental trends. In this interpretation, smooth random laser spectra are a consequence of competing modes for which the loss and gain are proportional. Spectral spikes are associated with modes that are uncoupled from the mode competition in the bulk of the sample. (paper)

Contribution to the study of turbulence spectra

Science.gov (United States)

Dumas, R.

1979-01-01

An apparatus suitable for turbulence measurement between ranges of 1 to 5000 cps and from 6 to 16,000 cps was developed and is described. Turbulence spectra downstream of the grills were examined with reference to their general characteristics, their LF qualities, and the effects of periodic turbulence. Medium and HF are discussed. Turbulence spectra in the boundary layers are similarly examined, with reference to their fluctuations at right angles to the wall, and to lateral fluctuations. Turbulence spectra in a boundary layer with suction to the wall is discussed. Induced turbulence, and turbulence spectra at high Reynolds numbers. Calculations are presented relating to the effect of filtering on the value of the correlations in time and space.

Direct synthesis of sp-bonded carbon chains on graphite surface by femtosecond laser irradiation

International Nuclear Information System (INIS)

Hu, A.; Rybachuk, M.; Lu, Q.-B.; Duley, W. W.

2007-01-01

Microscopic phase transformation from graphite to sp-bonded carbon chains (carbyne) and nanodiamond has been induced by femtosecond laser pulses on graphite surface. UV/surface enhanced Raman scattering spectra and x-ray photoelectron spectra displayed the local synthesis of carbyne in the melt zone while nanocrystalline diamond and trans-polyacetylene chains form in the edge area of gentle ablation. These results evidence possible direct 'writing' of variable chemical bonded carbons by femtosecond laser pulses for carbon-based applications

Modification of the surface properties of a polyimide film during irradiation with polychromic light

International Nuclear Information System (INIS)

Rosu, Liliana; Sava, Ion; Rosu, Dan

2011-01-01

The behaviour of a polyimide film with the aromatic structure during the exposure to UV light with λ > 290 nm was studied. Significant changes in color surface and gloss surface were identified during irradiation. Sample became lighten and less glossy after exposure to the light. These modifications were correlated with the structural changes in FTIR spectra. Based on changes in FTIR spectra recorded during irradiation, a mechanism for the photochemical degradation of polyimide film was proposed.

Reflectance spectra characteristics from an SPR grating fabricated by nano-imprint lithography technique for biochemical nanosensor applications

Science.gov (United States)

Setiya Pradana, Jalu; Hidayat, Rahmat

2018-04-01

In this paper, we report our research work on developing a Surface Plasmon Resonance (SPR) element with sub-micron (hundreds of nanometers) periodicity grating structure. This grating structure was fabricated by using a simple nano-imprint lithography technique from an organically siloxane polymers, which was then covered by nanometer thin gold layer. The formed grating structure was a very well defined square-shaped periodic structure. The measured reflectance spectra indicate the SPR wave excitation on this grating structure. For comparison, the simulations of reflectance spectra have been also carried out by using Rigorous Coupled-Wave Analysis (RCWA) method. The experimental results are in very good agreement with the simulation results.

Venus surface peeking through the atmosphere - gaining a global perspective on the surface composition through near infrared observations

Science.gov (United States)

Helbert, J.; Dyar, M. D.; Maturilli, A.; D'Amore, M.; Ferrari, S.; Mueller, N. T.; Smrekar, S. E.

2017-12-01

Venus is the most Earth-like of the terrestrial planets, though very little is known about its surface composition. Thanks to recent advances in laboratory spectroscopy and spectral analysis techniques, this is about to change. Although the atmosphere prohibits observations of the surface with traditional imaging techniques over much of the EM spectral range, five transparent windows between 0.86 µm and 1.18 µm occur in the atmosphere's CO2 spectrum. New high temperature laboratory spectra from the Planetary Spectroscopy Laboratory at DLR show that spectra in these windows are highly diagnostic for surface mineralogy [1]. The Venus Emissivity Mapper (VEM) [2] builds on these recent advances. It is proposed for NASA's Venus Origins Explorer where a radar will provided the needed high-resolution altimetry and ESA's EnVision would provide stereo topography instead. VEM is the first flight instrument specially designed to focus solely on mapping Venus' surface using the windows around 1 µm. Operating in situ from Venus orbit, VEM will provide a global map of composition as well as redox state of the surface, enabling a comprehensive picture of surface-atmosphere interaction on Venus. VEM will return a complex data set containing surface, atmospheric, cloud, and scattering information. Total planned data volume for a typical mission scenario exceeds 1TB. Classical analysis techniques have been successfully used for VIRTIS on Venus Express [3-5] and could be employed with the VEM data. However, application of machine learning approaches to this rich dataset is vastly more efficient, as has already been confirmed with laboratory data. Binary classifiers [6] demonstrate that at current best estimate errors, basalt spectra are confidently discriminated from basaltic andesites, andesites, and rhyolite/granite. Applying the approach of self-organizing maps to the increasingly large set of laboratory measurements allows searching for additional mineralogical indicators

Surface enhancement Raman scattering of tautomeric thiobarbituric acid. Natural bond orbitals and B3LYP/6-311+G (d, p) assignments of the Fourier Infrared and Fourier Raman Spectra.

Science.gov (United States)

Soto, C A Téllez; Ramos, J M; Costa Junior, A C; Vieira, Laís S; Rangel, João L; Raniero, L; Fávero, Priscila P; Lemma, Tibebe; Ondar, Grisset F; Versiane, Otavio; Martin, A A

2013-10-01

Surface enhancement Raman scattering (SERS) of two tautomer of thiobarbituric acid was obtained using silver and gold nanoparticles. Large band enhancement in the region of the ν(C=S), ν(C=C), δ(CH2), and δ(CNH) vibrational modes was found. Natural bond analysis of the tautomer species revealed expressive values of charge transfer, principally from lone pair electron orbitals of the S, N, and O atoms. Complete vibrational assignment was done for the two tautomers using the B3LYP/6-311+G (d, p) procedure, band deconvolution analysis, and from a rigorous interpretation of the normal modes matrix. The calculated spectra agree well with the experimental ones. Copyright © 2013 Elsevier B.V. All rights reserved.

The effect of ultraviolet irradiation on the photothermal, photoluminescence and photoluminescence excitation spectra of Mn-doped ZnS nanoparticles

International Nuclear Information System (INIS)

Briones Cruz, Almira; Shen Qing; Toyoda, Taro

2006-01-01

Research involving Mn doped nanocrystalline ZnS (ZnS:Mn) has grown in recent years, partly due to the high quantum luminescence efficiencies that have been reported. We measured the photoacoustic (PA), the photoluminescence (PL) and the photoluminescence excitation (PLE) spectra of surface-passivated and unpassivated ZnS:Mn. The effects of UV irradiation on the PL and PLE spectra were also studied. A decrease in the PA intensity after UV exposure was observed for the ZnS:Mn, indicating a decrease in the nonradiative relaxation probability. The observed increase in PL intensity indicates a corresponding increase in the radiative transition probability. For the PLE spectra, possible aggregation of the primary particles could have resulted in the lower measured energy of the PLE peak compared to the value predicted by the effective mass approximation theory

Three-dimensional hollow graphene efficiently promotes electron transfer of Ag3PO4 for photocatalytically eliminating phenol

Science.gov (United States)

Song, Shaoqing; Meng, Aiyun; Jiang, Shujuan; Cheng, Bei

2018-06-01

The effective transport of photo-induced carriers over semiconductor photocatalyst is critical for enhancing the photocatalytic performance under light excitation. Although oxidized graphene (GO) and/or reduced graphene oxide (rGO) has been used as cocatalyst to promote the transfer and utilization of electrons, however, random diffusion and transfer of photo-induced charges are inevitable from all sides over these actual graphene owing to the limitation of the preparation process and theory. Herein, we utilized three-dimensional hollow carbon graphene (HCG) to promote the efficient electron transfer of Ag3PO4 in the photocatalytic process. Owing to the confinement-induced electron field of HCG, the constructed HCG-Ag3PO4 photocatalytic system demonstrated the enhanced visible-light adsorption, improved transfer of photo-induced charges, and suitable redox potentials as revealed by transient photo-current spectroscopic, surface photovoltage spectroscopy, and electron paramagnetic resonance (EPR). EPR spectra of oxygen species and gas chromatography-mass spectra exhibited high efficiency activity over HCG-Ag3PO4 with Z-scheme photocatalytic mechanism for phenol decomposition by reaction between hexanoic acid and radOH and radO2-. It is noteworthy that photocatalytic performance over optimal HCG-Ag3PO4 is 6, 3.43, 1.92 times of pristine Ag3PO4, GO-Ag3PO4, and rGO-Ag3PO4, respectively. The results may supply a novel perspective to enhance transfer of photo-induced charges for the promotion of photocatalytic technology.

Surface-enhanced raman spectroscopy of quinomethionate adsorbed on silver colloids

International Nuclear Information System (INIS)

Kim, Mak Soon; Kang, Jae Soo; Park, Si Bum; Lee, Mu Sang

2003-01-01

We have studied the surface-enhanced Raman spectroscopy (SERS) spectrum of quinomethionate (6-methyl-1,3-dithiolo(4,5-b)quinoxalin-2-one), which is an insecticide or fungicide used on vegetables and wheat. We observed no signals in the ordinary Raman spectra of solid-state quinomethionate, but when it was adsorbed on a colloidal silver surface, strong vibrational signals were obtained at a very low concentration. The SERS spectra were obtained by silver colloids prepared by the Creighton et al. method. The influence of pH and the aggregation inductors (Cl - , Br - , I - , F - ) on the adsorption mechanism was investigated. Two different adsorption mechanisms were deduced, depending on the experimental conditions: The one N atom or two N atoms are chemisorbed on an Ag surface. An important contribution of the chemical mechanism was inferred when the one N atom was perpendicularly adsorbed on a surface. It is possible that quinomethionate can be detected to about 10 -5 M

Parametrization relating the fermionic mass spectra

International Nuclear Information System (INIS)

Kleppe, A.

1993-01-01

When parametrizing the fermionic mass spectra in terms of the unit matrix and a recursive matrix scrR 0 , which corresponds to an underlying scaling pattern in the mass spectra, each fermionic sector is characterized by three parameters: k, α, and R. Using the set of relations displayed by the parameters of the different sectors, it is possible to formulate a ''family Lagrangian'' which for each sector encompasses all the families. Relations between quark masses are furthermore deduced from these ''family Lagrangians.'' Using the relations between the parameters of the different charge sectors, it is also possible to ''derive'' the quark mass spectra from the (charged) leptonic mass spectrum

Size dependence in tunneling spectra of PbSe quantum-dot arrays.

Science.gov (United States)

Ou, Y C; Cheng, S F; Jian, W B

2009-07-15

Interdot Coulomb interactions and collective Coulomb blockade were theoretically argued to be a newly important topic, and experimentally identified in semiconductor quantum dots, formed in the gate confined two-dimensional electron gas system. Developments of cluster science and colloidal synthesis accelerated the studies of electron transport in colloidal nanocrystal or quantum-dot solids. To study the interdot coupling, various sizes of two-dimensional arrays of colloidal PbSe quantum dots are self-assembled on flat gold surfaces for scanning tunneling microscopy and scanning tunneling spectroscopy measurements at both room and liquid-nitrogen temperatures. The tip-to-array, array-to-substrate, and interdot capacitances are evaluated and the tunneling spectra of quantum-dot arrays are analyzed by the theory of collective Coulomb blockade. The current-voltage of PbSe quantum-dot arrays conforms properly to a scaling power law function. In this study, the dependence of tunneling spectra on the sizes (numbers of quantum dots) of arrays is reported and the capacitive coupling between quantum dots in the arrays is explored.

Effect of concentration and pH on the surface-enhanced Raman scattering of captopril on nano-colloidal silver surface

Science.gov (United States)

Gao, Junxiang; Gu, Huaimin; Liu, Fangfang; Dong, Xiao; Xie, Min; Hu, Yongjun

2011-07-01

In this report, Raman and surface-enhanced Raman scattering (SERS) spectra of captopril are studied in detail. Herein, the Raman bands are assigned by the density functional theory (DFT) calculations and potential energy distributions (PED) based on internal coordinates of the molecule, which are found to be in good agree with the experimental values. Furthermore, the concentration and pH dependence of the SERS intensity of the molecule is discussed. By analyzing the intensities variation of SERS bands of the different concentrations of captopril solution, it can be concluded that the molecules orientation adsorbed on the silver nanoparticles surface change with the change of the concentrations. The variation of SERS spectra of captopril with the change of pH suggests that the interaction among the adsorbates with Ag cluster depend on the protonated state of the adsorbate and the aggregation of silver nanoparticles.

Differential dpa calculations with SPECTRA-PKA

Science.gov (United States)

Gilbert, M. R.; Sublet, J.-Ch.

2018-06-01

The processing code SPECTRA-PKA produces energy spectra of primary atomic recoil events (or primary knock-on atoms, PKAs) for any material composition exposed to an irradiation spectrum. Such evaluations are vital inputs for simulations aimed at understanding the evolution of damage in irradiated material, which is generated in cascade displacement events initiated by PKAs. These PKA spectra present the full complexity of the input (to SPECTRA-PKA) nuclear data-library evaluations of recoil events. However, the commonly used displacements per atom (dpa) measure, which is an integral measure over all possible recoil events of the displacement damage dose, is still widely used and has many useful applications - as both a comparative and correlative quantity. This paper describes the methodology employed that allows the SPECTRA-PKA code to evaluate dpa rates using the energy-dependent recoil (PKA) cross section data used for the PKA distributions. This avoids the need for integral displacement kerma cross sections and also provides new insight into the relative importance of different reaction channels (and associated different daughter residual and emitted particles) to the total integrated dpa damage dose. Results are presented for Fe, Ni, W, and SS316. Fusion dpa rates are compared to those in fission, highlighting the increased contribution to damage creation in the former from high-energy threshold reactions.

Bulk photovoltaic effect in an organi c polar crystal

NARCIS (Netherlands)

Vijayaraghavan, R.K.; Meskers, S.C.J.; Abdul Rahim, M.; Das, S.

2014-01-01

Organic polar crystals from the donor–acceptor substituted 1,4-diphenybutadiene 1 can generate a short-circuit photocurrent and a photovoltage upon illumination with near UV light. The photocurrent and photovoltage are attributed to a bulk photovoltaic effect. The bulk photovoltaic effect has been

NLTE ANALYSIS OF HIGH-RESOLUTION H -BAND SPECTRA. I. NEUTRAL SILICON

Energy Technology Data Exchange (ETDEWEB)

Zhang, Junbo; Shi, Jianrong; Liu, Chao [Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, A20 Datun Road, Chaoyang District, Beijing 100012 (China); Pan, Kaike [Apache Point Observatory and New Mexico State University, P.O. Box 59, Sunspot, NM, 88349-0059 (United States); Prieto, Carlos Allende, E-mail: sjr@bao.ac.cn [Instituto de Astrofísica de Canarias, E-38205 La Laguna, Tenerife (Spain)

2016-12-20

We investigated the reliability of our silicon atomic model and the influence of non-local thermodynamical equilibrium (NLTE) on the formation of neutral silicon (Si i) lines in the near-infrared (near-IR) H -band. We derived the differential Si abundances for 13 sample stars with high-resolution H -band spectra from the Apache Point Observatory Galactic Evolution Experiment (APOGEE), as well as from optical spectra, both under local thermodynamical equilibrium (LTE) and NLTE conditions. We found that the differences between the Si abundances derived from the H -band and from optical lines for the same stars are less than 0.1 dex when the NLTE effects are included, and that NLTE reduces the line-to-line scatter in the H -band spectra for most sample stars. These results suggest that our Si atomic model is appropriate for studying the formation of H -band Si lines. Our calculations show that the NLTE corrections of the Si i H -band lines are negative, i.e., the final Si abundances will be overestimated in LTE. The corrections for strong lines depend on surface gravity, and tend to be larger for giants, reaching ∼−0.2 dex in our sample, and up to ∼−0.4 dex in extreme cases of APOGEE targets. Thus, the NLTE effects should be included in deriving silicon abundances from H -band Si i lines, especially for the cases where only strong lines are available.

NEW LUMINOUS ON SPECTRA FROM THE GALACTIC O-STAR SPECTROSCOPIC SURVEY

Energy Technology Data Exchange (ETDEWEB)

Walborn, Nolan R. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Morrell, Nidia I. [Las Campanas Observatory, Carnegie Observatories, Casilla 601, La Serena (Chile); Barbá, Rodolfo H. [Departamento de Física y Astronomía, Universidad de La Serena, Cisternas 1200 Norte, La Serena (Chile); Sota, Alfredo, E-mail: walborn@stsci.edu, E-mail: nmorrell@lco.cl, E-mail: rbarba@dfuls.cl, E-mail: sota@iaa.es [Instituto de Astrofísica de Andalucía—CSIC, Glorieta de la Astronomía s/n, E-18008 Granada (Spain)

2016-04-15

Two new ON supergiant spectra (bringing the total known to seven) and one new ONn giant (total of this class now eight) are presented; they have been discovered by the Galactic O-Star Spectroscopic Survey. These rare objects represent extremes in the mixing of CNO-cycled material to the surfaces of evolved, late-O stars, by uncertain mechanisms in the first category but likely by rotation in the second. The two supergiants are at the hot edge of the class, which is a selection effect from the behavior of defining N iii and C iii absorption blends, related to the tendency toward emission (Of effect) in the former. An additional N/C criterion first proposed by Bisiacchi et al. is discussed as a means to alleviate that effect, and it is relevant to the two new objects. The entire ON supergiant class is discussed; they display a fascinating diversity of detail undoubtedly related to the complexities of their extended atmospheres and winds that are sensitive to small differences in physical parameters, as well as to binary effects in some cases. Serendipitously, we have found significant variability in the spectrum of a little-known hypergiant with normal N, C spectra selected as a comparison for the anomalous objects. In contrast to the supergiants, the ONn spectra are virtual (nitrogen)-carbon copies of one another except for the degrees of line broadening, which emphasizes their probable unique origin and hence amenability to definitive astrophysical interpretation.

The spanwise spectra in wall-bounded turbulence

Science.gov (United States)

Wang, Hong-Ping; Wang, Shi-Zhao; He, Guo-Wei

2018-06-01

The pre-multiplied spanwise energy spectra of streamwise velocity fluctuations are investigated in this paper. Two distinct spectral peaks in the spanwise spectra are observed in low-Reynolds-number wall-bounded turbulence. The spectra are calculated from direct numerical simulation (DNS) of turbulent channel flows and zero-pressure-gradient boundary layer flows. These two peaks locate in the near-wall and outer regions and are referred to as the inner peak and the outer peak, respectively. This result implies that the streamwise velocity fluctuations can be separated into large and small scales in the spanwise direction even though the friction Reynolds number Re_τ can be as low as 1000. The properties of the inner and outer peaks in the spanwise spectra are analyzed. The locations of the inner peak are invariant over a range of Reynolds numbers. However, the locations of the outer peak are associated with the Reynolds number, which are much higher than those of the outer peak of the pre-multiplied streamwise energy spectra of the streamwise velocity.

Seismic spectra of events at regional distances

International Nuclear Information System (INIS)

Springer, D.L.; Denny, M.D.

1976-01-01

About 40 underground nuclear explosions detonated at the Nevada Test Site (NTS) were chosen for analysis of their spectra and any relationships they might have to source parameters such as yield, depth of burial, etc. The sample covered a large yield range (less than 20 kt to greater than 1 Mt). Broadband (0.05 to 20 Hz) data recorded by the four-station seismic network operated by Lawrence Livermore Laboratory were analyzed in a search for unusual explosion signatures in their spectra. Long time windows (total wave train) as well as shorter windows (for instance, P/sub n/) were used as input to calculate the spectra. Much variation in the spectra of the long windows is typical although some gross features are similar, such as a dominant peak in the microseismic window. The variation is such that selection of corner frequencies is impractical and yield scaling could not be determined. Spectra for one NTS earthquake showed more energy in the short periods (less than 1 sec) as well as in the long periods (greater than 8 sec) compared to those for NTS explosions

Sequential Analysis of Gamma Spectra

International Nuclear Information System (INIS)

Fayez-Hassan, M.; Hella, Kh.M.

2009-01-01

This work shows how easy one can deal with a huge number of gamma spectra. The method can be used for radiation monitoring. It is based on the macro feature of the windows XP connected to QBASIC software. The routine was used usefully in generating accurate results free from human errors. One hundred measured gamma spectra were fully analyzed in 10 minutes using our fast and automated method controlling the Genie 2000 gamma acquisition analysis software.

Skyshine spectra of gamma rays

International Nuclear Information System (INIS)

Swarup, Janardan

1980-01-01

A study of the spectra of gamma photons back-scattered in vertical direction by infinite air above ground (skyshine) is presented. The source for these measurements is a 650 Ci Cobalt-60 point-source and the skyshine spectra are reported for distances from 150 m to 325 m from the source, measured with a 5 cm x 5 cm NaI(Tl) detector collimated with collimators of 12 mm and 20 mm diameter and 5 cm length. These continuous spectra are unfolded with Gold's iterative technique. The photon-spectra so obtained have a distinct line at 72 keV due to multiply-scattered photons. This is an energy where photoelectric and Compton cross-sections for multiply-scattered photons balance each other. The intensity of the line(I) decreases exponentially with distance (d) from the source obeying a relation of the type I = Isub(o)esup(-μd) where μ is called as ''Multiply-Scatter Coefficient'', a constant of the medium which is air in these measurements. This relationship is explained in terms of a halo around the source comprising of multiply-scattered gamma photons, Isub(0) being the intensity of these scattered photons at the location of cobalt-source. A fraction called as ''Back-scattered Fraction'', the ratio of Isub(0) to the number of original photons from the cobalt-source entering the infinite air, is also calculated. It is shown that with a properly calibrated detector system, this fraction can be used to determine the strength of a large gamma source, viz. a nuclear explosion in air, and for mineral prospecting. These conclusions are general and can be applied to any other infinite medium. Some forward-scatter (transmission) spectra of cobalt-60 source through 10 cm of Pb and 2.5 cm of Al are also reported. (auth.)

Solid surfaces : some theoretical aspects

International Nuclear Information System (INIS)

Das, M.P.

1978-01-01

An appraisal of the current situation concerning some of the theoretical aspects of solid surfaces is presented. First of all the characterization of the surfaces that involves the surface geometry and atomic composition for both the clean and adsorbed surfaces is discussed. Under this, the methods for determining the surface structure (such as low energy electron diffraction, field electron and field ion microscopy, photo emission spectroscopy and atomic scattering) and methods for determining the surface composition by the Auger electron spectroscopy are outlined. In the second part, emphasis is on the electronic structure of the clean and adsorbed surfaces. The measurements of ultra-violet and X-ray photo electron spectra are shown to yield the information about the surface electronic structure. In this context the many body effects such as, shake-up and relaxation energy etc. are discussed. Finally the status of the theory in relation to the experiments on angular resolved and polarization dependent photo emission are presented. (auth.)

Mesoporous TiO2 Micro-Nanometer Composite Structure: Synthesis, Optoelectric Properties, and Photocatalytic Selectivity

Directory of Open Access Journals (Sweden)

Kun Liu

2012-01-01

Full Text Available Mesoporous anatase TiO2 micro-nanometer composite structure was synthesized by solvothermal method at 180°C, followed by calcination at 400°C for 2 h. The as-prepared TiO2 was characterized by X-ray diffraction (XRD, scanning electron microscope (SEM, transmission electron microscope (TEM, and Fourier transform infrared spectrum (FT-IR. The specific surface area and pore size distribution were obtained from N2 adsorption-desorption isotherm, and the optoelectric property of the mesoporous TiO2 was studied by UV-Vis absorption spectrum and surface photovoltage spectra (SPS. The photocatalytic activity was evaluated by photodegradation of sole rhodamine B (RhB and sole phenol aqueous solutions under simulated sunlight irradiation and compared with that of Degussa P-25 (P25 under the same conditions. The photodegradation preference of this mesoporous TiO2 was also investigated for an RhB-phenol mixed solution. The results show that the TiO2 composite structure consists of microspheres (∼0.5–2 μm in diameter and irregular aggregates (several hundred nanometers with rough surfaces and the average primary particle size is 10.2 nm. The photodegradation activities of this mesoporous TiO2 on both RhB and phenol solutions are higher than those of P25. Moreover, this as-prepared TiO2 exhibits photodegradation preference on RhB in the RhB-phenol mixture solution.

Hyperthermal surface ionization mass spectrometry of organic molecules: monoterpenes

International Nuclear Information System (INIS)

Kishi, Hiroshi; Fujii, Toshihiro.

1997-01-01

This paper describes an experimental study on the influence of kinetic energy of fast monoterpene molecules on the surface ionization efficiency and on the mass spectral patterns, using rhenium oxide (ReO 2 ) surface. Molecular kinetic energy, given to the molecules through the acceleration in the seeded supersonic molecular beam, ranged from 1 to 10 eV. Hyperthermal surface ionization mass spectra (HSIMS) were taken for various incident kinetic energies and surface temperatures. The observed mass spectra were interpreted in a purely empirical way, by means of evidence from the previous investigations, and they were compared with conventional EI techniques and with the thermal energy surface ionization technique (SIOMS; Surface Ionization Organic Mass Spectrometry). Ionization efficiency (β) was also studied. Under hyperthermal surface ionization (HSI) conditions, many kinds of fragment ions, including quite abundant odd electron ions (OE +· ) are observed. HSIMS patterns of monoterpenes are different among 6-isomers, contrary to those of SIOMS and EIMS, where very similar patterns for isomers are observed. HSIMS patterns are strongly dependent on the molecular kinetic energies. The surface temperature does not affect much the spectral patterns, but it controls the total amount of ion formation. We conclude from these mass spectral findings, HSI-mechanism contains an impulsive process of ion formation, followed by the fragmentation process as a results of the internal energies acquired through the collision processes. (author)

Algorithms for the rapid simulation of Rutherford backscattering spectra

Energy Technology Data Exchange (ETDEWEB)

Doolittle, L.R.

1985-06-01

A computer program which simulates Rutherford backscattering spectra is currently in use at Cornell University and other institutions. Straggling and detector resolution are among the effects included. Samples are considered to be made up of a finite number of layers, each with uniform composition. The emphasis in the mathematics is on accuracy beyond that of iterated surface approximation methods. Thicker layers can thus be analyzed without a net loss in accuracy. The mathematical description of the sample can then have fewer layers, and fewer calculations are required. This paper provides estimates of the number of arithmetic operations used by the program for any simulation to demonstrate the tradeoffs between accuracy, computation time, and algorithm sophistication.

Algorithms for the rapid simulation of Rutherford backscattering spectra

International Nuclear Information System (INIS)

Doolittle, L.R.

1985-01-01

A computer program which simulates Rutherford backscattering spectra is currently in use at Cornell University and other institutions. Straggling and detector resolution are among the effects included. Samples are considered to be made up of a finite number of layers, each with uniform composition. The emphasis in the mathematics is on accuracy beyond that of iterated surface approximation methods. Thicker layers can thus be analyzed without a net loss in accuracy. The mathematical description of the sample can then have fewer layers, and fewer calculations are required. This paper provides estimates of the number of arithmetic operations used by the program for any simulation to demonstrate the tradeoffs between accuracy, computation time, and algorithm sophistication. (orig.)

Identifying Broadband Rotational Spectra with Neural Networks

Science.gov (United States)

Zaleski, Daniel P.; Prozument, Kirill

2017-06-01

A typical broadband rotational spectrum may contain several thousand observable transitions, spanning many species. Identifying the individual spectra, particularly when the dynamic range reaches 1,000:1 or even 10,000:1, can be challenging. One approach is to apply automated fitting routines. In this approach, combinations of 3 transitions can be created to form a "triple", which allows fitting of the A, B, and C rotational constants in a Watson-type Hamiltonian. On a standard desktop computer, with a target molecule of interest, a typical AUTOFIT routine takes 2-12 hours depending on the spectral density. A new approach is to utilize machine learning to train a computer to recognize the patterns (frequency spacing and relative intensities) inherit in rotational spectra and to identify the individual spectra in a raw broadband rotational spectrum. Here, recurrent neural networks have been trained to identify different types of rotational spectra and classify them accordingly. Furthermore, early results in applying convolutional neural networks for spectral object recognition in broadband rotational spectra appear promising. Perez et al. "Broadband Fourier transform rotational spectroscopy for structure determination: The water heptamer." Chem. Phys. Lett., 2013, 571, 1-15. Seifert et al. "AUTOFIT, an Automated Fitting Tool for Broadband Rotational Spectra, and Applications to 1-Hexanal." J. Mol. Spectrosc., 2015, 312, 13-21. Bishop. "Neural networks for pattern recognition." Oxford university press, 1995.

Surface plasma resonance enhanced photocurrent generation in NiO photoanode based solar cells

Energy Technology Data Exchange (ETDEWEB)

Wang, Zhong; Cui, Jin [Michael Grätzel Center for Mesoscopic Solar Cells, Wuhan National Laboratory for Optoelectronics Department, Huazhong University of Science and Technology, 1037 Luoyu Road, Wuhan 430074, Hubei (China); Li, Junpeng [State Key Laboratory of Advanced Technologies for Comprehensive Utilization of Platinum Metals, Kunming Institute of Precious Metals, Kunming 650106 (China); Cao, Kun; Yuan, Shuai [Michael Grätzel Center for Mesoscopic Solar Cells, Wuhan National Laboratory for Optoelectronics Department, Huazhong University of Science and Technology, 1037 Luoyu Road, Wuhan 430074, Hubei (China); Cheng, Yibing [Michael Grätzel Center for Mesoscopic Solar Cells, Wuhan National Laboratory for Optoelectronics Department, Huazhong University of Science and Technology, 1037 Luoyu Road, Wuhan 430074, Hubei (China); Department of Materials Engineering, Monash University, Melbourne, Victoria 3800 (Australia); Wang, Mingkui, E-mail: mingkui.wang@mail.hust.edu.cn [Michael Grätzel Center for Mesoscopic Solar Cells, Wuhan National Laboratory for Optoelectronics Department, Huazhong University of Science and Technology, 1037 Luoyu Road, Wuhan 430074, Hubei (China)

2015-09-15

Highlights: • SPR effect from Au-nanostructures was first investigated in NiO-based solar cells. • Enhanced photocurrent generation was observed in p-DSC and perovskite solar cell. • Au-nanorods SPR effect induced charge kinetics were investigated. - Abstract: Surface plasma resonance (SPR) effect has been demonstrated to improve solar cell performance. This work reports on the SPR effect from Au nanorod@SiO{sub 2} on p-type dye-sensitized solar cells. Au nanorod@SiO{sub 2} works as an antenna to transform photons with long wavelength into electric field followed by an enhanced excitation of dye. The devices using the NiO electrode containing Au nanorod@SiO{sub 2} shows overall power conversion efficiencies of about 0.2% in combination with I{sup −}/I{sub 3}{sup −} electrolyte, and 0.29% with T{sup −}/T{sub 2} electrolyte, which are superior to those without adding Au nanorods. Detailed investigation including spectroscopy and transient photovoltage decay measurements reveals that plasma effect of Au nanorod@SiO{sub 2} contribute to charge injection efficiency, and thus on the photocurrent. The effect of Au NRs can be further extended to the inverted planar perovskite solar cells, showing obviously improvement in photocurrent.

One pot synthesis of Ag nanoparticle modified ZnO microspheres in ethylene glycol medium and their enhanced photocatalytic performance

International Nuclear Information System (INIS)

Tian Chungui; Li Wei; Pan Kai; Zhang Qi; Tian Guohui; Zhou Wei; Fu Honggang

2010-01-01

Ag nanoparticles (NPs) modified ZnO microspheres (Ag/ZnO microspheres) were prepared by a facile one pot strategy in ethylene glycol (EG) medium. The EG played two important roles in the synthesis: it could act as a reaction media for the formation of ZnO and reduce Ag + to Ag 0 . A series of the characterizations indicated the successful combination of Ag NPs with ZnO microspheres. It was shown that Ag modification could greatly enhance the photocatalytic efficiency of ZnO microspheres by taking the photodegradation of Rhodamine B as a model reaction. With appropriate ratio of Ag and ZnO, Ag/ZnO microspheres showed the better photocatalytic performance than commercial Degussa P-25 TiO 2 . Photoluminescence and surface photovoltage spectra demonstrated that Ag modification could effectively inhibit the recombination of the photoinduced electron and holes of ZnO. This is responsible for the higher photocatalytic activity of Ag/ZnO composites. -- Graphical abstract: A 'one-pot' strategy was developed for preparing the Ag/ZnO microspheres in ethylene glycol. The composites exhibited superior photocatalytic performance for photodegradation of Rhodamine B dye in water. Display Omitted

Enhanced visible-light activities for PEC water reduction of CuO nanoplates by coupling with anatase TiO2 and mechanism

International Nuclear Information System (INIS)

Li, Zhijun; Qu, Yang; He, Guangwen; Humayun, Muhammad; Chen, Shuangying; Jing, Liqiang

2015-01-01

Graphical abstract: - Highlights: • CuO nanoplates were successfully prepared as photocathodes for PEC water reduction. • Visible-light activity for PEC water reduction is improved after coupling with TiO 2 . • Improved PEC performance is attributed to the enhanced visible-excited charge separation. • Enhanced charge separation results from high-energy electron transfer from CuO to TiO 2 . - Abstract: CuO nanoplates were prepared by a feasible hydrothermal method, and then utilized as photocathodes for photoelectrochemical (PEC) water reduction in a neutral medium under visible-light irradiation. It is clearly demonstrated that the visible-light activities of the resulting nanoplates for PEC water reduction could be greatly improved after coupling with a proper amount of nanocrystalline anatase TiO 2 . This is attributed to the enhanced charge separation in the fabricated TiO 2 /CuO nanoplate composites mainly based on the atmosphere-controlled steady-state surface photovoltage spectra. Moreover, it is suggested that the enhanced charge separation resulted from the transfer of visible-light-excited high-energy electrons from CuO to TiO 2 as confirmed from the single-wavelength PEC behavior

A correlation between the defect states and yellow luminescence in AlGaN/GaN heterostructures

Science.gov (United States)

Jana, Dipankar; Sharma, T. K.

2017-07-01

AlGaN/GaN heterostructures are investigated by performing complementary spectroscopic measurements under novel experimental configurations. Distinct features related to the band edge of AlGaN and GaN layers are clearly observed in surface photovoltage spectroscopy (SPS) spectra. A few more SPS features, which are associated with defects in GaN, are also identified by performing the pump-probe SPS measurements. SPS results are strongly corroborated by the complementary photoluminescence and photoluminescence excitation (PLE) measurements. A correlation between the defect assisted SPS features and yellow luminescence (YL) peak is established by performing pump-probe SPS and PLE measurements. It is found that CN-ON donor complex is responsible for the generation of YL peak in our sample. Further, the deep trap states are found to be present throughout the entire GaN epilayer. It is also noticed that the deep trap states lying at the GaN/Fe-GaN interface make a strong contribution to the YL feature. A phenomenological model is proposed to explain the intensity dependence of the YL feature and the corresponding SPS features in a pump-probe configuration, where a reasonable agreement between the numerical simulations and experimental results is achieved.

SERS and in situ SERS spectroscopy of riboflavin adsorbed on silver, gold and copper substrates. Elucidation of variability of surface orientation based on both experimental and theoretical approach

Science.gov (United States)

Dendisová-Vyškovská, Marcela; Kokaislová, Alžběta; Ončák, Milan; Matějka, Pavel

2013-04-01

Surface-enhanced Raman scattering and in situ surface-enhanced Raman scattering spectra have been collected to study influences of (i) used metal and (ii) applied electrode potential on orientation of adsorbed riboflavin molecules. Special in situ SERS spectroelectrochemical cell was used to obtain in situ SERS spectra of riboflavin adsorbed on silver, gold and copper nanostructured surfaces. Varying electrode potential was applied in discrete steps forming a cycle from positive values to negative and backward. Observed spectral features in in situ SERS spectra, measured at alternate potentials, have been changing very significantly and the spectra have been compared with SERS spectra of riboflavin measured ex situ. Raman spectra of single riboflavin molecule in the vicinity to metal (Ag, Au and Cu) clusters have been calculated for different mutual positions. The results demonstrate significant changes of bands intensities which can be correlated with experimental spectra measured at different potentials. Thus, the orientation of riboflavin molecules adsorbed on metal surfaces can be elucidated. It is influenced definitely by the value of applied potential. Furthermore, the riboflavin adsorption orientation on the surface depends on the used metal. Adsorption geometries on the copper substrates are more diverse in comparison with the orientations on silver and gold substrates.

Sum-frequency spectroscopic studies: I. Surface melting of ice, II. Surface alignment of polymers

Energy Technology Data Exchange (ETDEWEB)

Wei, Xing [Univ. of California, Berkeley, CA (United States)

2000-01-01

Surface vibrational spectroscopy via infrared-visible sum-frequency generation (SFG) has been established as a useful tool to study the structures of different kinds of surfaces and interfaces. This technique was used to study the (0001) face of hexagonal ice (Ih). SFG spectra in the O-H stretch frequency range were obtained at various sample temperatures. For the vapor(air)/ice interface, the degree of orientational order of the dangling OH bonds at the surface was measured as a function of temperature. Disordering sets in around 200 K and increases dramatically with temperature, which is strong evidence of surface melting of ice. For the other ice interfaces (silica/OTS/ice and silica/ice), a similar temperature dependence of the hydrogen bonded OH stretch peak was observed; the free OH stretch mode, however, appears to be different from that of the vapor (air)/ice interface due to interactions at the interfaces. The technique was also used to measure the orientational distributions of the polymer chains on a rubbed polyvinyl alcohol surface. Results show that the polymer chains at the surface appear to be well aligned by rubbing, and the adsorbed liquid crystal molecules are aligned, in turn, by the surface polymer chains. A strong correlation exists between the orientational distributions of the polymer chains and the liquid crystal molecules, indicating that the surface-induced bulk alignment of a liquid crystal film by rubbed polymer surfaces is via an orientational epitaxy-like mechanism. This thesis also contains studies on some related issues that are crucial to the above applications. An experiment was designed to measure SFG spectra in both reflection and transmission. The result confirms that SFG in reflection is generally dominated by the surface contribution. Another issue is the motional effect due to fast orientational motion of molecules at a surface or interface. Calculations show that the effect is significant if the molecular orientation varies

Energetic Proton Spectra Measured by the Van Allen Probes

Science.gov (United States)

Summers, Danny; Shi, Run; Engebretson, Mark J.; Oksavik, Kjellmar; Manweiler, Jerry W.; Mitchell, Donald G.

2017-10-01

We test the hypothesis that pitch angle scattering by electromagnetic ion cyclotron (EMIC) waves can limit ring current proton fluxes. For two chosen magnetic storms, during 17-20 March 2013 and 17-20 March 2015, we measure proton energy spectra in the region 3 ≤ L ≤ 6 using the RBSPICE-B instrument on the Van Allen Probes. The most intense proton spectra are observed to occur during the recovery periods of the respective storms. Using proton precipitation data from the POES (NOAA and MetOp) spacecraft, we deduce that EMIC wave action was prevalent at the times and L-shell locations of the most intense proton spectra. We calculate limiting ring current proton energy spectra from recently developed theory. Comparisons between the observed proton energy spectra and the theoretical limiting spectra show reasonable agreement. We conclude that the measurements of the most intense proton spectra are consistent with self-limiting by EMIC wave scattering.

SpectraPLOT, Visualization Package with a User-Friendly Graphical Interface

Science.gov (United States)

Sebald, James; Macfarlane, Joseph; Golovkin, Igor

2017-10-01

SPECT3D is a collisional-radiative spectral analysis package designed to compute detailed emission, absorption, or x-ray scattering spectra, filtered images, XRD signals, and other synthetic diagnostics. The spectra and images are computed for virtual detectors by post-processing the results of hydrodynamics simulations in 1D, 2D, and 3D geometries. SPECT3D can account for a variety of instrumental response effects so that direct comparisons between simulations and experimental measurements can be made. SpectraPLOT is a user-friendly graphical interface for viewing a wide variety of results from SPECT3D simulations, and applying various instrumental effects to the simulated images and spectra. We will present SpectraPLOT's ability to display a variety of data, including spectra, images, light curves, streaked spectra, space-resolved spectra, and drilldown plasma property plots, for an argon-doped capsule implosion experiment example. Future SpectraPLOT features and enhancements will also be discussed.

Surface characterization of polymethylmetacrylate bombarded by charged water droplets

International Nuclear Information System (INIS)

Hiraoka, Kenzo; Takaishi, Riou; Asakawa, Daiki; Sakai, Yuji; Iijima, Yoshitoki

2009-01-01

The electrospray droplet impact (EDI), in which the charged electrospray water droplets are introduced in vacuum, accelerated, and allowed to impact the sample, is applied to polymethylmetacrylate (PMMA). The secondary ions generated were measured by an orthogonal time-of-flight mass spectrometer. In EDI mass spectra for PMMA, fragment ions originating from PMMA could not be detected. This is due to the fact that the proton affinities of fragments formed from PMMA are smaller than those from acetic acid contained in the charged droplet. The x-ray photoelectron spectroscopy spectra of PMMA irradiated by water droplets did not change with prolonged cluster irradiation, i.e., EDI is capable of shallow surface etching for PMMA with a little damage of the sample underneath the surface.

Monte Carlo simulation of x-ray spectra in mammography

Energy Technology Data Exchange (ETDEWEB)

Ng, K.P. [Department of Optometry and Radiography, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong (China). E-mail: benngkp at netvigator.com; Kwok, C.S.; Ng, K.P.; Tang, F.H. [Department of Optometry and Radiography, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong (China)

2000-05-01

A model for generating x-ray spectra in mammography is presented. This model used the ITS version 3 Monte Carlo code for simulating the radiation transport. Various target/filter combinations such as tungsten/aluminium, molybdenum/molybdenum, molybdenum/rhodium and rhodium/rhodium were used in the simulation. Both bremsstrahlung and characteristic x-ray production were included in the model. The simulated x-ray emission spectra were compared with two sets of spectra, those of Boone et al (1997 Med. Phys. 24 1863-74) and IPEM report 78. The {chi}{sup 2} test was used for the overall goodness of fit of the spectral data. There is good agreement between the simulated x-ray spectra and the comparison spectra as the test yielded a probability value of nearly 1. When the transmitted x-ray spectra for specific target/filter combinations were generated and compared with a measured molybdenum/rhodium spectrum and spectra generated in IPEM report 78, close agreement is also observed. This was demonstrated by the probability value for the {chi}{sup 2} test being almost 1 for all the cases. However, minor differences between the simulated spectra and the 'standard' ones are observed. (author)

Monte Carlo simulation of x-ray spectra in mammography

International Nuclear Information System (INIS)

Ng, K.P.

2000-01-01