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Chemical bonding and composition of silicon nitride films prepared by inductively coupled plasma chemical vapor deposition

Matsuoka, Masao; Isotani, Sadao; SUCASAIRE, W.; ZAMBOM, L. S.; OGATA, K.
Fonte: ELSEVIER SCIENCE SA Publicador: ELSEVIER SCIENCE SA
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
46.44%
Thin silicon nitride films were prepared at 350 degrees C by inductively coupled plasma chemical vapor deposition on Si(100) substrates under different NH(3)/SiH(4) or N(2)/SiH(4) gas mixture. The chemical composition and bonding structure of the deposited films were investigated as a function of the process parameters, such as the gas flow ratio NH(3)/SiH(4) or N(2)/SiH(4) and the RF power, using X-ray photoelectron spectroscopy (XPS). The gas flow ratio was 1.4, 4.3, 7.2 or 9.5 and the RF power, 50 or 100 W. Decomposition results of Si 2p XPS spectra indicated the presence of bulk Si, under-stoichiometric nitride, stoichiometric nitride Si(3)N(4), oxynitride SiN(x)O(y), and stoichiometric oxide SiO(2), and the amounts of these compounds were strongly influenced by the two process parameters. These results were consistent with those obtained from N 1s XPS spectra. The chemical composition ratio N/Si in the film increased with increasing the gas flow ratio until the gas flow ratio reached 4.3, reflecting the high reactivity of nitrogen, and stayed almost constant for further increase in gas flow ratio, the excess nitrogen being rejected from the growing film. A considerable and unexpected incorporation of contaminant oxygen and carbon into the depositing film was observed and attributed to their high chemical reactivity. (C) 2010 Elsevier B.V. All rights reserved.

X-ray photoelectron spectroscopy analysis of zirconium nitride-like films prepared on Si(100) substrates by ion beam assisted deposition

Matsuoka, Masao; Isotani, Sadao; SUCASAIRE, W.; KURATANI, N.; OGATA, K.
Fonte: ELSEVIER SCIENCE SA Publicador: ELSEVIER SCIENCE SA
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
66.44%
Thin zirconium nitride films were prepared on Si(l 00) substrates at room temperature by ion beam assisted deposition with a 2 keV nitrogen ion beam. Arrival rate ratios ARR(N/Zr) used were 0.19, 0.39, 0.92, and 1.86. The chemical composition and bonding structure of the films were analyzed with X-ray photoelectron spectroscopy (XPS). Deconvolution results for Zr 3d, Zr 3p(3/2), N 1s, O 1s, and C 1s XPS spectra indicated self-consistently the presence of metal Zr-0, nitride ZrN, oxide ZrO2, oxymnide Zr2N2O, and carbide ZrC phases, and the amounts of these compounds were influenced by ARR(N/Zr). The chemical composition ratio N/Zr in the film increased with increasing ARR(N/Zr) until ARR(N/Zr) reached 0.92, reflecting the high reactivity of nitrogen in the ion beam, and stayed almost constant for ARR(N/Zr) >= 1, the excess nitrogen being rejected from the growing film. A considerable incorporation of contaminant oxygen and carbon into the depositing film was attributed to the getter effect of zirconium. (C) 2007 Elsevier B.V. All rights reserved.

Quantification of Short and Medium Range Order in Mixed Network Former Glasses of the System GeO2-NaPO3: A Combined NMR and X-ray Photoelectron Spectroscopy Study

Ren, Jinjun; Eckert, Hellmut
Fonte: AMER CHEMICAL SOC; WASHINGTON Publicador: AMER CHEMICAL SOC; WASHINGTON
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
56.39%
Glasses in the system xGeO(2)-(1-x)NaPO3 (0 <= x <= 0.50) were prepared by conventional melting quenching and characterized by thermal analysis, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and P-31 nuclear magnetic resonance (MAS NMR) techniques. The deconvolution of the latter spectra was aided by homonuclear J-resolved and refocused INADEQUATE techniques. The combined analyses of P-31 MAS NMR and O-1s XPS lineshapes, taking charge and mass balance considerations into account, yield the detailed quantitative speciations of the phosphorus, germanium, and oxygen atoms and their respective connectivities. An internally consistent description is possible without invoking the formation of higher-coordinated germanium species in these glasses, in agreement with experimental evidence in the literature. The structure can be regarded, to a first approximation, as a network consisting of P-(2) and P-(3) tetrahedra linked via four-coordinate germanium. As implied by the appearance of P-(3) units, there is a moderate extent of network modifier sharing between phosphate and germanate network formers, as expressed by the formal melt reaction P-(2) + Ge-(4) -> P-(3) + Ge-(3). The equilibrium constant of this reaction is estimated as K = 0.52 +/- 0.11...

Corrosion protection of fluorzirconate glasses coated by a layer of surface modified tin oxide nanoparticles

Hammer, P.; Rizzato, A. P.; Alvarez, F.; Landers, R.; Pulcinelli, S. H.; Santilli, C. V.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Conferência ou Objeto de Conferência Formato: 94-98
ENG
Relevância na Pesquisa
46.44%
The protection efficiency against water corrosion of fluorozirconate glass, ZBLAN, dip-coated by nanocrystalline tin oxide film containing the organic molecule Tiron® was investigated by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The chemical bonding structure of the surface region and morphology were studied before and after two water exposure periods of 5 and 30 min. The results of the analysis for the as-grown sample revealed a SnO1.6 phase containing carbon and sulfur, related to Tiron®, and traces of elements related to ZBLAN (Zr, F, Ba). This fact and the clear evidence of the presence of tin oxifluoride specie (SnOxF y) indicates a diffusion of the glass components into the porous coating. After water exposure, the increase of the oxygen concentration accompanied by a strong increase of Zr, F, Ba and Na content is interpreted as filling of the nanopores of the film by glass compounds. The formation of a compact protective layer is supported by the morphological changes observed by AFM. © 2005 Elsevier B.V. All rights reserved.

Effect of experimental photopolymerized coatings on the hydrophobicity of a denture base acrylic resin and on Candida albicans adhesion

Lazarin, Andréa Azevedo; MacHado, Ana Lucia; Zamperini, Camila Andrade; Wady, Amanda Fucci; Spolidorio, Denise Madalena Palomari; Vergani, Carlos Eduardo
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 1-9
ENG
Relevância na Pesquisa
46.44%
Objective: This study investigated the effect of experimental photopolymerized coatings, containing zwitterionic or hydrophilic monomers, on the hydrophobicity of a denture base acrylic resin and on Candida albicans adhesion. Methods: Acrylic specimens were prepared with rough and smooth surfaces and were either left untreated (control) or coated with one of the following experimental coatings: 2-hydroxyethyl methacrylate (HE); 3-hydroxypropyl methacrylate (HP); and 2-trimethylammonium ethyl methacrylate chloride (T); and sulfobetaine methacrylate (S). The concentrations of these constituent monomers were 25%, 30% or 35%. Half of the specimens in each group (control and experimentals) were coated with saliva and the other half remained uncoated. The surface free energy of all specimens was measured, regardless of the experimental condition. C. albicans adhesion was evaluated for all specimens, both saliva conditioned and unconditioned. The adhesion test was performed by incubating specimens in C. albicans suspensions (1 × 10 7 cell/mL) at 37 °C for 90 min. The number of adhered yeasts were evaluated by XTT (2,3-bis[2-methoxy-4-nitro-5-sulfophenyl]-5-[{phenylamino} carbonyl]-2H-tetrazolium-hydroxide) method. Results: For rough surfaces...

Carbon nanotube-reinforced siloxane-PMMA hybrid coatings with high corrosion resistance

Hammer, P.; Dos Santos, F. C.; Cerrutti, B. M.; Pulcinelli, S. H.; Santilli, C. V.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 601-608
ENG
Relevância na Pesquisa
46.51%
Siloxane-polymethyl methacrylate hybrid films containing functionalized multiwall carbon nanotubes (CNTs) were deposited by dip-coating on carbon steel substrates from a sol prepared by radical polymerization of methyl methacrylate and 3-methacryloxy propyl-trimethoxysilane, followed by hydrolytic co-polycondensation of tetraethoxysilane. The correlation between the structural properties and corrosion protection efficiency was studied as a function of the molar ratio of nanotubes carbon to silicon, varied in the range between 0.1% and 5%. 29Si nuclear magnetic resonance and thermogravimetric measurements have shown that hybrids containing carbon nanotubes have a similar degree of polycondensation and thermal stability as the undoped matrix and exhibit and excellent adhesion to the substrate. Microscopy and X-ray photoelectron spectroscopy results revealed a very good dispersion of carbon nanotubes in the hybrid matrix and the presence of carboxylic groups allowing covalent bonding with the end-siloxane nodes. Potentiodynamic polarization curves and electrochemical impedance spectroscopy results demonstrate that CNTs containing coatings maintain the excellent corrosion protection efficiency of the hybrids, showing even a superior performance in acidic solution. The nanocomposite structure acts as efficient corrosion barrier...

Determinação estrutural da superfície de óxidos ordenados por difração de fotoelétrons: o caso de CrxOy sobre Pd(111) e SrTiO3(100); Structural determination of ordered oxide surface by photoelectron diffraction: the case CrxOy sobre Pd(111) e SrTiO3(100)

Alexandre Pancotti
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 09/12/2009 PT
Relevância na Pesquisa
46.55%
Este trabalho apresenta um estudo sobre a estrutura atômica da superfície de dois materiais com potencial para suportar nano partículas metálicas num catalisador modelo, o primeiro, Óxido de Cromo é um suporte usado comercialmente, e o segundo, SrTiO3(100) (STO) tem a característica interessante de induzir o crescimento de nano partículas de alguns metais com formatos definidos pelo tipo de tratamento térmico que o suporte recebeu. O Óxido de cromo estava na forma de filmes ordenados crescidos epitaxialmente sobre um cristal de Pd(111) enquanto que o SrTiO3 consistia de cristal dopado com Nb cortado segundo a face (100). Os filmes de óxido de cromo sobre Pd(111) foram crescidos "in-situ" na câmara de análises pela deposição de cromo metálico numa atmosfera de oxigênio (1,0.10-6 mBar) sobre o substrato aquecido (623K) o que produziu filmes com boa cristalinidade e estequiometria. Foram estudados filmes com duas estruturas diferentes: óxido de cromo com 3.5 Å de espessura que apresentava uma reconstrução tipo p(2x2) e um filme mais espesso com 12.0 Å que mostrava uma reconstrução (V3xV3)R30o, ambos determinados por LEED (Low Energy Electron Diffraction). A composição e a estrutura atômica foram determinadas por XPS (X-Ray Photoelectron Spectroscopy) e XPD (X-Ray Photoelectron Diffraction)...

Study and characterization of the ZnPc:C60/MoOx interface in organic solar cells by means of photoelectron spectroscopy

Stenta, Caterina
Fonte: Faculdade de Ciências e Tecnologia Publicador: Faculdade de Ciências e Tecnologia
Tipo: Dissertação de Mestrado
Publicado em //2013 ENG
Relevância na Pesquisa
46.57%
Dissertation to obtain the academic degree of Master in materials engineering submitted to the Faculty of science and engineering of Universidade Nova de Lisboa; The search for low cost photovoltaics has led to the use of organic materials as possible candidates to substitute silicon based solar devices. Organic materials have high absorption coe cients, allowing the use of very thin lms and low cost solution phase manufacturing techniques. Control over the electronic structure of organic/inorganic semiconductor interfaces is a key step for the development of these devices. In the present study this issue is addressed for an organic solar cell with an inverted structure: an organic absorber layer of zinc phthalocyanine: Fullerene heterojuntion, sandwiched between a front electrode of zinc oxide doped with aluminium, an intermediate bu er layer of molybdenum oxide and a silver electrode. The objective of this experimental work has been the investigation of the electronic properties of the MoOx/ZnPc:C60 interface. For this purpose photoelectron spectroscopy using di erent types of radiation has been carried out. Results will be presented on the interface analysis carried out by ultraviolet photoelectron spectroscopy (UPS) for the study of the valence electron levels and by X-ray photoelectron spectroscopy (XPS) to probe the core electron levels. Valence band o sets and work function values at MoOx/ZnPc:C60 interfaces have been characterized as a function of MoOx thickness and as a function of annealing temperature. Current-voltage characteristics (I-V) were measured as a function of annealing temperature and the optical properties of the MoOx layer were measured by transmission in the range 250-2500 nm. Near edge X-ray absorption ne structure (NEXAFS)spectroscopy was used to give additional insight into the situation of the electronic structure: spectra were taken from the electron storage ring for synchrotron radiation (BESSY II...

Facile hydrothermal synthesis and optical limiting properties of TiO2-reduced graphene oxide nanocomposites

Wang, Aijian; Yu, Wang; Fang, Yu; Song, Yinglin; Jia, Ding; Long, Lingliang; Cifuentes, Marie P.; Humphrey, Mark G.; Zhang, Chi
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica Formato: 12 pages
Relevância na Pesquisa
46.46%
TiO2/reduced graphene oxide (RGO) nanocomposites Gx (RGO titania nanocomposite, x grams tetrabutyl titanate per 0.03 g RGO, x = 0.25, 0.50, 1.00) were prepared by a hydrothermal method: graphene oxide was reduced to RGO in a 2:1 water:ethanol mixture in the presence of varying quantities of tetrabutyl titanate, which deposited as TiO2 on the RGO sheets. The nanocomposites were characterized by a combination of Fourier transform infrared spectroscopy, diffuse reflectance ultraviolet–visible spectroscopy, photoluminescence spectroscopy, Raman spectroscopy, X-ray powder diffraction, X-ray photoelectron spectroscopy and transmission electron microscopy studies. The nanocomposite G0.25 exhibits enhanced nonlinear optical properties compared to its individual components, which is ascribed to a combination of mechanisms. The role of defects and electron/energy transfer in the optical limiting performance of G0.25 was clarified with the help of Raman and photoluminescence spectroscopies. Intensity-dependent switching between reverse saturable absorption and saturable absorption behavior was observed with the G0.50 nanocomposite; Financial support from the National Natural Science Foundation of China (51432006, 50925207, 51172100), the Ministry of Science and Technology of China for the International Science Linkages Program (2009DFA50620...

Spektroskopie an Silberelektroden auf yttriumstabilisiertem Zirkondioxid; Spectroscopy on Silver Electrodes on Yttria Stabilized Zirconia

Rösch, Martin
Fonte: Universidade de Tubinga Publicador: Universidade de Tubinga
Tipo: Dissertação
DE_DE
Relevância na Pesquisa
56.55%
Ein neuer Messaufbau für in situ Spektroskopie an Elektroden auf Oxidionenleitern wurde entwickelt, der ein Referenzsystem aus porösen Platinelektroden und gasförmigem Sauerstoff besitzt und elektrochemisch gut definierte Messbedingungen ermöglicht. Die Austrittsarbeit von Silberelektroden auf yttriumstabilisiertem Zirkondioxid wurde mit Ultraviolett-Photoelektronenspektroskopie bestimmt, die chemische Natur der Oberflächenspezies mit Röntgen-Photoelektronenspektroskopie. Die Austrittsarbeit einer dichten Silberelektrode lässt sich durch elektrochemische Bildung von Oberflächendipolschichten aus Sauerstoffspezies beeinflussen. Die Eigenschaften der beobachteten Sauerstoffspezies decken sich mit den in der Literatur beschriebenen Eigenschaften von Sauerstoffspezies auf Silber, die durch Adsorption bei hohen Temperaturen erzeugt wurden. Bei Messungen an porösen Elektroden auf Ionenleitern muss der Einfluss des Elektrolyten berücksichtigt werden. Man findet eine Überlagerung der Eigenschaften der Silberelektrode und der des YSZ. Bei der Bestimmung der Austrittsarbeit poröser Elektroden mit UPS wird eine effektive Austrittsarbeit bestimmt. Die Ergebnisse der elektrochemischen Charakterisierung zeigen keine signifikanten Unterschiede im Elektrodenmechanismus zwischen dichter und poröser Elektrode. Die Erfassung des frequenzabhängigen Verhaltens von Druckschwankungen in der Analysenkammer des UHV-Systems liefert zur elektrochemischen Impedanzspektroskopie komplementäre Informationen zum Elektrodenmechanismus. Diese neue Methode wird als Oberflächenimpedanzspektroskopie bezeichnet. Die Messergebnisse zeigen...

Chemical reaction dynamics and coincidence imaging spectroscopy

Lee, Anthony M. D., 1976-
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado Formato: 5492593 bytes; application/pdf
EN
Relevância na Pesquisa
56.62%
This thesis describes and develops two experimental techniques, Time Resolved Photoelectron Spectroscopy (TRPES), and Time Resolved Coincidence Imaging Spectroscopy (TRCIS), to study ultrafast gas phase chemical dynamics. We use TRPES to investigate the effects of methyl substitution on the electronic dynamics of the simple alpha, beta-enones acrolein, crotonaldehyde, methylvinylketone, and methacrolein following excitation to the S2 state. We determine that following excitation, the molecules move rapidly away from the Franck-Condon region reaching a conical intersection promoting relaxation to the S1 state. Once on the S1 surface, the trajectories access another conical intersection leading them to the ground state. Only small variations between molecules are seen in their S2 decay times. However, the position of methyl group substitution greatly affects the relaxation rate from the S1 surface. Ab initio calculations used to compare the geometries, energies, and topographies of the S1/S0 conical intersections of the molecules are not able to explain the variations in relaxation behaviour. We propose a model that uses dynamical factors of specific motions in the molecules to explain the differing nonadiabatic S1/S0 crossing rates. The second part of this thesis examines the issues involved with design and construction of a Coincidence Imaging Spectrometer. This type of spectrometer measures the 3-dimensional velocities of both photoelectrons and photoions generated from probing of laser induced photodissociation reactions. Importantly...

High-resolution velocity-map-imaging photoelectron spectroscopy of the O¯ photodetachment fine-structure transitions

Cavanagh, Steven; Gibson, Stephen; Gale, M.N.; Dedman, Colin J; Roberts, E; Lewis, Brenton
Fonte: American Physical Society Publicador: American Physical Society
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
56.37%
A high-resolution photoelectron velocity-map-imaging study is reported for the photodetachment of the atomic oxygen anion at 532 nm, where five of the six possible spin-orbit fine-structure transitions have been resolved. A resolution of Δ E=0.38% was ac

Ab-initio angle and energy resolved photoelectron spectroscopy with time-dependent density-functional theory

De Giovannini, U.; Varsano, D.; Marques, M. A. L.; Appel, H.; Gross, E. K. U.; Rubio, A.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 25/06/2012
Relevância na Pesquisa
46.44%
We present a time-dependent density-functional method able to describe the photoelectron spectrum of atoms and molecules when excited by laser pulses. This computationally feasible scheme is based on a geometrical partitioning that efficiently gives access to photoelectron spectroscopy in time-dependent density-functional calculations. By using a geometrical approach, we provide a simple description of momentum-resolved photoe- mission including multi-photon effects. The approach is validated by comparison with results in the literature and exact calculations. Furthermore, we present numerical photoelectron angular distributions for randomly oriented nitrogen molecules in a short near infrared intense laser pulse and helium-(I) angular spectra for aligned carbon monoxide and benzene.; Comment: Accepted for publication on Phys. Rev. A

Probing the interface of Fe3O4/GaAs thin films by hard x-ray photoelectron spectroscopy

Paul, M.; Mueller, A.; Ruff, A.; Schmid, B.; Berner, G.; Mertin, M.; Sing, M.; Claessen, R.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 13/03/2009
Relevância na Pesquisa
46.44%
Magnetite (Fe3O4) thin films on GaAs have been studied with HArd X-ray PhotoElectron Spectroscopy (HAXPES) and low-energy electron diffraction. Films prepared under different growth conditions are compared with respect to stoichiometry, oxidation, and chemical nature. Employing the considerably enhanced probing depth of HAXPES as compared to conventional x-ray photoelectron spectroscopy (XPS) allows us to investigate the chemical state of the film-substrate interfaces. The degree of oxidation and intermixing at the interface are dependent on the applied growth conditions; in particular, we found that metallic Fe, As2O3, and Ga2O3 exist at the interface. These interface phases might be detrimental for spin injection from magnetite into GaAs.; Comment: 5 pages, 3 figures

Infrared and photoelectron spectroscopy study of vapor phase deposited poly (3-hexylthiophene)

Wei, Haoyan; Scudiero, L.; Eilers, Hergen
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 13/05/2011
Relevância na Pesquisa
46.48%
Poly (3-hexylthiophene) (P3HT) was thermally evaporated and deposited in vacuum. Infrared spectroscopy was used to confirm that the thin films were indeed P3HT, and showed that in-situ thermal evaporation provides a viable route for contaminant-free surface/interface analysis of P3HT in an ultrahigh vacuum (UHV) environment. Ultraviolet photoelectron spectroscopy (UPS) as well as X-ray photoelectron spectroscopy (XPS) experiments were carried out to examine the frontier orbitals and core energy levels of P3HT thin films vapor deposited in UHV on clean polycrystalline silver (Ag) surfaces. UPS spectra enable the determination of the vacuum shift at the polymer/metal interface, the valence band maximum (VBM), and the energy of the \Pi-band of the overlayer film. The P3HT vacuum level decreased in contrast to that of the underlying Ag as the film thickness increased. XPS and UPS data confirmed the chemical integrity (stoichiometry) of the polymer at high coverage, as well as the shift of the C 1s and S 2p binding energy peaks and the secondary-electron edge with increasing film thickness, indicating that band bending is present at the P3HT/Ag interface and that the measured onset of the valence band is about 0.8 +- 0.05 eV relative to the Fermi level.

Photoelectron spectroscopy at the graphene-liquid interface reveals the electronic structure of an electrodeposited cobalt/graphene electrocatalyst

Velasco-Velez, Juan J.; Pfeifer, Verena; H?vecker, Michael; Weatherup, Robert S.; Arrigo, Rosa; Chuang, Cheng-Hao; Stotz, Eugen; Weinberg, Gisela; Salmeron, Miquel; Schl?gl, Robert; Knop-Gericke, Axel
Fonte: Wiley Publicador: Wiley
Tipo: Article; accepted version
EN
Relevância na Pesquisa
66.48%
This is the author accepted manuscript. The final version is available from Wiley via http://dx.doi.org/10.1002/anie.201506044; Electrochemically grown cobalt on graphene exhibits exceptional performance as a catalyst for oxygen evolution reactions and provides the possibility of controlling the morphology and the chemical properties during deposition. However, the detailed atomic structure of this hybrid material is not well understood. To elucidate the Co/graphene electronic structure we have developed a flow cell closed by a graphene membrane that provides electronic and chemical information of active surfaces under atmospheric pressure and in the presence of liquids by means of X-ray photoelectron spectroscopy (XPS). We found that cobalt anchors on graphene via carbonyl-like species, i.e. Co(CO)_x promoting the reduction of Co^3+ to Co^2+, which is believed to be the active site of the catalyst.; HZB is acknowledged for granting beamtime at the ISSIS endstation under proposal #14201159. This work was funded from EU project GRAFOL grant 285275 and by SYNESTESia project grant 05K14EWA (BMBF). R.S.W. acknowledges a Research Fellowship from St. John?s College, Cambridge and a Marie Sk?odowska-Curie Individual Fellowship (Global) under grant ARTIST (no. 656870) from the European Union?s Horizon 2020 research and innovation programme.. C.H.C. acknowledges financial support from projects 103-2112-M-032-004 and 102-2632-M-032-001 -MY3. M.S. was supported by the Office of Science...

Time-resolved photoelectron spectroscopy of wavepackets through a conical intersection in NO_2

Arasaki, Yasuki; Takatsuka, Kazuo; Wang, Kwanghsi; McKoy, Vincent
Fonte: American Institute of Physics Publicador: American Institute of Physics
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em 28/03/2010
Relevância na Pesquisa
46.48%
We report the results of theoretical studies of the time-resolved femtosecond photoelectron spectroscopy of quantum wavepackets through the conical intersection between the first two ^2A′ states of NO_2. The Hamiltonian explicitly includes the pump-pulse interaction, the nonadiabatic coupling due to the conical intersection between the neutral states, and the probe interaction between the neutral states and discretized photoelectron continua. Geometry- and energy-dependent photoionization matrix elements are explicitly incorporated in these studies. Photoelectron angular distributions are seen to provide a clearer picture of the ionization channels and underlying wavepacket dynamics around the conical intersection than energy-resolved spectra. Time-resolved photoelectron velocity map images are also presented.

Monitoring the effect of a control pulse on a conical intersection by time-resolved photoelectron spectroscopy

Arasaki, Yasuki; Wang, Kwanghsi; McKoy, Vincent; Takatsuka, Kazuo
Fonte: Royal Society of Chemistry Publicador: Royal Society of Chemistry
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em //2011
Relevância na Pesquisa
46.61%
We have previously shown how femtosecond angle- and energy-resolved photoelectron spectroscopy can be used to monitor quantum wavepacket bifurcation at an avoided crossing or conical intersection and also how a symmetry-allowed conical intersection can be effectively morphed into an avoided crossing by photo-induced symmetry breaking. The latter result suggests that varying the parameters of a laser to modify a conical intersection might control the rate of passage of wavepackets through such regions, providing a gating process for different chemical products. In this paper, we show with full quantum mechanical calculations that such optical control of conical intersections can actually be monitored in real time with femtosecond angle- and energy-resolved photoelectron spectroscopy. In turn, this suggests that one can optimally control the gating process at a conical intersection by monitoring the photoelectron velocity map images, which should provide far more efficient and rapid optimal control than measuring the ratio of products. To demonstrate the sensitivity of time-resolved photoelectron spectra for detecting the consequences of such optical control, as well as for monitoring how the wavepacket bifurcation is affected by the control...

Optical spectrometry via photoelectron spectroscopy

Clemens, Marshall
Fonte: Rochester Instituto de Tecnologia Publicador: Rochester Instituto de Tecnologia
Tipo: Tese de Doutorado
EN_US
Relevância na Pesquisa
66.48%
The photoelectric effect has long been a phenomenon of great scientific and practical interest. Its application to photomultiplier and image pickup tubes has yielded a wealth of instruments. Most recently the field of photoelectron spectroscopy has developed as a tool for chemical analysis.

An Electron Momentum Spectroscopy and Density Functional Theory Study of the Outer Valence Electronic Structure of Stella-2,6-dione

Nixon, K L; Wang, Feng; Campbell, L.; Maddern, T; Winkler, D A; Gleiter, R.; Loeb, P; Weigold, Erich; Brunger, Michael J
Fonte: Institute of Physics Publishing Publicador: Institute of Physics Publishing
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
56.39%
We report on the first electron momentum spectroscopy (EMS) study into the outer valence electronic structure of the ground electronic state for the organic molecule stella-2,6-dione (C8H8O2). Experimentally measured binding-energy spectra are compared against a He(Iα) photoelectron spectroscopy result, while our derived momentum distributions (MDs) are compared against corresponding results from the plane wave impulse approximation (PWIA) level calculations. These computations employed density functional theory (DFT) basis states at the triple zeta valence polarization (TZVP) level, with a range of exchange-correlation (XC) functional. A detailed comparison between the experimental and PWIA DFT-XC/TZVP calculated MDs enabled us to evaluate the accuracy of the various functionals, the Becke-Perdew (BP) XC functional being found to provide the most accurate description here. The importance of the through-bond interaction to the molecular orbitals (MOs) of stella-2,6-dione is demonstrated using the orbital imaging capability of EMS. Finally we show that the molecular geometry of this molecule, as derived from BP/TZVP, is in quite good agreement with corresponding independent experimental data.