Search Results - (Author, Cooperation:R. Vasquez)
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1Latest Papers from Table of Contents or Articles in PressH. ter Steege ; N. C. Pitman ; D. Sabatier ; C. Baraloto ; R. P. Salomao ; J. E. Guevara ; O. L. Phillips ; C. V. Castilho ; W. E. Magnusson ; J. F. Molino ; A. Monteagudo ; P. Nunez Vargas ; J. C. Montero ; T. R. Feldpausch ; E. N. Coronado ; T. J. Killeen ; B. Mostacedo ; R. Vasquez ; R. L. Assis ; J. Terborgh ; F. Wittmann ; A. Andrade ; W. F. Laurance ; S. G. Laurance ; B. S. Marimon ; B. H. Marimon, Jr. ; I. C. Guimaraes Vieira ; I. L. Amaral ; R. Brienen ; H. Castellanos ; D. Cardenas Lopez ; J. F. Duivenvoorden ; H. F. Mogollon ; F. D. Matos ; N. Davila ; R. Garcia-Villacorta ; P. R. Stevenson Diaz ; F. Costa ; T. Emilio ; C. Levis ; J. Schietti ; P. Souza ; A. Alonso ; F. Dallmeier ; A. J. Montoya ; M. T. Fernandez Piedade ; A. Araujo-Murakami ; L. Arroyo ; R. Gribel ; P. V. Fine ; C. A. Peres ; M. Toledo ; C. G. Aymard ; T. R. Baker ; C. Ceron ; J. Engel ; T. W. Henkel ; P. Maas ; P. Petronelli ; J. Stropp ; C. E. Zartman ; D. Daly ; D. Neill ; M. Silveira ; M. R. Paredes ; J. Chave ; A. Lima Filho Dde ; P. M. Jorgensen ; A. Fuentes ; J. Schongart ; F. Cornejo Valverde ; A. Di Fiore ; E. M. Jimenez ; M. C. Penuela Mora ; J. F. Phillips ; G. Rivas ; T. R. van Andel ; P. von Hildebrand ; B. Hoffman ; E. L. Zent ; Y. Malhi ; A. Prieto ; A. Rudas ; A. R. Ruschell ; N. Silva ; V. Vos ; S. Zent ; A. A. Oliveira ; A. C. Schutz ; T. Gonzales ; M. Trindade Nascimento ; H. Ramirez-Angulo ; R. Sierra ; M. Tirado ; M. N. Umana Medina ; G. van der Heijden ; C. I. Vela ; E. Vilanova Torre ; C. Vriesendorp ; O. Wang ; K. R. Young ; C. Baider ; H. Balslev ; C. Ferreira ; I. Mesones ; A. Torres-Lezama ; L. E. Urrego Giraldo ; R. Zagt ; M. N. Alexiades ; L. Hernandez ; I. Huamantupa-Chuquimaco ; W. Milliken ; W. Palacios Cuenca ; D. Pauletto ; E. Valderrama Sandoval ; L. Valenzuela Gamarra ; K. G. Dexter ; K. Feeley ; G. Lopez-Gonzalez ; M. R. Silman
American Association for the Advancement of Science (AAAS)
Published 2013Staff ViewPublication Date: 2013-10-19Publisher: American Association for the Advancement of Science (AAAS)Print ISSN: 0036-8075Electronic ISSN: 1095-9203Topics: BiologyChemistry and PharmacologyComputer ScienceMedicineNatural Sciences in GeneralPhysicsKeywords: *Biodiversity ; Models, Biological ; Population ; *Rivers ; South America ; Trees/*classification/*physiologyPublished by: -
2Latest Papers from Table of Contents or Articles in PressI. Lazaridis ; N. Patterson ; A. Mittnik ; G. Renaud ; S. Mallick ; K. Kirsanow ; P. H. Sudmant ; J. G. Schraiber ; S. Castellano ; M. Lipson ; B. Berger ; C. Economou ; R. Bollongino ; Q. Fu ; K. I. Bos ; S. Nordenfelt ; H. Li ; C. de Filippo ; K. Prufer ; S. Sawyer ; C. Posth ; W. Haak ; F. Hallgren ; E. Fornander ; N. Rohland ; D. Delsate ; M. Francken ; J. M. Guinet ; J. Wahl ; G. Ayodo ; H. A. Babiker ; G. Bailliet ; E. Balanovska ; O. Balanovsky ; R. Barrantes ; G. Bedoya ; H. Ben-Ami ; J. Bene ; F. Berrada ; C. M. Bravi ; F. Brisighelli ; G. B. Busby ; F. Cali ; M. Churnosov ; D. E. Cole ; D. Corach ; L. Damba ; G. van Driem ; S. Dryomov ; J. M. Dugoujon ; S. A. Fedorova ; I. Gallego Romero ; M. Gubina ; M. Hammer ; B. M. Henn ; T. Hervig ; U. Hodoglugil ; A. R. Jha ; S. Karachanak-Yankova ; R. Khusainova ; E. Khusnutdinova ; R. Kittles ; T. Kivisild ; W. Klitz ; V. Kucinskas ; A. Kushniarevich ; L. Laredj ; S. Litvinov ; T. Loukidis ; R. W. Mahley ; B. Melegh ; E. Metspalu ; J. Molina ; J. Mountain ; K. Nakkalajarvi ; D. Nesheva ; T. Nyambo ; L. Osipova ; J. Parik ; F. Platonov ; O. Posukh ; V. Romano ; F. Rothhammer ; I. Rudan ; R. Ruizbakiev ; H. Sahakyan ; A. Sajantila ; A. Salas ; E. B. Starikovskaya ; A. Tarekegn ; D. Toncheva ; S. Turdikulova ; I. Uktveryte ; O. Utevska ; R. Vasquez ; M. Villena ; M. Voevoda ; C. A. Winkler ; L. Yepiskoposyan ; P. Zalloua ; T. Zemunik ; A. Cooper ; C. Capelli ; M. G. Thomas ; A. Ruiz-Linares ; S. A. Tishkoff ; L. Singh ; K. Thangaraj ; R. Villems ; D. Comas ; R. Sukernik ; M. Metspalu ; M. Meyer ; E. E. Eichler ; J. Burger ; M. Slatkin ; S. Paabo ; J. Kelso ; D. Reich ; J. Krause
Nature Publishing Group (NPG)
Published 2014Staff ViewPublication Date: 2014-09-19Publisher: Nature Publishing Group (NPG)Print ISSN: 0028-0836Electronic ISSN: 1476-4687Topics: BiologyChemistry and PharmacologyMedicineNatural Sciences in GeneralPhysicsKeywords: Agriculture/history/manpower ; Asia/ethnology ; Europe ; European Continental Ancestry Group/*classification/*genetics ; Genome, Human/*genetics ; History, Ancient ; Humans ; Population Dynamics ; Principal Component AnalysisPublished by: -
3Latest Papers from Table of Contents or Articles in PressD. Reich ; N. Patterson ; D. Campbell ; A. Tandon ; S. Mazieres ; N. Ray ; M. V. Parra ; W. Rojas ; C. Duque ; N. Mesa ; L. F. Garcia ; O. Triana ; S. Blair ; A. Maestre ; J. C. Dib ; C. M. Bravi ; G. Bailliet ; D. Corach ; T. Hunemeier ; M. C. Bortolini ; F. M. Salzano ; M. L. Petzl-Erler ; V. Acuna-Alonzo ; C. Aguilar-Salinas ; S. Canizales-Quinteros ; T. Tusie-Luna ; L. Riba ; M. Rodriguez-Cruz ; M. Lopez-Alarcon ; R. Coral-Vazquez ; T. Canto-Cetina ; I. Silva-Zolezzi ; J. C. Fernandez-Lopez ; A. V. Contreras ; G. Jimenez-Sanchez ; M. J. Gomez-Vazquez ; J. Molina ; A. Carracedo ; A. Salas ; C. Gallo ; G. Poletti ; D. B. Witonsky ; G. Alkorta-Aranburu ; R. I. Sukernik ; L. Osipova ; S. A. Fedorova ; R. Vasquez ; M. Villena ; C. Moreau ; R. Barrantes ; D. Pauls ; L. Excoffier ; G. Bedoya ; F. Rothhammer ; J. M. Dugoujon ; G. Larrouy ; W. Klitz ; D. Labuda ; J. Kidd ; K. Kidd ; A. Di Rienzo ; N. B. Freimer ; A. L. Price ; A. Ruiz-Linares
Nature Publishing Group (NPG)
Published 2012Staff ViewPublication Date: 2012-07-18Publisher: Nature Publishing Group (NPG)Print ISSN: 0028-0836Electronic ISSN: 1476-4687Topics: BiologyChemistry and PharmacologyMedicineNatural Sciences in GeneralPhysicsKeywords: Americas ; Asia ; Cluster Analysis ; Emigration and Immigration/*history/statistics & numerical data ; Gene Flow ; Genetics, Population ; History, Ancient ; Humans ; Indians, North American/*genetics/*history ; Models, Genetic ; *Phylogeny ; Polymorphism, Single Nucleotide/genetics ; SiberiaPublished by: -
4Latest Papers from Table of Contents or Articles in PressR. J. Brienen ; O. L. Phillips ; T. R. Feldpausch ; E. Gloor ; T. R. Baker ; J. Lloyd ; G. Lopez-Gonzalez ; A. Monteagudo-Mendoza ; Y. Malhi ; S. L. Lewis ; R. Vasquez Martinez ; M. Alexiades ; E. Alvarez Davila ; P. Alvarez-Loayza ; A. Andrade ; L. E. Aragao ; A. Araujo-Murakami ; E. J. Arets ; L. Arroyo ; C. G. Aymard ; O. S. Banki ; C. Baraloto ; J. Barroso ; D. Bonal ; R. G. Boot ; J. L. Camargo ; C. V. Castilho ; V. Chama ; K. J. Chao ; J. Chave ; J. A. Comiskey ; F. Cornejo Valverde ; L. da Costa ; E. A. de Oliveira ; A. Di Fiore ; T. L. Erwin ; S. Fauset ; M. Forsthofer ; D. R. Galbraith ; E. S. Grahame ; N. Groot ; B. Herault ; N. Higuchi ; E. N. Honorio Coronado ; H. Keeling ; T. J. Killeen ; W. F. Laurance ; S. Laurance ; J. Licona ; W. E. Magnussen ; B. S. Marimon ; B. H. Marimon-Junior ; C. Mendoza ; D. A. Neill ; E. M. Nogueira ; P. Nunez ; N. C. Pallqui Camacho ; A. Parada ; G. Pardo-Molina ; J. Peacock ; M. Pena-Claros ; G. C. Pickavance ; N. C. Pitman ; L. Poorter ; A. Prieto ; C. A. Quesada ; F. Ramirez ; H. Ramirez-Angulo ; Z. Restrepo ; A. Roopsind ; A. Rudas ; R. P. Salomao ; M. Schwarz ; N. Silva ; J. E. Silva-Espejo ; M. Silveira ; J. Stropp ; J. Talbot ; H. ter Steege ; J. Teran-Aguilar ; J. Terborgh ; R. Thomas-Caesar ; M. Toledo ; M. Torello-Raventos ; R. K. Umetsu ; G. M. van der Heijden ; P. van der Hout ; I. C. Guimaraes Vieira ; S. A. Vieira ; E. Vilanova ; V. A. Vos ; R. J. Zagt
Nature Publishing Group (NPG)
Published 2015Staff ViewPublication Date: 2015-03-20Publisher: Nature Publishing Group (NPG)Print ISSN: 0028-0836Electronic ISSN: 1476-4687Topics: BiologyChemistry and PharmacologyMedicineNatural Sciences in GeneralPhysicsKeywords: Atmosphere/chemistry ; Biomass ; Brazil ; Carbon/analysis/metabolism ; Carbon Dioxide/*analysis/metabolism ; *Carbon Sequestration ; Plant Stems/metabolism ; *Rainforest ; Trees/growth & development/metabolism ; Tropical Climate ; Wood/analysisPublished by: -
5Articles: DFG German National LicensesHecht, M. H. ; Vasquez, R. P. ; Grunthaner, F. J. ; Zamani, N. ; Maserjian, J.
[S.l.] : American Institute of Physics (AIP)
Published 1985Staff ViewISSN: 1089-7550Source: AIP Digital ArchiveTopics: PhysicsNotes: We report on the first nondestructive measurement of the chemical and physical characteristics of the interface between bulk SiO2 and thick aluminum films. Both x-ray photoelectron spectroscopy (XPS) and electrical measurements of unannealed, resistively evaporated Al films on thermal SiO2 indicate an atomically abrupt interface. Post metallization annealing (PMA) at 450 °C induces reduction of the SiO2 by the aluminum, at a rate consistent with the bulk reaction rate. The XPS measurement is performed from the SiO2 side after the removal of the Si substrate with XeF2 gas and thinning of the SiO2 layer with HF:ETOH. This represents a powerful new approach to the study of metal-insulator and related interfaces.Type of Medium: Electronic ResourceURL: -
6Articles: DFG German National LicensesVasquez, R. P. ; Hunt, B. D. ; Foote, M. C.
Woodbury, NY : American Institute of Physics (AIP)
Published 1989Staff ViewISSN: 1077-3118Source: AIP Digital ArchiveTopics: PhysicsNotes: Treatment of YBa2Cu3O7−x films with a nonaqueous solution of HF in absolute ethanol results in the formation of an oxyfluoride with relative Y:Ba:Cu concentrations of 1:4:3 on the surface, as determined by x-ray photoelectron spectroscopy. The passivation properties of chemically treated films were tested by monitoring the growth of the high binding energy O 1s peak, associated with nonsuperconducting surface species, as a function of air exposure time, for both HF-treated and untreated films. The native oxyfluoride is shown to reduce the reactivity of the superconductor to air.Type of Medium: Electronic ResourceURL: -
7Articles: DFG German National LicensesVasquez, R. P. ; Hunt, B. D. ; Foote, M. C.
Woodbury, NY : American Institute of Physics (AIP)
Published 1988Staff ViewISSN: 1077-3118Source: AIP Digital ArchiveTopics: PhysicsNotes: A nonaqueous chemical etch, with Br as the active ingredient, is described which removes the insulating hydroxides and carbonates that form on high-temperature superconductor surfaces as a result of atmospheric exposure. X-ray photoemission spectra have been recorded before and after etching YBa2Cu3O7−x films. It is found that, after the etch, the high binding energy O 1s and Ba 3d peaks associated with surface contaminants are greatly reduced, the Y:Ba:Cu ratio is close to the expected 1:2:3, and the oxidation state of the Cu(2+) is not affected. The resistance of an etched film reaches zero at 78 K, compared to 81 K for a similar unetched film. The suitability of other nonaqueous halogen-based etches is discussed, as is the applicability of this etch to other high Tc superconductors.Type of Medium: Electronic ResourceURL: -
8Articles: DFG German National LicensesHunt, B. D. ; Foote, M. C. ; Vasquez, R. P.
Woodbury, NY : American Institute of Physics (AIP)
Published 1990Staff ViewISSN: 1077-3118Source: AIP Digital ArchiveTopics: PhysicsNotes: Results on electrical characterization of YBa2Cu3O7−x thin-film surfaces treated with a Br/ethanol chemical etch are presented. Electrical measurements of YBa2Cu3O7−x/Au/Nb device structures fabricated using polycrystalline, post-annealed YBa2Cu3O7−x films with Br-etched surfaces, show improvements of approximately one or two orders of magnitude in current densities and resistivities (resistance-area products) relative to unetched devices. The existence of supercurrents in these structures has been confirmed by observation of the ac Josephson effect, and by magnetic field and temperature studies of the critical currents. The Br-etch process has produced 10×10 μm2 devices with critical current densities greater than 400 A/cm2 and resistivities as low as 4×10−7 Ω cm2.Type of Medium: Electronic ResourceURL: -
9Articles: DFG German National LicensesVasquez, R. P. ; Foote, M. C. ; Hunt, B. D.
Woodbury, NY : American Institute of Physics (AIP)
Published 1989Staff ViewISSN: 1077-3118Source: AIP Digital ArchiveTopics: PhysicsNotes: A nonaqueous solution of Br in absolute ethanol (EtOH) has recently been reported [R. P. Vasquez, B. D. Hunt, and M. C. Foote, Appl. Phys. Lett. 53, 2692 (1988)] to be effective at removing nonsuperconducting surface species from YBa2 Cu3 O7−x films, leaving the surface close to the ideal stoichiometry. This same etchant is shown here to be an effective bulk etchant in chemical depth profiling through 1-μm-thick films. The Cu remains in the 2+oxidation state and the stoichiometry, as determined by x-ray photoelectron spectroscopy, is close to ideal and nearly constant throughout the profile, indicating the absence of any large preferential etching effects. The reaction of YBa2 Cu3 O7−x films with HF/EtOH, HCl/ EtOH, and I/EtOH solutions is also reported.Type of Medium: Electronic ResourceURL: -
10Articles: DFG German National LicensesVasquez, R. P. ; Foote, M. C. ; Hunt, B. D.
Woodbury, NY : American Institute of Physics (AIP)
Published 1989Staff ViewISSN: 1077-3118Source: AIP Digital ArchiveTopics: PhysicsNotes: Wet chemical techniques are described for treatment of YBa2Cu3O7−x surfaces, resulting in the formation of native compounds with little or no reactivity to water. Promising native compounds include CuI, BaSO4, CuS, Cu2S, and the oxalates, all of which are either insoluble or have very low solubility in water. Treatment with dilute HI results in the formation of anative iodide film which is 80–90% CuI with small amounts of YI3 and BaI2. Treatment with dilute H2SO4 results in the formation of a film which is 95% BaSO4 and 5% Y2(SO4)3. Cu2S is formed on the surface with a dilute Na2S solution. An oxalate film with equal amounts of Y2(C2O4)3 and BaC2O4 results from treatment with dilute oxalic acid. X-ray photoelectron spectra show no significant changes when the sulfide, sulfate, or oxalate films are dipped in water, while the iodide film shows evidence of Cu(OH)2 formation.Type of Medium: Electronic ResourceURL: -
11Articles: DFG German National LicensesHecht, M. H. ; Orient, O. J. ; Chutjian, A. ; Vasquez, R. P.
Woodbury, NY : American Institute of Physics (AIP)
Published 1989Staff ViewISSN: 1077-3118Source: AIP Digital ArchiveTopics: PhysicsNotes: A silicon wafer has been oxidized at room temperature in vacuum using a pure, ground-state beam of O− ions. The beam was of sufficiently low energy that no displacement damage or implantation was energetically possible. The resulting SiO2 films were analyzed with x-ray photoelectron spectroscopy. A logarithmic dependence of oxide thickness on dose was observed, with an extrapolated oxidation efficiency of unity for the clean silicon surface. A distinct initial oxidation phase was observed, with an anomalously high level of silicon suboxides. In addition, the valence-band offset between the silicon and the oxide was unusually small, suggesting a large interfacial dipole.Type of Medium: Electronic ResourceURL: -
12Articles: DFG German National LicensesVasquez, R. P. ; Kuroda, R. T. ; Madhukar, A.
[S.l.] : American Institute of Physics (AIP)
Published 1987Staff ViewISSN: 1089-7550Source: AIP Digital ArchiveTopics: PhysicsNotes: The dielectric response of molecular-beam epitaxially grown single Al0.3Ga0.7As/GaAs/Al0.3Ga0.7As square quantum wells with thicknesses in the range 14–59 A(ring) is examined via spectroscopic ellipsometry in the energy range 1.6–5.7 eV. Shifts in the E1 transitions are observed and found to be consistent with the shifts calculated within a simple square well model with finite barrier height using appropriate L-point parameters of the bulk materials.Type of Medium: Electronic ResourceURL: -
13Articles: DFG German National LicensesVasquez, R. P. ; Madhukar, A. ; Grunthaner, F. J. ; Naiman, M. L.
[S.l.] : American Institute of Physics (AIP)
Published 1986Staff ViewISSN: 1089-7550Source: AIP Digital ArchiveTopics: PhysicsNotes: X-ray photoelectron spectroscopy (XPS) has been used to study the dependence of the nitrogen distribution in thermally nitrided SiO2 films on the nitridation time and temperature. Intensity analysis of the XPS data, of which a detailed derivation is presented, in conjunction with chemical depth profiling, has been used to determine the compositional variation with depth in the nitrided film. The experimental results show that, for a nitridation temperature of 1000 °C, the maximum nitrogen concentration in the interfacial region occurs at the interface in the initial stages of nitridation (within 10 min), while at later times (30 min and longer) the maximum occurs 20–25 A(ring) away from the interface. For a nitridation temperature of 1150 °C, the maximum interfacial nitrogen concentration occurs 20 A(ring) from the interface for nitridation times as short as 5 min, but saturates at a lower value than that observed at 1000 °C. For a nitridation temperature of 800 °C, the maximum interfacial nitrogen concentration remains at the interface for nitridation times up to 4 h. These data can be understood within a previously developed kinetic model which explicitly considers the effect of interfacial strain on the nitridation kinetics. In addition, the intensity of a fluorine marker is found to correlate with the nitrogen concentration. It is postulated that the fluorine bonds preferentially to defects, and it is shown that this postulate and the measured fluorine intensities are consistent with a strain-dependent energy of formation of defects, proposed recently to explain electrical results.Type of Medium: Electronic ResourceURL: -
14Articles: DFG German National LicensesStaff View
ISSN: 1089-7550Source: AIP Digital ArchiveTopics: PhysicsNotes: A kinetic model has been developed in order to understand the underlying reasons for observed nitrogen distributions in SiO2 films on Si which have been thermally nitrided in NH3. The calculations simulate the nitridation process, considering first-order chemical kinetics and Arrhenius dependence of the diffusion and reaction rates on temperature. The calculations show that as the substrate reacts with diffusing species, which initially consist primarily of nitrogen, a nitrogen-rich oxynitride forms at the interface. For nitridation temperature of 1000 °C and above, an oxygen-rich oxynitride subsequently forms at the interface due to reaction of the substrate with an increasing concentration of diffusion oxygen which has been displaced by the slower nitridation of the SiO2. This sequence of events results in a nitrogen distribution in which the peak in the interfacial nitrogen concentration occurs away from the the interface. The results of the calculations are compared with observed nitrogen distributions. The calculations correctly predict that, (i) for a nitridation temperature of 800 °C, the peak of the interfacial nitrogen concentration remains at the interface, while for nitridation temperatures≥1000 °C it moves away from the interface, and (ii) for a nitridation temperature of 1150 °C, the peak interfacial nitrogen concentration is lower than that which occurs at 1000 °C, even though the position of the peak is essentially the same. The effect of interfacial strain is included in the simulations, and is found to be necessary to account for the observed width of the interfacial nitrogen distribution.Type of Medium: Electronic ResourceURL: -
15Articles: DFG German National LicensesStaff View
ISSN: 1089-7550Source: AIP Digital ArchiveTopics: PhysicsNotes: The R-matrix propagation technique is shown to be a practical technique for estimating the electronic energy levels in aperiodic semiconductor structures within a simple one-dimensional potential model. As an example, the energy levels of an AlAs/GaAs quasiperiodic Fibonacci superlattice are calculated for electrons, light holes, and heavy holes. Those features which are unique to the quasiperiodic nature of the structure, rather than due to the choice of basis, are identified. These features are shown to be of a magnitude which makes detection using optical techniques possible.Type of Medium: Electronic ResourceURL: -
16Articles: DFG German National LicensesVasquez, R. P. ; Madhukar, A. ; Grunthaner, F. J. ; Naiman, M. L.
[S.l.] : American Institute of Physics (AIP)
Published 1986Staff ViewISSN: 1089-7550Source: AIP Digital ArchiveTopics: PhysicsType of Medium: Electronic ResourceURL: -
17Articles: DFG German National LicensesVasquez, R. P. ; Madhukar, A. ; Grunthaner, F. J. ; Naiman, M. L.
[S.l.] : American Institute of Physics (AIP)
Published 1986Staff ViewISSN: 1089-7550Source: AIP Digital ArchiveTopics: PhysicsNotes: Previously reported nitrogen distributions in SiO2 films on Si which have been thermally nitrided at 1000 °C have been explained by a kinetic model of the nitridation process which rests upon the effects of interfacial strain. A critical test of this kinetic model is the validity of the predictions regarding nitrogen distributions obtained at other nitridation temperatures. In this work, nitrogen distributions determined via x-ray photoelectron spectroscopy are reported for samples nitrided at 800 and 1150 °C, and are shown to be consistent with the kinetic model. In addition, the intensity of a fluorine marker is found to correlate with the nitrogen distribution, and is postulated to be related to kinetically generated defects in the dielectric film, consistent with the strain-dependent energy of formation of defects proposed recently to explain electrical data.Type of Medium: Electronic ResourceURL: -
18Articles: DFG German National LicensesVasquez, R. P. ; Madhukar, A. ; Tanguay, A. R.
[S.l.] : American Institute of Physics (AIP)
Published 1985Staff ViewISSN: 1089-7550Source: AIP Digital ArchiveTopics: PhysicsNotes: The dielectric functions of a-Si prepared by Si ion implantation in Si and of subsequently thermally annealed a-Si have been measured by means of spectroscopic ellipsometry. Differences are observed that may be accounted for only partially by differences in density, recrystallization during preparation of the anneal-stabilized a-Si state, or differences in the surface condition of the samples. Intrinsic changes in the bond polarizability are thus indicated. Comparison of the x-ray photoemission results for the Si 2p core levels and the valence band states of the as-implanted and anneal-stabilized a-Si samples reveals measurable changes in the valence charge distribution sufficient to substantiate a change in the bond polarizability.Type of Medium: Electronic ResourceURL: -
19Articles: DFG German National LicensesGeorge, T. ; Foote, M. C. ; Vasquez, R. P. ; Fortier, E. P. ; Posthill, J. B.
Woodbury, NY : American Institute of Physics (AIP)
Published 1993Staff ViewISSN: 1077-3118Source: AIP Digital ArchiveTopics: PhysicsNotes: A 248 nm excimer laser was used to thin naturally occurring type 1a diamond substrates at normal and glancing (22°) incidence. Perforation of a 250-μm-thick substrate was achieved in about 15 min at normal incidence. While the substrate thinned at glancing incidence was found to have large electron-transparent areas, that thinned at normal incidence required additional argon-ion milling to achieve electron transparency. X-ray photoelectron spectroscopy of the back surface of the diamond failed to detect any graphite or glassy carbon, confirming that damage due to laser ablation occurs only at the incident surface. Samples prepared using this technique imaged in the transmission electron microscope were observed to have retained the nitrogen platelets characteristic of such type 1a diamonds.Type of Medium: Electronic ResourceURL: -
20Articles: DFG German National LicensesVasquez, R. P. ; Fathauer, R. W. ; George, T. ; Ksendzov, A. ; Lin, T. L.
Woodbury, NY : American Institute of Physics (AIP)
Published 1992Staff ViewISSN: 1077-3118Source: AIP Digital ArchiveTopics: PhysicsNotes: Characterization of light-emitting porous Si films with x-ray photoelectron spectroscopy is reported. Only traces of O are detected on HF-etched samples, in contradiction to an earlier report that oxides are a significant component of porous Si. Si 2p and valence-band measurements demonstrate that the near-surface region of high porosity films which exhibit visible luminescence consists of amorphous Si.Type of Medium: Electronic ResourceURL:
