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Showing papers on "Inorganic compound published in 1991"


Journal ArticleDOI
TL;DR: In this article, the electron inelastic mean free paths (IMFPs) of 14 organic compounds were computed for a group of 14 compounds: 26-n-paraffin, adenine, β-carotene, bovine plasma albumin, deoxyribonucleic acid, diphenylhexatriene, guanine, kapton, polyacetylene, poly(butene-1-sulfone), polyethylene, polymethylmethacrylate, polystyrene and poly(2-vinyl
Abstract: We report calculations of electron inelastic mean free paths (IMFPs) of 50–2000 eV electrons for a group of 14 organic compounds: 26-n-paraffin, adenine, β-carotene, bovine plasma albumin, deoxyribonucleic acid, diphenylhexatriene, guanine, kapton, polyacetylene, poly(butene-1-sulfone), polyethylene, polymethylmethacrylate, polystyrene and poly(2-vinylpyridine). The computed IMFPs for these compounds showed greater similarities in magnitude and in the dependences on electron energy than was found in our previous calculations for groups of elements and inorganic compounds (Papers II and III in this series). Comparison of the IMFPs for the organic compounds with values obtained from our predictive IMFP formula TPP-2 showed systematic differences of ∼40%. These differences are due to the extrapolation of TPP-2 from the regime of mainly high-density elements (from which it had been developed and tested) to the low-density materials such as the organic compounds. We analyzed the IMFP data for the groups of elements and organic compounds together and derived a modified empirical expression for one of the parameters in our predictive IMFP equation. The modified equation, denoted TPP-2M, is believed to be satisfactory for estimating IMFPs in elements, inorganic compounds and organic compounds.

2,383 citations


Journal ArticleDOI
TL;DR: In this paper, annealing results for several Tl-superconductors in the series Tlm(Ba, Sr)2Can−1CunO2n+m+2+δ, for both m=1 and 2, revealing two general results for this class of Bi or TI superconductors: (1) effects on Tc due to labile oxygen occur for all m=2 compounds but are absent in m = 1 compounds with Sr.
Abstract: We have previously shown that Tc for Bi2 (Sr, Ca)n+1CunO2n+4+δ (n=1, 2 and 3) varies with oxygen stoichiometry δ determined by annealing in a variety of oxygen partial pressures and temperatures. Annealing results are now also presented for several Tl-superconductors in the series Tlm(Ba, Sr)2Can−1CunO2n+m+2+δ, for both m=1 and 2, revealing two general results for this class of Bi or TI superconductors: (1) effects on Tc due to labile oxygen occur for all m=2 compounds but are absent in m = 1 compounds with Sr. m=1 compounds with Ba do have variable oxygen but the effects on the c-axis are the opposite to m=2 compounds. This suggests for the latter that the labile oxygen resides in interstitial sites within the Bi2O2 or Tl2O2 bi layers; (2) the hole concentration per Cu decreases in progressing from n = 1 to 2 to 3 in either class so that the parent n = 3 and n = 2 compounds lie respectively on the low- and high-hole concentration sides of the peak in Tc while the n = 1 compounds extend out into the non-superconducting domain at very high hole concentration.

712 citations


Journal ArticleDOI
26 Apr 1991-Science
TL;DR: The toluene extract of the fluffy carbon material produced by resistive heating of graphite contains a variety of molecules larger than C60 and C70 in a total amount of 3 to 4% by weight that are identified as higher fullerenes.
Abstract: The toluene extract of the fluffy carbon material produced by resistive heating of graphite contains a variety of molecules larger than C(60) and C(70) in a total amount of 3 to 4% by weight. Repeated chromatography of this material on neutral alumina has led to the isolation of stable solid samples of C(76), C(84), C(90), and C(94). The characterization, which includes mass spectrometry, (13)C nuclear magnetic resonance, electronic absorption (ultraviolet/visible) and vibrational (infrared) spectroscopy identifies these all-carbon molecules as higher fullerenes. In addition, C(70)O, a stable oxide, has been isolated that is structurally and electronically closely related to D5h-C(70). This compound forms during the resistive heating process and probably has an oxygen atom inserted between two carbon atoms on the convex external surface of the C(70) skeleton.

598 citations


Journal ArticleDOI
TL;DR: In this article, X-ray photoelectron spectroscopy measurements of several silver compounds were made and precise photo-electron and Auger line energies reported for Ag(3d 5 2 ) and Ag(M4N 4,5N4,4,5) lines.

418 citations


Journal ArticleDOI
01 Jan 1991-Nature
TL;DR: In this paper, the isostructural compound Sr1-yNdyCuO2, in which the substitution of neodymium for strontium adds electrons to the CuO2 planes, is superconducting at 40 K.
Abstract: THE known copper oxide superconductors all have intergrowth structures consisting of superconducting layers of fixed oxygen content alternating with non-superconducting oxide layers. Siegrist et al.1 reported the synthesis of the 'infinite-layer' parent compound of the copper oxide superconductor—a structure comprising CuO2 planes separated only by calcium and strontium atoms, with the composition Ca086Sr014CuO2. Although this compound has not been made to superconduct, here we show that the isostructural compound Sr1–yNdyCuO2, in which the substitution of neodymium for strontium adds electrons to the CuO2 planes, is superconducting at 40 K. The difference in dopant type seems to distinguish this superconductor from the superconductivity found in a multiphase sample of nominal composition Sr1–yBayCuO2 by Takano et al.2, in an independent study.

391 citations


Journal ArticleDOI
P. Lacorre1, Jerry B. Torrance1, J. Pannetier, A. I. Nazzal1, P.W. Wang1, T.C. Huang1 
TL;DR: In this paper, the electrical conductivity of PrNiO3 is shown to be metallic at room temperature, but undergoes a transition at 130 K to an insulating state, with a ∼ 0.2% contraction upon heating into the metallic state.

316 citations


Journal ArticleDOI
TL;DR: In this article, X-ray photoelectron spectroscopy (XPS) measurements of core level binding energies and kinetic energies for a comprehensive set of 25 Sr and Ba compounds are reported, including many for which there have been no previous XPS measurements.

223 citations


Journal ArticleDOI
TL;DR: In this article, the electroabsorption spectra of metal-to-ligand and metal to metal charge transfer (MLCT and MMCT) transitions are reported for the charge transfer transitions of (NH3)SRuL2+ and [(NH3]5R~]2L4+*5+, where L is pyrazine (pz) or 4, 4'-bipyridine (4,4'-bpy).
Abstract: Electroabsorption (Stark effect) spectra are reported for the charge-transfer transitions of (NH3)SRuL2+ and [(NH3)5R~]2L4+*5+, where L is pyrazine (pz) or 4,4'-bipyridine (4,4'-bpy). The spectra permit experimental estimates of the susceptibility of the transition dipole moment to an electric field, the change in polarizability (TrAu), and the magnitude of the change in permanent electric dipole moment (IApI) associated with many of the metal-to-ligand and metal-to-metal charge-transfer (MLCT and MMCT, respectively) transitions in these complexes. The observed electroabsorption spectra of the MLCT transitions of the monoruthenium complexes are interpreted as arising predominantly from Au and Ap. When L = pz and 4,4'-bpy, the observed values of IApl are (5.3 0.8)lfand (15.8 * 0.2)/fD, respectively, compared with the values of 16.5 and 27.1 D expected for full charge transfer from the metal to the geometric center of the ligand (fis a local electric field correction). Protonation of the monoruthenium complexes has relatively small effects on the observed Au and Ap when L = 4,4'-bpy, but when L = pz, Au appears to change its sign while Ap virtually disappears. A simple electrostatic model qualitatively accounts for the results and indicates that pyrazine allows a much greater degree of delocalization from the ruthenium than 4,4'-bipyridine whose pyridyl rings are probably not coplanar. The electroabsorption spectra of the MLCT region of the biruthenium complexes are very complicated and not quantitatively interpretable on the basis of current information, though interesting and qualitatively suggestive features appear. For the MMCT transitions in the biruthenium mixed-valence complexes where L is pz and 4,4'-bpy, the observed values of lApl are (0.7 * O.l)/fand (28.5 A 1.5)/fD, respectively, compared with the values of 32.7 and 54.3 D expected fur charge transfer in fully localized complexes. These latter results demonstrate that electronic delocalization between the two metals is essentially complete when the bridging ligand is pyrazine, whereas it is significant but incomplete when the bridge is 4,4'-bipyridine. In all complexes, the angle dependence of the electroabsorption demonstrates that Ap and the other field-interactive molecular properties are parallel to the transition dipole moment, as expected if the transition moment lies along the metal-ligand axis. The electroabsorption spectra of all of the monoruthenium and [(NH3)5R~]2L4+ complexes also show evidence for transitions that are weak or obscured in conventional absorption spectra; possible assignments are discussed within the context of a molecular orbital model.

184 citations



Journal ArticleDOI
TL;DR: In this paper, high-order stable structures with planar tetracoordinate central atoms, such as Al4O, Al4N, Al3SiN, cis-Al2Si2C, trans-Al 2Si2c and AlSi3B, are predicted at the MP4SDTQ/6-311 + G*/MP2(full)/6-31G* level.
Abstract: Highly stable structures with planar tetracoordinate central atoms, Al4O, Al4N–, Al3SiN, cis-Al2Si2C, trans-Al2Si2C and AlSi3B, are predicted computationally at the ab initio MP4SDTQ/6-311 + G*//MP2(full)/6-31G* level.

167 citations


Journal ArticleDOI
TL;DR: In this article, the steady-state photoluminescence of (100)-oriented GaAs has been studied using x-ray photoelectron spectroscopy and steadystate photodynamic properties of GaAs surfaces exposed to inorganic and organic donors.
Abstract: Steady-state photoluminescence, time-resolved photoluminescence, and x-ray photoelectron spectroscopy have been used to study the electrical and chemical properties of GaAs surfaces exposed to inorganic and organic sulfur donors. Despite a wide variation in S2–(aq) concentration, variation of the pH of aqueous HS–solutions had a small effect on the steady-state n-type GaAs photoluminescence intensity, with surfaces exposed to pH=8, 0.1-M HS–(aq) solutions displaying comparable luminescence intensity relative to those treated with pH=14, 1.0-M Na2S·9H2O(aq). Organic thiols (R-SH, where R=–CH2CH2SH or –C6H4Cl) dissolved in nonaqueous solvents were found to effect increases in steady-state luminescence yields and in time-resolved luminescence decay lifetimes of (100)-oriented GaAs. X-ray photoelectron spectroscopy showed that exposure of GaAs surfaces to these organic systems yielded thiols bound to the GaAs surface, but such exposure did not remove excess elemental As and did not form a detectable As2S3 overlayer on the GaAs. These results imply that complete removal of As0 or formation of monolayers of As2S3 is not necessary to effect a reduction in the recombination rate at etched GaAs surfaces. Other compounds that do not contain sulfur but that are strong Lewis bases, such as methoxide ion, also improved the GaAs steady-state photoluminescence intensity. These results demonstrate that a general class of electron-donating reagents can be used to reduce nonradiative recombination at GaAs surfaces, and also imply that prior models focusing on the formation of monolayer coverages of As2S3 and Ga2S3 are not adequate to describe the passivating behavior of this class of reagents. The time-resolved, high level injection experiments clearly demonstrate that a shift in the equilibrium surface Fermi-level energy is not sufficient to explain the luminescence intensity changes, and confirm that HS– and thiol-based reagents induce substantial reductions in the surface recombination velocity through a change in the GaAs surface state recombination rate.



Journal ArticleDOI
TL;DR: In this paper, the authors give examples of XPS analysis, showing how O 1s bands can be affected by surface carbonates, and a proper peak assignment (e.g. to O− OH− species) needs the preliminary determination of a carbonate contribution.
Abstract: The aim of the paper is to give examples of XPS analysis, showing how O 1s bands can be affected by surface carbonates. A proper peak assignment (e.g. to O− OH− species) needs the preliminary determination of a carbonate contribution. Although the samples examined represent Co and La compounds only, the principal conclusions can be extended also to other oxide systems.

Journal ArticleDOI
TL;DR: In this article, time-of-flight neutron diffraction measurements were carried out on pure liquid water in the high-Q region and at high temperatures between 25 and 200°C.
Abstract: Time-of-flight neutron diffraction measurements were carried out on pure liquid water in the high-Q region and at high temperatures between 25 and 200°C. The observed data at high scattering angle ...




Journal ArticleDOI
01 Jan 1991-Nature
TL;DR: In this paper, an example of a synthetic process that produces composite materials analogous to those produced by natural biomineralization is presented, where the inorganic/organic in situ synthesized composites display controlled inorganic crystal size, morphology and orientation, which are determining features of type II, or matrix-mediated7, biocomposites.
Abstract: BIOLOGICAL composite materials such as bones, teeth and shells consist of a polymer matrix reinforced by an inorganic phase which forms in the matrix1. These materials are distinguished from synthetic composites by the high degree of organization and regularity displayed by the inorganic phase: inorganic minerals of uniform size, morphology and crystallographic orientation can be formed in ordered arrays in living cells. Such a process has until now not been realized in synthetic systems, although the recent interest in nanoscience2–6has stimulated much research in the area. We report here an example of a synthetic process that produces composite materials analogous to those produced by natural biomineralization. The inorganic/organic in situ synthesized composites display controlled inorganic crystal size, morphology and orientation, which are determining features of type II, or matrix-mediated7, biocomposites. The synthetic factors that must be optimized to give biomimetic properties to synthetic composites are strong binding of the inorganic reagents by the organic matrix (molecular complementarity); good 'solvation' of the inorganic reagents by the polymer; and an ordered, regular polymer environment in which to induce nucleation (matrix preorganization)1.


Patent
24 Apr 1991
TL;DR: In this paper, a method and apparatus for forming a dielectric thin film or pattern thereof is provided in which a positive or negative resist of a desired pattern if formed on various substrates including a semiconductor substrate by contact of the resist with a liquefied gas or super critical fluid of CO2, NH3 or the like.
Abstract: A method and apparatus for forming a dielectric thin film or pattern thereof is provided in which a positive or negative resist of a desired pattern if formed on various substrates including a semiconductor substrate by contact of the resist with a liquefied gas or super critical fluid of CO2, NH3 or the like. Alternatively, a thin film of an organic or inorganic compound dissolved or dispersed in an organic solvent which has been formed on substrate becomes substantially free of any organic matter or functional groups by contact with the liquefied gas or super critical fluid. Semiconductor devices of high performance and high reliability are ensured.



Journal ArticleDOI
TL;DR: In this paper, the properties of OI contact barrier diodes are discussed in terms of the thermionic emission-space-charge-limited (TE-SCL) current model.
Abstract: The properties are discussed of organic-on-inorganic (OI) semiconductor contact barrier diodes, where the 3, 4, 9, 10 perylenetetracarboxylic diimide (PTCDI) and the copper phthalocyanine (CuPc) serve as the organic thin film. The results presented can be fully understood in terms of the thermionic emission-space-charge-limited (TE-SCL) current model introduced for OI structures with prototypical aromatic compound; 3, 4, 9, 10 perylenetetracarboxylic dianhydride (PTCDA) vapour-deposited onto n- and p-Si substrates. Also, under moderate and high reverse bias voltages the results obtained can be understood in terms of the organic-on-inorganic heterojunction (OI-HJ) model. Comparisons between diode performances and theory are made. The contact barrier diodes exhibit high breakdown voltages and reverse dark currents limited by generation and recombination of carriers in the Si bulk. From the forward current-voltage characteristics at several temperatures, apparent OI contact barriers of Φbp = (0.63 ± 0.01) V for PTCDI and Φbp = (0.59 ± 0.02) V for CuPc, are formed with p-Si substrates. Studies of the I–U characteristics suggest the presence of an exponential trap distribution in the band-gap of the organic semiconductors used. The resulting diodes are superior in many respect to conventional Schottky diodes due to enhanced contact barriers and reduced edge effects.




Journal ArticleDOI
TL;DR: While the bulk spectra are isotropic, the surface and interface spectra exhibit a pronounced polarization dependence, which can be used to become surface and/or interface selective via polarization-modulation experiments, even for buried interfaces.
Abstract: The fine structure of the Ca 2p soft-x-ray-absorption edge is studied for a variety of bulk compounds (Ca metal, CaSi2, CaO, and CaF2), for surfaces and interfaces [CaF2(111), BaF2 on CaF2(111), Ca and CaF2 on Si(111)], and for defects (F centers in CaF2). The observed multiplet structure is explained by atomic calculations in a crystal field [cubic O(h) for the bulk and threefold C3-nu for the (111) surfaces and interfaces]. While the bulk spectra are isotropic, the surface and interface spectra exhibit a pronounced polarization dependence, which is borne out by the calculations. This effect can be used to become surface and/or interface selective via polarization-modulation experiments, even for buried interfaces. A change in valence from Ca2+ to Ca1+ causes a downwards energy shift and extra multiplet lines according to the calculation. The energy shift is observed for F centers at the CaF2 surface and for the CaF2/Si(111) interface.


Journal ArticleDOI
TL;DR: For the growth of III-VA/III-VB heterostructures with a sharp interface, it is important to suppress the interchanging reaction of column V elements between the impinging molecules (VA) and atoms of the substrates (VB) as discussed by the authors.