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1.
I. Nakamura M. Haneda H. Hamada T. Fujitani 《Journal of Electron Spectroscopy and Related Phenomena》2006,150(2-3):150-154
The influence of deposited potassium on the oxidation and NO reactivity of a Co(0 0 0 1) surface was studied using X-ray photoelectron spectroscopy. The formation of surface CoO was observed when the clean Co(0 0 0 1) surface was exposed to O2 at 500 K. In contrast, the Co atoms on the K-deposited Co(0 0 0 1) surface remained at a lower oxidation state, CoOx (0 < x < 1). No adsorption or dissociation of NO occurred on the CoO/Co(0 0 0 1) surface at 320 K, whereas a NO2− species formed on the oxidized K/Co(0 0 0 1) surface. This species is considered to be an intermediate in NO decomposition. It was concluded that the role of potassium was (i) to form the NO2− intermediate, and (ii) to keep the Co surface partially oxidized (CoOx) as the active site for the dissociation of the NO2− species. 相似文献
2.
The nature of the interaction of isocyanic acid (HNCO) with the active centers at the ideal anatase TiO2 (1 0 1) surface were studied using ab initio density functional theory (DFT) method with a cluster model. Two types of adsorption of isocyanic acid are found to be likely at (1 0 1) surface – dissociative and molecular adsorption. Only molecular adsorption of HNCO leads to the direct weakening and further splitting of the NC bond, which is a necessary step for the hydrolysis of isocyanic acid. During molecular adsorption of HNCO, an energetically stable intermediate surface complex is created with an adsorption energy of −1.33 eV, in which the HNCO skeleton is changing due to new strong bonds between C–Os and N–Tis. Based on the existence of this intermediate complex a probable reaction pathway for the hydrolysis of HNCO over the ideal anatase (1 0 1) surface was developed. A surface oxygen vacancy was formed after the decomposition of the intermediate complex and CO2 desorption. Afterwards, water adsorbs at the oxygen vacancy site and NH3 is successively formed. The HNCO hydrolysis over TiO2 was found to be energetically favorable with global energy gain of about −2.08 eV. 相似文献
3.
Giuseppe Spoto Evgueni Gribov Alessandro Damin Gabriele Ricchiardi Adriano Zecchina 《Surface science》2003,540(2-3):L605-L610
The FTIR spectroscopy of carbon monoxide adsorbed on polycrystalline MgO smoke has been investigated as a function of the CO equilibrium pressure at constant temperature (60 K) (optical isotherm) and of the temperature (in the 300–60 K range) at constant CO pressure (optical isobar). In both cases the spectra fully reproduce those of CO adsorbed on the (0 0 1) surface of UHV cleaved single crystals [Heidberg et al., Surf. Sci. 331–333 (1995) 1467]. This result, never attained in previous investigations on dispersed MgO, contribute to bridging the gap which is commonly supposed to exist between surface science and the study of “real” (defective) systems. Depending on the surface coverage θ the main spectral features due to the CO/MgO smoke interaction are a single band shifting from 2157.5 (at θ→0) to 2150.2 cm−1 (at θ=1/4) or a triplet, at 2151.5, 2137.2 and 2132.4 cm−1 (at θ>1/4). These manifestations are due to the ν(CO) modes of Mg5C2+· · · CO adducts formed on the (0 0 1) terminations of the cubic MgO smoke microcrystals. The formation of the CO monolayer is occurring in two different phases: (i) a first phase with CO oscillators perpendicularly oriented to the surface (2157–2150 cm−1) and (ii) a second phase constituted by an array of coexisting perpendicular and tilted species (triplet at 2151.5, 2137.2 and 2132.4 cm−1). A much weaker feature at 2167.5–2164 cm−1 is assigned to Mg4C2+· · · CO adducts at the edges of the microcrystals. The heat of adsorption of the perpendicular Mg5C2+· · · CO complex in the first phase has been estimated from the optical isobar and results to be 11 kJ mol−1. 相似文献
4.
A 35Cl nuclear quadrupole resonance (35Cl-NQR) investigation of polycrystalline Ca(ClO3)2·2H2O is described. The 35Cl-NQR frequencies (νQ) for two resonance lines (νQ1 and νQ2), the spin lattice relaxation time (T1Q) for νQ2 only and the line width δνQ2 were measured in the temperature range 292–345 K, except for the frequency measured up to 455 K. The observed decrease in the resonance frequencies with increasing temperature permitted the determination of the frequencies of librations of the ClO3− ion about two axes perpendicular to the three-fold axis of the ion mainly responsible for this effect. The temperature dependence of the relaxation time T1Q proved the occurrence of water diffusion and hindered rotation of ClO3− ions. The activation energies of these two molecular motions were determined, and their effect on the electric field gradient at the site of a chlorine nucleus was discussed. Temperature measurements of the line width δνQ2 confirmed the conclusions drawn from the analysis of T1Q(T). 相似文献
5.
The third-order nonlinear optical response of a triphenylmethane dye (Acid blue 7) was studied using the Z-scan technique with a continuous-wave He–Ne laser radiation at 633 nm. The magnitude and sign of the third-order nonlinear refractive index n2 of aqueous solution of Acid blue 7 dye were determined; the negative sign indicates a self-defocusing optical nonlinearity in the sample studied. The negative nonlinear refractive index n2 and nonlinear absorption coefficient β were estimated to be −1.88 × 10−7 cm2/W and −3.08 × 10−3 cm/W, respectively, corresponding to Re(χ(3)) = −8.35 × 10−6 esu, and Im(χ(3)) = −6.88 × 10−7 esu. The experimental results show that Acid blue 7 dye have potential applications in nonlinear optics. 相似文献
6.
To evaluate the interactions between the atoms of Au, Ag and Cu and clean Si(1 1 1) surface, two types of silicon clusters Si4H7 and Si16H20 together with their metal complexes were studied by using hybrid (U)B3LYP density functional theory method. Optimized geometries and energies on different adsorption sites indicate that: (1) the binding energies at different adsorption sites are large (ranging from 1.2 to 2.6 eV depend on the metal atoms and adsorption sites), suggesting a strong interaction between metal atom and silicon surface; (2) the most favorable adsorption site is the on top (T) site. Mulliken population analysis indicated that in the system of on top (T) site, a covalent bond is formed between metal atom and dangling bond of surface Si atom. 相似文献
7.
The adsorption of SH and OH radicals on Ni(111) is treated using an ab initio embedding theory. The Ni(111) surface is modeled as a three-layer, 28-atom cluster with the Ni atoms fixed at bulk lattice sites. The Ni(111) energy surface is very flat for SH adsorption if the H tilt angle is allowed to vary. At both atop and bridge sites, the S---H axis is tilted away from the surface normal by 70°, resulting in the sulfur atom being sp3-hybridized and the adsorption energy being 59 kcal mol−1. For SH at the three-fold site, the S---H axis is normal to the surface, the sulfur is sp-hybridized, and the adsorption energy is 58 kcal mol−1. OH is preferentially adsorbed at the three-fold site. The calculated adsorption energy is 90 kcal mol−1 and the O---H axis is perpendicular to the surface. OH adsorption at the atop and bridge sites is 16 and 5 kcal mol−1 less stable than at the three-fold site, respectively. Atomic H, O and S are preferentially adsorbed at the three-fold site. The calculated adsorption energies are 62, 92 and 87 kcal mol−1, for H, O and S, respectively. The calculated adsorbate---Ni bond distances of 1.86 Å for H, 1.86 Å for O and 2.29 Å for S are in good agreement with experimental data. SH and OH bonding to the surface involves a combination of ionic and covalent contributions and substantial mixing with the Ni 3d orbitals. Dipole-moment calculations indicate strong ionic bonding for the atomic O/Ni system and ionic plus covalent character for the atomic S/Ni interactions. Adsorption of S and O at the three-fold site blocks H adsorption at the nearby surface. Moving H away from the S or O adatom reduces the repulsion. The dissociation of SHad → Sad + Had is calculated to be exothermic by 5 kcal mol−1 and OHad → Oad + Had to be endothermic by 30 kcal mol−1 for infinite separation between S, O and H. 相似文献
8.
The coadsorption of carbon monoxide (CO) and water molecules on a Ru(0 0 1) surface has been studied by infrared spectroscopy, LEED and STM. At high CO coverage phases, a 2×2-(2CO+D2O) structure was observed on both UHV and electrode surfaces. Electrode potential dependent structures from CO and water adlayers on an electrode surface were reproduced on a UHV surface by controlling molecular orientations of the first layer and second over-layer water molecules. At lower CO coverages, a CO band center showed coverage dependent shift down to 1444 cm−1 due to an electron transfer from a lone pair of a water molecule to CO 2π*. 相似文献
9.
Quasi-elastic neutron scattering has been used to characterize the diffusivity of CH4 molecules condensed in single-wall carbon nanotubes. It is shown that the two sites of adsorption, previously observed by adsorption volumetry and calorimetry measurements, correspond to a solid-like phase for the more strongly bound site at T<120 K and to a liquid-like component for the more weakly bound site at 70<T<120 K. The diffusion coefficients of the mobile molecules range between 3×10−7 to 15×10−7 cm2 s−1. The fraction of this viscous liquid diminishes as the temperature is decreased; the adsorbate is fully solidified at 50 K and below. 相似文献
10.
The π0 spectrum in the KL0 → 3π decay was measured using a wire chambers magnetic spectrometer. In the usual approximation, the matrix element can be expressed as: M2 ≈ 1 + 2a0(MK/Mπ2)(2Tπ0−Tπ0max) + a1(MK2/Mπ4)(2Tπ0−Tπ0max)2. We obtained a0 = −0.282 ± 0.011 and a1 consistent with zero. 相似文献
11.
The results of the impedance spectroscopy measurements on eutectic samples based on zirconium oxide are presented here. Samples of CaZrO3---ZrO2(cubic) and MgO---ZrO2(cubic) have been grown by a directional solidification procedure such that the different phases appear nearly oriented along the growth direction (lamellae in the system of CaZrO3-ZrO2(cubic) and fibers of MgO in a ZrO2 matrix in the other system). The DC electrical conductivity has been measured by impedance spectroscopy along and across the growth axis. For CaZrO3---ZrO2 the coductivity is clearly anisotropic. The following values for σT have been obtained: the conductivity at 600 °C equals 2.0 × 10−6 Ω−1 cm−1 perpendicular to the fiber axis and 1.4 × 10−5 Ω−1 cm−1 parallel to it and with an activation energy of 1.3 eV for σT. For MgO---ZrO2(cubic) the isotropic value of the conductivity at 600 °C is 10−4 Ω−1 cm−1 with activation energy for σT of 1.5 eV. The anisotropic conductivity in the CaZrO3---ZrO2 (cubic) system has been explained by a model of an ordered stacking of oxygen conducting (cubic ZrO2) and non-conducting (CaZrO3 or MgO) phases. 相似文献
12.
The 1H and 23Na spin–lattice and spin–spin relaxation times of NaH3(SeO3)2 single crystals grown using the slow-evaporation method were measured as functions of temperature and frequency in the ferroelectric and paraelectric phases. The changes in the symmetry of the (SeO3)2− dimers as a result of the ferroelectric–paraelectric phase transition are associated with large changes in the spin–lattice and spin–spin relaxation times, and in the number of resonance lines. The large changes in the relaxation times at 195 K indicate that the H and Na ions are significantly affected by this transition. The change in the number of resonance lines for the 1H and 23Na nuclei means that the orientations of the (SeO3)2− dimers and the environments of the Na ions change at TC. Therefore, the orientations of the (SeO3)2− dimers and the environments of the Na ions play important roles in the phase transitions. In conclusion, the ferroelectric–paraelectric phase transition of NaH3(SeO3)2 is accompanied by changes in hydrogen-bond structure and distortions of the (SeO3)2− and Na+ ion lattices, which form a slightly distorted octahedron. 相似文献
13.
V. K. Dixit K. S. Keerthi H. L. Bhat Parthasarathi Bera M. S. Hegde 《Applied Surface Science》2003,220(1-4):321-326
The growth of epitaxial InBixAsySb(1−x−y) layers on highly lattice mis-matched semi-insulating GaAs substrates has been successfully achieved via the traditional liquid phase epitaxy. Orientation and single crystalline nature of the film have been confirmed by X-ray diffraction. Scanning electron micrograph shows abrupt interface at micrometer resolution. Surface composition of Bi(x) and As(y) in the InBixAsySb(1−x−y) film was measured using energy dispersive X-ray analysis and found to be 2.5 and 10.5 at.%, respectively, and was further confirmed with X-ray photoelectron spectroscopy. Variation of the composition with depth of the film was studied by removing the layers with low current (20 μA) Ar+ etching. It was observed that with successive Ar+ etching, In/Sb ratio remained the same, while the As/Sb and Bi/Sb ratios changed slightly with etching time. However after about 5 min etching the As/Sb and Bi/Sb ratios reached constant values. The room temperature band gap of InBi0.025As0.105Sb0.870 was found to be in the range of 0.113–0.120 eV. The measured values of mobility and carrier density at room temperature are 3.1×104 cm2 V−1 s−1 and 8.07×1016 cm−3, respectively. 相似文献
14.
K. M. A. Salam Hidekazu Konishi Masahiro Mizuno Hisashi Fukuda Shigeru Nomura 《Applied Surface Science》2002,190(1-4):88-95
Polycrystalline (1−x)Ta2O5−xTiO2 thin films were formed on Si by metalorganic decomposition (MOD) and annealed at various temperatures. As-deposited films were in the amorphous state and were completely transformed to crystalline after annealing above 600 °C. During crystallization, a thin interfacial SiO2 layer was formed at the (1−x)Ta2O5−xTiO2/Si interface. Thin films with 0.92Ta2O5–0.08TiO2 composition exhibited superior insulating properties. The measured dielectric constant and dissipation factor at 1 MHz were 9 and 0.015, respectively, for films annealed at 900 °C. The interface trap density was 2.5×1011 cm−2 eV−1, and flatband voltage was −0.38 V. A charge storage density of 22.8 fC/μm2 was obtained at an applied electric field of 3 MV/cm. The leakage current density was lower than 4×10−9 A/cm2 up to an applied electric field of 6 MV/cm. 相似文献
15.
Adsorption of HOCl on ice surface was studied using the ab initio molecular orbtial theory. We applied Hartree–Fock (HF) self-consistent field and the second-order Møller–Plesset (MP2) level of theory to cluster models of the (0001) surface ice Ih to optimize adsorption structures and binding energies. In all stable binding configurations, HOCl acts as a proton donor in a hydrogen bond. The presence of neighboring water molecules can strengthen the interaction of HOCl with ice. In the HOCl·(H2O)4 system, interaction hydrogen bond length is about 1.85 Å, and binding energies are −10.063−11.149 kcal mol−1. We also calculated the vibrational frequencies of HOCl affected by the ice surface. 相似文献
16.
M. Metcalf G. Neuhofer F. Niebergall M. Regler H. Stier K. Winter
J. J. Aubert
X. De Bouard V. Lepeltier L. Massonnet H. Pessard M. Vivargent T. R. Willitts M. YvertW. Bartl
M. Steuer 《Physics letters. [Part B]》1972,40(6):703-707The time-dependence of the decay rate of initially pure K0 into the final state (π+π−π0) has been studied in search for the decay kS0→π+π−π0. No evidence is found in a sample of 384 observed events. The ratio of the CP -violating KS0 amplitude and the KL0 amplitude is η+−0 = (0.13−0.20+0.17) + i(0.17−0.26+0.27); the ratio of the CP-conserving KS0 amplitude and the KL0 amplitude is < 0.4. The energy dependence of the K0→π+π−π0 matrix element is found to be a+−0 = −0.31 ± 0.03. 相似文献
17.
The molecular adsorption of NO on both the reconstructed (hex) and unreconstructed (1 × 1) surfaces of Pt{100} has been studied using a combination of infrared reflection-absorption spectroscopy (IRAS) and low energy electron diffraction (LEED) at temperatures between 90 and 300 K. On the (1 × 1) surface at 300 K adsorbed NO gives rise to an N-O stretching band at initially 1596 cm−1 shifting to 1641 cm−1 at a coverage of θ = 0.5. The LEED pattern at this coverage is interpreted in terms of a c(4 × 2) structure in which all the molecules occupy a single type of adsorption site between the on-top and bridge positions. At temperatures below 300 K, a higher coverage disordered phase is observed, giving rise to an N-O stretching band at 1680 cm−1 associated with an on-top NO species. On the (hex) phase surface above 210 K, NO adsorption gives rise to bands characteristic of adsorption on the (1 × 1) phase indicating that the reconstruction is immediately lifted. Below 200 K initial adsorption actually occurs directly on the (hex) phase, resulting in a band at 1680 cm−1, which is assigned to on-top NO. This band increases in intensity until, at a critical coverage dependent on temperature, the (hex) → (1 × 1) surface phase transition is induced. This is indicated by the disappearance of the band at 1680 cm−1 and its replacement by bands characteristic of adsorption on islands of the (1 × 1) structure. 相似文献
18.
Nikoleta Theodoropoulou Vinith Misra John Philip Patrick LeClair Geetha P. Berera Jagadeesh S. Moodera Biswarup Satpati Tapobrata Som 《Journal of magnetism and magnetic materials》2006,300(2):407-411
Clear evidence of ferromagnetic behavior at temperatures >400 K as well as spin polarization of the charge carriers have been observed in Zn1−xMnxO thin films grown on Al2O3 and MgO substrates. The magnetic properties depended on the exact Mn concentration and the growth parameters. In well-characterized single-phase films, the magnetic moment is 4.8 μB/Mn at 350 K, the highest moment yet reported for any Mn doped magnetic semiconductor. Anomalous Hall effect shows that the charge carriers (electrons) are spin-polarized and participate in the observed ferromagnetic behavior. 相似文献
19.
M. G. Olsson 《Physics letters. [Part B]》1997,410(2-4):311-314
A new evaluation of the universal ππ scattering length relation is used to extract the ππ s-wave scattering lengths from threshold pion production data. Previous work has shown that the chiral perturbation series relating threshold pion production to ππ scattering lengths appears to converge well only for the isospin-2 case, giving a2 = −0.031 ± 0.007mπ−1. A model-independent and data-insensitive universal curve then implies a0 = 0.235 ± 0.03mπ−1 for the isospin-0 scattering length. 相似文献
20.
The chemisorption of one monolayer Ag atoms on an ideal Si(1 0 0) surface is studied by using the self-consistent tight-binding linear muffin-tin orbital method. The adsorption energies (Ead) of different sites are calculated. It is found that the adsorbed Ag atoms are more favorable on C site (fourfold site) than on any other sites on Si(1 0 0) surface, the polar covalent bond is formed between Ag atom and surface Si atom, a Ag and Si mixed layer does not exist and does form an abrupt interface at the Ag–Si(1 0 0) interface. This is in agreement with the experiment results. The layer-projected density of states is calculated and compared with that of the clean surface. The charge transfer is also investigated. Comparing with the Au/Si(1 0 0) system, the interaction is weaker between Ag and Si than between Au and Si. 相似文献