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1.
The electron impact behavior of CO adsorbed on Pd 1/W(110) was investigated. The desorption products observed were neutral CO, CO +, and O +. After massive electron impact residual carbon, C/ W = 0.15, but not oxygen was also found, suggesting that energetic neutral O, not detected in a mass analyzer must also have been formed. Formation of β-CO, i.e., dissociated CO with C and O on the surface was not seen. The total disappearance cross section varies only slightly with coverage, ranging from 9 × 10 −18 cm 2 at low to 5 × 10 −18 cm 2 at saturation ( CO/ W = 0.75). The cross section for CO + formation varies from 4 × 10 −22 cm 2 at satura to 2 × 10 −21 cm 2 at low coverage. That for O + formation is 1.4 × 10 −22 cm 2 at saturation and 2 × 10 −21 cm 2 Threshold energies are similar to those found previously [J.C. Lin and R. Gomer, Surf. Sci. 218 (1989) 406] for CO/W(110) and CO/Cu 1/W(110) which suggests similar mechanisms for product formation, with the exception of β-CO on clean W(110). It is argued that the absence or presence of β-CO in ESD hinges on its formation or absence in thermal desorption, since electron impact is likely to present the surface with vibrationally and rotationally activated CO in all cases; β-CO formation only occurs on surfaces which can dissociate such CO. It was also found that ESD of CO led to a work function increase of the remaining Pd 1/W(110) surface of 500 meV, which could be annealed out only at 900 K. This is attributed to surface roughness, caused by recoil momentum of energetic desorbing entities. 相似文献
2.
The diffusion of W on a (211) plane of a W field emitter has been re-examined by means of the fluctuation autocorrelation method. Diffusion along channels yielded E = 16.8 ± 0.5 kcal, D0 = (3 ± 1) × 10 −5 cm2 s−1. For diffusion across channels E =6.6 kcal, D0 = 4 × 10 −9cm2 s−1 at T < 752 K, and E = 24 kcal, D0 = 5 × 10 −4 cm2 s−1 at T > 752 K. The results for diffusion along channels yield E and D0 values intermediate between recent results by Wang and Ehrlich [Surf. Sci. 206 (1988) 451] using field ion microscopy ( E = 19 kcal, D0 = 7.7 × 10 −3 cm2 s−1) and Tringides and Gomer [J. Chem. Phys. 84 (1986) 4049], using the same method as the present work but a larger slit ( E = 13.3 kcal, D0 = 7 × 10 −7 cm2 s−1). The results for cross channel diffus good agreement with those of Tringides and Gomer below 752 K, where these authors stopped. The new high temperature results suggest that the channel wall exchange mechanism postulated by Tringides and Gomer for cross channel diffusion at low T gives way to diffusion by climbing over the channel walls with higher E but also higher D0 above 752 K. Possible reasons for the discrepancies between these three sets of results and the absence of cross channel diffusion in the work of Wang and Ehrlich are briefly discussed. 相似文献
3.
The co-adsorption of oxygen and deuterium at 100 K on a Pd(110) surface has been studied by measurements of the change in work function (Δφ) and by thermal desorption spectroscopy (TDS). When the surface with co-adsorbed species is heated, the adsorbates O and D react to form D 2O which desorbs from the surface at T > 200 K. The D 2O desorption peaks shift continuously to lower temperatures as the surface D coverage (θ D) increases. The maximum production of D 2O is estimated to be 0.26 ML (1 ML = 9.5 × 10 14 atoms cm −2), resulting from reaction in a layer containing 0.65 ML D and 0.3 ML O. The maximum work function increase caused by adsorption of D to saturation onto oxygen precovered Pd(110) decreases almost linearly with Δφ O of the oxygen precovered surface. On a surface with pre-adsorbed D however, the maximum Δφ increase contributed by oxygen adsorption decreases abruptly at Δφ D > 200 mV. This sharp change occurs at θ D > 1 ML and is believed to be associated with the development of the reconstructed (1 × 2) phase of D/Pd(110). 相似文献
4.
Cross sections for absorption from excited vibrational levels of the ground X3Σ -g state of molecular oxygen to the repulsive 1 3Π u state are given. The potential energy curve for the 1 3Π u state of O 2 is constructed to be consistent with predissociation data for the B3Σ -u state and with recent ab initio calculations. In the photon wavelength range of 200–320 nm the cross sections are smoothly oscillatory and in no case larger than 1 × 10 -21 cm 2. In the region of the Schumann-Runge bands the cross sections are of order 0.4 × 10 -21 cm 2. 相似文献
5.
Nd2CuO4±δ is the non-superconducting prototype of the Re2−xMxCuO4t− y family (Re=Pr, Nd, Sm and M=Ceor Th) of n-type oxide superconductors. Four-probe DC conductivity, EMF in P(O 2) gradient, and thermopower measurements have been used to characterise its electric transport and defect structure between 300 and 900°C and between 5×10 −4 and 1 atm oxygen partial pressure. The results show that Nd2CuO4±δ can be oxygen under-stoichiometric (with n-type conductivity), near-stoichiometric, and over-stoichiometric (with p-type conductivity) in different T, P(O2) ranges. 相似文献
6.
A phenomenological Landau–Devonshire theory is developed to investigate the ferroelectric, dielectric, and piezoelectric properties of(110) oriented Pb(Zr_(1-x)Ti_x)O_3(x = 0.4, 0.5, 0.6, and 0.7) thin films. At room temperature, the tetragonal a_1 phase, the orthorhombic a_2c phase, the triclinic γ_1 phase, and the triclinic γ_2 phase are stable. The appearance of the negative polarization component P_2 in the a_2c phase and the γ_1 phase is attributed to the nonlinear coupling terms in the thermodynamic potential. The γ phase of the Pb(Zr_(1-x)Ti_x)O_3 thin films has better dielectric and piezoelectric properties than the a_2c phase and the a_1 phase. The largest dielectric and piezoelectric coefficients are obtained in the Pb(Zr_(0.5)Ti_(0.5))O_3 thin film. The piezoelectric coefficient of 110–150 pm/V is obtained in the(110) oriented Pb(Zr_(0.5)Ti_(0.5))O_3 thin film, and the Pb(Zr_(0.3)Ti_(0.7))O_3 thin film has the remnant polarization and relative dielectric constant of 50 μC/cm~2 and 100, respectively,which are in agreement with the experimental measurements reported in the literature. 相似文献
7.
A solid-state electrochemical cell of the type O 2(air), Pt La0.9Sr0.1MnO3/ Li2CO3(+5 mol% Li3PO4 + 6 mol% Al2O3)/Au, CO2, O2 was composed to determine CO 2 concentration, where Li 2CO 3, a lithium ion conductor, was used as an electrolyte, and the perovskite-type oxide ( La0.9Sr0.1MnO3)/ O2-electrode as a reference electrode. The electromotive force (EMF) of the cell was found to be proportional to the logarithm of CO/ 2 partial pressure in CO 2/O 2/N 2 gas mixtures at temperatures between 300 and 400 °C. The EMF responded to changes of CO 2 partial pressure within 1 min at 400 °C. The sensitivity to CO 2 of this cell was not affected by coexistence of O 2, and the EMF remained constant after the first 15 days. The mechanism for sensing CO 2 is discussed. 相似文献
8.
The kinetics of H 2 desorption from H/W(110) and H/Fe 1/W(110) were studied by measuring work function changes Δø vs time at a number of temperatures. Combination with previously determined Δø vs coverage data and differentiation at various fixed coverages gave rate vs T data from which activation energies of desorption could be obtained. E vs coverage results agree well with previously determine Δ Hdes results. In the case of H/Fe 1/W(110) this includes a rise from 20 to 30 kcal mol −1 of H 2 at H/Fe = H/W > 0.3. Plots of rate −dθ/d t vs θ (θ being coverage in units of H/W) vary much more steeply than θ 2 at most coverages for both systems. The θ dependence can be explained almost quantitatively in terms of the variations of Δ Hdes and surface entropy Ss with coverage, by assuming that rates of desorption are equal to the equilibrium rates of adsorption. The latter can be formulated thermodynamically, except for a sticking coefficient, s. Values for s(θ, T) can also be obtained and show relatively little temperature dependence. 相似文献
10.
YBa 2Cu 3O 7−δ (YBCO) films with high critical current density ( Jc) were successfully fabricated on nickel tapes buffered with epitaxial NiO. NiO was prepared on the textured nickel tape by the surface-oxidation epitaxy (SOE) method. We have reported so far a critical temperature ( Tc) of 87 K and Jc=4–6×10 4 A/cm 2 (77 K, 0 T) for the YBCO films on NiO/Ni tapes. To enhance the superconducting properties of the YBCO films on the SOE-grown NiO, depositions of thin oxide cap layers such as YSZ, CeO 2, and MgO on NiO were investigated. These oxide cap layers were epitaxially grown on NiO and provided the template for the epitaxial growth of YBCO films. Substantially improved data of Tc=88 K and Jc=3×10 5 A/cm 2 (77 K, 0 T) and 1×10 4 A/cm 2 (77 K, Hc, 4 T) were obtained for YBCO film on NiO, by using a MgO cap layer with a thickness of 50 nm. The method described in this paper is a simple way to produce long YBCO tape conductors with high- Jc values. 相似文献
11.
The electrical conductivity of single crystal lithium niobate (LiNbO 3) was determined as a function of temperature for various oxygen partial pressures. The electrical conductivity is proportional to Po2−1/4 which can be explained by a defect equilibrium involving singly ionized oxygen vacancies and electrons. Measurements of electrical transport numbers at 1000°K show the electrical conductivity of LiNbO3 to be ionic at one atmosphere of oxygen and electronic at low oxygen partial pressures. Thermoelectric measurements indicate that LiNbO3 at low oxygen partial pressures is n-type and that the concentration of electrons at 1000°K and in an atmosphere of 50% C0/50% CO2a is 4 × 1017cm3 with a mobility of 1.7 cm2V sec. The diffusion of oxygen in LiNbO3 was determined as a function of temperature at an oxygen partial pressure of 70 Torr. by measuring O18/O16 isotope exchange with the gas phase as a function of time. The diffusion data may be represented by D = 3.03 × 10−6 exp (−29.4 kcal mole−1/RT)cm2sec. Consideration of the Nernst-Einstein relation for oxygen and the variation in conductivity with Li2O activity indicate that the ionic conduction is caused by transport of lithium ions. 相似文献
12.
Magnetization σ vs. temperature T was measured from 80 to 700 K in polycrystalline DyFe 3 in a magnetic field H = 10 kOe. From σ = f( T), the Curie temperature was determined. Also, σ was measured vs. H from 0 to 70 kOe at 4.2 K. Magnetization at saturation σ 0 at 4.2 K and the magnetic moment of DyFe 3 were also determined. First observations of domain structure in DyFe 3 are reported. The mean domain with
is determined in its dependence on the grain size
. The magnetocrystalline anisotropy constant of polycrystalline DyFe 3 is determined as K1 = -1.2×10 7 erg/cm 3. 相似文献
13.
We study the N=2 supersymmetric E6 models on the 6-dimensional space–time where the supersymmetry and gauge symmetry can be broken by the discrete symmetry. On the space–time M4× S1/( Z2× Z2′)× S1/( Z2× Z2′), for the zero modes, we obtain the 4-dimensional N=1 supersymmetric models with gauge groups SU(3)× SU(2)× SU(2)× U(1) 2, SU(4)× SU(2)× SU(2)× U(1), and SU(3)× SU(2)× U(1) 3 with one extra pair of Higgs doublets from the vector multiplet. In addition, considering that the extra space manifold is the annulus A2 and disc D2, we list all the constraints on constructing the 4-dimensional N=1 supersymmetric SU(3)× SU(2)× U(1) 3 models for the zero modes, and give the simplest model with Z9 symmetry. We also comment on the extra gauge symmetry breaking and its generalization. 相似文献
14.
Thin films of Bi 2Sr 2CaCu 2O 8 and (Bi, Pb) 2Sr 2Ca 2Cu 3O 10 have been prepared on monocrystalline (100) MgO substrates, using a laser ablation method with post annealing treatment. The influence of substrate temperature and oxygen pressure during deposition were investigated. SEM observations, EDS analysis, electric and magnetic measurements have been used to characterize the films. Superconducting “2212” films, with Tc( R = 0) at 80–83 K and Jc (50 K) up to 5 × 10 5 A/cm 2, have been currently achieved, while Pb-doped “2223” films exhibit Tc as high as 110 K with Jc = 5 × 10 4 A/cm 2 at 77 K. The effect of annealing at low temperature (350°C) in an argon flow has been studied for the 2212 phase, it shows the influence of the oxygen non-stoichiometry, i.e. of the hole carrier density upon Tc's which can be measured up to 89 K (zero resistance). 相似文献
15.
We calculate the O( s) virtual corrections to the matrix element for b → sγ, taking into account the contributions of the four-Fermi operator O2 and the electromagnetic and color dipole-type operators. The results are combined with existing O( s) Bremsstrahlung corrections in order to obtain the relevant inclusive rate. The new result drastically reduces the large scale dependence of the leading logarithmic approximation. It implies that a very accurate prediction for the branching ratio for B → Xsγ will become possible once also the corrections to the Wilson coefficients are available. 相似文献
16.
We have measured the resistivity of textured Bi 1.84Pb 0.4Sr 2Ca 2Cu 3O y silver-clamped thick films as a function of temperature, current density ranging from 10 to 1×10 3 A/cm 2 and magnetic field up to 0.3 T. We find that the effective activation energy Ue follows Ue( T, J, H)= U0(1− T/ Tp) mln( Jc0/ J) H− with m=1.75 for Hab-plane and 2.5 for Hc-axis and =0.76 for Hab and 0.97 for Hc, for the current density regime above 100 A/cm 2, where Tp is a function of applied magnetic field and current density. This result suggests the effective activation energy Ue be correlated with the temperature, current density and magnetic field. The possible dissipative mechanisms responsible for the temperature, current density and magnetic field dependence of the effective activation energy are discussed. 相似文献
17.
本文用实空间重整化群方法讨论了准周期层状铁磁超晶格的磁自旋波,用Reduce语言推导了decimation变换公式,从而求得了局域格林函数、局域态密度和约化磁矩。发现局域态密度的带宽和约化磁矩与最近邻相互作用 J1、 J2及格点自旋 sa、 sb密切相关。 相似文献
18.
A micro kinetic model of the Pt, O 2(g)| c-zirconia electrode/electrolyte system was developed in state space form (model M3). The oxygen adsorption/desorption process was modeled as a precursor-mediated surface reaction. The surface diffusion of atomic oxygen and the electrochemical reduction of atomic oxygen near the three-phase boundary ( tpb) were considered. It was shown that the simulated charge-transfer behavior of M3 is significantly different from models with ordinary Langmuir kinetics (model M2). The electrochemical rate constant was estimated from selected experimental data as k10=(6.05±0.25)·10 6 m 3/(mol·s). From experimental results it was concluded that only one adsorbed oxygen species is relevant for the dynamic behavior. In porous Pt electrodes binary gas phase diffusion of oxygen in O 2/N 2 gas mixtures becomes relevant at oxygen partial pressures below 10 −3 atm. The general procedure for state and parameter estimation can be well adopted for the investigation of further reaction mechanisms. 相似文献
19.
The adsorption of CO 2 on the NaCl(100) surface was studied with a high-resolution LEED-system. Measurements without charging up at low electron energies and without damage by the e-beam could be performed by using ultrathin epitaxial films on a conducting Ge(100) substrate. The adsorption behavior was recorded as a function of time and pressure at constant substrate temperatures of 78 and 83 K and CO 2 partial pressures from 4 × 10 −8−2 × 10 −3 Pa. The adsorption system shows a first-order two-dimensional phase transition to a (2 × 1) superstructure including glide planes (herringbone-like structure) at p = 7.2 × 10 −8Pa ( T = 78 K). The condensation of the CO 2 solid is starting at p = 1.5 × 10 −4 Pa ( T = 78 K). The LEED-pattern shows in this c(2 × 2) superstructure, which corresponds to the pyrite-like structure of the CO 2 solid. Both observed superstructures are commensurable with the NaCl(100) surface. Observation of island growth shows that the domains of the (2 × 1) superstructures have already at coverage of 5% of a monolayer an average lateral size of at least 200 A. 相似文献
20.
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 cm 2/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
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