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1.
Atomic oxygen coverages of up to 1.2 ML may be cleanly adsorbed on the Au(111) surface by exposure to O 3 at 300 K. We have studied the adsorbed oxygen layer by AES, XPS, HREELS, LEED, work function measurements and TPD. A plot of the O(519 eV)/Au(239 eV) AES ratio versus coverage is nearly linear, but a small change in slope occurs at ΘO=0.9 ML. LEED observations show no ordered superlattice for the oxygen overlayer for any coverage studied. One-dimensional ordering of the adlayer occurs at low coverages, and disordering of the substrate occurs at higher coverages. Adsorption of 1.0 ML of oxygen on Au(111) increases the work function by +0.80 eV, indicating electron transfer from the Au substrate into an oxygen adlayer. The O(1s) peak in XPS has a binding energy of 530.1 eV, showing only a small (0.3 eV) shift to a higher binding energy with increasing oxygen coverage. No shift was detected for the Au 4f 7/2 peak due to adsorption. All oxygen is removed by thermal desorption of O 2 to leave a clean Au(111) surface after heating to 600 K. TPD spectra initially show an O 2 desorption peak at 520 K at low ΘO, and the peak shifts to higher temperatures for increasing oxygen coverages up to ΘO=0.22 ML. Above this coverage, the peak shifts very slightly to higher temperatures, resulting in a peak at 550 K at ΘO=1.2 ML. Analysis of the TPD data indicates that the desorption of O 2 from Au(111) can be described by first-order kinetics with an activation energy for O 2 desorption of 30 kcal mol −1 near saturation coverage. We estimate a value for the Au–O bond dissociation energy D(Au–O) to be 56 kcal mol −1. 相似文献
2.
This paper extends a previous study (Pehrsson and Mercer, submitted to Surf. Sci.) on unheated, hydrogenated, natural diamond (100) surfaces oxidized with thermally activated oxygen (O *2). In this paper, the oxidation is performed at substrate temperatures from Tsub=24 to 670°C. The diamond surface composition and structure were then investigated with high resolution electron energy loss spectroscopy (HREELS), Auger electron spectroscopy (AES), electron loss spectroscopy (ELS) and low energy electron diffraction (LEED). The oxygen coverage (θ) increased in two stages, as it did during oxidation at T<80°C. However, there are fundamental differences between the oxidation of nominally unheated and heated diamond surfaces. This difference is attributed to simultaneous adsorption and rapid desorption of oxygen species at higher temperatures; the desorption step is much slower without heating. The initial oxidation rates were similar regardless of the substrate temperatures, but the peak coverage (θ) was lower at higher temperatures. For example, θ plateaued at 0.4±0.1 ML at 600°C. The lower saturation coverage is again attributed to oxygen desorption during oxidation. Consistent results were obtained on fully oxidized surfaces, which when heated in vacuum to Tsub=600°C, lost 60% of their adsorbed oxygen. ELS revealed few C=C dimers on the oxidized surfaces, and more graphitization than on unheated surfaces. Oxidation at elevated temperatures also increased the carbonyl to ether ratio, reflecting etching-induced changes in the types of surface sites. The carbonyl and C–H stretch frequencies increased with oxygen dose due to formation of higher oxidation states and/or hydrogen bonding between adjacent groups. The oxygen types did not interconvert when the oxidized surfaces were heated in vacuum. Oxygen desorption generated a much more reactive surface than heating-induced dehydrogenation of the smooth, hydrogenated surface. 相似文献
3.
The interaction between submonolayer titania coverages and Pt foil has been studied by Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), temperature programmed desorption (TPD) and high-resolution electron energy loss spectroscopy (HREELS). The submonolayer titania can be fully oxidized to TiO 2 at 923 K under 10 −8 Torr O 2, and partially oxidized to TiO x at lower oxidation temperatures. The oxidized surface can be reduced by annealing to 1000 K or higher, or by heating in H 2 at 823 K, or by interacting with surface carbon formed from acetone decomposition. Under certain conditions (e.g., hydrogen reduction at 923 K), the surface titania can be fully reduced to metallic Ti which diffuses into bulk Pt readily. The reduced metallic Ti can resurface when the surface is oxidized at 923 K. Both XPS and HREELS data indicate the existence of subsurface oxygen, which plays an important role for the diffusion of Ti into and out of the Pt foil. Although no special interfacial active sites were revealed by HREELS studies of adsorbed acetone and CO, some TPD and XPS data suggest the presence of sites active for acetone decomposition. 相似文献
4.
The surface composition and structure of natural diamond (100) surfaces subsequently oxidized with activated oxygen at Tsub≤35°C were investigated with high-resolution electron energy loss spectroscopy (HREELS), Auger electron spectroscopy, electron loss spectroscopy (ELS) and low-energy electron diffraction (LEED). Complete surface oxidation (oxygen coverage θ=1 ML) required doses of hundreds of kilolangmuirs of O 2. HREELS vibrational spectra permitted identification of the specific surface oxygen species, and also provided information about the diamond surface states. Most surface sites lost their hydrogen at least once before becoming oxidized. The oxygen coverage θ increased quickly at first, and then more slowly as saturation was approached; different mechanisms or sites may have accounted for the decreased rate. The relative distribution of oxygen species varied with the oxidation conditions. Ether, carbonyl and hydroxyl groups appeared during the initial stages of oxidation, but the hydroxyl groups disappeared at higher coverages. Bridge-bonded ether groups dominated at saturation coverage, although smaller amounts of carbonyl and hydroxyl were still observed. The carbonyl and C---H stretch frequencies increased with oxygen dose due to formation of higher oxidation states and/or hydrogen bonding between adjacent groups. ELS revealed only a low concentration of C=C dimers on the oxidized surfaces, and no evidence of graphitization. Surfaces generated by oxygen addition and then desorption were more reactive than surfaces generated by hydrogen desorption. Oxidized surfaces that were heated in vacuum and then rehydrogenated did not recover the sharp LEED patterns and HREELS spectra of the original plasma-smoothed surface. This effect was presumably due to surface roughening caused by oxygen desorption as CO and CO2, and creation of reactive high-energy sites that quickly bonded to available background gases and prevented large areas of organized surface reconstruction. 相似文献
5.
Oxygen tracer diffusion ( D*) and surface exchange rate constant ( k*) have been measured, using isotopic exchange and depth profiling by secondary ion mass spectrometry (SIMS), in La 1−xSr xFe 0.8Cr 0.2O 3−δ ( x=0.2, 0.4 and 0.6). Measurements were made as a function of temperature (700–1000 °C) and oxygen partial pressure (0.21–10 −21 atm) in dry oxygen, water vapour and water vapour/hydrogen/nitrogen mixtures. At high oxygen activity, D* was found to increase with increasing temperature and Sr content. The activation energies for D* in air are 2.13 eV ( x=0.2), 1.53 eV ( x=0.4) and 1.21 eV ( x=0.6). As the oxygen activity decreases, D* increases as expected qualitatively from the increase in oxygen vacancy concentration. Under strongly reducing conditions, the measured values of D* at 1000 °C range from 10 −8 cm 2 s −1 for x=0.2 to 10 −7 cm 2 s −1 for x=0.4 and 0.6. The activation energies determined at constant H 2O/H 2 ratio are 1.21 eV ( x=0.2), 1.59 eV ( x=0.4) and 0.82 eV ( x=0.6). The surface exchange rate constant of oxygen for the H2O molecule is similar in magnitude to that for the O2 molecule and both increase with increasing Sr concentration. 相似文献
6.
The chromium(II) antimony(III) sulphide, [Cr((NH 2CH 2CH 2) 3N)]Sb 4S 7, was synthesised under solvothermal conditions from the reaction of Sb 2S 3, Cr and S dissolved in tris(2-aminoethyl)amine (tren) at 438 K. The products were characterised by single-crystal X-ray diffraction, elemental analysis, SQUID magnetometry and diffuse reflectance spectroscopy. The compound crystallises in the monoclinic space group P2 1/n with a=7.9756(7), b=10.5191(9), c=25.880(2) Å and β=90.864(5)°. Alternating SbS 33− trigonal pyramids and Sb 3S 63− semi-cubes generate Sb 4S 72− chains which are directly bonded to Cr(tren) 2+ pendant units. The effective magnetic moment of 4.94(6) μB shows a negligible orbital contribution, in agreement with expectations for Cr(II): d4 in a 5A ground state. The measured band gap of 2.14(3) eV is consistent with a correlation between optical band gap and framework density that is established from analysis of a wide range of antimony sulphides. 相似文献
7.
The adsorption and reaction of methyl nitrite (CH 3ONO, CD 3ONO) on Pt(111) was studied using HREELS, UPS, TPD, AES, and LEED. Adsorption of methyl nitrite on Pt(111) at 105 K forms a chemisorbed monolayer with a coverage of 0.25 ML, a physisorbed second layer with the same coverage that desorbs at 134 K, and a condensed multilayer that desorbs at 117 K. The Pt(111) surface is very reactive towards chemisorbed methyl nitrite; adsorption in the monolayer is completely irreversible. CH 3ONO dissociates to form NO and an intermediate which subsequently decomposes to yield CO and H 2 at low coverages and methanol for CH 3ONO coverages above one-half monolayer. We propose that a methoxy intermediate is formed. At least some C–O bond breaking occurs during decomposition to leave carbon on the surface after TPD. UPS and HREELS show that some methyl nitrite decomposition occurs below 110 K and all of the methyl nitrite in the monolayer is decomposed by 165 K. Intermediates from methyl nitrite decomposition are also relatively unstable on the Pt(111) surface since coadsorbed NO, CO and H are formed below 225 K. 相似文献
8.
LEED, AES and Δ φ measurements were used to investigate the growth of Fe, Ni, Rh and Pd layers on the tungsten (111) surface. The thermal stabilities of the layers and of the substrate were also examined. Both were found to be thermally unstable at coverages above one monolayer. In addition, Rh and Pd were found to cause faceting of the substrate surface. In thick Fe layers, a non-wetting-wetting transition was observed. 相似文献
9.
The adsorption of SO 2 on a CaO surface derived from Ca(OH) 2 has been studied by X-ray photoelectron Spectroscopy. It is shown that SO 2 adsorbs molecularly on the CaO surface forming SO 32− and SO 42−. The adsorbate SO 32− species shift the Ca2 p core levels about 2 eV toward higher binding energy. However, the formation of SO 42− species does not induce any further observable changes in the Ca core line spectra. These results are explained and discussed in terms of an electronic charge transfer from the substrate metal atoms to the adsorbed molecules and vice versa. 相似文献
10.
The interactions of gas phase oxygen with gadolinia-doped ceria (GDC) surfaces are investigated by electron stimulated desorption (ESD). The primary desorbed cationic species related to molecular oxygen adsorption is O 2+. The threshold energy for ESD of O 2+ is 13–14 eV, indicating electron impact ionization of molecular oxygen bound at oxygen vacancies. Dependence of O 2+ velocities upon incident electron energy and substrate temperature reveals the dominant influence of the effective charge of the adsorption complex. The O 2+ velocity distribution is bimodal, and the onset of the faster components at room temperature is related to the balance between fluxes of incident electrons and secondary electron emission, causing effective hole production and neutralization of trapped electrons at surface states. 相似文献
11.
The effects of adsorbed H on the Mo 1−xRe x(110), x=0, 0.05, 0.15, and 0.25, surfaces have been investigated using low-energy electron diffraction (LEED) and high-resolution electron energy loss spectroscopy (HREELS). For the x=0.15 alloy only, a c(2×2) LEED pattern is observed at a coverage Θ0.25 ML. A (2×2) pattern is observed for H coverages around Θ0.5 ML from surfaces with x=0, 0.05, and 0.15. Both c(2×2) and (2×2) patterns are attributed to reconstruction of the substrate. At higher coverages, a (1×1) pattern is observed. For the alloy surface with x=0.25, only a (1×1) pattern is obtained for all H coverages. Two H vibrations are observed in HREELS spectra for all Re concentrations, which shift to higher energies at intermediate coverages. Both peaks exhibit an isotopic shift, confirming their assignment to hydrogen. For Re concentrations of x=0.15 and higher, a third HREELS peak appears at 50 meV as H (D) coverage approaches saturation. This peak does not shift in energy with isotopic substitution, yet cannot be explained by contamination. The intrinsic width of the loss peaks depends on the Re concentration in the surface region and becomes broader with increasing x. This broadening can be attributed to surface inhomogeneity, but may also reflect increased delocalization of the adsorbed hydrogen atom. 相似文献
12.
Dynamical spin susceptibility χs( q, ω) of the d– p model in the over doping region is investigated by using the auxiliary boson technique. It includes higher order terms of the 1/ N-expansion within the random phase approximation (RPA) of the local vertex, where frequency dependence of the quasi-particle interaction is taken into account. The incommensurate spin fluctuation is obtained due to the nesting effect in the low energy region ( ωω*), whereas the commensurate one in the high energy region ( ωω*), the characteristic energy ω* is estimated to be about 30 meV. Both of the spin–lattice relaxation rate 1/ T1 and the spin–spin relaxation rate 1/ Tg monotonically increase as T decreases, while the spin Knight shift K is almost independent of T. 相似文献
13.
Ion desorption induced by a resonant excitation of O 1s of condensed amorphous H 2O has been studied by total ion and total electron yield spectroscopy, nonderivative Auger electron spectroscopy (AES) and Auger electron photo-ion coincidence (AEPICO) spectroscopy. The spectrum of total ion yield divided by total electron yield exhibits a characteristic threshold peak at hν = 533.4 eV, which is assigned to the 4a 1 ← O 1s resonant transition. The AES at the 4a 1 ← O 1s resonance is interpreted as being composed of the spectator-AES of the surface H 2O, and the normal-AES of the bulk H 2O, where the 4a 1 electron is delocalized before Auger transitions. H + is found to be the only ion species in AEPICO spectra measured at the 4a 1 ← O 1s resonance and at the O 1s ionization ( hν = 560 eV). The electron kinetic energy dependence of the AEPICO yield (AEPICO yield spectrum) at the 4a 1 ← O 1s resonance is found to be greatly different from that at the O 1s ionization. The peak positions of the AEPICO yield spectrum at the 4a 1 ← O 1s resonance are found to correspond to those of the spectator-AES of the surface H 2O, which is extracted from the AES at the 4a 1 ← O 1s resonance. Furthermore, the AEPICO yield is greatly enhanced at the 4a 1 ← O 1s resonance as compared with that at the O 1s ionization. On the basis of these results, a spectator-Auger-stimulated ion desorption mechanism and/or ultra-fast ion desorption mechanism are concluded to be responsible for the H + desorption at the 4a 1 ← O 1s resonance. The enhancement of the H + yield is ascribed to the O---H anti-bonding character of the 4a 1 orbital. 相似文献
14.
The profiles of the concentration and the exchange enthalpy at the solid-fluid interface are investigated with the framework of a layer model (or inhomogeneous cell model). It is shown that for systems consisting of isotropic units, concentration distributions in the interfacial phase obey an exponential law. This is in agreement with results obtained from other theories or computer simulations. Subsequently, a characteristic thickness δ * (or n*d) is defined. This factor, together with the surface characterist scaling factor Cℓ* and the value of bulk concentrations, will determine the shape of distribution profiles of the concentration and the exchange energy in the interfacial phase. As a result, it is found that this factor δ * is associated with Cℓ*. This is empl estimate Cℓ* from δ *. Finally, the connection between the attachment energy Eatt and Cℓ* is discussed f crystal. 相似文献
15.
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
16.
本文采用甚高频等离子体化学气相沉积技术 (VHF-PECVD) 制备薄膜硅/晶体硅异质结电池中的本征硅薄膜钝化层, 光发射谱 (OES) 测量技术研究了硅薄膜沉积过程中等离子体发光谱随时间的变化. 结果表明: 在实验优化条件下等离子体发光谱很快达到稳定 (大约25 s), 并且SiH */H α* 的比值随时间变化较小, 避免了生长过程中硅薄膜结构的不均匀性, 这主要是SiH 4没有完全耗尽避免了SiH 4的反向扩散. 进一步研究了沉积参数对稳态发光谱和硅薄膜性质的影响, 结果表明: 随着硅烷浓度增加, H α*峰强度减小, SiH *峰强度增加, 薄膜从微晶转变成非晶, 非晶硅薄膜钝化效果好; 随着沉积气压增大, H α*和 SiH *峰强度先增加后减小, 高气压下H α*和 SiH *峰强度下降主要是反应前驱物的聚合形成高聚合物, 不利于形成高质量的硅薄膜, 因此钝化效果下降; 随着反应功率密度增加, H α*和 SiH *峰强度增大, 当功率密度为150 mW/cm 2 趋于饱和, 硅薄膜的致密度和钝化效果也开始下降, 50 mW/cm 2的低功率密度下硅薄膜钝化效果差可能是由于原子H 浓度低, 不能完全钝化单晶硅表面的悬挂键.
关键词:
薄膜硅
异质结
光发射谱
钝化 相似文献
18.
利用密度泛函理论的方法研究了Mg原子修饰的封闭型六 硼烷B 6H 62-吸附氢的性能. Mg可以稳定地结合在B 6H 62-上, 它可以吸附六个氢分子. 电荷转移所导致的Mg周围电场的增强和体系更大的偶极矩使 得MgB 6H 62-比MgB 6H 6具有更好的储氢性能, 储氢密度达到11.1 wt%, 氢分子的平均结合能在0.23 eV/H 2至0.34 eV/H 2之间. 结果表明可以通过控制金属-有机物体系的电荷态来增强电场, 进而改善其储氢性能.
关键词:
6H 62-团簇')" href="#">MgB 6H 62-团簇
密度泛函理论(DFT)
储氢性能
电荷态 相似文献
19.
The electrical conductivity, optical and metal–semiconductor contact properties of the MEH-PPV:C 70 organic semiconductor have been investigated. The electrical conductivity results show that the MEH-PPV:C 70 film is an organic semiconductor. The optical band gap of the film was found to be 2.06 eV and the fundamental absorption edge in the film is formed by the direct allowed transitions. The refractive index dispersion curve of the film obeys the single oscillator model and Ed and Eo dispersion parameters were found to be 10.61 and 3.89 eV, respectively. The electrical characterization of the ITO/MEH-PPV:C 70 diode have been investigated by current–voltage characteristics. ITO/MEH-PPV:C 70 diode indicates a non-ideal current–voltage behavior with ideality factor n (2.50) and barrier height φB (0.90 eV) values. 相似文献
20.
MgO films were deposited by pulsed mid-frequency magnetron sputtering from metallic targets in the mixture of Ar and O 2 gas. The surface morphology, crystalline structure, and optical properties were characterized by using atomic force microscopy (AFM), X-ray diffraction (XRD), and spectroscopic ellipsometry, respectively. The secondary electron emission coefficients of MgO films were measured by using a self-made apparatus in He gas. A pronounced hysteresis phenomenon of target voltage, current, and deposition rate with increasing and decreasing O 2 flow rate was observed. The structure of films deposited at a metallic mode changes from Mg phase to the mixed Mg and MgO phase, and the films have a very rough surface. All the films deposited at oxide mode have high transparency and smooth surface, and show (2 2 0) preferred orientation growth. The refractive index and extinction coefficient at a wavelength of 670 nm for MgO films deposited at oxide mode with a O 2 flow rate of 3 sccm are 1.698 and 1.16×10 −4, respectively. The secondary emission coefficient at a E/ p of 57.8 V/(cm Torr) for MgO films deposited at a O 2 flow rate of 3 sccm is 0.16, which is higher than that of MgO films deposited by e-beam evaporation. 相似文献
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