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1.
用第一性原理的总能计算研究了Cu(100))面的表面结构、弛豫以及氧原子的(2×22)吸附状 态.计算给出了Cu(100) (2×22)R45°-O吸附表面的结构参数,并得到了上述结构下氧吸附 的Cu(100)表面氧原子和各层Cu原子的电子态密度.计算得到的吸附表面功函数为4.58 eV ,与清洁Cu(100)表面功函数(~4.53 eV)几乎相同.吸附氧原子与最外层铜原子之间的垂直 距离约为0.02 nm,其能带结构体现出一定的金属性,同时由于Cu-O的杂化作用在费米能以 下约6.4 eV附近出现了局域的表面态.可以认为,在Cu(100) (2×22)R45°的氧吸附表面结 构下,吸附氧原子和衬底之间的结合主要来源于表面最外层铜原子与氧原子的相互作用.
关键词:
Cu(100)(2×22)R45°-O表面
缺列再构
表面电子态 相似文献
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利用Scanning Tunneling Microscope(STM)和Scanning Tunneling Spectroscopy(STS)技术研究了La0.67Ca0.33MnO3(001)表面性质,研究发现表面呈现多相分离现象,在锰氧终端面观察到了绝缘性的( 2 × 2 )R45°重构表面和金属性的(1×1)重构表面,在镧钙氧终端面,观察到了表面呈现条纹状结构.La0.67Ca0.33
关键词:
镧钙锰氧薄膜
终端面
绝缘金属转变 相似文献
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用第一性原理的总能计算研究了Cu(100))面的表面结构、弛豫以及氧原子的(2×22)吸附状态.计算给出了Cu(100)(2×22)R45°-O吸附表面的结构参数,并得到了上述结构下氧吸附的Cu(100)表面氧原子和各层Cu原子的电子态密度.计算得到的吸附表面功函数为4.58eV,与清洁Cu(100)表面功函数(~4.53eV)几乎相同.吸附氧原子与最外层铜原子之间的垂直距离约为0.02nm,其能带结构体现出一定的金属性,同时由于Cu-O的杂化作用在费米能以下约6.4eV附近出现了局域的表面态.可以认为,在Cu(100)(2×22)R45°的氧吸附表面结构下,吸附氧原子和衬底之间的结合主要来源于表面最外层铜原子与氧原子的相互作用. 相似文献
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用能量为1千电子伏,束流为6微安的氮离子轰击含有痕量碳和氧的钼(001)和钼(110)表面10至15分钟,在俄歇能谱中出现了很强的氮的俄歇峰。从室温直到350℃退火,低能电子衍射观察表明,表面是无序层。样品加热到530℃和650℃之间,在钼(001)表面上得到c(2×2)-氮,p(2×2)-氮和(4(21/2)×21/2)R45°-氮、氧三种结构的低能电子衍射图;在密堆的钼(110)面得到单一结构的c(7×3)-氮的低能电子衍射图。低能电子衍射图与热脱附密切相关
关键词: 相似文献
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从中能电子向前散射产生的实空间图像研究了Cu(111)1×1,Si(111)(31/2×31/2)R30°-In及Ge(111)(31/2×31/2)R30°-Ag的表面结构.Cu(111)1×1的图像不仅说明表面有三重旋转轴对称性,而且还表明fcc结构一直保持到最表面一层原子.Si(111)(31/2×31/2)R30°-In表面的图像说明In原子占据T4位,而不是H3位.Ge(111)(31/2×31/2)R30°-Ag的图像说明HCT模型是正确的.这些成功的应用说明从中能电子向前散射图像可以直观而且快捷地获得表面结构类型的可靠信息,而无需类似于低能电子衍射(LEED)表面结构分析那样的复杂计算
关键词: 相似文献
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本文用X射线光电子能谱(XPS),紫外光电子能谱(UPS),电子能量损失谱(EELS)和低能电子衍射(LEED)研究了O与预覆盖K的Ag(110)表面相互作用及其性质。在低覆盖度K下,发现有两种O的吸附态,经鉴别为溶解到表面下的O2-和表面上吸附的Ox-增加K的覆盖度,出现分子状态的吸附物O2δ-,它与表面下存在的K相联系。XPS和UPS均清楚地显示出对应于三种不同吸附态的光电子发射峰。Ag(110)表面预覆盖K后的粘滞系数大大增加。K和O的共吸附引起它们彼此向Ag(110)表面下的溶解。LEED实验结果表明,清洁Ag(110)表面覆盖单层K原子后衍射图形从(1×1)变到(1×2),再吸附O后表面吸附层结构变为(2×1)。另外,结合UPS和EELS测量初步考察了O/K/Ag(110)共吸附系统的电子结构。本文还提出了一个共吸附模型来解释这些现象。
关键词: 相似文献
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用第一性原理的总能计算研究了Cu(100))面的表面结构、弛豫以及氧原子的(√2×2√2)吸附状态.计算给出了Cu(100)(√2×2√2)R45°-O吸附表面的结构参数,并得到了上述结构下氧吸附的Cu(100)表面氧原子和各层Cu原子的电子态密度.计算得到的吸附表面功函数φ为4.58 eV,与清洁Cu(100)表面功函数(~4.53 eV)几乎相同.吸附氧原子与最外层铜原子之间的垂直距离约为0.02 nm,其能带结构体现出一定的金属性,同时由于Cu-O的杂化作用在费米能以下约6.4 eV附近出现了局域的表面态.可以认为,在Cu(100)(√2×2√2)R45°的氧吸附表面结构下,吸附氧原子和衬底之间的结合主要来源于表面最外层铜原子与氧原子的相互作用. 相似文献
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The adsorption of SO2 on Ag(110) and the reaction of SO2 with oxygen adatoms have been studied under ultrahigh vacuum conditions using low energy electron diffraction, temperature programmed reaction spectroscopy and photoelectron spectroscopy. Below 300 K, SO2 adsorbs molecularly giving p(1×2) and c(4×2) LEED patterns at coverages of one half and three quarter monolayers. respectively. At intermediate coverages, streaked diffraction patterns, similar to those reported for noble gas and alkali metal adsorption on the (110) face of face-centered cubic metals were observed, indicating adsorption out of registry with the surface. A feature at low binding energy in the ultraviolet photoemission spectrum appeared which was assigned to a weak chemisorption bond to the surface via the sulfur, analogous to bonding observed in SO2-amine charge transfer complexes and in transition metal complexes. SO2 exhibited three binding states on Ag(110) with binding energies of 41, 53 and 64 kJ mol?1; no decomposition on clean Ag(110) was observed. On oxygen pretreated Ag(110), SO2 reacted with oxygen adatoms to form SO3(a), as determined by X-ray photoelectron spectroscopy. Reacting preadsorbed atomic oxygen in a p(2 × 1) structure with SO2 resulted in a c(6 × 2) pattern for SO3(a). The adsorbed SO3(a) decomposed and disproportionated upon heating to 500 K to yield SO2(g), SO4(a) and subsurface oxygen. 相似文献
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The adsorption/desorption characteristics of CO, O2, and H2 on the Pt(100)-(5 × 20) surface were examined using flash desorption spectroscopy. Subsequent to adsorption at 300 K, CO desorbed from the (5×20) surface in three peaks with binding energies of 28, 31.6 and 33 kcal gmol?1. These states formed differently from those following adsorption on the Pt(100)-(1 × 1) surface, suggesting structural effects on adsorption. Oxygen could be readily adsorbed on the (5×20) surface at temperatures above 500 K and high O2 fluxes up to coverages of of a monolayer with a net sticking probability to ssaturation of ? 10?3. Oxygen adsorption reconstructed the (5 × 20) surface, and several ordered LEED patterns were observed. Upon heating, oxygen desorbed from the surface in two peaks at 676 and 709 K; the lower temperature peak exhibited atrractive lateral interactions evidenced by autocatalytic desorption kinetics. Hydrogen was also found to reconstruct the (5 × 20) surface to the (1 × 1) structure, provided adsorption was performed at 200 K. For all three species, CO, O2, and H2, the surface returned to the (5 × 20) structure only after the adsorbates were completely desorbed from the surface. 相似文献
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Bromine gas adsorbs atomically on W(100) at room temperature to a saturation concentration of θ = 0.88 relative to the surface tungsten atom density (1019 m?2). Below θ ~ 0.4, a c(2 × 2) overlayer is formed. Beyond this a (√2 × √2)R45° structure is preferred and this saturates at θ = 0.67. Higher surface bromine concentrations result in hexagonal variable compression structures on W(100). The sequence begins w structures on W(100). The sequence begins with a c(4 × 2) coincidence mesh which at higher coverages is compressed in one 〈0,1〉 substrate direction. At certain compressions the overlayer achieves p(5 × 2), c(6 × 2), p(7 × 2) coincident configurations and perhaps c(8 × 2) at saturation. This would correspond to θ = 0.875 and is the closest coincidence structure to a perfect hcp overlayer. Bromine prefers a rectangular overlayer geometry on W(100) and compression into an hexagonal array greatly reduces the overlayer stability. The nn repulsions incurred limit room temperature adsorption as the overlayer compresses to perfect hep. Halogen behaviour on W(100) is compared with that on Fe(100). Most differences can be explained in terms of geometrical and bond strength differences but chlorine on W(100) appears to be an exception to this rule. 相似文献
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The adsorption of carbon monoxide on Cu(110)-Ni surfaces prepared by dissociation of nickel carbonyl
C.M.A.M. Mesters A.F.H. Wielers O.L.J. Gijzeman J.W. Geus G.A. Bootsma 《Surface science》1982,115(2):237-246
Cu(110)-Ni surface alloys were prepared by dissociation of nickel carbonyl on clean Cu(110). The adsorption of CO is reversible in the temperature region of 22–200°C and the pressure range of 5 × 10?8-0.7 Torr, as monitored with ellipsometry and AES. The amount of adsorbed CO depends on the amount of preadsorbed oxygen but not on the amount of carbon present at the surface. The isosteric heat of adsorption decreases from 31 ± 3kcal/mole to 18 ± 2 kcal/mole with increasing CO coverage (up to θ = 0.14θmax) but is constant for higher coverages (up to θ = 0.4θ max). 相似文献
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Cesium adsorption on oxygenated and oxidized W(110) is studied by Auger electron spectroscopy, LEED, thermal desorption and work function measurements. For oxygen coverages up to 1.5 × 1015 cm?2 (oxygenated surface), preadsorbed oxygen lowers the cesiated work function minimum, the lowest (~1 eV) being obtained on a two-dimensional oxide structure with 1.4 × 1015 oxygen atoms per cm2. Thermal desorption spectra of neutral cesium show that the oxygen adlayer increases the cesium desorption energy in the limit of small cesium coverages, by the same amount as it increases the substrate work function. Cesium adsorption destroys the p(2 × 1) and p(2 × 2) oxygen structures, but the 2D-oxide structure is left nearly unchanged. Beyond 1.5 × 1015 cm?2 (oxidized surface), the work function minimum rises very rapidly with the oxygen coverage, as tungsten oxides begin to form. On bulk tungsten oxide layers, cesium appears to diffuse into the oxide, possibly forming a cesium tungsten bronze, characterized by a new desorption state. The thermal stability of the 2D-oxide structure on W(110) and the facetting of less dense tungsten planes suggest a way to achieve stable low work functions of interest in thermionic energy conversion applications. 相似文献
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In this paper, we reexamine the surface structures of CO on (100) surfaces of copper, palladium, nickel and platinum. We use the types of site determined by High Resolution Energy Electron Loss Spectroscopy (HREELS), or Infra Red Spectroscopy (IRS), to propose new models for the arrangement of CO molecules at coverages exceeding , i.e. at coverages higher than those corresponding to simple structures c(2 × 2) and . Laser simulations allow us to decide the validity of the proposed models. The consequences of these models are the existence of at most two adsorption sites at all coverages, and the existence of antiphase domains separated by walls to form the complex structures. The transition between two consecutive structures due to an increase of coverage is a unidirectional compression, generating more wall regions. 相似文献
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The adsorption of oxygen on Ag(111) has been studied by ellipsometry in conjunction with AES and LEED. The oxygen pressure varied between 10?5 and 10?3 Torr and the crystal temperature between room temperature and 250° C. Changes in the Auger spectrum and the LEED pattern upon oxygen adsorption are very small. Oxygen coverages were derived from the changes in the ellipsometric parameter Δ. At room temperature a maximum coverage is reached within a few minutes. Its value increases with the damage produced by the preceding argon ion bombardment. The sticking coefficient derived from the initial rate of Δ-change amounts to 3 × 10?5 for well-annealed surfaces and 2.5 ? 5 × 10?4 for damaged surfaces. After evacuation no desorption takes place. Other types of adsorption, associated with much larger changes in Δ, were observed upon bombardment with oxygen ions and with oxygen activated by a hot filament. The reaction of CO with adsorbed oxygen was studied ellipsometrically at room temperature in the CO pressure range 10?7–10?6 Torr. The initial reaction rate is proportional to the CO pressure. The reaction probability (number of oxygen atoms removed per incident CO molecule) is 0.36. 相似文献