O在预覆盖K的Ag(110)表面的共吸附及其性质

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O^2-和表面上吸附的O^x-增加K的覆盖度,出现分子状态的吸附物O₂^δ-,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：     

NO在Ag/Pt(110)-(1×2)双金属表面的吸附：亚硝酸盐/硝酸盐表面物种的生成

以俄歇电子能谱、X射线光电子能谱和热脱附谱研究了室温下NO在Ag/Pt(110)-(1×2)双金属表面的吸附. 在该双金属表面上观察到了可能的亚硝酸盐/硝酸盐表面物种,其在更高温度下分解生成N₂. 然而,室温下NO在清洁Pt(110)表面和Ag-Pt合金表面上并不会生成这种亚硝酸盐/硝酸盐表面物种. 亚硝酸盐/硝酸盐表面物种的形成归因于高度配位不饱和Ag粒子的高活性及其与Pt基底之间的协同作用.     

利用原子集团多重散射理论决定HCOO-Cu(110)的结构

利用原子集团多重散射理论计算甲酸在Cu(110)表面催化分解中间产物HCOO(formate)的O原子K边X射线吸收精细结构谱,证实formate吸附在Cu(110)表面长方元胞的短桥位,求得C—O键长等于1.26±0.01?,Cu—O键长为1.975±0.02?,O—C—O键角处于130°—134°范围内。上述结果与光电子衍射谱的分析结论一致。 关键词：     

CO与K在Cu(111)面上共吸附的角分辨紫外光电子能谱

CO在有K沉积的Cu(111)面上吸附的角分辨紫外光电子能谱(ARUPS)测量结果表明:在室温下,有分子状态的CO吸附在该表面,CO分子的4σ态信号强度明显低于5σ/1π态的强度,这表明CO分子在该状态下是强烈倾斜的,低温下(～150K),有两种不同的CO吸附状态,一种只有在较高CO暴露量下才出现,而另一种则在任何暴露量下都存在,后者是一种类似于CO在室温时的吸附状态。 关键词：     

分子束外延GaN薄膜的X射线光电子能谱和俄歇电子能谱研究

用XPS和AES电子能谱的方法对等离子体辅助分子束外延(MBE)生长的GaN薄膜进行了表面分析和深度剖析.发现红外分子束外延(RFMBE)生长的富镓GaN薄膜实际表面存在O和C吸附层,C主要为物理吸附,而O在GaN表面形成局域化学键产生氧络合物覆盖层,并形成一定的深度分布.杂质O在GaN带隙中导带底形成杂质带同时引入深受主能级,使得带隙变窄室温光吸收谱向低能方向移动,光致发光谱出现宽带发光峰.从而影响GaN薄膜的电学和光学性质 关键词： GaN薄膜 X射线光电子能谱 俄歇电子能谱 表面分析     

利用扫描隧道显微镜研究水分子在Cu(110)表面的吸附与分解

利用扫描隧道显微镜研究水分子在吸附有氧原子的Cu(110)表面的吸附与分解过程.室温条件下,氧原子(O)在Cu(110)表面吸附并自组装形成规则的沿[001]方向的(2×1)Cu-O链状结构.将吸附有氧原子的Cu(110)样品置于77 K低温条件下观察水分子的吸附与分解,发现在低温下水分子通过氢键与Cu-O链中的氧原子键合而吸附于Cu-O链的顶部和周围,吸附于Cu-O链周围的水分子自组装形成规则的六边形网状结构.通过针尖隧穿电子激发,六边形网状结构中的水分子与氧原子发生化学反应,反应生成的羟基与未参与反应的水分子键合在裸露的Cu(110)表面形成蜂窝网状结构.研究结果表明,Cu(110)表面吸附的氧原子有助于水分子在金属表面的吸附和组装,同时可以催化金属表面水分子的分解反应,对水汽转换实验研究具有一定的指导意义.     

Cu-Zr合金在氢气氛中退火后表面Cu沉积物的光电子能谱研究

对不同成分的Cu-Zr合金,在超高真空(UHV)和在氢气氛中200—400℃退火后的光电子能谱(XPS)研究发现,与多数情况下因氧感应致使Zr发生表面分凝相反,富铜样品在氢气氛下退火,Cu发生强烈的表面分凝;扫描电子显微镜得出表面Cu沉积物的显微照片,显然,这是由于Cu上氢化吸附热的影响所形成。 关键词：     

碱金属促进CO在Ag(110)上分解的实验证据

本文用X射线光电子能谱(XPS)和紫外光电子能谱(UPS)研究了CO与预覆盖Ne的Ag(110)表面的相互作用。低温下CO饱和吸附在Na/Ag(110)上存在两种吸附态,随衬底温度升高仅留下一种吸附态。实验结果表明,该吸附态与Ag(110)上存在的Na有关它是CO解离的前驱态。 关键词：     

Cu/CeO2(110)界面特性的第一性原理研究

Cu-CeO₂体系因其特殊的催化能力而在固体氧化物燃料电池和水煤气转化反应等多个催化领域有重要应用. 采用基于密度泛函理论的第一性原理方法, 在原子和电子层面上系统地研究了单个Cu原子及Cu小团簇在CeO₂(110)面上的吸附构型, 价键特性和电子结构, 结果表明: 1) 单个Cu原子的最稳定吸附位是两个表面O的桥位; 2) Cu团簇的稳定吸附构型为扭曲的四面体结构; 3) Cu原子及Cu团簇的吸附在CeO₂(110)面的gap区域引入了间隙态, 这些间隙态主要来自于Cu及其近邻的O和表层还原形成的Ce³⁺, 间隙态的出现表明Cu的吸附增强了CeO₂(110)表面的活性; 4) 吸附的单个Cu原子及Cu团簇分别被CeO₂(110)面表层的Ce⁴⁺离子氧化形成了Cu^δ+和Cu₄^δ+, 并伴随着Ce³⁺离子的形成, 这个反应可归结为Cu_x/Ce⁴⁺→Cu_x^δ+/Ce³⁺; 5) Cu团簇的吸附比Cu单原子的吸附引入了更多的Ce³⁺离子, 进而形成了更多的Cu^δ+-Ce³⁺催化活性中心. 结合已报道的Cu/CeO₂(111)界面特性, 更加全面地探明了Cu与CeO₂(111)和(110)两个较稳定低指数表面的协同作用特性, 较为系统地揭示了Cu增强CeO₂催化特性的原因及Cu与CeO₂协同作用的内在机理. 关键词： 2')" href="#">Cu/CeO₂ U')" href="#">DFT+U 吸附 电子结构     

NO在清洁和Cs覆盖的Ru(100)表面上吸附的热脱附谱

用热脱附谱等方法研究了NO分别在清洁和Cs覆盖的Ru(1010)表面上的吸附.结果表明:存在两种NO分子吸附态(a1,a2),脱附温度分别处于325℃和550℃附近.Cs的存在增加了Ru(1010)表面上a2态的吸附位置,提高了该态的脱附温度.Cs在Ru(1010)表面上的存在同时促进了吸附NO分子的分解.NO在Ru(1010)表面上分解后形成吸附O原子和N原子.N原子复合以N2在约500℃附近脱附,同时Cs的存在也促进了N2O的形成.在Cs覆盖的Ru(1010)表面上,N2O的脱附温度约在425℃.     

Adsorption an Einkristall-Oberflächen von Cu/Ni-legierungen. I

The adsorption of O₂ and CO on the (110) face of a Cu/Ni alloy (55 at% Cu) has been studied by means of low energy electron diffraction (LEED), Auger electron spectroscopy, work function measurements, and flash desorption. A comparison with the behavior of Cu(110) and Ni(110) is made. It is shown that the height of an Auger peak is proportional to the surface concentration of the corresponding species and that the surface composition of the alloy is identical with the composition of the bulk. Adsorption of oxygen leads to the formation of an ordered 2 × 1 structure, as is the case for Cu(110) and Ni(110). Further exposure causes disordered adsorption in contrast to the pure components where c6 × 2 respectively 3 × 1 structures are formed. Oxygen increases the work function of Cu and Cu/Ni by about 0.25 eV whereas for Ni the increase is > 1 eV. CO is not irreversibly adsorbed on Cu at 25°C, but forms a stable 1 × 1 structure on Ni(110). With the alloy two ordered phases (2 × 1 and 2 × 2) are observed. The flash desorption spectrum shows three maxima which are similar to the binding states of CO on Ni(110) and Ni(100). The results are discussed in view of the electronic structure of Cu/Ni alloys and the parameters influencing the configuration of adsorbed particles.     

The adsorption of water on clean and oxygen covered Cu(110)

The water adsorption on clean and oxygen precovered Cu(110) surfaces is studied by means of UPS, LEED, work function measurements and ELS. At 90 K on the clean surface molecular water adsorption is indicated by UPS. The H₂O molecules are bonded at the oxygen end and the H-O-H angle is increased as compared with the free molecule. In the temperature range between 90 and 300 K distorted H₂O molecules and adsorbed hydroxyl species (OH) are detected, which are desorbed at room temperature. On an oxygen covered surface hydroxyl groups are formed by dissociation of adsorbed water molecules at a lower temperature than on the clean surface. Multilayers of condensed water are found below 140 K in both cases.     

Orientation and bonding of adsorbed CH3NCO on Pt{110} and Cu{110} from vibrational and photoelectron spectroscopies

The bonding and orientation of CH{in3}NCO on Pt{110} and Cu{110} are studied by HREELS, ARUPS, AES, and LEED. CH{in3}NCO is found to adsorb nondissociatively on both Cu{110} and Pt{110} at T = 160 K, bonding primarily through the 2π a′ orbital with the NCO group lying down on the surface and the methyl group largely unperturbed. We propose that the absence of a strong HREELS band at about 2290 cm^?1, which is the liquid phase frequency for the NCO asymmetric stretching mode, combined with the presence of strong bands between 1000 and 1450 cm^?1 provides a “finger-print” for NCO bonded to the surface in a lying-down configuration.     

Theoretical studies of CO and NO on CuO and Cu2O(110) surfaces

The characteristics of CO and NO adsorption on surfaces of CuO(110) and Cu₂O(110) have been studied by using the self-consistent-charge discrete variational X_a method (SCC-DV-X_a). The calculated results show that the CO and NO molecules are perpendicularly adsorbed on cuprous ions of Cu₂O and cupric ions of CuO, respectively and with oxygen pointing upward in both cases. The order of chemisorption energy of the four adsorbed systems is: CuO-NO > Cu₂O-CO > Cu₂O-NO > CuO-CO. In all chemisorptions discussed d orbitals of Cu do play an important role.     

Thermal stability of adsorbed CH3NCO on Cu{110} AND Pt{110} from vibrational and photoelectron spectroscopies

The thermal stability of CH₃NCO adsorbed on Cu{110} and Pt{110} is investigated using HREELS, TPD, and ARUPS. CH₃NCO desorbs largely without fragmentation from Cu{110}, but on Pt{110} only about 20% of the adsorbed CH₃NCO desorbs intact, with 80% decomposing on the surface at T > 200 K into CO(a), H(a), CH_x(a), N(a) and NH_y(a) fragments. The kinetics of the surface decomposition were characterised for 220 < T < 300 K by HREELS and the activation energy for CH₃NCO decomposition was found to vary strongly as a function of coverage.     

The surface chemistry of H2O on clean and oxygen-covered Cu(110)

Adsorption of water at 100 K. on clean and oxygen-covered Cu(110) has been studied using UPS, TDS, Δφ and LEED measurements. The results indicate that two-dimensional hydrogenbonded islands are formed on the clean surface. The long-range order in these islands is in registry with the substrate lattice and gives rise to a c(2×2) LEED pattern. Upon the formation of multilayer ice, the ordering disappears. The presence of oxygen on the surface disrupts the hydrogen bonding, and composite oxygen-water layers are formed. A model of the arrangement of oxygen atoms and water molecules is presented, based upon the LEED observations for these layers and an estimate of the relative oxygen and water coverages. The intensity variation of a thermal desorption peak at 290 K, attributed to adsorbed OH species, with oxygen coverage is in accordance with this model. For low oxygen coverages, the TDS and Δφ results indicate that small oxygen-water clusters with an enhanced ratio of water molecules per adsorbed oxygen atom are present.     

AES and LEED studies of xenon adsorption on (100)NaCl

The thermal and electro impact behaviour of NO adsorbed on Pt(111) and Pt(110) have been studied by LEED, Auger spectroscopy, and thermal desorption. NO was found to adsorb non-dissociatively and with very similar low coverage adsorption enthalpies on the two surfaces at 300 K. In both cases, heating the adlayer resulted in partial dissociation and led to the appearance of N₂ and O₂ in the desorption spectra. The (111) surface was found to be significantly more active in inducing the thermal dissociation of NO, and on this surface the molecule was also rapidly desorbed and dissociated under electron impact. Cross sections for these processes were obtained, together with the desorption cross section for atomically bound N formed by dissociation of adsorbed NO. Electron impact effects were found to be much less important on the (110) surface. The results are considered in relation to those already obtained by Ertl et al. for NO adsorption on Ni(111) and Pd(111), and in particular, the unusual desorption kinetics of N₂ production are considered explicitly. Where appropriate, comparisons are made with the behaviour of CO on Pt(111) and Pt(110), and the adsorption kinetics of NO on the (110) surface have been examined.     

ESR of adsorbates on single crystal metal surfaces under UHV conditions

Angular dependent electron spin resonance measurements were taken for paramagnetic molecules adsorbed on metallic single crystal surfaces in UHV. For the hydrated Cu(NO₃)₂ complex on a Cu[111] surface an angular dependent ESR signal is recorded. The plane ofthe molecule is found to lie preferentially out of the surface plane. Experiments on chemisorbed molecular O₂ on Ag[110] at 25 K and NO on Pt[111] at 110 K show no sharp ESR signal characteristic for well localized moments. If one assumes that NO on Pt (respectively Pd) carries an unpaired spin, one can estimate a lower limit for the spin flip rate of π^?1>2×10⁹s^?.     

A UPS and LEED/Auger study of adsorbates on Fe(110)

Ultraviolet photoemission spectroscopy (UPS) and LEED/Auger were used to study adsorbed species of C, N, O, S, CO, NO, and C₂H₂ on Fe(110). The complicated “carbon ring” LEED patterns were shown to be due to atomic carbon and/or nitrogen. Molecular nitrogen does not stick at or above room temperature on Fe(110). The optical excitation probability of the 3p electrons of segregated sulphur is found to have a Cooper minimum aroundhω=40.8 eV. Carbon monoxide chemisorbs molecularly at room temperature and then dissociates slowly. Only dissociative CO adsorption was observed atT=385 K. Acetylene also adsorbs molecularly but does not dissociate at room temperature. By contrast, nitric oxide chemisorption is completely dissociative at room temperature.     

Chemisorption and surface reactivity of nitric oxide on clean and sodium-dosed Ag(110)

The chemisorption of NO on clean and Na-dosed Ag(110) has been studied by LEED, Auger spectroscopy, and thermal desorption. On the clean surface, non-dissociative adsorption into the α-state occurs at 300 K with an initial sticking probability of ～0.1, and the surface is saturated at a coverage of about $\text{1}\text{25}$. Desorption occurs without decomposition, and is characterised by an enthalpy of E_d ～104 kJ mol^?1 — comparable with that for NO desorption from transition metals. Surface defects do not seem to play a significant role in the chemistry of NO on clean Ag, and the presence of surface Na inhibits the adsorption of αNO. However, in the presence of both surface and subsurface Na, both the strength and the extent of NO adsorption are markedly increased and a new state (β₁NO) with E_d ～121 kJ mol^?1 appears. Adsorption into this state occurs with destruction of the Ag(110)-(1 × 2)Na ordered phase. Desorption of β₁NO occurs with significant decomposition, N₂ and N₂O are observed as geseous products, and the system's behaviour towards NO resembles that of a transition metal. Incorporation of subsurface oxygen in addition to subsurface Na increases the desorption enthalpy (β₂NO), maximum coverage, and surface reactivity of NO still further: only about half the adsorbed layer desorbs without decomposition. The bonding of NO to Ag is discussed, and comparisons are made with the properties of α and βNO on Pt(110).