银(110)表面苝有序薄膜电子态的研究

运用紫外光电子能谱(UPS)和低能电子衍射(LEED)技术,对银(110)表面上有机分子苝（perylene）的生长进行了研究.有机分子价带的4个特征峰分别位于费米能级以下3.5、4.8、6.4和8.5 eV处.当有机薄膜约为单分子层(厚度为0.3 nm)时, 苝在银(110)表面上形成C(6×2)的有序结构.角分辨紫外光电子能谱(ARUSP)的测量显示:在界面处的苝分子平面平行于衬底.苝在银(110)表面稳定性很高,随着对衬底加热，有机材料发生脱附,在140 ℃以下没有观察到分解现象.     

COT-H在金属Ru表面上沉积的光电子能谱分析

采用紫外光电子能谱（UPS），分析了不对称四苯基四苯乙炔基环辛四烯（COT H）有机发光材料与金属之间的界面电子结构，研究了在金属/COT H界面上的逸出功变化.UPS谱中位于费米能级以下5.6、7.9和10.2 eV处的三个谱峰分别来自于COT H材料中苯环的πCC、σCC和σCH轨道.位于3.8 eV处的谱峰反映了八个苯环聚合后具有π轨道特性的C－C键.从UPS谱图中可以看到， COT H材料的最高占有态（HOS：highest occupied state）位于费米能级以下1.8 eV处.COT H材料的逸出功只有3.2 eV，比清洁Ru表面的逸出功小1.0 eV.角分辨紫外光电子能谱（ARUPS）的结果表明,组成COT H分子应该近似平行于衬底表面.     

Fluorescein有机薄膜在Ag(110)面上的生长研究

利用紫外光电子能谱(UPS)对在Ag(110)表面上荧光素(fluorescein)的生长进行研究. 研究表明, 与fluorescein分子轨道有关的4个特征峰分别位于费米能级以下2.70, 3.80, 7.40和9.80 eV处. 角分辨紫外光电子能谱(ARUPS)测量结果表明, fluorescein分子的三苯环平面平行衬底平面, 分子的C=O轨道轴向接近于[1-10]晶向.     

The growth of perylene on Ru(0001)

The structure of perylene adsorbed on Ru(0001) surface has been studied by ultraviolet photoemission spectroscopy (UPS) and low-energy electron diffraction. An ordered p(4x4) structure is observed from a monolayer (about 4 A thickness) of the perylene on Ru(0001) surface. UPS measurements show the molecular features, from the perylene multiplayer, between 2 and 10 eV below the Fermi level. Angle-resolved ultraviolet photoemission spectroscopy measurements suggest that the perylene molecular plane is parallel to the substrate. Temperature dependent UPS measurements show that the perylene multilayer is stable on Ru(0001) surface up to 125 degrees C. The desorption of the multilayer and the decomposition of the monolayer are observed above 125 degrees C.     

Chemisorption of carbon monoxide on the platinum(100) surface: A definition of electronic states by photoelectron spectroscopy

UPS studies are reported for carbon monoxide chemisorbed, at varying coverages, on a clean Pt(100) surface. A new assignment of surface states is obvious from the broadening and resolution of the emission peak, positioned at ca. 8 eV below the Fermi level, following pre-adsorption of propene and pyridine. The valence band density of states, determined by He(I) and He(II) emission spectroscopy, is compared with that reported earlier by X-ray electron emission spectroscopy.     

UPS和功函数研究氧在电解银上的吸附

本文报导了用紫外光电子能谱(UPS), 热脱附(TDS)和表面功函数连续测量等手段对氧与电解银表面相互作用过程中的电荷传递, 成键以及吸附动力学等研究的实验结果。     

Characterizing TiO2(110) surface states by their work function

The unreconstructed TiO(2)(110) surface is prepared in well-defined states having different characteristic stoichiometries, namely reduced (r-TiO(2), 6 to 9% surface vacancies), hydroxylated (h-TiO(2), vacancies filled with OH), oxygen covered (ox-TiO(2), oxygen adatoms on a stoichiometric surface) and quasi-stoichiometric (qs-TiO(2), a stoichiometric surface with very few defects). The electronic structure and work function of these surfaces and transition states between them are investigated by ultraviolet photoelectron spectroscopy (UPS) and metastable impact electron spectroscopy (MIES). The character of the surface is associated with a specific value of the work function that varies from 4.9 eV for h-TiO(2), 5.2 eV for r-TiO(2), 5.35 eV for ox-TiO(2) to 5.5 eV for qs-TiO(2). We establish the method for an unambiguous characterization of TiO(2)(110) surface states solely based on the secondary electron emission characteristics. This is facilitated by analysing a weak electron emission below the nominal work function energy. The emission in the low energy cut-off region appears correlated with band gap emission found in UPS spectra and is attributed to localised electron emission through Ti(3+)(3d) states.     

Deposition of tetracene on GaSe passivated Si(111)

The growth of tetracene on GaSe half-sheet passivated Si(111) is investigated under ultrahigh vacuum (UHV) using low-energy electron diffraction (LEED) and photoelectron spectroscopy (PS). A highly ordered thin-film growth was observed in the initial stages of the deposition process. All proposed structures form a coincidence lattice with the underlying substrate, due to the influence of the molecule-substrate interactions and are built up by either flat lying tetracene molecules at low coverage or tilted molecules at higher coverages. Photoelectron spectroscopy (XPS/UPS) shows that the deposited tetracene molecules induce band bending in the silicon substrate. No band bending was observed in the tetracene film, and an interface dipole potential of 0.45 eV was measured between the GaSe passivated Si(111) surface and the tetracene film.     

吸附O的Cu(110)c(2×1)表面原子结构和电子态

采用第一性原理的密度泛函理论方法计算了清洁Cu(110)表面和吸附O原子的Cu(110) c(2×1)表面的原子结构, 结构弛豫和电子结构, 得到了各种表面结构参数. 分别计算了O原子在Cu(110)表面三个可能吸附位置吸附后的能量, 并给出了能量最低的吸附位置上各层原子的弛豫特性和态密度. 结果表明O吸附后的Cu(110)表面有附加列(added-row)再构的特性, O原子吸附在最表层铜原子上方, 与衬底Cu原子的垂直距离为0.016 nm, 以氧分子为能量基准的吸附能为－1.94 eV; 同时由于Cu 3d- O 2p态的杂化作用使得低于费米能级5.5~6.0 eV的范围内出现了局域的表面态. 计算得到清洁的和氧吸附的Cu(110)表面的功函数分别为4.51 eV和4.68 eV. 电子态密度的结果表明：在Cu(110) c(2×1) 表面O吸附的结构下, 吸附O原子和金属衬底之间的结合主要是由于最表层Cu原子3d态和O原子2p态的相互作用.     

Ni(110)-p2mg(2×1)-CO表面的几何结构和电子态

利用密度泛函理论(DFT)总能计算研究了Ni(110)-p2mg(2×1)-CO表面的原子结构和电子态. 计算结果表明: CO分子吸附于该表面的短桥位附近, 分子吸附能为1.753 eV, CO分子的键长dC—O为0.117 nm, 分子与表面竖直方向的夹角为20.0°, 碳原子和短桥位中点的连线与竖直方向的夹角为20.9°; 吸附的CO分子内原子间的伸缩振动频率为1876和1803 cm-1. 态密度研究结果表明吸附作用主要来自CO分子π、σ轨道与衬底d轨道间的杂化作用. CO分子σ轨道和衬底表面镍原子dxz轨道杂化形成的表面电子态主要位于费米能以下-10.4 至-8.8 eV和-7.4至-5.1 eV 范围内. σ和dxz轨道间的杂化作用可能是形成p2mg表面对称性的重要因素之一.     

Local chemical reaction of benzene on Cu110 via STM-induced excitation

We have investigated the mechanism of the chemical reaction of the benzene molecule adsorbed on Cu(110) surface induced by the injection of tunneling electrons using scanning tunneling microscopy (STM). With the dosing of tunneling electrons of the energy 2-5 eV from the STM tip to the molecule, we have detected the increase of the height of the benzene molecule by 40% in the STM image and the appearance of the vibration feature of the nu(C-H) mode in the inelastic tunneling spectroscopy (IETS) spectrum. It can be understood with a model in which the dissociation of C-H bonds occurs in a benzene molecule that induces a bonding geometry change from flat-lying to up-right configuration, which follows the story of the report of Lauhon and Ho on the STM-induced change of benzene on the Cu(100) surface. [L. J. Lauhon and W. Ho, J. Phys. Chem. A 104, 2463 (2000)]. The reaction probability shows a sharp rise at the sample bias voltage at 2.4 V, which saturates at 3.0 V, which is followed by another sharp rise at the voltage of 4.3 V. No increase of the reaction yield is observed for the negative sample voltage up to 5 eV. In the case of a fully deuterated benzene molecule, it shows the onset at the same energy of 2.4 eV, but the reaction probability is 10(3) smaller than the case of the normal benzene molecule. We propose a model in which the dehydrogenation of the benzene molecule is induced by the formation of the temporal negative ion due to the trapping of the electrons at the unoccupied resonant states formed by the pi orbitals. The existence of the resonant level close to the Fermi level ( approximately 2.4 eV) and multiple levels in less than approximately 5 eV from the Fermi level, indicates a fairly strong interaction of the Cu-pi(*) state of the benzene molecule. We estimated that the large isotope effect of approximately 10(3) can be accounted for with the Menzel-Gomer-Redhead (MGR) model with an assumption of a shallow potential curve for the excited state.     

Directly probing the hybrid bonding of styrene on Cu111

The interfacial electronic structure of chemisorbed styrene on Cu(111) was successfully investigated with two-photon photoemission spectroscopy. We observed unoccupied states 3.5 eV above the Fermi level and occupied states 2.0 eV below the Fermi level. Polarization results reveal that the occupied and unoccupied states arise from bonding and antibonding orbitals formed by hybridization of copper (surface state and d-band orbitals) and styrene (pi1* and pi2* orbitals).     

First principles study of adsorption of O2 on Al surface with hybrid functionals

Adsorption of O(2) molecule on Al surface has been a long standing puzzle for the first principles calculation. We have studied the adsorption of O(2) molecule on the Al(111) surface using hybrid functionals. In contrast to the previous local-density approximation/gradient-corrected approximation, the present calculations with hybrid functionals successfully predict that O(2) molecule can be absorbed on the Al(111) surface with a barrier around 0.2-0.4 eV, which is in good agreement with experiments. Our calculations predict that the lowest unoccupied molecular orbital of O(2) molecule is higher than the Fermi level of the Al(111) surface, which is responsible for the barrier of the O(2) adsorption.     

Hot hole-induced dissociation of NO dimers on a copper surface

We use reflection-absorption infrared spectroscopy (RAIRS) to study the photochemistry of NO on Cu(110) in the UV-visible range. We observe that the only photoactive species of NO on Cu(110) is the NO dimer, which is asymmetrically bound to the surface. RAIRS shows that photoinduced dissociation proceeds via breaking of the weak N-N bond of the dimer, photodesorbing one NO(g) to the gas phase and leaving one NO(ads) adsorbed on the surface in a metastable atop position. We model the measured wavelength-dependent cross sections assuming both electron- and hole-induced processes and find that the photochemistry can be described by either electron attachment to a level 0.3 eV above the Fermi energy E(F) or hole attachment to a level 2.2 eV below E(F). While there is no experimental or theoretical evidence for an electron attachment level so close to E(F), an occupied NO-related molecular orbital is known to exist at E(F) - 2.52 eV on the Cu(111) surface [I. Kinoshita, A. Misu, and T. Munakata, J. Chem. Phys. 102, 2970 (1995)]. We, therefore, propose that photoinduced dissociation of NO dimers on Cu(110) in the visible wavelength region proceeds by the creation of hot holes at the top of the copper d-band.     

苯在Rh(111)表面化学吸附的DV-Xα研究

The chemisorption of benzene on the Rh(111) surface is calculated using DVX_a method. The electronic structure, the ground states valence levels, Mulliken overlap populations, and the density of states (LDOS and TDOS) of the adsorption system C_6H_6/Rh_6(111) are obtained. The results of DV-X_a calculations indicate that the adsorbed benzene structure is unpertured from its stable gas-phase structure, is π-bonded to the Rh surface with ring plane parallel to the metal plane, and has a C_(3ν)(σ_d) bonding symmetry. We also discuss the charge transfer between adsorbate and substrate. The π electrons of benzene transfer to the empty d orbitals of Rh, so is resonance stability decreases and is easy to be hydrogenated. The results of TDOS are in agreement with UPS, supporting the LEED structural analysis. From figure 3, it can be found that the two peaks at 5—6 eV and 7—9 eV under Fermi level (E_F) move to left by about 0.5 eV in the process of adsorption, which are mainly contributed by the 2π and 1π orbiatls of benzene respectively and are widened, and the peaks at 2 eV and 4 eV over Fermi level also move to left, which are contributed by the empty d orbitals of Rh.     

1-Phenyl-1-propyne on Cu(111): TOFMS TPD, XPS, UPS, and 2PPE Studies

The bonding properties of 1-phenyl-1-propyne (PP, C6H5CCCH3) on Cu(111) at 100 K have been studied using temperature-programmed desorption (TPD), and X-ray, ultraviolet, and two-photon photoemission spectroscopies (XPS, UPS, and 2PPE). In TPD, there is no evidence for dissociation. Multilayer desorption occurs at 187 K, and monolayer desorption occurs at 320 (83.5 kJ/mol) and 390 K (102.4 kJ/mol), with the latter dominating. Based on the calibrated C(1s) XPS, the saturation monolayer coverage is one PP per four surface Cu atoms. The broad and asymmetric C(1s) intensity profile of the monolayer can be resolved into three symmetric components, with peaks at 283.6, 284.5, and 285.2 eV and intensities of 2:6:1, respectively. These are attributed, respectively, to acetylenic carbons bound to Cu, phenyl, and methyl carbons. The monolayer valence band ultraviolet photoemission spectrum profile contains four resonances attributable to PP perturbed by interactions with the Cu(111) substrate. With the exception of the highest occupied molecular orbital (HOMO) that is shifted by 0.4 eV, these are uniformly shifted by 1 eV further from the Fermi level for the multilayer. Calculated electron density plots of the occupied orbitals coupled with UPS profiles suggest a spectator role for the phenyl group and bonding to Cu via the acetylenic carbons. The adsorption of 1.0 monolayer (ML) of PP on Cu(111) lowers the work function by 0.85 eV. Using 2PPE, two unoccupied orbitals were identified at 1.0 (U1*-LUMO) and 0.6 eV (U2*-image state) below the vacuum level. A chemisorption model consistent with these spectroscopic results and the major chemisorption peak in TPD involve di-sigma-bonding of the acetylenic carbons to a pair of second-nearest neighbor surface Cu atoms (cross-bridge).     

Valence electron orbitals of an oligo(p-phenylene-ethynylene)thiol on gold

This communication reports measurement of one-photon (21.2 eV) and one-color, two-photon (3.2-4.5 eV) photoemission spectra of 4,4'-bis-(phenylethynyl)benzenethiol chemisorbed on gold. Four features are observed in these spectra: two occupied, predominantly molecular levels below the Fermi level and two unoccupied, predominantly molecular levels above the Fermi level. The occupied and unoccupied bands closest to the Fermi level are assigned to delocalized pi-bands, and the other occupied and unoccupied bands, to localized pi-bands. With this assignment, the hole- and electron-injection barriers and the transport gap for those levels are deduced.     

GaAs(100)解理面的能带弯曲

在真空中解理后,用XPS测得了GaAs样品（110）断面能带弯曲的动态过程．两组重掺杂n型和p型GaAs样品的费米能级分别向禁带中间的方向移动了0.4eV和0．3eV.实验测得重掺杂n型和p型GaAs样品费米能级之差为1．3eV,它们的禁带宽度理论值为1．42eV,这说明结果是合理的．根据实验结果,对引起GaAs表面能带弯曲的可能原因进行了分析讨论．排除了本征表面态、真空中残留气体和X射线辐射等原因,认为解理过程在表面产生的缺陷和解理后表面晶格弛豫过程中产生的缺陷可能是导致能带弯曲的主要原因．     

Orbital interactions in large molecular systems: Adsorption of H2 on Ni surfaces

The concept of orbital interactions is applied to the adsorption of H₂ on to the Ni (110) and (111) surfaces. We calculate first two orbitals of a Ni cluster one of which forms an orbital pair with the σ MO and the other with the σ*MO of a H₂ molecule. Contributions of these paired orbitals of fragments to the density of states of the surface-adsorbate extended system are then examined. It is shown that the orbital of the surface that participates in electron delocalization to σ* of the H₂ molecule is located significantly below the Fermi level both in the (110) and in the (111) adsorption models. The σ MO of H₂ and its counterpart of the surface represent mainly overlap repulsion which is shown to be stronger on the (111) surface than on the (110) surface. It is feasible to understand chemical interactions of large systems by using the paired interacting orbitals.     

Comparison of the periodic slab approach with the finite cluster description of metal–organic interfaces at the example of PTCDA on Ag(110)

We present a comparative study of metal–organic interface properties obtained from dispersion corrected density functional theory calculations based on two different approaches: the periodic slab‐supercell technique and cluster models with 32–290 Ag atoms. Fermi smearing and fixing of cluster borders are required to make the cluster calculation feasible and realistic. The considered adsorption structure and energy of a PTCDA molecule on the Ag(110) surface is not well reproduced with clusters containing only two metallic layers. However, all clusters with four layers of silver atoms and sufficient lateral extension reproduce the adsorbate structure within 0.04 Å with respect to the slab‐supercell structure and provide adsorption energies of ( 0.08 eV) consistent with the slab result of −4.47 eV. Thus, metal–organic adsorbate systems can be realistically represented by properly defined cluster models. © 2018 Wiley Periodicals, Inc.