Organizing C60 molecules on a nanostructured Au(111) surface

We have studied, using scanning tunneling microscopy, the adsorption of C₆₀ molecules on a nanostructured Au(111) surface consisting of artificially created two-dimensional cavities. These cavities, one atomic layer deep, are found to be effective as molecular traps at room temperature. Gold atoms at step edges are found to respond to the adsorption of C₆₀ molecules and gross faceting is observed for steps connected with R30° oriented C₆₀ molecular islands. Structural models are proposed to establish the step structures related to all three types of molecular islands.     

Interactions of CO molecules adsorbed on oxidised Cu(111) and Cu(110)

Reflection absorption infrared spectroscopy has been used in conjunction with LEED and surface potential measurements to study low temperature CO adsorption on the oxidised Cu surfaces Cu(111)O|$\text{3}\text{2}\text{?}\text{2}$|, Cu(110)O(2 × 1) and Cu(110)Oc(6 × 2). On all three surfaces adsorption at 80 K yields surface potential changes in excess of 0.6 V and does not lead to the formation of an ordered overlayer. At high coverages the adsorption enthalpy is lower than on the clean surfaces. Infrared spectra show the growth of a doublet band with components initially at 2100 and 2117 cm^?1 on the oxidised Cu(111) surface. Similar features seen on the oxidised Cu(110) surfaces are accompanied by a band at 2140 cm^?1: a very weak band at the same frequency on oxidised Cu(111) is attributed to defect sites. Studies of the temperature dependence of the spectrum from oxidised Cu(111) lead to the conclusion that two different binding sites are occupied. Spectra of ${}^{12}\text{CO}{}^{13}\text{CO}$ mixtures show that the molecules occupying these sites are in close proximity to each other, and that the spectrum is subject to large but opposing coverage-dependent frequency shifts.     

Photoelectron spectroscopy from CO adsorbed on a Cu(111) surface

He II-ultraviolet photoelectron spectra (hv = 40.8 eV) from a carbon monoxide layer adsorbed on a Cu(111) surface exhibit two peaks at 8.5 and 11.6 eV below the Fermi level and a weaker maximum centered at about 13.5 eV. The emission from the Cu d-band is markedly suppressed after adsorption. The results are discussed in terms of the recent models for assigning the UPS peaks observed after adsorption of CO on transtion metals     

Au(111)表面单个钴酞菁分子的去氢过程

利用低温超高真空扫描隧道显微镜对单个钴酞菁分子实现了选键化学反应.通过对吸附于Au(111)表面的单个钴酞菁分子外围H原子的"剪裁",并用实验图像和谱学方法,结合第一性原理理论计算研究了逐步去除钴酞菁分子8个外围H原子的过程.理论计算结果再现了实验中所观测到的分子空间构型的变化,并阐明了吸附体系中局域自旋的恢复和变化过程.     

Quantitative analysis of long-range interactions between adsorbed dipolar molecules on Cu(111)

Highly dispersed superstructures of a dipolar iridium complex are formed on a Cu(111) surface. We show that the dilute superstructures with density-controlled intermolecular separations are stabilized by the strong and long-range repulsive intermolecular interactions. The repulsive intermolecular interactions are quantitatively evaluated by using low-temperature scanning tunneling microscopy, which are characterized by the surface-enhanced dipole-dipole interactions.     

The surface chemistry of methyl and methylene radicals adsorbed on Cu(111)

The interactions of methyl and methylene radicals on Cu(111) were investigated with XPS, AES and HREELS under various exposure conditions. The CH₂ and CH₃ radicals are generated through a hot nozzle source with ketene and azomethane gases. It is shown that with substrate at 300 K, the impinging CH₃ radicals are trapped mainly as CH₃(ads), while a part of the adsorbate decomposes to form CH₂(ads) and H(ads). H atoms are found to desorb at about 380 K, while the chemisorbed hydrocarbon adspecies desorb at about 420 K. In drastic contrast, exposing the clean Cu surface to methylene radicals results not only in the trapping of CH₂(ads), but also in the formation of complex aromatic species. The adlayer is sensitive to annealing at elevated temperatures. Desorption and partial conversion to methylidyne take place at around 420 K. The CH(ads) species can survive up to 700 K and then decomposes to form residual carbon above 800 K. In both radical-Cu(111) systems, surface coverage appears to saturate near one monolayer. The relative concentrations of different surface species in the adlayer, however, depend on the amount of radical exposure. The reaction properties of the two systems are compared and discussed.     

NEXAFS study of 1-butanethiol adsorbed on Cu(111) and square root of 7 x square root of 7 R19.1 degrees S/Cu(111)

The adsorption of 1-butanethiol on Cu(111) and square root of 7 x square root of 7 R19.1 degrees S/Cu(111) surfaces has been studied by S K-edge near edge X-ray absorption fine structure (NEXAFS) spectroscopy and thermal desorption spectroscopy. Upon adsorption on clean Cu(111) surface at room temperature, butanethiolate as well as atomic sulfur is formed. For the butanethiolate, the S-C bond is found predominately perpendicular to the surface as revealed by polarization analysis. In contrast, on square root of 7 x square root of 7 R19.1 degrees S/Cu(111) surface, the S-H and S-C bonds of the butanethiol stay intact, resulting in a weakly chemisorbed butanethiol.     

Origin of O 1s core-level shifts on oxygen adsorbed Si(111)-(7x7)

Density functional calculations are used to examine the chemical and structural origin of O 1s core-level shifts measured on the initial oxidation stage of Si(111)-(7x7). Our analysis of metastable core-level peaks leads to a conclusive identification of the long-sought metastable oxidation species as a tetrahedral SiO4 unit, formed by two successive O2 adsorptions on a Si adatom. The origin of a higher-binding core-level shoulder is clarified by the presence of a threefold-coordinated subsurface O atom, introduced as a decay product of the metastable SiO4 unit. The present study provides a detailed atomic-scale picture of the initial oxidation process of Si(111)-(7x7).     

Structural and optical properties of the Ge(111)-(2 x 1) surface

We study the two lowest-energy isomers of the Ge(111)-(2 x 1) surface, by a state-of-the-art first-principles calculation of their optical spectra, including the electron-hole interaction effects. A comparison of our results with the available experimental data suggests that, at difference with the silicon case, the stablest isomer differs from the standard "buckled Pandey chains" reconstruction. This conclusion is supported by accurate total-energy results.     

Orientationally ordered (7x7) superstructure of C60 on AU(111)

Long range orientational order within C60 monolayers on Au(111) is observed with low-temperature scanning tunneling microscopy. A unit cell comprised of 49 molecules which adopt 11 different orientations is found. It can be divided in a faulted and an unfaulted half similar to the (7x7) reconstruction of Si(111). A model is proposed which shows how, through a Moiré-like effect, the substrate induces minute changes in the orientation of the C60 molecules. Intermolecular interactions are shown to play a major role in stabilizing the superlattice.     

Monomer structures of water adsorbed on p(2 x 2)-Ni(111)-O surface at 25 and 140 K studied by surface X-ray diffraction

The structures of a monomeric water molecule adsorbed on p(2 x 2)-Ni(111)-O surface were determined by difference Fourier calculations. At temperatures of 25 K, water molecules chemisorb predominantly at 2 x 2 oxygen atom sites, forming an OH---O(ad) (2 x 2) hydrogen bond. A 2 x 2 oxygen atom (O(ad)) is surrounded by one to three monomeric water molecules, which take statistically disordered positions with threefold symmetry. At temperatures of 140 K, monomeric water molecules occupy a top site of Ni atoms via an oxygen lone pair and are stabilized as a singleton molecule on the surface.