Crystal growth of para-sexiphenyl on clean and oxygen reconstructed Cu(110) surfaces_Phys Chem Chem Phys 14675 (20113) (original) (raw)
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Morphology of Pd multilayers on Cu(110)
Surface Science, 1999
The growth of Pd films deposited on a Cu(110) single crystal surface and the resulting morphology of the film structure has been followed by STM for deposition at 310 K. For~1 ML films an ordered (2×1) surface alloy is formed which is also visible in LEED. The surface morphology is, however, not flat but has roughened step edges, raised islands and smaller trenches. For increased coverages of Pd the growth shifts to the formation of rectangular multilayered Pd islands. Upon annealing, AES shows a preferential segregation of Cu to the surface region that accompanies a flattening of the surface morphology in STM. Annealing thick films (>4 ML) to 603 K produces a surface morphology with larger flat terraces and small islands that have rough, non-crystallographically aligned step edges. With further annealing to 723 K these surfaces also display large-scale 'banding' in the STM images that we attribute to stress relaxation between the CuPd alloy and Cu. of a Cu 3 Pd(110) bulk alloy where the second layer 0039-6028/99/$ -see front matter
2008
The self organization of pentacene to form ordered film structures can be driven by the large structural anisotropy of suitable metal substrates [1]. We have prepared and studied pentacene films as grown on Cu(119) (Cu(100) vicinal surface with terrace width ~1,15 nm) with a surface science approach, i.e by LEED, STM, STS and ARPES measurements with polarized synchrotron radiation. These films show a long-range ordered structure, with the long molecular axis aligned along the step direction of the substrate. The formation of a single layer of pentacene molecules on the substrate kept at 373 K, results in longrange-ordered chain structures, as observed in STM images and in the 3 x 7 reconstruction observed by LEED. The character of the interface and molecular states was investigated by measuring ARPES in different experimental geometries, e.g. using linearly polarized synchrotron radiation oriented parallel or perpendicular to the steps of the vicinal surface (i.e. parallel or perpendicular to the longer molecular axis). As the thickness of the film increases, the intermolecular forces start to play a more important role than interface interaction in determining the relative orientation of the molecules and the electronic properties of the film. In a pentacene multilayer ~2nm thick the orientation of the molecules was observed by STM, which shows still an ordered array of the molecules lying almost flat on the surface. The extent of the intermolecular interaction was evaluated from the ARUPS measurements by looking at the energy dispersion of HOMO band along the molecular plane normal.
Influence of surface morphology on surface states for Cu on Cu(111)
Physical Review B, 2000
We have exploited angle-resolved one-photon photoemission, two-photon photoemission, and spot-profile analysis of low-energy electron diffraction to monitor the influence of surface morphology on the occupied and empty surface states observed at ⌫ on Cu͑111͒. Surface morphology changes were induced by homoepitaxial growth of Cu on Cu͑111͒. A simple model of electron localization on terraces successfully explains energy shifts and linewidth broadening of both surface states. Obviously, surface states may be used as sensitive probes of terrace-width distributions and other structural properties.
alpha-Sexithiophene Films Grown on Cu(110)-(2x1)O: From Monolayer to Multilayers
Interface Controlled Organic Thin Films, 2009
The growth of α-sexithiophene (6T) on copper (110) and oxygen reconstructed Cu(110) is studied by multiple techniques such as STM (scanning tunnelling microscopy), XRD (X-ray diffraction), XPS (X-ray photoelectron spectroscopy) and NEXAFS (near edge X-ray absorption fine structure). Selected data will be presented here and we will show that the long axes of the molecules on Cu and Cu -(2x1)O (CuO) are aligned along the valleys of the surface corrugations, i.e. along [1-10] and [001], respectively. With GIXD (grazing incidence X-ray diffraction) measurements the monolayer structure of 6T on Cu-O could be determined. Thicker films were studied by the X-ray diffraction pole figure technique. On all surfaces the (010) net planes of the bulk crystal structure are parallel to the surface i.e. the films grow exclusively (on Cu-O) or predominantly (on Cu) in the orientation. In the thick film the long molecular axes of the 6T molecules are found to be parallel to those of the monolayer. To study the transition from the monolayer to the multilayer structures NEXAFS measurements were carried out.
Quasi-1D pentacene structures assembled on the vicinal Cu(119) surface
Surface Science, 2004
We present a morphological study of pentacene (C 22 H 14 ) long range ordered molecular wires assembled on the Cu(1 1 9) vicinal surface. At low pentacene coverage, scanning tunneling microscopy (STM) shows single molecules adsorbed flat on the surface, presenting the long side parallel to the terrace direction. At the completion of the first layer, the molecules line up in regular rows extending along the step edges. By increasing the coverage, the rows of pentacene molecules form a densely packed structure, presenting a pyramid-like shape perpendicular to the steps.
The Journal of Physical Chemistry B, 1999
The room-temperature growth of palladium (Pd) on Cu(110) has been studied by X-ray photoelectron spectroscopy (XPS), scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), and temperature-programmed desorption (TPD). XPS signal versus deposition time plots rule out a simple layerby-layer growth mechanism. STM/LEED indicates formation of regions of (2 × 1) overlayer at low Pd coverages (θ Pd < 1 ML), with considerable disorder in the form of monolayer deep pits and islands. Higher Pd coverages lead to the formation of a granular film consisting of densely packed, flat-topped Pd clusters of average size 75 × 150 Å and with largely a rectangular shape. The favored growth mechanism is of multilayered Pd islands above a mixed (2 × 1) CuPd interface of two to three atomic layers thickness. The thermal stability of the Pd/Cu(110) system was investigated with XPS peak intensity versus annealing temperature plots that indicate that bulk intermixing takes place rapidly between 500 and 600 K. The Pd 3d 5/2 XPS peak widths narrow, suggesting the formation of a largely homogeneous CuPd surface alloy. STM indicates that heating to 500 K leaves the Pd clusters in a largely unaltered morphology with no sign of Ostwald ripening, whereas annealing to 600 K leads to considerable changes in topography. The granular structure of the Pd film is disrupted, leading to a surface with irregularly shaped flat domains separated by mono-atomic steps. High temperature (720 K) annealing leads to further flattening and appearance of regular parallel lines in STM images. The spacing of these lines varies with Pd loading, and they are assigned to strain due to lattice mismatch between the "capping" copper monolayer and the underlying mixed CuPd alloy. The reactivity of the Pd/Cu(110) surface has been probed by dosing formic acid and monitoring formate decomposition. High Pd coverages lead to a substantial destabilization of the formate relative to clean Cu(110), which is assigned to formate adsorption on mixed CuPd sites.
The Journal of Physical Chemistry C, 2014
The atomic structure of the pentacene/Cu(110) interface for coverages at and just below one monolayer has been determined by surface X-ray diffraction (SXRD), supported by state-of-the-art density functional theory (DFT) calculations. The in-depth sensitivity of SXRD to atom positions allows tracking the adsorption-induced distortions down to the fifth substrate layer. The main feature of the DFT model, namely, the buckling induced in the substrate, is fully confirmed by the experiment. The considerable atomic displacements which are the same for the two coverages under investigation are a signature of the strong molecule−substrate interaction, indicative of an adsorption mechanism of chemisorption type.