An STM investigation of the interaction and ordering of pentacene molecules on the Ag/Si(111)-(√3×√3)R30° surface (original) (raw)
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Pentacene on Ag(111): Correlation of Bonding Distance with Intermolecular Interaction and Order
ACS Applied Materials & Interfaces, 2013
We report coverage and temperature dependent bonding distances of vacuum-sublimed pentacene (PEN) submonolayers on Ag(111) obtained by the X-ray standing wave technique. The average vertical bonding distance of 2.98 Å at room temperature for 0.50 monolayer (ML) coverage increases to 3.12 Å for 0.75 ML due to competing intermolecular and adsorbate−substrate interactions. In contrast, decreasing the temperature from 295 to 145 K does not impact the bonding distance despite the concomitant transition from a "liquidlike" to an ordered molecular arrangement. In combination with X-ray photoelectron spectroscopy results, we could identify "soft chemisorption" with a subtle balance of molecule−molecule and substrate−molecule interactions as being responsible for this special adsorption behavior. Thus our study sheds light not only on the interface between PEN and Ag(111), but also on fundamental adsorption processes of organic adsorbates on metals in the context of chemi-and physisorption.
The Journal of Physical Chemistry C
Here we present a structural study of pentacene (Pn) thin films on vicinal Ag(111) surfaces by He atom diffraction measurements and density functional theory (DFT) calculations supplemented with van der Waals (vdW) interactions. Our He atom diffraction results suggest initial adsorption at the step edges evidenced by initial slow specular reflection intensity decay rate as a function of Pn deposition time. In parallel with the experimental findings, our DFT +vdW calculations predict the step edges as the most stable adsorption site on the surface. An isolated molecule adsorbs as tilted on the step edge with a binding energy of 1.4 eV. In addition, a complete monolayer (ML) with pentacenes flat on the terraces and tilted only at the step edges is found to be more stable than one with all lying flat or tilted molecules, which in turn influences multilayers. Hence our results suggest that step edges can trap Pn molecules and act as nucleation sites for the growth of ordered thin films ...
Langmuir, 2007
Evaporated pentacene thin films with thicknesses from several nm to 150 nm on gold and silver substrates have been studied by ultraviolet photoelectron spectroscopy (UPS), near-edge X-ray absorption fine structure (NEXAFS), scanning tunneling microscopy (STM), and atomic force microscopy (AFM). It was found that pentacene thin-film structures, particularly their molecular orientations, are strongly influenced by the metal substrates. UPS measurements revealed a distinct change in the valence band structures of pentacene on Au compared to those on Ag, which is attributed to the different packing between adjacent molecules. Using NEXAFS, we observed 74 ( 5°and 46 ( 5°m olecular tilt angles on Ag and Au, respectively, for all measured thicknesses. We propose that pentacene molecules stand up on the surface and form the "thin-film phase" structure on Ag. On Au, pentacene films grow in domains with molecules either lying flat or standing up on the substrate. Such a mixture of two crystalline phases leads to an average tilt angle of 46°for the whole film and the change in valence band structures. STM and distance-voltage (z-V) spectroscopy studies confirm the existence of two crystalline phases on Au with different conducting properties. z-V spectra on the low conducting phase clearly indicate its nature as "thin-film phase". Langmuir 2007, 23, [8336][8337][8338][8339][8340][8341][8342] 10.
Molecular-Scale Structure of Pentacene Interfaces with Si (111)
MRS Proceedings, 2006
ABSTRACTThe morphology and crystal structure of the first few molecular layers of organic semiconductor thin films at organic-inorganic interfaces are important from both electronic and structural perspectives. The first upright layer of pentacene on Si (111) forms on top of a disordered layer of strongly bonded pentacene molecules in a structure similar to the pentacene monolayers formed on insulators. We describe a high-resolution structural study of this crystalline phase of pentacene using low-temperature scanning tunneling microscopy (STM). The arrangement of molecules in these layers observed with STM agrees the results of with structural studies using scattering techniques. The imaging conditions and sample preparation techniques necessary to achieve molecular resolution can be adapted to subsequent STM and scanning tunneling spectroscopy experiments probing individual structural defects including vacancies, dislocations and grain boundaries within and between islands.
Langmuir, 2001
The structures of anthracene adlayers on Ag(111), Ag(100), and Ag(110) electrode surfaces in dilute perchloric acid have been investigated in detail by using in situ scanning tunneling microscopy (STM). Anthracene was found to form highly ordered molecular layers with a flat-lying orientation on the Ag single-crystal electrode surfaces in the double-layer region. High-resolution STM images allowed us to reveal packing arrangements of anthracene. Highly ordered anthracene adlayers with (2 3 × 2 3)R30°( θ ) 0.08), c(4 × 6) (θ ) 0.08), and c(4 × 4) (θ ) 0.125) symmetries were observed on
The Journal of Physical Chemistry C, 2008
Temperature programmed desorption (TPD) is used for examining surface binding, intermolecular interaction, and morphology of mono-and multilayer films of tetracene on Ag(111). TPD of monolayer tetracene revealed strong inter-adsorbate repulsion caused by interaction among interface dipoles resulted from charge-transfer bonding. A modified Albano model, in which a point interface dipole is assigned to each of the aromatic rings of tetracene, is proposed to account for the interfacial dipole interaction at short range. It is found that desorption energy at the zero-coverage limit is 142 (7 kJ/mol. The interface dipole is determined as 8.2 (2.1 D, which corresponds to a partial charge transfer of 0.4 e per tetracene molecule to the Ag substrate. At full monolayer coverage, the strong inter-adsorbate repulsion reduces the desorption energy to 105 (14 kJ/mol. Annealing at elevated temperature (350-400 K) but below desorption temperature, on minute time scale followed by cooling, appears to produce a more stable structure. Multilayer TPD spectra show three separate half-order desorption peaks that merge into one bulk peak at higher coverage. The half-order kinetics agrees with the previously reported Stranski-Krastanov growth mode in which islands with high height-towidth ratio are formed. The desorption energies for these peaks are 100 (7, 110 (10, and 116 (4 kJ/mol respectively. Upon annealing, the lower energy structure transform into the higher energy ones. † This article was originally intended to be a contribution to the "Giacinto Scoles Festschrift".
Adsorption of pentacene on a silicon surface
Surface Science, 2005
A computational description of the chemical bonding interactions of a pentacene molecule on a Si(1 0 0)-(2 · 1) surface is carried out using a combination of tight-binding and Gaussian 98 ab initio approaches. These computations identify the molecular configurations responsible for the adsorption sites parallel and perpendicular to the dimer row observed in STM studies to be a nearly flat, relatively strain-free ''tetra dimer''. The calculations confirm experimental evidence for strong monolayer adsorption dictated by the nature of the underlying reconstructed dimer row: The binding energies of the most stable perpendicular and parallel adsorption sites are 5.02 and 4.42 eV, respectively. The results are consistent with STM studies of sub-monolayer coverage of pentacene on silicon showing that the number of perpendicular adsorbed structures slightly exceeds those for parallel-adsorbed structures.
Physical Review Materials, 2021
Molecular adsorption on both quasicrystalline and approximant substrates has produced a number of pseudomorphic films, and has led to a deeper understanding of the chemistry of the surfaces of these materials. Here, the recently reported reconstructed (111) surface of the 1/1 Au-Al-Tb Tsai-type approximant has been used as a template for pentacene (Pn) adsorption, which is investigated using Scanning Tunnelling Microscopy (STM). This surface provides unique varieties of adsorption sites compared to normal metal surface. After room temperature deposition, the Pn molecules are mobile yet exhibit a structure which indicates a bond with the Tb atoms of the surface, while reflecting the 2-fold symmetrical nature of the reported Au/Al row reconstruction. Post-deposition annealing shows a linearised film of molecules which appears dependent on the relationship of the Tb atoms to the row structure.
Surface Science, 1998
Semi-empirical molecular orbital calculations reveal the local surface density of states for the adsorbed molecules on the Si surface. The organic molecules adenine, thymine, cytosine, and pentacene, which are adsorbed on Si(100)2×1 surfaces have been imaged by scanning tunneling microscopy (STM). The molecular images obtained by STM exhibit distinct shapes corresponding to the expected shapes for adsorption configurations. The energy level diagrams of the molecular orbitals (MOs) of the Si cluster on which the molecules are adsorbed are shown. The calculated MOs for adenine and thymine are in good agreement with the molecular images observed in STM. The bias dependence image of adsorbed cytosine is also explained by the calculated MOs of the molecule.
Ab initio study of pentacene on Au(001) surface
Surface Science, 2005
We report results of our first-principles density-functional studies on the nature of intermolecular interactions between pentacene (C 22 H 14 ) molecules and adsorption properties of the molecule on Au(0 0 1) surface. The energetics and electronic structure of two pentacene molecules in various configurations show an anisotropic nature of intermolecular interactions between the molecules. From total energy calculations, it is predicted that a single pentacene molecule adsorbed on Au(0 0 1) surface prefer to be centered at the bridge site, aligning its long-axis to the [1 1 0] direction of the Au(0 0 1) substrate. The structural distortions of the adsorbed molecule are closely related to the orbital characteristics of the HOMO and LUMO states and indicate a possible back-donation from the metal substrate to the molecule.