skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Orientation of pentacene molecules on SiO{sub 2}: From a monolayer to the bulk

Abstract

Near edge x-ray absorption fine structure (NEXAFS) spectroscopy is used to study the orientation of pentacene molecules within thin films on SiO{sub 2} for thicknesses ranging from monolayers to the bulk (150 nm). The spectra exhibit a strong polarization dependence of the {pi}{sup *} orbitals for all films, which indicates that the pentacene molecules are highly oriented. At all film thicknesses the orientation varies with the rate at which pentacene molecules are deposited, with faster rates favoring a thin film phase with different tilt angles and slower rates leading to a more bulklike orientation. Our NEXAFS results extend previous structural observations to the monolayer regime and to lower deposition rates. The NEXAFS results match crystallographic data if a finite distribution of the molecular orientations is included. Damage to the molecules by hot electrons from soft x-ray irradiation eliminates the splitting between nonequivalent {pi}{sup *} orbitals, indicating a breakup of the pentacene molecule.

Authors:
; ; ; ;  [1];  [2];  [2]
  1. Department of Physics, University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States)
  2. (United States)
Publication Date:
OSTI Identifier:
20991250
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Chemical Physics; Journal Volume: 126; Journal Issue: 15; Other Information: DOI: 10.1063/1.2717161; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ABSORPTION; ABSORPTION SPECTROSCOPY; CRYSTALLOGRAPHY; FINE STRUCTURE; IRRADIATION; ORIENTATION; PENTACENE; POLARIZATION; SEMICONDUCTOR MATERIALS; SILICON OXIDES; SOFT X RADIATION; SPECTRA; THIN FILMS; X-RAY SPECTROSCOPY

Citation Formats

Zheng, Fan, Park, Byoung-Nam, Seo, Soonjoo, Evans, Paul G., Himpsel, F. J., Materials Science Program University of Wisconsin, Madison, Wisconsin 53706 and Department of Materials Science and Engineering, University of Wisconsin, Madison, Wisconsin 53706, and Department of Physics, University of Wisconsin-Madison, Madison, Wisconsin 53706. Orientation of pentacene molecules on SiO{sub 2}: From a monolayer to the bulk. United States: N. p., 2007. Web. doi:10.1063/1.2717161.
Zheng, Fan, Park, Byoung-Nam, Seo, Soonjoo, Evans, Paul G., Himpsel, F. J., Materials Science Program University of Wisconsin, Madison, Wisconsin 53706 and Department of Materials Science and Engineering, University of Wisconsin, Madison, Wisconsin 53706, & Department of Physics, University of Wisconsin-Madison, Madison, Wisconsin 53706. Orientation of pentacene molecules on SiO{sub 2}: From a monolayer to the bulk. United States. doi:10.1063/1.2717161.
Zheng, Fan, Park, Byoung-Nam, Seo, Soonjoo, Evans, Paul G., Himpsel, F. J., Materials Science Program University of Wisconsin, Madison, Wisconsin 53706 and Department of Materials Science and Engineering, University of Wisconsin, Madison, Wisconsin 53706, and Department of Physics, University of Wisconsin-Madison, Madison, Wisconsin 53706. Sat . "Orientation of pentacene molecules on SiO{sub 2}: From a monolayer to the bulk". United States. doi:10.1063/1.2717161.
@article{osti_20991250,
title = {Orientation of pentacene molecules on SiO{sub 2}: From a monolayer to the bulk},
author = {Zheng, Fan and Park, Byoung-Nam and Seo, Soonjoo and Evans, Paul G. and Himpsel, F. J. and Materials Science Program University of Wisconsin, Madison, Wisconsin 53706 and Department of Materials Science and Engineering, University of Wisconsin, Madison, Wisconsin 53706 and Department of Physics, University of Wisconsin-Madison, Madison, Wisconsin 53706},
abstractNote = {Near edge x-ray absorption fine structure (NEXAFS) spectroscopy is used to study the orientation of pentacene molecules within thin films on SiO{sub 2} for thicknesses ranging from monolayers to the bulk (150 nm). The spectra exhibit a strong polarization dependence of the {pi}{sup *} orbitals for all films, which indicates that the pentacene molecules are highly oriented. At all film thicknesses the orientation varies with the rate at which pentacene molecules are deposited, with faster rates favoring a thin film phase with different tilt angles and slower rates leading to a more bulklike orientation. Our NEXAFS results extend previous structural observations to the monolayer regime and to lower deposition rates. The NEXAFS results match crystallographic data if a finite distribution of the molecular orientations is included. Damage to the molecules by hot electrons from soft x-ray irradiation eliminates the splitting between nonequivalent {pi}{sup *} orbitals, indicating a breakup of the pentacene molecule.},
doi = {10.1063/1.2717161},
journal = {Journal of Chemical Physics},
number = 15,
volume = 126,
place = {United States},
year = {Sat Apr 21 00:00:00 EDT 2007},
month = {Sat Apr 21 00:00:00 EDT 2007}
}
  • Thin film growth of pentacene on SiO{sub 2} using a supersonic source has been investigated with in situ real time synchrotron x-ray scattering and ex situ atomic force microscopy, focusing on the effects of incident kinetic energy E{sub i} and growth rate GR on the evolution of surface roughness and the crystalline structure of the thin films. For the conditions examined here, E{sub i}=2.5-7.2 eV and GR=0.0015-0.2 ML s{sup -1}, the thin film phase is always observed. We find that while the effect of E{sub i} on interlayer transport is minimal, at high growth rates, slightly smoother films are observed.
  • Infrared spectroscopy and [sup 29]Si MAS NMR are used to probe the structure of SiO[sub 2] on Al[sub 2]O[sub 3] catalysts prepared by chemical vapor deposition of Si(OCH[sub 3])[sub 4][center dot]SiO[sub 2] loadings from about 0.2-2.5 statistical monolayers are studied. Infrared shows a gradual disappearance of AlOH vibrations as the SiO[sub 2] loading is increased. A population of inaccessible AlOH is also observed. The Si-O-X asymmetric stretching frequency shows a continuous variation with SiO[sub 2] content, consistent with X varying from Al at low levels to Si at high levels of silica. [sup 29]Si NMR shows composite peaks at allmore » SiO[sub 2] levels. At the lowest level most intensity is concentrated in the -80 to -85 ppm range, corresponding to Si with attached -OAl groups. At the highest silica levels, the spectrum can be deconvoluted into peaks at -108, -100, and -92 ppm. These correspond to Si(OSi)[sub 4], Si(OSi)[sub 3]OH, and mixtures of Si(OSi)[sub 2](OH)[sub 2] with -OAl-containing species. A model is proposed for build up of the silica layer on these catalysts. Random deposition of silica on any available surface is shown to give a semiquantitative account of the experimental results. 31 refs., 6 fig., 2 tabs.« less
  • Experimental procedures for quantitative estimation of surface acid by [sup 31]P NMR of adsorbed phosphines are discussed. These procedures are illustrated by application to a commercial silica alumina cracking catalyst, and are applied to a series of silica on alumina monolayer catalysts prepared by chemical vapor deposition. The monolayer catalysts show a maximum in Broensted acidity for a deposition of 8 SiO[sub 2] groups per nm[sup 2] of Al[sub 2]O[sub 3] surface. The evolution of Broensted acid concentration as a function of amount of deposited silica can be accounted for by a simple kinetic model. 9 refs., 5 figs., 2more » tabs« less
  • This paper examines the damage created by an electron beam on layered specimens consisting of a (CH[sub 2])[sub 17] self-assembled monolayer (SAM) deposited on an oxidized Si wafer. Beam effects on both the SAM and substrate were observed. X-ray photoelectron spectroscopy (XPS) measurements indicate that less than 20% of the carbon from the film is lost during the beam damage, ion analysis shows hydrogen emission from the films, and residual gas analysis suggest loss of some CH[sub [ital x]] ([ital x]=2--4) molecules. Consistent with the conversion of some (CH)[sub [ital n]] chains to graphite,'' the C 1[ital s] photopeak ismore » broadened by the electron beam. In addition to the effects on the SAM layer, there are shifts for the O 1[ital s] and oxidized-Si[sub 2[ital p]] binding energies due to the electron beam exposure. Studies on SiO[sub 2] films formed in a wide variety of ways, without the SAM, show similar effects. These shifts are attributed to changes in potential at the Si--SiO[sub 2] interface.« less