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  4. Polyphenylsilole multilayers - an insight from X-ray electron spectroscopy and density functional theory
 
research article

Polyphenylsilole multilayers - an insight from X-ray electron spectroscopy and density functional theory

Diller, Katharina  
•
Ma, Yong
•
Luo, Yi
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2015
Physical Chemistry Chemical Physics

We present a combined investigation by means of X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine-structure (NEXAFS) spectroscopy of condensed multilayers of two polyphenylsiloles, namely hexaphenylsilole (HPS) and tetraphenylsilole (TPS). Both compounds exhibit very similar spectroscopic signatures, whose interpretation is aided by density functional theory (DFT) calculations. High-resolution XPS spectra of the Si 2p and C 1s core levels of these multilayers indicate a positively charged silicon ion flanked by two negatively charged adjacent carbon atoms in the silole core of both molecules. This result is corroborated quantitatively by DFT calculations on isolated HPS (TPS) molecules, which show a natural bond orbital partial charge of + 1.67 e (+1.58 e) on the silicon and -0.34 e (-0.58 e) on the two neighbouring carbon atoms in the silole ring. These charges are conserved in direct contact with a Cu(111) substrate for films of submonolayer coverage, as evidenced by the Si 2p XPS data. The C K-edge NEXAFS spectra of HPS and TPS multilayers exhibit distinct and differing features. Their main characteristics reappear in the simulated spectra and are assigned to the different inequivalent carbon species in the molecule. The angle-dependent measurements hardly reveal any dichroism, i.e., the molecular p-systems are not uniformly oriented parallel or perpendicular with respect to the surface. Changes in the growth conditions of TPS, i.e., a reduction of the substrate temperature from 240 K to 80 K during deposition, lead to a broadening of both XPS and NEXAFS signatures, as well as an upward shift of the Si 2p and C 1s binding energies, indicative of a less ordered growth mode at low temperature.

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Type
research article
DOI
10.1039/c5cp02935j
Web of Science ID

WOS:000365401700037

Author(s)
Diller, Katharina  
Ma, Yong
Luo, Yi
Allegretti, Francesco
Liu, Jianzhao
Tang, Ben Zhong
Lin, Nian
Barth, Johannes V.
Klappenberger, Florian  
Date Issued

2015

Publisher

Royal Society of Chemistry

Published in
Physical Chemistry Chemical Physics
Volume

17

Issue

46

Start page

31117

End page

31124

Editorial or Peer reviewed

REVIEWED

Written at

EPFL

EPFL units
LNS  
Available on Infoscience
February 16, 2016
Use this identifier to reference this record
https://infoscience.epfl.ch/handle/20.500.14299/123685
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