Münster 1999 – wissenschaftliches Programm

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CP: Chemische Physik

CP 4: Symposium: Benetzung und dünne Filme

CP 4.5: Vortrag

Montag, 22. März 1999, 17:45–18:00, Phy

Modification of self-assembled monolayers by low-energy electron irradiation — •M. Zharnikov, S. Frey, W. Geyer, K. Heister, H.U. M"uller, V. Stadler, B. V"olkel, W. Eck, A. G"olzh"auser, and M. Grunze — Angewandte Physikalische Chemie, Universit"at Heidelberg, Im Neuenheimer Feld 253, D-69120 Heidelberg

Low energy electron induced damage of aliphatic and aromatic self-assembled monolayers (SAM) has been investigated using angle-resolved near edge X-ray absorption fine structure spectroscopy (NEXAFS), X-ray photoelectron spectroscopy (XPS), infrared reflection absorption spectroscopy, and contact angle measurements. The films were exposed to electrons of energies 10 - 100 eV and doses between 30 and 14000 µC/cm². The characterization of the films was performed both in-situ by XPS and NEXAFS measurements interleaved with electron irradiations and ex-situ after an exposure of the irradiated samples to air. Progressive film damage was found to occur with increasing either electron energy or irradiation dose. In the case of aliphatic SAMs a breakdown of the conformational and orientational order, a radiation-induced cleavage of the C-H, C-F and C-C bonds, a cross-linking involving C=C double bonds, and disulfide formation at the gold interface were observed. Through the incorporation of specific molecular groups into the alkane chains a selectivity of the irradiation induced damage could be achieved. Aromatic SAMs were found to be less sensitive to the electron irradiation. This allowed a controlled modification of the tail group with the aromatic spacer remained intact. All the changes only occurred during irradiation and were not induced by chemical reactions with air constituents upon the subsequent exposure of the irradiated films to air.