Strong Temperature Dependence of Irradiation Effects in Organic Layers

Abstract

Radiation damage of self-assembled monolayers, which are prototypes of thin organic layers and highly organized biological systems, shows a strong dependence on temperature. Two limiting cases could be identified. Reactions involving transport of single atoms and small fragments proceed nearly independent of temperature. Reactions requiring transport of heavy fragments are, however, efficiently quenched by cooling. We foresee the combined use of temperature and irradiation by electrons or photons for advanced tailoring of self-assembled monolayers on surfaces. In addition, our results have direct implications for cryogenic approaches in advanced electron and x-ray microscopy and spectroscopy of biological macromolecules and cells.

Electronically induced modification of thin layers on surfaces

“…Apart from resonances at 288, 293 and 300 eV which are due to Rydberg, (C-H)-s* and (C-C)-s* excitations, respectively [8], an additional peak appears and grows at 285 eV for extended photon irradiation. This maximum has previously been assigned to double bond-derived [C1s]p* states formed as a result of radiation induced hydrogen abstraction [8,11]. Comparing data at 50 and 300 K, no significant temperature dependence is observed for the growth of this maximum as a function of photon exposure ( Fig.…”

“…We believe that the suppression of electronically stimulated desorption of large fragments from organic films at low temperatures is a phenomenon of general validity. It has been observed not only for thiolate bonded SAMs on Au and Ag, but also for alkyls on silicon [11] and diamond [14], and for phosphonate bonded SAMs on silicon oxide [15].…”

“…Here we summarize the main results of these studies. For details of sample preparation, data acquisition or data evaluation the reader is referred to [11,12].…”

Azobenzene-functionalized alkanethiols in self-assembled monolayers on gold

“…The deconvolution of the TF-Az6 compound suggests a small contribution at a binding energy of 161.0 eV (S 2p 3/2 ). The latter is attributed either to atomic sulphur or intact molecules bound at distinctly different adsorption sites [20,[22][23][24]. Such a doublet has also been observed for BP4 and BP6, Table 1 XPS data for S 2p 3/2 , C 1s, and N 1s for C6, Az6, and TF-Az6 films on Au(111) on mica, respectively.…”

“…In general it is believed that secondary electrons are responsible for beam damage, but also resonant X-ray core excitations are effective in bond breaking [36]. For aliphatic SAMs, cooling suppresses the transport of heavy fragments, but already an exposure of 5 × 10 16 photons/cm 2 leads to significant formation of carbon double-bonds and of atomic sulphur [23,24]. Combined aliphatic-aromatic SAMs are less sensitive to electron bombardment, and X-ray beam damage is believed to be reduced [37].…”