Low-Energy Electron-Induced Damage in Hexadecanethiolate Monolayers

Abstract

Low-energy electron-induced damage in hexadecanethiolate (HDT) monolayers on gold substrates has been investigated using infrared reflection−absorption spectroscopy (IRAS), angle-resolved near edge X-ray absorption fine structure spectroscopy (NEXAFS), and advancing water contact angle measurements. HDT films were exposed to electrons of energies 10−100 eV and doses between 30 and 14 000 μC/cm2. The induced damage was monitored both “in situ” by NEXAFS measurements interleaved with electron irradiations and “ex-situ” by NEXAFS, IRAS, and contact angle measurements after exposure of the irradiated samples to air. A progressive film damage was observed with increasing electron energy and dose of irradiation. This damage was found to occur during irradiation in UHV and was not induced by chemical reactions with airborne molecules during subsequent exposure of the irradiated films to air. The damage starts in the region of the terminal methyl groups of the HDT films and propagates into the bulk of the film. An analysis of the IRAS and NEXAFS data shows that the conformational and orientational order within the HDT film are most sensitive to low-energy electron irradiation. Electron-induced cleavage of C−H and C−C bonds resulting in a partial desorption of the film constituents also occurs and leads to formation of CC double bonds in the film as inferred from the appearance of a π*-resonance in the C 1s NEXAFS spectra. The obtained results are of importance for both the optimization of self-assembled-monolayers-based lithography processes and for the general understanding of irradiation-induced changes in organic films.

Doping Molecular Monolayers: Effects on Electrical Transport Through Alkyl Chains on Silicon

“…The results show a significant p à resonance after less than 20 s of electron irradiation, a resonance signature that grows with increase in irradiation time. These results agree with those of Muller et al [41] who found that damage induced by electron irradiation in hexanedecanethiolate SAMs on gold shows up in the NEXAFS spectrum as a rapid growth of the p à resonance.…”

Low‐Dimensional, Hinged Bar‐code Metal Oxide Layers and Free‐Standing, Ordered Organic Nanostructures from Turbostratic Vanadium Oxide

“…The positions and FWHM (~1.2 eV) of the S 2p 3/2 and S 2p 1/2 peaks are essentially equivalent to those for conventional self assembled monolayers of alkanethiols. [48] Thus, the upper surface of the thiol nanostructure ( Figure 7c) is similar to a monolayer of thiols where all the Scontaining head-group reside on the outside of the structure (also depicted schematically in Figure 7b). Indeed, dedicated STM measurements (Figure 7e) were acquired of the organic segment of a side-view barcoded nanofiber.…”

A Flexible Approach to the Fabrication of Chemical Gradients

“…This variation is mostly related to the dehydrogenation of the SAM-ambient interface. [15,16] Other irradiation-induced processes, such as desorption of the chain fragments, disordering, crosslinking, and cleavage of the primary Au-thiolate bonds contribute to a minor extent to the wetting properties. [16] The respective results are presented in Figure 1, where h a for the DT/Au sample, which was subsequently irradiated and immersed into the MUDA/EtOH solution (2 h) for the purpose of exchange, is given as a function of irradiation dose kept below 1 mC cm -2 .…”