Monolayer Damage in XPS Measurements As Evaluated by Independent Methods

Abstract

The damage caused to amphiphilic n-alkane monolayers under XPS measurement conditions was assessed in a combined XPS-FTIR study supplemented by additional AFM imaging and contact angle measurements. Nine different self-assembled monolayer/substrate systems were examined, comprising a long chain silane (C18, OTS), a short chain silane (C1, MTS), a functional (COOH-terminated) long chain silane (C18, NTSox), a long chain carboxylic acid (C20, AA), and four different solid substrates (silicon, quartz, glass, and ZnSe). Significant differences were observed in the behavior of the various examined monolayer systems under identical X-ray irradiation conditions. These are interpreted in terms of effects associated with the specific mode of layer-to-surface and intralayer coupling, the size of the monolayer hydrocarbon core, and the presence of radiation-sensitive functional groups in the layer. All these factors and their influence on the degradation path followed by a particular monolayer upon exposure to the X-rays were found to be interrelated, giving rise to a variety of possible damage patterns, including an unexpected overall stabilization effect initiated by the preferential rapid loss of a labile top functional group (NTSox). XPS is shown to be insufficient as a tool for the evaluation of the radiation-induced damage in such ultrathin films, because of its insensitivity to loss of hydrogen and to structural transformations that occur without a net loss of carbon from the surface. Independent methods of surface analysis (mainly FTIR), applied in conjunction with XPS, provide a more comprehensive picture of the induced damage, thus permitting a realistic interpretation of the XPS experimental data as well as the design of improved data acquisition procedures. This could also assist in the tailoring of monolayers with predetermined degradability, for specific purposes. Finally, results of combined AFM-XPS-FTIR-contact angle measurements suggest the possible formation of a “diamond-like” surface film upon extensive X-ray irradiation of an OTS/Si monolayer.

Mechanism of UV Photoreactivity of Alkylsiloxane Self-Assembled Monolayers

“…[25][26][27] Although there is little absorption of X-rays by organic monolayers, photoelectrons generated from the substrate can interact with the organic monolayers. Indeed, the damage of SAMs by X-ray degradation 26 is remarkably similar to the electron damage of SAMs. 28 Both involve dehydrogenation and cross-linking of the alkyl chains.…”

Phase transformation of PbSe/CdSe nanocrystals from core-shell to Janus structure studied by photoemission spectroscopy

“…Although radiation-induced phenomena can also be observed with intense fluxes in photons, the disordering effects are generally much reduced and are limited to the surfaces of the nanomaterials. [11][12][13] Through the use of spectroscopic techniques, light also offers the advantage of following the chemical changes that occur in nanoparticles during a reaction. 14 Thus, it should give invaluable details into the kinetic pathways that exist when nanomaterials undergo radiation effects.…”

Sensitivity of Transmission Surface Plasmon Resonance (T‐SPR) Spectroscopy: Self‐Assembled Multilayers on Evaporated Gold Island Films

“…Elimination of beam-induced damage effects [54] was achieved by first studying the evolution of these effects and then performing the analysis on fresh spots using optimal experimental conditions.…”