Chemical Manipulation by X-rays of Functionalized Thiolate Self-Assembled Monolayers on Au

Abstract

The chemical modification caused by prolonged exposure to X-rays on a series of para-substituted phenyl moieties (-NO2, -CN, -CHO, -COOH, -CO2Me, and -CO2(1)Bu) at the surface of thiolate-Au self-assembled monolayers (SAMs) has been investigated by X-ray photoelectron spectroscopy (XPS). Furthermore, the influence that the phenyl group has on the chemical modification induced by the X-ray irradiation on the SAMs was investigated by comparing the XPS results obtained from irradiation on a NO2-aromatic-terminated SAM (6-(4-nitro-phenoxy)-hexane-1-thiolate (NPHT)) and NO2-aliphatic-terminated SAM (thioacetic acid S-(12-nitrododecyl) ester (TNDDE)). The NPHT and TNDDE SAMs have been shown to behave differently to X-ray exposure. The irradiation of the NPHT SAM led to the reduction of the nitro (-NO2) moiety to the amine (-NH2) moiety, as shown by the decrease in the intensity of the N 1s photoelectron peak for -NO2 (406 eV) in the XPS spectra with the concomitant increase in the N 1s photoelectron peak for -NH2 (399 eV). On the TNDDE SAM, XPS showed the -NO2 photoelectron peak again decreasing with prolonged X-ray irradiation whereas no peak was observed at 399 eV; therefore, the -NO2 moieties are selectively cleaved. No change was observed on the other functionalized monolayers apart from the -CO2(t)Bu-functionalized monolayer, where after 100 min of X-ray irradiation approximately 11% of the carbon content was lost. The S 2p and O 1s spectra remained unchanged during the irradiation suggesting the conversion of the -CO2(t)Bu to the -COOH moiety, although the conversion was not complete because the tertiary butyl moiety contributes 25% to the total carbon content of the SAM. Also, there was no evidence of the molecules desorbing from the substrate for any of the SAMs studied during the X-ray irradiation as shown by no change in the S 2p and C 1s XPS spectra taken during the X-ray irradiation.

Silane coupling agent bearing a photoremovable succinimidyl carbonate for patterning amines on glass and silicon surfaces with controlled surface densities

“…However, the spectrum also had an unknown peak at 400 eV. Although gradual conversion of the NO 2 group to the NH 2 group by the prolonged X-ray exposure have been reported in literature [44,46], we speculated that the majority of the peak appeared at 400 eV in our experiments was composed of some decomposed products derived from the succinimidyl carbonate rather than the NO 2 group. This is because the peak intensity of the NO 2 group at 406 eV did not change significantly when the spectral accumulation time was decreased from 36 min to 1.5 min (Fig.…”

Lamellar Orientation of a Block Copolymer via an Electron-Beam Induced Polarity Switch in a Nitrophenyl Self-Assembled Monolayer or Si Etching Treatments

“…Chemical analysis of substrate pre-and post-EB modification was not performed as the EB exposure tool's time and analytical tools were limited. However, X-ray photoelectron spectroscopy (XPS) data of the SAM substrates by pre-and post-x-ray modification [52] and XPS data of different SAM substrates by post-EB modification [49] are available. EB patterning was chosen for controlling block copolymer features because EB lithography tools can pattern areas nearly as small as the domain of block copolymer.…”

Lamellar orientation of block copolymer using polarity switch of nitrophenyl self-assembled monolayer induced by electron beam

“…It has previously been reported that EB lithography and x-ray irradiation can induce conversion of the SAM terminal function aromatic nitro (NO 2 ) moieties to aromatic amino (NH 2 ) moieties. [46][47][48][49][50][51][52][53] pre-coated with SAM. It is known that the PMMA block preferentially wets on SAMs that contain polar groups.…”