Investigation of Solid Surfaces Modified by Langmuir−Blodgett Monolayers Using Sum-Frequency Vibrational Spectroscopy and X-ray Photoelectron Spectroscopy

Abstract

Langmuir-Blodgett (LB) monomolecular layers of alkylhydroxamic acids and alkylphosphonic acids on copper and iron substrates have been studied by X-ray photoelectron spectroscopy (XPS) and sum-frequency vibrational spectroscopy. According to the XPS results, the structures of the hydroxamic acid and phosphonic acid Langmuir-Blodgett films are very similar: the thickness of the layer of the hydrocarbon tails is typically 1.9-2.1 nm, while the layer of headgroups is about 0.3-0.35 nm thick. The tilt angle of the carbon chains is estimated to be 20-30 degrees with respect to the sample surface normal, and the molecules are connected to the substrate via their headgroups. Analysis of the P 2p and N 1s lines indicates the presence of deprotonated headgroups. The substrate Cu 2p line includes a component which can be assigned to Cu(2+) ions in a thin Cu(OH)(2) layer. The deposition of LB layers led to significant decrease of the hydroxide-related signal, which indicates that binding of the headgroups to the surface is accompanied by the elimination of water molecules. The sum-frequency spectra also clearly indicate that well-ordered monolayers can be formed by the Langmuir-Blodgett technique. Since the non-resonant background from the metal substrates renders the analysis of the spectra more difficult, model system samples on glass were prepared. It was found that the alkyl chains of the adsorbed acids predominantly adopt the all-trans conformation and form an ordered structure. Upper limits for the mean tilt angle of the terminal methyl groups are approximately 10-20 degrees.

Spectroscopic and Theoretical Study of the Grafting Modes of Phosphonic Acids on ZnO Nanorods

“…Note that similar shifts (around 0.8 eV) have also been reported for the grafting of phosphonic acids on transition metal oxide surfaces. 49 Figure 5a−c shows XPS C 1s region of bare NRs and of PPA and TDPA functionalized NRs (PPA-NRs and TDPA-NRs). The C 1s peak of bare NRs is a convolution of two components.…”

The use of nano-/microlayers, self-healing and slow-release coatings to prevent corrosion and biofouling

“…Phosphonic acid nanolayers have also been studied (1H,1H,2H,2H-perfluorodecyl phosphonic acid, 1-octyl-, decyl-and octadecyl phosphonic acids) (Hoque, 2009, Raman, 2010, Telegdi, 2005b, Rigó, 2005, Keszthelyi, 2006. This work showed that with increasing carbon length, the compactness of the surface SAM layer improves and the anticorrosion and antifouling effect significantly increases.…”

“…SFS is an efficient technique for obtaining information about the molecular level order of the prepared nanofilm, which is directly correlated with its performance as a protective layer (Keszthelyi, 2006). SFS is based on the nonlinear optical phenomenon which occurs when a light beam with a fixed wavelength in the visible part of the spectrum interacts with one at infrared wavelength which scans the surface.…”

“…On a copper surface, the amount of hydroxide species present decreased after surface modification, indicating that metal hydroxide is necessary for fixing the organic molecules. It is probable that water is desorbed during the measurement (Keszthelyi, 2006).…”

Adsorption of a PEO–PPO–PEO triblock copolymer on metal oxide surfaces with a view to reducing protein adsorption and further biofouling

“…The thickness and structure of OPA layer was studied in detail elsewhere (Keszthelyi et al 2006). Briefly, the mechanism of assembly is Table 3 and 4, and shape of O 1s peaks, not shown here).…”