Self thiol adlayers

The modification and functionabzation of metal electrodes with self-assembled thiol adlayers [66, 67] opens up many possibilities for electrochemical applications. At present, this very active field is centered on the studies of the electrochemical properties of self-assembled monolayers (SAMs) [68, 69]. In short, electrochemical deposition represents a promising technique for the preparation of Cu-NPs due to its ease of use, low cost, environmental friendliness and convenience of manufacture. In particular, the high sensitivity and low cost of the SPEs when using Cu-NPs should lead to their widespread use in a variety of scientific and medical fields, including medical diagnostics. 

If an enhancement of five to six orders of magnitude can be achieved routinely, TERS for small molecules, which are not in resonance with the laser line, is within reach. These molecules have cross sections of the order of (dff/dfJ) 10 cm sr and are barely seen as adlayers on smooth interfaces by normal Raman spectroscopy. To test this, benzenethiol was chosen, which assumes an essentially vertical orientation to the surface due to its thiol group. The adlayer preparation is quick and easy the adsorption occurs from an etha-nolic solution, and a self-assembled monolayer is formed on previously flame-annealed gold or platinum surfaces. Fig. 10.26 shows TERS spectra for benzenethiol at Au(llO) and Pt(llO) surfaces. The comparison of the spectra reveals the characteristic benzenethiol bands but with sHghtly different band positions and relative intensities for the two samples and a nearly 20-fold lower intensity level for benzenethiol at Pt(llO). The comparison of these data with SER spectra for... 

Electron transfer cannot occur in blocking films. However, for very thin self-assembled monolayers (SAMs] of alkane thiols or oxide films, electrons can tunnel through the film and cause Faradaic reactions. Monolayer of alkane thiols can form spontaneously ordered adlayers on substrate like Au(lll] due to a strong interaction between the sulphur of the thiol and the gold substrate. These SAMs have received tremendous attention in recent years [209,210]. 

VASE measurements reveal a thickness of 1.3—1.4 nm for densely packed monolayers of PFAND. The difference between molecular length (Rs 2.1 nm) and measured adlayer thickness is attributed to three considerations (i) relaxed PFAND molecules are most likely not straight but helical and bent as in the case of fluorinated alkyl thiols, (ii) adsorbed PFAND molecules, as fluorinated alkyls, might be tilted with respect to the surface normal by 30°-35° to optimize packing and intermolecular interactions, and (iii) VASE-determined thickness is systematically underestimated by the layer model that was employed, because of adventitious carbon/contamination, which is constantly replaced by PFAND during adsorption, a process referred to as self-cleaning by Buck et al. for thiols on gold. Comparison of C Is XP spectra allows an estimation of the replacement of surface contamination the amount of contamination on clean TiO surfaces is equivalent to a fraction (20-25%) of what is... 

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