Spectroscopy organic monolayer studies with

Organized multilayers of ferrocene alkyl thiol have been self-assembled on Au(lll) under conditions of controlled thiol concentration. Several methods, such as CV, ellipsometry, STM, AFM, and in situ FTIR spectroscopy have been applied in these studies in order to find out the differences between mono- and multilayers of the same compound [152]. Similar compounds, namely, short-chain alkyl thiols (n = 3-10) with ferrocene terminal group were allowed to form organized monolayers at Au(lll) surfaces [153]. 

In spite of the overall success of this particular scheme, there are some issues which need to be clarified especially when it comes to details of the structure of the electrode/monolayer/electrode crossings on an atomistic level [4]. In a recent review on the vapor deposition of metal atoms on organic monolayers [65], the complexity of the process and the subtle effects of the surface structure and composition on the outcome are illustrated. A reflection-absorption infrared spectroscopy study [66] of a system, which is similar to the actual cross-junction, suggests undamaged organic mono-layers with Ti coatings, but further research is needed for the complete characterization of these complex structures. 

Advanced synchrotron based characterization techniques of solid state applied to macromolecules are reported in Chapter 4. After an introduction to the physics and principles of NEXAFS and XPS spectroscopy, the main features of these techniques that allow a non conventional assessment of the electronic and chemical structure are depicted. The study of macromolecular organization and self-assembly can be nicely obtained by these spectroscopic tools. For example the formation of SAMs (Self Assembled Monolayers) of a variety of molecules arranged in supramolecular assemblies can be detected as well as the behaviour of biomolecules bound to surfaces mimicking biological substrates. Many examples of macromolecules studied with NEXAFS and XPS highlight the potential of these spectroscopic methods to give insight into the molecular and supramolecular structure which in turn determine the most desired properties. 

IR, X-ray photoelectron spectroscopy (XPS), and cyclic voltammetry study. The kinetics of monolayer formation vary dramatically for the two compounds. The alkanethiol assembles rapidly, within a few minutes, and forms a densely packed, highly organized monolayer with the alkylchains in an almost perfect all-trans conformation and the C -Cq axis of the thiophene moiety tilted about 14° away from the surface normal. The disulfide assembles much slowlier within at least one day. It forms an organized monolayer with a thiophene chain tilt of about 33° against the surface normal. 

NEXAFS spectroscopy can be applied for quantitative analyses of the chemical composition of polymer blends and copolymers [9]. An interesting application concerns NEXAFS microscopy (see Section 6.3). Moreover, the application of NEXAFS spectroscopy to surface studies -and in particular to studies related to the adsorption of organic molecules onto the surfaces of metals and polymers - is of particular interest. For example, the NEXAFS spectra of a monolayer of poly-3-methylthiophene, electrochemically grafted onto Pt, revealed that the aromatic rings in the polymeric layer are Jt-bonded to the Pt(lll) surface [16]. In addition, NEXAFS spectroscopy provides answers to questions such as Flow do molecules interact with surfaces or How do molecules orient on surfaces ... 

In contrast to the minimal activity in infrared reflection studies the technique of inelastic electron tunneling spectroscopy (IETS) recently has contributed a large amount of information on monolayer adsorption of organic molecules on smooth metal oxide surfaces,Q),aluminum oxide layers on evaporated aluminum. These results indicate that a variety of organic molecules with acidic hydrogens, such as carboxylic acids and phenols chemisorb on aluminum Oxide overlayers by proton dissociation - 1 — and that monolayer coverage can be attained quite repro-ducibly by solution doping techniques. - The IETS technique is sensitive to both infrared and Raman modes. — However, almost no examples exist in which Raman il and or infrared spectra have been taken for an adsorbate/substrate system for which IETS spectra have been observed. 

Biirgi and co-workers [154-156] have reported a series of conformational investigations of chiral ligands absorbed on AuNPs using VCD spectroscopy complemented with DFT calculations, a powerful spectroscopic tool for conformational studies of condensed matters. Three organic chiral molecules, namely /V-acetyl-cysteine, /V- isobutyry I -cysteine, and l,l -binaphthyl-2,2 -dithiol (BINAS), were used as chiral ligands in their studies. The details about how to prepare monolayer-protected AuNPs with these ligands can be found in the pertinent references [154-156]. The measured VA and VCD spectra of the AuPNs protected by /V-isobutyryl-L/D-cysteine monolayer are shown in Fig. 18, as examples. As one... 

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