Self-assembled monolayers characterization

Zhang, J.D., WeHnder, A.C., Chi, Q., and Ulstrup, J. (2011) Electrochemically controlled self-assembled monolayers characterized with molecular and sub-molecular resolution. Physical Chemistry Chemical Physics, 13, 5525-5545. 

The importance of surface characterization in molecular architecture chemistry and engineering is obvious. Solid surfaces are becoming essential building blocks for constructing molecular architectures, as demonstrated in self-assembled monolayer formation [6] and alternate layer-by-layer adsorption [7]. Surface-induced structuring of liqnids is also well-known [8,9], which has implications for micro- and nano-technologies (i.e., liqnid crystal displays and micromachines). The virtue of the force measurement has been demonstrated, for example, in our report on novel molecular architectures (alcohol clusters) at solid-liquid interfaces [10]. 

The parameters K1/ K2/ and K3 are defined by the refractive indices of the crystal and sample and by the incidence angle [32]. If the sample has uniaxial symmetry, only two polarized spectra are necessary to characterize the orientation. If the optical axis is along the plane of the sample, such as for stretched polymer films, only the two s-polarized spectra are needed to determine kz and kx. These are then used to calculate a dichroic ratio or a P2) value with Equation (25) (replacing absorbance with absorption index). In contrast, a uniaxial sample with its optical axis perpendicular to the crystal surface requires the acquisition of spectra with both p- and s-polarizations, but the Z- and X-axes are now equivalent. This approach was used, through dichroic ratio measurements, to monitor the orientation of polymer chains at various depths during the drying of latex [33]. This type of symmetry is often encountered in non-polymeric samples, for instance, in ultrathin films of lipids or self-assembled monolayers. 

Pham T., Jackson J.B., Halas N.J., Lee T.R., Preparation and characterization of gold nanoshells coated with self-assembled monolayers, Langmuir 2002 18 4915-4920. 

Maeda Y., Yamamoto H., Kitano H., Self-assembled monolayers as novel biomembrane mimetics. 1. Characterization of cytochrome-c bound to self-assembled monolayers on... 

Roberts C, Chen CS, Mrksich M, Martichonok V, Ingber DE, Whitesides GE (1998) Using mixed self-assembled monolayers presenting RGD and (EG)3OH groups to characterize long-term attachment of bovine capillary endothelial cells to surfaces. J Am Chem Soc 120 6548-6555... 

As the analytical, synthetic, and physical characterization techniques of the chemical sciences have advanced, the scale of material control moves to smaller sizes. Nanoscience is the examination of objects—particles, liquid droplets, crystals, fibers—with sizes that are larger than molecules but smaller than structures commonly prepared by photolithographic microfabrication. The definition of nanomaterials is neither sharp nor easy, nor need it be. Single molecules can be considered components of nanosystems (and are considered as such in fields such as molecular electronics and molecular motors). So can objects that have dimensions of >100 nm, even though such objects can be fabricated—albeit with substantial technical difficulty—by photolithography. We will define (somewhat arbitrarily) nanoscience as the study of the preparation, characterization, and use of substances having dimensions in the range of 1 to 100 nm. Many types of chemical systems, such as self-assembled monolayers (with only one dimension small) or carbon nanotubes (buckytubes) (with two dimensions small), are considered nanosystems. 

Chiechi RC, Weiss EA, Dickey MD, Whitesides GM (2008) Eutectic gallium-indium (EGaln) a moldable liquid metal for electrical characterization of self-assembled monolayers. Angew Chem Int Ed 47(1)442-144... 

Lee T, Wang W, Klemic JF, Zhang J, Su J, Reed MA (2004) Comparison of electronic transport characterization methods for alkanethiol self-assembled monolayers. J Phys Chem B 108 8742-8787... 

C. Yan, M. Zhamikov, A. Golzhauser, and M. Grunze, Preparation and characterization of self-assembled monolayers on indium tin oxide, Langmuir, 16 6208-6215, 2000. 

Su, J., Mrksich, M. Using mass spectrometry to characterize self-assembled monolayers presenting peptides, proteins, and carbohydrates. Angew. Chem. Int. Ed. 2002, 41, 4715-4718. 

Wang B, Xiao X, Sheng P (2000) Growth and characterization of Au clusters on alkanethiol self-assembled monolayers. J Vac Sci Technol B 18 2351-2358... 

A Au-coated substrate is another model surface, to which many surface characterization methods can be applied. To achieve surface-initiated ATRP on Au-coated substrates, some haloester compounds with thiol or disulflde group were developed [80-84]. Self-assembled monolayers (SAM) of these compounds were successfully prepared on a Au-coated substrate and used for ATRP graft polymerization. Because of the limited thermal stability of the S - Au bond, the ATRP was carried out at a relatively low temperature, mostly at room temperature, by using a highly active catalyst system and water as a (co)solvent (water-accelerated ATRP). 

Lastly, Polystyrene (PS) brushes on silicate substrates were grafted via carbocationic polymerization from self-assembled monolayer (SAM) initiators as reported by Brittain et al The carbocationic initiators, 2-(4-(ll-triethoxysilylundecyl))phenyl-2-methoxypropane and 2-(4-trichlorosilyl-phenyl)-2-methoxy-d3-propane, and their corresponding SAMs were prepared on various substrates. The monolayers were characterized by FTIR-ATR, contact angles, and X-ray reflectometry. The growth of the PS brushes from... 

Nakanishi T, Ohtani B, Uosaki K (1998) Fabrication and characterization of CdS-nanoparticle mono- and multilayers on a self-assembled monolayer of alkanedithiols on gold. J Phys Chem B 102 1571-1577... 

Chemically prepared colloidal gold nanoparticles were immobilized as a submonolayer on Au(lll) surface modified with self-assembled monolayers (SAMs) of 4-aminothiophenol [14]. This submonolayer of Au nanoparticles was subsequently characterized using STM. 

Another well-represented category was that of self-assembled monolayers (SAMS) and other supramolecular systems. The experiments on the SAMS included studies of the surface pKa of one system (110), the kinetics and thermodynamics of the self-assembly process (111), and the characterization of the SAM surface by study of solution contact angles (112). The experiments on supramolecular systems included studies on chemical equilibria in such systems (113, 114, 115), the kinetics of inclusion phenomena (116), and the use of solvatochromic probes in studying inclusion phenomena (117). 

Yamamoto, H., Butera, R. A., Gu, Y. and Waldeck, D. H. Characterization of the surface to thiol bonding in self-assembled monolayer films of C12H25SH on InP(100) by angle-resolved X-ray photoelectron spectroscopy. Langmuir 15, 8640 (1999). 

Like the currently popular area, called nanoscience , the field of supramolecular chemistry has rather hazy boundaries. Indeed, both areas now share much common ground in terms of the types of systems that are considered. From the beginning, electrochemistry, which provides a powerful complement to spectroscopic techniques, has played an important role in characterizing such systems and this very useful book goes considerably beyond the volume on this same topic by Kaifer and Gomez-Kaifer that was published about 10 years ago. Some of the classic supramolecular chemistry topics such as rotaxanes, catenanes, host-guest interactions, dendrimers, and self-assembled monolayers remain, but now with important extensions into the realms of fullerenes, carbon nanotubes, and biomolecules, like DNA. 

DePalma and Tillman investigated self-assembled monolayer films from three silanes, tridecafluorooctyltrichlorosilane, undecyltrichlorosilane, and octadecyl-trichlorosilane, on silicon, a popular model substrate for such studies with great relevance to potential semiconductor coating applications. They characterized the films by ellipsometry and contact angle measurements (data for trideca-fluorooctyltrichlorosilane are included in Table 1), but more usefully from an applicational viewpoint, they carried out friction and wear measurements with a pin-on-disk device where the silicon wafer substrate, coated with monolayer, is moved under a spherical glass slider. Optical microscopy was used to assess wear. Table 2 summarizes DePalma and Tillman s data and their comparison with the classical self-assembled monolayer friction studies of Levine and Zisman [18]. 

S. Campuzano, R. Galvez, M. Pedrero, F.J. Manuel de Villena and J.M. Pingarron, Preparation, characterization and application of alkanethiol self-assembled monolayers modified with tetrathiafulvalene and glucose oxidase at a gold disk electrode, J. Electroanal. Chem., 526(1-2) (2002) 92-100. 

Formation and characterization of a well-ordered monolayer prepared by adsorbing thiophene onto Au(l 1 1) (96L6167). Exposure of Au(l 1 1) surfaces to an ethanol solution of thiophene produces a stable SAM (self-assembled monolayer) which is strikingly similar to SAMs obtained by reacting Au(l 11) with alkanethiols or dialkylsulfides. 

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