Ellipsometry SAMs

TABLE 5.1. The ellipsometry SAM thickness data for the SAMs formed from 2 and 3. 

When cells are suspended in a biological fluid or culture medium, both serum proteins and cells interact with the surface substrate. Serum protein adsorption behavior on SAMs has been examined with various analytical methods, including SPR [58-61], ellipsometry [13, 62, 63], and quartz QCM [64—66]. These methods allow in situ, highly sensitive detection of protein adsorption without any fluorescence or radioisotope labeling. SPR and QCM are compatible with SAMs that comprise alkanethiols. In our laboratory, we employed SPR to monitor protein adsorption on SAMs. 

Wasserman [186] has described the use of both low-angle X-ray reflectivity and ellipsometry for the determination of thickness of Cio-Cig SAMs prepared on surface silanol groups of silicon plates. Ellipsometry is based on the reflection of polarized light from a sample and depends on the sample s thickness and refractive index. X-ray reflectivity measures the intensity of X-rays reflected from a surface (or interference pattern) that is characteristic of the distance between interfaces. The thickness of the SAMs was consistent with fully extended alkyl chains with all-trans conformations and excellent agreement was observed between the two methods. 

A number of methods are available for the characterization and examination of SAMs as well as for the observation of the reactions with the immobilized biomolecules. Only some of these methods are mentioned briefly here. These include surface plasmon resonance (SPR) [46], quartz crystal microbalance (QCM) [47,48], ellipsometry [12,49], contact angle measurement [50], infrared spectroscopy (FT-IR) [51,52], Raman spectroscopy [53], scanning tunneling microscopy (STM) [54], atomic force microscopy (AFM) [55,56], sum frequency spectroscopy. X-ray photoelectron spectroscopy (XPS) [57, 58], surface acoustic wave and acoustic plate mode devices, confocal imaging and optical microscopy, low-angle X-ray reflectometry, electrochemical methods [59] and Raster electron microscopy [60]. 

In the case of work on phenylhthium anionic initiators, the first reported work by Jordan et al. involved the use of a SAM of biphenyllithium moieties on gold substrates to initiate anionic polymerization of styrene [26]. The thickness of the resulting dry polystyrene brush, as estimated by ellipsometry... 

A series of SAMs formed on Au from mono- and dithiol conjugated aromatic molecules was characterized by cyclic voltammetry, grazing incidence Fourier transform infrared spectroscopy, contact angle measurement, and ellipsometry.43 The analyses indicated that the molecular orientation of conjugated phenylene- and thophene-based dithiols became less tilted with respect to the surface normal as the chain length of the organic molecules increased. 

Shortly after Chidsey and co-workers initial papers. Miller et al. reported full characterization of Au-S(CH2) OH monolayers (System 5, = 6-12, 14, 16) by ellipsometry, XPS and electrochemical methods [44]. The nearly defect-free nature of the monolayers was attributed to hydrogen-bonding interactions between neighboring adsorbate chains at the film-electrolyte interface. The level of defects was probed by varying bridging halides, which should change electron-transfer processes at pinholes from outer to inner sphere. Electrochemical annealing was found to improve the EBE [44]. Later, they showed that defects in the SAMs are on the... 

As an example, herein we explain the characterization of the combinatorial Libraries 1 and 2, mentioned above, which were synthesized using the solution-based procedure. Contact angle and ellipsometry data of the monolayer Libraries 1 and 2 are summarized in Fig. 4.1. Amino terminated SAMs formed from /V-13-(trimethoxysilyl)propyl]ethylenediamine (TPEDA) have an advancing contact angle (6j of 60°, and a hysteresis of 250.34 Hysteresis (0a - 6) values range from... 

One criterion for the quality of SAMs is the respective layer thickness, which, for example, can be determined by ellipsometry. As becomes elear in Table 7.1, the thicknesses of the monolayers deposited from ethanol are generally more consistent with the expected values. Most of the thiols used in this study are new, so the tilt angles eould only be estimated based on experiences with other araliphatie systems [36]. Even if the estimated tilt angle for the molecules were to be lower, the ealculated layer thieknesses would still be too low for the values determined for the THF-derived layers. The reason for this behaviour might be the formation of physisorbates. These layers were nevertheless used for the deposition study. 

The SAMs on a gold substrate of terthiophenes (219), where X-R-T3 is either a thiol (220) or a dithio (221) anchoring group were characterized by ellipsometry, contact angle goniometry, IR spectroscopy, XPS and cyclic voltametry. 220 organized in a few minutes... 

Fig. 14 Tapping-mode AFM height images of HPG on a SAM of 2.6% -S-(CH2)ioCOOH in a matrix of -S-(CH2>9CH3 for different growth times, (a) Average thickness of HPG film as a function of growth time from AFM (circles and solid line) and ellipsometry (triangles and dashed line), (b) Histogram analysis of the size of HPG molecules on surface for different growth times. Reprinted with permission from [142]. Copyright 2007 American Chemical Society...

The kinetics from the solution phase have been carried out by Bain etal. using ellipsometry [47]. Later, many research groups have studied the kinetics of SAM formation (more quantitatively) using various spectroscopic techniques [48,75], such as second-harmonic generation (SHG) [76,... 

Until now, numerous studies on the growth processes of SAM formation have been conducted using several instrumental techniques. In addition to wettability, ellipsometry, and UHV-STM described above, various other techniques, such as SHG [76, 77], SFG [78, 79], NEXAFS [80], EQCM [81], SPR[82], and FTIRRAS [83],... 

Rubinstein et al. [22] used the SAM of p-aminothiophenol to increase the polyaniline (PANI) film/substrate adhesion. It became possible to calculate the film density from the mass data using the QCM and thickness data by ellipsometry. They... 

---