The ability to produce monomolecular coatings with well-defined structural and functional properties is of key importance in biosensing, drug delivery, and many recently developed applications of nanotechnology. Organic chemistry has proven to be a powerful tool to achieve this in many research areas. Herein, we present the synthesis of three oligo(lactosides) glycosylated in a (1 → 3) manner, and which are further functionalized with amide-linked short alkanethiol spacers. The oligosaccharides (di-, tetra-, and hexasaccharide) originate from the inexpensive and readily available lactose disaccharide. These thiolated derivatives were immobilized onto gold surfaces, and the thus formed self-assembled monolayers (SAMs) on planar gold were characterized by wettability, ellipsometry and infrared reflection–absorption spectroscopy. Further, the ability of these SAMs to stabilize gold nanoparticles in saline solutions was also demonstrated, indicating that the oligosaccharides may be used as stabilizing agents in gold nanoparticle-based assays.

Switchable surfaces, also called smart surfaces or controllable surfaces, respond to changes in their local environment resulting in altered surface properties. There are various environmental perturbations that can cause changes to the surface properties but the focus of this thesis is on the affect of electrostatic potential. Significant evidence is provided from previous reports on electrochemical and infrared spectroscopic experiments suggesting that self-assembled monolayers (SAMs) of 4-mercaptobenzoic acid (4-MBA) undergo protonation-deprotonation by the application of an electric field. However, there are plenty of aspects of this electric field driven protonation-deprotonation mechanisms using carboxylic acid terminated SAMs that are not well understood. Most importantly, there is a lack of model independent measurements to validate this process. As such, experimental techniques utilizing infrared spectroscopy were employed to correlate electrochemical measurements and models.<p> This body of work demonstrates the importance of the intermolecular hydrogen bonding network on the measured voltammetric peak associated with the protonation-deprotonation of these SAMs. The voltammetric peak height diminishes with increasing exposure to an electrolyte solution. This behaviour is attributed to the replacement of the carboxylic acid protons with electrolyte cations and ultimately the disruption of the hydrogen bonded network.<p> We attempted to further our ex-situ infrared measurements by using an in-situ spectroelectrochemical technique. We had some initial successes, presented within, but more work is needed to complete this picture and is beyond the scope of this thesis. To summarize, the protonated state of SAMs of 4-MBA can be driven by the application of an electric field providing a potential platform to build a controllable smart surface.

Langmuir-Blodgett (LB) organic monomolecular (monolayer) films containing fatty acids and their perfluorinated counterparts separate into phases under certain conditions. These perfluorinated surfactant containing mixed-phase systems have been shown to exhibit many favourable attributes in comparison to non- perfluorinated surfactant monolayers. In this thesis project, two of these films were investigated. One film is a 2:1 ratio mixture of arachidic acid (C19H39COOH AA) to perfluorotetradecanoic acid (C13F27COOH PA), which phase-separates into hexagonal domains ~6 ìm large (2:1 ratio of AA to PA 2AA1PA). The other film is a 2:1 mixture of stearic acid (C17H35COOH - SA) to PA, which phase-separates into linear domains ~300 nm wide (2:1 ratio of SA to PA 2SA1PA).<p> Through the use of atomic force microscopy (AFM), and various synchrotron photoemission electron microscopy-based (PEEM) techniques, the films were characterized. As properties such as molecular organization, and dispersion of the molecules in the film, affect film function, it is necessary to use a variety of techniques to better understand order and composition in the films.<p> First, the well-known and previously-studied film, 2AA1PA, was used to better understand contrast mechanisms in the energy filtered x-ray photoemission electron microscope (X-PEEM) at the CLS. Through the use of techniques such as secondary electron emission microscopy (SEEM), ultraviolet photoelectron spectroscopy (UPS), and x-ray linear dichroism microscopy (XLDM), the effects of secondary electrons, valence character, and polarization dependence were studied so as to better understand their contribution to contrast in energy-filtered PEEM-based spectromicroscopy.<p> Second, the composition and organization of a novel system (2SA1PA), was characterized using traditional near-edge x-ray absorption fine-structure (NEXAFS) spectroscopy. As the size of the domains in the 2SA1PA system are below the spatial resolution limit of PEEM spectromicroscopy, methods involving selective phase dissolution, and spectrum subtraction, were used to acquire phase composition and molecular order information.<p> The high lateral and vertical spatial resolution of AFM allowed physical imaging and confirmation of sample structure, as well as very accurate domain height determination. X-PEEM supplements this with chemical sensitivity using high spatial resolution spectromicroscopy. Therefore, using AFM and X-PEEM as complimentary techniques, it is possible to physically and chemically characterize phase-separated monolayer films.

Switchable surfaces, also called smart surfaces or controllable surfaces, respond to changes in their local environment resulting in altered surface properties. There are various environmental perturbations that can cause changes to the surface properties but the focus of this thesis is on the affect of electrostatic potential. Significant evidence is provided from previous reports on electrochemical and infrared spectroscopic experiments suggesting that self-assembled monolayers (SAMs) of 4-mercaptobenzoic acid (4-MBA) undergo protonation-deprotonation by the application of an electric field. However, there are plenty of aspects of this electric field driven protonation-deprotonation mechanisms using carboxylic acid terminated SAMs that are not well understood. Most importantly, there is a lack of model independent measurements to validate this process. As such, experimental techniques utilizing infrared spectroscopy were employed to correlate electrochemical measurements and models.<p> This body of work demonstrates the importance of the intermolecular hydrogen bonding network on the measured voltammetric peak associated with the protonation-deprotonation of these SAMs. The voltammetric peak height diminishes with increasing exposure to an electrolyte solution. This behaviour is attributed to the replacement of the carboxylic acid protons with electrolyte cations and ultimately the disruption of the hydrogen bonded network.<p> We attempted to further our ex-situ infrared measurements by using an in-situ spectroelectrochemical technique. We had some initial successes, presented within, but more work is needed to complete this picture and is beyond the scope of this thesis. To summarize, the protonated state of SAMs of 4-MBA can be driven by the application of an electric field providing a potential platform to build a controllable smart surface.

Langmuir-Blodgett (LB) organic monomolecular (monolayer) films containing fatty acids and their perfluorinated counterparts separate into phases under certain conditions. These perfluorinated surfactant containing mixed-phase systems have been shown to exhibit many favourable attributes in comparison to non- perfluorinated surfactant monolayers. In this thesis project, two of these films were investigated. One film is a 2:1 ratio mixture of arachidic acid (C19H39COOH AA) to perfluorotetradecanoic acid (C13F27COOH PA), which phase-separates into hexagonal domains ~6 ìm large (2:1 ratio of AA to PA 2AA1PA). The other film is a 2:1 mixture of stearic acid (C17H35COOH - SA) to PA, which phase-separates into linear domains ~300 nm wide (2:1 ratio of SA to PA 2SA1PA).<p> Through the use of atomic force microscopy (AFM), and various synchrotron photoemission electron microscopy-based (PEEM) techniques, the films were characterized. As properties such as molecular organization, and dispersion of the molecules in the film, affect film function, it is necessary to use a variety of techniques to better understand order and composition in the films.<p> First, the well-known and previously-studied film, 2AA1PA, was used to better understand contrast mechanisms in the energy filtered x-ray photoemission electron microscope (X-PEEM) at the CLS. Through the use of techniques such as secondary electron emission microscopy (SEEM), ultraviolet photoelectron spectroscopy (UPS), and x-ray linear dichroism microscopy (XLDM), the effects of secondary electrons, valence character, and polarization dependence were studied so as to better understand their contribution to contrast in energy-filtered PEEM-based spectromicroscopy.<p> Second, the composition and organization of a novel system (2SA1PA), was characterized using traditional near-edge x-ray absorption fine-structure (NEXAFS) spectroscopy. As the size of the domains in the 2SA1PA system are below the spatial resolution limit of PEEM spectromicroscopy, methods involving selective phase dissolution, and spectrum subtraction, were used to acquire phase composition and molecular order information.<p> The high lateral and vertical spatial resolution of AFM allowed physical imaging and confirmation of sample structure, as well as very accurate domain height determination. X-PEEM supplements this with chemical sensitivity using high spatial resolution spectromicroscopy. Therefore, using AFM and X-PEEM as complimentary techniques, it is possible to physically and chemically characterize phase-separated monolayer films.

The speed of microelectronic devices is controlled by the size of the transistor gate. In order to create faster devices, the size of this transistor gate must shrink. Microlithography is the method used to define patterns in semiconductor devices, and it is optimized periodically to create smaller features. It is a subtractive process that relies on the selective removal of sections of a photosensitive polymeric film called photoresist. This photoresist is exposed to patterned ultraviolet radiation that changes the local solubility of the film and allows for the creation of relief patterns in the resist using a developing solvent. Decreasing the wavelength of the light used to expose the patterns is the primary method for decreasing the minimum feature size that can be printed by this process. There are a number of challenges associated with decreasing the exposure wavelength for conventional lithographic processes. First of all, the polymeric films must be transparent at the exposure wavelength in order to allow light to propagate through the entire thickness of the film. Secondly, there is a limit in the thickness of the photoresist films that can be used. This thickness limits the etch resistance of the film. In fact, the issues concerning etch resistance and transparency are generally in opposition. This makes designing photoresist platforms for future lithographic applications very difficult. Therefore, to overcome these limitations, we are developing an unconventional approach to microlithography. In our approach, entitled Surface Monolayer Initiated Polymerization, polymer structures are formed on a surface by polymerizing a monomer in a patterned fashion using a self-assembled monolayer that can be locally activated to initiate the reaction. This process has been demonstrated by creating patterned polystyrene films on native silicon dioxide surfaces. In these initial studies, it took more than one day to create features. This is unacceptable for a lithographic application. The kinetics of all the processes involved in making these patterned layers is described. Along with these rate constants, means of optimizing these rates are also presented. Additionally, the patterns grown in these initial studies exhibited poor uniformity. Methods of optimizing the patterns formed are also presented.

No description available.

Biologically-inspired materials have emerged as promising substrates for enhanced repair in various therapeutic and regenerative medicine applications, including nervous and vascular tissues, bone, and cartilage. These strategies focus on the development of materials that integrate well-characterized domains from biomacromolecules to mimic individual functions of the extracellular matrix (ECM), including cell adhesive motifs, growth factor binding sites, and protease sensitivity. A vital property of the ECM is the fibrillar architecture arising from supramolecular assembly. For example, the fibrillar structure of fibronectin (FN) matrices modulates cell cycle progression, migration, gene expression, cell differentiation, and the assembly of other matrix proteins. Current biomaterials do not actively promote deposition and assembly of ECM. In this research, we describe the rational design and investigation of non-fouling biomimetic surfaces in which an oligopeptide sequence (FN13) from the self-assembly domain of FN is tethered to non-fouling substrates. This surface modification directs cell-mediated co-assembly of robust fibrillar FN and type I collagen (COL) matrices reminiscent of ECM, and increases in cell proliferation rates. Furthermore, the effect of this peptide is surface-directed, as addition of the soluble peptide has no effect on matrix assembly. We have also identified a critical surface density of the immobilized peptide to elicit the full activity. These results contribute to the development and design of biomimetic surface modifications that direct cell function for biomedical and biotechnology applications.

High-resolution lattice periodicity images of a variety of well-defined surfaces, including graphite, mica, and Au(111), validated the good stability of our atomic force microscope (AFM) system. Combining self-assembled monolayer (SAM) and AFM technology, we demonstrated the capabilities of pattern fabrication as well as modification of surface functionality. AFM-based nanolithography operating conditions, such as scan rate, deflection setpoint, and number of scan were studied to obtain the optimized quality of the fabricated patterns. Thiolated-DNA probe molecules could be patterned at a nanometer scale on a gold substrate. However, we found that the surface coverage began to drop notably with the probe length (number of DNA bases). Therefore, the displaced DNA molecules during nanoshaving were reversibly adsorbed, and patterning became unreliable. We were unsuccessful in detecting the subsequent hybridization reactions at these nanopatterns from AFM measurements. To realize the DNA hybridization, further studies on the incubation temperature, probe length and even DNA sequences are required to demonstrate that this AFM-based gene diagnostic method is truly operational.

Nanostructured materials play a vital role in almost all aspects of science and technology in the 21st century. The materials include nanoparticles, nanofilms, biological membranes etc. whose physicochemical properties are size-dependent. Thin films have wide range of applications in various branches of science. One of the efficient methods to form miniaturized structures for device applications is to fabricate nanostructured films on different substrates. Surfactant assembly on metallic and non-metallic surfaces based on self assembly and Langmuir-Blodgett technique offers a unique way to form thin films at molecular levels. The process of formation of unimolecular assemblies gives the flexibility of tuning the properties of underlying substrates for various applications including wetting characteristics, lubrication, passivation, mimicking biological phenomena etc. Towards this direction, self assembled monolayers (SAMs) of alkanethiols on gold and silver surfaces have been studied comprehensively for the past two decades. The reported literature on short chain length thiol-based monolayers is however, limited since the formation using conventional methods yield poor quality monolayers. The short chain length monolayers are useful in various applications like tribology, layer-by-layer assemblies, biosensors etc. Hence, it is essential to reproducibly form SAMs of various chain lengths and understand their properties. The present study is related to the formation of SAMs of alkanethiols and diselenides on gold and silver surfaces to form ordered and well-oriented monolayers. Monolayers of varying chain lengths (CH3(CH2)nSH where n = 3, 5, 7, 9, 11, 15) have been formed on gold and silver surfaces using different methods, (1) adsorption from neat thiols; (2) adsorption under electrochemical control and (3) adsorption from alcoholic solutions of the thiols. The characteristics features of the SAMs have been followed based on three different aspects, (i) structure and stability of the methylene groups (ii) interfacial characteristics involving the end group and the solvent and (iii) metal-head group interactions. The structure and stability of the monolayers have been followed based on vibrational spectroscopy and electrochemistry under different environment including thermal perturbations. The stability of the SAMs at different temperatures and subsequent changes associated with the orientation / packing has been monitored both in the dry state using reflection absorption infrared spectroscopy (RAIRS) and under electrochemical conditions using cyclic voltammetry and impedance analysis. Monolayers adsorbed from neat thiols show superior quality in terms of stability and structural arrangement. Short chain thiols with n = 3, 5, 7 show substantial stability when the adsorption is carried out from neat thiols. Figure 1 shows the RAIR spectra of hexanethiol SAM on gold adsorbed by three different procedures. Monolayers adsorbed under potential control behave very similar to the monolayers adsorbed from neat thiol as for as stability and structural orientation are concerned. Monolayers prepared using conventional methods of adsorption from alcoholic solutions are of inferior quality in terms of stability and arrangement especially for the short chain lengths. This is likely to be due to the fact that monolayers prepared using conventional methods may have intercalated solvent molecules within the monolayer assembly that degrade the integrity of the SAM leading to poor quality. The blocking characteristics of the monolayers for diffusing redox couple have been followed by determining the heterogeneous electron transfer rate constant using electrochemical techniques. The spectroscopic data and the electrochemical data follow similar trend indicating the superior quality of monolayer adsorbed from neat thiol in terms of stability as compared to conventionally prepared monolayers. Figure 1. RAIR spectra of hexanethiol-SAMs on Au(111) surface at 25C. The monolayers are formed by adsorption (A) from neat thiol (B) under potential control and (C) from alcoholic solution of the thiol. Wavenumber (cm-1) The interfacial characteristics of the monolayers (effect of end group functionality on the solvent properties) have been monitored on the basis of capacitance, contact angle and atomic force microscopy- measurements. Well-organized monolayers behave like good capacitors with relatively low values of double layer capacitance in presence of a liquid electrolyte as compared to the expected values based on known thickness and dielectric constant of the SAMs. This behavior can be explained by invoking the depletion of water density at the methyl terminated SAM-water interface where the solvent properties are different from that of bulk. Variation of one such property, dielectric constant, has been mapped using force measurement based on AFM. Dielectric constant of water changes from the bulk value of 78 to a low value as given in figure 2. This cross-over occurs within a span of 1-3 nm depending on the chain length of the thiol. Of the three procedures used, the ones based on the use of neat thiol and electrochemical adsorption result in well-oriented alkyl chains followed by highly oriented methyl terminal groups. This is responsible for the high hydrophobic nature of the interface and the subsequent observation of interfacial water properties. The SAMs prepared from ethanol fail to show the hydrophobic effects. Hydrophilic monolayers (NH2 terminated monolayers) fail to show depletion of water density at the interface indicating the importance of end group functionality in altering the interfacial characteristics of the monolayer. Figure 2. Spatial variation of dielectric permittivity of water at the hexanethiol SAM - water interface. The SAM is formed on gold (111) surface; (a) from ethanolic solution of the thiol (b) under electrochemical control (c) from neat thiol. The origin on the x-axis is the position of the methyl groups of SAM and the direction towards right side is in to the bulk water. The well-oriented SAMs have been used to follow the adsorption of a biopolymer. Zein protein is a prolamine of maize and is projected to be a biocompatible coating for food products and food containers. Hence, it is essential to prepare impermeable coatings of zein with different surface wetting properties. The adsorption of zein on highly ordered SAMs with hydrophobic or hydrophilic end group functionality has been studied and the orientation of the protein followed using spectroscopy, microscopy and electrochemistry. It is observed that zein shows higher affinity towards hydrophilic than hydrophobic surfaces with small foot print size on the Figure 3. Orientation of zein protein on hydrophilic and hydrophobic SAM as deciphered from the experimental data. hydrophilic surface resulting in large surface coverage. Figure 3 shows the schematics of zein deposits on hydrophilic and hydrophobic SAM surfaces determined based on spectroscopy, quartz crystal microbalance and electrochemical studies. The AFM shows cylindrical, rod-like and disc-like features of zein on hydrophilic surfaces that form the base units for the growth of cylindrical structures of zein. The published literature on the studies on SAMs on silver surfaces reveals that there is no consensus on the structure of the monolayers on silver. This may be due to the difficulty in getting pristine oxide-free surfaces in the case of silver and this is likely to affect the monolayer quality. Hence, it is decided to prepare SAMs of alkanethiols on silver and study their characteristics. Subtle differences between the monolayers adsorbed from neat thiol and from alcoholic solutions of thiols have been observed in terms of stability and permeability. Atomic force microscopic studies illustrate the presence of depletion of water at the SAM-aqueous interface. Diselenide-based monolayers have been formed on gold to understand the head group-substrate interactions on the monolayer properties. The disorder observed on short chain diselenide-based monolayers formed from alcoholic solutions can be eliminated by adsorption from neat compounds as described for the thiols. A preliminary account on the stability of SAMs under hydrodynamic conditions has been given based on rotating disc electrode voltammetry. It is observed that the SAMs get well-ordered when the electrode is rotated at a fast rate leading to the hypothesis that the monolayer assembly gets annealed as a function of the rotation rate. The thesis is planned as follows: Chapter 1 gives general introduction about organic thin films with particular emphasis on self-assembled monolayers on gold and silver, their characteristics in terms of stability, interfacial properties and adsorption behaviour. Chapter 2 deals with the experimental methodologies and schematics used for the preparation and characterization of the monolayers. Chapter 3 is on the contribution of alkyl spacer to the stability of the monolayers studied using spectroscopy and electrochemistry. Chapter 4 deals with the interfacial properties of the SAMs in presence of aqueous medium. In order to emphasize the importance of the terminal functional groups, adsorption of zein has been demonstrated on surfaces of controlled wettablity. Chapter 5 explains the formation and stability of monolayers of short and long chain alkyl diselenides on gold surfaces. Chapter 6 gives the structural and interfacial characteristics of alkanethiol monolayers on silver surfaces. The stability and subsequent changes of alkanethiol monolayers under hydrodynamic conditions has been discussed in the appendix section.(For fig pl refer pdf file.)