"Retinal prostheses are becoming a viable therapy for inner retinal degeneration caused by age related macular degeneration (AMD) and retinitis pigmentosa (RP). The majority of ocular and periocular prosthetic devices employ photodiodes and a microelectrode interface to convert light into a nerve impulse within the retina. Problems with this design include the need of an external power source, the lack of biocompatibility of the microelectrode array, and the need for complicated surgical procedures. Self-assembled monolayer (SAM) technology offers an alternative strategy, where neurons can be stimulated by light activation of a single layer of a photovoltaic SAM. We have developed a SAM structure where the photoexcitable dye 2-[2-[4-(dibutylamino)phenyl]ethenyl]-3-caboxymethylbenzothiazolium bromide (NK5962) was covalently immobilized to an indium tin oxide (ITO) and 3-(aminopropyl) trimethoxysilane (APTMS) surface. The NK562 derivatized surface was characterized through contact angle goniometry, electrochemical impedance spectroscopy, grazing angle infrared spectroscopy, and ultraviolet-visible absorption spectrophotometry. NG108-15 neurons were differentiated onto the surface and neural responses from electrical stimulation and photostimulation of the system were measured using whole-cell current and voltage clamp methodologies. We found an average 2.9 mV decrease in NG108-15 threshold potential for every 10 mV increase in ITO surface potential. Following photostimulation, there was a 1.8±0.2 fold increase (p < 0.05) in the sodium channel current amplitude and a 2.00 ± 0.22 fold increase (p < 0.05 ) in voltage amplitude of NG108-15 neurons on the ITO-APTMS-NK5962 surface due to transfer of energy from the excited dye surface to the attached neurons. The degree of photostimulation decreased upon using 344, 430, and 603 nm optical filters to block increasing amounts of the wavelengths of incident light capable of being absorbed by NK5962. The sodium current amplitude slightly increased at 50% transmittance of incident light relative to 100% transmittance, then sharply decreased at 12.5%, 6.25%, 3.13% transmittance. Upon addition of tetrodotoxin (TTX), sodium channel blockage was observed and portrayed by decreased sodium current and voltage response amplitudes, validating the voltage and current clamp results described above. Our findings indicate that the NK5962 photoelectric film shows promise as an implant for restoring light sensitivity to the retina. "

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We examine the electrochemical properties of SAM of alkanethiols terminated with biferrocenyl group (complex 7) to understand the interactions between metal surface and molecules. The cyclic voltammogram of complex 8 shows two successive reversible one-electron redox waves corresponding to the oxidation of the biferrocenyl moiety and all peak-to-peak separations are smaller than 59 mV (ideal value of one electron transfer with diffusing controlling). In addition, the peak currents are linear to scan rate, i.e., i£\V. This observation is corresponding to the electrochemical property of SAM, and we would like to suggest that the electron transfer process in the electrochemical measurements is direct controlling. Furthermore, we synthesized a nano-material by using of redox stable biferrocenylalkanethiol attached to gold cluster (complex 10). The clusters are stable in air, soluble in nonpolar organic solvents and the characters could be examining by traditional chemical instruments such as NMR, IR, UV/Vis, TEM. The cyclic voltammogram shows that the electron transfer process in the electrochemical measurements is also direct controlling. Finally, the well-known mechanism of intramolecular electron transfer in mixed-valence biferroceniums and the stable biferrocene on Au (111) surface and on gold clusters let to the more advanced concept. We believe that the microstructure of biferrocene assembled on an electrode surface or on gold clusters might enable to carry out a particular function extraordinarily well, for example, optical switch.

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The development of metal-oxide-semiconductor field effect transistor (MOSFET) technology relies on new channel materials with higher carrier mobilities that allow faster switching but at lower voltages. III-V semiconductors are suitable for channel materials in n-type MOSFETs due to their higher electron mobility. However, the interface between the gate dielectric and the III-V surface shows defects that detriment the electrical performance of the transistor. These defects are attributed to interfacial oxides that create energy states in the band gap. Therefore, III-V oxides must be removed and the surface must be protected from reoxidation for the deposition of other functional layers. In this work, oxide etching and passivation of III-V semiconductors were studied to understand the oxide etching mechanism and to develop passivation techniques that allow the integration of these materials in device manufacturing. The etching of GaAs(100) was studied using aqueous HCl and H₂O₂ mixtures with and without the addition of alpha-hydroxy acids. Oxide etching depends on the strength of the acid. Without the addition H₂O₂, acetic, glycolic, tartaric and hydrochloric acids (pKₐ lower than 5) are able to remove oxides. Upon the addition of H₂O₂, only the stronger acids (glycolic, tartaric and hydrochloric) with a pKₐ lower than 4 are able to compete with H₂O₂ and etch the oxides. Oxide removal leaves an As-rich surface, and in the case of HCl, etching leaves a surface terminated with As-Cl species. As-As dimers are formed when oxides are etched with HCl and organic acids. After oxide removal with HF or HCl, the fresh GaAs and InP surfaces were passivated with a series of alkanethiols (C(n)H(2n+1)SH) to assess their effectiveness in protecting the substrate from reoxidation. Longer C chains provided increased protectiong due to their increased chain-chain interactions that allow them to form a denser and well-ordered monolayer. The surface is chemically passivated through S-X (where X = As, Ga for GaAs, and In for InP) bonding between the alkanethiolate layer and the surface. A layer formed by 1-eicosanethiol protected GaAs for 30 min, but prevented reoxidation of InP for at least 5 hours. Since the thickness of the alkanethiol layer is the same, the difference in protection is a result of the density of the layer and S bonding with the substrate.

A study to optimise an IgG based immunosensor is presented, that has been carried out by absorbing monolayers to a gold transducer surface at varying immersion times and temperatures. The theory and kinetics of monolayer adsorption are analysed and discussed. Existing mathematical models are reviewed and experimentally researched, to highlight gaps in knowledge that would facilitate high quality, cost effective immunosensor production. The creation of two mathematical models to predict monolayer adsorption kinetics and optimal immersion times are discussed. Details are provided of how the new mathematical models may be advanced, and how the production of immunosensors may be further improved. The first novel mathematical model (PTCS) has been created to model the presence of two sequentially forming structures on the surface of a substrate. It gives an insight into the percentages of each structure on the surface, along with the actual adsorption process. This model provides a good fit to all applicable experimental data and has allowed the deduction of optimum immersion times. The second novel model (PIF) provides a greater insight than existing models into the individual contributions to surface coverage by both random and island growth. This allows an insight into how the monolayer surface is covered, which is critical to determine the optimum conditions for adsorption. This model also provides a good fit to the isotherm data it has been applied to. To provide a thorough understanding of the bulk properties of monolayer formation over the gold transducer, and how these properties vary with immersion time and temperature, various measurement techniques have been employed. Electrochemical Impedance Spectroscopy (EIS) has been the principle measurement technique used to measure the bulk properties, but confirmation studies have also been carried out including, Contact angle measurements, FTIR microscopy with BSA molecular labels, Fluorescence microscopy for small adsorbed molecules and AFM for layers assembled from macromolecules. The data generated from the different techniques show consistency with the arguments discussed in each instance. Two different IgG adsorption processes have been compared. These include direct IgG addition and a multilayered streptavidin-based process. The results indicate that IgG molecules adsorbed via the streptavidin based multilayer process are more vertically orientated and have a higher packing density of IgG molecules. Keywords: Self Assembled Monolayer, impedance-based immunoassay, Streptavidin, biotinylated IgG, mathematical adsorption modelling.

Molecules that contain linear alkane chains self-assemble on a variety of surfaces changing the degree of wetting, lubricity, and reactivity. We report on the reoxidation of GaAs(100) in air after adsorbing five alkanethiols (C$_n$H$_{2n+1}$-SH where $n=$ 3, 6, 12, 18, 20) and one alkanedithiol (HS-(CH$_2$)$_8$-SH) deposited from the liquid phase. The alignment of the alkane chains forms a self-assembled layer, however, air diffuses readily through the carbon layer and reaches the surface. The impact of alignment is to improve the bonding of sulfur with the surface atoms which reduces the oxidation rate based on fitting the data to a reaction-diffusion model. The layer thickness and molecular density scale linearly with the number of carbon atoms in the alkane chain. The thickness of the alkanethiolate (RS$^{-}$) layer grows by $0.87 \pm 0.06$ {\AA} for each C atom in the chain and the surface density by $0.13 \pm 0.03$ molecule per nm$^2$ per C atom up to a coverage of 5.0 molecules/nm$^2$ for $n=20$ or 0.8 monolayer. The surface coverage increases with length because interactions between methylene (CH$_2$) groups in neighboring chains reduce the tilt angle of the molecules with the surface normal. The tight packing yields areas per alkanethiolate as low as 20 \AA$^2$ for $n=20$. The amount of C in the layer divided by the chain length is approximately constant up to $n=12$ but increases sharply by a factor of 2-4$\times$ for $n=18$ and 20 based on the C 1s x-ray photoelectron spectroscopy (XPS) peak. Fourier transform infrared (FTIR) spectroscopy shows that the asymmetric methylene stretch shifts continuously to lower wavenumber and the relative peak area increases sharply with the length of the alkane chain. Fitting the data to a reaction-diffusion model shows that for times less than 30 min the surface oxide coverage does not depend on the thickness of the self-assembled layer nor the diffusivity of oxygen through the layer. Instead increasing the layer thickness makes more S available for bonding with the predominately As termination and reduces the rate coefficient for reaction of oxygen with the GaAs surface.

In earlier research in our lab, the manipulation of microtubules on gold patterned silicon wafers was achieved by E-beam lithography, Poly (ethylene glycol) self assembled monolayers (PEG-SAMs) and electrophoresis. To develop a technique for delicate single microtubule manipulation, further studies need to be done on PEG-SAMs and electrophoresis. As a foundation of this goal, we examined the electric field in an aqueous solution between two planar electrodes and the compatibility of the antifouling property of PEG-SAMs with the electric field. For this purpose, the distribution of microbeads was analyzed using a Boltzmann distribution. The amount of adsorbed microtubules on a PEG-SAM was examined to test the compatibility of the antifouling property of a PEG-SAM with concomitant exposure to electric field. It is shown that the product of the electric field and the effective charge of the microbead does not have a linear relation with the applied electric potential but an exponentially increasing function with respect to the potential. The antifouling property of the PEG-SAM was not retained after an exposure to the electric field.

The thesis is divided into two parts. One is about the preparation of discotic liquid crystals Acid-6. The other is about the growth of Acid-6 thin film by thermal evaporation on silicon oxide surfaces and modified silicon oxide surfaces such as self-assembled monolayer(SAM) in different temperature. The surface morphology and molecular orientation of the thin film were studied by Atomic Force Microscopy(AFM) , X-ray Diffraction (XRD) , and then they were applicated to organic thin film transistor and measured properties by Semiconductor Parameter Analyzer. In the second part of our research, our expectative characteristics was not observed in different temperature and substructure. In the other side, we guessed that because discotic liquid crystals Acid-6 is negative semiconductor materials, so it is susceptible to hydrosphere, thus we can¡¦t observe the electric characteristic of OTFT in the atmosphere. In addition, due to discotic liquid crystals Acid-6 have biggish moleculer weight, thus its viscosity was so big that cause the diameter of Acid-6 crystals to be too small. Therefore, it influenced the carrier mobility. Finally, from the aspect of procedure about fabrication of the devices we can discuss whether this parameter of this device can apply to OTFT.