Dissertations / Theses on the topic 'Self-assembled monolayer'

Molecular self-assembly has recently attracted significant attention for possible application in organic electronic and optoelectronic devices, such as self-assembled monolayer field-effect transistors (SAMFETs) and functional self-assembled integrated circuits. Self-assembly combines the advantages of low temperature solution processability, regio-selective monolayer adsorption and nano-scale control of film thickness. Much progress has been made in improving device performance using self-assembled monolayers (SAMs). However, most SAMFET devices reported to date showed current modulation only with submicrometre channels, with low device yields and poor reproducibility as a result of limited lateral interconnection of the semiconducting layer.In an attempt to address these issues, this thesis presents an investigation of the synthesis and properties of conjugated SAM molecules for use as the charge transporting layer in SAMFETs. Chapter 1 gives a comprehensive introduction to SAM-based surface systems, organic semiconductors and their use in OFETs and SAMFETs. Chapter 2 discusses attempts to design and synthesise p-type conjugated molecules capable of self-assembly on oxide surfaces based on a phenylene-bithiophene semiconducting core. The optical and electrochemical properties, as well as the thermal behaviour of these molecules are studied in detail. This theme is carried over to Chapter 3, which describes the synthesis, chemical and physical characterisation of two families of n-type SAM molecules. These molecules consist of NTCDI cores with hexyl or cyclohexyl chains as end-capping groups. Incorporation of a selection of materials as the active layer in OFETs or SAMFETs to evaluate the charge transport is demonstrated in Chapter 4. Monolayer films based on p-type monochlorosilane-terminated SAM molecules are made using the solution assembly technique and characterised by contact angle and AFM. OFETs made from DH-PTTP by both thermal evaporation and spin coating show high mobilities comparable to the best values reported in the literature. Top-contact SAMFETs show a hole mobility of 1.1 × 10-3 cm2V-1s-1 in air, consistent with those of solution processed DH-PTTP based OFETs. Finally, an overview of the project and some suggestions for future work are presented in Chapter 5.

Zinc, cobalt and iron phenylthio substituted phthalocyanines have been synthesized and characterized. Cyclic and square wave voltammetry in dimethylformamide containing tetrabutylammonium perchlorate revealed five and six redox processes respectively for the cobalt and iron phenylthio substituted phthalocyanines. These complexes are easier to reduce compared to the corresponding unsubstituted MPc and to butylthio substituted derivatives. Spectroelectrochemistry (in dimethylformamide containing tetrabutylammonium perchlorate) was employed to assign the cyclic voltammetry peaks, and gave spectra characteristic of Fe(I)Pc for reduction of iron phenylthio substituted phthalocyanine and Co(I)Pc for the reduction of cobalt phenylthio substituted phthalocyanine. The spectrum of the former is particularly of importance since such species have not received much attention in literature. Cobalt and iron phenylthio substituted phthalocyanines have been deposited on Au electrode surfaces through the self assembled monolayer (SAM) technique. The so formed layers were studied using voltammetric techniques. These SAMs blocked a number of Faradic processes and electrocatalyzed the oxidation of L-cysteine. Amine substituted cobalt phthalocyanine (CoTAPc) was deposited on gold surfaces by using an interconnecting SAM of mercaptopropionic acid or dithiobis(N-succinimidyl propionate) through the creation of an amide. Reductive and oxidative desorption of the SAMs limit the useful potential window. The SAM-CoTAPc layers show electrocatalytic activities towards oxygen reduction through the Co(I) central metal ion. Both SAMs were highly stable and hence will be interesting tools for further research in surface modification and sensor development.

This study describes the covalent and the electrostatic attachment of molecules, nano-particles, and proteins to patterned self-assembled monolayers. A scanning probe nanografting technique was employed to produce patterns of various sizes, down to 10 nm. Thus, we are able to demonstrate a degree of surface patterning which is an order of magnitude smaller than that used in the semiconductor industry. One efficient strategy for creating chemically specific nanostructures is to use the extraordinary catalytic properties of enzymes. However, as the dimension of a catalyst patch is reduced down to nanometer scale, it is difficult to detect the very low concentration of product. This study resolves the problem by developing a new strategy: the surface trapping of a product generated by a nanometer-scale patch of surface-bound enzyme. An array of proteins finds use when the array contains a number of different proteins. Toward this end, a new and convenient method for immobilizing enzymes is developed, which will allow the preparation of thin films containing several different catalytically-active enzymes on the nanoscale. The disadvantage of scanning probe nanografting technique is that the AFM tip loses resolution through wear during the patterning procedure. This study examines the possibility of developing a new AFM lithographic method to avoid wear: the use of enzymes covalently attached to a tip as a site-specific catalyst.
Ph. D.

"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. "

The synthesis of the catenane components, a dithiol and a cyclophane, are described using previously reported methods. 1-3 The preparation techniques used to obtain a self-assembled dithiol monolayer and a self-assembled catenane monolayer from dilute solution onto a gold's surface are also reported. Grazing angle reflectance infrared spectroscopy was used to characterize the selfassembled dithiol and catenane monolayers. The infrared spectra revealed evidence for the existence of the dithiol monolayer and possible evidence for the existence of the catenane monolayer. A catenane transmission film spectrum was obtained to provide evidence for the existence of the catenane itself. When the transmission and the monolayer spectra were compared, shifts in a few of the absorption bands revealed some association between the dithiol and the cyclophane.
Department of Chemistry

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1999.
Includes bibliographical references.
Many areas of technology rely on interfacial events that are controlled by nanometer-level interactions present at solid/liquid interfaces. Properties of wetting, corrosion inhibition, and molecular recognition provide convenient examples. To investigate such interactions at the molecular level, self-assembled monolayers (SAMs) have been employed as a model system as they offer the ability to produce well-defined organic surfaces of controlled composition. This thesis addresses the development and characterization of such films for controlling the adsorptive properties of surfaces toward various surfactant-like molecules and for proteins. Adsorption is controlled to facilitate the organized assembly of molecular precursors, retard the non-specific adsorption of proteins, provide a specificity for the adsorption of select proteins, and the use of molecular adsorption to generate local surface energy gradients useful for directing self propelled drop movement. A common theme in these studies is the importance of controlling the energetics and compositions of surfaces at the molecular level to influence microscopic events that translate into macroscopically observable changes in behavior. The first part of this thesis details the formation of monolayer films by the solution-phase adsorption of n-alkyl-chained adsorbates [CH 3(CH2)~ Y] onto the polar surfaces of terminally substituted SAMs [Au/S(CH)mX]. The polar tail groups (X and Y) of the adsorbate and SAM included amine, carboxylic acid, and amide groups, and the formation of the adsorbed monomolecular films on the SAMs relied on non-covalent interactions between X and Y. Highly organized monomolecular adlayers could be produced that were as densely packed as the alkanethiolate SAMs on gold comprising the first layer. This thesis also used this molecular adsorption process to cause liquid drops to move spontaneously on surfaces by creating local changes in surface energy. The drops could be directed to move along specified paths using patterned substrates that contained inner tracks of polar functionality and exterior domains of oleophobic methyl groups. The adsorption process allowed sequential transport of two drops on a common track and also regeneration of the initial high energy surface for reuse. The developed system provides an experimental platform for examining reactive flow and offers a novel "pumpless" method for sequentially delivering multiple drops along surfaces and within microfluidic devices. The second part of this thesis discusses various oligo(ethylene glycol)-terminated alkyltrichlorosilanes [C13Si(CH2)11(OCH2CHnX; X = -OCH 3 or -O 2CCH 3, n= 2- 4] that can form robust films on glass and metal oxide surfaces and control the adsorption of proteins. The adsorption of the methyl-capped trichlorosilanes produces densely packed, oriented monolayer films that are 2-3 nm in thickness. The trichlorosilyl group anchors the molecules to the surface, and the resulting film exposes the ethylene glycol units at its surface, as noted by its moderate hydrophilicity. The films are robust with stabilities similar to those of other alkylsiloxane coatings. These oligo(ethylene glycol)-terminated silane reagents produce films that exhibit resistances against the non-specific adsorption of proteins and that are better than for films prepared from octadecyltrichlorosilane. These oligo(ethylene glycol)-siloxane coatings offer performance advantages and could easily provide a direct and superior replacement for protocols that presently use silane reagents to generate hydrophobic, "inert" surfaces. This thesis also discusses the development of an acetate-capped oligo(ethylene glycol)-terminated silane to produce a HO-terminated oligo(ethylene glycol)-based coating on glass and metal oxide surfaces. The HO-termini of these films provide sites for covalently grafting biomolecules to the parent surface. As a demonstration, biotin and mannose moieties were covalently attached to the HO-surfaces to provide a means to induce the specific adsorption of proteins. For these surfaces, the presence of oligo(ethylene glycol) groups reduces the nonspecific adsorption of other competing proteins. The results indicate that the developed systems could offer a strategy to arrange biomolecules selectively on glass and metal oxide surfaces.
by Seok-Won Lee.
Ph.D.

Formation and characterization of well-organized protein film assemblies are of high interest due to potential applications in biomolecular devices. The hypothesis that a macroscopically ordered protein film can be formed by site-directed, covalent binding of a protein to an appropriately derivatized surface formed the basis for the reported studies. The molecular architecture chosen to address this hypothesis consisted of yeast cytochrome c, a heme protein containing a unique binding site, immobilized on a surface derivatized with a silane self-assembled monolayer, (SAM). A combination of two techniques: total internal reflectance fluorescence (TIRF), to measure fluorescence anisotropy, and integrated optical waveguide-attenuated total reflectance (IOW-ATR) spectroscopy, to measure absorbance linear dichroism, was used to probe the macroscopic order of the heme groups in the film assemblies. Epifluorescence microscopy and absorbance (in an IOW-ATR geometry) were used to probe the nature of the surface-protein interactions and to determine relative protein affinities for different SAM-derivatized surfaces. The molecular orientation distribution for yeast cytochrome c immobilized on a 100% thiol-terminated SAM was 67° ± 39°. Partial protein removal was observed under a variety of rinse conditions, indicating that multiple protein-surface interactions may have contributed to the wide distribution value. Relative binding affinity constants and protein-surface interactions are compared for yeast cytochrome c and horse heart cytochrome c on 100% thiol-capped, 100% hydroxyl-capped, and mixed SAM-modified surfaces. These studies were also extended to include a variant of yeast cytochrome c, Thr8Cys/Cys102Thr. Similar adsorption and removal trends were observed for all the protein-SAM combinations. The adsorption isotherms indicated that at least two binding processes occur during formation of each protein film, high and low affinity binding. Removal studies indicated that the adsorption process is only partially reversible. It was concluded that employing a site-directed immobilization strategy does not necessarily produce a well-ordered protein film.

Mesenchymal stem cells (MSCs) have been proposed as a promising cell source for musculoskeletal tissue engineering due to their multipotentiality. So far, bioactive substances have been used to induce MSC differentiation in vitro, which can also act as a limiting factor when translating into the clinic. With these limitations in mind, efforts are now centred on controlling biomaterial surface properties as a tool to control MSC fate. In particular, modification of surface chemistry in biomaterials is an appealing option to obtain a desirable cell response for the intended function of a biomaterial. As such, chemical modifications on a surface can induce changes in focal adhesions, which in turn, could be used to promote the desired cellular response (e.g. induce chondrogenesis, osteogenesis or adipogenesis in MSCs). With a relatively high degree of reproducibility, self-assembled monolayers (SAMs) seem to be the most promising chemical modification as they are formed spontaneously on surfaces by chemical adsorption. The aim of this work was to explore and understand how different alkylsilane SAMs affected protein adsorption and how changes in adsorption could lead to induce MSC differentiation in vitro. The project focused on five different methyl-terminated alkylsilane SAMs, two amine SAMs and two hydroxyl SAMs that presented varying carbon chain lengths (CCLs) and surface energies (i.e. wettabilities). Following fabrication, the presence of SAMs, their wettabilities and topographical profiles were assessed using XPS, FTIR, contact angle tensiometer and AFM, respectively. Viability assays confirmed that none of the SAMs caused a cytotoxic effect on MSCs or enhanced proliferation when compared to control. Cell morphology on each chemistry was also assessed using immunofluorescence. Although no major differences were found in MSC shape, cell area was clearly reduced by all chemistries compared to control. Assessment of chondrogenic, adipogenic and osteogenic markers was then undertaken qualitatively and quantitatively. While none of the assessed chemistries promoted chondrogenesis, hydroxyl and amine SAMs induced osteogenic and adipogenic differentiation simultaneously with primary MSCs. The use of a clonal MSC line demonstrated that hydroxyl SAMs promoted osteogenesis while silencing adipogenesis in the absence of external stimuli. Overall, longer CCLs enhanced lineage-specific marker expression and secretion, which highlighted the importance of this parameter with regards to MSC behaviour. It is likely that the correlation between wettability, cell proliferation and differentiation was linked to the different protein adsorption profiles observed on alkylsilane SAMs, which was also influenced by the CCL of SAMs. Data suggested that vitronectin might be more important in mediating MSC adhesions on alkylsilane SAMs than fibronectin, which was not adsorbed on any substrates. In addition to this, these findings suggested that in the presence of complex media, ITGA8 and VCAM1 seem to play a key role in determining MSC fate. Altogether, this thesis has established that surface chemistry in the form of alkylsilane SAMs can influence MSC differentiation in the absence of external stimuli, and that CCL is a parameter that MSCs react to.

This dissertation investigates a label-free sensing platform which can be used to detect DNA, enzyme or protein, based upon electrochemical detection which is suitable for implementation in microarray form. Two implementations are proposed based on mixed Ferrocene self-assembled monolayer (SAM) and the Azurin (metalloprotein) SAM. We have shown for the first time that electro-active SAM, functionalized with suitable receptors, can be employed for the detection of biomolecular interactions. Detection of streptavidin by biotin-functionalized Ferrocene SAM was successfully demonstrated. These results were made possible by the development of the fabrication protocols that optimize the SAM stability and reproducibility. Reliable samples, combined with theoretical modelling and modification of existing published model for electro-active SAM, has enabled us to experiment and analyse in depth various electrochemical detection techniques, based on changes in capacitance, voltammetric formal potential and current, Open Circuit Potential (OCP). It was found that AC voltammetry and OCP are the best measurement techniques. The use of OCP with an electro-active SAM had not been previously demonstrated and the theoretical basis for this technique was presented. Essential for this technique was the development of micro-electrodes to reduce parasitic capacitances that would reduce the available signal, enabling real-time detection of bio-molecular interaction. We also made possible to characterize the binding of a protein (streptavidin) to a biotin-functionalized Azurin SAM. Also a numerical analysis has been developed to analyse the effect of design parameters of the platform, such as the probe density and buffer concentration, which can greatly affect the assay sensitivity. This is achieved using 3D simulation with finite element method in COMSOL.

Electrokinetics based microfluidic systems are potentially promising for lab-on-a-chip applications due to their effectiveness in manipulating nanoscale and biological objects, label-free operation, simple fabrication processes, small voltage requirements, and most importantly simple system integration strategy. Among various electrokinetics techniques, AC electrothermal flow (ACEF) is the most promising technique in microfluidic manipulation toward biomedical applications due to its effectiveness in high conductivity biological and physiological fluids. As relatively little is known about the ACEF induced fluid motion at highly conductive samples, the characteristics of electrothermal manipulation of fluid samples with different conductivities were investigated systematically. For low conductivity sample (below 1 S/m), the characteristics of the electrothermal fluid motion was in quantitative agreement with the theory. For high conductivity samples (greater than 1 S/m), the fluid motion appeared to deviate from the model as a result of electrochemical reactions and the temperature effect. Here, a universal electrode approach which directly implements ACEF-induced sample preparation on a SAM based electrochemical sensor for point-of-care diagnostics of urinary tract infections has also been demonstrated. Using uropathogenic E. coli clinical isolates as model systems, we demonstrate that "on-chip" ACEF-induced sample preparation can improve the sensor performance without complicated system integration strategy and presents a pathway for implementing truly lab on a chip, instead of chip in a lab. Finally an integrated chip approach has been proposed for transforming electrochemical sensing system from laboratory research into point-of-care diagnostics with multiple microelectrodes.

A scanning tunneling microscope (STM) was used to perform current-voltage (I-V) measurements over electroactive self-assembled monolayers (SAMs). It was hypothesized that the redox potential of an electroactive molecule influences the peak position of negative differential resistance (NDR). For this research, a ferrocene terminated alkanethiol, a ferrocenyl-ketone terminated alkanethiol, and a methyl viologen terminated alkanethiol were used, giving a range of redox potentials. Variability from the tip and the sample made the detection of any discernable differences impossible in the NDR peak position when the different SAMs were used. To address the variability, experiments were conducted where the order of the SAM was increased. The STM tip was also coated with 2,2,2-trifluoroethanethiol to make the tip surface more homogeneous. The results of the experiments discussed in this thesis suggest that the mechanism that leads to NDR is much more complicated than the resonant tunneling model suggests.

The surface of biomaterials can induce contacting blood to coagulate, similar to the response initiated by injured blood vessels to control blood loss. This poses a challenge to the use of biomaterials as the resulting coagulation can impair the performance of hemocompatible devices such as catheters, vascular stents and various extracorporeal tubings [1], what can moreover cause severe host reactions like embolism and infarction. Biomaterial induced coagulation processes limit the therapeutic use of medical products, what motivates the need for a better understanding of the basic mechanisms leading to this bio-incompatibility [2] in order to define modification strategies towards improved biomaterials [3]. Several approaches for the enhancement of hemocompatible surfaces include passive and active strategies for surface modifications. The materials’ chemical-physical properties like surface chemistry, wettability and polarity are parameters of passive modification approaches for improved hemocompatibility and are the focus of the present work. In the present study self assembled monolayers with different surface functionalities (-COOH, -OH, -CH3) were applied as well as two-component-layers with varying fractions of these, as they allow a defined graduation of surface wettability and charge. The ease of control over these parameters given by these model surfaces enables the evaluation of the influence of specific surface-properties on biological responses. To evaluate the effects of different surface chemistry on initial mechanisms of biomaterial induced coagulation, the surfaces were incubated with protein solution, human plasma, blood cell fractions or fresh heparinised human whole blood. Indicative hemocompatibility parameters were subsequently analysed focusing on protein adsorption, coagulation activation, contact activation (intrinsic/ enhancer pathway), impact of tissue factor (extrinsic/ activator pathway) and cellular systems (blood platelets and leukocytes).

Polyimides are frequently used as insulating layers in the microelectronics industry. These polymers are tough, have high thermal stability, and have favorable dielectric properties; consequently, polyimides are excellent materials for insulating layers in microelectronic devices. In this research, self-assembled monolayers are investigated for use as an adhesion promoter for metal substrates, and for corrosion protectors of the metal surface. Gold substrates modified by adsorption of 3- and 4-aminothiophenol monolayers, 3- and (4-mercaptophenyl) phthalimide (MPP) monolayers, and by reaction of the 3- and 4-aminothiophenol monolayers with the phthalic anhydride were studied using reflection absorption infrared spectroscopy, contact angle measurement, ellipsometry, and electrochemical measurements. Reactions on the monolayers are used to model the attachment of an insulating polyimide to the substrate. The covalent attachment of the anhydride is confirmed, and the efficiency of the reaction of the aminothiolphenol monolayers is investigated. The reactivity of the aminothiolphenol monolayers is found to depend on the position of the amino-group around the phenyl ring. Impedance spectroscopy is used to investigate the ionic insulating properties of these systems. The 4-mercaptophthalimide monolayer is found to have the highest monolayer resistance to ion transport. This result suggests that it forms the most densely packed monolayer. The monolayer resistance of the surfaces prepared by adsorption of the aminothiolphenol isomers followed by reaction with phthalic anhydride is much lower than the corresponding deposited mercaptophthalimide monolayers. These results suggest that the reaction efficiency is low. Impedance spectroscopy and polarization measurements suggests a higher protection efficiency for 3-mercaptophenylphthalimide. These results will be discussed in the context of the ability of the isomeric mercaptophthalimide monolayers to serve as protectors against substrate corrosion.
Ph. D.

Nanocomposites of multilayer structures of zirconia/polymer thin-film coatings have been fabricated on quartz and single-crystal silicon substrates by the Ionically Self-Assembled Monolayer (ISAM) technique. Particle size distribution was measured to calculate the grain diameter of the zirconia particles. UV/Vis spectroscopy and ellipsometry were used to characterize the ISAM technique. SEM and AFM were used to observe the microscopic structure of the multilayer structures. Some mechanical properties were characterized by adhesion, abrasion, and nano-hardness tests. It was shown that an important distinction of this novel technique over conventional coating processes is the fabrication of excellent molecular-level uniform films with precise control of film thickness at the à ngström-level at ambient temperature and pressure conditions. It was also shown the maximum Vickers microhardness of ZrO2/polymer nanocomposite thin-film coatings prepared by this method was greater than 25 GPa.
Master of Science

The functionalization of surfaces has received attention because the process allows the design and tailoring of substrate surfaces with a new or improved function. â Host-guestâ thin film complexes are composed of â hostâ molecules attached the substrate surface, either through physisorption or covalent bonds, with cavities for the inclusion of desired â guestâ molecules for the functionalization of the surface. Two methods for fabricating functional â host-guestâ thin films were investigated: Langmuir-Blodgett (LB) deposition and self-assembly monolayer (SAM). Langmuir films were created at the air-water interface using octadecanesulfonic acid (C18S) as the amphiphilic â hostâ molecules separated by hydrophilic guanidinium (G) spacer molecules, which created a cavity allowing the inclusion of desired â guestâ molecules. Surface pressure-area isotherms of the (G)C18S, with and without guests, are characterized by the lift-off molecular areas and are use to determine the proper deposition surface pressure. â Host-guestâ Langmuir films are deposited onto silicon substrates using the LB deposition technique. The LB films were then subjected to stability testing using different solvents over increasing periods of time. Grazing-angle incidence X-ray diffraction (GIXD), specular X-ray reflectivity (XRR) and transfer ratio measurements were used to characterize the crystallinity, film thickness, overall film stability and film coverage. The GIXD data revealed that the crystallinity of the deposited film varies with the â guestâ molecules and can be disrupted by the functional group on the â guestâ molecule through hydrogen bonding. After modeling the XRR data using StochFit, it was discovered that the more polar solvent, tetrahydrofuran (THF), removed the film completely while the nonpolar solvent, hexane, compacted the thin film and increased the electron density. With transfer ratios around 0.95 to 1.05, the deposited films were homogenous. The second method used was self-assembly monolayers, which differs from Langmuir films in that they are created by a spontaneous chemical synthesis from immersing a substrate into a solution containing an active surfactant. Octadecyltrichlorosilane (OTS) was used initially as a molecule to study the self-assembled monolayer procedure. To study a â host-guestâ self-assembled monolayer system, a compound is being synthesized from 9-bromoanthracene. This compound would already contain the cavity necessary for the inclusion of â guestâ molecules. The solution that contained OTS was composed of a 4:1 mixture of anhydrous octadecane: chloroform. Silicon substrates with a deposited oxide layer were hydroxylated for the surfactant binding chemical reaction to occur. The OTS SAMs were exposed to the same stability tests as the LB films. Surface contact angle measurements were taken of the OTS SAMs before and after the stability tests. The contact angle prior to the stability tests was 110° (±2°). The contact angle after immersion in THF was 101° (±2°) while the contact angle resulting from immersion in hexane was 105° (±2°). From the contact angle measurements, the degradation of the OTS SAMs was less extensive than that of the (G)C18S LB films.
Master of Science

The work presented on this thesis is focused on studies of the kinetics of electron transfer in bilayer lipid membranes (BLMs). Three different types of BLM were studied: i) tethered, ii) pore suspended (commonly known as ‘black’) and iii) based on the avidin – biotin interaction (these are part of the wider group of polymer cushioned BLMs). In order to produce tethered BLMs (tBLMs) of the best quality possible, self – assembled monolayers (SAMs) of a thiolipid (1,2 dipalmitoyl-sn-glycero-phosphothioethanol (DPPTE)) and of the same thiolipid mixed with L α phosphatidylcholine (EggPC) were characterised and their behaviour compared to that of SAMs of two alkanethiols (1 – heptanethiol and 1 – dodecanethiol). The SAMs that were formed by a mixture of lipids (DPPTE+EggPC) presented better kinetic parameters and were the chosen to produce tBLMs. Tethered BLMs were made by using the SAM described above as the lower leaflet; the second leaflet was deposited by vesicle fusion, the vesicles were made of EggPC. tBLMs are commonly used as model membranes, however in biophysical studies free-standing membranes or ‘black’ lipid membranes are more realistic models of cellular processes. The rates of electron transfer in both types of bilayer lipid membranes are compared. These BLMs were modified using two very important mitochondrial membrane associated molecules – ubiquinone-10 (UQ10) and α-tocopherol (VitE). The studies involved the use three redox couples, Fe(CN)_6^(3-/4-), Ru(NH_3 )_6^(3+/2+) and NAD+/NADH using cyclic voltammetry and electrochemical impedance spectroscopy. The NAD+/NADH couple is of particular interest as it is the key to several important biochemical processes. The last type of BLM that was studied was the BLMs based on the avidin – biotin interaction. Avidin was deposited on a platinum surface by electrodeposition and then vesicles composed of EggPC and 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine-N-(biotinyl) (sodium salt) (DOPE(B)) are burst by applying +0.7V (vs. Ag/AgCl, KCl 3.5M), leading to the formation of a supported BLM. The vesicles used had methylene blue (MB) inside; its release, when the vesicles burst, was monitored by cyclic voltammetry and UV-Vis. The kinetic parameters were determined based on the EIS measurements using Fe(CN)_6^(3-/4-) and Ru(NH_3 )_6^(3+/2+) as redox couples.

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.

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.

L'intégration de moteurs moléculaires aux interfaces permet de former des structures assemblées hautement organisées qui utilisent leur mouvement moléculaire afin d'obtenir des surfaces sensibles aux stimuli. Dans cette thèse, nous avons principalement étudié l'impact de l'irradiation par la lumière UV sur les moteurs moléculaires amphiphiles à l'interface dynamique air-eau et sur les moteurs moléculaires ancrés à la surface sur des interfaces solides. Nous montrons que la rotation des moteurs amphiphiles dans les monocouches de Langmuir peut induire d'importants changements dans la compressibilité et la structuration supramoléculaire, conduisant à un premier exemple de processus de polymérisation supramoléculaire induit par le mouvement aux interfaces. Nous rapportons également une première étude de moteurs ancrés à la surface par spectroscopie de force sur une seule molécule, montrant que la rotation des moteurs peut être utilisée pour modifier les propriétés mécaniques et conformationnelles des chaînes polymères attachées. De plus, nous décrivons un système basé sur des moteurs ancrés à la surface qui peut être utilisé pour imiter le mouvement induit par un moteur biologique. Enfin, nous avons cherché à étudier une application concrète pour la rotation des moteurs moléculaires en les intégrant dans des membranes d'ultrafiltration disponibles commercialement
The integration of molecular motors at interfaces allows to form highly organised assembled structures that use their molecular motion in order to obtain stimuli-responsive surfaces. In this thesis, we mainly studied the impact of UV light irradiation on amphiphilic molecular motors at the dynamic air-water interface and on surface-anchored molecular motors at solid interfaces. We show that the rotation of amphiphilic motors in Langmuir monolayers can induce large changes in the compressibility and the supramolecular structuration, leading to a first example of a motion induced supramolecular polymerisation process at interfaces. Herein, we also report a first study on surface-anchored motors by single molecule force spectroscopy, showing that the rotation of motors can be used to change the mechanical and conformational properties of the attached polymer chains. Further, we describe a system based on surface-anchored motors that can be used in mimicking the motion induced by a biological motor. Finally, we aimed to investigate a concrete application for the rotation of molecular motors by integrating them in commercially available ultrafiltration membranes

A novel cyclopentadienylruthenium(II) thiolato Schiff base, [Ru(SC6H4NC(H)C6H4OCH2CH2SMe)(&eta
5-C2H5]2 was synthesized and deposited as a selfassembled monolayer (SAM) on a gold electrode. Effective electronic communication between the Ru(II) centers and the gold electrode was established by electrostatically cycling the Shiff base-doped gold electrode in 0.1 M NaOH from -200 mV to +600 mV. The SAMmodified gold electrode (Au/SAM) exhibited quasi-reversible electrochemistry. The integrity of this electro-catalytic SAM, with respect to its ability to block and electro-catalyze certain Faradaic processes, was interrogated using Cyclic and Osteryoung Square Wave voltammetric experiments. The formal potential, E0', varied with pH to give a slope of about - 34 mV pH-1. The surface concentration, &Gamma
, of the ruthenium redox centers was found to be 1.591 x 10-11 mol cm-2. By electrostatically doping the Au/SAM/Horseradish peroxidase at an applied potential of +700 mV vs Ag/AgCl, a biosensor was produced for the amperometric analysis of hydrogen peroxide, cumene hydroperoxide and tert-butylhydroperoxide. The electrocatalytic-type biosensors displayed typical Michaelis-Menten kinetics with their limits of detection of 6.45 &mu
M, 6.92 &mu
M and 7.01 &mu
M for hydrogen peroxide, cumene hydroperoxide and tert-butylhydroperoxide respectively.

碩士
國立中正大學
機械工程所
94
In the MEMS and precision machine, particles and liquid films (capillary force) are often presented at contact interfaces. These two factors will enhance the adhesion, friction and wear of contacting surfaces. In the meantime, in order to minimize the adhesion and wear problems of moving MEMS, numerous coating methods are being designed to improve these surface properties. Self-assembled monolayer (SAM) coating has been demonstrated to achieve anti-stiction and low friction characteristics when properly integrated into microstructure release process. The objective is to establish analysis and manufacture technology of SAMs in MEMS. For this purpose, several kinds of SAMs, including alkyl and biphenyl spacer chains with different surface terminal groups (-CH3,-COOH), and head groups (-SH), were prepared. The influence of spacer chains, surface terminal groups, and head groups on adhesion, friction and surface energy properties were investigated by AFM, nano tester and contact angle analyser. The effect of self-assembled monlayers on matrix surface and coating film characteristics. Moreover, in order to design the optimal surface, the effects of adhesion and capillary force of surface micromaching on the real contact area of microparts are investigated. In this study, it is found that HDT exhibits the smallest adhesive force and friction force, because of low work of adhesion of -CH3 surface terminal group, and high-compliance long carbon chain. The influence of velocity on friction forces of HDT film is very small. In order to design the optimal surface, we found that Vicker’ surface has lowest surface energy, and adhesion properties.

碩士
國立臺灣科技大學
化學工程系
98
In this work, we studied the deposition of ITO and AZO on self-assembled monolayer (SAM) modified glass substrate with RF sputtering. In general , deposition of ITO and AZO thin films under low temperature condition result in the amorphous or less crystallinity structures, which needed to be improved by post annealing of thin film at high temperature. However, in this study, we have found that high crystallinity can be achieved in low temperature by modification of glass substrate by SAMs prior to ITO and AZO deposition.The ITO with high electrical conductivitycan be fabricated by using –SH SAM modified glass substrate. We attributed the improvement of electrical conductivity to larger quantity of Sn atoms attached on thiol functional group. In addition, for the deposition of AZO, the surface tension of glass substrate was modulated by fabrication of SAMs with different functional groups, which the preferential growth direction of AZO thin film could be controlled to along c-axis or a-axis.

碩士
國立中正大學
機械工程所
96
Self-assembled monolayers(SAMs) have proven to be an efficient biomimetic strategy in the development of material with controllable surface properties. Self-assembled monolayers is a process in which molecules spontaneouslyorganize into ordered assemblies by noncovalent intermolecular force. In past years, self-assembled monolayers have been developed widely in many application field, such as optical instruments, electronics, biomedical application. Adsorption and adhesion of SAMs is of interest for use in dental application in past year. According to atomic force microscopy imaging, the SAM growing process as the formation of islands on the surface. Therefore, the wear and surface roughness(aesthetic) properties have to the considered in the future application. The purpose of this study was to investigate the possibility of achieving better mechanical properties in the artificial tooth with self-assembled monolayers. Self-assembled monolayers (ODPA,ODT,OTS,ODS) must possess biocompatible. The influence of artificial denture and SAMs on adhesion, surface energy, water hydrophobic, friction and anti-attrition by AFM, nano test, contact angle, ESCA and FTIR analyzer. Moreover, the optimal SAMs were choiced to apply to coating surface of industrial optimal product. In this study, it is found that ODPA, ODS, OTS and ODT of SAMs exhibit lower surface energy than artificial teeth surface. All of them can reduce adhesive force and friction force. In contact angle, the contact angles on the SAMs surface are larger than that on the artificial teeth. The contact angles of SAMs for OTS at six hours larger than the other surface film cases. The maximum contact angle is about 123°. For adhesive force test by AFM, the OTS film at six hours exhibit the smallest value. However, the reaction time is the important issue during fabrication process, two hours fabrication time of OTS film is the better choice. In order to chew food, teeth surface need a certain value of friction coefficient. In pin on disc friction model of indentation tester, ODS and ODT films have the better friction properties for all SAMs films. In ESCA, It may discover the O1s element has the certain influence to the SAMs, the contact angle is increased with decrease of counts/sec. In FTIR, it is found that contact angle is increased with increase of peak, show the molecular arranges neatly. In this study, it is found SAMs for OTS at six hours has best contact angle, smallest adhesion force and reduces the particle adsorption situation. These results suggest that SAMs have proven to be an efficient in the artificial teeth surface.

碩士
國立成功大學
化學工程學系碩博士班
90
Abstract Due to the van der Waals forces between hydrocarbon chains and strong binding between gold and sulfur, the self-assembled monolayer formed by the long-chain alkanthiol has densely-packed, and well-oriented characteristics. On the other hand, varying the terminal functional groups of the self-assembled monolayer will affect various properties of the surface. This study is based on the structure of phospholipid, the most abundant component of the cell membrane. Due to the thermodynamic effect, phospholipid with long hydrophobic hydrocarbon chains and hydrophilic zwitterionic functional group has the self-assembly character. In other words, studying the self-assembled monolayer is just to mimic the structure of phospholipid properly. The starting material: 10-mercaptodecanyl phosphonic acid was synthesized according to the previous study. Because the solubility of this thiol in absolute ethanol was limited, other proper solvents were found to dissolve it. By the measurement of contact angle, it was found that different solvents would affect the structure of the self-assembled monolayer. Therefore, the surface would have the differences in hydrophilicity due to the solvent effect. To protect the monolayer formed from adsorbing contaminants in the air that could affect the following modification reaction, the phosphonic acid terminated SAM was stored in the proper solvent. Also, the measurement of contact angle had been done again before the surface was modified. As a result, it was proven the solvents can affect the reorganization of the monolayer structure. However, the hysteresis value of the surface in this study was similar to each other. According to the spectra of O1s、N1s、P2p、S2p in ESCA , the existence of the functional group on the surface has been proven. By correlating the variation within the spectrum characteristics and atomic ratio under different reaction conditions, it was found that thionyl chloride is indeed a strong oxidant, and may destroy the gold-sulfur binding on the surface. Consequently, the chances of choline acetate reacting with the monolayer were reduced. This indicates that both the amount of the thionyl chloride adding to the reaction system and the reaction time need to be considered carefully. As for the solvent used, both the reaction time of the reactants and the reaction temperature require further investigation.

The formation and desorption processes of a self-assembled monolayer, deposited from solution, have been observed in situ, at the liquid/solid interface, using atomic force microscopy. The growth begins with the nucleation of submonolayer islands, that grow and eventually coalesce. The submonolayer island nucleation rate was found to depend on the concentration of the deposition solution. The power-law dependence of the submonolayer island density on the solution concentration was consistent with the interpretation that the smallest stable island consists of two molecules. By following the time-dependence of the island nucleation, and the growth kinetics of individual islands, we found that the formation process can be quantitatively explained by a kinetic theory of 2D cluster growth typically used to describe vapor phase molecular beam epitaxy. During the desorption process, holes in the monolayer are observed to nucleate, grow, and percolate across the sample, leaving isolated monolayer islands that gradually decrease in size. The relative rates of hole growth and hole nucleation suggest that removing a molecule from the monolayer/hole boundary is about 105 times more likely than removing a molecule from within a continuous region of monolayer. The coverage kinetics and nucleation and growth rates are consistent with a picture of monolayer desorption where molecules detach from the monolayer/hole boundaries, remaining adsorbed in the 'hole' regions from which they eventually desorb into the solvent
acase@tulane.edu

碩士
國立臺灣大學
物理研究所
101
We report the surface, magnetic and charge transport in organic spin valve structure (Ferromagnetic/Organic/Ferromagnetic) with self-assembled monolayer barrier. We have built top ferromagnetic electrode by transfer printing and sputtering to prevent interdiffusion or pinhole and observed that the interdiffusion could be suppressed by lowering the fabrication energy of the top ferromagnetic layer. A through study of the device characteristics reveals that the hysteresis on I-V measurement is proposed to contribute from tunneling through junction and charge　trapping on the thiol and ferromagnetic interface. Magnetoresistance ratio is 1 %　have reported in our system. We have demonstrated how the device can switch between two pair of conducting state for the potential of develop multifunction memory　device which combine MRAM and RRAM properties

碩士
國立中央大學
生醫科學與工程學系
105
Reducing nonspecific interaction of biomolecules with an electrode is a key issue for increasing sensitivity and specificity for biosensors. Zwitterionic materials, carrying both positively and negatively charged moieties in a molecule, have shown excellent biocompatibility by resisting undesired biomolecules adsorption. In particular, zwitterionic carboxybetaine materials are the most attractive. Besides the high resistance to nonspecific biomolecules adsorption, the carboxylic acid group can be transformed to functionalizable intermediates to create a ligand-functionalized substrate. Self-assembled monolayers (SAMs) are well-established as a means to selectively modify surfaces to achieve desired chemical and physical properties. In this study, we used carboxybetaine and sulfobetaine terminated alkanethiol to form mixed SAMs on gold surface. The zwitterion terminated mixed SAMs can provide functionalizable antifouling properties. X-ray photoelectron spectroscopy showed the molar ratio of carboxybetaine and sulfobetaine terminated alkanethiol molecular mixing in solution was in agreement with the feed-in molecules ratio. It supported that the composition of the surface molecules can be controlled by varying feed-in molar ratio in the solution. Surface plasmon resonance biosensor showed that there were the best ability of anti-fouling when carboxybetaine and sulfobetaine terminated alkanethiol mixed SAM with a molar ratio of 1 : 9. Under this condition, we can successfully attach the antibody on the surface via amino-coupled NHS / EDC chemical modification. Then, the surface was applied to the surface plasmon resonance sensor. The limit of detection was 80 ng/ml. The new type of biosensor interface offers anti-fouling properties and functionalizable capacity. It can meet the needs of the market to facilitate the development of biological sensors

High-resolution and low-cost fabrication techniques are essential for nanotechnology to overcome the commercialization barrier to benefit our society. Since its inception nanoimprint has become the ideal technology to fabricate dense sub-micron structures over large areas with low cost, which are important to many applications such as high-density storage disks and diffractive optical devices. The decade-long development in nanoimprint equipment has reached a point where large-scale manufacturing of high-density nanostructures are possible. However, there are a few remaining issues that need to be studied before the advent of commercial application of nanoimprint. In this work we look at a pressing issue, long-term stability of the mold surfactant coating. It is important to understand the details of the surfactant wear during nanoimprint in order to limit defect density to a tolerable threshold in a high-volume manufacturing process. To study this we went through a nanoimprinting procedure and measured chemical and physical alterations in the coating. The surfactant wear information also helps to optimize the time interval for surfactant recoating to keep the fabrication throughput as high as possible. In this paper we characterize the stability of two commonly used surfactants as well as prescribe a new technique for mold anti-adhesion. Through this work we see that FDTS and OTS undergo significant degradation in air and gradual degradation by chain scission is observed during the nanoimprint procedure. It is also noted that an embedded anti-adhesion layer is effective for mold releasing.

碩士
國立中山大學
化學系研究所
96
An alkyl-containing self-assembled monolayer is grafted on the silicon surface by a nature process in solutions. The alkyl thin film was used as the lubricant for the silica interface, usually applied to the MEMS or NENS domains. The ability of reducing friction for silica device at room temperature was improved, but little was known as the thin films existed at higher temperature during device was working or operating. In this study, we used Hexyltrichlorosilane (C6), Dodecyltrichlorosilane (C12), and Octadecyltrichlorosilane (C18) molecules to form self-assembled monolayers (SAMs) on silicon, and these monolayers exhibited different molecular packing properties due to different interactions between the molecules. Fourier transform infrared spectroscopy (FTIR) revealed that the short chain-length (C6) molecules exhibited poor packing on the surface at room temperature, and that the molecular packing of C6 was thermally stable up to 500 K. But the C12 and C18 monolayers exhibited abrupt blue shifts in FTIR at temperatures between 300 and 575 K, with stable packing observed over several temperature ranges. Furthermore, water contact angle measurements showed the C6, C12, and C18 molecular films changed from hydrophobic to hydrophilic as the sample temperature was increased. Atomic force microscopy (AFM) images revealed that pits had formed in the C18 monolayer after the temperature was increased to 460 K, which were caused by the molecular reorganization of C18 on the surface. This resulted in an abrupt change in the friction coefficient for the C18 monolayer at 460K as compared to the short C6 and C12 monolayers. However, the friction coefficients for all the SAM films still increased with temperature. Understanding the temperature-dependent behavior of SAM film molecules will assist in the design of better anti-wear monolayers to improve performance and increase lifetimes in modern MEMS and NEMS devices.

碩士
國立成功大學
微電子工程研究所
103
In this thesis, we have investigated the characteristics of polymer photodetector fabricated on transparent electrode which is treated by self-assembled molecule (SAM) treatment and we also compared the characteristics of each the devices. After the SAM attach on the surface of the transparent electrode, the work function of transparent electrode can be modulated due to the molecular dipole moment. By choosing different functional group of the SAM, the direction and magnitude of the dipole moment can be changed. We obtained the result that 1H,1H,2H,2H-Perfluorooctanephosphonic acid (FOPA) is useful for indium-tin oxide (ITO) from all of the SAMs used in this experiment. In processing time investigation, we obtained the same result between short time treatment and long time treatment (24hr) which is often seen in journal. The device with FOPA short time treatment modified on ITO has incident photon to current conversion efficiency (IPCE) 50% and the dark current was 60% reduced compared to non-treatment device. Furthermore, the detectivity was enhanced by 1.7 times. In the treatment of Poly (3,4-ethylendioxythiophene) dope with poly (4-styrenesulfonate) (PEDOT:PSS) which is often used as hole transport layer, the dark current was increased by 122 times due to the erosion of the ITO. Thus, the PEDOT:PSS was not suitable for organic photodetector fabrication. We also used the gallium-doped zinc oxide (GZO) substrate for device fabrication and found that the 2,3,4,5,6-Pentafluorobenzylphosphonic acid (FBPA) is useful for GZO. The device with modified on GZO has IPCE 47% and dark current was 62% reduced compared to non-treatment device. Furthermore, the detectivity was enhanced by 1.78 times. In the PEDOT:PSS based GZO devices, the short circuit current was not increased as in ITO. This might mainly due to the increase of the sheet resistance which was caused by hard erosion of the GZO. In this thesis, instead of PEDOT:PSS by using SAM, the photocurrent could be increased and the dark current could be decreased at the same time which results in the improved photodetector detectivity.

碩士
國立中正大學
機械工程所
97
Macromolecular material Polymethyl Methacrylate (PMMA) has good nature in light transmission, bio-compatibility, chemical resistance, and mechanical strength. With its simple and cost-efficient production procedure, it is a very suitable for various material of bio-medical and chemical examination instruments. In this study, we tried to grow three self-assembled monolayers OTS, ODS, and HDT, with bio-compatibility, in the microchannel made of PMMA, in order to reduce time expense and increase examination accuracy of bio-microchannel chips. Findings of research were: in the contact angle experiment of three self-assembled layers, OTS illustrated the maximum contact angle 123° 24 hours after its reaction, while ODS and HDT showed 94° and 65° respectively. Through analysis by Fourier-Transform Infrared Spectrometer, we found that all the three self-assembled layers reached their maximum contact angles, which were caused by the increase of their terminal functionality CH3, indicating that self-assembled layers had better adhesion quality than the surface of its precursor PMMA. As experiment of static contact angle could not completely illustrate the flow ability of liquid which is to be examined, we suggested replacing the normal contact angle with dynamic inclination angle parameters as measurement indicator. The experiment showed that results of dynamic inclination angle parameters were inconsistent with those of contact angle, but more consistent with ability trend of friction coefficient. In the biotic experiment of protein concentration, OTS self-assembled film, after 24 hours reaction time, also showed the lowest protein residue. Therefore, more portion of the specimen could be maintained in the area of chip reaction and increased accuracy of test.

碩士
大同大學
化學工程學系(所)
94
The best mobility for organic semiconductors has been reported for vacuum-deposited pentacene film. Pentacene organic thin-film transistor (OTFT) has drawn great attention because of it is advantages over conventional inorganic electronics such as low cost, large-area, and low processing temperature. Pentacene interactions between molecules in the crystal are rather weak van der Weals interactions. Thus, the dielectric (ex: hydrophobic….) can influence the morphology of the pentacene semiconductor. The purpose of this work is to show the improvement of OTFT performance by controlling the surface treatments of dielectric/organic layer interface. We investigated the electrical properties of the OTFTs using pentacene fabricated by thermal evaporation in high vacuum with the five kinds of dielectric surface treatments: as-prepared, hexamethyldisilasane ((CH3)3-Si-O-Si-(CH3)3) (HMDS), octadecyltrichlorosilane (C18H37SiCl3) (OTS), phenyltrichlorosilane (C6H5SiCl3) (PTS), and phenethyltrichlorosilane (C6H5C2H4SiCl3) (PETS) treatment. And we use x-ray diffractometer (XRD), atom force microscope (AFM), X-ray photoelectron spectroscopy (XPS), water contact angle, and semiconductor parametric test system (HP 4155C) equipments to analyze the properties of self-assembled monolayer (SAM), pentacene thin film, and the performance of the device, respectively. From the result, the mobility and on/off current ratio of pentacene OTFT are 0.34 cm 2 V –1 s –1 and 1.21 x 10 5 (top-contact) and 0.011 cm 2 V –1 s –1 and 2.31 x 10 4 (bottom-contact), respectively. From the result of AFM images, it can be seen that grain size of pentacene thin film deposited on the electrode region are significantly smaller compared to that of the channel region on SiO2. That discontinuity causes for the inferior performance of bottom-contact pentacene transistors compared to that of top-contact devices. The mobility and on/off current ratio of bottom-contact pentacene OTFT with OTS-treated SiO2 can be achieved 0.1 cm 2 V –1 s –1 and 1.71 x 10 5, respectively. XPS detects the chemical composition of surfaces in the top 50-100 Å. The results confirm OTS adsorbed on the surface of gate dielectric. Similarly, HMDS, PTS, and PETS treatments can affect good influence in filed effect mobility. The mobility and on/off current ratio of pentacene OTFT are 0.11 cm 2 V –1 s –1, 1.92 x 10 6 of PTS-treated and 0.07 cm 2 V –1 s –1, 5.29 x 10 5 of HMDS-treated, respectively. The best performance of device can be obtained by using PETS as SAM reagent. The mobility, on/off current ratio, threshold voltage, and subthrshold slope of pentacene OTFT are 0.13 cm 2 V –1 s –1, 4.17 x 10 6, - 2.4 V, 0.8 V/decade of PETS, respectively, which are enhanced one to two orders of magnitude larger than those of untreated SiO2 device. Furthermore, the pentacene OTFT performance with PTS- and PETS-treated gate dielectric can be obtained an outstanding subthrshold slope.

碩士
南台科技大學
機械工程系
93
Characteristics and mechanism of the metal oxide structure produced by atomic force microscopy (AFM) anodization and dip-pen lithography (DPN) are studied. Effects of experimental parameters including the applied voltage, the anodization time and the electric field strength on the oxidation are discussed. Molecular dynamics (MD) simulation was employed to analyze the oxidation mechanism. The results show that the growth of the oxide structures increased as the applied voltage, the anodization time and the electric field strength were increased. The height and width of the nanodots was increased when the distance between the tip and the sample was increased. Furtheremore, the adhesion force and the contact angle of the self-assembled monolayers (SAM) were measured. The dip-pen lithography was developed with SAM.

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.)

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.)

This thesis proposes to use optical rectennae (rectifying antennae) for generating electricity by harvesting solar energy. Rectennae have theoretical efficiency over 90%, well above that of current photovoltaic devices. They could be built by arraying nano- antennae combined with a self-assembled monolayer for DC current rectification. Gold nanoarrays were built to absorb light by plasmonic resonance by depositing a gold layer on CdSe tetrapods or directly growing nanowires via template synthesis; various alkanethiolates were explored as rectifying units. The tunneling properties of alkanethiolates on gold nanoarrays were examined by electrochemical analysis. Preliminary photocurrent tests show that electric currents can be induced at different optical frequencies depending on the aspect ratios of the nanoarrays. However, gold contributes as an enhancement rather than an active material. Furthermore, by fitting the impedance spectroscopy data with equivalent electric circuits, the calculated tunneling barrier of the self-assembled monolayer on gold nanoarrays is ten times lower than on gold film, suggesting that the monolayer formed on gold nanoarrays is defective and cannot serve as a practical rectifying barrier. This concept will need further investigation to lead to an applicable photovoltaic cell.

碩士
國立清華大學
化學系
90
Abstract Self-assembled monolayers （SAMs） of n-hexadecanoic acid (1), p-terphenylcarboxylic acid (2), were prepared onto silver surface by adsorption from a solution of respective compound, all through the carboxylate/silver （CO2－/Ag） interaction. A brief exposure of the monolayer to H2S vapor leads to immediate protonation of the carboxylate head groups and reorganization of the resulting free acid molecules in the monolayer into clusters of H-bonded dimers of the acid. Mixed monolayer prepared from n-hexadecanoic acid (1) and p-terphenylcarboxylic acid (2) appears to form domains of respective component on silver surface. H2S-exposure of the mixed-monolayer also leads to a reorganization of the molecules in the monolayer. For mixed monolayer, the atomic force microscopy suggests that H2S-exposure leads to aggregates of respective compounds. The effect of a self-assembled monolayer on a substrate surface on the packing/orientation of vacuum-deposited p-terphenyl film was also investigated. The nearly perpendicular orientation of the terphenyl group in the SAM of p-terphenylcarboxylic acid caused perpendicular alignment of the p-terphenyl molecules in vacuum-deposited film, whereas H2S-treated SAM surface caused parallel alignment of the p-terphenyl molecules in the deposited film.

碩士
國立臺北科技大學
有機高分子研究所
99
Polymer solar cells have gained wide interest in recent years, but how to further cut down the fabrication cost and increase the device lifetime is still an important issue for their commercialization. In this study, a series of assembled monolayers (SAMs) of benzoic acid with various para-substituted groups on ITO was employed to replace PEDOT:PSS as the electron blocking layer of polymer solar cells. In the first part of this thesis, contact angle, X-ray photoelectron spectroscope, and AFM were applied to study the SAMs of benzoic acid derivatives on ITO. AFM images showed the presence of SAMs slightly reduced the surface roughness of ITO. In addition, the effect of SAMs on the work function of ITO was examined using AC-2. The experimental results indicated that the electron donating ability of the para-substituent on benzoic acid had decisive effect on the work function of ITO. An electron donating moiety will up-shift the work function but an electron withdrawing group will down-shift the work function of ITO. Finally, the SAMs-modified ITO was used as transparent anode to fabricate P3HT/PCBM bulk heterojunction solar cells. I-V measurements demonstrated that as the para-substituent was –CN or –CF3 group, the SAMs-based device reached a power conversion efficiency of 3.64%, which is comparable to that of a conventional solar cells with PEDOT:PSS as electron blocking layer. In the second part, the SAMs-covered ITO which was patterned with ordered line-shaped groove was utilized as the anode of solar devices to shorten the transport pathway of hole. Preliminary results showed this patterned ITO is helpful in rising the short-circuit current. Further optimization on the thickness of photoactive layer and the dimension of groove is still undertaking by our group members.