Understanding interfacial interactions at the molecular level is important for interpreting and predicting the dynamics and mechanisms of all chemistry processes. A thorough understanding of the interaction dynamics and energy transfer between gas molecules and surfaces is essential for the study of various chemical reactions. The collisions of diatomic molecules on organic surfaces are crucial to the study of atmospheric chemistry. Molecular beam scattering experiments performed in ultra-high vacuum chambers provide insight into the dynamics of gas-surface interactions. Many questions remain to be answered in the study of gas-surface interfacial chemistry. For example, what affects the energy transfer between gas molecules and surfaces? How do intermolecular forces affect the interfacial interaction dynamics? We have approached these questions by scattering diatomic gas molecules from functionalized self-assembled monolayers (SAMs). Our results indicate that the intermolecular forces between gas molecules and surfaces play an important role in the energy transfer processes. Moreover, the stronger the intermolecular forces, the more often the incident molecules come into thermal equilibrium with the surface. Furthermore, most of the previous approaches toward understanding gas-surface interaction dynamics considered the interactions as independent incidents. By scattering O2, N2, CO and NO on both CH3- and OH- terminated SAM, we found a correlation between the gas-surface interactions and a bulk property, solubility. Both being strongly affected by intermolecular forces, the gas-surface energy transfer and solubility of gases in surface-similar solvents (water for OH-SAM, n-hexane for CH3-SAM) have a positive correlation. This correlation facilitates the understanding of interfacial dynamics at the molecular level, and helps predict the outcome of the similar-size gas collisions on surfaces. / Master of Science

Detailed understanding of the kinetics and mechanisms of heterogeneous reactions between gas-phase nitrate radicals, a key nighttime atmospheric oxidant, and organic particles will enable scientists to predict the fate and lifetime of the particles in the atmosphere. In an effort to acquire knowledge of interfacial reactions of nitrate radical with organics, model surfaces are created by the spontaneous adsorption of methyl-/vinyl-/hydroxyl-terminated alkanethiols on to a polycrystalline gold substrate. The self-assembled monolayers provide a well-defined surface with the desired functional group (-CH3, H2C=CH-, or HO-) positioned precisely at the gas-surface interface. The experimental approach employs in situ reflection-absorption infrared spectroscopy (RAIRS) to monitor bond rupture and formation while a well-characterized flux of NO3 impinges on the organic surface. Overall, the reaction kinetics and mechanisms were found to depend on the terminal functional group of the SAM and incident energy of the nitrate radical (NO3). For reactions of the H2C=CH-SAM with NO3, the surface reaction kinetics obtained from RAIRS reveals that the consumption rate of the terminal vinyl groups is nearly identical to the formation rate of a surface-bound nitrate species and implies that the mechanism is one of direct addition to the vinyl group rather than hydrogen abstraction. Upon nitrate radical collisions with the surface, the initial reaction probability for consumption of carbon-carbon double bonds was determined to be (2.3 ± 0.5) -- 10-3. Studies of reactions of HO-SAM with the effusive source of NO3 suggest that the reaction between NO3 and the HO-SAM is initiated by hydrogen abstraction at the terminal - 'CH2OH groups with the initial reaction probability of (6 ± 1)-- 10-3. An Arrhenius plot was obtained to measure the activation energy of the H abstraction from the HO-SAM. Further, for reactions of the HO-SAM with the high incident energy of NO3 molecules created by molecular beam, the reaction probability for H abstraction at the hydroxyl terminus was determined to be ~0.4. The significant increase in the reaction probability was attributed to the promotion in the ability of NO3 abstracting hydrogen atom at the methylene groups along hydrocarbon chains. The reaction rates of NO3 with the model organic surfaces that have been investigated are orders of magnitude greater than the rate of ozone reactions on the same surfaces which suggests that oxidation of surface-bound organics by nighttime nitrate radicals may play an important role in atmospheric chemistry despite their relative low concentration. X-ray photoelectron spectroscopy (XPS) data suggests that oxidation of the model organic surfaces by NO3 leads to the production of organic nitrates, which are stable for a period time. In addition, the effect of background gases on reactions of NO3 with model organic surfaces needs further investigations at atmospheric pressures. The results presented in this thesis should help researchers to predict the fate and environmental impacts of organic particulates with which nitrate radicals interact. / Ph. D.

A técnica de Microbalança de Cristal de Quartzo (QCM) tem sido utilizada para a aplicação em biossensores. Esta técnica consiste no monitoramento da freqüência de oscilação do cristal de quartzo e a variação de freqüência está relacionada com a variação de massa na superfície do cristal por meio da equação de Sauerbrey. Porém, sabe-se que há discrepância entre a massa calculada pela equação de Sauerbrey e a massa real aderida na superfície do cristal de quartzo, sendo tal discrepância causada por fatores tais como a viscoelasticidade, o que é especialmente observado para macromoléculas e sistemas biológicos. Com a técnica de Admitância Eletroacústica (AE) é possível analisar a massa real devido à análise em separado dos parâmetros que compõem o circuito equivalente do cristal de quartzo e também inferir informações sobre a estrutura das monocamadas montadas sobre a superfície do cristal de quartzo. Neste trabalho foi utilizada técnica de AE para se potencializar e detalhar o estudo da formação de monocamadas automontadas e interações entre diferentes proteínas e carboidratos. Em muitos casos verificou-se que durante a formação de determinadas monocamadas, grande parte da variação de massa estava relacionada a interações fracas e não-específicas. Também durante a formação das monocamadas de tióis de cistamina, verificou-se que a estrutura da monocamada é extremamente dependente das concentrações iniciais de cistamina utilizadas para formar a monocamada. As interações entre proteínas e carboidratos foram realizadas após formação de multicamadas nas quais as proteínas eram imobilizadas para depois estudar-se, então, sua interação com carboidratos específicos. No caso da Jacalina, um tipo de lectina, observou-se interações bastante específicas com a fetuína e interações fracas com a alfa-lactose. A atividade da enzima GumH também foi testada com sucesso utilizando a técnica de AE. / The Quartz Crystal Microbalance (QCM) has been largely used for biosensor applications. This technique consists on monitoring quartz crystal oscillation frequency. The relationship of quartz crystal frequency variation with mass deposited on the crystal surface is described by Sauerbrey´s equation. However, the relationship is not directly inferred and discrepancy exists caused mainly by viscoelasticity features of mass adsorbed on the quartz crystal surface. The viscoelastic influence is very common to be observed especially for macro-molecules and biological systems. By using Electroacoustic Admittance (EA) technique it is possible to calculate and separate the real mass deposited over the quartz crystal from other contributions. Therefore, the EA was used to infer about self-assembly monolayer structure being deposited over the quartz crystal. In this work EA technique was used to study details of self-assembled monolayer formation and specific interactions between different proteins and carbohydrate molecules. It was observed that during monolayer formation the majority of mass variation was related to non-specific interactions. For instance, regarding cystamine monolayer formation it was observed that the monolayer structure is dependent on the cystamine concentrations in the liquid medium. The study of interactions between proteins and carbohydrates was conducted by means of multilayers approach in which the proteins are immobilized previously to study the interaction between its active sites and carbohydrates. In the specific case of Jacalin, a type of lectin, it was observed a large formation of specific bonding between this protein and alpha-lactose or fetuin. The GumH enzyme activity was also tested successfully by using of EA technique.

Made available in DSpace on 2017-07-24T19:38:05Z (GMT). No. of bitstreams: 1 Rosana Mossanha.pdf: 1591695 bytes, checksum: aac2e3d256b391dd0e8f113bb72eb620 (MD5) Previous issue date: 2011-03-03 / In this work were studied investigated different types of modifiers for the formation of self-assembled monolayers on the gold surface. The monolayers used were formed by different structural arrangements, alkyl chains and functional groups. The thiols groups used were: 3-mercaptopropionic acid (MPA), thiolactic acid (TLA), cystamine (CYS) and 11-mercaptoundecanoic acid. The electroactivity of films of different thiols was assessed by the probe molecule, Fe(CN)63-/4-. It was possible to observe through the cyclic voltammetry technique, the formation and organization of the films, monitoring the behavior of the redox couple. The voltammograms showed a decrease in the faradaic current response with the increase of immersion time of the gold substrate in ethanolic solution of thiols, suggesting that the process of electron transfer occurs through the pinholes of the electrodes surface and tunneling. The monolayers of 3-mercaptopropionic acid (MPA) and thiolactic acid (TLA) had a better coating of the surface in immersion time of 3 hours. While the 11-mercaptopropionic acid (MUA) and cystamine (CYS) needed more time to organize the monolayer, 24 hours, because the MUA is a long chain molecule and CYS because the cleavage of S-S. The size of thiol chain influenced the surface organization, short-chain thiols tend to form monolayers with a considerable amount of defects, leading to a lower coating on the electrode surface. Indeed, the MUA that contains a high number of carbons in the chain showed a higher surface coverage, which caused loss of voltammetric response. The electrode surface roughness and the active area, calculated by the voltammetric data, showed a decrease with the formation of the monolayers on gold surface. Aiming to estimate the amount of molecules immobilized on the surface, it was calculated the superficial excess ) by voltammetric charge obtained from the reductive desorption. The obtained values were of 1.88x10-10 for Au-CYS, 5.03x10-10 to Au-MPA, 1.06x10-8 for Au-MUA and 1.35x10-10 mol.cm-2 for the Au-TLA, demonstrating an almost complete coverage of active sites on the surface. By the electrochemical impedance spectroscopy technique, it was possible to determine the kinetic parameters of the SAMs, which were consistent with those obtained by cyclic voltammetry. Analyzing the performance of sensors for dopamine determination through the VC, it was found that the SAM formed by TLA presented the most satisfactory results regarding the sensitivity and selectivity compared to the analyte DA. Studies at different scan rates for the electrodes, Au-MPA, Au-TLA and Au-CYS in the presence of the analite showed that the anodic peak current linearly increases with the square root of scan rate, indicating that the electron transfer process is controlled by diffusion of species to the electrode surface. Dopamine was quantified by CV and SWV technique, in the linear range from 1.1 to 6.6x10-7 mol L-1 with detection limits of 1,42x10-7 mol L-1 and 4,77x10-8 mol L-1, respectively. Using the technique of VOQ, TLA-Au electrode was able to distinguish between AA and DA, when present in the same solution, with a potential difference of approximately 340 mV. / Neste trabalho foram investigados diferentes tipos de modificadores para a formação de monocamadas auto-organizadas sobre a superfície do ouro. As monocamadas utilizadas foram formadas por diferentes arranjos estruturais, tamanho da cadeia carbônica e grupos funcionais. Os tióis utilizados foram: ácido 3- mercaptopropiônico (MPA), ácido tioláctico (TLA), cistamina (CYS) e o ácido 11-mercaptoundecanóico. A eletroatividade dos filmes dos diferentes tióis foi avaliada pela molécula sonda, Fe(CN)6]3-/4-. Foi possível constatar através da técnica de voltametria cíclica, a formação e a organização dos filmes, monitorando o comportamento do par redox. Os voltamogramas mostraram um decréscimo nas respostas da corrente faradaica com o aumento do tempo de imersão do substrato ouro na solução etanólica dos tióis, sugerindo que o processo de transferência de elétrons ocorre através dos pinholes da superfície e por tunelamento. Os eletrodos com as monocamadas de ácido 3-mercaptopropiônico (MPA) e o ácido tioláctico (TLA) obtiveram melhor recobrimento da superfície no tempo de imersão de 3 horas. Enquanto que o ácido 11-mercaptopropiônico (MUA) e a cistamina (CYS) necessitaram de maior tempo de imersão para organização da monocamada, de 24 horas, devido o MUA ser uma molécula de cadeia longa e a CYS devido a quebra da ligação S-S. O tamanho da cadeia do tiol influenciou no empacotamento da superfície, tióis de cadeia curtas tendem a formar monocamadas com uma quantidade de defeitos considerável, levando ao um menor recobrimento na superfície eletródica. O MUA que contém um número elevado de carbonos na cadeia apresentou um maior recobrimento da superfície, o que ocasionou perda da resposta voltamétrica. A rugosidade e a área ativa dos diferentes eletrodos, calculadas a partir dos voltamogramas, diminuíram com a formação das monocamadas sobre a superfície do ouro. Com o objetivo de estimar a quantidade de moléculas imobilizadas sobre a superfície, foram calculados os excessos superficiais por meio da carga voltamétrica obtida da dessorção redutiva. Os valores obtidos foram de = 1,88x10-10 para Au-CYS, 5,03x10-10 para Au-MPA, 1,06x10-8 para Au-MUA e 1,35x10-10 mol.cm-2 para o Au-TLA, demonstrando uma cobertura quase completa dos sítios ativos da superfície. Pela técnica de espectroscopia de impedância eletroquímica foi possível determinar os parâmetros cinéticos das SAMs, os quais foram consistentes com os obtidos pelos voltamogramas cíclicos. Analisando o desempenho dos sensores para a determinação de dopamina (DA) através da VC, verificou que a SAM formada pelo TLA foi a que apresentou resultados mais satisfatórios quanto a sensibilidade e seletividade em relação a este analito. Estudos em diferentes velocidades de varredura para os eletrodos Au-MPA, Au-TLA e Au-CYS na presença do analito mostraram que a corrente de pico anódica aumenta linearmente com a raiz quadrada da velocidade de varredura, indicando que o processo de transferência de elétrons é controlado pela difusão das espécies à superfície do eletrodo. A dopamina foi quantificada pela técnica de VC e VOQ, na faixa linear de 1,1 a 6,6x10-7 mol L-1 com limites de detecção de 1,42x10-7 mol L-1e 4,77x10-8 mol L-1, respectivamente. Utilizando-se a técnica de VOQ, o eletrodo Au-TLA foi capaz de distinguir o ácido ascórbico (AA) e DA quando presentes na mesma solução, com uma diferença de potencial de aproximadamente 340 mV.

Este trabalho consistiu de estudos da viabilidade da geração e identificação de radicais livres envolvidos em processos oxidativos avançados por via eletroquímica. Para a geração e identificação de radicais livres em eletrodos modificados com organotióis via eletroquímica, escolheu-se uma técnica pouco aplicada para este fim; a espectroscopia de impedância eletroquímica, e o ajuste dos dados experimentais pela proposta de modelos de circuitos equivalentes. O eletrodo de trabalho utilizado (Au) foi caracterizado em meio ácido e básico e diversas monocamadas auto-organizadas conhecidas foram adsorvidas sobre o mesmo e também caracterizadas por esta técnica. Parâmetros importantes como constante dielétrica, capacitância de uma monocamada livre de defeitos e grau de recobrimento foram determinados com êxito. Também foram empregadas moléculas menos utilizadas como modificadoras de eletrodos (fenotiazinas e derivados). As mesmas foram caracterizadas no sistema Au/adsorvente/NaOH, pois, o pH alto garante a formação do radical superóxido e do ânion hidroperóxido. Os mesmos modelos de circuitos equivalentes puderam ser empregados na obtenção dos parâmetros físicos relativos a essas moléculas no sistema eletroquímico utilizado. Em uma etapa subsequente obteve-se a valiosa informação, se as moléculas adsorvidas sobre Au poderiam ser usadas para a geração de superóxido e outros radicais. As monocamadas de tióis, quando utilizadas para gerar radicais livres, se mostraram aptas a gerar superóxido em meio alcalino saturado com oxigênio molecular. Como se demonstrou na etapa de caracterização, as SAM-3 e SAM-6 não formaram um empacotamento totalmente hidrofóbico. Por este motivo, mesmo que superóxido tenha sido gerado, não pôde ser detectado. Já para a fenotiazina e seu metil-derivado, a cinética de adsorção e a utilização de soluções aquosas impediram a formação de um filme completo e homogêneo, imprescindível para a constituição de uma interface hidrofóbica e isolante. Além disso, possíveis reações de complexação entre as moléculas e superóxido, reações entre a fenotiazina cátion-radical e superóxido fazem necessários mais estudos acerca da natureza eletroquímica do sistema, que já é bastante conhecido fotoquimicamente. Posterior a modificação, todos os eletrodos se mostraram ser bastante sensíveis ao pH e aos eletrólitos utlizados, alterando-se a estrutura interna muito facilmente, o qual implica uma limitação no tempo de uso e reprodutibilidade quando da geração de um radical tão reativo quanto superóxido. / This work consisted in testing the viability of investigations into the electrochemical generation and identification of free radicals involved in advanced oxidative processes. In these studies, a technique which is rarely used for the electrochemical generation and identification of free radicals at organothiole-modified electrodes, electrochemical impedancy spectroscopy, was chosen and the experimental data obtained were fitted by equivalent circuit models. A working electrode (Au) was characterized in both acidic and basic media and several known self-assembled monolayers were adsorbed over this electrode and also characterized using this technique. Important parameters such as dielectric constants, capacitance of the monolayers free of defects and coverage were determined with success. Other lesser-known molecules such as phenothiazines and their derivatives were also used .The modified electrodes were characterized in NaOH solution, since the high pH assures the production of superoxide radicals and hydroperoxylate anions. The equivalent circuit model was employed to obtain physical parameters for these molecules in the electrochemical systems studied. In a subsequent step, a valuable piece of information was obtained; it was noted that the molecules adsorbed over Au could be used in order to generate superoxide and other radicals. The ability of thiol monolayers used in the generation of free radicals, to produce superoxides in alkaline media saturated with molecular oxygen was demonstrated. However, characterization of the self-assembled monolayers, SAM-3 and SAM-6, revealed that these were not able to pack in a completely hydrophobic manner. This may account for the fact that the superoxide could not be detected even when it was believed to have formed. For the phenothiazine-modified electrodes, the adsorption kinetics and the utilization of aqueous solutions prevented the formation of an intact and homogeneous film, which is essential in establishing a hydrophobic and isolating interface. Furthermore, possible complexation reactions between the molecules and the superoxide and reactions between the phenothiazine cation-radical and superoxide, point to the need for further studies regarding the electrochemical nature of this system, whose photochemical properties are very well known. Following modification, all the electrodes were shown to be too sensitive to pH and to the electrolytes used, since the inner structure was easily modified, which implies that they would have a limited time of use and in addition that the reproducibility of the rate of generation of reactive radical species such as superoxides could be compromised.

This thesis covers different topics in the field of synthetic organic chemistry combined with the field of surface science and glycobiology. First, the text presents a series of orthogonally protected oligosaccharides (tri-, penta-, and heptasaccharides) of varying length and structures, which are synthesized with the aim of developing novel heterobifunctional biocompatible cross-linkers. Successful conjugation with different chemical handles is also described and used to illustrate the potential implementation of defined carbohydrate based compounds have potential use in biosensing applications. The results of incubation experiments using living cells indicate that the linker is incorporated into cell surfaces and enriched in microdomains. Second, synthesis of various saccharide-terminated alkane thiols immobilized on gold surfaces is reported. The protein adsorption and antifouling characteristics of these surfaces were investigated using model proteins and the common fouling organisms, Ulva linza and Balanus amphitrite. Further, oligo(lactose)-based thiols (di-, tetra-, and hexasaccharides) were synthesized and immobilized on gold nanoparticles to investigate how well these rigid, rod-like oligosaccharides can stabilize such nanoparticles for future use in constructing hybrid nanoparticles. Finally, the thesis describes synthesis of a systematic series of oligo(ethylene) glycols possessing either hydrogen- or methyl-terminated groups. Investigation of the fundamental characteristics of self-assembled monolayers, will give important insights into the design of protein repellant surfaces.

Neste trabalho foi estudado o desenvolvimento de uma superfície modelo de silício monocristalino, SiO2/Si, modificada com organossilanos derivados de N-heterocíclicos que permitisse a imobilização de um complexo de coordenação, FeTIM. Estas superfícies modificadas poderão ser empregadas em estudos de reatividade frente a analitos de interesse, como o NO. Sob esse aspecto, a síntese desses novos silanos, contendo N-heterocíclicos, e o desenvolvimento de uma metodologia de formação dos filmes finos automontados, sobre a superfície de SiO2/Si, tornou-se de grande relevância na aplicabilidade deste trabalho. Para a obtenção dessas superfícies, fez-se necessária a compreensão dos parâmetros de formação dos filmes de silanos. Os parâmetros estudados foram os efeitos do tempo de adsorção, da concentração da solução dos silanos, da polaridade do solvente e do tamanho da cadeia alquílica do silano no processo de formação dos filmes. Deste modo, foi possível inferir sobre as alterações na morfologia e na estrutura química dos filmes formados, através de medidas de Espectroscopia de Fotoelétrons excitados por Raios-X (XPS), Microscopia de Força Atômica (AFM) e Microscopia Eletrônica de Varredura (MEV). A imobilização do complexo de FeTIM sobre a superfície organomodificada foi comprovada pela variação da linha de fotoemissão do Fe 2p nas medidas de XPS. / This work describes the study of model surfaces on oxidized silicon wafer, SiO2/Si, modified with N-heterocycles rings, that allows the grafting of a macrocycle iron complex, FeTIM, that could be used in reactivity studies, with biologically relevant molecules, as nitrogen monoxide (NO). On this way, the synthesis of these silanes and a new methodology of the formation of self-assembled monolayers had become a relevant question on this work applicability. These thin films contain silanes bearing nitrogenated Lewis bases on silicon surfaces. In order to obtain these modified surfaces, it was necessary a comprehensive study of the adsorption parameters of the thin films. The parameters studied were the effect of: adsorption time, the solution concentration, the role of the solvents polarity and the chain length alkylsilanes in the film formation. Then, it was possible to infer about the film\'s morphology differences and chemical structures by the XPS, AFM and MEV measurements. X-ray photoemission lines of Fe 2p were used to probe the iron chemical environment in the chemically adsorbed macrocycles complexes.

Lors de la mise au point de biocapteurs, le contrôle de l'état de surface sur laquelle sontimmobilisées les biomolécules est un paramètre crucial pour la fiabilité et la reproductibilité desmesures. Pour ce travail de Thèse, deux objectifs principaux ont été fixés :- obtenir de façon reproductible des films organiques fonctionnels capables de rendre lessurfaces inorganiques biocompatibles afin d'immobiliser des biomolécules sans les dénaturer.- se doter d'outils innovants afin d'analyser la distribution de biomolécules sur la surface etd'évaluer leur activité biologique à l'échelle de la molécule unique.L'immobilisation a été réalisée sur des SAMs terminées par une fonction acide carboxylique.Pour imager les surfaces nous avons choisi la Microscopie Atomique de Force (AFM) qui permetd'obtenir des informations à l'échelle nanométrique et de mesurer des interactions moléculaires del'ordre du piconewton (10-12 N).Des CNTs, générés par dépôt chimique en phase vapeur, sont fixés sur une pointe AFM. Puis Ilssont biofonctionnalisés selon un protocole de trempage original afin d'obtenir une modificationchimique sélective de leur apex. Les interactions entre un récepteur, immobilisé sur la surface, et sonligand, lié de façon covalente au CNT, sont mesurées à l'échelle de la molécule unique. / During the development of biosensors, control of the surface on which the biomolecules areimmobilized is a crucial parameter for the reliability and reproducibility of the measurements. For thisPhD work, two main objectives were set:- obtain in a reproducible way functional organic films able to make inorganic surfacebiocompatible for the immobilization of biomolecules without any denaturation.- develop innovative tools in order to analyze the distribution of biomolecules on the surface etevaluate their biological activity at single molecule scaleThe immobilization step was done on SAMs terminated by a carboxylic acid function.In order to image surfaces, Atomic Force Microscopy (AFM) was chosen. This technique permits toobtain information at nanometric scale and to measure molecular interactions in the range ofpiconewton forces (10-12 N).MWCNTs were linked to a commercial AFM tip by micro-welding under optical microscopy. CNTswere biofunctionalized at the nanotube apex by an original dipping procedure.The interactions between a ligand, immobilized on the surface, and a receptor covalently linked to aCNT have been characterized.

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.

Low energy (tens of eV) polyatomic cations were used as probes for characterization of monolayers of spontaneously chemisorbed thiols on gold. Characteristics including chemical composition, surface order and orientation of the self-assembled monolayers (SAMs) can be derived by monitoring the products of projectile ion neutralization, surface-induced dissociation (SID), and ion-surface reactions.To study the influence of the terminal group chemical structures and orientations of the SAMs on ion-surface interactions, a series of semi-fluorinated alkane thiols with difluoromethylenes buried underneath hydrocarbon terminal groups were examined (CH3CF2CH2− and CH3CH2CF2−). Compared to terminally fluorinated SAMs, they showed more projectile ion neutralization and less internal to vibrational energy deposition into precursor ions. Projectile ion-hydrocarbon reactions decreased significantly when difluoromethylenes are one or two bonds away from the terminal group. Furthermore, ion-surface reaction results on surfaces with odd and even chain lengths suggested that they have similar terminal methyl orientations to their hydrocarbon counterparts.Mixed monolayers of CF3CF2(CH2)14SH (F-SAMs) and CH3(CH2)15SH (H-SAMs) with systematically changing electron transfer, energy deposition and ion-surface reaction were prepared using mixed thiols solution and micro-contact printing (μ-CP). The solution mixture system showed linear variations in electron transfer and energy deposition with different F-SAM surface concentrations, while non-linear changes occur for ion-surface reaction suggesting strong lateral interactions between the two components. These interactions are minimized in the μ-CP system containing domains of each thiol. Energy deposition on the patterned surfaces varies non-linearly with changing F-SAM concentration which differs from the homogenously mixed system.To explore SID with a 90 collision angle, eV SID of a series of protonated peptide ions were performed in an in-line sector Time-Of-Flight (TOF) mass spectrometer. The results were compared to keV collision-induced dissociation (CID) data collected with the same instrument. Fragmentation efficiency for SID was higher than CID for those peptides. In addition to the excellent control over laboratory collision energies with SID, different amount of energy deposition can be achieved when varying surface composition, e.g. using mixed F-SAM/H-SAM.Reactive ion scattering spectrometry (RISS) results provided more in-depth knowledge of low energy ion-surface interactions that will promote usage of RISS as a novel surface characterization technique.