The treatment of polymer surfaces by low pressure plasmas is of technological interest in a variety of applications for modification and functionalisation. Until now the interactions of the individual plasma species (especially electrons) with polymeric material have not been subject of a microscopic study.In an anticipated chapter the inner plasma parameters were characterised by Langmuir probe measurements, leading to a precise knowledge about the density and energy distributions of plasma electrons and ions. The values for electrons were later used for an exclusive treatment with this species. The main part of this thesis describes and interprets the chemical composition after UV, plasma and electron treatment by x-ray photoelectron spectroscopy (XPS), structural changes by atomic force microscopy (AFM) and their combination to distinguish the fundamental interactions with polyethylene and polypropylene surfaces. It was found that all treatments show specific modification behaviour according to the chemical composition, topography and modification depth. For an argon microwave discharge, the plasma effects can also be obtained by a combination of UV and electron treatment. Fundamental radical reactions have been traced indirectly by chemical derivatisation as well as their passivation reactions through cross-linkage and the creation of double bonds.

Un-doped, Tb3+ as well as Yb3+ doped ZnO nanocrystals with different concentrations of RE3+ (Tb3+, Yb3+) ions were successfully synthesized via sol-gel method to produce rare earth activated zinc oxide nanophosphors. The phosphor powders were produced by drying the precursor gels at 200˚C in ambient air. Based on the X-ray diffraction results, it was found that the pure and RE3+ doped ZnO nanophosphors were highly polycrystalline in nature regardless of the incorporation of Tb3+ or Yb3+ ions. Moreover, the diffraction patterns were all indexed to the ZnO Hexagonal wurtzite structure and belong to P63mc symmetry group. The Raman spectroscopy confirmed the wurtzitic structure of the prepared samples. Elemental mapping conducted on the as prepared samples using Scanning electron microscope (SEM) equipped with energy dispersive X-ray spectrometer (EDX) revealed homogeneous distribution of Zn, O, and RE3+ ions. The high resolution transmission electron microscope (HR-TEM) analyses indicated that the un-doped and RE3+ doped samples were composed of hexagonal homogeneously dispersed particles of high crystallinity with an average size ranging from 4 to 7 nm in diameter, which was in agreement with X-ray diffraction (XRD) analyses. ZnO:Tb3+ PL study showed that among different Tb3+ concentrations, 0.5 mol% Tb3+ doped ZnO nanoparticles showed clear emission from the dopant originating from the 4f-4f intra-ionic transitions of Tb3+ while the broad defects emission was dominating in the 0.15 and 1 mol% Tb3+doped ZnO. Optical band-gap was extrapolated from the Ultraviolet Visible spectroscopy (UV-Vis) absorption spectra using TAUC‟s method and the widening of the optical band-gap for the doped samples as compared to the un-doped sample was observed. The PL study of ZnO:Yb3+ samples was studied using a 325 nm He-Cd laser line. It was observed that the ZnO exciton peak was enhanced as Yb3+ions were incorporated in ZnO matrix. Furthermore, UV-VIS absorption spectroscopic study revealed the widening of the band-gap in Tb3+ doped ZnO and a narrowing in the case of Yb3+ doped ZnO system. X-ray photoelectron spectroscopy demonstrated that the dopant was present in the doped samples and the result was found to be consistent with PL data from which an energy transfer was evidenced. Energy transfer mechanism was evidenced between RE3+ and ZnO nanocrystals and was discussed in detail. / Physics / M.Sc. (Physics)

No description available.

The production of higher alcohols from synthesis gas over Cu-Co-Cr-K catalysts has been studied. The production rate of alcohol was measured in the flow reactor, operating at 250 to 350°C, 3500 to 8000 gas hourly space velocity, and 900 to 1800 psig. The productivity as a function of temperature, pressure, gas hourly space velocity, carbon dioxide content of the feed, and reaction time was also examined. Physisorption data have been analyzed using the Langmuir model, the Brunauer-Emmett-Teller (BET) method, the Barret-Joyner-Halenda (BJH) method, and the de Boer and Halsey t-method. The surface areas of catalysts CB1(1), CB1(3), and CB1(1) after reaction were 39.9 ± .9 m2/g, 28.9 ± 1.7 m2/g, and 26.5 ± 0.3 m2/g, respectively. Moreover, information such as pore size distribution, pore shape, monolayer volume, micropore volume and thickness of adsorption layer were also obtained. The atomic concentration and oxidation states of near surface species were established by X-ray Photoelectron Spectroscopy.

My dissertation is primarily divided into two parts. The first deals with the preparation, functionalization, and characterization of carbon surfaces prepared by direct current magnetron sputtering (DCMS) and high power impulse magnetron sputtering (HiPIMS) as substrates for bioarrays. Part two discusses applications of XPS peak fitting in surface chemical analysis. Chapter 1, the introduction, includes (i) a discussion of the construction of bioarrays and the preparation of sputtered surfaces, e.g., by DCMS and HiPIMS, and also functionalization (bioconjugate) chemistry with special emphasis on the importance of covalent functionalization of surfaces, and (ii) a discussion of the surface characterization techniques and accompanying analysis methods I have primarily used, which include X-ray photoelectron spectroscopy (XPS), near-ambient pressure XPS (NAP-XPS), XPS peak fitting, and contact angle goniometry (wetting). Chapter 2 discusses the preparation, characterization, and functionalization of DCMS and HiPIMS carbon surfaces for bioarrays. Here, two functionalization chemistries are explored, where the activity of DCMS and HiPIMS carbon towards amidation and amination is compared. Chapter 3 focuses on the use of Gaussian-Lorentzian sum (GLS) and Gaussian-Lorentzian product (GLP) line shapes in the context of peak fitting XPS narrow scans. This discussion includes a comparison of the GLS and GLP line shapes with the Voigt function. Chapters 4 and 5 discuss the applications of XPS peak fitting in materials characterization. Chapter 4 talks about XPS data analysis in the context of the chemical vapor deposition of various aminosilanes and their effect on peptide stability and purity. Chapters 5 describes the surface chemical analysis of various materials by NAP-XPS, including accompanying data analysis and/or peak fitting. The materials probed here cannot be analyzed at ultra-high vacuum by conventional XPS, hence, they are analyzed by NAP-XPS. Chapter 5 is divided into 5 sections. Section 5.1.1 discusses the characterization and analysis of a solution of bovine serum albumin (BSA) by peak fitting the C 1s and O 1s peak envelopes. Section 5.1.2 discusses the analysis of polytetrafluoroethylene (PTFE) at different pressures. Here, the effect of increasing background pressure and X-ray illumination time on the equivalent widths of the F 1s narrows scans is shown. Environmental charge compensation is also discussed here. Section 5.1.3 includes the analysis of poly(γ-benzyl L-glutamate) (PBLG), where the C 1s and O 1s peak envelopes were peak fitted to determine/confirm the structure and composition of this polymer. Section 5.1.4 contains an analysis and comparison of three different human hair samples: (i) untreated, (ii) colored, and (iii) bleached. Here, a comparison of the Si 2p, S 2p, and C 1s peaks illustrates the effects of the different treatments. Section 5.1.5 shows the characterization and analysis of liquid and solid phosphate buffered saline (PBS). Chapter 6 presents conclusion of my work and discusses future work.

No description available.

No description available.

A catalytic route to hydrogen production via thermochemical water splitting is highly desirable because it directly converts thermal energy into stored chemical energy in the form of hydrogen and oxygen. Recently, the Davis group at Caltech reported an innovative low-temperature (max 850°C) catalytic cycle for thermochemical water splitting based on sodium and manganese oxides (Xu, Bhawe and Davis, PNAS, 2012). The key steps are thought to be hydrogen evolution from a Na₂CO₃/MnO mixture, and oxygen evolution by thermal reduction of solids formed by Na⁺ extraction from NaMnO₂. Our work is aimed at understanding the fundamental chemical processes involved in the catalytic cycle, especially the hydrogen evolution from water. In this project, efforts are made to understand the interactions between the key components (Na, O₂, CO₂, and water) in the hydrogen evolution steps on a well-defined MnO(100) single crystal surface, utilizing x-ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED) and temperature programmed desorption (TPD). While some of the behavior of the catalytic system is observed with the model system developed in this work, hydrogen is only produced from water in the presence of metallic sodium, in contrast to the proposal of Xu et al. that water splitting occurs from the reaction of water with a mixture of Na₂CO₃ and MnO. These differences are discussed in light of the different operating conditions for the catalytic system and the surface science model developed in this work. / Ph. D.

It was found that laser modified wood surfaces can be bonded together to create a wood composite without the need of any additive. This bonding method removes the need of applying adhesive, potentially lowers cost, and eliminates off gassing of petroleum resins, creating a wood product with many eco-friendly attributes. This body of work outlines a) initial chemical analysis of the laser modified surface b) its bond strength and c) the optimization of factors that control the strength of the bond. Surface chemical analysis on laser modified wood was conducted using photo acoustic Fourier transform infrared spectroscopy (PA-FTIR) and X-Ray photoelectron spectroscopy (XPS). Light microscopy and scanning electron microscopy were utilized for surface topology analysis.Differential scanning calorimetry (DSC) quantified the thermal properties of the modified wood surface. Screening of multiple factors that would contribute to surface modification and adhesion was performed utilizing mechanical testing. Optimization of significant factors that affect bond strength was determined statistically utilizing a design of experiment approach. Chemical analysis of the laser modified surface revealed changes in the carbonyl and aromatic regions indicating modification of the hemicellulose and lignin components, intensifying with increasing laser modification.The C1/C2 ratios found via XPS revealed that one or more of the following is occurring: more extractives have moved to the surface, condensation reactions among lignin units, and the loss of methoxy and breakage of aryl ether linkages occurred.Microscopy images showed color changes to a darker caramel color with a smoothing of surface topology, suggesting the occurrence of the softening and/or melting of wood polymers. DSC verified chemical and/or physical changes in the wood with the modified material now having a glass transition temperature between 130-150°C.DOE found that laser parameters (power and focus) as well as hot press parameters (temperature and pressure) were significant in optimizing the bond. The impact of the study is the first documentation of the ability to laser modifies wood surfaces and subsequently bond them together. The ability of the wood polymers at the surface to undergo flow at elevated temperature is implicated in the adhesion mechanism of the laser modified wood. / Master of Science

While Li-ion batteries (LIBs) are the prevailing electrochemical energy storage technology, development of batteries using earth abundant alkali metals (e.g., Na and K) is necessary to alleviate LIB supply chain concerns. K-ion batteries (KIBs) offer a compelling advantage over Na via their compatibility with commercialized graphite anodes, and therefore may be more readily adopted within existing battery production lines. K-ions present some inherent advantages as well, such as rapid diffusion and low energy barriers to desolvation in the battery electrolyte that may enable fast charging. Presently, research on KIBs is in early stages and it is unclear if the same battery design principles produced by decades of study on LIBs apply to KIBs. Here, I examine structure-performance relationships in KIB anodes and electrolytes to propose broad design rules. In the first chapter, I summarize the motivations and prominent advancements in materials used for KIBs, providing commentary on the direction of the field. I begin by summarizing present concerns over materials criticality facing LIBs and how KIBs address these concerns but do not necessarily achieve lower costs. I continue with a summary of popular materials choices for KIB anodes, cathodes, and electrolytes. I place particular emphasis on the discovery and development of graphite anodes and the advantages of using a weak Lewis acid such as K-ions in batteries. Finally, I discuss the challenges presented by using highly reactive K metal anodes in research. In the second chapter, I examine the mechanisms of potassiation/depotassiation of two high-capacity tin phosphide anodes, Sn₄P₃ and SnP₃, and discuss possible failure modes. Ex situ 31P and 119Sn solid-state nuclear magnetic resonance (NMR) analyses reveal that both Sn₄P₃ and SnP₃ exhibit phase separation of elemental P and the formation of KSnP-type environments (which are predicted to be stable based on DFT calculations) during potassiation, while only Sn₄P₃ produces metallic Sn as a byproduct. In both anode materials, K reacts with elemental P to form K-rich compounds containing isolated P sites that resemble K₃P, but K does not alloy with Sn during potassiation of Sn₄P₃. During charge, K is only fully removed from the K3P-type structures, suggesting that the formation of ternary regions in the anode and phase separation contribute to capacity loss upon reaction of K with tin phosphides. The third chapter addresses the use of fluorinated electrolyte additives in KIBs. Fluoroethylene carbonate (FEC) is a well-known additive used in Li-ion electrolytes, because the products of its sacrificial decomposition aid in forming a stable solid electrolyte interphase (SEI) on the anode surface. Here, we show that FEC addition to KIBs containing hard carbon anodes results in a dramatic decrease in capacity and cell failure. Using a combination of 19F solid-state NMR spectroscopy, X-ray photoelectron spectroscopy (XPS), and electrochemical impedance spectroscopy (EIS), we show that FEC decomposes during galvanostatic cycling to form insoluble KF and K₂CO₃ on the anode surface, which correlates with increased interfacial resistance in the cell. Our results strongly suggest KIB performance is sensitive to accumulation of an inorganic SEI, likely due to poor K transport in these compounds. The fourth chapter presents a nonflammable electrolyte mixture for use in KIBs. In this report, we show that a low-concentration (1 M) KPF6 electrolyte combining ethylene carbonate (EC), propylene carbonate (PC), and triethyl phosphate (TEP) is nonflammable, retains high ionic conductivity, and is compatible with graphite. Notably, we then show that this electrolyte is only usable in KIBs; the analogous Li electrolyte fails immediately due to the incompatibility of Li, PC, and graphite. We continue the study by characterizing the impact of TEP on the graphite interphase using a combination of EIS, XPS, and 1D and 2D NMR spectroscopy. We show that, compared to using EC/PC alone, the addition of TEP reduces resistance of the SEI layer, lessens reductive decomposition of carbonates to soluble organic species, and produces inorganic phosphate salts (that we posit contribute to passivation in lieu of fluorination in the SEI). The fifth chapter concludes by summarizing the design strategies learned in each of the preceding three chapters and makes recommendations for future studies. The proposed research emphasizes the need for fundamental studies on materials properties in KIBs, contradicting the current push towards optimizing capacity and longevity of KIBs to prove their relevance. Doing so will not only inform how to design high-performance batteries, but potentially uncover distinct advantages of KIBs that complement existing LIB technologies.