We quantified the chemical species present at polycrystalline cesium tin bromide perovskite, CsSnBr3 and cesium titanium bromide antifluorite, Cs2TiBr6. For CsSnBr3, experiments utilized the orthogonal reactivity of the Cs+ cation, the Sn2+ cation, and the Br– halide anion. Ambient- pressure exposure to BF3 solutions probed the reactivity of interfacial bromines. Reactions with p-trifluoromethylanilinium chloride probed the exchange reactivity of the Cs+ cation. A complex-forming ligand, 4,4’-bis(trifluoromethyl)-2,2’-bipyridine, probed for interfacial Sn2+- site cations. For Cs2TiBr6, both BF3 and (C6F5)3B probed the reactivity of interfacial bromines. Fluorine features in x-ray photoelectron spectroscopy (XPS) quantified reaction outcomes for each solution-phase species. XPS indicated adsorption of BF3 on CsSnBr3 and (C6F5)3B on Cs2TiBr6 indicating surface-available halide anions on both surfaces. For CsSnBr3, temperature- programmed desorption (TPD) quantified a ~215 kJ mol–1 desorption energy of BF3 on the surface. Adsorption of the fluorinated anilinium cation included no concomitant adsorption of chlorine as revealed by the absence of Cl 2p features within the limits of XPS detection. The bipyridine ligand demonstrated adsorption to CsSnBr3. We discuss the present results in the context of interfacial stability, passivation, and reactivity for solar-energy conversion devices.

We quantified the chemical species present at polycrystalline cesium tin bromide perovskite, CsSnBr3 and cesium titanium bromide antifluorite, Cs2TiBr6. For CsSnBr3, experiments utilized the orthogonal reactivity of the Cs+ cation, the Sn2+ cation, and the Br– halide anion. Ambient- pressure exposure to BF3 solutions probed the reactivity of interfacial bromines. Reactions with p-trifluoromethylanilinium chloride probed the exchange reactivity of the Cs+ cation. A complex-forming ligand, 4,4’-bis(trifluoromethyl)-2,2’-bipyridine, probed for interfacial Sn2+- site cations. For Cs2TiBr6, both BF3 and (C6F5)3B probed the reactivity of interfacial bromines. Fluorine features in x-ray photoelectron spectroscopy (XPS) quantified reaction outcomes for each solution-phase species. XPS indicated adsorption of BF3 on CsSnBr3 and (C6F5)3B on Cs2TiBr6 indicating surface-available halide anions on both surfaces. For CsSnBr3, temperature- programmed desorption (TPD) quantified a ~215 kJ mol–1 desorption energy of BF3 on the surface. Adsorption of the fluorinated anilinium cation included no concomitant adsorption of chlorine as revealed by the absence of Cl 2p features within the limits of XPS detection. The bipyridine ligand demonstrated adsorption to CsSnBr3. We discuss the present results in the context of interfacial stability, passivation, and reactivity for solar-energy conversion devices.

Optical properties (transmission and refractive index) and chemical structure (XPS) of diamond-like coating (DLC) film before and after focused ion beam milling (FIBM) process, were investigated in this paper. It is shown by our FIBM experiment that influence of FIBM on Optical properties and chemical structure of the DLC film is not apparent, especially in near-infra region. The film still can be used for optical applications. As an application example, diffractive optical element (DOE) was directly fabricated on the film by use of FIBM. Measured diffraction efficiency of the DOE is 73%, which is acceptable for conventional use. / Singapore-MIT Alliance (SMA)

This thesis examines the catalytic characteristics of two materials with respect to the decomposition of Formic Acid. The decomposition of formic acid proceeds via two principal reaction pathways: dehydration and dehydrogenation. Dehydrogenation is a valuable reaction producing Hydrogen suitable for use in fuel cells whereas the dehydration pathway produces carbon monoxide, a poison for many fuel cell materials. One of the surface species, the formate ion, is also implicated in other important chemical reactions, most notably the water gas shift and the decomposition of methanol. The author seeks to document various intermediate surface species associated with the two reaction pathways with hope to use this information to future tailoring of catalysts for greater selectivity.

This thesis examines the catalytic characteristics of two materials with respect to the decomposition of Formic Acid. The decomposition of formic acid proceeds via two principal reaction pathways: dehydration and dehydrogenation. Dehydrogenation is a valuable reaction producing Hydrogen suitable for use in fuel cells whereas the dehydration pathway produces carbon monoxide, a poison for many fuel cell materials. One of the surface species, the formate ion, is also implicated in other important chemical reactions, most notably the water gas shift and the decomposition of methanol. The author seeks to document various intermediate surface species associated with the two reaction pathways with hope to use this information to future tailoring of catalysts for greater selectivity.

There is a global need to find a permanent and readily implemented solution to the problem of heavy metal pollution in aqueous environments. A dithiol compound, benzene-1,3-diamidoethanethiol (BDETH2), also known as N,N'-bis(2-mercaptoethyl) isophthalamide or N,N'-bis(2-mercaptoethyl)-1,3-benzenedicarboxamide, capable of binding divalent metal ions, has been synthesized and characterized. A broad range of BDET-metal compounds, spanning the periodic chart, has been prepared and characterized by IR, MS, EA, Raman, XAFS and TGA. The characteristics of the BDET-M compounds were determined through secondary reactions. In an effort to derivatize BDET-M compounds through alkylalumination a new cyclic compound, 1,3- bis(4,5-dihydrothiazolo)benzene, has been synthesized by refluxing BDETH2 in the presence of AlMe3. Mineral coating studies have been performed and it was found that coating with BDET prevents metal leaching. XPS studies indicated that covalent bonds exist between BDET and metals at the mineral surfaces. BDETH2 is not water soluble and must be used as an ethanolic solution to precipitate metals from water. In an effort to find similar ligands that are water-soluble another dithiol compound, N,N'-bis(2-mercaptoethyl)oxalamide (MOA), and a monothiol compound, N-mercaptoethyl-furoylamide (MFA), have been synthesized. Each was found to precipitate Cd, Hg and Pb from water, to varying degrees. Some metal compounds of MOA, MFA and dithiothreitol (DTT), a watersoluble dithiol compound have been prepared and characterized. These compounds provide insight into the properties of the BDET-M compounds. For example, it was shown that insolubility in water is a common feature of thiol compounds and is not unique to BDET-M compounds.

We quantify the chemical species present at and reactivity of the tetragonal (100) face of single-crystal methylammonium lead iodide, MAPbI3(100). MAPbI3 is an ABX3 perovskite, experiments utilized the orthogonal reactivity of the A+-site cation, the B2+-site cation, and the X–-site halide anion. Ambient-pressure exposure to BF3 solutions probe the reactivity of interfacial halides. Reactions with p-trifluoromethylanilinium chloride probe the exchange reactivity of the A+-site cation. The ligand 4,4’-bis(trifluoromethyl)-2,2’-bipyridine probe for interfacial B2+-site cations. Fluorine features in x-ray photoelectron spectroscopy (XPS) quantify reaction extents with each solution-phase species. XP spectra reveals adsorption of BF3 indicating surface-available halide anions on tetragonal MAPbI3(100) and preliminary examinations on the (112), (110), and thin-film surfaces. Temperature-programmed desorption (TPD) established a ~200 kJ mol–1 desorption activation energy from tetragonal MAPbI3(100). Adsorption of the fluorinated anilinium cation includes no concomitant adsorption of chlorine as revealed by the absence of Cl 2p features within the limits of XPS detection on the tetragonal (100) and (112) faces with no discernable exchange in preliminary experiments on tetragonal (110). Within detection limits, bipyridine ligand demonstrate no adsorption to tetragonal MAPbI3(100) or (112), while it does demonstrate significant adsorption on the (110) in preliminary experiments. We discuss the present results in the context of interfacial stability, passivation, and reactivity for perovskite-based energy conversion materials and some preliminary investigations into bilayer graphene-based dye sensitized photovoltaic materials.

Colloidal quantum dots (QDs) are promising candidates for the next generation of solar cells due to their tunable band gaps, solution processability and the potential for multiple exciton generation. However their stability and the reduction of surface defects are big challenges and effective surface passivation is needed. Passivations via organic ligands have been shown to be imperfect and hinder the charge transfer in devices. Three different QD systems, chosen as exemplars of different approaches to surface passivation, have been investigated with synchrotron-radiation (SR) depth- profiling X-ray photoelectron spectroscopy (XPS). With this technique the chemical composition of the top few nanometres of a sample can be studied with depth. The study of CdTe QDs with and without a chloride treatment revealed the presence of stoichiometric particles prior to, and the likely coexistence of Cl atoms and organic ligands on the surfaces of the QDs after the treatment. The chloride treatment led to a better surface passivation of the QDs resulting in photoluminescence quantum yields of up to 97.2%. Shell thickness estimations using a core/shell/shell model were performed of the chloride treated sample and XPS highlighted the complexity of the structure of the sample. CdTe QDs passivated by a thick CdSe shell were investigated. Indications for an improvement of the stability of the QDs against oxidation were found. The Se:Te ratio was equivalent to a CdSe shell of 0.3-0.4 nm which was significantly smaller than intended, indicating that the butylamine ligand exchange and/or the washing of the sample reduced the thickness of the CdSe shell drastically. The third system studied was PbS QDs that were passivated with a thin CdS shell. XPS of the thoroughly washed QDs confirmed the presence of Cd in an amount equivalent to a 0.13-0.18 nm thick shell. This is thicker than the 0.05 nm shell expected from absorption spectroscopy. A study of ageing of the PbS/CdS QDs revealed that oxidation took place on the surface of the QDs. It was found that sulfur oxidised in stages leading to highly oxidised SO4^2- components. Upon long-term ageing Pb oxidised more rapidly than S, and either some Pb and/or Cd migration or some decomposition of the QDs occurred. The PbS/CdS nanoparticles were more stable than a comparable PbS colloidal quantum dot sample from the literature. The study of the PbS/CdS QDs prior to and after the second wash- ing cycle after a mercaptopropionic acid (MPA) ligand exchange revealed, amongst other things, the removal of MPA and a reduction of the Cd:Pb ratio indicating that (parts of) the QDs decomposed through the ligand exchange or the washing. In addition to the results of the nanoparticles studied some limitations of the study of colloidal QDs with SR depth-profiling XPS are discussed.

Zinc oxide (ZnO) is a promising photoanode material which has been used in quantum dot-based depleted heterojunction solar cells. The specific influence of the defect chemistry of ZnO on its n-type conductivity remains a focus for research. This thesis presents results from a series of near-ambient pressure (NAP) XPS experiments (at The University of Manchester, UK), used to characterise surface adsorption of O2 and H2O on ZnO(10-10) surfaces in high pressure environments. Water dosing is shown to lead to surface hydroxylation and a change in the surface band bending consistent with an increase in the surface conductivity. Oxygen dosing is also observed to lead to the formation of surface species on the ZnO surface, revealing that ZnO is prone to hydroxylation even in oxygen-rich environments. The role of surface OH on influencing the transient surface photovoltage (SPV) of the ZnO(10-10) surface is probed through a series of time-resolved, pump-probe XPS experiments (at SOLEIL synchrotron, France). It is shown that increasing the degree of surface hydroxylation leads to a decrease in surface band bending, leading to longer-lived transient SPV. Other factors influencing the SPV dynamics are explored, such as the role of the oxygen vacancy concentration. The transient SPV decay lifetime is shown to increase with increasing oxygen vacancy concentration, consistent with the presence of persistent photoconductivity (PPC) in ZnO, mediated by oxygen vacancy-related hole traps. The influence of the concentration of thermally excited carriers in ZnO on the surface band bending is also described, showing that the equilibrium band bending and the surface photovoltage are both reduced at low temperature. It is shown that thermal excitation of carriers from the valence band of ZnO and from neutral oxygen vacancies have negligible influence on the magnitude of equilibrium band bending at the surface. The energy regime consistent with the observed temperature dependence is also consistent with a perturbed-host state 0.2 eV below the conduction band minimum. This meta-stable state is associated with doubly-ionised oxygen vacancies, that mediate the PPC in ZnO. However this does not rule out the contribution from other shallow donor levels such as those associated with hydrogen impurities. The influence of hydrogen on the SPV dynamics in ZnO is explored, through angle-resolved photoemission spectroscopy (ARPES) after implanting hydrogen atoms into the ZnO surface. H implantation is shown to lead to the formation of a 2D electron gas (2DEG) at the surface, consistent with an increase in conductivity at the surface large enough to change the nature of the space-charge region at the ZnO surface from depletion to accumulation.

Diamond-Like Carbon (DLC) films have been deposited on ITO glass substrate. DLC thin film was electrodeposited at low DC potential using a mixture of acetic acid and DI water. The DLC film deposition parameters include DC potential, deposited temperature, the concentration of electrolyte were used to study the characteristics of DLC film measured by the Ellipsometer, XPS, SEM and Raman spectroscopy in detail. The Raman spectra shows two peaks located near 1358cm-1 and 1580cm-1 assigned as the characteristics peaks of DLC films. That is an evidence for DLC film deposited successfully on ITO glass. Scanning electron microscopy (SEM) can make insight into accurately the surface morphology and uniformity of DLC films so as used to grow the best quality of DLC films. From the variations of the I-t curve and the surface morphology observed by SEM, the properties of DLC film depend on a verity of growth parameters such as applied voltage, the concentration of electrolyte and deposition temperature. The shift of G-peak increase with the applied voltage, and the sp2/sp3 ratio of the content C1s decreases with the applied voltage. Finally, based on the I-t curve and results of SEM, XPS, Raman, and Ellipsometer for n, k coefficients measured, we obtain a deeply understanding for the growth conditions of DLC films and their surface morphology. We achieve the consistent results between various measurements. Finally, the optimizing growth of DLC film is to be studied and discussed in future