Incorporation of nitrogen into ¢»-¢½ materials such as GaAsN and InGaAsN, have recently drawn much attention, due to the unique properties as well as potential device applications of such materials. The purpose of this thesis is to probe microscopic compositions and electronic structures in a series of N-based semiconductor compounds. For the material and electronic structure characterizations, X-ray photoelectron spectroscopy (XPS) with synchrotron radiation beam was adopted to analyze the sample quality under different growth and post-growth thermal annealing. Through detection of samples of InGaAsN in comparison with a series of samples of GaAsN, InAsN, InN, GaN, InGaAs and GaAs, the experimental result and analysis. Now X-ray photoelectron spectroscopy investigation on ¢»-¢½alloys containing a few percentage of nitrogen demonstrated the success of nitrogen incorporation. X-ray photoelectron spectroscopy investigation on InGaAsN films and curve fitting analysis, it can provide evidence of the existence of two principle N configurations, indicating the formation of N-In, N-Ga bonds. Through an estimation of the sample surface composition was made on the basis of the peak area: N-In/N-Ga larger than 3, it can provid direct evidence of the presence of preferential bonding of N to In. The incorporation of atomic nitrogen was added during the annealing. Right through X-ray photoelectron spectroscopy in annealed InGaAsN film can N-In and N-Ga bonds be observed to be increase, but N-In/N-Ga larger than 2, The bonds of atomic nitrogen is still N-Ga bonds.

Methanation of CO2, a greenhouse gas component, using bimetallic catalysts is considered. Rh, Pd and Ru were combined separately with Co on silica support to form bimetallic catalysts with 5 % metal loading and atomic ratio to Co equal to 1. Pore volume of the silica was measured using physisorption analysis. The unreduced catalyst samples were characterized using XPS, TPR and SEM-EDS. XPS results showed low Rh, Pd, Ru and Co concentrations at the surface for the three bimetallic catalysts. The oxidation states of metals detected by XPS supported the likely presence of metals in their oxide form. Detection of alloys and/or bimetallic particles on the surface of the catalysts was difficult through the XPS results, but presence of bimetallic particles was confirmed in Ru-Co and Pd-Co catalysts through the TPR results. Surface segregation of cobalt was observed. This was supported and extended to other metals through the SEM-EDS results.

Yes / The properties of nitrogen centres acting either as hydrogen-bond or Brønsted acceptors in solid molecular acid–base complexes have been probed by N 1s X-ray photoelectron spectroscopy (XPS) as well as 15N solid-state nuclear magnetic resonance (ssNMR) spectroscopy and are interpreted with reference to local crystallographic structure information provided by X-ray diffraction (XRD). We have previously shown that the strong chemical shift of the N 1s binding energy associated with the protonation of nitrogen centres unequivocally distinguishes protonated (salt) from hydrogen-bonded (co-crystal) nitrogen species. This result is further supported by significant ssNMR shifts to low frequency, which occur with proton transfer from the acid to the base component. Generally, only minor chemical shifts occur upon co-crystal formation, unless a strong hydrogen bond is formed. CASTEP density functional theory (DFT) calculations of 15N ssNMR isotropic chemical shifts correlate well with the experimental data, confirming that computational predictions of H-bond strengths and associated ssNMR chemical shifts allow the identification of salt and co-crystal structures (NMR crystallography). The excellent agreement between the conclusions drawn by XPS and the combined CASTEP/ssNMR investigations opens up a reliable avenue for local structure characterization in molecular systems even in the absence of crystal structure information, for example for non-crystalline or amorphous matter. The range of 17 different systems investigated in this study demonstrates the generic nature of this approach, which will be applicable to many other molecular materials in organic, physical, and materials chemistry. / EPSRC, Sanofi-Aventis

SiGe 25% substrates were treated with aqueous solutions of ammonium sulfide with and without added acid to understand the adsorption of sulfur on the surface. X-ray photoelectron spectroscopy showed no sulfide layer was deposited from aqueous (NH4)(2)S alone and instead both Si and Ge oxides formed during immersion in the sulfur solution. The addition of hydrofluoric and hydrochloric acids dropped the pH from 10 to 8 and deposited sulfides, yet increased the oxide coverage on the surface and preferentially formed Ge oxides. The sulfur coverage grew with increasing concentrations of acid in the aqueous (NH4)(2)S. The simultaneous deposition of O and S is suspected to be the result of oxidized sulfur species in solution. Metal-insulator-semiconductor capacitor (MISCAP) devices were fabricated to test the electrical consequences of aqueous ammonium sulfide wet chemistries on SiGe. MISCAPs treated with acidic ammonium sulfide solutions contained fewer interface defects in the valence band region. The defect density (D-it) was on the order of 10(+12) cm(-2) eV(-1). The flat band voltage shift was lower after the acidic ammonium sulfide treatment, despite the presence of surface oxides. Adsorption of S and potentially O improved the stability of the surface and made it less electrically active. (C) 2017 American Vacuum Society.

This work is to study the interface properties of Gallium-Gadolinium oxide / GaAs structures. The samples we probed were produced by depositing oxide films in situ on freshly grown n type GaAs (100) surface. Three different oxides were deposited : Ga2O3, Gd2O3, and (Ga2O3-Gd2O3) oxide mixture. Structural properties of the interfaces have been investigated by X-ray photoelectron spectroscopy (XPS). Using Ar+ sputtering to remove the oxide layer step by step, we are able to observe the depth profiles of these samples. No Asenic or Asenic oxides are observed at the interfaces of these samples. The Ga(3d) of Ga2O3 / GaAs interface shows three different oxidation states, whose binding energies are 21.5eV, 21.0eV and 20.3eV, respectively. The binding energy of O (1s) core level is about at 530eV. For (Ga2O3-Gd2O3) / GaAs, Ga(3d) peaks exhibit at 21.0eV and 20.3eV. Also, two O (1s) peaks were clearly observed: one is Ga-O at 532.2eV and the other is Gd-O at 530.1eV. For the Gd2O3 / GaAs, only one Ga(3d) peak shows at 20.3eV, and the O (1s) spectra exhibit two peaks related to Ga-O at 532eV and Gd-O at 530eV, similar to the data of (Ga2O3-Gd2O3) sample. In conclusion, the Ga2O3 / GaAs interface has a Ga2O3 and two non-fully oxidized GaxOy states (i.e. Ga+1, Ga+2). The (Ga2O3-Gd2O3) layer consists two non-fully oxidized GaxOy states. For the Gd2O3 / GaAs interface, the GaxOy (Ga+1) state is formed possibly by the competitive oxidation of Ga, which diffused from the GaAs substrate, with the Gd2O3.

The purpose of this thesis is to probe microscopic compositions and electronic structures at the high-£edielectric-semiconductor interfaces. The samples are prepared by electron beam evaporation, including Y2O3/Si, (Ga2O3-Gd2O3)/GaAs, Gd2O3/GaAs, Gd2O3/GaN and (Ga2O3-Gd2O3)/GaN. The thermal annealing effects on the interfacial properties have been investigated by depth-profiling X-ray photoelectron spectroscopy (XPS) with synchrotron radiation beam. The depth-profiling XPS data show the O-H bonding in all the measured oxide layers. For Y2O3/Si, the hydroxide can be removed by surface desorption at 300¢J, while a Y-Si-O-H state maintained at the interface. The data suggests that the Y-Si-O-H state is possibly formed in the deposition process. For (Ga2O3-Gd2O3)/GaAs, the hydroxide can be removed by surface desorption at 100¢J, and GaOx and GaOy intermediary states have been observed. For Gd2O3/GaAs, the hydroxide can be removed by surface desorption at 250¢J, and a GaOx intermediary state has been observed, and no arsenic oxides have been detected. For Gd2O3/GaN and (Ga2O3-Gd2O3)/GaN, a GaOx intermediary state and little N-O bonding have been observed. Comparing the XPS relative intensity of the N 1s states, (Ga2O3-Gd2O3)/GaN shows a more stable interface than Gd2O3/GaN.

No description available.

One form of surface modification was primarily investigated in this work on glassy carbon electrodes. The form of modification is comprised of a series of steps in which electrografting is first applied to the glassy carbon surface, which is then followed up with click chemistry to ultimately immobilise a phthalocyanine onto the surface. The modified glassy carbon electrodes and surfaces were characterised with a combination of scanning electrochemical microscopy, X-ray photoelectron spectroscopy and various electrochemical methods. In this work, three alkyne substituted phthalocyanines were used. Two novel phthalocyanines, with nickel and cobalt metal centres, were studied alongside a manganese phthalocyanine reported in literature. Each of the three phthalocyanines was modified at the peripheral position with a 1-hexyne group, via a glycosidic bond, yielding the terminal alkyne groups that were used for subsequent click reactions. In situ diazotisation was used to graft 4-azidoaniline groups to the surface of the glassy carbon electrode. The azide bearing 4- azidoaniline groups were thus used to anchor the tetra substituted phthalocyanines to the surface of the electrodes. This method yielded successful modification of the electrodes and lead to their application in sensing studies. The modified electrodes were primarily used to catalyse the common agricultural oxidising agent hydrazine.

A detailed, fundamental understanding of the surface properties of molecular crystals and their interaction with adsorbing molecules (e.g. excipients) is important for tailoring the stability of formulations and the bioavailability of Active Pharmaceutical Ingredient (APIs). Few fundamental experimental studies with surface sensitive probes have been carried out for organic molecular crystals. X-ray photoelectron spectroscopy (XPS) is an established surface analysis method in the fields of adsorption, catalysis and surface chemistry of inorganic crystals. It has high surface sensitivity, probing approximately the top 1-3 nm of a crystal, and allows surface elemental analysis combined with the determination of the chemical state of the elements. To explore the possibilities and limitations of XPS for the surface characterisation of molecular crystal systems, investigation has been made on a range of paracetamol systems, three different poloxamers and blends of paracetamol with poloxamer 188. It was found by investigations of a range of polycrystalline paracetamol forms that the C1s, N1s and O1s core level emissions from the amide group of paracetamol allow to quantify, for the first time, the influence of surface contamination and adsorbed species on the paracetamol XPS data. Results of quantitative XPS analyses must be critically evaluated taking the material and energy-specific escape depth of the photoelectron signals into account. Analysis of the polycrystalline powder samples, including two different polymorphs and various partially amorphous forms of paracetamol, indicated that the core-level shifts associated with varying intermolecular interactions do not perturb the local electronic structure variations in paracetamol enough to become detectable through chemical shifts in the core level photoemission spectra. Subsequently, large, high quality single crystals of the monoclinic form I (with facet diameters between ~5 and ~10 mm) were obtained from different solvents (methanol, ethanol, acetone) to examine the influence of the crystallisation medium on the surface properties. Small spot XPS analysis was performed in several areas across facets to examine the possible influence of roughness and other lateral inhomogeneities. Careful curve-fitting of all results reveals only minor variations in the XPS data as a function of facet orientation, crystallisation medium or degree of crystallinity. Moreover, results indicate that any variations seen in XPS data very likely stem from low-level surface contamination, which is very difficult to avoid, even in a clean-room laboratory environment. In fact, the results indicate that the level of surface contamination depends significantly on the crystallisation apparatus cleanliness. Even minute concentrations of surface active components in the solutions, i.e. below the detection level of techniques for routine analytical methods, are likely to cause significant surface concentrations on crystal facets emersed from the solutions. The study thus highlights the paramount importance of microscopic surface cleanliness when assessing macroscopic facet-specific phenomena such as contact angles. Finally, XPS was employed to analyse milled and physical mixtures of paracetamol with poloxamer 188 at different percent. At minimum mass percentages poloxamer 188 adsorbs on the paracetamol surfaces; in the presence of poloxamer 188 excess the conformation of adsorbed poloxamer on the paracetamol surface changes. Studies of radiation damage on the poloxamer samples were performed both for several pure polxamers as well as for milled mixtures with paracetamol. They allowed the proposal of radiation-induced degradation mechanisms.

The ageing of polymer insulation occurs under long-term exposure to high electric fields and has attracted research due its relevance to high voltage insulation. In this work, polymers that have been electrically aged via a number of methods have been investigated using X-ray photoelectron spectroscopy (XPS). Despite some use in the investigation of outdoor insulation surfaces, XPS has not been used for investigations of polymer bulk electrical ageing before now. The first XPS measurements, using both small spot analysis and XPS imaging, are presented from the exposed inner surfaces of electrically aged artificial voids and electrical breakdown channels, as well as corona discharge aged surfaces and spark discharge by-products. XPS is shown to be a valuable technique for the investigation of polymer electrical ageing. Investigations into breakdown channels are supported by data acquired using X-ray photoemission electron microscopy (XPEEM) and scanning electron microscopy (SEM).Results show that the chemistry present at these surfaces takes the form of significant oxidation over a wide area with localised production of graphitic carbon. C-O-, C=O, and O-C=O species are detected in all cases. It is found that similar ageing products are present regardless of the ageing process or material investigated. However, the level of oxidation and relative ratio of the species seen with XPS is shown to be highly dependant on oxygen availability. Greater intensity of carbon oxides, and a shift towards highly oxidised species, is observed when there is more oxygen in the system. XPS imaging of breakdown channels reveals that high concentrations of oxidised components form on the outer edges of the channel, with graphitic carbon forming in the central regions. In addition, evidence for degradation is seen to extend at least 300 μm from channels in XPS imaging and at least ~650 μm in XPS line scans. Variation with the applied discharge energy was investigated for breakdown channels and spark discharge ageing. Evidence is seen for an energy dependence on the breakdown products, with higher energies producing relatively higher graphitic carbon and reduced oxidation products. Further, the relationship between the applied voltage and graphitic carbon concentration suggests an activated process with an energy barrier before graphitic carbon formation starts. XPS observations are supported by confocal Raman microprobe spectroscopy (CRMS) results from artificial voids and electrical breakdown channels, which identify graphitic carbon on a fluorescent background as the main features. XPS data indicate oxidised species are the origin of the fluorescence seen and provides quantitative information on the levels, chemical states and spatial distribution of these species and of graphitic carbon.