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

A novel class of semi-conducting ortho-carborane (B10C2H12) based polymer films with enhanced electronic and chemical properties has been developed. The novel films are formed from electron-beam cross-linking of condensed B10C2H12 and B10C2H12 co-condensed with aromatic linking units (Y) (Y=1,4-diaminobenzene (DAB), benzene (BNZ) and pyridine (PY)) at 110 K. The bonding and electronic properties of the novel films were investigated using X-ray photoelectron spectroscopy (XPS), UV photoelectron spectroscopy (UPS) and Mulliken charge analysis using density functional theory (DFT). These films exhibit site-specific cross-linking with bonding, in the pure B10C2HX films, occurring at B sites non-adjacent to C in the B10C2H12 icosahedra. The B10C2H12:Y films exhibit the same phenomena, with cross-linking that creates bonds primarily between B sites non-adjacent to C in the B10C2H12 icosahedra to C sites in the Y linking units. These novel B10C2HX: Y linked films exhibit significantly different electron structure when compared to pure B10C2HX films as seen in the UPS spectra. The valence band maxima (VBM) shift from - 4.3 eV below the Fermi level for pure B10C2HX to -2.6, -2.2, and -1.7 for B10C2HX:BNZ, B10C2HX:PY, and B10C2HX:DAB, respectively. The top of the valence band is composed of states derived primarily from the Y linking units, suggesting that the bottom of the conduction band is composed of states primarily from B10C2H12. Consequently these B10C2HX:Y films may exhibit longer electron-hole separation lifetimes as compared to pure B10C2HX films. This research should lead to an enhancement of boron carbide based neutron detectors, and is of potential significance for microelectronics, spintronics and photo-catalysis.

Paddlewheel complexes are molecules in which two interacting metal atoms are bridged by four chelating ligands. This class of complexes has a large range of electronic variability while keeping a rigid geometric structure. This variability has led to their use as catalysts, strong reductants, anti-tumor agents, and electron transfer agents. This dissertation examines the effects of changing both the dimetal core and the surrounding ligands on the electronic structure properties of the paddlewheel complexes. Examination of Bi₂(O₂CCF₃)₄, a p-orbital dimetal paddlewheel complex, provided a way to probe the orbitals that are important in metal-ligand σ bonding. The b(1g) and b(2u) ligand orbitals of Bi₂(O₂CCF₃)₄ have no dimetal orbital counterpart, unlike the case of the more familiar d-orbital dimetal paddlewheel complexes such as Mo₂(O₂CCF₃)₄. This had the effect of destabilizing these ligand orbitals compared to d-orbital paddlewheel complexes. The ligand a1g orbital in Bi₂(O₂CCF₃)₄ was also destabilized due to nodal differences in the dimetal σ orbital. The unusual coincidence of Mo-Mo σ and π ionization bands is due to a greater amount of ligand character in the Mo-Mo σ orbital compared to its ditungsten analogue, which has separate ionization bands for the σ and π bonds. A series of p-substituted dimolybdenum tetrabenzoate complexes was synthesized and studied by photoelectron spectroscopy in order to further examine the delocalization of electron density from the metals to the ligands in these complexes. A 0.89 eV shift in the δ ionization band was observed from Mo₂(O₂CPh-p-OMe) ₄ and Mo₂(O₂CPh-p-CF₃)₄. Overlap effects are the major factor causing the shift in the δ bond ionization, as the calculated charges on the molybdenum and oxygen atoms did not vary significantly on change of substituent. Molybdenum and tungsten guanidinate paddlewheel complexes have promise as good reducing agents due to their extremely low ionization energies. The solubility of the complexes poses a problem for their widespread adoption for use as reducing agents. Alkyl substituents were added to the complexes to increase their solubility. W₂(TEhpp)₄ was observed to have the lowest ionization energy at 3.71 eV (vertical ionization) and 3.40 eV (onset ionization) of any molecule yet prepared.

The ease of electron loss of fifty alipathic thioethers was studied by electrochemistry, charge transfer and photoelectron spectroscopy. These compounds consisted of mesocyclic thioethers and S-methyl norbornane derivatives. Comparison of charge transfer and photoelectron ionization potential showed a good correlation. Correlation of ionization potential with anodic peak potentials showed the existence of two groups of compounds. Those compounds having an electron rich neighboring group capable of an intramolecular interaction were found to have a good correlation of ionization potential with electrochemical peak potential. For those compounds without this capability, no observable correlation was seen. Photoelectron ionization potentials of thioethers are a function of the alkyl groups attached to the sulfur atom. With substituent constants assigned to alkyl groups from measurements on simple thioethers, the ionization potential of more complicated thioethers can be calculated. Compounds whose experimental value was found to be less than the calculated value were found to fall in the group where an intramolecular neighboring group could facilitate the ease of electron loss by stabilization of the cation radical. Electrochemical peak potentials were seen to be dramatically affected by intramolecular stabilization of the cation radical. Shifts of 600-800 mV were seen for structurally similar compounds whose only difference was the availability of an electron rich neighboring group. Since the electrochemistry of these compounds exhibits irreversible behavior, the shift in peak potential could be due to a change in the formal potential, the heterogeneous rate constant, the rate of a following chemical reaction or a combination of these. Changes in the heterogeneous rate constant or chemical step rate constant alone cannot account for the magnitude of the shift seen. Thus the differences observed must be due to two different processes. In the noninteracting case, E⁰' is a measure of the formation of the cation radical, whereas, in the case of interacting compounds E⁰') is a measure of the formation of an intramolecularly stabilized cation radical where bond formation has occurred. Evidence for the structure of some intramolecular stabilized intermediates is presented. An electron deficient thioether which is a model for biological systems was shown to be capable of phosphorylating adenine nucleotides.

The bonding in a series of ligand-bridged metal dimer complexes has been characterized by He(I) and He(II) photoelectron spectroscopy and approximate molecular orbital calculations. Bridging ligands such as carbonyl, nitrosyl, methylene and pyrazolyl in the complexes [CpFe(NO)]₂, [Cp*Fe(NO)]₂, [CpRu(NO)]₂, [Cp*Co(CO)]₂, [CpFe(CO)₂]₂, [Cp*Fe(CO)₂]₂, [CpFe(CO)]₂-μCO-μCH₂, [Cp*Fe(CO)]₂-μCO-μCH₂, [CpFe(NO)]₂- μCh₂, [CpRu(NO)]₂-μCH₂, [CpCo(CO)]₂-μCH₂, [CpRh(CO)]₂-μCH₂, [Ir(pyrazolyl)(CO)₂]₂, [Ir(3-methylpyrazolyl)(CO)₂]₂ and [Ir(3,5-dimethylpyrazolyl)(CO)₂]₂ are investigated and their effects upon metal-metal interactions are surveyed. Due to the presence of two d⁷ or d⁸ late metal atoms per molecule, these complexes display many overlapping ionization bands in a narrow valence ionization region. Attention has been given to modelling the photoelectron single ionization with asymmetric and symmetric Gaussians. The overlapping ionizations are successfully represented in terms of the model bandshapes. Thermodynamic relationships between bond dissociation and photoelectron ionization energies are also investigated. With relationships of this type, trends in bond energies may be correlated with ionization energies. Ligand inductive and bonding effects as well as small changes in molecular geometry cause shifts in the metal-based ionizations, which aid chemical understanding and interpretation of the molecular orbital picture. By comparing a series of related metal dimers, the assignment of related ionizations in the photoelectron spectra becomes apparent. Changes in ligand π accepting ability and changes in metal and formal oxidation states are also probed. Addition information is provided by vibrational fine structure in Cp₂Os, [CpFe(NO)]₂, and [Cp*Co(CO)]₂ and spin-orbit splitting in Cp₂Os. The metal-ligand backbonding combinations are found to be the most stable interactions and are responsible for the stability of the metal dimers. Metal-metal interactions are found to be relatively unimportant. Ligands with stronger π accepting abilities allow for more stabilized supported metal dimer complexes.

Principles of transition metal electronic structure are presented to enable an understanding of the activation of C-H and C=C bonds by metals. A multitechnique approach utilizing core and valence photoelectron spectroscopies (p.e.s.) and molecular orbital calculations has been used to gain these insights. In the first half of the dissertation three principles are developed: ligand additivity, core-valence ionization correlation, and ring methylation. In the latter half of the dissertation these principles are seen to be crucial for understanding ionization data for the C-H and C=C activated species. Additive (with respect to ligand substitution) electronic effects, including additive core and valence ionization potentials, are shown in the p.e.s. of phosphine substituted molybdenum carbonyls. These additive effects demonstrate that the electronic effects of ligand substitution are predictable from empirical models. The core-valence ionization correlation enables direct comparison of XPS (core) and UPS (valence) ionization data and allows separation of bonding and overlap induced valence shift effects from Coulombic and relaxation shift effects. In the study of trimethylphosphine substituted cyclopentadienylmanganese tricarbonyl complexes, both the ligand additivity and core-valence ionization correlation principles are less valid than for the molybdenum carbonyl complexes because of loss of the very influential carbonyl backbonding. Methylation of the cyclopentadienyl ring in this system adds another independent variable of electronic structure perturbation and enables separation of the one-center and two-center Coulombic contributions to the core shifts. The above principles are used in the later chapters to show that the initial activation of the C-H bond in alkenylmanganese tricarbonyl complexes is dominated by the interaction of the C-H sigma bonding level with empty metal acceptor levels. The activation stops at the agostic stage rather than proceeding to full β-hydribe abstraction because there is, in these molecules, no gain in the number of pi electrons between the allyl and diene hydride endpoints of the abstraction cycle. Activation of the C=C bond in the cyclopentadienylmetal olefins is similar for Co and Rh complexes despite little similarity in the valence ionization spectra. The spectral differences are largely caused by the relaxation energy differences between Co and Rh. These complexes also provide interesting examples of electron delocalization through the metal. Permethylation of the cyclopentadienyl ring shifts the olefin pi ligand ionizations more than the expected Coulombic shift.

An experimental apparatus has been constructed to investigate ionisation mechanisms of complex molecules and nanoparticles after femtosecond and/or picosecond laser excitation. The photoproducts are detected by time-of-flight mass spectrometry and velocity-map imaging (VMI) photoelectron spectroscopy. Test measurements on C60 and Xe have successfully reproduced previously published work indicating that the setup is working in a satisfactory manner. New detailed investigations of mass spectra and angle resolved photoelectron spectra (PES) have been carried out as a function of laser intensity, wavelength and pulse duration for C60 and C70, providing new insights into the electronic structure and ionisation mechanisms of these molecules. For 400 nm, 130 fs laser excitation, an isotropic contribution from thermally emitted electrons is found. A series of peaks are seen superimposed on the thermal background with binding energies in agreement with the recently discovered superatom molecular orbitals (SAMOs) of C60 [Feng et.al. Science 320 (2008) p. 359]. Furthermore, the angular dependence of the peak in the PES corresponding to the s-SAMO is in agreement with this assignment. To confirm the assignment of the other observed peaks it is concluded that the measured photoelectron angular distributions (PADs) need to be compared to calculated angular distributions. Measurements have also been made with the same wavelength but with a pulse duration of about 5 ps. Mass spectra, PES and PADs for these measurements show that the main ionisation mechanism for these laser conditions is delayed (thermionic) ionisation. For 800 nm, 130 and 180 fs laser excitation, thermally emitted electrons are observed. In contrast to the 400 nm measurements, the PADs show an asymmetry with higher apparent temperatures along the laser polarisation direction. Measurements were also made for longer pulse durations (1.0 – 3.8 ps). For pulse durations above 1 ps the asymmetry is gradually reduced while the delayed ionisation component in the mass spectrum increases with increasing pulse duration. The asymmetry is compared to calculations made assuming a field-assisted thermal electron emission. Similarly to the 400 nm experiments, a series of peaks are seen superimposed on the thermal background. PADs are presented for these peaks. PADs for peaks with the same binding energy as peaks seen in the 400 nm experiments follow the same trend. Isotropic PADs after ns laser excitation are also presented confirming delayed ionisation for these pulse durations.

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.

by Ka-wai Wong. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1995. / Includes bibliographical references (leaves 106-109). / TABLE OF CONTENTS --- p.i / ABSTRACT --- p.v / LIST OF FIGURES --- p.vi / LIST OF TABLES --- p.xi / LIST OF ABBREVIATIONS --- p.x / Chapter Chapter 1 --- Research Background --- p.1 / Chapter 1.1 --- Introduction --- p.1 / Chapter 1.2 --- The effect of solid acceptance angle --- p.2 / Chapter 1.3 --- Research goals --- p.4 / Chapter 1.3.1 --- Determination of the electron spectrometer transmission function --- p.4 / Chapter 1.3.2 --- Novel depth profiling technique by adjusting the solid acceptance angle --- p.6 / Chapter 1.3.3 --- Correction to conventional ARXPS --- p.8 / Chapter 1.4 --- Thesis Structure --- p.8 / Chapter Chapter 2 --- Fundamentals of X-ray Photoelectron Spectroscopy --- p.9 / Chapter 2.1 --- Introduction --- p.9 / Chapter 2.2 --- X-ray Photoelectron Spectroscopy (XPS) --- p.9 / Chapter 2.2.1 --- Basic principles --- p.9 / Chapter 2.2.2 --- Surface sensitivity --- p.11 / Chapter 2.2.3 --- A typical XPS spectrum --- p.13 / Chapter 2.3 --- Qualitative analysis --- p.16 / Chapter 2.3.1 --- Binding energy --- p.16 / Chapter 2.3.2 --- Chemical state information --- p.17 / Chapter 2.4 --- Quantitative analysis --- p.20 / Chapter 2.4.1 --- Factors affecting intensity --- p.20 / Chapter 2.4.2 --- Homogeneous materials --- p.22 / Chapter 2.4.3 --- Layer structure --- p.23 / Chapter Chapter 3 --- Instrumentation --- p.26 / Chapter 3.1 --- XPS spectrometer --- p.26 / Chapter 3.1.1 --- Magnetic immersion lens system --- p.26 / Chapter 3.1.2 --- Tunable iris --- p.29 / Chapter 3.1.3 --- Scan plates --- p.29 / Chapter 3.1.4 --- Input lens aperture --- p.32 / Chapter 3.2 --- Calibration of the iris --- p.32 / Chapter 3.3 --- Applications --- p.35 / Chapter 3.3.1 --- Two dimensional XPS imaging --- p.35 / Chapter 3.3.2 --- ARXPS --- p.37 / Chapter 3.4 --- Summary --- p.37 / Chapter Chapter 4 --- Determination of electron spectrometer transmission function --- p.38 / Chapter 4.1 --- Introduction --- p.38 / Chapter 4.2 --- Traditional method of determination --- p.39 / Chapter 4.3 --- Methodology of the novel approach --- p.40 / Chapter 4.4 --- Calculation Procedures and Results --- p.48 / Chapter 4.5 --- Results and Discussions --- p.50 / Chapter 4.6 --- Conclusions --- p.57 / Chapter Chapter 5 --- "Depth Profiling by Adjusting the Solid Acceptance Angle: a Starting Point to “ Three-Dimensional Imaging""" --- p.59 / Chapter 5.1 --- Introduction --- p.59 / Chapter 5.2 --- Theoretical Background --- p.60 / Chapter 5.2.1 --- Quantification of Intensity --- p.60 / Chapter 5.3 --- Experimental --- p.69 / Chapter 5.3.1 --- Operation --- p.69 / Chapter 5.3.2 --- Calibration of iris --- p.70 / Chapter 5.3.3 --- Novel depth profile by adjusting the solid acceptance angle --- p.71 / Chapter 5.4 --- Results and Discussions --- p.71 / Chapter 5.4.1 --- Depth Profiles --- p.71 / Chapter 5.4.2 --- "Concept of ""Three-Dimensional XPS Imaging""" --- p.72 / Chapter 5.5 --- Conclusions --- p.76 / Chapter Chapter 6 --- Correction to Quantitative X-ray Photoelectron Spectroscopy with Consideration of the Solid Acceptance Angle --- p.79 / Chapter 6.1 --- Introduction --- p.79 / Chapter 6.2 --- The effect of the solid acceptance angle --- p.80 / Chapter 6.3 --- Theoretical Background --- p.83 / Chapter 6.4 --- Results and Discussions --- p.87 / Chapter 6.4.1 --- Homogeneous Sample --- p.87 / Chapter 6.4.2 --- Layer structure --- p.90 / Chapter 6.4.3 --- Simulation plots and further investigation --- p.92 / Chapter 6.5 --- Conclusions --- p.101 / Chapter Chapter 7 --- Conclusion --- p.103 / Acknowledgment --- p.105 / References --- p.106

<p>In order to develop blood biocompatible materials a heparin surface and a phosphorylcholine (PC) functionalized polymer surface were characterized using photoelectron spectroscopy (PES). The formation of the heparin surface was studied by quartz crystal microbalance with dissipation monitoring (QCM-D). This heparin surface consists of heparin conjugates deposited on a conditioning layer, applied once or twice. The PC functionalized polymer, poly(trimethylene carbonate), was linked to a silicon substrate through 3-amino- propyltrimethoxysilane (APTMS), also studied using PES. </p><p>Synchrotron radiation based PES showed that the thicker heparin film resulted in complete coverage of the substrate, while the thinner did not. This could explain the difference in blood biocompatibility between the two films, as observed by others. It was also found that the heparin chains bend down towards the substrate (under vacuum). </p><p>For the thinner heparin film the modifications, resulting from extensive irradiation of the sample, were studied with synchrotron radiation based PES. This was done at a pressure of about 10^-7 mbar and in 0.5 mbar water vapor. It was found that the modification is slower under water vapor than at low pressures and that the damaged film incorporates water upon exposure.</p><p>The heparin coating was found to be stable and wear resistant enough to still be present on artificial heart valves after three weeks testing in circulating plasma. It then had about the same antithrombin uptake as a non-tested surface. The film was, however, partly destroyed by the durability test and plasma proteins were deposited. </p><p>The PC functionalized, APTMS linked polymer was found to be much shorter than could be expected from random reactions. One plausible explanation is an interaction between the PC group and the silane surface, favoring aminolysis close to the PC group. This is consistent with our finding that the PC group bends down towards the surface.</p>