The mechanism by which chiral selectivity takes place is complicated by the surface morphology, the possible involvement of the solvent, and the characteristics of the chiral molecules at the surface. My goal is to model and understand the factors which lead to significant discrimination in the case of three closely related chiral stationary phases: N-(1-phenylethyl)-N’-[3-(triethoxysilyl)propyl]-urea (PEPU), [(3,5-dinitrobenzoyl)-amino]-N-[3-(triethoxysilyl)propyl]-2-phenylacetamide (DNB-phenyglycine), and [(3,5-dinitrobenzoyl)amino]-N-[3-(triethoxysilyl)propyl]-4-methylpentanamide (DNB-leucine). Ab initio calculations are used to develop molecular models of these chiral selectors. These models are employed in molecular dynamics (MD) simulations, which provide the theoretical framework for modelling chiral interfaces in different solvent mixtures. The MD simulations of PEPU interfaces show that, in alcohol/water mixtures, the alcohols form domains at the interface with the hydrophobic portions of the molecule tending to orient towards the surface. This disrupts the water hydrogen bonding networks at the interface and leads to the exclusion of water from the surface region relative to the bulk. The MD simulations of DNB-phenylglycine and DNB-leucine selectors in hexane/2-propanol mixtures demonstrate that the interfaces are distinct both in terms of the selector orientations at the surface and in the number of hydrogen bonds formed with 2-propanol. This occurs despite the structural similarity between these two selectors. The interfaces are also prepared experimentally by attaching the chiral selectors onto oxidized Si(111) samples and AFM tips. In particular, for DNB-phenylglycine and DNB-leucine samples, two synthetic routes have been explored. Using AFM, the morphologies of the resulting chiral interfaces are obtained. X-ray photoelectron spectroscopy and refraction-absorption infrared spectroscopy provide information regarding the relative distribution of the compounds on the surface. Using chemical force microscopy (CFM) measurements, chiral self-selectivity is examined in various solvent mixtures. For PEPU interfaces, the extent of hydrogen bonding at the surface is the dominant contributor to the measured forces. In the case of DNB-phenylglycine and DNB-leucine, CFM measurements of the chiral self-selectivity in 2-propanol demonstrate that chiral discrimination is present in both systems, but larger forces are observed for DNB-phenylglycine, consistent with the molecular dynamics study that shows much weaker solvent interactions with this species. / Thesis (Ph.D, Chemistry) -- Queen's University, 2008-08-14 11:26:37.436

Darbo tikslas yra ištirti etaloninių vanadžio pentoksido ir dioksido Rentgeno fotoelektronų spektrus siekiant nustatyti cheminį poslinkį tarp oksidų V 2p spektrų smailių. Darbe išsamiai aprašytos vanadžio dioksido ir prntoksido struktūros, oksidų savybės, Rentgeno fotoelektronų spektroskopijos metodo pagrindai bei V2O5 ir VO2 Rentgeno fotoelektronų spektrų ypatumai. Aprašyti atliktų eksperimentų metodai. Pateikti eksperimentų ir literatūrinės duomenų bazės analizės rezultatai. Atliktas darbas leido nustatyti sekančius faktus: cheminis poslinkis tarp vanadžio dioksido ir pentoksido etaloninių bandinių Rentgeno fotoelektronų spektrų V 2p3/2 smailių lygus 0.7 eV matuojant spektrus spektrometru XSAM 800 (Kratos Analytical, Anglija); literatūrinių duomenų analizę parodė, kad tikimiausia cheminio poslinkio vertė tarp V 2p3/2 smailių įvairiuose vanadžio junginiuose lygi 1.1 eV; skirtumas tarp eksperimentiškai gautos cheminio poslinkio vertės ir analogiško dydžio gauto iš literatūrinių duomenų analizės sąlygotas tuo, kad buvo matuojami gryni VO2 ir V2O5 bandiniai, o analizei buvo naudojama duomenų visumą apie įvairius vanadžio junginius. / The main aim of the presented work was to investigate the chemical shift between XPS V 2p peaks of standard V2O5 and VO2 samples. The structure and physical properties of vanadium dioxide and pentoxide, X-ray photoelectron spectroscopy basis and some singularities of these oxides XPS spectra are presented. The experimental methods, the results of experiments and the literature analysis results are described. The executed work has allowed establishing following facts: the chemical shift between vanadium dioxide and pentoxide standard samples XPS V 2p peaks is equal to 0.7 eV; the analysis of the literature base shows that this shift for various vanadium compounds is 1.1 eV; the difference between measured chemical shift and chemical shift value established from literature analysis is caused because XPS spectra of pure oxides samples was measured in present work and the analysis of the literature base was performed for various vanadium compounds.

No description available.

This thesis describes studies of materials which can be exploited for hydrogen production from water and sunlight. The materials investigated are maghemite (γ-Fe2O3), magnetite (Fe3O4) and especially hematite (α-Fe2O3), which is an iron oxide with most promising properties in this field. Hematite has been deposited using Atomic Layer Deposition (ALD) - a thin-film technique facilitating layer-by-layer growth with excellent thickness control and step coverage. The iron oxides were deposited using bis-cyclopentadienyl iron (Fe(Cp)2) or iron pentacarbonyl (Fe(CO)5) in combination with an O2 precursor. Since it is crucial to have good control of the deposition process, the influence of substrate, process temperature, precursor and carrier gas have been investigated systematically. By careful control of these deposition parameters, three polymorphs of iron oxide could be deposited: hematite (α-Fe2O3), maghemite (γ-Fe2O3) and magnetite (Fe3O4). The deposited materials were characterized using X-ray Diffraction, Raman and UV-VIS Spectroscopy, and Scanning Electron Microscopy. Hard X-ray Photoelectron Spectroscopy (HAXPES) was also used, since it is a non-destructive, chemically specific, surface sensitive technique – the surface sensitivity resulting from the short mean escape depth of the photoelectrons. The depth probed can be controlled by varying the excitation energy; higher photoelectron energies increasing the inelastic mean-free-path in the material. HAXPES studies of atomic diffusion from F-doped SnO2 substrates showed increased doping levels of Sn, Si and F in the deposited films. Diffusion from the substrate was detected at annealing temperatures between 550 °C and 800 °C. Films annealed in air exhibited improved photocatalytic behavior; a photocurrent of 0.23 mA/cm2 was observed for those films, while the as-deposited hematite films showed no photo-activity whatsoever. The optical properties of low-dimensional hematite were studied in a series of ultra-thin films (thicknesses in the 2-70 nm range). The absorption maxima were shifted to higher energies for films thinner than 20 nm, revealing a different electronic structure in thin films.

The present research focuses on the coupling of mechanical and electrical properties of materials and culminates in a direct connection between applied strain to thin-films, thin-film electron binding energy, the energy loss via plastic deformation provided by an indentation, and the substrate resistance. The methods used in this research include X-ray photoelectron spectroscopy (XPS), nanoindentation, digital optical microscopy, and sputter coat deposition. It is discovered that there is a shift in electron binding energy on the scale of 0.2 eV to 1.4 eV in gold and palladium thin-films sputtered on polyvinylidene fluoride (PVDF) through the application of strain induced by a convex shape. There is a change in the area beneath the load-displacement curve measured via indentation from 5.55 x 10^-10 J to 4.78 x 10^-10 J when the gold-palladium thin-film sputtered on PVDF is changed from the flat arrangement to the convex arrangement. Furthermore, the strain also changed the electrical resistance of aluminum foil, which indicates that the substrate electrical resistance is affected by the induced strain. The internal resistance of a circuit developed for this research changed from 7.76 ohms for flat samples to 8.03 ohms and 8.33 ohms for flat and convex samples, respectively. It is expected that the research can be used to estimate the strain in nanogears and other devices at small length scales.

Corrosion is a common issue which must be accounted for when designing all metal products in our society. Many factors need to be considered when new alloys are created, and further knowledge of the corrosion process would be of great use for companies worldwide. The purpose of this thesis was to investigate if X-ray Photoelectron Spectroscopy, XPS, can be used to characterise and quantify corrosion products. With the goal to develop a method that can be used for further studies to increase our understanding of the corrosion process. Aluminium alloy AA3003 was subjected to an immersion corrosion test in an acidified salt solution for different periods of time and the produced chemical compounds were characterised using XPS. The results revealed a direct connection between corrosion time and formed product, which after characterisation proved to be aluminium hydroxide, Al(OH)3. It was concluded that XPS can be used for corrosion studies and is a method that shows great potential and should be further developed. / I metallindustrin är korrosion ett ständigt förekommande problem som måste tas i beaktande vid design av metallprodukter. Många faktorer är avgörande när nya legeringar utvecklas och en djupare kunskap om korrosionsprocessen och dess mekanismer är av stort värde för företag världen över. Syftet med detta examensarbete var att undersöka huruvida röntgen-fotoelektron-spektroskopi, XPS, kan användas för att kvalitativt och kvantitativt karakterisera de korrosionsprodukter som bildas vid korrosion. Med målet att presentera en metod som kan användas för att vidare undersöka och öka vår förståelse för korrosionsprocessen. Aluminiumlegering AA3003 utsattes för accelererad korrosion i en surgjord saltlösning under varierande tid och korrosionsprodukter karakteriserades med XPS. Resultatet påvisade direkt korrelation mellan korrosionstid och mängd produkt. Korrosionsprodukten visade sig vara aluminiumhydroxid, Al(OH)3, och med det i åtanke kunde slutsatsen dras att XPS kan användas vid studier av korrosion. Den utvärderade metoden visar stor potential och detta examensarbete öppnar upp för vidare forskning som kan komma att öka förståelsen för korrosionsprocessen och hur den kan kontrolleras.

Metallophthalocyanines and metal nanoparticles were successfully synthesized and applied for the electrooxidation of amitrole, nitrite and hydrazine individually or when employed together. The synthesized materials were characterized using the following techniques: predominantly scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), electrochemistry and scanning electrochemical microscopy (SECM). Different electrode modification methods were used to modify the glassy carbon substrates. The methods include adsorption, electrodeposition, electropolymerization and click chemistry. Modifying the glassy carbon substrate with MPc (electropolymerization) followed by metal nanoparticles (electrodeposition) or vice versa, made a hybrid modified surface that had efficient electron transfer. This was confirmed by electrochemical impedance studies with voltammetry measurements having lower detection potentials for the analytes. This work also describes for the first time the micropatterning of the glassy carbon substrate using the SECM tip. The substrate was electrografted with 4-azidobenzenediazonium salt and then the click reaction was performed using ethynylferrocene facilitated by Cu⁺ produced at the SECM tip. The SECM imaging was then used to show the clicked spot.

III-V semiconductors have higher charge carrier mobilities than silicon and are used in photovoltaic devices, optical sensors, and emitters. The high injection velocities obtained with III-V channels allow for faster transistors with low power consumption. However, the large-scale implementation in electronic devices is currently limited by the defective interface formed between III-Vs and their oxides. Clean III-V surfaces are highly reactive in air and form amorphous oxides that lead to a high density of dangling bonds. Satisfying these dangling bonds has been associated with an improvement in electrical performance, directing the development of strategies that decrease the surface reactivity (chemical passivation) and the density of surface states that cause power dissipation (electrical passivation). Sulfur bonds easily to III-V surfaces and has been used to chemically and electrically passivate GaAs. In this work, we investigated liquid phase sulfur chemistries in the chemical passivation of clean InSb(100) and In0.53Ga0.47As(100) surfaces terminated by their group V elements. Our strategy consisted of maximizing the number of bonds between sulfur and antimony or arsenic. A long alkane chain thiol, 1-eicosanethiol (ET, 20 carbon atoms), was used to produce a hydrophobic surface and deposit a dense organic layer by taking advantage of the van der Waals interactions between thiol molecules. The first part of the study involved the optimization of the thiol deposition process on InSb. Self-assembled alkanethiol monolayers were formed by immersing clean InSb substrates in ET solutions in ethanol for 20 h. The layers prevented the formation of detectable oxides for 20 min based on the O Auger x-ray photoelectron spectroscopy (XPS) peak. The thiol layer was completely removed by heating the surface to 227 C in vacuum. In the second part of the study, a 20 h ET deposition was performed on In0.53Ga0.47As(100), and re-oxidation was prevented for up to 4 min based on the O 1s XPS peak. The alkanethiolate layer was removed by heating the samples to 350 C in vacuum. The sulfur coverage after 20 min and 20 h ET depositions was increased by performing a second immersion in (NH4)2S without modifying the thickness of the layer. The best process studied consisted of a 20 h immersion in ET solution followed by a short (NH4)2S step, preventing the formation of oxides for up to 9 min. This is due to the presence of available surface sites and weakly bonded molecules in the layer after a long 20 h ET process. The chemical passivation effect is not uniquely influenced by surface termination, roughness, or lattice constant, but is rather a result of a combination of these factors. Future work will involve the fabrication and electrical characterization of III-V devices modified with various chemical passivation strategies.

Doctor of Philosophy / Department of Chemistry / Peter M. Sherwood / This work is a detailed study of the interaction between two phosphorous-containing acids and the metals chromium and 316L stainless steel. The objective of this work is to investigate the formation of unique thin films on the two metals and to probe the surface chemistry of these films through the use of core level and valence band X-ray photoelectron spectroscopy (XPS). Chromium forms a wide array of oxides and can exist at several valencies. Valence band XPS is used in conjunction with band structure and multiple scattered wave X[alpha] calculations to distinguish which states are present in the resultant films. Both 99.99% chromium and 316L stainless steel foils were treated with orthophosphoric acid and 1-hydroxyethylidene-1,1-diphosphonic acid, otherwise known as etidronic acid. Two methods developed in the Sherwood research laboratory for forming oxide-free films on metal surfaces are utilized in this work. Core level XPS results did not provide sufficient information to draw conclusions regarding the products formed in the reactions. The valence band results showed clear evidence of multiple forms of phosphates forming on the metal surfaces as evidenced by the subtle differences in separation between the phosphorous 3p and 3s peaks as well as differences in separation between the O2s and phosphorous 3s peaks. The Valence Band XPS results were interpreted by X-[alpha] cluster and band structure calculations. Films formed on chromium foil from the orthophosphoric acid were found to be condensed phosphates that are stable in air. Etidronic acid formed very thin phosphate films on chromium with both treatment methods as well as on 316L stainless steel when the bench top method was applied. Treatment of etched 316L steel in the anaerobic cell generated an etidronate film. This sample was the only etidronate film formed, all other etidronate-based films were generated from disassembled portions of the etidronate ion to form phosphate films.

>Magister Scientiae - MSc / In the wide search for advanced materials for next generation lithium-ion batteries, lithium manganese orthosilicate, Li₂MnSiO₄ is increasingly gaining attention as a potential cathode material by virtue of its ability to facilitate the extraction of two lithium ions per formula unit, resulting in a two-electron redox process involving Mn²⁺/Mn³⁺ and Mn³⁺/Mn⁴⁺ redox couples. This property confers on it, a higher theoretical specific capacity of 333 mAhg⁻¹ which is superior to the conventional layered LiCoO₂ at 274 mAhg⁻¹ and the commercially available olivine LiFePO₄ at 170 mAhg⁻¹. Its iron analogue, Li₂FeSiO₄ has only 166 mAhg⁻¹ capacity as the Fe⁴⁺ oxidation state is difficult to access. However, the capacity of Li₂MnSiO₄ is not fully exploited in practical galvanostatic charge-discharge tests due to the instability of the delithiated material which causes excessive polarization during cycling and its low intrinsic electronic conductivity. By reducing the particle size, the electrochemical performance of this material can be enhanced since it increases the surface contact between the electrode and electrolyte and further reduces the diffusion pathway of lithium ions. In this study, a versatile hydrothermal synthetic pathway was employed to produce nanoparticles of Li₂MnSiO₄, by carefully tuning the reaction temperature and the concentration of the metal precursors. The nanostructured cathode material was further coated with a thin film of aluminium oxide in order to modify its structural and electronic properties. The synthesized materials were characterized by microscopic (HRSEM and HRTEM), spectroscopic (FTIR, XRD, SS-NMR, XPS) and electrochemical techniques (CV, SWV and EIS). Microscopic techniques revealed spherical morphologies with particle sizes in the range of 21-90 nm. Elemental distribution maps obtained from HRSEM for the novel cathode material showed an even distribution of elements which will facilitate the removal/insertion of Li-ions and electrons out/into the cathode material. Spectroscopic results (FTIR) revealed the vibration of the Si-Mn-O linkage, ascertaining the complete insertion of Mn ions into the SiO₄⁴⁻ tetrahedra. XRD and ⁷Li MAS NMR studies confirmed a Pmn21 orthorhombic crystal pattern for the pristine Li₂MnSiO₄ and novel Li₂MnSiO₄/Al₂O₃ which is reported to provide the simplest migratory pathway for Li-ions due to the high symmetrical equivalence of all Li sites in the unit cell, thus leading to high electrochemical reversibility and an enhancement in the overall performance of the cathode materials. The divalent state of manganese present in Li₂Mn²⁺SiO₄ was confirmed by XPS surface analysis. Scan rate studies performed on the novel cathode material showed a quasi-reversible electron transfer process. The novel cathode material demonstrated superior electrochemical performance over the pristine material. Charge/discharge capacity values calculated from the cyclic voltammograms of the novel and pristine cathode materials showed a higher charge and discharge capacity of 209 mAh/g and 107 mAh/g for the novel cathode material compared to 159 mAh/g and 68 mAh/g for the pristine material. The diffusion coefficient was one order of magnitude higher for the novel cathode material (3.06 x10⁻⁶ cm2s⁻¹) than that of the pristine material (6.79 x 10⁻⁷ cm2s⁻¹), with a charge transfer resistance of 1389 Ω and time constant (τ) of 1414.4 s rad⁻¹ for the novel cathode material compared to 1549 Ω and 1584.4 s rad-1 for the pristine material. The higher electrochemical performance of the novel Li₂MnSiO₄/All₂O₃ cathode material over the pristine Li₂MnSiO₄ material can be attributed to the alumina nanoparticle surface coating which considerably reduced the structural instability intrinsic to the pristine Li₂MnSiO₄ cathode material and improved the charge transfer kinetics.