With an increasing demand for renewable energy sources, research efforts on different solar cell technologies are increasing rapidly. The dye-sensitized solar cell (DSC) is one such technology, taking advantage of light absorption in dye molecules. The liquid based DSC contains several interesting and important interfaces, crucial for the understanding and development of the solar cell performance. Examples of such interfaces include dye-semiconductor, electrode-electrolyte and solute-solvent interfaces. Ultimately, complete interfaces with all these components included are of particular interest. One major challenge is to understand the key functions of these systems at an atomic level and one way to achieve this is to use an element specific and surface sensitive tool, such as photoelectron spectroscopy (PES). This thesis describes the use and development of PES for studying interfaces in the DSC. The materials part of the thesis focuses on interfaces in DSCs studied with PES and the methodology development parts focus on methods to use PES for investigations of solvated heterogeneous interfaces of interest for photoelectrochemical systems such as the DSC. More specifically, beginning with standard vacuum techniques, dye molecules bound to a semiconductor surface have been studied in terms of energy level alignment, surface coverage and binding configuration. To increase the understanding of solvation phenomena present in the liquid DSC, liquid jet experiments have been performed in close combination with theoretical quantum calculations. As a step towards an in-situ method to measure a complete, functioning (in operando) solar cell, methodology development and measurements performed with higher sample pressures are described using new high pressure X-ray photoelectron spectroscopy techniques (HPXPS).

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 work in this thesis was aimed at the preparation of low energy surfaces via the surface attachment of fluorinated surfactant molecules. Such surface functionalisation routes are highly dependent on the chemical nature of the substrate surface. For this reason the choice of substrate materials is both all important and extremely limited. To make the process of more general appeal a method for pre-treating the substrate, using cold plasma polymerisation reactions, followed by surfactant coupling to the plasma polymer has been devised. Using this approach, the surfactant coupling process is now dependent on the surface chemistry of deposited plasma polymers and independent of substrate characteristics. In order to form highly functionalised surfaces, likely to undergo further reactions, the plasma polymerisation of acrylic acid, ally! amine and allyl alcohol was investigated. Highly functionalised acid, amine and alcohol surfaces, as shown by X-ray Photoelectron Spectroscopy (XPS) and Infrared Spectroscopy (IR), were produced by optimisation of pulsed plasma conditions. Measurement of deposition rates during plasma polymerisation reactions indicated that polymerisation can occur during the off-time of the pulsed plasma period, most likely via free radical polymerisation pathways. Highly functionalised plasma polymer surfaces thus formed were shown to couple to fluorinated surfactant molecules. The mechanism of surfactant attachment has been suggested to be ionic attraction between opposite charges on the surfactant molecule and the plasma polymer in aqueous solution. The surfaces formed give rise to oleophobic/hydrophilic behaviour. This is in marked contrast to the usual liquid repellent attributes of conventional polyelectrolyte- fluorosurfactant complexes formed by solution phase synthesis.

Femtosecond time-resolved photoelectron spectroscopy (fsTRPES) experiments have been used to study the photoelectron energy spectra of simple molecules since the 1980’s. Analysis of these spectra provides information about the ultrafast internal conversion dynamics of the parent ions. However, ultraviolet pulses must be used for these pump-probe experiments in order to ionize the molecules. Since current solid state lasers, such as the Ti:sapphire laser, typically produce pulses centered at 800nm, it is necessary to generate UV pulses with nonlinear frequency mixing techniques. I therefore constructed an optical setup to generate the 3rd and 4th harmonics, at 266.7nm and 200nm, respectively, of a Ti:sapphire (Ti:sa) chirped-pulse amplified (CPA) laser system that produces 35fs pulses centered at 800nm. Thin Beta-Barium Borate (β-BaB2O4 or BBO) crystals were chosen to achieve a compromise between short pulse durations and reasonable conversion efficiencies, since ultrashort pulses are quite susceptible to broadening from group velocity dispersion (GVD). Output energies of around 11μJ and 230nJ were measured for the 266.7nm and 200nm pulses, respectively. The transform limits of the 3rd and 4th harmonic pulse lengths were calculated from their measured spectral widths. We found that the 266.7nm bandwidth was large enough to support sub-30fs pulses, and due to cutting at the lower-wavelength end of the 200nm spectrum, we calculated an upper limit of 38fs. The pulses were compressed with pairs of CaF2 prisms to compensate for dispersion introduced by transmissive optics. Two-photon absorption (TPA) intensity autocorrelations revealed fully compressed pulse lengths of 36 ± 2 fs and 42 ± 4 fs for the 3rd and 4th harmonics, respectively.

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.

The photosensitive molecule adsorption on titanium dioxide (TiO2) forms the so-called “dye sensitized TiO2” system, a typical organic/oxide heterojunction, which is of great interest in catalysis and energy applications, e.g. dye-sensitized solar cell (DSSC). Traditionally, the transition metal complex dyes are the focus of the study. However, as the fast development of the organic semiconductors and invention of new pure organic dyes, it is necessary to expand the research horizon to cover these molecules and concrete the fundamental understanding of their basic properties, especially during sensitization.In this work, we focus on two different photosensitive molecules: phthalocyanines and triphenylamine-based dyes. Phthalocyanines are organic semiconductors with symmetric macro aromatic molecular structures. They possess good photoelectrical properties and good thermal and chemical stability, which make them widely used in the organic electronic industries. Triphenylamine-based dyes are new types of pure organic dyes which deliver high efficiency and reduce the cost of DSSC. They can be nominated as one of the strong candidates to substitute the ruthenium complex dyes in DSSC. The researches were carried out using classic surface science techniques on single crystal substrates and under ultrahigh vacuum condition. The photosensitive molecules were deposited by organic molecular beam deposition. The substrate reconstruction and ordering were checked by low energy electron diffraction. The molecular electronic, geometric structures and charge transfer properties were characterized by photoelectron spectroscopy, near edge X-ray absorption fine structure spectroscopy and resonant photoelectron spectroscopy (RPES). Scanning tunneling microscopy is used to directly image the molecular adsorption.For phthalocyanines, we select MgPc, ZnPc, FePc and TiOPc, which showed a general charge transfer from molecule to the substrate when adsorbed on rutile TiO2(110) surface with 1×1 and 1×2 reconstructions. This charge transfer can be prevented by modifying the TiO2 surface with pyridine derivatives (4-tert-butyl pyridine (4TBP), 2,2’-bipyridine and 4,4’-bipyridine), and furthermore the energy level alignment at the interface is modified by the surface dipole established by the pyridine molecules. Annealing also plays an important role to control the molecular structure and change the electronic structure together with the charge transfer properties, shown by TiOPc film. Special discussions were done for 4TBP for its ability to shift the substrate band bending by healing the oxygen vacancies, which makes it an important additive in the DSSC electrolyte. For the triphenylamine-based dye (TPAC), the systematic deposition enables the characterization of the coverage dependent changes of molecular electronic and geometric structures. The light polarization dependent charge transfer was revealed by RPES. Furthermore, the iodine doped TPAC on TiO2 were investigated to mimic the electrolyte/dye/TiO2 interface in the real DSSC.The whole work of this thesis aims to provide fundamental understanding of the interaction between photosensitive molecules on TiO2 surfaces at molecular level in the monolayer region, e.g. the formation of interfacial states and the coverage dependent atomic and electronic structures, etc. We explored the potential of the application of new dyes and modified of the existing system by identifying their advantage and disadvantage. The results may benefit the fields of dye syntheses, catalysis researches and designs of organic photovoltaic devices. / QC 20111114

Thesis (Ph. D.)--University of Washington, 1998. / Vita. Includes bibliographical references (leaves [97]-102).

Thesis (Ph.D.)--McMaster University, 2003. / Advisor: N. Werstiuk. Includes bibliographical references (leaves 148-156). Also available via World Wide Web.

A new multi-purpose surface analytical instrument (the Hallam instrument) is described, which combines the surface specific information obtained using x-ray photoelectron spectroscopy (XPS), with bulk information obtained using Energy Dispersive X-ray (EDX) detection. A 15kV electron gun and an ultra high vacuum EDX detector give the instrument an EDX mapping capability. To exploit this to its full potential, spatial alignment of EDX maps acquired at various electron beam energies, E[o], was required. The misalignment of images acquired at various E[o] values was investigated, and a means of describing the misalignment as a function of E[o] was presented. An algorithm was developed which would allow the alignment of offline images acquired at different E[o] values. This was demonstrated on images acquired on both the Hallam instrument and on a Phillips XL40 electron microscope. The small area XPS system developed by Kratos analytical gave a spatial resolution of 30pm at the centre of the field of view, although this deteriorated away from the centre. The reasons for this deterioration in spatial resolution were investigated, and two methods of improving the system were presented. The improvements were implemented on the Hallam instrument and demonstrated using a standard silver grid sample. The small area XPS was applied to a TiAINi coated stainless steel sample to demonstrate its application to real samples, and to display the spatial alignment between the XPS and EDX maps. Finally, the instrument was calibrated for quantitative XPS studies. This involves determining the response of the instrument as a function of the photoelectron kinetic energy. From several methods presented in the literature, the most appropriate was chosen for calibration of the 'Hallam' instrument. The effectiveness of the method used was assessed by recording spectrum intensity from pure elemental standards, and comparing the results with intensity values calculated using the calibration curves.

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.