This thesis focuses on the synthesis and characterisation of titanium dioxide (TiO2) thin films for photocatalytic applications and use in semi-transparent dye-sensitised solar cells for energy efficient glazing. Several synthetic methods for the production of TiO2 thin films are explored including sol-gel, aerosol-assisted chemical vapour deposition (CVD) and hybrid combinatorial CVD. For sol-gel processing two different precursors were studied; titanium tetra-isopropoxide (TTIP) and titanium bis-ammonium lactato dihydroxide (TiBALD). Non-ionic surfactants (Tween 20, 40, 60 and Brij 58 and 98) were successfully incorporated into all three methods for the production of TiO2 thin films modified morphology, microstructure and enhanced functional properties in some cases. All films are fully characterised using scanning electron microscopy, X-ray diffraction, atomic force microscopy, Raman spectroscopy, UV-Vis spectroscopy, contact angle analysis, as well as assessment for photocatalytic performance with resazurin 'intelligent' ink. Photocatalytic performance has been used as an indicator for performance in dye-sensitised solar cells (DSSCs). The best photocatalytic performances with half-lives of up to 2 minutes were obtained for thin films produced with the addition of Brij surfactants. A selection of thin films were tested in semi-transparent DSSC devices with up to 70% transparency, to determine their overall potential for use as energy-efficient glazing. Three DSSC device configurations were tested, whereby the optimum configuration used N3 "black" dye with a dye loading time of 42 hours in combination with a high performance iodine electrolyte and a platinum counter electrode. The highest power conversion efficiencies (PCE) obtained were within the region of 0.1 - 0.3 %, with the highest PCE of 0.3814 % obtained with a 3-layer TTIP sol-gel derived Brij 58 thin film (0.0006 mol dm3) which exhibited an short-circuit current of 0.857 mA/cm2, an open-circuit voltage of 0.71 V and a fill factor of 0.60.

The scaling down of Complementary Metal Oxide Semiconductor (CMOS) transistors requires replacement of conventional silicon dioxide layer with higher dielectric constant (K) material for gate dielectric. In order to reduce the gate leakage current, and also to maximize gate capacitance, ‘high K’ gate oxide materials such as Al2O3, ZrO2, HfO2, Ta2O5, TiO2, Er2O3, La2O3, Pr2O3, Gd2O3, Y2O3, CeO2 etc. and some of their silicates such as ZrxSi1–xOy, HfxSi1–xOy, AlxZr1–xO2 etc. are under investigation. A systematic consideration of the required properties of gate dielectrics indicates that the key guidelines for selecting an alternate gate dielectric are (a) permittivity, band gap and band alignment to silicon, (b) thermodynamic stability, (c) film morphology, (d) interface quality, (e) compatibility with the materials/process used in CMOS devices and (f) reliability. In this study titanium dioxide (TiO2) is chosen as an alternate to silicon dioxide (SiO2). This thesis work is aimed at the study of the influence of process parameters like deposition rate, substrate temperature and annealing temperature on the electrical properties like maximum capacitance, dielectric constant, fixed charge, interface trapped charge and leakage current. For making this analysis we have used p–type single crystal silicon (<100>) as substrates and employed direct current (DC) reactive magnetron sputtering method with Titanium metal as target and Oxygen as reactive gas. TiO2 thin films have been deposited with an expected thickness of 50 nm with different deposition rates starting from 0.8 nm/minute to 2 nm/minute with different substrate temperatures (ambient temperature to 500ºC). Some of the samples are annealed at 750ºC in oxygen atmosphere for 30 minutes. SENTECH make Spectroscopic Ellipsometer is used for analyzing the optical properties such as thickness, refractive index etc. The thicknesses of all the samples that are extracted from the Ellipsometry are varying from 35 ± 2 nm to 50 ± 5 nm. Agilent make 4284A model L−C−R meter along with KarlSUSS wafer probe station is used for the C − V measurements and Keithley make 6487 model Pico ammeter/Voltage source is used for the I−V measurements. MOS capacitors have been fabricated with Aluminium as top electrode to perform the bi directional Capacitance−Voltage and also Current−Voltage analysis. The X–ray diffraction studies on the samples deposited at 500ºC showed that the films are amorphous. Dielectric constant (K) and effective substrate doping concentration (Na), flat band voltage (VFB), hysteresis, magnitude of fixed charges (Qf) as well as interface states density (Dit') and Equivalent Oxide Thickness (EOT) are obtained from the bi directional C−V analysis. A maximum dielectric constant of 18 is achieved with annealed samples. The best value of fixed charge density we have achieved is 1.2 x1011 per cm2 corresponding to the deposition rate of 2.0 nm/minute and with 500ºC substrate temperature. The ranges of Qf values that we have obtained are varying from 1.2x 1011 − 1.0 x1012 per cm2. It was also found that, the samples deposited at higher substrate temperatures show lower Qf values than the samples deposited at lower temperatures. The same trend is observed in case of interface states density also. The range of Dit' values we have obtained are in the range of 1.0 x 1012 cm–2eV–1 to 9x1012 cm–2eV–1. The best value of Dit' we have obtained is 1.0x1012 cm–2 eV–1 for the sample deposited at 0.8 nm/minute deposition rate and with substrate temperature of 400ºC. From the flat band voltage values of different set of samples, it was found that the flat band voltage is decreasing and in turn trying to approach the analytical value for the films deposited at higher deposition rates. The minimum EOT that we have achieved is 11 nm that corresponds to the film, which is annealed at 750ºC in oxygen atmosphere. From the I−V analysis it was found that the leakage current density is increasing with increase in substrate temperature and the same trend is observed with annealed films also. The minimum leakage current density achieved is 1.72x10–6 A/cm2 at a gate bias of 1V (corresponding field of 0.3 MV/cm). From the time dependent dielectric breakdown analysis it was found that the leakage current is exhibiting a constant value during the entire voltage stress time of 23 minutes. From the I–V characteristics it was found that the leakage current is following the Schottky emission characteristics at lower electric fields (< 1MV/cm) and is following the Fowler–Nordheim tunneling mechanism at higher electric fields. Since our aim is to study the electrical properties of titanium dioxide thin films for the application as high K gate dielectric in microelectronic applications more emphasis is given on the electrical properties. The maximum dielectric constant we have achieved is in the comparable range of the values for this parameter. The leakage current density values obtained are higher than the required for the microelectronic devices, where as the interface state density values and fixed charge density values are in the same range of values that are reported with this particular oxide and more care has to be taken to minimize these parameters. The EOT values we have achieved are also falling into the range of values that it actually takes as it was reported in the literature.

In dieser Arbeit wurde eine systematische Untersuchung der Abscheidung von TiO2 mittels reaktiver Ionenstrahlzerstäubung von einem metallischen Ti-Target sowie von einem keramischen TiO2-Target durchgeführt. Der Einfluss der Prozessparameter, d.h. der Ionensorte, der Ionenenergie, des Einfalls- und Emissionswinkels sowie des Targetmaterials, auf die Eigenschaften der Sekundärteilchen und der TiO2-Schichten wurde untersucht. Der Ionenstrahl wurde mit einer Faradaysonde, einem Gegenfeldanalysator und einem energieselektiven Massenspektrometer charakterisiert. Das Massenspektrometer wurde auch zur Untersuchung der Massen- und Energieverteilung der Sekundärionen eingesetzt. Mit SDTrimSP simulierte Energieverteilungen der Sekundärteilchen zeigten eine gute Übereinstimmung mit den gemessenen Energieverteilungen der Sekundärionen. Die TiO2-Schichten wurden mittels Ellipsometrie, Röntgendiffraktometrie, -reflektometrie, Rutherford-Rückstreu-Spektrometrie und Rasterkraftmikroskopie untersucht. Eine Verringerung des Streuwinkel führte zu einer Erhöhung der Sekundärteilchenenergien, resultierend daraus wurde eine verstärkte Implantation von Primärteilchen, eine Oberflächenglättung sowie eine systematischen Änderung der Massendichte und folglich der optischen Eigenschaften beobachtet. Die Ionenenergie und das Targetmaterial spielten dabei eine untergeordnete Rolle. / A systematic investigation of the reactive ion beam sputter deposition of TiO2 from a metallic Ti and a ceramic TiO2 target was performed. The influence of the process parameters, i.e. the ion species, ion energy, ion incidence angle, emission angle, and the target material, on the properties of the secondary particles and the TiO2 films was investigated. The ion beam was characterized with a Faraday probe, a retarding potential analyzer, and an energy-selective mass spectrometer. The mass spectrometer was also used to determine the mass and energy distribution of the secondary ions. The experimentally obtained energy distributions were compared to the energy distributions of the secondary particles that were simulated with SDTrimSP. A good agreement was found. The TiO2 films were investigated by spectroscopic ellipsometry, X-ray diffraction, X-ray reflectivity, Rutherford backscattering spectrometry, and atomic force microscopy. Reducing the scattering angle lead to an increase of the secondary particle energies, resulting in an enhanced implantation of primary particles, surface smoothing, and a systematic change of the mass density and consequently of the optical properties. The ion energy and the target material had a minor influence.