Magister Scientiae - MSc / TiO2 has been broadly used as a standard photocatalyst due to its high stability, low cost, relatively low toxicity, and excellent photocatalytic performance in comparison to other semiconductor materials. However, the large band gap of TiO2 limits its use as a photocalyst due to the high energy required for excitation of the electrons in the UV region. Research on the reduction of TiO2 band gap to the visible region of the spectrum has been explored with little success. Therefore, this study focusses on shifting the band gap of TiO2 catalyst from the UV region to the visible region by doping with graphene and nitrogen-doped graphene to form TiO2-G and TiO2-NG nanocomposites, respectively. The N-doped graphene support was prepared by doping the graphene oxide with nitrogen through Hydrothermal process, followed by the reduction of the materials. Fourier Tranform Infrared (FTIR) spectroscopy confirmed the successful doping of graphene to N-graphene by the appearance of C-N and N-H vibrational modes on the spectra. The XRD results show the fingerprint patterns of TiO2 and N-graphene, which confirms the successful preparation of the nanocomposites. Morphological studies of the nanocomposites using transmission electron microscopy (TEM) show the TiO2 nanowires dispersed on graphene related supports. The optical band gap of TiO2 from UV-Vis spectroscopy was found to be 3.2eV, which decreased to 2.7eV and 2.5eV upon incorporation of grapheme and N-graphene, respectively. These results prove the success in the achievement of the aim in this study. When electrochemical studies were further conducted on the materials, TiO2-NG was found to possess better electrochemical properties with fast electron kinetics observed on the impendance spectroscopy results. The results obtained justified use of TiO2-NG photocatalyst the optimal material for organic mineralisation in Advanced Oxidation Processes (AOPs).

In this study, the characteristics of atomic layer deposited TiO2 films on silicon substrate were investigated. The physical and chemical properties were measured and surveyed. And an Al/ALD-TiO2/Si MOS structure was used for the electrical characterizations. For the electrical property improvements, we investigated the atomic layer deposited TiO2 films by the post-anneal treatments in nitrogen and oxygen ambient. Furthermore, the TiO2 films were passivated by fluorine ions to decrease the leakage current density that came from the liquid phase deposited SiO2 stacks. After the post-annealing and fluorine ions passivation treatments, the dielectric constant of atomic layer deposited TiO2 film was maintained and the leakage current density was improved.

As the electronic device scale down, replacing conventional SiO2 with high dielectric constant material is very important. Due to its have high dielectric constant (£`// = 170, £`¡æ = 90), high refractive index (~2.5) and high chemical stability. TiO2 is a promising candidate for fabricating thin dielectrics in dynamic random access memory (DRAM) storage capacitors and as gate dielectrics of metal-oxide-semiconductor field effect transistor (MOSFET) without the problem of conventional SiO2 thickness scaling down in ULSI processes because of its high dielectric constant. TiO2 thin films deposited on p-type (100) Si substrate were investigated by a cold wall horizontal MOCVD system using Ti(i-OC3H7)4, N2O as precursors in the deposition temperature range from 400 ¢J to 650 ¢J. XRD results indicate that the structures of TiO2 films are polycrystalline and mixture of anatase and rutile phases coexist in the film at the deposition temperature of 650 ¢J. Electrical properties are strongly influenced by deposition temperature. The electrical properties of as-deposited TiO2 films can be improved by annealing treatment. The TiO2 film at the deposition temperature of 650 ¢J has the highest dielectric constant of 100.3 and at the deposition temperature of 550 oC has the lowest leakage current density of 2.07¡Ñ10-7 A/cm2 under the applied electric field of 5 MV/cm after annealing for 20 minutes at 750 ¢J in O2 ambient. In order to obtain the better electrical properties of TiO2 films on Si substrate, LPD-SiO2 thin films were deposited on the polycrystalline MOCVD-TiO2 films. The minimum equivalent oxide thickness of LPD-SiO2/post-annealed TiO2 film is 51.13

Scaling down of DRAM¡¦s dimensions is a continuous trend since its inception. Therefore, the high dielectric constant material is necessary because the application of conventional SiO2 will reach its physical limits. Due to TiO2 have high dielectric constant (£`// = 170, £`¡æ = 90), high refractive index (~2.5) and high chemical stability, it is a promising candidate for fabricating thin dielectrics in DRAM storage capacitors and as gate dielectrics of MOSFET without the problem of conventional SiO2 thickness scaling down in ULSI processes. TiO2 thin films grown on p-type (100) Si substrate are investigated by a cold wall horizontal MOCVD system using Ti(i-OC3H7)4, N2O as precursors at the growth temperature which ranges from 400 oC to 650 oC. The dielectric constant of poly-crystalline titanium oxide (TiO2) films grown on silicon (Si) by metal organic chemical vapor deposition (MOCVD) is high. The leakage current is also high, which is dominated by the film defect and the grain boundary. The electrical characteristics are also strongly associated with growth temperature. After oxygen annealing, the leakage current is improved due to the reduction of the oxygen vacancy of TiO2 film. However, the electrical characteristics can be further improved by the postmetallization annealing treatment especially under the negative electric field. Post-metallization annealing (PMA) is an effective method in MOS technology to reduce the effective charge density and the interface state density. The mechanism of PMA is to use the reaction between the aluminum contact and hydroxyl groups existed on oxide surface to form active hydrogen and diffuse through the oxide to passivate the oxide traps. Therefore, MOCVD-TiO2/Si films which treated by O2-annealing and PMA with high dielectric constant and low leakage current can be obtained. The leakage current can reach 3.44¡Ñ10^-6 A/cm2 under a negative electric field of 5 MV/cm. The hysteresis loop shift voltage and the interface state densities are 5 mV and 1.17 ¡Ñ 10^11 cm−2 eV^−1, respectively.

The dielectric constant of poly-crystalline titanium oxide (TiO2) films grown on silicon (Si) by metal organic chemical vapor deposition (MOCVD) is high. The leakage current is also high, which is dominated by the grain boundary and lower barrier height. Silicon oxide (SiO2) film is used as an interfacial layer for the structure of MOCVD-TiO2/SiO2/Si. The leakage current is much improved due to the high quality and high barrier height of SiO2/Si, but the total capacitance is lost due to the series of low-dielectric constant SiO2 films and amorphous low dielectric constant of TiO2 film grown on SiO2. Liquid-phase-deposited SiO2 is used as a cap layer for the structure of LPD-SiO2/MOCVD-TiO2/Si, the high dielectric constant of MOCVD-TiO2/Si is preserved. The leakage current is much improved due to the high barrier height SiO2 and the passivation of the dangling bonds of the grain boundary of poly-crystalline MOCVD-TiO2 films by the F from LPD-SiO2 films. Therefore, high dielectric constant and low leakage current LPD-SiO2/MOCVD-TiO2/Si films were obtained. Therefore, MOSFET with LPD-SiO2/MOCVD-TiO2 gate oxide can have lower off state leakage current, smaller subthreshold swing, higher transconductance, and higher field effect mobility. On the other hand, LPD-SiO2/MOCVD-TiO2 film on (NH4)2Sx-treated InP not only can lower leakage current but can lower interface state density. The leakage current densities are 1.37¡Ñ10-7 A/cm2 and 1.45¡Ñ10-7A/cm2 under positive and negative electric fields at 1.5 MV/cm, respectively. The lowest interface state density is 4.7¡Ñ1011 cm-2eV-1 in the band gap. Moreover, the dielectric constant can reach 61.2. Therefore, LPD-SiO2/MOCVD-TiO2 structure is a high dielectric constant and low leakage current film.

For MOCVD-TiO2/Si MOS structure, oxygen vacancy and grain boundary are the main defects of polycrystalline TiO2 films. They are the main mechanisms for the leakage current. In order to improve the problems, oxygen annealing treatment is often used for filling oxygen vacancies. The electrical characteristics of as-grown MOCVD-TiO2 films can be improved. However, it is from the lattice mismatch between the TiO2 film and Si substrate. In order to release the stress, the TiO2 film will produce a lot of defects and degrade its stoichiometry. Besides, the thermal ionic emission is due to lower conduction band offset between TiO2/Si than that of SiO2/Si. These problems need further improvement. In order to solve the above mentioned problems, fluorinated liquid phase deposition (LPD) SiO2 deposited upon polycrystalline MOCVD-TiO2/Si. Higher barrier height (Eg = 9 eV) of fluorinated LPD-SiO2 could avoid the thermal ionic emission from lower conduction band offset of TiO2/Si. Moreover, the LPD-SiO2 film can provide fluorine (F-) from the hydrofluosilicic acid (H2SiF6) aqueous solution. Fluorine could passivate grain boundaries of poly-crystalline MOCVD-TiO2 films and interface state density (Dit) of the MOCVD-TiO2/Si interface. The main leakage current of polycrystalline MOCVD-TiO2 films could be .effective to reduce. Furthermore, nitrogen (N2) annealing was used to enhance fluorine passivation of LPD-SiO2/O2-annealed MOCVD-TiO2 films. Therefore, it can be expected that higher dielectric constant and lower leakage current density will be obtained from LPD-SiO2/O2-annealed MOCVD-TiO2/Si MOS structure. Therefore, MOSFET with fluorinated MOCVD-TiO2 gate oxide can have lower off state leakage current, smaller subthreshold swing, higher transconductance, and higher field effect mobility. On the other hand, LPD-SiO2/MOCVD-TiO2 film on (NH4)2Sx-treated GaAs not only can lower leakage current but can lower interface state density. The leakage current densities are 2.3¡Ñ10-7 A/cm2 and 3.6¡Ñ10-7A/cm2 under positive and negative electric fields at 10V, respectively. The lowest interface state density is 4.7¡Ñ1011 cm-2eV-1 in the band gap. Moreover, the dielectric constant can reach 62. Therefore, LPD-SiO2/MOCVD-TiO2/(NH4)2Sx-treated GaAs structure is a high dielectric constant and low leakage current film. This structure has high potential for the further development of GaAs MOSFETs.

The goal of this experiment is to explore the absorption and reflection of UV light by TiO2/MCA in physical mixing and chemical synthesis. The experiment shows that TiO2/MCA in anatase structure is better than in amorphous structure (with FT-IR. UV-VIS. XRD and Raman spectrum). The first experiment shows that the small TiO2 particle size (290 nm) has better UV absorption than large TiO2 particle (400 nm) in the same mole. After TiO2/MCA(P) exposed to the UV source, the concentration of MCA in TiO2 anatase structure will decrease much than in TiO2 amorphous structure. In the second experiment, the raman peak in 1070 cm-1 proofs that the existence of the Ti-O-C structure. In addition, the FT-IR spectrums peck shows a part of TiO2/MCA has no chemical bonding, and also produces sparse ester (1100 cm-1 . 1300 cm-1). If the peak (1100 cm-1 . 1300 cm-1) were not exist, compare with the previous step, the level of chemical bonding will increase, and it will produce even less ester. In conclusion, The direction of UV absorption of TiO2/MCA(C1. C2. C3) and TiO2/MCA(P) are extremely similar.

ABSTRACT The purpose of this research was to investigate the modified photocatalyst(TiO2) from the heterogeneous photocatalysis of perchloroethylene(PCE) products distribution by different operating conditions using near UV/TiO2 hope that could enhance the PCE¡¦s conversion and mineralization rate and explore the reaction pathways.The modified photocatalyst of this research was completed with Ag/TiO2¡BAu/TiO2¡BPt/TiO2¡BWO3/TiO2 and AC/TiO2. The added species except activied carbon was 10 % weight of photocatalyst(TiO2) others the noble metal (sillver¡Bgold and platinum) and tungsten oxide(WO3) were 0.5 % weight of TiO2. Then the experiments were conducted by varying relative humidity(R.H.=0~60 %), oxygen concentration(0~21 %), and retention time(0.38~0.89 sec). Glass beds coated with modified Degussa P-25 anatase TiO2 were filled in a Pyrex glass reactor. TiO2 was illuminated by four 10 watts ultraviolet(UV) lamps. Results from QA/QC experiments indicated that PCE could not be photodegradated by near UV of wavelength 365 nm. However, It can be decomposed quickly through heterogeneous photocatalysis. And it also find that no modified photocatalyst would be envenomed in photoactivied continuance test. The best PCE conversion and mineralization rate of modified photocatalyst were WO3/TiO2 and AC/TiO2. The modified photocatalyst Ag/TiO2 were the same as TiO2 but Au/TiO2 and Pt/TiO2 were worse to TiO2. The highest converstion rate of PCE could top to 99.5 %¡F The experiment showed that PCE was decomposed as oxygen concentration and retention time increased. But a higher concentration of oxygen was not efficient on the increase of PCE conversion. The conversion ratio of PCE could be inhibited at higher relative humidities. The end products observed from UV/TiO2 heterogeneous photocatalytic reactions included CHCl3, CCl4, C2HCl5, C2Cl6, COCl2, CCl3CClO, Cl2, HCl, CO, and CO2. The major chlorinated compound was Cl2 when the photocatalytic reactions proceed at higher oxygen concentration and less humid conditions. As water vapor existed, the major chlorinated compound became HCl. The major product was CO2 during the entire experimental process of heterogeneous photocatalytic reactions.

Recently, many dielectric materials have been considered as future promising candidates for a thin dielectric in DRAM storage capacitors. Due to its properties of high dielectric constant (£`// = 170, £`¡æ = 89), high refractive index (~2.5) and high chemical stability. TiO2 is a promising candidate for fabricating thin dielectrics in dynamic random access memory (DRAM) storage capacitors and as gate dielectrics of metal-oxide-semiconductor field effect transistor (MOSFET) without the problem of conventional SiO2 thickness scaling down in ULSI processes because of its high dielectric constant. TiO2 thin films grown on p-type (100) Si substrate are investigated by a cold wall horizontal MOCVD system using Ti(i-OC3H7)4, N2O and O2 as precursors in the growth temperature range from 400¢J to 700¢J. The growth rate of using N2O as the oxidizer is quicker than the growth rate of using O2 as the oxidizer because N2O is the more efficient in producing free O atoms. XRD results indicate that the structures of TiO2 films are polycrystalline and the phase transformation temperature of TiO2 films from the anatase phase to the rutile phase is about 650¢J. Electrical properties are strongly influenced by the growth temperature. The electrical properties of as-grown TiO2 films can be improved by annealing treatment. The TiO2 films using O2 as the oxidizer at the growth temperature of 600¢J has the highest dielectric constant of 119.3 and the lowest leakage current density of 1.43¡Ñ10-6 A/cm2 at the applied electric field of 1 MV/cm after annealing for 20 minutes in O2. In order to obtain the better electrical properties of TiO2 films on Si substrate, we prepared TiO2 films by combination of MOCVD and LPD. The dielectric constant of post-annealed TiO2 films prepared by combination of MOCVD and LPD is 34.1. And the leakage current density of it is 3.7¡Ñ10-6 A/cm2 at the applied electric field of 1 MV/cm. It is lower than the films prepared in the same MOCVD-TiO2 growth condition (about 8.2¡Ñ10-6 A/cm2). It suggests that this growth method can reduce the leakage current density.

¡@Silver nanowires prepared by the the reduction of AgNO3 at low temperature with thermocatalystic biphase (anatase and brookite phases) TiO2 nanoparticles are described. Furthermore, the possible mechanism to grow silver nanowires without the help of the Ag seed and capping reagent is proposed. ¡@Firstly, the amorphous TiO2 nanoparticles prepared by sol-gel method were spin-coated on the silicon wafer to form amorphous TiO2 matrix. Then an aqueous AgNO3 (1 &#x00B5;L 0.7 M) solution was dropped on the amorphous TiO2 matrix. Following the heat treatment at 200 ¢XC for 8 h, the silver nanowires (length~10 &#x00B5;m, line width~100 nm) were grown on the silicon wafer. We found that amorphous phase of TiO2 was changed to the anatase and brookite phases during the thermal reduction of the aqueous solution of AgNO3. ¡@Silver nanowires were characterized as f.c.c. structure by XRD. The TiO2 particles play an important role in providing electrons and holes for redox reaction and nucleation. With the controlling of the heating temperature and the amount of AgNO3, the silver nanowires were selectively grown in one dimension with large energetic surface. A combination of HR-TEM imaging and selected area electron diffraction reveals that the growing direction for the Ag wires is <011>.