No description available.

Here we investigate the organic ionic plastic crystal (OIPC) 1,2-bis[N-(N\'-hexylimidazolium-d2(4,5))]C2H4 2PF6- in one of its solid plastic crystal phases by means of multi-nuclear solid-state (SS) NMR and pulsed-field-gradient (PFG) NMR. We quantify distinct cation and anion diffusion coefficients as well as the diffusion activation energies (Ea) in this dicationic imidazolium-based OIPC. Our studies suggest a change in transport mechanism for the cation upon varying thermal and magnetic treatment (9.4 T), evidenced by changes in cation and anion Ea. Moreover, variable temperature 2H SSNMR lineshapes further support a change in local molecular environment upon slow cooling in B0. Additionally, we quantify the percentage of mobile anions as a function of temperature from variable temperature 19F SSNMR, where two distinct spectral features are present. We also comment on the pre-exponential factor (D0), giving insight into the number of degrees of freedom for both cation and anion as a function of thermal treatment. In conjunction with previously reported conductivity values for this class of OIPCs and the Stokes-Einstein relation, we propose that ion conduction is dominated by anion diffusion between crystallites (i.e., grain boundaries). Using our experimentally determine diffusion coefficient and previously reported PF6- hydrodynamic radius (rH), viscous (" = 4.1 Pa " s) ionic liquid (IL) is present with a cation rH of 0.34 nm. NMR measurements are very powerful in elucidating fundamental OIPC properties and allow a deeper understanding of ion transport within such materials. / Master of Science

In this master thesis, electrical characterization of thin film CuInxGa(1−x)Se2 solar cells produced by Midsummer AB were performed with the aim of determining the dominant recombination path of these cells. Current-Voltage (IV), Quantum Effinciency (QE), temperature dependent IV (IVT) and Drive-Level Capacitance Profiling (DLCP) was used with the objective to investigate the dominant recombination path as well as provide some insight of the solar cells in order to create a baseline model using the modelling software SCAPS (Solar cell CAPacitance Simulator). The IV produced mostly consistent results with slight variation, most likely due to non uniformity of equipment. The QE showed consistent results between all cells indicating a stable process for the sample preparation. Using IVT measurements were taken from a temperature of 115K −300K in order to obtain the activation energy for the dominant recombination path. By comparing it with the band gap energy from the QE measurement, it was found that the dominant recombination path is in either the space charge region or in the bulk of the CIGS and not at the hetero interface. DLCP measurement were made at both low temperature and at room temperature and revealed that the cells had a similar doping as other comparable cells at 7×1016cm−3 . The initial baseline model created in SCAPS show a good agreement with the measured IV and currently indicates a spike in the band alignment, supporting the results for the IVT measurement.

京都大学 / 新制・課程博士 / 博士(工学) / 甲第24633号 / 工博第5139号 / 新制||工||1982(附属図書館) / 京都大学大学院工学研究科物質エネルギー化学専攻 / (主査)教授 安部 武志, 教授 阿部 竜, 教授 作花 哲夫 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

No description available.

No description available.

Silicon carbide is a very promising semiconductor material for high-power, highrequency, and high-temperature applications. SiC distinguishes from traditional narrow bandgap semiconductors, such as silicon, in that common doping impurities in SiC have activation energies larger than the thermal energy kT even at room temperature. This causes incomplete ionization of such impurities, which leads to strong temperature and frequency dependence of the semiconductor junction differential admittance and, if carrier freeze-out effects are not taken into account, errors in doping profiles calculated from capacitance-voltage data. Approaches commonly used to study the influence of incomplete impurity ionization on the junction admittance are based on the truncated space charge approximation and/or the small-signal approximation. The former leads to impurity ionization time constant and occupation number errors, while the latter fails if the measurement ac signal amplitude is larger than kT/q. In this work, a new reverse bias Schottky junction admittance model valid for the general case of an arbitrary temperature, measurement signal frequency and amplitude, and doping occupation number and time constant distributions is developed. Results of junction admittance calculations using the developed model are compared with the results of traditional models. Based on the general model, a new method of admittance spectroscopy data analysis is created and used to determine impurity parameters more accurately than allowed by traditional approaches. Incomplete impurity ionization is investigated for the case of nitrogen donors and aluminum and boron acceptors in 4H- and 6H-SiC. It is shown that the degree of carrier freeze-out is significant in heavily N-doped 6H-SiC and in Al- and B-doped SiC. Frequency dispersion of the junction admittance is shown to be significant at room temperature in N- and B-doped SiC. Junction capacitance calculations as a function of applied dc bias show that calculated doping profiles deviate from the actual impurity concentration profiles if the impurity ionization time constant is comparable with the ac signal period. This is the case for N- and B-doped SiC with certain values of the impurity activation energy and capture cross-section. Validity of the new model and its predictions are successfully tested on experimental admittance data for N- and B-doped SiC Schottky diodes.

No description available.

京都大学 / 新制・課程博士 / 博士(工学) / 甲第23196号 / 工博第4840号 / 新制||工||1756(附属図書館) / 京都大学大学院工学研究科材料工学専攻 / (主査)教授 辻 伸泰, 教授 田中 功, 教授 乾 晴行 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

Sulfide minerals are a major source of metals; however, certain sulfide minerals, such as pyrite and pyrrhotite, are less desirable. Froth flotation is a commonly used separation technique, which requires the use of several reagents to float and depress different sulfide minerals. Xanthate, a thiol collector, has gained immense usage in sulfide minerals flotation. However, some sulfides are naturally hydrophobic and may float without a collector. Iron sulfides, such as pyrite and pyrrhotite, are few of the most abundant minerals, yet economically insignificant. Their existence with other sulfide minerals leads to an inefficient separation process as well as environmental problems, such as acid mine drainage during mining and processing and SO2 emissions during smelting process. A part of the present study is focused on understanding their behavior, which leads to undesired flotation and difficulties in separation. The major reasons for the undesired flotation are attributed to the collectorless hydrophobicity and the activation with heavy metal ions. To better understand the collectorless hydrophobicity of pyrite, Electrochemical Impedance Spectroscopy (EIS) of freshly fractured pyrite electrodes was used to study the oxidation and reduction of the mineral. The EIS results showed that the rate of reaction increases with oxidation and reduction. At moderate oxidizing potentials, the rate of reaction is too slow to replenish hydrophilic iron species leaving hydrophobic sulfur species on the surface. However, at higher potentials, iron species are replaced fast enough to depress its flotation. Effects of pH and polishing were also explored using EIS. Besides collectorless hydrophobicity, the activation of pyrrhotite with nickel ions and interaction with xanthate ions makes the separation more difficult. DETA and SO2 are commonly used as pyrrhotite depressants; however, the mechanism is not very well understood. Contact angle measurements, cyclic voltammetry and Tafel studies have been used to elucidate the depressing action of DETA and SO2. It was observed that DETA and SO2 complement each other in maintaining lower pulp potentials and removing polysulfides. DETA also helps in deactivating pyrrhotite. Therefore, the combined use of DETA and SO2 leads to the inhibition of both the collectorless flotation and the adsorption of xanthate. The adsorption of xanthate on sulfide minerals is a mixed-potential mechanism, i.e., the anodic oxidation of xanthate requires a cathodic counterpart. Normally, the cathodic reaction is provided by the reduction of oxygen. However, oxygen can be replaced by other oxidants. Ferric ions are normally present in the flotation pulp. Their source could be either iron from the grinding circuit or the ore itself. The galvanic studies were carried out to test the possibility of using ferric ions as oxidants and positive results were obtained. Tafel studies were carried out to measure the activation energies for the adsorption of ethylxanthate on several sulfide minerals. Pyrite, pyrrhotite (pure and nickel activated), chalcocite and covellite were studied in 10-4 M ethylxanthate solution at pH 6.8 at temperatures in the range of 22 – 30 0C. The Tafel studies showed that xanthate adsorbs as dixanthogen (X2) on pyrite and pyrrhotite, nickel dixanthate (NiX2) on nickel-activated pyrrhotite and cuprous xanthate (CuX) on both chalcocite and covellite. However, the mechanism for xanthate adsorption on each mineral is different. The free energy of reaction estimated from the activation energies are in good agreement with thermodynamically calculated ones. / Ph. D.