Photoelectrochemical cells (PEC) and microbial fuel cells (MFC) are two promising environmental technologies with the purposes of energy production and pollutant degradation. In this study, p-type Cu2O thin film electrodes were synthesized by electrodeposition on the ITO glass. The influences of various electrodeposition conditions, including the deposition potential, temperature, electrolyte pH, substrates and deposition duration on the morphology and the photoelectrochemical properties of the Cu2O films were investigated. The so-called p-type micro-crystal Cu2O thin film photocathodes were synthesized at -0.4 V, 70 °C and pH 10. An innovative composite Cu2O/TiO2 photoelectrode was developed by dip-coating TiO2 on the surface of the Cu2O film. The outer TiO2 layer would help reduce the electron-hole recombination and hence improve the catalyst stability. The photocatalyst was shown to be capable of photocatalytic degradation of model pollutants. Under simulated solar irradiation, methylene blue, acridine orange, and bromocresso brilliant blue G were effectively degraded in the Cu2O-based PEC. The composite Cu2O/TiO2 photoelectrode could further enhance the photodegradation of the dyes. For the study on MFC with the saline wastewater-inoculated MFCs, an electricity output of 581 mW/m2 could be achieved at a NaCl concentration of 200 mM. Based on the characterization of the bioande using the electrochemical impedance spectroscopy (EIS) technique, the R(QR)(QR) model, instead of the conventional R(QR) model, was found to fit well with the EIS data of the carbon cloth bioanode. The results support the two-interface-based physical model for the description of the bioanode, including an interface on the flat electrode and the other for the porous biofilm matrix. The new model was employed to monitor the biofilm formation and development on the carbon clothe anode during the MFC start-up. In addition, photocatalytic MFC was developed by using the Cu2O film as the photocathode for the MFC. With the simulated solar light illumination, the PMFC open circuit voltage could be increased by 200 mV comparing to the MFC test. Moreover, the cathode material (Cu2O) is much less expensive than Pt used by common MFCs. / published_or_final_version / Civil Engineering / Master / Master of Philosophy

The observation of ferromagnetism of (Ga,Mn)As by Ohno in 1998 has inspired great interest in diluted magnetic semiconductors (DMS). DMS’s features combining ferromagnetism and semiconducting make them of great potential for conceptual spintronic devices, which is a promising field of research for the emerging electronics. The practical application of DMS requires a Curie temperature well above room temperature and an intrinsic ferromagnetism. There are several types of DMS materials. The typical ones are transition-metal (TM) doped GaAs, GaN and ZnO. The TM-doped ZnO has drawn particular attention due to the observation of room temperature ferromagnetism in this system including cobalt-doped ZnO.But the origin of ferromagnetic TM-doped ZnO is still unknown after a decade’s theoretical and experimental effort on this material. In this thesis, we do the magnetic circular dichroism(MCD) and Hall measurement of high quality Cobalt-doped ZnO thin films grown by molecular beam epitaxy (MBE). Room temperature ferromagnetism is observed in these samples. Combining the data from MCD and Hall measurement, we attribute the room temperature ferromagnetism in this system to the impurity band of the doped Cobalt cations. / published_or_final_version / Physics / Master / Master of Philosophy

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There is significant interest in understanding and exploiting the extraordinary property enhancements of polymers, enabled by adding small concentrations of nanoparticles to polymer hosts to create polymer nanocomposites (PNCs). Thin film PNCs hold potential for novel technological applications in areas such as optoelectronics or photovoltaic devices. One of the key challenges that limits the potential of PNC-based technologies is the control of nanofiller dispersion throughout the matrix. This requires a fundamental understanding of the energetic interactions that affect dispersion. Thin film PNCs pose a greater challenge than bulk PNCs, largely because interfacial interactions become increasingly important as the material is confined. It is equally important to find effective processing schemes that promote nanofiller dispersion in a manner that can be readily scalable for industrial operations. Accordingly, the last few years have seen an upsurge in processing schemes involving supercritical solvents, due in part to their tunable solvent strength. To this end, our research is aimed at gaining control of nanoparticle dispersion within thin film hosts using supercritical CO₂ (scCO₂) as a processing aid. This research examined a series of related problems. For the first project, we investigated the effects of scCO₂ sorption on the structural stability and kinetics of destabilization of homopolymer films. We showed that the films are metastable under these conditions, and the barrier to nucleation is larger than that encountered in air/vaccum. We also examined the issue of nanofiller dispersion within homopolymer thin films. In a model athermal mixture, polystyrene-coated gold nanoparticles in polystyrene hosts, interfacial segregation was generally observed, and was shown to be a function of the wetting characteristics of the brush-matrix interface and the ratio of the size of the particles to the unperturbed dimensions of the host chains. In a separate system, we show how scCO₂ can serve to prevent coarsening, which is ubiquitous in air/vacuum environments at elevated temperatures, for these nanofillers. Finally, we made nanocomposite micellar structures from block copolymers, with a fluorinated block. Gold nanoparticles were sequestered within the discontinuous domain. We then showed how scCO₂ could be used to invert the structure, placing the nanoparticles in the continuous phase.

This dissertation explores magnetic-field- and electric-current-driven domain-wall motion in thin-film-based magnetic microstructures. Conventional thin-film growth and microstructure fabrication techniques including electron-beam lithography and focused ion beam milling are used to fabricate nanometer-scale one-dimensional and two-dimensional magnetic structures that support magnetic domains (regions of different magnetization orientation separated by domain walls). A high-spatial resolution, hightemporal resolution technique for measuring the field- or current- driven dynamics of the domain walls, based on the magneto-optic Kerr effect, is developed and used to study the wall dynamics. Field-driven domain-wall motion at slow magnetic field sweep rates is dominated by Barkhausen jumps, the discontinuous random movement of domain-wall displacements. The experiments described represent one of the first successful attempts to extend the study of Barkhausen effects into the two-dimensional region. The experiments successfully probe velocity distributions, jump amplitude distributions, and attempt to address issues that pertain to the universal exponents that describe the scaling behavior of Barkhausen jump distribution function including effects of dimensionality and sweep-rate effects on the exponents. A novel dual-beam magneto-optical experiment is performed on thin-film microstructure that probes negative Barkhausen jumps (jumps that oppose the direction favored by Zeeman energy driving the magnetic reversal). A new mechanism for negative Barkhausen jumps is proposed that accounts for the observed effects. Domain-wall motion driven by (spin-polarized) electric current is studied in nanoscale thin-film based wires. The experiments address issues pertaining to the basic mechanisms responsible for current-driven domain-wall motion, which are believed to be the adiabatic spin-torque mechanism and non-adiabatic mechanisms. The experiments described are the first true time-resolved measurements of current-driven displacements, and the results reveal new information about the stochastic properties of current-driven domain wall displacements. The results also provide information on domain-wall velocities and spin-flip efficiencies that address issues related to spin-torque mechanisms.

No description available.

Two-photon optical bistability in commercial thin-film interference filters with ZnS and ZnSe spacers is observed with switching times ≳ 200 μs. The accompanying drifting of the bistability loop in time and laser-induced "damage" indicate a thermal mechanism. The problem of water vapor absorption in such filters must be addressed before the inherent potential and advantages of these devices in two-dimensional image processing applications can be realized. Trans- verse effects in GaAs superlattice etalons are observed which cannot be explained on the basis of a plane-wave analysis. The optical nonlinearity in GaAs and diffraction combine to produce drastic effects on the measured beam profiles and bistable loops, due to an intensity-dependent virtual focus. Lastly, the first observation of optical bistability due to a biexcitonic nonlinearity in CuCl etalons is reported with detector-limited switching times of 600 ps. In addition, lasing action along the pump axis in a cavity defined by the end mirrors is observed in a very thin (2.0 μm) CuCl etalon. The lasing transition is unique in that it involves the creation of a virtual excitation of biexcitons which decay to the longitudinal exciton state.

To augment the monitoring capabilities of a Balzers 760 coating chamber, we replaced the simple, single wavelength optical monitor with a wide-band scanning monochromator system which records transmission data over the visible region of the spectrum. The system is controlled by an IBM-PC. The same computer is also interfaced to a quartz crystal monitoring system which was purchased with the Balzers chamber. The scanning monochromator system required a new brighter light source to deliver sufficient signal to the detector array through the more complex, dispersive optical train. Above the chamber the filter and the photomultiplier pair were removed, and replaced by a flat mirror which diverts the beam horizontally into the scanning monochromator system. The beam passes first through a telescope-slit configuration onto a Jobin-Yvon holographic grating, built to disperse the 400-800 nm band of which we use approximately 360 nm. This reflective grating images the spectrum of the slit onto a Fairchild CCD array, which consists of 1728 elements. These elements are then averaged into 173 data points and recorded by the IBM-PC. The 173 data points allows us a wavelength resolution of about 2 nm. The IBM incorporates a Tecmar A/D board in accepting data from both the quartz crystal monitor and the scanning monochromator system. Although the system is capable of recording data at a faster rate, it is generally stored once every three seconds. This is adequate since at normal deposition rates this gives us information every 10 - 20 Angstroms of deposited material. The system has been used in several applications which will be discussed in this dissertation. They include in situ measurements of water adsorption into a film, derivation of optical constant profiles during the film deposition, both of which may lead us to a better understanding of the growth of a thin film. The monochromator has also been used to analyze the components of a multilayer coating by monitoring the film's transmission spectra while it was sputter-etched off. The extension of the system into the ultraviolet region of the spectrum and some future applications are also considered.