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Hole-doped manganite La0.7Ca0.3MnO3 materials has been extensively studied because of its colossal magnetoresistance (CMR) characteristic in a magnetic field. Recently, a new member of CMR family La0.7Ce0.3MnO3 , an electron-doped manganite, raises a new wave of attention for possible application of p-n junctions. Single Phase La0.7Ce0.3Mn3 films were usually grown by the pulse laser deposition (PLD) technique with a relatively narrow growth window around 755¢J¡Ó5¢J. In this study, we use a RF sputtering technique to grow La0.7Ce0.3Mn3 epitaxial films, which has not been tried yet. Films are grown on SrTiO3, MgO and LaAlO3 substrates. The best film have the metal-insulator transition temperature (TP) 304K and the curie temperature (TC) 310K, which are higher than that of grown by PLD method

The breakthrough technology in dry fiber fabrication has opened the possibility for using fiber bandwidths all the way from 1.3 to 1.6 £gm. However, the fiber amplifier used in commercial product, such as erbium-doped fiber amplifier (EDFA), can not fully cover the whole fiber bandwidths from 1.3 to 1.6 £gm with a single fiber amplifier. Recently, the Cr4+-doped fiber has shown a broadband emission from 1.3 to 1.6 £gm. Therefore, it is interesting to develop a single fiber amplifier which can operate the wide bandwidth of the 1.3 ~ 1.6 £gm emission. In this study, we have successfully fabricated and measured the Cr-doped fibers by using a commercial drawing-tower technique. The Cr-doped YAG preform was firstly fabricated by a rod-in-tube method. By employing a negative pressure control in drawing-tower technique on the YAG preform, the Cr-doped fibers with a better core circularity and uniformity, and good interface between core and cladding were fabricated. The drawing speed was up to 200m/min. The core diameters were 26 and 16 £gm and the non-circularity was smaller than 3%. The spontaneous emission spectrum showed a broadband emission of 1.2 to 1.6 £gm with the output power density about a few nW/nm. The Cr-doped fibers fabricated by drawing tower are beneficial when integrated with the standard single-mode fibers and broadband WDM couplers for lightwave communication systems. Therefore, the Cr-doped fibers may be used as a broadband fiber amplifier to cover the whole 1.3-1.6 £gm range of silica fibers and have a potential for commercial production and application to lightwave communication systems.

Recently, Iwamoto[1] has proposed a passive-matrix LCD called VA-STN-LCD (Verically Aligned Super Twist Nemetic LCD), in which excellent electro-optic (EO) performance under high-multiplexing conditions has been demonstrated. It was pointed out that such a high EO performance was realized by achieving a pretilt angle of about 80 degree. In this study, we want to learn the different EO characteristic of separate pretilt angle and separate chiral-doped concentration of Negative Dielectric Anisotropy nemetic liquid crystal in vertically aligned cell.

Study of rare-earth manganites has been a very active research area in the last few years in condensed matter physics. This is due to the interesting phenomena such as (1) colossal magneto resistance (2) charge, orbital and spin ordering and (3) phase separation exhibited by these materials as a function of doping, pressure and temperature [1-3]. There is a lot of experimental data available in literature on different doped manganites, but no satisfactory and complete theoretical understanding is available yet. Though different theoretical models proposed are able to explain certain individual physical properties, a unified theory is missing which can comprehensively explain the full phase diagram. The study of such complex systems requires a probe that is sensitive to various interactions observed in manganites such as spin-spin interactions, spin-lattice interactions, spin-orbit interactions, crystal field interactions and the magnetic environment of the spins. Electron paramagnetic resonance (EPR) being sensitive to these interactions is an ideal probe for investigating these strongly correlated systems. A number of EPR studies have been reported in the paramagnetic phase of manganites, throwing light on the complex spin dynamics present in the manganites [4-10]. There are a few reports in the ferromagnetic state of manganites [11-12]. In recent years, a few studies reporting the observation of phase separation using EPR have also been published [13-15]. Charge ordering phase is the other interesting phase, which is not understood from EPR point of view [16-19]. Recently there are a few reports on suppression of CO phase by reducing the particle size from micro to nano range [20-22]. In this thesis we present the results of Electron Magnetic Resonance (EMR) (EPR in the paramagnetic phase and FMR: ferromagnetic resonance in the ferromagnetic phase) studies supported by magnetization and magneto-transport studies of the following : (1) various magnetic phases in the two electron doped manganite Ca1-xCexMnO3 (CCMO) (2) Charge ordered phase vs. ferromagnetic metallic phase as a function of Cr and Ni doping at the Mn site of Nd0.5Ca0.5MnO3 (NCMO) and comparison between the effect of the two dopants, and (3) a study of nano-sized particles (with different particle size) of Cr doped NCMO. Chapter 1 of the thesis consists of a brief introduction to the general features of manganites describing various phenomena and the interactions underlying them. Further we have written a detailed overview of EPR studies in manganites describing the current level of understanding in the area. In this chapter we have also described the experimental methodology and the analysis procedure adopted in this work. Chapter 2 reports the magnetization, transport and electron paramagnetic resonance studies (EPR) on two electron-doped manganites Ca1-xCexMnO3 (0.075 ≤ x ≤ 0.20). The various compositions of CCMO were prepared by solid-state synthesis and characterized by different techniques like XRD, SEM, EDX, and ICPAES. Our magnetization and transport results are consitent with the earlier reports [23-25]. For compositions x ≥ 0.13, all the EPR parameters viz. intensity, linewidth and the resonance field show signatures of a CO phase and at low temperature coexistence of two magnetic phases. x = 0.1 composition shows the most interesting results. Though the EPR intensity and resonance field indicate the presence of a CO phase, the EPR linewidth shows behaviour of a spin-disordered phase which we attribute to a possible spin-liquid phase [26]. The linewidth for x = 0.11 composition shows a combination of a CO and a spin-disorderd phase. For low composition x = 0.075, we observe a weak ferromagnetic phase and later on at low temperatures an antiferromagnetic phase. We do not observe the CO phase for this composition. In chapter 3, we present the magnetization, magnetotransport and EMR studies on Cr doped NCMO (0.0 ≤ x ≤ 0.10) [27]. The samples were prepared by solid-state synthesis and characterized by various techniques like XRD, SEM, EDX, and ICPAES. The magnetization studies show that the Cr doping induces ferromagnetic phase at low temperatures. With the increase of Cr doping the magnetization increases at the expense of the CO phase and for higher doping CO phase disappears completely. The Cr doping induces insulator-metal transition and with increase of Cr doping the metallic phase increases. The doped samples show high CMR, almost 100%, near the TC. The EMR studies in the paramagnetic phase indicate a CO phase for low Cr doping and the presence of short-range dynamical CO-OO correlations for higher Cr doping, which were not observed in magnetization studies. We observe two EPR signals at low temperatures for the Cr doped samples. For 3% doping, the two signals appear well above TC whereas for higher doping (5%, 10%) the two signals were observed in the FM phase. We rule out the possibility of the two-signal behaviour arising from the coexistence of two magnetic phases. For higher doping, the presence of two signals in FM phase can be attributed to magnetic anisotropy. With increase of Cr doping, magnetic anisotropy decreases which is also supported by reduction of magnetic anisotropy in magnetization measurements. But it cannot explain the observation of two signals above TC in the 3% doped sample. In chapter 4, we present the magnetization, magnetotransport and EMR studies on Ni doped NCMO (0.0 ≤ x ≤ 0.10). The samples were prepared by solid-state synthesis and characterized by various techniques like XRD, SEM, EDX, and ICPAES. The magnetization studies show that the Ni doping induces ferromagnetic phase at low temperatures. With the increase of Ni doping, though the CO phase is suppressed, the FMM phase also weakens which is different from the behaviour observed in Cr doped NCMO. The Ni doping induces insulator-metal transition and with increase of Ni doping, the metallic phase weakens. The magnetic anisotropy increases with increase of Ni doping as obtained from magnetization measurements and the EMR data also corroborates the same fact. The EMR studies in the paramagnetic phase indicate a CO phase for low Ni doping and the presence of short-range dynamical CO-OO correlations for higher Ni doping, which were not observed in magnetization studies. We observe two signals in the FM phase, which again can be attributed to the magnetic anisotropy. In chapter 5, we present EMR studies on nano-particles of Cr doped NCMO for x = 0.03. We have prepared nano-particles of three different sizes by the sol-get route. The samples were characterized by various techniques like XRD, SEM, EDX, and ICPAES. The particle sizes are 50, 100, 200 nm. We also compare the results of nano samples with the bulk samples. The ac susceptibility measurements show that the FM phase increases with the reduction of particle size. The EMR measurements show that the magnetic anisotropy decreases with decrease of particle size. The EMR linewidth in the paramagnetic phase increases with the decrease of particle size. The EMR intensity also increases with the reduction of particle size consitent with the magnetization results. The EMR results show that the reduction of particle size is one more way of inducing FM phase more effectively. Also the CO phase gets suppressed with the reduction of particle size. The two-signal feature is observed for all the particles. For nano-sized particles, the two signals appear in FM phase whereas in bulk sample they appeared well above TC. For 50 nm sized particles, the two signals appear well below 40 K. Thus we conclude that with decrease of particle size, the magnetic anisotropy decreases. The thesis concludes with a brief writeup summarizing the results and indicating possible future directions of research in the area.

Tungsten doped tantalum oxide films on titanium substrates were investigated for use as anodes in the electrochemical disinfection of wastewater (measured through e. coli inactivation). A sol-gel method for fabricating these films was developed that allowed for control of both the doping concentration (through volumes of tantalum and tungsten ethoxide added to the solutions), and the thickness (through the number of layers applied). The morphology and composition of these films were investigated using SEM and EDX mapping; the morphology was found to be connected to the fabrication heating procedure. Three different doping concentrations (0%, 8% and 14% tungsten by volume of added metals) were investigated for: 1) electrochemical activity; 2) long-term stability; and 3) disinfection capabilities. The 14% samples demonstrated the highest conductivity (0.06μS/cm), good long-term stability (verified using ICPMS, SEM and EDX analysis) and the best electrochemical activity for removal of e. coli (based on wastewater tests).

Tungsten doped tantalum oxide films on titanium substrates were investigated for use as anodes in the electrochemical disinfection of wastewater (measured through e. coli inactivation). A sol-gel method for fabricating these films was developed that allowed for control of both the doping concentration (through volumes of tantalum and tungsten ethoxide added to the solutions), and the thickness (through the number of layers applied). The morphology and composition of these films were investigated using SEM and EDX mapping; the morphology was found to be connected to the fabrication heating procedure. Three different doping concentrations (0%, 8% and 14% tungsten by volume of added metals) were investigated for: 1) electrochemical activity; 2) long-term stability; and 3) disinfection capabilities. The 14% samples demonstrated the highest conductivity (0.06μS/cm), good long-term stability (verified using ICPMS, SEM and EDX analysis) and the best electrochemical activity for removal of e. coli (based on wastewater tests).

No description available.

The combination of the arsenic trisulfide (As2S3) waveguide and titanium diffused lithium niobate (Ti:LiNbO3) waveguide provide us compact and versatile means for transmitting and processing optical signals, which benefits from the high index contrast between these two materials and the electro-optical properties of Ti: LiNbO3. Furthermore, waveguide gain is introduced through selective surface erbium (Er) doping which yields high quality loss-compensated or even amplifying waveguides without disturbing the excellent electrooptical, acoustooptical and nonlinear properties of the waveguide substrate LiNbO3. The integration of these waveguides allows the development of a whole class of new waveguide devices of higher functionality and complexity. As one kind of the hybrid waveguide devices, a new configuration consisting of an As2S3 channel waveguide on top of an Er doped titanium diffused x-cut lithium niobate waveguide has been investigated by simultaneous analytical expressions, numerical simulations, and experimentation. Both simulation and experimental results have shown that this structure can enhance the optical gain, as predicted by the analytical expressions. An As2S3 channel waveguide has been fabricated on top of a conventional Er:Ti:LiNbO3 waveguide, where the higher refractive index As2S3 waveguide is used to pull the optical mode towards the substrate surface where the higher Er concentration yields an improved propagation gain. The relationship between the gain and As2S3 layer thickness has been evaluated and the optimal As2S3 thickness was found by simulation and experimentation. Side integration was applied to reduce the extra propagation loss caused by the titanium diffusion bump. The propagation gain (dB/cm) has been improved from 1.1 to 2 dB/cm. Another hybrid device which combines the As2S3 and LiNbO3 is to make an As2S3 racetrack ring resonator on top of an x-cut y-propagation Er:Ti:LiNbO3 waveguide which is the potential structure for integrated lossless all-path filter. The ring was side-coupled with the Ti:LiNbO3 waveguide and the optical gain was achieved when the 5mm long coupling region where has been diffused with Er in advance pumped by 144mW pump laser. The free spectral range (FSR) of the measured ring response for TM mode is 0.0587nm (7.33GHz) at 1550nm. The roundtrip loss are 4.4dB (2.60dB/cm) when pump on and 5.8dB (3.44dB/cm) when pump off. The optical gain in the Er diffused area is 0.72dB/cm.

Thesis (Ph. D.)--Ohio University, June, 2000. / Title from PDF t.p.