Vertically aligned nanocomposite (VAN) thin films have recently stimulated significant research interest to achieve better material functionality or multifunctionalities. In VAN thin films, both phases grow epitaxially in parallel on given substrates and form a unique nano-checkerboard structure. Multiple strains, including the vertical strain which along the vertical interface and the substrate induced strain which along the film and substrate interface, exist in VAN thin films. The competition of these strains gives a promise to tune the material lattice structure and future more the nanocomposite film physical properties. Those two phases in the VAN thin films are selected based on their growth kinetics, thermodynamic stability and epitaxial growth ability on given substrates. In the present work, we investigated unique epitaxial two-phase VAN (BiFeO3)x:(Sm2O3)1-x and (La0.7Sr0.3MnO3)x:(Mn3O4)1-x thin film systems by pulsed laser deposition. These VAN thin films exhibit a highly ordered vertical columnar structure with good epitaxial quality. The strain of the two phases can be tuned by deposition parameters, e.g. deposition frequency and film composition. Their strain tunability is found to be related directly to the systematic variation of the column widths and domain structures. Their physical properties, such as dielectric loss and ferromagnetisms can be tuned systematically by this variation. The growth morphology, microstructure and material functionalities of VAN thin films can be varied by modifying the phase ratio, substrate orientation or deposition conditions. Systematic study has been done on growing (SrTiO3)0.5:(MgO)0.5 VAN thin films on SrTiO3 and MgO substrates, respectively. The variation of column width demonstrates the substrate induced strain plays another important role in the VAN thin film growth. The VAN thin films also hold promise in achieving porous thin films with ordered nanopores by thermal treatment. We selected (BiFeO3)0.5:(Sm2O3)0.5 VAN thin films as a template and get uniformly distributed bi-layered nanopores. Controllable porosity can be achieved by adjusting the microstructure of VAN (BiFeO3):(Sm2O3) thin films and the annealing parameters. In situ heating experiments within a transmission electron microscope column provide direct observations into the phases transformation, evaporation and structure reconstruction during the annealing. Systematic study in this dissertation demonstrate that the vertically aligned nanocomposite microstructure is a brand new architecture in thin films and an exciting approach that promises tunable material functionalities as well as novel nanostructures.

The primary target of this paper is to fabricate bidirectional transceiver modules based on single mode fiber (SMF) and ultra-thin thin-film filter (TFF). Two major components, namely, SMF and ultra-thin TFF are hybrid integrated on the silicon bench using V-groove and U-groove techniques. A 1310 nm wavelength light was launched into the input SMF of the module. After passing through the filter, the light was received by the output SMF of the module. On the other hand, a 1550 nm wavelength light input to the SMF is reflected by the filter and collected by the output multimode fiber (MMF). Transceiver modules using two different fiber structures were fabricated. The first kind of the module uses standard SMF for 1310 nm light transmission. The insertion loss of the module for the 1310 nm wavelength light was 5.66 dB. In the second kind of the module lens fibers were used to replace the standard SMF. The insertion loss for the 1310 nm wavelength light was reduced to 0.98 dB. A reduction of 4.6 dB was achieved. For both modules, the insertion loss for the 1550 nm wavelength light reflected from the filter was around 0.5 dB.

The primary target of this paper is to fabricate triplexer modules based on Si-bench technology. The triplexer modules were formed by hybrid integration of single mode lensed fibers and ultra-thin thin-film filters (TFF) on silicon bench as using V-groove and U-groove techniques. The output light at 1.31 µm was launched into the input lensed fiber of the module. After passing through two filters, the light was received by the output lensed fiber of the module. The insertion loss of the module at the 1.31 µm light was 1.25 dB. On the other hand, incoming lights at 1.49µm and 1.55µm were received from the output lensed fiber. Lights at 1.49µm will pass through the first filter, and be reflected by the second filter, and eventually be collected into the second multimode fiber. The insertion loss of the module at the 1.49 µm light was 1.14 dB. The 1.55µm wavelength lights received at the lensed fiber are reflected by the first filter and collected by the first multimode fiber. The insertion loss of the module at the 1.55 µm light was 0.68 dB.

kein Abstract vorhanden

Thesis (doctoral)--Helsinki University of Technology, 2009. / Includes bibliographical references. Also available on the World Wide Web.

Thesis (Ph. D. in Electrical Engineering)--Vanderbilt University, Aug. 2003. / Title from title screen. Includes bibliographical references.

Thesis (M.S.) in Electrical Engineering--University of Maine, 2001. / Includes vita. Includes bibliographical references (leaves 128-129).

This dissertation presents the development of methods based on microfabricated devices for combined structure and thermoelectric characterizations of individual nanowire and thin film materials. These nanostructured materials are being investigated for improving the thermoelectric figure of merit defined as ZT=S²[sigma]T/K, where S is the Seebeck coefficient, [sigma] is the electrical conductivity, K is the thermal conductivity, and T is the absolute temperature. The objective of the work presented in this dissertation is to address the challenges in the measurements of all the three intrinsic thermoelectric properties on the same individual nanowire sample or along the in plane direction of a thin film, and in correlating the measured properties with the crystal structure of the same nanowire or thin film sample. This objective is accomplished by the development of a four-probe thermoelectric measurement procedure based on a micro-device to measure the intrinsic K, [sigma], and S of the same nanowire or thin film and eliminate the contact thermal and electrical resistances from the measured properties. Additionally the device has an etched through hole that facilitates the structural characterization of the sample using transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS). This measurement method is employed to characterize individual electrodeposited Bi[subscript 1-x]Te[subscript x] nanowires. A method based on annealing the nanowire sample in a forming gas is demonstrated for making electrical contact between the nanowire and the underlying electrodes. The measurement results show that the thermoelectric propertied of the nanowires are sensitive to the crystal quality and impurity doping concentration. The highest ZT found in three nanowires is about 0.3, which is still lower than that of bulk single crystals at the optimum carrier concentration. The lower ZT found in the nanowires is attributed to the high impurity or carrier concentration and defects in the nanowires. The micro-device is further modified to extend its use to characterization of the in-plane thermoelectric properties of thin films. Existing practice for thermoelectric characterization of thin films is obtaining K in the cross plane direction using techniques such as the 3[omega] method or time domain laser thermal reflectance technique whereas the [sigma] and S are usually obtained in the in-plane direction. However, transport properties of nanostructured thin films can be highly anisotropic, making this combination of measurements along different directions unsuitable for obtaining the actual ZT value. Here, the micro-device is used to measure all three thermoelectric properties in the in-plane direction, thus obtaining the in-plane ZT. A procedure based on a nano-manipulator is developed to assemble etched thin film segments on the micro-device. Measurement results of two different types of thin films are presented in this dissertation. The first type is mis-oriented, layered thin films grown by the Modulated Elemental Reactant Technique (MERT). Three different structures of such thin films are characterized, namely WSe₂, W[subscript x](WSe₂)[subscript y] and (PbSe₀.₉₉)[subscript x](WSe₂)[subscript x] superlattice films. All three structures exhibit in-plane K values much higher than their cross-plane K values, with an increased anisotropy compared to bulk single crystals for the case of the WSe₂ film. The increased anisotropy is attributed to the in-plane ordered, cross-plane disordered nature of the mis-oriented, layered structure. While the WSe₂ film is semi-insulating and the W[subscript x](WSe₂)[subscript y] films are metallic, the (PbSe₀.₉₉)[subscript x](WSe₂)[subscript x] films are semiconducting with its power factor (S²[sigma]) greatly improved upon annealing in a Se vapor environment. The second type of thin films is semiconducting InGaAlAs films with and without embedded metallic ErAs nanoparticles. These nanoparticles are used to filter out low energy electrons with the introduction of Schottky barriers so as to increase the power factor and scatter long to mid range phonons and thus suppress K. The in-plane measurements show that both the S and [sigma] increase with increasing temperature because of the electron filtering effect. The films with the nanoparticles exhibited an increase in [sigma] by three orders of magnitude and a decrease in S by only fifty percent compared to the films without, suggesting that the nanoparticles act as dopants within the film. On the other hand, the measured in-plane K shows little difference between the films with and without nanoparticles. This finding is different from those based on published cross-plane thermal conductivity results. / text

Not available / text

Not available / text