A steady state, axial flow thermal conductivity test apparatus was designed and constructed to operate between room temperature and approximately 4 Kelvin, and to be compatible with existing electronic instrumentation and a continuous flow cryostat. The test design included a radiation shield that had its temperature profile matched to that of the sample to minimize radiation heat transfer losses. The cryostat was used to provide the controllable, low temperature test environment in which the test apparatus would operate. A special wiring bundle was constructed to ensure proper connection of the test device to the required electronic instrumentation, which was controlled from a computer by custom written software. Once assembled, the thermal conductivity of a high purity copper sample was measured over the temperature range from 45 to 300 Kelvin and compared to literature recommended values. The test was performed a second time to check repeatability of the measurements over a range of temperature. Next, the thermal conductivity of a high purity niobium sample was measured and compared to literature recommended values. This test was also performed twice. When completed, these tests had demonstrated the accuracy and repeatability of the measurement of thermal conductivity by the test apparatus over the range of temperatures specified and over a range of conductivities. Finally, the thermal conductivity of a sample of the bulk metallic glass Vitreloy 1 was measured over the same temperature range. As far as was known, this was the first time the thermal conductivity of this particular material had been tested below 400 Kelvin. / Graduation date: 2003

Transition edge sensors are the detectors of choice for a wide range of applications; from dark matter search, neutrino search, to cosmic radiation detection from near infrared to millimeter wavelengths. We are developing transition edge sensors using superconducting iridium thin films and we are proposing their use for future dark matter and neutrino search experiments. Our Ir films are deposited using an radio frequency (RF) magnetron sputtering and photolithographic techniques and measured using an adiabatic refrigerator capable of reaching temperatures of a few tens of mK. This thesis presents a detailed description of superconducting iridium thin films from the fabrication process to the characterization of the film properties at room temperature and low temperature. Alternative options for the bias circuit used to read out the TES signals will be discussed, we are proposing the use of RLC resonant circuits and transformers instead of SQUIDS.

The recent pollution norms have brought a strong emphasis on the reduction of diesel engine emissions. Low temperature combustion technology such as premixed compression ignition (PCI) has the capability to significantly and simultaneously reduce nitric oxides (NOx) and particulate matter (PM), thus meeting these specific pollution norms. There has been, however, observed loss in fuel conversion efficiency in some cases. This study analyzes how energy transfer and brake fuel conversion efficiency alter with (or are affected by) injection timings and exhaust gas recirculation (EGR) rate. The study is conducted for PCI combustion for four injection timings of 9°, 12°, 15° and 18° before top dead center (BTDC) and for four exhaust gas recirculation (EGR) rates of 39%, 40%, 41% and 42%. The data is collected from the experimental apparatus located in General Motors Collaborative Research Laboratory at the University of Michigan. The heat release is calculated to obtain various in-cylinder energy transfers. The brake fuel conversion efficiency decreases with an increase in EGR. The decrease in the brake fuel conversion efficiency is due to the decrease in work output. This decrease is due to an increase in the pumping work and an increase in friction and decrease in gross indicated work. The decrease in the combustion efficiency is because of the increased formation of unburnt products due to increased ignition delay caused by the application of EGR and decreasing air-fuel (A/F) ratio. A definite trend is not obtained for the contribution of heat transfer to the total energy distribution. However the total heat transfer decreases with retardation of injection timing because of decreasing combustion temperature. As the injection timing is retarded, the brake fuel conversion efficiency is found to decrease. This decrease is because of a decrease in net work output. This is because the time available for utilization of the energy released is less because of late combustion. The total heat transfer decreases with retardation of injection timing because of decreasing combustion temperature. The contribution of heat transfer to the total energy distribution decreases with increase in EGR.

In recent years, in order to promote the MOSFET¡¦s frequency and performance, the dimension keeping scale down, we can get more transistors in the same area. But nowadays the development of the lithography technology has come to the bottleneck, we must find the other way to improve the performance of transistor. In this study, the strained silicon effect and reliability of CMOS are fully discussed. In order to get strain from the channel, by process, deposit Si3N4 at NMOS and adopt the silicon-germanium epitaxy on source/drain by PMOS, can effective improve NMOS and PMOS electronic characteristic. Besides, silicon substrate is bent by applying external mechanical stress, the lattice of channel will have strain due to uniaxial tensile stress by NMOS and strain due to uniaxial compressive stress by PMOS. By these ways, we successfully improve drain current and mobility of NMOS and PMOS. Furthermore, this study is also probing into strain silicon at low temperature, the impacts on electronic characteristic by different scattering mechanism.

Transport measurements and fabrication of superconductor-exchange spring magnet-superconductor systems

In order to explore how electrons and holes in 2D semiconductors behave at 3He temperatures under millimeter wave irradiation, we developed a new probe and measurement technique. Our samples are specially grown high-mobility GaAs/AlGaAs 2D electron or hole systems that have been modulation doped with Si or C respectively and etched into Hall bars. We also use microwave irradiation waveguide techniques to probe edge magnetoplasmons in 2D electron systems and find that the periodic resistance oscillations in the magnetic field are independent of the length between the leads measured. This demonstrates that the propagation of edge states is a non-local effect, contrary to previously established research. We confirm microwave induced resistance oscillations using a newly developed probe that delivers microwaves from a frequency generator down to the sample via a coax line and coplanar waveguides. Due to the low frequency range (2 -- 40 GHz) and high irradiation powers available, we are able to observe microwave induced resistance oscillations and newly revealed fractional microwave induced resistance oscillations. The probe that we develop for this new measurement makes previously unattainable non-Faraday as well as Faraday irradiation geometries accessible. In addition to measuring quantum transport, it also allows us to measure the transmission of microwaves across the sample. We establish a differential measurement technique that instantaneously removes the background signal leaving only the transmission from the 2D system, also reducing the preparation time required. This is accomplished with a gated high-mobility sample prepared to allow for microwaves to be irradiated from the back. The advantage of this new technique is that it accommodates any gated/polished sample which can be mounted on the specially designed sample holder. From this arrangement we are able to measure the cyclotron resonance transmission minima of both the 2D electron and hole systems. We can then use the known values for the effective mass and cyclotron time constant as a confirmation that our new probe can successfully make the expected measurements.

In this report a novel low temperature synthesis approach of CdS nanocrystals is described starting from well known precursors, Cd(SA) and TOP-S, in a ligand system of aliphatic long chain alcohols. A one-pot synthesis approach is applied using a laboratory microwave heating source. The resulting CdS nanocrystals exhibit an absorbance with a pronounced fine-structure, a photoluminescence with a very high ratio between the band gap peak and the defect peak and a fluorescence quantum yield of 33%. Different synthesis approaches have been investigated by changing heating rate, temperature, precursor concentration and chain length of the aliphatic alcohol ligand as well as chain length of the Cadmium precursor. It was found that small changes in the heating rate do not affect the reaction. Changing the reaction temperature between 200°C and 160°C has no visible effects on the quality of the resulting CdS nanocrystals. At 140°C the nanoparticles experience a significant drop in quality, probably because there is a major change in the growth mechanism of the nanocrystals at that low temperature. At 100°C and 120°C the creation of so-called CdS nanoclusters is observed, and a growth mechanism towards nanocrystals based on cluster aggregation is suggested. For the synthesis of high quality nanoparticles it was found that a ratio of 1:25 between precursor and aliphatic alcohol is preferable as well as a ratio of 1:1 between the two precursors. If the chain length of both the precursors and the alcohol is short, the reaction rate is enhanced. If the chain length is too short the nanocrystals grow very fast and the size distribution gets broad, the photoluminescence intensity decreases and the ratio between band gap luminescence and defect luminescence decreases. The best Cd-precursor was found to be Cd-Laurate and the most suitable ligand evaluated was Tetradecanol.

The catalytic properties of gold have been widely investigated. In Dr. Chao-Ming Chiang¡¦s study, department of chemistry of NSYSU, they found that the organic molecules, propanal, form heterocyclic 2, 4, 6- triethyl-1, 3, 5-trioxane ring on Au(110) missing row surface at 180 K by temperature programmed desorption (TPD) and reflection absorption infrared spectra (RAIR). In this study, we used low energy electron diffraction (LEED) and scanning tunneling microscopy (STM) to study the detailed catalytic process on surface. Residual gas analyzer (RGA) was used to measure the thermal desorption of the propanal on Au(110) at 130 K and 185 K. This can be used to calibrate the temperature on the surface, which can not be directly measured by the thermal couple on the manipulator. The combination between the LEED pattern from the experiment and the DFT model shows the propanal adsorbed on the inclined plane with about 64 deg. to 71 deg. companing the (110) plane. The STM results also show that some of the surface after adsorption have trench wider atomic rows. In our experiment, the real temperature of the sample was not exactly determined. More experiments need to be taken to confirm the temperature.

Since the discovery of high superconducting transition temperature in layered copper oxides, many researchers have searched for similar behavior in other layered metal oxides, such as cobalt and nickel. The sodium cobalt oxyhydrate is the first cobalt-oxide layered superconductor. We present the studies of low-temperature specific heat C(T, H) in NaxCoO2¡EyH2O (x ~ 0.35, y ~ 1.3). At H = 0, a very sharp anomaly was observed at T ~ 4.7 K indicating the existence of bulk superconductivity. There exists an £\T2 term in C(T, H=0) in the superconducting state manifesting the line nodal superconducting order parameter. The feature at the superconducting transition is rather sharp, becoming broad and strongly suppressed in an applied magnetic field. The transition temperature also changed in an applied magnetic field. Thus an abrupt change of slope in H vs. Tc curve was observed. Possible scenarios such as the multiple phase transitions in the mixed state are discussed.

In this thesis we propose several novel configurations of bandpass filters (BPFs) with two transmission zeros by using the fractal theory. By means of the fractal theory, the dimension of the proposed BPFs can be effectively reduced. Furthermore, the proposed BPFs can be easily fabricated by using multilayer structure based on low-temperature cofired ceramic (LTCC) technology. Under the condition of the same dielectric thickness and coupling coefficient, we compared the conventional square open-loop BPF with the proposed fractal ones. The results show that the reduction in the dimension of the proposed BPFs is evident. Specifically, the dimension of the proposed Koch¡¦s, Minkowski_1st, and Minkowski_2nd filters can be reduced by about 36.5%, 32%, and 51.5%, respectively. Finally, the simulation and measurement results are reported in this thesis.