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Semiconductor nanowire synthesis provides a promising route to engineer novel nanoscale materials for applications in energy conversion, electronics, and photonics. The addition of methylgermane (GeH₃CH₃) to standard GeH₄/H₂ chemistry is demonstrated to induce a transition from <111> to <110> oriented growth during the vapor-liquid-solid synthesis of Ge nanowires. This hydride-based chemistry is subsequently leveraged to rationally fabricate kinking superstructures based on combinations of <111> and <110> segments with user defined angles and segment lengths. The addition of GeH₃CH₃ also eliminates sidewall tapering and enables Ge nanowire growth at temperatures exceeding 475 °C, which greatly expands the process window. User-programmable diameter modulation is demonstrated without kinking using tetramethyltin (Sn(CH₃)₄) or trimethylsilane (SiH(CH₃)₃) reacting directly on the sidewalls of growing nanowires to either block or allow conformal deposition. Catalyst modification with tetramethyltin is demonstrated to tune growth kinetics and provides further control over nanowire design. Morphological markers, generated via user-defined changes to diameter along the nanowire axial direction, enable a new approach to rapid, accurate, and facile extraction of growth rate information from electron microscopy images. The ability to engineer nanowire structure by tuning chemistry either at the nucleation point or on the sidewall is demonstrated in this work, thus enabling the rational fabrication of complex superstructures.

Geólogo / En este trabajo se desarrollan los fundamentos de la energía geotérmica de baja entalpia (EGBE), y su uso en la climatización de espacios, especialmente en el ámbito domiciliario. Se introduce el concepto de bomba de calor geotérmica, con todos los aspectos conceptuales que esto conlleva. Se analizara la demanda energética para una casa dentro de la región del Maule, con el fin de generar un sistema de apoyo en la toma de decisiones, aplicado a la evaluación de proyectos relacionados con este tipo de energía. Esta región es una de las dos zonas estudiadas por el proyecto "Determinación de parámetros termales en el subsuelo de las cuencas de Santiago y Talca: implicancias para el uso directo de la energía geotérmica". Se estudiará la cobertura sedimentaria presente en la cuenca del Maule con el objetivo de describir la sedimentología y las propiedades hidráulicas de los acuíferos que estén contenidos en ella, esto con el fin de analizar en profundidad el intercambio calórico con el subsuelo. A esto se le suman las variables hidrogeológicas, como el flujo subterráneo y abatimiento, ya que estas pueden generar quiebres hidráulicos y térmicos, que pueden afectar a una futura implementación y/o operación. Se generaran dos metodologías de estimación, para dos tipos de bombas de calor, ambas asociadas a pozos verticales, pero con distinta fuente calórica. Las bombas BHP (Borehole Heat Pump), que obtiene el calor de los sedimentos y la bomba GWHP (Ground Water Heat Pump) que obtiene el calor del agua subterránea. La generación de este sistema de apoyo requiere una perspectiva multidisciplinaria, ya que necesita la incorporación de todas las variables hidrogeológicas involucradas, además de una correcta estimación en términos de demanda energética y patrones de consumo. Los resultados muestran que ambas tecnologías son aplicables dentro de la zona, pero existe una gran diferencia de costos de implementación. A través de esta diferencia es posible determinar que las bombas GWHP son más favorables cuando se trata de calefacción domiciliaria.

The Large Binocular Telescope Interferometer uses a near-infrared camera to measure the optical path length variations between the two AO-corrected apertures and provide high-angular resolution observations for all its science channels (1.5-13 microns). There is however a wavelength dependent component to the atmospheric turbulence, which can introduce optical path length errors when observing at a wavelength different from that of the fringe sensing camera. Water vapor in particular is highly dispersive and its effect must be taken into account for high-precision infrared interferometric observations as described previously for VLTI/MIDI or the Keck Interferometer Nuller. In this paper, we describe the new sensing approach that has been developed at the LBT to measure and monitor the optical path length fluctuations due to dry air and water vapor separately. After reviewing the current performance of the system for dry air seeing compensation, we present simultaneous H-, K-, and N-band observations that illustrate the feasibility of our feedforward approach to stabilize the path length fluctuations seen by the LBTI nuller.

CIVINS / Carbon nanotubes (CNTs) exhibit exceptional electrical, thermal, and mechanical properties that could potentially transform such diverse fields as composites, electronics, cooling, energy storage, and biological sensing. For the United States Navy, composites potentially provide a significant decrease in lifetime maintenance costs of ships by eliminating hull corrosion. A stronger composite could also improve naval ship survivability or increase combat payloads by reducing the hull weight of ships and submarines. Further, cooling requirements of ship borne electronics have grown exponentially and represent a significant weight penalty for advanced ship designs. Any improvement in thermal transport could significantly improve future naval ship designs. In order to realize these benefits, methods must be discovered to fully characterize CNT growth mechanisms, consistently produce CUTs in manufacturable quantities, and to integrate CUTs into macroscale structures which reflect the properties of individual CUTs. While growth of CNTs in laboratory scale chemical vapor deposition (CVD) tube furnaces has shown great promise, existing low cost tube furnace designs limit the researcher's ability to fully separate critical reaction parameter such as temperature and flow profiles and limit the rate of temperature change during the growth process. Conventional tube furnace designs also provide limited mechanical access to the growth Site and prevent optical monitoring of the growth site, removing the ability to observe and interact in situ during growth. This thesis presents the SabreTube, a low-cost desktop cvD apparatus that decouples temperature and flow variables, provides mechanical and optical access to the reaction site during growth, and provides modular fixturing to enable versatile experimentation with and characterization of CUT growth mechanisms. This thesis also presents the Nanosled, a device designed to translate a substrate through a CVD furnace. / Contract number: N62271-97-G-0026. / CIVINS

Approved for public release; distribution is unlimited / Heat-transfer measurements were made for condensation of R-113 and steam on a smooth tube and on three finned tubes with rectangular shape fins. These tubes had a fin height and width of 1.0 mm and spacings of 0.25, 1.5, and 4.0 mm (tubes A, B, and C respectively) . Data were taken by increasing the vapor velocity from 0.4 to 1.9 m/s for R-113 and 4.8 to 31.3 m/s for steam. For both fluids, the improvement of the condensing heat-transfer coefficient with vapor velocity was smaller for the finned tubes than for the smooth tube. For R-113, the smooth tube experienced a 32 percent improvement with vapor velocity, where the finned tubes (tubes A, B and C respectively) experienced improvements of only 0, 5 and 10 percent. For steam, the smooth tube experienced a 62 percent improvement, whereas the finned tubes (tubes A, B, and C respectively) experienced improvements of only 31, 11, and 9 percent. These test results show that, although finned tubes can provide significant heat transfer enhancement over smooth tubes at low vapor velocities, the degree of enhancement becomes smaller as vapor velocity increases. / CBT-8603582 (NSF) / http://archive.org/details/effectofvaporvel00hopk / National Science Foundation / Lieutenant Commander, United States Navy

Discover of new energy sources and solutions are one of the important global issues nowadays, which has a big impact on economy as well as environment. One of the methods to help to mitigate this issue is to recover wasted heat, which is produced in large quantities by the industry, through vehicle exhausts and in many other situations where we consume energy. One way to do this would be using thermoelectric (TE) materials, which enable direct interconversion between heat and electrical energy. This thesis investigates how the novel material combinations and nanotechnology could be used for fabricating more efficient TE materials and devices. The work presents synthesis, processing, and electrical characterization of group IV materials for TE applications. The starting point is epitaxial growth of alloys of group IV elements, silicon (Si), germanium (Ge) and tin (Sn), with a focus on SiGe and GeSn(Si) alloys. The material development is performed using chemical vapor deposition (CVD) technique. Strained and strain-relaxed Ge1-x Snx (0.01≤x≤0.15) has been successfully grown on Ge buffer and Si substrate, respectively. It is demonstrated that a precise control of temperature, growth rate, Sn flow and buffer layer quality is necessary to overcome Sn segregation and achieve a high quality GeSn layer. The incorporation of Si and n- and p-type dopant atoms is also investigated and it was found that the strain can be compensated in the presence of Si and dopant atoms.  Si1-xGexlayers are grown on Si-on-insulator wafers and condensed by oxidation at 1050 ᵒC to manufacture SiGe-on-insulator (SGOI) wafers. Nanowires (NWs) are processed, either by sidewall transfer lithography (STL), or by using conventional lithography, and subsequently manufactured into nanoscale dimensions by focused ion beam (FIB) technique. The NWs are formed in an array, where one side is heated by a resistive heater made of Ti/Pt. The power factor of NWs is measured and the results are compared for NWs manufactured by different methods. It is found that the electrical properties of NWs fabricated with FIB technique can be influenced due to Ga doping during ion milling. Finally, the carrier transport in SiGe NWs formed on SGOI samples is tailored by applying a back-gate voltage on the Si substrate. In this way, the power factor is improved by a factor of 4. This improvement is related to the presence of defects and/or small fluctuation of nanowire shape and Ge content along the NWs, generated during processing and condensation of SiGe layers. The SiGe results open a new window for operation of SiGe NWs-based TE devices in the new temperature range of 250 to 450 K. / <p>QC 20160907</p>

As part of the effort to increase the reliability of the MMT Observatory (MMTO) 6.5m Primary Mirror Coating System, the specified filament has changed from a configuration in which the aluminum charge is hand wound around a tungsten filament to a configuration in which the aluminum is integrally wound with the tungsten at the time of filament manufacture. In the MMTO configuration, this filament consists of the three strands of tungsten wire and one strand of aluminum wire. In preparation of a full system test utilizing two hundred filaments fired simultaneously, an extensive testing program was undertaken to characterize these filaments using a four filament configuration in the MMTO small coating chamber (0.5m) and then a forty filament configuration in the University of Arizona Steward Observatory coating chamber (2m). The testing using the smaller coating chambers has shown these filaments provide very predicable coatings from test to test, and with the proper heating profile, these filaments greatly reduce the likelihood of aluminum drips. The initial filament design was modified during the course of testing by shortening the unwound filament length to closer match the aluminum load required in the MMTO coating chamber. This change increased the aluminum deposition rates without increasing the power delivered of the filament power supplies (commercial welders). Filament power levels measured at the vacuum chamber feedthroughs, currents, and deposition rates from multiple coating tests, including a full system test, are presented.

In recent years, quasi-one-dimensional materials have attracted a lot of research attention due to their remarkable properties, and their potential as building blocks for nanoscale electronic and optoelectronic devices. A modified chemical vapor deposition (CVD) method has been used to synthesize ZnO nanowires. Electron microscopy and other characterization techniques show that nanowires having distinct morphologies when grown under different conditions. The effects of reaction parameters including reaction time, temperature, carrier gas flow rate, substrates and catalyst material upon the size, shape, and density of ZnO nanowire arrays have been investigated. Excitonic solar cells —including Gratzel-type cells, organic and hybrid organic/inorganic solar cells—are promising devices for inexpensive, large-scale solar energy conversion. Hybrid organic/inorganic solar cells are made from composites of conjugated polymers with nanostructure metal oxides, in which the polymer component serves the function of both light absorber and hole conductor, and the ZnO nanowire arrays act as the electron conductors. Organic solar cells have been fabricated from environmentally friendly water-soluble polymers and ZnO nanowire arrays.