Hybrid nanomaterial and its applications: IR sensing and energy harvesting

In this dissertation, a hybrid nanomaterial, single-wall carbon nanotubes-copper sulfide nanoparticles (SWNTs-CuS NPs), was synthesized and its properties were analyzed. Due to its unique optical and thermal properties, the hybrid nanomaterial exhibited great potential for infrared (IR) sensing and energy harvesting. The hybrid nanomaterial was synthesized with the non-covalent bond technique to functionalize the surface of the SWNTs and bind the CuS nanoparticles on the surface of the SWNTs. For testing and analyzing the hybrid nanomaterial, SWNTs-CuS nanoparticles were formed as a thin film structure using the vacuum filtration method. Two conductive wires were bound on the ends of the thin film to build a thin film device for measurements and analyses. Measurements found that the hybrid nanomaterial had a significantly increased light absorption (up to 80%) compared to the pure SWNTs. Moreover, the hybrid nanomaterial thin film devices exhibited a clear optical and thermal switching effect, which could be further enhanced up to ten times with asymmetric illumination of light and thermal radiation on the thin film devices instead of symmetric illumination. A simple prototype thermoelectric generator enabled by the hybrid nanomaterials was demonstrated, indicating a new route for achieving thermoelectricity. In addition, CuS nanoparticles have great optical absorption especially in the near-infrared region. Therefore, the hybrid nanomaterial thin films also have the potential for IR sensing applications. The first application to be covered in this dissertation is the IR sensing application. IR thin film sensors based on the SWNTs-CuS nanoparticles hybrid nanomaterials were fabricated. The IR response in the photocurrent of the hybrid thin film sensor was significantly enhanced, increasing the photocurrent by 300% when the IR light illuminates the thin film device asymmetrically. The detection limit could be as low as 48mW mm-2. The dramatically enhanced sensitivity and detection limit were due to the temperature difference between the two junctions formed by the nanohybrid thin film and copper-wire electrodes under asymmetric IR illumination, and the difference between the effective Seebeck coefficient of the nanohybrid thin film and that of the Cu wires. The IR sensor embedded in polydimethylsiloxane (PDMS) layers was also fabricated and tested to demonstrate its potential application as a flexible IR sensor. In another application, energy harvesting, a new type of thermoelectric microgenerator enabled with the SWNTs-CuS nanoparticles hybrid nanomaterial, was fabricated. This type of microgenerator did not require any cooling or heat sink element to maintain the temperature difference or gradient in the device. Instead, the integrated nanomaterials in the device enhanced the local temperature and thus produced and maintained an intrinsic temperature difference or gradient across the microgenerator, thereby converting light and heat directly into electricity. In order to enhance the maximum output voltage, the incoming light had to be focused on the thin film region. A tunable lens was fabricated to collect and focus the ambient light on the thin film to enhance the output voltage of the microgenerators. The tunable lens was fabricated with a flexible polymer, PDMS. Therefore, the focal length of the tunable lens can be adjusted by pumping oil into the lens chamber to deform a PDMS membrane, resulting in the changed focus of the lens. In order to enhance the output power, two different arrays of thermoelectric generators in series and in parallel were fabricated. A hybrid nanomaterial thin film was also used to enhance the temperature gradient of the thermoelectric generators. For the devices in series, the generated voltage of all thermoelectric generators was combined together to enhance the output voltage. With the device in parallel, it can be used to combine all of the current of thermoelectric generators together to enhance the output current

Concentrating solar thermoelectric generators with a peak efficiency of 7.4%

Concentrating solar power normally employs mechanical heat engines and is thus only used in large-scale power plants; however, it is compatible with inexpensive thermal storage, enabling electricity dispatchability. Concentrating solar thermoelectric generators (STEGs) have the advantage of replacing the mechanical power block with a solid-state heat engine based on the Seebeck effect, simplifying the system. The highest reported efficiency of STEGs so far is 5.2%. Here, we report experimental measurements of STEGs with a peak efficiency of 9.6% at an optically concentrated normal solar irradiance of 211 kW m⁻², and a system efficiency of 7.4% after considering optical concentration losses. The performance improvement is achieved by the use of segmented thermoelectric legs, a high-temperature spectrally selective solar absorber enabling stable vacuum operation with absorber temperatures up to 600 °C, and combining optical and thermal concentration. Our work suggests that concentrating STEGs have the potential to become a promising alternative solar energy technology.United States. Department of Energy (DE-EE0005806)Solid-State Solar-Thermal Energy Conversion Center (DE-SC0001299)Solid-State Solar-Thermal Energy Conversion Center (DE-FG02-09ER46577

Fabrication and characterization of hybrid energy harvesting microdevices

In this dissertation, a hybrid energy harvesting system based on a lead zirconate titanate (PZT) and carbon nanotube film (CNF) cantilever structure has been designed, fabricated and studied. It has the ability to harvest light and thermal radiation energy from ambient energy and convert them to electricity. The proposed micro-scale energy harvesting device consists of a composite cantilever beam (SU-8/CNF/Pt/PZT/Pt) which is fixed on a silicon based anchor and two electrode pads for wire bonding. The CNF acts as an antenna to receive radiation energy and convert it to heat energy and then transfer to the whole cantilever structure. The CNF will also convert the radiation energy to a non-uniform distributed static charge. These are two major reasons that cause the cantilever to bend and give the ability of cyclic bending back and forth of the cantilever. The PZT layer, in turn, converts the mechanical energy of repeated deformation of the cantilever to electricity by the piezoelectric effect. First, the cyclic bending capability of the composite cantilever when receiving radiation energy, named self-reciprocation, has been evaluated by copper-CNF cantilever structures and the proposed mechanisms have been discussed. Based on this idea, a prototype macro-scale device with PZT and CNF integrated has been used to verify the possibility of harvesting energy from light and thermal sources by the self-reciprocation phenomenon. Open circuit voltage (OCV) output recorded from the prototype device showed continuous oscillation while a constant radiation source was presented. The proposed micro-scale energy harvesting device was then designed and the fabrication process flow has been developed using surface and bulk micromachining techniques. The fabricated device was polarized in a strong electric field at raised temperature to boost the piezoelectric coefficient. A validation step is designed to pick out the working devices before testing. The functioned device was then tested and successfully demonstrated to harvest energy from light and thermal sources. The result showed the power density of the micro-scale device is 4,445 times higher than the macro-scale prototype device calculated from the maximum power transfer theorem. It was found that the electric output of the micro-scale device contains not only the AC component as the prototype device but also a DC bias shift added to the AC component. An equivalent structure model of the micro-scale device was established to study the electric output characteristic. It was realized that the DC bias shift is generated from the thermoelectric effect (Seebeck effect) by controlled experiments and analysis. The performance of the micro device was studied under different levels of light and thermal radiation conditions. The relationship between output (both DC and AC components of open circuit voltage and short circuit current) and input (light and thermal energy) were analyzed by the least square regression method. The device was taken out of the laboratory to demonstrate its ability to harvest energy in ambient conditions. Both the DC and AC components of the open circuit voltage (electricity) were able to be generated from the solar and wind energy. The power density generated from a single device was about 4 µW/cm2. Further enhancement of the power density was proved by concentrating solar energy on the device with a magnifier and operating an arrayed device

Index to nasa tech briefs, issue number 2

Annotated bibliography on technological innovations in NASA space program

Index to 1984 NASA Tech Briefs, volume 9, numbers 1-4

Short announcements of new technology derived from the R&D activities of NASA are presented. These briefs emphasize information considered likely to be transferrable across industrial, regional, or disciplinary lines and are issued to encourage commercial application. This index for 1984 Tech B Briefs contains abstracts and four indexes: subject, personal author, originating center, and Tech Brief Number. The following areas are covered: electronic components and circuits, electronic systems, physical sciences, materials, life sciences, mechanics, machinery, fabrication technology, and mathematics and information sciences

Index to NASA Tech Briefs, 1975

This index contains abstracts and four indexes--subject, personal author, originating Center, and Tech Brief number--for 1975 Tech Briefs

Index to NASA Tech Briefs, January - June 1967

Technological innovations for January-June 1967, abstracts and subject inde

High Temperature VO2 based Microbolometer with Enhanced Light Absorption

Department of Materials Science and EngineeringMicrobolometer depends on the change in electrical resistance of material as the temperature of the material changes. As element technology of microbolometer, VOx thin films are widely used due to high temperature resistance coefficients (TCR) and low noise . However, due to the metal insulator transition (MIT) property of the VO2 thin film, it is difficult to fabricate a micro bolometer at 68oC which can operate at high temperatures. Also, high light absorption is required . Here, we developed VO2 thin films a nd nanowires. And we developed a light absorber to increase the responsivity of microbolometer through high light absorption and applied it to various application. In order to obtain high quality of thermal sensitive material, we fabricated the resistor in cluded in micro bolometer which has a low resistance and a high temperature resistance coefficient (TCR) by growing the tetragonal VO2 crystal phase on the oxide thin film of the perovskite structure. In addition, infrared absorber has multilayer structure in which Ti metal layer and an MgF2 dielectric layer are alternately deposited with a several repetition cycle. The absorber layer shows about 70 % infrared absorption in the range of 8 14 ??m. In this paper, we used VO2 for the TCR material and the infrar ed absorber, showing the enhanced performance compared to that of the conventional micro bolometer. The micro bolometer operates even at high temperature of 100??C. The micro bolometer has a responsivity and detectivity of 4.90 x 10^3 V/W and 1.45 x 10^8 cmHz 1/2 /W at 100oC.clos

Development and Characterization of Nanofiber-Based Thermoelectric and Piezoelectric Composites

This study focuses on the development and characterization of nanofiber-based composites with the goal of developing flexible, lightweight, and cost effective thermoelectric and piezoelectric devices. The following materials were used in the development of the composites: polyvinylidene fluoride (PVDF) with polyaniline (PANI), polypyrrole (PPY), polyindole (PIN), polyanthranilic acid (PANA), polycarbazole (PCZ), polyacrylonitrile (PAN), functionalized multi-walled carbon nanotubes (MWCNT-COOH), and camphorsulfonic acid (CSA). Blends and in-situ polymerization techniques were utilized to increase the desired thermoelectric/piezoelectric response. Nanofiber systems were produced utilizing the Forcespinning® technique. The morphology, structure, electrochemical, thermal stability, thermoelectric, and piezoelectric performance was analyzed. All of the nanofiber PVDF/CP systems displayed higher piezoelectric performance than the pure PVDF nanofiber systems. The PVDF/PPY nanofiber system showed the highest piezoelectric performance of 15.56 V. Thermoelectric devices consisting of 1-17 modules were created, connected electrically in series and thermally in parallel. The maximum voltage output of the 17 modules thermoelectric device was 8.8 mV. The maximum power output obtained from the thermoelectric device was 15 nW with a figure of merit ZT of 0.0002