Index to 1981 NASA Tech Briefs, volume 6, 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 1981 Tech 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

Development Of Titanium Nitride/molybdenum Disulphide Composite Tribological Coatings For Cryocoolers

Hydrogen is a clean and sustainable form of carrier of energy that can be used in mobile and stationary applications. At present hydrogen is produced mostly from fossil sources. Solar photoelectrochemical processes are being developed for hydrogen production. Storing hydrogen can be done in three main ways: in compressed form, liquid form and by chemical bonding. Near term spaceport operations are one of the prominent applications for usage of large quantities of liquid hydrogen as a cryogenic propellant. Efficient storage and transfer of liquid hydrogen is essential for reducing the launch costs. A Two Stage Reverse Turbo Brayton Cycle (RTBC) CryoCooler is being developed at University of Central Florida. The cryocooler will be used for storage and transport of hydrogen in spaceport and space vehicle application. One part in development of the cryocooler is to reduce the friction and wear between mating parts thus increasing its efficiency. Tribological coatings having extremely high hardness, ultra-low coefficient of friction, and high durability at temperatures lower than 60 K are being developed to reduce friction and wear between the mating parts of the cryocooler thus improving its efficiency. Nitrides of high-melting-point metals (e.g. TiN, ZrN) and diamond-like-carbon (DLC) are potential candidates for cryogenic applications as these coatings have shown good friction behavior and wear resistance at cryogenic temperatures. These coatings are known to have coefficient of friction less than 0.1 at room temperature. However, cryogenic environment leads to increase in the coefficient of friction. It is expected that a composite consisting of a base layer of a hard coating covered with layer having an ultra-low coefficient of friction would provide better performance. Extremely hard and extremely low friction coatings of titanium nitride, molybdenum disulphide, TiN/MoS2 bilayer coatings, DLC and DLC/MoS2 bilayer coatings have been chosen for this application. TiN film was deposited by reactive DC magnetron sputtering system from a titanium target and MoS2 film was deposited by RF magnetron sputtering using a MoS2 target. Microwave assisted chemical vapor deposition (MWCVD) technique was used for preparation of DLC coatings. These composite coatings contain a solid lubricating phase and a hard ceramic matrix phase as distinctly segregated phases. These are envisioned as having the desired combination of lubricity and structural integrity. Extremely hard coatings of TiN and DLC were chosen to provide good wear resistance and MoS2 was chosen as the lubricating phase as it provides excellent solid lubricating properties due to its lamellar crystal structure. This thesis presents preparation; characterization (SEM and XRD), microhardness and tribological measurements carried out on TiN and TiN/MoS2 coatings on aluminum and glass substrate at room temperature. It also presents initial development in preparation of DLC coatings

DIRECT PRINTING/COATING/PLATING OF KEY COMPONENTS FOR ELECTRONIC DEVICES

Miniaturization has been a technological trend for several decades for electronic devices. From the practical point of view, the successful miniaturization of fully integrated systems mainly depends on their components. This dissertation examines the inkjet printing of copper oxide inks on flexible substrates for applications in microfluidic valving systems. We expand the knowledge of low-cost and high-performance electrowetting valves and fabricate the microfluidic device for fluidic control, which is necessary to enable the next-generation microfluidic devices. In addition, we also study the electromagnetic interference (EMI) shielding material, which is a crucial part of electronic devices. The basic theory of EMI shielding is discussed in this dissertation. We explore the high-performance shielding materials with novel fabrication methods, such as spray coating, laser carbonizing and electroplating. Chapter 1 describes the fabrication of flexible inkjet-printed copper electrowetting valves. We study the effects of dielectric layer thickness as well as applied voltage to the contact angle decreasing process. Taking this one step further, an electrowetting valve with two controlled channels is described for demonstration. Chapter 2 explores the fabrication of high-performance EMI shielding material of silver-coated carbon fiber fabrics (CFFs) via spray coating. EMI shielding theory is discussed in detail. The silver/CFF composite material is introduced at the lab-scale as well as at the roll-to-roll large fabrication scale. Chapter 3 introduces the high-performance optically transparent copper mesh. The laser carbonizing and electroplating techniques are described. We study the effect of different patterns to the EMI shielding performance. Chapter 4 evaluates the EMI shielding performance of graphite/polymer composites. Microwave exfoliation and acid treatment are explained from the mechanism aspect. Furthermore, future work is described for potential improvement on their performance

Carbon nanotubes for thermal interface materials in microelectronic packaging

As the integration scale of transistors/devices in a chip/system keeps increasing, effective cooling has become more and more important in microelectronics. To address the thermal dissipation issue, one important solution is to develop thermal interface materials with higher performance. Carbon nanotubes, given their high intrinsic thermal and mechanical properties, and their high thermal and chemical stabilities, have received extensive attention from both academia and industry as a candidate for high-performance thermal interface materials. The thesis is devoted to addressing some challenges related to the potential application of carbon nanotubes as thermal interface materials in microelectronics. These challenges include: 1) controlled synthesis of vertically aligned carbon nanotubes on various bulk substrates via chemical vapor deposition and the fundamental understanding involved; 2) development of a scalable annealing process to improve the intrinsic properties of synthesized carbon nanotubes; 3) development of a state-of-art assembling process to effectively implement high-quality vertically aligned carbon nanotubes into a flip-chip assembly; 4) a reliable thermal measurement of intrinsic thermal transport property of vertically aligned carbon nanotube films; 5) improvement of interfacial thermal transport between carbon nanotubes and other materials. The major achievements are summarized. 1. Based on the fundamental understanding of catalytic chemical vapor deposition processes and the growth mechanism of carbon nanotube, fast synthesis of high-quality vertically aligned carbon nanotubes on various bulk substrates (e.g., copper, quartz, silicon, aluminum oxide, etc.) has been successfully achieved. The synthesis of vertically aligned carbon nanotubes on the bulk copper substrate by the thermal chemical vapor deposition process has set a world record. In order to functionalize the synthesized carbon nanotubes while maintaining their good vertical alignment, an in situ functionalization process has for the first time been demonstrated. The in situ functionalization renders the vertically aligned carbon nanotubes a proper chemical reactivity for forming chemical bonding with other substrate materials such as gold and silicon. 2. An ultrafast microwave annealing process has been developed to reduce the defect density in vertically aligned carbon nanotubes. Raman and thermogravimetric analyses have shown a distinct defect reduction in the CNTs annealed in microwave for 3 min. Fibers spun from the as-annealed CNTs, in comparison with those from the pristine CNTs, show increases of ~35% and ~65%, respectively, in tensile strength (~0.8 GPa) and modulus (~90 GPa) during tensile testing; an ~20% improvement in electrical conductivity (~80000 S m⁻¹) was also reported. The mechanism of the microwave response of CNTs was discussed. Such an microwave annealing process has been extended to the preparation of reduced graphene oxide. 3. Based on the fundamental understanding of interfacial thermal transport and surface chemistry of metals and carbon nanotubes, two major transfer/assembling processes have been developed: molecular bonding and metal bonding. Effective improvement of the interfacial thermal transport has been achieved by the interfacial bonding. 4. The thermal diffusivity of vertically aligned carbon nanotube (VACNT, multi-walled) films was measured by a laser flash technique, and shown to be ~30 mm² s⁻¹ along the tube-alignment direction. The calculated thermal conductivities of the VACNT film and the individual CNTs are ~27 and ~540 W m⁻¹ K⁻¹, respectively. The technique was verified to be reliable although a proper sampling procedure is critical. A systematic parametric study of the effects of defects, buckling, tip-to-tip contacts, packing density, and tube-tube interaction on the thermal diffusivity was carried out. Defects and buckling decreased the thermal diffusivity dramatically. An increased packing density was beneficial in increasing the collective thermal conductivity of the VACNT film; however, the increased tube-tube interaction in dense VACNT films decreased the thermal conductivity of the individual CNTs. The tip-to-tip contact resistance was shown to be ~1×10⁻⁷ m² K W⁻¹. The study will shed light on the potential application of VACNTs as thermal interface materials in microelectronic packaging. 5. A combined process of in situ functionalization and microwave curing has been developed to effective enhance the interface between carbon nanotubes and the epoxy matrix. Effective medium theory has been used to analyze the interfacial thermal resistance between carbon nanotubes and polymer matrix, and that between graphite nanoplatlets and polymer matrix.PhDCommittee Chair: Wong, C. P.; Committee Member: Graham, Samuel; Committee Member: Hess, Dennis; Committee Member: Jacob, Karl; Committee Member: Wang, Z. L.; Committee Member: Yao, Don

Manufacture and Investigation of Organic Composite Polymer Based Films for Advanced Flexible Solar Cells

Modern society has created big challenges in the area of sustainable supply of energy to satisfy the needs of growing population and to account for depleting fossil fuel resources. The Irish Government has set targets for the energy sector by 2020, with 33% of electricity to be generated from renewable sources. Organic photovoltaic devices offer several advantages over expensive silicon solar cells, including deposition of ultra-thin films by spin-coating, printing and spray-coating. This in turn provides for the exciting possibility to make lightweight, flexible solar cells for a broad range of existing and emerging applications for security, military and medicine. This research project was inspired by the current drive into finding alternative technologies and materials for the design and manufacture of advanced solar cells. The primary objective was to tailor the properties of Poly3Hexylthiophene: PhenylC60 Buturic Acid Methyl Esther composite (P3HT:PCBM) thin films for flexible organic solar cells performance. The extensive experimental work was conducted to reveal the effect of the solar irradiation and thermal annealing on the dielectric, optical and electrical properties of P3HT:PCBM thin films. A common degradation pattern was demonstrated in the films after UV exposure whereby the optical absorbance and the resistivity were shown to be inversely proportionate. These two correlating techniques showed similar patterns after exposure. It was also shown that annealing the structure after deposition increased the absorbance in the thin film and the quantum efficiency of the final prototype device was related to film morphology. The dielectric properties of these films were studied using a novel microwave spectroscopy technique and it is believed to be the first report on the application of this novel technique to photovoltaic materials characterisation. To examine the dielectric properties of the P3HT:PCBM films using microwave spectroscopy, two types of Electro Magnetic (EM) wave sensors were fabricated, one on a Rogers substrate with Cu patterns and a second on a flexible substrate with Ag patterns. Both types of EM sensors exhibited shifts in resonant peak frequencies and amplitude during exposure to solar irradiation. All other experimental parameters and environmental conditions were kept constant. Therefore it is reasonable to conclude that the proposed method of microwave spectroscopy is a reliable tool to trace the changes in the properties of the materials caused by solar irradiation. The optical properties of the P3HT:PCBM films displayed a decrease in absorbance after 40mins solar simulator irradiation and then an increase in absorbance from 40 min to 20hrs. The electrical properties of P3HT:PCBM films showed a resistance decrease as the films were illuminated by a solar simulator from 0 to 40 min, and a subsequent increase in resistance up to 20hrs. In addition, a bespoke solar cell on flexible Polyethylene terephthalate (PET) was constructed and tested. It exhibited a fill factor and an efficiency of 0.3238 and 0.49% respectively. Although the performance is poor compared to reported state of the art for organic solar cells, the work demonstrates that operational devices can be manufactured under non-optimised laboratory conditions

The systematic development of Direct Write (DW) technology for the fabrication of printed antennas for the aerospace and defence industry

Low profile, conformal antennas have considerable advantages for Aerospace and Military platforms where conventional antenna system add weight and drag. Direct Write (DW) technology has been earmarked as a potential method for fabricating low profile antennas directly onto structural components. This thesis determines the key design rules and requirements for DW fabrication of planar antennas. From this, three key areas were investigated: the characterisation of DW ink materials for functionality and durability in harsh environments, localised processing of DW inks and the optimisation of DW conductive ink material properties for antenna fabrication. This study mainly focused on established DW technologies such as micro-nozzle and inkjet printing due to their ability to print on conformal surfaces. From initial characterisation studies it was found that silver based micro-nozzle PTF inks had greater adhesion then silver nano-particle inkjet inks but had lower conductivity (2% bulk conductivity of silver as opposed to 8% bulk conductivity). At higher curing temperatures (>300°C) inkjet inks were able to achieve conductivities of 33% bulk conductivity of silver. However, these temperatures were not suitable for processing on temperature sensitive surfaces such as carbon fibre. Durability tests showed that silver PTF inks were able to withstand standard aerospace environments apart from Skydrol immersion. It was found that DW inks should achieve a minimum conductivity of 30% bulk silver to reduce antenna and transmission line losses. Using a localised electroplating process (known as brush plating) it was shown that a copper layer could be deposited onto silver inkjet inks and thermoplastic PTF inks with a copper layer exhibiting a bulk conductivity of 66% bulk copper and 57% bulk copper respectively. This was an improvement on previous electroless plating techniques which reported bulk copper conductivities of 50% whilst also enabling DW inks to be plated without the need for a chemical bath. One of the limitations of many DW ink materials is they require curing or sintering before they become functional. Conventional heat treatment is performed using an oven which is not suitable when processing DW materials onto large structural component. Previous literature has investigated laser curing as means of overcoming this problem. However, lasers are monochromatic and can therefore be inefficient when curing materials that have absorption bands that differ from the laser wavelength. To investigate this, a laser diode system was compared to a broadband spot curing system. In the curing trials it was found that silver inks could be cured with much lower energy density (by a factor of 10) using the broadband white light source. Spectroscopy also revealed that broadband curing could be more advantageous when curing DW dielectric ink materials as these inks absorb at multiple wavelengths but have low heat conductivity. Themodynamical modelling of the curing process with the broadband heat source was also performed. Using this model it was shown that the parameters required to cure the ink with the broadband heat source only caused heat penetration by a few hundred micro-metres into the top surface of the substrate at very short exposure times (~1s). This suggested that this curing method could be used to process the DW inks on temperature sensitive materials without causing any significant damage. Using a combination of the developments made in this thesis the RF properties of the DW inks were measured after broadband curing and copper plating. It was found that the copper plated DW ink tracks gave an equivalent transmission line loss to a copper etched line. To test this further a number of GPS patch antennas were fabricated out of the DW ink materials. Again the copper plated antenna gave similar properties to the copper etched antenna. To demonstrate the printing capabilities of the micro-nozzle system a mock wireless telecommunications antenna was fabricated on to a GRP UAV wing. In this demonstrator a dielectric and conductive antenna pattern was fabricated on to the leading edge of the wing component using a combination of convection curing and laser curing (using an 808nm diode laser)

Electromagnetic Energy Coupled to Nanomaterial Composites for Polymer Manufacturing

Polymer nano-composites may be engineered with specific electrical properties to achieve good coupling with electromagnetic energy sources. This enables a wide range of novel processing techniques where controlling the precise thermal profile is critical. Composite materials were characterized with a variety of electrical and thermographic analysis methods to capture their response to electromagnetic energy. COMSOL finite element analysis software was used to model the electric fields and resultant thermal profiles in selected samples. Applications of this technology are demonstrated, including the use of microwave and radio frequency energy to thermally weld the interfaces of 3D printed parts together for increased interlayer (Z) strength. We also demonstrate the ability to bond various substrates with carbon nanotube/epoxy composite adhesives using radio frequency electromagnetic heating to rapidly cure the adhesive interface. The results of this work include 3D printed parts with mechanical properties equal to injection molded samples, and RF bonded joints cured 40% faster than traditional oven curing

ADHESION ENHANCEMENT OF DIAMOND AND DIAMOND-LIKE CARBON THIN FILMS ON TITANIUM ALLOY

Titanium (Ti) and its alloys have been widely used in aerospace, biomedical, chemical processing, marine facilities, and sports equipment because of their low density, very high tensile strength and toughness, and high corrosion resistance. However, the poor tribological properties has been a major problem and limited their widespread applications. Deposition of wear/corrosion resistant diamond-like carbon (DLC) coatings on Ti alloys is promising to significantly enhance the durability and service performances of these materials. However, the adhesion between DLC coatings and Ti alloy substrates is too weak to meet the application requirements. Up to now, approaches including optimization of deposition conditions, surface treatment of the substrate, deposition of an interlayer, and incorporation of metallic or nonmetallic elements have been used for adhesion enhancement of DLC on Ti alloys. In this research, a new method, nanodiamond particles incorporation, was developed for adhesion enhancement of DLC coatings on Ti alloys. In order to achieve high diamond nucleation without damaging the Ti alloy, nucleation enhancement of diamond on Ti alloys by nanodiamond seeding, tungsten (W) interlayers, and high methane concentration were studied. Diamond, DLC and W deposition were carried out by microwave assisted chemical vapor deposition, direct ion beam deposition and hot filament assisted chemical vapor deposition, respectively. Scanning electron microscopy, Atomic force microscopy, X-ray diffraction, Raman spectroscopy and synchrotron-based near edge extended X-ray absorption fine structure spectroscopy were used to characterize the microstructure and chemical bonding of the as-deposited particles and films, and indentation testing was used to evaluate the adhesion of the as-deposited coatings. By nanodiamond seeding or applying a W interlayer, significantly enhanced diamond nucleation has been obtained on Ti alloys, and consequently high quality nanocrystalline diamond thin films have been obtained on Ti alloys at decreased deposition temperature and reduced deposition time, which mitigates the deterioration of Ti alloy substrates due to hydrogen diffusion during diamond deposition and also enhances the adhesion of diamond on Ti alloys. Based on these results, nanodiamond particles (NDP) with high nucleation density and high adhesion were deposited on Ti alloys initially to enhance the adhesion of DLC films on Ti alloys. Results show that the pre-deposited NDP can significantly increase the adhesion of DLC on Ti6Al4V, probably due to the increased interfacial bonding, mechanical interlocking, and stress relief by the incorporation of NDP into DLC to form NDP/DLC composite films

Conducting metal oxide materials for printed electronics

Printed electronics as a manufacturing process has many advantages, mainly, it allows for the high throughput rapid fabrication of thin, flexible electronic components with minimal waste. There are many printing processes that can be utilised for printing electronics and although each process can differ vastly, the materials currently used in these processes are generally the same, silver and carbon. However, to develop printing as a more mainstream manufacturing method for electronics, a wider variety of materials are required which can provide better stability and longevity of components, new functionality for printed applications and allow for in-situ processing and tuning of components. Conducting metal oxides are a good candidate for integrating into printed electronics processes, these materials are typically semiconductors, they have bandgaps, and properties can be altered via altering the band gap. They are also oxides, so they cannot oxidise further and therefore atmospheric damage is reduced compared to pure metals. They can also be fabricated into a wide range of particle morphologies, all with advantages in different fields and electronic applications. Therefore, the ability to print these materials is valuable to the field. In this thesis, the integration of conducting metal oxide electro-ceramic materials into the field of printed electronics has been explored. This was performed through the completion of five research objectives including, the selection of appropriate materials for the research, the formulation of conductive inks with the materials, the investigation of post-processing techniques for printed films and further research into passive component fabrication and sensor applications. Firstly, following an extensive literature review, four materials were selected including three doped zinc oxide materials synthesised via different methods. The fourth material is commercially sourced indium tin oxide (ITO). A nitrocellulose vehicle was determined to be the most compatible with the oxides and selected for ink formulation. Inks were then formulated with all four materials, with optical and electrical properties analysed. Gallium doped Zinc Oxide (GZO) and ITO were selected for further investigation based on the excellent conductivity of the indium tin oxide (57.77Ω□-1) and the highly transparent optical properties of the gallium doped zinc oxide (>84% transmittance). Laser processing was selected as a post processing method. It was found that the laser processing dramatically increased conductivity. The GZO improving from a non-conductive film to 10.21% of bulk conductivity. The ITO improved from 3.46% to 40.47% of the bulk conductivity. It was also found that the laser processing invoked a carbothermal reduction process allowing for a rapid manufacturing process for converting spherical particles into useful nanoparticle morphologies (nanorods, nanowires etc). Following this, resistive and capacitive applications involving laser processing and conventionally heat-treated conductive oxide inks were developed. Combining the new materials and manufacturing processes, tuneable printed resistors with a tuning range of 50 to 20M could be fabricated. All metal oxide, ITO based capacitors were also fabricated and characterised. These were then developed into humidity sensors which provided excellent humidity sensing properties, showing linearity between 5 and 95% relative humidity (RH) and sensitivities of up to 7.76pF/RH%, demonstrating higher performance than commercial equivalents (0.2 – 0.5pF/RH%). In conclusion, this work provides a breakthrough for conductive metal oxide materials research and its place in Printed Electronics research by providing insight into the processes required to make these materials conduct and by developing useful manufacturing methods, post processing techniques and applications.</div