SEARCH · Search NASA
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Past and present planetary exploration is briefly reviewed, and the planned 1996 Cassini mission to Saturn and Titan is examined. The CIRS experiment aboard Cassini, which will retrieve information on the atmospheres of Titan and Saturn, is discussed. Ongoing efforts to build a high-sensitivity, high-Tc bolometer that would greatly improve detection in Titan's atmosphere are addressed.
This publication is comprised of abstracts for oral and poster presentations scheduled for AMSAHTS '90. The conference focused on understanding high temperature superconductivity with special emphasis on materials issues and applications. AMSAHTS 90, highlighted the state of the art in fundamental understanding of the nature of high-Tc superconductivity (HTSC) as well as the chemistry, structure, properties, processing and stability of HTSC oxides. As a special feature of the conference, space applications of HTSC were discussed by NASA and Navy specialists.
It has been proposed that the Abrikosov flux lattice in high-Tc superconductors is melted over a significant fraction of the phase diagram. A thermodynamic argument is provided which establishes that the angular dependence of the melting temperature is controlled by the superconducting mass anisotropy. Using a low-frequency torsional-oscillator technique, this relationship has been tested in untwinned single-crystal YBa2Cu3O(7-delta). The results offer decisive support for the melting proposal.
An approach to the application of high-Tc ceramic superconductors to practical circuit elements was developed and demonstrated. This method, known as the rigid conductor process (RCP), involves the mounting of a preformed, sintered, and tested superconductor material onto an appropriate, rigid substrate with an epoxy adhesive which also serves to encapsulate the element from the ambient environment. Circuit elements such as straight conductors, coils and connectors were fabricated from YBa2Cu3O(7-x) superconducting material. Performance results are included for a low-noise low-thermal-conductivity superconducting grounding link for NASA.
An infrared detector called the magnetic susceptibility bolometer is introduced which is based on the tmperature dependence of the diamagnetic screening of a high-Tc superconductor film near Tc. Results are reported for the response of a prototype model to modulated blackbody radiation. Possible improvements are discussed as is the potential sensitivity of an improved device.
The paper describes the processing and electrical transport measurements for achieving reproducible high-Tc and high-Jc sputtered TlCaBaCuO thin films on LaAlO3 substrates, for microelectronic applications. The microwave properties of TlCaBaCuO thin films were investigated by designing, fabricating, and characterizing microstrip ring resonators with a fundamental resonance frequency of 12 GHz on 10-mil-thick LaAlO3 substrates. Typical unloaded quality factors for a ring resonator with a superconducting ground plane of 0.3 micron-thickness and a gold ground plane of 1-micron-thickness were above 1500 at 65 K. Typical values of penetration depth at 0 K in the TlCaBaCuO thin films were between 7000 and 8000 A.
Recent developments in X-ray and hard X-ray imaging detector, high-intensity sources, hard X-ray imaging optics, calibration, and detection technologies are discussed. Particular attention is given to a high-MTF X-ray image intensifier, application of monolithic CdZnTe linear solid state ionization detectors for X-ray imaging, magnetic response of high-Tc superconductors to X-ray radiation and detection of X-rays, laboratory soft X-ray source with foil target, detection of explosive materials using nuclear radiation, energy response of astronomical CCD X-ray detectors, calibration techniques for high-flux X-ray detectors, fabrication of grazing-incidence optics using flow-polishing techniques, and numerical simulations for capillary-based X-ray optics. (No individual items are abstracted in this volume)
Devices offer switching speeds greater than semiconducting counterparts. High-Tc superconducting field-effect transistors (SUPEFETs) investigated for use as electronic switches in delay-line-type microwave phase shifters. Resemble semiconductor field-effect transistors in some respects, but their operation based on different principle; namely, electric-field control of transition between superconductivity and normal conductivity.
A status report based on the applied high temperature superconductivity (HTS) research at Materials Research Laboratories (MRL), Industrial Technology Research Institute (ITRI) is given. The aim is to develop fabrication technologies for the high-TC materials appropriate to the industrial application requirements. To date, the majorities of works have been undertaken in the areas of new materials, wires/tapes with long length, prototypes of magnets, large-area thin films, SQUID's and microwave applications.
Mossbauer research using the 21.54 kev resonance radiation of Eu-151 on the high temperature superconductors Bi(2)Ca(0.5)Eu(0.5)Sr(2)CU2O(x), and EuBa(2)CU(3)O(7-x) is performed. For the Bismuth compound the Mossbauer measurements gave a weak signal at room temperature but improved at lower temperatures. Experimental data indicated that europium is located at only one crystallographic site. Isomer shift measurements were .69 + 0.02 mm/s with respect to EuF(3). The linewidth at room temperature was found to be 2.54 mm/s. This value falls within the values observed by other researchers on Eu based 1,2,3 high-Tc compounds. Our results also show the Eu to be trivalent with no trace of divalent europium present. Superconducting europium based 1,2,3 compounds were prepared and measurements completed. Our results show the Eu to be trivalent with no trace of divalent europium present. These compounds had an average isomer shift of .73 mm/s +/- O.02 for all samples made. One of these was irradiated with 3.5 X 10(exp 16) neutrons and a comparison made of the Mossbauer parameters for the irradiated and non-irradiated samples. Experimental results showed no difference between linewidths but a measurable effect was seen for the isomer shift.
A multi-axis accelerometer which utilizes a magnetically-suspended, high-TC proof mass is under development. The design and performance of a single axis device which is stabilized actively in the axial direction but which utilizes ring magnets for passive radial stabilization is discussed. The design of a full six degree-of-freedom device version is also described.
In 1959, during a famous lecture entitled "There's Plenty of Room at the Bottom", Richard Feynman focused on the startling technical possibilities that would exist at the limit of miniaturization, that being atomically precise devices with dimensions in the nanometer range. A nanometer is both a convenient unit of length for medium to large sized molecules, and the root of the name of the new interdisciplinary field of "nanotechnology". Essentially, "nanoelectronics" denotes the goal of shrinking electronic devices, such as diodes and transistors, as well as integrated circuits of such devices that can perform logical operations, down to dimensions in the range of 100 nanometers. The thirty-year hiatus in the development of nanotechnology can figuratively be seen as a period of waiting for the bottom-up and atomically precise construction skills of synthetic chemistry to meet the top-down reductionist aspirations of device physics. The sub-nanometer domain of nineteenth-century classical chemistry has steadily grown, and state-of-the-art supramolecular chemistry can achieve atomic precision in non-repeating molecular assemblies of the size desired for nanotechnology. For nanoelectronics in particular, a basic understanding of the electron transport properties of molecules must also be developed. Quantum chemistry provides powerful computational methods that can accurately predict the properties of small to medium sized molecules on a desktop workstation, and those of large molecules if one has access to a supercomputer. Of the many properties of a molecule that quantum chemistry routinely predicts, the ability to carry a current is one that had not even been considered until recently. "Currently", there is a controversy over just how to define this key property. Reminiscent of the situation in high-Tc superconductivity, much of the difficulty arises from the different models that are used to simplify the complex electronic structure of real materials. A model-independent approach has been proposed, that sacrifices the plentiful molecular orbitals and Bloch functions of conventional approaches, for a single three-dimensional observable quantity, the electron momentum density Pi(sub rho). This quantity is simply the probability of any electron having momentum rho, multiplied by the total number of electrons in the system (the position of the electron is uncertain). We have explored the utility of this new approach in providing a fundamental understanding of the electron transport properties of molecules that have provi been nominated as candidates for components in the design of nanoelectronics; phenylene-ethynylene oligomers. Some of the molecular systems that have been studied are sketched below.
As a Bose condensate, superconductors provide novel conditions for revisiting previously proposed couplings between electromagnetism and gravity. Strong variations in Cooper pair electron density, large conductivity and low magnetic permeability define superconductive and degenerate condensates without the traditional density limits imposed by the Fermi energy (about 10-6 g/cu cm). Recent experiments have reported anomalous weight loss for a test mass suspended above a rotating Type II, YBCO superconductor, with the percentage change (0.05-2.1%) independent of the test mass' chemical composition and diamagnetic properties. A variation of 5 parts per 10(exp 4) was reported above a stationary (non-rotating) superconductor. In the present experiments reported using a sensitive gravimeter (resolution <10(exp -9) unit gravity or variation of 10(exp -6) cm/sq s in accelerations), bulk YBCO superconductors were stably levitated in a DC magnetic field (0.6 Tesla) subject to lateral AC fields (60 Gauss at 60 Hz) and rotation. With magnetic shielding, thermal control and buoyancy compensation, changes in acceleration were measured to be less than 2 parts in 10(exp 8) of the normal gravitational acceleration. This result puts new limits on the strength and range of the proposed coupling between high-Tc superconductors and gravity. Latest test results will be reported, along with status for future improvements and prospects.
High temperature superconductors(HTS) and microwaves devices form the ideal partnership. The application of superconductors in microwave devices, components and systems allows the reduction in size, power consumption and insertion loss. The surface resistance of high-Tc superconductors has been found to be two orders of magnitude lower than normal conducting copper materials. The reduction in size and power requirements, which together both lead to a reduction in system mass, coupled with reasonably accessible operating temperatures, suggest that HTS microwave components should find ready application in satellite communications systems. At present, multi- channeling communication networks demand filters with narrow bandwidth in order to allow the available RF frequency spectrum to be partitioned into small frequency bands, -and possible variation of dielectric constant from substrate to substrate is undesirable. Microwave multiplexers demand the fabrication of two identical filters in each channel. Thus, the filter with tuning function is preferable. Tunable filters are the critical component for phased array antennas in order to electronically steer the radiated beam. To fabricate a tunable filter that uses an electric field for operation, one would like a material that provides a large change on dielectric constant for a given electric field, yet has a relatively low tangent in order to minimize the insertion loss of the device. Ferroelectrics have been the materials of choice. Their large dielectric constant sufficiently increases the coupling between microwave resonators and its dependence on electric field provides timability. Development of technology promises to diminish tangent loss. The use of thin ferroelectric films sufficiently decreases insertion losses keeping considerable potential for applications. NASA Lewis Research Center is the one of the leading centers in investigation of superconductors/ferroelectric tunable components for microwave devices. A large number of possible microwave devices were fabricated and tested on the basis of thin film multilayer superconductor-ferroelectric structures. In major cases the systems with edge-coupling scheme were investigated. Dr. Genkin has recently focused on the new potentialities which implements the using of thin ferroelectric films in filters fabricated with end-coupled microstrip lines. Numerical modeling shows that these systems have large potential for application in tunable narrow- and wide-bandpass filters in the frequency range 10-20 GHz. The phase shifter with end-coupled resonant sections was fabricated and tested. Experimental results show large tunability, particular in low voltages. The possible optimization of this structure promises to improve the obtained result and to reach the low level of insertion losses.
Scanning tunneling spectroscopy was performed at 4.2K on epitaxial thin-film heterostructures comprising YBa2Cu3O7 and La0.7Ca0.3MnO3, to study the microscopic effects of spin-polarized quasiparticle injection from the half-metallic ferromagnetic manganite on the high-Tc cuprate superconductor.
We report on the development of a scanning eddy-current imaging system designed to detect deep subsurface flaws in conducting materials. A high transition temperature (high-T c) superconducting quantum interference device (SQUID) magnetometer is employed to provide the required sensitivity at low frequencies, while a combination of small cylindrical high-Tc superconducting and A-metal shields enable the instrument to be scanned in a magnetically noisy environment, rather than the object under test. The shields are arranged to prevent unwanted excitation and ambient noise fields from reaching the SQUID, and to enhance spatial resolution and minimize undesirable edge effects. Thus far, the instrument has successfully detected cracks and pits through 10 layers of aluminum, with a combined thickness of 5 cm at room temperature.
Quantum devices require coherent coupling over macroscopic distances. Recently, resonances due to Klein tunneling and Andreev reflection states (KARS) have been observed in a naturally occurring p-n junction at the interface between Bi 2 Sr 2 CaCu 2 O 8+𝑥 (BSCCO), a high−𝑇 c superconductor (HTS), and graphene. The resonances appear as conductance oscillations with gating. Here, in this study, we show coupling between the KARS in BSCCO-graphene-BSCCO devices of varying separation (L). The coupling is evidenced by a power-law decay of resonance period as L increases from tens of nanometers to microns. These results demonstrate the long-distance coupling of KARS cavities in graphene-HTS junctions. The length dependence seen in experiments is supported by single-particle spectral functions which show KARS are coupled by transport modes in graphene. The strong coupling between KARS in BSCCO-graphene-BSCCO devices showcases the possibility of HTS-graphene junctions for quantum circuits and unconventional Josephson junctions.