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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.

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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS2014

A Novel Instrument and Methodology for the In-Situ Measurement of the Stress in Thin Films

We introduce a novel methodology for the in-situ measurement of mechanical stress during thin film growth utilizing a highly sensitive non-contact variation of the classic spherometer. By exploiting the known spherical deformation of the substrate the value of the stress induced curvature is inferred by measurement of only one point on the substrate's surface-the sagittal. From the known curvature the stress can be calculated using the well-known Stoney equation. Based on this methodology, a stress sensor has been designed which is simple, highly sensitive, compact, and low cost. As a result of its compact nature, the sensor can be mounted in any orientation to accommodate a given deposition geometry without the need for extensive modification to an already existing deposition system. The technique employs the use of a double side polished substrate that offers good specular reflectivity and is isotropic in its mechanical properties, such as <111> oriented crystalline silicon or amorphous soda lime glass, for example. The measurement of the displacement of the uncoated side during deposition is performed with a high resolution (i.e. 5nm), commercially available, inexpensive, fiber optic sensor which can be used in both high vacuum and high temperature environments (i.e. 10(exp-7) Torr and 480oC, respectively). A key attribute of this instrument lies in its potential to achieve sensitivity that rivals other measurement techniques such as the micro cantilever method but, due to the comparatively larger substrate area, offers a more robust and practical alternative for subsequent measurement of additional characteristics of the film that can might be correlated to film stress. We present measurement results of nickel films deposited by magnetron sputtering which show good qualitative agreement to the know behavior of polycrystalline films previously reported by Hoffman.

Broadway, David M.↗
NASA NTRS1980

Tribological properties of sputtered MoS2 films in relation to film morphology

Thin sputter-deposited MoS2 films with thicknesses ranging from 2000 to 6000 A have shown excellent lubricating properties when sputtering parameters and substrate conditions are properly selected and controlled. The lubricating properties are strongly influenced by the crystalline-amorphous structure, morphology, and composition of the films. The coefficient of friction can range from 0.04 (which is effective lubrication) to 0.4 (no lubricating action).

Spalvins, T.↗
NASA NTRS1985

Optical properties of hydrogenated amorphous carbon films grown from methane plasma

A 30 kHz ac glow discharge formed from methane gas was used to grow carbon films on InP substrates. Both the growth rate, and the realitive Ar ion sputtering rate at 3 keV varied monotonically with deposition power. Results from the N-15 nuclear reaction profile experiments indicated a slight drop in the hydrogen concentration as more energy was dissipated in the ac discharge. Values for the index of refraction and extinction coefficient ranged from 1.721 to 1.910 and 0 to -0.188, respectively. Optical bandgaps as high as 2.34 eV were determined.

Pouch, J. J.↗
NASA NTRSDate not supplied

The PCM is Dead! Long Live O-PCM!

The ability to reconfigure the optical behavior of a device enables free-space applications ranging from imaging to sensing and signal control. Such optical devices can be compacted via meta-surfaces, patterned structures with feature sizes below the incident wavelength. Leveraging geometry in addition to material properties and CMOS fabrication techniques has allowed meta-surfaces for lenses, holograms, beam steerers and more. To incorporate multiple optical functions into one device, various methods of device control have been implemented, such as stretching of flexible substrates, tuning the refractive index of the comprising meta-atoms via the electro-optic or the thermo-optic effects, phase transition materials such as VO2 and more. Chalcogenide glasses used as optical phase change materials, such as Ge¬2Sb2Te5 (GST), have gained increased traction in the optics community for potential use in the near infrared (NIR) and mid infrared (MIR) bands, including the telecom bands. Various chalcogenides such as Sb2Se3, Sb2S3, Ge2Sb¬2Se5 and Ge2Sb2Se4Te (GSST) have been investigated due to their broad NIR or MIR transparency window and large changes in refractive index. In their amorphous phase, these materials usually display a lower refractive index and low absorption when compared to their crystalline state which display a higher refractive index and typically larger extinction coefficients. The amorphous-crystalline reversible switching can be done via fast melt-quenching thermal processes triggered by laser or electrical impulses, relying on a substrate as a heat sink. The potential of PCMs in photonic devices can be limited by intrinsic material limitations as well as by device fabrication issues. To explore the cyclability of GSST, a PCM with large refractive index contrast and on-chip electrothermal switching on a silicon-on-insulator platform has been done to analyze potential failure mechanisms from both a material and device perspective. A brief outline of the instrumentation and phase change contrast analysis is provided. Dewetting of the PCM, delamination of and damage in the PECVD SiNx protective layer, elemental migration in the PCM and optical contrast decay have been observed in cycled GSST devices. Guidelines for device performance improvement are proposed, and an improved design with larger endurance is shown in progress.

reconfigurable photonics↗
NASA NTRS1972

Investigation of phase-change coatings for variable thermal control of spacecraft

An investigation was conducted to determine the feasibility of producing a spacecraft coating system that could vary the ratio of its solar absorptance to thermal emittance to adjust automatically for changes in the thermal balance of a spacecraft. This study resulted in a new concept called the phase-change effect which uses the change that occurs in the optical properties of many materials during the phase transition from a crystalline solid to an amorphous material. A series of two-component model coatings was developed which, when placed on a highly reflecting substrate, exhibited a sharp decrease in solar absorptance within a narrow temperature range. A variable thermal control coating can have a significant amount of temperature regulation with the phase-change effect. Data are presented on several crystallite-polymer formulations, their physical and optical properties, and associated phase-change temperatures. Aspects pertaining to their use in a space environment and an example of the degree of thermal regulation attainable with these coatings is also given.

Kelliher, W. C.↗
NASA NTRS2003

Elastic Properties of Films of Water and Noble Gases Condensed at Low Temperatures

We have shown that there are extensive similarities between the quench-condensed noble gas films and those of amorphous water ice. In particular, both can be quite soft upon deposition and can stiffen considerably when annealed. Furthermore, this stiffening follows a logarithmic time dependence for all substances. The temperature dependence of these behaviors scales with the triple point. The results shown here show a strong thickness dependence, which has implications for any study of mechanical properties of films on substrates. The temperature dependence of the stiffening and the stiffening rate have now been characterized for the noble gases, and these observations provide a roadmap for new experiments on amorphous water ice.

Pohl, Robert O.↗
NASA NTRS1975

Morphological growth of sputtered MoS2 films

Sputtered MoS2 films from 300 A to 20,000 A thick were deposited on metal and glass surfaces. The substrate effects such as surface temperature, finish, pretreatment and chemistry as they affect the film formation characteristics were investigated by optical, electron transmission, electron diffraction, and scanning electron microscopy. Substrate temperature and surface chemistry were found to be the prime variables as to the formation of a crystalline or amorphous film. The friction characteristics are strictly influenced by the type of film formed. Surface chemistry and surface pretreatment account for compound formation and corresponding grain growth, which directly affect the adhesion characteristics, resulting in poor adherence. The type of surface finish (topography) as related to scratches, impurities, inhomogeneities, etc., are favorable nucleation sites for the growth of isolated and complex nodules within the film, and various complex surface overgrowths on the film. These nodular growth features have progressively more undesirable effects on the film behavior as the film thickness increases.

Spalvins, T.↗
NASA NTRS1975

Morphological growth of sputtered MoS2 films

Sputtered MoS2 films from 300 A to 20,000 A thick were deposited on metal and glass surfaces. The substrate effects such as surface temperature, finish, pretreatment, and chemistry as they affect the film formation characteristics were investigated by optical, electron transmission, electron diffraction, and scanning electron microscopy. Substrate temperature and surface chemistry were found to be the prime variables as to the formation of a crystalline or amorphous film. The friction characteristics are strictly influenced by the type of film formed. Surface chemistry and surface pretreatment account for compound formation and corresponding grain growth, which directly affect the adhesion characteristics, resulting in poor adherence. Scratches, impurities, inhomogeneities, etc., are favorable nucleation sites for the growth of isolated and complex nodules within the film.

Spalvins, T.↗
NASA NTRS1984

Metallic glass as a temperature sensor during ion plating

The temperature of the interface and/or a superficial layer of a substrate during ion plating was investigated using a metallic glass of the composition Fe67Co18B14Si1 as the substrate and as the temperature sensor. Transmission electron microscopy and diffraction studies determined the microstructure of the ion-plated gold film and the substrate. Results indicate that crystallization occurs not only in the film, but also in the substrate. The grain size of crystals formed during ion plating was 6 to 60 nm in the gold film and 8 to 100 nm in the substrate at a depth of 10 to 15 micrometers from the ion-plated interface. The temperature rise of the substrate during ion plating was approximately 500 C. Discontinuous changes in metallurgical microstructure, and physical, chemical, and mechanical properties during the amorphous to crystalline transition in metallic glasses make metallic glasses extremely useful materials for temperature sensor applications in coating processes.

Miyoshi, K.↗
NASA NTRS1985

Metallic glass as a temperature sensor during ion plating

The temperature of the interface and/or a superficial layer of a substrate during ion plating was investigated using a metallic glass of the composition Fe67Co18B14Si1 as the substrate and as the temperature sensor. Transmission electron microscopy and diffraction studies determined the microstructure of the ion-plated gold film and the substrate. Results indicate that crystallization occurs not only in the film, but also in the substrate. The grain size of crystals formed during ion plating was 6 to 60 nm in the gold film and 8 to 100 nm in the substrate at a depth of 10 to 15 micrometers from the ion-plated interface. The temperature rise of the substrate during ion plating was approximately 500 C. Discontinuous changes in metallurgical microstructure, and physical, chemical, and mechanical properties during the amorphous to crystalline transition in metallic glasses make metallic glasses extremely useful materials for temperature sensor applications in coating processes.

Miyoshi, K.↗
NASA NTRS2006

New Optical Constants for Amorphous and Crystalline H2O-ice and H2O-mixtures.

We will present the products of new laboratory measurements of ices relevant to Trans-Neptunian Objects. We have calculated the real and imaginary indices of refraction for amorphous and crystalline H2O-ice and also H2O-rich ices containing other molecular species. We create ice samples by condensing gases onto a cold substrate. We measure the thickness of the sample by reflecting a He-Ne laser off of the sample and counting interference fringes as it grows. We then collect transmission spectra of the samples in the wavelength range from 0.7-22 micrometers. Using the thickness and the transmission spectra of the ice we calculate the imaginary part of the index of refraction. We then use a Kramers-Kronig calculation to calculate the real part of the index of refraction (Berland et al. 1994; Hudgins et al. 1993). These optical constants can then be used to create model spectra for comparison to spectra from Solar System objects, including TNOs. We will summarize the difference between the amorphous and crystalline H2O-ice spectra. These changes include weakening of features and shifting of features to shorter wavelength. One important result is that the 2 pm feature is stronger in amorphous H2O ice than it is in crystalline H2O-ice. We will also discuss the changes seen when H2O is mixed with other components, including CO2, CH4, HCN, and NH3 (Bernstein et al. 2005; Bernstein et al. 2006).

Mastrapa, Rachel↗
NASA NTRS1980

Tribological properties of sputtered MoS sub 2 films in relation to film morphology

Thin sputter deposited MoS2 films in the 2000 to 6000 A thickness range have shown excellent lubricating properties, when sputtering parameters and substrate conditions are properly selected and precisely controlled. The lubricating properties of sputtered MoS2 films are strongly influenced by their crystalline-amorphous structure, morphology and composition. The coefficient of friction can range from 0.04 which is effective lubrication to 0.4 which reflects an absence of lubricating properties. Visual screening and slight wiping of the as-sputtered MoS2 film can identify the integrity of the film. An acceptable film displays a black-sooty surface appearance whereas an unacceptable film has a highly reflective, gray surface and the film is hard and brittle.

Spalvins, T.↗
NASA NTRS1979

Development of RF sputtered chromium oxide coating for wear application

The radio frequency sputtering technique was used to deposite a hard refractory, chromium oxide coating on an Inconel X-750 foil 0.1 mm thick. Optimized sputtering parameters for a smooth and adherent coating were found to be as follows: target-to-substrate spacing, 41.3 mm; argon pressure, 5-10 mTorr; total power to the sputtering module, 400 W (voltage at the target, 1600 V), and a water-cooled substrate. The coating on the annealed foil was more adherent than that on the heat-treated foil. Substrate biasing during the sputter deposition of Cr2O3 adversely affected adherence by removing naturally occurring interfacial oxide layers. The deposited coatings were amorphous and oxygen deficient. Since amorphous materials are extremely hard, the structure was considered to be desirable.

Bhushan, B.↗
NASA NTRS1998

Photonic and Opto-Electronic Applications of Polydiacetylene Films Photodeposited from Solution and Polydiacetylene Copolymer Networks

Polydiacetylenes (PDAS) are attractive materials for both electronic and photonic applications because of their highly conjugated electronic structures. They have been investigated for applications as both one-dimensional (linear chain) conductors and nonlinear optical (NLO) materials. One of the chief limitations to the use of PDAs has been the inability to readily process them into useful forms such as films and fibers. In our laboratory we have developed a novel process for obtaining amorphous films of a PDA derived from 2-methyl4-nitroaniline using photodeposition with Ultraviolet (UV) light from monomer solutions onto transparent substrates. Photodeposition from solution provides a simple technique for obtaining PDA films in any desired pattern with good optical quality. This technique has been used to produce PDA films that show potential for optical applications such as holographic memory storage and optical limiting, as well as third-order NLO applications such as all-optical refractive index modulation, phase modulation and switching. Additionally, copolymerization of diacetylenes with other monomers such as methacrylates provides a means to obtain materials with good processibility. Such copolymers can be spin cast to form films, or drawn by either melt or solution extrusion into fibers. These films or fibers can then be irradiated with UV to photopolymerize the diacetylene units to form a highly stable cross-linked PDA-copolymer network. If such films are electrically poled while being irradiated, they can achieve the asymmetry necessary for second-order NLO applications such as electro-optic switching. On Earth, formation of PDAs by the above mentioned techniques suffers from defects and inhomogeneities caused by convective flows that can arise during processing. By studying the formation of these materials in the reduced-convection, diffusion-controlled environment of space we hope to better understand the factors that affect their processing, and thereby, their nature and properties. Ultimately it may even be feasible to conduct space processing of PDAs for technological applications.

Paley, Mark S.↗
NASA NTRS2002

Space and Terrestrial Photovoltaics: Synergy and Diversity

A historical view of the research and development in photovoltaics from the perspective of both the terrestrial and the space communities is presented from the early days through the '70s and '80s and the '90s and beyond. The synergy of both communities in the beginning and once again in the present and hopefully future are highlighted, with examples of the important features in each program. The space community which was impressed by the light-weight and reliability of photovoltaics drove much of the early development. Even up to today, nearly every satellites and other scientific space probe that has been launched has included some solar power. However, since the cost of these power systems were only a small fraction of the satellite and launch cost, the use of much of this technology for the terrestrial marketplace was not feasible. It was clear that the focus of the terrestrial community would be best served by reducing costs. This would include addressing a variety of manufacturing issues and raising the rate of production. Success in these programs and a resulting globalization of effort resulted in major strides in the reduction of PV module costs and increased production. Although, the space community derived benefit from some of these advancements, its focus was on pushing the envelope with regard to cell efficiency. The gap between theoretical efficiencies and experimental efficiencies for silicon, gallium arsenide and indium phosphide became almost non-existent. Recent work by both communities have focused on the development thin film cells of amorphous silicon, CuInSe2 and CdTe. These cells hold the promise of lower costs for the terrestrial community as well as possible flexible substrates, better radiation resistance, and higher specific power for the space community. It is predicted that future trends in both communities will be directed toward advances through the application of nanotechnology. A picture is emerging in which the space and terrestrial solar cell communities shall once again share many common goals and, in fact, companies may manufacture both space and terrestrial solar cells in III-V materials and thin film materials. Basic photovoltaics research including these current trends in nanotechnology provides a valuable service for both worlds in that fundamental understanding of cell processes is still vitally important, particularly with new materials or new cell structures. It is entirely possible that one day we might have one solar array design that will meet the criteria for success in both space and on the Earth or perhaps the Moon or Mars.

Bailey, Sheila↗
NASA NTRS1985

'Diamondlike' carbon films - Optical absorption, dielectric properties, and hardness dependence on deposition parameters

An RF plasma deposition system was used to prepare amorphous 'diamondlike' carbon films. The source gases for the RF system include methane, ethylene, propane, and propylene, and the parameters varied were power, dc substrate bias, and postdeposition anneal temperature. Films were deposited on various substrates. The main diagnostics were optical absorption in the visible and in the infrared, admittance as a function of frequency, hardness, and Auger and ESCA spectroscopy. Band gap is found to depend strongly on RF power level and band gaps up to 2.7 eV and hardness up to 7 Mohs were found. There appears to be an inverse relationship between hardness and optical band gap.

Natarajan, V.↗
NASA NTRS2001

Band-gap Engineering in Sputter Deposited Amorphous/Microcrystalline Sc(x)Ga(1-x)N

Reactive sputtering was used to grow thin films of Sc(x)Ga(1-x)N with scandium concentrations of 20%-70% on quartz substrates at temperatures of 300-675 K. X-ray diffraction (XRD) of the films showed either weak or no structure, suggesting the films are amorphous or microcrystalline. Optical absorption spectra were taken of each sample and the optical band gap was determined. The band gap varied linearly with increasing Ga concentration between 2.0 and 3.5 eV. Ellipsometry was used to confirm the band gap measurements and provide optical constants in the range 250-1200 nm. ScN and GaN have different crystal structures (rocksalt and wurzite, respectively), and thus may form a heterogeneous mixture as opposed to an alloy. Since the XRD data were inconclusive, bilayers of ScN/GaN were grown and optical absorption spectra taken. A fundamental difference in the spectra between the bilayer films and alloy films was seen, suggesting the films are alloys, not heterogeneous mixtures.

Little, Mark E.↗