Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “carbon films”

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.

At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Single-beam plasma source deposition of carbon thin films

A single-beam plasma source was developed and used to deposit hydrogenated amorphous carbon (a-C:H) thin films at room temperature. The plasma source was excited by a combined radio frequency and direct current power, which resulted in tunable ion energy over a wide range. The plasma source could effectively dissociate the source hydrocarbon gas and simultaneously emit an ion beam to interact with the deposited film. Using this plasma source and a mixture of argon and C 2 H 2 gas, a-C:H films were deposited at a rate of ~26 nm/min. The resulting a-C:H film of 1.2 µm thick was still highly transparent with a transmittance of over 90% in the infrared range and an optical bandgap of 2.04 eV. Young’s modulus of the a-C:H film was ~80 GPa. The combination of the low-temperature high-rate deposition of transparent a-C:H films with moderately high Young’s modulus makes the single-beam plasma source attractive for many coatings applications, especially in which heat-sensitive and soft materials are involved. Here, the single-beam plasma source can be configured into a linear structure, which could be used for large-area coatings.

14 SOLAR ENERGY↗
NASA NTRS2005

Optical and Thermo-optical Properties of Polyimide-Single-Walled Carbon Nanotube Films: Experimental Results and Empirical Equations

The incorporation of single-walled carbon nanotubes (SWNTs) into the bulk of space environmentally durable polymers at loading levels greater than or equal to 0.05 wt % has afforded thin films with surface and volume resistivities sufficient for electrostatic charge mitigation. However, the optical transparency at 500 nm decreased and the thermo-optical properties (solar absorptivity and thermal emissivity) increased with increaed SWNT loading. These properties were also dependent on film thickness. The absorbance characteristics of the films as a function of SWNT loading and film thickness were measured and determined to follow the classical Beer-Lambert law. Based on these results, an empirical relationship was derived and molar absorptivities determined for both the SWNTs and polymer matrix to provide a predictive approximation of these properties. The molar absorptivity determined for SWNTs dispersed in the polymer was comparable to reported solution determined values for HiPco SWNTs.

Smith, Joseph G., Jr.↗
DOE OSTI2020

Nano-engineering the material structure of preferentially oriented nano-graphitic carbon for making high-performance electrochemical micro-sensors

Direct synthesis of thin-film carbon nanomaterials on oxide-coated silicon substrates provides a viable pathway for building a dense array of miniaturized (micron-scale) electrochemical sensors with high performance. However, material synthesis generally involves many parameters, making material engineering based on trial and error highly inefficient. Here, we report a two-pronged strategy for producing engineered thin-film carbon nanomaterials that have a nano-graphitic structure. First, we introduce a variant of the metal-induced graphitization technique that generates micron-scale islands of nano-graphitic carbon materials directly on oxide-coated silicon substrates. A novel feature of our material synthesis is that, through substrate engineering, the orientation of graphitic planes within the film aligns preferentially with the silicon substrate. This feature allows us to use the Raman spectroscopy for quantifying structural properties of the sensor surface, where the electrochemical processes occur. Second, we find phenomenological models for predicting the amplitudes of the redox current and the sensor capacitance from the material structure, quantified by Raman. Our results indicate that the key to achieving high-performance micro-sensors from nano-graphitic carbon is to increase both the density of point defects and the size of the graphitic crystallites. Our study offers a viable strategy for building planar electrochemical micro-sensors with high-performance.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
NASA NTRS1976

The critical currents in superconducting tin films

The nonlinear current-voltage curves exhibited by tin films in the flux flow state have made studies of the amount of heating present in the sample necessary. The samples in this work consisted of an evaporated tin film on one side of a 2 mm thick crystal quartz substrate and a carbon film of the same configuration as the tin film on the back of the substrate. The carbon film was used as a thermometer to measure the temperature rise of the tin film above the bath temperature. The heating results indicate negligible effects in the samples. Temperature ratios as small as 0.80 for the tin samples have been investigated and the current-voltage characteristics are still nonlinear, indicating that the source of the nonlinearity is not Joule heating in the samples.

Payne, J. E.↗
NASA NTRS2000

Nano-crystalline porous tin oxide film for carbon monoxide sensing

A tin oxide sol is deposited on platinum electrodes (12) of a sensor (10). The sol is calcined at a temperature of 500 to 800.degree. C. to produce a thin film of tin oxide with a thickness of about 150 nm to 2 .mu. and having a nano-crystalline structure with good stability. The sensor rapidly detects reducing gases, such as carbon monoxide, or hydrocarbons and organic vapors. Sensors using films calcined at around 700.degree. C. have high carbon monoxide selectivity with a response time of around 4 minutes and a recovery time of 1 minute, and therefore provide good detection systems for detection of trace amounts of pollutants such as toxic and flammable gases in homes, industrial settings, and hospitals.

Liu, Chung-Chiun↗
NASA NTRS1981

Vapor phase diamond growth technology

Ion beam deposition chambers used for carbon film generation were designed and constructed. Features of the developed equipment include: (1) carbon ion energies down to approx. 50 eV; (2) in suit surface monitoring with HEED; (3) provision for flooding the surface with ultraviolet radiation; (4) infrared laser heating of substrate; (5) residual gas monitoring; (6) provision for several source gases, including diborane for doping studies; and (7) growth from either hydrocarbon source gases or from carbon/argon arc sources. Various analytical techniques for characterization of from carbon/argon arc sources. Various analytical techniques for characterization of the ion deposited carbon films used to establish the nature of the chemical bonding and crystallographic structure of the films are discussed. These include: H2204/HN03 etch; resistance measurements; hardness tests; Fourier transform infrared spectroscopy; scanning auger microscopy; electron spectroscopy for chemical analysis; electron diffraction and energy dispersive X-ray analysis; electron energy loss spectroscopy; density measurements; secondary ion mass spectroscopy; high energy electron diffraction; and electron spin resonance. Results of the tests are summarized.

Angus, J. C.↗
DOE OSTI2021

Connection between the physicochemical characteristics of amorphous carbon thin films and their electrochemical properties

Connecting a material's surface chemistry with its electrocatalytic performance is one of the major questions in analytical electrochemistry. This is especially important in many sensor applications where analytes from complex media need to be measured. Unfortunately, today this connection is still largely missing except perhaps for the most simple ideal model systems. Here we present an approach that can be used to obtain insights about this missing connection and apply it to the case of carbon nanomaterials. In this paper we show that by combining advanced computational techniques augmented by machine learning methods with x-ray absorption spectroscopy (XAS) and electrochemical measurements, it is possible to obtain a deeper understanding of the correlation between local surface chemistry and electrochemical performance. As a test case we show how by computationally assessing the growth of amorphous carbon (a-C) thin films at the atomic level, we can create computational structural motifs that may in turn be used to deconvolute the XAS data from the real samples resulting in local chemical information. Then, by carrying out electrochemical measurements on the same samples from which x-ray spectra were measured and that were further characterized computationally, it is possible to gain insight into the interplay between the local surface chemistry and electrochemical performance. To demonstrate this methodology, we proceed as follows: after assessing the basic electrochemical properties of a-C films, we investigate the effect of short HNO 3 treatment on the sensitivity of these electrodes towards an inner sphere redox probe dopamine to gain knowledge about the influence of altered surface chemistry to observed electrochemical performance. Overall, these results pave the way towards a more general assessment of electrocatalysis in different systems and provide the first steps towards data driven tailoring of electrode surfaces to gain optimal performance in a given application.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Stable support films for electron microscopy

This disclosure provides systems, methods, and apparatus related to arrangements including electron microscopy grids. In one aspect an arrangement includes an electron microscopy grid. The electron microscopy grid comprises a first surface and a second surface, with the first surface having a holey carbon film disposed thereon. A plurality of lipid molecules are disposed in a hole in the holey carbon film. Each lipid molecule of the plurality of lipid molecules has a hydrophilic head and a hydrophobic tail. A biotin-binding protein is attached to the hydrophilic heads of the plurality of lipid molecules. The biotin-binding protein is crystalline.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1982

Growth of diamondlike films for power applications

Diamond has a high thermal conductivity (approximately 5 times that of copper) and is an ideal heat sink material for high power semiconductor devices as well as being of interest as a semiconductor material. Numerous vacuum deposition processes are being evaluated by NASA-LeRC which have demonstrated the capability to deposit carbon films having some of the properties of diamond. Current activities include Investigation of high deposition rate vacuum processes suitable for synthesis of diamondlike carbon films. The results of recent film characterization tests are reported.

Banks, B. A.↗
NASA NTRS1984

Plasma deposited diamondlike carbon on GaAs and InP

The properties of diamond like carbon films grown by RF flow discharge 30 kHz plasma using methane are reported. The Cls XPS line shape of films showed localized hybrid carbon bonds as low as 40 to as high as 95 percent. Infrared spectroscopy and N(15) nuclear reaction profiling data indicated 35 to 42 percent hydrogen, depending inversely on deposition temperature. The deposition rate of films on Si falls off exponentially with substrate temperature, and nucleation does not occur above 200 C on GaAs and InP. Optical data of the films showed bandgap values of 2.0 to 2.4 eV increasing monotonically with CH4 flow rate.

Warner, J. D.↗
NASA NTRS1985

Plasma deposited hydrogenated carbon on GaAs and InP

The properties of diamond like carbon films grown by RF flow discharge 30 kHz plasma using methane are reported. The Cis XPS line shape of films showed localized hybrid carbon bonds as low as 40 to as high as 95 percent. Infrared spectroscopy and N(15) nuclear reaction profiling data indicated 35 to 42 percent hydrogen, depending inversely on deposition temperature. The deposition rate of films on Si falls off exponentially with substrate temperature, and nucleation does not occur above 200 C on GaAs and InP. Optical data of the films showed bandgap values of 2.0 to 2.4 eV increasing monotonically with CH4 flow rate.

Warner, J. D.↗
DOE OSTI2021

Stress- and Time-Dependent Formation of Self-Lubricating In Situ Carbon (SLIC) Films on Catalytically-Active Noble Alloys

Abstract Low shear strength (30 MPa) organic films were grown in situ on Pt 0.9 Au 0.1 surfaces via cyclic sliding contact in dry N 2 with trace concentrations of ambient hydrocarbons. We present a systematic investigation of the stress- and time-dependent film formation. Steady-state friction coefficients were found to be as low as µ ~ 0.015 and inversely proportional to contact pressure, revealing non-Amontonian behavior. Above a Hertzian contact pressure of ~500 MPa, shear strength dropped, indicating an activated process. Raman spectroscopy identified non-uniformity in areal coverage and relative order with contact pressure. Regions of steady-state low-friction behavior exhibited spectra similar to DLC coatings. Atomic force microscopy was used to study the formation and growth of films at the nanoscale. Stress- and time-dependent measurements suggested a sublinear increase of film volume with time, and a transition from growth to wear at a Hertzian contact pressure of ~1.2 GPa.

Jones, Morgan R.↗