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Procedures for fabricating large sheets of CR-39 with uniform chemical reactivity and sensitivity and which retain a clear, smooth surface after prolonged etching were investigated. Very thin sheets for certain Spacelab applications were fabricated.
Continuous single-crystal Al2O3 fibers have been incorporated into a variety of metal and intermetallic matrices and the results have consistently indicated that the fiber strength had been reduced by 32 to 50% during processing. Two iron-based alloys, FeNiCoCrAl and FeAlVCMn, were chosen as matrices for Al2O3 fiber reinforced metal matrix composites (MMC) with the goal of maintaining Al2O3 fiber strength after composite processing. The feasibility of Al2O3/FeNiCoCrAl and Al2O3/FeAlVCMn composite systems for high temperature applications were assessed in terms of fiber-matrix chemical compatibility, interfacial bond strength, and composite tensile properties. The strength of etched-out fibers was significantly improved by choosing matrices containing less reactive elements. The ultimate tensile strength (UTS) values of the composites could generally be predicted with existing models using the strength of etched-out fibers. However, the UTS of the composites were less than desired due to a low fiber Weibull modulus. Acoustic emission analysis during tensile testing was a useful tool for determining the efficiency of the fibers in the composite and for determining the failure mechanism of the composites.
Plasma-enhanced chemical vapor deposition (PECVD) and high-throughput manufacturing techniques for integrating single, aligned carbon nanotubes (CNTs) into novel 3D nanoscale architectures have been developed. First, the PECVD growth technique ensures excellent alignment of the tubes, since the tubes align in the direction of the electric field in the plasma as they are growing. Second, the tubes generated with this technique are all metallic, so their chirality is predetermined, which is important for electronic applications. Third, a wafer-scale manufacturing process was developed that is high-throughput and low-cost, and yet enables the integration of just single, aligned tubes with nanoscale 3D architectures with unprecedented placement accuracy and does not rely on e-beam lithography. Such techniques should lend themselves to the integration of PECVD grown tubes for applications ranging from interconnects, nanoelectromechanical systems (NEMS), sensors, bioprobes, or other 3D electronic devices. Chemically amplified polyhydroxystyrene-resin-based deep UV resists were used in conjunction with excimer laser-based (lambda = 248 nm) step-and-repeat lithography to form Ni catalyst dots = 300 nm in diameter that nucleated single, vertically aligned tubes with high yield using dc PECVD growth. This is the first time such chemically amplified resists have been used, resulting in the nucleation of single, vertically aligned tubes. In addition, novel 3D nanoscale architectures have been created using topdown techniques that integrate single, vertically aligned tubes. These were enabled by implementing techniques that use deep-UV chemically amplified resists for small-feature-size resolution; optical lithography units that allow unprecedented control over layer-to-layer registration; and ICP (inductively coupled plasma) etching techniques that result in near-vertical, high-aspect-ratio, 3D nanoscale architectures, in conjunction with the use of materials that are structurally and chemically compatible with the high-temperature synthesis of the PECVD-grown tubes. The techniques offer a wafer-scale process solution for integrating single PECVD-grown nanotubes into novel architectures that should accelerate their integration in 3D electronics in general. NASA can directly benefit from this technology for its extreme-environment planetary missions. Current Si transistors are inherently more susceptible to high radiation, and do not tolerate extremes in temperature. These novel 3D nanoscale architectures can form the basis for NEMS switches that are inherently less susceptible to radiation or to thermal extremes.
This paper primarily reviews the potential of using the sputtering process as a deposition technique; however, the manufacturing and sputter etching aspects are also discussed. Since sputtering is not regulated by classical thermodynamics, new multicomponent materials can be developed in any possible chemical composition. The basic mechanism for dc and rf sputtering is described. Sputter-deposition is described in terms of the unique advantageous features it offers such as versatility, momentum transfer, stoichiometry, sputter-etching, target geometry (coating complex surfaces), precise controls, flexibility, ecology, and sputtering rates. Sputtered film characteristics, such as strong adherence and coherence and film morphology, are briefly evaluated in terms of varying the sputtering parameters. Also described are some of the specific industrial areas which are turning to sputter-deposition techniques.
Procedures and chemical baths were developed for chem-milling aluminum alloy 2219. Using a series of sample etchings, it was found that good etching results could be obtained by using 'white plastic for porcelain repair (toluol, xylol, and petroleum distillates)' on top of cellosolve acetate as resist coatings and ferric chloride as on etchant.
A finite-element analysis of possible silicon carbide (SIC) folded-beam, lateral-resonating accelerometers is presented. Results include stiffness coefficients, acceleration sensitivities, resonant frequency versus temperature, and proof-mass displacements due to centripetal acceleration of a blade-mounted sensor. The surface micromachined devices, which are similar to the Analog Devices Inc., (Norwood, MA) air-bag crash detector, are etched from 2-pm thick, 3C-SiC films grown at 1600 K using atmospheric pressure chemical vapor deposition (APCVD). The substrate is a 500 gm-thick, (100) silicon wafer. Polysilicon or silicon dioxide is used as a sacrificial layer. The finite element analysis includes temperature-dependent properties, shape change due to volume expansion, and thermal stress caused by differential thermal expansion of the materials. The finite-element results are compared to experimental results for a SiC device of similar, but not identical, geometry. Along with changes in mechanical design, blade-mounted sensors would require on-chip circuitry to cancel displacements due to centripetal acceleration and improve sensitivity and bandwidth. These findings may result in better accelerometer designs for this application.
Experimental dry etching technique strips photoresists from semiconductor wafers without damaging semiconductor materials. Makes use of afterglow existing downstream from plasma generated by radio-frequency electric field. Constituents of afterglow react with sacrificial polymer to make reactive gases that quickly etch-away photoresist. Strips quickly at room temperature; not necessary to heat substrates. No hazardous or toxic chemicals used.
Surface halogenation experimental technique of postgrowth nonaqueous chemical processing of high-temperature superconductors. Research continues in use of technique to obtain superconducting and/or passivated surfaces, to etch bulk superconductors, and to make low-resistance electrical contacts. Most promising etchant is bromine dissolved in such polar nonaqueous solvents as alchols, acetone, or ether. Etchant appears to act only on surface without adversely affecting superconducting bulk of film.
Geometrically structured surfaces have become increasingly important to solar cell efficiency improvements and radiation tolerance. Gallium arsenide solar cells with a V-grooved front surface which demonstrate improved optical coupling and higher short-circuit current compared to planar cells were fabricated. GaAs homojunction cells were fabricated by organometallic chemical vapor deposition (OMCVD) on an n+ substrate. The V-grooves were formed on the surface with an anisotropic etch, and an n-type buffer and p-type emitter were grown by OMCVD, followed by ohmic contacts. Reflectivity measurements show significantly lower reflectance for the microgrooved cell compared to the planar structure. The short circuit current of the V-grooved solar cell is consistently higher than that of the planar controls.
The term plasma process diagnostics (PPD) refers to a spectroscopic technique and sensing hardware that have been proposed for monitoring plasma processes used to fabricate electronic devices that feature sizes as small as several nanometers. Nanometer dimensions are characteristic of the quantum level of miniaturization, where single impurity atoms or molecules can drastically change the local properties of the nanostructures. Such changes may be purposely used in nanoscale design but may also be extremely damaging or cause improper operation of the fabricated devices. Determination of temperature and densities of reactants near the developing features is important, since the structural synthesis is affected by characteristics of the local microenvironment. Consequently, sensors capable of nonintrusive monitoring with high sensitivity and high resolution are essential for real-time atomistic control of reaction kinetics and minimizing trace contamination in plasma processes used to fabricate electronic nanodevices. Such process-monitoring sensors are required to be compact, multiparametric, and immune to the harsh environments of processing plasmas. PPD is intended to satisfy these requirements. The specific technique used to implement plasma diagnostics with a PPD sensor would be an advanced version of continuous-wave cavity-ringdown spectroscopy (CW-CRDS) capable of profiling spectral line broadenings in order to derive both Doppler and Stark components. CRDS is based on measurements of the rate of absorption of laser light in an optical resonator. The ultimate sensitivity results from a very long absorption path length within the cavity and immunity to variations in incident laser intensity. The proposed version of this technique would involve the use of multiplexing tunable laser diodes and an actively modulated high-reflectivity optical resonator, thus offering a synergistic combination of simplicity, compactness, high sensitivity, and high resolution. The multiplexing capabilities of diode lasers could be utilized to make the PPD sensor a single, simple, compact, and inexpensive tool for the acquisition of multiparametric data. A PPD sensor would be capable of continuous measurement of such physical parameters as gas temperature, gas velocity, electron number density, and absolute densities of reacting chemical species. A laser beam can be easily adjusted to analyze the immediate vicinity of the growing nanostructures (or features etched down) in real time. The absorption enhancement in an optical cavity would afford the sensitivity needed for measurement of the temperature and densities of species at concentrations significantly lower than measurable by other nonintrusive techniques. It is anticipated that fully developed PPD sensors would enable simultaneous measurement of local temperature and determination of plasma species responsible for the synthesis and functionalization of nanodevices. These sensors would also enable tracking the pathways and origins of damaging contaminants, thereby providing feedback for adjustment of processes to optimize them and reduce contamination. The PPD sensors should also be useful for optimization of conventional microelectronics manufacturing plasma processes. Going beyond plasma processes for fabrication of electronic devices, PPD sensors could be used for monitoring of atoms, molecules, ions, radicals, clusters, and particles in a variety of other settings, including outer space. Because of their high sensitivity, such sensors could also prove useful for detecting traces of illegal drugs and explosives.
Acid spray machining technique chemically mills aluminum alloy panels without immersing them in an etchant. The spray does not require artificial heating to initiate the etching process.
Wear tests were performed on 304 stainless steel lubricated with pure mineral oil with and without dibenzyl-disulfide. Both mild and severe wear were observed. The type of wear was distinguished by a marked change in wear rate, friction coefficient, and wear scar appearance. The chemical composition of the wear scar surface was examined with X-ray photoelectron spectroscopy in conjunction with argon ion sputter etching. In severe wear scars, a sulfide was formed at the expense of the normal oxide layer. In mild wear scars, there were only superficial sulfur compounds, but there was a substantial increase in the oxide thickness.
An Auger spectrometer in ultrahigh vacuum was used to measure the secondary emission properties of a number of candidate collector-materials including beryllium, carbon, (soot and pyrolytic graphite), copper, titanium carbide and tantalum. The advantage of the technique used is that the surface chemical constituents could be determined just before the secondary emission characteristics of the surface were measured. Pyrolytic graphite roughened by sputter etching showed the most favorable results for depressed collector use.
In this investigation sputtered silicon carbide annealed at 300 C for one hour is used as a conformal thin film package. A RF magnetron sputterer was used to deposit 500 nm silicon carbide films on gold metal structures on alumina wafers. To determine the reliability and resistance to immersion in harsh environments, samples were submerged in gold etchant for 24 hours, in BOE for 24 hours, and in an O2 plasma etch for one hour. The adhesion strength of the thin film was measured by a pull test before and after the chemical immersion, which indicated that the film has an adhesion strength better than 10(exp 8) N/m2; this is similar to the adhesion of the gold layer to the alumina wafer. MIM capacitors are used to determine the dielectric constant, which is dependent on the SiC anneal temperature. Finally, to demonstrate that the SiC, conformal, thin film may be used to package RF circuits and sensors, an LC resonator circuit was fabricated and tested with and without the conformal SiC thin film packaging. The results indicate that the SiC coating adds no appreciable degradation to the circuits RF performance. Index Terms Sputter, silicon carbide, MIM capacitors, LC resonators, gold etchants, BOE, O2 plasma
Introduction Hydrophobicity is the tendency of a fluid to repel another material or fluid. Hydrophobiciy can be measured through the wetting angle of the fluid on the surface of the other material. The greater the wetting angle, the more hydrophobic the surface is against the fluid. Hydrophobicity properties can be caused by one of two means, either through physical properties or chemical properties [\citenum{NARBUTT2020121}]. Physical hydrophobicity due to the surface of a solid creating surface roughness/patterning, minimizing the contact area between the fluid and the surface. This can be observed throughout nature, such as the surface of lotus leaves or butterfly wings. This physical property can be induced on a variety of surfaces, namely through laser etching, allowing a surface to be finely lineated to imitate these natural surfaces while controlling quantity, depth, and patterns of the etching on the surface [\citenum{10.1063/1.4905616}]. Physical hydrophobicity is therefore dependent on several variables, including the surface that the fluid is on and properties of the fluid itself, such as density and surface tension, both of which are dependent on temperature and/or pressure. Chemical hydrophobicity [\citenum{MadeiraHydrophobocicicici}] is due to the inherent chemical properties of the materials being used. This is most commonly due to the molecular structures changing the polarity of the materials. Depending on a nonpolar material will repel a polar material, proving to be hydrophobic, conversely if the polarity of the materials is the same (polar – polar, nonpolar – nonpolar), they will attract each other. Cryogenics refers to the behavior of materials at very low temperatures (<\ang{-100} C) [\citenum{ZOHURI20181}]. In space applications many things are inherently cryogenic, therefore this is an important field. There has been little research in how hydrophobicity changes at cryogenic temperatures. Cryogenic fluids are commonly used as fuels for spacecraft, therefore, integrating a hydrophobic surface can increase the transfer rate of the fuel. To test this, several experiments were set up to determine the hydrophobic properties of cryogenic fluids, including nitrogen (LN2), argon (LAr), oxygen (LOx), hydrogen (LH2), and methane (CH4), at cryogenic temperatures. Etched Wafer Testing A silicon wafer cut from a crystal of silicon [100] was used to model the potential hydrophobicity of various cryogenic fluids. Silicon [100] references to the crystallographic orientation of the silicon crystals in the wafer. These wafers were then laser etched to create a surface that is more likely to be hydrophobic. To test the hydrophobicity of the wafers at cryogenic temperatures, the temperatures of the wafers must be reduced to the same temperature as the cryogenic fluid being used to prevent rapid boil-off. To achieve this a double-walled vacuum insulated glass chamber was utilized. The chamber is open, with a double-walled glass that can be placed in a vacuum to remove condensation from the outside to allow easier viewing of the experiment. Furthermore, the silicon wafer's temperature must be lowered to the temperature of LN2, as well as maintain the temperature throughout the experiment. To achieve this a piece of 6061 aluminum was used, creating a stand-off for the wafer and it would allow for the insulation of the temperature of the wafers. The container was then filled with LN2 and once the LN2 stabilized the vaporization and the levels of LN2 dropped under the height of the wafer, the wafer was then allowed to air dry. Once the wafer was dry from the LN2, drops of LN2 were placed on the surface of the wafer for observation. During the first trial, the LN2 that was dropped on the surface displayed nonhydrophobic behaviors, spreading out along the surface, with a minimal wetting angle (too small to be measured). This process was repeated for liquid argon. Further testing with other cryogenic liquids will require different testing apparatuses due to being more volatile. Furthermore, several papers [\citenum{voltvolt7}] have suggested that running a voltage can induce a hydrophobic effect throughout a surface, further testing will include a voltage (constant and oscillating) to determine if voltage influences inducing hydrophobicity at cryogenic temperatures. Chemical Testing Coating the interior walls of the fuel tanks and fuel lines can successfully create a hydrophobic surface. The inherent problem is finding a material that can be used to coat the surface, furthermore, at these temperatures, the coating will remain solid, which could pose issues in maintaining the hydrophobic properties. To test this water (polar) is hydrophobic against oils and fats (nonpolar), therefore the same experiment as the etched wafer testing was conducted to determine if the hydrophobic properties will persist as the nonpolar material remains solid and the polar material remains a fluid. The water remained hydrophobic, allowing testing can expand to the cryogenic fluids. However, another hurdle is faced in finding a chemically opposite material to the cryogenic fluids being tested. As many of the cryogenic fluids being tested are diatomic, they are inherently nonpolar, therefore, the material used for the hydrophobic coating must be polar. Polar greases and lubricants are difficult to come by, however, lithium stearate, appears to be a potential candidate for creating a coated hydrophobic surface for cryogenic fluids at cryogenic temperatures.
It is shown that the efficiency of a solar cell can be improved if minority carriers are confined by use of a wide-bandgap heterojunction window. For silicon (lattice constant a = 5.43 A), nearly lattice-matched wide-bandgap materials are ZnS (a = 5.41 A) and GaP (a = 5.45 A). Isotype n-n heterojuntions of both ZnS/Si and GaP/Si were grown on silicon n-p homojunction solar cells. Successful deposition processes used were metalorganic chemical vapor deposition (MO-CVD) for GaP and ZnS, and vacuum evaporation of ZnS. Planar (100) and (111) and texture-etched - (111)-faceted - surfaces were used. A decrease in minority-carrier surface recombination compared to a bare surface was seen from increased short-wavelength spectral response, increased open-circuit voltage, and reduced dark saturation current, with no degradation of the minority carrier diffusion length.
In order to understand the influence of etch pits on the material properties of carbon fiber microstructures, we use the Porous Microstructure Analysis (PuMA) software to create realistic pitted structures from virgin fiber structures and then analyze their degradation as the degree of pitting increases. For that purpose, we developed a pitting module within PuMA that creates pits with user-defined geometry (shape, size) and distribution (defect density) on the surface of arbitrary microstructures. In this work, we consider FiberForm microstructures, which are commonly used as the base material for ablative thermal protection systems (TPS). Using the new pitting module, we mimic the evolution of etch pits on FiberForm as it occurs from oxidation in ablative heating environments, by first importing the virgin FiberForm structure from a micrograph scan and then imposing different pitting conditions by varying pit radii and defect densities. We then leverage PuMA’s capabilities to calculate material properties for each structure. The results clearly show the degradation of thermal conductivity and structural integrity as etch pits grow, and furthermore highlight the complex evolution of the surface topology, which results in significant changes of the flowgeometry and chemical gas-surface interactions. Furthermore, a comparison of these changes with the case of shrinking fibers, which has heretofore been the standard for modelling ablation of carbon structures, yields significant differences. For example, we observe the formation of small chunks of fibers as pits grow in size, which could be released into the surrounding flow environment as spallation particles. This motivates us to continue our efforts of modelling pitting as an integral part of the structural degradation of carbon fiber structures in oxidation environments, which will ultimately improve our understanding of failure mechanisms in those materials.
In order to understand the influence of etch pits on the material properties of carbon fiber microstructures, we use the Porous Microstructure Analysis (PuMA) software to create realistic pitted structures from virgin fiber structures and then analyze their degradation as the degree of pitting increases. For that purpose, we developed a pitting module within PuMA that creates pits with user-defined geometry (shape, size) and distribution (defect density) on the surface of arbitrary microstructures. In this work, we consider FiberForm microstructures, which are commonly used as the base material for ablative thermal protection systems (TPS). Using the new pitting module, we mimic the evolution of etch pits on FiberForm as it occurs from oxidation in ablative heating environments, by first importing the virgin FiberForm structure from a micrograph scan and then imposing different pitting conditions by varying pit radii and defect densities. We then leverage PuMA’s capabilities to calculate material properties for each structure. The results clearly show the degradation of thermal conductivity and structural integrity as etch pits grow, and furthermore highlight the complex evolution of the surface topology, which results in significant changes of the flowgeometry and chemical gas-surface interactions. Furthermore, a comparison of these changes with the case of shrinking fibers, which has heretofore been the standard for modelling ablation of carbon structures, yields significant differences. For example, we observe the formation of small chunks of fibers as pits grow in size, which could be released into the surrounding flow environment as spallation particles. This motivates us to continue our efforts of modelling pitting as an integral part of the structural degradation of carbon fiber structures in oxidation environments, which will ultimately improve our understanding of failure mechanisms in those materials.