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A Stennis Space Center researcher investigating the effectiveness of photocatalytic materials for keeping the Center's buildings free of grime turned to a solution created by PURETi Inc. of New York City. Testing proved successful, and NASA and the company now share a Dual Use Technology partnership. PURETi's coatings keep surfaces clean and purify surrounding air, eliminating pollution, odors, and microbes.
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Low energy electron diffraction method of identifying atomically clean surface after laser surface interaction
The effects of direct plasma chemistries on carbon removal from silicon nitride (SiN{sub x}) and oxynitride (SiO{sub x}N{sub y}) surfaces have been studied by in-situ x-ray photoelectron spectroscopy (XPS) and ex-situ contact angle measurements. The data indicate that O{sub 2} and NH{sub 3} capacitively coupled plasmas are effective at removing adventitious carbon from silicon nitride (SiN{sub x}) and Si oxynitride (SiO{sub x}N{sub y}) surfaces. O{sub 2} plasma treatment results in the formation of a silica overlayer. In contrast, the exposure to NH{sub 3} plasma results in negligible additional oxidation of the SiN{sub x} or SiO{sub x}N{sub y} surface. Ex-situ contact angle measurements show that SiN{sub x} and SiO{sub x}N{sub y} surfaces exposed to oxygen plasma are initially more hydrophilic than surfaces exposed to NH{sub 3} plasma, indicating that the O{sub 2} plasma-induced SiO{sub 2} overlayer is highly reactive toward ambient. At longer ambient exposures (≳10 h), however, surfaces treated by either O{sub 2} or NH{sub 3} plasma exhibit similar steady state contact angles, correlated with rapid uptake of adventitious carbon, as determined by XPS. Surface passivation by exposure to molecular hydrogen prior to ambient exposure significantly retards the increase in contact angle upon exposure to ambient. The results suggest a practical route to enhancing the time available for effective bonding to surfaces in microelectronics packaging applications.
Cleaning of surfaces by ion bombardment and abrasion, and measuring of surface cleanliness
Investigating nanometer and micron sized materials thought to exhibit topological surface properties that can present a challenge, as clean surfaces are a pre-requisite for band structure measurements when using nano-ARPES or laser-ARPES in ultra-high vacuum. This issue is exacerbated when dealing with nanometer or micron sized materials, which have been prepared ex-situ and so have been exposed to atmosphere. We present the findings of an XPS study where various cleaning methods have been employed to reduce the surface contamination and preserve the surface quality for surface sensitive measurements. Microcrystals of the topological crystalline insulator SnTe were grown ex-situ and transferred into ultra high vacuum (UHV) before being treated with either atomic hydrogen, argon sputtering, annealing, or a combination of treatments. The samples were also characterised using the scanning electron microscopy, both before and after treatment. It was found that atomic hydrogen cleaning with an anneal cycle (200 °C) gave the best clean surface results.
Surface processing of a rubrene single crystal immersed in ionic liquids is valuable for further development of low voltage transistors operated by an electric double layer. We performed a precise and clean surface processing based on the tip-induced dissolution of rubrene molecules at the ionic liquid/rubrene single crystal interfaces by using frequency modulation atomic force microscopy. Molecular resolution imaging revealed that the tip-induced dissolution proceeded via metastable low density states derived from the anisotropic intermolecular interactions within the crystal structure.
This chapter presents the adhesion, friction, and wear behaviors of smooth, atomically clean surfaces of solid-solid couples, such as metal-ceramic couples, in a clean environment. Surface and bulk properties, which determine the adhesion, friction, and wear behaviors of solid-solid couples, are described. The primary emphasis is on the nature and character of the metal, especially its surface energy and ductility. Also, the mechanisms of friction and wear for clean, smooth surfaces are stated.
This paper investigates efficiency of specially designed atomizer used to spray water and cavitate microbubbles in water flow. Surface cleaning system was used to clean machined (grinded) aluminum surface from abrasive particles. It is established that cleaning efficiency depends on diameter of the diffuser, water pressure and distance between nozzle and metal surface. It is obtained that the best cleaning efficiency (100%) is achieved at pressure 36 bar, when diameter of diffuser is 0.4 mm and distance between nozzle and surface is 1 mm. It is also established that satisfactory cleaning efficiency (80%) is achieved not only when atomizer is placed closer to metal surface, but also at larger (120 mm) distances.
We report on the influence of variations in the process parameters of an in-situ surface cleaning procedure, consisting of alternating cycles of nitrogen plasma and trimethylaluminum dosing, on the interface trap density of highly scaled HfO{sub 2} gate dielectrics deposited on n-In{sub 0.53}Ga{sub 0.47}As by atomic layer deposition. We discuss the interface chemistry of stacks resulting from the pre-deposition exposure to nitrogen plasma/trimethylaluminum cycles. Measurements of interface trap densities, interface chemistry, and surface morphology show that variations in the cleaning process have a large effect on nucleation and surface coverage, which in turn are crucial for achieving low interface state densities.
Q spoiled laser bombardment to obtain atomically clean surfaces in vacuum, noting damages
This project developed new methods for cleaning the inside surfaces of very long, narrow vacuum tubes used in particle accelerators. Traditional cleaning approaches are expensive, slow, or difficult to implement in accelerator tunnels. We designed and tested a portable plasma discharge cleaning system that uses lower-cost microwave and magnetron technologies to reduce outgassing and secondary electron emission from stainless steel and copper surfaces. The system, called the Plasma Discharge Test System (PDTS), allows accelerator components to be scrubbed more efficiently, which can improve performance and reduce maintenance costs for research and industrial applications.
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Q switched lasers for obtaining clear surfaces in vacuum
N-polar aluminum nitride (AlN) is an important building block for next-generation high-power radio frequency electronics. We report successful homoepitaxial growth of N-polar AlN by molecular beam epitaxy (MBE) on large-area, cost-effective N-polar AlN templates. Direct growth without any in situ surface cleaning leads to films with inverted Al polarity. It is found that Al-assisted cleaning before growth enables the epitaxial film to maintain N-polarity. The grown N-polar AlN epilayer with its smooth, pit-free surface duplicates the structural quality of the substrate, as evidenced by a clean and smooth growth interface with no noticeable extended defects generation. Near band-edge photoluminescence peaks are observed at room temperature on samples with MBE-grown layers but not on the bare AlN templates, implying the suppression of nonradiative recombination centers in the epitaxial N-polar AlN.
The morphological stability of atomically clean silicon (100) surface after low-energy microwave plasma-chemical etching in various plasma-forming media is studied. It is found that relaxation changes in the surface density and atomic bump heights after plasma processing in inert and chemically active media are multidirectional in character. After processing in a freon-14 medium, the free energy is minimized due to a decrease in the surface density of microbumps and an increase in their height. After argon-plasma processing, an insignificant increase in the bump density with a simultaneous decrease in bump heights is observed. The physicochemical processes causing these changes are considered.
Bonding labs at both MSFC and the northern Utah production plant prepare bond test specimens which simulate or witness the production of NASA's Reusable Solid Rocket Motor (RSRM). The current process for preparing the bonding surfaces employs 1,1,1-trichloroethane vapor degreasing, which simulates the current RSRM process. Government regulations (e.g., the 1990 Amendments to the Clean Air Act) have mandated a production phase-out of a number of ozone depleting compounds (ODC) including 1,1,1-trichloroethane. In order to comply with these regulations, the RSRM Program is qualifying a spray-in-air (SIA) precision cleaning process using Brulin 1990, an aqueous blend of surfactants. Accordingly, surface preparation prior to bonding process simulation test specimens must reflect the new production cleaning process. The Bonding Lab Statistical Process Control (SPC) program monitors the progress of the lab and its capabilities, as well as certifies the bonding technicians, by periodically preparing D6AC steel tensile adhesion panels with EA-91 3NA epoxy adhesive using a standardized process. SPC methods are then used to ensure the process is statistically in control, thus producing reliable data for bonding studies, and identify any problems which might develop. Since the specimen cleaning process is being changed, new SPC limits must be established. This report summarizes side-by-side testing of D6AC steel tensile adhesion witness panels and tapered double cantilevered beams (TDCBs) using both the current baseline vapor degreasing process and a lab-scale spray-in-air process. A Proceco 26 inches Typhoon dishwasher cleaned both tensile adhesion witness panels and TDCBs in a process which simulates the new production process. The tests were performed six times during 1995, subsequent statistical analysis of the data established new upper control limits (UCL) and lower control limits (LCL). The data also demonstrated that the new process was equivalent to the vapor degreasing process.
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