bluuebunny/crossref_metadata_2025_split huggingface dataset:
Kinetics of Linear Defect Formation in Gallia-Doped Rutile.
Authors: Empie Nathan , Edwards Doreen 
Published: April 2011

ABSTRACTThe diffusion of Ga2O3 into the surface of single crystal[001] rutile leads to the insertion of β-gallia subunits along {210} planes of the parent rutile structure. These linear defects introduce hexagonally shaped tunnels, approximately 2.5 å in diameter, normal to the]001] surface. Because these tunnels may serve as highly reactive sites for the attachment of macromolecules, we are exploring the application of these linear defects for creating nanostructures. The current work investigates the kinetics of defect formation and the factors that affect defect periodicity and orientation. Gallium oxide was applied to the surfaces of [001]-oriented TiO2 single-crystal substrates via a sol-gel spin-coating process using a gallium-containing precursor. Thermal treatments were systematically varied to obtain different defect surface structures. Defect orientation and the surface concentration of rows of defects were characterized via tapping mode atomic force microscopy.
Temperature and Flux dependence of ion induced ripple: a way to study defect and relaxation kinetics during ion bombardment
Authors: Chan Wai Lun 
Published: April 2011

ABSTRACTWe have measured the temperature and ion flux dependence of the ripple wavelength on a Cu(001) surface during low energy ion sputtering. We analyze these results in terms of a linear instability model and identify different experimentally observed behavior with different mechanisms of relaxation and surface defect kinetics. In a high temperature regime, diffusing species on the surface are mainly thermally induced while in a lower temperature range, the diffusing species are ion beam induced. At even lower temperature, thermal diffusion is deactivated and the surface relaxes through an athermal mechanism. We define a transition between different defects formation kinetics in temperature and flux phase space and discuss how the defect kinetics model can be extended to different materials system.
On the Formation Kinetics of Thin Nanopatterned Layers on Silicon Wafers Created by Hydrogen Plasma Exposure
Authors: Job R. , Huang Y. L. , Ma Y. , Zölgert B. , Düngen W. 
Published: April 2011

ABSTRACTCzochralski silicon wafers which are treated by hydrogen plasma at ca. 260 °C are structured at the surface due to the high reactivity of atomic hydrogen. “Nanopatterned” (np) Si layers with average structure diameters below 100 nm are created. The thickness of the np-Si layer is on the order of 100 nm. The morphology of np-Si layers depend on the applied plasma power and the exposure time. The formation of np-Si layers is discussed in the frame of a combined etching/ redeposition mechanism. Annealing at T ≥ 800 °C causes a reconstruction of np-Si layers and the appearance of tensile stress in the wafers up to a depth of several micrometers.
Dynamic spatial ordering of thin film nanostructures by rapid spatio-temporal surface modulations
Authors: Zhang Wei , Zhang Chi , Kalyanaraman Ramki 
Published: April 2011

AbstractWe present novel results showing that the application of a rapid spatio-temporal surface modulation in-situ with film deposition directs the assembly of ordered nanostructures. Co nanoclusters of approximately 50 nm in size were assembled into one-dimensionally ordered arrays spaced 400 nm apart on Si (100) substrates during film growth of a 0.5 nm thick film. This ordered arrangement was achieved under e-beam evaporation of Co with simultaneous two-beam pulsed laser interference irradiation. The ordering length scale was consistent with the theoretical two-beam fringe spacing. For a thicker Co film, the particles were irregularly shaped, like that of a rapidly solidified liquid-like structure. From this evidence, the mechanism for ordering is partly attributed to thermal effects due to the spatially periodic laser interference heating of the cobalt nanoparticles. This dynamic in-situ process, without the need of any pre-or post-patterning of the substrate or film, is promising as an economical and simple approach to assemble ordered nanostructured films. The author can be reached via e-mail at ramkik@wuphys.wustl.edu
laser ablation of carbon films used for transfer of electronic device
Authors: Sameshima Toshiyuki , Andoh Nobuyuki 
Published: April 2011

ABSTRACTPulsed laser-induced ablation using diamond-like carbon (DLC) films is reported. Pulsed XeCl excimer laser induced heating revealed that 200-nm DLC films formed by sputtering method had high heat resistivity and structural relaxation was induced by laser heating. SiO2 layers formed on the DLC films were successively removed from the DLC surface by laser heating at 350 mJ/cm2. C-O bond reaction probably occurred and stickiness of SiO2 to carbon was reduced. Laser induced forward transfer of Al/SiO2 was also demonstrated using DLC films with laser heating.
The Mechanical Properties of Thin Polymer Films from Nanoindentation
Authors: Jones F R , Hayes S A 
Published: April 2011

ABSTRACTThe thermomechanical properties of thermoset polymeric materials are shown to be suitable for detecting relevant degradative processes in the matrix of a fibre composite. In space environments, the surface of the material will be modified first because of the diffusion of the active molecules. Nanoindentation has been shown to be capable of determining changes in viscoelastic properties of thin polymer films and at surfaces of bulk material. The Hysitron Triboscope has been used to characterise an epoxy resin and polycyanurate in dynamic and static scanning modes. Dynamic nanoindentation has been shown to provide a full description of the viscoelastic response. Progress has been made in analysing static indentation for time dependence.
Developing Glassy Magnets from simulated Composition of Moon/Mars Regolith for Exploration Applications
Authors: Ray C. S. , Ramachandran N. , Rogers J. 
Published: April 2011

ABSTRACTThe feasibility of preparing glasses and developing glass-ceramic materials that display magnetic characteristics using the simulated compositions of Lunar and Martian regoliths have been demonstrated. The reported results are preliminary at this time, and are part of a larger ongoing research activity at the NASA Marshall Space Flight Center (MSFC) with an overall goal aimed at (i) developing glass, ceramic and glass-ceramic type materials from the Lunar and Martian soil compositions in their respective simulated atmospheric conditions, (ii) exploring the potential application areas of these materials through extensive materials characterization, and (iii) further improving the related materials properties through a variation of the processing methods. This research activity is an important component of NASA's current space exploration program, which encourages feasibility studies for materials development using in situ resources on planetary bodies to meet the technological and scientific needs of future human habitats on these extra terrestrial outposts. This paper presents an overview of this on-going work at NASA (MSFC) and reports on a few selected results obtained to date.
Vertically Aligned Carbon Nanotubes as the Sputter Resist in Space Propulsive Systems
Authors: Yap Yoke Khin , Kayastha Vijaya , Menda Jitendra , Vanga Lakshman Kumar , Wang Jiesheng , Kieckhafer Alex , Massey Dean , King Lyon B. 
Published: April 2011

ABSTRACTTwo-types of vertically aligned multi-walled carbon nanotubes (VA-MWNTs) are evaluated as the protective coatings against ion erosion in electric propulsion systems. A series of experiments have been conducted to understand the erosion rate and erosion mechanism of these VA-MWNTs. These experiments were carried out with Xe propellant at an ion current density of 5 mA/cm2. We found that the erosion rates of both types of VA-MWNTs were changing with time. Such a nonlinear erosion process is explained according to a possible erosion mechanism.
Advanced life support for space exploration: Air revitalization using amine coated single wall carbon nanotubes.
Authors: Moloney Padraig , Huffman Chad , Gorelik Olga , Nikolaev Pasha , Arepalli Sivaram , Allada Ramakumar , Springer Micah , Yowell Leonard 
Published: April 2011

ABSTRACTThe challenges posed by long duration human space flight have made regenerable air revitalization a critical technology. Current systems using disposable lithium hydroxide do not address the difficulties presented by long duration missions. Solid amine systems offer the capability to regeneratively adsorb CO2 using an amine—impregnated porous substrate. Desorption of CO2 is then achieved by exposing the system to vacuum or by increasing temperature. However, thermal inefficiencies and system size constraints prevent adoption of regenerable systems on current and future space vehicles. A key challenge is the thermal management of the adsorbing bed. The adsorbing surface increases in temperature which reduces adsorbing efficiency. The removal of CO2 reduces temperature, which in turn produces a loss in regeneration efficiency. These thermal inefficiencies necessitate prohibitively large volumes of traditional solid-amine materials, which do not have optimized surface areas and pore distributions. Single-wall carbon nanotubes (SWCNTs) may provide a means to increase surface area of the amine support and thermal efficiency. Recent work by Cinke et. al. provided a method of functionalizing SWCNTs and increasing the surface area to the order of 1500 m2/g [1]. We will report on the production of free standing, high surface area carbon nanotube structures currently being impregnated with amines. This novel SWCNT/amine approach will be compared with the current state of the art polymer structure-based system and characterized using SEM, TEM, surface area analysis through Brunauer-Emmett-Teller (BET), and also thermogravimetric equilibrium absorption. Results of SWCNT material improvements from processing modifications will also be presented.
Multifunctional Power-Generating and Energy-Storing Structural Composites for U.S. Army Applications
Authors: South Joseph T. , Carter Robert H. , Snyder James F. , Hilton Corydon D. , O'Brien Daniel J. , Wetzel Eric D. 
Published: April 2011

ABSTRACTMany U.S. Army systems, such as ground vehicles and fully equipped soldiers, are comprised of multiple subcomponents which each typically perform unique functions. Combining these functions into single, multifunctional components could reduce mass and improve overall system efficiency. In particular, creating structural materials that also provide power generating or energy storing capacity could provide significant weight savings over a range of platforms. In this study, structural composite batteries, fuel cells, and capacitors are proposed. To ensure performance benefits, these multifunctional composites are designed so that the materials involved in power and energy processes are also load bearing, rather than simply packaged within monofunctional structural materials. Fabrication and design details for these multifunctional systems, as well as structural and power/energy performance results, are reported. Critical material properties and fabrication considerations are highlighted, and important technical challenges are identified.
Screening Of The Thermal Endurance Of Spacecraft Materials By Kinetic Modelling
Authors: Moser M. , Heltzel S. , Semprimoschnig C. O. A. , Garcia Martin G. 
Published: April 2011

ABSTRACTFuture science missions of the European Space Agency (ESA) to the inner part of the solar system will require the use of materials at an extreme radiation and temperature environment. A major concern regarding the selection of these materials is the thermal behaviour and the thermal stability. In this paper ways are shown to assess the thermal endurance of polymers by kinetic modelling. Two commonly used kinetic models, the one following the ASTM E 1641 and ASTM E 1877 standards and the other following the Model Free Kinetics (MFK) approach, are presented and compared to each other with the given example of two competing polyimide films, Kapton HN® of DuPont and Upilex S® of Ube Industries1, which were tested within ESA's critical materials technology program.
Advanced Carbon-based Material as Space Radiation Shields
Authors: Gupta Sanju , Patel Rishi J. , Smith Nathaniel D. 
Published: April 2011

ABSTRACTCarbon-based materials including microcrystalline diamond, nanocrystalline diamond, and carbon nanotubes films were prepared by microwave plasma-assisted chemical vapor deposition (MWCVD) technique. While the former were submitted to gamma radiation doses of 1, 5, and 20 Mrad, the latter to low energy electron beam of 30 keV or to 30 GeV/cm2) to study the radiation-induced structural transformation. The characterizations were performed prior to and after irradiation using Raman spectroscopy, scanning electron microscopy, and X-ray diffraction, techniques. Microcrystalline diamond showed a dramatic modification in the structural properties only after a cumulative dose of 26 Mrad (2 Grad/cm2), while nanocrystalline carbon showed a relatively small but systematic transformation with increasing gamma radiation dose. The results indicate that nanocrystalline carbon tends to reach a state of saturation when submitted to 26 Mrad doses of gamma radiation, suggesting the possibility of fabricating radiation buffer materials that would undergo internal sp3 ⇔ sp2 inter-conversion while absorbing ionizing radiation without changing their average microstructure and protecting the device/material underneath. Single- and multi-walled nanotubes exhibited structural modifications after 5.5–8 hrs of continuous exposure to electron beam. The variation in the characteristic X-ray peaks for multi-walled and single-walled corresponding to intertube spacing and the high frequency Raman band around 1580 cm−1 (G band) are reflected in their corresponding spectra. The results indicate that there is an increase in the intertube spacing for multi-walled nanotubes due to electron irradiation. While single-wall nanotubes tends to ‘collapse’ after > 8 hours of exposure forming multi-wall nanotubes analyzed using scanning electron microscopy and Raman spectroscopy. These C materials can be employed for preventing space radiation from reaching sensitive materials and electronic devices at least for short term experiments and entitled them as ‘space radiation shields’.
Electron Beam Radiation of Carbon Nanotubes-Polymer Composites
Authors: Najafi Ebrahim , Lee Jong-Oh , Shin Kwanwoo 
Published: April 2011

ABSTRACTThe degradation of PMMA-CNT thin film composites was examined, using electron beam radiation as a function of CNTs concentration. The findings show that the addition of CNT fillers can significantly reinforce composites against the irradiation induced degradation of PMMA, in which polymer free radicals are mainly responsible for the progress of the degradation. The results show that CNT networks are able to effectively disperse irradiated electrons through the matrix. The saturation of reinforcement effects was observed at a concentration of CNTs of approximately 0.5 wt%. This concentration was interpreted in terms of the critical concentration needed for percolation of the CNTs network, and this was further verified by sheet resistivity measurements. Free radical interactions with CNTs were also investigated by accelerated electron beam radiation and thermogravimetric analysis. CNTs were able to inhibit the free radical proliferation during a degradation process and to reduce the extent of degradation of the composites.
Radiation Effects and Defects in Cubic Boron Nitride. A Promising Multifunctional Material for Severe Environment Conditions.
Authors: Nistor S. V. 
Published: April 2011

ABSTRACTCubic boron nitride (c-BN) is a synthetic material which exhibits exceptional physicochemical properties such as: hardness, thermal conductivity, thermo-chemical stability, semiconducting properties and radiations resistance. Such outstanding properties make it a promising multifunctional material for applications in extreme conditions, as those found in the outer space environment. Its further use for such applications requires, however, a much better understanding of the lattice defects and radiation damage properties. Here we present the results of multifrequency ESR studies concerning the native and radiation induced point defects in crystalline c-BN under irradiation with high intensity 1MeV electron beams.
Low Earth Orbital Atomic Oxygen Interactions with Spacecraft Materials
Authors: Banks Bruce A. , de Groh Kim K. , Miller Sharon K. 
Published: April 2011

ABSTRACTAtomic oxygen, formed in Earth's thermosphere, interacts readily with many materials on spacecraft flying in low Earth orbit (LEO). All hydrocarbon based polymers and graphite are easily oxidized upon the impact of ∼4.5 eV atomic oxygen as the spacecraft ram into the residual atmosphere. The resulting interactions can change the morphology and reduce the thickness of these materials. Directed atomic oxygen erosion will result in the development of textured surfaces on all materials with volatile oxidation products. Examples from space flight samples are provided. As a result of the erosive properties of atomic oxygen on polymers and composites, protective coatings have been developed and are used to increase the functional life of polymer films and composites that are exposed to the LEO environment. The atomic oxygen erosion yields for actual and predicted LEO exposure of numerous materials are presented. Results of in-space exposure of vacuum deposited aluminum protective coatings on polyimide Kapton indicate high rates of degradation are associated with aluminum coatings on both surfaces of the Kapton. Computational modeling predictions indicate that less trapping of the atomic oxygen occurs, with less resulting damage, if only the space-exposed surface is coated with vapor deposited aluminum rather than having both surfaces coated.
Materials Testing Activities within ESA in Support of Future Inner Solar System Missions
Authors: Semprimoschnig Christopher O. A. , Heltzel Stan , Eesbeek Marc van 
Published: April 2011

ABSTRACTIn this paper the ESA internal approach regarding the assessment of materials for inner solar system missions is presented. A main part of the work is devoted to the assessment of thermal control materials and space environmental testing at elevated temperature. As these materials are the most exposed it is important to understand how they will interact with the relevant space environment at elevated temperature. Driving parameters for materials degradation are discussed and on-going testing efforts are described. An important input parameter for thermal models is the knowledge of the end of life values for the thermo-optical properties as these determine the equilibrium temperatures. In certain cases end of life testing needs to be done when the uncertainty of extrapolation is too high.
The Role of βFeOOH in the Corrosion of Archaeological Iron
Authors: Watkinson David , Lewis Mark R. T. 
Published: April 2011

ABSTRACTThe chloride bearing corrosion product akaganéite (βFeOOH) can form during postexcavation corrosion of chloride infested archaeological iron and is able to corrode iron in contact with it. Its action on iron is examined using βFeOOH synthesized from ferrous chloride and iron powder. Using weight measurements the hygroscopicity of βFeOOH is established. The influence of relative humidity on the corrosion of iron powder mixed with βFeOOH is examined by dynamic mass change within a climatic chamber. At 20°C and 12% relative humidity, iron in contact with βFeOOH did not corrode. At 15% relative humidity slight iron corrosion was detected after 160 hours, but at 35% relative humidity corrosion occurred after a few hours. Surface adsorbed chloride was removed from βFeOOH by aqueous washing and this reduced its hygroscopicity. The reported metastability of βFeOOH was examined via XRD of a 23 year old sample, which was found to be still entirely composed of βFeOOH. These results provide better understanding of βFeOOH corrosion of iron, corrosion control of chloride infested iron using dry storage and the effect of aqueous washing on archaeological iron.
Linseed Oil Paint as Ionomer: Synthesis and Characterization
Authors: Tumosa Charles S. , Erhardt David , Mecklenburg Marion F. , Su Xingfang 
Published: April 2011

ABSTRACTAs linseed oil ages, hydrolysis and oxidation produce acid groups on the polymer chain that may lead to ionomeric behavior. The effect of these changes is difficult to determine in old paints because of the lack of records of environmental and treatment histories that can alter the physical properties significantly. A series of paints were made that have chemical properties similar to those of aged paints and that mimic old paints. Their properties seem to show flexibility as well as coherency but low strength and a high susceptibility to solvents.
Analysis of Stucco Floors from the Citadel of the Archaeological Zone of Teotihuacan, Mexico
Authors: Montes Luis Torres , García Manuel Reyes , Gazzola Julie , Gómez Sergio 
Published: April 2011

ABSTRACTSevere decay of the stone façade of the Pyramid of Quetzalcoatl, one of the more remarkable structures in the World Heritage Site archaeological zone of Teotihuacan, Mexico, is caused by the presence of humidity and salt crystallization. The floors were analyzed to determine whether water and salts were filtering up from the ground and to find a way to reduce the penetration of water. Analyses of the lime plaster and organic matter were carried out by traditional wet chemical methods in order to discover the possible recipe that is the basis of the technology used by Pre-Columbian masons. The presence of an organic mucilage and fiber was identified. The organic components of the floors were analyzed using FTIR of extracts, while mucilage from leaves of a local cactus, Opuntia sp, that is used traditionally as a cementing material in plasters, was analyzed for comparative purposes to determine whether the mucilage was also used in pre-Columbian times. X-ray spectrometry and x- ray diffraction were also used to complement the study to identify the mineralogy of the plasters. This study shows that the Teotihuacanos used a composite material that has great durability, permitting the survival of the floors for almost 2000 years, but that also is succeptible to damage in a modern, stressed environment with high tourist traffic.
The Provenance of Ancient Glass through Compositional Analysis
Authors: Freestone Ian C. 
Published: April 2011

ABSTRACTRecent developments in the understanding of the low-magnesia soda-lime-silica or “natron” glasses of the first millennium A.D. are reviewed. It appears that glass production was divided between a small number of primary glass making centres, situated mainly in the Near East, and a large number of secondary fabrication workshops that remelted and shaped the lumps of raw, premelted glass. Glass may be related to its primary production group by elemental analysis and, where there are data from workshops, to the production centre or region. The recycling of old glass is revealed by trace element analysis, due to the contamination of primary glass compositions by small quantities of coloured glass incorporated in the recycled material. The analysis of isotopes of Sr and Pb allows the geological environment of the raw materials to be inferred and in some cases, provenance to be predicted.