Effect of diffusion processes and temperature on smoking tendencies of laminar diffusion flames
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Schalla, Rose L↗
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Atomic scale analysis of Nb3Sn on Nb prepared by a vapor-diffusion process for superconducting radiofrequency cavity applications
We report an atomic-scale analysis of the microstructure of Nb3Sn coating on Nb prepared by vapor diffusion process for superconducting radiofrequency (SRF) cavity application using transmission electron microscopy (TEM). Epitaxial growth of Nb3Sn on the Nb substrate is found and four types of orientation relationships at the Nb3Sn/Nb interface are identified by electron diffraction or high-resolution scanning transmission electron microscopy (STEM) analysis. Thin Nb3Sn grains are observed in regions with low Sn flux and they have the specific orientation relationship, Nb3Sn (1-20)//Nb (-111) and Nb3Sn (002)//Nb (0-11). The Nb3Sn/Nb interface of thin grains had a large lattice mismatch, 12.3 at.%, and a high density of misfit dislocations was observed by HR-STEM. Based on our microstructural analysis of the thin grains, we conclude that the thin regions are probably a result of a slow interfacial reaction with this particular orientation relationship at the interface. The Sn-deficient regions are seen to form initially at the Nb3Sn/Nb interface and remain in the grains due to the slow diffusion of Sn in bulk Nb3Sn. The formation of Sn-deficient regions and the effects of strain and interfacial energies on the formation of Sn-deficient regions at various interfaces were also estimated by first-principle calculation. The finding of orientation relationships at the Nb3Sn/Nb interface provides important information about the formation of defects in Nb3Sn coatings such as large thin regions, Sn-deficient regions, which are critical to the performance of Nb3Sn superconducting radiofrequency cavities for accelerators.
43 PARTICLE ACCELERATORS↗
Solar cells in bulk InP using an open tube diffusion process
A simple open tube diffusion technique for the fabrication of n+p junction solar cells is described. Large area (greater than 0.25 square cm) solar cells have been made by this process with a photovoltaic conversion efficiency of 15.2 percent under simulated AMO illumination. An ideality factor is 1.04 and a saturation current density of 9.6 times 10 to the minus 16th power A/square cm have been observed for these cells. These are the lowest (best) values reported to date for diffused structures in bulk InP.
Parat, K. K.↗
Growth of Nb 3 Sn coating in tin vapor-diffusion process
The potential of Nb 3 Sn for superconducting radio frequency (SRF) cavities is widely recognized and renewed R&D efforts continue to bring new insights about the material's structure and properties. Here, we have systematically coated niobium with Nb 3 Sn for different durations, and several of them were coated over ("overcoat") multiple times, to elucidate the growth kinetics of Nb 3 Sn during tin vapor diffusion process. Analysis of coated samples is consistent with the model in which tin diffuses via grain boundaries to the Nb 3 Sn-Nb interface, where the growth of Nb 3 Sn into the Nb bulk takes place. Similar scaling laws were found for Nb 3 Sn grain growth and layer thickness. Non-parabolic layer growth is consistent with significant grain growth, which reduces the number of Sn transport channels. Examination of patchy region in Nb 3 Sn coating, revealing large single crystalline grains, points to impeded Nb 3 Sn layer growth due to low grain boundary density, resulting in a significantly thinner coating in those areas.
36 MATERIALS SCIENCE↗
A study of solid-propellant vaporization and diffusion processes Final technical report
Vaporization rate and diffusion coefficient determined for organic additives to polyurethane solid propellants - dioctyl adipate and ferrocene
SOLID PROPELLANT↗
Cosmic Ray Hysteresis as Evidence for Time-dependent Diffusive Processes in the Long Term Solar Modulation
A simple one-dimensional time-dependent diffusion-convection model for the modulation of cosmic rays is presented. This model predicts that the observed intensity at a given time is approximately equal to the intensity given by the time independent diffusion convection solution under interplanetary conditions which existed a time iota in the past, (U(t sub o) = U sub s(t sub o - tau)) where iota is the average time spent by a particle inside the modulating cavity. Delay times in excess of several hundred days are possible with reasonable modulation parameters. Interpretation of phase lags observed during the 1969 to 1970 solar maximum in terms of this model suggests that the modulating region is probably not less than 10 a.u. and maybe as much as 35 a.u. in extent.
Ogallagher, J. J.↗
Effect of a diffusion process on the stress concentration near a circular hole
System of differential equations that reflects interrelationships of deformation, diffusion, and thermoconductivity used to study stress concentration around holes in elastic body
DIFFERENTIAL EQUATION↗
Inverse gas chromatography. V - Computer simulation of diffusion processes on the column
The elution behavior of low molecular weight probes on inverse gas chromatography (IGC) columns is simulated using a computer. The IGC model is based on a polymer stationary phase of uniform thickness with a nonnegligible resitance to probe penetration. Three characteristic numbers are found to determine the whole process: Z(p) characterizing the distribution of the probe between phases, Z(f) describing the diffusion in the polymer phase, and Z(g) related to diffusion in the gaseous phase. For situations when Z(p)/Z(f) is less than 2, the standard evaluation procedures are virtually useless. The actual behavior of such systems is described.
Hattam, Paul↗
Transformation of TiN to TiNO Films via In-Situ Temperature-Dependent Oxygen Diffusion Process and Their Electrochemical Behavior
Titanium oxynitride (TiNO) thin films represent a multifaceted material system applicable in diverse fields, including energy storage, solar cells, sensors, protective coatings, and electrocatalysis. This study reports the synthesis of TiNO thin films grown at different substrate temperatures using pulsed laser deposition. A comprehensive structural investigation was conducted by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Non-Rutherford backscattering spectrometry (N-RBS), and X-ray absorption spectroscopy (XAS), which facilitated a detailed analysis that determined the phase, composition, and crystallinity of the films. Structural control was achieved via temperature-dependent oxygen in-diffusion, nitrogen out-diffusion, and the nucleation growth process related to adatom mobility. The XPS analysis indicates that the TiNO films consist of heterogeneous mixtures of TiN, TiNO, and TiO2 phases with temperature-dependent relative abundances. The correlation between the structure and electrochemical behavior of the thin films was examined. The TiNO films with relatively higher N/O ratio, meaning less oxidized, were more electrochemically active than the films with lower N/O ratio, i.e., more oxidized films. Films with higher oxidation levels demonstrated enhanced crystallinity and greater stability under electrochemical polarization. These findings demonstrate the importance of substrate temperature control in tailoring the properties of TiNO film, which is a fundamental part of designing and optimizing an efficient electrode material.
Cherono, Sheilah↗
Magnetic fields and diffusion processes in peculiar A stars
The detailed effects of a magnetic field on the equilibrium surface abundances of Ap stars as well as on the diffusion velocity are considered. The equivalent widths of the magnetic null lines are shown to be functions of the magnetic field strength. Furthermore, null lines can be used to help distinguish between inhomogeneities in abundance and in magnetic field strength and to determine ionization temperatures. The results of the diffusion mechanism with magnetic fields are used to interpret the phenomenon of spectrum variability. A review of the observational aspects of null lines in the magnetic Ap stars is presented.
Shore, S. N.↗
Diffusion Processes at the Magnetopause: POLAR Waves
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cross-field diffusion magnetosheath plasma POLAR↗
Microscopic diffusion processes measured in living planarians
Living planarian flatworms were probed using quasielastic neutron scattering to measure, on the pico-to-nanosecond time scale and nanometer length scale, microscopic diffusion of water and cell constituents in the planarians. Measurable microscopic diffusivities were surprisingly well defined in such a complex system as living animals. The overall variation in the microscopic diffusivity of cell constituents was found to be far lower than the variation in the microscopic diffusivity of water in planarians in a temperature range of 284.5 to 304.1K.
77 NANOSCIENCE AND NANOTECHNOLOGY↗
Analysis of Al diffusion processes in TiN barrier layers for the application in silicon solar cell metallization
An evaporated Al layer is known as an excellent rear metallization for highly efficient solar cells, but suffers from incompatibility with a common solder process. To enable solar cell-interconnection and module integration, in this work the Al layer is complemented with a solder stack of TiN/Ti/Ag or TiN/NiV/Ag, in which the TiN layer acts as an Al diffusion barrier. X-ray photoelectron spectroscopy measurements prove that diffusion of Al through the stack and the formation of an Al{sub 2}O{sub 3} layer on the stack's surface are responsible for a loss of solderability after a strong post-metallization anneal, which is often mandatory to improve contact resistance and passivation quality. An optimization of the reactive TiN sputter process results in a densification of the TiN layer, which improves its barrier quality against Al diffusion. However, measurements with X-ray diffraction and scanning electron microscopy show that small grains with vertical grain boundaries persist, which still offer fast diffusion paths. Therefore, the concept of stuffing is introduced. By incorporating oxygen into the grain boundaries of the sputtered TiN layer, Al diffusion is strongly reduced as confirmed by secondary ion mass spectroscopy profiles. A quantitative analysis reveals a one order of magnitude lower Al diffusion coefficient for stuffed TiN layers. This metallization system maintains its solderability even after strong post-metallization annealing at 425 °C for 15 min. This paper thus presents an industrially feasible, conventionally solderable, and long-term stable metallization scheme for highly efficient silicon solar cells.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Diffusion processes in Al2O3 scales - Void growth, grain growth, and scale growth
The internal microstructure and growth kinetics of Al2O3 scales on Ni-15Cr-13Al (wt percent) are investigated by TEM and analyzed in relation to models of diffusivity. Polished arc-melted specimens were oxidized in 1-atm air at 1100 C for 0.1, 1.0, and 20 hours and ion-thinned for TEM at 100 kV. The frequency distribution of void size and grain size is determined for different oxidation times and scale depths. The kinetics of microvoid growth and of grain and scale growth are plotted and related via simplified models to lattice and grain-boundary oxygen diffusivity, respectively. Good agreement is found between model predictions and data obtained by Oishi and Kingery (1960) on oxygen diffusion in bulk Al2O3. The further implications and limitations of these findings are discssed.
Smialek, J. L.↗
Current understanding of point defects and diffusion processes in silicon
The effects of oxidation of Si which established that vacancies (V) and Si self interstitials (I) coexist in Si at high temperatures under thermal equilibrium and oxidizing conditions are discussed. Some essential points associated with Au diffusion in Si are then discussed. Analysis of Au diffusion results allowed a determination of the I component and an estimate of the V component of the Si self diffusion coefficient. A discussion of theories on high concentration P diffusion into Si is then presented. Although presently there still is no theory that is completely satisfactory, significant progresses are recently made in treating some essential aspects of this subject.
Tan, T. Y.↗
Diffusion processes in the magnetopause boundary layer
A quantitative estimate is calculated for the effect of wave-particle scattering on the structure of the magnetopause boundary layer. It is assumed that large cross-B electric fields are absent in the observed penetration of magnetosheath plasma into the magnetopause boundary layer, thus allowing for cross-field transport comparable to 10% of the Bohm diffusion. It is shown that magnetosheath ions, resonant with low frequency electrostatic waves, can account for the typical boundary layer thickness when transported at 10% of the diffusion rate 1000 sq km/sec. The conditions are required to occur at all local times and under all interplanetary conditions. Significant mass and momentum transfer are then possible across the magnetopause when field merging is not occurring.
Tsurutani, B. T.↗
X-ray background, discrete sources, and diffuse processes
Possible sources are discussed for the cosmic residual X-ray background (XRB) radiation at energies from 3-50 keV. Sources have been identified that can account for at least 50 percent of the XRB. The residual has a spectrum with a flat slope up to 30 keV. Comptonized thermal gas emission is ruled out as the origin of the radiation since the emitting regions would be diffuse and Comptonization would require regions no more than a parsec across. Optically thin bremsstrahlung from discrete sources is a more viable candidate, although the associated spectra would not have been accessible with the Einstein Observatory. Future observations with the AXAF and ROSAT satellites in imaging and spectroscopic modes are discussed for gaining definitive data on the real sources of the XRB.
Giacconi, Riccardo↗
Elemental Mercury Diffusion Processes and Concentration at the Lunar Poles
In 2009, the Lyman Alpha Mapping Project (LAMP) spectrograph onboard the Lunar Reconnaissance Orbiter (LRO) spacecraft made the first detection of element mercury (Hg) vapor in the lunar exosphere after the Lunar Crater Observing and Sensing Satellite (LCROSS) Centaur rocket impacted into the Cabeus crater in the southern polar region of the Moon. The lunar regolith core samples from the Apollo missions determined that Hg had a devolatilized pattern with a concentration gradient increasing with depth, in addition to a layered pattern suggesting multiple episodes of burial and volatile loss. Hg migration on the lunar surface resulted in cold trapping at the poles. We have modeled the rate at which indigenous Hg is lost from the regolith through diffusion out of lunar grains. We secondly modeled the migration of Hg vapor in the exosphere and estimated the rate of cold-trapping at the poles using a Monte Carlo technique. The Hg vapor may be lost from the exosphere via ionization, Jeans escape, or re-impact into the surface causing reabsorption.
Moxley, Frederick↗