Induced Surface Degradation Research Articles

Structural electronic and magnetic properties of BaBiO3 single crystals

We report on growth of high quality BaBiO3 single crystals and their characterization via x-ray diffractometry (XRD), atomic force microscopy, surface nanoindentation, electronic transport, and magnetic susceptibility. The grown crystals are mildly twinned, which was analyzed and twin law with twinning factor is obtained. Surface studies revealed very peculiar adsorbate assisted and mechanically induced degradation. The XRD and induced surface degradation point to micro twinning with large strains on the twin boundaries. The observed as-grown surface morphology suggests high sensitivity of crystal growth to the growth temperature variations and might be related to twinning. Electronic transport and magnetization measurements are consistent with previous works, but systematic comparison of latter with earlier works renders an interesting question: can local moments be structurally induced in BaBiO3?

Resurfacing asteroids from thermally induced surface degradation

The spectral slopes of S and Q-type asteroids are altered by the weathering of their surfaces due to solar wind interactions and micrometeorite impacts, as well as any processes that work to remove that weathered material. These processes of space weathering and asteroid resurfacing compete with each other to determine the spectral slope of each asteroid, with space weathering raising the spectral slope and resurfacing lowering it. By considering the distribution of spectral slopes with respect to orbital location and size, we can determine which potential resurfacing processes are the most dominant. In this study, we show that the spectral slopes of S and Q-type Near-Earth Asteroids (NEAs) decrease with decreasing perihelion, but only for perihelia q≲0.9 AU. We then use this distribution of spectral slopes vs. perihelion as a constraint for modeling two proposed resurfacing mechanisms. For both models, we numerically integrate the orbits of NEAs over their lifetimes and track their spectral slopes. First, we model the resurfacing of asteroids due to close encounters with the terrestrial planets and found that no combination of parameters could explain the spectral slope vs. perihelion trend at q≲0.9 AU. We also model the resurfacing of asteroids due to thermally induced surface degradation, by assuming a power law relationship between the resurfacing timescale and the solar distance. For a space weathering timescale of an asteroid on a circular orbit at 1 AU of τSW0≲5 Myr, we find a range of resurfacing timescales and power law exponents that generate a spectral slope vs. perihelion distribution consistent with observations. We discuss that previous studies supporting the resurfacing of asteroids due to close encounters could be a result of confounding variables, as the correlation of Q-type asteroids' past orbits with the terrestrial planets are confounded by the higher fraction of Q-type asteroids at low perihelia, which could be created by another mechanism. We also discuss previous studies that qualitatively support the process of thermally induced surface degradation at low perihelia, and conclude that thermal processes are the most consistent explanation for resurfacing of asteroids with low perihelia q≲0.9 AU.

Oxidation behaviour of amorphous steel: impact on electromagnetic properties

PurposeHigh silicon amorphous steels are gaining preference as the material of choice for the fabrication of the core of low and medium power electrical transformers because they present a better electromagnetic behaviour compared to that offered by common grain-oriented and non-oriented high silicon steels. This study aims to investigate the effects that the environmental conditions present during the high temperature annealing of cores exert on the surface oxidation and electromagnetic changes experienced by a commercial amorphous steel alloy.Design/methodology/approachThe effect of environmental impact on the correct development of annealing practices during the manufacture process of amorphous steel cores used in distribution transformers was studied by the development of an oxidation reactor. With this installation, it was possible to simulate environmental conditions that could affect the surface of magnetic cores made from amorphous steel.FindingsIt was found that: the surface oxidation of amorphous steels affects their electromagnetic behaviour, environmentally induced surface degradation can be modelled at laboratory scale and oxide formation does not affect the amorphous condition of the alloy.Originality/valueThe effect of surface oxidation induced by the existence of water vapour in the annealing process of cores made from amorphous steels and its impact on the electromagnetic behavior of these alloys has been barely studied.

ORR Activity for Pt/Pd(111) Bimetallic Surface Prepared By Molecular Beam Epitaxy

Background From the view-points of reduction in usage of expensive Pt and enhancement in oxygen reduction reaction (ORR) activity [1], Pt-shell and Pd-core, core-shell type nano-particles attract much interest as cathode-electrode materials for polymer electrolyte fuel cells. Relation between topmost surface structures of the core-shell nano-particles and ORR activities is a key for developing highly-active, low-Pt-content catalysts. However, disscussion of ORR mechanism is complicated. In this study, we prepared well-defined Pt/Pd(111) bimetallic surfaces by molecular beam epitaxy (MBE) in ultra-high vacuum (UHV) and performed EC measurements in an inert gas atomosphere. Experimental The MBE apparatus and UHV-EC sample transfer system have been described earlier [2]. All sample fabrication processes were conducted in UHV. Pd(111) single crystal substrate was cleaned by Ar+ sputtering and annealing. Various-thick Pt was deposited onto the clean Pd(111) by an electron-beam evaporation method at 673K. The resulting surface structures were verified with low energy electron diffraction (LEED), scanning tunelling microscope in UHV (UHV-STM). Then, the MBE-prepared Ptxnm/Pd(111) surfaces were transferred without being exposed to air to the EC system set in an N2-purged glove box. Cyclic voltammogram (CV) of the samples were recorded in N2-purged 0.1M HClO4, and, then, linear sweep voltammetry (LSV) was conducted by a rotating electrode (RDE) method at 1600 rpm after saturating the solution with O2. EC degradation of the Ptxnm/Pd(111) was evaluated by applying potential cycles between 0.6V (3s) and 1.0V (3s) vs. RHE. The potential-cycled Ptxnm/Pd(111) were re-transferred to the UHV-STM system to evaluate the potential-cycle-induced topmost surface structural changes. Results and discussion From the results obtained by LEED and IRRAS for carbon monoxide adsorption, we deduce that 0.6nm-thick Pt almost covers the Pd(111) substrate surface. A UHV-STM image of the Pt0.6nm/Pd(111) (inset in Fig. 1 (a)) clearly shows atomically-flat, wide terraces. Fig. 1 (a) shows CV curves of the Pt0.6nm/Pd(111) (blue). CV curves for clean Pt(111) (black) and Pd(111) (grey) are also presented as references. EC charge of the H-related features (0.15V-0.3V ; Qab&de) for the Pt0.6nm/Pd(111) markedly shirinks in comparison to that of clean Pd(111), suggesting that the topmost surface of the Pt0.6nm/Pd(111) is epitaxial Pt(111). Fig. 1 (b) shows LSV curves for the respective surfaces. A half-wave potential of the as-prepared Pt0.6nm/Pd(111) (blue) shifts positively relative to clean Pt(111), indicating ORR activity enhancement. The LSV curve of the as-prepared Pt0.6nm/Pd(111) shifts to lower potentials after the 1000 potential cycles (red), revealing potential-cycle induced surface degradation. One might notice that the red LSV curve is almost identical to that for 0.15nm-thick-Pd deposited Pt(111) (Pd0.15nm/Pt(111);green). The results obtained in this study suggest that the topmost surface of MBE-prepared Pt0.6nm/Pd(111) is degraded through dissolution and precipitation of the substrate Pd atoms during the potential cycles. Acknowledgement This work was supported by New Energy and Industrial Technology Development Organization (NEDO).

Feasibility of macrophage mediated on-demand drug release from surface eroding poly(ethylene carbonate)

Macrophage induced surface degradation of poly(ethylene carbonate) (PEC) was investigated under in vitro conditions. Degradation of PEC with the MW of 41 kDa (PEC41) was slower than that of PEC with the MW of 200 kDa (PEC200). In terms of macrophage mediated drug release from PEC matrix, in cell-free medium, less than 1% of levofloxacin was released from both PEC samples in 10 days, while more than 60 and 20% of the drug, levofloxacin, can be detected in medium with macrophages from PEC200 and PEC41 films, respectively. This work indicated that on-demand drug delivery induced by macrophages can be achieved with PEC polymer.

Effects of optical beam angle on quantitative optical coherence tomography (OCT) in normal and surface degenerated bovine articular cartilage

Quantitative measurement of articular cartilage using optical coherence tomography (OCT) is a potential approach for diagnosing the early degeneration of cartilage and assessing the quality of its repair. However, a non-perpendicular angle of the incident optical beam with respect to the tissue surface may cause uncertainty to the quantitative analysis, and therefore, significantly affect the reliability of measurement. This non-perpendicularity was systematically investigated in the current study using bovine articular cartilage with and without mechanical degradation. Ten fresh osteochondral disks were quantitatively measured before and after artificially induced surface degradation by mechanical grinding. The following quantitative OCT parameters were determined with a precise control of the surface inclination up to an angle of 10° using a step of 2°: optical reflection coefficient (ORC), variation of surface reflection (VSR) along the surface profile, optical roughness index (ORI) and optical backscattering (OBS). It was found that non-perpendicularity caused systematic changes to all of the parameters. ORC was the most sensitive and OBS the most insensitive to the inclination angle. At the optimal perpendicular angle, all parameters could detect significant changes after surface degradation (p < 0.01), except OBS (p > 0.05). Nonsignificant change of OBS after surface degradation was expected since OBS reflected properties of the internal cartilage tissue and was not affected by the superficial mechanical degradation. As a conclusion, quantitative OCT parameters are diagnostically potential for characterizing the cartilage degeneration. However, efforts through a better controlled operation or corrections based on computational compensation mechanism should be made to minimize the effects of non-perpendicularity of the incident optical beam when clinical use of quantitative OCT is considered for assessing the articular cartilage.

Surface electrical degradation for low mass ion implanted SiO 2: Dependence on ion mass, energy and dose rate

KS-4V quartz glass (SiO 2) is a candidate material to be used in ITER diagnostic systems where it will play an important role for optical components and possibly as electrical insulator. In addition to neutron and gamma radiation, the material will be subjected to bombardment by low energy ions and neutral particles. Previous work has shown severe electrical and optical degradation with a marked temperature dependence when the material is subjected to proton or alpha particle bombardment, due to loss of oxygen from the surface caused by preferential sputtering by energetic ions. In this work, a systematic study of ion bombardment induced surface degradation as a function of the ion mass, energy and dose rate has been carried out. A clear dependence on ion mass has been observed, with degradation occurring much more rapidly for heavier ions. Also the surface electrical degradation depends strongly on the implanted particle energy, degradation is higher for higher energy. No dependence on dose rate was observed.

Hydrogenation and Electrochemical Characteristics of Amorphous-nanostructured Mg-based Alloys

In the development of new hydrogen absorbing materials for a next generation of metal hydride electrodes for rechargeable batteries, metastable Mg-Ni-based compounds find currently special attention. Amor phous-nanocrystalline <TEX>$Mg_{63}Ni_{30}Y_7$</TEX> and <TEX>$Mg_{50}Ni_{30}Y_{20}$</TEX> alloys were produced by mechanical alloying and melt-spinning and characterized by means of XRD, TEM and DSC. On basis of mechanically alloyed Mg-Ni-Y powders, complex hydride electrodes were fabricated and their electrochemical behaviour in 6M KOH (pH=14,8) was investigated. The electrodes made from <TEX>$Mg_{63}Ni_{30}Y_7$</TEX> powders, which were prepared under use of a SPEX shaker mill, with a major fraction of nanocrystalline phase reveal a higher electrochemical activity far hydrogen reduction and a higher maximum discharge capacity (247 mAh/g) than the electrodes from alloy powder with predominantly amorphous microstructure (216 mAh/g) obtained when using a Retsch planetary ball mill at low temperatures. Those discharge capacities are higher that those fur nanocrystalline <TEX>$Mg_2Ni$</TEX> electrodes. However, the cyclic stability of those alloy powder electrodes was low. Therefore, fundamental stability studies were performed on <TEX>$Mg_{63}Ni_{30}Y_7$</TEX> and <TEX>$Mg_{50}Ni_{30}Y_{20}$</TEX> ribbon samples in the as-quenched state and after cathodic hydrogen charging by means of anodic and cathodic polarisation measurements. Gradual oxidation and dissolution of nickel governs the anodic behaviour before a passive state is attained. A stabilizing effect of higher fractions of yttrium in the alloy on the passivation was detected. During the cathodic hydrogen charging process the alloys exhibit a change in the surface state chemistry, i.e. an enrichment of nickel-species, causing preferential oxidation and dissolution during subsequent anodization. The effect of chemical pre-treatments in 1% HF and in <TEX>$10\;mg/l\;YCl_3/1%\;H_2O_2$</TEX> solution on the surface degradation processes was investigated. A HF treatment can improve their anodic passivation behavior by inhibiting a preferential nickel oxidation-dissolution at low polarisation, whereas a <TEX>$YCl_3/H_2O_2$</TEX> treatment has the opposite effect. Both pre-treatment methods lead to an enhancement of cathodically induced surface degradation processes.

Secondary molecular ion emission from aliphatic polymers bombarded with low energy ions: Effects of the molecular structure and the ion beam induced surface degradation

The influence of the molecular structure on the secondary ion production is studied for three saturated aliphatic polymers (low-density polyethylene, polypropylene and polyisobutylene) bombarded with low energy ions. These polymers differ only by the presence and nature of the pendant group. The intensities of the most characteristic secondary molecular ions are followed as a function of the primary ion dose in the (10 12 ions/cm 2–10 14 ions/cm 2) range for two primary ion bombardment conditions (4 keV Xe + and 15 keV Ga +). The results show that there is a direct relationship between the polymer degradation and the emission of molecular fragments. No truly “static” conditions are found, rather, the polymer surface undergoes a continuous transformation under ion beam bombardment. The most spectacular effect is its dehydrogenation. By rationalizing the competition between the two related processes, surface degradation and molecular ion production, a kinetic model is proposed in order to explain the behavior of molecular fragments belonging to the C8 cluster.

A mechanism for induced surface degradation of high-resistive GaAs during device fabrication

Undoped, liquid-encapsulated-Czochralski (LEC)-grown, semi-insulating (SI) GaAs crystals were electrically characterized by temperature-dependent Hall effects and conductivity measurements to establish the mechanism for thermally induced surface degradation. X-ray photoelectron spectroscopy (XPS) was used to obtain depth profiles of the Ga and As composition, and the nature of the defect complexes and their changes were determined using Fourier-transform infrared spectroscopy (FTIR). Boron-related inhomogeneities were found to occur, and although it is normally considered a passive impurity, we conclude that it was in fact responsible for the detrimental p-conversion through the formation of BGa–Ga(i), BGa–GaAs, and BGa–VAs defect complexes. We propose that boron homogenization inhibits the escape of Ga from the crystal surface during annealing, leaving an excess of Ga in the p-converted layers. With FTIR we observed changes in the local vibrational-mode absorption of the acceptor defects SiAs, CAs, and the donors BGa, SiGa, and BGa–SiAs upon annealing. We present a theoretical analysis, which explains the observed changes in electrical characteristics on the basis of variations in deep-donor compensators, less deep donors, and net shallow acceptors, and conclude that higher device yields are achievable in SI GaAs if boron contamination can be reduced.

Surface Weatherability of Glass-Fiber-Reinforced Polyester Sheeting. I. Effect of Modification of Resin Chemical Composition

An accelerated weathering test (2 to 0.67 cycle) has been applied to glass-fiber-reinforced polyester (GRP) to determine the effect on surface durability of modifiying the chemical composition of the resin matrix. The nature and rate of induced surface degradation were monitored by scanning electron microscopy. For GRP based on general purpose polyester resin (o-phthalic anhydride-propylene glycol-maleic anhydride-based) the nature of surface damage was not significantly influenced by chemical modification, although the time of initiation was altered. The average overall durability of GRP improved 60% by substitution of propylene glycol with neopentyl glycol, 30% by incorporation of a greater amount of maleic anhydride, and 20% by replacement of both anhydride and glycol with isophthalic acid and neopentyl glycol, respectively. By inference, replacement of anhydride with isophthalic acid reduced the durability of neopentyl glycol-based GRP by 40%.

Surface Weatherability of Glass-Fiber Reinforced Polyester Sheeting. II. Effect of Constituents

An accelerated weathering test (2 to 0.67 cycle) has been applied to glass-fiber reinforced polyester (GRP) to evaluate the effect of constituents on the surface durability of GRP. The nature and rate of induced surface degradation was assessed by scanning electron microscopy. For general-purpose GRP (GRP (GP)), replacement of chopped glass roving reinforcement with chopped glass mat reinforcement did not change the nature and rate of surface degradation. Incorporation of a glass surfacing veil, to provide a resin-rich surface layer, however, improved the durability of GRP (GP) to fiber pop out by 100%. Moreover, replacement of styrene with a styrene-methyl methacrylate cross-linking agent enhanced the resistance of GRP (GP) to fiber pop out, erosion, and surface microcracking an average of 70%. Substitution of an ultraviolet absorber Tinuvin P with Tinuvin 327 did not alter the durability of ethylene glycol-based GRP, while replacement of Tinuvin P with Tinuvin P/Tinuvin 144 in neopentyl glycol-based GRP improved the resistance to fiber pop out by 17% but decreased the durability to erosion and surface microcracking by 19 and 12%, respectively.

Application of Accelerated Weathering Test to Glass-Fiber Reinforced Polyester Sheets of Improved Surface Durability

Abstract An accelerated weathering test has been applied to three types of commercial glass-fiber reinforced polyester (GRP), the durability of which has been improved by the application of various surface finishes. The nature and rate of induced surface degradation were monitored throughout the exposure period by scanning electron microscopy and, where possible, compared with those produced by horizontal outdoor exposure at Ottawa, Canada. Acrylic-lacquer-coated GRP underwent six types of surface damage leading to exposure and surface microcracking of the GRP substrate. The first three types of damage produced by artificial weathering were similar to those induced so far after six years of outdoor weathering, resulting in an acceleration factor of 6. Gel-coated GRP sustained surface microcracking as for outdoor exposure with an acceleration factor of 9. Poly(vinyl fluoride)-laminated (PVF) GRP underwent five types of damage, resulting in delamination of PVF and surface microcracking of the unprotected GRP resin. The first two types of damage have been verified to date after six years of outdoor exposure and were accelerated by a factor of 5.

Analysis of Defects in Laser Annealed GaAs

ABSTRACTThe nature and depth distributions of residual damage in ion implanted and pulsed ruby laser annealed GaAs have been studied using both plan-view and cross-section transmission electron microscopy (TEM) specimens for high dose (1.0 × 1015 cm−2) Zn+, Se+ and Mg+ implants. It was found that laser energy densities above 0.36 J/cm2 were required to remove the implantation damage, this threshold energy density giving good agreement with that indicated by electrical activation measurements. Laser induced surface degradation of the GaAs was present even for energy densities as low as 0.25 J/cm2, and more severe damage, with the introduction of dislocations near the surface, was present for energy densities above 0.8 J/cm2. The use of thin SiO2 layers for encapsulation during laser annealing was found to substantially reduce this surface degradation.