The Combination of Morphology and Surface Chemistry Defines the Immunological Identity of Nanocarrie
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Vincent, Michael P.↗
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Stable Rate of Slip Along the Karakax Section of the Altyn Tagh Fault from Observation of Interglacial and Postglacial Offset Morphology and Surface Dating
Digital elevation maps obtained using TanDEM-X and Pleiades data combined with newly obtained surface age estimates using cosmogenic radionuclide (CRN) and optically simulated luminescence (OSL) methods are used to quantify the slip rate along the western section of the Altyn Tagh Fault in southern Xinjiang. The reconstruction of the conical shape of massive alluvial fans inferred to be from the Eemian (115±7 ka) from CRN dating shows consistent left-lateral offsets of 300±20 m, yielding a slip rate of 2.6±0.3 mm/year. Successive episodes of incision have left cut terraces inset in wide canyons, 10–25 m below the fans' surface. The incision was followed by the deposition of a broad terrace of early Holocene age, which is reincised by modern stream channels. Near the village of Shanxili, a 200 m wide valley is partially dammed by a shutter ridge displaced by the fault. A fill terrace deposited upstream from the ridge has an OSL age of 8.8±0.6 ka. The 23±2 m offset of the riser incising the terrace indicates a minimum postdepositional movement on the fault, yielding a Holocene rate of 2.6±0.5 mm/year, consistent with the 115-ka average slip rate. Furthermore, scarp degradation analysis using mass diffusion reveals a nonlinear relationship between fault displacement and degradation coefficient along the progressively exposed fault scarp, a pattern suggesting either seismic clustering or variable diffusion rate since the Eemian. Together with the Gozha Co-Longmu Co fault to the south, the Karakax section of the Altyn Tagh Fault contributes to the eastward movement of the western corner of Tibet.
58 GEOSCIENCES↗
Plasma Surface Interactions: Predicting the Performance and Impact of Dynamic PFC Surfaces
The objective of this project is to develop, and integrate, high-performance simulation tools capable of predicting plasma-facing component (PFC) operating lifetime and the impact of the evolving surface morphology of tungsten-based PFCs on plasma contamination, including the dynamic recycling of fuel species and tritium retention, in future magnetic fusion devices. Establishing a fundamental physical understanding and developing predictive capabilities of plasma-surface interactions (PSI) requires simultaneously addressing complex and diverse physics occurring over a wide range of length (Angstroms to meters) and time (femtoseconds to years) scales, as well as integrating extensive physical processes across the plasma–surface interface. This requires development of not only detailed physics models and computational strategies at each scale, but also algorithms and methods to couple them effectively in a way that can be robustly validated. Deploying these tools requires the continued development and coupling of leadership-scale computational codes to describe the boundary plasma and the evolving PFC surface, as well as a host of simulations that bridge disparate scales to address complex physical and computational issues at the plasma–surface interface in multi-component materials systems for magnetic fusion energy development beyond ITER.
36 MATERIALS SCIENCE↗
Comparative performance of bio-based coatings formulated with cellulose, chitin, and chitosan nanomaterials suitable for fruit preservation
Sustainable nanomaterials (SNMs) from wood, sugarcane and crab shell were prepared and used to coat selected fruits. The properties of SNMs and selected fruits were characterized and strawberry was used as an example to test antifungal activity and freshness preservation of the SNMs. The SNMs with their nano-structured morphology form strong shear-thinning dispersions for easy spraying on fruit surfaces. The fruit surface free energy was influenced by its surface morphology, predominant surface wax components, and cutin monomers. The antifungal activity of SNMs was influenced by their surface functional groups and particle size (crystals vs fibers). The coblend of wood nanocrystals (WCNCs) and chitosan nanofiber (CSNFs) exhibited the best antifungal property, which was comparable with the performance of the fungicide thiabendazole (80 mg L -1 ). The weight loss and color change of the WCNC/CSNF coated strawberries decreased by nearly half compared with the control samples, showing coating effectiveness on preserving fruit freshness.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Artificial linear brush abrasion of coatings for photovoltaic module first-surfaces
Natural soiling and the subsequent necessary cleaning of photovoltaic (PV) modules result in abrasion damage to the cover glass. The durability of the front glass has important economic consequences, including determining the use of anti-reflective and/or anti-soiling coatings as well as the method and frequency of operational maintenance (cleaning). Artificial linear brush abrasion using Nylon 6/12 bristles was therefore examined to explore the durability of representative PV first-surfaces, i.e., the surface of a module incident to direct solar radiation. Specimens examined include silane surface functionalized-, roughened (etched)-, porous silica-coated-, fluoropolymer-coated-, and ceramic (TiO 2 or ZrO 2 /SiO 2 /ZrO 2 /SiO 2 )-coated-glass, which are compared to monolithic-poly(methyl methacrylate) and -glass coupons. Characterization methods used in this study include: optical microscopy, ultraviolet–visible–near-infrared (UV-VIS-NIR) spectroscopy, sessile drop goniometry, white-light interferometry, atomic force microscopy (AFM), and depth-profiling X-ray photoelectron spectroscopy (XPS). The corresponding characteristics examined include: surface morphology, transmittance (i.e., optical performance), surface energy (water contact angle), surface roughness, scratch width and depth, and chemical composition, respectively. The study here was performed to determine coating failure modes; identify characterization methods that can detect nascent failures; compare the durability of popular contemporary coating materials; identify their corresponding damage characteristics; and compare slurry and dry-dust abrasion. This study will also aid in developing an abrasion standard for the PV industry.
14 SOLAR ENERGY↗
Artificial Linear Brush Abrasion of Coatings for Photovoltaic Module First Surfaces
Natural soiling and the subsequent requisite cleaning of photovoltaic (PV) modules result in abrasion damage to the cover glass. The durability of the front glass has important economic consequences, including determining the use of anti-reflective and/or anti-soiling coatings as well as the method and frequency of operational maintenance (cleaning). Artificial linear brush abrasion using Nylon 6/12 bristles was therefore examined to explore the durability of representative PV first-surfaces, i.e., the surface of a module incident to direct solar radiation. Specimens examined include silane surface functionalized-, roughened (etched)-, porous silica-coated-, fluoropolymer-coated-, and ceramic (TiO2 or ZrO2/SiO2/ZrO2/SiO2)-coated-glass, which are compared to monolithic-poly(methyl methacrylate) and -glass coupons. Characterization methods used in this study include: optical microscopy, ultraviolet-visible-near-infrared (UV-VIS-NIR) spectroscopy, sessile drop goniometry, white-light interferometry, atomic force microscopy (AFM), and depth-profiling X-ray photoelectron spectroscopy (XPS). The corresponding characteristics examined include: surface morphology, transmittance (i.e., optical performance), surface energy (water contact angle), surface roughness, scratch width and depth, and chemical composition, respectively. The study here was performed to determine coating failure modes; identify characterization methods that can detect nascent failures; compare the durability of popular contemporary coating materials; identify their corresponding damage characteristics; and compare slurry and dry-dust abrasion. This study will also aid in developing an abrasion standard for the PV industry.
41 EE - Solar Energy Technologies Office (EE-4S)↗
Basic Research of Intrinsic Tamper indication Markings and Patterns defined by Pulsed Laser Irradiation
With our previous research, it was found that surface asperities or roughness must be present to create periodic surface structures upon laser exposure. In particular, an initial rough surface morphology (such as that found with a machined surface) provides multiple sites for light scattering, which underlies the formation of periodic ripple morphologies. Light scattering from a random surface creates patterns of periodic structures (with complex orientations) that could be used as intrinsic markings for tagging materials and equipment. Despite these initial findings, the fundamental mechanisms that give rise to periodic surface structures and their characteristic shapes were not identified in prior research.
36 MATERIALS SCIENCE↗
Surface Self-Diffusion Induced Sintering of Nanoparticles
Despite the critical role of sintering phenomena in constraining the long-term durability of nanosized particles, a clear understanding of nanoparticle sintering has remained elusive due to the challenges in atomically tracking the neck initiation and discerning different mechanisms. Through the integration of in situ transmission electron microscopy and atomistic modeling, this study uncovers the atomic dynamics governing the neck initiation of Pt–Fe nanoparticles via a surface self-diffusion process, allowing for coalescence without significant particle movement. Real-time imaging reveals that thermally activated surface morphology changes in individual nanoparticles induce significant surface self-diffusion. Further, the kinetic entrapment of self-diffusing atoms in the gaps between closely spaced nanoparticles leads to the nucleation and growth of atomic layers for neck formation. This surface self-diffusion-driven sintering process is activated at a relatively lower temperature compared to the classic Ostwald ripening and particle migration and coalescence processes. The fundamental insights have practical implications for manipulating the morphology, size distribution, and stability of nanostructures by leveraging surface self-diffusion processes.
36 MATERIALS SCIENCE↗
Surface modification of bamboo fiber with sodium hydroxide and graphene oxide in epoxy composites
Bamboo fibers (BFs) have high mechanical properties and are candidate reinforcement for epoxy matrix composites. However, to improve performance, good fiber-matrix interaction is required. In this work, unidirectional long BF reinforced epoxy composites at fiber volume content of 22%, 40%, and 50% were made by compression molding. The 40 v% untreated BF reinforced composites exhibited 107% and 439% increase for flexural strength and modulus, respectively, compared to neat epoxy. Sodium hydroxide (NaOH) treatment was used to modify the surface of the BFs, and then the NaOH modified BFs were coated with graphene oxide (GO). The 40 v% NaOH modified BF composites showed an improvement from 259.9 to 327.5 MPa for flexural strength and from 16.7 to 21.5 GPa for flexural modulus, compared to 40 v% untreated BF composites. Slight improvement in properties up to 334.6 MPa for flexural strength and up to 23.8 GPa for flexural modulus was achieved for composites made of 40 v% NaOH/GO modified BF. Surface modification of BF after the NaOH and NaOH/GO treatment was confirmed by X-ray photoelectron spectroscopy and by scanning electron microscopy, which showed differences on the fiber surface morphology and on the composite fracture surface. This BF surface modification approach with GO has potential to impart other properties beyond mechanical to produce multifunctional composite and lead to the use of sustainable plant fibers as alternatives to synthetic fibers.
36 MATERIALS SCIENCE↗
Observation of tantalum deposition and growth on TiB2 and ZrB2 from PISCES-RF deuterium and helium plasma exposures
Deuterium and helium plasma exposures on bulk TiB2 and ZrB2 samples were performed using the PISCES-RF linear plasma device. 40 and 90 eV deuterium ion plasma exposures were performed at 240 and 800 °C sample temperatures, and 80 eV helium ion plasma exposures were performed at 800 °C sample temperatures. Following plasma exposures, it was discovered that two plasma conditions (90 eV deuterium and 80 eV helium at 800 °C) resulted in thick (>200 nm) tantalum-rich (>10 at%) surface features on the targets, presumably from tantalum sourced from a tantalum adapter mask or cap used as part of the target holder. This work aims to characterize these tantalum-rich features and examine the mechanisms of impurity deposition.Plasma-induced surface morphology of the tantalum-rich surface layers depends on plasma properties and target temperature and chemistry. Greater titanium sputtering compared to zirconium resulted in more distinct surface features in the TiB2 samples compared to the ZrB2 samples via increased, prompt deposition onto tantalum surface impurities. There is still uncertainty as to why thick tantalum deposition only occurred under some plasma exposure conditions but not others; it is likely due to tantalum sputtering by a combination of boron molecules from the targets and carbon-impurities in the tantalum mask or targets. Impurity driven surface features are a well-documented phenomena in samples exposed to plasma from linear plasma device facilities—this work confirms the occurrence of this and emphasizes the need for chemistry characterization of isolated post-mortem surface features in plasma-exposed samples.
Nuckols, Lauren↗
Pool boiling critical heat flux studies of accident tolerant fuel cladding materials
Pool boiling experiments have been performed at atmospheric pressure on potential accident tolerant fuel (ATF) cladding materials (Zirlo®, Cr coated Zirlo®, FeCrAl coated Zirlo®, and monolithic SiC) to evaluate the Critical Heat Flux (CHF) points. Corrosion resistant coatings of Cr and FeCrAl alloy were deposited on flat Zirlo® samples using cold spray technology. The as-prepared samples after uniform surface polishing were subjected to autoclave tests at 360 °C water and 18.6 MPa for 360 h to simulate prototypic corrosion of the ATF cladding materials in LWR normal operation. Surface characteristics potentially influencing CHF such as surface morphology, roughness, static contact angle, and surface chemistry were characterized using a suite of characterization methods including scanning electron microscopy, 3D optical profilometry, optical contact angle measurements, and x-ray photoelectron spectroscopy (XPS). Thermo-physical properties of the samples such as density, thermal conductivity, and heat capacity were measured by differential scanning calorimetry and laser flash thermal diffusivity measurement. FeCrAl coatings showed CHF values comparable to bare Zirlo® samples, while slightly lower CHF values were observed for Cr coated samples and bulk SiC flats (produced by chemical vapor deposition, CVD). As-deposited Cr coatings showed 67% higher CHF than the as-polished Cr coatings due to its higher surface roughness level. The autoclave testing for the prepared samples generally increased the CHF except for the surface polished Cr coatings. Similar CHF values of bare Zirlo®, FeCrAl coating, and CVD SiC samples were observed after autoclave test but there were negligible change CHF of Cr coatings. XPS studies indicated that the formation or deposition of a few monolayers of hydrophobic carbonaceous species on surface can affect CHF values. The trends in CHF data are discussed in terms of evolution of the surface characteristics of the ATF materials.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Stability Enhancement and Microstructural Modification of Ni-Rich Cathodes via Halide Doping
In this study, elemental doping is an effective strategy to modify surface and bulk chemistry in NMC cathode materials. By adding small amounts of lithium halide salts during the calcination process, the Ni-rich NMC811 cathode is doped with Br, Cl, or F halogens. The dopant type has a significant impact on the lithiation process and heavily influences the final cathode porosity and surface morphology. Utilizing a variety of electrochemical, surface, and bulk characterization techniques, it is demonstrated that an initial content of 5 mol % LiBr or LiCl in the lithium source is effective in improving capacity retention while also providing excellent rate performance. The improvements are attributed to a substantial increase in specific surface area, the formation of a stable cathode electrolyte interface (CEI) layer, and suppressed surface reconstruction. In addition, the particle microstructure is better equipped to handle cyclic volume changes with increased values of critical crack lengths. Overall, it is demonstrated that anion doping via the addition of lithium halide salts is a facile approach toward Ni-rich NMC modification for enhanced cathode performance.
25 ENERGY STORAGE↗
Hydrogen Sulfide Passivation for p-Type Passivated Emitter and Rear Contact Solar Cells
This work reports on the application of sulfur (S)-passivation to passivated emitter and rear contact (PERC) solar cells. The emitter surface was passivated by hydrogen sulfide (H 2 S) gas phase reaction and capped by a hydrogenated amorphous silicon nitride (a-SiN x :H) layer. The sulfur passivation on a symmetrically n + diffused emitter is shown to lead to an emitter saturation current density (J 0n+ ) of 30 fA/cm 2 at R sheet,n+ ≈ 100 Ω/sq. The application of S-passivation to the emitter surface in the PERC cell structure, with the rear surface passivated by an aluminum oxide (Al 2 O 3 )/a-SiN x :H stack, showed a promising implied open-circuit voltage (iV OC ) of 686 mV before metallization. This iV OC was higher than that for the a-SiN x :H or SiO 2 /a-SiN x :H passivated emitter surfaces (675 and 674 mV, respectively) on PERC cells processed in the same run. However, a significant drop in cell V OC is observed for the S-passivated PERC cell after the completion of device fabrication with laser patterning, screen-printed metal contact deposition, and firing. Nonetheless, an efficiency of ~20% and a V OC of ~650 mV was achieved with an emitter surface passivated by sulfur. We identified that the 760°C contact firing process degrades the S-passivation quality. Furthermore, the surface morphology was studied, and a detailed surface analysis was performed to study the causes of the S-passivated surface degradation.
14 SOLAR ENERGY↗
Effects of surface undulations on asymmetric X-ray diffraction: a rocking-curve topography study
The results are reported of an X-ray diffraction study of an Si crystal designed and fabricated for very asymmetric diffraction from the 333 reflection for X-ray energies of 8.100 and 8.200 keV. A crystal with an asymmetry angle of 46 ± 0.1° between the surface and the (111) planes was studied. The grazing angles of incidence were near 1.08 and 0.33° for these two energies, respectively. Features arising from surface undulations were not observed at 8.100 keV, but were observed at 8.200 keV. The results at 8.100 keV allow an alternative explanation based on strain near the surface to be ruled out. Topographic images were obtained as a function of rocking angle, and in the case of 8.200 keV the surface morphology is evident. Finally, the results are found to be in agreement with dynamical X-ray diffraction calculations made with the Takagi–Taupin equations specialized to a surface having convex or concave features, as reported in the accompanying paper [Macrander (2020). J. Appl. Cryst. 53 , 793–799].
36 MATERIALS SCIENCE↗
Mechanisms of dissolution from gibbsite step edges elucidated by ab initio molecular dynamics with enhanced sampling
Surface reactions underpin our collective understanding of mineral dissolution. This impacts a range of predictive geochemical models (for weathering, the fate and transport of metals) as well as industrial utilization of minerals. Yet atomistic details are rarely known due to the complex mineral/fluid interfacial environment. There is significant need to understand the mechanistic details of dissolution reactions and how they depend on surface morphology and solution conditions. This work utilizes surface pit models in conjunction with changes to solution composition that mimic pH to explore surface detachment of aluminate from gibbsite, which is a primary source of Al in soils and within the industrial processing of aluminum. Ab initio molecular dynamics simulations with enhanced sampling has been used to explore the detailed process of the detachment, the results of which indicate two potential pathways that are differentiated based upon the extent of water hydration. Here, the heights of the energy barriers depend upon the local morphology which influence the number of bridges (quasi-)simultaneously broken (1 or 2) or the Al-O coordination of the neighboring aluminum atoms (5 or 6) at the armchair edge. pH effects are significant, with a nearly 50% reduction in barrier height under alkaline conditions that are relevant to geothermal fluids and Al extraction from minerals.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
A Comparison of Emerging and Industry Benchmark Photovoltaic Backsheets Between Different Outdoor Locations
Recent interest within the photovoltaic (PV) module industry is largely directed toward enhanced lifetimes in the field, balanced with improved recyclability. Traditionally, fluoropolymer-based backsheets have been used, however, are difficult to recycle. Emerging polyolefin (PO)-based backsheets are more recyclable and can be formulated to be robust. Properties of different fluoropolymer- and non-fluoropolymer-based backsheet coupons and in encapsulated silicon mini modules that have been fielded in Albuquerque, NM and Cocoa, FL are reported here. Seven backsheets were examined: two novel PO's, TPT, APO, PPE, AAA, and KPf. Methods of examination include module electrical performance (I - V flash test), surface morphology (optical microscope and gloss), polymer chemical structure (FTIR), EL imaging, mechanical tensile testing, DC breakdown voltage, DSC (phase transitions), and optical performance (reflectance spectra).
industries↗
Epitaxial growth and characterization of magnesium gallate (MgGa 2 O 4 ) thin films by pulsed laser deposition
To advance high power device application of MgGa 2 O 4 , it is imperative to achieve crystalline epitaxial thin films and to observe its materials’ characteristics within a wide range of growth conditions. However, there is no published work on the growth of this promising ultrawide bandgap material till this day. In this study, we report the crystalline growth of MgGa 2 O 4 thin films on c-plane (006) sapphire substrates using the pulsed laser deposition (PLD) technique in a broad range of temperature and oxygen pressure. The temperature range for this crystalline growth was within the temperature range of 300°C to 700°C and a pressure range of 1x10 -1 to 1x10 -3 Torr. Within this parameter range, the structural, chemical, optical, and surface property of MgGa 2 O 4 thin films have been investigated. Specifically, the acquired XRD patterns confirmed the film growth along the [111] preferential crystal orientation in the lattice. Here, the rocking curve measurement of the prominent (222) plane showed an increasing trend of the crystallinity with growth temperature and pressure. Furthermore, the XRD phi (φ) scan demonstrated the six-fold rotational symmetry of the MgGa 2 O 4 films and the epitaxial relationship of 30° between the film and the sapphire substrate. The XPS spectra confirmed the presence of +2 and +3 oxidation state for Mg and Ga respectively, in the films. The direct bandgap of MgGa 2 O 4 films was obtained ~5.27±0.03 eV by analyzing the UV-Vis absorbance spectra using the Tauc equation. The SEM images exhibited a granular surface morphology of the MgGa 2 O 4 films with an increasing trend in the grain size from low to high temperature and pressure. The refractive index and thickness of these films were in the range of ~1.90±0.02 and ~70±2.0 nm, respectively determined by fitting the spectroscopic ellipsometry data.
36 MATERIALS SCIENCE↗
Thermal Behavior During the Selective Laser Melting Process of Ti-6Al-4V Powder in the Point Exposure Scan Pattern
Currently, there are two main scan patterns, including the continuous exposure scan pattern and the point exposure scan pattern, during the selective laser melting (SLM) process. The point exposure scan pattern allows a three-dimensional (3-D) printer to build finer detail features as a static molten pool that is more stable than a dynamic one. However, there has been limited theoretical research on the thermal behavior characteristics during the process in the point exposure scan pattern. Therefore, in this study, the simulation of thermal behavior during SLM of Ti-6Al-4V powder in the point exposure scan pattern was performed. The temperature evolution behavior of different positions and the effects of exposure time on the temperature evolution behavior of different positions, temperature distributions, and dimensions of the molten pool were investigated. The results showed that the direct exposure position and unexposed position had significantly different temperature evolution behaviors under a given condition, and the changed exposure time had the greatest influence on the direct exposure position compared with unexposed position. Moreover, the thermal accumulation effect of a former exposure point on a later one decreased with increasing exposure time. In addition, with the increase of exposure time, the maximum temperature of the molten pool was enhanced and the surface morphology of the molten pool changed from an approximate ellipse to an approximate circle. Besides, the molten pool dimensions were found to increase with exposure time, which indicated that the exposure time played an important role in the stability of the molten pool and the metallurgical bonding in the process. Furthermore, the dimensions of the molten pool and metallurgical bonding in the cross-sectional view were obtained through experiments. Good agreement was obtained when comparing the simulated results with the experimental ones.
36 MATERIALS SCIENCE↗