Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “TEXTURE”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,477 records · Page 82
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Effect of cold rolling on the microstructural evolution of new β-typed Ti–6Mo–6V–5Cr–3Sn–2.5Zr alloys

A Ti–6Mo–6V–5Cr–3Sn–2.5Zr (wt.%) alloy was designed as a new metastable β-Ti alloy. The effect that cold rolling had on the microstructural evolution of the material was investigated via optical microscopy (OM), X-ray diffraction (XRD), electron back-scattered diffraction (EBSD) and transmission electron microscopy (TEM) measurements. A single β phase formed in the alloy after solution treatment at 780 °C for 30 min followed by water quenching. The solution-treated alloy was cold rolled with thickness reductions of 10%, 30%, 50% and 70%, and the hardness values increased as the thickness of the specimen decreased. The textures of the cold rolled specimen were characterized according to the 〈110〉 partial parallel to the rolling direction as the rolling reduction increased. The crystallographic orientation showed principal α-fiber textures for (111)〈110〉 and (112)〈110〉. The cold deformation led to the appearance of martensite α″ phases, particularly stress-induced martensite (SIM) α″ phases. - Highlights: • Effect of cold rolling on new β-typed Ti-6Mo-6V-5Cr-3Sn-2.5Zr alloy was studied. • A single β phase was obtained after solution treatment at 780 °C for 30 min. • α-Fiber textures became dominated with the increase in cold rolling reduction. • A stress-induced α″ martensite was caused by cold rolling.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Enhanced strength and electrical conductivity of ultrafine-grained Al-Mg-Si alloy processed by hydrostatic extrusion

Highlights: • Al-Mg-Si alloy was subjected to hydrostatic extrusion combined with aging treatment. • UFG Al-Mg-Si alloy with UTS of 332 MPa and conductivity of 58% IACS was obtained. • Precipitation process depended on applied strains and crystallographic texture. • Strengthening effect was achieved by UFG structure and needle-like β″ precipitates. • Precipitation of β″ and spherical β′/β particles at GB provided high conductivity. - Abstract: The effect of hydrostatic extrusion combined with an artificial aging on microstructure, mechanical and electrical properties of 6101 Al-Mg-Si alloy was investigated. It has been shown that such thermo-mechanical treatment is an effective method for producing of long wires with an ultrafine-grained microstructure (grain size of 300–400 nm) and enhanced ultimate tensile strength (> 330 MPa) and electrical conductivity (up to 58% IACS). The mechanical behavior of 6101 Al-Mg-Si alloy depended strongly on applied strains by hydrostatic extrusion and crystallographic texture. Higher accumulative strain accelerated the precipitation kinetics but decreased the age hardening response. The double fiber <100> and <111> texture was observed for hydrostatically extruded samples. The <001> grains with homogenously distributed needle-like β″ precipitates provided precipitation strengthening of material while <111> grains resulted in more efficient grain boundary strengthening. Quantitative microstructure characterization allowed adjusting physical model to estimate the electrical conductivity and compare it with experimental data. The high conductivity was provided mainly by decomposition of solid solution due to precipitation of needle-like β″ precipitates in the grain interior and spherical β′ or β particles located at grain boundaries.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Microstructure and mechanical properties of extruded Mg-Gd-Y-Zn-Zr alloys filled with intragranular LPSO phases

Highlights: • Intragranular thin-platelet LPSO phases strongly restrict the DRX. • The low extrusion ratio fails to widely break the intragranular LPSO. • The large extrusion ratio results in the full DRX via the CDRX mechanism. • Finer DRX-ed grains and LPSO induce the higher yield strength and elongation. • The larger grain size causes an increase in the strain hardening rate. - Abstract: A comparison has been made on the dynamic recrystallization (DRX), texture, and mechanical properties of the Mg-5.5Gd-4.4Y-1.1Zn-0.5Zr (wt%) alloys extruded with different ratios (ER, 36 and 7.1). Intragranular long-period stacking ordered (LPSO) phases strongly restrict the DRX by restraining the lattice rotation of α-Mg grains and hindering the migration of the boundaries of DRX-ed grains. Extrusion with ER of 36 can widely break the intragranular LPSO phases and create a fully DRX-ed microstructure with a relatively random texture, while the lower ER of 7.1 fails to break the LPSO and leads to a bimodal microstructure with a strong basal fiber texture. Finer DRX-ed grains and smaller LPSO phases account for the superior tensile yield strength and elongation of the ER36 alloy. However, the ultimate tensile strength of the ER7.1 alloy catches up because its larger grain size causes an increase in the strain hardening rate.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Magnetic Barkhausen noise characterization of two pipeline steels with unknown history

Highlights: • The hardness, microstructure, texture and MBN of two pipeline steels were analyzed. • The angular MBN results revealed possible manufacturing histories of the two pipelines. • The MBN is closely related to the processing history, microstructure and stress state. • The use of MBN technique can help address the integrity issues in the pipeline industry. Steel samples cut from two line pipes with unknown processing history were analyzed using magnetic Barkhausen noise (MBN), electron backscatter diffraction (EBSD) and Vickers hardness techniques on the pipe surface and on sections through the wall thickness. The results show that the MBN responses vary significantly not only between the two pipe steels, but also among different thickness layers of each steel. Both steels show considerable variations in MBN at different locations on the surfaces. For one steel, the surface MBN illustrates an inverse linear relationship with respect to the hardness, while the other does not depict such a relation since the variation in hardness at different locations is very small. Across the thickness, the microstructure (phase and grain size) of both steels is quite similar, but the texture shows significant differences. Again, there is a large difference in hardness across the thickness for one steel, while the other only shows very small variation in hardness across the thickness. The variations in average MBN across the wall thickness for both steels are quite large. Angular MBN measurements on the sectioned samples revealed significant discrepancies in the magnetic anisotropy in the two steels. Based on the analysis of the angular MBN data with respect to the single and dual easy axis models, one pipe can be determined to have been manufactured through a seam welding process, while the other may have been formed by spiral welding. Due to the residual stresses in the steel samples, the effect of the crystallographic texture on the anisotropy in MBN response has essentially been suppressed.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Obtaining aluminas from the thermal decomposition of their different precursors: An {sup 27}Al MAS NMR and X-ray powder diffraction studies

Graphical abstract: - Highlights: • We synthesized three precursors of alumina from different methods. • The calcination of the precursors generated several alumina polymorphs. • XRD and NMR were used for structural investigation of the polymorphs. • The synthesis route determines the structural and textural properties of the solids. - Abstract: A commercial sample of Boehmite was used as precursor of alumina polymorphs. For comparison, three other precursors were synthesized from different methods. Particularly, the use of excess of urea promoted a very crystalline form of basic aluminum carbonate. The characteristics of the four precursors were investigated by thermal, vibrational and X-ray powder diffraction (XRD) analysis. Additionally, the nuclear magnetic resonance, with magic angle spinning ({sup 27}Al MAS NMR), was used to verify the coordination of aluminum cations. Each precursor was calcined at various temperatures generating alumina polymorphs, which were structurally analyzed by XRD and {sup 27}Al MAS NMR. Due to interest in catalysis supports, special attention was given to the γ-Al{sub 2}O{sub 3} phase, which in addition to structural investigation was subjected to textural analysis. The results showed that, from different synthesis procedures and common route of calcination, one can obtain materials with the same composition but with different structural and textural properties, which in turn can significantly influence the performance of a supported catalyst.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Fully implicit crystal plasticity models representing orientations with modified Rodrigues parameters

Here, this work describes a crystal plasticity formulation combining several mathematical, numerical, and implementation choices to produce a highly efficient model. Specifically, the key choices in the implementation are (1) representing orientations with modified Rodrigues parameters, (2) implementing a fully coupled implicit time integration for the elastic stretch, the crystal orientations, and the model internal variables, (3) implementing the model in the NEML2 constitutive modeling framework, based on PyTorch, to vectorize the calculations and port the computation to GPUs and other hardware accelerators, and (4) an exact implementation of the consistent tangent matrix, even for arbitrary coupling to other field variables beyond the displacements, like temperature, neutron fluence, etc. The first two features of the model are, to our knowledge, novel. The paper considers each of these choices individually as well as the final model as a whole. This includes a full description of modified Rodrigues parameters, their advantages over other representations of orientations, the mathematical formulae and tools required to implement a model with modified Rodrigues parameters, and a detailed description of the geometry of the space of modified Rodrigues parameters (in an appendix). It also includes a description of a fully implicit time integration scheme for the orientations and the advantages in representing orientations with modified Rodrigues parameters in implementing such a model. The work then assess, via numerical examples, the advantages of fully coupled implicit time integration versus more common decoupled and explicit time integration schemes. These studies demonstrate the computational advantages of fully coupled integration versus other time integration algorithms, though the performance of the competing models depends on the complexity of the underlying single crystal model. The study concludes by demonstrating that the choice of time integration method affects the sharpness of the predicted texture, with explicit methods for integrating the orientations overestimating texture sharpness and implicit methods underestimating texture sharpness.

Crystal plasticity↗
DOE OSTI2022

Effects of surface treatments on ABS mechanical properties from fused filament fabrication

This paper examines the influence of surface treatments on the mechanical properties of acrylonitrile butadiene styrene (ABS) samples printed by fused filament fabrication (FFF). Prior efforts have applied brushing, painting, solvent dipping, infiltration, and vapor smoothing as post-processing surface treatments to improve the mechanical properties of FFF components. Additionally, because FFF can produce components with undesirable surface roughness, mechanical abrasion, epoxy coating, and acetone treatment may increase tensile strength by decreasing stress concentrations. Ridged surface texture may provide desirable tribological or handling properties. Based on these opportunities, this paper investigates abrasive media blasting, epoxy coating, acetone immersion, and ridged texturing surface treatments on the tensile strength and other mechanical properties of FFF ABS samples. ASTM D638-14 Type-I samples were printed, treated on all sample sides, and tested. From tensile tests, the elastic modulus, tensile strength, and fracture strain for both the untreated and treated ABS samples were calculated. For each sample, the surface finish and fracture macromorphology were observed with optical microscopy and the roughness values for the surface finish were calculated from profilometer data. Furthermore, samples were submerged in water and weighed periodically to measure mass changes due to water absorption. From surface profilometry and optical miscopy data, mechanical media blasting, epoxy coating, and immersion in all concentrations of acetone decreased surface roughness. Overall, on average, grit blasting with large beads and epoxy coating led to 2.6% and 1.2% increases in tensile strength, respectively; immersion in 40% acetone led to a 1.9% increase in tensile strength while treatment in 60% and 80% acetone decreased tensile strength by 4.9% and 1.9%, respectively. The study concludes that only grit blasting with large beads, immersion in 60% acetone, and the ridged texture significantly affected the tensile strength.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Influence of the as-built microstructure on the recrystallization of an additively manufactured Inconel939 Ni-based superalloy

This study investigates the influence of the as-built microstructure on the recrystallization (RX) behavior and mechanical properties of the Ni-based superalloy Inconel 939 produced by laser powder bed fusion (PBF-LB/M). Two distinct as-built microstructures were obtained by varying the hatch distance (h d ): a columnar, strongly textured condition (h d =50, termed h d 50) and an equiaxed, weakly textured condition (h d =70, termed h d 70)). Both were subjected to nine solution treatments combining three temperatures (1100, 1150, and 1200 °C) and three holding times (1, 4, and 8 h). Comprehensive microstructural characterization was conducted to assess grain morphology, texture, grain boundary character, dislocation density, and precipitate distribution. Recrystallization was found to be significantly slower than in cast counterparts, requiring higher temperatures and longer times for completion. The initial microstructure plays a decisive role: full RX was achieved only in hd70 specimens after treatment at 1200 °C for 8 h, whereas hd50 samples exhibited delayed and incomplete RX under identical conditions. This behavior is attributed to the finer grain size and higher fraction of high-angle grain boundaries in hd70, which promote recrystallization. Mechanical testing revealed that hd70 samples subjected to a 1200 °C/8 h treatment followed by standard double ageing show higher yield and tensile strengths across the investigated temperature range than both printed and cast Inconel939 processed under conventional conditions, albeit with slightly reduced ductility. The enhanced mechanical performance is attributed to the larger grain size, which limits grain boundary sliding. These results demonstrate the critical importance of controlling the as-built microstructure and tailoring post-processing strategies to optimize high-temperature performance of PBF-LB/M Inconel939.

Inconel939↗
DOE OSTI2022

Compositionally graded aluminum-silicon alloy fabricated via friction extrusion

Herein, a novel solid-phase gradient alloying technique was developed for a high throughput composition-microstructure-mechanical property assessment. Friction extrusion of a two-piece billet setup facilitated the formation of a seamless compositionally graded aluminum (Al)-silicon (Si) extrudate rod, with Si concentration in Al matrix gradually increasing from ~1 at% at one end to ~7 at% at the other end of the rod. We observed a strong dependence of the Al grain size, morphology, and texture on the Si concentration. The Si particles pinned the recrystallized grain boundaries resulting in refined (< 10 µm) and textured grains in the high Si content region, while the Al grains in the low Si region are equiaxed, randomly textured, and with a larger average size (~50 µm). The hardness of Al-Si gradient extrudate increases by ~50% percent with a 6 at% increase in Si content due to Hall Petch and particle strengthening effects. Our approach demonstrates the use of a solid phase processing technique to successfully produce a defect-free continuously compositionally graded bulk components thus overcoming the limitations of porosity and material heterogeneities commonly observed in other techniques such as by additive laser deposition.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Controlling mechanical properties of laser powder bed fused AlSi10Mg through manipulation of laser scan rotation

The microstructure and mechanical properties of laser powder bed fused (LPBF) AlSi10Mg alloys can be controlled by many processing parameters. This study focuses on the scan rotation angle, α, between adjacent layers, and establishes the relationship between α and tensile behavior of the as-built LPBF-processed AlSi10Mg alloy. Near-full density cubic coupons were manufactured using the same processing parameters but with systematic variation of α from 0° to 90°. Microscopic observations and X-ray diffraction analysis showed that differences among various coupons mainly include orientations of the melt pools with respect to the build direction and development of the crystallographic texture. The α=0° coupon and α=30° coupon showed the highest and lowest texture index, although the overall crystallographic texture was mild. Tensile specimens were manufactured horizontally and vertically using either α=0° or α=30°, but with various first layer laser direction with respect to the build plate. Notably, the α=0° specimen that was tested along the laser scan direction showed the largest yield strength (283 MPa) and highest tensile ductility (10.1 %). Quantitative image analysis and fractography were performed on all specimens. Results showed that the melt pool orientation with respect to the tensile direction affected the tensile behavior across the different specimens. This was closely related to the localized strain distribution within the melt pool and along the melt pool boundary for the different melt pool orientations observed. Further, these results demonstrate that the laser scan rotation angle between layers can be used to fine tune the mechanical properties of LPBF AlSi10Mg alloy.

36 MATERIALS SCIENCE↗
DOE OSTI2017

SIMS microanalysis of the Strelley Pool Formation cherts and the implications for the secular-temporal oxygen-isotope trend of cherts

The significance of oxygen isotope ratios in Archean chert has long been debated. Cherts from the c. 3.4 Ga Strelley Pool Formation (SPF) (Pilbara Craton, Western Australia) host some of the oldest stromatolite and microfossil evidence for life, but the genesis and timing of silica cements has been unclear. Field relations, petrography and a combination of laser fluorination and in-situ SIMS measurements of δ 18 O in quartz show that bedded cherts of the SPF were originally precipitated as carbonates and were later widely replaced by quartz. Three localities were studied and analyzed for δ 18 O(Qz) in chert: 1) Camel Creek: foliated, metamorphosed, bedded cherts and meter-scale black chert veins; 2) Unconformity Ridge and ABDP8 drill core: stromatolitic and bedded chert overlying basal detrital quartz sandstone; and 3) the Trendall locality: “bedded” stromatolitic chert replacing original dolomite, low temperature hydrothermal quartz, and mm- to decimeter-scale chert-quartz veins. Laser fluorination (mm-scale) values of δ18O(Qz) range from: 14.2 to 18.2‰ VSMOW at Camel Creek; 9.3 to 18.9‰ at Unconformity Ridge; and 13.7 to 25.7‰ at Trendall. Values of δ 18 O(Qz) in cm to decimeter-scale hydrothermal chert veins cutting bedded carbonates at Trendall range from ca. 15 to 16‰, whereas “bedded cherts” are 17 to 26‰. These laser data include the highest δ 18 O values reported for cherts in Paleoarchean sediments and are up to 4‰ higher than the upper limit of ~22‰ reported in other studies, in apparent contrast to the long-standing secular-temporal trend which shows such high δ 18 O only in younger chert. However, analysis by laser fluorination at the 1-mm scale cannot resolve microtextures seen petrographically. In contrast, in-situ SIMS analyses can resolve petrographic microtextures and show δ 18 O(Qz) at 10-μm scale have an even greater range of 7–31‰ in “bedded” cherts at the Trendall locality, up to 9‰ above the secular-temporal trend. Textures observed optically at the Trendall locality were classified as: microquartz, mesoquartz, chalcedony, megaquartz veins, and cavity megaquartz. SEM-CL imaging shows two generations of meso- and megaquartz; bright CL with well-developed growth zoning, and dark CL with massive or mottled texture. Microquartz is the earliest textural generation of quartz and has a maximum δ 18 O(Qz) of ~22‰ by SIMS. Dark-CL mesoquartz has similar δ 18 O to microquartz and is interpreted to also be early. Bright-zoned-CL mesoquartz, which formed post-Archean, has even higher δ 18 O, up to 29‰. Vein megaquartz crosscuts most quartz generations and has a restricted range of δ 18 O, mostly from 16 to 19‰. Chalcedony pseudomorphs rhombic cavities and fractures, lines the edges of veins, and has similar δ 18 O to veins (16–19‰). Late cavity megaquartz is bright and zoned by CL, grows into late open cavities, and has the highest δ 18 O(Qz) values reported from the Pilbara, up to 31.3‰. Thus, the highest-δ 18 O quartz cements at the Trendall locality are the youngest and may be related to weathering. Early silicification and the formation of microquartz, chalcedony and low δ 18 O mesoquartz occurred during low temperature hydrothermal activity in the Archean. None of the SPF quartz examined is interpreted to have formed as a direct precipitate from Paleoarchean seawater. Thus, values of δ 18 O(Qz) do not record either water chemistry or temperature of Archean oceans. In-situ SIMS analysis shows that high-δ 18 O(Qz) values above 22‰ are only found in late-forming cavity megaquartz and bright-zoned-CL mesoquartz at the Trendall locality. The SPF results from our sample suite demonstrate the ability to resolve complex history using detailed petrography and SIMS analysis. Similar studies may show equal complexity of δ 18 O(Qz) data for other localities that are interpreted to show secular-temporal trends for chert. The apparent increase of δ 18 O(Qz) through time may reflect differences in diagenesis, and/or an inherent and previously unrecognized sampling bias that compares fundamentally different populations of quartz, such as Archean hydrothermal chert from volcanic greenstone belts, with unrelated Phanerozoic biogenic quartz.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2016

Systematic analysis of diffuse rear reflectors for enhanced light trapping in silicon solar cells

Simple diffuse rear reflectors can enhance the light path length of weakly absorbed near infrared light in silicon solar cells and set a benchmark for more complex and expensive light trapping structures like dielectric gratings or plasmonic particles. We analyzed such simple diffuse rear reflectors systematically by optical and electrical measurements. We applied white paint, TiO 2 nanoparticles, white backsheets and a silver mirror to bifacial silicon solar cells and measured the enhancement of the external quantum efficiency for three different solar cell geometries: planar front and rear side, textured front and planar rear side, and textured front and rear side. We showed that an air-gap between the solar cell and the reflector decreases the absorption enhancement significantly, thus white paint and TiO 2 nanoparticles directly applied to the rear cell surface lead to the highest short circuit current density enhancements. Here, the short circuit current density gains for a 200 um thick planar solar cell reached up to 1.8 mA/cm 2 , compared to a non-reflecting black rear side and up to 0.8 mA/cm 2 compared to a high-quality silver mirror rear side. For solar cells with textured front side the short circuit current density gains are in the range between 0.5 and 1.0 mA/cm 2 compared to a non-reflecting black rear side and do not significantly depend on the angular characteristic of the rear side reflector but mainly on its absolute reflectance.

14 SOLAR ENERGY↗
DOE OSTI2024

Enhanced passivation and stability of negative charge injected SiN x with higher nitrogen content on the boron diffused surface of n-type Si solar cells

This paper explores the potential of the negatively charged SiN x using plasma charge injection technology to passivate the front textured boron-diffused emitter of n-type Si solar cells. The high-x value single SiN x layer with x ≥ 1.30 (x = N/Si) previously developed for the planarized rear-side passivation of p-type silicon solar cells, with an excellent passivation and charge stability, was found to be unacceptable for the passivation on the front textured boron emitter of n-type cells due to a severe bulk lifetime degradation issue. Therefore, in this study, we investigated a new concept of depositing a dual-x SiN x with a low-x SiN x layer (x~1.01) on top of a high-x SiN x layer (x~1.30) for passivation of the front textured rough surface of boron diffused emitter in n-type cells. Here, the optimized dual-x SiN x stack reveals the promise of charge retention for more than 25 years in field operation as well as excellent passivation of boron-doped emitter without bulk lifetime degradation. N-type cells with the optimized dual-x SiN x after charge injection show comparable cell performance to Al 2 O 3 passivated reference cells. The results of cell-level light stability tests using one-cell minimodules exhibit cell performance decay characteristics similar to the traditional Al 2 O 3 /SiN x passivated reference module.

14 SOLAR ENERGY↗
DOE OSTI2024

Tuning Surface Adhesion Using Grayscale Electron-beam Lithography

Surface texturing of manufactured products tailors their properties, such as friction, adhesion, biocompatibility, or fluid interactions. However, advancements in this area are largely the result of trial-and-effort testing and generally lack a science-guided framework for determining the surface topography that will optimize performance. The present investigation explores grayscale electron-beam lithography as a means to create multiscale surface patterns to control surface performance. Here, we created and characterized a set of surface textures on a silicon wafer; the textures were superpositions of sine waves of varying wavelengths and amplitudes. First, the multiscale topography of the patterned surface was characterized, using profilometry and atomic force microscopy, to understand its fidelity to the designed-in pattern. The results of this analysis demonstrated how grayscale lithography accurately controlled the lateral size of features but was less precise on the vertical height of the surface, and also introduced inherent roughness below the scale of patterning. Second, a micromechanical tester was used to characterize the adhesion of the surfaces with large-scale polished silicon spheres. The results showed that adhesion could be tailored, with significant contribution from all of the designed-in length scales of topography. The strength of adhesion did not correlate with conventional roughness parameters but could be accurately modeled using simple numerical integration. Taken together, this investigation demonstrates the promise and challenges of grayscale e-beam lithography with multiscale patterns as a method for the tailoring of surface performance.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2026

Spin-Valley Locking in 2 H -TaS 2 and Its Co-Intercalated Counterpart: Roles of Surface Domains and Co Intercalation

Tuning and probing spin-valley coupling is key to understanding correlated ground states in 2H-TaS 2 . Its magnetically intercalated analogue, Co 1/3 TaS 2 , introduces additional degrees of freedom, including modified interlayer coupling and magnetism, to modulate spin-valley physics. Surface-sensitive probes like ARPES are essential for accessing surface spin texture, yet previous studies on 2H-TMDs have reported conflicting results regarding spin-polarized bands, leaving open whether these discrepancies are intrinsic or extrinsic. Here, in this study, we performed spatially resolved spin-ARPES measurements on 2H-TaS 2 and Co 1/3 TaS 2 . Our results reveal robust spin-valley locking on both compounds. Importantly, Co intercalation enhances interlayer hybridization and introduces magnetism while preserving the TaS 2 -derived spin texture. We further observe a spatial reversal of the out-of-plane spin polarization, which we attribute to different surface domains. This effect complicates quantifying spin textures and may underlie prior inconsistent observations. Our findings provide microscopic insight into how interlayer interactions and surface domains together govern spin-valley phenomena in layered TMDs.

Spin-resolved angle-resolved photoemission spectro↗
DOE OSTI2021

Sub-10 nm Probing of Ferroelectricity in Heterogeneous Materials by Machine Learning Enabled Contact Kelvin Probe Force Microscopy

Reducing the dimensions of ferroelectric materials down to the nanoscale has strong implications on the ferroelectric polarization pattern and on the ability to switch the polarization. As the size of ferroelectric domains shrinks to the nanometer scale, the heterogeneity of the polarization pattern becomes increasingly pronounced, enabling a large variety of possible polar textures in nanocrystalline and nanocomposite materials. Critical to the understanding of fundamental physics of such materials and hence their applications in electronic nanodevices is the ability to investigate their ferroelectric polarization at the nanoscale in a nondestructive way. We show that contact Kelvin probe force microscopy (cKPFM) combined with a k-means response clustering algorithm enables to measure the ferroelectric response at a mapping resolution of 8 nm. In a BaTiO 3 thin film on silicon composed of tetragonal and hexagonal nanocrystals, we determine a nanoscale lateral distribution of discrete ferroelectric response clusters, fully consistent with the nanostructure determined by transmission electron microscopy. Moreover, we apply this data clustering method to the cKPFM responses measured at different temperatures, which allows us to follow the corresponding change in the polarization pattern as the Curie temperature is approached and across the phase transition. This work opens up perspectives for mapping complex ferroelectric polarization textures such as curled/swirled polar textures that can be stabilized in epitaxial heterostructures and more generally for mapping the polar domain distribution of any spatially highly heterogeneous ferroelectric materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Boiling Transitions During Droplet Contact on Superheated Nano/Micro-Structured Surfaces

Manipulating surface topography is one of the most promising strategies for increasing the efficiency of numerous industrial processes involving droplet contact with superheated surfaces. In such scenarios, the droplets may immediately boil upon contact, splash and boil, or could levitate on their own vapor in the Leidenfrost state. In this work we report the outcomes of water droplets coming in gentle contact with designed nano/micro-textured surfaces at a wide range of temperatures as observed using high-speed optical and X-ray imaging. Further, we report a paradoxical increase in the Leidenfrost temperature ($T_{\text{LFP}}$) as the texture spacing is reduced below a critical value (~10 μm) that represents a minima in $T_{\text{LFP}}$. Although droplets on such textured solids appear to boil upon contact, our studies suggest that their behavior is dominated by hydrodynamic instabilities implying that the increase in $T_{\text{LFP}}$ may not necessarily lead to enhanced heat transfer. On such surfaces, the droplets display a new regime characterized by splashing accompanied by a vapor jet penetrating through the droplets before they transition to the Leidenfrost state. We provide a comprehensive map of boiling behavior of droplets over a wide range of texture spacings that may have significant implications towards applications such as electronics cooling, spray cooling, nuclear reactor safety and containment of fire calamities.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Interplay between Topological States and Rashba States as Manifested on Surface Steps at Room Temperature

The unique spin texture of quantum states in topological materials underpins many proposed spintronic applications. However, realizations of such great potential are stymied by perturbations, such as temperature and local fields imposed by impurities and defects, that can render a promising quantum state uncontrollable. Here, in this study, we report room-temperature scanning tunneling microscopy/spectroscopy observation of interaction between Rashba states and topological surface states, which manifests local electronic structure along step edges controllable by the layer thickness of thin films. The first-principles theoretical calculation elucidates the robust Rashba states coexisting with topological surface states along the surface steps with characteristic spin textures in momentum space. Furthermore, the Rashba edge states can be switched off by reducing the thickness of a topological insulator Bi 2 Se 3 to bolster their interaction with the hybridized topological surface states. The study unveils a manipulating mechanism of the spin textures at room temperature, reinforcing the necessity of thin film technology in controlling the quantum states.

36 MATERIALS SCIENCE↗