Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “tunable”

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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

SnSe 1-x S x Alloys: Anisotropic Van der Waals Semiconductors with Tunable Bandgaps

Alloying is one of the main tools of bandgap engineering, allowing the tuning of crystal structure, lattice parameters, and electronic structure of 3D and 2D/layered semiconductors. Among the latter, it can play a key role in tailoring the properties of tin monochalcogenides, a class of van der Waals semiconductors of interest for optoelectronics, thermoelectrics, ferroelectrics, and valleytronics. Here, the study investigates the synthesis and properties of large flakes of the anion substitution alloys SnSe 1-x S x . Alloy flakes across a wide range of compositions are obtained systematically by repeated growth from the same mixed (SnS, SnSe) powder precursor. Combined experiment and theory show full miscibility for all compositions, along with tunable lattice constants, bandgaps, and vibrational modes. Atomic resolution imaging demonstrates the accumulation of S and Se in alternating layers in the SnSe 1-x S x unit cell, attributed to growth kinetics. Polarized Raman spectroscopy confirms anisotropic vibrational modes; the calculated and measured band structure shows systematic changes in the band edge energies and anisotropic electronic structure due to the anisotropic in-plane lattice of the monochalcogenides. Cathodoluminescence, finally, indicates that a unique configuration of two non-degenerate, direct valleys along orthogonal k-space directions persists all the way from SnS to SnSe, making SnSe 1-x S x alloys interesting for valleytronics.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Tunable amorphous carbon films formed on ultralow wear, Pt–Au alloys

The mechanocatalytic formation of carbonaceous films at the interface between sliding metallic contacts is simultaneously advantageous for reducing friction and adhesion in several tribological applications and detrimental for electrical contacts as they can induce device failure by increasing the contact resistance. Yet, remarkably little is still known about the chemistry, structural and mechanical properties, and tunability of these interfacial layers. In this study, we performed contact pressure-dependent tribological experiments in dry nitrogen containing trace organics on four, nanocrystalline Pt–Au alloys ([Au] from 0 at.% to 10 at.%) – a promising class of alloys for ultralow wear and electrical contact applications. The ex-situ, multi-technique characterization results did not only provide insights into the chemical nature and mechanical behavior of the mechanocatalytic, carbon-rich films formed on Pt–Au surfaces, but also revealed the interplay between catalytic and mechanochemical tribofilm formation controlled by the composition-dependent electronic structure of the Pt–Au substrate and the applied contact pressure. The results of this work provide guidelines for tailoring nanocrystalline alloys to control their mechanocatalytic activity on the basis of variations of the alloy mechanical properties and element's electronic structure with the alloy stoichiometry.

AFM↗
DOE OSTI2024

Microwave-assisted synthesis of mixed-linker covalent organic frameworks enabling tunable and ultrahigh iodine capture

The use of covalent organic frameworks (COFs) for hazardous radioiodine capture has been highly sought after recently. However, the synthesis of high-performance COF adsorbents while circumventing the limitations of traditional solvothermal methods remains largely unexplored. Herein, we for the first time combine microwave-assisted synthesis and mixed-linker strategy to fabricate multivariate COF adsorbents (X% OMe-TFB-BD COFs, X% = 0, 33, 50, 67, and 100 mol%) with varying ratios of benzidine (BD) and 3,3'-dimethoxylbenzidine (BD-OMe) linkers in a rapid and facile manner. Adjusting the BD-OMe/BD mole ratios has led to distinct variations in density, crystallinity, porosity, morphology, and thermal/chemical stability of the resultant COFs, which empowered fine-tuning of the adsorption performance towards static iodine vapor. Remarkably, the 50% OMe-TFB-BD COF exhibited an ultrahigh iodine adsorption capability of 8.2 g g –1 , surpassing those of single-component COFs, mixed-linker COFs with other methoxy content, physically blended mixtures, and most existing COF adsorbents. Moreover, 50% OMe-TFB-BD COF was recyclable seven times without obvious loss in its adsorption capacity. Finally, this work underscores the substantial potential of microwave-assisted mixed-linker strategy as a viable approach for developing multivariate COFs with shortened reaction times, precisely tailored pore environment, and tunable sorption properties, which are of considerable promise for environmental remediation and other niche applications.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Design principles for intrinsically circular polymers with tunable properties

This perspective discusses a set of design principles for next-generation kinetically trapped, intrinsically circular polymers (iCPs) that are inherently, selectively, and expediently depolymerizable to their monomer state once their kinetic barriers of deconstruction are overcome, thereby enabling not only the ideal shortest chemical circularity but also tunable performance properties. After describing four elements of the design principles - thermodynamics and kinetics, strategies to overcome trade-offs and unify conflicting properties, predictive modeling, and supply-chain life-cycle assessment and techno-economic analysis, which are illustrated with state-of-the-art examples - it concludes with presenting key challenges and opportunities for sustainable development of iCPs.

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

Retrieving images from tarnished daguerreotypes using X-ray fluorescence imaging with an X-ray micro beam with tunable energy

We report recent observations using a synchrotron X-ray micro-beam to retrieve images from tarnished 19th century daguerreotypes. We confirm that high quality image can always be retrieved from tarnished plates using Hg L α XRF as long as the bulk of the image particles and their distribution remains intact. We also report results from using tunable tender X-rays (2 - 7 keV) to conduct imaging in high vacuum at energy above the Ag L-edge and the Hg M-edge, extracting images using Ag L α and Hg M α , respectively among others (e.g., S to track corrosion). Images obtained with the surface sensitive total electron yield (TEY) and the bulk sensitive fluorescence yield (FLY) as well as corresponding micro-XANES are reported. Flux tolerance to high intensity X-beam is also explored. These results and their implications for cultural heritage research are discussed.

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

A scalable and tunable thermoreversible polymer for 3D human pluripotent stem cell biomanufacturing

Human pluripotent stem cells (hPSCs) are an exciting and promising source to enable cell replacement therapies for a variety of unmet medical needs. Though hPSCs can be successfully derived into numerous physiologically relevant cell types, effective translation to the clinic is limited by challenges in scalable production of high-quality cells, cellular immaturity following the differentiation process, and the use of animal-derived components in culture. To address these limitations, we have developed a fully defined, reproducible, and tunable thermoreversible polymer for high-quality, scalable 3D cell production. Our reproducible synthesis method enables precise control of gelation temperature (24°C–32°C), hydrogel stiffness (100–4000 Pa), and the prevention of any unintended covalent crosslinking. After material optimization, we demonstrated hPSC expansion, pluripotency maintenance, and differentiation into numerous lineages within the hydrogel. Overall, this 3D thermoreversible hydrogel platform has broad applications in scalable, high-quality cell production to overcome the biomanufacturing burden of stem cell therapy.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2020

Tunable structural and magnetic properties of NiAs-type Mn x Sb (1.00≤x≤1.30) compounds

Mn-based alloys can exhibit a variety of magnetic properties related to their tunable exchange interactions. Here, structural and magnetic properties of hexagonal NiAs-type Mn x Sb (1.00≤x≤1.30) compounds are studied with a combination of X-ray diffraction, neutron diffraction, and magnetic measurements. It is found that the magnetization, Curie temperature, and magnetocrystalline anisotropy of Mn x Sb compounds can be tuned by controlling Mn concentration and doping at interstitial (2d) sites. With increasing Mn concentration, magnetic moments of Mn atoms decrease and deviate gradually from the ab-plane to the c-axis for 1.20≤x≤1.22 at room temperature, which leads to a decrease of the Curie temperature T c and the spin reorientation temperature T SR . By doping with nonmagnetic elements, a substantial room-temperature magnetocaloric effect without magnetic hysteresis was achieved for Mn 1.12 Zr 0.1 Sb compound, which is highly beneficial to the practical magnetic refrigeration application.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Tunable broadband luminescence in lead-free hybrid copper halides

Metal halides are an important class of optoelectronic materials combining exceptional optical and electronic properties. An inherent advantage of metal halides is their solution synthesis and processability, which render them as low-cost and environmentally friendly materials for a range of applications from photovoltaics and photodetection to solid-state lighting (SSL). Here, in this study, we synthesized three previously unreported lead-free organic–inorganic hybrid copper halides: (OA) 4 CuX 5 (X = Br, I; OA + = C 8 H 17 NH 3+ , n-octylammonium cation) and (HA) 2 CuI 3 (HA + = C 6 H 13 NH 3 + , n-hexylammonium cation), all of which exhibit broadband emissions arising from self-trapped excitons (STEs). Among these compounds, (OA) 4 CuI 5 demonstrates tunable dual-band white-light emission with a high color rendering index value of 91 at room temperature. Temperature-dependent photoluminescence measurements and first-principles calculations reveal distinct behaviors between the two emission states in (OA) 4 CuI 5 . These findings highlight the potential of copper halide compounds for optoelectronic applications, particularly in the development of environmentally friendly solid-state lighting technologies.

36 MATERIALS SCIENCE↗
DOE OSTI2020

An all-oxide electrolysis cells for syngas production with tunable H 2 /CO yield via co-electrolysis of H 2 O and CO 2

High-rate production of syngas with tunable H 2 /CO and coke-free operation is achieved in a solid-oxide electrolysis cell (SOEC). Prior to operation, controlled pre-reduction of La 0.7 Sr 0.3 Fe 0.9 Ni 0.1 O 3-δ (LSFNi) cathode is used to trigger the in-situ exsolution of Ni-Fe alloy nanoparticles with an average size of ~45 nm uniformly distributed and socketed on LSFNi backbone, enabling efficient co-electrolysis of H 2 O and CO 2 to H 2 and CO. At 1.5 V, the current density reaches ~1.0 A cm-2 at 750 °C and ~2.4 A cm -2 at 850 °C with near 100% Faradaic Efficiency. We demonstrate the feasibility of tuning the output H 2 /CO ratio by nearly two orders of magnitude (from ~0.1 to ~7) by manipulating H 2 O/CO 2 ratio of feed gas, operating temperature, and current density. Finally, stable operation for >100 h is obtained without evidence of carbon deposition, although high current density operation leads to observable deterioration of anode/electrolyte interface due to the rapid oxygen evolution.

25 ENERGY STORAGE↗
DOE OSTI2020

Tunable Second Harmonic Generation in Twisted Bilayer Graphene

Twisted stacking of van der Waals (vdW) materials introduces a new way in bandstructure engineering and has given rise to numerous extraordinary physical phenomena. Despite the absence of second harmonic generation (SHG) in non-gated monolayer graphene, artificially twisted bilayer graphene (tBLG) possesses more possible point-group symmetries including those with broken inversion-symmetry. Here, we report twist-angle-dependent SHG from tBLG, which is the first demonstration of an elemental material with intrinsically tunable nonlinearity. We show that depending on the twist angle, the susceptibility of the dominant chiral tensor component of tBLGs can vary from 0 to 28×10 4 pm 2 /V, which is at the same order of magnitude as on-resonance susceptibility of monolayer MoS 2 . These results shed light on the underlying symmetry of tBLG systems and electronic band-structure near van Hove singularities (vHs). More importantly, they introduce a new degree of freedom, the twisting, in creating efficient second-order nonlinear material form centrosymmetric constituents

36 MATERIALS SCIENCE↗
DOE OSTI2020

Tunable mechanical behavior of graphene nanoribbon-metal composites fabricated through an electrocharge-assisted process

This work investigates the role of a carbon nanophase on the local mechanical behavior of nanocarbon metal matrix composites (NCMCs) produced through an electrocharge-assisted process. Nanoindentation experiments on single crystal Al, Al 1350 parent alloys, and Al 1350 NCMCs revealed variable mechanical properties, caused by an interplay between microstructure and graphitic reinforcements. TEM and AFM studies also reveal nanoscale structural changes based on the incorporation of a carbon nanophase. In order to decouple the effects of the aforementioned mechanical behaviors, molecular dynamics nanoindentation simulations were performed on the (111) surface of Al and Al NCMC samples containing semi-infinite graphene nanoribbons to examine the evolution of plasticity over time. Findings indicate that the arrangement of a finite graphene nanophase within a host matrix can alter plasticity mechanisms and therefore yield strength in near-surface mechanical behavior with little effect on elastic properties. Here, this understanding enables further study into tunable bulk properties of Al-based NCMCs while isolating microstructural effects and reinforcement effects of the carbon phase. Such an understanding will lead to application-specific material geometries ranging from highperforming vehicle structures to next-generation electrical devices.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Tunable, room-temperature multiferroic Fe-BaTiO 3 vertically aligned nanocomposites with perpendicular magnetic anisotropy

Room-temperature ferromagnetic materials with perpendicular magnetic anisotropy are widely sought after for spintronics, magnetic data storage devices, and stochastic computing. To address this need, a new Fe-BaTiO 3 vertically aligned nanocomposite (VAN) has been fabricated—combining both the strong room-temperature ferromagnetic properties of Fe nanopillars and the strong room-temperature ferroelectric properties of the BaTiO 3 matrix. Furthermore, the Fe-BaTiO 3 VAN allows for highly anisotropic magnetic properties with tunable magnetization and coercivity. Additionally, to demonstrate the multiferroic properties of the Fe-BaTiO 3 system, the new metal-oxide hybrid material system has been incorporated in a multilayer stack. Overall, this new multiferroic VAN system possesses great potential in magnetic anisotropy and property tuning and demonstrates a new material family of oxide-metal hybrid systems for room-temperature multiferroic material designs.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Tunable high spin Chern-number insulator phases in strained Sb monolayer

High spin Chern-number insulators (HSCI) have emerged as a novel 2D topological phase of condensed matter that is beyond the classification of topological quantum chemistry. The HSCI phase with two pairs of gapless helical edge states is robust even in the presence of spin–orbit coupling due to the protection of a “hidden” feature spectrum topology. Here, in this work, we report the observation of a semimetallic Sb monolayer carrying the same band topology as HSCI with the spin Chern number equal to 2. Our calculations further indicate a moderate lattice strain can make Sb monolayer an insulator or a semimetal with a tunable spin Chern number from 0 to 3. The results suggest strained Sb monolayers as a promising platform for exploring exotic properties of the HSCI topological matter.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Field-tunable BKT and quantum phase transitions in spin-$\frac{1}{2}$ triangular lattice antiferromagnet

Quantum magnetism is one of the most active fields for exploring exotic phases and phase transitions. The recently synthesized Na 2 BaCo(PO 4 ) 2 (NBCP) is an ideal material incarnation of the spin-$\frac{1}{2}$ easy-axis triangular lattice antiferromagnet (TLAF). Experimental evidence shows that NBCP hosts the spin supersolid state with a giant magnetocaloric effect. Theory further predicts that magnetic fields can drive NBCP through Berezinskii-Kosterlitz-Thouless (BKT) and other richer quantum phase transitions. However, detecting these transitions is challenging, as they onset at ultralow temperatures near 60 mK and require high magnetization sensitivity. Using a newly developed gradient force magnetometer in a dilution refrigerator, we mapped the magnetic susceptibility phase diagram down to 30 mK. Our results provide a more comprehensive and accurate understanding of BKT melting of spin supersolidity and several field-tunable quantum phase transitions, which establish NBCP as a model platform for frustrated magnetism and highlight potential applications of its giant magnetocaloric effects.

BKT transition↗
DOE OSTI2020

Hyperfine structures and isotopic shifts of uranium transitions using tunable laser spectroscopy of laser ablation plumes

We report isotopic shifts and hyperfine structures of selected U transitions employing tunable spectroscopy viz: laser-induced fluorescence and laser absorption spectroscopy of laser ablation plumes. The laser-produced plasmas were produced during ns laser ablation on a natural U metal which contains 0.7% 235U. Our results show that isotopic shifts between 238U and 235U are entangled with hyperfine structures of 235U. The isotopic ratio obtained using laser-induced fluorescence is affected by optical saturation effect. Time-resolved laser absorption spectroscopy is carried out for evaluating the optical absorption and estimating the hyperfine constants.

(020.3260) Isotope shifts↗
DOE OSTI2021

Perovskite oxynitrides as tunable materials for electrocatalytic nitrogen reduction to ammonia

The electrocatalytic nitrogen reduction reaction (ENRR) to ammonia is a potentially sustainable alternative to the Haber-Bosch (HB) process, but low Faradaic efficiencies and rates hinder its implementation. Perovskite oxynitrides are a tunable class of materials with unique chemistry for ENRR. As a result, elucidating structure–property–mechanism relations for perovskite oxynitrides will aid ENRR catalyst design.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Morphology Control of Self-Assembled Three-Phase Au-BaTiO 3 –ZnO Hybrid Metamaterial for Tunable Optical Properties

Microstructural control in metal-dielectric hybrid metamaterials presents enormous opportunities in tailoring the physical properties including the magnetic and optical properties. In this paper, we demonstrate a strong tunability achieved in the microstructure of self-assembled ordered three-phase Au-BaTiO 3 –ZnO hybrid metamaterial along with its optical properties, grown by a pulsed laser deposition method. Varying the growth temperature, deposition frequency, and template thickness evolves the microstructure by tuning the Au and ZnO pillar geometry as well as the shape and size of the Au nanoparticles capping the ZnO nanowires. The three-phase hybrid metamaterials exhibit unique optical properties, including enhanced nonlinear optical properties, hyperbolic dispersion in the visible and near-infrared wavelength region, and tuned epsilon-near-zero (ENZ) wavelength upon varying the deposition parameters. This study suggests that the three-phase hybrid metamaterials present great potential in the microstructure and optical property tuning that can also be applied to other two-phase and three-phase nanocomposite systems.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Annealing-Driven Phase Control Enables Plasmonic Tunability in Alloy Nanoparticles

A critical aspect of designing and realizing useful solid state materials is controlling phase and structure to tailor physical properties. While common for semiconductor and quantum materials, plasmonic materials have inhabited a narrow phase space typically comprising one or two elements, e.g., face-centered cubic metals. While this simplicity has enabled robust use and understanding of Au and Ag nanoparticles, it has also limited the design and manipulation of solid state properties. Here, we show that by tuning the phase and elemental composition of binary Au−Sn nanoparticles, the steady-state absorbance and ultrafast thermalization properties of plasmonic nanoparticles can be controlled. Solid state characterization suggests this is due to the dealloying of Sn and destabilization of the AuSn phase, leading to higher quality Au 5 Sn intermetallic phases alongside Au. Consequently, this work shows that phase control can profoundly influence the properties of plasmonic nanoparticles, providing important tunability for applications in catalysis, photothermal heating, and sensing.

Gold↗