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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.

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At least 1,153 records · Page 64
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Beyond electrical conductance: progress and prospects in single-molecule junctions

The idea of using individual molecules as conducting wires, regulators, and interconnects for charges in electronic circuitry has catalyzed the vibrant development of the field of single-molecule electronics. The ability to reliably and repeatedly construct single-molecule junctions (SMJs) has enabled the study of charge transport through a broad spectrum of individual molecules. Over the past decade, the capability of the SMJ platform has been greatly expanded thanks to the development of new experimental techniques and the integration of knowledge and methodologies from other disciplines. New opportunities beyond electrical conductance have emerged at the atomic and molecular scale. It has been demonstrated in many recent studies that the SMJ can now serve as a powerful and versatile tool to address critical physical and chemical questions that are otherwise inaccessible. Furthermore, this perspective focuses on the new capabilities and functionalities of the SMJ beyond conductance measurements and how they have enabled the investigation of crucial single-molecule processes and advanced our understanding beyond molecular electronics.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2023

Small angle X-ray studies of short-range order in non-stoichiometric pseudoprotic ionic liquids: the influence of chemical structure

Mixtures of organic acids and amines have been studied extensively owing to their unusual physicochemical properties and applications as solvents for extraction. In equimolar ratios they represent pseudoprotic ionic liquids, and in other, “nonstoichiometric” ratios they display a range of odd physicochemical behaviors. We report the results of small-angle X-ray scattering studies of a series of such systems with a range of chemical structures chosen to explore the link between molecular geometry and the character of the emergent nanoscale local liquid structure. We find that while the details vary, structure can emerge even when the hydrogen-bonding character of the components is changed significantly, and the character of their hydrocarbon substituents is altered. The consistent emergence of local order in the face of varying chemical structures indicates that the process is robust. Furthermore, this implies that the emergence of such structure may in fact be far more common in liquid mixtures than is currently recognized, and a great many structures may be suitable for the synthesis of pseudoprotic ionic liquids.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2023

Chirality and dislocation effects in single nanostructures probed by whispering gallery modes

Nanostructures such as nanoribbons and -wires are of interest as components for building integrated photonic systems, especially if their basic functionality as dielectric waveguides can be extended by chiroptical phenomena or modifications of their optoelectronic properties by extended defects, such as dislocations. However, conventional optical measurements typically require monodisperse (and chiral) ensembles, and identifying emerging chiral optical activity or dislocation effects in single nanostructures has remained an unmet challenge. Here we show that whispering gallery modes can probe chirality and dislocation effects in single nanowires. Wires of the van der Waals semiconductor germanium(II) sulfide (GeS), obtained by vapor–liquid–solid growth, invariably form as growth spirals around a single screw dislocation that gives rise to a chiral structure and can modify the electronic properties. Cathodoluminescence spectroscopy on single tapered GeS nanowires containing joined dislocated and defect-free segments, augmented by numerical simulations and ab-initio calculations, identifies chiral whispering gallery modes as well as a pronounced modulation of the electronic structure attributed to the screw dislocation. Further, our results establish chiral light-matter interactions and dislocation-induced electronic modifications in single nanostructures, paving the way for their application in multifunctional photonic architectures.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Enriching 2D transition metal borides via MB XMenes (M = Fe, Co, Ir): Strong correlation and magnetism

Recently, two-dimensional (2D) FeSe-like anti-MXenes (or XMenes), composed of late d-block transition metal M and p-block nonmetal X elements, have been both experimentally and theoretically investigated. Here, we select three 2D borides FeB, CoB and IrB for a deeper investigation by including strong correlation effects, as a fertile ground for understanding and applications. Using a combination of Hubbard corrected first-principles calculations and Monte Carlo simulations, FeB and CoB are found to be ferro- and anti-ferro magnetic, contrasting with the non-magnetic nature of IrB. The metallic FeB XMene monolayer, superior to most of the MXenes or MBenes, exhibits robust ferromagnetism, driven by intertwined direct-exchange and super-exchange interactions between adjacent Fe atoms. The predicted Curie temperature ($T$ C ) of the FeB monolayer via the Heisenberg model reaches an impressive 425 K, with the easy-axis oriented out-of-plane and high magnetic anisotropic energy (MAE). The asymmetry in the spin-resolved transmission spectrum induces a thermal spin current, providing an opportunity for spin filtration. In conclusion, this novel 2D FeB material is expected to hold great promise as an information storage medium and find applications in emerging spintronic devices.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2023

Surface enrichment dictates block copolymer orientation

Orientation of block copolymer (BCP) morphology in thin films is critical to applications as nanostructured coatings. Despite being well-studied, the ability to control BCP orientation across all possible block constituents remains challenging. Here, in this study, we deploy coarse-grained molecular dynamics simulations to study diblock copolymer ordering in thin films, focusing on chain makeup, substrate surface energy, and surface tension disparity between the two constituent blocks. We explore the multi-dimensional parameter space of ordering using a machine-learning approach, where an autonomous loop using a Gaussian process (GP) control algorithm iteratively selects high-value simulations to compute. The GP kernel was engineered to capture known symmetries. The trained GP model serves as both a complete map of system response, and a robust means of extracting material knowledge. We demonstrate that the vertical orientation of BCP phases depends on several counter-balancing energetic contributions, including entropic and enthalpic material enrichment at interfaces, distortion of morphological objects through the film depth, and of course interfacial energies. BCP lamellae are found more resistant to these effects, and thus more robustly form vertical orientations across a broad range of conditions; while BCP cylinders are found to be highly sensitive to surface tension disparity.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2023

DNA-caged nanoparticles via electrostatic self-assembly

DNA-modified nanoparticles enable DNA sensing and therapeutics in nanomedicine and are also crucial for nanoparticle self-assembly with DNA-based materials. However, methods to conjugate DNA to nanoparticle surfaces are limited, inefficient, and lack control. Inspired by DNA tile nanotechnology, we demonstrate a new approach to nanoparticle modification based on electrostatic attraction between negatively charged DNA tiles and positively charged nanoparticles. This approach does not disrupt nanoparticle surfaces and leverages the programmability of DNA nanotechnology to control DNA presentation. We demonstrated this approach using a variety of nanoparticles, including polymeric micelles, polystyrene beads, gold nanoparticles, and superparamagnetic iron oxide nanoparticles with sizes ranging from 5–20 nm in diameter. DNA cage formation was confirmed through transmission electron microscopy (TEM), neutralization of zeta potential, and a series of fluorescence experiments. DNA cages present “handle” sequences that can be used for reversible target attachment or self-assembly. Handle functionality was verified in solution, at the solid–liquid interface, and inside fixed cells, corresponding to applications in biosensing, DNA microarrays, and erasable immunocytochemistry. Finally, these experiments demonstrate the versatility of the electrostatic DNA caging approach and provide a new pathway to nanoparticle modification with DNA that will empower further applications of these materials in medicine and materials science.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2023

Manipulating topological Hall-like signatures by interface engineering in epitaxial ruthenate/manganite heterostructures

Topologically protected non-trivial spin textures (e.g. skyrmions) give rise to a novel phenomenon called the topological Hall effect (THE) and have promising implications in future energy-efficient nanoelectronic and spintronic devices. Here, we have studied the Hall effect in SrRuO 3 /La 0.42 Ca 0.58 MnO 3 (SRO/LCMO) bilayers. Our investigation suggests that pure SRO has hard and soft magnetic characteristics but the anomalous Hall effect (AHE) in SRO is governed by the high coercivity phase. Here, we have shown that the proximity effect of a soft magnetic LCMO on SRO plays a critical role in interfacial magnetic coupling and transport properties in SRO. Upon reducing the SRO thickness in the bilayer, the proximity effect becomes the dominant feature, enhancing the magnitude and temperature range of THE-like signatures. The THE-like features in bilayers can be explained by a diffusive Berry phase transition model in the presence of an emergent magnetic state due to interface coupling. This work provides an alternative understanding of THE-like signatures and their manipulation in SRO-based heterostructures, bilayers and superlattices.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2023

Ultrafast transient absorption measurements of photocarrier dynamics in PdSe 2

We investigate the photocarrier dynamics in bulk PdSe 2 , a layered transition metal dichalcogenide with a novel pentagonal structure and unique electronic and optical properties. Using femtosecond transient absorption microscopy, we study the behavior of photocarriers in mechanically exfoliated bulk PdSe 2 flakes at room temperature. By employing a 400 nm ultrafast laser pulse, electron–hole pairs are generated, and their dynamics are probed using an 800 nm detection pulse. Our findings reveal that the lifetime of photocarriers in bulk PdSe 2 is approximately 210 ps. Furthermore, by spatially resolving the differential reflection signal, we determine a photocarrier diffusion coefficient of about 7.3 cm 2 s –1 . Based on these results, we estimate a diffusion length of around 400 nm and a photocarrier mobility of approximately 300 cm 2 V –1 s –1 . Furthermore, these results shed light on the ultrafast optoelectronic properties of PdSe 2 , offer valuable insights into photocarriers in this emerging material, and enable design of high-performance optoelectronic devices based on PdSe 2 .

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2023

Expanding the color palette of bicolor-emitting nanocrystals

Owing to their bright and tunable luminescence spectra, nanocrystals appear as a unique playground for light source design. Displays and lighting require white light sources that combine several narrow lines. As Kasha's rule prevents the emission of hot carriers, blends of multiple nanocrystal populations are currently the obvious strategy for broad-band source design. However, a few reports suggest that bicolor emission can also be obtained from a single particle even under weak excitation if a careful design of the exciton scattering mechanism sufficiently slows down its relaxation pathways. A key challenge remains to maintain quantum confinement for color tunability in the same structure, while simultaneously achieving a large size to leverage the critical, slower exciton diffusion or relaxation down to the ground state. In this work, we demonstrate that 2D nanoplatelets offer an original opportunity for the design of confined and large heterostructures. We demonstrate that bicolor emission is not limited to green–red pair and show that blue–yellow and purple–green emissions can be obtained from CdSe/CdTe/CdSe core/crown/crown and CdSe/CdS core/crown heterostructures, respectively.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2024

GeSn-on-GaAs with photoconductive carrier lifetime >400 ns: role of substrate orientation and atomistic simulation

Group IV GeSn quantum material finds application in electronics and silicon-compatible photonics. Synthesizing these materials with low defect density and high carrier lifetime is a potential challenge due to lattice mismatch induced defects and tin segregation at higher growth temperature. Recent advancements in the growth of these GeSn materials on Si, Ge, GaAs, and with substrate orientations, demonstrated different properties using epitaxial and chemical deposition methods. This article addresses the effect of GaAs substrate orientation and misorientation on the materials’ properties and carrier lifetimes in epitaxial Ge 0.94 Sn 0.06 layers. With starting GaAs substrates of (100)/2°, (100)/6°, (110) and (111)A orientations, Ge 0.94 Sn 0.06 epitaxial layers were grown with an intermediate Ge buffer layer by molecular beam epitaxy and analyzed by several analytical tools. X-ray analysis displayed good crystalline quality, and Raman spectroscopy measurements showed blue shifts in phonon wavenumber due to biaxial compressive strain in Ge 0.94 Sn 0.06 epilayers. Cross-sectional transmission electron microscopy analysis confirmed the defect-free heterointerface of Ge 0.94 Sn 0.06 /Ge/GaAs heterostructure. Minority carrier lifetimes of the unintentionally doped n-type Ge 0.94 Sn 0.06 epilayers displayed photoconductive carrier lifetimes of >400 ns on (100)/6°, 319 ns on (100)/2°, and 434 ns on (110) GaAs substrate at 1500 nm excitation wavelength. On the other hand, Ge 0.94 Sn 0.06 layer showed poor carrier lifetime on (111)A GaAs substrate. The observed differences in carrier lifetimes were correlated with the formation energy of the Ge on (100)/6° and (100)/2° GaAs heterointerface using Stillinger–Weber interatomic potential model-based atomistic simulation with different heterointerfacial bonding by Synopsys QuantumATK tool. Total energy computation of 6280-atom Ge/GaAs supercell on (100)/6° leads to lower formation energy than (100)/2°, making it more thermodynamically stable. Hence, the growth of the GeSn/III–V material system using misoriented (100) substrates that are more thermodynamically stable will enhance the performances of optoelectronic devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Effects of radiation damage on the yielding and fracture of nanowires

Irradiated nanowires' strength can change with their diameter. Though damaged by radiation, defects get cleaned during loading, returning the nanowires to their pristine state. This suggests that radiation has little impact on their fracture behavior.

77 NANOSCIENCE AND NANOTECHNOLOGY↗