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At least 1,567 records · Page 87
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Single-Step Nonthermal Plasma Synthesis of Water-Soluble and Near-Infrared-Emitting Si Quantum Dots for Bioimaging Applications

Here, we present a single-step nonthermal plasma method for the synthesis of near-infrared (NIR)-emitting and water-soluble Si quantum dots (QDs) for bioimaging applications. Oxygen gas and water vapor were introduced together with acrylic acid (AA) into the afterglow region of the synthesis plasma leading to the surface functionalization of the upstream synthesized Si QDs. The simultaneous surface oxidation and ligand grafting enabled solubility and colloidal stability of the Si QDs in water, as evidenced by strongly reduced hydrodynamic diameters. Aged Si QDs in water emitted NIR photoluminescence (PL) at around 830 nm. The PL quantum yield of the Si QDs in water increased over time from initially undetectable to ~30% after 8 days. Cell viability tests showed that >70% of 3T3 cells survived for 24 h at a concentration of 200 μg/mL of oxidized AA grafted Si QDs. The water solubility, NIR emission with a high quantum yield, and cell viability make the Si QDs promising for bioimaging applications.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Focused Electron Beam Induced Deposition Synthesis of 3D Photonic and Magnetic Nanoresonators

While many plasmonic phenomena have been realized by using standard nanoscale synthesis in a single 2-dimensional plane, enhanced functionality should be possible by extending into the third dimension. Several nanoscale synthesis approaches have been explored to achieve 3-dimensional (3d) geometries; however, a robust strategy for synthesizing complex 3d plasmonic architectures is lacking. In this study, we utilize a hybrid of direct-write 3d nanoprinting and thin film deposition to fabricate 3d plasmonic structures. Focused electron beam induced deposition (FEBID) is used to deposit nonplasmonic 3d scaffolds, which are subsequently isolated with a conformal SiO 2 layer and coated with a gold layer to create functional 3d plasmonic nanostructures. A variety of rod antennae, split-ring nanoresonators, and ring resonators are synthesized, and low-loss electron energy loss spectroscopy (EELS) is utilized to characterize their full plasmonic spectra with nanoscale resolution. Complementary EELS simulations are performed to interpret the spectra and elucidate the associated electric and magnetic field distributions of the infrared and near optical modes. This work demonstrates the flexibility that FEBID scaffolds offer for the advancement of 3d plasmonic devices and future advanced optical and magnetic metamaterials.

3d printing↗
DOE OSTI2020

A Review on Challenges and Successes in Atomic-Scale Design of Catalysts for Electrochemical Synthesis of Hydrogen Peroxide

Hydrogen peroxide is a valuable chemical oxidant with a wide range of applications in a variety of industrial processes, especially in water sanitization. Electrochemical synthesis of hydrogen peroxide (H 2 O 2 ) through a two-electron oxygen reduction reaction (2e-ORR) or a two-electron water oxidation reaction (2e-WOR) has emerged as an appealing process for onsite production of this chemically valuable oxidant. On-site produced H 2 O 2 can be applied for wastewater treatment in remote locations or any applications where H 2 O 2 is needed as an oxidizing agent. Overall, this Review studies the theoretical efforts in understanding the challenges in catalysis for electrochemical synthesis of H 2 O 2 as well as providing design principles for more efficient catalyst materials.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Synthesis Gas Conversion over Rh/Mo Catalysts Prepared by Atomic Layer Deposition

Conversion of synthesis gas into value-added products, including oxygenates and C 2+ hydrocarbons, was studied at 523 K, 580 psi, and a 1/1 CO/H 2 ratio over Rh catalysts on catalyst supports prepared by atomic layer deposition (ALD) of molybdenum and tungsten species on silica. The reactivity measurements showed that coating the silica support with molybdenum and tungsten species helped to suppress the methane selectivity and promote the overall conversion rate. When the silica support was coated with five cycles of β-Mo 2 C, the methane selectivity decreased from 32% (1% Rh/SiO 2 ) to 13% (1% Rh/5c-Mo 2 C/SiO 2 ), and the overall product rate increased 33 times from 0.4 to 12.7 mmol min –1 (g of Rh) –1 . CO-FTIR results showed that supporting Rh on silica led to the formation of Rh(211) facets, which favored the formation of methane and had a higher CO conversion rate. Rh on a MoO 3 /SiO 2 support prepared by ALD was found to be the most active catalyst while maintaining the suppression of methane selectivity, showing an overall rate ~60 times higher than that of 1% Rh/SiO 2 . A reaction pathway is proposed, in which hydrogenation steps are promoted most significantly by Mo and W species, followed by promotion of CO insertion steps for ethanol synthesis and C–C coupling steps for hydrocarbon formation. CO-FTIR results showed that 1% Rh/MoO 3 /SiO 2 has the highest proportion of gem-dicarbonyl adsorption sites and the lowest proportion of bridge-bonded CO adsorption sites. As a result, the rate of methanol formation shows a positive correlation with the number of sites that form gem-dicarbonyl species.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Nanoporous Dielectric Resistive Memories Using Sequential Infiltration Synthesis

Resistance switching in metal–insulator–metal structures has been extensively studied in recent years for use as synaptic elements for neuromorphic computing and as nonvolatile memory elements. However, high switching power requirements, device variabilities, and considerable trade-offs between low operating voltages, high on/off ratios, and low leakage have limited their utility. Here, we have addressed these issues by demonstrating the use of ultraporous dielectrics as a pathway for high-performance resistive memory devices. Using a modified atomic layer deposition based technique known as sequential infiltration synthesis, which was developed originally for improving polymer properties such as enhanced etch resistance of electron-beam resists and for the creation of films for filtration and oleophilic applications, we are able to create ~15 nm thick ultraporous (pore size ~5 nm) oxide dielectrics with up to 73% porosity as the medium for filament formation. We show, using the Ag/Al 2 O 3 system, that the ultraporous films result in ultrahigh on/off ratio (>10 9 ) at ultralow switching voltages (~±600 mV) that are 10× smaller than those for the bulk case. In addition, the devices demonstrate fast switching, pulsed endurance up to 1 million cycles. and high temperature (125 °C) retention up to 10 4 s, making this approach highly promising for large-scale neuromorphic and memory applications. Additionally, this synthesis methodology provides a compatible, inexpensive route that is scalable and compatible with existing semiconductor nanofabrication methods and materials.

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

cm 2 -Scale Synthesis of MoTe 2 Thin Films with Large Grains and Layer Control

Owing to the small energy differences between its polymorphs, MoTe 2 can access a full spectrum of electronic states from the 2H semiconducting state to the 1T' semimetallic state and from the T d Weyl semimetallic state to the superconducting state in the 1T' and T d phase at low temperature. Thus, it is a model system for phase transformation studies as well as quantum phenomena such as the quantum spin Hall effect and topological superconductivity. Careful studies of MoTe 2 and its potential applications require large-area MoTe 2 thin films with high crystallinity and thickness control. Here, we present cm 2 -scale synthesis of 2H-MoTe 2 thin films with layer control and large grains that span several microns. Layer control is achieved by controlling the initial thickness of the precursor MoO x thin films, which are deposited on sapphire substrates by atomic layer deposition and subsequently tellurized. Despite the van der Waals epitaxy, the precursor–substrate interface is found to critically determine the uniformity in thickness and grain size of the resulting MoTe 2 films: MoTe 2 grown on sapphire show uniform films while MoTe 2 grown on amorphous SiO 2 substrates form islands. Furthermore, this synthesis strategy decouples the layer control from the variabilities of growth conditions for robust growth results and is applicable to growing other transition-metal dichalcogenides with layer control.

2D materials↗
DOE OSTI2024

Vapor Infiltration Synthesis of Indium Sulfide Magic Size Cluster

The energetically favorable formation of atomically precise clusters, known as magic size clusters, in the solution phase enables a precision nanoscale synthesis with exquisite uniformity. Here, we report the synthesis of magic size clusters via vapor infiltration of atomic layer deposition precursors directly in a polymer thin film. Sequential infiltration of trimethylindium vapor and hydrogen sulfide gas into poly(methyl methacrylate) leads to the formation of clusters with uniform properties consistent with a magic size cluster-In 6 S 6 (CH 3 ) 6 . While an increase in cluster size might be expected with additional sequential infiltration cycles of the reactive In and S precursors, uniform properties consistent with magic size clusters form in multiple polymers under a range of processing conditions. Ultraviolet-visible absorption spectra of In 6 S 6 (CH 3 ) 6 are largely independent of the number of sequential infiltration cycles and exhibit air stability, both of which are attributed to an energetically favorable synthetic pathway that is evaluated with density functional theory.

atomic layer deposition↗
DOE OSTI2016

Facile synthesis of silver nanocubes with sharp corners and edges in an aqueous solution

It remains a challenge to synthesize Ag nanocubes in an aqueous system, although the polyol process was successfully adopted more than one decade ago. Here, we report an aqueous method for the synthesis of Ag nanocubes with an average edge length of 35–95 nm. It involves the formation of AgCl octahedra by mixing CF 3 COOAg with cetyltrimethylammonium chloride, followed by the nucleation and growth of Ag nanocrystals in the presence of ascorbic acid (AA) and FeCl 3 . The Fe 3+ /Fe 2+ redox pair is responsible for the removal of multiply twinned seeds through oxidative etching. Here, the Cl – ions play two critical roles in the nucleation and growth of Ag nanocubes with a single-crystal structure. First, the Cl – ions react with Ag + ions to generate nanometer-sized AgCl octahedra in the initial stage of a synthesis. In the presence of room light and a proper reducing agent such as AA, the AgCl can be reduced to generate Ag n nuclei followed by their evolution into single-crystal seeds and then Ag nanocrystals. Second, the Cl – ions can act as a specific capping agent toward the Ag(100) surface, enabling the formation of Ag nanocubes with sharp corners and edges. Based on the results from a set of time-lapse studies and control experiments, we formulate a plausible mechanism to account for the formation of Ag nanocubes that resembles the formation and development of latent image centers in silver halide grains in the photographic process.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2026

Direct Ab Initio Simulation of the Synthesis of BaZrO 3 and the Microstructure Impacts on Proton Transport

Controlling and predicting the processing-structure-performance relationship in functional materials is a grand challenge in materials science, with important implications for a wide range of emerging applications; a high fidelity understanding of the performance impact of microstructures formed under synthesis conditions is required to develop advanced materials, such as solid-state fuel cells and electrolyzers. Using the ceramic BaZrO 3 as a case study, we directly simulate the synthesis and investigate how proton transport is dictated by microstructures. We develop a framework that couples density functional theory (DFT), machine-learning interatomic potential (MLIP) driven molecular dynamics, and grand canonical Monte Carlo to perform large-scale, microstructure-resolved, atomistic simulations of proton transport in experimentally representative polycrystalline structures. Our fully ab initio approach, using a MLIP as a proxy for DFT, allows us to quantify the competition between two distinct diffusion mechanisms: one associated with grain-boundary regions and another within grains. When the impacts of grain boundaries are taken into account, proton transport exhibits substantial deviation from the bulk oxide limit. This addresses long-standing discrepancies between theory and experiments. Our integrated approach provides atomistic insight into microstructure-dependent proton pathways in BaZrO 3 and establishes a general protocol for predicting processing-structure-performance relationships.

organic↗
DOE OSTI2018

Selective Laser-Assisted Synthesis of Tubular van der Waals Heterostructures of Single-Layered PbI{sub 2} within Carbon Nanotubes Exhibiting Carrier Photogeneration

The electronic and optical properties of two-dimensional layered materials allow the miniaturization of nanoelectronic and optoelectronic devices in a competitive manner. Even larger opportunities arise when two or more layers of different materials are combined. Here, we report on an ultrafast energy efficient strategy, using laser irradiation, which allows bulk synthesis of crystalline single-layered lead iodide in the cavities of carbon nanotubes by forming cylindrical van der Waals heterostructures. In contrast to the filling of van der Waals solids into carbon nanotubes by conventional thermal annealing, which favors the formation of inorganic nanowires, the present strategy is highly selective toward the growth of monolayers forming lead iodide nanotubes. The irradiated bulk material bearing the nanotubes reveals a decrease of the resistivity as well as a significant increase in the current flow upon illumination. Both effects are attributed to the presence of single-walled lead iodide nanotubes in the cavities of carbon nanotubes, which dominate the properties of the whole matrix. The present study brings in a simple, ultrafast and energy efficient strategy for the tailored synthesis of rolled-up single-layers of lead iodide (i.e., single-walled PbI{sub 2} nanotubes), which we believe could be expanded to other two-dimensional (2D) van der Waals solids. In fact, initial tests with ZnI{sub 2} already reveal the formation of single-walled ZnI{sub 2} nanotubes, thus proving the versatility of the approach.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2019

Borophene Synthesis on Au(111)

Borophene (the first two-dimensional (2D) allotrope of boron) is emerging as a groundbreaking system for boron-based chemistry and, more broadly, the field of low-dimensional materials. Exploration of the phase space for growth is critical because borophene is a synthetic 2D material that does not have a bulk layered counterpart and thus cannot be isolated via exfoliation methods. Furthermore, we report synthesis of borophene on Au(111) substrates. Unlike previously studied growth on Ag substrates, boron diffuses into Au at elevated temperatures and segregates to the surface to form borophene islands as the substrate cools. These observations are supported by ab initio modeling of interstitial boron diffusion into the Au lattice. Borophene synthesis also modifies the surface reconstruction of the Au(111) substrate, resulting in a trigonal network that templates growth at low coverage. This initial growth is composed of discrete borophene nanoclusters, whose shape and size are consistent with theoretical predictions. As the concentration of boron increases, nanotemplating breaks down and larger borophene islands are observed. Spectroscopic measurements reveal that borophene grown on Au(111) possesses a metallic electronic structure, suggesting potential applications in 2D plasmonics, superconductivity, interconnects, electrodes, and transparent conductors.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Supramolecular Effects of Alkyl Sulfonates in Silver Nanocrystal Synthesis

While cationic surfactants such as hexadecyltrimethylammonium bromide (CTAB) are ubiquitous in the synthesis of noble metal nanocrystals, anionic surfactants are rarely used. This work explores the addition of sodium alkyl sulfonates with chain lengths ranging from one to eight carbons to a silver nanoplatelet reaction. Short-chain sulfonates comprised of one to four carbons show little effect on the nanocrystal synthesis, but alkyl sulfonates comprised of five or more carbons at concentrations above 1 mM have a pronounced effect on the absorbance of the nanocrystals, causing a blueshift in the wavelength of maximum absorbance (λ max ) from approximately 800 to 400 nm as the sulfonate concentration is increased to 7 mM. Higher concentrations of sulfonate result in a subsequent red-shift of the peak. Investigation into the possible formation mechanisms responsible for this synthetic control revealed the absence of sulfonate micelles under the reaction conditions. Instead, we hypothesize that sulfonate bilayers are nucleated around the silver nanocrystals at concentrations below the critical micelle concentration and interact with either the citrate ligands or the silver surface to influence nanocrystal morphology, and thus absorbance. Strikingly, the addition of long-chain alkyl sulfonates to already-synthesized nanocrystals results in similar changes to the nanocrystal absorbance that occur within seconds, providing further support for the proposal that these effects are related to the surface chemistry of the nanocrystals, which appear to be highly dynamic.

alkyls↗
DOE OSTI2022

Simple Setup Miniaturization with Multiple Benefits for Green Chemistry in Nanoparticle Synthesis

The development of nanomaterials often relies on wet-chemical synthesis performed in reflux setups using round-bottom flasks. Here, an alternative approach to synthesize nanomaterials is presented that uses glass tubes designed for NMR analysis as reactors. This approach uses less solvent and energy, generates less waste, provides safer conditions, is less prone to contamination, and is compatible with high-throughput screening. The benefits of this approach are illustrated by an in breadth study with the synthesis of gold, iridium, osmium, and copper sulfide nanoparticles.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

Synthesis, Crystal Structure, and Elastic Properties of Novel Tungsten Nitrides

Among transition metal nitrides, tungsten nitrides possess unique and/or superior chemical, mechanical, and thermal properties. Preparation of these nitrides, however, is challenging because the incorporation of nitrogen into tungsten lattice is thermodynamically unfavorable at atmospheric pressure. To date, most materials in the W-N system are in the form of thin films produced by nonequilibrium processes and are often poorly crystallized, which severely limits their use in diverse technological applications. Here we report synthesis of tungsten nitrides through new approaches involving solid-state ion exchange and nitrogen degassing under pressure. We unveil a number of novel nitrides including hexagonal and rhombohedral W{sub 2}N{sub 3}. The final products are phase-pure and well-crystallized in bulk forms. For hexagonal W{sub 2}N{sub 3}, hexagonal WN, and cubic W3N4, they exhibit elastic properties rivaling or even exceeding cubic-BN. All four nitrides are prepared at a moderate pressure of 5 GPa, the lowest among high-pressure synthesis of transition metal nitrides, making it practically feasible for massive and industrial-scale production.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Synthesis and Coordination Chemistry of Phosphine Oxide Decorated Dibenzofuran Platforms

A four-step synthesis for 4,6-bis(diphenylphosphinoylmethyl)dibenzofuran (4) from dibenzofuran and a two-step synthesis for 4,6-bis(diphenylphosphinoyl)dibenzofuran (5) are reported along with coordination chemistry of 4 with In(III), La(III), Pr(III), Nd(III), Er(III), and Pu(IV) and of 5 with Er(III). Crystal structure determinations for the ligands, 4 {center_dot} CH{sub 3}OH and 5, the 1:1 complexes [In(4)(NO{sub 3}){sub 3}], [Pr(4)(NO{sub 3}){sub 3}(CH{sub 3}CN)] {center_dot} 0.5CH{sub 3}CN, [Er(4)(NO{sub 3}){sub 3}(CH{sub 3}CN)] {center_dot} CH{sub 3}CN, [Pu(4)Cl4] {center_dot} THF and the 2:1 complex [Nd(4){sub 2}(NO{sub 3}){sub 2}]{sub 2}(NO{sub 3}){sub 2} {center_dot} (H{sub 2}O) {center_dot} 4(CH{sub 3}OH) are described. In these complexes, ligand 4 coordinates in a bidentate POP{prime}O{prime} mode via the two phosphine oxide O-atoms. The dibenzofuran ring O-atom points toward the central metal cations, but in every case it is more than 4 {angstrom} from the metal. A similar bidentate POP{prime}O{prime} chelate structure is formed between 5 and Er(III) in the complex, {l_brace}[Er(5){sub 2}(NO{sub 3}){sub 2}](NO{sub 3}) {center_dot} 4(CH{sub 3}OH){r_brace}0.5, although the nonbonded Er{hor_ellipsis} O{sub furan} distance is reduced to 3.6 {angstrom}. The observed bidentate chelation modes for 4 and 5 are consistent with results from molecular mechanics computations. The solvent extraction performance of 4 and 5 in 1,2-dichloroethane for Eu(III) and Am(III) in nitric acid solutions is described and compared against the extraction behavior of n-octyl(phenyl)-N,N-diisobutylcarbamoylmethyl phosphine oxide (O{Phi}DiBCMPO) measured under identical conditions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

Synthesis, Improved Antisense Activity and Structural Rationale for the Divergent RNA Affinities of 3;#8242;-Fluoro Hexitol Nucleic Acid (FHNA and Ara-FHNA) Modified Oligonucleotides

The synthesis, biophysical, structural, and biological properties of both isomers of 3'-fluoro hexitol nucleic acid (FHNA and Ara-FHNA) modified oligonucleotides are reported. Synthesis of the FHNA and Ara-FHNA thymine phosphoramidites was efficiently accomplished starting from known sugar precursors. Optimal RNA affinities were observed with a 3'-fluorine atom and nucleobase in a trans-diaxial orientation. The Ara-FHNA analog with an equatorial fluorine was found to be destabilizing. However, the magnitude of destabilization was sequence-dependent. Thus, the loss of stability is sharply reduced when Ara-FHNA residues were inserted at pyrimidine-purine (Py-Pu) steps compared to placement within a stretch of pyrimidines (Py-Py). Crystal structures of A-type DNA duplexes modified with either monomer provide a rationalization for the opposing stability effects and point to a steric origin of the destabilization caused by the Ara-FHNA analog. The sequence dependent effect can be explained by the formation of an internucleotide C-F {hor_ellipsis} H-C pseudo hydrogen bond between F3' of Ara-FHNA and C8-H of the nucleobase from the 3'-adjacent adenosine that is absent at Py-Py steps. In animal experiments, FHNA-modified antisense oligonucleotides formulated in saline showed a potent downregulation of gene expression in liver tissue without producing hepatotoxicity. Our data establish FHNA as a useful modification for antisense therapeutics and also confirm the stabilizing influence of F(Py) {hor_ellipsis} H-C(Pu) pseudo hydrogen bonds in nucleic acid structures.

08 HYDROGEN↗
DOE OSTI2025

Autonomous Synthesis and Inverse Design of Electrochromic Polymers with High Efficiency and Accuracy

Here, the design and synthesis of functional polymers, aimed at targeted properties through specific structures, have long been challenged by their complex and often nonlinear structure–property relationships. Key processes, including knowledge accumulation for predictive design and experimental refinement and validation, are traditionally labor-insensitive and time-consuming, making it difficult to balance accuracy and efficiency. Here, we introduce an accelerated, autonomous system for the on-demand synthesis of electronic polymers that achieves the desired electrochromic functionality with high accuracy and efficiency. Our approach leverages large language model-assisted data mining, a physics-informed copolymer machine learning model, and an AI-driven autonomous robotic workflow in the Polybot lab. Within 72 h, Polybot autonomously synthesized electrochromic polymers (ECPs) with targeted, previously-unreported color values, including green polymers with specific absorption profiles, precisely fine-tuning copolymer structures with a 5% step size in comonomer composition within a three-monomer system. A publicly accessible ECP informatics database has also been created to foster knowledge exchange.

AI-driven Robotic Lab↗
DOE OSTI2024

Electrochemical Synthesis of Zeolite Coatings with Controlled Crystal Polymorphism and Self-Regulating Growth

Zeolite coatings are studied as molecular sieves for membrane separation, membrane reactors, and chemical sensor applications. They are also studied as anticorrosive films for metals and alloys, antimicrobial and hydrophobic films for heating, ventilation, and air conditioning, and dielectrics for semiconductor applications. Zeolite coatings are synthesized by hydrothermal, ionothermal, and dry-gel conversion approaches, which require high process temperatures and lengthy times (ranging from hours to days). Here, we report the first zeolite coatings synthesized via electrochemical deposition on a cathodic electrode, with controlled crystal polymorphism achieved within subhourly duration. We demonstrate this approach by developing sodium zeolite (e.g., sodalite (SOD), NaA (LTA), and Linde Type N (LTN)) coatings on a titanium electrode and extending the synthesis method to porous stainless steel. The coating morphology and crystallinity depend on the temperature, time, and applied current. The coating thickness is independent of the applied current, showing the presence of a self-regulating mechanism to ensure a uniform coating thickness across the metal surface. The electrochemical zeolite growth mechanism was elucidated with high-resolution transmission electron microscopy, and applications of the resultant zeolite coatings for oil/water separation and ethanol/water pervaporation were exploited. Electrochemical synthesis represents a novel, simple, fast, and environmentally friendly approach to preparing zeolite coatings. It can potentially be generalized for developing zeolite materials with diverse framework structures, morphologies, and orientations for substrates with complicated geometries.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗