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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 505 records · Page 28
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Local Lattice Deformation of Tellurene Grain Boundaries by Four-Dimensional Electron Microscopy

Two-dimensional (2D) tellurene is a promising competitor for the fabrication of ultrathin optoelectronic devices belonging to a new family of monoelemental 2D materials. Furthermore, the precise fabrication and characterization of tellurene and its lattice defects is of utmost importance to determine device reliability and predict functionality, yet it remains experimentally challenging. The rapid growth of the four-dimensional scanning transmission electron microscopy (4D-STEM) technique as well as postprocessing tools now allows for structural analysis with nanometer-scale resolution over a broad range of length scales. Here, we use 4D-STEM to reveal the three-dimensional (3D) atomic structure of the characteristic grain boundary in 2D tellurium formed through a new microwave-enabled chemical self-assembly. Strain and lattice parameter maps permit the reconstruction of the roughness of the grain boundary and suggest that its formation is promoted by a wedge of helical atomic chains along the [0001] crystallographic direction. The observation of wrinkles at the grain boundary is found to be the dominant relaxation mechanism. Insights into the formation mechanism are elucidated by mapping the lattice parameters as the first demonstration of local in-plane and out-of-plane unit cell variation in a nanometer-by-nanometer real-space array.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Doping of Cr in Graphene Using Electron Beam Manipulation for Functional Defect Engineering

Chromium atoms in graphene have been proposed to exhibit magnetic moments and spin-selective conducting states depending on the local bonding geometry within the graphene structure, which could lead to interesting applications in spintronics. Despite this interest, there are few direct experimental reports of Cr dopants in graphene even though it is theorized to be stable. Here, we demonstrate the introduction of single Cr dopant atoms into the graphene lattice and onto graphene edges through the controlled use of a focused electron beam in a scanning transmission electron microscope. Here, we show local control of doping locations, and when coupled with targeted in situ milling during scanning of the e-beam, these strategies demonstrate an important component of the fabrication of tailored nanostructured devices in the electron microscope. The approach is validated with first-principles calculations to understand synthesis pathways during fabrication and reveal the energetics and local properties of Cr atoms embedded in graphene; for example, Cr doping can convert graphene into a magnetic and semiconducting material, which suggests Cr-doped graphene can be used as a building block for potential electronic devices and a means to construct them.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Selective nano-patterning of graphene using a heated atomic force microscope tip

In this study, we introduce a selective thermochemical nano-patterning method of graphene on insulating substrates. A tiny heater formed at the end of an atomic force microscope (AFM) cantilever is optimized by a finite element method. The cantilever device is fabricated using conventional micromachining processes. After preliminary tests of the cantilever device, nano-patterning experiments are conducted with various conducting and insulating samples. The results indicate that faster scanning speed and higher contact force are desirable to reduce the sizes of nano-patterns. With the experimental condition of 1 μm/s and 24 mW, the heated AFM tip generates a graphene oxide layer of 3.6 nm height and 363 nm width, on a 300 nm thick SiO{sub 2} layer, with a tip contact force of 100 nN.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Local structure of solid Rb at megabar pressures

We have investigated the local and electronic structure of solid rubidium by means of x-ray absorption spectroscopy up to 101.0 GPa, thus doubling the maximum investigated experimental pressure. This study confirms the predicted stability of phase VI and was completed by the combination of two pivotal instrumental solutions. On one side, we made use of nanocrystalline diamond anvils, which, contrary to the more commonly used single crystal diamond anvils, do not generate sharp Bragg peaks (glitches) at specific energies that spoil the weak fine structure oscillations in the x-ray absorption cross section. Second, we exploited the performance of a state-of-the-art x-ray focussing device yielding a beam spot size of 5 × 5 μm{sup 2}, spatially stable over the entire energy scan. An advanced data analysis protocol was implemented to extract the pressure dependence of the structural parameters in phase VI of solid Rb from 51.2 GPa up to the highest pressure. A continuous reduction of the nearest neighbour distances was observed, reaching about 6% over the probed pressure range. We also discuss a phenomenological model based on the Einstein approximation to describe the pressure behaviour of the mean-square relative displacement. Within this simplified scheme, we estimate the Grüneisen parameter for this high pressure Rb phase to be in the 1.3–1.5 interval.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Collisionless Larmor coupling and blob formation in a laser-plasma expanding into a magnetized ambient plasma

Collisionless Larmor coupling is a fundamental process in space and astrophysical plasmas that enables momentum transfer between an expanding plasma and a magnetized ambient medium. Here, in this paper, we report on the laboratory experimental study of Larmor coupling leading to the formation of a plasma blob associated with a laser-driven, super-Alfvénic plasma flow on the Large Plasma Device at the University of California, Los Angeles. The high-repetition rate enables systematic spatial and temporal scans of the plasma evolution using Doppler spectroscopy, as well as measurements of the magnetic field, electrostatic field, and self-emission of both debris and ambient ions using filtered imaging. We observe the self-focusing of the laser-produced plasma and the formation of a secondary diamagnetic cavity associated with a blob composed of background ions. Doppler spectroscopy reveals the transverse velocity distribution of the background ions, providing direct evidence of ion energization via Larmor coupling. The systematic spatial and temporal scans enabled by the high-repetition-rate experiment allow for a detailed characterization of the ion dynamics. These experimental observations are supported by numerical simulations that provide more insight into the kinetic-scale physics associated with blob formation as well as the role of the ambient plasma density.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2019

The existence and impact of persistent ferroelectric domains in MAPbI 3

Methylammonium lead iodide (MAPbI 3 ) exhibits exceptional photovoltaic performance, but there remains substantial controversy over the existence and impact of ferroelectricity on the photovoltaic response. We confirm ferroelectricity in MAPbI 3 single crystals and demonstrate mediation of the electronic response by ferroelectric domain engineering. The ferroelectric response sharply declines above 57°C, consistent with the tetragonal-to-cubic phase transition. Concurrent band excitation piezoresponse force microscopy–contact Kelvin probe force microscopy shows that the measured response is not dominated by spurious electrostatic interactions. Large signal poling (>16 V/cm) orients the permanent polarization into large domains, which show stabilization over weeks. X-ray photoemission spectroscopy results indicate a shift of 400 meV in the binding energy of the iodine core level peaks upon poling, which is reflected in the carrier concentration results from scanning microwave impedance microscopy. As a result, the ability to control the ferroelectric response provides routes to increase device stability and photovoltaic performance through domain engineering.

14 SOLAR ENERGY↗
DOE OSTI2024

Material and Interface Engineering Strategies to Mitigate Decoherence in Superconducting Qubits

While significant strides have been made to increase the coherence time of superconducting qubits, further advancements are essential for realizing scalable quantum computing. Decoherence is often a result of loss and noise stemming from two-level systems and excess quasiparticles, arising due to material defects, fabrication processes, and ambient exposure, particularly at surfaces and interfaces. Our recent efforts to mitigate these decoherence mechanisms have employed a variety of strategies, including low-loss surface encapsulation materials, advanced substrate preparation techniques, modifications to metal film growth, and the development of novel fabrication processes. The structural and chemical properties of materials, surfaces, and interfaces are studied using scanning probe microscopy, electron microscopy, photoelectron spectroscopy, mass spectrometry, and X-ray diffraction, which is correlated to device performance metrics, including superconducting resonator internal quality factor and qubit T1 time. This information is used to identify and understand material sources of loss and their origins in the device fabrication process. Through multi-institution efforts within SQMS we have identified the loss mechanism of interstitial hydrogen in niobium-based devices and shown how standard fabrication processes introduce these hydrides, developing strategies to mitigate their formation.1 Furthermore, we have characterized the metal-substrate interface, including the loss of niobium-silicides formed at that interface, and developed silicon surface treatments that reduce atomic scale roughness and oxygen content at the metal-substrate and Josephson junction interfaces.2-4 By developing the connection between materials properties and the overall performance of superconducting quantum circuitry, we can develop fabrication strategies to mitigate material losses, thus supporting the ongoing efforts to enhance coherence time in superconducting quantum devices. 1. Torres-Castanedo, C. G.*, Goronzy, D. P.*, et al., Adv. Funct. Mater., 2401365 (2024) 2. Lu, X., et al., Phys. Rev. Materials 6, 064402 (2022) 3. Berti, G., Appl. Phys. Lett. 122, 192605 (2023) 4. Kopas, C. J., Goronzy, D. P., et al., arXiv:2408.02863 (2024)

Goronzy, Dominic P.↗
DOE OSTI2012

Broad-emission nanocrystals and methods of making and using same

In one aspect, the invention relates to an inorganic nanoparticle or nanocrystal, also referred to as a quantum dot, capable of emitting white light. In a further aspect, the invention relates to an inorganic nanoparticle capable of absorbing energy from a first electromagnetic region and capable of emitting light in a second electromagnetic region, wherein the second electromagnetic region comprises an at least about 50 nm wide band of wavelengths and to methods for the preparation thereof. In further aspects, the invention relates to a frequency converter, a light emitting diode device, a modified fluorescent light source, an electroluminescent device, and an energy cascade system comprising the nanoparticle of the invention. This abstract is intended as a scanning tool for purposes of searching in the particular art and is not intended to be limiting of the present invention.

Bowers, Michael J.↗
DOE OSTI2015

Preparation, characterization and electroluminescence studies of ZnO nanorods for optoelectronic device applications

In this work, ZnO nanorods were achieved by a simple chemical precipitation method in the presence of capping agent Poly Vinyl Pyrrolidone (PVP) at room temperature. X-Ray Diffraction (XRD) result indicates that the synthesized undoped ZnO nanorods have wurtzite hexagonal structure without any impurities. It has been seen that the growth orientation of the prepared ZnO nanorods were (101). XRD analysis revealed that the nanorods having the crystallite size 49 nm. The Scanning Electron Microscopy (SEM) image confirmed the size and shape of these nanorods. The diameter of nanorods has been found that 1.52 µm to 1.61 µm and the length of about 4.89 µm. It has also been found that at room temperature Ultra Violet Visible (UV-VIS) absorption band is around 355 nm (blue shifted as compared to bulk). Electroluminescence (EL) studies show that emission of light is possible at very small threshold voltage and increases rapidly with increasing applied voltage. It is seen that smaller ZnO nanoparticles give higher electroluminescence brightness starting at lower threshold voltage. The brightness is also affected by increasing the frequency of AC signal.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

High-Temperature Interaction of Liquid Gd with Y{sub 2}O{sub 3}

The sessile drop method combined with contact heating procedure was applied for the investigation of high-temperature interaction between liquid Gd and Y{sub 2}O{sub 3} substrate. Real-time behavior of Gd sample in flowing inert gas (Ar) atmosphere upon heating to and at temperature of 1362 °C was recorded using high-speed high-resolution CCD camera. The results evidenced that molten Gd wets Y{sub 2}O{sub 3} substrate (the contact angle θ < 90°) immediately after melting of metal sample observed at T = 1324 °C (T{sub m} = 1312 °C). During the first 3 min of the sessile drop test, the contact angle dropped from θ = 52° to θ = 24° and then stabilized at the final value of θ{sub f}{sup *} = 33°. The solidified Gd/Y{sub 2}O{sub 3} couple was subjected to structural characterization using optical microscopy, scanning electron microscopy coupled with x-ray energy-dispersive spectroscopy. The results evidenced that the wettability in the Gd/Y{sub 2}O{sub 3} system has a reactive nature and the leading mechanism of the interaction between liquid Gd and Y{sub 2}O{sub 3} is the dissolution of the ceramic in the liquid metal responsible for the formation of a deep crater in the substrate under the drop. Therefore, the final contact angle θ{sub f}*, estimated from the side-view drop image, should be considered as an apparent value, compared to the more reliable value of θ{sub f} = 70° measured on the cross section of the solidified couple.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Sol–gel Synthesis and Upconversion Luminescent Properties of Yb{sup 3+},Er{sup 3+},Eu{sup 3+} Triply-Doped in YVO{sub 4} Phosphors

Yb{sup 3+},Er{sup 3+},Eu{sup 3+} triply-doped in YVO{sub 4} with varying molar ratio of Er/Eu were synthesized in a sol–gel method with a subsequent heat treatment for the first time. The optimal molar ratio of Er/Eu for the maximum energy transfer efficiency was 1/39. After molar ratio, the influences of different heat treatment temperatures were also researched and the maximal heat temperature was 1300 °C. Besides, the properties of YVO{sub 4}:Yb{sup 3+},Er{sup 3+},Eu{sup 3+} upconversion phosphors were investigated by X-ray diffraction, scanning electron microscopy and photo luminescent spectra, respectively. In sum, XRD results indicate the crystal structure of as-prepared samples, which is the tetragonal phase of YVO{sub 4} with no other diffraction peaks. SEM images show the morphology of as-prepared samples, which are granular-like nanoparticles. PL spectra demonstrate the upconversion luminescence of as-prepared samples, which emit strong green lights (at 525 nm, 550 nm) and slight red lights (at 590 nm, 615 nm, 695 nm) under the NIR irradiation at 980 nm. Two strong green emissions are attributed to the {sup 2}H{sub 11/2}→{sup 4}I{sub 15/2} and {sup 4}S{sub 3/2}→{sup 4}I{sub 15/2} transitions of Er{sup 3+} ions. Meanwhile, three slight red emissions are attributed to the {sup 5}D{sub 0}→{sup 7}F{sub 1}, {sup 5}D{sub 0}→{sup 7}F{sub 2} and {sup 5}D{sub 0}→{sup 7}F{sub 4} transitions of Eu{sup 3+} ions. All in all, the colorful emissions endow YVO{sub 4}:Yb{sup 3+},Er{sup 3+},Eu{sup 3+} phosphors great potential for some applications, such as display devices, bio-labeling and infrared detection.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Direct Visualization and Manipulation of Tunable Quantum Well State in Semiconducting Nb 2 SiTe 4

We report quantum well states (QWSs) can form at the surface or interfaces of materials with confinement potential. They have broad applications in electronic and optical devices such as high mobility electron transistor, photodetector, and quantum well laser. The properties of the QWSs are usually the key factors for the performance of the devices. However, direct visualization and manipulation of such states are, in general, challenging. In this work, by using angle-resolved photoemission spectroscopy (ARPES) and scanning tunneling microscopy/spectroscopy (STM/STS), we directly probe the QWSs generated on the vacuum interface of a narrow band gap semiconductor Nb 2 SiTe 4 . Interestingly, the position and splitting of QWSs could be easily manipulated via potassium (K) dosage onto the sample surface. Our results suggest Nb 2 SiTe 4 to be an intriguing semiconductor system to study and engineer the QWSs, which has great potential in device applications.

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

Thermodynamic origin of nonvolatility in resistive memory

Electronic switches based on the migration of high-density point defects, or memristors, are poised to revolutionize post-digital electronics. Despite significant research, key mechanisms for filament formation and oxygen transport remain unresolved, hindering our ability to predict and design device properties. For example, experiments have achieved 10 orders of magnitude longer retention times than predicted by current models. Here, using electrical measurements, scanning probe microscopy, and first-principles calculations on tantalum oxide memristors, we reveal that the formation and stability of conductive filaments crucially depend on the thermodynamic stability of the amorphous oxygen-rich and oxygen-poor compounds, which undergo composition phase separation. Including the previously neglected effects of this amorphous phase separation reconciles unexplained discrepancies in retention and enables predictive design of key performance indicators such as retention stability. Furthermore, this result emphasizes non-ideal thermodynamic interactions as key design criteria in post-digital devices with defect densities substantially exceeding those of today’s covalent semiconductors.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Microwave heating device for internal heating convection experiments, applied to Earth's mantle dynamics

We report the design, construction, and performances of a microwave (MW) heating device for laboratory experiments with non-contact, homogeneous internal heating. The device generates MW radiation at 2.47 GHz from a commercial magnetron supplied by a pulsed current inverter using proprietary, feedback based command and control hardware and software. Specially designed MW launchers direct the MW radiation into the sample through a MW homogenizer, devised to even the MW power distribution into the sample's volume. An adjustable MW circuit adapts the MW generator to the load (i.e., the sample) placed in the experiment chamber. Dedicated heatsinks maintain the MW circuits at constant temperature throughout the experiment. Openings for laser scanning for image acquisition with a CCD camera and for the cooling circuits are protected by special MW filters. The performances of the device are analyzed in terms of heating uniformity, long term output power stability, and load matching. The device is used for small scale experiments simulating Earth's mantle convection. The 30 × 30 × 5 cm{sup 3} convection tank is filled with a water‑based viscous fluid. A uniform and constant temperature is maintained at the upper boundary by an aluminum heat exchanger and adiabatic conditions apply at the tank base. We characterize the geometry of the convective regime as well as its bulk thermal evolution by measuring the velocity field by Particle Image Velocimetry and the temperature field by using Thermochromic Liquid Crystals.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Formation of conductive copper lines by femtosecond laser irradiation of copper nitride film on plastic substrates

In this paper, we report a simple method to form conductive copper lines by scanning a single-beam femtosecond pulse laser on a plastic substrate covered with copper nitride (Cu{sub 3}N) film. The Cu{sub 3}N films were prepared by DC magnetron sputtering in the presence of an Ar + N{sub 2} atmosphere at 100 °C. The influence of the laser power and scanning speed on the formed copper line width, surface features, and morphology was analyzed by means of optical microscopy, X-ray diffraction, non-contact 3D profilometer, and scanning electron microscopy. The experimental results demonstrate that low laser power and low scanning speed favor the formation of uniform and flat Cu lines. After process optimization, copper lines with a width less than 5 μm were obtained, which provides an attractive application prospect in the field of flexible electronic devices.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Carbon nanotube quantum dots on hexagonal boron nitride

We report the fabrication details and low-temperature characteristics of carbon nanotube (CNT) quantum dots on flakes of hexagonal boron nitride (hBN) as substrate. We demonstrate that CNTs can be grown on hBN by standard chemical vapor deposition and that standard scanning electron microscopy imaging and lithography can be employed to fabricate nanoelectronic structures when using optimized parameters. This proof of concept paves the way to more complex devices on hBN, with more predictable and reproducible characteristics and electronic stability.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Nanoscale Control of Oxygen Defects and Metal–Insulator Transition in Epitaxial Vanadium Dioxides

Strongly correlated vanadium dioxide (VO 2 ) is one of the most promising materials that exhibits a temperature-driven, metal–insulator transition (MIT) near room temperature. The ability to manipulate the MIT at nanoscale offers both insight into understanding the energetics of phase transition and a promising potential for nanoelectronic devices. In this work, we study nanoscale electrochemical modifications of the MIT in epitaxial VO 2 thin films using a combined approach with scanning probe microscopy (SPM) and theoretical calculations. We find that applying electric voltages of different polarity through an SPM tip locally changes the contact potential difference and conductivity on the surface of VO 2 by modulating the oxygen stoichiometry. We observed nearly 2 orders of magnitude change in resistance between positive and negative biased-tip written areas of the film, demonstrating the electric field modulated MIT behavior at the nanoscale. Density functional theory calculations, benchmarked against more accurate many-body quantum Monte Carlo calculations, provide information on the formation energetics of oxygen defects that can be further manipulated by strain. In conclusion, this study highlights the crucial role of oxygen vacancies in controlling the MIT in epitaxial VO 2 thin films, useful for developing advanced electronic and iontronic devices.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Controllable spin-charge transport in strained graphene nanoribbon devices

We theoretically investigate the spin-charge transport in two-terminal device of graphene nanoribbons in the presence of a uniform uniaxial strain, spin-orbit coupling, exchange field, and smooth staggered potential. We show that the direction of applied strain can efficiently tune strain-strength induced oscillation of band-gap of armchair graphene nanoribbon (AGNR). It is also found that electronic conductance in both AGNR and zigzag graphene nanoribbon (ZGNR) oscillates with Rashba spin-orbit coupling akin to the Datta-Das field effect transistor. Two distinct strain response regimes of electronic conductance as function of spin-orbit couplings magnitude are found. In the regime of small strain, conductance of ZGNR presents stronger strain dependence along the longitudinal direction of strain. Whereas for high values of strain shows larger effect for the transversal direction. Furthermore, the local density of states shows that depending on the smoothness of the staggered potential, the edge states of AGNR can either emerge or be suppressed. These emerging states can be determined experimentally by either spatially scanning tunneling microscope or by scanning tunneling spectroscopy. Our findings open up new paradigms of manipulation and control of strained graphene based nanostructure for application on novel topological quantum devices.

77 NANOSCIENCE AND NANOTECHNOLOGY↗