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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 595 records · Page 33
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Design and construction of a quantum matter synthesizer

The quantum matter synthesizer (QMS) is a new quantum simulation platform in which individual particles in a lattice can be resolved and re-arranged into arbitrary patterns. The ability to spatially manipulate ultracold atoms and control their tunneling and interactions at the single-particle level allows full control of a many-body quantum system. We present the design and characterization of the QMS, which integrates into a single ultra-stable apparatus a two-dimensional optical lattice, a moving optical tweezer array formed by a digital micromirror device, and site-resolved atomic imaging. We demonstrate excellent mechanical stability between the lattice and tweezer array with relative fluctuations below 10 nm, diffraction-limited imaging at a resolution of 655 nm, and high-speed real-time control of the tweezer array at a 2.52 kHz refresh rate, which will be adopted to realize fast rearrangement of atoms. The QMS also features new technologies and schemes, such as nanotextured anti-reflective windows and all-optical long-distance transport of atoms.

47 OTHER INSTRUMENTATION↗
DOE OSTI2024

Optimizing spectral phase transfer in four-wave mixing with gas-filled capillaries

Four-wave mixing (FWM) in gas-filled hollow-core capillaries, a nonlinear optical process that mixes signal and pump photon frequencies to generate idler frequency photons, offers a method for precise spectral phase transfer from signal to idler at ultrashort timescales and extreme powers. However, this regime is challenged by competing linear and nonlinear dynamics, leading to significant trade-offs between spectral phase transfer and conversion efficiency. Our computational investigation focuses on the upconversion of femtosecond pulses from the infrared (IR) to the ultraviolet (UV), a range notoriously difficult to manipulate. We explore an intermediate energy regime that strikes an optimal balance between FWM-mediated phase-transfer fidelity and nonlinear conversion efficiency. By adjusting the energy ratios and spectral phase profiles of the input signal, we achieve conversion efficiencies of approximately 5-15% while maintaining an effective quasi-linear spectral phase transfer. These findings will contribute to establishing first-principles and scaling laws essential for applications such as high-precision imaging, spectroscopy, quantum transduction, and distributed entangled interconnects, facilitating advanced control of ultrafast photonic and electronic wavepackets in quantum materials with unprecedented spatial and temporal precision.

Zhang, Hao↗
DOE OSTI2019

Effect of Annealing Temperature on Structure and Magnetic Properties of Zn{sub 0.94}Mg{sub 0.01}Mn{sub 0.05}O Nanoparticles

Structural and magnetic characteristics of Zn{sub 0.94}Mg{sub 0.01}Mn{sub 0.05}O (ZnMgMnO) nanoparticles synthesized by Sol-Gel preparation technique in a wide temperature range were reported. The influence of annealing temperature on the crystal structure of ZnMgMnO nanoparticles was figured out by X-ray diffraction technique (XRD). To optimize the annealing temperature and reveal the particle formation and size, Scanning Electron Microscope (SEM) imaging technique was performed. The required stoichiometry of the synthesized samples was obtained by an energy dispersive X-ray analysis technique (EDX). Quantum Design Vibrating Sample Magnetometer (QDVSM) tool was used for the magnetic characterizations of Zn{sub 0.94}Mg{sub 0.01}Mn{sub 0.05}O composition. Magnetization measurements as a function of magnetic field (M-H) were performed in the magnetic field up to 10 kOe. Temperature dependence of magnetization measurements (M-T) was taken between 10 and 320 K temperature ranges.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2013

Synchrotron nanoimaging of single In-rich InGaN nanowires

This work reports on the elemental distribution and local structure of single In{sub x}Ga{sub 1-x}N nanowires (NWs) grown by molecular beam epitaxy on Si (111) substrates using X-ray fluorescence nanoprobe. Ga and In maps reveal an inhomogeneous elemental distribution along the NWs, with a higher Ga concentration at the bottom of the NW. Scanning electron microscopy images show that the inhomogeneous axial distribution is not correlated with a X-ray beam induced damage, and therefore, should be an intrinsic characteristic of the NWs arising from the growth process. Spatially resolved X-ray absorption near edge structure spectroscopy data acquired around the In K-edge show that the tetrahedral structure is preserved around the absorbing In-atoms all along the NW, and suggests that the compositional modulation could be affecting its long-range order.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Automated detection of rear contact voids in perc cells with photoluminescence imaging

An image-processing method combined with Fourier analysis is introduced here in this work as a rapid and highly-automated method of detecting rear contact voids in passivated emitter and rear contact cells (PERC). This approach utilizes photoluminescence (PL) imaging to locate the central point of the most detrimental type of voids and associate a void fraction to each cell in a manner of seconds. Acoustic microscopy and scanning electron microscopy are also used as complementary tools to confirm the presence of voids detection using PL imaging and provide more insight into the actual physical mechanism of what is observed in PL measurements.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2014

Stochastic solution of population balance equations for reactor networks

This work presents a sequential modular approach to solve a generic network of reactors with a population balance model using a stochastic numerical method. Full-coupling to the gas-phase is achieved through operator-splitting. The convergence of the stochastic particle algorithm in test networks is evaluated as a function of network size, recycle fraction and numerical parameters. These test cases are used to identify methods through which systematic and statistical error may be reduced, including by use of stochastic weighted algorithms. The optimal algorithm was subsequently used to solve a one-dimensional example of silicon nanoparticle synthesis using a multivariate particle model. This example demonstrated the power of stochastic methods in resolving particle structure by investigating the transient and spatial evolution of primary polydispersity, degree of sintering and TEM-style images. Highlights: •An algorithm is presented to solve reactor networks with a population balance model. •A stochastic method is used to solve the population balance equations. •The convergence and efficiency of the reported algorithms are evaluated. •The algorithm is applied to simulate silicon nanoparticle synthesis in a 1D reactor. •Particle structure is reported as a function of reactor length and time.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2013

Effect of annealing on SiO{sub x}-TiO{sub 2} axial heterostructure nanowires and improved photodetection

Glancing angle deposition technique has been used to synthesize the axial heterostructure SiO{sub x}-TiO{sub 2} nanowires (NWs) on the Si substrate. The field emission gun scanning electron microscope image shows the formation of perpendicular NWs on Si substrate. A typical transmission electron microscope image confirms the heterostructure NW which consists of SiO{sub x} of length ∼130 nm and TiO{sub 2} of length ∼170 nm. The amorphous NWs transformed to polycrystalline nature after annealing. The trap assisted radiative recombination process is absent for the annealed NWs. An averagely 1.1 fold enhanced photoabsorption was exhibited by the annealed NWs in the 200–350 nm region and 1.5 fold in the 500–850 nm region. The leakage current (2.6 × 10{sup −8} A/cm{sup 2} at −0.5 V) significantly reduced for annealed NWs device. A maximum 1.4 × 10{sup 3} times enlarged photodetection has been observed for annealed device.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

The iQID Camera: An Ionizing-Radiation Quantum Imaging Detector

We have developed and tested a novel, ionizing-radiation Quantum Imaging Detector (iQID). This scintillation-based detector was originally developed as a high-resolution gamma-ray imager, called BazookaSPECT, for use in single-photon emission computed tomography (SPECT). Recently, we have investigated the detectors response and imaging potential with other forms of ionizing radiation including alpha, neutron, beta, and fission fragment particles. The detector’s response to a broad range of ionizing radiation has prompted its new title. The principle operation of the iQID camera involves coupling a scintillator to an image intensifier. The scintillation light generated particle interactions is optically amplified by the intensifier and then re-imaged onto a CCD/CMOS camera sensor. The intensifier provides sufficient optical gain that practically any CCD/CMOS camera can be used to image ionizing radiation. Individual particles are identified and their spatial position (to sub-pixel accuracy) and energy are estimated on an event-by-event basis in real time using image analysis algorithms on high-performance graphics processing hardware. Distinguishing features of the iQID camera include portability, large active areas, high sensitivity, and high spatial resolution (tens of microns). Although modest, iQID has energy resolution that is sufficient to discrimate between particles. Additionally, spatial features of individual events can be used for particle discrimination. An important iQID imaging application that has recently been developed is single-particle, real-time digital autoradiography. In conclusion, we present the latest results and discuss potential applications.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2012

One-step synthesis of lightly doped porous silicon nanowires in HF/AgNO{sub 3}/H{sub 2}O{sub 2} solution at room temperature

One-step synthesis of lightly doped porous silicon nanowire arrays was achieved by etching the silicon wafer in HF/AgNO{sub 3}/H{sub 2}O{sub 2} solution at room temperature. The lightly doped porous silicon nanowires (pNWs) have circular nanopores on the sidewall, which can emit strong green fluorescence. The surface morphologies of these nanowires could be controlled by simply adjusting the concentration of H{sub 2}O{sub 2}, which influences the distribution of silver nanoparticles (Ag NPs) along the nanowire axis. A mechanism based on Ag NPs-induced lateral etching of nanowires was proposed to explain the formation of pNWs. The controllable and widely applicable synthesis of pNWs will open their potential application to nanoscale photoluminescence devices. - Graphical abstract: The one-step synthesis of porous silicon nanowire arrays is achieved by chemical etching of the lightly doped p-type Si (100) wafer at room temperature. These nanowires exhibit strong green photoluminescence. SEM, TEM, HRTEM and photoluminescence images of pNWs. The scale bars of SEM, TEM HRTEM and photoluminescence are 10 {mu}m, 20 nm, 10 nm, and 1 {mu}m, respectively. Highlights: Black-Right-Pointing-Pointer Simple one-step synthesis of lightly doped porous silicon nanowire arrays is achieved at RT. Black-Right-Pointing-Pointer Etching process and mechanism are illustrated with etching model from a novel standpoint. Black-Right-Pointing-Pointer As-prepared porous silicon nanowire emits strong green fluorescence, proving unique property.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Nanoscale imaging of photocurrent and efficiency in CdTe solar cells

The local collection characteristics of grain interiors and grain boundaries in thin film CdTe polycrystalline solar cells are investigated using scanning photocurrent microscopy. The carriers are locally generated by light injected through a small aperture (50-300 nm) of a near-field scanning optical microscope in an illumination mode. Possible influence of rough surface topography on light coupling is examined and eliminated by sculpting smooth wedges on the granular CdTe surface. By varying the wavelength of light, nanoscale spatial variations in external quantum efficiency are mapped. We find that the grain boundaries (GBs) are better current collectors than the grain interiors (GIs). The increased collection efficiency is caused by two distinct effects associated with the material composition of GBs. First, GBs are charged, and the corresponding built-in field facilitates the separation and the extraction of the photogenerated carriers. Second, the GB regions generate more photocurrent at long wavelength corresponding to the band edge, which can be caused by a smaller local band gap. As a result, resolving carrier collection with nanoscale resolution in solar cell materials is crucial for optimizing the polycrystalline device performance through appropriate thermal processing and passivation of defect and surfaces.

14 SOLAR ENERGY↗
DOE OSTI2017

Circular dichroism in photoelectron images from aligned nitric oxide molecules

We have used velocity map photoelectron imaging to study circular dichroism of the photoelectron angular distributions (PADs) of nitric oxide following two-color resonanceenhanced two-photon ionization via selected rotational levels of the A 2 Σ + , v' = 0 state. By using a circularly polarized pump beam and a counter-propagating, circularly polarized probe beam, cylindrical symmetry is preserved in the ionization process, and the images can be reconstructed using standard algorithms. The VMI set up enables individual ion rotational states to be resolved with excellent collection efficiency, rendering the measurements considerably simpler to perform than previous measurements conducted with a conventional photoelectron spectrometer. The results demonstrate that circular dichroism is observed even when cylindrical symmetry is maintained, and serve as a reminder that dichroism is a general feature of the multiphoton ionization of atoms and molecules. Furthermore, the observed PADs are in good agreement with calculations based on parameters extracted from previous experimental results obtained by using a time-offlight electron spectrometer.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Self-aligned process for forming microlenses at the tips of vertical silicon nanowires by atomic layer deposition

The microlens is a key enabling technology in optoelectronics, permitting light to be efficiently coupled to and from devices such as image sensors and light-emitting diodes. Their ubiquitous nature motivates the development of new fabrication techniques, since existing methods face challenges as microlenses are scaled to smaller dimensions. Here, the authors demonstrate the formation of microlenses at the tips of vertically oriented silicon nanowires via a rapid atomic layer deposition process. The nature of the process is such that the microlenses are centered on the nanowires, and there is a self-limiting effect on the final sizes of the microlenses arising from the nanowire spacing. Finite difference time domain electromagnetic simulations are performed of microlens focusing properties, including showing their ability to enhance visible-wavelength absorption in silicon nanowires.

36 MATERIALS SCIENCE↗
DOE OSTI2014

High power THz sources for nonlinear imaging

Many biological and chemical compounds have unique absorption features in the THz (0.1 - 10 THz) region, making the use of THz waves attractive for imaging in defense, security, biomedical imaging, and monitoring of industrial processes. Unlike optical radiation, THz frequencies can pass through many substances such as paper, clothing, ceramic, etc. with little attenuation. The use of currently available THz systems is limited by lack of highpower, sources as well as sensitive detectors and detector arrays operating at room temperature. Here we present a novel, high power THz source based on intracavity downconverison of optical pulses. The source delivers 6 ps pulses at 1.5 THz, with an average power of >300 μW and peak powers >450 mW. We propose an imaging method based on frequency upconverison that is ideally suited to use the narrow bandwidth and high peak powers produced by the source. By upconverting the THz image to the infrared, commercially available detectors can be used for real time imaging.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Investigation of combinatorial coevaporated thin film Cu{sub 2}ZnSnS{sub 4}. I. Temperature effect, crystalline phases, morphology, and photoluminescence

Cu{sub 2}ZnSnS{sub 4} is a promising low-cost, nontoxic, earth-abundant absorber material for thin-film solar cell applications. In this study, combinatorial coevaporation was used to synthesize individual thin-film samples spanning a wide range of compositions at low (325 °C) and high (475 °C) temperatures. Film composition, grain morphology, crystalline-phase and photo-excitation information have been characterized by x-ray fluorescence, scanning electron microscopy, x-ray diffraction, Raman spectroscopy, and photoluminescence imaging and mapping. Highly textured columnar grain morphology is observed for film compositions along the ZnS-Cu{sub 2}ZnSnS{sub 4}-Cu{sub 2}SnS{sub 3} tie line in the quasi-ternary Cu{sub 2}S-ZnS-SnS{sub 2} phase system, and this effect is attributed to structural similarity between the Cu{sub 2}ZnSnS{sub 4}, Cu{sub 2}SnS{sub 3}, and ZnS crystalline phases. At 475 °C growth temperature, Sn-S phases cannot condense because of their high vapor pressures. As a result, regions that received excess Sn flux during growth produced compositions falling along the ZnS-Cu{sub 2}ZnSnS{sub 4}-Cu{sub 2}SnS{sub 3} tie line. Room-temperature photoluminescence imaging reveals a strong correlation for these samples between film composition and photoluminescence intensity, where film regions with Cu/Sn ratios greater than ∼2 show strong photoluminescence intensity, in comparison with much weaker photoluminescence in regions that received excess Sn flux during growth or subsequent processing. The observed photoluminescence quenching in regions that received excess Sn flux is attributed to the effects of Sn-related native point defects in Cu{sub 2}ZnSnS{sub 4} on non-radiative recombination processes. Implications for processing and performance of Cu{sub 2}ZnSnS{sub 4} solar cells are discussed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

Imaging regenerating bone tissue based on neural networks applied to micro-diffraction measurements

We monitored bone regeneration in a tissue engineering approach. To visualize and understand the structural evolution, the samples have been measured by X-ray micro-diffraction. We find that bone tissue regeneration proceeds through a multi-step mechanism, each step providing a specific diffraction signal. The large amount of data have been classified according to their structure and associated to the process they came from combining Neural Networks algorithms with least square pattern analysis. In this way, we obtain spatial maps of the different components of the tissues visualizing the complex kinetic at the base of the bone regeneration.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2016

In Situ Real-Time Radiographic Study of Thin Film Formation Inside Rotating Hollow Spheres

Hollow spheres with uniform coatings on the inner surface have applications in optical devices, time- or site controlled drug release, heat storage devices, and target fabrication for inertial confinement fusion experiments. The fabrication of uniform coatings, which is often critical for the application performance, requires precise understanding and control over the coating process and its parameters. Here, we report on in-situ real-time radiography experiments that provide critical spatio-temporal information about the distribution of fluids inside hollow spheres during uniaxial rotation. Image analysis and computer fluid dynamics simulations were used to explore the effect of liquid viscosity and rotational velocity on the film uniformity. The data were then used to demonstrate the fabrication of uniform sol-gel chemistry derived porous polymer films inside 2mm inner diameter diamond shells.

aerogel↗
DOE OSTI2022

Integration of Highly Luminescent Lead Halide Perovskite Nanocrystals on Transparent Lead Halide Nanowire Waveguides through Morphological Transformation and Spontaneous Growth in Water

The integration of highly luminescent CsPbBr 3 quantum dots on nanowire waveguides has enormous potential applications in nanophotonics, optical sensing and quantum communications. On the other hand, CsPb 2 Br 5 nanowires have also attracted a lot of attention due to their unique water stability and controversial luminescent property. Here we first report the growth of CsPbBr 3 nanocrystals on CsPb 2 Br 5 nanowires by simply immersing CsPbBr 3 powder into pure water, CsPbBr 3-γ X γ (X = Cl, I) nanocrystals on CsPb 2 Br 5-γ X γ nanowires are then synthesized for tunable light sources. Systematic structure and morphology studies, including in-situ monitoring, revealed that CsPbBr 3 powder was first converted to CsPb 2 Br 5 microplatelets in water, followed by a morphological transformation from CsPb 2 Br 5 microplatelets to nanowires, which is a kinetic dissolution-recrystallization process controlled by electrolytic dissociation and supersaturation of CsPb 2 Br 5 . CsPbB r3 nanocrystals are spontaneously formed on CsPb 2 Br 5 nanowires when nanowires are collected from the aqueous solution. Raman spectroscopy, combined photoluminescence and SEM imaging confirm that the bright emission originates from CsPbBr 3-γ X γ nanocrystals while CsPb 2 Br 5-γ X γ nanowires are transparent waveguides. In conclusion, the intimate integration of nanoscale light sources with a nanowire waveguide is demonstrated through the observation of the wave guiding of light from nanocrystals and Fabry-Perot interference modes of the nanowire cavity.

42 ENGINEERING↗
DOE OSTI2023

A Platform for Atomic Fabrication and In Situ Synthesis in a Scanning Transmission Electron Microscope

Here, the engineering of quantum materials requires the development of tools able to address various synthesis and characterization challenges. These include the establishment and refinement of growth methods, material manipulation, and defect engineering. Atomic-scale modification will be a key enabling factor for engineering quantum materials where desired phenomena are critically determined by atomic structures. Successful use of scanning transmission electron microscopes (STEMs) for atomic scale material manipulation has opened the door for a transformed view of what can be accomplished using electron-beam-based strategies. However, serious obstacles exist on the pathway from possibility to practical reality. One such obstacle is the in situ delivery of atomized material in the STEM to the region of interest for further fabrication processes. Here, progress on this front is presented with a view toward performing synthesis (deposition and growth) processes in a scanning transmission electron microscope in combination with top-down control over the reaction region. An in situ thermal deposition platform is presented, tested, and deposition and growth processes are demonstrated. In particular, it is shown that isolated Sn atoms can be evaporated from a filament and caught on the nearby sample, demonstrating atomized material delivery. This platform is envisioned to facilitate real-time atomic resolution imaging of growth processes and open new pathways toward atomic fabrication.

36 MATERIALS SCIENCE↗