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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 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Accelerator physics at NSLS-II: research accomplishments in 2020

NSLS-II accelerator physicists provide scientific support for user operations, as well as for improvements and developments of the accelerator systems. This work includes optimization of the NSLS-II performance with high beam current and low vertical emittance, improvement of the beam stability, development of new software tools for operations and beam studies. The accelerator physicists productively worked on a number of research activities such as the conceptual design of NSLS-II accelerator upgrade; design and optimization of advanced low-emittance lattices; development of novel methods to study nonlinear beam dynamics; ultrafast electron diffraction and microscopy. The physicists also contributed to the BNL electron-ion collider project, to the APS and ALS upgrade projects. Research accomplishments achieved in 2020, are summarized in this report.

43 PARTICLE ACCELERATORS↗
DOE OSTI2017

Dose-rate dependence of damage buildup in 3 C -SiC

The influence of the defect generation rate on radiation damage processes in SiC remains poorly understood. Here, we use a combination of ion channeling and transmission electron microscopy to systematically study the dose-rate dependence of damage buildup in 3C-SiC bombarded in the temperature range of 25–200 °C with 500 keV Ar ions. The results reveal a pronounced dose-rate effect, whose magnitude increases close-to-linearly with temperature. When ion dose and temperature are held constant, the dose-rate dependence of the damage level is nonlinear, with saturation at high dose rates. Electron microscopy reveals that the average size of stable defect clusters increases with increasing dose rate. These findings have important implications for understanding and predicting radiation damage in SiC.

Bayu Aji, L. B. (ORCID:0000000315573023)↗
DOE OSTI2016

Local, global, and nonlinear screening in twisted double-layer graphene

Significance Using scanning tunneling microscopy and numerical simulations we demonstrate that a graphene buffer sheet placed underneath an atomically thin layer is an extremely effective method to increase the quality of 2D electron systems without modifying their electronic structure and without compromising the gating capabilities. We show that owing to its remarkable nonlinear screening capability the graphene buffer layer provides better shielding from substrate-induced perturbations than either increasing the distance to the substrate or doubling the carrier density, or even than using a graphene bilayer.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Giant nonlinear optical responses from photon-avalanching nanoparticles

Avalanche phenomena use steeply nonlinear dynamics to generate disproportionately large responses from small perturbations, and are found in a multitude of events and materials. Photon avalanching enables technologies such as optical phase-conjugate imaging, infrared quantum counting and efficient upconverted lasing. However, the photon-avalanching mechanism underlying these optical applications has been observed only in bulk materials and aggregates, limiting its utility and impact. In this study we report the realization of photon avalanching at room temperature in single nanostructures-small, Tm 3+ -doped upconverting nanocrystals-and demonstrate their use in super-resolution imaging in near-infrared spectral windows of maximal biological transparency. Avalanching nanoparticles (ANPs) can be pumped by continuous-wave lasers, and exhibit all of the defining features of photon avalanching, including clear excitation-power thresholds, exceptionally long rise time at threshold, and a dominant excited-state absorption that is more than 10,000 times larger than ground-state absorption. Beyond the avalanching threshold, ANP emission scales nonlinearly with the 26th power of the pump intensity, owing to induced positive optical feedback in each nanocrystal. This enables the experimental realization of photon-avalanche single-beam super-resolution imaging with sub-70-nanometre spatial resolution, achieved by using only simple scanning confocal microscopy and without any computational analysis. Pairing their steep nonlinearity with existing super-resolution techniques and computational methods, ANPs enable imaging with higher resolution and at excitation intensities about 100 times lower than other probes. The low photon-avalanching threshold and excellent photostability of ANPs also suggest their utility in a diverse array of applications, including sub-wavelength imaging and optical and environmental sensing.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Dynamically tunable second-harmonic generation using hybrid nanostructures incorporating phase-change chalcogenides

Nonlinear metasurfaces with high conversion efficiencies have been vastly investigated. However, strong dynamic tunability of such devices is limited in conventional passive plasmonic and dielectric material platforms. Germanium antimony telluride (GST) is a promising phase-change chalcogenide for the reconfiguration of metamaterials due to strong nonvolatile changes of the real and imaginary parts of the refraction index through amorphous-crystalline phase change. The orderly structured GST has an even higher potential in tunable second-harmonic generation (SHG) with a non-centrosymmetric crystal structure at the crystalline phase, while the amorphous phase of GST does not exhibit bulk second-order nonlinearity. Here, we experimentally demonstrate SHG switches by actively controlling the crystalline phase of GST for a GST-based hybrid metasurface featuring a gap-surface plasmon resonance, and a quarter-wave asymmetric Fabry–Perot (F–P) cavity incorporating GST. We obtain SHG switches with modulation depths as high as ~ 20 dB for the wavelengths at the on-state resonance. We also demonstrate the feasibility of multi-level SHG modulation by leveraging three controlled GST phases, i.e., amorphous, semi-crystalline, and crystalline, for the gap-surface plasmon hybrid device, which features stronger light–matter interaction and has higher resonant SHG efficiencies than the asymmetric F–P cavity device at respective GST phases. This research reveals that GST-based dynamic SHG switches can be potentially employed in practical applications, such as microscopy, optical communication, and photonic computing in the nonlinear regime.

42 ENGINEERING↗
DOE OSTI2015

A micromechanics model for bread dough

The mechanical behaviour of dough and gluten was studied in an effort to investigate whether bread dough can be treated as a two phase (starch and gluten) composite material. The dough and gluten show rate dependent behaviour under tension, compression and shear tests, and non-linear unloading-reloading curves under cyclic compression tests. There is evidence from cryo-Scanning Electron Microscopy (SEM) that damage in the form of debonding between starch and gluten occurs when the sample is stretched. A composite finite element model was developed using starch as filler and gluten as matrix. The interaction between the starch and gluten was modelled as cohesive contact. The finite element analysis predictions agree with trends seen in experimental test data on dough and gluten, further evidence that debonding of starch and gluten is a possible damage mechanism in dough.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Fabrication and characterization of electrospun single-crystal lead manganese borate nanofibers

Highlights: • Single crystal PbMnBO4 nanofibers were successfully fabricated by electrospinning process. • The PbMnBO4 nanofibers synthesized for the first time and unprecedented in the literature. • Characterization of PbMnBO{sub 4} nanofibers in mineralogical, optical and thermal properties was revealed. • The nanofibers exhibit single crystalline features with an average size between 120 and 250 nm. • These nanofibers can be used in optic or photonic fields as a flexible sensor due to its nonlinear and ferromagnetic properties. - Abstract: Anhydrous borate compounds are important materials in optical applications as nonlinear optical materials (NLO), due to the presence of structural B{sub x}O{sub y} subunits. Herein, lead manganese borate (PbMnBO{sub 4}) nanofibers have been firstly fabricated via a facile approach using a simple and inexpensive electrospinning technique. All of the synthesized samples were analyzed with X-Ray Diffractometer (XRD), Transmission Electron Microscope (TEM), Scanning Electron Microscope (SEM), Fourier Transform Infrared (FTIR), and Ultraviolet-visible Spectroscopy (UV–vis) method. In addition, they were thermally analyzed with Thermal Gravimetric and Differential Thermal Analyzer and TG-DTA diagrams were discussed in detail. All of the characterization results showed that the obtained PbMnBO{sub 4} nanostructures have nanofiber structures and good crystalline features. PbMnBO{sub 4} nanofiber synthesized for the first time and unprecedented in the literature is promising absorber materials for nonlinear optic applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Growth of dopamine crystals

Many nonlinear optical (NLO) crystals have been identified as potential candidates in optical and electro-optical devices. Use of NLO organic crystals is expected in photonic applications. Hence organic nonlinear optical materials have been intensely investigated due to their potentially high nonlinearities, and rapid response in electro-optic effect compared to inorganic NLO materials. There are many methods to grow organic crystals such as vapor growth method, melt growth method and solution growth method. Out of these methods, solution growth method is useful in providing constraint free crystal. Single crystals of Dopamine have been grown by evaporating the solvents from aqueous solution. Crystals obtained were of the size of orders of mm. The crystal structure of dopamine was determined using XRD technique. Images of crystals were obtained using FEG SEM Quanta Series under high vacuum and low KV.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Wavefront distortion correction in scanning tunneling microscope image

Here, we report an algorithm to identify and correct distorted wavefronts in atomic resolution scanning tunneling microscope images. This algorithm can be used to correct nonlinear in-plane distortions without prior knowledge of the physical scanning parameters, the characteristics of the piezoelectric actuator, or individual atom positions. The 2D image is first defined as a sum of sinusoidal plane waves, where a nonlinear distortion renders a curve for an otherwise ideal linear wavefront. Using the Fourier transforms of local areas of the image, the algorithm generates a wavefront vector field. The identified wavefronts are subsequently linearized for each plane wave without changing lattice orders, giving rise to distortion corrections. Our algorithm is complementary to conventional post-processing algorithms that require prior detection of real space features, which can also be used to correct nonlinear distortions in 2D images acquired by other microscopy techniques.

47 OTHER INSTRUMENTATION↗
DOE OSTI2015

Domain Wall Motion Across Various Grain Boundaries in Ferroelectric Thin Films

Domain wall movement at and near engineered 10°, 15°, and 24° tilt and 10° and 30° twist grain boundaries was measured by band excitation piezoresponse force microscopy for Pb(Zr,Ti)O 3 films with Zr/Ti ratio of 45/55 and 52/48. A minimum in nonlinear response was observed at the grain boundary for the highest angle twist and tilt grain boundaries, while a maximum in nonlinear response was observed at the 10° tilt grain boundaries. Lastly, the observed nonlinear response was correlated to the domain structure imaged in cross section by transmission electron microscopy.

36 MATERIALS SCIENCE↗
DOE OSTI2019

A data-driven approach to construct a quantitative relationship between microstructural features of fatigue cracks and contact acoustic nonlinearity

This study demonstrates the feasibility of a data-driven approach to construct a quantitative relationship between nonlinear acoustic parameters and microstructural features of contact interfaces. The near-surface nonlinearity is measured using dynamic acousto-elastic testing (DAET) with a surface wave probe, while the microstructural features are extracted from scanning electron microscopy (SEM) images of fatigue cracks. Four aluminum alloy samples, each having a fatigue crack are prepared. Six local nonlinearity parameters are measured at different locations along the crack propagation direction. A total of 40 local measurements are acquired. A principal component analysis (PCA) reveals that all six nonlinearity parameters are correlated and hence can be replaced by one principal component (PC). Fifteen crack micro-geometrical features at each measurement point were extracted from the SEM images. Regression analysis is used to relate the PC of the nonlinearity parameters to the microstructural features at the crack interface. We compare three regression models that take variable selection into account: stepwise multiple linear regression (MLR), stepwise principal component regression (PCR), and least absolute shrinkage and selection operator (LASSO). Despite having different principles, the three predictive models identify two features as the most significant in predicting the interface nonlinearity: the crack aperture (opening) distribution and the distance to the crack tip. The differences between the three models and the physical interpretation of the data-driven predictions are discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Environmental Gating and Galvanic Effects in Single Crystals of Organic–Inorganic Halide Perovskites

Understanding the impact of environmental gaseous on the surface of organometal halide perovskites (OMHPs) couples to the electronic and ionic transport is critically important. Here, we explore the transport behavior and origins of the gas sensitivity in MAPbBr 3 single crystals (SCs) devices using impedance spectroscopy and current relaxation measurements. Strong resistive response occurs when crystals are exposed to different environments. It was shown that SC response to the environment is extremely different at the surface as compared to the bulk due to the disorder surface chemistry. The nonlinear transport properties studied using ultrafast Kelvin probe force microscopy (G-KPFM) to unravel spatio-temporal charge dynamics at SC/electrode interface. The relaxation processes observed in pulse relaxation and G-KPFM measurements along with gas sensitivity of crystals suggest the presence of a triple-phase boundary between environment, electrode, and crystal. Results indicate that the environment is a nontrivial component in the operation of OMHP devices which is reminiscent of fuel cell systems. Furthermore, the triple-phase boundary can play a significant role in the transport properties of OMHPs due to the possibility of the redox processes coupled to the concentration of bulk ionic species. Finally, although instrumental for understanding the device characteristics of perovskites, our studies suggest a new opportunity of coupling the redox chemistry of the Br 2 –Br – pair that defines the bulk ionic conductivity of MAPbBr 3 with the redox chemistry of gaseous (or liquid) environment via a suitable electrocatalytic system to enable new class of energy storage devices and gas sensors.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Emergent room temperature polar phase in CaTiO 3 nanoparticles and single crystals

Polar instabilities are well known to be suppressed on scaling materials down to the nanoscale, when the electrostatic energy increase at surfaces exceeds lowering of the bulk polarization energy. Surprisingly, here we report an emergent low symmetry polar phase arising in nanoscale powders of CaTiO 3 , the original mineral named perovskite discovered in 1839 and considered nominally nonpolar at any finite temperature in the bulk. Using nonlinear optics and spectroscopy, X-ray diffraction, and microscopy studies, we discover a well-defined polar to non-polar transition at a T C = 350 K in these powders. The same polar phase is also seen as a surface layer in bulk CaTiO 3 single crystals, forming striking domains with in-plane polarization orientations. Density functional theory reveals that oxygen octahedral distortions in the surface layer lead to the stabilization of the observed monoclinic polar phase. These results reveal new ways of overcoming the scaling limits to polarization in perovskites.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Femtosecond wavelength-tunable laser system using gain managed nonlinear amplifier

Optical parametric amplifiers require a seed energy at the spectral range of interest for amplification. In the case of pulsed laser systems, seed pulse characteristics such as spectral energy density and spectral uniformity influence laser system design and performance. In this letter, we present the design and modeling of a few micro-joules, wavelength-tunable, femtosecond parametric amplifier system. We employ a gain-managed nonlinear fiber amplifier output as the seed pulse. This seed pulse is relatively uniform across its bandwidth from 1010 to 1180 nm. Its spectral energy density averages 600 pJ/nm, 30 times higher than conventional counterparts. The overall amplification gain is 175, and the conversion efficiency is 17.5%. The inherent quasi-linear chirp of the seed pulse is utilized to alter the output wavelength. Our tunable femtosecond laser is an enabling technology for high-demand applications such as time-resolved spectroscopy, nonlinear and advanced material research, and biomedical imaging and microscopy modalities.

47 OTHER INSTRUMENTATION↗
DOE OSTI2014

Graphene folding on flat substrates

We present a combined experimental-theoretical study of graphene folding on flat substrates. The structure and deformation of the folded graphene sheet are experimentally characterized by atomic force microscopy. The local graphene folding behaviors are interpreted based on nonlinear continuum mechanics modeling and molecular dynamics simulations. Our study on self-folding of a trilayer graphene sheet reports a bending stiffness of about 6.57 eV, which is about four times the reported values for monolayer graphene. Our results reveal that an intriguing free sliding phenomenon occurs at the interlayer van der Waals interfaces during the graphene folding process. This work demonstrates that it is a plausible venue to quantify the bending stiffness of graphene based on its self-folding conformation on flat substrates. The findings reported in this work are useful to a better understanding of the mechanical properties of graphene and in the pursuit of its applications.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2021

Disentangling Ferroelectric Wall Dynamics and Identification of Pinning Mechanisms via Deep Learning

Field-induced domain-wall dynamics in ferroelectric materials underpins multiple applications ranging from actuators to information technology devices and necessitates a quantitative description of the associated mechanisms including giant electromechanical couplings, controlled nonlinearities, or low coercive voltages. While the advances in dynamic piezoresponse force microscopy measurements over the last two decades have rendered visualization of polarization dynamics relatively straightforward, the associated insights into the local mechanisms have been elusive. This work explores the domain dynamics in model polycrystalline materials using a workflow combining deep-learning-based segmentation of the domain structures with nonlinear dimensionality reduction using multilayer rotationally invariant autoencoders (rVAE). The former allows unambiguous identification and classification of the ferroelectric and ferroelastic domain walls. Here, the rVAE discovers the latent representations of the domain wall geometries and their dynamics, consequently providing insight into the intrinsic mechanisms of polarization switching, that can further be compared to simple physical models. The rVAE disentangles the factors affecting the pinning efficiency of ferroelectric walls, offering insights into the correlation of ferroelastic wall distribution and ferroelectric wall pinning.

36 MATERIALS SCIENCE↗
DOE OSTI2023

In situ high-harmonic microscopy of a nanostructured solid

Nanostructured optical surfaces allow exquisite control over linear and nonlinear light interactions, where the surface actively creates new frequencies up to high-order harmonics of an intense infrared driving laser field. The function and performance of these surfaces depend sensitively on the distribution of the high-harmonic fields in and between the nanostructured elements, as the high-harmonic wavelength becomes comparable to the nanoscale features of the surface. Imaging the nonlinear response at the active surface with nanometer resolution would greatly benefit the optimization of the metasurface's function. Here we demonstrate an approach to lensless imaging of extreme ultraviolet high harmonics that resolves the amplitude and phase of nonlinear polarization at the active nanostructured surface of an MgO crystal. Imaging the near-field distribution of high harmonics is the gateway to optimized functional high-harmonic metasurfaces and the integration of high harmonics on a chip.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Polymer Composition Influence on Optical Properties of Laser-Generated Au Nanoparticles Based Nanocomposites

Au nanoparticles (AuNPs) stable colloid solution were prepared by laser ablation and fragmentation in liquid monomer isodecyl acrylate (IDA). Sizes of obtained nanoparticles were determined by scanning transmission electron microscopy (STEM) and were about 20 nm. Nanocomposites films were prepared from obtained stable colloid solution by UV-photocuring. To prepare solid polymer films different crosslinking diacrylates were used. Third-order nonlinear optical responses of prepared nanomaterials with different polymer matrix compositions were estimated by z-scan technique and compared.

36 MATERIALS SCIENCE↗