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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Direct observation of anisotropic growth of water films on minerals driven by defects and surface tension

Knowledge of the occurrences of water films on minerals is critical for global biogeochemical and atmospheric processes, including element cycling and ice nucleation. The underlying mechanisms controlling water film growth are, however, misunderstood. Using infrared nanospectroscopy, amplitude-modulated atomic force microscopy, and molecular simulations, we show how water films grow from water vapor on hydrophilic mineral nanoparticles. We imaged films with up to four water layers that grow anisotropically over a single face. Growth usually begins from the near edges of a face where defects preferentially capture water vapor. Thicker films produced by condensation cooling completely engulf nanoparticles and form thicker menisci over defects. The high surface tension of water smooths film surfaces and produces films of inhomogeneous thickness. Nanoscale topography and film surface energy thereby control anisotropic distributions and thicknesses of water films on hydrophilic mineral nanoparticles.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Topological Surface States of Dirac Fermions in n-Bi 2 Te 3-y Se y Thermoelectrics

In n-Bi{sub 2}Te{sub 3} and n-Bi 2 Te 3-y Se y thermoelectrics, the surface states of Dirac fermions of the interlayer Van der Waals surface (0001) are studied by scanning tunneling microscopy and spectroscopy. The surface morphology and modulated line profiles of the tunneling microscopy images are determined by local distortions of the surface density of electronic states and depend on the composition. The Dirac point E D in the studied compositions is localized in the band gap and shifts to the top of the valence band with increasing Se content in n-Bi 2 Te 3-y Se y alloys. The dependence between the parameters of the surface states of Dirac fermions (Dirac-point position, Fermi velocity, surface fermion concentration) and thermoelectric properties (Seebeck coefficient and power parameter) in the thermoelectrics under study is determined.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Polyacids as Modulators for the Synthesis of UiO-66

Poly(acrylic acid) (PAA) and poly(vinylbenzoic acid) (PBA) were synthesized via reversible addition–fragmentation chain transfer (RAFT) polymerization and used as modulators for the synthesis of the metal–organic framework (MOF) UiO-66 (UiO = University of Oslo). Whereas typical syntheses of UiO-66 require large excesses of acid modulators, such as acetic acid or benzoic acid, to achieve controlled particle size and morphology of the resulting MOF particles, the use of polymerized acids allows for narrow particle size distributions at sub-stoichiometric quantities of modulator. Here, we show using scanning electron microscopy and dynamic light scattering techniques that polyacids can act as alternative modulators for the growth of UiO-66.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

In-situ angle-resolved photoemission spectroscopy of copper-oxide thin films synthesized by molecular beam epitaxy

We present that angle-resolved photoemission spectroscopy (ARPES) is the key momentum-resolved technique for direct probing of the electronic structure of a material. However, since it is highly surface-sensitive, it has been applied to a relatively small set of complex oxides that can be easily cleaved in ultra-high vacuum. Here we describe a new multi-module system at Brookhaven National Laboratory (BNL) in which an oxide molecular beam epitaxy (OMBE) is interconnected with an ARPES and a spectroscopic-imaging scanning tunneling microscopy (SI-STM) module. This new capability largely expands the range of complex-oxide materials and artificial heterostructures accessible to these two most powerful and complementary techniques for studies of electronic structure of materials. Lastly, we also present the first experimental results obtained using this system — the ARPES studies of electronic band structure of a La 2-x Sr x CuO 4 (LSCO) thin film grown by OMBE.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Mapping the catalytic conformations of an assembly-line polyketide synthase module

Assembly-line polyketide synthases, such as the 6-deoxyerythronolide B synthase (DEBS), are large enzyme factories prized for their ability to produce specific and complex polyketide products. By channeling protein-tethered substrates across multiple active sites in a defined linear sequence, these enzymes facilitate programmed small-molecule syntheses that could theoretically be harnessed to access countless polyketide product structures. Additionally, using cryogenic electron microscopy to study DEBS module 1, we present a structural model describing this substrate-channeling phenomenon. Our 3.2- to 4.3-angstrom-resolution structures of the intact module reveal key domain-domain interfaces and highlight an unexpected module asymmetry. We also present the structure of a product-bound module that shines light on a recently described “turnstile” mechanism for transient gating of active sites along the assembly line.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2019

Simulating noncontact atomic force microscopy images

A scanning probe with an atomically sharp tip is used in atomic force microscopy. As the probe is rastered over the specimen of interest, changes in its vibration mode can be ascribed to changes in the interatomic forces between the specimen and the tip. Various modes for implementing atomic force measures exist. One of the most successful modes is frequency-modulation noncontact atomic force microscopy. Here we address the role of replicating accurate forces on the probe tip to simulate images within this mode. In this work, we examine several approaches. One involves the use of classical force fields based on interatomic potentials, where the potentials are often fit to experiment. Other approaches center on the use of forces generated from quantum-based calculations. We consider the development of a “virtual tip” approximation wherein the probe tip senses electrostatic forces generated by the specimen. This approach treats the specimen quantum mechanically, while the tip is treated as a classical object. We also consider the use of an embedding approximation to avoid direct computations of the specimen in the presence of the tip. In this method, the tip and specimen are treated quantum mechanically. However, the electronic structure of the specimen is computed in the absence of the probe tip. The electronic density of the specimen is then fixed and the electronic structure of the tip is then computed in the presence of the fixed density. As a general approach, we outline new methods for the full computation of quantum forces between the tip and specimen. We note that quantum-based forces are particularly important as they directly contain the chemical nature of the forces present without the use of any adjustable parameters. We illustrate recent algorithmic developments to computing quantum forces that can produce accurate simulations of atomic force microscopy images for large and complex molecular species. We also suggest new pathways to overcome current challenges in this rapidly evolving field.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Operando X-ray Nanocharacterization of Polycrystalline Thin Film Modules

Non-destructive measurement techniques, with high spatial resolution, capable of correlating composition and structure with device properties, are few and far between. For the case of polycrystalline and inhomogeneous materials, the added challenge is that large sampling areas are necessary in order to have a statistical representation of the specimen under study. For the study of grain cores and grain boundaries in polycrystalline solar absorbers this is of particular importance since their dissimilar behavior and variability throughout the samples makes it difficult to draw conclusions and ultimately optimize the materials and devices. Our approach to use state-of-the-art x-ray microscopy to study full module stacks under operating conditions is unique. Understanding the effects of elemental and charge migration under full encapsulation and operating conditions will allow CIGS and CdTe manufactures and in particular our partners in this proposal to modify materials, stacks, architectures, and processing steps to minimize the performance losses through time.

14 SOLAR ENERGY↗
DOE OSTI2022

Super-resolution Imaging of Plasmonic Near-Fields: Overcoming Emitter Mislocalizations

Plasmonic nano-objects have shown great potential in enhancing applications like biological/chemical sensing, light harvesting and energy transfer, and optical/quantum computing. Therefore, an extensive effort has been vested in optimizing plasmonic systems and exploiting their field enhancement properties. Super-resolution imaging with quantum dots (QDs) is a promising method to probe plasmonic near-fields but is hindered by the distortion of the QD radiation pattern. Here, we investigate the interaction between QDs and “L-shaped” gold nanoantennas and demonstrate both theoretically and experimentally that this strong interaction can induce polarization-dependent modifications to the apparent QD emission intensity, polarization, and localization. Based on FDTD simulations and polarization-modulated single-molecule microscopy, we show that the displacement of the emitter’s localization is due to the position-dependent interference between the emitter and the induced dipole, and can be up to 100 nm. Our results help pave a pathway for higher precision plasmonic near-field mapping and its underlying applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Critical nematic correlations throughout the superconducting doping range in Bi 2–z Pb z Sr 2–y La y CuO 6+x

Charge modulations have been widely observed in cuprates, suggesting their centrality for understanding the high-T c superconductivity in these materials. However, the dimensionality of these modulations remains controversial, including whether their wavevector is unidirectional or bidirectional, and also whether they extend seamlessly from the surface of the material into the bulk. Material disorder presents severe challenges to understanding the charge modulations through bulk scattering techniques. We use a local technique, scanning tunneling microscopy, to image the static charge modulations on Bi 2–z Pb z Sr 2–y La y CuO 6+x . The ratio of the phase correlation length ξ CDW to the orientation correlation length ξ orient points to unidirectional charge modulations. By computing new critical exponents at free surfaces including that of the pair connectivity correlation function, we show that these locally 1D charge modulations are actually a bulk effect resulting from classical 3D criticality of the random field Ising model throughout the entire superconducting doping range.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Large-Area Junction Damage in Potential-Induced Degradation of c-Si Solar Modules

We report a large area of millimeter-scale p-n junction damage caused by potential-induced degradation (PID) of lab-stressed crystalline-Si modules. Kelvin probe force microscopy results show electrical potential change across the junction, and a recovery was observed after heat treatment. Electron-beam induced current results support the large-area damage instead of local shunts and a much lower collected current for the affected junction area. Furthermore, secondaryion mass spectrometry indicates that the large-area damage correlates with sodium contamination. The consistent results shed new light on PID mechanisms to investigate that are essentially different than the widely reported local junction shunts.

14 SOLAR ENERGY↗
DOE OSTI2018

Grain Boundary Diffusion Characterized by KPFM

Materials aging is a high-consequence failure mode in electronic systems. Such mechanisms can degrade the electrical properties of connectors, relays, wire bonds, and other interconnections. Lost performance will impact, not only that of the device, but also the function and reliability of next-level assemblies and the weapons system as a whole. The detections of changes to materials surfaces at the nanometer-scale resolution, provides a means to identify aging processes at their early stages before they manifest into latent failures that affect system-level performance and reliability. Diffusion will be studied on thin films that undergo accelerated aging using the nanometer scale characterization technique of Frequency Modulated Kelvin Probe Force Microscopy (FM-KPFM). The KPFM provides a relatively easy, non-destructive methodology that does not require high-vacuum facilities to obtain nanometer spatial resolution of surface chemistry changes. The KPFM method can provide the means to measure surface, and near-surface, elemental concentrations that allow the determination of diffusion rate kinetics. These attributes will be illustrated by assessing diffusion in a thin film couple. Validation data will obtained from traditional techniques: (a) Auger electron spectroscopy (AES), x-ray fluorescence (XRF), and xray photoelectron spectroscopy (XPS).

36 MATERIALS SCIENCE↗
DOE OSTI2018

Grain Boundary Diffusion Characterized by KPFM

Materials aging is a high-consequence failure mode in electronic systems. Such mechanisms can degrade the electrical properties of connectors, relays, wire bonds, and other interconnections. Lost performance will impact, not only that of the device, but also the function and reliability of next-level assemblies and the weapons system as a whole. The detections of changes to materials surfaces at the nanometer-scale resolution, provides a means to identify aging processes at their early stages before they manifest into latent failures that affect system-level performance and reliability. Diffusion will be studied on thin films that undergo accelerated aging using the nanometer scale characterization technique of Frequency Modulated Kelvin Probe Force Microscopy (FM-KPFM). The KPFM provides a relatively easy, non-destructive methodology that does not require high-vacuum facilities to obtain nanometer spatial resolution of surface chemistry changes. The KPFM method can provide the means to measure surface, and near-surface, elemental concentrations that allow the determination of diffusion rate kinetics. These attributes will be illustrated by assessing diffusion in a thin film couple. Validation data will obtained from traditional techniques: (a) Auger electron spectroscopy (AES), x-ray fluorescence (XRF), and xray photoelectron spectroscopy (XPS).

36 MATERIALS SCIENCE↗
DOE OSTI2018

Grain Boundary Diffusion Characterized by KPFM

The nanometer scale characterization technique of Frequency Modulated Kelvin Probe Force Microscopy (FM-KPFM) will be used to assess a preliminary diffusion study on thin metal films that undergo accelerated aging. The KPFM technique provides a relatively easy, non-destructive methodology that does not require high-vacuum facilities to obtain nanometer spatial resolution of surface chemistry changes and will be exercised in an effort to explore its capacity to map surface potential contrast caused by Cu diffusion in a manner that allows for a qualitative assessment of diffusion rate kinetics. Supporting data will be obtained from traditional techniques: AES, XPS and UPS. An aging study was conducted on thin metal test specimens comprised of Ti or Cr/Cu/Au layer thicknesses of 50nm/500nm/500nm up to 4μm respectively. The accelerated aging process, was performed in air at aging temperatures of 60°C, 100°C, and 125°C for aging times of 8 hours, 24 hours, 96 hours (4 days), and 216 hours (9 days). A calibration method was developed using Au, Al and Ni standards to establish precision and repeatability of the KPFM technique. Average CPDs and standard deviations for each metal were found and summarized.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Cu/Al Through Au Diffusion Characterized by KPFM

The nanometer scale characterization technique of Frequency Modulated Kelvin Probe Force Microscopy (FM-KPFM) will be used to assess a diffusion study on thin metal films that undergo accelerated aging. The KPFM technique provides a relatively easy, non-destructive methodology that does not require high-vacuum facilities to obtain nanometer-scale spatial resolution of surface chemistry changes. The KPFM technique will be exercised in an effort to explore its capacity to map surface potential contrast caused by diffusion in a manner that allows for a qualitative assessment of diffusion of Cu or Al through Au. Supporting data will be obtained from traditional techniques: AES, XPS and UPS. An aging study was conducted on thin metal test specimens comprised of 500nm Cu or Al then 500nm Au on Si. The accelerated aging process was performed under inert conditions at aging temperatures of 100°C for Cu/Au film stack and 175°C for Al/Au film stack at aging times of 8 hours, 24 hours, 96 hours (4 days), and 216 hours (9 days).A calibration method was developed using Au, Al and Cu standards to establish precision and repeatability of the KPFM technique. The average Contact Potential Difference (CPD)s and standard deviations for each metal were found and summarized. Averages from surface roughness of the AFM topography images and roughness analysis of KPFM potential images which yield an average CPD of each area of unaged vs aged coupon surfaces were compared and show trends that indicate surface chemistry.

36 MATERIALS SCIENCE↗
DOE OSTI2026

The incommensurate modulation of tetragonal tungsten bronze quantified by high resolution 4D STEM

Many members of the tetragonal tungsten bronze (TTB) family of oxides display an incommensurate periodic lattice distortion, the nature of which has been the subject of some controversy. Here we present a study of this structural modulation in the relaxor ferroelectric Ba 5 SmSn 3 Nb 7 O 30 (BSSN) by quantitative scanning transmission electron microscopy (STEM). Additionally, we characterize the modulation in BSSN by employing a fast, pixelated direct electron detector to perform high resolution phase contrast STEM imaging of the crystalline lattice. By quantitatively analyzing the images, we visualize the atomic structural correlations present in the material on both the cation and anion sublattices. This analysis reveals the incommensurate structure to have an octahedral tilting pattern and cooperative A2 site cation displacements, analogous to an Ama2 commensurate cell. Finally, we show that the modulation is composed of a structural motif with a period of 3 x $d_{1\bar{1}0}$ and modified by discommensurations, likely arise from frustrated octahedral tilting in the odd-valued periodicity.

Differential phase contrast↗
DOE OSTI2018

Analytical (S)TEM Studies of Defects Associated with PID in Stressed Si PV Modules

We report the results of analytical transmission electron microscopy studies of defects associated with potentialinduced degradation (PID) of a laboratory stressed multicrystalline silicon mini-module. Shunt defects were first identified using dark lock in thermography (DLIT) and scanning electron microscopy (SEM) electron beam induced current (EBIC) imaging. Transmission electron microscopy (TEM) crosssection samples were then prepared of selected shunt defects using conventional focused ion beam (FIB) lift out techniques and examined by TEM and scanning transmission electron microscopy (STEM). The defects were identified as {111} planar defects and compositional mapping of the defects revealed elevated levels of both Na, expected from previous work, and also surprisingly O at some of the defect cores.

14 SOLAR ENERGY↗