SEARCH · Engineering Papers
Results for “Visualization”
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.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Nano-optical Visualization of Interlayer Interactions in WSe 2 /WS 2 Heterostructures
Not Available
Visualizing Stereodynamics in Cold Collisions through Shape Resonance Wavefunctions
Shape resonances in cold collisions are often strongly affected by stereodynamics. These resonances can sometimes be assigned by single-channel quantization along the scattering coordinate. However, sensitive steric control of collision implies strong anisotropy of the interaction potential energy surface, which usually leads to coupling among multiple scattering channels in the strongly interacting region. Hence, the resonances might be the result of quantization in a multidimensional space. Using the cold rotationally inelastic collision between para-H 2 (v 1 = 1, j 1 = 2) and HF (v 2 = 0, j 2 = 0) as an example, we analyze four low-lying shape resonances via diagonalization of the full-dimensional Hamiltonian with a stabilization method. While some resonances can indeed be assigned with a single partial wave, others apparently involve more than one scattering channel. Furthermore, a new model based on these resonance wavefunctions is developed to better understand the stereodynamics through shape resonances in cold collisions.
Atomically Visualizing Elemental Segregation-Induced Surface Alloying and Restructuring
Using in situ transmission electron microscopy that spatially and temporally resolves the evolution of the atomic structure in the surface and subsurface regions, we Find that the surface segregation of Au atoms in a Cu(Au) solid solution results in the nucleation and growth of a (2 × 1) missing-row reconstructed, half-unit-cell thick L1 2 Cu 3 Au(110) surface alloy. Our in situ electron microscopy observations and atomistic simulations demonstrate that the (2 × 1) reconstruction of the Cu 3 Au(110) surface alloy remains as a stable surface structure as a result of the favored Cu-Au diatom configuration.
Direct Visualization of Counter-Propagating Surface Plasmons in Real Space-Time
We deploy two-dimensional nano-hole arrays as resonant surface plasmon polariton (SPP) couplers that enable counter-propagation and interference-free imaging of SPP wave-packets. We monitor the spatiotemporal evolution of the resulting SPPs using two-color photoemission electron microscopy (PEEM). The measurements track the electric field envelope of the SPP in real space and time and enable direct characterization of their spatiotemporal properties in a regime where the SPP wave-packet is the principle observable. We provide an analysis of the observables for both the co- and counter-propagating directions via SPP trajectories that are recorded in tandem. Our results highlight the advantages of isolating SPPs through counter-propagation, where field-SPP interactions are suppressed.
IsoForma: An R Package for Quantifying and Visualizing Positional Isomers in Top-Down LC-MS/MS Data
Proteoforms, the different forms of a protein with sequence variations including post-translational modifications (PTMs), execute vital functions in biological systems such as cell signaling and epigenetic regulation. Precisely defining the stoichiometry of PTMs has been challenging because, in the widely used bottom-up proteomics methods, the detection occurs at the peptide level and thus the link between peptides and their specific modification site is lost, resulting in proteoform ambiguity. Advances in top-down mass spectrometry (MS) technology have permitted the direct characterization of intact proteoforms and their exact number of modification sites, allowing for the relative quantification of positional isomers (PI). Proteins with positional isomers refers to proteoforms with identical total mass and set of modifications but varying PTM site combinations. The relative abundance of PI can be estimated by matching proteoform-specific fragment ions to top-down tandem MS (MS2) data to localize and quantify modifications. However, current approaches heavily rely on manual annotation. Here, we present IsoForma, an open-source R package for relative quantification of PI within a single tool. We benchmarked IsoForma’s performance against two existing workflows and highlight the similarity of the results and improvements in speed. Overall, IsoForma provides a streamlined process, reduces the time of conducting isoform-based analyses, and offers an essential framework for developing customized proteoform analysis workflows. Finally, the software is open source and available at https://github.com/EMSL-Computing/isoforma-lib.
In Situ Visualization of Solvent Swelling Dynamics in Block Copolymer Films with Atomic Force Microscopy
Not provided.
Direct Visualization of Drug–Polymer Phase Separation in Ritonavir–Copovidone Amorphous Solid Dispersions Using in situ Synchrotron X-ray Fluorescence Imaging of Thin Films
Amorphous solid dispersions (ASDs) are new formulations currently being used in pharmaceutical industry. The ASDs, in which amorphous drug and polymeric excipients are intimately mixed at a molecular level, exhibit dramatically enhanced solubility and dissolution characteristics relative to their crystalline drug counterparts. In the process of achieving an ever-increasing drug loading (DL), it is noticed however, that the drug release profile deteriorates significantly beyond a certain DL. As an example, a ritonavir-copovidone ASD achieves continuous and full drug release when DL ≤ 25 wt%. The release drops at 30 wt% and when DL > 30 wt% there is virtually no drug release, behaving like a pure amorphous drug. In this communication, the dissolution behavior of ASD thin films has been investigated by in situ synchrotron X-ray fluorescence (XRF) imaging to elucidate the mechanism for the unique change in extent of drug release as a function of DL. It is found that the drug release profile correlates well with the amorphous-amorphous phase separation (AAPS) onset. At a lower drug loading (up to 20 wt%), it takes more than 12 hours for AAPS to happen while in sharp contrast, it only needs less than 10 minutes for DL > 30 wt%. During AAPS amorphous drug accumulates on the surface of the film which prevents further dissolution from the interior of the ASD. The current study provides a mechanistic understanding of the confounding drug release profile of ASDs as a function of DL, and opens the door for studying drug-excipient (e.g. polymer, surfactant) interactions via XRF imaging in the future.
Visualization of Multifractal Superconductivity in a Two-Dimensional Transition Metal Dichalcogenide in the Weak-Disorder Regime
Eigenstate multifractality is a distinctive feature of noninteracting disordered metals close to a metal–insulator transition, whose properties are expected to extend to superconductivity. While multifractality in three dimensions (3D) only develops near the critical point for specific strong-disorder strengths, multifractality in 2D systems is expected to be observable even for weak disorder. Here we provide evidence for multifractal features in the superconducting state of an intrinsic, weakly disordered single-layer NbSe 2 by means of low-temperature scanning tunneling microscopy/spectroscopy. The superconducting gap, characterized by its width, depth, and coherence peaks’ amplitude, shows a characteristic spatial modulation coincident with the periodicity of the quasiparticle interference pattern. The strong spatial inhomogeneity of the superconducting gap width, proportional to the local order parameter in the weak-disorder regime, follows a log-normal statistical distribution as well as a power-law decay of the two-point correlation function, in agreement with our theoretical model. Furthermore, the experimental singularity spectrum f(α) shows anomalous scaling behavior typical from 2D weakly disordered systems.
Visualization of Plasmonic Couplings Using Ultrafast Electron Microscopy
Hybrids of graphene and metal plasmonic nanostructures are promising building blocks for applications in optoelectronics, surface-enhanced scattering, biosensing, and quantum information. An understanding of the coupling mechanism in these hybrid systems is of vital importance to its applications. Previous efforts in this field mainly focused on spectroscopic studies of strong coupling within the hybrids with no spatial resolution. In this study, we report direct imaging of the local plasmonic coupling between single Au nanocapsules and graphene step edges at the nanometer scale by photon-induced near-field electron microscopy in an ultrafast electron microscope for the first time. The proximity of a step in the graphene to the nanocapsule causes asymmetric surface charge density at the ends of the nanocapsules. Computational electromagnetic simulations confirm the experimental observations. The results reported here indicate that this hybrid system could be used to manipulate the localized electromagnetic field on the nanoscale, enabling promising future plasmonic devices.
In Situ Visualization of the Pinning Effect of Planar Defects on Li Ion Insertion
Longevity of Li ion batteries strongly depends on the interaction of transporting Li ions in electrode crystals with defects. However, detailed interactions between the Li ion flux and structural defects in the host crystal remain obscure due to the transient nature of such interactions. Here, by in situ transmission electron microscopy and density function theory calculations, we reveal how the diffusion pathways and transport kinetics of a Li ion can be affected by planar defects in a tungsten trioxide lattice. We uncover that changes in charge distribution and lattice spacing along the planar defects disrupt the continuity of ion conduction channels and dramatically increase the energy barrier of Li diffusion, thus, arresting Li ions at the defect sites and twisting the lithiation front. In conclusion, the atomic-scale understanding holds critical implications for rational interface design in solid-state batteries and solid oxide fuel cells.
Direct Visualization of the Charge Transfer in a Graphene/α-RuCl 3 Heterostructure via Angle-Resolved Photoemission Spectroscopy
Not Available
Subnanometer Visualization of Spatially Varying Local Field Resonances that Drive Tip-Enhanced Optical Spectroscopy
Our knowledge of the electromagnetic fields that power modern nanoscale optical measurements, including (non)linear tip-enhanced Raman and photoluminescence, chiefly stems from numerical simulations. Aside from idealized in silico vs heterogeneous (nano)structures in the laboratory, challenges in quantitative descriptions of nanoscale light–matter interactions more generally stem from the very nature of the problem, which lies at the interface of classical and quantum theories. This is particularly the case in ultrahigh spatial resolution measurements that are sensitive to local optical field variations that take place on subnanometer length scales. Here this work approaches this challenge through extinction-based spectral nanoimaging experiments. We demonstrate <1 nm spatial resolution in hyperspectral extinction measurements that track spatially varying plasmon resonances. We describe the principles behind our experiments and highlight more general implications of our observations.
Visualization of Mesoscopic Conductivity Fluctuations in Amorphous Semiconductor Thin-Film Transistors
Charge transport in amorphous semiconductors is considerably more complicated than the process in crystalline materials due to abundant localized states. In addition to device-scale characterization, spatially resolved measurements are important to unveiling electronic properties. Here, we report gigahertz conductivity mapping in amorphous indium gallium zinc oxide (a-IGZO) thin-film transistors by microwave impedance microscopy (MIM), which probes conductivity without Schottky barrier’s influence. The difference between the dc and microwave conductivities reflects the efficacy of the injection barrier in an accumulation-mode transistor. The conductivity exhibits significant nanoscale inhomogeneity in the subthreshold regime, presumably due to trapping and release from localized states. The characteristic length scale of local fluctuations, as determined by the autocorrelation analysis, is about 200 nm. Using a random-barrier model, we can simulate the spatial variation of the potential landscape, which underlies the mesoscopic conductivity distribution. Furthermore, our work provides an intuitive way to understand the charge transport mechanism in amorphous semiconductors at the microscopic level.
Visualization of Bacterial Microcompartment Facet Assembly Using High-Speed Atomic Force Microscopy
Not Available
Twist-Angle-Dependent Excitons in Moiré MoTe 2 Visualized by Cryogenic STEM and Monochromated EELS
van der Waals twisted bilayers of transition-metal dichalcogenides exhibit diverse excitonic phenomena arising from moiré superlattices and lattice reconstruction. While interlayer strain and relaxation reshape their electronic bands, their nanoscale influence on the excitonic fine structure remains poorly understood. Here, we study the interplay between spin–orbit coupling (SOC) and the moiré lattice by probing excitons in H-type twisted (∼8-layer × 8-layer) MoTe 2 using atomic-resolution scanning transmission electron microscopy (STEM) combined with monochromated electron energy loss spectroscopy (EELS) at cryogenic temperature. Spatially resolved spectra reveal moiré-site-dependent variations in excitonic absorption, including modulation of the X B exciton across the moiré unit cell. We find that SOC in MoTe 2 increases with the twist angle within the studied range (2–4.5°), with the largest value observed at 4°. Furthermore, these findings establish the twist angle as a tunable parameter for SOC via moiré engineering and link local structural relaxation to excitonic fine structure in twisted MoTe 2 .