skip to main content

Title: Quantitative agreement between dynamical rocking curves in ultrafast electron diffraction for x-ray lasers
Electron diffraction through a thin patterned silicon membrane can be used to create complex spatial modulations in electron distributions. By precisely varying parameters such as crystallographic orientation and wafer thickness, the intensity of reflections in the diffraction plane can be controlled and by placing an aperture to block all but one spot, we can form an image with different parts of the patterned membrane, as is done for bright-field imaging in microscopy. The patterned electron beams can then be used to control phase and amplitude of subsequent x-ray emission, enabling novel coherent x-ray methods. The electrons themselves can also be used for femtosecond time resolved diffraction and microscopy. As a first step toward patterned beams, we demonstrate experimentally and through simulation the ability to accurately predict and control diffraction spot intensities. We simulate MeV transmission electron diffraction patterns using the multislice method for various crystallographic orientations of a single crystal Si(001) membrane near beam normal. The resulting intensity maps of the Bragg reflections are compared to experimental results obtained at the Accelerator Structure Test Area Ultrafast Electron Diffraction (ASTA UED) facility at SLAC. Furthermore, the fraction of inelastic and elastic scattering of the initial charge is estimated along with the more » absorption of the membrane to determine the contrast that would be seen in a patterned version of the Si(001) membrane. « less
Authors:
; ; ; ; ; ; ;
Award ID(s):
1935994 1632780
Publication Date:
NSF-PAR ID:
10290943
Journal Name:
Ultramicroscopy
Volume:
223
Issue:
113211
ISSN:
0304-3991
Sponsoring Org:
National Science Foundation
More Like this
  1. In this study, we describe reducing the moisture vapor transmission through a commercial polymer bag material using a silicon-incorporated diamond-like carbon (Si-DLC) coating that was deposited using plasma-enhanced chemical vapor deposition. The structure of the Si-DLC coating was analyzed using scanning electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy, selective area electron diffraction, and electron energy loss spectroscopy. Moisture vapor transmission rate (MVTR) testing was used to understand the moisture transmission barrier properties of Si-DLC-coated polymer bag material; the MVTR values decreased from 10.10 g/m2 24 h for the as-received polymer bag material to 6.31 g/m2 24 hmore »for the Si-DLC-coated polymer bag material. Water stability tests were conducted to understand the resistance of the Si-DLC coatings toward moisture; the results confirmed the stability of Si-DLC coatings in contact with water up to 100 °C for 4 h. A peel-off adhesion test using scotch tape indicated that the good adhesion of the Si-DLC film to the substrate was preserved in contact with water up to 100 °C for 4 h.« less
  2. A free-standing film composed of bilayered vanadium oxide nanoflakes is for the first time synthesized using a new low-energy process. The precursor powder, δ-Li x V 2 O 5 · n H 2 O, was prepared using a simple sol–gel based chemical preintercalation synthesis procedure. δ-Li x V 2 O 5 · n H 2 O was dispersed and probe sonicated in N -methyl pyrrolidone to exfoliate the bilayers followed by vacuum filtration resulting in the formation of a free-standing film with obsidian color. X-ray diffraction showed lamellar ordering of a single-phase material with a decreased interlayer distance compared tomore »that of the precursor powder. Scanning electron microscopy images demonstrated stacking of the individual nanoflakes. This morphology was further confirmed with scanning transmission electron microscopy that showed highly malleable nanoflakes consisting of ∼10–100 vanadium oxide bilayers. One of the most important consequences of this morphological rearrangement is that the electronic conductivity of the free-standing film, measured by the four-probe method, increased by an order of magnitude compared to conductivity of the pressed pellet made of precursor powder. X-ray photoelectron spectroscopy measurements showed the coexistence of both V 5+ and V 4+ oxidation states in the exfoliated sample, possibly contributing to the change in electronic conductivity. The developed approach provides the ability to maintain the phase purity and crystallographic order during the exfoliation process, coupled with the formation of a free-standing film of enhanced conductivity. The produced bilayered vanadium oxide nanoflakes can be used as the building blocks for the synthesis of versatile two-dimensional heterostructures to create innovative electrodes for electrochemical energy storage applications.« less
  3. Nanocrystalline MnFe2O4 has shown promise as a catalyst for the oxygen reduction reaction (ORR) in alkaline solutions, but the material has been sparingly studied as highly ordered thin-film catalysts. To examine the role of surface termination and Mn and Fe site occupancy, epitaxial MnFe2O4 and Fe3O4 spinel oxide films were grown on (001)- and (111)-oriented Nb:SrTiO3 perovskite substrates using molecular beam epitaxy and studied as electrocatalysts for the oxygen reduction reaction (ORR). High-resolution X-ray diffraction (HRXRD) and X-ray photoelectron spectroscopy (XPS) show the synthesis of pure phase materials, while scanning transmission electron microscopy (STEM) and reflection high-energy electron diffraction (RHEED)more »analysis demonstrate island-like growth of (111) surface-terminated pyramids on both (001)- and (111)-oriented substrates, consistent with the literature and attributed to the lattice mismatch between the spinel films and the perovskite substrate. Cyclic voltammograms under a N2 atmosphere revealed distinct redox features for Mn and Fe surface termination based on comparison of MnFe2O4 and Fe3O4. Under an O2 atmosphere, electrocatalytic reduction of oxygen was observed at both Mn and Fe redox features; however, a diffusion-limited current was only achieved at potentials consistent with Fe reduction. This result contrasts with that of nanocrystalline MnFe2O4 reported in the literature where the diffusion-limited current is achieved with Mn-based catalysis. This difference is attributed to a low density of Mn surface termination, as determined by the integration of current from CVs collected under N2, in addition to low conductivity through the MnFe2O4 film due to the degree of inversion. Such low densities are attributed to the synthetic method and island-like growth pattern and highlight challenges in studying ORR catalysis with single-crystal spinel materials.« less
  4. Metal nitrides are intensely investigated because they can offer high melting points, excellent corrosion resistance, high hardness, electronic and magnetic properties superior to the corresponding metals/metal oxides. Thus, they are used in diverse applications including refractory materials, semiconductors, elec- tronic devices, and energy storage/conversion systems. Here, we present a sim- ple, novel, scalable and general route to metal nitride precursors by reactions of metal chlorides with hexamethyldisilazane [HMDS, (Me3 Si)2 NH] in tetrahydro- furan or acetonitrile at low temperatures (ambient to 60◦C/N2). Such reactions have received scant attention in the literature. The work reported here focuses primarily on the Al-HMDSmore »precursor pro- duced from the reaction of AlCl3 with HMDS (mole ratio = 1:3) characterized by matrix-assisted laser desorption/ionization-time of flight, Fourier-transform infrared spectroscopy, thermogravimetric analysis-differential thermal analysis, and multinuclear nuclear magnetic resonance spectroscopy (NMRs) for chemi- cal and structural analyses. The Al-HMDS precursor heated to 1600◦C/4 h/N2 produces aluminum nitride, characterized by X-ray powder diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy/energy-dispersive X- ray spectroscopy, and magic-angle spinning NMR. On heating to 800–1200◦C/4 h/N2, the precursor transforms to an amorphous, oxygen-sensitive powder with very high surface areas (>200 m2/g) indicating nanosized particles, which can be used as additives to polymer matrices to modify their thermal stabilities. Al2O3 is also presented in the final product after heating, due to its high susceptibility to oxidation. This approach was extended via proof-of-concept studies to other metal chloride systems, including Zn-HMDS, Cu-HMDS, Fe-HMDS, and Bi-HMDS. The formed precursors are volatile, offering the potential utility as gas-phase deposition pre- cursors for their corresponding metal nitrides.« less
  5. This study examines membrane performance data of a pilot-scale gas-sparged anaerobic membrane bioreactor (AnMBR) over its 472 day operational period and characterizes the foulant cake constituents through a membrane autopsy. The average permeability of 336 ± 81 LMH per bar during the first 40 days of operation decreased by 92% by the study's conclusion. While maintenance cleaning was effective initially, its ability to restore permeability decreased with time. Wasting bioreactor solids appeared to be effective in restoring permeability where chemical cleans were unable to. The restoration mechanism appears to be a decrease in colloidal material, measured by semi-soluble chemical oxygenmore »demand (ssCOD), rather than bioreactor total solids concentration. This is further supported through the use of fluorometry during AnMBR operation, which showed an increase in tyrosine-like compounds during heavy fouling conditions, suggesting that proteinaceous materials have a large influence on fouling. This was corroborated during membrane autopsy using Fourier transform infrared spectroscopy (FTIR). FTIR, scanning electron microscopy with energy dispersive X-ray spectroscopy, and transmission electron microscopy were used to characterize inorganic scalants and predominantly found phosphate salts and calcium sulfate. Fundamentally characterizing foulants and introducing novel and dynamic monitoring parameters during AnMBR operation such as ssCOD and fluorometry can enable more targeted fouling control.« less