InAs nanowire hot-electron Josephson transistor

At a superconductor (S)-normal metal (N) junction pairing correlations can "leak-out" into the N region. This proximity effect [1, 2] modifies the system transport properties and can lead to supercurrent flow in SNS junctions [3]. Recent experimental works showed the potential of semiconductor nanowires (NWs) as building blocks for nanometre-scale devices [4-7], also in combination with superconducting elements [8-12]. Here, we demonstrate an InAs NW Josephson transistor where supercurrent is controlled by hot-quasiparticle injection from normal-metal electrodes. Operational principle is based on the modification of NW electron-energy distribution [13-20] that can yield reduced dissipation and high-switching speed. We shall argue that exploitation of this principle with heterostructured semiconductor NWs opens the way to a host of out-of-equilibrium hybrid-nanodevice concepts [7, 21].Comment: 6 pages, 6 color figure

Confined Polymer Dynamics on Clay Platelets

The structure and dynamics of poly(ethylene oxide) adsorbed on dispersed clay platelets are investigated by small-angle neutron scattering and neutron spin-echo spectroscopy. The intermediate scattering function has a mobile contribution described by the Zimm theory and an immobile contribution that is constant within the time window. The immobile fraction as a function of the scattering vector Q is described by a Lorentz function, from which a localization length is determined. The relaxation rates grow with polymer concentration in agreement with dielectric measurements but contrary to pure polymer gels

Stabilizing the Solid-Electrolyte Interphase with Polyacrylamide for High-Voltage Aqueous Lithium-Ion Batteries

The introduction of “water-in-salt” electrolyte (WiSE) concept opens a new horizon to aqueous electrochemistry that is benefited from the formation of a solid-electrolyte interphase (SEI). However, such SEI still faces multiple challenges, including dissolution, mechanical damaging, and incessant reforming, which result in poor cycling stability. Here, we report a polymeric additive, polyacrylamide (PAM) that effectively stabilizes the interphase in WiSE. With the addition of 5 molar % PAM to 21 mol kg−1 LiTFSI electrolyte, a LiMn2O4∥L-TiO2 full cell exhibits enhanced cycling stability with 86 % capacity retention after 100 cycles at 1 C. The formation mechanism and evolution of PAM-assisted SEI was investigated using operando small angle neutron scattering and density functional theory (DFT) calculations, which reveal that PAM minimizes the presence of free water molecules at the anode/electrolyte interface, accelerates the TFSI− anion decomposition, and densifies the SEI

In Situ Investigations on the Structural and Morphological Changes of Metal Phosphides as Anode Materials in Lithium-Ion Batteries

The binary metal phosphides (MP, M = Cu, Fe, Sn, Sb) compounds are of great interest as negative electrode materials for high energy density lithium-ion batteries. However, the morphology and structural changes at the nanoscale upon electrochemical (de)lithiation are not clear yet, which require further detailed investigation. In situ neutron scattering technique is utilized to investigate and compare the morphological changes of copper phosphide and tin phosphide during the initial cycle. By coupling with scanning electron microscopy investigation, the surface activities of the electrodes at different electrochemical states, including the solid electrolyte interphase formation, swelling and recovering, cracks appearance, and stripping at nanoscale of the material particles are evaluated. With in situ X-ray diffraction measurement, the energy storage mechanism is further explained. This work demonstrates useful techniques to analyze the detailed fatigue mechanisms of the active material, and provides new insights of the nanostructural changes of anode materials reacting with lithium via conversion and alloying

Fluorine-free water-in-ionomer electrolytes for sustainable lithium-ion batteries

The continuously increasing number and size of lithium-based batteries developed for large-scale applications raise serious environmental concerns. Herein, we address the issues related to electrolyte toxicity and safety by proposing a “water-in-ionomer” type of electrolyte which replaces organic solvents by water and expensive and toxic fluorinated lithium salts by a non-fluorinated, inexpensive and non-toxic superabsorbing ionomer, lithium polyacrylate. Interestingly, the electrochemical stability window of this electrolyte is extended greatly, even for high water contents. Particularly, the gel with 50 wt% ionomer exhibits an electrochemical stability window of 2.6 V vs. platinum and a conductivity of 6.5 mS cm −1 at 20 °C. Structural investigations suggest that the electrolytes locally self-organize and most likely switch local structures with the change of water content, leading to a 50% gel with good conductivity and elastic properties. A LiTi 2 (PO 4 ) 3 /LiMn 2 O 4 lithium-ion cell incorporating this electrolyte provided an average discharge voltage > 1.5 V and a specific energy of 77 Wh kg −1 , while for an alternative cell chemistry, i.e., TiO 2 /LiMn 2 O 4 , a further enhanced average output voltage of 2.1 V and an initial specific energy of 124.2 Wh kg −1 are achieved

A 3D porous Li-rich cathode material with an: In situ modified surface for high performance lithium ion batteries with reduced voltage decay

High crystallinity Li-rich porous materials integrated with an in situ formed surface containing carbonaceous compounds are synthesized through a facile approach. The rationally designed procedure involves the formation of a specific morphology of a hydroxide precursor assisted by a self-made template and subsequent high temperature treatment to obtain a Li1.2Mn0.56Ni0.16Co0.08O2 target product. The porous morphology is investigated using field-emission scanning electron microscopy and its surface area is quantitatively examined by gas sorption analysis coupled with the Brunauer-Emmett-Teller method. The crystallinity is characterized by X-ray diffraction and high-resolution transmission electron microscopy. X-ray photoelectron spectroscopy, CHN elemental analysis and small angle neutron scattering confirm the presence of carbonaceous compounds in the surface composition. The prepared material exhibits superior discharge rate capability and excellent cycling stability. It shows minor capacity loss after 100 cycles at 0.5C and retains 94.9% of its initial capacity after 500 cycles at 2C. Even more notably, the "voltage decay" during cycling is also significantly decreased. It has been found that carbonaceous compounds play a critical role in reducing the layered to spinel structural transformation during cycling. Therefore, the present porous Li-rich material with surface modified carbonaceous compounds represents an attractive material for advanced lithium-ion batteries

A grazing incidence neutron spin echo study of near surface dynamics in p(MEO2MA-co-OEGMA) copolymer brushes

Surface-attached architectures of p(MEO2MA-co-OEGMA) copolymers are thermoresponsive PEG analogues with potential applications in biotechnology and medicine. In this respect, structure and dynamics of polymer brushes made of these copolymers are of great interest. In this work, the near surface dynamics of a p(MEO2MA-co-OEGMA) brush with a height of 250 nm was investigated with neutron spin echo spectroscopy under grazing incidence (GINSES) conditions. The brush dynamics was studied at two penetration depths of the neutrons. An influence of the distance from the confining surface on the collective diffusion was found. For the first time, the experiment demonstrates the feasibility of studying thermal fluctuations of macromolecules at a single planar liquid/solid interface by neutron spin echo spectroscopy under grazing incidence

Host-Guest Self-assembly in Block Copolymer Blends

Ultrafine, uniform nanostructures with excellent functionalities can be formed by self-assembly of block copolymer (BCP) thin films. However, extension of their geometric variability is not straightforward due to their limited thin film morphologies. Here, we report that unusual and spontaneous positioning between host and guest BCP microdomains, even in the absence of H-bond linkages, can create hybridized morphologies that cannot be formed from a neat BCP. Our self-consistent field theory (SCFT) simulation results theoretically support that the precise registration of a spherical BCP microdomain (guest, B-b-C) at the center of a perforated lamellar BCP nanostructure (host, A-b-B) can energetically stabilize the blended morphology. As an exemplary application of the hybrid nanotemplate, a nanoring-type Ge[subscript 2]Sb[subscript 2]Te[subscript 5] (GST) phase-change memory device with an extremely low switching current is demonstrated. These results suggest the possibility of a new pathway to construct more diverse and complex nanostructures using controlled blending of various BCPs.United States. Dept. of Energy. Office of Basic Energy Sciences (Award DE-SC0001088