Aspartic acid adsorbed on Cu surfaces is doubly deprotonated. On chiral Cu(643) its enantiomers undergo enantiospecific decomposition via an autocatalytic explosion. Once initiated, the decomposition mechanism proceeds via sequential cleavage of the C3-C4 and C1-C2 bonds each yielding CO, followed by conversion of the remaining species into N[triple bond, length as m-dash]CCH.
Deformable temperature sensors are required for applications such as soft robotics, biometric sensing, cryopreservation of organs, and flexible electronics. In this paper, we demonstrate Cu–CuNi temperature sensors on flexible Kapton substrates by a novel method consisting of rapid aerosol jet printing of nanoparticles followed by laser sintering at low powers of 100 mW and 400 mW under a shroud of an inert gas to minimize oxidation. The sensors showed a highly linear response as a function of the temperature and the highest sensitivity among film-based sensors yet reported in literature (RajagopalM. C. Rajagopal, M. C. Sens. Actuators, A2018272253; YangF. Yang, F. Sci. Rep.201771721; MurakamiR. Murakami, R. J. Cryst. Growth20184877277). The sensor film microstructure was investigated using scanning electron microscopy (SEM), X-ray photoemission spectroscopy (XPS), transmission electron microscopy (TEM), and selective area electron diffraction (SAED). The Cu and CuNi film morphology consisted of fused nanoparticles with varying degrees of coalescence and porosities ranging from 9% to 24% through the thickness of the films. No surface oxidation was observed for CuNi films but oxide phase was detected for the Cu films, which did not affect the sensor performance after repeated tests up to a temperature of 140 °C. The sensor performance was independent of the manufacturing conditions of the aerosol jet printing process. Flexibility tests showed a stable device performance (variation of Seebeck coefficient within 2.5%) after 200 bending cycles at three different radii and 200 twisting cycles. The superior performance of the sensor films to the bending and twisting tests was attributed to the porosity of the sintered nanoparticles that allows significant strain without a proportional build-up of the stresses in the film. These results demonstrate the suitability of nanoparticle-based bottom-up fabrication methods for a range of deformable high-performance electronic devices.
Garnet solid-electrolyte-based Li-metal batteries can be used in energy storage devices with high energy densities and thermal stability. However, the tendency of garnets to form lithium hydroxide and carbonate on the surface in an ambient atmosphere poses significant processing challenges. In this work, the decomposition of surface layers under various gas environments is studied by using two surface-sensitive techniques, near-ambient-pressure X-ray photoelectron spectroscopy and grazing incidence X-ray diffraction. It is found that heating to 500 °C under an oxygen atmosphere (of 1 mbar and above) leads to a clean garnet surface, whereas low oxygen partial pressures (i.e., in argon or vacuum) lead to additional graphitic carbon deposits. The clean surface of garnets reacts directly with moisture and carbon dioxide below 400 and 500 °C, respectively. This suggests that additional CO2 concentration controls are needed for the handling of garnets. By heating under O2 along with avoiding H2O and CO2, symmetric cells with less than 10 Ωcm2 interface resistance are prepared without the use of any interlayers; plating currents of >1 mA cm–2 without dendrite initiation are demonstrated.
Surface explosion reactions have highly nonlinear reaction kinetics that exhibit autoacceleration under isothermal conditions. These can lead to phenomena such as oscillatory surface reaction rates and to highly enantiospecific reactions of chiral adsorbates on chiral surfaces. Tartaric acid (TA) decomposes on Cu surfaces by an explosion mechanism that is propagated by vacancies, empty adsorption sites that self-replicate autocatalytically during TA decomposition. Surface explosion kinetics result from chain-branching steps in which one vacancy decomposes an adsorbate to yield two vacancies. In the absence of vacancies, surface explosions cannot occur; they require some initiation step that creates vacancies. By comparison with the chain-branching explosion step, little is known about the processes that initiate or nucleate surface explosion reactions. Time-resolved XPS measurements during the early stages of explosion initiation of TA/Cu(hkl) reveal a process that involves direct loss of TA from the surface to create the initial vacancies. In the presence of a gas phase flux to the surface, such vacancy nuclei can be repopulated to suppress the onset of explosion. Measurements on 18 different Cu(hkl) surface orientations demonstrate that the kinetics of the initiation process are structure-insensitive. This implies that the highly enantiospecific TA decomposition kinetics observed on chiral Cu(hkl) surfaces must arise from the structure sensitivity of the chain-branching explosion kinetics.
The mechanism and kinetics of aspartic acid (Asp, HO2CCH(NH2)CH2CO2H) decomposition on Cu(100) have been studied using X-ray photoemission spectroscopy and temperature-programmed reaction spectroscopy. We investigate the Asp decomposition mechanism in detail using unlabeled d-Asp and isotopically labeled l-Asp-4-13C (HO2CCH(NH2)CH2 13CO2H), l-Asp-d 7 (DO2CCD(ND2)CD2CO2D), l-Asp-2,3,3-d 3 (HO2CCD(NH2)CD2CO2H), and l-Asp-15N-2,3,3-d 3 (HO2CCD(15NH2)CD2CO2H). The monolayer of Asp adsorbed on the Cu(100) surface is in a doubly deprotonated bi-aspartate form (−O2CCH(NH2)CH2CO2−). During heating, Asp decomposes on Cu(100) with kinetics consistent with a vacancy-mediated explosion mechanism. The mechanistic steps yield CO2 by sequential cleavage of the C3–C4 and C1–C2 bonds, and NCCH3 and H2 via decomposition of the remaining CH(NH2)CH2 intermediate. Deuterium labeling has been used to demonstrate that scrambling of H(D) occurs during the decomposition to acetonitrile of the CD(NH2)CD2 intermediate formed by decarboxylation of l-Asp-2,3,3-d 3 and l-Asp-15N-2,3,3-d 3.
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