103 research outputs found
Direct single-molecule dynamic detection of chemical reactions.
Single-molecule detection can reveal time trajectories and reaction pathways of individual intermediates/transition states in chemical reactions and biological processes, which is of fundamental importance to elucidate their intrinsic mechanisms. We present a reliable, label-free single-molecule approach that allows us to directly explore the dynamic process of basic chemical reactions at the single-event level by using stable graphene-molecule single-molecule junctions. These junctions are constructed by covalently connecting a single molecule with a 9-fluorenone center to nanogapped graphene electrodes. For the first time, real-time single-molecule electrical measurements unambiguously show reproducible large-amplitude two-level fluctuations that are highly dependent on solvent environments in a nucleophilic addition reaction of hydroxylamine to a carbonyl group. Both theoretical simulations and ensemble experiments prove that this observation originates from the reversible transition between the reactant and a new intermediate state within a time scale of a few microseconds. These investigations open up a new route that is able to be immediately applied to probe fast single-molecule physics or biophysics with high time resolution, making an important contribution to broad fields beyond reaction chemistry
Interface-engineered hole doping in Sr2IrO4/LaNiO3 heterostructure
The relativistic Mott insulator Sr2IrO4 driven by large spin-orbit
interaction is known for the Jeff = 1/2 antiferromagnetic state which closely
resembles the electronic structure of parent compounds of superconducting
cuprates. Here, we report the realization of hole-doped Sr2IrO4 by means of
interfacial charge transfer in Sr2IrO4/LaNiO3 heterostructures. X-ray
photoelectron spectroscopy on Ir 4f edge along with the X-ray absorption
spectroscopy at Ni L2 edge confirmed that 5d electrons from Ir sites are
transferred onto Ni sites, leading to markedly electronic reconstruction at the
interface. Although the Sr2IrO4/LaNiO3 heterostructure remains non-metallic, we
reveal that the transport behavior is no longer described by the Mott variable
range hopping mode, but by the Efros-Shklovskii model. These findings highlight
a powerful utility of interfaces to realize emerging electronic states of the
Ruddlesden-Popper phases of Ir-based oxides.Comment: 9 pages including 3 figures and reference
Direct Determination of Electron-Phonon Coupling Matrix Element in a Correlated System
High-resolution electron energy loss spectroscopy measurements have been
carried out on an optimally doped cuprate Bi2Sr2CaCu2O8+{\delta}. The
momentum-dependent linewidth and the dispersion of an A1 optical phonon are
obtained. Based on these data as well as the detailed knowledge of the
electronic structure from angle-resolved photoemission spectroscopy, we develop
a scheme to determine the full structure of electron-phonon coupling for a
specific phonon mode, thus providing a general method for directly resolving
the EPC matrix element in systems with anisotropic electronic structures
Strengthened proximity effect at grain boundaries to enhance inter-grain supercurrent in Ba1-xKxFe2As2 superconductors
Iron-based superconductors have great potential for high-power applications
due to their prominent high-field properties. One of the central issues in
enhancing the critical current density of iron-based superconducting wires is
to reveal the roles and limitations of grain boundaries in supercurrent
transport. Here, we finely tuned the electronic properties of grain boundaries
by doping Ba1-xKxFe2As2 superconductors in a wide range (0.25<x<0.598). It is
found that the intra-grain Jcintra peaks near x~0.287, while the inter-grain
Jcinter has a maximum at about x~0.458. Remarkably, the grain boundary
transparency parameter defined as Jcinter/Jcintra rises monotonically with
doping. Through detailed microscopic analysis, we suggest that the FeAs
segregation phase commonly existing at grain boundaries and the adjacent grains
constitute superconductor-normal metal-superconductor (SNS) Josephson junctions
which play a key role in transporting supercurrent. A sandwich model based on
the proximity effect and the SNS junction is proposed to well interpret our
data. It is found that overdoping in superconducting grains largely strengthens
the proximity effect and consequently enhances the intergrain supercurrent. Our
results will shed new insights and inspirations for improving the application
parameters of iron-based superconductors by grain boundary engineering.Comment: 22 pages, 6 figure
CoveâEdged Nanographenes with Localized Double Bonds
The efficient synthesis and electronic properties of two largeâsize coveâedged nanographenes (NGs), CN1 and CN2, are presented. Xâray crystallographic analysis reveals a contorted backbone for both molecules owing to the steric repulsion at the inner cove position. Noticeably, the dominant structures of these molecules contain four (for CN1) or six (for CN2) localized C=C double bonds embedded in nine (for CN1) or twelve (for CN2) aromatic sextet rings according to Clar's formula, which is supported by bond length analysis and theoretical (NICS, ACID) calculations. Furthermore, Raman spectra exhibit a band associated with the longitudinal CC stretching mode of olefinic double bonds. Owing to the existence of the additional olefinic bonds, both compounds show a small band gap (1.84â
eV for CN1 and 1.37â
eV for CN2). They also display moderate fluorescence quantum yield (35â% for CN1 and 50â% for CN2) owing to the contorted geometry, which can suppress aggregation in solution.J.W. acknowleges financial support from the MOE Tier 3 programme (MOE2014-T3-1-004) and NRF Investigatorship (NRF-NRFI05-2019-0005). J.C. acknowledges MINECO and Junta de AndalucĂa of Spain projects (PGC2018-098533-BI00 and UMA18FEDERJA057). M.A.D.-G. and R.M.-M. thank support from MINECO through the research project MAT2015-66586-R and the FPI fellowship (no. BES-2016-077681), respectively
Flexible but Refractory Single-Crystalline Hyperbolic Metamaterials
The fabrication of flexible single-crystalline plasmonic or photonic
components in a scalable way is fundamentally important to flexible electronic
and photonic devices with high speed, high energy efficiency, and high
reliability. However, it remains to be a big challenge so far. Here, we have
successfully synthesized flexible single-crystalline optical hyperbolic
metamaterials by directly depositing refractory nitride superlattices on
flexible fluoro phlogopite-mica substrates with magnetron sputtering.
Interestingly, these flexible hyperbolic metamaterials show dual-band
hyperbolic dispersion of dielectric constants with low dielectric losses and
high figure-of-merit in the visible to near-infrared ranges. More importantly,
the optical properties of these nitride-based flexible hyperbolic metamaterials
show remarkable stability under either heating or bending. Therefore, the
strategy developed in this work offers an easy and scalable route to fabricate
flexible, high-performance, and refractory plasmonic or photonic components,
which can significantly expand the applications of current electronic and
photonic devices.Comment: 15 page
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