10 research outputs found
Edge-pinning effect of graphene nanoflakes sliding atop graphene
Edge effect is one of the detrimental factors preventing superlubricity in
laminar solid lubricants. Separating the friction contribution from the edge
atom and inner atom is of paramount importance for rational design of ultralow
friction across scales in van der Waals heterostructures. To decouple these
contributions and provide the underlying microscopic origin at the atomistic
level, we considered two contrast models, namely, graphene nanoflakes with
dimerized and pristine edges sliding on graphene monolayer based on extensive
ab initio calculations. We found the edge contribution to friction is lattice
orientation dependence. In particular, edge pinning effect by dimerization is
obvious for misaligned contact but suppressed in aligned lattice orientation.
The former case providing local commensuration along edges is reminiscent of
Aubry's pinned phase and the contribution of per edge carbon atom to the
sliding potential energy corrugation is even 1.5 times more than that of an
atom in bilayer graphene under commensurate contact. Furthermore, we
demonstrated that the dimerized edges as high frictional pinning sites are
robust to strain engineering and even enhanced by fluorination. Both structural
and chemical modification in the tribological system constructed here offers
the atomic details to dissect the undesirable edge pinning effect in layered
materials which may give rise to the marked discrepancies in measured friction
parameters from the same superlubric sample or different samples with the same
size and identical preparation.Comment: 18 pages,6 figure
MoSe2 nanosheets and their graphene hybrids: synthesis, characterization and hydrogen evolution reaction studies
MoSe2 nanosheets and MoSe2/graphene hybrids have been prepared by a facile hydrothermal method. The number of layers of the MoSe2 nanosheets is typically <10 as confirmed directly by transmission electron microscopy and indirectly by a red shift of the characteristic A(1g) Raman peak. The hydrogen evolution reaction ( HER) studies show that the onset potentials of MoSe2 and MoSe2/RGO hybrids are only similar to 0.15 V vs. RHE and similar to 0.05 V vs. RHE, respectively, about 20-30 mV lower than those of MoS2 and its graphene hybrids reported previously. Density functional theory calculations reveal that the Gibbs free energy for atomic hydrogen adsorption (Delta G(H)(0)) on MoSe2 edges is closer to thermoneutral than that on MoS2, with an H coverage of about 75% on the edge under operating conditions, which is also higher than that of MoS2 reported in the literature. The consistency between the experimental and computational results indicates that MoSe2 nanosheets have potential to be a better HER catalyst than their MoS2 counterpart
Annealing process optimization of 3D coil core based on annealing simulation experiment and thermal mechanical coupling model
Annealing is necessary to reduce the residual stress and no-load loss of 3D coil core. In production, because monitoring the changes in temperature and stress of 3D coil core in real time is impossible, the trial and error method is usually used to formulate the annealing process parameters. The annealing simulation experiment of grain-oriented electrical steel (GOES) is carried out to explore the influence of soaking time on iron loss and magnetic flux density. The mechanical properties of GOES are tested, and the true stress–strain curves at different temperatures are obtained. Based on the existing research and experimental results, an anisotropic thermal mechanical coupling model of 3D coil core is established. An optimization scheme of 3D coil core annealing process is obtained, considering the temperature difference, stress and strain. According to the onsite measured parameters, the annealing process is simulated and optimized by the coupling model. Results show that the total annealing time is shortened by about 18.7% without increasing the stress and strain
Flexoelectricity Driven Fano Resonance in Slotted Carbon Nanotubes for Decoupled Multifunctional Sensing
Multifunctionality, interference-free signal readout, and quantum effect are important considerations for flexible sensors equipped within a single unit towards further miniaturization. To address these criteria, we present the slotted carbon nanotube (CNT) junction features tunable Fano resonance driven by flexoelectricity, which could serve as an ideal multimodal sensory receptor. Based on extensive ab initio calculations, we find that the effective Fano factor can be used as a temperature-insensitive extrinsic variable for sensing the bending strain, and the Seebeck coefficient can be used as a strain-insensitive intrinsic variable for detecting temperature. Thus, this dual-parameter permits simultaneous sensing of temperature and strain without signal interference. We further demonstrate the applicability of this slotted junction to ultrasensitive chemical sensing which enables precise determination of donor-type, acceptor-type, and inert molecules. This is due to the enhancement or counterbalance between flexoelectric and chemical gating. Flexoelectric gating would preserve the electron–hole symmetry of the slotted junction whereas chemical gating would break it. As a proof-of-concept demonstration, the slotted CNT junction provides an excellent quantum platform for the development of multistimuli sensation in artificial intelligence at the molecular scale
C/SiO2 meta-composite: Overcoming the λ/a relationship limitation in metamaterials
Metamaterials usually require that the unit size a should be comparable to the wavelength λ. Although the λ/a relationship could tell us what size of unit we need and which method we should choose for the fabrication, it limits the application of metamaterials in the kHz and MHz frequency range, as the unit size would be on the order of 10 2 m, making the overall size of the metamaterial too large for practical application. In this paper, we firstly demonstrate that the λ/a relationship limitation could be overcome by a new kind of composite, which we have called carbon-based \u27meta-composite\u27. A SiO 2 matrix with periodic microstructure is fabricated by using self-assembly of SiO 2 microspheres, and amorphous carbon fills in the gaps to form a three-dimensional periodic carbon network. The experimental results indicate that the carbon network will introduce tunable electromagnetic properties, which could be precisely tailored by controlling the geometric size of the carbon network. It is worth pointing out that the unit size of the periodic carbon network is on the sub-micrometre level, but the wavelength is on the order of 10 2 m. This means that the meta-composite overcomes the λ/a relationship limitation in the kHz and MHz frequency range, which shows great potential for the miniaturization of electronic devices
Design and Numerical Analysis of an Infrared Cassegrain Telescope Based on Reflective Metasurfaces
Reflective imaging systems such as Cassegrain-type telescopes are widely utilized in astronomical observations. However, curved mirrors in traditional Cassegrain telescopes unavoidably make the imaging system bulky and costly. Recent developments in the field of metasurfaces provide an alternative way to construct optical systems, possessing the potential to make the whole system flat, compact and lightweight. In this work, we propose a design for a miniaturized Cassegrain telescope by replacing the curved primary and secondary mirrors with flat and ultrathin metasurfaces. The meta-atoms, consisting of SiO2 stripes on an Al film, provide high reflectance (>95%) and a complete phase coverage of 0~2Ď€ at the operational wavelength of 4 ÎĽm. The optical functionality of the metasurface Cassegrain telescope built with these meta-atoms was confirmed and studied with numerical simulations. Moreover, fabrication errors were mimicked by introducing random width errors to each meta-atom; their influence on the optical performance of the metasurface device was studied numerically. The concept of the metasurface Cassegrain telescope operating in the infrared wavelength range can be extended to terahertz (THz), microwave and even radio frequencies for real-world applications, where metasurfaces with a large aperture size are more easily obtained
Sr-Doped Cubic In2O3/Rhombohedral In2O3 Homojunction Nanowires for Highly Sensitive and Selective Breath Ethanol Sensing: Experiment and DFT Simulation Studies
In recent years, it is urgent and challenging to fabricate highly sensitive and selective gas sensors for breath analyses. In this work, Sr-doped cubic In2O3/rhombohedral In2O3 homojunction nanowires (NWs) are synthesized by one-step electrospun technology. The Sr doping alters the cubic phase of pure In2O3 into the rhombohedral phase, which is verified by the high-resolution transmittance electron microscopy, X-ray diffraction, and Raman spectroscopy, and is attributable to the low cohesive energy as calculated by the 2 a 4 density functional theory (DFT). As a proof-of-concept of fatty liver biomarker sensing, ethanol sensors are fabricated using the electrospun In2O3 NWs. The results show that 8 wt % Sr-doped In2O3 shows the highest ethanol sensing performance with a high response of 21-1 ppm, a high selectivity over other interfering gases such as methanol, acetone, formaldehyde, toluene, xylene, and benzene, a high stability measured in 6 weeks, and also a high resistance to high humidity of 80%. The outstanding ethanol sensing performance is attributable to the enhanced ethanol adsorption by Sr doping as calculated by DFT, the stable rhombohedral phase and the preferred (104) facet exposure, and the formed homojunctions favoring the electron transfer. All these results show the effective structural modification of In2O3 by Sr doping, and also the great potency of the homojunction Sr-doped In2O3 NWs for highly sensitive, selective, and stable breath ethanol sensing