Minjie Zhou

Selectively enhanced sensing performance for oxidizing gases based on ZnO nanoparticle-loaded electrospun SnO2 nanotube heterostructures

In this work, we present gas sensors based on ZnO nanoparticle-loaded electrospun SnO2 nanotube (ZnO/SnO2) n–n heterostructures (HSs) synthesized by electrospinning combined with facile thermal decomposition. The sensing properties of the pristine SnO2 nanotubes (NTs) and ZnO/SnO2 HSs were investigated toward the representative oxidizing (NO2) and reducing (H2, CO) gases. Results show that the as-prepared ZnO/SnO2 HSs exhibit selectively enhanced and diminished sensing performances for oxidizing and reducing gases, respectively. These phenomena are closely associated with the modulation of the local depletion layer on the surface of SnO2 nanoparticles (NPs) caused by charge transfer at the heterojunctions due to work function difference. A modified grain boundary-controlled sensing mechanism is proposed to describe charge transport in sensing layers based on the contact potential barriers between nanoparticles. Our study indicates that the selection of material system and their synergism are keys to the effective design of gas sensors with semiconducting metal oxide HSs.

Synthesis and characterization of aligned ZnO/BeO core/shell nanocable arrays on glass substrate

By sequential hydrothermal growth of ZnO nanowire arrays and thermal evaporation of Be, large-scale vertically aligned ZnO/BeO core/shell nanocable arrays on glass substrate have been successfully synthesized without further heat treatment. Detailed characterizations on the sample morphologies, compositions, and microstructures were systematically carried out, which results disclose the growth behaviors of the ZnO/BeO nanocable. Furthermore, incorporation of BeO shell onto ZnO core resulted in distinct improvement of optical properties of ZnO nanowire, i.e., significant enhancement of near band edge (NBE) emission as well as effective suppression of defects emission in ZnO. In particular, the NBE emission of nanocable sample shows a noticeable blue-shift compared with that of pristine ZnO nanowire, which characteristics most likely originate from Be alloying into ZnO. Consequently, the integration of ZnO and BeO into nanoscale heterostructure could bring up new opportunities in developing ZnO-based device for application in deep ultraviolet region.PACS61.46.K; 78.67.Uh; 81.07.Gf.

Unique Zigzag-Shaped Buckling Zn2C Monolayer with Strain-Tunable Band Gap and Negative Poisson Ratio

Designing new materials with reduced dimensionality and distinguished properties has continuously attracted intense interest for materials innovation. Here we report a novel two-dimensional (2D) Zn2C monolayer nanomaterial with exceptional structure and properties by means of first-principles calculations. This new Zn2C monolayer is composed of quasi-tetrahedral tetracoordinate carbon and quasi-linear bicoordinate zinc, featuring a peculiar zigzag-shaped buckling configuration. The unique coordinate topology endows this natural 2D semiconducting monolayer with strongly strain tunable band gap and unusual negative Poisson ratios. The monolayer has good dynamic and thermal stabilities and is also the lowest-energy structure of 2D space indicated by the particle-swarm optimization (PSO) method, implying its synthetic feasibility. With these intriguing properties the material may find applications in nanoelectronics and micromechanics.

Low Energy Conformations and Gas-Phase Acidity and Basicity of Pyrrolysine

The gas-phase conformational potential energy surfaces (PES) of the last, 22nd amino acid pyrrolysine and related derivatives (neutral, deprotonated, and protonated) were extensively searched for the first time. By considering all possible combinations of the single-bond rotational degrees of freedom with a semiempirical and ab initio combined computational approach, a large set of unique low-energy conformers was identified for each pyrrolysine species, and essential properties such as vibrational frequencies, dipole moments, rotational constants, and intramolecular hydrogen bonding configurations were presented and characterized. The conformational electronic energies and thermochemical properties of proton affinity/dissociation energy (PA/PDE) and gas-phase acidity/basicity (GA/GB) were determined by the density functional BHandHLYP, B3LYP, and M062X, and Møller-Plesset MP2 methods. The MP2 and DFT methods are found to predict disparate PES for neutral and protonated conformations and sufficiently different thermochemical data. The measurements of dipole moments and characteristic IR modes at low temperature as well as GA/GB are demonstrated to be feasible approaches to verify the theoretical predictions.

Enhanced quantum interference transport in gold films with random antidot arrays

We report on the quantum interference transport of randomly distributed antidot arrays, which were prepared on gold films via the focused ion beam direct writing method. The temperature dependence of the gold films’ resistances with and without random antidot arrays were described via electron–phonon interaction theory. Compared with the pristine gold films, we observed an unexpected enhancement of the weak localization signature in the random antidot array films. The physical mechanism behind this enhancement may originate from the enhancement of electron–electron interactions or the suppression of electron–phonon interactions; further evidence is required to determine the exact mechanism.

The collimation of intense relativistic electron beams generated by ultra-intense femtosecond laser in nanometer-scale solid fiber array

A scheme to collimate the ultra-intense laser generated MeV electrons by nanometer-scale solid fiber array is proposed. Unlike previous resistivity-structured target schemes, not the magnetic field but the electric field due to the anisotropic resistivity acts to collimate the divergent fast electrons. This concept is well supported by analytical estimation and numerical calculation. The measurements of collimated MeV electron beams at rear of carbon nanotube arrays irradiated by intense femtosecond laser show the viability of this scheme. These results indicate that potential applications include radiography, fast electron beam focusing, and perhaps the electron collimation for fast ignition of inertial confined fusion.

Suppression of magnetoresistance in PtSe2 microflakes with antidot arrays

Suppression of magnetoresistance (MR) is meaningful for sensor applications to immure magnetic fields. Herein, we report the observation of suppressed MR in PtSe2 microflakes by introducing the antidot arrays (AAs). We have compared the magnetotransport properties of PtSe2 microflakes before and after milling of AAs. The enhanced resistivity and notable MR suppression were observed while the AAs are milled in the PtSe2 microflakes. Their physical mechanism has been ascribed to the enhanced electron scattering rate due to the additional electron-antidot interactions. This work gave an example to suppress MR in materials by introducing AAs, which may be useful for sensor applications in magnetic fields.

Linear magnetoresistance in gold foams

The electrical transport properties of metal foams may not only be of fundamental research interest but can also lead to wide application in sensors. We report the magnetotransport properties of gold foams prepared by a chemical template–dealloying method. The temperature dependence of the resistivity of gold foams represents a metallic behavior with zero magnetic field. With increasing magnetic field, a crossover from quadratic to linear dependence of the magnetoresistance in gold foams is observed in the studied temperature range (2–50 K). The physical mechanisms resulting in this observation may be ascribed to the classical linear magnetoresistance theory based on the spatial mobility fluctuations or current distribution effect. However, further evidence is required to determine the exact mechanism.

Anomalous magnetotransport behaviours in PtSe2 microflakes

Platinum diselenide (PtSe2) is a newly discovered 2D transition metal dichalcogenide, and is further theoretically identified as a candidate of type-II Dirac semimetals. The electrical transport study of PtSe2 microflakes may provide great potential not only in fundamental physics, but also for future electronic applications. We report the anomalous magnetotransport properties of PtSe2 microflakes. The anisotropic magnetoresistance of PtSe2 microflakes can be normalized by introducing a 3D scaling factor [Formula: see text], where θ is the magnetic field angle with respect to the c axis of the crystal and γ is the mass anisotropic constant of electrons. Additionally, the non-monotonic temperature-dependent magnetoresistance of PtSe2 microflakes is observed both in the perpendicular and in-plane magnetic field orientations. This anomalous magnetotransport behaviour may be ascribed to the novel features of type-II Dirac fermions; however, the exact physical mechanism deserves further investigation.

Large-scale synthesis of novel vertically-aligned helical carbon nanotube arrays

Abstract The large-scale synthesis of vertically-aligned carbon nanotube arrays with different helical pitches and diameters was achieved using the floating catalyst method. Results indicate that they are aligned perpendicular to the substrate surface and have a well-graphitized structure and their growth is accompanied by the production of pentagonal, heptagonal and hexagonal carbon rings. The hexagonal carbon ring is the basic structure unit to form the graphite lattice. When paired pentagon-heptagon atomic rings arrange themselves periodically within the hexagonal carbon network, helical carbon nanotubes are formed. The growth rate of the helical carbon nanotubes is about 4.5mg/cm 2 ·h.