Nano

Cobalt-doped MoSe₂/nitrogenated graphene composite has been successfully synthesized via a facile hydrothermal route and is investigated as an electrocatalyst for hydrogen evolution reaction (HER). The as-prepared samples are well characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS) and Raman spectrum. The results reveal that Co-doped MoSe₂ nanosheets which are characteristic of few layers (2–4 layers) and abundant exposed active edge sites are well anchored on the nitrogen-doped graphene sheets to constitute robust composites. When evaluated as catalysts for HER, the obtained composites demonstrate superior electrocatalytic activities toward HER.

Herein, we report a facile one-pot method for the synthesis of orange/red-emitting fluorescent copper nanoclusters (Cu NCs), in which bovine serum albumin (BSA) served as the capping scaffold (Cu NCs@BSA) and hydroxylamine hydrochloride (NH₂OH$\cdot$HCl) as the reducing agent. To the best of our knowledge, this is the first time to adopt this mild reductant to synthesize fluorescent Cu NCs. The as-prepared Cu NCs@BSA exhibits strong orange or red fluorescence at room temperature depending on the synthesis process, and the maximum excitation and emission peaks were at 355nm and 615nm, 395nm and 645nm, respectively. Synthesis conditions including the amounts of NH₂OH$\cdot$HCl, the selection of reducing agent, the molar ratio of BSA/Cu(NO₃)₂, the pH value, the reaction temperature, the reaction time, and various kinds of Cu sources have been systematically studied. Importantly, these Cu NCs exhibit excellent stability for at least 2 months when stored at 4${}^{\circ }$C in the dark, and they also show strong oxidation resistance toward H₂O₂. Moreover, the prepared Cu NCs have been successfully applied to sensitively and selectively sensing Hg${}^{2+}$ without suffering any interference from other metal ions and anions.

Photoelectric spectra of heterostructures containing InAs quantum dots (QDs) produced in different technological regimes were studied. A simple nondestructive method to reveal a bimodality of the QDs’ size distribution was described. The method based on the analysis of the shape of InAs/GaAs QDs’ photoelectric spectra and their temperature dependencies. The quantitative analysis of the temperature dependencies of the photoelectrical spectra was performed. All possible emission processes occurring from quantum confined levels to the semiconductor matrix were considered at the simulation. The surface concentration of the QDs was estimated.

The metal–semiconductor composites with unique optical properties are highly desirable. Here we report that Ag–TiO₂ nanorod composites with two distinctive absorption peaks exhibit tunable plasmon coupling behaviors. The intensity of the long-wave absorption could be enhanced by modifying the geometry of TiO₂ particles, while such absorption is due to the plasmon coupling between the Ag particles. The long-wave absorption bands can be tuned by varying the reaction time and changing the amount of silver acetate. Furthermore, the Ag–TiO₂ composites were also prepared by photochemical reduction method which confirmed the previous properties. These results may help to design metal–semiconductor systems with desirable optical properties.

The effect of an alternating external field on the pattern of an axon’s action potential and its propagation has been investigated by incorporating the effect of an alternating electric field in the nonlinear Hodgkin–Huxley cable model. The results illustrate that for a wide range of frequencies, the applied field is capable of stimulating the resting potential of the membrane. In addition to hyper-polarization state of the neuron which is inevitable for certain values of the electric field amplitude, there will be additional effects on the propagation of action potentials in the neuron. We have also studied the action potentials velocity and amplitude change in the presence of the external field while the fiber is firing. The initiation of action potential for an axon at rest exposed to external field is possible and during the firing of the neuron and under the influence of the external field, it will act as a velocity modifier, and the neuron will lower the amplitude of the action potentials.

This article has been retracted. A statement of retraction is published in Nano Volume 11, Issue 12 (2016).

Noble metal sculptured thin films are of great interest during last decade as excellent surface-enhanced Raman scattering (SERS) substrates due to remarkable plasmonic properties in the visible and near-infrared range. In this work, Ag columnar thin films (Ag-CTFs) have been prepared by the glancing angle deposition technique. Finite-difference time-domain simulations has been utilized to study plasmonic properties of Ag-CTFs with a more accurate model based on binary scanning electron microscope (SEM) images by taking account of the shape irregularities, size distributions and random arrangement. The calculated absorption spectra based on the model of binarized SEM images show the best agreement with the measured spectra compared with models of periodic array with a regular shape. The near-field plasmonic properties are simulated based on the verified model. The distributions of electric field enhancement and hot spots are confirmed to be spectral and polarization dependent. There are multiple resonance peaks from visible to near-infrared and multiple eigenmodes coexist at the same wavelength and electric field enhancement are mainly excited by the polarized light vertical to the gap orientation. The electric field enhancement is found to distribute unevenly in the films with surface-localized feature. The equations to calculate the simulation SERS enhancement factor (EF) and total number of hot spots (tHN) are modified according to the above discussions. The experimental SERS EFs are on the order of 10⁷–10⁸, which indicates the high sensitivity of the films and the simulation SERS EFs and tHNs show good agreement with the experimental EFs. It is found that the SERS performance of Ag-CTFs is decided by both the cross-section structural characteristics and film thickness, which affect the electric filed enhancement and number of adsorbed molecules, respectively. Our work could be helpful in understanding the SERS mechanism and useful to the optimization of metal sculptured thin films for designing SERS biosensor.

Few-layered MoS₂ nanostructures were successfully synthesized by a simple hydrothermal method without the addition of any catalysts or surfactants. Their morphology, structure and photocatalytic activity were characterized by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, transmission electron microscopy, electrochemical impedance spectra and UV-Vis absorption spectroscopy, respectively. These results show that the MoS₂ nanostructures synthesized at 180${}^{\circ }$C exhibit an optimal visible light photocatalytic activity (99%) in the degradation of Rhodamine B owing to the relatively easier adsorption of pollutants, higher visible light absorption and lower electron–hole pair recombination.

Hydroxyapatite and strontium-substituted hydroxyapatite nanoparticles (n-HA and Sr-HA) were prepared by microwave-assisted solution synthesis with aqueous solutions of various Sr/(Sr$+$Ca) molar ratios ranging from 0% to 15%. The structural properties of the hydroxyapatite powders were investigated by X-ray powder diffraction, Fourier transform infrared spectroscopy and Raman spectra, field emission scanning electron microscopy coupled with energy dispersive X-ray spectrometry and transmission electron microscopy. The results confirmed that strontium ions had been incorporated into the hydroxyapatite lattice. The synthetic n-HA and Sr-HA nanocrystalline consisted of hydroxyapatite crystalline phase with hexagonal structure, and the particle size was 30–40 × 60–70nm and 40–50 × 70–80nm, respectively. The calcined HA particle size ranged from about 120nm to 150nm, the calcined Sr-HA products were composed of spherical aggregates with a size of about 70–100nm. The incorporation of Sr ions lead to the formation of vacancies in the crystal structure of the HA. The results indicated that the strontium substitution did not change the crystal structures. More Sr resulted in less calcined crystallites and formed agglomerates owing to the size effect.

A novel nonenzymatic electrochemical immunosensor was fabricated for quantitative detection of $\alpha$-fetoprotein (AFP). The immunosensor was constructed by modifying gold electrode with electrochemical reduction of graphene oxide-carboxyl multi-walled carbon nanotube composites (ERGO–CMWCNTs) and electrodeposition of gold nanoparticles (AuNPs) for effective immobilization of primary antibody (Ab${}_1)$. Ferroferric oxide–manganese dioxide–reduced graphene oxide nanocomposites (Fe₃O₄@MnO₂–rGO) were designed as labels for signal amplification. On one hand, the excellent electroconductivity and outstanding electron transfer capability of ERGO–CMWCNTs/AuNPs improved the sensitivity of the immunosensor. On the other hand, introduction of rGO could not only increase the specific surface area for immobilization of secondary antibody (Ab${}_2)$ but also build a synergetic effect to reinforce the electrocatalytic properties of catalysts. Fe₃O₄@MnO₂–rGO nanocomposites were characterized by scanning electron microscope, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Using AFP as a model analyte, the proposed sandwich-type electrochemical immunosensor exhibited a wide linear range of 0.01–50$\mathrm{\text{ng}}\cdot {\mathrm{\text{mL}}}^{-1}$ with a low detection limit of 5.8$\mathrm{\text{pg}}\cdot {\mathrm{\text{mL}}}^{-1}$. Moreover, the Fe₃O₄@MnO₂–rGO-based peroxidase mimetic system displayed an excellent analytical performance with low cost, satisfactory reproducibility and high selectivity, which could be further extended for detecting other disease-related biomarkers.

The paper reports a comparative analysis between the dual material gate double gate (DMG-DG) nMOSFET and the tri material gate double gate (TMG-DG) nMOSFET in terms of their analog and RF performance. Three different devices having the DMG-DG structure have been considered. Each of the devices have different higher workfunction material gate length (L1) to lower workfunction material gate length (L2) ratio (L1:L2). Along with the three devices, the performance of the TMG-DG nMOSFET is compared. The analog parameters considered for the comparison are the drain current ($I_{\mathrm{\text{ds}}}$), the transconductance ($g_m$), the transconductance generation factor ($g_m$/$I_{\mathrm{\text{ds}}}$) and the intrinsic gain ($g_m$Ro). The drain induced barrier lowering (DIBL) of the devices is compared. The RF analysis is performed using the non quasi static (NQS) approach. We consider the intrinsic gate to source capacitances ($C_{\mathrm{\text{gs}}}$), the intrinsic gate to drain capacitance ($C_{\mathrm{\text{gd}}}$), the intrinsic gate to source resistances ($R_{\mathrm{\text{gs}}}$), the intrinsic gate to drain resistance ($R_{\mathrm{\text{gd}}}$), the transport delay (${\tau }_m$), the unity current gain cut-off frequency ($f_T$) and the max frequency of oscillation ($f_{\max }$) for the RF comparisons. A single stage amplifier is also implemented using the devices for a circuit comparison.

Sintering of the active metallic nanoparticles and carbon deposition are the key problems faced for CO methanation catalysts. For overcoming those problems, bimetallic nanocatalyst is a promising route. In this work, a series of Al₂O₃ supported Ni-Co alloy catalysts were prepared by reducing NiCoAl layered double hydrotalcite (LDHs), and characterized with X-ray diffraction (XRD), temperature programmed reduction TPR, N₂ adsorption-desorption, transmission electron microscopy (TEM) and temperature programed oxidation (TPO) techniques. The resultant catalysts were mesoporous with nanoparticles of Ni-Co alloy ranging from 7.9nm to 9.2nm which were highly dispersed in alumina matrix. The sample Ni₇Co₃-Al₂O₃ catalysts showed very good catalytic performance during the stability test at 500/600${}^{\circ }$C for 300h, meanwhile exhibited excellent anti-sintering ability and anti-carbon deposition ability, owing to the formation of Ni-Co alloy and the feature of LDHs. This strategy for improving anti-sintering and anti-carbon deposition should be extendable for catalysts of other reactions.