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Viologen derivatives with non-conjugated substituent groups sharply promoted photocatalytic HER performance under o-CTF photocatalysis, while viologen derivatives with conjugated substituent groups decreased the photocatalytic HER rate.

The ultraviolet to terahertz band forms the main focus of optoelectronics research, while light detection in different bands generally requires the use of different materials and processing methods. However, researchers are aiming to realize multi-band detection simultaneously in the same device in certain specific application scenarios and ultra-wideband photoelectric detectors can also realize multi-function and multi-system integration. Therefore, the research and development work on ultra-wideband photoelectric detectors has important practical application value. Here, we produced self-powered suspended Pd-reduced graphene oxide-Ti (Pd-rGO-Ti) photodetectors. We varied the properties of the rGO films by using different annealing temperatures and achieved p-doping and n-doping of the films by evaporating palladium films and titanium films, respectively, thus enabling preparation of photothermoelectric (PTE) photodetectors based on rGO films. The resulting detectors have excellent photoelectric responses over a wideband illumination wavelength range from 375 nm to 118.8 μm (2.52 THz). At the same time, we determined the best experimental conditions and device structure by varying the channel width, the laser spot irradiation position and the experimental atmospheric pressure. The maximum responsivity obtained from our detectors is 142.08 mV W−1, the response time is approximately 100–200 ms and the devices have high detection sensitivity. Based on this work, we assumed in the subsequent experiments that detectors with higher performance can be obtained by reducing the channel width and atmospheric pressure. With advantages that include simple fabrication, low cost, large-scale production potential and ultra-wideband responses, these Pd-rGO-Ti photodetectors have broad application prospects in high-performance integrated optoelectronics.

A series of imine-linked covalent organic frameworks (COF) are constructed under Sc(OTf)3 catalysis in a 1,4-dioxane/mesitylene mixture. The amount of Sc(OTf)3 catalyst strongly affects the structure of the as-synthesized COFs. When 0.005 equivalent Sc(OTf)3 is used, a crystalline COF with uniform micropores and high surface area is obtained. The as-synthesized COF evolves to a disordered structure with increase in the catalyst amount. Several imine-linked COFs show NH3 sensing ability at room temperature, and the NH3 sensing performance is strongly dependent on their electric conductivity. The imine-linked COF with a disordered structure has better electric conductivity than the crystalline imine-linked COF. The NH3 sensing ability of the imine-linked COF with a disordered structure is far better than that of the imine-linked COF with a crystalline structure. The excellent NH3 sensing ability, including a short response time, large response value and high sensing selectivity, as well as lower sensor baseline resistance were observed on the imine-linked COF with a disordered structure. The imine linkage was recognized as the active site for NH3 adsorption on the imine-linked COF. Both density functional theory (DFT) calculations and an in situ UV-Vis spectra experiment confirm a hydrogen bond formation between NH3 and imine linkage during the NH3 sensing process.

Graphene has excellent electrical, optical, thermal, and mechanical properties that make it an ideal optoelectronic material. However, it still has some problems, such as a very low light absorption rate, which means it cannot meet the application requirements of high-performance optoelectronic devices. Here, we produce a high-responsivity photodetector based on a monolayer graphene/RbAg4I5 composite nanostructure. With the aid of poly(methyl methacrylate), we suspend the monolayer graphene on a hollow carving groove with a width of 100 μm. A RbAg4I5 film evaporated on the back of the graphene causes the composite nanostructure to generate a large photocurrent under periodic illumination. Experimental results show that the dissociation and recombination of ion-electron bound states (IEBSs) are responsible for the excellent photoresponse. The device has very high (>1 A W-1) responsivity in wide-band illumination wavelength from 375 nm to 808 nm, especially at 375 nm, where it shows a responsivity of up to ∼5000 A W-1. We designed the dimensions of the carving groove to allow the light spot to cover the entire groove, and we cut the graphene sheet to match the length of the carving groove. With the structural optimizations, the energy of light can be used more efficiently to dissociate the IEBSs, which greatly improves the photoresponse of optoelectronic devices based on the proposed monolayer graphene/RbAg4I5 composite nanostructure.

Photothermoelectric materials have important applications in many fields. Here, we joined a silver nanostructure film (AgNSF) and a carbon nanotube film (CNTF) by van der Waals force to form a AgNSF/CNTF heterojunction, which shows excellent photothermal and photoelectric conversion properties. The local temperature difference and the output photovoltage increase rapidly when the heterojunction is irradiated by lasers with wavelengths ranging from ultraviolet to terahertz. The maximum of the local temperature difference reaches 205.9 K, which is significantly higher than that of other photothermoelectric materials reported in literatures. The photothermal and photoelectric responsivity depend on the wavelength of lasers, which are 175-601 K/W and 9.35-40.4 mV/W, respectively. We demonstrate that light absorption of the carbon nanotube is enhanced by local surface plasmons, and the output photovoltage is dominated by Seebeck effect. The AgNSF/CNTF heterostructure can be used as high-efficiency sensitive photothermal materials or as ultra-wideband fast-response photoelectric material., 11 figures

To estimate the prevalence and distribution of tooth wear among groups of adolescents and adults in Shanghai, China through an epidemiological survey, and explore the associated factors.Multistage, stratified, constant volume and cluster sampling methods were used in an epidemiological survey conducted in Shanghai in 2014. The basic erosive wear examination (BEWE) index was used to screen for tooth wear in different age groups: 12 years, 15 years, 18 to 35 years, 36 to 49 years and 50 to 74 years. A previously published questionnaire collected information including dietary habits, oral hygiene habits and general conditions.This survey reports the results for 1806 participants in Shanghai. The prevalence of tooth wear was 59.7% in adolescents (BEWE ≥ 1) and 93.1% in adults (BEWE ≥ 2). The prevalence and severity of disease increased with age (P0.01). The teeth most susceptible to wear were the central incisors and first molars. Multivariate analysis of covariance (ANCOVA) results showed that soft drinks, alcoholic drinks, pickled vegetables and hard food, gastroesophageal reflux disease (GERD), xerostomia and poor tooth brushing habits were statistically correlated with tooth wear in different age groups.The prevalence of tooth wear appears to be high in adolescents and adults in Shanghai. Frequent consumption of soft or alcoholic drinks, GERD, xerostomia and poor tooth brushing habits were positively associated with tooth wear in different age groups.

Graphene has excellent electrical, optical, thermal, and mechanical properties that make it an ideal optoelectronic material. However, it still has some problems, such as a very low light absorption rate, which means it cannot meet the application requirements of high-performance optoelectronic devices. Here, we produce a high-responsivity photodetector based on a monolayer graphene/RbAg

Graphene is receiving significant attention for use in optoelectronic devices because it exhibits a wide range of desirable electrical properties. Although modified graphene that is fabricated on quantum dots (or similar integration strategies) has shown promise, it has not met the requirements for high-speed applications and highly sensitive detection. Herein, we report ion-modulated graphene composite nanostructures that were incorporated into photodetectors. We focus on the dynamical properties of the novel photodetectors, and they exhibit extraordinary photoelectric performances (photoresponsivity ∼1 A/W, response time ∼100 μs) over a broad range of wavelengths from 405 to 1064 nm (the maximum external quantum efficiency is greater than 300% at 635 nm with a 10 kHz chopping frequency). A theoretical model is proposed in this paper, and it is in good agreement with our experimental results. The dynamic analyses further confirmed the dissociation and recombination of ion-electron bound states to be responsible for the fast and sensitive photoresponse from the composite samples. Although ion-modulated optoelectronic nanomaterials are rarely studied, they require further exploration as they offer new insights and alternatives in nanomaterial research.

A new kind of phototransistor based on graphene and a superionic conductor is fabricated by depositing a layer of RbAg4I5 on transferred graphene by a vacuum thermal evaporation method. Electrons in graphene and silver ions in RbAg4I5 form an ion–electron bound state (IEBS) at the interface due to Coulomb interactions. The bound state, which can be dissociated by photons, greatly influences the electronic conductivity of graphene. The binding energy between ions and electrons is an important parameter to determine the photon energy that can be absorbed to set the free bound state. Through the back-gate bias, we realize controllable modulation of binding energy. The binding energy between electrons and silver ions linearly decreases with the increase of gate voltage, resulting in the increased number of IEBSs that can be dissociated by photons, which is proved by experimental measurement and theoretical analysis. Owing to the decrease in binding energy, the response amplitudes can be increased by up to two orders of magnitude under the illumination of lasers. This phototransistor based on graphene and RbAg4I5 achieves controllable responsivity from several mA W−1 to several hundred mA W−1 while the response speed remains unchanged on the order of 100 milliseconds. This study, on the one hand, gives a better understanding of the modulation of ions on electron transport; on the other hand, it offers a new road for us to achieve modulation of photo-responses, and it is very promising to be applied in optoelectronic devices with current circuit technology.

An interdigitated gold (Au) nanofilm was introduced on graphene, supported by a p-type silicon (p-Si) substrate, as an optoelectronic photodetector based on an Au/graphene/p-Si heterojunction by a low-cost method. Tunable photocurrent (photoconductivity) response to laser power density was realized under the modulation of the Au nanofilm and the Si layer on the carrier transport through graphene. Photoelectric measurements demonstrated that the device generated positive photocurrent when illuminated at low laser power density and negative photocurrent when illuminated at high laser power density. Positive photocurrents of 9 μA and 5 μA were generated at 1.13 μW cm−2 (power ∼ 20 nW) and 0.32 μW cm−2 (power ∼ 40 nW) under irradiation of 532 nm and 1064 nm lasers, respectively; responsivities of up to 450 A W−1 and 125 A W−1, were achieved, respectively, owing to the increase in carrier density caused by photo-induced carrier injection. At high power density, the mobility of graphene declined due to the scattering effect between carriers and phonons (bolometric effect), which was further strengthened by the local high-temperature field caused by the Au nanofilm. The negative photocurrent of up to several milliamperes was clearly observed under irradiation of 532 nm and 1064 nm lasers. The photocurrent response versus power density behavior of the photodetector could be modulated by the source–drain bias and laser wavelength. The device had a rapid response rate of the order of several hundred microseconds and good stability. The photodetector realized high-speed conversion of light density to photocurrent with different signs, demonstrating good potential for future applications in optoelectronic devices.

Objectives To compare the prevalence of chronic periodontitis between men who had semen abnormalities and those who had normozoospermia through a case-control study. Materials and methods Male patients who visited the assisted reproduction clinic of a large general hospital and were diagnosed with semen abnormalities were included in the case group. The control group was composed of patients of the same clinic with normozoospermia. The semen analysis included sperm concentration, count and progressive and total motility, which were measured in the laboratory. A questionnaire and clinical periodontal examination were conducted for all participants. Logistic regression was performed to explore the relationship between chronic periodontitis and male infertility. Results A total of 192 participants were included: 63 participants (32.8%) had some type of semen abnormality (case group), while 129 participants (67.2%) had normozoospermia (control group). The case group had a significantly higher prevalence of moderate/severe periodontitis than the control group (33.3% vs. 17.8%, P=0.012). The logistic regression showed that participants who had moderate/severe periodontitis had a greater chance of having semen abnormalities after adjusting for other confounding factors (OR=3.377, P=0.005). Conclusions Periodontitis is associated with semen abnormalities and sperm motility in men.

Variant selection during solid–solid phase transformation in titanium alloys affects greatly the microstructure and mechanical properties of the alloys. Theoretical investigations of the variant selection were generally performed by using phase field simulation that considers solely the elastic coherency strain energy. In the present work, we develop a model to determine the variant selection directly from first-principles calculations. The source of the variant selection is considered to be the varying free energy gains (including both bulk and interface contributions) induced by the transformation from the parent phase to different variants of the product phase. This model is applied to investigate the effects of shear stress and alloy composition on ω variant selection during athermal β → ω transformation in binary Ti-xMo ( x ≤ 25 at.%) alloys. The random distribution of the atoms in the alloy is described by using virtual crystal approximation (VCA). We show that the tendency of variant selection becomes stronger with increasing shear stress. With increasing Mo concentration, the favorable ω variant transfers from one to another, except for the ω phase with very small particle size (e.g., radius R ≤ 1 nm) where one variant is always selected. The critical Mo concentration for the transfer of the favorable ω variant approaches to 5 at.% with increasing size of the ω phase particles and remains almost unchanged against the shear stress. At the critical Mo concentration, the considered variants have equal free energy gains and there is no variant selection. This finding opens the possibility of controlling the variant selection and the associated microstructure by changing the composition of the alloys.

Ultra-broad spectral detection is critical for several technological applications in imaging, sensing, spectroscopy, and communication. Carbon nanotube (CNT) films are a promising material for ultra-broadband photodetectors because their absorption spectra cover the entire ultraviolet to the terahertz range. However, because of the high binding energy of excitons, photodetectors based on CNT films always require a strong electric field, asymmetric electrical contacts, or hybrid structures with other materials. Here, we report an ultra-broadband bolometric photodetector based on a suspended CNT film. With an abundant distribution of tube diameters and an appropriate morphology (spider web-like), the CNT films display a strong absorption spectrum from the ultraviolet up to the terahertz region. Under illumination, heat generated from the electron-photon interaction dominates the photoresponse of our devices. For small changes in temperature, the photocurrent shows a convincing linear dependence with the absorbed light's power across 3 orders of magnitude. When the channel length is reduced to 100 μm, the device demonstrates a high performance with an ultraviolet responsivity of up to 0.58 A/W with a bias voltage of 0.2 V and a short response time of ∼150 μs in vacuum, which is better than that of many other photodetectors based on CNTs. Moreover, this performance could be further enhanced by optimization.

Eutectic gallium-indium (EGaIn) alloy is a kind of liquid metal and has attracted much attention due to good properties. In order to satisfy the trend of miniaturization and realize more practical applications, the exploration for preparation method and properties of EGaIn at nanoscale are very important. Here, facile vacuum thermal evaporation method is developed to fabricate EGaIn nanostructures. The EGaIn nanoparticle and nanofilm with naturally formed 5 nm thick oxide layers are well prepared. The oxide film formed on the EGaIn surface is an important factor, making the properties of the nanostructure different from the properties of the bulk. Compared with ignorance of oxide layer in bulk materials, the proportion of oxide layer increases evidently in nanostructures, which produce obvious influence on the electric and optical properties. The rectifying characteristic and optoelectronic performance are experimentally observed. The EGaIn nanostructures can generate evident photocurrent responses with good responsivities (∼1 mA W-1) and response speed (∼1 s) under irradiation of 206 nm, 405 nm, 532 nm, 635 nm, 808 nm, 1064 nm and 10.6 μm lasers. These properties are completely different from the metallic properties of EGaIn bulk material.

A macroscopic silver nanowire (AgNW) network is grown by solid state ionics method. The ion flow during growth of the AgNW network is controlled by maintaining a current in the order of 10-7 A. Scanning electron microscopy (SEM) analysis reveals that the growth direction of AgNWs in the network is irregular and spread evenly in all directions and the nanowires are 40-160 nm in diameter. The microcosmic mechanism of silver nanostructures grown by the solid state ionics method is established by real time and in situ SEM analysis of the growth process of the AgNW networks. To study the photoelectric properties of the network, a self-supported AgNW network sample (∼1 mm wide and 8 mm long) is irradiated with lasers of different wavelengths of 375, 405, 532, 633, 808, and 1064 nm and 10.6 μm, and changes in the current between the two ends of the sample are recorded. The network displays negative photoconductance effect, and the maximum light responsivity is 43 mA W-1. The network displays light responsivity in the ultraviolet light-to-mid-infrared light region, with response times of tens of milliseconds. These findings indicate that the AgNW network has broad application prospect in ultra-wide spectrum photoelectric detection.

Herein, we propose a new strategy to fabricate gold (Au) micro/nanostructure arrays by photocatalytic solid-state electrochemical reaction between superionic conductor RbAg

In this reply to R. Van Pottelberge, M. Zarenia, and F. M. Peeters's comment on our original paper, ``Impurity spectra of graphene under electric and magnetic fields,'' we discuss the existence of bound states of a Coulomb impurity in graphene through the regular and irregular solution of the Dirac equation, and clarify its relation to the term ``atom collapse'' in our original paper.

Vibration monitoring of machinery and equipment plays a very important role in judging the equipment maintenance and operational status. This paper discussed the mechanical vibration amplitude measurement system scheme based on PVDF piezoelectric sensors. The entire test system is mainly composed of PVDF piezoelectric film sensors, charge amplifiers, data acquisition and processing and display of valid values. It can display the amplitude of vibration signals in real time and alarm. The measurement system has the advantages of a simple structure and convenient operation.

The quantum properties of topological insulator magnetic quantum rings formed by inhomogeneous magnetic fields are investigated using a series expansion method for the modified Dirac equation. Cycloid-like and snake-like magnetic edge states are respectively found in the bulk gap for the normal and inverted magnetic field profiles. The energy spectra, current densities and classical trajectories of the magnetic edge states are discussed in detail. The bulk band inversion is found to manifest itself through the angular momentum transition in the ground state for the cycloid-like states and the resonance tunneling effect for the snake-like states.

Fast and sensitive detection of terahertz radiation is notoriously difficult, especially the detection at the ambient condition. Here, we fabricated bolometric terahertz photodetectors based on suspended carbon nanotube (CNT) fibers. Because the CNT fibers exhibit a very small heat dissipation area, the heat transport from the CNT fibers to the air is negligible. It ensures the devices can work well at the ambient condition. Additionally, the CNT fibers demonstrate a high responsivity up to 0.54 A W−1 and a short response time of 200 μs. This implies a performance that is competitive among the terahertz photodetectors based on CNT.

In this paper, we present an acoustic-structure couple interaction model of partial discharge (PD) in Gas Insulated Switchgear, the interaction between the internal acoustic source of partial discharge and structure of GIS is simulated with the finite element analysis, and the internal and external acoustic pressure levels distribution of GIS is obtained. The results based on the frequency sweep shown that the internal acoustic pressure levels is bigger than the external acoustic pressure levels of GIS in the ultrasonic frequency spectrum,it suggests that it should use the ultrasonic sensor with a broadband spectrum response to measure partial discharge in GIS, which can obtain high sensitivity. In addition, the external sound pressure of GIS is very small, and the signal of the Ultrasonic sensors must be amplified for measurement. Meanwhile, the outside acoustic pressure of the epoxy insulator is so small that it can properly judge the adjacent GIS unit partial discharge conditions.

In this paper, we produced the 0-3 PZT/P(VDF-TFE) piezoelectric composite film with 80μm thickness using PZT piezoelectric ceramics and fluorine resin P(VDF-TFE) by weight 85/15 ingredients through the hot rolling machine and corona-discharge method. A sensor with 4cm×1.3cm area is designed and produced by using this film. We have carried out the breaking of a pencil lead pressed against an aluminum plate acoustic emission testing. The result shown that the sensor is with fast response and high sensitivity advantage, the sensor can be used as acoustic emission sensor. Meanwhile the sensor is very easy to use due to it is a soft film sensor.

Charge amplifier is the key component in the pre-processing circuit of the sensors. With the development of the sensor technology, the charge amplifier on the market has not been able to meet the requirement of the actual measurement. In this paper, a LF356-based charge amplifier is suitable for the conversion circuit of the polyvinylidene fluoride (PVDF) piezoelectric sensor, duing to its small volume, low power consumption and strong anti-interference. The fesibility and reliability of the charge amplifier are verified by simulating the circuit with Multisim10 and testing the hardware circuit. This charge amplifier achieves a volume of 19.32 cm3 and a bandwidth between 20kHz and 150kHz at a power consumption of 1 mW. Performance of this charge amplifier is investigated when it is connected to a standrad signal source, achieving a gain of 10 times.

We exposed single- and double-walled carbon nanotube (SWCNT and DWCNT) fibers to microwave radiation. Small carbon clusters of C2 were detached from the nanotubes, and the process was accompanied by intense heat release. The exfoliation of C2 made the nanotubes break, while the high temperature made the nanotube bundles transform into large diameter CNTs. Strong visible light emission was observed from the vicinity of the nanotube fibers. The emission spectra excited by the microwaves from the as-grown CNT fibers correspond to the Swan band of C2 clusters. In the case of the purified SWCNT fibers, two characteristic peaks at 584 nm and 769 nm emerge in the spectra beyond the Swan band of C2.

We address the quantum capacitance of a bilayer graphene device in the presence of Rashba spin–orbit interaction (SOI) by applying external magnetic fields and interlayer biases. Quantum capacitance reflects the mixing of the spin-up and spin-down states of Landau levels and can be effectively modulated by the interlayer bias. The interplay between interlayer bias and Rashba SOI strongly affects magnetic oscillations. The typical beating pattern changes tuned by Rashba SOI strength, interlayer bias energy, and temperature are examined as well.

In this paper, the basic principles of the surface acoustic wave (SAW) formed in the periodically poled piezoelectric ceramic has been elaborated theoretically. The modal and harmonic analyses has been performed by utilizing ANSYS software for the periodically poled piezoelectric composite structure (adjacent piezoelectric polarization direction opposite) which composed by piezoelectric ceramic (PZT-4). The data of simulation result have been processed and obtained the following conclusion: the surface wave can be formed in the periodically poled piezoelectric domain with a relatively large amplitude, the motion track of each particle in the SAW is an ellipse by combined the transverse modal displacement and longitudinal modal displacement of each surface node. These conclusions are same as the theoretical values, the simulation results are very useful for designing SAW device with periodically poled piezoelectric ceramic.

A novel photodetector based on double-walled carbon nanotube (DWCNT) film/TiO2 nanotube array (TNA) heterojunctions was fabricated, which exhibited high photoresponse in a broad spectral range. The photoresponse of the detector was dramatically dependent on the length of the TNAs. High photocurrent-to-dark current ratio with a value of 3360 was observed in the visible range by optimizing the lengths of the TNAs. The photosensitive regions could be extended into the near-infrared range. These results reveal that DWCNT film/TNA heterojunctions show potential applications for broad band photodetectors.

We investigated the resistive switching characteristics of Au/Ar+ bombarded SrTi0.993Nb0.007O3/In sandwiches. The evolution of the resistive switching polarity with sweeping voltage was observed. Our experiments showed that under a macroscopic electrode the homogeneous trapping-detrapping-type conduction and filament-type conduction coexist and compete with each other. For a large sweeping voltage range, the trapping-detrapping-type conduction dominates. However, for a small range the latter dominates. If the bias voltage is too large, the filament conduction could be destroyed. These results will help deepen the understanding of the resistive switching polarity, and will aid in future device design.

The electric current effects on (La,Ca)MnO3 thin films epitaxially grown on SrTiO3 and LaAlO3 substrates were carefully investigated. When the applied electric current density exceeds a sample dependent critical value, apparent asymmetric I – V curves are clearly observed on the stimulated (La,Ca)MnO3/SrTiO3 films. The larger current and longer processed time enhance the asymmetry. No asymmetry was observed on all the (La,Ca)MnO3/LaAlO3 films independent of applied electric current and stimulated time. The comparison study indicates that the observed asymmetric I – V behavior of the (La,Ca)MnO3/SrTiO3 films is closely related to the electric field induced conductivity of the underlying SrTiO3 substrates. We proposed an equivalent circuit to qualitatively explain our results. Our results also imply that in dealing with the electric current (field) effects on the thin films fabricated on SrTiO3 substrates, the electric field induced conductivity of the substrates should be considered.

A new kind of photodetector based on a double-walled carbon nanotube (DWCNT) film and a TiO2 nanotube array with hetrodimensional non-ohmic contacts has been fabricated. Due to the dimensionality difference effect, the DWCNT film/TiO2 nanotube array photodetector exhibits a much higher photocurrent-to-dark current ratio and photoresponse relative to an Au film/TiO2 nanotube array device, even at small bias voltage. The photocurrent-to-dark current ratio reached four orders of magnitude and a high photoresponse of 2467 A/W was found upon irradiation at 340 nm. Furthermore, the photosensitive regions could be extended into the visible range. The photocurrent-to-dark current ratio reached approximately three orders of magnitude upon irradiation at 532 nm, where the photon energy is much lower than the band gap of TiO2. Open image in new window

Heterojunction structures were fabricated, which consisted of a double-walled carbon nanotube (DWCNT) thin film coated either on an n-type silicon wafer or an n-type silicon nanowires (SiNW) array with varied lengths. Current–voltage characteristics measured under laser (532 nm) irradiation showed that the photoresponse [(light current − dark current)/dark current] of the heterojunctions dramatically depends on the length of SiNWs. Increase in the length of SiNWs led first to increase and then to decrease in the photoresponse of DWCNT/SiNW heterojunction. The heterojunction with a SiNW length of ca. 600 nm has the highest the photoresponse value of 10.72.

Herein, we propose a new strategy to fabricate gold (Au) micro/nanostructure arrays by photocatalytic solid-state electrochemical reaction between superionic conductor RbAg4I5 and Au films. The Au and RbAg4I5 films were successively deposited on a clean quartz substrate by vacuum thermal deposition method. A copper microgrid possessing periodic holes 100 μm in diameter was put above the RbAg4I5 film as a mask plate, whereupon irradiation from a 405 nm wavelength laser was used to diffuse gold ions (Au+ ions) into vacant silver sites of RbAg4I5 and transfer Au+ through ion passageways in the RbAg4I5 film. When the laser was turned off, the Au+ ions were easily reduced due to low activity compared to the silver (Ag+) ions. After multiple on/off cycles of the 405 nm laser, the irradiated area of uniform Au film exhibited a periodic structural unit array whose period was the same as that of the mask plate hole array. Atomic force microscope and scanning electron microscope images revealed that a self-assembled needle-like nanostructure array grew perpendicular to the substrate surface inside each circle's structural unit. The height of the grown nanostructure array increased with laser power density. Raman enhancement of the gold nanostructure array as substrate was detected using Rhodamine 6G (R6G) ethanol solutions as probe molecules. The enhancement effect increased with the height of the grown nanostructure array, and could increase by two orders of magnitude greater than that of unirradiated Au film. This strategy offers a new method for the micro/nanostructure processing of gold and provides microscale-array-mediated surface-enhancement Raman-scattering (SERS) substrates comprising Au nanostructures for application in high-sensitivity spectrum analysis.

By proposing an effective method for the coupled modified Dirac equation, the effects of structure inversion asymmetry on the confined states in quantum dots of three-dimensional topological ultrathin films are investigated. It is found that the presence or absence of the quantized edge states can be controlled by the inversion asymmetry potential. The tuning of the potential to the spins of edge and nonedge states is quite different. In the presence of impurities, the mixing between the edge and nonedge states can be largely enhanced and effectively tuned by the potential. The finding will be useful to design relevant nanodevices.

We study the shot noise spectrum of the system composed of a semiconductor quantum dot coupled to two ferromagnetic leads with arbitrary relative magnetization direction. A general formula for the spin-dependent noise spectrum is obtained within the formalism of the nonequilibrium Green functions. We show that the noise spectrum and Fano factor can increase or decrease with the relative angle between the magnetizations of the two leads, which depends on the system parameters. The spin current correlations strongly depend on the spin orientations and show a nonmonotonic behavior versus the relative magnetization angle.

A two-dimensional double-barrier nanoring under in-plane electric fields is proposed to investigate field-controlled two-electron spectra and entanglements. It has been found that changing the direction of the field can destroy the symmetries of the wavefunctions and has great impact on the spectra. The angle between the barriers, along with the intensity and direction of the field, can be used for controlling the entanglements of both the ground and excited states. The structure-dependent and field-controlled far-infrared spectroscopies are useful in such investigations. It is helpful for manipulating the entanglements of indistinguishable particles in nanostructures.

The effects of transverse field and a single defect on the conductance of an achiral carbon nanotube have been investigated. It is found that armchair nanotubes under the transverse field are always metallic, and that field-induced metal–semiconductor (MS) and semiconductor–metal (SM) transitions are shown for zigzag nanotubes. MS transition fields are independent of the defect while SM transition fields are sensitive to the field-defect azimuth, defect type and its strength. Most importantly, the field-defect azimuth is a new freedom and can be used to tailor and control the electronic behaviour. The experimental confirmation of the prediction may be possible.

Finite-temperature spectral density for metallic single-walled carbon nanotubes (SWNTs) with a magnetic impurity is studied theoretically. A single orbital Anderson model and a rapidly convergent perturbation method for dilute magnetic alloy are applied to investigate the effect of magnetic impurities on density of states (DOS) of both thin and thick SWNTs at various temperatures. It is found that for nanotubes of different diameter the DOS exhibit different resonance properties and different changing trend with increase of temperature. Rules behind the behavior are manifested.

The tunneling of a giant spin at excited levels is studied theoretically in mesoscopic magnets with a magnetic field at an arbitrary angle in the easy plane. Different structures of the tunneling barriers can be generated by the magnetocrystalline anisotropy, the magnitude and the orientation of the field. By calculating the nonvacuum instanton solution explicitly, we obtain the tunnel splittings and the tunneling rates for different angle ranges of the external magnetic field ($\theta_{H}=\pi/2$ and $\pi/2, Comment: 27 pages, 4 figures, accepted by Euro. Phys. J. B

We address atomic collapse and its magnetic modulation in gapped graphene. Based on the exact solution of the Dirac equation, we obtain the complete supercritical Coulomb impurity spectra and accurate wave functions. The unique degeneracy, electron probability densities, pseudospin of supercritical states, and mass and core-size effects are investigated in the supercritical region. When a magnetic field is applied, atomic collapse can be effectively restrained. Both supercritical and subcritical impurity states exhibit obviously different behaviors in two valleys in the magnetic field. The Landau levels also exhibit different changes in supercritical and subcritical impurity potentials. This study is helpful in understanding relativistic quantum phenomena in graphene and related systems.

Using the coupled series expansion method developed in this paper, we have investigated the quantum behavior of Coulomb impurity states under external electric and magnetic fields in graphene. Under magnetic field, we have obtained an accurate full spectrum of the attractive and repulsive Coulomb impurities for both massless and massive Dirac electrons and have found that bound states can be tuned between in and out of the gap by Coulomb impurities and a magnetic field. When a linear radial electric field in combination with a magnetic field are applied, the energy levels of Coulomb impurity states experience intercrossing, and they disappear because of Klein tunneling as the electric field exceeds the magnetic field. The results are helpful in controlling Coulomb impurity states by external fields in graphene and the method proves to be an efficient way to obtain accurate solutions of the Dirac equation with various fields.

The phenomenon of quantum nucleation is studied in a nanometer-scale antiferromagnet with biaxial symmetry in the presence of a magnetic field at an arbitrary angle. Within the instanton approach, we calculate the dependence of the rate of quantum nucleation and the crossover temperature on the orientation and strength of the field for bulk solids and two-dimensional films of antiferromagnets, respectively. Our results show that the rate of quantum nucleation and the crossover temperature from thermal-to-quantum transitions depend on the orientation and strength of the field distinctly, which can be tested with the use of existing experimental techniques., Comment: 21 pages, 5 figures, Final version and accepted by Eur. Phys. JB