Showing papers in "Physica E-low-dimensional Systems & Nanostructures in 2019"
TL;DR: In this article, the features of Hall current on hybrid nanofluid flow over a revolving disk are described. And the foremost PDE equations of the model are renovated into ODEs by employing similarity variables and then sketched out via RK-4 method in conjunction with shooting procedure.
Abstract: The present literature exhibits the features of Hall current on hybrid nanofluid flow over a revolving disk. Impacts of magnetic field and thermal radiation have been also included to explore the fine points of the flow. An innovative class of nanofluid i.e. hybrid nanofluid is being used here, which are assemble of Copper (Cu) and Titanium Dioxide ( T i O 2 ) with water. The foremost PDE equations of our model are renovated into ODEs by employing similarity variables and then sketched out via RK-4 method in conjunction with shooting procedure. Impact of embedding flow factors on velocity, temperature, concentration have been framed in the light of parametric study. Favorable comparison with existing literatures has been revealed and it depicts tremendous similarity. Result addresses that radial skin frictional factor is enhanced for Hall parameter, while transverse frictional component illustrates opposite scenario. Investigation extracts that temperature declines for Hall parameter and heat transport rises for radiative factor. Also, hybrid nanosuspension exhibits elevated temperature profile than usual nanoliquids.
101 citations
TL;DR: In this article, the performance of ZnO nanoparticles loaded on multi-wall carbon nanotubes for removing congo red dye from aqueous solutions was investigated and the effect of various parameters such as contact time, temperature and adsorbent dosage are investigated and discussed.
Abstract: The present work investigates the performance of ZnO nanoparticles loaded on multiwall carbon nanotubes for removing of congo red dye from aqueous solutions . The prepared nanocomposites are characterized by XRD, TEM, FTIR, FESEM and EDX. The effect of various parameters such as contact time, temperature and adsorbent dosage are investigated and discussed. The obtained results show that the optimum adsorption conditions are contact time of 50 min., 55 °C and dosage of 9 mg. These optimum parameters give a high removal ratio of 99.8%.The adsorption data were well fitted by pseudo-second-order model. The obtained results reveal that ZnO/MWCNTs is a promising, environmentally friendly and efficient adsorbent for some wastewater treatment.
89 citations
TL;DR: In this article, density functional theory calculations are performed to investigate the adsorption characteristics of NO2 and H2S on the graphene surface decorated with group 10 transition metals (Ni, Pd and Pt).
Abstract: NO2 and H2S are highly toxic and corrosive gases that severely pollute the environment and damage the health of human beings. Developing sensitive sensor for efficiently detecting NO2 and H2S molecules is highly demanded. In this work, density functional theory calculations are performed to investigate the adsorption characteristics of NO2 and H2S on the graphene surface decorated with group 10 transition metals (Ni, Pd and Pt). NO2 and H2S molecules are physically adsorbed on pristine graphene due to weak interactions. Decorating graphene with metals can significantly enlarge the interactions between gas molecules and graphene, in which the adsorption energy and charge transfer are 7–10 times and 3–10 folds higher than those on pristine graphene, respectively, demonstrating the strong chemisorption on the metal-decorated graphene. Especially, Ni and Pt decorated graphene are highly sensitive to the NO2, while for H2S molecule detection, Pt-decorated graphene is more preferable. Besides, we demonstrate that graphene with group 10 metal decoration can capture the NO2 gas more effectively than H2S because H2S molecule fails to dope graphene by Fermi level shifts (Δ(Ef-ED) = 0 eV). The as-obtained insights could provide useful guidance on the design of graphene-based sensor for advanced performances.
77 citations
TL;DR: In this article, a full-wave EM solver CST Microwave Studio (Computer Simulation Technology) based on finite integrate technique has been used to simulate and investigate the absorption of the metamaterial structure with chemicals liquids depending on the electrical properties.
Abstract: In this work, sensor abilities of the metamaterial absorber based on swastika shaped resonator are developed both theoretically and experimentally at X-band frequency range. The structure is consisted of a swastika shaped resonator on the top of dielectric layer and have an air gap to fill chemicals liquids between the copper plate and backside resonator. In this study, a full-wave EM solver CST Microwave Studio (Computer Simulation Technology) based on finite integrate technique has been used to simulate and investigate the absorption of the metamaterial structure with chemicals liquids depending on the electrical properties. A vector network analyzer 85070E probe kit has been used to measure the relative dielectric constants and loss tangent of some chemical liquids (ethanol content, methanol content, acetone, methanol, ethanol, Polyethylene Glycol 300, water) in the related frequency range. Absorption value of the sensor structure for selected chemicals placed in the air gaphas been investigated. It is obtained that there is a significant difference in absorption ratios between each chemicals and overall resonance frequency shifts have been observed which provides information to accurately estimate density rate of the sensed liquids. The absorption mechanisms of the metamaterial has been explained by using electric field, magnetic field and surface current distributions. Furthermore, the resonance absorption properties of the metamaterial based absorber sensor can be modified and adjusted easily by varying the dimensions of the resonator. Experimental and simulated results demonstrate that the resonance frequency of the swastika metamaterial based sensor is linearly related to the permittivity of selected chemicals which creates an appropriate approach for multipurpose sensor devise and electrochemical sensor.
62 citations
TL;DR: In this paper, the spin gauge field has adiabatic and nonadiabatic components, consisting an SU(2) gauge field, which gives rise to spin Berry's phase, topological Hall effect and spin motive force.
Abstract: The aim of this paper is to present a comprehensive theory of spintronics phenomena based on the concept of effective gauge field, the spin gauge field. An effective gauge field generally arises when we change a basis to describe system and describes low energy properties of the system. In the case of ferromagnetic metals we consider, it arises from structures of localized spin (magnetization) and couples to spin current of conduction electron. The first half of the paper is devoted to quantum mechanical arguments and phenomenology. We show that the spin gauge field has adiabatic and nonadiabatic (off-diagonal) components, consisting an SU(2) gauge field. The adiabatic component gives rise to spin Berry's phase, topological Hall effect and spin motive force, while nonadiabatic components are essential for spin-transfer torque and spin pumping effects by inducing nonequilibrium spin accumulation. In the latter part of the paper, field theoretic approaches are described. Dynamics of localized spins in the presence of applied spin-polarized current is studied in a microscopic viewpoint, and current-driven domain wall motion is discussed. Recent developments on interface spin-orbit interaction are also mentioned.
60 citations
TL;DR: In this paper, the structural, electronic, and magnetic properties of 10 transition metals (TMs) doped with Puckered arsenene were investigated, and it was shown that all the substitutional systems have large binding energy, suggesting the formation of chemical bonds and consequently robust structural stability.
Abstract: Puckered arsenene is a new two-dimensional group V elemental material which has sparked much research interest owing to its fascinating properties and potential applications in various fields. To further widen its application, we studied arsenene doped with 10 different transition metals (TMs) by using first-principles calculations, focusing on the structural, electronic, and magnetic properties of TM-doped arsenene. Our calculation results show that all the substitutional systems have large binding energy, suggesting the formation of chemical bonds and consequently robust structural stability. The substitution of Ti, V, Cr, Mn, Fe and Ni atoms for As atoms induces a magnetic moment of 1, 2, 3, 4, 3, and 1 μB in arsenene, respectively. Moreover, the V-, Mn- and Fe-doped systems exhibit half-metallic properties, while the Ti-, Cr-, and Ni-doped systems exhibit magnetic semiconductor properties. Adsorption of a single oxygen molecule on TM-doped arsenene was also investigated to determine whether O 2 can widen the application of substitutional arsenene systems for spintronic devices. The adsorption of a single oxygen molecule turns the Ti-, V-, Cr-, Mn-, Fe-, Co-, Ni-, and Pt-arsenene systems to magnetic metals which can be used as spin sources and drains in spintronic circuits. Interestingly, all the substitutional systems show good catalytic activity for CO oxidation since they can elongate the O O bond. In particular, after O2 is adsorbed on the Sc-arsenene system, the O2 molecule is almost decomposed, which provides much information on the requirements for a suitable CO oxidization catalyst with high activity and low cost. Our results are expected to lead to new opportunities for arsenene in spintronics and catalysts.
59 citations
TL;DR: In this article, an aligned ZnO nanorods (NRs) were synthesized by a simple and inexpensive hydrothermal method, which lead to good photocatalytic activity in the presence of visible light.
Abstract: Aligned ZnO nanorods (NRs) were synthesized by a simple and inexpensive hydrothermal method. Morphological, structural, photoabsorbance and photoluminescence studies have been carried out using field emission scanning electron microscopy (FE-SEM), grazing incidence X-ray diffraction (GIXRD), Raman, UV–visible and Photoluminescence spectroscopy. Results show that crystallinity and alignment of ZnO NRs lead to good photocatalytic activity in the presence of visible light. The Photoluminescence spectra revealed a decrease in the UV emission, suggesting a reduced recombination of the photo generated carriers. The visible region emission is due to the surface oxygen vacancies. Increase of charge separation rate observed from emission spectra and the vacancy related sub-bands in the absorbance spectra are together responsible for the enhanced visible light photocatalytic activity of ZnO NRs. Vertically aligned 1-D morphology of ZnO NRs and the presence of oxygen vacancy states assist in the visible light photocatalytic degradation of Methylene Blue dye.
58 citations
TL;DR: In this paper, a patterned textile based PENG (ZnO-T-PENG) was developed, which consists of vertically arranged ZnO nanorod arrays sandwiched between two symmetrically layers of silver (Ag) coated-fabrics.
Abstract: With the development of wearable and flexible electronics, PENGs based on ZnO nanorod arrays patterned-textile have aroused great interests. Nevertheless, the currently used hydrothermal method to fabricate ZnO nanorods and the performance of ZnO strucures prepared at present still need to be further improved. Hence, ZnO nanorods patterned textile based-PENG (ZnO-T-PENG) has been developed in this paper, which consists of vertically arranged ZnO nanorod arrays sandwiched between two symmetrically layers of silver (Ag) coated-fabrics. A facile screen printing method was utilized to plate Ag paste on the fabric surface as electrodes . In particular, a novel hydrothermal method which requires single precursor solution was employed to synthesize ZnO nanorod arrays. Results reveal ZnO nanorod arrays which are uniformly, densely, and vertically arranged on the surface of Ag coated-fabric, have been synthesized successfully. Atomic force microscope (AFM) analysis proves the ZnO nanorods possess excellent coupled piezoelectric and semiconducting properties. This PENG can harvest the energy from human bodies with output voltages of 4 V, 0.8 V and output currents of 20 nA, 5 nA for palm clapping and finger bending respectively. This kind of ZnO-T-PENG exhibits superior flexibility and wearability with the capability of powering for micro electronic devices, which can promote the development of wearable electronics.
57 citations
TL;DR: In this paper, the free vibration of viscoelastic nanotubes under longitudinal magnetic field is investigated and the governing equation is formulated by utilizing Timoshenko beam model and Kelvin-Voigt model based on the nonlocal strain gradient theory.
Abstract: In this paper, the free vibration of viscoelastic nanotube under longitudinal magnetic field is investigated The governing equation is formulated by utilizing Timoshenko beam model and Kelvin-Voigt model based on the nonlocal strain gradient theory The local adaptive differential quadrature method (LADQM) is applied in the analyzing procedure We also investigated the influences of the nonlocal parameter, structural damping coefficient, material length scale parameter and the longitudinal magnetic field on the natural frequencies of the system The results of this research may be helpful for understanding the potential applications of nanotubes in Nano-Electromechanical System
56 citations
TL;DR: In this paper, the authors performed a theoretical study on the adsorption behaviors of O 3 and SO 3 molecules on two-dimensional stanene sheet in order to fully exploit the promising gas sensing capability of these materials.
Abstract: Recent findings shed light on performing fundamental experiments for preparation of metal monolayer stanene, which is a zero band gap semiconductor material with buckled honeycomb structure . Stanene possesses outstanding physical and mechanical properties , and has been extensively investigated in the field of nanoelectronic devices. We performed a theoretical study on the adsorption behaviors of O 3 and SO3 molecules on two-dimensional stanene sheet in order to fully exploit the promising gas sensing capability of these materials. We examined the most stable structures of O3 and SO3 molecules adsorbed on the stanene, and examined the adsorption process in view of the energetics , charge transfers and electronic structure of the adsorption systems. The results indicate that the adsorption of gas molecules on the B-doped stanene is more favorable in energy than that on the pristine one, representing the superior sensing performance of B-doped system. Our charge analysis based on Mulliken charges reveals a charge transfer from the stanene sheet to the adsorbed O 3 and SO3 molecules, as evidenced by charge accumulation on the adsorbed molecules. This indicates the gas molecules act as charge acceptors from the stanene sheet. The significant overlaps between the PDOS spectra of the interacting atoms indicate the formation of chemical bonds between these atoms. Our findings thus suggest that B-doped stanene could be a highly efficient gas sensor device for SO3 and O3 detection in the environment.
55 citations
TL;DR: In this paper, the uniaxial strain behaviors and carrier mobilities of monolayer 2D GeP are investigated by first principles calculations, and the upper limits of some possible carrier mobility are presented.
Abstract: Recently, two-dimensional (2D) GeP semiconductor was successfully obtained from single crystals using mechanical exfoliation method. In this study, uniaxial strain behaviors and carrier mobilities of monolayer GeP are investigated by first principles calculations. The stretching simulation shows that monolayer GeP can maintain a stable elastic deformation for x axis strain from zero to ɛ = 12.9%, and y axis strain from zero to ɛ = 26.2%. The structural stability can be further verified by the phonon dispersion. Carrier mobility based on acoustic deformation potential scattering mechanism is predicted by the calculations of effective mass, elastic modulus and deformation potential. The upper limits of some possible carrier mobilities are presented, and they can be tuned by uniaxial strain. Combining excellent mechanical properties with moderate band gap and tunable carrier mobility, 2D GeP has a potential application in nanoelectronics and optoelectronics.
TL;DR: One dimensional ternary photonic crystal based refractive index sensor is numerically proposed for the blood plasma sensing applications by introducing the defects or cavity cell, where the blood samples are infiltrated and surrounded by the graphene layers at the middle region of the teranary structures.
Abstract: One dimensional ternary photonic crystal based refractive index sensor is numerically proposed for the blood plasma sensing applications. It is achieved by introducing the defects or cavity cell, where the blood samples are infiltrated and surrounded by the graphene layers at the middle region of the ternary structures. Introduction of the graphene layer is to avoid the change in blood sample characteristics due to few ambient factors. The whole structure is then tuned to observe the transmittance spectrum over the infrared region (800 nm–1200 nm). It is noticed that the resonance spectral shift occurs for variation of the blood plasma samples as 10 g/l, 20 g/l, 30 g/l, 40 g/l & 50 g/l. These spectral shifts report the device sensitivity and it is optimized for different filling factor of nanocomposite material and different thickness of the graphene coating.
TL;DR: In this paper, the capacity of classical interatomic potentials to describe elastic properties of graphene is tested and linear and non-linear elastic response of graphene under uniaxial stretching is investigated by static energy calculations.
Abstract: The capacity of popular classical interatomic potentials to describe elastic properties of graphene is tested. The Tersoff potential, Brenner reactive bond-order potentials REBO-1990, REBO-2000, REBO-2002 and AIREBO as well as LCBOP, PPBE-G, ReaxFF-CHO and ReaxFF-C2013 are considered. Linear and non-linear elastic response of graphene under uniaxial stretching is investigated by static energy calculations. The Young's modulus , Poisson's ratio and high-order elastic moduli are verified against the reference data available from experimental measurements and ab initio studies. The density functional theory calculations are performed to complement the reference data on the effective Young's modulus and Poisson's ratio at small but finite elongations. It is observed that for all the potentials considered, the elastic energy deviates remarkably from the simple quadratic dependence already at elongations of several percent. Nevertheless, LCBOP provides the results consistent with the reference data and thus realistically describes in-plane deformations of graphene. Reasonable agreement is also observed for the computationally cheap PPBE-G potential. REBO-2000, AIREBO and REBO-2002 give a strongly non-linear elastic response with a wrong sign of the third-order elastic modulus and the corresponding results are very far from the reference data. The ReaxFF potentials drastically overestimate the Poisson's ratio. Furthermore, ReaxFF-C2013 shows a number of numerical artefacts at finite elongations. The bending rigidity of graphene is also obtained by static energy calculations for large-diameter carbon nanotubes. The best agreement with the experimental and ab initio data in this case is achieved using the REBO-2000, REBO-2002 and ReaxFF potentials. Therefore, none of the considered potentials adequately describes both in-plane and out-of-plane deformations of graphene.
TL;DR: In this article, a square-shaped plasmonic cavity (SSPC) was laterally coupled to two metal-insulator-metal (MIM) waveguides to create a single-mode plasmoronic bandpass filter.
Abstract: In this paper, first a square-shaped plasmonic cavity (SSPC), which is laterally coupled to two metal-insulator-metal (MIM) waveguides , is used to create a single-mode plasmonic bandpass filter . Thereafter, we try to modify the SSPC topology so that the resonance wavelength (λ r ) of the filter be transferred to higher wavelengths (without increasing the SSPC size). Such a technique is equivalent to less footprint for a fixed operational wavelength. Similar ideas are already being used to decrease the size of microstrip antennas, where defects and slots are introduced to the ground plate and the radiating microstrip patch to make the antenna wideband and compact. For this purpose, we discuss the effect of different possible types of defects on the filter's performance. It is shown that among the studied topologies, the best results are obtained for circular defects with square and triangular patterns in the original SSPC. The proposed topologies can provide an approximately 50% increase in the resonance wavelength. All results are obtained using finite difference time domain method . It is worth mentioning that the metals and insulators used in this paper are silver and air and the Drude model has been used for characterization of the silver.
TL;DR: In this article, the structure, electronic and vibrational properties of all three possible conformations (chair, stirrup and boat) of stanane are studied in detail using density functional theory (DFT) based on an ab-initio technique.
Abstract: The monolayer stanane in chair form is reported to be a novel sensor for environmentally toxic and non-toxic gas molecules for the first time. The structure, electronic and vibrational properties of all three possible conformations (chair, stirrup and boat) of stanane are studied in detail using density functional theory (DFT) based on an ab-initio technique. The interactions and charge transfer of environmentally toxic (NO 2, SO2 and NH3) and non-toxic (CO2) gas molecules on the dynamically most stable hexagonal chair type hydrogenated stanene, viz. stanane has been investigated in detail. The most stable configuration, electronic properties, adsorption energies and charge transfer of these gases on stanane are systematically studied and discussed. The band gap of the pure stanane (0.52 eV) is noticed to be changed after interaction with gases. Moreover, the changes in the energy band gap and charge density is observed upon adsorption of NO2, SO2, NH3 and CO2 gases on p -type stanane based material. The results show that the selectivity of hydrogenated stanene based gas sensors is very important to enhance their sensitivity. It is found that all the gas molecules act as charge donors in which NO 2 gas shows maximum adsorption on the stanane surface along with the maximum charge transfer. The nontrivial affectability and selectivity of stanane demonstrate its potential application in the field of gas sensors and superior impetuses.
TL;DR: In this article, the influence of transition metal atoms (Au, Ag) doping on the structure parameters and electronic properties of MoS2 monolayer was studied based on DFT calculations.
Abstract: The influence of transition metal (TM) atoms (Au, Ag) doping on the structure parameters and electronic properties of MoS2 monolayer was studied based on DFT calculations. In order to realize the adsorption mechanism, the adsorption structures, adsorption energy, charge transfer, density of states (DOS), and electron density difference of water (H2O) molecule absorbed on two kinds of doped-MoS2 monolayer were analyzed. The results show that the electronic properties of TM (Au, Ag) doped-MoS2 monolayer have significantly changes and the chemical activity is obviously enhanced compared with the MoS2 monolayer. Moreover, Au or Ag doped-MoS2 monolayer both exhibits excellent adsorption capacity to H2O molecule and the processes of absorption both are chemical.
TL;DR: In this article, first-principles calculations are carried out to study the structural and electronic properties of square phase MX2 and Janus MXY (M, W; X, Y =S, Se, Te) transition metal dichalcogenide monolayers.
Abstract: In this paper, first-principles calculations are carried out to study the structural and electronic properties of square phase MX2 and Janus MXY (M = Mo, W; X, Y =S, Se, Te) transition metal dichalcogenide monolayers. The bandgaps of unstrained 1S- MX2 range from 25 to 188 meV, while the values of unstrained Janus 1S-MXY range from 30 to 165 meV. For both systems, the octagon bonds are more sensitive than the square bonds in the structure under biaxial strain. The shape of their lowest conduction band near Γ point is observed like a Mexican-hat and it will gradually vanish from the conduction band under increasing tensile strain . 1S-MoSe 2, 1S-MoTe2, 1S-WS2, 1S-WSe2, 1S-MoSeTe, 1S-WSSe and 1S-WSeTe turn to be metallic under certain compressive strains within the range from −6% to −3%. More importantly, Janus 1S-MXY systems intrinsically possess spin splitting due to the broken out-of-plane structural symmetry compared with 1S-MX2. The conduction band and valence band of unstrained 1S-WSTe split about 29 meV and 31 meV, respectively. The results show that compressive strain can enhance the spin splitting and 1S-WSTe monolayer presents the largest splitting of 129 meV under −3% compressive strain.
TL;DR: In this paper, the Monte Carlo simulation has been used to study the magnetic and thermodynamic properties of a cylindrical ferrimagnetic Ising nanowire system with core/shell structure.
Abstract: The Monte Carlo simulation has been used to study the magnetic and thermodynamic properties of a cylindrical ferrimagnetic Ising nanowire system with core/shell structure Phase diagrams are attained with diverse single-ion anisotropies and exchange couplings It is discovered plentiful phase transitions in the nanowire system, for example, the compensation behaviors, the second-order and first-order phase transitions as well as the tricritical point phenomena We have discussed the significant effects of single-ion anisotropies, exchange couplings and temperature on the magnetization, the susceptibility, the internal energy and the specific heat for the cylindrical core/shell nanowire system In addition, we have also found the existence of two types of triple hysteresis loops behaviors for certain physical parameters It is interesting to achieve satisfying results to compare our results obtained with other theoretical and experimental studies
TL;DR: In this paper, the effect of strain engineering and electric field on the electronic properties of single-layer SnSe 2 using density functional theory was investigated, and it was shown that the single layer SnSe2 is a semiconductor with a small band gap of 0.715
Abstract: In this study, we investigate systematically the effect of strain engineering and electric field on electronic properties of single-layer SnSe 2 using density functional theory . Our calculated results indicate that the single-layer SnSe2 is a semiconductor with a small band gap of 0.715 eV at the equilibrium state. The electronic states near the Fermi level are mainly contributed by Sn- d and Se-p orbitals, especially the contribution of the Se-p orbital to the valence band is dominant. Under biaxial strain, the band gap of the single-layer SnSe2 changes abnormally. While compressive biaxial strain reduces band gap rapidly, the band gap of the single-layer SnSe2 only increases slightly when increasing the tensile biaxial strain. In contrast to the strain-dependence case, the influence of the external electric field on the electronic properties of the single-layer SnSe2 is quite small and the energy gap of the single-layer SnSe2 does not depend on the direction of the perpendicular electric field. Our calculated results can provide more information for application possibility of the single-layer SnSe2 in nanoelectronic devices.
TL;DR: In this article, a 2% Ag-TiO2 -rGO microspheres composite showed the best degradation efficiency when degrading Rhodamine B, which caused RhB to degrade 96% in 100min.
Abstract: Photocatalysis technology is considered to be the most industrially feasible way to degrade industrial pollutants due to its low energy consumption and high efficiency. Graphene is considered to be the most potential carrier. Therefore, introducing it into TiO 2 has great significance. In this study, We report Ag nanoparticles - modified TiO2 microspheres deposited on reduced graphene oxide (rGO) sheets material was prepared by two-step hydrothermal method . X-ray diffraction (XRD) analysis confirmed that the TiO 2 microspheres are typical anatase phases and has the presence of Ag nanoparticles. The characterization of Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) indicated that the graphene oxide was well reduced to rGO, which binds well to Ag-TiO 2 microspheres. The prepared 2% Ag-TiO2 -rGO microspheres composite showed the best degradation efficiency when degrading Rhodamine B, which caused RhB to degrade 96% in 100 min. At the same time, The modification of Ag nanoparticles on TiO 2 microspheres facilitates the separation of photogenerated electron-hole pairs of TiO2, and electrons are further transferred to rGO to participate in photocatalytic reactions. In addition, the composite of rGO also increases the specific surface area of the sample, which is more favorable for the adsorption of dye molecules, so that 2% Ag-TiO2-rGO microspheres composite showed the highest efficiency for photodegradation of RhB.
TL;DR: In this article, the authors present an overview of key experimental and theoretical results concerning the thermoelectric properties of nanowires, including phonon scattering at surfaces and interfaces, enhancement of the power factor by quantum effects and topological protection of electron states.
Abstract: Miniaturization of electronic devices aims at manufacturing ever smaller products, from mesoscopic to nanoscopic sizes. This trend is challenging because the increased levels of dissipated power demands a better understanding of heat transport in small volumes. A significant amount of the consumed energy in electronics is transformed into heat and dissipated to the environment. Thermoelectric materials offer the possibility to harness dissipated energy and make devices less energy-demanding. Heat-to-electricity conversion requires materials with a strongly suppressed thermal conductivity but still high electronic conduction. Nanowires can meet nicely these two requirements because enhanced phonon scattering at the surface and defects reduces the lattice thermal conductivity while electric conductivity is not deteriorated, leading to an overall remarkable thermoelectric efficiency. Therefore, nanowires are regarded as a promising route to achieving valuable thermoelectric materials at the nanoscale. In this paper, we present an overview of key experimental and theoretical results concerning the thermoelectric properties of nanowires. The focus of this review is put on the physical mechanisms by which the efficiency of nanowires can be improved. Phonon scattering at surfaces and interfaces, enhancement of the power factor by quantum effects and topological protection of electron states to prevent the degradation of electrical conductivity in nanowires are thoroughly discussed.
TL;DR: In this paper, the effect of GQDs content on the gas sensing responses and the gas-sensing selectivity of the ZnFe2O4/GQDs nanocomposites was investigated.
Abstract: ZnFe2O4 /graphene quantum dots (GQDs) nanocomposites were prepared via hydrothermal method . The as-prepared nanocomposites were characterized by XRD, SEM, TEM, HRTEM , TG, FTIR, Raman, XPS and N 2 adsorption-desorption, respectively. The effect of GQDs content on the gas-sensing responses and the gas-sensing selectivity of the ZnFe2O4/GQDs nanocomposites was investigated. It was found that the sensor based on ZnFe2O4/GQDs nanocomposite (S-15) exhibited good response and good selectivity to acetone vapor at room temperature, the responses of the sensor based on ZnFe2O4/GQDs nanocomposite (S-15) to 1000 ppm acetone and 5 ppm acetone reached 13.3 and 1.2, respectively; the response times and the recovery times for 1000-5 ppm acetone were all shorter than 12 s. The ZnFe2O4/GQDs nanocomposite (S-15) will be a potential acetone sensing materials if its long-term gas sensing stability is improved.
TL;DR: In this article, the magnetic and thermodynamic properties of a ferrimagnetic mixed-spin (1/2, 1, 3/2) nanoisland with a double-layer quadrangle core-shell structure has been investigated by Monte Carlo simulation.
Abstract: Based on the Ising model, the magnetic and thermodynamic properties of a ferrimagnetic mixed-spin (1/2, 1, 3/2) nanoisland with a double-layer quadrangle core-shell structure has been investigated by Monte Carlo simulation. The magnetization of the total system and three sublattices, susceptibility, blocking temperature, internal energy and hysteresis loops have been discussed in detail. The phase diagrams of the TB under the influence of various parameters have been given. We have obtained the critical exponents β and γ for the system. Multiple hysteresis loops behaviors such as single, triple, quintuple and septuple loops have been found, originating from the competitions among various parameters. The results are comparable with some theoretical and experimental studies given in advance.
TL;DR: In this paper, the density functional theory type of first-principles methods was adopted to study the sensitivity of Sc2CO2 to NO and CO in a gas sensor.
Abstract: One of the most important and indispensable applications for 2D materials is toxic gas sensor. By adopting the density functional theory type of first-principles methods, we studied MXenes X 2CO2 (X = Sc, Ti, Zr and Hf) as the gas sensor material to NO and CO. Our calculations show that Sc2CO2 is sensitive to NO molecule due to the chemical interaction and large charge transfer of 0.303 e between them, which will induce current change and then be detected. More importantly, the interaction is further enhanced by applying the external strain, indicating the potential of Sc2CO2 as the gas capturer material. Additionally, the adsorption of CO on Sc2CO2 is significantly improved by Mn doping, which is also detectable due to the strong adsorption energy of −0.85 eV. Our study broadens the application of Sc2CO2 in gas sensor and provides feasible way to enhance the CO sensibility of MXene materials.
TL;DR: In this article, different sizes of Ag2S nanoparticles as a non-toxic semiconductor are prepared onto TiO2 (Titania) electrodes using successive ionic layer adsorption and reaction (SILAR) method for environmental-friendly applications.
Abstract: In this work, different sizes of Ag2S nanoparticles as a non-toxic semiconductor are prepared onto TiO2 (Titania) electrodes using successive ionic layer adsorption and reaction (SILAR) method for environmental-friendly applications. The surface morphology of the prepared Ag 2 S quantum dots (QDs) has been investigated using a scanning electron microscope (SEM). The structural properties of the prepared Ag 2 S photoanodes are studied using an energy dispersive X-ray spectrometer and X-ray diffractometer . The XRD measurements show the formation of the crystalline monoclinic acanthite phase of Ag 2S (α-Ag2 S). The optical properties of the prepared photoanodes were measured using a UV–visible spectrophotometer . The deduced energy band gap of the Ag 2S photoanodes decreases from 3.20 eV to 1.31 eV as the number of SILAR deposition cycles increases from 1 to 9 cycles. This result is mainly attributed to the increase in the size of Ag2S QDs. The prepared Ag2S QDs photoanodes were utilized to fabricate Ag2 S QDs sensitized solar cells (QDSSCs). The photovoltaic performance of the assembled QDSSCs is studied under AM1.5 conditions (100 mW/cm 2). The optimal photovoltaic performance is achieved for six SILAR deposition cycles. This result is mainly attributed to the increase in the absorption of the incident solar power. Ag2S QDSSCs show good reproducibility with rapid sensitivity undercutting ON-OFF illumination.
TL;DR: In this article, the effects of using different precursors on the main properties of the α-Fe2O3 nanoparticles synthesized were studied, namely, the energy band gap and phase purity and chemical bonds of the synthesized nanoparticles.
Abstract: The aim of this study, beside the development of an eco-friendly method for the synthesis α-Fe2O3 nanoparticles, is to study the effects of using different precursors on the main properties of the α-Fe2O3 nanoparticles synthesized. In this regards, we have used a biosynthesis method to synthesis two α-Fe2O3 samples from two different salts as precursors, namely, ferric nitrate and ferric chloride. XRD results confirmed a rhombohedral (hexagonal) structure with the space group R 3 ¯ c in all samples. TEM morphology analysis revealed different shapes for the different samples based on different precursors. The ferric nitrate sample showed quasi-spherical shape with average particles size of 70 nm, while ferric chloride showed growth of a nanorod-based structure with average diameter of 50 nm and length of 400 nm. UV study revealed that the ferric nitrate sample exhibits better optical properties than the ferric chloride sample. The energy band gap Eg obtained from the optical study is 2.53 eV for the ferric nitrate sample and 2.70 eV for the ferric chloride sample. FT-IR study confirms the phase purity and chemical bonds of the nanoparticles synthesized. Mossbauer spectroscopy investigation revealed the weak ferromagnetic nature of the samples.
TL;DR: In this paper, the authors predict and calculate two 1T phase monolayer telluride materials SnTe 2 and SiTe2 with soft mechanics, ultralow κ L and electronic properties.
Abstract: 2H phase (trigonal prismatic D3h ) of layered two-dimensional (2D) transition metal dichalcogenides (TMDs) have attracted a lot of interests due to the superior electronic and optoelectronic properties. However, flexible electronic devices and thermoelectric performances based on 2H phase have been potentially limited by the strain sensitive electronic band gap and high lattice thermal conductivity ( κ L ). Here, we predict and calculate two 1T (octahedral Oh ) phase monolayer telluride materials SnTe 2 and SiTe2 with soft mechanics, ultralow κ L and electronic properties. The calculated in-plane Young's modulus of monolayer SnTe 2 is softer than most of 1T-MX2 compounds. Furthermore, monolayer SiTe2 and SnTe2 also have relatively flexible electronic properties under large biaxial strain, indicating potential flexible electrode materials. Meanwhile, monolayer SiTe 2 and SnTe2 both exhibit ultralow κ L (2.27 W/mK of SiTe2 and 1.62 W/mK of SnTe2) at room temperature. Considering both acoustic and polar optical phonon scattering of the electronic relaxation time, the figure of merit (ZT) can achieve 0.46 at 600 K and 0.71 at 900 K for monolayer SiTe2 and SnTe2 respectively.
TL;DR: In this paper, a ZrO2/Fe2O3/RGO nanocomposite was synthesized via insitu-hydrothermal method and characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (FESEM), energy dispersive x-ray (EDX), UV-Visible diffuse reflectance spectrophotometer (DRS), Raman, Photoluminescence (PL) and BET analysis to study the structural, morphological and optical properties.
Abstract: We report a ZrO2/Fe2O3/RGO nanocomposite was synthesized via insitu -hydrothermal method and characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (FESEM), energy dispersive X-ray (EDX), UV–Visible diffuse reflectance spectrophotometer (DRS), Raman, Photoluminescence (PL) and BET analysis to study the structural, morphological and optical properties. FESEM images declares that ZrO 2 particles are uniform discs like nanostructure shape with clear facets and narrow size distribution; Fe 2O3 were agglomerated, which leads to have completely dispersed with the rGO and forms a ZrO2/Fe2O3/RGO nanocomposite. The elemental composition (Zr, Fe, O and C) of as-prepared ZrO2/Fe2O3 /RGO nanocomposite was confirmed using EDX. FTIR and Raman analysis confirmed the GO was reduced into RGO during the synthesis of ZrO 2/Fe2O3 /RGO nanocomposite. The synthesized catalysts were examined for photocatalytic activity by the degradation of Congo Red (CR) and Acetophenone (AP) under visible light illumination, these results clearly prompted that ZrO 2/Fe2O3/RGO nanocomposite shows a high photodegradation efficiency of CR and AP under visible light illumination than ZrO2/Fe2O3, pure Fe2O3 and pure ZrO2.
TL;DR: In this paper, the effects of metal and non-metal doping on the structural and electronic properties of stanene were examined in detail, and it was shown that codoping of aluminum and phosphorous atoms into stanenes opens up a wider band gap.
Abstract: Density functional theory calculations were carried out to investigate the band gap variations in stanene, and the effects of metal and nonmetal doping on the structural and electronic properties of stanene were examined in detail. Various metal and nonmetals were considered to be substituted into the tin vacancy of stanene. The results suggest that Al P codoped stanene shows a sizeable band gap of about 0.07 eV, while the pristine stanene is a gapless material. Moreover, codoping of aluminum and phosphorous atoms into stanene monolayer opens up a wider band gap in comparison with the individual aluminum-doped and phosphorous-doped systems. Band structure calculations were performed to further investigate the band gap tuning in stanene. In Al-doped stanene, the Fermi level is shifted to the valence band edge, indicating that Al-doped stanene is a metallic system. In contrast, in P-doped system, the Fermi level shifts to the conduction band edge. Formation energy calculations indicate that Al P codoping is energetically more favorable than P-doping than Al-doping. Charge analysis based on Mulliken charges indicates that the Al atoms were positively charged, whereas P atoms negatively charged. Total electron density distribution plots show the charge accumulation on the surface, and consequently formation of chemical bonds between the dopants and tin atoms. Based on the obtained results, we found that AlP-codoped stanene exhibits a semiconductor characteristics, whereas mon-doping of Al or P atoms provides a metallic system. Our results thus suggest a theory basis for AlP-codoped stanene monolayer for application in next-generation nanoelectronic devices.
TL;DR: In this paper, the authors reported the synthesis of CdSe/ZnS/CdSe core-shell quantum dots and their optical properties using TEM, absorbance and photoluminescence emission.
Abstract: We report the synthesis of CdSe, CdSe/ZnS core-shell and CdSe/ZnS/CdSe core-shell-shell quantum dots (QDs) and their optical properties. These core-shell QDs are characterized by using TEM, absorbance and photoluminescence emission. The absorption spectra of QDs reveals that blue and red shift observed as shells capped onto the core. The luminescence spectra of core-shell QDs have shown two bands, one is due to the coupling of core and shell and the second band is because of defect states. From TEM, the size of the core and shell are found. Nonlinear optical properties such as nonlinear absorption and nonlinear refraction of the QDs are investigated by the Z-scan technique using 532 nm with picosecond laser. The nonlinear absorption of QDs show reverse saturable absorption due to two-photon absorption and have large nonlinear refractive indexes . CdSe/ZnS and CdSe/ZnS/CdSe core-shell QDs have high third-order susceptibility about on order of 10 −12 esu. The large optical nonlinearities allow these QDs to be one kind of candidate materials for fluorescence label, bioimaging, optical limiting and all-optical switching of photonics .