Screening of Water Dipoles Inside Finite-Length Armchair Carbon Nanotubes

The electronic structure and dielectric screening of finite-length armchair carbon nanotubes are studied with both tight-binding and ab initio methods. Good agreement is found in the band gap oscillation patterns and dielectric constants, which validates the tight-binding method as a reliable and fast approach to describe the screening effect of carbon nanotubes. For an illustration, our method is applied to a system consisting of a short (6,6) nanotube filled with six water molecules. Substantial screening of the water dipoles through the nanotube is observed. This polarization effect should have an important influence on the permeation of water and other biomolecules inside carbon nanotubes.     

Electronic properties of graphyne nanotubes filled with small fullerenes: a density functional theory study

The encapsulation of small fullerenes into graphyne nanotubes was studied to investigate the possibility of band gap engineering in these nanotubes. The electronic properties of zigzag (4,0) and (5,0) graphyne nanotubes filled with small \(\hbox {C}_{20}\) and \(\hbox {C}_{30}\) fullerenes were studied using density functional theory. It was found that the zigzag (4,0) and (5,0) graphyne nanotubes were semiconductors. These graphyne nanotubes filled with \(\hbox {C}_{20}\) and \(\hbox {C}_{30}\) fullerenes were shown p-type and n-type semiconducting properties, respectively. The energy band gap was dependent on the number of the encapsulated fullerenes. Our results demonstrated the ability of band gap engineering through the encapsulation of small fullerenes into graphyne nanotubes.     

Basis-set choice for DFT/NEGF simulations of carbon nanotubes

We investigate the effect of the choice of the basis set on the results of ab initio (density functional theory/non-equilibrium Green’s function) calculations of the bandgap of semiconducting carbon nanotubes, and near-zero-bias conductance of metallic carbon nanotubes. Both ideal and deformed carbon nanotubes are studied, as well as nanotubes with an adsorbed biomolecule. The results show that the near-zero-bias conductance of armchair nanotubes can be calculated accurately with a minimal basis set, with the exception of the (2,2) tube, where a polarized basis set is necessary to accurately predict the metallic behaviour of this tube. For zigzag tubes, a double-zeta polarized basis set is in general required for accuracy in bandgap and near-zero-bias conductance calculations.     

超支化聚芳酰胺接枝氮化硼/环氧复合材料的制备与性能研究

采用两步法将超支化聚芳酰胺接枝到氮化硼粒子表面,并将其掺入到环氧树脂中,制备了一系列复合材料,并对复合材料的微观形貌、玻璃化转变温度、导热性能及电气强度进行了测试研究。结果表明:超支化聚芳酰胺接枝氮化硼粒子在环氧树脂中有较好的分散性,复合材料的电气强度、玻璃化转变温度和导热系数均得到了提高。     

Studies of the mechanism of boron nitride thin-film formation by means of nitrogen-argon gas mixture plasma jet

The mechanism of boron nitride thin-film formation using the nitrogen-argon gas mixture plasma jet, which is a new method reported in our previous paper, has been studied. The electron temperature, electron density, and magnitudes of various ion and radical species in the plasma jet have been measured by an electrostatic probe and by optical spectroscopic methods. The amount of recombination of free nitrogen atoms by three-body conversion was estimated using the emission intensity of the first positive band system from nitrogen B state vibrational level v = 11. The emission intensity from vibrational level v = 11 in the vicinity of the boron target shows a more than one order of magnitude increase than when the boron target is absent, and the peak value occurs at a gas pressure of approximately 5 Torr to 10 Torr. Experimental data are discussed in connection with the optimum discharge condition of BN synthesis in the plasma. It is concluded that enhanced recombination on the boron target and substrate surface supplies large amounts of molecular nitrogen ions and vibrationally excited nitrogen molecules in the vicinity of the substrate, and thus that the high-energy ion-rich condition makes it possible to form a cubic BN film on the substrate surface placed in the plasma jet. © 1997 Scripta Technica, Inc. Electr Eng Jpn, 120(4): 1–6, 1997     

DFT study on structural,electronic, and optical properties of cubic and monoclinic CuO

First-principles calculations were made to explore the structural, electronic, and optical properties of copper oxide (CuO) with monoclinic (m-CuO) and cubic (c-CuO) structures. We calculated the equilibrium structural parameters: lattice parameters (a, b, and c), angle \(\beta \), and volume V. The obtained results were in good agreement with the experimental data reported in the literature. The cohesive energy showed that m-CuO is more stable than c-CuO. The band structure indicated that c-CuO is an indirect band gap semiconductor with a band gap of 0.87 eV along R–G, while m-CuO has a metallic behavior. Furthermore, electrovalent and covalent bonds were observed in both c-CuO and m-CuO. The linear optical properties were calculated and analyzed along different polarization directions of the incident light. The results indicated that m-CuO possesses optical anisotropic properties. In particular, c-CuO can be used as a potential UV detector material because of its high absorption coefficient (356351.3).     

Structural,electronic, and optical properties of C-type $$\hbox {Gd}_{2}\hbox {O}_{3}$$: a density functional theory investigation

Recently, \(\hbox {Gd}_{2}\hbox {O}_{3}\) has gained considerable interest in industry, and its optical applications have been of interest in optoelectronic. The band structure and optical properties of cubic \(\hbox {Gd}_{2}\hbox {O}_{3}\) are investigated using the density functional theory framework. Calculations are performed within the local density approximation and generalized gradient approximation, adding the empirical Hubbard potential U. Calculation of the electronic band structure indicates a direct \({\Gamma }\) band gap. Further, the total and partial densities of states were presented, and the contribution of different orbitals is analyzed. Moreover, the behavior of optical spectra such as real and imaginary part of dielectric function, refractive index, extinction coefficient, optical conductivity, and electron energy-loss function is analyzed. There is a good agreement between the computed results and reported experimental data.     

Effect of Fe – substitution on phase transformation,optical, electrical and dielectrical properties of BaTiO<Subscript>3</Subscript> nanoceramics synthesized by sol-gel auto combustion method

The structural, microstructural, optical, electrical and dielectrical properties of nanocrystalline Fe substituted BaTiO₃ synthesized by sol-gel auto combustion have been investigated. The X-ray diffraction (XRD) analysis revealed the existence of the tetragonal phase for lower Fe content (x = 0.0–0.3) whereas, coexistence of the tetragonal and hexagonal structure of higher Fe content (x = 0.4 and 0.5). The lattice constant (a and c) and unit cell volume (V) increases with increase in Fe content; and an average crystallite size (t) was recorded in the range of ~14–20 nm. The surface morphology as examined using field emission scanning electron microscopy (FESEM) and the compositional stoichiometry was confirmed by energy dispersive spectrum (EDS) analysis. The UV-Vis spectra showed that the band gap energy sensitively depends on the Fe concentration x. DC-electrical conductivity (σ) was recorded in the temperature range of 333–714 K which was found to be increases with increasing temperature and Fe concentration; indicating that an electrical conduction was a thermally activated process. The type of temperature dependent DC conductivity indicates that the electrical conduction in the material is a thermally activated process. The dependencies of the conductivity contributions were predicted from the simple defect model presented, in which oxygen vacancies charge compensate Fe substitution of Ti. Dielectrical property was measured as a function of frequency in the range 50 Hz - 5 MHz at room temperature which was found to be higher at lower frequencies. Dielectric constant (ε’) and loss tangent (tan δ) shows strong compositional as well as frequency dependences.     

First-Principle Study of Cl Functionalized Zigzag AlN Nanoribbons

Abstract

We employed density functional theory (DFT)-based first-principle calculations to reveal the structural stability and electronic properties of zigzag AlN nanoribbons (ZAlNNR) functionalized with Cl. Considered structures were found to be energetically feasible. A pure metallic character has been observed for one edge Cl functionalization, whereas for rest of the others, the band gap varies from 2.2?eV to 3.9?eV. Interestingly, a transition from indirect to direct band gap has been obtained for semiconducting ribbons due to Cl functionalization. Present findings show that Cl functionalization could be useful for the band gap engineering and absolute shifting of Fermi level in ZAlNNR.     

A first-principles study of the structural,elastic, electronic,vibrational, and optical properties of BaSe<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Te<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>

The structural, elastic, electronic, vibrational, and optical properties of BaSe_1?xTe_x alloys are investigated by means of the full-potential linearized augmented plane wave method. The exchange–correlation effects are treated with the local density approximation, as well as the GGA-PBE, GGA-PBEsol, and GGA?+?mBJ schemes of the generalized gradient approximation. Ternary BaSe_1?xTe_x compounds have not yet been synthesized. Improved predictions of the structural parameters are obtained using the GGA-PBEsol approach. Calculations of the electronic and optical properties with the GGA?+?mBJ approach yield accurate results. Ternary BaSe_1?xTe_x alloys are wide-band-gap semiconductors with a direct gap Γ–Γ. The upper valence band is mainly due to Se p and Te p states, while the bottom of the conduction band results essentially from Ba d states. The dielectric function, refractive index, reflectivity, absorption coefficient, and energy-loss function are calculated in the range 0–35 eV. The increase in x gives rise to a redshift of the optical spectra. BaSe_1?xTe_x alloys exhibit reflective properties of metals in some energy ranges. The static dielectric constant ?₁(0) and the static refractive index n₀ are calculated. The investigation of the elastic and vibrational properties shows that ternary BaSe_1?xTe_x should be mechanically and dynamically stable, elastically anisotropic, brittle, and relatively soft.     

Design and analysis of a gate-all-around CNTFET-based SRAM cell

This paper proposes a highly stable and low power 6-T static random access memory (SRAM) cell design using a gate-all-around carbon nanotube field effect transistor (GAA-CNTFET). The 6-T SRAM cell is designed and analyzed in HSPICE for different performance metrics viz. SNM, read SNM, write SNM, delay, and leakage power for both the top gate CNTFET and the GAA-CNTFET. The effect of variation of the power supply voltage on the leakage current is also presented, and it was found that the GAA-CNTFET accounts for low power dissipation at higher supply voltage. The 6-T SRAM cell is analyzed for different flat band conditions of the p-type CNTFET taking flatband of the n-type as constant, which is called a dual flat band voltage technique. Through simulations, it is found that by increasing the flatband voltage of a p-type CNTFET, the SRAM gives better performance. The dual flatband variation technique is compared with dual chirality technique, and it is observed that both techniques give the same results.     

模板法合成的CoFe2O4纳米管的结构与磁性

利用阳极氧化铝(AAO)模板,用化学方法合成了三种不同孔径的CoFe2O4(CFO)纳米管.X射线衍射(XRD)分析表明,纳米管由无择尤取向、立方尖晶石结构的多晶CoFe2O4构成;透射电镜(TEM)观察显示,随着纳米管直径的增大,管壁厚度和CoFe2O4颗粒直径随之增大;进一步的磁性测量表明,纳米管阵列的矫顽力、磁滞回线的矩形比也随着纳米管直径的增大而增大.     

Corrosive resistance of nitride coatings of steam turbine blades

Results from tests of multilayer nitride Ti _x N and (TiAlZrMo) _x N coatings resistance to downtime and high-temperature corrosion in steam are presented.     

Impact of channel length,gate insulator thickness,gate insulator material,and temperature on the performance of nanoscale FETs

Aggressive technology scaling as per Moore’s law has led to elevated power dissipation levels owing to an exponential increase in subthreshold leakage power. Short channel effects (SCEs) due to channel length reduction, gate insulator thickness change, application of high-k gate insulator, and temperature change in a double-gate metal–oxide–semiconductor field-effect transistor (DG MOSFET) and carbon nanotube field-effect transistor (CNTFET) were investigated in this work. Computational simulations were performed to investigate SCEs, viz. the threshold voltage (V_th) roll-off, subthreshold swing (SS), and I_on/I_off ratio, in the DG MOSFET and CNTFET while reducing the channel length. The CNTFET showed better performance than the DG MOSFET, including near-zero SCEs due to its pure ballistic transport mechanism. We also examined the threshold voltage (V_th), subthreshold swing (SS), and I_on/I_off ratio of the DG MOSFET and CNTFET with varying gate insulator thickness, gate insulator material, and temperature. Finally, we handpicked almost similar parameters for both the CNTFET and DG MOSFET and carried out performance analysis based on the simulation results. Comparative analysis of the results showed that the CNTFET provides 47.8 times more I_on/I_off ratio than the DG MOSFET. Its better control over the threshold voltage, near-zero SCEs, high on-current, low leakage power consumption, and ability to operate at high temperature make the CNTFET a viable option for use in enhanced switching applications and low-voltage digital applications in nanoelectronics.     

Fabrication and Characterization of Titania (TiO2) Nanotube Dye-Sensitized Solar Cells by Anodization Method

Titania (TiO₂) nanotubes were synthesized on Ti metal sheets by anodization method. The anodization condition was the variation of the anodization voltage. The nanotubes were characterized by using scanning electron microscopy (SEM), X-ray diffraction (XRD) and UV-vis Spectrometer. The nanotubes can be used to make working electrodes for dye-sensitized solar cells. The pore diameter of TiO₂ nanotube increases with the higher anodization voltage. The TiO₂ nanotube diameters prepared at applied voltages of 40, 50, 60 and 70 V were approximately 200, 170, 140 and 100 nm, respectively. Furthermore, the dye-sensitized solar cells device based on the N719 dye and electrolytes shows the photovoltaic performance at different voltages of 40, 50, 60 and 70 V were 4.21%, 4.77%, 6.10% and 6.89%, respectively, under irradiation of 60 mW/cm². The energy conversion efficiency of the dye-sensitized solar cells increased with increasing pore diameter of titania nanotubes.     

Atomistic tight-binding simulations of quaternary-alloyed $$\hbox {Zn}_{x}\hbox {Cd}_{1-x}\hbox {S}_{y}\hbox {Se}_{1-y}$$ nanocrystals

Advancement of alloyed nanocrystals with attractive structural and optical properties for use in a wide range of physical, chemical, and biological applications represents a growing research field. Employing atomistic tight-binding theory combined with the virtual crystal approximation, the electronic structure and optical properties of quaternary-alloyed \(\hbox {Zn}_{{x}}\hbox {Cd}_{1-{x}} \hbox {S}_{{y}}\hbox {Se}_{1-{y}}\) nanocrystals with experimentally synthesized compositions (x and y) and sizes were investigated. Analysis of the results shows that the physical properties are mainly sensitive to the concentrations (x and y) and the diameter. With decreasing x and y contents, the optical bandgap is reduced because the contributions of the materials with narrower bulk bandgap (ZnSe and CdSe) is mostly promoted. The optical bandgap is reduced with increasing diameter due to the quantum confinement effect. The optical bandgap calculated based on tight-binding calculations shows discrepancy of less than 0.4 eV from experiment. Most importantly, the optical emission is continuously tunable across the entire visible spectrum. The conduction and valence bands are predominantly contributed by cation and anion atoms, respectively. The optical properties are obviously improved in Cd- and Se-rich quaternary \(\hbox {Zn}_{{x}}\hbox {Cd}_{1-{x}} \hbox {S}_{{y}}\hbox {Se}_{1-{y}}\) nanocrystals with large diameter. The atomistic electron–hole interactions can be hybrid-engineered by tuning either the contents (x and y) or diameter. The Stokes shift becomes more pronounced with decreasing alloy concentrations (x and y) and diameter, as described by the trend of the atomistic electron–hole exchange interaction. The present systematic study provides a new avenue to understand the unique size- and composition-dependent structural and optical properties of quaternary-alloyed \(\hbox {Zn}_{{x}}\hbox {Cd}_{1-{x}} \hbox {S}_{{y}}\hbox {Se}_{1-{y}}\) nanocrystals for broad use in multicolor bioimaging, biosensing, light-emitting diodes, solar cells, and other nanodevice applications.     

Electromechanical properties of ternary BiFeO<Subscript>3</Subscript>−0.35BaTiO<Subscript>3</Subscript>–BiGaO<Subscript>3</Subscript> piezoelectric ceramics

In the present work, composition dependent crystal structure, ferroelectric, piezoelectric, and temperature dependent dielectric properties of the BiGaO₃-modified (1–x)(0.65Bi_1.05FeO₃–0.35BaTiO₃) (BFBT35–xBG, where x?=?0.00–0.03) lead-free ceramics were systematically investigated by solid-state reaction method, followed by water quenching process. The substitution of BG successfully diffuses into the lattice of the BFBT ceramics, without changing the pseudo-cubic structure of the samples. The scanning electron microscopy (SEM) results revealed that the average grain size was increased with BG-content in BFBT system. The BFBT–xBG ceramics showed a maximum in permittivity (?_max) at temperatures (T_max) above 500 °C in the compositional range of 0.00?≤?x?≤?0.03. The electro-strain is measured to be 0.125% (d^*₃₃ ~ 250 pm/V) under unipolar fields (5 kV/mm) for BFBT–0.01BG ceramics. The same composition (x?=?0.01), large static piezoelectric constant (d₃₃ ~ 165 pC/N) and electromechanical coupling factor (k_p ~ 25%) were obtained. The above investigated characterizations suggests that BFBT–BG material is favorable for piezoelectric and high temperature applications.     

Fabrication of MgO-coated TiO2 nanotubes and application to dye-sensitized solar cells

Dye-sensitized solar cells (DSCs) are more spotlighted than conventional photovoltaic devices due to their relatively low cost, easy fabrication and high efficiency. However, there are limitations to increase the conversion efficiency of DSCs. The limiting factors are the quantity of dye adsorption and charge recombination between TiO₂ electrode and electrolyte. Coating other materials such as high energy band gap insulators or semiconductors on the TiO₂ electrode enhances dye adsorption and reduces charge recombination. We fabricated DSCs based on bare TiO₂ nanotube arrays and 0.02 and 0.04 M MgO coated TiO₂ nanotube arrays. MgO layer increased the photovoltage and photocurrent. The overall conversion efficiency of DSCs using 0.02 M MgO coated TiO₂ nanotubes was 1.61%. MgO formed insulating layers between TiO₂ nanotube array electrode and electrolyte. Charge recombination was inhibited at the interfaces of TiO₂ nanotube array electrode and electrolyte by MgO insulating layers. MgO coating also improved dye adsorption because iso-electric point (IEP) of MgO was larger than TiO₂. When the IEP of coating material is larger than TiO₂, the chemical attraction between the electrode surface and Ru-based dye molecule is increased.     

Effects of Al<Superscript>3+</Superscript> substitution on the luminescence properties of LuNbO<Subscript>4</Subscript> doped with Eu<Superscript>3+</Superscript> and Tb<Superscript>3+</Superscript> ions

The effect of Al³⁺ substitution on the enhancement of the luminescence of Lu_1–xAl_xNbO₄:Eu³⁺ and Lu_1–xAl_xNbO₄:Tb³⁺ was investigated. X-ray diffraction patterns confirmed that the Eu³⁺, Tb³⁺, and Al³⁺ ions were fully incorporated into the Lu³⁺ sites. In the case of Lu_1–xAl_xNbO₄:Eu³⁺, the predominant red emission (614 nm) was assigned to the ⁵D₀?→?⁷F₂ transition of Eu³⁺ and for x?=?0–0.05, its intensity increased up to ~125 and 108% under 395 nm (⁷F₀ → ⁵L₆) and a charge transfer band excitation, respectively. For Lu_1–xAl_xNbO₄:Tb³⁺, the strongest emission band peaking at 551 nm was attained in the green region among multiple emission bands corresponding to the ⁵D₄?→?⁷F_J transitions of Tb³⁺. Increasing the x values from 0 to 0.05 increased the green emission significantly by ~137%. These phenomena were explained by the local structural distortions and crystal field asymmetry surrounding Eu³⁺ and Tb³⁺, which were attributed to a large difference in the ionic radii of Al³⁺ and Lu³⁺.