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1.
This work presents a study of the adsorption properties of defective nanostructures. The calculations have quantum mechanical detail and are based on a semi-empirical Hamiltonian, which is applied to the evaluation of both the electronic structure and of the conductance. The material considered in this study, i.e. SnO2, has a widespread use as gas sensor and oxygen vacancies are known to act as active catalytic sites for the adsorption of small molecules. In the following calculations crystalline SnO2 nanograins, with a size and shape comparable with the experimental ones, have been considered. The grains lattice, which has the rutile structure of the bulk material, includes oxygen vacancies and the adsorbed system is generated by depositing a gaseous molecule, either CO or O2, above an atom on the grain surface. The calculations show that the presence of the defects enhances the grain cohesion and favors adsorption. The conductance has a functional relationship with the structure and the defective state of the nanograins and its dependence on these quantities parallels the one of the binding energy. 相似文献
2.
Gd-doped SnO2 nanoparticles were chemically prepared doping 0-12.5% Gd into SnO2 and calcined at 600 °C. X-ray diffraction and Fourier transformed infrared spectroscopy measurements show the formation of single phase of Sn1−xGdxO2 up to x=0.0625 while at x=0.125, an additional secondary phase of tetragonal GdO2 (not cubic Gd2O3) is detected. The transmission electron microscopy studies show that the individual particles are single crystalline with an average size in the range of 10-12 nm. Magnetization measurements show the absence of ferromagnetic and antiferromagnetic ordering in all samples; however surface spin effects and enhanced Gd-O-Gd interactions are proposed to account for the observed magnetic properties of the samples. 相似文献
3.
在室温及不同的氧氩比条件下,采用射频磁控溅射Ag层和直流磁控溅射SnO2层,在载玻片衬底上制备出了SnO2/Ag/SnO2多层薄膜.用霍尔效应测试仪、四探针电阻测试仪和紫外-可见-近红外光谱仪等表征了薄膜的电学性质和光学性质.实验结果表明:当氧氩比为1:14时,所制得的薄膜的光电性质优良指数最大,为1.69×10-2 Ω-1;此时,薄膜的电阻率为9.8×10-5 Ω·cm,方电阻为9.68 Ω/sq,在400~800 nm可见光区的平均光学透射率达85%;并且,在氧氩比为1:14时,利用射频磁控溅射Ag层和直流磁控溅射SnO2层在PET柔性衬底上制备出了光电性质优良的柔性透明导电膜,其在可见光区的平均光学透过率达85%以上,电阻率为1.22×10-4 Ωcm,方电阻为12.05 Ω/sq. 相似文献
4.
First-principles calculations have been carried out to investigate intrinsic defects including vacancies, interstitials, antisite defects, Frenkel and Schottky defects in the 312 MAX phase Ti3SiC2. The formation energies of defects are obtained according to the elemental chemical potentials which are determined by the phase stability conditions. The most stable self-interstitials are all found in the hexahedral position surrounded by two Ti(2) and three Si atoms. For the entire elemental chemical potential range considered, our results demonstrated that Si and C related defects, including vacancies, interstitials and Frenkel defects are the most dominant defects. Besides, the present calculations also reveal that the formation energies of C and Si Frenkel defects are much lower than those of all Schottky defects considered. In addition, the calculated profiles of densities of states for the defective Ti3SiC2 indicate that these defects should have great influence on its thermal and electrical properties. 相似文献
5.
Hui Yang Ruilin Han Yu Yan Xiaobo Du Qing Zhan Hanmin Jin 《Journal of magnetism and magnetic materials》2012
The electronic structures and magnetic properties of Zn- and Cd-doped SnO2 are investigated using first-principles calculations within the generalized gradient approximation (GGA) and GGA+U scheme. The substitutional Zn and Cd atoms introduce holes in the 2p orbitals of the O atoms and the introduced holes are mostly confined to the minority-spin states. The magnetic moment induced by doping mainly comes from the 2p orbitals of the O atoms, among which the moment of the first neighboring O atoms around the dopant are the biggest. The U correction for the anion-2p states obviously increases the moment of the first neighboring O atoms and transforms the ground states of the doped SnO2 from half-metallic to insulating. The magnetic coupling between the moments induced by two dopants is ferromagnetic and the origin of ferromagnetic coupling can be attributed to the p–d hybridization interaction involving holes. 相似文献
6.
Pascal Ifeacho Hartmut Wiggers Paul Roth 《Proceedings of the Combustion Institute》2005,30(2):2577-2584
SnO2/TiO2 mixed oxides with primary particle size ranging between 5 nm dp 12 nm were synthesized by doping a H2/O2/Ar flame with Sn(CH3)4 and Ti(OC3H7)4 co-currently. The effects of “flow coordinate,” concentration and flame configurations were investigated with respect to particle size and morphology of the generated mixed oxides. In situ characterization of the mixed oxides was performed using the particle mass spectrometer (PMS), while XRD, TEM, BET and UV–Vis were performed ex situ. Results obtained showed that primary particle size of mixed oxides can be controlled by varying experimental parameters. The mixed oxides have interesting properties compared to those of the pure oxides of TiO2 and SnO2, which were also synthesized in flames earlier. Band gap tuning opportunities are possible using mixed oxides. 相似文献
7.
Experimental and theoretical study of silicon-doped Sb2Te3 thin films: Structure and phase stability
Xuelai Li Feng RaoZhitang Song Kun Ren Weili LiuZhimei Sun 《Applied Surface Science》2011,257(10):4566-4568
The influence of Si in Sb2Te3 on structure and phase stability was studied by experiments and ab initio calculations. With the increase of Si content in Sb2Te3 samples, the crystallization temperature increases and the crystalline grain size decreases. The incorporation of Si atoms into Sb2Te3 lattice is energetically unfavorable and hence Si atoms most probably accumulated in the boundaries of Sb2Te3 grains. 相似文献
8.
Surachet Phadungdhitidhada Suvit Thanasanvorakun Pongsri Mangkorntong Supab Choopun Nikorn Mangkorntong Duangmanee Wongratanaphisan 《Current Applied Physics》2011,11(6):1368-1373
Mixed morphology of SnO2 nanowires and nanodendrites was synthesized on the gold-coated alumina substrates by carbothermal reduction of SnO2 in closed crucible. The products were characterized by scanning electron microscopy, x-ray diffractometer, and transmission electron microscopy. Results showed the SnO2 nanowires and the SnO2 nanodendrites branched out from the main nanowires. Both SnO2 nanostructures were pure tetragonal rutile structure. The nanowires were grown in [101] and directions with the diameter of 50–150 nm and the length of a few 10 μm. The nanodendrites were about 100–300 nm in diameter. The growth mechanism of the SnO2 nanostructures was also discussed. Characterization of ethanol gas sensor, based on the mixed morphology of the SnO2 nanostructures, was carried out. The optimal temperature was about 360 °C and the sensor response was 120 for 1000 ppm of ethanol concentration. 相似文献
9.
Byeong-Guk KimDong-Gun Lim Jae-Hwan Park Young-Jin ChoiJae-Gwan Park 《Applied Surface Science》2011,257(10):4715-4718
A simple and efficient way of making highly sensitive SnO2 nanowire-based gas sensors without an individual lithography process was studied. The SnO2 nanowires network was floated upon the Si substrate by separating the Au catalyst layer from the substrate. As the electric current is transported along the networks of the nanowires, not along the surface layer on the substrate, the gas sensitivities could be maximized in this networked and floated structures. The sensitivity was 5-30 when the NO2 concentration was 1-10 ppm. The response time was ca. 20-60 s. 相似文献
10.
Results of magnetic measurements suggested that Bi2S3 and ZnS nanocrystalline powders prepared by hydrothermal method could possibly exhibit room temperature ferromagnetism. The measured saturation magnetization of the powders increases with an increase of annealing temperature from 300 to 500 °C. Ab initio calculations suggested that the cation vacancies on the surface of Bi2S3 and ZnS nanograins could be responsible for the observed magnetic moments. Heat-treatment of Bi2S3 or ZnS nanocrystalline powders in Bi or Zn vapor could bring about an enhancement of ferromagnetism. The calculation results indicated that the interstitial Bi or Zn atoms in Bi2S3 (0 0 1) or ZnS (0 0 1) surface could induce magnetic moments. 相似文献
11.
Ashok B. Bhise Niranjan S. Ramgir Imtiaz S. Mulla Dilip S. Joag 《Applied Surface Science》2007,253(23):9159-9163
Field emission studies of a bunch and a single isolated RuO2:SnO2 wire have been performed. A current density of 5.73 × 104 A/cm2 is drawn from the single wire emitter at an applied field of 8.46 × 104 V/μm. Nonlinearity in the Fowler-Nordheim (F-N) plot has been observed and explained on the basis of electron emission from both the conduction and the valence bands of the semiconductor. The current stability recorded at the preset value of 1.5 μA is observed to be good. Overall the high emission current density, good stability and mechanically robust nature of the RuO2:SnO2 wires offer advantages as field emitters for many potential applications. 相似文献
12.
We studied in detail the atomic and electronic structure of the LaMnO3 surfaces, in both cubic and orthorhombic phases, combining GGA-plane wave approach, as implemented into the VASP-4.6.19 computer code, with a slab model. These studies are complemented by a thermodynamic analysis of the surface stability at different gas pressures and temperatures. The obtained results are compared with similar studies for other ABO3-perovskites. 相似文献
13.
We focused on the effects of the inorganic acid HNO3 on the gas-sensing properties of nanometer SnO2 and prepared the powders via a dissolution-pyrolysis method. Furthermore, the powders were characterized by means of X-ray diffraction (XRD), scanning electron microscope (SEM), field emission scanning electron microscopy (FESEM) and energy-dispersive X-ray spectra (EDS). Several aspects were surveyed, including the calcining temperature, concentration of nitric acid and the working temperature. The results showed that the gas response of 3 wt% HNO3-doped SnO2 powders (calcined at 500 °C) to 10 ppm Cl2 reached 316.5, at the working temperature 175 °C. Compared with pure SnO2, appropriate HNO3 could increase the gas sensitivity to Cl2 gas more significantly. 相似文献
14.
Aligned tin dioxide (SnO2) nanotubes have been synthesized by high-frequency inductive heating. Nanotubes with high yield were grown on silicon substrates in less than 5 min, using SnO2 and graphite as the source powder. Scanning electron microscopy and transmission electron microscopy showed nanotube with diameters from 50 to 100 nm and lengths up to tens of mircrometers. The SnO2 nanotubes synthesized under the optimum condition have better field-emission characteristics. The turn-on field needed to produce a current density of 10 μA/cm2 is found to be 1.64 V/μm. The samples show good field-emission properties with a fairly stable emission current. This type of SnO2 nanotubes can be applied as field emitters in displays as well as vacuum electric devices. 相似文献
15.
SnO2 crystals with various morphologies were prepared by a facile hydrothermal method in the simple solution systems of SnCl2 and SnCl4, respectively. This process was carried out under mild conditions and required no high-temperature heat treatment. The morphological evolution with the preparation conditions was investigated. Various self-assembled hierarchical structures including microspheres assembled with nanoparticles, oriented nanocones, and flower-like, cabbage-like structures consisting of single-crystalline nanosheets were obtained by varying the solvent and the introduction of polyethylene glycol. A possible mechanism for the formation of the spherical hierarchically structures assembled by cone-like nanocrystals was proposed. 相似文献
16.
SnO2 thin films undoped and doped with antimony (Sb), erbium (Er) and Si nanocrystals (Si-nc) have been grown on silicon (Si) substrate using sol-gel method. Room-temperature photoluminescence (PL) measurement of undoped SnO2, under excitation at 280 nm, shows only one broad emission at 395 nm, which is related to oxygen vacancies. The PL of Er3+ ions was found to be enhanced after doping SnO2 with Sb and Si-nc. The excitation process of Er is studied and discussed. The calculation of cross-section suggests a sensitisation of Er PL by Si-nc. 相似文献
17.
The structural, elastic, magnetic and electronic properties of the layered tetragonal phase KCo2Se2 have been examined in details by means of the first-principles calculations and analyzed in comparison with the isostructural KFe2Se2 as the parent phase for the newest group of ternary superconducting iron-chalcogenide materials. Our data show that KCo2Se2 should be characterized as a quasi-two-dimensional ferromagnetic metal with highly anisotropic inter-atomic bonding owing to mixed ionic, covalent, and metallic contributions inside [Co2Se2] blocks, and with ionic bonding between the adjacent [Co2Se2] blocks and K sheets. This material should behave in a brittle manner, adopt enhanced elastic anisotropy rather in compressibility than in shear, and should show very low hardness. 相似文献
18.
The extensive investigation of the annealing effect in nitrogen atmosphere on the structural optical and electrical properties of chemically deposited CdS films on SnO2 has been performed. The as-deposited film shows 2.45 eV band gap (Eg) and decreases with increasing annealing temperature. The film annealed at 623 K having pure hexagonal phase (a = 4.14 Å, c = 6.71 Å for [1 0 0] plane) and Eg = 2.36 eV shows 10 times higher conductivity for all temperature range, and shows two different activation energies Ea = 0.114 eV and Ea = 0.033 eV for the temperature range 395 K ≤ T ≤ 515 K and 515 K ≤ T ≤ 585 K, respectively. The structural parameters such as dislocation density, strain and optical parameters such as absorption and extinction coefficient are calculated and compared for all the films. 相似文献
19.
In this study, SnO2/TiO2 thin films are fabricated on SiO2/Si and Corning glass 1737 substrates using a R.F. magnetron sputtering process. The gas sensing properties of these films under an oxygen atmosphere with and without UV irradiation are carefully examined. The surface structure, morphology, optical transmission characteristics, and chemical compositions of the films are analyzed by atomic force microscopy, scanning electron microscopy and PL spectrometry. It is found that the oxygen sensitivity of the films deposited on Corning glass 1737 substrates is significantly lower than that of the films grown on SiO2/Si substrates. Therefore, the results suggest that SiO2/Si is an appropriate substrate material for oxygen gas sensors fabricated using thin SnO2/TiO2 films. 相似文献
20.
SnO2:Eu and SnO2:Eu nanoparticles dispersed in silica matrix were prepared at a relatively low temperature of 185 °C in ethylene glycol medium. For as-prepared SnO2:Eu nanoparticles there exists a weak energy transfer from the SnO2 host to the Eu3+ ions. However, the energy transfer can be significantly improved by dispersing the Eu3+-doped SnO2 nanoparticles in silica matrix. Effective shielding of surface Eu3+ ions in SnO2:Eu nanoparticles from the stabilizing ligand by silica matrix is the reason for the improved extent of energy transfer. Increase in asymmetric ratio of luminescence (ratio of the intensity of the electric dipole allowed transition, 5D0→7F2, to magnetic dipole allowed transition, 5D0→7F1) for SnO2:Eu nanoparticles dispersed in silica compared to that of SnO2:Eu nanoparticles, has been attributed to the distorted environment around surface Eu3+ ions brought about by the presence of both tin and silicon structural units. 119Sn and 29Si MAS NMR studies on this sample confirmed that there is no interaction between the tin and silicon structural units even after heating the samples at 900 °C. 相似文献