Comparison of electronic structures of doped ZnS and ZnO calculated by a first-principle pseudopotential method

Electronic band calculations of doped and undoped ZnO and ZnS have been done using density functional theory under the local density approximation so as to clarify the reason of the difference in behaviors of doped ZnO and ZnS. The reason why the electrical conductivity of ZnS is difficult to be increased by doping was discussed. In the case of doped ZnS, an impurity level was generated at deep position below the bottom of the conduction band of the host ZnS lattice and Fermi level was located at this impurity level. On the contrary, the shape of the density of states curve and the band structures of doped and undoped ZnO are alike with each other and the donor band is hybridized with the conduction band of the ZnO host material. This seems to result in contribution of doped electrons to electrical current in the case of doped ZnO.     

Electronic structures of Mg3Pn2 (Pn=N, P, As, Sb and Bi) and Ca3N2 calculated by a first-principle pseudopotential method

Electronic structure calculations for Mg₃N₂, Mg₃P₂, Mg₃As₂ (low and high temperature modifications), Mg₃Sb₂, Mg₃Bi₂, and Ca₃N₂ have been performed. Mg₃Sb₂ is predicted to be an indirect semiconductor with the gap value of about 0.41 eV. Mg₃As₂ with a high temperature modification is also predicted to be a semiconductor with the gap value of about 1.1 eV, but the valence band maximum and the conduction band minimum of Mg₃Bi₂ contacts at Γ which would make it a semimetal. Mg₃N₂, Mg₃P₂, and Mg₃As₂ (low temperature phase) are semiconductors with the direct band gaps of 1.64 eV, 1.73 eV, and 1.57 eV, respectively. Ca₃N₂ is a semiconductor with a gap of about 1.2 eV.     

Deposition of Al doped ZnO layers with various electrical types by atomic layer deposition

AlZnO thin films with various Al/Zn composition ratios were deposited by atomic layer deposition (ALD) at 200 °C. The effect of the composition of the AlZnO films on their electrical and optical characteristics was investigated. The AlZnO films with an Al content of up to 10 at.% showed high conductivity, while further increasing in the Al content resulted in the abrupt formation of an insulating oxide film. The lowest electrical resistivity of the ALD-deposited AlZnO film was 6.5 × 10^− 4 [Ω cm] at 5 at.% Al. The AlZnO films with up to 5 at.% Al exhibited crystalline phases and a near-band-edge emission. With increasing Al content, the optical band edge showed a blue shift, and a sudden shift associated with an insulating bandgap was observed in the AlZnO films containing 20 at.% Al.     

Controllable synthesis of ZnO with various morphologies by hydrothermal method

ZnO microstructures with various morphologies have been controllably synthesized by hydrothermal route using different precipitant and zinc source in liquid solution. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize the ZnO2, Zn(OH)2 and ZnO structures to understand the role of precipitant and precursors in the growth of various morphologies. The nucleation and growth process can regulate by changing the precipitant. When H2O2 was used as precipitant, ZnO particles with a rather uniform particle size of -500 nm and a rather rough surface was obtained. While, ZnO synthesized in this polyvinyl pyrrolidone (PVP) solution has the same granular morphology with particle size of 300-1000 nm. In contrast, ZnO sunflower and polyhedron aggregates composed of several smaller polyhedron were formed, when ammonium hydroxide and NH4HCO3 was applied, respectively. Meanwhile, precursors play an important role in the determination of the morphology of ZnO. Sunflower and dumbbell like ZnO composed of nanosheets were obtained, when different centrifugal component of Zn(OH)2 suspension was applied as zinc source. In contrast, sunflower and dumbbell like ZnO composed of nanorods and ZnO rods were obtained, when different centrifugal components of ZnO2 suspension were used as zinc sources. The growth mechanism of ZnO nanostructures fabricated by the hydrothermal process using different zinc sources was tentatively investigated.     

Synthesis of linear ZnO structures by a thermal decomposition method and their characterisation

The semiconductor zinc oxide (ZnO) is a promising material for applications in optoelectronics, photochemistry and chemical sensing. Furthermore, ZnO structures can be grown with a large variety of sizes and shapes. Devices with ZnO rods or wires as their core elements can be used in solar cells, gas sensors or biosensors. In this article, an easy approach for the non-aqueous wet chemical synthesis of ZnO structures is presented that employs the solvent trioctylamine (TOA) and the surfactant hexamethylenetetramine (HMTA). Using the thermal decomposition method, rod-shaped structures were grown that are suitable for the fabrication of electrical devices. A detailed study was carried out to investigate the effects of various reaction parameters on the growth process. Both the concentration of the surfactant HMTA and the zinc precursor zincacetylacetonate (Zn(acac)₂) were found to show strong effects on the resulting morphology. In addition to structural characterisation using XRD, SEM and TEM, also optical properties of rod-shaped ZnO structures were measured. Rod-shaped structures were obtained for the following conditions: reaction time 4 h, reaction temperature 70 °C, 1 mmol of Zn(acac)₂, 4 mmol of HMTA and 25 mL of the solvent TOA. Photoluminescence and photoluminescence excitation spectroscopy of samples grown under these conditions provided information on levels of defect states that could be critical for chemical sensing applications. Two narrow peaks around 254 and 264 nm were found that are well above the band gap of ZnO.     

Optical and magnetic properties of copper doped ZnO nanorods prepared by hydrothermal method

Surfactant free ZnO and Cu doped ZnO nanorods were synthesized by hydrothermal method. The formation of ZnO:Cu nanorods were confirmed by scanning electron microscopy, X-ray diffraction and Raman analysis. Diffuse reflectance spectroscopy results shows that band gap of ZnO nanorods shifts to red with increase of Cu content. The orange-red photoluminescent emission from ZnO nanorods originates from the oxygen vacancy or ZnO interstitial related defects. ZnO:Cu nanorods showed strong ferromagnetic behavior, however at higher doping percentage of Cu the ferromagnetic behavior was suppressed and paramagnetic nature was enhanced. The presence of non-polar E ₂ ^high and E ₂ ^low Raman modes in nanorods indicates that Cu doping didn’t change the wurtzite structure of ZnO.     

Optical properties of Ag doped ZnO nanocrystals prepared by hydrothermal and photodeposition method

Ag/ZnO nanocomposites have been synthesized by facile hydrothermal and photodeposition method. The effect of different concentration of Ag on the luminous intensity of ZnO was studied. The morphology, structure and optical properties of Ag/ZnO were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence (PL), respectively. The XRD patterns show that intensities of diffraction peaks of Ag/ZnO were enhanced. The weak diffraction peak at 38.28° can be assigned to Ag₂O when the concentration of Ag increased to 0.09 M. PL results demonstrate that the UV luminous intensity of ZnO was significantly influenced by the concentration of Ag. The UV luminous intensity of Ag/ZnO nanocomposites increased by 11 times as compared with undoped ZnO when the concentration of Ag was 0.03 M due to the local surface plasma resonance effect of Ag nanoparticles.     

The effect of annealing on properties of europium doped ZnO nanopowders obtained by a microwave hydrothermal method

Europium doped ZnO nanopowders made by microwave hydrothermal method are investigated. As zinc oxide precursor zinc nitrate(V) hexahydrate (Zn(NO₃)₂·6H₂O) was used. Two types of nanopowder samples are examined: as grown and annealed at 750 °C in air atmosphere. We investigate the structural, morphological and optical prosperities of europium doped ZnO. Results of scanning electron microscopy, X-ray diffraction, photo- and cathodoluminescence investigations and also CIE1961 chromaticity diagram are presented.     

Fabricating Co doped ZnO nanocrystallines by hydrothermal method with high pulsed magnetic field

Co-doped ZnO nanocrystallines were fabricated by hydrothermal method with high pulsed magnetic field. As a new preparation method, more refined grains and diluted magnetic semiconductors (DMSs) with better performance could be obtained by the hydrothermal synthesis process under pulsed magnetic field. The samples were tested by X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM), Vibrating Sample Magnetometer (VSM) and Raman scattering spectrum. The results show that the sample prepared under pulsed magnetic field has wurtzite structure with tiny crystal lattices changes. Doping Co ions into ZnO crystal lattice is also improved. Curie temperature of 2% Co doped ZnO nanocrystallines synthesized with 4T pulsed magnetic field is higher than that for without magnetic field process, and very close to the room temperature.     

Study of thermodynamic properties of liquid binary alloys by a pseudopotential method

On the basis of the Percus–Yevick hard-sphere model as a reference system and the Gibbs–Bogoliubov inequality, a thermodynamic perturbation method is applied with the use of the well-known model potential. By applying a variational method, the hard-core diameters are found which correspond to a minimum free energy. With this procedure, the thermodynamic properties such as the internal energy, entropy, Helmholtz free energy, entropy of mixing, and heat of mixing are computed for liquid NaK binary systems. The influence of the local-field correction functions of Hartree, Taylor, Ichimaru–Utsumi, Farid–Heine–Engel–Robertson, and Sarkar–Sen–Haldar–Roy is also investigated. The computed excess entropy is in agreement with available experimental data in the case of liquid alloys, whereas the agreement for the heat of mixing is poor. This may be due to the sensitivity of the latter to the potential parameters and dielectric function.     

Luminescent properties of ZnO structures grown with a vapour transport method

ZnO structures were synthesised on the sapphire (112?0) substrate by a vapour transport method in a gas flowing furnace. The influence of the oxygen content in the gas mixture on the morphology and luminescent properties of ZnO structures grown on a strip-like substrate was investigated, with all other growth parameters being kept nominally identical. Integrated electron microscopy and cathodoluminescence analysis shows gradual variations of structural and optical emission properties for ZnO structures grown on the long substrate. Defect-related green luminescence of ZnO is found to be highly dependent on the oxygen vapour in the growth region of the furnace. Our findings demonstrate that the green luminescence is associated with oxygen deficiency in ZnO.     

Optical and magnetic properties of Mn doped ZnO thin films grown by SILAR method

Polycrystalline Mn doped ZnO (MZO) semiconductor thin films were deposited onto glass substrates employing different number of dipping at room temperature using Successive Ionic Layers by Adsorption Reaction (SILAR) technique. The thin film deposition conditions were optimized by altering the various deposition parameters based on their structure. The structural study was carried out using X-ray diffractometer (XRD). The XRD analysis indicated that there is no change in the structure of ZnO thin films due to Mn doping. The films exhibited hexagonal wurtzite structure. The structural studies on Mn doped samples revealed that the predominant orientation is (002) lattice plane and the position of this orientation shifted toward lower angle during doping. The intensity of photoluminescence (PL) emission of ZnO is found to be augmented for Mn doped samples. The room temperature Raman spectra measurements revealed the presence of additional modes. The Vibrating Sample Magnetometer (VSM) studies show that MZO thin film has ferromagnetic properties.     

高压对Gd掺杂ZnO的电子结构和磁性影响研究

压力可以作用于物质的晶体结构内部,影响并改变物质整体性质.为进一步探究高压对Gd掺杂ZnO试样的电子结构及磁性影响,运用金刚石对顶砧压机和Materials Studio4.4软件包中的CASTEP运算程序,完成高压实验制备工作;利用基于密度泛函理论的第一性原理计算高压作用下Gd掺杂ZnO试样内部分子的变化情况,并对G...     

The properties of Al doped ZnO thin films deposited on various substrate materials by RF magnetron sputtering

Transparent conductive Al-doped ZnO (AZO) thin films were deposited on various substrates including glass, polyimide film (PI) and stainless steel, using radio frequency magnetron sputtering method. The structural, electrical and optical properties of AZO thin films grown on various substrates were systematically investigated. We observe that substrate materials play important roles in film crystallization and resistivity but little on optical transmittance. X-ray diffractometer study shows that all obtained AZO thin films have wurtzite phase with highly c-axis preferred orientation, and films on glass present the strongest (002) diffraction peaks. The presence of compression stress plays critical role in determining the crystalline structure of AZO films, which tends to stretch the lattice constant c and enlarge the (002) diffraction angle. Although the films on the glass present the finest electrical properties and the resistivity reaches 12.52 × 10-4 Ωm, AFM study manifests that films on flexible substrates, especially stainless steel, bestrew similar inverted pyramid structure which are suitable for window material and electrode of solar cells. The average optical transmittance of AZO thin films deposited on glass and PI are both around 85% in the visible light range (400–800 nm).     

In situ formation of Mn-doped ZnO aligned structures by rapid heating method

ZnO tetrapods and Mn doped multipods have been prepared by a rapid thermal oxidation at 1220 °C during 6 min. Moreover, Mn doped ZnO nearly aligned nanostructures forming carpets over sintered pellets have been produced by the same method without the use of catalyst or gas flow. These rods show two different diameters, one of 500 nm and the other one of 300 nm, with lengths of 5 µm. XRD and Raman spectra demonstrate a good crystalline quality of the doped nanostructures. The room temperature photoluminescence shows a quenching of the intrinsic UV emission band on the ZnO tetrapods, due to an increase of material defects.     

Ca掺杂纤锌矿ZnO电子结构和光学性质的第一性原理研究

采用第一性原理的超软赝势方法,对ZnO、Ca掺杂ZnO的电子结构和光学性质进行了研究。结果表明,能隙宽度随掺杂浓度的增大而增大;掺杂后ZnO的光学性质发生了一些变化,静态介电常数总趋势随着掺杂浓度的增大而减小;与纯ZnO吸收谱相比,Ca掺杂后出现了新吸收峰,吸收边发生蓝移,介电函数虚部也出现了新波峰。