High‐mobility solution‐processed zinc oxide thin films on silicon nitride

A high effective electron mobility of 33 cm² V^–1 s^–1 was achieved in solution‐processed undoped zinc oxide (ZnO) thin films. The introduction of silicon nitride (Si₃N₄) as growth substrate resulted in a mobility improvement by a factor of 2.5 with respect to the commonly used silicon oxide (SiO₂). The solution‐processed ZnO thin films grown on Si₃N₄, prepared by low‐pressure chemical vapor deposition, revealed bigger grain sizes, lower strain and better crystalline quality in comparison to the films grown on thermal SiO₂. These results show that the nucleation and growth mechanisms of solution‐processed films are substrate dependent and affect the final film structure accordingly. The substantial difference in electron mobilities suggests that, in addition to the grain morphology and crystalline structure effects, defect chemistry is a contributing factor that also depends on the particular substrate. In this respect, interface trap densities measured in high‐κ HfO₂/ZnO MOSCAPs were about ten times lower in those fabricated on Si₃N₄ substrates. (© 2014 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)

     

Mn掺杂ZnO稀磁半导体材料的制备和磁性研究

采用共沉淀方法制备了名义组分为Zn_1-xMn_xO(x=0.001,0.005,0.007,0.01)的Mn掺杂的ZnO基稀磁半导体材料,并研究了在大气气氛下经过不同温度退火后样品的结构和磁性的变化.结果表明：样品在600℃的大气条件下退火后, 仍为单一的六方纤锌矿结构的ZnO颗粒材料;当样品经过800℃退火后,Mn掺杂量为0.007,0.01的样品中除了ZnO纤锌矿结构外还观察到ZnMnO₃第二相的存在.磁性测量表明,大气条件下600℃退火后的样品,呈现出室温铁磁性;而800℃退火后的样品,其室温铁磁性显著减弱,并表现为明显的顺磁性.结合对样品的光致发光谱的分析,认为合成样品的室温铁磁性是由于Mn离子对ZnO中的Zn离子的替代形成的. 关键词： ZnO 掺杂 稀磁半导体 铁磁性     

Vibrational spectroscopic study of poly(dimethylsiloxane)-ZnO nanocomposites

A series of poly(dimethylsiloxane)-zinc oxide (PDMS-ZnO) nanocomposites having different concentrations of ZnO nanoparticles (0, 1, 5, 10 and 20 wt%) have been prepared. Raman and FTIR-ATR spectroscopic analysis was performed in order to determine the interaction between the ZnO nanoparticles and PDMS polymer matrix. Density functional theory (DFT) using the (B3-LYP)/6-311++G(2df,2p) method was used to investigate the vibrational spectra of PDMS. A complete vibrational assignment is supported by the normal coordinate analysis, calculated Raman activities as well as IR intensities.The presence of ZnO nanoparticles in PDMS gives rise to significant differences in relative intensities of the characteristic vibrational bands with respect to the cross-linked polymer. The changes in relative intensities of Raman bands, as well as swelling measurements, were used to explain the effect of ZnO nanoparticles on the cross-linked structure of PDMS nanocomposites. It is established that ZnO nanoparticles influence the cross-linking density of the polymer matrix.     

High-quality oriented ZnO films grown by sol-gel process assisted with ZnO seed layer

High-quality oriented ZnO films were prepared on silicon and quartz glass by sol-gel, assisted with a ZnO seed layer. The effects of the seed layer on the orientation, morphology and optical properties of ZnO films were investigated. Results show that the seed layer can effectively induce the growth of high-quality oriented ZnO films on two substrates, and the effectiveness of the seed layer strongly depends on preparation conditions, i.e., the spin-coating layer number and the preheating temperature. ZnO films with five layers on the seed layer preheated at 500 °C exhibit the single (0 0 2) orientation, which is much stronger than that on the flat substrate. Additionally, ZnO films on the seed layer show a denser internal structure and higher optical quality than that on the flat substrate. At ten layers, however, ZnO films on the seed layer show the multiple-orientation, which is similar to that on the flat substrate. Finally, the physical mechanism underlying the growth behavior of ZnO films assisted with the seed layer was discussed.     

Imidazole derivatives as the organic precursor of ZnO nano particle

N₁-Hydroxy-2,4,5-trisubstituted imidazoles were synthesized starting from 1,2-diketones. The crystal structure of 4,5-dimethyl-2-(3-nitrophenyl)-1H-imidazol-1-ol has been determined. An unusual intermolecular hydrogen bonding through the association of water molecule has been reported. These imidazole derivatives can be thought of as the organic precursor for the synthesis of zinc oxide nano particles.     

First-principle study on the effect of high Li-2N co-doping on the conductivity of ZnO

Based on the density functional theory (DFT), using first-principles plane-wave ultrasoft pseudopotential method, the models of the unit cell of pure ZnO and two highly Li-2N co-doped supercells of Zn_0.9375Li_0.0625O_0.875N_0.125 and Zn_0.9167Li_0.0833O_0.8333N_0.1667 were constructed, and the geometry optimization for the three models was carried out. The total density of states (TDOS) and the band structures (BS) were also calculated. The calculation results showed that in the range of high doping concentration, when the co-doping concentration is more than a certain value, the conductivity decreased with the increase of co-doping concentration of Li-2N in ZnO, which agrees with the change trend of the experimental results.     

Synthesis and Photocatalytic Properties of Coupled Nanocrystalline ZnO/ZnS in Nation Membrane

T The coupled nanocrystalline ZnO/ZnS was fabricated and immobilized in Nafion membrane by using sodium sulfide (Na_2S) as the single anion precursor. The molar ratio of ZnO to ZnS can be controlled by simply adjusting the reaction time. The as-prepared ZnO/ZnS-Nafion samples were characterized by various methods, including optical absorption, X-ray diffraction and high-resolution transmission electron microscopy. These coupled ZnO/ZnS nanocrystals embedded in Nafion membrane displayed excellent photocatalytic activities for their efficient charge separation properties. A mechanism of ZnO/ZnS nanoparticle fabrication in Nation was deduced from the solubility difference, and the photocatalytic mechanism of coupled ZnO/ZnS was discussed as well.     

Room-temperature ferromagnetism of Cu ion-implanted Ga-doped ZnO

1 MeV Cu²⁺ ions have been implanted into un-doped ZnO and Ga-doped ZnO films with a dose of 1 × 10¹⁷ ions/cm² at room-temperature. Cu ion-implanted Ga-doped ZnO had ferromagnetism at room-temperature and the saturation magnetization of this sample was estimated to be 0.12 μ_B per Cu, while the Cu ion-implanted un-doped ZnO did not show ferromagnetic behavior. Near-edge X-ray fine structure (NEXAFS) spectroscopy revealed that a partial amount of implanted Cu ions existed as Cu²⁺ (d⁹) state in Ga-doped ZnO film. On the other hand, almost Cu atoms existed as Cu¹⁺ (d¹⁰) state in un-doped ZnO film. However, the subsequent annealing at temperature above 800 °C on this ferromagnetic sample induced the annihilation of ferromagnetism due to the formation of non-ferromagnetic Cu₂O phase.     

单晶ZnO、TiO_2纳米线拉伸力学特性的分子动力学研究

采用分子动力学方法,模拟了不同加载速度、不同温度下单晶ZnO、TiO_2纳米线的拉伸破坏过程.通过模拟结果,对比、分析了两种单晶金属氧化物纳米线拉伸力学特性的差异.研究表明,1)ZnO纳米线的断裂机制为:表面微裂纹-微孔-微裂纹与微孔贯穿-断裂,而TiO_2纳米线的断裂机制为:局部屈服-颈缩-断裂;2)TiO_2纳米线的承载能力优于ZnO纳米线,而承受变形的能力劣于ZnO纳米线;3)温度较低的情况下,纳米线的抗拉性能较好;加载速度越高,纳米线的抗载性能越好,而抗变形能力越差.