Electron field emission from ZnO self-organized nanostructures and doped ZnO:Ga nanostructured films

Self-organized ZnO nanostructures were grown by thermal decomposition of metalorganic precursors as well as by carbothermal reduction process. Nanostructured undoped and gallium-doped ZnO nanostructured films were deposited by plasma-enhanced chemical vapor deposition from metalorganic compounds. Electron field emission follows Fowler-Nordheim equation. Efficient electron emission was obtained from self-organized nanostructures due to their geometric shape. Enhanced field emission from ZnO:Ga nanostructured films in comparison with undoped ZnO films is obliged to lowering work function at doping by gallium.     

B掺杂ZnO纳米薄膜的结构和光学特性研究

采用脉冲磁控溅射法制备了B掺杂ZnO(ZnO:B)纳米薄膜,并用X射线衍射(XRD)、扫描电子显微镜(SEM)和紫外-可见-近红外分光光度计分别研究了薄膜的结构和光学特性。结果表明:ZnO:B为多晶纳米薄膜,具有六方钎锌矿结构,且薄膜沿着c轴取向择优生长;在可见光和近红外光谱区的透光性能良好,其中在可见光区的平均透光率大于84%,而在近红外区的透光率随着波长增加而逐渐降低至45%。运用逐点无约束最优化法分析计算了薄膜的光学常数,在可见光区,ZnO:B纳米薄膜的光学常数随波长的变化很小且数值基本恒定,折射率约为2.0,而在紫外区,光学常数随波长的变化显著。     

Magnetic Properties of Fe-Implanted ZnO Nanotips Grown by Metal-Organic Chemical Vapor Deposition

Fe ions were implanted into well-aligned single-crystal ZnO nanotips grown on SiO₂/quartz substrates using metal-organic chemical vapor deposition (MOCVD). The Fe ion concentration distribution within a single nanotip is mapped by electron energy loss spectroscopy (EELS) and energy dispersive spectroscopy (EDS) and the nanotips imaged by high-resolution transmission electron microscopy (TEM). X-ray absorption spectroscopy (XAS) identified the presence of Fe²⁺ and Fe³⁺ ions in both as-implanted and annealed samples. However, Fe³⁺ ion concentration increased during postannealing. Superconducting quantum interference device (SQUID) measurements show that the as-implanted and postannealed ZnO nanotips are ferromagnetic at room temperature. The observed ferromagnetism in the as-implanted nanotips is primarily attributed to the near surface 10-nm region that has high Fe concentration. The saturation magnetization reduces after annealing.     

锰掺杂ZnO稀磁半导体的制备及铁磁性能

用溶胶-凝胶法,在超声波辅助条件下制备了Mn掺杂ZnO(Zn1-xMnxO,x≤0.05)稀磁半导体(DMS)纳米晶粉末样品.用透射电子显微镜(TEM)、X射线衍射(XRD)仪、超导量子干涉(SQUID)测磁仪分别对样品形貌、结构和磁性能进行了表征.较低的掺杂浓度下样品很好地保持ZnO的纤锌矿结构,随着掺杂浓度x的增加,样品的晶格常数近似线性增大,没有观察到杂质相.样品Zn0.98Mn0.02O显示了很好的铁磁性,居里温度在350 K以上.     

掺杂钛酸钡薄膜的合成及性能研究

通过化学溶液沉积法制备的BiFeO3-BaTiO3薄膜在室温下能够同时显现铁电性和铁磁性。在600℃至700℃的条件下,以Pt/TiOx/SiO2/Si为载体,能够成功得到钙钛矿单相0.7BiFeO3-0.3BaTiO3薄膜。随着结晶温度上升,晶粒持续增长,最终在700℃时到达更高的结晶度。由于0.7BiFeO3-0.3BaTiO3薄膜的绝缘电阻较低,它所显现的极化(P)-电场(E)磁滞回线较弱。尽管如此,在0.7BiFeO3-0.3BaTiO3薄膜铁的位置上添加锰,高作用场的漏电流有效地减少,最终铁电性质得到了提高。在室温下,添加了摩尔分数5%的锰的0.7BiFeO3-0.3BaTiO3薄膜同时显现铁电极化和铁磁磁化磁滞回线。     

Properties of nanostructured Al doped ZnO thin films grown by spray pyrolysis technique

Aluminium doped zinc oxide thin films were deposited on glass substrate by using spray pyrolysis technique. The X-ray diffraction study of the films revealed that the both the undoped and Al doped ZnO thin films exhibits hexagonal wurtzite structure. The preferred orientation is (002) for undoped and up to 3 at % Al doping, further increase in the doping concentration to 5 at % changes the preferred orientation to (101) direction. The surface morphology of the films studied by scanning electron microscope, reveal marked changes on doping. Optical study indicates that both undoped and Al doped films are transparent in the visible region. The band gap of the films increased from 3.24 to 3.36 eV with increasing Al dopant concentration from 0 to 5 at % respectively. The Al doped films showed an increase in the conductivity by three orders of magnitude with increase in doping concentration. The maximum value of conductivity 106.3 S/cm is achieved for 3 at % Al doped films.     

绒面AZO最新研究进展及应用

掺铝氧化锌(AZO)透明导电膜作为一种光电性能优异的透明导电膜(TCO)受到研究人员的广泛关注,并被认为是当前大规模使用的传统铟锡氧化物(ITO)的替换材料。绒面AZO薄膜因其电阻率低、高透过率且具有良好的陷光效果,可以提高太阳能电池的光电转换效率,而被认为是太阳能电池前电极的理想材料。综述了绒面AZO透明导电膜的制备方法和性能研究现状,并针对AZO的国内外研究状况提出了今后的发展趋势和研究方向。     

Elaboration and characterization of Co-doped ZnO thin films deposited by spray pyrolysis technique

The structure and the nature of magnetism of ZnO and Zn_1−xCo_xO (CZO) thin films (0?x?0.09) deposited on glass substrate at 450 °C by spray pyrolysis technique is investigated. All the CZO thin films have the ZnO wurtzite structure with a preferential orientation along the c-axis and had no impurity phase. This was also confirmed by transmission electron microscopy analysis. Transmission UV-visible spectroscopy showed that Co²⁺ was well substituted for the Zn²⁺ ions in the ZnO matrix. Magnetization measurements at low temperature show that CZO thin films present a paramagnetic behaviour and no sign of ferromagnetism.     

Growth and characterization of OMVPE grown (In,Mn)As diluted magnetic semiconductor

In_1−xMn_xAs diluted magnetic semiconductor (DMS) thin films with x 0.14 have been grown using organometallic vapor phase epitaxy. Tricarbonyl-(methylcyclopentadienyl)manganese was successfully used as the Mn source. Single phase, epitaxial films were achieved for compositions as high as x=0.14 using growth temperatures ≥475°C. For lower growth temperatures or x>0.14, nanometer scale MnAs precipitates were observed within the In_1−xMn_xAs matrix. Transport properties were investigated using the Hall effect. All Mn doped films were p-type with single phase films exhibiting hole concentrations 2≤×10¹⁹ cm⁻³. Magnetization was measured as a function of temperature and applied field for a single phase film with x=0.1. Ferromagnetic ordering was observed at 5 K with a saturation magnetization of M_s=68 emu/cm³, a remnant magnetization, M_r=10 emu/cm³, and a coercive field H_c=400 Oe.     

退火气氛对稀土Eu3+掺杂ZnO薄膜结构和发光性质的影响

采用脉冲激光沉积(PLD)法在Si(111)衬底上制备稀土Eu3+掺杂ZnO薄膜材料,分别在纯氧和真空气氛中进行退火处理。XRD图谱中仅观察到尖锐的ZnO(002)衍射峰,表明ZnO:Eu3+,Li+薄膜具有良好的c轴取向。薄膜的结构参数显示：在纯氧气氛中退火的样品具有较大的晶粒尺寸且应力较小,表明在纯氧中退火的样品具有较好的结晶质量。通过光致发光谱发现,在纯氧中退火的样品的IUV/IDL比值较大,说明在纯氧中退火的样品缺陷去除更充分,结晶质量更好。当用395nm光激发样品时,仅发现Eu3+位于595nm附近的5D0→7F1磁偶极跃迁峰。并没有发现Eu3+在613 nm附近的特征波长发射,表明掺杂的Eu3+占据了ZnO基质反演对称中心格位。     

Al-Zr共掺杂ZnO透明导电薄膜制备及光电性能研究

采用直流磁控溅射法,在室温水冷玻璃衬底上制备出Al-Zr共掺杂的ZnO透明导电薄膜。研究结果表明,Ar气压强对Al-Zr共掺杂ZnO透明导电薄膜的结构和电阻率有显著影响。X射线衍射(XRD)表明,Al-Zr共掺杂ZnO透明导电薄膜为六角纤锌矿结构的多晶薄膜,且具有C轴择优取向。扫描电镜(SEM)观察表明,Ar气压强对Al-Zr共掺杂ZnO透明导电薄膜的微观结构影响较大。薄膜的厚度随Ar气压强的增加而变薄,在Ar气压强为2.5Pa时,制备的Al-Zr共掺杂ZnO薄膜电阻率具有最小值1.01×10-3Ω.cm,在可见光区(500～800nm)平均透过率超过93%。     

Characterization of ZnO and ZnO:Al films deposited by MOCVD on oriented and amorphous substrates

Zinc oxide (ZnO) and ZnO:Al-doped films were deposited by metal organic chemical vapour deposition (MOCVD) using the Zn(tta)₂·tmeda (H-tta=2-thenoyltrifluoroacetone, tmeda=N,N,N′,N′-tetramethylethylendiamine) and Al(acac)₃ (H-acac=acetylacetone) precursors on different substrates. The deposited layers were characterised by X-ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM). Film structure is strongly dependent on the substrate nature and deposition conditions. AFM and XRD measurements show a good film texture and a preferential orientation along the c-axis. The Al concentration of ZnO:Al film has been confirmed by energy dispersive X-ray (EDX) analysis. Optical transparency of these ZnO layers has been studied in order to evaluate their applications as a transparent conducting oxide (TCO) material.     

低压高温退火对Ag掺杂ZnO薄膜性质的影响

采用电子束蒸发在n-Si(100)衬底上沉积Ag掺ZnO(ZnO:Ag)薄膜,随后在200 Pa的O<,2>气氛下分别在500、600、700和800℃退火4 h.用X射线衍射(XRD)仪、荧光光谱仪以及Van der Pauw方法测量ZnO:Ag薄膜的结构和光电学性质.结果表明,ZnO:Ag薄膜为多晶结构,且随着退火...     

Spin-coated ZnO thin films using ZnO nano-colloid

Using ZnO nano-colloids, thin films of ZnO have been deposited and characterized. The nano-colloid has been synthesized using a top-down wet chemistry method starting from submicron ZnO particles. The steric stabilization technique is implemented using stearic acid as a capping agent to prevent agglomeration of the ZnO nanoparticles. A stable suspension is achieved, exhibiting strong optical absorbance and a band edge at 376 nm. The simple chemistry enables a uniform film on a variety of substrates using spin coating. Current-voltage (I–V) measurements of ZnO films deposited on quartz after annealing treatment show a resistivity of 1.89×10⁵ Ω · cm.     

Facile deposition of ZnO:Cu films: Structural and optical characterization

Sol–gel technology has been applied for preparation of ZnO:Cu films. The proposed facile approach allows obtaining a wide variety of copper doped zinc oxide systems, revealing different structural and optical behaviors. The work presents structural and optical studies depending on Cu concentration and thermal treatments in the range of 500–800 °C. The structural analysis is performed by X-Ray diffraction (XRD). It reveals that small Cu addition enhances the film crystallization. Increasing copper concentration results in deterioration of ZnO:Cu crystallization. XRD study manifests no Cu oxide phases in ZnO:Cu film structure for lower Cu additions. For a specific higher copper concentration, an appearance of a small fraction of copper oxide is detected. Vibrational properties have been characterized by FTIR spectroscopy. The effect of the copper introduction into ZnO reveals a slight change of optical properties compared to ZnO films for certain Cu ratios. ZnO:Cu films with higher copper contents manifest different optical behaviors with very high transparency in spectral visible range.     

Multifunctional device based on ZnO:Fe nanostructured films with enhanced UV and ultra-fast ethanol vapour sensing

Extensive application requests on high-performance gas sensors and photodetectors reveal the importance of controlling semiconducting oxide properties. Sensing properties of ZnO nano- and micro-structures can be tuned and their functional performances can be enhanced more efficiently by metal-doping. Here, we report the synthesis of crystalline Fe-doped ZnO (ZnO:Fe) nanostructured films via a cost-effective and simple synthesis from chemical solutions (SCS) approach followed by rapid thermal annealing (RTA) with excellent potential for the development of multifunctional devices for UV and ethanol (C₂H₅OH) vapour sensing. The effects of two types of thermal annealing on the ZnO:Fe morphology, the crystallinity, the electronic and the vibrational properties, the UV radiation and the gas sensing properties are investigated. The experimental results indicate an increase in UV response (I_UV/I_DARK~10⁷) of as-grown ZnO nanostructured films by Fe-doping, as well as an essential improvement in rise and decay times due to RTA effects at 725 °C for 60 s. In comparison with un-doped samples, ZnO:Fe (0.24 at%) specimens showed a response to ethanol which is enhanced by a factor of two, R_air/R_gas~61. It was demonstrated that by using Fe-doping of ZnO it is possible to reduce essentially the response τ_r and recovery times τ_d of the multifunctional device. The involved gas sensing mechanism is discussed in detail in this paper. The presented results could be of great importance for the application of RTA and doping effects for further enhancement of UV detection and gas sensing performances of the ZnO:Fe nanomaterial-based multifunctional device.     

Ga掺杂ZnO氧化物的热学性能的研究

在密度泛函理论和线性响应的密度泛函微扰理论基础上通过第一性原理计算的方法研究了Ga掺杂ZnO氧化物的热学参数和热学性能.计算结果表明,Ga掺杂使ZnO氧化物晶胞增大;在所研究温度范围内,纯的ZnO和Ga掺杂的ZnO的晶格热容均随温度升高不断增大,其晶格热容在最高温度900 K分别达到16.5 Cal.mol^-1K^-1和31.3 Cal.mol^-1K^-1.纯的ZnO和Ga掺杂的ZnO的德拜温度θ_D均随温度升高不断增大.Ga掺杂在ZnO中引入了新的振动模式.     

Growth and characterization of ZnO thin films on GaN epilayers

Dense ZnO(0001) films formed at 500°C via coalescence of islands grown via metalorganic vapor phase epitaxy (MOVPE) either on GaN/AlN/SiC(0001) substrates or on initial, coherent ZnO layers. Conical crystallites formed due to thermal expansion-induced stresses between the ZnO and the substrate. Interfaces between the ZnO films on GaN epilayers exposed either simultaneously to diethylzinc and oxygen or only to diethylzinc at the initiation of growth were sharp and epitaxial. Interfaces formed after the exposure of the GaN to O₂ were less coherent, though an interfacial oxide was not observed by cross-sectional transmission electron microscopy (TEM). Threading dislocations and stacking faults were observed in all films.     

Sb-implanted ZnO ultra-thin films

Mild heating of the Zn(C₅F₆HO₂)₂·2H₂O·CH₃(OCH₂CH₂)₂OCH₃ precursor allowed MOCVD deposition of ZnO films, in a low-pressure horizontal hot-wall reactor, on ITO substrates. The ZnO films were subsequently implanted with Sb ions. XRD measurements provided evidence that they consist of hexagonal, (002) and (101) oriented, crystals. UV–vis spectra showed that the transmittance of these films in the visible region is about 90%. The Sb implanted ZnO film showed a current-voltage characteristic that resembles that of a rectifying diode. This study represents the first example of Sb-implantation in ZnO films obtained by MOCVD.     

Effect of Co doping on structural, optical, electrical and thermal properties of nanostructured ZnO thin films

Nanocrystalline Zn1-x CoxO(where x varies from 0 to 0.04 in steps of 0.01) thin films were deposited onto glass substrate by the spray pyrolysis technique at a substrate temperature of 350 ℃. The X-ray diffraction patterns confirm the formation of hexagonal wurtzite structure. The crystal grain size of these films was found to be in the range of 11–36 nm. The scanning electron micrographs show a highly crystalline nanostructure with different morphologies including rope-like morphology for undoped ZnO and nanowalls and semispherical morphology for Co-doped Zn O. The transmittance increases with increasing Co doping. The optical absorption edge is observed in the transmittance spectra from 530 to 692 nm, which is due to the Co2C absorption bands corresponding to intraionic d–d shifts. The direct and indirect optical band gap energies decrease from 3.05 to 2.75 eV and 3.18 to 3.00 eV, respectively for 4 mol% Co doping. The electrical conductivity increases with increasing both the Co doping and temperature, indicating the semiconducting nature of these films. The temperature dependence thermal electromotive force measurement indicates that both undoped and Co-doped ZnO thin films show p-type semiconducting behavior near room temperature. This behavior dies out beyond 313 K and they become n-type semiconductors.