Effect of vacuum magnetic annealing on the structural and physical properties of the Ni and Al co-doped ZnO films

About 300 nm-thick Zn_0.87Al_0.06Ni_0.07O, Zn_0.83Al_0.06Ni_0.11O and Zn_0.81Al_0.04Ni_0.15O films were deposited on glass substrates at 300 K by co-sputtering ZnO:Al and Ni targets. The films were annealed in vacuum at 673 K for 2 h under a magnetic field of 4.8 × 10⁴ A/m applied along the film plane and then were cooled down to room temperature without magnetic field. All the films have a wurtzite structure and consist of thin columnar grains perpendicular to the substrate. The annealing promotes the (002) orientation growth in the film growing direction for the Zn_0.87Al_0.06Ni_0.07O and Zn_0.83Al_0.06Ni_0.11O films as well as the (100) orientation growth for the Zn_0.81Al_0.04Ni_0.15O film. The annealing results in a slight increase in the grain size. A weak Ni diffraction peak was detected for the annealed films with high Ni content. The annealing enhances the room temperature ferromagnetism of the films. A temperature dependence of magnetization confirms that the Curie temperature is above 400 K for the annealed films. The films magnetically annealed exhibit an anisotropic magnetization behavior. The annealed Zn_0.87Al_0.06Ni_0.07O film has the lowest resistivity (8.73 × 10⁻³ Ω cm), the highest free electron concentration (1.73 × 10²⁰ cm^− 3) and Hall mobility (4.16 cm²V^− 1 s^− 1). A temperature dependence of the resistivity from 50 K to 300 K reveals that the carrier transport mechanism is Mott's variable range hopping in the low temperature range and thermally activated band conduction in the high temperature range.     

Optical and electrical properties of ZnO films, codoped with Al and Ga deposited at room temperature by an RF sputtering method

ZnO thin films, codoped with Al and Ga, were prepared on fused quartz (FQ) and cyclo-olefin polymer (COP) substrates using a radial frequency magnetron sputtering technique at room temperature, without the introducing of oxygen. The elemental distributions of Al, Ga, Zn and O throughout the films were found and no compositional variation in working pressure was observed. A resistivity of 0.03-4.07 Ω cm in AGZ/FQ films (Fig. 2b and 0.04-5.73 Ω cm in AGZ/COP films as well as a transmittance of above 85% were obtained by appropriate control of the working pressure. Compared with the band gap energy of single crystal ZnO, the band gap energy of the AGZ/FQ thin film was somewhat higher. The band gap energy of the AGZ/FQ films showed a tendency to increase with the working pressure employed.     

ZnO缓冲层上低温生长Al掺杂的ZnO薄膜

采用射频磁控溅射法在ZnO缓冲层上制备了不同Al掺杂量的ZnO（AZO）薄膜。利用X射线衍射（XRD）、扫描电子显微镜（SEM）和光致发光（PL）等表征技术,研究了AZO薄膜的微观结构、表面形貌和发光特性。结果表明,随着Al掺杂量的增加,ZnO薄膜的择优取向性发生了改变,且当Al的掺杂量为0.81%（原子分数）时,（002）衍射峰与其它衍射峰强度的比值达到最大,表明适合的Al掺杂使ZnO薄膜的择优取向性得到了改善。在可见光范围内薄膜的平均透过率超过70%。通过对样品光致发光（PL）谱的研究,发现所有样品出现了3个发光峰,分别对应于以444nm（2.80eV）、483nm（2.57eV）为中心的蓝光发光峰和以521nm（2.38eV）为中心较弱的绿光峰。并对样品的发光机理进行了详细的探讨。     

溅射Ni和Ni/Al对SiC陶瓷真空钎焊性能的影响

本工作采用磁控溅射的方法在SiC陶瓷表面分别溅射Ni薄膜和Ni/Al双层薄膜,然后将表面改性的SiC陶瓷片用真空钎焊的方法制备了以Al为钎料的钎焊接头,研究了表面溅射Ni和Ni/Al对SiC真空钎焊接头界面结合的影响。结果表明,表面溅射Ni薄膜的SiC钎焊接头平均剪切强度为69.4 MPa,表面溅射Ni/Al薄膜的SiC钎焊接头平均剪切强度为113.8 MPa,均高于未改性处理的SiC钎焊接头的平均剪切强度(48.4 MPa),其原因在于SiC表面溅射沉积Ni和Ni/Al薄膜,一方面能够避免脆性反应相Al₄C₃的生成对界面结合强度的降低,另一方面有助于改善铝钎料对SiC陶瓷表面的润湿。另外,相比于溅射单层Ni薄膜,采用Ni/Al双层薄膜改性的SiC钎焊接头,由于界面生成的强化相Al₃Ni分布更为集中,起到了“锚定”钎缝的作用,使接头剪切强度得到了更大的提高。     

Effect of the nanostructure on room temperature ferromagnetism and resistivity of undoped ZnO thin films grown by chemical vapor deposition

Undoped zinc oxide thin films having various types of morphology and nanostructure were deposited by metal organic chemical vapor deposition (MOCVD) on single-crystalline substrates. Water-assisted MOCVD process at low temperatures (300-500 °C) was applied along with conventional MOCVD in oxygen-containing atmosphere at 500 and 600 °C. The strong correlation between room-temperature ferromagnetism of the films, their electrical properties and morphology at nano-scale was demonstrated.     

Corrosion behavior of Al, Sc-co-doped ZnO thin films in 3.5% NaCl solution

The corrosion behavior of Al, Sc-co-doped zinc oxide films (with Sc-dopant varying in 0, 0.01, 0.13, 0.24 and 1.07 wt.% Sc) in 3.5% NaCl solution has been investigated. It was compared to that of the commercial indium tin oxide (ITO) thin film. The films were prepared by sputtering on the ZnO (4 N) target with RF and on the targets of Al (4 N), Al-0.4 wt.% Sc, Al-0.8 wt.% Sc, Al-1.7 wt.% Sc alloy and pure Sc with DC. The electrochemical studies revealed that the corrosion resistance of the films increases in the order AZO < Sc-doped AZO < ITO < annealed AZO (at 300 °C for 1 h). The AZO doped with higher Sc-content is more resistant to corrosion. Examining the surface morphology through atomic force microscope (AFM) and scanning electron microscope (SEM), the film, which is more susceptible to corrosion depicted a rougher surface. The electrical resistivity of the films maintained almost unchanged in 120-h test. However, the optical transmittance varied with the concentration of Sc-dopant in the films. The higher Sc-dopant in the film the more stable it is to maintain higher transmittance. Higher corrosion resistance for the Sc-doped AZO in comparison with the monotonic AZO is attributed to a release of lattice strain by the Sc (III)-dopant which its size is similar to Zn (II). The most corrosion-resistant specimen (i.e., Sc-doped AZO annealed at 300 °C for 1 h) is considered to have the complete release of the lattice strain.     

磁控共溅射Ni3 Al合金薄膜的微观结构及电阻特性

研究了室温下采用直流磁控共溅射法在抛光玻璃和Si基底上沉积Ni3Al合金薄膜的制备工艺、微观结构和电阻特性.采用SEM、EDX、AFM、TEM等测试分析了不同基底、溅射功率、工作气压等因素对薄膜微观结构、成分比和电阻特性的影响.结果表明:采用大功率混合溅射可以得到多晶态Ni3Al纳米合金薄膜,且呈多层岛状生长.所得薄膜具有良好的导电性,与玻璃相比,在Si基底上的薄膜表面光滑平整,晶粒更小,电阻率略大.然而随着厚度的减小,薄膜的电阻率增加迅速,发生金属向绝缘体过渡的相变,而厚度较大时这种现象不明显,这表明Ni3Al薄膜相变与厚度及晶格中氧含量有关.     

Preparation and characterization of sol-gel Li and Al codoped ZnO thin films

Li and Al codoped ZnO (LAZO) thin films have been prepared by a sol-gel method and their structural and optical properties have been investigated. The prepared LAZO films had an average transmittance of over 85% in the visible range. The UV absorption edge was red-shifted with Li-doping, whereas it was blue-shifted with Al-doping. A broad yellowish-white emission was observed from the LAZO films annealed above 600 °C. The visible emission was enhanced with increasing annealing temperature and dopant concentration.     

Influence of preparation condition and doping concentration of Fe-doped ZnO thin films: Oxygen-vacancy related room temperature ferromagnetism

Fe-doped and Fe-Ga co-doped ZnO diluted magnetic semiconductor thin films on quartz substrate were studied. Rapid annealing enhanced the ferromagnetism (FM) of the films grown in Ar/O₂. All the films grown in Ar are n-type and the carrier concentration could increase significantly when Ga is doped. The state of Fe in the films was investigated exhibiting Fe³⁺. Magnetic measurements revealed that room temperature ferromagnetism in the films were doping concentration dependent and would enhance slightly with Ga doping. The origin of the observed FM is interpreted by the overlapping of polarons mediated through oxygen vacancy based on the bound magnetic polaron model.     

用铝丝掺杂溅射ZnO薄膜的光电性能研究

本文采用射频磁控反应溅射法于常温下在硅片和玻璃基片上制备ZnO和掺铝ZnO薄膜,将铝丝置于ZnO靶材上共同溅射来达到掺杂的效果,利用不同长度的铝丝以获得不同的掺杂量。通过X射线衍射法对薄膜进行结构分析,利用紫外-可见分光光度计获得薄膜的透过率光谱,霍尔效应仪测量薄膜的电学性能。发现所制备的样品在可见光区域透过率达到80%以上,达到了透明膜的要求;掺Al后的ZnO膜电阻率最低达到了4.25×10-4Ω·cm;结构表征发现样品的(002)晶面有明显衍射峰。基于包络线方法通过透射谱拟合计算了薄膜样品的折射率和厚度。     

Effect of the annealing temperature on transparency and conductivity of ZnO:Al thin films

Highly aluminum-doped zinc oxide (ZnO:Al) films were grown by rf-magnetron sputtering at low temperature from aerogel nanoparticles and characterized by structural, electrical and optical techniques. Nanoparticles with a size of about 30 nm were synthesized by sol–gel method using supercritical drying in ethyl alcohol and annealed at different temperatures with different gas atmospheres. The ZnO films were polycrystalline textured, preferentially oriented along the (002) crystallographic direction normal to the film surface. The films show within the visible wavelength region an optical transmittance of more than 90% and low electrical resistivity of 10^− 3 Ω cm at room temperature.     

On the structure and characterization of Al, Sc-co-doped ZnO-films varying with 0-2.37 wt.% Sc contents

Thin films of Al, Sc-co-doped ZnO varying with Sc-contents were sputtered on the glass substrate. X-ray diffraction (XRD) of the films revealed wurtzite crystals that were confirmed through the analysis of high resolution transmission electron microscopy (HRTEM). With increasing the Sc-content from 0 to 2.37 wt.% in the films, the optical energy band gap (Eg) was estimated to decrease from 3.25 to 3.20 eV, and the electrical resistivity (Ω cm) decreased from 3.8 × 10^− 3 to 1.3 × 10^− 3. The decrease in resistivity may be ascribed to electrons tunneling through the horizontal stacking faults induced by Sc-dopants in the films.     

Structural, electrical and optical properties of ZnO:Al films deposited on flexible organic substrates for solar cell applications

Aluminum doped ZnO thin films (ZnO:Al) were deposited on glass and poly carbonate (PC) substrate by r.f. magnetron sputtering. In addition, the electrical, optical properties of the films prepared at various sputtering powers were investigated. The XRD measurements revealed that all of the obtained films were polycrystalline with the hexagonal structure and had a preferred orientation with the c-axis perpendicular to the substrate. The ZnO:Al films were increasingly dark gray colored as the sputter power increased, resulting in the loss of transmittance. High quality films with the resistivity as low as 9.7 × 10^− 4 Ω-cm and transmittance over 90% have been obtained by suitably controlling the r.f. power.     

以PVA为溶剂ZnO薄膜的液相法制备及其机理研究

以聚乙稀醇(PVA)水溶液为溶剂,采用液相法制备了高度c轴取向的ZnO薄膜。采用XRD、Raman以及AFM分析了退火温度与涂层厚度对ZnO薄膜的影响。结果表明,随着退火温度的提高,ZnO薄膜的结晶度及其均方根粗糙度有所提高;同时厚度的增加使得ZnO薄膜的单一取向性减弱。其生长机理可表述为:在每一层涂层中一致或不一致的成核同时产生,通过层内与层间晶粒的聚合、联并,最后形成具有(002)取向的柱状与颗粒状并存的ZnO连续膜。     

Preparation of LaNiO3 thin films with very low room-temperature electrical resistivity by room temperature sputtering and high oxygen-pressure processing

LaNiO₃ (LNO) thin films were deposited by radio frequency magnetron sputtering on n-type Si (100) wafers at room temperature (RT). The as-sputtered LNO thin films were amorphous and had very high RT electrical resistivity even after post-annealing at 800 °C. The amorphous as-sputtered LNO films could be transformed to polycrystalline LNO films in rhombohedral phase by heating at 400 °C in an O₂ atmosphere at pressure ranging from 1.5 to 8.0 MPa. Very low RT resistivity of LNO films were obtained by this high oxygen-pressure processing. The lowest value was as low as 1.09 × 10^− 4 Ω cm by processing at oxygen pressure of 8 MPa. Such preparation of LNO thin films is compatible with the Si-based readout integrated circuits. Highly (100)-oriented perovskite structure of Pb(Zr_0.52Ti_0.48)O₃ thin films was formed on this rhombohedral phase LNO, and good ferroelectricity could also be obtained on these HOPP-processed rhombohedral phase LNO films.     

Structural,electrical and photoluminescence properties of ZnO:Al films grown on MgO(0 0 1) by direct current magnetron sputtering with the oblique target

ZnO:Al films were deposited on MgO(0 0 1) substrates at 300 K and 673 K by direct current magnetron sputtering with the oblique target. The Ar pressure was adjusted to 0.4 Pa and 1.2 Pa, respectively. All the films have a wurtzite structure and a c-axis orientation in the film growth direction. The films deposited at 300 K initially grow with thin columnar grains and subsequently grow with large granular grains on the thin columnar grains. However, the films grown at 673 K consist mainly of dense columnar grains perpendicular to the substrate surface. The ZnO:Al film deposited at 673 K and 0.4 Pa has the lowest resistivity, the highest free electron concentration and Hall's mobility. A temperature dependence of the resistivity within 5–300 K reveals that the films grown at 300 K exhibit a semiconducting behavior and those grown at 673 K show a metal–semiconductor transition. The carrier transport mechanism is Mott's variable range hopping in the temperature range below 90 K for all the films and thermally activated band conduction above 215 K for the films grown at 300 K. Room temperature photoluminescence spectra for wavelengths between 300 nm and 800 nm reveal mainly blue-green emissions centered at 452 nm, 475 nm and 515 nm.     

Optical, electrical and structural characteristics of Al:ZnO thin films with various thicknesses deposited by DC sputtering at room temperature and annealed in air or vacuum

Transparent and conductive Al-doped ZnO (AZO) films have been grown with various thicknesses between 0.3 and 1.1 μm by magnetron sputtering at room temperature onto soda lime glass substrates. After deposition, the samples have been annealed at temperatures ranging from 150 to 450 °C in air or vacuum. The optical, electrical, and structural characteristics of the AZO coatings have been analyzed as a function of the film thickness and the annealing parameters by spectrophotometry, Hall effect measurements, and X-ray diffraction. As-grown layers are found polycrystalline, with hexagonal structure that shows some elongation of the unit cells along the c-axis, having visible transmittance ∼85-90% and resistivity ∼1.6-2.0 mΩ cm, both parameters slightly decreasing when the film thickness increases. Heating in air or vacuum produces further elongation of the crystalline lattice together with some increase of the visible transmittance and a decrease of the electrical resistance that depends on the heating temperature and atmosphere. The best characteristics have been obtained after treatment in vacuum at 350 °C, where the highest carrier concentrations are achieved, giving visible transmittance ∼90-95% and resistivity ∼0.8-0.9 mΩ cm for the AZO layers with various thicknesses. Some relationships between the analyzed properties have been established, showing the dependence of the lattice distortion, the band gap energy and the mobility on the carrier concentration.     

Effect of metal (Al, Ga, and In)-dopants and/or Ag-nanoparticles on the optical and electrical properties of ZnO thin films

ZnO thin films were deposited by a sol-gel process using zinc acetate dihydrate and 2-methoxyethanol as starting precursor and solvent, respectively. Ag-nanoparticles were prepared with uniform size (4.4 nm) by the spontaneous reduction method of Ag 2-ethylhexanoate in Dimethyl sulfoxide. The optical and electrical characteristics of ZnO films with the introduction of 3A metal (Al, Ga, and In)-dopants and/or Ag-nanoparticles were evaluated. The optical and electrical properties of metal-doped ZnO films were improved and light scatter, charge emission and the scattering behavior of Ag-nanoparticles incorporated into the ZnO thin film were measured. The introduction of Ag-nanoparticles into metal-doped ZnO films induced a slight decrease in the optical transmittance but an increase in the electrical sheet resistance.     

Fabrication of Ta3N5-Ag nanocomposite thin films with high resistivity and near-zero temperature coefficient of resistance

In this study, we investigate as-deposited Ta₃N₅-Ag nanocomposite thin films with near-zero temperature coefficients of resistance (TCRs) that are fabricated by a reactive co-sputtering method; these films can be used in thin-film embedded resistors. In these films, the TCR approaches zero due to compensation between Ag (+TCR) and Ta-N (−TCR) at resistivities higher than 0.005 Ω-cm.Taking into account the fact that Ag counterbalances the resistivity of the Ta₃N₅-Ag thin film, we performed reactive co-sputtering at a nitrogen partial pressure of 55%, corresponding to a resistivity of 0.384 Ω-cm. The resistivity and power density changed, respectively, from 1.333 Ω-cm and 0.44 W/cm² for silver to 0.0059 Ω-cm and 0.94 W/cm² for the Ta₃N₅-Ag thin film. A near-zero TCR of + 34 ppm/K was obtained at 0.94 W/cm² in the Ta₃N₅-Ag thin film without heat treatment.