Effects of ZnO Buffer Layer Thickness on Properties of MgxZn1-xO Thin Films Deposited by MOCVD

High-quality MgxZn1-xO thin films were grown on sapphire（0001 ） substrates with a ZnO buffer layer of different thicknesses by means of metal-organic chemical vapor deposition. Diethyl zinc, bis-cyclopentadienyl-Mg and oxygen were used as the precursor materials. The crystalline quality, surface morphologies and optical properties of the Mg, Zn1-xO films were investigated by X-ray diffraction, atomic force microscopy and photoluminescence spectrometry. It was shown that the quality of the MgxZn1-xO thin films depends on the thickness of the ZnO buffer layer and an Mg, Zn1-xO thin film with a ZnO buffer layer whose thickness was 20 nm exhibited the best crystal-quality, optical properties and a flat and dense surface.     

Photoinduced hydrophilicity of heteroepitaxially grown ZnO thin films

Single crystalline ZnO thin films were heteroepitaxially grown on sapphire substrates by rf-magnetron sputtering. The ZnO films on sapphire A and C face were oriented along the (0001) direction, whereas the ZnO film on sapphire R face was oriented along the (11-20) direction. The rate of photoinduced hydrophilic conversion strongly depended on the surface crystal structure. The ZnO film oriented along the (11-20) direction exhibited a higher hydrophilicizing rate than those oriented along the (0001) direction. The high hydrophilicizing rate of the ZnO oriented along the (11-20) direction is due to its surface atomic arrangement. The outermost layer of the ZnO surface of the (11-20) face contains oxygen ions, which are considered to be energetically reactive sites and responsible for the hydrophilic conversion.     

Preparation and characterization of nanocomposite ZnO–Ag thin film containing nano-sized Ag particles: influence of preheating,annealing temperature and silver content on characteristics

Nanocomposite ZnO–Ag thin film containing nano-sized Ag particles have been grown on glass substrate by spin-coating technique using zinc acetate dihydrate as starting precursor in 2-propanol as solvent and monoethanolamine as stabilizer. Silver nanoparticles were added in the ZnO sol using silver nitrate dissolved in ethanol-acetonitrile. Their structural, electrical, crystalline size and optical properties were investigated as a function of preheating, annealing temperature and silver content. The results indicated that the crystalline phase was increased with increase of annealing temperature up to 550 °C at optimum preheating temperature of 275 °C. Thermal gravimetric differential thermal analysis results indicated that the decomposition of pure ZnO and nanocomposite ZnO–Ag precursors occurred at 225 and 234 °C, respectively with formation of ZnO wurtzite crystals. The scanning electron microscopy and atomic force microscopy revealed that the surface structure (the porosity and grain size) of the ZnO–Ag thin film (the film thickness is about 379 nm) was changed compared to pure ZnO thin film. The result of transmission electron microscopy showed that Ag particles were about 5 nm and ZnO particles 58 nm with uniform silver nanoclusters. Optical absorption results indicated that optical absorption of ZnO–Ag thin films decreased with increase of annealing temperature. Nanocomposite ZnO–Ag thin films with [Ag] = 0.068 M and [Ag] = 0.110 M showed an intense absorption band, whose maximum signals appear at 430 nm which is not present in pure ZnO thin films. The result of X-ray photoelectron spectroscopy revealed that the binding energy of Ag 3d_5/2 for ZnO–Ag shifts remarkably to the lower binding energy compared to the pure metallic Ag due to the interaction between Ag and ZnO.     

Studies on the Structure of Gel during Preparing ZnO Thin Films by Sol-gel Method

<正>Transparent thin films of ZnO have been prepared on ordinary glass substrates by the inorganic sol-gel method using citric acid as chelating agent and zinc nitrate as the starting material.A novel structure on zinc citrate complex was put forward by using DTA-TG and FT-IR absorbance spectrum of citrate gels.Phase formation,morphology and optical properties of ZnO films are investigated by XRD,AFM and UV-vis transmittance spectra.The experimental results show that ZnO thin films derived from zinc citrate sol-gel method showed a(002)oriented hexagonal wurtzite structure,good crystalline property,a uniform range of grain size(40 nm), smooth surface of films,band gap of 3.28 eV and optical transmittances ratio over 90%in the visible range.     

Influence of rapid thermal annealing on structure and interfacial characteristic of ZnO thin films

Highly C‐axis oriented ZnO thin film was manufactured by radio‐frequency magnetron sputtering technique on Si (111) substrate. The main objective was to study the influence of rapid thermal annealing (RTA) temperature on the structure and interfacial characteristic of ZnO thin films. X‐ray diffraction results showed that the ZnO thin films annealed at 600 °C by RTA technique had a perfect C‐axis preferred orientation compared to the other ZnO thin films, and the full width at half maximum of ZnO (002) rocking curve measurements indicted that the RTA‐annealed ZnO thin films possessed better crystal structure. Atom force microscopy displayed that the grain size of RTA‐annealed ZnO thin films was fine and uniform compared with the as‐deposited ZnO thin films, although the grains grew in RTA process and the root meant square roughness was smaller than that of as‐deposited films. High‐resolution transmission electron microscopy showed that there was an obvious amorphous layer between ZnO thin films and Si substrate, but the RTA‐annealed ZnO thin films exhibited larger and denser columnar structure and a preferred orientation with highly c axis perpendicular to the amorphous layer. Copyright © 2012 John Wiley & Sons, Ltd.     

Ordered porous ZnO thin films formed by dip-coating method using PS templates

Monolayer polystyrene spheres (∼400 nm) array templates were assembled orderly on clean glass substrates by dip-coating method from emulsion of polystyrene (PS). Porous ZnO thin films were also prepared by dip-coating method to fill the interstices among the close-packed PS templates with ZnO and annealing to remove the PS templates. Results showed that ZnO sol concentration and dipping time of PS templates in sol had great influences on the morphology of ordered porous ZnO thin films. There was a shrinkage ratio of about 30% from pore to PS. SEM observation showed that the PS array templates had face-centered cubic close-packing. X-ray diffraction (XRD) spectra showed the porous ZnO thin film was wurtzite structure. The optical transmittance decreased with decreasing wavelength of lights, but was kept above 80% beyond the wavelength of 550 nm. Optical band-gap of the porous ZnO thin film annealed at 500°C was 3.22 eV.     

Preparation and optical–electrical properties of Al-doped ZnO films

Among the various semiconducting metal oxide materials, ZnO thin films are highly attractive in the development of materials area. In this paper, Al-doped ZnO thin films were prepared by sol–gel dipping and drawing technology and their composition, structure and optical–electrical properties were investigated. XRD results shows that the Al-doped ZnO thin film is of polycrystalline hexagonal wurtzite structure, and the (002) face of the thin film has the strongest orientation at the annealing temperature of 550 °C. The surface resistance of Al-doped ZnO thin film firstly drops and then increases with the increase in annealing temperature. Al doping concentration is also an important factor for improving the conductivity of modified ZnO thin films, and the surface resistance has the tendency to drop at first and then to increase when the Al concentration is increasing. The surface resistance of modified ZnO thin films drops to the lowest point of 139 KΩ sq^?1 when the Al concentration is 1.6 at% and the annealing temperature is 500 °C. The light transmission measurements show that the doping concentration has little influence on light transmittance. The transmittance at the visible region of films is all over 80 %, and the highest value is up to 91 %.     

Enhancement of optical conductivity in the ultra-violet region of Cs doped ZnO sol gel thin films

Nano crystalline cesium (Cs) doped ZnO thin films were deposited on glass substrate by sol gel spin coating method with 1–3 mol.% doping concentration and different annealing temperatures. The deposited films were characterized by X-ray diffraction (XRD), Hall Effect, Photoluminescence (PL) and UV–Visible studies. XRD measurements reveal that all the samples abound in the wurtzite structure with polycrystalline nature. An increase in crystalline size from 19.60 to 44.54 nm is observed with the increase of doping concentration. Electrical conductivity of Cs doped ZnO films were observed from Hall effect measurements and the maximum carrier concentration obtained is 7.35 × 10¹⁸ cm^?3. The near band emission (384 nm) peak intensity increases with the increase of Cs doping concentration and a maximum intensity 55,280 was observed for CZ3 film from PL spectrum. Also a low energy near infrared (NIR) emission peak centered at 1.62 eV appears for the Cs doped ZnO films. The average transmission of CZ film is 88 % and the absorption edge is red shifted with the increase of Cs doping concentration and also the optical conductivity increases in the UV region.     

溶胶浸渍模板法制备有序多孔氧化钛、氧化锌薄膜

采用溶胶浸渍模板法制备了有序多孔的氧化钛(TiO₂)和氧化锌(ZnO)薄膜。首先，在洁净的玻璃基片上通过浸渍-提拉工艺组装有序的聚苯乙烯微球(PS)阵列模板；然后再采用溶胶浸渍法将TiO₂和ZnO溶胶灌充到PS模板微球的间隙内；最后通过煅烧去除PS而得多孔薄膜。采用SEM观察了薄膜的表面形貌，并用XRD对薄膜的性能进行了表征。结果表明，溶胶的浓度对薄膜形貌有着显著的影响。经煅烧后，TiO₂和ZnO薄膜分别为锐钛矿和六方纤锌矿结构。此外，对模板的组装及溶胶的灌注过程进行了分析。     

Fabrication of surface-patterned ZnO thin films using sol–gel methods and nanoimprint lithography

Surface-patterned ZnO thin films were fabricated by direct imprinting on ZnO sol and subsequent annealing process. The polymer-based ZnO sols were deposited on various substrates for the nanoimprint lithography and converted to surface-patterned ZnO gel films during the thermal curing nanoimprint process. Finally, crystalline ZnO films were obtained by subsequent annealing of the patterned ZnO gel films. The optical characterization indicates that the surface patterning of ZnO thin films can lead to an enhanced transmittance. Large-scale ZnO thin films with different patterns can be fabricated by various easy-made ordered templates using this combination of sol–gel and nanoimprint lithography techniques.     

Preparation, structure and ultraviolet photoluminescence of ZnO films by a novel chemical method

A novel and simple chemical method was developed for the deposition of ZnO films from aqueous solution, integrating the merits of successive ionic layer adsorption and reaction with the chemical bath deposition technology. By this new method, dense and continuous ZnO thin films with good crystallinity can be prepared in a very short time, e.g., in about 20 min. Results show that as-deposited ZnO films on glass and Si (1 0 0) exhibit hexagonal wurtzite crystalline structure and the preferential orientation along (0 0 2) plane. With a dense and continuous appearance, the film is composed of ZnO particles in even size of 200-300 nm. The strong and sharp emission at 391 nm and several weak emissions at the wavelength band of 440-500 nm indicate the high optical quality and the stoichiometrical nature of obtained film. Mechanism analysis shows that the reaction duration in hot water and the drying process are vital important factors affecting the deposition process and the crystallization behavior of the film prepared via the aqueous solution route.     

White light emission from nano-fibrous ZnO thin films/porous silicon nanocomposite

Nanocomposites composed of nano-fibrous ZnO thin films and porous silicon (PS) were prepared and examined by atomic force microscopy (AFM), X-ray diffraction (XRD), Raman spectroscopy, and photoluminescence (PL) to investigate their structural and optical properties. PS, consisting of irregular and random nanosized-pores, was prepared by electrochemical anodization. The nano-fibrous ZnO thin films were grown on PS by the sol-gel spin-coating method. The texture coefficient (TC _(hkl)) of the nano-fibrous ZnO thin films was calculated to determine the preferred orientation. The nano-fibrous ZnO thin films were grown with a c-axis preferred orientation. The residual stress in the films was reduced in the case of PS. The observed broad PL emission peak from 460 to 598 nm was attributed to coupled emission from ZnO to PS. The results show that white light luminescence with blue, green, and red emission peaks having highly uniform intensities can be obtained from the nanocomposite via a relatively simple and low-cost sol-gel spin-coating method.     

聚苯胺-TCNQ复合薄膜的微观结构与电学特性

聚苯胺 (ＰＡＮＩ)作为高聚物材料 ,具有稳定性好 ,易于合成等优点．它在化学传感器、显示器、光化学电池等光电器件上有着许多潜在的应用前景．目前导电聚苯胺材料的合成、薄膜的制备与表征正在受到人们的重视．由于聚苯胺很难溶于一般的有机溶剂 ,用化学方法通过聚合物溶液用旋涂或自组装的方法成膜具有很大的局限性 ,特别是不易得到实用化的薄膜产物．而用真空蒸发沉积方法制备聚苯胺薄膜却有成膜质量高、易于控制 ,能很好与电子及微电子加工工艺相接轨等优点［１ -３］．国外已有一些关于真空蒸发沉积聚苯胺薄膜的研究报导［２ -５］,但…     

Optical and structural characteristics of yttrium doped ZnO films using sol–gel technology

Yttrium-doped ZnO gel was spin-coated on the SiO₂/Si substrate. The as-prepared ZnO:Y (YZO) thin films then underwent a rapid thermal annealing (RTA) process conducted at various temperatures. The structural and photoluminescence characteristics of the YZO films were discussed thereafter. Our results indicated that the grain size of YZO thin films being treated with various annealing temperatures became smaller as compared to the ones without being doped with yttrium. Furthermore, unlike other ZnO films, the grains of YZO thin films appeared to separate from one another rather than aggregating together as both types of the films were annealed under the same environment. The photoluminescence characteristic measured showed that the UV emission was the only radiation obtained. However, the UV emission intensity of YZO thin film was much stronger than that of the ZnO thin film after annealing them with the same condition. It was also found that the intensity increased with an increase in the annealing temperature, which was caused by the exciton generated and the texture surface of the YZO thin film.     

Chemical Solution Deposition of ZnO Thin Films by an Aqueous Solution Gel Precursor Route

An aqueous chemical solution deposition method was used to prepare thin films of ZnO on SiO₂/Si (1 1 1) substrates. Starting from an aqueous solution of Zn acetate, citric acid and ammonia, very thin films could be deposited by spin coating. Heating parameters, necessary for thin film annealing, were determined using FTIR experiments on dried gel precursors, heated up to different temperatures. The morphology and the thickness of the films were investigated by SEM. It is found that homogeneous thin films with grain sizes of about 20 nm are formed. XRD experiments show that there is an indication that the films, crystallized at 500°C, exhibit preferential grain growth along the c-axis.     

Preparation of ZnO Film on 2024Al Surface for Hydrophobicity Investigation

A uniform ZnO film with microscale rod-like structure has been obtained on 2024Al surface by the hydrothermal method and perfluorooctanoicacid has been used to enhance the surface hydrophobic performance of the ZnO film. The as-prepared ZnO film was characterized by scan electron microscope (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectrum (XPS). The results indicate that the ZnO film is uniform and the ZnO microrods are 2 um in length. The water contact angle of hydrophobic surface is 146° and the sliding angle is 10°.     

Influence of Mn incorporation on the structural and optical properties of sol gel derived ZnO film

Undoped and manganese doped ZnO (ZnO:Mn) films were prepared by sol gel method using spin coating technique. The effect of Mn incorporation on the structural and optical properties of the ZnO film has been investigated. The crystalline structure and orientation of the films have been investigated by using their X-ray diffraction spectra. The films exhibit a polycrystalline structure. Mn incorporation led to substantial changes in the structural characteristics of the ZnO film. The scanning electron microscopy (SEM) images of the films showed that the surface morphology of the ZnO film was affected by the Mn incorporation. The transparency of the ZnO film decreased with the Mn incorporation. The optical band gap and Urbach energy values of the ZnO and ZnO:Mn films were found to be 3.22, 3.19 eV and 0.10, 0.23 eV, respectively. The optical constants of these films, such as refractive index, extinction coefficient and optical dielectric constants were determined using transmittance and reflectance spectra. The refractive index dispersion curve of the films obeys the single oscillator model with dispersion parameters. The oscillator energy, E _o , and dispersion energy, E _d, of the films were determined 5.30 and 16.26 eV for ZnO film and 5.80 and 12.14 eV for ZnO:Mn film, respectively.     

Aligned ZnO nanorods: A useful film to fabricate amperometric glucose biosensor

A novel amperometric glucose biosensor has been fabricated on the basis of aligned ZnO nanorod film grown on ITO directly. Glucose oxidase immobilized on the surface of ZnO nanorods are very stable with highly catalytic activity during the measurements, Because of the novel properties of ZnO, such as biocompatibility, non-toxicity, chemical stability, electrochemical activities and high isoelectric point, and the protection effect of Nifion membrane cast on the surface of the film. This biosensor displays excellent analytical performance over a wide linear range along with good selectivity. Interference from uric acid and ascorbic acid which usually coexist with glucose in practical samples has been found to be negligible. This method may be used to construct other amperometric biosensors using aligned nanorod/nanowire films.     

Morphology effects on the biofunctionalization of nanostructured ZnO

A stepwise surface functionalization methodology was applied to nanostructured ZnO films grown by metal organic chemical vapor deposition (MOCVD) having three different surface morphologies (i.e., nanorod layers (ZnO films-N), rough surface films (ZnO films-R), and planar surface films (ZnO films-P). The films were grown on glass substrates and on the sensing area of a quartz crystal microbalance (nano-QCM). 16-(2-Pyridyldithiol)-hexadecanoic acid (PDHA) was bound to ZnO films-N, -R, and -P through the carboxylic acid unit, followed by a nucleophilic displacement of the 2-pyridyldithiol moiety by single-stranded DNA capped with a thiol group (SH-ssDNA). The resulting ssDNA-functionalized films were hybridized with complementary ssDNA tagged with fluorescein (ssDNA-Fl). In a selectivity control experiment, no hybridization occurred upon treatment with non complementary DNA. The ZnO films' surface functionalization, characterized by FT-IR-ATR and fluorescence spectroscopy and detected on the nano-QCM, was successful on films-N and -R but was barely detectable on the planar surface of films-P.     

溶胶-凝胶方法制备ZnO:Al薄膜及其制备工艺条件研究

采用Sol-Gel工艺在玻璃基片上制备出C轴择优取向性、高可见光透过率以及高电导率的Al³⁺离子掺杂的ZnO透明导电薄膜ZnO:Al(ZAO薄膜).并研究了退火温度、Al掺杂量等对其光电性能的影响.结果表明,溶胶-凝胶法制备ZAO薄膜的最佳工艺条件为:溶胶浓度0.75 mol/L、掺杂量1.5 atm%,镀膜层数10层(厚度约为136 nm)、退火温度600℃.