Synthesis and characterizations of new morphological ZnO and Ce-doped ZnO powders by sol–gel process

ZnO micro-tori and cerium-doped hexangulars ZnO have been prepared by the sol–gel method under methanol hypercritical conditions of temperature and pressure. X-ray diffraction (XRD) measurement has revealed the high crystalline quality and the nanometric size of the samples. Scanning electron microscopy (SEM) has shown that the ZnO powder has a torus-like shape while that of ZnO:Ce has a hexangular-like shape, either standing free or inserted into the cores of ZnO tori. Transmission electron microscopy (TEM) has revealed that the ZnO particles have sizes between 25 and 30 nm while Ce-doped ZnO grains have diameters ranging from 75 nm to 100 nm. It is demonstrated from photoluminescence (PL) spectra at room temperature that the introduction of cerium in ZnO reduces the emission intensity lines, particularly the ZnO red and green ones.     

The structure and optical properties of SiC film on Si (111) substrate with a ZnO buffer layer by RF-magnetron sputtering technique

We have fabricated a multiply layer SiC/ZnO on Si substrates using the RF-magnetron sputtering technique with the targets of a single crystalline SiC and a polycrystalline ZnO. The as-deposited films were annealed in the temperature range of 600–1000 °C under nitrogen ambient. We have observed a strong ultraviolet (UV) emission (370 nm) from the as-deposited SiC/ZnO film and an intense violet emission (412 nm) from the film annealed at high temperature (1000 °C) under nitrogen ambient. The SiC film quality and the PL intensities are considered to be strongly dependent on the crystalline quality of the ZnO buffer layer. With the increase of the annealing temperature, the crystalline quality of the ZnO buffer layer is improved, resulting in the improvement of the SiC film quality and the increase of the PL intensities. The thin films have been characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) to provide the evidences of photoluminescence (PL). We suggest that the UV emission could be attributed to the nanocrystal silicon particles, that the 395 nm band is related to ZnO buffer layer and has a great relation to the crystalline quality of the ZnO film, and that the violet emission is associated with the emission luminescence from 6H-SiC, which bears on the SiC film quality. The obtained results are expected to have important applications in modern optoelectronic devices.     

Cubic ZnO films obtained at low pressure by molecular beam epitaxy

A zinc oxide thin film in cubic crystalline phase, which is usually prepared under high pressure, has been grown on the Mg O(001) substrate by a three-step growth using plasma-assisted molecular beam epitaxy. The cubic structure is confirmed by in-situ reflection high energy electron diffraction measurements and simulations. The x-ray photoelectron spectroscopy reveals that the outer-layer surface of the film(less than 5 nm thick) is of ZnO phase while the buffer layer above the substrate is of ZnMgO phase, which is further confirmed by the band edge transmissions at the wavelengths of about 390 nm and 280 nm, respectively. The x-ray diffraction exhibits no peaks related to wurtzite ZnO phase in the film. The cubic ZnO film is presumably considered to be of the rock-salt phase. This work suggests that the metastable cubic ZnO films, which are of applicational interest for p-type doping, can be epitaxially grown on the rock-salt substrates without the usually needed high pressure conditions.     

Centimetre-Long Single Crystalline ZnO Fibres Prepared by Vapour Transportation

Centimetre-long ZnO fibres are synthesized by vapour transportation via thermal evaporation of ZnO powders. The growth process is carried out in a graphite crucible, in which ZnO powder is loaded as the source material, and a silicon wafer is positioned on the top of the crucible as the growth substrate. During the growth process, the source temperature is kept at 800℃ and the substrate temperature is kept at 600℃. Typical growth time to obtain centimetre-long ZnO fibres is 5-10 hours. Scanning electron microscopy （SEM）, x-ray diffraction （XRD）, transmission electron microscopy （TEM）, and selected area electron diffraction （SAED） measurement results show that ZnO fibres are single crystalline with high crystalline quality and very low defects concentration.     

ZnO薄膜的性质对水热生长ZnO纳米线阵列的影响

用水热法在ZnO薄膜上制备了直径、密度及取向可控的ZnO纳米线阵列。ZnO薄膜是通过原子层沉积(ALD)方法制备并在不同温度下退火处理得到的,退火温度对ZnO薄膜的晶粒尺寸、结晶质量和缺陷性质有很大的影响。而ZnO薄膜的性质对随后生长的ZnO纳米线的直径、密度及取向能起到调节控制的作用。通过扫描电子显微镜(SEM)、X射线衍射(XRD)仪和光致发光(PL)测试对ZnO薄膜和ZnO纳米线进行了表征。最后得到的垂直取向的ZnO纳米线阵列适合在发光二极管和太阳能电池等领域使用。     

纳米ZnO微晶的合成及其发光特性

以醋酸锌和尿素为主要原料,利用沉淀-水热法一步合成了纳米ZnO微晶。用XRD,TEM,FTIR等测试技术及光致发光光谱(PL)对纳米ZnO微晶进行了表征,并对其发光特性进行了分析。研究表明：该合成方法操作简单,得到的纳米ZnO颗粒基本无团聚,结晶性较好,平均粒径约为17.2 nm,并在500～750 nm范围内出现宽的PL峰, 呈现出纳米材料的发光特征。     

Synthesis and structural characterization of Zn_3N_2 powder

1 Introduction In the field of wide band gap semiconductors, many studies have been carried out on zinc compounds. For example, ZnO, as a semiconductor material of n-type with a wide direct band gap of 3.37 eV[1—3], can function as transparent conducting films of low cost; ZnO, with an extremely large exciton binding energy of 60 meV and a strong ultra- violet (UV) stimulated emission at room temperature, has enormous potential for serving as short-wave light devices[4], such as light-emit…     

低温CVD法在玻璃衬底上制备ZnO纳米线阵列

采用化学气相沉积(CVD)法在镀Cr(20nm)的玻璃衬底上,低温制备了ZnO纳米线阵列。利用扫描电子显微镜(SEM)和X射线衍射(XRD)对样品的表面形貌和微结构进行了分析表征。结果表明:源分解温度1350℃,衬底温度450～500℃,氩气流量为35sccm时,ZnO纳米线在玻璃衬底上呈现有序生长;XRD谱图中只观测到ZnO(002)衍射峰。表明制备的纳米线阵列具有高度c轴择优取向生长特性和较高的结晶质量。     

Photocatalytic performance of ZnO:Fe array films under sunlight irradiation

ZnO:Fe array thin films were prepared by the hydrothermal method using the sol-gel grown film as a seed layer. The samples were characterized by X-ray diffraction (XRD), ultraviolet/visible absorption spectra (UV-vis) and scanning electron microscopy (SEM). The photocatalytic activities of the prepared samples were investigated for the photodegradation of methylene blue (MB) under sunlight irradiation. The results show that the lattice constant a and the cell volume of ZnO:Fe film increase due to the substitution of Fe for Zn. The absorption edge of Fe-doped ZnO displays a red shift with a significant absorption between 600 and 700 nm. The ZnO:Fe array film is composed of disk particles with uniformity and compactness. Doping Fe ions enhances the photodegradation rate of ZnO array film for MB. 1.5% Fe doped ZnO sample exhibits the highest activity under irradiation time of 4 h. Its degradation rate increases about 1.6 times compared to the undoped ZnO.     

Synthesis and luminescent property of single-crystal ZnO nanobelts by a simple low temperature evaporation route

Large-scale ZnO nanobelts in aligned fashion have been prepared via a simply conducted low temperature evaporation route using the oxidization of metallic zinc plates at 450±10 °C under ambient pressure. The produced nanobelt array has been structurally characterized by powder X-ray diffraction (XRD), scanning electron microscopy, and transmission electron microscopy (TEM). The microscope images show that the nanobelts are about 120-micron long, ranging on average from 80 to 160 micron, with about 30 nm in thickness. In addition to XRD, high-resolution TEM images and electron-diffraction patterns show that the nanobelts are single crystalline with wurtzite structure and mostly grow along the [0001] direction. The photoluminescence spectra of the single nanobelts show that the nanobelts have a dominant near-band-edge emission at about 388 nm with a very weak defect emission band centered at about 514 nm. PACS 81.05.Ys; 81.15.Gh; 78.66.Jg     

退火温度对Cu:ZnO薄膜绿光发射的影响

利用溶胶-凝胶法在Si衬底上制备了不同退火温度的Cu:ZnO薄膜.利用X射线衍射(XRD)、X射线光电子能谱(XPS)、扫描电子显微镜和光致发光谱研究了样品的晶格结构、表面形貌、成分及其发光特性.结果表明:所有样品均具有高度的c轴择优取向,随着退火温度的升高,样品的结晶质量变好,样品的表面都被晶粒覆盖,强而稳定的绿光发射被观察到.绿光强度随退火温度的升高先增加后减小,发光中心位置不随退火温度的变化而改变,这样的绿光发射强而稳定.XRD和XPS结果表明,随退火温度的升高Cu2+还原为Cu+,导致Cu:ZnO薄膜形成的缺陷是VZn,所以绿光发射是由VZn引起的.Cu2+还原为Cu+时,Cu:ZnO薄膜中VZn浓度增加,使绿光发射强度增大.当退火温度超过800?C时,Cu2+的还原能力变差,绿光发射强度减弱.     

纳米ZnO薄膜可见发射机制研究

利用溶胶－凝胶法 （Sol-Gel）制备了纳米ZnO薄膜,获得了高强的近紫外发射室温下测量了样品的光致发光谱(PL )、吸收谱(ABS)、X射线衍射谱(XRD).X射线衍射(XRD)的结果表明：纳米ZnO薄膜呈多晶态,具有六角纤锌矿结构和良好的C轴取向;发现随退火温度升高,（002）衍射峰强度显著增强,衍射峰的半高宽（FWHM）减小、纳米颗粒的粒径增大.由吸收谱(ABS)给出了样品室温下带隙宽度为3.30 eV.在PL谱中观察到二个荧光发射带,一个是中心波长位于392 nm附近强而尖的紫带,另一个是519 nm附近弱而宽的绿带研究了不同退火温度样品的光致发光峰值强度的变化关系,发现随退火温度升高,紫带峰值强度增强、绿带峰值强度减弱,均近似呈线性变化.证实了纳米ZnO薄膜绿光发射主要来自氧空位(Vo)形成的浅施主能级与锌空位(VZn)形成的浅受主能级之间的复合,或氧空位(Vo)形成的深施主能级上的电子至价带顶的跃迁;紫带来自于导带中的电子与价带中的空位形成的激子复合.     

紫外吸收光谱法研究ZnO/碳纳米管复合材料催化降解偶氮染料

以Zn(NO₃)₂和酸化多壁碳纳米管为原料采用水热法合成了ZnO/碳纳米管复合材料,产物经X射线粉末衍射(XRD)和透射电子显微镜(TEM)表征,表明六方晶相的ZnO颗粒大小约为28 nm。紫外吸收光谱研究表明, 该复合材料在太阳光照下具有较高的光催化降解偶氮染料的活性。探究了光照时间﹑催化剂用量﹑染料浓度以及不同的染料结构等因素对催化效率的影响,结果表明随光照时间的延长,偶氮染料位于400 nm的特征峰强度逐渐减弱,且偶氮染料的降解呈准一级的反应。该复合材料对三种染料：酸性橙﹑酸性大红﹑酸性嫩黄的溶液都具有较好的降解能力,反应速率分别为0.09,0.28,0.22 mg· L-1·min-1,此光催化降解速率的差异是由于偶氮染料分子中有机官能团的不同所造成。当选用最优条件时,该复合材料可以迅速降解染料,且经过五次循环后,其催化效率仍高于50％。     

衬底温度对ZnO薄膜的结构和光学特性的影响

利用等离子体辅助分子束外延(P-MBE)设备在蓝宝石衬底上通过改变生长温度,制备了不同的ZnO样品.研究了衬底温度对ZnO的结构、光学和电学性质的影响.样品的晶体结构利用X射线衍射谱进行表征.X射线衍射谱表明,所有的ZnO样品都是(002)取向的六角纤锌矿结构.随着生长温度的升高,X射线的(002)衍射峰的半峰全宽逐渐...     

高分子网络凝胶法制备ZnO超细粉体及其光学性能

采用高分子网络凝胶法制备球形ZnO超细粉体。通过聚乙烯醇(PVA)亚浓溶液交联网络的空间位阻作用,经过烧结,获得了具有球形形貌的粒径为1~3μm的ZnO粉体颗粒。利用X射线衍射(XRD)、扫描电镜(SEM)分析了不同PVA浓度以及退火温度对产物形貌、结构的影响,发现在PVA溶液浓度为5%,并且经500℃热处理所形成的ZnO球形颗粒最为均匀规整。研究了球形ZnO粉体的光致发光性能,室温下经325nm波长激发,观察到两个中心波长分别位于407,468nm的微弱的荧光发射带,在合适温度下,在385nm处还出现了较强的紫外峰。PL光谱表明,退火温度对ZnO的光致发光影响较大,随着退火温度升高,由于表面缺陷和结晶性能发生变化,407nm处发射峰逐渐减弱消失,而紫外发光先增强后减弱,经500℃热处理样品的紫外发光性能达到最佳。     

溶胶-凝胶法纳米ZnO薄膜的绿光发射

利用溶胶-凝胶法制备了纳米ZnO薄膜,室温下测量了样品的光致发光谱(PL)和X射线衍射谱(XRD),观测到中心波长在523 nm附近的绿色荧光发射,研究了纳米ZnO薄膜的绿光发射机制,证实了纳米ZnO薄膜绿光可见发射带来自氧空位(Vo)形成的浅施主能级和锌空位(Vzn)形成的浅受主能级之间的复合。     

Influence of nitrogen and magnesium doping on the properties of ZnO films

Undoped ZnO and doped ZnO films were deposited on the MgO(111) substrates using oxygen plasma-assisted molecular beam expitaxy. The orientations of the grown ZnO thin film were investigated by in situ reflection high-energy electron diffraction and ex situ x-ray diffraction(XRD). The film roughness was measured by atomic force microscopy, which was correlated with the grain sizes determined by XRD. Synchrotron-based x-ray absorption spectroscopy was performed to study the doping effect on the electronic properties of the ZnO films, compared with density functional theory calculations.It is found that, nitrogen doping would hinder the growth of thin film, and generate the NOdefect, while magnesium doping promotes the quality of nitrogen-doped ZnO films, inhibiting(N_2)Oproduction and increasing nitrogen content.     

Crystalline structure and morphological properties of undoped and Sn doped ZnO thin films

Undoped and tin (Sn) doped ZnO thin films have been prepared by spray pyrolysis method. Effect of Sn dopant on the crystalline structure and morphological properties of ZnO thin films has been investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM) method. XRD patterns confirm that the films have polycrystalline nature. While undoped ZnO film has (101) as the preferred orientation, Sn doped ZnO thin films have (002) as the preferred orientation. Grain sizes, lattice parameters and texture coefficient values of the films were determined. Microstructure was analyzed by SEM and the influence of the doping concentration in the microstructure of the films is investigated.     

Improved performance of a crystalline silicon solar cell based on ZnO/PS anti-reflection coating layers

A porous silicon (PS) layer was prepared by photoelectrochemical etching (PECE), and a zinc oxide (ZnO) film was deposited on a PS layer using a radio frequency (RF) sputtering system. The surface morphology of the PS and ZnO/PS layers was characterised using scanning electron microscopy (SEM). Nano-pores were produced in the PS layer with an average diameter of 5.7 nm, which increased the porosity to 91%. X-ray diffraction (XRD) of the ZnO/PS layers shows that the ZnO film is highly oriented along the c-axis perpendicular to the PS layer. The average crystallite size of the PS and ZnO/PS layers are 17.06 and 17.94 nm, respectively. The photoluminescence (PL) emission spectra of the ZnO/PS layers present three emission peaks, two peaks located at 387.5 and 605 nm due to the ZnO nanocrystalline film and a third located at 637.5 nm due to nanocrystalline PS. Raman measurements of the ZnO/PS layers were performed at room temperature (RT) and indicate that a high-quality ZnO nanocrystalline film was formed. Optical reflectance for all the layers was obtained using an optical reflectometer. The lowest effective reflectance was obtained for the ZnO/PS layers. The fabrication of crystalline silicon (c-Si) solar cells based on the ZnO/PS anti-reflection coating (ARC) layers was performed. The I–V characteristics of the solar cells were studied under 100 mW/cm² illumination conditions. The ZnO/PS layers were found to be an excellent ARC and to exhibit exceptional light-trapping at wavelengths ranging from 400 to 1000 nm, which led to a high efficiency of the c-Si solar cell of 18.15%. The ZnO/PS ARC layers enhance and increase the efficiency of the c-Si solar cell. In this paper, the fabrication processes of the c-Si solar cell with ZnO/PS ARC layers are an attractive and promising technique to produce high-efficiency and low-cost of c-Si solar cells.     

ZnO/SiO2 复合薄膜的光学性能

采用溶胶-凝胶法在玻璃衬底上制备ZnO/SiO₂复合薄膜,分别用XRD、TEM、SEM对样品的结构和形貌进行表征,并研究了不同ZnO含量对复合薄膜透过率及荧光特性的影响。结果表明,样品经500 ℃退火处理生成了SiO₂和ZnO,其晶粒尺寸为18.7 nm,薄膜具有双层结构。复合薄膜的透过率随着其中ZnO含量的增加而降低,禁带宽度减小,光学吸收边红移。样品在355 nm波长激发下产生了384 nm的紫外发射峰和440 nm的蓝光发射带,并随ZnO含量的增加而增强,它们分别来自ZnO的电子-空穴复合发光和缺陷发光,及ZnO/SiO₂复合薄膜双层结构的缺陷发光。