Observation of magnetic domains in undoped ZnO grains at room temperature

The present study reports the room temperature ferromagnetism in undoped ZnO thin films grown by PVD method. The 500 nm film with small (90 nm) ZnO grains possess isolated magnetic domains with coercivity of 520 Oe. However, long range magnetic ordering with smaller coercivity of 230 Oe is observed for 1000 nm film. The long range ordering is caused by the reduction in domain wall pinning effect due to the presence of bigger (270 nm) ZnO grains. PL measurements show that these grains are semiconducting in nature. Results presented here suggest that oxygen vacancies at the surface may be responsible for the observed ferromagnetism.     

A grain boundary defect model for ZnO ceramic varistors by deep heat treatment

Studies on ZnO ceramic varistors by deep heat treatment at 650–900 C are reported. The current creep time curve exhibits a peak during the continuous action of a dc biasing voltage; the forwardV-l characteristic is improved rather than degraded after the action of the biasing voltage. We assume that the zinc interstitial cations Zn_i are out diffused rapidly and the concentration of Zn_i in the depletion layer is decreased rapidly during deep heat treatment; the oxygen anions O’_o could be accumulated at the grain interface if the out diffusion quantity of Zn_i is not enough to react with the O’_o; the current creep phenomenon above results from the migration of the interface O’_o by the biasing voltage. We suggest an improved grain boundary defect model for the ZnO varistors by deep heat treatment, and examine the model using the experimental data of lifetime positron-annihilation spectroscopy. Project supported by the National Natural Science Foundation of China.     

缓冲层厚度对Ti/Si模板上生长ZnO薄膜的影响

采用常压MOCVD法,以二乙基锌和去离子水为源,在不同厚度的ZnO缓冲层上生长了一组ZnO薄膜.分别采用X射线衍射(XRD)、干涉显微镜和光致发光谱(PL)对样品的结晶性能、表面形貌和发光性能进行分析,结果表明,随着缓冲层的引入,ZnO外延膜的质量得到很大提高,缓冲层的厚度对外延ZnO薄膜的质量有很大的影响,当缓冲层厚度为60 nm时,ZnO薄膜的结晶性能最好,表现出高度的择优取向,(002)面的ω摇摆曲线半峰全宽仅为1.72°,其表面平整,表现出二维生长的趋势,室温光致发光谱中只有与自由激子复合有关的近紫外发光峰,几乎观察不到与缺陷有关的深能级发光.     

氧化锌微米花的共振拉曼和“负热淬灭”效应

利用化学气相沉积(CVD)的方法通过热氧化高纯锌粉在硅衬底上得到氧化锌微米花. X射线衍射(XRD)结果表明，其具有六角纤锌矿晶体结构.场发射扫描电子显微镜(FE-SEM)图像表明，合成的样品是由很多长且直的ZnO亚微米棒组成的微米花， 具有六角棱柱端面，棒的长度在30μm到50μm之间.在背向共振拉曼散射光谱测量中，观测到ZnO A₁(LO)的五阶声子紫外共振拉曼散射，表明样品具有较高的晶体质量.在变温光致发光谱测量中，观察到明显的中性受主束缚激子(A⁰X)的 关键词： ZnO微米花 光致发光 共振拉曼 “负热淬灭”效应     

掺杂和未掺杂氧化锌薄膜的拉曼光谱

利用拉曼光谱分别对不同衬底上,未掺杂和掺杂以及掺杂浓度不同的ZnO薄膜进行了系统的分析研究。其中ZnO薄膜均由溶胶-凝胶法制得,掺杂源为LiCl。测得的拉曼光谱显示,Pt/Ti/SiO2/Si衬底上生长的ZnO薄膜的拉曼特征峰(437cm-1)的强度明显高于SiO2/Si衬底上ZnO薄膜的拉曼特征峰的强度,说明Pt/Ti/SiO2/Si衬底上ZnO的晶化程度比SiO2/Si上ZnO的晶化程度高;但ZnO拉曼特征峰的位置和半高宽并没有发生变化,说明两种衬底上ZnO薄膜中应力大小没有发生变化。掺Li+后,580cm-1处的峰位向高频方向移动,且掺杂浓度越大频移量越大,说明掺杂已经在不同程度上引起了ZnO晶体中自由载流子浓度的变化。此外,还分析了掺Li+未在很大程度上引起ZnO晶格畸变的原因。     

ZnO-Bi2O3系压敏陶瓷的导电过程与等效势垒高度

研究了ZnO-Bi₂O₃系压敏陶瓷等效势垒高度_eff随着归一化电压的变化规律，发现等效势垒高度_eff随着归一化电压的增加先逐渐增大，达到最大值后持续下降.由于在外加电压作用下反偏势垒高度高于正偏势垒高度，等效势垒高度_eff主要取决于反偏势垒.因此，这种变化规律说明了ZnO压敏陶瓷晶界的导电过程可能存在三个阶段.在低归一化电压区，晶界区域中的电子从正偏势垒区注入到晶界无序层的速率低于电子从晶界无序 关键词： ZnO压敏陶瓷 归一化电压 等效势垒高度 导电过程     

Materials characterization of n - ZnO / p - GaN : Mg / c - Al2O3 UV LEDs grown by pulsed laser deposition and metal–organic chemical vapor deposition

n-ZnO/p-GaN:Mg hybrid heterojunctions grown on c-Al₂O₃ substrates showed 375 nm room temperature electroluminescence. It was suggested that the high materials and interface quality obtained using pulsed laser deposition for the n-ZnO growth and metal–organic chemical vapor deposition for the p-GaN:Mg were key factors enabling the injection of holes and the radiative near band edge recombination in the ZnO. In this paper we present the materials characterization of this structure using x-ray diffraction, scanning electron microscopy and atomic force microscopy.     

柱状ZnO阵列薄膜的生长及其发光特性

采用一种设备简单、原料低廉的新型方法，在镀有ZnO先驱薄膜的(0001)蓝宝石上利用水热 法制备出了柱状ZnO阵列薄膜.用扫描电镜(SEM)，X射线衍射(XRD)对样品的形貌和结构进行 了表征，结果显示ZnO薄膜为柱状阵列，基于蓝宝石衬底沿c轴择优生长，且(0004)摇摆曲线 半高宽度(FWHM)约为1.8°.此ZnO阵列薄膜具有很强的紫外发射光谱(PL). 关键词： 柱状ZnO阵列薄膜 水热法 (0001)蓝宝石 PL谱     

Room-temperature growth of carbon nanofibers on plastic substrates

A very simple method to synthesize densely distributed carbon nanofibers (CNFs) on flexible plastic substrates at room temperature with no catalyst is demonstrated. Carbon film was deposited onto polyimide, poly-ethylene-terephthalate (PET) films, Si plates and a Ni mesh, which were then sputtered with obliquely incident Ar⁺ ions at 3 keV at room temperature. Linear-shaped CNFs oriented in the incidence direction of the ion beam grew on the sputtered substrates, as confirmed by scanning (SEM) and transmission electron microscopes (TEM). CNF growth on a PET substrate, which is a non-heat-tolerant plastic, has never been reported so far. CNFs thus grown were characterized as amorphous without a hollow structure. The diameter of CNFs was almost identical (20-30 nm) despite a large difference in CNF length (0.1-4 μm). In addition, the CNF-tipped cones were demonstrated to act successfully as a template to fabricate one dimensional (1-D) zinc oxide (ZnO) nanostructures on a PET substrate. Thus, it was believed that the ion-irradiation technique would open up a new approach to fabricate any kinds of 1-D nanomaterials on flexible substrates at room temperature.