【作者】 刘延霞；

【导师】 谢二庆；

【作者基本信息】 兰州大学 ， 凝聚态物理， 2011， 博士

【摘要】 ZnO是一种非常重要的新型半导体功能材料,其独特的电学、光学性质引起了极大的关注。由于ZnO在气体传感器、发光器件制作和场发射领域具有广泛的应用前景,其气敏特性、光致发光性质以及场发射性质成为了研究的热点。本论文的研究工作就是基于ZnO以上三个方面的性质展开的。论文中的主要研究结果总结如下：1.采用激光脉冲沉积方法在蓝宝石衬底上沉积了厚度大约为10nm的ZnO以及掺杂ZnO薄膜,并对部分ZnO薄膜进行了金属Pd颗粒包覆或者空气中高温退火,然后对这些样品进行了H2气敏测试,实验结果表明P、Mn和Sb元素掺杂后,样品对H2的灵敏度没有提高,而Mg0.1Zn0.9O薄膜对H2的灵敏度明显提高,并通过气敏机制分析解释了实验结果；而包覆Pd颗粒后样品对H2的响应温度显著地降低了,在室温下对低浓度的H2(10ppm)就有较好的响应；此外对ZnO薄膜进行空气退火后样品对H2的灵敏度显著地提高了。在对样品进行H2气敏测试的过程中发现ZnO薄膜在低温下为p型导电类型,随着温度的升高又变为n型导电类型,文中分析了导电类型转变的原因,并给出了p型ZnO薄膜中存在的本征缺陷。2.采用电纺丝技术制备了不同形貌的ZnO一维纳米结构,并测试了样品的气敏特性。首先发现排列的ZnO纳米管对H2的敏感度要优于同条件下制备的ZnO薄膜；其次在研究不同浓度Tb掺杂ZnO纳米纤维对乙醇和丙酮气体的敏感特性时发现低浓度的Tb掺杂(<3%)可以提高样品对乙醇气体的灵敏度,而Tb掺杂浓度为2%或3%时,样品对丙酮气体的敏感度较高；最后制备了SnO2/ZnO并排纳米管,并对其生长机制做出了解释,同时测试样品对乙醇和丙酮气体的敏感特性,发现测试温度高于200℃时,样品对乙醇气体具有很好的敏感特性,而其作为丙酮气敏材料的最佳工作温度为300℃。3.用电纺丝方法分别制备了Al和Tb掺杂的ZnO纳米纤维,此外还制备了Eu和Tb掺杂的ZnO/ZrO2纳米带,研究了样品的光致发光(PL)特性。实验结果表明：首先Al掺杂可以同时抑制ZnO纳米纤维PL谱中的绿光和橙光发射,由对比实验得出绿光和橙光发射分别源于样品中存在的O空位和间隙O缺陷,而这两种缺陷在晶粒中分布的区域不相同,Al的掺入促进了两种相对立的缺陷的中和,因此同时减弱了两种缺陷发光峰的强度；其次实验证明在325nm的激光激发下掺Tb的ZnO纳米纤维不能为Tb3+离子发光提供很好的基质,因此稀土发光效率很低；而Tb掺杂的ZnO/ZrO2纳米带的PL谱可以观察到Tb3+离子的特征发光谱线。另外,掺Eu的ZnO/ZrO2纳米带可以激发Eu3+离子的特征谱线,并且其中ZnO的O空位有可能为Eu3+离子发光提供了敏化剂。4.结合了电纺丝技术和低温水溶液方法制备了ZnO一维同质外延结构,场发射测试结果表明该结构具有非常高的场发射性能,其开启电场仅为4.8V/μm,当场强为6.7V/μm时样品的发射电流密度就达到了100μA/cm2,场发射增强因子为3361。通过分析得出ZnO同质外延结构优异的场发射性能可以归因于三方面的因素：纳米棒的针状形貌、ZnO纳米针的高长径比和ZnO纳米针在衬底上的高低起伏分布。更多还原

【Abstract】 ZnO, considered as one of the most important semiconductor functional material, has attracted great attention due to its unique electrical and optical characteristics. ZnO is a very promising candidate in the fields of gas sensors, optoelectronic devices and field emitters. Thus the sensing, photoluminescence (PL) and field emission properties of ZnO have been widely investigated. This thesis is focused on these three properties of ZnO. The main research work and the results as listed as follows:1. Undoped and doped ZnO thin films with the thickness of about 10 nm were deposited on sapphire substrates by pulsed laser deposition (PLD) technique. Some of the undoped films were covered with Pd particles or annealed in air. The H2 sensing properties of all these samples were measured. When P, Mn and Sb elements were doped into the ZnO films, the sensitivities were not improved. And Mg doping could greatly improve the H2 sensitivity of the ZnO film. The sensing mechanism was analyzed to explain the great improvement of sensitivity for Mg doped ZnO film. The ZnO films coated with Pd particles showed good response to H2 at low temperatre. It could detect 10 ppm H2 even at room temperature. Moreover, post-annealing in air could also improve the H2 sensitivity of the ZnO films. Basing on the H2 sensing measurement, we found that the conductivity of the undoped ZnO films converted from p-type at low temperature to n-type at higher temperature. Opposite responses to H2 were observed for ZnO with different conduction type. We explained the reason for such a conversion and the origins of the p-type ZnO were proposed.2. Different structures of one-dimensional ZnO have been fabricated by electrospinning method and the sensing properties of them were tested. It was found that the aligned ZnO nanotubes showed better H2 sensitivity than the ZnO films did. The ethanol and acetone sensing properties of the Tb doped ZnO nanofibers were measured. The results indicated that low concentration (<3%) of Tb doping could improve the sensitivity of the ZnO nanofibers to ethanol and the ZnO nanofibers with the Tb concentration of 2% and 3% showed higher acetone sensitivities among all the Tb doped ZnO nanofibers. Besides, bicomponent SnO2/ZnO nanotubes were fabricated by electrospinning with a side-by-side dual spinneret. The side-by-side SnO2/ZnO nanotubes sample showed good sensing properties to both ethanol and acetone. Its gas sensitivity to ethanol was high at the operation temperature higher than 200℃. And the optimal operation temperature for it to detect acetone was 300℃.3. Al doped ZnO (AZO) nanofibers, Tb doped ZnO (TZO) nanofibers and Eu or Tb doped ZnO/ZrO2 nanaobelts were fabricated by electrospinning technique. The Al doping could simultaneously suppress the green and orange emissions in the PL spectra of the ZnO nanofibers, which derived from oxygen vacancies and excess oxygen in the ZnO nanofibers respectively. This phenomenon could be explained as the separate distribution of these two kinds of the defects in the ZnO nanograins and Al doping could facilitate the neutralization of the two kinds of defects. The PL spectra of the Tb doped ZnO nanofibers showed that using a 325 nm laser as the excitation source, Tb3+ ions could not be well excited and the characteristic peaks of the Tb3+ ions were very weak. That is to say ZnO nanofibers could not be a good matrix for Tb3+ ions. On the other hand, Tb3+ in the ZnO/ZrO2 nanobelts showed strong characteristic peaks of Tb3+ ions, which could be attributed to ZrO2 in the nanobelts. Furthermore, the emissions corresponding to intra-5D0→7Fj(j=0,1,2,3 and 4) transitions of Eu3+ ions in the ZnO/ZrO2 nanobelts could be observed with a high emission intensity. And ZnO oxygen vacancy in the host matrix might act as an effective sensitizer for adjacent Eu ions.4. Homogeneous hierarchical-structure ZnO with ZnO nanoneedles growing on ZnO nanofibers has been fabricated by combining electrospinning and aqueous solution processes. High field emission performance of the hierarchical-structure ZnO, including low turn-on field, high current density at low applied field and high field enhancement factor was obtained. This good FE performance of the hierarchical-structure ZnO is due to the tapered tips of the ZnO nanoneedles, the high aspect ratio of the ZnO nanoneedles and the undulant space distribution of the ZnO nanoneedles.更多还原