纳米氧化锌掺杂.doc

ZnO纳米材料的可控合成是实现材料性能调控与应用的基础。ZnO纳米材料真正走向应用领域，首先需要解决的就是ZnO纳米材料的可控合成问题，以获得尺寸、形貌、结构、单分散和重复性等稳定可靠的ZnO纳米材料。针对这个问题，人们发展了多种物理和化学的手段来合成ZnO纳米材料，如气相的热蒸发法1-3、化学气相沉积法4-7、脉冲激光沉积法8-9和液相的水热法10-12、溶剂热法13-15、溶胶凝胶法16-17、模板法18和微乳液法汇19-20等。ZnO纳米材料具有极为丰富的形貌和结构。迄今为止，人们已经成功地合成了各种形貌的ZnO纳米结构，如零维的纳米点4，一维的纳米线11、纳米棒1023、纳米管23-24和纳米带2，二维的米片25，此外还有一些复杂的形貌如tetrapod26-29和纳米梳30-32等。ZnO纳米材料的掺杂半导体中的掺杂是指人为地将杂质原子引入到本征半导体中，以调控半导体电学、磁学等材料性能的目的。在半导体工业中根据掺杂原子在半导体中的含量，掺杂可以分为轻掺和重掺，其中轻掺的杂质浓度在10-8数量级，而重掺的杂质浓度在0.1%数量级。当掺杂原子的浓度更高时，一般称为半导体的合金化，如SIGe、AIGaN和CuInSe:等。在研究半导体低维纳米材料的掺杂问题时，通常纳米材料中掺杂原子的浓度在千分之几到百分之几，有时可以达到10%以上，实际上已形成了合金，但是与传统的半导体工业所有不同，在纳米材料中引入特定的杂质时，一般对掺杂和合金化不作细致的划分，本文中沿用掺杂这个概念在ZnO纳米材料中通过引入特定的杂质原子可以有效地调控其光学、电学和磁性等材料性能，接下来将针对ZnO纳米材料中的掺杂现状作介绍。Mg、cd等掺杂在ZnO纳米材料进行Mg或Cd的掺杂，可以在纳米尺度实现ZnO的能带工程33-43。Wu等人36采用金属有机化学气相沉积方法阿(MOCVD)在高温下成功地制备了Mg掺杂的ZnO纳米棒阵列，他们系统地研究了Mg掺杂引起的ZnO纳米棒能带调节现象，Mg在ZnO纳米棒中的掺杂浓度可达到16.5at.%。该方法的主要问题是Mg的金属有机源种类非常有限，同时MOCVD需要使用昂贵的高真空设备和较高的生长温度，在一定程度上限制了其发展。为了降低生长温度，Lee等44人利用水热方法在75一100生长了Mg掺杂的ZnO纳米线，Mg的含量可以达到 25at.%，其光学禁带宽度在 3.21一 3.95eV之间可调，但是较低温度下生长的Mg掺杂zno纳米线的形貌和结晶质量不够理想。Ghosh等人45报道了采用低温水热的方法可以合成Cd掺杂的ZnO纳米晶，随着Cd掺杂浓度的增加，可以观察到明显的吸收边红移现象，但是实验发现容易出现CdO的分相，需要经过分离提纯才能得到Cd掺杂的ZnO纳米晶。OBrien等人46将金属有机盐在三辛胺有机溶剂中进行热分解反应，得到了Mg掺杂和Cd掺杂的Zno纳米晶，通过Cd或Mg的掺杂，ZnO纳米晶的光学禁带宽度可以在2.92一 3.77eV之间可调，该方法的优点是反应温度不高，获得的掺杂ZnO纳米晶具有很好的结晶质量和可调的光学性能，但是形貌与尺寸可控性不够理想。Mn、Ni、Co、Fe等过渡元素掺杂将含有3d电子的Mn、Ni、Co和Fe等过渡元素掺杂引入到ZnO材料中，可以形成所谓的稀磁半导体，稀磁半导体可能会对未来的信息存储技术带来变革。迄今为止，关于ZnO纳米材料中Mn、Ni、CO和Fe等元素掺杂和相关性能的文献报道较多47-68。Kang等人50通过气相热蒸发的方法制备了Mn掺杂的ZnO纳米线。Mn的掺杂浓度可以在5-20at.%之间调节，研究发现Mn原子成功地进入到ZnO的晶格并占据Zn的替代位置，X射线吸收测试表明Mn掺杂的ZnO纳米线在室温下具有铁磁性。Wang等人68报道了大面积衬底上生长的Ni掺杂ZnO纳米棒阵列，具有优异的晶体质量和改善的电学性能，为研究Ni掺杂ZnO纳米材料中的磁性性能提供了基础。HenS等人69报道了Co掺杂浓度为 2at.%的ZnO量子点，研究发现一部分Co原子进入ZnO晶格并占据Zn的替代位置，大部分的Co原子(50一60%)仅仅吸附在量子点的表面，此外还有一部分Co原子进入ZnO的晶格并处于间隙位置。Palomino等人70合成了单分散性较好的Fe掺杂ZnO纳米晶，尺寸约6一8nm，研究发现Fe掺杂ZnO纳米晶的磁性性能与纳米晶的成分和尺寸密切相关。Inamdar等人71合成了Co掺杂和Mn、Co共掺杂的ZnO纳米晶，研究发现ZnO纳米晶中的磁性性能与ZnO纳米晶中的缺陷密切相关。AI、Ga等掺杂通过族元素如Al和Ga等原子的有效掺杂，人们可以制备n型的ZnO纳米材料，显著地提高其电导率和载流子浓度。Yang等人71采用溶剂热的方法制备了Al掺杂的ZnO纳米晶，纳米晶的尺寸约为40nm，具有可控的形貌。当Al的掺杂浓度为 2at.%时，其制成的薄膜具有最低的电阻率，经过后续的退火处理后，Al掺杂ZnO纳米晶薄膜的电阻率最低可以达到22.38欧cm，比纯ZnO的电阻率低了6个数量级，研究认为Al掺杂ZnO显著增强的电导率是由于Al掺杂进入了ZnO晶格并占据了Zn原子的位置。Hidayat等人72报道了采用低压喷雾热解法生长的Al掺杂ZnO纳米颗粒，颗粒尺寸约为20nm，热解温度为800一1000，Al掺杂浓度为 4at.%的ZnO纳米颗粒薄膜经退火处理后，在400一800nm范围内具有97%以上的透过率，厚度为250nm的薄膜其电阻率最低为4* 103欧cm。Hartner等人73通过化学气相沉积方法的制备了高度结晶的Al掺杂ZnO纳米颗粒，研究发现Al掺杂浓度在7一 8at.%之间时制备的ZnO纳米薄膜具有较好的电学性能，在氢气气氛下它的电阻率最低可以达到1.9*102欧cm。Yuan等人74报道了采用简单的CVD方法可以制备Ga掺杂的ZnO纳米线，通过改变Ga的掺杂含量，即从0到 1at.%，ZnO纳米线的电阻率降低了两个数量级。Wei等人75采用液相热注入的方法合成了Ga掺杂的ZnO纳米晶，纳米晶的尺寸约为5一10nm，将Ga掺杂的ZnO纳米晶旋涂成纳米晶薄膜，经过退火处理后其电阻率最低可以达到7.5*10-2欧cm。1 M. 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