摘要
半导体材料在湿度传感器研究领域越来越受到重视。金属氧化物ZnO纳米材料,由于其独特的物理和化学特性,在太空、汽车、航天、火警探测、工业尾气检测、气候监测等诸多行业中得到应用。课题组利用水热腐蚀法获得具有微米／纳米层次结构的硅纳米孔柱阵列(Si-NPA),其独特的形貌和结构特点为其良好的湿敏特性提供了良好的条件。本文通过利用操作简单,成本低廉的溶胶凝胶法制备氧化锌纳米颗粒,并通过高分子有机物聚乙烯吡咯烷酮(PVP)进行表面修饰。利用旋涂法将PVP修饰过的ZnO纳米颗粒涂覆到Si-NPA上,制得ZnO@PVP/Si-NPA复合结构湿敏元件。通过一系列表征和测试得到如下结果：
1.通过场发射扫描电子显微镜、透射电镜观察了氧化锌与PVP形成氧化锌纳米颗粒的形貌,并结合电子衍射、高分辨透射电镜和傅里叶变换验证了ZnO纳米颗粒的存在。利用X射线衍射证明溶胶凝胶法合成ZnO纳米颗粒的物相为六方纤锌矿结构。傅里叶变换红外吸收光谱证实了PVP与Zn2+的相互作用,该相互作用带来PVP对生成的ZnO表面的修饰,并能影响ZnO合成过程。紫外-可见光吸收光谱证明氧化锌纳米颗粒的大小受到PVP摩尔量的影响,通过计算发现ZnO纳米颗粒粒径随着PVP摩尔量的增加呈现先减小再增大的趋势。
2.比较PVP/Si-NPA和Si-NPA的湿敏性能发现,PVP对Si-NPA衬底的影响较大,由原来电容-相对湿度(C-RH)曲线的接近线性关系转换成为接近指数变化。而ZnO/Si和ZnO@PVP/Si湿敏元件的比较发现,电容出现两种不同的结果,ZnO/Si湿敏元件的电容函数关系基本保持为线性,而ZnO@PVP/Si湿敏元件随着PVP的加入由线性关系转变为指数关系。结合ZnO、PVP和Si-NPA得到不同Zn2+与PVP摩尔比的ZnO@PVP/Si-NPA湿敏元件,经过测试发现,其电容变化在原来的基础上变化更大,并且在Zn2+:PVP=5:5时达到最大值。因此PVP作为ZnO纳米颗粒的修饰剂,以及自身高分子聚合物的特性,能对以Si-NPA为衬底的复合结构湿度传感器产生了极大的增强作用,为后续的湿敏器件性能优化提供了参考和实验基础。
Semiconductor materials have attracted more and more attention in the field of humidity sensor in resent years. As one of the metallic oxides semiconductor materials, zinc oxide nanometer are widely used in space technology, automotive industry, aerospace application, fire detection, industrial exhaust gas testing, climate monitoring, and many other industries for its unique physical and chemical properties. Our team obtained a novel silicon nanoporous pillar array (Si-NPA) with mocron/nanometer hierarchical structure by the hydrothermal etching method, which showed promising prospect in humidity-sensing for its unique morphology and structure feature. In this paper, by simple and low cost sol-gel method we synthesized ZnO nanoparticles, and choosed macromolecule organic matter polyvinylpyrrolidone(PVP) to modify the surface of ZnO nanoparticles. Then the PVP modified ZnO nanoparticles were coated onto the Si-NPA by the spin-coating method, obtaining a ZnO@PVP/Si-NPA composite moisture sensor. A series of characterization and the test were conducted, the results are as follows:
1.The surface morphology as well as the microstructure of ZnO nanoparticles was characterized by field emission scanning electron microscope (SEM), transmission electron microscope (TEM).Combining with electron diffraction, high resolution pictures, and the Fourier transform the existence of ZnO nanoparticles was verified. X-ray diffraction (XRD) proved the as-synthesized ZnO nanoparticles had wurzite hexagonal structure. Fourier transform infrared absorption spectra (FTIR) proved the interaction of PVP with Zn2+,which caused the modification of the ZnO and influence the synthesization of ZnO nanoparticles. Ultraviolet-visible absorption spectra showed the size of the ZnO nanoparticles influenced by PVP molar weight. Through theoretical calculation we found that the ZnO nanoparticles size decrease and then increase with the increase of the molar amount of PVP.
2.Comparison of PVP/Si-NPA and Si-NPA humidity-sensitive performance found that PVP has had a biggish impact on Si-NPA substrate performance, the near linear relative humidity capacitance functional relationship converted into near exponential. Comparing the ZnO/Si and ZnO@PVP/Si moisture sensing performance showed the capacitance of the ZnO/Si moisture sensor remained linear and the ZnO@PVP/Si moisture sensor C-RH curve changed from linear relationship to the exponential relationship with increase of PVP. Combining ZnO, PVP, and Si-NPA we got different ZnO@PVP/Si-NPA moisture sensor with different molar ratio of Zn2+:PVP. Trough testing different sensors we found that the sensor with a molar ratio of Zn2+:PVP=5:5reached maximum improvement comparing with the original sample with no PVP. So by modifying the ZnO nanoparticles, and combined with the characteristics of the polymer itself, PVP had enormous enhancement effect on performance of humidity sensor on Si-NPA substrate composite structure, which provided experimental basis and reference for subsequent humidity sensor optimization.
引文
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