热等离子体强化氧化锌表面缺陷的形成及对气敏性能作用机理研究

One of the challenges in realizing high performance of metal oxide semiconductor based gas sensors is to enhance their sensitivity in order to respond to the low concentration of detecting hazard gases. Gas sensing process of metal oxide semiconductor is achieved by the change of the surface electric conductivity, and the critical point to realize advanced sensing properties relies on the efficient adjusting of the crystal defects on the surface of semiconductor materials. Furthermore, the function mechanism of the crystal defects on sensing properties is also a critical scientific issue need to be resolved urgently. In this project, the typical enhanced properties of thermal plasma will utilized to design and synthesis of doped ZnO nanoparticles. The ultra-high temperature and active reaction atmosphere in thermal plasma dramatically promote the chemical reaction and the crystal growth, which greatly favors the formation of crystal defects and increasing the carrier concentration in the materials. The detailed crystal defects species and their concentration could be achieved by control the rapid quenching rate in the plasma torch tail. Furthermore, the formaldehyde gas sensing performance of synthesized product will be investigated to the couple the correlation between crystal defects and gas sensing property, which will provides scientific direction for further design and synthesis of materials used in efficient gas sensors. The proposed project is supposed to develop a novel strategy to synthsize metal oxide semiconductor with excellect gas sensing performance, and understand the inherent function mechanism of microstructures to their device performances. This research plan probably not only results in the establishment of the growth model of particle inthermal plasma, but also theoretic development of materials design for sensoring materials to further extent.

低浓度毒害气体的有效检测对氧化物半导体基的气敏传感器气体响应性能提出了很高的要求，半导体材料主要是依靠表面电导变化进行检测，因此对材料表面缺陷的有效调控是实现高灵敏度气敏材料的关键，其对气敏性能的作用机制也是亟待解决的科学问题。本项目拟采用热等离子体合成技术开展氧化锌颗粒制备及掺杂结构调控研究，利用等离子体高温及高活性气氛强化反应进行及颗粒的快速生长，促进颗粒表面缺陷的形成及载流子浓度的控制，通过不同淬冷条件下“冻结”产物实现缺陷种类的调控。在此基础上开展缺陷结构对甲醛气体响应性能的作用规律研究，通过建立二者之间的内在联系并深入分析其作用机理，为高性能的气敏材料设计提供理论依据。本项目的研究不但可以探索出一条制备具有优异气敏性能半导体材料的新技术，阐明产物缺陷对气敏性能的作用机理，推动气敏材料理论研究的发展。而且能够进一步揭示等离子体中颗粒结构调控规律，促进高频热等离子体技术的发展。

在本项目的研究工作中，我们采用热等离子体合成技术开展了氧化锌颗粒制备及掺杂结构调控研究，利用等离子体高温及高活性的反应环境强化反应及颗粒的快速生长，从而促进氧化锌颗粒表面缺陷的形成。实验结果表明通过反应参数及元素掺杂的控制，能够实现产物中缺陷种类及浓度的有效调控。通过不同条件产物显微结构以及生长动力学的分析，阐明了等离子合成过程中缺陷调控的机理。在此基础上进一步探究了不同缺陷结构对气敏性能的影响。研究结果表明对于甲醛等还原性气体，施主缺陷释放的电子容易与吸附的氧结合，使颗粒表面的自由电子数量的增多，从而造成电阻改变明显，气敏性能提高，而受主缺陷的作用正好相反。根据这一机理，我们通过工艺优化得到了对甲醛及乙醇气体具有优异性响应性能的掺杂氧化锌产品。同时利用第一性原理计算对实验结果进行了验证，计算结果表明氧化锌中施主缺陷的存在极大地降低了氧的吸附能，由于吸附氧的增强导致耗尽层内电子数量的增强，从而有效地促进了产物的气敏性能，这一结论与实验结果得到了很好的吻合。同时我们对研究内容进行了延伸，在掺杂氧化锌产物表面负载第二相形成异质结构，利用能带匹配实现载流子的有效分离，进一步促进了气敏性能的提升，取得了很好的结果。