一维ZnO纳米材料甲醛光电气敏性能的研究

发布时间：2018-09-18 12:39

【摘要】：气体传感器技术在工业自动化控制过程、汽车排放控制系统以及家庭、公共场所气体泄漏检测中发挥了重要的作用,特别是基于金属氧化物半导体热阻式气体传感器在检测H2、CO、Volatile Organic Compounds(VOCs)等气体方面取得了显著的成果。热阻式的金属氧化物半导体气体传感主要是利用其暴露在还原或者氧化性气氛中电阻的变化来检测气体浓度。由于该种类型的气体传感器具有较高的灵敏度,并且价格便宜,被认为是很有前景的传感器。然而,低的选择性和相对较高的工作温度使热阻式气体传感器在使用过程中稳定性较差、能耗高,而且不适合在易燃易爆的环境中使用。更重要的是,由于工作中需要额外消耗能量,使器件的小型化受到限制。因此,发展能够在室温下工作、低能便携的新型传感器对研究人员来说依然是个严峻的挑战。近来已经被实验证实光激发可以增加半导体材料光生载流子浓度,促进半导体材料表面气体的吸附脱附,因此,对金属氧化物半导体材料来说,使用光激发代替加热是可以实现在室温下对目标气体检测的。而Zn O作为n型宽带隙、气体敏感的半导体材料是构建光电气体传感器的理想材料。但是,目前光电气体传感器对气体的响应度、选择性能相比于热阻式气体传感器是有一定差距的,这是目前极需要解决的问题,同时,为了提高Zn O材料光电气体传感的性能,深入了解在气体检测过程中材料的光物理过程,即光照后,光生载流子的分离、传输以及复合过程是十分必要。本文选用Zn O作为气敏材料,气敏响应测试采用的是在室温下选用紫外光为激发光源的表面光电流系统。通过贵金属修饰、金属离子掺杂的手段改善Zn O气敏材料的光电性能,借助于表面光电压技术(SPV)深入讨论了光生电荷对光电气敏的微观的影响。基于以上内容,本文的工作从以下几个方面展开:1.采用水热方法合成了贵金属Ag修饰的Zn O纳米棒光电气敏材料。TEM测试证实Ag单质成功沉积在Zn O纳米棒表面,光电气敏测试的结果说明一定Ag修饰量的Zn O材料展现出良好的HCHO气敏性能,对40 ppm浓度的HCHO响应度是纯Zn O气敏材料的5.3倍。Ag修饰在Zn O表面,一方面是由于Ag具有催化作用,可以加速氧气在Zn O表面的吸附;另一方面Ag作为电子受体能够捕获Zn O导带中的电子,会使Zn O表面富集更多的氧负离子基团,也会在光照下促进光生电子-空穴的分离,我们用表面光电压技术论证了这一解释。但是多的修饰量并不利于材料的光电气敏性能,可能是由于过多的Ag单质会占据Zn O表面活性位点,不利于氧气吸附,也会阻碍材料对光的吸收,不利于光生电荷分离,因此,表面修饰要有一个最佳量。2.采用静电纺丝的方法合成了Ni2+离子掺杂的Zn O纳米纤维光电气敏材料。通过系统地表征证明了Ni2+离子存在于Zn O的晶格中,有Ni-O-Zn键的形成。荧光测试结果证明适量的Ni2+离子掺杂可以增加气敏材料的给体缺陷密度,促进更多的氧气分子吸附,有利于表面催化氧化反应。表面光电压和瞬态光电压谱图直观的表明了适量的Ni2+离子掺杂能有效的促进Zn O纳米纤维光生电荷的分离和传输,抑制其复合,使更多的光生空穴参与到气敏反应中,提高了材料对HCHO的光电气敏响应。3.采用静电纺丝的方法合成了Al3+离子掺杂的Zn O纳米纤维光电气敏材料。一系列的表征证实了Al3+离子取代Zn2+进入到Zn O晶格中。根据O 1s的XPS测试结果,说明Al3+离子掺杂增加了材料的表面氧空位,促使更多的氧气分子在其表面的吸附。表面光电压测试证实了多的氧负离子有助于样品光生电荷的分离以及促进更多的光生空穴向表面迁移。气敏测试表明Al3+离子掺杂Zn O气敏材料对低浓度(1 ppm)HCHO有很好的响应,其最低检测限为0.14 ppb。另外,我们在气敏检测过程中选用365 nm的UV-LED灯珠为光源,成功的简化了光电气敏测试系统,这将有利于器件的集成化发展。
[Abstract]:Gas sensor technology plays an important role in industrial automation control process, automotive emission control system and gas leakage detection in households and public places. Especially, metal oxide semiconductor thermal resistance gas sensor has made remarkable achievements in detecting H2, CO, Volatile Organic Compounds (VOCs) and other gases. Thermal resistive metal oxide semiconductor gas sensors are mainly used to detect gas concentration by changing the resistance of the gas exposed to reductive or oxidative atmosphere. Due to their high sensitivity and low cost, these sensors are considered to be promising sensors. However, they have low selectivity and relatively high selectivity. The working temperature makes the thermistor gas sensor unstable, high energy consumption and unsuitable for use in flammable and explosive environments. More importantly, the miniaturization of the device is limited because of the need for additional energy consumption in the work. Therefore, the development of new low-energy and portable sensors that can work at room temperature will be studied. Recently, it has been proved that photoexcitation can increase the concentration of photogenerated carriers in semiconductor materials and promote the adsorption and desorption of gases on the surface of semiconductor materials. As an n-type wide-band gap, gas-sensitive semiconductor material is an ideal material for constructing photoelectric gas sensors. However, the response and selectivity of photoelectric gas sensors to gases are different from those of thermal resistive gas sensors. This is a problem that needs to be solved at present. At the same time, in order to improve the photoelectric properties of Zn O materials. The performance of gas sensing, in-depth understanding of the material in the process of gas detection photophysical process, that is, after illumination, photogenerated carrier separation, transmission and recombination process is very necessary. Noble metal modification and metal ion doping are used to improve the photoelectric properties of Zn O gas sensing materials. The micro-effects of photoinduced charges on the photoelectric properties of Zn O gas sensing materials are discussed by means of surface photovoltaic technique (SPV). TEM test confirmed that Ag was successfully deposited on the surface of Zn O nanorods. The results showed that Zn O with a certain amount of Ag modified exhibited good HCHO gas sensing properties. The HCHO responsiveness to 40 ppm concentration was 5.3 times higher than that of pure Zn O. Ag modified on the surface of Zn O was due to the catalysis of Ag. On the other hand, Ag as an electron acceptor can capture electrons in the conduction band of Zn O, enrich more oxygen anion groups on the surface of Zn O, and promote the separation of photogenerated electrons and holes under light. We have demonstrated this explanation by surface photovoltaic technique. However, the amount of modification is not favorable. It may be that too much Ag will occupy the active sites on the surface of Zn O, which is not conducive to oxygen adsorption, but also hinder the absorption of light and the separation of photogenerated charges. Therefore, the surface modification should have an optimum amount. 2. Ni2+ doped Zn O nanofibers were synthesized by electrospinning. Gas sensitive materials. It is proved by systematic characterization that Ni2+ ions exist in the lattice of Zn O and form Ni-O-Zn bonds. Fluorescence measurements show that appropriate doping of Ni2+ ions can increase the density of donor defects, promote more oxygen molecules adsorption and facilitate surface catalytic oxidation. Surface photovoltage and transient photovoltage The spectra show that the appropriate amount of Ni2+ ion doping can effectively promote the separation and transmission of photogenerated charge of Zn O nanofibers, inhibit their recombination, make more photogenerated holes participate in the gas-sensitive reaction, and improve the material's photoelectric response to HCHO. 3. Al3+ ion doped Zn O nanofibers were synthesized by electrospinning method. Electrical sensitive materials. A series of characterizations confirm that Al 3+ ions replace Zn 2+ into the Zn O lattice. According to the XPS results of O 1s, it is shown that Al 3+ ion doping increases the surface oxygen vacancy of the material and promotes the adsorption of more oxygen molecules on its surface. Gas sensing tests show that Al 3+ doped Zn O gas sensing materials have a good response to low concentration (1 ppm) HCHO, and the minimum detection limit is 0.14 ppb. In addition, we choose 365 nm UV-LED beads as the light source in the gas sensing process, which simplifies the photoelectric gas sensing testing system successfully. It will facilitate the integrated development of devices.
【学位授予单位】：吉林大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：O614.241;TP212

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