|关键词||肖特基结 传感器阵列 爆炸物检测 光电检测 气敏检测|
爆炸恐怖袭击严重危害国家安全和社会稳定，爆炸物的快速探测与排除是一个热点研究领域。爆炸物气氛检测具有非接触、采样简单、可靠性高等优点。然而，室温下爆炸物的饱和蒸气压通常比较低，尤其是实际环境中爆炸物气氛浓度更低。因此，开发针对爆炸物气氛的高灵敏传感材料及器件，是爆炸物气氛检测中亟需解决的难题。基于电学传感器的气敏检测方法具有稳定性高、制备工艺成熟、结构简单和成本低廉等优点，被广泛应用于气体检测领域。在电学气敏传感器中，相比于传统的欧姆接触传感器，基于肖特基结的传感器灵敏度更高。其检测的基本原理为：在反向偏压下，输出电流与肖特基势垒高度呈指数关系，肖特基势垒高度的微小变动可引起输出电流的极大变化。然而，目前关于肖特基结传感器用于爆炸物气氛检测的研究十分有限，且存在灵敏度较低、响应时间较长等问题，不能实现爆炸物识别。因此，需要进一步提升肖特基结传感器的各项性能指标，从而实现爆炸物气氛的高灵敏、快速、识别检测。本论文从设计、构建基于肖特基结的气敏传感器入手，致力于痕量爆炸物气氛检测，最终实现对爆炸物的识别检测。主要的研究内容和结果分为如下四个部分：1、ZnO/rGO（reduced graphene oxide，还原氧化石墨烯）核壳微观肖特基结传感器用于硝基爆炸物气氛的高灵敏检测通过一步水热法合成了ZnO/rGO核壳结构，并采用传统涂膜方法构建了ZnO/rGO核壳微观肖特基结传感器。该微观肖特基结传感器实现了对ppb（part per billion，十亿分之一）级TNT（2, 4, 6-trinitrotoluene，2，4，6-三硝基甲苯）、DNT（2, 4-dinitrotoluene，2，4-二硝基甲苯）和PNT（para-nitrotoluene，对硝基甲苯）以及ppt（part per trillion，万亿分之一）级PA（picric acid，苦味酸）和RDX（hexagen，黑索金）5种硝基爆炸物气氛的高灵敏、快速检测。其中，对TNT、DNT和RDX的响应大小分别可达到56.8%、58.4%和80%，且响应时间均小于6 s。该传感器对浓度高达ppm（parts per million，百万分之一）级的NO2、NH3和乙醇气氛均表现出良好的抗干扰性能。相比于ZnO纳米球传感器，ZnO/rGO核壳微观肖特基结传感器对TNT和RDX的响应分别提高了5.5和3.4倍。结果表明，微观肖特基结的引入，极大地简化了肖特基结制备工艺，有效地提升了传感材料对爆炸物气氛的响应灵敏度，为开发高灵敏传感材料提供了新的思路。2、Si/ZnO NWs（nanowires，纳米线）/rGO肖特基结传感器用于爆炸物气氛检测的研究为了充分发挥肖特基结的优势，通过引入比表面积大的ZnO NWs阵列，构建了基于Si/ZnO NWs/rGO的三元宏观肖特基结传感器。然而，该传感器对爆炸物室温饱和蒸气的灵敏度较低，响应时间较长。该研究说明构建肖特基结传感器需要选择合适的材料组成和结构。3、基于单个SiNWs（silicon nanowires，硅纳米线）/ZnO/rGO光电肖特基结的传感器阵列对爆炸物气氛的半定量检测首次通过SiNWs阵列表面包覆生长ZnO纳米晶和转移rGO顶电极构建了SiNWs/ZnO/rGO肖特基结。通过调节468 nm单色LED（light-emitting diode）光源形成8种不同光强周期性照射肖特基结传感器，即可得到由8个传感器组成的传感器阵列。该设计中，光的施加会产生三种作用：1）调控肖特基势垒的高度；2）调控载流子浓度；3）调控分析物的吸附-脱附平衡。因此，对于同一种爆炸物气氛，在8种不同光强下，肖特基结传感器会产生8个不同的响应值。另外，由于不同的爆炸物分子得到电子和失去电子的能力不同，因而，对于不同的爆炸物，肖特基结传感器在同一种光强下呈现出的响应大小也不一样。最后，通过PCA（principal component analysis，主成分分析）方法对响应数据进行分析处理，实现了对TNT、DNT、PNT、PA、RDX、Urea、BP（black powder，黑火药）和AN（ammonium nitrate，硝酸铵）等8种制式及非制式爆炸物的高灵敏、快速识别检测。相比于传统的传感器阵列，该传感器阵列基于单个传感器即可实现阵列检测的功能，同时，大大简化了传感器阵列的制备工序，并从原理上显著提升了阵列的稳定性。不仅如此，该方案在检测不同浓度的同一种爆炸物时，其响应数据在主成分空间中会落在一个线性区。因此，利用该光电肖特基结传感器检测未知爆炸物时，不仅能够实现爆炸物的识别，还可以实现半定量分析。4、SiNWs/rGO光电肖特基结传感器阵列对痕量爆炸物气氛的识别检测首次通过将制备的SiNWs/APTS（3-aminopropyltriethoxysilane，3-氨基丙基-三乙氧基硅烷）/rGO、SiNWs/TiO2/rGO和SiNWs/ZnO/rGO肖特基结传感器自由组合及施加光源调制，将传感器数量从3个增加到21个，借助LDA（linear discriminant analysis，线性判别分析）方法，对爆炸物气氛的区分能力从无提高到可对TNT、DNT、PNT、PA、BP和AN等6种制式及非制式爆炸物的严格识别区分。在此基础上，实验证明，该传感器阵列能够实现对ppb级未知爆炸物气氛，如TNT的准确识别。该研究进一步为肖特基结传感器阵列的构建做出了有力尝试。
The terrorist attack based on explosives has become a major threat to the homeland security and social stability, while the rapid detection and elimination of explosives is a hot research field. The detection method of vapor-phase explosives has the merits of non-contacting, simple sampling and high reliability. However, the saturated vapor pressures of explosives are usually ultralow, especially, the concentrations of the explosives are even lower in the real-world atmosphere. Therefore, it is an urgent demand to exploit sensing materials and devices with high sensitivity for trace explosive vapors detection.Fortunately, electrical sensor-based gas sensing method is widely applied in the field of gas detection owing to the high stability, mature processing technique, simple structure and low cost. Among electrical sensors for gas detection, the Schottky junction-based sensors could be much more sensitive compared with the traditional Ohmic contact-based sensors theoretically. The fundamental working principle of Schottky junction-based sensor is that the output current has exponential relation to the Schottky barrier height while reverse biased. Hence, a small change in Schottky barrier height would lead to a significant change in output current. However, there is only very limited research on the detection of explosive vapors by Schottky junction-based sensors, along with unresolved issues like low sensitivity and long response time, preventing the realization of the discriminative detection of explosive vapors. Therefore, it is necessary to improve the sensing performance of Schottky junction-based sensor to realize supersensitive, fast and recognizable detection of explosive vapors.Aiming at the recognizable detection of explosives, here, in this thesis, we focuse on the design and fabrication of the Schottky junction-based sensors, including the following four parts: 1. Highly sensitive detection of nitro-explosive vapors realized by ZnO/rGO (reduced graphene oxide) core/shell micro-Schottky junctionThe ZnO/rGO core/shell structure was successfully prepared via a facile one-step hydrothermal method. A sensor composed by micro Schottky junction of ZnO/rGO core/shell structure was further constructed using the traditional coating method. It is found that this gas sensor exhibited excellent performance for the vapor detection of TNT (2, 4, 6-trinitrotoluene), DNT (2, 4-dinitrotoluene) and PNT (para-nitrotoluene) in ppb (part per billion) level, and PA (picric acid) and RDX (hexogen) in ppt (part per trillion) level. Especially, the responses towards TNT, DNT and RDX achieved 56.8%, 58.4% and 80%, respectively, while all the response times are less than 6 s. More importantly, superior anti-interfering property is shown even towards interfering gases in ppm level. Furthermore, it is demonstrated that with the wrapping of rGO, the response values of the pure ZnO-based sensor towards TNT and RDX vapors were boosted by 5.5 and 3.4 times, respectively. These results show that the introduction of micro Schottky junction not only greatly simplifies the preparation process of Schottky sensor, but also effectively improves the sensitivity of the sensing materials towards explosive vapors, which shines light on the development of sensing materials with high sensitivity.2. Si/ZnO NWs (nanowires)/rGO Schottky sensor for nitro-explosive vapors detectionIn order to further bring the advantages of Schottky junction, the sensor based on Si/ZnO NWs/rGO tri-component macro Schottky junction was built by introducing the ZnO NWs array with large surface area. However, the corresponding response values toward explosive vapors are quite low, and the response times were too long. This work demonstrates that the selection of appropriate junction components and structure is essential for the building of a high performance Schottky sensor.3. Semi-quantitative detection of explosive vapors realized by sensory array based on a single SiNWs (silicon nanowires)/ZnO/rGO optoelectronic Schottky sensorThe SiNWs/ZnO/rGO Schottky junction were prepared for the first time via decorating ZnO nanocrystals on the SiNWs surface and transferring rGO top electrode. By using 468 nm monochromatic LED (light-emitting diode) with eight light intensities to periodically illuminate the Schottky sensor, a sensory array with 8 sensors was built. Here, light illumination plays three important role by regulating the Schottky barrier height, controlling the carrier concentration, and controlling the adsorption-desorption equilibrium of the analytes. Therefore, for the same explosive species, the present Schottky sensor could produce 8 different response values under 8 light intensities. Besides, due to the fact that the ability of gaining or losing electrons for different explosive molecules are different, the responses of the sensor towards different explosives are different even under the same light intensity. With the help of the PCA (principal component analysis) method to analyze the response data, the sensory array could realize the rapid, ultrasensitive and discriminative detection of TNT, DNT, PNT, PA, RDX, Urea, BP (black powder) and AN (ammonium nitrate) vapors. Thus, an individual optoelectronic sensor is able to realize the function of a sensory array, which was traditionally composed by a group of sensors, simply by periodically adjusting the intensity of the illuminated light. Besides, the preparation process of the sensory array is greatly simplified, and the stability of the array is significantly enhanced in principle. Furthermore, the clusters representing one explosive with different concentrations could line up separately in the PCA diagram. Therefore, the present optoelectronic Schottky sensor can not only distinguish explosive species, but also semi-quantitatively define the concentration of unknown explosive vapors, which is similar as an artificial olfactory system.4. SiNWs/rGO optoelectronic Schottky junction-based sensory array for the recognizable detection of trace explosive vaporsTo enhance the recognization ability of a sensory array, for the first time, Schottky sensors of SiNWs/APTS(3-aminopropyltriethoxysilane)/rGO, SiNWs/TiO2/rGO and SiNWs/ZnO/rGO were randomly combined and regulated by the illuminated light to increase the sensor number. Remarkably, the sensor number was increased from 3 to 21. And with the assistance of LDA (linear discriminant analysis) method, the distinguishing ability of the sensory array toward explosive vapors were promoted from no performance to strict identification of TNT, DNT, PNT, PA, BP and AN vapors. Furthermore, it shows that the sensory array could achieve accurate identification of unknown explosive vapors in ppb level, such as TNT. We hope this work could contribute to the development of novel Schottky junction-based sensory array.
|郭林娟. 肖特基结传感器的设计、构建及其在痕量爆炸物气氛检测中的应用[D]. 北京. 中国科学院大学,2017.|
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