石墨烯机械谐振式光纤氢传感器研究

Fiber-optic hydrogen sensors are intrinsically safe compared with their electrical counterparts; however, their sensing performance needs further improvement, in terms of sensitivity, response speed and temperature cross-sensitivity, for real applications. Here, we propose a new fiber-optic hydrogen sensor based on mechanical resonance of graphene with nanoscale thickness. The sensor is constructed by first decorating a thin layer of hydrogen-sensitive material onto a graphene film, and then transfer the graphene film onto a fiber with an air cavity at the end. When the hydrogen-sensitive material interacts with hydrogen molecules, the crystal lattice of the material expands, which stretches the graphene film. The stretching force changes the resonant frequency of the graphene film, and the frequency shift is measured by using two laser beams with separated wavelengths, to optically exciting and detecting the mechanical resonance of the graphene film, respectively. This project will focus on the study of the characteristics of the graphene resonance under optical driving, the construction of the sensor, the mechanism of hydrogen sensitivity and the optimization of sensing performance. By detecting the dynamic mechanical resonance of nanoscale graphene films, instead of optical response in conventional microscale optical fibers, a novel fiber-optic hydrogen sensor with high sensitivity, fast response and immunity to environmental disturbance can be achieved. This study can also provide fundamental theoretical basis and research methodology for investigating other micro/nano-mechanical resonators.

光纤氢传感器与传统电学传感器相比具有本质安全的特性，但在灵敏度、响应速度、温度交叉敏感等方面仍存在不足。针对此问题，本项目提出一种基于石墨烯机械谐振的光纤氢传感器：在石墨烯薄膜表面修饰氢敏材料，将薄膜转移到光纤空腔端面形成谐振结构；薄膜吸氢后固有谐振频率改变，通过光纤导光以激励薄膜振动并读取谐振频率变化。项目将重点围绕石墨烯机械谐振特性与光激励振动过程、传感器构建、氢敏机理与性能提升等几个方面展开研究。区别于传统光纤氢传感器检测光学参量的变化，本项目基于石墨烯纳米薄膜力学谐振特性改变这一新机理，实现灵敏度高、响应速度快、抗环境干扰的氢气探测，同时为研究这类纳米光机械谐振器件的物理机制提供理论基础和研究方法。

随着环境污染与全球变暖等问题的日益加重，清洁能源的开发和使用对绿色可持续发展尤为重要。氢气燃烧效率高、产物无污染，是理想的清洁能源，但与甲烷等其它可燃气体相比，氢气分子质量小，容易泄露，空气中浓度在4%-75%的范围内时，遇到明火就会爆炸。因此，在氢气生产、存储、运输及使用过程中需要对其浓度进行快速、准确检测。传统的电化学、电阻型氢气传感器可能因产生电火花而引发爆炸等安全事故。与之相比，光纤氢传感器以光波作为信号载体，具有本质安全、灵敏度高、体积小、抗电磁干扰等优点。但目前的光纤氢传感器在灵敏度、响应速度等方面仍存在不足。.针对上述问题，本项目将二维材料石墨烯与高精度光纤干涉仪相结合，构建基于石墨烯机械形变的高灵敏、快响应光纤氢气传感器，项目主要围绕石墨烯光纤氢传感器光学与力学特性、传感器制备、传感器氢敏机理与性能提升三个方面开展了研究：.1.理论研究了氢敏材料（钯膜）厚度对石墨烯光学反射率的影响；在此基础上，研究了石墨烯膜、钯膜厚度对传感器反射谱条纹对比度的影响，通过优化参数获得了1550nm处对比度大于20dB的器件；建立了石墨烯-钯复合薄膜挠曲与薄膜内部应力关系的理论分析模型。.2.掌握了光纤微结构制作以及石墨烯高质量转移工艺，制备出直径25μm、厚度3nm的悬空石墨烯膜；掌握了石墨烯表面修饰钯膜的工艺方法，实验摸索出5nm左右厚度的均匀连续钯膜制备参数。.3.理论推导出传感器的氢气灵敏度数学表达式，通过光学干涉方法检测复合薄膜吸氢后的机械形变，实现了检测极限低至20ppm、响应速度短至18s的高灵敏、快速氢气检测。.本项目研究的传感器，结构紧凑且工作于反射模式，不仅适用于狭窄空间与远距离的气体检测，所取得的氢气传感指标领先于绝大多数已报道的光纤氢传感器。未来以该光纤-石墨烯结构为传感基元，将氢敏材料替换为其它功能材料，还可用于其它不同生化量的高灵敏、快速检测。