微机电系统（MEMS）和透射电子显微镜（TEM）的结合使原位TEM表征技术取得了巨大的进步，原位TEM能够以超高的空间分辨率对样品的微观动态过程进行观测。通过MEMS工艺，现已成功将各种原位刺激施加到样品上，各种原位TEM表征已被开发研究。其中， TEM原位加热技术吸引了广泛关注，因为温度是多类实验中的重要参数，如相变、材料生长等。但TEM微加热芯片仍存在一些未解决的问题，如芯片在加热过程中悬空窗口的膨胀变形问题，会对芯片的原位TEM观测产生影响。本文首先对TEM微加热MEMS芯片的结构进行了详细的拆解和分析，并讨论了芯片的结构对芯片性能的影响。TEM微加热芯片一般由电子透明悬空薄膜及加热电阻丝组成。这样的微加热芯片热容量较低，设计灵活，可以实现低功耗以及快速、精确的温度控制，均匀加热至较高的温度。然而，电阻层和悬空薄膜是一个双层复合结构，强界面相互作用以及热膨胀系数的失配使得窗口在高温下会发生显著的膨胀变形。低维碳纳米材料如石墨烯、碳纳米管是结构稳定、性能优良的焦耳加热材料，并且表面没有悬挂键，与其他材料通过弱的范德华力相结合，因此本论文提出将这类新材料集成到微加热芯片中用作加热元件来提升器件的性能。我们成功设计并制备了低维碳纳米材料微加热芯片，包括石墨烯微加热芯片和碳纳米管微加热芯片。通过光谱测温对芯片温度进行校准，测量了芯片的加热范围、温度均匀性、响应速度、功耗、热漂移速率和高温形变等性能。这些分析表明低维碳纳米材料微加热芯片可以在短时间内快速、均匀加热至高温，且功耗低于同类型MEMS芯片，薄膜在高温下的加热形变仅为几十纳米，比其它MEMS加热器小两个数量级。快速的高温响应、低功耗和对膨胀变形的有效抑制均可归因于低维碳纳米材料的优异性能和范德华接触。微加热芯片被成功应用到TEM中观察锡纳米颗粒的熔化过程，展示了其在研究动态热力学过程中的潜力。可以在微加热芯片中进一步集成其他刺激，开发多功能原位芯片；也可将加热功能引入到其它仪器中，如光学显微镜、扫描电子显微镜等。我们的工作为低维碳纳米材料和原位表征技术开辟了新的发展方向，相关成果将在纳米科学、材料科学、电化学等领域具有广阔的应用前景。
The combination of micro electro mechanical system (MEMS) and transmission electron microscopy (TEM) have led great progress on in situ TEM characterization techniques, enabling the observation on micro dynamic processes of samples with ultra-high spatial resolution. MEMS makes it possible to integrate various stimuli to the sample, and a variety of in situ TEM techniques have been developed. Among them, TEM in situ heating technique attracts lots of attention, as temperature is an important parameter for experiments, like phase transition, materials growth, etc. However, there are still some unresolved issues with TEM microheaters, such as the bulging deformation of the suspended membrane during heating, which affects the in situ TEM observation seriously.This article first provided a detailed dissection and analysis of the structure of TEM MEMS microheaters, and discussed the effect of structure on its performance. Generally, TEM MEMS microheaters consist of an electron-transparent suspended membrane and a heating resistive wire. Such microheaters have low heat capacity and high design flexibility, which enables low power consumption, fast and precise control on temperature as well as high uniformity at high temperature. However, the resistive layer and the suspended membrane form a bimorph structure, and the strong interface interaction and mismatch of the coefficient of thermal expansion lead to significant bulging deformation of the membrane at high temperatures. Low dimensional carbon nanomaterials, such as graphene and carbon nanotubes, are structurally stable and preeminent as Joule heating materials. They have no dangling bonds on their surfaces, combining with other materials via weak van der Waals forces. Therefore, this paper proposes the integration of such new materials into MEMS microheaters as heating elements to improve device performance.We’ve designed and fabricated low dimensional carbon nanomaterial microheaters successfully, including graphene microheaters and carbon nanotube microheaters. The temperature of the microheaters was calibrated by spectral thermometry method, and the properties of the microheaters were then characterized, such as the heating temperature range, temperature uniformity, response time, power consumption, thermal drift and bulging deformation. These characterizations demonstrated that the low dimensional carbon nanomaterial microheaters can be rapidly and uniformly heated to high temperatures, the power consumption is much lower than that of similar MEMS chips, and the bulging deformation of the membrane at high temperatures is only tens of nanometers, which is two orders of magnitude smaller than that of other MEMS heaters. The fast high-temperature response, low power consumption, and suppressed bulging effect can be attributed to the distinguished properties and van der Waals interaction of low dimensional carbon nanomaterials. The as-fabricated microheaters were conducted to observe the melting process of Sn nanoparticles in TEM successfully, verifying their great potential in studying dynamic thermodynamics processes. Other stimuli can be further integrated into microheaters to develop multifunctional in situ chips, and these microheaters can also be introduced into other instruments, such as optical microscopes, scanning electron microscope, etc. Therefore, our work could become a new strategy for application development of low dimensional carbon nanomaterials and in situ characterization techniques, and the related achievements may have broad application prospects in the fields of nanoscience, materials science, electrochemistry, etc.
