Recent years have seen a growing interest in graphene, a ground-breaking material which continues to reveal exciting properties and find useful applications. One of the most promising applications of graphene is in the field of nanoelectromechanical systems (NEMS) such as for mechanical resonators. These devices exploit graphene`s one-atom thick membrane profile with ultrahigh strength and stiffness and low mass per unit area. Potential applications of such devices include ultrasensitive mass, force and displacement detection as well as label-free chemical and biological identification. A central problem for these devices is motion detection as they are scaled down in order to improve sensing performance because of diffraction effects of optical interferometric techniques currently used. Furthermore, large-scale production of graphene resonators is not feasible with the exfoliated graphene that is still the most commonly-used graphene production method.
A displacement detection scheme for graphene nanomechanical resonators by slot waveguide integration is proposed and investigated. This is based on the lossy characteristic of graphene and the high field confinement of a slot waveguide. The electrostatically-actuated graphene vibrates in and out of the slot thereby causing the confined mode to be periodically attenuated. Its motion can then be monitored by the transmission of the optical signal. The attenuation and the corresponding attenuation depth have been computed as a function of graphene-slot gap with 2D FEM using COMSOL. They have been found to be strongly influenced by waveguide dimensions especially by slot width which can be explained by the degree of mode confinement. The number of graphene layers as well as its frequency of operation were determined to affect the performance of the device. Optical signal control such as switching was suggested to be a feasible extension of this work.
Fabrication of suspended circular CVD graphene membranes was demonstrated using a dry support-layer removal process. This process can be used as a basis for the scalable production of graphene mechanical resonators arrays for improved sensing performance.
이 논문은 틈새 도파관을 이용하여 그래핀 나노기계 공진기의 변위를 감지하는 방법을 제안한다. 이는 그래핀의 손실 특성과 전기장을 잘 집속하는 틈새 도파관의 특성을 기반으로 하며, 틈새 위의 그래핀을 전기적으로 진동시킴으로써 집속된 모드가 주기적 감쇄하는 원리를 이용한 것이다. 이를 증명하기 위해 2차원 FEM 방식으로 그라핀과 틈새 사이의 간격에 따른 감쇄를 시뮬레이션 하였다. 감쇄 되는 정도는 도파관의 크기 특히 틈새 폭에 크게 영향을 받았다. 이는 틈새 폭에 따라 모드 집속이 영향을 받기 때문이다. 소자 동작특성은 그라핀 층 수 뿐만 아니라 동작 주파수에 의해 결정되며, 이를 이용하면 향후 광 스위치 등과 같이 광 신호를 조절하는 응용 소자로 개발될 수 있을 것으로 예상된다.
실험적으로 이를 증명하기 위해 열처리로 PMMA support-layer를 제거하는 새로운 방식의 그래핀 막 제조방법을 고안하였다. 이 공정방식을 이용하여 향상된 감지 특성을 가진 기계적 그래핀 공진기 배열을 대량 생산할 수 있을 것으로 기대된다.