Investigation on the Optical, Mechanical, and Electrical Applications of Integrated Graphene Nanostructures

Abstract

Graphene has remarkable characteristics such as high electron mobility, high Youngs modulus, and high thermal conductivity. Moreover, it intrinsically is a one-atom layered material therefore has an absolute dimensional advantage to be exploited in the application fields. On the other hand, the absence of an energy band gap between the conduction and valence bands sets a limitation and challenges for applying graphene in electronic applications. That is mainly because the band gap is one of the necessities to make active components such as diode or transistor from semiconducting material. The research to overcome this weakness is categorized into two parts. First part is to reform the electron band structure of the graphene so that it becomes similar to the conventional semiconductor such as Si and GaAs. Second part is to directly build a fundamental electronic component such as diode and memory without the necessity of the band gap. In this thesis, two novel approaches to accomplish electronic components are introduced and those are classified as second type of endeavor explained above. The first one is to make a p-n junction by using the locally focused laser and the second is to realize mechanical memory by nonlinear response of NEMS. The basic principles of corresponding structures are following. Local irradiation causes the charge trapping between graphene and SiO2 substrate and the trapped charge changes the electrochemical potential. Since the polarity of the charge carrier in graphene depends on the local electrochemical potential, the p-n junction can be developed under the certain proper condition. On the other hand, mechanical resonator shows hysteresis on vibration amplitude attributed to nonlinear oscillating. The amplitude and the frequency of resonance are controllable by DC modulation. Combined with that, exploiting the dependence of the vibrating amplitude on the state of previous time step makes a DC modulated mechanical memory.