Mechanical and Electrical Properties of Modified Graphene Devices
- Author(s): ZHANG, HANG
- Advisor(s): Lau, Chun Ning
- et al.
Compared with traditional semiconductor materials, graphene has unparalleled advantages on mobility, thermal conductivity, mechanical strength and so on. Thus it was considered as a promising candidate material for the future semiconductor industry. However, since its band structure is gapless, band gap engineering has become a significant task for scientists. My dissertation focuses on chemical and physical modification methods that could pave the way to applications of graphene based devices and reveal a number of interesting phenomena.
The critical roadblock for graphene electronics is the absence of a band gap. We first focus on chemical functionalization of graphene as a route to band gap engineering. This is first achieved via grafting nitrophenyl groups onto single layer graphene sheets. The functionalized graphene samples behave like semiconductors. Substrate supported and suspended samples demonstrate transport gaps as large as ~0.1eV and ~1eV, respectively. Secondly, we developed a different chemical functionalization approach based on organometallic chemistry. Apart from behaving like semiconductors, functionalized samples also retains the high mobility of the pristine state.
The second part of the thesis focuses on physical modifications of graphene a. Suspended graphene-based switch was developed using a special pulsing breakdown technique. Voltage pulses of 2.5V~4V and 8V can turn a switch device to ON (high conductance) state and OFF (low conductance) state, respectively. We provide experimental evidence that these behaviors arise from motions of atomic-scale carbon chains and reformation of chemical bonds.
Finally, strain engineering is another approach for modifying transport properties of graphene. We proposed and developed novel nano-electromechanical system (NEMS)-like devices that allows in situ modulation of strain on suspended graphene flakes, which in turn induces interesting changes in both transport and morphological properties of graphene.
In summary, this dissertation presents our studies on chemical and physical modification approaches of graphene samples, and related novel phenomena that emerge amid these devices, with implications on next generation electronic devices.