[Reminder] MSE PhD Dissertation Defense: Sangwon Lee (Tomorrow, 10am)

Department of Materials Science & Engineering

University PhD Dissertation Defense

Graphene: Synthesis, Structure & Properties

Sangwon Lee

Advisor: Prof. Alberto Salleo

Date: Monday, February 13th, 2012
Time: 10 am (Refreshments served at 9:45 am)

Location: Jerry Yang and Akiko Yamazaki Environment and Energy Building (Y2E2)

Conference room # 299 (Bechtel conference room)

(http://campus-map.stanford.edu/index.cfm?ID=04-070)

Abstract

The discovery of free-standing graphene in 2004 has attracted wide attention in both scientific communities and industries because of its unusual electronic structure and properties. Due to the possible applications of graphene, many attempts to produce high-quality wafer-scale graphene films have been actively tried in the materials science and other scientific communities. Thermal decomposition of silicon carbide (SiC) is considered as one of the most promising routes toward the synthesis of well-controlled and characterized graphene films.

Since the argon (Ar) atmosphere produced higher quality graphene films on SiC than in vacuum, the inert-gas mediated thermal decomposition of SiC is regarded so far as the most effective method for the controlled epitaxial graphene (EG) growth. Most studies and progresses have been demonstrated with the Si-face of basal plane oriented SiC substrates because of its slower reaction kinetics, which results from higher surface energy than the C-face. Nevertheless, there is significant interest in obtaining few-layer, smooth EG on the C-face of SiC due to its superior electrical properties as compared to EG on the Si-face. The first part of the presentation will focus on the structural properties of EG layers grown on the C-face of 4H-SiC in vacuum or Ar environments by X-ray diffraction using synchrotron radiation. The qualities and characteristics of layers will be also correlated with carrier mobilities from Hall measurements.

The high temperatures required in this method (~ 1400°C) are not compatible with large-scale device integration where different materials must be deposited and patterned prior to the formation of the semiconductor layers and limit the synthesis to single-crystal SiC substrates. In the second part of the presentation, an alternative low-temperature, spatially controlled and scalable epitaxial graphene synthesis technique based on laser-induced surface decomposition of SiC will be proposed. This technique is compatible and amenable to large-scale device integration. Furthermore, laser synthesis of graphene offers the advantage of combining synthesis and patterning in one step as the process can be designed to form graphene devices in predetermined locations on the substrate. Our results in this research show that epitaxial graphene (EG) forms on SiC as a result of laser irradiation. Various characterization techniques such as RHEED, synchrotron-based X-ray diffraction, Raman, TEM and STM were used to confirm the graphitization of SiC and to measure the properties of graphene films.