LIQUID-BASED CHEMICAL VAPOR DEPOSITION SYNTHESIS OF GRAPHENE WITH VARIATIONS ON THE DOPANTS AND THE NUMBER OF LAYERS

Restricted (Penn State Only)
Author:
Zhu, Haoyue
Graduate Program:
Chemistry
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
May 16, 2018
Committee Members:
  • Mauricio Terrones Maldonado, Dissertation Advisor
  • Thomas E Mallouk, Committee Chair
  • Harry R Allcock, Committee Member
  • Thomas E Mallouk, Committee Member
  • James Hansell Adair, Outside Member
Keywords:
  • graphene
  • solar cell
  • raman
  • GERS
  • surface enhanced raman
  • sensing
  • sensor
  • heterostructure
  • heterolayer
  • CVD
  • chemical vapor deposition
  • doping
  • dopant
Abstract:
Graphene is an atomically thin carbon material with high carrier mobility and transparency to visible light. But because graphene lacks a bandgap and is chemically inert, significant amount of research has been dedicated to making it more suitable for applications such as transistors and molecular sensors. The research within this dissertation investigates the synthesis of graphene using Chemical Vapor Deposition (CVD) with liquid precursors, and the synthetic conditions are varied in ways so that the number of layers and dopant incorporations are changed for graphene. Chapter 1 briefly introduces the properties, synthesis, and characterization of graphene. In Chapter 2, the synthesis of monolayer graphene is demonstrated using toluene in an atmospheric pressure CVD (APCVD) system. The properties of monolayer graphene were characterized by Raman Spectroscopy, UV-Vis Spectroscopy, and High-resolution Transmission Electron Microscopy. The synthesized monolayer graphene was used as the transparent conducting film for a graphene/silicon Schottky junction solar cell, and it is suggested that the photo-conversion efficiency (PCE) of the cell can be maximized with a suitable coating of PMMA and HNO3 treatment. In Chapter 3, bi-layer graphene is synthesized in an APCVD system using toluene, and a graphene/WS2 vertical heterolayer was constructed by transferring CVD-synthesized monolayer WS2 flakes onto monolayer and bi-layer graphene. It is demonstrated that while monolayer WS2 only shows a single exciton peak when it was transferred on top of monolayer graphene, the underlying bi-layer graphene in the hetero-layer induced an extra trion peak in monolayer WS2. The construction of graphene/WS2 vertical heterolayer using a transfer process and the trion peak generation using CVD-synthesized bi-layer graphene has not been reported before. Finally, the synthesis of N-doped graphene (N-G) using pyridine and its application in Graphene-Enhanced Raman Spectroscopy (GERS) is investigated in Chapter 5. It is suggested that the Raman signals of the Crystal Violet, a fluorescent dye, were enhanced after they were deposited on top of N-G when compared to those deposited on Pr-G. The synthetic parameters of N-G were also found to be correlated to the GERS efficiency of it.