N-Doped Graphene with Low Intrinsic Defect Densities via a Solid Source Doping Technique

Bo Liu,Zhiwei Liu,Chao-Sung Lai,Chia-Ming Yang

doi:10.3390/nano7100302

Abstract

N-doped graphene with low intrinsic defect densities was obtained by combining a solid source doping technique and chemical vapor deposition (CVD). The solid source for N-doping was embedded into the copper substrate by NH3 plasma immersion. During the treatment, NH3 plasma radicals not only flattened the Cu substrate such that the root-mean-square roughness value gradually decreased from 51.9 nm to 15.5 nm but also enhanced the nitrogen content in the Cu substrate. The smooth surface of copper enables good control of graphene growth and the decoupling of height fluctuations and ripple effects, which compensate for the Coulomb scattering by nitrogen incorporation. On the other hand, the nitrogen atoms on the pre-treated Cu surface enable nitrogen incorporation with low defect densities, causing less damage to the graphene structure during the process. Most incorporated nitrogen atoms are found in the pyrrolic configuration, with the nitrogen fraction ranging from 1.64% to 3.05%, while the samples exhibit low defect densities, as revealed by Raman spectroscopy. In the top-gated graphene transistor measurement, N-doped graphene exhibits n-type behavior, and the obtained carrier mobilities are greater than 1100 cm2·V−1·s−1. In this study, an efficient and minimally damaging n-doping approach was proposed for graphene nanoelectronic applications.

Highlights

Graphene is a promising generation electronic material, and its electronic properties can be modified by the substitutional doping of heteroatoms
The synthesis methods for N-doped graphene can be briefly classified into two main categories [14]: (i) post-treatment in which nitrogen is incorporated into graphene or graphene oxide by post-annealing in NH3 gas or by NH3 plasma [7,11,15,16,17] or via Ultraviolet illumination in NH3 [18] and (ii) direct doping during synthesis in which carbon/nitrogen precursors such as CH4/H2/NH3 [19] and pyridine [9] are simultaneously introduced during the graphene growth, in chemical vapor deposition (CVD)
A CVD synthesis process for low defect density N-doped graphene based on the NH3 plasma pretreatment of the Cu foil catalyst was proposed

Summary

Introduction

Graphene is a promising generation electronic material, and its electronic properties can be modified by the substitutional doping of heteroatoms (e.g., boron [1], nitrogen [2], fluorine [3], and sulfur [4]). To obtain N-doped graphene with low defect densities, Cory et al determined the ion energy window for nitrogen doping in the graphene lattice with the balance between the substitutional reaction efficiency and the vacancies or defect formation [22]. To overcome the bottleneck in the direct synthesis of N-doped graphene in the conventional chemical vapor deposition (CVD) process and to obtain high transport properties for N-doped graphene, a solid state doping technique was introduced in this study. Cu foils were pre-treated by NH3 plasma at room temperature, and atomic force microscopy (AFM) was performed to examine the surface morphology variation This process embeds nitrogen atoms into the Cu substrate, which are subsequently used as the solid-state doping source.

Conclusions

NH3 Plasma Pretreatment and AFM Scanning

Graphene Growth and Transfer Process

Raman Spectral Analysis and X-ray Photoelectron Spectroscopy

Findings

Top-Gated Graphene Field-Effect Transistors Fabrication and Measurement