Abstract
In this article, we report the modification of the electronic and magnetic properties of few-layered graphene (FLG) nanoflakes by nitrogen functionalization carried out using radio-frequency plasma-enhanced chemical vapor deposition (rf-PECVD) and electron cyclotron resonance (ECR) plasma processes. Even though the rf-PECVD N 2 treatment led to higher N-doping levels in the FLG (4.06 atomic %) as compared to the ECR process (2.18 atomic %), the ferromagnetic behavior of the ECR FLG (118.62 × 10 -4 emu/g) was significantly higher than that of the rf-PECVD FLG (0.39 × 10 -4 emu/g) and pristine graphene (3.47 × 10 -4 emu/g). Although both plasma processes introduce electron-donating N atoms into the graphene structure, distinct dominant nitrogen bonding configurations (pyridinic, pyrrolic) were observed for the two FLG types. Whereas the ECR plasma introduced more sp 2 -type nitrogen moieties, the rf-PECVD process led to the formation of sp 3 -coordinated nitrogen functionalities, as confirmed through Raman measurements. The samples were further characterized using X-ray absorption near-edge spectroscopy (XANES), and X-ray and ultraviolet photoelectron spectroscopies revealed an increased electronic density of states and a significantly higher concentration of pyrrolic groups in the rf-PECVD samples. Because of the formation of reactive edge structures and pyridinic nitrogen moieties, the ECR-functionalized FLG samples exhibited highest saturation magnetization behavior with the lowest field hysteretic features. In comparison, the rf-PECVD samples displayed the lowest saturation magnetization owing to the disappearance of magnetic edge states and formation of stable nonradical-type defects in the pyrrole type structures. Our experimental results thus provide new evidence regarding the control of the magnetic and electronic properties of few-layered graphene nanoflakes through control of the plasma-processing route.
| Original language | English |
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| Pages (from-to) | 14073-14082 |
| Number of pages | 10 |
| Journal | Journal Of Physical Chemistry C |
| Volume | 121 |
| Issue number | 26 |
| DOIs | |
| Publication status | Published (in print/issue) - 7 Jun 2017 |
Funding
S.C.R. and S.S. (UNISA) gratefully acknowledge the financial support received from the National Research Foundation (NRF), South Africa (Grants EQP13091742446 and PDTWAS150813137166). A.M.S. thanks SA-NRF (93549) and the FRC and URC of University of Johannesburg for financial assistance. The authors also thank D. Britz for his help with magnetic property characterizations.