Magnetic behavioural change of silane exposed graphene nanoflakes

Abstract

The electronic structures and magnetic properties of graphene nanoflakes (GNFs) exposed to an organo-silane precursor [tetra-methyl-silane, Si(CH 3) 4 ] were studied using atomic force microscopy, electron field emission (EFE), x-ray photoelectron spectroscopy (XPS), and magnetization. The result of XPS indicates that silyl radical based strong covalent bonds were formed in GNFs, which induced local structural relaxations and enhanced sp 3 hybridization. The EFE measurements show an increase in the turn-on electric field from 9.8 V/lm for pure GNFs to 26.3 V/lm for GNFs:Si having highest Si/(Si þ C) ratio (ffi 0.35) that also suggests an enhancement of the non-metallic sp 3 bonding in the GNFs matrix. Magnetic studies show that the saturation magnetization (Ms) is decreased from 172.53 Â 10 À6 emu/g for pure GNFs to 13.00 Â 10 À6 emu/g for GNFs:Si with the highest Si/(Si þ C) ratio 0.35, but on the other side, the coercivity (Hc) increases from 66 to 149 Oe due to conversion of sp 2 ! sp 3-hybridization along with the formation of SiC and Si-O bonding in GNFs. The decrease in saturation magnetization and increase in coercivity (Hc) in GNFs on Si-functionalization are another routes to tailor the magnetic properties of graphene materials for magnetic device applications.

Electronic, Electrical, and Magnetic Behavioral Change of SiO2-NP-Decorated MWCNTs

“…These XPS spectra for Si 2p and 2s are also observed in Figure j–l for MWCNTs/SiO 2 -NP nanocomposites with different peak positions. Different decomposed peaks between ∼99.0 and 102 eV for Si 2p are assigned to Si–C/Si–C–O and that at ∼103.0 eV to Si–O. − The peaks at ∼151.1–153.0 eV range for Si 2s XPS spectra are Si–Si peaks and those above 153.0 eV are assigned to Si–O . These results clearly indicate that SiO 2 -NPs are responsible for the change in the electronic and bonding structure of the MWCNT/SiO 2 -NP composites.…”

“…37−39 The peaks at ∼151.1–153.0 eV range for Si 2s XPS spectra are Si–Si peaks and those above 153.0 eV are assigned to Si–O. 40 These results clearly indicate that SiO 2 -NPs are responsible for the change in the electronic and bonding structure of the MWCNT/SiO 2 -NP composites. Based on the XPS decomposed peak intensity, it can be hypothesized that SiO 2 -NPs are responsible for the change in structural properties of MWCNTs and can make a material rich in sp 3 .…”

“…The interaction of silicon atoms with other elements in MWCNTs has been explained elsewhere with possibilities of reducing sp 2 while increasing sp 3 hybridization. 40,43…”

“…The strong interaction (tetrahedral bonding Si–C) between the atoms of Si and C may be responsible for the rapid decrease in the magnetization of MWCNTs due to an increase in the SiO 2 -NPs content. 40 The relationship between the electrical and magnetic properties of MWCNT:SiO 2 -NPs can be clarified by the transport properties of the MWCNTs/SiO 2 -NP nanocomposites. The ferromagnetism induced in MWCNT/SiO 2 -NPs was also based on the delocalized electrons not trapped by O vacancy.…”

“…The reduction of M S is due to the formation of Si–C bonding along with Si–O, making the material rich in sp 3 . The interaction of silicon atoms with other elements in MWCNTs has been explained elsewhere with possibilities of reducing sp 2 while increasing sp 3 hybridization. , …”