Limits...
Visualizing chemical states and defects induced magnetism of graphene oxide by spatially-resolved-X-ray microscopy and spectroscopy.

Wang YF, Singh SB, Limaye MV, Shao YC, Hsieh SH, Chen LY, Hsueh HC, Wang HT, Chiou JW, Yeh YC, Chen CW, Chen CH, Ray SC, Wang J, Pong WF, Takagi Y, Ohigashi T, Yokoyama T, Kosugi N - Sci Rep (2015)

Bottom Line: Magnetic hysteresis loop reveals that the GO is ferromagnetic whereas photo-thermal moderately reduced graphene oxide (M-rGO) and heavily reduced graphene oxide (H-rGO) gradually become paramagnetic behavior at room temperature.The results of X-ray magnetic circular dichroism further support the finding that C 2p(σ*)-derived states are the main origin of the magnetism of GO.Based on experimental results and first-principles calculations, the variation in magnetic behavior from GO to M-rGO and to H-rGO is interpreted, and the origin of ferromagnetism is identified as the C 2p(σ*)-derived states that involve defects/vacancies rather than the C 2p(π*) states that are bound with oxygen-containing and hydroxyl groups on GO sheets.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, Tamkang University, Tamsui 251, Taiwan.

ABSTRACT
This investigation studies the various magnetic behaviors of graphene oxide (GO) and reduced graphene oxides (rGOs) and elucidates the relationship between the chemical states that involve defects therein and their magnetic behaviors in GO sheets. Magnetic hysteresis loop reveals that the GO is ferromagnetic whereas photo-thermal moderately reduced graphene oxide (M-rGO) and heavily reduced graphene oxide (H-rGO) gradually become paramagnetic behavior at room temperature. Scanning transmission X-ray microscopy and corresponding X-ray absorption near-edge structure spectroscopy were utilized to investigate thoroughly the variation of the C 2p(π*) states that are bound with oxygen-containing and hydroxyl groups, as well as the C 2p(σ*)-derived states in flat and wrinkle regions to clarify the relationship between the spatially-resolved chemical states and the magnetism of GO, M-rGO and H-rGO. The results of X-ray magnetic circular dichroism further support the finding that C 2p(σ*)-derived states are the main origin of the magnetism of GO. Based on experimental results and first-principles calculations, the variation in magnetic behavior from GO to M-rGO and to H-rGO is interpreted, and the origin of ferromagnetism is identified as the C 2p(σ*)-derived states that involve defects/vacancies rather than the C 2p(π*) states that are bound with oxygen-containing and hydroxyl groups on GO sheets.

No MeSH data available.


Related in: MedlinePlus

Total DOS, spin-polarized PDOS, and spin density of (a) symmetric and (b) J-T defect structures. Contributions from π and σ electrons in defect structures are represented in blue and red curves, respectively. Data for pristine graphene are also included for reference. Fermi level (EF) is set to 0 eV for alignment.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4612711&req=5

f6: Total DOS, spin-polarized PDOS, and spin density of (a) symmetric and (b) J-T defect structures. Contributions from π and σ electrons in defect structures are represented in blue and red curves, respectively. Data for pristine graphene are also included for reference. Fermi level (EF) is set to 0 eV for alignment.

Mentions: Figure 6(a,b) plot the total DOS, PDOS and spin density that correspond to the defect structures in Fig. 5(a,b) and to pristine graphene as a reference. First, the calculations herein demonstrate that the total DOS close to the EF of perfect graphene is dominated by π electron (black curves), agreeing closely with earlier studies175. Similar electronic structures, but with some new features of π character [blue curves in Fig. 6(a)] at 1–3 eV below EF, are identified in the graphene with a symmetrically distorted vacancy. Also, a rather sharp feature associated with the occupied π orbital (blue curves) next to EF reveals the origin of the local magnetic moment and demonstrates that the magnetic property associated with the symmetric vacancy geometry is dominated by π electrons, even though an unoccupied σ orbital (red curves) emerges very close to EF. However, in asymmetric J-T defect configuration, the J-T splitting redshifts a spin-up σ orbital (red curves) down to 0.5 eV below EF and blue-shifts its spin counterpart [the first red peak above EF in the spin-down channel of Fig. 6(b)] to 1.7 eV above EF. This huge J-T splitting of more than 2 eV is responsible for the local magnetic moment at the unsaturated C atom [Fig. 5(b)] adjacent to the vacancy. Therefore, the calculated PDOS demonstrates that the J-T distortion-induced imbalance of carbon σ orbitals close to the defect is critical to enhance local magnetic moments in GO.


Visualizing chemical states and defects induced magnetism of graphene oxide by spatially-resolved-X-ray microscopy and spectroscopy.

Wang YF, Singh SB, Limaye MV, Shao YC, Hsieh SH, Chen LY, Hsueh HC, Wang HT, Chiou JW, Yeh YC, Chen CW, Chen CH, Ray SC, Wang J, Pong WF, Takagi Y, Ohigashi T, Yokoyama T, Kosugi N - Sci Rep (2015)

Total DOS, spin-polarized PDOS, and spin density of (a) symmetric and (b) J-T defect structures. Contributions from π and σ electrons in defect structures are represented in blue and red curves, respectively. Data for pristine graphene are also included for reference. Fermi level (EF) is set to 0 eV for alignment.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4612711&req=5

f6: Total DOS, spin-polarized PDOS, and spin density of (a) symmetric and (b) J-T defect structures. Contributions from π and σ electrons in defect structures are represented in blue and red curves, respectively. Data for pristine graphene are also included for reference. Fermi level (EF) is set to 0 eV for alignment.
Mentions: Figure 6(a,b) plot the total DOS, PDOS and spin density that correspond to the defect structures in Fig. 5(a,b) and to pristine graphene as a reference. First, the calculations herein demonstrate that the total DOS close to the EF of perfect graphene is dominated by π electron (black curves), agreeing closely with earlier studies175. Similar electronic structures, but with some new features of π character [blue curves in Fig. 6(a)] at 1–3 eV below EF, are identified in the graphene with a symmetrically distorted vacancy. Also, a rather sharp feature associated with the occupied π orbital (blue curves) next to EF reveals the origin of the local magnetic moment and demonstrates that the magnetic property associated with the symmetric vacancy geometry is dominated by π electrons, even though an unoccupied σ orbital (red curves) emerges very close to EF. However, in asymmetric J-T defect configuration, the J-T splitting redshifts a spin-up σ orbital (red curves) down to 0.5 eV below EF and blue-shifts its spin counterpart [the first red peak above EF in the spin-down channel of Fig. 6(b)] to 1.7 eV above EF. This huge J-T splitting of more than 2 eV is responsible for the local magnetic moment at the unsaturated C atom [Fig. 5(b)] adjacent to the vacancy. Therefore, the calculated PDOS demonstrates that the J-T distortion-induced imbalance of carbon σ orbitals close to the defect is critical to enhance local magnetic moments in GO.

Bottom Line: Magnetic hysteresis loop reveals that the GO is ferromagnetic whereas photo-thermal moderately reduced graphene oxide (M-rGO) and heavily reduced graphene oxide (H-rGO) gradually become paramagnetic behavior at room temperature.The results of X-ray magnetic circular dichroism further support the finding that C 2p(σ*)-derived states are the main origin of the magnetism of GO.Based on experimental results and first-principles calculations, the variation in magnetic behavior from GO to M-rGO and to H-rGO is interpreted, and the origin of ferromagnetism is identified as the C 2p(σ*)-derived states that involve defects/vacancies rather than the C 2p(π*) states that are bound with oxygen-containing and hydroxyl groups on GO sheets.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, Tamkang University, Tamsui 251, Taiwan.

ABSTRACT
This investigation studies the various magnetic behaviors of graphene oxide (GO) and reduced graphene oxides (rGOs) and elucidates the relationship between the chemical states that involve defects therein and their magnetic behaviors in GO sheets. Magnetic hysteresis loop reveals that the GO is ferromagnetic whereas photo-thermal moderately reduced graphene oxide (M-rGO) and heavily reduced graphene oxide (H-rGO) gradually become paramagnetic behavior at room temperature. Scanning transmission X-ray microscopy and corresponding X-ray absorption near-edge structure spectroscopy were utilized to investigate thoroughly the variation of the C 2p(π*) states that are bound with oxygen-containing and hydroxyl groups, as well as the C 2p(σ*)-derived states in flat and wrinkle regions to clarify the relationship between the spatially-resolved chemical states and the magnetism of GO, M-rGO and H-rGO. The results of X-ray magnetic circular dichroism further support the finding that C 2p(σ*)-derived states are the main origin of the magnetism of GO. Based on experimental results and first-principles calculations, the variation in magnetic behavior from GO to M-rGO and to H-rGO is interpreted, and the origin of ferromagnetism is identified as the C 2p(σ*)-derived states that involve defects/vacancies rather than the C 2p(π*) states that are bound with oxygen-containing and hydroxyl groups on GO sheets.

No MeSH data available.


Related in: MedlinePlus