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

OD images and corresponding stack mapping from STXM images of GO, M-rGO and H-rGO are shown in panels I and II.Panels III-VI present stack mappings from C K-edge STXM images of GO, M-rGO and H-rGO, which are decomposed into blue, yellow, red and green regions that are associated with the different thicknesses of samples. Spectra of all samples typically present background (blue), flat (yellow), medium (red) and wrinkle (green) regions.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f2: OD images and corresponding stack mapping from STXM images of GO, M-rGO and H-rGO are shown in panels I and II.Panels III-VI present stack mappings from C K-edge STXM images of GO, M-rGO and H-rGO, which are decomposed into blue, yellow, red and green regions that are associated with the different thicknesses of samples. Spectra of all samples typically present background (blue), flat (yellow), medium (red) and wrinkle (green) regions.

Mentions: Figure 2 presents optical density (OD) images (panel I), C K-edge STXM stack mappings (panel II) and decomposed STXM mappings (panels III-VI) of the surfaces of randomly selected single sheets of GO, M-rGO and H-rGO. The bright areas in the OD images represent thick regions; dim areas represent thin regions and grey areas represent the regions of intermediate thickness, as observed in GO [panel I(a)], M-rGO [panel I(b)] and H-rGO [panel I(c)], respectively. Based on the OD, the selected regions of GO, M-rGO and H-rGO are typically attributed to wrinkle, medium and flat regions of the GO, M-rGO and H-rGO sheets. As presented in panels I(a)-I(c), the brightest region of H-rGO has a higher average OD (1.29) than does GO (0.93) or M-rGO (0.64), suggesting that the thickest regions were preferably formed in the H-rGO sheets, even though they were the most heavily reduced. The various colors shown in the C K-edge STXM stack mapping in panels II(a)-II(c) of Fig. 2 correspond to the randomly varying thickness of GO, M-rGO and H-rGO. The decomposed STXM stack mappings (panels III-VI) are shown in blue (background), yellow (flat), red (medium) and green (wrinkle), which relate directly to the regions of the samples with various thicknesses1728. The maps were divided into four regions by principle component analysis (PCA) for cluster analysis, based on spectroscopic differences. The PCA spectrum of each region is the average from all image pixels in that region. The background is shown in blue; the OD or absorbance of the background is nearly zero, corresponding to the near- intensity of the C K-edge STXM spectrum. A more intense average spectrum generally indicates a thicker sample, with the thickness’ increasing form flat, through medium to wrinkle regions. All chemical species in these regions can affect thickness and the thick regions are typically attributed to wrinkle regions of GO sheets. As shown panels IV-VI in Fig. 2, the flat, medium and wrinkle regions are present at random locations on the surface of GO, M-rGO and H-rGO. GO cannot be formed with a perfectly flat geometry because the wrinkle geometry of GO sheets is generally more stable than their flat geometry3637, so the formation of wrinkle regions of GO sheets is simply observed in both GO and rGOs. More details concerning STXM-XANES measurement can be found elsewhere172838.


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)

OD images and corresponding stack mapping from STXM images of GO, M-rGO and H-rGO are shown in panels I and II.Panels III-VI present stack mappings from C K-edge STXM images of GO, M-rGO and H-rGO, which are decomposed into blue, yellow, red and green regions that are associated with the different thicknesses of samples. Spectra of all samples typically present background (blue), flat (yellow), medium (red) and wrinkle (green) regions.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f2: OD images and corresponding stack mapping from STXM images of GO, M-rGO and H-rGO are shown in panels I and II.Panels III-VI present stack mappings from C K-edge STXM images of GO, M-rGO and H-rGO, which are decomposed into blue, yellow, red and green regions that are associated with the different thicknesses of samples. Spectra of all samples typically present background (blue), flat (yellow), medium (red) and wrinkle (green) regions.
Mentions: Figure 2 presents optical density (OD) images (panel I), C K-edge STXM stack mappings (panel II) and decomposed STXM mappings (panels III-VI) of the surfaces of randomly selected single sheets of GO, M-rGO and H-rGO. The bright areas in the OD images represent thick regions; dim areas represent thin regions and grey areas represent the regions of intermediate thickness, as observed in GO [panel I(a)], M-rGO [panel I(b)] and H-rGO [panel I(c)], respectively. Based on the OD, the selected regions of GO, M-rGO and H-rGO are typically attributed to wrinkle, medium and flat regions of the GO, M-rGO and H-rGO sheets. As presented in panels I(a)-I(c), the brightest region of H-rGO has a higher average OD (1.29) than does GO (0.93) or M-rGO (0.64), suggesting that the thickest regions were preferably formed in the H-rGO sheets, even though they were the most heavily reduced. The various colors shown in the C K-edge STXM stack mapping in panels II(a)-II(c) of Fig. 2 correspond to the randomly varying thickness of GO, M-rGO and H-rGO. The decomposed STXM stack mappings (panels III-VI) are shown in blue (background), yellow (flat), red (medium) and green (wrinkle), which relate directly to the regions of the samples with various thicknesses1728. The maps were divided into four regions by principle component analysis (PCA) for cluster analysis, based on spectroscopic differences. The PCA spectrum of each region is the average from all image pixels in that region. The background is shown in blue; the OD or absorbance of the background is nearly zero, corresponding to the near- intensity of the C K-edge STXM spectrum. A more intense average spectrum generally indicates a thicker sample, with the thickness’ increasing form flat, through medium to wrinkle regions. All chemical species in these regions can affect thickness and the thick regions are typically attributed to wrinkle regions of GO sheets. As shown panels IV-VI in Fig. 2, the flat, medium and wrinkle regions are present at random locations on the surface of GO, M-rGO and H-rGO. GO cannot be formed with a perfectly flat geometry because the wrinkle geometry of GO sheets is generally more stable than their flat geometry3637, so the formation of wrinkle regions of GO sheets is simply observed in both GO and rGOs. More details concerning STXM-XANES measurement can be found elsewhere172838.

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