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Probing substrate influence on graphene by analyzing Raman lineshapes.

Huang CH, Lin HY, Huang CW, Liu YM, Shih FY, Wang WH, Chui HC - Nanoscale Res Lett (2014)

Bottom Line: Distinguishing the substrate influences or the doping effects of charged impurities on graphene can be realized by optically probing the graphene surfaces, included the suspended and supported graphene.For the Gaussian part, the suspended graphene exhibits much greater Gaussian bandwidths than those of the supported graphene.It reveals that the doping effect on supported graphene is stronger than that of suspended graphene.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Photonics, National Cheng Kung University, Tainan 70101, Taiwan. hcchui@mail.ncku.edu.tw.

ABSTRACT
We provide a new approach to identify the substrate influence on graphene surface. Distinguishing the substrate influences or the doping effects of charged impurities on graphene can be realized by optically probing the graphene surfaces, included the suspended and supported graphene. In this work, the line scan of Raman spectroscopy was performed across the graphene surface on the ordered square hole. Then, the bandwidths of G-band and 2D-band were fitted into the Voigt profile, a convolution of Gaussian and Lorentzian profiles. The bandwidths of Lorentzian parts were kept as constant whether it is the suspended and supported graphene. For the Gaussian part, the suspended graphene exhibits much greater Gaussian bandwidths than those of the supported graphene. It reveals that the doping effect on supported graphene is stronger than that of suspended graphene. Compared with the previous studies, we also used the peak positions of G bands, and I2D/IG ratios to confirm that our method really works. For the suspended graphene, the peak positions of G band are downshifted with respect to supported graphene, and the I2D/IG ratios of suspended graphene are larger than those of supported graphene. With data fitting into Voigt profile, one can find out the information behind the lineshapes.

No MeSH data available.


Related in: MedlinePlus

Structural illustration (a), optical image (b), and AFM image (c) and its cross section of suspended and supported graphene sample.
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Figure 1: Structural illustration (a), optical image (b), and AFM image (c) and its cross section of suspended and supported graphene sample.

Mentions: Suspended graphene was fabricated by mechanical exfoliation of graphene flakes onto an oxidized silicon wafer, and the illustration of that is shown in Figure 1a. First, ordered squares with areas of 6 μm2 were defined by photolithography on an oxidized silicon wafer with an oxide thickness of 300 nm. Reactive ion etching was then used to etch the squares to a depth of 150 nm. Micromechanical cleavage of highly ordered pyrolytic graphite was carried out using scotch tape to enable the suspended graphene flakes to be deposited over the indents. The thickness of the monolayer grapheme is about 0.35 nm. The optical image of suspended graphene, atomic forced microscopy (AFM) image, and its cross section are shown in Figure 1b,c. The surface of suspended graphene is like a hat, and the top of graphene surface can reach 100 nm high with respect to supported graphene. To identify the number of graphene layers and their properties, a micro-Raman microscope (Jobin Yvon iHR550, HORIBA Ltd., Kyoto, Japan) was utilized to obtain the Raman signals of monolayer graphene. A 632-nm He-Ne laser was the excitation light source. The polarization and power of the incident light were adjusted by a half-wave plate and a polarizer. The laser power was monitored by a power meter and kept constant as the measurements were made. The experimental conditions for Raman measurement were as follows. In order to avoid the local heating effect, the excited laser power on the graphene surface was 0.45 mW and the integration time was 180 s. The laser beam was focused by a × 50 objective lens (NA = 0.75) on the sample with a focal spot size of about 0.5 μm, representing the spatial resolution of the Raman system. Finally, the Raman scattering radiation was sent to a 55-cm spectrometer for spectral recording.


Probing substrate influence on graphene by analyzing Raman lineshapes.

Huang CH, Lin HY, Huang CW, Liu YM, Shih FY, Wang WH, Chui HC - Nanoscale Res Lett (2014)

Structural illustration (a), optical image (b), and AFM image (c) and its cross section of suspended and supported graphene sample.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3924919&req=5

Figure 1: Structural illustration (a), optical image (b), and AFM image (c) and its cross section of suspended and supported graphene sample.
Mentions: Suspended graphene was fabricated by mechanical exfoliation of graphene flakes onto an oxidized silicon wafer, and the illustration of that is shown in Figure 1a. First, ordered squares with areas of 6 μm2 were defined by photolithography on an oxidized silicon wafer with an oxide thickness of 300 nm. Reactive ion etching was then used to etch the squares to a depth of 150 nm. Micromechanical cleavage of highly ordered pyrolytic graphite was carried out using scotch tape to enable the suspended graphene flakes to be deposited over the indents. The thickness of the monolayer grapheme is about 0.35 nm. The optical image of suspended graphene, atomic forced microscopy (AFM) image, and its cross section are shown in Figure 1b,c. The surface of suspended graphene is like a hat, and the top of graphene surface can reach 100 nm high with respect to supported graphene. To identify the number of graphene layers and their properties, a micro-Raman microscope (Jobin Yvon iHR550, HORIBA Ltd., Kyoto, Japan) was utilized to obtain the Raman signals of monolayer graphene. A 632-nm He-Ne laser was the excitation light source. The polarization and power of the incident light were adjusted by a half-wave plate and a polarizer. The laser power was monitored by a power meter and kept constant as the measurements were made. The experimental conditions for Raman measurement were as follows. In order to avoid the local heating effect, the excited laser power on the graphene surface was 0.45 mW and the integration time was 180 s. The laser beam was focused by a × 50 objective lens (NA = 0.75) on the sample with a focal spot size of about 0.5 μm, representing the spatial resolution of the Raman system. Finally, the Raman scattering radiation was sent to a 55-cm spectrometer for spectral recording.

Bottom Line: Distinguishing the substrate influences or the doping effects of charged impurities on graphene can be realized by optically probing the graphene surfaces, included the suspended and supported graphene.For the Gaussian part, the suspended graphene exhibits much greater Gaussian bandwidths than those of the supported graphene.It reveals that the doping effect on supported graphene is stronger than that of suspended graphene.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Photonics, National Cheng Kung University, Tainan 70101, Taiwan. hcchui@mail.ncku.edu.tw.

ABSTRACT
We provide a new approach to identify the substrate influence on graphene surface. Distinguishing the substrate influences or the doping effects of charged impurities on graphene can be realized by optically probing the graphene surfaces, included the suspended and supported graphene. In this work, the line scan of Raman spectroscopy was performed across the graphene surface on the ordered square hole. Then, the bandwidths of G-band and 2D-band were fitted into the Voigt profile, a convolution of Gaussian and Lorentzian profiles. The bandwidths of Lorentzian parts were kept as constant whether it is the suspended and supported graphene. For the Gaussian part, the suspended graphene exhibits much greater Gaussian bandwidths than those of the supported graphene. It reveals that the doping effect on supported graphene is stronger than that of suspended graphene. Compared with the previous studies, we also used the peak positions of G bands, and I2D/IG ratios to confirm that our method really works. For the suspended graphene, the peak positions of G band are downshifted with respect to supported graphene, and the I2D/IG ratios of suspended graphene are larger than those of supported graphene. With data fitting into Voigt profile, one can find out the information behind the lineshapes.

No MeSH data available.


Related in: MedlinePlus