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Raman modes in transferred bilayer CVD graphene

100%

Niilisk A., Kahro T., Kiisk V., Rähn M., Alles H., Aarik J., Sammelselg V.

Open Physics

2015

vol. 13

issue 1

A systematic experimental Raman spectroscopic study of twisted bilayer graphene (tBLG) domains localized inside wide-area single layer graphene (SLG) produced by low-pressure CVD on Cu foil and transferred onto SiO2/Si substrate has been performed. According to the Raman characterization the tBLG domains had a great variety of twisting angles θ between the bottom and top graphene layers (6° < θ < 25°). The twisting angle θ was estimated from the spectral position of the rotating R and R' modes in the Raman spectrum.Under G band resonance conditions the breathing mode ZO' with a frequency of 95- 97 cm−1 was detected, and a breathing mode ZO was found in the spectra between 804 cm−1 and 836 cm−1, its position depending on the twisting angle θ. An almost linear relationship was found between the frequencies ωZO and ωR. Also a few other spectral peculiarities were found, e.g. a high-energy excitation of the G band resonance, the 2G overtone appearing at 3170-3180 cm−1 by the G band resonance, revealing a linear dispersion of 80 cm−1/eV of the 2D band in tBLG

Atomic layer deposition of HfO2 on graphene from HfCl4 and H2O

68%

Alles H., Aarik J., Aidla A., Fay A., Kozlova J., Niilisk A., Pärs M., Rähn M., Wiesner M., Hakonen P., Sammelselg V.

Open Physics

2011

vol. 9

issue 2

319-324

Atomic layer deposition of HfO2 on unmodified graphene from HfCl4 and H2O was investigated. Surface RMS roughness down to 0.5 nm was obtained for amorphous, 30 nm thick hafnia film grown at 180°C. HfO2 was also deposited in a two-step temperature process where the initial growth of about 1 nm at 170°C was continued up to 10–30 nm at 300°C. This process yielded uniform, monoclinic HfO2 films with RMS roughness of 1.7 nm for 10–12 nm thick films and 2.5 nm for 30 nm thick films. Raman spectroscopy studies revealed that the deposition process caused compressive biaxial strain in graphene, whereas no extra defects were generated. An 11 nm thick HfO2 film deposited onto bilayer graphene reduced the electron mobility by less than 10% at the Dirac point and by 30–40% far away from it.

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2 Open Physics

1 2015

1 2011

2 Aarik J.

2 Alles H.

2 Niilisk A.

2 Rähn M.

2 Sammelselg V.

1 Aidla A.

1 Fay A.

1 Hakonen P.

1 Kahro T.

1 Kiisk V.

1 Kozlova J.

1 Pärs M.

1 Wiesner M.

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Raman modes in transferred bilayer CVD graphene

Atomic layer deposition of HfO2 on graphene from HfCl4 and H2O