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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

Structural study of TiO2 thin films by micro-Raman spectroscopy

84%

Niilisk A., Moppel M., Pärs M., Sildos I., Jantson T., Avarmaa T., Jaaniso R., Aarik J.

Open Physics

2006

vol. 4

issue 1

105-116

The Raman spectroscopy method was used for structural characterization of TiO2 thin films prepared by atomic layer deposition (ALD) and pulsed laser deposition (PLD) on fused silica and single-crystal silicon and sapphire substrates. Using ALD, anatase thin films were grown on silica and silicon substrates at temperatures 125–425 °C. At higher deposition temperatures, mixed anatase and rutile phases grew on these substrates. Post-growth annealing resulted in anatase-to-rutile phase transitions at 750 °C in the case of pure anatase films. The films that contained chlorine residues and were amorphous in their as-grown stage transformed into anatase phase at 400 °C and retained this phase even after annealing at 900 °C. On single crystal sapphire substrates, phase-pure rutile films were obtained by ALD at 425 °C and higher temperatures without additional annealing. Thin films that predominantly contained brookite phase were grown by PLD on silica substrates using rutile as a starting material.

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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3 Open Physics

1 2015

1 2011

1 2006

3 Aarik J.

3 Niilisk A.

2 Alles H.

2 Pärs M.

2 Rähn M.

2 Sammelselg V.

1 Aidla A.

1 Avarmaa T.

1 Fay A.

1 Hakonen P.

1 Jaaniso R.

1 Jantson T.

1 Kahro T.

1 Kiisk V.

1 Kozlova J.

1 Moppel M.

1 Sildos I.

1 Wiesner M.

Search results

Raman modes in transferred bilayer CVD graphene

Structural study of TiO2 thin films by micro-Raman spectroscopy

Atomic layer deposition of HfO2 on graphene from HfCl4 and H2O