Raman Spectroscopy of 2D Materials

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Transcript Raman Spectroscopy of 2D Materials

Kevin Cai, AMSA Charter School Matthew Greenlaw, Pioneer Charter School of Science Dr. Birol Ozturk, Northeastern University Professor Swastik Kar, Physics, Northeastern University Laboratory for Graphene Research 31 July 2014

 ◦ ◦ ◦ Graphene 2D sheet of carbon Conductor Stronger than steel  Mechanical exfoliation, CVD  ◦ ◦ ◦ Applications Films, composite materials Biological engineering Storage Image from http://en.wikipedia.org/wiki/Graphene

   Laser at set wavelength aimed at sample Reflected beam has a different wavelength due to vibrations Raman shift (wavenumber, cm -1 )

 ◦ ◦ ◦ Three peaks D peak (~1350 cm -1 ) – defect G peak (~1600 cm -1 ) – in-plane vibrations G’ peak (~2700 cm -1 ) – out-of-plane vibrations

 Creates ◦ ◦ topographical image Scanning probe (with laser aimed at the tip) vibrates at a set frequency/amplitude Changes in amplitude are recorded

~4 nm

1.

How does the thickness of a graphene sample correlate to its Raman spectrum?

2.

How does O 2 flow rate affect the doping of graphene with boron nitride?

 Procedure: 1.

2.

3.

4.

Exfoliate HOPG Raman Spectroscopy AFM Graph IG’/IG ratio vs. thickness

 IG’/IG ratio generally decreases as thickness increases  Along with lower intensity, G’ peak becomes wider with increasing thickness (multilayer)

 Graphene – conductor, zero band gap   ◦ Boron nitride – semiconductor Boron nitride domains are isostructural to  graphene 2D semiconductor alloy with controlled band gap Image from: Servincli, H., et.al. “Effects of domains in phonon conduction through hybrid boron nitride and graphene sheets.” American Physical Society . 2011.

 ◦ ◦ ◦ Procedure Samples grown by CVD; B, N, C, and O present  O 2 flow rates (sccm): 0, 2, 4, …, 10 Raman Spectroscopy Broad peak at ~1355 cm -1 decomposed  1330 cm -1

cm -1

(B-C peak), 1352 cm

(h-BN peak)

-1 (D peak), 1368

 No clear trend found between O 2 ◦ and h-BN domain coverage More data needed flow rate

 ◦ Mechanically Exfoliated Graphene Improve exfoliation strategy, scan/measure more samples  ◦ ◦ BN-doped Graphene Use curve fitting on more Raman spectra of domains Limit domain loss at higher O 2 flow rate

 [1] Servincli, H., et.al. “Effects of domains in phonon conduction through hybrid boron nitride and graphene sheets.” American Physical Society. 2011.

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 [2] Wang, Lifeng, et.al. “Monolayer Hexagonal Boron Nitride Films with Large Domain Size and Clean Interface for Enhancing the Mobility of Graphene Based Field-Effect Transistors.”Wiley Online Library. 2014. .

 [3] Zhou, H., Yu, F., Yang, H., Qiu, C., Chen, M., Hu, L., ... & Sun, L.. “Layer dependent morphologies and charge transfer of Pd on n-layer graphenes”. Chem. Commun., 47(33), 9408-9410. (2011).

 Dan Rubin and Dr. Birol Ozturk – Research mentors  Center for STEM Education  ◦ ◦ Young Scholars Program and Team Claire Duggan – Director Kassi Stein, Jake Holstein, Chi Tse – Coordinators  Professor Swastik Kar