Raman Spectroscopy of 2D MaterialsKevin Cai, AMSA Charter SchoolMatthew Greenlaw, Pioneer Charter School of ScienceDr. Birol Ozturk, Northeastern UniversityProfessor Swastik Kar, Physics, Northeastern UniversityLaboratory 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

Introduction

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)

Raman Spectroscopy

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

Graphene’s Raman Spectrum

Creates topographical image◦Scanning probe

(with laser aimed at the tip) vibrates at a set frequency/amplitude

◦Changes in amplitude are recorded

Atomic Force Microscope (AFM)

~4 nm

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

2. How does O2 flow rate affect the doping of graphene with boron nitride?

Objectives

Procedure:1. Exfoliate HOPG2. Raman Spectroscopy3. AFM 4. Graph IG’/IG ratio vs. thickness

I - Mechanically Exfoliated Graphene

IG’/IG ratio generally decreases as thickness increases

Along with lower intensity, G’ peak becomes wider with increasing thickness (multilayer)

Mechanically Exfoliated Graphene - Conclusions

Graphene – conductor, zero band gap

Boron nitride – semiconductor◦Boron nitride domains are isostructural

to graphene 2D semiconductor alloy with controlled band gap

II – BN-doped Graphene

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 O2 flow rates (sccm): 0, 2, 4, …, 10

◦Raman Spectroscopy◦Broad peak at ~1355 cm-1 decomposed 1330 cm-1 (B-C peak), 1352 cm-1 (D

peak), 1368 cm-1 (h-BN peak)

II – BN-doped Graphene

No clear trend found between O2 flow rate and h-BN domain coverage◦More data needed

Conclusions

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 O2 flow rate

Future Work

[1] Servincli, H., et.al. “Effects of domains in phonon conduction through hybrid boron nitride and graphene sheets.” American Physical Society. 2011.<http://journals.aps.org/prb/abstract/10.1103/PhysRevB.84.205444>.

[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. <http://onlinelibrary.wiley.com/doi/10.1002/adma.201304937/full>.

[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).

References

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

Acknowledgements

Questions?