Raman Analysis of Carbon Nanostructures

Div. 683: Semiconductor and Dimensional Metrology

Physical Measurement Laboratory

Advisor: Dr. Angela Hight Walker

SURF Student Talks

Thursday, August 8th 2013

Nadav KravitzUMD: Electrical Engineering (Physics)

Overview

• Carbon Nanostructures and their Applications

• Raman Spectroscopy

– Fitting and Mapping Raman spectra.

– Designing a MATLAB toolbox and environment.

• TERS: Tip-Enhanced Raman Spectroscopy

• AFM: Atomic Force Microscopy

• Future Work

• Acknowledgements

Summer Plan

1) Collect and analyze Raman images of single-wall carbon nanotubes (SWCNTs) on a silicon wafer

a) Develop MATLAB routines to process large amounts of Raman data for general use

2) Develop AFM (Atomic Force Microscopy) techniques for imaging SWCNT sample

a) Learn details of tuning fork AFM

3) Develop TERS (Tip-Enhanced Raman Spectroscopy) techniques for simultaneous Raman and AFM

a) Ambitious goal.

b) May require additional time during academic year

Carbon Nanostructures

• sp2 Carbon Allotropes– Elemental carbon

– Each atom bonded to three others

• Graphene– Hexagonal lattice in a single sheet

• Graphite– Parallel sheets of graphene

• Nanotubes– Cylindrical, rolled up graphene

• Fullerenes– Carbon polyhedra

http://uef.saske.sk/en/dtp/research/

Carbon Nanostructures: Potential Applications

• Extraordinary properties (graphene)– Lightweight

• 0.77 mg/m2

– Mechanically strong• 1 m2 of graphene can support 4 kg.

– Conductive • Resistivity: 10-6 ohm cm.

• Electron mobility: 1.5 m2/V s

– Metallic/semiconducting • (nanotubes) depending on chirality

http://www.scientificamerican.com

• Prospective uses– Technology:

• Transistors

• Photovoltaics

• Medicine

• Textiles, etc.

– Research

– Reference materials 2010 Nobel laureates

Geim and Novoselov

http://inhabitat.com

Raman Spectroscopy

• Sample irradiated with monochromatic visible laser light

• Some light is inelastically scattered (wavelength is changed)

– Some energy lost to vibration/rotation

• Scattered light spectrum is collected and analyzed

– Plotted as intensity vs. wavenumber shift

• Peaks give valuable information about composition, bonding, chemical makeup, molecular structure and properties

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Carbon Nanotube Raman Spectrum

Raman Spectroscopy: Analysis

• Peak Position Chemical Makeup

– unique chemical signatures due to geometry and bond strength

• Peak Amplitudes Relative scattering strengths, quantity

• Peak Shifts Strains, chemical changes

• Peak Width Sample purity

• Peak Shape Physical properties and effects2x104 3500

Raman shift (cm-1) Raman shift (cm-1)

Inte

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ty (

a.u

.)

Inte

nsi

ty (

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H=1.8x104

W=30

H=2.9x103

W=50

Raman Spectroscopy: Fitting

• Fitting : taking a spectrum and fitting it with a sum of specified functions

– Polynomials, Gaussians: , Lorentzians:

• Involves multiple steps: ray removal, smoothing,background-subtraction, least-squares fitting

1000 1500 2000 2500 3000 35000

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Raman shift (cm-1)

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Raman Spectroscopy: Mapping

• Mapping : taking spectra at points in a spatial array and extracting parameters

– E.g. peak heights, widths, areas, etc.

• Involves fitting each spectrum in the array and using that to deduce parameter values, and plotting

Fitted Amplitude Fitted Width Error

Making an Analysis Environment

• Developed MATLAB user interface for Raman data handling.

• Emphasis on usability, adaptability, efficiency, speed, scalability, and transparency.

• Much effort into making user friendly, and providing comments and documentation.

TERS: Tip-Enhanced Raman Spectroscopy

• TERS involves simultaneous AFM (atomic force microscopy) and Raman data collection.

• Sharp, conducting tip near surface enhances Raman signal.

• Allows greater imaging power, greater signal to noise, greater spatial resolution.

http://www.nanonics.co.il/galleries/image-gallery/afm-raman-ters/afm-raman-of-cnt.html

AFM: Atomic Force Microscopy

• Atomic force microscopy uses a physical probe to “feel” surface topology

• Typical probes use optics to determine cantilever deflection

• Tuning-fork AFMs use a two-prong fork and dynamic sensing to determine deflections based on the resonance in the fork– Can be done without optical interference (better for TERS)

www.azom.com www2.warwick.ac.uk

AFM: Atomic Force Microscopy• SiC Step-Edge Calibration Standard

– 1 nm step edges

– Used as a standard for AFM calibration , (SI traceable)

6.13 nm

-15.12 nm

2.79 nm

-3.99 nm

3.67 nm

-2.88 nm

Summer Plan Recap

1) Collect and analyze Raman images of single-wall carbon nanotubes (SWCNTs) on a silicon wafer.

a) MATLAB interface is complete and works well for Raman data. Improvements will continue.

2) Develop AFM (Atomic Force Microscopy) techniques for imaging SWCNT sample.

a) AFM is highly developed. Application to SWCNTs is ongoing.

3) Develop TERS (Tip-Enhanced Raman Spectroscopy) techniques for simultaneous Raman and AFM.

a) On the horizon. Foreseeable next step.

Future Work

• Continue to develop, improve and expand data handling and user interface.

• Work on developing AFM and TERS techniques.

• Apply both to research in technology and standardization.

AcknowledgementsThe SURF Program for the opportunity to have this experience. The NSF for providing the grant for my fellowship.Dr. Gordon Shaw and Dr. John Melcher for their patient efforts and tireless commitment.

Dr. Erlon Ferriera for his help and feedback.Dr. Angela Hight Walker and her team for their guidance, support, encouragement and feedback. I thank each of them greatly for all their work and assistance on my behalf.

Questions?

http://www.flickr.com/photos/cambridgeuniversity-engineering/

“A CNT ribbon self-organizes into a question mark morphology.

Credit: Chen; UC.”