10836_Raman Characterization of Carbon Nano Materials and Obtaining Representative Measurements

8/2/2019 10836_Raman Characterization of Carbon Nano Materials and Obtaining Representative Measurements

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Raman Characterization of

Carbon Nanotubes and Carbon

Materials: ObtainingRepresentative Measurements

Presenter: Mark Wall

Product Specialist Raman Spectroscopy

E-mail: [email protected]
mailto:[email protected]:[email protected]


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Presentation Overview

What is Raman spectroscopy?

What can Raman tell you about Carbon?

What is involved in a collecting a Raman

measurement?

Questions and Answers


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Brief Description of Raman Spectroscopy

Raman spectroscopy is a laser light scattering technique

A form of Vibrational Spectroscopy

Records vibrations of covalent bonds

Provides detailed molecular information

Most sensitive to symmetric bonds

A good tool for characterizing molecular backbones

Sensitive to even slight changes in bond angle or strength

Highly sensitive to geometric structure

Highly sensitive to stresses in molecules or modifications which impactbond properties

R

RH

H


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What Can Raman Tell You About Carbon?

First, Raman can identify it and distinguish it from other materials

The Diamond spectrum is very similar to that of crystalline Silicon and Germanium except that the lighter

weight Carbon bonds vibrate at higher frequency.


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What Can Raman Tell You About Carbon?

Raman easily differentiates different allotropes D band may represent sp3 bonds (tetrahedral configurations) or it

may represent disorder in hybridized sp2 bonds (graphene edge

configurations) G band represents sp2 bonds (planar configurations) These two bands form the core of Raman carbon spectrum

Silicon

D band known as the

disorder, defect, or

diamond band.

G band known as the

graphite or tangential band
http://upload.wikimedia.org/wikipedia/commons/d/d9/Diamond_and_graphite2.jpg


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Other Forms of Carbon Nanocrystalline Diamond

Raman is very sensitive to morphology differences

Nanocrystalline diamond has a slightly different structure to bulk diamond

due to the increased surface area on the nanocrystals

The effect on the Raman spectrum is dramatic


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Other Forms of Carbon Diamond like Carbon (DLC)

The band position shows us that this Diamond like Carbon film probablyhas both sp2 and sp3 carbon


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Other Forms of Carbon Fullerenes

Raman tells us that C60 bonds are much more uniform than C70


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Other Forms of Carbon Graphene

Graphene consists of the single layer units that make up graphite

G' G


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Other Forms of Carbon Graphene

Examination of G' band is revealing Graphene has one primary mode

Multilayer Graphite exhibits multiple modes

Graphite Graphene

Graphene

Graphite


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1587.

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1581.

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15501560157015801590160016101620Raman shift (cm-1)

OMNIC

Raman Spectroscopy

Software

Single Layer

Double Layer

Graphite

Wang,Hui; Cao,Xuewei; Feng,Min; and Lan,Guoxian

Other Forms of Carbon Graphene Layer Thickness


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145015001550160016501700

Raman shi ft (cm-1)

Single Layer

Double Layer

Triple Layer



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160018002000220024002600

Raman sh ift (cm-1)

2D

G

Single Layer Graphene

I2D/IG= 2



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Single-wall Carbon Nanotubes (SWCNT)

Represent a rolled up sheet of graphene in the form of a tube

Multi-wall Carbon Nanotubes (MWCNT)

Consist of concentric nanotubes

Other Forms of Carbon Carbon Nanotubes (CNT)

Graphene SWCNT


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Single-Walled Carbon Nanotubes (SWCNT) introduce a new mode

Radial Breathing Modes (RBM) Characteristic of SWCNT

2D RBMG D


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Other Forms of Carbon SWCNTs

RBM Frequency correlates to tube diameter

Theoretical calculation is diameter (nm) = 248/(RBM frequency cm -1)

In practice, exact RBM frequency can be shifted by other factors so it is better used forrelative comparisons


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Other Forms of Carbon SWCNTs

Metallic and Semiconducting properties

SWCNTs can have either semiconducting or metallic properties depending on thechirality of the tube.

Differences are less pronounced, but relative comparisons can be made

GiTOLA M

Red Semiconducting and Metallic Mix

Blue

Semiconducting only


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MWCNTs

Do not exhibit RBM modes

Typically have a higher D/G ratio than SWCNTs

RBMDG


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Other Forms of Carbon MWCNTs

Collection of MWCNTs ranging in diameter from 50 nm


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Raman Measurements Sample Preparation

Raman samples materials neat under atmosphere

This means there is relatively little sample preparation Samples typically run under a microscope

Loose powders can be compressed between two slides

CNTs are often cast onto slides in a surfactant matrix

Films are run in their native state


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CNT Sample Preparation for Raman Characterization

Light compression of raw CNT Compacts sample to increase the density of CNTs

Place second slide over sampleTake small sample from bag Transfer sample to slide

Apply pressure to top slide Remove top slide CNT ready for measurement


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Raman Measurements Laser Sensitivity

Many Carbon materials are sensitive to laser power at sample

Spectral changes may represent different excited modes at different laser power

MWCNTs excited at 3 different laser powers peak height normalized

1.0 mW2.0 mW

3.0 mW

with increasinglaser power

with increasinglaser power

DG


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Spectral changes may represent different excited modes at different laser power

G band of SWCNTs excited at different laser powers peak height normalized


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In some cases spectral changes may indicate damage to the material

C60 excited over a range of laser power peak height not normalized

Decomposition products

Thermal baseline


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Laser Power Regulation

Legend:Zone A: The Laser Power Regulator controls the laser powerreaching the sample to ensure reproducible results.Zone B: As the laser power declines over its lifetime,measurements become non-reproducible on instrumentslacking a Laser Power Regulator.Zone C: Beyond the expected laser lifetime. The Ramaninstrument can still be used reproducibly at lower power levels.

Precise and fine laser power control at sample!


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Raman Measurements Selection of Excitation Laser

Many CNT bands are subject to resonance enhancement

RBM bands and G band in particular are highly resonant

RBMDG2D

Blowup of RBM bands


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Raman Measurements Types of Measurements

Microscope measurements

Single point collection

Mapping

Bulk measurements

Only applicable if sample is densely packed

Sometimes this applicable to liquidsuspensions

Even investigation of single CNTs


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Single Point Raman measurements - Spectrum Variability

50010001500200025003000

Raman shift (cm-1)

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Raman shift (cm-1)

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Raman shift (cm-1)

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Multipoint Measurements - Raman Mapping

532nm Excitation contour map is based upon G band intensity


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Position (micrometers)=-321 m ;-206 m Number: 473

150200250300350400

Raman shift (cm-1)

260 cm-1Positio n (micrometers)=-71 m ;-176 m Number: 753

80100120140160180200220240260

Raman shift (cm-1)

150 cm-1

Multipoint Measurements - Raman Mapping

Diameter (nm) = 248/RBM(cm-1)

1nm SWCNT 1.7nm SWCNT


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Calculating a Representative Raman Spectrum Chemical Map

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Raman shi ft (cm-1)

Average Spectrum = RamanSpectra / total number of spectra

417 spectra: Average

417 spect ra: Variance

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Raman shi ft (cm-1)

AverageVariance

R id R t ti R M t


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Rapid Representative Raman Measurements

Alternative method for obtaining a representative Raman spectrum Based upon rastering the laser rapidly across sample (100 hz) Collect Raman scatter continuously during multiple passes of the laser across the sample

Raman spectrum indicative of the area traversed by the laser

Variable Dynamic Point Sampling (VDPS)

C i f A M S t t VDPS


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Comparison of Average Map Spectrum to VDPS

VDPS

Map

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Raman shift (cm-1)

H R i A li d I d t i l A li ti


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How Raman is Applied Industrial Applications

Measurements of consistency of

product DLC films

Purity of CNTs

Incoming QC

Outgoing QC

Sometimes the range of variationis important

Distribution mapping

Verifying that processing is notaltering the material

Functionalization steps

SWCNT with a peak near 313 cm -1

SWCNT with a peak near 276 cm-1



Diameter

Sm

Lg

Distribution of SWCNTs within MWCNT matrix

H R i A li d R h A li ti


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How Raman is Applied Research Applications

Quick characterization of materials before utilization

Formation of CNTs pretty well established as this time

Still useful for quick checking of formation process before moving on Current research focuses on purification, separation, and integration within end commercial

materials and devices.

G' G

C l i


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Conclusions

Raman is an extremely powerful tool for characterizing Carbon

nanomaterials Raman sampling is easy and faster than many other techniques

Raman has a role to play in both research and QC

The limits to the information that Raman can provide on Carbonmaterials are still unfolding

As this field continues to develop, the role of Raman is most likely going to increase

S ti f F th L i


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Suggestions for Further Learning

Additional reading on interpretation of Raman spectra of CNTs:

Raman spectroscopy of carbon nanotubesM.S. Dresselhaus, G. Dresselhaus, R. Saito, A. Jorio

10.1016/j.physrep.2004.10.0006

Additional reading on sorting CNTs:

Sorting carbon nanotubes by electronic structure using density differentiation

M.S. Arnold, A.A. Green, J.F. Hulvat, S.I. Stupp, M.C. Hersam

nature nanotechnology, vol 1, October 2006, pages 60-65

Q ti ?


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Questions?

Thank You For Your Time!

Email survey Your feedback is important

Presentation slides and recording will be available on the Materials Todaywebsite

Additional Thermo Fisher Scientific Raman webinars

www.thermoscientific.com/ramanwebinars

Any additional questions?

E-mail: [email protected]

Please include subject line: Raman CNT Webinar Request

For product information please see:

http://www.thermoscientific.com/dxr

Mark Wall
http://www.thermoscientific.com/ramanwebinarsmailto:[email protected]://www.thermoscientific.com/dxrhttp://www.thermoscientific.com/dxrmailto:[email protected]://www.thermoscientific.com/ramanwebinars

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10836_Raman Characterization of Carbon Nano Materials and Obtaining Representative Measurements