The Effect of Thermal and Gas Exposure on the ...

RAMAN SPECTROSCOPIC CHARACTERIZATION OF CARBON NANOTUBES & TUNGSTEN OXIDE OF RELEVANCE TO ENERGY STORAGE AND GAS SENSING APPLICATIONS P. Misra, D. Casimir, R. Garcia-Sanchez Howard University, Washington, DC S. Baliga General Monitors Inc., Lake Forest, CA June 15, 2015

OUTLINE Background  Goals  Methodology and Results 

 Raman

Spectroscopy  Temperature Experiments  Gas Exposure Experiments  Molecular Dynamics 

Conclusions

CARBON NANOTUBE LATTICE Chiral

Achiral “Armchair”





“Zigzag”

Nanotubes can be separated into two major classifications, namely chiral and achiral Fortunately, using a folding construction on a flat graphene lattice, the primitive lattice of any single wall nanotube based on these two classifications can be constructed.

P. Wong; D. Akinwande, (2011). Carbon Nanotube and Graphene Device Physics. Cambridge University Press

APPLICATIONS Field Emission Sources

Li-Ion batteries

A. Hutchinson, Popular Mechanics, May, 2010

Gas sensors

Sergei Skarupo, Nanomix, Evaluation Engineering, June 2007 “New Coating Turns Nanotubes Into Dense, Strong Batteries” Developed at MIT How It Works: 1. Heat the Tube One end of a microscopic carbon nanotube, coated with reactive fuel, is ignited by a laser.

Applied Physics Letters, March 26, 2007, Vol. 90, 133108.

2. Herd the Particles A wave of heat races through the inside of the tube, pushing electrons toward the other end. 3. Harvest the Energy The movement of the electrons forms an electric current.

BACKGROUND 

Metal Oxides Gas Sensors (MOGS)…  are

solid-state devices used for the detection of reducing and/or oxidizing gases through conductive measurements.  are suitable for detecting a variety of reducing and oxidizing gases in environmental and sensing applications through conductive measurements.  have been extensively used in the detection of a wide variety of gases.

GOALS Measurements and calculations of the axial coefficient of thermal expansion of carbon nanotubes exhibit an unusual and debated temperature dependence where it is negative at low temperatures exhibiting contraction then gradually becomes positive, transitioning to thermal expansion. There are some studies that contradict this behavior.

Kwon, et.al PRL 92, no. 1, (2004)

There is also a large variation in the reported values for the temperatures where the transition from contraction to expansion take place, and also the temperature where maximum contraction occurs. H. Jiang, et. al. J. Eng. Mat. & Tech., (2004)

GOALS 





Determine if the Raman spectrum of metal oxides changes under certain conditions and whether these conditions can be correlated into patterns. Develop a supplemental technique (to the current way of measuring changes in the conductance/resistivity) using Raman Spectroscopy. Utilize Raman Spectroscopy with computational techniques to supplement the model.

METHODOLOGY – RAMAN SPECTROSCOPY 



Raman Spectroscopy is a laser technique used for determining the vibrational modes of samples. We utilize a DXR Smart Raman spectrometer: 

    

455/532/780 nm Laser source (Frequency-stabilized single mode diode, High Brightness), wavelength stability < 1 cm-1 over 1 hr. period Full range grating, spectral range of 50 – 3500 cm-1 spectral resolution 5.0 cm-1 Triplet Spectrograph, (No moving parts), Spectral Dispersion, 2cm-1 per CCD pixel (average value) Automated aperture selections 





Imaging Spectrometer

CCD Detector

Collection Lens

Notch Filter

780 nm Narrowband Mirror Objective Lens Sample

25 – 50 µm apertures

Temperature Controlled Environmental Chamber

Rayleigh filters (Stokes only)

We also utilize a Renishaw inVia Raman Microscope for 514 nm wavelength studies.

CW Laser (780 nm)

DXR Smart Raman setup

RAMAN FEATURES

G-Band: Strong peak centered at ~ 1580 cm-1. (Tuinstra & Koenig, 1970). In-plane bond stretching in the Graphene lattice. This Raman feature is present in all graphitic materials, hence the G label stands for “graphite

Graphite 780 nm excitation

G’-Band: Usually at ~ 2600 cm-1 was shown by Nemanich and Solin to be due to a second order two phonon scattering process at non-zero wavenumber, q ≠ 0.

Corresponding SEM Image of graphite sample

Graphene 532nm excitation

D – “Defect” Band: Located at ~ 1300 – 1400 cm-1, this peak is associated with defects, disorders, boundaries and edge effects. (Tuinstra & Koenig 1970) A. Jorio, R.Saito, M.Dresselhauss, G.Dresselhauss, (2011) Raman Spectroscopy in Graphene Related Systems. Wiley

Corresponding optical Image of graphene sample

RAMAN FEATURES (CARBON NANOTUBES) Radial Breathing Mode-Band (RBM) 𝑨𝑨 𝝎𝝎𝑹𝑹𝑹𝑹𝑹𝑹 = + 𝑩𝑩 𝒅𝒅𝒕𝒕

Corresponding SEM Image of purified Hipco SWCNT sample

Multi-walled carbon nanotube     

780 nm excitation, 9 mW Power 4.00 sec Exposure time, (2 Exposures) 400 lines/mm Grating 25 um slit entrance aperture 1.9285 cm-1 Resolution

RAMAN SPECTROSCOPY RESULTS

L.I. Espinosa-Vega et al., Spectroscopy Letters, “Determination of the Thermal Expansion Coefficient of Single-Wall Carbon Nanotubes by Rama Spectroscopy”, (48), pp. 139-143, 2013

CHIRAL INDEX DETERMINATION

Laser Excitation (nm)

SEM image of SWCNT Sample analyzed via a Kataura Plot.

Radial Breathing Mode (cm-1)

1/dt (nm-1)

Resonant Chiralities

780

150.51

0.632

***

532

166.04

0.697

***

455

171.57

0.721

(15,4), (17,3), (18,1)

CHIRAL INDEX DETERMINATION Optical Transition, Eii (ev)

Kataura Plot (Type 2 Semi conductor chiralities) 6 5 4 3 2 1 0

0

0.2

0.4

0.6

0.8

1

1.2

Series5

Series6

1.4

1.6

1/dt (nm-1) Series1

Series2

Laser Excitation (nm)

SEM image of SWCNT Sample analyzed via a Kataura Plot.

Series3

Series4

Radial Breathing Mode (cm-1)

1/dt (nm-1)

780

150.51

0.632

532

166.04

0.697

455

171.57

0.721

Resonant Chiralities *** (14,7), (15,5), (16,3), (17,1) ***

THERMODYNAMICS OF THE PHONON FREQUENCY SHIFT ∆𝛚𝛚 =

𝛛𝛛𝛛𝛛 𝛛𝛛𝛛𝛛

𝐕𝐕

∆𝐓𝐓 + (1st

𝛛𝛛𝛛𝛛 𝛛𝛛𝛛𝛛

𝐓𝐓

“Pure Thermal” contribution term) Inter-mixing of phonon modes, with the cubic and higher order an-harmonic terms in the expansion of the interaction potential gaining in importance

𝛛𝛛𝛛𝛛 𝛛𝛛𝛛𝛛

𝐏𝐏

∆𝐓𝐓

30°C

200°C

“Volume” contribution (2nd term), shift of phonon frequency to lower values due to bond-softening caused by volume increases with temperature. 30°C

𝜔𝜔(𝑇𝑇) = 𝜔𝜔0 − 𝑎𝑎1 𝑇𝑇 − 𝑎𝑎2 𝑇𝑇 2 a2 ≈ 0

Dominance of the intrinsic thermal effect yields an essentially linear frequency variation with temperature.

200°C

METHODOLOGY – TEMPERATURE EXPERIMENTS

Heated Cell used for temperature experiments

TEMPERATURE SHIFT OF RAMAN FREQUENCIES PURIFIED HIPCO SAMPLE 267.80

Temperature Variation of Radial Breathing Mode

267.60 267.40

y = -0.0093x + 270.33

267.20 267.00 RBM Frequency, 266.80 (cm-1) 266.60 266.40 266.20 266.00

SEM image of purified Hipco SWCNT used.

265.80

300

350

1595 1566.00

Temperature Variation of G- Frequency

1565.50

G+ Frequency (cm-1)

G1564.00 Frequency (cm-1) 1563.50 1563.00

1561.50

500

1594

1564.50

1562.00

450

Temperature Variation of G+ Frequency

1594.5

1565.00

1562.50

400 Temperature (K)

350

400 Temperature, (K)

1593 1592.5 1592

y = -0.0204x + 1571.8 300

1593.5

1591.5 450

500

y = -0.0187x + 1600

1591 300

350

400 Temperature, (K)

450

500

TEMPERATURE SHIFT OF RAMAN FREQUENCIES (2ND SWCNT SAMPLE) 1591.00 1590.00 1589.00

167

y = -0.0219x + 1595.4

166.5

y = -0.0096x + 168.61

166

G+ 1588.00 Frequency, (cm-1) 1587.00

ωRBM, (cm-1)

1586.00

165.5 165 164.5

1585.00 1584.00 300.00

Temperature Shift of Radial Breathing Mode

Temperature Shift of G+ Frequency

164 350.00

400.00

450.00

500.00

163.5 300.00

350.00

400.00

450.00

500.00

Temperature, (K)

Temperature, (K) 1569.00 1568.00 1567.00

Temperature Shift of G- Frequency

y = -0.0184x + 1571.6

1566.00 G1565.00 Frequency (cm-1) 1564.00 1563.00 1562.00 1561.00

SEM image of SWCNT used

1560.00 300.00

350.00 400.00 Temperature, (K)

450.00

500.00

WO3 TEMPERATURE RESULTS 



As temperature increases, the Raman spectrum exhibits a peak at ~1550 cm-1 related to W-OH bonding. Unlike the thermal effects at 780 nm, the Raman spectrum at 532 nm does not show other changes.

Change in Raman Spectra with increasing temperature (30140°C) for WO3 on Silicon substrate at 532nm

METHODOLOGY – GAS EXPOSURE EXPERIMENTS 



Synthesize NO2/N2O4 gas mixture through the reaction of Nitric acid and copper. 3Cu + 8HNO3 => 2NO + 3Cu(NO3)2 + 4H2O Sample is placed in shortpath gas cell and exposed to the synthesized gas.

Gas Synthesizer Setup

Short-path gas cell

WO3 GAS EXPOSURE RESULTS 455 NM

•

•

780 NM

We observe that no differences occur at 455 nm between the unexposed and the 24 hour exposure Raman spectra. • This suggests gas exposure has no effect on the Raman spectrum of WO3 at 455 nm. 780 nm shows a very different result and the differences can be easily discerned. • The key differences appear to be the 203 cm-1 and 239 cm-1 peaks. • The 203 cm-1 peak, it does not seem to correspond to any known related vibrational modes (i.e. W-O, O-H, N-O bonds) but has been observed in all samples that were exposed to the NO2-N2O4 gas. • Previously, the 239 cm-1 peak corresponded to O-W-O bending in one type of WO3 sample; this suggested a non-monoclinic behavior in the part of these nanopowder samples.

MOLECULAR DYNAMICS The theoretical basis of this computer based technique involves little more than Newton’s laws of motion

Relation to thermodynamics Temperature Equipartition Theorem

Relation to Statistical Mechanics

Pressure, (Virial Theorem) Ergodic Hypothesis

MOLECULAR DYNAMICS SIMULATION RESULTS

P. Schelling, P. Keblinski, PRB, 8, 2003

Radial linear thermal expansion (blue): -8.61883*10-6 K-1 Axial linear thermal expansion (red): 2.31296*10-6 K-1

VIBRATIONAL ANALYSIS

0.997 Tera-Hertz 1.93 Tera-Hertz

Lateral frequencies, from the transverse motion of the center of mass of one of the cylindrical disk sections during an 800K MD Simulation.

100 K Temperature

800 K Temperature

CONCLUSIONS (SWCNT) 











Using the above mentioned temperature shift of the RBM band we were able to model the linear decrease in the volume thermal expansion of a SWCNT sample. Besides Espinosa-Vega et al, this study the only one demonstrating the volumetric contraction of a “bundled” SWCNT sample based on the linearly decreasing volume CTE obtained via the thermally shifted radial breathing mode Raman frequency. Our extreme values of 0.2*10-6 and -0.5*10-7 K-1, of the volume CTE β, at the minimum and maximum experimental temperatures were an order of magnitude lower than those of Espinosa-Vega et al. This was due to different sample preparation, and environmental conditions of the SWCNTs in both of our studies, which demonstrated the influence of inter-tubule interactions via dispersion forces, suggesting a possible path in attempting to better quantify this effect in SWCNT characterization without the use of expensive Scanning Probe Methods (TEM, AFM, etc.). A robust efficient method of predicting this thermo-mechanical property of SWCNTs will be critical to the applications of Li-Ion Batteries, Gas Sensors, and other potential applications based on SWCNTs mentioned earlier. Future work will also involve including computational data and results not only from MD simulations, but also from ab-initio calculations.

25

CONCLUSIONS (WO3) 

We were able to determine the effect of:  



Previous work done has studied the effect of:  



Temperature at 780 nm on three different types of WO3 materials. Humidity.

We also studied the effects of:    



Temperature at 532 nm. 24 hour NO2/N2O4 exposure on WO3 at 455 nm and 780 nm.

NO2/N2O4 exposure on WO3 at 514 nm and 532 nm. Incremental NO2/N2O4 exposure at 780 nm (up to 5 exposures for the first sample) Cooling. Prolonged underwater exposure.

Through the study of Raman spectra that results from gas exposure and temperature effects on the sample, we are able to further the understanding of the vibrational configuration of metal oxide materials that are commonly used for gas sensing applications.

ACKNOWLEDGEMENTS Support from the College of Arts and Science and the Graduate School is gratefully acknowledged.  Support from NSF HBCU-UP and REU in Physics grants is gratefully acknowledged. 