SYNTHESIS OF SINGLE-WALLED CARBON NANOTUBES (SWCNTs) FROM OPTICALLY

PUMPED CARBON MONOXIDE

Elke Ploenjes, Vish V. Subramaniam, J. William Rich

Department of Mechanical Engineering and Department of Chemistry

The Ohio State University

Presented by Jennifer McFerran Ohio Nanotechnology Summit

March 2005

INTRODUCTION

• Potential applications:– fiber-based electronic devices

– High-strength, high-stiffness fibers for composite materials

– Field-emitting lamps and displays

– Clathrates for fuel cells

• November 1999: Smalley’s group publishes growth of SWNTs from equilibrium high-pressure, high-temperature process involving CO with trace amounts of Fe(CO)5.

• December 1999: OSU group develops scalable non-equilibrium process for synthesis of SWNTs based on optical pumping of CO.

• Summer 2000: Patent application filed (J. W. Rich, V. V. Subramaniam, & E. Ploenjes).

• December 2001: Journal paper published, see Chemical Physics Letters 352 (2002) 342-347.

BACKGROUND: V-V PUMPING

• Most probable single quantum vibrational energy transfer process:

)1()1()()( wBvAwBvA

• Due to anharmonicity, E < 0 for w > v. – V-V transfer energetically favored for w > v because excess energy

can go into translational or rotational (i.e. external) modes. – Reverse process requires energy to be supplied from external

modes.– Therefore, if v = 1 is populated slightly above equilibrium levels,

excess energy re-distributed to higher vibrational levels.– Super-equilibrium population of v > 1 levels results as long as v = 1

is maintained above equilibrium. – This anharmonic VV pumping gives a non-Boltzmann distribution

called the Treanor-Rich-Rehm (TRR) distribution.

BACKGROUND: VV PUMPING

• Characteristic times for vibration to equilibrate with rotation and translation are long.

• VV transfer occurs preferentially over VT transfer as long as VV rates dominate VT rates.

• Typically, this means that as long as low translational temperatures (less than about 1500 K) are maintained, VV rates can dominate VT rates.

Gas-phase Boudouard Reaction:

Catalyzed Boudouard Reaction:

2catalystCO CO C CO

catalystn C Carbon nanotubes

2( ) ( )CO v CO w C CO

EXPERIMENTAL SETUP

• Total gas pressure 100 Torr, equal amounts CO and Ar.

• Gaseous metal carbonyls, Fe(CO)5 and Ni(CO)4, used as catalyst precursors.

• A few watts of the CO laser radiation is absorbed by the CO/Ar mixture, resulting in vibrational excitation of CO.

• FT-IR spectrometer used to determine non-equilibrium vibrational population of CO and rotational mode temperature by emission spectroscopy.

0 1 0 2 0 3 0

1 E - 5

1 E - 4

1 E - 3

1 E - 2

1 E - 1

1 E + 0

V i b r a t i o n a l q u a n t u m n u m b e r

R e l a t i v e p o p u l a t i o n

B o l t z m a n n d i s t r ibutiona t Tv= 4 1 0 0 K

M e a s u r e d n o n e q u i l i b r i u md i s t r i b u t i o n

Tv T = 1200 K

NON-EQUILIBRIUM POPULATIONS OF VIBRATIONAL STATES OF CO (1+) IN OPTICALLY PUMPED CO/Ar

PLASMA

RESULTS

• TEM images are obtained from raw material without any post-synthesis purification.

• Typically, bundles or ribbons appear in a range of lengths from 0.5 m to 1 m. Diameters of individual tubes are ~ 1 nm.

• 70% of deposit estimated to be SWCNTs.

• Total deposition rate is 10–20 mg/h at PCO = 50 Torr.

HIGH-RESOLUTION TEM IMAGES OF AS-DEPOSITED MATERIAL

10 nm

SWNTs among amorphous material Bundles of SWNTs

TEM IMAGES OF CNT’s PRODUCED IN AN OPTICALLY-PUMPED CO/Ar PLASMA

10 nm 10 nm

A bundle of SWNTs Ribbons of carbon nanotubes (as grown)

SUMMARY

• Optical pumping of CO in the presence of a catalyst can result in production of SWCNTs.

• Although this non-equilibrium process has not been optimized, it is capable of high yield.

• The process is scalable to higher pressures and to condensed phases; produces only SWCNTs and amorphous carbon.

• Potential exists to control tube diameter, length and chirality using macroscopic process parameters.