Carbon Nanotubes

Carbon Nanotubes

Deanna Zhang

Chuan-Lan Lin

May 12, 2003

Overview

• Introduction

• History

• Fabrication

• Application

• Summary

Introduction I:What is nanotube?

•Responsible bond:•Unit cell: honeycomb pattern•Wrapping these patterns back on top of themselves and joining the edges Carbon nanotube

2SP

Introduction II:Single and Multi-wall nanotube

• Single wall nanotube: – SWNT– single atomic layer wall,

diameter of 1-5 nm – excellent mechanical property– hot topic now

• Multi wall nanotube:– MWNT– Inner diameter: 1.5 – 15 nm– Outer diameter: 2.5 – 30 nm– ~50 layers – containing more structure

defects (http://www.lbl.gov)

Introduction III:The Electrical Properties of nanotube

• Can be either Metal or semiconductor– Controlled by Rolling Direction

Ch (rolling vector)= na + mb (unit vector)

Rule: = integer metallic

non-integer semiconductor

• Electrical Conductivity– Four Point Probe Method to determine sheet resistance and conductivity

3

mn

Introduction IV:The Other Properties of Nanotube

•Mechanical:

–Young’s Modulus ~ 1TPa (SWNT), 1.25 TPa (MWNT)

(Steel: 230 GPa)

–Density ~ 1.3 g/cm^3

•Thermal:

–Conductivity: 2000W/m.K ( copper: 400W/m.K)

•High Aspect Ratio: Length ~1µm, Diameter ~ 1nm to 50nm

History IBuckyball ( )

• The discovery of nanotubes comes from Buckyball

• The discovery of Buckyball is by accident, from Radio-astronomy

• Around 1970s

60C

(http://www.slb.com )

History IIThe History of Nanotubes

When Who Events

1970s Harry Kroto & Dave Walton Try to synthesize long carbon chains

Late 1980s Scientists around the world Buckyball was synthesized and confirmed as C60

1991 Japanese Scientist, Sumio Iijima Discovery of multi wall carbon nanotubes

1993S, Iijima and T, Ichihashi Synthesis of single wall carbon

nanotubes

1996 Robert F. Curl, Harry Kroto ,

Richard E. Smalley Nobel Prize in Chemistry for the discovery of Buckyball

1999 Samsung Flat Panel display prototype

2001 IBM The first computer circuit composed of only one single carbon nanotube

Fabrication of Carbon Nanotubes

• Laser Ablation or Pulsed Laser Vaporization

• Carbon Arc or Arc Discharge

• Chemical Vapor Deposition (CVD)

• High pressure (HiPCO)

Fabrication ILaser Ablation

• Target: 1 at.% each of Ni and Co uniformly mixed with graphite• 500 m Torr Ar flowing at 50 sccm• In the oven at 1473 K• Nd:YAG Pulse laser at 60Hz• PUREST but yield is very small (~0.4 gram/hour)• Developed by NASA JSC Group based on Rice University facility

Fabrication IICarbon Arc or Arc Discharge

• The first available method• Electric arc vaporizes an carbon anode containing the catalysts (Ni and Co)• He: 500 Torr, Current: 100 amp and 35 volts• Chamber is cooled by water• Nanotube takes place at the wall inside the chamber• Developed by the group at the University of Monpellier, France

Fabrication IIIChemical Vapor Deposition

(CVD)

• Idea: prepattern the substrate with a catalyst and to grow nanotubes onto these by CVD

• The key step : deposit the catalyst at predefined locations • Advantage: SELECTIVE GROWTH: we can grow

nanotube at the place we expect • First developed by Xie group in China in 1996• Use hydrocarbons as source

Fabrication III:Steps of CVD

• Deposit photoresist

• Expose resist

• Deposit catalyst

• Etch resist

• CVD growth of Carbon Nanotube on catalyst

Fabrication IVHiPCO

2CO

• Single wall nanotube in gas phase (1200C, 10 atm)• CO+CO C+ catalyst: (25 mTorr)• Flow high pressure carbon monoxide past catalyst particles at high temperatures• Can now produce largely single-walled nanotubes in kilogram quantities • Purification steps are unnecessary due to use CO instead of hydrocarbons•(P. Nikolaev et al.)

5FeCO

Application

• Transistor– Field Effect transistor– Single electron transistor

• SPM Tips

• Field Emission Display Device

• More Possible Applications

Nanotube transistor

• Field Effect transistor– Similar to MOSFET– Formation of P-type– Annealing or doping with K to form N-type– Use both N and P to

make CMOS typecircuits

SPM Tips

• Tips of Scanning Probe Microscopes are usually cantilevers or metal wires but seldom survive a tip crash

• Nanotubes: large aspect-ratio, well-defined end, far more resistant

A nanotube was directly grown by CVD on

a cantilever (From J. Hafner et al, Nature 398, 761 (1999))

Field Emission Display Device• Take advantage of the properties of

high current containing and high aspect ratio

• Useful as the electron source for Flat Panel Display with lower power consuming and high voltage circuit is unneeded

• Samsung has shown the prototype of 9” full color display with 576 X 242 pixels

• The first nanotube flat screen TV is expected to be manufactured by the end of 2003

The Samsung 4.5” full-color nanotube display

Schematic structure of nanotube flat panel display.(Choi et al.)

(Cathode)

(Anode)

More Possible Applications• Nanotube sensors (Kong et al.):

– The electrical conductivities of SWNT change dramatically when they expose to gaseous molecules

• Hydrogen storage (Heben et al.):– 5~10 wt% hydrogen storage density at room temperature for

SWNT

• Light Elements (Saito et al. ):– Electrons from nanotube bombard a phosphor-coated surface to

produce light – 2 times brighter, 8000h lifetime, can be used for giant outdoors

displays

• Memory device (Fuhrer et al.):Capable to store single electronic charge– High mobility

Summary and Future work• Carbon Nanotubes have unique properties• Unique properties lead to fabrication of different

devices.• Improvements of current fabrication of carbon

nanotubes needed to make available commercial products.

• The totally new world constructed by nanotube is close.

• Little knowledge about growth mechanism

Questions?Questions?