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Preparation and Characterization of Carbon Nanotubes. Timothy Day and Tyrone Hill ECE 345 November 28, 2001. Overview. Objectives Background Information Original Design Successes and Challenges Testing Conclusions. Project Goals.

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preparation and characterization of carbon nanotubes

Preparation and Characterization of Carbon Nanotubes

Timothy Day and Tyrone Hill

ECE 345

November 28, 2001

  • Objectives
  • Background Information
  • Original Design
  • Successes and Challenges
  • Testing
  • Conclusions
project goals
Project Goals
  • Objective: “To perfect a process for creating H-passivated Si [100] wafers with a sparse enough CNT density to allow manipulation and characterization with an STM.”
  • 5 nanotubes/square m
project features and equipment
Characterization of CNT bonding with Si H-passivated layer

Knowledge of CNT electrical properties

Recipe for preparing CNT deposition

UHV Chamber

Atomic Force Microscope

Scanning Electron Microscope

Scanning Tunneling Microscope

Project Features and Equipment
cnt background info
CNT Background Info
  • Discovered by S. Ijima in 1991
  • Tubular hexagonal arrays of graphene sheets
  • Can be single-walled or multi-walled (~2 nm SWNT diameter)
  • Have metallic or semiconducting properties
  • Nanoelectronic Applications
cnt background info1
CNT Background Info

Chiral vector:

    • Ch= aV1 + bV2
  • Metallic:
    • a=b
  • Semi-conducting:
    • (a-b)=3N
  • Types:
    • Armchair: (a,a)
    • Zigzag : (a,0)
    • Chiral: (a,b) angle > 30°
original design
Original Design
  • Degrease Wafers
  • UHV Passivation
  • Deposition of CNT
  • STM/AFM Characterization
  • Deposit Metal Contacts
  • Electrical Characterization


ultra high vacuum system
Ultra High Vacuum System
  • Main Chamber- Ion Pump w/ base pressure ~5 * 10-11 Torr
  • Scanning Tunneling Microscope Chamber off main chamber designed by Dr. Lyding
  • Bake- ~300˚ C for 7 days
  • Estimated Cost = $300,000
ultra high vacuum system1
Ultra High Vacuum System


Main Chamber




ultra high vacuum chamber basic operation
Ultra High Vacuum Chamber Basic Operation
  • Proper Handling of Samples and Sample Holders
  • Procedure for Inserting Samples into Chamber using load-lock
  • Maneuvering of Sample Holder with Dipstick and Manipulators
uhv passivation
UHV Passivation
  • Degas Si sample (~700˚ C, 24 hrs)
  • Cool Dipstick to 40ºC/Perform temperature calibration with pyrometer
    • Passivation temp: 377° C
  • Expose Si to two 30 second heat flashes
  • Introduce H2 gas
uhv passivation1
UHV Passivation
  • Step 1: Diatomic Hydrogen (H2) is introduced into the chamber
  • Step 2: The tungsten “cracking” filament breaks the H bonds
  • Step 3: The atomic hydrogen atoms attach to the dangling bond on the Si surface
h passivation
  • Dangling Bonds
  • Dimer rows
  • Si Terraces
  • Si Defects
adjustments and new directions
Adjustments and New Directions
  • Began using “wet” H-passivation
    • 50:1 HF dip for 30 seconds, DI for 15 seconds, blow dry with N2 gas
  • Concentrated on CNT deposition
    • Made 1:10 dilution and 1:100 dilution of original CNT solution
    • Deposited using volume-controlled syringe
  • Atomic Force Microscope
atomic force microscope
Atomic Force Microscope
  • Two modes: Contact & Tapping*
  • Tip diameter used was 5-10 nm
    • Diameter will affect spreading effects
  • Atomic Resolution
  • Small Damage Effects
  • Slow Scanning Speed
atomic force microscopy
Atomic Force Microscopy
  • 1. Laser
  • 2. Mirror
  • 3. Photodetector
  • 4. Amplifier
  • 5. Register
  • 6. Sample
  • 7. Probe
  • 8. Cantilever
environmental scanning electron microscopy
Environmental Scanning Electron Microscopy
  • Column generates electron beam that is aimed at sample and focused with EM fields
  • Images are obtained by detecting and processing primary electron scattering
  • Resolution of 5-10 nm
  • Scanning speed faster than AFM
problems and solutions
Problems and Solutions
  • CNTs appeared only in concentrated islands
  • Amorphous carbon particles contaminated CNT islands
  • Made new CNT solution
    • Anthony Bollinger, Physics Dept. UIUC
    • Dried CNT in DCE
    • Sonicated for 15 min
conclusions from esem
Conclusions from ESEM
  • Use second CNT solution with 1:5 dilution
  • Sonicate diluted solution for at least 15 min
  • Deposit 2 L drop and allow solvent(DCE) to evaporate
  • Scanning Tunneling Microscopy
scanning tunneling microscopy
Scanning Tunneling Microscopy
  • A biased sharp tip at nm distances causes a tunneling current to flow between sample and tip
  • Feedback of tunneling current keeps current constant while varying height of tip using a voltage controlled piezoelectric tube
  • Movements are recorded and converted to topographical map of sample surface

UHV STM Design

Piezoelectric Scanning Unit

Tunneling Probe

Sample Holder

image after sample degas
Image After Sample Degas

3000x3000 Å2



Large rope like structure

present, as well as, the atomic

steps of silicon surface are


image of rope section
Image of Rope Section

Initial Image of Bundle

Tip is Multiple

After Several Scans Bundle

Appears to be Unraveling

600x600 Å2



600x600 Å2



magnified swnt and dos characterization
Magnified SWNT and DOS Characterization



300x300 Å2-3.5V 8.6x10-12A

multiple tip image of potential single wall nanotube
Multiple Tip Image of Potential Single Wall Nanotube

650x650 Å2



~ 17Å

Attempted todamage

tube using nano-

lithography routine,

tube was clearly

perturbed, but more work

is needed before we can

draw any conclusions.

final conclusions
Final Conclusions
  • Possible to image CNTs with STM on semiconducting substrate
  • Van der Waals interactions make isolation of single tube very difficult
  • Could get better data with sharper STM tip
  • Use cleaner solvent to avoid organic contamination
special thanks
Special Thanks
  • Dr. Joe Lyding for guidance and use of his facilities
  • Frankie Liu and Nathan Guisinger for their help and technical expertise
  • Anthony Bollinger for his CNTs
  • Matt Olson for his advice