1. Characterization of CNT using Electrostatic Force Microscopy
Vadim Karagodsky
Probing induced defects in individual carbon nanotubes using electrostatic force
microscopy, T. S. Jespersen et al., Appl. Phys. A 88, 309–313 (2007).
Charge Trapping in Carbon Nanotube Loops Demonstrated by Electrostatic Force
Microscopy, T. S. Jespersen et al., Nano Lett, 5, (2005).
Characterization of Carbon Nanotubes on Insulating Substrates using
Electrostatic Force Microscopy, T.S. Jespersen et al. Electronic Properties of Novel
Nanostructures, 786, (2005)

2. AFM basic operation – oscillating mode
The cantilever is oscillated
at its resonant frequency.
The oscillation is detected
by the reflected laser at the
photodiode.
The atomic forces between
the tip and the sample
modulate the oscillation.
The cantilever is raised
until the oscillations get
back to initial state.
The raised distance is
proportional to the surface
topography.

3. AFM tip and resolution

4. AFM tip and resolution

5. AFM tip and resolution
Atoms of sodium chloride
sensed by AFM (2007).

6. EFM - basic operation (Vs=-5V h=60nm) Similar to AFM, but:
Voltage Vs is applied.
The tip is raised to tens nm
above the surface.
At this height, the atomic
forces can be neglected but
the Coulomb force remains.
The information is
obtained from phase shift.
The Coulomb force has a
longer range, and therefore
the CNTs appear hugely
amplified in diameter.
(Vs=-5V h=60nm)

7. AFM vs. EFM AFM: (-) Relatively slow (-) Small scanning areas
(tens m across)
(+) high resolution
(CNT diameter)
(+) can work on
conducting surfaces.

8. AFM vs. EFM AFM: (-) Relatively slow (-) Small scanning areas
(tens m across)
(+) high resolution
(CNT diameter)
(+) can work on
conducting surfaces.
EFM:
(+) Rapid
(+) Larger surfaces
(hundreds m across)
(+) Provides electrical info.
(-) low resolution.
(-) Does not work on
conducting surfaces.

9. EFM – phase shift information

10. EFM – Basic theory
Harmonic oscillator equation:

11. EFM – Basic theory
Harmonic oscillator equation:
Solution:

12. EFM – Basic theory Harmonic oscillator equation: Solution:
Frequency shift and phase shift:

13. EFM – Basic theory Harmonic oscillator equation: Solution:
Frequency shift and phase shift: 0
60kHz k
2.8N/m Q
225
||
<2 deg

14. EFM – Basic theory Harmonic oscillator equation: Solution:
Frequency shift and phase shift: 0
60kHz k
2.8N/m Q
225
||
<2 deg

15. Experiments relying on EFM
Quick estimation of CNT density
using phase-shift histogram.

16. Experiments relying on EFM
Proving that CNT loops can trap surface charges.
Two loops initially contain charges

17. Experiments relying on EFM
Proving that CNT loops can trap surface charges.
Two loops initially contain charges
The lower loop was discharged by grounded AFM tip.

18. Experiments relying on EFM
Identification of special CNT structures (loops) with respect to predefined alignment marks in large samples (100m X 100m).
Low resolution EFM scan
resolved the CNTs.
AFM scan with the same
resolution did not
resolve the CNTs.

19. Conclusions EFM is a powerful technique for rapid
characterization of CNTs on insulating surfaces.
EFM can operate under ambient conditions.
In the experiments reported here, EFM was found to
be at least 100 times more time efficient than AFM.
EFM provides electrostatic information that is not
available through topographic AFM scans.
EFM cannot be used on conducting surfaces.
EFM does not provide CNT diameter information.