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Characterization of CNT using Electrostatic Force Microscopy

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).

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Characterization of CNT using Electrostatic Force Microscopy

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  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, 1838-41 (2005). • Characterization of Carbon Nanotubes on Insulating Substrates using • Electrostatic Force Microscopy, T.S. Jespersen et al. Electronic Properties of Novel • Nanostructures, 786, 135-138 (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 • 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 EFM: (+) Rapid (+) Larger surfaces (hundreds m across) (+) Provides electrical info. (-) low resolution. (-) Does not work on conducting surfaces. AFM: (-) Relatively slow (-) Small scanning areas (tens m across) (+) high resolution (CNT diameter) (+) can 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:

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

  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.

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