Carbon Nanotubes: theory and applications

1. Carbon Nanotubes: theory and applications Yijing Fu1, Qing Yu2 1 Institute of Optics, University of Rochester 2 Department of ECE, University of Rochester Institute of Optics, University of Rochester

2. Outline • Definition • Theory and properties • Ultrafast optical spectroscopy • Applications • Future Institute of Optics, University of Rochester

3. Definition: Carbon Nanotube and Carbon fiber • The history of carbon fiber goes way back… • The history of carbon nanotube starts from 1991 Institute of Optics, University of Rochester

4. Schematic of a CNT STM image of CNT Carbon nanotube CNT: Rolling-up a graphene sheet to form a tube Institute of Optics, University of Rochester

5. Carbon nanotube Properties depending on how it is rolled up. a1, a2 are the graphene vectors. OB/AB’ overlaps after rolling up. OA is the rolling up vector. Institute of Optics, University of Rochester

6. Carbon nanotube properties: Electronic Electronic band structure is determined by symmetry: • n=m: Metal • n-m=3j (j non-zero integer): Tiny band-gap semiconductor • Else: Large band-gap semiconductor. Band-gap is determined by the diameter of the tube: • For tiny band-gap tube: • For large band-gap tube: Institute of Optics, University of Rochester

7. Band structure of 2D graphite (7,7) (7,0) Carbon nanotube : band structure Institute of Optics, University of Rochester

8. Carbon nanotube: Density of state • 1D confined system DOS should give spikes • Experimental results do show some spikes • Also there are some deviations, further study is needed to explain this. Institute of Optics, University of Rochester

9. Carbon nanotube properties: Mechanical • Carbon-carbon bonds are one of the strongest bond in nature • Carbon nanotube is composed of perfect arrangement of these bonds • Extremely high Young’s modulus Institute of Optics, University of Rochester

10. Ultrafast Optical spectroscopy of CNT • Pump-probe experiment is used • Provides understanding of CNT linear and nonlinear optical properties • Time-domain measurement provides lifetime measurement • 1-D confined exciton can be studied Institute of Optics, University of Rochester

11. Auger recombination of excitons • Theoretical results show strong bound excitons in semiconducting CNTs with binding energy up to 1eV • Auger recombination : Nonradiative recombination of excitons • Auger rates is enhanced in reduced dimension materials compared to bulk materials Institute of Optics, University of Rochester

12. Experimental results • Quantized auger recombination in quantum-confined system is shown here • Τ2 , Τ3 ~ 4ps, very fast loss of exciton due to auger recombination. Therefore, optical performance of CNT is severely limited. Institute of Optics, University of Rochester

13. Confined exciton effect: blue shift • Exciton energy levels are stable when bohr radius is smaller than the exciton-exciton distance • At intense laser excitation, many-body effects renormalize the exciton energy levels • Due to fast auger recombination, exciton energy level shift is only observed in very short time scale Institute of Optics, University of Rochester

14. Confine exciton effect: experiment • At zero time-delay, the absorption spectrum for pumping wavelength of 1250nm and 1323nm are shown as At low pumping level, this effect disappears. Thus many-body effect is proposed to explain this exciton blue-shift. Institute of Optics, University of Rochester

15. Applications • Electrical • Field emission in vacuum electronics • Building block for next generation of VLSI • Nano lithography • Energy storage • Lithium batteries • Hydrogen storage • Biological • Bio-sensors • Functional AFM tips • DNA sequencing Institute of Optics, University of Rochester

16. Biological applications: Bio-sensing • Many spherical nano-particles have been fabricated for biological applications. • Nanotubes offer some advantages relative to nanoparticles by the following aspects: • Larger inner volumes – can be filled with chemical or biological species. • Open mouths of nanotubes make the inner surface accessible. • Distinct inner and outer surface can be modified separately. Institute of Optics, University of Rochester

17. Resolution of ~ 12nm is achieved Biological applications: AFM tips Carbon nanotubes as AFM probe tips: • Small diameter – maximum resolution • Excellent chemical and mechanical robustness • High aspect ratio Institute of Optics, University of Rochester

18. Biological applications:Functional AFM tips Molecular-recognition AFM probe tips: • Certain bimolecular is attached to the CNT tip • This tip is used to study the chemical forces between molecules – Chemical force microscopy Institute of Optics, University of Rochester

19. Biological applications: DNA sequencing • Nanotube fits into the major grove of the DNA strand • Apply bias voltage across CNT, different DNA base-pairs give rise to different current signals • With multiple CNT, it is possible to do parallel fast DNA sequencing Top view and side view of the assembled CNT-DNA system Institute of Optics, University of Rochester

20. Challenges and future • Future applications: • Already in product: CNT tipped AFM • Big hit: CNT field effect transistors based nano electronics. • Futuristic: CNT based OLED, artificial muscles… • Challenges • Manufacture: Important parameters are hard to control. • Large quantity fabrication process still missing. • Manipulation of nanotubes. Institute of Optics, University of Rochester