Institute of Optics, University of Rochester1 Carbon Nanotubes: theory and applications Yijing Fu 1, Qing Yu 2 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 Carbon nanotube CNT: Rolling-up a graphene sheet to form a tube Schematic of a CNT STM image of CNT

Institute of Optics, University of Rochester 5 Carbon nanotube Properties depending on how it is rolled up. a 1, a 2 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 Carbon nanotube : band structure Band structure of 2D graphite (7,7)(7,0)

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 MaterialYoung’s modulus (GPa) Steel SWNT1,000+ Diamond1,050-1,200

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 Τ 2, Τ 3 ~ 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 1. Field emission in vacuum electronics 2. Building block for next generation of VLSI 3. Nano lithography Energy storage 1. Lithium batteries 2. Hydrogen storage Biological 1. Bio-sensors 2. Functional AFM tips 3. 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: 1. Larger inner volumes – can be filled with chemical or biological species. 2. Open mouths of nanotubes make the inner surface accessible. 3. Distinct inner and outer surface can be modified separately.

Institute of Optics, University of Rochester 17 Biological applications: AFM tips Carbon nanotubes as AFM probe tips: 1. Small diameter – maximum resolution 2. Excellent chemical and mechanical robustness 3. High aspect ratio Resolution of ~ 12nm is achieved

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: 1. Already in product: CNT tipped AFM 2. Big hit: CNT field effect transistors based nano electronics. 3. Futuristic: CNT based OLED, artificial muscles… Challenges 1. Manufacture: Important parameters are hard to control. 2. Large quantity fabrication process still missing. 3. Manipulation of nanotubes.