1. SWNT Periodic Table
Primary and secondary gap semiconductors

2. After R Smalley and B Weisman

3. After R Smalley and B Weisman

4. Pulsed photovoltaics
Picosecond excitation with continuously tunable wavelength:
high sensitivity detection even with blocking contacts
high spectral resolution (0.1 nm), high time resolution
spectroscopy of amplitude and dynamics of photoresponse
Nd:Yag with regenerative amplifier 30 ps long light pulses 80 mJ output energy nm, 532 nm, 355 nm.
Optical Parameteric Generator/Amplifier
Tunable continuously from nm to 2300 nm output energy > 100 µJ

5. Pulsed photovoltaics
Photovoltaic signal induced by picosecond pulses is a good spectroscopic “observable”.
The spectra we observe depend on nanotube coverage on the contacts.
Use these basic observation to develop a rapid, useful spectroscopy tool to study the distribution of different nanotubes characteristics in a given sample: such as band gaps, chiralities, etc.

6. SWNT Sample 8 7 6 5 4 3 2 1 9 10 11 12 13 14 15 16

7. First results 8 7 6 5 4 3 2 1 9 10 11 12 13 14 15 16

8. First results 8 7 6 5 4 3 2 1 9 10 11 12 13 14 15 16

9. After R Smalley and B Weisman

10. Additional results 8 7 6 5 4 3 2 1 9 10 11 12 13 14 15 16

11. Summary of first observations
No voltage applied, we measured photoinduced voltage change between contacts
Transient voltage change, less than 20 ns long, the photoinduced charge on the illuminated contact appears to be negative (to be double-checked).
The transient appears to be due to a what is effectively a photoinduced dipole that relaxes back in a few nanoseconds. However, the strength of the transient is wavelength-dependent showing bands characteristic of nanotube spectral features.
Further investigation will focus on identifying the origin of the photovoltaic response by comparing different contact configurations and different kinds of nanotube coverage.