SWNT Periodic Table Primary and secondary gap semiconductors

After R Smalley and B Weisman

After R Smalley and B Weisman

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. 1064 nm, 532 nm, 355 nm. Optical Parameteric Generator/Amplifier Tunable continuously from 420 nm to 2300 nm output energy > 100 µJ

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.

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

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

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

After R Smalley and B Weisman

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

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.