Chip-Scale Aligned Chiral Carbon Nanotubes Exhibiting Giant Second Harmonic Generation

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Chiral carbon nanotubes (CNTs) are direct-gap semiconductors with unique optical properties due to 1D excitons.
• While theoretical studies predicted strong nonlinear optical effects in chiral CNTs, experimental verification was lacking due to difficulties in creating ordered, single-enantiomer assemblies.
• Enantiomer-dependent phenomena are expected in chiral CNTs, particularly in nonlinear optical processes.

Purpose of the Study:

• To report the synthesis of macroscopically ordered, single-enantiomer chiral CNT films.
• To experimentally verify and quantify the predicted strong second-order nonlinearities in chiral CNTs.
• To explore the potential of these materials for advanced electronic and photonic applications.

Main Methods:

• Synthesis of centimeter-scale, densely packed, aligned single-enantiomer chiral CNT films compatible with microfabrication.
• Observation and measurement of second harmonic generation (SHG) emission from the chiral CNT films.
• Theoretical calculations using many-body theory to estimate optical nonlinearity.

Main Results:

• Successful synthesis of aligned single-enantiomer chiral CNT films.
• Observation of giant second harmonic generation (SHG) emission, attributed to intrinsic chirality and broken inversion symmetry.
• Measured nonlinear susceptibility of 4.9 × 10^2 pm/V, with an estimated χ_xyz = 1.6 × 10^3 pm/V for a perfectly aligned crystal.
• Theoretical calculations accurately predicted the spectrum and magnitude of the observed nonlinear optical effects.

Conclusions:

• The study provides the first experimental quantitative verification of strong second-order nonlinearities in chiral CNTs.
• The developed fabrication method enables scalable production of ordered chiral CNT films.
• These findings pave the way for novel chiral-CNT based electronics and nonlinear photonic devices.