Infrared spectroscopic studies on unoriented single-walled carbon nanotube films under hydrostatic pressure

TL;DR

This study investigates how hydrostatic pressure affects the electronic and optical properties of unoriented single-walled carbon nanotube films, revealing pressure-induced deformations, hybridization effects, and a structural phase transition.

Contribution

It provides new insights into pressure-dependent optical transitions and structural changes in SWCNT films using broad-spectrum transmission measurements.

Findings

Optical transition energies decrease with pressure.

Low-energy absorbance diminishes under pressure, indicating carrier localization.

A structural phase transition occurs around 2 GPa.

Abstract

The electronic properties of as-prepared and purified unoriented single-walled carbon nanotube films were studied by transmission measurements over a broad frequency range (far-infrared up to visible) as a function of temperature (15 K - 295 K) and external pressure (up to 8 GPa). Both the as-prepared and the purified SWCNT films exhibit nearly temperature-independent properties. With increasing pressure the low-energy absorbance decreases suggesting an increasing carrier localization due to pressure-induced deformations. The energy of the optical transitions in the SWCNTs decreases with increasing pressure, which can be attributed to pressure-induced hybridization and symmetry-breaking effects. We find an anomaly in the pressure-induced shift of the optical transitions at $\sim$2 GPa due to a structural phase transition.