HOMO band structure and anisotropic effective hole mass in thin crystalline Pentacene films

TL;DR

This study uses photoemission spectroscopy to analyze the HOMO band structure in thin crystalline Pentacene films, revealing discrepancies with theoretical predictions and highlighting the impact on hole mobility.

Contribution

It provides experimental band structure data for Pentacene films, showing weaker molecular interactions and anisotropic effective hole masses, contrasting with prior theoretical models.

Findings

Smaller band width than predicted by first-principles calculations

Larger band separation indicating weaker molecular interactions

Anisotropic effective hole mass correlating with mobility measurements

Abstract

The band dispersion of the two highest occupied molecular orbital (HOMO)-derived bands in thin crystalline Pentacene films grown on Bi(001) was determined by photoemission spectroscopy. Compared to first-principles calculations our data show a significantly smaller band width and a much larger band separation indicating that the molecular interactions are weaker than predicted by theory--a direct contradiction to previous reports by Kakuta et al. [Phys. Rev. Lett. 98, 247601 (2007)]. The effective hole mass m* at M-bar is found to be anisotropic and larger than theoretically predicted. Comparison of m* to field effect mobility measurements shows that the band structure has a strong influence on the mobility even at room temperature where we estimate the scattering rate to be tau ~3 fs.