Dual-wavelength control of charge accumulation in rubrene microcrystals with anisotropic conductivity

TL;DR

This study investigates the anisotropic electronic properties of rubrene microcrystals with distinct sector shapes, demonstrating controlled charge accumulation and neutralization via dual-wavelength illumination, advancing understanding of their charge dynamics.

Contribution

It reveals the anisotropic charge accumulation behavior in rubrene microcrystals and introduces a model explaining band shifts due to surface capacitance and drift-diffusion effects.

Findings

Diamond sectors accumulate charge under photoemission; triangular sectors do not.

Charge in diamond sectors can be neutralized with sub-threshold illumination.

The band shifting behavior is quantitatively explained by a combined surface capacitance and drift-diffusion model.

Abstract

Previously, a novel type of rubrene microcrystals was reported, forming two distinct sectors -- diamond- and triangular-shaped -- that exhibit pronounced contrasts in photoluminescence (PL) spectra and exciton dynamics. In the present work, their internal electronic structure is investigated using time-of-flight photoemission electron spectroscopy (TOF-PES), revealing that the two sector's different charging characteristics arising from anisotropic conductivities. Upon photoemission via a one-photon photoemission (1PPE) process excited by 6.2 eV (200 nm) photons, the diamond-shaped sectors accumulate significant charge, whereas the triangular sectors remain essentially uncharged. The charge accumulation in the diamond sectors can be neutralized by additional sub-threshold illumination, which generates charge carriers through internal photoeffect. The dynamics and energetics of the observed band shifting is described quantitatively by a model combining surface capacitance and drift-diffusion. These crystalline systems enable the creation of built-in charge landscapes that can be manipulated both spatially and temporally.