Identification of an organic semiconductor superlattice structure of pentacene and perfluoro-pentacene through resonant and non-resonant X-ray scattering

S Kowarik,A Hexemer,A Hinderhofer,F Schreiber,C Weber,A Gerlach,C Wang,S R Leone

doi:10.1063/1.4936884

Abstract

Highly crystalline and stable molecular superlattices are grown with the smallest possible stacking period using monolayers (MLs) of the organic semiconductors pentacene (PEN) and perfluoro-pentacene (PFP). Superlattice reflections in X-ray reflectivity and their energy dependence in resonant soft X-ray reflectivity measurements show that PFP and PEN MLs indeed alternate even though the coherent ordering is lost after ∼ 4 ML. The observed lattice spacing of 15.9 Å in the superlattice is larger than in pure PEN and PFP films, presumably because of more upright standing molecules and lack of interdigitation between the incommensurate crystalline PEN and PFP layers. The findings are important for the development of novel organic quantum optoelectronic devices.

Highlights

Superlattices and quantum wells are widely used in inorganic semiconductor devices, for example to tailor the electronic structure, tune the emission wavelength, and lower stimulated emission thresholds
Superlattice reflections in X-ray reflectivity and their energy dependence in resonant soft X-ray reflectivity measurements show that PFP and PEN MLs alternate even though the coherent ordering is lost after ∼ 4 ML
Hybrid organic-inorganic quantum well structures have been demonstrated for excitonic energy transfer,[6] and negative differential resistance based on resonant tunneling has been realized in crystalline organic quantum wells,[5] which may lead to the realization of new functionality in novel organic “quantum” optoelectronic devices

Summary

Introduction

Superlattices and quantum wells are widely used in inorganic semiconductor devices, for example to tailor the electronic structure, tune the emission wavelength, and lower stimulated emission thresholds. Crystalline and stable molecular superlattices are grown with the smallest possible stacking period using monolayers (MLs) of the organic semiconductors pentacene (PEN) and perfluoro-pentacene (PFP).

Results

Conclusion