Organic Step Edge Driven Heteroquasiepitaxial Growth of Organic Multilayer Films

Abstract

bottom-up exploiting a new non-surface energy driven mechanism. Each layer is shown to grow with a well-defi ned quasiepitaxial registry regardless of the incommensurate unit cells, where the multilayer pair growth is maintained for multiple cycles. While there is a close surface energy matching between the LES of DIP and NTCDA, it is a non-lowest energy plane of DIP that is formed in the multilayer structure. While surface energy matching of the lowest energy surface is likely to play an important role in many other organic-organic systems, the ability to grow this multilayer system with sustained ordering provides an intriguing new mechanism in organic-organic quasiepitaxy. A combination of in situ real time diffraction techniques, energy landscape calculations, and sub-monolayer microscopy on the initial growth reveals that the molecular orientation is driven by step edge driven nucleation instead of surface energy potentials of the intraterrace landscape. This case of organic step edge driven growth stems from a different mechanism than that for atomic step edge growth [24][25][26] due to the additional degrees of molecular freedom and molecular bonding. The ability to grow epitaxial superlattice structures has had signifi cant importance in inorganic quantum wells and quantum dots applications, such as with photodetectors, light emitting diodes, and solid state laser diodes. [27][28][29][30][31][32][33] The organic equivalent could have similarly substantial impact but has not been widely accessible previously. Thus, this new growth mode for achieving quasiepitaxial multilayers could provide novel pathways to fabricate highly ordered organic superlattices with tunable orientation for enhanced excitonic electronic devices.We start with NTCDA, a wide bandgap semiconductor, which we have already demonstrated to grow quasiepitaxially on KBr crystals with excellent ordering and well-defi ned registry at room temperature. [ 23 ] The archetypal perylene derivation, DIP, was paired with NTCDA due to its (1) promising electron and hole mobilities in thin-fi lm transistors >1 cm 2 V −1 s −1 ; [ 34 ] (2) good crystallization behavior, stability against decomposition and oxidation at high temperature, and moderate photoluminescence effi ciency; [34][35][36] and (3) close surface energy matching of LES to that of NTCDA. A number of studies have investigated DIP growth on inorganic surfaces like SiO 2 [37][38][39][40][41] showing an upright crystalline orientation with little in-plane ordering. The 3D growth of upright DIP has also been observed on organic layers including F 16 CoPc and F 16 CuPc [ 42,43 ] with inplane disorder.A typical series of refl ection high-energy electron diffraction (RHEED) patterns for the growth of NTCDA/DIP alternating layer structures grown at room temperature are shown in Figure 1 . Bulk structures for NTCDA and DIP are shown in Figure S1 in the Supporting Information. Although there The presence of excitons in organic semiconductors at room temperature distinguishes them from traditional se...

Homoepitaxial Growth of Metal Halide Crystals Investigated by Reflection High-Energy Electron Diffraction

“…By using ultra-low current, the damage and charging of the film is negligible over the growth times investigated enabling the use of this technique on organic and insulating surfaces45. RHEED oscillations are monitored with substrates fixed at various in-plane orientations (KSA400).…”

Epitaxial Growth of C60 on Rubrene Single Crystals for a Highly Ordered Organic Donor/Acceptor Interface

“…The heteroepitaxy of organic thin films has been studied for a long time on the basis of the concept of van der Waals epitaxy, where the substrate and deposited films have a weak interaction. However, the studies of heteroepitaxy using different types of organic materials are still underway. − Materials with similar molecular structures tend to form well-ordered heterointerfaces because of the small mismatch in their lattice constants. − In the field of organic transistor, organic heteroepitaxy has been studied for fabricating ordered thin films on wetting layers. The growth of C 60 on pentacene monolayer films, the growth of C8BTBT on nanopatterned graphene, and the growth of pentacene on BN were reported, and field-effect-transistor characteristics were demonstrated.…”

Epitaxial growth of copper phthalocyanine on a large single-grain of thin film alkyl perylene diimide

“…The above results suggest that the mechanism of epitaxial growth is driven by step-induced epitaxy 13,35) or graphoepitaxy. [36][37][38] In this scenario, CuPc first nucleates at the molecular steps of the PTCDI-C8 large grain surface.…”

“…On the other hand, the heteroepitaxial structure of organic thin films provides a well-defined and controlled interface for systematic investigation of its electronic properties emerging from the interactions between the films. [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] However, there have not been so many studies on organic-organic heteroepitaxial growth. Although the use of organic single crystals as substrates is beneficial for the fabrication of organicorganic heteroepitaxial structures, 6,7,9,[14][15][16][17][18][19] their applications are limited because of some difficulties in handling the crystals and fabricating practical devices with such heterostructures in large areas.…”