Epitaxial growth of sexi-thiophene and para-hexaphenyl and its implications for the fabrication of self-assembled lasing nano-fibres

Abstract

Over the last few years, epitaxially grown self-assembled organic nano-structures became of increasing interest due to their high potential for implementation within opto-electronic devices. Exemplarily, the epitaxial growth of the rod-like molecules para-hexaphenyl (p-6P) and α-sexi-thiophene (6T) is discussed within this review. Both molecules tend to crystallize in highly asymmetric elongated entities which are also called nano-fibres. It is demonstrated that the obtained needle orientations and morphologies result from a complex interplay between various parameters e.g. substrate surface symmetry, molecular adsorption, crystal structure and contact plane. The interplay and its implications on the fabrication of self-assembled waveguiding nano-fibres and optical resonator structures are discussed and substantiated by a comparison with the reported literature. In further consequence, it is demonstrated that a precise control on the molecular adsorption geometry and the crystal contact plane represents a fundamental key parameter for the fabrication of self-assembled nano-fibres. As both parameters are basically determined by the chosen molecule-substrate material couple, the possible spectrum of molecular building blocks for the fabrication of waveguiding and lasing nano-structures can be predicted by the discussed growth model. A possible expansion of this common valid concept is presented by the utilization of organic-organic heteroepitaxy. Based on the reported p-6P/6T heterostructures which have been fabricated on various substrate surfaces, it is substantiated that the fabrication of organic-organic interfaces can be effectively used to gain control on the molecular adsorption geometry. As the proposed strategy still lacks a precise control of the obtained crystal contact plane, further strategies are discussed which potentially lead to a controlled fabrication of opto-electronic devices based on self-assembled organic nano-structures.

From Chiral Islands to Smectic Layers: A Computational Journey Across Sexithiophene Morphologies on C60

“…[49][50][51] For instance, Campione and co-workers [ 52 ] showed that the homoepitaxy of T6 is reduced by increasing temperature, at which even needles of lying molecules can form, indicating that the differences in free energy between the possible orientations are small, as well acknowledged for organic-organic epitaxy. [ 31,53,54 ] Interestingly, in reference [ 52 ] it was also observed a roughening at (100) terrace edges upon increasing temperature, which was attributed to desorption, but that in the light of the present results it could be also related to the peculiar shape of islands, as discussed above. Indications of a reduced interlayer correlation in T6 fi lms grown on SiO 2 are also provided by Raman scattering measurements, in which lattice phonons polarized in the direction perpendicular to molecular layers are not found for thicknesses lower than 10 ML, [ 50 ] while conversely grazing incidence X-ray experiments showed that a layered structure still exists.…”

A scale-bridging modeling approach for anisotropic organic molecules at patterned semiconductor surfaces

“…On the other hand, the anisotropic character of the COMs allows them to self-assemble into a variety of structures each characterized by different features in terms of functionality (charge transfer, optimization of band-gaps, excitation transfer). Combining these materials thus leads to tunable hybrids whose characteristic properties, such as the work-function and charge carrier mobility, can be tailored through the choice molecules and substrates [1][2][3], as well as through the self-assembled structures formed by the adsorbed molecules [4][5][6]. This wide range of possibilities could not be achieved with an organic or inorganic component alone.…”

Layer Dependent Wetting in Parahexaphenyl Thin Film Growth on Graphene

“…Thin film growth control is also a central issue in organic electronics [19], because the intrinsic film properties as well as the formed interfaces significantly determine the device performance [20][21][22]. Especially, the use of Gr as possible transparent and mechanically flexible * This paper was presented at the 12th International Conference on Atomically Controlled Surfaces, Interfaces and Nanostructures (ACSIN-12) in conjunction with the 21st International Colloquium on Scanning Probe Microscopy (ICSPM21), Tsukuba International Congress Center, Tsukuba, Japan, November 4-8, 2013.…”

“…An intensively studied model system for organic thin film growth on solid surfaces is parahexaphenyl (6P) [23][24][25][26][27][28][29][30]. The rodlike, conjugated 6P molecule (C 36 H 24 ) crystallizes in a herringbone bulk structure [31] and exhibits a gap of ∼3.1 eV between its lowest unoccupied molecular orbital and the highest occupied molecular orbital which makes it suitable for OLED applications [22]. So far, a few studies have been dedicated to the growth of 6P on Ir(111) supported Gr [32,33].…”