Dipartimento di Fisica

giovedì 3 maggio, ore 15:00, Aula D del Dipartimento di Fisica 

il Dr. C. Simbrunner del Institute of Semiconductor and Solid State Physics, Johannes Kepler University Linz, Austria 

terrà il seguente seminario: "The Epitaxial Growth of Rod-Like Molecules and Implications for the Fabrication of

Lasing Nano-Fibers"

Abstract

Motivated by the affinity to form highly crystalline organic nano-needles the

epitaxial growth of rod-like molecules e.g. para-hexaphenyl (p-6P) or sexi-thiophene

(6T) on various substrates e.g. muscovite-, phlogopite-mica and KCl has been

investigated intensively [1, 2, 3].It turned out that p-6P in combination with

muscovite mica represents an outstanding material combination [1]. In particular,

the low substrate surface symmetry in combination with the resulting molecular

alignment is the key to well ordered, parallel aligned nano-fibers providing highly

polarized blue fluorescence and laser action [4].

In a first step we will highlight the growth mechanisms of p-6P and 6T

self-assembled nano-fibers by comprehensive morphological and structural

investigations. Based on this analysis the potential of other material systems e.g.

6T to obtain optical resonators and in further consequence lasing will be discussed.

We will demonstrate that more complex approaches have to be found in order to

fabricate highly parallel self-assembled nano-structures being the key to shift the

lasing wavelength from the blue to the green or red spectral range.

In the second part we will focus and introduce an alternative approach to obtain

highly parallel nano-fibers. In recent years, heteroepitaxy of organic-organic

nanostructures has been demonstrated as a valuable technique to explore the full

potential of organic semiconductors for optoelectronic applications. It has been

shown that crystalline and highly ordered heterostructures with different morphology

and molecular orientations can be realized by heteroepitaxy starting from conjugated

oligomers, aimed at tailoring their optical properties and transport characteristics

[1-4]. We demonstrate that organic-organic heteroepitaxy can also be applied to

produce multilayered organic nanofibers with high crystallinity, well-defined

epitaxial relationship along different materials’ phases, sharp molecular azimuthal

order, and long-range morphological homogeneity [9]. In consequence, we are

convinced that the presented advance could lead to a general approach in order to

tune the polarized fluorescence and lasing action of nano-fibers in a broad spectral

range.

References

[1] C. Simbrunner et al., J. Am. Chem. Soc. 133, 3056 (2011) 

 [2] C. Simbrunner et. al., Phys. Rev. B, 83, 115443 (2011)

 [3] T. Haber et. al., J. Cryst. Growth, 312, 333 (2010)

[4] F. Quochi, J. Opt. 12, 024003 (2010)

 [5] S. C. B. Mannsfeld et. al.,  Phys. Rev. Lett. 94, 056104 (2005)

[6] S. Timpanaro et. al. Adv. Mater. 13, 127-130 (2001)

 [7] M. Oehzelt et.al., Adv. Mater. 18, 2466-2470 (2006)

 [8] G. Koller et.al., Nano Lett. 6, 1207-1212 (2006)

 [9] C. Simbrunner et al., ACS Nano 4, 6244 (2010)