Parallelly and Normally Surface-Aligned Organic Nanofiber Arrays

Abstract

Results are presented from a direct comparison of 2,7-diphenylcarbazole (DPC) nanofibers fabricated in the form of parallel to the surface plane aligned arrays by means of organic molecular beam deposition (OMBD) and fabricated in the form of normal to the surface aligned arrays by solution-assisted wetting of porous anodic alumina (PAA) membranes. The former method leads to the formation of mutually aligned needlelike nanoaggregates on muscovite mica substrates, while the latter method allows fabrication of arrays of closely packed upright standing nanofibers. The dimensions of the DPC nanofibers obtained by the OMBD technique depend strongly on the nominal film thickness and on the substrate temperature during deposition. The DPC nanofibers obtained by template wetting possess the same shape and dimensions as those of the pores of the PAA template. All of the obtained nanofibers show strong polarization anisotropy, but the polarization dependent measurements indicate a higher degree of mutual alignment of the DPC molecules in the fibers obtained by OMBD as compared to those obtained by membrane wetting. Temperature dependent fluorescence spectra from the DPC nanoaggregates reveal blue shifts and narrowing of the spectral peaks with decreasing temperature as well as a redistribution of peak intensities.