Paper SE+TF+NC-ThM11
Crystalline Organic Nanocolumn Arrays

Thursday, October 23, 2008, 11:20 am, Room 204

Nanocolumn arrays based on organic semiconductor materials have significant potential for realizing various devices, such as sensors, field emitters, and nanoelectronic devices, on large-area flexible substrates at room temperature. In our work, crystalline nanocolumnar arrays of two widely studied organic semiconductors, i.e., Fullerene (C₆₀) and pentacene were fabricated by glancing angle deposition (GLAD), and characterized by scanning electron microscopy and X-ray diffraction. For both materials, column diameters of typically 100 nm are found on the transparent conductive oxide ITO at the rotation speed of 3 rpm (rounds per minute), essentially independent of column height (up to 360 nm for pentacene). However, on Si-oxide only C₆₀ formed nanocolumns, while pentacene exhibited a morphology resembling that obtained by regular normal incidence deposition. The difference is attributed to the different molecular surface diffusion lengths on the substrate. Furthermore, the morphology of nanocolumns on ITO grown by GLAD is studied for molecular materials forming amorphous and crystalline solids. Amorphous tris(8-hydroxyquinoline)aluminum nanocolumn arrays were obtained at sample rotation speeds varying from 0.3 rpm to 30 rpm. For crystalline pentacene, a nanocolumn array formed at a rotation speed of 3 rpm, while a wide distribution of column heights and shapes was formed at rotation speeds of 0.3 rpm and 30 rpm. The incoming molecular flux and molecular diffusion length on column surface, both determined by rotation speed, were found to govern the resulting morphology of crystalline pentacene nanocolumns on ITO.