Narrow Results

3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA) nanostructures with different morphologies are prepared on glass substrates at different substrate temperature (T_s) in a molecular beam epitaxy (MBE) system. Scanning/transmission/scanning transmission electron microscopy (SEM/TEM/STEM), X-ray diffraction (XRD), selected area electron diffraction (SAED) and nanobeam diffraction (NBD) techniques are employed in the systematical characterizations of the nanostructures. It is found that the PTCDA nanosheets (NSs), nanowires and nanorods are facile to produce at T_s = 350°C, 330°C and 240°C, respectively; the continuous films are obtained at 180°C and 50°C. XRD studies indicate that only the α-phase polymorph is formed regardless of the T_s. SAED and NBD results show that the nanowire and NS are single crystalline. The optical properties of the prepared PTCDA nanostructures are also found to be influenced by T_s and are correlated with the crystal quality and size. PTCDA nanowires and NSs exhibit an obvious redshift and broadening in the adsorption spectra, and enhanced emission intensity. The improved optical properties facilitate potential applications of these nanostructures in organic optoelectronic devices.