Rectangular Nanotubes of Copper Phthalocyanine: Application to a Single Nanotube Transistor

We report on the structural transformation of organic copper phthalocyanine (CuPc) nanowires to hollowed rectangular nanotubes through the use of a hydrothermal process. The CuPc molecules have been chemically self-assembled into a form of nanowires, through reaction with trifluoroacetic acid. The mechanism of the chemical self-assembly for the CuPc nanowires is studied through analyzing the Fourier transform infrared spectra. After the hydrothermal process, it is observed that the alpha-phase CuPc nanowires are transformed to beta-phase CuPc rectangular nanotubes, with crystallinity in the (-101) direction. From X-ray diffraction patterns, the crystallinity of the CuPc nanowires is enhanced by annealing. The optical and electrical characteristics of the beta-phase crystalline CuPc rectangular nanotubes are compared with those of alpha-phase CuPc nanowires, using ultraviolet and visible absorption spectra and current voltage (I-V) characteristics. From the gate field-dependent I-V characteristics for a single nanowire/nanotube transistor, improved device performance in terms of the charge carrier mobility and the current on and off ratio have been observed in the beta-phase CuPc crystalline rectangular nanotube compared with the self-assembled alpha-phase CuPc nanowire, because of the relatively strong pi-pi interaction between the CuPc molecules.