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 --phase CuPc nanowires are transformed to ß-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 ß-phase crystalline CuPc rectangular nanotubes are compared with those of 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 ß-phase CuPc crystalline rectangular nanotube compared with the self-assembled phase CuPc nanowire, because of the relatively strong interaction between the CuPc molecules.