Temperature effect on structure of copper phthalocyanine thin films

In situ deposited heteroepitaxial thin films of copper phthalocyanine (CuPc) on Ag(111) surfaces have been investigated by scanning tunneling microscopy. The molecules lay flat on the substrate forming a well ordered closed pack square lattice. A lattice vector of ordered film makes 4$^{0 }\pm $ 0.5$^{0 }$with [0-11] direction of Ag (111) lattice. The lattice vectors of the overlayer have been measured 14{\AA}x14{\AA} corresponding to the surface molecular density of 5.10 x 10$^{13 }$molecules/cm$^{2}$. The close packed square lattice remains highly ordered when annealed up to 500$^{0}$K. However further annealing of film to $\sim $ 700$^{0}$K desorbs 75 {\%} of molecules leaving submonolayers coverage of molecules. The remaining molecules aggregate to form dendrite like form, which appears to result from dimerization and polymerization. Molecular orientation in well ordered film, structural change of molecules in dendrite like form, and further discussion of temperature effects on CuPc thin films will be presented.