The nano-structure of C-60 photopolymers has been investigated using in situ Fourier-Transform Infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and scanning tunneling microscopy (STM). The FTIR and XPS studies revealed that the C-60 photopolymer has a cross-linking via a [2+2] cycloaddition four-membered ring and formed a 2D rhombohedral structure when the polymerization was saturated. Using STM, we have successfully observed the direct real-space imaging of the C-60 dimers and trimers in a C-60 monolayer supported on a clean semiconductor surface.