Near-field optical chemical vapor deposition (NFO-CVD), proposed by us, is a kind of optical CVD using the optical near field (ONF). Its application to nanostructure fabrication has the potential to realize high-density nanometric structures with extremely high accuracies in size and position. So far, we have deposited 20-nm-wide Zn wire, 40-nm Zn and 25-nm Al dots, and ZnO dot with 85-nm spot size of UV emission. The localized property of ONF also causes a unique photochemical reaction. Conventional optical CVD is based on the adiabatic photochemical process and requires the UV light in order to excite molecules from the ground electronic state to the excited state for dissociation (the Frank-Condon principle). For NFO-CVD, however, nonadiabatic photodissociation can take place, i.e., even by a visible light, which arises from the steep spatial gradient of optical power of ONF. We succeeded to deposit 20-nm Zn dot by using this nonadiabatic process, which can be explained by the exciton-phonon polariton model. According to this model, ONF generated at the apex of the fiber probe can directly excite the molecular vibrational state with its photon energy. Such nonadiabatic process rejects the requirement of resonant light for photochemical reaction. This unique process makes it possible to use visible lights and optically inactive gas sources to deposit a variety of nanometric materials, and is also applicable to other photochemical processes, e.g., photolithography.