Diamond-like carbon film with gradient germanium-doped buffer layer by pulsed laser deposition

Germanium-doped diamond-like carbon film with different germanium concentrations on the germanium substrate were prepared by double laser beams emitted from the femtosecond and nanosecond lasers. Diamond-like carbon film with gradient germanium-doped buffer layer, which was named as GDBL-DLC film, was prepared. The germanium concentration could be controlled easily by adjusting the repetition frequency of one of the lasers. Infrared transmission and hardness of the GDBL-DLC film kept high levels of above 60% and 45.4GPa. On the other hand, the critical load of the GDBL-DLC film on the germanium substrate increased to 143.7mN from 65.5mN of the pure diamond-like carbon film. In addition, the GDBL-DLC film had not been damaged after being rubbed by rubber stick and stuck by tape. It was shown that the GDBL-DLC film could be used as protective film for infrared windows.