Effects of the femtosecond laser irradiation for carbon nanowalls as a sacrificed layer generating shock waves

The surface structures and electronic states of various semiconductors, which were covered with carbon nanowalls (CNWs) and then irradiated by a femtosecond laser, were investigated. The studied semiconductors are silicon on insulator, alkali-free glass, gallium nitride, and sapphire. Applying the femtosecond laser to each substrate covered with CNWs caused melting or phase transition of the interior material. These results can be attributed to shock waves driven by the femtosecond laser and showed that a high-temperature/pressure field can be induced by using CNWs as a sacrificial layer. In addition, it was confirmed that femtosecond laser-driven shock waves are very effective in varying the physical properties such as crystallinity and conductivity of wide band gap materials.