Micro/Nano-structures On Silicon Surface By Pulse Laser

In nature, biological surfaces with orderly micro-nano structures make it show unique properties, such as structural color, hydrophobic membranes, super adhesion and so on, which cause people having great interest on it. As an important semi-conductor material, silicon with micro-nano structured surface has broad applications in infrared detectors, solar cells, flat panel displays and so on. It has a great interest to explore the micro-nano structures on the silicon surface. Laser direct-inducing micro-nano surface structure has been demonstrated to be a promising method. In this thesis, the silicon surfaces with micro-nano structure are formed by using femtosecond and nanosecond laser under certain conditions and the properties are researched.Different micro-nano structures such as periodic ripple structures and conical spikes are prepared on silicon surfaces by the cumulative Nd:YAG nanosecond laser pulses (wavelength 1064 nm, 532 nm and 355 nm) and Ti:Sapphire femtosecond laser pulses (wavelength 800 nm). The effects of laser parameters, atmosphere conditions and crystal orientation to the forming of the micro-structures have been studied. Qualitative theoretical explanations to the formation of microstructure have been given.We discovered that silicon surface will appear different colors after scanning with femtosecond laser. The results show that sub-wavelength periodic structures appear on the colored silicon surfaces under air, nitrogen and vacuum atmosphere. The color for the silicons prepared under vacuum is much clearer. The periods of the ripple structures on colored silicon surfaces produced on vacuum have the maximum value, and the ones prepared on air are the smallest. The study of reflection spectrum shows that the reflectivity of colored silicon's surfaces is not higher than 30% in the wavelength range 500-1500 nm.Black silicon is firstly achieved efficiently by using the nanosecond laser with low frequency (10Hz), which is much cheaper and easier to maintain than the femtosecond laser. The wettability of micro-structure silicon surface formed under different atmosphere has different performances: super-hydrophilic under air, superhydrophobic under vacuum and hydrophilic under SF6. The study of absorption spectrum in the wavelength 500-2400 nm indicates that the silicon surface with the microstructure fabricated under SF6 atmosphere has strong infrared absorption characteristics which are due to the multiple reflections within surface microstructures and the doped sulfur in silcon.