TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Method: The method preferably comprises immersing the monocrystalline silicon in the mixed solution containing alkaline solution and isopropanol, carrying out anisotropic etching to the monocrystalline silicon substrate via the mixed solution, forming the traditional pyramid structure on the surface of the monocrystalline silicon substrate, placing the monocrystalline silicon substrate with the traditional pyramid structure in the plasma immersion ion implantation device, adjusting the process parameter of the plasma immersion ion implantation device so that the device generates plasma, forming the nanometer structure on the pyramid structure by adjusting the process parameter using the plasma immersion ion implantation method, forming the porous pyramid structure on the surface of the monocrystalline silicon substrate. The process parameter comprises the process gas type and the flow ratio implanted in the chamber of the plasma immersion ion implantation device, the work pressure implanted in the chamber, the power used for generating the radio frequency power of the plasma, the power kind of the bias voltage, the bias voltage and the implantation time. The process gas is formed by mixing the gas having etching function and the gas having passivating function. Preferred Components: The mass percentage of the alkaline solution in the mixed solution is 0.1%-50%. The volume percentage of isopropanol is 1%-80%, and the immersion time of the monocrystalline silicon substrate in the mixed solution is 10-50 minutes. The characteristic dimension of the traditional pyramid structure is 1-10 mu m. The gas having etching function comprises sulfur hexafluoride, carbon tetrafluoride, trifluoromethane, octafluorocyclobutane, nitrogen trifluoride, tetrafluorosilane, hexafluoroethane, hydrogen fluoride, boron trifluoride, phosphorus trifluoride, chlorine, hydrogen chloride, dichlorosilane, tetrachlorosilane, boron trichloride or hydrogen bromide, and the gas having passivating function comprises oxygen, nitrous oxide or nitrogen. The flow ratio of gas having etching function and the gas having passivating function is 0.01-100. The range of the work pressure is 10-3-1000 Pa. The range of the bias voltage is -100000-100000 V. The implantation time is 0-1000 minutes. The shape of the nanometer structure is pore-, needle- or dendriform.