In the past 50 years there has been great effort to develop porous structures based on silicon. Commonly use technique preparation of porous silicon base on electrochemical etching. The thickness of the porous layer is usually in the micrometer range and the porosity of such prepared layer is in the range of 20-80%. Porous silicon is a material composed from wires and open spaces. In the nanometer size range such structure can be prepared as a quantum wires and quantum dots. Recent investigations shows that ultrafine silicon particles shows luminescence comparable to those reported for porous silicon films. Hence the ball milling can be accurate to achieve highly dispersed structures with properties comparable to electrochemically etched wafer.
The formation of porous silicon by high-energy ball-milling and sintering was studied. The coarsely crushed silicon wafer was ball milled in a time up to 72h. After that, the average crystallite size is close to 15nm. Between 24 and 72h there was not significant change in crystallite size. The fine particles were then isostatically pressed at a pressure of 300 and 400 MPa. The green compacts are porous and after sintering at 1173K/60min the samples have still porous nature. In comparison etching of silicon wafer in diluted NH₄F was done, which results in regular porous layer. The advantage of powder metallurgy is a preparation of the porous structure in whole volume of the sample in spite of etching.

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