Synthesis of Nanoscaled Powders by Laser-Evaporation of Materials

Abstract

ABSTRACTUltra fine powders with particle diameters less than 100 nm are becoming increasingly important for various electronic, magnetic and chemical applications as well as in nanostructured materials with extremely fine grained components. Nowadays there are a lot of methods available to synthesize nanoscaled powders. One of the most versatile production methods delivering clean particle surfaces is laser evaporation. Interaction of high intensity laser beams with materials leads to evaporation and subsequent condensation of very small mostly spherical particles with diameters in the order of 10 nm. This means specific surfaces of the powders in the order of 100 m2/g. Depending on the lasers intensity, the surrounding gas, its pressure, and the evaporated material the particles have mean diameters ranging from 4 to 20 nm. Their distribution is generally lognormal with a geometrical standard deviation in the narrow range between 1.5 and 1.7. These properties of the powders can be explained by their originating mechanism, nucleation and particle growth in the surrounding gas. With this method nanosized powders of various materials can be produced like pure metals, alloys, metal oxides, other ceramics and new phases which are probably stabilized by the small particle size. Using a 1 kW - Nd:YAG - laser powder production rates of up to 100 g/h can be achieved for alumina. Contrary to other synthesis methods e.g. the sol-gel method the produced nanoparticles are in particular free of solvents or other residuals. This makes laser synthesised powders extremely usefiil for catalytic or gas sensor applications where defined surface qualities are necessary.