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Metallic Nanoparticles, Top- Down and Bottom-Up


In metallic nanoparticles part I, the interesting and unique properties of metallic nanoparticles were mentioned and some examples for these fascinating nanoparticles such as gold and silver nanoparticles were given. Here we discover some methods for the preparation of the metallic nanoparticles.
Preparation of nanoparticles can be done by two main approaches. The first is top- down approach, in which the starting material is in the macro or micro scale and using different techniques the particles are transformed to the nano-scale. The second technique is the bottom-up approach. In this approach, which is the most used for the preparation of the nanoparticles, the nanoparticles are formed starting from atomic level to the nano-scale level. The goal of these approaches is to prepare nanoparticles with specific nano-sizes and similar sizes for all particles in which the unique properties can function.
Image retrieved from: http://nanotechnologyjd.weebly.com/
The top-down approach as its name indicate means from top (bigger) to bottom (lesser). It is similar to the manufacturing of statue from stone. The bulk or the giant stone is taken and carving plus cutting is done to the stone until the desired shape is accomplished. Similarly for metallic nanoparticles either mechanical or chemical fabrication techniques are used. Mechanical techniques include mechanical milling in which a suitable powderis placed in a high energy mill, along with a suitable milling medium. Chemical techniques can be applied by etching the metal by acids to obtain the desired particles.
The bottom-up approach starts from the atoms of the metals by chemical processes based on transformations in different mediums. It can be done in solutions such as sol-gel and colloidal methods or it can be done in gaseous medium such as, chemical vapor deposition (CVD), plasma or flame spraying synthesis, laser pyrolysis, and atomic or molecular condensation. There are also other methods that are used for the production of the metallic nanoparticles using the bottom-up approach. The details for these processes and the difference between them will be mention in the following blogs.

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