Nanofabrication and Characterization of Plasmonic Structures

The nanofabrication processes can be divided into two well defined approaches: 1) ‘topdown’ and 2) ‘bottom-up’. The ‘top-down’ approach uses traditional methods to guide the synthesis of nanoscale materials. The paradigm proper of its definition generally dictates that in the ‘top-down’ approach it all begins from a bulk piece of material, which is then gradually or step-by-step removed to form objects in the regime of nanometer-size scale. Well known techniques such as photo lithography, electron beam lithography, anodization, and ionand plasma-etching, that will be later described, all belong to this type of approach. The top-down approach for nanofabrication is the method firstly suggested by Feynman in his famous American Physical Society lecture in 1959. Top down fabrication can be likened to sculpting from a block of stone. A piece of the base material is gradually eroded until the desired shape is achieved. That is, you start at the top of the blank piece and work your way down removing material from where it is not required. Nanotechnology techniques for top down fabrication vary but can be split into mechanical and chemical fabrication techniques. The most top down fabrication technique is nanolithography. In this process, required material is protected by a mask and the exposed material is etched away. Depending upon the level of resolution required for features in the final product, etching of the base material can be done chemically using acids or mechanically using ultraviolet light, and x-rays or electron beams. This is the technique applied to the manufacture of computer chips. Bottom up fabrication can be described as building a brick house. Instead of placing bricks one-by-one at a time to produce a house from bottom, bottom up fabrication technology places atoms or molecules one-by-on at a time to build the desired nanostructure. Such processes are time consuming and so self assembly techniques appeared where the atoms arrange themselves as required. Self assembling nanomachines are regularly mentioned by science fiction writers but significant obstacles including the laws of physics will need to be overcome or circumvented before this becomes a reality. Other areas involving bottom up fabrication are already quite successful. Manufacturing quantum dots by self-assembly