Nanotechnology is an emerging field concerned with the controlled study of matter, manipulated and created at the atomic and molecular scale. This technology has the ability to design and fabricate the structures, devices, and systems further, characterizing their performance. Naturally occurring and synthetic are the two types of nanoparticles. Nanofabrication is a very active area of research, referred to as the design and manufacture of devices for the development of innovative products. Patterns or devices at the nanoscale level (1-100 nm) can be generated through this technique and it also achieves macroscopic systems from devices with dimensions in the nano-scale range. Nanostructures generated through this technique have a relatively high degree of functionality, structural complexity, and hierarchy. Nanofabrication can be categorized into top-down and bottom-up approaches. Some of the applications of nanofabrication are-
- Manufacturing nanoscale objects with special properties
- Making nanoscale structures
- Enabling special functionality by incorporating nanoscale objects into larger objects
- Assembling nanoscale objects into more complex structures
Top-down approaches are good for producing structures at the scale of a micrometer, where the building blocks are removed from the substrate to form nanostructures with long-range order. This method is widely used for the fabrication of integrated circuits and severe plastic deformation by controlling shape and size from bulk material to create small structures as desired. In order to define the fabrication process, patterning, etching, and depositing are the elements on which the top-down approach is based upon.
The bottom-up approach is used in the formation and establishing short-range order at nanoscale dimensions, where building blocks are added onto the substrates to form nanostructures. This approach involves building more complex molecular devices atom by atom and is widely used for chemical synthesis. Fabrication technique involves both these approaches to work together. High-energy ball milling, photolithography, and gas condensation are some of the methods of top-down approach for fabrication and nano-synthesis. The Sol-gel process and chemical vapor deposition are the methods of a bottom-down approach for fabricating nanostructures.
Photolithography is the technique to prepare nanostructures through light exposure and is widely used in technological processes. But it suffers some limitations also such as lack of absolute state-of-art equipment and unable to fabricate the mask which leads to a slow iteration cycle. Electron beam lithography which appeared in the late 60s utilizes an electron beam to scan the material and create features at the nanoscale level but the maintenance of the system is very expensive and can have genetic aberrations. Electron beam lithography produces masks for other lithographic techniques and reaches higher resolution since this technique involves attain deeper comprehension.
Focused ion beam lithography is an extremely versatile fabrication process that utilizes ions to pattern features directly to a substrate but this technique is slower than electron beam lithography. Colloid monolayer lithography utilizes self-organized 1D or 2D colloidal systems as layers which are used as a protective barrier against etching. These monolayers can be generated through a number of self-assembly processes further, used for nanofabrication. Molecular self-assembly is a technique that has the ability to fabricate 3D structures and has the potential for molecular control of the material.
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