Which fabrication methods are used to create nanostructures?

The fabrication of nanostructures is generally divided into two main approaches: "Top-Down" and "Bottom-Up."

Top-Down (Subtractive) Methods:
These methods are like sculpting. You start with a large, bulk piece of material and "carve" or etch away material to create the nanoscale structure.

• Example - Photolithography: This is the primary method used to make computer chips. A pattern is projected using light (or electrons) onto a light-sensitive material (a photoresist) on top of a silicon wafer. The pattern is then etched into the wafer using chemicals, removing material to create billions of tiny transistors.
• Other examples include e-beam lithography and milling.

Bottom-Up (Additive) Methods:
These methods are like building with LEGO bricks. You start with individual atoms and molecules and assemble them one by one into the desired nanostructure.

• Example - Chemical Vapor Deposition (CVD): This is a common method for creating high-quality thin films and nanotubes (like carbon nanotubes). A gas containing the desired atoms (e.g., carbon) is passed over a hot surface (substrate). The gas reacts or decomposes on the surface, "building" the structure atom by atom.
• Other examples include molecular self-assembly (where molecules are designed to "snap" together on their own) and atomic layer deposition (ALD).