Types of Nanotechnology
- [California Institute of Technology - Los Angeles Times]
- Overview
Nanotechnology can be classified by its method of creation - either "top-down" or "bottom-up" - and by the environmental medium in which it operates - either "wet" or "dry".
A. Top-down vs. bottom-up methods:
1. Top-down nanotechnology:
This approach starts with a large, bulk-sized material and uses fabrication techniques to remove material and carve it down to the nanoscale. The top-down method is more conventional and typically involves physically creating nanoscale features.
Process: Starts large, ends small.
Examples:
- Photolithography: Uses light to transfer a pattern to a light-sensitive chemical ("resist") on a substrate. It is a standard technique in the semiconductor industry for creating microchips and electronic devices.
- Ball Milling: A method of grinding material with tiny, hard balls to reduce it to a nano-sized powder.
- Etching: The process of removing layers from a material's surface to create patterns.
- Nano-imprint Lithography: A technique that stamps or prints nanoscale features onto a surface.
B. Bottom-up nanotechnology:
This method involves building larger structures by assembling them atom by atom or molecule by molecule. This approach is often compared to building with LEGOs, as it assembles components from the ground up.
1. Process: Starts small, ends large.
2. Examples:
- Self-Assembly: A process where components spontaneously organize themselves into stable, larger structures. A natural example is the formation of a DNA double helix.
- Chemical Vapor Deposition (CVD): Reactants are transported to a surface where they react to form a thin, solid film.
- DNA Nanotechnology: Uses the self-assembling properties of DNA to create designed nanoscale structures and devices.
- Sol-gel Process: A chemical method where nanoparticles dispersed in a liquid (sol) are used to form a solid gel.
C. Dry vs. wet nanotechnology:
1. Dry nanotechnology:
This type of nanotechnology operates in a dry environment and is used to create structures from inorganic materials like carbon, silicon, metals, and semiconductors.
Medium: Primarily a non-aqueous, low-humidity environment.
Examples:
- Carbon Nanotubes: Can be used to create smaller, faster, and more efficient microchips.
- Protective Coatings: Thin layers of nanocoatings can protect surfaces from wear, corrosion, and water damage. This technology is used on items like scratch-resistant eyeglasses, car paint, and stain-repellent fabrics.
- High-tech Electronics: Dry methods are fundamental to the creation of advanced transistors and other electronic components.
2. Wet nanotechnology:
Wet nanotechnology involves biological systems that exist in aqueous environments, such as genetic material, enzymes, and other cellular components. It is based on the principles of molecular recognition used by nature to create complex structures.
Medium: An aqueous (water-based) environment.
Examples:
- Drug Delivery: Nanoparticles are used to transport drugs and therapeutic compounds to specific cells in the body, such as targeted cancer therapies.
- Bio-nanosensors: Nanobiosensors can be used to detect pathogens in food.
- Water Purification: Nanofiltration systems utilize nanomaterials to purify water by removing heavy metals and microbial pathogens.
- Bio-mimicry: Researchers replicate natural phenomena, like the self-cleaning "lotus effect" on leaves, to create water-repellent surfaces.
[More to come ...]
