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Bottom Up

No, 'bottom up' isn't something related to drinking.  It's the new paradigm for synthesis in the nanotechnology world that could revolutionize the way we make materials.  It takes the idea of 'top down' and flips it right on its behind.  Instead of starting with large materials and chipping away to reveal small materials, the bottom up approach starts with atoms and molecules and creates larger (but not too large!) nanostructures.

The bottom up approach requires a thorough understanding of forces of attraction.  You can't have things come together without some attractive force or active field of force in the region.

The simplest such bottom up synthesis route is electroplating.  By inducing an electric field with an applied voltage, you can attract charged particles to the surface of a substrate where bonding will occur.  Most nanostructured metals with high hardness values are created with this approach.  It's already been proven that electroplating creates a material layer-by-layer, atom-by-atom.

Chemical Vapor Deposition is another big favorite with chemists.  Using a mix of volatile gases and taking advantage of some simple thermodynamic principles, it's possible to have your source material migrate its way to the substrate and then bond to the surface due to high chemical potentials.  This is the one proven method for creating nanowires and carbon nanotubes.  It's also a method of choice for creating quantum dots.  Right now, CVD is the most popular and readily available method for creating nanostructures of all kinds.

Self-assembly promises to be the revolutionary new way of creating materials from the bottom up.  Ideally, with self-assembly you can throw a bunch of tailored molecules in a mix, and they should do all the hard work for you.  One way to achieve self-assembly is through physical attractive forces.  Stuff like static electricity, Van der Waals forces, and a variety of other short-range attractive forces can be used to orient constituent molecules in a regular array.  This method has proven very effective in creating large grids of quantum dots in a proven periodic lattice.

As it stands, our ability to build things from the bottom up is fairly limited in scope.  We can create simple structures but we can't create integrated devices from the bottom up.  Any sort of overall order aside from repeating grids can't be done without some sort of top-down influence like lithographic patterning.  Until we've fully mastered the bottom up synthesis routes we won't be able to take full advantage of its speed and accuracy.