Top Down
Top down, in nanotechnology, refers to a manufacturing technique whereby an object is created by carefully removing pieces of a larger object--essentially carving out the desired object. An example of this process is lithography. Bottom up manufacturing, in contrast, refers to a manufacturing technique whereby systems are assembled from their basic components--atoms and molecules. Bottom up manufacturing is thought to provide much greater control over the end products that can be made, but is technologically very challenging. Top down techniques are in use today but the products they can produce are, in the context of nanotechnology and its promise, quite limited.
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