The proposed solution to the 'lithographic challenge,' attributed to nanotechnology, is to convert to a 'bottom-up' approach. The traditional lithographic paradigm is called 'top-down' because it involves starting with a large chunk of matter, and carving it into ever smaller features until the desired (micro or nano) structure is obtained. The bottom-up approach suggests that it might be more convenient to build using nanometre sized building blocks (atoms, molecules, monomers, etc.), putting the device together piece by nanometre-sized piece, until the overall, macroscopic, device is constructed. This naturally includes the nanometre resolution desired. Of course, at first glance it would seem more difficult to build things this way (manipulating molecules is difficult, and usually a serial process).

      The bottom-up approach has many challenges associated with it. First, designing the building blocks so as to include the precise functionality desired is nontrivial. Second, assembling the pieces together into the desired device is difficult. Another way of looking at this second challenge is that it is difficult to bridge the gap between the nano and the macro (or even micro) world. Lithography can define features down to 100's or even 20nm, with addressability into the macroscopic world. Other techniques (such as clever synthetic chemistry, genetic engineering, etc.) can build nanometre-sized objects of exquisite shape and function. Getting the two techniques to interface properly would lead to fantastically powerful devices. For example, if a lithographically defined array of wires could have single-molecule transistors bonded to it at specific locations, we could push Moore's Law much further.

1.Physics. Worth, 1991
2.Chem. Mater. 2001, 13, 1023.
3. Biology. Benjamin/Cummings, 1996
4.Electrophoresis 2001, 22, 191.

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