Chemical routes to top-down nanofabrication.

In fabricating materials at the nanometer scale, nanotechnologists typically employ two general strategies: bottom-up and top-down. While the bottom-up approach constructs nanomaterials from basic building blocks like atoms or molecules, the top-down approach produces nanostructures by deconstructing larger materials with the use of lithographic tools (i.e., physical top-down) or through chemical-based processes (i.e., chemical top-down). This tutorial review summarizes the various top-down nanofabrication methods, with great emphasis on the chemical routes that can generate nanoporous materials and ordered arrays of nanostructures with three-dimensional features. The chemical top-down routes that are discussed in detail include (1) templated etching, (2) selective dealloying, (3) anisotropic dissolution, and (4) thermal decomposition. These emerging nanofabrication tools open up new avenues in the creation of functional nanostructures with a wide array of promising applications.