Dip-Pen Nanolithography: Automated Fabrication of Custom Multicomponent Sub-100-Nanometer Surface Architectures
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Dip-Pen
Nanolithography: Automated Fabrication of Custom Multicomponent, Sub-100-Nanometer Surface Architectures Chad A. Mirkin
As physical processes for generating miniaturized structures increase in resolution, the types of scientific questions one can ask and answer become increasingly refined. Indeed, if one had the capability to control surface architecture on the 1–100-nm length scale with reasonable speed and accuracy, one could ask and answer some of the most important questions in science and, in the process, develop technologies that could allow for major advances in surface science, chemistry, biology, and human health. This length scale, which is exceedingly difficult to control, comprises the length scale of much of chemistry and most of biology. Indeed, chemical and biochemical recognition events are essentially sophisticated examples of pattern-recognition processes. Therefore, if one could pattern on this length scale with control over feature size, shape, registration, and composition, one could systematically uncover the secrets
MRS BULLETIN/JULY 2001
of recognition processes involving extraordinarily complex molecules. A recent invention, dip-pen nanolithography (DPN), may provide access to this type of control over surface architecture and entry into a new realm of structure-versus-function studies for chemists, biologists, physicists, and materials scientists. Since the invention of scanning probe microscopes (SPMs) and the realization that one could manipulate matter one atom at a time, many scientists have thought that this elusive goal of controlling surface architecture may be possible. However, although early attempts to develop patterning methodologies from SPMs demonstrated the high-resolution capabilities of these instruments, the resulting methods were fraught with speed limitations or restrictions on the types of molecules and the patterning conditions. Indeed, throughout the 1980s and most of the 1990s, SPM surface-patterning methods
focused on either impressive (but inherently slow) serial scanning tunneling microscope (STM) methods that move individual atoms around on a surface under ultrahighvacuum and low-temperature conditions, or indirect multiple-step STM or atomic force microscope (AFM) etching and backfilling methods.1 But it is difficult to create parallel patterning methods using these approaches that are general with respect to controlling both feature size and the types of molecules that can be patterned. In other words, one can utilize a multipletip SPM instrument with multiple independent feedback systems to control parallel etching procedures, but it is difficult, if not impossible, to selectively fill in such features with different types of molecules on the sub-100-nm length scale. In 1999, we introduced DPN to the scientific community as a new direct-write SPM-based lithographic method2–5 (Figure 1). DPN allows one to transport molecules to a surface, much like a macroscopic dip pen transfers ink to paper, but with the resolution of an AFM. Two important obser
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