Nanolithography by Molecular Deposition
Another way to create a nanopattern is by dip-pen nanolithography™. With DPN™ method, ink molecules are adsorbed on the AFM tip and transferred by diffusion through the liquid meniscus (formed between the probe tip and the substrate surface) onto the substrate. The DPN™ process is patented by NanoInk, Inc. NanoInk is the sole manufacturer of DPN™ process solutions. The technique is illustrated in Figure 4. The liquid can be water or another suitable solvent in which a material (the "pigment") is dissolved. The ink could also be in liquid form and require no solvent. Inks include organic compounds such as alkane thiols, dendrimers, polymers, or large biomolecules such as antibodies, proteins, or DNA. (A dendrimer - from Greek dendra for tree - is a small, high-molecular weight globular molecule built up from branched units forming a tree-like structure.)  Figure 4: Illustration of the AFM probe being used to deposit molecules on a sample's surface. As the probe moves across the surface, molecules move down the probe and attach to the surface. Figure 5 shows patterns formed by the DPN™ process on a gold substrate using open loop control of the AFM tip. Note that the box drawn around the LLL pattern is not closed - the open loop control did not allow accurate location of the endpoint. Advanced DPN™ experiments involve the overlay of patterned ink layers with the precise deposition of molecules, and this process requires more complex instrumentation. NanoInk has developed a dedicated DPN Writer™ tool called NSCRIPTOR™. Built upon advanced PNI scanner technology, NSCRIPTOR™ offers a sophisticated, user-friendly DPN™ experience with integrated environmental control.  Figure 5: Lateral force microscope image of a pattern written with the DPN™ process. This pattern was written with an AFM that does not have X-Y calibrations sensors. As a result, at the right upper corner of the image two of the lines did not connect as intended. Image courtesy of Brandon Weeks - Lawrence Livermore National Labs -52000-01-12
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