Raymond G. Sanedrin

Generation of Metal Photomasks by Dip‐Pen Nanolithography

Since the invention of dip-pen nanolithography (DPN) in 1999, the technique has been developed into an effective and powerful nanofabrication tool for a wide variety of metal and semiconductor substrates with many types of deposition materials, including small organic molecules, polymers, DNA, proteins, peptides, viruses, metal ions, and nanoparticles. The high resolution and materials flexibility of DPN make it particularly attractive for many applications in the life sciences and semiconductor industry, and many research groups have used it to prepare gene chips and proteomic arrays for applications ranging from biodiagnostics to studies of cell-surface interactions. Although there are a variety of potential applications of DPN in the semiconductor industry, to date there have been no examples of the use of DPN to prepare functional devices. One application in which DPN is potentially well suited is the fabrication, inspection, and repair of photomasks. Single-pen DPN, however, does not provide the throughput to make it a viable approach for photomask fabrication. However, with the advent of massively parallel DPN through the use of cantilever arrays, it may be possible to fabricate photomasks on a reasonable timescale. With respect to nanostructures made of noble metals, features can be fabricated by using DPN-generated monolayers of alkanethiols as positive wet-chemical-etching resists. Alternatively, one can pattern polymers by DPN, carry out passivation with alkanethiols, and subsequently remove the polymers followed by wet chemical etching to create a system that behaves as a negative resist. Herein, we address the challenge of using DPN and associated chemistry to make photomasks of chromium on quartz and then evaluate their utility as masters to prepare microelec-

Electrically Biased Nanolithography with KOH-Coated AFM Tips

This letter provides the first study aimed at characterizing the desorption and nanolithographic processes for SAM-coated, gold-coated silicon substrates oxidatively patterned with an AFM with a tip under potential control. The process either results in recessed patterns where the monolayer has been removed or raised structures where the monolayer has been removed and silicon oxidation has taken place. Eleven different SAMs have been studied, and the type of pattern formed depends markedly upon SAM chain length, end functional group, and applied bias. We show how local pH and choice of monolayer can be used to very effectively control the type of pattern that is ultimately formed. Interestingly, we show that hydroxide anion accessibility to the substrate surface is one of the most significant factors in determining the pattern topography. Moreover, control over the pattern topography can be achieved by controlling the concentration of the KOH in the water meniscus formed at the point of contact between tip and surface in the context of a bias-controlled DPN experiment with a KOH-coated tip. The work provides important insight into the factors that control SAM desorption and also ways of controlling the topography of features made in a potential-controlled scanning probe nanolithographic process.