Sub-100 nm, centimeter-scale, parallel dip-pen nanolithography.

Novel methods for fabricating nanostructures have become essential in nanoscience and nanotechnology, and have subsequently fueled significant advances in fields ranging from molecular electronics to medical diagnostics. 2] A suite of nanofabrication technologies now exist for patterning a wide range of surfaces with many types of materials. These include focused ion-beam (FIB) lithography, electronbeam lithography, nano-imprint lithography (NIL), dippen nanolithography (DPN), 10] and in a few select cases, microcontact printing (m-CP) techniques. Each of these techniques has a set of capabilities that differentiate it from the others, and all possess both strengths and weaknesses with regard to resolution, speed, materials compatibility, complexity, and cost. DPN, a scanning-probe-based lithography in which an AFM tip is used to generate nanoscale chemical patterns by directly transferring molecules to a surface, offers a number of realized and potential advantages over other nanofabrication methods. For example, since DPN is a maskless lithography, it does not require an expensive master or resist and is capable of rapid prototyping. It is substrate general and allows one to directly deposit inks made of both soft and hard matter. It is typically performed under ambient conditions, which is critical for patterning biologically active materials such as proteins, nucleic acids, viruses, and even cells. Finally, unlike scanning probe methods that rely on resists, DPN is, in principle, amenable to massive parallelization where either the same or different inks can be confined to the tips that make up a single cantilever array. Indeed, the single biggest limitation of DPN in its current state of development is its speed, especially when carried out in the context of a single-pen experiment, where the patterning area is typically limited to 100 mm 8 100 mm. Many of the potential benefits attributed to the field of scanning probe lithography (SPL) will not be realized beyond the proof-of-concept until significant advances are made in their parallelization. There are two general approaches to extending serial-based SPL to parallel array systems: those that involve feedback control at each tip in an array and those that require minimal, often single-tip feedback control. For arrays that utilize individual feedback at each tip, researchers have demonstrated impressive capabilities in terms of array fabrication and implementation in anodic oxidation experiments and for polymer hole melting in data-storage applications. These approaches work, but are limited in scope because of their complexity and therefore are currently used by only a few research laboratories. The capabilities afforded by these approaches thus far do not provide the throughput, materials generality, and feature quality required for many research-scale and production lithographic applications. DPN is ideally suited for parallelization for the following reasons: 1) Feature size is independent of the contact force between tip and surface over a large contact-force range (0–10 mN). Importantly, this attribute is critical for performing parallel patterning experiments, since the need to perfectly align probe arrays to the substrate, and therefore, the need for complicated multiple-pen feedback systems are minimized. Using this observation, researchers have developed crude proof-of-concept methods for using pairs of cantilevers or small arrays of blunt AFM tips to demonstrate parallel DPN capabilities with a single feedback system in a conventional AFM; 2) precise horizontal and vertical movements of the scanner control the path of the tip, and subsequently the dimensions of the resulting patterns, an advantage over beam-based lithographic methods; 3) scanning probe instrumentation is readily available to most researchers at a fraction of the cost of the instrumentation and facilities for other nanofabrication techniques. The greatest challenges in performing parallel-probe lithography include fabricating large arrays of sharp tips, developing simple and widely accessible tip–surface alignment protocols, maintaining tip feedback, patterning a wide variety of molecules, and characterizing large arrays of nanostructures. Herein, we demonstrate parallel-probe DPN in a high-throughput fashion using as many as 250 tips operating in parallel over the centimeter length scale. This is performed using three different types of linear tip arrays (Figure 1A–C): 1) Commercially available 26-pen arrays (A-26), 2) custom-made 250-pen arrays, and 3) arrays of 26-pen arrays. Importantly, we demonstrate that one can generate nanostructures at a rate of 0.935 cmmin 1 distributed over a distance of 1.25 centimeters, by simply utilizing a linear array of cantilevers operating in parallel. In all three cases, only a conventional single-tip feedback system is required, and an AFM configured for lithography, or an Nscriptor (a dedicated DPN instrument), can perform this high-throughput patterning. The goal of this manuscript is to demon[*] K. Salaita, Dr. S. W. Lee, Dr. L. Huang, Prof. C. A. Mirkin Department of Chemistry and Institute for Nanotechnology Northwestern University, Evanston, IL 60208 (USA) Fax: (+1)847-467-5123 E-mail: chadnano@northwestern.edu