No abstract

Low cost, direct writing of conductive traces is highly desired for applications in nanoelectronics, photonics, circuit repair, flexible electronics, and nanoparticle-based gas detection. The unique ability of Dip Pen Nanolithography ͑DPN ® ͒ to direct write a variety of materials onto suitable surfaces with nanoscale resolution and area-specific patterning is leveraged in this work. We present a direct-write approach toward creating traces with commercially available silver nanoparticle ͑AgNP͒-based inks using DPN. In this work we demonstrate submicron AgNP feature creation together with a discussion on the ink transport mechanism.

We report the first demonstration of subµm, sub-50-µΩ · cm conductive traces directly written by Dip Pen Nanolithography (DPN). We achieved subµm Ag lines with 28.8 µΩ · cm average resistivity after directwrite printing from a silver nanoparticle-based ink suspension and annealing at 150°C for 10 min. This compares to Ag bulk resistivity of 1.63 µΩ · cm, where the difference is within the range of previously reported variations in conductivity of Ag-based inks due to annealing conditions and larger width scales. We leveraged DPN's ability to directly place materials at specific locations in order to fabricate and characterize these conductive silver (Ag) traces on electrode patterns and multiple substrates (SiO 2 , Kapton, mica). The low viscosity of the AgNP ink solution allowed write speeds up to 1600 µm/s, almost 4 orders of magnitude higher than typical thiol-on-gold DPN writing speeds. This direct-write methodology paves the way for sitespecific deposition of metallic materials for use in applications such as circuit repair, sensor element functionalization, failure analysis, gas sensing, and printable electronics.

The ability to perform controllable nanopatterning with a broad range of "inks" at ambient conditions is a key aspect of the dip pen nanolithography (DPN) technique. The traditional ink system to demonstrate DPN is n-alkanethiols on a gold substrate, but the DPN method has found numerous other applications since. This article is meant to outline recent advances in the DPN toolkit, both in terms of research and patterning technology, and to discuss applications of DPN as a viable nanofabrication method. We will summarize new DPN developments, and introduce our concept of the "Desktop Nanofab." In addition, we outline our efforts to commercialize DPN as a viable nanofabrication technique by demonstrating massively parallel nanopatterning with the 55,000 tip 2D nano PrintArray. This demonstrates our ability to overcome the serial nature of DPN patterning and enable high-throughput nanofabrication.

Scanning probe lithography (SPL) has witnessed a dramatic transformation with the advent of two-dimensional (2D) probe arrays. Although early work with single probes was justifiably assessed as being too slow to practically apply in a nanomanufacturing context, we have recently demonstrated throughputs up to 3x10(7) microm(2)/h--in some cases exceeding e-beam lithography--using centimeter square arrays of 55,000 tips tailored for Dip Pen Nanolithography (DPN). Parallelizing DPN has been critical because there exists a need for a lithographic process that is not only high throughput, but also high resolution (DPN has shown line widths down to 14 nm) with massive multiplexing capabilities. Although previous methods required non-trivial user manipulation to bring the 2D array level to the substrate, we now demonstrate a self-leveling fixture for NanoInk's 2D nano PrintArray. When mounted on NanoInk's NLP 2000, the 55,000 tip array can achieve a planarity of <0.1 degrees with respect to the substrate in a matter of seconds, with no user manipulation required. Additional fine-leveling routines (<2 min of user interaction) can improve this planarity to <0.002 degrees with respect to the substrate-a Z-difference of less than 600 nm across 1 cm(2) of surface area. We herein show highly homogeneous etch-resist nanostructure results patterned from a self-leveled array of DPN pens, with feature size standard deviation of <6% across a centimeter square sample. We illustrate the mechanisms and methods of the self-leveling fixture, and detail the advantages thereof. Finally, we emphasize that this methodology brings us closer to the goal of true nanomanufacturing by automating the leveling process, reducing setup time by at least a factor of 10, enhancing the ease of the overall printing process, and ultimately ensuring a more level device with subsequently homogeneous nanostructures.

For the first time, we have shown that spin coating and Dip pen nanolithography (DPNTM) are simple methods of preparing energetic materials such as PETN and HMX on the nanoscale, requiring no heating of the energetic material. Nanoscale patterning has been demonstrated by the DPN method while continuous thin films were produced using the spin coating method. Results are presented for preparing continuous PETN thin films of nanometer thickness by the spin coating method and for controlling the architecture of arbitrary nanoscale patterns of PETN and HMX by the DPN method. These methods are simple for patterning energetic materials and can be extended beyond PETN and HMX, opening the door for fundamental studies at the nanoscale.

The ability to deposit different materials with nanoscale precision at user-specified locations is a very important attribute of dip pen nanolithography (DPN). However, the potential of DPN goes beyond simple deposition since DPN used in conjunction with lateral force microscopy (LFM) allows site-specific investigations of nanoscale properties. In this work, we use two different inks, 16-mercaptohexadecanoic acid (MHA) and 1-octadecanethiol (ODT) to show site-specific dual ink DPN enabled exclusively by our proprietary software. A diamond-dot pattern was created by using a layer-to-layer alignment (LLA) algorithm, which enables a MHA pattern (diamond) to be written concentric with another ODT (central dot) pattern. This simple demonstration of multi-ink DPN is not specific to alkanethiol ink systems, but is also applicable to other multi-material patterning, interaction, and exchange studies.

Precision nanoscale deposition is a fundamental requirement for much of current nanoscience research. Further, depositing a wide range of materials as nanoscale features onto diverse surfaces is a challenging requirement for nanoscale processing systems. As a high resolution scanning probe-based direct-write technology, Dip Pen Nanolithography ® (DPN ® ) satisfies and exceeds these fundamental requirements. Herein we specifically describe the massive scalability of DPN with two dimensional probe arrays (the 2D nano PrintArray™). In collaboration with researchers at Northwestern University, we have demonstrated massively parallel nanoscale deposition with this 2D array of 55,000 pens on a centimeter square probe chip. (To date, this is the highest cantilever density ever reported.) This enables direct-writing flexible patterns with a variety of molecules, simultaneously generating 55,000 duplicates at the resolution of single-pen DPN. To date, there is no other way to accomplish this kind of patterning at this unprecedented resolution. These advances in high-throughput, flexible nanopatterning point to several compelling applications. The 2D nano PrintArray can cover a square centimeter with nanoscale features and pattern 10 7 µm 2 per hour. These features can be solid state nanostructures, metals, or using established templating techniques, these advances enable screening for biological interactions at the level of a few molecules, or even single molecules; this in turn can enable engineering the cell-substrate interface at sub-cellular resolution.