DPN-generated nanostructures as positive resists for preparing lithographic masters or hole arrays

Electrochemical etching of gold within nanoshaved self-assembled monolayers

Wet etching of metal substrates with patterned self-assembled monolayers (SAMs) is an inexpensive and convenient method to produce metal nanostructures. For this method to be relevant to the fabrication of high precision plasmonic structures, the kinetics of nanoscale etching process, particularly in the lateral direction, must be elucidated and controlled. We herein describe an in situ atomic force microscopy (AFM) study to characterize the etching process within patterned SAMs with nanometer resolution and in real time. The in situ study was enabled by several unique elements, including single crystalline substrates to minimize the variability of facet-dependent etch rate, high-resolution nanoshaved SAM patterns, electrochemical-potential-controlled etching, and AFM kymographs to improve temporal resolution. Our approach has successfully quantified the extent of both lateral etching and vertical etching at different potentials. Our study reveals the presence of an induction period prior to the onset of significant lateral etching, which would be difficult to observe with the limited time resolution and sample-to-sample variation of ex situ studies. By increasing the vertical etch rate during this induction period with higher potentials, gold was etched up to 40 nm in the vertical direction with minimal lateral etching. High-resolution etching was also demonstrated on single crystal gold microplates, which are high quality gold thin films suitable for plasmonics studies.

Mass-producible nano-featured polystyrene surfaces for regulating the differentiation of human adipose-derived stem cells

In this study, we report an efficient and cost-effective method of fabricating polystyrene (PS) nano-featured substrates containing nanopore (NPo) and nanopillar (NPi) arrays based on hot embossing using nickel nano-stamps. We investigate the behavior of adipose-derived stem cells (ASCs), including adhesion, morphology, proliferation and differentiation, on the replicated PS surfaces. Compared to a flat substrate, NPo- and NPi-featured substrates do not alter the morphology of stem cells. However, both NPo- and NPi-featured substrates induce different integrin expression and lower formation of focal adhesion complexes. In addition, ASCs on the NPo-featured substrate exhibit greater adipogenic differentiation, while the NPi-featured substrate induces higher osteogenic differentiation.

Biomimetic nanopatterns as enabling tools for analysis and control of live cells

It is becoming increasingly evident that cell biology research can be considerably advanced through the use of bioengineered tools enabled by nanoscale technologies. Recent advances in nanopatterning techniques pave the way for engineering biomaterial surfaces that control cellular interactions from the nano- to the microscale, allowing more precise quantitative experimentation capturing multi-scale aspects of complex tissue physiology in vitro. The spatially and temporally controlled display of extracellular signaling cues on nanopatterned surfaces (e. g., cues in the form of chemical ligands, controlled stiffness, texture, etc.) that can now be achieved on biologically relevant length scales is particularly attractive enabling experimental platform for investigating fundamental mechanisms of adhesion-mediated cell signaling. Here, we present an overview of bio-nanopatterning methods, with the particular focus on the recent advances on the use of nanofabrication techniques as enabling tools for studying the effects of cell adhesion and signaling on cell function. We also highlight the impact of nanoscale engineering in controlling cell-material interfaces, which can have profound implications for future development of tissue engineering and regenerative medicine.

Temperature controlled dip-pen nanolithography

Dip-pen nanolithography (DPN) has emerged as a powerful tool for creating sophisticated micron- and nanoscale features of various molecules, such as small organic molecules, on a variety of substrates. Despite significant advances in recent years, the influence of temperature on molecular transport for nanostructure fabrication has not been fully explored. Herein, it is shown how the dimensions of patterned organic nanostructures can be controlled by using a cooling/heating module. This method allows nanometer-sized feature fabrication of a variety of small organic molecules, including 'inks' that have been deemed very difficult to write under ambient conditions. Features with dimensions as small as 30 nm have been successfully reproduced using the newly developed temperature control device in conjunction with DPN.

Self-leveling two-dimensional probe arrays for Dip Pen Nanolithography

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.

Dip-pen-nanolithographic patterning of metallic, semiconductor, and metal oxide nanostructures on surfaces

Dip-pen nanolithography (DPN) is a powerful method to pattern nanostructures on surfaces by the controlled delivery of an "ink" coating the tip of an atomic force microscope upon scanning and contacting with surfaces. The growing interest in the use of nanoparticles as structural and functional elements for the fabrication of nanodevices suggests that the DPN-stimulated patterning of nanoparticles on surfaces might be a useful technique to assemble hierarchical architectures of nanoparticles that could pave methodologies for functional nanocircuits or nanodevices. This Review presents different methodologies for the nanolithographic patterning of metallic, semiconductor, and metal oxide nanostructures on surfaces. The mechanisms involved in the formation of the nanostructures are discussed and the effects that control the dimensions of the resulting patterns are reviewed. The possible applications of the nanostructures are also addressed.

Dip Pen Nanolithography: a "Desktop Nanofab" approach using high-throughput flexible nanopatterning

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.

Unconventional methods for forming nanopatterns

Nanostructured materials have become an increasingly important theme in research, in no small part due to the potential impacts this science holds for applications in technology, including such notable areas as sensors, medicine, and high-performance integrated circuits. Conventional methods, such as the top-down approaches of projection lithography and scanning beam lithography, have been the primary means for patterning materials at the nanoscale. This article provides an overview of unconventional methods - both top-down and bottom-up approaches - for generating nanoscale patterns in a variety of materials, including methods that can be applied to fragile molecular systems that are difficult to pattern using conventional lithographic techniques. The promise, recent progress, advantages, limitations, and challenges to future development associated with each of these unconventional lithographic techniques will be discussed with consideration given to their potential for use in large-scale manufacturing.

Applications of dip-pen nanolithography

The ability to tailor the chemical composition and structure of a surface at the sub-100-nm length scale is important for studying topics ranging from molecular electronics to materials assembly, and for investigating biological recognition at the single biomolecule level. Dip-pen nanolithography (DPN) is a scanning probe microscopy-based nanofabrication technique that uniquely combines direct-write soft-matter compatibility with the high resolution and registry of atomic force microscopy (AFM), which makes it a powerful tool for depositing soft and hard materials, in the form of stable and functional architectures, on a variety of surfaces. The technology is accessible to any researcher who can operate an AFM instrument and is now used by more than 200 laboratories throughout the world. This article introduces DPN and reviews the rapid growth of the field of DPN-enabled research and applications over the past several years.