Role of Absorbed Solvent in Polymer Pen Lithography

Simultaneous Writing and Erasing Using Probe Lithography Synchronized Erasing and Deposition (PLiSED)

Simultaneous writing and erasing of two and three molecules in one single step at the microscale using Polymeric Lithography Editor (PLE) probes is demonstrated. Simultaneous writing and erasing of three molecules was accomplished by rastering a nanoporous probe that was loaded with rhodamine B and fluorescein over a quinine-coated glass substrate. The solvated quinine molecules were erased and transported into the probe matrix, whereas both rhodamine and fluorescein molecules were simultaneously deposited and aligned with the path of the erased quinine on the substrate. The simultaneous writing and erasing of molecules is referred to as PLiSED. The writing and erasing speed can be easily tuned by adjusting the probe speed to as large as 10,000 μm²/s. The microscale patterns on the orders of square millimeter area were fabricated by erasing fluorescein with an efficiency (η_e) > 95% while simultaneously depositing rhodamine molecules at the erased spots. The roles of the probe porosity, transport medium, and kinetics of solvation for editing were also investigated─the presence of a transport medium at the probe-substrate interface is required for the transport of the molecules into and out of the probe. The physical and mechanical properties of the polymeric probes influenced molecular editing. Young's modulus values of the hydrated hydrogels composed of varying monomer/cross-linker ratios were estimated using atomic force microscopy. Probes with the highest observed erasing capacity were used for further experiments to investigate the effects of relative humidity and erasing time on editing. Careful control over experimental conditions provided high-quality editing of microscale patterns at high editing speed. Combining erasing and deposition of multiple molecules in one single step offers a unique opportunity to significantly improve the efficiency and the accuracy of lithographic editing at the microscale. PLiSED enables rapid on-site lithographic rectification and has considerable application values in high-quality lithography and solid surface modification.

Closed-Loop Nanopatterning of Liquids with Dip-Pen Nanolithography

The ability to reliably manipulate small quantities of liquids is the backbone of high-throughput chemistry, but the continual drive for miniaturization necessitates creativity in how nanoscale samples of liquids are handled. Here, we describe a closed-loop method for patterning liquid samples on pL to sub-fL scales using scanning probe lithography. Specifically, we employ tipless scanning probes and identify liquid properties that enable probe-sample transport that is readily tuned using probe withdrawal speed. Subsequently, we introduce a novel two-harmonic inertial sensing scheme for tracking the mass of liquid on the probe. Finally, this is combined with a fluid mechanics-based iterative control scheme that selects printing conditions to meet a target feature mass to enable closed-loop patterning with better than 1% accuracy and ∼4% precision in terms of mass. Taken together, these advances address a pervasive issue in scanning probe lithography, namely, real-time closed-loop control over patterning, and position scanning probe lithography of liquids as a candidate for the robust nanoscale manipulation of liquids for advanced high-throughput chemistry.

Nanocombinatorics with Cantilever-Free Scanning Probe Arrays

The effectiveness of combinatorial experiments is determined by the rate at which distinct experimental conditions can be prepared and interrogated. This has been particularly limiting at the intersection of nanotechnology and soft materials research, where structures are difficult to reliably prepare and materials are incompatible with conventional lithographic techniques. For example, studying nanoparticle-based heterogeneous catalysis or the interaction between biological cells and abiotic surfaces requires precise tuning of materials composition on the nanometer scale. Scanning probe techniques are poised to be major players in the combinatorial nanoscience arena because they allow one to directly deposit materials at high resolution without any harsh processing steps that limit material compatibility. The chief limitation of scanning probe techniques is throughput, as patterning with single probes is prohibitively slow in the context of large-scale combinatorial experiments. A recent paradigm shift circumvents this problem by fundamentally altering the architecture of scanning probes by replacing the conventionally used cantilever with a soft compliant film on a rigid substrate, a substitution that allows a densely packed array of probes to function in parallel in an inexpensive format. This is a major lithographic advance in terms of scalability, throughput, and versatility that, when combined with the development of approaches to actuate individual probes in cantilever-free arrays, sets the stage for scanning-probe-based tools to address scientific questions through nanocombinatorial studies in biology and materials science. In this review, we outline the development of cantilever-free scanning probe lithography and prospects for nanocombinatorial studies enabled by these tools.

Size-tunable, highly sensitive microelectrode arrays enabled by polymer pen lithography

By combining polymer pen lithography (PPL) patterning with in situ polymerization, we report a straightforward and bottom-up approach for bench-top fabrication of microelectrode arrays (MEAs) with well-controlled dimensions. The as-fabricated MEAs can be used to electrodeposit prussian blue in situ and work as a biosensor for H₂O₂ with a detection limit as low as 5 nM at a sensitivity of 0.7 A cm^-2 M^-1.

Liquid-Phase Beam Pen Lithography

Beam pen lithography (BPL) in the liquid phase is evaluated. The effect of tip-substrate gap and aperture size on patterning performance is systematically investigated. As a proof-of-concept experiment, nanoarrays of nucleotides are synthesized using BPL in an organic medium, pointing toward the potential of using liquid phase BPL to perform localized photochemical reactions that require a liquid medium.

Ink transport modelling in Dip-Pen Nanolithography and Polymer Pen Lithography

Dip-pen nanolithography (DPN) and Polymer pen lithography (PPL) are powerful lithography techniques being able to pattern a wide range of inks. Transport and surface spreading depend on the ink physicochemical properties, defining its diffusive and fluid character. Structure assembly on surface arises from a balance between the entanglement of the ink itself and the interaction with the substrate. According to the transport characteristics, different models have been proposed. In this article we review the common types of inks employed for patterning, the particular physicochemical characteristics that make them flow following different dynamics as well as the corresponding transport mechanisms and models that describe them.

Apertureless cantilever-free pen arrays for scanning photochemical printing

A novel, apertureless, cantilever-free pen array can be used for dual scanning photochemical and molecular printing. Serial writing with light is enabled by combining self-focusing pyramidal pens with an opaque backing between pens. The elastomeric pens also afford force-tuned illumination and simultaneous delivery of materials and optical energy. These attributes make the technique a promising candidate for maskless high-resolution photopatterning and combinatorial chemistry.

Capillary bridge rupture in dip-pen nanolithography

Here, we explore fluid transfer from a nanoscale tip to a surface and elucidate the role of fluid flows in dip-pen nanolithography (DPN) of liquid inks. We find that while fluid transfer in this context is affected by dwell time and tip retraction speed from the substrate, their specific roles are dictated by the contact angle of the ink on the surface. This is shown by two observations: (1) the power law scaling of transferred fluid with dwell time depends on contact angle, and (2) slower retraction speeds result in more transfer on hydrophilic surfaces, but less transfer on hydrophobic surfaces. These trends, coupled with the observation of a transition from quasi-static to dynamic capillary rupture at a capillary number of 6 × 10(-6), show that the transfer process is a competition between surface energy and viscosity. Based on this, we introduce retraction speed as an important parameter in DPN and show that it is possible to print polymer features as small as 14 nm. Further explorations of this kind may provide a useful platform for studying capillary phenomena at the nanoscale.