Liquid Ink Deposition from an Atomic Force Microscope Tip: Deposition Monitoring and Control of Feature Size

Abstract

The controlled deposition of attoliter volumes of liquid inks may engender novel applications such as targeted drug delivery to single cells and localized delivery of chemical reagents at nanoscale dimensions. Although the deposition of small organic molecules from an atomic force microscope tip, known as dip-pen nanolithography (DPN), has been extensively studied, the deposition of liquid inks is little understood. In this work, we have used a set of model ink-substrate systems to develop an understanding of the deposition of viscous liquids using an unmodified AFM tip. First, the growth of dot size with increasing dwell time is characterized. The dynamics of deposition are found to vary for different ink-substrate systems, and the change in deposition rate over the course of an experiment limits our ability to quantify the ink-transfer dynamics in terms of liquid properties and substrate wettability. We find that the most critical parameter affecting the deposition rate is the volume of ink on the cantilever, an effect resulting in a 10-fold decrease in deposition rate (aL/s) over 2 h of printing time. We suggest that a driving force for deposition arises from the gradient in Laplace pressure set up when the tip touches the substrate. Second, the forces acting upon the AFM cantilever during ink deposition were measured in order to gain insight into the underlying ink-transfer mechanism. The force curve data and simple geometrical arguments were used to elucidate the shape of the ink meniscus at the instant of deposition, a methodology that may be used as an accurate and real-time means of monitoring the volume of deposited dots. Taken together, our results illustrate that liquid deposition involves a very different transfer mechanism than traditionally ascribed to DPN molecular transport.

A diffusive ink transport model for lipid dip-pen nanolithography

“…This is also true for the development of DPN with lipids (L-DPN) by enabling a systematic informed choice of ideal materials and/or a combination of materials for a given application need, as well as to improve the quality of the outcome. [3][4][5] Basically, the competition between surface energy and ink viscosity connected by a variable shaped meniscus decides the outcome, while surface diffusion and spreading as well as tip ink solubility kinetics are expected to play a minor role. 2 The factors that govern the transport and assembly of the different ink/substrate systems patterned with DPN mainly depend on the physicochemical properties of the ink: one main distinction that can be made here is the difference in molecular (diffusive) inks and liquid inks.…”

Nanoscale platinum printing on insulating substrates

“…The ink we have developed in this paper is liquid based and should be analysed in terms of the mechanism of liquid deposition from an AFM tip, rather than molecular diffusion from an AFM tip. Several phenomena unique to liquid deposition may contribute to the transition in deposition rate observed in Figure 5 C. For liquid inks, the volume of ink on the cantilever affects ink flow from tip to substrate [37]. More particularly, the deposition rate depends on the local volume of ink on the tip apex, and ink distribution along the cantilever is subject to dynamic reorganisation during printing [40].…”

“…We noticed that the success rate in deposition decreased over the course of a long print run. Our group has recently shown how deposition dynamics in liquid ink deposition from an AFM tip can change as a result of decreased volume of ink on the cantilever [37]. The ink available at the tip apex is also liable to reorganise during printing, which may explain why some dots print and some do not [40].…”

Selective three-dimensional hydrophilization of microstructured polymer surfaces through confined photocatalytic oxidation

“…In addition, with the needle as a transfer tip, patterning and depositing of viscous liquid is also possible. Moreover, the robot technique provides a quicker and microscaled liquid patterning alternative to the slow nanoscaled dip-pen lithography with the AFM tip [17,18]. The topographical structuring of the polymer surfaces increases the surface area, which in turn improves the surface adherence properties [19].…”