Abstract
Despite diverse applications, phospholipid membrane stacks generated by dip-pen nanolithography (DPN) still lack a thorough and systematic characterization that elucidates the whole ink transport process from writing to surface spreading, with the aim of better controlling the resulting feature size and resolution. We report a quantitative analysis and modeling of the dependence of lipid DPN features (area, height and volume) on dwell time and relative humidity. The ink flow rate increases with humidity in agreement with meniscus size growth, determining the overall feature size. The observed time dependence indicates the existence of a balance between surface spreading and the ink flow rate that promotes differences in concentration at the meniscus/substrate interface. Feature shape is controlled by the substrate surface energy. The results are analyzed within a modified model for the ink transport of diffusive inks. At any humidity the dependence of the area spread on the dwell time shows two diffusion regimes: at short dwell times growth is controlled by meniscus diffusion while at long dwell times surface diffusion governs the process. The critical point for the switch of regime depends on the humidity.
Highlights
In dip-pen nanolithography (DPN), modeling is a key element of the nanofabrication process, required to identify the critical parameters of the ink transfer and subsequent reorganization and to quantify their influence and the process sensitivity to them in order to achieve accurate writing control
Our results provide a deeper understanding of ink transport in L-DPN, thereby helping in making an informed choice of experiment conditions to control L-DPN features
The procedure employed can be used in the analysis of any DPN ink transport as it provides useful information concerning the ink state within the transport, its transport mechanism, the influence of substrate surfaces and so on
Summary
In dip-pen nanolithography (DPN), modeling is a key element of the nanofabrication process, required to identify the critical parameters of the ink transfer and subsequent reorganization and to quantify their influence and the process sensitivity to them in order to achieve accurate writing control. This is 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.[1] As a striking example, a multilayer structure (height and width) decisively determines the functionality of lipid multilayer gratings.[2].
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