One-Dimensional Grating Patterns of Poly (Dimethoxysiloxane) Line Arrays by Dip-Pen Nanolithography

Almog Azulay, Electrical and Electronics Engineering, Sami Shamoon College of Engineering, Beer-Sheva, Israel
Moshe Zohar, Electrical And Electronics Engineering, Sami Shamoon College Of Engineering, Beer-sheva, Israel
Zeev Fradkin, Electrical And Electronics Engineering, Sami Shamoon College Of Engineering, Beer-sheva, Israel
Saad Tapuchi, Electrical And Electronics Engineering, Sami Shamoon College Of Engineering, Beer-sheva, Israel

Scanning probe lithography (SPL) is a set of techniques that employs a scanning probe or an array of probes for surface patterning [1]. The invention of dip-pen nanolithography (DPN) in 1999 introduced possibilities for creative SPL, forming surface architectures through delivering materials directly with an inked scanning probe [2, 3].

Dip-pen nanolithography (DPN) is a low-cost bench-top versatile method for directly patterning materials on surfaces with sub-50 nm resolution, it involves the use of a cantilever tip to transfer a selected ink onto a various surfaces to create dot and line array patterns, which are then cross-linked and bonded irreversibly to the substrate [1-3].

There are many parameters to consider when attempting to utilize DPN due to the direct transfer of materials to the patterning surface and the chemical interaction between them. DPN tip deposition of liquid inks is not well understood for lack of thorough study of the various parameters which need to be controlled in order to achieve uniform patterning [4].

This work focuses on printing complex patterns incorporating 200µm or longer lines over an SiO2 substrate. We have prepared seven different types of Sylgard 184 PDMS based inks diluted with hexane to give varying percentage mixtures (wt/wt). The patterning procedures were performed at a temperature of 24oC, and we examined the effect of the different parameters over the patterning. In addition to the different hexane percentage mixtures, we also observed the effect of humidity and patterning tip velocity. Overall we tested five humidity conditions at twenty different patterning velocities.

The attached graph (Fig. 1) describes the line widths obtained at 60% humidity for various hexane percentages mixtures (wt/wt); for other humidity conditions the effect is significant mainly at high tip velocities. We have created a databank which allows the selection of operating conditions and ink types for obtaining the desirable line thickness and height.

[1] Z. Xie, X. Zhou, X. Tao, and Z. Zheng, “Polymer nanostructures made by scanning probe lithography: recent progress in material applications,” Macromol. Rapid Commun., vol. 33, pp. 359-373, 2012.

[2] K. A. Brown, D. J. Eichelsdoerfer, X. Liao, S. He, and C. A. Mirkin, “Material transport in dip-pen nanolithography,” J. Front. Phys., vol. 9, pp. 385-397, 2014.

[3] H. Santana, E. Irvine, K. Faulds, and D. Graham, ”Rapid prototyping of poly (dimethoxysiloxane) dot arrays by dip-pen nanolithography,” Chem. Sci., vol. 2, pp. 211-215, 2011.

[4] C. D. O’Connell, M. J. Higgins, R. P. Sullivan, S. E. Moulton, and G. G. Wallace, ”Ink-On-Probe Hydrodynamics in Atomic Force Microscope Deposition of Liquid Inks,” Small, vol. 10, pp. 3717-3728, 2014.

Fig. 1: PDMS inks line widths as a function of DPN tip velocity and various hexane percentage mixtures (wt/wt) at 60% humidity.

Fig. 2: An AFM image of a 1-D PDMS grating pattern with a 8.25µm pitch. The pattern was made using an NLP 2000 device at 60% humidity.