Polymer Pen Lithography (PPL): Establishing the Field of Cantilever-Free Scanning Probe Lithography

Above: TERA-print’s TERA-Fab M series is the first commercial tool for performing PPL. Taken from: https://www.tera-print.com/m-series.

In 2008, the Mirkin group invented polymer pen lithography (PPL) to couple the tight feature size control of dip-pen nanolithography (DPN) with the high throughput nature of microcontact printing. In PPL, a large-scale array of millions of elastomeric pyramidal tips replaces the atomic force microscopy (AFM) tips utilized in DPN, and PPL allows force- and time-dependent ink transport (and hence force- and time-dependent control over feature size and shape) to be realized. Indeed, with PPL, arrays of features with sizes ranging from the nanoscale to the microscale can be patterned by the same pen by varying either the dwell time or the pressure on the pen.  In addition, pens can be individually actuated using heat. Subsequently, hard-tip, soft-spring lithography (HSL), was invented to increase the resolution of the PPL technique; HSL utilizes hard silicon tips, rather than soft elastomeric ones that are prone to deformation. PPL and related cantilever-free scanning probe lithography techniques have been commercialized by TERA-print, a company founded by Prof. Chad A. Mirkin.

Left: Schematic of the platform design used in polymer pen lithography (PPL).

Right: 2008 Beijing Olympic logo prepared using PPL. Patterns of 16-mercaptohexadecanoic acid (MHA) were written on a gold substrate using a centimeter-scale polymer pen array, and this ink was used as a mask for the subsequent wet chemical etching of the exposed gold areas. Taken from Science, 2008, 321, 1658.