New Microprinting Technique Improves Nanoscale Fabrication
Scientists at Penn State developed a new technique called microdisplacement printing, which makes possible the highly precise placement of molecules during the fabrication of nanoscale components for electronic and sensing devices. The new technique, which also extends the library of molecules that can be used for patterning, will be described in Nano Letters by a team led by Paul S. Weiss, professor of chemistry and physics at Penn State.
The new microdisplacement technique is based on a widely used patterning method known as microcontact printing--a simple way of fabricating chemical patterns that does not require clean rooms and other kinds of special and expensive environments. Both methods involve "inking" a patterned rubber-like stamp with a solution of molecules, then applying the inked stamp to a surface.
One of the limitations of microcontact printing is that its precision is limited at the edges of a stamped pattern by the tendency of the applied molecules to skitter across the stamped surface, blurring or obliterating the applied pattern and destroying its usefulness. Weiss's improved microdisplacement technique solves this problem by applying a self-assembled-monolayer film--a single ordered layer of spherical adamantanethiolate molecules--to keep the stamped molecules in place on the surface. "We specifically engineered the adamantanethiol molecule to have a very weak chemical bond with the surface so that it would detach easily when bumped by a stronger-bonding molecule," Weiss explains. The molecules inked on the stamp replace the adamantanethiolate molecules wherever they touch the monolayer film, but the surrounding molecules in the film remain attached to the surface to prevent the applied molecules from wandering.
In addition to providing more control over the precision of stamped patterns, the new microdisplacement technique also relaxes the requirements in precisely positioning a series of stamps used to apply consecutive patterns with different molecular inks.
Adamantanethiol is related to the family of alkanethiol molecules, which have been studied extensively as a model systems for their ability to form well-ordered monolayer films on gold. Weiss and his team were studying the adamantanethiolate-on-gold system when graduate student Arrelaine Dameron discovered that stronger-bonding molecules easily displaced the adamantanethiolate molecules. Her discovery has led to further studies of this system by the Weiss team, including how the displacement can be applied in a broad range of applications using a variety of materials.
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