Pillar Arrays Formed Via Electric Field Assisted Assembly


Arrays of pillars form across a thin gap when an electric field is applied normal to a thin film (see figure). This “directed assembly” based process is an attractive patterning technique since pillars form spontaneously using simple, inexpensive equipment.
Figure: A thin film is placed between two parallel plates that resemble a capacitor. Applying a voltage across the gap generates an electrostatic force at the film-air interface that amplifies surface undulations until pillars span the gap.


Initial work on the pillars process was done by the research groups of Steven Chou (Princeton), Tom Russell (University of Massachusetts, Amherst), and Ulrich Steiner (University of Cambridge).
Much of the initial work in the literature focused on polymer systems, which require heat to raise the temperature of the film above the glass transition temperature so it can flow.  Most of the work done in our group has been in collaboration with the Russell research group (Suresh Gupta and Dr. Amanda Leach) to further explore the capabilities of electric field assisted assembly.    The work has focused on the use of Polystyrene / Polymethyl methacrylate (PMMA) bilayers to study the resulting hierarchical structures that are formed (see figure).  Publications generated from this collaboration are listed below ([1] and [2]).
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  1. Chou, S. Y.; Zhuang, L.; Guo, L. Applied Physics Letters 1999, 75, 1004-1006. Schaffer, E.; Thurn-Albrecht, T.; Russell, T. P.; Steiner, U. Nature (London) 2000, 403, 874-877.
  2. M. D. Dickey, S. Gupta, K.A. Leach, C.G. Willson, and T. P. Russell. “Novel 3-D structures in polymer films by coupling external and internal fields,” Langmuir (submitted).
  3. K.A. Leach, S. Gupta, M. D. Dickey, C.G. Willson, and T. P. Russell. “Electric Field and Dewetting Induced Hierarchical Structure Formation in Polymer/Polymer/Air Trilayers,” Chaos (in press).