Jun 30, 2009
Growing nanowires pinpoint on-chip targets
Precise nanowire placement in on-chip circuitry is vital to the development of nanoelectronic devices. Recently, Kansas State University physicists have shown how to apply electric fields to lithographic electrode arrays to enable the directional growth of metallic and polymeric nanowires from a given electrode up to a user-selected target on the array. The target may be another electrode or even a living cell and the technique is called directed electrochemical nanowire assembly (DENA).
Growth occurs along the straight-line path from a user selected electrode to a second electrode lying within a ~140° angular range and a ~100 µm radius of the initial electrode (see image). The applied voltage defines a ridge of electric field maxima that extends between the selected electrodes. This ridge serves as an electrochemical growth channel for the wires, analogous to the mechanical channels of templated nanowire-growth techniques. However, this template can be removed by simply switching off the voltage.
By readily attaching nanowires to macroscopic electrode pairs, this technology provides a convenient means of characterizing nanowire-transport properties. Alternatively, targets such as living cells may be located along the growth path prior to growth. DENA may then be used to grow a nanowire into contact with the cell for electrophysiological applications.
DENA is executed by depositing a ~10 µl aliquot of aqueous solution containing the growth material onto lithographically prepared electrode arrays. Growth is induced by applying a square-wave voltage across an electrode-pair and proceeds until the wire bridges the gap or the user terminates the voltage signal. The wire material is changed by swapping growth solutions: a 50 mM In(CH3COO)3 solution was used to grow In wires whereas a 10 mM ethylenedioxy-thiophene was used to grow polythiophene wires.
Electrode kits available by 2010
The range of known DENA-active materials is almost certainly incomplete, so an important future direction is the identification interesting wire-types. The on-chip production of biological filaments, like f-actin or sickle hemoglobin, are current goals. We have recently started the company NanoGenix to fabricate nanoelectrode growth-kits for sale to researchers and educators who require nanowire-growth capabilities. We expect these kits to be available by 2010.
The group published its research in Nanotechnology.
About the author
Bret N Flanders is an associate professor in the Department of Physics at Kansas State University, US. His group fabricates nanoelectronic devices for measuring electromechanical properties at selected sites on living cells.