Delicate heating builds robust nanowires
By Chappell Brown , EE Times
13, 2004 (11:07 AM EDT)

Hancock, N.H. - The problem of delivering exactly the right amount of heat to build the small features on ICs only gets worse as design rules shrink. For nanotechnologists, the picture is even worse, but a recent development suggests a universal approach to the problem.

A pair of researchers at the Hebrew University of Jerusalem have announced a heat-management process for nanostructures that could be applied to just about any materials system. Gabriel Kerner and Micha Asscher combined some previous methods to produce their versatile approach, demonstrating the fabrication of wires 50 nanometers thick and millimeters in length.

The first step is to deposit a thin buffer layer of neutral atoms on a substrate. A key property of the layer is a weak bond between the atoms and the substrate. Next, a layer of potassium atoms is deposited over the neutral layer. Normally, the potassium would bond strongly to the substrate, requiring more heat to remove it. But the weakly bound neutral layer responds much more readily to laser-pulse heating.

By firing nanosecond laser pulses through a diffraction grating, periodic heating of the potassium layer removes alternate lines of material, leaving an array of nanowires sitting on top of underlying neutral atoms. When the system is gently heated, the neutral atoms disperse and the potassium wires "land" on the substrate, forming a strong bond.

The width of the wires was controlled by varying the amount of heat delivered by the laser pulse. More heat produced thinner wires.

Not only is the process versatile with respect to the kinds of materials that can be used, it is also potentially fast since it is accomplished in a high vacuum without the need for laser masks and wet etching processes. More-complex structures could be formed by using different laser-pulse patterns.

The researchers are also looking at the effects created by using chemically active buffer layers.

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