CHEMICAL & ENGINEERING
NEWS OF THE WEEK MAY 3 2004 - ED TED BY WILL AM G. SCHUllZ & LINDA WANG
MATERIALS
actions and alaser-patterning technique, chemistry professor Micha Asscher and graduate student Gabriel Kerner prepared periodic designs (parallel stripes) of monolayer-thick potassium on ruthemwn[SurfSa, 557,5 (2004)}. And in recent follow-up experiments, the team patterned ruthenium surfaces with long parallel lines of gold with widths vides new opportunities for fun- and periodicities as narrow as a few hundred nanometers. Ultidamental investigations. When one material is deposit- mately, the technique should be ed on top of another—for exam- capable of patterning surfaces ple, through vapor deposition with closely spaced lines of metal less than 50 nm wide and 5 mm long, the group says. To form the patterns, the researchers cool the support metal and expose it first to xenon and then to the second metal, which results in a sandwich of methods, which are common in weakly interacting layers. Then semiconductor processing—the they use a pair of low-intensity behavior of the top layer depends laser beams to create abright-andon the strength of its interactions dark diffraction pattern of parwith the bottom layer. If the two allel lines on the surface. In the materials interact only weakly, bright areas, just enough energy then the top material will form is pumped into the system to rebonds to other atoms or molecules move the xenon layer and the in the top layer, causing the mate- metal above it without damaging rial to ball up. But if the top mate- the surface.Then, by warming the rial prefers to associate with the surface slighdy the remainder of bottom material, the top layer the gas desorbs, allowing the metwill wet the layer below and re- al to be deposited gendy, thereby mamtaining the pattern. main firmly attached. In a commentary in the same The upshot is that weakly interacting materials are easily ma- issue of Surface Science, John H. nipulated by a variety ofmethods Weaver and Vassil N. Antonov, and can be coaxed into forming materials scientists at the Unicomplex patterns. But materials versity of Illinois, Urbana-Chamthat interact strongly, such as paign, describe the work as "novpairs of metals, or metals and el and exciting." Weaver, who semiconductors, bond tightly to developed the buffer-layer proceone another and resist patterning. dure to prepare metal clusters on What the Israeli team has dem- semiconductors, remarks that the onstrated is a technique for form- laser-plus-buffer approach is a ing complex patterns of one met- general technique useful for "synal on top ofanother. By combining thesis and patterning of nanosthe use of a gaseous buffer layer to tructures of almost anything on sidestep strong metal-metal inter- anytrimg."-MITCH JACOBY
SCIENCE
UNLIKELY PARTNERS IN PATTERNING Laser-based method provides route to previously inaccessible structures
LINE UP Narrow parallel lines of gold on ruthenium demonstrate a new technique's control in forming patterns using pairs of strongly interacting materials that cannot be patterned using other methods.
S
UCCESS I N MATCHMAKING
depends on choosing partners with just the right character traits. If the parties are incompatible, the union won't succeed. The same is true « of materials. Scientists 5 who combine materials < to make complex struc- 5 § tures are mindful of ma- Ï terials compatibility is- £ |] sues and often are limited | g | by them. But those limi- ° tations have now become less restrictive, thanks to a new study Researchers at Hebrew University of Jerusalem have devised a versatile method for forming nanometer-scale patterns using pairs of materials that don't lend themselves to patterning via other methods. The technique may form the basis for future nanofabrication strategies and pro-
EXPERIMENTALISTS Hebrew University chemists Asscher (left) and Kerner combine surface science and laser methods to pattern materials with nanoscale features. 6
C & E N / MAY 3, 2 0 0 4
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