Chemical origami

Click on picture to see a neat animation of folding some paper

US chemists have brought the Japanese art of origami into the lab to help them build minute 3D objects from silver that might lead to a new technique for making micromechanical devices.

In the microelectronics industry tiny 3D objects, such as transistors and diodes, are usually made by laying down multiple layers of silicon, printing a patterned mask over the top and then using a corrosive chemical, such as an acid, to "etch" away the exposed parts. Curved objects and ones made from non-traditional materials are not amenable to the technique though.

	George Whitesides

According to Harvard University's George Whitesides and colleagues at McGill University in Montreal Quebec, other techniques, have allowed engineers to use elaborate systems of mirrors to project planar patterns for printing on to spherical surfaces. However, while all these methods can be used to make tiny and complex 3D objects, such approaches beggar a less complicated approach. Chemists would prefer to be able to design a straightforward reaction scheme where they simply mix the ingredients in a pot and out pops the object. The Harvard-McGill team have now taken the first steps towards such an ideal with micro-origami.

The researchers have combined microcontact printing, with standard chemical etching to create 2D patterns in thin silver films. Micro-CP involves first making a flat mould of the pattern they want to create, using a rubbery plastic, known as an elastomer. The elastomer is then painted on one side with an organic sulfur "ink", which is then "stamped" on to a thin sheet of silver. It is rather like a hi-tech version of a child's potato prints.

The sulfur-layer on the silver sheet then acts as a protective mask covering those parts that the researchers wish to keep. They then pour a corrosive compound over the masked silver sheet and watch as it etches away the exposed areas. They are left with the raw template for their micro-origami.

Once they have the template in hand, or rather on a microscope slide, they use a pair of tweezers to fold it along the pre-defined lines and perforations patterned into the silver, bending each flap to make their 3D object. Coating with nickel "welds" the edges together, making a tough little object.

The team reports its results in more detail in J. Phys. Chem. B, 2001, 105, 347.^*

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