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IBM prints with molecules

Tuesday, September 11, 2007
Think of it as an atomic rubber stamp.

Researchers at IBM and ETH Zurich have devised a way to print patterns with molecules. Using the technique, particles are precisely arranged on a soft, rubbery template. A glass or silicon plate is laid on top of the soft template, and the particles transfer to the glass or silicon.

The pattern on the solid substrate then can be exploited in a number of ways, according to Heiko Wolf, researcher in nano-patterning at the IBM Zurich Research Laboratory. It can be used to mass-produce patterns. The picture included here is a reproduction of a 17th century drawing of the sun originally done by Robert Fludd. It was created by placing 20,000 gold particles, each about 60 nanometers in diameter, with the IBM-ETH technique. At 60 nanometers, each particle is one one-hundredth the size of a human blood cell. The technique could be used to place particles as small as 2 nanometers wide. (A nanometer is a billionth of a meter. A human hair is about 60 microns, or 60,000 nanometers, wide.)


IBM used the system to arrange gold particles onto a piece of silicon. The gold particles in turn served as a catalyst to make nanowires. Some believe nanowires could one day replace components in transistors.

Conceivably, the technique could also be used to produce sensor arrays. By placing a blood drop on a chip embedded with rows of different nanoparticles, a doctor could quickly get information on a patient's vital statistics.

Controlling the placement of particles is a fundamental building block for nanotechnology. The ultimate dream for nanotechnologists is self-assembly, where particles will arrange themselves into complex structures through physical and chemical forces. Self-assembly is common in nature: abalone shells are primarily made of calcium carbonate chalk, the same thing that's found inside chalk and antacids. Proteins secreted by shellfish, however, set off a chain reaction directing the growth of calcium carbonate that results in a hard, resilient, complex cavity.

IBM's printing technology uses directed self-assembly, which is akin to self-assembly with some human assistance. The gold particles, for instance, are intricately placed onto the soft, rubbery substrate, which contains microscopic pits. The pits then help the molecules fine-tune their position through physical forces like capillary action.

Another experimental technique for ordering particles is nano imprinting, in which a signet-ring-like mold is pressed into a layer of materials. This technique can produce lines that measure only a few nanometers wide.

The scientists published a paper on the experiments in the September issue of Nature Nanotechnology.
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