Nanoscience – working small, thinking big
Box 2 | Nanomanipulation
Researchers are increasingly able to manipulate objects of nanometre dimensions – often atoms or molecules. The manipulation can be done atom by atom or by using some form of automated assembly.
Moving atoms
One aspect of manipulation at the nanoscale involves the ability to move atoms from one location to another to build different structures. This is much easier said than done. There are no tweezers small enough to pick up an atom. However, the tip of a scanning probe microscope (SPM) can be used to the same effect. One method simply involves placing the tip of the probe between two atoms and pushing one aside.
Another method involves picking up an atom on the tip of the probe and moving it to the desired location. In a famous example that was published in 1990, researchers moved 35 xenon atoms to spell the letters IBM on top of a crystal of nickel. The entire logo measured less than 3 nanometres. But the challenge is to construct useful materials and structures using this technique. This will involve not single SPM tips but whole arrays of tips working in parallel.
Researchers at Cornell University in the USA recently created an ultra-tiny SPM with a silicon tip only 20 nanometres wide and powered by a motor one-fifth of a millimetre in diameter. An army of these tiny SPMs could be used for patterning computer circuits on an incredibly fine scale, allowing millions of bits of information to be stored in an area no larger than the width of a human hair.
Spray painting with atoms
Another form of nanomanipulation involves laying down atoms in precise arrangements as atom-thin coatings. There are a variety of techniques that allow scientists to lay down multiple thin layers of different atoms in a carefully controlled way. Individual layers might only be a couple of atoms thick. It's like spray painting with atoms.
Semiconductor wafers made of silicon or compound semiconductors like gallium arsenide are coated in a variety of layers. The layers then have circuits cut into them using acids, lasers or ultraviolet radiation. Depending on the optical and electrical properties of individual layers, it is possible to create an enormous range of devices ranging from the laser-emitting semiconductors that read your CDs to computer chips and advanced memory chips.
Boxes
Box 1. Room at the bottom
Box 3. In nature's footsteps
Related sites
Biotechnology as a route to nanotechnology (Ralph C Merkle, July 1999, Trends in Biotechnology, USA)
Nanorobotics
(Laboratory for Molecular Robotics, University of Southern California, USA)
Layered nanoassembly of three-dimensional structures
(Laboratory for Molecular Robotics, University of Southern California, USA)
Posted September 2003.