At the heart of semiconductor fabrication are crucial additives called dopants. These impurities change the electronic properties of silicon or other material to make the transistors and other components of a chip. Currently these dopants are added in bulk, their exact location usually no more a problem than the exact location of grains of baking soda or raisins stirred into cake batter. But as electronic devices shrink - and the hope is to get them down to the size of a molecule - serious problems with doping are expected. At that small a scale, the location of a needed doping...