'World's smallest electric motor' consists of a single molecule
By Ben Coxworth
September 5, 2011
Remember back in the old days, when nano-scale motors were a clunky 500 nanometers across? That record was subsequently broken with a 200-nanometer model, but has now been broken again, by a motor that's just one nanometer wide. By comparison, the width of a human hair is about 60,000 nanometers. The new motor, created by scientists at Tufts University in Massachusetts, is reportedly the first one ever to consist of a single molecule.
More specifically, the motor consists of a butyl methyl sulfide molecule that is located on a conductive copper surface. Arm-like structures made up of carbon and hydrogen atoms protrude from either side of the molecule, with one containing four carbon atoms, and the other containing one. While the sulfur in the molecule causes it to bond with the copper surface, the two arms are free to rotate around its base.
By providing electricity from the metal tip of a low-temperature scanning tunneling microscope, the team was able to cause the molecule to rotate. Altering the temperature of the molecule was shown to affect the speed of its rotation, with a temperature of 5 Kelvin (-268C/-450F) turning out to be ideal for tracking its motion. While higher temperatures caused it to spin significantly faster, it proved difficult to track and control its rotation at such speeds.
"Once we have a better grasp on the temperatures necessary to make these motors function, there could be real-world application in some sensing and medical devices which involve tiny pipes," said associate professor of chemistry, E. Charles H. Sykes. "Friction of the fluid against the pipe walls increases at these small scales, and covering the wall with motors could help drive fluids along. Coupling molecular motion with electrical signals could also create miniature gears in nanoscale electrical circuits; these gears could be used in miniature delay lines, which are used in devices like cell phones."