A new way to reduce friction at the nanoscale could enable the commercialization of nano mechanical devices, including ones for data storage 10 to 100 times denser than current memory. Now physicists at the University of Basel in Switzerland have developed a dry “lubrication” method that uses tiny vibrations to keep parts from wearing out.
The method, described in the current issue of Science, could be particularly useful for a new class of memory devices, pioneered by IBM with its Millipede technology, which uses thousands of atomic force microscope tips to physically “write” bits to a surface by making divots in a polymer substrate and later reading them. The “nano lube” could also find uses with tiny rotating mirrors that might serve as optical routers in communications and mechanical switches, replacing transistors in computer processors, so cutting power consumption.
Devices based on NEMS and MEMS are some of the most promising new nanotechnologies. Yet the commercialization of applications such as Millipede — which could store well over 25 DVDs in an area the size of a postage stamp — has been held up in part by wear caused by friction. Indeed, friction is a particular problem in micro- or nanodevices, where contacts between surfaces are tiny points that can do a lot of damage.
In their experiments, the Swiss researchers moved an atomic force microscope tip made of silicon across a test material of sodium chloride or potassium bromide. Ordinarily, the ultra-sharp tip would travel in a “stick-and-slip” fashion, as friction repeatedly builds up until the tip suddenly breaks free. (The same physical mechanism accounts for squeaky door hinges.) The researchers solved the sticky-tip problem by oscillating the tips using changing voltages. The vibrations, which are so small that the tip stays in continuous contact with the material, keep energy from building up and being suddenly released. As a result, friction decreases 100-fold.