No matter how small devices are, all moving parts need to be lubricated. Otherwise, the nano- and micro-scale devices eventually fail due to adhesion and friction. Self-assembled monolayers and other coatings have been widely investigated for this purpose; but it is well known that without continuous replenishment or self-healing, these coatings will eventually fail. Our group is addressing these issues in nanotribology.* We are currently exploring the use of gas adsorption isotherms for continuous formation and replenishment of nanofilms of lubricating molecules on the surface of working microelectromechancial systems (MEMS) devices. We have studied the alcohol adsorption isotherm and demonstrated that it can be used to reduce adhesion and friction and most of all prevent wear of silicon oxide even under the extreme pressure condition of AFM. In collaboration with Dr. Michael T. Dugger at the Sandia National Laboratory, we are studying the efficacy of alcohol vapor lubrication in tests of MEMS friction diagnostic structures.**
New task in our group is to understand tribological contacts of noble metallic surfaces involved in MEMS applications. Metal contacts allow for an electrical current to pass through the device, opening a broad range of new applications. However it has been shown that the noble metals, used for their beneficial hardness and electrical resistance properties, can also act as catalysts under tribological conditions. This can result in deposition of insulating organic layers at device interfaces. These deposits can negatively affect the friction and electrical resistivity of the device and cause device failure. This leads to two important questions; can we stop the formation of this tribochemical organic deposition while still lubricating the surface, or can we manipulate this organic layer to reduce friction while keeping electrical resistivity low. Answering these questions should help broaden the range of applications for MEMS devices.
(a, b) SEM images of MEMS side-wall tribometer. (c) Friction coefficient measured with MEMS tribometer as a function of cycles (bottom axis) and operation time (top axis) in dry nitrogen and n-pentanol vapor environments.