(654f) Microtribology Control Provided by CO2-Expanded Liquid Nanoparticle Deposition
AIChE Annual Meeting
Thursday, November 20, 2008 - 2:15pm to 2:35pm
The technology to fabricate microeletromechanical systems (MEMS) and micromachines has been around for over 20 years. However, due to reliability issues that are inherent in microelectromechanical systems (MEMS) and microdevices, only the most simple structures and devices are currently available commercially. These reliability concerns include stiction, or permanent adhesion, and friction. One approach to overcome the inherent forces which can lead to stiction and friction related problems is to reduce the real area of contact, and effectively increasing the separation distance, between two contacting surfaces. This can be accomplished by a fundamentally new technique to increase the surface roughness of the microstructures by depositing nanoparticles of a specified size and surface number density onto MEMS and microdevices.
Our work has shown that ligand-stabilized gold nanoparticles can be precipitated out of an organic solution and deposited into nanoparticle thin films and coatings using CO2- or gas-expanded liquids (GXLs). Following nanoparticle deposition, the liquid CO2/organic solvent mixture can be transitioned into the supercritical region which allows for a particled-coated sample or microdevice to be dried in absence of the liquid-vapor interface. This supercritical drying step negates the detrimental effects of capillary forces that can destroy nanoparticle films as well as render microstructured devices useless. In this work, polysilicon cantilever beam arrays (CBAs) coated with gold nanoparticles via GXL deposition were tested and exhibited a drastic decrease in the apparent work of adhesion compared to uncoated beam arrays. The deposition of nanoparticles by GXLs onto MEMS and microdevices is a fundamentally new concept and, therefore, a number of fundamental studies were undertaken to determine the effect of particle deposition on stiction and friction of microstructures.