Applied Materials and Surface Science Laboratory
Due to the large surface-to-volume ratio of MEMS and especially NEMS, surface forces dominate over body forces. While this leads to many of the key advantages of technology at this scale, some of the major issues that inhibit widespread application of MEMS/NEMS are strong adhesion and wear that halt device operations or eventually destroy devices. We have created series of micro-instruments and methods for measuring adhesion, friction, wear and corrosion. With the knowledge these measurements provide, we have developed hard coatings (such as SiC) and self assembled monolayers (SAMs) to tailor surface properties such as wettability, adhesion, and biocompatibility, among others. We have developed liquid and vapor phase methods to deposit SAMs on various semiconductor surfaces and use atomic force microscopy (AFM) and Kelvin probe force microscopy (KPFM) to probe the effects of varying deposition parameters, post-deposition treatments, and wear on SAMs and coatings.
For many potential applications for MEMS/NEMS, specialized coatings must be deposited on device surfaces in a controlled manner. With this in mind, we have explored chemistries to chemically functionalize semiconductor surfaces for the fabrication of MEMS-based chemical sensor arrays. Beyond chemical functionalization, noble metals are finding increased use as refractive/conductive coatings for optical MEMS, microswitches and microrelays, catalytically active coatings in microchemical reactors, catalytic centers for bottom-up nanostructure growth, and substrates for surface enhanced Raman spectroscopy (SERS). Our group has pioneered the application of galvanic displacement methodologies to create (and subsequently) characterize micro- and nano-structures by selective metallization of silicon. Galvanic displacement is an electroless deposition process involving reduction of metal ions via the oxidation of the substrate underneath. Thus, it is selective to oxidizable substrates (such as Si or Ge) and requires no external voltage. For example, we are currently developing low-friction Pt coatings deposited by galvanic displacement on Si substrates.