Optically Defined Chemical Functionalization of Silicon Nanomechanical Resonators for Mass Sensing

Nanomechanical resonators with their extremely small mass and high surface/volume ratio present a unique opportunity for mass sensing [1-4]. However, functionalization with selective vapor adsorptive functional groups has been an impediment to the realization of nanomechanical systems for mass sensing. Functional groups that adsorb analytes of interest should be patterned only on the nanoresonator itself, and should not be located on structural elements or micro-channel walls, which would greatly limit the minimum detectible limit of the overall device. Also, traditional spin cast polymer films present the problem of being many times thicker than the nanomechanical resonator, essentially burying the resonator in the adsorptive polymer and completely damping the resonator. To address this, we are using a generic monolayer functionalization scheme based on a UV-mediated reaction between terminal alkenes and a hydrogen terminated silicon surface [5]. Specifically, we report the selective surface functionalization with a vapor adsorptive monolayer of hexafluoro-dimethylcarbinol on polycrystalline silicon nanomechanical resonators.