Axial-stressed piezoresistive nanobeam for ultrahigh chemomechanical sensitivity to molecular adsorption

This study proposes nanothickness piezoresistive double-clamped beams that are used in a double-side adsorbing mode. The axially stressed clamped beam exhibits continually increasing sensitivity as it is thinned down to nanoscale, and the thinning is theoretically without limitation. Sensing experiments to part-per-million levels of trimethylamine vapor well verify the proposal. A 93 nm thick beam sensor exhibits higher than 1 order of magnitude sensitivity compared to typical piezoresistive cantilever sensors, and its chemomechanical sensing resolution is comparable with that obtained by the off-cantilever optical detection method. With the nanobeam, a surprisingly ultrahigh sensitivity to surface molecular self-assembly induced surface stress is also obtained that is about 150 times higher than that obtained from a conventional cantilever. With additional advantages of elimination of single-sided adsorption induced bimetallic effect noise, tinier size, and easier fabrication, the ultrasensitive nanothick beam sensors show promise to replace the state-of-the-art piezoresistive cantilevers for bio/chemical nanomechanical detection.