(Invited) Multi-Modal Nanowire Sensors Using Electrical Resonance Approach

Abstract

There is an ever increasing demand for nanosensors with enhanced characteristics such as miniature size, low power consumption, higher sensitivity and selectivity, ease of manufacturing, decreased cost, simultaneous detection of multi-analytes, etc. As a result, the area of nanoscale sensing remains an area of rich opportunity to develop new ideas for immediate applications ranging from health and environmental monitoring to military and homeland defense. Therefore, these sensor technologies have great potential to revolutionize science and to influence major economic, agricultural, environmental, social, and health issues. Recent advances in our understanding of 1-D nanomaterials are paving the way for developing novel platforms for sensors and devices based on multi-physics, multi-modal approaches. Optically induced surface state (or defect states) population-depopulation in nanomaterials with extremely small thermal mass changes its electrical resonance and serves as a bridge to nano-world for developing next-generation, miniature spectrometers and molecular sensors with unprecedented selectivity and sensitivity. Modulating the defect state population in wide bandgap materials using optically-induced thermal pathways offers a new approach for designing advanced sensors and devices based on nanowire resonators with extremely low thermal mass. Resonant excitation of molecules adsorbed on these nanowires using tunable mid-infrared radiation heats the nanowires during the de-excitation process affecting the surface state population which can be sensitively monitored as changes in the dissipation at its electrical resonance frequency as a function of illumination wavelength and mimics the infrared absorption spectra of the physisorbed molecules offering excellent molecular selectivity. Since the mid-IR spectra are free of overtones (molecular fingerprint regime) and the spectrum of individual molecular species are linearly independent, this approach offers a new paradigm for chemical vapor sensing with high sensitivity and selectivity. Further, monitoring the dissipation variations at resonance as a function of temperature can provide information on thermally induced desorption and polarization or depolarization of adsorbed chemical species. The temperature response of the nanowire at resonance can be used to discriminate different vapors based on differential calorimetry due to a difference in the dipole moments.