Development of compact and fast modulators of infrared light has garnered strong research interests in recent years due to their potential applications in communication, imaging, and sensing. In this study, electric field induced fast modulation near-infrared light caused by phase change in VO2 thin films grown on GaN suspended membranes has been reported. It was observed that metal insulator transition caused by temperature change or application of electric field, using an interdigitated finger geometry, resulted in 7% and 14% reduction in transmitted light intensity at near-infrared wavelengths of 790 and 1550 nm, respectively. Near-infrared light modulation has been demonstrated with voltage pulse widths down to 300 µs at 25 V magnitude. Finite element simulations performed on the suspended membrane modulator indicate a combination of the Joule heating and electric field is responsible for the phase transition.

Transport property variation in O2 plasma treated graphene and related enhancement in NH3 sensing.

Strong enhancement in a photoacoustic signal due to plasmonic absorption in Au nanostructures was measured using piezotransistive GaN microcantilevers. A pulsed 790 nm laser focused on the Au metallization of the piezotransistor resulted in a much larger photoacoustic signal compared to the non-metallized areas. Upon deposition of a 5 nm Au layer, the photoacoustic signal increased significantly for both previously metallized and non-metallized areas, while 2 nm Ni deposition decreased the photoacoustic signal, confirming the role of Au nanostructures in facilitating plasmonic absorption. Infrared microscopy images covering the boundary of Au metallized and non-metallized surfaces indicated a much larger rise in temperature of the former region with laser exposure, explaining the generation of photoacoustic signals through plasmonic absorption.

A graphene-based ISFET has been developed and demonstrated high sensitivity and direct measurement of K+ ion efflux from live cells.

We have investigated nonlinear dynamic characteristics of piezotransistive GaN microcantilevers, with integrated AlGaN/GaN heterostructure field effect transistor as a highly sensitive deflection transducer. When excited with a piezochip actuator, both softening and hardening type of nonlinear behavior were exhibited by the GaN microcantilevers in their first flexural mode. The nonlinear behavior was found to strongly depend on the dimensions of these microcantilevers. While the hardening behavior was found to be enhanced with increase in length of the cantilever for a fixed width, the nonlinear behavior changed much more sharply with width, exhibiting a clear switchover from hardening to softening type, with an increase in width of the cantilever for a constant length. The nonlinear characteristics of the cantilevers were modeled using a Duffing equation with excellent agreement observed between the theoretical model and experimental data for both nonlinearity types and frequency sweep directions.

Detection of H 2 using plasmonic amplification of surface photoacoustic (SPA) waves generated in Pd nanoparticle-deposited GaN piezotransistive microcantilevers has been investigated using a pulsed 520 nm laser. Using 1.5 nm thickness of the Pd functionalization layer, H 2 detection down to 1.5 ppm was demonstrated with a high signal-to-noise ratio, underscoring the feasibility of sub-ppm level detection using this novel sensing method. Adsorption of H 2 in Pd nanoparticles (NPs) changes their plasmonic absorption spectra because of Pd lattice expansion, in addition to changing their work function. The high sensitivity exhibited by the SPA-based H 2 detection method is attributed to a combination of changes in the plasmonic spectrum and work function of Pd NPs and was observed to be a strong function of Pd thickness, biasing conditions, and probe laser power. A comparison of the SPA-based detection technique with traditional chemidiode and chemiresistor sensors, integrated in the functionalized piezotransistor, indicated a superior detection performance of the former.

Surface work function (SWF) measurements using a piezotransistive III–nitride cantilever has been demonstrated on multiple surfaces. The minimum detectable surface potential change of 10 mV was achieved with a signal to noise ratio of 3. This method was applied to determine the surface potential changes due to exposure of 5 ppm NO2 in graphene and In2O3 thin film, simultaneously with conductivity changes. The potentiometric measurements yielded 100 and 80 mV potential changes in SWFs of graphene and In2O3 respectively, which matches very well with experimental data published earlier indicating the efficacy of this readily miniaturizable measurement technique.

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