The authors report on the formation and evaluation of V-based Ohmic contacts to n-AlGaN films in the entire alloy composition. The films were produced by plasma assisted molecular beam epitaxy and doped n-type with Si. The conductivity of the films was determined to vary from 103to10−2(Ωcm)−1 as the AlN mole fraction increases from 0% to 100%. Ohmic contacts were formed by e-beam evaporation of V(15nm)∕Al(80nm)∕V(20nm)∕Au(100nm). These contacts were rapid thermal annealed in N2 for 30s at various temperatures. The optimum annealing temperature for this contact scheme to n-GaN is about 650°C and increases monotonically to about 1000°C for 95%–100% AlN mole fraction. The specific contact resistivity was found to be about 10−6Ωcm2 for all films up to 70% AlN mole fraction and then increases to 0.1–1Ωcm2 for films from 95%–100% AlN mole fraction. These results were accounted for by hypothesizing that vanadium, upon annealing, interacts with the nitride film and forms vanadium nitride, which is consistent with reports that it is a metal with low work function.

Traditional electrochemical biosensing electrodes (e.g., gold disk, glassy carbon electrode, etc.) can undergo sophisticated design to detect chemicals/biologicals from cells. However, such electrodes are typically rigid and nonstretchable, rendering it challenging to detect cellular activities in real-time and in situ when cells are in mechanically deformed states. Here, we report a new stretchable electrochemical cell-sensing platform based on vertically aligned gold nanowires embedded in PDMS (v-AuNWs/PDMS). Using H2O2 as a model analyte, we show that the v-AuNWs/PDMS electrode can display an excellent sensing performance with a wide linear range, from 40 μM to 15 mM, and a high sensitivity of 250 mA/cm2/M at a potential of −0.3 V. Moreover, living cells can grow directly on our stretchable high-surface area electrodes with strong adhesion, demonstrating their excellent biocompatibility. Further cell stimulation by adding chemicals induced H2O2 generation, which can be detected in real-time and in situ using our v-AuNWs/PDMS platform for both natural and stretched states of cells. Our results indicate the v-AuNWs/PDMS electrochemical biosensor may serve as a general cell-sensing platform for living organisms under deformed states.

No abstract

No abstract

No abstract