A comparison is made of the sensitivities for detecting hydrogen with Pt-coated single ZnO nanorods and thin films of various thicknesses (20–350 nm). The Pt-coated single nanorods show a current response of approximately a factor of 3 larger at room temperature upon exposure to 500ppmH2 in N2 than the thin films of ZnO. The power consumption with both types of sensors can be very small (in the nW range) when using discontinuous coatings of Pt. Once the Pt coating becomes continuous, the current required to operate the sensors increases to the μW range. The optimum ZnO thin film thickness under our conditions was between 40–170 nm, with the hydrogen sensitivity falling off outside this range. The nanorod sensors show a slower recovery in air after hydrogen exposure than the thin films, but exhibit a faster response to hydrogen, consistent with the notion that the former adsorb relatively more hydrogen on their surface. Both ZnO thin and nanorods cannot detect oxygen.

Articles you may be interested inThermal neutron detection using a silicon pad detector and 6LiF removable converters Rev. Sci. Instrum. 84, 033503 (2013); 10.1063/1.4794768Self-powered micro-structured solid state neutron detector with very low leakage current and high efficiency Development of a thermal neutron detector based on scintillating fibers and silicon photomultipliers Rev. Sci. Instrum. 81, 093503 (2010); 10.1063/1.3480995 6:1 aspect ratio silicon pillar based thermal neutron detector filled with B 10

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Pd and Pt Schottky diodes were fabricated on free-standing 2-in.-diameter GaN substrates prepared by a combination of hydride vapor phase epitaxy of ϳ350 m onto sapphire, substrate removal and subsequent growth of 3 m of epi GaN by metalorganic chemical vapor deposition. Vertical diodes with Ti/ Al/ Pt/ Au back contacts annealed at 850°C for 30 s showed excellent rectification with an on/off ratio of ϳ100 at 1.5 V / −10 V. Both forward turn-on and reverse breakdown voltages showed negative temperature coefficients. Pd and Pt diodes showed detection of 10 ppm H 2 in N 2 at 25°C, with fast ͑Ͻ10 s͒ recovery times upon removal of hydrogen from the measurement ambient. The Pt showed higher detection sensitivity than Pd. Detection of C 2 H 4 and C 2 H 6 required much higher temperatures ͑ϳ450°C͒ and concentrations ͑10%͒ of the gases in N 2 than hydrogen detection.

Solid-state thermal neutron detectors are desired to replace 3 He tube tube-based technology for the detection of special nuclear materials. 3He tubes have some issues with stability, sensitivity to microphonics and very recently, a shortage of 3 He. There are numerous solid-state approaches being investigated that utilize various architectures and material combinations. Our approach is based on the combination of high-aspect-ratio silicon PIN pillars, which are 2 µm wide with a 2 µm separation, arranged in a square matrix, and surrounded by 10 B, the neutron converter material. To date, our highest efficiency is ~ 20 % for a pillar height of 26 µm. An efficiency of greater than 50 % is predicted for our device, while maintaining high gamma rejection and low power operation once adequate device scaling is carried out. Estimated required pillar height to meet this goal is ~ 50 µm. The fabrication challenges related to 10 B deposition and etching as well as planarization of the three-dimensional structure is discussed.