Schottky-contacted vertically self-aligned ZnO nanorods for hydrogen gas nanosensor applications

Abstract

Vertically well aligned ZnO nanorods (NRs) were grown on Si(100) substrate using RF magnetron sputtering technique. Scanning electron microscopy images confirms uniform distribution of NRs on 2 in. wafer with average diameter, height and density being $75 nm, $850 nm, and $1.5 Â 10 10 cm À2 , respectively. X-ray diffraction reveals that the ZnO NRs are grown along c-axis direction with wurtzite crystal structure. Cathodoluminescence spectroscopy, which shows a single strong peak around 3.24 eV with full width half maxima 130 meV, indicates the high crystalline and optical quality of ZnO and very low defect density. Vertically aligned nanosensors were fabricated by depositing gold circular Schottky contacts on ZnO NRs. Resistance responses of nanosensors were observed in the range from 50 to 150 C in 1% and 5% hydrogen in argon environment, which is below and above the explosive limit (4%) of hydrogen in air. The nanosensor's sensitivity increases from 11% to 67% with temperature from 50 to 150 C and also shows fast response time (9-16 s) and moderate recovery time (100-200 s). A sensing mechanism is proposed based on Schottky barrier changes at heterojunctions and change in depletion region of NRs. V C 2015 AIP Publishing LLC. [http://dx.

A self-healing, adaptive and conductive polymer composite ink for 3D printing of gas sensors

“…‫ݕ‬ ൌ ‫ݕ‬ ‫ܣ‬ ଵ ݁ ି௧/௧ భ ‫ܣ‬ ଶ ݁ ି௧/௧ మ (5) where y 0 , A 1 , t 1 , A 2 and t 2 are fitting parameters 57 ,. The equation fit the dynamic resistance data well for all the six organic chemical vapors with R-squared coefficients (R 2 ) in the range of 0.985 ~ 0.999.…”

Hydrogen gas sensor based on mesoporous In2O3 with fast response/recovery and ppb level detection limit

“…Many different types of semiconducting metal oxides have been investigated in the literature as potential materials for fabricating hydrogen gas sensors. These are summarized in Table 1, and mainly include WO3 [11][12][13][14], ZnO [15][16][17][18], NiO [19][20][21], SnO2 [22][23][24], TiO2 [25,26], MoO3 [27,28], CuO [29], MgO [30] and In2O3 [31,32].…”

“…H2 + O − (ads) = H2O + e − (100 o C ~ 300 o C) WO3 thin films 200 1000 9 a 60s/80s - [11] WO3 nanosheets 250 1% 80% b 120s/235s - [12] WO3 nanotube 450 500 17.6 a 25s/-10 ppm [13] WO3 thin films 300 3600 1.32 a 12s/40s - [14] ZnO nanorods 180 500 264% b 127s/203s - [15] ZnO nanorods 150 10000 77% b 10s/116s - [16] ZnO nanorods 100 10000 67% b 14s/100s - [17] ZnO nanorod array 250 1000 1370% b 20s/25s - [18] NiO nanostructure 150 1000 119.63% b 6s/0.5s 30 ppm [19] NiO nanowires 300 1000 91% b 88s/39s 50 ppm [20] NiO thin film 175 1000 46.3 a 81s/322s - [21] SnO2 thin film 300 250 28 a 15s/4s 100 ppm [22] SnO2 nanofibers 150 10000 2.4 a 21s/33s 600 ppm [23] Honeycombed SnO2 340 1 8.4 a 4s/10s 0.05 ppm [24] p-TiO2 thin film 150 1000 28.5% b 2.4s/34.6s - [25] TiO2 thin film 225 10000 8100 a 120s/420s - [26] a-MoO3 nanowires 260 15000 0.85 c 3.0s/2.7s 100 ppm [27] CuO NW networks 300 100 340 a 60s/2s - [29] MgO nanocube 200 5000 25.4 a 140 s/130 s - [30] In2O3 flower-like spherical nanostructure 210 100 1.4 a 11s/12s 10 ppm [31] In2O3 nanowires 200 500 0.1 c 31s/80s 500 ppm [32] Note: a : Rair/RH2; b : 100(Rair-RH2)/RH2; c : (Rair-RH2)/RH2 4 Decrease of the electrical resistance of sensors is corresponding to the change of hydrogen concentration. As summarized in Table 1, there are many types of hydrogen gas sensors based on various semiconducting metal oxides.…”

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“…The function of MOS chemoresistive gas sensors is based on the physical absorption of trace species (with redox interactions) on the surface states and subsequent changes in their surface electron density and conductivity [5]. Among various MOSs, ZnO nanostructures are the most important candidates because of their preparation simplicity, low cost, thermal and chemical stability, high electron mobility and exquisite response to several gases or volatile organic compounds [6][7][8].…”