Defect-free ZnO nanorods for low temperature hydrogen sensor applications

Kim

et al. 2019

Small

ZnO is a potential candidate for photodetection utilizing the pyroelectric effect. Here, a self‐biased and translucent photodetector with the configuration of Cu4O3/ZnO/FTO/Glass is designed and fabricated. In addition, the pyroelectric effect is effectively harvested using indium tin oxide (ITO), silver nanowires (AgNWs), and a blend of AgNWs‐coated ITO as the transparent selective contact electrode. The improved rise times are observed from 1400 µs (bare condition; without the selective electrode) to 69, 60, 7 µs, and fall times from 720 µs (bare condition) to 80, 70, 10 µs for corresponding ITO, AgNWs, and AgNWs‐coated ITO contact electrodes, respectively. Similarly, the responsivity and detectivity are enhanced by about 4.39 × 107 and 5.27 × 105%, respectively. An energy band diagram is proposed to explain the underlying working mechanism based on the workfunction of the ITO (4.7 eV) and AgNWs (4.57 eV) as measured by Kelvin probe force microscopy, which confirms the formation of type‐II band alignment resulting in the efficient transport of photogenerated charge carriers. The functional use of the transparent selective contact electrode can effectively harness the pyro‐phototronic effect for next‐generation transparent and flexible optoelectronic applications.

Section: Resultssupporting

confidence: 82%

Section: Schematics X-ray Diffraction Device Transmittance and Orisupporting

confidence: 73%

Section: Methodsmentioning

confidence: 99%

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Translucent Photodetector with Blended Nanowires–Metal Oxide Transparent Selective Electrode Utilizing Photovoltaic and Pyro‐Phototronic Coupling Effect

Abbas

Kim

et al. 2019

Small

“…Moreover, the conduction of ZnO nanorods is correlated with cross section and given as follow 44 ,where G, n, e, l, and µ are electrical conductivity, electron concentration, length of NR and electron mobility, respectively. Fast oxygen desorption will take place when ZnO NRs are exposed to hydrogen and increase the conduction cross section channel area.…”

Section: Discussionmentioning

confidence: 99%

Pd/ZnO nanorods based sensor for highly selective detection of extremely low concentration hydrogen

Bhati

Ranwa

et al. 2017

Sci Rep

Self Cite

111

We report highly hydrogen selective Pd contacted ZnO nanorods based sensor detecting low concentration even at low operating temperature of 50 °C. The sensor performance was investigated for various gases such as H2, CH4, H2S and CO2 at different operating temperatures from 50 °C to 175 °C for various gas concentrations ranging from 7 ppm to 10,000 ppm (1%). The sensor is highly efficient as it detects hydrogen even at low concentration of ~7 ppm and at operating temperature of 50 °C. The sensor’s minimum limit of detection and relative response at 175 °C were found 7 ppm with ~38.7% for H2, 110 ppm with ~6.08% for CH4, 500 ppm with ~10.06% for H2S and 1% with ~11.87% for CO2. Here, Pd exhibits dual characteristics as metal contact and excellent catalyst to hydrogen molecules. The activation energy was calculated for all the gases and found lowest ~3.658 kJ/mol for H2. Low activation energy accelerates desorption reactions and enhances the sensor’s performance.

“…Currently, low operating temperature with low level of gas detection using ZnO based nanostructure is prime goal for many researchers. Ranwa et al 25 fabricated ZnO NRs/Si Schottky heterojunction based hydrogen sensor which showed fast response time $21.6 s at low operating temperature ($70 C) in pure hydrogen gas. Das et al 26 fabricated Pt/ZnO single nanowire Schottky diode by using e-beam lithography.…”

Section: Introductionmentioning

confidence: 99%

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

Ranwa

Journal of Applied Physics

Singh

et al. 2015

Self Cite

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.