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Significance Statement
Hydrogen is a green energy and this has led to it application in fuel cells and since it is a colorless and odorless, with a wide explosion limit. The introduction of nanomaterials has opened the door for improved sensor development. Researchers from East China Normal University carried out a research on the detection of H2 at room temperature using Pd/SiNW/P-Si schlocky diode. The work was published in the journal Sensors and Actuators B: Chemical.
Prior to this research, ‘room temperature H2 detection based on Pd/SiNWs/P-Si schottky diode structure, the hydrogen gas sensors previously used is the field effect transistor FET structure. The FET sensor works on the mechanism of selective adsorption H2 on metallic Pd, forming the reversible PdHx and changes in characteristics of the FET. According to the research team, the hydrogen gas sensor has short comings like limited detection range, high working temperature, require expensive facilities and complex production processes. Due to this limitation, attention is now shifted to use of schottky diode sensor.
Schottky diode sensor or Pd/SiNWs/P-Si is a simple production process with excellent performance. It is expected that the newly fabricated sensor overcome the disadvantages of FET, said Zhu et al. (2016). The novelty of the work is that the sensor can detect H2 at room temperature. The new sensor has simple structure and high response. The SiNWs were fabricated by chemical etching and coated with palladium layers. The Pd films were deposited on top of the SiNWs by electroless plating, the Pd/SiNWs/P-Si schottky diode were studied by using constant potential chronoamperometry, the research team make use of SEM scanning electron microscopy to characterized the structural properties of Pd/SiNWs/P-Si and an X-ray energy spectrum EDS analysis was used to analyzed the material chemical composition. The team suspected the presence of Pd particles deposited at the top of SiNWs, to verify the chemical component of the deposited material, the research team make use of the EDS analysis which indicate peak corresponding to the Pd and Si element.
In their experiments researchers also tested the effect of humidity and found out that humidity has small effect which was eventually ignored. The research team also noted that the inversely relation of the current to the H2 concentration. It was observed that the higher the concentration, the faster the current amplitude decline. The response time and recovery time decrease monotonically with the H2 concentration and for 3000ppmH2, the time response is approximately 2 minute while the shortest recovery time is approximately 9 minute. Due to the variation in electrical current, diode tends to deteriorates. To avoid diode deterioration, the team fixed the applied bias at +1V. The etching time used to determine nanowire length is found to be increasing with response factor. Longer etching time leads to the longer SiNW arrays and in turn lead to larger surface to volume ratio enhance the adsorption and desorption of H2 gas and led to the improved response factor.
The incorporation interaction of Pd nanoparticles and silicon nanowires has been confirmed as barrier to the high performance of Pd/SiNW/P-Si/Al schottky. The current through the Pd/SiNW/P-Si/Al schottky barrier is capable of causing the localized electrical field between SiNW and PdNPs to be enhanced due to the large curvature of SiNWs. This will enhance the catalytic capability of PdNPs which make the H2 dissociation easier and also makes the depletion layer change which in turn improve the sensitivity of the sensor.
The hydrogen detecting sensor of Pd/SiNW/P-Si schottky diode structure by electroless plating Pd has shown visibility and reliability with its improvement over the previous method of detecting hydrogen gas. The newly developed detector has small response and can detect hydrogen at room temperature.
Journal Reference
L.S. Zhu, J. Zhang, X.W. Xu, Y.Z. Yu, X. Wu, T. Yang, X.H. Wang, Room temperature H2 detection based on Pd/SiNWs/p-Si Schottky diode structure, Sensors and Actuators B: Chemical, Volume 227, May 2016, Pages 515–523.
State Key laboratory of Transducer Technology, Shanghai Key Laboratory of Multidimensional Information and Processing, and Key Laboratory of Poling Materials and Devices, MOE, Department of Electrical Engineering, East China Normal University, 500 Dongchuan Road, Shanghai 200241, China.
Abstract
In this paper, the Schottky diode sensor composed of silicon nanowires (SiNWs) coated with palladium layers was used for room temperature H2 detection. Pd films were deposited on silicon nanowire via electroless plating. The structural and morphological properties of the Pd/SiNWs were analyzed firstly. The current–voltage (I–V) curves of Pd/SiNWs Schottky diode structure were measured. Variations of the electrical current in the presence of H2 at room temperature revealed that the diode sensors can sense H2 in a wide range of concentration of 300–3000 ppm. This novel sensor has great potential for the detection of H2 at room temperature.
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