Realization of palladium-based optomechanical cantilever hydrogen sensor

Abstract

Hydrogen has attracted attention as an alternative fuel source and as an energy storage medium. However, the flammability of hydrogen at low concentrations makes it a safety concern. Thus, gas concentration measurements are a vital safety issue. Here we present the experimental realization of a palladium thin film cantilever optomechanical hydrogen gas sensor. We measured the instantaneous shape of the cantilever to nanometer-level accuracy using diffraction phase microscopy. Thus, we were able to quantify changes in the curvature of the cantilever as a function of hydrogen concentration and observed that the sensor's minimum detection limit was well below the 250 p.p.m. limit of our test equipment. Using the change in curvature versus the hydrogen curve for calibration, we accurately determined the hydrogen concentrations for a random sequence of exposures. In addition, we calculated the change in film stress as a function of hydrogen concentration and observed a greater sensitivity at lower concentrations.Keywords: hydrogen detection; imaging and sensing; interference microscopy; optomechanics; optical sensors; surface dynamics INTRODUCTIONHydrogen has always been viewed as a promising alternative to fossil fuels, and it can also function as an effective energy storage medium for intermittent energy sources. In addition, hydrogen is used in a range of other industries, including chemical production, metal refining, and food processing. A major safety concern with hydrogen is combustibility. Therefore, early leak detection and concentration determination of hydrogen have been areas of intense research 1-3 . There are various types of hydrogen sensors that use a wide range of detection mechanisms. Lundström et al. 4 proposed metal oxide semiconductor (MOS)-type hydrogen sensors 5 . However, MOS sensors suffer from drawbacks such as premature saturation of detectable hydrogen concentrations and low sensitivity. Other MOS-based devices have been used as hydrogen sensors, such as MOS field-effect transistors (FETs) 6,7 , high electron mobility transistors [8][9][10] , and Schottky diode-type FETs 11,12 . However, these devices require complicated fabrication processes and have high production costs. Optical gas sensors 13-21 not only overcome these disadvantages but also have other unique advantages, such as negligible electrical interference, no risk of ignition from an electrical spark, and the ability to work at high temperatures or in harsh environments.Palladium (Pd) can absorb up to 900 times its own weight in hydrogen gas at room temperature 22 . Compared with platinum 23 , Pd film is more popular because of its lower cost. Pd alloys with Ag, Au, Ni, and WO 3 have also been studied 24-29 because of their improved response time 24,25,27 , sensitivity 28,29 , and durability 26 as a sensing material. The alloys can avoid blistering effects 26 and the α to β phase transition at higher hydrogen concentrations 25,27 .

Diffraction phase microscopy imaging and multi-physics modeling of the nanoscale thermal expansion of a suspended resistor

“…A background phase image was first collected without an applied voltage and subtracted from each subsequent phase image. This is commonly done with the DPM method to reduce the background noise 17 – 25 and enables us to obtain an image sequence of the change in phase versus time. To reduce the propagation of phase errors during unwrapping, we temporally unwrapped the image sequence at each pixel 36 .…”

“…Diffraction phase microscopy (DPM) is a real-time quantitative phase imaging (QPI) method 17 . As a single-shot non-destructive method, DPM can accurately monitor nanoscale dynamics in - situ 18 – 25 . Epi-illumination diffraction phase microscopy (epi-DPM) provides a solution for reconstructing the three-dimensional (3D) shape of reflective structures.…”

Hydrogen Sensors Using 2‐Dimensional Materials: A Review

“…[173] However, Schottky diode-type and MOSFET sensors are costly and require complicated fabrication. [174] Due to the zero gap of the energy band in graphene, graphene lacks a sub-threshold region. Therefore, a large enhancement of the sensor response is generally unexpected by optimizing the gate-induced field.…”

Gas sensors based on mass-sensitive transducers. Part 2: Improving the sensors towards practical application

“…Viespe and Miu reported good hydrogen detection (59 ppmv LDL and 0.51 Hz/ppmv sensitivity) with Pd/Zn bilayers produced by pulsed laser deposition (PLD) on 70MHz Q-SAWs [ 497 ]. Using only Pd films on silicon micro-cantilevers and static bending operating mode, McKeown et al detected 250 ppmv of hydrogen in air [ 498 ]. Humidity.…”