Abstract
The fast growth of hydrogen usage as a clean fuel in civil applications such as transportation, space technology, etc. highlights the importance of the reliable detection of its leakage and accumulation under explosion limit by sensors with a low power consumption at times when there is no accumulation of hydrogen in the environment. In this research, a new and efficient mechanism is presented for hydrogen detection—using the Coulomb blockade effect in a well-arranged 2D array of palladium nano-islands—which can operate at room temperature. We demonstrated that under certain conditions of size distribution and the regularity of palladium nano-islands, with selected sizes of 1.7, 3 and 6.1 nm, the blockade threshold will appear in current-voltage (IV) characteristics. In reality, it will be achieved by the inherent uncertainty in the size of the islands in nano-scale fabrication or by controlling the size of nanoparticles from 1.7 to 6.1 nm, considering a regular arrangement of nanoparticles that satisfies single-electron tunneling requirements. Based on the simulation results, the threshold voltage is shifted towards lower ones due to the expansion of Pd nanoparticles exposed to the environment with hydrogen concentrations lower than 2.6%. Also, exploring the features of the presented structure as a gas sensor, provides robustness against the Gaussian variation in nano-islands sizes and temperature variations. Remarkably, the existence of the threshold voltage in the IV curve and adjusting the bias voltage below this threshold leads to a drastic reduction in power consumption. There is also an improvement in the minimum detectable hydrogen concentration as well as the sensor response.
Highlights
Hydrogen is an essential gas for many industrial processes
Many hydrogen gas sensors have been developed and studied, including electrochemical [3,4], conductometric [5,6], Schottky junction [7], field effect [8], optical [9], surface acoustic wave (SAW) [10,11,12], single-electron tunneling-based [13], and bulk acoustic wave [14], which operate based on different mechanisms
The most common operation mechanisms of hydrogen sensors are based on the changes in the electrical resistance, work function, optical properties and electrical current of selective material employed upon the adsorption and desorption of hydrogen gas [15,16,17,18]
Summary
Hydrogen is an essential gas for many industrial processes. In recent years, the consumption of hydrogen has become more popular due to its potential capabilities as a clean fuel and its intrinsic versatility as a reagent. If the widths of the gaps between the adjacent palladium nanoparticles are small (less than 10 nm), an applied potential difference greater than the Coulomb blockade threshold voltage between the electrodes can transport electrons into or out of the islands by quantum mechanical tunneling [25]. The advantages in contrast with single-island single-electron transistors (SETs)—in similar conditions in terms of dimensions of the islands and tunneling junctions—are ability to stand a higher threshold voltage of Coulomb blockade; lower sensitivity to unwanted effects such as defects, background charges, and uncertainty in the size of the palladium nanoparticles; higher operation temperature; and ease of fabrication [32,37,38]. We investigated the possibility of single-electron tunneling in well-arranged arrays of palladium nano-islands at room temperature In this respect, the study of IV characteristics for the emergence and disappearance of the Coulomb blockade by controlling the size of nanoparticles was performed. The minimum tunnel resistance of all the tunnel barriers must be much higher than the quantum unit of resistance
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