With the development of the Internet-of-Things (IoT) technology, the applications of gas sensors in the fields of smart homes, wearable devices, and smart mobile terminals have developed by leaps and bounds. In such complex sensing scenarios, the gas sensor shows the defects of cross sensitivity and low selectivity. Therefore, smart gas sensing methods have been proposed to address these issues by adding sensor arrays, signal processing, and machine learning techniques to traditional gas sensing technologies. This review introduces the reader to the overall framework of smart gas sensing technology, including three key points; gas sensor arrays made of different materials, signal processing for drift compensation and feature extraction, and gas pattern recognition including Support Vector Machine (SVM), Artificial Neural Network (ANN), and other techniques. The implementation, evaluation, and comparison of the proposed solutions in each step have been summarized covering most of the relevant recently published studies. This review also highlights the challenges facing smart gas sensing technology represented by repeatability and reusability, circuit integration and miniaturization, and real-time sensing. Besides, the proposed solutions, which show the future directions of smart gas sensing, are explored. Finally, the recommendations for smart gas sensing based on brain-like sensing are provided in this paper.

https://www.mdpi.com/1424-8220/19/17/3760/pdf

Review on Smart Gas Sensing Technology.

Detection and quantification of hydrogen sulfide (H2S) gas is important as it influences directly human health, our environment, and operations of several industries including food and beverages, oil, construction, and medicine. It also acts as biomarker in diagnosis of halitosis at early stage. We report herein liquid exfoliated MoSe2 nanoflakes based stable chemiresistive H2S gas sensor which operate at moderate temperature of 200℃. The response of p-type MoSe2 gas sensor device (when operated in ambient environment) was found to be varying between 15.87%–53.04% when the concentration of H2S was varied between 50 ppb – 5.45 ppm. The response of the device decreases when the measurements were done in synthetic air environment and it varies between 7.13%–19.87% for the concentration range of 500 ppb - 5.45 ppm. The response (%), recovery rate (%), hysteresis, experimental lowest detection limit etc. of the device suggest that the device performs better when operated in ambient than in synthetic air which suggest its real time device application. The response time and recovery time of the sensor are 15 s and 43 s respectively for 100 ppb of H2S. The sensor performance was found to be highly repeatable with sensitivity of 5.57%/ppm of H2S. The theoretical limit of detection and limit of quantization of the device were found to be 6.73 ppb and 22.44 ppb respectively. Based on chemical analysis, a plausible mechanism based on charge transfer phenomenon has been proposed for this sensor.

/pdf/mose2-nanoflakes-based-chemiresistive-sensors-for-ppb-level-3qn1n2ubih.pdf

MoSe2 nanoflakes based chemiresistive sensors for ppb-level hydrogen sulfide gas detection

A review of photovoltaic performance of organic/inorganic solar cells for future renewable and sustainable energy technologies

https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1279&context=ameslab_manuscripts

Highly efficient and stable p-type ZnO nanowires with piezotronic effect for photoelectrochemical water splitting

Effect of sputter pressure on UV photodetector performance of WO3 thin films

Mg x Zn1– x O ( $x = 0.05$ , 0.15 and 0.20) based metal–semiconductor–metal ultraviolet (UV) photodetectors were fabricated on Si substrate using dual-ion-beam sputtering. The performances of fabricated photodetectors were studied by current–voltage, spectral photoresponse, and temporal response measurements. The values of peak responsivity of photodetectors were 0.4, 0.31, and 0.27 A/W with corresponding external quantum efficiency of 146%, 110%, and 105% for $x = 0.05$ , 0.15 and 0.20, respectively. The cutoff wavelength and UV/visible rejection ratio of fabricated photodetectors decrease over 360–330 nm and 341.8–115.3, respectively, with increase in Mg concentration. The variation in specific detectivity and noise equivalent power with Mg concentration variation is also reported.

High Responsivity Mg x Zn 1– x O Based Ultraviolet Photodetector Fabricated by Dual Ion Beam Sputtering

Sb-doped p-Mg
 0.1
Zn
 0.9
O/n-Si-based heterojunction ultraviolet photodetectors were fabricated using dual ion beam sputtering. Current-Voltage measurements showed good rectifying behavior in fabricated devices with rectifying ratio as high as 251.35 at ± 4 V. The detectors exhibited good ultraviolet spectral response having peak responsivity of 0.025 A/W (at 310 nm) and 0.32 A/W (at 320 nm) at -30 V. The values of peak responsivity and external quantum efficiency increased from 1.7 mA/W and 0.75% (at 0 V) to 0.32 A/W and 134.26% (at -30 V), respectively. The value of detectivity of heterojunction devices was calculated to be 3.65 × 10
 11
 cm · Hz
 1/2
·W
 -1
 at -5 V.

Sb-Doped $p$ -MgZnO/ $n$ -Si Heterojunction UV Photodetector Fabricated by Dual Ion Beam Sputtering

The development of a new type of hybrid material comprising naphthalene-based π-conjugated amine (NBA) and zinc oxide (ZnO) nanohybrid, grown in situ on polydimethylsiloxane (PDMS) flexible substra...

π-Conjugated Amine-ZnO Nanohybrids for the Selective Detection of CO2 Gas at Room Temperature

In this work, we report a high-performance p-ZnO/n-Si heterojunction-based ultraviolet (UV) photodetector fabricated by dual ion beam sputter deposition. The lithium–phosphorus (Li–P) codoping route was used to realize low resistive and stable p-type ZnO. The current–voltage characteristics of p-ZnO/n-Si heterojunction photodiode showed good rectifying behavior with a rectification ratio of 170 at ±3 V. The spectral response measurements of the photodiode showed excellent responsivity with a peak observed around ~325 nm and cutoff wavelength around 370 nm. The maximum responsivity achieved was 2.6 A W−1 at an applied reverse bias of −6 V. The external quantum efficiency determined was of the order of ~1000% which is attributed to the trap assisted multiplication of charge carriers.

https://iopscience.iop.org/article/10.1088/1361-6463/aa98fb/pdf

Trap assisted charge multiplication enhanced photoresponse of Li-P codoped p-ZnO/n-Si heterojunction ultraviolet photodetectors

An analytical study has been carried out to obtain the device performance parameters of InGaN/GaN-based multiple quantum well solar cell (MQWSC). Significant improvements are made upon the preexisting models reported in the literature for predicting device performance matrix for MQWSC. The American Society for Testing and Materials (ASTM) standards data sheets are utilized for attaining photon flux density instead of blackbody radiation formula. Furthermore, the photon flux density is utilized to evaluate the performance parameters of MQWSC and bulk p-i-n solar cell. Results suggest that by incorporating QWs in the intrinsic region ( ${x} = {0.1}$ in $\text{In}_{x}\text{Ga}_{{1}-{x}}\text{N}$ ), ∼27% increment in the conversion efficiency can be achieved as compared to that from the bulk solar cell. Moreover, the impact of operating temperature in the solar cell performance is also studied. The rise in temperature leads to an increase in short-circuit current density; however, open-circuit voltage and conversion efficiency decrease. A decrement of ∼9.7% in the conversion efficiency of MQWSC is observed with the rise in temperature from 200 to 400 K as compared to ∼11.6% decline in p-i-n solar cell.

Ritesh Bhardwaj

Papers

High Responsivity Mg x Zn 1– x O Based Ultraviolet Photodetector Fabricated by Dual Ion Beam Sputtering

Sb-Doped $p$ -MgZnO/ $n$ -Si Heterojunction UV Photodetector Fabricated by Dual Ion Beam Sputtering

π-Conjugated Amine-ZnO Nanohybrids for the Selective Detection of CO2 Gas at Room Temperature

Trap assisted charge multiplication enhanced photoresponse of Li-P codoped p-ZnO/n-Si heterojunction ultraviolet photodetectors

Analytical Study of Performance Parameters of InGaN/GaN Multiple Quantum Well Solar Cell