The excellent and promising gas sensors not only have high response, but also can be easily integrated with other semiconductor devices to form an intelligent chip. In order to realize this goal, an effective strategy is proposed to combine the magnetron sputtering and Ar plasma treatment. As a result, a high-performance sensor based on Au-ZnO films is achieved at the optimal technology parameter, with high response (Ra/Rg) of 190 to 100 ppm isopropanol (IPA), rapid response/recovery speed of 1 s/18 s, and low detection limit of 100 ppb at 300℃. Moreover, the mechanisms of the improvement on the sensing properties of the as-fabricated sensor are discussed. The present work provides new ideas for the future development of integrating gas sensors with functional circuits to form a smart chip that can perform data acquisition, processing and storage.
We demonstrate the highly sensitive and fast response/recovery gas sensors for detecting isopropanol (IPA), in which the Au-nanoparticles-modified ZnO (Au@ZnO) nanofilms act as the active layers. The data confirm that both the response and the response/recovery speed for the detection of IPA are significantly improved by adding Au nanoparticles on the surface of ZnO nanofilms. The gas sensor with an Optimum Au@ZnO nanofilm exhibits the highest responses of 160 and 7 to the 100 and 1 ppm IPA at 300 °C, which indicates high sensitivity and a very low detecting limit. The sensor also exhibits a very short response/recovery time of 4/15 s on the optimized Au@ZnO nanofilm, which is much shorter than that of the sensor with a pure ZnO nanofilm. The mechanisms of the performance improvement in the sensors are discussed in detail. Both the electronic sensitization and the chemical sensitization of the ZnO nanofilms are improved by the modified Au nanoparticles, which not only regulate the thickness of the depletion layer but also increase the amount of adsorbed oxygen species on the surfaces. This work proposes a strategy to develop a highly sensitive gas sensor for real-time monitoring of IPA.
A detailed analysis of the electrical response of In0.3Ga0.7As surface quantum dots (SQDs) coupled to 5-layer buried quantum dots (BQDs) is carried out as a function of ethanol and acetone concentration while temperature-dependent photoluminescence (PL) spectra are also analyzed. The coupling structure is grown by solid source molecular beam epitaxy. Carrier transport from BQDs to SQDs is confirmed by the temperature-dependent PL spectra. The importance of the surface states for the sensing application is once more highlighted. The results show that not only the exposure to the target gas but also the illumination affect the electrical response of the coupling sample strongly. In the ethanol atmosphere and under the illumination, the sheet resistance of the coupling structure decays by 50% while it remains nearly constant for the reference structure with only the 5-layer BQDs but not the SQDs. The strong dependence of the electrical response on the gas concentration makes SQDs very suitable for the development of integrated micrometer-sized gas sensor devices.
A new grating structure with cladding etched as the sinusoidal function along the length direction is introduced. The cladding area of the grating varies as the sinusoidal function along fiber axes. The coupled mode theory is used to analyze its performance. Compared with the linearly chirped grating, the new structure exhibits an ideal box spectrum with steep edges when the tension is applied on the gratings in two different ways. For the type B grating, without tension after writing, it has a bigger bandwidth utilization (BWU) than that of the type A grating with tension after writing. Compared with the type A grating, the type B one is more adaptable in fiber-optic communications and sensor systems.
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