A highly transparent humidity sensor with fast response speed based on α-MoO₃ thin films

Abstract

<p>A transparent and rapid humidity sensor based on α-MoO₃ thin films was fabricated by a facile chemical route.</p>

Flexible Ni/NiOx-Based Sensor for Human Breath Detection

“…We believe that the Ni 3+ increase in the NiO x -sensing channel can contribute to the enhancement of the breath-sensing ability due to the following reasons: The increase in the Ni 3+ states led to an increase in hole concentration in the hall accumulation layer on the NiO x surface. As the sensor is exposed to human breath, the absorbed water molecules from the breathing gas under the applied electricity are ionized into H 3 O + and free electrons [ 53 , 54 , 55 ]. These electrons are injected into the NiO x , and the resultant hole concentration in the hole accumulation layer on the surface of the NiO x decrease via electron–hole recombination, thereby increasing the sensor’s resistance [ 56 ].…”

“…It is noteworthy that NiO x is known as a p-type semiconductor. On the other hand, H 3 O + could act as the charge carriers by proton hopping [ 55 , 57 ], which leads to a decrease in the resistance. Therefore, the electron injection mechanism and proton hopping mechanism have opposite effects on resistance change.…”

Contemporary Advances in Humidity Sensing Materials, Methods, and Performances

“…The film was prepared by the single-step spin coating method using the green reaction bath. The observed sensing parameters are 85% transparency in the visible region along with a small response time of 0.97, recover time of 12.11 s and sensing range of 11 to 95% [36]. The oxide coated substrate also generates an optimized refractive index for the quantification of interacting water molecules.…”

Advances in the designs and mechanisms of MoO3 nanostructures for gas sensors: a holistic review

“…The 2-D materials are strong adsorbents to organic molecules, and at high temperatures, they tend to partially lose oxygen to become oxygen-deficient and so are considered as the most suitable candidates in VOCs sensing 144 . Among the various 2-D nanostructures of MoO3, the nanosheets 64,80,81,145 , nanoflakes [146][147][148] , nanoplates 79,149,150 , nanolamella 151 , nanopaper 152 , thin film [153][154][155][156] , microsheet 157 and microplanks 158 morphology of MoO3 have recently received great research interest in gas sensing applications as they can be used in designing nanodevices with desired crystal orientation due to their anisotropic structures. An overview of gas sensors based on 2-D MoO3 nanostructures is listed in Table 2.…”

“…In addition, most of the sensors fabricated so far have been based on the deposition of sensing layers on mechanically rigid substrates such as alumina, glass, quartz, or Silicon. In addition, the precise detection of humidity in the indoor climate has also emerged as a research hotpot in recent times 136,140,[162][163][164] and so the group of Ma and coworkers 156 prepared α-MoO3 TFm by a simple solution method and prepared a transparent humidity sensor which consisted of laser-etched Fluorine-doped tin oxide (FTO) electrode onto which the annealed α-MoO3 thin film was coated (Figure 14i). The SEM image in Figure 14j revealed that the FTO substrate has an important influence on the film formation process as the morphologies of the film on the channels and FTO electrodes are not exactly the same.…”