A metal-semiconductor-metal photoconductive detector was fabricated using Ce-doped ZnO nanofibers synthesized by electrospinning and calcinations. UV photocurrents were carried out to study optoelectronic properties of Ce-doped ZnO nanofibers. The current-voltage (I–V) characteristics of photodetector device were analyzed under different wavelength UV illumination. The photocurrent increased by about 300 times under UV illumination. Results showed that the photocurrent of the device increased with the decrease of the wavelengths. A maximum photocurrent and photo-responsivity was observed at 365 nm, 308 nm, 254nm, respectively, under 30 V bias. The response and recovery time of the nanofibers was 16 s and 16 s at 365 nm, 10 s and 12 s at 308nm, 4 s and3 s at 254nm under 30 V bias, respectively.
We developed a novel sensor structure by synthesizing Pd nanocubes (NCs) decorated on ZnO nanostructures (NSs) applied to resistive-type H2 gas sensor with micro-length in sensing channel. The ZnO NSs were selectively grown between micro-size finger-like interdigital electrodes
through microelectromechanical technology. The novel H2 sensor structure with the sensing channel was reduced to micro-size by this proposed method to obtain a sensor with fast response/recovery time. The as-prepared structure exhibited robust sensing performance with a response
of 11% at optimal temperature of 150 °C, good linearity, and fast response/recovery time within 10 s. The speed of chemisorption through the diffusion pathway in Pd NCs combined with micro-length in sensing channel in sensor showed fast response and recovery times of 9 and 15 s, respectively,
toward 10,000 ppm (1%) H2 at 150 °C. The result showed approximate linearity response in H2 concentration range of 5÷10,000 ppm and a large operating temperature range from room temperature to 200 °C.
Novel Ni-doped wurtzite ZnS nanospheres decorated with Au nanoparticles (Au NPs–ZnS NSs) have been successfully fabricated using a simple method involving vacuum evaporation followed by an annealing process. This transition metal-doped gas sensor had high responsivity, extremely fast response and recovery time, and excellent selectivity to formaldehyde at room temperature. The response and recovery time are only 29 s and 2 s, respectively. Since ZnS is transformed into ZnO at a high temperature, superior room temperature-sensing performance can improve the stability and service life of the sensor. The improvement in sensing performance could be attributed to the reduced charge-transfer distance resulting from the creation of a local charge reservoir layer, and the catalytic and spillover effect of Au nanoparticles. The rough and porous spherical structure can also facilitate the detection and diffusion of gases. The as-prepared Au NPs–ZnS NSs are considered to be an extremely promising candidate material for gas sensors, and are expected to have other potential applications in the future.
Breath monitoring is significant in assessing human body conditions, such as cardiac and pulmonary symptoms. Optical fiber-based sensors have attracted much attention since they are immune to electromagnetic radiation, thus are safe for patients. Here, a microfiber (MF) humidity sensor is fabricated by coating tin disulfide (SnS2) nanosheets onto the surface of MF. The small diameter (~8 μm) and the long length (~5 mm) of the MF promise strong interaction between guiding light and SnS2. Thus, a small variation in the relative humidity (RH) will lead to a large change in optical transmitted power. A high RH sensitivity of 0.57 dB/%RH is therefore achieved. The response and recovery times are estimated to be 0.08 and 0.28 s, respectively. The high sensitivity and fast response speed enable our SnS2-MF sensor to monitor human breath in real time.
A new type of gas sensor was realized by directly depositing carbon nanotube on nano
channels of the anodic alumina oxide (AAO) fabricated on p-type silicon substrate. The carbon
nanotubes were synthesized by thermal chemical vapor deposition at a very high temperature of
1200 oC to improve the crystallinity. The device fabrication process was also developed. The
contact of carbon nanotubes and p-type Si substrate showed a Schottky behavior, and the Schottky
barrier height increased with exposure to gases while the overall conductivity decreased. The
sensors showed fast response and recovery to ammonia gas upon the filling (400 mTorr) and
evacuation.
A novel composite based on a polymer (P(VDF-TrFE)) and a two-dimensional material (graphene flower) was proposed as the active layer of an interdigitated electrode (IDEs) based humidity sensor. Silver (Ag) IDEs were screen printed on a flexible polyethylene terephthalate (PET) substrate followed by spin coating the active layer of P(VDF-TrFE)/graphene flower on its surface. It was observed that this sensor responds to a wide relative humidity range (RH%) of 8–98% with a fast response and recovery time of 0.8 s and 2.5 s for the capacitance, respectively. The fabricated sensor displayed an inversely proportional response between capacitance and RH%, while a directly proportional relationship was observed between its impedance and RH%. P(VDF-TrFE)/graphene flower-based flexible humidity sensor exhibited high sensitivity with an average change of capacitance as 0.0558 pF/RH%. Stability of obtained results was monitored for two weeks without any considerable change in the original values, signifying its high reliability. Various chemical, morphological, and electrical characterizations were performed to comprehensively study the humidity-sensing behavior of this advanced composite. The fabricated sensor was successfully used for the applications of health monitoring and measuring the water content in the environment.
Development of tungsten doped Ni-Zn nano-ferrites with fast response and recovery time for hydrogen gas sensing application