Humidity sensing properties of La^(3+)/Ce^(3+)-doped TiO_2-20 wt.% SnO_2 thin films derived from sol-gel method

The humidity sensing properties of La3+/Ce3+-doped TiO2-20 wt.%SnO2 thin films were studied.Sol-gel method was employed to prepare the films on alumina substrates.By constructing a humidity-impedance measuring system,the sensing behaviors were inspected for the films sintered at different temperatures.Experimental results showed that,0.5 wt.% of La2O3 or Ce2O3 doped films sintered at 500 °C for 2 h had the best humidity sensing properties,the impedance decreasing from 109 ? to below 104 ? in the humidity ra...

Humidity sensing properties of spray deposited Fe doped TiO_(2)thin film

In the present work,ferrite(Fe)doped TiO_(2)thin films with different volume percentage(vol%)were synthesized using a spray pyrolysis technique.The effect of Fe doping on structural properties such as crystallite size,texture coefficient,microstrain,dislocation densities etc.were evaluated from the X ray diffratometry(XRD)data.XRD data revealed a polycrystalline anatase TiO_(2)phase for sample synthesized up to 2 vol%and mixed anatase and rutile crystalline phase for sample synthesized at 4 vol%Fe doped TiO_(2).The crystalline size was observed to decrease with increase in Fe dopant vol%and also other structural parameters changes with Fe dopant percentage.In the present work,electrical resistance was observed to decrease with a rise in Fe dopant vol%and temperature of the sample.Thermal properties like temperature coefficient of resistance and activation energy also showed strong correlation with Fe dopant vol%.Humidity sensing properties of the synthesized sample altered with a change in Fe dopant vol%.In the present paper,maximum sensitivity of about 88.7%for the sample synthesized with 2 vol%Fe doped TiO_(2)and also the lowest response and recovery time of about 52 and 3 s were reported for the same sample.

Synthesis,Proton Conductivity and Humidity Sensing Property ofγ-Type Zirconium Hydrogen Phosphate,Zr(HPO_4)_2·2H_2O

A γ - type of layered zirconium hydrogen phosphate, Zr(HPO 4) 2·2H 2O( γ ZrP), was synthesized under hydrothermal conditions and characterized by powder X ray diffraction and thermogravimetric analysis. The temperature dependence of the proton conductivity in γ ZrP was investigated in a temperature range of 23￣413 ℃ by ac impedance spectroscopy. The variation of the conductivity with water loss and phase transitions was observed. The best proton conductivity in γ ZrP is 6×10 -4 S·cm -1 at 60 ℃. The proton conductivities in the dehydrated sample are ￣10 -5 at 150 ℃ and ￣10 -4 S·cm -1 at 350 ℃, respectively. The conductivities as a function of humidity in the temperature range of 120￣200 ℃ were measured.

Polyimide-Coated Fiber Bragg Grating for Relative Humidity Sensing

A fiber-optic humidity sensor has been fabricated by coating a moisture sensitive polymer film to the fiber Bragg grating （FBG）. The Bragg wavelength of the polyimide-coated FBG changes while it is exposed to different humidity conditions due to the volume expansion of the polyimide coating. The characteristics of sensors, including sensitivity, temporal response, and hysteresis, were improved by controlling the coating thickness and the degree of imidization during the thermal curing process of the polyimide. In the relative humidity （RH） condition ranging from 11.3%RH to 97.3%RH, the sensitivity of the sensor was about 13.5pm/%RH with measurement uncertainty of ±1.5%RH.

Humidity sensing properties of Ce-doped nanoporous ZnO thin film prepared by sol-gel method

The humidity sensitive characteristics of the sensor fabricated from Ce-doped nanoporous ZnO by screen-printing on the alumina substrate with Ag-Pd interdigital electrodes were investigated at different sintering temperatures.The nanoporous thin films were prepared by sol-gel technique.It was found that the impedance of the sensor sintered at 600 oC changed more than four order of magnitude in the relative humidity（RH） range of 11%-95% at 25 oC.The response and recovery time of the sensor were about 13 and 17 s,respectively.The sensor showed high humidity sensitivity,rapid response and recovery,prominent stability,good repeatability and narrow hysteresis loop.These re-sults indicated that Ce-doped nanoporous ZnO thin films can be used in fabricating high-performance humidity sensors.

Humidity sensing properties of La^(3+) and K^+ co-doped Ti_(0.9)Sn_(0.1)O_2 thin films

The humidity sensing properties of La^3＋ and K^＋ co-doped Ti0.9Sn0.1O2 thin films were investigated. The humidity sensitive thin films were prepared by sol-gel method on alumina substrates. The sensing behaviors of thin films were inspected at different sintering temperatures by constructing a humidity-impedance measuring system. It was found that the addition of rare earth ion La^3＋ and alkali ion K^＋ was beneficial for improving the humidity sensitive properties of the samples and La0.003K0.5Ti0.9Sn0.1O2 sintered at 500 ℃ for 4 h showed the best humidity sensing properties. The impedance of this thin film decreased from 109 to 104 Ω with excellent linearity in the humidity range of 11%-95%. Narrow hysteresis loop, prominent stability and high sensitivity were obtained. The effects of dopant con-tent and doping mechanism on humidity sensitivity were also discussed in terms of segregation of rare earth ions at grain boundaries and granularity of crystalline and influence of K^＋ on the decrease in the intrinsic resistance of the materials, and increase in the number of wa-ter adsorption sites.

Whispering-gallery mode lasing from polymer microsphere for humidity sensing

Microlasers based on high quality （Q） whispering-gallery mode （WGM） resonance are pronfising low threshold laser sources for bio-sensing and imaging applications. In this Letter, dye-doped polymer microspheres were fabricated by a controlling emulsion solvent evaporation method. WGM lasing with low threshold and high Q factors was realized in an individual microsphere under femtosecond laser pumping. The slight change of environmental relative humidity （RH） can be monitored by measuring the shift of the lasing modes at tile ex- posure of water molecules, which dcmonstrates the sensitivity is as high as 6 pm/RH%. The results would offer an insight into employing microlasers as sensors.

Hydrophobic ionic liquid-in-polymer composites for ultrafast,linear response and highly sensitive humidity sensing

Traditional ionic liquids are sensitive to humidity but with long response time and nonlinear response.Pure liquid-state ionic liquids are usually hard for dehydration which have ultralong response time for humidity sensing.The immobilization of ionic liquids provide a possible way for high performance humidity sensing.Hydrophobic materials and structures also promised faster response in humidity sensing,because of easier desorption of water.In this work,we prepared flexible humidity sensitive composites based on hydrophobic ionic liquid and polymer.The combination of hydrophobic ionic liquid with hydrophobic polymer realized linear response,high sensitivity with low hysteresis to humidity.By adjusting the ratio of ionic liquid,not only the impedance but also the hydrophobicity of composite could be modulated,which had a significant influence on the humidity sensing performance.The morphology and microstructure of the material also affected its interaction with water molecules.Due to the diverse processing methods of polymer,highly transparent film fabricated by spinning-coating and nanofibrous membrane fabricated by electrospinning could be prepared and exhibited different response time,which could be used for different application scenarios.Especially,the fibrous membrane made with electrospinning method showed an ultrafast response and could distinguish up to 120 Hz humidity change,due to its fibrous structure with high specific surface area.The humidity sensors with ultrafast,linear response and high sensitivity showed potential applications in human respiratory monitoring and flexible non-contact switch.To better show the multifunction of ionic liquid-polymer composite,as a proof of concept,we fabricated an integrated humidity sensitive color change device by utilizing lower ionic liquid content composite for sensing in the humidity sensing module and higher ionic liquid content composite as the electrolyte in the electrochromic module.

Synthesis，Proton Conductivity and High－Temperature Humidity Sensing Property of Zr（HPO_4）_2·H_2O and Its Aluminium－substituted Compositions

A series of aluminium-containing α-type hydrated zirconium hydrogen phosphates,Zr_(1-x)Alx (H_(1+x/2)PO_4 )_2 with x=0-0.06,were hydrothermally synthesized and characterizedby means of X-ray diffraction,differential thermal analysis and thermogravimetric analysis.The proton conductivity,1.2×10￣(-4) S·cm￣(-1)at 180℃ was found in Zr_(0.98)Al_(0.02)(H_(1.01)PO_4)_2·H_2O.Humidity-sensing measurements were carried out at 120℃ and 140℃ respectively.Even a limited substitution of Al for Zr can enhance both proton conductivity and humidity sensitivity.

Humidity Sensing Properties of the Sensor Based on V-doped Nanoporous Ti0.9Sn0.1O2 Thin Film

Vanadium doped nanoporous Ti0.9Sn0.1O2 thin film has been prepared on an alumina substrate by sol-gel method with Pluronic P123 as the organic template, and humidity sensing properties of it has been investigated. It is found that V-doped nanoporous Ti0.9Sn0.1O2 thin film shows good humidity sensing properties, and impendence of it de- creases more than four orders of magnitude in the relative humidity （RH） range of 11%--95% at 25 ℃. The response and recovery time of this sensor are about 13 and 17 s, respectively. High sensitivity, narrow hysteresis loop, rapid response and recovery, prominent stability and good repeatability are obtained. A possible mechanism is sug- gested to explain the humidity sensitive properties.

Applied whispering gallery modes on ZnO nanorods coated glass for humidity sensing application

In this letter,a humidity sensor is demonstrated by applying a whispering gallery mode(WGM)from a microsphere resonator onto the ZnO nanorods coated glass surface.The diameter of the microsphere was 234μm and the glass surface was coated with ZnO nanorods using the hydrothermal method at growth duration of 12 h.A significant response to humidity level ranging from 35%RH to 85%RH has been observed with the sensitivity of 0.0142 nm/%RH.The proposed humidity sensor has successfully employed to enhance interaction between the whispering gallery mode evanescent and surrounds analyte with the assistance of ZnO nanorods coated glass.

Dielectric Properties of Capacitive-Type Humidity Sensor Made under Different Pressures

Capacitive humidity sensors were made of nanometer barium titanate.The pellets were prepared under different pressures between 3920N to 7850N force.The capacitance changes in three orders of magnitude in the relative humidity range of 10%～98%,indicating high humidity sensitivity of the sensors.At a certain measuring frequency,the capacitance of the sensors increases as increasing of the preparation pressure,while the sensitivity of the sensors basically remains the same.The frequencies corresponding to the peaks of the dielectric loss of the sensors move to the higher frequency direction as increasing of the relative humidity.At a certain humidity,the frequencies corresponding to the peaks of the dielectric loss move to the higher frequency direction as increasing of the preparation pressure.

Study on Porous Silicon with P-N Junction Sensor for Humidity Measurement

Porous materials used for humidity sensing have been commercialized.In this paper,the preparation and humidity sensing characteristics of porous silicon with P-N junctions (PNJPS)are studied.PNJPS is made by electro-chemical anodic etched method from silicon wafers with P-N junctions.Its porous structure is verified by scanning electronic micrograph. Experiments also show that PNJPS has high sensitivity,short response time (less than 30 seconds),and long-term stability.

Angle-independent responsive organogel retroreflective structural color film for colorimetric sensing of humidity and organic vapors

The angle dependence of photonic crystals(PCs)dramatically limits their practical applications in the colorimetrical sensing of humidity and volatile organic compound(VOC)vapors.In addition,it is challenging for inverse opal PCs to colorimetrically distinguish between vapors with similar refractive indices.Different from the mechanism of PC-based sensors,here,we report an angle-independent polyacrylamide(PAAm)organogel structural color film based on the mechanisms of retroreflection,total internal reflection(TIR)and interference with a shape similar to a single-sided“egg waffle”.During the process of responding to humidity and VOC vapors,the color of the film remains angle-independent in the normal angle range of 0°to 45°under coaxial illumination and observation conditions.At the same time,the film can colorimetrically distinguish between vapors with similar refractive indices,such as methanol and ethanol,which is mainly due to the differences in their polarity and solubility parameters.The film shows good stability,reversibility and selectivity when exposed to vapors.A colorimetric sensor with a new response mechanism is proposed and has the potential to effectively distinguish between vapors with similar refractive indices.Furthermore,this responsive retroreflective structural color film(RRSCF)provides a universal strategy to develop targeted angle-independent structural color sensors by selecting optimized materials.

Enhanced positive humidity sensitive behavior of p-reduced graphene oxide decorated with n-WS_(2) nanoparticles

Most resistance-type humidity sensors exhibit negative humidity sensitivity,i.e.,their resistance decreases with a corresponding increase in humidity.This is primarily attributed to the dominant role of ionic conduction in adsorbed water.In this work,a humidity sensor based on a p-type reduced graphene oxide(p-rGO)with positive humidity sensitivity is proposed.Moreover,its positive humidity sensing response is further enhanced by n-type WS_(2) nanoparticles modification.The results show that both rGO and r GO/WS_(2) humidity sensors have good linear response in the relative humidity(RH)range of0%-91.5%.The sensitivity of the rGO/WS_(2) humidity sensor is 1.87 times that of rGO humidity sensor,which is mainly attributed to p-n heterojunction between rGO and WS_(2).Besides,the r GO/WS_(2) humidity sensor has small humidity hysteresis(-3%RH)and good repeatability.This work demonstrates a humidity sensor based on rGO/WS_(2) composite film and provides a facile route for fabricating humidity sensor with positive humidity sensing properties.

Atomically Thin 2D TiO_(2) Nanosheets with Ligand Modified Surface for Ultra-sensitive Humidity Sensor

As a kind of two-dimensional(2D)nanostructured materials,metal oxide nanosheets(MONS)are attractive and promising humidity sensing materials due to their considerable surface area,good charge carrier transportation,and designable surface functional groups properties.Nevertheless,the ultra-thin MONS modified with active functional groups for humidity sensing are still rare.As a proof of concept,the atomically thin TiO_(2)nanosheets with high surface area and electron-donating amino groups are prepared by a structure-maintained post-ligand modification strategy.The fabricated TiO_(2)-based sensors demonstrate superior humidity sensing performance with high response,short response time,narrow hysteresis,and ultra-low theoretical limit of detection of about 15 ppm.Additionally,the possible mechanism is proposed from the AC complex impedance measurements and DC instantaneous reverse polarity experiments.This work provides a possible path for developing the high-performance 2D nanostructured metal oxides-based humidity materials through the surface chemical method.

Water-driven photoluminescence reversibility in CsPbBr_(3)/PDMSPUa composite

Strong ionic character endows all-inorganic perovskite nanocrystals(NCs)with particular optoelectronic features when interacting with common polar solvents,such as water.However,the interaction mechanism of water affecting perovskite NCs is still lack of in-depth understanding.This study systematically explores the roles of water on CsPbBr_(3) nanocrystals(CNCs)by finely controlling the polymer coating degree of polydimethylsiloxane-based polyurea(PDMS-PUa).Through this coating,the effect of water on CNCs is found to experience from“fluorescence quenching”owing to irreversible crystal decomposition towards“forward fluorescence reversibility”by crystal destruction and recrystallization.With gradually enhanced coating,a phenomenon of“reverse fluorescence reversibility”is further observed in that water begins to passivate the CNCs’defect states.Finally,“fluorescent balance”can be achieved with a thick enough coating,where water can hardly contact with the CNCs.Inspired by the fluorescence reversible mechanism discovered,a new wearable intelligent sensing skin is demonstrated by using the CsPbBr_(3)/PDMS-PUa composite as raw material.Both water contact and humidity change can be perceived through photoluminescence(PL)intensity,corresponding to stimuli-responsive sensory nerves of human skin.It is expected that these findings will shed some new lights on perovskite NCs.