Opto-electronic Humidity Sensor Research Articles

Fabrication of leaf shaped SnO2 nanoparticles via sol–gel route and its application for the optoelectronic humidity sensor

In this report, synthesis of nanostructured SnO2via sol–gel technique and its application for the detection of humidity level has been studied. Scanning electron microscopy (SEM) micrographs showed the formation of uniform leaf like structured SnO2 nanoparticles. The average crystalline size is discovered as 9 nm calculated by Debye Scherrer’s formula using X-ray diffraction (XRD) which shows tetragonal crystal structure. The crystallite size is further confirmed by transmission electron microscopy (TEM). The optical band gap is estimated as 3.63 eV by UV–Visible absorption spectra. The prepared SnO2 based thin film with leaf like structure enhances the feasibility for the detection of humidity, especially in the high range of 65–90 %RH. The prepared SnO2 samples shows good sensitivity towards the relative humidity. It shows 1.8nW/% RH in the humidity range 65–90% RH at 25 °C.

An installation for studying optoelectronic humidity sensor

An installation for studying optoelectronic humidity sensor

Catalytic growth of MWCNT using CVD and its application as opto-electronic humidity sensor

The present paper describes the effect of co-catalyst on the growth of multiwall carbon nanotube (MWCNT) by chemical vapor deposition (CVD) technique. The fascinating properties of CNT make them a suitable material for optoelectronic devices such as sensors, LED, solar cell, and field emission displays. MWCNTs were fabricated using CVD, by decomposing ethanol over finely dispersed Co metal as a catalyst at 750 °C. The effects of growth condition on the quality and morphology of MWCNTs were investigated by SEM, FTIR and XRD. SEM photographs show that the nanotubes are densely packed having a diameter of 10–15 nm. The bandgap was calculated by UV–visible spectroscopy and it was found varying from 3.08 to 3.5 eV by changing the substrates. The average size of tubes (length) was found to be 250 nm. FTIR exhibited that the synthesized MWCNTs were semiconducting in nature with the oxygen vacancies causing the variations in refractive index with the exposure of moisture.

Synthesis and characterization of highly porous hexagonal shaped CeO2-Gd2O3-CoO nanocomposite and its opto-electronic humidity sensing

The present paper reports the synthesis and fabrication of CeO2-Gd2O3-CoO nanocomposite films using metal carboxylates as precursors. The refractive index of the film was found as 1.445538. The crystallinity was confirmed from XRD and the minimum crystallite size calculated was 9 nm. TEM analysis showed the hexagonal crystals where the minimum dimension was obtained as 6 nm. The dimensionality was further confirmed by Particle Size Analyzer. The film was then examined using SEM which revealed highly porous nature of the material. UV–Vis spectrophotometer found the absorption of the film taking place in UV-region and the optical band-gap as determined from Tauc plot was 3.987 eV. The film was used as transmission based opto-electronic humidity sensor. Owing to the highly porous nature of the film, the maximum sensitivity was found as ~2.006 μW/%RH, which is showing the quite efficient behavior of the film towards humidity. Response and recovery times were found as 71 s and 86 s respectively, also ~91% reproducible results were found while repeating the experiment.

Development of nanostructured nickel reinforced polyacrylamide via frontal polymerization for a reliable room temperature humidity sensor

The present paper reports the polymer matrix of Ni(NO3)2(AAm)4·2H2O thin film as an electrical and opto-electronic humidity sensor. For this purpose, films were prepared by spin-coating method to investigate the adsorption/desorption of humidity at room ambient. The sensing element was investigated through X-ray diffraction (XRD), Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM) and UV–Vis absorption techniques. XRD exhibited the crystalline nature of the nanomaterial thin film and evaluated average crystallite size was 30 nm. SEM showed highly porous nanostructures of different size distributed throughout the film. Energy band-gap of the film was estimated as 4.034 eV. TEM image showed the nanostructures with the average grain size of 4-21 nm and SAED confirmed the crystalline nature of the material. The film was further employed for two different modes of humidity sensing i.e., impedance-based electrical humidity measurement and transmission based opto-electronic humidity measurement which gave a maximum average sensitivity of 37.79 MΩ/%RH and 1.31 µW/%RH respectively at room temperature.

Synthesis and investigation of cubical shaped barium titanate and its application as opto-electronic humidity sensor

In the current scenario, nanoscience and nanotechnology are playing a vital role in the upliftment of the quality of human life. The quantum confinement effect that arises at the nano-dimensional particles, changes the properties of the material in a drastic way. The present paper reports the successful synthesis of BaTiO3 using rotary evaporator and fabrication of sensing elements by deposition of films on flat borosilicate glass substrates using 2-methoxy ethanol and homogeneous precursor in the ratio of 1:4, 2:4, 3:4 and 4:4. These films were then annealed at 650 °C and characterized through various techniques. Morphological investigation as obtained from SEM reported the cubical clusters and the dimensionality of these clusters, decreases with increase in the concentration of 2-methoxy ethanol. An optical investigation done through UV–Vis spectrum showed the absorbance in the UV range and Tauc plot estimated the optical band gaps of 3.842, 3.854, 3.864 and 3.872 eV for the respective films. Structural information as obtained from XRD of the film having 2-methoxy ethanol and homogeneous precursor in the ratio of 4:4 gave minimum crystallite size of ~ 18 nm. Further, these films were employed as opto-electronic humidity sensor where the maximum sensitivity of the sensing elements was found as 2.15, 2.79, 3.28 and 3.67 µW/%RH respectively. Thus as the concentration of 2-methoxy ethanol in the solution increases, the properties of the material increases and hence the humidity sensing potency also increases.

Nanostructured Spherical-Shaped Sc(III) Polyacrylate for Monitoring the Moisture Level

This paper reports the investigation of transmitted power through the nanostructured scandium polyacrylate (Sc(III) PAcr) deposited on flat borosilicate substrates to examine the adsorption/desorption of humidity at room temperature. For this purpose, the precursor of Sc(CH2 = CH-COO)3 was prepared and used for film deposition. The film was then investigated using scanning electron microscope (SEM) and UV–Visible (Vis) absorption techniques. SEM showed the spherical-shaped clusters of the material. Energy band gap of the film was estimated as 3.887 eV by UV–Vis spectrophotometer. Transmission electron microscope revealed the minimum grain diameter of ~21 nm and selected-area electron diffraction showed its polycrystalline nature. From Zeta nanosizer, minimum particle size was found as 18 nm. Fourier transforms infra-red spectroscopy confirmed the bond formation in the material. The surface area analysis shows that the pore volume of Sc(III) PAcr is 0.15 cm3/g, which is quite small, whereas the surface area and mean pore radius of the spherical structure are 60.1 m2/g and 41.2 A, respectively. The film was employed as transmission-based opto-electronic humidity sensor. Maximum sensitivity was found as 2.1 $\mu \text{W}$ /%RH with 89% reproducibility. Response and recovery times of the sensor were found as 25 and 155 s, respectively.

Preparation of zinc (II) nitrate poly acryl amide (PAAm) and its optoelectronic application for humidity sensing

The present paper reports the investigation of transmitted power through the nanostructured zinc (II) nitrate polyacrylamide deposited substrate to investigate the adsorption/desorption of humidity at room temperature. For this purpose, the precursor of Zn(NO3)2·(AAm)4·2H2O was prepared and used for the deposition of films on borosilicate flat substrates. The film was then investigated using SEM, XRD and UV–Vis absorption techniques. Scanning Electron Microscope showed the macroporous nature of the film with multiple pores in situ. XRD revealed the nature of monomer and polymer. Energy band-gap of the film was estimated as 3.865 eV by UV–Vis spectrophotometer. SAED confirmed the crystalline nature of the material. From Zeta nanosizer, the minimum range of particles was found as 5–20 nm. The film was employed as transmission based opto-electronic humidity sensor. Maximum sensitivity was found as 1.831 µW/%RH. Response and recovery times of the sensor were found as 250 and 37 s respectively. Experiments were repeated time to time and found that the sensor was ~ 96% stable after a long run. Thus the investigated opto-electronic sensor being polymeric is flexible in nature.

Fabrication of tin substituted nickel ferrite (Sn-NiFe2O4) thin film and its application as opto-electronic humidity sensor

A well nanocrystalline structured tin substituted nickel ferrite thin film was prepared by chemical co-precipitation method. XRD analysis reveals the average crystallite size as 51 nm and most preferential peak (311) affirms the formation of tin substituted nickel ferrite. The SEM morphology shows the large number of active sites. FT-IR analysis reveals the general nature of ferrite materials. TEM analysis shows the inhomogeneous distribution of particles. Also, the SAED pattern exhibits the polycrystalline nature. From UV analysis, it was observed that material has absorption in visible region at ∼201 nm. Humidity sensing analysis reveals that material has average sensitivity is 2.08 MΩ/%RH and excellent reproducibility with response and recovery times of 44 and 180 s respectively.

Synthesis and characterization of copper (II) nitrate polyacrylamide & its application as opto-electronic humidity sensor

The present paper reports the effect of humidity on the transmitted power through the nanostructured copper (II) nitrate polyacrylamide (AAm) complex film at room temperature. For this purpose, the precursor of Cu(II) nitrate polyAAm was prepared and used for the deposition of a film on the substrates of borosilicate. The film was then investigated using SEM which revealed the uniform leaf-like structured morphology. By UV–vis spectrophotometer, it was found that the absorption of light took place in UV-region and the corresponding optical energy band-gap was observed as 4.02eV. The diffraction pattern obtained from TEM showed the crystalline nature of the material. Powder XRD revealed the minimum crystallite size as 9nm and average size as 13nm which was further confirmed by the Zeta Nano-sizer. The film was employed as transmission based opto-electronic humidity sensor. Maximum sensitivity was found as∼0.838μW/%RH. Response and recovery times were found as 31s and 76s respectively. Experiments were repeated time to time and reproducibility was found ∼96% with negligible ageing effect. The investigated sensor being optical in nature has the capability of multiplexing the information with the signal.

Fabrication of nanostructured yttria stabilized zirconia multilayered films and their optical humidity sensing capabilities based on transmission

The present paper reports the study of modulation in intensity of light transmitted through the thin films of nanostructured yttria stabilized zirconia (YSZ) with the exposure of moisture at room temperature. For this purpose the precursor of YSZ was prepared and used for the deposition of multilayered thin films on borosilicate substrates. The film was then investigated using SEM, XRD and UV–vis absorption techniques. The refractive index of the sensing material was found as 1.448829. SEM showed the macroporous nature of the film and XRD revealed the minimum crystallite size as 5nm which was further confirmed using TEM and Zeta Nanosizer. Energy band-gaps of one-, two-, three- and four- layered films were estimated as 3.927, 3.919, 3.873 and 3.830eV respectively by UV–vis spectrophotometer. These films were employed as transmission based opto-electronic humidity sensor. Maximum sensitivity was found as∼1.937, 1.642, 1.393 and 1.143μW/%RH for one, two, three and four- layered films, respectively. Response and recovery times of the sensor were found as 28s and 30s respectively. Experiments were repeated time to time and found that the sensor was ∼94% stable after long run. Thus the investigated opto-electronic sensor has excellent potential to replace an electrical humidity sensor.

Experimental investigations on barium titanate nanocomposite thin films as an opto-electronic humidity sensor

This article reports the synthesis and characterisation of Barium titanate (BaTiO3) nanocomposite and its application as opto-electronic humidity sensor. Titanium tetrachloride and barium hydroxide were mixed in molar ratio 1 : 1 in deionised water under continuous stirring at room temperature. Later, sodium hydroxide solution was added to above solution with continuous stirring. Finally, BaTiO3 gel was obtained. The synthesised nano-composite material was characterised using a scanning electron microscope, X-ray diffraction (XRD) and UV-Visible spectrophotometer. SEM image of the composite film shows that the film is porous having uniform grains. From XRD the minimum crystallite size of BaTiO3 was found to be 8 nm using Debye–Scherer formula. UV-Visible absorption spectroscopy was used for optical characterisation of the film. It was found that the optical band gap of the composite material was 3.50 eV. Barium titanate thin film was deposited on the base of an equilateral prism using sol–gel spin coating process at 4000 rpm. The humidity sensing properties of the film was investigated at different angles of incidence. It was observed that the intensity of reflected light increased with an increase in relative humidity (%RH) in the range 5–95% at a particular angle of incidence. Sensing element has maximum sensitivity ∼6 µW/%RH, which is quite significant for sensor fabrication purposes.

Nanocrystalline SnO2–TiO2 thin film deposited on base of equilateral prism as an opto-electronic humidity sensor

Present paper reports the synthesis of SnO2–TiO2 nanocomposite, its characterization and performance as opto-electronic humidity sensor. Nanocrystalline SnO2–TiO2 film was deposited on the base of an equilateral prism using a photo resist spinner and the as prepared film was annealed at 200°C for 2h. The crystal structure of the prepared film was investigated using X-ray diffraction (XRD). Minimum crystallite size of the material was found 7nm. Surface morphology of the film was investigated by Scanning electron microscope (SEM LEO-0430, Cambridge). SEM image shows that the film is porous. Differential scanning calorimetry (DSC) of as synthesized material shows two exothermic peaks at about 40 and 110°C, respectively which are due to the evaporation of chemical impurities and water. Further the prepared film was investigated through the exposure of humidity and relative humidity (%RH) was measured directly in terms of modulation in the intensity of light recorded on a digital power meter. The maximum sensitivity of sensor was found 4.14μW/%RH, which is quite significant for sensor fabrication purposes.

Sol–gel processed (Mg–Zn–Ti) oxide nanocomposite film deposited on prism base as an opto-electronic humidity sensor

Nanocrystalline (Mg–Zn–Ti) oxide films were deposited on an equilateral prism using sol–gel spin process and then annealed at 450 °C for 4 h. The humidity sensing properties of the films were investigated at different angles of incidence. It was observed that the intensity of reflected light increased with an increase in relative humidity (%RH) in the range 10–95% at a particular angle of incidence, which is quite significant for sensor fabrication purposes. The X-ray diffraction reveals the formation of TiO 2, ZnTiO 3 and MgTiO 3 nanocomposites having minimum crystallite size 14 nm. UV–vis absorption spectroscopy was used for optical characterization of the film. It was found that the optical band gap of the composite material was 3.925 eV. Surface morphological study of the film and compositional analysis of elements were carried out using scanning electron microscopy and energy dispersive X-ray spectroscopy. The average sensitivity and reproducibility of the sensor for θ i = 60° were found 2 and ∼88%, respectively. Response and recovery time of the sensor were 18 and 30 s respectively. These experimental results have well matches with the theory.

Pulsed laser deposited ZnO films and their humidity sensing behavior

The present paper describes an opto-electronic humidity sensor based on thin film of zinc oxide prepared by pulsed laser deposition method. Being optical in nature it gives electromagnetic disturbance-free monitoring. The sensing element is a right-angled isosceles prism with its base coated with ZnO thin film. Films have been characterized by XRD, SEM, and optical transmission. Film grown with substrate at room temperature is amorphous whereas that grown at elevated temperature is single crystalline with grain size 38.52 nm. Film deposited at room temperature is sensitive to humidity over a wide range i.e. 5–90RH% while that deposited at elevated temperature is found to be insensitive to humidity. The sensor shows better sensitivity for higher range of humidity. The response and recovery time of the sensor element have also been evaluated. This sensor configuration can be used for on-line applications and in-situ monitoring.

ZnO Thick Film Based Opto-electronic Humidity Sensor for a Wide Range of Humidity

Sensitivity of zinc oxide film to humidity is studied using prism based opto-electronic sensor configuration. Film is deposited on the base of the prism by screen printing. The film is crystalline in nature and has micropores on its surface which is suitable for humidity sensing. The sensing mechanism, here, is the modulation in emergent light intensity with change in ambient humidity. Response of the sensor configuration is repeatable and the configuration is found to be sensitive to relative humidity (RH%) ranging from 5 to 90 RH%.