Gas sensors are important in many fields such as environmental monitoring, agricultural production, public safety, and medical diagnostics. Herein, Tamm plasmon resonance in a photonic bandgap is used to develop an optical gas sensor with high performance. The structure of the proposed sensor comprises a gas cavity sandwiched between a one-dimensional porous silicon photonic crystal and an Ag layer deposited on a prism. The optimised structure of the proposed sensor achieves ultra-high sensitivity (S = 1.9×10⁵ nm/RIU) and a low detection limit (DL = 1.4×10⁻⁷ RIU) compared to the existing gas sensor. The brilliant sensing performance and simple design of the proposed structure make our device highly suitable for use as a sensor in a variety of biomedical and industrial applications.

Gold/one-dimensional photonic crystal (Au/1D-PC) is fabricated and applied for sensitive sensing of glucose and different chemical molecules of various refractive indices. The Au layer thickness is optimized to produce surface plasmon resonance (SPR) at the right edge of the photonic band gap (PBG). As the Au deposition time increased to 60 sec, the PBG width is increased from 46 to 86 nm in correlation with the behavior of the SPR. The selectivity of the optimized Au/1D-PC sensor is tested upon the increase of the environmental refractive index of the detected molecules. The resonance wavelength and the PBG edges increased linearly and the transmitted intensity increased nonlinearly as the environment refractive index increased. The SPR splits to two modes during the detection of chloroform molecules based on the localized capacitive coupling of Au particles. Also, this structure shows high sensitivity at different glucose concentrations. The PBG and SPR are shifted to longer wavelengths, and PBG width is decreased linearly with a rate of 16.04 Å/(μg/mm³) as the glucose concentration increased. The proposed structure merits; operation at room temperature, compact size, and easy fabrication; suggest that the proposed structure can be efficiently used for the biomedical and chemical application.

Nanocrystalline undoped and Cr-doped PbS thin films were prepared on glass substrates by a simple chemical bath deposition method. The X-ray diffraction analyses of the films showed their polycrystalline nature with cubic structure and preferential growth along the (111) orientation. Cr incorporation decreases the average PbS crystallite size from 59.97 to 37.59 nm, whereas the strain and dislocation density showed an increasing trend. The atomic ratio of doping for Cr is about 0.63, 1.75, and 4.70% according to energy-dispersive X-ray (EDX) spectroscopy. Morphological analysis showed that the average sizes of nanoclusters decreased from 73 to 41 nm as the Cr concentration increased. The optical band gap values are increased with increasing Cr doping. The photoelectrochemical (PEC) behaviors and the stability of the Cr doped PbS photoelectrodes were studied in 0.3 M Na₂SO₃ electrolyte solution. Also, the incident photon-to-current efficiency and applied bias photon-to-current efficiency are calculated and showed optimized values of 13.5% and 1.44% at 0.68 V and 390 nm. Moreover, the optimized electrode shows high chemical stability and a long lifetime. Finally, the effect of temperature on the PEC behaviors is evaluated and the different thermodynamic parameters are calculated.

In this work, a polyaniline/lead sulfide (PANI/PbS) nanocomposite was prepared by combining the in situ oxidation polymerization method and the surface adsorption process. This nanocomposite was applied as a supercapacitor electrode. The crystal structure, nanomorphology, and optical analysis of PANI and PANI/PbS were investigated. The electrochemical performance of the designed PANI/PbS electrode-based supercapacitor was tested by using cyclic voltammetry (CV), chronopotentiometry (CP), and AC impedance techniques in HCl and Na₂SO₄ electrolytes. The average crystallite size of the PANI/PbS nanocomposite is about 43 nm. PANI/PbS possesses an agglomerated network related to PANI with additional spherical shapes from PbS nanoparticles. After the PANI/PbS nanocomposite formation, there are enhancements in their absorption intensities. At a current density of 0.4 A g⁻¹, the specific capacitance of PANI/PbS in Na₂SO₄ and HCl was found to be 303 and 625 F g⁻¹, respectively. In HCl (625 F g⁻¹ and 1500 mF cm⁻²), the gravimetric and areal capacitances of the PANI/PbS electrode are nearly double those of the Na₂SO₄ electrolyte. Also, the average specific energy and specific power density values for the PANI/PbS electrode in HCl are 4.168 Wh kg⁻¹ and 196.03 W kg⁻¹, respectively. After 5000 cycles, the capacitance loses only 4.5% of its initial value. The results refer to the high stability and good performance of the designed PANI/PbS as a supercapacitor electrode.

Thin films of ZnO and ZnO/carbon nanotubes (CNTs) are prepared and used as CO₂ gas sensors. The spray pyrolysis method was used to prepare both ZnO and ZnO/CNTs films, with CNTs first prepared using the chemical vapor deposition method (CVD). The chemical structure and optical analyses for all the prepared nanomaterials were performed using X-ray diffraction (XRD), Fourier transformer infrared spectroscopy (FTIR), and UV/Vis spectrophotometer devices, respectively. According to the XRD analysis, the crystal sizes of ZnO and ZnO/CNTs were approximately 50.4 and 65.2 nm, respectively. CNTs have average inner and outer diameters of about 3 and 13 nm respectively, according to the transmitted electron microscope (TEM), and a wall thickness of about 5 nm. The detection of CO₂ is accomplished by passing varying rates of the gas from 30 to 150 sccm over the prepared thin-film electrodes. At 150 sccm, the sensitivities of ZnO and ZnO/CNTs sensors are 6.8% and 22.4%, respectively. The ZnO/CNTs sensor has a very stable sensitivity to CO₂ gas for 21 days. Moreover, this sensor has a high selectivity to CO₂ in comparison with other gases, in which the ZnO/CNTs sensor has a higher sensitivity to CO₂ compared to H₂ and C₂H₂.