Carbon nanotubes/polyaniline as hydrogen gas sensor: Optical bandgap, micro-morphology, and skin depth studies

In this study, multiwall carbon nanotubes (MWCNTs)/polyaniline nanocomposites deposited on ITO coated glass as substrate by the spin-coating technique were applied to the investigation of the effect of different contents of MWCNTs on the optical and electrical properties of polyaniline. Micrographs from an atomic force microscope were taken to analyze the 3-D microtexture parameters of surface texture factors and fractal dimension. By using optical spectroscopy of samples with different concentrations of MWNCTs in visible and ultraviolet regions, the transmission variations vs photon wavelength, optical bandgap, absorption coefficient, and skin depth were studied. The variation in the resistance of nanocomposite films exposed to 0.4 %vol of H2 gas at room temperature was monitored, and the results indicated that the sensitivity and responsibility of the composites increased with an increase in the MWCNT amount

ZnO, Cu-doped ZnO, Al-doped ZnO and Cu-Al doped ZnO thin films: Advanced micro-morphology, crystalline structures and optical properties

The thin film coatings composed of: undoped ZnO film, ZnO doped with Al, ZnO doped with Cu, and ZnO simultaneously doped with Al and Cu (co-doping) were separately deposited on quartz substrates using RF sputtering method with different targets. The advanced fractal features, crystalline structure and optical properties of sputtered samples were investigated by atomic force microscopy (AFM), X‐ray diffraction (XRD) and UV–vis spectroscopy. Microstructural studies revealed homogeneously granular structure of ZnO layer and axially oriented granular structure of AZO thin film.The transmission spectra of undoped, mono-doped and co-doped ZnO thin films were measured revealing relatively large transmittance of more than 80 % for un-doped and co-doped samples and less than that value for mono-doped thin films in both visible and infrared regions. CAZO thin film was found the most transparent thin film in the visible area being a prerequisite for good TCO. Analysis of absorption coefficients demonstrated that excitonic effects are invisible in mono-doped and co-doped samples. Also, PL spectra show that in these samples there are very high densities of free carriers and presence of impurities, which is important for conductivity of thin films as well as their optical applications. The optical band gap of ZnO thin films decreases by Cu doping from 3.12 eV to 3.09 eV and increases by Al doping to 4.30 eV, but remains exactly between those values in terms of co-doped sample (3.75 eV)

Nanoscale morphology, optical dynamics and gas sensor of porous silicon

Abstract We investigated the multifaceted gas sensing properties of porous silicon thin films electrodeposited onto (100) oriented P-type silicon wafers substrates. Our investigation delves into morphological, optical properties, and sensing capabilities, aiming to optimize their use as efficient gas sensors. Morphological analysis revealed the development of unique surfaces with distinct characteristics compared to untreated sample, yielding substantially rougher yet flat surfaces, corroborated by Minkowski Functionals analysis. Fractal mathematics exploration emphasized that despite increased roughness, HF/ethanol-treated surfaces exhibit flatter attributes compared to untreated Si sample. Optical approaches established a correlation between increased porosity and elevated localized states and defects, influencing the Urbach energy value. This contributed to a reduction in steepness values, attributed to heightened dislocations and structural disturbances, while the transconductance parameter decreases. Simultaneously, porosity enhances the strength of electron‒phonon interaction. The porous silicon thin films were further tested as effective gas sensors for CO2 and O2 vapors at room temperature, displaying notable changes in electrical resistance with varying concentrations. These findings bring a comprehensive exploration of some important characteristics of porous silicon surfaces and established their potential for advanced industrial applications