Nanoscale morphology, optical dynamics and gas sensor of porous silicon.

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.

Advanced nano-texture, optical bandgap, and Urbach energy analysis of NiO/Si heterojunctions.

Due to the large number of industrial applications of transparent conductive oxides (TCOs), this study focuses on one of the most important metal oxides. The RF-magnetron sputtering method was used to fabricate NiO thin films on both quartz and silicon substrates at room temperature under flow of Argon and Oxygen. The sputtered samples were annealed in N2 atmosphere at 400, 500, and 600 °C for 2 hours. Using the AFM micrographs and WSXM 4.0 software, the basic surface parameters, including root mean square roughness, average roughness, kurtosis, skewness, etc., were computed. Advanced surface parameters were obtained by the Shannon entropy through a developed algorithm, and the power spectral density and fractal succolarity were extracted by related methods. Optical properties were studied using a transmittance spectrum to achieve the optical bandgap, absorption coefficient, Urbach energy, and other optical parameters. Photoluminescence properties also showed interesting results in accordance with optical properties. Finally, electrical characterizations and I-V measurements of the NiO/Si heterojunction device demonstrated that it can be used as a good diode device.

Evaluating structural, morphological, and multifractal aspects of n-ZnO/p-ZnO homojunctions and n-ZnO/p-NiO heterojunctions.

We have investigated the evolution of the structure and surface morphology of n-ZnO/p-ZnO homojunctions and n-ZnO/p-NiO heterojunctions transparent structures deposited by radio frequency-sputtering on quartz (Q)/ITO substrates. X-ray diffraction (XRD) analysis of the as-deposited and annealed ZnO, n-ZnO/p-NiO/Q/ITO, and n-ZnO/p-ZnO/Q/ITO thin films showed that ZnO had a wurtzite hexagonal structure and (002) preferred growth direction. The annealing temperature played a key role in improving the crystalline structure of the films, as evidenced by the changes in the intensity and position of the XRD (002) peak. Morphological analysis revealed that the roughness of the film varies with increasing annealing temperature. Particle size dictates the vertical growth of p-ZnO homojunctions, while particle shape dictated the p-NiO heterojunctions growth. Fractal analysis showed that p-ZnO homojunctions have similar spatial complexity, surface percolation, and topographical uniformity and are dominated by low dominant frequencies. Moreover, a robust multifractal character was observed, where n-ZnO/p-ZnO homojunctions follow similar vertical growth dynamics, which differed from the n-ZnO/p-NiO heterojunctions growth dynamics. These results prove that annealing temperature plays a key role in the n-ZnO/p-ZnO homojunctions and n-ZnO/p-NiO heterojunctions structure, surface morphology, and vertical growth dynamics.

ITO:n-ZnO:p-NiO and ITO:n-ZnO:p-NZO thin films: Study of crystalline structures, surface statistical metrics, and optical properties.

The article presents results on fabrication and characterization of transparent, oxide-based junction diodes on quartz substrates. The devices are made by radio frequency magnetron sputtering in the form of sandwich structures: ITO:n-ZnO:p-NiO (homojunction) and ITO:n-ZnO:p-NZO (heterojunction). The microstructure, crystalline structure, and micromorphology features of deposited samples are studied by means of X-ray diffraction, Atomic Force Microscopy, and Scanning Electron Microscopy. Obtained results are used to derive statistical, fractal and functional surface characteristics that exhibited secondary alignment patterns. Apart from that, optical and electrical measurements are carried out as well. Optical transmittance peaked at 80% in visible range, but substantially increased after annealing. Due to structural differences, heterojunction was found to follow linear current-voltage dependence specific of ohmic contacts, whereas homojunction was found to follow non-linear characteristics as in junction diode.

Advanced microstructure, morphology and CO gas sensor properties of Cu/Ni bilayers at nanoscale.

In this study, we investigated the morphology of synthesized Cu/Ni nanoparticles in trace of carbon sources by the co-deposition process of RF sputtering and RF-PECVD methods and localized surface plasmon resonance of CO gas sensing of Cu/Ni nanoparticles. The surface morphology was studied by analyzing 3D micrographs of atomic force microscopy using image processing techniques and fractal/multifractal analyses. The MountainsMap® Premium software with the two-way ANOVA (Variance analysis) and least-significant differences tests were used for statistical analysis. The surface nano-patterns have a local and global particular distribution. Experimental and simulated Rutherford backscattering spectra confirm the quality of nanoparticles. Then, prepared samples were exposed to CO gas flue to study their gas sensor application using the localized surface plasmon resonance method. Increasing the Ni layer over Cu one shows an interesting result in both morphology and gas sensing sides. Advanced stereometric analyses for the surface topography of thin films in conjunction with Rutherford backscattering spectrometry and Spectroscopic analysis make a unique study in the field.

Surface dynamics, fractal features, and micromorphology analysis of kefir biofilms.

We introduce a study of image analysis of kefir biofilms associated with Acai extract prepared by fermentation of fresh kefir grains natural. Atomic force microscopy data were studied, aiming to understand how the concentration of acai berry (Euterpe oleracea Mart.) influences the surface morphology as well as the texture complexity, evaluated by the fractal dimension. The results showed that the superficial morphology was affected by the increase of Acai concentration in the biofilms, as well as the fractal dimension. It has also been observed that the surface of the biofilm presented saturation when concentration changes from 40 to 60 ml. On the other hand, it was observed that the intermediate sample produced with 20 ml of acai berry seems to be the best point for biofilms production that can serve as a skin dressing since other studies related to mechanical properties and in vitro and in vivo tests can confirm this applicability. Thus, the characterization of the surface morphology of kefir biofilms by the evaluation of surface statistical parameters and fractal geometry may provide promising results regarding the applicability of these films. RESEARCH HIGHLIGHTS: We characterized the structural complexity of the 3-D surface of the kefir biofilms associated with açaí extract. The 3-D surface analysis of the samples was performed using an atomic force microscope operating in contact mode. We determined the stereometric and fractal dimension of the analyzed samples.

Topographic Characterization of Cu-Ni NPs @ a-C:H Films by AFM and Multifractal Analysis.

In the present work three-dimensional (3-D) surface topography of Cu-Ni nanoparticles in hydrogenated amorphous carbon (Cu-Ni NPs @ a-C:H) with constant thickness of Cu and three thicknesses of Ni prepared by RF-Plasma Enhanced Chemical Vapor Deposition (RF-PECVD) system were investigated. The thin films of Cu-Ni NPs @ a-C:H with constant thickness of Cu and three thicknesses of Ni deposited by radio frequency (RF)-sputtering and RF-PECVD systems, were characterized. To determine the mass thickness and atomic structure of the films, the Rutherford backscattering spectroscopy (RBS) spectra was applied. The absorption spectra were applied to study localized surface plasmon resonance (LSPR) peaks of Cu-Ni NPs (observed around 608 nm in visible spectra), which is widened and shifted to lower wavelengths as the thickness of Ni over layer increases, and their changes are also evaluated by the 3-D surface topography. These nanostructures were investigated over square areas of 1 µm × 1 µm using atomic force microscopy (AFM) and multifractal analysis. Topographic characterization of surface samples (in amplitude, spatial distribution, and pattern of surface characteristics) highlighted 3-D surfaces with multifractal features which can be quantitatively estimated by the multifractal measures. The 3-D surface topography Cu-Ni NPs @ a-C:H with constant thickness of Cu and three thicknesses of Ni prepared by RF-PECVD system can be characterized using the multifractal geometry in correlation with the surface statistical parameters.