Bioactive glasses are known for their surface reactivity and ability to bond with bone tissue through the formation of hydroxyapatite. This study investigates the effects of substituting ultrapure water with natural geothermal waters from the Azores in the sol–gel synthesis of 45S5 and MgO-modified bioglasses. Using high-resolution X-ray photoelectron spectroscopy (XPS), we examined how the mineral composition of the waters influenced the chemical environment and network connectivity of the glass surface. The presence of trace ions, such as Mg²⁺, Sr²⁺, Zn²⁺, and B³⁺, altered the silicate structure, as evidenced by binding energy shifts and peak deconvolution in O 1s, Si 2p, P 2p, Ca 2p, and Na 1s spectra. Thermal treatment further promoted polymerization and reduced hydroxylation. Our findings suggest that mineral-rich waters act as functional agents, modulating the reactivity and structure of bioactive glass surfaces in eco-sustainable synthesis routes.

This study investigates the structural and electronic transitions of sol–gel derived titanium dioxide (TiO₂) thin films using vacuum ultraviolet (VUV) spectroscopy, to elucidate the impact of annealing-induced phase evolution. As the annealing temperature increased from 400 °C to 800 °C, the films transitioned from amorphous to anatase, mixed anatase–rutile, and finally rutile phases. VUV spectroscopy revealed distinct absorption features: a high-energy σ → π* transition below 150 nm, associated with bonding to antibonding orbital excitations, and lower-energy absorption bands in the range 175–180 nm and near 280 nm, attributed to π → π* and t_2g(π) → t*_2g(π*) transitions, respectively. These spectral features highlight the material’s intrinsic electronic states and defect-related transitions. A slight redshift of the absorption band from 176 nm to 177 nm with annealing reflects bandgap narrowing, attributed to increased rutile content, crystallite growth, and defect-induced effects. Broadening and additional absorption features around 280 nm were attributed to oxygen vacancies and reduced titanium oxidation states (Ti³⁺), as corroborated by X-ray photoelectron spectroscopy (XPS). XPS further confirmed the presence of Ti³⁺ species and oxygen vacancies, providing complementary evidence of defect-mediated transitions observed in the VUV spectra. While complementary techniques such as X-ray diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR) confirmed phase transitions and the reduction of hydroxyl groups, respectively, VUV spectroscopy uniquely captured the dynamic interplay between structural defects, phase evolution, and optical properties. This study underscores the utility of VUV spectroscopy as a powerful tool for probing the electronic structure of TiO₂ films, offering insights critical for tailoring their functional properties in advanced applications.

TiO₂ thin films of about 50, 100, and 150 nm thicknesses and their n-TiO₂/p-Si heterojunctions (HJs) were prepared by physical evaporation of TiO₂ powders. The role of thickness on the electrical properties of the HJ diodes and the optical properties of the films were compared. The morphological roughness and granularity of the films were determined by the SEM imaging. UV–vis spectroscopy of the films showed that the optical transmittance and bandgap values decreased with increasing thickness, whilst the refractive index, extinction coefficient, and Urbach energy increased. The 50 nm thick TiO₂ thin film has a relatively high FOM value of 7.99 × 10^–5 Ω⁻¹. Electrical characteristics of the HJs were studied by current–voltage (I–V), and capacitance/conductance–voltage (C/G–V) measurements with the thickness variable. Important diode parameters of the HJs such as ideality factor ( $$n$$ n ), barrier height (ϕ_b), series resistance ( $${R}_{\text{s}}$$ R s ), interface state density ( $${N}_{\text{ss}}$$ N ss ), built-in potential ( $${V}_{\text{bi}}$$ V bi ), and acceptor density ( $${N}_{\text{A}})$$ N A ) were calculated. The n and ϕ_b of the HJs were determined by the I–V method to be 2.27, 2.48, 2.11 and 0.61, 0.55, 0.58, respectively. The ϕ_b values obtained from the C–V properties were 0.73, 0.62 and 0.64, respectively, which were higher than those obtained from the I–V method and decreased with thickness. The $${N}_{\text{ss}}$$ N ss of the HJs, calculated by the I–V approach are 2 × 10¹⁷, 3.33 × 10¹⁷ and 1.09 × 10¹⁸ eV⁻¹cm⁻², respectively. The capacitance–voltage/frequency (C–V/F), conductance–voltage/frequency (G–V/F), and impedance–frequency (Z–F) characteristics of the HJs were investigated as a function of TiO₂ layer thickness. All measurements showed that the optical and electrical properties of the films and HJs are affected by the thickness of the TiO₂ layer, and that the thinner one (~ 50 nm) may be suitable for optoelectronic device designs.

This study investigates the rheological behavior of cellulose microfiber suspensions derived from kahili ginger stems (Hedychium gardnerianum), an invasive species, in two adhesive matrices: a commercial water-based adhesive (Coplaseal^®) and a casein-based adhesive made from non-food-grade milk, referred to as K and S samples, respectively. Rheological analyses were performed using oscillatory and rotational shear tests conducted at 25 °C, 50 °C, and 75 °C to assess the materials’ viscoelastic properties more comprehensively. Oscillatory tests across a frequency range of 1–100 rad/s assessed the storage modulus (G′) and loss modulus (G″), while rotational shear tests evaluated apparent viscosity and shear stress across shear rates from 0.1 to 1000 s⁻¹. Fiber-free samples consistently showed lower moduli than fiber-containing samples at all frequencies. The incorporation of fibers increased the dynamic moduli in both K and S samples, with a quasi-plateau observed at lower frequencies, suggesting solid-like behavior. This trend was consistent in all tested temperatures. As frequencies increased, the fiber network was disrupted, transitioning the samples to fluid-like behavior, with a marked increase in G′ and G″. This transition was more pronounced in K samples, especially above 10 rad/s at 25 °C and 50 °C, but less evident at 75 °C. This shift from solid-like to fluid-like behavior reflects the transition from percolation effects at low frequencies to matrix-dominated responses at high frequencies. In contrast, S samples displayed a wider frequency range for the quasi-plateau, with less pronounced moduli changes at higher frequencies. At 75 °C, the moduli of fiber-containing and fiber-free S samples nearly converged at higher frequencies, indicating similar effects of the fiber and matrix components. Both fiber-reinforced and non-reinforced suspensions exhibited pseudoplastic (shear-thinning) behavior. Fiber-containing samples exhibited higher initial viscosity, with K samples displaying greater differences between fiber-reinforced and non-reinforced systems compared to S samples, where the gap was narrower. Interestingly, S samples exhibited overall higher viscosity than K samples, implying a reduced influence of fibers on the viscosity in the S matrix. This preliminary study highlights the complex interactions between cellulosic fiber networks, adhesive matrices, and rheological conditions. The findings provide a foundation for optimizing the development of sustainable biocomposites, particularly in applications requiring precise tuning of rheological properties.

The morphology of solid surfaces encodes fundamental information about the physical mechanisms that govern their formation. Here, we reinterpret scanning electron microscopy (SEM) micrographs of oxide thin films as two-dimensional self-affine morphology fields (not height-metrology) and analyze them using a multiscale statistical-physics framework that integrates spectral, multifractal, geometric, and topological descriptors. Fourier-based power spectral density (PSD) provides the spectral slope $\beta$ and apparent Hurst exponent $H$, while multifractal scaling yields the information dimensions $D_q$, the singularity spectrum $f\left(\alpha \right)$, and its width $\mathsf{\Delta }\alpha$, which quantify scale hierarchy and intermittency. Lacunarity captures intermediate-scale heterogeneity, and Minkowski functionals—especially the Euler characteristic $\chi \left(\theta \right)$—probe connectivity and identify the onset of a percolation-like network structure. Two representative surfaces with contrasting morphologies are used as model systems: one exhibiting an anisotropic, porous, strongly multifractal structure with fragmented domains; the other showing a compact, nearly isotropic, and nearly monofractal organization. The porous surface/topography displays steep PSD decay, broad multifractal spectra, and positive $\chi$, consistent with a sub-percolated, diffusion-limited, Edwards–Wilkinson-like (EW-like) growth regime. Conversely, the compact surface/topography exhibits gentler spectral slopes, narrower $f\left(\alpha \right)$, enhanced lacunarity at intermediate scales, and a $\chi \left(\theta \right)$ zero-crossing indicative of a connectivity transition where a surface becomes a percolating network, consistent with a Kardar–Parisi–Zhang-like (KPZ-like) correlated growth regime. These results demonstrate that individual SEM micrographs encode quantitative fingerprints of nonequilibrium universality classes and topology-driven transitions from fragmented surfaces to connected networks, showing that SEM intensity maps can serve as a quantitative probe for testing theories of rough surfaces and kinetic growth in experimental thin-film systems.