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Surfaces

Surfaces is an international, peer-reviewed, open access journal on all aspects of surface and interface science published quarterly online by MDPI.

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Prof. Dr. Gaetano Granozzi

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All Articles (377)

Article

When a Surface Becomes a Network: SEM Reveals Hidden Scaling Laws and a Percolation-like Transition in Thin Films

Helena Cristina Vasconcelos,
Telmo Eleutério and
Reşit Özmenteş
+ 1 author

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 $β$ and apparent Hurst exponent $H$ , while multifractal scaling yields the information dimensions $D_{q}$ , the singularity spectrum $f (α)$ , and its width $Δ α$ , which quantify scale hierarchy and intermittency. Lacunarity captures intermediate-scale heterogeneity, and Minkowski functionals—especially the Euler characteristic $χ (θ)$ —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 $χ$ , consistent with a sub-percolated, diffusion-limited, Edwards–Wilkinson-like (EW-like) growth regime. Conversely, the compact surface/topography exhibits gentler spectral slopes, narrower $f (α)$ , enhanced lacunarity at intermediate scales, and a $χ (θ)$ 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.

30 January 2026

$Representative analyses of the two thin-film samples. (a,e) scanning electron microscopy (SEM) micrographs of Sample A (porous, fragmented) and Sample B (compact, connected); (b,f) Isotropic power spectral density (PSD) functions S ( k ) ∼ k − β , including fitted slopes and apparent Hurst exponents; (c,g) Multifractal singularity spectra f ( α ) derived from normalized partition functions Z q ( ε ) , with widths Δα indicating intermittency; (d,h) Euler characteristic density χ(θ) as a function of threshold, showing positive χ for fragmented regimes and a zero-crossing (θ ≈ 0.53) for the connected regime. SEM panels are shown with consistent grayscale/contrast for readability; all quantitative analyses were performed on the normalized intensity field after ROI cropping and label removal. The horizontal dashed line marks χ(θ)=0, and the vertical dashed line indicates the selected threshold θ (≈0.53 in panel (h)).$

Article

Immobilization of Hydroxyapatite on the Surface of Porous Piezoelectric Fluoropolymer Implants for the Improved Stem Cell Adhesion and Osteogenic Differentiation

Alexander Vorobyev,
Igor Akimchenko and
Semen Goreninskii
+ 6 authors

Owing to their high strength characteristics, chemical stability, and piezoelectric activity, vinylidene fluoride (VDF) copolymers have become promising materials for creating implants to replace bone tissue defects. However, a significant drawback of these materials is the biological inertness of their surface, which leads to unsatisfactory integration with the patient’s bone tissue. In this study, we propose a single-step approach for immobilizing hydroxyapatite (HAp) on the surface of porous implants made of vinylidene fluoride and tetrafluoroethylene copolymer (P(VDF-TeFE)). This method consists of treating the surface of the product with a mixture of solvents while simultaneously capturing HAp microparticles. Using scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS), it was shown that the proposed method preserves the morphology of model implants (pore diameter and printed line thickness) and allows HAp to cover up to 63 ± 14% of their surface, reaching concentrations of calcium and phosphorus up to 6.0 ± 1.3 and 3.6 ± 0.7 at. %, respectively, imparting superhydrophilic properties to them. Optical profilometry revealed that the surface roughness of samples increased by more than seven times as a result of HAp immobilization. X-ray diffraction analysis (XRD) confirmed that the piezoelectric phase of P(VDF-TeFE) is preserved after treatment, as are the compressive strength characteristics of the samples. Hydroxyapatite immobilization significantly improved the adhesion and osteogenic differentiation of multipotent stem cells cultured with P(VDF-TeFE)-based samples. Thus, the proposed method can significantly enhance the biological activity of implants based on the piezoelectric VDF copolymer.

25 January 2026

SEM images of the control sample and the samples with HAp immobilized from suspensions with various concentrations (magnification ×100, magnification ×1000 in the inserts).

Article

Biosynthesis, Characterisation, and Antimicrobial Activities of Nickel-Doped Silver Nanoparticles Using Caralluma umbellata Plant Root Extract

Gundeti Bhagyalaxmi,
Kothamasu Suresh Babu and
Srinivas Ravella
+ 2 authors

Greenly synthesised Ni-doped Ag nanoparticles utilising Caralluma umbellata root extracts, and an investigation into their optical properties, biological properties, and characterisation, is the focus of the study. Characterisation was performed using FTIR analysis, UV-Vis, X-ray diffraction, and field emission scanning electron microscopy. The synthesis of Ni-doped Ag nanoparticles was confirmed through UV-Vis spectroscopy, revealing a peak at 396 nm and a band gap energy of 3.24 eV. XRD analysis revealed a face-centred cubic structure with a crystallite size of 55.22 nm (as-prepared) and 18.56 nm (annealed at 200 °C). Reduction and capping were demonstrated by FTIR, as evidenced by the presence of phytochemicals. The Ag NPs demonstrated potent antibacterial activity against both Gram-positive and Gram-negative bacteria, with a minimal inhibitory concentration of 1.25 μg/mL observed against Streptococcus mutans. Their vigorous anti-oxidant activity, as well as in vitro anti-diabetic potential through alpha-amylase and alpha-glucosidase inhibition, also proves suitable for biomedical applications.

23 January 2026

Extraction of Ni-doped Ag Nanoparticles using Caralluma umbellata root extract.

Article

On the Effective Medium Theory for Silica Nanoparticles with Size Dispersion

Feng Liu,
Yao Xu and
Xiaowei Li

Silica nanoparticles (SNPs) are pivotal in designing functional optical films, but accurately modeling their properties is hindered by the limitations of classical effective medium theories, which break down for larger particles and complex morphologies. We introduce a robust, effective medium theory that overcomes these limitations by incorporating full Mie scattering solutions, thereby accounting for size-dependent and multipolar effects. Our model is comprehensively developed for unshelled, shelled, mixed, and hollow SNPs randomly dispersed in a host medium. Its accuracy is rigorously benchmarked against 3D finite-element method simulations. This work establishes a practical and reliable framework for predicting the optical response of SNP composites, significantly facilitating the rational design of high-performance coatings, such as anti-glare layers, with minimal computational cost.

17 January 2026