Surfaces, Volume 8, Issue 2 (June 2025) – 17 articles

Porous PZT films offer significant potential due to tunable electromechanical properties, yet the polarization behavior remains insufficiently understood because of discontinuous morphology and domain structures. In this work, we study the impact of porosity on the spontaneous polarization and electromechanical response of PZT thin films fabricated using a multilayer spin-coating technique with various concentrations (0–14%) of polyvinylpyrrolidone (PVP) as a porogen. Atomic force microscopy (AFM) and piezoresponse force microscopy (PFM) were employed to analyze the local topography, domain distribution, and polarization behavior of the films. The results indicate that increasing porosity leads to substantial changes in grain morphology, dielectric permittivity, and polarization response. Films with higher porosity exhibit a more fragmented polarization distribution and reduced piezoresponse, while certain orientations demonstrate enhanced domain mobility. Despite the decrease in overall polarization, the local coercive field remains relatively stable, suggesting structural stability during the local polarization switching. The findings highlight the crucial role of grain boundaries and local charge redistribution in determining local polarization behavior. Full article

Titanium thin films with thicknesses of up to 105 nm were deposited on borosilicate glass implementing low-power continuous (25 W) and pulsed (85 W, with an ultra-low duty cycle) DC magnetron sputtering. The characteristics of the resulting films were studied via atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), VIS spectroscopy, and four-point-probe measurements. Both deposition modes yield films with low surface roughness, and AFM analysis showed no topographical features indicative of columnar-and-void structures. The films exhibited high optical reflectivity and stable transmittance and reflectance across the visible spectrum. The electric resistivity could be measured even at single nanometer thickness, emphasizing the metallic character of the films and approaching the bulk titanium value at higher film thicknesses. The low power regime of magnetron sputter deposition not only offers the possibility of studying the development of physical characteristics during the growth of ultra-thin films but also provides the advantage of extremely low heat development and no evident mechanical stress on the substrate during the coating process. These results outline a path for low-power DC sputtering as a reliable approach for studying the evolution of functional properties in ultra-thin films and for the gentle fabrication of coatings where thermal stress must be avoided, making the method compatible with temperature-sensitive applications. Full article

Magnetic shape memory alloys have attracted considerable attention due to their multifunctional properties. Among these materials, Ni-Mn-Ga alloys are distinguished by their ability to achieve up to 10% strain when exposed to a magnetic field, a characteristic predominantly observed in single-crystal samples. Consequently, it is essential to develop nanomaterials with a crystal structure closely resembling that of a single crystal. In this study, an epitaxial Ni-Mn-Ga thin film was fabricated using Pulsed Laser Deposition on an Al₂O₃ $\left(11\overline{2}0\right)$ single-crystal substrate. The crystal structure was characterised through X-ray diffraction methodologies, such as symmetrical $2\theta -\omega$ scans, pole figures, and reciprocal space maps. The results indicated that the sample was mainly in a slightly distorted cubic austenite phase, and some incipient martensite phase also appeared. A detailed microstructural analysis, performed by transmission electron microscopy, confirmed that certain regions of the sample exhibited an incipient transformation to the martensite phase. Regions closer to the substrate retained the austenite phase, suggesting that the constraint imposed by the substrate inhibits the phase transition. These results indicate that it is possible to grow high crystalline quality thin films of Ni-Mn-Ga by Pulsed Laser Deposition. Full article

The combination of the catalytic properties of Al₂O_3/TiO₂ formed an efficient system to degrade the ubiquitous pollutants TPA and PET. The coating (Al₂O₃)_0.75TiO₂ was characterized by X-ray diffraction. Stainless steel disks with photo-catalyst coating were placed transversely in a 3.0 L vertical glass reactor with ascending airflow for supplying oxygen to the reaction medium and visible light lamps for photo-activation. The analysis of the coating homogeneity, morphology and particle size distribution of the TiO₂ coatings and (Al₂O₃)_0.75TiO₂ system were confirmed by SEM. Optical properties and band-gap energy were calculated by using the Tauc equation. UV–Vis spectrophotometry (UV–Vis) and chemical oxygen demand (COD) were the quantitative techniques to measure the reduction in the initial TPA and PET concentrations. Full article

In this study, polymer films based on the inorganic sorbents Al₂O₃, ZrO₂ and SiO₂-phenyl with repellent N,N-diethyl-3-methylbenzamide were prepared and used as functional textile coatings. The high sorption activity of oxides with respect to N,N-diethyl-3-methylbenzamide (63–239 mg/g) allows for the use of these compounds as repellent carrier materials, and their mixture with polyacrylates allows for the formation of functional coatings–polymer films. Scanning electron microscopy and Fourier transform infrared spectroscopy results revealed that the inorganic sorbents Al₂O₃, ZrO₂ and SiO₂-phenyl were successfully anchored in the polyacrylate structure, and the FTIR spectra confirmed the presence of repellent molecules. The thermal diffusion parameters of N,N-diethyl-3-methylbenzamide were also calculated via thermogravimetric analysis and high-performance liquid chromatography with diode array detection. The highest thermal diffusion rates and concentrations were observed for the material with Al₂O₃ (up to 148.3∙10⁻⁹ mol at 200 °C), and lower values for ZrO₂ and SiO₂-phenyl (up to 15.2∙10⁻⁹ mol and 34.3∙10⁻⁹ mol at 200 °C, respectively). The heat flux parameter J_f was also calculated according to Onsager’s theory and Fourier’s law. The release of repellent from polymeric materials can be achieved by applying less heat than that required to reach the boiling point of N,N-diethyl-3-methylbenzamide. Full article

The main goal of the present study was to verify in detail whether the use of a cluster model for Stone–Wales (SW) defect-containing graphene (SWG) to study the adsorption of Ln atoms yields results similar to those previously obtained by employing a periodic model. We addressed this question by analyzing the optimized geometries of SWG + Ln complexes, their formation energies, and selected electronic parameters (in particular, the frontier orbital energies and atomic charges and spins). Within the frame of density functional theory, we used the computational methodology of the PBE-D2/DNP theoretical level using ECP pseudopotentials. The most important conclusion is that the use of a cluster model gives qualitatively similar results to those of the periodic model. While the corresponding plots of the dihedral angles θ versus the Ln atoms differ considerably, the two models have many common features in the trends of the bonding strength despite the use of two very different theoretical tools, namely periodic (plane waves) versus cluster calculations (localized basis sets). In comparing the results for SW defect-free and SW defect-containing cluster models, it is evident that SW defects serve as much more preferential adsorption sites compared to the conditions in the defect-free graphene model. Full article

The surface diffusion flux is known to dominate mass transport within many amorphous porous materials, used as adsorbents, heterogeneous catalysts, and membranes, employed in many chemical processes. However, while the impact of surface coverage has been widely studied and reviewed, relatively little attention has been paid to the impact of surface geometric and energetic heterogeneity on the surface diffusion rate, which would inform intelligent materials selection. It was, thence, the aim of this work to survey studies of the impact of surface structure on surface diffusion. Since the so-called “maximally realistic” modelling approach is found to be infeasible, due to limitations on the degree of structural characterisation possible for complex disordered surfaces, and the level of detail and length scales it is possible to represent with current computing power, a range of alternative approaches have been adopted. It has been seen that the Galilean idealisation of atomistic models has rendered them sufficiently tractable in order to study the impact of certain surface features, such as traps or ruts, on surface diffusion. Theoretical justifications have been used to develop minimalist models of amorphous surfaces, and mass transport thereon, that do selectively include the key surface parameters, and have, therefore, been successfully empirically validated for a range of different surfaces and adsorbate types. Full article

In this study, we detailed the fabrication and characterization of photovoltaic structures based on PTB7:ICBA (1:1, wt.%) bulk-heterojunction on optical glass substrates by spin-coating. Some samples were deposited on a flat substrate, and others were placed on a patterned substrate obtained by nano-imprinting lithography; the induced effects were analyzed. We demonstrated that using a patterned substrate enhanced the maximum output power, primarily because the short-circuit current density increased. This can be considered a direct consequence of reduced optical reflection and improved optical absorption. The topological parameters evaluated by atomic force microscopy, namely, the root mean square, Skewness, and Kurtosis, had small values of around 2 nm and 1 nm, respectively. This proves that the mixture of a conductive polymer and a fullerene derivative creates a thin film network with a high flatness degree. The samples discussed in this paper were fabricated and characterized in air; we can admit that the results are encouraging, but further optimization is needed. Full article

Ionic liquids (ILs) have been explored as a way of improving the performance of ZnO-based optoelectronic devices; however, there are few fundamental studies of the IL/ZnO interface. Here, the adsorption of the IL 1-octyl-3-methylimidazolium tetrafluoroborate [C₈C₁Im][BF₄] on ZnO (0001) and ZnO ($10\overline{1}0$) has been studied using synchrotron-based soft X-ray photoelectron spectroscopy. The results indicate that [C₈C₁Im][BF₄] is deposited intact on the ZnO (0001) surface; however, there is some dissociation of [BF₄]⁻ anions, resulting in boron atoms attaching to the oxygen atoms in the ZnO surface and forming B₂O₃. In contrast, the deposition of [C₈C₁Im][BF₄] on the ZnO ($10\overline{1}0$) surface at −150 °C results in the appearance of more chemical environments in the spectra. We propose that the high temperature of the IL evaporator causes some conversion of [C₈C₁Im][BF₄] to a carbene–borane adduct, resulting in the deposition of both the IL and adduct onto the ZnO surface. The adsorption and desorption of the analogous IL 1-butyl-3-methylimidazolium tetrafluoroborate [C₄C₁Im][BF₄] was investigated on ZnO (0001) using synchrotron-based soft X-ray photoelectron spectroscopy. The results indicate that [C₄C₁Im][BF₄] is deposited largely intact at −150 °C and forms islands when heated to room temperature. When heated to over 80 °C, it begins to react with the ZnO surface and decomposes. This is a much lower temperature than the long-term thermal stability of the pure IL, quoted in the literature as ~400 °C, and of IL on powdered ZnO, quoted in the literature as ~300 °C. This indicates that the ZnO surface may catalyse the thermal decomposition of [C₄C₁Im][BF₄] at lower temperatures. This is likely to have a negative impact on the potential use of ILs in ZnO-based photovoltaic applications, where operating temperatures can routinely reach 80 °C. Full article

Enzymatic catalysis has gained significant attention in green chemistry due to its high specificity and efficiency under mild conditions. However, challenges related to enzyme immobilization and spatial control often limit its practical applications. In this work, we report a Marangoni flow-driven strategy to fabricate a biomimetic jellyfish-like hydrogel with tunable tentacle-like structures. The formation process occurs entirely in an aqueous system without organic solvents or post-treatment, enabling the construction of ultra-thin, free-standing hydrogels through spontaneous interfacial self-assembly. The resulting structure exhibits high surface-area geometry and excellent biocompatibility, providing a versatile platform for localized enzyme loading. This method offers a simple and scalable route for engineering soft materials with complex morphologies, and expands the design space for bioinspired hydrogel systems. Full article

The invasive presence of nanoplastics in various ecosystems makes them a significant environmental problem nowadays. One of the main production mechanisms of nanoplastics is mechanical wear. The combination of friction, abrasion, and shear forces can indeed lead to the progressive fragmentation of polymeric materials. The high surface area–volume ratio of the resulting nanoparticles not only alters the physicochemical properties of the polymers but also leads to increased interaction with biological systems, which raises questions about the persistence of nanoplastics in the environment and their potential toxicity. Despite the growing body of research on microplastics, studies specifically addressing the formation, characterization, and impact of wear-induced nanoplastics remain limited. This article describes current research on the formation mechanisms of nanoplastics generated by mechanical wear, highlighting the tribological processes underlying their release. Advanced characterization techniques used to identify the morphology and composition of these particles are also mentioned. The techniques include atomic force microscopy (AFM), scanning electron microscopy (SEM), and, to some extent, Raman spectroscopy. In the case of AFM, an example of application to the extrusion of nanoplastics from polystyrene surfaces subjected to repeated nanoscratching is also provided. Full article

Environmental humidity is a determining factor in the degradation of concrete structures, particularly in the corrosion process of reinforcement bars. This study analyzed four concrete mixtures with different mucilage contents replacing mixing water: 0, 5, 10, and 15%. Two sets of specimens were fabricated and subjected to a 420-day test period under two different working conditions: natural environmental conditions and high-humidity conditions. Open-circuit potential parameters were analyzed to compare the behavior of the mixtures and determine the corrosion rate. It was observed that under environmental conditions, the mixtures with 0% and 15% mucilage exhibited higher corrosion rates, with values of 0.046 and 0.049 mm/year, respectively, compared to the mixtures with low mucilage additions of 5% and 10%, which showed values of 0.041 and 0.038 mm/year, respectively. The corrosion rates of the mixtures under high-humidity conditions were 0.010 for M0, 0.009 for M1 and M2, and 0.014 for M3. The results indicate that mixtures with 5% and 10% mucilage show better corrosion protection, suggesting that this approach could be a sustainable, low-cost solution to enhance the durability of concrete structures, particularly in coastal areas with high humidity levels. It is concluded that adding nopal mucilage in low concentrations as a substitute for mixing water in concrete formulations not only modifies the properties of concrete, but also reduces the corrosion rate of reinforcement steel under high-humidity conditions, thereby extending the service life of constructions. Full article

Platinum exhibits essential characteristics for enhancing electrochemical processes, but the use of electrodes made entirely of Pt is not cost-effective. A more affordable alternative is electrodepositing Pt black on accessible metallic surfaces, such as brass, to ensure that the electrodes are both resistant to corrosive environments and possess catalytic capabilities. Pourbaix and kinetic analyses were performed to establish the optimal potential and current conditions for electrodepositing Pt black on brass utilizing a Pb-free Pt solution. The Pourbaix analysis indicated that Pt electrodeposition is achieved from the PtCl₆⁻ ionic species and occurs before hydrogen evolution. Kinetic studies further revealed that Pt black nanoscale deposition on a brass surface requires mechanical surface treatment and electrochemical polishing, followed by metallic Pt electrodeposition under potentiostatic control at −295 mV vs. SCE. Subsequent Pt black deposition was achieved under galvanostatic control at −500 A cm⁻². Scanning electron microscopy (SEM) and X-ray diffraction (XRD) confirmed the formation of nanostructures of metallic Pt and Pt black on brass, with the latter presenting a larger surface area to enhance the active sites for catalysis in electrochemical processes. Full article

In this study, we report a green, one-step synthesis of fluorescent carbon quantum dots (PET-FCQDs) derived from polyethylene terephthalate (PET) waste using an environmentally friendly pyrolytic method. The PET-FCQDs were systematically characterized using techniques such as UV-Vis spectroscopy, fluorescence spectroscopy, ATR-FTIR, TGA, and fluorescence microscope, confirming their nanoscale size (2–50 nm), rich functional groups and thermal stability. Thermal stability and dynamics evaluated by the Coats–Redfern method showed endothermic reactions with an activation energy of 88.84–125.05 kJ/mol. Density functional theory studies showed a binding energy, highest occupied molecular orbital, lowest unoccupied molecular orbital, and energy gap of −675.39, −5.23, −5.07, and 0.17 eV, respectively. The as-synthesized PET-FCQDs demonstrated excellent optical properties with quantum yield ($\Phi$) of 49.6% and were applied as a dual-mode fluorescent sensing probe for the detection of Pd²⁺, ciprofloxacin (CIP), and fluoxetine (FLX) in aqueous systems via fluorescence quenching and enhancement mechanisms. For Pd²⁺, the fluorescence emission intensity at 470 nm was quenched proportionally to the increasing concentration, while CIP and FLX induced fluorescence enhancement. The Stern–Volmer analysis confirmed strong interaction between the analytes and PET-FCQDs, distinguishing dynamic quenching for Pd²⁺ and static interactions for CIP and FLX. The method exhibited linear detection ranges of 1–10 mg/L for Pd²⁺, 50–150 µg/L for CIP, and 100–400 ng/L for FLX, with corresponding limits of detection (LOD) of 1.26 mg/L, 3.3 µg/L, and 134 ng/L, respectively. Recovery studies in spiked tap water and river water samples demonstrated the practical applicability of PET-FCQDs, although matrix effects were observed, particularly for FLX. This work not only highlights a sustainable route for PET waste upcycling but also demonstrates the potential of PET-FCQDs as cost-effective, sensitive, and versatile fluorescent probes for environmental monitoring of heavy metal ions and pharmaceutical pollutants. Further optimization of the sensing platform could enhance its selectivity and performance in real-world applications. Full article

Polypyrrole (PPy) is cationic in its conducting form, requiring a charge-balancing counterion, or dopant. The release of bioactive dopants, driven by the reduction of PPy films, offers a route to controlled drug delivery. Thiol-terminated long chain poly (ethylene glycol) (PEG) reacts with a dodecylbenzene sulfonate (DBSA)-doped PPy, forming a dense overlayer and partially liberating DBSA via the chemical reduction of the film. The resulting PEG brush acts as a barrier to dopant diffusion from the film, but proteins have been shown to disrupt this layer, releasing the DBSA. The mechanism by which this disruption occurs has not been thoroughly investigated. In this study, dopant release from PEG-PPy composites was examined via systematic exposure to a variety of chemical stimuli, including macromolecules such as poly (ethylene imine), polyethylene glycol, and poloxamers, as well as small-molecular-weight alcohols, carboxylic acids, and amines. Dopant release was quantified by quartz crystal microbalance. Poly (ethylene imine) efficiently released DBSA, while anionic and uncharged macromolecules did not. All classes of small molecules triggered dopant release, with longer homologues magnifying the response. The mechanisms of dopant removal are dependent on the functional groups of the stimulating agent and include ion exchange and nucleophilic reduction of the polycationic backbone. Tosylate, salicylate, and penicillin dopants showed release behaviors similar to DBSA, demonstrating the generality of the PEG barrier. Full article

The realization of novel electronic devices based on 2D materials, i.e., field-effect transistors, has recently stimulated a renewed interest regarding ultrathin fluoride epitaxial films. Thanks to their chemical and dielectric properties, ionic fluorides could have the potential to be used as insulators in many applications that require high processing control down to the nanoscale. Here we provide a review of some of the principal results that have been achieved in the past decades regarding the controlled growth of epitaxial fluorides on different types of materials relevant for electronics. The aim is to provide a concise summary of the growth modes, crystallinity, film morphologies, and chemical interactions of different types of fluorides on different type of substrates, highlighting the possibilities of applications and the future perspectives. Full article

Green diesel is a high-quality biofuel obtained through the transformation of triglycerides into linear alkanes. In order to obtain green diesel, this study investigates the impact of impregnation pH on the surface species of NiMo/Al₂O₃ catalysts in the hydroprocessing of soybean oil. NiMo catalysts supported on Al₂O₃ were synthesized at different pH values (pH = 7 and 9). In the oxide state, solids were characterized by UV-Vis diffuse reflectance, Raman, and FT-IR spectroscopies, and, in the sulfide state, they were characterized by HR-TEM. The results show that the pH of impregnation significantly determines the surface species formed. An impregnation at pH = 7 favors the formation of Ni²⁺_(Oh) and Ni²⁺_(Oh-dis) interacting with non-crystalline molybdenum trioxide, while the formation of Ni²⁺/Al₂O₃, Ni_2+(Oh-dis), and MoO₃ species is favored at pH = 9. These surface species play a fundamental role in the hydrogenolysis and deoxygenation steps. Catalyst impregnated at pH = 7 shows higher activity due to the formation of shorter MoS₂ slabs. This study emphasized the importance of controlling impregnation conditions for optimizing catalyst performance. Full article