Surfaces

13 pages, 4356 KiB

Open AccessArticle

Highly Reproducible Automated Tip Coater for In Situ and Operando EC-STM Measurements

by Robert Kurczak, Paulina Wira, Anna Futyma, Radosław Wasielewski and Tomasz Kosmala

Surfaces 2024, 7(4), 990-1002; https://doi.org/10.3390/surfaces7040065 - 18 Nov 2024

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High-quality, reproducible tip coatings are essential for minimizing faradaic currents in electrochemical scanning tunneling microscopy (EC-STM), especially during in situ and operando measurements. The variability inherent in manual coating methods, influenced by the operator’s skill and a lack of standardization, can lead to [...] Read more.

High-quality, reproducible tip coatings are essential for minimizing faradaic currents in electrochemical scanning tunneling microscopy (EC-STM), especially during in situ and operando measurements. The variability inherent in manual coating methods, influenced by the operator’s skill and a lack of standardization, can lead to inconsistent results, increased research costs, and a greater workload. This study introduces an Automated Tip Coater (ATC) designed to automate and standardize the tip coating process. The ATC features a tip movement system using stepper motors, a rotation module with a DC motor, and a heating block based on a soldering iron. It is controlled by an Arduino development board, supported by motor drivers, and has a user-friendly interface with an OLED display and encoder. The ATC coating mechanism includes a redesigned plate with a reduced gap size and a milled tray to precisely control the amount of insulating material applied to the tip. A fast cyclic voltammetry test in a 0.1 M HClO₄ electrolyte demonstrated that over 75% of ATC-coated tips achieved excellent insulation with leakage currents below ±50 pA—and 30% below ±10 pA—suitable for highly sensitive experiments. Further measurements with EC-STM using the newly coated tips investigated the electrochemical behavior of highly oriented pyrolytic graphite (HOPG), revealing detailed atomic structures under dynamic electrochemical conditions. The ATC significantly enhances reproducibility, reduces dependency on operator skills, and lowers research costs while improving the accuracy and reliability of EC-STM measurements. Full article

(This article belongs to the Special Issue In Situ and Operando Catalyst Characterization)

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11 pages, 1993 KiB

Open AccessArticle

Modeling the Terminal Velocity of Rising Electrocharged Microbubbles

by Roberto Pérez-Garibay, Arturo Bueno-Tokunaga, Francisco Andrés Acosta-González and Ramón Arellano-Piña

Surfaces 2024, 7(4), 979-989; https://doi.org/10.3390/surfaces7040064 - 8 Nov 2024

Viewed by 388

Abstract

The generation of electrocharged microbubbles is very important for several separation processes (e.g., water treatment, paper industry, and mineral processing). However, their rising terminal velocities are not fully understood. This work presents a laboratory study of the terminal velocity of single microbubbles (bubble [...] Read more.

The generation of electrocharged microbubbles is very important for several separation processes (e.g., water treatment, paper industry, and mineral processing). However, their rising terminal velocities are not fully understood. This work presents a laboratory study of the terminal velocity of single microbubbles (bubble diameter (

D_{b}

) < 100 µm) rising in stagnant aqueous solutions with different pH levels (from 2 to 12) and reagent types (frother and collector; 30 ppm). The measurements were compared with the respective predicted velocities computed from the Stokes and Hadamard–Rybczynski models. It was found that the terminal velocities of electrocharged microbubbles were larger than the respective predictions from the Stokes equation. A regression equation was proposed to predict the terminal velocity as a function of the bubble diameter, which showed considerable dispersion depending on the type of reagent adsorbed on its surface, the concentration of these reagents, and the physical characteristics that the boundary layer acquires by modifying the zeta potential of the microbubbles; this effect has not yet been addressed in the literature. Full article

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10 pages, 4340 KiB

Open AccessArticle

Study on the Thermal Control Performance of Mg-Li Alloy Micro-Arc Oxidation Coating in High-Temperature Environments

by Wentao Zhang, Shigang Xin, Qing Huang and Haiyang Jiao

Surfaces 2024, 7(4), 969-978; https://doi.org/10.3390/surfaces7040063 - 8 Nov 2024

Viewed by 583

Abstract

This paper reports on the successful preparation of a low absorption–emission thermal control coating on the surface of LAZ933 magnesium–lithium alloy using the micro-arc oxidation method. This study analyzed the microstructure, phase composition, and thermal control properties of the coating using Scanning Electron [...] Read more.

This paper reports on the successful preparation of a low absorption–emission thermal control coating on the surface of LAZ933 magnesium–lithium alloy using the micro-arc oxidation method. This study analyzed the microstructure, phase composition, and thermal control properties of the coating using Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), UV–visible near-infrared spectroscopy (UV-VIS-NIR) and infrared emissivity measurements. The results indicate that the hemispherical emissivity of the coating remains unaffected with an increase in temperature and holding time, while the solar absorption ratio gradually increases. The thermal control performance of the coating after a high-temperature experiment was found to be related to the diffusion of the Li metal element in the magnesium lithium alloy matrix, as determined by X-ray photoelectron spectroscopy (XPS), flame graphite furnace atomic absorption spectrometry (GFAAS) and Glow Discharge Optical Emission Spectroscopy (GD-OES). As the holding time is extended, the coating structure gradually loosens under thermal stress. The Li metal element in the substrate diffuses outward and reacts with O₂, H₂O and CO₂ in the air, forming LiO₂, LiOH, Li₂CO₃ and other products. This reaction affects the coating’s solar absorption ratio in the end. Full article

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18 pages, 3903 KiB

Open AccessArticle

A Comprehensive Approach to Optimization of Silicon-Based Solar Cells

by Nikolay Chuchvaga, Nazira Aubakirova, Nurlan Tokmoldin, Vasiliy Klimenov and Danil W. Boukhvalov

Surfaces 2024, 7(4), 951-968; https://doi.org/10.3390/surfaces7040062 - 5 Nov 2024

Viewed by 483

Abstract

In this work, we report a detailed scheme of computational optimization of solar cell structures and parameters using PC1D and AFORS-HET codes. Each parameter’s influence on the properties of the components of heterojunction silicon-based solar cells (HIT) has been thoroughly examined. The proposed [...] Read more.

In this work, we report a detailed scheme of computational optimization of solar cell structures and parameters using PC1D and AFORS-HET codes. Each parameter’s influence on the properties of the components of heterojunction silicon-based solar cells (HIT) has been thoroughly examined. The proposed approach follows a stringent sequence of steps to optimize various parameters of the studied HITs. Furthermore, we have revealed the effects of the metal-semiconductor contact, and a model of a photocell with an ohmic contact and a Schottky contact has been simulated. The optimal model of HIT for available materials has been proposed and fabricated based on the results of these simulations. A comparison of predicted and measured performance unequivocally demonstrates the efficiency of the proposed scheme in developing silicon-based HITs, providing reassurance about its practical application. Full article

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13 pages, 15943 KiB

Open AccessArticle

Studying the Photoactivity of Ag-Decorated TiO₂ Nanotubes with Combined AFM and Raman Spectroscopy

by Manjunath Veeranna Shinnur, Marco Menegazzo, Gianlorenzo Bussetti, Lamberto Duò, MariaPia Pedeferri and Maria Vittoria Diamanti

Surfaces 2024, 7(4), 938-950; https://doi.org/10.3390/surfaces7040061 - 2 Nov 2024

Viewed by 738

Abstract

The drive for the development of systems that can simultaneously investigate chemical and morphological information comes from the requisite to fully understand the structure and chemical reactivity relationships of materials. This is particularly relevant in photocatalysis, a field ruled by surface interactions. An [...] Read more.

The drive for the development of systems that can simultaneously investigate chemical and morphological information comes from the requisite to fully understand the structure and chemical reactivity relationships of materials. This is particularly relevant in photocatalysis, a field ruled by surface interactions. An in-depth understanding of these complex interactions could lead to significant improvements in materials design, and consequently, in photocatalytic performances. Here, we present a first approach to a combined atomic force microscopy (AFM) and Raman spectroscopy characterization of anodic TiO₂ nanotubes arrays decorated with Ag nanoparticle electrodeposition from either the same anodizing organic electrolyte or from an aqueous one. Photocatalytic substrates were used in up to 15 consecutive photocatalysis tests to prove their possible deterioration with reuse. Sample aging can, in principle, produce changes in both the morphology and the chemical compounds that characterize the photocatalyst surface. Adopting multiple characterization techniques, such as a combination of AFM and Raman spectroscopy in an original setup, can profitably enable the observation of surface contamination. A significant drop in photocatalytic activity was observed after 10 cycles on samples where silver was deposited from the organic electrolyte, while the others remained stable. Such a drop was ascribed to photocatalyst deactivation. While in other cases, a simple recovery treatment allowed the initial photoactivity to be restored, this deactivation was not restored even after chemical and thermal cleaning treatments. Full article

(This article belongs to the Special Issue In Situ and Operando Catalyst Characterization)

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18 pages, 17356 KiB

Open AccessArticle

A Study of the Features of Coating Deposition on a Carbide Substrate Using Preliminary Etching with Glow-Discharge Plasma

by Sergey Grigoriev, Marina Volosova, Yuri Bublikov, Catherine Sotova, Filipp Milovich, Anton Seleznev, Ilya Shmakov and Alexey Vereschaka

Surfaces 2024, 7(4), 920-937; https://doi.org/10.3390/surfaces7040060 - 2 Nov 2024

Viewed by 479

Abstract

The properties of coatings obtained using two surface preparation methods were compared: heating and etching by ion bombardment with plasma generation by arc evaporators and heating and etching by a glow discharge. A Ti-TiN-(Ti,Cr,Al)N coating was deposited. The use of a glow discharge [...] Read more.

The properties of coatings obtained using two surface preparation methods were compared: heating and etching by ion bombardment with plasma generation by arc evaporators and heating and etching by a glow discharge. A Ti-TiN-(Ti,Cr,Al)N coating was deposited. The use of a glow discharge provides better resistance of the coating to destruction during the scratch test and wear resistance of metal-cutting tools when turning steel. As the cutting speed increases, the advantage in wear resistance of the coating deposited using a glow discharge increases. During the process of heating and etching by ion bombardment with metal ions, a nanolayer rich in cobalt and tooling elements (iron, molybdenum) is formed in the area of the interface of the coating and the carbide substrate. When heated and etched by a glow discharge, such a layer does not form. When using both methods, there is identical diffusion of tungsten into the coating and diffusion of chromium and possibly titanium into the substrate. Thus, the glow-discharge heating and etching method can be effectively used in the process of PVD coating deposition. Full article

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22 pages, 5242 KiB

Open AccessArticle

Photoelectrochemical and Structural Insights of Electrodeposited CeO₂ Photoanodes

by Alberto E. Molina-Lozano, Marcos R. V. Lanza, Pablo Ortiz and María T. Cortés

Surfaces 2024, 7(4), 898-919; https://doi.org/10.3390/surfaces7040059 - 19 Oct 2024

Viewed by 898

Abstract

Cerium dioxide (CeO₂) is a promising material for photoelectrochemical applications, requiring a thorough understanding of the interplay between its properties and structure for optimal performance. This study investigated the photoelectrochemical performance of CeO₂ photoanodes immobilized by electrodeposition on glass substrates, [...] Read more.

Cerium dioxide (CeO₂) is a promising material for photoelectrochemical applications, requiring a thorough understanding of the interplay between its properties and structure for optimal performance. This study investigated the photoelectrochemical performance of CeO₂ photoanodes immobilized by electrodeposition on glass substrates, focusing on the correlation between the annealing temperature and structural, optical, and electrical changes. CeO₂ coatings were obtained via chronoamperometry in an aqueous solution of 25 mM CeCl₃ and 50 mM NaNO₃. The photoelectrochemical characterization included the evaluation of photoactivity, current density, stability, and recombination using linear sweep voltammetry (LSV) and chronoamperometry (CA). Charge transfer resistance, flat-band potential, and capacitance were assessed through impedance spectroscopy. The optimal annealing temperature for this material was found to be 600 °C as it resulted in the lowest charge transfer resistance and increased photocurrent, which was attributed to enhanced crystallinity and variations in the Ce³⁺/Ce⁴⁺ ratio. Full article

(This article belongs to the Collection Featured Articles for Surfaces)

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19 pages, 5186 KiB

Open AccessArticle

Development of Natural Fungicidal Agricultural Defensives Using Microbial Glycolipid and Vegetable Oil Blends

by Anderson O. de Medeiros, Maria da Gloria C. da Silva, Attilio Converti, Fabiola Carolina G. de Almeida and Leonie A. Sarubbo

Surfaces 2024, 7(4), 879-897; https://doi.org/10.3390/surfaces7040058 - 16 Oct 2024

Viewed by 608

Abstract

The use of pesticides causes significant environmental problems, which drives the search for natural and non-toxic alternatives. In this study, a glycolipid biosurfactant (BS), produced by the yeast Starmerella bombicola ATCC 22214, was utilized as an active ingredient in natural agricultural defensive blends. [...] Read more.

The use of pesticides causes significant environmental problems, which drives the search for natural and non-toxic alternatives. In this study, a glycolipid biosurfactant (BS), produced by the yeast Starmerella bombicola ATCC 22214, was utilized as an active ingredient in natural agricultural defensive blends. The mixtures were tested for their fungicidal potential against phytopathogenic fungi isolated from fruits such as papaya, orange, and banana, demonstrating strong inhibition of fungal growth. The genera Penicillium, Colletotrichum, and Aspergillus were the pathogens present in the deterioration of the fruits used in the experiment. The biosurfactant was produced in a fermenter, yielding 10 g/L and reducing the surface tension to 31.56 mN/m, with a critical micelle concentration (CMC) of 366 mg/L. Blends of BS with oleic acid (T1) and lemongrass oil (T2) were found to be effective in controlling fungi. Additionally, the phytotoxicity of these formulations was assessed using Cucumis anguria (gherkin) seeds, where the blend of BS with castor oil (T4) showed the best performance, promoting seed germination. These results indicate the potential of such mixtures as natural alternatives for fungal control in plants and for application in sustainable agricultural systems. Full article

(This article belongs to the Collection Featured Articles for Surfaces)

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15 pages, 9791 KiB

Open AccessArticle

Synthesis of BiOCl Colloidal Particles by Laser Ablation of Solids in Liquids

by Abril Vázquez Francisco, Armando Pérez-Centeno, Laura P. Rivera and José G. Quiñones-Galván

Surfaces 2024, 7(4), 864-878; https://doi.org/10.3390/surfaces7040057 - 15 Oct 2024

Viewed by 478

Abstract

Colloidal bismuth nanoparticles (NPs) were synthesized in sodium chloride (NaCl) solutions at different concentrations using the laser ablation of solids in liquids technique. The obtained materials were characterized using various techniques. The morphology, size, and crystalline phases were determined through scanning electron microscopy [...] Read more.

Colloidal bismuth nanoparticles (NPs) were synthesized in sodium chloride (NaCl) solutions at different concentrations using the laser ablation of solids in liquids technique. The obtained materials were characterized using various techniques. The morphology, size, and crystalline phases were determined through scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and Fourier-transform infrared spectroscopy (FTIR). The optical properties were studied using UV–visible spectroscopy, employing the Tauc method to determine the band gap of the particles. Two types of materials were identified depending on the NaCl concentration: spherical nanoparticles of α-Bi₂O₃ and the coexistence of α-Bi₂O₃ and BiOCl particles with irregular morphology. NaCl concentrations higher than 11.6% enable the coexistence of α-Bi₂O₃ and BiOCl. The photocatalytic response of the colloids was evaluated by the degrading rhodamine B under visible light irradiation. The sample synthesized at a NaCl concentration of 31.6% showed the best photocatalytic activity. Full article

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18 pages, 3712 KiB

Open AccessReview

The Usefulness of Infrared Spectroscopy for Elucidating the Degradation Mechanism of Metal Industrial Heritage Coatings

by Ernest Konadu-Yiadom, Ethan Bontrager and Anna Staerz

Surfaces 2024, 7(4), 846-863; https://doi.org/10.3390/surfaces7040056 - 15 Oct 2024

Viewed by 735

Abstract

As society moves away from heavy industry, large metallic structures will be abandoned. As an alternative to dismantling, these structures could be repurposed. Beyond being a practical solution, the conservation of these structures would serve as an ode to the role of these [...] Read more.

As society moves away from heavy industry, large metallic structures will be abandoned. As an alternative to dismantling, these structures could be repurposed. Beyond being a practical solution, the conservation of these structures would serve as an ode to the role of these industries in shaping modern society. Conservation, however, requires suitable coatings that hinder corrosion long-term while not significantly altering the outward appearance. Traditionally, the stability of coatings has been tested by comparing fresh samples to those aged naturally or in a UV chamber. This method of testing provides no temporal information. Additionally, measuring many different conditions, e.g., UV, humidity, temperature, and pollutants, is tedious. In this review, we highlight how by implementing infrared spectroscopy in different configurations, temporally resolved information about the coating chemistry, the metal–coating interface chemistry, and gas emissions could be gained during degradation. These insights would be essential to enable the intentional design of coatings while simultaneously revealing their environmental impact. Full article

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8 pages, 4310 KiB

Open AccessCommunication

Synthesis and Properties of Novel Acrylic Fluorinated Surfactants

by Chao Lin, Jinhua Li, Yejun Qin, Ping Xing and Biao Jiang

Surfaces 2024, 7(4), 838-845; https://doi.org/10.3390/surfaces7040055 - 14 Oct 2024

Viewed by 415

Abstract

Branched fluorinated surfactants with creatively introduced acrylate in the hydrophilic group were designed and prepared by adopting perfluoro-2-methyl-2-pentene as the raw substrate. These new compounds showed excellent surface properties, and the surface tension of their aqueous solution at 25 °C could be below [...] Read more.

Branched fluorinated surfactants with creatively introduced acrylate in the hydrophilic group were designed and prepared by adopting perfluoro-2-methyl-2-pentene as the raw substrate. These new compounds showed excellent surface properties, and the surface tension of their aqueous solution at 25 °C could be below 20.00 mN/m at the critical micelle concentration. Compared with similar structures we have synthesized previously, these synthesized compounds exhibit a great improvement with regard to their molecular arrangement at the gas–liquid interface, their polymerizability, and the antibacterial properties of their polymer form, which can provide new ideas in the work to replace perfluorooctane sulfonate/perfluorooctanoic acid. Full article

(This article belongs to the Special Issue Recent Advances in Catalytic Surfaces and Interfaces)

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14 pages, 11777 KiB

Open AccessArticle

Increasing the Wear and Corrosion Resistance of a CP-Ti Surface by Plasma Electrolytic Borocarburizing and Polishing

by Marina A. Volosova, Sergei A. Kusmanov, Ivan V. Tambovskiy, Tatiana L. Mukhacheva, Artem P. Mitrofanov, Igor V. Suminov and Sergey N. Grigoriev

Surfaces 2024, 7(4), 824-837; https://doi.org/10.3390/surfaces7040054 - 7 Oct 2024

Viewed by 949

Abstract

The paper examines the possibility of increasing the wear and corrosion resistance of a CP-Ti surface by duplex plasma electrolytic treatment (borocarburizing and polishing). The structure and composition of diffusion layers, their microhardness, surface morphology and roughness, wear resistance during dry friction and [...] Read more.

The paper examines the possibility of increasing the wear and corrosion resistance of a CP-Ti surface by duplex plasma electrolytic treatment (borocarburizing and polishing). The structure and composition of diffusion layers, their microhardness, surface morphology and roughness, wear resistance during dry friction and corrosion resistance in Ringer’s solution were studied. The formation of a surface-hardened layer up to 200 μm thick with a microhardness of up to 950 HV, including carbides and a solid solution of boron and carbon, is shown. Subsequent polishing makes it possible to reduce surface roughness and remove weak areas of the porous oxide layer, which are formed during high-temperature oxidation in aqueous electrolyte vapor during borocarburizing. Changing the morphology and structural-phase composition of the CP-Ti surface helps reduce weight wear by a factor of three (the mode of frictional interaction changes from microcutting to oxidative wear) and corrosion current density by a factor of four after borocarburizing in a solution of boric acid, glycerin and ammonium chloride at 950 °C for 5 min and subsequent polishing in an ammonium fluoride solution at a voltage of 250 V for 3 min. Full article

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12 pages, 7742 KiB

Open AccessArticle

PVD Coatings for Lightweight Bipolar Plates

by Parnia Navabpour, Liam Cooper, Shicai Yang, Jinlong Yin, Kun Zhang, Ahmad El-Kharouf and Hailin Sun

Surfaces 2024, 7(4), 812-823; https://doi.org/10.3390/surfaces7040053 - 2 Oct 2024

Viewed by 767

Abstract

Bipolar plates are one of the main components of proton exchange membrane fuel cells (PEMFCs). Their functions include distributing reactants, supporting the cell, and conducting heat and electricity. They account for a significant proportion of the fuel cell stack’s weight and volume. The [...] Read more.

Bipolar plates are one of the main components of proton exchange membrane fuel cells (PEMFCs). Their functions include distributing reactants, supporting the cell, and conducting heat and electricity. They account for a significant proportion of the fuel cell stack’s weight and volume. The main materials currently used for bipolar plates are graphite and stainless steel. Aluminium has a much lower density than steel and is easier to form than both steel and graphite. Its use, therefore, would allow fuel cells with higher power densities but is hindered due to it being prone to corrosion. This work focused on the development of corrosion-resistant and conductive coatings to address this issue. Carbon coatings with Ti and Cr adhesion layers were deposited on aluminium substrates using closed-field unbalanced magnetron sputtering. These coatings were tested for corrosion properties and performance on the cathode side of a single-cell fuel cell. Coated aluminium samples were also tested for their ability to maintain their corrosion protection after being formed. Coating with a Cr adhesion layer outperformed that with a Ti adhesion layer in both forming and fuel cell tests, demonstrating much lower performance degradation after accelerated stress testing. Full article

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11 pages, 3574 KiB

Open AccessArticle

Charged Microdroplets Deposition for Nanostructured-Based Electrode Surface Modification

by Rosaceleste Zumpano, Marco Agostini, Franco Mazzei, Anna Troiani, Chiara Salvitti, Marta Managò, Alessia Di Noi, Andreina Ricci and Federico Pepi

Surfaces 2024, 7(4), 801-811; https://doi.org/10.3390/surfaces7040052 - 1 Oct 2024

Viewed by 676

Abstract

Accelerated synthesis of gold nanoparticles (AuNPs) in charged microdroplets produced by electrospray ionization (ESI) was exploited to modify the surface of graphite screen-printed electrodes (GSPEs). The deposited AuNPs were then functionalized by the charged microdroplets deposition of 6-ferrocenyl-hexanethiol (6Fc-ht) solutions that act as [...] Read more.

Accelerated synthesis of gold nanoparticles (AuNPs) in charged microdroplets produced by electrospray ionization (ESI) was exploited to modify the surface of graphite screen-printed electrodes (GSPEs). The deposited AuNPs were then functionalized by the charged microdroplets deposition of 6-ferrocenyl-hexanethiol (6Fc-ht) solutions that act as reducing and stabilizing agents and provide electrochemical properties for the modified electrodes. The morphology and composition of the AuNPs were characterized by scanning electron microscopy (SEM). Cyclic voltammetry (CV), differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS) were used to investigate the electrochemical behavior of the modified electrodes. The results showed that the ESI microdroplets deposition technique produces uniform and well-dispersed AuNPs on GSPE, and optimal conditions for deposition were identified, enhancing GSPE electrocatalytic performance. Further functionalization by ESI microdroplets of AuNPs with 6Fc-ht demonstrated improved redox properties compared with the conventional self-assembled monolayer (SAM) method, highlighting the technique’s potential for the easy and fast functionalization of electrochemical sensors. Full article

(This article belongs to the Special Issue Recent Advances in Catalytic Surfaces and Interfaces)

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Surfaces, Volume 7, Issue 4 (December 2024) – 14 articles

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