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Fabrication, Characterization, and Application of Coatings and Thin Films

A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Thin Films and Interfaces".

Deadline for manuscript submissions: closed (10 March 2023) | Viewed by 30639

Special Issue Editor


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Guest Editor
Faculty of Mechanical Engineering, University of Applied Sciences Schmalkalden, 98574 Schmalkalden, Germany
Interests: smart materials; carbon-based thin films and carbon modifications; coatings with actuator and sensor functions; materials for robotics
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Coatings and thin films improve and fine-tune the properties of material surfaces. Moreover, materials deposited in the geometry of a thin film or a designed coating offer different functionalities in comparison to bulk materials. Today’s equipment and technologies for m-structuring and patterning provide sophisticated tools for further perfection of the surface. The art of coating and thin film technologies starts before their deposition by placing proper emphasis on the processing of precursors and particles for adjusted monolayered films or hybrid coatings. Sometimes, the fixation of nanomaterials in coatings or at surfaces is not only the cherry on the cake but also enables specific features. Last but not least, signals from the coating or thin film enable smart interactions and coating communication with or coating reaction on the environment.

Ensuring a long durability, wear and corrosion resistance, as well as friction adjustment are desired. These aspects need to be tested before coated materials are released for practical applications. Though this is a long-standing topic, this Special Issue aims to address the latest trends in surface engineering and coatings technology. Our aim is to combine results from experts in different fields, to stimulate interest in the trends and successes from one special field and application to another.

Prof. Dr. Annett Dorner-Reisel
Guest Editor

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Keywords

  • wear
  • friction
  • micropatterning
  • nanostructured surfaces
  • smart coatings and thin films
  • percursor and powder design
  • film and coating characterisation

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Published Papers (15 papers)

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Research

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18 pages, 3315 KiB  
Article
Comprehensive Analysis of Different Coating Materials on the POM Substrate
by Tonica Bončina, Srečko Glodež, Brigita Polanec, Lara Hočuršćak and Franc Zupanič
Materials 2023, 16(12), 4365; https://doi.org/10.3390/ma16124365 - 13 Jun 2023
Cited by 1 | Viewed by 800
Abstract
This study presents a comprehensive analysis of different coating materials on the POM substrate. Specifically, it investigated physical vapour deposition (PVD) coatings of aluminium (Al), chromium (Cr), and chromium nitride (CrN) of three various thicknesses. The deposition of Al was accomplished through a [...] Read more.
This study presents a comprehensive analysis of different coating materials on the POM substrate. Specifically, it investigated physical vapour deposition (PVD) coatings of aluminium (Al), chromium (Cr), and chromium nitride (CrN) of three various thicknesses. The deposition of Al was accomplished through a three-step process, particularly plasma activation, metallisation of Al by magnetron sputtering, and plasma polymerisation. The deposition of Cr was attained using the magnetron sputtering technique in a single step. For the deposition of CrN, a two-step process was employed. The first step involved the metallisation of Cr using magnetron sputtering, while the second step involved the vapour deposition of CrN, obtained through the reactive metallisation of Cr and nitrogen using magnetron sputtering. The focus of the research was to conduct comprehensive indentation tests to obtain the surface hardness of the analysed multilayer coatings, SEM analyses to examine surface morphology, and thorough adhesion analyses between the POM substrate and the appropriate PVD coating. Full article
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15 pages, 9508 KiB  
Article
Self-Healing and Self-Adhesive Substrate-Free Tattoo Electrode
by Yuanfen Chen, Xiaoming Yuan, Chunlin Li, Ruicheng Ruan and Hui You
Materials 2023, 16(9), 3499; https://doi.org/10.3390/ma16093499 - 01 May 2023
Cited by 2 | Viewed by 1541
Abstract
Electronic tattoos have great potential application in the biomedical field; moreover, the substrate-free electronic tattoo offers better comfortability and conformal contact. However, the substrate-free electronic tattoo is more prone to malfunction, including fall off and fracture. In this paper, a self-healing and self-adhesive [...] Read more.
Electronic tattoos have great potential application in the biomedical field; moreover, the substrate-free electronic tattoo offers better comfortability and conformal contact. However, the substrate-free electronic tattoo is more prone to malfunction, including fall off and fracture. In this paper, a self-healing and self-adhesive substate-free tattoo based on PEDOT: PSS is studied and reported. The dry composite electrode will turn into self-healing material while it transforms into hydrogel, and a cut with a width up to 24 μm could be healed in 1 s. In terms of adhesion performance, the substrate-free electrode can hang a 28.2 g weight by a contact area of 8 mm × 8 mm. Additionally, the substate-free electrode could maintain fully conformal contact with porcine skin in 15 days by its self-adhesiveness. When applied as a substrate-free tattoo, the contact impedance and ECG signal measurement performance before and after self-healing are almost the same. At a frequency of 10 Hz, the contact impedance of the undamaged electrode, healed electrode, and Ag/AgCl gel electrode are 32.2 kΩ, 39.2 kΩ, and 62.9 kΩ, respectively. In addition, the ECG signals measured by the undamaged electrode and healed electrode are comparable to that of Ag/AgCl electrode. The self-healing and self-adhesive substrate-free tattoo electrode reported here has broad application in health monitoring. Full article
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15 pages, 29860 KiB  
Article
Preparation and Performance of Multilayer Si-B-C-N/Diamond-like Carbon Gradient Films
by Jiaqi Duan, Minghan Li, Wenzhi Wang, Ziming Huang, Hong Jiang and Yanping Ma
Materials 2023, 16(4), 1665; https://doi.org/10.3390/ma16041665 - 16 Feb 2023
Cited by 2 | Viewed by 1528
Abstract
Si-B-C-N/diamond-like carbon (DLC) gradient films with different layers were prepared on a glass substrate by radio frequency magnetron sputtering, and the structure and surface morphology of the resulting films were analyzed by scanning electron microscopy, Raman spectrometry, and X-ray photoelectron spectroscopy. The mechanical [...] Read more.
Si-B-C-N/diamond-like carbon (DLC) gradient films with different layers were prepared on a glass substrate by radio frequency magnetron sputtering, and the structure and surface morphology of the resulting films were analyzed by scanning electron microscopy, Raman spectrometry, and X-ray photoelectron spectroscopy. The mechanical and optical properties of the films were studied using a multifunctional material mechanical testing system, UV-Vis spectrophotometer, and micro-Vickers hardness tester. The gradient structure promotes the formation of sp3 bonds and improves the hardness and optical transmittance of the resulting films. Among the prepared films, the single-layer Si-B-C-N/DLC gradient film shows the highest optical transmittance (97%). Film–substrate adherence is strengthened by the introduction of the gradient structure. The best adhesion was obtained with a double-layer Si-B-C-N/DLC gradient film. Suitable anti-wear properties were exhibited in both dry (0.18) and wet (0.07) conditions. In this paper, evaluation of the microstructural, optical, and mechanical properties of the films could provide new insights into improvements in the bonding force of glass-based DLC films and enrich the experimental data of DLC multilayer film systems. Full article
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18 pages, 16588 KiB  
Article
Effects of Cold Rolling Reduction on Microstructure, Thickness, Adhesive Force of Al-Si Coating and on Bending Toughness of Al-Si Coated Press-Hardened Steel
by Xue Feng, Xianlei Hu and Xianghua Liu
Materials 2023, 16(1), 4; https://doi.org/10.3390/ma16010004 - 20 Dec 2022
Viewed by 3735
Abstract
Al-Si coated press-hardened steel (PHS) is widely used along with the development of light-weight vehicles, and the tailor-rolled blank parts based on Al-Si coated PHS have attracted much attention. The preparation process includes cold rolling, austenitization, hot-stamping, and quenching. The most widely used [...] Read more.
Al-Si coated press-hardened steel (PHS) is widely used along with the development of light-weight vehicles, and the tailor-rolled blank parts based on Al-Si coated PHS have attracted much attention. The preparation process includes cold rolling, austenitization, hot-stamping, and quenching. The most widely used AS60/60 coating will change after cold rolling and austenitization, which has been little-studied. Herein, the effects of cold rolling reduction on the microstructure, thickness, adhesive force of AS60/60 coating and on bending toughness of AS60/60 coated PHS were studied. As the cold rolling reduction ratio increased from 0% to 50%, the coatings were gradually thinned, but the overall continuity was unchanged. When the reduction ratio was 40% or above, rapid diffusion channels were formed. The adhesive force of coatings was 21.50–22.15 MPa. After austenitization, the coating thickness gradually decreased as the cold rolling reduction ratio rose from 0% to 50%, but the structure and overall continuity were both unchanged, and the adhesive force was 21.60–22.40 MPa. The rapid diffusion channels promoted the transition from brittle Fe2Al5 to tough FeAl during austenitization, leading to a rapid increment in bending toughness after Al-Si coated PHS was quenched. When the reduction ratio was 50%, the bending angle was improved by 23%. Full article
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12 pages, 8846 KiB  
Article
Morphology and Anti-Corrosive Performance of Cr(III) Passivated Zn–Fe Alloy Coating on NdFeB Substrate
by Ba Li, Xiaoshun Zhou, Xiaoping Chen, Song Fu, Xiangdong Wang and Dongliang Zhao
Materials 2022, 15(21), 7523; https://doi.org/10.3390/ma15217523 - 27 Oct 2022
Cited by 2 | Viewed by 1066
Abstract
In this study, low-iron Zn–Fe alloy coatings and pure Zn coatings, with or without trivalent chromium passivation treatment, were electrodeposited onto a sintered NdFeB magnet from a weak acid chloride bath. The surface morphology and structure of the coatings were then examined using [...] Read more.
In this study, low-iron Zn–Fe alloy coatings and pure Zn coatings, with or without trivalent chromium passivation treatment, were electrodeposited onto a sintered NdFeB magnet from a weak acid chloride bath. The surface morphology and structure of the coatings were then examined using the X-ray diffraction, a scanning electron microscope and 3D white-light interfering surface analysis. Meanwhile, the electrodeposition behavior and anti-corrosive properties of the coatings were investigated using cyclic voltammetry, potentiodynamic polarization, electrochemical impedance spectroscopy, and natural salt spray tests. The results indicate that a passivated Zn–Fe alloy coating with a 0.9 wt.% Fe content provided much better corrosion resistance than a pure Zn coating and could provide both anodic protection and physical barrier function in the NdFeB substrates. The Fe element in Zn–Fe alloy coating was predominantly in solid solution in η-phase and small amounts in elemental form, which was beneficial to acquire a compact coating and passivation film. Finally, the passivated Zn–Fe alloy coating withstood 210 h against a neutral 3.5 wt.% NaCl salt spray without any white rust, which was 3–4 times longer than the pure Zn coating. Full article
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15 pages, 3321 KiB  
Article
Effect of Surface Topology on the Apparent Thermal Diffusivity of Thin Samples at LFA Measurements
by Robert Szczepaniak
Materials 2022, 15(14), 4755; https://doi.org/10.3390/ma15144755 - 07 Jul 2022
Cited by 3 | Viewed by 1054
Abstract
This paper deals with the problem of the influence of surface topography on the results of thermal diffusivity measurements when determined using the instantaneous surface heat source method, also called the pulse method. The analysis was based on numerical tests carried out using [...] Read more.
This paper deals with the problem of the influence of surface topography on the results of thermal diffusivity measurements when determined using the instantaneous surface heat source method, also called the pulse method. The analysis was based on numerical tests carried out using Comsol Multiphysics software. The results of experimental investigations on the actual material structure using an electron microscope, an optical microscope and a profilometer were used to develop a numerical model. The influence of the non-uniformity of the surface of the tested sample on the determined values of half-time of the thermal response of the sample’s rough surface to the impulse forcing on the opposing flat surface was determined by developing the data for simulated measurements. The effect of the position of the response data reading area on the obtained simulation results was also analyzed. The obtained results can be used to improve the accuracy of experimental heat transfer studies performed on thin-film engineering structures depending on the uniformity and parallelism of the material applied to engineering structures. The difference in half-life determination error results for various analyzed models can be as high as 16.7%, depending on the surface from which the responses of the heating impulse are read. With an equivalent model in which 10% of the material volume corresponds to the rough part as a single inclusion, hemisphere, the error in determining thermal diffusivity was equal to 3.8%. An increase in the number of inclusions with smaller weight reduces an error in the determination of thermal diffusivity, as presented in the paper. Full article
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14 pages, 3178 KiB  
Article
Antimicrobial TiN-Ag Coatings in Leather Insole for Diabetic Foot
by Sandra M. Marques, Isabel Carvalho, Teófilo R. Leite, Mariana Henriques and Sandra Carvalho
Materials 2022, 15(6), 2009; https://doi.org/10.3390/ma15062009 - 08 Mar 2022
Cited by 3 | Viewed by 2195
Abstract
This work reports on TiN-Ag antimicrobial coatings deposited by d.c. magnetron sputtering on leather used for insoles on the footwear industry, studies involving the antimicrobial properties of Ag-based functionalized leathers by sputtering techniques are shown. The X-ray diffraction (XRD) results suggested the presence [...] Read more.
This work reports on TiN-Ag antimicrobial coatings deposited by d.c. magnetron sputtering on leather used for insoles on the footwear industry, studies involving the antimicrobial properties of Ag-based functionalized leathers by sputtering techniques are shown. The X-ray diffraction (XRD) results suggested the presence of crystalline fcc-TiN phase for the sample without silver, and also a fcc-Ag phase in the samples containing silver. According to the Scanning Electron Microscopy (SEM) analysis, the coatings were homogeneous and dispersed Ag clusters were detected on the surface of samples with silver content above 8 at. %. The Inductively coupled plasma—optical emission spectrometry (ICP-OES) analysis showed that the ionization of silver over time depends on the morphology of the coatings. The samples did not present cytotoxicity and only samples with incorporated silver presented antibacterial and antifungal activity, highlighting the potential of the TiN-Ag insole coatings for diseases such as diabetic foot. Full article
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12 pages, 3575 KiB  
Article
Research on Atomic Oxygen Erosion Influence of Structural Damage and Tribological Properties of Mo/MoS2-Pb-PbS Thin Film
by Cuihong Han, Guolu Li, Guozheng Ma, Jiadong Shi, Aobo Wei, Zhen Li, Qingsonge Yong, Haidou Wang and Huipeng Wang
Materials 2022, 15(5), 1851; https://doi.org/10.3390/ma15051851 - 01 Mar 2022
Cited by 2 | Viewed by 1407
Abstract
To investigate atomic oxygen effects on tribological properties of Mo/MoS2-Pb-PbS film and further enlarge application range, atomic oxygen exposure tests were carried out for 5 h, 10 h, 15 h, and 20 h by the atomic oxygen simulator with atomic oxygen [...] Read more.
To investigate atomic oxygen effects on tribological properties of Mo/MoS2-Pb-PbS film and further enlarge application range, atomic oxygen exposure tests were carried out for 5 h, 10 h, 15 h, and 20 h by the atomic oxygen simulator with atomic oxygen flux of 2.5 × 1015 atoms/cm2·s. The exposure time in test was equivalent to the atomic oxygen cumulative flux for 159.25 h, 318.5 h, 477.75 h, and 637 h at the height of 400 km in space. Then, the vacuum friction test of Mo/MoS2-Pb-PbS thin film was performed under the 6 N load and 100 r/min. By SEM, TEM, and XPS analysis of the surface of the film after atomic oxygen erosion, it was observed that atomic oxygen could cause serious oxidation on the surface of Mo/MoS2-Pb-PbS film, and the contents of MoS2, PbS, and Pb, which were lubricating components, were significantly reduced, and oxides were generated. From AES analysis and the variation in the main element content, Mo/MoS2-Pb-PbS thin film showed self-protection ability in an atomic oxygen environment. Hard oxide generated after atomic oxygen erosion such as MoO3 and Pb3O4 could cause the friction coefficient slight fluctuations, but the average friction coefficient was in a stable state. Full article
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13 pages, 2847 KiB  
Article
Method for High-Yield Hydrothermal Growth of Silica Shells on Nanoparticles
by Max Willinger, Martin Felhofer, Erik Reimhult and Ronald Zirbs
Materials 2021, 14(21), 6646; https://doi.org/10.3390/ma14216646 - 04 Nov 2021
Cited by 3 | Viewed by 2609
Abstract
Coating processes are commonly used in materials science to protect a core or modify material properties. We describe a hydrothermal coating process using TEOS (tetraethyl orthosilicate), a widely used precursor for silica coatings, on three representative template materials (carbon nanotubes, silica, and polystyrene [...] Read more.
Coating processes are commonly used in materials science to protect a core or modify material properties. We describe a hydrothermal coating process using TEOS (tetraethyl orthosilicate), a widely used precursor for silica coatings, on three representative template materials (carbon nanotubes, silica, and polystyrene nanoparticles) with different properties and shapes. We compare the efficiency of previously published protocols for silica coatings at room temperature and atmospheric pressure with the hydrothermal process at 160 °C and 3 bar. The hydrothermal method achieves higher yields and thicker silica coatings with the same amount of precursor when compared to the conventional way, thus offering higher effectiveness. Furthermore, the hydrothermal coating process yields more homogeneous shells with a higher density, making hydrothermal coating the method of choice when mechanical integrity and low permeability of the coating are required. Full article
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18 pages, 3615 KiB  
Article
Cr-Based Sputtered Decorative Coatings for Automotive Industry
by Edgar Carneiro, Nuno M. G. Parreira, Todor Vuchkov, Albano Cavaleiro, Jorge Ferreira, Martin Andritschky and Sandra Carvalho
Materials 2021, 14(19), 5527; https://doi.org/10.3390/ma14195527 - 24 Sep 2021
Cited by 14 | Viewed by 2199
Abstract
The present work aims to study the impact of O and N addition on Cr-sputtered coatings on plastic (polycarbonate, PC) used in automobile parts, as a promisor alternative for auto part metallization, while eliminating the usage of toxic hexavalent chromium. The coatings were [...] Read more.
The present work aims to study the impact of O and N addition on Cr-sputtered coatings on plastic (polycarbonate, PC) used in automobile parts, as a promisor alternative for auto part metallization, while eliminating the usage of toxic hexavalent chromium. The coatings were deposited using DC magnetron sputtering from a single pure Cr target in a reactive atmosphere (N2 and/or O2). The deposition of the coatings was performed maintaining the total pressure constant and close to 1 Pa by tuning Ar pressure while reactive gases were added. The target current density was kept at JW = 20 mA·cm−2. Structural characterization revealed a mixture of α-Cr, δ-Cr, β-Cr2N, and CrN crystalline structures as well as amorphous oxides. The coating hardness ranged from 9 GPa for the CrON coating to 15 GPa for the CrN coating. All deposited coatings showed a particularly good interface adhesion; adjusting the amount of O and N made it possible to tune the optical properties of the Cr-based coatings as desired. The promising results open future industrialization of sputtered Cr-based coatings for automotive industries. Full article
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16 pages, 28795 KiB  
Article
Performance of MoS2/Zr Composite Coatings at Different Deposition Temperatures
by Wenlong Song, Kai Sun, Guangming Zhao, Long Zhu, Shoujun Wang and Tianya Li
Materials 2021, 14(17), 5100; https://doi.org/10.3390/ma14175100 - 06 Sep 2021
Cited by 3 | Viewed by 1469
Abstract
The properties of the MoS2/Zr coatings can be significantly affected by the deposition temperature. In this study, the MoS2/Zr composite coatings were fabricated on the cemented carbide surface, utilizing the duplex deposition technology at various deposition temperatures. The effects [...] Read more.
The properties of the MoS2/Zr coatings can be significantly affected by the deposition temperature. In this study, the MoS2/Zr composite coatings were fabricated on the cemented carbide surface, utilizing the duplex deposition technology at various deposition temperatures. The effects of deposition temperature on the mechanical and friction properties of the MoS2/Zr coatings were systematically studied. Results exhibited that as the deposition temperature increased, the adhesion force increased first and then decreased, and the coating thickness and micro-hardness gradually increased. Dry sliding tests against a hardened steel ring showed that the tribological behaviors and wear mechanisms of the MoS2/Zr coatings varied with deposition temperature, which were due to the changing mechanical properties of coatings caused by the temperature. The coatings deposited at a temperature of 180 °C and 200 °C possessed preferable comprehensive mechanical and tribological properties. Full article
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9 pages, 1766 KiB  
Article
Oxygen Adsorption Induced Superconductivity in Ultrathin FeTe Film on SrTiO3(001)
by Wei Ren, Hao Ru, Kun Peng, Huifang Li, Shuai Lu, Aixi Chen, Pengdong Wang, Xinwei Fang, Zhiyun Li, Rong Huang, Li Wang, Yihua Wang and Fangsen Li
Materials 2021, 14(16), 4584; https://doi.org/10.3390/ma14164584 - 15 Aug 2021
Cited by 5 | Viewed by 2464
Abstract
The phenomenon of oxygen incorporation-induced superconductivity in iron telluride (Fe1+yTe, with antiferromagnetic (AFM) orders) is intriguing and quite different from the case of FeSe. Until now, the microscopic origin of the induced superconductivity and the role of oxygen are far from [...] Read more.
The phenomenon of oxygen incorporation-induced superconductivity in iron telluride (Fe1+yTe, with antiferromagnetic (AFM) orders) is intriguing and quite different from the case of FeSe. Until now, the microscopic origin of the induced superconductivity and the role of oxygen are far from clear. Here, by combining in situ scanning tunneling microscopy/spectroscopy (STM/STS) and X-ray photoemission spectroscopy (XPS) on oxygenated FeTe, we found physically adsorbed O2 molecules crystallized into c (2/3 × 2) structure as an oxygen overlayer at low temperature, which was vital for superconductivity. The O2 overlayer were not epitaxial on the FeTe lattice, which implied weak O2 –FeTe interaction but strong molecular interactions. The energy shift observed in the STS and XPS measurements indicated a hole doping effect from the O2 overlayer to the FeTe layer, leading to a superconducting gap of 4.5 meV opened across the Fermi level. Our direct microscopic probe clarified the role of oxygen on FeTe and emphasized the importance of charge transfer effect to induce superconductivity in iron-chalcogenide thin films. Full article
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21 pages, 7507 KiB  
Article
Stoichiometry Dependence of Physical and Electrochemical Properties of the SnOx Film Anodes Deposited by Pulse DC Magnetron Sputtering
by Yibo Ma, Xiaofeng Zhang, Weiming Liu, Youxiu Wei, Ziyi Fu, Jiuyong Li, Xuan Zhang, Jingjing Peng and Yue Yan
Materials 2021, 14(7), 1803; https://doi.org/10.3390/ma14071803 - 06 Apr 2021
Cited by 2 | Viewed by 1875
Abstract
A batch of Sn oxides was fabricated by pulse direct current reactive magnetron sputtering (pDC−RMS) using different Ar/O2 flow ratios at 0.3 Pa; the influence of stoichiometry on the physical and electrochemical properties of the films was evaluated by the characterization of [...] Read more.
A batch of Sn oxides was fabricated by pulse direct current reactive magnetron sputtering (pDC−RMS) using different Ar/O2 flow ratios at 0.3 Pa; the influence of stoichiometry on the physical and electrochemical properties of the films was evaluated by the characterization of scanning electron microscope (SEM), X-ray diffraction (XRD), X-ray reflection (XRR), X-ray photoelectron spectroscopy (XPS) and more. The results were as follows. First, the film surface transitioned from a particle morphology (roughness of 50.0 nm) to a smooth state (roughness of 3.7 nm) when Ar/O2 flow ratios changed from 30/0 to 23/7; second, all SnOx films were in an amorphous state, some samples deposited with low O2 flow ratios (≤2 sccm) still included metallic Sn grains. Therefore, the stoichiometry of SnOx calculated by XPS spectra increased linearly from SnO0.0.08 to SnO1.71 as the O2 flow ratios increased, and the oxidation degree was further calibrated by the average valence method and SnO2 standard material. Finally, the electrochemical performance was confirmed to be improved with the increase in oxidation degree (x) in SnOx, and the SnO1.71 film deposited with Ar/O2 = 23/7 possessed the best cycle performance, reversible capacity of 396.1 mAh/g and a capacity retention ratio of 75.4% after 50 cycles at a constant current density of 44 μA/cm2. Full article
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14 pages, 5241 KiB  
Article
Effect of Functionalization of Reduced Graphene Oxide Coatings with Nitrogen and Sulfur Groups on Their Anti-Corrosion Properties
by Karolina Ollik, Jakub Karczewski and Marek Lieder
Materials 2021, 14(6), 1410; https://doi.org/10.3390/ma14061410 - 14 Mar 2021
Cited by 6 | Viewed by 1956
Abstract
Electrophoretic production of anticorrosion carbonaceous coatings on copper could be successfully performed by anodic oxidation of negatively charged graphene platelets suspended in an aqueous solution. The various platelets were synthesized by Hummer’s method followed by a hydrothermal reduction in the presence of NH [...] Read more.
Electrophoretic production of anticorrosion carbonaceous coatings on copper could be successfully performed by anodic oxidation of negatively charged graphene platelets suspended in an aqueous solution. The various platelets were synthesized by Hummer’s method followed by a hydrothermal reduction in the presence of NH4SCN which was expected to substitute some parts of graphene structure with nitrogen and sulfur groups. X-ray photoelectron spectroscopy analysis confirmed that the graphene precursors, as well as the coatings, contained typical nitrogen groups, such as pyridinic and pyrrolic, and sulfur groups, such as thiol, thiophene, or C-SO2. However, due to oxidation during deposition, the qualitative and quantitative composition of the graphene coatings changed relative to the composition of the precursors. In particular, the concentration of nitrogen and sulfur dropped and some thiophene groups were oxidized to C-SO2. Studies showed the functionalized coatings had a uniform, defect-free, hydrophobic, more adhesive surface than nonmodified films. The corrosion measurements demonstrated that these coatings had better protective properties than the ones without these heteroatoms. This behavior can be assigned to the catalytic activity of nitrogen towards oxidation of C-SO2 groups to C-SO3H with oxygen. Full article
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Review

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21 pages, 5571 KiB  
Review
Recent Advances in Multi-Functional Coatings for Soft Magnetic Composites
by Emir Pošković, Fausto Franchini, Luca Ferraris, Elisa Fracchia, Jana Bidulska, Federico Carosio, Robert Bidulsky and Marco Actis Grande
Materials 2021, 14(22), 6844; https://doi.org/10.3390/ma14226844 - 12 Nov 2021
Cited by 31 | Viewed by 3332
Abstract
During the past 50 years, the aim to reduce the eddy current losses in magnetic cores to a minimum led to the formulation of new materials starting from electrically insulated iron powders, today called Soft Magnetic Composites (SMC). Nowadays, this promising branch of [...] Read more.
During the past 50 years, the aim to reduce the eddy current losses in magnetic cores to a minimum led to the formulation of new materials starting from electrically insulated iron powders, today called Soft Magnetic Composites (SMC). Nowadays, this promising branch of materials is still held back by the mandatory tradeoff between energetic, electrical, magnetic, and mechanical performances. In most cases, the research activity focuses on the deposition of an insulating/binding layer, being one of the critical points in optimizing the final composite. This insulation usually is achieved by either inorganic or organic layer constituents. The main difference is the temperature limit since most inorganic materials typically withstand higher treatment temperatures. As a result, the literature shows many materials and process approaches, each one designed to meet a specific application. The present work summarizes the recent advances in state of the art, analyzing the relationship among material compositions and magnetic and mechanical properties. Each coating shows its own processing sets, which vary from simple mechanical mixing to advanced chemical methods to metallurgical treatments. From state of the art, Aluminum coatings are characterized by higher current losses and low mechanical properties. In contrast, higher mechanical properties are obtained by adopting Silicon coatings. The phosphates coatings show the best-balanced overall properties. Each coating type was thoroughly investigated and then compared with the literature background highlighting. The present paper thus represents a critical overview of the topic that could serve as a starting point for the design and development of new and high-performing coating solutions for SMCs. However, global research activity continuously refines the recipes, introducing new layer materials. The following steps and advances will determine whetherthese materials breakthrough in the market. Full article
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