Two-Dimensional Materials-Based Thin Films and Coatings

Abstract

Here, we highlight the research presented in this Special Issue, focusing on the innovative use of graphene and other two-dimensional (2D) materials to develop advanced coating technologies. The contributions herein address critical challenges such as the scalable fabrication and stable dispersion of such materials and their compatibility with conventional coating systems, offering solutions that enhance their mechanical strength, chemical stability, and multifunctionality. The featured studies demonstrate the diverse applications of these materials, from protective anticorrosive barriers to high-performance optoelectronic devices and environmental remediation. Moving forward, future research is encouraged to explore novel 2D materials, hybrid coating strategies, and advanced computational modeling to overcome existing limitations and unlock new possibilities.

1. Introduction and Scope

Since the isolation of graphene in 2004 [1], the field of two-dimensional (2D) materials has experienced unprecedented growth, drawing extensive interest from researchers and industry alike [2]. The unique properties of graphene [3,4]—such as its remarkable mechanical strength, high electrical conductivity, and near-perfect impermeability to gasses—have positioned it as a transformative material for a range of applications, particularly in thin films and coatings [5]. These attributes, coupled with its high diameter-to-thickness ratio, make graphene and its derivatives ideal candidates for creating robust protective barriers against moisture, oxygen, and corrosive agents. As a result, graphene-based materials have become the focus of intense research aimed at developing innovative coatings with enhanced performance in terms of their corrosion resistance, mechanical stability, and environmental resilience [6,7,8]. Despite these promising characteristics, the practical application of graphene-based coatings faces significant challenges. Issues such as the scalable, stable, and non-destructive dispersion of graphene, as well as its compatibility with various resin interfaces, have hindered its widespread use in industrial settings [9]. These limitations necessitate a deeper understanding and exploration of both graphene and alternative 2D materials, including graphene oxide, molybdenum disulfide, boron nitride, and MXenes, among others [10]. Such materials offer complementary properties that can be tailored to specific applications, ranging from anticorrosive coatings to high-performance electronics.

With this in mind, the scope of this Special Issue encompasses a wide range of topics related to 2D materials-based thin films and coatings (Figure 1). It covers recent developments in multifunctional graphene-based coatings, including novel fabrication techniques and hybrid composite structures designed to enhance the mechanical, thermal, and chemical properties of such coatings. The issue also delves into the theoretical and experimental research that has been carried out into protective and preventive mechanisms using beyond-graphene materials, such as molybdenum disulfide and boron nitride, which offer promising alternatives for specific applications. Additionally, this Special Issue highlights innovative coating technologies, including additive manufacturing processes, thermal spray, laser and plasma processing, chemical vapor deposition (CVD), and plating. These techniques are crucial for fabricating coatings that can withstand extreme conditions, such as high temperatures and mechanical stress, making them suitable for use in aerospace, automotive, and other high-performance industries.

Theoretical and computational studies are also a key focus of this Special Issue, providing insights into the degradation mechanisms of coatings under dynamic loading conditions, such as friction and wear, and exploring the use of modeling and simulations to predict the performance, durability, and reliability of coatings. Understanding these mechanisms is essential for developing coatings that can maintain their functionality over long periods and in harsh environments. Finally, this Special Issue aims to not only showcase cutting-edge research but also to foster collaboration among scientists, engineers, and industry professionals. By providing a comprehensive overview of the current state-of-the-art and emerging trends, it hopes to inspire further innovation and contribute to the development of next-generation thin films and coatings based on 2D materials.

2. Contributions

Table 1. Summary of research articles published in this Special Issue.

Author	Results	Conclusions
Jiao T. et al. [11]	Achieved 5H pencil hardness which was maintained over an 85% light transmittance.	The coatings significantly improve surface hardness while maintaining high levels of transparency, making them ideal for protective applications.
Abdelazeez A. et al. [12]	Produced high-quality graphene nanosheets (~7 nm thickness) suitable for photovoltaic applications.	The EPD method provides uniform and controlled graphene films with enahnced applications in optoelectronics.
Ben Gouider Trabelsi A. et al. [13]	High photoresponsivity and detectivity, suitable for solar cells.	The free-standing Ppy/GO composite offers a high potential for light sensors and solar cells.
Martyanov A. et al. [14]	High-quality PCD films produced at lower temperatures, optimal growth at 20% methane.	Controlling methane and temperature can fine-tune PCD properties, aiding diamond production for various uses.
Sedov V. et al. [15]	Improved thermal conductivity and reduced bow by 57% compared to HF CVD alone.	Combined MW+HF CVD improves PCD film properties, making them beneficial for thermal management applications.
Kovalev A. et al. [16]	Strong oxidation resistance thanks to the critical roles of silicon and yttrium.	Silicon and yttrium enhance oxidation resistance, confirming their importance in PVD coatings.
Tene T. et al. [17]	Enhanced plasmon frequency by up to 40 THz with tunable responses.	GNR arrays offer significant potential for nanoplasmonic devices and molecular sensing.
Zhang Y. et al. [18]	Developed a 2DU2-Net† model with a high accuracy and strong generalization ability.	Deep learning methods improve layer identification, and are applicable in 2D material research.
Laszlo E. et al. [19]	Films exhibited good hardness, adhesion, and tailored electrical properties.	High-entropy alloy films are promising for applications requiring wear resistance and tailored properties.
Tene T. et al. [20]	rGO showed 75% Hg(II) removal efficiency, reaching equilibrium in 20 min.	rGO offers a sustainable solution for mercury removal, which is effective for water treatment applications.
Tang T. et al. [21]	Accurate replication of lacquer pattern formation with 3D simulation.	Combining traditional craftsmanship with technology enhances the production of lacquerware.
Liu H. et al. [22]	Fe-adsorbed germanene showed ferromagnetism with a bandgap of 0.22 eV.	TM-adsorbed germanene exhibits unique properties, and is applicable in spintronic devices.
Roy P. et al. [23]	PSCs achieved PCE up to 25.8%, but stability issues remain.	Major improvements in stability and manufacturing are needed for the commercialization of PSCs.

shows the advancements across various published works in the Special Issue with a particular focus on graphene-based and 2D nanomaterials.

Summary of Contributions

The development of graphene-based coatings is a prominent theme in this Special Issue. Jiao and colleagues [11] engineered transparent polyurethane/laponite/graphene coatings with remarkable surface hardnesses, setting a new benchmark for protective films that do not compromise on visual clarity. Abdelazeez et al. [12] took a different approach by focusing on the scalable production of graphene films through a green, liquid-phase exfoliation method. Their work not only supports the drive for sustainable manufacturing but also paves the way for the enhanced performance of graphene films in photovoltaic and optoelectronic applications. Ben Gouider Trabelsi et al. [13] extended the functional scope of graphene composites by creating a photodetector material with heightened sensitivity, leveraging the synergy between graphene oxide and polypyrrole to improve photoresponsivity across a broad optical spectrum.

Moving beyond graphene, the synthesis and optimization of diamond and thin films have garnered considerable attention. Martyanov et al. [14] explored the influence of methane concentration on the growth of polycrystalline diamond films, revealing the nuanced interplay between process parameters and material properties. Meanwhile, Sedov et al. [15] demonstrated how combining microwave plasma and hot filament chemical vapor deposition can significantly enhance the thermal conductivity and structural integrity of diamond films. These studies underscore the potential of diamond films in high-performance applications where thermal management and durability are vital.

In the exploration of nanostructured and composite coatings, Kovalev and colleagues [16] delved into the oxidation behavior of multilayer nanolaminated PVD coatings, finding that the inclusion of silicon and yttrium notably boosts resistance against high-temperature degradation. This insight is crucial for industries reliant on robust, heat-resistant coatings, such as the aerospace and automotive sectors. Additionally, Tene et al. [17] contributed to the field of nanoplasmonics by examining the properties of graphene nanoribbon arrays. Their findings suggest new avenues for developing tunable plasmonic devices, which could revolutionize molecular sensing and communication technologies.

Computational methods are playing an increasingly vital role in advancing material science. Zhang et al. [18] harnessed deep learning to update the method for identifying atomic layers in 2D materials, presenting a significant leap forward in material characterization. Their approach enhances both the precision and efficiency of analyzing complex nanomaterials. Laszlo et al. [19], on the other hand, focused on the synthesis of high-entropy alloy films, revealing how variations in nickel content can be fine-tuned to tailor the mechanical and electrical properties of these versatile materials, potentially broadening their possible applications in fields that demand high performance and resilience.

Environmental sustainability remains a critical concern, one which is addressed thoughtfully by Tene et al. [20], who explored the use of oxidized graphene for the removal of mercury from water. Their work not only highlights the efficacy of graphene-based materials in environmental remediation but also emphasizes the need for eco-friendly solutions to tackle pollution. Meanwhile, Tang et al. [21] merged traditional lacquerware craftsmanship with advanced 3D modeling techniques to innovate the production process of rhinoceros skin lacquer coatings. This fusion of technology and heritage underscores the potential of modern methods to preserve and enhance traditional arts sustainably.

In the realm of electronic properties, Liu et al. [22] investigated the effects of transition-metal adsorption on germanene, uncovering unique electronic and magnetic behaviors that could have significant implications for the development of spintronic devices. Finally, Roy et al. [23] provided a comprehensive review of perovskite solar cells, discussing recent breakthroughs in efficiency and stability. They highlight the challenges of scaling up production and achieving long-term durability, which are critical hurdles that must be overcome for these materials to fulfill their potential as cost-effective alternatives to conventional solar technologies.

3. List of Contributions by Topic

Figure 2 shows the distribution of the research articles contained in this Special Issue across seven distinct topics. Topic 1 (Fabrication and Functionalization of Graphene-Based Coatings) accounts for the largest share, representing 27.3% of the total articles. This indicates a strong research focus on developing and optimizing graphene-based coatings for various applications. Topic 2 (Diamond and Thin Film Coatings for High-Performance Applications) and Topic 4 (Computational Approaches and Modeling) each comprise 18.2% of the articles, suggesting significant interest in high-performance coatings and the use of computational methods to enhance material properties. Topic 6 (Novel Coating Technologies and Methodologies) also holds an 18.2% share, highlighting the ongoing exploration of innovative coating techniques and their practical applications. Topic 3 (Nanostructured and Composite Coatings for Enhanced Properties), Topic 5 (Environmental and Sustainable Applications), and Topic 7 (Reviews and Advanced Insights) each comprise 9.1% of the total, indicating these areas are less represented but are still crucial for a comprehensive understanding of the field.

3.1. Topic 1: Fabrication and Functionalization of Graphene-Based Coatings

• Jiao, T.; Shui, L.; Lin, M.; Huang, W.; Chen, G. Fabrication of Polyurethane/Laponite/Graphene Transparent Coatings with High Surface Hardness. Coatings 2024, 14(12), 12.
• Abdelazeez, A.A.A.; Trabelsi, A.B.G.; Alkallas, F.H.; AlFaify, S.; Shkir, M.; Alrebdi, T.A.; Almugren, K.S.; Kusmatsev, F.V.; Rabia, M. Reproducible Preparation of Thin Graphene Films Using a Green and Efficient Liquid-Phase Exfoliation Method for Applications in Photovoltaics. Coatings 2023, 13, 1628.
• Ben Gouider Trabelsi, A.; Elsayed, A.M.; Alkallas, F.H.; AlFaify, S.; Shkir, M.; Alrebdi, T.A.; Almugren, K.S.; Kusmatsev, F.V.; Rabia, M. Photodetector-Based Material from a Highly Sensitive Free-Standing Graphene Oxide/Polypyrrole Nanocomposite. Coatings 2023, 13, 1198.

3.2. Topic 2: Diamond and Thin Film Coatings for High-Performance Applications

• Martyanov, A.; Tiazhelov, I.; Savin, S.; Voronov, V.; Konov, V.; Sedov, V. Synthesis of Polycrystalline Diamond Films in Microwave Plasma at Ultrahigh Concentrations of Methane. Coatings 2023, 13, 751.
• Sedov, V.; Popovich, A.; Linnik, S.; Martyanov, A.; Wei, J.; Zenkin, S.; Zavedeev, E.; Savin, S.; Gaydaychuk, A.; Li, C.; et al. Combined HF+MW CVD Approach for the Growth of Polycrystalline Diamond Films with Reduced Bow. Coatings 2023, 13(2), 380.

3.3. Topic 3: Nanostructured and Composite Coatings for Enhanced Properties

• Kovalev, A.I.; Vakhrushev, V.O.; Konovalov, E.P.; Fox-Rabinovich, G.S.; Wainstein, D.L.; Dmitrievskii, S.A.; Mukhsinova, A.D. Features of the Oxidation of Multilayer (TiAlCrSiY)N/(TiAlCr)N Nanolaminated PVD Coating during Temperature Annealing. Coatings 2023, 13(2), 287.

3.4. Topic 4: Computational Approaches and Modeling

• Tene, T.; Guevara, M.; Cevallos, Y.; Sáez Paguay, M.Á.; Bellucci, S.; Vacacela Gomez, C. THz Surface Plasmons in Wide and Freestanding Graphene Nanoribbon Arrays. Coatings 2024, 13, 28.
• Zhang, Y.; Zhang, H.; Zhou, S.; Liu, G.; Zhu, J. Deep Learning-Based Layer Identification of 2D Nanomaterials. Coatings 2024, 12(10), 1551.

3.5. Topic 5: Environmental and Sustainable Applications

• Tene, T.; Arias Arias, F.; Guevara, M.; González García, J.C.; Arias Polanco, M.; Scarcello, A.; Caputi, L.S.; Bellucci, S.; Vacacela Gomez, C. Adsorption Kinetics of Hg(II) on Eco-Friendly Prepared Oxidized Graphenes. Coatings 2024, 12(8), 1154.

3.6. Topic 6: Novel Coating Technologies and Methodologies

• Tang, T.; Li, D.; Li, M.; He, J.; Zhang, Y. Three-Dimensional Construction Method for Two-Dimensional Film Pattern Design in Sustainable Rhinoceros Skin Coating Technology. Coatings 2024, 12(8), 1132.
• Liu, H.-Y.; Wu, J.-Y. Fundamental Properties of Transition-Metals-Adsorbed Germanene: A DFT Study. Coatings 2022, 12(7), 948.

3.7. Topic: Reviews and Advanced Insights

• Roy, P.; Ghosh, A.; Barclay, F.; Khare, A.; Cuce, E. Perovskite Solar Cells: A Review of the Recent Advances. Coatings 2024, 12(8), 1089.

4. Conclusions and Outlook

This Special Issue highlights the transformative potential of 2D materials in the development of advanced thin films and coatings. From enhancing the mechanical and chemical stability of protective barriers to enabling innovative electronic and optoelectronic applications, 2D materials such as graphene, graphene oxide, and molybdenum disulfide are paving the way for next-generation technologies. Despite the impressive progress made, several challenges persist, particularly in the areas of large-scale fabrication, stable dispersion, and compatibility with conventional coating systems. Addressing these issues is crucial for the broader adoption of 2D materials in industrial applications. The insights gained from the contributions in this Issue highlight the need for a multifaceted approach to overcoming these barriers. Continued research into novel synthesis and processing techniques, such as additive manufacturing and hybrid deposition methods, will be essential for achieving the scalability and reproducibility required for commercial use. Additionally, advancing our understanding of the interactions between 2D materials and various substrates will help optimize their integration into complex coating systems, enhancing their performance and longevity.

Future research should also focus on expanding the range of 2D materials that are explored as potential coatings, beyond graphene and its derivatives. Materials such as MXenes, boron nitride, and layered double hydroxides offer unique properties that can be tailored to specific applications, from high-temperature environments to electrochemical sensors. Exploring these materials in combination with existing technologies could lead to the development of multifunctional coatings with unprecedented capabilities. Furthermore, the role of computational modeling and simulation cannot be overstated. As the field progresses, advanced modeling techniques will become increasingly important for predicting the behavior of 2D materials under various conditions, guiding the design of more effective and durable coatings. Such models will be instrumental in bridging the gap between laboratory research and practical applications, accelerating the development of reliable, high-performance coatings.