Recent Advances in Graphene and Other Two-Dimensional Materials

1. Introduction

Research on breakthroughs in the synthesis and characterization of graphene [1], graphene oxide (GO) and reduced graphene oxide (rGO) [2], Molybdenum Disulfide (MoS₂) [3], and two-dimensional (2D) topological materials [4] has emerged as a critical area due to their unique electronic, optical, and mechanical properties, which enable transformative applications in electronics, energy storage, and quantum technologies [5].

Despite remarkable progress over the past two decades, the transition from fundamental discoveries to practical applications remains challenging. It has become increasingly evident that the key obstacles facing research in graphene and 2D materials lie not merely in understanding their intrinsic properties, but in developing the capability to reliably synthesize, characterize, model, and seamlessly integrate these materials into functional architectures at scale. Critical challenges persist in several interconnected areas: the lack of predictive theoretical models that can guide experimental design; the profound complexity introduced by structural disorder, edge effects, and chemical functionalization; the difficulties in achieving large-area synthesis with controlled quality, and the integration of 2D materials into practical electronic, optoelectronic, energy, and environmental applications while maintaining their exceptional properties.

This Special Issue (SI), titled Recent Advances in Graphene and Other Two-Dimensional Materials, brings together cutting-edge research that directly addresses these fundamental challenges. The collection showcases innovative approaches spanning advanced theoretical modeling, novel synthesis and fabrication strategies, comprehensive spectroscopic characterization, and demonstration of functional devices and applications. By bridging the gap between fundamental understanding and technological implementation, these contributions collectively advance the field toward realizing the full potential of graphene and other 2D materials in next-generation technologies.

2. An Overview of Published Articles

This SI attracted a number of submissions on graphene and other 2D materials. Nine high-quality papers were accepted following the peer-review process.

These contributions span a broad spectrum of topics, yet they naturally converge into four coherent thematic areas that capture the current frontiers of the field:

• From Modeling to Functional Graphene Nanoribbon Devices;
• Properties and Applications of Graphene Oxide and Reduced Graphene Oxide;
• Graphene-Based Silicon Heterostructures for Optoelectronic Applications;
• Two-Dimensional Materials Beyond Graphene.

Together, these thematic clusters provide a comprehensive overview of recent advances while highlighting promising directions for future research. In the following sections, we present each thematic area and discuss the individual contributions within their broader scientific context.

3. From Modeling to Functional Graphene Nanoribbon Devices

Graphene nanoribbons (GNRs) [6] have emerged as key building blocks for plasmonic and photonic technologies, owing to their reduced dimensionality, tunable electronic structure, and strong light–matter interaction. Recent advances [7] highlight the importance of combining accurate theoretical modeling with device-oriented design strategies to fully exploit their plasmonic response across different frequency regimes. Within this context, two contributions in this SI address complementary aspects of plasmonic engineering in GNRs, spanning from fundamental modeling to functional device implementation.

The article “Modeling 2D Arrangements of Graphene Nanoribbons” (contribution 3) focuses on GNRs. Owing to their sizeable bandgaps and tunable electronic properties, GNRs represent promising platforms for photonic and plasmonic applications. While significant experimental progress has been achieved in the synthesis of GNRs, the theoretical description of their electronic and optical properties has largely relied on ab initio methods, which become impractical for wide systems due to the large number of atoms involved. The authors present a semi-analytical model based on the Dirac cone approximation to describe the electronic and plasmonic properties of widely and experimentally relevant GNRs, considering both freestanding and non-freestanding configurations.

The results show that, in the terahertz regime, the plasmon–momentum dispersion is highly sensitive to variations in ribbon width and charge carrier concentration. The model successfully reproduces the electronic properties of GNRs on Ge(001) and Au(111), as well as the plasmon spectra of graphene microribbon arrays (4 μm wide) on Si/SiO₂ and GNR arrays on Si, in good agreement with experimental observations. Finally, the potential application of GNRs for molecular sensing is discussed by considering chlorpyrifos-methyl as a test molecule, showing that the plasmon resonances of all investigated GNR systems occur at the same frequency (0.95 THz).

Main Message: Terahertz plasmon dispersion in graphene nanoribbons is highly sensitive to ribbon width and charge carrier concentration, and the model reliably matches experimental plasmon spectra across multiple substrates. These results also support GNR-based molecular sensing, with all systems showing a common resonance at ~0.95 THz using chlorpyrifos-methyl as a test molecule.

In the article “A Novel High-Performance 2-to-4 Decoder Design Utilizing a Plasmonic Well and Suspended Graphene Nanoribbon” (contribution 8), the authors present a compact 2-to-4 optical decoder based on a plasmonic well structure incorporating suspended GNRs. The device exploits the tunability of graphene chemical potential to dynamically control the propagation and confinement of surface plasmon polaritons, enabling efficient routing of optical signals toward the output ports. Finite-difference time-domain simulations are used to investigate the effects of channel geometry and graphene chemical potential on surface plasmon polariton propagation, refractive index, and transmission loss. The proposed structure, consisting of a plasmonic well 30 nm wide and 10 nm high, exhibits a low propagation loss of 0.188 dB/µm and a high figure of merit of 1950 at 40 THz. The decoder achieves a contrast ratio of 36.93 dB and crosstalk suppression of −36.93 dB, while occupying a footprint of 0.05 µm². These results demonstrate the high optical performance and compactness of the proposed plasmonic well-based decoder.

Main message: Tunable graphene’s chemical potential enables dynamic control of surface plasmon polariton propagation, resulting in low loss, high contrast ratio, strong crosstalk suppression, and an ultra-compact footprint, demonstrating excellent potential for integrated plasmonic logic and signal-routing applications.

4. Properties and Applications of Graphene Oxide and Reduced Graphene Oxide

GO and rGO have attracted considerable attention as versatile graphene-derived materials, owing to their tunable chemical composition and surface functionality [8]. The presence of oxygen-containing groups and structural defects not only influences their optical and electronic behavior, but also enables a wide range of practical applications. In this SI, three contributions address GO- and rGO-based systems from complementary perspectives, spanning fundamental modeling, spectroscopic characterization, and application-driven studies.

The article “Modelling the Structure and Optical Properties of Reduced Graphene Oxide Produced by Laser Ablation: Insights from XPS and Time-Dependent DFT” (contribution 5) investigates graphene derivatives, specifically rGO and graphene-based composites, which are regarded as promising materials for optoelectronic and photodetection applications. Motivated by the growing interest in simple and environmentally friendly graphene production methods, the study addresses unresolved fundamental issues related to the structure of these materials and the interactions between their components.

The authors propose several atomistic models of oxidized graphene fragments based on X-ray photoelectron spectroscopy compositional analysis and density functional theory calculations, representing rGO produced by laser irradiation. Using these models, they determine the composition of oxygen-containing functional groups, their equilibrium configurations, and their influence on the electronic and optical properties of graphene sheets. The nature of the low-lying excited states and the photoactive regions is also examined. Finally, the calculated absorption spectra of the graphene sheets are compared with the experimental UV–Vis spectrum of rGO obtained by laser ablation.

Main message: The work clarifies the role of oxygen functional groups in electronic structure, low-energy excited states, and optical absorption, showing good agreement between calculated spectra and experimental UV–Vis data and providing insight into photoactive regions of rGO.

The article “Unleashing the Power of Graphene-Based Nanomaterials for Chromium(VI) Ion Elimination from Water” (contribution 6) studies GO-based nanomaterials for heavy metal removal from water. GO and graphene-oxide-coated silica nanoparticles (GO/SiO₂) are synthesized and evaluated for the removal of Cr(VI) ions. The prepared nanosorbents are characterized using FTIR, Raman spectroscopy, and transmission electron microscopy. The effects of pH and Cr(VI) ion concentration on the adsorption process are examined through batch experiments for both GO and GO/SiO₂. The results show that the highest removal efficiency occurs at pH 3 for both adsorbents. At a Cr(VI) concentration of 50 ppm, GO/SiO₂ exhibits a higher removal percentage (92.28%) compared to GO (86.15%). The study confirms that Cr(VI) removal is strongly dependent on both pH and ion concentration and demonstrates that both GO and GO/SiO₂ are effective adsorbents, with GO/SiO₂ showing enhanced performance relative to GO for Cr(VI) removal from water.

Main message: This study investigates GO and GO-coated silica nanoparticles for Cr(VI) removal from water. Batch adsorption experiments show strong pH and concentration dependence, with optimal performance at pH 3. GO/SiO₂ achieves higher removal efficiency (92.28% at 50 ppm) than GO (86.15%), demonstrating enhanced adsorption capability for water remediation applications.

The review “Recent Advances in the Raman Investigation of Structural and Optical Properties of Graphene and Other Two-Dimensional Materials” (contribution 1) summarizes recent progress in the investigation of graphene and other 2D materials. The review includes studies on GO thin films deposited on different substrates, such as titanium and silver thin films. Particular attention is devoted to the role of surface-enhanced Raman scattering (SERS) and to the effects of film thickness and laser power on the Raman response. Studies on a silver/GO/gold sandwich configuration reveal the appearance of sharp Raman modes associated with localized surface plasmon resonances.

Main message: Recent progress in the investigation of graphene and other 2D materials is summarized.

5. Graphene-Based Silicon Heterostructures for Optoelectronic Applications

The interaction between graphene-based materials and silicon (Si) has attracted growing interest for applications in optoelectronics, photovoltaics, and sensing [9]. A detailed understanding of charge transport, interfacial effects, and defect-related phenomena is essential to fully exploit the potential of these hybrid systems. Accordingly, two studies in this SI investigate graphene-based layers on Si substrates, providing insights into their electrical performance and transport mechanisms.

In the paper “Low-Frequency Noise Characteristics of Graphene/h-BN/Si Junctions” (contribution 7), the authors investigate graphene/h-BN/Si heterostructures, which are considered promising for infrared detection and photovoltaic applications due to their tunable electrical properties and well-matched interfaces. The near lattice matching between graphene and hexagonal boron nitride (h-BN) enables the growth of graphene layers with low defect density on h-BN substrates. The study provides a detailed analysis of the low-frequency electrical noise behavior of graphene/h-BN/Si heterojunctions under both forward and reverse bias at room temperature. Graphene nanolayers are directly grown on h-BN films by microwave plasma-enhanced chemical vapor deposition, while the h-BN layers are deposited by reactive high-power impulse magnetron sputtering (HiPIMS). Four different h-BN thicknesses (1 nm, 3 nm, 5 nm, and 15 nm) are examined, together with a reference graphene/Si junction fabricated under the same conditions without the h-BN interlayer. Low-frequency noise measurements are used to identify the dominant charge transport mechanisms in the different structures. The results show that grain boundaries act as major defects leading to increased noise levels under high forward bias. A statistical analysis of the voltage noise spectral density over multiple devices, supported by Raman spectroscopy, indicates that hydrogen-related defects play a significant role in the 1/f noise observed in the linear region of the current–voltage characteristics. This work provides a detailed assessment of the influence of h-BN interlayers on low-frequency noise in graphene/Si heterojunctions.

Main message: Graphene/h-BN/Si junctions are investigated to understand how electrical noise affects their performance in optoelectronic applications. By comparing different h-BN thicknesses, the authors show that defects at grain boundaries and hydrogen-related imperfections strongly influence low-frequency noise, highlighting the role of material quality in improving device reliability.

In the paper “Cyclic Voltammetry and Impedance Measurements of Graphene Oxide Thin Films Dip-Coated on n-Type and p-Type Silicon” (contribution 2), the authors address a comparatively less explored aspect of graphene research, namely the enhancement of silicon performance through interaction with graphene-based materials. Cyclic voltammetry and electrical impedance measurements are carried out on GO dip-coated on both n-type and p-type Si substrates. The results show a significant improvement in the electrical properties of GO on n-type Si, with a marked increase in conductivity and photocurrent compared to bare n-type Si. These findings highlight the potential of GO to enhance silicon-based devices and suggest possible applications in optoelectronics, contributing to the future integration of GO within the silicon semiconductor industry.

Main message: This work highlights the potential of GO to enhance silicon-based devices and outlines possible optoelectronic applications, supporting the future integration of GO within the silicon semiconductor industry.

6. Two-Dimensional Materials Beyond Graphene

Beyond graphene, a broad class of 2D materials has emerged, exhibiting physical properties that differ markedly from their bulk counterparts and enable novel functionalities. In this SI, two contributions address two-dimensional materials beyond graphene.

The article “The Pressure Response of Bulk and Two−Dimensional MoS₂ Crystals Studied by Raman and Photoluminescence Spectroscopy: Dimensionality and Pressure Transmitting Medium Effects” (contribution 9) investigates the pressure response of bulk and 2D MoS₂ crystals, including monolayer, bilayer, and multilayer samples, directly transferred onto the diamond surface of a diamond anvil cell (DAC). Raman and photoluminescence (PL) spectroscopy are employed to probe the pressure-induced changes. For high-pressure experiments on 2D MoS₂, Daphne 7474 oil and a 4:1 methanol–ethanol mixture are alternatively used as pressure-transmitting media (PTM), while Daphne 7474 oil is also used in the case of bulk MoS₂. The authors observe distinct differences in the pressure evolution of the Raman spectral features and in the pressure coefficients of the vibrational modes between bulk and 2D MoS₂ crystals of different thicknesses, with an additional dependence on the PTM employed.

Main message: Distinct pressure-dependent vibrational and optical behaviors are observed between bulk and mono-, bi-, and multilayer MoS₂, with additional sensitivity to the pressure-transmitting medium, highlighting the combined effects of dimensionality and experimental conditions on MoS₂ under compression.

In the article “Double-Heterostructure Resonant Tunneling Transistors of Surface-Functionalized Sb and Bi Monolayer Nanoribbons” (contribution 4), the authors investigate zigzag nanoribbons derived from chemically surface-modified antimony (Sb) and bismuth (Bi) monolayers, which are two-dimensional topological materials, using first-principles electronic-structure calculations. Surface functionalization with methyl, amino, or hydroxyl groups is considered to assess their potential for applications in topological transport nanoelectronics. The presence of Dirac-point-like energy dispersion near the Fermi level confirms that the scattering-forbidden edge states in these nanoribbons provide topological conductive channels with extremely high electron mobility. Based on these properties, Sb/SbXHn/Sb and Bi/BiXHn/Bi nanoribbon double heterostructures (XHn = CH₃, NH₂, OH) are designed as resonant tunneling transistors. Their electron transport characteristics are evaluated using nonequilibrium Green’s function methods combined with first-principles calculations. The calculated ballistic equilibrium conduction spectra and current–voltage characteristics demonstrate that the quantum conductance arises from resonant electron tunneling between the topological edge states of the two Sb or Bi monolayer nanoribbons through the central SbXHn or BiXHn barrier. This mechanism leads to pronounced resonant current peaks accompanied by strong negative differential conductance, highlighting the suitability of these nanoribbon heterostructures for zero-loss and ultrahigh-frequency resonant tunneling applications.

Main message: This article explores antimony and bismuth nanoribbons as promising building blocks for future nanoelectronic devices. By modifying their surfaces, the authors show that these materials can efficiently control electron flow, enabling resonant tunneling behavior with high performance.

7. Conclusions

The nine papers collected in this SI exemplify the versatility and transformative potential of graphene and other 2D materials in addressing fundamental scientific questions and practical technological challenges.

Looking forward, the continued advancement of research on this topic will require sustained efforts in several key areas: the development of scalable synthesis methods that maintain high material quality; the refinement of theoretical and computational tools that can handle the complexity of real-world systems, including defects, disorder, and environmental effects; and the engineering of robust integration strategies that bridge the gap between laboratory demonstrations and commercial technologies.

The integration of experimental advancements with theoretical insights, as demonstrated throughout this SI, will undoubtedly drive future breakthroughs in the field. The diverse approaches, innovative methodologies, and significant findings presented here provide both inspiration and practical guidance for the next generation of investigations. We sincerely hope that the insights and advances reported in this SI will stimulate further research and contribute to the second Volume of the SI (https://www.mdpi.com/journal/crystals/special_issues/4824H80143, accessed on 2 February 2026).