Layered platinum diselenide (PtSe₂) grown by molecular beam epitaxy provides a reliable and reproducible alternative to mechanical exfoliation, making it suitable for scalable device integration. In this work, we thoroughly investigate the in-plane thermal conductivity of multilayer suspended PtSe 2 membranes. For this study, we first achieved the transfer of large-scale epitaxially grown PtSe 2 and demonstrate a highly efficient process that enables the fabrication of multiple suspended membranes in a single transfer while maintaining the structural quality of the material. Optothermal Raman Technique is then used to investigate the in-plane thermal conductivity of the suspended PtSe₂ membranes. This approach leverages millimeter-scale transfer to conduct systematic ORT measurements, enabling statistical refined thermal conductivity of 11.92 ± 1.78 W·m −1 ·K −1 , with negligible dependence on vacuum/air environments. Finally, our results are supported by numerical simulations using a COMSOL model. This work provides significant insights into the thermal properties of PtSe₂, paving the way for the design of high-performance electronic devices with enhanced thermal management capabilities.

On-chip integration of two-dimensional transition metal dichalcogenides (TMDs) with photonic waveguides underpins a growing class of compact optoelectronic and sensing devices, whose performance depends on the optical absorption of the 2D material in this integrated environment. We demonstrate source-free, on-chip evanescent absorption spectroscopy of MoS_2 and WS_2 flakes integrated on Si_3N_4 waveguides, in which the broadband defect-related photoluminescence of the Si_3N_4 core itself acts as the internal probe. Light generated inside the core propagates under the TMD flake and is spectrally attenuated by evanescent interaction with the 2D material, and normalizing the transmitted spectrum to a reference waveguide without TMD yields the energy-dependent absorption response without any external illumination. The extracted guided absorption agrees with Raman and local micro-photoluminescence characterization and resolves differences between spatially uniform and non-uniform flakes. A complementary top-pumping scheme recovers guided WS_2 photoluminescence, whose spectral reshaping during propagation is quantitatively reproduced by the measured absorption. This source-free platform qualifies 2D materials in their integrated photonic environment and provides a direct route toward waveguide-integrated TMD photodetectors and sensors.

Accurate prediction of phonon propagation is crucial for modeling temperature-dependent properties in solid-state systems-particularly in two-dimensional (2D) materials and their heterostructures, where interfacial effects strongly influence vibrational and thermal behavior. Here, we employ density functional theory to investigate the impact of anharmonicity on thermal expansion and temperature-dependent phonon frequencies in semiconducting monolayers of transition metal dichalcogenides (TMDCs), specifically MoS2 and WS2, and their vertical heterostructures with insulating hexagonal boron nitride. We specifically examine the often-overlooked rotational invariance condition (RIC) of interatomic force constants, a fundamental symmetry requirement. Our results show that thermal expansion significantly affects all geometric parameters in monolayers and heterostructures, including in-plane lattice constants, monolayer thickness, and interlayer separation (with the expansion of the latter reaching similar to 2.1 & times; 10-5 K-1 at 300 K). We also provide first-principles predictions of the temperature dependence of prominent Raman-active E '-like and A1 '-like phonon modes in TMDC-based systems, highlighting the roles of thermal expansion and phonon-phonon interactions. Notably, we find that anharmonicity alone can alter the frequency difference of a given Raman-active phonon mode between monolayer and heterostructure forms-by >= 0.4 cm-1 at 300 K. Furthermore, we demonstrate that neglecting RIC leads to incorrect phonon redshifts, with errors >= 0.5 cm-1 in monolayers and >= 0.1 cm-1 in heterostructures at 300 K-potentially exceeding Raman spectroscopy resolution. It also distorts thermal expansion coefficients, with deviations of up to similar to 30%. These discrepancies arise primarily from the mischaracterization of out-of-plane acoustic (ZA) phonons, which may exhibit unphysical imaginary frequencies or erroneous quasi-linear dispersion, instead of the symmetry-preserving quadratic behavior. The framework enables accurate modeling of temperature-dependent vibrational and thermal phenomena in a range of 2D systems.

The large-scale synthesis of van der Waals heterostructures (vdWHSs) is required to adopt these materials in electronic devices. However, the repeatable and controllable growth of vdWHSs has proven challenging. Here, we investigate the technological aspects of solid-source chemical vapor deposition (CVD) of two-dimensional heterostructures, with WS2/graphene and MoS2/graphene as examples. We show that by modification of one variable at least one another is unintentionally altered. For example, change in the growth pressure influences the evaporation rate of sulfur and shifts the position of one of the growth zones. We also perform a statistical screening of the 11 process parameters, indicating which of them impact the evaporation of the precursors. The screening indicates that the evaporation depends on weight of growth promoter (NaCl), growth temperature, precursors temperature, time difference between main and sulfur growth zones reaching the set temperatures, pressure, carrier gas flow, and process time. Finally, the five consecutive, identical growth processes show the seemingly inherent variability in synthesizing vdWHSs. We suggest that the high but limited airtightness of the CVD system or the substrate features can cause repeatability issues. Our study can facilitate future research on van der Waals heterostructures growth.

Anharmonicity is a crucial feature of solid-state systems, affecting phenomena such as thermal expansion and temperature-dependent heat conductivity. Here, phonon anharmonicity in monolayer MoS2, WS2, and their heterostructures with graphene is comprehensively investigated, using ab-initio calculations and Raman spectroscopy. The presented theoretical approach yields exceptionally accurate predictions of temperaturedependent phonon frequencies in these systems. It is demonstrated that the friction regime between monolayers strongly affects thermal expansion in heterostructures - resulting in a tenfold difference in-plane expansion coefficients. Furthermore, significant impact of four-phonon processes is unveiled, contributing to approximately 1/3 of temperature-dependent frequency slopes (d omega/dT) in MoS2 and WS2 monolayers, although this factor has been commonly ignored in state-of-the-art theoretical works. This effect changes noticeably if a graphene cap layer is present, which, combined with the evolved thermal expansion, can flatten the d omega/dT slopes by 20 %. Our work introduces a novel approach to calculating phonon anharmonicity in complex, multi-layered two-dimensional structures, which might also support determining their macroscopic thermal properties.

In this work, we present a new graphene-based sensor designed to monitor a set of photovoltaic panels on a sound-absorbing screen in terms of their potential mechanical damage. The innovative design of the photovoltaic module and consequently its sound-reflecting and sound-absorbing parameters play a vital role. The light transmittance of the sensor layer composed of graphene flakes in a cellulose matrix, confirmed by optical studies, allows its use directly over the photovoltaic cells. All the sensors are interconnected with metallic connections to reduce their internal resistance on larger surfaces. The sensor state is monitored through the resistance value as a zero-one operation/damaged response. Two sensor damage, scenarios, repetitive scratching, and cutting-out were described. The sensor measurements were performed in the potential ranging from 2.1 to 51.1 V, and the current response allowed to calculate the total resistance. The change in sensor resistance ranged between 9.3 and 24.1%, depending on the damaged area. The resistance for the scratched surface oscillated between 25 and 26 Ω, whereas the cut-out surface showed values more than 1.5 times higher. The proposed sensor based on graphene, cellulose, and ethylene–vinyl acetate allows the registration of immediate information about the destruction or theft of a power node.

Technological progress in producing graphene nanoplatelets on a large scale and using them in perspective applications requires a statistical approach to their properties characterization. Here, a novel approach to analyzing graphene nanoplatelets' properties using Raman spectroscopy with the support of X-ray diffraction is presented. An illustrative method for analyzing two parameters of the 2D band in Raman spectra - full width at half maximum Gamma 2D and its coefficient of determination R2 is introduced. The trends of R2(Gamma 2D) graph allows for tracking exfoliation effects from graphite with 90 nm thickness to a monolayer of graphene nanoplatelets. It is proposed to classify the quality of graphene nanoplatelets based on the trends of the R2(Gamma 2D) graph in terms of the number of layers as well as defects of structure, inter-layer distances, and stacking between layers, which analysis was supported by X-ray diffraction. This analysis is particularly useful for analyzing graphene nanoplatelets' properties during the development of innovative, large-scale production methods and for characterizing graphene materials available on the market from an industrial point of view.

Sub-wavelength metasurfaces offer opportunities to develop efficient stealth technologies that are increasingly significant in modern civil and military applications. Here, we demonstrate that a highly efficient flexible graphene-based composite sub-THz radiation absorber can also act as an ultra-low reflection material with reflectivity as low as 0.12%. To enable this, we employ a surface modification of the composite with periodic shapes designed to harness the sub-wave low reflection mechanism for a given frequency- at 96.9 GHz that is within the range of the atmospheric radio window. The terahertz goniometric system measurements show that the fabricated metasurface works for terahertz waves with two polarization directions (S and P) and exhibits material characteristics with polarization independence. Our work offers an alternative approach for designing and fabricating a flexible metasurface for efficient antireflection and stealth application. (c) 2024 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

Commonly used materials for protection against ionizing radiation (gamma and X-ray energy range) primarily rely on high-density materials, like lead, steel, or tungsten. However, these materials are heavy and often impractical for various applications, especially where weight is a key parameter, like in avionics or space technology. Here, we study the shielding properties of an alternative light material—a graphene-based composite with a relatively low density ~ 1 g/cm3. We demonstrate that the linear attenuation coefficient is energy of radiation dependent, and it is validated by the XCOM model, showing relatively good agreement. We also show that the mass attenuation coefficient for selected radiation energies is at least comparable with other known materials, exceeding the value of 0.2 cm2/g for higher energies. This study proves the usefulness of a commonly used model for predicting the attenuation of gamma and X-ray radiation for new materials. It shows a new potential candidate for shielding application.

Dipole-dipole interactions provide a route to couple excitons across materials of different dimensionality. Here, we introduce hybrid films as a cross-dimensional excitonic platform and develop a theory of resonant Raman scattering in the presence of dipolar exciton coupling. Combining a coupled-oscillator model with perturbation theory, we show that coupling renormalizes the exciton-photon matrix elements and modifies nanotube Raman excitation profiles. We test this framework in vacuum-filtered films containing InP/ZnS quantum dots and mixed chirality metallic single-walled carbon nanotubes. The quantum-dot exciton remains near 1.83 eV, while chirality-dependent nanotube excitons span 1.7-1.93 eV, enabling systematic control of excitonic detuning. Relative to pristine nanotube films, the hybrids exhibit detuning-dependent redshifts and blueshifts, Raman intensity enhancement, reduced effective linewidths, and near-resonant two-branch profiles. The model yields an effective splitting of approximately 110 meV. Resonant Raman scattering thus provides component-selective access to dipolar interactions that are only weakly apparent in ensemble absorption spectra.

One of the primary factors hindering the development of 2D material-based devices is the difficulty of overcoming fabrication processes, which pose a challenge in achieving low-resistance contacts. Widely used metal deposition methods lead to unfavorable Fermi level pinning effect (FLP), which prevents control over the Schottky barrier height at the metal/2D material junction. We propose to harness the FLP effect to lower contact resistance in field-effect transistors (FETs) by using an additional 2D interlayer at the conducting channel and metallic contact interface (under-contact interlayer). To do so, we developed a new approach using the gold-assisted transfer method, which enables the fabrication of heterostructures consisting of TMDs monolayers with complex shapes, prepatterned using e-beam lithography, with lateral dimensions even down to 100 nm. We designed and demonstrated tungsten disulfide (WS2) monolayer-based devices in which the molybdenum disulfide (MoS2) monolayer is placed only in the contact area of the FET, creating an Au/MoS2/WS2 junction, which effectively reduces contact resistance by over 60% and improves the Ion/Ioff ratio 10 times in comparison to WS2-based devices without MoS2 under-contact interlayer. The enhancement in the device operation arises from the FLP effect occurring only at the interface between the metal and the first layer of the MoS2/WS2 heterostructure. This results in favorable band alignment, which enhances the current flow through the junction. To ensure the reproducibility of our devices, we systematically analyzed 160 FET devices fabricated with under-contact interlayer and without it. Statistical analysis shows a consistent improvement in the operation of the device and reveals the impact of contact resistance on key FET performance indicators.

Van der Waals heterostructures (vdWHSs) enable the fabrication of complex electronic devices based on two-dimensional (2D) materials. Ideally, these vdWHSs should be fabricated in a scalable and repeatable way and only in the specific areas of the substrate to lower the number of technological operations inducing defects and impurities. Here, we present a method of selective fabrication of vdWHSs via chemical vapor deposition by electron-beam (EB) irradiation. We distinguish two growth modes: positive (2D materials nucleate on the irradiated regions) on graphene and tungsten disulfide (WS2) substrates, and negative (2D materials do not nucleate on the irradiated regions) on the graphene substrate. The growth mode is controlled by limiting the air exposure of the irradiated substrate and the time between irradiation and growth. We conducted Raman mapping, Kelvin-probe force microscopy, X-ray photoelectron spectroscopy, and density-functional theory modeling studies to investigate the selective growth mechanism. We conclude that the selective growth is explained by the competition of three effects: EB-induced defects, adsorption of carbon species, and electrostatic interaction. The method here is a critical step toward the industry-scale fabrication of 2D-materials-based devices.

The objective of this study was to obtain a geopolymer composite with semi-conductive or conductive properties for self-control of abnormal symptoms caused by damages to its microstructure. For that purpose effects of different content of fly ash, waste glass powder, as well as two types of graphene and hydrophilic and hydrophobic nanosilica on electrical, physical and mechanical properties were tested. Measurements of resistivity showed the capacity for electrical charge flow in composites, which depended on their composition and products of the geopolymer hardening process. Based on results of the electrical charge flow intensity and observations of geopolymer composite microstructure by means of XRD and scanning microscopy, a possible course of the electrical conductivity mechanism in geopolymer materials was indicated. It was found that geopolymer composites containing fly ash, as well as addition of graphene and hydrophobic nanosilica, showed the most favourable electrical charge conductivity parameters and the highest strength gain.

In this study, we comprehensively investigate the shape of Raman spectra in titanium disulfide (TiS2) and its temperature dependence, using first-principles calculations and a rigorous theoretical approach to evaluate the corresponding Raman scattering cross sections. Our analysis includes anharmonicity-induced effects: phonon-phonon interactions and the thermal expansion of the 1T-TiS2 crystal. We aim to establish the origin of a not yet fully understood Raman feature often observed at the high-energy side of the band corresponding to the out-of-plane A(1g) phonon mode-commonly called the "shoulder" band. We show that TiS2 is an example of a counterintuitive situation in which a relatively large anharmonicity of the system and its specific two-phonon density of states can lead to a highly asymmetric A(1g) band-consisting of the main band and a high-energy shoulder. Although the presence of the "shoulder" band is confirmed for ideal 1T-TiS2 crystals, we also consider realistic TiS2 systems characterized by the often-reported presence of excess interlayer titanium atoms. According to our simulation, such defects lead to the splitting of the A(1g) phonon mode, resulting in the formation of a high-energy shoulder independent of the anharmonicity-induced mechanism depicted above. The dependence of the phonon splitting on the amount and spatial distribution of the extra titanium atoms is also investigated.

High-quality and high-yield production of graphene nanoplatelets (GNPs) is the ultimate challenge in today's graphene technology that would allow mature commercialization. Recently demonstrated new methods still suffer from low quantities of exfoliated graphene and a lack of controllable qualities, processability, and costs. Here, we developed a simple yet compelling chemical route for industry-scale production of turbostratic-like GNPs (similar to 10 layers) that relies on simultaneous, nonoxidative intercalation and exfoliation of raw graphite with 100% weight efficiency. High yield is enabled because unbounded SO3 molecules dissolved in heated, fuming sulfuric acid can effectively intercalate into the graphite, boosting spontaneous exfoliation during ultrasound treatment. The density functional theory calculation indicates a two-step subsequent intercalation mechanism with SO3 and H2SO4 molecules before final exfoliation. X-ray diffraction, vibrational spectroscopy, and elemental analysis confirm very low concentration of defects and lack of strong oxidization effects in the graphene layers, whereas electron microscopy and diffraction show a fine structure.

This work is dedicated to a non-destructive technique that allows modeling-based extraction of the surface resistance, resistivity and conductivity maps of graphene-based polymer composites. The technique is based on the use of a 10 GHz inverted Single-Post Dielectric Resonator (iSiPDR) incorporated into a 2D scanner. Retro-modeling is then applied to convert the measured microwave signal parameters to material characteristics. Retro-modeling requires the actual modeling to be performed may times, over a grid of parameters (material parameters and sample dimensions), and therefore, an ultra-fast conformal FDTD Bodies-of-Revolution (BoR) formulation of the FDTD method is utilized here. The maps of material parameters allow non-destructive testing of the developed composites and will be used for their assessment for different applications, such as electromagnetic shielding.

Insufficient homogeneity is one of the pressing problems in nanocomposites’ production as it largely impairs the properties of materials with relatively high filler concentration. Within this work, it is demonstrated how selected mixing techniques (magnetic mixer stirring, calendaring and microfluidization) affect filler distribution in poly(dimethylsiloxane)-graphene based nanocomposites and, consequently, their properties. The differences were assessed via imaging and thermal techniques, i.a. Raman spectroscopy, differential scanning calorimetry and thermogravimetry. As microfluidization proved to provide the best homogenization, it was used to prepare nanocomposites of different filler concentration, whose structural and thermal properties were investigated. The results show that the concentration of graphene significantly affects polymer chain mobility, grain sizes, defect density and cross-linking level. Both factors considered in this work considerably influence thermal stability and other features which are crucial for application in electronics, EMI shielding, thermal interface materials etc.

This article presents an attempt to determine the effect of the MXene phase addition and its decomposition during sintering with the use of the spark plasma sintering method on mechanical properties and residual stress of silicon carbide based composites. For this purpose, the unreinforced silicon carbide sinter and the silicon carbide composite with the addition of 2 wt.% of Ti3C2Tx were tested. The results showed a significant increase of fracture toughness and hardness for composite, respectively 36% and 13%. The numerical study involving this novel method of modelling shows the presence of a complex state of stress in the material, which is related to the anisotropic properties of graphitic carbon structures formed during sintering. An attempt to determine the actual values of residual stress in the tested materials using Raman spectroscopy was also made. These tests showed a good correlation with the constructed numerical model and confirmed the presence of a complex state of residual stress.

Anharmonicity is an essential property of two-dimensional materials due to its significant impact on lattice dynamics - involving interactions between phonons, thermal expansion of the structure, and interaction with the substrate. The effects manifest in temperature-dependent redshifts of the phonon frequencies and reduced lifetime. In this work, we investigate phonon anharmonicity in supported 1-5 layered WS(2 )by performing Raman measurements in the temperature range of 80-500 K and explore the results by ab-initio DFT study. An ab-initio model including three-phonon interaction processes and thermal expansion of all geometrical degrees of freedom (in-plane lattice constant, interlayer distance, and monolayer thickness) well describes the experimental temperature trends of the fundamental E-2g(1) (in -plane) and A(1g) (out-of-plane) phonon modes, giving a great promise of using simulation to quantitatively analyze phonon propagation and heat transport in multi-layered two-dimensional materials. The models predict a noticeable increase in the temperature-induced slope of A(1g) vibrations' frequency with the number of layers - primarily due to the thermal expansion of interlayer distance. Additionally, we study the impact of the substrate on the phonon properties - concerning cumulated effects of induced strain and electron doping. We show that the effect of biaxial strain is the most significant in the E-2g(1) phonon mode and independent of the number of layers, while the excess charge is more significant in thin films and affects mainly the A(1g) mode. The presented studies based on a combination of ab-initio and experimental approaches can be extended to quantitatively analyze phonon evolution with structural modification and external stimuli. (c) 2022 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Polymer composites with high dielectric constant and low loss tangent are highly regarded as substrates for modern high-speed electronics. In this work, we analyze the high-frequency dielectric properties of two types of composites based on polypropylene infused with high-dielectric-constant microparticles. Two types of fillers are used: commercial ceramics or titanium oxide (TiO 2 ) with different concentrations. The key observation is that adding the fillers causes an increase of dielectric constants by around 100% (for highest loading) up to 4.2 and 3.4, for micro-ceramics and TiO 2 based composites, respectively. Interestingly, for the TiO 2 composite, the loss tangent depends on the filler loading volume, whereas the other composite has a slightly increasing tendency, however, being at the level ~ 10 –3 . To explain the experimental results, a theoretical model determined by microwave reflection and transmission through a representative volume element is proposed, which allows the investigation of the impact of volume ratio, grain shape, aggregation, and size on the loss tangent and permittivity evolution. This approach could be used for modeling other low dielectric loss materials with inclusions.