The construction of hybrid organic-inorganic systems is usually aimed at increasing the electrical conductivity and modifying the work function of transparent and conductive electrodes. Here, we describe the fabrication and photoelectrical studies of a light-emitting diode incorporating graphene/molybdenum oxide as an anode and poly(para-phenylene vinylene) copolymer as an organic emitting layer. We observed increased hole injection from the anode relative to electron injection from the cathode, as well as undesirable hole-electron recombination at the graphene-polymer interface responsible for a significant charge leakage. Modeling the multilayer structure of organic light emitting diodes using electrical equivalent circuits based on the results of impedance spectroscopy measurements, we analyzed the electronic processes in the graphene/metal-oxide/organic layer junction. We developed a complex mathematical model to analyze and interpret impedance data. The original method that we present here provides a way to monitor the charge density of the main charge carriers as well as the leaked ones. The work paves the way towards understanding the interface charge transport phenomena in multilayer systems, in particular polymer light-emitting diodes.

We investigate degradation and surface protection of epitaxial 2H-MoTe2 films grown by molecular beam epitaxy on GaAs(111)B substrates. Using X-ray photoelectron spectroscopy (XPS), scanning tunneling microscopy, atomic force microscopy (AFM), Kelvin probe microscopy (KPM), Raman spectroscopy, and density functional theory (DFT), we examine the structural, chemical, and electronic evolution of MoTe2 protected by Co and Ni capping layers. XPS shows that the metallic caps effectively suppress oxidation during short-term air transfer, while revealing a pronounced Te-rich near-surface composition. With time, the caps become increasingly difficult to remove, suggesting gradual interfacial bonding promoted by excess tellurium and defect-rich MoTe2 interfaces. AFM and KPM reveal pronounced thickness-dependent ageing, with ultrathin regions showing markedly different contact-potential evolution from thicker films. DFT calculations support the sensitivity of work function and density of states to thickness and surface chemistry. Raman measurements through approximately 20 nm thick metallic caps demonstrate partial optical access to the protected material. Additional AFM and Raman observations suggest local formation of Te-rich nanostructures under laser illumination or near mechanically damaged regions. These results provide practical guidelines for protecting, transferring, delaminating, and optically characterizing air-sensitive MoTe2 and related van der Waals materials.

The application of two-dimensional (2D) semiconductors, such as monolayer MoS2, is limited by the high contact resistance commonly attributed to interfacial barriers at metal contacts. Furthermore, the dependence of electrical conductivity on MoS2 thickness is still unsettled, as both increasing and decreasing trends with layer number have been reported. By showing the contrast between electrical transport of mono- and multilayer MoS2 exfoliated on Au under ultra-high vacuum (UHV) and ambient conditions, we experimentally prove that, contrary to the prevailing view in the literature, the intrinsic MoS2/Au junction is highly conductive and exhibits ohmic behaviour. Our results indicate that interfacial contamination is responsible for the high contact resistances reported to date and affects the thickness dependence of electrical transport, explaining the discrepancies observed in the literature. We rationalize those findings using electrical transport simulations. Lastly, we show that local force-mediated lamination on lightly contaminated contacts can recover pristine, ohmic contacts, offering a route towards nanoscale patterning.

The article presents a positioning control system for adjustment screws in a mapping Raman spectroscopy setup. The solution employs inductive sensors based on LC resonant circuits and LDC1614 converters, enabling contactless measurement of metal component positions with high precision. The developed electronic hardware and Raspberry Pi Pico microcontroller firmware provide integration with the spectrometer control system. Tests confirmed the method’s effectiveness in compensating for errors caused by hysteresis and thermal drift, making the proposed solution useful for high-precision spectroscopic and measurement applications.

Crystal symmetries in solids give rise to spin–momentum locking, which determines how an electron's spin orientation depends on its momentum. This relationship, often referred to as spin texture, influences both charge-to-spin conversion and spin relaxation, making it one of the essential characteristics for spin–orbit-driven phenomena. Materials with strong spin–orbit coupling and broken inversion symmetry can host persistent spin textures (PSTs)—unidirectional spin configurations in momentum space, supporting efficient charge-to-spin conversion and extended spin lifetimes. Monolayer WTe2, a topological material crystallizing in a rectangular lattice, is a notable example; its symmetry enforces a canted PST, enabling the quantum spin Hall effect with the nontrivial spin orientation. Here, we use first-principles calculations to explore how these properties are modified when WTe2 is interfaced with graphene. We find that the PST is preserved by the local symmetry present in different regions of the heterostructure, while the system develops extended electron and hole pockets, resulting in semimetallic behavior. Although the bandgap closes and eliminates the quantum spin Hall phase, spin Hall effects remain robust in both conventional and unconventional geometries. The computed spin Hall conductivities are comparable to those of other two-dimensional materials, and the survival of the PST suggests the possibility of long-range spin transport even in the absence of topological edge states. In addition, the graphene layer serves as an oxidation barrier, helping protect the intrinsic properties of WTe2 and supporting the potential of this heterostructure for spintronic applications.

Correction for 'Correction: The coexistence of Dirac cones and Fermi arcs in a graphene/WTe2 heterostructure' by Wojciech Ryś et al., Nanoscale, 2025, 17, 28209, https://doi.org/10.1039/D5NR90229K.

Crystal symmetries in solids give rise to spin-momentum locking, which determines how an electron's spin orientation depends on its momentum. This relationship, often referred to as spin texture, influences both charge-to-spin conversion and spin relaxation, making it one of the essential characteristics for spin-orbit-driven phenomena. Materials with strong spin-orbit coupling and broken inversion symmetry can host persistent spin textures (PSTs) - unidirectional spin configurations in momentum space, supporting efficient charge-to-spin conversion and extended spin lifetimes. Monolayer WTe_2, a topological material crystallizing in a rectangular lattice, is a notable example; its symmetry enforces a canted PST enabling quantum spin Hall effect with the nontrivial spin orientation. Here, we use first-principles calculations to explore how these properties are modified when WTe_2 is interfaced with graphene. We find that the PST is preserved by the local symmetry present in different regions of the heterostructure, while the system develops extended electron and hole pockets, resulting in semimetallic behavior. Although the band gap closes and eliminates the quantum spin Hall phase, spin Hall effects remain robust in both conventional and unconventional geometries. The computed spin Hall conductivities are comparable to those of other two-dimensional materials, and the survival of the PST suggests the possibility of long-range spin transport even in the absence of topological edge states. In addition, the graphene layer serves as an oxidation barrier, helping protect the intrinsic properties of WTe_2 and supporting the potential of this heterostructure for spintronic applications.

We report here a comprehensive study of thickness-dependent Raman measurements at the wavelength of 532 nm of five ultrathin van der Waals materials, namely, 2H-MoS2, 1T-TaS2, 1T'-MoTe2, T d-WTe2, and alpha-MoO3, and interpret using Fabry-Perot (F-P) interferences. We point out the importance of extinction coefficient k for F-P phenomena, which together with optical contrast are stronger for materials characterized by low k values. Conducted simulations indicate that in first approximation, one can expect enhancement of the Raman signal from regions of low optical contrast. Additionally, we find also that for the 532 nm light, the tellurides have a higher absorption coefficient than the sulfides. Moreover, we observe edge states amplified by plasmonic effects in the trench formed in the tear of a MoS2 flake. Finally, we show that laser irradiation of MoTe2 and WTe2 can lead to generation of metallic tellurium. This result is an alternative explanation to many recent reports claiming a transition in MoTe2 from 1T' to T d phase.

Metal halide perovskites are ideal candidates for indoor photovoltaics (IPVs) due to their tunable bandgaps, which allow the active layers to be optimized for artificial light sources. However, significant non-radiative carrier recombination under low-light conditions has limited the full potential of perovskite-based IPVs. To address this challenge, an integration of perylene diimide (PDI)-based sulfobetaines as cathode interlayers (CILs) is proposed and the impact of varying alkyl chain length (from 1,2-ethylene to 1,5-pentylene) between the cationic and the anionic moieties is examined. The respective four PDI materials are synthesized almost qualitatively using a one-step microwave-assisted process. All of them show adequate thermal stability and energy levels suitable for the desired application as CILs. Moreover, their degradation temperature, LUMO level, conductivity, and performance in model devices are found to change positively along with the alkyl chain length increase. Among the tested derivatives, the compound equipped with the longest alkyl chain (PDI-C5-S3) stands out for its superior electrical conductivity and enhanced ability to lower the silver cathode work function. When incorporated into Cs0.18FA0.82Pb(I0.8Br0.2)-based wide-bandgap perovskite solar cells (PSCs), the PDI-C5-S3 interlayer lead to an outstanding power conversion efficiency (PCE) of 19.04% under one-sun illumination and a remarkable 40.72% under 3000K LED (1000 lux) conditions.

We report on the electronic properties of a van der Waals heterostructure formed by graphene and a type-II Weyl semimetal (Td-WTe2), hosting features of both Dirac and Weyl semimetals. By combining angle-resolved photoemission spectroscopy (ARPES), scanning tunnelling microscopy and spectroscopy (STM/STS), and density functional theory (DFT) calculations, we directly visualise how the interlayer interaction modifies the electronic structures of both materials in the heterostructure. Furthermore, STM reveals that the local twist angle between the graphene and the Weyl semimetal affects the appearance of moiré patterns in the heterostructure, which in turn suggests a twist-angle-dependent modulation of the interlayer interaction. Finally, we also show XPS 4d lines splitting for Te related to the local environment of tellurium atoms. Our findings highlight the importance of controlling twist angles and interlayer interactions for electronics and twistronics applications based on novel quantum materials.

This study examines the thermal stability and structural behavior of bismuth chloride telluride BiTeCl, a layered thermoelectric material with significant potential for energy conversion applications. Our investigations reveal that the chlorine-terminated surface exhibits poorer quality and increased defectivity compared to the tellurium-terminated side. The crystals were subjected to thermal annealing up to 520 K and green laser irradiation. Through techniques such as low-energy electron diffraction (LEED) and X-ray photoelectron spectroscopy (XPS), we found that while annealing enhances the crystallinity of the chlorine side up to 470 K, it ultimately suffers from thermal degradation above this temperature. The event leads to transformation into bismuth telluride - Bi2Te3 characterized by a lower BE shift of the Bi and Te bands by ~ 0.35 eV. The identity of the product was later confirmed via Raman spectroscopy while irradiating it with little laser power. With an increase in the power to 3.1 mW, it was however observed that the samples become locally modified undergoing similar degradation as during the annealing. The research demonstrates and characterizes the phenomena occurring during the decomposition either via irradiation or annealing. The explanation of such phenomena is then proposed based on the results of our theoretical DFT calculations. Additionally, we assess the usefulness of BiTeCl as a thermoelectric material, compare it in regard to the literature, and suggest new potential applications that may benefit from the transformation into Bi2Te3.

An electronic control system developed by our team for spatial mapping in Raman spectroscopy integrated with a glove box is described in this article. Key features include a Positioning and Optical Preview System with a 3-axis NanoMax stage for precise sample mapping, a Control Module based on the STM32F207 microcontroller for managing stage movements and synchronisation, and a custom software solution enabling measurement synchronisation via TTL signals. To validate our Raman mapping methodology, we analysed mechanically ground alpha-MoO3 powder deposited on glass. The acquired spectra clearly exhibited all the characteristic vibrational modes of the orthorhombic phase, confirming the reliability of our mapping technique.

We present our integration of a Raman spectrometer with a glove box, which opens the possibility to conduct studies in a high-purity inert gas conditions. This innovative setup allows for the fabrication, optical inspection, and characterization of reactive materials under strictly controlled conditions, ensuring seamless operation without exposing samples to the external environment and thus significantly enhancing research reliability. Our development work included designing a system for point, line, and mapping analysis. The open architecture allows easy modifications and the addition of new components, synchronized via software or electronics. As a proof of concept, we show results recorded on Re2O7 powder and ultrathin films of 2H-MoTe2 grown on GaAs (111)B, which are highly unstable in air and provide clear evidence that sample stability is maintained, allowing in-depth, long-lasting investigations. This research validates the key advantages of our solution in real-world applications.

We report on the electronic properties of a van der Waals heterostructure formed by graphene and a type-II Weyl semimetal ( T d -WTe 2 ), hosting features of both Dirac and Weyl semimetals.

The heterostructure consisting of graphene and two-dimensional (2D) crystalline molybdenum trioxide (MoO3) layers was fabricated through a wet transfer method using a polymer to transfer the MoO3 layers from the mica crystal surface. Using a heating plate method, this crystalline MoO3 was initially grown on mica under normal atmospheric air conditions. Furthermore, the authors demonstrated that the only MoO3 phase forms on the molybdenum foil following annealing in air, as confirmed by X-ray photoelectron spectroscopy (XPS) study. The resulting graphene heterostructure was examined using optical and atomic force microscopy (AFM). The fabrication method introduced here offers a cost-effective alternative to the more costly and complex ultra-high vacuum techniques used for epitaxial layer fabrication. This graphene heterostructure holds potential as a conductive and transparent anode for the organic light-emitting diode (OLED) technology.

Incommensurate heterostructures of two-dimensional (2D) materials, despite their attractive electronic behaviour, are challenging to simulate because of the absence of translation symmetry. Experimental investigations of these structures often employ scanning tunneling microscopy (STM), however there is to date no comprehensive theory to simulate and predict a STM image in such systems. In this paper, we present a new approach to simulate STM images in arbitrary van der Waals (vdW) heterostructures, using a moir\'e plane wave expansion model (MPWEM). Contrary to computationally demanding conventional methods such as density functional theory that in practice require periodic boundaries, our method only relies on the description of the noninteracting STM images of the separate materials, and on a narrow set of intuitive semi-empirical parameters, successfully simulating experimental STM images down to angstrom-scale details. We illustrate and benchmark the model using selected vdW 2D systems composed of structurally and electronically distinct crystals. The MPWEM, generating reliable STM images within seconds, can serve as an initial prediction tool, which can prove to be useful in the investigation of vdW heterostructures, offers an avenue towards fast and reliable prediction methods in the growing field of twistronics.

The diverse and intriguing phenomena observed in twisted bilayer systems, such as graphene and transitionmetal dichalcogenides, prompted new questions about the emergent effects that they may host. However, the practical challenge of realizing these structures on a scale large enough for spectroscopic investigation, remains a significant hurdle, resulting in a scarcity of direct measurements of the electronic band structure of twisted transition metal dichalcogenide bilayers. Here, we present a systematic nanoscale angle-resolved photoemission spectroscopy investigation of bulk, single-layer, and twisted bilayer WS2 with a small twist angle of 4.4 degrees. The experimental results are compared with theoretical calculations based on density functional theory along the high-symmetry directions P- K and t'-M. Surprisingly, the electronic band structure measurements suggest a structural relaxation occurring at 4.4 degrees twist angle and the formation of large, untwisted bilayer regions replacing most of the twisted area.

Transition metal dichalcogenides exhibit giant spin-orbit coupling, and intriguing spin-valley effects, which can be harnessed through proximity in van der Waals (vdW) heterostructures. Remarkably, due to the prismatic crystal field, the Zeeman-type band splitting of valence bands reach values of several hundreds of meV. While this effect is suppressed in the commonly studied hexagonal (H)-stacked bilayers due to the presence of inversion symmetry, the recent discovery of sliding ferroelectricity in rhombohedral (R-)stacked MX$_2$ bilayers (M=Mo, W; X=S, Se) suggests that the Zeeman effect could be present in these non-centrosymmetric configurations, making it even more intriguing to investigate how the spin-resolved bands would evolve during the phase transition. Here, we perform density functional theory calculations complemented by symmetry analysis to unveil the evolution of ferroelectricity during sliding and the behavior of Zeeman splitting along the transition path. While the evolution of the out-of-plane component of the electric polarization vector resembles the conventional ferroelectric transition, we observe significant in-plane components parallel to the sliding direction, reaching their maximum at the intermediate state. Moreover, we demonstrate that the R-stacked bilayers exhibit persistent Zeeman-type band splitting throughout the transition path, allowed by the lack of inversion symmetry. Further analysis of different stacking configurations generated by sliding along various directions confirms that the Zeeman effect in MX$_2$, primarily arising from the polarity of prismatic ligand coordination of the metal atom, is remarkably robust and completely governs the spin polarization of bands, independently of the sliding direction. This resilience promises robust spin transport in vdW based MX$_2$ bilayers, opening new opportunities for ferroelectric spintronics.

A graphene/NPB structure with Re2O7 as an interfacial layer in the context of its potential use in the design of an organic light-emitting diode (OLED) is investigated. The X-ray photoelectron spectroscopy (XPS) study shows the formation of the Re2O7 phase on a monolayer graphene on quartz during thermal deposition in ultra-high vacuum (UHV). The ultraviolet photoelectron spectroscopy (UPS) study shows an enhancement of the work function of the graphene heterostructure after deposition of the Re2O7 layer up to 5.4 eV. The hole injection barrier between the Re2O7/graphene heterostructure and the N-bis-(1naphthyl)-N,N-diphenyl-(1,1-biphenyl)-4,4-diamine (NPB) layer was estimated to be 0.35 eV, which is very promising for a good OLED performance.