Understanding charge transport in networks of 2D crystals is essential for developing reliable applications such as chemiresistors or electromagnetic shields. For this purpose, intra- and inter-flake contributions to the network resistance must be disentangled. MXenes such as Ti3C2Tx, are prime examples of 2D crystals often employed as thin networks of interconnected flakes for functional devices. While a significant number of studies focused on transport in individual MXene flakes, inter-flake transport remains scarcely explored. Here, we demonstrate that charge transport in multi-flake conductive paths of Ti3C2Tx is dominated by interflake junctions and provide quantitative estimates of junction resistances. Scanning probe measurements reveal that in a MXene multi-flake conductive path, individual flakes behave as isopotential domains, since the voltage drop is localized precisely at inter-flake junctions. The chemiresistive response to humidity is further investigated at the single flake, multi-flake and flake network scale, evidencing the crucial impact of junctions on sensing kinetics. These findings underline the dominant role of inter-flake junctions in MXene charge transport and sensing capabilities.

Three-dimensional woodpile photonic crystals constitute one of the most successful architectures for realizing photonic band gaps, yet their optical response is traditionally fixed by the geometry established during fabrication. Here, we introduce a twist-controlled woodpile photonic crystal in which the relative angular orientation between successive rod layers acts as an additional, in situ-tunable geometrical degree of freedom. Using an extension of rigorous coupled-wave analysis adapted to multilayer structures with rotated reciprocal lattices, we systematically investigate the evolution of the transmission spectrum as a function of twist angle. We show that twisting drives the structure through three distinct photonic regimes. In the fully aligned configuration, broad frequency intervals exhibit near-unity transmission. At intermediate twist angles, the spectrum becomes populated by strongly dispersive resonances displaying characteristic Fano line shapes, high quality-factor and pronounced angular sensitivity. As the twist angle approaches 90°, the conventional woodpile structure is recovered, and these resonances evolve into a broad photonic stop band characteristic of three-dimensional photonic crystals. A simplified analytical model based on reciprocal-lattice considerations accurately reproduces the principal resonance modification observed in the numerical calculations. Our results demonstrate a continuous twist-induced transition from broadband transmission to photonic stop bands through an intermediate Fano-resonant regime, establishing twisted woodpiles as a versatile platform for three-dimensional twist-engineered photonics.

Charge transport in two-dimensional (2D) crystals is critical for a large variety of future applications, and it is therefore highly desirable to get a better understanding of the underlying mechanisms. While the in-plane resistivity of 2D crystals is usually relatively easy to extract, the out-of-plane component is much more difficult to access, especially at the flake-scale. Here, we focus on individual metallic single crystal Ti3C2Tx flakes. Ti3C2Tx belongs to the MXenes family, which has recently garnered significant attention for excellent prospects of applications in printable electronics, energy storage and electromagnetic interference shielding, for which electrical properties play a leading role. To answer the need for experimental data on charge transport in Ti3C2Tx, we combine local-probe measurements (Conductive AFM), conventional four-contact measurements, finite element and ab initio simulations on individual few-layer flakes of Ti3C2Tx. This effort establishes new methods to study charge transport both in in-plane and out-of-plane directions and yields consistent quantitative value of resistivity anisotropy in individual Ti3C2Tx flakes, an essential ingredient in the understanding and modeling of charge transport in MXenes, in particular considering the role of interlayer interactions and surface functionalization in these materials.

Two-dimensional (2D) materials have attracted significant interest due to their tunable physical properties when stacked into homo- and heterostructures. Twisting adjacent layers introduces moiré patterns that strongly influence the material's electronic and thermal behavior. In twisted graphene systems, the twist angle critically alters phonon transport, leading to reduced thermal conductivity compared to Bernal-stacked configurations. However, experimental investigations into thermal transport in twisted structures remain limited. Here, we study the local thermal properties of low-angle (<1°) twisted double bilayer graphene using scanning thermal microscopy. We find an increase in thermal resistance of 0.3±0.1×106 KW−1 compared to untwisted bilayers, attributed to changes in both intrinsic thermal conductivity and the tip–sample interface. Analytical modeling shows that such variations may be attributed to intrinsic conductivity changes or modifications of the tip–sample interface resistance, or a combination of both. Our study highlights how twist alters the overall thermal resistance network in graphene heterostructures, providing direct nanoscale evidence that moiré engineering impacts multiple pathways of heat dissipation. These insights advance understanding of thermal transport in twisted 2D systems and open avenues for thermal management in twistronic devices.

We report fast atom diffraction through single-layer graphene using hydrogen atoms at kinetic energies from 150 to 1200 eV. High-resolution images reveal overlapping hexagonal patterns from coexisting monocrystalline domains. Time-of-flight tagging confirms negligible energy loss, making the method suitable for matter-wave interferometry. The diffraction is well described by the eikonal approximation, with accurate modeling requiring the full 3D interaction potential from density functional theory. Simpler models fail to reproduce the data, highlighting the exceptional sensitivity of diffraction patterns to atom-surface interactions and their potential for spectroscopic applications.

Charge transport in two-dimensional crystals is critical for a large variety of future applications, and it is therefore highly desirable to get a better understanding of the underlying mechanisms. Here, we focus on the MXene Ti3C2Tx, which has recently garnered significant attention for its potential in printable electronics, energy storage and electromagnetic interference shielding, for which electrical properties play a leading role. To answer the need for experimental data on charge transport in Ti3C2Tx, we combine local-probe measurements (Conductive AFM), conventional four-contact measurements, finite element and ab initio simulations on individual few-layer flakes of Ti3C2Tx. This effort establishes new methods to study charge transport both in in-plane and out-of-plane directions and yields a consistent quantitative value of resistivity anisotropy in individual Ti3C2Tx flakes, an essential ingredient in the understanding and modeling of charge transport in MXenes, in particular considering the role of interlayer interactions and surface functionalization in these materials. Accessing charge transport along the out-of-plane direction in 2D crystals is challenging, yet essential to understanding their anisotropic properties. Here, both in-plane and out-of-plane transport are measured in Ti3C2Tx with experimental and computational tools, enabling quantitative analysis.

Over the few decades, terahertz radiation has attracted attention for its applications in imaging, spectroscopy, communications, and security. Recently, this electromagnetic spectral range became highly interesting for research of quantum materials, as ultra-microscopies are now able to operate at those frequencies. In this work, we demonstrate the use of a cryogen-free compact quantum cascade laser as THz source for scattering scanning near-field microscopy to study the nano-optics of 2D materials such as Bi₂Se₃ and twisted-bilayer graphene. Custom-designed probes with tailored shaft lengths enabled high-contrast imaging at 2.5 THz, achieving spatial resolutions comparable to those in the mid-infrared range and delivering high sensitivity in THz nano-imaging. An in-depth analysis of probe performance across different lengths is also included.

To expand the possible applications, chemical vapor deposition grown graphene needs to be transferred to appropriate substrates such as a silicon wafer. Although enormous efforts have been devoted to transfer graphene to various substrates using many different methods, the quality of the final product is still insufficient. We develop a new process named semi-dry transfer, which combines wet etching and dry transfer to obtain graphene with a clean interface with the substrate. For this purpose, an adhesive tape is attached to a sacrificial polymer deposited on the synthesized graphene, which allows the graphene to be easily manipulated so that it can be carefully cleaned before being precisely transferred onto target substrates, here silicon (Si) surfaces. We used this technique to transfer up to 4 × 4 cm2 of graphene onto SiO2/Si substrates. Using various analysis techniques such as low energy electron diffraction, scanning electron microscopy, scanning tunneling microscopy/spectroscopy, Raman, Auger electron and X-ray photoelectron spectroscopies, we demonstrate that our transferred graphene on Si is continuous, clean and that it is very promising for device fabrication. Graphene transistors show transport properties comparable with the state-of-the-art.

Electronic devices continue to shrink in size while increasing in performance, making excess heat dissipation challenging. Traditional thermal interface materials (TIMs) such as thermal grease and pads face limitations in thermal conductivity and stability, particularly as devices scale down. Carbon nanotubes (CNTs) have emerged as promising candidates for TIMs because of their exceptional thermal conductivity and mechanical properties. However, the thermal conductivity of CNT films decreases when integrated into devices due to defects and bundling effects. This study employs a novel cross-sectional approach combining high-vacuum scanning thermal microscopy (SThM) with beam-exit cross-sectional polishing (BEXP) to investigate the nanoscale morphology and thermal properties of vertically aligned CNT bundles at low and room temperatures. Using appropriate thermal transport models, we extracted effective thermal conductivities of the vertically aligned nanotubes and obtained 4 W m-1 K-1 at 200 K and 37 W m-1 K-1 at 300 K. Additionally, non-negligible lateral thermal conductance between CNT bundles suggests more complex heat transfer mechanisms in these structures. These findings provide unique insights into nanoscale thermal transport in CNT bundles, which is crucial for optimizing novel thermal management strategies.

Nanomechanical measurements of minimally twisted van der Waals materials remained elusive despite their fundamental importance for device realisation. Here, we use Ultrasonic Force Microscopy (UFM) to locally quantify the variation of out-of-plane Young's modulus in minimally twisted double bilayer graphene (TDBG). We reveal a softening of the Young's modulus by 7% and 17% along single and double domain walls, respectively. Our experimental results are confirmed by force-field relaxation models. This study highlights the strong tunability of nanomechanical properties in engineered twisted materials, and paves the way for future applications of designer 2D nanomechanical systems.

Copper foil impurities are hampering scalable production of high-quality graphene by chemical vapor deposition (CVD). Here, we conduct a thorough study on the origin of these unavoidable contaminations at the surface of copper after the CVD process. We identify two distinct origins for the impurities. The first type is intrinsic im-purities, originating from the manufacturing process of the copper foils, already present at the surface before any high-temperature treatment, or buried into the bulk of copper foils. The buried impurities diffuse towards the copper surface during high-temperature treatment and precipitate. The second source is external: silica contamination arising from the quartz tube that also precipitate on copper. The problem of the extrinsic silica contamination is readily solved upon using an adequate confinement the copper foil samples. The intrinsic impurities are much more difficult to remove since they appear spread in the whole foil. Nevertheless, elec-tropolishing proves particularly efficient in drastically reducing the issue.

The weak disorder potential seen by the electrons of a two-dimensional electron gas in high-mobility semiconductor heterostructures leads to fluctuations in the physical properties and can be an issue for nanodevices. In this paper, we show that a scanning gate microscopy (SGM) image contains information about the disorder potential, and that a machine learning approach based on SGM data can be used to determine the disorder. We reconstruct the electric potential of a sample from its experimental SGM data and validate the result through an estimate of its accuracy.

Coulomb diamonds are the archetypal signatures of Coulomb blockade, a well-known charging effect mainly observed in nanometer-sized electronic islands tunnel-coupled with charge reservoirs. Here, we identify apparent Coulomb diamond features in the scanning gate spectroscopy of a quantum point contact carved out of a semiconductor heterostructure in the quantum Hall regime. Varying the scanning gate parameters and the magnetic field, the diamonds are found to smoothly evolve to checkerboard patterns. To explain this surprising behavior, we put forward a model which relies on the presence of a nanometer-sized Fabry-P??rot quantum Hall interferometer at the center of the constriction with tunable tunneling paths coupling the central part of the interferometer to the quantum Hall channels running along the device edges. Both types of signatures, diamonds and checkerboards, and the observed transition, are reproduced by simply varying the interferometer size and the transmission probabilities at the tunneling paths. The proposed interpretation of diamond phenomenology will likely lead to revisiting previous data, and opens the way toward engineering more complex interferometric devices with nanoscale dimensions.

This work reports information on the transience of hole doping in epitaxial graphene devices when nitric acid is used as an adsorbent. Under vacuum conditions, desorption processes are monitored by electrical and spectroscopic means to extract the relevant timescales from the corresponding data. It is of vital importance to understand the reversible nature of hole doping because such device processing can be a suitable alternative to large-scale, metallic gating. Most measurements are performed post-exposure at room temperature, and, for some electrical transport measurements, at 1.5 K. Vacuum conditions are applied to many measurements to replicate the laboratory conditions under which devices using this doping method would be measured. The relevant timescales from transport measurements are compared with results from X-ray photoelecton spectroscopy and Fourier transform infrared spectroscopy measurements, with the latter performed at ambient conditions and accompanied by calculations of the spectra in the Reststrahlen band.

This work reports information on the transience of hole doping in epitaxial graphene devices when nitric acid is used as an adsorbent. Under vacuum conditions, desorption processes are monitored by electrical and spectroscopic means to extract the relevant timescales from the corresponding data. It is of vital importance to understand the reversible nature of hole doping because such device processing can be a suitable alternative to large-scale, metallic gating. Most measurements are performed post-exposure at room temperature, and, for some electrical transport measurements, at 1.5 K. Vacuum conditions are applied to many measurements to replicate the laboratory conditions under which devices using this doping method would be measured. The relevant timescales from transport measurements are compared with results from X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy measurements, with the latter performed at ambient conditions and accompanied by calculations of the spectra in the Reststrahlen band.

Complete absorption of electromagnetic waves is paramount in today's applications, ranging from photovoltaics to cross-talk prevention into sensitive devices. In this context, we use a genetic algorithm (GA) strategy to optimize absorption properties of periodic arrays of truncated square-based pyramids made of alternating stacks of metal/dielectric layers. We target ultra-broadband quasi-perfect absorption of normally incident electromagnetic radiations in the visible and near-infrared ranges (wavelength comprised between 420 and 1600 nm). We compare the results one can obtain by considering one, two or three stacks of either Ni, Ti, Al, Cr, Ag, Cu, Au or W for the metal, and poly(methyl methacrylate) (PMMA) for the dielectric. More than 10^17 configurations of geometrical parameters are explored and reduced to a few optimal ones. This extensive study shows that Ni/PMMA, Ti/PMMA, Cr/PMMA and W/PMMA provide high-quality solutions with an integrated absorptance higher than 99% over the considered wavelength range, when considering realistic implementation of these ultra-broadband perfect electromagnetic absorbers. Robustness of optimal solutions with respect to geometrical parameters is investigated and local absorption maps are provided. Moreover, we confirm that these optimal solutions maintain quasi-perfect broadband absorption properties over a broad angular range when changing the inclination of the incident radiation. The study also reveals that noble metals (Au, Ag, Cu) do not provide the highest performance for the present application.

Quantum Hall edge states offer avenues for quasiparticle interferometry, provided that the ratio between phase coherence length and quantum Hall interferometer (QHI) size is large enough. Maximizing this ratio by shrinking the QHI area favors Coulomb interactions, impairing clear interferences observation. Here, we use scanning gate spectroscopy to probe interference regime in antidots-based graphene nano-QHIs, free of localized states (LS). A simple Fabry-Perot model, without Coulomb interaction, reproduces the QHI phenomenology, even in the smallest QHI, highlighting the LS detrimental role.

Walking droplets represent an ideal playground to explore wave-particle duality at the macroscopic scale. The proper control and measurement of such system requires several experimental tools that are not often easily affordable at undergraduate level. This paper proposes a complete low-cost and open-source experimental setup for walking droplets with a performance characterization. The setup is tested by examining the behaviour of droplets in the stadium billiard, a two-dimensional concave cavity that yields chaotic trajectories. Drastic differences between classical and quantum particles behaviour were observed in such geometry. In particular, the long-term evolution of walking droplets in a stadium billiard presents clear scarring patterns, informing on the existence of preferred "probable positions" within the billiard.