The Emergence of Mem-Emitters.

The advent of memristors and resistive switching has transformed solid-state physics, enabling advanced applications such as neuromorphic computing. Inspired by these developments, we introduce the concept of Mem-emitters, devices that manipulate light-emission properties of semiconductors to achieve memory functionalities. Mem-emitters, influenced by past exposure to stimuli, offer a new approach to optoelectronic computing with potential for enhanced speed, efficiency, and integration.

Acoustic Modulation of Excitonic Complexes in hBN/WSe/hBN Heterostructures.

The interaction of high-frequency surface acoustic waves (SAWs) and excitons in van der Waals heterostructures (vdWHs) offers challenging opportunities to explore novel quantum effects and functionalities. We probe the interaction of neutral excitons, trions, and biexcitons with SAWs in a hBN/WSe/hBN vdWH. We show that neutral excitons respond weakly to the SAW stimulus at 5 K.

Ultrathin natural biotite crystals as a dielectric layer for van der Waals heterostructure applications.

Biotite, an iron-rich mineral belonging to the trioctahedral mica group, is a naturally abundant layered material (LM) exhibiting attractive electronic properties for application in nanodevices. Biotite stands out as a non-degradable LM under ambient conditions, featuring high-quality basal cleavage-a significant advantage for van der Waals heterostructure (vdWH) applications. In this work, we present the micro-mechanical exfoliation of biotite down to monolayers (1Ls), yielding ultrathin flakes with large areas and atomically flat surfaces.

The impact of different flexible substrates on the photothermal reduction quality of graphene oxide.

In this work, we demonstrate the impact of the photothermal reduction quality of graphene oxide (GO), which is affected by the material composition, roughness, and thermal properties of the membrane substrates. We show high efficiency reduced graphene oxide (rGO) conversion by applying a 405 nm pulsed laser in ambient conditions onto different flexible substrates. Three filter membranes, such as nylon, cellulose acetate, and nitrocellulose, are used as rGO thin film substrates, achieving sheet resistance of 51 ± 2, 58 ± 3, and 620 ± 40 Ω sq, respectively, which has been the lowest resistance reported in ambient conditions.

Nature of Long-Lived Moiré Interlayer Excitons in Electrically Tunable MoS/MoSe Heterobilayers.

Interlayer excitons in transition-metal dichalcogenide heterobilayers combine high binding energy and valley-contrasting physics with a long optical lifetime and strong dipolar character. Their permanent electric dipole enables electric-field control of the emission energy, lifetime, and location. Device material and geometry impact the nature of the interlayer excitons via their real- and momentum-space configurations.

Ultrafast Coherent Exciton Couplings and Many-Body Interactions in Monolayer WS.

Transition metal dichalcogenides (TMDs) are quantum confined systems with interesting optoelectronic properties, governed by Coulomb interactions in the monolayer (1L) limit, where strongly bound excitons provide a sensitive probe for many-body interactions. Here, we use two-dimensional electronic spectroscopy (2DES) to investigate many-body interactions and their dynamics in 1L-WS at room temperature and with sub-10 fs time resolution. Our data reveal coherent interactions between the strongly detuned A and B exciton states in 1L-WS.

Ultrafast Charge Transfer and Recombination Dynamics in Monolayer-Multilayer WSe Junctions Revealed by Time-Resolved Photoemission Electron Microscopy.

The ultrafast carrier dynamics of junctions between two chemically identical, but electronically distinct, transition metal dichalcogenides (TMDs) remains largely unknown. Here, we employ time-resolved photoemission electron microscopy (TR-PEEM) to probe the ultrafast carrier dynamics of a monolayer-to-multilayer (1L-ML) WSe junction. The TR-PEEM signals recorded for the individual components of the junction reveal the sub-ps carrier cooling dynamics of 1L- and 7L-WSe, as well as few-ps exciton-exciton annihilation occurring on 1L-WSe.

Ultrafast Electronic Relaxation Dynamics of Atomically Thin MoS Is Accelerated by Wrinkling.

Strain engineering is an attractive approach for tuning the local optoelectronic properties of transition metal dichalcogenides (TMDs). While strain has been shown to affect the nanosecond carrier recombination dynamics of TMDs, its influence on the sub-picosecond electronic relaxation dynamics is still unexplored. Here, we employ a combination of time-resolved photoemission electron microscopy (TR-PEEM) and nonadiabatic molecular dynamics (NAMD) to investigate the ultrafast dynamics of wrinkled multilayer (ML) MoS comprising 17 layers.

Review on infrared nanospectroscopy of natural 2D phyllosilicates.

Phyllosilicates have emerged as a promising class of large bandgap lamellar insulators. Their applications have been explored from the fabrication of graphene-based devices to 2D heterostructures based on transition metal dichalcogenides with enhanced optical and polaritonics properties. In this review, we provide an overview of the use of infrared (IR) scattering-type scanning near-field optical microscopy (s-SNOM) for studying nano-optics and local chemistry of a variety of 2D natural phyllosilicates.

Identification of Exciton Complexes in Charge-Tunable Janus W Monolayers.

Janus transition-metal dichalcogenide monolayers are artificial materials, where one plane of chalcogen atoms is replaced by chalcogen atoms of a different type. Theory predicts an in-built out-of-plane electric field, giving rise to long-lived, dipolar excitons, while preserving direct-bandgap optical transitions in a uniform potential landscape. Previous Janus studies had broad photoluminescence (>18 meV) spectra obfuscating their specific excitonic origin.

Redox exfoliated NbS: characterization, stability, and oxidation.

Niobium disulfide is a layered transition metal dichalcogenide that is being exploited as a two-dimensional material. Although it is a superconductor at low temperatures and demonstrates great potential to be applied as a catalyst or co-catalyst in hydrogen evolution reactions, only a few reports have demonstrated the synthesis of a few-layer NbS. However, before applications can be pursued, it is essential to understand the main characteristics of the obtained material and its stability under an atmospheric environment.

Low-Loss Integrated Nanophotonic Circuits with Layered Semiconductor Materials.

Monolayer transition-metal dichalcogenides with direct bandgaps are emerging candidates for optoelectronic devices, such as photodetectors, light-emitting diodes, and electro-optic modulators. Here we report a low-loss integrated platform incorporating molybdenum ditelluride monolayers with silicon nitride photonic microresonators. We achieve microresonator quality factors >3 × 10 in the telecommunication O- to E-bands.

Weak Distance Dependence of Hot-Electron-Transfer Rates at the Interface between Monolayer MoS and Gold.

Electron transport across the transition-metal dichalcogenide (TMD)/metal interface plays an important role in determining the performance of TMD-based optoelectronic devices. However, the robustness of this process against structural heterogeneities remains unexplored, to the best of our knowledge. Here, we employ a combination of time-resolved photoemission electron microscopy (TR-PEEM) and atomic force microscopy to investigate the spatially resolved hot-electron-transfer dynamics at the monolayer (1L) MoS/Au interface.

Second harmonic generation in defective hexagonal boron nitride.

Determining the role of defects in materials can be an important task both for the fundamental understanding of their influence on material properties and for future applications. In this work, we studied the influence of defects on the second harmonic generation (SHG) in hexagonal boron nitride (h-BN). We characterized the sample by photoluminescence imaging and spectroscopy, showing strong and sharp photoluminescence emission at visible range from h-BN flakes due to single defect states.

Anisotropic Flow Control and Gate Modulation of Hybrid Phonon-Polaritons.

Light-matter interaction in two-dimensional photonic or phononic materials allows for the confinement and manipulation of free-space radiation at sub-wavelength scales. Most notably, the van der Waals heterostructure composed of graphene (G) and hexagonal boron nitride (hBN) provides for gate-tunable hybrid hyperbolic plasmon phonon-polaritons (HP). Here, we present the anisotropic flow control and gate-voltage modulation of HP modes in G-hBN on an air-Au microstructured substrate.

Charge-tuneable biexciton complexes in monolayer WSe.

Monolayer transition metal dichalcogenides have strong Coulomb-mediated many-body interactions. Theoretical studies have predicted the existence of numerous multi-particle excitonic states. Two-particle excitons and three-particle trions have been identified by their optical signatures.

Anomalous Nonlinear Optical Response of Graphene Near Phonon Resonances.

In this work we probe the third-order nonlinear optical property of graphene and hexagonal boron nitride and their heterostructure by the use of coherent anti-Stokes Raman spectroscopy. When the energy difference of the two input fields matches the phonon energy, the anti-Stokes emission intensity is enhanced in h-BN, as usually expected, while for graphene an anomalous decrease is observed. This behavior can be understood in terms of a coupling between the electronic continuum and a discrete phonon state.

Graphene/h-BN plasmon-phonon coupling and plasmon delocalization observed by infrared nano-spectroscopy.

We observed the coupling of graphene Dirac plasmons with different surfaces using scattering-type scanning near-field optical microscopy integrated into a mid-infrared synchrotron-based beamline. A systematic investigation of a graphene/hexagonal boron nitride (h-BN) heterostructure is carried out and compared with the well-known graphene/SiO2 heterostructure. Broadband infrared scanning near-field optical microscopy imaging is able to distinguish between the graphene/h-BN and the graphene/SiO2 heterostructure as well as differentiate between graphene stacks with different numbers of layers.

Asymmetric effect of oxygen adsorption on electron and hole mobilities in bilayer graphene: long- and short-range scattering mechanisms.

We probe electron and hole mobilities in bilayer graphene under exposure to molecular oxygen. We find that the adsorbed oxygen reduces electron mobilities and increases hole mobilities in a reversible and activated process. Our experimental results indicate that hole mobilities increase due to the screening of long-range scatterers by oxygen molecules trapped between the graphene and the substrate.

Metal-doped carbon nanotubes interacting with vitamin C.

In this paper, the structural, electronic and magnetic properties of carbon nanotubes doped with Al, Fe, Mn and Ti atoms interacting with vitamin C molecules are studied through first principles simulations based on the density functional theory. The charge transfers are obtained from the vitamins into the tubes for adsorption and substitutional doping cases. The highest binding energies of vitamin C molecules are calculated for the Al substitutional and Ti adsorbed cases, with values of about 1.