In a self-driven mode, a graphene/InSe/MoS ₂ photodetector exhibits high photoresponsivity, fast photoresponse and high operational stability under ambient conditions.

Significance: Two-dimensional electron gases are an essential building block of today’s technology and attract broad interest in the context of material science or nanoengineering. Their widespread applications in many strategical sectors call for a direct visualization of hot electrons relaxation in an accumulation layer. In this work, we make use of time-resolved photoelectron spectroscopy to acquire snapshots of the electronic distribution after a strong and impulsive drive. We identified and quantified the remote coupling of the confined electrons to phonon modes of the adjacent polar material. The far-reaching outcomes provide insights on the screening of electron–phonon coupling in constrained dimensions and will be of high relevance for the development of aggressively downscaled circuits.

Electrostatic gating or alkali metal evaporation can be successfully employed to tune the interface of layered black phosphorus (BP) from a semiconductor to a 2D Dirac semimetal. Although Angle Resolved Photoelectron Spectroscopy (ARPES) experiments have captured the collapse of the band gap in the inversion layer, a quantitative estimation of band structure evolution has been hindered by the short escape depth and matrix elements of the probed photoelectrons. Here, we precisely monitor the evolution of electronic states using time-resolved ARPES at a photon energy of 6.3 eV. The probing depth of laser-based ARPES is long enough to observe the buried electronic states originating from the valence band maximum. Our data shows that the band gap has a maximal value of 0.32 eV in the pristine sample, and that it shrinks down monotonically by increasing the carrier concentration in the topmost layer. Most interestingly, the band velocity of the valence band increases by a factor of two along the armchair direction, surpassing the value reported in graphene on silicon carbide (SiC). This control of band structure via external gating will be of interest with regard to the design of optoelectronic devices.

The number of two-dimensional (2D) materials has grown steadily since the discovery of graphene. Each new 2D material demonstrated unusual physical properties offering a large flexibility in their tailoring for high-tech applications. Here, we report on the formation and characterization of an uncharted 2D material: ‘Cu₂Te alloy monolayer on Cu(111) surface’. We have successfully grown a 2D binary Te-Cu alloy using a straightforward approach based on chemical deposition method. Low electron energy diffraction (LEED) and scanning tunneling microscopy (STM) results reveal the existence of a well-ordered alloy monolayer characterized by (√3 × √3)R30° superstructure, while the x-ray photoemission spectroscopy (XPS) measurements indicate the presence of single chemical environment of the Te atoms associated with the Te-Cu bonding. Analysis of the valence band properties by angle resolved photoemission spectroscopy (ARPES); in particular the electronic states close to the Fermi level suggests a strong hybridization between Te and Cu electronic states leading to an appearance of new dispersive bands localized at the surface alloy, which is confirmed by first-principles calculations. These bands are strongly influenced by the surface reconstruction and undergo a back-folding at the boundaries of the reduced surface Brillouin zone (SBZ). More interesting, a band gap of about 0.91 eV and a Rashba splitting in the conduction band are obtained. These findings taken together clearly prove the presence of 2D-type electron system within the Cu₂Te alloy layer, which is promising for spintronic application.

Interlayer coupling in 2D heterostructures can result in a reduction of the rotation symmetry and the generation of quantum phenomena. Although these effects have been demonstrated in transition metal dichalcogenides (TMDs) with mismatched interfaces, the role of band hybridization remains unclear. In addition, the creation of flat bands at the valence band maximum (VBM) of TMDs is still an open challenge. In this work, we investigate the electronic structure of monolayer MoS₂-black phosphorus heterojunctions with a combined experimental and theoretical approach. The disruption of the rotational symmetry of the MoS₂ bands, the creation of anisotropic minigaps and the appearance of flat bands at the Γ valley, accompanied by the switch of VBM from K to Γ, are clearly observed with micro-ARPES. Unfolded band structures obtained from first principles simulations precisely describe these multiple effects – all independent of the twist angle – and demonstrates that they arise from strong band hybridization between Mo \({d}_{{z}^{2}}\) and P \({p}_{x}\) orbitals. The underlying physics revealed by our results paves the way for innovative electronics and optoelectronics based on TMDs superlattices, adding further flexibility to the approaches adopted in twisted hexagonal superlattices.