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.

Manipulation of intrinsic electronic structures by electron or hole doping in a controlled manner in van der Waals layered materials is the key to control their electrical and optical properties. Two-dimensional indium selenide (InSe) semiconductor has attracted attention due to its direct band gap and ultrahigh mobility as a promising material for optoelectronic devices. In this work, we manipulate the electronic structure of InSe by in situ surface electron doping and obtain a significant band gap renormalization of ∼120 meV directly observed by high-resolution angle resolved photoemission spectroscopy. This moderate doping level (carrier concentration of 8.1 × 1012 cm–2) can be achieved by electrical gating in field effect transistors, demonstrating the potential to design of broad spectral response devices.

LEED, STM and XPS techniques were used to systematically study a temperature-dependent phase transition on a PtSe2 film grown on the surface of Pt(111) by a chemical deposition method.

Two-dimensional (2D) chalcogen-based layers have proven to be the next generation of materials for potential high-tech applications, and it is very important to control their properties at the nanoscale. Herein, we discuss the structural and electronic properties of Au(111) surface after being exposed to high temperature vapor deposition of Tellurium (Te) in ultrahigh vacuum. The scenarios entailing the formation of 2D AuTe2 metal dichalcogenide or rather Au–Te alloy monolayer (ML) or even Tellurene single layer deserved to be addressed. In this purpose, low energy electron diffraction (LEED) supported by scanning tunneling microscopy (STM) shows the existence of several surface reconstructions depending on the Te film thickness in the sub-monolayer regime. We observed that the well-known spin-split Shockley state of the Au(111) surface survives the Te deposition and is even shifted to higher binding energy, suggesting a charge transfer at the interface. For a coverage of 0.33 ML of Te, new dispersive bands are observed by angle-resolved photoemission (ARPES), which arise from a strong hybridization between the electronic states of Te and Au. With a substantially low intensity and a back-folding at the boundaries of the reduced surface Brillouin zone (R-SBZ), these electronic bands represent a proof of the existence of a naturel 2D electron gas, strongly disturbed by the surface reconstruction. It is therefore possible that an Au–Te alloy is formed at the surface. By increasing the coverage to 0.5 ML, a rich, thickness-dependent transition develops from the surface alloy to Tellurene-like structure and completely excludes the growth of AuTe2 monolayer. Both the surface alloy and the Tellurene monolayer have a semiconductor character with a gap in the occupied states of about 0.65 eV.

We report the design of an electrochemical aptasensor for ampicillin detection, which is an antibiotic widely used in agriculture and considered to be a water contaminant. We studied the transducing potential of nanostructure composed of MoS2 nanosheets and conductive polypyrrole nanoparticles (PPyNPs) cast on a screen-printed electrode. Fine chemistry is developed to build the biosensors entirely based on robust covalent immobilizations of naphthoquinone as a redox marker and the aptamer. The structural and morphological properties of the nanocomposite were studied by SEM, AFM, and FT-IR. High-resolution XPS measurements demonstrated the formation of a binding between the two nanomaterials and energy transfer affording the formation of heterostructure. Cyclic voltammetry and electrochemical impedance spectroscopy were used to analyze their electrocatalytic properties. We demonstrated that the nanocomposite formed with PPyNPs and MoS2 nanosheets has electro-catalytic properties and conductivity leading to a synergetic effect on the electrochemical redox process of the redox marker. Thus, a highly sensitive redox process was obtained that could follow the recognition process between the apatamer and the target. An amperometric variation of the naphthoquinone response was obtained regarding the ampicillin concentration with a limit of detection (LOD) of 10 pg/L (0.28 pM). A high selectivity towards other contaminants was demonstrated with this biosensor and the analysis of real river water samples without any treatment showed good recovery results thanks to the antifouling properties. This biosensor can be considered a promising device for the detection of antibiotics in the environment as a point-of-use system.