Epitaxial graphene/Ge interfaces: a minireview

Single-Layer Graphene/Germanium Interface Representing a Schottky Junction Studied by Photoelectron Spectroscopy

We investigated the interfacial electronic structure of the bidimensional interface of single-layer graphene on a germanium substrate. The procedure followed a well-established approach using ultraviolet (UPS) and X-ray (XPS) photoelectron spectroscopy. The direct synthesis of the single-layer graphene on the surface of (110) undoped Ge substrates was conducted via chemical vapor deposition (CVD). The main graphitic properties of the systems were identified, and it was shown that the Ge substrate affected the electronic structure of the single-layer graphene, indicating the electronic coupling between the graphene and the Ge substrate. Furthermore, the relevant features associated with the Schottky contact's nature, the energy level's alignments, and the energy barrier's heights for electron and hole injection were obtained in this work. The results are useful, given the possible integration of single-layer graphene on a Ge substrate with the complementary metal-oxide-semiconductor (CMOS) technology.

2D magnetic phases of Eu on Ge(110)

2D magnetic materials are at the forefront of research on fundamentals of magnetism; they exhibit unconventional phases and properties controlled by external stimuli. 2D magnets offer a solution to the problem of miniaturization of spintronic devices. A technological target of materials science is to find suitable magnetic materials and scale their thickness down as much as possible, a single monolayer being a natural limit. However, magnetism does not halt at one monolayer - it may persist beyond this boundary, to sparse but regular lattices of magnetic atoms. Here, we report 2D magnetic phases of Eu on the Ge(110) surface. We synthesized two submonolayer structures Eu/Ge(110) employing molecular beam epitaxy. The phases, identified by electron diffraction, differ in the surface density of Eu atoms. At low temperature, they exhibit magnetic ordering with magnetic moments lying in-plane. Strong dependence of the effective magnetic transition temperature on weak magnetic fields points at the 2D nature of the observed magnetism. The results are set against those on the Eu/Si system. The study of Eu/Ge(110) magnets demonstrates that a variety of substrates of different structure and symmetry can host submonolayer 2D magnetic phases, suggesting the phenomenon to be rather general.

Electronic and Magnetic Properties of the Graphene/Y/Co(0001) Interfaces: Insights from the Density Functional Theory Analysis

The effect of Y intercalation on the atomic, electronic, and magnetic properties of the graphene/Co(0001) interface is studied using state-of-the-art density functional theory calculations. Different structural models of the graphene/Y/Co(0001) interface are considered: (i) graphene/Y/Co(0001), (ii) graphene/1ML-YCo₂/Co(0001), and (iii) graphene/bulk-like-YCo₂(111). It is found that the interaction strength between graphene and the substrate is strongly affected by the presence of Y at the interface and the electronic structure of graphene (doping and the appearance of the energy gap) is defined by the Y concentration. For the Co-terminated interfaces between graphene and the metallic support in the considered systems, the electronic structure of graphene is strongly disturbed, leading to the absence of the linear dispersion for the graphene π band; in the case of the Y-terminated interfaces, a graphene layer is strongly n-doped, but the linear dispersion for this band is preserved. Our calculations show that the magnetic anisotropy for the magnetic atoms at the graphene/metal interface is strongly affected by the adsorption of a graphene layer, giving a possibility for one to engineer the magnetic properties of the graphene/ferromagnet systems.

Selectivity in trace gas sensing: recent developments, challenges, and future perspectives

Selectivity is one of the most crucial figures of merit in trace gas sensing, and thus a comprehensive assessment is necessary to have a clear picture of sensitivity, selectivity, and their interrelations in terms of quantitative and qualitative views.

Correlations in the Electronic Structure of van der Waals NiPS3 Crystals: An X-ray Absorption and Resonant Photoelectron Spectroscopy Study

The electronic structure of high-quality van der Waals NiPS₃ crystals was studied using near-edge X-ray absorption spectroscopy (NEXAFS) and resonant photoelectron spectroscopy (ResPES) in combination with density functional theory (DFT) approach. The experimental spectroscopic methods, being element specific, allow one to discriminate between atomic contributions in the valence and conduction band density of states and give direct comparison with the results of DFT calculations. Analysis of the NEXAFS and ResPES data allows one to identify the NiPS₃ material as a charge-transfer insulator. Obtained spectroscopic and theoretical data are very important for the consideration of possible correlated-electron phenomena in such transition-metal layered materials, where the interplay between different degrees of freedom for electrons defines their electronic properties, allowing one to understand their optical and transport properties and to propose further possible applications in electronics, spintronics, and catalysis.

Tuning the Doping of Epitaxial Graphene on a Conventional Semiconductor via Substrate Surface Reconstruction

Combining scanning tunneling microscopy and angle-resolved photoemission spectroscopy, we demonstrate how to tune the doping of epitaxial graphene from p to n by exploiting the structural changes that occur spontaneously on the Ge surface upon thermal annealing. Furthermore, using first-principle calculations, we build a model that successfully reproduces the experimental observations. Since the ability to modify graphene electronic properties is of fundamental importance when it comes to applications, our results provide an important contribution toward the integration of graphene with conventional semiconductors.