ABSTRACT
It is known that carrier mobility in layered semiconductors generally increases from two-dimensions (2D) to three-dimensions due to fewer scattering channels resulting from decreased densities of electron and phonon states. In this work, we find an abnormal decrease of electron mobility from monolayer to bulk MoS2. By carefully analyzing the scattering mechanisms, we can attribute such abnormality to the stronger intravalley scattering in the monolayer but weaker intervalley scattering caused by few intervalley scattering channels and weaker corresponding electron-phonon couplings compared to the bulk case. We show that it is the matching between the electronic band structure and phonon spectrum rather than their densities of electronic and phonon states that determines scattering channels. We propose, for the first time, the phonon-energy-resolved matching function to identify the intra- and inter-valley scattering channels. Furthermore, we show that multiple valleys do not necessarily lead to strong intervalley scattering if: (1) the scattering channels, which can be explicitly captured by the distribution of the matching function, are few due to the small matching between the corresponding electron and phonon bands; and/or (2) the multiple valleys are far apart in the reciprocal space and composed of out-of-plane orbitals so that the corresponding electron-phonon coupling strengths are weak. Consequently, the searching scope of high-mobility 2D materials can be reasonably enlarged using the matching function as useful guidance with the help of band edge orbital analysis.
ABSTRACT
Silicene-based van der Waals heterostructures are theoretically predicted to have interesting physical properties, but their experimental fabrication has remained a challenge because of the easy oxidation of silicene in air. Here, the fabrication of graphene/silicene van der Waals heterostructures by silicon intercalation is reported. Density functional theory calculations show weak interactions between graphene and silicene layers, confirming the formation of van der Waals heterostructures. The heterostructures show no observable damage after air exposure for extended periods, indicating good air stability. The I-V characteristics of the vertical graphene/silicene/Ru heterostructures show rectification behavior.
ABSTRACT
Two-dimensional (2D) Dirac materials and boron sheets have attracted intensive interest recently. However, 2D Dirac materials remain rare and difficult to be realized experimentally, and 2D boron sheets generally have high dynamical instability. Stimulated by the experimental observation of Dirac cones in nongraphene-like ß12 boron sheets and based on the understanding of boron sheet electronic organization, we theoretically design new 2D Dirac materials ß12-XBeB5 (X = H, F, Cl) with high stability. We confirm ß12-HBeB5 as the global energy minimum among its 2D allotropes based on global structure search methods, a strong indication of its experimental feasibility. Our designed ß12-HBeB5 has not only a high Fermi velocity, but also a Dirac state very robust against extraordinary large tensile strains, an advantage for flexible electronics applications. Our work opens a new avenue to designing feasible 2D Dirac materials and stabilizing borophene sheets.
ABSTRACT
Single-layer transition-metal dichalcogenides (TMDs) receive significant attention due to their intriguing physical properties for both fundamental research and potential applications in electronics, optoelectronics, spintronics, catalysis, and so on. Here, we demonstrate the epitaxial growth of high-quality single-crystal, monolayer platinum diselenide (PtSe2), a new member of the layered TMDs family, by a single step of direct selenization of a Pt(111) substrate. A combination of atomic-resolution experimental characterizations and first-principle theoretic calculations reveals the atomic structure of the monolayer PtSe2/Pt(111). Angle-resolved photoemission spectroscopy measurements confirm for the first time the semiconducting electronic structure of monolayer PtSe2 (in contrast to its semimetallic bulk counterpart). The photocatalytic activity of monolayer PtSe2 film is evaluated by a methylene-blue photodegradation experiment, demonstrating its practical application as a promising photocatalyst. Moreover, circular polarization calculations predict that monolayer PtSe2 has also potential applications in valleytronics.
Subject(s)
Photochemical Processes , Platinum/chemistry , Selenium Compounds/chemistry , SemiconductorsABSTRACT
The site-dependent g factor of a single magnetic molecule, with intramolecular resolution, is demonstrated for the first time by low-temperature, high-magnetic-field scanning tunneling microscopy of dehydrogenated Mn-phthalocyanine molecules on Au(111). This is achieved by exploring the magnetic-field dependence of the extended Kondo effect at different atomic sites of the molecule. Importantly, an inhomogeneous distribution of the g factor inside a single molecule is revealed. Our results open up a new route to access local spin properties within a single molecule.
