arXiv subjects

Yangfan Shao

Publications and source records attributed to Yangfan Shao.

4 recordsLinked to original sources

arXiv2019

Fermi-level depinning in metal-2D multilayered semiconductor junctions

Thicknesses-dependent performance of metal-two-dimensional (2D) semiconductor junctions (MSJ) in electronics/optoelectronics have attracted increasing attention, but till present, people have little knowledge about the micro-mechanism of the thicknesses (or layer-number) dependence. Here, by first-principles calculations based on density functional theory, we show that the Fermi-level pinning (FLP) factor of MSJ depends sensitively on the layer-number of few-layer 2D semiconductors, and, an extended FLP theory is proposed for metal-2D multilayered semiconductor junctions (MmSJ). Taking multilayered MoS2 as a typical example for van der Waals (vdW) semiconductor in MmSJ, the extended FLP theory has the following character: strong pinning right at the metal-1st-layer semiconductor interface while depinning occurs between MoS2 layers. This depinning effect between vdW layers has several important consequences: 1) the overall pinning in MmSJ is greatly weakened; 2) p-type contact, rarely obtained in metal-monolayer MoS2 junctions, becomes favored in MmSJ, which is important for CMOS logical devices; 3) depinning between MoS2 layers result in type II band alignment in MoS2 'homojunction' supported on metals, which is useful for optoelectronics. Moreover, our extended FLP theory sheds light on the recent controversial experimental observation and paves a new and universal route to type II band alignment in vdW 'homojunctions'.

cond-mat.mtrl-sci↗

arXiv2019

Charge distribution at metal-multilayered semiconductor interfaces

Thicknesses-dependent performances of metal-multilayered semiconductor junctions have attracted increasing attention, but till present, the mechanism of interaction and the resulting charge distribution at interfaces which control the Schottky barrier and band offset between the semiconductor layers have not been systematically studied. Based on first-principles calculations, the nature and strength of the non-bonding interactions at Metal-MoS2 (M-S) and MoS2-MoS2 (S-S) interfaces in meta-multilayered MoS2 are investigated. We show that the charge distribution at M-S interfaces depends sensitively on the dimensionality and work function of metal substrates: 1) push back effect and metal induced gap states play a main role at 3D metal-MoS2 interfaces; 2) charge transfer occurs in Mo2C(OH)2 (or Mo2CO2)-MoS2 interfaces which means electron distribution is determined by the band alignment of metal and MoS2; 3) covalent-like feature appears at Mo2CF2-MoS2 interface. The S-S interface inherit the charge redistribution at M-S interface for 2D metal-2L MoS2 junction, and have a depinning effect for M-S interface in 3D metal-2L MoS2 junction. We are trying to start drawing general conclusions and developing new concepts to understand metal-multilayered semiconductor interfaces in the strong interaction limit, where charge-transfer effects must be taken into consideration in this paper.

cond-mat.mtrl-sci↗

arXiv2016

Fullerene antiferromagnetic reconstructed spinterface subsurface layer dominates multi-orbitals spin-splitting and large magnetic moment in C60

The interfaces between organic molecules and metal surfaces with layered antiferromagnetic order have gained increasing interests in the field of antiferromagnetic spintronics. The C60 layered AFM spinterfaces have been studied for C60 bonded only to the outermost ferromagnetic layer. Using density functional theory calculations, here we demonstrate that C60 adsorption can reconstruct the layered AFM Cr(001) surface so that C60 bonds to the top two Cr layers with opposite spin direction. Surface reconstruction drastically changes C60 s spintronic properties 1 the spin-split p-d hybridization involve multi-orbitals of C60 and metal double layers, 2 the subsurface layer dominates the C60 spin properties, and 3) reconstruction induces a large magnetic moment in C60 of 0.58 B, which is a synergetic effect of the top two layers as a result of a magnetic direct-exchange interaction. Understanding these complex spinterfaces phenomena is a crucial step for their device applications. The surface reconstruction can be realized by annealing at above room temperature in experiments.

physics.comp-ph↗

arXiv2015

Stability of Two-Dimensional Iron-Carbides Suspended across Graphene Pores: First-principles Particle Swarm Optimization

Inspired by recent experimental realizations of two-dimensional (2D) metals and alloys, we theoretically investigate the stability and electronic properties of monolayer (ML) Fe-C compounds and pure Fe. According to our and others theoretical results, the experiment [Science 343, 1228 (2014)] proposed ML pure Fe square-lattices embedded in graphene (Gr) pores are energetically unstable compared to that of the Fe triangular-lattices in Gr. To solve the above contradiction, we search for the stable structures of ML Fe-C with various Fe to C ratios (as a generalization of ML Fe in Gr) using ab initio particle swarm optimization technique. A Fe1C1 square-lattice embedded in Gr is found. We propose and demonstrate that the square-lattices observed in the experiment were iron-carbides (Fe-C) but not pure Fe from the square-lattice shape, Fe-Fe lattice constant and energetic considerations. Note that the coexistence of C with Fe cannot be excluded from the experiment. More importantly, we find a lowest energy and dynamically stable structure, ML Fe2C2 with Fe atoms form distorted square lattices. High spin polarization around the Fermi level is predicted for different 2D Fe-C structures due to significant orbital hybridization between C and Fe.

cond-mat.mtrl-sci↗