Pairing of $π$ electronic state structures with functional or metallic atoms makes them possible to engineer physical and chemical properties. Herein, we predict the reorientation of magnetization of Co on hexagonal BN (h-BN) and graphene multilayers. The driving mechanism is the formation of the tetrahedral bonding between sp$^3$ and d orbitals at the interface. More specifically, the intrinsic $π$-bonding of h-BN and graphene is transformed to sp$^3$ as a result of strong hybridization with metallic $d_{z^2}$ orbital. The different features of these two tetrahedral bondings, sp$^2$ and sp$^3$, are well manifested in charge density and density of states in the vicinity of the interface, along with associated band structure near the $\bar{K}$ valley. Our findings provide a novel approach to tailoring magnetism by means of degree of the interlayer hybrid bonds in 2D layered materials.
To accelerate development of innovative materials, their modelings and predictions with useful functionalities are of vital importance. Here, based on a recently developed crystal structure prediction method, we find a new family of stable two-dimensional crystals with an open-channel tetrahedral bonding network, rendering a potential for electronic and energy applications. The proposed structural prototype with a space group of Cmme hosts at least thirteen different freestanding T$_{3}$X compounds with group IV (T=C, Si, Ge, Sn) and VI (X=O, S, Se, Te) elements. Moreover, the proposed materia…
Based on ab initio calculations, we study the effect of intercalating twisted bilayer graphene with carbon. Surprisingly, we find that the intercalant pulls the atoms in the two layers closer together locally when placed in certain regions in between the layers, and the process is energetically favorable as well. This arises because in these regions of the supercell, the local environment allows the intercalant to form tetrahedral bonding with nearest atoms in the layers. Intercalating AB- or AA-bilayer graphene with carbon does not produce this effect; therefore, the nontrivial effect owes it…
On the basis of density functional calculations and using Bader's atom in molecule theory, this article presents quantitative microscopic analyses on the bonding properties of amorphous silicon (a-Si) which could reflect in the observable mechanical and electronic behaviors of this material. In addition, the occurrence and strength of quantum confinement of charge carriers in a composition of silicon crystal nano slabs (SiNSs) embedded in hydrogenated a-Si (a-Si:H) semiconductor are studied. It is shown that the strongest confinement effect happens for Si slabs limited in [100] direction. The …
New intercalation compounds Cr$_x$ZrTe$_2$ were synthesized in the Cr concentration range of x=0-0.3. A thorough study of the crystal and electronic structure has been performed. It was found that there is competition in the distribution of the Cr atoms over the octa- and tetrahedral sites in the van der Waals gap, depending on the Cr content. The ordering of the Cr atoms was found at x = 0.25; at the same time, the lattice symmetry decreases from trigonal P-3m1 to monoclinic F2/m. This ordering stabilizes the octahedral coordination of the Cr atoms by Te atoms. The analysis of the experimenta…
The bonding properties of tilt boundary in poly-silicon and the effect of interstitial impurities are investigated by first-principles. In order to obtain thorough information on the nature of chemical bondings in these solid systems, an accurate topological analysis is performed, through partitioning of the electron localization function. Although the mechanism of segregation of single light impurities, such as carbon, nitrogen, and oxygen in Si-based systems is known, it is only in the presence of multiple segregations that the distinctive structures of the various interstitial impurities em…
Interatomic forces that bind materials are largely determined by an often complex interplay between the electronic band-structure and the atomic arrangements to form its equilibrium structure and dynamics. As these forces also determine the phonon dispersion, lattice dynamics measurements are often crucial tools for understanding how materials transform between different structures. This is the case for the mono-chalcogenides which feature a number of lattice instabilities associated with their network of resonant bonds and a large tunability in their functional properties. SnSe hosts a novel …
Ultra-wide band gap (UWBG) materials are poised to play an important role in the future of power electronics. Devices made from UWBG materials are expected to operate at higher voltages, frequencies, and temperatures than current silicon and silicon carbide based devices; and can even lead to significant miniaturization of such devices. In the UWBG field, aluminum nitride and boron nitride have attracted great interest, however, the B$_x$Al$_{1-x}$N alloys are much less studied. In this article, using first-principles simulations combining density-functional theory and cluster expansion method…
New ultra-hard rhombohedral B2N2 and BC2N - or hexagonal B6N6 and B3C6N3 - are derived from 3R graphite based on crystal chemistry rationale schematizing a mechanism for 2D => 3D transformation. Full unconstrained geometry optimizations leading to ground state energy structures and energy derived quantities as energy-volume equation of states (EOS) were based on computations within the density functional theory (DFT) with generalized gradient approximation (GGA) for exchange-correlation (XC) effects. The new binary and ternary phases are characterized by tetrahedral stacking alike diamond, vis…
Scanning tunneling microscopy (STM) and spectroscopy (STS) in combination with density functional theory (DFT) calculations are employed to study the surface and subsurface properties of the metastable phase of the phase change material Ge$_{2}$Sb$_{2}$Te$_{5}$ as grown by molecular beam epitaxy. The (111) surface is covered by an intact Te layer, which nevertheless allows to detect the more disordered subsurface layer made of Ge and Sb atoms. Centrally, we find that the subsurface layer is significantly more ordered than expected for metastable Ge$_{2}$Sb$_{2}$Te$_{5}$. Firstly, we show that …
We theoretically investigate Sn(II) phosphates as optoelectronic materials using first principles calculations. We focus on known prototype materials Sn$_n$P$_2$O$_{5+n}$ (n=2, 3, 4, 5) and a previously unreported compound, SnP$_2$O$_6$ (n=1), which we find using global optimization structure prediction. The electronic structure calculations indicate that these compounds all have large band gaps above 3.2 eV, meaning their transparency to visible light. Several of these compounds show relatively low hole effective masses ($\sim$2-3 m$_0$), comparable the electron masses. This suggests potentia…
We report a combined theoretical and experimental investigation of half-metallic ferromagnetism in equiatomic quaternary Heusler alloy CoRuMnSi. Room temperature XRD analysis reveals that the alloy crystallizes in L21 disorder instead of pristine Y-type structure due to 50% swap disorder between the tetrahedral sites, i.e., Co and Ru atoms. Magnetization measurements reveal a net magnetization of 4 $μ_B$ with Curie temperature of ~780 K. Resistivity measurement reveals the presence of localization effect below 35 K while above 100 K, a linear dependence is observed. Resistivity behavior indica…
Diverse interlayer tunability of physical properties of two-dimensional layers mostly lies in the covalent-like quasi-bonding that is significant in electronic structures but rather weak for energetics. Such characteristics result in various stacking orders that are energetically comparable but may significantly differ in terms of electronic structures, e.g. magnetism. Inspired by several recent experiments showing interlayer anti-ferromagnetically coupled CrI3 bilayers, we carried out first-principles calculations for CrI3 bilayers. We found that the anti-ferromagnetic coupling results from a…
Synergistic doping and stabilization of magnetically tunable LnTi$_3$(Sb,Sn)$_4$ (Ln:Ce--Gd) kagome metals
Oak Ridge National Laboratory（橡树岭国家实验室）；Norfolk State University（诺福克州立大学）；University of Central Florida（中佛罗里达大学）；Gdansk University of Technology（格但斯克理工大学）
Enhancing Quasi-Two-Dimensional Electronic Structure in Bi2O2Se via Chlorine Substitution
ShanghaiTech University（上海科技大学）；Nanjing University（南京大学）；Diamond Light Source（钻石光源）；Shanghai Synchrotron Radiation Facility, Shanghai Advanced Research Institute, Chinese Academy of Sciences（中国科学院上海高级研究院同步辐射实验室）；National Key Laboratory of Materials for Integrated Circuits, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences（中国科学院上海微系统与信息技术研究所国家集成电路材料重点实验室）
2D abrupt nano-junctions blending sp-sp2 bonds on atomically precise heterostructures
Politecnico di Milano（米兰理工大学）；Università degli Studi di Milano（米兰大学）；INFN Sezione di Milano（意大利国家核物理研究所米兰分部）；Università di Pavia（帕维亚大学）；Università Degli Studi Di Padova（帕多瓦大学）；Instituto de Nanociencia y Materiales de Aragon (INMA), CSIC-Universidad de Zaragoza（阿拉贡纳米科学与材料研究所（INMA），西班牙国家科学研究委员会-萨拉戈萨大学）
