We investigate energetic and electronic properties of TiS2 , an archetypal van der Waals (vdW) material, from first principles, in the framework of the Density Functional Theory (DFT). In this system a recent experimental study showed a puzzling discrepancy between the distribution of the electron density in the interlayer region obtained by X-ray diffraction data and that computed by DFT, even adopting DFT functionals that should properly include vdW effects. Such a discrepancy could indicate a partial failure of state-of-the-art DFT approaches in describing the weak interlayer interactions of TiS2 and, possibly, of similar systems too. In order to shed light on this issue, we have carried out simulations based on different DFT functionals, basically confirming the mentioned discrepancy with the experimental findings. Subsequently, we have tried to reproduce the experimental interlayer electronic density deformation both by changing the parameters characterizing the rVV10 DFT functional (in such a way to artificially modify the strength of the vdW interactions at short or long range), and also by adopting a modified pseudopotential for Sulfur atoms, involving d orbitals. The latter approach turns out to be particularly promising. In fact, using this novel, more flexible pseudopotential, we obtain not only an electronic density deformation closer to the experimental profile, but also a better estimate of the interlayer binding energy. Interestingly, this improvement in the theoretical DFT description is not limited to TiS2 but also applies to other similar layered systems involving S atoms, such as TaS2 , HfS2 , and MoS2 .
Recent studies have revealed that the interlayer interaction in two-dimensional (2D) layered materials is not simply of van der Waals character but could coexist with quasi-bonding character. Here we classify the interlayer quasi-bonding interactions into two main categories (I: homo-occupancy interaction, II: hetero-occupancy interaction) according to the occupancy of the involved energy bands near the Fermi level. Then we investigate the quasi-bonding-interaction-induced band structure evolution of several representative 2D materials based on density functional theory calculations. Further c…
We present a method for low temperature plasma-activated direct wafer bonding of III-V materials to Si using a transparent, conductive indium zinc oxide interlayer. The transparent, conductive oxide (TCO) layer provides excellent optical transmission as well as electrical conduction, suggesting suitability for Si/III-V hybrid devices including Si-based tandem solar cells. For bonding temperatures ranging from 100$^{\circ}$C to 350$^{\circ}$C, Ohmic behavior is observed in the sample stacks, with specific contact resistivity below 1 $Ω$cm$^2$ for samples bonded at 200$^{\circ}$C. Optical absorp…
A methodology to test the interlayer bonding strength of two-dimensional (2D) surfaces and associated one (1D)- and two (2D)- dimensional surface defects using scanning tunneling microscope tip-induced deformation, is demonstrated. Surface elastic deformation characteristics of soft 2D monatomic sheets of graphene and graphite in contrast to NbSe2 indicates related association with the underlying local bonding configurations. Surface deformation of 2D graphitic moire patterns reveal the inter-layer van der Waals strength varying across its domains. These results help in the understanding of th…
Proposed special requirements exist for the rheological properties and time varying characteristics of 3D printing cementitious materials (3DPC). In this study, high dispersion polycarboxylate superplasticizer (HD PC) and fluidity retaining polycarboxylate superplasticizer (FR PC) were used to control the rheological behaviors of 3DPC. The correlation of the time interval, the time varying characteristics of the rheological properties and the interlayer bonding strength were investigated. The results indicated that FR PC improved the fluidity retention ability and thixotropy of the fresh paste…
When single-layer h-BN is subjected to a high-energy electron beam, triangular pores with nitrogen edges are formed. Because of the broken sp2 bonds, these pores are known to possess magnetic states. We report on the magnetism and electronic structure of triangular pores as a function of their size. Moreover, in the Bernal-stacked h-BN (AB-h-BN), multilayer pores with parallel edges can be created, which is not possible in the commonly fabricated multilayer AA'-h-BN. Given that these pores can be manufactured in a well-controlled fashion using an electron beam, it is important to understand th…
Due to the noticeable structural similarity and being neighborhood in periodic table of group-IV and -V elemental monolayers, whether the combination of group-IV and -V elements could have stable nanosheet structures with optimistic properties has attracted great research interest. In this work, we performed first-principles simulations to investigate the elastic, vibrational and electronic properties of the carbon nitride (CN) nanosheet in the puckered honeycomb structure with covalent interlayer bonding. It has been demonstrated that the structural stability of CN nanosheet is essentially ma…
Two pressure-induced phase transitions have been theoretically studied in the layered iron phosphorus triselenide (FePSe3). Topological analysis of chemical bonding in FePSe3 has been performed based on the results of first-principles calculations within the periodic linear combination of atomic orbitals (LCAO) method with hybrid Hartree-Fock-DFT B3LYP functional. The first transition at about 6 GPa is accompanied by the symmetry change from R-3 to C2/m, whereas the semiconductor-to-metal transition (SMT) occurs at about 13 GPa leading to the symmetry change from C2/m to P-31m. We found that t…
The interlayer bonding in two dimensional materials is particularly important because it is not only related to their physical and chemical stability but also affects their mechanical, thermal, electronic, optical, and other properties. To address this issue, we report the direct characterization of the interlayer bonding in 2D SnSe using contact-resonance atomic force microscopy in this study. Site specific CR spectroscopy and CR force spectroscopy measurements are performed on both SnSe and its supporting SiO2 substrate comparatively. Based on the cantilever and contact mechanic models, the …
The direct integration of GaN with Si can boost great potential for low-cost, large-scale, and high-power device applications. However, it is still challengeable to directly grow GaN on Si without using thick strain relief buffer layers due to their large lattice and thermal-expansion-coefficient mismatches. In this work, a GaN/Si heterointerface without any buffer layer is successfully fabricated at room temperature via surface activated bonding (SAB). The residual stress states and interfacial microstructures of GaN/Si heterostructures were systematically investigated through micro-Raman spe…
For the moment, there is no exact description of van der Waals (vdW) interactions. ACFD-RPA \cite{Gould1} is expected to better describe vdW bonding, but it is not exact. The PBE/DFT-D2 method is less satisfactory, however, its results are in good agreement with experimental data. Although our fitting technique may weaken (not neglect) the vdW interactions and produce interlayer potentials with weakened vdW, the obtained interlayer potentials reproduce energetics of graphite near the equilibrium interlayer distance very well, as shown in Ref. \cite{Chen}. If having inputs which fully include v…
Thickness-Dependent Interlayer Coupling and Semiconductor-to-Semimetal Crossover in Arsenene Multilayers
The Anthony J. Leggett Institute for Condensed Matter Theory, Department of Physics, University of Illinois at Urbana-Champaign（伊利诺伊大学厄巴纳-香槟分校）；Materials Science and Technology Division, Oak Ridge National Laboratory（橡树岭国家实验室）；Research Center for Technology Commercialization, Korea Institute of Science and Technology Information (KISTI)（韩国科学技术信息研究院）
Although the precise microscopic knowledge of van der Waals interactions is crucial for understanding bonding in weakly bonded layered compounds, very little quantitative information on the strength of interlayer interaction in these materials is available, either from experiments or simulations. Here, using many-body perturbation and advanced density-functional theory techniques, we calculate the interlayer binding and exfoliation energies for a large number of layered compounds and show that, independent of the electronic structure of the material, the energies for most systems are around 20…
Based on geometry optimization and magnetic structure investigations within density functional theory, unique uranium nitride fluoride UNF, isoelectronic with UO2, is shown to present peculiar differentiated physical properties. Such specificities versus the oxide are related with the mixed anionic sublattices and the layered-like tetragonal structure characterized by covalent like [U2N2]2+motifs interlayered by ionic like [F2]2- ones and illustrated herein with electron localization function graphs. Particularly the ionocovalent chemical picture shows, based on overlap population analyses, st…
In van der Waals bonded or rotationally disordered multilayer stacks of two-dimensional (2D) materials, the electronic states remain tightly confined within individual 2D layers. As a result, electron-phonon interactions occur primarily within layers and interlayer electrical conductivities are low. In addition, strong covalent in-plane intralayer bonding combined with weak van der Waals interlayer bonding results in weak phonon-mediated thermal coupling between the layers. We demonstrate here, however, that Coulomb interactions between electrons in different layers of multilayer epitaxial gra…
We investigate the behaviour of the $π$-electrons under compression and the effect of the stacking order of graphene layers. First we find that electrons can hardly be squeezed through the $sp^2$ network, regardless of the stacking order. The largely deformed electronic orbitals (mainly those of $π$-electrons) under compression along the $\textit{c}$-axis increase interlayer interaction between graphene layers as expected, but surprisingly in a similar way for the A-A and Bernal stacking. On the other hand, the large out-of-plane compression shifts the in-plane phonon frequencies of A-A stacke…
Moire superlattices are twisted bilayer materials, in which the tunable interlayer quantum confinement offers access to new physics and novel device functionalities. Previously, moire superlattices were built exclusively using materials with weak van der Waals interactions and synthesizing moire superlattices with strong interlayer chemical bonding was considered to be impractical. Here using lead sulfide (PbS) as an example, we report a strategy for synthesizing of moire superlattices coupled by strong chemical bonding. We use water-soluble ligands as a removable template to obtain free-stand…
Two-dimensional (2D) graphene-like layered semiconductors provide a new platform for materials research because of their unique mechanical, electronic and optical attributes. Their in-plane covalent bonding and dangling-bond-free surface allow them to assemble various van der Waals heterostructures (vdWHSs) with sharply atomic interfaces that are not limited by lattice matching and material compatibility. Interlayer coupling, as a ubiquitous phenomenon residing among 2D materials (2DMs) systems, controls a thin layer exfoliation process and the assembly of vdWHSs and behaves with a unique degr…
Twisted bilayer graphene (TBG), in which two monolayer graphene are stacked with an in-plane rotation angle, has recently become a hot topic due to unique electronic structures. TBG is normally produced in air by the tear-and-stack method of mechanical exfoliation and transferring graphene flakes, by which a sizable, millimeter-order area, and importantly clean interface between layers are hard to obtain. In this study, we resolved these problems by directly transferring the easy-to-exfoliate CVD-grown graphene on SiC substrate to graphene in a high vacuum without using any transfer assisting …
Using density functional theory calculations, we have investigated the interlayer cation exchange phenomena in muscovite mica, which is motivated by a necessity to develop flexible high-insulating covering materials. The crystalline structures, chemical bonding properties, energetics, and electronic properties of muscovites before and after exchange of interlayer K$^+$ cation with ammonium (NH$_4^+$) or methylammonium (CH$_3$NH$_3^+$) ion were calculated. It was found that the unit cell volume changes are negligibly small upon exchange with NH$_4^+$ ion, while the unit cells are expanded with …
Unmasking charge transfer in the Misfits: ARPES and ab initio prediction of electronic structure in layered incommensurate systems without artificial strain
Two-dimensional (2D) van der Waals (vdW) materials and their bilayers have stimulated enormous interests in fundamental researches and technological applications. Recently, a group of 2D vdW III2-VI3 materials with out-of-plane ferroelectricity have attracted substantial attentions. In this work, the structural, electronic and optical properties of 2D ferroelectric Ga2O3 bilayer system are systematically studied using ab-initio computational method. Intrinsic dipoles of the two freestanding monolayers lead to three distinct dipole models (one ferroelectric and two antiferroelectric models). Th…
The spin-density functional theory (DFT) and DFT+$U$ with Hubbard $U$ term accounting for on-site Coulomb interactions were applied to investigate structure, stability, and electronic properties of different terminations of the Fe$_3$O$_4$(111) surface. All terminations of the ferrimagnetic Fe$_3$O$_4$(111) surface exhibit very large (up to 90%) relaxations of the first four interlayer distances, decreasing with the oxide layer depth. Our calculations predict the iron terminated surface to be most stable in a wide range of the accessible values of the oxygen chemical potential. The adsorption …
Van der Waals (vdW) layered materials have rather weaker interlayer bonding than the intra-layer bonding, therefore the exfoliation along the stacking direction enables the achievement of monolayer or few layers vdW materials with emerging novel physical properties and functionalities. The ferroelectricity in vdW materials recently attracts renewed interest for the potential use in high-density storage devices. As the thickness going thinner, the competition between the surface energy, depolarization field and interfacial chemical bonds may give rise to the modification of ferroelectricity and…
In this work, we study structural and vibrational properties of multilayer graphene using density-functional theory (DFT) with van der Waals (vdW) functionals. Initially, we analyze how different vdW functionals compare by evaluating the lattice parameters, elastic constants and vibrational frequencies of low energy optical modes of graphite. Our results indicate that the vdW-DF1-optB88 functional has the best overall performance on the description of vibrational properties. Next, we use this functional to study the influence of the vdW interactions on the structural and vibrational properties…
Directionally Locked Heteroepitaxy with a Structurally Modulated van der Waals Material
Princeton University（普林斯顿大学）；Princeton Materials Institute（普林斯顿材料研究所）；Donostia International Physics Center（圣塞巴斯蒂安国际物理中心）；University of the Basque Country (UPV/EHU)（巴斯克大学）；Boston College（波士顿学院）；The Hong Kong University of Science and Technology（香港科技大学）；Indian Institute of Technology Guwahati（印度理工学院古瓦哈提分校）；National Institute for Materials Science（日本国立材料研究所）；Centro de Física de Materiales (CSIC-UPV/EHU)（材料物理中心）；Université de Sherbrooke（舍布鲁克大学）
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）
Herein, we performed ab initio screening to identify the best doping of LiNiO2 to achieve improved cycle performance in lithium ion batteries. The interlayer interaction that dominates the c-axis contraction and overall performance was captured well by density functional theory using van der Waals exchange-correlation functionals. The screening indicated that Nb-doping is promising for improving cycle performance. To extract qualitative reasonings, we performed data analysis in a materials informatics manner to obtain a reasonable regression to reproduce the obtained results. LASSO analysis im…
SCAN+rVV10 has been demonstrated to be a versatile van der Waals (vdW) density functional that delivers good predictions of both energetic and structural properties for many types of bonding. Recently, the r$^{2}$SCAN functional has been devised as a revised form of SCAN with improved numerical stability. In this work, we refit the rVV10 functional to optimize the r$^{2}$SCAN+rVV10 vdW density functional, and test its performance for molecular interactions and layered materials. Our molecular tests demonstrate that r$^{2}$SCAN+rVV10 outperforms its predecessor SCAN+rVV10 in both efficiency (nu…
We investigate theoretically the adhesion and electronic properties of graphene on a muscovite mica surface using the density functional theory (DFT) with van der Waals (vdW) interactions taken into account (the vdW-DF approach). We found that irregularities in the local structure of cleaved mica surface provide different mechanisms for the mica-graphene binding. By assuming electroneutrality for both surfaces, the binding is mainly of vdW nature, barely exceeding thermal energy per carbon atom at room temperature. In contrast, if potassium atoms are non uniformly distributed on mica, the diff…
