Ab Initio Density Functional Theory Research Articles

In situ characterization of vacancy ordering in Ge-Sb-Te phase-change memory alloys

Tailoring the degree of structural disorder in Ge-Sb-Te alloys is important for the development of non-volatile phase-change memory and neuro-inspired computing. Upon crystallization from the amorphous phase, these alloys form a cubic rocksalt-like structure with a high content of intrinsic vacancies. Further thermal annealing results in a gradual structural transition towards a layered structure and an insulator-to-metal transition. In this work, we elucidate the atomic-level details of the structural transition in crystalline GeSb2Te4 by in situ high-resolution transmission electron microscopy experiments and ab initio density functional theory calculations, providing a comprehensive real-time and real-space view of the vacancy ordering process. We also discuss the impact of vacancy ordering on altering the electronic and optical properties of GeSb2Te4, which is relevant to multilevel storage applications. The phase evolution paths in Ge-Sb-Te alloys and Sb2Te3 are illustrated using a summary diagram, which serves as a guide for designing phase-change memory devices.

Experimental and DFT studies on spinel NiMn2O4 flower derived from bimetallic MOF as an efficient electrode for next-generation supercapacitor

Metal-organic frameworks (MOF) have recently emerged as an intriguing template for developing morphologically pre-designed metal oxide nanostructures. MOFs offer excellent control over morphology, extremely high porosity and large surface area, which is highly beneficial for supercapacitor electrode applications. We report the synthesis of bimetallic MOF-derived Nickel Manganese oxide for an electrode in supercapacitor by an efficient solvothermal and subsequent calcination route. The physical characterization was carried out by X-ray diffraction (XRD), Scanning electron microscope (SEM), Transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Thermogravimetric analysis (TGA) and Bruner-Emmert-Teller (BET). We performed the cyclic voltammetry (CV), chronopotentiometry (CP), and electronic impedance spectroscopy (EIS) test in a 1 M KOH electrolyte to examine the electrochemical characteristics of the prepared samples. NiMn2O4 electrode material revealed high specific capacitance of 1387 F/g at 1 A/g current density and prominent cycle life (80% capacitance retention after 6500 cycles) and the porous structure of the material has a good BET surface area of 84.3 m2/g. Further, we performed spin-polarized ab-initio density functional theory calculations to study the structural, electronic, and magnetic properties of the spinel NiMn2O4 structure. Our calculated results are close to the experimentally determined structural parameters, and the enthalpy of formation confirms the thermodynamical stability of the spinel structure with ΔHF = −1.6 eV/atom. The orbital projected electronic structure is further investigated to understand the contribution of elements near the Fermi region, which paves the way for further understanding of the distribution of electrons at a particular energy interval of our system. The present findings will aid in fabricating the bimetallic MOF-derived metal oxide nanostructures for the next-generation supercapacitors.

Towards the Growth of Hexagonal Boron Nitride on Ge(001)/Si Substrates by Chemical Vapor Deposition.

The growth of hexagonal boron nitride (hBN) on epitaxial Ge(001)/Si substrates via high-vacuum chemical vapor deposition from borazine is investigated for the first time in a systematic manner. The influences of the process pressure and growth temperature in the range of 10−7–10−3 mbar and 900–980 °C, respectively, are evaluated with respect to morphology, growth rate, and crystalline quality of the hBN films. At 900 °C, nanocrystalline hBN films with a lateral crystallite size of ~2–3 nm are obtained and confirmed by high-resolution transmission electron microscopy images. X-ray photoelectron spectroscopy confirms an atomic N:B ratio of 1 ± 0.1. A three-dimensional growth mode is observed by atomic force microscopy. Increasing the process pressure in the reactor mainly affects the growth rate, with only slight effects on crystalline quality and none on the principle growth mode. Growth of hBN at 980 °C increases the average crystallite size and leads to the formation of 3–10 well-oriented, vertically stacked layers of hBN on the Ge surface. Exploratory ab initio density functional theory simulations indicate that hBN edges are saturated by hydrogen, and it is proposed that partial de-saturation by H radicals produced on hot parts of the set-up is responsible for the growth.

Bringing the promises of microreactors and gold catalysis to lignocellulosic biomass valorization: A study on oxidative transformation of furfural

Valorization of lignocellulosic biomass is a key to a sustainable chemical production industry. Furfural has been recognized as a major biomass-derived platform compound and a precursor of various value-added chemicals, including alkyl furoates with a wide range of applications. The conventional production of alkyl furoate utilizes concentrated acids and strong oxidants, making it an environmentally taxing process. A greener alternative is the one-pot direct conversion of furfural to alkyl furoate in an alcohol medium through oxidative esterification using molecular oxygen. However, the explosive mixtures of O2 and alcohols pose a major challenge to this process. To circumvent this issue, for the first time in the literature, we employed a catalytic microchannel reactor that enabled us to carry out the reaction over a wide range of reaction conditions, including the conventionally explosive regions. The conversion of furfural to methyl 2-furoate (MF) was carried out over a silica-supported Au catalyst coated on the inner wall of a microcapillary. A thorough experimental investigation of the reaction was conducted to obtain kinetic information while accounting for possible mass transfer effects on the process. The barely addressed mechanism of gold-assisted oxidative esterification is then investigated, taking advantage of ab initio density functional theory to examine plausible mechanisms. Experimental and computational evidence suggested that surface regeneration by O2 and decomposition of methanol to methoxy species are the crucial steps in the reaction pathway, while furfural was found to have no involvement in the rate-determining step. This work attempts to provide further insights into the reaction engineering and mechanistic aspects of furfural oxidative esterification to potentially contribute to rational catalyst design and process development.

Implications of electron and hole doping on the magnetic properties of spin–orbit entangled Ca4IrO6 from DFT calculations

We investigate the electronic structure and magnetic properties of a Jeff=1/2 iridate Ca4IrO6 and the implications of doping electrons and holes using ab initio density functional theory. Our calculations considering spin–orbit interaction reveal that although the Mott-insulating parent compound transforms into a conductor upon doping, antiferromagnetism sustains in the doped system, albeit with a grossly noncollinear arrangement of the spins. We find a strong spin–orbit interaction and magneto-crystalline anisotropy, causing frustration in the system, possibly leading to the highly noncollinear arrangement of spins upon non-magnetic doping. Our results may be important from the viewpoint of spintronics using iridates or other 5d materials.

Disentangling the electronic structure of an adsorbed graphene nanoring by scanning tunneling microscopy

Graphene nanorings are promising model structures to realize persistent ring currents and Aharonov–Bohm effect at the single molecular level. To investigate such intriguing effects, precise molecular characterization is crucial. Here, we combine low-temperature scanning tunneling imaging and spectroscopy with CO functionalized tips and algorithmic data analysis to investigate the electronic structure of the molecular cycloarene C108 (graphene nanoring) adsorbed on a Au(111) surface. We demonstrate that CO functionalized tips enhance the visibility of molecular resonances, both in differential conductance spectra and in real-space topographic images. Comparing our experimental data with ab-initio density functional theory reveals a remarkably precise agreement of the molecular orbitals and enables us to disentangle close-lying molecular states only separated by 50 meV at an energy of 2 eV below the Fermi level. We propose this combination of techniques as a promising new route for a precise electronic characterization of complex molecules and other physical properties which have electronic resonances in the tip-sample junction.

Modeling the temporal evolution and stability of thin evaporating films for wafer surface processing.

The interaction of thin evaporating fluid films with solids is studied using the example of water on LiTaO3 (LTO). Adsorption energies are computed by ab initio density functional theory (DFT) and used to calculate the Gibbs free energy of adsorption of water on LTO. Integrating the disjoining pressure, consisting of molecular and structural components, with respect to film thickness gives an expression for the Gibbs free energy. In this way, parameters for the disjoining pressure can be calculated by fitting its integral to the Gibbs free energy computed by ab initio DFT. A combination of literature-known models for spin drying and evaporation is utilized to describe the temporal evolution of the water layer. The vapor above the water layer is modeled by diffusion and a mass balance is applied at the water-air interface. For thick initial layers, an analytical approximation is derived which only depends on fluid and ambient conditions but not on the substrate properties.

Theoretical investigations on the excited-state intramolecular proton transfer in the solvated 2-hydroxy-1-naphthaldehyde carbohydrazone

Abstract The vast applications of 2-hydroxy-1-naphthaldehyde-derived systems in the sensors originate from their unusual excited-state intramolecular proton transfer (ESIPT) fluorescence in the molecules. The mechanism of ESIPT fluorescence in the solvated 2-hydroxy-1-naphthaldehyde carbohydrazone (HNLSC) system was investigated by ab initio time-dependent density functional theory (TDDFT) calculation. The solvation stabilized both ground state and excited state in the enol form, and the medium intramolecular interaction ensured the bond break, bond-forming and proton transfer in the conversion from excited enol form to keto form. ESIPT reaction from the enol form to the keto form had a low barrier of 2.54 kcal mol−1 in the cyclohexane solvation, and all the calculated emission was consistent with the experimental findings. Moreover, the disaggregation of excited enol form was favoured instead of the IPT conversion to keto form, vanishing the specific ESIPT pathway in the protic surroundings. Our research can give a meaningful insight into the two kinds of fluorescence spectroscopy in the HNISC system found by experimental measurement and be potential guidance to the application of 2-hydroxy-1-naphthaldehyde-derived systems in the development of new-type sensors, nonlinear optical materials and biochemical probes.

Multilevel Computational Studies Reveal the Importance of Axial Ligand for Oxygen Reduction Reaction on Fe-N-C Materials.

The systematic improvement of Fe-N-C materials for fuel cell applications has proven challenging, due in part to an incomplete atomistic understanding of the oxygen reduction reaction (ORR) under electrochemical conditions. Herein, a multilevel computational approach, which combines ab initio molecular dynamics simulations and constant potential density functional theory calculations, is used to assess proton-coupled electron transfer (PCET) processes and adsorption thermodynamics of key ORR intermediates. These calculations indicate that the potential-limiting step for ORR on Fe-N-C materials is the formation of the FeIII-OOH intermediate. They also show that an active site model with a water molecule axially ligated to the iron center throughout the catalytic cycle produces results that are consistent with the experimental measurements. In particular, reliable prediction of the ORR onset potential and the Fe(III/II) redox potential associated with the conversion of FeIII-OH to FeII and desorbed H2O requires an axial H2O co-adsorbed to the iron center. The observation of a five-coordinate rather than four-coordinate active site has significant implications for the thermodynamics and mechanism of ORR. These findings highlight the importance of solvent-substrate interactions and surface charge effects for understanding the PCET reaction mechanisms and transition-metal redox couples under realistic electrochemical conditions.

Active Surface Structure of SnO2 Catalysts for CO2 Reduction Revealed by Ab Initio Simulations

Tin oxide (SnO2) is an efficient catalyst for the CO2 reduction reaction (CO2RR) to formic acid; however, the understanding of the SnO2 surface structure under working electrocatalytic conditions and the nature of catalytically active sites is a current matter of debate. Here, we employ ab initio density functional theory calculations to investigate how the selectivity and reactivity of SnO2 surfaces toward the CO2RR change at varying surface stoichiometry (i.e., reduction degree). Our results show that SnO2(110) surfaces are not catalytically active for the CO2RR or hydrogen evolution reaction, but rather they reduce under an applied external bias, originating surface structures exposing few metal tin layers, which are responsible for formic acid selectivity.

Spectroscopic investigations, ab-initio DFT calculations, molecular docking and in-vitro assay studies of novel oxovanadium(V)chalcone complexes as potential antidiabetic agents

A series of four novel oxovanadium(V)chalcone complexes ([VO(LI-IV)2Cl]; where HLI=1-(2-Hydroxy-phenyl)-3-phenyl-propenone, HLII=1-(1-Hydroxy-naphthalen-2-yl)-3-phenyl-propenone, HLIII = 1-(2-Amino-phenyl)-3-phenyl-propenone, HLIV = 4-Hydroxy-6-methyl-3-(3-phenyl-acryloyl)-pyran-2-one) were designed and synthesized by performing chemical reaction between VOCl3 and respective chalcone derivatives in 1:2 molar ratio. Their formation as well as chemical structures were confirmed by FTIR, UV-Visible, 1H-NMR, SEM, EDS, and mass spectrometry spectroscopic techniques. The geometry of the synthesized complexes was purposed to be octahedral on the basis of the characterization. Further computational and structural parameters of the synthesized complexes were determined in order to establish their thermodynamic stability/chemical reactivity of the synthesized complexes. Density Functional Theory (DFT) method was employed to calculate the molecular geometry and vibrational frequencies of the synthesized complexes using B3LYP hybrid functional at 6-31G* level of basis set. Further, Spartan'20 V1.0.0 program package was used to calculate the 1H-NMR spectra with (DFT/ B3LYP) in the gaseous phase to validate the structure of oxovanadium(V) complexes. The experimentally obtained results were found to be well correlated with theoretical results with a correlation value > 0.96. Global reactivity descriptors helps to explain the bioactivity of complexes hence, were calculated from the HOMO-LUMO energies. The enzymatic assay experiments indicated that all the four synthesized complexes have significant to moderate inhibition potential against α-glucosidase, and α-amylase enzymes. Among all the oxovanadium(V)chalcone complexes, complex 4showed excellent and superior inhibition potency almost equivalent to the commercially available Acarbose drug and even better in case of α-amylase. The observed IC50 value of complex 4 for the inhibition of α-amylase and α-glucosidase was calculated to be 16.36 µg/mL and 57.27 µg/mL, respectively. The Kinetic parameters calculated from the Lineweaver-Burk plot showed that complex 4 were uncompetitive and mixed inhibitor of α-amylase and α-glucosidase respectively. Thereafter,the antiradical activity of synthesized vanadium(V)chalcone complexes was assessed with the help of DPPH radical scavenging assay. The results demonstrated that all the complexes were remarkable free radical scavengers for the DPPH. The complex 1 was observed to be best among them with the 0.03 µg/mL IC50 value. The AutoDockTools-1.5.6 software was used to examine structure-activity relationship and the binding interactions between oxovanadium(V) complexes and protein target alpha-amylase, alpha-glucosidase, and Myeloperoxidase respectively. The in-vitro as well as in-silico biological activity studies showed significant and major improvements after complexation of chalcone derivatives with vanadium oxychloride (VOCl3). Thus, oxovanadium(V)chalcone complexes were found to be potent inhibitors of the α-glucosidase and α-amylase enzyme.

Silicene: an excellent material for flexible electronics

The outstanding properties of graphene have laid the foundation for exploring graphene-like 2D systems, commonly referred to as 2D-Xenes. Among them, silicene is a front-runner due to its compatibility with current silicon fabrication technologies. Recent works on silicene have unveiled its useful electronic and mechanical properties. The rapid miniaturization of silicon devices and the useful electro-mechanical properties of silicene necessitate the exploration of potential applications of silicene flexible electronics in nano electro-mechanical systems. Using a theoretical model derived from the integration of ab initio density-functional theory and quantum transport theory, we investigate the piezoresistance effect of silicene in the nanoscale regime. As with graphene, we obtain a small value of the piezoresistance gauge factor (GF) of silicene, which is sinusoidally dependent on the transport angle. The small GF of silicene is attributed to its robust Dirac cone and strain-independent valley degeneracy. Based on the obtained results, we propose to use silicene as an interconnect in flexible electronic devices and as a reference piezoresistor in strain sensors. This work will hence pave the way for exploring flexible electronics applications in other 2D-Xene materials.

Deep Insights into Complicated Superdislocation Dissociation and Core Properties of Dislocation in L1 2 ‐Al 3 RE Compounds: A Comprehensive First‐Principles Study

The complicated superdislocation dissociation, dislocation core properties, and slip mechanism of L12 structural alloys have been controversial. Herein, the generalized stacking-fault energy surfaces (γ-surfaces) of the {001}, {110}, and {111} planes in L12-Al3RE (RE = Er, Tm, Yb, Lu) compounds are first calculated according to ab initio density functional theory. Based on the γ-surfaces, the superdislocation dissociation modes are preliminarily estimated using the unstable and stable stacking-fault energies and their ratio. The result shows that the possible type of dissociations cannot be determined just from these ratios. Then, the 2D Peierls–Nabarro (PN) model is applied to simulate the ⟨110⟩{111} superdislocation dissociation configuration evolution in L12-Al3RE, and the complete dislocation properties, including the dissociation width, the dislocation movement, and the Peierls energy and stress, are also investigated. The present study indicates that the combination of the γ-surface and the 2D PN model can comprehensively elucidate the superdislocation properties and deformation mechanisms of L12 structural alloys.

Performance and mechanism of lignin and quercetin as bio-based anti-aging agents for asphalt binder: A combined experimental and ab initio study

• FTIR is used to assess the inhibitory effect of anti-aging agents on asphalt aging. • The capability of lignin to inhibit asphalt aging is lower than that of quercetin. • AIMD simulation and DFT method are used to explore aging mechanism of asphalt. • Bond strength and electrostatic potential are important for anti-aging properties. The addition of lignin to petroleum asphalt as a bio-based anti-aging agent has attracted significant attention owing to its antioxidant property and similar molecular structure to asphalt. To guide the structural modification of lignin to improve its performance in inhibiting asphalt aging, we conducted a combined experimental and ab initio study to reveal the mechanism by which lignin competitively blocks the asphalt aging pathway and to identify the factors affecting the anti-aging property of lignin. Fourier transform infrared spectroscopy was used to evaluate the capability of lignin to prevent asphalt aging. Although lignin inhibited asphalt aging, its activity was significantly lower than that of quercetin, which is another natural phenolic antioxidant. To explain the different performances of lignin and quercetin, ab initio molecular dynamics and density functional theory methods were employed to investigate the aging mechanism of asphalt and the anti-aging mechanism of these two natural phenolics. The results indicate that the H abstraction by O 2 or free radicals is important in asphalt aging and triggers other reactions. Phenolic hydroxyls on lignin and quercetin have strong ability for H atom transfer and positive local electrostatic potential, and so they attract and react with oxidants to prevent the latter from abstracting H atoms from asphalt. Quercetin has a higher content of phenolic hydroxyls than lignin and therefore exhibits superior anti-aging activity. Based on these theoretical results, it is suggested to improve the anti-aging capability of lignin by modifying its structure to lower the molecular weight and increase the phenolic hydroxyl content.

First principles DFT analysis on the diffusion kinetics of hydrogen isotopes through bcc iron (Fe): Role of temperature and surface coverage

The diffusion of interstitial H, D, and T in Fe metal at different temperature are evaluated using ab-initio density functional theory and transition state theory. The thermal expansion coefficient, Helmholtz free energy of activation, jump factor of diffusion was determined by use of activation energy and phonon calculations. The calculated diffusion coefficient was well described by a constant activation energy, (D = D0exp (-Ea)/kT)) with Ea = 0.016, 0.041, and 0.050 eV and D0 = 1.042 × 10−7, 0.736 × 10−7 and 0.572x10−7 m2.s−1for H, D, and T, respectively using harmonic transition state theory (hTST) with temperature correction. The calculated permeability and solubility also followed the Arrhenius relation.The earlier experimentally reported higher diffusivity of H atom at lower temperatures than that at higher temperature (200–600 K) was well explained by Wigner + hTST model with temperature correction and semi-classical transition state theory (SC-TST). The present computed results followed the similar trend of experimental findings. Further, the ideal fracture energy was evaluated using the Born-Haber thermodynamic cycle for varied coverage of H, D and T to account for decohesion-based embrittlement. The lighter H atom was seen to cause more decohesion-based embrittlement compared to D and T due to reduced cohesion. Additionally, the effect of temperature on ideal fracture energy was evaluated for H, D and T in Fe. The decohesion-based embrittlement was increased with increase in the temperature for H, D and T up to certain temperature (for H lower than 500 K, for D around 500 K and for T above 500 K) but with further increase in the temperature, the ideal fracture energy was reduced due to decrease in the adsorption energy and increase in the solution enthalpy of H isotopes. Further, the path and kinetics of dissociation and reassociation of H2 molecule were established on Fe (100) surface at 0.5 and 2.0 ML coverage. At lower concentration (0.5 ML), dissociation of H2 molecule on Fe (100) surface was favored, whereas at high concentration (2.0 ML), reassociation of H2 molecule was favored.

Magnetic properties of equiatomic CrMnFeCoNi

Magnetic, specific heat, and structural properties of the equiatomic Cantor alloy system are reported for temperatures between 5 kelvin and 300 kelvin, and up to fields of 70 kilo-oersted. Magnetization measurements performed on as-cast, annealed, and cold-worked samples reveal a strong processing history dependence and that high-temperature annealing after cold-working does not restore the alloy to a pristine state. Measurements on known precipitates show that the two transitions, detected at 43 kelvin and 85 kelvin, are intrinsic to the Cantor alloy and not the result of an impurity phase. Experimental and ab initio density functional theory (DFT) computational results suggest that these transitions are a weak ferrimagnetic transition and a spin-glass-like transition, respectively, and magnetic and specific heat measurements provide evidence of significant Stoner enhancement and electron-electron interactions within the material.

Evolution of the Electronic and Optical Properties of Meta-Stable Allotropic Forms of 2D Tellurium for Increasing Number of Layers.

In this work, ab initio Density Functional Theory calculations are performed to investigate the evolution of the electronic and optical properties of 2D Tellurium—called Tellurene—for three different allotropic forms (-, - and -phase), as a function of the number of layers. We estimate the exciton binding energies and radii of the studied systems, using a 2D analytical model. Our results point out that these quantities are strongly dependent on the allotropic form, as well as on the number of layers. Remarkably, we show that the adopted method is suitable for reliably predicting, also in the case of Tellurene, the exciton binding energy, without the need of computationally demanding calculations, possibly suggesting interesting insights into the features of the system. Finally, we inspect the nature of the mechanisms ruling the interaction of neighbouring Tellurium atoms helical chains (characteristic of the bulk and -phase crystal structures). We show that the interaction between helical chains is strong and cannot be explained by solely considering the van der Waals interaction.

Probing Strain-Induced Effects on Performance of Low-Dimensional Hybrid Perovskites for Solar Energy Harvesting.

The application of strain to photovoltaics (PVs), thermoelectrics (TEs), and semiconductors often has substantial impacts on the fundamental properties governing the efficiency of these materials. In this work, we investigate two stable phases of hybrid organic-inorganic two-dimensional (2D) perovskites (2DPKs) and their response to the application of tensile and compressive strain of up to 5%. These 2D MAPbI3 analogues are known to exhibit strongly anisotropic properties and have been put forward as excellent candidates for application in mixed PV-TE devices. Our results, stemming from ab initio density functional theory calculations and investigation of transport properties through the Boltzmann transport equations, further elucidate the key properties contributing to the success of these materials. In particular, both the M1 and M2 phases exhibit stable structures between -5 and 5% biaxial strains. The M2 phase exhibits an excellent 23.8% power conversion efficiency under the application of 5% tensile strain. Furthermore, we analyze the effects of spin-orbit coupling on the band structures of both phases, revealing great potential for spintronic applications with the M2 phase, demonstrating Rashba coefficients up to 3.67 eV Å.

Intrinsic electronic property and adsorption of organic molecules on specific iron surface: an ab initio DFT and DFTB study

An ab initio density functional theory (DFT) calculation revealed the electronic properties of azomethine functionalised epoxy, namely, 4-((oxiran-2-yl)methoxy)-N-(4-(4-(4-((oxiran-2-yl)methoxy)benzylideneamino)phenoxy)benzylidene)benzenamine (DSBE) and amine based curing agent namely diethylenetriamine (DETA), triethylenetetraamine (TETA) and para-phenylenediamine (PPD) responsible for its adsorption on the mild steel surface. The frontiers molecular orbitals (FMOs) and the corresponding energies as well as global softness values revealed the reactive nature of the studied organic molecules. The probable trends of the chemical properties of different amine cured epoxy have been predicted. The insights of the adsorption of these organic molecules have been visualized through density functional tight binding calculation. It revealed that these organic molecules are able to adsorb onto targeted metal surface viz. Fe(110), FeO(110) and Fe2O3(110) plane through charge density sharing occurring at the molecule-iron layer interface. Thus, a complete theoretical insight analysis and modelled simulated adsorption study provided a clear picture regarding the adsorptions of the organic molecules onto metallic surfaces.

Universal Principle for Large-Scale Production of a High-Quality Two-Dimensional Monolayer via Positive Charge-Driven Exfoliation

On the basis of the intrinsic characteristics of the layered materials, here we report a universal principle for the production of intact monolayers via layer-by-layer exfoliation from their bulk via positive charge doping. At experimental accessible densities (nc) of ∼1014 cm-2, various multilayer crystals, including graphite, hexagonal boron nitride, transition metal dichalcogenides, MXenes, and black phosphorus, can be exfoliated into the corresponding monolayers through ab initio density functional theory stimulations. The carrier critical thresholds for exfoliating are found to be nearly independent of thickness but dependent on surface size. The universality of positive charge-driven exfoliation originates from the common intrinsic characteristics of electronic structures for layered materials. The positively doped charges that preferentially accumulate near the surface induce interlayer repulsion, leading to layer-by-layer exfoliation when repulsion surpasses interlayer van der Waals force. This strategy may open the possibility of producing diverse high-quality two-dimensional monolayers with a small number of defects toward large-scale manufacturing.