First-principles Calculations Research Articles

Conformational Tuning of Magnetic Interactions in Coupled Nanographenes.

Phenalenyl (C13H9) is an open-shell spin-1/2 nanographene. Using scanning tunneling microscopy (STM) inelastic electron tunneling spectroscopy (IETS), covalently bonded phenalenyl dimers have been shown to feature conductance steps associated with singlet-triplet excitations of a spin-1/2 dimer with antiferromagnetic exchange. Here, we address the possibility of tuning the magnitude of the exchange interactions by varying the dihedral angle between the two molecules within a dimer. Theoretical methods ranging from density functional theory calculations to many-body model Hamiltonians solved within different levels of approximation are used to explain STM-IETS measurements of phenalenyl dimers on a hexagonal boron nitride (h-BN)/Rh(111) surface, which exhibit signatures of twisting. By means of first-principles calculations, we also propose strategies to induce sizable twist angles in surface-adsorbed phenalenyl dimers via functional groups, including a photoswitchable scheme. This work paves the way toward tuning magnetic couplings in carbon-based spin chains and two-dimensional lattices.

Phonon transport manipulation in TiSe2 via reversible charge density wave melting

Titanium diselenide (TiSe2) is a layered material that under a critical temperature of Tc ≈ 200 K features a periodic modulation of the electron density, known as charge density wave (CDW), which finds applications in quantum information and emerging electronic devices. Here, we present first-principles calculations showing the suppression of the CDW via photoexcitation and consequent stabilization of the undistorted high-temperature phase, in agreement with experimental observations. Interestingly, the unfolded CDW melting is accompanied by a sizable reduction in the thermal conductivity, κ, of up to 25% and a large entropy increase of ~10 J K−1 kg−1. The significant κ variation is almost entirely originated from photoinduced changes in the phonon–phonon scattering processes involving a high-symmetry soft phonon mode. Our results open new possibilities in the design of devices for thermal management and phonon-based logic, and suggest original applications in the of context solid-state cooling.

Comparative First-Principles Study of the Y2Ti2O7/Matrix Interface in ODS Alloys

Oxide-dispersion-strengthened (ODS) alloys generally exhibit extraordinary service performance under severe conditions through the formation of ultrafine nano oxides. Y2Ti2O7 has been characterized as the major strengthening oxide in Fe-based ODS alloys. First-principles energetic analyses were performed to investigate the structural, elastic and interface properties of Y2Ti2O7 in either Fe-based or Ni-based ODS alloys. Y2Ti2O7 has comparable elastic constants to bcc-Fe and fcc-Ni and similar elastic deformation compatibility in Y2Ti2O7-strengthened Fe-based and Ni-based ODS alloys is therefore expected. The Ni/oxide interface has generally better thermostability than Fe/oxide across the whole range of the concerned oxygen chemical potential. Further interface bonding and adhesion calculations revealed that Y2Ti2O7 can enhance the bonding strength of Ni/Y2Ti2O7 through d-d orbital interaction between the interfacial YTi layer and Ni layer, while the interface bonding between the Fe layer and YTi layer is weakened compared to the metal matrix. First-principles calculations suggest that Y2Ti2O7 can be a candidate for strengthening nano-oxides in either Fe-based or Ni-based ODS alloys with well-behaved mechanical properties for fourth-generation fission reactors and further experimental validations are encouraged.

Pseudo-proper two-dimensional electron gas formation

Abstract In spite of the interest in the two-dimensional electron gases (2DEGs) experimentally found at surfaces and interfaces, important uncertainties remain about the observed insulator–metal transitions (IMTs). Here we show how an explicit pseudo-proper coupling of carrier sources with a relevant soft mode significantly affects the transition. The analysis presented here for 2DEGs at polar interfaces is based on group theory, Landau-Ginzburg theory, and illustrated with first-principles calculations for the prototypical case of the LaAlO3⁄SrTiO3 interface, for which such a structural transition has recently been observed. This direct coupling implies that the appearance of the soft mode is always accompanied by carriers. For sufficiently strong coupling an avalanchelike first-order IMT is predicted.

Discovery of Bimetallic Hexagonal MBene Mo2ErB3T2.5 (T = O, F, and Cl).

Exfoliation from quaternary hexagonal MAB (h-MAB) phases has been suggested as a method for producing 2D in-plane ordered MBenes (i-MBenes) with the general formula (M'2/3M″1/3)2AB2. However, experimental realization of defect-free i-MBenes has not been achieved yet due to the absence of a suitable parent quaternary h-MAB phase. In this study, a machine learning (ML)model is used to predict the stability of 15771 quaternary h-MAB phases generated by considering 33 transition metals for the M site and 16 p-block elements for the A site. Out of these compounds, only 195 are identified as potentially stable. Subsequent high-precision first-principles calculations confirm that 47 of them exhibit both thermodynamic and dynamic stability. Their potential for exfoliation into bimetallic i-MBenes is investigated by bonding analysis. Leveraging these theoretical insights, a bimetallic i-MBene is successfully synthesized, namely 2D Mo2ErB3T2.5 (T = F, Cl and O). Further experimental scrutiny reveals its excellent performance for the hydrogen evolution reaction (HER), highlighting the application potential of bimetallic i-MBenes.

Realizing multiorbital Hubbard model with commensurate fillings in the paramagnetic phase of triangular magnets Na2BaX(PO4)2 (X = Mn, Co, Ni)

Abstract The multiorbital Hubbard model is renowned for its rich phase diagram, characterized by various filling-dependent Mott transitions. However, controlling electron filling to explore the complete phase diagram within a single material remains challenging. In this study, we investigate three members of a correlated magnet family: Na2BaX(PO4)2 (where X = Mn, Co, Ni). Our focus is on revealing their unusual electronic structure and magnetic properties. Despite differences in their effective angular momentum, our first-principles calculations reveal a strikingly similar flat-band electronic structure across all three systems. Remarkably, we found that their distinct valence configurations lead to a similar response to electronic correlations in the high-temperature paramagnetic phases, which nicely realizes Mott states with different electron concentrations. Thus, these systems can be conceptualized as multiorbital Hubbard models with differing electron fillings. Our work unifies the understanding of these structurally similar systems and opens new avenues for exploring correlated electronic structures with distinct fillings.

First-principles prediction of high carrier mobility for β-phase MX2N4 (M = Mo, W; X = Si, Ge) monolayers

The recently synthesized monolayer MoSi2N4 (Science 2020, 369, 367) exhibits exceptional environmental stability, a moderate band gap, and excellent mechanical properties, presenting exciting opportunities for the exploration of two-dimensional (2D) MX2Z4 materials. However, the low carrier mobility of α-phase MoSi2N4 significantly limits its potential applications in field-effect transistor (FET) devices. In this study, we systematically investigate the structural stability, elastic properties, and carrier mobility of a novel family of β-phase MX2N4 (M = Mo, W; X = Si, Ge) monolayers through first-principles calculations. Our findings reveal that these β-phase MX2N4 monolayers demonstrate remarkable dynamic, thermal, and mechanical stability. Specifically, we identify the MoSi2N4, MoGe2N4, WSi2N4, and WGe2N4 monolayers as semiconductors with band gaps of 2.70 eV, 1.57 eV, 3.12 eV, and 1.93 eV, respectively, as calculated using the HSE06 functional. Moreover, the MX2N4 monolayers exhibit significant elastic anisotropy, characterized by high ideal tensile strengths and a critical tensile strain exceeding 25%. Notably, the WGe2N4 monolayer displays exceptional anisotropic in-plane charge transport, achieving mobility levels of up to 104 cm2V− 1S− 1, surpassing those of the α-phase MX2N4 monolayers. These novel ternary monolayer structures have the potential to broaden the 2D MX2Z4 material family and emerge as promising candidates for applications in field-effect transistors.

Encapsulation of linear carbon chains in single-walled carbon nanotubes: Towards 1D van der Waals heterostructures for high-efficiency excitonic solar cells

One-dimensional van der Waals heterostructures (1D vdW HTs) based on single-walled carbon nanotubes (SWCNTs) encapsulating linear carbon chains (LCCs) with tunable optoelectronic properties provide a fresh ground for efficient excitonic solar cells (XSCs) alternative to those based on 2D monolayer materials. As an effort to identify for the first time 1D vdW HTs for efficient XSCs application, we perform here a systematic theoretical investigation on the energetic and structural stability, optoelectronic and photovoltaic properties of 1D vdW HTs based on SWCNTs encapsulating 50 symmetrical LCCs of different lengths, and capped with different conjugated endgroups through comprehensive first-principles calculations. We showed the fundamental role of the length and the endgroups effects in modulating the optoelectronic properties of LCCs. Through exploration of the energetic stability of the 1D vdW HTs of LCCs@SWCNTs from the universal force field (UFF) including vdW interactions, we determined the optimal SWCNTs diameters for which the resulting 1D vdW HTs are stable. Then, the band alignment in the 50 stable 1D vdW HTs of LCCs@SWCNTs is examined. Intriguingly, stable LCCs@SWCNTs are identified as type-II 1D vdW HTs complying the prerequisite of XSCs with strong optical absorption in the UV–visible-NIR spectral regions, and power conversion efficiency (PCE) reaching well over 21 %. These findings unravel the enormous potential of the 1D vdW HTs in designing next-generation XSCs devices competitive with state-of-the-art solar cells.

Designed Polar Cosolvent-Prepared Zinc Oxide Film for Efficient and Stable Inverted Organic Solar Cells.

Here, a simple method of applying dimethylformamide (DMF) as cosolvent in the sol-gel technology is used to improve the quality of ZnO bulk films. First-principles calculations show that with the addition of polar solvent DMF, the adsorption energy (Eads) between the solvent and Zn(OH)₂ increases from -1.42 to -1.74eV, which can stabilize the existence of Zn(OH)₂, thereby promoting the ZnO synthesis. Besides, the elimination of amine residues in the DMF-ZnO film significantly suppress the photocatalytic activity induced by amine-induced coordination or redox reactions. Inverted organic solar cells (OSCs) based on PM6:Y6 and PM6:BTP-eC9 achieves impressive power conversion efficiencies (PCE) of 17.58 and 18.14%, respectively. Furthermore, benefiting from the reduced defects of bulk ZnO, pseudo-bilayer bulk heterojunction (PBHJ) devices based on the optimized ZnO film exhibited superior stability, the PM6:Y6 devices based on DMF-ZnO ETLs can maintain 90.28% of their initial PCE after 1000 h of thermal aging at 85°C, and 80.98% of their initial PCE after 168 h of UV aging. This simple solvent optimization strategy can significantly improve the charge transport of ZnO bulk films, making it a reliable strategy for the preparation of electron transport layers in OSCs.

First-principles study of CoMn2O4-Cr2O3 coherent interface analysis

The CoMn2O4 coating can effectively protect the metallic interconnect of solid oxide fuel cells, which come into direct contact with the naturally occurring Cr2O3 on the matrix surface. However, the properties of CoMn2O4-Cr2O3 interface remain unclear. In this study, the first-principles calculations are utilized to investigate the atom staking, stability, and electronic properties of the CoMn2O4(101)-Cr2O3(001) interface, along with examining the diffusion behavior of Cr atom at the interface. By comparing the adhesion work, the most stable model is determined. Based on the most stable model, the results of electronic structure analysis show that Mn atoms providing vacant orbitals near the conduction band minimum, enhancing the overall conductivity of the interface. The projected density of states metal atoms validates the formation priority of Cr-O bonds. The climbing image nudged elastic band (CI-NEB) method is used to simulate the interstitial diffusion properties of Cr atom at the interface, revealing that the energy barrier is about 3.05 eV. The diffusion coefficients of Cr atom are calculated accordingly. The obtained results can provide theoretical support for relevant experiments and deepen the understanding of the protective effects of spinel coatings on metallic interconnects of solid oxide fuel cells.

Lattice dynamics and vibrational properties of scheelite-type alkali-metal perrhenates

The present work provides insight into the structural, vibrational, and elastic properties of scheelite-type alkali-metal perrhenates AReO4(A= Na, K, Rb, and Cs) via first-principles calculations. Sodium, potassium, and rubidium perrhenates are isostructural and crystallize in a tetragonal structure, whereas cesium perrhenate crystallizes in an orthorhombic structure. All the phonon frequencies and their corresponding mode assignments were estimated through the linear response method within density-functional-perturbation theory. The phonon density of states highlights the participation of the oxygen anions and both the A-type and rhenium (Re) cations in the low-frequency range. In contrast, the oxygen and Re atoms make relatively high and moderate contributions to the remaining phonon frequency spectrum. Considerable splitting of the longitudinal and traverse optic modes was observed. Elastic constants and phonon dispersion calculations confirmed the mechanical and dynamic stability of the studied AReO4compounds. A redshift was observed with the frequency of the phonons following the sequence Na→Cs. The low value calculated for the bulk modulus (ranging from 28.36 GPa to 14.15 GPa) and shear modulus indicates the perrhenates have a low resistance to deformation. The values of these moduli decrease in the order of Na→Cs, which correlates with an increase in an ionic radius of the cation. The response to pressure was found to be anisotropic. This characteristic and the ductile nature of the alkali-metal perrhenates were confirmed through elastic analysis.

Magneto-chemical effects in the elastic properties of Co3Al-based compounds

The thermodynamic and mechanical properties of the L12Co3Al type of compounds are fundamental for understanding and designing Co-based superalloys. In these systems, both compositional and magnetic changes can occur upon service due to the elevated temperature. Here, using first-principle calculations, we study the bulk properties of three families of Co3Al-based compounds: (Co1−xNix)3Al (0⩽x⩽0.5), Co3(Al1−yWy) (0⩽y⩽1), and (Co0.5Ni0.5)3(Al0.5TizTa0.5−z) (0⩽z⩽0.5). The calculated lattice constants, Curie temperatures, and formation energies show good agreement with the limited available theoretical and experimental data. Our results reveal the impact of chemistry and magnetism on the elastic parameters. We find that both chemical composition and magnetic state alter the elastic parameters and the elastic anisotropy, which in turn makes the predictions based on common ductile–brittle criteria challenging. We separate the volume and chemical effects for both ferromagnetic and paramagnetic states and show that in most cases, the chemical effect gives the dominant contribution to the alloying trends in the elastic parameters. The present findings reveal the complex relationship between alloying elements and elastic parameters in the Co3Al-based precipitates, providing insights into their mechanical properties for engineering applications.

Transition metal-loaded C2N catalysts for selective CO2 reduction to CH4: Insights from first-principles calculations

The escalating atmospheric CO2 levels due to fossil fuel consumption pose significant environmental challenges, including the greenhouse effect and ocean acidification. Converting CO2 into valuable fuels and chemicals through electrochemical CO2RR is a promising strategy to mitigate these issues. However, the high thermodynamic stability of CO2 and the competing HER present challenges in achieving high selectivity and efficiency. This study employs first-principles calculations to investigate the performance of transition metal trimer catalysts (3TM-C2N, TM = Mn, Mo, Ru, Ti) supported on porous graphitic C2N for CO2RR to CH4. The catalysts were constructed and their stability, electronic structure, and CO2 adsorption mechanisms were systematically analyzed using DFT. The results indicate that 3TM-C2N catalysts are structurally stable, efficiently adsorb and activate CO2, and effectively suppress HER. Notably, 3Mn-C2N demonstrated optimal selectivity for CH3OH and CH4 with a limiting potential of −0.44 V, while 3Ru-C2N showed superior selectivity for the same products at limiting potentials of −0.86 V and −0.73 V, respectively. These findings provide theoretical insights for the experimental optimization of C2N-based catalysts and guide the development of efficient CO2RR electrocatalysts.

Oxygen Vacancy Compensation-Induced Analog Resistive Switching in the SrFeO3-δ/Nb:SrTiO3 Epitaxial Heterojunction for Noise-Tolerant High-Precision Image Recognition.

Neuromorphic computing, inspired by the brain's architecture, promises to surpass the limitations of von Neumann computing. In this paradigm, synaptic devices play a crucial role, with resistive switching memory (memristors) emerging as promising candidates due to their low power consumption and scalability advantages. This study focuses on the development of metal/oxide-semiconductor heterojunctions, which offer several technological advantages and have broad potential for applications in artificial neural synapses. However, constructing high-quality epitaxial interfaces between metal and oxide semiconductors and designing modifiable contact barriers are challenging. Herein, we construct high-quality epitaxial metal/semiconductor interfaces based on the metallicity of the perovskite phase SrFeO3-δ (PV-SFO) and a small Schottky barrier in contact with Nb-doped SrTiO3 (NSTO). X-ray diffraction patterns, reciprocal space mapping results, and cross-sectional transmission electron microscopy images reveal that the prepared PV-SFO film exhibits a perfect single-crystal structure and an excellent epitaxial interface with the NSTO (111) substrate. The corresponding memristor exhibits analog-type resistive-variable characteristics with an ON/OFF ratio of ∼1000, stable data retention after 10,000 s, and no noticeable fluctuation in resistance after 10,000 pulse cycles. Electron energy loss spectroscopy, first-principles calculations, and electrical measurements reveal that compensating or restoring oxygen vacancies at the NSTO surface decreases or increases the contact barrier between PV-SFO and NSTO, respectively, thereby gradually regulating the resistance value. Furthermore, high-quality epitaxial PV-SFO/NSTO devices achieve up to 98.21% recognition accuracy for handwriting recognition tasks using LeNet-5-based network structures and 92.21% accuracy for color images using visual geometry group (VGG) network structures. This work contributes to the advancement of interface-type memristors and provides valuable insights into enhancing synaptic functionality in neuromorphic computing systems.

Robust topological insulating property in C2X-functionalized III-V monolayers.

Two-dimensional (2D) topological insulators (TIs) show great potential applications in low-power quantum computing and spintronics due to the spin-polarized gapless edge states. However, the small bandgap limits their room-temperature applications. Based on first-principles calculations, a series of C2X (X = H, F, Cl, Br, and I) functionalized III-V monolayers are investigated. The nontrivial bandgaps of GaBi-(C2X)2, InBi-(C2X)2, TlBi-(C2X)2 and TlSb-(C2X)2 are found to between 0.223 and 0.807 eV. For GaBi-(C2X)2 and InBi-(C2X)2, the topological insulating properties originate from the s-px,y band inversion induced by the spin-orbital coupling (SOC) effect. While for TlBi-(C2X)2 and TlSb-(C2X)2, the topological insulating properties are attributed to the SOC effect-induced band splitting. The robust topological characteristics are further confirmed by topological invariants Z2 and the test under biaxial strain. Finally, two ideal substrates are predicted to promote the applications of these TIs. These findings indicate that GaBi-(C2X)2, InBi-(C2X)2, TlBi-(C2X)2 and TlSb-(C2X)2 monolayers are good candidates for the fabrication of spintronic devices.

Rational construction of ZnIn2S4/Co3Se4 with boosted photocatalytic hydrogen production through cooperate with S-scheme heterojunction and photothermal effect

The rational design of excellent visible light photocatalysts that efficiently utilize the solar spectrum is urgently needed. In this work, ZnIn2S4 (ZIS) and Co3Se4 (CS) were coupled by a multistep process involving simple ultrasonic self-assembly and calcination to form ZnIn2S4/Co3Se4 (ZIS/CS) photocatalysts with synergistic S-scheme heterojunctions and photothermal effects, which realized efficient photocatalytic hydrogen (H2) production with optimal H2 yield of 2.46 mmol h−1 g−1, superior to pure ZIS (0.47 mmol h−1 g−1) by a factor of 5.23. The excellent cyclic stability and wide environmental adaptability to the ionic environment of water of ZIS/CS were proved. The positive impaction of photothermal effect on the H2 yield of ZIS/CS was investigated and confirmed by the temperature change of photocatalysts powder or photocatalytic system under light irradiation. In addition, based on a series of characterization analyses and first-principle simulation calculations, a charge transfer pathway for ZIS/CS S-scheme heterojunctions was proposed. This work provides valuable ideas and feasible research methods for the design of stable and practical photocatalysts.

Effects of transition elements additions on interfacial properties of Al (111)/B4C (0001) interface based on first-principles study

In this study, the structural stability and adhesion performance of the Al (111)/B4C (0001) interface are explored by performing first-principles calculations, as well as the effects of the additions of the transition elements Sc, Zr, and V on the interfacial adhesion work and electron structures are further investigated. The results of interfacial structure calculations demonstrate that the B-terminated interface with FCC site stacking modality is the optimal configuration of the Al (111)/B4C (0001) interface. The results of adhesion work and electronic properties indicate that the d orbitals of Sc, Zr, and V elements are hybridized with the p orbital of B to form Sc-B, Zr-B, and V-B bonds, respectively, at the interface, which are more covalent than the Al-B bond. In particular, the hybridization between the d orbital of the V element and the p-orbital of B is more intense. Therefore, the best improvement of the interfacial wettability is obtained by the V element, in which the interfacial adhesion work is enhanced by 41.18% compared to the undoped interface. A theoretical guide to enhance the wettability and interfacial properties of the Al/B4C system by adding transition elements can be provided by our calculations.

Effect of sulfur on synergistic corrosion behavior of Q235 and 16Mn steel in sodium aluminate solution

In this study, the corrosion electrochemistry and corrosion behavior of two steels were studied under the simulated alumina production conditions. The corrosion rate of 16Mn steel is greater than that of Q235 steel. The effect of S2− concentration on corrosion rate was significantly higher than that of S2O32−. The synergistic corrosion rates of Q235 and 16Mn steels increase at first and then decrease with the sulfur content, and the peak value appears when the concentration of S2− and S2O32− is 4 g/L and 3 g/L respectively. There are two main types of corrosion products: one is surface octahedral grain, which is composed of Fe2O3, Fe3O4 and Al2O3.The other is the interlayer corrosion between the surface layer and the matrix, which is composed of FeS, FeS2 and NaFeO2.The formation mechanism of the corrosion and corrosion mechanism were obtained by analyzing the phenomenon of ion competitive adsorption. Further validation and analysis of ion competition adsorption phenomenon were conducted using first-principles calculations based on density functional theory (DFT). The formation of corrosion products on the steel surface was investigated at an ion level, and the adsorption energies of OH− and S2− at the top site of Fe(110) surface were calculated. It was found that S2− is more likely to be adsorbed on the Fe(110) surface compared to OH−. The corrosion mechanism of steel is discussed preliminarily.

Achieving high thermal conductivity and strong bending strength diamond/aluminum composite via nanoscale multi-interface phase structure engineering

Diamond/aluminum composites, as a new generation of thermal management materials, are caught in the dilemma between inhibiting the formation of Al4C3 and improving the performance. Herein, we proposed a strategy for nanoscale multi-interface phase structure engineering, utilizing a combination of magnetron sputtering and vacuum heat treatment to obtain diamond particles with nanoscale TiC-Ti layers. Prolonging the vacuum heating time increases the content of TiC, but results in significant differences in the morphology and coverage of TiC formed on the diamond(100) and (111) facets. First-principles calculations reveal that the work of adhesion and C-Ti reaction tendency of diamond(100)/Ti are stronger than those of diamond(111)/Ti, clarifying the difference in interfacial properties between diamond/Ti and diamond/TiC. Diamond-TiC-Ti configuration obtained in advance contributes to fabricating the composite with diamond-TiC-Al(Al3Ti) structure, and the multi-interface phase structure is beneficial to improve the interface bonding, adjust the acoustic mismatch, and inhibit the formation of Al4C3. (800 °C 0.5 h)@Ti-coated diamond(100 μm)/aluminum composite with the multi-interface phase exhibits excellent thermal conductivity(646 W m−1 K−1) and outstanding bending strength(358 MPa), exceeding 90 % of the theoretical prediction of the differential effective medium model. The performance of (800 °C 0.5 h)@Ti-coated diamond/aluminum composite is about 30 % higher than that of traditional Ti-coated diamond/aluminum composite. The TiC layer formed by increasing the heat treatment time is thicker and discontinuous, leading to a decrease in the thermal conductivity of the composite and a weakening effect of Al4C3 inhibition. We clarified the formation mechanism of interface structure related to diamond orientation by multi-scale characterization. Based on the thermal conductivity prediction models, the interface structures corresponding to different diamond orientations were considered, and the predicted values showed good consistency with the experimental results. By interface modification engineering, we overcome the dilemma of introducing modified layer to inhibit Al-C reaction while leading to additional interface thermal resistance, providing insights into the interfacial thermal transport mechanism.

Perspective: imaging atomic step geometry to determine surface terminations of kagome materials and beyond

Here we review scanning tunneling microscopy research on the surface determination for various types of kagome materials, including 11-type (CoSn, FeSn, FeGe), 32-type (Fe3Sn2), 13-type (Mn3Sn), 135-type (AV3Sb5, A = K, Rb, Cs), 166-type (TbMn6Sn6, YMn6Sn6 and ScV6Sn6), and 322-type (Co3Sn2S2 and Ni3In2Se2). We first demonstrate that the measured step height between different surfaces typically deviates from the expected value of ±0.4 ∼0.8Å, which is owing to the tunneling convolution effect with electronic states and becomes a serious issue for Co3Sn2S2 where the expected Sn-S interlayer distance is 0.6Å. Hence, we put forward a general methodology for surface determination as atomic step geometry imaging, which is fundamental but also experimentally challenging to locate the step and to image with atomic precision. We discuss how this method can be used to resolve the surface termination puzzle in Co3Sn2S2. This method provides a natural explanation for the existence of adatoms and vacancies, and beyond using unknown impurity states, we propose and use designer layer-selective substitutional chemical markers to confirm the validity of this method. Finally, we apply this method to determine the surface of a new kagome material Ni3In2Se2, as a cousin of Co3Sn2S2, and we image the underlying kagome geometry on the determined Se surface above the kagome layer, which directly visualizes the p-d hybridization physics. We emphasize that this general method does not rely on theory, but the determined surface identity can provide guidelines for first-principles calculations with adjustable parameters on the surface-dependent local density of states and quasi-particle interference patterns.