Interface Atomic Structures Research Articles

Location preference of boron and nitrogen dopants at graphene/copper interface

Controlling the placement of dopants can significantly tailor graphene's properties, but this process is influenced by copper substrates during vapor deposition. Understanding the influence of interfacial atomic structures on the preference for dopant locations is crucial. In this work, we conducted a systematic first-principles study of boron- and nitrogen-doped graphene on copper {111}, considering both sublattice and superlattice configurations. Our calculations revealed that the formation energy is minimized at the top-fccb site (−0.60 eV) for boron and the hcp-fcca site (1.94 eV) for nitrogen, suggesting a possible selective distribution of dopants in both sublattice and superlattice arrangements at the graphene/copper interface. Furthermore, a lower formation energy indicates a higher release of energy during doping, resulting in a stronger interfacial binding. Since formation energy is closely associated with out-of-plane interactions, while in-plane interactions remain relatively stable, these differences offer potential avenues for modifying dopant distribution at graphene/copper interfaces.

Real-time observation of liquid-gallium ordering on epitaxially-grown GaN(0001) by X-ray scattering measurements

X-ray crystal truncation rod (CTR) measurements are commonly used to analyze surface or interfacial atomic structures quantitatively. However, it is difficult to expand the measurement range to determine three-dimensional atomic structures in real time. We developed a method for CTR measurements that involves the simultaneous intensity measurements of X-rays and electron diffraction under molecular beam epitaxial conditions. Using the proposed method, we observed the formation of liquid gallium ordering on the GaN(0001) surface and determined the ordered structure within each layer.

Lattice-Plane-Dependent Distribution of Ce3+ at Pt and CeO2 Interfaces for Pt/CeO2 Catalysts.

The interaction between a metal and a support, which is known as the metal-support interaction, often plays a determining role in the catalytic properties of supported metal catalysts. Herein, we have developed model Pt/CeO2 catalysts, which enabled us to investigate the interface atomic and electronic structures between Pt and the {001}, {011}, and {111} planes of CeO2 using scanning transmission electron microscopy and electron energy-loss spectroscopy. We found that the number of Ce3+ ions around the Pt nanoparticles followed the order {001} > {011} > {111}, which was the opposite order of the generally accepted stability of low index surfaces of CeO2. Systematic first-principles calculations revealed that the presence of Pt nanoparticles facilitated the formation of oxygen vacancies and that the appearance of the Ptδ+ state was preferred when Pt nanoparticles were in contact with CeO2 {001} planes due to direct charge transfer from Pt to CeO2. These results provide important insights into the nature of the metal-support interaction for a comprehensive understanding of the properties of supported metal catalysts.

Formation of Dewetted Epitaxial Structures of Fe3O4/Fe and Their Magnetic Switching Properties

Herein, it is demonstrated that the solid‐state dewetting of patterned Fe(100) films can lead to the formation of epitaxial heterostructures of Fe3O4 and Fe. Fe3O4 layers can be grown conformally on multiple facets of dewetted Fe patterns, without buckle delamination, creating epitaxial interfaces. The dewetted line patterns show switching behaviors that are indicative of parallel and antiparallel coupling of Fe3O4 and Fe magnetization, when magnetic fields are applied along their long and short axes, respectively. By comparing this behavior with the results of micromagnetic simulations, it is suggested that the anisotropic switching behavior cannot be solely attributed to the shape anisotropy of the dewetted patterns; their interfacial atomic structures should also be considered.

Molecular dynamics study of thermal transport properties across covalently bonded graphite-nanodiamond interfaces

The groundbreaking experiment [Luo et al. Nature 2022, 607 (7919) 486–491] recently led to the development of new ultrastrong Carbon/Carbon composites, in which graphene and nanodiamond are strongly connected via covalent bonding. This covalently bonded interface endows the composites with spectacular high strength and other exceptional properties. Herein, non-equilibrium molecular dynamic simulations are conducted to examine the interfacial thermal conductance of graphite-diamond structures by considering the effects of size, environmental temperature, interfacial atomic structures, and tensile strain. Further insight into the microscopic heat transport mechanism of various effects is obtained by analyzing the phonon vibration modes, structural deformation and atomic stress distribution. The variations of interfacial thermal conductance at various temperatures and interfacial configurations are explained qualitatively by the phonon coupling factor. Interestedly, our findings indicate that the interfacial thermal conductance is nearly independent of the graphene size, while it is dependent on the length of the diamond in the direction of heat transport. Furthermore, our study reveals that the interfacial structure retains its heat transport properties even subject to large tensile strain due to interface propagation. Our research provides valuable insights into the heat transport properties of these newly developed Carbon/Carbon composites.

2D layered BP/InSe and BP/Janus In2SeX (X = S or Te) type-II van der Waals heterostructures for photovoltaics: insight from first-principles calculations.

Constructing van der Waals (vdW) heterostructures provides an effective and feasible method for 2D materials to improve their properties and extend their possible applications. Using first-principles calculations, we explored the atomic and electronic structures of Janus In2SeX (X = S or Te) and revealed the existence of a vertical internal intrinsic electric field in these Janus monolayers. Then, we stacked the pristine InSe and Janus In2SeX (X = S or Te) with black phosphorus (BP) vertically to construct vdW heterostructures with a mismatch of less than 5% and systematically investigated their interface atomic structures and possible applications in photovoltaics. The calculation results reveal that the constructed vdW heterostructures can be synthesized experimentally, and the type-II band alignment can be found in all vdW heterostructures, which is independent of the internal electric field of Janus monolayers, the built-in dipole at the interface between two domains, and the number of layers. In addition, the vdW heterostructures show stronger light absorption compared to monolayer individuals, and the type-II band alignment can help the photo-excited carriers to separate and achieve an excellent photovoltaic power conversion efficiency of up to about 21% in these heterostructures. These extraordinary results suggest that these vdW heterostructures have great potential for more efficient solar photovoltaic applications.

Interfacial quality to control tunnelling magnetoresistance

Theoretically, coherent tunnelling through an MgO barrier can achieve over 1,000% magnetoresistance at room temperature. To date, this has not been demonstrated experimentally. In this article, we have categorised magnetic tunnel junctions into four groups and have investigated possible causes of the reduction in their magnetoresistance by correlating their interfacial atomic structures and spin-polarised electron transport. We have concluded that the spin fluctuation induced by dislocations and disordering at a ferromagnet/barrier interface reduced the corresponding magnetoresistance.

First-principles investigation on adsorption of anchors on two-dimensional halide perovskite material

Anchoring groups are important to immobilize the organic species on emerging energy materials such as the halide perovskite material surfaces to tailor their optoelectronic performance. In this manuscript, we employ first-principles calculations to closely examine the interfacial atomic structures, electronic and optical properties of the anchor/perovskite system, using Cs2PbBr4 as an example. 13 small molecular anchors with various functional anchoring groups, including halogen species (-F, -Cl, -Br and –I) and Lewis acids/bases (–COOH, –NH2, –NO2, –OH, -SH and thiophene) are investigated to comprehensively understand the fundamental interactions between the anchors and the two-dimensional halide perovskite surface. The hydrogen bonds play predominant role in the anchor/perovskite interfacial structural stabilization, while the halogen bonds are suggested to initiate weak interactions. These anchoring groups initiate disparate charge transfer characters at the halide perovskite surface, and the nitrobenzene anchor containing the –NO2 group presents perovskite → molecule surface charge transfer direction while most other anchors cause charge transfer in the reverse direction. In addition, the adsorption of the anchors causes blue-shifts in the UV–vis absorption spectra and optical bleaching effects in the resulting halide perovskite systems. The present study facilitates the fundamental understanding on the basic interactions between the anchoring species and the halide perovskite materials toward the photovoltaic applications.

Interfacial Behavior and Atomic Structures of Femtosecond Laser Self-Limiting Covalent Joining Carbon Nanotubes

Interfacial Behavior and Atomic Structures of Femtosecond Laser Self-Limiting Covalent Joining Carbon Nanotubes

Manipulating interfacial atomic structure of Pt/Ce1−xYxO2−δ to improve charge transfer capacity and catalytic activity in aerobic oxidation of HMF

The electronic interaction between metal and support plays a significant role in varying catalytic activity of oxide-supported metal catalysts for the aerobic oxidation of biomass-based alcohols and aldehydes. Employing Y3+-doped ceria supported Pt catalysts, Pt/Ce1-xYxO2-δ, different interfacial atomic structures, including Pt/Ce-Vo(-Ce)2, Pt/Y-Vo(-Ce)2, Pt/Ce-Vo(-Y)2, and Pt/Y-Vo(-Y)2 (Vo represents an oxygen vacancy), were created in this work to modulate the interfacial electron transfer capacity. The results of experimental and theoretical investigations showed that the Pt/Y-Vo(-Ce)2 interfacial structure owned the highest electron transfer capacity from Pt to the support, resulting in more Ptδ+/Y-Vo(-Ce)2 sites. Accordingly, the catalyst Pt/Ce0.75Y0.25O2-δ owning the largest amount of Ptδ+/Y-Vo(-Ce)2 sites exhibited notably promoted catalytic activity for the oxidation of 5-hydroxymethylfurfural (HMF) toward 2,5-furandicarboxylic acid (FDCA), affording a complete conversion of HMF and 96.6% yield of FDCA in 6 h. This work provided a facile and versatile strategy to modulate the electron transfer capacity of oxide supported metal catalysts by manipulating the interfacial atomic structure for promoting their activities in various catalytic oxidation reactions.

Role of Atomic Structure on Exciton Dynamics and Photoluminescence in NIR Emissive InAs/InP/ZnSe Quantum Dots

The development of bright, near-infrared-emissive quantum dots (QDs) is a necessary requirement for the realization of important new classes of technology. Specifically, there exist significant needs for brighter, heavy metal-free, near-infrared (NIR) QDs for applications with high radiative efficiency that span diverse applications, including down-conversion emitters for high-performance luminescent solar concentrators. We use a combination of theoretical and experimental approaches to synthesize bright, NIR luminescent InAs/InP/ZnSe QDs and elucidate fundamental material attributes that remain obstacles for development of near-unity NIR QD luminophores. First, using Monte Carlo ray tracing, we identify the atomic and electronic structural attributes of InAs core/shell, NIR emitters, whose luminescence properties can be tailored by synthetic design to match most beneficially those of high-performance, single-band-gap photovoltaic devices based on important semiconductor materials, such Si or GaAs. Second, we synthesize InAs/InP/ZnSe QDs based on the optical attributes found to maximize LSC performance and develop methods to improve the emissive qualities of NIR emitters with large, tunable Stokes ratios, narrow emission linewidths, and high luminescence quantum yields (here reaching 60 ± 2%). Third, we employ atomistic electronic structure calculations to explore charge carrier behavior at the nanoscale affected by interfacial atomic structures and find that significant exciton occupation of the InP shell occurs in most cases despite the InAs/InP type I bulk band alignment. Furthermore, the density of the valence band maximum state extends anisotropically through the (111) crystal planes to the terminal InP surfaces/interfaces, indicating that surface defects, such as unpassivated phosphorus dangling bonds, located on the (111) facets play an outsized role in disrupting the valence band maximum and quenching photoluminescence.

Theoretical Insights for Improving the Schottky-Barrier Height at the Ga2O3/Pt Interface

In this work we study the Schottky barrier height (SBH) at the junction between $\beta$-Ga$_2$O$_3$ and platinum, a system of great importance for the next generation of high-power and high-temperature electronic devices. Specifically, we obtain interfacial atomic structures at different orientations using our structure matching algorithm and compute their SBH using electronic structure calculations based on hybrid density functional theory. The orientation and strain of platinum are found to have little impact on the barrier height. In contrast, we find that decomposed water (H.OH), which could be present at the interface from Ga$_2$O$_3$ substrate preparation, has a strong influence on the SBH, in particular in the ($\overline{2}$01) orientation. The SBH can range from $\sim$2 eV for the pristine interface to nearly zero for the full H.OH coverage. This result suggests that SBH of $\sim$2~eV can be achieved for the Ga$_2$O$_3$($\overline{2}$01)/Pt junction using the substrate preparation methods that can reduce the amount of adsorbed water at the interface.

Effect of interfacial structures on phonon transport across atomically precise Si/Al heterojunctions

Phonons are important carriers of energy and information in many cryogenic devices used for quantum information science and in fundamental physics experiments such as dark matter detectors. In these systems phonon behaviors can be dominated by interfaces and their atomic structures; hence, there is increasing demand for a more detailed understanding of interfacial phonon transport in relevant material systems. Previous studies have focused on understanding thermal transport over the entire phonon spectrum at and above room temperature. At ultralow temperatures, however, knowledge is missing regarding athermal phonon behavior due to the challenge in modeling the extreme conditions in microscale, heterogeneous cryogenic systems, as well as extracting single-phonon information from a large ensemble. In this paper, we delineate the effects of interfacial atomic structures on phonon transport using a combination of classical molecular dynamics (MD) and phonon wave-packet simulations, to illustrate the consistency and differences between the ensemble- and single-phonon dynamics. We consider three single-crystal Si surface reconstructions---$(1\ifmmode\times\else\texttimes\fi{}1), (\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3})$ and $(7\ifmmode\times\else\texttimes\fi{}7)$---and model both experimentally observed $\mathrm{Si}(1\ifmmode\times\else\texttimes\fi{}1)/\mathrm{Al}$ interfaces and hypothesized $\mathrm{Si}(\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3})$/Al and $\mathrm{Si}(7\ifmmode\times\else\texttimes\fi{}7)/\mathrm{Al}$ interfaces. The overall interfacial thermal conductance calculated from non-equilibrium MD shows that for the $\mathrm{Si}(1\ifmmode\times\else\texttimes\fi{}1)/\mathrm{Al}$ system, the presence of Al twin boundaries can hinder phonon transport and reduce thermal conductance by 2--12% relative to single-crystal Al; whereas the Si $(\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3})$ and $(7\ifmmode\times\else\texttimes\fi{}7)$ reconstructions can enhance it by 6--19%. Normal mode decomposition reveals that both the increase and decrease in conductance are related to inelastic phonon scattering. Single-phonon wave-packet simulations predict phonon transport properties consistent with non-equilibrium MD, while further suggesting that phonon polarization conversion is significant even when elastic transmission dominates, and that the interfacial structures have anisotropic impacts on atomic vibrations along different lattice directions. Our findings suggest avenues for achieving selective phonon transport via controlling interfacial structures of materials using atomically precise fabrication techniques, and that the phonon wave-packet formalism is a potentially powerful method for developing a detailed understanding of non-equilibrium phenomena in the low-temperature limit.

Tuning the high-κ oxide (HfO2, ZrO2)/4H-SiC interface properties with a SiO2 interlayer for power device applications

SiC based power devices are promising for the next generation energy-efficient power converters. But its device performance is always largely limited by the tradition thermal SiO2 gate dielectric. The high-κ dielectric gate oxides have been widely used in Si and III-V devices. However, high quality dielectric layer using high-κ oxide for SiC power device is still lacking sufficient theoretical investigation. In this paper, the properties of XO2/4H-SiC (X = Hf or Zr) interfaces with a SiO2 interlayer are systematically studied by density-functional supercell calculations. Reliable interface atomic structures without any gap states have been built according to the electron counting rule. Based on the models, the electronic structure of each interface is obtained by hybrid functional. The interfacial characteristics including the averaged potential and charge transfer analysis are calculated in detail. The calculated band edge line-ups are comparable with the experimental reports. In term of the band alignment, HfO2 and ZrO2 directly bonding to SiC are not suitable dielectric materials for SiC based power device, due to the relatively smaller conduction band offsets (CBO). While introducing the SiO2 interlayer can effectively tune the interface properties, especially the band alignment. With HfO2(ZrO2)/SiO2 stack as the dielectric layer for 4H-SiC, the interface has the large CBO (>1 eV) to efficaciously confine the channel carriers, indicating that the HfO2(ZrO2)/SiO2/4H-SiC stack is the promising strategy for SiC based power device applications.

Prediction of orientation relationships and interface structures between α-, β-, γ-FeSi2 and Si phases.

A pure crystallogeometrical approach is proposed for predicting orientation relationships, habit planes and atomic structures of the interfaces between phases, which is applicable to systems of low-symmetry phases and epitaxial thin film growth. The suggested models are verified with the example of epitaxial growth of α-, γ- and β-FeSi2 silicide thin films on silicon substrates. The density of near-coincidence sites is shown to have a decisive role in the determination of epitaxial thin film orientation and explains the superior quality of β-FeSi2 thin grown on Si(111) over Si(001) substrates despite larger lattice misfits. Ideal conjunctions for interfaces between the silicide phases are predicted and this allows for utilization of a thin buffer α-FeSi2 layer for oriented growth of β-FeSi2 nanostructures on Si(001). The thermal expansion coefficients are obtained within quasi-harmonic approximation from the DFT calculations to study the influence of temperature on the lattice strains in the derived interfaces. Faster decrease of misfits at the α-FeSi2(001)||Si(001) interface compared to γ-FeSi2(001)||Si(001) elucidates the origins of temperature-driven change of the phase growing on silicon substrates. The proposed approach guides from bulk phase unit cells to the construction of the interface atomic structures and appears to be a powerful tool for the prediction of interfaces between arbitrary phases for subsequent theoretical investigation and epitaxial film synthesis.

Manipulating Atomic Structures at the Au/TiO2 Interface for O2 Activation.

The metal/oxide interface has been extensively studied due to its importance for heterogeneous catalysis. However, the exact role of interfacial atomic structures in governing catalytic processes still remains elusive. Herein, we demonstrate how the manipulation of atomic structures at the Au/TiO2 interface significantly alters the interfacial electron distribution and prompts O2 activation. It is discovered that at the defect-free Au/TiO2 interface electrons transfer from Ti3+ species into Au nanoparticles (NPs) and further migrate into adsorbed perimeter O2 molecules (i.e., in the form of Au-O-O-Ti), facilitating O2 activation and leading to a ca. 34 times higher CO oxidation activity than that on the oxygen vacancy (Vo)-rich Au/TiO2 interface, at which electrons from Ti3+ species are trapped by interfacial Vo on TiO2 and hardly interact with perimeter O2 molecules. We further reveal that the calcination releases those trapped electrons from interfacial Vo to facilitate O2 activation. Collectively, our results establish an atomic-level description of the underlying mechanism regulating metal/oxide interfaces for the optimization of heterogeneous catalysis.

Interfacial ferromagnetism and atomic structures in high-temperature grown Fe3O4/Pt/Fe3O4 epitaxial trilayers

Induced Pt ferromagnetism in Fe3O4/Pt/Fe3O4 epitaxial trilayer films has been investigated by means of X-ray magnetic circular dichroism (XMCD) at the Pt L3,2-edges at various temperatures from 300K to 12K, including the metal-insulator transition temperature of Fe3O4 (TV∼114K). At all the temperatures, we observed clear XMCD signals due to Pt ferromagnetism, the amplitude of which was determined to be 0.39μB at 300K and 0.52μB at 12K for the sample with the Pt thickness of ∼2nm. Interestingly, these values are comparable to or even greater than those in Pt/3d-ferromagnetic-metal (Fe, Ni, Co, and Ni81Fe19) junction systems. The results can be interpreted in terms of a possible Fe interdiffusion into the Pt layer and also possible Fe-Pt alloying due to its high-temperature deposition.

Real-time Observation of Interface Atomic Structures by an Energy-Dispersive Surface X-ray Diffraction

Surface X-ray diffraction is a powerful tool for studying the atomic structure of buried interfaces nondestructively. The analysis is often limited to the static structures, since the acquisition of crystal truncation rod (CTR) profile dataset is lengthy. Recently, high-speed methods have been developed by several groups, aiming for the in operando study of interface phenomena. Our method uses energy-dispersive convergent X-rays and area detector, and allows the quantitative structure analysis during irreversible phenomena in a typical time frame of 1 s. In this review, the energy-dispersive method is compared with the other high-speed methods which use high-energy X-rays with a grazing incidence geometry and transmission geometry, and then two examples of the real-time monitoring are presented, the photo-induced wettability transition of the rutile-TiO2(110) surface and an electrochemical reaction on the Pt(111) electrode surface, to show the capability of the energy-dispersive method.

(Invited) Engineering Au/TiO2 Interface for Electron-Driven Heterogeneous Catalysis

Interfacial electronic properties of Metal/oxide have been extensively studied due to its importance for heterogeneous catalysis, however, to date, the exact role of interfacial atomic structures in governing catalytic processes still remains elusive. Herein, we demonstrate how the manipulation of atomic structures at the Au/TiO2 interface significantly alters the interfacial electron distribution and prompts O2 activation. It is discovered that at the defect-free Au/TiO2 interface, electrons transfer from Ti3+ species into Au nanoparticles (NPs) and further migrate into adsorbed perimeter O2 molecules (i.e., in the form of Au-O-O-Ti), facilitating O2 activation and leading to a 34 times higher CO oxidation activity than that on the oxygen vacancy (V o)-rich interface, at which electrons from Ti centers are trapped by interfacial V o ­on TiO2 and hardly interact with perimeter O2 molecules. Collectively, our results establish an atomic-level description of the underlying mechanism regulating the atomic structure at metal/oxide interfaces for optimizing heterogeneous catalysis.

Tuning Interfacial Cu-O Atomic Structures for Enhanced Catalytic Applications.

Cu2 O/CuOx (x=0, 1) nanocomposites with well-defined morphologies have been widely applied in catalytic reactions. However, people still understand less about tuning interfacial Cu-O atomic structures for enhanced catalytic applications, and a special review on this topic has not been reported so far. Herein, we summarize our understanding on tuning interfacial Cu-O atomic structures based on the literature, including the formation as well as evolution mechanism of Cu-O interfaces in Cu2 O/CuO and Cu2 O/Cu systems, and the improved performances in the fields of CO oxidation, NOx oxidation, photoelectrocatalysis, water gas shift reaction, photodegradation of organic dyes, hydrogen evolution, and photoreduction of CO2 . Finally, we briefly propose several potential research directions.