Corrected Scanning Transmission Electron Microscopy Research Articles

Nanoscale mechanisms of carboxyl carbon preservation during Fe(II)-induced ferrihydrite transformation

The persistence of organic carbon (OC) in natural environments is widely attributed to OC associations with minerals such as iron (Fe) minerals. Carboxyl, a critical structure of OC, can form strong complexes with Fe minerals, but it is still largely unknown about the effects of carboxyl groups on the transformation of Fe oxides and the stabilization mechanisms of OC on Fe oxides at nanoscales. In this study, four carboxylic acids with varying numbers of carboxyl groups (2, 3, 4, and 27 carboxyls) and molecular weight (ranging from 100 to 2000 Da) were added during the coprecipitation of Fe oxides and OC. This approach was taken to systematically elucidate the nanoscale distribution and sequestration mechanisms of carboxyl-containing OC on Fe oxides over different aging periods. Results suggested that ferrihydrite transformed quickly into lepidocrocite, goethite, and magnetite with the presence of Fe(II). The transformation rate of lepidocrocite to goethite slowed with increasing carboxyl number in OC molecules for the low molecular weight carboxylic acids (100–300 Da), but the high molecular weight carboxylic acid (∼2000 Da) promoted ferrihydrite transformation into goethite. Meanwhile, the particle sizes of produced magnetite decreased with increasing carboxyl number in OC molecules. During the mineral transformation, the release of OC from Fe oxides to aqueous solution decreased with increasing numbers of carboxyl groups. Spherical aberration corrected scanning transmission electron microscopy (Cs-STEM) coupled with electron-energy-loss spectroscopy (EELS) suggested that carboxyl-rich OC promoted the formation of abundant defective or porous structures in goethite, resulting in OC accumulation in the bulk areas of goethite, which provided an effective way to sequester OC. The aggregation of high molecular weight OC containing more carboxyl groups with magnetite nanoparticles also played an important role in the preservation of OC. Furthermore, Fourier-transform infrared spectroscopy (FTIR) and near edge X-ray absorption fine structure spectroscopy (NEXAFS) indicated that OC may form bidentate binding with Fe oxides and the binding strength of Fe(III) and OC may change with varying numbers of carboxyl groups. Results in this study provided a comprehensive understanding of the dynamic interactions between OC with different numbers of carboxyl groups and Fe oxides, and shed insights into the nanoscale mechanisms of OC stabilization during Fe oxide transformation process.

The role of high-resolution transmission electron microscopy and aberration corrected scanning transmission electron microscopy in unraveling the structure-property relationships of Pt-based fuel cells electrocatalysts.

Platinum-based fuel cell electrocatalysts are structured on a nano level in order to extend their active surface area and maximize the utilization of precious and scarce platinum. Their performance is dictated by the atomic arrangement of their surface layers atoms via structure-property relationships. Transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) are the preferred methods for characterizing these catalysts, due to their capacity to achieve local atomic-level resolutions. Size, morphology, strain and local composition are just some of the properties of Pt-based nanostructures that can be obtained by (S)TEM. Furthermore, advanced methods of (S)TEM are able to provide insights into the quasi-in situ, in situ or even operando stability of these nanostructures. In this review, we present state-of-the-art applications of (S)TEM in the investigation and interpretation of structure-activity and structure-stability relationships.

Structural investigation of nanovoids around the interface of micro-vias by spherical aberration corrected scanning transmission electron microscopy

In this study, we investigated the microstructural characteristics of nanovoids that form during the electroless Cu plating process for micro-vias using a spherical aberration-corrected scanning transmission electron microscope. The nanovoids, which form during the early stages of the plating process, have a spherical shape with an outermost layer covered with Pd. They are not only empty spaces but partly filled with complexing agent elements, reaction production gas, and other materials.

In situ preparation and determination of CeO2 high-index surface atomic structures

Understanding the properties regarding the high-index surfaces of the oxide nanocrystals is of great importance, but it remains challenging to obtain atomic-level information due to the lack of efficient preparation methods for high-index surfaces. Herein, we presented a work to in situ prepare and determine the intrinsic atomic structures of nanocrystalline CeO2 high-index surfaces via in situ spherical aberration (Cs)-corrected scanning transmission electron microscopy (STEM). By utilizing a reshaping process driven by the Wulff reconstruction, high-index surfaces of CeO2 nanocrystals including {210} {311}, and {533} were successfully prepared. Combined STEM with the density functional theory calculations, these high-index surface structures were determined with atomic precision, and interestingly {533} exhibited a unique atomic pit feature with low-coordinated Ce atoms exposure and unique electrical properties. This work has revealed new information about CeO2 high-index surfaces through experiments, enhancing our understanding of these surfaces, and also providing a new route for preparing high-index surfaces.

Interface effects on titanium growth on graphene

Poor quality interfaces between metal and graphene cause non-linearity and impair the carrier mobility in graphene devices. Here, we use aberration corrected scanning transmission electron microscopy to observe hexagonally close-packed Ti nano-islands grown on atomically clean graphene, and establish a 30∘ epitaxial relationship between the lattices. Due to the strong binding of Ti on graphene, at the limit of a monolayer, the Ti lattice constant is mediated by the graphene epitaxy, and compared to bulk Ti, is strained by ca. 3.7% to a value of 0.306(3) nm. The resulting interfacial strain is slightly greater than what has been predicted by density functional theory calculations. Our early growth stage investigations also reveal that, in contrast to widespread assumptions, Ti does not fully wet graphene but grows initially in islands with a thickness of 1–2 layers. Raman spectroscopy implies charge transfer between the Ti islands and graphene substrate.

Organic Matter Counteracts the Enhancement of Cr(III) Extractability during the Fe(II)-Catalyzed Ferrihydrite Transformation: A Nanoscale- and Molecular-Level Investigation.

Phase transformation of ferrihydrite to more stable Fe (oxyhydr)oxides, catalyzed by iron(II) [Fe(II)], significantly influences the mobility of heavy metals [e.g., chromium (Cr)] associated with ferrihydrite. However, the impact of organic matter (OM) on the behavior of Cr(III) in the Fe(II)-catalyzed transformation of ferrihydrite and the underlying mechanisms are unclear. Here, the Fe(II)-catalyzed transformation of the coprecipitates of Fe(III), Cr(III), or rice straw-derived OM was studied at the nanoscale and molecular levels using Fe and Cr K-edge X-ray absorption spectroscopy and spherical aberration corrected scanning transmission electron microscopy (Cs-STEM). Batch extraction results suggested that the OM counteracted the enhancement of Cr(III) extractability during the Fe(II)-catalyzed transformation. Cs-STEM and XAS analysis suggested that Cr(III) could be incorporated into the goethite formed by Fe(II)-catalyzed ferrihydrite transformation, which, however, was inhibited by the OM. Furthermore, Cs-STEM analysis also provided direct nanoscale level evidence that residual ferrihydrite could re-immobilize the released Cr(III) during the Fe(II)-catalyzed transformation process. These results highlighted that the decreased extractability of Cr(III) mainly resulted from the inhibition of OM on the Fe(II)-catalyzed transformation of ferrihydrite to secondary Fe (oxyhydr)oxides, which facilitates insightful understanding and prediction of the geochemical cycling of Cr in soils with active redox dynamics.

Local Structure in Sodium Antiperovskite Ionic Conductors

Antiperovskites, which can serve as solid state electrolytes, have recently received great attention due to their high ionic conductivity[1]. Compared to typical solid-state ionic conductors, Na3OCl antiperovskite exhibits a unique ionic conductivity behavior that deviates from a linear Arrhenius behavior, in which the ionic conductivity increases rapidly with increasing temperature[2,3]. Many different structural origins affecting the ion conduction mechanism in antiperovskite have been proposed using calculation, such as vacancy/dumbbell migration[4]. The lack of direct experimental local structural investigations makes it challenging to fully understand the structural origins for high ionic conductivity, even resulting in limitations in the development of material designs for good ionic conductors. Complicating their investigation, these materials are also extremely sensitive to air, preventing many structural studies.Here, local structural investigations of Na3OCl are performed using aberration corrected scanning transmission electron microscopy (STEM) to elucidate the atomistic mechanisms underlying its high ionic conduction. To avoid degradation in air, we use an inert gas transfer system that has several advantages. First, transfer in an inert gas environment without air/moisture exposure enables the sample to retain the on-stoichiometry. Second, both room temperature and cryo experiments are possible, which allows pristine structure investigation at application relevant temperatures. Beyond the environment, Na3OCl is also very electron beam sensitive. We will show that low-dose imaging methods, such as parallel beam electron diffraction and electron ptychography, can provide new insights and allow for direct imaging of the local structure. For example, diffuse electron scattering (scattering between the Bragg reflections) is used to investigate subtle differences resulting from local structure, atomic defects, and phonon dispersion relations through combination with electron scattering simulations and Molecular Dynamics (MD) using machine learned potentials. We will then demonstrate how electron ptychography can achieve deep sub-angstrom spatial resolution with low dose conditions and provide direct insights into the migration of Na-ions. Overall, the inert gas transfer system and low-dose diffraction and STEM ptychography enable direct imaging of local structures even for reactive and electron beam sensitive materials, such as antiperovskite electrolytes. The understanding of local structure related to the high ionic conductivity will be crucial for designing high-performance solid electrolytes.

Origin of spin glass magnetic behavior and phase stability of flux-grown RE(Al, Cr, Fe)B4 (RE = Ho and Er) single crystals

The YCrB4 type (α-phase, orthorhombic with space group Pbam) α-HoAlB4 and α-ErAlB4 single crystals which were self-flux grown exhibit the spin glass magnetic behavior, which is anomalous compared to the other reported rare earth system phases of α-REAlB4. Local atomic arrangements with the atomic-resolution for α-HoAlB4 and α-ErAlB4 compounds have been investigated by spherical aberration (Cs)-corrected scanning transmission electron microscopy (STEM) with high-angle annular detector dark-field (HAADF) and annular bright-field (ABF), and STEM-energy-dispersive X-ray spectroscopy (EDS) techniques to elucidate the origin of the exotic magnetic behavior. Observed HAADF- and ABF-STEM images and STEM-EDS chemical maps taken with the incident beam parallel to the [001] direction clearly indicate the existence of substitutions for Al atom sites. The phase stability of RAlB4 (R = Ho ∼ Lu) compounds was discussed from the viewpoint of crystallographic features with lattice parameters and compositions. Based on the presented results, it could be concluded that the origin of the spin glass behavior for self-flux grown α-HoAlB4 and α-ErAlB4 single crystals is the unexpected substitution of Cr/Fe atoms for Al ones. Simultaneously, the substitution by Cr/Fe atoms for Al atoms is indicated to play a significant role to stabilize the YCrB4-type α-HoAlB4 and α-ErAlB4 compounds.

Determination of short-range order in TiVNbHf(Al)

The presence of short-range chemical order can be a key factor in determining the mechanical behavior of metals, but directly and unambiguously determining its distribution in complex concentrated alloy systems can be challenging. Here, we directly identify and quantify chemical order in the globally single phase BCC-TiVNbHf(Al) system using aberration corrected scanning transmission electron microscopy (STEM) paired with spatial statistics methods. To overcome the difficulties of short-range order (SRO) quantification with STEM when the components of an alloy exhibit large atomic number differences and near equiatomic ratios, “null hypothesis” tests are used to separate experiment from a random chemical distribution. Experiment is found to deviate from both the case of an ideal random solid solution and a fully ordered structure with statistical significance. We also identify local chemical order in TiVNbHf and confirm and quantify the enhancement of SRO with the addition of Al. These results provide insight into local chemical order in the promising TiVNbHf(Al) refractory alloys while highlighting the utility of spatial statistics in characterizing nanoscale SRO in compositionally complex systems.

Bi-Deficiency Leading to High-Performance in Mg3 (Sb,Bi)2 -Based Thermoelectric Materials.

Mg3 (Sb,Bi)2 is a potential nearly-room temperature thermoelectric compound composed of earth-abundant elements. However, complex defect tuning and exceptional microstructural control are required. Prior studies have confirmed the detrimental effect of Mg vacancies in Mg3 (Sb,Bi)2 . This study proposes an approach to mitigating the negative scattering effect of Mg vacancies (VMg ) by Bi deficiency, synergistically modulating the electrical and thermal transport properties to enhance the thermoelectric performance. Positron annihilation spectrometry and Cs -corrected scanning transmission electron microscopy analyses indicated that the VMg tends to coalesce due to the introduced VBi . The defects created by Bi deficiency effectively weaken the scattering of electrons from the intrinsic VMg and enhance phonon scattering. A peak zT of 1.82 at 773 K and high conversion efficiency of 11.3% at ∆T = 473 K are achieved in the optimized composition of Mg3 (Sb,Bi)2 by tuning the defect combination. This work demonstrates a feasible and effective approach to improving the performance of Mg3 (Sb,Bi)2 as an emerging thermoelectric material. This article is protected by copyright. All rights reserved.

Exploring the Nanoscale Origin of Performance Enhancement in Li1.1Ni0.35Mn0.55O2 Batteries Due to Chemical Doping

AbstractDespite significant potential as energy storage materials for electric vehicles due to their combination of high energy density per unit cost and reduced environmental and ethical concerns, Co‐free lithium ion batteries based on layered Mn oxides presently lack the longevity and stability of their Co‐containing counterparts. Here, a reduction in this performance gap is demonstrated via chemical doping, with Li1.1Ni0.35Mn0.54Al0.01O2 achieving an initial discharge capacity of 159 mAhg−1 at C/3 rate and a corresponding capacity retention of 94.3% after 150 cycles. The nanoscale origins of this improvement are subsequently explored through a combination of advanced diffraction, spectroscopy, and electron microscopy techniques, finding that optimized doping profiles lead to an improved structural and chemical compatibility between the two constituent sub‐phases that characterize the layered Mn oxide system, resulting in the formation of unobstructed lithium ion pathways between them. A structural stabilization effect of the host compound is also directly observed near the surface using aberration corrected scanning transmission electron microscopy and integrated differential phase contrast imaging.

Uncovering Structure-Activity Relationships in Pt/CeO2 Catalysts for Hydrogen-Borrowing Amination.

The hydrogen-borrowing amination of alcohols is a promising route to produce amines. In this study, experimental parameters involved in the preparation of Pt/CeO2 catalysts were varied to assess how physicochemical properties influence their performance in such reactions. An amination reaction between cyclopentanol and cyclopentylamine was used as the model reaction for this study. The Pt precursor used in the catalyst synthesis and the properties of the CeO2 support were both found to strongly influence catalytic performance. Aberration corrected scanning transmission electron microscopy revealed that the most active catalyst comprised linearly structured Pt species. The formation of these features, a function result of epitaxial Pt deposition along the CeO2 [100] plane, appeared to be dependent on the properties of the CeO2 support and the Pt precursor used. Density functional theory calculations subsequently confirmed that these sites were more effective for cyclopentanol dehydrogenation-considered to be the rate-determining step of the process-than Pt clusters and nanoparticles. This study provides insights into the desirable catalytic properties required for hydrogen-borrowing amination but has relevance to other related fields. We consider that this study will provide a foundation for further study in this atom-efficient area of chemistry.

Influence of the shell thickness on the degradation of Ru@Pt core-shell catalysts in PEM fuel cells

Polymer electrolyte membrane fuel cells, which are fueled by reformate, are reliant on highly active, CO tolerant Ru@Pt core-shell anode catalysts. As little is known of the degradation behaviour of these catalysts, the herein presented study investigated membrane electrode assemblies (MEAs), which were stressed under fuel cell relevant conditions, via electrochemical and physical methods. Two catalysts with different shell thicknesses (Ru@1 Pt and Ru@2 Pt) were incorporated in the MEAs to investigate how the shell thickness influences the degradation behaviour. While the MEA incorporating Ru@1 Pt as anode catalyst was higher in performance than Ru@2 Pt MEA under reformate conditions in the beginning, it strongly degraded during stress testing to end up with a lower performance than Ru@2 Pt afterwards. Due to cyclic voltammetry experiments, it was evidenced that for both catalysts Ru was leached from the anode and crossed over to the cathode – but to a significantly lower extent for Ru@2 Pt. This was further quantified by advanced corrected (scanning) transmission electron microscopy coupled with energy dispersive spectroscopy detector. Additionally, due to imaging local degradation effects were observed for the anode, while Ru poisoning the Pt catalyst was found to be a global problem in the cathode.

Nano and sub-nano scale distribution of organic carbon species on soil particles revealed by Cs-STEM EELS

Understanding the heterogeneous distribution of soil organic matter (SOM) on soil particles is essential for predicting the stability of organic carbon (C) in soil, but direct visualization of the microscopic distribution of organic C in soil is still challenging due to the complexity of soil particles. In this study, a paddy soil was fractionated and spherical aberration corrected scanning transmission electron microscopy (Cs-STEM) coupled with electron energy loss spectroscopy (EELS) was employed to analyze the microscopic distribution of organic C species on clay-sized soil particles (<2000 nm) from the different size fractions (800–2000 nm, 100–800 nm and 0–100 nm) at the nano and sub-nano scale. The EELS results demonstrated that the relative abundance of both phenolic and aliphatic C was quite independent of the particle size fractions, while aromatic and carboxyl carbon demonstrated the largest variations between fractions. With the decrease in soil particle size from 800 to 2000 nm to 0–100 nm, the median abundance of carboxyl (oxidized) C increased from 23% to 35%, and aromatic (reduced) C decreased accordingly from 40% to 16%. The statistical analysis demonstrated that the local organic C concentration was the major factor accounting for the variations in oxidized and reduced C species in soil particles, in which selective sorption of the organic C abundant of acidic functional groups by reactive minerals was responsible for the enrichment of oxidized C in small clay size soil particles. Overall, the results of this study contribute to an improved understanding of the chemical diversity of SOM in organo-mineral interfaces and provide insights in the microscopic C stabilization mechanisms in natural soils.

Atomic-Scale Strucural Analysis of Pt-Based Nanoparticles Using Scanning Transmission Electron Microscopy

Polymer electrolyte fuel cells (PEFCs) is proposed as an alternative to the power generation system in fuel cell vehicles. The performance of the PEFCs is significantly affected by the catalytic activity of the cathode, which contains platinum in general. Recent theoretical studies show that the Pt-Pt interatomic distance at the subsurface of the Pt-based catalysts might considerably influence the catalytic activity. However, experimental evidence remains a challenge due to the requirement of measurement accuracy in picometers at the subsurface. The present work attempts to achieve precise measurements on the Pt-Pt interatomic distance of Pt particles by high-angle annular dark-field (HAADF) imaging in scanning transmission electron microscopy (STEM). Further, we also aim to understand the effects of the change in Pt-Pt interatomic distance on the catalytic activity.A catalyst of 10 wt.% Pt-loaded on graphitized carbon (Sigma-Aldrich) was used in this work. TEM specimen was prepared by dispersing the catalyst on a carbon film supported copper grid. Structural characterizations were examined by a spherical aberration corrected scanning transmission electron microscope (JEM-2100F, JEOL) operated at 200 kV.In order to determine the Pt atomic coordinate accurately, images were first taken under the optimized conditions. Further, a series of images were taken and integrated to form one image with high signal-to-noise ratio and minimized drifting. Finally, the Pt atomic coordinates were extracted precisely on a picometer scale by fitting of the individual atomic columns to two-dimensional Gaussian functions using a custom code developed by MatLab software. To gain insight into the atomic changes in Pt particle, a map of Pt-Pt interatomic displacement vector was constructed and superimposed on the HAADF-STEM image. Intriguingly, a significant Pt-Pt interatomic displacement occurs at the surface of the Pt particle, corresponding to changes in surface morphology and particle size.The state-of-the-art methodology demonstrated here could greatly advance our understanding of surface chemistry of Pt-based catalysts such as Pt3Co alloys. Further understanding of the correlation between the interatomic distances on the catalyst surface and the catalytic activity may give considerable interests and guidelines for future developments of PEFCs.

Magnetocaloric properties of transition metal doped high entropy LaFe11Si2 alloys on Fe sites

The working temperature range of magnetic refrigeration (MR) is severely limited by the narrow range of magnetic entropy change (ΔSM) of magnetocaloric (MC) materials, which especially hinders MR applications near room temperature. Here, high-entropy La(Fe, Si)13 based MC materials with increasing number of equimolar transition metal elements such as Mn, Co, Ni, and Cr occupying Fe sites were synthesized using arc melting and annealing, to stabilize the La(Fe, Si)13 phase, and to increase δFWHM. Atomic resolution aberration corrected scanning transmission electron microscopy and elemental mapping confirmed that the doped transition metal elements uniformly occupy the Fe sites. Due to enhanced configuration entropy, the high entropy alloy has achieved La(Fe, Si)13 single phase structure. Magnetic property measurements reveal that the working temperature range of the high entropy alloy has increased by 141.3%. This work provides a new method to design novel MC materials for better stability and larger temperature range.

Structural investigation of the temperature-stable relaxor dielectric Ba0.8Ca0.2TiO3-Bi(Mg0.5Ti0.5)O3

Aberration corrected scanning transmission electron microscopy (STEM) and electron diffraction have been used to disclose local structure and nano-chemistry in a Ca modified BaTiO3-Bi(Mg0.5Ti0.5)O3 relaxor dielectric ceramic which exhibits high and near-invariant relative permittivity over a wide temperature range. High-resolution, synchrotron X-ray diffraction indicated a globally cubic structure (Pm3̅m), but direct atomic-scale imaging by STEM revealed local tetragonal distortions. Nanopolar clusters were identified from B-site atomic displacement vectors measured relative to oxygen ion positions along < 100 > and < 110 > zone axes of integrated differential phase contrast (iDPC) STEM images, highlighting cluster sizes of 2–5 nm. Chemical analysis by STEM-energy dispersive X-ray spectroscopy and full pattern refinements of X-ray powder diffraction data each implied high levels of Bi vacancies within the matrix. The possibility that these A-site vacancies modulate the nanopolar structure and promote flattening of the permittivity-temperature response in this class of dielectric is discussed.

Enhanced optical emission at MoS2-WS2 heterostructure interface with n-N junction

Atomically thin transition metal dichalcogenide based heterostructures are of significant interest for the electronic and optoelectronic device applications. Growth of atomically thin heterostructures have gained remarkable importance due to the unusual electrical response and optical emission at the interface. Here, facile chemical vapour deposition growth of n-N type MoS2-WS2 heterostructure is demonstrated. Multifold enhancement in photoluminescence emission at the interface of MoS2-WS2 heterostructure with local excitonic amplifications arising at the interface is observed. The atomic level structure of interface has been investigated with the aid of aberration corrected scanning transmission electron microscopy. Electrical properties of MoS2-WS2 heterostructure with n-N semiconductor junction are systematically probed using micromanipulators interfaced with scanning electron microscope. Our microscopic and spectroscopic investigations along with electrical and optical responses at the interface contribute to the fundamental knowledge to empower the development of optical devices based on two dimensional heterostructures with enhanced emissions.

Nanoscale mapping of shifts in dark plasmon modes in sub 10 nm aluminum nanoantennas

In this work, we report the fabrication and spectroscopic characterization of subwavelength aluminum nanocavities—consisting of hexamer or tetramer clusters of sub 10 nm width Al nanorods—with tunable localized surface plasmon resonance (LSPR) energies on suspended SiN x membranes. Here the volume plasmon (VP) and LSPR modes of lithographically-fabricated Al nanocavities are revealed by low-loss electron energy-loss spectroscopy (EELS) in an aberration corrected scanning transmission electron microscope (STEM). We show that the existence of grain boundaries (GBs) in these nanocavities results in shifts in the VP energy and a reduction in the VP lifetime. We map the VP energy and lifetime across GBs and we observe a decrease in VP energy and lifetime at GBs that is consistent with a reduction in free carrier density and increased plasmon scattering at these locations. Dipolar LSPR modes resonant in the UV and blue regions of the electromagnetic spectrum as well as higher-energy optically dark quadrupolar and hexapolar LSPR modes are also observed and mapped by STEM and EELS. All LSPR modes are confirmed via electromagnetic simulations based on the boundary element method. Both tetramer and hexamer structures support the excitation of dipolar bright and dipolar dark modes. Finally, we find that asymmetries in fabricated nanorod hexamer and tetramer nanocavities result in a mode mixing leading to a shift in dipolar dark LSPR modes.

One-Stage Hydrothermal Growth and Characterization of Epitaxial LaMnO3 Films on SrTiO3 Substrate.

Epitaxial LaMnO3 thin films were grown on SrTiO3 substrate using a one-stage hydrothermal route from La(NO3)3, MnCl2 and KMnO4 in an aqueous solution of 10 M KOH at 340 °C. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) indicate full coverage of LaMnO3 on the substrate. X-ray diffraction in the symmetric ω/2θ mode suggests the film has an out-of-plane preferred orientation along the [001] direction of the substrate. The LaMnO3 epitaxial thin film growth mechanism is proposed based on the analysis of the atomic sharp interface formed between LaMnO3 and the SrTiO3 substrate, as seen by aberration−corrected scanning transmission electron microscopy (AC−STEM) imaging in combination with electronic energy loss spectroscopy (EELS). Compared with the conventional vapor deposition methods, the one-stage hydrothermal route opens up a new way to fabricate complex oxide epitaxial heterostructures.