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The article presents a study which demonstrated operando spectrum imaging of a lithium (Li)-ion battery anode over multiple charge-discharge cycles using electron energy-loss spectroscopy (EELS) in a scanning transmission electron microscope (STEM). Topics discussed include observation on the growth of Li and LiH dendrites in the solid-electrolyte interphase (SEI), STEM spectrum imaging and in situ biasing, and fluid cell fabrication.

Transmission electron microscopy is a powerful imaging tool that has found broad application in materials science, nanoscience and biology (1-3). With the introduction of aberration-corrected electron lenses, both the spatial resolution and the image quality in transmission electron microscopy have been significantly improved (4,5) and resolution below 0.5 angstroms has been demonstrated (6). To reveal the three-dimensional (3D) structure of thin samples, electron tomography is the method of choice (7-11), with cubic-nanometre resolution currently achievable (10,11). Discrete tomography has recently been used to generate a 3D atomic reconstruction of a silver nanoparticle two to three nanometres in diameter (12), but this statistical method assumes prior knowledge of the particle's lattice structure and requires that the atoms fit rigidly on that lattice. Here we report the experimental demonstration of a general electron tomography method that achieves atomic-scale resolution without initial assumptions about the sample structure. By combining a novel projection alignment and tomographic reconstruction method with scanning transmission electron microscopy, we have determined the 3D structure of an approximately ten-nanometre gold nanoparticle at 2.4-angstrom resolution. Although we cannot definitively locate all of the atoms inside the nanoparticle, individual atoms are observed in some regions of the particle and several grains are identified in three dimensions. The 3D surface morphology and internal lattice structure revealed are consistent with a distorted icosahedral multiply twinned particle. We anticipate that this general method can be applied not only to determine the 3D structure of nanomaterials at atomic-scale resolution (13-15), but also to improve the spatial resolution and image quality in other tomography fields (7,9,16-20)., Since its introduction in 1968, electron tomography has been primarily used to determine the 3D structure of biological samples (7,9). In the past decade, electron tomography has been increasingly applied [...]

The deformation mechanism of the Ti-6Al-4V (wt.%) alloy with globular structure was studied under conditions of quasi-static and high-strain compression with rates 10−3 s−1 and 2.1–3.3 × 103 s−1, respectively. High-strain compression was conducted using a Split Hopkinson Pressure Bar (SHPB). The details of the deformation mechanism were evaluated based on the analysis of the deformation hardening curves using the strain hardening exponent concept developed for titanium alloys in tension conditions. The used approach allowed us to identify the stages of plastic deformation observed and the controlling phase in deformation of two-phase alloy through the assessment of the strengthening index, n. It has been found that three deformation stages can be identified in quasi-static conditions. However, when the alloy is compressed at a high strain rate, the third deformation stage does not develop due to the high process rate. Further analysis of deformation curves reveals the leading role of the β-phase under the quasi-static conditions and the essential contribution of the second, α-phase, at a high compression rate. The findings on the deformation mechanism based on the analysis of hardening curves were supported by a detailed structural study. [ABSTRACT FROM AUTHOR]

Dielectric breakdown (DB) controls the failure, and increasingly the function, of microelectronic devices. Standard imaging techniques, which generate contrast based on physical structure, struggle to visualize this electronic process. Here in situ scanning transmission electron microscopy (STEM) electron beam‐induced current (EBIC) imaging of DB in Pt/HfO2/Ti valence change memory devices is reported. STEM EBIC imaging directly visualizes the electronic signatures of DB, namely local changes in the conductivity and in the electric field, with high spatial resolution and good contrast. DB is observed to proceed through two distinct structures arranged in series: a volatile, "soft" filament created by electron injection; and a non‐volatile, "hard" filament created by oxygen‐vacancy aggregation. This picture makes a physical distinction between "soft" and "hard" DB, while at the same time accommodating "progressive" DB, where the relative lengths of the hard and soft filaments can change on a continuum. [ABSTRACT FROM AUTHOR]

Orientation-controlled growth of two-dimensional (2D) transition metal dichalcogenides (TMDCs) may enable many new electronic and optical applications. However, previous studies reporting aligned growth of WSe2 usually yielded very small domain sizes. Herein, we introduced gold vapor into the chemical vapor deposition (CVD) process as a catalyst to assist the growth of WSe2 and successfully achieved highly aligned monolayer WSe2 triangular flakes grown on c-plane sapphire with large domain sizes (130 µm) and fast growth rate (4.3 µm·s−1). When the aligned WSe2 domains merged together, a continuous monolayer WSe2 was formed with good uniformity. After transferring to Si/SiO2 substrates, field effect transistors were fabricated on the continuous monolayer WSe2, and an average mobility of 12 cm2·V−1·s−1 was achieved, demonstrating the good quality of the material. This report paves the way to study the effect of catalytic metal vapor in the CVD process of TMDCs and contributes a novel approach to realize the growth of aligned TMDC flakes. [ABSTRACT FROM AUTHOR]

Transition metal dichalcogenides such as molybdenum disulfide (MoS2) may see service in the heart of next-generation nanoelectronic devices, where highly localized power dissipation can produce nontrivial temperature gradients over nanometer-scale distances. Here, we demonstrate that MoS2 is a promising target for plasmon energy expansion thermometry (PEET), a high-spatial resolution temperature mapping technique employed in a scanning transmission electron microscope (STEM) equipped with electron energy loss spectroscopy (EELS). We first use a calibrated, commercial MEMS-style TEM sample heater chip to measure the temperature dependence of the MoS2 bulk plasmon. We corroborate the chip's temperature calibration with Raman thermometry and determine the bulk thermal expansion coefficient (TEC) of MoS2 in the temperature range of 300–1100 K. Applying this TEC value to PEET measurements on a suspended MoS2 flake, we map 70–90 K/μm temperature gradients with a submicrometer spatial resolution. [ABSTRACT FROM AUTHOR]

As Moore's law comes to an end, the search for additional integrated circuit functionality has shifted from scaling down lateral dimensions to combining multiple materials onto a single substrate. However, the quality of crystalline semiconductors is highly sensitive to the substrate upon which it is grown, preventing multiple materials from being directly grown on single substrates. To circumvent this challenge, many complex growth strategies have been developed, such as strain relaxation buffer-layers, nanostructure growth, and template selective epitaxy. However, even with these advanced growth techniques, the growth of manufacturable crystalline materials is still limited to crystalline surfaces. Here, the authors show that using templated liquid phase (TLP) growth, single crystalline indium phosphide on Si can be grown using a variety of buffers, both crystalline and amorphous. Moreover, by performing detailed optoelectronic characterization, the authors find that the quality of the grown material not only closely matches commercial single crystalline InP wafers but is also highly insensitive to the buffer layer used. This unique feature of TLP growth could enable the next generation of crystalline material integration. [ABSTRACT FROM AUTHOR]

Surface properties of electrode materials play a critical role in the function of batteries. Therefore, surface modifications, such as coatings, have been widely used to improve battery performance. Understanding how these coatings function to improve battery performance is crucial for both scientific research and applications. In this study the electrochemical performance of coated and uncoated LiNi0.5Mn1.5O4 (LNMO) electrodes is correlated with ensemble-averaged soft X-ray absorption spectroscopy (XAS) and spatially resolved scanning transmission electron microscopy-electron energy loss spectroscopy (STEM-EELS) to illustrate the mechanism of how ultrathin layer Al2O3 coatings improve the cycle life of LiNi0.5Mn1.5O4. Mn2+ evolution on the surface is clearly observed in the uncoated sample, which results from the reaction between the electrolytic solution and the surfaces of LiNi0.5Mn1.5O4 particles, and also possibly atomic structure reconstructions and oxygen loss from the surface region in LiNi0.5Mn1.5O4. The coating effectively suppresses Mn2+ evolution and improves the battery performance by decelerating the impedance buildup from the surface passivation. This study demonstrates the importance of combining ensemble-averaged techniques (e.g., XAS) with localized techniques (e.g., STEM-EELS), as the latter may yield unrepresentative information due to the limited number of studied particles, and sheds light on the design of future coating processes and materials. [ABSTRACT FROM AUTHOR]

Heterostructure devices with specific and extraordinary properties can be fabricated by stacking two-dimensional crystals. Cleanliness at the inter-crystal interfaces within a heterostructure is crucial for maximizing device performance. However, because these interfaces are buried, characterizing their impact on device function is challenging. Here, we show that electron-beam induced current (EBIC) mapping can be used to image interfacial contamination and to characterize the quality of buried heterostructure interfaces with nanometer-scale spatial resolution. We applied EBIC and photocurrent imaging to map photo-sensitive graphene-MoS2 heterostructures. The EBIC maps, together with concurrently acquired scanning transmission electron microscopy images, reveal how a device's photocurrent collection efficiency is adversely affected by nanoscale debris invisible to optical-resolution photocurrent mapping. [ABSTRACT FROM AUTHOR]

The vapor diffusion sol–gel (VDSG) method was employed for the room-temperature synthesis of ∼10 nm, aliovalently doped 0.4, 0.8, and 1.6 mol% La:BaTiO3 and 0.4, 0.6, and 1.2 mol% Dy:BaTiO3 nanocrystals. Maximum ensemble relative permittivities of 176 and 208 were observed in the 0.8 mol% La:BaTiO3 and the 1.2 mol% Dy:BaTiO3 nanocrystals, respectively, relative to 89 for undoped BaTiO3 (at 1 MHz, 25 °C) due to local disorder induced by aliovalent substitution. [ABSTRACT FROM AUTHOR]

Graphene's stmcture bears on both the material's electronic properties and fundamental questions about long- range order in two-dimensional crystals. We present an analytic calculation of selected area electron diffraction from multilayer graphene and compare it with data from samples prepared by chemical vapor deposition and mechanical exfoliation. A single layer Scatters Olll~ 0.5% of the incident electrons, so this kinematical calculation can be considered reliable for five or fewer layers. Dark-field transmission electron micrographs of multilayer graphene illustrate how knowledge of the diffraction peak intensities can be applied for rapid mapping of thickness, stacking, and grain boundaries. The diffraction peak intensities also depend on the mean-square displacement of atoms from their ideal lattice locations, which is parameterized by a Debye-Waller factor. We measure the Debye-Waller factor of a suspended monolayer of exfoliated graphene and find a result consistent with an estimate based on the Debye model. For laboratory-scale graphene samples, finite size effects are sufficient to stabilize the graphene lattice against melting, indicating that ripples in the third dimension are not necessary. [ABSTRACT FROM AUTHOR]

Using scanning transmission electron microscopy we image∼4nm platinum nanoparticles deposited on an insulating membrane, wherethe membrane is one of two electron-transparent windows separatingan aqueous environment from the microscope’s high vacuum. Uponreceiving a relatively moderate dose of ∼104 e/nm2, initially immobile nanoparticlesbegin to move along trajectories that are directed radially outwardfrom the center of the field of view. With larger dose rates the particlemotion becomes increasingly dramatic. These observations demonstratethat, even under mild imaging conditions, the in situelectron microscopy of aqueous environments can produce electrophoreticcharging effects that dominate the dynamics of nanoparticles underobservation. [ABSTRACT FROM AUTHOR]

Objects that are small compared to their thermal photon wavelengths violate the assumptions underlying optical pyrometry and can show unusual coherence effects. To investigate this regime, we measure the absolute light intensity from individual, incandescent multiwalled carbon nanotubes. The nanotube filaments' physical dimensions and composition are determined using transmission electron microscopy and their emissivities are calculated in terms of bulk conductivities. A single-color pyrometric analysis then returns a temperature value for each wavelength, polarization, and applied bias measured. Compared to the more common multiwavelength analysis, single-color pyrometry supports a more consistent and complete picture of the carbon nanotube lamps, one that describes their emissivity, optical conductivity, and thermal conductivity in the range 1600-2400 K. [ABSTRACT FROM AUTHOR]