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Abstract: Annular dark field TEM images exhibit a dominant mass-thickness contrast that can be quantified to extract single atom scattering cross sections. On top of this incoherent background, additional lattice fringes appear with a nonlinear information limit of 1.2Å at 150kV. The formation of these fringes is described by coherent nonlinear imaging theory and good agreement is found between experimental and simulated images. Calculations furthermore predict that the use of aberration corrected microscopes will improve the image quality dramatically. [Copyright &y& Elsevier]

Decomposition of the solid solution of an Al–3Mg–0.4Cu–0.12Si (wt.%) alloy has been studied by examining samples aged for periods of 1–16 h at a temperature of 180 °C. High resolution transmission electron microscopy (HRTEM) was the primary method of investigation. Within the 4–16 h aging interval, nanometer scale, homogeneously dispersed, coherent, lath-like particles were detected in the matrix. The orientation of the lath particles in the matrix is such that the edges are aligned along the 〈1 0 0〉Al directions. From the Fourier transformation of the HRTEM images obtained on 〈1 0 0〉Al zones, it was possible to confirm that two variants give rise to diffraction spots that were previously associated with the presence of S″-phase in “Cu lean” Al–Mg–Cu alloys. Two other variants give rise to streaked diffraction spots positioned around the (1 1 0)Al. The detected particles are termed GPBII in this study, instead of previously suggested S″-phase notation. The findings of this study are also compared with those of the frequently studied “Cu rich” Al–Cu–Mg alloying system. [Copyright &y& Elsevier]

Microstructure evolution of an age hardenable Al–3Mg–0.4Cu–0.12Si (wt%) alloy has been studied during artificial aging at 180 °C prior to the formation of the stable S-phase. The primary investigation method used in this study was high-resolution transmission electron microscopy (HRTEM), coupled with image processing and image simulation. After 1 h of aging, the presence of super-lattice reflections was detected in the Fourier spectra of the HRTEM images, suggesting an L10 type ordering of Mg and Cu atoms in the Al matrix. After 4 and 8 h of aging, coherent particles were observed in the microstructure. These particles give rise to diffraction spots that in previous literature have been considered to be characteristic of the S″-phase in the “Cu-lean” Al–Mg–Cu alloys. It is shown that these diffraction spots can be indexed in terms of a crystal structure that is closely related to the L10 ordering formed at the shorter aging times. The crystal structure is orthorhombic with lattice parameters a=1.2 nm, b=0.4 nm, c=0.4 nm and space group Cmmm. We propose to identify these coherent particles as GPB-II zones, and the ordering that precedes them as GPB zones. [Copyright &y& Elsevier]

Presents a study that investigated homoepitaxial deposition of a GaN overlayer onto a bulk single-crystal GaN substrate using molecular beam epitaxy. Comparison of structural quality of deposited GaN overlayer with heteroepitaxially grown layers; Photoluminescence of bulk GaN and the deposited homoepitaxial GaN layer; Benefits for the development of benchmark values for the optoelectronic properties of GaN thin films.

The crystal structure of FePt nanoparticles of mean size of 6 nm produced by gas-phase condensation is characterized using a combination of high-resolution transmission electron microscopy (HRTEM) and high-angle annular dark field (HAADF) imaging in scanning transmission electron microscopy (STEM). These FePt nanoparticles are found to be chemically ordered, decahedral shaped, and Pt enriched at the surfaces. The experimentally determined crystallographic lattice constants and distribution of Fe and Pt atoms are compared with first-principles calculations of ordered decahedral FePt nanoparticles to confirm the discovery of a unique decahedral structure with Fe/Pt ordedng and Pt surface segregation. [ABSTRACT FROM AUTHOR]

Atomically precise tailoring of graphene can enable unusual transport pathways and new nanometer-scale functional devices. Here we describe a recipe for the controlled production of highly regular "5-5-8" line defects in graphene by means of simultaneous electron irradiation and Joule heating by applied electric current. High-resolution transmission electron microscopy reveals individual steps of the growth process. Extending earlier theoretical work suggesting valley-discriminating capabilities of a graphene 5-5-8 line defect, we perform first-principles calculations of transport and find a strong energy dependence of valley polarization of the charge carriers across the defect. These findings inspire us to propose a compact electrostatically gated "valley valve" device, a critical component for valleytronics. [ABSTRACT FROM AUTHOR]

Abstract: Aberration corrected Transmission Electron Microscope (TEM) images can currently resolve information at significantly better than 0.1nm. Aberration corrected imaging conditions seek to optimize the transfer of high-resolution information but in doing so they prevent the transfer of low spatial frequency information. To recover low spatial frequency information, aberration corrected images must be acquired at a large defocus which compromises high spatial frequency information transfer. In this paper we present two a posteriori solutions to this problem in which the information bandwidth in an exit wave reconstruction is increased. In the first we reconstruct the electron exit wavefunction from two focal series datasets, with different, uniform focal steps, experimentally demonstrating that the width of the transfer interval can be extended from 0.2nm−1 (∼5nm) to better than 10nm−1 (0.1nm). In the second we outline the use of a focal series recorded with a non-uniform focal step to recover a wider range of spatial frequencies without the need for a large number of images. Using simulated data we show that using this non-uniform focal step the spatial frequency interval for a five image data set may be increased to between 0.25nm−1 (4nm) and 8.3nm−1 (0.12nm) compared to between 0.74nm−1 (1.4nm) and 8.3nm−1 (0.12nm) for the standard focal series geometry. [Copyright &y& Elsevier]

Abstract: Using two levels of electron beam lithography, vapor phase deposition techniques, and FIB etching, we have fabricated an electrostatic Boersch phase plate for contrast enhancement of weak phase objects in a transmission electron microscope. The phase plate has suitable dimensions for the imaging of small biological samples without compromising the high-resolution capabilities of the microscope. A micro-structured electrode allows for phase tuning of the unscattered electron beam, which enables the recording of contrast enhanced in-focus images and in-line holograms. We have demonstrated experimentally that our phase plate improves the contrast of carbon nanotubes while maintaining high-resolution imaging performance, which is demonstrated for the case of an AlGaAs heterostructure. The development opens a new way to study interfaces between soft and hard materials. [Copyright &y& Elsevier]

Although the physics of materials at surfaces and edges has been extensively studied, the movement of individual atoms at an isolated edge has not been directly observed in real time. With a transmission electron aberration-corrected microscope capable of simultaneous atomic spatial resolution and 1-second temporal resolution, we produced movies of the dynamics of carbon atoms at the edge of a hole in a suspended, single atomic layer of graphene. The rearrangement of bonds and beam-induced ejection of carbon atoms are recorded as the hole grows. We investigated the mechanism of edge reconstruction and demonstrated the stability of the "zigzag" edge configuration. This study of an ideal low-dimensional interface, a hole in graphene, exhibits the complex behavior of atoms at a boundary. [ABSTRACT FROM AUTHOR]

Employing exit-plane wave function (EPWF) reconstruction in high-resolution transmission electron microscopy (HRTEM), we have developed an approach to atomic scale compositional analysis of III-V semiconductor interfaces, especially suitable for analyzing quaternary heterostructures with intermixing in both cation and anion sub-lattices. Specifically, we use the focal-series reconstruction technique, which retrieves the complex-valued EPWF from a thru-focus series of HRTEM images. A study of interfaces in Al0.4Ga0.6As–GaAs and In0.25Ga0.75Sb–InAs heterostructures using focal-series reconstruction shows that change in chemical composition along individual atomic columns across an interface is discernible in the phase image of the reconstructed EPWF. To extract the interface composition profiles along the cation and anion sub-lattices, quantitative analysis of the phase image is performed using factorial analysis of correspondence. This enabled independent quantification of changes in the In–Ga and As–Sb contents across ultra-thin interfacial regions (approximately 0.6 nm wide) with true atomic resolution, in the In0.25Ga0.75Sb–InAs heterostructure. The validity of the method is demonstrated by analyzing simulated HRTEM images of an InAs–GaSb–InAs model structure with abrupt and graded interfaces. Our approach is general, permitting atomic-level compositional analysis of heterostructures with two species per sub-lattice, hitherto unfeasible with existing HRTEM methods. [ABSTRACT FROM AUTHOR]

Abstract: A novel reconstruction procedure is proposed to achieve atomic resolution in electron tomography. The method exploits the fact that crystals are discrete assemblies of atoms (atomicity). This constraint enables us to obtain a three-dimensional (3-D) reconstruction of test structures from less than 10 projections even in the presence of noise and defects. Phase contrast transmission electron microscopy (TEM) images of a gold nanocrystal were simulated in six different zone axes. The discrete number of atoms in every column is determined by application of the channelling theory to reconstructed electron exit waves. The procedure is experimentally validated by experiments with gold samples. Our results show that discrete tomography recovers the shape of the particle as well as the position of its 309 atoms from only three projections. Experiments on a nanocrystal that contains several missing atoms, both on the surface and in the core of the nanocrystal, while considering a high noise level in each simulated image were performed to prove the stability of the approach to reconstruct defects. The algorithm is well capable of handling structural defects in a highly noisy environment, even if this causes atom count “errors” in the projection data. [Copyright &y& Elsevier]

Abstract: Electron channelling occurs when the incident electron beam is parallel to the atom columns of an object, such as a crystal or a particular crystal defect. Then, the electrons are trapped in the electrostatic potential of an atom column in which they scatter dynamically. This picture provides physical insight and explains why a one-to-one correspondence is maintained between the exit wave and the projected structure, even in case of strong dynamical scattering. Moreover, the theory is very useful to invert the dynamical scattering, that is, to derive the projected structure from the exit wave. Finally, it can be used to determine the composition of an atom column with single atom sensitivity or to explain dynamical electron diffraction effects. In this paper, an overview of the channelling theory will be given together with some recent applications. [Copyright &y& Elsevier]

Abstract: The interface of an annealed GaN/InN heterostructure was investigated by valence electron energy loss spectroscopy (VEELS). A monochromated electron beam provides an energy resolution of 180meV at a beam size of 1nm in scanning transmission electron microscopy mode. Although simulteanously performed energy dispersive spectra (EDS) scans reveal an 80nm wide InGaN interdiffusion area, alloying is locally minimal and phase separation is commonly found. Various defect transitions in the range between 1 and less than 0.7eV were observed together with room temperature band transitions of 1.7 and 3.3eV for InN and GaN, respectively. An enhanced concentration of vacancies accumulated at the interface may explain the pronounced interdiffusion and some of the observed defect transitions. [Copyright &y& Elsevier]

Abstract: Zincblende and wurtzite phases of InN are found in InN epilayers deposited by molecular beam epitaxy on GaN buffers which were grown by metal organic chemical vapor deposition. Valence electron energy loss spectroscopy (VEELS) was applied to determine band transitions in both phases of InN. GaN buffer layers were used as VEELS reference. The chemistry and crystalline structure of the observed areas was recorded simultaneously to exclude a contribution from oxides and/or metal clusters or extended defects such as grain boundaries. At room temperature a band transition for wurtzite InN was found at and for zincblende InN at (1.4±0.2)eV that are ascribed to the fundamental bandgaps of the respective polytypes. Those values correlate well with recent results of various research groups measuring the bandgap in InGaN alloys with VEELS. [Copyright &y& Elsevier]

Abstract: High efficient green light emitting diodes (LED) on the basis of GaN/InGaN exhibit indium-rich nanoclusters inside the quantum wells (QW) due to InN–GaN phase decomposition. By direct measurements of the variations in the electronic structure, we show for the first time a correlation between indium-rich nanoclusters and local energy band gap minima. Our investigations reveal the presence of 1–3nm wide indium rich clusters in these devices with indium concentrations x as large as x∼0.30–0.40 that narrow the band gap locally to energies as small as 2.65eV. These clusters are able to act as local traps for migrating photon-emitting carriers and seem to boost the overall device performance. [Copyright &y& Elsevier]

Abstract: Valence electron energy loss spectroscopy (VEELS) was applied to determine band transitions in wurtzite InN, deposited by molecular beam epitaxy on (0001) sapphire substrates or GaN buffer layers. The GaN buffer layer was used as VEELS reference. At room temperature a band transition for wurtzite InN was found at (1.7±0.2eV) and for wurtzite GaN at (3.3±0.2eV) that are ascribed to the fundamental bandgap. Additional band transitions could be identified at higher and lower energy losses. The latter may be related to transitions involving defect bands. In InN, neither oxygen related crystal phases nor indium metal clusters were observed in the areas of the epilayers investigated by VEELS. Consequently, the obtained results mainly describe the properties of the InN host crystal. [Copyright &y& Elsevier]

Within the last few years indium nitride (InN) gained substantial interest due to its controversially discussed apparent band gap and its predicted highest maximum electron mobility among several III–V compounds, including Al(Ga)N and GaAs. The band gap of epitaxial InN has been recently reported to be around 0.7 eV rather than the previously accepted value of 1.9 eV obtained from polycrystalline films. Thus, InN could be a promising material for applications in infrared opto-electronics or high-speed electronics. However, the structural quality of the InN epilayers is still inferior to GaN and needs to be improved. Also, the role of many contaminants in InN and their effect on the epilayer''s conductivity and/or luminescence properties is still under investigation.This work describes recent studies of InN growth by molecular beam epitaxy on sapphire (0 0 0 1) substrates. The effect of buffer layer variations including a prior substrate nitridation step is discussed. Structural properties (X-ray diffraction, AFM and TEM images) and chemical profiles (SIMS) will be correlated to Hall data and Photo-luminescence spectra. The role of oxygen and hydrogen as possible donors in InN will be discussed. [Copyright &y& Elsevier]

Annular objective apertures are fabricated for a CM300 transmission electron microscope using a focused ion beam system. A central beam stop in the back focal plane of the objective lens of the microscope blocks all electrons scattered up to a semi-angle of approximately 20 mrad. In this manner, contributions to the image from Bragg scattering are largely reduced and the image contrast is sensitive to the atomic number Z. Experimentally, we find that single atom scattering cross sections measured with this technique are close to Rutherford scattering values. A comparison between this new method and STEM-HAADF shows that both techniques result in qualitatively similar images although the resolution of ADF-TEM is limited by contrast delocalization caused by the spherical aberration of the objective lens. This problem can be overcome by using an aberration corrected microscope. [Copyright &y& Elsevier]

We demonstrate the deposition of CuInS2 films on single-crystalline (0 0 0 1)-sapphire by radio frequency reactive sputtering with a Cu–In alloy target and H2S gas. X-ray diffraction (XRD) revealed that the as-sputtered films are of mainly (1 1 2)-oriented CuInS2 incorporating a minor CuIn2 phase. XRD rocking curve of CuInS2 (1 1 2) showed a full width at half maximum of 0.1°, indicating an epitaxial-like growth of (1 1 2)-CuInS2 films on (0 0 0 1)-sapphire. Six peaks dominantly show up in the XRD φ–2θ map, between which there are additional regular modulations present, suggesting a multi-domain structure of the thick double-layered films. Furthermore, the morphology and internal microstructure of the quasi-epitaxially sputtered CuInS2 films were characterized by scanning electron microscopy and transmission electron microscopy, respectively. [Copyright &y& Elsevier]

Intensities in high-resolution phase-contrast images from electron microscopes build up discretely in time by detecting single electrons. A wave description of pulse-like coherent-inelastic interaction of an electron with matter implies a time-dependent coexistence of coherent partial waves. Their superposition forms a wave package by phase decoherence of 0.5 - 1 radian with Heisenbergs energy uncertainty ΔEH = ħ/2 Δt-1 matching the energy loss ΔE of a coherent-inelastic interaction and sets the interaction time Δt. In these circumstances, the product of Planck's constant and the speed of light hc is given by the product of the expression for temporal coherence λ2/Δλ and the energy loss ΔE. Experimentally, the self-coherence length was measured by detecting the energy-dependent localization of scattered, plane matter waves in surface proximity exploiting the Goos-Hänchen shift. Chromatic-aberration Cc-corrected electron microscopy on boron nitride (BN) proves that the coherent crystal illumination and phase contrast are lost if the self-coherence length shrinks below the size of the crystal unit cell at ΔE > 200 eV. In perspective, the interaction time of any matter wave compares with the lifetime of a virtual particle of any elemental interaction, suggesting the present concept of coherent-inelastic interactions of matter waves might be generalizable., Competing Interests: Conflict of Interest. The authors declare that they have no competing interest., (Published by Oxford University Press on behalf of the Microscopy Society of America 2024.)

The relation between the energy-dependent particle and wave descriptions of electron-matter interactions on the nanoscale was analyzed by measuring the delocalization of an evanescent field from energy-filtered amplitude images of sample/vacuum interfaces with a special aberration-corrected electron microscope. The spatial field extension coincided with the energy-dependent self-coherence length of propagating wave packets that obeyed the time-dependent Schrödinger equation, and underwent a Goos-Hänchen shift. The findings support the view that wave packets are created by self-interferences during coherent-inelastic Coulomb interactions with a decoherence phase close to Δ φ = 0.5 rad. Due to a strictly reciprocal dependence on energy, the wave packets shrink below atomic dimensions for electron energy losses beyond 1000 eV, and thus appear particle-like. Consequently, our observations inevitably include pulse-like wave propagations that stimulate structural dynamics in nanomaterials at any electron energy loss, which can be exploited to unravel time-dependent structure-function relationships on the nanoscale.

Modifiers are commonly used in natural, biological, and synthetic crystallization to tailor the growth of diverse materials. Here, we identify tautomers as a new class of modifiers where the dynamic interconversion between solute and its corresponding tautomer(s) produces native crystal growth inhibitors. The macroscopic and microscopic effects imposed by inhibitor-crystal interactions reveal dual mechanisms of inhibition where tautomer occlusion within crystals that leads to natural bending, tunes elastic modulus, and selectively alters the rate of crystal dissolution. Our study focuses on ammonium urate crystallization and shows that the keto-enol form of urate, which exists as a minor tautomer, is a potent inhibitor that nearly suppresses crystal growth at select solution alkalinity and supersaturation. The generalizability of this phenomenon is demonstrated for two additional tautomers with relevance to biological systems and pharmaceuticals. These findings offer potential routes in crystal engineering to strategically control the mechanical or physicochemical properties of tautomeric materials., (© 2023. The Author(s).)

Reconstruction of the exit wave function is an important route to interpreting high-resolution transmission electron microscopy (HRTEM) images. Here we demonstrate that convolutional neural networks can be used to reconstruct the exit wave from a short focal series of HRTEM images, with a fidelity comparable to conventional exit wave reconstruction. We use a fully convolutional neural network based on the U-Net architecture, and demonstrate that we can train it on simulated exit waves and simulated HRTEM images of graphene-supported molybdenum disulphide (an industrial desulfurization catalyst). We then apply the trained network to analyse experimentally obtained images from similar samples, and obtain exit waves that clearly show the atomically resolved structure of both the MoS 2 nanoparticles and the graphene support. We also show that it is possible to successfully train the neural networks to reconstruct exit waves for 3400 different two-dimensional materials taken from the Computational 2D Materials Database of known and proposed two-dimensional materials., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 The Author(s). Published by Elsevier B.V. All rights reserved.)

Advances in electron microscopy have enabled visualizations of the three-dimensional (3D) atom arrangements in nano-scale objects. The observations are, however, prone to electron-beam-induced object alterations, so tracking of single atoms in space and time becomes key to unravel inherent structures and properties. Here, we introduce an analytical approach to quantitatively account for atom dynamics in 3D atomic-resolution imaging. The approach is showcased for a Co-Mo-S nanocrystal by analysis of time-resolved in-line holograms achieving ~1.5 Å resolution in 3D. The analysis reveals a decay of phase image contrast towards the nanocrystal edges and meta-stable edge motifs with crystallographic dependence. These findings are explained by beam-stimulated vibrations that exceed Debye-Waller factors and cause chemical transformations at catalytically relevant edges. This ability to simultaneously probe atom vibrations and displacements enables a recovery of the pristine Co-Mo-S structure and establishes, in turn, a foundation to understand heterogeneous chemical functionality of nanostructures, surfaces and molecules., (© 2021. The Author(s).)

The scientific bounty resulting from the successful isolation of few to single layers of two-dimensional materials suggests that related new physics resides in the few- to single-chain limit of one-dimensional materials. We report the synthesis of the quasi-one-dimensional transition metal trichalcogenide NbSe 3 (niobium triselenide) in the few-chain limit, including the realization of isolated single chains. The chains are encapsulated in protective boron nitride or carbon nanotube sheaths to prevent oxidation and to facilitate characterization. Transmission electron microscopy reveals static and dynamic structural torsional waves not found in bulk NbSe 3 crystals. Electronic structure calculations indicate that charge transfer drives the torsional wave instability. Very little covalent bonding is found between the chains and the nanotube sheath, leading to relatively unhindered longitudinal and torsional dynamics for the encapsulated chains., (Copyright © 2018 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.)

Quaternary alloys are essential for the development of high-performance optoelectronic devices. However, immiscibility of the constituent elements can make these materials vulnerable to phase segregation, which degrades the optical and electrical properties of the solid. High-efficiency III-V photovoltaic cells are particularly sensitive to this degradation. InAlAsSb lattice matched to InP is a promising candidate material for high-bandgap subcells of a multijunction photovoltaic device. However, previous studies of this material have identified characteristic signatures of compositional variation, including anomalous low-energy photoluminescence. In this work, atomic-scale clustering is observed in InAlAsSb via quantitative scanning transmission electron microscopy. Image quantification of atomic column intensity ratios enables the comparison with simulated images, confirming the presence of nonrandom compositional variation in this multispecies alloy.

Artificial photosystems are advanced by the development of conformal catalytic materials that promote desired chemical transformations, while also maintaining stability and minimizing parasitic light absorption for integration on surfaces of semiconductor light absorbers. Here, we demonstrate that multifunctional, nanoscale catalysts that enable high-performance photoelectrochemical energy conversion can be engineered by plasma-enhanced atomic layer deposition. The collective properties of tailored Co 3 O 4 /Co(OH) 2 thin films simultaneously provide high activity for water splitting, permit efficient interfacial charge transport from semiconductor substrates, and enhance durability of chemically sensitive interfaces. These films comprise compact and continuous nanocrystalline Co 3 O 4 spinel that is impervious to phase transformation and impermeable to ions, thereby providing effective protection of the underlying substrate. Moreover, a secondary phase of structurally disordered and chemically labile Co(OH) 2 is introduced to ensure a high concentration of catalytically active sites. Application of this coating to photovoltaic p + n-Si junctions yields best reported performance characteristics for crystalline Si photoanodes.

This article summarizes core aspects of beam-sample interactions in research that aims at exploiting the ability to detect single atoms at atomic resolution by mid-voltage transmission electron microscopy. Investigating the atomic structure of catalytic Co 3 O 4 nanocrystals underscores how indispensable it is to rigorously control electron dose rates and total doses to understand native material properties on this scale. We apply in-line holography with variable dose rates to achieve this goal. Genuine object structures can be maintained if dose rates below ~100 e/Å 2 s are used and the contrast required for detection of single atoms is generated by capturing large image series. Threshold doses for the detection of single atoms are estimated. An increase of electron dose rates and total doses to common values for high resolution imaging of solids stimulates object excitations that restructure surfaces, interfaces, and defects and cause grain reorientation or growth. We observe a variety of previously unknown atom configurations in surface proximity of the Co 3 O 4 spinel structure. These are hidden behind broadened diffraction patterns in reciprocal space but become visible in real space by solving the phase problem. An exposure of the Co 3 O 4 spinel structure to water vapor or other gases induces drastic structure alterations that can be captured in this manner.

It is now established that the 3D structure of homogeneous nanocrystals can be recovered from in-line hologram of single projections. The method builds on a quantitative contrast interpretation of electron exit wave functions. Since simulated exit wave functions of single and bilayers of graphene reveal the atomic structure of carbon-based materials with sufficient resolution, we explore theoretically how the approach can be expanded beyond periodic carbon-based materials to include non-periodic molecular structures. We show here theoretically that the 3D atomic structure of randomly oriented oleic acid molecules can be recovered from a single projection.

The radiation-sensitive nature of halide perovskites has hindered structural studies at the atomic scale. We overcome this obstacle by applying low dose-rate in-line holography, which combines aberration-corrected high-resolution transmission electron microscopy with exit-wave reconstruction. This technique successfully yields the genuine atomic structure of ultrathin two-dimensional CsPbBr 3 halide perovskites, and a quantitative structure determination was achieved atom column by atom column using the phase information of the reconstructed exit-wave function without causing electron beam-induced sample alterations. An extraordinarily high image quality enables an unambiguous structural analysis of coexisting high-temperature and low-temperature phases of CsPbBr 3 in single particles. On a broader level, our approach offers unprecedented opportunities to better understand halide perovskites at the atomic level as well as other radiation-sensitive materials.

Atomic scale features of polyvinylidene fluoride molecules (PVDF) were observed with aberration corrected transmission electron microscopy. Thin, self-supporting PVDF nanofibers were used to create images that show conformations and relative locations of atoms in segments of polymer molecules, particularly segments near the surface of the nanofiber. Rows of CF2 atomic groups, at 0.25 nm intervals, which marked the paths of segments of the PVDF molecules, were seen. The fact that an electron microscope image of a segment of a PVDF molecule depended upon the particular azimuthal direction, along which the segment was viewed, enabled observation of twist around the molecular axis. The 0.2 nm side-by-side distance between the two fluorine atoms attached to the same carbon atom was clearly resolved. Morphological and chemical changes produced by energetic electrons, ranging from no change to fiber scission, over many orders of magnitude of electrons per unit area, promise quantitative new insights into radiation chemistry. Relative movements of segments of molecules were observed. Promising synergism between high resolution electron microscopy and molecular dynamic modeling was demonstrated. This paper is at the threshold of growing usefulness of electron microscopy to the science and engineering of polymer and other molecules.