High-resolution Lattice Images Research Articles

The Construction of a Lattice Image and Dislocation Analysis in High-Resolution Characterizations Based on Diffraction Extinctions.

This paper introduces a method for high-resolution lattice image reconstruction and dislocation analysis based on diffraction extinction. The approach primarily involves locating extinction spots in the Fourier transform spectrum (reciprocal space) and constructing corresponding diffraction wave functions. By the coherent combination of diffraction and transmission waves, the lattice image of the extinction planes is reconstructed. This lattice image is then used for dislocation localization, enabling the observation and analysis of crystal planes that exhibit electron diffraction extinction effects and atomic jump arrangements during high-resolution transmission electron microscopy (HRTEM) characterization. Furthermore, due to the method's effectiveness in localizing dislocations, it offers a unique advantage when analyzing high-resolution images with relatively poor quality. The feasibility of this method is theoretically demonstrated in this paper. Additionally, the method was successfully applied to observed edge dislocations, such as 1/6[211-], 1/6[2-11-], and 1/2[01-1], which are not easily observable in conventional HRTEM characterization processes, in electro-deposited Cu thin films. The Burgers vectors were determined. Moreover, this paper also attempted to observe screw dislocations that are challenging to observe in high-resolution transmission electron microscopy. By shifting a pair of diffraction extinction spots and superimposing the reconstructed images before and after the shift, screw dislocations with a Burgers vector of 1/2[011-] were successfully observed in electro-deposited Cu thin films.

Perpendicular magnetic anisotropy induced by La2/3Sr1/3MnO3–YBaCo2O5+δ interlayer coupling

Heterostructure with a symmetry-mismatched interface provides a promising playground for the exploration of emergent phenomena. Herein, we report a systematic investigation on La2/3Sr1/3MnO3/YBaCo2O5+δ (LSMO/YBCO) grown on SrTiO3, a heterostructure formed by perovskite oxides of different symmetry. A high-resolution lattice image shows the formation of high-quality perovskite LSMO and A-site cation-ordered oxygen-deficient double perovskite YBCO, without any signatures of atomic reconfiguration at the interface. Surprisingly, the YBCO-buffered LSMO exhibits perpendicular magnetic anisotropy (PMA), though bare LSMO film is in-plane anisotropic. The PMA is robust, appearing even when the thickness of YBCO is only one unit cell. The typical anisotropy constant is ∼4 × 106 erg cm−3. X-ray absorption spectroscopy analysis reveals a preferential occupation of the orbital compared with , which is confirmed by density functional theory calculations. This orbital reconstruction accounts for the PMA. The formation of a covalent bond between Mn and Co caged by different oxygen polyhedrons, an octahedron and a square pyramid, respectively, stabilizes the orbital reconstruction, resulting in anomalous spin orientation.

Te-rich Bi2Te3 thin films by electron−beam deposition: Structural, electrical, optical and thermoelectric properties

Tellurium-rich Bi2Te3 thin films are deposited by electron−beam evaporation technique at 300 K. These as-deposited thin films are further annealed at 100 °C, 200 °C and 300 °C for 1 h at a pressure of 3 × 10−4 Pa. X-ray diffraction (XRD) patterns of as-deposited films distinctly show Te phase along with Bi2Te3. Peak intensity ratio suggests the polycrystalline nature of as-deposited Bi2Te3 films. On vacuum annealing Te-rich Bi2Te3 films exhibit improved crystallinity with a c-axis preferred orientation. In addition, structural features related to Te and Bi2Te3 composition change with Te fraction diminishing on annealing at 300 °C. From Raman spectral studies, the presence of distinct Te-rich regions, predominantly within the interlayers of Bi2Te3, are discerned. Te becomes structurally integrated within the quintuples of Bi2Te3 lattice as intergrown layers. Disordered planar structures, mostly concentrated on crystallite surfaces result from Te accumulations as evidenced in high-resolution transmission electron microscopy lattice images and energy dispersive X-ray spectroscopy mapping. These are consistent with the observations from XRD and Raman studies further confirming Te-rich Bi2Te3 characteristics. Electrical properties of Te-rich Bi2Te3 thin films exhibit n-type semiconductor behaviour. Seebeck coefficient for as-deposited film is ~ 32 μV/K, which increases to ~ 97 μV/K on 200 °C annealing. Resistivity increases from 1.39 × 10−4 Ωcm to 18.76 × 10−4 Ωcm and power factor changes from 7.4×10−4W/K2m to 27.17×10−4W/K2m going through a maximum at 200 °C upon systematic annealing. Te-rich Bi2Te3 thin films annealed at 200 °C exhibit high power factor (∼29×10−4W/K2m) for a wide range of temperature gradients ( ΔT from 30 °C to 165 °C).

Electro-work hardening of metals induced by the athermal electromigration effect

Direct current stressing treatment has been proposed as an effective potential method to modify the microstructures and optimize the mechanical properties of metals. Two contributions that could give rise to variations in the microstructure and mechanical properties of metals are involved in the direct current stressing treatment: thermal effects from Joule heat generation and athermal effects from electron-lattice interaction. The present study, for the first time, provides direct evidence of the work hardening behavior of pure Sn metals induced by the athermal electromigration effect, which is referred to the “electro-work hardening.” The micro-hardness of the Sn strip increased for all of the current densities (4–7 × 103 A/cm2) and current stressing times (1 h and 6 h) that were investigated. The maximum micro-hardness increment achieved could be as high as 27.3% at 5 × 103 A/cm2 for 1 h as compared with the as-annealed Sn strip benchmark. The thermal benchmark experiment further evidences that the thermal Joule heating effect did not contribute to any variations in the micro-hardness, suggesting the predominant athermal effect of electromigration. The high-resolution transmission electron microscope lattice images further revealed a high volume of dislocations produced in the Sn matrix, which was responsible for the electro-work hardening behavior. The electro-work hardening mechanism incorporated in a direct current stressing treatment can be applied in metals without the need for macroscopic mechanical deformation pre-treatment, which is regarded as a non-deformation material treatment. This innovative method for inducing work hardening is considered to have great potential for applications in which products have already been shaped.

Perpendicular magnetic anisotropy in La1−xSrxCoO2.5+δ/La2/3Sr1/3MnO3/La1−xSrxCoO2.5+δ trilayers (x=0.05–0.5)

Perpendicular magnetic anisotropy (PMA) of magnetic materials has received much attention because of its potential application to spintronics devices. In general, the tensely strained $(001)\text{\ensuremath{-}}\mathrm{L}{\mathrm{a}}_{2/3}\mathrm{S}{\mathrm{r}}_{1/3}\mathrm{Mn}{\mathrm{O}}_{3}$ (LSMO) layer is easy plane. Here we demonstrate that the tensile LSMO layer will exhibit an out-of-plane magnetic anisotropy if it is sandwiched between two $\mathrm{L}{\mathrm{a}}_{1\ensuremath{-}x}\mathrm{S}{\mathrm{r}}_{x}\mathrm{Co}{\mathrm{O}}_{2.5+\ensuremath{\delta}}$ (LSCO) layers. The most remarkable observation is that the PMA enhances with the increase of the Sr content in LSCO. It is $\ensuremath{\sim}2.7\ifmmode\times\else\texttimes\fi{}{10}^{6}\phantom{\rule{0.16em}{0ex}}\mathrm{erg}/\mathrm{c}{\mathrm{m}}^{3}$ for $x=0.05$ and $\ensuremath{\sim}4.3\ifmmode\times\else\texttimes\fi{}{10}^{6}\phantom{\rule{0.16em}{0ex}}\mathrm{erg}/\mathrm{c}{\mathrm{m}}^{3}$ for $x=0.5$. This value is two orders of magnitude greater than that obtained by compressively straining the LSMO film $(\ensuremath{\sim}{10}^{4}\phantom{\rule{0.16em}{0ex}}\mathrm{erg}/\mathrm{c}{\mathrm{m}}^{3})$. Analysis of high resolution lattice image shows the formation of perovskite/brownmillerite-type interfaces in the multilayers: Brownmillerite-like lattice structure forms in the interfacial layers of LSCO, resulting in a coherent tilting of adjacent $\mathrm{Mn}{\mathrm{O}}_{6}$ octahedra. This in turn leads to, as evidenced by the analysis of x-ray linear dichroism, selective orbital occupation thus spin reorientation. There is evidence that the brownmillerite-structured LSCO is more easily formed when $x$ is high, which explains the growth of anisotropy constant with the increase of Sr content.

Unravelling the polarity of InN quantum dots using a modified approach of negative-spherical-aberration imaging.

InN quantum dots (QDs) are considered to be promising nanostructures for different device applications. For any hexagonal AB-stacking semiconductor system, polarity is an important feature which affects the electronic properties. Therefore, the determination of this characteristic on any wurtzite (semi)polar III-N compound or alloy is essential for defining its applicability. In this paper, the polarity of InN QDs grown on silicon by indium droplet epitaxy plus nitridation and annealing was determined by a modified approach combining exit wave reconstruction with negative-spherical-aberration high-resolution lattice imaging using TEM. Comparing the micrographs of two QDs from the same TEM specimen with the simulated images of InN slab structures generated under the same conditions as of the experiments, it was confirmed that the QDs of the present study are N polar. Given that the settlement of material's polarity has always been a tedious, indirect and controversial issue, the major value of our proposal is to provide a straightforward procedure to determine the polar direction from atomic-resolution focal series images.

Collagen functionalized graphene sheets decorated with in situ synthesized nano hydroxyapatite electrospun into fibers

We report the in situ synthesis of hydroxyapatite nanoparticles on 1–3 layers of colloidal collagen-graphene composites. Varying calcium and phosphate: graphene ratio two different composites were synthesized. Crystallite size, particle size and degree of crystallinity of hydroxyapatite nanoparticles changes with a change in graphene concentration. Transmission electron microscopy shows that these graphene composites change shape from spherical to elongated needle-like structures because of the varying nitrogen content in collagen-graphene. Fourier-transform Infrared Spectroscopy peaks suggests an interaction between calcium and the colloidal composites. X-ray Photo Electron spectroscopy data shows the interaction between graphene, collagen and hydroxyapatite through pyridinic N-oxide moiety. High-resolution lattice images confirm the co-existence of both graphene and hydroxyapatite. Anti-bacterial tests of the colloidal composites with two different bacteria S. Marcences and E. Coli show improved anti- bacterial property with increased graphene concentration. The colloidal composites were further electrospun into fibers, and their electrochemical stability in simulated body fluids estimated. The electrochemical test data show that the fiber made of composites would be extremely useful for biomedical applications such as internal bandages and burns.

Structure of crystallized particles in sputter-deposited amorphous germanium films

Pristine thin films of amorphous Ge prepared by sputtering are unstable and form coarse crystalline particles of 100 nm in size upon crystallization by electron irradiation. These crystalline particles exhibit unusual diffraction patterns that cannot be understood from the diamond cubic structure. The structure has previously been assumed to be a metastable hexagonal form. In the present work, the structure of the coarse crystalline particles has been analysed in detail by transmission electron microscopy, considering the possibility that those diffraction patterns might occur with the diamond cubic structure if the particle consists of thin twin layers. By high-resolution lattice imaging the particles have been shown to be of the diamond cubic structure containing a high density of twins and stacking faults parallel to {111}. With such defects, diffraction patterns can be complex because of the following effects: superposition of two or more diffraction patterns of the same structure but of different orientations, double diffraction through twin crystals, and streaks parallel to the thin crystal which give rise to extra diffraction spots. It is found that diffraction patterns taken from various orientations can be explained in terms of these effects.

The mechanism of an increase in electrical resistance in Al thin film induced by current stressing

A 10mm×2mm×500nm Al thin film was stressed with electric current at 1.5–3.0×105Acm−2 for 1h under an ambient atmosphere. Ex situ variations in the sheet resistance induced by current stressing were measured with a four-point probe. The critical current density for the resistance change was observed between 1.5×105 and 2.0×105Acm−2. The electrical resistance reached a maximum increment of 5.47% at 2.5×105Acm−2. The lattice structure of the Al thin film was investigated with a high resolution transmission electron microscope to determine the fundamental effects of electric current stressing on the electrical property of the metal film. The high resolution lattice images incorporating a selected area fast Fourier transform indicated a large degree of lattice distortion and high dislocation density, up to 8.60×1016m−2, in the metal film after current stressing at 3.0×105Acm−2. The dislocations are believed to have been generated by the impingement of electron wind. In situ synchrotron X-ray diffraction further evidenced a high degree of lattice strain, as great as 1.1% at 3.0×105Acm−2, as estimated from the low angle shifts in the diffraction peaks. The generation of dislocations and the lattice strain induced by current stressing were orientation-dependent, as determined by the d-spacing of the lattice orientation. The formation of a high dislocation density and the subsequent buildup of lattice strain caused to an increase in electrical resistance of the Al thin film.

Self-formed grain boundary healing layer for highly efficient CH3NH3PbI3 perovskite solar cells

Perovskite solar cells have attracted significant research efforts due to their remarkable performance, with certified power conversion efficiency now reaching 22%. Solution-processed perovskite thin films are polycrystalline, and grain boundaries are thought to be responsible for causing recombination and trapping of charge carriers. Here we report an effective and reproducible way of treating grain boundaries in CH3NH3PbI3 films deposited by means of a Lewis acid–base adduct approach. We show by high-resolution transmission electron microscopy lattice images that adding 6 mol% excess CH3NH3I to the precursor solution resulted in a CH3NH3I layer forming at the grain boundaries. This layer is responsible for suppressing non-radiative recombination and improving hole and electron extraction at the grain boundaries by forming highly ionic-conducting pathways. We report an average power conversion efficiency of 20.1% over 50 cells (best cell at 20.4%) together with significantly reduced current–voltage hysteresis achieved by this grain boundary healing process. The grain boundaries in thin-film perovskite solar cells are responsible for non-radiative carrier recombination, which is deleterious for the optoelectronic performance. Son et al. show how to passivate the grain boundaries by using excess CH3NH3I in the precursor solution, achieving efficiencies of 20.4%.

Asbestiform Talc From a Talc Mine Near Talcville, New York, U.S.A.: Composition, Morphology, and Genetic Relationships With Amphiboles

We analyzed the chemical composition and observed morphological relationships of mineral phases in a thin section and grain mount of a talc-bearing amphibole schist collected at a former talc mine near Talcville, New York at scales ranging from hand sample to crystal lattice. The main mineral phases are tremolite, anthophyllite, and talc. Tremolite exists as unaltered crystals throughout the sample. Anthophyllite has an acicular habit and a series of fractures running perpendicular to crystal elongation ( i.e. , its c crystallographic axis). Talc occurs as a fine-grained mass in anthophyllite fractures, between acicular anthophyllite partings, and as pseudomorphs after anthophyllite, with some occurring with an asbestiform habit. Thus, the talc alterations occur both parallel and perpendicular to the elongate anthophyllite, with the latter producing very high-aspect ratio ( i.e. , greater than 20 times longer than wide) non-asbestiform anthophyllite particles. Based on wavelength-dispersive spectroscopy (WDS) analysis the three phases have near endmember formulas: tremolite [K0.03Na0.17Ca1.74Mn0.01Fe0.01Mg5.21Al0.03Si7.94O22(OH1.65F0.35)], anthophyllite [Na0.04Ca0.04 Mn0.04Fe0.02Mg6.96Al0.02Si7.95O22(OH1.82F0.18)], fracture-filling talc [Mg3.10Mn0.02Fe0.01Al0.01Si3.93O10(OH1.92F0.08)], and talc pseudomorph [Mg3.03Mn0.02Fe0.01Al0.01Si3.96O10(OH1.92F0.08)]. Microscopic examination in light and electron microscopes showed intergrowths of talc and anthophyllite, but it was only with the aid of high-resolution lattice imaging perpendicular to the c crystallographic axis where the formation mechanism of asbestiform talc could be ascertained.

Crystal structure and defects visualization of Cu2ZnSnS4 nanoparticles employing transmission electron microscopy and electron diffraction

A detailed analysis of the structure of Cu2ZnSnS4 (CZTS) nanocrystals synthesized by hot-injection in the presence of oleylamine is provided employing high resolution TEM, selected area electron diffraction (SAED) and convergent beam electron diffraction (CBED). The nanostructures were investigated as-grown and after vacuum thermal treatment at 550°C. As-grown materials consisted of polycrystalline particles with an average size of 7±3nm, which grow an average size of 53±13nm after the vacuum annealing step. This thermal treatment allows investigating the initial stages of high quality film growth required in photovoltaic devices. Sets of SAED and CBED patterns, where individual crystals after annealing were viewed down different prominent zone axes, enabled us to reveal the presence of weak reflections due to cation ordering, and confirm a tetragonal unit cell consistent with either the kesterite or stannite structure. We demonstrate how these approaches enable to distinguish CZTS from secondary phases such as ZnS. Structure defects of partially annealed CZTS crystals were also investigated using bright and dark field images taken in 2-beam diffraction conditions as well as by high resolution lattice imaging. The material exhibited dislocations, along with lamellar twins and stacking faults characterized by local hexagonal structure on {112} planes. High resolution TEM images showed preferential growth on {112} planes during vacuum annealing, which is consistent with X-ray diffraction patterns. These studies provide key information on nanoscale crystal defects which may have important consequence on the performance of CZTS photovoltaic devices.

Zn nanodot patterning in borosilicate glasses by electron irradiation

Abstract

Formation of endogenous MgO and MgAl2O4particles and their possibility of acting as substrate for heterogeneous nucleation of aluminum grains

Aluminum containing 4 wt.% magnesium was oxidized at a temperature for different oxidation times and analyzed by high-resolution electron microscopy. A thin oxidized layer of about 5 µm, which is composed of MgO, forms at short oxidation time and gradually increases. High-resolution microstructures reveal that the oxidized layers are porous regardless of oxidation time. After extended oxidation time, discrete MgAl2O4 particles formed as a result of the reaction of initially formed MgO, liquid aluminum, and oxygen introduced from air through the porous MgO. Furthermore, it is clear by high-resolution lattice images that MgAl2O4 particles are covered with thin Al2O3, whereas MgO is bonded intimately to aluminum. Therefore, MgAl2O4 particles that form naturally during oxidation are difficult to act as a direct substrate for nucleation of aluminum grains because of the coverage of Al2O3. In contrast, MgO shows the possibility of acting as a substrate for the aluminum nucleation. The formation mechanism of MgO and MgAl2O4 and their possibility of acting as substrates for nucleation of aluminum grains suggest that atomic level bonding and mismatches of nucleant/nucleus metal should be considered for correct evaluation of the possibility of heterogeneous nucleation of metallic matrix on a potent nucleant. © 2015 The Authors. Surface and Interface Analysis Published by John Wiley & Sons, Ltd.

An investigation into the relationship between processing, structure and properties for high-modulus PBO fibres: part 3: analysis of fibre microstructure using transmission electron microscopy

A detailed morphological study of the microstructure of poly(p-phenylene benzobisoxazole) (PBO) fibres (HM and HM+) and a polypyridobisimidazole (PIPD) (HT) fibre has been undertaken using transmission electron microscopy. Both PBO and PIPD fibres are composed of rigid-rod polymers having p-phenylene rings in the molecular backbone and show high modulus (280–360 GPa) and high strength (4–6 GPa). It is found that the PBO HM+ fibre has the highest degree of molecular orientation of the three fibres and the longest crystal length along the fibre axis, while the PIPD fibre shows a lower degree of orientation and a shorter crystal length than the PBO fibres. To understand the effect of crystalline size and fine structure of the fibres upon mechanical properties, dark-field and high-resolution lattice images were obtained and analysed in detail.

Reversible H+/Li+ Ion Exchange and Structure Stability of Garnet-Type Nb-Doped Li7La3Zr2O12 in Water

The lithium garnet-type oxide is considered as a promising candidate of solid electrolytes to be applied in all solid lithium batteries for its high ion conductivity, chemical stability vs. metal lithium and wide electrochemical potential window. In order to further improve the ion conductivity, dopants like Nb and Ta have been adopted and much progress has been achieved. The total lithium-ion conductivity of Nb-doped Li7La3Zr2O12 was as high as 0.8mS/cm. In this work, its reversible H+/Li+ion exchange reaction and the structural stability in aqueous solutions are systematically investigated.Cubic garnet phase Li6.25La3Zr1.75Nb0.25O12 (LLNZO) was prepared by a conventional solid-state reaction process at 950oC. The H+/Li+ion exchange reaction of the LLNZO powder was performed in distilled water and the pH value was recorded simultaneously. The process was carried out continuously for 4 times. The lithium content and crystal structure of the garnet powder were measured by ICP and XRD.The pH value of the distilled water increased quickly after the cubic garnet powder was added in it and finally reached a constant value. The garnet powder was then filtered and the dispersion was repeated with fresh water for deeper ion exchange. The products with different H+/Li+ ion exchange rate were obtained via this way for further dynamics analysis of ion exchange process. The remaining lithium content of the garnet powder was gradually declined after the ion exchange happened. FTIR spectra was tested to identify the ion exchange. It was found that the cubic garnet phase was maintained even the ion exchange rate of lithium ion was up to 74.8% and was confirmed by the high resolution lattice imaging and XRD analysis. The stoichiometry of garnet-type Li6.25-xHxLa3Zr1.75Nb0.25O12, as well as the crystal lattice parameters, was evolved with the H+/Li+ ion exchange reaction in aqueous solutions. It is noticeable that the reverse ion exchange of H+ by Li+was achieved by controlling the reaction temperature, pressure, the lithium concentration and the pH of the solutions. The successful re-exchange indicated the high stability of the Nb doped cubic garnet phase.Fig.1 XRD results of Li6.25La3Zr1.75Nb0.25O12powder and products from distilled water treatmentFig.2 The evolution of the constant pH value and remaining lithium content versus water treating stagesFig.3 TEM and electron diffraction images of Li6.25La3Zr1.75Nb0.25O12with 74.8% lithium ion exchange Reference (1) Truong, L. and V. Thangadurai (2011). Chemistry of Materials 23(17): 3970-3977. (2) Shimonishi, Y., A. Toda, et al. (2011). Solid State Ionics 183(1): 48-53 (3) Ishiguro, K., Y. Nakata, et al. (2013). Journal of the Electrochemical Society 160(10): A1690-A1693.

Formation of Fine Clusters in High-Temperature Oxidation of Molten Aluminum

High-temperature oxidation of molten aluminum was investigated by high-resolution electron microscopes in order to determine the possibility of heterogeneous nucleation of aluminum grains on oxide for the grain refinement and structural uniformity of intensively melt-sheared aluminum alloys. High-resolution observations detect initial amorphous phase and gamma-alumina phase and show fine clusters with size of about 150 to 200 nm composed of extremely fine aluminum grains and gamma-alumina or amorphous aluminum oxide. Furthermore, high-resolution lattice images and diffraction patterns show no orientation relationship, although there is a specific orientation between gamma-alumina and aluminum along (111)[110] with high potency of heterogeneous nucleation. The volumetric shrinkage by the transformation of gamma- into alpha-alumina causes the surface oxide films to repeatedly rupture and leads to the creation of channels to the base melt surface for further oxidation of fresh metal. Based on the observations, the mechanism of high-temperature oxidation of molten aluminum and formation of the fine clusters as well as the possibility of the heterogeneous nucleation of aluminum grains are discussed.

Surface modification of carbon fiber by direct growth of zinc oxide nanowalls using a radio-frequency magnetron sputtering technique

Zinc oxide nanowalls have been grown uniformly on a carbon fiber substrate at room temperature using a radio-frequency magnetron sputtering technique. The synthesis process involved two steps; application of catalyst using a solution process and subsequent radio-frequency sputter deposition of zinc oxide. The nanowalls were examined by field emission scanning electron microscopy for their microstructure and morphology while their nanostructure was studied by high resolution transmission electron microscopy. Both the X-ray and the electron diffraction techniques were used for crystallographic analysis of the produced nanowalls. Selected area electron diffraction and high resolution lattice image showed highly crystalline structure of the nanowalls. Photoluminescence analysis was carried out for the determination of their optical characteristics which showed a strong ultra violet peak at 393nm and violet peak centered at 401nm. The latter is a characteristic peak of zinc oxide which demonstrates oxygen rich composition of nanowalls.

Growth of crystalline Al2O3 via thermal atomic layer deposition: Nanomaterial phase stabilization

We report the growth of crystalline Al2O3 thin films deposited by thermal Atomic Layer Deposition (ALD) at 200 °C, which up to now has always resulted in the amorphous phase. The 5 nm thick films were deposited on Ga2O3, ZnO, and Si nanowire substrates 100 nm or less in diameter. The crystalline nature of the Al2O3 thin film coating was confirmed using Transmission Electron Microscopy (TEM), including high-resolution TEM lattice imaging, selected area diffraction, and energy filtered TEM. Al2O3 coatings on nanowires with diameters of 10 nm or less formed a fully crystalline phase, while those with diameters in the 20–25 nm range resulted in a partially crystalline coating, and those with diameters in excess of 50 nm were fully amorphous. We suggest that the amorphous Al2O3 phase becomes metastable with respect to a crystalline alumina polymorph, due to the nanometer size scale of the film/substrate combination. Since ALD Al2O3 films are widely used as protective barriers, dielectric layers, as well as potential coatings in energy materials, these findings may have important implications.

Unveiling the electronic origin of anion order in CrO2−xFx

Electron-diffraction and high-resolution lattice images reveal superstructure stripes with wave vectors of (1/3, 0, 1/3) and (-1/3, 0, 1/3), which are associated with the ordered arrangement of F(-). Charge density distribution suggests that these stripes manifest themselves electronically as F(-)-Cr(3+)-F(-) zigzag chains, driven by the anisotropic charge interaction of F(-) anions.