High-resolution Transmission Electron Microscopy Observations Research Articles

Vibrational and optical spectroscopies integrated with environmental transmission electron microscopy.

Here, we present a measurement platform for collecting multiple types of spectroscopy data during high-resolution environmental transmission electron microscopy observations of dynamic processes. Such coupled measurements are made possible by a broadband, high-efficiency, free-space optical system. The critical element of the system is a parabolic mirror, inserted using an independent hollow rod and placed below the sample holder which can focus a light on the sample and/or collect the optical response. We demonstrate the versatility of this optical setup by using it to combine in situ atomic-scale electron microscopy observations with Raman spectroscopy. The Raman data is also used to measure the local temperature of the observed sample area. Other applications include, but are not limited to: cathodo- and photoluminescence spectroscopy, and use of the laser as a local, high-rate heating source.

In Situ HRTEM Observation of Electron-Irradiation-Induced Amorphization and Dissolution of the E (Al18Cr2Mg3) Phase in 7475 Al Alloy

Electron irradiation effects on phase stability of the E (Al18Cr2Mg3) phase have been investigated by high-angle annular dark-field scanning transmission electron microscopy and high-resolution transmission electron microscopy (HRTEM). The in situ HRTEM observations show that the Al18Cr2Mg3 particles with different thickness undergo amorphization and dissolution under 300 keV electron irradiation at 25 °C. The results indicate that the intermetallic compound Al18Cr2Mg3 is unstable under electron irradiation, and structural changes mainly depend on the thickness of particles. Amorphization in the thick particles is caused by a combination of chemical disordering and an increase in point defect concentration. Dissolution after amorphization in the thin particles is attributed to the diffusion of point defect towards the Al matrix.

Holes drilling in gold and silver decahedral nanoparticles by the convergent beam electron diffraction electron beam

The 200 kV focused electron beam in the convergent beam electron diffraction patterns mode in a transmission electron microscope (TEM) with field emission gun is able to drill holes in gold and silver decahedral nanoparticles. However, although they are done under the same circumstances, the holes are shapeless in the silver and faceted in gold nanoparticles. In addition to this, the holes are closed during their high-resolution TEM observation in both materials. To comment their differences, displacement energy considerations are taken into account as function of the sputtering energy in order to modify the displacement cross-section of the processes.

Impact of the structure of Mo(S,Se)2 interfacial region in electrodeposited CuIn(S,Se)2 solar cells

In this study, we investigate the formation of Mo(S,Se)2 layers in the interface region between the absorber and the back contact in electrodeposited CuIn(S,Se)2 (CISSe) solar cells, and its influence on the resulting devices. Mo(S,Se)2 layers are formed spontaneously in the Mo/CI(S,Se) interface during the annealing of the absorber, but have a serious impact on the solar cell performance, being responsible of the conductivity at this interface. In this paper, we demonstrate that the crystal orientation of the Mo(S,Se)2 layer is the relevant parameter that governs the electrical properties of the interface by the generation of an energy barrier. For this, we have analysed two different groups of cells, with high and low Voc, to determine the origin of the differences. C–V analysis suggested the presence of an energy barrier at the back contact that was related to the existence of a Mo(S,Se)2 layer with c-axis oriented perpendicular to the substrate. Simulations taking into account this feature reproduced the behaviour of the low performing cells. Finally, high-resolution transmission electron microscopy observations were performed to clarify the orientation of the Mo(S,Se)2 layers at the CISSe/Mo(S,Se)2 interface, which is determining for the thickness of the Mo(S,Se)2 layer.

Blue-emitting photoluminescence of rod-like and needle-like ZnO nanostructures formed by hot-water treatment of sol–gel derived coatings

The morphological evolution of the zinc oxide (ZnO) nanostructures generated by hot-water treatment (HWT) of sol–gel derived coatings as a function of temperature from 30 to 90°C was investigated. With increasing HWT temperature, the ZnO crystals evolved from nanoparticles to rod-like and needle-like nanostructures. High-resolution transmission electron microscope observations of rod-like and needle-like nanostructures generated at 60 and 90°C indicated single crystal ZnO wurtzite structure was obtained. All the hot-water treated samples exhibited blue emission at approximately 440nm in room temperature. The intensity of blue emission increased with higher HWT temperatures. The unique photoluminescence emission characteristic remained even after heat-treatment at 400°C for 1h. As the emission peak obtained in our work is approximately 440nm (2.82eV), the emission peak is corresponding to the electron transition from the interstitial Zn to the top of valence band. This facile formation of blue-emitting ZnO nanostructures at low-temperature can be utilized on substrate with low thermal stability for optoelectronic applications such as light emitting devices and biological fluorescence labeling.

Interplay between Point Defects and Thermal Conductivity of Chemically Synthesized Bi2Te3 Nanocrystals Studied by Positron Annihilation

In this work, Bi2Te3 nanocrystals were synthesized via a hydrothermal method. They were treated by spark plasma sintering (SPS) at 350 °C and further annealed between 350 and 500 °C. The crystal structures and morphologies of these annealed Bi2Te3 samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HRTEM) measurements. SEM observation indicates an obvious increase of particle size with increasing annealing temperature, but the grain size estimated from HRTEM observation and the broadening of X-ray diffraction lines show little change in the annealing temperature range between 350 and 500 °C. Positron annihilation lifetime measurements reveal vacancy defects in all of the samples, which exist most probably in the grain boundary region. The average positron lifetime shows a monotonic decrease from 301 to 273 ps with increasing annealing temperatures up to 500 °C. Detailed analysis of the positron lifetime indicates ...

High resolution transmission electron microscopic in-situ observations of plastic deformation of compressed nanocrystalline gold

Nanocrystalline (nc) metals possess extremely high strength, while their capability to deform plastically has been debated for decades. Low ductility has hitherto been considered an intrinsic behavior for most nc metals, due to the lack of five independent slip systems actively operating during deformation in each nanograin. Here we report in situ high resolution transmission electron microscopic (HRTEM) observations of deformation process of nc gold under compression, showing the excellent ductility of individual and aggregate nanograins. Compression causes permanent change in the profile of individual nanograins, which is mediated by dislocation slip and grain rotation. The high rate of grain boundary sliding and large extent of widely exited grain rotation may meet the boundary compatibility requirements during plastic deformation. The in situ HRTEM observations suggest that nc gold is not intrinsically brittle under compressive loading.

In-situ synthesis of MgAl2O4 nanowhiskers reinforced 6061 aluminum alloy composites by reaction hot pressing

In-situ generated MgAl2O4 nanowhiskers, with diameters ranging from 30 to 200 nm, reinforced 6061 aluminum alloy composites have been successfully synthesized by reaction hot pressing under a relatively low temperature (600 °C). The effects of temperature and pressure on the morphology of MgAl2O4 whiskers, as well as microstructure, densification and mechanical properties of the composites were investigated in detail. The results indicate that the MgAl2O4 nanowhiskers with aspect ratio about 10–50 are uniformly distributed and firmly bonded with the matrix. Most of the nanowhiskers acting as bridges penetrate into the Al particles to form a framework bearing and transferring extrinsic loads. The high-resolution transmission electron microscope observation reveals that the MgAl2O4/Al interface is clean, smooth and free from interfacial product, and the whiskers have well-bonded interfaces with matrix. Additionally, the composites, prepared by sintering at 600 °C under the pressure of 50 MPa, exhibit the optimal performance.

Dissecting the mechanism of martensitic transformation via atomic-scale observations.

Martensitic transformation plays a pivotal role in the microstructural evolution and plasticity of many engineering materials. However, so far the underlying atomic processes that accomplish the displacive transformation have been obscured by the difficulty in directly observing key microstructural signatures on atomic scale. To resolve this long-standing problem, here we examine an AISI 304 austenitic stainless steel that has a strain/microstructure-gradient induced by surface mechanical attrition, which allowed us to capture in one sample all the key interphase regions generated during the γ(fcc) → ε(hcp) → α′(bcc) transition, a prototypical case of deformation induced martensitic transformation (DIMT). High-resolution transmission electron microscopy (HRTEM) observations confirm the crucial role of partial dislocations, and reveal tell-tale features including the lattice rotation of the α′ martensite inclusion, the transition lattices at the ε/α′ interfaces that cater the shears, and the excess reverse shear-shuffling induced γ necks in the ε martensite plates. These direct observations verify for the first time the 50-year-old Bogers-Burgers-Olson-Cohen (BBOC) model, and enrich our understanding of DIMT mechanisms. Our findings have implications for improved microstructural control in metals and alloys.

Facile synthesis of Zn-doped SnO2 dendrite-built hierarchical cube-like architectures and their application in lithium storage

Abstract Zn-doped SnO 2 dendrite-built hierarchical cube-like architectures were successfully synthesized by a facile hydrothermal approach without the use of any surfactants or templates. The as-prepared samples were characterized by the X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), and Raman spectroscopy. The observation of FESEM and HRTEM showed that Zn-doped SnO 2 hierarchical cube-like architectures were composed of numerous oriented dendrites. Each dendrite is assembled by a pronounced trunk with highly ordered branches distributing on the both sides. The as-prepared Zn-doped SnO 2 dendrite-built hierarchical cube-like architectures were used as anode materials for Li-ion battery, and a stable capacity of 488.3 mA h g −1 was achieved after 50 cycles. The results of electrochemical measurements indicated that the as-prepared Zn-doped SnO 2 dendrite-built hierarchical cube-like architectures have potential application in Li-ion battery.

Effective control of nanodefects in multiwalled carbon nanotubes by acid treatment

Abstract The defect-type evolution and gradual increase in nanodefects in the outer walls of multiwalled carbon nanotubes (MWCNTs) in a chemically oxidizing environment were thoroughly investigated using a mixture of sulfuric acid (H2SO4) and nitric acid (HNO3). A fairly low temperature of 323 K was employed for the acid treatment, and this limited the reaction rate to provide a mild acidic environment for gradual chemical oxidation compared to commonly used treatment conditions. High-resolution transmission electron microscopy (HRTEM) observations clearly demonstrated the formation of groove-type defects in the outer walls of MWCNTs in the early period around 0.5–3 h, followed by a morphological change into circumference-type defects and further into unzipped graphene nanoribbons. A unique parabolic variation in the intensity ratio of D and G bands (ID/IG) was observed. This observation supports the gradual oxidation of graphitic walls with increasing acid treatment time and corresponds well with the formation and evolution of nanodefects. Herein, the appropriate acid treatment time that would result in an effective number of nanodefects via suitable carboxyl functionalization, providing preferential nanocarbide sites for interfacial improvement as well as uniform dispersibility of MWCNTs, has been discussed.

Structural and Electrochemical Characterization of Ethylenediaminated Single-Walled Carbon Nanotubes Prepared from Fluorinated SWCNTs

We prepared ethylenediaminated single-walled carbon nanotubes (SWCNTs) from fluorinated SWCNTs by substituting fluorine groups with ethylenediamine groups. The ethylenediaminated SWCNTs were characterized by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), Raman scattering spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Brunauer–Emmett–Teller surface area measurement by nitrogen adsorption, contact angle measurement, zeta potential analysis, and thermogravimetry. In addition, the properties of 30 wt % sulfuric acid aqueous electrolyte-based electric double-layer supercapacitors (EDLSCs) with free-standing ethylenediaminated SWCNT electrodes were investigated. The degree of ethylenediamine functionalization was 0.603 mmol/g and 1.46 μmol/m2, and the specific surface area was ∼413.3 m2/g. From HRTEM observation, isolated nanotubes disentangled from the bundled SWCNTs were present in many observed areas, and the structures retained a nanotube sk...

Nucleation and growth of boron nanowires on diamond particles

Abstract Crystalline boron nanowires (BNWs) are grown on the entire surface of diamond powders by a solid–solid reaction approach. The as-grown BNWs have diameters in the range of 20–200 nm, lengths of several micrometers. High-resolution transmission electron microscopy (HRTEM) observation indicated the boron nanowires are composed of two structures, the interior of the nanowire is well crystalline in hexagonal structure and the surface of the nanowire is covered by a 5–10 nm thick tetragonal structure layer. Systematic analysis reveals that the conventional VLS (vapor–liquid–solid) growth model is not applicable to explain this kind of BNWs’ growth mechanism. Hereby, an extended VLS model is proposed which can perfectly interpret the BNW's growth process on diamond surface and match experiment results very well.

Site-occupation behavior and solid-solution hardening effect of rhenium in Mo5SiB2

The site-occupation behavior of Re in Mo5SiB2 (T2) was studied both theoretically and experimentally, and the effect of Re on the solid-solution hardening of T2 was investigated by taking into account the off-stoichiometry of the T2 phase. Mo–Si–B quaternary alloys containing 1.4 at.% Re were produced using a conventional Ar arc-melting technique, and the cast samples were homogenized at 1800 °C for 24 h in an Ar atmosphere. High-resolution high-angle annular dark-field scanning transmission electron microscopy observations strongly suggest that Re preferentially occupies the Mo sites in the Mo–B layers of the T2 unit cell, which was confirmed by the site-occupation behavior predicted by first-principles calculations. Nanoindentation measurements indicate that the hardness of the T2 phase is affected by both the off-stoichiometry and Re addition.

Growth and local structure of BiFeO3 thin films with giant tetragonality on SrRuO3-buffered SrTiO3(001) substrate by ion beam sputtering

Rhombohedral (R-) and tetragonal-like (T-) BiFeO3 (BFO) mixed-phase thin films and single R-phase BFO thin films have been grown on SrRuO3-buffered SrTiO3 (STO) (001) substrate by ion beam sputtering. From X-ray diffraction study, it was found that T-BFO and R-BFO mixed-phase thin films can be grown at a low oxygen partial pressure of 1 mPa, and the lattice parameters of the T-BFO and R-BFO were a = 0.381 nm, c = 0.461 nm (c/a = 1.22), and a = 0.394 nm and c = 0.400 nm (c/a = 1.02), respectively. High-resolution high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) observation and energy dispersive X-ray analysis (EDXA) mappings have revealed a clear T-BFO lattice and a–c domain in the middle of the thin films. However, Bi-rich and Fe-rich secondary phases were also found with the T-BFO phase. Therefore, it can be concluded that secondary phases such as Bi2O3 or Bi-poor phase are needed for T-BFO formation on STO (001) substrate, and the a–c domain formation does not occur by stress relaxation but matching of the growth directions of different domains.

Formation of two-dimensional ZnO nanosheets by rapid thermal oxidation in oxygenated environment.

Crystalline 2-D (dimensional) ZnO nanosheets were formed by rapid thermal oxidation of etched Zn foil in oxygen at 300 degrees C and 400 degrees C. Short oxidation time was varied from 10, 20 and 30 min. The morphologies and optical properties of the ZnO nanosheets evolved with the oxidation temperature and time. At 300 degrees C, ZnO nanosheets with thickness ranging from 32 nm to 80 nm were obtained while at 400 degrees C, the thickness of the nanosheets increased from 88 nm to approximately 200 nm after 10 and 30 min of oxidation, respectively. The surface roughness of the ZnO nanosheets and grain size increased with oxidation time and temperature. Photoluminescence of the oxidized samples shows ultraviolet (UV) and visible emissions indicating good crystallinity of ZnO which was further confirmed by high-resolution transmission electron microscope observation of ZnO wurtzite interplanar spacing. Photocatalytic activity of ZnO was also investigated by using degradation of methyl orange (MO) and all the samples exhibit photocatalytic activity. The sample oxidized at 400 degrees C for 10 min show better MO degradation after 2 h of exposure due to higher surface area and better crystallinity of the ZnO nanosheets obtained.

Phase determination of zinc selenide nanocrystals depending on the ligand species of precursor complexes

The two polytypes of ZnSe nanocrystals (NCs), the wurtzite (WZ) and zincblende (ZB) phases, were synthesized in hot organic solutions using zinc acetate as the zinc monomer with oleic acid and oleylamine as ligands. The growth rate, number and size of NCs during the growth stage were evaluated based on the X-ray diffraction profiles, high-resolution transmission electron microscope observations and optical absorption spectra. Experimental results suggested that in these systems, the phase that appeared was not determined during the growth stage but during the nucleation stage. High supersaturation during the nucleation stage resulted in the thermodynamically stable ZB phase, while low supersaturation resulted in the metastable WZ phase. The reason why supersaturation during nucleation determined the phase was discussed on the basis of the size of the critical nucleus influenced by the total free energy change in the system during nucleation.

Low-frequency magnetic susceptibility and photoelectric properties of glass/Fe40Pd40B20/ZnO and glass/ZnO/Fe40Pd40B20

The following conditions are deposited: (a) glass/Fe40Pd40B20(Xnm)/ZnO(50nm) and (b) glass/ZnO(50nm)/Fe40Pd40B20(Ynm), where each of X and Y is 2.5nm, 5nm, 7.5nm or 10nm. The sputtering sequence and the thickness of the FePdB film were varied to investigate their effects on the low-frequency alternative-current magnetic susceptibility (χac), maximum phase angle (θmax), maximum χac and corresponding optimal resonance frequency (fres), electrical resistivity (ρ), and transmission and reflection percentages. Experimental results reveal that Fe40Pd40B20(Xnm)/ZnO(50nm) is better than ZnO(50nm)/Fe40Pd40B20(Ynm) because the nanocrystallization Fe40Pd40B20 at the bottom of the material can improve its magneto nanocrystalline anisotropy and increase the crystallization of ZnO, improving its magnetic and electrical properties. X-ray diffraction patterns (XRD) demonstrate that the ZnO (002) peak of Fe40Pd40B20(Xnm)/ZnO(50nm) is stronger than that of ZnO(50nm)/Fe40Pd40B20(Ynm). In particular, a comparison of high-resolution cross-sectional transmission electron microscopic (HR X-TEM) observations of Fe40Pd40B20(10nm)/ZnO(50nm) and ZnO(50nm)/Fe40Pd40B20(10nm) indicates that the Fe40Pd40B20 texture induces magneto nanocrystalline anisotropy into the nanocrystalline FePdB layer of Fe40Pd40B20(10nm)/ZnO(50nm), yielding the highest χac of around 0.79 with an fres of 10Hz and an θmax of 179°. Furthermore, ρ is reduced as the thickness of FePdB increases, because grain boundaries and the surface of thin films scatter electrons, causing thinner films to have greater resistance. The ρ of Fe40Pd40B20(Xnm)/ZnO(50nm) is lower than that of ZnO(50nm)/Fe40Pd40B20(Ynm) because stronger ZnO crystallization and nanocrystalline FePdB improve the scattering of electrons by the surface of the films. Finally, with respect to the optical transmittance and reflectance of Fe40Pd40B20(Xnm)/ZnO(50nm) and ZnO(50nm)/Fe40Pd40B20(Ynm), as the FePdB thickness increases, the transmittance gradually decreases, because transmittance and reflectance are inversely related to film thickness, increasing reflective efficiency. The results reveal that the magnetic and photoelectric properties of glass/Fe40Pd40B20(Xnm)/ZnO(50nm) are better than those of glass/ZnO(50nm)/Fe40Pd40B20(Ynm) owing to the tightly nanocrystalline FePdB crystallization and stronger ZnO crystallization. Glass/Fe40Pd40B20(10nm)/ZnO(50nm) is particularly effective for magnetic and photoelectric applications.

Structural features of epitaxial graphene on SiC {0 0 0 1} surfaces

We investigated the atomic-scale structural properties of graphene epitaxially grown on SiC {0 0 0 1} surfaces by high-resolution transmission electron microscope observations. In this review paper, we summarize our results about the interface structure, the growth mechanisms and the growth techniques. Graphene on the Si-terminated surface has a buffer layer that is strongly bonded to the substrate and has a low carbon atom density. Multilayer graphene on the Si-face exhibited an ABC-stacking selectively. Graphene on the Si-face nucleates at the step-edge, and grows layer-by-layer over the upper terrace. Based on the mechanism, we succeeded in growing high-quality and homogeneous monolayer and bilayer graphene on the Si-terminated surface with low-height and low-density steps using our original technique. Graphene on the C-face has weaker bonds with the substrate, and the resulting multilayer contains the rotational stacking disorder. The origin of the rotational stacking is closely related to the growth mechanism, where graphene layers nucleate on a terrace at a lower temperature and grow in all directions on the surface.

Characterization of grain-boundary phases in Li7La3Zr2O12 solid electrolytes

Two types of Li7La3Zr2O12 (LLZ) pellets were prepared containing Al and Si impurities, and their grain boundaries characterized using scanning electron microscopy (SEM) with energy-dispersed X-ray (EDX) elemental mapping, transmission electron microscopy (TEM), selected-area electron diffraction (SAED), electron energy-loss spectroscopy (EELS), and high-resolution transmission electron microscopy (HRTEM). In the LLZ pellets containing a small amount of both Al and Si, the total conductivity and density were found to be greater than that of LLZ containing Al alone. Using EDX and TEM, the Al and Si were confirmed to accumulate predominantly at grain-boundary regions. EELS and SAED were used to determine the presence of crystallites of LiAl5O8 and LiAlSiO4 in the Al-only and Si and Al containing specimens, respectively. HRTEM observations clarified that in the case of LiAlSiO4, nano-sized particles exist within an amorphous phase matrix, with a microstructure similar to that in a glass-ceramic. The presence of grain-boundary phases is shown to greatly affect the grain boundary resistance, in the case of the LiAlSiO4 glass-ceramic-type phase resulting in a noticeable improvement of the total conductivity.