Electron Diffraction Studies Research Articles

Electron microscopy and diffraction studies of suspension-plasma-sprayed ZrO2 + 8 wt.% Y2O3 coatings

The microstructure of ZrO2+8wt.% Y2O3 coatings has been studied by means of transmission electron microscopy (TEM) including selected-area electron diffraction (SAED) and electron backscatter diffraction (EBSD). The coatings were suspension-plasma-sprayed onto stainless steel substrates. The parameters spray distance and torch scan speed had been varied. Both diffraction methods have confirmed the tetragonal lattice structure of the suspension-plasma-sprayed zirconia. The combination of TEM and EBSD allowed a detailed analysis of the size, shape and orientation of grains. The microstructure of the coatings is mainly lamellar, consisting of columnar grains. Additional microstructural features indicate that powder particles have been subjected to different modifications during spraying. The influence of the variation of spraying parameters on the microstructure is marginal.

Synthesis of gold nanoparticles using ethonolic leaf extract of Bacopa monnieri and UV irradiation

Here we report the green synthesis of gold nanoparticles (AuNPs) using UV irradiation and ethanolic leaf extract of Bacopa monnieri (BLE). The reducing and capping functions provided by BLE can replace synthetic reducing and stabilizing agents required for nanoparticle synthesis. UV-Visible spectra and TEM indicated the successful formation of AuNPs whose size ranged from 3-45 nm with a mean diameter of 11 nm. Selected-area electron diffraction and X-ray diffraction studies revealed the crystalline nature of AuNPs. Fourier transform infra-red and thermo gravimetric analysis showed that the AuNPs were capped with bioactive molecules obtained from BLE and most likely contributes towards their nontoxic nature as revealed by cytotoxicity assays.

An electron energy loss spectroscopy and electron diffraction study of the Pmnb polymorph of Li2MnSiO4

The Mn valency and the crystallinity of Li2MnSiO4 cathodes (Pmnb form) were examined with electron energy-loss spectroscopy (EELS) and selected area electron diffraction (SAED) both before and after electrochemical lithium extraction. A decrease in the crystallinity of the delithiated charged cathode particles compared to the as-prepared material was observed. The decrease in crystallinity varied from particle to particle. EELS analysis showed that the non-uniform decrease in crystallinity was due to a non-uniform extraction of lithium from the particles. The observed decrease in discharge capacity of the Pmnb polymorph of Li2MnSiO4 with cycling was attributed to the progressive loss of crystallinity and the structural collapse of Li diffusion pathways.

Magneto-dielectric effect in Pb(Zr0·52Ti0·48)O3 filled nanoporous Ni 0 ·5Zn 0 ·5Fe 2 O 4 composite

Nanoporous Ni0·5Zn0·5Fe2O4 particles of diameter, ~ 9·5 nm, were synthesized by citric acid assisted thermal decomposition in an autoclave. The BET surface area measured was 80 m2 g − 1 and the average pore diameter was 2·5 nm. By soaking the particles in a suitable precursor solution and then subjecting them to a heat treatment at 923 K for 3 h, Pb(Zr0·52Ti0·48)O3 was grown within the nanopores. X-ray and electron diffraction studies confirmed the presence of both these phases. The nanocomposites showed ferromagnetic behaviour over the temperature range 2–300 K. No ferroelectric hysteresis loop could be found which was consistent with the earlier theoretical prediction of loss of ferroelectricity below a critical thickness of 2·4 nm. Good magneto-dielectric response of the order of 7% at a magnetic field of 9 kOe was recorded for the present system. This is believed to arise due to a negative magnetostriction coefficient of Ni0·5Zn0·5Fe2O4 which exerted a compressive strain on Pb(Zr0·52Ti0·48)O3 thereby lowering the tetragonality in its crystal structure.

Complex structural phase transitions in slightly Ca modified Na0.5Bi0.5TiO3

A temperature dependent neutron powder diffraction study, in conjunction with dielectric and ferroelectric characterization, of slightly Ca modified Na0.5Bi0.5TiO3 (NBT) revealed an instability with regard to a non-polar orthorhombic (Pbnm) distortion above room temperature. This intermediate orthorhombic phase has earlier been reported for unmodified NBT by electron diffraction studies, but has never been captured by global (x-ray/neutron) diffraction techniques. Calcium substitution seems to amplify the magnitude of this intermediate orthorhombic distortion thereby making the corresponding superlattice reflections become visible in the neutron diffraction pattern. The study revealed the following sequence of very complex structural evolution with temperature: .

Hydrothermal Synthesis and Magnetic Property Studies of Multiferroic YMnO<sub>3</sub> Nanorods

Multiferroic YMnO3nanorods were synthesized by hydrothermal process at 200°C. Hexagonal structure of the synthesized sample was confirmed by powder X-ray diffraction analysis. High resolution scanning electron microscope analysis shows uniform nanorods with average diameter of about 350nm and length of 10µm. Transmission electron microscope and selected area electron diffraction studies reveal the single crystalline nature of nanorods and the lattice fringe width of nanorod is about 0.296nm for the (111) plane with the growth direction along (001) plane (c-axis). The zero-field-cooled and field-cooled magnetization studies show a complicated magnetic transition occurred in the temperature range from 20 to 300K as confirmed by magnetic hysteresis loops.

In situ grown Ge in an arsenic-free environment for GaAs/Ge/GaAs heterostructures on off-oriented (100) GaAs substrates using molecular beam epitaxy

High-quality epitaxial Ge layers for GaAs/Ge/GaAs heterostructures were grown in situ in an arsenic-free environment on (100) off-oriented GaAs substrates using two separate molecular beam epitaxy (MBE) chambers, connected via vacuum transfer chamber. The structural, morphological, and band offset properties of these heterostructures are investigated. Reflection high energy electron diffraction studies exhibited (2 × 2) Ge surface reconstruction after the growth at 450 °C and also revealed a smooth surface for the growth of GaAs on Ge. High-resolution triple crystal x-ray rocking curve demonstrated high-quality Ge epilayer as well as GaAs/Ge/(001)GaAs heterostructures by observing Pendellösung oscillations and that the Ge epilayer is pseudomorphic. Atomic force microscopy reveals smooth and uniform morphology with surface roughness of ∼0.45 nm and room temperature photoluminescence spectroscopy exhibited direct bandgap emission at 1583 nm. Dynamic secondary ion mass spectrometry depth profiles of Ga, As, and Ge display a low value of Ga, As, and Ge intermixing at the Ge/GaAs interface and a transition between Ge/GaAs of less than 15 nm. The valence band offset at the upper GaAs/Ge-(2 × 2) and bottom Ge/(001)GaAs-(2 × 4) heterointerface of GaAs/Ge/GaAs double heterostructure is about 0.20 eV and 0.40 eV, respectively. Thus, the high-quality heterointerface and band offset for carrier confinement in MBE grown GaAs/Ge/GaAs heterostructures offer a promising candidate for Ge-based p-channel high-hole mobility quantum well field effect transistors.

Oxygen defects: The key parameter controlling the activity and selectivity of mesoporous copper-doped ceria for the total oxidation of naphthalene

Mesoporous CeO2 modified by the addition of copper has shown high efficiency for the total oxidation of naphthalene. High activity and 100% selectivity to carbon dioxide throughout the whole range of temperatures studied were achieved for copper loadings of 3.6% and lower. The catalytic behaviour has been related to the concentration of surface oxygen defects. A clear correlation between the concentration of surface oxygen defects (determined by XPS and DRIFTS) and the catalytic performance has been identified. Catalytic activity increased as copper was incorporated into the ceria up to 3.6%. In this range of copper content the copper was incorporated into the cubic fluorite lattice of CeO2 and this was confirmed using XRD and electron diffraction studies. For copper ceria catalysts with higher copper contents the concentration of oxygen defects decreased and an additional dispersed monoclinic CuO phase with a low intrinsic activity was formed, thus leading to a decrease of both the activity and the selectivity to CO2.

Molecular packing of fullerenes inside single-walled carbon nanotubes

We report a first electron diffraction study of the C60s packing inside individual single-walled carbon nanotubes (C60s at SWCNT or peapod). Diffraction patterns from a single peapod were recorded using a nanometer-sized electron beam at 80kV. Determination of the peapod structure, including the diameter (D) and chiral angle of the SWCNT, and the average spacing between C60s along the tube direction (ZC60) are performed. The determined ZC60 increases from around 9.03 to 9.69Å as D increases from around 14.17 to 14.38Å, while in large diameter SWCNTs with D larger than 14.5Å, a significant reduction in ZC60 takes place. Molecular dynamics (MD) simulations reproduce the same reduction in ZC60, due to the well-known linear-to-zigzag transition. More importantly, prior to the linear-to-zigzag transition, a 1D-to-3D transition of C60s configuration is predicted. The resulting expansion of accessible volume is likely to contribute to the observed increasing ZC60 as a function of increasing SWCNT diameter before D reaching 14.5Å.

Vapor phase synthesis of hexagonal shaped single crystal yttria stabilized zirconia nanoparticles using CO2 laser

Growth of hexagonal shaped single crystal yttria stabilized zirconia nanoparticles has been observed in the vapors emanating from solid targets vaporized using CO2 laser in CW and pulsed modes of operation. The mean size and yttrium concentration in these nanoparticles are found to be in the range of 5–40nm and ∼10.4–11.6wt% respectively, which depend on the laser power density and the gaseous environment used during the growth process. Nanoparticles synthesized with pulsed mode of laser operation were found to be smaller in size compared to those generated in the CW mode. It was also found that formation of these nanoparticles was more pronounced in helium gas environment compared to those in nitrogen and argon. X-ray and electron diffraction studies showed that in all experimental conditions the generated nanoparticles were in cubic phase. From high resolution TEM it was observed that the nanoparticles with identical orientations coalesced with each other in line with the oriented attachment theory.

Structural Variations of BiMnO3+x Revealed by Electron Diffraction

Electron diffraction studies have been performed on a number of samples within the series BiMnO3+x (for the range –0.11 < x < 0.16). Samples with a large value of x (either positive or negative) crystallize as a monoclinic perovskite supercell structure not dissimilar from the stoichiometric ideal. However, the variation of oxygen composition manifests itself as disorder in either the cation or anion sub-lattices, leading to a reduction in symmetry (to C2, P21 or P2). In addition, three new structures have been identified at compositions closer to the perovskite ideal. One structure is similar to a mixed cation phase reported by Hughes et al, while another is an n = 2 Ruddlesden-Popper phase; importantly both of these phases are acentric and so could support multiferroic properties. The third is as yet not fully characterised but seems to crystallise into a different monoclinic structure than the stoichiometric ideal phase.

Ultrathin MoS2 membranes and their characterization through HRTEM and electron diffraction studies

Extended abstract of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, USA, July 29 – August 2, 2012.

Scanned Electron Diffraction Studies of Self-assembled Monolayers

Extended abstract of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, USA, July 29 – August 2, 2012.

Molecular structure and relative stability of trans and cis isomers of formanilide: gas-phase electron diffraction and quantum chemical studies

Molecular structure of formanilide is determined by gas-phase electron diffraction (GED) augmented by quantum chemical calculations (B3LYP/cc-pVTZ and MP2/cc-pVTZ) and literature microwave (MW) data. The combined GED and MW data are well reproduced for the mixture of trans and cis isomers with the relative abundance of 59 ± 5 and 41 ± 5 %, respectively, at T = 410 K. The trans isomer (C s symmetry) is planar, while the cis isomer (C 1 symmetry) has the twisted structure with the amide group rotated by 36.7 ± 2.7° with respect to the phenyl ring. In accord with theoretical calculations, the amide bond –NH–C(O)– is planar in trans formanilide and a somewhat nonplanar in cis isomer. Accurate structural parameters were obtained by a simultaneous fit of the rotational constants reported in the literature and GED intensities obtained in this study. The N–C(O) and N–CPh bond dissociation energies in formanilide are calculated using Gaussian-4 method. It is revealed that the strength of N–C(O) bond in formanilide is 50 kJ/mol less than that in benzamide. On the contrary, the strength of adjacent bond (N–CPh) increases by 35 kJ/mol compared to aniline. It is rather unexpectedly that the bond strength weakening does not result in the bond elongating, and vice versa.

Structure and high-temperature properties of the (Sr,Ca,Y)(Co, Mn)O3−y perovskites — perspective cathode materials for IT-SOFC

Oxygen deficient perovskites Sr0.75Y0.25Co1−xMnxO3−y, x=0.5 and 0.75, were prepared by using the citrate route at 1373–1573K for 48h. The cubic Pm-3m perovskite structure for x=0.5 was confirmed by electron diffraction study and refined using neutron powder diffraction (NPD) data. For x=0.75, the superstructure corresponding to a=2×aper, b=2×aper, c=2×aper (a0b−b− tilt system, space group Imma) was revealed by electron diffraction. The solid solution Sr0.75−xCaxY0.25Co0.25Mn0.75O3−y, 0.1≤x≤0.6 and compound Ca0.75Y0.25Mn0.85Co0.15O2.92 were prepared in air at 1573K for 48h. The crystal structure of Ca0.75Y0.25Mn0.85Co0.15O2.92 was refined using NPD data (S.G. Pnma, a=5.36595(4), b=7.5091(6), c=5.2992(4)Å, Rp=0.057, Rwp=0.056, χ2=4.26). High-temperature thermal expansion properties of the prepared compounds were studied in air using both dilatometry and high-temperature X-ray powder diffraction data (HTXRPD). They expanding non-linearly at 298–1073K due to the loss of oxygen at high temperatures. Calculated average thermal expansion coefficients (TECs) for Sr0.75Y0.25Co1−xMnxO3−y, x=0.5, 0.75 and Ca0.75Y0.25Mn0.85Co0.15O2.92(1) are 15.5, 15.1, and 13.8ppmK−1, respectively. Anisotropy of the thermal expansion along different unit cell axes was observed for Sr0.15Ca0.6Y0.25Co0.25Mn0.75O3−y and Ca0.75Y0.25Mn0.85Co0.15O2.92. Conductivity of Sr0.75Y0.25Co1−xMnxO3−y, x=0.5 and 0.75 increases with the temperature reaching 110S/cm for x=0.5 and 44S/cm for x=0.75 at 1173K. Samples of Sr0.75−xCaxY0.25Co0.25Mn0.75O3−y, 0.1≤y≤0.6 were found to be n-type conductors at room temperature with the similar temperature dependence of the conductivity and demonstrated the increase of the σ value from ∼1 to ∼50S/cm as the temperature increases from 300 to 1173K. Their conductivity is described in terms of the small polaron charge transport with the activation energy (Ep) increasing from 340 to 430meV with an increase of the calcium content from x=0 to x=0.6.

Generation and characterization of zirconium nitride nanoparticles by wire explosion process

In the present study, wire explosion process (WEP) has been used to produce zirconium nitride (ZrN) nanoparticles. The produced ZrN nanoparticles were characterized through X-ray diffraction (XRD) and by the selected area electron diffraction (SAED) studies. The size and shape of the particles were analyzed using Transmission Electron Microscope (TEM). An analysis based on Log-normal probability distribution was used to quantify the particle size distribution of the powder. High speed photography was used to observe the wire explosion process.

Electron diffraction study of 1M illites with interstratified trans- and cis-vacant 2 : 1 layers

Illites from the volcanogenic Zn-Au-Ag sulfide deposit Galkinskoe (Northern Urals) have been investigated using oblique-texture electron diffraction patterns in combination with the simulation of diffraction effects. Along with single-phase tv/cv1M illites, the structures of which are formed by statistically interstratified dioctahedral 2: 1 layers with vacant trans- or cis-octahedra, illites in the form of a mixture of two interstratified tv/cv1M phases, with the dominance of tv- or cv layers, are identified. It is shown that in the latter case the diffraction pattern can also be interpreted within the single-phase tv/cv model, provided that the tv- and cv layers are distributed with some tendency to segregate. The structural features indicating the preference of the two-phase model are analyzed.

Effect of Ammonia Water on the Morphology of Monoethanolamine-Assisted Sonochemicaly Synthesized ZnO Nanostructures

In the present work, ZnO nanostructures were synthesized by monoethanolamine (MEA)-assisted ultrasonic method at low temperature. Structural analysis was carried out by X-ray diffraction (XRD) confirmed the formation of hexagonal wurtzite structure of ZnO. The effect of ammonia water on the molecular structure of MEA, and its effect on the morphology of ZnO nanostructures were monitored by electron microscopy. Scanning electron microscopy (SEM) results suggest that ZnO nanoparticles with 100 nm in diameter were produced in case of MEA-assisted ultrasonic method. However, as ammonia water was added into the reaction system the morphology of ZnO nanoparticles changed into nanorods, flower-like nanostructures and finally microrods. Transmission electron microscopy (TEM) and selected area electron diffraction (SAED) studies showed that as prepared ZnO nanostructures were single crystalline in nature and grew in different directions resulted in the formation of various structures. The growth mechanism of as prepared ZnO nanostructures was discussed in detail. It was proposed that the addition of ammonia water into the reaction system resulted into the formation of ethylene diamine (EDA) which directed the growth of ZnO. The optical property was studied by photoluminescence (PL) spectroscopy showed only UV emission and no defects mediated visible emission.

Growth and Surface Structure of Thin Co Films on Au(001) Studied by Scanning Tunneling Microscopy

We have studied the room-temperature growth of Co films on Au(001) substrate in the thickness range up to 3.4 monolayers (ML) and also studied the effects of annealing at 500 K. The surface morphology and structure at various Co coverages (θCo) were investigated in scanning tunneling microscopy (STM) and low-energy electron diffraction studies. As-grown Co films up to 3.4 ML thick show bcc structures with Co islands. Annealing at 500 K activates several diffusion mechanisms, inducing surface segregation of Au and phase separation between Au and Co. These mechanisms change the structure and surface morphology of the films significantly. Consequently, regular nanostructures aligned in the <100> direction and consisting of buried Co islands are formed and characteristic reconstruction of the Au(001) surface were observed on annealed Co films. From the observed STM height profile data we have inferred detailed surface and interface structures due to the large difference between the monolayer heights of the bcc Co(001) and fcc Au(001). In samples with θCo=3.4 ML we observed a regular network structure with the (2 ×1) reconstruction. The mechanism by which the buried Co islands form is discussed based on thermodynamic considerations.

Growth and Surface Structure of Thin Co Films on Au(001) Studied by Scanning Tunneling Microscopy

We have studied the room-temperature growth of Co films on Au(001) substrate in the thickness range up to 3.4 monolayers (ML) and also studied the effects of annealing at 500 K. The surface morphology and structure at various Co coverages (θCo) were investigated in scanning tunneling microscopy (STM) and low-energy electron diffraction studies. As-grown Co films up to 3.4 ML thick show bcc structures with Co islands. Annealing at 500 K activates several diffusion mechanisms, inducing surface segregation of Au and phase separation between Au and Co. These mechanisms change the structure and surface morphology of the films significantly. Consequently, regular nanostructures aligned in the <100> direction and consisting of buried Co islands are formed and characteristic reconstruction of the Au(001) surface were observed on annealed Co films. From the observed STM height profile data we have inferred detailed surface and interface structures due to the large difference between the monolayer heights of the bcc Co(001) and fcc Au(001). In samples with θCo=3.4 ML we observed a regular network structure with the (2 ×1) reconstruction. The mechanism by which the buried Co islands form is discussed based on thermodynamic considerations.