Selected Area Diffraction Patterns Research Articles

A high‐resolution electron microscopy study of MgxZn1–xO films grown on MgO/c‐sapphire

AbstractWe report on the microstructure of MgxZn1–xO films grown on MgO/c‐sapphire by P‐MBE. Cross sectional specimens of three layers with rock salt, wurtzite, and mixed crystal structure were studied by high‐resolution transmission electron microscopy (HRTEM). Selected area diffraction pattern (SADP) and fast fourier transform (FFT) were also employed to analyze the samples. The results indicate the growth of cubic‐MgZnO along the [111] direction accompanied by twinning. HRTEM micrograph of wurtzite‐MgZnO confirmed that initial stage of the growth starts with a cubic structure and then changes to the wurtzite phase. Our results demonstrate that by introducing a thin MgO buffer layer, growth of cubic‐MgZnO with low Mg content is feasible. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Reaction products of Al/TiC composites fabricated by the pressureless infiltration technique

The interfacial reaction products of the Al-Mg/TiC p composite fabricated by the pressureless infiltration method were analyzed using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and transmission electron microscopy (TEM). During the fabrication of composites, reaction products with various morphologies and sizes were formed in the A1 matrix as well as in the vicinity of the TiC particles by the interfacial reaction between the Al alloy and the TiC particles. From the EDS and selected-area diffraction pattern (SADP) analysis, Al4C3, Al18Ti2Mg3, Ti2AlC, Al3Ti, and TiAl could be identified to form as interfacial reaction products. Both the size and the amount of the reaction products were increased with increasing fabrication temperature as well as fabrication time. Coarse Al3Ti was barely observed in water-quenched composites, while it was observed at all fabrication temperatures (700 °C to 1000 °C) in furnace-cooled conditions.

Coexistence of chalcopyrite and CuAu-type ordered structures in In 0.52Al 0.48As epilayers grown on InP substrates

Ordering formation in In 0.52Al 0.48As alloys grown on (0 0 1) InP substrates by metalorganic chemical vapor deposition was investigated using transmission electron microscopy (TEM). In the plan-view selective area diffraction pattern, the 12 superlattice reflections around the transmitted spot and the {2 0 0} spots were observed, which are associated with the chalcopyrite- and CuAu-type ordered structures. In the InAlAs consisting of III–III–V elements, these ordered phases with the rod-shaped domains elongated along the [2 2 0] show the coexistence of CuAu- and chalcopyrite-type ordered structures. An atomic model showing the formation process of the diffraction pattern of the chalcopyrite- and CuAu-type ordered structures is presented here based on the TEM results.

HRTEM Study of α-Phase in Cu-Zn-Si Alloy

The α-phase in 60/40 brass added Si was investigated by transmission electron microscope (TEM) in order to understand the relationship between the ability of hardening during annealing and phase decomposition. The ability of hardening ( Δ HV), which is the value of difference between the maximum hardness during annealing and the value of as-quenched sample, was obtained measurement from the alloy. As a result, the Si-bearing alloy is higher in ΔHV than a base alloy without Si. The α-phase in the Si-bearing alloy showed fringes in its TEM image like as stacking faults, and extra reflected spots in its selected area diffraction pattern (SADP), which is corresponding to the 9R structure. Streaks were also observed together with spots in its SADP. Extra reflected spots and streaks in SADP became weak or disappeared when the annealing time increased. After 600 ks annealing, SADP obtained from the α-phase could be indexed as FCC lattice. Change in chemical composition of α-phase was also measured by the energy dispersive X-ray spectroscopy (EDS).

Role of electronic and nuclear energy losses in swift heavy ion beam induced epitaxial crystallization of a buried Si3N4 layer

This paper reports on swift heavy ion beam induced epitaxial crystallization of a buried Si3N4 layer. Transmission electron microscopy and selected area diffraction patterns are used to study the epitaxial growth of the buried Si3N4 layer. We observe good epitaxial crystallization at 150°C and 200°C, respectively, for 70MeV Si and 100MeV Ag ions at an ion fluence of 1×1014ionscm−2. The fact that recrystallization is achieved at a lower temperature for Si ions is attributed to the higher ratio (one order of magnitude) of the electronic to nuclear energy loss values compared to that of Ag ions. The possible role of the electronic and nuclear energy loss processes in the mechanism of recrystallization has also been discussed.

Crystallography, microstructure and morphology of Mg 4Nb 2O 9/MgO and Mg 4Ta 2O 9/MgO interfaces formed by topotaxial solid state reactions

Mg 4Nb 2O 9/MgO and Mg 4Ta 2O 9/MgO interfaces of definite crystallography were formed by topotaxial thin film solid state reactions in the systems MgO–Nb 2O 5 and MgO–Ta 2O 5. MgO (0 0 1) single crystal substrates, heated to different temperatures, were subjected to Nb–O and Ta–O vapors generated by e-beam evaporation in high vacuum. Thin films mainly containing the phases Mg 4Nb 2O 9 and MgNb 2O 6, respectively Mg 4Ta 2O 9 and MgTa 2O 6, were formed by gas–solid reactions. The crystallographic relationships between the product phases and the MgO substrate were systematically studied by X-ray diffractometry and transmission electron microscopy (TEM). Surprisingly pole figure analysis revealed more than one orientation relationship for some of the phases: Mg 4Nb 2O 9 and Mg 4Ta 2O 9 grew with (1 1 .4), (1 1 .6) and (1 1 .9) orientations, depending on temperature. Selected area diffraction patterns and high resolution TEM images show that these three orientations have a common Mg 4(Nb/Ta) 2O 9 [ 1 1 ¯ .0 ] /MgO [ 1 1 ¯ 0 ] axis and differ by the angle between the Mg 4(Nb/Ta) 2O 9 (0 0 .1) and MgO (1 1 1) planes. Crystallographic illustrations of this phenomenon are given, and possible origins and consequences for the solid state reaction are discussed. Indications for two different interfacial reaction mechanisms are found.

MeV heavy ion beam induced epitaxial crystallization of buried Si3N4 layer

We report on swift heavy ion beam induced epitaxial crystallization of a buried Si3N4 layer. High-resolution transmission electron microscopy and selected area diffraction patterns are used to study the 70MeV Si5+ ion beam induced epitaxial growth of the Si3N4 layer. We observe good epitaxial crystallization at 150°C, which is a much lower temperature as compared to the conventional solid phase epitaxial growth. A possible mechanism of recrystallization is discussed on the basis of formation of vacancies along the track of the swift heavy ion and their migration at elevated temperatures during irradiation.

TEM observation of Eu-doped GaN and fabrication of n-GaN/Eu:GaN/p-GaN structure

Structural properties of Eu-doped GaN with the Eu concentration of about 2 at% were studied by cross sectional transmission electron microscope (TEM) observation, and electrical and optical properties of n-GaN/Eu-doped GaN/p-GaN structure were discussed. Selected area diffraction pattern from Eu-doped GaN showed hexagonal structure and no other anomalous pattern was observed. These results suggest that the segregation of Eu and EuN were not formed. From the high resolution TEM observation of Eu-doped GaN, in addition to a small portion of cubic phase of GaN, high density of stacking irregularity which was hardly observed in undoped GaN was detected. Heterostructure of n-GaN/Eu:GaN/p-GaN was grown by molecular beam epitaxy on the p-type GaN template which was prepared by metalorganic chemical vapor deposition. Although the rectification behavior was observed, the electroluminescence was obtained not from the Eu-doped layer but from p-GaN layer. These results suggest that the hole mobility in Eu-doped GaN is extremely low probably due to the high density of stacking irregularity.

Structure and optical properties of polyvinyle alcohol capped GaAs nanocrystals

Polyvinyl alcohol capped GaAs nanocrystals, assembled in thin film form, have been synthesized by a simple electrochemical technique. Transmission electron microscopy (TEM) study reveals the presence of 20–50 nm size GaAs nanoparticles embedded in the polymer host. Selected area diffraction pattern contains a series of spotted rings indicative of textured nature of the thin film. The excitonic peak broadening and the blue shift of its spectral position with respect to the bulk band gap depend upon the concentration of the polyvinyle alcohol. The X-ray photoelectron spectrum shows C(1s) peak corresponding to the surface bonded polyvinyl alcohol along with the Ga3d and As3d peaks of the GaAs core. Room temperature micro-Raman spectrum shows one surface phonon mode that shifts to the lower energy side with decrease in the crystallite size.

In situ templated synthesis of anatase single-crystal nanotube arrays

Anatase single-crystal nanotubes were obtained using an in situ templated method.First, highly ordered titania arrays were formed through an anodization process inH3PO4 electrolytes containing 0.5 wt% HF. Under optimized conditions titaniananotubes with a diameter of up to 100 nm and a length of up to1.1 µm were prepared. Second, the crystallization and stability of the titaniananotubes were studied in air at elevated temperatures. Anatasesingle-crystal nanotubes were fabricated after annealing the sample in air at450 °C. The anatase single-crystal structure was verified by selected area diffraction pattern andHRTEM images.

Crystallographic Orientation Relationships Between Hexagonal and Tetragonal Barium Titanate

The high‐temperature hexagonal (h) phase has been found to retain metastability at room temperature and co‐exist with the room‐temperature tetragonal (t) phase in hot‐pressed BaTiO3 ceramics. The crystallographic orientation relationships between two polytypes have been analyzed by TEM and selected‐area diffraction patterns (SADPs). The relationships are illustrated using transformation matrices for both the forward h→t phase transformation (Mf) and the backward t→h phase transformation (Mb) based on two independent microstructures containing h‐particle in t‐matrix and t‐particle in h‐matrix, respectively. Self‐consistent transformation matrices are derived from the coincident reflections in corresponding SADPs. The forward and backward matrices are inverse matrix to each other.

Improving the Electrochemical Performance of LiCoO2 Cathode by Nanocrystalline ZnO Coating

The cycle life of cathodes cycled at a high cutoff voltage can be largely improved by surface modification with ZnO coating. The bright-field transmission electron microscopy (TEM) images and selected area diffraction patterns of as-coated particles reveal the existence of continuous ZnO films with a thickness deposited on surfaces, indicating a Li-Zn-O phase formed on the surface region. Besides high-voltage cycleability, cycle-life degradation caused by inappropriate conductive carbon can also be moderated by ZnO coating. Furthermore, the rate capability at high current density can also be notably improved. The role ZnO coating played in the charge-discharge process is discussed from the viewpoint of surface chemistry with the aid of data from scanning electron microscopy, TEM, energy-dispersive X-ray, and impedance spectra. Moreover, the correlation between electrochemical performance and surface properties of ZnO-coated is explored.

Swift heavy-ion-induced epitaxial crystallization of buried Si3N4 layer

We report on swift heavy-ion-beam-induced epitaxial crystallization of a buried Si3N4 layer. We observe good epitaxial crystallization at 200 °C, which is a much lower temperature than that required for the conventional solid phase epitaxial growth. High-resolution transmission electron microscopy and selected area diffraction patterns have been used to study the 100-MeV Ag8+-ion-beam-induced epitaxial growth of the Si3N4 layer. A possible mechanism of recrystallization is discussed on the basis of synergetic effects of electronic and nuclear energy-loss processes along the trajectory of the swift heavy ions at elevated temperatures.

Electron microscopic study on SrGdMnO 4

Single crystals of SrGdMnO 4 have been synthesized by the floating zone method. The structure was characterized as the K 2NiF 4-type, using X-ray diffraction (XRD) and a transmission electron microscope (TEM). Presence of weak reflections breaking the archetypal tetragonal symmetry was observed from the selected area diffraction (SAD). The compound was found to have an orthorhombic unit cell of a ≅ b = 0.532(4) nm, c = 1.271(6) nm, by taking the a and b axes along the diagonal directions on the basal plane of the tetragonal archetype. Structural change occurred around 1018 K. The weak reflections disappeared in the SAD pattern, suggesting that crystal is of the archetype above 1018 K.

The influence of yttrium on a typical SnO 2 varistor system: Microstructural and electrical features

The influence of yttrium oxide, Y 2O 3, on the microstructure development of the SnO 2·Co 3O 4·Nb 2O 5 typical varistor system was studied with scanning (SEM) and transmission (TEM) electron microscopies. The different phases present in the studied samples were characterized through XRD, EDS and selected area diffraction patterns (SAD). Particles of Co 2SnO 4 were observed with TEM in every sample, whereas clusters of the pyrochlore phaseY 2Sn 2O 7 were observed with SEM in samples with 0.05, 0.10 and 0.25 mol% of Y 2O 3. The higher non-linearity ( α = 16) was achieved with the addition of 0.05 mol% of Y 2O 3. The influence of the secondary phases on the electrical properties is also addressed in this work.

Characteristics of SnO2 fishbone‐like nanostructures prepared by the thermal evaporation

AbstractWe have successfully grown the tin oxide (SnO2) fishbone‐like nanostructures on titanium nitride (TiN)‐coated substrates by the thermal evaporation of Sn powders. X‐ray diffraction indicated that the product had the phase structure of the rutile form of SnO2. Transmission electron microscopy (TEM) revealed that the product consisted of fishbone‐like structure, with branches and sub‐branches attached to the main stem. High‐resolution TEM and selected area diffraction pattern coincidentally indicated that both branches and sub‐branches were single crystalline rutile SnO2 structures. Room temperature photoluminescnece (PL) spectrum of the as‐synthesized SnO2 nanostructures exhibited peaks associated with the visible light emission. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Critical assessment of the speckle statistics in fluctuation electron microscopy and comparison to electron diffraction

The technique of fluctuation electron microscopy (FEM) is applied to thin films of amorphous germanium and of polycrystalline gold in a transmission electron microscope. Even though the method was introduced as a tool for quantitative analysis of structural fluctuations in amorphous materials, the basic principles are applicable to any disordered specimen independent of the dimension of disorder. Hence, we extended the technique of FEM to a well-known specimen, gold, whereby it was possible to reinterpret the results of the measurements on amorphous germanium. The hollow-cone dark field images, the statistical analysis of which is the basis of FEM, are examined with respect to the effects of frequency filtering, and are compared to electron diffraction. We find that the angular dependence of the normalised variance, as measured by FEM, yields information similar to the average intensity of hollow-cone dark field image series. Both plots are basically identical to a scan through a selected-area diffraction pattern convoluted by the corresponding angular resolution function. Hence, it appears questionable whether standard FEM analysis provides more information than the classical pair distribution function, which is experimentally limited to short-range order. Frequency selective analysis of the normalised variance, however, gives supplementary information on preferred inter-atomic distances related to the medium-range order of the specimen.

Dielectric Properties and Microstructures of Ba(Ti,Zr)O3 Multilayer Ceramic Capacitors with Ni Electrodes

The microstructures and dielectric properties of multilayer ceramic capacitors based on reoxidized Ba(Ti0.88,Zr0.12)O3 (BTZ) materials with Ni electrodes were studied using transmission electron microscopy. Dielectric measurements showed that the BTZ materials exhibited frequency relaxation effects. Although X‐ray diffraction showed a single pseudocubic phase, split and elongated electron diffraction spots were observed using selected area diffraction (SAD). There were no super‐lattice diffraction spots in the SAD pattern. The microstructures of BTZ dielectric materials were observed at dynamical diffraction conditions, and multidomain structures coexisting in one grain were imaged with high contrast. Bright field and centered dark field images revealed the pseudocubic (100) and (110) domain walls had developed in some regions of the same grain with normal ferroelectric macro‐domain features, and bend contours and distorted domain walls were seen. Defects with the features of low angle grain boundaries, dislocations, and phase boundaries were also observed. Uneven distribution of internal stress and coexistence of multiphases and multidomains in individual grains were considered to be responsible for the frequency relaxor behavior observed in these materials. A model of the evolution of the microstructures with the decrease of temperature is presented.

Sol–gel auto-igniting synthesis and structural property of cerium-doped titanium dioxide nanosized powders

Anatase-type TiO 2 (titania) doped with cerium up to 5 mol% was directly formed as nanometer-sized particles from TiO(NO 3) 2–Ce(NO 3) 2–NH 4NO 3–citric acid complex compound system by sol–gel auto-igniting synthesis process. The precursor gel was characterized by infrared spectroscopy and TG/DSC analysis. The XPS measurement showed that Ce(III) was easily oxidized to Ce(IV) at 550 °C and above. The XRD data, XPS spectra, and TEM selected-area diffraction patterns confirmed that cerium(IV) formed a solid solution in the anatase-type TiO 2 powders. Doping of CeO 2 into TiO 2 shifted the phase transformation from anatase- to rutile-type structure to a high temperature. On the other hand, CeO 2 was segregated on the surface of TiO 2 and the rutile formation was accelerated during phase transformation from anatase to rutile at elevated temperature. When the cerium content was increased in the anatase phase, onset of optical absorption shifted to longer wavelengths, and absorption in the UV-light region and in the visible-light region over 400–500 nm clearly appeared in the diffuse reflectance spectra of the as-prepared Ce-doped TiO 2.

Raman spectroscopy study of C/Cr coatings deposited by the combined steered cathodic ARC/unbalanced magnetron sputtering technique

C/Cr coatings were prepared by the combined steered cathodic arc/unbalanced magnetron sputtering technique with a wide range of bias voltages, Ub from −65 to −350 V. The paper focuses on the microstructure evolution and phase transformations in the coatings and their influence on the tribological performance of C/Cr coatings as a function of the bias voltage. Raman spectroscopy on the surface of the as deposited coatings and in the wear track generated in pin-on-disc tests has been carried out in conjunction with TEM and SEM studies of coatings microstructure and XPS analysis of the chemical bonding in the films. The Raman spectra from the surface of the C/Cr coatings consists of two main Raman features on a strong photoluminescence background: broad bands around ∼1380 cm−1 and ∼1572 cm−1, which are designated to D (disorder) and G (graphitic) peaks, respectively. The broad D and G bands further confirm the TEM-selected area diffraction (SAD) analysis, which shows an amorphous character of the coating. The downshift of the G-band by ∼2–10 cm−1 from the planar graphite (1582 cm−1) is ascribed as the shell curvature of the carbon plane, which could be due to the presence of Cr. We assume the D-band position has a close dependence on the stress in the coating, which results in shifting of the D-band to higher wave number as the stress in the coatings increases. The Raman spectra show better resolution of the D and G peaks for samples deposited at low bias voltage (Ub=−65 to Ub=−75 V). However, these peaks become more diffused and difficult to resolve, with a much lower intensity as the applied bias voltage increases and completely disappears at Ub=−350 V, which suggests formation of metal carbides in the coating. This interpretation was further confirmed by the XRD, TEM and SAD pattern observations. The ID/IG ratio correlates well with the friction behaviour of the films. The friction coefficient decreases and reaches its minimum of μ=0.16 at Ub=−95 V due to the increase in the sp2 content in the film, which is accompanied by a maximum ID/IG ratio of 7.15.