High resolution electron microscopy of long range ordered alloys

In this paper a survey is given of the application of high resolution electron microscopy and selected area electron diffraction to the study of long range ordered alloys. The characteristic features of the diffraction effects and of the imaging of ordered alloys are discussed. Group theoretical considerations allow prediction of microtexture of such alloys. A number of simple alloy structures are imaged and it is shown, by means of simulated images, that under suitable diffraction conditions the columns of minority atoms are represented as bright dots. The columns of majority atoms are only visible at very small thicknesses. Subsequently a number of one- and two-dimensional long period superstructures derived from these simple structures are analysed, using high resolution micrographs. Finally the observed microtexture of the same alloy superstructures is compared with the predictions of group theory. Strongly non-conservative antiphase boundaries are found to dissociate inapb’s which are as close to conservative as is compatible with thefcc lattice.     

Optimization of diffraction grating profiles in fabrication by electron-beam lithography

We propose a new design method for periodic diffraction gratings to be fabricated with direct-writing electron-beam lithography. When the grating has a small period, the proximity effect of electron scattering restricts the grating profile after developing. Our design method optimizes the electron-dose profile and grating profile simultaneously to obtain the desired diffraction efficiency under the restriction of the proximity effect. The optimization is made with rigorous electromagnetic grating analysis and the resist development simulator. When we designed the diffraction grating with a period of 1.0 microm to obtain the highest efficiency of the first-order diffracted light of a 633-nm wavelength, the calculated grating profile was really different from the profile optimized only with rigorous electromagnetic grating analysis. Moreover, the diffraction grating of the electron-beam resist was fabricated according to the simulation result. The estimated diffraction efficiency was 82%, and the measured efficiency was 70%.     

Lattice imaging studies on the structure and non-random disorder in SiC crystals

A number of SiC crystals having extremely large period unit cells and one-dimensionally disordered structures have been studied by x-ray diffraction and lattice imaging in the electron microscope. It has been observed that structures of extremely large periodicities (>100 nm) can be conveniently studied by lattice imaging technique which simply give continuous streaks in their x-ray diffraction patterns. This has been shown in the case of 150R, 150R_A, 900R and another structure whosec-repeat period is more than 100 nm. SiC crystals showing streaks alongc*-direction in x-ray diffraction are found to possess either completely ordered structures with extremely large periodicities or non-random disorder.     

Helical Diffraction from Tubular Structures

An electron diffraction technique is described that enables both the calculation of electron diffraction intensity distribution from a given tubule structure and the deduction of its true helicity from an experimental electron diffraction pattern of the nanotube. The cylindricality and the helicity of nanotubes are taken into full account. An example of the applications is also presented as an illustration for the simulation of the electron diffraction pattern and the deduction of its true helicity of a single-walled helical carbon nanotube of indices [12, 1].     

Biosynthesised silver nanoparticles using aqueous leaf extract of Tagetes patula L. and evaluation of their antifungal activity against phytopathogenic fungi

In the recent decades, nanotechnology is gaining tremendous impetus due to its capability of modulating metals into their nanosize, which drastically changes the chemical, physical, biological and optical properties of metals. In this study, silver nanoparticles (AgNPs) synthesis using aqueous leaf extracts of Tagetes patula L. which act as reducing agent as well as capping agent is reported. Synthesis of AgNPs was observed at different parameters like temperature, concentration of silver nitrate, leaf extract concentration and time of reduction. The AgNPs were characterized using UV‐vis spectroscopy, scanning electron microscope with energy dispersive spectroscopy, transmission electron microscopy with selected area electron diffraction, X‐ray diffraction, Fourier transform infrared and dynamic light scattering analysis. These analyses revealed the size of nanoparticles ranging from 15 to 30 nm as well revealed their spherical shape and cubic and hexagonal lattice structure. The lower zeta potential (−14.2mV) and the FTIR spectra indicate that the synthesized AgNPs are remarkably stable for a long period due to the capped biomolecules on the surface of nanoparticles. Furthermore, these AgNPs were found to be highly toxic against phytopathogenic fungi Colletotrichum chlorophyti by both in vitro and in vivo and might be a safer alternative to chemical fungicides.Inspec keywords: silver, nanoparticles, nanofabrication, nanobiotechnology, ultraviolet spectra, visible spectra, scanning electron microscopy, X‐ray chemical analysis, electron diffraction, X‐ray diffraction, Fourier transform infrared spectra, crystal structure, electrokinetic effects, antibacterial activityOther keywords: biosynthesised silver nanoparticles, aqueous leaf extract, Tagetes patula L, antifungal activity, phytopathogenic fungi, nanotechnology, UV–vis spectroscopy, scanning electron microscope, energy dispersive spectroscopy, transmission electron microscopy, selected area electron diffraction, X‐ray diffraction, Fourier transform infrared spectra, dynamic light scattering analysis, hexagonal lattice structure, zeta potential, phytopathogenic fungi Colletotrichum chlorophyti, cubic lattice structure, size 15 nm to 30 nm, Ag     

An electron microscopy and X-ray diffraction study of the microstructures of melt-drawn polyethylene films

Electron microscopy and X-ray diffraction have been used to study microstructures of melt-drawn polyethylene films. During the drawing process, uniplanar structures are formed which consist of crystals with theirb andc axes in the film plane. On annealing the films, the crystal size and orientation increase. Quantitative measures of the crystal thickness, lateral crystallite size and long period were obtained from bright-field and dark-field electron micrographs as well as from wide and small angle X-ray diffraction of stacked layers of the films.     

The lamellar structure of oriented high-density polyethylene

The lamellar structure of a high-density polyethylene oriented to give a single-crystal type of texture has been studied by electron microscopy and X-ray diffraction. Structures shown by the Kanig technique [6, 7] and a replication technique of electron microscopy are consistent with one another and with the small-angle X-ray diffraction patterns of this type of material, but the electron microscope observations show local regions of highly misoriented lamellae which are not detectable by X-ray diffraction. In regions where the lamellar orientation is that expected from the X-ray patterns the lamellae are wide and irregularly wavy.     

Elektronenbeugung zur Analyse dünner Funktionsschichten

Electron Diffraction for Analysis of thin Functional Layers A short history of the diffraction techniques in crystallography is given and the basics of electron diffraction in transmission electron microscopy are explained: electrons as waves, Bragg's law, selected area and convergent beam electron diffraction. The possibilities of the often used selected area electron diffraction are demonstrated by two typical examples: determination of the crystallographic orientation in single crystalline layers (piezoelectric LiTaO₃) and phase analysis in polycrystalline structures (Ni‐Al‐O hard coatings).     

Microstructure of a thermotropic random copolymer of hydroxybenzoic acid,isophthalic acid and hydroquinone (HBA-IA-HQ)

Transmission electron microscopy has been used to study microstructural features in a thermotropic copolyester composed of 4-hydroxybenzoic acid, isophthalic acid and hydroquinone residues. Selected-area electron diffraction patterns indicate that thin sheared samples of the pure copolymer, and of an analogue containing glass filler, exhibit a dual molecular orientation in which the meridional maxima are closely periodic in scattering angle. Dark-field (DF) imaging in one set of the diffuse equatorial reflections reveals “bands” which have an average period of 200 nm. Annealing the material in the solid state at 250 °C leads eventually to a change in the structure in which the banded texture is replaced by regions of uniform orientation within which the molecules are aligned with the shear axis. Needle-like diffracting crystalline entities, measuring approximately 80 nm long, in the direction of the molecular chain axis, and 5–8 nm thick, have been imaged in DF using the first meridional reflection as the source of diffraction contrast.     

Comparative determination of the α/β phase fraction in α+β-titanium alloys using X-ray diffraction and electron microscopy

A comparison is made between the measured α/β phase fractions in Ti-6246 using X-ray diffraction (XRD) and electron microscopy. Image analysis of SEM and TEM images was compared to the phase fraction estimate obtained using electron backscattered diffraction, lab and high-energy synchrotron XRD. There was a good agreement between the electron microscopic and diffraction techniques, provided that the microstructural parameters of grain size and texture are estimated correctly when using quantitative Rietveld refinement.     

Molten salt route of single crystal barium titanate nanowires

Rather long barium titanate nanowires have been synthesised by molten salt method without any organic surfactants. The crystal structure of barium titanate nanowires is identified by X-ray diffraction to be the tetragonal structure phase, Raman spectroscopy and selected area electron diffraction measurements. Furthermore, scanning electron microscopy and transmission electron microscopy observations show that the barium titanate nanowires have uniform cylindrical structure, with lengths from 20 to 80 μm and diameters from 100 nm to 1 μm. Moreover, high resolution transmission electron microscopy observations and selected area electron diffraction analysis show that the barium titanate nanowires are single crystals with a tetragonal structure in nature.     

TiN／AIN纳米多层膜的调制周期及力学性能研究

采用一种新型的离子束辅助非平衡反应磁控溅射设备制备了TiN／AlN纳米多层复合膜。采用XRD衍射、TEM、显微硬度计和干涉显微镜对TiN／AlN纳米多层膜的微结构和力学性能进行了表征。结果表明：TiN／AlN多层膜有良好的周期；调制结构影响薄膜的择优取向，薄膜整体表现出硬度增强的效果，硬度随调制周期的变化而变化并在调制周期为7、5nm时达到最大值。     

Electron diffraction studies of Langmuir-Blodgett film structures with potential for optical applications

The Langmuir-Blodgett film technique is currently being researched as a deposition process for many optical applications. The performance of these coatings is dependent on both the quality of deposition and the film structure. A structural investigation, using transmission electron diffraction and microscopy, on materials with potential for second harmonic generation and optical data storage is reported on this paper.

Transmission electron diffraction patterns are presented for an optically non- linear stilbene derivative. Results indicate that monolayer quality is good but for the formation of multilayers causes the film quality to deteriorate. The technique of alternating this material with tricosanoic acid has improved deposition, and electron microscopy has been used to indicate this. High quality transmission electron diffraction patterns of tricosanoic acid are interpreted in terms of a pseudo- hexagonal packing arrangement with a grain size of approximately 5 μm.

Organic dyes which absorb in the near-IR have also been studied. These have potential for use in ablative optical hole burning for optical data storage. Electron diffraction results are presented, showing good structure, with a grain size suitable for this application.     

Al-doped single-crystalline SiC nanowires synthesized by pyrolysis of polymer precursors

Al-doped 6H-SiC nanowires are synthesized by catalyst-assisted pyrolysis of polymer precursors. The obtained nanowires were characterized using scanning electron microscopy, X-ray diffraction, transmission electron microscopy and selective area electron diffraction. We demonstrate that doping concentrations can be controlled by tailoring the Al concentrations in the precursors. We also find that Al-doping has a profound effect on the morphology and emission behavior of the SiC nanowires. The current results suggest a simple technique for synthesizing Al-doped SiC nanomaterials in a controlled manner, which are promising for applications in optical and electronic nanodevices.     

A possible crystallographic explanation for the five-fold diffraction symmetry in icosahedral phases

X-ray and electron diffraction data from the Al-Cu-Fe icosahedral phase are compared and analysed on the basis of the microcrystalline and multi-domain model developed by the author. It is shown that a crystallographic explanation is now possible for both the enigmatic five-fold symmetry and non-periodicity of reflections observed in electron diffraction patterns of icosahedral phases.     

Structural investigations of homoepitaxial Si films grown at low temperature by pulsed magnetron sputtering on Si(111) substrates

Using pulsed magnetron sputtering at low substrate temperature (T_s = 580 °C) the homoepitaxial growth on Si(111) was studied. The films were comprehensively characterized by cross-section transmission electron microscopy and various diffraction methods. Up to a film thickness of 1240 nm no breakdown of the epitaxial growth was observed. The surface microstructure, characterized by electron backscatter diffraction, exhibits exclusively crystalline structure with (111) orientation. Careful analysis of selected area electron diffraction patterns and high-resolution X-ray diffraction data clearly proves the existence of twinning/stacking faults in the {111} planes. Besides these defects – which are typical for low-temperature epitaxy – no additional significant defects related to the energetic particle bombardment by the sputter deposition method are observed.     

Kikuchi rings from polycrystalline platinum films with a 〈111〉 fiber axis

Platinum films were grown on mica substrates in ultrahigh vacuum. These films have a strong 〈111〉 fiber axis orientation as found by low energy electron diffraction, reflection high energy electron diffraction and transmission electron diffraction studies. A new form of Kikuchi pattern, namely Kikuchi rings, was found in the diffraction pattern of these oriented polycrystalline films. This is the first time that a Kikuchi pattern has been reported from a polycrystalline film with a fiber axis.     

Ultrafast Kikuchi diffraction: nanoscale stress-strain dynamics of wave-guiding structures

Complex structural dynamics at the nanoscale requires sufficiently small probes to be visualized. In conventional imaging using electron microscopy, the dimension of the probe is large enough to cause averaging over the structures present. However, by converging ultrafast electron bunches, it is possible to select a single nanoscale structure and study the dynamics, either in the image or using electron diffraction. Moreover, the span of incident wave vectors in a convergent beam enables sensitivity levels and information contents beyond those of parallel-beam illumination with a single wave vector Bragg diffraction. Here, we report the observation of propagating strain waves using ultrafast Kikuchi diffraction from nanoscale volumes within a wedge-shaped silicon single crystal. It is found that the heterogeneity of the strain in the lateral direction is only 100 nm. The transient elastic wave gives rise to a coherent oscillation with a period of 30 ps and with an envelope that has a width of 140 ps. The origin of this elastic deformation is theoretically examined using finite element analysis; it is identified as propagating shear waves. The wedge-shaped structure, unlike parallel-plate structure, is the key behind the traveling nature of the waves as its angle permits "transverse" propagation; the parallel-plate structure only exhibits the "longitudinal" motion. The studies reported suggest extension to a range of applications for nanostructures of different shapes and for exploring their ultrafast eigen-modes of stress-strain profiles.     

Coherent twinning phenomena: towards twinning superlattices in III-V semiconducting nanowires

We report evidence in GaP and InP nanowires for a coherent modulation of the structure along the wire axis. By using electron diffraction, we have observed an additional series of diffraction peaks consistent with a quasiperiodic placement of twinning boundaries along the wire. This observation is indeed unexpected, as the vapor-liquid-solid growth conditions used to produce the nanowires were not modulated. The averaged repeat distance of the structure, i.e., the distance between twin boundaries, has been found to depend on the temperature gradient imposed in the growth zone. Future control of the twinning superlattice period should allow significant design possibilities for electronic, thermoelectric, thermal and electro-optic applications of semiconducting nanowires.     

金相学史话(6):电子显微镜在材料科学中的应用

Ruska在三十年代研制出第一台电子显微镜 ,战后 (195 4年 )又在极端困难条件下发展出带有电子衍射功能的高分辨电镜ElmiskopI。但是 ,从专利优先权角度看 ,他不是电镜的发明人。直到半个世纪后 ,有关的争议人都已过世 ,他才在 1986年获得这个迟到的但却是当之无愧的诺贝尔物理奖。材料科学的几次突破性进展充分说明电子显微镜的重要性。首先是电子衍射与成像的结合使位错的直接观察得以实现。在双束 (透射束与一个强衍射束 )条件下 ,位错产生的畸变区的衍射强度与基体不同从而显示衬度差异 (衍衬像 )。位错等晶体缺陷因此得以成为六、七十年代的研究热点。选区衍射使晶体结构分析进入到微米甚至到纳米层次。迄今为止 ,八十年代发现的各种类型的准晶 (五重、八重、十重、十二重旋转对称准晶 )都是使用这种手段实现的 ,从而扩大了晶体的范围 ,把无周期性的准晶也包括进去。高分辨电镜已发展到分辨单个原子的水平 ,这就为九十年代发现和研究纳米碳管创造了条件 ,开辟了纳米技术的新纪元