Resolution Electron Microscopy Images Research Articles

Application of phase extension method to sub-Å transmission electron microscopy

A sub-A resolution analysis of a Si crystal structure was performed successfully using a phase extension technique that combined the high-voltage electron microscopy (HVEM) and energy-filtered precession electron diffraction (EF-PED) methods. The high resolution electron microscopy (HREM) image of Si [211] was obtained with a spatial resolution of 0.12 nm using HVEM. The electron diffraction of Si [211] was acquired with a spatial resolution of 0.06 nm by employing the EF-PED method. The phase information of Si [211] was extracted from a deconvoluted image by applying instrumental parameters. Its amplitude information with higher spatial resolution was quasi-kinematically extracted from EF-PED data. Finally, it was revealed that Si atoms were clearly separated with a resolution of 0.78 A in the enhanced resolution image. Therefore, it is expected that the combination of the HVEM and EF-PED methods will be a useful and powerful tool for the quantitative characterization of nanostructured materials.

Microstrain in nanocrystalline copper by high resolution electron microscopy

The elastic microstrains in a crystallite of electrodeposited nanocrystalline copper were investigated by analyzing the high resolution electron microscopy (HRTEM) image. The microstrain was considered as consisting of two parts, in which the uniform part was determined with fast Fourier transformation of the HRTEM image, while the non-uniform part of the microstrain in the crystallite was measured by means of peak finding. Atomic column spacing measurements show that the crystal lattice is contracted in the longitudinal direction, while expanded in the transverse direction of the elliptical crystallite, indicating that the variation of microstrain exists mainly near the grain boundary.

Crystal Structure of New Approximant Phase in Al-Fe-V-Si System

AbstractA model proposed for the atomic structure of the new hexagonal Al-Fe(V)-Si phase which was found in rapidly solidified Al-Fe(V)-Si alloys is discussed in terms of relation this phase to approximants. The structure of this new phase was described as hexagonal packing of double Mackay icosahedral units similar to those of which the cubic α-(AlFeSi) approximant phase is built up. On the basis of this model the experimental high resolution electron microscopic (HREM) images of the hexagonal phase were successfully interpreted. Like the á phase this structure is characterized by the local icosahedral ordering and can be regarded as an approximant.

Atomic Level Studies of Dislocation Networks in Niobium-Sapphire Interfaces

In this paper we present atomistic modelling of the (0001) Al2 O 3 || (111) Nb interface using a simple description of atomic interactions. The goal is to reveal the influence of the strength of bonding between the two materials upon the misfit dislocations formed in Nb at or near the interface. The calculations show that two types of networks of misfit dislocations may be formed depending on the strength of bonding but only the triangular network with 1/2 dislocations occurs if the transport of material, for example by diffusion, can take place. This is, indeed, the network found by electron microscopic studies [1]. The core structure of the misfit dislocations also depends on the strength of bonding. Comparison of simulated high resolution electron microscope (HREM) images, based on the atomistic model, with observations leads to an excellent agreement for a reasonable strength of bonding and provides means for assessment of this physical quantity.

Quantitative Analysis of Co Silicide/SiC Interfaces

The structure of the interfaces between Co silicide and (0001) SiC has been characterized mostly by high resolution electron microscopy and electron spectroscopic imaging. It has been found that, in general, there is no simple and systematic relationships at the silicide/ceramic interface and that there is no noticeable interdiffusion: the interfaces are chemically abrupt over 1.5 nm.

Relaxation of Metamorphic III-V Heterostructures Studied by Digital Processing of HREM Images

AbstractThe crystalline structure of metamorphic heterostructures grown by epitaxy has been studied by digital processing of High Resolution Electron Microscopy (HREM) images. Two systems have been investigated: the GaSb/(001)GaAs, known to be fully relaxed by a perfect Lomer dislocation network and the GaAs/(001)InP relaxed by partial and 60° dislocations randomly distributed. A transition zone can be defined between the perfect substrate and the relaxed epitaxial layer: its thickness is less than 20Å in GaSb/GaAs and more than 80Å in GaAs/InP. These results indicate that the misfit dislocations are only one of the elements involved in the relaxation of misfit stress.

Electron crystallography of zeolites: structure information from HREM images and electron diffraction patterns

High resolution electron microscope (HREM) images of zeolites have typically been used for crystal structure interpretation of frameworks. Only under strict conditions (weak phase object approximation), do HREM images represent directly the projected framework potential, otherwise the images are distorted. A large part of those distortions can be determined and compensated for by crystallographic image processing (CIP). This technique has been used to show that new zeolites SSZ-25 and porosil ITQ-1 are isomorphous to the MCM-22 zeolite. CIP and filtering can also be useful in HREM images of zeolite crystals doped with small particles, revealing directly the size and distribution of particles lying on the surface of zeolite matrix.

Cross sectional Tem Sample Preparation Using E-Beam Lithography and Reactive ion Etching

AbstractA simple method to make cross sectional TEM samples of Si and GaAs semiconductor devices at specific device locations using electron beam (e-beam) lithography and reactive ion etching is described. The basic idea of this technique is to form pillar or line type patterns thin enough to be transparent to electron beams used in transmission electron microscopy. Since the entire process is conducted in the semiconductor fabrication facility, reliable samples were efficiently obtained within a short time without mechanical polishing or ion milling. High Resolution Electron Microscopy (HREM) images of SiGe and GaAs multilayer structures were obtained by this method. Using the alignment function of the e-beam lithography system, cross sectional TEM samples at specific locations of MOS transistors were obtained. The samples were thin enough to obtain HREM images of atomic level defects in the device.

Transmission Electron Microscopy Study of Room Temperature Lasing Epitaxial ZnO Films on Sapphire

AbstractWe have studied the microstructures of lasing and non-lasing ZnO films on sapphire in plan-view and cross-section by transmission electron microscopy (TEM). While ZnO films in general are made up of cloumnar close-packed c-axis misoriented nanocrystals, the misorientation in nonlasing film, typically 5°, is considerably larger than lasing film, typically less than 1°. A rather high density of pinholes or nanotubes is associated with the highly misoriented films. The misorientation between adjacent grains is taken up by grain boundary dislocations. Room temperature lasing films contain a high density of threading boundary edge dislocations, in excess of 1010 cm−2. But faceting in the columnar nanocrystals is not well developed so that the grain boundaries are not clearly visible. Tilting of (0001) lattice planes between grains originating from substrate surface step and growth fault step, however, has been observed in high resolution electron microscopy (HREM) images.

Simulated Chemical Imaging of InGaAs/InAlAs Interfaces

For many semiconductor devices, a detailed knowledge of interface composition on an atomic scale is important for understanding the device performance. One technique for obtaining such knowledge is “chemical imaging”. This technique has previously been applied to Si/Ge and GaAs/AlAs interfaces. Recently, there has been interest in constructing quantum wells using the (In0.532Ga0.468)As/(In0.522Al0.478)As system (hereafter InGaAs/InAlAs), which is lattice-matched to InP (lattice constant of 5:869Å).The chemical imaging technique uses high resolution electron microscopy (HREM) images taken under special conditions of microscope defocus df, and specimen thickness t. Under the correct conditions, the images contain features which are linearly dependent on composition x. For heterogeneous structures (e.g. InGaAs/InAlAs), a change in x affects <200> beams preferentially. In this case, imaging in the <100> orientation is favorable, because four <200> beams occur. It is necessary to define a function of the image intensity h(I) which is proportional to x for some values of t and df. Here we follow the approach of Thoma and Cerva and use h(I) equal to the <200> frequency component of the image intensity (I200) normalized relative to I200 for x=0 and x=1. The resolution of h(I) is limited to one <200> period, or 1/2 unit cell (2.93Å).

High Resolution Electron Microscopy of InGaAs/InAIAs Interfaces

Recently, quantum wells (QW) have been constructed using the (In0.532Ga0.468)As/ (In0.522Al0.478)As system (hereafter InGaAs/In Al As), which is lattice matched to InP (lattice constant of 5.869Å). In order to understand the properties of such QWs, it is important to have knowledge of the structure and composition of interfaces. For III-V materials, compositional changes affect the <200> frequency component of the high resolution electron microscopy (HREM) image intensity (I200). This underlies the “chemical imaging” approach. Simulations for InGaAs/InAlAs interfaces suggest optimum conditions of microscope defocus df=-50nm and sample thickness t=14nm in the <100> orientation. A double-QW structure, consisting of InGaAs/ InAlAs/ InGaAs layers with nominal thicknesses of 4nm/ 2nm/ 4nm (respectively), and embedded in InAlAs layers, has been studied. All the layers were grown by molecular beam epitaxy at 500°C on a <100> InP substrate, with 60s growth interrupts between layers in the QW region.

The measurement of the period and strain of semiconductor superlattice systems using HREM

The quantification of local strains in semiconductor epilayer systems is of technological importance since strain can affect the physical, electrical and optical properties of the material. For the measurement of strains in epitaxial structures on the nanometer scale, high resolution electron microscopy (HREM) images recorded using slow scan charged-coupled device cameras and analyzed using Fourier filtering techniques can provide reliable, quantitative results that are independent of image contrast.Fig. 1a is a HREM image of about 3 periods from a 20 period In.82Al.18Sb / InSb coherently strained superlattice in [110] zone axis projection. The superlattice was grown by magnetron sputter epitaxy and the growth direction is along [001]. The image was recorded at 200 kV using a Philips CM20 TEM. Displayed is a 128×697 pixel subset of the original 256×1024 image. This image was Fourier transformed to obtain the digital diffractogram and all reflections apart from the [002] were filtered out using elliptical masks of approximately the first Brillouin zone in size. The inverse Fourier transform, displaying the [002] lattice fringes, is presented in Fig. 1b.

Anomalous Lattice Parameters in Iron-Copper Multilayers

AbstractX-ray, magnetism and electron loss spectroscopy data were obtained for a series of coherent Fe-Cu face-centred multilayers which suggest that there is a lattice parameter anomaly in the structure. The use of high resolution electron microscopy (HREM) and dark field imaging to measure spacing changes along the layer normal are compared. Experimental dark field images suggest that the Fe has expanded lattice spacings in the growth direction in contradiction to the predictions of a conventional elastic model for a coherent multilayer structure.

Phase refinement of copper perchlorophthalocyanine from a 0.23 nm-resolution electron micrograph using the Sayre equation

The use of direct methods of phasing for electron diffraction (ED) presents opportunities which cannot be matched with x-ray diffraction. High-resolution lattice images of thin crystals obtained on the electron microscope can provide crystallographic phases after image averaging and correction for the contrast transfer function--a procedure which has no analog for x-rays. This procedure has been used for protein crystallography, where such images are often the primary source for phase information.The method has also been used in the analysis of organic molecules.A high resolution (0.23 nm) electron microscope image of epitaxially oriented copper perchlorophthalocyanine obtained at 500 kV (Fig. 1) was used to provide a basis set of 39 phases for refinement in conjunction with a set of ED amplitudes obtained at 1200 kV (Fig 2). Portions of the image were digitized with a CCD camera and a frame-grabber and analyzed using the CRISP software package. The ED pattern was scanned using a Joyce-Loebl Mk. IIIC flatbed microdensitometer to produce integrated intensities, to which no Lorenz correction was applied.

Quantitative analysis of low-dose high-resolution images and diffraction patterns from zeolites using a slow-scan CCD camera

Zeolites are an important class of low-density aluminosilicates framework structures with applications to the field of catalysis and molecular sieves. In order to understand die origin of die unique properties of these materials and hence optimize their performance, it is essential to have a detailed description of their structures. Zeolite structure is often described in terms of the secondary building unit (SBU) which is a specific configuration of the SiO4 tetrahedrons. Structure determination of zeolites is then reduced to determine the types of SB Us and their connectivities when forming the 3-D framework structure.It has been recognized that zeolites undergo rapid structural damage under electron beam irradiation. The use of a slow-scan CCD camera to record low-dose high resolution electron microscope (HREM) images from zeolites with the combination with real-space averaging techniques has been shown to be successful in obtaining the averaged unit cell with high signal-to-noise ratio (SNR).

Structure of the Σ=5 (310) interface in NiAl

The atomic structure of the Σ=5 [001] (310) grain boundary in NiAl was examined by high resolution electron microscopy and multislice image simulation. As in most other intermetallic compounds, the grain boundaries in NiAl are intrinsically brittle at low temperatures. Although there have been few studies on this alloy, the energies of NiAl grain boundaries have been calculated using embedded atom potentials for both stoichiometric and non-stoichiometric structures. These studies are consistent with the results of Bradley and Taylor, which indicate that nickel-rich compositions result from nickel antisite defects on the aluminum sublattice, while aluminum-rich compositions produce constitutional vacancies on the nickel sublattice, and with recent field ion microscopy results on nickel-rich alloys.The Σ=5 grain boundary was prepared by diffusion bonding at 1000 °C. A JEOL 4000EX was used for HREM imaging and the NUMIS multislice simulation program was used to simulated images. Analysis of these images considered the effects of grain boundary expansion, rigid body displacements along the boundary, grain boundary stoichiometry, and point defects at the boundary.

Microstructural Evaluation of Silicon Carbide Whisker Reinforced Alumina Fabricated with Carbon-Coated Whiskers

The presence of interfacial films at the whisker-matrix interface can significantly influence the fracture toughness of ceramic composites. The film may alter the interface debonding process though changes in either the interfacial fracture energy or the residual stress at the interface. In addition, the films may affect the whisker pullout process through the frictional sliding coefficients or the extent of mechanical interlocking of the interface due to the whisker surface topography.Composites containing ACMC silicon carbide whiskers (SiCw) which had been coated with 5-10 nm of carbon and Tokai whiskers coated with 2 nm of carbon have been examined. High resolution electron microscopy (HREM) images of the interface were obtained with a JEOL 4000EX electron microscope. The whisker geometry used for HREM imaging is described in Reference 2. High spatial resolution (< 2-nm-diameter probe) parallel-collection electron energy loss spectroscopy (PEELS) measurements were obtained with a Philips EM400T/FEG microscope equipped with a Gatan Model 666 spectrometer.

Quantification of High Resolution Electron Microscopy and Electron Diffraction by the Imaging Plate

Taking advantages of “Imaging Plate” (IP), i.e., a wide dynamic range and good linearity for electron intensity, high resolution electron microscope (HREM) images and electron diffraction (ED) patterns were quantitatively investigated. Observations of HREM images and ED patterns were made by the TEM-IP System (PIXsys TEM) using electron microscopes JEM-4000EX and JEM-2000FX, respectively. The data on the IP with an effective size of 102×77 mm2 was converted into digital data of 2048 × 1536 pixels with 4096 gray levels and analyzed with the IP-processor of the PIXsys TEM and a large-computer ACOS-2020.Since the IP is highly sensitive to incident electrons, the beam convergence can be lowered for HREM observations, and so the effect of the dumping envelope due to the beam divergence can be reduced. In Fig. 1, an HREM image of an oxide W-Ta-O, taken at a direct magnification of 1,500,000x and an exposure time of 2 s, shows fine contrast of partially ordered cation distributions. Although the phase contrast of the HREM image is rather weak, the image was recorded with about 1100 effective gray levels which are much larger than the 256 gray levels normally used in a conventional image processing system. Intensity distributions in two parts of the image near the crystal edge (A) and at a relatively thicker region (B) are visualized with perspective drawings in Figs. 2(a) and 2(b), and compared quantitatively with contour maps in Figs. 3(a) and 3(b), respectively. It was noticed that projected atomic potentials of the block structure unit (see the inset of Fig. 1) were revealed faithfully in A, having intensity minima at heavy atomic columns (H), whereas the low potential regions (L) have sharp intensity maxima at the thicker region B. These observed images will be compared quantitatively with calculated ones, taking into account the dynamical diffraction effect.

Dynamic TEM Observation on Oxide Glass Materials

AbstractIntensity fluctuation in high resolution electron microscope (HREM) images of amorphous Tl-Ba-Ca-Cu-O oxide films is observed. The fluctuation with a frequency of few tens of Hertz and an amplitude of about 0.3nm, occurs under an intense electron beam irradiation. It is shown experimentally that atom migration in the films is responsible for the fluctuations. The result is also supported by computer image simulations on a model structure for amorphous film.

A NEW METHOD FOR SIMULATING HIGH RESOLUTION ELECTRON MICROSCOPE IMAGES FROM NON-PERIODIC OBJECTS

It is shown that the dynamical diffraction calculation using periodic extension of the sampling boundary points leads to serious and artificial errors in the High Resolution Electron Microscope (HREM) image simulation for a non-periodic object in FFT Multi-Slice (FFTMS) method which is now routinely used for the simulation of HREM images from periodic objects.In a systematic study of the problem of induced numerical artifacts, a new method has been proposed for the HREM image simulation of non-periodic objects. It is based on some improvements in the calculation of the phase grating and the propagation operator to the Real Space Multi-Slice (RSMS) method, which are compatible with a non-periodic object.It can be seen from the comparison with the experimental HREM images that much more better agreement can be obtained by using Real Space Multi-Slice method for Non-periodic objects (RSMSN).