Showing papers on "Transmission electron microscopy published in 1979"

Principles of Thin Film X-Ray Microanalysis

Abstract: The scanning electron microscope-electron probe microanalyzer (SEM-EPMA) and transmission electron microscope (TEM) are two established tools for microscopy. The first instrument enables one to obtain high magnification pictures as well as microchemical information from micron sized areas in solid samples. The second instrument enables one to obtain high magnification pictures and diffraction data from electron transmission thin specimens. Over 10 years ago DUNCUMB (1968) mounted a wavelength dispersive x-ray spectrometer on a TEM in order to obtain chemical and structural as well as diffraction data from the same area of a thin specimen. This idea of a combination instrument has developed rapidly in the last few years into the scanning transmission electron microscope—analytical electron microscope (STEM-AEM) instrument of today. In the modern version of this instrument a 60 to 200 kV electron beam is focused to < 100 and often to < 10 nm diameter at the specimen surface. Scanning coils move the focused beam over the specimen to obtain a STEM image. The emitted x-rays are measured with an energy dispersive x-ray spectrometer (EDS). Quantitative electron probe microanalysis can be accomplished when the focused beam is positioned at selected points on a specimen. In addition, particle identification and x-ray scanning can be performed with this instrument.

Aluminum‐silicide reactions. I. Diffusion, compound formation, and microstructure

Abstract: Material reactions as a result of thermal treatment were studied on thin‐film Al/silicide/Si systems with CoSi2, PtxNi1−xSi, and MoSi2 for the silicide. Auger electron spectroscopy and Rutherford backscattering analysis showed the transport of Si and the metal released from the silicide into the Al and transport of Al into the silicide. X‐ray diffraction showed the formation of Co2Al9 at 400 °C, PtAl2, NiAl3, and PtNiAl2 at 275 °C, of which the latter disappeared above 450 °C, and MoAl12 at 535 °C, as well as free Si. The Co2Al9 formation followed a linear time dependence with an activation energy of 2.3 eV. The MoAl12 formation followed a parabolic time dependence with an activation energy of 3.6 eV. A thin tungsten layer between Al and the silicide proved to be effective as a diffusion barrier below 500 °C, at which temperature WAl12 was formed. The microstructure was studied by scanning and transmission electron microscopy, electron microprobe analysis, and scanning Auger electron spectroscopy. The reaction resulted in the formation of Si islands with a size up to about 10 μm, containing Al‐rich inclusions, and the intermetallic compound with Si inclusions in between the islands.

The change in properties of the stratum corneum as a function of depth.

Abstract: The constancy of stratum corneum thickness suggests an ordered decrease in intracorneal cohesion binding forces. In this study, intracorneal cohesion was measured in the vertical dimension by cohesography and the number of cells released after applying a standardized stimulus was determined before and after repeated stripping of the same sites with adhesive tape. In addition, surface replicas and the corneocytes from different levels were examined by scanning and transmission electron microscopy and differential phase interference microscopy. The results indicate a gradual loss of cohesion within the stratum corneum towards the surface and that anatomical changes take place in the corneocytes as they progress towards the surface.

Interstitial supersaturation near phosphorus‐diffused emitter zones in silicon

Abstract: Bipolar transistors with consecutively diffused boron base and phosphorus emitter showing the ’’emitter‐push effect’’ have been investigated by transmission electron microscopy. The analysis of isolated dislocation helices in the emitter and base regions indicates the presence of a self‐interstitial supersaturation in front of the phosphorus‐diffused zone. This result refutes the widely accepted explanation of the ’’emitter‐push effect’’ in terms of a phosphorus‐induced vacancy supersaturation.

Initial stages of recrystallization in aluminum of commercial purity

Abstract: In commercial aluminum with a purity of 99.4 pct, the formation and growth of recrystallization nuclei were studied by techniques such asin-situ annealing in a high voltage electron microscope, transmission electron microscopy and light microscopy. Sample parameters were the initial grain size (370 and 19 microns) and the degree of deformation (50 and 90 pct reduction in thickness by cold-rolling). It was found that the initial grain boundaries and high angle boundaries within the original grains are preferential sites for recrystallization nuclei, and that the effect of such sites is enhanced by the FeAl3 particles present in the commercial aluminum as impurities. The nucleation temperatures determined by high voltage electron microscopy and transmission electron microscopy decrease markedly when the initial grain size is decreased both after 50 and 90 pct cold rolling; a less pronounced temperature decrease is obtained by increasing the degree of deformation. The size of the recrystallization nuclei, the recrystallization temperature and the recrystallized grain size are reported for the four sample states, and finally the structural and kinetic observations are discussed.

Microstructural evaluation of multicomponent ZnO ceramics

Abstract: A microstructural evaluation was made of experimental non‐Ohmic ZnO ceramics by optical, scanning, and transmission electron microscopy complemented with electron beam microprobe and x‐ray analyses. Four crystalline phases were identified: a major phase of ZnO grains containing Co and Mn in solid solution and three minor phases of bismuth silicate (12 Bi2O3⋅2SiO2), pyrochlore (Bi2[Zn4/3Sb2/3]O6) and spinel (Zn7Sb2O12) in the intergranular region. Transmission electron microscopy revealed that the ZnO grains are mostly in direct contact with each other and that the intergranular phase is located primarily in the multiple grain junctions. In those regions where ZnO grains are in contact with each other, the measured grain‐boundary width was ?25 A. It is suggested that the barrier to conduction in ZnO varistors resides in the vicinity of the grain boundary within the ZnO grains and not in the intergranular insulating layer.

Crystallization Mechanisms in Glass‐Ceramics

Abstract: Transmission electron microscopy, electron diffraction, and microprobe X-ray analysis were used to study crystallization of glasses in the systems Li2O-SiO2, BaO-SiO2, and Li2O-A12O3-SO2. The ternary system, with 4 mol% TiO2 added to an Li2O-Al2O3-4SiO2 composition, crystallizes with a simple morphology of equiaxed grains of the β-quartz metastable phase which transforms at higher temperatures to the stable β-spodumene structure. The binary systems exhibit a more complex crystallization morphology dictated by crystal anisotropy, temperature, impurity content, and susceptibility either to intermediate-phase formation (BaO-SiO2) or to liquid immiscibility (Li2O-SiO2). The initial crystal growth units formed in these systems are frequently two-phase branched morphologies many micrometers in diameter. They may be recrystallized to form polycrystalline glass-ceramics with submicrometer grain sizes.

Visualization of subsurface structures in cells and tissues by backscattered electron imaging.

Abstract: A fraction of the beam electrons which interact with a specimen scatter back. The number of backscattered electrons (BE's) increases with the atomic number of the elements encountered. Cell and tissue structures lacking a heavy metal content yield few BE's compared to structures affixed with heavy metals, either vitally or by means of staining methods applied after fixation. The BE imaging mode of a scanning electron microscope (SEM) provides an intensity map of the BE yield from the specimen. BE imaging of selectively stained structures in cells and tissues renders these structures visible in contrast to the unstained surround. Since BE's can emerge from a significant depth within the material, BE imaging can be used to view such heavy metal stained structures beneath intact cell surfaces. The microcontours of the overlying surface can be viewed concurrently by using the surface scanning (i.e., the secondary electron imaging; SEI) mode of the microscope. Methods for selectively contrasting subsurface structures can be adapted from existing light microscope (LM) and transmission electron microscope (TEM) methods. Staining methods have been devised for subsurface viewing of cell organelles, including nuclei, mitochondria, peroxisomes, lysosomes, and phagosomes. A physical model is presented which describes these observations and suggests future possible trends in this subject. Specifically the image contrast and resolution are described in terms of the physical properties of the stain and specimen and of the SEM operating conditions of energy and current. Finally a summary of instrumentation considerations describes present and potential BE detectors, their ancillary electronics, and image processing.

The characterization of highly‐zinc‐doped InP crystals

Abstract: Highly‐zinc‐doped InP crystals, grown along the 〈111〉 direction by the liquid‐encapsulated Czochralski technique, have been characterized by x‐ray topography, transmission cathodoluminescence, and transmission electron microscopy. It is observed that high zinc doping improves the perfection of crystals insofar as dislocations are concerned. However, not all of the dopant atoms are in solid solution, and it appears that some have clustered to form a high density (∼4×108 cm−2) of fine precipitates with an average size of ∼675 A.

Optical and electron microscopy of niobium crystals deformed below room temperature

Abstract: Pure niobium crystals have been deformed at 77 and 158 K at a strain rate 8 × 10−1 s−1. For crystals with a wide range of Orientations the deformation took place mainly by slip on the anomalous (011) plane. The nature and extent of the slip lines were studied by optical microscopy using Nomarski interference contrast. Thin foils were prepared from many crystals, with sections being taken parallel to a number of planes, and examined in a transmission electron microscope. The dislocation structures observed are described in some detail. A model for anomalous (011) slip is proposed which explains many of its characteristics.

Spherical-Aberration Correction of an Electron Lens by Holography

Abstract: Electron image holograms of a crystalline fine particle are made with a field emission electron microscope. The spherical aberration of the electron lens is corrected in the optical reconstruction stage, using an optical lens as a compensator. Lattice images separated from the particle in the exactly focused electron microscopic image are formed inside the particle in the spherically corrected image and give correct information on the crystal lattice of the gold particle.

A transmission electron microscopy study of the defect microstructure of Al2O3, subjected to ion bombardment

Abstract: The defect microstructure induced in single-crystal aluminum oxide by bombardment with high-energy ions has been studied by transmission electron microscopy (TEM). The effects of the irradiation temperature, the type of ion used for irradiation, and the presence of inert gas atoms upon the microstructure were examined in detail. The intrinsic, displacement-induced defect structures which resulted from ion bombardment appeared quite similar to the microstructures of aluminum oxide subjected to fast neutron or high energy electron irradiation at similar temperatures and doses. The most significant changes in the microstructure were caused by bombardment with helium ions. Implantation of helium into alumina at low temperature followed by annealing at high temperature resulted in the formation of a dense dislocation network. The large number of defects required to account for this network may have arisen from strong trapping of helium by radiation-induced vacancies, which left a large population of i...

Electron Microscopic Studies of Structure and Crystallization of Amorphous Metal Oxide Films

Abstract: High-resolution transmission electron microscopy using axial beam illumination was carried out on vacuum-deposited WO3, TiO2, and MoO3 films. In as-deposited WO3 films thinner than 100 A and films heated at 350°C for 2~5 h which gave rise to amorphous haloes in electron diffraction, crossed fringe-like structure images of the order of 10~20 A was observed. This means that the amorphous films consisted of micro-crystallites in which the W–O6 octahedra were arrayed like crystalline WO3. When the films were heated at 350°C for 10 h, they grew to crystallites of WO3 as large as 100 A. On the other hand, in WO3 films thicker than about 200 A, crystals of a few microns grew after shorter heat treatment. Similar results were obtained for the TiO2 and MoO3 films. The differnce in crystallization between the very thin films and the thicker films is interpreted by considering the heat generated during crystallization and its dispersion.

The identification of single-domain titanomagnetite particles by means of transmission electron microscopy

Abstract: A basalt sample dredged from the axis of the Mid-Atlantic Ridge has been ion-thinned and examined by transmission electron microscopy. Finely dispersed particles as small as 0.04 μm in diameter, occurring in amorphous patches of the rock, have been identified as titanomagnetite by means of electron diffraction and microanalysis. These small particles have dimensions appropriate to single magnetic domain behaviour, and are considered to be largely responsible for the strong and very stable natural remanent magnetization of this rock.

The Measurement Of Excess Volume At Grain Boundaries Using Transmission Electron Microscopy

Abstract: SUMMARY A technique enabling accurate measurements of relative displacements between adjacent coincidence related crystals has been described previously. The technique depends on intensity measurements of stacking-fault-like fringes by comparison of experimental and theoretically simulated fringe profiles. This matching procedure is illustrated in the present work for a (l2l) boundary between twin related aluminium crystals. The main part of the paper describes the application of the technique for measuring excess volume at certain coincidence boundaries, and considers in detail the measurement for (l2l) boundaries. The excess volume per unit area at (l2l) boundaries is found to be 0·02 nm.

Laser‐induced metal‐to‐semiconductor phase transition in mixed Al‐Sb films

Abstract: Metallic films consisting of overlapping polycrystalline layers of, alternatively, Al or Sb atoms in overall equal proportions are irradiated at 300 °K with 80‐mJ/cm2 microsecond dye laser pulses of 2‐eV photon energy. Using transmission electron microscopy, electron diffraction, optical transmission, and conductivity measurements, the presence of semiconducting AlSb is fully identified in systematically all the irradiated films after one single pulse, giving unambiguous evidence for a phase transition between the layered fcc‐rhomboedric metallic structure and the blende structure of AlSb.

The mechanism of optically induced degradation in InP/In1−xGaxAsyP1−y heterostructures

Abstract: Optically degraded regions in In1−xGaxAsyP1−y layers, grown on (001) InP substrates by liquid phase epitaxy, have been examined in detail by transmission electron microscopy. It is shown that these areas are associated with dislocation clusters or bundles which are aligned parallel to the 〈100〉 directions. We conclude that the observed features develop by nonradiative‐recombination‐enhanced glide of threading and inclusion‐generated dislocations present in the layers.

Experimental coarsening of antiphase domains in a silicate mineral.

Abstract: Combined annealing experiments and observations by transmission electron microscopy show that in natural pigeonite crystals antiphase domains coarsen approximately according to a rate law in which the tenth power of the average domain size is proportional to time. This result suggests that certain cations (possibly Ca 2+ ) were segregated preferentially onto the antiphase boundaries. The domain size in samples quenched from above the high-low transformation temperature is large and apparently independent of annealing time and temperature. It appears that large domains can be generated either by very fast or by very slow cooling; thus the estimation of geological cooling rates from the sizes of antiphase domains in natural samples becomes rather difficult.

Tem Study Of Amorphous Alloys Produced By Ion Implantation

Abstract: SUMMARY Ion implantation is a technique for introducing foreign elements into surface layers of solids. Ions, as a suitably accelerated beam penetrate the surface, slow down by collisions with target atoms to produce a doped layer. This non-equilibrium technique can provide a wide range of alloys without the restrictions imposed by equilibrium phase diagrams. This paper reports on the production of some amorphous transition metal-metalloid alloys by implantation. Thinned foils of Ni, Fe and stainless steel were implanted at room temperature with Dy+ and P+ ions at doses between 1018 and 1021 ions m−2 at energies of 20 and 40 keV respectively. Transmission electron microscopy and selected area diffraction analysis were used to investigate the implanted specimens. Radial diffracted intensity measurements confirmed the presence of an amorphous implanted layer. The peak positions of the maxima are in good agreement with data for similar alloys produced by conventional techniques. Only certain ion/target combinations produce these amorphous layers. Implantations at doses lower than those needed for amorphization often result in formation of new crystalline phases such as an h.c.p. phase in nickel and a b.c.c. phase in stainless steel.

Electron Microscopical Techniques For The Observation Of Cavities

Abstract: SUMMARY The full range of methods by means of which cavities can be examined using a transmission electron microscope are reviewed. Different techniques are required in different circumstances and the extent to which a quantitative interpretation can be given is discussed for a number of examples. These range from the use of structure factor contrast for relatively large pores through the use of Fresnel contrast for intermediate sized pores with a dimension in the 0·4–20 nm range to elastic side band imaging and atomic resolution techniques for pores with sizes less than about 0·6 nm.