Showing papers on "Transmission electron microscopy published in 1974"

Conversion of Si to epitaxial SiC by reaction with C2H2

Abstract: The growth of β‐SiC films on Si by reaction of a Si single crystal with C2H2 has been studied for the conditions 10−7 ≤PC2H2≤5×10−4 Torr, 800≤T≤1100°C, in both high‐ and ultrahigh‐vacuum chambers. At C2H2 pressures below approximately 10−5 Torr, linear growth kinetics were observed over the temperature range investigated and the reaction probability was determined as 0.02–0.03. In this pressure range growth occurs by the diffusion of Si through porous defects incorporated in the growing film. We have studied in detail the structure of defected films formed under various growth conditions by scanning electron microscopy, scanning transmission electron microscopy, and transmission electron microscopy. We conclude that the occurrence of defects is intrinsic to the mechanism of film growth. The predominant defect type consists of a shallow (∼ 2000 A) pit in the Si substrate, over which the growing SiC assumes a porous polycrystalline morphology. The number and areal densities of these defects are proportional to the C2H2 partial pressure and the SiC film thickness, respectively. The defects act as sources of Si for reaction, and film growth occurs via diffusion of Si from the substrate through the porous overgrowth to the epitaxial SiC/vacuum interface, where reaction occurs. For C2H2 pressures exceeding approximately 10−5 Torr the porous defects are sealed off at an early stage in the growth and further reaction is virtually arrested due to the extremely small bulk and/or grain boundary diffusivity for Si in SiC over the experimental temperature range. No significant effect on growth rate due to the type of vacuum system used was found.

The microstructures of silicon nitride ceramics during hot-pressing transformations

Abstract: The microstructure of silicon nitride hot-pressed with a magnesium oxide additive has been studied by transmission electron microscopy. This includes material at various stages in a hot-pressing process: the initial (∼ 90%α) silicon nitride powder; specimens partially densified and partially transformed from α-silicon “nitride” (Si11.5N15O0.5) to β-silicon nitride (Si3N4); and almost fully dense and fully transformed β-Si3N4. The observations substantiate a solid/liquid/solid transformation mechanism, whereby Si and N are transported from α grains through a silicate liquid phase to nucleation sites for β at α/liquid interfaces or to β grains nucleated homogeneously in the liquid phase.

An energy filter for biological electron microscopy.

Abstract: SUMMARY A prism-mirror-prism electron energy filter has been inserted into a fixed beam transmission electron microscope. The insertion of the filter has not degraded the spatial resolution of the microscope, while providing an energy resolution of 2.5 eV. The filter greatly reduces the chromatic aberration of the images, increasing resolution in dark field and contrast in bright field. Images of bacteriophage T4 and of polyoma virus indicate that thick unstained and unshadowed biological specimens can now be observed at high resolution in dark field. In addition, the increased contrast and definition observed in bright-field images of conventional liver sections suggest that it should be possible to obtain sufficient contrast from stains containing atoms of lower atomic numbers than those employed at present.

New methods for surface ultrastructure: Comparative studies of scanning electron microscopy, transmission electron microscopy and replica method.

Abstract: When we have talked about electron microscopy in the past 10-15 years, it meant transmission electron microscopy (TEM). In TEM the thickness of the section should be less than 0.1 /x, preferably 0.05 IX, because, like light in light microscopy, the electron beam which is relatively weak should pass through the specimen to form an image. Resin instead of paraffin should be used for embedding the specimen and for cutting of such thin sections, a diamond knife is usually used in a sophisficated microtome. Although the resolution of the image (4/10,000 /x) in TEM was fantastically better than that of the light microscope, (1/10 /i) as applied to biological materials, TEM was a poor instrument to observe the surface of relatively thick materials. We definitely needed an ultrastructural counterpart of phase contrast or Nomarski differential interference contrast optics.

Dislocation Structures in Sapphire Deformed by Basal Slip

Abstract: Dislocation structures in sapphire deformed by basal slip at 1200° to 1500°C were studied by transmission electron microscopy. Long dislocation dipoles of edge character are formed by interactions of dislocations on parallel basal planes (“edge-trapping”); screw dislocations annihilate by cross-slip. The accumulation of dislocation dipoles leads to work-hardening, but the dipoles also break up into smaller loops by climb, causing recovery. Eventually a steady state of zero work-hardening is reached, where the rate of accumulation of dipoles by edge-trapping is equal to their rate of annihilation by climb. From these observations, it is suggested that dislocation climb plays an important role in the deformation process for basal slip in the range 1200° to 1500°C.

Electron microscopic study of the crystallization kinetics of the amorphous alloy Pd80Si20

Abstract: Amorphous Pd 80 Si 20 foils, prepared by the rapidly rotating mill device method, were quenched from the liquid state, temperatures of the melt being 1100, 1500 and 1600°C. The foils were linearly heated at a rate of 1.5 °C/min over a temperature range of 20–600°C. The structural changes were observed by methods of optical microscopy, transmission electron microscopy and electron diffraction. The beginning of crystallization of the amorphous phase is affected by the temperature of the melt. The crystallization of the amorphous phase was terminated at a temperature of 390–400°C. Silicides Pd 9 Si 2 and Pd 3 Si, the morphology of which varied with temperature, were formed during crystallization.

Transmission electron microscopy of ion beam thinned dentine.

Abstract: Transmission electron microscopy (TEM) samples of dentine were prepared by ion beam thinning using a liquid nitrogen cooled holder, 4 to 5 kV Ar+, 70–100 μA beam. The samples were fresh, unfixed, and not subjected to mechanical deformation or dissolution. They were examined at 80 or 100 kV in the TEM, when contrasts were due entirely to the mineral component. Parallel pairs of elongated electron dense features extended for distances exceeding the collagen D period, appearing as electron dense circles in “transverse section”. These images are interpreted as indicating the deposition of mineral around collagen microfibrils. The repeat distance between close packed pairs of dark lines ranged from 38 A upwards. There was little regular packing of the electron dense circles (or dots) seen in “transverse section”.

Study of crystallization in lithium silicate glasses using high-voltage electron microscopy

Abstract: The early stages of crystallization in a lithium disilicate glass were studied by high-voltage transmission electron microscopy and diffraction at 1000 kV, using thin sections prepared from the bulk material. Heat treatment of the glass in the range 450°-500°C produced large numbers of internally-nucleated lithium disilicate crystals. These consisted of small faceted single-crystal plates parallel to (010) planes and elongated along [001]. Within the crystals, regions of a darker contrast and distinct shape were observed, which contained a high defect concentration. The presence of planar growth-faults in the crystals was indicated by streaking of the diffraction spots. New branches formed on many of the crystals, probably by a twinning mechanism. The regular nature of this branching explains the morphology of crystallization observed after prolonged growth. The effect of an addition of P2O5to the glass composition on the crystal morphologies was also studied.

Re-Exposure of Tapes at High Temperature and Pressure in the Lycopodium Clavatum Spore Exine

Abstract: Lamellations are visualizable through the staining commonly used in transmission electron microscopy during exine formation on Lycopodium and other spores, and the nexine of pollen grains. The lamellations so exposed consist-of dark tapes at either side of an unstained (white) line. Neither tapes nor white lines are visualizable in the exine of mature spores of Lycopodium. The continued presence of lamellations having tape-white line spacing has been demonstrated with inorganic tracers in the nexine of pollen in which lamellations otherwise appeared to be absent. Through high contrast staining methods for TEM we have observed lamellations in the residual exine following heat treatment (350[ddot]C) of mature spores of Lycopodium clavatum. The surface of these residual exines was etched by treatment with hot 2-aminoethanol and filaments were observed to protrude from the etched surfaces. The residual exine stained darkly. Lycopodium spores heated to 300[ddot]C at 1 kb pressure had long filaments ex...

Electro-erosion of metal surfaces

Abstract: Craters produced by single electrical discharges in kerosene under conditions similar to Electro-Discharge Machining were formed on the following metals: Al, Cr, Cu, Fe, Mg, Mo, Nb, Ni, Ta, Ti, V, W, and Zn. Anode and cathode crater volumes were measured by a profilometer imaging technique and except for Nb, Mo and Ta, the cathode craters were always found to be larger. An empirical equation was developed to relate the volume of the electro-erosion craters formed to the physical properties of the electrodes. Crater morphology and surface texture were studied using both Scanning and Transmission Electron Microscopy. An Electron Microprobe was used to determine the distribution of cross deposited metal in the case of dissimilar electrodes. Crater volumes and morphologies resulting from single electrical discharges in liquid and dry nitrogen were shown to be radically different from those produced in kerosene.

Studies of voids in neutron-irradiated aluminium single crystals: I. Small-angle X-ray scattering and transmission electron microscopy

Abstract: Small-angle X-ray scattering and transmission electron microscopy experiments have been performed on high-purity (99·9999+ %) aluminium single crystals that were neutron-irradiated to a fluenoe of 1·5 × 1021 n/cm2 (>0·18MeV) at 50°C. The volume changes determined by each technique are in reasonably good agreement. Evidence for scattering effects resulting from faceting of the voids is presented. Assuming a truncated octahedral void shape, the ratios of the third to the second moment of the distribution of void sizes determined by both SAXS and TEM are in excellent agreement. The effects of isochronal annealing on the swelling have been followed to near the melting point. The annealing-out of voids was clearly seen; no evidence was found for bubble formation at elevated temperatures.

A study of the adhesion of polyethylene to porous alumina films using the scanning electron microscope

Abstract: An adhesive bond was formed by sintering low-density polyethylene onto aluminum with a porous anodic film. The topography of the polymer surface in contact with the anodized aluminum was studied in a scanning electron microscope, having removed the aluminum and alumina by dissolution in aqueous sodium hydroxide. The surface of the polymer appeared very rough with large projections of various forms, all of which were many times larger than the pores revealed in the anodic films by transmission electron microscopy. These projections are shown to consist, most probably, of “stacks” or “tufts” of much smaller polyethylene fibers, each of which had entered a pore in the anodic film. Thus, the scanning electron-microscopic investigation confirms the keying mechanism for the adhesionof polyethylene to porous anodic films on aluminum proposed in an earlier paper.

The X-ray diffraction and electron microscopic investigation of stable and metastable equilibria in Al-rich Al-Zn alloys

Abstract: The solvus line for the metastable cubic α′-phase and for the stable α- and α′-solubility limit for Al-Zn alloys with zinc content from 15 to 50 wt.% were determined. X-ray diffraction on single crystals was used to study the structures of phases developed during the applied heat-treatments. The dissolution of α′-phase at temperatures close below and above the determined solvus temperatures was observed by the transmission electron microscopy. The shift of the known (α+α′)-phase boundary to lower temperatures of about 8 °C was found. Similarly, small changes were obtained in the shape of the curve giving the solid solubility limit of Zn in Al.

Evidence of a precipitatelike zone in as‐grown GaAs and its influence on optical absorptivity

Abstract: A defect structure, consisting of very small roughly cylindrical zones, was found in as‐grown GaAs during observation by transmission electron microscopy. The zones are one atomic plane thick and 10–20 A in length, lying parallel to 〈110〉. The density of defects in all samples observed was uniform at approximately 1017 cm−3. By using the results of a calculation of the optical absorptivity attributable to these defects and by assuming intermediate metallic conductivity, excellent agreement between theoretical and observed absorptivity was obtained.

Direct observation and identification of long‐period structures of SiC by transmission electron microscopy

Abstract: Transmission electron microscopy has been used for the observation of polytypes of SiC having very long periods. The periodicity of these structures can be observed from the direct resolution of structural lattice periods and from the diffraction patterns. The actual structures can be determined from the intensity distribution in the diffraction pattern, and this has been done for two of the structures. These have been identified as [(33)1632]3 or 303R and [(33)634(33)434]3 or 222R, two hitherto unknown structures. A mechanism for conveying the long‐distance information concerning the stacking order which leads to stabilization of the long‐period structures in SiC is suggested. This mechanism essentially involves a transformation from a basic structure of short period to accommodate a constraint from the surroundings.

Oxide structure in evaporated aluminum films

Abstract: Transmission electron microscopy, small‐angle and selected‐area diffraction, and surface‐plasmon dispersion studies are used to characterize the microstructure of evaporated aluminum films. The grain size of the films is obtained from the width of the Bragg reflections. Energy‐loss studies show that the surface‐plasmon dispersion is a function of the average grain size for films grown at low condensation rates, i.e., ``dirty'' films, while the average surface‐plasmon energy for all films, ``clean'' and ``dirty'', is close to 6.7 eV, the value characteristic of an aluminum‐aluminum oxide interface. In clean films the dispersion depends on thickness in the normal fashion and no dependence on grain size is detected. We conclude that in dirty films a thin layer of oxide surrounds each grain. Small‐angle electron scattering and out‐of‐focus transmission electron microscopy identify a cluster effect in which somewhat larger oxide boundaries surround clusters of approximately 36 grains (in most films). A similar...

Particle growth in flowing inert gases

Abstract: Fine particles of Zn, Mn, and Se are produced in a flowing system of argon gas. The experimental geometry is described, and the effect of experimental parameters (metal vapor pressure, gas flow rate, and oxidants) is characterized. These particles are studied using a transmission electron microscope in both imaging and electron diffraction modes. Mn and Zn formed well‐defined crystals as verified by electron diffraction, while Se did not. Even small amounts of oxygen inhibited the proper crystal growth.

The application of X-ray analysis in the transmission electron microscope to a study of drug distribution in the parasite Schistosoma monsoni (Platyhelminthes)

Abstract: SUMMARY The distribution of sodium antimony dimercaptosuccinate in the helminth parasite Schistosoma monsoni was determined using a transmission electron microscope (TEM) fitted with an X-ray non-dispersive analysis system. Both Araldite and cryosections of the parasite were examined. The drug was found to have a marked effect on some cells of the ovary and vitelline gland and it was within these cells that the drug was demonstrated. Within the vitelline cells the drug was confined to the vitelline droplets and the analysis of both Araldite and cryosections confirmed that the absence of drug from other tissues was genuine and not due to loss during processing. Maximum retention of elements was achieved in cryosections and this type of material also enabled one to distinguish elements genuinely associated with the tissues from those present in the Araldite matrix. The combination of X-ray analysis with TEM and cryosectioning has provided a most valuable tool for the study of drug distribution at tissue and subcellular levels and also enabled the elemental characteristics of the tissue at the precise drug locus to be determined.

Light and electron microscopic studies of retzius lines in human cervical enamel.

Abstract: Unaltered mature enamel and partially demineralized mature enamel from the cervical third of human permanent teeth were examined by means of transmission electron microscopy, microradiography, phase contrast and Nomarski differential interference microscopy. The Retzius lines in the outer third of the cervical enamel had a staircase configuration. The steps in the stair-case pattern formed the bases of triangular regions which were radiolucent and ultrastructurally contained fewer crystallites than the adjacent enamel. In the outer prismless layer, the Retzius lines had a curvilinear configuration and were also crystallite deficient. The structure of the Retzius lines in the inner portion of the cervical enamel was not nearly as well defined.

Fine structure of the cuticle of female Onchocerca volvulus.

Abstract: The fine structure of the cuticle of adult female Onchocerca volvulus, a tissue-dwelling nematode parasite of man, was studied. Although the cuticle is composed of the 3 layers characteristic of nematodes (cortex, matrix, and fiber), there were also unusual features. The most notable modification is in the trilaminate membrane, which covers the external surface of the cuticle. Scanning (SEM) and transmission (TEM) electron microscopy disclose that this membrane is projected into numerous folds, substantially increasing the surface area. Many authors have described the fine structural morphology of the cuticle of various species of nematodes (Watson, 1965a, b; Lee, 1966a, b, 1970; Bonner and Weinstein, 1972). Most nematode surfaces are smooth except for annulations (Weise, 1973), but microvilli have been observed on the surface of Bradynema sp. (Riding, 1970), which inhabits the hemocoel of insects. A light microscopy study of Onchocerca volvulus (Neafie, 1972) shows little more than a deeply striated cuticle. Since this nematode resides within a subcutaneous fibrotic nodule of host origin for long periods of time, the possibility of cuticular structural specialization exists. Therefore a study of the fine structure of the cuticle of adult female 0. volvulus in situ was undertaken. MATERIALS AND METHODS Transmission electron microscopy (TEM) Nodules containing 0. volvulus adults were excised from the subcutaneous tissue of persons living in the endemic area of San Pedro Yepocapa, Guatemala. These nodules were placed immediately into either ice-cold glutaraldehyde buffered with 0.1 M cacodylate (pH 7.2) or into 10% formalin. The nodules were then cut into small pieces and placed into fresh fixative overnight, rinsed in 0.25 M cacodylate buffer, and postfixed Received for publication 4 February 1974. * Supported, in part, by Research Grant AI-02347 from the NIH. in ice-cold 1% OO04 in 0.25 M cacodylate-HCl (pH 7.2) for 3 hr. Adult female worms were teased free from formalin-fixed tissue, rinsed in 0.25 M cacodylate-HCl (pH 7.2), and postfixed in 1% OO,4 in 0.25 M cacodylate-HCl (pH 7.2). Dehydration in all cases was in ethanol and propylene oxide with embedment in Araldite 502. Thin sections were cut with diamond knives on a Reichert OmU2 ultratome, mounted on naked 200/300 mesh copper girds, and stained with uranyl acetate (Watson, 1958) followed by lead citrate (Reynolds, 1963). A Hitachi HU-11A electron microscope, operating at 50 kv, was used for viewing and recording at initial magnifications up to 60,000X. Scanning electron microscopy (SEM) Adult female worms were teased from nodules fixed in 10% formalin, followed by postfixation in 1% Os04 in 0.25 M cacodylate-HCl (pH 7.2). Anterior, middle, and posterior portions were selected. These were then dehydrated through ethanol to amyl acetate, critical point dried and coated with gold-paladium. Viewing was on an AMR Model 1000 scanning electron microscope, operating at 10 kv, with original magnifications of 1,000 and 5,000X.

Transmission Electron Microscopy of Hydrated Dicalcium Silicate Thin Films

Abstract: A method of preparing calcium silicate hydration products for transmission electron microscopy is presented. Thin films of dicalcium silicate are evaporated onto substrates and hydrated in a vacuum chamber. Since the resulting hydration products are undisturbed, the interrelations of the species can be studied. The technique provides specimens suitable for high-resolution microscopy. This method produces hydration products like those reported when conventional specimen preparation techniques are used. Calcium silicate hydrate gel, two forms of C-S-H II (fans and fiber bundles), afwillite, and Ca(OH)2 morphologies were observed. Coevaporated CaCl2 additions improve the electron diffraction patterns obtained from the C-S-H II fan structures but increase shrinkage of these structures on drying.

Electron microscope study of silver colloids in KCl : Ag

Abstract: Transmission electron microscope studies of the colloids of silver in KCl : Ag crystals show that the colloidal particles are spherical in shape and have a size distribution among them. Using the observed size distribution and modified optical constants for small metal particles by the Kawabata‐Kubo method and Mie's theory, the calculated shapes of the optical bands agree well with the observed band shape.