Showing papers on "Transmission electron microscopy published in 1975"

The preparation, examination and analysis of frozen hydrated tissue sections by scanning transmission electron microscopy and x-ray microanalysis.

Abstract: A method is reported for preparing, examining and analysing frozen hydrated tissue sections using transmission electron microscopy and X-ray microanalysis. Use of this method permits localization and measurement of water soluble or diffusible elements within the hydrated cell matrix. Since any change in total fresh weight of the specimen will affect the concentration of all components, great care has been taken to demonstrate that the mass neither increases nor decreases and to ensure that the tissue remains frozen-hydrated. Criteria for assessing whether or not the tissue remains frozen-hydrated are reported. After quench freezing, 1-2 mum thick sections of mouse liver were cut at 193 degrees K and picked up on a specially designed annular specimen holder covered with an aluminium coated nylon film. Using a transfer device which prevents contamination of the tissue sections while maintaining them at a low temperature (below 143 degrees K), the sections are transferred either to the vacuum evaporator cold stage or the scanning microscope cold stage. The tissue sections may be coated with an aluminium layer to improve electrical and thermal conductivity. The specimens are examined in the scanning transmission imaging mode and analysed using an energy dispersive X-ray analyser. Concentration of intra-nuclear and intra-cytoplasmic K, P, S and Cl are reported for mouse hepatocytes as ratios of the characteristic radiation to the continuum radiation used as a measure of mass. Ratios for all four elements were higher in the nucleus than the cytoplasm. Examples are given of this method as applied to plant and insect tissue.

In situ observations of crystalline oxide formation during aluminum and aluminum alloy oxidation

Abstract: Anin situ morphological study of the oxidation of electron transparent specimens of aluminum and aluminum alloys containing zinc and magnesium has been carried out in the temperature range 400 to 520°C using the hot stage of a 1 MeV transmission electron microscope. The structure and morphology of the crystalline oxide produced in each alloy has been carefully examined by selected area electron diffraction and stereomicroscopy. In pure aluminum, oxidation takes place after a temperature dependent induction period, by the nucleation of crystalline γ-Al2O3 at the amorphous oxide/metal interface. This process is delayed by additions of zinc which modify the structure of the oxide. In alloys containing magnesium, oxidation takes place by the rapid nucleation and growth of MgAl2O4 or MgO, with a secondary form of magnesia developing from the reduction of the amorphous γ-Al2O3 surface layer.

Additive and Impurity Distributions at Grain Boundaries in Sintered Alumina

Abstract: Additive and impurity distributions at grain boundaries in sintered Al2O3 were determined using a scanning Auger microprobe, transmission electron microscopy, metallography, and electron probe analysis. The results indicated that Ca was present uniformly at the boundaries as a segregant, whereas the Mg or Ni levels observed resulted from nonequilibrium spinel particles. The Ca concentrations were consistent with equilibrium segregation theory and followed an equilibrium segregation isotherm.

Scanning electron microscopy of the subarachnoid space in the dog. III. Cranial levels.

Abstract: Young dogs were anesthetized by intrathoracic injection of sodium pentobarbital and perfused with buffered aldehydes. Lining tissue samples from the cranial subarachnoid space were prepared for scanning electron microscopy (SEM) by postfixing in buffered OSO4. Samples were then dehydrated, dried in a Critical Point Drying System, and coated with carbon and palladium-gold. Specimens were viewed in a Cambridge S4 scanning electron microscope. After thorough scanning, selected samples were routinely prepared for transmission electron microscopy (TEM) and viewed in a Philips EM-200 transmission electron microscope. This study depicts the surface morphology of the meningeal linings of the cranial subarachnoid space. The cranial pia mater possesses natural gaps or fenestrations between cells. SEM reveals a more complex morphology of arachnoid trabeculae than previously interpreted from light and transmission electron microscopy. Many free cells are observed on the meningeal linings of the subarachnoid space. The present study establishes that these free cells are macrophages by means of definitive TEM correlates. Microvillous-like processes extending between macrophages and the pial surface are present. The frequency and the nature of these thin processes suggest the possibility of a plasmalemma-mediated system of communication.

Study of the diffusion of Au and Ag in Be using ion beams

Abstract: The diffusion of Au and Ag in single−crystal α−Be has been studied using ion beam techniques. The time−dependent diffusion profiles were monitored by ion backscattering. Diffusion couples were created both by ion implantation and by vapor deposition, with consistent results. Diffusion data were obtained at two temperatures, 665 and 780 °C, for both c and a crystallographic directions. Because of the low solid solubilities of Au and Ag in Be, ≲0.1 at.% at the above temperatures, a surface layer of ∼ 1000 A thickness was always present in which the solubility was greatly exceeded. During annealing this layer served as a source from which the solute diffused into the underlying Be. The surface layer was characterized by transmission electron microscopy in the case of Au implantation. No evidence of precipitation was found following the room−temperature implantation, but subsequent annealing above about 300 °C caused regions of AuBe5 to form in the layer. In the underlying bulk, the observed diffusion behavio...

Crystal growth and precipitation in thin films of amorphous Fe-Au alloys

Abstract: Metastable alloys of the Fe–Au system have been prepared by the vapour quenching technique. The films so obtained are studied by resistivity measurements and by transmission electron microscopy and diffraction. Alloys containing more than 60 at. % Fe are amorphous at low temperature and a transformation to a metastable b.c.c. solid solution occurs at a temperature ranging from 80 to 250 K when the concentration varies from 80 to 60 at. % Fe. A further annealing at higher temperature leads to the precipitation of a gold-rich f.c.c. phase which grows, in a platelet structure, from linear defects formerly observed in the metastable b.c.c. phase. Kinetic parameters of the crystallization and orientation relationship between the phases during the precipitation are determined.

Electron microscopy of silicon monophosphide precipitates in P-diffused silicon

Abstract: Precipitates of a second phase in P-diffused (111) and (110) silicon wafers were revealed by X-ray topography and studied by transmission electron microscopy. The structural data derived from the analysis of the images and the corresponding diffraction patterns resulted in agreement with the ones recently reported by Wadsten, in his X-ray study on synthetic SiP single crystals. Therefore the precipitates were assigned a SiP base-centred orthorhombic structure with a=3.51 A, b=20.59 A and c=13.60 A. The sign of the calculated values of the misfit parameters between the two phases and the morphology of the precipitates were related to the tensile stress induced by the phosphorus diffusion into silicon.

An examination of tellurium ion-implanted GaAs by transmission electron microscopy

Abstract: The effect of implanting high energy tellurium ions into single crystal GaAs has been investigated by transmission electron microscopy Results from annealing experiments on specimens implanted at room temperature show that two anneal stages centred near 200 and 600° C occur, the actual anneal temperature being dose dependent Non-crystalline surface layers were formed after implanting doses in the range 5×1013 to 5×1015 ions cm−2 at room temperature However, implanting similar doses at 180° C caused no change in crystallinity Thus the low temperature anneal stage which is the epitaxial recrystallization of the non-crystalline material, does not occur for the higher implant temperature The high temperature anneal stage is associated with the annealing out of tiny defects such as twins and/or stacking faults leaving a single crystal containing only dislocation loops The anneal stages observed by electron microscopy correlate with changes in sheet resistivity and Rutherford backscattering measurements on similar material It is suggested that changes in dislocation loop size and density at high temperatures are coincident with the attainment of electrical activity

High resolution electron microscope study of lattice images in biological apatites.

Abstract: SUMMARY Lattice (Fourier) images of crystallites in human bone and teeth, and calcified atherosclerotic plaque were studied using high resolution transmission electron microscope techniques. The lattice images observed in the normal and diseased calcified tissue were compared with the images of synthetic hydroxyapatite crystallites.

A comparative study in the transmission electron microscope and scanning electron microscope of intracellular structures in sheep heart muscle cells.

Abstract: The internal cellular structures of the sheep ventricular myocardium have been comparatively studied in the transmission electron microscope (TEM) and in the scanning electron microscope (SEM). For TEM studies the tissue was prepared according to standard methods. Thick sections (10 mum) of paraffin embedded material were, after they had been deparaffinized in toluene, critical point dried, coated with gold and examined in the SEM. The comparative TEM and SEM investigations revealed very good correspondence, and it is evident that the described preparation procedure for SEM has preserved the fine structures of myofibrils, mitochondria, T-Tubules and sarcoplasmic reticulum in an excellent life-like pattern. Of special interest was the three-dimensional demonstration of triads and circumferentially arranged T-tubules.

Epitaxial Growth and Structure of CdSe Evaporated in Vacuum onto Ge

Abstract: Films of were grown by focused electron beam evaporation in vacuain the 10−6 Torr range on the three singular faces of Ge. The structures of the films were examined by transmission electron microscopy. On (100) oriented substrates, epitaxy was obtained throughout the range of substrate temperatures from 350° to 450°C, and the films had the sphalerite structure in parallel alignment with the Ge. The diffraction patterns contained no satellite spots but streaks were present. On (110) oriented substrates the epitaxial growth range of temperatures was 300°–450°C. The films again had basically the sphalerite structure in (110) orientation but the domain‐form faulted structure was found in all the films. On (111) Ge surfaces, grew epitaxially at all temperatures from 350° to 450°C and had the sphalerite structure in (111) orientation. Streaks but no satellite spots were observed in the electron diffraction patterns. Well‐defined rosettes of Moire spots were observed in the transmission electron diffraction patterns of areas where comparable thicknesses of and Ge were present in the cases of both (100) and (111) substrates. These Moire diffraction patterns confirmed the parallel alignment of the films on (100) substrates but showed that on (111) substrates the films were azimuthally rotated through a small angle from the parallel orientation.

Electron microscopy studies of long‐period polytypes of SiC

Abstract: The structures of four long-period polytypes of SiC found in a sample of reaction-sintered material have been analyzed using transmission electron microscopy. Those structures which have been positively identified are 303R or [(33)16(32)]3, 180R or [(23)11(32)]3 and 222R or [(33)6(34) (33)4(34)]3. The fourth structure is tentatively identified as 150R or [(34)5(23)3]3. The lack of conclusive identification for this structure is due to structural irregularities throughout the very small size of this grain. The frequency of observing long-period structures in reaction-sintered SiC is quite high, especially when the grain size is small.

Void formation during annealing of neutron-irradiated molybdenum

Abstract: Examination by transmission electron microscopy of molybdenum specimens neutron-irradiated at 60°C with doses of 2·16 × 1018 and 10·6 × 1018 fast neutrons cm−2 has revealed the presence of voids with diameters up to 60 A. This observation corroborates earlier conclusions based on positron annihilation measurements.

Enhanced crystallinity of silicon film deposited at low temperature

Abstract: Silicon thin films were vacuum deposited onto fused quartz at 600 °C with a prior coating of ultrathin aluminum layer (∼ 500 A). Significant increase in crystallinity was observed from both x−ray diffraction and transmission electron microscopy studies. The problem of handling aluminum film at this temperature in a vacuum of 1×10−6 Torr is discussed, and distribution of aluminum in the silicon film is studied using Auger spectroscopy.

High resolution scanning electron microscopy at the subcellular level.

Abstract: SUMMARY Recently developed scanning electron microscopes provide sufficient resolution to allow useful observation of subcellular biological objects. Preparation methods for such objects need not be limited to the traditional coating and mounting procedures. Many methods developed for transmission electron microscopy are immediately adaptable to scanning electron microscopy. We show that a number of techniques are available to the microscopist which yield adequate contrast and high resolution. As examples we show skeletal muscle myofibrils dispersed to reveal thick filaments, uncoated on a thin carbon film; a tropomyosin tactoid, negatively stained with uranyl acetate; oncornavirus, conventionally coated; and T4 bacteriophage on an aluminium substrate.

Conditions critical for optimal visualization of bacteriophage adsorbed to bacterial surfaces by scanning electron microscopy.

Abstract: The potential of scanning electron microscopy as a tool for the detection of viruses on cell surfaces has been studied using bacteriophage P1 adsorbed to Shigella dysenteriae as a model system. Viral particles were readily detectable by scanning electron microscopy on the surface of infected cells which were fixed with glutaraldehyde followed by postfixation in OsO4 and prepared by critical point drying. The virus-studded surface of the infected cells differed markedly from the relatively smooth surfaces of uninfected control cells. Examination of the same preparations with transmission electron microscopy revealed numerous viral particles adsorbed to the surfaces of infected cells, whereas the control cells were free of viruses as expected. Glutaraldehyde fixation alone did not preserve the surface detail of infected cells: cells adsorbed with viruses were not distinguishable from control cells by scanning electron microscopy although by transmission electron microscopy viruses could be visualized. Air drying from water or absolute alcohol resulted in unsatisfactory preservation as compared to the appearance of infected cells prepared by the critical point method. Thus, scanning electron microscopy is capable of resolving viral particles on cell surfaces, but detection of these particles is completely dependent both on the method of fixation and on the technique of drying used.

Domain Growth in Au3Cu

Abstract: Domain patterns in Au 3 Cu have been investigated by means of transmission electron microscopy. Samples were quenched from 800°C and subsequently annealed at temperatures between 100°C and 165°C for various periods of time. The electron microscopic observations are correlated with measurements of the electrical resistivity.

Electron microscopic study on nucleation and growth of silver particles in a thin glass film

Abstract: Nucleation and crystal growth of silver particles in a thin glass film of Li 2 O·2.6SiO 2 glass containing 0.1 wt% of Ag 2 O were observed by transmission electron microscopy and studied by an electron diffraction technique. Anomalies of the image contrast which appeared in the heat-treated specimens were explained to be caused by phase separation of the glass. Nucleation of silver particles was found to occur on the surface of the phase-separated silica-rich droplets. As the silver particles grew, their shape changed into that of a regular cube which was covered with a thin diffusion layer of silver ions about 50 A in thickness. The presence of this thin layer and the cubic shape suggest that the growth of silver particles proceeds by a layer-by-layer growth mechanism.