Journal of electron microscopy technique最新文献

The sequence of events leading to the development of freeze-fracture replication is described. Subsequent developments discussed include complementary replicas, replica interpretation with stereo micrograph and reversal negatives, replica reinforcement, and control of resistance evaporation.

Particle counting and measuring techniques are now widely used to characterize normal membranes and to identify molecular changes occurring during development, maturation, and aging during progression of disease and following pharmacological manipulation. However, the use of particle counting and measuring for the identification of molecular changes in membranes has been premature. We show that current procedures rarely yield replicas that are free of cryogenic or mechanical prefractures, and as a result, the "complementarity" of membrane faces is severely compromised. However, with simple alterations of procedure, combined with the resolve to recognize and discard images of pre-fractured membrane faces, a high degree of "complementarity" may be obtained. Criteria for recognizing the occurrence and relative frequency of noncomplementarity are presented and a cleaving method for avoiding a primary source of water vapor contamination is described. In such replicas, membrane pits are found in equivalent numbers and near-identical diameters as the intramembrane particles (IMPs) in the complementary-type membrane faces. When conditions of "cold fracture" and immediate replication are demonstrated, fracture faces are minimally contaminated by frozen water vapor, yielding images where 1) diameters of IMPs vs. pits are very nearly identical, 2) large diameter IMPs are very rare, and 3) the numbers of IMPs and pits are increased substantially over the numbers currently reported. Thus, we reiterate previous proposals that complementarity of membrane faces is the single most important criterion that must be met before accepting the validity of IMP counts or for attributing perceived changes in IMP density or size to conditions of experimental manipulation, to normal developmental processes, or to disease etiology.

A scanning electron microscope of ultra-high-vacuum (UHV-SEM) with a field emission gun (FEG) is operated at the primary electron energies of from 100 eV to 3 keV. The instrument can form the images that contain information on surface chemical composition, chemical bonding state (electronic structure), and surface crystal structure in a microscopic resolution of several hundred angstroms (A) using the techniques of scanning Auger electron microscope, scanning electron energy loss microscope, and scanning low-energy electron diffraction (LEED) microscope. A scanning tunneling microscope (STM) also has been combined with the SEM in order to obtain the atomic resolution for the solid surface. The instrumentation and examples of their applications are presented both for scanning LEED microscopy and STM.

The critical voltages for systematic reflections and splits of Kikuchi lines were measured using a high-voltage electron microscope to investigate the atomic temperature factors in cubic crystals. The split of the Kikuchi line at the intersection with the forbidden 222 Kikuchi line as well as the critical voltage of the 333 reflection for Si and Ge decreased steeply with temperature. The temperature dependence showed that the anharmonic contribution to the atomic-temperature factor for Si and Ge is extremely weak in the temperature range 300 approximately 1078 K. On the contrary, the B factors obtained from the measured critical voltages for Al, Cu, and Fe varied nonlinearly with temperature, suggesting the importance of the anharmonic effect in the vibration of atoms. The observed temperature dependence of the critical voltages for the metals were compared with calculations based on harmonic, quasi-harmonic, and anharmonic approximations. The quasi-harmonic approximation that takes into account the thermal expansion modification reproduces well the observed values for Fe but not those for Al and Cu. The effect of intrinsic anharmonic vibration should be considered for reproducing the results for Al and Cu. Fitting the measured critical voltages with the calculated ones, we estimated the values for coefficients of the isolated atom potentials. The results are in good agreement with those obtained by neutron and X-ray diffraction.

Recent studies of high-resolution electron microscopy on the high-Tc superconductors of Y-Ba-Cu-O and Bi-Ca-Sr-Cu-O are presented. The observed images of crystals thinner than 3 nm, taken under conditions that approached the Scherzer defocus condition, directly show the arrangements of cations and oxygen-vacant positions. The results reveal structural characteristics of the atomic scale; this offers important insights into the origin of the high-Tc superconductivity. The usefulness of high-resolution electron microscopy for studying complicated crystal structures is demonstrated for the high-Tc oxides.

Three observations described here were chosen not only to represent our recent interface studies in ceramics, but also to demonstrate how different the present status of interface research is with respect to the level of high-resolution electron microscopy. Certain common features may be found among the problems of ceramic interface studies. Importance of basal plane grain boundary, for example, is one of the characteristics of this type of heterogeneous compound. The crystalline heterogeneity has been ignored largely in the grain boundary structure study since it has been developed primarily for cubic metals. The new area of basic grain boundary interface structure study is opened now that description of this type of interface has become engineeringly important.

Single crystalline composite films of iron and MgO are prepared by a simultaneous vacuum deposition technique. The structures of the composite films, especially of the iron crystallites embedded, are studied by high-resolution electron microscopy and nanometer-area electron diffraction. The alpha-iron (b.c.c.) crystallites of 1 nm in size are epitaxially embedded in single crystalline MgO films, the orientation being (011)[100]Fe parallel (001)[100]MgO and (001)[110]Fe parallel (001)[100]MgO. A heat treatment of the as-grown films at 500-1,000 degrees C brings about a phase transformation of the crystallites from alpha-iron to gamma-iron (f.c.c.), followed by a grain growth of alpha-iron and finally the growth of the spinel, MgFe2O4. The gamma-iron crystallites transformed are circular plates and have strains at the periphery to accommodate the surrounding MgO-matrix. The magnetic property of the composite films is also reported.