Showing papers on "Transmission electron microscopy published in 1985"

Structural analysis of Si(111)‐7×7 by UHV‐transmission electron diffraction and microscopy

Abstract: Structural analysis of the surface reconstructions investigated by ultrahigh vacuum (UHV) transmission electron microscopy (TEM) and diffraction (TED) is shown. By TED intensity analysis a new structural model of Si(111)‐7×7 is derived. The model basically consists of 12 adatoms arranged locally in the 2×2 structure, nine dimers on the sides of the triangular subunits of the 7×7 unit cell and a stacking fault layer. UHV–HREM of Si (111)‐7×7 surface is commented.

Surface roughness at the Si(100)-SiO 2 interface

Abstract: We have studied the statistical properties of random surface roughness at the Si-${\mathrm{SiO}}_{2}$ interface using high-resolution transmission electron microscopy (HRTEM). The spectral properties of the HRTEM roughness on normally prepared and intentionally roughened samples appears to be well characterized as a first-order autoregressive or Markovian process which corresponds to an exponential decay in the autocovariance function rather than the usual Gaussian approximation which has been widely used. Such an exponential decay is characterized by tails in the spectrum which are directly attributable to the discrete or steplike nature of the interface roughness which is restricted to occur on crystalline atomic sites. Using a simplified model, we have estimated the effect of projecting the two-dimensional interface roughness through the cross-section thickness to form the one-dimensional boundary studied here. For an isotropic medium, we find that the statistical character of the roughness is preserved during this transformation, but that the rms fluctuation of the roughness is attenuated so that the actual interface is rougher than indicated by the HRTEM technique. After correcting for such averaging, the parameters estimated from the HRTEM are more in agreement with the same parameters used to fit the surface-roughness-limited Hall mobility in metal-oxide-semiconductor field-effect transistor devices.

The microstructure of rapidly solidified Al 6 Mn

Abstract: The microstructure of rapidly solidified Al−Mn alloys containing 18 to 25.3 wt pct Mn was studied by transmission electron microscopy. One of the phases found in the microstructure exhibits icosahedral symmetry manifested in electron diffraction patterns having five-fold symmetry. A new structural concept is proposed to account for the observed electron diffraction patterns. The structure is assumed to be composed of many connected polyhedra. Although not forming a regular lattice, such structures are able to produce sharp diffraction peaks. The terminal stability and transformation of the icosahedral phase was also studied and reported.

Polymer decoration: The orientation of polymer folds as revealed by the crystallization of polymer vapors

Abstract: A new technique of decoration of the fold surface of polymer crystals is described. It is similar in methodology to gold decoration, but makes use of vapors of crystallizable polymers, principally polyethylene, as decorating material. Upon condensation and crystallization, the highly anisometric decorating molecules become oriented parallel to the fold direction. They build up small crystalline lamellae which, seen edge-on, appear as elongated rods and can be easily observed by conventional transmission electron microscopy. This decoration technique reveals the sectorization of polymer single crystals grown from solution. It can be used to determine the local fold orientation (with a resolution of ca. 10 nm) of polymers crystallized under a wide range of conditions, including crystallization from the bulk. The technique reveals that under all crystallization conditions so far investigated the outermost part of the polymer fold surface is relatively ordered, and the folds and/or loops are, as a rule, oriented nearly parallel to the macroscopic growth front.

The Formation of Filamentous Carbon on iron and Nickel Catalysts

Abstract: The microstructure of primary carbon filaments formed on supported iron and nickel catalysts has been investigated using transmission electron microscopy, dark-held imaging, and (selectedarea) electron diffraction. It has been established that the filaments consist of cone-shaped graphite layers, stacked with their c-axes in a direction normal to the metal-carbon interface. A growth mechanism is proposed involving the excretion of cone-shaped graphite layers. To explain the constancy of the filament diameter, slippage of these layers over one another is invoked. Edge dislocations are brought about by differences in the rate of carbon excretion.

Micromechanism for metallic-glass formation by solid-state reactions.

Abstract: Metallic-glass formation by solid-state reactions has been observed in multilayer Zr-Co diffusion couples and studied by cross-sectional transmission electron microscopy. Planar growth of a Corich amorphous phase proceeds from each interface of the unreacted sample, thus consuming the Co layers at a higher rate. Further annealing results eventually in a reaction of the Co-rich glassy phase with remaining Zr. Because of the high diffusivity of the Co in the amorphous phase, Kirkendall voids are formed during this homogenizing process and are lined up with the periodicity of the original layered structure.

Microstructures of SrTiO3 Internal Boundary Layer Capacitors During and After Processing and Resultant Electrical Properties

Abstract: The microstructure of strontium titanate internal boundary layer capacitors at various stages in their processing was studied by transmission electron microscopy of rapidly quenched and normally cooled samples. Compositions containing excess TiO2, Al2O3, and SiO2 have a completely wetting liquid phase at the sintering temperature; during cooling TinO2n−1, Magneli phases precipitate at multiple grain junctions. Diffused metal oxides and flux (Bi2O3, PbO, CuO, and B2O3) rapidly penetrate as a liquid phase along boundaries in postsintering heat treatment. This liquid phase disappears during slow cooling.

Lattice images from ultrathin sections of cellulose microfibrils in the cell wall of Valonia macrophysa Kütz.

Abstract: The crystalline ultrastructure and orientation of cellulose microfibrils in the cell wall of Valonia macrophysa were investigated by means of high-resolution electron microscopy of ultrathin (approx. 28 nm) sections. With careful selection of imaging conditions, ultrastructural aspects of the cell wall that had remained unresolved in previous studies were worked out by direct imaging of crystal lattice of cellulose microfibrils. It was confirmed that each microfibril is a single crystal having a lateral dimension of 20·20 nm2, because lattice images of 0.39 nm resolution were clearly recorded with no major disruption in the whole area of the cross section of the microfibril. There was no evidence for the existence of 3.5-nm elementary fibrils which have been considered to be basic crystallographic and morphological units of cellulose in general. It was also confirmed that the axial directions (crystallographic fiber direction) of adjacent microfibrils in each single lamella of the cell wall are opposite to each other.

Raman, transmission electron microscopy, and conductivity measurements in molecular beam deposited microcrystalline Si and Ge: A comparative study

Abstract: The structure of molecular beam deposited microcrystalline silicon and germanium films prepared under different growth conditions has been analyzed by conventional transmission electron microscope (TEM) and Raman scattering (RS) and compared to electrical conductivity experiments. The TEM measurements yield an average grain size L0 ranging from 200 A to 1.5 μm. On the other hand, the line shape of the RS is determined by a mean free path related to the average separation l between defects (or impurities), where l≤150 A. We find in a number of cases that the electrical conductivity is determined by l rather than L0. This experiment demonstrates the significance of RS as a structural characterization method when used in conjunction with other techniques such as TEM.

Microstructure of silicon implanted with high dose oxygen ions

Abstract: Buried implanted oxide layers have been formed by high dose implantation of oxygen ions (3×1018 ions cm−2) into 〈100〉 silicon wafers, at a constant temperature of 500 °C. The implanted layers were studied by cross‐sectional transmission electron microscopy and secondary ion mass spectroscopy. The defects at both the top Si/SiO2 and the SiO2/bulk Si interfaces are shown to be SiO2 precipitates. The precipitates are unstable and can be eliminated by heat treatment, and a homogeneous top silicon layer with a low density of dislocations can be obtained.

Interdiffusion at the polyimide-Cu interface

Abstract: Interdiffusion at the polymide‐Cu interface has been studied with high resolution medium energy ion scattering (MEIS) and cross section transmission electron microscopy (TEM). Cu was evaported on polyimide in UHV and studied in situ with ion scattering. In the temperature range from 293 to 593 K Cu is found to diffuse into polyimide and form small spherical particles. The size of these spheres and the depth at which they occur increase with increasing temperature. Once the Cu spheres have been formed they become relatively immobile. It is argued that the kinetics of Cu‐polyimide interdiffusion is determined by atomic diffusion of Cu. Chemical effects do not appear to play an important role.

Transmission electron microscope and transmission electron diffraction observations of alloy clustering in liquid-phase epitaxial (001) GaInAsP layers

Abstract: Transmission electron microscope examinations performed on liquid‐phase epitaxial GaInAsP layers grown on (001) InP substrates showed a coarse tweed structure (∼150‐nm scale) and a fine granular structure (∼15‐nm scale). Transmission electron diffraction patterns revealed main spots with associated satellite spots, indicating the presence of periodic variations in lattice parameter along the [100] and [010] directions and of wavelength corresponding to the fine granular structure. The particular behavior depended on the alloy layer composition. Both structures are attributed to alloy clustering arising from spinodal decomposition.

Microstructure and magnetic properties of CoCr thin films formed on Ge layer

Abstract: To improve the c-axis oriented columnar growth, the nucleation of CoCr crystals on various underlayers which are formed on substrates prior to CoCr alloy deposition is studied. Microstructures of vacuum deposited CoCr alloy films are examined by transmission electron microscopy (TEM). It is found that an amorphous-like Ge is a suitable underlayer material to prepare highly oriented CoCr films. Cross-sectional TEM study indicates that the CoCr film formed on Ge layer consists of pillarlike crystals grown vertically throughout the film thickness. The CoCr film formed on Ge layer has a large perpendicular magnetic anisotropy. The read-write (R/W) characteristics have been markedly improved using the highly oriented CoCr film and a very high recording density of D 50 =230 kFCI is achieved, The role of the Ge layer on nucleation of CoCr crystal is discussed.

Surface layer spinodal decomposition in In1−xGaxAsyP1−y and In1−xGaxAs grown by hydride transport vapor‐phase epitaxy

Abstract: Composition modulation due to spinodal decomposition in In1−xGaxAsyP1−y quaternary and In1−xGaxAs ternary alloys is observed by transmission electron microscopy in epitaxial layers grown by hydride transport vapor phase epitaxy at 700 °C on (001) InP substrate A quasi‐periodic fine contrast oriented along [100] and [010] directions is found in all samples over a composition range of 020≤x≤053 and 037≤y≤1 Contrary to the result reported on materials grown by liquid‐phase epitaxy, complete mixing at composition outside the miscibility gap predicted by thermodynamics for bulk crystals is not observed The evidence indicates a rapid spinodal decomposition by surface diffusion during vapor phase deposition Furthermore, transmission electron microscopy diffraction contrast experiments on the (110) cross‐sectional view of planar and nonplanar epitaxial layers reveal a columnar structure oriented along the growth direction which is consistent with the surface layer spinodal formation Additional coarse cont

Optical properties and microstructure of gold-fluorocarbon-polymer composite films

Abstract: The optical transmittance of plasma-deposited composite gold\char21{}fluorocarbon-polymer thin films is analyzed in terms of effective-medium theories. The effect of increasing gold volume fraction is shown to be correctly described by the Sheng model, provided the gold-cluster and polymer-inclusion sizes and shapes analyzed by transmission electron microscopy are properly taken into account. Moreover, good consistency is obtained between the present results and our previous study of the electrical conductivity variation at and above the percolation threshold. An extension of the Sheng model has been developed to deal with three-phase systems and has been applied in this work to test the possible existence of an interfacial carbon layer at the gold-polymer interface. The effects of topological disorder and higher-order multipole interactions between the clusters are discussed. Annealing of the films above the glass transition temperature of the polymer results in a drastic change of the film optical properties which is attributed to an increase of gold volume fraction, due to the collapse of the polymer phase, and above all to a modification of the cluster sizes and shapes by sintering and coalescence of gold particles as confirmed by transmission electron microscopy.

Electron-microscopic investigation of the morphology of a melt-crystallized polyaryletherketone

Abstract: We have studied the structure and morphology of the useful high‐temperature/high‐strength polymer polyaryletherketone (PEEK) by transmission electron microscopy and three‐dimensional electron diffraction after finding suitable solvents (α‐chloronaphthalene and benzophenone) that allowed casting of the required ultrathin polymer films. When crystallized from the melt, PEEK grows in the form of spherulites consisting of narrow lamellae and having the b axis of the unit cell radial. Additionally, at high temperatures in these ultrathin films, the spherulites attain an extraordinary cylindrical symmetry as a result of growth of their lamellae on edge, with the c crystallographic direction parallel to the film plane and the a direction corresponding to the cylinder axis. Reasons for this mode of growth are attributed to the highly anisometric molecular cross section normal to the chain direction, which favors crystal nucleation on the substrate with the bc plane. At lower temperatures during crystallization from the melt, a more random lamellar disposition is seen in these thin‐film spherulites, although lamellae on edge still predominate. Crystallization by heating from the quenched glassy phase yields random lamellar aggregates and small spherulites. The glassy phase in ultrathin PEEK shows no consistent morphological features down to a level of resolution of 1.0 nm. Scanning electron microscopic examination of the free surfaces of bulk samples crystallized under controlled conditions both from the melt and from the glass, show that our findings from ultrathin films (with the exception of the quasicylindrical spherulitic substructure) also apply to these thicker specimens.

Composition dependence of equal thickness fringes in an electron microscope image of GaAs/AlxGa1−xAs multilayer structure

Abstract: A new method is presented for the composition analysis of GaAs/AlxGa1-xAs multilayer structure using transmission electron microscopy. It is found that the position of equal thickness fringe observed at the edge of a cleaved chip is closely related to the composition. Change in Al composition in GaAs/AlxGa1-xAs superstructure is observed as a shift of the equal thickness fringe. Compositional abruptness at the heterointerface and compositional fluctuation in the thin layer can be estimated in the electron microscope image.

Temperature dependence of semiconducting and structural properties of Cr‐Si thin films

Abstract: Electrical and structural properties of coevaporated Cr‐Si thin alloy films and bilayer Cr/Si films as a function of annealing temperature from 10 to 1000 °K have been studied by in situ electrical resistivity and Hall measurements, and structural analysis including MeV 4He+ ion backscattering, x‐ray diffraction, Auger electron spectroscopy combined with Ar sputtering, electron microprobe, and scanning and transmission electron microscopy. In the as‐deposited state, the coevaporated alloy film was amorphous. Upon annealing, a sharp increase in resistivity occurred near 270 °C and the increase has been determined to be amorphous to crystalline CrSi2 phase transformation. The resistivity increased further with annealing up to 550 °C then a gradual decrease took place beyond 600 °C. In cooling, the resistivity increased monotonically with decreasing temperature. For the bilayer Cr/Si films, the annealing behavior is similar except the sharp increase in resistivity occurred around 450 °C due to the formation ...

Elastic relaxation in transmission electron microscopy of strained‐layer superlattices

Abstract: We demonstrate that thin, cross‐sectioned transmission electron microscopy samples from strained‐layer superlattices undergo elastic relaxation such that the local lattice parameter modulation amplitude can be reduced by a large fraction. Relaxation is dependent on the ratio of the superlattice wavelength to the local sample thickness and is demonstrated experimentally for molecular beam expitaxially grown GexSi1−x superlattices both by selected‐area diffraction and high‐resolution electron microscopy. The results can be qualitatively explained by a simple linear elasticity theory model. Reports of anomalies in the elastic properties of semiconductor superlattices from electron microscopy can be resolved. Evidence is also presented for expected lattice plane bending due to relaxation which can cause strong diffraction contrast. This thin‐sample ‘‘artefact’’ allows unexpectedly weak strain fields to be imaged and permits probing of local elastic properties of individual layers within a superlattice. Simila...

The effect of the H2O/TEOS ratio on the structure of gels derived by the acid catalysed hydrolysis of tetraethoxysilane

Abstract: Silica gels were produced by the acid catalysed hydrolysis of tetraethoxysilane (TEOS) using H 2 O/TEOS ratios from 2 to 50. After heat treatment the structure of the gels was studied using nitrogen adsorption, small angle X-ray scattering (SAXS), transmission electron microscopy (TEM) and bulk density measurements. All the gels possessed microporosity in the region of 30 A or less. For H 2 O/TEOS = 25 and 50 the matrix density was found to be uniform, but for gels from solutions with H 2 O/TEOS = 2,4 and 10, density fluctuations in the matrix were detected from Porod analysis of the SAXS data. These results indicate that in higher water content solutions, rearrangement of the polymeric chains leads to small densified particles, but for lower water content solutions, gelation results from the entanglement of linear chains leaving free volume on a molecular scale between the chains.

Mesophase texture and defects in thermotropic liquid-crystalline polymers

Abstract: Two rigid/flexible thermotropic polyesters based on 1,10-decane bisterephthaloyl chloride with hydroquinone or methyl hydroquinone have been investigated by transmission electron microscopy. Oriented thin films were prepared by melt spreading on phosphoric acid. After thermal quenching to freeze-in the liquid-crystalline state, films were examined at room temperature using electron microscopy and electron diffraction. High local orientation within 10 µm diameter areas was observed by electron diffraction. Layer-line spacings showed that the molecules adopted a highly aligned conformation. Multiple equatorial reflections in the unsubstituted polymer and the formation of a single-crystal-like texture on annealing the frozen liquid-crystalline state in the methyl-substituted polymer suggest biaxial chain packing in the liquid-crystalline state. Bright-field images of the quenched films were essentially featureless, but equatorial dark field and polarized-light optical images revealed an alternating band structure. Annealing below the crystal-melting transition results in the growth of lamellae which decorate the overall pattern of molecular order in the precursor frozen liquid-crystalline state. The 200 A thick lamellae provide high contrast and resolution for observation of characteristic mesophase texture and defects. The molecular trajectory across the transverse bands is found to be sawtoothed rather than serpentine. Two types of disclination lines have been observed: non-singular S=±1 disclination loops lying in the plane of the films with their loop axes oriented along the overall chain-axis direction and S=±½ disclination lines lying normal to the film surface.The semicrystalline microstructure consists of thin lamellae separated by frozen liquid-crystal regions. The single-crystal-like texture of the oriented lamellae, together with the nature of the meridional scattering, suggests a biaxial smectic liquid-crystalline phase for these polymers. The liquid-crystalline state is not believed to consist of an intrinsic polydomain structure but rather a continuous liquid-crystalline medium containing various types of disclinations.