Formation and structure of polymeric carbons

1972 ◽  
Vol 327 (1571) ◽  
pp. 501-517 ◽  
Keyword(s):  
Glassy Carbon ◽  
Molecular Orientation ◽  
Early Stage ◽  
Structural Difference ◽  
Direct Consequence ◽  
High Resolution Electron Microscopy ◽  
Polymer Chains ◽  
Resolution Electron ◽  
Ribbon Structure ◽  
Phenolic Polymer

Glassy carbon has been prepared in the shape of disk and fibre by direct pyrolysis of a phenolic resin. Carbonization studies indicate that the unique structure of the final glassy carbon is a direct consequence of the production of very stable aromatic ribbon molecules by the coalescence of phenolic polymer chains at an early stage of pyrolysis. It is shown that molecular orientation induced in the initial polymer before pyrolysis is 'memorized’ to some extent after carbonization. Molecular orientation imposed in this type of carbon is not an intrinsic structural feature, but a physical characteristic which can be varied by the formation process or by extension at high temperatures; there is no essential structural difference apart from preferred orientation between polymeric units or microfibrils in well-oriented carbon fibres and isotropic glassy carbon. High resolution electron microscopy confirms this directly. We thus identify a new class of ‘polymeric carbons’, that consist of intertwined microfibrils comprising stacks of narrow graphitic ribbons. The fibrils are held together with covalent interfibrillar links of strength lower than that in the ribbons themselves. A ribbon structure has been proposed previously by Ruland (1971) for the specific case of high modulus carbon fibre. The structure is elaborated and extended here to cover all polymeric carbons and the steps in its development during carbonization are decisively detailed.

Precipitation behavior in the early stage of aging in an Al–Li°Cu–Mg–Zr–Ag (Weldalite 049) alloy

1999 ◽  
Vol 14 (2) ◽  
pp. 384-389 ◽  
Author(s):  
Kap Ho Lee ◽  
Yeung Jo Lee ◽  
Kenji Hiraga
Keyword(s):  
Aging Process ◽  
Early Stage ◽  
High Resolution Electron Microscopy ◽  
S Phase ◽  
Precipitation Behavior ◽  
Ordered Structures ◽  
Resolution Electron ◽  
The Matrix ◽  
Habit Planes

The precipitation behavior of various phases during the aging process of an Ag–Li°Cu–Mg–Zr–Ag (Weldalite 049) alloy was investigated by high-resolution electron microscopy and in situ hot-stage microscopy. Two kinds of domains with L12-type ordered structures, which are considered to be δ′ and β′ phases, are observed with different domain sizes in the alloy quenched from 530 °C. In the early stage of aging at 190 °C, the δ′ phase is precipitated as surrounding the β' phase, and the δ′ domains appear with in-phase and antiphase relationships to the β′ lattices. In situ observations at 190 °C clearly show that the T1 phase precipitates predominantly on dislocations at subgrain boundaries and then is homogeneously formed in the matrix with increasing aging time. The nucleation of the S′ phase is associated with clustering of Cu and Mg in the matrix, and the S0 domains are grown with {210} habit planes.

The Early Stages of the Spinel-Alumina Phase Transformation

1987 ◽  
Vol 94 ◽  
Author(s):  
Y. Kouh Simpson ◽  
C. B. Carter
Keyword(s):  
Electron Microscopy ◽  
Phase Transformation ◽  
Early Stage ◽  
Spinel Phase ◽  
High Resolution Electron Microscopy ◽  
Solid State Reactions ◽  
Alumina Phase ◽  
Transmission Electron ◽  
Resolution Electron ◽  
In Situ Experiments

ABSTRACTThe initial stage of topotactic growth of Ni-Al spinel into Al2O3 has been examined using transmission electron microscopy. A new experimental approach to the study of solid-state reactions, which may be adapted for in-situ experiments for low-temperature systems, has been used in this study. In its present form, the technique involves heating a thin film of one oxide in the presence of a vapor of the second oxide. In the study of the growth characteristics of Ni-Al spinel phase, the orientation of the Al2O3 substrate has been found to influence greatly both the structural and morphological aspects of the spinel growth. In particular, the topotactic relationship between the spinel and the alumina are very different for (0001) and {1120} substrate orientations. The very early stage of the kinetics of the spinel growth, in which the length and the width of the spinel particles are only a few hundred angstroms, is illustrated with the results obtained from the re-heating experiments. The structure of the spinel-alumina interface has also been studied using high-resolution electron microscopy. These results are discussed in relation to the different models proposed for the spinel-alumina phase transformation.

Crystallization of Sputter Deposited Ti-Al Amorphous Alloy

1995 ◽  
Vol 400 ◽  
Author(s):  
M. Ohnuma ◽  
T. Abei ◽  
H. Onodera
Keyword(s):  
Amorphous Alloy ◽  
Early Stage ◽  
Metastable Phase ◽  
High Resolution Electron Microscopy ◽  
Lattice Parameter ◽  
Tetragonal Symmetry ◽  
Thin Sample ◽  
Thick Sample ◽  
Resolution Electron ◽  
Sputter Deposited

AbstractThe crystallization process of Ti-Al amorphous alloy has been studied by X-ray diffraction, small-angle neutron scattering and high resolution electron microscopy. In the early stage of crystallization of a thick sample with 55at%Al, a metastable hcp(α, α2) phase appeares. For a thin sample with 52at%Al, a new metastable phase having primitive tetragonal symmetry is found in the early stage of crystallization. The lattice parameter of this tetragonal phase is a=c=0.69nm. The prototype structure which has the same atomic arrangement as this phase is only Cu4Pd type structure (P42/m) in the Peason's Handbook.

scholarly journals Determination of the structural aspects of favored grain boundary reaction sites

1978 ◽  
Vol 36 (1) ◽  
pp. 408-409
Author(s):  
Ronald Gronsky ◽  
Gareth Thomas
Keyword(s):  
Grain Boundary ◽  
Early Stage ◽  
Structural Characteristics ◽  
High Resolution Electron Microscopy ◽  
Growth Front ◽  
Grain Boundary Plane ◽  
Nucleation Sites ◽  
Resolution Electron ◽  
Boundary Reaction

Of the techniques which have been employed in the study of grain boundary precipitation reactions, none have demonstrated sufficient resolution to directly reveal the structural characteristics of active nucleation sites. This information is vital since many existing interpretations of conventional TEM data are in conflict.The present paper describes an application of high resolution electron microscopy which distinguishes atomic level details in both the boundary and growth front regions of grain boundary precipitates, and indicates the structure and mechanisms responsible for enhanced reaction kinetics.Experiments were performed on an Al-9.5 at.% Zn alloy aged for 30 mins, at 180°C to encourage heterogeneous nucleation at grain boundaries. Two examples of early stage grain boundary precipitates are shown in Fig. 1, both of which have been nucleated in the lower grain. It is seen that in (b) the precipitate is much more sharply faceted than in (a). Notably the orientation of the grain boundary plane is very near to that of the close-packed {111} matrix planes of the lower grain for precipitate (b), whereas the boundary is sharply inclined to {111} for precipitate (a).

In situ heating studies at high resolution

1991 ◽  
Vol 49 ◽  
pp. 656-657
Author(s):  
Robert Sinclair
Keyword(s):  
High Resolution ◽  
Structural Information ◽  
Direct Consequence ◽  
High Resolution Electron Microscopy ◽  
Spectroscopic Characterization ◽  
Characterization Methods ◽  
Intermediate Phases ◽  
Resolution Electron ◽  
Interfacial Defects

It is well-known that interfaces in solids have a crucial influence on the properties of materials. The structures of such interfaces are a direct consequence of their means of formation, be it by deposition, reaction, interdiffusion or epitaxial growth. Even subtle changes during processing or service can alter the anticipated behavior. High resolution electron microscopy (HREM) has become an invaluable, and virtually routine, characterization tool in understanding the influence of structure on properties. Its strength lies in the ability to derive direct structural information at the atomic level, not only about topography but also about interfacial defects such as dislocations or ledges, contamination residue, intermediate phases etc. It complements well the broad-beam spectroscopic characterization methods such as Auger, ECSA, SIMS and RBS, which do not provide structural information and can be ambiguous to interpret.

Morphology and molecular orientation of thin-film bis(triisopropylsilylethynyl) pentacene

2007 ◽  
Vol 22 (6) ◽  
pp. 1701-1709 ◽  
Author(s):  
Jihua Chen ◽  
David C. Martin ◽  
John E. Anthony
Keyword(s):  
Crystal Structure ◽  
Thin Films ◽  
Molecular Orientation ◽  
Crystalline State ◽  
High Resolution Electron Microscopy ◽  
Good Solubility ◽  
Resolution Electron ◽  
Local Crystal Structure ◽  
Individual Crystallite ◽  
Unit Edge

As a modification to the insoluble and herringbone-structured pentacene, bis(triisopropylsilylethynyl) (TIPS) pentacene has two bulky side groups, leading to good solubility in common organic solvents and regular π–π stacking arrangements in the crystalline state. Solution processing of TIPS–pentacene thin films was investigated as a function of various process parameters in this work. Electron diffraction results suggested that TIPS–pentacene molecules tended to align with the acene unit edge on to the substrate, touching down with their bulky side groups. In a TIPS–pentacene polycrystalline film, the long axis of individual crystallite is [2 1 0], while the shorter axis is [1 ¯20]. High-resolution electron microscopy was used to study the local crystal structure and characteristic defects of TIPS–pentacene thin films. Due to the nonaromatic side groups, TIPS–pentacene was found to be significantly more sensitive to the electron beam (critical dose Jc= 0.05 C/cm2at 300 kV) than pentacene itself (Jc= 0.2 C/cm2at 100 kV).

Short-Range-Ordering and Fe-Clustering in Au-Fe Alloys

1990 ◽  
Vol 205 ◽  
Author(s):  
Chen-Chia Chou ◽  
F.-R. Chen ◽  
C. M. Wayman
Keyword(s):  
Short Range ◽  
Early Stage ◽  
High Resolution Electron Microscopy ◽  
Electron Microscopic ◽  
Transmission Electron ◽  
Fe Content ◽  
Resolution Electron ◽  
Short Range Ordering ◽  
Fe Alloys ◽  
Microscopic Techniques

AbstractAs an “archtypal” spin-glass system, the local atomic arrangement in Au-Fe alloys is still a controversial subject. In the present experiment, Au-Fe alloys with Fe content from 10.7 to 33% were studied as to microstructure evolution, through various transmission electron microscopic techniques. Information derived from aging experiments using real and reciprocal spaces appears to suggest the coexistence of short-range-order and Fe-clusters. At early stages of aging, lobe-like and/or rod-shaped strain contrast images, identified as clusters, were revealed after specimens were further cleaned by an ion-miller. The (1 1/2 0) special point diffuse reflections were prominent in the as-quenched condition and/or early stage aging, and the intensifies decrease gradually as aging proceeds. After a certain period, (1 1/2 0) diffuse reflections disappear but strain contrast images still remain similar. This suggests that the strain contrast images are not related to the (1 1/2 0) diffuse reflections. High resolution electron microscopy was also employed. The results are consistent with the arguments derived from aging experiments.

Initial stage Fe-clustering in the Au–Fe spin-glass system

1992 ◽  
Vol 7 (2) ◽  
pp. 321-328 ◽  
Author(s):  
Chen-Chia Chou ◽  
C.M. Wayman
Keyword(s):  
Electron Microscopy ◽  
Early Stage ◽  
Theoretical Calculations ◽  
High Resolution Electron Microscopy ◽  
Initial State ◽  
Transmission Electron ◽  
Initial Stage ◽  
Fe Content ◽  
Resolution Electron ◽  
Fe Alloys

Aging experiments were conducted to study initial state Fe-clustering in Au–Fe alloys with Fe content from 10.7 to 33%. Information derived from experiments using transmission electron microscopy, electron diffraction, and high resolution electron microscopy suggests the coexistence of short-range-order and Fe-clusters. At early stages of aging, lobe-like and/or rod-shaped strain contrast images, identified as clusters, were revealed after specimens were further cleaned by an ion-miller. The (11/20) special point diffuse reflections were prominent in the as-quenched condition and/or early stage aging, and the intensities decrease gradually as aging proceeds. After a certain period, (11/20) diffuse reflections disappear but strain contrast images still remain similar. This suggests that the strain contrast images are not related to the (11/20) diffuse reflections. The cluster characteristics of Au–Fe alloys are differentiated from those of Al–Cu and Cu–Be based upon theoretical calculations.

Recent Applications of High Resolution Electron Microscopy to Crystalline Arrays of Virus Particles

1978 ◽  
Vol 36 (3) ◽  
pp. 470-482 ◽  
Author(s):  
R.W. Horne
Keyword(s):  
Electron Microscopy ◽  
Image Processing ◽  
Analytical Techniques ◽  
Staining Technique ◽  
High Resolution Electron Microscopy ◽  
Optical Diffraction ◽  
Full Potential ◽  
Virus Particles ◽  
Resolution Electron ◽  
Wide Range

The technique of surrounding virus particles with a neutralised electron dense stain was described at the Fourth International Congress on Electron Microscopy, Berlin 1958 (see Home & Brenner, 1960, p. 625). For many years the negative staining technique in one form or another, has been applied to a wide range of biological materials. However, the full potential of the method has only recently been explored following the development and applications of optical diffraction and computer image analytical techniques to electron micrographs (cf. De Hosier & Klug, 1968; Markham 1968; Crowther et al., 1970; Home & Markham, 1973; Klug & Berger, 1974; Crowther & Klug, 1975). These image processing procedures have allowed a more precise and quantitative approach to be made concerning the interpretation, measurement and reconstruction of repeating features in certain biological systems.

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