The conversion of an organometallic compound into an intercalated thin-layer amorphous structure

In this form of electron microscopy, photoelectrons emitted from a metal by ultraviolet radiation are accelerated and imaged onto a fluorescent screen by conventional electron optics. image contrast is determined by spatial variations in the intensity of the photoemission. The dominant source of contrast is due to changes in the photoelectric work function, between surfaces of different crystalline orientation, or different chemical composition. Topographical variations produce a relatively weak contrast due to shadowing and edge effects.Since the photoelectrons originate from the surface layers (e.g. ∼5-10 nm for metals), photoelectron microscopy is surface sensitive. Thus to see the microstructure of a metal the thin layer (∼3 nm) of surface oxide must be removed, either by ion bombardment or by thermal decomposition in the vacuum of the microscope.

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Observations on the Structure of Ta2O5

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100095959 ◽

1972 ◽

Vol 30 ◽

pp. 540-541

Author(s):

P. S. Kotval ◽

C. J. Dewit

Keyword(s):

Electron Microscope ◽

Structural Features ◽

Amorphous Structure ◽

Polished Surface ◽

Distilled Water ◽

Anodic Films ◽

Amorphous Films ◽

Beam Heating ◽

Diffraction Patterns ◽

Hexagonal Arrays

The structure of Ta2O5 has been described in the literature in several different crystallographic forms with varying unit cell lattice parameters. Earlier studies on films of Ta2O5 produced by anodization of tantalum have revealed structural features which are not consistent with the parameters of “bulk” Ta2O5 crystalsFilms of Ta2O5 were prepared by anodizing a well-polished surface of pure tantalum sheet. The anodic films were floated off in distilled water, collected on grids, dried and directly examined in the electron microscope. In all cases the films were found to exhibit diffraction patterns representative of an amorphous structure. Using beam heating in the electron microscope, recrystallization of the amorphous films can be accomplished as shown in Fig. 1. As suggested by earlier work, the recrystallized regions exhibit diffraction patterns which consist of hexagonal arrays of main spots together with subsidiary rows of super lattice spots which develop as recrystallization progresses (Figs. 2a and b).

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Spherulite Structures in a Melt Spun Fe-Ni Austenitic Steel

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100117339 ◽

1985 ◽

Vol 43 ◽

pp. 52-53

Author(s):

G. M. Michal ◽

T. K. Glasgow ◽

T. J. Moore

Keyword(s):

Austenitic Steel ◽

Room Temperature ◽

Elevated Temperatures ◽

Large Range ◽

Amorphous Structure ◽

Nucleation And Growth ◽

Ni Alloys ◽

Melt Spun ◽

Crystal Fibers ◽

Rapidly Solidified

Large additions of B to Fe-Ni alloys can lead to the formation of an amorphous structure, if the alloy is rapidly cooled from the liquid state to room temperature. Isothermal aging of such structures at elevated temperatures causes crystallization to occur. Commonly such crystallization pro ceeds by the nucleation and growth of spherulites which are spherical crystalline bodies of radiating crystal fibers. Spherulite features were found in the present study in a rapidly solidified alloy that was fully crysstalline as-cast. This alloy was part of a program to develop an austenitic steel for elevated temperature applications by strengthening it with TiB2. The alloy contained a relatively large percentage of B, not to induce an amorphous structure, but only as a consequence of trying to obtain a large volume fracture of TiB2 in the completely processed alloy. The observation of spherulitic features in this alloy is described herein. Utilization of the large range of useful magnifications obtainable in a modern TEM, when a suitably thinned foil is available, was a key element in this analysis.

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Devitrification products of rapidly solidified Ni-Nb amorphous alloys.

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s042482010017788x ◽

1990 ◽

Vol 48 (4) ◽

pp. 950-951

Author(s):

G. A. Bertero ◽

W.H. Hofmeister ◽

N.D. Evans ◽

J.E. Wittig ◽

R.J. Bayuzick

Keyword(s):

Electron Microscopy ◽

Amorphous Structure ◽

Sulphuric Acid Solution ◽

X Ray Diffraction ◽

High Fracture ◽

Transmission Electron ◽

Xrd Techniques ◽

Rapidly Solidified ◽

Electromagnetically Levitated

Rapid solidification of Ni-Nb alloys promotes the formation of amorphous structure. Preliminary results indicate promising elastic properties and high fracture strength for the metallic glass. Knowledge of the thermal stability of the amorphus alloy and the changes in properties with temperature is therefore of prime importance. In this work rapidly solidified Ni-Nb alloys were analyzed with transmission electron microscopy (TEM) during in-situ heating experiments and after isothermal annealing of bulk samples. Differential thermal analysis (DTA), scanning electron microscopy (SEM) and x-ray diffraction (XRD) techniques were also used to characterize both the solidification and devitrification sequences.Samples of Ni-44 at.% Nb were electromagnetically levitated, melted, and rapidly solidified by splatquenching between two copper chill plates. The resulting samples were 100 to 200 μm thick discs of 2 to 3 cm diameter. TEM specimens were either ion-milled or alternatively electropolished in a methanol-10% sulphuric acid solution at 20 V and −40°C.

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