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.

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.

HIGH RESOLUTION ELECTRON MICROSCOPY OF THE HIGH Tc SUPERCONDUCTOR Bi2Sr2CaCu2O8+δ

1988 ◽  
Vol 02 (06) ◽  
pp. 835-839 ◽  
Author(s):  
M. HERVIEU ◽  
B. DOMENGES ◽  
C. MICHEL ◽  
B. RAVEAU
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Electron Diffraction Study ◽  
High Resolution Electron Microscopy ◽  
Basic Structure ◽  
Tetragonal Symmetry ◽  
High Tc ◽  
Resolution Electron ◽  
High Resolution Images ◽  
New Superconductor

The new superconductor Bi 2 Sr 2 CaCu 2 O 8+δ with T c ranging from 80 to 105K, was studied by electron microscopy. The electron diffraction study shows a pseudo-tetragonal symmetry with a≈b≈5.4 Å and c≈30.7 Å and satellites along a, which settle in an incommensurate way. The high resolution images agree with the proposed basic structure. The stacking of the ( BiO y)2 and [ Sr 2 CaCu 2 O 6] layers is quite regular, with only some defects corresponding to c≈24 Å. The lamellar character of the oxide results in splitting and bending of the crystals.

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.

Epitaxial Growth and Structure of Cubic and Pseudocubic Perovskite Films on Perovskite Substrates

1995 ◽  
Vol 401 ◽  
Author(s):  
P. A. Langjahr ◽  
T. Wagner ◽  
M. RÜhle ◽  
F. F. Lange
Keyword(s):  
Electron Microscopy ◽  
Epitaxial Growth ◽  
Lattice Mismatch ◽  
High Resolution Electron Microscopy ◽  
Lattice Parameter ◽  
Ternary Oxide ◽  
Misfit Dislocations ◽  
X Ray Diffraction ◽  
Transmission Electron ◽  
Resolution Electron

AbstractCubic and pseudocubic perovskite films on perovskite substrates are used to study the influence of the lattice mismatch on the epitaxial growth of thin films on substrates of the same structure. For the growth of the films, a metalorganic decomposition route (MOD) using 2-ethylhexanoates and neodecanoates as precursors, was developed. The decomposition of the precursors was investigated with thermogravimetric analysis (TGA) and x-ray diffraction (XRD). The films were spin-coated on (001)-oriented SrTiO3- and LaAlO3-substrates, pyrolyzed and afterwards annealed between 600°C and 1200°C. XRD-nvestigations and conventional transmission electron microscopy (CTEM) show, that epitaxial films with the orientation relationship [100](001) film ║ [100](001) substrate can be grown. With XRD, it could be shown, that not only ternary oxide films (SrZrO3, BaZrO3 and BaCeO3), but also perovskite solid solution films (SrTi0.5Zr0.5O3and BaCe0.5Zr0.5O3) can be prepared. Strong interdiffusion, detected by a shift of the film lattice parameter towards the substrate lattice parameter was found in SrZrO3- and BaZrO3-films on SrTiO3, annealed at temperatures above 1050°C. High resolution electron microscopy (HREM) studies of SrZrO3 on SrTiO3 show that a crystalline semicoherent interface with a periodical array of misfit dislocations is present.

Degradation mechanisms of Cu2-xS/CdS solar cells as revealed by high-resolution electron microscopy

1983 ◽  
Vol 41 ◽  
pp. 104-105
Author(s):  
T. Sands
Keyword(s):  
Solar Cells ◽  
Metastable Phase ◽  
High Resolution Electron Microscopy ◽  
Thin Film Solar Cells ◽  
Degradation Mechanisms ◽  
Copper Loss ◽  
Cell Efficiency ◽  
Cds Thin Film ◽  
Resolution Electron ◽  
Formation Conditions

A major factor preventing the production of inexpensive and efficient p-Cu2S/n-CdS thin film solar cells is the inherent sensitivity of the electronic and optical properties of the copper sulfide layer to small changes in composition. This layer can act as an efficient absorber-emitter only if the predominant phase is low chalcocite (CU2S). A small amount of copper loss due to non-optimum formation conditions, in-service oxidation, or electromigration under load result in the formation of djurleite (Cu1.97S) and a corresponding reduction in cell efficiency. The structures of both low chalcocite and djurleite are based on an hep sulfur network. However, further copper loss encourages the nucleation and growth of low digenite (Cu1.82S), a metastable phase based on an fee sulfur network.This study addresses the problem of determining the dominant factors influencing these degradation transformations so that methods to produce more stable layers or device configurations can be systematically developed.

Structure of long-period tetragonal lattice formed by solid-state alloying in Bi-Mn double-layer thin films

1990 ◽  
Vol 48 (4) ◽  
pp. 160-161
Author(s):  
Kentaroh Yoshida ◽  
Takashi Yamada
Keyword(s):  
Thin Films ◽  
Solid State ◽  
Double Layer ◽  
Metastable Phase ◽  
High Resolution Electron Microscopy ◽  
Ferromagnetic Phase ◽  
Amorphous Films ◽  
Long Period ◽  
Tetragonal Lattice ◽  
Resolution Electron

It has been a well known fact that BI and Mn are, by melting, immiscible with each other and only a ferromagnetic phase, MnBi, forms by a peritectic reaction at 446°C between solid Mn and the melt. However, the authors succeeded in mixing these two atomic elements by simultaneous vacuum deposition and found that a new metastable phase, Mn3Bi, appears as a crystallization product of the as-deposited amorphous films at 180°C, when their composition is in a range 85 to 65 at% Mn. They derived its atomic arrangement only by means of high resolution electron microscopy. In the present investigation, double layer thin films, consisting of Bi layer (300 Å) and of Mn layer (200°Å), were prepared by successive deposition and were heated at 265°C, just below the melting point of Bi (271°C), for 150 to 200 hr. By this heat treatment, solid-state alloying reaction takes place at the interface between the two layers and as many as four kinds of new alloy phases were found to appear.

Microstructural determination of a metastable phase during rhodium oxidation

1989 ◽  
Vol 47 ◽  
pp. 262-263
Author(s):  
A. David Logan
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Volume Expansion ◽  
Lattice Structure ◽  
Metastable Phase ◽  
Active Surface ◽  
High Resolution Electron Microscopy ◽  
Silica Spheres ◽  
Resolution Electron

In heterogeneous catalysis, oxidation of the catalyst is frequently used as a means of removing impurities from the active surface. However, bulk oxidation severely alters the microstructure of the metal due to atom repositioning and valence changes. Transformation of Rh to Rh2O3 causes the lattice structure to change from fcc to hexagonal with a resulting volume expansion of 90% due to density changes. This is the reported cause for fracturing of crystallites and variations in reactivity. In this study, microstructural changes during progressive oxidation of 5 nm metal Rh particles have been examined.A 2 wt% Rh/Silica catalyst was prepared using Rh(III)-2,4 pentanedionate as a precursor and nonporous silica spheres as a support. The catalyst was then reduced in flowing H2 at 473 K. High resolution electron microscopy (HREM) was performed on a JEM-4000EX having a point resolution of 0.17 nm. The catalyst was oxidized in research purity O2 (Matheson 99.99%) using an all glass volumetric chemisorption system.

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.

Preparation and structural characterization of sputtered CoO, NiO, and Ni0.5Co0.5O thin epitaxial films

1991 ◽  
Vol 6 (12) ◽  
pp. 2680-2687 ◽  
Author(s):  
M.J. Carey ◽  
F.E. Spada ◽  
A.E. Berkowitz ◽  
W. Cao ◽  
G. Thomas
Keyword(s):  
Single Phase ◽  
High Resolution Electron Microscopy ◽  
Lattice Parameter ◽  
Epitaxial Films ◽  
X Ray Diffraction ◽  
Cross Sectional ◽  
Resolution Electron ◽  
Axis Parallel ◽  
Oxide Substrate

Single phase CoO, NiO, and Ni0.5Co0.5O epitaxial films have been prepared by reactive sputtering onto 〈0001〉 α−Al2O3 substrates maintained at 373 K. Epitaxy was confirmed by x-ray diffraction (XRD) and high resolution electron microscopy (HREM) techniques. XRD experiments indicate that these monoxide films are cubic and contain rotation twins with the twin axis parallel to 〈111〉. Lattice parameters for the CoO and NiO films are 0.4254 ± 0.0001 nm and 0.4173 ± 0.0006 nm, respectively, and agree with published values for the corresponding bulk oxides. The lattice parameter 0.4220 ± 0.0001 nm for the Ni0.5Co0.5O film lies between those of CoO and NiO and suggests that the mixed oxide film is compositionally homogeneous. Cross-sectional HREM images of the Ni0.5Co0.5O specimen show Σ3(12) twin boundaries perpendicular to the oxide-substrate interface. The twin regions are approximately 30 nm in size and are uniformly distributed throughout the film. The epitaxial orientation of the monoxide films with respect to the substrate can be summarized by the relationships [111] monoxide // [0001] α−Al2O3, [10] monoxide // [100] α−Al2O3, and [11] monoxide // [110] α−Al2O3.

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).

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