TEM studies of amorphization processes and amorphous structures

1988 ◽  
Vol 46 ◽  
pp. 448-449
Author(s):  
T. E. Mitchell ◽  
R. B. Schwarz
Keyword(s):  
Amorphous Materials ◽  
Fission Products ◽  
Rapid Quenching ◽  
Surface Films ◽  
List Type ◽  
Oxide Glasses ◽  
Crystalline Materials ◽  
Amorphous Structures ◽  
Amorphous Surface ◽  
Interfacial Films

Traditional oxide glasses occur naturally as obsidian and can be made easily by suitable cooling histories. In the past 30 years, a variety of techniques have been discovered which amorphize normally crystalline materials such as metals. These include [1-3]:Rapid quenching from the vapor phase.Rapid quenching from the liquid phase.Electrodeposition of certain alloys, e.g. Fe-P.Oxidation of crystals to produce amorphous surface oxide layers.Interdiffusion of two pure crystalline metals.Hydrogen-induced vitrification of an intermetal1ic.Mechanical alloying and ball-milling of intermetal lie compounds.Irradiation processes of all kinds using ions, electrons, neutrons, and fission products.We offer here some general comments on the use of TEM to study these materials and give some particular examples of such studies.Thin specimens can be prepared from bulk homogeneous materials in the usual way. Most often, however, amorphous materials are in the form of surface films or interfacial films with different chemistry from the substrates.

Formation and Stability of Extended Solid Solutions Made by Rapid Quenching from the Melt

1981 ◽  
Vol 8 ◽  
Author(s):  
Howard Jones
Keyword(s):  
Heat Treatment ◽  
Solid Solutions ◽  
Solid Solubility ◽  
Rapid Quenching ◽  
List Type ◽  
Type Number ◽  
Alloy Development ◽  
Equilibrium Conditions ◽  
Present Contribution ◽  
Bulk Production

ABSTRACTExtension of solid solubility by rapid quenching from the melt (RQM) enormously increases scope for alloy development in metals such as aluminium for which solid solubility is particularly limited under equilibrium conditions. The present contribution reviews mainly recent work concerned with matching of experimental observations with predictions affecting:(1)conditions for solidification without change in composition(2)temperatures and modes of deconposition on subsequent heating(3)hardening effects as-quenched and on heat treatment.The significance of such findings for bulk production and consolidation of wrought products for engineering applications is briefly discussed.

Characterization of Amorphous Materials by Electron Diffraction and Atomistic Modeling

2000 ◽  
Vol 6 (4) ◽  
pp. 329-334 ◽  
Author(s):  
D.J.H. Cockayne ◽  
D.R. McKenzie ◽  
W. McBride ◽  
C. Goringe ◽  
D. McCulloch
Keyword(s):  
Molecular Dynamics ◽  
Electron Diffraction ◽  
Diffraction Data ◽  
Amorphous Materials ◽  
Atomistic Modeling ◽  
Amorphous Structures

AbstractThe technique of energy selected electron diffraction gives information about amorphous structures which can be used to characterize amorphous materials in terms of their structure. The diffraction data can be used to refine models obtained using molecular dynamics, resulting in physically reasonable models consistent with the diffraction data.

scholarly journals Tunable continuous wave emission via phase-matched second harmonic generation in a ZnSe microcylindrical resonator

2015 ◽  
Vol 5 (1) ◽  
Author(s):  
N. Vukovic ◽  
N. Healy ◽  
J. R. Sparks ◽  
J. V. Badding ◽  
P. Horak ◽  
...  
Keyword(s):  
Second Harmonic Generation ◽  
Harmonic Generation ◽  
Amorphous Materials ◽  
Continuous Wave ◽  
Frequency Comb ◽  
Second Harmonic ◽  
Red Light ◽  
Nonlinear Phenomena ◽  
Optical Processing ◽  
Crystalline Materials

Abstract Whispering gallery mode microresonators made from crystalline materials are of great interest for studies of low threshold nonlinear phenomena. Compared to amorphous materials, crystalline structures often exhibit desirable properties such as high indices of refraction, high nonlinearities and large windows of transparency, making them ideal for use in frequency comb generation, microlasing and all-optical processing. In particular, crystalline materials can also possess a non-centrosymmetric structure which gives rise to the second order nonlinearity, necessary for three photon processes such as frequency doubling and parametric down-conversion. Here we report a novel route to fabricating crystalline zinc selenide microcylindrical resonators from our semiconductor fibre platform and demonstrate their use for tunable, low power continuous wave second harmonic generation. Visible red light is observed when pumped with a telecommunications band source by a process that is phase-matched between different higher order radial modes, possible due to the good spatial overlap between the pump and signal in the small volume resonator. By exploiting the geometrical flexibility offered by the fibre platform together with the ultra-wide 500–22000 nm transmission window of the ZnSe material, we expect these resonators to find use in applications ranging from spectroscopy to quantum information systems.

MULTISCALE MODELING FOR AMORPHOUS MATERIALS — MAPPING ATOMISTIC DISPLACEMENTS TO MACROSCOPIC DEFORMATION

2012 ◽  
Vol 04 (04) ◽  
pp. 1250037 ◽  
Author(s):  
ZHOU CHENG SU ◽  
TONG-EARN TAY ◽  
YU CHEN ◽  
VINCENT B. C. TAN
Keyword(s):  
Amorphous Materials ◽  
Amorphous Material ◽  
Multiscale Simulations ◽  
Mathematical Form ◽  
Computational Domain ◽  
Crystalline Materials ◽  
Macroscopic Deformation ◽  
T Matrix ◽  
Representative Points ◽  
Good Agreement

A method to relate the displacements of atoms within a representative volume element (RVE) of amorphous material to the deformation of the RVE is presented. The displacement relationship is expressed as a mapping matrix, T, which operates on the displacements of representative points in the RVE to return the atom displacements within it. While the mapping operation has the same mathematical form as an interpolation operation, the T matrix is not an interpolant. It is derived taking into account atom displacements in amorphous materials which cannot be simplified as a continuous, much less homogenous, field. It is shown that the computational domain of a material can be partitioned into nonintersecting sub-domains comprising representative cells — pseudo-amorphous cells (PAC) — and sub-domains of atoms for concurrent multiscale simulations of amorphous materials through the T matrix. Multiscale simulations of nanoindentation on a polymer substrate using the T matrix show good agreement with pure molecular mechanics simulations. When homogenization techniques commonly used for crystalline materials were employed for the same simulations, they gave much less accurate predictions.

scholarly journals PDF Analysis on a Laboratory System: Adapting the Experiment to the Material

2014 ◽  
Vol 70 (a1) ◽  
pp. C870-C870
Author(s):  
Céleste Reiss ◽  
Milen Gateshki ◽  
Marco Sommariva
Keyword(s):  
Distribution Function ◽  
Pair Distribution Function ◽  
Amorphous Materials ◽  
Nearest Neighbors ◽  
High Energy ◽  
Experimental Point ◽  
Laboratory System ◽  
Crystalline Materials ◽  
X Ray ◽  
Pdf Analysis

The increased interest in recent years regarding the properties and applications of nanomaterials has also created the need to characterize the structures of these materials. However, due to the lack of long-range atomic ordering, the structures of nanostructured and amorphous materials are not accessible by conventional diffraction methods used to study crystalline materials. One of the most promising techniques to study nanostructures using X-ray diffraction is by using the total scattering (Bragg peaks and diffuse scattering) from the samples and the pair distribution function (PDF) analysis. The pair distribution function provides the probability of finding atoms separated by a certain distance. This function is not direction-dependent; it only looks at the absolute value of the distance between the nearest neighbors, the next nearest neighbors and so on. The method can therefore also be used to analyze non-crystalline materials. From experimental point of view a typical PDF analysis requires the use of intense high-energy X-ray radiation (E ≥ 20 KeV) and a wide 2θ range. After the initial feasibility studies regarding the use of standard laboratory diffraction equipment for PDF analysis [1-3] this application has been further developed to achieve improved data quality and to extend the range of materials, environmental conditions and geometrical configurations that can be used for PDF experiments. Studies performed on different nanocrystalline and amorphous materials of scientific and technological interest, including organic substances, oxides, metallic alloys, etc. have demonstrated that PDF analysis with a laboratory diffractometer can be a valuable tool for structural characterization of nanomaterials. This contribution presents several examples of laboratory PDF studies, in which the experimental conditions have been successfully adapted to match the specific requirements of materials under investigation.

scholarly journals EVALUATION OF REFLECTANCE FOR BUILDING MATERIALS CLASSIFICATION WITH TERRESTRIAL LASER SCANNER RADIATION

2021 ◽  
Vol 61 (1) ◽  
pp. 174-198
Author(s):  
Domenica Costantino ◽  
Massimiliano Pepe ◽  
Maria Giuseppa Angelini
Keyword(s):  
Laser Scanning ◽  
Amorphous Materials ◽  
Building Materials ◽  
Phase Measurement ◽  
Laser Scanner ◽  
Optical Diffraction ◽  
Degree Of Crystallinity ◽  
Crystalline Materials ◽  
Oblique Position ◽  
Reflectance Analysis

The main purpose of this work is the evaluation of the potential of Terrestrial Laser Scanning (TLS) technology to perform a reflectance analysis of scanned objects. A laser beam, having a coherent beam in the field of visible light (wavelength between 532nm and 680 nm), can lead to optical diffraction phenomena that allow a correlation between the degree of crystallinity of solids (in particular dispersed crystalline materials) and its reflectivity. Different materials with known crystallinity values have been examined and the diffraction value has been analysed for two types of lasers, one pulsed and the other phase measurement, with two different acquisition conditions (nadiral and oblique position). The results demonstrated the correlation by verifying that the incident laser light beam is more refracted by materials with a higher degree of crystallinity than less crystalline or amorphous materials.

scholarly journals Local structure analysis of amorphous materials by angstrom-beam electron diffraction

Microscopy ◽  
2020 ◽  
Author(s):  
Akihiko Hirata
Keyword(s):  
Electron Diffraction ◽  
Structure Analysis ◽  
Local Structure ◽  
Amorphous Materials ◽  
Rotational Symmetry ◽  
Diffraction Method ◽  
Beam Electron ◽  
Structure Information ◽  
Amorphous Structures ◽  
Global And Local

Abstract The structure analysis of amorphous materials still leaves much room for improvement. Owing to the lack of translational or rotational symmetry of amorphous materials, it is important to develop a different approach from that used for crystals for the structure analysis of amorphous materials. Here, the angstrom-beam electron diffraction method was used to obtain the local structure information of amorphous materials at a sub-nanometre scale. In addition, we discussed the relationship between the global and local diffraction intensities of amorphous structures, and verified the effectiveness of the proposed method through basic diffraction simulations. Finally, some applications of the proposed method to structural and functional amorphous materials are summarized.

Determination of Crystal Thickness from Relative Transmission Measurements

1975 ◽  
Vol 33 ◽  
pp. 242-243 ◽  
Author(s):  
D. C. Joy ◽  
D. M. Maher
Keyword(s):  
Amorphous Materials ◽  
Accurate Estimate ◽  
Foil Thickness ◽  
Specimen Thickness ◽  
Crystal Thickness ◽  
Crystalline Materials ◽  
Transmission Electron ◽  
Relative Transmission ◽  
History Of ◽  
Electron Intensity

An accurate knowledge of the specimen foil thickness often is required in quantitative transmission electron microscopy. The methods used for thickness determinations of thin crystalline materials (e.g. the trace method, thickness fringe counts and stereoscopic measurements) generally are selected according to the history of the specimen and nature of the microstructure. For amorphous materials a measurement of the relative transmission of electrons I/I0, where I is the transmitted and I0 the incident electron intensity, affords an accurate estimate of the specimen thickness. In this case, for a sufficiently large specimen thickness, I/I0 varies exponentially according to the mass thickness relationship e-μt, where μ is the mass absorption coefficient and t is the specimen thickness. The purpose of this paper is to demonstrate that the thickness of a crystalline specimen also may be determined accurately from a measurement of I/I0, provided that well defined diffracting conditions are used. The results presented here are for silicon.

Atomic Transport in Irradiated Solids

1993 ◽  
Vol 311 ◽  
Author(s):  
R.R. Averback ◽  
Mai Ghaly ◽  
Y.Y. Lee ◽  
H. Zhu
Keyword(s):  
Ion Beam ◽  
Rapid Quenching ◽  
Primary Role ◽  
Melting Points ◽  
Crystalline Materials ◽  
Enhanced Diffusion ◽  
Atomic Transport ◽  
Radiation Enhanced Diffusion ◽  
Radiation Induced ◽  
Kinetics Of

ABSTRACTAtomic transport in irradiated solids has been investigated in both the prompt and delayed regimes. Prompt effects are revealed on an atomic level through molecular dynamics computer simulations. It is demonstrated that for metals like gold, which have high atomic numbers and low melting points, thermal spikes play a primary role in the cascade dynamics and that concepts like melting and rapid quenching are useful descriptions. Surface effects in these metals are also discussed. For metals with higher melting points and lower atomic numbers, the cascade dynamics are determined almost exclusively by energetic collisions far above thermal energies. This is illustrated by simulations of cascades in NiAl. The effect of the high ordering energy in this intermetallic compound on the radiation-induced defect structure has also been studied.Atomic transport in the delayed regime is illustrated by two examples: an order-disorder alloy, Cu3Au, and an amorphous alloy, NiZr. The first example is used to illustrate various aspects of radiation enhanced diffusion (RED): ion beam mixing, diffusion kinetics, the effects of primary recoil spectrum, and the importance of chemical order. The second example illustrates that the basic theory of RED, which was developed to describe crystalline materials, appears to work adequately for amorphous metal alloys, suggesting that similar mechanisms may be operating. It is shown, however, that the kinetics of RED observed in amorphous alloys are not unique to point defect models.

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