On The Melting of Amorphous Ge and Si

1981 ◽  
Vol 7 ◽  
Author(s):  
David Turnbull
Keyword(s):  
Glass Transition ◽  
External Surface ◽  
Rapid Heating ◽  
Diffusion Constant ◽  
Nucleation And Growth ◽  
The Self ◽  
Metallic State ◽  
Equilibrium Melting Temperature ◽  
Self Diffusion ◽  
Limiting Values

ABSTRACTThe amorphous semiconducting phase (a-sc) of Si or Ge is so resistant to crystallization that rapid heating may bring it into a temperature regime in which it melts. Such melting might occur in one or the other of two ways, either homogeneously, by the reverse of the glass transition, to a viscous semi-conducting melt (ℓ-sc) or by transition, probably by nucleation and growth, to the molten metallic state (ℓm). Using the self-diffusion constant of the crystalline elements in conjunction with the Stokes-Einstein equation, upper limiting values of the glass transition (a-sc→ℓ-sc) temperatures of Si and Ge were calculated. These were of the order 0.6 to 0.65 Tcℓ for slow and 1.1 Tcℓ for ultra rapid heating, where Tcℓ is the equilibrium melting temperature of the crystal. Arguments are given that superheating to a temperature 1.15 to 1.25 Taℓ (a-sc↔ℓm in equilibrium at temperature T = Taℓ< Tcℓ) may be required for copious internal nucleation of im in a-sc. At lesser superheating the transition must be initiated at internal flaws (e.g. voids) or at the external surface of the a-sc film. Therefore the superheating at perceptible onset of the transition during rapid heating can vary widely from specimen to specimen, depending on the flaw concentration and how the external surface of a-sc was treated.

scholarly journals Self-Diffusion Coefficients, Aggregation Numbers and the Range of Existence of Spherical Micelles of Oxyethylated Alkylphenols

2021 ◽  
Author(s):  
Victor P. Arkhipov ◽  
Natalia A. Kuzina ◽  
Andrei Filippov
Keyword(s):  
Aqueous Solutions ◽  
Diffusion Coefficients ◽  
The Self ◽  
Self Diffusion ◽  
Aggregation Numbers ◽  
Temperature Ranges ◽  
Spherical Micelles ◽  
Limiting Values

AbstractAggregation numbers were calculated based on measurements of the self-diffusion coefficients, the effective hydrodynamic radii of micelles and aggregates of oxyethylated alkylphenols in aqueous solutions. On the assumption that the radii of spherical micelles are equal to the lengths of fully extended neonol molecules, the limiting values of aggregation numbers corresponding to spherically shaped neonol micelles were calculated. The concentration and temperature ranges under which spherical micelles of neonols are formed were determined.

Molecular-Dynamics Analysis of the Structural Properties of Silica during Cooling

2008 ◽  
Vol 139 ◽  
pp. 101-106 ◽  
Author(s):  
Byoung Min Lee ◽  
Shinji Munetoh ◽  
Teruaki Motooka ◽  
Yeo Wan Yun ◽  
Kyu Mann Lee
Keyword(s):  
Molecular Dynamics ◽  
Glass Transition ◽  
Transition Temperature ◽  
Structural Properties ◽  
Diffusion Coefficients ◽  
The Self ◽  
Dynamics Analysis ◽  
Self Diffusion ◽  
Dynamics Simulations ◽  
Potential Parameters

The structural properties of SiO2 liquid during cooling have been investigated by molecular dynamics simulations. The interatomic forces acting on the particles are calculated by the modified Tersoff potential parameters. The glass transition temperature and structural properties of the resulting SiO2 system at various temperatures have been investigated. The fivefold coordinations of Si and threefold coordinations of O atoms were observed, and the coordination defects of system decrease with decreasing temperature up to 17 % at 300 K. The self-diffusion coefficients for Si and O atoms drop to almost zero below 3000 K. The structures were distorted at high temperatures, but very stable atomic network persisted up to high temperature in the liquid state.

scholarly journals Evidence for Glass Behavior in Amorphous Carbon

2020 ◽  
Vol 6 (3) ◽  
pp. 50 ◽  
Author(s):  
Steven Best ◽  
Jake B. Wasley ◽  
Carla de Tomas ◽  
Alireza Aghajamali ◽  
Irene Suarez-Martinez ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Diffusion Coefficient ◽  
Glass Transition ◽  
Transition Temperature ◽  
Amorphous Carbon ◽  
The Self ◽  
Self Diffusion ◽  
Dynamics Simulations ◽  
Self Diffusion Coefficient ◽  
Glass Behavior

Amorphous carbons are disordered carbons with densities of circa 1.9–3.1 g/cc and a mixture of sp2 and sp3 hybridization. Using molecular dynamics simulations, we simulate diffusion in amorphous carbons at different densities and temperatures to investigate the transition between amorphous carbon and the liquid state. Arrhenius plots of the self-diffusion coefficient clearly demonstrate that there is a glass transition rather than a melting point. We consider five common carbon potentials (Tersoff, REBO-II, AIREBO, ReaxFF and EDIP) and all exhibit a glass transition. Although the glass-transition temperature (Tg) is not significantly affected by density, the choice of potential can vary Tg by up to 40%. Our results suggest that amorphous carbon should be interpreted as a glass rather than a solid.

scholarly journals Time-of-flight modulated intensity small-angle neutron scattering measurement of the self-diffusion constant of water

2021 ◽  
Vol 54 (3) ◽  
Author(s):  
Stephen J. Kuhn ◽  
Niels Geerits ◽  
Christian Franz ◽  
Jeroen Plomp ◽  
Robert M. Dalgliesh ◽  
...  
Keyword(s):  
Neutron Scattering ◽  
Small Angle ◽  
Small Angle Neutron Scattering ◽  
Spin Echo ◽  
Time Of Flight ◽  
Diffusion Constant ◽  
The Self ◽  
Neutron Resonance ◽  
High Energy Resolution ◽  
Self Diffusion

The modulated intensity by zero effort small-angle neutron scattering (MI-SANS) technique is used to measure scattering with a high energy resolution on samples normally ill-suited for neutron resonance spin echo. The self-diffusion constant of water is measured over a q–t range of 0.01–0.2 Å−1 and 70–500 ps. In addition to demonstrating the methodology of using time-of-flight MI-SANS instruments to observe diffusion in liquids, the results support previous measurements on water performed with different methods. This polarized neutron technique simultaneously measures the intermediate scattering function for a wide range of time and length scales. Two radio frequency flippers were used in a spin-echo setup with a 100 kHz frequency difference in order to create a high-resolution time measurement. The results are compared with self-diffusion measurements made by other techniques and the general applicability of MI-SANS at a pulsed source is assessed.

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