scholarly journals Computational Study of Quenching Effects on Growth Processes and Size Distributions of Silicon Nanoparticles at a Thermal Plasma Tail

Nanomaterials ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 1370
Author(s):  
Masaya Shigeta ◽  
Yusuke Hirayama ◽  
Emanuele Ghedini
Keyword(s):  
Thermal Plasma ◽  
Silicon Nanoparticles ◽  
Computational Study ◽  
Melting Point Depression ◽  
Type Model ◽  
Size Distributions ◽  
Growth Processes ◽  
Cooling Rates ◽  
Nanoparticle Growth ◽  
Plasma Tail

In this paper, quenching effects on silicon nanoparticle growth processes and size distributions at a typical range of cooling rates in a thermal plasma tail are investigated computationally. We used a nodal-type model that expresses a size distribution evolving temporally with simultaneous homogeneous nucleation, heterogeneous condensation, interparticle coagulation, and melting point depression. The numerically obtained size distributions exhibit similar size ranges and tendencies to those of experiment results obtained with and without quenching. In a highly supersaturated state, 40–50% of the vapor atoms are converted rapidly to nanoparticles. After most vapor atoms are consumed, the nanoparticles grow by coagulation, which occurs much more slowly than condensation. At higher cooling rates, one obtains greater total number density, smaller size, and smaller standard deviation. Quenching in thermal plasma fabrication is effectual, but it presents limitations for controlling nanoparticle characteristics.

A Model for Heterogeneous Nucleation and Growth of Silicon Nanoparticles on Silicon Dioxide from Disilane

2001 ◽  
Vol 686 ◽  
Author(s):  
William T. Leach ◽  
Jian-Hong Zhu ◽  
John G. Ekerdt ◽  
Supika Mashiro ◽  
Junro Sakai ◽  
...  
Keyword(s):  
Silicon Dioxide ◽  
Silicon Nanoparticles ◽  
Chemical Vapor ◽  
Model Parameters ◽  
Size Distributions ◽  
Temperature Influence ◽  
Growth Pressure ◽  
Nanoparticle Deposition ◽  
Nanoparticle Growth ◽  
Pressure Chemical

AbstractA model is presented that describes silicon nanoparticle deposition in terms of disilane decomposition on silicon dioxide, adatom diffusion, nucleation, nanoparticle growth and coalescence. Total nanoparticle densities are output as a function of time, and segregation of nanoparticles into subsets with common size allows size distributions to be reported for all times during the simulation. Model parameters are fit to low pressure chemical vapor deposition data with disilane pressures ranging from 5×10−4 to 5×10−3 Torr and surface temperatures from 510 to 570 °C. Simulations are used to explain how growth pressure and surface temperature influence incubation time, nanoparticle density and size distribution.

Impact of Graupel Parameterization Schemes on Idealized Bow Echo Simulations

2013 ◽  
Vol 141 (4) ◽  
pp. 1241-1262 ◽  
Author(s):  
Rebecca D. Adams-Selin ◽  
Susan C. van den Heever ◽  
Richard H. Johnson
Keyword(s):  
Complete Removal ◽  
Cold Pool ◽  
Size Distributions ◽  
Pressure Gradients ◽  
Cooling Rates ◽  
Cold Pools ◽  
Highly Sensitive ◽  
Bow Echo ◽  
Mean Size ◽  
Microphysical Processes

Abstract The effect of changes in microphysical cooling rates on bow echo development and longevity are examined through changes to graupel parameterization in the Advanced Research Weather Research and Forecasting Model (ARW-WRF). Multiple simulations are performed that test the sensitivity to different graupel size distributions as well as the complete removal of graupel. It is found that size distributions with larger and denser, but fewer, graupel hydrometeors result in a weaker cold pool due to reduced microphysical cooling rates. This yields weaker midlevel (3–6 km) buoyancy and pressure perturbations, a later onset of more elevated rear inflow, and a weaker convective updraft. The convective updraft is also slower to tilt rearward, and thus bowing occurs later. Graupel size distributions with more numerous, smaller, and lighter hydrometeors result in larger microphysical cooling rates, stronger cold pools, more intense midlevel buoyancy and pressure gradients, and earlier onset of surface-based rear inflow; these systems develop bowing segments earlier. A sensitivity test with fast-falling but small graupel hydrometeors revealed that small mean size and slow fall speed both contribute to the strong cooling rates. Simulations entirely without graupel are initially weaker, because of limited contributions from cooling by melting of the slowly falling snow. However, over the next hour increased rates of melting snow result in an increasingly more intense system with new bowing. Results of the study indicate that the development of a bow echo is highly sensitive to microphysical processes, which presents a challenge to the prediction of these severe weather phenomena.

Generation and Structural Analysis of Silicon Nanoparticles

1994 ◽  
Vol 358 ◽  
Author(s):  
Ping Li ◽  
Klaus Sattler
Keyword(s):  
Structural Analysis ◽  
Atomic Force Microscope ◽  
Silicon Nanoparticles ◽  
Pyrolytic Graphite ◽  
Silicon Wafers ◽  
Silicon Substrates ◽  
Size Distributions ◽  
Particle Interactions ◽  
Atomic Force ◽  
Silicon Vapor

ABSTRACTWe have generated 20 to 100 nm sized silicon nanoparticles and analyzed their morphologies using an atomic force microscope (AFM). The particles are formed by deposition of silicon vapor onto silicon wafers and highly oriented pyrolytic graphite (HOPG). On silicon substrates, the particles are close to spherical with relatively narrow size distributions and they are randomly located. On graphite substrates the particles are arranged in chains. Within the chains they show strong deformations in the contact areas. We relate this to covalent inter-particle interactions.

Crystallization Kinetics of Plasma-Produced Amorphous Silicon Nanoparticles

2013 ◽  
Vol 1536 ◽  
pp. 213-218 ◽  
Author(s):  
Thomas Lopez ◽  
Lorenzo Mangolini
Keyword(s):  
Experimental Evidence ◽  
Residence Time ◽  
Thermal Plasma ◽  
Silicon Nanoparticles ◽  
Plasma Reactor ◽  
Crystallization Kinetic ◽  
Plasma Heating ◽  
Particle Interaction ◽  
Crystalline Powder ◽  
Non Thermal Plasma

ABSTRACTThe use of a continuous flow non-thermal plasma reactor for the formation of silicon nanoparticles has attracted great interest because of the advantageous properties of the process [1]. Despite the short residence time in the plasma (around 10 milliseconds), a significant fraction of the precursor, silane, is converted and collected in the form of nanopowder. The structure of the produced powder can be tuned between amorphous and crystalline by adjusting the power of the radio-frequency excitation source, with higher power leading to the formation of crystalline particles. Numerical modeling suggests that higher excitation power results in a higher plasma density, which in turn increases the nanoparticle heating rate due to the interaction between ions, free radicals and the nanopowder suspended in the plasma [2]. While the experimental evidence suggests that plasma heating may be responsible for the formation of crystalline powder, an understanding of the mechanism that leads to the crystallization of the powder while in the plasma is lacking. In this work, we present an experimental investigation on the crystallization kinetic of plasma-produced amorphous powder. Silicon nanoparticles are nucleated and grown using a non-thermal plasma reactor similar to the one described in [1], but operated at low power to give amorphous nanoparticles in a 3-10 nm size range. The particles are then extracted from the reactor using an orifice and aerodynamically dragged into a low pressure reactor placed in a tube furnace capable of reaching temperatures up to 1000°C. Raman and TEM have been used to monitor the crystalline fraction of the material as a function of the residence time and temperature. It is expected that for a residence time in the annealing region of approximately ∼300 milliseconds, a temperature of at least 750 °C is needed to observe the onset of crystallization. A range of crystalline percentages can be observed from 750 °C to 830 °C. A discussion of particle growth and particle interaction, based on experimental evidence, will be presented with its relation to the overall effect on crystallization. Further data analysis allows extrapolating the crystallization rate for the case of this simple, purely thermal system. We conclude that thermal effects alone are not sufficient to explain the formation of crystalline powder in non-thermal plasma reactors.

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