Date: May 31, 2021

Dataset Title: On the growth of Si nanoparticles in non-thermal plasma: physisorption to chemisorption conversion

Dataset Creators: Xuetao Shi, Paolo Elvati, Angela Violi

Dataset Contact: Angela Violi avioli@umich.edu

Funding: US Army Research Office MURI grant W911NF-18-1-0240


Key Points:

- The collisions of SiHx (x=1-4) fragments and silicon cluster (Si4, Si2H6, and Si29H36) surfaces, responsible for the sticking coefficients, are simulated by molecular dynamics (MD) with a reactive force field. 
- The dependence of sticking coefficients on temperature, H coverage of both silane fragments and cluster surfaces, and the size of the cluster, are systematically examined.
- The mechanism underlying the sticking events, specifically the conversion of physical aggregation to chemisorption is investigated to better understand the complex interplay between factors influencing the surface growth.


Research Overview:
Non-thermal plasma systems offer unique opportunities in the fields of bio-imaging, drug delivery, photovoltaics, microelectronics manufacturing. Such interests are largely inspired by the fact that hot plasma electrons coexist with neutral species and ions close to room-temperature under non-thermal plasma conditions. Modeling of these systems requires a deep understanding of the atomistic processes underlying the rich chemistry of the various radicals and ions with the nascent nanoparticle surface. A key parameter for determining the contribution of a certain radical/ion species to the nanoparticle surface growth, called sticking coefficient, is computed as a weighted sum from the simulated sticking outcomes with different collision velocities drawn from a Maxwell-Boltzmann distribution at certain temperatures. In this work, the collisions of SiHx (x=1-4) fragments and silicon cluster (Si4, Si2H6, and Si29H36) surfaces, responsible for the sticking coefficients, are simulated by molecular dynamics (MD) with a reactive force field. The dependence of sticking coefficients on temperature, H coverage of both silane fragments and cluster surfaces, and the size of the cluster, are systematically examined. And the mechanism underlying the sticking events, specifically the conversion of physical aggregation to chemisorption is investigated to better understand the complex interplay between factors influencing the surface growth. The detailed and multi-parameter model of sticking coefficients, accompanied by the mechanism study of physisorption to chemisorption conversion, provides a more accurate and robust approximation of surface growth rate using sticking coefficients, and a deeper understanding of surface growth processes, for the wider non-thermal plasma simulation community.

Methodology:
The data are mechanism labeling of the Molecular Dynamics (MD) simulation trajectories at the end of allocated simulation time. The MD simulation is carried out using LAMMPS and the atomic interactions were modeled using a classical all-atom reactive force field. The labeling is made by computing the composition and the number of clusters in the system.
Two atoms were assigned to the same cluster if their distance was less than twice their typical bond length, namely 0.44, 0.32 and 0.148 nm for Si/Si, Si/H, and H/H pairs, respectively. 

If the trajectory outcome is non-sticking (more than one cluster), the label is "-1";
If the trajectory outcome is  physisorption (one cluster, but no chemical bond formed), the label is "0";
If the trajectory outcome is chemisorption (one cluster, chemical bonds formed), the label is "1", "2", "3", "4", where the numerical value corresponds to the number new bonds formed. 

Instrument and/or Software specifications: NA


Files contained here:
The 12 CSV files corresponds to the 12 collision systems studied in this work. 
Each entry corresponds to the label of one of the MD trajectories for this system with the system temperature, molecular orientation configurations, and impact velocity interval percentages in CDF. 
There are 5 temperatures: 300K, 400K, 500K, 600K, and 900K. 
There are 5 configurations, denoted "2, 4, 6, 8, 10", for both impacting fragments. 
And therefore there could be 5*5=25 configurations (not all of them may be sampled).


Related publication(s):
Shi, X., Elvati, P., Violi, A. (2021). On the growth of Si nanoparticles in non-thermal plasma: physisorption to chemisorption conversion. J. Phys. D. Submitted.

Use and Access: 
This data set is made available under a Creative Commons Public Domain license (CC0 1.0).