Simulating the translation of silicon nanowires in a liquid using thermophoresis
(2025) PHYM01 20242Solid State Physics
Department of Physics
- Abstract
- This study explores the potential of thermophoresis as a method of translating silicon nanowires in a liquid. Thermophoresis, the movement of particles against a temperature gradient, provides a scalable method of manipulating the particles. Simulations conducted in COMSOL examined both spherical and cylindrical approximations of nanowires, focusing on their translation under varying temperature gradients. In the cylindrical approximation, an electric field was defined around the nanowires to induce alignment and the strength of this field decided the degree of alignment with a higher field strength increasing the probability of a wire being aligned. A significant factor influencing nanowire motion is Brownian motion, which introduces... (More)
- This study explores the potential of thermophoresis as a method of translating silicon nanowires in a liquid. Thermophoresis, the movement of particles against a temperature gradient, provides a scalable method of manipulating the particles. Simulations conducted in COMSOL examined both spherical and cylindrical approximations of nanowires, focusing on their translation under varying temperature gradients. In the cylindrical approximation, an electric field was defined around the nanowires to induce alignment and the strength of this field decided the degree of alignment with a higher field strength increasing the probability of a wire being aligned. A significant factor influencing nanowire motion is Brownian motion, which introduces randomness to the particle's movement. Here translational Brownian motion was defined and simulated using a normal distribution and rotational Brownian motion was incorporated in the probability of having aligned wires. Results indicate that increasing temperature gradients and electric field strengths can significantly increase the wire velocities. In the spherical approximation, velocities of around 6 µm/min were achieved in a temperature gradient of 200 K/mm in a viscous liquid. Using the more realistic cylindrical approximation, velocities of around 4 to 5 µm/min were achieved in the same gradient. Brownian motion remains a limiting factor, contributing to wider wire velocity distributions and worsening the efficiency of wire translation. While several approximations were employed, the results provide conservative estimates of induced thermophoretic velocities when fighting against Brownian motion. (Less)
- Popular Abstract
- With a size one thousand times smaller than the width of a human hair, nanowires are an interesting area of research thanks to all of the intricate properties and phenomena that arise at this tiny scale, many of which are unheard of in our regular lives. Their small size is what makes them useful. You can find them in solar cells, LEDs, transistors, and DNA-sequencing, to name a few areas. The tiny scale is also what makes them difficult to handle. Many applications require thousands, if not millions, of wires to work together. Consequently, it is not practical to handle them one by one to put them in the correct location and rotation. You would be better off finding a method to manipulate them in bulk.
Placing your nanowires in an... (More) - With a size one thousand times smaller than the width of a human hair, nanowires are an interesting area of research thanks to all of the intricate properties and phenomena that arise at this tiny scale, many of which are unheard of in our regular lives. Their small size is what makes them useful. You can find them in solar cells, LEDs, transistors, and DNA-sequencing, to name a few areas. The tiny scale is also what makes them difficult to handle. Many applications require thousands, if not millions, of wires to work together. Consequently, it is not practical to handle them one by one to put them in the correct location and rotation. You would be better off finding a method to manipulate them in bulk.
Placing your nanowires in an electric field induces a dipole in them which can be used to control their rotation. This dipole can be compared to a compass needle. Just like a compass needle, the nanowires will tend to align with the field lines, making them point to the `north'.
This is the starting point of this thesis. It attempts to find a way to move the wires lengthwise after they have aligned with the field. This is done with a focus on a phenomenon called thermophoresis which can push particles away from hot areas to cold ones. Intuitively, this effect can be explained using the kinetic energy of the fluid surrounding the nanowire. If the fluid on one side of the particle is hotter than on the other, the fluid molecules will have a higher kinetic energy on the hot side compared to the cold. This results in a pressure-difference on the two sides which pushes the wire toward colder regions.
The effects of thermophoresis in a liquid are simulated based on existing models of its inner workings. Each nanowire is also affected by Brownian motion. This is a phenomenon first explained by Einstein which causes small particles to rotate and move around randomly. As a result, each nanowire follows a unique path. Hundreds of wires are tracked to explore how Brownian motion and thermophoresis contribute to the nanowires' overall behaviour.
The results show that Brownian motion is completely dominant on a short time scale of a few tens of seconds. However, thermophoresis wins in the long run if the parameters governing its magnitude are optimised, although this requires a very high temperature difference between the hot and cold areas. This suggests that thermophoresis can effectively manipulate nanowires in bulk, making it a valuable method for large-scale transport in manufacturing. (Less)
Please use this url to cite or link to this publication:
http://lup.lub.lu.se/student-papers/record/9182572
- author
- Froste, Sebastian LU
- supervisor
- organization
- course
- PHYM01 20242
- year
- 2025
- type
- H2 - Master's Degree (Two Years)
- subject
- keywords
- thermophoresis, nanowires, electric field, temperature gradient, particle tracing, Brownian motion
- language
- English
- id
- 9182572
- date added to LUP
- 2025-01-24 12:52:36
- date last changed
- 2025-01-24 12:52:36
@misc{9182572,
abstract = {{This study explores the potential of thermophoresis as a method of translating silicon nanowires in a liquid. Thermophoresis, the movement of particles against a temperature gradient, provides a scalable method of manipulating the particles. Simulations conducted in COMSOL examined both spherical and cylindrical approximations of nanowires, focusing on their translation under varying temperature gradients. In the cylindrical approximation, an electric field was defined around the nanowires to induce alignment and the strength of this field decided the degree of alignment with a higher field strength increasing the probability of a wire being aligned. A significant factor influencing nanowire motion is Brownian motion, which introduces randomness to the particle's movement. Here translational Brownian motion was defined and simulated using a normal distribution and rotational Brownian motion was incorporated in the probability of having aligned wires. Results indicate that increasing temperature gradients and electric field strengths can significantly increase the wire velocities. In the spherical approximation, velocities of around 6 µm/min were achieved in a temperature gradient of 200 K/mm in a viscous liquid. Using the more realistic cylindrical approximation, velocities of around 4 to 5 µm/min were achieved in the same gradient. Brownian motion remains a limiting factor, contributing to wider wire velocity distributions and worsening the efficiency of wire translation. While several approximations were employed, the results provide conservative estimates of induced thermophoretic velocities when fighting against Brownian motion.}},
author = {{Froste, Sebastian}},
language = {{eng}},
note = {{Student Paper}},
title = {{Simulating the translation of silicon nanowires in a liquid using thermophoresis}},
year = {{2025}},
}