Discussion Forum

Apologies, as I am fairly new to COMSOL.

I am trying to simulate using a pulsed laser to melt and recrystallize silicon. Right now, I am just trying to model the rapid solidification after the melting has been done. I am doing a 2D simulation with a 10 um x 10 um piece of Si using heat transfer in solids and liquids with a time-dependent study. I am starting with a 100 nm thick layer of liquid Si at the top of the sample. For the sides, I have periodic boundary conditions, and the bottom is held at constant temperature. I also have surface-to-ambient radiation on the top surface. I give it an initial temperature distribution where the interface is at the melting point of Si, and then there is a linear temp distribution in the solid that goes from the melting temp to room temp. In the liquid layer, I set the top surface to be at a temperature higher than the melting temp and again use a linear temp distribution in that layer.

What I am ultimately trying to get is the position of the liquid/solid interface as a function of time. Right now, it is working to the point that I can see the interface move towards the top surface with time, but the simulation gets an error at one point that is due to the mesh. Then it stops the simulation at that point, but it does give me all the data for the time points before that happens. I believe that when the liquid part is completely solidified, it has zero thickness, so when it tries to mesh, it can't make an appropriate mesh element, which is why it gives the error.

I have two questions:

1. Is there a way to tell the simulation to stop once the top layer is fully solidified so that I don't get this error?

2. How can I extract the position of the interface as a function of time?