Grain boundaries in overlayer on a substrate

Let’s assume there are only two ways to get grain boundaries in the universe of grain boundaries in layers materials. First, the overlayer is feeling strain due to the existence of the substrate under it. Second, due to multiple nucleation sites result in multiple domains which results merging of those domains and hence the grain boundaries.

In below paper, the authors are working on the second reason by neglecting the first on the basis of interaction between substrate and overlayer is too weak to produce any strain in overlayer due to lattice mismatch or any other reason.

Now let’s apply the limits on these scenarios and see what we get. First case, let’s assume the overlayer was grown by only a single nucleation site and hence single grain and hence no grain boundary. And starting from 0 interaction between overlayer and sublayer, we are increasing the interaction gradually to infiniti. A question can be asked in this hypothetical scenario of increasing the interaction gradually, do we reach a point (before hitting infinity) where the single-crystal-overlayer will start experiencing a distortion in its crystal in a way to have more than one crystal. If yes then what is that threshold. We know from our real-life experience that this threshold do exist and it is way less than infinity because whenever we grow overlayer in a lab over substrate it HAS multiple domains and hence grain boundaries.

On the second grain boundary reason, we can setup a hypothetical scenarios like following. For a given interaction between substrate and overlayer, do at least one combination of all growth parameters exist (among all their permutations and combinations) so that we will have more than one nucleation site but the grains originating from all nucleation sites will have SAME orientation and no grain boundaries!* A let’s take it one step further, how this combination varies as a function of the interaction between substrate and overlayer.

I got the above thoughts from this paper

A few days after writing this blog post I came across this paper[1]. It almost demonstrates the same idea i.e. they observed orientation dispersion of MoS2 resulting into wafer scale MoS2.

Thank you for stopping-by, have a good day/night ahead.


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