How to shrink the grid at will?

Hello everyone, I now have a model of a 2mm × 2mm rectangle, and I want to refine the mesh on a side thickness of 100nm, each mesh size is about 1nm, how do I achieve this?
I have tried using the refine method, but this does not work because the mesh is too small and the scale is too different. Thank you very much!

Given the length scale approaching machine precision, nondimensionalising your problem to some degree is likely the best approach.

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Oh, this seems to be a blind spot that I dare not touch, how can I achieve this process? Can you recommend some tutorials? I need to solve a reaction-diffusion model, thank you!

It’s a very common technique and nothing to fear, e.g:

Bear in mind that you’re not obliged to commit a complete nondimensionalisation. You could simply introduce a length scale in your underlying problem. This would mitigate numerical precision issues with the computational geometry.

There are also various works on this.
Here is a free springer brief:

All right, thank you.