how I can define a infinite layer of Vacuum. It is no clear the substrate how can be defined in the structure
Hello and welcome to the forum 
This is a general forum about the Julia programming language, your question is missing a lot of vital information for people to know what you are talking about. I assume you are talking about a specific package, and not “general usage of Julia”?
Ok you right my question is on pakages TransmissionMatrix
As far as I know there is no such package. Perhaps you mean the package TransferMatrix.jl? Or the package RigorousCoupledWaveAnalysis.jl ?
sorry [[ANN] TransferMatrix.jl
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You could define the vacuum as custom material as described here: Tutorial · TransferMatrix.jl. The refractive index of vacuum is 1.
Not so sure about the substrate, but isn’t it also be made of a specific material?