The simplest way to generate a hollow object or an object with a coated core (core-shell) is to add two solid concentric objects which overlap in the central region, and set the mesh order of the objects appropriately.
The mesh order is a property which can either be set from the material database, or in the object properties. In regions where several objects overlap, the material with a smaller mesh order number will take priority. For more information about setting the mesh order property, see this page:
A common example is a coated spherical nanoparticle. To create this, you can add two concentric sphere objects centered at the same location. If the core object with a smaller radius has a mesh order of 1, and the coating object with a larger radius has the default mesh order of 2, then the core material will included in the simulation.
For a hollow object, you can set the material of the core object to “Etch” which will use the background index of the simulation region. The “Etch” material is the only material in the material database with a default mesh order of 1, so without modifying any of the mesh order properties, you can simulate a hollow core structure.
core_shell.fsp (231.8 KB) This simulation file contains an example of a core-shell structure with a gold core and dielectric shell where the mesh order of the core is set to 1. Using the refractive index monitor, you can plot the index profile over space to verify the structure which gets simulated.