Guilin Sun
Ansys Employee

This is a little tedious but you can do it:

you know the center locations for each nano particle, and know the radius, you can use script to add them. eg

1: specify the center xyz coordinates 
2: write a loop or nested loop, eg
for (n=1:10){

3: since they have the same radius and material, you  can use
set("material","Au (Gold) - CRC");

You could optimize the location parameters to use few loops in some cases. You know the triangle slope so it can be easy to find an analytical solution.

The script can be inside a structure group, or independent. It may need trial and error but I am sure you can do it by your own. Please refer some structure groups  in the object library.

PS: usually you would not include the air/Si interface inside the simulation region. otherwise it will beed large simulation volume and long simulation time, except the Sillicon is only a few um thick.