# Thin layers
This example shows how to add layers in a specific material to your structure and can be reproduced with `examples/layers.py` input file. The structure contains an array of layers (or "interfaces") defined in the input file as:
```
INTERFACES = []
period = 20e-9 # modify this value to change the distance between two interfaces
start_x = -WIDTH / 2 + period
end_x = WIDTH / 2 - period
INTERFACE_ROUGHNESS = 1.5e-9 # roughness of the interfaces
x = start_x
while x <= end_x:
INTERFACES.append(VerticalPlane(position_x=x, roughness=INTERFACE_ROUGHNESS, inner_material='Ge', outer_material=MEDIA, depth = THICKNESS)) # add the material of the layers here
x += period
```
Here, the `INTERFACE` list is filled with the `VerticalPlane` objects. This will create a structure that looks like the figure below, where the thin layers are indicated by the black lines:
If we increase the number of phonons to several thousand, we can see some interesting curves. For example, the transmission factor as a function of the incident angles. Each curve corresponds to one frequency, and each color corresponds to one mode.
To better observe the influence of frequency on transmission, this curve shows the phonon incident angle as a function of its frequency, with the transmission factor represented as a color map.
The file `information.txt` also contains various statistical insights, like the average transmission:
```
95% of particles reached the cold side
8.62% - scattering on side walls (99.88% - diffuse, 0.12% - specular)
1.60% - scattering on top and bottom walls (90.00% - diffuse, 10.00% - specular)
0.78% - rethermalization at the hot side
71.27% - internal scattering processes
18.33% - scattering on interfaces (24.08% - diffuse, 75.92% - specular)
67.81% - transmission through interfaces (24.72% - diffuse, 75.28% - specular)
```
