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Defining Layers

Similar to a range of different materials, there are a few different ways that a layer can be defined in :py:mod:`easyreflectometry`.

:py:class:`Layer`

The :py:class:`Layer` is the simplest possible type of layer, taking a :py:class:`Material` and two floats associated with the thickness and upper (that is closer to the source of the incident radiation) roughness. So we construct a :py:class:`Layer` as follows for a 100 Å thick layer of boron with a roughness of 10 Å.

from easyreflectometry.sample import Material
from easyreflectometry.sample import Layer

boron = Material(
    sld=6.908,
    isld=-0.278,
    name='Boron'
)
boron_layer = Layer(
    material=boron,
    thickness=100,
    roughness=10,
    name='Boron Layer'
)

This type of layer is used extensively in the tutorials

To create a semi-infinite layer one needs to set the thickness to 0 and the roughness to 0.

from easyreflectometry.sample import Material
from easyreflectometry.sample import Layer

si = Material(
    sld=2.07,
    isld=0,
    name='Si'
)
semi_infinite_layer = Layer(
    material=si,
    thickness=0,
    roughness=0,
    name='Si layer'
)

:py:class:`LayerAreaPerMolecule`

The :py:class:`LayerAreaPerMolecule` layer type is the fundation of the :py:class:`SurfactantLayer` assemblies type (further information on this can be found in the assemblies library). The purpose of the :py:class:`LayerAreaPerMolecule` is to allow a layer to be defined in terms of the chemical formula of the material and the area per molecule of the layer. The area per molecule is a common description of surface density in the surfactant monolayer and bilayer community.

We can construct a 10 Å thick :py:class:`LayerAreaPerMolecule` of phosphatidylcholine, with an area per molecule of 48 Å squared and a roughness of 3 Å that has 20 % solvent surface coverage with D2O using the following.

from easyreflectometry.sample import Material
from easyreflectometry.sample import LayerAreaPerMolecule

d2o = Material(
    sld=6.36,
    isld=0,
    name='D2O'
)
molecular_formula = 'C10H18NO8P'
pc = LayerAreaPerMolecule(
    molecular_formula=molecular_formula,
    thickness=10,
    solvent=d2o,
    solvent_fraction=.2,
    area_per_molecule=48,
    roughness=3,
    name='PC Layer'
)

It is expected that the typical user will not interface directly with the :py:class:`LayerAreaPerMolecule` assembly type, but instead the :py:class:`SurfactantLayer` assemblies library will be used instead.