Layer

A layer is made of a Material and has a certain thickness. The other two lateral dimensions are assumed to be infinite. It also holds information on the thickness distribution via the thickness_fwhm in forward scattering or via the roughness in grazing-incidence geometry.

The following parameters are Var objects and can be fit:

• thickness

• roughness

• thickness fwhm

All values are given in nanometer.

Thickness

The thickness defines the only dimension given for a Layer. In forward geometry the thickness is given along the beam propagation direction. In gracing incidence geometry the thickness is assumed to be almost perpendicular to the beam propagation direction, depending on the incidence angle specified in the Sample.

Thickness FWHM

This parameter is only used in forward scattering geometry. The thickness_fwhm value gives the full width half maximum of an assumed Gaussian distribution of thickness values around thickness. Contributions to the scattering intensity originating from different thicknesses are treated incoherently, see Thickness and divergence distributions.

Roughness

The roughness is only taken into account in grazing incidence geometry. The roughness specifies the \(\sigma\) value of a Gaussian distribution around the thickness value. In contrast to the thickness_fwhm, the roughness is treated coherently. How the roughness is treated is defined in the Sample by the specified roughness model, see Sample.

Setting up a layer

import nexus as nx

mat = nx.Material.Template(nx.lib.material.Fe2O3)

layer = nx.Layer(id = "my iron oxide layer",
                 thickness = 1000,  # in nanometer
                 material = mat,
                 roughness = 30,
                 thickness_fwhm = 50)

print(layer)

Here, we have defined a material first, followed by the Layer definition. You can define the Material directly in the layer initialization. Then, a new Material object is automatically created by the Layer. This is helpful in setting up the experiment for non-resonant calculations and fitting.

layer = nx.Layer(id = "my iron oxide layer",
                 thickness = 1000,  # in nanometer
                 roughness = 30,
                 thickness_fwhm = 50
                 composition = [["Fe", 2], ["O", 3]],
                 density = 5.3)

print(layer)

For convenience, the density and composition of a Material can also be accessed via the Layer directly. This is not possible for nuclear properties of the Material.

# access density via material properties
layer.material.density = 6.1

print(layer)

# access density via layer directly
layer.density = 4.9

print(layer)

Note

Changing material properties via one Layer will change all Layers referencing to the same material. Therefore, this procedure should only be done when the material was defined automatically in the Layer initialization. Then, no other Layer is using this Material.

Layer methods

There are several methods to retrieve the scattering matrix, refractive index, critical angle and many other properties of a layer. For example,

# refractive index of a layer
ref_index = layer.ElectronicRefractiveIndex(energy = 14412.5)

print(ref_index)

# outputs (0.9999952911043145+1.4925088081386838e-07j)

# critical angle at 16 keV
ang = layer.CriticalAngle(energy=16e3)

print(ang * 180/np.pi)

# outputs (0.1583868640530339)

Notebooks

layer - nb_layer.ipynb.

Please have a look to the API Reference for more information.