Creating Multilayers and Surfactant Layers

EasyReflectometry is designed to be used with a broad range of different assemblies. Assemblies are collective layers behaving as a single object, for example, a multilayer or a surfactant layer. These assemblies offer flexibility for the user and enable more powerful analysis by making chemical and physical constraints available with limited code. In this page, we will document the assemblies that are available with simple examples of the constructors that exist. Full API documentation is also available for the easyreflectometry.sample.assemblies module.

Multilayer

This assembly should be used for a series of layers that should be thought of as a single object. For example, in the simple fitting tutorial this assembly type is used to combine the silicon and silicon dioxide layer that is formed into a single object. All of the separate layers in these objects will be fitted individually, i.e. there are no constraints present, however, there is some cognitive benefit to grouping layers together.

To create a Multilayer object, we use the following construction.

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

si = Material(sld=2.07, isld=0, name='Si')
sio2 = Material(sld=3.47, isld=0, name='SiO2')
si_layer = Layer(material=si, thickness=0, roughness=0, name='Si layer')
sio2_layer = Layer(material=sio2, thickness=30, roughness=3, name='SiO2 layer')

subphase = Multilayer(layers=[si_layer, sio2_layer], name='Si/SiO2 subphase')

This will create a Multilayer object named subphase which we can use in some Structure for our analysis.

RepeatingMultilayer

The RepeatingMultilayer assembly type is an extension of the Multilayer for the analysis of systems with a multilayer that has some number of repeats. This assembly type imposes some constraints, specifically that all of the repeats have the exact same structure (i.e. thicknesses, roughnesses, and scattering length densities), which brings with it some computational saving as the reflectometry coefficients only need to be calculated once for this structure and propagated for the correct number of repeats. There is a tutorial that discusses the utilisation of this assembly type for a nickel-titanium multilayer system.

The creation of a RepeatingMultilayer object is very similar to that for the Multilayer, with the addition of a number of repetitions.

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

ti = Material(sld=-1.9493, isld=0, name='Ti')
ni = Material(sld=9.4245, isld=0, name='Ni')
ti_layer = Layer(material=ti, thickness=40, roughness=0, name='Ti Layer')
ni_layer = Layer(material=ni, thickness=70, roughness=0, name='Ni Layer')
ni_ti = RepeatingMultilayer(layers=[ti_layer, ni_layer], repetitions=10, name='Ni/Ti Multilayer')

The number of repeats is a parameter that can be varied in the optimisation process, however given this is a value that depends on the synthesis of the sample this is unlikely to be necessary.