Particles Crossing an Interface

In this example, very similar to the one on Cylinders and Prisms, it is shown how to position particles in order to cross multilayer interfaces: the $z$ position of particles originally located within the air layer must be adjusted slightly downwards in order to cross the air-substrate interface.

The simulation kernel automatically detects particles crossing interfaces and adjusts the calculations accordingly, causing a drop on speed to complete each simulation.

The script below models a air-substrate bilayer in which cylindrical particles made of two materials are added to the air layer and their $z$ coordinate is shifted downwards in order to cross the air-substrate interface.

Intensity image

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#!/usr/bin/env python3
"""
This example demonstrates new experimental feature of release-1.8.0:
particles can now cross interfaces.

Given example is similar to simulation/ex01_BasicParticles/CylindersAndPrisms.py,
with the difference, that z-position of particles is adjusted to move them slightly
down from vacuum layer and to make them cross substrate/air interface.

Note:
1) Simulation kernel automatically detects particles crossing interface and
adjusts calculations accordingly.

2) Particle crossing interface requires more time to simulate.

3) Crossing of interface is possible only for limited number of geometries.
For example, X or Y rotated particles can not yet cross interfaces (exception
will be thrown when trying to simulate such geometries).
"""
import bornagain as ba
from bornagain import deg, nm, kvector_t


def get_sample():
    """
    Returns a sample with uncorrelated cylinders and prisms on a substrate.
    """

    # Define materials
    material_Particle = ba.HomogeneousMaterial("Particle", 0.0006, 2e-08)
    material_Substrate = ba.HomogeneousMaterial("Substrate", 6e-06, 2e-08)
    material_Vacuum = ba.HomogeneousMaterial("Vacuum", 0.0, 0.0)

    # Define form factors
    ff_1 = ba.FormFactorCylinder(5.0*nm, 5.0*nm)
    ff_2 = ba.FormFactorPrism3(10.0*nm, 5.0*nm)

    # Define particles
    particle_1 = ba.Particle(material_Particle, ff_1)
    particle_1_position = kvector_t(0.0*nm, 0.0*nm, -3.0*nm)
    particle_1.setPosition(particle_1_position)
    particle_2 = ba.Particle(material_Particle, ff_2)
    particle_2_position = kvector_t(0.0*nm, 0.0*nm, -3.0*nm)
    particle_2.setPosition(particle_2_position)

    # Define interference functions
    iff = ba.InterferenceFunctionNone()

    # Define particle layouts
    layout = ba.ParticleLayout()
    layout.addParticle(particle_1, 0.5)
    layout.addParticle(particle_2, 0.5)
    layout.setInterferenceFunction(iff)
    layout.setWeight(1)
    layout.setTotalParticleSurfaceDensity(0.01)

    # Define layers
    layer_1 = ba.Layer(material_Vacuum)
    layer_1.addLayout(layout)
    layer_2 = ba.Layer(material_Substrate)

    # Define sample
    sample = ba.MultiLayer()
    sample.addLayer(layer_1)
    sample.addLayer(layer_2)

    return sample


def get_simulation(sample):
    beam = ba.Beam(1.0, 0.1*nm, ba.Direction(0.2*deg, 0*deg))
    detector = ba.SphericalDetector(100, 2*deg, 0*deg, 1*deg)
    simulation = ba.GISASSimulation(beam, sample, detector)
    return simulation


if __name__ == '__main__':
    import ba_plot
    sample = get_sample()
    simulation = get_simulation(sample)
    ba_plot.run_and_plot(simulation)
ParticlesCrossingInterface.py