Source code for irfpy.util.sputtering

''' A formulation of sputtering

.. codeauthor:: Yoshifumi Futaana

.. autosummary::
    
    ThompsonSigmund
'''
import numpy as np

class ThompsonSigmund:
    ''' Thompson-Sigmund energy spectrum.

    >>> ts0 = ThompsonSigmund(1, 0.5, 1.5, 1000., 1, 25)
    >>> print('%.3f' % ts0.ei)
    147.929
    
    .. todo::
        
        Clarify the unit system. Energy looks eV.
        What about the energy spectrum?
    '''

    def __init__(self, n0, y, ene_bind, ene_in, m1, m2):
        r''' Initialize the formulation.

        .. math::

            F(E) = nC\frac{E}{(E+E_b)^3}\Bigl(1-\sqrt{\frac{E+E_b}{Ei'}}\Bigr)

        Note that C is a parameter including the yield.  The unit of C is the energy.
        After several argebla, C is obtained from yield, Y, like

        .. math::

            C = \frac{Y}{\frac{1}{2E_b}-\frac{4}{3\sqrt{EbEi'}}}

        :param n0: Density.
        :param y: Yeild.
        :param ene_bind: Binding energy, :math:`E_b`
        :param ene_in: Impinging beam energy, :math:`E_i`
        :param m1: Mass of impinging beam. Unitless.
        :param m2: Mass of target. Unitless.
        '''

        self.n0 = float(n0)
        self.yld = float(y)
        self.eb = float(ene_bind)
        self.m1 = float(m1)
        self.m2 = float(m2)
        self.ei0 = float(ene_in)
        self.ei = self.ei0 * 4 * self.m1 * self.m2 / ((self.m1 + self.m2) ** 2)

        c1 = 1. / (2 * self.eb)
        c2 = 4. / (3 * np.sqrt(self.eb * self.ei))

        self.c =self.yld / (c1 - c2)

        if self.c <= 0:
            raise ValueError('C becomes negative (%g)...' % self.c)

    def f(self, e):
        ''' Return the energy distribution at certain e.
        '''
        eeb = (e + self.eb)
        eeb3 = eeb ** 3
        sqterm = np.sqrt(eeb / self.ei)

        fval = self.n0 * self.c * e / eeb3 * (1 - sqterm)
        return fval


import unittest
import doctest


def doctests():
    return unittest.TestSuite((
        doctest.DocTestSuite(),
        ))
if __name__ == '__main__':
    unittest.main(defaultTest='doctests')