  A versatile X-ray/neutron reflectivity (specular) simulator using
LabVIEW(National Instruments Corp.) for structural study of a multi-layer thin
film having any combination, including the repetitions, of nano-scale layers of
different materials is presented here (available to download from the link
provided at the end of the paper). Inclusion of absorption of individual
layers, inter-layer roughnesses, background counts, beam width, instrumental
resolution and footprint effect due to finite size of the sample makes the
simulated reflectivity close to practical one. The effect of multiple
reflection is compared with simulated curves following the exact dynamical
theory and approximated kinematical theory. The applicability of further
approximation (Born theory) that the incident angle does not change
significantly from one layer to another due to refraction is also considered.
Brief discussion about reflection from liquid surface/interface and
reflectivity study using polarized neutron are also included as a part of the
review. Auto-correlation function in connection with the data inversion
technique is discussed with possible artifacts for phase-loss problem. An
experimental specular reflectivity data of multi-layer erbium stearate
Langmuir-Blodgett (LB) film is considered to estimate the parameters by
simulating the reflectivity curve.
