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Combined specular and off‐specular reflectometry: elucidating the complex structure of soft buried interfaces
Author(s) -
Hafner Aljoša,
Gutfreund Philipp,
Toperverg Boris P.,
Jones Andrew O. F.,
de Silva Johann P.,
Wildes Andrew,
Fischer Henry E.,
Geoghegan Mark,
Sferrazza Michele
Publication year - 2021
Publication title -
journal of applied crystallography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.429
H-Index - 162
ISSN - 1600-5767
DOI - 10.1107/s1600576721003575
Subject(s) - specular reflection , reflectometry , neutron reflectometry , scattering , x ray reflectivity , materials science , optics , surface finish , reciprocal lattice , diffraction , dewetting , neutron scattering , molecular physics , small angle neutron scattering , chemistry , thin film , nanotechnology , physics , composite material , computer science , time domain , computer vision
Neutron specular reflectometry (SR) and off‐specular scattering (OSS) are nondestructive techniques which, through deuteration, give a high contrast even among chemically identical species and are therefore highly suitable for investigations of soft‐matter thin films. Through a combination of these two techniques, the former yielding a density profile in the direction normal to the sample surface and the latter yielding a depth‐resolved in‐plane lateral structure, one can obtain quite detailed information on buried morphology on length scales ranging from the order of ångströms to ∼10 µm. This is illustrated via quantitative evaluation of data on SR and OSS collected in time‐of‐flight (ToF) measurements of a set of films composed of immiscible polymer layers, protonated poly(methyl methacrylate) and deuterated polystyrene, undergoing a decomposition process upon annealing. Joint SR and OSS data analysis was performed by the use of a quick and robust originally developed algorithm including a common absolute‐scale normalization of both types of scattering, which are intricately linked, constraining the model to a high degree. This, particularly, makes it possible to distinguish readily between different dewetting scenarios driven either by the nucleation and growth of defects (holes, protrusions etc. ) or by thermal fluctuations in the buried interface between layers. Finally, the 2D OSS maps of particular cases are presented in different spaces and qualitative differences are explained, allowing also the qualitative differentiation of the in‐plane structure of long‐range order, the correlated roughness and bulk defects by a simple inspection of the scattering maps prior to quantitative fits.