String Fit: a new structurally oriented X-ray and neutron reflectivity evaluation technique

A novel method for the analysis of neutron and X-ray reflectivity measureme nts is presented. In contrast to existing methods, the new data fitting app roach is structurally oriented and therefore only requires information abou t the chemical structure of studied molecules and no other ad hoc assumptio ns. Apart from the inversion of reflectivity into scattering length density profile, the inversion of scattering length density profile into molecular arrangement is addressed systematically for non-trivial molecular conforma tions for the first time. This includes the calculation of structural chara cteristics, such as radius of gyration or chain order parameters, based on measured reflectograms. Another important option is the possibility to eval uate simultaneously neutron and X-ray reflectograms of a given sample. For better convergence, especially for complex simultaneous evaluations, an eff ective extension of the normally used least-squares deviation function is i ntroduced. Different simulated molecular ensembles are used to illustrate t he features of the new approach; typically, excellent agreement between the simulated starting and final deduced data sets is achieved.