The synergic interplay between nuclear physics, detector technology and solid state and surface sciences is a fundamental aspect of the development of new neutron detection devices. The synthesis technique and the physical-chemical properties of the B4C films used as a neutron-to-charged particle converter are described in relation to the GEM side-on thermal neutron detector. Neutron detection is performed allowing scattered neutrons to be converted into charged particles by means of a series of sheets covered by B-10-enriched boron carbide (B4C) layers placed along their flight path inside the detector. The extremely interesting performance shown by the detector in neutron diffraction measurements at the ISIS spallation neutron sources are discussed and related to the chemical-physical properties of the converting layers.