Inelastic Neutron Scattering: A Powerful Probe of Condensed Matter *

Inelastic neutron scattering (INS) is a powerful tool to probe the dynamic and static properties of condensed matter at the atomic scale.  As neutrons are sensitive to hydrogen, they provide key information about the structure and dynamics of the water species in materials.  Neutrons have a magnetic moment, so neutron studies reveal information about the magnetic properties of materials. Neutrons can also be used as a probe of molecular vibrations.  INS determines the full lattice vibrational spectrum from which the thermodynamic driving forces, including entropic factors, can be determined.  It is therefore a complementary method to infrared and Raman spectroscopy and has the advantage over these techniques as it is not subject to selection rules.  In this presentation, examples that display each of these unique features of INS will be discussed. First, INS studies of water species confined to the surfaces of metal-oxide surfaces of nanoparticles are given and shown how this affects their stabilities.  Second, novel magnetic spin transitions observed at low energies in metal-oxide nanoparticles are discussed.  Third, INS spectra for a set of zeolitic imidazolate framework (ZIF) polymorphs synthesized by mechanochemistry are presented. The low-frequency vibrations observed in the INS spectra control the thermodynamic stabilities of the polymorphs and are correlated with physical phenomena such as gate-opening and / or shear-induced phase transitions that signify the onset of structural instability.  The results from these studies have immense broader impact as they contribute to our fundamental knowledge of condensed matter by relating structures with their lattice dynamics, energetics and entropies.