Recent research has been concerned with the interaction between charged particles and solid surfaces in several fields of physics. Especially, collective excitations near the surface play an important role in particle-surface collisions (e. g. image force, energy loss, surface resonant state) . A systematic review of the interaction between charged particles and collective modes near the surface is made, and some examples or topics are taken in this review; image-induced surface state, inelastic scattering of fast charged particles, effective interactions between ion-pairs at the surface (surface wake potential), etc.
Molecular crystals and ionic crystals which consist of polyatomic groups exhibit “orientational transitions” accompanied by an orientational disorder of polyatomic groups. Some topics on X-ray studies of the orientational disorder, which have been studied by the present author and his collaborators in a recent decade, are summarized. The observed X-ray diffuse scatterings due to the orientational disorder of NO3-ions in the CsCI-type cubic phases of NH4NO3 and RbNO3 are analysed on the basis of “12-orientation” model. The intensity formulae of X-ray diffuse scattering for polyorientation system, which have been given by Matsubara (Zernike's theory), by Naya (random phase approximation) and recently by Nagai (Bethe's method), are discussed. Anomalies of X-ray temperature diffuse scatterings due to C44 mode are observed in the NaCI-type cubic phases of RbNO3 and NaCN. By taking account of a linear coupling between the orientations and acoustic phonons, the observed temperature dependences of the diffuse scatterings are explained.