Aspects of Structure and Interactive Processes at Solid Crystal Surfaces.
Recent experimental evidence shows solid like behavior for submonolayer He('3) and He('4) films on argon plated copper. From low temperature heat capacity measurements, the latent heat of vaporization for submonolayer helium was estimated to be about 0.7 mev higher than the corresponding value for the bulk. In Part A, the quantum vibronic zero -point interaction energy is investigated in an effort to determine its contribution to the observed enhancement of the lateral binding energy. It is found that the many -body zero-point indirect interaction energy per particle is almost an order of magnitude greater than the two-body result, while the direct interaction energy is an additional four orders of magnitude greater. The effects of next -nearest-neighbor as well as direct Lennard-Jones (L-J) interactions are estimated using a simple model for helium on the (001) surface of argon to be (TURN) 0.3 mev per particle which is greater than the corresponding L-J 6 -12 gas-phase potential energy. Physisorbed submonolayer and monolayer films on solid surfaces are of interest also because they serve as models for experimental investigations of properties of lower-dimensional systems. In Part B, substrate effects on long-range crystalline order and scattering characteristics of simple 1D and 2D systems are investigated. It is shown that a finite interchain coupling strength, between the adlayer and the substrate, introduces a gap to the normal mode frequency spectrum which damps-out the divergencies in the long-range crystalline order parameter and introduces Bragg peaks to the static structure factor for both 1D and 2D modes. The growth of thin films, particularly, epitaxial crystallization from a melt is a subject of considerable interest. However, experiments which probe the solid-liquid interface are very difficult to perform and theories of the growth mechanisms are inadequate. Thus, investigations through computer simulation become an important tool. In Part C, a surface molecular dynamics investigation of the epitaxial crystallization from a supercooled (SCL) and hot liquid (HL) with the parameters of argon is presented. The analysis of the phase space of the systems is given for several quantities. It is shown that an initial ordering event occurs in the liquid near the solid interface in which the liquid stratifies into layers. This occurs in both the SCL and the HL systems. This layering of the liquid occurs before any intralayer ordering. Once the intralayer ordering begins, it proceeds sequentially for both systems.
- Pub Date:
- Physics: Condensed Matter