Studies of melting, crystallization, and commensurate-incommensurate transitions in two dimensions. Terminal year progress report.

摘要

The four year period of this contract was devoted to the study of two dimensional (2D) systems of particles in their fluid and crystalline phases and especially in their behavior on passage through the freezing/melting (F/M) transition. Monolayers of microspheres both on the surface of water and trapped in water films between parallel quartz plates were used in these studies. In addition, macroscopic-size steel spheres were used in similar studies jointly with Noel Clark's group. There was only partial agreement with the predictions of theory in the F/M behavior of these 3 systems. The air/water (A/W) interface experiments displayed a two-step continuous F/M transition in agreement with theory for 2.99 (mu)m particles with a definite intermediate phase. An A/W system of 1.01 (mu)m spheres exhibits what we interpreted to be a first order transition with a very narrow coexistence region in place of the hexatic phase. The trapped water film monolayer experiments using 1.01 (mu)m spheres showed the same behavior, i.e., a narrow range of two-phase coexistence and a first order F/M transition. The steel spheres displayed a definite first order F/M transition. The techniques of electron-beam lithography and plasma etching were used to produce square arrays of wells and parallel linear channels on a quartz plate. This together with a second parallel smooth plate confined a monolayer if 1.01 (mu)m spheres in a water film. Damped lattice dynamics and hydrodynamics interactions were studied using the techniques of autocorrelation spectroscopy on a crystalline monolayer on the surface of water. Thermal relaxation times and Lame coefficients were obtained. Experiments were initiated to measure the variation of the surface tension of an A/W interface containing a crystalline monolayer at different states of compression.