טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentKauffmann Yaron
SubjectOrdering at a Model Solid-Liquid Interface
DepartmentDepartment of Materials Science and Engineering
Supervisor Professor Wayne D. Kaplan


Abstract

Understanding the nature of solid-liquid interfaces is very important for many processes of technological interest, such as solidification, epitaxial growth, wetting, liquid phase joining, crystal growth, and lubrication. In recent years, many published theoretical works report on interesting structural effects occurring at solid-liquid interfaces. These works concluded that ordering of a liquid at an interface with a solid crystalline substrate is governed by both the structure of the solid substrate, and the properties of the liquid.


Real-time observations of the dynamic S-L interfaces at the atomic scale were conducted using the MPI-Stuttgart high voltage atomic resolution TEM (JEM-ARM 1250, JEOL) operating at 1.25 MeV. In addition, interesting contrast perturbations were observed in the liquid at the interface. The main problem with direct high resolution electron microscopy (HRTEM) is that the imaging conditions (such as delocalization and defocus) have a significant influence on the contrast in the image, and may lead to inaccurate conclusions about the structure of the interface.


A new method was developed, single image iterative wave function reconstruction (SIIWFR), which is based on the concept of reconstructing the complex electron wave function at the exit surface of the specimen iteratively. A comprehensive analysis, using this new method combined with computer simulations, show that these perturbations are due to real structural ordering in the liquid. This analysis allowed, for the first time, direct extraction of quantitative information regarding the degree of ordering at such interfaces.


The degree of ordering at the Al2O3-Al interface at 750ºC was quantified. The layering in the liquid extends to about 4-5 layers (about 1 nm from the edge of the crystal). The in-plane ordering was observed only in the 3 first layers of the liquid. In addition, the interlayer spacings measured in the liquid may point to the fact that the liquid atoms at the interface are influenced by the structure of the crystal and further away the ordering of the liquid atoms gradually vanishes until it adopts the characteristics of bulk liquid.


In view of the structural ordering occurring at the S-L interface, many interfacial phenomena have to be reconsidered, such as interfacial segregation. Since the ordering effect is probably always present to some extent, it may be exploited to obtain novel nano-structures that were unavailable before. One example, which might be useful in the field of nano-eletronic and nano-optics, is the formation of new crystallographic structures during liquid phase epitaxial growth.