Masters Theses

Date of Award

5-2002

Degree Type

Thesis

Degree Name

Master of Science

Major

Materials Science and Engineering

Major Professor

Carl McHargue

Committee Members

Tom Meek, George Pharr

Abstract

The effects of crystallographic orientation (c-plane versus a-plane), crystallographic structure (crystalline versus amorphous), implantation-produced damage at the surface, and a combination of implantation-produced damage and chemistry changes upon the wetting behavior of α-Al2O3 was studied. One would rather study the surface free energy of sapphire and the interfacial free energies of the sapphire/liquid interfaces but there is no method for independently determining the changes in the individual quantities of Ysv and Ysl. However, a qualitative approach was used to approximate the individual changes in (Ysv and Ysl) for the implanted crystalline samples. This qualitative approach was necessary only for the implanted samples because Ylv was known and acted as a constant for all conditions of the substrates and Ysv was known and acted as a constant for the unimplanted crystalline samples. The wetting behavior for each study was determined by measuring the contact angles with water and methylene iodide (CH2I2). The contact angles were measured by means of the Sessile Drop Method using water and methylene iodide and the Tantec Half-Angle TM Measuring Method. The work of adhesion (Wad) was determined for each sample for both water and methylene iodide using a form of the Young - Dupré Equation. The work of adhesion values did not give any new information regarding the individual Ysv and Ysl values but were helpful in examining the results. The contact angle values for water were determined to be greater than the contact angle values for methylene iodide. This trend was true for the unimplanted and the implanted crystalline and amorphous samples. The contact angle values for the unimplanted crystalline c-plane samples were greater than the unimplanted crystalline a-plan samples. These results were found to be consistent with the polarity of the sapphire surfaces (c-plane and a-plane), the polar nature of water and the non-polar nature of methylene iodide. The results for both the c-plane and the a-plane in terms of crystallographic structure were explained by using the calculated surface free energy values of Mackrodt. All orientations have greater Ysv values than the c-plane, [0001], in the relaxed condition. Therefore, destroying the order of the c-plane by the amorphous condition could increase the c-plane Ysv value. This "randomizing" of the sample might be expected to expose elements of symmetry possessed by the planes having higher values of surface free energy leading to a decrease in the Ysl value for the sapphire/water interface but the Ysl value for the sapphire/methylene iodide interface would not be affected. The number of Al3+ terminations may be reduced due to the "randomizing" of the c-plane decreasing the Ysl value by reducing the OH attraction to the c-plane. All axis orientations except [1011] have smaller Ysv values than the a-plane, [1120], in the relaxed condition. Therefore, destroying the order of the a-plane by the amorphous condition could decrease the a-plane Ysv value. However, for the a-plane this increased disorder might be expected to increase the YsI value for the sapphire/water interface but not for the sapphire/methylene iodide interface. There are two possible explanations for the effects implantation-produced surface damage has upon the surface free energy and the interfacial free energies. The two possible explanations are (1) the same arguments used in discussing the results for the crystallographic structure study (Mackrodt's calculations), and (2) the creation of an image charge at the surface due to the presence of charged defects and the differences in dielectric constants of the sapphire and surroundings (air, water, or methylene iodide). Qualitatively determining the individual changes in Ysv and YsI was rather straight forward. However, it is difficult to determine if these changes are dependent on either the implantation-produced damage or the implantation produced chemistry changes. Based on the TRIM calculations, there is an increase in both the vacancy and implanted ions concentrations. Therefore, it is most likely that the individual changes in the solid-vapor and solid-liquid interfacial free energies depend upon both the damage and chemistry changes due to the implantation process.

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