Microstructural characterization of porous thin films
- PDF / 5,730,372 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 103 Downloads / 250 Views
W5.4.1
Microstructural characterization of porous thin films B. Djurfors1, M.J. Brett2 and D.G. Ivey1 1 Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta, Canada, T6G 2G6. 2 Department of Electrical and Computer Engineering, University of Alberta, Edmonton, Alberta, Canada, T6G 2V4. ABSTRACT A preliminary TEM investigation of porous films fabricated by glancing angle deposition has shown the importance of surface diffusion and crystal structure in determining the final microstructure of the film. Although the process variables are extremely important in defining the morphology of the film, their effects are limited in terms of final microstructure. INTRODUCTION Using a highly oblique substrate angle (>80°) during a physical vapor deposition process, it is possible to produce a highly porous film that is inclined towards the vapor source. When combined with substrate motion control, these types of films have been previously referred to as GLAD (glancing angle deposition) films and their fabrication and properties have been well documented [1-4]. There are four major structures that can be produced: slanted posts, zigzags, helices, and vertical posts. Individual slanted posts are produced when no substrate rotation is used, just an extreme oblique vapor incidence. Discontinuous substrate rotation of 180° at a time will result in a zigzag structure, while continuous substrate rotation will result in a helical structure. When the rotation speed is increased sufficiently, the helical pitch will become so small that the film will resemble a series of vertical posts. Previous analysis of these films has revealed the importance of adatom surface diffusion on the final microstructure of the film, often described in terms of the dimensionless ratio Ts/Tm where Ts is the substrate temperature and Tm is the melting temperature, both quoted in Kelvin [5-7]. Materials with low surface adatom diffusion rates (low Ts or high Tm) tend to exhibit branching or bifurcation due primarily to a combination of shadowing and limited diffusion, while those materials with high surface diffusion (high Ts, or low Tm) rates tend not to exhibit these characteristics because bulk and surface diffusion suppress branching [5,6]. The purpose of this research is to expand the knowledge base of the growth mechanism of the GLAD technique on a microscopic level by studying the effect of material, annealing, and rotation speed on microstructure. EXPERIMENTAL DETAILS GLAD film preparation The films were grown in a diffusion-pumped vacuum system using a rotating substrate holder without substrate heating, at an angle of 85°. Earlier measurements of substrate temperature have shown a maximum of 430K. All samples were deposited on silicon wafers for ease of post-fabrication cleaving.
W5.4.2
TEM sample preparation and imaging TEM samples were prepared on carbon coated Cu grids as this was the simplest method for producing an electron transparent sample. As the individual columns that make up the films are themselves
Data Loading...
