AVS 49th International Symposium
    Thin Films Tuesday Sessions
       Session TF-TuM

Paper TF-TuM6
Role of Interface Free Energy in Hardness Enhancement in PTFE/Al, PTFE/Cu, and PTFE/Ti Nanomultilayered Thin Films

Tuesday, November 5, 2002, 10:00 am, Room C-101

Session: Mechanical Properties of Thin Films
Presenter: E. Kusano, Kanazawa Institute of Technology, Japan
Authors: E. Kusano, Kanazawa Institute of Technology, Japan
N. Kikuchi, Kanazawa Institute of Technology, Japan
I. Yoshimura, Kanazawa Institute of Technology, Japan
A. Kinbara, Kanazawa Institute of Technology, Japan
H. Nanto, Kanazawa Institute of Technology, Japan
Correspondent: Click to Email
In nanostructured materials, interface or surface affects their mechanical properties strongly. In this study internal stress and hardness in polytetrafluoroethylene (PTFE)/Al, PTFE/Cu, and PTFE/Ti nanomultilayered thin films have been investigated as a function of modulation period, i.e., the number of interfaces in the films. PTFE, which has a low surface energy of 17 mJ/m@super 2@ was used to introduce a large interface energy in thin films. The designed value of interface energy accumulated in thin films is up to 80 J/m@super 2@. PTFE thin film was deposited by rf magnetron sputtering using the target of a PTFE sheet. Al, Cu, and Ti were deposited by dc magnetron sputtering. Multilayers were fabricated sequentially without breaking vacuum on aluminosilicate glass. The total thickness of films was about 200 nm for all samples. Modulation period was changed from 10 nm to 200 nm. Internal stress in metal layers was evaluated from strain obtained by X-ray diffraction measurements. Hardness was measured by nanoindentation. The surface energy of a monolithic PTFE film deposited by sputtering was about 18 mJ/m@super 2@. The compressive internal stress evaluated by XRD increases with decreasing the modulation period. Hardness enhancements were also investigated for films with a short modulation period. Further it was shown that the hardness has a linear relationship to internal stress. A large compressive stress introduced in thin films increases the energy needed to drive cracks made by a nanoindentation deep into the film, resulting in the increase in hardness. The results emphasize an important role of interfaces in mechanical properties of nanomultilayered thin films.