| AVS 60th International Symposium and Exhibition | |
| Thin Film | Monday Sessions |
| Session TF+EN-MoM |
| Session: | ALD for Energy |
| Presenter: | A.S. Cavanagh, University of Colorado at Boulder |
| Authors: | A.S. Cavanagh, University of Colorado at Boulder L. Baker, University of Colorado at Boulder J. Clancey, University of Colorado at Boulder J. Yin, University of Colorado at Boulder A. Kongkanand, General Motors Research and Development F.T. Wagner, General Motors Research and Development S.M. George, University of Colorado at Boulder |
| Correspondent: | Click to Email |
Platinum is an excellent catalyst for many applications. The high cost of Pt requires that Pt be used as efficiently as possible. For the oxygen reduction reaction in H2 fuel cells, experiments show that a continuous Pt film is 5-10 times more active per Pt surface atom than a 3 nm Pt nanoparticle. Consequently, understanding the process conditions under which thin continuous films of Pt can be deposited is critical.
Pt has a high surface energy of ~2.5 J/m and does not readily wet most substrates which typically have much lower surface energies. Pt nanoparticles are generally formed during Pt atomic layer deposition (ALD) on oxide substrates. A continuous Pt film is possible only after the coalescence of the Pt nanoparticles. The result is a thick Pt film and the inefficient use of Pt resulting from the thickness.
One possible route to obtain a continuous and ultrathin Pt film is to deposit on an adhesion layer that has a higher surface energy than Pt. In this case, the Pt should wet the adhesion layer because the deposited Pt film will lower the surface energy. One material that has a higher surface energy than nearly all other metals, including Pt, is W. The surface energy of W is ~3.5 J/m.
In situ spectroscopic ellipsometry (SE) allowed for the characterization of Pt ALD nucleation on W ALD adhesion layers. In situ measurements of nucleation during plasma-assisted ALD provided rapid feedback on the process variables including plasma power, plasma exposure time and the process gas mixture. Ex situ characterization with X-ray photoelectron spectroscopy and X-ray reflectivity was used to verify the SE models employed during in situ monitoring of the nucleation of plasma-assisted Pt ALD.