AVS 49th International Symposium
    Surface Engineering Tuesday Sessions
       Session SE+NS-TuM

Paper SE+NS-TuM2
Optical Behavior of Zirconia-Titania Nanolaminate Films

Tuesday, November 5, 2002, 8:40 am, Room C-111B

Session: Nanocomposite and Nanolayered Coatings
Presenter: C.R. Aita, University of Wisconsin-Milwaukee
Authors: C.R. Aita, University of Wisconsin-Milwaukee
J.D. DeLoach, Texas Instruments
Correspondent: Click to Email
Nanolaminate films of wide band gap semiconductors have bilayer periodicity much less than the wavelength of optical photons. These films are excellent candidates for high refractive index coatings througout the visible spectrum, coupled with optical band gap tailorability in the near-ultraviolet region. Here, we demonstrate this concept using ZrO@sub 2@-TiO@sub 2@ nanolaminates. Multilayer films were grown at room temperature by sequential reactive sputter deposition from metal targets using O@sub 2@-bearing discharges. Bilayer periodicity ranged from several to tens of nanometers. Total film thickness was in the 200 to 500 nm range. Optical transmission and reflection measurements were carried out in the 190 to 1100 nm wavelength range. Optical parameters were determined from these measurements. The results show that the refractive index throughout the region of high transmission was constant, equal to 2.2, and independent of nanolaminate architecture. On the other hand, the onset of fundamental optical absorption was strongly dependent upon bilayer architecture. A blue shift of the optical absorption edge was observed as the bilayer ZrO@sub 2@ increased. Optical band gap values spanned a range of 2 eV, from appproximately 3 eV for TiO@sub 2@ to 5 eV for ZrO@sub 2@, giving the system tailorability. The results are discussed in terms of the primacy of the coordination of a central cation (Zr or Ti) with its nearest neignbor O atoms in determining the features of the fundamental optical absorption edge. We show that the model developed to explain the results for the ZrO@sub 2@-TiO@sub 2@ system can be applied to other nanolaminates or nanocomposites in which the spatial extent of the wavefunctions describing near edge optical transitions is comparable to the short-range order in the film.