It was further ion-milled to electron transparency in a TechNoorg Linda IV4 ion miller (Budapest, Hungary). High-resolution transmission electron microscopy (HRTEM) studies of XTEM specimens were

carried out in a JEOL 2000 EX II (T) transmission electron microscope (Akishima-shi, Japan) operated at 200 kV. Surface morphology of the samples was examined using an atomic force microscope (AFM; Nanoscope E Digital instruments Inc, Model: NSE, Santa Barbara, CA, USA) in contact mode using Si3N4 cantilever. Results and discussion Microstructural characterization XRD and HTXRD studies The S63845 mw sintered alumina pellet was found to be phase-pure α-alumina with a hexagonal structure (a = 4.75 Å, c = 12.99 Å) and in agreement with JCPDS data

(#46-1212) [17]. The sintered zirconia pellet was found to have higher volume fraction of monoclinic (approximately 75%) and small fraction (25%) of tetragonal PCI-34051 chemical structure phases [1]. These two targets were used to deposit multilayers of Al2O3/ZrO2. Figure  1 shows the XRD pattern of the 10:10-, 5:10-, 5:5-, and 4:4-nm multilayers with 40 bilayers deposited at room temperature on Si (100). The films showed a broad peak buy GSK2118436 at an angle of 30.5°, which represents the nanocrystalline nature and tetragonal structure of ZrO2[19, 20]. The zirconia is stabilized in its tetragonal phase at room temperature in all these films. The typical 5:5-nm film is further analyzed by HTXRD in the temperature range 298 -1,273 K to study phase transformation and thermal stability. Figure  2 shows the HTXRD pattern of the Al2O3/ZrO2 multilayer of 5:5 nm with 40 bilayers. The multilayer showed reflections of (101), (110), (002), (200), (103), and (310), and all these reflections correspond to the tetragonal phase of ZrO2. The multilayer also showed the preferred orientation for (103), and the intensity of this peak increases steadily with temperature. Figure  2 also shows the XRD pattern of the annealed PRKD3 film after cooling down the sample

to room temperature (RT), and it showed strong tetragonal peaks and was evident that there was no tetragonal to monoclinic phase transformation. The 5:5-nm multilayer film showed excellent thermal stability and had only tetragonal phase after cooling down to RT. It is interesting to note that the alumina remains in amorphous state throughout the range of annealing temperature. If the alumina layer is formed with a thickness less than the critical thickness, the temperature of crystallization also increases significantly, and therefore, the films are amorphous when the thickness is about 5 nm [21]. The crystallite sizes were determined from the HTXRD data using the Scherrer formula and found to be 2 to 5 nm for (101) and 4 to 8 nm for (103) orientations in the temperature range 298-1,273 K. The contribution of instrumental broadening is subtracted while measuring the crystallite size.