Investigations on the influence of the substrate on the crystal structure of sputtered LiCoO2

The influence of the uppermost substrate layer on the structural properties of sputtered lithium cobalt oxide (LiCoO2) is discussed in this work. For this purpose, bare, oxidized, and platinum-coated silicon wafers, as well as stainless steel and titanium sheets, were used as substrates. The resulting crystal structure of LiCoO2 deposited on these substrates was analyzed and discussed. The LiCoO2 thin films were deposited by RF magnetron sputtering with different film thicknesses. A subsequent annealing step at 700 A degrees C was performed to induce the crystallinity of LiCoO2. The crystal orientation was determined by X-ray diffraction. The obtained results show a strong dependency of LiCoO2's crystal structure on the surface the film is deposited on. However, the strong influence of the film thickness reported in previous publications could not be observed. If LiCoO2 is deposited on the substrates with a metallic surface, a strong (003) preferential orientation is obtained for a wide range of film thicknesses. In contrast, sputtering of LiCoO2 on bare and on oxidized silicon wafers results in a (101) dominated crystal structure for the different film thicknesses. These experiments show the importance of the characterization of LiCoO2's crystal structure in the intended battery setup.