Transport Properties and X-ray Absorption Spectroscopy in Layered Cobaltate Na$_{x}$CoO$_{2}$ thin films

Na$_{x}$CoO$_{2}$ ($x\sim $0.7) thin films ($\sim $200 nm) were fabricated on sapphire (0001) substrates via lateral diffusion of sodium into Co$_{3}$O$_{4}$ (111) epitaxial films. From the results of x-ray diffraction and in-plane resistivity \textit{$\rho $}$_{ab}$, the single phase and the metallic behaviors of these Na$_{x}$CoO$_{2}$ films were identified, and consisting with the results of single crystals [1] and Ohta's films [2]. The anomalous Hall effect and the magnetoresistance were also measured in Na$_{x}$CoO$_{2}$ thin films. In addition, the O 1$s$ x-ray absorption spectra of thin films show different anisotropy to those of single crystals. The electronic structures of Na$_{x}$CoO$_{2}$ single crystals and thin films will be discussed to investigate the splitting of $e_{g}$ and $t_{2g}$ states in Co 3$d$ bands of Na$_{x}$CoO$_{2}$ thin films. *This work was supported by the National Science Council of Taiwan, under Grant Nos. NSC-94-2112-M-009-006. [1] Maw Lin Foo \textit{et al}., Phys. Rev. Lett. \textbf{92}, 247001 (2004). [2] Hiromichi Ohta \textit{et al}., Crystal Growth {\&} Design \textbf{5}, 25 (2005).