Chemical Vapor Deposition of Cobalt and Nickel Ferrite Thin Films: Investigation of Structure and Pseudocapacitive Properties
Dennis Zywitzki, Raoul Schaper, Engin Çiftyürek, Jan‐Lucas Wree, Dereje H. Taffa, Daniel M. Baier, Detlef Rogalla, Yujiao Li, Michael Meischein, Alfred Ludwig, Zheshen Li, Klaus Schierbaum, Michael Wark, Anjana Devi
Abstract
Abstract Transition metal ferrites, such as CoFe 2 O 4 (CFO) and NiFe 2 O 4 (NFO), have gained increasing attention as potential materials for supercapacitors. Since chemical vapor deposition (CVD) offers advantages like interface quality to the underlying substrates and the possibility for coverage of 3D substrates, two CVD processes are reported for CFO and NFO. Growth rates amount to 150 to 200 nm h −1 and yield uniform, dense, and phase pure spinel ferrite films according to X‐ray diffraction (XRD), Raman spectroscopy, Rutherford backscattering spectrometry and nuclear reaction analysis (RBS/NRA) and scanning electron microscopy (SEM). Atom probe tomography (APT) and synchrotron X‐ray photoelectron spectroscopy (XPS) give insights into the vertical homogeneity and oxidation states in the CFO films. Cation disorder of CFO is analyzed for the first time from synchrotron‐based XPS. NFO is analyzed via lab‐based XPS. Depositions on conducting Ni and Ti substrates result in electrodes with pseudocapacitive behavior, as evidenced by cyclovoltammetry (CV) experiments. The interfacial capacitances of the electrodes are up to 185 µF cm −2 .