Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

Iron and iron oxide nanostructures are of broad interest for numerous applications, such as in the fields of magnetic data
storage, spintronics, biosensing and catalysis. In all of these cases, defined deposition on nanometer scale is essential for
functionality. For conventional electrodeposition of transition metals, precise thickness control and layer stability at the
nanoscale are difficult due to dissolution tendencies in acidic electrolytes after the voltage is switched off. In contrast to
previous studies that focused on self-termination of Ni and Ni-based alloys, we investigate the thickness control of nanoscale
iron oxide/iron layers using self-terminated electrodeposition from sulfate electrolytes. Electrochemical quartz crystal
microbalance measurements show that self-terminated thickness can be controlled by both deposition potential and iron ion
concentration. Comparison of experimental results with model calculations based on diffusion theory reveal two different
growth modes for self-termination. At low iron ion concentration, self-termination of iron proceeds via the formation of an
ultrathin iron hydroxide layer. At larger iron ion concentration, precipitation of bulk Fe(OH)2 dominates the film growth and
self-termination is shifted to more negative potentials. All self-terminated layers exhibit enhanced stability in the electrolyte
after the voltage is switched off compared to those deposited in the conventional deposition regime. With in situ Rutherford
backscattering spectrometry measurements, we can follow the self-terminating deposition and the stability after voltage
switch-off for longer times online. Surface analytical and morphological analyses show that the self-terminated layers exhibit
a higher iron oxide/iron ratio and are smoother than layers obtained by conventional electrodeposition.