In-situ monitoring of electro-deposition for iron-nickle thin film by time-resolved X-ray absorption spectroscopy

Abstract

The crystal structure of iron-nickel thin films depends on the composition of iron and nickel dissolved with electrolytes. However, it is believed that in electro-deposition the iron and nickel ions are homogenous distribute in the solution and should provide the uniformly homogenous alloy thin film. Due to differences in ion mobility and sticking condition of iron and nickel ions, the real time investigation of electro-deposition of these alloy thin films were investigated by TRXAS during the applying current into the solution. In this work, the electrochemical cell consists of two 2.0 x 2.0 cm2 indium tin oxide (ITO) coated on thin plastic sheets for anode and cathode. These two electrodes separate by placing other two thin plastic sheets at the edges with the total thickness of 0.1 cm. The electrochemical cell is electro-deposited at the current density value of 0.25 mA/cm-2 for 10 minutes and collect the TRXAS data every 20 s with Fe K-edge (7112 eV) and Ni K-edge (8333 eV) at beam line 2.2, Synchrotron Light Research Institute (SLRI). Moreover, the intensity of X-ray at Fe edge dramatically decreases as the Fe ion deposits on the electrode. The slightly shift of Fe edge indicate the metal film forming i.e. Fe(II) ions convert to Fe(0) film. In addition, the signal of Fe(II) ion in R space also decrease as increasing the deposition time while the component at the nearest neighbor position of Fe metal alloy (at about 2Å) slight increase. However, the scattering signal of alloy at 1st nearest neighbor cannot determine the BCC and FCC crystal structure. These are needed the signal at the third and fourth nearest neighbor which are very weak at this initial deposition.