ABSTRACT
The atomic layer deposition (ALD) method was applied to grow thin polycrystalline BiFeO3 (BFO) films on Pt/SiO2/Si substrates. The 50 nm thick films were found to exhibit high resistivity, good morphological integrity, and homogeneity achieved by the applied ALD technique. Magnetic characterization revealed saturated magnetization of 25 emu/cm(3) with temperature-dependent coercivity varying from 5 to 530 Oe within the temperature range from 300 to 2 K. Magnetism observed in the films was found to change gradually from ferromagnetic spin ordering to pinned magnetic domain interactions mixed with weak spin-glass-like behavior of magnetically frustrated antiferromagnetic/ferromagnetic (AFM-FM) spin ordering depending on the temperature and magnitude of the applied magnetic field. Antiferromagnetic order of spin cycloids was broken in polycrystalline films by crystal sizes smaller than the cycloid length (â¼60 nm). Uncompensated spincycloids and magnetic domain walls were found to be the cause of the high magnetization of the BFO films.
ABSTRACT
Electrodes have become more and more popular in biomedical and bioengineering applications, where they are used mostly to apply/measure potentials or currents to/from biological systems. Under such conditions, electrochemical reactions commonly occur at the electrode surface. With the aim to better describe these processes we applied constant currents using transparent indium tin oxide microelectrodes to induce a local change in pH, associated with electrolysis. The pH change was monitored optically within the first lateral 170 microm vicinity using microscopy and a pH sensitive fluorescent dye combination as indicator. The data were then fitted with a simple diffusion model. The effect of such an induced pH change was also assessed by measuring the desorption of a cationic polyelectrolyte (poly(l-lysine)-grafted-poly(ethylene glycol)) as a function of the local pH. Since this polymer interacts electrostatically with surfaces in a pH dependent manner, we could show a strong effect in unbuffered solutions while buffered solutions restricted the electrochemically induced pH change below the optical resolution of the microscope. The effect of applied current on the behavior of cells was also studied on myoblasts cultured directly on the microelectrodes. We have found that current densities larger than 0.57 A m(-2) induced cell death within 2 min of exposure. Based on our model we could attribute this to the change in local pH although the effect of other electrochemically created reactive molecules could not be excluded.
