Effect of Temperature on Dissipative Electron Tunneling through Co Nanoparticles in HfO2 Films

The influence of temperature on the processes of dissipative electron tunneling through individual Co nanoparticles (NPs) in an HfO₂ film (10 nm thick) on a conductive substrate with a Co sublayer has been experimentally studied by atomic force microscopy (AFM) with a conducting probe. Co NPs were formed by local anodic oxidation of the Co sublayer using an AFM probe with subsequent drift of Co ions to the AFM probe, their reduction, and growth of Co NPs near the contact of the AFM probe tip with the HfO₂ film surface. In the experiment, the tunnel current–voltage characteristics (CVC) of the formed Co NPs were measured when voltage was applied between the AFM probe and the Co sublayer at different temperatures in the range of 20–105°С. The experimental results were interpreted on the basis of the theory of one-dimensional dissipative tunneling for a model double-well oscillatory potential in an external electric field. At one of the voltage polarities on the AFM probe, kinks in I–V characteristics were observed, accompanied by current oscillations through the AFM probe I, which, according to the theory, corresponds to the situation when the initially asymmetric double-well potential becomes symmetrical. The amplitude of the mentioned oscillations ΔI falls slightly non-linearly with increasing temperature. The results of the experiment were compared with the results of calculations of the temperature dependence of the maximum amplitude of oscillations on the field dependence of the probability of 1D dissipative tunneling. The obtained qualitative agreement between the experimental 19 and theoretical temperature dependences indicates that the experimentally observed features of I–V characteristics are associated with the effect of macroscopic quantum tunneling with dissipation. A qualitative agreement was obtained between the experimental and theoretical results that allow us to assume the possibility of experimental observation of the macroscopic dissipative tunneling effects [1] and thereby confirm the hypothesis expressed in the groundbreaking works of A.J. Leggett, A.I. Larkin, Yu.N. Ovchinnikov, and other authors.