Ran Ji

Wafer-scale arrays of epitaxial ferroelectric nanodiscs and nanorings

Wafer-scale arrays of well-ordered Pb(Zr(0.2)Ti(0.8))O3 nanodiscs and nanorings were fabricated on the entire area (10 mm x 10 mm) of the SrRuO3 bottom electrode on an SrTiO3 single-crystal substrate using the laser interference lithography (LIL) process combined with pulsed laser deposition. The shape and size of the nanostructures were controlled by the amount of PZT deposited through the patterned holes and the temperature of the post-crystallization steps. X-ray diffraction and transmission electron microscopy confirmed that (001)-oriented PZT nanostructures were grown epitaxially on the SrRuO3(001) bottom electrode layer covering the (001)-oriented single-crystal substrate. The domain structures of PZT nano-islands were characterized by reciprocal space mapping using synchrotron x-ray radiation. Ferroelectric properties of each PZT nanostructure were characterized by scanning force microscopy in the piezoresponse mode.

Magnetization dynamics in optically excited nanostructured nickel films

In this work, the laser-induced magnetization dynamics of nanostructured nickel films is investigated. The influence of the nanosize is discussed considering the timescale of hundreds of femtoseconds as well as the GHz regime. While no nanosize effect is observed on the short timescale, the excited magnetic mode in the GHz regime can be identified by comparison with micromagnetic simulations. The thickness dependence reveals insight into the dipole interaction between single nickel structures. Also, transient reflectivity changes are discussed.

Manipulating feature sizes in Si-based grating structures by thermal oxidation

We report a method for manipulating feature sizes in Si-based grating structures by thermal oxidation, which allows the realization of fin width/period ratios not directly accessible by laser interference lithography. Taking advantage of the expansion in volume associated with the thermal oxidation of Si, grating structures with very high fin width/period ratios of the order of 0.96 were obtained, whereas subsequent chemical etching of the oxide yields grating structures with fin width/period ratios as small as ∼0.06.