Yil-Hwan You

Impedance spectroscopy characterization of resistance switching NiO thin films prepared through atomic layer deposition

To understand electrical/dielectric phenomena and the origins of bistable resistive switching, impedance spectroscopy was applied to NiO thin films prepared through atomic layer deposition. The dc current-voltage characteristics of the NiO thin films were also determined. Frequency-dependent characterizations indicated that the switching and memory phenomena in NiO thin films did not originate from the non-Ohmic effect at the electrode/NiO interfaces but from the bulk-related responses, i.e., from an electrocomposite where highly conducting components are distributed in the insulating NiO matrix. Low dielectric constants and bias-independent capacitance appeared to corroborate the bulk-based responses in resistive switching in NiO thin films.

Crystallization of amorphous silicon thin films using self-limiting ALD of nickel oxide

The crystallization of amorphous Si (a-Si) thin films was performed using atomic layer deposition (ALD) of nickel oxide. Nickel oxide layers were deposited using nickel aminoalkoxide as a precursor in Ni and water as a precursor in oxygen. The presence of nickel oxide caused significant crystallization to occur in a-Si at 575 °C under a reducing atmosphere. Even one single ALD layer of nickel oxide was high enough to crystallize the a-Si thin films. Self-limiting layer controllability in ALD is useful in providing a catalytic layer for formation of polycrystalline Si thin films for application to large-scale flat panel displays.

Extraction of quantitative parameters for describing the microstructure of solid oxide fuel cells.

Digital quantification of a two-dimensional structure was applied to a GDC(Gd₂O₃-doped CeO₂)/LSM(La₀.₈₅Sr₀.₁₅MnO₃) composite cathode employed for solid oxide fuel cells. With the aid of high-resolution imaging capability based on secondary and backscattered electron images, two-dimensional electron micrographs were converted to digital binary files using an image processing tool combined with the line intercept method. Statistical analysis combined with a metallurgical tool was employed to determine microstructural factors, i.e., volume fraction, size distribution, and interconnectivity. The current work reports the quantification of the two-dimensional structural images of GDC/LSM composites applicable to solid oxide fuel cells, with the aim of obtaining the volume fraction, size distribution, and interconnectivity as functions of composite composition. The volume fractions of the solid constituent phases exhibit compositional dependence in cathodes; however, LSM interconnectivity increases gradually as a function of LSM composition, whereas that of GDC decreases significantly at 50 wt% LSM.