Jungsik Bang

Highly stable colloidal ZnO nanocrystals by MgO passivation

The surface of ZnO nanocrystals was engineered by the creation of an MgO shell layer that prevents the particle aggregation and improves the luminescent properties. The ZnO core with a diameter of ~3.0?nm and ~0.3?nm thick MgO-passivated ZnO nanocrystals were prepared at 0??C using the reaction between Zn(CH3COO)2, Mg(CH3COO)2 and NaOH dissolved in ethanol medium. While unpassivated or organically capped ZnO nanocrystals are lacking in a colloidal stability against ageing, MgO-passivated ones show a remarkable colloidal stability, demonstrating that the surface passivation of ZnO nanocrystals by an MgO shell is effective. Luminescent efficiencies of green emission of ZnO/MgO nanocrystals versus bare ZnO counterparts are compared, and combined EDS/XPS and Raman spectroscopic data are further provided to verify the core/shell structure of ZnO/MgO nanocrystals.

Process estimation and optimized recipes of ZnO: Ga thin film characteristics for transparent electrode applications

Ga-doped zinc oxide (ZnO:Ga) thin films were prepared on glass substrate by magnetron sputtering at room temperature (RT) and thermally annealed in hydrogen atmosphere for 1h. The effects of film thickness and annealing temperature on sheet resistance, transmittance and figure of merit of ZnO:Ga thin films were analyzed and modeled using the artificial neural networks (NNets). The NNet models presented the good prediction on sheet resistance, transmittance and figure of merit of ZnO:Ga thin films and it was found that the electrical and optical properties of ZnO:Ga thin films were enhanced by thermal annealing. After NNet models were verified, genetic algorithm (GA) was used to search the optimized recipe for the desired figure of merit of ZnO:Ga thin films. The methodology allows us to estimate the optimal process condition with a small number of experiments.

Wet Chemical Etching of Transparent Conducting Ga-Doped ZnO Thin Films by Oxalic and Formic Acid

Wet etching behaviors of highly crystalline, well-textured Ga-doped zinc oxide (GZO) film with a thickness of 150 nm are investigated by using oxalic and formic acids. These two organic acids showed strikingly different etching characteristics with respect to etch rate and etch profile under 0.02 M of concentration and 30°C of temperature. Under these conditions, a faster vertical etch rate of 90 nm/min and sharp edge lines of the patterned GZO film resulted from a formic acid etchant while an oxalic acid solution generated a slower vertical rate of 22 nm/min and uneven line features. These etching behaviors were schematically described by monitoring the intermediate etching stages for each etchant. The mobility of hydronium ions in the oxalic and formic acid solutions, which should be associated with their chemical structures, presumably plays an important role in determining characteristic etching behaviors. Activation energies for the vertical etching of oxalic and formic acids were also experimentally determined to be 14.60 and 6.58 kcal/mol, respectively.