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Ahn Y.N.,Corning Technology Center Korea | Yoon H.,Corning Technology Center Korea | Lee S.H.,Corning Technology Center Korea | Lee H.-H.,Corning Technology Center Korea | Kim H.,Corning Technology Center Korea
Materials and Design | Year: 2016

Kirkendall diffusion, an unbalanced interdiffusion process through an interface of two materials, has attracted attention for decades as one of the promising techniques to fabricate nanoporous materials. In particular, a lot of efforts have been focused on the study of Kirkendall diffusion occurred in ZnO-based material couples due to the unique optoelectronic properties of ZnO. In this study, we fabricate nanoporous planar multilayered structures composed of Al2O3/Ga-doped ZnO (GZO)/Glass with different Ga concentrations by utilizing Kirkendall effect-induced diffusion. It is demonstrated that Ga-doping leads to the formation of internal (not interfacial) voids in the GZO layers, and the features of formed voids clearly depend on the Ga concentration. Through atomistic computational analyses, we elucidate that grain boundaries (GBs) whose density increases as the Ga doping concentration increases promote the local atomic diffusivity, and consequently act as the initiators of voids formed in the GZO layers. In addition, the doped Ga atoms and GBs induce a compressive stress within the GZO layers, which suppresses the growth rate of each individual void. Fundamental understandings of atomic diffusion mechanism demonstrated in this study may provide a simple approach to fabricate nanoporous materials with controlled porosity by modulating the Ga doping concentration. © 2015 Elsevier Ltd.

Choi Y.,Corning Technology Center Korea | Jung Y.,Corning Technology Center Korea | Kim H.,Corning Technology Center Korea
Thin Solid Films | Year: 2016

Highly dense and highly crystalline vanadium dioxide (VO2) thermochromic thin films were successfully sputter-deposited on glass substrates at a low substrate temperature of 300 °C. By superimposition of RF and DC magnetron sputtering, we were able to fabricate VO2 films with high solar transition efficiency (△Tsol) of 12.8% at a substrate temperature of 300 °C, which was comparable to the results attained at 450 °C by conventional DC sputtering. The VO2 crystallization at a lower temperature of 300 °C could be achieved using a high-energy and high-density plasma induced by RF-superimposed DC sputtering. The hysteresis curves of transmittance as a function of temperature revealed that the VO2 films by RF-superimposed DC sputtered at 300 °C exhibited a reduced transition temperature of 59 °C and a narrow hysteresis width of 3 °C. The enhanced transition properties might result from the compressive stress in the b and c axes as well as the densification of the films due to ion bombardment effect. © 2016

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