Junghan Lee

A Light Incident Angle Switchable ZnO Nanorod Memristor: Reversible Switching Behavior Between Two Non‐Volatile Memory Devices

A light incident angle selectivity of a memory device is demonstrated. As a model system, the ZnO resistive switching device has been selected. Electrical signal is reversibly switched between memristor and resistor behaviors by modulating the light incident angle on the device. Moreover, a liquid passivation layer is introduced to achieve stable and reversible exchange between the memristor and WORM behaviors.

Resistive Switching WOx‐Au Core‐Shell Nanowires with Unexpected Nonwetting Stability Even when Submerged Under Water

The resistive switching (RS) characteristics of a tungsten oxide (WO(x) )-Au core-shell nanowire device array is demonstrated for the first time. In addition to the stable bipolar RS characteristics, the nanowire structure of our RS devices provides superhydrophobic properties. The superhydrophobic RS nanowires repelled water that was poured over, such that the device was protected from failure by water contact-driven leakage currents. Moreover, surprisingly, the devices still work even with when the device is submerged underwater.

Fabrication of a novel hierarchical assembly of ZnO nanowires on WOx nanowhiskers for highly efficient field electron emission

A novel hierarchical heteronanostructure of ZnO nanowires/WOx nanowhiskers was fabricated using a simple two-step process called the thermal evaporation and solution reaction. A high density of thin ZnO nanowires was uniformly deposited on a WOx nanowhisker backbone. The density and morphology of the ZnO nanowires were observed to be tunable as a function of reaction parameters, such as reaction time, growth temperature and solution composition. A solution-mediated solid (SS) growth mechanism was proposed for the formation of the ZnO/WOx hierarchical heteronanostructures. The developed schematic model is consistent with the experimental results as shown in SEM and TEM analyses. Our hierarchical ZnO/WOx heteronanostructures demonstrated enhanced field electron emission properties in comparison to pristine WOx nanowhiskers. The turn-on-field voltage and field enhancement factor were comparable to other nanostructured materials, suggesting that ZnO/WOx hierarchical nanostructures are promising electron emitters in future field emission devices.

Surface chemistry controlled superhydrophobic stability of W18O49 nanowire arrays submerged underwater

Superhydrophobic surfaces with quasi-aligned W18O49 nanowire (NW) arrays were fabricated using a simple thermal evaporation and surface chemistry modification method. The fabricated superhydrophobic W18O49 NW surface has shown reliable stability in submerged underwater conditions, exhibiting silvery surfaces caused by total reflection between the water layer and air pockets. The stability of superhydrophobicity in underwater conditions decreased exponentially as the hydrostatic pressure applied to the substrates increased. In addition, variations in stability were investigated according to changes in the surface energy of W18O49 NW arrays. As surface energy decreased, the underwater stability of the superhydrophobic surface increased sharply. Based on these results, the models explaining tendencies of superhydrophobic stability underwater resulting from hydrostatic pressure and surface energy were designed. This study on fabrication and modeling of underwater superhydrophobic stability will help in designing highly stable superhydrophobic surfaces and broadening fields of superhydrophobic applications.

Bio-inspired dewetted surfaces based on SiC/Si interlocked structures for enhanced-underwater stability and regenerative-drag reduction capability.

Drag reduction has become a serious issue in recent years in terms of energy conservation and environmental protection. Among diverse approaches for drag reduction, superhydrophobic surfaces have been mainly researched due to their high drag reducing efficiency. However, due to limited lifetime of plastron (i.e., air pockets) on superhydrophobic surfaces in underwater, the instability of dewetted surfaces has been a sticking point for practical applications. This work presents a breakthrough in improving the underwater stability of superhydrophobic surfaces by optimizing nanoscale surface structures using SiC/Si interlocked structures. These structures have an unequaled stability of underwater superhydrophobicity and enhance drag reduction capabilities,with a lifetime of plastron over 18 days and maximum velocity reduction ratio of 56%. Furthermore, through photoelectrochemical water splitting on a hierarchical SiC/Si nanostructure surface, the limited lifetime problem of air pockets was overcome by refilling the escaping gas layer, which also provides continuous drag reduction effects.