Sohyeon Kim

Room-temperature (RT) gas sensors for nitrogen dioxide (NO₂) detection face persistent challenges, including reliance on high operating temperatures and inefficient charge carrier utilization under UV activation. To address these limitations, we engineered a p-n nano-heterojunction (NHJ) gas sensor by integrating p-type nickel oxide (NiO) nanoparticles onto n-type zinc oxide (ZnO) nanorods. This architecture leverages UV-driven carrier generation and interfacial electric fields at the NHJ to suppress recombination, enabling unprecedented RT performance. By optimizing thermal annealing conditions, we achieved a well-defined heterojunction with uniform NiO distribution on the top of the ZnO nanorods, validated through electron microscopy and X-ray photoelectron spectroscopy. The resulting sensor exhibits a 5.4-fold higher normalized response to 50 ppm NO₂ under 365 nm UV illumination compared to pristine ZnO, alongside rapid recovery and stable cyclability. The synergistic combination of UV-assisted carrier generation and heterojunction-driven interfacial modulation offers a promising direction for next-generation RT gas sensors aimed at environmental monitoring.

Hydrogen sensors play a crucial role in ensuring safety in various industrial applications. In this study, we demonstrated the use of a room-temperature hydrogen gas sensor based on Pt-nanoparticle-decorated TiO₂ nanorods (TiO₂ NRs/Pt NP). The TiO₂ NRs were synthesized via a hydrothermal method, followed by Pt deposition using sputtering and thermal annealing. Under UV illumination, the TiO₂ NR/Pt NP gas sensor exhibited a remarkable response of 2.4 at a 1% hydrogen concentration, which is approximately 5.9 times higher than that of bare TiO₂ NRs measured in the dark. This enhancement is attributed to the synergistic effect of Pt NPs, which promote charge separation and spillover for oxygen molecules, and UV activation, which generates additional carriers. Moreover, the sensor demonstrated stable and reliable detection of hydrogen concentrations up to 1% without the need for external heating, underscoring its practical applicability under ambient conditions. These results demonstrate that TiO₂ NRs/Pt NP, combined with UV activation, provide a promising approach for highly sensitive and room-temperature hydrogen detection, offering significant potential for hydrogen monitoring and hydrogen energy systems.

The increasing demand for advanced transparent and flexible display technologies has led to significant research in thin-film transistors (TFTs) with high mobility, transparency, and mechanical robustness. In this study, we fabricated all-transparent TFTs (AT-TFTs) utilizing amorphous indium-zinc-tin-oxide (a-IZTO) as a dual-functional material for both the channel layer and transparent conductive electrodes (TCEs). The a-IZTO was deposited using radio-frequency magnetron sputtering, with its composition adjusted for both channel and electrode functionality. XRD analysis confirmed the amorphous nature of the a-IZTO layers, ensuring structural stability post-thermal annealing. The a-IZTO TCEs demonstrated high optical transparency (89.57% in the visible range) and excellent flexibility, maintaining a low sheet resistance with minimal degradation even after 100,000 bending cycles. The fabricated AT-TFTs exhibit superior field-effect mobility (30.12 cm²/V·s), an on/off current ratio exceeding 10⁸, and a subthreshold swing of 0.36 V/dec. The AT-TFT device demonstrated a minimum transmittance of 75.46% in the visible light range, confirming its suitability for next-generation flexible and transparent displays.

Zinc oxide (ZnO) is a promising material for nitrogen dioxide (NO₂) gas sensors because of its nontoxicity, low cost, and small size. We fabricated one-dimensional (1D) and zero-dimensional (0D) convergence gas sensors activated via ultraviolet (UV) photonic energy to sense NO₂ gas at room temperature. One-dimensional ZnO nanorod (ZNR)-based and ZnO nanotube (ZNT)-based gas sensors were synthesized using a simple hydrothermal method. All the sensors were tested under UV irradiation (365 nm) so that they could be operated at room temperature rather than a high temperature. In addition, we decorated 0D Pt nanoparticles (NPs) on the gas sensors to further improve their sensing responsivity. The NO₂-sensing response of the ZNT/Pt NP convergence gas sensor was 2.93 times higher than that of the ZNR gas sensor. We demonstrated the complex effects of UV radiation on 1D ZnO nanostructures and 0D metal nanostructures in NO₂ gas sensing.

GaN nanorod (GNR)-integrated photonic emitters (GIPEs) with horizontally self-arrayed GNRs were fabricated for the next generation displays. The self-array performance of GNRs was enhanced by the effective electric-field area.