Seok Joon Kwon

A myriad of studies and strategies have already been devoted to improving the stability of perovskite films; however, the role of the different perovskite crystal facets in stability is still unknown. Here, we reveal the underlying mechanisms of facet-dependent degradation of formamidinium lead iodide (FAPbI₃) films. We show that the (100) facet is substantially more vulnerable to moisture-induced degradation than the (111) facet. With combined experimental and theoretical studies, th

Abstract Hardware-based cryptography that exploits physical unclonable functions is required for the secure identification and authentication of devices in the Internet of Things. However, physical unclonable functions are typically based on anticounterfeit identifiers created from randomized microscale patterns or non-predictable fluctuations of electrical response in semiconductor devices, and the validation of an encrypted signature relies on a single-purpose method such as microscopy or elec

Abstract Structurally and chemically defective activated‐crumbled graphene (A‐CG) is employed to achieve unique synergy of large reversible potassium (K) and sodium (Na) ion storage capacity with fast charging and extended cyclability. A‐CG synthesis consists of low temperature spraying of graphene oxide slurry, followed by partial reduction annealing and air activation. For K storage, the reversible capacities are 340 mAh g −1 at 0.04 A g −1 , 261 mAh g −1 at 0.5 A g −1 , and 210 mAh g −1 at 2

We report on the wrinkle formation in a thin film produced by the sol-gel method. Through the relaxation of stress, which results from the removal of the solvent during the drying process, an isotropic wavy pattern is generated in the form of skeletal branches. The patterns have a dominant wavelength satisfying a relationship of three-fourths order of thickness. Densification of the gelated film is enhanced by an increase in the volumetric strain caused by the evaporation of the remaining solven

Abstract Solar‐thermal materials have been intensively studied in the context of production and localization of thermal energy, targeting an industry level application. Although photonic and optical strategies for enhancing light absorption have increased the efficiency of photo excitation/conversion into thermal energy, most of them have several limitations such as large area fabrication, thermal stability and broadband/omnidirectional light absorption. In this study, a gold‐coated hierarchical

Advanced materials with low density and high strength impose transformative impacts in the construction, aerospace, and automobile industries. These materials can be realized by assembling well-designed modular building units (BUs) into interconnected structures. This study uses a hierarchical design strategy to demonstrate a new class of carbon-based, ultralight, strong, and even superelastic closed-cellular network structures. Here, the BUs are prepared by a multiscale design approach starting

MXene-blanketed Au nanoparticle assembly with energy level alignment effectively facilitates the charge transfer effect while securing the electromagnetic effect by guiding the analyte near to hotspot center for surface enhanced Raman scattering.

Achieving defect-free block copolymer (BCP) nanopatterns with a long-ranged orientation over a large area remains a persistent challenge, impeding the successful and widespread application of BCP self-assembly. Here, we demonstrate a new experimental strategy for defect annihilation while conserving structural order and enhancing uniformity of nanopatterns. Sequential shear alignment and solvent vapor annealing generate perfectly aligned nanopatterns with a low defect density over centimeter-sca

The planar spin glass pattern is widely known for its inherent randomness, resulting from the geometrical frustration. As such, developing physical unclonable functions (PUFs)-which operate with device randomness-with planar spin glass patterns is a promising candidate for an advanced security systems in the upcoming digitalized society. Despite their inherent randomness, traditional magnetic spin glass patterns pose considerable obstacles in detection, making it challenging to achieve authentic

Photoelectrochemical (PEC) H2O2 production has gained interest as a green, promising route to produce valuable chemicals. However, it suffers from low H2O2 Faradaic efficiency due to competing O2 generation. Here, we propose a plasmon-driven band structure engineering strategy to thermodynamically regulate the product selectivity of a metal oxide based PEC photoanode. It is demonstrated that the plasmonic near-field generated by the periodically patterned Au nanosphere arrays (Au-PAT) effectivel

Abstract The significant performance decay in conventional graphite anodes under low‐temperature conditions is attributed to the slow diffusion of alkali metal ions, requiring new strategies to enhance the charge storage kinetics at low temperatures. Here, nitrogen (N)‐doped defective crumpled graphene (NCG) is employed as a promising anode to enable stable low‐temperature operation of alkali metal‐ion storage by exploiting the surface‐controlled charge storage mechanisms. At a low temperature o

Nanophotonics relies on precise control of refractive index (RI) which can be designed with metamaterials. Plasmonic superstructures of nanoparticles (NPs) can suggest a versatile way of tuning RI. However, the plasmonic effects in the superstructures demand 1 nm-level exquisite control over the interparticle gap, which is challenging in a sub-wavelength NPs. Thus far, a large-area demonstration has been mostly discouraged. Here, heteroligand AuNPs are prepared, which are stable in oil but becom

We report on the morphological dynamics of surface patterns induced by swelling of metal-capped polymer bilayer on a substrate. When the bilayer is subject to solvent vapor, the strain is generated in the polymer layer that is confined by the substrate and the metal capping layer. An increase in the strain induces the development of the stress in the bilayer to deform the lower polymer layer perpendicularly to the surface of the bilayer. Isotropic surface wave patterns results from the stress re

We report on the formation of self-organized surface patterns on a thin metal film capped polymer bilayer on a substrate by swelling. The self-organization is directed by a periodically corrugated elastomeric mold which exerts a nodal effect that confines the intrinsic swelling wave, and the resulting self-organized patterns are anisotropic and quite periodic. The corrugated pattern confined by the elastomeric mold was observed from the earlier stages of swelling while the small wrinkles (the fi