Yong‐Hoon Kim

We demonstrate a high-performance organic thin-film transistor array fabricated on a flexible paper substrate. As a water and chemical barrier layer, 6-μm-thick parylene has been coated on the paper substrate by using the vacuum deposition. The parylene layer protects the paper substrate from becoming damp during the wet chemical process. Using poly (3-hexylthiophene) as an active layer, a high-performance organic transistor with field effect mobility up to 0.086 cm <sup xmlns:mml="http://www.w3

We investigate the behavior of three-dimensional (3D) exchange-correlation energy functional approximations of density-functional theory in anisotropic systems with two-dimensional (2D) character. Using two simple models, the quasi-2D electron gas and two-electron quantum dot, we show a fundamental limitation of the local density approximation (LDA) and its semilocal extensions, generalized gradient approximation (GGA) and meta-GGA (MGGA), the most widely used forms of which are worse than the L

Applying a novel exact-exchange (EXX) approach within time-dependent density-functional theory, we obtained the optical absorption spectrum of bulk silicon in good agreement with experiments including excitonic features. Analysis of the EXX kernel shows that inclusion of the Coulomb coupling of electron-hole pairs and the correct long-wavelength behavior in the kernel is crucial for the proper description of excitonic effects in semiconductors.

We developed an on-packaging colorimetric sensor label that can detect the aldehyde emission of apples based on Methyl Red. The sensor label was constructed using printable inks on paper medium and relied on the change in basicity caused by the nucleophilic addition reaction between aldehyde and hydroxide via the Cannizzaro reaction. The sensor can be used to detect aldehyde in solution and vapor. Sensitivity and stability toward changes in humidity were achieved by altering the concentration of

We present a first-principles study of the coherent charge transport properties of bistable [2]catenane molecular monolayers sandwiched between Au(111) electrodes. We find that conduction channels around the Fermi level are dominated by the two highest occupied molecular orbital levels from tetrathiafulvalene (TTF) and dioxynaphthalene (DNP) and the two lowest unoccupied molecular orbital levels from tetracationic cyclophane (CBPQT4+), and the OFF to ON switching results from the energetic shift

We present an exact expression for the frequency-dependent Kohn-Sham exact-exchange (EXX) kernel for periodic insulators, which can be employed for the calculation of electronic response properties within time-dependent (TD) density-functional theory. It is shown that the EXX kernel has a long-wavelength divergence behavior as the exact full exchange-correlation kernel and thus rectifies one serious shortcoming of the adiabatic local-density approximation and generalized gradient approximations

We report on the development of an accurate first-principles computational scheme for the charge transport characteristics of molecular monolayer junctions and its application to hexanedithiolate (C6DT) devices. Starting from the Gaussian basis set density-functional calculations of a junction model in the slab geometry and corresponding two bulk electrodes, we obtain the transmission function using the matrix Green's function method and analyze the nature of transmission channels via atomic pro

MAPbBr₃ (MA: CH₃NH₃⁺) undergoes surface degradation under dark and vacuum conditions that leads to the formation of surface PbBr₂ species.

A hierarchical architecture fabricated by integrating ultrafine titanium dioxide (TiO 2 ) nanocrystals with the binder‐free macroporous graphene (PG) network foam for high‐performance energy storage is demonstrated, where mesoporous open channels connected to the PG facilitate rapid ionic transfer during the Li‐ion insertion/extraction process. Moreover, the binder‐free conductive PG network in direct contact with a current collector provides ultrafast electronic transfer. This structure leads t

We investigate anion-π binding modes in a cis-isomer of 3,5-dinitrophenyl-substituted calix[4]pyrrole with various anions via X-ray crystallographic analyses and compare its binding affinities with those of the corresponding trans-isomer. Sandwich-type anion-π interactions prove to not only enhancing anion binding abilities but also altering the anion-binding selectivity of the calix[4]pyrrole framework.