Lee Byeongchan

We report the results of first-principles density functional theory calculations of the Young's modulus and other mechanical properties of hydrogen-passivated Si⟨001⟩ nanowires. The nanowires are taken to have predominantly {100} surfaces, with small {110} facets according to the Wulff shape. The Young's modulus, the equilibrium length, and the constrained residual stress of a series of prismatic beams of differing sizes are found to have size dependences that scale like the surface area to volu

We report the results of first-principles density functional theory calculations of the Young's modulus and other mechanical properties of hydrogen-passivated Si ⟨001⟩ anowires. The nanowires are taken to have predominantly {100} surfaces, with small {110} facets. The Young's modulus, the equilibrium length, and the residual stress of a series of prismatic wires are found to have a size dependence that scales like the surface area to volume ratio for all but the smallest wires. We analyze the ph

Recent diamond-anvil-cell (DAC) experiments revealed a new phase in vanadium metal at high pressure. Here we present results from first-principles electronic-structure calculations confirming the existence of this phase. The structure corresponds to a rhombohedral distortion of the bcc ambient-pressure phase. The calculated transition pressure $(0.84\phantom{\rule{0.3em}{0ex}}\mathrm{Mbar})$ and density compare reasonably with the measured data. Interestingly, a reentrant bcc phase is discovered

We present results from ab initio calculations of the mechanical properties of the rhombohedral phase $(\ensuremath{\beta})$ of vanadium metal reported in recent experiments, and other predicted high-pressure phases ($\ensuremath{\gamma}$ and bcc), focusing on properties relevant to dynamic experiments. We find that the volume change associated with these transitions is small: no more than 0.15% (for $\ensuremath{\beta}\text{\ensuremath{-}}\ensuremath{\gamma}$). Calculations of the single crysta

Icosahedral clusters in Ti and Ni are studied with first-principles density functional calculations. We find significant distortion on the Ti icosahedron caused by the strong interaction between surface atoms on the icosahedron but not between the center atom and surface atoms, whereas no such distortion is observed on Ni clusters. In addition, distortion becomes more severe when atoms are added to the Ti(13) cluster resulting in short bonds. Such distorted icosahedra having short bonds are esse

A prototype 1 × 4 microstrip array antenna for the IMT-2000 base station using +/–45° slanted polarisation diversity is proposed to overcome the problems of space diversity. ‘T’ shaped aperture coupled feeds are used to obtain good isolation. For a single radiating element, isolation of up to 50 dB between the two ports has been obtained. Stacked patches are also used for broadband operation. For the 1 × 4 array, the distance between each radiating element is 0.92λ0 and a corporate feed is used.

Despite their well-defined and intrinsic porous structures, metal–organic cages (MOCs) readily lose their crystalline arrangement upon solvent exchange and desolvation, which significantly reduces their porosity. Herein, we report a novel bridging and fixing strategy for retaining the ordered arrangement of MOCs. In the bridging process, electrophilic aromatic substitution reactions involving the 4,6-dihydroxy-1,3-benzenedicarboxylate (m-DOBDC2–) ligands of cuboctahedral MOCs and formaldehyde co

Abstract Metal–organic cages (MOCs) have garnered significant attention due to their unique discrete structures, intrinsic porosity, designability, and tailorability. However, weak inter‐cage interactions, such as van der Waals forces and hydrogen bonding can cause solid‐state MOCs to lose structural integrity during desolvation, leading to the loss of porosity. In this work, a novel strategy to retain the permanent porosity of Cu‐paddlewheel‐based MOCs, enabling their use as heterogeneous catal

Local order of liquid Ti is studied by ab initio molecular dynamics to address the unique liquid structure factor in experiments reported recently. The present study reveals that the local order of liquid Ti is in the form of fragments of the distorted icosahedral short range order, where the distortion is induced by strong bond order effects. We show that the fragments in the short-bond rich region separated from the background liquid account for the pronounced feature in structure factor of li

We investigate the mechanics of Si nanowires using first-principles theory and find that the nanowires exhibit the same softening (decreased Young's modulus) as the wire diameter is reduced, regardless of the surface reconstruction or passivation. This invariance is contrary to the expectation that the lower coordination of the bare surfaces affects the bond order and leads to stiffer nanowires than the H-passivated nanowires. We rigorously connect electronic structures and mechanical properties

Abstract Metal–organic polyhedra (MOPs) are intrinsically porous cage‐like structures; however, they frequently display low porosity due to their agglomeration caused by solvent exchange and removal, which results in the blockage of pore windows. This study presents the unprecedented single‐crystal‐to‐single‐crystal transformation of a cuboctahedral MOP‐OH ([Cu 24 L 24 ], H 2 L = 5‐hydroxybenzene‐1,3‐dicarboxylic acid) using a simple solvent exchange from coordinating N , N ‐diethylformamide to

Liquid-liquid transitions under high pressure are found in many elemental materials, but the transitions are known to be associated with either sp-valent materials or f-valent rare-earth elements, in which the maximum or a negative slope in the melting line is readily suggestive of the transition. Here we find a liquid-liquid transition with a positive melting slope in transition metal Ti from structural, electronic, and thermodynamic studies using ab-initio molecular dynamics calculations, show

A light‐weight and wideband X‐band absorber employing a resistive silver nanowire (AgNW) film is presented. One unit of the absorber is composed of a cross‐shaped AgNW resistive film and a conducting plane separated by a 7.5 mm ( λ 0 /4 at 10 GHz) Styrofoam ( ε r = 1.03) layer. The used surface resistance of the film is 42 Ω per square. The 90% absorption bandwidth of the absorber is 80% from 6 to 14 GHz with a near complete absorption at the centre frequency of 10 GHz. Besides, it is also shown