김성곤 교수

We report a molecular dynamics simulation of melting and evaporation of the carbon fullerenes ${\mathrm{C}}_{20}$, ${\mathrm{C}}_{60}$, and ${\mathrm{C}}_{240}$. Several phases, among them a previously unknown ``pretzel'' phase with a three-dimensional structure of multiply connected carbon rings, can be identified above the high initial melting temperature T\ensuremath{\approxeq}4000 K. At T\ensuremath{\gtrsim}${10}^{4}$ K, a complete conversion of compact fullerenes to carbon chain fragments i

Copper (Cu) nanoparticles (NPs) have received extensive interest owing to their advantageous properties compared with their bulk counterparts. Although the natural oxidation of Cu NPs can be alleviated by passivating the surfaces with additional moieties, obtaining non-oxidized bare Cu NPs in air remains challenging. Here we report that bare Cu NPs with surface excess electrons retain their non-oxidized state over several months in ambient air. Cu NPs grown on an electride support with excellent

Abstract An electride, a generalized form of cavity-trapped interstitial anionic electrons (IAEs) in a positively charged lattice framework, shows exotic properties according to the size and geometry of the cavities. Here, we report that the IAEs in layer structured [Gd 2 C] 2+ ·2e − electride behave as ferromagnetic elements in two-dimensional interlayer space and possess their own magnetic moments of ~0.52 μ B per quasi-atomic IAE, which facilitate the exchange interactions between interlayer

We report local-density-approximation calculations of the electronic structure and thermoelectric properties of $\ensuremath{\beta}\ensuremath{-}{\mathrm{Zn}}_{4}{\mathrm{Sb}}_{3}$. The material is a low carrier density metal with a complex Fermi-surface topology and a nontrivial dependence of the Hall concentration on the band filling. The band structure is rather covalent, consistent with experimental observations of good carrier mobility. At a band filling corresponding to the experimental Ha

We report that the spin-alignment of interstitial anionic electrons (IAEs) in two-dimensional (2D) interlayer spacing can be tuned by chemical pressure that controls the magnetic properties of 2D electrides. It was clarified from the isovalent Sc substitution on the Y site in the 2D Y 2 C electride that the localization degree of IAEs at the interlayer becomes stronger as the unit cell volume and c -axis lattice parameter were systematically reduced by increasing the Sc contents, thus eventually

Abstract Magnetic order has been proposed to arise from a variety of defects, including vacancies, antisites, and grain boundaries, which are relevant in numerous electronics and spintronics applications. Nevertheless, its magnetism remains controversial due to the lack of structural analysis. The escalation of ferromagnetism in vanadium‐doped WSe 2 monolayer is herein demonstrated by tailoring complex configurations of Se vacancies (Se Vac ) via post heat‐treatment. Structural analysis of atomi

Discoveries of two-dimensional (2D) magnetism originated from confined atomic layers in van der Waals (vdW) crystals provide an interesting arena for elucidating its fundamentals and enrich magneto-electric and quantum properties. However, a material that exhibits intrinsic 2D magnetism of interstitial electrons occupying layered space, as a root system of magnetic vdW crystals, remains obscure. In this work, 2D ferromagnetic vdW electride, [RECl]2+·2e− (RE = Y and La) is reported with perfectly

Electrides, which are ionic crystals composed of excess anionic electrons, are of great interest as an exotic material for fundamental research and practical applications in broad fields of science and technology. However, an inherent chemical instability under ambient conditions at room temperature has been a fatal drawback to be addressed. Here, we report that transition metal-rich monochalcogenides are an emerging class of low-dimensional electrides with excellent chemical and thermal stabili

General theory of semi-empirical potential methods including embedded-atom method and modified-embedded-atom method (MEAM) is reviewed. The procedures to construct these potentials are also reviewed. A multi-objective optimization (MOO) procedure has been developed to construct MEAM potentials with minimal manual fitting. This procedure has been applied successfully to develop a new MEAM potential for magnesium. The MOO procedure is designed to optimally reproduce multiple target values that con

We report first-principles calculations of the electronic and geometric structure of the (110) cross-sectional surfaces on InAs/GaSb superlattices, and compare the results with scanning tunneling microscopy images of filled electronic states. In both the predicted and measured images the InAs surfaces appear lower than GaSb, a height difference we show is caused primarily by differences in the electronic structure of the two materials. In contrast, local variations in the apparent height of surf

Constructing a mono-atom step-level ultra-flat material surface is challenging, especially for thin films, because it is prohibitively difficult for trillions of clusters to coherently merge. Even though a rough metal surface, as well as the scattering of carriers at grain boundaries, limits electron transport and obscures their intrinsic properties, the importance of the flat surface has not been emphasised sufficiently. In this study, we describe in detail the initial growth of copper thin fil

In superconductors, cracks (of width w ≳ ξs) are effective in enhancing local supercurrent, and we calculate the size of these supercurrent hot spots as a function of the crack length a and the London penetration depth λ using the two-dimensional (2D) London theory. In the λ→∞ limit and constant injected current density, we show that this 2D solution is also exact for the current flow in a thin film containing a through crack. We argue that large local supercurrents near a surface crack nucleate

Abstract Magnetism of pure electrons is fundamental for understanding diverse magnetic phenomena in condensed matters but has not been fully investigated in experiments due to the lack of a tractable model system. Such an exotic material necessitates an exclusive magnetic interaction of electrons being devoid of orbital and lattice degrees of freedom. Here, we report the two-dimensional mixed-cation [YGdC] 2+ ∙2e − electride, showing ferrimagnetic nature from the direct exchange interaction of m