Hyejin Jang

Seoul National University | SNU · Department of Materials Science and Engineering

Halide perovskites have emerged as promising candidates for various applications, such as photovoltaic, optoelectronic, and thermoelectric applications. The knowledge of the thermal transport of halide perovskites is essential for enhancing the device performance for these applications and improving the understanding of heat transport in complicate...

Nonequilibrium of electrons, phonons, and magnons in metals is a fundamental phenomenon in condensed-matter physics and serves as an important driver in the field of ultrafast magnetism. In this work, we demonstrate that the magnetization of a subnanometer-thick Co layer with perpendicular magnetic anisotropy can effectively serve as a thermometer...

Spin-dependent charge transport in magnetic tunnel junctions (MTJs) can be manipulated by a temperature gradient, which can be utilized for spintronic and spin caloritronic applications. Evaluation of the thermally induced phenomena requires knowledge of the temperature differences across the oxide tunnel barrier adjacent to the ferromagnetic (FM)...

Non-equilibrium of electrons, phonons, and magnons in metals is a fundamental phenomenon in condensed matter physics and serves as an important driver in the field of ultrafast magnetism. In this work, we demonstrate that the magnetization of a sub-nm-thick Co layer with perpendicular magnetic anisotropy can effectively serve as a thermometer to mo...

Spin-dependent charge transport in magnetic tunnel junctions (MTJs) can be manipulated by a temperature gradient, which can be utilized for spintronic and spin caloritronic applications. Evaluation of the thermally induced phenomena requires knowledge of the temperature differences across the oxide tunnel barrier adjacent to the ferromagnetic (FM)...

A significant experimental challenge in testing proposed relationships between structure and properties is the synthesis of targeted structures with atomistic control over both structure and composition. SnSe2(MoSe2)1.32 was synthesized to test the hypothesis that the low temperature synthesis of two interleaved structures would result in complete...

Films containing 8, 16, 24, 32 and 64 MoSe2 layers were synthesized using the modulated elemental reactants method. X-ray reflectivity patterns showed that the annealed films were the targeted number of MoSe2 layers thick with atomically smooth interfaces. In-plane x-ray diffraction (XRD) scans contained only hk0 reflections for crystalline MoSe2 m...

ReS2 represents a different class of 2D materials, which is characterized by low symmetry having 1D metallic chains within the planes and extremely weak interlayer bonding. Here, the thermal conductivity of single-crystalline ReS2 in a distorted 1T phase is determined at room temperature for the in-plane directions parallel and perpendicular to the...

Thermoelectric power generation can play a key role in a sustainable energy future by converting waste heat from power plants and other industrial processes into usable electrical power. Current thermoelectric devices, however, require energy intensive manufacturing processes such as alloying and spark plasma sintering. Here, we describe the fabric...

Large-scale, polycrystalline WTe2 thin films are synthesized by atmospheric chemical vapor reaction of W metal films with Te vapor catalyzed by H2Te intermediates, paving a way to understanding the synthesis mechanism for low bonding energy tellurides and toward synthesis of single-crystalline telluride nanoflakes. Through-plane and in-plane therma...

We ascertain the anisotropic thermal conductivity of alumina passivated black phosphorus (BP), a reactive 2D nanomaterial with strong in-plane anisotropy. We measure the room temperature thermal conductivity by time-domain thermoreflectance for the three crystalline axes of exfoliated BP. The thermal conductivity along the zigzag direction (86 +/-...

SrRuO3, a p-type metallic conductor with a small thermopower, and SrTiO3, a p-type insulator with a large thermopower in its hyperstoichiometric state, have been reported to make a complete solid solution. It is, thus, suggested that the thermoelectric power factor, conductivity times thermopower squared (sigma theta(2)), may be best optimized by m...

Defect structures of BaTiO(3) and the like co-doped with variable-valence acceptors and donors are not clear particularly in transition from acceptor domination to donor domination with increasing oxygen activity. We have, thus, examined the electrical conductivity and thermoelectric power of BaTiO(3) co-doped with a variable-valence acceptor Mn(Mn...