In Hwan Oh

Structure and magnetism in VO2 nanorods

The structural and magnetic properties in vanadium dioxide (VO2) nanorods prepared by the hydrothermal treatment are shown to be markedly different from the case of the bulk system. A peculiar mixed phase of an insulating monoclinic structure (M2) that is observed in the bulk systems under doping or stress and a rutile (R) structure was revealed and confirmed by transmission electron microscopy, x-ray diffraction, and electron spin resonance measurements. Besides, a broad transition from a high-temperature magnetic phase to a low-temperature one, with quite distinct magnetic correlation strengths, was observed.

Crystal Structure of LiH2PO4 Studied by Single-Crystal Neutron Diffraction

Structure of a LiH 2 PO 4 (LDP) single crystal has been studied at room temperature and at 100 K by means of neutron diffraction. The LiO 4 tetrahedra in LDP are linked by vertices forming chains along the a -axis, and a three-dimensional network is formed by PO 4 groups connected by two different hydrogen bonds. The Li + ions in this structure were found to be quite immobile in spite of their very light mass; The very high proton conductivity in the system may have directly to do with the relatively weak hydrogen bonds and the relatively long interoxygen distances facilitating reorientation of the proton acceptor complexes, rather than with the Li + ionic motions.

Charge dynamics in KH2PO4 systematically modified by proton irradiation

Our systematic study employing high-resolution nuclear magnetic resonance measurements shows that the hydrogen bonds and proton transport in the KH2PO4 (KDP) system may be tuned sensitively by proton irradiation. In particular, the hydrogen-bond length in KDP increased by a properly chosen dose of proton irradiation is shown to give rise to a minimum in the activation energy of proton hopping in the hydrogen-bond direction.

Solvent-dependent self-assembly of two dimensional layered perovskite (C6H5CH2CH2NH3)2MCl4 (M = Cu, Mn) thin films in ambient humidity

Two dimensional layered organic-inorganic halide perovskites offer a wide variety of novel functionality such as solar cell and optoelectronics and magnetism. Self-assembly of these materials using solution process (ex. spin coating) makes crystalline thin films synthesized at ambient environment. However, flexibility of organic layer also poses a structure stability issue in perovskite thin films against environment factors (ex. moisture). In this study, we investigate the effect of solvents and moisture on structure and property in the (C6H5(CH2)2NH3)2(Cu, Mn)Cl4 (Cu-PEA, Mn-PEA) perovskite thin films spin-coated on Si wafer using three solvents (H2O, MeOH, MeOHu2009+u2009H2O). A combination of x-ray diffraction (XRD) and x-ray absorption spectroscopy (XAS) show that relative humidity (RH) has a profound effect on perovskite thin films during sample synthesis and storage, depending on the kind of solvent used. The ones prepared using water (Cu-PEA:H2O, Mn-PEA:H2O) show quite different behavior from the other cases. According to time-dependent XRD, reversible crystalline-amorphous transition takes place depending on RH in the former cases, whereas the latter cases relatively remain stable. It also turns out from XAS that Mn-PEA thin films prepared with solvents such as MeOH and MeOHu2009+u2009H2O are disordered to the depth of about 4u2009nm from surface.