Eunmo Lee

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.

Electrical transport and quasipersistent photocurrent in vanadium oxide nanowire networks

Electrical conductivity and photoconductivity measurements were carried out on semiconducting vanadium oxide nanowire networks synthesized through the polycondensation of vanadic acid. The temperature-dependent conductivity was described well by Mott’s optical multiphonon assisted hopping model at high temperatures and by the variable-range hopping mechanism at low temperatures. The photoconductivity showed a weak temperature dependence. Besides, quasipersistent photocurrent with a single-exponential decay behavior was observed right after switching off the light and was explained in terms of the random local-potential fluctuation model.

Charge transport and photoresponses in a single-stranded DNA/single-walled carbon nanotube composite film

Electrical conductivity and photoresponse measurements have been carried out on a single-stranded DNA (ssDNA)/single-walled carbon nanotube (SWNT) composite film in comparison to those of a SWNT film. While the temperature-dependent electrical conductivity of the pristine SWNT film was described well by the combined mechanism of a three-dimensional variable-range hopping and hopping conduction, that of the ssDNA/SWNT composite film followed a fluctuation-induced tunneling model. Besides, competition of photoexcited charge carrier generation and oxygen adsorption/photodesorption in the photoresponses of the films was observed and discussed in view of the role of the DNA wrapping. Thus, the biopolymer coating of the SWNTs is shown to play a significant role in modifying the charge dynamics of the composite system.