This project was supported by MOST through the NRL program and in part by the BK21 program.We have investigated the key factors determining the performance of supercapacitors constructed using single-walled carbon nanotube (SWNT) electrodes. Several parameters, such as composition of the binder, annealing temperature, type of current collector, charging time, and discharging current density have been optimized for the best performance of the supercapacitor with respect to energy density and power density. We find a maximum specific capacitance of 180 F/g and a measured power density of 20 kW/kg at energy densities in the range from 7 to 6.5 Wh/kg at 0.9 V in a solution of 7.5 N KOH (the currently available supercapacitors have energy densities in the range 6±7 Wh/kg and power density in the range 0.2±5 kW/kg at 2.3 V in non-aqueous solvents).

We have measured polarized Raman spectra of MnWO 4 single crystals at low temperatures, and studied the temperature dependence of the various phonon modes. From our Raman studies of the MnWO 4 , a new transition temperature, ∼180 K, was found. We have completely assigned the symmetries of the 18 observed Raman modes of the MnWO 4 , as expected from a group theoretical analysis. These Raman modes have been classified into three groups according to weak, intermediate and strong temperature dependence of the modes in each group. Six internal modes have been identified by their weak temperature dependence of the Raman wavenumbers. The temperature dependence of the wavenumbers of the B g modes in Mg-O bonds, modes of intermediate temperature dependence group, shows an anomalous behavior under 50 K. The phonon modes of strong temperature dependence show an anomalous change at ∼180 K in the linewidths. This is believed to be a new transition temperature which involves the changes in the inter-WO 6 octahedra structure.

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We investigated the magnetic and optical properties of [(LaMnO 3 ) n /(SrTiO 3 ) 8 ] 20 (n = 1, 2, and 8) superlattices grown by pulsed laser deposition. We found a weak ferromagnetic and semiconducting state developed in all superlattices. An analysis of the optical conductivity showed that the LaMnO 3 layers in the superlattices were slightly doped. The amount of doping was almost identical regardless of the LaMnO 3 layer thickness up to eight unit cells, suggesting that the effect is not limited to the interface. On the other hand, the magnetic ordering became less stable as the LaMnO 3 layer thickness decreased, probably due to a dimensional effect.