Ruchira Dharmasena

Mesoporous TiO2 coating on carbon–sulfur cathode for high capacity Li–sulfur battery

In this paper, a meso-porous TiO2 (titania) coating is shown to effectively protect a carbon–sulfur composite cathode from polysulfide dissolution. The cathode consisted of a sulfur impregnated carbon support coated with a few microns thick mesoporous titania layer. The carbon–sulfur cathode is made using activated carbon powder (ACP) derived from biomass. The mesoporous titania coated carbon–sulfur cathodes exhibit a retention capacity after 100 cycles at C/3 rate (433 mA g −1) and stabilized at a capacity around 980 mA h g−1. The electrochemical impedance spectroscopy (EIS) of the sulfur cathodes suggests that the charge transfer resistance at the anode, (Ract) is stable for the titania coated sulfur electrode in comparison to a continuous increase in Ract for the uncoated electrode implying mitigation of polysulfide shuttling for the protected cathode. Stability in the cyclic voltammetry (CV) data for the first 5 cycles further confirms the polysulfide containment in the titania coated cathode while the uncoated sulfur electrode shows significant irreversibility in the CV with considerable shifting of the voltage peak positions. Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) studies confirm the adsorption of soluble polysulfides by mesoporous titania.

Photoluminescence in Functionalized/Doped Graphene Quantum Dots: Role of SurfaceStates

Photoluminescence in Functionalized/Doped Graphene Quantum Dots: Role of Surface States It has been shown that functionalization/doping of Graphene Quantum Dots (GQDs) can lead to further tuning of their already existing band gap. We have successfully functionalized GQDs (synthesized by hydrothermal process) with oxygen, hydrogen, fluorine, and doped with nitrogen using capacitively coupled plasma of respective gas as evidenced by Raman and X-ray photo emission spectroscopy (XPS). Room temperature photoluminescence (PL) of each functionalized GQD shows distinctive features and can be explained as due to charge transfers between the functional groups/dopants and GQDs as well as presence of mid gap states as a result of functionalization and doping. An energy diagram model is proposed to elucidate the PL modulation resulting from functionalization and doping.

MOS tunneling strain sensor using an AC measurement technique

The increasing requirement for low power sensors is motivating research on new techniques. MOS tunneling sensors consume only nW of power, compared to typical piezoresistive and capacitive sensors which consumes μW to mW. The strain was measured by measuring the tunneling current through a Metal-Oxide-Semiconductor sandwich from a DC voltage. To overcome the electronic noise, substantial averaging was utilized. In this paper an improved method of measuring the strain from the tunneling current is demonstrated in which an AC signal is utilized, and the AC current is measured. This approach substantially reduces the noise by avoiding the 1/f noise. The optimal conditions for the AC technique are to use a high frequency to avoid 1/f noise and a low DC bias.