Dielectrophoretic assembly and surface treatment of carbon nanomolecules

This dissertation describes experimental studies on the surface treatment and functionalisation of carbon nanomolecules. For characerisation of the disaggregation state of single-walled carbon nanotube bundles, dielectrophoresis with Raman spectroscopy has been investigated. The presence of semiconducting nanotubes in the Raman spectrum following dielectrophoretic assembly indicates incomplete disaggregation. I show that this novel technique is a more effective measure than two existing conventional techniques: (a) optical absorption measurement and (b) the reduction of (10, 2) semiconducting nanotube peak in the Raman spectrum. Excimer lamp processing has been used for three applications: (i) preferential destruction of metallic nanotubes, (ii) nitrization of nanotubes and (iii) instantaneous removal of nanotube caps by ozonolysis. Preferential destruction was undertaken by ultraviolet irradiation in an argon atmosphere. The Raman spectrum after radiation reveals that more metallic nanotubes were destroyed than semiconducting nanotubes. The radial breathing mode peak intensity of (13, 4) metallic nanotubes dropped by about 67 %. Nitrization of carbon nanotubes was undertaken by dissociation of nitric oxide using excimer lamp irradiation. Spectroscopic studies by FTlR and XPS on the irradiated nanotubes suggest that nitric oxide was chemically functionalised on the surface of the nanotubes. The change of surface morphology of the nanotubes was shown by transmission electron microscopy. Removal of nanotube caps was done by excimer lamp induced ozonolysis. Contact angle measurement and electron microscopy on the nanotubes which had been irradiated for ten seconds showed that the end-caps had been removed. Electrophoresis has been utilised for fabrication of a glass-like carbon film. Raman spectroscopy and scanning electron microscopy has shown the presence of glass-like carbon. This fabrication can be done at room temperature, whereas most fabrication processes are undertaken by high temperature processes exceeding 1000 oC

Bottom-contact pentacene thin-film transistors on silicon nitride

We fabricate high-performance pentacene thin-film transistors (TFTs) using lithographic processes compatible with industry standard amorphous silicon (a-Si) TFT fabrication. Bottom-contact bottom-gate pentacene TFTs realized with silicon nitride SiNx gate dielectric show effective mobility values of 0.59 cm2Vs, contact resistances as low as 2.4 kΩ cm, and low threshold voltages. These results demonstrate the viability of using SiNx as a gate dielectric for vacuum-deposited organic TFTs for large-area and flexible electronic applications. © 2011 IEEE

Emergence of electrochemical catalytic activity via an electrochemical-probe on defective transition metal dichalcogenide nanosheets

Two-dimensional transition metal dichalcogenides (2D TMDs) have shown exceptional electrochemical catalytic activity for the efficient generation of hydrogen through electrochemical water splitting. In the case of molybdenum disulfide (MoS2), a prominent member of 2D TMDs, the electrochemically active sites primarily reside at the edges, while the basal plane, which constitutes the majority of the MoS2 structure, remains relatively inactive. In this study, we aimed to activate the inert sites of the basal plane with some defective structure for hydrogen evolution reaction (HER) by employing an electrochemical-probe in combination with voltage sweeping. The initiation of HER at these previously inactive sites was visualized and confirmed using scanning electrochemical cell microscopy (SECCM). Our findings reveal that the enhanced HER activity originates from surface defects induced by the probing process