Growth of Carbon Nanotubes on Carbon/Cobalt Films with Different sp 2

The need of barrier layer such as SiO2 for carbon nanotubes (CNTs) growth limits their performance in electronic applications. In this study, conductive carbon/metal (carbon/cobalt—C:Co) composite films with the same metal content, but different sp2/sp3 ratios, were deposited using dual-source filtered cathodic vacuum arc (FCVA) technique. Three different C:Co composite films were deposited at different temperatures; visible Raman spectroscopy indicates that the sp2-rich C:Co composite film forms at high temperature (500°C), and high-resolution transmission electron microscopy (HRTEM) shows the formation of conducting graphitic-like sp2 clusters and with Co nanoclusters embedded within them. Electrical measurement shows a significant decrease in film resistivity as sp2/sp3 ratio increases. CNTs were successfully grown on the composite films by plasma-enhanced vapor deposition (PECVD) approach. Scanning electron microscopy (SEM) shows minor effect on the density of CNTs by varying the sp2/sp3 ratio. The dependence of defect level of the as-grown CNTs is found to reduce as sp2/sp3 ratio increases

Localized anneal

US8268733Granted Paten

Experimental characterization and modelling of electromigration lifetime under unipolar pulsed current stress

The electromigration behaviour of Cu/SiCOH interconnects carrying unipolar pulsed current with long periods (i.e. 2, 16, 32 and 48 h) is presented in this study. Experimental observations suggest that the electromigration behaviour during void growth can be described by the ON-time model and that the lifetime of the Cu/SiCOH interconnects is inversely related to the duty cycle. Numerical simulation is carried out to compute the time required to nucleate a void under unipolar pulsed current stress conditions. The time to void nucleation is found to vary proportionally to the inverse square of the duty cycle and is independent of frequency at 1 Hz and higher. By computing the stress evolution in interconnects with short length, it was shown that the product of the unipolar pulsed current’s duty cycle and current density, i.e. average current density, is equivalent to the current density of a constant current (D.C.) stress. The simulation results suggest (d · jL)crit as the equivalent critical current density-length product under unipolar pulsed current condition. Both the experimental and simulation results show that duty cycle has an effect on the electromigration lifetime of interconnects carrying unipolar pulsed current

Tailor and functionalize TiO2 compact layer by acid treatment for high performance dye-sensitized solar cell and its enhancement mechanism

Surface tailoring and functionalization of an annealed TiO2 compact layer by H2SO4 acid was performed to improve the dye-sensitized solar cell (DSSC) performance. Compared to untreated counterpart, the acid-treated compact layer possesses a rougher surface and more hydroxyl groups, which result in increased surface area and enhanced adherence of the compact layer with the mesoporous TiO2 film by Ti–O–Ti bonds formed by a followed heating process. Impedance measurement was further used to investigate the enhancement mechanism, indicating the acid post treatment of the TiO2 compact layer reduces the ohmic bulk resistivity while effectively suppressing charge recombination at FTO/electrolyte interface. In DSSCs with untreated TiO2 compact layer, a significantly increased series resistivity is very likely to be the rate determining factor to limit the charge separation process. Thus, an optimal post acid treatment could reduce the resistivity for high charge transport, resulting in larger short-circuit current for further improvement of power conversion efficiency from 6.60% in DSSC with untreated compact layer to 7.21% in DSSC with acid-treated compact layer. This work also provides fundamental insight of the compact layer for DSSC performance improvement

TiO2 composing with pristine, metallic or semiconducting single-walled carbon nanotubes : which gives the best performance for a dye-sensitized solar cell

Different types of single-walled carbon nanotubes (SWCNTs), pristine (p-), metallic (m-) and semiconducting (s-) are incorporated into TiO2 photoanodes to improve the dye-sensitized solar-cell (DSSC) performance and their effects on the device performance are further investigated. Although all three types of SWCNTs are found to have comparable structural morphologies and a reduced charge transport resistivity for the photoanodes, only the semiconducting one was able to suppress charge-recombination events, resulting in even greater improvement of DSSC performances. This is very likely to be ascribed to the higher energy barrier of s-SWCNTs compared to both m- and p-SWCNTs to block the back flowing of dye-injected electrons for I3− reduction in the charge recombination process

Electrical properties of textured carbon film formed by pulsed laser annealing

Previous works have showed that textured carbon film can be fabricated by applying suitable ion energy and substrate temperature. In this experiment, the effect of laser annealing on amorphous carbon films was studied. Atomic force microscopy shows the effect of laser irradiation on surface morphology of carbon film, and visible Raman spectroscopy shows that the G peak position shifted from 1540 cm− 1 to 1600 cm− 1, and the increase in I(D)/I(G) intensity ratio indicates the formation of more graphitic film at higher laser energy. High resolution transmission electron microscopy (HRTEM) shows the vertical alignment formation at suitable laser energy. Electrical measurement shows that the vertical aligned carbon films exhibit low resistance, ohmic current–voltage characteristics, which suggests that vertical aligned films formed by laser irradiation may be promising material for future nano-device interconnects

Effect of initial sp3 content on bonding structure evolution of amorphous carbon upon pulsed laser annealing

Previous work has shown that pulsed laser annealing can be used to change the bonding structure of amorphous carbon films. In this paper, the effect of initial sp3 content on bonding structure of amorphous carbon upon pulsed laser annealing was studied. Visible Raman spectroscopy was used to examine the bonding structure evolution. Here we show a detailed analysis of the Raman features—G peak position and I(D)/I(G) ratio of carbon film with initial sp3 content of 80%, 65% and 50%. The laser energy level required to induce the change of the bonding structure of carbon film decreases with the decreasing sp3 content. High resolution transmission electron microscopy (HRTEM) shows the formation of graphitic sp2 clusters form at proper laser energy. Electrical measurement also shows that the electrical property such as electrical resistivity has a close relation with the graphitic sp2 clusters

Dark ambient degradation of Bisphenol A and Acid Orange 8 as organic pollutants by perovskite SrFeO3−δ metal oxide

Current advanced oxidation processes (AOPs) are chemically and energetically intensive processes, which are undesirable for cost-effective and large-scale system water treatment and wastewater recycling. This study explored the Strontium Ferrite (SFO) metal oxide on the degradation of highly concentrated organic pollutants under dark ambient condition without any external stimulants. The SFO particles with single perovskite structure were successfully synthesized with a combined high temperature and high-energy ball milling process. An endocrine disruptor, Bisphenol A (BPA) and an azo dye, Acid Orange 8 (AO8) were used as probe organic pollutants. BPA was completely degraded with 83% of mineralization in 24 h while rapid decoloration of AO8 was achieved in 60 min and complete breakdown into primary intermediates and aliphatic acids occurred in 24 h under the treatment of dispersed SFO metal oxide in water. Such efficient degradation could be attributed to the enhanced adsorption of these anionic pollutants on positively charged ball-milled SFO metal oxide surface, resulted in higher degradation activity. Preliminary degradation mechanisms of BPA and AO8 under the action of SFO metal oxide were proposed. These results showed that the SFO metal oxide could be an efficient alternative material as novel advanced oxidation technology for low cost water treatment.ASTAR (Agency for Sci., Tech. and Research, S’pore)EDB (Economic Devt. Board, S’pore

Method for fabricating semiconductor devices with shallow diffusion regions

US8101487Granted Paten

Graphene-Pt\ITO counter electrode to significantly reduce Pt loading and enhance charge transfer for high performance dye-sensitized solar cell

A graphene-Pt\ITO (ITO-PG) counter electrode is fabricated by electrochemical deposition of a porous graphene film on a low-loaded Pt\ITO electrode. Compared to both plain graphene and Pt films, the graphene-coated Pt composite film provides large and superior conductive interface for significant improvement of Pt utilization efficiency and charge transfer, which in turn leads to higher power conversion efficiency of the dye-sensitized solar cell (DSSC). As compared to conventional Pt-coated counter electrode, the Pt loading of ITO-PG electrode can be reduced by more than 60% to 1.9 μg cm−2 while achieving even better performance. The performance enhancement mechanism is proposed. This work renders an economical manufacturing process to fabricate high performance DSSC for potential commercial production