80 GHz field-effect transistors produced using high purity semiconducting single-walled carbon nanotubes

This paper presents the high frequency performance of single-walled carbon nanotube (SWNT) field-effect transistors, with channel consisting of dense networks of high purity semiconducting SWNTs. Using SWNT samples containing 99% pure semiconducting SWNTs, we achieved operating frequencies above 80 GHz. This record frequency does not require aligned SWNTs, thus demonstrating the remarkable potential of random networks of sorted SWNTs for high frequency electronics

alex.buchner @ synergy-learning.com

wd.patterson @ ulster.ac.uk A considerable amount of e-learning content is being delivered via virtual or managed learning environments. These platforms keep track of learners’ activities including content viewed, time spent and quiz results. This monitoring trawl provides appropriate data to enable personalised e-learning experiences through the application of existing data mining and knowledge discovery techniques. The reasons for not providing this type of bespoke teaching is, in addition to technical and financial constraints, largely due to the plethora of educational and pedagogical issues which have to be overcome. This paper presents these obstacles and suggests solutions thus challenging the community to focus on a new research area which concentrates on facilitating the specification and application of pedagogical domain knowledge for incorporation into existing data mining and knowledge discovery frameworks. This includes educational thresholds, constraints, taxonomies and previously discovered knowledge as well as pedagogical interestingness and metrics. 1

Surfactant-nanotube interactions in water and nanotube separation by diameter: atomistic simulations

A non-destructive sorting method to separate single-walled carbon nanotubes (SWNTs) by diameter was recently proposed. By this method, SWNTs are suspended in water by surfactant encapsulation and the separation is carried out by ultracentrifugation in a density gradient. SWNTs of different diameters are distributed according to their densities along the centrifuge tube. A mixture of two anionic surfactants, namely sodium dodecylsulfate (SDS) and sodium cholate (SC), presented the best performance in discriminating nanotubes by diameter. Unexpectedly, small diameter nanotubes are found at the low density part of the centrifuge tube. We present molecular dynamics studies of the water-surfactant-SWNT system to investigate the role of surfactants in the sorting process. We found that surfactants can actually be attracted towards the interior of the nanotube cage, depending on the relationship between the surfactant radius of gyration and the nanotube diameter. The dynamics at room temperature showed that, as the amphiphile moves to the hollow cage, water molecules are dragged together, thereby promoting the nanotube filling. The resulting densities of filled SWNT are in agreement with measured densities.Brazilian Agencies FAPESP (Fundacao de Amparo a Pesquisa do Estado de Sao Paulo)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)CNPq (Conselho Nacional de Desenvolvimento Cientifico e Tecnologico)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Photophysics of polymer-wrapped single-walled carbon nanotubes

Single-walled carbon nanotubes (SWNTs) are successfully dispersed in two conjugated polymer poly(9,9-dioctylfluorenyl-2,7-diyl) (PFO) and poly[2-methoxy-5-(2’-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEHPPV) solutions. Steady-state and time-resolved photoluminescence spectroscopy in the near-infrared and visible spectral regions are used to study the interaction of the dispersed carbon nanotube and the wrapped polymer in the nano-hybrids. The SWNTs infrared emission is the signatures of the separation of single semiconducting tubes, the lifetime of the photoluminescence of these tubes is bi-exponential with the first component varying from 6 ps (in MEHPPV wrapped SWNTs) to 14 ps (in PFO wrapped SWNTs), while the second component of the decay for all samples is in the range of 30−40 ps, revealing the intrinsic lifetime of the SWNTs. The study of the photoluminescence of the nano-hybrids in the visible spectral range shows, in the case of the PFO, a relatively strong quenching, the photoluminescence lifetime for the hybrid is more than 100 ps shorter than the one of the pristine polyfluorene solution. For the MEHPPV-SWNT hybrid an opposite behavior is revealed with the photoluminescence lifetime surprisingly longer than the polymer solution. The possible mechanism for the interaction of the two conjugated polymers and the SWNTs is discussed in terms of their electronic band structure