Theoretical and Experimental Studies of Schottky Diodes That Use Aligned Arrays of Single Walled Carbon Nanotubes

We present theoretical and experimental studies of Schottky diodes that use aligned arrays of single walled carbon nanotubes. A simple physical model, taking into account the basic physics of current rectification, can adequately describe the single-tube and array devices. We show that for as grown array diodes, the rectification ratio, defined by the maximum-to-minimum-current-ratio, is low due to the presence of m-SWNT shunts. These tubes can be eliminated in a single voltage sweep resulting in a high rectification array device. Further analysis also shows that the channel resistance, and not the intrinsic nanotube diode properties, limits the rectification in devices with channel length up to ten micrometer.Comment: Nano Research, 2010, accepte

A statistical framework for identifying past PRDM9 binding targets in primates

Recombination is a basic biological force, which, with mutation, plays an important role in generating new combinations of alleles in each chromosome, by shuffling and exchanging genetic material between maternal and paternal chromosomes. Multiple lines of evidence suggest that the rapidly evolving zinc-finger (ZF) protein, PRDM9, is responsible for initiating much or all of recombination in human. PRDM9 shows extreme variation in both the number and sequence of its ZFs, between species and amongst individuals, across mammals. The rapid evolution of the PRDM9 ZF array may be a response to escape a self-destructive drive called biased gene conversion, which can cause preferential transmission of hotspot disrupting alleles, and leading to erosion of vital recombination sites – and hotspot signaling motifs – in the genome through time. This research attempts to uncover ancestral PRDM9 binding targets in humans and primates. By using six primate genomes, this work involves the development of statistical methods that identifies the locations where meiotic recombination could have occurred in the past. This is achieved by looking for short words that have undergone rapid losses or gains in each lineage. As a result, we found many short and different words across lineages. In conclusion, our findings imply a rapidly evolving mechanism landscape of past PRDM9 binding targets

Brittle and Ductile Behavior in Carbon Nanotubes

Article discussing research on the response of carbon nanotubes to a tensile load

Pitfalls in Using Electrical Conductivity to Monitor the Chloride Ingress of Concrete

Chloride ingress in the field structure is influenced by many factors. A non-destructive monitoring is a useful tool for assessing the health of reinforced structures. This study used array sensors to measure the temperature and electrical conductivity of concrete at depths from 10 mm to 140 mm. The electrical conductivity in concrete showed a continuous decrease during the exposure to 3% NaCl solution. A numerical modelling of multi-ion species migration in pore solution can explain the evolution of conductivity profile over exposing time. By comparing with several previous investigations, this study identified the pitfalls in using electrical conductivity or resistivity to monitor the chloride ingress in the exposed concrete. To obtain a correct information from the electrical monitoring system, the experimental and analysing process should consider the saturation degree of concrete, the hydration induced structure change, the leaching of ions, the ingress of chloride and composition of binders

High‐Volume Processed, ITO‐Free Superstrates and Substrates for Roll‐to‐Roll Development of Organic Electronics

The fabrication of substrates and superstrates prepared by scalable roll‐to‐roll methods is reviewed. The substrates and superstrates that act as the flexible carrier for the processing of functional organic electronic devices are an essential component, and proposals are made about how the general availability of various forms of these materials is needed to accelerate the development of the field of organic electronics. The initial development of the replacement of indium‐tin‐oxide (ITO) for the flexible carrier materials is described and a description of how roll‐to‐roll processing development led to simplification from an initially complex make‐up to higher performing materials through a more simple process is also presented. This process intensification through process simplification is viewed as a central strategy for upscaling, increasing throughput, performance, and cost reduction

Project MoonDust: Characterization and Mitigation of Lunar Dust

The feasibility of extended exploration and human presence on the Moon and Mars depends critically on dealing with the environmental factors, especially the intrusive effects of dust. The prior Apollo landed missions found that the lunar dust exhibited high adherence to exposed surfaces and a restrictive friction-like action causing premature wear of the EVA suits. MoonDust is a project being performed in collaboration with the Canadian Space Agency to study the effects of lunar dust on optics and mechanics, and to develop innovative solutions to extend their operational lifetime within a lunar or Mars environment based on the unique properties of carbon nanotube (CNT) nanocomposites. To assist this work, a small lunar environment simulation vacuum chamber has been set-up at MPB Communications to enable the study of lunar dust effects on optics and rotary mechanisms at pressures to below 10-5 Torr. New lunar dust simulants have been developed at the University of Winnipeg, characteristic of lunar Mare (UW-M1) and highland (UW-H1) compositions, that incorporate nanophase Fe in the silica particles. This paper describes the preliminary characterization of the various available lunar dust simulants that has included IR Raman for composition, Atomic Force and SEM Microscopy for morphology, and Vibrating Sample Magnetometer (VSM) for magnetic properties. Trial CNT dust deflectors/traps were fabricated and experimentally validated for magnetic and electrostatic interactions with lunar dust simulants. Good deflection and retention of submicron dust particles for device dust protection was observed. The preliminary experimental results are discussed

Carbon nanotube assisted formation of sub-50 nm polymeric nano-structures

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2008.Includes bibliographical references (p. 39-43).A novel processing method was developed for sub-50 nm structures by integrating quantum dots (QDs) on patterned polymer substrates. Poly(styrene-alt-maleic anhydride) (PSMa) was prepared by the initiated chemical vapor deposition (iCVD) method, an alternative to spin-on deposition. The sub-50 nm PSMa polymer patterns were prepared by low energy oxygen plasma etching by using CNTs as the masks. The water soluble, amine-functionalized QDs underwent the nucleophilic acyl substitution reaction with the PSMa containing anhydride functional groups. This integration method is use to incorporate high performance QDs on inexpensive, lightweight flexible substrate.by Chia-Hua Lee.S.M

Randomized Network of Single Walled Carbon Nanotubes Thin Film Transistor: Fabrication, Simulation and Application as Biosensor

2011 - 2012Nanoelectronic devices based on nanomaterials, such as carbon nanotubes (CNTs) have attracted remarkable attention as a promising building block for future nanoelectronic circuits due to their exceptional electrical, mechanical and chemical characteristics. The electrical characteristics of CNTs, such as high mobility, quasiballistic conductance and resistance against electromigration, allow to surpass the properties of current Si based complementary metal oxide semiconductor (CMOS) devices. In particular, the large surface area and nanoscale structure makes SWCNTs promising candidates for chemical and biological sensing applications as well. Current research covers broad scientific fields, such as study of materials properties at nanoscale, development, fabrication and simulation of nanoscale structures, for electronics and biomedical applications. However, there is ample space for advancements in both theoretical studies and practical applications for CNT-based systems. This thesis addresses the design and manufacture of thin film transistor (TFT) based on randomized network of single walled carbon nanotubes (SWCNTs) that exploit the unique properties of such materials to create a label-free biosensor for detection of variety biomolecules, particularly proteins. In addition, in order to analyze the electric transport of SWCNTs network in the TFT channel a numerical 3-dimensional (3D) model for the thin film layer is developed. The SWCNTs-TFTs are fabricated by using microfabrication to obtain a micro-interdigitated electrode (μ-IDE) as drain-source electrode. The sizes vary between 2 to 50 μm. Thin-film transistors (TFTs) are fabricated by using SWCNTs thin film as the semiconducting layer and SiO2 thin film as the dielectric layer. The high purity semiconducting network of SWCNTs layer is deposited with an effective technique that combines the silanization of the substrate with vacuum filtration process from dispersed SWCNTs in surfactant solution. . The adopted technique provides a low-cost, fast, simple, and versatile approach to fabricate high-performance SWCNTs-TFTs at room temperature. The morphological arrangement of SWCNTs forming the active layer in the channel of the transistor is checked with scanning electron microscopic (SEM). The TFTs obtained exhibit p-type transistor characteristics and operate in 2 accumulation mode. The results are interpreted by considering the percolation theory. The exponent a of the power law describing the conductivity can be linked to the structural complexity of the SWCNT network. In particular an exponent = 1.7 was found experimentally, showing that the obtained thin film is relatively dense and near percolation. In addition, the experimental data have been compared with the results of the 3D model simulating the charge transport in the SWCNT structures formed in the TFT channel. The simulation results lead to an exponent = 1.8 that is in good agreement with the experimental data. The proposed model seems to be able to reliably reproduce the transport characteristics of the fabricated devices and could be an effective tool to improve the SWCNTs-TFTs structure. Moreover, the fabricated SWCNTs-TFT devices provide a suitable platform for high-performance biosensors in label-free protein detection. The sensing mechanism is demonstrated on a proof of principle level for the interaction of biotin and streptavidin on the SWCNTs surface. It is used as a research model for biosensor application. The SWCNTs thin-film biosensor has high sensitivity and it is capable of detecting streptavidin at concentration of 100 pM. [edited by author]XI n.s