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Abstract: Lateral porous anodic alumina (PAA) templates were used to organize carbon nanotubes (CNTs) grown by a hot-filament assisted chemical vapor deposition (HFCVD) process. For the CNT growth, we used a modified “home-made” HFCVD system with two independently powered filaments which are fitted respectively on the methane (CH4) gas line, which serves as a carbon precursor and on the hydrogen (H2) gas line, which acts as an etching agent for the parasitic amorphous carbon. Various activation powers of the hot filaments were used to directly or indirectly decompose the gas mixtures at relatively low substrate temperatures. A parametric study of the HFCVD process has been carried out for optimizing the confined CNTs growth inside the lateral PAA templates. [Copyright &y& Elsevier]

Abstract: We investigated the single-walled carbon nanotubes (SWCNTs) growth on Ru nanoparticle catalyst via hot filament assisted chemical vapor deposition (HFCVD) with two independent W filaments for the carbon precursor (methane) and the hydrogen dissociation respectively. The Ru nanoparticles were obtained following a two-step strategy. At first the growth substrate is functionalized by silanisation, then a self assembly of a ruthenium porphyrin complex monolayer on pyridine-functionalized metal oxide substrates. We have studied the impact of the filaments power and we optimized the SWCNTs growth temperature. The as grown SWCNTs were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM) and Raman spectroscopy. It was found that the quality, density and the diameter of SWCNTs depends on the filament and growth temperature. Results of this study can be used to improve the understanding of the growth of SWCNTs by HFCVD. [Copyright &y& Elsevier]

Abstract: Carbon nanofibres (CNFs) obtained by plasma-enhanced chemical vapour deposition are made of cone-shaped graphene layers, the opening angle of which has a significant influence on their properties: the smaller the angle, the closer the properties to those of carbon nanotubes. That angle is determined by the shape of the metal nanoparticle used to catalyse the growth. We show in this paper that the shape of Ni nanoparticle catalysts, and in turn the CNF properties, can be tuned during plasma-enhanced chemical vapour deposition, by the choice of the etchant gas. We show in particular that a water-containing etchant (H2O or H2O+H2) increases the growth rate by an order of magnitude at 600°C compared to an ammonia-containing etchant (NH3 or NH3 +H2), and leaves more elongated Ni particles with a cone angle three times smaller. We conclude that the cone angle and the growth rate are directly related, and propose a mechanism to explain that large difference between the two etchants [ABSTRACT FROM AUTHOR]

Background: Identifying functions for all gene products in all sequenced organisms is a central challenge of the post-genomic era. However, at least 30-50% of the proteins encoded by any given genome are of unknown or vaguely known function, and a large number are wrongly annotated. Many of these 'unknown' proteins are common to prokaryotes and plants. We set out to predict and experimentally test the functions of such proteins. Our approach to functional prediction integrates comparative genomics based mainly on microbial genomes with functional genomic data from model microorganisms and post-genomic data from plants. This approach bridges the gap between automated homology-based annotations and the classical gene discovery efforts of experimentalists, and is more powerful than purely computational approaches to identifying gene-function associations. Results: Among Arabidopsis genes, we focused on those (2,325 in total) that (i) are unique or belong to families with no more than three members, (ii) occur in prokaryotes, and (iii) have unknown or poorly known functions. Computer-assisted selection of promising targets for deeper analysis was based on homology-independent characteristics associated in the SEED database with the prokaryotic members of each family. In-depth comparative genomic analysis was performed for 360 top candidate families. From this pool, 78 families were connected to general areas of metabolism and, of these families, specific functional predictions were made for 41. Twenty-one predicted functions have been experimentally tested or are currently under investigation by our group in at least one prokaryotic organism (nine of them have been validated, four invalidated, and eight are in progress). Ten additional predictions have been independently validated by other groups. Discovering the function of very widespread but hitherto enigmatic proteins such as the YrdC or YgfZ families illustrates the power of our approach. Conclusions: Our approach correctly predicted functions for 19 uncharacterized protein families from plants and prokaryotes; none of these functions had previously been correctly predicted by computational methods. The resulting annotations could be propagated with confidence to over six thousand homologous proteins encoded in over 900 bacterial, archaeal, and eukaryotic genomes currently available in public databases. [ABSTRACT FROM AUTHOR]

The electrochemical and structural responses of silicon nanowires deposited by chemical vapor deposition are investigated. Transmission electron microscopy and X-ray diffraction experiments show the electrochemical lithiation of SiNWs is not a quantitative process in good agreement with cycling experiments performed as a function of cycling limits. The SiNWs are not deeply lithiated as revealed by TEM micrographs. Our results suggest the existence of two well-defined lithiation steps, first at ∼0.2 V into amorphous silicon and then into crystalline silicon at ∼0.1 V. Cycling SiNWs above 100 mV avoid the lithiation of c-Si which preserves the silicon 3-D architecture and results in good cycling performances. A stable capacity value of ∼500 mAh g−1 is achieved over at least 50 cycles. [ABSTRACT FROM AUTHOR]

Vertically aligned multi-walled carbon nanofibers (CNFs) were grown by plasma-enhanced chemical vapor deposition with Ni catalysts on the top of nanofibers. Transmission electron microscopy was used to study the morphology and crystallography of Ni catalysts, which are essential for the nucleation and growth of CNFs. A model for the faceted shape of Ni catalytic particles is proposed. It is shown that the exposed polyhedral surfaces of Ni catalytic particles for vertically aligned CNFs are composed of {111}, {110}, and {100}, a faceting that appears to be characteristic of the growth atmosphere. [ABSTRACT FROM AUTHOR]

Abstract: A fabrication method for silicon beams and membranes defined in lateral and vertical dimensions, as well as superposed silicon membranes, all realized in bulk silicon using only one lithographic step is proposed. This proposal is based on observations made on structures obtained by High Temperature Annealing (HTA) in hydrogen atmosphere process. The combination of design configuration and materials technology (hard mask) with the process shows the possibility of new 3D devices and cavities beyond previously reported capabilities of with this technique. The specific design and hard mask engineering presented can lead to structures used in a bulk silicon platform for 3D devices with optical and electronic functions for the fabrication of bulk silicon waveguides and transistors on stressed membranes with enhanced mobility. [Copyright &y& Elsevier]

Abstract: The increasingly demand on secondary batteries with higher specific energy densities requires the replacement of the actual electrode materials. With a very high theoretical capacity (4200mAhg−1) at low voltage, silicon is presented as a very interesting potential candidate as negative electrode for lithium-ion microbatteries. For the first time, the electrochemical lithium alloying/de-alloying process is proven to occur, respectively, at 0.15V/0.45V vs. Li+/Li with Si nanowires (SiNWs, 200–300nm in diameter) synthesized by chemical vapour deposition. This new three-dimensional architecture material is well suited to accommodate the expected large volume expansion due to the reversible formation of Li–Si alloys. At present, stable capacity over ten to twenty cycles is demonstrated. The storage capacity is shown to increase with the growth temperature by a factor 3 as the temperature varies from 525 to 575°C. These results, showing an attractive working potential and large storage capacities, open up a new promising field of research. [Copyright &y& Elsevier]

The effects of an atomic hydrogen (Hat) pretreatment of the catalyst layer on the low temperature growth of single-walled carbon nanotubes (SWCNTs) have been investigated using a modified catalytic chemical vapor deposition system. Well-defined and isolated individual Fe nanoparticles as a catalyst are successfully formed on the defects with high trapping energy which are created on the Al2O3 surface by Hat pretreatment, yielding highly dense SWCNTs. The pretreatment mechanism of Hat, compared to H2, is also discussed. It was also found that the quality of SWCNTs can be enhanced when Hat is flowed with CH4 during nanotubes growth at low temperature. In this case, the undesired carbon products and defects on catalyst seeds and nanotube walls can be selectively removed by Hat. Therefore it is essential to use Hat in the pretreatment stage for increasing catalytic activity and to keep the size of nanoparticles in the nm range. Hat can also be employed in growth stage for enhancing SWCNTs quality and density at low temperature. [ABSTRACT FROM AUTHOR]

Abstract: We report on the growth mechanism and density control of vertically aligned carbon nanotubes using a triode plasma enhanced chemical vapor deposition system. The deposition reactor was designed in order to allow the intermediate mesh electrode to be biased independently from the ground and power electrodes. The CNTs grown with a mesh bias of +300 V show a density of ∼1.5 μm−2 and a height of ∼5 μm. However, CNTs do not grow when the mesh electrode is biased to −300 V. The growth of CNTs can be controlled by the mesh electrode bias which in turn controls the plasma density and ion flux on the sample. [Copyright &y& Elsevier]

Membrane-based synthesis, also called template synthesis, is a very general approach used to prepare arrays of nanomaterials with monodispersed geometrical features. The most commonly used porous templates are track-etched polycarbonate and porous anodic alumina membranes. Common to all these templates is the fact that the pores are perpendicular to the surface of the membrane. Here, a novel approach is presented, where the pores are synthesized parallel to the surface of the membrane. For the first time, the anodic oxidation of an aluminum thin film is performed laterally, i.e., parallel to the surface of the substrate, instead of perpendicular as usually done. For low anodic oxidation voltages (between 3 and 5 V) we obtain highly regular and ordered pore arrays, at least over a few hundred nanometers length, with a minimum pore size of ~3 to 4 nm. With such porous alumina structures, the controlled in-plane organization of arrays of template-grown nanowires and carbon nanotubes for reproducible device fabrication should be much easier. [ABSTRACT FROM AUTHOR]

We demonstrate the production of integrated-gate nanocathodes which have a single carbon nanotube or silicon nanowire/whisker per gate aperture. The fabrication is based on a technologically scalable, self-alignment process in which a single lithographic step is used to define the gate, insulator, and emitter. The nanotube-based gated nanocathode array has a low turn-on voltage of 25 V and a peak current of 5 μA at 46 V, with a gate current of 10 nA (i.e., 99% transparency). These low operating voltage cathodes are potentially useful as electron sources for field emission displays or miniaturizing electron-based instrumentation. [ABSTRACT FROM AUTHOR]

Either at pixel or driver levels, low-temperature polysilicon (LTPS) is becoming a standard technology for the fabrication of thin-film transistors (TFTs) used in active matrix liquid crystal displays and in active matrix organic light emissive displays. Given the complexity of addressing or pixel circuits, simulation is becoming more and more necessary. In order to reach the required level of simulation efficiency, an accurate model has been developed. This model takes into account all the operating regimes, capacitors contributions, and frequency dispersion effects. In order to be able to simulate large number of matrix pixels and/or integrated drivers, this model is simple enough to allow simulator convergence. Based on 38 parameters, it presents an easy electrical parameters characterization methodology. Moreover, physical parameters use allows an easy modification of the model performances depending on polycrystalline silicon TFT technology properties and evolution. [ABSTRACT FROM AUTHOR]

Plasma enhanced chemical vapour deposition (PECVD) is a controlled technique for the production of vertically aligned multiwall carbon nanotubes for field emission applications. In this paper, we investigate the electrical properties of individual carbon nanotubes which is important for designing field emission devices. PECVD nanotubes exhibit a room temperature resistance of 1–10 kΩ/μm length (resistivity 10−6 to 10−5 Ω m) and have a maximum current carrying capability of 0.2–2 mA (current density 107–108 A/cm2). The field emission characteristics show that the field enhancement of the structures is strongly related to the geometry (height/radius) of the structures and maximum emission currents of ∼10 μA were obtained. The failure of nanotubes under field emission is also discussed. [Copyright &y& Elsevier]

This work reports the non-covalent functionalization of SWNTs with Fe-porphyrin, Co-porphyrin and Co-phthalocyanine molecules. The functionalized SWNTs were first characterized using Raman and X-ray photoelectron spectroscopies. Observations down to nanoscale resolution were also performed by atomic force microscopy, as well as scanning and transmission electron microscopies. The spectroscopic methods evidenced an electronic interaction between the metal-centered molecules and the SWNTs, ensuring the robustness of the functionalization. High resolution microscopy characterizations reveal that the porphyrin and phthalocyanine molecules are adsorbed on the surface of SWNTs. The electrical characterizations show a weak charge transfer between those grafted molecules and the SWNTs, confirming the electronic interaction between the molecules and the SWNTs. Density functional theory (DFT) supports experimental data and helps understanding the experimental results of selective interaction of metal complexes with one type of semiconducting SWNTs. [Display omitted] • The non-covalent assembly of metalloporphyrin (MPo) and metallophthalocyanines (MPc) onto CNTFETs. • These molecules strongly bind to the side walls of SWNTs via physi-adsorption and п-п interactions. • The theoretical study evidences that the molecules are electron donors and the SWNTs are n-doped. • The electrical measurements showed a charge transfer between the metal-centered molecules and SWNTs. [ABSTRACT FROM AUTHOR]

A structure composed of zinc oxide nanowires (ZNWs) grown hydrothermally on an array of vertically aligned carbon nanofibers (CNFs) was fabricated and its field emission properties determined and compared with bare CNF arrays. The combination produced a macroscopic turn-on field of 1.2 V/μm which was found to be the lowest reported from ZNWs deposited on a two-dimensional substrate and much less than the equivalent CNFs array (5.2 V/μm). Crucially, field emission was found to be much more stable at higher pressures of 5×10-6 mbar without exhibiting current degradation for a fixed external field, while emitting with a current density of 1 mA/cm2, the current density typically required for backlighting and field emission displays. We propose a self-ballasting mechanism, in which the low carrier density in the zinc oxide prevents current runaway in the presence of adsorbed species. [ABSTRACT FROM AUTHOR]

A versatile chemical vapor deposition (CVD) based method for the fabrication and electrical measurement of individual carbon nanotube junctions was developed. ferritin or Fe particles were grafted on multiwalled carbon nanotubes (MWNTs) and used as catalysts for the subsequent growth of secondary MWNT by CVD. Junctions were then individually connected. The conductivities of the MWNTs and of the junction were measured. Statistical data show that the conductance of the MWNT-MWNT junction is similar to that of MWNT. This result paves the way for the use of carbon nanotubes as electrical interconnects in electronic applications. [ABSTRACT FROM AUTHOR]

Here we report the reversible change in the nonlinear conductance of a multiwall carbon nanotube (MWNT) when it is bent longitudinally. As the nanotube is compressed and bent, its resistance decreases dramatically. This behavior is fully recoverable. The observed drop in resistance during bending must be the result of increasing number of conduction channels in the nanotube and parallel transport through them. Using this concept of parallel transport, we show that it is indeed possible to electrically model the behavior of the MWNT under compression. The reversible electrical characteristics of a MWNT under bending opens new possibilities for these structures to be applied as nanoscale displacement sensors. [ABSTRACT FROM AUTHOR]

The Enhancer of Zeste Polycomb group proteins, which are encoded by a small gene family in Arabidopsis thaliana, participate to the control of plant development. In the tomato (Solanum lycopersicum), these proteins are encoded by three genes (SlEZ1, SlEZ2 and SlEZ3) that display specific expression profiles. Using a gene specific RNAi strategy, we demonstrate that repression of SlEZ2 correlates with a general reduction of H3K27me3 levels, indicating that SlEZ2 is part of an active PRC2 complex. Reduction of SlEZ2 gene expression impacts the vegetative development of tomato plants, consistent with SlEZ2 having retained at least some of the functions of the Arabidopsis CURLY LEAF (CLF) protein. Notwithstanding, we observed significant differences between transgenic SlEZ2 RNAi tomato plants and Arabidopsis clf mutants. First, we found that reduced SlEZ2 expression has dramatic effects on tomato fruit development and ripening, functions not described in Arabidopsis for the CLF protein. In addition, repression of SlEZ2 has no significant effect on the flowering time or the control of flower organ identity, in contrast to the Arabidopsis clf mutation. Taken together, our results are consistent with a diversification of the function of CLF orthologues in plants, and indicate that although partly conserved amongst plants, the function of EZ proteins need to be newly investigated for non-model plants because they might have been recruited to specific developmental processes.

A paralog (here termed COG0212) of the ATP-dependent folate salvage enzyme 5-formyltetrahydrofolate cycloligase (5-FCL) occurs in all domains of life and, although typically annotated as 5-FCL in pro- and eukaryotic genomes, is of unknown function. COG0212 is similar in overall structure to 5-FCL, particularly in the substrate binding region, and has distant similarity to other kinases. The Arabidopsis thaliana COG0212 protein was shown to be targeted to chloroplasts and to be required for embryo viability. Comparative genomic analysis revealed that a high proportion (19%) of archaeal and bacterial COG0212 genes are clustered on the chromosome with various genes implicated in thiamin metabolism or transport but showed no such association between COG0212 and folate metabolism. Consistent with the bioinformatic evidence for a role in thiamin metabolism, ablating COG0212 in the archaeon Haloferax volcanii caused accumulation of thiamin monophosphate. Biochemical and functional complementation tests of several known and hypothetical thiamin-related activities (involving thiamin, its breakdown products, and their phosphates) were, however, negative. Also consistent with the bioinformatic evidence, the COG0212 proteins from A. thaliana and prokaryote sources lacked 5-FCL activity in vitro and did not complement the growth defect or the characteristic 5-formyltetrahydrofolate accumulation of a 5-FCL-deficient (ΔygfA) Escherichia coli strain. We therefore propose (a) that COG0212 has an unrecognized yet sometimes crucial role in thiamin metabolism, most probably in salvage or detoxification, and (b) that is not a 5-FCL and should no longer be so annotated.

Tetrahydropterin-dependent aromatic amino acid hydroxylases (AAHs) are known from animals and microbes but not plants. A survey of genomes and ESTs revealed AAH-like sequences in gymnosperms, mosses, and algae. Analysis of full-length AAH cDNAs from Pinus taeda, Physcomitrella patens, and Chlamydomonas reinhardtii indicated that the encoded proteins form a distinct clade within the AAH family. These proteins were shown to have Phe hydroxylase activity by functional complementation of an Escherichia coli Tyr auxotroph and by enzyme assays. The P. taeda and P. patens AAHs were specific for Phe, required iron, showed Michaelian kinetics, and were active as monomers. Uniquely, they preferred 10-formyltetrahydrofolate to any physiological tetrahydropterin as cofactor and, consistent with preferring a folate cofactor, retained activity in complementation tests with tetrahydropterin-depleted E. coli host strains. Targeting assays in Arabidopsis thaliana mesophyll protoplasts using green fluorescent protein fusions, and import assays with purified Pisum sativum chloroplasts, indicated chloroplastic localization. Targeting assays further indicated that pterin-4a-carbinolamine dehydratase, which regenerates the AAH cofactor, is also chloroplastic. Ablating the single AAH gene in P. patens caused accumulation of Phe and caffeic acid esters. These data show that nonflowering plants have functional plastidial AAHs, establish an unprecedented electron donor role for a folate, and uncover a novel link between folate and aromatic metabolism.

Like other forms of engineering, metabolic engineering requires knowledge of the components (the 'parts list') of the target system. Lack of such knowledge impairs both rational engineering design and diagnosis of the reasons for failures; it also poses problems for the related field of metabolic reconstruction, which uses a cell's parts list to recreate its metabolic activities in silico. Despite spectacular progress in genome sequencing, the parts lists for most organisms that we seek to manipulate remain highly incomplete, due to the dual problem of 'unknown' proteins and 'orphan' enzymes. The former are all the proteins deduced from genome sequence that have no known function, and the latter are all the enzymes described in the literature (and often catalogued in the EC database) for which no corresponding gene has been reported. Unknown proteins constitute up to about half of the proteins in prokaryotic genomes, and much more than this in higher plants and animals. Orphan enzymes make up more than a third of the EC database. Attacking the 'missing parts list' problem is accordingly one of the great challenges for post-genomic biology, and a tremendous opportunity to discover new facets of life's machinery. Success will require a co-ordinated community-wide attack, sustained over years. In this attack, comparative genomics is probably the single most effective strategy, for it can reliably predict functions for unknown proteins and genes for orphan enzymes. Furthermore, it is cost-efficient and increasingly straightforward to deploy owing to a proliferation of databases and associated tools.

Dihydroneopterin aldolase (FolB) catalyzes conversion of dihydroneopterin to 6-hydroxymethyldihydropterin (HMDHP) in the classical folate biosynthesis pathway. However, folB genes are missing from the genomes of certain bacteria from the phyla Chloroflexi, Acidobacteria, Firmicutes, Planctomycetes, and Spirochaetes. Almost all of these folB-deficient genomes contain an unusual paralog of the tetrahydrobiopterin synthesis enzyme 6-pyruvoyltetrahydropterin synthase (PTPS) in which a glutamate residue replaces or accompanies the catalytic cysteine. A similar PTPS paralog from the malaria parasite Plasmodium falciparum is known to form HMDHP from dihydroneopterin triphosphate in vitro and has been proposed to provide a bypass to the FolB step in vivo. Bacterial genes encoding PTPS-like proteins with active-site glutamate, cysteine, or both residues were accordingly tested together with the P. falciparum gene for complementation of the Escherichia coli folB mutation. The P. falciparum sequence and bacterial sequences with glutamate or glutamate plus cysteine were active; those with cysteine alone were not. These results demonstrate that PTPS paralogs with an active-site glutamate (designated PTPS-III proteins) can functionally replace FolB in vivo. Recombinant bacterial PTPS-III proteins, like the P. falciparum enzyme, mediated conversion of dihydroneopterin triphosphate to HMDHP, but other PTPS proteins did not. Neither PTPS-III nor other PTPS proteins exhibited significant dihydroneopterin aldolase activity. Phylogenetic analysis indicated that PTPS-III proteins may have arisen independently in various PTPS lineages. Consistent with this possibility, merely introducing a glutamate residue into the active site of a PTPS protein conferred incipient activity in the growth complementation assay, and replacing glutamate with alanine in a PTPS-III protein abolished complementation.

Effects of an extract from Y. enterocolitica 0:3 biotype 4 on mouse splenocytes and human lymphocytes cultures were examined. Low doses had a mitogenic action on splenocytes, while high doses inhibited tritiated thymidine incorporation into the cells. With human lymphocytes only inhibitory effect was observed.