JOURNAL OF PHYCOLOGY, Issue 5 2002
Pascal Claquin
The elemental composition and the cell cycle stages of the marine diatom Thalassiosira pseudonana Hasle and Heimdal were studied in continuous cultures over a range of different light- (E), nitrogen- (N), and phosphorus- (P) limited growth rates. In all growth conditions investigated, the decrease in the growth rate was linked with a higher relative contribution of the G2+M phase. The other phases of the cell cycle, G1 and S, showed different patterns, depending on the type of limitation. All experiments showed a highly significant increase in the amount of biogenic silica per cell and per cell surface with decreasing growth rates. At low growth rates, the G2+M elongation allowed an increase of the silicification of the cells. This pattern could be explained by the major uptake of silicon during the G2+M phase and by the independence of this process on the requirements of the other elements. This was illustrated by the elemental ratios Si/C and Si/N that increased from 2- to 6-fold, depending of the type of limitation, whereas the C/N ratio decreased by 10% (E limitation) or increased by 50% (P limitation). The variations of the ratios clearly demonstrate the uncoupling of the Si metabolism compared with the C and N metabolisms. This uncoupling enabled us to explain that in any of the growth condition investigated, the silicification of the cells increased at low growth rates, whereas carbon and nitrogen cellular content are differently regulated, depending of the growth conditions. [source]

Aerogel and Xerogel Catalysts Based on ,-Alumina Doped with Silicon for High Temperature Reactions

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 3 2005
Aurelien Florin Popa
Abstract Numerous materials (supports and catalysts) based on alumina have been prepared using the sol-gel process and carbon dioxide supercritical drying. In this work two types of solids, i.e. xerogels and aerogels, were systematically compared and a way of introducing platinum metal with a content of 5% percent by weight was examined. The structural data, the surface area, Pt dispersion and catalytic activity for the decomposition of the propellant were measured for the various samples. The (Al2O3)0.88(SiO2)0.12 samples prepared show very interesting porosity values, especially for the aerogel. For this reason, they were chosen as supports for the synthesis of 5 wt% platinum on alumina catalysts. The results presented in this work allowed us to obtain an overall view of the influence of the preparation mode on the properties of platinum on alumina supported catalysts. The dispersion of the metal phase is directly dependent on the specific surface of the support. A significant value for the surface area implies a large amount of centers for interaction with the metal precursor and, consequently, the appearance of more centres of simultaneous germination. Although aerogels obtained by carbon dioxide supercritical drying always show superior properties compared with xerogels, for catalytic decompositions the xerogels still remain superior. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]

Combined Analytical and Phonon-Tracking Approaches to Model Thermal Conductivity of Etched and Annealed Nanoporous Silicon

ADVANCED ENGINEERING MATERIALS, Issue 10 2009
Jaona Randrianalisoa
A combination of analytical and phonon-tracking approaches is proposed to predict thermal conductivity of porous nanostructured thick materials. The analytical approach derives the thermal conductivity as function of the intrinsic properties of the material and properties characterizing the phonon interaction with pore walls. [source]

Suppression of Premature Fracture of Silicon under Three-Point Bending: Role of Nanoscale Localized Deformation of Metallic Multilayered Coating,

ADVANCED ENGINEERING MATERIALS, Issue 1-2 2009
Yuan-Ping Li
Brittle single crystal Si with and without Au/Cu multilayer coating was investigated via three-point bending test. Load-bearing capacity of the Si coated with the Au/Cu multilayer is improved evidently compared with the bare Si. Especially the nanoscale plastic deformation of the multilayer was observed to be effective in delaying instable crack propagation within the Si. That would shed significant light in toughening methods of brittle materials. [source]

Porous Silicon-Based Optical Microsensors for Volatile Organic Analytes: Effect of Surface Chemistry on Stability and Specificity

ADVANCED FUNCTIONAL MATERIALS, Issue 17 2010
Anne M. Ruminski
Abstract Sensing of the volatile organic compounds (VOCs) isopropyl alcohol (IPA) and heptane in air using sub-millimeter porous silicon-based sensor elements is demonstrated in the concentration range 50,800 ppm. The sensor elements are prepared as one-dimensional photonic crystals (rugate filters) by programmed electrochemical etch of p++ silicon, and analyte sensing is achieved by measurement of the wavelength shift of the photonic resonance. The sensors are studied as a function of surface chemistry: ozone oxidation, thermal oxidation, hydrosilylation (1-dodecene), electrochemical methylation, reaction with dicholorodimethylsilane and thermal carbonization with acetylene. The thermally oxidized and the dichlorodimethylsilane-modified materials show the greatest stability under atmospheric conditions. Optical microsensors are prepared by attachment of the porous Si layer to the distal end of optical fibers. The acetylated porous Si microsensor displays a greater response to heptane than to IPA, whereas the other chemical modifications display a greater response to IPA than to heptane. The thermal oxide sensor displays a strong response to water vapor, while the acetylated material shows a relatively weak response. The results suggest that a combination of optical fiber sensors with different surface chemistries can be used to classify VOC analytes. Application of the miniature sensors to the detection of VOC breakthrough in a full-scale activated carbon respirator cartridge simulator is demonstrated. [source]

High-Temperature Contact Formation on n-Type Silicon: Basic Reactions and Contact Model for Seed-Layer Contacts

ADVANCED FUNCTIONAL MATERIALS, Issue 3 2010
Matthias Hörteis
Abstract Contact formation on n-type silicon, especially using a high-temperature process, has been the subject of research for more than 40 years. After its application in microelectronics, n-type silicon is widely used in silicon solar cells as the emitter layer. The formation of a low ohmic contact grid using an industrially feasible process step is one of the key features required to improve the solar-cell efficiency. The contact materials, typically deposited in a printing step, have to fulfil several functions: opening the dielectric antireflection layer and forming an intimate metal-semiconductor contact with good mechanical adhesion and low specific contact resistance. As the used contact inks typically contain several functional materials, such as silver and a glass frit, the detailed contact formation is still not entirely understood. Therefore, the chemical reactions during the contact firing process have been studied in detail by thermogravimetric differential thermal analysis in combination with mass spectroscopy. Based on these studies, a contact ink has been developed, optimized and tested on silicon solar cells. In this paper, the mechanism of the etching process, the opening of a dielectric layer, the influence of different atmospheres and the impact of the glass-frit content are investigated. The observed microscopic contact structure, the resulting electrical solar-cell parameters and the studied reactions are combined to clarify the physics behind the high-temperature contact formation. [source]

A Porous Silicon-Based Ionomer-Free Membrane Electrode Assembly for Miniature Fuel Cells

FUEL CELLS, Issue 5 2006
T. Pichonat
Abstract Previous work showed the pertinence of using grafted porous silicon as the proton exchange membrane for miniature fuel cells. One of the limitations was the membrane-electrodes assembly, which required an ionomer, in the current study a 5% Nafion®-117 solution, to ensure a proton-conducting link between the commercial carbon cloth electrodes and the membrane. Here, new developments for this fuel cell, with a totally Nafion®-free process, are reported. The Pt catalyst is sputtered and electrodeposited onto the surface of the proton conducting porous silicon membrane. The initial performance of this fuel cell is shown and demonstrates the validity of the technique. [source]

Nanostructured Bulk Silicon as an Effective Thermoelectric Material

ADVANCED FUNCTIONAL MATERIALS, Issue 15 2009
Sabah K. Bux
Abstract Thermoelectric power sources have consistently demonstrated their extraordinary reliability and longevity for deep space missions and small unattended terrestrial systems. However, more efficient bulk materials and practical devices are required to improve existing technology and expand into large-scale waste heat recovery applications. Research has long focused on complex compounds that best combine the electrical properties of degenerate semiconductors with the low thermal conductivity of glassy materials. Recently it has been found that nanostructuring is an effective method to decouple electrical and thermal transport parameters. Dramatic reductions in the lattice thermal conductivity are achieved by nanostructuring bulk silicon with limited degradation in its electron mobility, leading to an unprecedented increase by a factor of 3.5 in its performance over that of the parent single-crystal material. This makes nanostructured bulk (nano-bulk) Si an effective high temperature thermoelectric material that performs at about 70% the level of state-of-the-art Si0.8Ge0.2 but without the need for expensive and rare Ge. [source]

Identification of Nucleation Center Sites in Thermally Annealed Hydrogenated Amorphous Silicon

ADVANCED FUNCTIONAL MATERIALS, Issue 14 2009
A. Harv Mahan
Abstract Utilizing the concepts of a critical crystallite size and local film inhomogeneity, it is shown that nucleation in thermally annealed hydrogenated amorphous silicon occurs in the more well ordered spatial regions in the network, which are defined by the initial inhomogeneous H distributions in the as-grown films. Although the film H evolves very early during annealing, the local film order is largely retained in the still amorphous films even after the vast majority of the H is evolved, and the more well ordered regions which are the nucleation center sites for crystallization are those spatial regions which do not initially contain clustered H, as probed by H NMR spectroscopy. The sizes of these better ordered regions relative to a critical crystallite size determine the film incubation times (the time before the onset of crystallization). Changes in film short range order upon H evolution, and the presence of microvoid type structures in the as grown films play no role in the crystallization process. While the creation of dangling bonds upon H evolution may play a role in the actual phase transformation itself, the film defect densities measured just prior to the onset of crystallization exhibit no trends which can be correlated with the film incubation times. [source]

Silicon Inverse-Opal-Based Macroporous Materials as Negative Electrodes for Lithium Ion Batteries

ADVANCED FUNCTIONAL MATERIALS, Issue 12 2009
Alexei Esmanski
Abstract Several types of silicon-based inverse-opal films are synthesized, characterized by a range of experimental techniques, and studied in terms of electrochemical performance. Amorphous silicon inverse opals are fabricated via chemical vapor deposition. Galvanostatic cycling demonstrates that these materials possess high capacities and reasonable capacity retentions. Amorphous silicon inverse opals perform unsatisfactorily at high rates due to the low conductivity of silicon. The conductivity of silicon inverse opals can be improved by their crystallization. Nanocrystalline silicon inverse opals demonstrate much better rate capabilities but the capacities fade to zero after several cycles. Silicon,carbon composite inverse-opal materials are synthesized by depositing a thin layer of carbon via pyrolysis of a sucrose-based precursor onto the silicon inverse opals. The amount of carbon deposited proves to be insufficient to stabilize the structures and silicon,carbon composites demonstrate unsatisfactory electrochemical behavior. Carbon inverse opals are coated with amorphous silicon producing another type of macroporous composite. These electrodes demonstrate significant improvement both in capacity retentions and in rate capabilities. The inner carbon matrix not only increases the material conductivity but also results in lower silicon pulverization during cycling. [source]

UV-Light-Driven Immobilization of Surface-Functionalized Oxide Nanocrystals onto Silicon,

ADVANCED FUNCTIONAL MATERIALS, Issue 2 2007
E. Fanizza
Abstract TiO2 nanorods (NRs) and ,-Fe2O3 nanocrystals (NCs) passivated with unsaturated long-chain carboxylic acids, namely 10-undecylenic acid (10UDA) and oleic acid (OLEA), are covalently anchored to Si(100) at room temperature by UV-light-driven reaction of hydrogenated silicon with the carbon,carbon double bond (,CC,) moieties of the capping surfactants. The high reactivity of vinyl groups towards Si provides a general tool for attaching particles of both materials via Si,C bonds. Interestingly, TiO2 NRs were efficiently attached to silicon even when capped by OLEA. This latter finding has been explained by a photocatalytic mechanism involving the primary role of hydroxyl radicals that can be generated upon bandgap TiO2 photoexcitation with UV light. The increased oxide coverage achievable on Si opens access to further surface manipulation, as demonstrated by the possibility of depositing an additional film of Au nanoparticles onto TiO2 via TiO2 -catalyzed visible-light-driven reduction of aqueous AuCl4, ions. Extensive morphological and chemical characterization of the obtained NC-functionalized Si substrates is provided to support the effectiveness of proposed photochemical approaches. [source]

Silicon-Based Near-Visible Logpile Photonic Crystal

ADVANCED MATERIALS, Issue 37 2010
Ganapathi Subramania
A nanocavity structure is embedded inside a silicon logpile photonic crystal that demonstrates tunable absorption behavior at near visible wavelengths well beyond the absorption edge of silicon. This is due to silicon's indirect bandgap resulting in a relatively slow increase in the absorption of silicon with decreasing wavelength. Our results open up the possibility of utilizing the wide, complete three dimensional photonic gap enabled by the large refractive index of silicon to create three dimensional photonic crystal based devices well into the visible regime. [source]

Reversible Storage of Lithium in Silver-Coated Three-Dimensional Macroporous Silicon,

ADVANCED MATERIALS, Issue 20 2010
Yan Yu
Three-dimensional macroporous silicon (see image) was synthesized by a magnesiothermic reduction method as an anode material for lithium ion batteries. An improved lithium storage performance was obtained after coating silver nanoparticles on the surface of the silicon. The silver-coated 3D macroporous silicon shows promise as an anode material in lithium ion batteries. [source]

Carbon Nanotubes Anchored to Silicon for Device Fabrication

ADVANCED MATERIALS, Issue 5 2010
Kristina T. Constantopoulos
Abstract This report highlights recent progress in the fabrication of vertically aligned carbon nanotubes (VA-CNTs) on silicon-based materials. Research into these nanostructured composite materials is spurred by the importance of silicon as a basis for most current devices and the disruptive properties of CNTs. Various CNT attachments methods of covalent and adsorptive nature are critically compared. Selected examples of device applications where the VA-CNT on silicon assemblies are showing particular promise are discussed. These applications include field emitters, filtration membranes, dry adhesives, sensors and scaffolds for biointerfaces. [source]

Fullerene Sensitized Silicon for Near- to Mid-Infrared Light Detection

ADVANCED MATERIALS, Issue 5 2010
Gebhard J. Matt
A novel light-sensing scheme based on a silicon/fullerene-derivative heterojunction allows optoelectronic detection in the near- to mid-infrared (IR), which is fully compatible with complementary metal oxide semiconductor (CMOS) technology. Although silicon and the fullerene derivative do not absorb in the IR, a heterojunction of these materials absorbs and generates a photocurrent (PC) in the near- to mid-IR, presumably caused by an interfacial absorption mechanism. [source]

Diatomaceous Lessons in Nanotechnology and Advanced Materials

ADVANCED MATERIALS, Issue 29 2009
Dusan Losic
Abstract Silicon, in its various forms, finds widespread use in electronic, optical, and structural materials. Research on uses of silicon and silica has been intense for decades, raising the question of how much diversity is left for innovation with this element. Shape variation is particularly well examined. Here, we review the principles revealed by diatom frustules, the porous silica shells of diatoms, microscopic, unicellular algae. The frustules have nanometer-scale detail, and the almost 100,000 species with unique frustule morphologies suggest nuanced structural and optical functions well beyond the current ranges used in advanced materials. The unique frustule morphologies have arisen through tens of millions of years of evolutionary selection, and so are likely to reflect optimized design and function. Performing the structural and optical equivalent of data mining, and understanding and adopting these designs, affords a new paradigm in materials science, an alternative to combinatorial materials synthesis approaches in spurring the development of new material and more nuanced materials. [source]

Ultrahigh-Crystalline-Quality Silicon Pillars Formed by Millimeter-Wave Annealing of Amorphous Silicon on Glass

ADVANCED MATERIALS, Issue 29 2009
Fude Liu
Silicon pillars are formed by millisecond-long, single-pulse annealing of 110,GHz millimeter-wave radiation incident upon intrinsic amorphous silicon (a-Si) thin films deposited on glass by hot-wire chemical vapor deposition. The image was taken at a sample tilt angle of 52° for a better 3D view. [source]

Characterization of Charge Collection in Photodiodes under Mechanical Strain: Comparison between Organic Bulk Heterojunction and Amorphous Silicon

ADVANCED MATERIALS, Issue 18 2009
Tse Nga Ng
Both gradual electrical changes and device failure mechanisms caused by mechanical strain in organic photodiodes are investigated and compared to a-Si:H deposited on plastic substrates. [source]

The Origin of the Magnetism of Etched Silicon

ADVANCED MATERIALS, Issue 1 2009
Patrick J. Grace
A recent report of ferromagnetism appearing in silicon after etching in hot KOH (Kopnov et al., Adv. Mater.2007, 19, 925) is shown to be due to iron from the pyrex glassware, which precipitates on the silicon surface in the form of well-separated ferromagnetic nanoparticles. The reaction is explained in terms of the Pourbaix diagram. [source]

Cover Picture: Enhancement of Radiative Recombination in Silicon via Phonon Localization and Selection-Rule Breaking (Adv. Mater.

ADVANCED MATERIALS, Issue 7 2006
7/2006)
Abstract The cover shows a low-magnification TEM image of a periodically nanopatterned all-silicon structure exhibiting enhanced light emission at room temperature. The microstructure was studied using high-resolution TEM, allowing direct observation of high densities of structural defects in the nanopatterned silicon surface layer, which are held responsible for the phonon-localization effect leading to enhanced radiative recombination, as reported on p.,841 by Xu and co-workers. [source]

Integration of Erbium-Doped Lithium Niobate Microtubes into Ordered Macroporous Silicon,

ADVANCED MATERIALS, Issue 3 2006
L. Zhao
Er3+ -doped LiNbO3 microtubes have been prepared by the infiltration of ordered macroporous silicon with Er:LiNbO3 melts (see Figure). The microtubes consist of single-crystalline segments and exhibit the characteristic photoluminescence of Er3+, which coincides with the transmittance maximum of silica-based optical components. [source]

Patterned Gold-Nanoparticle Monolayers Assembled on the Oxide of Silicon,

ADVANCED MATERIALS, Issue 12 2005
W. Foster
Patterned monolayers of gold nanoparticles are selectively formed on Hf4+ -modified silicon dioxide. The 1.5,nm diameter particles are functionalized with a phosphonic acid ligand shell and assembled from solution on a native oxide surface that has been patterned with Hf4+ ions, as shown in the Figure. This system integrates nanoscale components and lithographic patterning. The technique used is precise and compatible with other lithographic techniques. [source]

Photolithographic Patterning of Ring-Opening Metathesis Catalysts on Silicon,

ADVANCED MATERIALS, Issue 1 2005
F. Harris
Ruthenium-based metathesis catalysts have been successfully covalently bound to a thermal oxide layer on a Si(100) wafer. Selective inactivation of the catalyst is achieved via exposure to UV light using standard photolithographic techniques. Subsequent exposure of the wafer to a suitable monomer results in the formation of a patterned polymeric film that is covalently attached to the oxide layer (see Figure). [source]

Comment on "Luminescent Nanoring Structures on Silicon"

ADVANCED MATERIALS, Issue 17 2004
D. Jones
No abstract is available for this article. [source]

Multibit Memory Using Self-Assembly of Mixed Ferrocene/Porphyrin Monolayers on Silicon,

ADVANCED MATERIALS, Issue 2 2004
Q. Li
An alternative strategy for achieving multi-bit functionality, which uses mixed self-assembled monolayers of a benzyl alcohol-tethered ferrocene (Fc-BzOH) and a benzyl alcohol-tethered porphyrin (Por-BzOH) on silicon surfaces to achieve a four-state (2-bit) memory element, is presented. The four states include the neutral state and three distinct cationic states obtained upon oxidation of Fc-BzOH (monopositive) and Por-BzOH (monopositive, dipositive) molecules. Conventional cyclic voltammetry, capacitance, and conductance methods have been used to characterize the mixed monolayer. [source]

Asymmetric Synthesis with Silicon-Based Bulky Amino Organocatalysts

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 2-3 2010
Li-Wen Xu
Abstract Recent years have witnessed an explosive growth in the field of amino organocatalysis, especially in asymmetric enamine and iminium catalysis. Except for the obvious interaction between organocatalyst and substrate, the impact of bulky side group ons stereoselectivity is not as simple as one could imagine. Within the development of bulky site-stereoselective organocatalysts, functional silyl organocatalysts with a bulky silicon group are promising and meet the high standards of modern synthetic methods. This review focuses on the recent advances in the synthetic applications of silicon-based, bulky amino organocatalysts in which catalysts containing an organosilicon moiety or group play a formative role in controlling both the course of the reaction as well as the stereoselectivity. [source]

DIOS-MSEED: A chip-based method for measurement of enantiomeric excess by kinetic resolution/mass spectrometry

ISRAEL JOURNAL OF CHEMISTRY, Issue 4 2001
Zhouxin Shen
The determination of enantiomeric excess by kinetic resolution mass spectrometry has been implemented with the Desorption/Ionization On Silicon (DIOS) MS technique. Measurements can thereby be made much more rapidly than was previously possible, bringing this general methodology for screening asymmetric catalysts closer to true high-throughput status. [source]

Influence of plant silicon and sugarcane cultivar on mandibular wear in the stalk borer Eldana saccharina

AGRICULTURAL AND FOREST ENTOMOLOGY, Issue 3 2009
Olivia L. Kvedaras
Abstract 1,Silicon can increase the resistance of plants to attack by herbivorous insects. The present study aimed to determine the effect of silicon and cultivar on mandibular wear in larvae of the sugarcane stalk borer Eldana saccharina Walker (Lepidoptera: Pyralidae). 2,Four sugarcane cultivars, resistant (N21, N33) and susceptible (N11, N26) to E. saccharina were grown in a pot trial in silicon deficient river sand, with (Si+) and without (Si,) calcium silicate. Individual third-instar larvae were confined on the sugarcane stalk at three known feeding sites (leaf bud, root band and internode) and left to feed for 21 days. 3,Eldana saccharina larval heads were mounted on stubs, with the mandibles oriented horizontally and photographed under a scanning electron microscope. Mandibular wear was measured from the digital images using a quantitative method. 4,Although there was a trend for increased wear in larvae that developed on Si+ cane, no significant effect of silicon, cultivar or site on mandibular wear of E. saccharina was shown. 5,This is the first study to accurately and quantitatively measure the mandibular wear of an insect fed on Si+ plants. [source]

Silicon Suppresses Phytophthora Blight Development on Bell Pepper

JOURNAL OF PHYTOPATHOLOGY, Issue 7-8 2010
Ronald D. French-Monar
Abstract The application of silicon (Si) reduces the intensity of diseases in several economically important crops. This study aimed at determining the potential of this element to decrease the symptoms of Phytophthora blight development on bell pepper, caused by Phytophthora capsici. Bell pepper plants (Sakata Hybrid X pp6115) were initially grown in plastic pots with substrate composed of 1 : 1 mixture of sterile fine sand and Fafard No. 2 peat mix amended with calcium silicate (+Si) or calcium carbonate (,Si). Six weeks later, plants were transplanted to new pots that contained the same +Si and ,Si substrate but were infested with finely ground wheat grains (1- to 2-mm diameter) colonized by two isolates of P. capsici, Cp30 (compatibility type A1) and Cp32 (compatibility type A2). At the end of the experiment, roots and stems from plants of each treatment were collected to determine Si concentration. The presence of lesions on crowns and stems and wilting of plants were monitored up to 9 days after transplanting (DAT). Data obtained were used to calculate the area under diseased plants progress curve (AUDPPC) and area under wilting plants progress curve (AUWPPC). Relative lesion extension (RLE) was obtained as the ratio of vertical lesion extension to stem length at 9 DAT. There was a 40% increase in the concentration of Si in the roots but not in the stems of bell pepper plants in the +Si treatment compared to the ,Si treatment. When comparing +Si to ,Si treatments, the AUDPPC was reduced by 15.4 and 37.5%, while AUWPPC was reduced by 29.1 and 33.3% in experiments 1 and 2, respectively. RLE values were reduced by 35% in the +Si treatment. Dry root weights increased by 23.7%, and stem weights were increased by 10.2% in the +Si treatment. Supplying Si to bell peppers roots can potentially reduce the severity of Phytophthora blight while enhancing plant development. [source]