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ABSTRACT: The origin of the bias stress effect related only to semiconductor properties is investigated in "air-gap" organic field-effect transistors (OFETs) in the absence of a material gate dielectric. The effect becomes stronger as the density of trap states in the semiconductor increases. A theoretical model based on carrier trapping and relaxation in localized tail states is formulated. Polar molecular vapors in the gap of "air-gap" OFETs also have a significant impact on the bias stress effect via the formation of bound states between the charge carriers and molecular dipoles at the semiconductor surface.
Advanced Materials 04/2012; 24(20):2679-84. · 13.88 Impact Factor
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ABSTRACT: Integration of organic and inorganic electronic materials is one of the emerging approaches to achieve novel material functionalities. Here, we demonstrate a stable self-assembled monolayer of an alkylsilane grown at the surface of graphite and graphene. Detailed characterization of the system using scanning probe microscopy, X-ray photoelectron spectroscopy, and transport measurements reveals the monolayer structure and its effect on the electronic properties of graphene. The monolayer induces a strong surface doping with a high density of mobile holes (n > 10(13) cm(-2)). The ability to tune electronic properties of graphene via stable molecular self-assembly, including selective doping of steps, edges, and other defects, may have important implications in future graphene electronics.
Nano Letters 07/2010; 10(7):2427-32. · 13.20 Impact Factor
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ABSTRACT: Soil compaction is a big challenge in managing poorly drained clay soils. An on-farm field study was conducted over 2 years in a poorly drained, heavy clay soil, Red River Valley, Manitoba, Canada, where soil compaction, crop growth and root development were perceived as serious concerns. To address these concerns, no-tillage and sub-soiling tillage were proposed and compared with the traditional tillage system in which light-duty field cultivators were used at tillage depths ranging from 50 to 75 mm. Measurements of soil cone index indicated that a hardpan existed at approximately 175 mm soil depth in each fall as a result of wheel traffic during the growing season. It may not be necessary to break the hardpan with fall tillage operations in the studied region, as the hardpan was naturally removed over winter. Effects of tillage practices were evaluated using seeding performance and plant development. No-tillage resulted in the similar speed of emergence, plant population and crop yield, but more uniform seeding depth and more roots in the topsoil layer (0–75 mm), when compared with the conventional tillage. Sub-soiling promoted much faster crop emergence, higher plant populations and crop yield as well as deeper root penetration than the conventional tillage. However, the draft force required for sub-soiling was four times that of the conventional tillage.
Soil and Tillage Research.
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ABSTRACT: In 1986, Gleiter and co-workers introduced the concept of synthesis of non-agglomerated nanoparticles by rapid condensation from the vapor phase in a reduced pressure environment. The source of the material was an evaporative source, which is ideally suited for low vapor pressure and low melting point metals. In order to broaden the scope of the materials synthesis, we have developed a variation in this process in which the source of the nanophase material is a metalorganic precursor. In this new Chemical Vapor Condensation (CVC) process, the key parameters are gas phase residence time, temperature of the hot-wall reactor, and precursor concentration in the carrier gas. The CVC processing unit is an effective nanoparticle generator which is suitable for many different types of materials. Examples are, SiC, Si3N4, Al2O3, TiO2, ZrO2 and other refractory compounds. More recently, we have extended our processing capabilities to include a flat flame combustor unit which is particularly suited to synthesis of oxide phases either as powders, films, coatings or free standing forms. We are laying the groundwork of computer-integrated manufacturing of nanophase oxides by combining a high rate nanopowder production technology with laser diagnostics and computer modeling.
Nanostructured Materials.
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ABSTRACT: Measurement are presented for the fuel-related properties of pure and fire-retarded cellulose used in diffusion flame calculations. The items measured are (1) heat of combustion of the volatile products of cellulose pyrolysis, (2) heat of gasification, (3) fuel and inert gas fractions in the pyrolysate and (4) stoichiometric ratio of the fuel volatiles. Cellulose samples were subjected to a radiant heat flux in a special apparatus designed for this purpose, and the pyrolysate was analyzed using a gas chromatograph. Heats of combustion of cellulose and of the char produced by pyrolysis were measured by a bomb calorimeter. Results are given for pure cellulose and for cellulose that has been fire retarded by up to 3 wt.% sodium hydroxide. For heat fluxes simulating those in diffusion flames, the char yield is found to increase from 9 wt.% percent for pure cellulose to 30 wt.% for retarded cellulose. The effect of retardant addition is to decrease the heat of combustion per unit mass of (total) volatiles, but to increase the heat of combustion per unit mass of combustible volatiles. The heat of gasification (defined as the energy input required to generate a unit mass of volatiles) is determined from measurements of mass loss, surface temperature, and surface emissivity. For pure cellulose, the mass loss rate and surface temperature increase for higher applied heat fluxes while the heat of gasification decreases. At a fixed heat flux, retardant addition increases both the mass loss rate and surface temperature, which results in a decrease in the heat of gasification. Analysis of the volatiles shows that retardant addition increases the fraction of inert gases (carbon dioxide and water) in the pyrolysate, which reduces the fuel fraction from 69 wt.% for pure cellulose to 35 wt.% for retarded cellulose. The corresponding change in stoichiometric ratio is from 1.6 for pure cellulose to a maximum value of 2.3 for retarded cellulose.
Combustion and Flame.
