Impact of Mole Fractions due to Work Function Variability (WFV) of Metal Gate on Electrical Parameters in Strained SOI-FinFET

In the recent sub-20 nm technology node, the process variability issues have become a major problem for scaling of MOS devices. We present a design for a strained Si/SiGe FinFET on an insulator using a 3D TCAD simulator. The impact of metal gate work function variability (WFV) on electrical parameters is studied. Such impact of WFV for different mole fractions (x) of the SiGe layer in a strained SOI-FinFET with varying grain size is presented. The results show that as the mole fraction is increased, the variability in threshold voltage (σVT) and off current (σIoff) is decreased; while, the variability of on-current (σIon) is increased. A notable observation is the distribution of electrical parameters approaches a normal distribution for smaller grain sizes.     

Preparation of polymer nanocapsules for use as carriers via one-step redox interfacially initiated miniemulsion polymerization

In this work, one-step redox interfacially initiated miniemulsion polymerization (IMEP) was employed to fabricate polystyrene (PS) nanocapsules 80 nm in diameter with a 2,2′-bipyridine core by the redox-initiated coupling of cumene hydroperoxide (CHPO) to iron(II) sulfate (FS) using waterborne polyurethane (WPU) as surfactant and hexadecane (HD) as costabilizer. The morphology of the nanocapsules was characterized by transmission electron microscopy (TEM) and field emission scanning electron microscopy (FESEM). Dynamic light scattering (DLS) was used to determine the size and polydispersity of the nanocapsules. It was found that the latexes prepared by miniemulsion polymerization via the redox-initiated method had relatively small diameters (40–100 nm) and a relatively narrow particle size distribution index (PDI: 0.086–0.124), which indicated that polymeric nanoparticles with small diameters and a narrow PDI can easily be prepared via one-step IMEP. The release of 2,2′-bipyridine from the nanocapsules was monitored by UV-visible spectroscopy. These results indicate that polymeric nanocapsules with a functional liquid core can be successfully fabricated via IMEP.     

Preparation of Protein-Stabilized β-Carotene Nanodispersions by Emulsification–Evaporation Method

This work was initiated to prepare protein-stabilized β-carotene nanodispersions using emulsification–evaporation. A pre-mix of the aqueous phase composed of a protein and hexane containing β-carotene was subjected to high-pressure homogenization using a microfluidizer. Hexane in the resulting emulsion was evaporated under reduced pressures, causing crystallization and precipitation of β-carotene inside the droplets and formation of β-carotene nanoparticles. Sodium caseinate (SC) was the most effective emulsifier among selected proteins in preparing the nanodispersion, with a monomodal β-carotene particle-size distribution and a 17-nm mean particle size. The results were confirmed by transmission-electron microscopy analysis. SC-stabilized nanodispersion also had considerably high ζ-potential (−27 mV at pH 7), suggesting that the nanodispersion was stable against particle aggregation. Increasing the SC concentration decreased the mean particle size and improved the polydispersity of the nanodispersions. Nanodispersions prepared with higher β-carotene concentrations and higher organic-phase ratios resulted in larger β-carotene particles. Although increased microfluidization pressure did not decrease particle size, it did improve the polydispersity of the nanodispersions. Repeating the microfluidization process at 140 MPa caused the nanodispersions to become polydisperse, indicating the loss of emulsifying capacity of SC due to protein denaturation.     

New measures of polydispersity from rheological data on polymer melts

The rheological properties of polymer melts depend strongly on the underlying molecular structure: molecular weight distribution, and long chain branching. It is of considerable importance, both fundamental and practical, to relate the molecular architecture to polymer melt rheology. The focus of the present work is in extracting a measure of polydispersity from rheological data. Various polydispersity measures that have been proposed in the literature are critically examined and their limitations are pointed out. New measures of polydispersity are proposed that overcome these limitations. The evaluation of the various polydispersity measures is performed by reference to rheology fundamentals, with model calculations and examples drawn from industrial practice. The issues of eliminating molecular weight and temperature effects in characterizing polydispersity are comprehensively addressed. The presence of small levels of long chain branching in an otherwise linear polymer alters most of these measures of polydispersity dramatically, while no detectable change appears in the molecular weight distribution obtained using a gel permeation chromatograph. It is demonstrated that the polydispersity measures proposed in the present work, and which are extracted from frequency response data in the linear viscoelastic region, can be used reliably to characterize polydispersity in polymer melts. © 1995 John Wiley & Sons, Inc.     

One-step process to create porous structures in cross-linked polymer films via breath-figure formations during in situ cross-linking reactions

This work demonstrates a new strategy of producing honeycomb-like porous structures in cross-linked polymer films via a simple one-step synthesis/fabrication process. This is based on the “breath figure” formation during the in situ cross-linking of reactive monomer solutions. A chloroform solution, containing tert-butyl acrylate monomer and tetraethylene glycol dimethacrylate cross-linker, was cross-linked upon UV radiation under a moist and nitrogen saturated chamber. Micron-sized pores with reasonable uniformity were obtained in the cross-linked polymer films. The size, shape, uniformity and ordering of the pores show significant dependences on the processing conditions. Using this method, porous structures were also achieved in a commercially available photo-active resin, NOA 65, illustrating the generality of this approach.     

NO adsorption on Pd clusters. A density functional study

The interaction of NO with Pd clusters has been studied by means of the LCGTO-DF method. Metal cluster models (up to 13 atoms) with different size and geometry have been used to describe the atop, bridge and three-fold sites. The use of different model core potentials to increase the size of the cluster model treated and to save computational time has been discussed. The binding energies of N(1s), 4σ, 5σ and 1π electrons are calculated and compared directly to the experimental XPS and UPS data available. The NO is tilted with respect to the surface normal axis when adsorbed on top and bridge sites by about 52.6 and 46.7 degrees, respectively. On the two types of three-fold sites (hcp and fcc) the NO remains upright. The bending angle is very sensitive to the cluster size and affects the binding energies of N(1s), 4σ, 5σ and 1π orbitals. The NO adsorption energies on the different adsorption sites have been estimated using different cluster models. The vibrational frequencies have been calculated in the harmonic approximation and they are in reasonable agreement with the available experimental values. The cluster model approach is discussed in terms of its reliability to determine the adsorption energies and the favored site of adsorption. This revised version was published online in June 2006 with corrections to the Cover Date.     

Simultaneous effects of adhesion and poly-dispersity on microstructures and geometrical properties in particle deposition

The simultaneous effects of adhesion and polydispersity on packing (or deposit) microstructures and their bulk properties are examined. The results show that the microstructures and bulk properties of the deposits vary sharply with the introduction of even small adhesion and polydispersity. A structural phase diagram is obtained as functions of adhesion and polydispersity. Increases in adhesion lead to noticeable or large fluctuations in packing fractions for polydisperse systems. However, the packing fraction can be stabilized and the fluctuations greatly reduced regardless of the magnitude of the polydispersity index by keeping the adhesion relatively low (i.e., s≤0.1).     

Formation and degeneration of cellular detonation in bidisperse gas suspensions of aluminum particles

The effect of polydispersity on formation of heterogeneous cellular detonation in gas suspensions of aluminum particles in oxygen is studied by means of numerical simulations and an acoustic analysis. The influence of the suspension composition on the character and size of the cellular structures being formed is found. Partial (and sometimes complete) degeneration of cellular detonation in bidisperse suspensions into a plane detonation wave is observed. Numerical predictions agree with the results of the acoustic analysis of steady detonation structures in bidisperse suspensions. A similar analysis performed for mixtures containing three and five fractions predicts difficulties in formation of cellular detonation in the case of a large scatter in the particle size. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 3, pp. 109–120, May–June, 2008.     

Highly Uniform Epitaxial ZnO Nanorod Arrays for Nanopiezotronics

Highly uniform and c-axis-aligned ZnO nanorod arrays were fabricated in predefined patterns by a low temperature homoepitaxial aqueous chemical method. The nucleation seed patterns were realized in polymer and in metal thin films, resulting in, all-ZnO and bottom-contacted structures, respectively. Both of them show excellent geometrical uniformity: the cross-sectional uniformity according to the scanning electron micrographs across the array is lower than 2%. The diameter of the hexagonal prism-shaped nanorods can be set in the range of 90–170 nm while their typical length achievable is 0.5–2.3 μm. The effect of the surface polarity was also examined, however, no significant difference was found between the arrays grown on Zn-terminated and on O-terminated face of the ZnO single crystal. The transmission electron microscopy observation revealed the single crystalline nature of the nanorods. The current–voltage characteristics taken on an individual nanorod contacted by a Au-coated atomic force microscope tip reflected Schottky-type behavior. The geometrical uniformity, the designable pattern, and the electrical properties make the presented nanorod arrays ideal candidates to be used in ZnO-based DC nanogenerator and in next-generation integrated piezoelectric nano-electromechanical systems (NEMS).     

The mixing effect on the free radical MMA solution polymerization

Mathematical models of reactors for the polymerization of methylmethacrylate (MMA) have been developed and analyzed to elucidate reactor dynamics and to determine conditions for improved operation. The effects of mixing and heat transfer in an MMA polymerization reactor system have been explored by the development of an imperfect mixing model. To model imperfect mixing in polymerization, a reactor configuration using two tanks in parallel was used. Bifurcation diagrams developed using numerical analysis of the model have been drawn with two variable parameters, an exchange ratio, σ, and a volume ratio, κ. We use feed and coolant temperatures as bifurcation parameters. If variable parameters are small, the lower solution branch of the steady state solutions is quite different from that of a simple model that assumes perfect macro-mixing as bifurcation parameters change. If σ increases (κ=0.1, σ=1.0), the shape of a steady state solution curve differs significantly from that of a simple model as the feed temperature decreases.     

Synthesis of hard mesoporous macro-spheres with silicate and aluminosilicate compositions

This study reports the synthesis mechanism and the influence of different variables in the preparation of mesoporous macro-spheres having silicate and aluminosilicate compositions. The spheres possess sizes in the range 200–1000 μm with a narrow particle size distribution and a significant mechanical resistance (hard macro-spheres). In addition, the presence of a highly regular mesoporosity (around 3 nm) and of a high surface area (normally about 1000 m²/g) make these materials as very interesting self-supported adsorbents or catalysts that could be directly applied without no binder, which is a great advantage compared to materials in powder form. The synthesis of the hard mesoporous spheres takes place in a biphasic system, generated by the use of tetrabutoxysilane as silica source, which is reacted with water and NaOH leading to the formation of small primary particles which initially do not present any mesoscopic ordering. However, after about 5 h of synthesis, the presence of cetyltrimethylammonium chloride, as surfactant, gives rise to the detection of a mesostructured silica material. Subsequently, after 9 h of synthesis the small mesostructured particles, with sizes in the micrometer range, acquire a spherical shape. Finally, the reorganization and fusion of these particles cause the formation of the silica macrospheres, with a particle size of several hundreds of micrometers. When the synthesis is carried in the presence of an aluminium source, the aluminosilicate materials so obtained exhibit smaller surface area and pore volume and greater particle size than the pure silica ones.     

Vanadium oxide supported γ-alumina with bimodal porous structure for intra-particle diffusion enhancement in styrene oxidation reaction

Porous γ-alumina with well arranged secondary mesopores has been contrived using nanosized templating units. The pore size of templated mesopores is precisely controlled as the pore shrinkage is insignificant. The primary pore diameter is ca. 4 nm and the secondary pore diameter is ca. 50 nm. The porous material was characterized using N₂ adsorption/desorption, TEM, XRD and FT-IR. γ-alumina with bimodal pore size distribution shows improved intra-particle diffusion compared to γ-alumina with unimodal pore size distribution in a simple dye adsorption test. γ-alumina with different porous structures were then impregnated with vanadium oxide for catalytic effect comparison. It was perceived that secondary pores improve the styrene oxidation rate after the conversion of styrene reaches 30%.     

Analytical Expression on Characteristic Time Scale of Black Carbon Aging due to Condensation of Hygroscopic Species

In this study, the characteristic time scale of black carbon (BC) aging due to condensation of hygroscopic species was parameterized as a function of the condensing species concentration and the size distribution of BC particles. The aging time scale defined based on the BC mass concentration was shown to increase with BC particle size as well as with polydispersity of the size distribution. The effects of the BC particle size distribution on the aging time scale are shown to be considerable in the continuum regime, whereas the aging time scale tends to converge to a constant value in the free-molecule regime. The polydispersity effect was shown to be significant except for extraordinarily small particles. When the aging time scale was defined based on the BC number concentration, the dependency of the aging time scale on polydispersity is much smaller because the effect of slow aging of largest particles is compensated by fast aging of smallest particles. The aging time scale was also shown to be a strong function of the condensing species concentration. The result of this study implies that the aging time scale parameterizations suggested in the previous studies, which did not take into account the effects of condensing species concentration and particle size distribution, cannot be easily generalized for being applied to global model simulations.

Copyright 2012 American Association for Aerosol Research     

Poly(BMA-co-NVP)/NiS core-shell hybrid materials via Interfacial-initiated miniemulsion copolymerization and gamma-irradiation

In this work, N-butyl methacrylate (BMA)/N-vinyl-2-pyrrilidone (NVP) amphiphilic core-shell nanoparticles were successfully prepared via miniemulsion copolymerization, the emulsion was initiated by the redox initiation couple of cumene hydroperoxide (CHPO) and ferrous sulfate hydrate (FS). The synthetic waterborne polyurethane (WPU) was used as surfactant and hexadecane (HD) as co-stabilizer, respectively. FTIR and XPS were used to confirm the occurrence of copolymerization between two monomers. TEM and DLS were used to observe the particle morphology and determine the particle size and its polydispersity index (PDI). It was found that the core-shell poly(BMA-co-NVP) nanoparticles prepared via interfacial-initiated miniemulsion copolymerization (IMEP) had relatively small diameters (40–120 nm) and narrowly particle size distribution (0.066–0.243). Only about 2 wt% surfactants based on the solution was enough to prepare a stable miniemulsion. The results demonstrated that IMEP prompted the copolymerization of water-soluble NVP monomer with oil-soluble BMA monomer to form core-shell nanoparticles. The effects of surfactant and co-stabilizer affect on the miniemulsion copolymerization were discussed. All the results indicate that the fabrication amphiphilic core-shell nanoparticles via IMEP were successful. Then the poly(BMA-co-NVP)/NiS hybrid materials were fabricate via the reaction of NiSO₄ and CH₃CSNH₂ on the copolymers surface under ⁶⁰Co γ-irradiation at room temperature and ambient pressure. The hybrid materials were characterized by FESEM.     

Acrolein Adsorption on Gold Clusters,A Theoretical Study of Conjugation Effect on C=C and C=O Interaction with Au Clusters

Abstract  

We studied acrolein (AC) adsorption on gold clusters Au _n (n = 1–5) using density functional theory. It is demonstrated that conjugation effect reduces the adsorbate–substrate interaction through π-(C=C), π-(C=O) and di-σ-(C=O) modes whereas it facilitates the di-σ-(C=C) and the σ-O configurations. Analysis reveals that in π-(C=C) and π-(C=O) modes acrolein uses the HOMO-1 orbital to interact with the clusters while in σ-O mode the HOMO of AC plays the role. For di-σ-(C=C), di-σ-(C, O) and di-(C=O), the HOMO orbital of the cluster donates electrons to acrolein. Acrolein adsorption through the C=C bond is more favorable than that via the C=O group, which explains why the yields of C=C hydrogenation is higher than that of C=O reduction.     

Anionic polymerisation of methyl methacrylate with complex initiator system

Summary Polymerisation of methyl methacrylate was conducted by using alkyl lithium/dimethylsulfoxide (DMSO) system as initiator in toluene. A special attention was focused on using some lithium polyetheralkoxides as polymerisation promoters at ambient temperatures. Poly(methyl methacrylate) samples were characterized with Gel Permeation Chromatography (GPC), Nuclear Magnetic Resonance Spectroscopy (¹H NMR) and Differential Scanning Calorimetry (DSC). The positive effect of the μ/σ type ligands such as lithium 2-(2-methoxyethoxy)ethoxide (LiOEEM), 2-(methoxy)ethoxide (LiOEM) on controlling the living character, molecular weight, stereo regularity and the yield of the produced polymers was demonstrated. It has been found that this approach provided high polymerisation yields and low polydispersity but low initiator efficiency. Received: 9 April 2002 / Revised version: 10 May 2002 / Accepted: 15 June 2002     

Adsorption mode of ethyl pyruvate on platinum: an in situ XANES study

The adsorption of ethyl pyruvate on Pt(111) has been studied by in situ XANES measurements in the presence and absence of hydrogen. Depending on the hydrogen and ethyl pyruvate pressure, the C and O K‐edge spectra exhibit distinctly different angular dependence. Without hydrogen ethyl pyruvate is oriented preferentially perpendicular to the surface, indicating bonding via the O lone pairs. In the presence of hydrogen the mean orientation is more tilted towards the surface. Likely, ethyl pyruvate also interacts with Pt via its π system under these conditions. The observed angle‐dependent shift of the energy of the π* and σ* resonances indicates the coexistence of differently adsorbed ethyl pyruvate species. The experimental findings demonstrate the importance of the in situ approach for unraveling the adsorption mode of ethyl pyruvate in the enantioselective hydrogenation over cinchona‐alkaloid‐modified Pt. This revised version was published online in July 2006 with corrections to the Cover Date.     

A nuclear magnetic resonance spectroscopic investigation of the headgroup motions of lysophospholipids in bilayers

Fully hydrated lysophospholipids in both the gel and the liquid crystalline states have been shown to exhibit negative phosphorus chemical shift anisotropies (Δσ) by³¹P nuclear magnetic resonance (NMR). The magnitude of Δσ for monoacyl lysophospholipids is found to be smaller than that of the corresponding diacyl phosphospholipids in bilayers by about a factor of two. We present evidence to suggest that the reduction in Δσ can be attributed primarily to an additional motional averaging of the lysophospholipid headgroup, and the additional motion can best be explained by rapid rotational motions of the headgroup about the C(1)-C(2) glycerol bond.     

Synthesis of δ-stearolactone from oleic acid

δ-Stearolactone was prepared from oleic acid using concentrated sulfuric acid under various conditions in the presence of polar, nonparticipating solvents. δ-Stearolactone was formed in as high as 15∶1 ratios over the thermodynamic product, ψ-lactone, in the presence of methylene chloride, 100% wt/vol, at room temperature with two equivalents of sulfuric acid for 24 h. This procedure is applicable to other olefinic fatty acids such as estolides and fatty acid methyl esters. Temperature plays a role in the regioselectivity of the cyclization for δ-lactone, as lower temperatures (20°C) gave higher σ/ψ ratios. At higher temperatures (50°C) in the presence of sulfuric acid and methylene chloride the yield of lactone was 75% but with a σ/ψ ratio of only 0.3∶1. Cyclization of oleic acid to lactone also occurred with other acids. Oleic acid underwent reaction with perchloric acid, one equivalent, in the absence of solvent at 50°C, which yielded σ-lactone in a modest yield with a 3.1 σ/ψ ratio. The same temperature effect was observed with perchloric acid that was observed in the case of sulfiric acid. Because σ-stearolactone is much more reactive than the corresponding fatty acid, fatty acid ester, or ψ-lactone, we believe that it will be a useful synthon for many new industrial products including new biodegradable detergents.     

Determination of individual tocopherols by derivative spectrophotometry

The second order derivative UV spectra of α-, β-, γ- and σ-tocopherols showed small differences that allowed development of a derivative spectrophotometric method for determining individual tocopherols in a mixture. The procedure consists of measuring the second derivative spectrum of the sample at four specified wavelengths and calculating each concentration by means of a method for multicomponent analysis that uses mixtures as standards. Vegetable oils and other fatty products usually require a previous clean-up process (under study) in order to remove interfering substances.