Maximum Substrate Research Articles

Dilute hydrogen plasma cleaning of boron from silicon after etching of HfO2 films in BCl3 plasmas: Substrate temperature dependence

The authors have investigated the effects of elevated substrate temperature (Ts) on cleaning of boron residues from silicon substrates in 1%H2–Ar plasmas, following etching of HfO2 in BCl3 plasmas. Vacuum-transfer x-ray photoelectron spectroscopy (XPS) provided a measure of total B removal rates, as well as information on individual BClxOy moities. B cleaning rates increased with Ts in an Arrhenius manner, with an apparent activation energy of 1.7kcal∕mol. Conversely, the Si etching rate decreased with increasing substrate temperature with an apparent activation energy of −0.8kcal∕mol. Therefore, when considering selectivity with respect to Si etching, it is advantageous to remove B at higher Ts. For example, at Ts=235°C, ∼90% of B is cleaned from Si in 10s, while <1.5nm of Si is removed. An apparent diffusion of H into the near-surface region of Si at higher temperatures, detected indirectly by a shift and broadening of the Si(2p) XPS peak, may limit the maximum optimum substrate temperature, however. It was also found that Si does not etch in 1%H2∕Ar plasmas if an oxide layer is present.

Application of desirability function based on neural network for optimizing biohydrogen production process

A fractional factorial design was carried out to investigate the effects of temperature, initial pH and glucose concentration on fermentative hydrogen production by mixed cultures in batch tests and then the experimental data of substrate degradation efficiency, hydrogen yield and average hydrogen production rate were described by a neural network, based on which the simultaneous optimization of the three responses was performed by the method of desirability function. The analysis showed that the neural network could successfully describe the effects of temperature, initial pH and glucose concentration on the substrate degradation efficiency, hydrogen yield and average hydrogen production rate of this study. The maximum substrate degradation efficiency of 95.3%, hydrogen yield of 305.3 mL/g glucose and average hydrogen production rate of 23.9 mL/h were all obtained at the optimal temperature of 39.0 °C, initial pH of 7.0 and glucose concentration of 24.6 g/L identified by the method of desirability function based on a neural network. In sum, the method of desirability function based on a neural network was a useful tool to optimize several responses for fermentative hydrogen production processes simultaneously.

Large grain Cu(In,Ga)Se 2 thin film growth using a Se-radical beam source

Cu(In,Ga)Se 2 (CIGS) thin films were grown by the three-stage process using a rf-plasma cracked Se-radical beam source. CuGaSe 2 (CGS) films grown at a maximum substrate temperature of 550 °C and CuInSe 2 (CIS) and CIGS films grown at the lower temperature of 400 °C exhibited highly dense surfaces and large grain size compared with films grown using a conventional Se-evaporative source. This result is attributed to the modification of the growth kinetics due to the presence of active Se-radical species and enhanced surface migration during growth. The effect on CIGS film properties and solar cell performance has been investigated. Enhancements in the cell efficiencies of 400 °C-grown CIS and CIGS solar cells have been demonstrated using a Se-radical source.

L-Methioninase Production by Filamentous Fungi: I-Screening and Optimization Under Submerged Conditions

Findings show 21 fungal isolates belonging to eight genera recovered from Egyptian soils that have the potential to attack L-methionine under submerged conditions. Aspergillus flavipes had the most methioninolytic activity, giving the highest yield of L-methioninase (10.78 U/mg protein), rate of methionine uptake (93.0%), and growth rate (5.0 g/l), followed by Scopulariopsis brevicaulis and A. carneus. The maximum L-methioninase productivity (11.60 U/mg protein) by A. flavipes was observed using L-methionine (0.8%) as an enzyme-inductive agent and glucose (1%) as a co-dissimilated carbon source. A significant reduction in L-methioninase biosynthesis by A. flavipes was detected using carbon-free medium, suggesting the lack of ability to use L-methionine as a carbon and nitrogen source. Potassium dihydrogen phosphate (0.25%), the best source of phosphorus, favors enzyme biosynthesis and enhances the level of methionine uptake by A. flavipes. The maximum L-methioninase productivity (12.58 U/mg protein) and substrate uptake (95.6%) were measured at an initial pH of 7.0.

Efficient non-viral transfection of primary human adult chondrocytes in a high-throughput format

The development of a reliable high-throughput transfection protocol for primary human articular chondrocytes. Primary human chondrocytes were isolated from adult knee cartilage by an optimized enzymatic digestion protocol and cultivated in high-density monolayer culture for 3-5 days. Isolated chondrocytes were transfected with a green fluorescent protein (GFP)-expressing reporter construct using amaxa's Nucleofector 96-well Shuttle System. Transfection efficiencies were measured by fluorescence activated cell sorting and cell viability was determined by an adenosine-5'-triphosphate (ATP) assay. siRNA oligonucleotides (against glyceraldehyde-3-phosphate dehydrogenase (GAPDH)) were transfected into the cells using the optimized nucleofection protocol and mRNA knockdown values were determined by a branched-DNA assay. Transfection efficiencies of more than 70% of surviving cells were achieved routinely with the nucleofection protocol presented in this article. Cell viability 24h post transfection was around 80%. The cell number used per transfection was reduced to 2x10(5) per sample. In addition, the protocol proved to be well suited for the transfer of siRNA molecules into primary human chondrocytes with suppression rates on the mRNA level of more than 95% (for GAPDH). We present the successful use of nucleofection on primary human chondrocytes using a microtiter plate compatible format that for the first time allows the efficient transfection of up to 96 samples in parallel. The optimized nucleofection protocol is offering maximum substrate flexibility by allowing transfer of DNA and siRNA oligonucleotides with the same set of parameters. Moreover, the transfection procedure requires substantially lower cell numbers than single cuvette protocols and is therefore perfectly suited for applications requiring multiple experimental replicates.

Biodegradation of diesel oil in a baffled roller bioreactor

AbstractBACKGROUND: Ex situ bioremediation is a feasible and economical way to remove petroleum pollutants from contaminated soil or water. A baffled roller bioreactor was shown to be effective for biodegradation of diesel oil as a model petroleum pollutant. Microorganisms enriched from an industrially contaminated soil with heavy hydrocarbons were shown to be the best inoculum source for diesel biodegradation.RESULTS: The baffled roller bioreactor demonstrated better performance than control (roller bioreactor without baffles) or bead mill roller (control bioreactor filled partially with spherical beads) bioreactors. Biodegradation consisted of both fast and slow stages for degradation of light and heavy compounds, respectively. Among the tested temperatures ranging from 15 to 35 °C, room temperature (23 °C) was found to be the optimum temperature for biodegradation. The values of maximum specific growth rate and substrate yield (µmax and YXS) for the indigenous microorganisms in the baffled roller bioreactor at room temperature were found to be 0.72 ± 0.08 h−1 and (7.0 ± 1.0) × 107 cells mg−1 diesel, respectively. Biodegradation of diesel concentrations up to 200 g L−1 was achieved with the highest biodegradation rate of 266 mg L−1 h−1 at the highest rotation rate of 45 rpm in the baffled roller bioreactor.CONCLUSION: Using indigenous bacteria enriched from industrial contaminated soil at room temperature, a baffled roller bioreactor is able to biodegrade high diesel oil concentrations at high biodegradation rates. Copyright © 2008 Society of Chemical Industry

Aerobic Composting of Poultry Manure and Wheat Straw-Kinetic and Reactor Model

Laboratory-scale aerobic composting tests with mixture of poultry manure and wheat straw were conducted in closed thermally insulated column reactors with effective volumes of 1 L and 32 L. Two 14-day experiments with two different mixture ratios (manure to straw, 2.77:1 and 5.25:1 on dry weight, respectively) were performed in order to compare the performances of composting process in both reactors as well to obtain the parameter values in the kinetic model and to validate proposed kinetic and reactor model in this work. The maximum temperature of 64.6°C was reached after 2.1 days in the large reactor and 64.5°C after 1.3 days in the small reactor. The temperature in these reactors was maintained above 55°C for 2 days, which should be sufficient to maximize sanitation and to destroy pathogens. The greatest mass of carbon dioxide was generated during the first 3 days. The maximum consumption of oxygen was noticed in the exit gas mixtures from both reactors after the first day of the process (the small reactor 16.0 vol. %, the large reactor 11.7 vol. %). The maximum emission of ammonia was observed from the small reactor after first day and from large reactor after the third day. The organic matter content of the materials decreased in both reactors during the process, but this reduction was greater in the large reactor (47.60%) than in the small reactor (41.36%). The proposed kinetic and reactor model was described by a differential equation set with 12 dynamic state variables: mass of organic matter, mass of oxygen, mass of dissolved carbon dioxide, mass of dissolved ammonia, mass of water in the substrate, molar amount of O2 (gas phase), molar amount of CO2 (gas phase), molar amount of NH3 (gas phase), molar amount of H2O vapour (gas phase), molar amount of N2 (gas phase), temperature of gas phase, temperature of solid-liquid phase. In the proposed kinetic model, four kinetic parameters were calculated. The model was validated by the results of several experimentally measured dynamic state variables (temperature of substrate, conversion of organic matter conversion, concentration of carbon dioxide, concentration of oxygen). Comparisons of experimental and simulation results showed good agreement during the whole duration of the process in a reactor, except for ammonia (good agreement was achieved for the first four days and for the last three days of the process). Different simulation scenarios were performed with the model in order to study the effects of initial moisture content, airflow rates and air temperature on the substrate temperature and organic matter conversion. A sensitivity analysis showed that two of four kinetic parameters had a great influence on all three objective functions (maximum conversion of organic matter, maximum concentration of carbon dioxide and maximum substrate temperature).

Substrate atom enriched carbon nanostructures fabricated by focused electron beaminduced deposition

Carbon nanostructures fabricated using focused electron beam induced deposition (FEBID)in a residual vacuum atmosphere or in the presence of low pressure precursor gas exhibitenrichment with the atoms of the substrate element. Nanostructures having base sizes upto 100 nm and height up to 250 nm with maximum substrate atom enrichment of 50% havebeen fabricated. The size of the structures (nanocones) and the substrate atomenrichment depends on the electron beam current density and irradiation time. Apossible explanation of the phenomenon has been sought on the basis of localtemperature rise and diffusion of the substrate atoms in the nanostructure duringthe growth process. The phenomenon can be used to fabricate dense 2D carbonnanopatterns enriched with a desired element used as the substrate material.

Optimization of fermentative hydrogen production process by response surface methodology

The effect of temperature, initial pH and glucose concentration on fermentative hydrogen production by mixed cultures was investigated in batch tests, and the optimization of fermentative hydrogen production process was conducted by response surface methodology with a central composite design. Experimental results showed that temperatures, initial pH and glucose concentrations had impact on fermentative hydrogen production individually and interactively. The maximum hydrogen yield of 289.8 mL/g glucose was estimated at the temperature of 38.6 °C, the initial pH of 7.2 and the glucose concentration of 23.9 g/L. The maximum hydrogen production rate of 28.2 mL/h was estimated at the temperature of 37.8 °C, the initial pH of 7.2 and the glucose concentration of 27.6 g/L. The maximum substrate degradation efficiency of 96.9% was estimated at the temperature of 39.3 °C, the initial pH of 7.0 and the glucose concentration of 26.8 g/L. Response surface methodology was a better method to optimize the fermentative hydrogen production process. Modified logistic model could describe the progress of cumulative hydrogen production in the batch tests of this study successfully.

Mechanical Properties of Polycrystalline Silicon formed by Al-2%Si Induced Crystallization

Due to their low thermal process budget, polycrystalline silicon (poly-Si) films formed by Al-2%Si induced crystallization (AIC) are potentially attractive for monolithic integration of MEMS with CMOS electronics using a "MEMS-last" process flow. In this work, the mechanical properties of AIC poly-Si films formed with a maximum substrate temperature of 350C are investigated. Residual stress, Young's modulus, and strain gradient are extracted from pull-in voltage measurements of cantilever and clamped-clamped beams. A post-AIC pulsed excimer laser annealing (ELA) treatment is found to be beneficial for completing the Al-2%Si and Si layer exchange process, although it results in a larger strain gradient within the poly-Si layer. The mechanical properties of AIC poly-Si films compare favorably with those of low-thermal-budget poly-Si0.4Ge0.6 films, so that AIC poly-Si is a promising structural material for MEMS.

A Cobalt(II)‐containing Metal‐Organic Framework Showing Catalytic Activity in Oxidation Reactions

AbstractA metal‐organic framework (MOF) containing redox active CoII atoms, [CoII(BPB)]·3DMF (1), has been prepared from the solvothermal reaction of CoII nitrate and 1,4‐bis(4′‐pyrazolyl)benzene (H2‐BPB) in dimethylformamide (DMF). Compound 1 constitutes a porous coordination framework that is built up by interconnecting 1D CoII polymer chains with (BPB)2− ligands. The thermal stability of 1 was investigated by thermogravimetric (TG) analysis and variable‐temperature X‐ray powder diffraction (VTXRPD), which indicate that the framework of 1 is stable upon removal of solvent molecules. The argon adsorption isotherm of 1 at 77 K indicates a porous structure with a BET surface area of 1207 m2/g. As a test reaction for catalytic activity of 1, the oxidation of cyclohexene was examined employing tert‐butyl hydroperoxide as oxidant. The maximum substrate conversion achieved after 12 h was 62 % with an estimated turn‐over number (TON) of 44 based on the number of converted substrate molecules (cyclohexene) per CoII atom.

Self-immobilization of acidogenic mixed consortia on mesoporous material (SBA-15) and activated carbon to enhance fermentative hydrogen production

The influence of self-immobilization of enriched acidogenic mixed consortia on fermentative hydrogen (H 2) production was studied on different supporting materials [SBA-15 (mesoporous) and activated carbon (granular; GAC and powder; PAC)] using chemical wastewater as substrate. Batch fermentation experiments were performed with same substrate at different organic loading rates (OLRs) under acidophilic microenvironment (pH 5.5) and room temperature (28 ± 2 °C). Experimental data evidenced the effectiveness of attached growth on both the H 2 yields and substrate degradation efficiency, particularly at higher loading rates. Among the three materials evaluated, immobilization on SBA-15 material showed comparatively effective performance in enhancing both H 2 yield and substrate degradation. Suspended growth (SG-control) culture showed inhibition in terms of both H 2 production and substrate degradation especially at applied higher loading rates. Immobilization on SBA-15 resulted in nine times higher H 2 production (7.29 mol/kg COD R-day at OLR of 0.83 kg COD/m 3-day) than the lowest yield observed (suspended growth at OLR of 2.55 kg COD/m 3-day). Maximum substrate degradation rate (SDR) of 0.96 kg COD/m 3-day (OLR 2.55 kg COD/m 3-day) was also observed with SBA-15 immobilization, which is 1.62 times higher than the lowest substrate degradation observed with SG-control experiments with the same OLR. Attached growth on GAC and PAC also showed remarkable improvement in the process performance at higher OLRs compared to SG-control.

Rapid and high biodegradation of phenols catalyzed by Candida tropicalis NCIM 3556 cells

Cells of 19 yeast cultures, belonging to genus Candida were screened for biodegradation of phenol. The cultures procured from NCIM culture collection and were selected so as to contain a representative of varied strains of the species. These were grown in MGYP medium and tested for biodegradation of phenol. C. tropicalis (CT) nos. 3118, 3556 and C. lipolytica 3472 effectively degraded >90% 2 g l −1 phenol. The C. tropicalis 3556 strain was selected for further studies as it metabolized >95% phenol in just 16 h as compared to the other two which took 48 h. The maximum substrate concentration that could be completely degraded was 2 g l −1. A study of induction, of different concentration of phenol in the growth medium showed that toxicity to cell growth increased with increasing phenol levels in growth media. Biodegradation of phenol derivatives – o-cresol, m-cresol, 2,6-dimethyl phenol, α-naphthol, o-chlorophenol and p-nitrophenol, by the selected three strains indicated that the specificity of each culture varied for different substrate.

Novel Brønsted acidic ionic liquids based on benzimidazolium cation: Synthesis and catalyzed acetalization of aromatic aldehydes with diols

In this article, a new group of Bronsted acidic task-specific ionic liquids based on benzimidazolium cation was synthesized and used as environmentally benign catalysts for acetalization of aromatic aldehydes with diols. Hammett method had been used to determine the acidity order of these ionic liquids, which was consistent with the catalytic activities observed in acetalization reaction. Maximum substrate conversion of 98% and product selectivity of 100% were obtained using [PSebim]HSO4 as catalyst, which could be reused at least 10 times without obvious loss of catalytic activity.

Use of an ionic liquid to improve asymmetric reduction of 4′-methoxyacetophenone catalyzed by immobilized Rhodotorula sp. AS2.2241 cells

Rhodotorula sp. AS2.2241, a newly isolated strain, was used as biocatalyst for asymmetric reduction of 4′-methoxyacetophenone (MOAP) to enantiopure ( S)-1-(4-methoxyphenyl)ethanol {( S)-MOPE}. Despite the improved efficiency of the reaction with immobilized cells compared to free cells, the inhibition of the reaction by substrate and product in monophasic aqueous system proved to be big problem. For high efficient biotransformation, several water-immiscible ionic liquids (ILs) were employed as green solvents to construct ionic liquid-involving biphasic systems. Of the six ILs tested, C 4MIM·PF 6 exhibited the best biocompatibility with the cells, and consequently the biocatalytic reduction proceeded with the fastest initial reaction rate and the highest maximum substrate conversion in the C 4MIM·PF 6-based biphasic system. To better understand the bioreduction conducted in the C 4MIM·PF 6-based biphasic system, various variables that influenced the performance of the reaction were examined. The optimal buffer pH, reaction temperature, volume ratio of buffer to C 4MIM·PF 6 and substrate concentration were 7.5, 25 °C, 4/1 and 40 mM, respectively. Under the optimal conditions, the initial reaction rate, maximum substrate conversion and product e.e. were 1.6 μmol/h, 95.5% and >99%, respectively. Additionally, the cells still remained above 90% of their original activity in the C 4MIM·PF 6-based biphasic system, which was much higher than that in the monophasic buffer system (about 25% of their original activity), after being repeatedly used for 8 batches (50 h per batch), indicating that C 4MIM·PF 6 markedly enhanced the operational stability of the cells.

Large-Scale Molecular Dynamics Simulations of Energetic Ni Nanocluster Impact onto the Surface

On the atomic scale, Molecular Dynamics (MD) Simulation of Nano Ni cluster impact on Ni (100) substrate surface have been carried out for energies of Ea = 1–5 eV/atom and total energy of ET = 195 eV (the total energy of cluster is ET = nEa, n is the number of cluster atoms) to understand quantitatively the interaction mechanisms between the cluster atoms and the substrate atoms. The many-body Embedded Atom Method (EAM) was used in this simulation. We investigated the maximum substrate temperature Tmax and the time tmax within which this temperature is reached as a function of cluster sizes and the total energy ET. The temperature Tmax is linearly proportional to total cluster energy. For the constant energy per atom and for the cluster size increase, the correlated collisions rapidly transfers energy to the substrate, and the time tmax approached a constant value. For constant total energy the temperature Tmax and the time tmax versus different cluster sizes was studied. We showed that the cluster implantation and sputtering atoms from the surface are affected by the cluster size and total kinetic energy of the clusters. Finally time dependence of the number Ndis of disordered atoms in the substrate was observed.

Application of the Stover–Kincannon kinetic model to nitrogen removal by Chlorella vulgaris in a continuously operated immobilized photobioreactor system

AbstractBACKGROUND: The aim of this study was to evaluate the ammonium nitrogen removal performance of algae culture Chlorella vulgaris in a novel immobilized photobioreactor system under different operating conditions and to determine the biokinetic coefficients using the Stover–Kincannon model.RESULTS: The photobioreactor was continuously operated at different initial ammonium nitrogen concentrations (NH4‐N0 = 10–48 mg L−1), hydraulic retention times (HRT = 1.7–5.5 days) and nitrogen/phosphorus ratios (N/P = 4/1–13/1). Effluent NH4‐N concentrations varied between 2.1 ± 0.5 mg L−1 and 26 ± 1.2 mg L−1 with increasing initial NH4‐N concentrations from 10 ± 0.6 mg L−1 to 48 ± 1.8 mg L−1 at θH = 2.7 days. The maximum removal efficiency was obtained as 79 ± 4.5% at 10 mg L−1 NH4‐N concentration. Operating the system for longer HRT improved the effluent quality, and the percentage removal increased from 35 ± 2.4% to 93 ± 0.2% for 20 mg L−1 initial NH4‐N concentration. The N/P ratio had a substantial effect on removal and the optimum ratio was determined as N/P = 8/1. Saturation value constant, and maximum substrate utilization rate constant of the Stover–Kincannon model for ammonium nitrogen removal by C. vulgaris were determined as KB = 10.3 mg L−1 d−1, Umax = 13.0 mg L−1 day−1, respectively.CONCLUSION: Results indicated that the algae‐immobilized photobioreactor system had an effective nitrogen removal capacity when the operating conditions were optimized. The optimal conditions for the immobilized photobioreactor system used in this study can be summarized as HRT = 5.5 days, N/P = 8 and NH4‐N0 = 20 mg L−1 initial nitrogen concentration to obtain removal efficiency greater than 90%. Copyright © 2008 Society of Chemical Industry

Accurate Raman spectroscopy of diamond-like carbon films deposited by an anode layer source

Diamond-like carbon (DLC) films deposited by a new room-temperature deposition method were critically investigated by Raman spectroscopy. A gridless, linear anode layer source was fed with acetylene at different flow rates at varying applied voltages producing highly adhesive and transparent DLC films. Raman spectra showed a correlation between the intensity ratio I D/ I G and the voltage applied to the ion source. When increasing the voltage from 1 to 3kV, the intensity ratio increased from 0.48 ± 0.02 to 0.59 ± 0.01 (measured at an excitation wavelength of 532nm and fitted with Gaussian functions). These observations were confirmed by stress measurements, where an increase of the voltage from 1 to 3kV resulted in a decrease of the compressive stress from − 2.34 ± 0.17 to − 0.85 ± 0.02GPa, indicating a decreased sp 3-hybridised carbon fraction at elevated voltage. Under the described conditions we observed maximum substrate temperatures of 70°C after deposition processes for several hours which clearly show the unique features of this relatively new deposition technique for hydrogenated tetrahedral DLC films.

Nickel inhibition of calcium precipitation by ureolytic mixed microorganisms under batch conditions

The respirometric assessment of the inhibitory impact of Ni(II) on substrate utilization and microbial carbonate precipitation (MCP) by ureolytic mixed microorganisms was investigated with a glucose containing mineral medium under batch conditions over an incubation period of 134 h. The IC 25 was determined as 224 mg Ni(II) L −1 from the BOD values of samples. The interpretation of kinetic data showed that the substrate removal rate fitted a zero-order at the beginning of the incubation period and first-order during the last period, for a range of Ni(II) concentrations between 0 and 512 mg L −1. Increasing Ni(II) concentrations from 0 to 512 mg L −1 reduced the substrate degradation rate constant from 10.8 to 5.3 mg L −1 h −1 for zero-order rate constant ( k 0), and from 0.015 to 0.002 h −1 for first-order rate constant ( k 1). The zero- and first-order reaction rates during incubation period were equalized to the reaction rate of the Monod equation in order to determine the kinetic constants, half saturation concentration ( K S) and maximum substrate removal rate ( R max). BOD removal rate was inhibited accordingly to mixed inhibition model with increasing Ni(II) concentrations during the calcification process. Also, the inhibition of calcium precipitation was observed at a higher Ni(II) concentration because of inhibition of ammonium production in these samples.

Biodegradation of pyridine by the new bacterial isolates S. putrefaciens and B. sphaericus

In this study, two bacterial strains capable of utilizing pyridine as a sole carbon source were isolated from biofilters. Based on the biochemical test, the organisms were identified as Shewanella putrefaciens and Bacillus sphaericus. In liquid cultures, S. putrefaciens and B. sphaericus degraded pyridine quite effectively up to 500 mg L −1. S. putrefaciens degrades 500 mg L −1 of pyridine completely within 140 h, whereas the B. sphaericus degrades 500 mg L −1 of pyridine only nearly 75% and takes a longer duration of 150 h. S. putrefaciens used pyridine as sole carbon and energy source better than B. sphaericus. Monod's and Haldane's inhibitory growth models were used to obtain maximum specific growth rate ( μ max), half saturation ( K s) and substrate inhibition ( K i) constant for pyridine by using S. putrefaciens and B. sphaericus. The high value of K i for S. putrefaciens than B. sphaericus indicates that the inhibition effect can be observed only in a high concentration range. The S. putrefaciens degrades pyridine with a faster rate than B. sphaericus. S. putrefaciens can be used effectively for the treatment of pyridine bearing wastewater and as an inoculum in a biofilter treating pyridine-laden gas.