Automation of a Mass Flow Controller for Application in Time‐Multiplex SF6+CH4 Plasma Etching of Silicon

In this work is proposed the automation of a gas injection (mass flow) system in order to generate timemultiplex SF₆/CH₄ radiofrequency plasma applied for silicon (Si) etching process. The control of the gas injection system is important in order to better control the process anisotropy, i.e., the high‐aspect‐ratio of mask pattern transfer to substrate surface. In other words, this control allows the attainment of deep Si etching process. Here, the automation of the gas injection system was realized through the interface between a computer and a data acquisition board. The automation software developed allows controlling the gas flow rate switching it on and off during whole process through the use of a square waveform routine, intermittent flow, beyond the conventional condition of a fixed value for gas flow rate, continuous flow. In order to investigate the time‐multiplex SF₆/CH₄ plasma etching of Si, the residual gas analysis was performed. The investigations were made keeping the following process parameters: flow of SF₆: 10 sccm, flow of CH₄: 6 sccm, 100 W rf power, wave period: 20 sec. It were monitored the partial pressure of SF⁺ ₅ (parent neutral specie: SF₆), CH⁺₄ (CH4) and SiF+ ₃ (SiF4) species as a function of time for different gas flow switching and duty cycle. The results showed that with the generation of plasma occurs a drastic change in behavior of partial pressures of SF⁺ ₅ and CH⁺₄ species. Moreover, it is evidenced that the interactions between the SF₆ and CH₄ fragments promotes a high production rate of HF molecule and consequently a decrease of atomic fluorine, mainly when plasma is on. Finally, the behavior of partial pressure of SiF⁺ ₃ specie for alternatively intermittent SF₆ and CH₄ flow operation shows us that both the etching processes and the deposition of a polymer passivation layer are occurring alternatively, a desirable feature for multi‐step etching process (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Fabrication of phytic acid sensor based on mixed phytase-lipid Langmuir-Blodgett films

This paper reports the surface activity of phytase at the air-water interface, its interaction with lipid monolayers, and the construction of a new phytic acid biosensor on the basis of the Langmuir-Blodgett (LB) technique. Phytase was inserted in the subphase solution of dipalmitoylphosphatidylglycerol (DPPG) Langmuir monolayers, and its incorporation to the air-water interface was monitored with surface pressure measurements. Phytase was able to incorporate into DPPG monolayers even at high surface pressures, ca. 30 mN/m, under controlled ionic strength, pH, and temperature. Mixed Langmuir monolayers of phytase and DPPG were characterized by surface pressure-area and surface potential-area isotherms, and the presence of the enzyme provided an expansion in the monolayers (when compared to the pure lipid at the interface). The enzyme incorporation also led to significant changes in the equilibrium surface compressibility (in-plane elasticity), especially in liquid-expanded and liquid-condensed regions. The dynamic surface elasticity for phytase-containing interfaces was investigated using harmonic oscillation and axisymmetric drop shape analysis. The insertion of the enzyme at DPPG monolayers caused an increase in the dynamic surface elasticity at 30 mN m(-)(1), indicating a strong interaction between the enzyme and lipid molecules at a high-surface packing. Langmuir-Blodgett (LB) films containing 35 layers of mixed phytase-DPPG were characterized by ultraviolet-visible and fluorescence spectroscopy and crystal quartz microbalance nanogravimetry. The ability in detecting phytic acid was studied with voltammetric measurements.     

Multi-technique surface characterization of bio-based films from sisal cellulose and its esters: a FE-SEM, μ-XPS and ToF-SIMS approach

Bio-based films were prepared from LiCl/DMAc solutions containing sisal cellulose esters (acetates, butyrates and hexanoates) with different degrees of substitution (DS 0.7–1.8) and solutions prepared with the cellulose esters and 20 wt% sisal cellulose. A novel approach for characterizing the surface morphology utilized field emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS) and contact angle analysis. XPS and ToF-SIMS were a powerful combination while investigating both the ester group distribution on the surface and effects of cellulose content on the film. The surface coverage by ester aliphatic chains was estimated using XPS measurements. Fibrous structures were observed in the FE-SEM images of the cellulose and bio-based films, most likely because the sisal cellulose chains aggregated during dissolution in LiCl/DMAc. Therefore, the cellulose aggregates remained after the formation of the films and removal of the solvent. The XPS results indicated that the cellulose loading on the longer chain cellulose esters films (DS 1.8) increased the surface coverage by ester aliphatic chains (8.2 % for butyrate and 45 % for hexanoate). However, for the shortest ester chains, the surface coverage decreased (acetate, 42 %). The ToF-SIMS analyses of cellulose acetate and cellulose hexanoate films (DS 1.8) revealed that the cellulose ester groups were evenly distributed across the surface of the films.     

Hybrid neural network model of an industrial ethanol fermentation process considering the effect of temperature

In this work a procedure for the development of a robust mathematical model for an industrial alcoholic fermentation process was evaluated. The proposed model is a hybrid neural model, which combines mass and energy balance equations with functional link networks to describe the kinetics. These networks have been shown to have a good nonlinear approximation capability, although the estimation of its weights is linear. The proposed model considers the effect of temperature on the kinetics and has the neural network weights reestimated always so that a change in operational conditions occurs. This allow to follow the system behavior when changes in operating conditions occur.     

Green synthesis of colloidal silver nanoparticles using natural rubber latex extracted from Hevea brasiliensis

Colloidal silver nanoparticles were synthesized by an easy green method using thermal treatment of aqueous solutions of silver nitrate and natural rubber latex (NRL) extracted from Hevea brasiliensis. The UV–Vis spectra detected the characteristic surface plasmonic absorption band around 435 nm. Both NRL and AgNO₃ contents in the reaction medium have influence in the Ag nanoparticles formation. Lower AgNO₃ concentration led to decreased particle size. The silver nanoparticles presented diameters ranging from 2 nm to 100 nm and had spherical shape. The selected area electron diffraction (SAED) patterns indicated that the silver nanoparticles have face centered cubic (fcc) crystalline structure. FTIR spectra suggest that reduction of the silver ions are facilitated by their interaction with the amine groups from ammonia, which is used for conservation of the NRL, whereas the stability of the particles results from cis-isoprene binding onto the surface of nanoparticles. Therefore natural rubber latex extracted from H. brasiliensis can be employed in the preparation of stable aqueous dispersions of silver nanoparticles acting as a dispersing and/or capping agent. Moreover, this work provides a new method for the synthesis of silver nanoparticles that is simple, easy to perform, pollutant free and inexpensive.     

Performance of biodegradable microcapsules of poly(butylene succinate), poly(butylene succinate-co-adipate) and poly(butylene terephthalate-co-adipate) as drug encapsulation systems

Poly(butylene succinate) (PBSu), poly(butylene succinate-co-adipate) (PBSA) and poly(butylene terephthalate-co-adipate) (PBTA) microcapsules were prepared by the double emulsion/solvent evaporation method. The effect of polymer and poly(vinyl alcohol) (PVA) concentration on the microcapsule morphologies, drug encapsulation efficiency (EE) and drug loading (DL) of bovine serum albumin (BSA) and all-trans retinoic acid (atRA) were all investigated. As a result, the sizes of PBSu, PBSA and PBTA microcapsules were increased significantly by varying polymer concentrations from 6 to 9%. atRA was encapsulated into the microcapsules with an high level of approximately 95% EE. The highest EE and DL of BSA were observed at 1% polymer concentration in values of 60 and 37%, respectively. 4% PVA was found as the optimum concentration and resulted in 75% EE and 14% DL of BSA. The BSA release from the capsules of PBSA was the longest, with 10% release in the first day and a steady release of 17% until the end of day 28. The release of atRA from PBSu microcapsules showed a zero-order profile for 2 weeks, keeping a steady release rate during 4 weeks with a 9% cumulative release. Similarly, the PBSA microcapsules showed a prolonged and a steady release of atRA during 6 weeks with 12% release. In the case of PBTA microcapsules, after a burst release of 10% in the first day, showed a parabolic release profile of atRA during 42 days, releasing 36% of atRA.     

Evaluation of tocopherol recovery through simulation of molecular distillation process

DISMOL simulator was used to determine the best possible operating conditions to guide, in future studies, experimental works. This simulator needs several physical-chemical properties and often it is very difficult to determine them because of the complexity of the involved components. Their determinations must be made through correlations and/or predictions, in order to characterize the system and calculate it. The first try is to have simulation results of a system that later can be validated with experimental data. To implement, in the simulator, the necessary parameters of complex systems is a difficult task. In this work, we aimed to determe these properties in order to evaluate the tocopherol (vitamin E) recovery using a DISMOL simulator. The raw material used was the crude deodorizer distillate of soya oil. With this procedure, it is possible to determine the best operating conditions for experimental works and to evaluated the process in the separation of new systems, analyzing the profiles obtained from these simulations for the falling film molecular distillator.     

Solid-State Si, Cd, Sn, and P NMR Studies of II-IV-P2 Semiconductors

Solid-state ²⁹Si, ¹¹³Cd, ¹¹⁹Sn, and ³¹P MAS NMR spectra are reported on a series of II-IV-P₂ compounds. In favorable cases (e.g., high degree of crystallinity, low concentration of unpaired electrons), well-defined spectra, with sharp lines for each specific nearest-neighbor configuration, are observed; in such cases, expected J coupling patterns are also seen. High-resolution solid-state NMR studies of this type provide useful information on structure (disorder), doping, and electron-mediated coupling in semiconductor systems.     

Fermi-edge singularities in the photoluminescence spectrum of modulation-doped GaAs v-groove quantum wires

We report the observation of strong Fermi-edge singularities in the photoluminescence spectrum of strongly-confined, modulation-doped GaAs v-groove quantum wires. The behaviour of the singularity has been investigated at high excitation intensity, and both lattice and electrical heating. The latter produces a strong reduction of the singularity due to Fermi surface smearing, whereas, increased photoexcitation produces complex electron–hole correlation effects.