New low-stress PECVD poly-SiGe layers for MEMS

Thick poly-SiGe layers, deposited by plasma-enhanced chemical vapor deposition (PECVD), are very promising structural layers for use in microaccelerometers, microgyroscopes or for thin-film encapsulation, especially for applications where the thermal budget is limited. In this work it is shown for the first time that these layers are an attractive alternative to low-pressure CVD (LPCVD) poly-Si or poly-SiGe because of their high growth rate (100-200 nm/min) and low deposition temperature (520/spl deg/C-590/spl deg/C). The combination of both of these features is impossible to achieve with either LPCVD SiGe (2-30 nm/min growth rate) or LPCVD poly-Si (annealing temperature higher than 900/spl deg/C to achieve structural layer having low tensile stress). Additional advantages are that no nucleation layer is needed (deposition directly on SiO/sub 2/ is possible) and that the as-deposited layers are polycrystalline. No stress or dopant activation anneal of the structural layer is needed since in situ phosphorus doping gives an as-deposited tensile stress down to 20 MPa, and a resistivity of 10 m/spl Omega/-cm to 30 m/spl Omega/-cm. With in situ boron doping, resistivities down to 0.6 m/spl Omega/-cm are possible. The use of these films as an encapsulation layer above an accelerometer is shown

Enhanced initial growth of atomic-layer-deposited metal oxides on hydrogen-terminated silicon

A route is presented for activation of hydrogen-terminated Si(100) prior to atomic layer deposition. It is based on our discovery from in situ infrared spectroscopy that organometallic precursors can effectively initiate oxide growth. Narrow nuclear resonance profiling and Rutherford backscattering spectrometry show that surface functionalization by pre-exposure to 108 Langmuir trimethylaluminum at 300 °C leads to enhanced nucleation and to nearly linear growth kinetics of the high-permittivity gate dielectrics aluminum oxide and hafnium oxide

Impact of redox agents on the extractability of gluten proteins during bread making

The gluten proteins gliadin and glutenin are important for dough and bread characteristics. In the present work, redox agents were used to impact gluten properties and to study gliadin-glutenin interactions in bread making. In control bread making, mixing increased the extractability of glutenin. The level of SDS-extractable glutenin decreased during fermentation and then further in the oven. The levels of extractable alpha- and gamma-gliadin also decreased during bread baking due to gliadin-glutenin polymerization. Neither oxidizing nor reducing agents had an impact on glutenin extractabilities after mixing. The redox additives did not affect omega-gliadin extractabilities during bread making due to their lack of cysteine residues. Potassium iodate (0.82-2.47 mumol/g of protein) and potassium bromate (1.07-3.17 mumol/g of protein) increased both alpha- and gamma-gliadin extractabilities during baking. Increasing concentrations of glutathione (1.15-3.45 mumol/g of protein) decreased levels of extractable alpha- and gamma-gliadins during baking. The work not only demonstrated that, during baking, glutenin and gliadin polymerize through heat-induced sulfhydryl-disulfide exchange reactions, but also demonstrated for the first time that oxidizing agents, besides their effect on dough rheology and hence bread volume, hinder gliadin-glutenin linking during baking, while glutathione increases the degree of covalent gliadin to glutenin linking. Keywords: Bread making; wheat gluten; gliadin-glutenin interaction; protein extractability.status: publishe

Mechanism of gliadin-glutenin cross-linking during hydrothermal treatment

The gluten proteins, gliadin and glutenin, are important for wheat flour functionality and they undergo changes during heat treatment involving sulfhydryl (SH) groups. To change the level of SH-groups during hydrothermal treatment, the oxidant, potassium iodate (2.1 mu mol/g protein) and the reducing agent dithiothreitol (DTT, 6.1 mu mol/g protein) were added to 20% (w/w) gluten-in-water suspensions at room temperature, at 90 degrees C and after 15 min at 95 degrees C, and the viscosity was measured by the Rapid Visco Analyser (RVA). Protein extractabilities after hydrothermal treatment were determined by size-exclusion and reversed-phase HPLC. DTT decreased maximal RVA viscosity and the levels of extractable alpha- and gamma-gliadin and this decrease was independent of the time of addition during hydrothermal treatment. In contrast, potassium iodate increased the levels of extractable alpha- and gamma-gliadin. Its impact was less when added at later times during RVA analysis. A SH-blocking agent (N-ethylmaleimide, 8.0 mu mol/g protein), added at room temperature to the gluten suspension, decreased RVA viscosity at 95 degrees C and increased the extractabilities of glutenin and alpha- and gamma-gliadin after hydrothermal treatment. Subsequent addition, at 90 degrees C, of a reducing agent (glutathione, 3.1 and 6.2 mu mol/g protein) recovered the control RVA profile and restored the control protein extractabilities after RVA analysis. This shows the importance of heat-induced gliadin-glutenin reactions for gluten viscosity and of the presence of free SH-groups for the polymerization of gluten proteins. A model explaining gliadin-glutenin polymerization through a sulfhydryl-disulfide exchange mechanism and demonstrating the effects of redox agents is put forward. (C) 2007 Elsevier Ltd. All rights reserved.status: publishe

Reaction kinetics of gliadin-glutenin cross-linking in model systems and in bread making

The gluten proteins gliadin and glutenin are important for wheat flour functionality in bread making, where, during baking, they polymerize through a heat-induced sulfhydryl-disulfide exchange mechanism. A model system was used to study the kinetics of this reaction. Thus, gluten was subjected to hydrothermal treatment with the rapid visco analyzer (RVA) with holding temperatures of 80, 90, and 95 degrees C. At these temperatures, omega-gliadin solubility did not change, but the solubilities of alpha- and gamma-gliadin in 60% ethanol decreased according to first-order reaction kinetics. All reaction rate constants increased with temperature. The activation energies for the heat-induced exchange reaction were 110 and 147 kJ/mol for alpha- and gamma-gliadin, respectively. Starch did not influence the reaction rates of the association of alpha- and gamma-gliadin with glutenin. During gluten-starch model bread baking, glutenin oxidized first, and when the internal crumb temperature reached 100 degrees C, alpha- and gamma-gliadin crosslinked to glutenin, again following first-order reaction kinetics. The experimental findings and similarities in temperature conditions and reaction kinetics suggest that the RVA system can be instrumental in understanding gluten behavior in concentrated food systems, such as bread making.status: publishe

Impact of redox agents on the physico-chemistry of wheat gluten proteins during hydrothermal treatment

The impact of the oxidants potassium bromate and potassium iodate and the reducing agent dithiothreitol (DTT) on the theological behaviour of 20% (w/v) gluten-in-water suspensions during thermal treatment was monitored with the rapid visco analyser (RVA). The suspensions were subjected to a linear temperature increase from 40 to 95 degrees C in 14 min, a holding step of 40 min at 95 degrees C, a cooling step (7 min) with a linear temperature decrease to 50 degrees C, and a final holding step at 50 degrees C (13 min). Potassium iodate (1.18 and 1.77 mu mol/g protein) and potassium bromate (1.52 and 15.2 mu mol/g protein) decreased RVA viscosities in the holding step and increased sodium dodecyl sulphate (SDS) protein extractabilities suggesting a greater heat resistance and decreased gliadin-glutenin cross-linking. In contrast, in the presence of DTT (1.65 and 3.30 mu mol/g protein) RVA viscosity increased at lower temperatures and lowered SDS extractabilities. It is postulated that low concentrations of reducing agent facilitate gliadin-glutenin cross-linking during heating while oxidants hinder gluten polymerization due to decreased levels of free sulphydryl groups and less flexibility of the glutenin chains. (c) 2006 Elsevier Ltd. All rights reserved.status: publishe

The impact of heating and cooling on the physico-chemical properties of wheat gluten-water suspensions

The rapid visco analysis (RVA) system was used to measure rheological behaviour in 20% (w/v) gluten-in-water suspensions upon applying temperature profiles. The temperature profiles included a linear temperature increase, a holding step, a cooling step with a linear temperature decrease to 50 degrees C, and a final holding step at 50 degrees C. Temperature and duration of the holding phase both affected RVA viscosity and protein extractability. Size-exclusion and reversed-phase HPLC showed that increasing the temperature (up to 95 degrees C) mainly decreased glutenin extractability. Holding at 95 degrees C resulted in polymerisation of both gliadin and glutenin. Above 80 degrees C, the RVA viscosity steadily increased with longer holding times while the gliadin and glutenin extractabilities decreased. Their reduced extractability in 60% ethanol showed that gamma-gliadins were more affected after heating than alpha-gliadins and omega-gliadins. Enrichment of wheat gluten in either gliadin or glutenin showed that both gliadin and glutenin are necessary for the initial viscosity in the RVA profile. The formation of polymers through disulphide bonding caused a viscosity rise in the RVA profile. The amounts of free sulphydryl groups markedly decreased between 70 and 80 degrees C and when holding the temperature at 95 degrees C. (c) 2005 Elsevier Ltd. All rights reserved.status: publishe