Silicon In Ambient Research Articles

Increased root herbivory under elevated atmospheric carbon dioxide concentrations is reversed by silicon‐based plant defences

Summary Predicted increases in atmospheric concentrations of CO2 may alter the susceptibility of many plants to insect herbivores due to changes in plant nutrition and defences. Silicon plays a critical role in plant defence against herbivores, so increasing such silicon‐based defences in plants may help remediate situations where plants become more susceptible to herbivores. Sugar cane (Saccharum spp. hybrid) was subjected to fully factorial treatment combinations of ambient (aCO2) or elevated (eCO2) atmospheric CO2 concentrations; ambient silicon or silicon supplementation; insect‐free or subject to root herbivory by greyback canegrub (Dermolepida albohirtum). A glasshouse study was used to determine how these factors affected rates of photosynthesis, growth, chemistry (concentrations of silicon, carbon, nitrogen and non‐structural carbohydrates). Changes in canegrub mass were determined in the glasshouse pot study, together with more detailed assessment of how eCO2 and silicon supplementation affected performance and feeding behaviour (relative growth rate and relative consumption) in a 24‐h feeding efficiency assay. Elevated CO2 and silicon supplementation increased rates of photosynthesis (+32% and 14%, respectively) and sugar cane biomass (+45% and 69%, respectively). Silicon supplementation increased silicon concentrations in both leaves and roots by 54% and 75%, respectively. eCO2 caused root C : N to increase by 12%. Canegrub performance and consumption increased under eCO2; relative growth rate (RGR) increased by 116% and consumed 57% more root material (suggestive of compensatory feeding). Silicon application reversed these effects, with large decreases in mass change, RGR and root consumption (65% less root mass consumed). Synthesis and applications. Our results suggest future atmospheric carbon dioxide concentrations could lead to increased crop damage by a below‐ground herbivore. Increasing bioavailable silicon in soil stimulated silicon‐based defences which dramatically decreased herbivory and herbivore performance. Our findings suggest future pest management strategies could benefit from characterising deficiencies in bioavailable silicon in agricultural soils and targeted application of silicon fertilisers. Moreover, future breeding programmes should exploit variation in silicon uptake between cultivars to enhance silicon uptake in new crop varieties. Silicon‐based plant defence proved to be highly beneficial for remediating the negative effects of atmospheric change on sugar cane susceptibility to herbivory and could be applicable in other crops.

Thermal Oxidation of Silicon in Nitrous Oxide at High Pressures

Thermal oxidation of silicon in nitrous oxide ambient at pressures from 1 to 4 atm has been studied. We show that the oxidation rate is different from the one predicted by the Deal-Grove model for normal oxidation in dry oxygen. In our case, the dependence observed for the oxide thickness as a function of the oxidation time is of the form where is a native oxide thickness. For the temperature range between 900 and 1200°C, and 2 atm of pressure, the activation energy for γ is around 1.18 eV. In addition, the exponential factor β (at 1000°C) varies as the square root of the pressure. These results indicate that thermal oxidation in behaves in a completely different way than normal oxidation, very likely due to the influence of chemical reactions in the gas phase, to the catalytic influence of the interface, and to the incorporation of nitrogen into the oxide film itself. The results presented here establish the basis for the development of a more complete model for thermal oxidation of silicon in a ambient. © 2001 The Electrochemical Society. All rights reserved.

Growth Rate and Characterization of Silicon Oxide Films Grown in N 2 O Atmosphere in a Rapid Thermal Processor

A rapid thermal oxidation process of silicon in ambient was investigated using a commercially available reactor with a fixed wafer position and a gas flow parallel to the wafer surface. For such a configuration, thickness uniformities in the 2% range were obtained for the first time. The oxidation rate as a function of process temperature and time was investigated. A retardation in the oxidation rate as compared to the oxidation in ambient is explained by the formation of a nitrided interfacial layer. A comparison of experimental results with an oxidation model calculation shows that this interface can affect either the oxidant diffusivity through the oxide or the reaction rate at the silicon surface. Infrared spectra of nitrided oxide films reveal a regular arrangement in the Si‐O network, similar to that of high quality thermally grown oxides. A vibrational contribution to that spectrum from a Si‐O‐N subnetwork is displayed. The accumulated charge to breakdown on metal‐oxide‐semiconductor capacitors as a function of the injected current density revealed different slopes for oxides either thermally grown or grown in . Hence, the projected lifetime for devices with grown oxide under low operating fields is extended by one order of magnitude in comparison with the thermal oxide.