Experimental results are presented which identify the following chemical reaction as being responsible for compensation of shallow-acceptor impurities when single-crystal silicon is exposed to monatomic hydrogen: A + h + + Ho~( A H), where A represents an ionized shallow acceptor, h + is a (positively charged) free hole, and H is a neutral hydrogen atom. Infrared absorption spectroscopy on boron-doped silicon, combined with recent defect-model calculations, reveals that the hydrogen atom forms a Si -H bond at the site of a substitutional boron atom; the absorption band for the stretch mode appears at 1870 cm . Measurements by secondary-ion mass spectrometry of impurity profiles in deuterated silicon reveal that shallow-acceptor passivation is suppressed by counter doping to produce n-type conductivity.These new results identify both the defect complex responsible for hydrogen compensation of shallow acceptors and the essential role of free holes, or equivalently neutral acceptors, in the chemical reaction.Shallow-acceptor impurities in single-crystal silicon can be compensated or neutralized by exposing the crystal to monatomic hydrogen. This conclusion has been well established from electrical measurements (e.g. , spreadingresistance and capacitance-voltage measurements) of the change in apparent dopant concentration before and after hydrogenation. ' ' Although models have been proposed, the specific chemical reaction and defect complex which are responsible for acceptor compensation have not yet been identified. In the first reports of this phenomenon, Sah, Sun, and Tzou' proposed that hydrogen diffuses into silicon and reacts with an acceptor impurity (e.g. , boron) to form a 8 H+ complex. Subsequently, Pankove, Carlson, Berkeyheiser, and Wance proposed that the hydrogen atom specifically bonds to the silicon dangling orbital that is immediately adjacent to the substitutional trivalent acceptorimpurity.This qualitative model was further defined and theoretically examined by DeLeo and Fowler. 7 Their model involves a hydrogen-acceptor pair in a lattice vacancy with both the acceptor and hydrogen off center and situated along the (111) axis. The hydrogen passivates the single silicon dangling orbital in the (111) direction, which leaves the acceptor impurity to threefold coordinate with the remaining silicon neighbors. In addition, total-energy calculations predict that the hydrogen-boron pair is stable, at a separation of 1.62 A, and will form spontaneously if an interstitial hydrogen atom approaches a neutral substitutional acceptor impurity. A different chemical model has been proposed by Hansen, Pearton, and Haller4 based on electrical measurements of boron-doped silicon after treatment in 02, H2, and H20 plasmas. They concluded that acceptor compensation requires the rapid diffusion of monatomic oxygen as well as hydrogen which combine at the acceptor site to form a neutral acceptor-OH complex. However, by applying isotopic substitution it has recently been shown that oxygen does not diffuse into silicon un...

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Natural populations evolve in response to biotic and abiotic changes in their environment, which shape species interactions and ecosystem dynamics. Agricultural systems can introduce novel conditions via herbicide exposure to non-crop habitats in surrounding fields. While herbicide drift is known to produce a variety of toxic effects in plants, little is known about its impact on non-target wildlife species interactions. In a two-year study, we investigated the impact of herbicide drift on plant-herbivore interactions with common weed velvetleaf (Abutlion theophrasti) as the focal species. The findings reveal a significant increase in the phloem feeding silverleaf whitefly (Bermisia tabaci) abundance on the plants exposed to herbicide at drift rates of 0.5% and 1% of the field dose. Additionally, we found evidence that drift imposes correlated selection on whitefly resistance and growth rate as well as positive linear selection on herbicide resistance. We also identified a significant phenotypic tradeoff between whitefly resistance and herbicide resistance in addition to whitefly resistance and relative growth rate in the presence of dicamba drift. These findings suggest herbicide exposure to non-target communities can significantly alter herbivore populations, potentially impacting biodiversity and community dynamics of weed populations found at the agro-ecological interface.