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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Ammonia Photodissociation Promoted by Si(100)
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Ammonia Photodissociation Promoted by Si(100)

机译：Si（100）促进的氨光解离

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摘要

Using in situ X-ray photoelectron spectroscopy measurements after reaction, we show that hydrogen-terminated Si(100) perturbs the bonding of physisorbed NH3 enabling a photochemical decomposition pathway at wavelengths different from those characteristic of either the molecule in the gas phase or the semiconductor bandgap. UV illumination only of gas phase NH_3 at partial pressures from 0.1 to 100 Torr produced a maximum at 10 Torr in the N surface coverage. This is in good agreement with a model of the radical production rate showing that at this pressure the gas density balances the flux of photons at the surface with energies sufficient to dissociate NH_3. UV illumination of both the gas phase and the surface produced a monotonic increase in the N coverage with pressure as well as coverages that were 3?10 times higher than when only the gas phase was illuminated. The amine saturation coverage scaled with the UV fluence at 10 Torr and 75 °C, reaching 6.9 × 10_(14) atoms/cm~2 (～1 N atom per Si surface atom) at 19 mW/cm~2 and 12 × 10_(14) atoms/cm~2 (～1.8 N per Si) at 35 mW/cm2. Monochromatic illumination showed that the wavelengths driving deposition were not correlated with the Si bandgap, but instead were roughly the same as gas phase photodissociation (λ > 220 nm). The primary driving force to replace the hydrogen termination with amine groups was direct photodissociation of NH3 molecules whose electronic structure was perturbed by interaction with the surface. Amine groups enhanced the surface reaction of water present as a contaminant in the source gas. These results show that molecules in weakly bound surface states can have a dramatic impact on the photochemistry.
机译：反应后使用原位X射线光电子能谱测量，我们显示氢封端的Si（100）扰乱了物理吸附的NH3的键合，从而使光化学分解途径的波长不同于气相或半导体分子的特征波长带隙。在0.1至100 Torr的分压下，仅气相NH_3的UV照射在N表面覆盖物中产生的最大值为10 Torr。这与自由基产生速率的模型非常吻合，该模型表明在此压力下，气体密度以足以解离NH_3的能量平衡了表面上的光子通量。气相和表面的紫外线照射都会使N覆盖率随压力而单调增加，并且覆盖率比仅照射气相时高3至10倍。在10 Torr和75°C下，胺饱和覆盖度随UV能量密度成比例变化，在19 mW / cm〜2和12×10_时达到6.9×10_（14）原子/ cm〜2（每个Si表面原子〜1 N原子）。 （14）原子/ cm〜2（每Si约1.8 N）在35 mW / cm2时。单色照明表明，驱动沉积的波长与Si带隙无关，而与气相光解离大致相同（λ> 220 nm）。用胺基取代氢封端的主要驱动力是NH 3分子的直接光解离，其电子结构因与表面的相互作用而受到干扰。胺基团增强了源气体中作为污染物存在的水的表面反应。这些结果表明，处于弱结合表面状态的分子可以对光化学产生巨大影响。

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