Wang Yimin, Watkins Erik, Ilavsky Jan, Metroke Tammy L, Wang Peng, Lee Byeongdu, Schaefer Dale W
Department of Chemical and Materials Engineering, University of Cincinnati, Cincinnati, Ohio 45221-0012, USA.
J Phys Chem B. 2007 Jun 28;111(25):7041-51. doi: 10.1021/jp0679212. Epub 2007 May 26.
X-ray and neutron reflectivity were employed to elucidate the morphologies of bis[trimethoxysilylpropyl]amine silane (A) and vinyltriacetoxysilane (V) mixed films on Si wafers at different A/V ratios, and the response of these films to saturated water vapor. Due to its insensitivity to chemical composition, X-ray reflectivity was used to assess the film density, whereas neutron reflectivity was used to probe water absorption and chemical change on exposure to water. NMR was employed to determine the reaction mechanism in neat AV mixtures and stoichiometry of the initial reaction. X-ray reflectivity reveals about 30% void volume in the films with the least void volume detected near stoichiometry. Grazing incidence small-angle scattering (GISAXS) shows that the void volume is at the molecular level, with no distinct pores. Neutron reflectivity on D2O-conditioned films shows that silane film is not an effective water barrier with about 30 vol % water being absorbed with only a slight thickness increase. Most water is physically absorbed in the void space with the least amount being absorbed near the stoichiometric A/V ratio. The scattering length density of the films almost returns to the virgin state after re-dry following D2O vapor exposure. The film thickness, however, remains at the water-vapor-conditioned state. The slight increase in scattering length density and irreversible thickness change after re-dry indicate some reaction with water during D2O conditioning. A D-rich layer is also observed at the air side surface in D2O-conditioned films regardless of A/V ratio.
采用X射线和中子反射率来阐明双[三甲氧基硅丙基]胺硅烷（A）和乙烯基三乙酰氧基硅烷（V）在不同A/V比下在硅片上混合膜的形态，以及这些膜对饱和水蒸气的响应。由于X射线反射率对化学成分不敏感，因此用于评估膜密度，而中子反射率用于探测暴露于水时的吸水率和化学变化。利用核磁共振（NMR）确定纯AV混合物中的反应机理和初始反应的化学计量。X射线反射率显示，在接近化学计量比时检测到的膜中空隙体积最小，约为30%。掠入射小角散射（GISAXS）表明，空隙体积处于分子水平，没有明显的孔隙。对经D2O处理的膜进行中子反射率测量表明，硅烷膜不是有效的水屏障，约30体积%的水被吸收，膜厚度仅略有增加。大多数水被物理吸附在空隙空间中，在化学计量比的A/V比附近吸收的水量最少。在D2O蒸汽暴露后重新干燥后，膜的散射长度密度几乎恢复到原始状态。然而，膜厚度保持在水蒸气处理后的状态。重新干燥后散射长度密度的轻微增加和不可逆的厚度变化表明在D2O处理过程中与水发生了一些反应。无论A/V比如何，在经D2O处理的膜的空气侧表面也观察到富含D的层。
