不同受限状态下链硫醇的非线性光学响应

以和频(SFG)振动光谱技术探测了正十二硫醇(DDT)在不同受限状态下的分子振动信号,包括金属基底上的自组装单层(SAM)分子,放置在二氧化硅基底上的表面DDT化的金纳米粒子以及金纳米粒子的甲苯溶液.在三种状态下都探测到了来自于DDT分子的振动光谱,振动光谱的区别提供了在不同受限态下DDT分子的结构信息.在金属基底上DDT分子排列规整,放置在二氧化硅基底上的金纳米粒子表面的DDT分子具有一定的柔性,在空气-甲苯溶液界面金纳米粒子表面的DDT分子高度无序.此外,光谱实验显示,金纳米粒子表面的分子振动信号产生了局域场增强的效应,相对于金基底上的自组装单层分子而言,增强系数为102-103,取决于光谱的偏振组合.

Nonlinear Optical Responses of Thiol Chains in Different Confined States

The molecular vibrational signals of n-dodecanethiol (DDT) were detected in different confined states using sum frequency generation (SFG) vibrational spectroscopy. Samples with three different confined states were used, including a self-assembled monolayer (SAM) of DDTmolecules on a gold (Au) substrate, DDT surface-functionalized Au nanoparticles on a silica substrate, and surface-functionalized Au nanoparticles dispersed in a toluene solution. The vibrational spectra of the DDT molecules were successfully captured for all three samples, and the spectral differences provided evidence of the different confined structures. On the Au substrate, the DDT molecules orderly packed together; on the silica substrate, the DDT molecules attached to the Au nanoparticle surfaces were somehow flexible; and at the air-toluene interface, the DDT molecules attached to the Au nanoparticle surfaces were highly disordered. The spectral analysis indicated that the molecular vibrational signals generated from the Au nanoparticle surfaces were enhanced because of the localized enhanced fields near the Au nanoparticle surfaces, with the enhancement factors of 10²-10³ over the SAM of DDT molecules on the Au substrate, depending on the selected polarization combination.