Depth profiling of APTES self-assembled monolayers using surface-enhanced confocal Raman microspectroscopy

Abstract The internal structure of self-assembled monolayers (SAMs) such as 3-aminopropyltriethoxysilane (APTES) fabricated on a glass substrate is difficult to characterize and analyze at nanometer level. In this study, we employed surface-enhanced Raman spectroscopy (SERS) to study the internal molecular structure of APTES SAMs. The sample APTES SAMs were deposited with Ag nanoparticles to enhance the Raman signal and to obtain subtler structure information, which were supported by density functional theory calculations. In addition, in order to carry out high-resolution analysis, especially for vertical direction, a fine piezo electric positioner was used to control the depth scanning with a step of 0.1 nm. We measured and distinguished the vertical Raman intensity variations of specific groups in APTES, such as Ag/NH 2 , CH 2 , and Si O, with high resolution. The interfacial bond at the two interfaces of Ag-APTES and APTES-SiO 2 was identified. Moreover, APTES molecule orientation was demonstrated to be inhomogeneous from frequency shift.