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

Yingying Sun; Masahiro Yanagisawa; Masahiro Kunimoto; Masatoshi Nakamura; Takayuki Homma

doi:10.1016/j.saa.2017.04.036

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

Spectrochim Acta A Mol Biomol Spectrosc. 2017 Sep 5:184:1-6. doi: 10.1016/j.saa.2017.04.036. Epub 2017 Apr 20.

Authors

Yingying Sun¹, Masahiro Yanagisawa², Masahiro Kunimoto², Masatoshi Nakamura¹, Takayuki Homma³

Affiliations

¹ Department of Applied Chemistry, Waseda University, 3-4-1 Okubo, Shinjuku, Tokyo 169-8555, Japan.
² Nanotechnology Research Center, Waseda University, 513 Wasedatsurumakicho, Shinjuku, Tokyo 162-0041, Japan.
³ Department of Applied Chemistry, Waseda University, 3-4-1 Okubo, Shinjuku, Tokyo 169-8555, Japan; Nanotechnology Research Center, Waseda University, 513 Wasedatsurumakicho, Shinjuku, Tokyo 162-0041, Japan. Electronic address: t.homma@waseda.jp.

PMID: 28475958
DOI: 10.1016/j.saa.2017.04.036

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 0.1nm. We measured and distinguished the vertical Raman intensity variations of specific groups in APTES, such as Ag/NH₂, CH₂, and SiO, with high resolution. The interfacial bond at the two interfaces of Ag-APTES and APTES-SiO₂ was identified. Moreover, APTES molecule orientation was demonstrated to be inhomogeneous from frequency shift.

Keywords: APTES self-assembled monolayers; Depth profile; Nano resolution; Surface-enhanced confocal Raman microspectroscopy.