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

Area of Science:

• Materials Science
• Surface Chemistry
• Nanotechnology

Background:

• Characterizing the nanometer-level internal structure of self-assembled monolayers (SAMs) like 3-aminopropyltriethoxysilane (APTES) on glass is challenging.
• Understanding SAM internal structure is crucial for advanced material applications.

Purpose of the Study:

• To investigate the internal molecular structure of APTES SAMs using advanced spectroscopic techniques.
• To achieve high-resolution analysis of SAMs, particularly in the vertical direction.

Main Methods:

• Employed surface-enhanced Raman spectroscopy (SERS) with silver nanoparticles to enhance Raman signals.
• Utilized density functional theory (DFT) calculations for theoretical support.
• Implemented a piezoelectric positioner for precise 0.1nm depth-scanning resolution.

Main Results:

• Successfully measured and distinguished vertical Raman intensity variations for specific APTES groups (Ag/NH2, CH2, SiO).
• Identified interfacial bonds at the Ag-APTES and APTES-SiO2 interfaces.
• Demonstrated inhomogeneous APTES molecule orientation through frequency shift analysis.

Conclusions:

• SERS provides high-resolution insights into the internal structure and interfacial properties of APTES SAMs.
• The study confirms the utility of SERS for detailed nanoscale surface analysis.
• Inhomogeneous molecular orientation in APTES SAMs was quantitatively observed.