Depth resolution during C60+ profiling of multilayer molecular films

Area of Science:

• Materials Science
• Surface Science
• Analytical Chemistry

Background:

• Langmuir-Blodgett (LB) multilayers are advanced materials with applications in electronics and sensors.
• Characterizing the molecular structure and depth of LB films is crucial for understanding their properties.
• Buckminsterfullerene (C60) primary ions offer unique sputtering characteristics for mass spectrometry.

Purpose of the Study:

• To investigate the effectiveness of time-of-flight secondary ion mass spectrometry (TOF-SIMS) using C60 ions for depth profiling of LB multilayers.
• To evaluate the influence of temperature on the sputtering process and signal stability.
• To determine the depth resolution achievable with this technique.

Main Methods:

• Time-of-flight secondary ion mass spectrometry (TOF-SIMS) was employed.
• Langmuir-Blodgett multilayers of barium arachidate and barium dimyristoyl phosphatidate on a silicon substrate were analyzed.
• Experiments were conducted at both cryogenic (liquid nitrogen) and room temperatures.
• Primary ion bombardment utilized buckminsterfullerene (C60) ions.

Main Results:

• C60 ion bombardment enabled successful molecular depth profiling of single-component and alternating LB multilayers.
• High mass signals remained stable at cryogenic temperatures but decreased with ion dose at room temperature.
• Cryogenic temperatures resulted in a higher average sputter yield.
• Depth resolution ranged from 20 to 50 nm, improvable by reducing primary ion energy or using glancing incidence angles.

Conclusions:

• TOF-SIMS with C60 ions is a viable technique for molecular depth profiling of LB multilayers.
• Cryogenic temperatures significantly improve signal stability and sputter yield, enhancing analytical performance.
• Optimizing ion energy and incidence angle can further refine depth resolution for nanoscale characterization.