Energy deposition during molecular depth profiling experiments with cluster ion beams

Area of Science:

• Materials Science
• Surface Science
• Analytical Chemistry

Background:

• Molecular depth profiling is crucial for analyzing thin films.
• Cluster ion bombardment offers advantages for preserving molecular integrity.
• Understanding energy deposition effects is key to optimizing profiling quality.

Purpose of the Study:

• To investigate the impact of incident angle on molecular depth profiling quality.
• To determine the optimal geometry for minimizing chemical damage during erosion.
• To elucidate the relationship between energy deposition location and profiling fidelity.

Main Methods:

• Erosion of cholesterol films using 40-keV C60(+) at varying incident angles (5°–73°).
• Evaluation of sputtering yield, damage cross section, altered layer thickness, and interface width.
• Development of an extended erosion model incorporating fluence-dependent sputter yield decay.

Main Results:

• Total sputtering yield relative to damage cross section and altered layer thickness maximized at 73° incidence.
• Chemical damage accumulation was least at glancing incident geometries.
• Signal decay in the quasi-steady-state regime was minimized at off-normal and glancing angles.
• Interface width calculations showed the smallest damaged depth at glancing incidence.

Conclusions:

• Decreased chemical damage is achieved by depositing incident energy nearer the surface, reducing the altered layer thickness.
• Glancing incident angles are optimal for preserving chemical information during molecular depth profiling with 40-keV C60(+).
• The study provides insights into optimizing cluster ion bombardment parameters for high-fidelity depth profiling.