Intermittent-contact local dielectric spectroscopy of nanostructured interfaces

Area of Science:

• Materials Science
• Surface Science
• Physical Chemistry

Background:

• Local dielectric spectroscopy (LDS) is a scanning probe technique utilizing dynamic-mode atomic force microscopy (AFM) for nanoscale dielectric property analysis.
• Previous LDS resolutions were insufficient to probe fundamental physical phenomena like cooperativity length (2-3 nm) in glass formers.
• Achieving sub-10 nm resolution is critical for understanding nanoscale dielectric behavior and interfacial phenomena.

Purpose of the Study:

• To introduce and explore a variant of AFM's intermittent-contact mode, constant-excitation frequency modulation, for enhanced LDS resolution.
• To assess the optimal operational parameters for achieving the best possible resolution in LDS.
• To demonstrate the capability of this method for high-resolution dielectric imaging and spectroscopy at the nanoscale.

Main Methods:

• Utilized a specialized constant-excitation frequency modulation mode of dynamic-force AFM for LDS measurements.
• Systematically investigated the influence of operational parameters (oscillation amplitude, frequency shift, feedback gain) on resolution and contrast.
• Employed thin films of phase-separated polystyrene (PS) and polymethylmethacrylate (PMMA) diblock copolymers as a model system.

Main Results:

• Demonstrated a lateral resolution of at least 3 nm in both dielectric imaging and localized spectroscopy.
• Successfully mapped the interface of lamellar PS/PMMA structures with an interface width of 1-3 nm.
• Tracked changes in the characteristic time of the secondary (β) relaxation process of PMMA across the PS interface.

Conclusions:

• The developed LDS technique significantly advances nanoscale dielectric analysis, achieving resolutions below 10 nm.
• This method provides unprecedented insights into interfacial dielectric properties and molecular dynamics in nanostructured materials.
• The findings open new avenues for studying fundamental physical processes at the nanoscale, relevant to materials science and condensed matter physics.