Infrared absorption nano-spectroscopy using sample photoexpansion induced by tunable quantum cascade lasers

Area of Science:

• Spectroscopy
• Nanotechnology
• Materials Science

Background:

• Mid-infrared (MIR) spectroscopy is crucial for chemical identification.
• Achieving high spatial resolution in MIR absorption spectroscopy is challenging.
• Existing techniques often require high laser power or lack nanoscale precision.

Purpose of the Study:

• To develop a novel, low-power technique for nanoscale spatial resolution MIR absorption spectroscopy.
• To demonstrate the capability of detecting light absorption via thermal expansion.
• To achieve sub-50 nm spatial resolution in MIR spectral measurements.

Main Methods:

• Utilizing tunable quantum cascade lasers (QCLs) for MIR light generation.
• Employing atomic force microscopy (AFM) to detect sample thermal expansion.
• Resonating the QCL pulse repetition frequency with the AFM cantilever's mechanical frequency to amplify thermal expansion detection.

Main Results:

• Successfully obtained MIR absorption spectra with nanoscale spatial resolution.
• Demonstrated a spatial resolution better than 50 nm.
• The technique operates effectively under low-power illumination.

Conclusions:

• This simple technique enables high-resolution MIR absorption spectroscopy at the nanoscale.
• The resonant detection method significantly enhances sensitivity to minute thermal expansion.
• The approach is promising for detailed chemical mapping of materials.