Electronic Action Spectroscopy on Single Nanoparticles in the Gas Phase

Area of Science:

• Spectroscopy
• Nanoparticle Science
• Physical Chemistry

Background:

• Characterizing individual nanoparticles (NPs) is crucial for understanding their properties.
• Direct absorption spectroscopy often faces limitations with scattering effects, especially for free nanoparticles.

Purpose of the Study:

• To present a novel method, messenger-mediated single nanoparticle action spectroscopy at cryogenic temperatures (cryo-SNAS), for obtaining electronic excitation spectra of individual NPs.
• To demonstrate the capability of cryo-SNAS in determining photoabsorption spectra of single, free NPs independently of scattering.

Main Methods:

• Trapping individual SiO2 nanoparticles (∼100 nm diameter) in a cryogenic quadrupole ion trap (100 K).
• Coating NPs with nitrogen (N2) as messenger molecules.
• Monitoring NP mass via light scattering while irradiating with a tunable supercontinuum laser (400-800 nm).
• Measuring N2 evaporation triggered by laser absorption to derive the NP spectrum.

Main Results:

• Cryo-SNAS successfully obtained electronic excitation spectra for individual, gas-phase SiO2 nanoparticles.
• The spectra showed narrower bands compared to suspension spectra due to the low NP temperature (100 K).
• The method yielded spectra similar to direct absorption but was independent of scattering processes.

Conclusions:

• Cryo-SNAS is a viable technique for the high-resolution spectroscopic analysis of single nanoparticles.
• This method overcomes scattering limitations inherent in traditional spectroscopy of nanoparticles.
• Cryo-SNAS enables detailed characterization of nanoparticle photoabsorption properties in a controlled, low-temperature environment.