Electronic Action Spectroscopy on Single Nanoparticles in the Gas Phase

Abstract

We present electronic excitation spectra of individual nanoparticles (NPs) in the gas phase obtained by messenger-mediated single nanoparticle action spectroscopy at cryogenic temperatures (cryo-SNAS). Single ∼100 nm diameter SiO 2 NPs, either colorless or dye-loaded, are trapped and coated with multiple layers of N 2 in a temperature-controllable modified quadrupole ion-trap at 100 K. The NP's mass is monitored quasi-continuously and nondestructively by light scattering. Absorption of electromagnetic radiation from a tunable (400−800 nm), quasi-continuous, supercontinuum laser leads to heating of the NP and subsequent evaporation of N 2 molecules. The average change in NP mass as a function of the irradiation wavelength then yields the cryo-SNAS spectrum without further correction. The obtained spectra are similar to direct absorption spectra of the corresponding NP suspensions but reveal narrower bands due to the lower NP temperature. These experiments demonstrate that cryo-SNAS allows the determination of photoabsorption spectra of single, free NPs independently of scattering processes.

UV‐vis spectroscopy of gas‐phase ions

“…At the high‐mass end of action spectroscopy measurements, dye‐loaded silicon oxide nanoparticles have been reported to absorb at 600 nm when irradiated in an ion trap. These experiments used a cold ion trap, and light absorption was monitored by desorption of N 2 molecules adhering to the cold nanoparticle ion surface (Hoffmann et al, 2020).…”

A Chemical Nanoreactor Based on a Levitated Nanoparticle in Vacuum

“…Therefore, the properties of these small particles and processes in which they can be involved are of interest because they determine the presence of accumulationmode particles in the atmosphere, 19 but their optical levitation and control still remain challenging. 20,21 Single NPs are typically characterized in Paul traps, [12][13][14]22,23 while the additional use of optical tweezers enables an increased coupling of the particle with the probing laser beam. 24 In fact, the diameter d of the NP strongly affects the scattering cross section σ scat , which scales as d 6 , making small particles hard to detect.…”

“…The substrate itself and neighboring NPs strongly affect the NPs properties. The levitation of individual particles with optical tweezers or Paul traps has become a well-established approach to characterize single microparticles in controlled conditions and evades both ensemble averages and disturbance from substrates, therefore enabling fundamental research in aerosol science , and nanochemistry. − In the case of aerosol science, most studies have been performed with single microparticles with diameters larger than 2 μm. Less is known about the behavior of single particles in the so-called accumulation mode (diameter 0.1–2 μm), which typically requires ensemble averages to provide meaningful data .…”

“…Single NPs are typically characterized in Paul traps, − ,, while the additional use of optical tweezers enables an increased coupling of the particle with the probing laser beam . In fact, the diameter d of the NP strongly affects the scattering cross section σ scat , which scales as d 6 , making small particles hard to detect.…”