Charge measurement of $\text{SiO}_2$ nanoparticles in an RF-plasma by IR absorption

TL;DR

This study measures the IR absorption of SiO2 nanoparticles in RF plasma to determine their charge, using shifts in absorption peaks caused by charge-dependent features, and introduces the IRPRS method for charge estimation.

Contribution

The paper presents a novel IRPRS method to accurately measure nanoparticle charge in plasma via IR absorption peak shifts, validated through pressure and duty cycle variations.

Findings

Charge-dependent IR absorption shifts observed in SiO2 nanoparticles.

Particle charge estimated from IR absorption shifts using IRPRS.

Relative charge change with pressure and absolute charge with duty cycle.

Abstract

We have performed measurements of the IR absorption of $\text{SiO}_2$ nanoparticles confined in an argon radio-frequency plasma discharge using an FTIR spectrometer. By varying the gas pressure of the discharge and duty cycle of the applied radio-frequency voltage we observed a shift of the absorption peak of $\text{SiO}_2$. We attributed this shift to charge-dependent absorption features of $\text{SiO}_2$. The charge-dependent shift has been calculated for $\text{SiO}_2$ particles and from comparisons with the experiment the particle charge has been retrieved using our IRPRS (Infrared Phonon Resonance Shift) method. With the two different approaches of changing the gas pressure and altering the duty cycle we are able to deduce a relative change of the particle charge with pressure variations and an absolute estimate of the charge with the duty cycle.