Abstract
We have performed measurements of the ir absorption of SiO_{2} nanoparticles confined in an argon radiofrequency plasma discharge using a Fourier transform infrared spectrometer. By varying the gas pressure of the discharge and duty cycle of the applied radiofrequency voltage, we observed a shift of the absorption peak of SiO_{2}. We attributed this shift to charge-dependent absorption features of SiO_{2}. The charge-dependent shift has been calculated for SiO_{2} particles, and from comparisons with the experiment the particle charge has been retrieved using our 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.
Highlights
INTRODUCTIONDusty (or complex) plasmas consist of electrons, ions, neutral gas atoms, and additional massive particles
Dusty plasmas consist of electrons, ions, neutral gas atoms, and additional massive particles
We have measured the ir absorption of SiO2 nanoparticles of 40 nm radius confined in a plasma
Summary
Dusty (or complex) plasmas consist of electrons, ions, neutral gas atoms, and additional massive particles. Heinisch et al have suggested a complementary approach, where the charge-dependent absorption of infrared light by nanoscaled particles is exploited [32,33] They have shown analytically that the electrons residing as charges on the particles cause a change in the effective refractive index of the particles. Heinisch et al have performed calculations for a variety of materials (Al2O3, Cu2O, LiF, MgO, PbS) For these materials, it is found that the absorption line of the transverse optical phonon in the infrared spectral range shifts towards higher wave numbers with increasing particle charge and smaller particle radius.
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