Quantum dot on a plasma-facing microparticle surface: Thermal balance

TL;DR

This study analyzes the thermal balance of quantum dots on plasma-facing microparticles, demonstrating that under pulsed plasma conditions, spectral shifts are primarily due to the Stark effect, enabling charge measurement.

Contribution

It provides a quantitative analysis of quantum dot thermal contact with microparticles, clarifying conditions where spectral shifts indicate microparticle charge rather than thermal effects.

Findings

Spectral shift due to temperature oscillations becomes undetectable at thermal flux ~10^9 s$^{-1}$.

Spectral shifts during plasma pulsing are mainly due to the Stark effect, not thermal effects.

Lower-bound estimate for thermal flux in direct contact is ~10^{12} s$^{-1}.

Abstract

Semiconductor nanocrystals, quantum dots, are known to exhibit the quantum-confined Stark effect which reveals itself in the shift of their photoluminescence spectra in response to external electric field. It was, therefore, proposed to use quantum dots deposited on the microparticle surface for the optical measurement of the charge acquired by the microparticles in low-temperature plasmas. Thermal balance of a quantum dot residing on the surface of a microparticle immersed in a plasma is considered in this work. It is shown for typical plasma parameters that under periodically pulsed plasma conditions, the spectral shift of the photoluminescence of the quantum dot caused by the oscillations of its temperature becomes undetectable at the effective thermal flux characterizing the thermal contact between the quantum dot and the microparticle $\sim 10^9$~s$^{-1}$. Under these conditions, the entire spectral shift observed during the period of plasma pulsing should be attributed to the quantum-confined Stark effect due to the microparticle charge. Lower-boundary estimate for the effective thermal flux for the direct contact between the quantum dot and the microparticle is $\sim 10^{12}$~s$^{-1}$.