Towards a new method to measure low energy electron sticking coefficients using dusty plasmas

尘埃等离子体界对不同材料的充电特性进行了广泛的研究。它们与粒子的电子粘附系数直接相关，因为它对使用不同电极材料的射频驱动等离子体反应器的放电性能有很大影响，因此与等离子体技术高度相关。粉尘电荷的高精度测量为低能电子粘着系数的测定开辟了新途径。在过去的几年里，我们开发了一套诊断工具，用于高精度测量等离子体护套中的电荷质量比和尘埃颗粒的大小。结合这些方法，可以高精度地确定粒子电荷。这使得在非常低的电子冲击能量（小于10 eV）下测量不同材料的电子粘附系数成为可能。与其他方法相比，该方法的优点是可以测量等离子体中小固体的全部电荷，避免了大固体表面电荷会扩散而使电荷测量模糊的问题。新方法的另一个优点是不依赖于材料的导电性，因此可以对导电和介电材料进行研究。在这个项目中，我们将进行实验来验证理论预测，即不同材料的尘埃颗粒在低压等离子体中电荷不同。•建立了测量两种材料低能电子粘着系数之比的诊断装置。•开发一种方法来测量绝对，能量分辨电子粘附系数的变化等离子体参数和校准与完美的吸收材料。•测试等离子体中非球形粒子充电的“封闭球形外壳”近似。

The charging properties of different materials are widely discussed in the dusty plasma community. They are directly related to the electron sticking coefficient of the particles, which is highly relevant for plasma technology because of its strong impact on the discharge properties of rf driven plasma reactors using different electrode materials. The high precision measurement of the dust charge opens the door to a new method for the determination of low energy electron sticking coefficients. In the last years, we developed a set of diagnostic tools for the high precision measurement of the charge-to-mass-ratio and the size of dust particles in the sheath of a plasma. Combining these methods allows to determine the particle charge with high precision. This makes it possible to measure the electron sticking coefficient for different materials at very low electron impact energies (less than 10 eV). Compared to other methods, the proposed method has the advantage that it measures the full charge of a small solid in a plasma, avoiding the problem that charges on a large solid surface will diffluence and obscure the charge measurement. Another advantage is that the new method does not rely on the electric conductivity of the material, therefore, conductive and dielectric materials canbe investigated.In this project, we will• Perform experiments to verify the theoretical prediction that dust particles of different materials charge up differently in a low pressure plasma.• Set up a diagnostic which measures the ratio of the low energy electron sticking coefficient of two materials.• Develop a method to measure the absolute, energy resolved electron sticking coefficient by a variation of the plasma parameters and calibration with a perfect absorbing material.• Test an ’enclosing spherical hull’ approximation for the charging of nonspherical particles in the plasma.