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

不同材料的电荷性质在尘埃等离子体领域得到了广泛的讨论。它们与粒子的电子附着系数直接相关，与等离子体技术高度相关，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特性有很大的影响。尘埃电荷的高精度测量为低能电子粘着系数的测定开辟了一条新的途径。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鞘中的荷质比和尘埃粒子的大小。将这些方法结合起来，可以高精度地确定粒子的电荷。这使得在非常低的电子碰撞能(小于10 eV)下测量不同材料的电子粘着系数成为可能。与其他方法相比，该方法的优点是测量等离子体中小固体的全部电荷，避免了大固体表面上的电荷分流和遮蔽电荷测量的问题。另一个优点是，新方法不依赖于材料的导电性，因此可以研究导电和介电材料。在这个项目中，我们将·进行实验，以验证理论预测，即不同材料的尘埃颗粒在低压等离子体中充电不同。·建立一个诊断程序，测量两种材料的低能电子粘连系数的比率。·开发一种方法，通过改变等离子体参数并用理想的吸收材料校准来测量绝对的、能量分辨的电子粘合系数。·测试非球形颗粒在等离子体中带电的‘封闭球壳’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.