Model and experimental evidence of heating of nanoparticles in low-pressure silane plasmas*

Recently we developed a nanoparticle-plasma charging-heating model which included the effect of collisions between ions and neutrals in proximity of the particles and showed that for pressures of a few Torr a charge distribution that is less negative than collisionless orbital motion limited theory is obtained. The model also predicted the nanoparticle temperature distribution and morphology (amorphous or crystalline) to be a function of ion density. To support the theory a batch plasma reactor was used to nucleate, grow and crystallize silicon nanoparticles. The nanoparticle size distribution and morphology were characterized using transmission electron microscopy, x ray diffraction and Raman light scattering. Experimental results indeed show a strong correlation between crystallinity and ion density, here measured with time and space resolution using a capacitive probe technique. The use of a simple floating potential probe method is also presented. The probe traces show distinctive features belonging to a nucleation and growth phase and a successive diffusional loss phase. A simple theoretical model is proposed to explain probe measurements as a function of the other plasma properties.