LICVD法纳米硅制备过程中的成核及生长

自行设计制备了激光诱导化学气相沉积法(LICVD)纳米制粉装置,利用该装置制备的纳米硅粉其粒度波动在30～60nm之间.通过对不同反应气体流量条件下的激光能量阈值研究表明,随反应气体流量的增加,所需激光能量阈值大致成线性增加.利用透射电镜和高分辨电镜对其形貌进行了表征,并对其成核与生长进行了分析,在成核长大初期,晶核周围的Si原子浓度较高,纳米硅晶应以层状长大方式为主.当纳米晶中有螺型位错等晶体缺陷形成时,会为Si原子的"落座"提供生长所需的台阶源,晶粒将以螺旋状生长方式长大.在长大过程中,纳米晶会发生跳跃式长大现象.以跳跃方式长大的晶粒通常在两晶粒的结合面处伴有晶体缺陷发生或亚晶界产生.较低的反应气体流速条件下,纳米硅的择优生长方向为<112>晶向;而在较高的反应气体流速条件下其择优生长方向变为<111>晶向.

Growth and Nucleation of Silicon Nano-particle in LICVD Preparation

Silicon nano-powder was prepared by self-designed and made LICVD nano-powder equipment. The particle size is 30-60nm. Laser energy threshold with different gas flux was studied, which indicated that if the content of SiH_4 keeps constant, the laser energy threshold increases linearly with the increase of reactive gas flux. The microstructure of the powder was studied by TEM and HREM. The growth and nucleation of nano-powder was examined. The analysis of dynamics of nucleation and growth indicated that at the beginning the main growing mode of nano-crystal is laminar. When the helix dislocation formed in nano-crystal, step resources required for Si atoms' growth can be supplied and crystal grains grow up by the way of helix. During growing process, the nano-crystal might grow with jumping mode and crystal defect and some sub-crystal boundaries would emerge in the combined face of grains. The crystal orientation of nano-silicon is <112> at the lower reaction gas flux and <111> at the higher flux.