Mechanisms of Ti nanocluster formation by inert gas condensation

The mechanisms involved in the formation of titanium (Ti) nanoclusters produced by sputtering and inert gas condensation were investigated experimentally and numerically. Ti nanoclusters were generated inside an ultrahigh vacuum compatible system under different source parameters, i.e., inert gas flow rate (f(Ar)), length of the aggregation region (L), and sputtering discharge power (P). Nanocluster size and yield were measured using a quadrupole mass filter (QMF). The variation of the above source parameters enabled fine-tuning of the nanocluster size and yield. Herein, Ti nanoclusters were produced within the size range 3.0-10.0 nm. The combination between the nanocluster size and yield as a function of source parameters enabled understanding Ti nanocluster formation mechanisms, i.e., three-body and two-body collisions. The results show that two-body collisions dominate nanocluster production at low f(Ar) while the three-body collisions dominate at high f(Ar). In addition, nanocluster size increases as L increases due to the increase in nanocluster nucleation and growth times. The maximum nanocluster yield was obtained at f(Ar) that maximize the probability of three-body and two-body collisions. Nanoclusters could be produced within an optimum range of the sputtering discharge power wherein the nanocluster size and yield increase with increasing the discharge power as a result of increasing the amount of sputtered material. The experimental results were compared with a theoretical model of nanocluster formation via three-body collision. Detailed understanding of the evolution of size and yield of Ti (and Ti-oxide) nanoclusters is essential for producing nanoclusters that can be utilized for environmental applications such as conversion of carbon dioxide and water vapor into hydrocarbons.