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SmB₆ nanowires, as a prototype of nanostructured topological Kondo insulator, have shown rich novel physical phenomena relating to their surface. Catalyst-assisted chemical vapor deposition (CVD) is a common approach to prepare SmB₆ nanowires and Ni is the most popular catalyst used to initiate the growth of SmB₆ nanowires. Here, we study the effect of growth mechanism on the surface of SmB₆ nanowires synthesized by CVD. Two types of SmB₆ nanowires are obtained when using Ni as the catalyst. In addition to pure SmB₆ nanowires without Ni impurity, a small amount of Ni is detected on the surface of some SmB₆ nanowires by element analysis with transmission electron microscopy. In order to eliminate the possible distribution of Ni on nanowire surface, we synthesize single crystalline SmB₆ nanowires by CVD without using catalyst. The difference between catalyst-assisted and catalyst-free growth mechanism is discussed.