u201d extend into the next indicating simultaneous growth fig2 d therefore the nanotube structure is clearly not simply aggregates of gold nanoshells furthermore the apparent one dimensional or linear structure is inconsistent with randomly aggregated structures that tend to be three dimensional the linear structure suggests that something is directing the formation of the nanotube structure in an ordered manner one possible clue to explaining the formation of the au nanotubes comes from the magnetic property of the seeding co nanparticles and the application of an external magnetic field to drive a magnetic stir bar during synthesis to test this we then intentionally examined the effect of an external magnetic field on the synthesis process and the final product we have found that the magnetic field has a strong influence on the formation of the nanotubes without an external magnetic field we observed little or no nanotube formation this led us to suggest that the mechanism of growth depends on the ordering of the co nanoparticles by a magnetic field the initial finding of nanotubes was the result of an unintended use of a magnetic stir bar and plate that uses a strong magnetic field that caused alignment of the co nanoparticles even though co nanoparticles are magnetic and could align by themselves this self alignment is apparently insignificant at room temperature when the magnetic field is strong enough the co nanoparticles align into chains along the field lines by the applied external magnetic field as illustrated in fig2 reduction of au salt into au metal with these aligned co chains resulted in the formation of the au nanotube.