Selective functionalization of carbon nanotubes based upon distance traveled

Method and system for functionalizing a collection of carbon nanotubes (CNTs). A selected precursor gas (e.g., H.sub.2 or NH.sub.3 or NF.sub.3 or F.sub.2 or CF.sub.4 or C.sub.nH.sub.m) is irradiated to provide a cold plasma of selected target particles, such as atomic H or F, in a first chamber. The target particles are directed toward an array of CNTs located in a second chamber while suppressing transport of ultraviolet radiation to the second chamber. A CNT array is functionalized with the target particles, at or below room temperature, to a point of saturation, in an exposure time interval no longer than about 30 sec. The predominant species that are deposited on the CNT array vary with the distance d measured along a path from the precursor gas to the CNT array; two or three different predominant species can be deposited on a CNT array for distances d=d1 and d=d2>d1 and d=d3>d2.