Carbon nanotips were grown on a silicon substrate without catalyst by plasma-enhanced hot filament chemical vapor deposition using a mixture of methane, ammonia and hydrogen as the reaction gases. Due to production of plasma during growing the carbon nanotips, the reaction gases were ionized into various kinds of ions and these ions played different roles in the process of growing the carbon nanotips. Based on different effects of the ions and combined with theory related to plasma, a model of the self-organized carbon nanotips without catalyst was put forward. © 2004 Elsevier B.V. All rights reserved.