Self-organized carbon nanotubes grown at the grain boundary of iron-nitride

Chemical vapor deposition of carbon nanotubes (CNTs) is the most promising method for fabricating CNTs based nanodevices [1] and sensors [2] because CNTs can be selectively grown by structuring the catalyst in a predefined arrangement. However, only dense aligned CNTs can be produced using transition metal catalysts (Fe, Co, and Ni) by plasma-enhanced chemical vapor deposition (PECVD) [3]. It is well known that electric field shielding effects from closely packed arrays of nanotubes adversely affect their field emission characteristics [3] and [4]. Therefore, it is desirable to control the density of CNTs so as to reduce the electric field shielding effect from adjacent CNTs. Although the density of CNTs can be controlled by various patterning technologies [3], [4] and [5], it is still crucial to develop self-organizing techniques that do not require any pre-patterning for the growth of CNT arrays. In addition, it has been found that the nucleation and growth of CNTs may be significantly enhanced by introducing N2 or NH3 in the CVD process [6]. Although the mechanism of the enhanced CNT growth in N2/NH3 environment is not yet clear, nitriding the catalyst surface seems to play an important role in CNT growth [7] and [8]. In this work, we show that aligned CNTs are preferably grown at the grain boundaries of iron nitride (Fe–N) films. This simple growth technique may lead to the development of controllable self-assembled CNT arrays for electron emitter and sensor applications.