Controlled synthesis of ultra-long AlN nanowires in different densities and in situ investigation of the physical properties of an individual AlN nanowire.

The controlled synthesis of different growth densities of ultra-long AlN nanowires has been successfully realized by nitridation of Al powders for the first time. These AlN nanowires have an average diameter of about 100 nm and their mean length is over 50 μm. All the synthesized ultra-long nanowires are pure single crystalline h-AlN structures with a growth orientation of [0001]. We preferred the self-catalyzing vapor-liquid-solid (VLS) mechanism to illustrate their growth process. Although the sample with the middle growth density (3.2×10(7) per cm2) of AlN nanowire performs the best field emission (FE) properties, the emission uniformity is not good enough for field emission display applications, which may be attributed to their low intrinsic conductivity. Moreover, the electrical transport and FE properties of an individual ultra-long AlN nanowire are further investigated in situ to find the decisive factor responsible for their FE behaviors. An individual AlN nanowire is observed to have a mean 1 nA field of 440 V μm(-1) and 1 μA field of 480 V μm(-1) as well as an average electrical conductivity of about 2.7×10(-4)Ω(-1) cm(-1), which is lower than that of some cathode materials with excellent FE properties. Therefore we come to the conclusion that the electrical conductivity of the AlN nanowire must be improved to a higher level by some effective ways in order to realize their practical FE device applications.