Synchronous growth of vertically aligned carbon nanotubes with pristine stress in the heterogeneous catalysis process

The formation of a vertically aligned carbon nanotube (VA-CNT) array in a floating catalyst process was described as a synchronous growth that resulted from the interaction of fast growth and slow growth CNTs. The array growth was characterized by the observations that straight and curved CNTs were formed during growth, and the tortuosity change of the curved CNTs and a G band Raman shift during growth. These were used to deduce that pristine stress was present in the CNTs. A model of the stresses as caused by space limitation and different growth rates was used to explain the development of a synchronous growth of the VA-CNT array. The tortuosity of the curved CNTs and Raman shift decreased and were constant after the growth of a certain length of the array, indicating that constant stresses were maintained in the growing array after the growth of this length. This indicated that an ordered CNT structure was formed and a transition from random structure to ordered structure growth had taken place in the growth. The transition was explained by a thermodynamic argument using the Onsager virial theory. Based on the vapor-liquid-solid model and bottom up growth for a single CNT, the description of a synchronous growth made possible by existent stresses gives a view that accounts for the interaction between CNTs in an array, and it can provide guidelines for a more precise control of the array structure.