Mechanisms of size-dependent shape evolution of one-dimensional nanostructure growth

The size-dependent morphological evolution of one-dimensional (1D) $\mathrm{Sn}{\mathrm{O}}_2$ nanostructures has been observed in experiment. It was found that the shape formations of nanowire and nanobelt of $\mathrm{Sn}{\mathrm{O}}_2$ are size dependent, i.e., the wire is favorable when the size is less than $90\mathrm{nm}$ and the belt is favorable when the size more than $90\mathrm{nm}$, respectively, indicating that a critical size exists in the growth of $\mathrm{Sn}{\mathrm{O}}_2$ nanostructures to determine their morphologies. The nucleation thermodynamics, growth kinetics, and morphological transition thermodynamics were established to elucidate the size-dependent morphological evolution. The theoretical predictions are consistent with experiments, suggesting that the thermodynamic driving force seems to be the physical origin of the shape evolution.

Figure 1

(a) Low-magnifying FESEM image of $\mathrm{Sn}{\mathrm{O}}_2$ nanowires and nanobelts. (b) High-magnifying FESEM image of a nanowire, in which a corresponding HRTEM image and SAD are shown below left right, respectively. (c) High-magnifying FESEM image of a nanobelt (the white line contrast on the nanobelt is another nanobelt whose wider plane of the cross-section inclines extremely towards left inside so as to seem thinner than the practical size), in which a corresponding HRTEM image and SAD are shown below left right, respectively. (d) The SEM statistics result of the radial size distribution of nanowires and nanobelts in the total prepared 1D nanostructures.

Figure 2

The nucleation energies of a column-shape nucleus of nanowires and a rectangle-shape nucleus of nanobelts growing along the [211] and the [301] directions, respectively.

Figure 3

(a) The growth mechanism sketch map of the 1D nanostructure (the radial cross section of the nanowire or nanobelt is shown here). (b) The growth rates of nanowire and nanobelt.

Figure 4

Dependence of the Gibbs free energy of the shape transition during the initial stage of the nuclei growth. (a) The shape transition from the wire nuclei to the belt nuclei that grows along the [211] direction on the radial size of the nanowires nuclei under conditions of $d_1=150$, 175, and $200\mathrm{nm}$, respectively, and $L_1=12\mathrm{nm}$. (b) The shape transition from the wire nuclei to the belt nuclei that growing along the [301] direction on the radial size of a nanowires nuclei under conditions of $d_1=150$, 175, and $200\mathrm{nm}$, respectively, and $L_1=12\mathrm{nm}$.