Meanwhile, the growth of nanowires via the VLS mechanism

competes with the counter growth of interfacial thin layer via the VS mechanism. Generally, the VS mechanism is simple as compared to the VLS mechanism, which involves three phases and two interfaces [26, 27]. Thus, the activation Temsirolimus chemical structure energy for the VS mechanism is lower than that for the VLS mechanism and thus could initiate earlier. This interfacial layer interrupts the epitaxial relationship between the nanowires and the substrate, Z-IETD-FMK purchase as this layer is polycrystalline and thus has a surface with various crystalline directions. This results in the random growth of GaN nanowires, as shown in Figure 1a. Figure 1b shows the nanowires grown by Au-Ni bi-metal catalysts. It shows the vertical growth of nanowires. Figure 1d shows the interfaces between the nanowires and the substrate click here without the interfacial layer. That is, the GaN nanowires grow directly from the substrate.

The result indicates that Au has a critical role in preventing the formation of the interfacial layer, thereby enabling the epitaxial vertical growth of GaN nanowires. The inset of Figure 1d shows the end of nanowires grown by the Au/Ni catalyst. It shows the metal globule at the end of nanowires and clearly indicates that the nanowires are grown by the catalyst via VLS mechanism. The diameter and length of nanowires were 80 to 100 nm and several hundred micrometers, respectively. One of the possible explanations of the role of Au in the vertical growth of nanowires is its ability to lower the liquid formation temperature as well as the activation energy of the VLS mechanism that leads to the growth of

nanowires on the substrate prior to the deposition of the interfacial layer. It is well known that the liquidus temperature of the multicomponent metal system decreases with the number of components. In this regard, the addition of Au to Ni should decrease the liquidus temperature of the Au-Ni-Ga system as compared to that of Nitroxoline the Ni-Ga system and can thus lead to the growth of nanowires via the VLS mechanism at low temperature, prior to the VS deposition of the interfacial layer [23, 25]. Based on these results, the growth processes of random growth and vertical growth GaN nanowires can be outlined in Figure 1e, f, respectively. In the case of random growth, the GaN interfacial layers are first deposited on the substrate, after which, the catalyst is reassembled on the interfacial layer; finally, the GaN nanowires randomly grow on the interfacial layer by the VLS mechanism. In the case of vertical growth, the Au/Ni catalyst works before the deposition of the interfacial layer, and the GaN nanowires vertically grow on the substrate. Figure 2a, b shows the TEM images of an individual nanowire. The TEM analysis also shows that the nanowires are single crystalline without defects.