Fig. 1a and b shows FE-SEM images of droplets formed by the deposition of 20 and 40 nm layers of Indium on Si/SiO2 at 210 °C, respectively. As expected, the thinner layer formed smaller droplets and exhibited a more spherical appearance. The number of droplets per unit area for the 20 nm Indium layer was 4.8 μm−2, which was almost 1.5 times higher than that BML-190 for the 40 nm layer (3.3 μm−2).
Fig. 1. SEM images of (a) 20 nm and (b) 40 nm In layers deposited on Si/SiO2 at 210 °C.Figure optionsDownload full-size imageDownload as PowerPoint slide
The small liquid Indium droplets acted as seeds and played a significant role in the VLS mechanism. However, under the relatively low temperatures used in the process, the additional Indium deposited during the growth was very important for determining the formation of the nanowires. In order to confirm this fact, a deposition of ITO with the catalyst layer was conducted during 60 min, without the additional Indium deposition, and the obtained structure is shown in Fig. 2a. This deposition produced short and thick nanorods, which are much different from the expected nanowires (Fig. 2b). The morphology and dimensions of these nanorods suggest sarcomeres are not suitable for Raman signal intensification.