Miao and Zhang Nanoscale Research Letters 2012, 7:321 http://www.nanoscalereslett.com/content/7/1/321 Page 3 of 6 Figure 2 SEM images of InP nanowires grown for 10 min without indium droplet fabrication before nanowire growth. (a) Top-view image. (b) Lateral-view image. provides the initial seed for nanowire growth, is scatter distributed on the substrate and there is large space be- tween the droplets. In the nanowire growing process, the TMIn in these spaces is decomposed and accumu- lates to fabricate indium droplets. These droplets are the seeds for new nanowire growth. By comparing the images of Figure 1, it is found that the density of nanowires had almost no change in the first 3 min. After 5 min, the density obviously increased. This means that the indium droplets take more than 3 min to be fabricated, as the space and the material TMIn for indium droplet fabrication are not as sufficient as the catalyst-fabricating step. Since the density of the nanowires in Figure 2a is quite low, the new nanowires fabricated in the growing process take a limited part in the catalyst-free nanowire growth. The nanowires grown for less than 5 min can hardly be examined by X-ray diffraction as they are too short and their density is so low. As shown in Figure 3, the diffraction peaks of patterns (a) to (c) are all at 26.3°, proving that the nanowires grow along the <111 > dir- ection. As the InP nanowires increase in unit area along with the growing time, the intensity of the diffraction peak rises from (a) to (c). The diffraction peak of the nanowires grown without a catalyst is at 26.3° too, indi- cating that the nanowires fabricated in the growing process are along the <111 > direction. The optical properties of InP nanowires were evalu- ated by PL measurements at room temperature and shown in Figure 4. Nanowires grown for different times have different PL peaks. From traces (a) to (c), the PL in- tensity increases with the increasing time of the nano- wire growth. This is due to the increase in dimension and density of the nanowires. The PL peaks are separ- ately at 1.416, 1.397, and 1.368 eV, corresponding to the growing time of 2, 5, and 7 min, respectively. Compared Figure 3 X-ray powder diffraction pattern of the grown InP nanowires. (a) 5, (b) 7, and (c) 15 min. (d) Nanowires grown for 10 min with no indium droplet fabrication.