The indium droplet deposition was calibrated in terms of growth rate, deposition thickness and growth temperature by growing a series of samples at various temperatures of 145°C to 310°C using In-flux in the range of 2.2 to 6.0 × 10−7 mbar. Results and discussion Figure 1a is the atomic force microscope (AFM) image of optimal sample showing that the droplets have an average diameter of approximately 70 nm, height of approximately 20 nm and density of approximately 6 × 108 cm−2. We found that 3 ML indium deposition Selleck Compound C grown at 220° with a growth rate of 0.01 ML/s gives uniform droplets suitable for NWs’ growth. Figure 1b shows the 45°-tilted SEM image of InAs NWs grown on HOPG for 20 min. All

the NWs are vertically aligned on the surface without tapering, i.e. highly uniform diameter along the entire length. The NWs also have a Selleckchem ARN-509 homogeneous diameter distribution with a hexagonal cross-section, and no metal droplets are present on the top of the NWs. The CRT0066101 average diameter, length and number density of the NWs are 78 ± 5 nm, 0.82 ± 0.28 μm and approximately 4 × 108 cm−2 respectively. The SEM image also shows that parasitic InAs islands were formed on the surface during growth.

Based on an estimate from large-area SEM images, the InAs islands cover 38% of the surface. As the areal coverage of NWs is approximately 2%, almost 60% of the surface remains bare. As growths on graphite without indium droplets led to NWs with a density one order of magnitude lower than that with droplets, we assume that droplets activate the growth of NWs. Figure 1 AFM image of pre-calibrated In droplets and SEM image of grown InAs NWs. A 1 × 1 μm AFM image of pre-calibrated indium droplets grown at optimal conditions (a) and 45°-tilted SEM image of InAs NWs grown for 20 min on (b) graphite and Si (111) (c). The scale bar is 400 nm. The vertical alignment of the NWs is due to the low surface Resveratrol energy along the (111) orientation. The morphological

parameters of the resulting NWs are similar to those of GaAs NWs on graphite by MBE [6]. However, in comparison with MOCVD grown InAs NWs on graphite (diameter of approximately 42 nm [2] and 30 nm [4] with a density of 6 to 7 × 108 cm−2), our MBE-grown InAs NWs are doubled in diameter with half the density. This is probably because of the non-requirement of activation and dissociation at the surface during the growth in MBE leading to longer surface diffusion of the adatoms, resulting in larger diameter and lower density [26]. In addition, the absence of surface dangling bonds on the graphite surface gives rise to van der Waals epitaxy which is proposed to be different from general Frank-van der Merwe growth mode in MBE (layer-by-layer growth). In order to understand this effect, a few samples of InAs NWs were grown on Si (111) under identical growth conditions. These led to repeatable NWs as shown in SEM image (Figure 1c) for typical resulting NWs.