We now consider the influence of the annealing time t a on nanohole morphology at constant temperature T = 650℃. Figure 3a,b shows Ga droplets on a GaAs surface prepared with immediate quenching of the sample after selleck kinase inhibitor droplet deposition (t a= 0). The occurrence

of Ga droplets at temperatures above the GaAs congruent evaporation temperature has already been studied previously [25, 26], but there the droplets were formed by Langmuir evaporation. In the present samples, the droplet density of 1.9 ×106 cm −2 is almost equal to the nanohole density obtained at the same temperature (Figure 2d), which establishes that every initial droplet forms SIS3 a nanohole. These droplets have an average height of 120 nm and average diameter of 470 nm (Figure 3c). This yields an average ratio between the droplet height and its radius of 0.51 ± 0.03 corresponding to a contact angle of 54°. Previous experiments [23] for Al-LDE on AlGaAs yielded a contact angle of 66°, which neither depends on temperature

nor on droplet material coverage. Figure 3 GaAs surface with as-grown droplets. (a) AFM micrograph of a GaAs surface with MG-132 in vitro as-grown droplets after deposition of 2 ML Ga at T = 650℃ without annealing. (b) Color-coded perspective view of a single Ga droplet. (c) Linescans of the droplet from (b). The average contact angle is 54°. At t a= 120 s, all initial Ga droplets have been transformed into nanoholes with walls (Figure 2). This process is called local droplet etching and has already been studied previously [1, 6, 13]. The time during which droplet etching takes place is given by the time up tuclazepam to complete removal of the droplet material. Using a model of the LDE process described in [13], for Ga-LDE at T = 650℃, an etching time of 12 s is predicted. After this time, the droplet material is removed and droplet etching stops. A central result of this work is obtained during long-time annealing at high temperature where the droplet etched holes are observed to widen. Figure 4 shows an example of a sample prepared at t a= 1,800 s. Large holes are visible with an average diameter of

the hole opening of 1,050 nm. The density of these large holes is 1.4 ×106 cm −2, which is almost equal to the density of droplet etched nanoholes obtained for t a= 120 s at the same temperature (Figure 2d). This supports our assumption that the large holes are modifications of the nanoholes drilled by droplet etching. Beyond the widening of the hole diameter, the long-time annealing also substantially modifies the shape of the holes. In detail, the side facet angle of the holes after droplet etching is in the range of 27° to 33°, whereas the average side facet angle of the large holes is about 5°. Furthermore, the bottom part of the inverted cone-like shaped LDE holes is rather peaked, whereas the large widened holes have a flat bottom plane of about 250 nm in diameter (Figure 4c). Finally, no walls are visible around the deep hole openings.