Thermal decomposition of GaAs (111)A and (111)B surfaces in ultrahigh vacuum results in self-running Ga droplets. Although Ga droplets on the (111)B surface run in one main direction, those on the (111)A surface run in multiple directions, frequently taking sharp turns and swerving around pyramidal etch pits, leaving behind mixed smooth-triangular trails as a result of simultaneous in-plane driving and out-of-plane crystallographic etching. The droplet motion is partially guided by dislocation strain fields. The results hint at the possibilities of using subsurface dislocation network and prepatterned, etched surfaces to control metallic droplet motion on single-crystal semiconductor surfaces.

The nucleation and dynamics of multiple generations of In droplets formed from Langmuir evaporation of InP ( 001), (111)A, and (111)B surfaces are reported. In situ mirror electron microscopy reveals that the majority of first-generation, or mother, droplets break up immediately before they run from the nucleation sites, leaving behind daughter droplets and etch trails where more droplets emerge. These subsequent droplets grow with time and run once a critical size is reached. The breakup and running characteristics are explained in terms of crystallography, viscosity, chemical potential, and temperature and will likely affect the growth processes and designs of various droplet-catalyzed nanostructures and devices.

Articles you may be interested inGrowth by molecular beam epitaxy of self-assembled InAs quantum dots on InAlAs and InGaAs lattice-matched to InP High-temperature operation of self-assembled Ga In N As ∕ Ga As N quantum-dot lasers grown by solid-source molecular-beam epitaxy Self-assembled InAs quantum-dot ͑QD͒ molecules having high dot density and aligned dot set structure, which is defined by nanotemplates, were realized by thin capping and regrowth technique in a molecular-beam epitaxy process. Thin capping of GaAs on InAs QDs leads to the creation of nanoholes having a camel-like nanostructure due to anisotropic strain fields along the ͓110͔ crystallographic direction and anisotropic surface diffusion accompanying the QD collapse. Regrowth of InAs QDs on the nanohole templates initially results in the formation of QDs with good size uniformity in the middle of features with the shape of propeller blades. This takes place at the regrowth thickness of 0.6 monolayer ͑ML͒. The strain at propellers' edge starts to play its role, creating sets of quantum dots surrounding the initial and centered dots at the regrowth thickness of 1.2 ML. The elongated configuration of propellers' blades defines the pattern of QD sets having five to six dots on each side. The dot density of the QD molecules is 3 ϫ 10 10 cm −2 , one order of magnitude higher than that of initial dot density ͑2 ϫ 10 9 cm −2 ͒.

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