Bi-stability of contact angle and its role in tuning the morphology of self-assisted GaAs nanowires

We demonstrate the existence of two stable contact angles for the gallium droplet on top of self-assisted GaAs nanowires grown by MBE on patterned silicon substrates. Contact angle around 130
^ο
features a continuous increase in the nanowire radius, while 90
^ο
allows for the nanowire thinning, followed by the stable growth of ultra-thin tops. We develop a model that explains the observed morphological evolution under the two different scenarios.