Crystalline surface phases of the liquid Au-Si eutectic alloy

Abstract

A two dimensional crystalline layer is found at the surface of the liquid\neutectic Au$_{82}$Si$_{18}$ alloy above its melting point $T_M=359 ^{\\circ}$C.\nUnderlying this crystalline layer we find a layered structure, 6-7 atomic\nlayers thick. This surface layer undergoes a first-order solid-solid phase\ntransition occurring at $371 ^{\\circ}$C. The crystalline phase observed for\nT$>$371 $^{\\circ}$C is stable up to at least 430 $^{\\circ}$C. Grazing Incidence\nX-ray Diffraction data at T$>$371 $^{\\circ}$C imply lateral order comprising\ntwo coexisting phases of different oblique unit cells, in stark contrast with\nthe single phase with a rectangular unit cell found for low-temperature\ncrystalline phase $359 ^{\\circ}$C$<T<371 ^{\\circ}$C.\n