Large Reaction Rate Enhancement in Formation of Ultrathin AuSi Eutectic Layers

Abstract

Metal-semiconductor eutectic liquids play a key role in both the fundamental understanding of atomic interactions and nanoscale synthesis and catalysis. At reduced sizes they exhibit properties distinct from the bulk. In this work we show an unusual effect that the formation of AuSi eutectic liquid layers is much easier for smaller thicknesses. The alloying reaction rate is enhanced by over 20 times when the thickness is reduced from 300 to 20 nm. The strong enhancement is attributed to a strain-induced increase in the chemical potential of the solid layer prior to the alloying reaction.

Degradation of the charge collection efficiency of an n-type Fz silicon diode subjected to MeV proton irradiation

“…In this paper, we report on a morphological investigation, which provides results in excellent agreement with those reported in [1] and extend the analysis to a differently oriented substrate.…”

“…3). In the former case, transmission electron microscopy analysis reported in [1] reveals that surface squares are the bases of inverted pyramids embedded in the silicon wafer with the four triangular sides lying along the In order to complete the validation of the model, we carried out a microPIXE and microRBS analysis of circular structures in order to map the elemental distribution of gold. The sample results from the annealing at 600°C for 7 minutes of 50 nm gold layer deposited on the native oxide of a (100) oriented silicon substrate.…”

“…A model has been recently proposed in [1], where the formation of such circular structures is attributed to the interdiffusion of gold and silicon through holes in the native oxide induced by the weakening of the amorphous silica matrix occurring during the annealing process. The rupture of the liquid Au/Si eutectic disc surrounding the pinhole in the oxide causes the debris to be pulled to the edges of the disk, forming Au droplets around it and leaving an empty zone of bare silicon oxide.…”

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AbstractWhen a thin gold layer is deposited onto the native oxide of a silicon wafer and is annealed at temperatures greater than 600°C, peculiar circular features, few micrometers in diameter, with a regular polygon at the centre of each circle, reminiscent of so called "alien" crop circles, can be observed.A model has been recently proposed in [1], where the formation of such circular structures is attributed to the interdiffusion of gold and silicon through holes in the native oxide induced by the weakening of the amorphous silica matrix occurring during the annealing process. The rupture of the liquid Au/Si eutectic disc surrounding the pinhole in the oxide causes the debris to be pulled to the edges of the disk, forming Au droplets around it and leaving an empty zone of bare silicon oxide.

In this paper, we present a morphological study and a RBS/PIXE analyses of these circular structures, carried out by scanning electron microscopy and by 4 MeV C microbeam, respectively.

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“…In a recent paper [1], a systematic investigation on the role of the annealing temperature and of the Au layer thickness allowed the formation mechanism of these circular nano-structures to be properly modelled: the opening of narrow channels in the native oxide induces the formation of a liquid AuSi eutectic layer with a thickness determined by the thickness of the deposited Au film. The central polygons occur in correspondence of the oxide channel openings and represent regions filled with a AuSi alloy which, during cooling, segregated into pure Au and Si.…”