# Molecular sp3‑like Reactivity of Metastable Au4Si near Its Deep Eutectic Point Enables Low-Temperature SiC Formation

## TL;DR

A metastable Au4Si compound near its eutectic point shows molecule-like reactivity, enabling SiC formation at low temperatures.

## Contribution

Demonstrates that metastable Au–Si configurations can enable Si–C bonding at low temperatures through sp3-like reactivity.

## Key findings

- Au–Si species react with carbon clusters to form SiC at 636 K, while elemental Si remains inert.
- SiC formation occurs only within a narrow temperature window around the eutectic point.
- The reaction mechanism differs from conventional catalytic or vapor–liquid–solid processes.

## Abstract

Metastable states
near deep eutectic points are typically
regarded
as transient intermediates preceding phase separation, yet their potential
chemical reactivity remains largely unexplored. Here, we demonstrate
that metastable Au–Si bonding configurations derived from Au4Si near its deep eutectic temperature exhibit molecule-like
reactivity associated with an sp3-like local bonding environment,
enabling direct Si–C bond formation at temperatures as low
as 636 K. Using a high-vacuum coevaporation platform, Au–Si
species generated during coevaporation react with carbon clusters
to produce SiC accompanied by Au segregation, whereas elemental Si
under identical conditions remains chemically inert. Raman spectroscopy
and X-ray photoelectron spectroscopy reveal that SiC formation occurs
only within a narrow temperature window centered at the eutectic point
and displays nonmonotonic temperature dependence inconsistent with
conventional catalytic or vapor–liquid–solid mechanisms.
These results provide experimental evidence that eutectic metastable
bonding configurations can transiently adopt molecule-like characteristics,
thereby enabling unconventional low-temperature reaction pathways
in metal–semiconductor systems.