  Chemically stable quantum-confined 2D metals are of interest in
next-generation nanoscale quantum devices. Bottom-up design and synthesis of
such metals could enable the creation of materials with tailored, on-demand,
electronic and optical properties for applications that utilize tunable
plasmonic coupling, optical non-linearity, epsilon-near-zero behavior, or
wavelength-specific light trapping. In this work, we demonstrate that the
electronic, superconducting and optical properties of air-stable
two-dimensional metals can be controllably tuned by the formation of alloys.
Environmentally robust large-area two-dimensional InxGa1-x alloys are
synthesized by Confinement Heteroepitaxy (CHet). Near-complete solid solubility
is achieved with no evidence of phase segregation, and the composition is
tunable over the full range of x by changing the relative elemental composition
of the precursor. The optical and electronic properties directly correlate with
alloy composition, wherein the dielectric function, band structure,
superconductivity, and charge transfer from the metal to graphene are all
controlled by the indium/gallium ratio in the 2D metal layer.
