  Heterostructures increasingly attracted attention over the past several years
to enable various optoelectronic and photonic applications. In this work,
atomically thin interfaces of Ir/Al2O3 heterostructures compatible with
micro-optoelectronic technologies are reported. Their structural and optical
properties were determined by spectroscopic and microscopic techniques (XRR,
XPS, HRTEM, spectroscopic ellipsometry, and UV/VIS/NIR spectrophotometry). The
XRR and HRTEM analyses reveal a layer-by-layer growth mechanism of Ir in atomic
scale heterostructures, which is different from the typical island-type growth
of metals on dielectrics. Alongside, XPS investigations imply the formation of
Ir-O-Al bonding at the interfaces for lower Ir concentrations, in contrast to
the nanoparticle core-shell structure formation. Precisely tuning the ratio of
the constituents ensures the control of the dispersion profile along with a
transition from effective dielectric to metallic heterostructures. The Ir
coating thickness was varied ranging from a few {\AA} to films of about 7 nm in
the heterostructures. The transition has been observed in the structures
containing individual Ir coating thicknesses of about 2-4 nm. Following this,
show epsilon-near-zero metamaterials with tunable dielectric constants by
precisely varying the composition of such heterostructures. Overall, a
comprehensive study on structural and optical properties of the
metal-dielectric interface of Ir/Al2O3 heterostructures was addressed
indicating an extension of the material portfolio available for optical system
design.
