Optical Trajectory of the Insulator-to-metal Transition of Ultra-thin Gold Films

TL;DR

This study uses interferometric picometrology to track the optical properties of ultra-thin gold films as they transition from insulator to metal, revealing three distinct regimes in their dielectric behavior.

Contribution

It provides a detailed optical characterization of gold films from 0.2 nm to 10 nm, uncovering the insulator-to-metal transition through complex refractive index analysis.

Findings

Identified three regimes in the dielectric constant trajectory.

Observed a circular trajectory consistent with the Drude model.

Revealed the atom-to-bulk transition of gold from optical measurements.

Abstract

We apply interferometric picometrology to measure the complex refractive index and dielectric properties of ultra-thin gold films as a continuous function of thickness from 0.2 nm to 10 nm deposited on thermal oxide on silicon. Three distinct regimes are found for the dielectric constant trajectory in the complex plane. The first regime shows a circular trajectory predicted by the Drude equation tracing the gold bulk-to-thin film transition. The second and third regimes are manifested as metal clusters range from large to small size and sparse coverage. The entire atom-to-bulk transition of gold is revealed from the optical perspective.