As performance of
van der Waals heterostructure devices
is governed
by the nanoscale thicknesses and homogeneity of their constituent
mono- to few-layer flakes, accurate mapping of these properties with
high lateral resolution becomes imperative. Spectroscopic ellipsometry
is a promising optical technique for such atomically thin-film characterization
due to its simplicity, noninvasive nature and high accuracy. However,
the effective use of standard ellipsometry methods on exfoliated micron-scale
flakes is inhibited by their tens-of-microns lateral resolution or
slow data acquisition. In this work, we demonstrate a Fourier imaging
spectroscopic micro-ellipsometry method with sub-5 μm lateral
resolution and three orders-of-magnitude faster data acquisition than
similar-resolution ellipsometers. Simultaneous recording of spectroscopic
ellipsometry information at multiple angles results in a highly sensitive
system, which is used for performing angstrom-level accurate and consistent
thickness mapping on exfoliated mono-, bi- and trilayers of graphene,
hexagonal boron nitride (hBN) and transition metal dichalcogenide
(MoS2, WS2, MoSe2, WSe2) flakes. The system can successfully identify highly transparent
monolayer hBN, a challenging proposition for other characterization
tools. The optical microscope integrated ellipsometer can also map
minute thickness variations over a micron-scale flake, revealing its
lateral inhomogeneity. The prospect of adding standard optical elements
to augment generic optical imaging and spectroscopy setups with accuratein situellipsometric mapping capability presents potential
opportunities for investigation of exfoliated 2D materials.