  CVD growth is capable of producing multiple single crystal islands of
atomically thin TMDs over large area substrates, with potential control of
their morphology, lateral size, and epitaxial alignment to substrates with
hexagonal symmetry. Subsequent merging of epitaxial domains can lead to
single-crystal monolayer sheets - a step towards scalable production of high
quality TMDs. For CVD growth to be effectively used for such production it is
necessary to be able to rapidly assess the quality of material across entire
large area substrates. To date characterisation has been limited to sub 0.1 mm2
areas, where the properties measured are not necessarily representative of an
entire sample. Here, we apply photoluminescence (PL) imaging and computer
vision techniques to create an automated analysis for large area samples of
semiconducting TMDs, measuring the properties of island size, density of
islands, relative PL intensity and homogeneity, and orientation of triangular
domains. The analysis is applied to 20x magnification optical microscopy images
that completely map samples of WSe2 on hBN, 5.0 mm x 5.0 mm in size, and
MoSe2-WS2 on SiO2/Si, 11.2 mm x 5.8 mm in size. For the latter sample 100,245
objects were identified and their properties measured, with an orientation
extracted from 27,779 objects that displayed a triangular morphology. In the
substrates studied, two prevailing orientations of epitaxial growth were
observed in WSe2 grown on hBN and four predominant orientations were observed
in MoSe2, initially grown on c-plane sapphire. The proposed analysis will
greatly reduce the time needed to study freshly synthesised material over large
area substrates and provide feedback to optimise growth conditions, advancing
techniques to produce high quality TMD monolayer sheets for commercial
applications.
