  Contact interface properties are important in determining the performances of
devices based on atomically thin two-dimensional (2D) materials, especially
those with short channels. Understanding the contact interface is therefore
quite important to design better devices. Herein, we use scanning transmission
electron microscopy, electron energy loss spectroscopy, and first-principles
calculations to reveal the electronic structures within the metallic
(1T')-semiconducting (2H) MoTe2 coplanar phase boundary across a wide spectral
range and correlate its properties and atomic structure. We find that the
2H-MoTe2 excitonic peaks cross the phase boundary into the 1T' phase within a
range of approximately 150 nm. The 1T'-MoTe2 crystal field can penetrate the
boundary and extend into the 2H phase by approximately two unit cells. The
plasmonic oscillations exhibit strong angle dependence, i.e., a red-shift
(approximately 0.3 eV-1.2 eV) occurs within 4 nm at 1T'/2H-MoTe2 boundaries
with large tilt angles, but there is no shift at zero-tilted boundaries. These
atomic-scale measurements reveal the structure-property relationships of
1T'/2H-MoTe2 boundary, providing useful information for phase boundary
engineering and device development based on 2D materials.
