  The field of two-dimensional (2D) materials has expanded to multilayered
systems where electronic, optical, and mechanical properties change-often
dramatically-with stacking order, thickness, twist, and interlayer spacing
[1-5]. For transition metal dichalcogenides (TMDs), bond coordination within a
single van der Waals layer changes the out-of-plane symmetry that can cause
metal-insulator transitions [1, 6] or emergent quantum behavior [7]. Discerning
these structural order parameters is often difficult using real-space
measurements, however, we show 2D materials have distinct, conspicuous
three-dimensional (3D) structure in reciprocal space described by near infinite
oscillating Bragg rods. Combining electron diffraction and specimen tilt we
probe Bragg rods in all three dimensions to identify multilayer structure with
sub-Angstrom precision across several 2D materials-including TMDs (MoS2, TaSe2,
TaS2) and multilayer graphene. We demonstrate quantitative determination of key
structural parameters such as surface roughness, inter- & intra-layer spacings,
stacking order, and interlayer twist using a rudimentary transmission electron
microscope (TEM). We accurately characterize the full interlayer stacking order
of multilayer graphene (1-, 2-, 6-, 12-layers) as well the intralayer structure
of MoS2 and extract a chalcogen-chalcogen layer spacing of 3.07 +/- 0.11
Angstrom. Furthermore, we demonstrate quick identification of multilayer
rhombohedral graphene.
