  Strain is a powerful tool to modify the optical properties of semiconducting
transition metal dichalcogenides like MoS2, MoSe2, WS2 and WSe2. In this work
we provide a thorough description of the technical details to perform uniaxial
strain measurements on these two-dimensional semiconductors and we provide a
straightforward calibration method to determine the amount of applied strain
with high accuracy. We then employ reflectance spectroscopy to analyze the
strain tunability of the electronic properties of single-, bi- and tri-layer
MoS2, MoSe2, WS2 and WSe2. Finally, we quantify the flake-to-flake variability
by analyzing 15 different single-layer MoS2 flakes.
