Table 1 The measured electronic band gap, the optical band gap (direct/indirect for bilayer sample) by photoluminescence spectroscopy, and the estimated exciton binding energy of four representative common TMDCs of different thicknesses

MoS₂

monolayer

2.24 ± 0.04

2.11∼2.4^{3,18,24,25,26}

1.891

1.81∼1.9^25,26,27

0.352

0.09∼0.57^{3,25,26,28,29}

bilayer

1.91 ± 0.05

2.1²⁴

1.88/1.60

1.59∼1.6^27,30

0.311

multilayer

1.52 ± 0.03

1.29−1.75^24,31

MoSe₂

monolayer

2.22 ± 0.02

1.9∼2.25^{32,33,34,35,36}

1.575

1.56∼1.657^34,37,38

0.641

0.59³⁴

bilayer

1.66 ± 0.04

1.56∼1.81^33,34

1.57/1.52

1.55^34,37,38

0.142

0.21³⁴

multilayer

1.51 ± 0.04

1.32³³

WS₂

monolayer

2.63 ± 0.05

2.14∼2.73^{18,26,39,40,41}

2.021

2.02∼2.09^40,41

0.611

0.32∼0.71^{26,28,40,41,42}

bilayer

2.21 ± 0.03

1.82∼2.1^39,43

1.99/1.76

1.68∼1.73^40,44

0.45

multilayer

1.77 ± 0.04

1.4∼2.1^40,45

WSe₂

monolayer

2.27 ± 0.06

1.75∼2.39^25,34

1.647

1.61∼1.735^25,34,38,46

0.618

0.14∼0.655^25,34,46,47

bilayer

1.81 ± 0.05

1.83³⁴

1.64/1.43

1.54∼1.605^34,38

0.377

0.23³⁴

multilayer

1.65 ± 0.03