Atomically thin semiconducting transition metal dichalcogenides (TMDs) offer tunable optoelectronic properties, making them prime candidates for next-generation electronic and photonic devices. A key challenge is understanding how their electronic structure evolves with thickness, a crucial step toward optimizing device performance. Here, we investigate the layer-dependent work function of $2H$-${\mathrm{Mo}\mathrm{Te}}_2$ nanoflakes using Kelvin probe force microscopy and first-principles calculations down to the monolayer limit. Contrary to earlier theoretical predictions, we experimentally observe a monotonic increase in work function, from 4.73 eV in the bulk to 4.92 eV in the monolayer. This trend correlates with the change in electronic structures below 5 nm, while, beyond this regime, dielectric screening dominates, as captured by nonlinear Thomas-Fermi theory. Our analysis identifies strong out-of-plane interlayer hopping ($t_{\perp }\simeq 0.214\mathrm{eV}$) as a key contributor to the screening behavior. These results reconcile experimental observations with theoretical models, revealing the interplay of quantum confinement and electrostatic screening. These findings provide practical guidance for tailoring band alignment and charge transport in two-dimensional (2D) TMD-based optoelectronic devices.

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• Band gap
• Electrical properties
• Optoelectronics
• Photonics
• 2-dimensional systems
• Layered crystals
• Transition metal dichalcogenides
• Noncontact atomic force microscopy