  Ionic liquids provide versatile pathways for controlling the structures and
properties of quantum materials. Previous studies have reported electrostatic
gating of nanometre-thick flakes leading to emergent superconductivity,
insertion or extraction of protons and oxygen ions in perovskite oxide films
enabling the control of different phases and material properties, and
intercalation of large-sized organic cations into layered crystals giving
access to tailored superconductivity. Here, we report an ionic-liquid gating
method to form three-dimensional transition metal monochalcogenides (TMMCs) by
driving the metals dissolved from layered transition metal dichalcogenides
(TMDCs) into the van der Waals gap. We demonstrate the successful
self-intercalation of PdTe$_2$ and NiTe$_2$, turning them into high-quality
PdTe and NiTe single crystals, respectively. Moreover, the monochalcogenides
exhibit distinctive properties from dichalcogenides. For instance, the
self-intercalation of PdTe$_2$ leads to the emergence of superconductivity in
PdTe. Our work provides a synthesis pathway for TMMCs by means of ionic liquid
gating driven self-intercalation.
