Fig. 1: 2D iontronic thermometer based on ABP₂X₆-gated MoS₂ field effect transistor (FET).

a,b, A schematic (a) and false-coloured angled SEM image (b) of a dual-gated 2D FET incorporating LiInP₂S₆ as the top-gate dielectric, monolayer MoS₂ as the semiconducting channel and 25 nm Al₂O₃ as the back-gate dielectric. c, An AFM image of an exfoliated LiInP₂S₆ flake with a measured thickness of ~70 nm. d, The top view of the ABP₂X₆ crystal structure, where A represents Li, Cu, Ag and so on; B corresponds to In, Sc and similar elements; P stands for phosphorus in the ABP₂X₆ family; and X denotes chalcogens such as S and Se. e, The XRD pattern of LiInP₂S₆ crystals confirms phase purity with no secondary phases. f, The SEM combined with EDS verifies the presence of LiInP₂S₆ constituents, except Li, which is undetectable by EDS. g, XPS spectra of exfoliated LiInP₂S₆ display a Li 1s peak at ~55.2 eV, confirming its ionic state, along with dominant In²⁺ signals and minor In³⁺ contributions due to surface oxidation.