Fig. 1: Nanoscale solid-state intercalation of vdW crystals and pristine heterostructures.

a Schematic of depositing Fe precursors onto 2H–TaS₂ crystals on SiO₂/Si support followed by vacuum annealing to yield Fe-intercalated 2H–TaS₂ (Fe_xTaS₂). High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) atomic-resolution images along the \([10\overline{1}0]\) zone axis of 2H–TaS₂ flakes labeled S1 and S3 immersed in Fe(CO)₅/acetone for 24 hours at 48 °C and subsequently vacuum annealed at 100 °C for 12 hours (S1) (b) and 350 °C for 30 minutes (S3) (c). Micrographs are overlaid with the structure of 2H–TaS₂ (ref. ⁷¹). Intercalants are marked in (c). The thickness of flakes S1, S2, and S3 are 12 nm, 7.8 nm, and 23 nm, respectively. Scale bars in (b, c): 1 nm. d Cumulative electron energy loss (EEL) spectra of 2H–TaS₂ flakes labeled S1–S3 treated in Fe(CO)₅/acetone and vacuum annealed with distinct thermal conditions. Spectra are normalized by total acquisition time. e Cumulative EEL spectra of flake S3 and the composite Fe_xC_yO_z that formed during the Fe(CO)₅/acetone treatment. Experimental spectra, normalized by the L₃ peak maxima, are overlaid with literature spectra for (Fe²⁺)TiO₃²⁹ and \({({{{\rm{Fe}}}}^{3+})}_{2}{{{\rm{TiO}}}}_{5}\)²⁹. Data in (d) and (e) was obtained at  ~ 100 K. f High-resolution STEM micrograph of a 2H–TaS₂ flake that was partially capped with hexagonal boron nitride (hBN), treated with Fe(CO)₅/isopropanol, and vacuum annealed at 350 °C for 1.5 hours. Scale bar: 2 nm. g Schematic of the thermally activated reaction between hBN/2H–TaS₂ and Fe_xC_yO_z.