Direct Formation of Layer-Controlled and Selectively Patterned PtSe2 Films by Focused Ion Beam-Assisted Deposition

Platinum diselenide (PtSe2), a noble-metal transition metal dichalcogenide, has attracted increasing attention for next-generation electronics owing to its air stability, thickness-dependent electronic structure, and compatibility with low-temperature processing. However, achieving simultaneous control over crystallinity, thickness, and spatial patterning at back-end-of-line (BEOL)-compatible temperatures remains a major challenge. Here, we report a mask-free and site-selective strategy for the direct formation of patterned few-layer PtSe2 films by combining focused-ion-beam (FIB) deposition of a Pt precursor with subsequent low-temperature selenization. The FIB process enables deterministic control of lateral geometry and thickness of the precursor, which is translated into thickness-controlled PtSe2 after conversion. Compared with e beam deposited precursors, the FIB derived Pt rich films form more continuous networks prior to selenization, leading to PtSe2 channels with more linear ID-VD behavior and improved electrical continuity. Structural characterization confirms the formation of layered PtSe2 with polycrystalline stacking and thickness-dependent morphology. Raman spectroscopy reveals systematic evolution of the Eg and A1g modes, consistent with enhanced interlayer coupling in thicker films. Importantly, we observe a strong substrate-dependent behavior in the low-temperature regime. At reduced temperature (200 °C), PtSe2 formation is more pronounced on SiO2/Si substrates, consistent with more efficient nucleation and selenium incorporation on the amorphous oxide surface. At elevated temperature (350 °C), PtSe2 grown on sapphire substrates exhibits sharper Raman features and improved structural ordering together with enhanced electrical characteristics. This behavior is consistent with a transition from nucleation‑limited growth at low temperature to crystallinity‑limited growth at higher temperature, governed by substrate‑dependent growth kinetics rather than a universally superior substrate. Field-effect transistors fabricated from the patterned films exhibit p-type transport behavior, demonstrating electrical continuity of the directly formed PtSe2 channels. This work provides a BEOL-compatible pathway for spatially selective integration of 2D materials and highlights the importance of substrate-dependent growth kinetics in low-temperature 2D material synthesis.