Oxygen Trick Yields First Uniform Semiconducting Monolayer PtSe2 Films for Transistors

For more than a decade, the promise of two-dimensional semiconductors has been shadowed by a stubborn manufacturing problem: the best atomically thin materials are notoriously difficult to grow as large, uniform, defect-free films that actual devices can use. Now a research team in South Korea reports a breakthrough that could change that calculus for one of the most intriguing members of the two-dimensional family. Writing in Advanced Science, the researchers describe the first successful growth of a uniform, large-area monolayer of platinum diselenide (PtSe2) using metal-organic chemical vapor deposition, the workhorse technique of industrial chip fabrication. The film spans a 1.5 by 1.5 centimeter substrate, exhibits a clear semiconducting bandgap of roughly 1.5 electron volts, and has already been turned into an array of field-effect transistors that set new performance records for this material class.

The excitement around PtSe2 stems from a remarkable property: its electronic character depends dramatically on how many atomic layers are stacked together. A single layer behaves as a true semiconductor with a bandgap of about 1.2 to 1.5 electron volts. Add a second layer and the gap collapses to roughly 0.3 electron volts; a third layer pushes it below 0.1 electron volts; and by four layers the material has become a semi-metal with no gap at all. This steep transition arises from strong interlayer coupling, and it cuts both ways. On one hand, it means a single material can serve as both the semiconducting channel and the metallic electrode in an all-PtSe2 transistor. On the other, it makes thickness control absolutely unforgiving: even a stray bilayer island in an otherwise monolayer film creates a semi-metallic leak path that would ruin a transistor’s ability to switch off.

That unforgiving requirement is precisely why monolayer PtSe2 has eluded researchers for so long. Earlier attempts using thermally assisted conversion, powder-source chemical vapor deposition, or molecular beam epitaxy produced nonuniform multilayer films, tiny grains of only 10 to 20 nanometers, or multilayer flakes dotted with small monolayer patches. None of these could deliver the precise thickness control and wafer-scale uniformity that transistor manufacturing demands. The new work overcomes this barrier through two clever chemical innovations: a custom-designed platinum precursor and an unexpected growth partner, oxygen gas.

The precursor, Pt(dipivaloylmethane-sulfonate)2, was synthesized specifically for thermal stability, refusing to decompose until temperatures reach approximately 300 degrees Celsius, higher than any other platinum precursor available. That stability matters because in a typical metal-organic deposition process, precursors that break apart too easily in the gas phase release highly reactive fragments that nucleate particles in mid-air, raining uncontrolled defects onto the growing film. By keeping the precursor intact until it reaches the heated substrate, the team suppressed these gas-phase reactions entirely, allowing the film to assemble itself in an orderly, layer-by-layer fashion at a growth temperature of 470 degrees Celsius on muscovite mica substrates.

Oxygen played an equally decisive role, and here the choice of material proved fortuitous. Metal-organic precursors carry organic ligands that, if left behind on the substrate, contaminate the film with amorphous carbon and create unwanted nucleation sites that shrink grain size. Most two-dimensional semiconductors, such as molybdenum disulfide, would be damaged by oxygen during growth, but PtSe2 belongs to the noble-metal dichalcogenides, which possess a high energy barrier to oxygen dissociation and are inherently resistant to oxidation. The researchers exploited this resilience by co-injecting a small, precisely metered flow of oxygen into the growth chamber. The oxygen triggers a combustion reaction that burns the organic ligands into volatile carbon dioxide and water vapor, sweeping them away while leaving the platinum and selenium atoms untouched to form pristine PtSe2.

The spectroscopic evidence for this chemistry is striking. Films grown with oxygen show no Raman signals in the 1300 to 1600 per centimeter range, where carbon’s characteristic D and G bands would appear, while films grown with hydrogen instead of oxygen display both bands, betraying amorphous carbon contamination. X-ray photoelectron spectroscopy reinforced the picture: oxygen-grown films exhibited sharp, symmetric platinum 4f and selenium 3d peaks consistent with a clean, stoichiometric crystal, whereas hydrogen-grown films showed sub-stoichiometric phases and oxidized selenium species, signs that lingering organic residue had interfered with proper bonding. The team also demonstrated that the resulting films are exceptionally stable in air, with Raman peak positions shifting by less than 0.001 percent over seven months of ambient exposure.

Uniformity across the full substrate was verified through a battery of optical and structural measurements. Raman spectroscopy at 36 points across the film found the characteristic in-plane vibrational peak at 181.35 per centimeter, exactly where a monolayer should sit, with a standard deviation of just 0.16 per centimeter, and a narrow peak width indicating few point defects. Ultraviolet-visible absorption confirmed an optical bandgap of approximately 1.5 electron volts, matching theoretical predictions. Atomic force microscopy captured the growth in action: after four hours, triangular grains roughly 100 nanometers across had nucleated simultaneously and grown laterally, with step heights of 0.75 nanometer confirming single-layer thickness; after eight hours, the grains had merged into a fully continuous monolayer. The triangular grains even showed preferential alignment with the six-fold symmetry of the underlying mica, hinting that single-crystalline films may be within reach.

At the atomic scale, high-angle annular dark-field scanning transmission electron microscopy revealed the textbook 1T crystal structure, with each platinum atom coordinated by six selenium atoms and all three atomic sublayers clearly resolved. The measured lattice constant of 3.78 angstroms closely matched the theoretical value of 3.79 angstroms, and selected-area electron diffraction showed diffraction spots arranged in hexagonal patterns, confirming that most grains align with the mica substrate, though the film is not yet fully epitaxial.

The ultimate test came when the team fabricated arrays of bottom-gate field-effect transistors using the monolayer film as the channel, with standard photolithography, hafnium oxide gate dielectric, and gold contacts. The devices delivered a maximum on/off current ratio of 8.31 times ten to the fourth power and a minimum off-current of 3.40 times ten to the negative twelfth amperes per micrometer, the highest ratio and lowest off-current ever reported for PtSe2 film-based transistors. The large monolayer bandgap suppresses the thermally activated carriers that plague thicker, semi-metallic films in the off state. Field-effect mobility reached up to 1.37 square centimeters per volt-second, modest compared with the theoretical ceiling of nearly 1900 for monolayer PtSe2, a gap the researchers attribute to grain boundaries in the roughly 100-nanometer grains, transfer-related residues, interface traps at the dielectric, and unoptimized metal contacts, all of which they identify as targets for future optimization.

Beyond the record numbers, the significance of this work lies in its industrial compatibility. Metal-organic chemical vapor deposition is already the standard route for depositing thin films in commercial semiconductor fabs, and the growth temperature of 470 degrees Celsius is low enough for back-end integration schemes. By demonstrating that a properly designed precursor combined with oxygen-assisted ligand removal can tame a material whose layer count must be controlled to a single atomic plane, the team has established not just a new channel material candidate but a general framework for growing other emerging two-dimensional semiconductors at scale. If grain size and contact engineering can be improved in subsequent work, PtSe2 could graduate from laboratory curiosity to a serious contender in the post-silicon roadmap, with the added possibility that its own semi-metallic thicker form could one day serve as the contacts in entirely platinum-diselenide circuits.

Subject of Research: Oxygen-assisted MOCVD growth of semiconducting monolayer platinum diselenide films for field-effect transistors

Article Title: Oxygen‐Assisted MOCVD Growth of Monolayer PtSe2 Films With Bandgap Opening for Semiconducting FET Channels

Article References: Kim, Y., So, H.-S., Yoo, M., Oh, S., Kim, D., Gyeon, M., Jo, M.-K., Noh, G., Kim, T. S., Kim, M.-G., Park, J., Chai, H.-J., Kang, M., Kim, S., Ham, A., Lee, J., Lim, J., Song, S., Kwak, J. Y., … Kang, K. (2026). Oxygen‐Assisted MOCVD Growth of Monolayer PtSe 2 Films With Bandgap Opening for Semiconducting FET Channels. Advanced Science, 13(53), Article e76362. https://doi.org/10.1002/advs.76362

Image Credits: AI Generated

DOI: 10.1002/advs.76362

Keywords: PtSe2, two-dimensional materials, MOCVD, monolayer semiconductor, field-effect transistor, bandgap engineering, transition metal dichalcogenides, nanoelectronics, thin film growth, oxygen-assisted growth, crystallography, semiconductor manufacturing