The work, published in Nature, describes a technique the authors call etching-flux-mediated single-centred nucleation, or EF-SCN. Conventional area-selective growth relies on a difference in surface binding energy between a growth region and a surrounding barrier: precursor molecules stick preferentially to the growth area, so deposition occurs only where intended. The problem is that the entire growth region behaves as a nucleation-active zone with a roughly uniform probability of crystal birth. Nuclei appear at random positions, often clustering at pattern corners and edges, and even when the region is shrunk enough to permit only one nucleus, its position remains a matter of chance. EF-SCN changes the physics of the problem by adding an in-plane chemical flux that reshapes the nucleation probability landscape itself.

The key ingredient is the barrier material. The researchers found that amorphous hafnium oxide, a common high-k dielectric, is thermally unstable at the temperatures used for molybdenum disulfide growth. X-ray diffraction showed monoclinic crystallization peaks appearing above roughly 550 degrees Celsius, and X-ray photoelectron spectroscopy revealed that at the typical growth temperature of 750 degrees Celsius the oxygen content of the film dropped rapidly from HfO1.95 to HfO1.83 within ten minutes before saturating. In other words, the barrier steadily exhales oxygen during the deposition process. Because oxygen is a known etchant for molybdenum disulfide, this released gas acts as a lateral etching flux that sweeps across the growth region from the pattern boundary inward.

The consequence is a spatially graded competition between growth and etching. Close to the barrier, the oxygen concentration is high enough that any nascent molybdenum disulfide nucleus is etched away as fast as it forms, creating a nucleation-suppressed region hugging the pattern edge. Farther toward the centre, the oxygen flux decays exponentially, following a diffusion model the team derived from Fick’s first law, and at some critical distance the net growth rate turns positive. Only the central core of the pattern remains a viable nucleation-active region, and within that core the probability of nucleation peaks at the geometric centre. The result, confirmed by scanning electron microscopy across large arrays of triangular and square patterns, is that a single molybdenum disulfide flake nucleates dead centre and then grows laterally until it fills the entire region as one seamless crystal.

What makes the demonstration compelling is not just the concept but the statistics. Across a two-centimetre substrate divided into sixteen regions of twenty-five patterns each, four hundred growth sites in total, the team achieved a single-crystal yield exceeding 99 percent. The resulting flakes reached approximately ten micrometres across, an order of magnitude relevant to practical device layouts, and atomic force microscopy confirmed monolayer thickness of 0.75 nanometres. Rigorous structural characterization, including transmission electron diffraction, atomic-resolution scanning transmission electron microscopy, atomic-force imaging and angle-resolved second-harmonic-generation mapping, consistently showed that the flakes were genuinely single-crystalline rather than stitched-together polycrystals, a distinction that matters enormously for carrier transport.

Perhaps most striking is the breadth of process compatibility. The technique worked on crystalline sapphire but also on amorphous silicon dioxide, where uniform single-crystal growth was achieved over a four-hundred-micrometre area even though crystal orientations varied randomly between sites, as expected on a non-epitaxial surface. Pattern densities spanning nearly an order of magnitude still yielded effective single-crystal growth. And by swapping the hafnium oxide barrier for zirconium dioxide, which releases its etching flux at lower temperature, the researchers pushed the entire process down to 430 degrees Celsius, producing well-defined centred single crystals and even fully filled ten-micrometre single-crystalline films. Low-temperature growth is a prerequisite for back-end-of-line integration, where atomically thin transistors would be fabricated atop finished silicon circuitry without damaging it.

Beyond demonstrating the phenomenon, the team distilled it into a quantitative design rule. By varying the growth-region size, the process time and the precursor flows during metal-organic chemical vapour deposition, they mapped out three distinct regimes: zero nucleation, when the nucleation-active region never forms; single nucleation, when only the central point survives; and multiple nucleation, when the active region broadens enough to host several nuclei. Growth regions of three, five and seven micrometres produced exactly these three outcomes under fixed conditions, while tuning the diethyl sulfide chalcogenine flow from 0.5 to 7 standard cubic centimetres per minute traced the same progression. The chalcogen flow primarily governed nucleation density, whereas the molybdenum hexacarbonyl flow controlled lateral growth rate, giving engineers two independent knobs. A kinetic Monte Carlo emulation with spatially separated precursor and etchant reservoirs reproduced all three regimes, reinforcing the physical picture.

The device implications follow directly. Because nucleation position and growth region can be decoupled, the researchers joined a large nucleation zone to a narrow growth-only channel, coaxing a single crystal to nucleate in one place and extend as a line-shaped stripe into another. These line-shaped channels, roughly 6.8 micrometres long, became the backbones of field-effect transistors exhibiting a peak field-effect mobility of 117 square centimetres per volt-second, the highest reported for selectively grown molybdenum disulfide, with an on-current density of 12 microamperes per micrometre. Even more intriguingly, four separate transistors were defined along a single ten-micrometre crystal, and their mobility variation collapsed to a relative standard deviation of 7.8 percent, a 65 percent improvement over devices carved from separate crystals. Sharing one flawless lattice apparently irones out much of the device-to-device scatter that has plagued two-dimensional electronics.

The same spatial programming enabled something previously out of reach: self-aligned contacts built from aligned lateral heterostructures. By alternating precursor supplies, the team grew stripe-shaped molybdenum disulfide and molybdenum diselenide superlattices with interfaces sharper than two nanometres, positioned and oriented identically across whole arrays. Because local strain at the heterojunction makes area-selective atomic layer deposition of ruthenium favour the diselenide segment, metal contacts deposited themselves precisely where the heterostructure dictated, yielding self-aligned field-effect transistors with on/off ratios above ten million and subthreshold swings of 170 millivolts per decade, achieved despite the harsh oxygen exposure of the ruthenium process. Taken together, the results suggest that the hardest part of two-dimensional manufacturing, deciding where a crystal begins, may finally be a matter of barrier design rather than luck, opening a route toward wafer-scale integration of atomically thin logic, optoelectronics and strain-engineered devices built crystal by crystal, site by site.

Subject of Research: Deterministic control of nucleation site in the selective growth of two-dimensional semiconductor single crystals using an oxygen etching flux released from oxide barriers

Article Title: Spatially deterministic nucleation of 2D semiconductors by etching flux

Article References: Park, J., Kim, J., Kang, S., Oh, J., Sunwoo, Y., Oh, S., Shin, S., Yang, S., Jo, S., Lee, J., Lee, D., Kim, M., Eom, C., Jeong, S., Lim, C., Moon, G., Kang, M., Kim, M.-G., Kim, J., … Kang, K. (2026). Spatially deterministic nucleation of 2D semiconductors by etching flux. Nature, 658(8135), 398-406. https://doi.org/10.1038/s41586-026-11095-1

Image Credits: AI Generated

DOI: 10.1038/s41586-026-11095-1

Keywords: two-dimensional materials, molybdenum disulfide, nucleation control, area-selective growth, chemical vapor deposition, single crystals, field-effect transistors, lateral heterostructures, hafnium oxide, semiconductor manufacturing, etching flux, 2D electronics

The challenge the team set out to solve is fundamental rather than merely technical. Two-dimensional intermetallic compounds, in which two or more metal species arrange themselves into ordered crystallographic sublattices, and high-entropy metallic alloys, in which four or more elements share a single disordered lattice, are both thermodynamically precarious when squeezed into a few atomic layers. Their intrinsic instability means that conventional vapor-phase or solution-based growth tends to produce three-dimensional particles rather than flat crystals, and kinetic factors during growth are equally difficult to control. Without a way to stabilize flat nuclei and steer their lateral expansion, the rich emergent physics predicted for these systems remained largely out of experimental reach.

The researchers call their solution an adsorption–conversion strategy, and its mechanics are worth unpacking. In a typical growth run, a metal halide precursor such as copper chloride is deposited onto a metallic matrix, for example copper germanide, in the presence of a potassium chloride salt flux. As the precursor decomposes on the hot surface, the liberated metal atoms do not simply sit there: they embed themselves into the metallic matrix below, converting the local composition into a new intermetallic phase. Meanwhile, the residual chlorine atoms adsorb onto the exposed crystal faces. Theoretical calculations show that this double action is what tips the energetic balance in favor of two dimensions.

The numbers from the team’s density functional theory calculations illustrate the effect vividly. For the copper–germanium system, embedding additional copper into a copper germanide matrix to form the richer Cu3Ge phase lowers the surface energy of the (001) facet from 0.069 electronvolts to 0.044 electronvolts, a critical first step that triggers the conversion of bulky three-dimensional Cu2Ge particles into flat Cu3Ge nanostructures. Chlorine adsorption then drives the surface energy down further, to 0.01 electronvolts. Because different crystal facets respond differently to chlorine, the energy gap between competing faces widens, and in the language of classical crystal morphology dating back to Wulff’s 1901 analysis, the crystal is pushed to grow laterally as thin plates rather than isotropically as cubes. The potassium chloride flux plays a supporting role, enhancing the wettability and fluidity of the molten system so that the flat nuclei can spread into large, uniform nanoflakes.

Control experiments confirm that both ingredients are essential. When only potassium chloride is present, the growth yields nothing but three-dimensional particles. Replace it with copper chloride, and two-dimensional nucleation begins. The team extended the same logic to iron, demonstrating through ab initio molecular dynamics simulations of the iron chloride and iron germanide interface that the identical mechanism of metal incorporation and chlorine-mediated surface stabilization operates there too, underscoring the generality of the approach rather than a lucky quirk of one chemistry.

The breadth of the resulting materials library is arguably the paper’s most striking feature. Using the adsorption–conversion route, the researchers synthesized ultrathin single crystals based on iron, cobalt, nickel, copper and palladium, spanning ordered intermetallics such as Fe3Sn2, Pd2Bi3, Ni3Sn2 and Co6Ga, multicomponent compounds such as CoFe2Ge2 and (Fe, Co, Cu)3Sn2, and genuine high-entropy alloys including (Cr, Fe, Co, Cu)3(Ge, Sn, Sb)2. Atomic-resolution scanning transmission electron microscopy confirmed that the flakes are high-quality single crystals with well-ordered atomic arrangements, and energy-dispersive mapping showed homogeneous elemental distributions without discernible aggregation even in the most compositionally complex samples. Most of the twenty-five characterized nanoflake compositions could be thinned below five nanometers, with the thinnest, Pd2Bi3, reaching just 1.9 nanometers.

Synthesis did not proceed blindly; the team distilled clear design principles that should guide future attempts. The valence electron concentration of the constituent elements governs which crystal lattice is stable, with higher values favoring close-packed hexagonal and face-centered structures and lower values permitting body-centered arrangements, while substrate symmetry can occasionally impose hexagonal stacking even on bcc-forming chemistries through quasi-van-der-Waals epitaxy. Oxygen affinity proved to be the other decisive variable. An Ellingham-type analysis of oxidation free energies explains why early transition metals such as vanadium, chromium and manganese are difficult to incorporate, since their high oxygen affinity leads to oxide contamination, whereas late transition metals like copper, palladium and nickel form readily. Even the difficult cases are not hopeless: when a hygroscopic precursor such as vanadium dichloride is rigorously dried in an oxygen-free environment, two-dimensional vanadium antimonide can indeed be grown.

The payoff for all this synthetic effort shows up in the electrical measurements. The ultrathin alloys exhibit conductivities reaching 3 × 10^7 siemens per meter, a figure that places them among the most conductive thin-film materials ever reported, and an ultralow temperature coefficient of resistance of just 2 parts per million per kelvin. That second number is the one likely to excite engineers: a resistance that barely changes between room temperature and cryogenic conditions is exactly what precision electronics, sensors and metrology instruments demand, and high-entropy alloys have long been theorized to achieve such behavior by balancing multiple electron-scattering channels. Magnetotransport measurements on CoFe2Ge2 flakes of roughly 9 and 22 nanometers revealed room-temperature ferromagnetism in both thickness regimes, opening a path toward combining high conductivity, temperature-stable resistance and magnetism in a single ultrathin platform.

What emerges from this work is less a single new material than a versatile materials platform. By establishing a reproducible, mechanistically understood route to two-dimensional single crystals of intermetallics and high-entropy alloys across much of the transition-metal series, the researchers have handed condensed-matter physicists a fresh playground in which ordered and disordered metallic lattices can be stacked, patterned and tuned at the nanometer scale. The same platform may serve technologists pursuing interconnects, magnetic devices and precision resistors. Given that the field of two-dimensional metals only reached the ångström thickness limit in 2025, the rapid arrival of a general synthesis for ultrathin intermetallics and high-entropy alloys suggests that the metallic frontier of two-dimensional materials science is now opening in earnest.

Subject of Research: Synthesis of two-dimensional intermetallic compounds and high-entropy metallic alloys via an adsorption–conversion growth strategy

Article Title: Adsorption–conversion synthesis of ultrathin intermetallics and high-entropy alloys

Article References: Zhang, P., Zhao, F., Wang, X., Wang, H., Si, K., Gong, Y., Li, B., Wei, J., Jia, Y., Gao, B., Liu, Z., Zou, X., & Duan, X. (2026). Adsorption–conversion synthesis of ultrathin intermetallics and high-entropy alloys. Nature Materials. https://doi.org/10.1038/s41563-026-02752-x

Image Credits: AI Generated

DOI: 10.1038/s41563-026-02752-x

Keywords: two-dimensional materials, intermetallic compounds, high-entropy alloys, adsorption–conversion synthesis, chloride-mediated growth, surface energy, single crystals, electrical conductivity, temperature coefficient of resistance, ferromagnetism, nanoflakes, materials synthesis