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In 2018, a South Korean research team reported a 3 × 3 cm film of single-crystal hexagonal boron nitride (hBN), then described as the largest “perfect” 2D crystal of its kind. The key was growing it on molten gold: hBN islands could rotate and align before joining, helping avoid the mismatched grain boundaries that can form when randomly oriented islands meet. “Perfect” is the report’s characterization, not evidence that every possible defect was absent, and the result should be understood as a record claim made at the time—not a verified current world record.
What the team made
The material was hexagonal boron nitride, an insulating two-dimensional material. The reported sample was a continuous film or wafer measuring 3 cm × 3 cm—not a naturally occurring crystal or a consumer product. Chemistry World reported that its size was limited by the vacuum chamber used for growth.
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The report appeared on 20 November 2018 and describes work by J. S. Lee and colleagues, published in Science 362, 817 (2018), DOI 10.1126/science.aau2132. The primary study is identified in that report; the dimensions and process details here are those reported by Chemistry World.
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1Clear out junk files and repair common Windows errors2Scan for outdated or missing drivers - takes under a minute3Repair Windows errors before they cause bigger problemsHow molten gold helped the film form
The researchers used chemical vapor deposition at 1100 °C on tungsten covered with gold foil. During growth, the gold melted to form a liquid surface. Small hBN islands on that surface could rotate before they met and joined. As they coalesced, the report says interactions between boron and nitrogen edges helped stitch them together.
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That mobility matters because islands that meet in different orientations can leave grain boundaries—interfaces that interrupt a uniform crystal lattice. In this approach, islands could align before merging, producing a film reported as a single crystal with uniform orientation. The mechanism is different from simply allowing misaligned islands to grow together on a fixed surface.
The word “perfect” needs care. The report calls the film perfect and a single crystal, but the available account does not give a numeric defect density or establish that the film was free of every kind of defect. It is most accurate to read “perfect” as the source’s description of the reported crystal quality, not as a literal guarantee of zero defects.
What “largest” means—and what it does not
Chemistry World presented the 3 × 3 cm sample as the largest perfect 2D crystal made from boron nitride at the time. That is a historical claim tied to a particular kind of result: a large-area, continuous single-crystal hBN film. It does not establish that the film remains the largest under every later definition of crystal size or quality.
Subsequent hBN research has pursued different forms and growth methods. A 2024 Nature Communications paper describes continuous, high-quality single-crystal monolayer films formed from aligned islands. Work published in 2025 examines bulk hBN boules grown by traveling-solvent floating-zone and lithium-flux methods. Bulk crystals and monolayer films are not directly comparable by a single “largest” measure: thickness, lateral area, continuity, orientation, defect characterization, and growth method all affect the comparison. The available evidence does not establish a current, universally comparable record ranking.
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Why the hBN film mattered for graphene
The team used the hBN film as a substrate for chemical vapor deposition of similarly sized single-crystal graphene, creating a two-layer heterostructure. The demonstration showed a way to grow graphene on a large-area single-crystal hBN surface; it was not a finished commercial electronic device.
Young Hee Lee, identified by Chemistry World with the Institute for Basic Science and Sungkyunkwan University, said: “You get an electronic mobility improvement in graphene on single crystalline hBN.” Nanoscientist Jiwoong Park of the University of Chicago described the result as “a clever way to produce a film with very uniform direction everywhere.” Park also cautioned, as quoted in the report, that the obvious graphene application mattered mainly at low temperature, while noting that the work could encourage further research.
From a growth demonstration to possible applications
The report raised thinner, flexible electronics as a future possibility, conditional on scaling the approach. The 2018 demonstration established a material-growth and substrate concept, not that flexible electronics made with this process were ready for practical use. Its significance lies in showing how a mobile growth surface might help produce a more uniformly oriented hBN film and support growth of graphene on it.
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