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In 2018, researchers reported a 3 cm × 3 cm film of hexagonal boron nitride (hBN), described at the time as the largest “perfect” two-dimensional crystal of its kind. They grew it on liquid gold so small crystal islands could rotate into alignment before joining. The result was a wafer-scale single-crystal film and a substrate for growing graphene—not proof of a defect-free material or a universally confirmed record that still holds today.
What “largest perfect 2D crystal” means
The phrase comes from a Chemistry World report published on 20 November 2018. The material was hexagonal boron nitride, an insulating two-dimensional material made of boron and nitrogen atoms. The researchers reported a continuous, 3 cm × 3 cm film—often described as a wafer-scale single crystal.
“Perfect” is a characterization in the report, not a measurement establishing that the film contained no defects whatsoever. The available account does not provide a numeric defect density or enough metrology to interpret that word as an absolute claim. Likewise, “largest” should be read as the claim made around this particular 2018 result, not as a current record across every type of hBN crystal or every definition of size.
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How the researchers grew the film
The South Korean team used chemical vapor deposition (CVD) at 1100 °C on tungsten covered with gold foil. During growth, the gold melted and provided a liquid surface. Small hBN islands could rotate on that surface, allowing them to align as they met and joined. The report attributes the stitching between islands to interactions between their boron and nitrogen edges.
That rotation addresses a problem with ordinary island coalescence: islands with different orientations can meet at grain boundaries. If islands align before merging, the resulting film can have a more uniform crystal orientation. The report says the finished wafer measured 3 cm × 3 cm and that the vacuum chamber, rather than a demonstrated material limit, constrained its size. These are details reported by Chemistry World; the cited primary study is J. S. Lee et al., Science 362, 817 (2018), DOI 10.1126/science.aau2132.
What the film demonstrated
The researchers used the hBN film as a substrate to grow a similarly sized single-crystal graphene layer, creating a two-layer heterostructure. The result demonstrated a growth approach and a potential substrate for graphene, rather than a finished commercial electronic device.
Rank #2
- Product name:Monolayer boron nitride film（HBN）
- Substrate: SiO2/Si
- Grain size: >4 um
- Oxide layer: 300 nm
- Silicon: 500 um
Young Hee Lee of the Institute for Basic Science and Sungkyunkwan University told Chemistry World: “You get an electronic mobility improvement in graphene on single crystalline hBN.” Nanoscientist Jiwoong Park of the University of Chicago praised the uniform direction of the film, while cautioning that the obvious graphene application mattered mainly at low temperature. The report presented thinner, flexible electronics as a possibility for future work, contingent on scaling—not as an application already delivered by this experiment.
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The evidence here does not establish whether the 2018 film remains the largest under a consistent, current global standard. Later studies illustrate why comparisons need care: a 2024 Nature Communications paper describes continuous high-quality single-crystal monolayer films formed from aligned islands, while 2025 studies address bulk hBN boules grown by traveling-solvent floating-zone and lithium-flux methods. A bulk boule is not directly comparable to a monolayer film by lateral area alone.
Rank #3
- Product name:Monolayer boron nitride film（HBN）
- Substrate: SiO2/Si
- Grain size: >4 um
- Oxide layer: 300 nm
- Silicon: 500 um
A meaningful comparison would need to distinguish:
- Form: monolayer film versus bulk crystal.
- Size: lateral film area or wafer dimensions versus bulk dimensions.
- Continuity: a continuous film versus separate grains or a boule.
- Crystal quality: orientation, grain boundaries, defects, and how these were characterized.
- Growth method and substrate: which can affect both scale and quality.
Without a record comparison that applies consistent criteria to these different forms, the careful description is that the 3 cm × 3 cm film was reported at the time as the largest “perfect” 2D hBN crystal.
Quick Recap
Best Value
- Bonds well with substrates and forms a coating film
- Excellent lubricating properties. Good chemical inertness. Electrical insulator.
- High temperature stability (1000 deg C in air, 1400 deg C in vacuum & 1800 deg C in inert gas)
- Low thermal expansion. Low dielectric constant. Non-wetting.
- Thermal conductor (result: better heat dissipation). Contains no fluorocarbons or lead. Not harmful to Ozone
Rank #4
- Excellent lubricity: Coefficient of Friction (COF) as low as 0.15
- Appearance: Ultra-white, crystalline, free-flowing powder
- High purity: 99%
- High temperature resistance: Temperature stability in air is 1800ºF (1000ºC)
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