A team at the University of Amsterdam has transferred roughly 1 mm-sized two-dimensional (2D) material layers onto patterned substrates with near-unity yield, addressing a long-standing bottleneck in 2D device fabrication. The method, described in ACS Nano, uses low-density polyethylene (LDPE) — the polymer found in kitchen cling film — as a transfer stamp.

"The method we developed allows us to, for the first time, pick up, transfer and place large (roughly 1-mm-sized) 2D layers on almost arbitrarily patterned surfaces," says Jorik van de Groep, who leads the 2D Nanophotonics group at the UvA-Institute of Physics. "Most importantly, the transfer is no longer probabilistic (as were most other methods) but has a near-unity yield."

That shift from probabilistic to deterministic is the meaningful change for R&D managers planning pilot runs. Existing dry-transfer techniques crack monolayers or fail to seat them on non-flat interfaces, making wafer-scale device integration a hit-or-miss proposition. Van de Groep's group, working with colleagues at UvA's Van 't Hoff Institute for Molecular Sciences, ARCNL and AMOLF, frames the new process as a controllable, sensor-monitored step.

What does the process actually look like?

The Amsterdam workflow starts with a gold-assisted-exfoliated monolayer of tungsten disulphide (WS₂) on a silica substrate. Researchers mount an LDPE-coated half-sphere stamp on an xyz precision stage and bring it into contact at controlled speed. The reported process parameters are:

• Contact approach speed: 0.5 µm/s
• Substrate temperature during approach: 70 °C
• Normal force at first contact (Fz): 120 mN
• Adhesion temperature: 140 °C (melts LDPE)
• Retraction speed after cooling: 0.5 µm/s

"We used force sensors in the stage to measure the forces involved during the stamping procedure, both in the plane of the 2D material and perpendicular to it," van de Groep explains. "This not only offers better control and repeatability of the transfer, it also provides crucial information on the contact and friction dynamics throughout the process."

The LDPE phase transition does the actual gripping work. The film adheres strongly to the monolayer at 140 °C, releases the layer during cooling back to 70 °C, and leaves residue that a final cleaning step removes.

How much damage does the monolayer sustain?

Pre- and post-transfer imaging showed crack coverage rising from 8% before transfer to 14% after, with most new cracks forming at the edges of the stamp's contact area. Van de Groep frames that as a "modest increase" that largely preserves topography. The transferred WS₂ also retained its good photoluminescence signature — the key optoelectronic property — though the paper does not report quantum-yield or carrier-mobility numbers.

The reported sample size is small: a single WS₂ monolayer plus one hexagonal boron nitride/monolayer heterostructure. R&D teams will want averaged yield data across many runs and varied substrates before treating "near-unity" as a production-grade specification rather than a per-trial claim.

What devices is the team targeting?

Van de Groep tells Physics World the lab is already feeding the stamp into development of atomically thin optical elements, optical modulators and single-photon emitters. He also flags van-der-Waals heterostructures for quantum materials as a longer-term target.

Near-term work centres on a humidity-controlled enclosure around the stamping rig. "2D materials and the (van-der-Waals) adhesion between them strongly depends on the surface chemistry and, as such, on the relative humidity during the stamping procedure," van de Groep notes. The group is also building in-situ thickness metrology to characterise layers during stamping.

If the group's next publication extends yield data across humidity ranges and a wider set of patterned substrate geometries, the cling-film stamp will have cleared its prototype-stage hurdle.