High-resolution patterning of reusable membranes for spatially predesigned single-walled carbon nanotube films for advanced optical and sensing applications

The development of high performance optical and sensing devices in the terahertz (THz) range is severely constrained by the lack of robust, scalable materials that can be patterned with high precision over large areas. Thin films of single walled carbon nanotubes (SWCNTs) are particularly attractive because they combine strong light–matter interaction, mechanical flexibility and compatibility with a wide range of substrates. However, existing patterning routes either rely on wet processing and complex lithography, or cut away large fractions of the material after growth, which wastes costly nanotubes and degrades their intrinsic properties. There is a strong need for a simple, dry and material efficient approach that can directly define complex SWCNT film geometries while keeping the films transferable and preserving quality of nanotubes.

 

In a new paper published in Light: Advanced Manufacturing, a team of researchers from Skolkovo Institute of Science and Technology (Russia), Moscow Institute of Physics and Technology (Russia), Prokhorov General Physics Institute (Russia), ITMO University (Russia), and Harbin Institute of Technology (China) report such a solution. They have designed reusable filtration membranes whose pore structure is locally “modified” by mechanical imprinting with laser machined metallic stencils. During aerosol chemical vapor deposition, an aerosol of SWCNTs is filtered through these pre imprinted membranes. Pressed regions become strongly clogged and block the aerosol flow, while unpressed regions remain permeable and collect nanotubes. As a result, the CNT film is deposited only where required, forming the target pattern in a single, dry step without adding extra wet processing or necessity for any post growth etching. The patterned films are then dry transferred onto any rigid or flexible substrates for further application.

 

The authors implement two complementary imprinting approaches to balance resolution, pressure requirements and design freedom. In the stencil-supported approach, a thin copper foil stencil is laser cut through, attached to the nitrocellulose membrane, and left in place after pressing. The combined blocking by the compressed pores and the metal stencil enables nearly perfect suppression of nanotube deposition in the “blocked” areas at relatively low pressures of around 50–100 MPa. This approach replicates line widths and gaps down to the laser beam limit of about 100 micrometers with clean, sharp edges and almost 100 percent optical transmittance in nominally empty regions. In the stencil-free mode, the pattern is engraved as recesses in a thick stainless-steel plate, which is used once to locally compress the membrane and then removed. This variant requires higher pressures, above about 200 MPa, but offers much greater freedom in pattern topology because the rigid plate can support isolated or weakly connected features that are difficult or impossible to realize with through cut foils.

 

 

To rigorously evaluate pattern quality, the team combines optical microscopy, spectroscopy and electrical testing. Resolution charts adapted from standard optical test patterns confirm that the lateral dimensions of lines and gaps in the SWCNT films closely follow the stencil geometry once the imprinting pressure exceeds a certain threshold. Measurements of visible transmittance at 550 nm show that properly imprinted membranes leave almost no nanotubes in nominally empty gaps. At the same time, percolation tests that probe the electrical resistance between neighboring elements are used to detect even ultrathin, optically invisible CNT residues. For stencil supported membranes, resistance between adjacent pads rapidly diverges with increasing pressure, indicating an almost complete absence of conductive bridges at around 100 MPa. For membranes prepared with stencil-free method, similar electrical isolation is achieved at higher pressures, especially for gaps smaller than about 200 micrometers.

 

Beyond small test areas, the researchers also explore the scalability and reusability of the modified membranes. They fabricate larger stencils compatible with manual rollers and demonstrate that the same imprinted membrane can be used multiple times to collect patterned SWCNT films with only a few percent variation in optical absorbance between runs. This suggests that the method can be extended to large area manufacturing of patterned carbon nanotube films. Importantly, the imprinting process itself does not introduce foreign materials into the membrane, which preserves the efficiency of subsequent dry transfer and avoids additional contamination steps.

 

To highlight the versatility of their approach, the authors realize two distinct classes of devices that exploit both the electrical and optical functionality of the patterned films. First, they design and fabricate SWCNT based strain sensors with geometries inspired by conventional metal foil gauges. These sensors are dry transferred onto epoxy substrates and tested under uniaxial tensile loading. The resistance change under strain translates into gauge factors that are at least about three times higher than typical values reported for SWCNT based strain gauges prepared by more conventional routes. At the same time, the sensors benefit from the intrinsic flexibility and robustness of nanotube networks, pointing toward applications in structural health monitoring, soft robotics and wearable electronics.

 

Second, the team uses their stencil-free approach to pattern a spiral zone plate tailored for operation around 327 GHz in the THz range. The resulting SWCNT structure is transferred onto a thin elastomer film, creating a mechanically stretchable THz lens. In a dedicated THz imaging setup, the spiral zone plate demonstrates well defined focusing and the generation of structured beams carrying orbital angular momentum. By stretching the elastomer by about 12 percent, the focal distance can be shifted by tens of percent, enabling continuous, reversible tuning of the beam focusing properties without changing the source or the detector. Numerical simulations based on the angular spectrum method agree well with the experimental intensity maps, confirming that the patterned SWCNT film behaves as a reliable diffractive optical element.

 

Taken together, these results establish mechanically imprinted membranes as a powerful platform for in situ patterning of aerosol grown SWCNT films. The method eliminates liquid processing, reduces nanotube waste, and decouples the resolution from the mechanical fragility of the final substrate by patterning at the membrane level rather than on the device itself. Because the same principles can be applied to a wide range of stencil designs and membrane types, the authors foresee applications not only in THz optics and high-performance strain sensing, but also in transparent conductors, bioelectrodes, thermoelectric modules and heating grids. By leveraging inexpensive laser cutting and standard pressing tools, their approach lowers the barrier for integrating sophisticated nanotube patterns into future electronic and photonic systems.

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