Researchers from Skoltech — a VEB.RF group institution — and their colleagues from Harbin Institute of Technology in China and ITMO University, Russia, have devised a way to deposit elaborate geometrical patterns of carbon nanotubes without wasting this precious material. Such patterns are used in advanced optical devices and mechanical strain sensors for structure integrity monitoring. The new technique will make nanotube patterning cheaper, faster, and more resource efficient, lowering the barrier for integrating the high-tech material into optical and electronic devices. Published in Light: Advanced Manufacturing, the study was supported by the Russian Science Foundation.

“Single-walled carbon nanotube films are a material with outstanding properties useful in optical and electronic devices,” one of the authors of the study, Associate Professor Dmitry Krasnikov of Skoltech Photonics, explained. “The challenge is that in fabricating a device, nanotube films have to be structured as conductive nanopatterns. The way this is usually done is by depositing a continuous film and then etching away the ‘excess’ material where it is not needed. This, however, is fairly wasteful, because as much as 90% of the nanotubes can be lost, and they are pretty expensive. Also, etching deteriorates the quality of the remaining nanotubes. We came up with a better solution.”

The team demonstrated a way to deposit nanotube patterns in a single-stage process that does not waste material or introduce additional reactants. The new technique involves the use of a conventional pressing tool and a nitrocellulose membrane — a type of filter commonly used in molecular biology experiments. Before nanotube deposition, the membrane is pressed with a laser-cut hot metal stencil that carries the inverse of the desired pattern. At about 200 megapascals, the stencil press clogs the pores in the filter, which effectively prevents nanotube deposition in the clogged regions.

Prepared in this way, the membrane becomes a sturdy reusable template that serves as a substrate for aerosol chemical vapor deposition — a standard technique for producing single-walled carbon nanotube films. The nanotube aerosol is filtered through the membrane, but since only the unclogged areas are permeable, it is there that the flow passes and the nanotubes are collected, ready for transfer to another substrate. Importantly, the method does not introduce foreign materials into the membrane (e.g., organic solvents), which eliminates postprocessing, avoids contamination, preserves nanotube quality, and facilitates subsequent transfer of the patterned film.

“The key insight comes from aerosol science: Single-walled carbon nanotubes are so light that their inertia is negligible, so they follow the carrier gas wherever it flows. By pairing that principle with a structured membrane — where we simply close off the pores we do not need — we let the gas flow itself draw the pattern, depositing nanotubes only where they belong and nowhere else. Nothing is etched away, no solvents or foreign materials are introduced, and the template can be reused many times over. In effect, we turn a fundamental property of the aerosol into a precision manufacturing tool — and that is what makes the method fast, clean, and scalable enough to move carbon nanotubes from the laboratory into real optical and electronic devices,” study co-author and RAS Professor Albert Nasibulin, who heads Skoltech Photonics, commented.

In an earlier version of the technique, the team prevented nanotube deposition in select areas on the nitrocellulose membrane filter by sputtering copper on them. This, however, imposed certain limitations on the geometry of the pattern that could be obtained. The pattern had to be continuous, without any isolated or weakly connected features. Also, some of the copper stuck to the nanotubes, degrading their properties. By eliminating copper from the equation, the hot pressing approach resolves both issues.

The team evaluated the resulting pattern quality via optical microscopy, scanning electron microscopy, and electrical measurements. These tests confirmed that the lines and gaps in the carbon nanotube films closely followed stencil geometry. Nearly no nanotubes were deposited in the areas intended as empty. The researchers also explored the scalability and reusability of the pressed membranes: Larger stencils were fabricated, and repeated use tests showed a variation of only a few percent in optical properties of the deposited films between runs.

The lead author of the study, Skoltech research intern Nikita Raginov emphasized: “The new method is highly scalable, opening up promising possibilities in optics, electronics, and sensorics.” To highlight the versatility of the approach, the authors implemented devices of two distinct classes that exploit both the electrical and the optical functionality of the patterned films.

The first device is a mechanical strain sensor. It uses a W-shaped pattern of nanotubes on an epoxy substrate subjected to uniaxial tensile loading. When the component is stretched, its electrical conductivity changes, and that way the device senses strain. Notably, the change in conductivity proved to be at least three times greater than previously reported for analogous strain sensors based on single-walled carbon nanotubes created by conventional methods. Tests over 3,000 load-unload cycles confirmed a stable and reliable response to stress. The intrinsic flexibility of nanotube networks suggests applications in wearable electronics, soft robotics, and structural health monitoring — sensors embedded in aircraft wings, bridge pillars, etc.

The second device functions as a tunable lens for manipulating terahertz waves — an intermediate band of electromagnetic radiation between infrared light and microwaves. The spiral-shaped structure was transferred onto a thin elastomer film, in effect creating a stretchable lens. This diffractive optical element demonstrated well-defined focusing, with the focal distance reversibly tuned by stretching without any changes to the radiation source or detector. The lens can encode information into terahertz waves for wireless communication or data transmission over optical fibers.

Beyond THz optics and high-performance strain sensing, the team foresees applications in transparent conductors, bioelectrodes, thermoelectric modules, and heating grids.

The patterned carbon nanotube structures reported in this story were modeled at ITMO University and Harbin Institute of Technology, manufactured at Skoltech, and tested at the Moscow Institute of Physics and Technology and Prokhorov General Physics Institute of the Russian Academy of Sciences.