Lithography-free carbon nanotube arrays are a simple approach to create an army of tiny superheroes

A microscope in the NanoScience Lab at The University of Melbourne. Credit: Gavan Mitchell & Michelle Gough, University of Melbourne
A microscope in the NanoScience Lab at The University of Melbourne. Credit: Gavan Mitchell & Michelle Gough, University of Melbourne

One of science's best-kept mysteries is carbon nanotubes. These small, man-made materials have astonishing properties: they are the darkest substance humans can build, they absorb light so efficiently that they can generate thermal energy, and they can mimic nature to aid the body in fighting germs.

Researchers in Australia and China have discovered a cheaper and easier method of organizing big groups of carbon nanotubes, possibly opening up numerous new paths for their usage by more scientists worldwide.

Carbon nanotubes are typically formed on the surface of a material by a chemical process that includes a carbon source and nanoscale metal catalysts such as iron, nickel, and cobalt. The nanotubes are grown vertically and free-standing using a glow-discharge plasma to generate a nanoscopic forest.

A catalyst template is required for pre-defined nanotube patterns. Creating such templates frequently necessitates an expensive and time-consuming procedure known as lithography. Lithography is justified in highly specialized sectors such as microelectronics, but less expensive alternatives are required for large-scale, low-tech applications.

Scientists have now revealed an alternate method for building and aligning strong collections of carbon nanotubes that do not require lithography. The team is spread throughout South China Normal University, the ARC Centre of Excellence in Exciton Science, and the University of Melbourne's Doherty Institute. Their findings were reported in the journal Nanotechnology.

According to Dr. Eser Akinoglu, "we aim to employ carbon nanotubes to cover medical implants and emulate the antibacterial capabilities of insect wings, to have a mechanical structure that can kill germs and maybe accelerate the formation of bone cells at the same time (osteoblasts). The main concept is to duplicate the structures on insect wings that destroy germs mechanically, without the need of antibiotic drugs."

To arrange nickel catalyst particles in a certain way, the researchers used a "dewetting" method. Dewetting is the process by which a fluid, in this example molten metal, is withdrawn from a surface. When heat is applied to a thin metal film atop a layer of silica nanospheres, it functions as a template to construct a precise arrangement of tiny nickel islands. The diameter of the silica particles affects the "pitch" of the hexagonal nanotube arrangement, but the thickness of the metal layer impacts the width of the nickel islands, which dictates the final width of the carbon nanotubes. Using this method, all of the geometric properties of the nanotubes may be selected without the requirement for costly lithography.

Normally, lithography would be required to create a template, according to Eser. This might be accomplished using light, X-rays, or electron beams. All of it is unnecessary because of what we do here. It's a lot easier to generate these carbon nanotubes in periodic, preset patterns this way. It is the first time that periodic arrays of carbon nanotubes have been manufactured without the use of lithography.

The resultant carbon nanotubes reject water and resemble similar structures seen in nature, which implies they might aid in the development of biomimetic devices tools that solve complicated issues by copying items found in nature. One example is the "lotus effect," in which the nanostructures in a plant's leaves dictate its ability to self-clean.

The researchers will now try to figure out if the carbon nanotube arrays can actually eliminate the microorganisms that harm medical devices.

Journal Information: Ruiting Chen et al, Lithography-free synthesis of periodic, vertically-aligned, multi-walled carbon nanotube arrays, Nanotechnology (2021). DOI: 10.1088/1361-6528/ac345a

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