Lithography-Free Carbon Nanotubes: New Biomimetic Supplies

A staff of researchers from China, Australia and Poland has developed a lithography-free methodology to synthesize vertically aligned multi-walled carbon nanotubes (VA-MWCNTs). These VA-MWCNTs – synthesized by plasma enhanced chemical vapor deposition (PECVD) on a nickel catalyst – have tunable pitch and dimension.

Synthesizing arrays of VA-MWCNTs requires periodically patterned arrays of nanoparticle catalysts. The multidisciplinary staff developed a dewetting methodology on a skinny nickel (Ni) catalyst movie. They used a hexagonal silica (SiO₂) monolayer as an array template. The diameters and lengths of the MWCNTs have been adjusted as a operate of the nickel particle dimension and PECVD software time.

This distinctive methodology of lithography-free synthesis of VA-MWCNT arrays opens up alternatives for the large-scale manufacture of biomimetic (nature mimicking) supplies.

Synthesizing Carbon Nanotubes

Ever since carbon nanotubes entered public consciousness in 1991, their distinctive properties have captured the curiosity of researchers internationally.

They’re comprised of rolled up “sheets” (“tubes”) of graphene which may be single-walled (SWCNTs) or multi-walled (MWCNTs). MWCNTs are nested SWCNTs certain by van der Waals interactions. They will attain lots of of nanometers in diameter.

MWCNTs possess distinctive electrical, thermal and mechanical properties, excessive mild absorption functionality and an prolonged floor space. They’ve a variety of purposes in supercapacitors, batteries, composite supplies, cell tradition scaffolds and near-perfect mild absorbers.

Of explicit curiosity is the replication of the properties of supplies present in nature. For instance, the self-cleaning properties of lotus leaves ensuing from their hierarchical nanostructure are a topic of continued curiosity.

Carbon nanotubes are sometimes synthesized on the floor of a cloth utilizing chemical vapor deposition (CVD). On this course of, a liquid steel catalyst resembling iron, nickel or cobalt reacts with a carbon-carrying fuel to kind carbon nanotubes.

To help perpendicular progress (vertical alignment) of VA-MWCNTs, an electrical subject is utilized to the fuel, thus making a plasma. This course of is named plasma-enhanced chemical vapor deposition (PECVD).

To rearrange nanotubes into patterns, a catalyst-based template is required. Historically, that is fabricated utilizing electron beam lithography, photolithography or nanosphere lithography. These require pricey manufacturing strategies resembling etching and will not be reproducible at a big scale.

Nonetheless, the multidisciplinary staff developed a dewetting methodology that entails retracting a fluid from a non-wettable floor resembling nickel. This course of yields a sample of distributed nickel particles on a substrate which will develop vertically into nanotubes. To make sure an orderly distribution of nanotubes, the staff patterned a silica (SiO₂) monolayer substrate.

Lithography-Free Synthesis of Carbon Nanotubes

The staff from South China Regular College, the College of Melbourne, The College of Queensland and the Polish Academy of Sciences demonstrated a lithography-free synthesis of periodically separated and vertically aligned multi-walled carbon nanotube (VA-MWCNT) arrays.

Utilizing a dewetting course of, they achieved a random distribution of nickel on a silica floor. As a skinny nickel movie was annealed (heat-treated), nickel islands appeared on the apices of silica nanospheres.

The silica floor was hexagonally patterned, leading to a periodic distribution of MWCNTs as they grew perpendicular to the floor.

Utilizing electron beam evaporation (EBE), a nickel thickness of 10 nm was deposited on silica nanospheres with 160 nm to 600 nm in diameter. A 25 nm movie thickness was deposited on 500 nm nanospheres and a 30 nm movie thickness on 600 nm nanospheres.

The VA-MWCNTs have been then grown at 700°C, with a C₂H₂ carbon precursor to NH₃ provider fuel.

The sizes of the silica spheres managed the pitch of the array, and subsequently the closest neighbor distance of the VA-MWCNTs. The size of the nickel particles and the nickel movie thickness managed the VA-MWCNT widths. Their lengths relied on progress instances in the course of the PECVD course of.

Curiously, the ensuing VA-MWCNT arrays displayed hydrophobic properties, reminding us of the properties discovered on the lotus leaf.

The distinctive management of dimensions and buildings on the nanoscale achieved by the staff of researchers opens the door to the large-scale improvement of low-cost biomimetic supplies.

References and Additional Studying

Chen R., et al. (2021). Lithography-free synthesis of periodic, vertically-aligned, multi-walled carbon nanotube arrays. [Online] Nanotechnology. Obtainable at: https://doi.org/10.1088/1361-6528/ac345a

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