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September 2023
By: Marina-Irina Suvac
In the realm of scientific breakthroughs, 1991 marked a milestone year. It was the year when Sumio Iijima, a visionary Japanese electron microscopist, made a groundbreaking discovery - carbon nanotubes (CNTs). These remarkable structures, often referred to as buckytubes, have since captured the imaginations of researchers worldwide, leading to thousands of research papers published annually.
The Essence of Carbon Nanotubes
Carbon nanotubes are not your ordinary materials; they possess extraordinary properties that have both academia and industry buzzing with excitement. These elongated, hollow structures are composed of sp2 carbon atoms, boasting a nanoscale diameter and one or more walls. The secret to their strength and rigidity lies in the well-ordered arrangement of carbon atoms, connected by sp2 bonds.
Diving into the Varieties
Depending on the number of walls, carbon nanotubes come in two main flavors: single-walled CNTs (SWCNTs) and multi-walled CNTs (MWCNTs). MWCNTs, resembling a Russian nesting doll, consist of multiple concentric cylinders with increasing diameters, reaching sizes of about 100 nanometers. Interestingly, the space between their walls mimics the gap between two graphene layers in graphite, measuring approximately 3.5 angstroms.
But the innovation doesn't stop there. Enter double-walled CNTs (DWCNTs), bridging the best of both worlds. Comprising only two concentric cylinders, DWCNTs combine the slender diameter and bundling characteristics of SWCNTs with superior mechanical stability, particularly when covalently functionalized. Moreover, the inner tube's mechanical and electrochemical properties remain unscathed when the outer wall undergoes functionalization, akin to MWCNTs.
Unleashing the Potential
The potential of carbon nanotubes spans a vast array of applications. In the realm of biomedicine, CNTs have made remarkable strides. Thanks to their substantial surface area, they can adsorb or conjugate with therapeutic and diagnostic agents like drugs, genes, vaccines, antibodies, and biosensors. Their prowess as carriers for drug delivery directly into cells, bypassing metabolism, has garnered particular attention.
Beyond medicine, carbon nanotubes play pivotal roles in the fields of electronics, optoelectronics, and sensors. Their unique properties, such as electrical and optical sensitivity to biomolecules, make them ideal for biosensors. Their incredible electric current-carrying capacity, surpassing that of copper wires by a factor of 1000, positions them as promising electrode materials.
Continuing the Journey
While the journey of carbon nanotubes has been nothing short of astounding, challenges remain. Researchers have made substantial strides in overcoming issues like yield, purity, and alignment. However, the precise control of chirality and diameter remains a challenging endeavor.
For applications such as sensors, existing levels of control may suffice for commercial deployment. Yet, to fully unlock the potential of nanotubes in advanced electronics, including nanotube FETs and interconnects, further research and innovation are necessary.
In conclusion, the tale of carbon nanotubes is one of scientific marvels and limitless possibilities. With their exceptional properties and versatility, they continue to push the boundaries of what is achievable in fields as diverse as medicine, electronics, and materials science. As we advance further into the nanotechnology era, the saga of carbon nanotubes promises to be an exciting and transformative one, full of discoveries yet to be made.
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