Dynamics and Structural Transformations of Carbon Onion-Like under High-Velocity Impacts

Carbon is the element of life, but it is also the element of extremes. In the right conditions, it forms the soft graphite in a pencil; in others, it becomes the hardest natural material on Earth, the diamond. Between these two familiar states lies a vast landscape of exotic structures, including tiny, hollow spheres made entirely of carbon atoms. These are fullerenes, often called buckyballs, and when they nest inside one another like Russian dolls, they form carbon nano-onions. Scientists have long been fascinated by these objects because their unique shape and electronic properties make them promising candidates for everything from medical imaging to advanced batteries. However, a critical question remained unanswered: what happens when these delicate, multi-layered spheres are struck with tremendous force? Understanding how these structures behave under high-speed impact is not just a matter of curiosity; it is essential for designing materials that can withstand extreme environments or for using high-speed collisions as a tool to create new forms of matter.

To answer this, a team of researchers in Brazil turned to a powerful computer simulation technique that treats every single atom as a distinct player. They modeled carbon nano-onions, ranging from a single shell of sixty atoms to massive structures with six nested shells containing nearly six thousand atoms. They then launched these virtual objects at a rigid, unyielding surface at speeds ranging from 2 to 7 kilometers per second. This is not a gentle tap; at the lower end, the speed is already twice that of a high-performance rifle bullet, and at the upper end, it approaches the velocity of a meteorite entering the atmosphere. By watching the atomic dance unfold in their digital laboratory, the researchers could observe exactly how the bonds between carbon atoms stretched, broke, and reformed under the stress of the crash.

The results revealed that the outcome of such a collision depends entirely on how fast the nano-onion is moving. At the slowest speeds, up to 2 kilometers per second, the impact acts almost like a bounce. The nano-onion squashes slightly against the surface and then springs back, retaining its original spherical shape with only minor, temporary deformations. The atoms shift just enough to absorb the energy, but the structure remains intact, much like a rubber ball hitting a wall. As the speed increases to a moderate range between 3 and 5 kilometers per second, the story changes dramatically. The collision becomes violent and permanent. The outer layers of the nano-onion collapse inward, and the intense pressure forces the carbon atoms to rearrange themselves into a dense, diamond-like core. In this middle ground, the impact is strong enough to crush the hollow shells but not so strong that it shatters the material entirely, instead forging a new, harder center within the wreckage.

When the speed climbs even higher, exceeding 5 kilometers per second, the nano-onion is completely destroyed. The impact is so energetic that the structure fragments into a chaotic spray of atoms. Instead of a single object or a compressed core, the collision produces long, thin chains of carbon atoms, essentially turning the solid sphere into a gas of linear atomic strings. The researchers observed that the way the stress travels through the material is also unique. Unlike other carbon structures, such as nanotubes, which tend to break at specific weak points like their edges or centers, the carbon nano-onion distributes the stress evenly across its entire surface. This uniform distribution means the material does not have a single predictable breaking point; it simply yields to the pressure as a whole.

Perhaps the most striking discovery was the transformation of the chemical bonds themselves. Carbon atoms can link together in different ways, creating soft graphite-like sheets or hard diamond-like networks. Before the collision, the nano-onions were made entirely of the graphite-like type. After hitting the surface at moderate speeds, a significant portion of these bonds were forced to change into the diamond-like type, creating that solid core. At the highest speeds, the bonds became a chaotic mix of all types, with the material breaking down into linear chains. The simulations showed that regardless of the size of the nano-onion or the speed of the impact, the energy conversion was remarkably consistent. The kinetic energy of the moving object was transformed into potential energy stored in the deformed bonds at a rate of about 0.7 electron-volts per atom. This suggests that the fundamental physics of how these structures absorb and dissipate energy is universal, whether the object is small or large.

These findings provide a clear map of how carbon nano-onions react to the extreme forces of high-velocity impacts. The research demonstrates that these structures are not merely fragile shells but dynamic systems capable of undergoing profound structural changes. They can bounce back, transform into diamond-like cores, or disintegrate into atomic chains, depending on the force applied. This knowledge helps scientists understand the limits of carbon-based materials and opens the door to potentially using high-speed impacts as a method to synthesize new materials with tailored properties, such as creating diamond-like cores inside hollow spheres or generating specific atomic chains for future technologies. The work confirms that even in the chaotic violence of a high-speed crash, the behavior of matter follows precise, predictable rules.