Carbon Jet Experiment

Astrophysical Motivation

• To date, approximately 175 different molecules have been discovered in the interstellar medium and in the vicinity of stars; the overwhelming majority of these compounds contain carbon atoms. In a variety of extrasolar sources—such as comet tails and the envelopes of carbon stars—molecules consisting exclusively of carbon (so-called carbon clusters) have even been detected. Carbon clusters do not occur naturally on Earth but can be formed in the laboratory in supersonic jets, where pressure and temperature are very low.

Applications in Materials Research

• 
  Fullerenes are the third stable form of carbon, alongside graphite and diamond. However, their exact formation process remains unclear. They can occur in many different structures (e.g., carbon nanotubes) and thus exhibit a wide variety of electrical, thermal, and mechanical properties.

• Production of Synthetic Diamonds
  In the so-called CVD (Chemical Vapor Deposition) process for producing synthetic diamonds, a CVD diamond layer several micrometers thick is deposited onto substrates—such as carbide tools—in a vacuum chamber.

Theoretical calculations of the structure of pure carbon clusters yield very different cluster geometries depending on the molecular size:

• _Cn ≤ 10
  Small clusters with fewer than 10 carbon atoms generally have a linear shape. However, starting at n = 4, cyclic forms also exist, which—due to the total spin of the molecular orbitals—are fundamentally limited to even numbers of atoms (i.e., C₄, C₆, C₈, C₁₀, while C₅, C₇, and C₉ ... are not stable).

• 10 ≤_Cn ≤ 30
  In this range, cyclic structures dominate; depending on the number of atoms, these may consist of several interconnected rings. Furthermore, for n ≥ approx. 20, three-dimensional bowl-like structures are expected in addition to planar ring structures.

• _Cn ≥ 30
  When a molecule contains more than 30 atoms, closed three-dimensional shapes—known as fullerenes—can form. For these molecules to be stable, they must consist of at least 12 carbon pentagons and any number of hexagons. C₆₀ is therefore the smallest possible fullerene.