Kinetic-energy and mass analysis of carbon cluster ions in pulsed-laser-stimulated field evaporation

Unraveling the Metastability of C n2+ ( n = 2-4) Clusters

Pure carbon clusters have received considerable attention for a long time. However, fundamental questions, such as what the smallest stable carbon cluster dication is, remain unclear. We investigated the stability and fragmentation behavior of C _n²⁺ ( n = 2-4) dications using state-of-the-art atom probe tomography. These small doubly charged carbon cluster ions were produced by laser-pulsed field evaporation from a tungsten carbide field emitter. Correlation analysis of the fragments detected in coincidence reveals that they only decay to C _n-1⁺ + C⁺. During C₂²⁺ → C⁺ + C⁺, significant kinetic energy release (∼5.75-7.8 eV) is evidenced. Through advanced experimental data processing combined with ab initio calculations and simulations, we show that the field-evaporated diatomic ¹²C₂²⁺ dications are either in weakly bound ³Π_u and ³Σ_g^- states, quickly dissociating under the intense electric field, or in a deeply bound electronic ⁵Σ_u^- state with lifetimes >180 ps.

HIGH-FIELD FORMATION OF LINEAR CARBON CHAINS AND ATOMIC CLUSTERS

Linear forms of carbon are important in a wide variety of applications, ranging from highly conducting interconnects to field emission materials. By methods of field ion microscopy (FIM) and mass-spectrometry, it was revealed that linear carbon chains were present at the surface of carbon fibers after high-voltage treatment. The carbon chains attached to the specimen tips were produced in situ in a field ion microscope by unraveling of nanofibers using low-temperature evaporation in electric fields of the order of 1011 Vm-1. The unraveling of graphite is possible due to the ultimate strength of the monoatomic carbon chain. The maximum force before failure of carbon chains at 0 K is 7.916 nN at a strain of 0.19 and the ideal tensile strength is equal to 252.1 GPa. Molecular dynamics simulations and high resolution FIM experiments are performed to assess the evaporation of atomic chains under high-field conditions. One can conclude that ions are field evaporated from a graphite surface initially in linear cluster forms, which decompose mostly into smaller atomic clusters and individual ions because of the ultrahigh-temperature excitation during unraveling.

Invited review article: Atom probe tomography

The technique of atom probe tomography (APT) is reviewed with an emphasis on illustrating what is possible with the technique both now and in the future. APT delivers the highest spatial resolution (sub-0.3-nm) three-dimensional compositional information of any microscopy technique. Recently, APT has changed dramatically with new hardware configurations that greatly simplify the technique and improve the rate of data acquisition. In addition, new methods have been developed to fabricate suitable specimens from new classes of materials. Applications of APT have expanded from structural metals and alloys to thin multilayer films on planar substrates, dielectric films, semiconducting structures and devices, and ceramic materials. This trend toward a broader range of materials and applications is likely to continue.