We report the observation and structural analysis of novel indium carbide gas phase cluster ions generated by bombardment of a clean indium surface by keV C60(–) ions. Positive In(m)C(n)(+) (m = 1–21, 1 ≤ n ≤ 9) ions were ejected off the surface and analyzed mass spectrometrically. C60(–) ion beam irradiation is shown to be an efficient way of producing new kinds of gas phase carbide ions with relatively balanced stoichiometries. The rise kinetics of the ion signal (immediate jump within the beam opening time to a plateau value) indicates that the formation/ejection of the carbide ions constitute a single impact event. In3C2(+) was found to be the most abundant carbide cluster ion. Optimal geometries of the different clusters were derived via density functional theory calculations. The acetylenic/cumulenic nature of the impact emitted cluster ions is manifested by the high abundance of In2C2(+), In3C2(+), and the calculated structures for In(m)C(n)(+) (m = 3–4, n = 2–8). Odd/even intensity alternations in the In3C(n)(+) (n = 1–8) and In4C(n)(+) (n = 1–9) abundances are observed and rationalized by the calculations.

We have measured kinetic energy distributions (KEDs) of large clusters emitted from five different solid targets following a single impact of C60− ion at 14 keV kinetic energy. It was found that all the large clusters emitted from a given target move with nearly the same velocity and that their KEDs can be described by a thermal distribution riding on a common center-of-mass velocity (shifted Maxwellian) of some precursor. This behavior is in sharp contrast to that observed when the incoming projectile ion is monoatomic. Different trends were observed when comparing the behavior of the KED families of group 5 early transition metal elements (Ta and Nb) with those of group 11 late transition metals (Cu, Ag, and Au). We propose a model for the initial phase of formation of the precursor and show that the measured KEDs can serve as both pressure and temperature probes for the impact excited, highly energized subsurface nanovolume, driving the ejection of the clusters. It is also shown that under the proposed impact scenario, thermally equilibrated conditions (of the atomic subsystem) can be established at the subsurface nanovolume on the early subpicosecond time scale relevant for the emission process. This conclusion is demonstrated both experimentally by the KEDs of the emitted large clusters (very high temperatures and center-of-mass velocity) and by molecular dynamics simulation of the temporal evolution of the thermal characteristics of the impact energized subsurface nanovolume.

In order to study the photodegradation of molecules located at the vicinity of a titanium dioxide photocatalyst, a well-defined structure comprised of alternating micro-stripes of TiO

We report the experimental observation and computational analysis of the binary tin-carbon gas phase species. These novel ionic compounds are generated by impact of C60(-) anions on a clean tin target at some kiloelectronvolts kinetic energies. Positive Sn(m)C(n)(+) (m = 1-12, 1 ≤ n ≤ 8) ions were detected mass spectrometrically following ejection from the surface. Impact induced shattering of the C60(-) ion followed by sub-surface penetration of the resulting atomic carbon flux forces efficient mixing between target and projectile atoms even though the two elements (Sn/C) are completely immiscible in the bulk. This approach of C60(-) ion beam induced synthesis can be considered as an effective way for producing novel metal-carbon species of the so-called non-carbide forming elements, thus exploring the possible onset of molecular level miscibility in these systems. Sn2C2(+) was found to be the most abundant carbide cluster ion. Its instantaneous formation kinetics and its measured kinetic energy distribution while exiting the surface demonstrate a single impact formation/emission event (on the sub-ps time scale). Optimal geometries were calculated for both neutral and positively charged species using Born-Oppenheimer molecular dynamics for identifying global minima, followed by density functional theory (DFT) structure optimization and energy calculations at the coupled cluster singles, doubles and perturbative triples [CCSD(T)] level. The calculated structures reflect two distinct binding tendencies. The carbon rich species exhibit polyynic/cummulenic nature (tin end capped carbon chains) while the more stoichiometrically balanced species have larger contributions of metal-metal bonding, sometimes resulting in distinct tin and carbon moieties attached to each other (segregated structures). The Sn2C(n) (n = 3-8) and Sn2C(n)(+) (n = 2-8) are polyynic/cummulenic while all neutral Sn(m)C(n) structures (m = 3-4) could be described as small tin clusters (dimer, trimer, and tetramer, correspondingly) attached to a nearly linear carbon chain. For example, the 1:1 (Sn:C) Sn3C3 and Sn4C4 clusters are composed of all-tin triangle and rhombus, correspondingly, with a short carbon chain (C3, C4) attached on top. The cationic Sn3C(n)(+) (n = 1-5) and Sn4C(n)(+) (n = 1-4) species exhibit various intermediate geometries. Structure calculations at the CCSD(T) level are essential since the segregation effect is not as easily evident based on the most stable structures calculated by DFT alone. Dependences of bond energies (per atom) reflect the evolution of the segregation effect. The mass spectral abundances could be reasonably rationalized in terms of calculated stabilities of the cluster ions with respect to various dissociation channels.

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