Distributions of C2 and C3 radical densities in laser-ablation carbon plumes measured by laser-induced fluorescence imaging spectroscopy

Abstract

We measured temporal variations of the distributions of C2 and C3 radical densities in carbon plumes produced by laser ablation of graphite in ambient He gas. Laser-induced fluorescence imaging spectroscopy was used for the measurement. The temporal variations of total numbers of C2 and C3 contained in plumes were evaluated by integrating the density distributions. The experimental observations have shown that the gas-phase production of C2 is comparable to the direct production from the target, while C3 is mainly produced in gas phase by three-body reactions between C and C2. In addition, we have discussed a scenario for the temporal evolution of heavy clusters (Cn with n⩾4). The present results are useful for understanding initial formation processes of carbon clusters in laser-ablation plumes.

Particle formation from pulsed laser irradiation of soot aggregates studied with a scanning mobility particle sizer, a transmission electron microscope, and a scanning transmission x-ray microscope

“…Evidence suggests that single-crystal (i.e., well ordered) graphite targets produce larger clusters than do amorphous carbon targets. 49,58 With laser irradiation in the visible and IR, small clusters consisting of a few carbon atoms are produced, 44,55,56,[59][60][61][62][63][64][65][66][67][68][69][70][71][72] but larger clusters (with as many as 100 carbon atoms) are also commonly observed in these wavelength regions under vacuum. 46,56,61,62,73 At these wavelengths large clusters, fullerenes, and nanoparticles can be formed at higher pressures 53,54,64,[74][75][76][77][78] or when expanded in a buffer gas into a vacuum.…”

“…The main products are C, C 2 , and C 3 and their cationic counterparts. [43][44][45][46][47][48][49][50][51][52] Small clusters initially produced are thought to form larger clusters via termolecular reactions, [53][54][55][56] and at higher pressures larger clusters have been observed. 57 The fine structure of the graphite substrate also appears to have an impact on the size of clusters produced.…”

“…This mechanism is consistent with observations of laser-induced particle production from graphite, particularly at wavelengths in the visible 65,74,[77][78][79] and infrared 53,64,75,76 regions at ambient pressures above 1 Torr or in free jet expansions into vacuum. Previous work on graphite has shown that small carbon clusters can react to form larger clusters, [53][54][55][56]81 which can then act as nucleation sites for particle growth. As indicated by the combined results of TEM images, STXM images, and NEXAFS spectra, this process leads to apparent changes in the sp 2 hybridization.…”

Dynamics of confined plumes during short and ultrashort pulsed laser ablation of graphite

“…The spectrum at x = 5 mm is still dominated by the C 2 * emission, which also increases in intensity slightly compared to the signal at x = 0 mm. This either indicates an increased production of C 2 fragments during the initial ablation, compared with ns pulse ablation, or more collision induced formation 30 of, and/or excitation to, C 2 * . Simulations of the fs ablation of graphite 14 have shown that ultrafast pulses produce significant carbon chains and clusters in addition to fast monomers, so it is likely that the enhanced C 2 * signal for fs pulses indicates an increased production of C clusters by fs pulses.…”

“…Monchicourt also concludes that binary collisions of C atoms in excited states would not lead to C 2 * production as the internal energy of the initial system would be too large to form a stable molecule. For 1.06 m Nd:YAG PLA of graphite in He, Sasaki et al 30 monitored the spatial distribution of C 2 and C 3 radicals by laser induced fluorescence. They concluded that the number of C 2 radicals produced by gas phase reactions was comparable with the direct ablation from the target.…”