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AFM images and particle size distributions of nickel particles obtained with laser fluences of [(a) and (b)] and [(c) and (d)]. Inset of (c) shows a smashed-droplet-like shape of a very large particle. Note that the density of the particles larger than is exaggerated by ten times in (b) and (d).
Dependences of (a) particle density, (b) particle size, and (c) ion current on laser fluence. The vertical dashed lines indicate a possible threshold fluence across which laser ablation and particle formation mechanisms are different.
(a) Schematic illustration of Gaussian beam profiles and two ablation thresholds. (b) Transient ion signal obtained with a fluence of . The distance between the ion probe and the target is .
HRTEM images of two particles with diameters of (a) and (b) . An interface is apparent in (b), suggesting a core-shell structure. Moiré fringes are also discernable as marked by the arrows. (c) displays the SAED pattern (left) and FFT patterns taken at the core (middle) and the shell (right) regions of the particle shown in (b). The SAED pattern can be indexed as the  zone axis of fcc nickel.
TEM (a) and HRTEM (b) images of the particles obtained by ultrafast laser ablation of nickel in oxygen. Inset of (b) is a nanobeam electron diffraction pattern, which can be indexed as the  zone axis of NiO.
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