Surface particularities in pulsed laser ablation/deposition of the ferromagnetic alloy NiMnSb

In this work we investigate the surface morphology and stoichiometry of the ablated targets employed with pulsed laser deposition (PLD) of thin films of the ferromagnetic half-Heusler alloy NiMnSb. The NiMnSb targets were: a pressed and sintered pellet and, respectively, polycrystalline discs grown by RF melting. The films were deposited using a KrF excimer laser (λ=248nm, τ=30ns, 600mJ/pulse maximum) delivering pulses at a repetition rate of 10Hz. SEM observations show different morphologies of the ablated surfaces in the two cases, which are further correlated with EDX analyses to explore surface segregation phenomena. The corresponding films are also considered. Apparently, the crystalline targets keep better the initial stoichiometry than the pressed ones, which in principle would indicate higher film stoichiometry and hence enhanced quality.