New Insight into the Gas Phase Reaction Dynamics in Pulsed Laser Deposition of Multi-Elemental Oxides

Abstract

The gas-phase reaction dynamics and kinetics in a laser induced plasma are very much dependent on the interactions of the evaporated target material and the background gas. For metal (M) and metal–oxygen (MO) species ablated in an Ar and O2 background, the expansion dynamics in O2 are similar to the expansion dynamics in Ar for M+ ions with an MO+ dissociation energy smaller than O2. This is different for metal ions with an MO+ dissociation energy larger than for O2. This study shows that the plume expansion in O2 differentiates itself from the expansion in Ar due to the formation of MO+ species. It also shows that at a high oxygen background pressure, the preferred kinetic energy range to form MO species as a result of chemical reactions in an expanding plasma, is up to 5 eV.

PLD plasma plume analysis: a summary of the PSI contribution

“…The electrons ejected from the surface originate either from the photoeffect and those formed due to the ionization of atoms. The laser-generated electrons are accelerated away from the vapour layer forming an electric field gradient with the ions via an electric double layer [ 35 , 36 , 41 ], an electric field in which the subsequently created ions are also accelerated gaining their often-observed large kinetic energy [ 28 , 41 , 42 ]. Here, the maximum kinetic energies of ionic species in the ablated plasma are strongly dependent on their masses, with higher masses yielding higher kinetic energies [ 41 ].…”

“…The dividing line is ~ 5 eV, which represents either the photon energy of the 248 nm laser or the dissociation energy of O 2 ( E diss (O 2 ) = 5.12 eV). At this O 2 pressure, it is E diss (O 2 ) because the amount of MO + species increases with increasing O 2 pressure, which means that more of these species are created than dissociated [ 42 , 60 ].

Fig.

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“…6 a The ratio of MO + /(M + + MO + ) vs. dissociation energy of MO + species as determined at 0.15 mbar O 2 . The dashed line represents the dissociation energy of O 2 , E diss (O 2 ) = 5.12 eV [ 42 , 60 ]; b Pressure dependence of La + , O + and LaO + in O 2 and Ar. Figure from [ 42 ].…”

“…The dashed line represents the dissociation energy of O 2 , E diss (O 2 ) = 5.12 eV [ 42 , 60 ]; b Pressure dependence of La + , O + and LaO + in O 2 and Ar. Figure from [ 42 ]. c Time-resolved plasma images from an LuMnO 3 target show in the left column the Lu I emission at 499 nm and in the right column the LuO I at 518.5 nm [ 74 ] …”

“…As for La + , the corresponding Ar and O 2 pressure dependencies show a decrease in the number of species with increasing pressure, whereas the number of LaO + species increases over the same pressure range by almost two orders of magnitude. This indicates that La + species are actively involved in the formation of LaO + species with increasing O 2 pressure a kinetic energy window of up to 5 eV to be the most effective energy regime to form LaO + species [ 42 ].…”