The effect of the molecular mass on the sputtering by electrosprayed nanodroplets

The Effect of the Molecular Mass on the Sputtering of Si, SiC, Ge, and GaAs by Electrosprayed Nanodroplets at Impact Velocities up to 17 km/s

“…The present values continuously extend previous measurements at lower stagnation pressures (up to 39 GPa), of the bombardment of these semiconductors by EMI-Im (Borrajo-Pelaez et al 2013). The only anomaly in the topography of these targets is the very strong dependence of the roughness of silicon on stagnation pressure below 30 GPa, for the case of liquids with high molecular mass: in this lower velocity range, the roughness produced by liquids like EMI-Im and TPP is much higher than that produced by liquids with light molecules like EAN and formamide; furthermore the roughness for the high molecular mass liquids displays a strong maximum around 20 GPa, and drops sharply afterward transitioning toward the values measured in the present study (Borrajo-Pelaez et al 2013;Borrajo-Pelaez and Gamero-Castaño 2015). Figure 5a shows the sputtering yield as a function of the kinetic energy of the EAN and EMI-Im molecules.…”

“…Instead, Figures 5a and b suggest that the physics of nanodroplet sputtering are driven by collisions between atoms and molecules proceeding in the absence of local thermodynamic equilibrium. This conclusion, previously proposed for the sputtering of silicon (Borrajo-Pelaez and Gamero-Castaño 2015), is now shown to be an intrinsic characteristic of nanodroplet sputtering. Figure 6 shows the sputtering rate as a function of the acceleration voltage.…”

“…Although the presence of fluorine in the EMI-Im molecule, its absence in EAN, and the strong reactivity of this element suggest that chemical enhancement could be the reason for the more efficient sputtering of EMI-Im compared to EAN, we expect this effect to be minor based on the following arguments: the sputtering phenomenology of the ionic liquid TPP, which does not contain fluorine but has a high molecular mass, is similar to that of EMI-Im and different to the low molecular mass liquids EAN and formamide (Borrajo-Pelaez and Gamero-Castaño 2015); at the impact energies used in this study it is unlikely that a significant number of covalent bonds in the liquid molecule will break, which is required to produce fluorine radicals (Anders et al 2007); and the molecular dynamics simulations, which do not account for chemical effects, do reproduce the experimental sputtering trends.…”

“…Molecular dynamics simulations of the impact of EMIIm nanodroplets on single-crystal silicon have shown that the ejection is a combination of knock-on and thermal sputtering, both driven by the initial phase of the impact characterized by intense collisionality (Saiz and Gamero-Castaño 2014). Finally, a study of the effect of the projectile's molecular mass on the sputtering of silicon using six different liquids covering the mass range between 45 and 773 amu has revealed an important dependence on this parameter, the larger the mass the higher the sputtering yield and the roughness of the bombarded surface at fixed impact velocity (Borrajo-Pelaez and Gamero-Castaño 2015). This finding suggests that nanodroplet sputtering is an atomic-scale phenomenon proceeding under non-equilibrium conditions, and which is not amenable to continuum modeling.…”

“…We bombard targets of single-crystal Si, SiC, Ge, and GaAs with nanodroplets of EMI-Im and ethylammonium nitrate, EAN, whose impacts are known to have distinct effects on Si as a result of their significantly different molecular masses, 391 and 108 amu, respectively (Borrajo-Pelaez and Gamero-Castaño 2015). In addition, we use molecular dynamics to simulate the impacts of EMI-Im and EAN nanodroplets on Si and explain the role of the molecular mass on sputtering.…”