Scaling law for the ion-induced electronic sputtering of intact biomolecules: Evidence of thermal activation

Abstract

A linear scaling is found for intact biomolecules in the form of $\ln (Y∕S_e)-1∕S_e$ where $Y$, and $S_e$ are the sputtering yield and the electronic stopping power, respectively. The law is in good agreement with the experimental data for valine, leucine, and insulin molecules in various charge states in a broad range of $S_e$. The thermal spike model of the author is applied and the activation energies of desorption $U$ are obtained from the slope of the semilogarithmic lines. $U$ is considerably higher for neutral leucine molecules than for ions. The Coulomb contribution to $U$ for molecular ions does not depend on $S_e$ in a broad range. During sputtering, the specific heat is approximately 10% of its room temperature value for valine and leucine.