Mechanisms of molecular emission from phenylalanine monolayer deposited on free-standing graphene bombarded by C60 projectiles

Abstract

The Molecular Dynamics (MD) computer simulations are used to gain insight into the mechanism of molecular ejection from a monolayer of phenylalanine (C9H11NO2) molecules deposited on free-standing two-layer graphene. The system is bombarded with C60 projectiles with different kinetic energy and angle of incidence. Mass spectra, sputtering yields, and angular distributions of emitted particles are recorded in two bombardment geometries, in which the projectile hits the sample from above and below.The sputtering yields increase with the primary kinetic energy. There is an optimal angle of incidence for each kinetic energy, leading to the most effective molecular emission. The value of this angle increases with kinetic energy. The interplay between the area energized by the impinging projectile, the energy back-reflection, and molecular fragmentation determines the shape of the yield dependence on the angle of incidence. The bombardment geometry has little effect on the efficiency of molecular emission. Generally, organic molecules are emitted by interaction with the projectile and/or a graphene substrate. The main factor affecting the relative contribution of each of these interactions is whether graphene is punctured. The implications of current results for the potential use of graphene supports in Secondary Ion Mass Spectrometry are discussed.