Putting the Incoming/Outgoing Correlation (INOUTCO) Ion Imaging Surface Scattering Technique to the Test in O Atom Scattering from Graphite

The interaction of hyperthermal oxygen atoms with graphitic carbon surfaces is of fundamental interest due to its importance in aerospace material degradation and in nanomaterials and nanodevice fabrication by plasma etching. In this work, we report the results of O(³P) atomic beam scattering from highly oriented pyrolytic graphite with incidence kinetic energies in the range 0.7–1.2 eV. Well-characterized incident beams of O(³P) are generated by VUV photolysis of carbon monoxide by a free-electron laser, and the scattering kinetic energy and angular distributions are measured by off-axis ion imaging. The results are used to benchmark an incoming/outgoing correlation ion imaging technique that is performed using a much simpler discharge source to generate O(³P) beams. By using the velocity information available from ion imaging to correlate the departure time of each scattered atom from the surface with the arrival time of atoms with a particular range of incidence velocities, the technique can achieve an incidence kinetic energy resolution much higher than the kinetic energy distribution of the incident beam. Good agreement is achieved between the two experimental approaches up to incidence energies of 1.0 eV, as long as the discharge source is used under conditions where background signal is kept low. The results are in qualitative agreement with trajectory simulations performed on a machine-learned spin-constrained triplet potential energy surface, which suggests that under the conditions used in this study, direct scattering takes place with limited triplet-to-singlet spin relaxation at the surface.