Hydrogen negative ion formation on a graphite HOPG surface

We report a study of hydrogen negative ion formation on highly oriented pyrolytic graphite (HOPG) as a result of proton scattering. In spite of the large workfunction of the surface, the negative ion formation probability was found to be quite large: significantly larger than for metal surfaces such as Mg or Al. As opposed to higher angle measurements, suggesting a decrease in anion yield on the exit angle with respect to the surface, measurements show an increase that resembles that of metals, as predicted by recent calculations for HOPG. However the magnitude is much larger.