TOF measurement of electron volt energy hydrogen atoms reflected by stainless-steel surface

Reflection behavior of hydrogen ions with electron volt energy on stainless-steel surface was investigated by time-of-flight (TOF) measurement. First, the flight time of atomic hydrogen ions (not molecular ions or neutral atoms) from the RF plasma was measured. Good agreement with a Maxwell-Boltzmann (M-B) distribution was found, with a temperature of 11,000 or 12,000 K depending on plasma and vacuum conditions. Next, the flight time of atomic hydrogen ions reflected 90° by a stainless-steel surface was measured. In this case, the velocity distribution consisted of two components, corresponding to M-B distributions, one with 9500 or 6000 K and a second one with 300 K. The former and the latter correspond to direct reflection and desorption, respectively. In case of direct reflection, the observed energy reflection coefficient for hydrogen is in the range 0.86-0.5. Lower values of the energy reflection coefficient are an indication that the incident hydrogen atom has interacted with two or more hydrogen atoms on the surface before being released. In case of desorption, a hydrogen atom will be desorbed by a non-thermal process such as electron-induced or particle-induced desorption, since by thermal desorption hydrogen particles are desorbed as molecules, not as atoms.