Atom probe analysis of the dissociation of CO and N-2 gases on a W(110)-oriented tip

We studied the dissociation of CO and N-2 gases on a W(110)-oriented tip by an atom probe (AP) technique. We paid attention to the effect of electric field induced dissociation as well as the temperature dependence of dissoci ation probabilities. We first show that the AP can discriminate between phy sisorbed and trapped states based on the difference in desorption field str ength. Then we show that field-induced dissociation can be properly measure d. Finally, we conclude the activation energy required for the conversion f rom the trapped state to the dissociated state to be 30 meV for CO gas and 22 meV for N-2 gas. (C) 1999 American Vacuum Society. [S0734-2101(99)17004- 0].