AVS 45th International Symposium
    Surface Science Division Monday Sessions
       Session SS-MoP

Paper SS-MoP12
Atom Probe Analysis of Dissociation of CO and N@sub 2@ Gas on a W(110) Oriented Tip

Monday, November 2, 1998, 5:30 pm, Room Hall A

Session: Surface Science Division Poster Session
Presenter: T. Shimizu, JRCAT, Japan
Authors: T. Shimizu, JRCAT, Japan
A. Ohi, JRCAT, Japan
H. Tokumoto, JRCAT, Japan
Correspondent: Click to Email
An atom probe ( AP ) is an attractive mass spectrometer of single-ion sensitivity. But the application of the AP technique to gas-surface phenomena is less advanced than the corresponding study of metallurgical processes. Because the high electric field for desorption induces the dissociation of gases, which hinders us from investigating the gas-surface catalytic phenomena themselves. We measured the dissociative and non-dissociative ions and estimated the temperature dependence of the dissociation probability. Here we introduced 10@super -7@ Torr x 10 s of CO and N@sub 2@ gas and investigated the dissociation on a W(110) oriented tip by using voltage-pulsed AP without a probe hole. The temperature of introduced gas was kept at RT and the tip temperature was changed from 50 K to RT. The count of gas ions increased with lowering temperature. Further AP at 50 K could detect two different states by the desorption field strength. A state desorbing at low field strength is related to the physisorption at low temperature, which was not observed at higher temperature. A state desorbing at high field strength is related to the trapping state following the dissociation. The dissociation probability decreased with lowering temperature. But below 100 K, the dissociation probability became almost constant ( 41% ( CO ), 45% ( N@sub 2@) ), which is caused by the field induced dissociation of chemisorbed gas. We postulated the ratio of field induced dissociation is almost constant up to RT and estimated the energy barrier from the trapped to the dissociation state as 30 meV (CO) and 22 meV ( N@sub 2@ ).