Nitrogen adsorption and desorption at iron pyrite FeS2{100} surfaces.
We have investigated the interaction of nitrogen with single-crystal iron pyrite FeS(2){100} surfaces in ultra-high vacuum. N(2) adsorbs molecularly at low temperatures, desorbing at 130 K, but does not adsorb dissociatively even at pressures up to 1 bar. Atomic surface N can, however, be obtained with nitrogen ions and/or excited neutral species, generated by passing N(2) through an ion gun. Substantial nitrogen-induced disorder is seen with both ions and neutrals, and no ordered N overlayers form; a decrease in the S/Fe ratio is seen when exposing to nitrogen ions. Recombinative desorption leads to temperature-programmed desorption peaks at 410 and 520-560 K which we associate with interstitial atomic N and substitutional ionic N, respectively, in the surface regions. Thermal repair of sputter damage necessitates segregation of bulk S to the surface, which, over repeated experiments, leads to gross cumulative damage to the bulk crystal. The desorption temperatures associated with recombinative desorption of atomic N from FeS(2){100} are significantly lower than those measured for Fe surfaces. This is linked to the inability of FeS(2){100} to dissociate N(2), but suggests that N(ads) will be significantly more able to react with other species than it is on Fe surfaces.
Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB2 1EW, UK.
Tao
T
Liu
Israel
I
Temprano
Stephen J
SJ
Jenkins
David A
DA
King
Stephen M
SM
Driver
D000327:Adsorption; D003460:Crystallization; D007501:Iron / Q000737:chemistry*; D008958:Models, Molecular; D009584:Nitrogen / Q000302:isolation & purification*; D013440:Sulfides / Q000737:chemistry*; D013499:Surface Properties; D013696:Temperature; D014618:Vacuum
D013440:Sulfides; C011342:pyrite; D007501:Iron; D009584:Nitrogen