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>The stepwise dissociation of NH3on the Si(111)ndash;(7times;7) surface: Lowhyphen;temperature dissociative adsorption and thermal effects
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The stepwise dissociation of NH3on the Si(111)ndash;(7times;7) surface: Lowhyphen;temperature dissociative adsorption and thermal effects
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机译：The stepwise dissociation of NH3on the Si(111)ndash;(7times;7) surface: Lowhyphen;temperature dissociative adsorption and thermal effects
The molecular and dissociative adsorption of NH3on a clean Si(111)ndash;(7times;7) surface has been studied using highhyphen;resolution electronhyphen;energyhyphen;loss spectroscopy (HREELS), Auger electron spectroscopy, and temperaturehyphen;programmed desorption (TPD). All NHx(3ge;xge;1) species have been observed vibrationally under varying experimental conditions. Adsorbed molecular ammonia is observed by both HREELS and TPD below 200 K. The absence of a strong dgr;s(NH3) mode in our vibrational spectra suggests that NH3is bound as a tilted species to the Si(111)ndash;(7times;7) surface. Ammonia exposures above 1.7times;1014NH3/cm2at 110 K populate a weakly bound NH3(a) state which desorbs upon heating with a peak desorption temperature of 115 K. The NH2(a) species is observed to form at 80 K at all coverages and exhibits an enhanced thermal stability at higher ammonia exposures. The NH(a) species is detected above 200 K by an energyhyphen;loss feature at 1100 cmminus;1, which we assign to the dgr;(NH) mode. NH(a) is stable to 750 K on high coverage layers. Finally, we observe an increase in the Sindash;H stretching frequency as the concentration of NH(a) and N(a) species is increased by heating.
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