DESORPTION PRODUCT YIELDS FOLLOWING CL2 ADSORPTION ON SI(111)7X7 - COVERAGE AND TEMPERATURE-DEPENDENCE

Desorption product yields obtained following adsorption of Cl2 on Si(111)7 x 7 were studied using temperature-programmed desorption (TPD) and laser-induced thermal desorption (LITD) techniques. At low chloride coverages of THETA/THETA-s < 0.6, where THETA-s is the saturation chloride coverage, TPD experiments monitored SiCl2 as the only desorption product at approximately 950 K. At higher chloride coverages of THETA/THETA-s > 0.6, a small SiCl4 TPD signal was also monitored at 950 K along with an additional SiCl2 TPD feature at 690 K. LITD experiments detected SiCl2 as the only desorption product in the LITD yield at low chloride coverages of THETA/THETA-s < 0.6. SiCl2 and SiCl3 LITD signals were both observed at higher chloride coverages of THETA/THETA-s > 0.6. In temperature-programmed LITD studies, the SiCl2 LITD signals persisted until 950 K, whereas the SiCl3 LITD signals were only observed up to 700 K. The magnitude of the SiCl3 LITD signal following saturation chlorine exposures also decreased as a function of adsorption temperature. The SiCl2 desorption products were assigned to the recombinative desorption of SiCl + Cl --> SiCl2. The SiCl3 LITD signals were attributed to either the direct desorption of SiCl3 surface species or the recombinative desorption of SiCl2 + Cl --> SiCl3. Based on photoemission and scanning tunneling microscopy investigations, the SiCl2 and SiCl3 desorption yields were correlated with the existence of mono-, di- and trichloride species on the Si(111)7 x 7 surface. Many similarities were also observed between the chlorides and hydrides on the Si(111)7 x 7 surface.