In situ investigation of hydrogen interacting with Si(100)

摘要

Silicon surfaces are subject to intense interaction with hydrogen ambient common in vapor phase epitaxy. We distinguish characteristic configurations of vicinal Si(100) by in situ reflectance anisotropy spectroscopy: covered by protective oxides, cleaned by thermal annealing, and the formation of monohydrides during cooling. Even above 1000 K, most dangling bonds of the (2 X l)-reconstructed surface are saturated by hydrogen, while stability of Si-H bonds in the process gas ambient requires temperatures well below 750 K. Adjustment of hydrogen coverage employing alternative process gases provides experimental access to hydrogen adsorption and desorption characteristics valid for annealing in vapor phase epitaxy ambient. ;The magnetoresistance (MR) of Ni_2Mn_(1+x).Sn_(1-x) (0.40≤x≤0.52) is studied as functions of temperature and magnetic field in austenitic and martensitic phases. The maximum MR obtained is -36% (x=0.4) at 170 K with 7 T magnetic field during martensitic transition. The MR in the martensitic phase (maximum -2.2%) is less than that in austenitic phase (maximum -4.6%). The origin of less MR below and above martensitic transition is understood through the experimental data fitting with magnetic field dependence (H~n) of MR.