ADSORPTION OF ALKALI METALS ON Si(111) SURFACE.

Second derivative energy loss spectroscopy (ELS) is a surface sensitive technique when the incident primary electron energy, E//p, is kept around 100 ev. This is because the electron penetration depth is minimal at this energy, and also the second derivative technique is sensitive to even minute changes in the ELS profile. Measurements similar to ours have already been made on Si(111)2 multiplied by 1 and Si(111)7 multiplied by 7 surfaces. For low primary energies (E//p equals 50-200) bulk transitions in ELS (Im 1/ epsilon ) compare well with optical absorption results (Im epsilon ), where epsilon is the complex dielectric function. A polished n-type (phosphorus doped, 0. 044 OMEGA -cm resistivity) single Si crystal was mounted in a Varian ultrahigh vacuum (UHV) chamber at approx. 2 multiplied by 10**-**1**0 torr base pressure. The sample was cleaned by Ar-ion sputtering and by heating to approx. 1000 degree C by an e-beam heating unit in back of the sample. Auger electron spectroscopy (AES) was used to monitor sample cleanness. AES indicated no trace of C or O after several hours of cleaning. The major contaminant was nickel, which was not removed with usual cleaning procedures. However, when annealed 30-45 min from 1000 degree C, Ni was observed to diffuse into the bulk Si and no trace of impurity was detected. LEED showed a clean 7 multiplied by 7 pattern.