The effective mass of a free-electron-like surface state of the Si(1 1 1)3×3-Ag surface investigated by photoemission and scanning tunneling spectroscopies

A small electron pocket composed of a metallic and parabolic surface-state band of Si(1 1 1)3×3-Ag was investigated in detail by high-resolution angle-resolved photoemission spectroscopy (ARPES) and scanning tunneling spectroscopy (STS). The Fermi surface was a complete circle (Fermi ring), and the band dispersion was determined three dimensionally in energy–momentum space. The effective mass (m*) was extracted by a new method, two-dimensional (2D) fitting to the band dispersion, and compared with the results of conventional analyses of energy and momentum distribution curves (EDC and MDC). The EDC (MDC) analysis gave a m* value larger (smaller) than that obtained by the 2D fitting method by about 20%. The m* obtained by the 2D fitting was in good agreement with the value obtained by the STS measurements of electron standing waves, giving the most plausible value of m*=(0.13±0.03)me (me is the free-electron mass) for the parabolic band.