Angle-resolved photoelectron spectroscopy investigation of intrinsic surface states on the Ge(001)-(2 × 1) reconstructed surface

Optical anisotropy of Ge(001)

“…The energy states related to this anisotropic ordering are probably outside the photon energy region studied. UPS measurements [4] showed that the low binding energy features especially are changed into a structureless electron distribution on adsorption of molecular oxygen. Auger electron spectroscopy measurements clearly indicated that additional states were found at higher binding energies due to oxygen exposure on the comparable Si(001) surface [18,19].…”

“…It is assumed that the influence of the matrix elements and the joint density of states is independent, which results in the factorization used in eqn. (4). In this qualitative interpretation we let the matrix elements determine whether a transition is optically active or not, using the symmetry properties of the initial and final states.…”

“…This well-defined surface with a small surface unit cell provides a unique opportunity to study the surface induced optical reflection anisotropy and to compare spectra obtained experimentally with theoretical calculations. In the past decade the geometric and electronic structure of the clean Ge(001)2 x 1 surface has been studied with ultraviolet photo-electron spectroscopy (UPS) [2][3][4][5][6][7], characterizing the occupied surface states. Scanning tunneling microscopy (STM) has provided an additional tool for obtaining spectroscopic information on the electronic structure around the Fermi energy [8][9][10].…”

Surface states on clean Ge(001)2×1 surfaces

“…The difference in the transitions measured with the tunneling microscope and that measured by ellipsometry may arise from the difference in k space emphasized by these techniques; the 1.8 and 3.3 eV transitions are a threshold energy difference that needs not occur at the T point of the surface Brillouin zone, which is emphasized in the tunneling spectrum. The filled state features have been determined by photoemission [8,14,18,25]. The difference could also arise from the different ranges of k ,, sampled by these different techniques.…”

“…Also during sputtering the crystal was heated to -700 K for about 15 min, followed by slow cooling. Auger spectra showed only a small residual carbon contamination of the surface [6,8]. We believe that this cleaning procedure results in a clean Ge(001)2 x 1 surface with a low density of defects; Alonso et al [9] applied a similar surface cleaning treatment, called SIBA (simultaneous ion bombardment and annealing), to GaAs surfaces.…”