Photoemission Structure Factor Effect for Fermi Rings of the Si(111)√3×√3-Ag Surface

Abstract

The energy contour at Fermi level (Fermi surface) of the Si(111) √ 3 × √ 3-Ag superstructure was measured in several surface Brillouin zones (SBZs) by high resolution angle-resolved photoemission spectroscopy (ARPES). Fermi rings centered at Γ points were observed only in the second SBZs, but missing in the first SBZ. This phenomenon was successfully reproduced by a calculation of the optical transition matrix based on a simple tightbinding approximation for the surface topmost-layer Ag atoms; the intensity in the first SBZ is diminished by destructive interferences in the matrix elements (i.e., photoemission structure factor). Thus with the known atomic orbital components of the surface structure, we can predict the photoemission intensity distribution and correctly understand the band structure. [DOI: 10.1380[DOI: 10. /ejssnt.2004 Keywords: Angle-resolved photoemission spectroscopy; Fermi surface; Photoemission structure factor; Surface state; Band dispersion; Ag; Si Angle-resolved photoemission spectroscopy (ARPES) has been a powerful tool to determine electronic structures (band dispersion and Fermi surface) of a solid material, especially crystal surfaces. However, the technique often enables to detect the bands only in the limited (surface) Brillouin zones though the band structures should repeat in every Brillouin zone. In other cases the observed intensity distributions of band structures sometimes look asymmetric depending on the polarization of exciting light. These phenomena are in many cases due to k-dependent transition probability of electrons from the initial to the final states in the photoemission process. This complication sometimes raises discrepancies among researchers in the band structure determination. A solution for this issue is to record the photoemission intensity distribution across the full hemisphere for both polar and azimuthal emission angles covering several Brillouin zones [1][2][3]. This is owing to recent developments of bright excitation sources and high-resolution electron analyzers with parallel detectors.It is well known that ARPES measurements of the Si(111) √ 3 × √ 3-Ag surface, one of the most widely studied prototype of metal-on-semiconductor systems, show such a property. Previous ARPES studies revealed a parabolic surface-state band (S 1 band) crossing Fermi level, having a circular Fermi surface (Fermi ring) around Γ points. However, the rings were observed only in the second √ 3 × √ 3-surface Brillouin zones (SBZs), but not in the first SBZ [4][5][6][7][8][9][10][11][12]. It has been proposed that the phenomenon is originated from a coupling of the S 1 surface state with the bulk states of Si substrate crystal, because there is an overlap in energy-momentum space between the S 1 state and bulk states only in the first SBZ [9]. Here, we show another explanation for it in terms of the k-dependent transition probability, i.e., an interference effect in the matrix elements of optical transition, socalled photoemission structure factor (PSF) or Brillouinzone-selection e...

Electrical Resistance of a Monatomic Step on a Crystal Surface

“…This is supported by experimentally observed linear I-V curves in the present conductivity measurements and theoretically by the WKB tunneling regime typically used in STM theories [22]. Inserting T determined above and k F (0:1 A ÿ1 ) determined in the previous ARPES measurements for the 3 p 3 p -Ag surface [2,3,21] into Eq. (2), 2D at a monatomic step on this particular surface is determined to be 2D 94 10 3 ÿ1 m ÿ1 .…”

“…In the figure, the energy position on the horizontal axis is referred to as the bottom of the surface-state band, E min . According to previous ARPES studies [2,3], E min is located at a binding energy 0:3 eV below E F , so that E F is located at 0:3 eV in Fig. 3(c).…”

“…Its physical properties have been well studied on noble metal surfaces [15][16][17][18][19]. The wavelength varied with tip bias (not shown here) [15,16], and the energy versus wave number dispersion obtained through the bias-dependent standing waves showed a parabola with an effective mass equal to that obtained by angle-resolved photoemission spectroscopy (ARPES) [2,3,20,21]. Figure 3(b) shows topographic STM and dI=dV profiles over a step.…”

“…The surface has a parabolic electronic band crossing the Fermi level with a circular Fermi surface, indicating an isotropic twodimensional free-electron like metal of monolayer thickness [2,3]. Recently, transport measurements with stateof-the-art monolithic micro-four-point probes (MFPP) and four-tip scanning tunneling microscope (STM) probes have been reported to be successful in obtaining (anisotropic) conductance values of atomic-scale structures on semiconductor surfaces, including the Si111 3 p 3 p -Ag surface [4 -9].…”

Electrical conduction through a monatomic surface step

“…[7] Since reflection phase shift at a scatter is related with transmission through it, a research of a standing wave will lead to obtaining its conductivity. Using an isotropic two-dimensional (2D) metallic surface, Si(111) √ 3 × √ 3-Ag, [8][9][10][11] described below, we have examined the issue. In this research, we studied conductance of a single atomic step through detailed analyses on standing waves near the steps and surface transport measurements.…”