VLEED from O-Cu OOl

VLEED (with E 16 eV, or lower than the plasma excitation energy) spectral collects simultaneously comprehensive yet nondestructive information from the outermost two atomic layers about the bond geometry, surface potential barrier (SPB), valence electrons (DOS features), Brillouin zones, and work function, reaction dynamics [69, 70]. VLEED is very insensitive to dislocations of atoms in the third layer and below [69, 70]. In the VLEED, electron beams interact with the valence electrons of atoms in the outermost two layers and resonant within the barrier of surface potential. 

With respect to the clean Cu(OOl) surface, the SPB is parameterized by varying Zo over —2.5 1.25 [for pure Cu(OOl)] in a step of 0.25 (atomic unit). A contour plot of Zo versus E is then drawn with a matching between the calculated intensity and the measured data, 7c(zoi, = 1.0 0.05. The ZoiE) contour plot is the 

2 Angular-resolved VLEED Brillouin Zones, Band Structure, and Bond Geometry 

Decoding the angular-resolved VLEED profiles from the O-Cu(001) surface has yielded static information about the Brillouin zones, band stmcture, and bond geometry (Fig. 3.7 [71, 72]). Calculations also reveal the nonuniformity and anisotropy of the SPB, and the distribution of the DOS in the upper part of the valence band. Oxygen adsorption has reduced the inner potential constant (Vo) by 9.6 % (from 11.56 to 10.5 a.u.) and the work function by 1.2 eV from 5.0 to 3.8 eV. The oxygen-induced reduction in Vq is due to the transportation of atoms and valence electrons at the surface. The lowered work function arises from surface dipole formation that increases the local charge density. 

VLEED profiles. The VLEED I—E profiles were collected from a Cu(OOl) surface exposed to 300-L oxygen. For the symmetry consideration, angles from 18.5° to 63.5° with 5° increment are sufficient to represent the fiiU azimuth of the surface. The following feamres the VLEED fine-structure in Fig. 3.7  

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C.Q. Sun, Angular-resolved VLEED from O-Cu(OOl) Valence bands, chemical bonds, potential barrier, and energy states. Int. J. Mod. Phys. B 11(25), 3073-3091 (1997)... 

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