H. Nishimoto

Structure factor in photoemission from valence band

Abstract Two-dimensional angular distribution of photoelectrons from valence band was analyzed using a tight-binding initial state. In simple cases, the angular distribution can be understood as a product of “ one-dimensional density of states (ODDOS)”, “ photoemission structure factor ”, and “ angular distribution from atomic orbital ”. This newly introduced “ photoemission structure factor ” is an intensity distribution in a reciprocal space similar to the X-ray or electron diffraction structure factor replacing scattering factor by the coefficient for each atomic orbital in the LCAO wavefunction. The remarkable symmetry-broken patterns observed from π band of single-crystalline graphite was clearly explained. The two-fold symmetry was obvious as the result of the “angular distribution from the pz atomic orbital” for the s- and linearly-polarized synchrotron radiation. The difference of the intensity in different BZs was clearly explained by the photoemission structure factor . Hence, the two-dimensional measurement can give us information not only (1)about the ODDOS, but also (2)about the symmetry of the initial state, and even more (3)about the coefficients in the initial state wavefunction.

Simultaneous angle-resolved measurement of the band structure of single-crystal graphite by an improved two-dimensional display analyzer

We have embodied a new version of two‐dimensional display‐type spherical mirror analyzer [H. Daimon and S. Ino, Rev. Sci. Instrum. 61, 57(1990)]. A couple of concentric hemispherical small grids and 12 pairs of obstacle rings have been attached to the original type of analyzer in order to operate with a constant pass‐energy mode and improve the uniformity of the energy resolution of the analyzer all over the detection area, respectively. We performed a test on the resolution of the analyzer, and applied it to the simultaneous angle‐resolved photoelectron spectroscopy on the band structures of single‐crystal graphite (Kish graphite) within the acceptance cone of ±50°. The observed band structure is in good agreement with those reported by other investigators. We observed a ring‐like pattern which enlarged as the binding energy approached the Fermi level. This ring is ascribed to the cross section of the π band. Although the designed energy resolution is 1% of the pass energy, the minimum value realized rea...

Photoelectron holography of the si(001) surface.

Three-dimensional images of the near-surface atom arrangement were calculated from two-dimensional photoelectron diffraction data by several imaging algorithms: (i) a basic method with a Fourier transformation at one kinetic energy over k space, considering the phase factor due to the path-length difference; (ii) energy summation of the above results; (iii) Fourier transformation within small k-space windows; and (iv) their combinations. Atomic images produced by these methods from the experimental Si 2p photoelectron diffraction patterns of an Si(001) surface are compared with the crystal geometry. The results show that the energy-summed small-window method, called SWEEP, gives the best images.

Two-dimensional angular distribution of photoemission spectra from the valence band of 1T-TaS2

Two-dimensional band structures of single-crystalline 1T-TaS2 have been directly observed by using a new version of two-dimensional display-type spherical mirror analyzer. The intensity distribution patterns for linearly-polarized synchrotron radiation normally incident on the cleaved surface have shown unusual angular distributions. The non three-fold symmetry is discussed by considering the angular dependence of the dipole transition probability for the s-polarized synchrotron radiation from each atomic orbital with particular symmetry, as well as the tight-binding initial state and a free electron like final state. In addition, circular dichroism in angular distribution (CDAD) of the photoemission pattern from the valence band is predicted for 1T-TaS2.

Unusual two-dimensional angular distribution of photoelectrons of kish graphite and 1T-TaS2

Abstract Two-dimensional patterns of angle-resolved photoemission are measured on Kish graphite and 1T-TaS 2 for s -polarized synchrotron radiation. Observed symmetry-broken patterns are theoretically discussed. The effect of the dipole selection rules by the s -polarized light is clarified. It is found for the first time that an interference of photoelectron waves from non-equivalent sites provides uneven intensity distribution in different Brillouin zones. The patterns of 1T-TaS 2 measured at 40 eV are remarkably different from those at 22 eV, which is explained by the resonant photoemission in the Ta 5 p core excitation region breaking the dipole selection rule due to the direct recombination type Auger transition.

Unusual photoelectron angular distribution of Kish graphite

Two-dimensional patterns of angle-resolved photoemission are measured on Kish graphite for s-polarized synchrotron radiation. Very wide acceptance cone allowed us to discuss the photoelectron intensity variation up to second Brillouin zone(BZ) in detail. Observed symmetry-broken patterns are theoretically discussed. It is found that an interference of photoelectron waves from non-equivalent sites provides imbalance in different BZs and the gross feature tells us the symmetry of the initial state.