Two-dimensional phase transformation probed by second harmonic generation: Oscillatory transformation of the K/Al(111) system

The technique of optical second harmonic generation is used to study phase transformations at two-dimensional surfaces and interfaces. Examples are given to illustrate that changes in surface symmetry, adsorption configuration, and electronic structure can be detected by this nonlinear optical technique. An oscillatory phase transformation of potassium adsorbed atoms on Al(111) probed by second harmonic generation is analyzed in detail

Pb0.4Bi1.6Sr2Ca1Cu2O8+xPb_{0.4}Bi_{1.6}Sr_{2}Ca_{1}Cu_{2}O_{8+x} and Oxygen Stoichiometry: Structure, Resistivity, Fermi Surface Topology and Normal State Properties

$Pb_{0.4}Bi_{1.6}Sr_2CaCu_2O_{8+x}$ ($Bi(Pb)-$2212) single crystal samples were studied using transmission electron microscopy (TEM), $ab-$plane ($\rho_{ab}$) and $c-$axis ($\rho_c$) resistivity, and high resolution angle-resolved ultraviolet photoemission spectroscopy (ARUPS). TEM reveals that the modulation in the $b-$axis for $Pb(0.4)-$doped $Bi(Pb)-$2212 is dominantly of $Pb-$type that is not sensitive to the oxygen content of the system, and the system clearly shows a structure of orthorhombic symmetry. Oxygen annealed samples exhibit a much lower $c-$axis resistivity and a resistivity minimum at $80-130$K. He-annealed samples exhibit a much higher $c-$axis resistivity and $d\rho_c/dT<0$ behavior below 300K. The Fermi surface (FS) of oxygen annealed $Bi(Pb)-$2212 mapped out by ARUPS has a pocket in the FS around the $\bar{M}$ point and exhibits orthorhombic symmetry. There are flat, parallel sections of the FS, about 60\% of the maximum possible along $k_x = k_y$, and about 30\% along $k_x = - k_y$. The wavevectors connecting the flat sections are about $0.72(\pi, \pi)$ along $k_x = k_y$, and about $0.80(\pi, \pi)$ along $k_x = - k_y$, rather than $(\pi,\pi)$. The symmetry of the near-Fermi-energy dispersing states in the normal state changes between oxygen-annealed and He-annealed samples.Comment: APS_REVTEX 3.0, 49 pages, including 11 figures, available upon request. Submitted to Phys. Rev. B

Scanning tunneling microscopy study of intermediates in the dissociative adsorption of closo-1,2-dicarbadodecaborane on Si(111)

Closo-1,2-dicarbadodecaborane (C2B10H12) is a source compound found to be suitable for the deposition of a high resistivity form of boron-carbide (B5C), and the fabrication of boron-rich semiconductor devices. A scanning tunneling microscope (STM) was used to image these molecular icosahedra on Si(111)-(7 x 7). Molecular decomposition (tip induced and otherwise) produced a boron-carbide/silicon interface with pronounced heterojunction electronic characteristics. In STM, this interface is characterized by a disordering of the Si(111)-(7 x 7) reconstruction. We suggest, based on Auger electron spectroscopy data and low-energy electron diffraction observations, that boron atoms from the dissociated source molecules substitutionally occupy selvedge sites, as in the boron-induced (√3 x √3)R30° reconstruction of Si(111)

Surface-Wave-Induced Interference Effects in Angle-Resolved Photoemission

New features are observed in normal-emission photoelectron spectra from Ni(100) in a narrow range of photon energies around 25 eV. These features are inconsistent with either direct transitions from the bulk or emission from occupied surface states or resonances. We suggest that they are a consequence of interference between the ordinary direct transition emitting an electron in the normal direction and the excitation from the same initial state into a final state that would normally be emitted from the surface at Γ― in the second surface Brillouin zone, but at this energy is trapped in a surface wave