Haruo Kuroda

The formation of hydrogen passivated silicon single-crystal surfaces using ultraviolet cleaning and HF etching

We have tried to develop a new procedure to prepare the clean surface of a silicon single crystal. We successfully prepared the contamination free bare silicon surface with ultraviolet cleaning followed by HF dipping with low concentration HF obtained by dilution by organic free ultrapure water, at room temperature under the atmospheric condition. X‐ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and ultraviolet photoelectron spectroscopy measurements proved thus prepared surface has a hydrogen monoatomic layer terminating the dangling bonds of silicon. The hydrogen termination was found to have remarkable passivation effect against surface oxidation reaction. A silicon thin‐film epitaxially grown on the prepared surface was confirmed to have perfect crystal structure and high‐purity level by scanning electron microscopy, reflection high‐energy electron diffraction, Raman spectroscopy and secondary ion mass spectroscopy.

X-ray photoelectron spectroscopic studies of CrO2 and some related chromium compounds

Core-electron and valence-band regions of crystalline CrO2, CrOOH, Cr2O3, and K2Cr2O7 have been studied. The XPS spectrum of the valence band region of CrO2 is interpretable in terms of Goodenoughs band-structure model, and the finite density of states at the Fermi level for this metallic compound is readily apparent, but the band profile shows no detectable change on traversing the Curie temperature. Whereas the ratio of the multiplet splittings recorded for Cr 3s levels in CrO2 and Cr2O3 are in reasonable agreement with theory, discrepancies were noted between observed and expected multiplet intensity ratios. Some evidence for shake-up satellites was also noted. The smaller binding energies of core-electron levels in the Cr4+ solid (CrO2) compared with the corresponding binding energies in Cr3+ compounds (Cr2O3 and CrOOH) are also discussed.

Efficient methods for solving the open-shell scf problem and for obtaining an initial guess. The “one-hamiltonian” and the “partial scf” methods

Abstract The “one-hamltonian” method combined with the “partial SCF” method for obtaining an initial guess of the orbitals is tested on open-shell restricted SCF calculations of the 2 Σ + state of PO and several excited states of o 3 , which showed pathological and slow convergence behavior in SCF calculations. The method is very efficient to obtain stable SCF solutions.

Polarized Cu K-edge XANES of square planar CuCl42− ion. Experimental and theoretical evidence for shake-down phenomena

To elucidate the origin of the shoulder structure which is known to appear about half-way up the Cu K-edge in the X-ray absorption spectra of Cu(II) compounds, polarized X-ray absorption spectra were measured on the single crystal of (creatinium)2CuCl4 by using synchrotron radiation. The transition responsible for the shoulder structure was found to be exclusively polarized in the direction normal to the molecular plane of the CuCl42− ion. The polarization dependence of other structures in the XANES spectra was also examined and compared with the results of ab initio SCF CI calculation. It is shown that the structure half-way up the Cu K-edge is due to the shake-down accompanying the 1s-4p= excitation, arising from the ligand-to-metal charge transfer induced by the core-hole creation. Structures attributable to the shake-down accompanying the 1s-4pσ and 1s-5p=, σ excitations were also found.

Bimetallic promotion of alcohol production in CO hydrogenation and olefin hydroformylation on RhFe, PtFe, PdFe, and IrFe cluster-derived catalysts

Iron-containing bimetallic catalysts were prepared from carbonyl clusters as precursors deposited on SiO2. FeRh4 and Fe2Rh4 cluster-derived catalysts showed high activity and selectivity for formation of ethanol and methanol in CO hydrogenation. Fe3Pt3, Fe6Pd6 and FeIr4 cluster catalysts gave methanol in high selectivity, while Fe-rich Fe4Pt and Fe4Pd were not selective catalysts. The RhFe cluster catalysts showed improved activity in hydroformylation of olefins; C4-alcohols were substantially obtained from C3 + CO + H2. Mossbauer and EXAFS studies on the Fe2Rh4/SiO2 catalyst show that highly dispersed RhFe bimetallic particles are located on the SiO2 surface, where Fe atoms exist preferentially in the state of Fe3+ even after H2 reduction. FTIR spectra of CO chemisorbed on Fe2Rh4/SiO2 exhibit a low-frequency band possibly due to the G and O-bonded CO on Rh-Fe3+ sites. Bimetallic promotion of alcohol production in CO hydrogenation and olefin hydroformylation is proposed to originate from the two-site interaction of Rh-Fe3+ (or Pt-Fe3+, Pd-Fe3+, IrFe3+) sites with CO to enhance migratory CO insertion.

Semiconductive Properties of Tetracyanoethylene Complexes and Their Absorption Spectra

The absorption bands characteristic of the solid molecular complexes of tetracyanoethylene are attributed to the charge transfer interaction between tetracyanoethylene and donor molecules.In the complexes with polycyclic aromatic hydrocarbons the energy gap associated with the semiconductivity agrees well with the energy of the charge transfer excitation in the crystalline state, while the former is much smaller than the later in the complexes with polymethylbenzenes and azulene.

Control of the chemical reactivity of a silicon single‐crystal surface using the chemical modification technique

A technique is developed to control the chemical reactivity of a silicon single‐crystal surface through chemical modification with atomic hydrogen. The reactivity of the reconstructed single‐crystal surface prepared by high‐temperature treatment in an ultrahigh vacuum is significantly decreased by capping the dangling bonds of top‐layer silicon atoms with hydrogen atoms. The Si—H bonds on the hydrogenated surface are found to be much more stable against oxidation than the Si—Si back bonds. The hydrogen‐passivated silicon surface is reactivated by electron beam irradiation. An ultrathin oxide layer pattern can be prepared using preferential oxidation of the area reactivated by a focused electron beam.

Fluorine-containing species on the hydrofluoric acid etched silicon single-crystal surface

The chemical structure and property of fluorine‐containing species on the hydrofluoric acid (HF) etched Si surface was examined by use of x‐ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. The fluorine content on the surface was found to increase with increase of HF concentration. A silicon surface etched by 50% HF has fluorine of 2.6×1014 atoms/cm2 as Si–F. Most of the Si–F bondings are rapidly hydrolyzed to Si–OH by rinsing the wafer in water. Thus prepared Si–OH groups are found to be useful as active sites for chemical modification of the bare silicon single‐crystal surface. The Si–F was observed not to influence the oxidation rate of HF etched silicon surface.

Cu K-edge XANES of (La1-xSrx)2CuO4, YBa2Cu3Oy and related Cu oxides. valence, structure and final-state effects on 1s-4pπ and 1s-4pσ absorption

Abstract The Cu K-edge absorption spectra of high- T c superconductors and related oxides, (La 1- x Sr x ) 2 CuO 4 (L(S)CO, x =0, 0.075 YBa 2 Cu 3 O y (YBCO, y ≈7−6), YBa 2 (Cu 1- x Co x ) 3 O y (Co substitution for Cu(1), x =0.33, y ≈7) ( y ≈7, ≈6) are interpreted by comparing with those of some divalent Cu complex oxides, Sr 2 CuO 3 and Ca 2 CuO 3 with the 1D CuO chain structure and Nd 2 CuO 4 and Gd 2 CuO 4 with the 2D CuO sheet structure. The twin-peak structure observed in the main absorption band arises from the final-state (core-hole screening) effect through ligand-to-metal charge transfer and can be assigned to the 1s-4pσ 1 (3d 10 L −1 ) and 4pσ 2 (3d 9 ) transitions. In the 1s-4pπ energy region below the 1s-4pσ main absorptio the onset and shoulder structures A–F are observed; the structures C and F are assigned to 1s-4pπ 1 and 1s-4pπ 2 transitions in the 2D CuO sheets of pyramidally coordinated [Cu(2)O 5 ] in YBCO and octahedrally coordinated [CuO 6 ] in L(S)CO, the structures B and E to those in the 1D CuO chain at the Cu(1) site of oxygen-rich YBCO, and the structures A and D to those in the linearly coordinated [Cu(1)O 2 ] ions of oxygen-deficient YBCO. The twin-peak structure both in the 1s-4pπ and 1s-4pσ energy regions indicates that the valence of Cu in YBCO and LSCO always has both d 9 and d 10 components; that is, the oxygen atoms coordinated to Cu take an important part in the balance of holes in the systems and in the hole conductivity on the 2D CuO sheet.

Preparation of diamondlike carbon films by electron cyclotron resonance chemical vapor deposition

Diamondlike carbon films were prepared by electron cyclotron resonance chemical vapor deposition. Structures of the carbon films were characterized by Raman spectroscopy and Fourier‐transform infrared spectroscopy. The relationship between the properties of films and growth conditions has been examined. High‐energy ion species extracted from a discharge of methane in the electron cyclotron resonance cavity, which is positively‐biased electrically against the earthed substrate, have an important role in the growth behavior of hard diamondlike carbon films.