Yukihiro Taguchi

Adsorbed state of benzene on the Si(100) surface: Thermal desorption and electron energy loss spectroscopy studies

The adsorbed state of benzene on the Si(100) surface at 90 and 300 K has been investigated by the use of thermal desorption spectroscopy (TDS) and high resolution electron energy loss spectroscopy (EELS). Benzene is chemisorbed nondissociatively on Si(100) at 300 K, and the fractional saturation coverage corresponds to 0.27 benzene molecule per surface Si atom. It is proposed that chemisorbed benzene is di‐σ bonded to two adjacent Si atoms saturating the dangling bonds on Si(100). At 90 K, physisorbed multilayers of benzene molecules are formed in addition to the chemisorbed layer. The multilayers consist of the metastable transition layer (α2) and ‘‘bulk’’ multilayers (α3). These results are markedly different from those of benzene on the Si(111)(7×7) surface, and the origin of the crystal‐face specificity is discussed.

Adsorbed state of benzene on the Si(111) (7×7) surface

Abstract High-resolution electron energy loss spectroscopy and thermal desorption spectroscopy have been applied to the study of the adsorbed state of benzene molecules on the Si(111) (7×7) surface. Both physisorbed and chemisorbed states were found at 90 K. Physisorbed benzene is desorbed by heating to ≈ 200 K; chemisorbed benzene 315 and ≈ 325 K. It is proposed that benzene in the chemisorbed state is π-bonded to the Si(111) surface.

Temperature-Dependent Angle-Resolved Photoemission Spectra of TlInSe2: Manifestations of Incommensurate and Commensurate Phases

The energy band structures of the valence band of the TlInSe2 material with a quasi one-dimensional chain structure and a giant Seebeck coefficient at temperatures below 413 K were investigated by angle-resolved photoemission spectroscopy at 280 and 50 K. The obtained energy bands and the calculated band structure were found to correspond well in main futures. A detailed analysis using both experimental and theoretical data was performed and the obtained results were evident of the presence of the incommensurate phase linked to a certain point on the A line of the Brillouin zone of TlInSe2. A self-consistent picture of the phase transition in TlInSe2 was drawn after discussion using available data for this material. According to this picture, TlInSe2 at 50 K is already a commensurate material while the incommensurate-commensurate phase transition occurs between 280 and 50 K.

Photoemission study of benzene adsorbed on Si surfaces

Abstract Chemisorbed states of C 6 H 6 onSi(111)7 × 7 andSi(100)2 × 1 surfaces are studied by Si2 p core-level photoemission and polarization dependent C K photoabsorption measurements. The Si2 p spectrum of theSi(111)7 × 7 surface shows that charge transfer from the rest atom possibly to the adatom occurs upon C 6 H 6 chemisorption. It is considered that the charge transfer plays an important role in chemisorption of C 6 H 6 on theSi(111)7 × 7 surface. The C K photoabsorption spectra of chemisorbed C 6 H 6 show that the C ring plane is nearly parallel to both surfaces. However, C 6 H 6 on theSi(100)2 × 1 surface is distorted by chemisorption.

Photoemission Study of CeO2 and SrCeO3

Photoemission spectra of CeO2 and SrCeO3 have been measured in the Ce 4d → 4f photoabsorption region. The yield spectra of these compounds resemble each other in shape. The valence-band emission of SrCeO3 shows the resonant enhancement in the giant absorption region and the 4f-derived emission exhibits a single-peak distribution such as obtained in CeO2. Moreover, the Ce 3d photoemission spectrum of SrCeO3 has a three-peak structure. These results indicate the strength of the hybridization between the Ce 4f and O 2p states in the ground state of SrCeO3 is similar to that in CeO2.

Resonant x-ray emission spectra of CuO and La2CuO4

The 3d → 2p x-ray emission spectra of CuO and La2CuO4 are measured under the selective excitation from the Cu 2p core-level to the Cu 3d level. The main peak is observed at about 1.5 eV below the absorption peak in both materials. The width of the main peak in CuO is somewhat narrower than that in La2CuO4. In La2CuO4, a satellite is observed at 3.5 eV below the main peak, while the spectrum of CuO does not show a satellite clearly. The main peaks in both materials are ascribed to the transition to the 3d9 excited state and the satellite is attributed to the 3d10v-charge-transfer excited state. From the above results, it is confirmed that the hybridization between the 3d9 and 3d10v states is larger in La2CuO4 than in CuO.

3p - 3d resonant photoemission study of at low temperature

We have studied the Co 3d state of in the temperature range 20 - 110 K by using resonant photoemission spectroscopy in the Co photoabsorption region. By raising the sample temperature from 20 to 110 K, the Co 3d derived emission near the top of the valence band is transferred to higher binding-energies, and the relative peak intensity of two peaks in the satellite is changed. This is interpreted by a spin-state transition of the Co ion.

Temperature-Induced Valence Transition of EuPd2Si2 Studied by Hard X-ray Photoelectron Spectroscopy

We have studied the electronic structure of EuPd2Si2 by hard X-ray photoelectron spectroscopy (HX-PES) from 300 to 20 K. The temperature-dependent HX-PES spectra clearly show the valence transition, namely, the intensities of the divalent and trivalent Eu 3d components are abruptly changed. The change in Eu 3d spectral shape, especially the drastic change in the trivalent Eu 3d feature with temperature, can be explained within the framework of the Anderson model. The peak shift of Pd 3d core level with temperature indicates that the valence electrons of Pd contribute to the temperature-induced valence transition of EuPd2Si2.

High-resolution photoemission spectroscopy of CeSi single crystal

Abstract We have investigated the valence-band electronic structures for a CeSi single crystal using high-resolution ultraviolet photoemission spectroscopy at 7 and 290 K. The spectra do not show a so-called tail of Kondo resonance even at 7 K. This indicates that the Kondo effect is very weak in CeSi, that is, the Kondo temperature is very low. In comparing the spectrum measured at 7 K with that at 290 K, the spectral intensity at 7 K near the Fermi edge decreases and that in the energy range 20–100 meV increases. The redistribution of the spectral intensity is related to the formation of magnetic ordering in CeSi at low temperature.

Dispersion-Compensation Electron-Energy-Loss Spectrometer

A dispersion-compensation electron-energy-loss spectrometer which consists of two 90° spherical sectors has been constructed and its characteristics have been tested. We have obtained the detector current of 160 pA with the full-width at half maximum of 25 meV for the primary electron energy of 19.5 eV in the direct mode, where electrons passing through the monochromator are directly detected by the analyzer without reflection from a sample. The obtained characteristics have been discussed, and suggestions for the design of an advanced spectrometer have been given.