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We have investigated bulk-derived electronic structure of the valence transition system Eu(Rh 1– x Co x ) 2 Si 2 with x = 0 and 0.4 by means of hard x-ray photoemission spectroscopy. The Eu mean valence evaluated from the Eu 3 d spectrum for x = 0.4 gradually changes from 2.57 at 300 K to 2.92 at 20 K. On the other hand, the valence for x = 0 retains ∼2.1 in the temperature range from 300 to 20 K. Furthermore, the Eu 2+ 4 f component in the valence band for x = 0.4 was shifted by 150 meV towards the Fermi level compared to that for x = 0. Present results suggest that the increase in the hybridization strength between Eu 4 f and conduction electrons induces the valence transition, which is consistent with the Kondo volume collapse model.

We investigated the bulk-derived electronic structure of the temperature-induced valence transition system ${\mathrm{EuNi}}_{2}$(${\mathrm{Si}}_{1\ensuremath{-}x}{\mathrm{Ge}}_{x}$)${}_{2}$ ($x=0.70$, 0.79, and 0.82) by means of hard x-ray photoemission spectroscopy (HAXPES). The HAXPES spectra clearly show distinct temperature dependencies in the spectral intensities of the ${\mathrm{Eu}}^{2+}$ and ${\mathrm{Eu}}^{3+}\phantom{\rule{4pt}{0ex}}3d$ components. For $x=0.70$, the changes in the ${\mathrm{Eu}}^{2+}$ and ${\mathrm{Eu}}^{3+}\phantom{\rule{4pt}{0ex}}3d$ spectral components with temperature reflect a continuous valence transition, whereas the sudden changes for $x=0.79$ and 0.82 reflect first-order valence transitions. The Eu $3d$ spectral shapes for all $x$ and particularly the drastic changes in the ${\mathrm{Eu}}^{3+}\phantom{\rule{4pt}{0ex}}3d$ feature with temperature are validated by a theoretical calculation based on the single-impurity Anderson model (SIAM). SIAM analysis reveals that the valence transition for each $x$ is controlled by the $c\ensuremath{-}f$ hybridization strength and the charge-transfer energy. Furthermore, the $c\ensuremath{-}f$ hybridization strength governs the valence transition of this system, which is either first order or continuous, consistent with Kondo volume collapse.

Electronic structures of the ternary-layered semiconductor TlGaSe2 have been investigated by hard and soft X-ray photoemission spectroscopies (HAXPES and SXPES). The spectral shape of all core levels obtained from HAXPES and SXPES can be represented by a symmetric Lorentzian, reflecting the semiconducting nature of TlGaSe2. Peak positions of the same bulk components, obtained from HAXPES and SXPES, are almost the same. This suggests that the recoil effect is ignorable for TlGaSe2 and that the HAXPES spectra of this material provide us the information on the intrinsic bulk electronic structures. The valence-band HAXPES spectrum is composed of two main features and is well reproduced by the theoretical calculation. The estimated value of 2.0 eV for the energy gap is consistent with the results from the optical measurements. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Bulk electronic structures of covalent-chain antiferromagnets TlFeS2 and TlFeSe2 have been investigated by hard X-ray photoemission spectroscopy (HAXPES) and band calculations based on the full-potential linearized augmented plane wave method. Competition between localized and delocalized characters of Fe 3d electrons has been suggested by the slight discrepancies between valence-band HAXPES spectra and calculated density of states, as well as Fe 2p spectra with a broad charge-transfer satellite. It is assumed that this competition closely related to the crystallographic onedimensionality of these materials. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The temperature dependence of the core-level and valence-band electronic structures of TlGaTe2 and TlInSe2 that exhibits high values of Seebeck coefficient has been studied by hard X-ray photoemission spectroscopy over the temperature range 40–450 K. The relative peak position and peak width for Tl 4f, Ga 2p and Te 3d in TlGaTe2 are determined. It is shown that not only chemical shift defying the peak position but also electron-phonon interaction responsible for temperature line-broadening has rather peculiar temperature behaviour that reflects incommensurate phase transition. Thermoelectric power of TlGaTe2 is evaluated and found to be very close to that of TlInSe2. It is shown that Tl 4f spectra of both compounds also display close similarity (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

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.

TlInSe 2 with a quasi one-dimensional chain structure and a giant Seebeck coefficient of more than 10 6 μV/K below 140 °C has been investigated by means of angle-resolved photoemission spectroscopy at 50 K and 280 K. The obtained energy bands favorably agree with the calculated band structure and show quite noticeable dispersion in the direction normal to the chains. A rigid shift toward lower binding energies, a splitting and the formation of the mini-gap-like structures are clearly observed in the experimental electronic bands with the temperature reduced to 50 K. These features are indicative of an incommensurate superlattice phase emerging in TlInSe 2 with temperature, and causing the record-breaking values of Seebeck coefficient.

We have measured Ir 4f core-level photoemission spectra using an excitation photon energy of 6 keV for single crystalline CuIr 2 S 4 at 250 and 200 K across the metal–insulator transition temperature of about 226 K . The Ir 4f spin–orbit doublet shifts by about 0.25 eV towards higher binding energy with decreasing temperature. Tails and satellites around 1 and 13 eV , respectively, higher in binding energy than the peaks of Ir 4f doublets are observed in the 250-K spectrum, but they almost disappear at 200 K . The peak analysis here done indicates that the Ir 4f spectrum at 200 K consists of two components 0.2 eV apart corresponding to the charge separation of Ir ions in CuIr 2 S 4 .

High-resolution Ce 4d–4f resonant photoemission spectra near the Fermi level of CeSi with the Neel temperature of 5.9 K have been measured at temperatures from 5.6 to 200 K, in order to investigate the competition between the Ruderman–Kittel–Kasuya–Yoshida (RKKY) interaction and the Kondo effect. As temperature is decreasing down to 30 K, the intensity due to the Ce 4 f 5 / 2 1 final state increases because of the evolution of the heavy Fermion behaviour caused by the Kondo effect. The intensity, however, decreases gradually from 30 to 5.6 K. This indicates that the heavy Fermion behaviour is strongly suppressed by the anti-ferromagnetic ordering due to the RKKY interaction.

Mn 3s photoemission spectroscopy has been performed at 300 and 100 K for Pr 0.5 Ca 0.5 MnO 3− δ which undergoes a charge-ordering transition around 235 K with decreasing temperature. We have observed in the Mn 3s spectrum the change in the Mn valency of Pr 0.5 Ca 0.5 MnO 3− δ accompanied by the transition. The Mn 3s spectrum at 300 K for Pr 0.5 Ca 0.5 MnO 3− δ is nearly identical to that of La 1.2 Sr 1.8 Mn 2 O 7 in which the formal valence of the Mn ion is +3.4. This is consistent with the fact that the oxygen deficiency δ is 0.05 for the present sample. On the other hand the Mn 3s spectrum at 100 K is well reproduced by a superposition of those for LiMnO 2 with Mn 3+ and for SrMnO 3 with Mn 4+ , while the mean Mn valency at 100 K remains being +3.4. This indicates that the Mn ions in Pr 0.5 Ca 0.5 MnO 3− δ are in the two different valence states below the transition temperature.

Eu 4f electronic structures of a temperature-induced valence transition system EuPd2Si2 have been investigated by bulk-sensitive high-resolution photoemission spectroscopy at temperatures from 20 to 300 K. The bulk Eu2+ 4f component is definitely distinguished from two surface Eu2+ 4f components. The changes in the spectral intensity of the bulk Eu2+ and Eu3+ 4f configurations and in the energy separation between these states are observed in the temperature dependent photoemission spectra. These temperature dependences are related to the valence transition of EuPd2Si2. The Eu mean valence is evaluated to be 2.75±0.03 at 20 K and 2.30±0.05 at 300 K. These values are in good agreement with those evaluated from Mossbauer and Eu LIII-edge X-ray absorption measurements.

Co 3d → 2p X-ray emission spectra of LaCoO 3 in the Co 2p photoabsorption region are measured at 40 and 300 K. The spectra mainly reveal features nearly independent of excitation photon energy. This indicates the highly covalent or strongly hybridized nature of the Co 3d state. The emission component showing resonant behavior is also observed. The temperature dependence of the resonant emission confirms that the wave function of Co 3d electrons is totally symmetric in the low-spin ground state and that for the spin state excited thermally through the magnetic transition around 100 K is not.

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.

Temperature-dependent change in core-level electronic structures of the layered semiconductor-ferroelectric TlInS2 with incommensurate phase has been investigated by means of X-ray photoemission spectroscopy. The temperature dependence of the relative peak position for each core level (Tl 4f, In 3d and S 2p) is found to differ very much in the regions bordering each other at the normal-incommensurate phase transition point of 218 K. The obtained data suggest that the charge distribution in TlInS2 dramatically changes upon passing from the normal phase (T > 218 K) to the spatially modulated incommensurate phase (T

We have investigated the layered manganite La0.5Sr1.5MnO4 surface at 100 K by scanning tunneling microscopy (STM). The surface roughness at 100 K below the charge and orbital order transition temperature (TCO = 220 K) is less than that at room temperature. By electron injection from the tip, STM measurements generate protrusions of about 2.5 nm diameter and 0.3 nm height in the scanned area on the surface. The induced protrusions at 100 K are aligned along the specific crystallographic directions, [100] or [010], whereas those at 300 K are randomly distributed.

Pr0.5 Ca0.5 MnO3−δ ( δ ∼ 0.05 ) exhibits a charge-order transition around 240 K. We have investigated the Mn 3d states of Pr0.5 Ca0.5 MnO3−δ above and below the transition temperature by using valence-band photoemission spectroscopy in the Mn 2 p → 3 d photoabsorption region. We have examined the Mn 3d electronic structure of Pr0.5 Ca0.5 MnO3−δ by comparing the photoemission spectra taken with photon energies well above the Mn 2p1/2 absorption peak and below the Mn 2p absorption edge in order that the spectrum may not be influenced by particular photo-excited states at different temperatures. After the charge ordering is developed, the obtained Mn 3d spectrum clearly shows increase in intensity around 0.8 eV below the Fermi level, whereas the off-resonance photoemission spectrum shows decrease there. These indicate that the hybridization between the Mn 3d eg orbitals with oxygen 2p decreases and the 3d eg electron is localized on the Mn3+ site when the charge ordering of Mn ions takes place and that there exists the polaron above the transition temperature.

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.

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.

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.

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.

Eu 4f states in EuPd 2 Si 2 have been investigated by bulk-sensitive high-resolution photoemission spectroscopy at temperatures from 20 to 300 K. A bulk Eu 2+ 4f component is definitely distinguished from two surface components. As the temperature is increasing, the spectral intensity of bulk Eu 2+ drastically increases around 150 K, while that of bulk Eu 3+ decreases. The bulk Eu 3+ 4f component is shifted by 0.2 eV from 100 to 200 K. The changes associated with the valence transition of EuPd 2 Si 2 are thus successfully observed in the temperature-dependent photoemission spectra.

In the present study, we used culture-independent methods to investigate the diversity of methanogenic archaea and their distribution in five permafrost samples collected from a borehole in the Kolyma River Lowland (north-east of Russia). Total DNA was extracted from methane-containing permafrost samples of different age and amplified by PCR. The resulting DNA fragments were cloned. Phylogenetic analysis of the sequences showed the presence of archaea in all studied samples; 60%-95% of sequences belonged to the Euryarchaeota. Methanogenic archaea were novel representatives of Methanosarcinales, Methanomicrobiales, Methanobacteriales and Methanocellales orders. Bathyarchaeota (Miscellaneous Crenarchaeota Group) representatives were found among nonmethanogenic archaea in all the samples studied. The Thaumarchaeota representatives were not found in the upper sample, whereas Woesearchaeota (formerly DHVEG-6) were found in the three deepest samples. Unexpectedly, the greatest diversity of archaea was observed at a depth of 22.3 m, probably due to the availability of the labile organic carbon and/or due to the migration of the microbial cells during the freezing front towards the bottom.

The 4f electronic state and the decay process of the photoexcited 4${\mathit{d}}^{9}$4${\mathit{f}}^{\mathit{n}+1}$ states in ${\mathrm{CeO}}_{2}$ are investigated by means of a resonant photoemission technique in the Ce 4d\ensuremath{\rightarrow}4f photoabsorption region. Resonant enhancement of the valence-band emission is clearly observed in the giant-absorption region. This confirms the existence of the 4f electron in the ground state of ${\mathrm{CeO}}_{2}$. The 4f-derived emission exhibits a single-peak distribution rather than a double-peak structure such as observed in other Ce compounds. The Ce 5p emission band, which spreads over about 10 eV and consists of at least three or more fine structures, also shows the resonant enhancement in the giant-absorption region. In the prethreshold region, the Ce 5p fine structures as well as the 4f emission band show enhancements, but these constant-initial-state spectra are different from each other. The obtained results are discussed in terms of the mixed valence in the ground state of ${\mathrm{CeO}}_{2}$ and of possible intermediate configurations in the resonant photoemission process.

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.

The Ir 5d state in CuIr 2 S 4 is investigated by using IrS 6 -cluster-model calculations for the Ir 4f core-level and valence-band photoemission and bremsstrahlung isochromat spectra. The three experimental spectra are consistently reproduced in such a localized picture with a single parameter set of the model. The average d-d Coulomb energy between Ir 5d electrons in CuIr 2 S 4 is 3.5 eV smaller than those for 3d transition-metal oxides, while the hybridization between Ir 5d and S 3p orbitals is larger. This indicates that the lattice distortion is important in the charge-order transition of CuIr 2 S 4 .

Two peculiar types of electronic dispersive structures, irreproducible in bulk band calculations, have been observed in quasi-one-dimensional TlSe studied by angle-resolved photoemission spectroscopy. One is of the cross type centered at the Γ point and extending along the Γ–H–T direction parallel to the chains, which are formed along the crystallographic c-axis. The other is of the pyramid type with truncated pyramids regularly arranged along the Γ–N direction perpendicular to the chains. To an extent given by the obtained excitation photon energy dependence, the above electronic structures can be assigned to high-lying surface conduction bands resulting from secondary electron emission.

Valence-band photoemission and S L X-ray emission spectroscopies have been performed for CuIr 2 S 4 in order to investigate the electronic structure of the valence band. A structure around 1 eV below the Fermi level in the photoemission spectrum consists of Ir 5d as well as S 3p by taking into account its photon-energy dependent intensity. The S L 2 , 3 emission spectrum also shows a structure around 1 eV below the Fermi level, indicating that the state around 1 eV has the d-like or s-like character. These results indicate that S 3p has contribution to the electronic states near the Fermi level to some extent, and that the hybridization of Ir 5d with S 3p is important in understanding the electronic property of CuIr 2 S 4 .

Photoelectron spectra of a [110]-oriented epitaxial thin film of Ba0.6K0.4BiO3 have been studied by use of the synchrotron radiation to elucidate its electronic structure. Observed spectra shows a clear Fermi edge and agree with published band calculations. A normal emission study for the (110) surface shows a band crossing the Fermi level between the M and Γ points, which is assigned to the Bi-O sp orbital.

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.

Electronic energy bands of the Tl-based ternary chalcogenide TlGaTe2 with a quasi one-dimensional crystalline structure have been studied by means of high resolution angle-resolved photoemission spectroscopy (ARPES) in order to check for dispersive structures similar to the Dirac cone observed in the surface bands of Bi-based binary chalcogenides. Two linear dispersive structures which are not reproduced in band calculations for bulk material have been observed in the energy band along the Γ–N direction perpendicular to the chains. These dispersions form a cross-type structure that is centered at the Γ point and extends along the Γ–H–T direction parallel to the chains, reflecting, in our opinion, one-dimensional features of surface morphology of TlGaTe2. The cross-type structure, the energy position of which linearly varies with excitation photon energy, is observed only for high-grade quality surfaces of TlGaTe2. It is therefore assumed that the observed peculiar dispersive structure is caused by the Dirac-type dispersion of high-lying surface conduction bands and that ARPES detects the joint density of states.

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.

High-resolution vibrational electron energy loss spectroscopy has been used to study the adsorbed state of NO on the Si(100)(2×1) surface. At 300 K, NO is adsorbed dissociatively on the Si(100) surface in the disordered structure, and the Si 3 N and SiOSi species are formed. By heating at 1200–1300 K, the O adatoms are removed from the surface and the silicon nitride is formed; the (2×1) structure is recovered, which is interpreted to indicate that the nitride is formed mainly in the subsurface region.

High-resolution vibrational electron-energy-loss spectroscopy has been used to study the interaction of ${\mathrm{NH}}_{3}$ with the Si(100)-(2\ifmmode\times\else\texttimes\fi{}1) surface. ${\mathrm{NH}}_{3}$ is decomposed on the Si(100) surface at 300 K to form the ${\mathrm{SiNH}}_{2}$ and SiH species. It is proposed that the amino (${\mathrm{NH}}_{2}$) species is bonded to the dangling bond of the Si(100) surface atom. Changes in the adsorbed state of both species under heat treatment are discussed.