Electronic and magnetic properties of ruthenocuprates

We report on X-ray photoemission of core levels, valence band studies using angle-integrated photoemission, and magnetization measurements of ruthenocuprate and SrRuO₃ polycrystalline samples. The data indicate that the RuO₂ planes are the source of the energetics of the magnetic ordering. We also find that adding hydrogen leads to changes in the many-body response on both the CuO₂ and EuO planes. Received 23 August 2000     

New nuclide 139Tb and (EC +β+) decay of 138,139Gd

Excited levels in ¹³³Sn and ¹³⁴Sb, populated in spontaneous fission of ²⁴⁸Cm, were studied by means of prompt-γ spectroscopy, using the EUROGAM 2 multidetector array. The neutron i _13/2 single-particle energy has been determined for the first time in the ¹³²Sn region. The energy of the h _9/2 neutron level, proposed previously, has been confirmed. Received: 13 January 1999 / Revised version: 22 March 1999     

Influence of Sb doping on crystal structure and electrical property of SnO2 nanoparticles prepared by chemical coprecipitation

Sb doped SnO₂ (ATO) nanoparticles with Sb doping concentrations ranging from 0% to 20% (Sb/Sb+Sn) have been prepared by chemical coprecipitation using metallic Sn and SbCl₃ as raw materials. The influence of Sb doping concentration on crystal structure and electrical property was studied in detail. Results indicated that all ATO nanoparticles possessed the same tetragonal rutile structure as that of bulk SnO₂. The average crystal size of the ATO nanoparticles decreased from 16 to 7 nm by increasing the Sb doping concentration. The unit-cell volume of ATO nanoparticles was either expanded or contracted, strongly depending on the Sb doping concentration. The electrical resistivity decreased sharply from 111 to minimum of 1.05 Ω cm when the Sb doping concentration was increased from 0% to 15% and then increased slightly to 1.42 Ω cm when the Sb doping concentration was increased from 15% to 20%. Finally, high resolution X-ray photoelectron spectroscopy (XPS) measurement was employed to investigate the valence state of Sb in samples with various Sb doping levels.     

<Superscript>119</Superscript>Sn CEMS study of Sb doped SnO<Subscript>2</Subscript> film

Sb doped SnO₂ films prepared by DC sputtering and heating were characterized by ¹¹⁹Sn conversion electron Mössbauer spectrometry (CEMS). An asymmetric doublet was observed in the Mössbauer spectra of 1 %, 3 %, and 10 % Sb doped SnO₂ films. The peak ratios of doublets are considered to be due to the columnar crystal growth on the substrate. With the doping level of Sb, both the isomer shift (δ) and the quadrupole splitting (Δ) increased. After annealing, δ increased and Δ decreased for each sample. These results suggest the followings. The electron doping of the SnO₂ lattice by pentavalent Sb induces the increase of the electron density at the Sn^IV nucleus. The annealing process leads to more complete accommodation of the Sb dopant that results in more effective electron doping and therefore increasing isomer shift for tin. Simultaneously, the distortion of the lattice caused by Sb is relaxed and the quadrupole splitting decreases.     

A density functional study of plutonium dioxide

The electronic and geometric structures of bulk PuO₂ and its (110) surface have been studied using a periodic model within the generalized gradient approximation (GGA) of density functional theory (DFT). The sixty core electrons of the Pu atom have been represented by a relativistic effective core potential and scalar relativistic effects have been incorporated on the valence orbitals. For bulk PuO₂, we predict an equilibrium lattice constant of 10.10 a.u. and a cohesive energy of 17.28 eV, in good agreement with experimental data. For the (110) surface, upon relaxation, the distance between the top layer and the next layer is found to decrease by 0.12 ?, i.e. 5.3% of the corresponding interlayer distance in the bulk. The distance between the two oxygen atoms on the top layer is found to increase by 0.15 ?, i.e. 5.6% of the corresponding bulk value. The small surface relaxation energy of 0.268 eV per unit cell indicates the fair stability of this surface. The effective charges on Pu and O atoms show that the chemical bonding in this system is not purely ionic. Together with the metallic feature of the density of states (DOS) on the surface, the effective charge distribution provides some basis for understanding surface reactivity and corresponding support for catalysis. Received 16 June 2000     

<Superscript>119</Superscript>Sn Mössbauer studies on ferromagnetic and photocatalytic Sn–TiO<Subscript>2</Subscript> nanocrystals

Diluted Sn doped TiO₂ nanocrystals (Sn/Ti ratio: x ≤ 1.37 %) were synthesized by a simple hydrothermal method using pure reagents without any surfactant and dispersant material. The XRD of these samples showed an anatase phase, anatase and rutile mixed phases, and a rutile phase of TiO₂ and SnO₂ with the increase of Sn dopant concentrations. ¹¹⁹Sn Mössbauer spectra gave the broad peaks, which were decomposed into doublets and sextets because almost all these samples showed magnetic hysteresis even at room temperature. The titanium oxides doped with x ≤ 0.12 % showed the relatively large magnetic hysteresis and high photocatalytic activity. Mössbauer spectra of samples doped with x > 0.3 % were analyzed by one doublet and two sextets although the samples showed weak ferromagnetism. Three kinds of Sn species may be distinguished as Sn ⁴⁺ substituted TiO₂ and two different magnetic arrangements of Sn doped TiO₂: one with more oxygen defects and other at the interface of TiO₂ and precipitated SnO₂ containing Ti atoms. The correlation between various amounts of Sn sites and photocatalytic activity and/ or magnetic property was discussed.     

In-beam Mössbauer study of 57Fe using a secondary 57Mn beam and ion implantation

We have succeeded in obtaining well-resolved M?ssbauer spectra of ⁵⁷Fe arising from short-lived ⁵⁷Mn ( T _1/2 = 1.45 min) in Si and KMnO₄. The M?ssbauer spectra of ⁵⁷Fe in Si are well fitted with a curve consisting of two singlet lines, one being assigned as the interstitial Fe atoms and the other as substitutional ones. The relative intensities of the two lines infer that 60% of ⁵⁷Fe ( ←⁵⁷Mn) atoms land at the interstitial sites and 40% at the substitutional sites at temperatures between 30 K and 296 K. The result for the KMnO₄ sample suggests a presence of an exotic chemical species corresponding to a higher valence state than Fe^{6 +}. Received: 1 May 2001 / Accepted: 4 December 2001     

Comparative photoemission study of the electronic properties of L-CVD SnO2 thin films

In this work we present the results of comparative XPS and PYS studies of electronic properties of the space charge layer of the L-CVD SnO₂ thin films after air exposure and subsequent UHV annealing at 400 °C, with a special emphasis on the interface Fermi level position.From the centre of gravity of binding energy of the main XPS Sn 3d_5/2 line the interface Fermi level position E_F − E_v in the band gap has been determined. It was in a good correlation with the value estimated from the offset of valence band region of the XPS spectrum, as well as from the photoemission yield spectroscopy (PYS) measurements. Moreover, from the valence band region of the XPS spectrum and PYS spectrum two different types of filled electronic band gap states of the L-CVD SnO₂ thin films have been derived, located at 6 and 3 eV with respect to the Fermi level.     

Structural,magnetic and XPS studies of Sn0.95Co0.05O2-0.05 and Sn0.95Fe0.05O2-0.05 nanoparticles

Structural, microstructural, X-ray photoemission spectra (XPS) and magnetic properties of transition metal ion [5 mol% of Co (SC5) and Fe (SF5)]-doped SnO₂ nanoparticles have been studied. The SC5 and SF5 nanoparticles were synthesized by a chemical route using polyvinyl alcohol as surfactant. The doped SnO₂ crystallites were found to exhibit a tetragonal rutile structure and the average grains size was measured by the Scherer relation of X-ray diffraction. Transmission electron micrographs showed that the average grain size of SC5 is smaller than SF5. SC5 nanoparticles showed strong ferromagnetic behaviour but SF5 exhibited an F-centre exchange (FCE) mechanism. Temperature-dependent magnetization showed the values of phase transition temperature. XPS confirmed the presence of Sn–O–Co and Sn–O–Fe bonds in these SC5 and SF5 nanoparticles. The oxidation states of Sn, Co and Fe were found to be +4, +2 and +2, respectively, while the core level XPS peaks of Sn 3d, O 1s, Co 2p and Fe 2p were analyzed.     

Solvation and chemical reaction of sodium in water clusters

Na_m(H₂O)_n Clusters ( n = 1...200, m = 1...50) are formed in a recently build pick-up arrangement. Preformed water clusters traverse a sodium oven, where sodium atoms are picked up. At low sodium vapour pressure ( < 1×10^-4 mbar) pure Na(H₂O)_n clusters are observed in the mass spectra. At high sodium vapour pressure ( > 1×10^-3 mbar) the water cluster pick up more than 50 Na atoms and reaction products Na(NaOH)_n ( n = 2, 4...50) dominate the mass spectra. The even number of NaOH units in the products indicate that also in a finite cluster the reaction occurs in pairs as in the macroscopic reaction. Received 4 December 2000     

Structural and photoluminescence characters of SnO2:Sb films deposited by RF magnetron sputtering

The Antimony-doped tin oxide (SnO₂:Sb) films have been prepared on glass substrates by RF magnetron sputtering method. The prepared samples are polycrystalline films with rutile structure of pure SnO₂ and have preferred orientation of (1 1 0) direction. XRD measurement did not detect the existence of Sb₂O₃ phase and Sb₂O₅ phase; Sb ions occupy the site of Sn ions and form the substitution doping. An intensive UV-violet luminescence peak near 392 nm is observed at room temperature. Photoluminescence (PL) properties influenced by sputtering power and annealing for the SnO₂:Sb films are investigated in detail and corresponding PL mechanism is discussed.     

X-ray photoemission study of a sodalimesilica glass

A comparison is made between the X-ray photoemission spectra of the core levels and the valence band of a high purity sodalimesilica glass (21.3 wt.% Na₂O5.2 wt.% CaO73.5 wt.% SiO₂) with those for fused silica. In the valence band of fused silica three peaks are observed whereas in the compound glass an additional peak is found above the high binding energy edge of the valence band. The presence of non-bridging oxygen in the sodalimesilica glass not only broadens the oxygen core level asymmetrically to lower binding energy, but also broadens the lowest energy peak in the valence band. It is this latter broadening which certainly contributes to the shift in the fundamental optical absorption edge to lower energy in this glass with respect to pure SiO₂. An energy-level model is proposed for this glass. The diffusion of Na⁺ ions to the surface is also observed.     

Magnetic circular dichroism in Co 2p photoemission of Co/Cu(1 1 13): Separation of the fundamental spectra

We measured high-quality Co 2p magnetic circular dichroism (MCD) spectra in photoemission for > 5 ML Co films grown on Cu(1 1 13) using a “complete” experiment, where the sample magnetization and the light helicity vector were reversed separately. We show how the four measured spectra, M^±P^±, can be used to make new linear combinations, which correspond to the circular dichroism in the angular dependence (CDAD), magnetic linear dichroism in the angular dependence (MLDAD) and MCD spectra. The integrated signals of the MLDAD and CDAD can be used to estimate the error caused by the difference in the degrees of magnetization and light polarization, respectively, in the opposite alignments. The MCD signal integrated over the entire 2p region does not average to zero, as one would have expected from the sum rule for photoemission to a non-interacting continuum state. There is a strong MCD signal in the entire region between the 2p _3/2 and 2p _1/2 main lines with pronounced satellite structure. The differences between the measured and calculated results for an independent-particle and an atomic model indicate the presence of interatomic electron correlation effects and configurational mixing. Received 26 September 2000     

Experimental evidence for molecular ultrafast dissociation in O<Subscript>2</Subscript> clusters

Resonant Auger spectra of O₂ clusters excited at the O1s edge are reported. After excitation to the repulsive 1s^-13σ^* state, the resulting resonant Auger spectrum displays features that remain constant in kinetic energy as the photon energy is detuned. The shift between known atomic fragment features and these features is consistent with that observed for atoms and clusters in singly charged states in direct photoemission. These findings are strong evidence for the existence of molecular ultrafast dissociation processes within the clusters or on their surface.     

The neutron and proton two-particle nucleus 134Sb: New low-spin states observed in the decay of 134Sn and an estimate of the energy of the 7- isomer

Excited states in the ¹³⁴Sb nucleus, populated in the β^--decay of ¹³⁴Sn, have been studied at the mass separator OSIRIS. The ¹³⁴Sn activity was produced via fast neutron-induced fission of ²³⁸U target. A main result was the discovery of a very low-lying first-excited state of ¹³⁴Sb, at 13keV, which has led to a strong revision of the level scheme. The new results are compared with different theoretical calculations and with the known data for the analogous neutron and proton two-particle nucleus in the ²⁰⁸Pb region. On the basis of this comparison, the energy of the ( πg _7/2νf _7/2)_7- isomer is estimated to be about 250keV, some 100keV lower than previously reported. Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002 RID="a" ID="a"e-mail: anovak@fuw.edu.pl     

Influence of vacancies on the electronic structure of Co ZrSn Heusler alloys

The electronic structure of the Co_2-xZrSn Heusler alloys has been studied by X-ray photoelectron spectroscopy (XPS). XPS valence band spectra can be compared with ab initio electronic structure calculations using the linearized muffin-tin orbital (LMTO) method. The calculated magnetic moments per Co atom agree well with the moments obtained from experiment. The LMTO calculations also show the energy shifts of the Co, Zr and Sn valence electron states towards the Fermi level when the concentration of vacancies increases in these alloys. Received 9 March 1999 and Received in final form 6 May 1999     

Synthesis and microstructure of metal oxide thin films containing metal nanoparticles by liquid phase deposition (LPD) method

Au nanoparticles dispersed SiO₂-TiO₂ composite films have been prepared by a novel wet process, Liquid Phase Deposition (LPD) method. The composite films were characterized by XRD, XPS, TEM, ICP, SEM and UV-VIS absorption spectroscopy. The results showed that the SiO₂-TiO₂ composite films containing Au^III and Au^I ionic species were co-deposited from a mixed solution of ammonium silicofluoride, ammonium hexafluorotitanate, boric acid and tetrachloroauric acid. The heat treatment induced the reduction of Au ions and formation of Au nanoparticles in the film. TEM observation revealed that the Au nanoparticles with 5-10 nm in diameter were found to be dispersed uniformly in the SiO₂-TiO₂ matrix. The optical absorption band due to the surface plasmon resonance of dispersed Au particles were observed at the wavelength of 550 nm and shifted toward longer wavelength with increasing heat treatment temperature. Received 28 November 2000     

X-ray photoemission spectra measurements of CeNi2Sb2 and CeCu2Sb2

X-ray photoemission spectra, resistivity and susceptibility of CeNi₂Sb₂ and CeCu₂Sb₂ were measured and are discussed. The results indicate that these alloys are Kondo systems. For comparison of the valence band properties, the spectra of the isostructural alloys of RT₂X₂-type with R = La, Gd, T = Cu, Ni and X = Sn, Sb were investigated, too.     

SiC bonding in ( C 60 ) n Si m clusters

This paper deals with a new type of SiC bonding where silicon atom seems to bridge C₆₀ molecules. We have studied films obtained by deposition of (C₆₀)_nSi_m clusters prepared in a laser vaporization source. Prior deposition, free ionized clusters were studied in a time-of-flight mass spectrometer. Mixed clusters (C₆₀)_nSi_m were clearly observed. Abundance and photofragmentation mass spectroscopies revealed the relatively high stability of the (C₆₀)_nSi _n ⁺ , (C₆₀)_nSi _{n - 1} ⁺ and (C₆₀)_nSi _{n - 2} ⁺ species. This observation is in favor of the arrangement of these complexes as polymers where the C₆₀ cages may be bridged by a silicon atom. Free neutral clusters are then deposited onto substrate making up a nanogranular thin film (≃ 100 nm). The film is probed by Auger and X-ray photoemission spectroscopies, but above all by surface enhanced Raman scattering. The results suggest an unusual chemical bonding between silicon and carbon and the environment of the silicon atom is expected to be totally different from the sp³ lattice: ten or twelve carbon neighbors might surround silicon atom. The bonding is discussed to the light of the so-called fullerene polymerization as observed for pure fullerite upon laser irradiation. This opens a new route for bridging C₆₀ molecules together with an appreciable energy bonding, since the usual van der Waals bonding in fullerite could be replaced by an ionocovalent bond. Such an assumption must be checked in the future by XAS and EXAFS experiments. Received 15 November 2000