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The difference between La-deficient and Sr-substituting effects for La in LaCoO${}_{3}$ has been investigated by using x-ray photoelectron spectroscopy (XPS). On the basis of the relationship between the intensity of the ${}^{2}{T}_{2}$ line and the amount of low-spin Co${}^{3+}$ ions in these compounds, it is pointed out that La${}_{0.9}$CoO${}_{3\ensuremath{-}\ensuremath{\delta}}$ is in a highly covalent low-spin state and La${}_{0.8}$Sr${}_{0.2}$CoO${}_{3\ensuremath{-}\ensuremath{\delta}}$ is in a mixed spin state. From the Co $2p$ and valence-band XPS results, it is pointed out that the electronic state of La${}_{0.9}$CoO${}_{3\ensuremath{-}\ensuremath{\delta}}$ is quite different from that of Sr-substituting La${}_{0.8}$Sr${}_{0.2}$CoO${}_{3\ensuremath{-}\ensuremath{\delta}}.$ In order to explain the difference between La-deficiency and Sr-substitution effects in valence controlling of LaCoO${}_{3}$, it is considered that Sr substitution produces the Co $3d$ holes and La deficiency yields the O $2p$ holes.

The LaCuO{sub 3-y} perovskite is considered as the first member of the 01 (n-1)n series of {open_quotes}layered cuprates.{close_quotes} Highly oxidized, stoichiometric LaCuO{sub 3} is stabilized under very high oxygen pressures, and was synthesized in a cubic-anvil-type high-pressure apparatus at 5 GPa and 1400{degrees}C using excess amounts of KClO{sub 4} as an external oxidizing agent. Upon heating under ambient pressure the rhombohedral high-pressure phase loses oxygen yielding tetragonal, monoclinic, and orthorhombic forms of LaCuO{sub 3-y} as intermediate products before the final decomposition into La{sub 2}CuO{sub 4} and CuO or Cu{sub 2}O around 800{degrees}C. All three oxygen-deficient LaCuO{sub 3-y} phases could be isolated and their stability limits and corresponding oxygen contents conveniently investigated by annealing stoichiometric LaCuO{sub 3} in a thermo-balance of high sensitivity in order to in situ detect the exact amount of oxygen loss. The nominal copper valence values calculated from the oxygen contents are compared and discussed with XPS data as well as with the results evaluated from magnetic susceptibility measurements.

The surface of cleaved Bi2Sr2 CaCu2O3 (Bi2212) single crystals has been studied by means of scanning tunneling microscope (STM) and scanning tunneling spectroscopy (STS) at room temperature in ultrahigh vacuum. We obtain atomic images of the BiO surface using logarithmic current mode and conventional mode. It is demonstrated that the Bi atoms in the BiO plane are not missing. Some Bi atoms are depressed down below the BiO surface. STS obtained at different places of the surface shows more or less the same feature, indicating that local electronic density of states does not change much due to the depression or the well-known structural modulation. The possible origins of the variation in the period of the structural modulation in the BiO plane of cleaved Bi2212 single crystals extracted from STM images are also studied.

We have studied the effects of the kinetic energy of mass-separated O+ beams on the growth of CuO thin films deposited on unheated MgO(001) and at 510 °C, in energy ranging from 10 to 200 eV by x-ray photoemission spectroscopy, x-ray diffraction, reflection high-energy electron diffraction, and scanning electron microscopy. The films deposited at 510 °C show a full width at the half maximum (FWHM) of 0.06°for the rocking curve through the (111) peak, regardless of the kinetic energy of oxygen ions. CuO has been epitaxially grown on MgO(001) without heating it in a vacuum of 4 × 10−7 Pa. The x-ray diffraction intensity of the CuO(111) increases with an increase in the kinetic energy of O+, and its FWHM approaches that of the CuO film grown at 510 °C. The surface morphology is improved for the films deposited on unheated substrates.

X-ray and ultraviolet photoelectron spectroscopic (XPS and UPS) data were obtained for ${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{NbO}}_{3}$ (x=0.8,0.85,0.9). The valency of the Nb ion was found to be between pentavalent and tetravalent. No shifts of the XPS core-level spectra, such as O 1s, Sr 3p, and Sr 3d, were observed in this system even when x was varied. For all samples, sharp Fermi edges were observed with He I (21.2 eV) photon excitation. The results indicate that this valence band was mainly caused by the hybridization between the O 2p and Nb 4d orbitals, as had been proposed for the tungsten bronze by Goodenough. Eu substituted samples, (Sr,Eu${)}_{0.9}$${\mathrm{NbO}}_{3}$, were also studied. An additional sharp peak, due to Eu 4f state, was clearly observed in the valence-band region close to the Fermi level.

A detailed analysis of the Ols core-levels of p- and n-type high-Tc copper oxides is reported. The binding energies of Ols core-level in La 2−x Sr x CuO 4 and Nd 2−x Ce x Cu04 are found to be different. We also find that, for the p-type La 2−x Sr x CuO 4 . the Ols peak shifts towards lower binding energy when hole-carriers are introduced, while, for the n-type Nd 2−x Ce x CuO 4 , the Ols peak shifts towards higher binding energy when electron-carriers are introduced. Taking into account the different crystal structures and the chemical environment of oxygen sites, our observations are analyzed and explained consistently. It follows that, we are able to understand why holes (electrons) can be doped into p- (n-) type high-Tc copper oxides. The results also confirm that p- and n-type high-Tc copper oxides are quite distinct in nature.

We investigated the structural and physical properties of (Sr,M${)}_{\mathit{x}}$${\mathrm{NbO}}_{3}$ (M=Ca and Eu) compounds. Polycrystalline samples of ${\mathrm{Sr}}_{0.9\mathrm{\ensuremath{-}}\mathit{y}}$${\mathrm{Eu}}_{\mathit{y}}$${\mathrm{NbO}}_{3}$ (0\ensuremath{\le}y\ensuremath{\le}0.9) were synthesized with a solid-state reaction using TiO as the reducing agent. Powder-x-ray-diffraction analysis indicated that the samples with y\ensuremath{\le}0.9 were nearly a single phase of the cubic perovskite structure. For each of the samples, the electrical resistivity (\ensuremath{\rho}) and the magnetic susceptibility (\ensuremath{\chi}) exhibited, respectively, metallic and Curie-Weiss behavior at temperatures below 300 K. The valence of the doped Eu ion was found to be in between +2 and +3 according to an x-ray-photoelectron spectroscopic analysis. Furthermore, nearly single-phase samples of ${\mathrm{Sr}}_{0.9\mathrm{\ensuremath{-}}\mathit{z}}$${\mathrm{Ca}}_{\mathit{z}}$${\mathrm{NbO}}_{3}$ (0\ensuremath{\le}z0.2) were successfully synthesized with the same preparation technique. For the samples with z\ensuremath{\le}0.2, \ensuremath{\rho} exhibited metallic behavior at temperatures below 300 K and \ensuremath{\chi} was nearly temperature independent, i.e., Pauli paramagnetic.

We designed and constructed an ultrahigh vacuum scanning tunneling microscope (UHV‐STM) which is available for the measurement of tunneling spectra at low temperature. The sample holder is cooled by thermal conduction to the stage that thermally connects with the refrigerator head. We cleaved Bi2Sr2CaCu2Oy (Bi2212 high Tc superconductor) single crystals under ultrahigh vacuum conditions, and measured tunneling spectra of the Bi–O surface at 35 K. The spectra were smeared due to the fact that the STM tip was at high temperature (≳100 K).

Heteroepitaxial Y1Ba2Cu3O7−x films were grown on MgO(100) substrates by using the reactive evaporation method. The in situ streak reflection high energy electron diffraction pattern of films gradually faded with an increasing thickness when the hydrogen partial pressure during growth was higher than 1×10−6 Torr. Transmission electron microscope observation revealed that the film showed heteroepitaxial growth in the early stage of coevaporation. However, as with the increase of film thickness, the quality of the film became worse and finally reached polycrystalline. These results are attributed to the accumulation of hydrogen induced defects during heteroepitaxial growth of Y1Ba2Cu3O7−x films.

We observed STM images of the Bi-O surfaces of the cleaved Bi2212 single crystals with and without substituted Y ions. A series of STM images obtained showed that the period of the superstructure decreased with increasing Y-substitution ratio. We also measured the tunneling spectra of these crystals. It turns out that the electronic states on the Bi-O surfaces are different between the superconductive and non-superconductive crystals.

A photoelectron spectroscopic study was performed to investigate both the fluorine sites in and the electronic structure of superconductive ${\mathrm{Nd}}_{2}$${\mathrm{CuO}}_{4\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{F}}_{\mathit{x}}$ (x=0, 0.1, 0.16, 0.2, and 0.3). The x-ray photoelectron spectroscopic (XPS) results for F 1s spectra showed that the doped fluorine ions were located on the oxygen sites in the tetragonal ${\mathrm{Nd}}_{2}$${\mathrm{CuO}}_{4}$ lattice. Furthermore, comparison between the XPS spectra of ${\mathrm{Nd}}_{2}$${\mathrm{CuO}}_{4\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{F}}_{\mathit{x}}$, ${\mathrm{CuF}}_{2}$, ${\mathrm{NdF}}_{3}$, and NdOF suggested that the fluorine ions were not located on the O(2) sites around the ${\mathrm{Nd}}^{3+}$ ion but rather on the O(1) sites in the ${\mathrm{CuO}}_{2}$ planes. The XPS result for Cu 2p spectra indicated that the amount of ${\mathrm{Cu}}^{1+}$ ions increased as x increased. In addition, according to the ultraviolet photoelectron spectroscopic measurements, the density of states in the vicinity of the Fermi level seemed to increase as the F content increased.

Scanning tunneling microscopic and spectroscopic studies were made on cleaved of Bi2Sr2CuOy single crystals using an ultrahigh-vacuum scanning tunneling microscope (UHV-STM). The modulation structures of the BiO surface were observed at room temperature with atomic resolution. The tunneling spectra showed electronic gap structures similar to those observed for the BiO surface of superconducting Bi2212 single crystals. This suggests that superconductivity is not directley related to the electronic structure observed in the BiO plane.

X-ray and ultraviolet photoelectron-spectroscopic (XPS and UPS) studies to investigate the core levels and valence-band spectra of ${\mathrm{BaV}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Ti}}_{\mathit{x}}$${\mathrm{S}}_{3}$, with x=0 and 0.2, is reported. The XPS results indicate that the valence of V as well as Ti is not 4 as would be expected nominally, but between 3 and 4. Essentially no difference of the core-level binding energies was observed between the two samples. The valence-band spectra exhibit three peak features at about 1, 2.5, and 4 eV. From the enhancement of the peak at 1 eV by the He ii photon, it is concluded that the V 3d orbitals are strongly incorporated in this peak that is close to the Fermi level. It is shown that the bond-valence-sum method can be useful as a quantitative tool for discussion of XPS results. The possibility of using the bond-valence-sum calculation for discussions on the transport properties of the system is also shown.

Shifts of the binding energies of x-ray-photoelectron core levels are observed in the Bi{sub 2}Sr{sub 2}Ca{sub 1{minus}{ital x}}Y{sub {ital x}}Cu{sub 2}O{sub {ital y}} system when {ital x} is varied. It is pointed out that this is due to the change in the chemical environment associated with the changes of the interatomic distances. We show that the so-called bond-valence-sum calculation is useful for the explanation of the shift; and propose that this method is generally applicable in explaining or predicting the shift of core levels in any system with a variable composition.

A photoelectron spectroscopic study to investigate the electronic structure of a noncuprate oxide superconductor Ba{sub 1{minus}{ital x}}Rb{sub {ital x}}BiO{sub 3} (0{le}{ital x}{le}0.4) system is reported. Comparison of the results with those inconclusively reported for Ba{sub 1{minus}{ital x}}K{sub {ital x}}BiO{sub 3} and BaPb{sub 1{minus}{ital x}}Bi{sub {ital x}}O{sub 3} is discussed. It is concluded that the chemical environment of substituted Rb in this system is similar to that of Rb metal, core-level binding energies of Bi and Ba are unaffected by Rb substitution, and the shift of the valence band towards lower binding energy upon hole-carrier doping is observed. A characteristic change of the density of states in the vicinity of the Fermi level with composition {ital x} is observed, suggesting that the nonmetal-to-metal transition occurs through a continuous change of the electronic states of the system.

Observations of the Bi–O surface of superconductive Bi2212 single crystals were carried out using an ultrahigh-vacuum scanning tunneling microscope (UHV-STM). In the atomic resolution images, surface corrugations, which correspond to the superstructure of the Bi–O surface in addition to Bi atom deficiencies, were observed. There were hollow lines along the ridges of the corrugations, which may be due to missing atom rows.

Recently, superconductive Nd1Ba2Cu3Oy (Nd123) thin films with high superconducting transition temperature (Tc) have been successfully fabricated at our institute employing the standard laser ablation method. In this paper, we report parts of the results of surface characterization of the Nd123 thin films using an ultrahigh vacuum scanning tunneling microscope/spectroscopy (UHV- STM/STS) and an atomic force microscope (AFM) system operated in air. Clear spiral pattern is observed on the surfaces of Nd123 thin films by STM and AFM, suggesting that films are formed by 2D island growth mode at the final growing stage. Contour plots of the spirals show that the step heights of the spirals are not always the integer or half integer numbers of the c-axis parameter of the structure. This implies that the surface natural termination layer of the films may not be unique. Surface atomic images of the as-prepared Nd123 thin films are obtained employing both STM and AFM. STS measurements show that most of the surfaces are semiconductive, or sometimes even metallic. The results of STS measurements together with the fact that we are able to see the surface atomic images using scanning probe microscopes suggest that exposure to air does not cause serious degradation to the as-prepared surfaces of Nd123 thin films.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

An ultrahigh vacuum scanning tunneling microscope/spectroscopy (UHV-STM/STS) system has been used to characterize the surfaces of high quality as-prepared Nd1Ba2Cu3Oy (Nd123) single crystals. A quasi-square lattice with average lattice spacings of 4×4 A2 has been observed. The natural termination layer of Nd123 single crystals is determined to be the CuO chain layer. Several surface lattice defect structures have been detected by STM. The influence of the defect structures on the surface electronic properties of Nd123 single crystals is also studied.

We have investigated the surface of high quality YBa2Cu2Ox single crystal substrates, fabricated from YBa2Cu3Ox single crystals grown by the crystal pulling method, for homoepitaxy. They have good crystallinity with χmin of under 2% evaluated by Rutherford backscattering spectrometry and good surface morphology with unit-cell steps observed by atomic force microscopy. Furthermore, we also discuss the initial stage of homoepitaxial growth by using metalorganic chemical vapor deposition method and YBa2Cu3Ox single crystal substrates as mentioned above.

Highly flat, clean, and stable surfaces of as-prepared Nd1Ba2Cu3Oy (Nd123) single crystals have been studied using an ultrahigh vacuum scanning tunneling microscope/spectroscopy (UHV-STM/STS) system. The results of large area STM scans together with the results of STS measurements, magnetization loops measured at several temperatures below Tc, and critical current density measurements reveal the presence of a new magnetic flux pinning center in Nd123 single crystals prepared in a reduced oxygen partial pressure. The new pinning center is more conductive on the surface than the matrix and has a size ranging from several to several tens nanometers as seen by STM.

We have studied the effects of the kinetic energy of mass-separated O + beams on the growth of CuO thin films deposited at room temperature and 510°C, in the energy ranging from 10 to 200eV by x-ray photoemission spectroscopy, x-ray diffraction, reflection high-energy electron diffraction and scanning electron microscopy. CuO has epitaxially grown on MgO(001) even at room temperature in a vacuum 3×10-9 Torr. As the energy of O + increased, the x-ray diffraction intensity of the CuO(111) increased and the full width at the half maximum of the peak approached that of the CuO film grown at 510°C. The surface morphology is surprising improvement for films deposited on an unheated substrate, compared with that deposited at 510°C.

Recently we have found that Ba4CuPt209 (Pt-0412) may play an important role on the grain growth inhibition of Y2BaCuO5 (211) inclusions in the Pt doped melt growth processing of Y- Ba-Cu-O superconductor. This compound is formed as the result of reaction between Pt and Y- Ba-Cu-O system in the heat treatment. The crystal structure is characteristic of one dimensional -(Cu/Pt)-O3- chain, where Cu and Pt are not necessarily stoichiometric and expected to have a certain substitutional disorder. Rh substituent of Pt-0412: Ba4CuRh2O9 (Rh-0412) takes the same crystal structure but Rh-0412 seems to be the mixed valence of Rh3+ and Rh4+. Rh-0412 is semiconductor with activation energy of 0.18eV from the transport measurement. Temperature dependence of conductivity at lower temperature is well fitted by one dimensional variable range hopping model.

We observed STM images of the Bi-O surfaces of cleaved Bi2212 single crystals with and without substituted Y ions. A series of STM images obtained showed that the period of the superstructure decreased with increasing Y substitution ratio. We also measured the tunneling spectra of these crystals. The electronic states on the Bi-O surfaces are shown to have a large (semiconducting) energy gap in the non-superconductive crystals.

We report the epitaxial growth of CuO thin films prepared by lowenergy and high-density O+ ion beams mass-separated from an oxygen plasma. We have successfully produced O+ beams of 50 μA/cm2 while maintaining an ambient pressure of 3×10−9 Torr during the growth. CuO grows on MgO(100) with epitaxial relationship of (111)CuO // (100)MgO and [110]CuO // [110]MgO at room temperature and even under conditions where the flux density of O+ beams is at least one order of magnitude lower than the minimum flux density of O2 required to form CuO.

X-ray photoelectron spectra (XPS) of Cu 2p have been studied for oxygen- and air-sintered samples of Bi2(La,Pr)0.5Ca2.5Cu2Oy and Bi2Nd0.5Ca2.5Cu2Oy. We estimated the number of Cu 3d electrons, n d , and charge transfer energy, Δ, from these results. We point out the possibility that the difference of T C between these compounds with the same doped hole concentrations is associated with the difference of n d . The role of the Cu 3d – O2p charge transfer in superconductivity is discussed.

For the first time, CuO thin films have been synthesized by means of low‐energy and high‐density O+‐ion beams, mass separated from an oxygen plasma. A 50‐eV, 47‐μA/cm2 O+‐ion beam has successfully produced CuO at a growth rate of 0.04 A/s by simultaneous deposition of Cu metal on MgO(100). O+ beams have greater potential for oxidation than O2 gas from the viewpoint of the flux necessary to form CuO.

Recently, high quality single crystals of Nd1Ba2Cu3O y (Nd123) high temperature superconductors (HTSC) have been successfully fabricated in our laboratory. In this paper, parts of the results of surface characterization of Nd123 single crystals employing an ultrahigh vacuum scanning tunneling microscope/spectroscopy (UHV-STM/STS) are reported. Atomic images are shown. The surface natural termination layer is unambiguously determined. It is demonstrated that the surfaces of the as-prepared single crystals of Nd123 HTSC are stable and clean in air. The effect of surface defect structures on the surface electronic properties is also investigated.

The authors developed a scanning tunneling spectroscopy system which enables the current imaging tunneling spectroscopy (CITS) to be measured under an ultrahigh vacuum environment. The scanning tunnel microscope and CITS of Bi–O surfaces of Bi2Sr2CaCu2Oy superconductors were studied. No remarkable difference was found for the tunneling spectra at different positions in the modulated surface structures. It is concluded that the missing atom rows in the modulated structure do not originate in the local density of states, but in the real‐spatial structure.