H. J. Song

Electronic structure of Zn1−xCoxO using photoemission and x-ray absorption spectroscopy

Electronic structures of homogeneous bulk samples of Zn0.9Co0.1O which do not exhibit diluted ferromagnetic semiconducting (DMS) behavior have been investigated using photoemission spectroscopy and x-ray absorption spectroscopy. We have found that the Co ions in Zn1−xCoxO are in the divalent Co2+(d7) states under the tetrahedral symmetry. Our finding indicates that the DMS properties will not be produced when Co ions are properly substituted for Zn sites, implying that the DMS properties observed in Zn1−xCoxO thin films are likely to be extrinsic.

Magnetic and electronic properties of transition-metal-substituted perovskite manganites—La0.7Ca0.3Mn0.95X0.05O3 (X=Fe,Co,Ni)

The magnetic and electronic properties of Fe-, Co-, Ni-substituted La0.7Ca0.3MnO3 were studied. Ferromagnetic–paramagnetic and metal–insulator transitions were significantly affected by Mn-site substitution although no observable differences were found in their crystal structures from x-ray diffraction analysis. Valence-band photoemission studies also showed that there were no appreciable changes in the electronic structures of each sample. Peak temperatures (Tp) at maximum resistivity decreased from 265 K of virgin LaCaMnO to 217, 203, and 171K for Ni-,Co-, and Fe-substituted LaCaMnO samples, respectively. As the Tp decreased, the electrical resistivity increased and the saturation magnetization decreased. The overall experimental results were well explained by considering superexchange interactions induced by substitution with magnetic ions having different magnetic moments. From our study, it is suggested that the magnetic properties of substituting elements should also be considered to deal with the p...

X-ray absorption and photoelectron spectroscopic study of plasma-nitrided SiO2 film

Plasma-nitrided SiO2 thin film has been analyzed by synchrotron-radiation-based x-ray absorption and photoelectron spectroscopies (XAS and XPS). High-resolution N 1s XAS and N 1s, O 1s, and Si 2p XPS spectral changes were obtained for different annealing temperatures. N 1s XPS and XAS spectra show that at room temperature, besides the main species of N[Si(O−)3−x]3, there exist free moleculelike N2 and HN[Si(O−)3]2, H2NSi(O−)3, and N–Si2O species with surface contaminants. The spectral intensities of the N2 and the HN[Si(O−)3]2, H2NSi(O−)3, and N–Si2O species decrease as the annealing temperature increases, and finally the nitrogen exists dominantly in the form of N[Si(O)3]3 species above 820K, indicating out-diffusion of molecular N2 and structural reconstruction to form a stable structure upon annealing. The Si 2p and O 1s XPS spectra show that Si>4+ 2p peak and O 1s peak appear at 103.7 and 534.0eV, respectively, which are higher binding energies than those of thermally grown oxynitride films with lower...

Photoelectron energy shift induced by microfocused x rays in micrometer-thick insulating layers

The temporal changes of the kinetic energy spectra of photoelectrons emitted from micrometer-thick insulating layers, SiO2, and photoresist layers, were investigated with microfocused soft x rays in soft x-ray spectromicroscopy. The energy spectra of the insulators shifted up to several tens of electronvolts toward lower energies within seconds of the initial exposure. The amount of the energy shift depended on the thickness of the insulators. For the photoresist insulator, which was susceptible to radiation damage, the energy shift then decreased as the exposure time increased. The main cause of this decrease is attributed to the increase of conductivity by the x-ray-induced chemical state change of the insulator along the x-ray path. It was also demonstrated that by choosing appropriate time and energy in detecting photoelectrons the spectromicroscopy could be used as a depth probe of the conducting microstructures covered by insulating layers.

An effective medium model applied to the conductivity of La–Ca–Mn–O across the phase transition temperature

Abstract Colossal magnetoresistance is closely related to (but is not) the abrupt change of electrical resistivity in the vicinity of Curie temperature, which is caused by the temperature-dependent paramagnetic–ferromagnetic phase transition and concurrent change of electrical conducting mechanism. A model equation based on the effective medium theory is presented to explain the abrupt change of resistivity in the vicinity of Curie temperature of La–Ca–Mn–O (LCMO). It is assumed that LCMO is in the form of mixture of ferromagnetic and paramagnetic phase in the magnetic transition region. The main ingredients of the equation are a simple effective medium theory and a function for the temperature-dependent fraction of ferromagnetic phase. This model fits very well to the measured resistance–temperature curves of La 0.7 Ca 0.3 MnO 3 .

Scanning photoelectron microscopy study of Ge1−xTx (T=Cr, Fe) diluted ferromagnetic semiconductor single crystals

The chemical distributions and electronic structures of Ge1−xTx (T=Cr, Fe) diluted ferromagnetic semiconductors have been investigated by employing scanning photoelectron microscopy (SPEM), x-ray absorption spectroscopy (XAS), and photoemission spectroscopy (PES). The SPEM images and PES spectra of Ge1−xTx show the stripe-shaped regions due to the inhomogeneous concentration distributions of T ions. T2p XAS spectra indicate that T ions are mainly in the divalent states, and that they do not form pure metal clusters. This study reveals that Ge1−xTx crystals are chemically phase-separated, suggesting that the observed ferromagnetic ordering in Ge1−xTx arises from the magnetic properties of the T-rich Ge1−xTx phases.

Photoemission spectroscopy and x-ray absorption spectroscopy study of delafossite AgTO2 (T=Fe,Co,Ni)

Electronic structures of delafossite AgTO2 (T=Fe,Co,Ni) have been investigated by using photoemission spectroscopy (PES) and x-ray absorption spectroscopy (XAS). The T 2p XAS spectra of AgTO2 show that Fe and Co ions are in the trivalent states but that Ni ions are mainly in the divalent states, suggesting that the metallic nature of AgNiO2 arises from hole carriers due to divalent Ni ions. The valence-band PES study of AgTO2 (T=Co,Ni) reveals that T 3d states are located close to EF and that the Ni 3d band is more metalliclike than the Co 3d band.

Electronic structures of AgNi1-xCoxO2AgNi1-xCoxO2 delafossite oxides

Electronic structures of AgNi1-xCoxO2AgNi1-xCoxO2(0⩽x⩽1)(0⩽x⩽1) delafossite oxides have been investigated by using photoemission spectroscopy (PES) and soft X-ray absorption spectroscopy (XAS). T 2p XAS (T=CoT=Co, Ni) spectra of AgNi1-xCoxO2AgNi1-xCoxO2 show that the valence states of Co ions are trivalent and do not change with xx. In contrast, Ni ions are in the Ni2+–Ni3+Ni2+–Ni3+ mixed-valent states and the trivalent component increases with increasing xx. This finding suggests that the metallic nature of AgNi1-xCoxO2AgNi1-xCoxO2 for low values of xx arises from the divalent Ni ions. The valence-band PES study of AgNi1-xCoxO2AgNi1-xCoxO2 reveals that the Ni 3d states are more metallic like than the Co 3d states.

Photon Energy Calibration and Measure of Spectral Resolving Power of the Monochromator by the use of N 1s NEXAFS from a Solid Sample

The energy calibration and the measurement of spectral resolving power (E/▵E) of the monochromator are important, especially in near‐edge x‐ray absorption fine structure (NEXAFS) and x‐ray photoemission spectroscopy (XPS) application. For the soft x‐ray beam lines covering 100 – 1000 eV photon energy range, the best way of these is to use a gas cell and an XPS setup with a well‐defined work function and a cooling system. Typically, the N 1s → π* absorption spectrum has been used as a reference for energy calibration and the visibility of the spectrum has been a good measure of the monochromator energy resolution. However, the gas cell is rather inconvenient in case of frequent uses, because it needs a dedicated experimental setup. In this manuscript, we introduce a solid sample that can be used for the energy calibration and for the measurement of spectral resolving power (RP) of the monochromator. The sample is a plasma nitrided SiON. The N 1s absorption spectrum of the sample at room temperature shows a...

On factors inducing the (101̄0) texture of hexagonal-close-packed Co63Cr31Mn6 layers in magnetic recording media

We investigate factors affecting the movement of sputtered species and the (1010) texture formation of hexagonal-close-packed Co63Cr31Mn6 (CoCrMn) layers in magnetic recording media. Deposition conditions and underlayers rendering high mobility of the sputtered species promote the (1010) texture of the CoCrMn film. Elemental effects are studied by substituting manganese with a series of 3d transition elements (Ti, V, Cr, Fe, Ni, and Cu) in the CoCrMn films. The results suggest that the chemical characteristics of manganese, the preference of bonding with different elements (especially with cobalt), is important in the texture formation of CoCrMn films.