Yuta Sakamoto

Electronic structure and magnetism of the diluted magnetic semiconductor Fe-doped ZnO nanoparticles

We have studied the electronic structure of Fe-doped ZnO nanoparticles, which have been reported to show ferromagnetism at room temperature, by x-ray photoemission spectroscopy, resonant photoemission spectroscopy, x-ray absorption spectroscopy, and x-ray magnetic circular dichroism (XMCD). From the experimental and cluster-model calculation results, we find that Fe atoms are predominantly in the Fe3+ ionic state with mixture of a small amount of Fe2+ and that Fe3+ ions are dominant in the surface region of the nanoparticles. It is shown that the room temperature ferromagnetism in the Fe-doped ZnO nanoparticles primarily originated from the antiferromagnetic coupling between unequal amounts of Fe3+ ions occupying two sets of nonequivalent positions in the region of the XMCD probing depth of ∼2–3 nm.

Surface- and bulk-sensitive x-ray absorption study of the valence states of Mn and Co ions in Zn1-2xMnxCoxO nanoparticles

We have performed x-ray absorption spectroscopy (XAS) measurements on Zn1−2xMnxCoxO nanoparticles. From the XAS results, it seems that the Mn and Co ions are in a mixed-valence (2+, 3+, and 4+) state and the relative concentrations of the high-valence (3+ and 4+) Mn and Co ions are higher in the surface region than in the deep core region. We suggest that this is a distinct trend of nanoparticle diluted magnetic semiconductor (DMS) unlike the case of DMS in film and bulk forms, where the transition-metal ions are expected to be 2+.

Ferromagnetism in ZnO co-doped with Mn and N studied by soft x-ray magnetic circular dichroism

We have investigated the electronic structure of ZnO:Mn and ZnO:Mn,N thin films using x-ray magnetic circular dichroism (XMCD) and resonance-photoemission spectroscopy. From the Mn 2p -> 3d XMCD ...

Electronic configuration of Mn ions in the π-d molecular ferromagnet β-Mn phthalocyanine studied by soft X-ray magnetic circular dichroism

Abstract We have studied the electronic structure of the molecular ferromagnet β -Mn phthalocyanine ( β -MnPc) in a polycrystalline form, which has been reported to show ferromagnetism at T 8.6 K , by X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD). From the experimental results and subsequent cluster-model calculation, we find that the ferromagnetic Mn ion in β -MnPc is largely in the 4 E g ground state arising from the ( e g ) 3 ( b 2 g ) 1 ( a 1 g ) 1 [ ( d x z , y z ) 3 ( d x y ) 1 ( d z 2 ) 1 ] configuration of the Mn2+ state. Considering that the highest occupied molecular orbital (HOMO) of MnPc with the 4 E g ground state originates from the a 1 g orbital of the Mn2+ ion, it is proposed that a 1 g – a 1 g exchange coupling via the π orbitals of the phthalocyanine ring plays a crucial role in the ferromagnetism of β -MnPc.

Performance of Integrated Cu Gap-Filling Process with Chemical Vapor Deposition Cobalt Liner

Cu interconnects are used in semiconductor devices and their dimensions are downscaled markedly. Cu interconnects are fabricated by a damascene process, and it becomes difficult to fill Cu into trenches and vias structures by electroplating below the 20 nm feature size. We evaluated the process integration for Cu interconnects using a Co wetting layer by chemical vapor deposition (CVD), a Cu seed by magnetic-field-assisted ionized sputtering (MFIS) and a Cu reflow technique. The properties of a CVD-Co film, such as composition, resistivity, step coverage, and adhesion between Cu and Co, were investigated. By using CVD-Co as the wetting layer, the properties of Cu gap filling in a trench structure were improved, and the filling of Cu into a 14-nm-wide trench structure was achieved.

X-Ray Absorption Spectroscopy and X-Ray Magnetic Circular Dichroism Studies of Transition-Metal-Codoped ZnO Nano-Particles

We report on x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) studies of the paramagnetic (Mn,Co)-co-doped ZnO and ferromagnetic (Fe,Co)-co-doped ZnO nano-particles. Both the surface-sensitive total-electron-yield mode and the bulk-sensitive total-fluorescence-yield mode have been employed to extract the valence and spin states of the surface and inner core regions of the nano-particles. XAS spectra reveal that significant part of the doped Mn and Co atoms are found in the trivalent and tetravalent state in particular in the surface region while majority of Fe atoms are found in the trivalent state both in the inner core region and surface region. The XMCD spectra show that the Fe

Bulk and surface magnetization of Co atoms in rutile Ti1 − xCoxO2 − δ thin films revealed by x-ray magnetic circular dichroism

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X-ray Magnetic Circular Dichroism Investigations of the Origin of Room Temperature Ferromagnetism in Fe-Doped ZnO Nanoparticles

ions in the surface region give rise to the ferromagnetism while both the Co and Mn ions in the surface region show only paramagnetic behaviors. The transition-metal atoms in the inner core region do not show magnetic signals, meaning that they are antiferromagnetically coupled. The present result combined with the previous results on transition-metal-doped ZnO nano-particles and nano-wires suggest that doped holes, probably due to Zn vacancy formation at the surfaces of the nano-particles and nano-wires, rather than doped electrons are involved in the occurrence of ferromagnetism in these systems.

Improved Step Coverage of Cu Seed Layers by Magnetic-Field-Assisted Ionized Sputtering

We have studied magnetism in Ti(1-x)Co(x)O(2-δ) thin films with various x and δ by soft x-ray magnetic circular dichroism (XMCD) measurements at the Co L(2, 3) absorption edges. The estimated ferromagnetic moment by XMCD was 0.15-0.24 µ(B)/Co at the surface, while in the bulk it was 0.82-2.25 µ(B)/Co, which is in the same range as the saturation magnetization of 1.0-1.5 µ(B)/Co. These results suggest an intrinsic origin of the ferromagnetism. The smaller moment of the Co atom at the surface is an indication of a magnetically dead layer of a few nanometers thick at the surface of the thin films.

Formation method of cobalt film

We have studied the electronic structure of Zn0.9Fe0.1O nanoparticles, which have been reported to be ferromagnetic at room temperature, by using soft X-ray absorption (XAS) and magnetic circular dichroism (XMCD). The XAS results indicate that Fe ions are predominantly in the Fe3+ state with mixture of a small amount of Fe2+. It is shown that the room temperature ferromagnetism in the Zn0.9Fe0.1O nanoparticles is primarily originated from the antiferromagnetic coupling between unequal amounts of Fe3+ ions occupying two sets of nonequivalent positions in the region of the XMCD probing depth of ~2–3 nm.