Magnetoresistance at Room Temperature of Oleic Acid Coated Fe3-xCoxO4 (x = 0, 0.1 and 0.3) Nanocrystal Drop-Cast Films

Oleic acid coated Fe3-xCoxO4 (x = 0, 0.1 and 0.3) nanocrystal self-assembled films were fabricated via drop-casting of colloidal particles on a SiO2/Si substrate. Nanocrystals of the Fe3-xCoxO4 exhibited bifurcation of the zero-field-cooled and field-cooled magnetizations at 300 K. The Fe3-xCoxO4 nanocrystal drop-cast films demonstrated nonlinear current-voltage characteristics between the source and drain electrodes in magnetic fields of zero and 0.2 T, and magnetoresistance reached into −46% for the x = 0 film and −50% for both the x = 0.1 and 0.3 films at 300 K. Oleic acid coated Fe3-xCoxO4 (x = 0.1 and 0.3) nanocrystal would boost developments of a high performance current switching device using negative magnetoresistance

Electron-energy-loss function of LiTaO3 and LiNbO3 by x-ray photoemission spectroscopy: Theory and experiment

We report experimental energy-loss structures in x-ray photoemission spectra of single crystalline LiTaO3 and LiNbO3, and then compare these with theoretical electron-energy-loss functions calculated from first principles using the full-potential linearized augmented plane-wave method in the local-density approximation. The energy-loss structure of core electrons can be approximated by a sum of four components: for LiTaO3, the peaks positioned at 8.0, 13.4, 15.8, and 22.6 eV; for LiNbO3, those positioned at 7.0, 12.0, 14.5, and 21.8 eV. The momentum matrix elements between Bloch functions were evaluated to determine the electron energy-loss functions. The theoretical electron-energy-loss functions agreed fairly well with the experimental one. The experimental peaks positioned at 8.0, 13.4, and 15.8 eV for LiTaO3 and those at 7.0, 12.0, and 14.5 eV for LiNbO3 were assigned to the interband transitions from the valence band to the conduction bands. The peaks at 22.6 eV for LiTaO3 and 21.8 eV for LiNbO3 were ascribed to the electron excitation from the O 2s level to the lower conduction band

Coupling of codoped In and N impurities in ZnS:Ag: Experiment and theory

A vapor-phase-grown epitaxial ZnS:Ag layer simultaneously codoped with In and N on GaAs substrate exhibited a 436-nm light emission and p-type conduction with a low resistivity. X-ray photoemission spectroscopy revealed that the In 3d5/2 electron binding energy of the codoped ZnS:In,N layer was smaller by 0.5 eV than that of the ZnS:In independently doped layer, although the 2p3/2 electron binding energies of Zn and S of the codoped layer agreed well with those of the independently doped layer, respectively. The reduction of binding energy was ascribed to an increase in the electronic relaxation energy for core-hole states in photoemission and reflects a large charge transfer between the In and N atoms at the first neighbor sites through covalent sp3 bonding orbitals. An increase of the spectral intensity at around 4 eV relative to the valence band maximum observed for the codoped layer corresponds to a new state at –3.67 eV from the valence band maximum due to a strong coupling between the In 5s and N 2p orbitals at the first neighbor sites, derived from a first-principle band structure calculation for ZnS:(In,2N)

Response to "Comment on `Quantum-confinement effects on the optical and dielectric properties for mesocrystals of BaTiO3 and SrBi2Ta2O9\u27"

In this reply, the authors show that the argument by Scott regarding the band gap of bulk SrBi2Ta2O9 (SBT) is not based on concrete evidence. The authors will also show additional data from a Raman study of a powdered SBT sample to prove that the surface of the specimen was not covered by Bi2O3

Magnetoresistance of Drop-Cast Film of Cobalt-Substituted Magnetite Nanocrystals

An oleic acid-coated Fe2.7Co0.3O4 nanocrystal (NC) self-assembled film was fabricated via drop casting of colloidal particles onto a three-terminal electrode/MgO substrate. The film exhibited a large coercivity (1620 Oe) and bifurcation of the zero-field-cooled and field-cooled magnetizations at 300 K. At 10 K, the film exhibited both a Coulomb blockade due to single electron charging as well as a magnetoresistance of ∼−80% due to spin-dependent electron tunneling. At 300 K, the film also showed a magnetoresistance of ∼−80% due to hopping of spin-polarized electrons. Enhanced magnetic coupling between adjacent NCs and the large coercivity resulted in a large spin-polarized current flow even at 300 K

Threshold of photoelectron emission from CNx films deposited at room temperature and at 500 °C

The threshold of photoelectron emission was measured for amorphous CNx films deposited at room temperature (RT) and at 500 °C. The x values of the films deposited at RT and at 500 °C by magnetron sputtering of a graphite target in a mixed N2/Ar gas were 0.6 and 0.3, respectively. Ratios of the sp2- to sp3-hybridized components of both C and N for the film deposited at 500 °C were larger by 4 times than those for the film deposited at RT. The onsets of the electron emission by photon irradiation were 5.0 and 4.7 eV for the films deposited at RT and at 500 °C, respectively

Photoelectron energy-loss functions of SrTiO3, BaTiO3, and TiO2: Theory and experiment

We compare experimental O 1s electron energy-loss structures below 30 eV of single crystalline SrTiO3 ,BaTiO3, and TiO2 with their theoretical electron energy-loss functions. The photoelectron energy-loss structuresof in situ fractured surface in ultrahigh vacuum can be approximated by a sum of four components forSrTiO3 and BaTiO3, and of three components for TiO2. Electronic structures were calculated from first principlesusing the full-potential linearized augmented plane-wave method in the local-density approximation. Themomentum matrix elements between Bloch functions were evaluated to determine the electron energy-lossfunctions. The theoretical electron energy-loss functions agree well with experimental spectra except a structureat around 20 eV of SrTiO3 and that at around 18 eV of BaTiO3. The difference of high binding energypeaks is explained from the positions of semicore states

Response to "Comment on `Quantum-confinement effects on the optical and dielectric properties for mesocrystals of BaTiO3 and SrBi2Ta2O9

In this reply, the authors show that the argument by Scott regarding the band gap of bulk SrBi2Ta2O9 (SBT) is not based on concrete evidence. The authors will also show additional data from a Raman study of a powdered SBT sample to prove that the surface of the specimen was not covered by Bi2O3

Hydrogen effects on crystallinity, photoluminescence, and magnetization of indium tin oxide thin films sputter-deposited on glass substrate without heat treatment

Indium tin oxide (ITO) thin films were sputter deposited by using working gas containing hydrogen on glass substrate without any heat treatments. The films demonstrated X-ray diffraction due to polycrystalline ITO, blue-green photoluminescence (PL) due to oxygen defects in nano-structured ITO crystals, and paramagnetic behaviour in temperature dependence of magnetization overlapped with diamagnetic signal from the substrate. The carrier density n of the films was of the order of 1020 cm−3, and varied as an inverse of V-character with the hydrogen concentration [H] in the gas. The n value peaked at [H] = 1%. Spectral features at ≈430 and ≈470 nm of the PL emission were invariant with [H]. The order of the density of electrons N with spins obeying the Curie law was 1023 cm−3, and the variation in N with [H] was almost parallel to that in n with [H]

Large frequency dependence of lowered maximum dielectric constant temperature of LiTaO3 nanocrystals dispersed in mesoporous silicate

A large frequency dependence of the maximum dielectric constant temperature was observed for LiTaO3 nanocrystals (the diameter 20 Å) dispersed in mesoporous silicate. At the applied field frequency of 100 kHz, the maximum temperatures in the real and imaginary parts were 365 and 345 °C, respectively. The maximum temperature in the real part is apparently lower than the paraelectric–ferroelectric transition temperature (645 °C) of bulk LiTaO3. The maximum temperature in the imaginary part rose from 285 to 420 °C with increasing frequency from 10 to 1000 kHz. Since the bulk LiTaO3 shows no relaxor behavior, such superparaelectric behavior is obviously a consequence of nanominiaturization of LiTaO3 crystal and insignificant cooperative interactions between the nanoparticles