Hironobu Sakata

Electrical conductivity of Co3O4 films prepared by chemical vapour deposition

Polycrystalline Co3O4 films were prepared by normal pressure chemical vapour deposition, and the d.c. electrical conduction was investigated at temperatures from 170 to 400 K. A minimum resistivity of 14.2 Ω cm was obtained at a film forming temperature of 773 K. The Seebeck coefficient of films indicated the films to be p-type semiconductors. For the temperature range 220–400 K conduction of the films was confirmed to be due to polaronic hopping of holes. For temperatures from 170–220 K. the conduction was attributed to variable-range hoping of holes. Optical absorption edge analysis gave band gap energies of 1.50–1.52 eV corresponding to the edge of the charge transfer band (Co3+-Co2+), which was responsible to variable-range hoping, and 1.88–1.95 eV relative to the O2−-Co2+ charge transfer band.

Copper (II) oxide as a giant dielectric material

Bulk copper (II) oxide (CuO), heat treated at 1223K, shows extraordinarily high dielectric constant (er∼104), almost independent of temperature (above 230K) and frequency in the kilohertz region. A sudden decrease of er is observed at lower temperature (below 150K). X-ray photoelectron spectroscopy and high resolution transmission electron microscopy studies confirm the presence of a microscopic amount of Cu3+ in annealed CuO. The dielectric behavior of CuO can be explained by Maxwell-Wagner-type polarization mechanism and thermally activated mechanism.

D.c. conductivity of V2O5–MnO–TeO2 glasses

Semiconductive oxide glasses in the system V2O5–MnO–TeO2 were prepared, and the mechanism of d.c. conduction was studied. The Seebeck coefficient measurements at temperatures from 375–475 K indicated the glasses to be n-type semiconducting. The d.c. conductivity ranged from 5×10−5 to 1.9×10−6 S cm−1 at 405 K for V2O5=60 mol% and MnO=0–20 mol%, and decreased with increasing MnO content. The conduction was confirmed to obey the adiabatic small polaron hopping model, and was due to mainly hopping between V-ions in the glasses. The polaron band width J was estimated to be J=0.10–0.20 eV. The electron–phonon interaction coefficient γp was very large (21–26). The hopping mobility evaluated as 2.3×10−7–2.7×10−6 cm2 V−1 s−1 increased with increasing V2O5 content. The estimated carrier concentration was the order of 1019 cm−3. The principal factor determining conductivity was the polaron hopping mobility in these glasses.

Electrical conductivity of V2O5Sb2O3TeO2 glasses

Abstract The dc conductivity of ternary V 2 O 5 Sb 2 O 3 TeO 2 glasses was studied from room temperature to 473 K. The structure of these glasses was found to become more open with increasing in TeO 2 content based upon calculation of oxygen molar volume. The glasses were found to be n-type semiconductors with conductivity of σ = 2.63 × 10 −6 to 1.46 × 10 −3 S cm −1 at 473 K for 11–62 mol% V 2 O 5 . The conduction was confirmed to be due to small polaron hopping between vanadium ions and was adiabatic for V 2 O 5 > 50 mol% and non-adiabatic for V 2 O 5 J = 0.02 to 0.11 eV which depended on the VV spacing. The carrier concentration was evaluated to be the order of 10 21 cm −3 . Estimated carrier mobility was from 10 −7 to 10 −5 cm 2 V −1 s −1 and varied significantly with V 2 O 5 content. The dominant factor determining conductivity was mobility in these glasses.

Small polaron hopping conduction in V2O5–Sb–TeO2 glasses

Abstract The dc electrical conductivity of glasses in the system V2O5–Sb–TeO2 prepared by press quenching was studied at temperatures between 303 and 473 K. The composition range of the glass formation region was found to be 10⩽TeO2⩽100 mol%, 0⩽V2O5⩽70 mol%, and 0⩽Sb⩽20 mol%, respectively. The glasses indicated n-type semiconductors from the measurement of thermoelectric power. The dc conductivities at 473 K for the present glasses were determined to be 6.38×10 −6 –7.13×10 −3 S cm −1 , indicating that the conductivity increased with increasing V2O5 concentration. Sb content also contributed to increase the conductivity and decrease activation energy for electrical conduction. A model of redox reaction during melting was proposed and quantitatively explained the reaction between V2O5 and Sb. A glass of composition 70 V 2 O 5 · 20 Sb · 10 TeO 2 (mol%) having a conductivity of 7.13×10 −3 S cm −1 at 473 K was found to be the highest conductive glass among the previous vanadium–tellurite glasses. From the conductivity-temperature relation, it was found that small polaron hopping model was applicable at the temperature above 1 2 Θ D (ΘD : the Debye temperature); the electrical conduction at T> 1 2 Θ D was due to adiabatic small polaron hopping of electrons between vanadium ions for V2O5⩾50 mol%, and non-adiabatic for 30⩽V2O5 2.90×10 −4 cm 2 V −1 s −1 at 473 K. The carrier density was obtained to be of the order of 10 20 –10 21 cm −3 , and temperature dependence of the carrier density was barely present between 423 and 473 K. The conductivity of the present glasses was primarily determined by hopping carrier mobility.

Low-temperature dc conductivity of V2O5SnOTeO2 glasses

Abstract The dc conductivity of glasses in the V2O5SnOTeO2 system was studied at temperatures between 200 and 473 K. At temperatures from room temperature (RT) to 200 K, a T − 1 4 (T is temperature) dependence of the conductivity was found, and variable-range hopping conduction was confirmed for these glasses. Mott parameters analysis gave the density of states at the Fermi level, N(EF) = 7.33 × 1019−8.45 × 1020cm−3 eV−1 at 230 K, and N(EF) increased with increasing V2O5 content (V2O5 = 40–50 mol%). At RT, variable-range hopping conduction was observed, which was attributable to large values of the disorder energy of the glasses, WD (= 0.08–0.09 eV), dominating the conduction.

Synthesis and electrical properties of Fe2O3-MoO3-TeO2 glasses

Abstract Semiconducting glasses of the Fe2O3-MoO3-TeO2 system were prepared by the press-quenching method and their d.c. conductivities in the temperature range 373–573 K were measured. The glass formation region was found to be Fe2O3 = 0–20 mol.%, MoO3 = 0–40 mol.%, TeO2 = 50–100 mol.%. The Seebeck coefficients showed these glasses to be n-type semiconductors. The glasses had conductivities σ ranging from 10−8 to 10−4 S cm−1 at temperatures from 373 to 573 K. The d.c. conductivity increased with increasing Fe2O3 content or MoO3/TeO2 at fixed amount of Fe2O3. Because of its slight effect on the conductivity. MoO3 was considered to act as a reducing agent for redox reaction during glass synthesis. Electrical conduction of the glasses was confirmed to be due to nonadiabatic small polaron hopping, and the conductivity was primarily determined by hopping carrier mobility. The polaron band width, J, ranged from 0.09 to 0.18 eV depending on the Fe-Fe spacing.

Electrical conduction in V2O5-NiO-TeO2 glasses

Abstract Semiconducting oxide glasses in the V2O5-NiO-TeO2 system are prepared and the d.c. conductivity is studied at temperatures ranging from 333 to 475 K. The Seebeck coefficient measurements at temperatures from 375 to 475 K indicate the glasses to be n-type semiconducting. The d.c. conductivity ranges from 6.6×10−7 to 1.3×10−5 Scm−1 at 405 K for V2O5 = 30–55 mol% and NiO = 10 mol%, and decreases with increasing NiO content. The conduction is confirmed to be due to a non-adiabatic small polaron hopping which occurs between V-ions in the glasses. The polaron bandwidth J is estimated to be J=0.003–0.083 eV. The estimated hopping mobility is 8.2×10−9−4.9×10−5 cm2 V−1 s−1 at 416 K and increases with increasing V2O5 content. The carrier density is evaluated to be 5.3×1018−7.3×1020cm−3.

DC conductivity of V2O5PbOTeO2 glasses and the effect of pressure

Abstract The dc conductivity of V2O5PbOTeO2 glasses was investigated from 300 to 473 K, and the effect of pressure on conductivity was studied to 6 GPa. Glasses were found to be n-type semiconductors with conductivity σ = 1.5 × 10−6−1.2 × 10 S−4 cm−1 at 408 K. The conduction was confirmed to be due to small polaron hopping between vanadium ions and was adiabatic for V2O5 = 40–70 mol%. The carrier density determined was 0.96–3.18 × 1021 cm−3. Estimated carrier mobility was from 8.61 × 10−9 to 1.02 × 10−7 cm2 V−1 s−1. The dominant factor determining conductivity was mobility in these glasses. The application of pressure to 6 GPa increased conductivity about a factor of 2–4. Reversible changes in conductivity on applying or releasing pressure were observed and attributed to variations in vanadium ion spacing, R, assuming small polaron hopping conduction in compacted glasses.

Laser-induced forward transfer of TiO2–Au nanocomposite films for maskless patterning

Laser-induced forward transfer is investigated for maskless pattering of thin films. A 89TiO2–11Au (mol %) nanocomposite polycrystalline (100 nm thick) film fabricated by a sol-gel method shows a surface plasmon absorption produced by Au nanoclusters formed in the film. A second-harmonic generation sheet beam of a Q-switched Nd:YAG laser was irradiated on the film in air in contact with another glass substrate or with a 0.14 mm air gap. Regular stripe patterns of laser-induced transferred films were obtained. Transmittance spectra of laser-induced transferred films showed shifts of the surface plasmon absorption peak. Analysis of the spectra using the Mie scattering model revealed the porous character of transferred films.