Spherical Cu2-xS nanoparticles with an average diameter of 4.6 nm were synthesized by a colloidal method, and their optical nonlinearities around localized surface plasmon resonance in the near-infrared region were investigated. Resonant enhancement of nonlinear absorption, which is similar to that in the case of the noble metal nanoparticles in the visible region, was observed. The nonlinear absorption coefficients of the Cu2-xS nanoparticles were smaller as compared with those of Au nanoparticles with the same dimensions and concentrations. Theoretical simulation of electric field distributions around individual nanoparticles suggested that the free carrier concentration in Cu2-xS nanoparticles was one order of magnitude smaller than that in Au nanoparticles, which led to a weaker local electric field and weaker optical nonlinearity.

We investigated electrical and structural properties of Ta-doped SnO2 (TTO) films on anatase TiO2 seed layers with various growth parameters of pulsed laser deposition. We found that anatase TiO2 seed layers induced pseudo-epitaxial (100) growth of TTO films with enhanced mobility (μ) in a wide range of growth parameters. The highest μ of 83 cm2V-1s-1 [resistivity (ρ) of 2.8 × 10-4 Ωcm] and the lowest ρ of 1.8 × 10-4 Ωcm (μ of 60 cm2V-1s-1) were obtained at a substrate temperature of 600 °C. Amorphization and (101)-preferred growth competed with (100) growth on the TiO2 seed layer at low temperatures. Introducing sufficient process oxygen suppressed such unwanted film growth, resulting in improved transport properties.

We investigated electrical conduction of anatase Ti0.94Nb0.06O2 (TNO) epitaxial thin films in relation to oxygen defects generated by post-annealing. Annealing of TNO in oxygen was found to cause dramatic decreases in ne. Resonant photoemission spectroscopy measurements revealed that a deep acceptor state just above the top of valence band evolves, synchronized with the decrease of ne. We proposed that the acceptor state originates from interstitial oxygen atoms combined with Nb dopants and compensates electron carriers.

We have discovered new transparent conducting oxides (TCOs), anatase Ti1-xMxO2 (M=Nb,Ta), in thin film form. Both films with 0.03 ≤ × ≤ 0.06 showed resistivity of 2−3 × 10−4 Ωcm and internal transmittance of ∼95% in the visible light region (40 nm in thickness), at room temperature. These values are comparable to those of typical TCOs, such as In2−xSnxO3 (ITO).