Kenji Adachi

Absorption and scattering of near-infrared light by dispersed lanthanum hexaboride nanoparticles for solar control filters

Optical absorption and scattering behaviors of lanthanum hexaboride (LaB 6 ) nanoparticulate dispersion coatings with various particle sizes have been investigated in the ultraviolet to near-infrared (NIR) wavelengths for application to solar control filters. Large characteristic near-infrared absorption is introduced as the decreased particle size falls into nanoscale, and its origin is discussed in terms of a localized surface plasmon resonance (LSPR) of conduction electrons. Optical constants of LaB 6 have been measured and Mie scattering theory analysis was conducted. The theory was found to generally replicate the optical characteristics, and variations of absorbed and scattered wave fractions as well as the LSPR wavelength have been discussed with varying particle size. The absorption peaks are found as shaped narrower and located at shorter wavelength in theory than in experiment, which is suggested as ascribed mainly to the nonspherical distorted shape of LaB 6 nanoparticles.

Ruthenium clusters in lead-borosilicate glass in thick film resistors

An interparticle glass matrix in ruthenium dioxide-based thick film resistors has been studied intensively by means of analytical and high resolution transmission electron microscopy. The ruthenium dioxide phase interacts with lead-borosilicate glass at high temperature by dissolving ruthenium ions and incorporating a small number of lead and aluminum ions on the surface. Ruthenium ions diffuse through the glass network at least over a distance of 1 μm during firing, but are accommodated in the glass structure by an amount only less than 7 at. % at room temperature. High resolution electron microscopy reveals numerous ruthenium-pyrochlore crystallites in high-lead glasses, but hardly any Ru-based clusters/crystallites in low-lead glasses, where lead-rich glass clusters due to glass immiscibility and reduced lead metal clusters are more commonly observed instead of ruthenium clusters. Lead oxide is prone to reduction both in high- and low-lead glasses upon irradiating with a high-energy incident electron beam. Comparison with gold-based resistor and estimation of average dispersion length of ruthenium clusters, 2 to 4 nm, prefer the model of electron hopping via ruthenium clusters/crystallites as a dominant conduction mechanism in thick film resistors.

Microstructural glass modifications in as-fired and high-voltage-surged RuO2-based thick film resistors

Electrical conduction in thick film resistors has been studied, and microstructures, especially around conducting RuO{sub 2} phases in lead-borosilicate glass matrix in as-fired and high-voltage-surged thick film resistors, have been observed in detail using transmission electron microscopy. Lattice images of as-fired thick film resistors have suggested the presence of subtle structural modifications in the very thin area across the RuO{sub 2}/glass interface, whereas in the glass matrix very small dot-like contrasts on the order of 1 nm were occasionally observed and, were interpreted as being small crystallites or Ru clusters. Heavy electrical loadings of thick film resistors were found to induce the local formation of plate-like crystals in glass, which were identified by electron diffraction to be a slightly modified anorthite. The significance of these observations in terms of the conduction network and the degradation due to the electrical overloading of thick film resistors are discussed.

Optical properties of group-3 metal hexaboride nanoparticles by first-principles calculations

LaB6 nanoparticles are widely used as solar control materials for strong near-infrared absorption and high visible transparency. In order to elucidate the origin of this unique optical property, first-principles calculations have been made for the energy-band structure and dielectric functions of R(III)B6 (R(III) = Sc, Y, La, Ac). On account of the precise assessment of the energy eigenvalues of vacant states in conduction band by employing the screened exchange method, as well as to the incorporation of the Drude term, dielectric functions and various physical properties of LaB6 have been reproduced in excellent agreement with experimental values. Systematic examinations of dielectric functions and electronic structures of the trivalent metal hexaborides have clarified the origin of the visible transparency and the near-infrared plasmon absorption of R(III)B6 nanoparticles.