Kenjiro Miyano

Resonant light scattering from metal nanoparticles: Practical analysis beyond Rayleigh approximation

We propose a simple analytical formula that can quantitatively predict resonant light scattering from metal nanoparticles of arbitrary shape, whose sizes are too large for Rayleigh approximation to be applicable. The formula has been derived as an empirical extension of Mie’s rigorous calculation for light scattering from spheres. It can very well reproduce the experimental characteristics of light scattering from Au nanorods.

Resonant light scattering from individual Ag nanoparticles and particle pairs

Light scattering by individual Ag nanoparticles and structures have been studied spectroscopically. Individual particles were selected and manipulated with a micromanipulator installed inside a scanning electron microscope (SEM). With typical particle dimensions of some 100 nm, the plasma resonances of particles and the coupled modes of particle pairs were observed in the visible region. The polarization dependence of the resonance frequencies strongly reflects the shape anisotropy; the effect that would be averaged out for experiments on ensembles. With a simple approximation to take the glass substrate into account, the results are in good agreement with the analytical calculations by Mie scattering, and with numerical calculations by the finite-difference time-domain method, both of which are performed with the morphological parameters obtained from the SEM observation for the corresponding particle or particle pair.

Photoconductivity in Semiconducting Single-Walled Carbon Nanotubes

We have observed the photoconductive response of film samples of single-walled carbon nanotubes for the first time. Two peaks in the photoconductivity excitation spectra around 0.7 and 1.2 eV are observed at room temperature, which can be interpreted as a photocurrent in semiconducting nanotubes. At a low temperature, we found a marked change in the intensity of the spectrum. In this paper, we discuss this temperature dependence and the mechanism of photoconductivity.

Raman depolarization ratios and order parameters of a nematic liquid crystal

The depolarization ratios of the Raman vibrational bands from the terminal C≡N and the central C–C biphenyl link of an oriented nematic liquid crystal [p‐n‐pentyl‐p′‐cyanobiphenyl (5CB)] have been measured. The orientational order parameters 〈P2〉 and 〈P4〉 were calculated. The parameter 〈P4〉 remained far less than the mean‐field theory prediction although a systematic discrepancy between the order parameters obtained from the two bands was noted. The Raman tensor of C≡N band was found not to be uniaxial, contrary to the previous assumption, and a strong association of molecules is suggested. Problems associated with this technique are discussed.

Hysteresis-free and highly stable perovskite solar cells produced via a chlorine-mediated interdiffusion method

Although lead-halide perovskite-based solar cells hold the promise of a breakthrough in the production of next-generation photovoltaic devices, anomalous hysteresis in current–voltage curves and inadequate stability remain as major challenges. Here, we demonstrate the production of low-temperature solution-processed perovskite solar cells (ITO/PEDOT:PSS/perovskite/PC61BM/Ca/Ag) with hysteresis-free current–voltage characteristics, excellent photostability, and high reproducibility via the inclusion of methyl ammonium chloride (MACl) using the interdiffusion method. The best-performing devices exhibited a power conversion efficiency of over 12%. Our devices showed promising stability by maintaining more than 90% of their initial performance over long periods of time at ambient conditions with encapsulation using common techniques, as well as no obvious degradation after 2 h of continuous light exposure. We statistically compared fabrication processes using the interdiffusion method with or without MACl by creating a histogram of over 120 devices for each method. The results clearly indicated that including MACl gave better reproducibility and a higher average efficiency of 9.5%, as well as improved device stabilities.

Phase control through anisotropic strain in Nd0.5Sr0.5MnO3 thin films

Strain effect in charge- and orbital-ordered state has been investigated for Nd0.5Sr0.5MnO3 thin films deposited on (100), (110), and (111)-oriented substrates of SrTiO3. Films on (001) and (111) substrates have a monotonous temperature dependence for magnetic and transport properties showing no first-order phase transition. On the other hand, films on (110) substrate show a clear ferromagnetic-antiferromagnetic and metal-insulator transition around 170K similar to that in a bulk single crystal, which is a manifestation of the charge and orbital order. Precise control of the hole concentration was also demonstrated around half doping.

Determination of the primary elastic constants from thin foils having a strong texture

A new method is described for determining the primary elastic constants (stiffnesses cij’s and compliances sij’s) with respect to the crystallographic axes. Although we will consider only cubic materials the method can be applied to materials of lower symmetry. The method utilizes the symmetry present in a textured (preferred growth) foil and can be used for cases when bulk single crystals are difficult to prepare for ultrasonic experiments. The method involves the use of expressions, that have not been previously derived, relating the biaxial, flexural, Young’s and shear modulus to the primary elastic constants for textured foils. The agreement of the experimentally observed moduli with ones calculated from the expressions to be presented demonstrates that the accuracy is comparable with existing methods.

Novel technique for dynamic surface tension and viscosity measurements at liquid–gas interfaces

A novel means of generating and detecting surface waves at liquid-gas interfaces has been successfully developed. Electrocapillarity is used to generate the waves which are detected via specular reflection of a laser beam from the fluid surface to a position sensitive photodiode. Such a scheme is compact, sensitive, and does not mechanically touch the fluid surface. A preliminary study of highly damped waves on the magnetically oriented liquid crystal MBBA is reported.

Surface-induced ordering of a liquid crystal in the isotropic phase

A detailed account of a measurement of order parameter of a liquid crystal at the boundary by means of the wall‐induced pretransitional birefringence is given. Several surface treatments were studied including surfactants and evaporated films. Although all treatments produced good alignment in the nematic phase, the boundary order parameter (hence the strength of the aligning force) in the isotropic phase differed very much depending on the treatment, indicating the diverse nature of the alignment process.

Longitudinal surface waves for the study of dynamic properties of surfactant systems. II: Air-solution interface

Abstract A recently developed longitudinal wave apparatus was employed to study the dynamic interfacial properties; the Gibbs elasticity, the diffusion parameter, the surface (excess) dilational viscosity, and the surface (excess) shear viscosity. The dynamic interfacial properties were calculated from the dispersion equation of the surface waves using the wave numbers and the damping coefficients of the longitudinal wave at different frequencies. The wave number and the damping coefficient were obtained by measuring, at different locations, the surface tension oscillations induced by the longitudinal wave. The system used in this study is the octanoic acid aqueous solution in a concentration range from 0.2 to 2.0 × 10 −6 mole/cm 3 . The Gibbs elasticity was observed to pass through a maximum, approximately 25 dyn/cm, at a concentration of 0.3 × 10 −6 mole/cm 3 . The diffusion parameter exhibited two apparent discontinuities. The results also indicate that the surface dilational viscosity is two orders of magnitude larger than the surface shear viscosity, corroborating with the previous findings.