We demonstrate that Pd nanospheres exhibit much higher susceptibility of the localized surface plasmon resonance (LSPR) peak to medium refractive index changes than commonly used plasmonic sensing materials such as Au and Ag. The susceptibility of spherical Au nanoparticle-core/Pd-shell nanospheres (Au/PdNSs, ca. 73 nm in diameter) was found to be 4.9 and 2.5 times higher, respectively, than those of Au (AuNSs) and Ag nanospheres (AgNSs) having similar diameters. The experimental finding was theoretically substantiated using the Mie exact solution. We also showed from a quasi-static (QS) approximation framework that the high susceptibility of Pd LSPR originates from the smaller dispersion of the real part of its dielectric function than those of Au and Ag LSPR around the resonant wavelength. We conclude that the Pd nanoparticle is a promising candidate of "the third plasmonic sensing material" following Au and Ag to be used in ultrahigh-sensitive LSPR sensors.

The hydrogen absorption/desorption processes of (111)-textured and normal palladium (Pd) thin films of thickness ranging from 8 to 48 nm are investigated using X-ray diffractometry. The one-dimensional expansion of Pd lattice due to the substrate clamping is observed at the low hydrogen composition phase while both out-of-plane and in-plane expansions are detected at the high hydrogen composition phase. Accordingly, using a biaxial Poisson’s ratio, an anisotropic expansion factor is proposed for describing such phenomenon quantitatively and the hydrogen composition dependence on this factor is investigated.

This paper reports that a fine-tuning of orbital hybridization opens a door to atomic-level engineering of spin-orbit physics.

Oxide‐based memristor devices are being extensively studied as one of the most promising technologies for next generation nonvolatile memory and neuromorphic computing. However, the switching process of such devices relying on the formation and rupture of conductive filaments has not been easily controlled, and thus induces large cycle‐to‐cycle and device‐to‐device variations in resistive switching, which hinders the development of high‐performance memristors. High‐performance memristors that meet the requirements for truly electroforming‐free, highly uniform, and low‐power switching are yet to be developed. Here, a phase‐separated oxide memristor is demonstrated based on a spontaneous phase separation process to form amorphous TiO2 switching medium distributed among the crystalline CoO grains. The confinement of conductive filaments into the intergrain amorphous oxide phase effectively minimizes the stochasticity of filament formation and rupture, resulting in drastically enhanced switching uniformity. The designed microstructure also facilitates filament formation and dissolution during switching processes and leads to truly electroforming‐free switching and low switching power (simultaneous low switching voltage 0.4 V and low current 2.5 µA).

We investigated the dependence of the surface-enhanced Raman scattering (SERS) activity of densely arranged two-dimensional assemblies of spherical Au(core)-Ag(shell) nanoparticles (Au/AgNSs) on the nanoparticle diameter. The size-controlled Au/AgNSs were synthesized using the Au nanosphere seed-mediated growth method without any bulky stabilizers. The diameters of the Au/AgNSs were 38, 53, and 90 nm and the ratio of the total diameter to the Au core diameter was adjusted to ca. 2.0. Extinction spectra of the colloidal solutions of these nanoparticles exhibited the prominent peak of the localized surface plasmon resonance (LSPR) of Ag and therefore the Au/AgNSs exhibited LSPR properties almost the same as Ag nanospheres. It was confirmed from SEM observation that the organic solvent-mediated liquid-liquid interface assembly technique easily generated densely arranged two-dimensional assemblies of the nanospheres. The extinction spectra of all the assemblies exhibited a prominent broad peak ranging from 500 nm to the near-infrared region, which is assigned to the longitudinal LSPR mode of the coupling nanospheres. The extinction intensity increased with increasing nanosphere diameter. The SERS activities of these assemblies were investigated using p-aminothiophenol as a probe molecule. The result revealed that the enhancement factor (EF) of the Raman signal dramatically increased upon increasing the particle diameter. The maximum EF obtained with a laser excitation wavelength of 785 nm was 1.90 × 10(6) for a nanosphere diameter of 90 nm. This renders the two-dimensional assemblies of the plasmonic Au/AgNSs promising for the development of highly sensitive SERS sensor platforms due to their strong electromagnetic effect.