Anomalous spin-orbit torque switching due to field-like torque-assisted domain wall reflection.

Spin-orbit torques (SOTs) allow the electrical control of magnetic states. Current-induced SOT switching of the perpendicular magnetization is of particular technological importance. The SOT consists of damping-like and field-like torques, and understanding the combined effects of these two torque components is required for efficient SOT switching. Previous quasi-static measurements have reported an increased switching probability with the width of current pulses, as predicted considering the damping-like torque alone. We report a decreased switching probability at longer pulse widths, based on time-resolved measurements. Micromagnetic analysis reveals that this anomalous SOT switching results from domain wall reflections at sample edges. The domain wall reflection was found to strongly depend on the field-like torque and its relative sign to the damping-like torque. Our result demonstrates a key role of the field-like torque in deterministic SOT switching and the importance of the sign correlation of the two torque components, which may shed light on the SOT switching mechanism.

Near-Room Temperature Synthesis of Core/Shell-Structured Quantum Dots.

Core/shell-structured quantum dots (QDs) are considered as important active materials for optoelectronic devices. There have been a lot of synthesis procedures developed so far. Real epitaxial growth of shell layer, however, has not been reported yet. Here, a simple method for the synthesis of CdSe/CdS core/shell QDs is presented. Epitaxial growth of CdS shell on CdSe core is carried out by near room temperature successive ion layer adsorption and reaction (RT-SILAR). Our method for shell formation is conducted at room temperature, which facilitates the separation of resulting products from shell growth solution. After full coverage with one monolayer (ML) of CdS on CdSe QDs surface, photoluminescence (PL) quantum yield (QY) reaches up to 60%. Produced CdSe/CdS QDs have an elongated morphology, implying that CdS layers are formed in an epitaxial manner without etching or deteriorating CdSe QDs surface. We believe that our synthesis method for core/shell-structured QDs would be an ideal model for practical implication of QDs as well as fundamental studies.

Shifting of surface plasmon resonance due to electromagnetic coupling between graphene and Au nanoparticles.

Shifting of the surface plasmon resonance wavelength induced by the variation of the thickness of insulating spacer between single layer graphene and Au nanoparticles is studied. The system demonstrates a blue-shift of 29 nm as the thickness of the spacer layer increases from 0 to 15 nm. This is due to the electromagnetic coupling between the localized surface plasmons excited in the nanoparticles and the graphene film. The strength of the coupling decays exponentially with a decay length of d/R = 0.36, where d is the spacer layer thickness and R is the diameter of the Au nanoparticles. The result agrees qualitatively well with the plasmon ruler equation. Interestingly, a further increment of the spacer layer thickness induces a red-shift of 17 nm in the resonance wavelength and the shift saturates when the thickness of the spacer layer increases above 20 nm.

Enhancement of optical transmission with random nanohole structures.

We demonstrate an enhancement of optical transmission by creating randomly distributed nanoholes in a glass surface using a simple bottom-up fabrication process. V-shaped holes with sub-100 nm diameter are created by anodized aluminum oxide template and dry etching on glass substrates. The broadband and omnidirectional antireflective effect of the proposed nanostructures is confirmed by measuring the transmittance of the patterned glasses, leading to 3% better transmission. Subsequently, the short-circuit current and the open-circuit voltage of a solar cell with nanostructures are enhanced by 3-4%, improving the solar cell efficiency from 10.47% to 11.20% after two weeks of outdoor testing.