Rabi-like splitting and refractive index sensing with hybrid Tamm plasmon-cavity modes

Rabi-like splitting and self-referenced refractive index sensing in hybrid plasmonic-1D photonic crystal structures have been theoretically demonstrated. The coupling between Tamm plasmon and cavity photon modes are tuned by incorporating a low refractive index spacer layer adjacent to the metallic layer to form their hybrid modes. Anticrossing of the modes observed at different values of spacer layer thickness validates the strong coupling between the two modes and causes Rabi-like splitting with different splitting energy. The modes coupling has been supported by coupled mode theory. Rabi-like splitting energy decreases with increasing number of periods (N) and refractive index contrast (η) of two dielectric materials used to make the 1D photonic crystals, and the observed variation is explained by an analytical model. Angular and polarization dependency of the hybrid modes shows that the polarization splitting of the lower hybrid mode is much stronger than that of the upper hybrid mode. On further investigation, it is seen that one of the hybrid modes remains unchanged while other mode undergoes significant change with varying the cavity medium. This nature of the hybrid modes has been utilized for designing self-referenced refractive index sensors for sensing different analytes. For η=1.333 and N=10 in a hybrid structure, the sensitivity increases from 51 nm/RIU to 201 nm/RIU with increasing cavity thickness from 170 nm to 892 nm. For the fixed cavity thickness of 892 nm, the sensitivity increases from 201 nm/RIU to 259 nm/RIU by increasing η from 1.333 to 1.605. The sensing parameters such as detection accuracy, quality factor, and figure of merit for two different hybrid structures ([η=1.333, N=10] and [η=1.605, N=6]) have been evaluated and compared. The value of resonant reflectivity of one of the hybrid modes changes considerably with varying analyte medium which can be used for refractive index sensing.

Analysis of current-in-plane giant magnetoresistance using Co2FeAl0.5Si0.5 half-metallic Heusler alloy

Current-in-plane giant magnetoresistance (CIP-GMR) devices receive revived interest for high-sensitivity magnetic sensors. However, further improvement in MR ratios is necessary to achieve sufficiently magnetic field sensitivity. The usage of half-metallic Co-based Heusler alloy ferromagnetic (FM) layer has been demonstrated to be effective in enhancing GMR in current-perpendicular-to-plane (CPP) configuration; however, only small MR ratios are obtained in the CIP configuration. To understand the origin of the disappointingly low MR in the CIP configuration using the Heusler alloy FM layers, we investigated magnetotransport properties of CIP-GMR devices using half-metallic Co2FeAl0.5Si0.5 (CFAS) Heusler alloy and conventional CoFe alloy as ferromagnetic (FM) layers in combination with Ag or Cu as nonmagnetic (NM) spacer layer. Regardless of high lattice and electronic band matching at the CFAS/Ag interface, CFAS/Ag CIP spin valves (SVs) shows the MR ratio of only 1.2% at RT, which is much smaller than those of reference CoFe/Cu and CoFe/Ag SVs, 21.6 and 8.4%, respectively. Current density distribution simulations suggest that large current shunting occurs in the Ag layer due to significant resistivity gap between CFAS and Ag, which limits the generation of highly spin-polarized current from the CFAS layer, resulting in the very small MR ratios. To enhance the MR ratio in CIP-GMR using half-metallic materials, resistivity matching between FM layers and NM layer is required in addition to the high electronic band match that has been considered as key factors to obtain high MR ratio in CIP-GMR.

3D hotspot matrix of Au nanoparticles on Au island film with a spacer layer of dithiol molecules for highly sensitive surface-enhanced Raman spectroscopy

Engineering of efficient plasmonic hotspots has been receiving great attention to enhance the sensitivity of surface-enhanced Raman scattering (SERS). In the present study, we propose a highly sensitive SERS platform based on Au nanoparticles (AuNPs) on Au island film (AuIF) with a spacer layer of 1,4-benzenedimethanethiol (BDMT). The three-dimensional (3D) hotspot matrix has been rationally designed based on the idea of employing 3D hotspots with a vertical nanogap between AuIF and AuNPs after generating large area two-dimensional hotspots of AuIF. AuNPs@BDMT@AuIF are fabricated by functionalizing BDMT on AuIF and then immobilizing AuNPs. The SERS performance is investigated with Rhodamine 6G as a probe molecule and the determined enhancement factor is 1.3 × 105. The AuNPs@BDMT@AuIF are then employed to detect thiram, which is used as a fungicide, with a detection limit of 13 nM. Our proposed platform thus shows significant potential for use in highly sensitive SERS sensors.

The Local Structure of the BiS2 Layer in RE(O,F)BiS2 Determined by In-Plane Polarized X-ray Absorption Measurements

We have investigated the local structure of BiS2-based layered materials by Bi L3-edge extended X-ray absorption fine structure (EXAFS) measurements performed on single crystal samples with polarization of the X-ray beam parallel to the BiS2 plane. The results confirm highly instable nature of BiS2 layer, characterized by ferroelectric like distortions. The distortion amplitude, determined by the separation between the two in-plane (Bi-S1) bonds, is found to be highest in LaO0.77F0.23BiS2 with ΔR∼0.26 Å and lowest in NdO0.71F0.29BiS2 with ΔR∼0.13 Å. Among the systems with intrinsic doping, CeOBiS2 shows smaller distortion (ΔR∼0.15 Å) than PrOBiS2 (ΔR∼0.18 Å) while the highest distortion appears for EuFBiS2 revealing ΔR∼0.22 Å. It appears that the distortion amplitude is controlled by the nature of the RE(O,F) spacer layer in the RE(O,F)BiS2 structure. The X-ray absorption near edge structure (XANES) spectra, probing the local geometry, shows a spectral weight transfer that evolves systematically with the distortion amplitude in the BiS2-layer. The results provide a quantitative measurements of the local distortions in the instable BiS2-layer with direct implication on the physical properties of these materials.

Tribofilm Formation of Simulated Gear Contact Along the Line of Action

In this paper, an experimental simulation method was used for evaluating the tribofilm formation in rolling/sliding contact at different points in the line of action. A ball-on-disc test method was employed by which the pressure and slide to roll ratio of gear contact could be simulated. In order to reach a general conclusion, four different oils and two surface roughness were involved in the experiments. The tribofilm evolution was captured using spacer layer interferometry method, and the correlation of tribofilm with the location at the line of action was studied. Results showed that there is a threshold pressure for the tribofilm formation around which the tribofilm growth rate is maximum. Above this threshold pressure, the tribofilm formation is not stable, and the wear is dominant. Below this threshold pressure, the tribofilm growth rate rises by increasing the pressure and the gear contact is safely protected by a stable tribofilm. Graphic Abstract

3D Hotspot Matrix of Au Nanoparticles on Au Nanostructures with a Spacer Layer of Dithiol Molecules for Highly Sensitive Surface-Enhanced Raman Spectroscopy

Engineering of efficient plasmonic hotspots has been receiving great attention to enhance the sensitivity of surface-enhanced Raman scattering (SERS). In the present study, we propose a highly sensitive SERS platform based on Au nanoparticles (AuNPs) on Au nanostructures (AuNSs) with a spacer layer of 1,4-benzenedimethanethiol (BDMT). The three-dimensional (3D) hotspot matrix has been rationally designed based on the idea of employing 3D hotspots with a vertical nanogap between AuNSs and AuNPs after generating large area two-dimensional hotspots of AuNSs. AuNP@BDMT@AuNSs are fabricated by functionalizing BDMT on AuNSs and then immobilizing AuNPs. The Raman signal of the AuNP@BDMT@AuNSs is approximately twelve times higher than that of AuNSs at 100 nM of rhodamine 6G. The AuNP@BDMT@AuNSs are then employed to detect thiram, which is used as a fungicide, with a detection limit of 13 nM. Our proposed platform thus shows significant potential for use in highly sensitive SERS sensors.