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Employing gap-mode plasmons in a scanning tunneling microscope junction, we studied tip-enhanced Raman spectroscopy (TERS) of MoS2on Au(111). We observed a mode denoted as “m”, positioned to the right of A1'by a difference of approximately 6 cm–1. In the MoS2region that is not in direct contact with the Au(111) substrate, the m peak still exists, indicating that the m mode originates from MoS2. The m mode could originate from non-G-point phonon modes in the ZO branch or LA(K) + TA(K). Additionally, our investigation reveals that the TERS intensity reaches its maximum by continuing to approach MoS2after the tip contacts MoS2. The tip displacement required to reach the maximum TERS intensity depends on the tip conditions. Our results provide guidance for obtaining the optimal TERS intensity for MoS2and have potential application to other two-dimensional transition metal dichalcogenides.

As a lattice interference effect, moiré superlattices feature a magnification effect that they respond sensitively to both the extrinsic mechanical perturbations and intrinsic atomic reconstructions. Here, using scanning tunneling microscopy and spectroscopy, we observe that long-wavelength WS2superlattices are reconstructed into various moiré morphologies, ranging from regular hexagons to heavily deformed ones. We show that a dedicated interplay between the extrinsic nonuniform heterostrain and the intrinsic atomic reconstruction is responsible for this interesting moiré structure evolution. Importantly, the interplay between these two factors also introduces a local inhomogeneous intralayer strain within a moiré. Contrary to the commonly reported electronic modulation that occurred at the valence band edge due to interlayer hybridization, we find that this local intralayer strain induces a strong modulation at Kpoint of the conduction band, reaching up to 300 meV in the heavily deformed moiré. Our microscopic explorations provide valuable information in understanding the intriguing physics in TMD moirés.

Planar plasmonic focusing of surface plasmon polaritons (SPPs) by an in-plane nanostructure consisting of Ag-column arrays and an in-plane Fresnel zone plate (FZP) with a Cu grating underneath for energy compensation was demonstrated. The CdS-based hybrid plasmonic waveguide generated in the Ag-column arrays was characterized with a scanning near-field optical microscope. By using the FZP focusing structure, the SPP modes were separated from the CdS photoluminescence background and focused at the FZP focus area, and in this way, were used as the source for the SPP waveguide. Finite-difference time-domain simulations correspond with the experimental observations, suggesting that this is indeed an effective approach to control SPP coupling within the dielectric nanoribbon waveguide.

We leached samples of the A1, A2, B2, and C horizons of Lakehurst soil with phosphate solution and measured total phosphorus, labile phosphorus, nonlabile phosphorus, and maximum retention capacity for each horizon. A1 and A2 horizons proved to have a limited capacity for phosphate retention, and the B2 and C horizons were capable of removing phosphate from solution.

This paper reports a model for the flow of two incompressible and immiscible fluids in soils, developed by combining a modified Darcy's law with the continuity equations. The resulting equations are of a system of nonlinear partial differential equations. Numerical analysis, based on the finite element method and Newton-Raphson's method, to solve the equations is given and discussed. Computer simulations of the flow of water and trichloroethylene in sands are also shown.

A mathematical model was developed to simulate phosphate reactions with minerals in acidic soils. Phosphate in solution was assumed to react with kaolinite, gibbsite, and goethite simultaneously. Each reaction had a two‐step sorption mechanism, i.e., mineral + solution P ⇄ labile P ⇄ nonlabile P, where labile and nonlabile forms are defined as isotopically exchangeable and nonexchangeable, respectively. The first step of the sorption mechanism followed the kinetic version of the Langmuir adsorption isotherm and was a second‐order reaction in nature. The second step of the sorption mechanism was a linear reversible kinetic equation. Seven ordinary differential equations describing the system were solved by numerical methods. The model effectively simulated the trend of phosphate reactions with soil minerals. Using the model to study the adsorption isotherm, we found that the Langmuir plot, i.e., concentration/adsorption vs. concentration, was linear when minerals had relatively homogeneous adsorption rates (or adsorption energies) and was nonlinear for widely differing rates, implying that a homogeneous surface provides a sufficient condition but not a necessary condition for a linear Langmuir plot. Simulation and analysis of a two‐surface Langmuir equation supported this finding.

A kinetic model of phosphate reactions with minerals in acidic soils was used to simulate experimental results obtained under a variety of conditions based on three factors—solution pH, solution concentration, and mineral specific surface area. Three minerals with different reactivity (kaolinite, gibbsite, goethite) were studied to check the adaptability of the model and show the effect of mineral properties on reaction with phosphate. The experimental data as well as the kinetic models showed that high pH values, low concentrations of the phosphorus in the reacting solution, and small specific surface area will reduce retention of phosphate. Any other change of the three factors increases the retention capability. The model shows its flexibility in simulating phosphate reactions with different minerals. The results show promise for the miltifactor approximation of phosphate reactions with soil minerals in acid to neutral soils.