Spectral Visualization of Near-Infrared Enhancement in 2D Layered WS₂

Abstract

Field enhancement of semiconductors is highly dependent on the wavelength of light. The wavelength dependence is particularly promising for light− matter interaction applications, such as sensors, photocatalysts, and solar cells, as well as to achieve an understanding of plasmon-free field enhancement. However, there are few reports on the field enhancement of two-dimensional (2D) semiconductors and no reports on the wavelength dependence to date. Here, we present the field enhancement of tungsten disulfide (WS 2 ) for a 2D layered semiconductor. The enhancement factor (EF) of a single WS 2 flake was evaluated by using confocal fluorescence microspectroscopy. The wavelength dependence was investigated both by experiment and with theoretical calculations for the range from the visible to the near-infrared (NIR) region (400−2000 nm). As a result, the EFs for a single WS 2 flake were visualized as maps upon six different excitation wavelengths. The maps were compared with maps of electric fields from finite-difference time-domain calculations, based on the x−y−z position of a single WS 2 flake at the same position measured by using atomic force microscopy. The EF in the NIR region showed the largest enhancement, and the maximum EF was demonstrated at a specific number of layers (150 layers) as EF = 100.

Large Field Enhancement of Nanocoral Structures on Porous Si Synthesized from Rice Husks

“…Interestingly, the size of ∼200 nm is in good agreement with that predicted by Mie scattering for a spherical Si particle producing the highest efficiency, as shown in Figure m. − According to Mie scattering theory, the value of Q sca is proportional to the square of the electric field of the scattered light, corresponding to the magnitude of EF Figure e.…”

“…An objective lens (SMLPLN, 100×, Olympus) with a long working distance was used to obtain the spectrum for the CV solution under a cover glass. The optical cell for collection of the spectrum was designed to provide a solution layer between the cover glass and the Si powder. − The EF values associated with the fluorescence intensities were obtained by acquiring four spectra, wherein the enhanced spectrum of the CV was divided by the spectrum of the CV, both of which had the background signals subtracted, as described in our reports previously. − Fluorescence mapping measurements were conducted by collecting CV spectra with the same instrument and by scanning the sample in the cell on an x–y translation stage, as described in our report previously. ,, The grid size of the mapping data was due to the scan step of the stage, which was set to 500 nm, and the data collection time of the spectrum was 1 s. Using the mapping data, EFs were obtained and layered over the SEM image of the same sample.…”

“…58−62 Fluorescence mapping measurements were conducted by collecting CV spectra with the same instrument and by scanning the sample in the cell on an x−y translation stage, as described in our report previously. 60,61,68 The grid size of the mapping data was due to the scan step of the stage, which was set to 500 nm, and the data collection time of the spectrum was 1 s. Using the mapping data, EFs were obtained and layered over the SEM image of the same sample.…”

Brush Printing Creates Polarized Green Fluorescence: 3D Orientation Mapping and Stochastic Analysis of Conductive Polymer Films

“…The mapping of the polarized fluorescence spectra to evaluate the oriented film was carried out as described elsewhere. 58,59 Briefly, the position of the film was controlled by a fine x-y stage. The polarized fluorescence spectra were measured over an area of 30 × 30 mm 2 , which was divided into 900 pixels (30 × 30 pixels, 1 μm 2 for each pixel).…”

“…To evaluate the anisotropy of the film using polarized fluorescence spectral measurements, the electric field of the polarized light was oriented either parallel or perpendicular to the brushing direction. The mapping of the polarized fluorescence spectra to evaluate the oriented film was carried out as described elsewhere. , Briefly, the position of the film was controlled by a fine x-y stage. The polarized fluorescence spectra were measured over an area of 30 × 30 mm 2 , which was divided into 900 pixels (30 × 30 pixels, 1 μm 2 for each pixel).…”