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Large-area graphene is commonly prepared through chemical vapor deposition (CVD); in situ and nondestructive methods for its characterization are desirable. In this paper, we demonstrate a practical method—exploiting magnetic dipole resonance and coupling effects—with which the Raman signals of graphene on copper (Cu) foil can be directly, faithfully, and greatly enhanced. The magnetic dipole resonance of a silicon nanoparticle (SiNP) can effectively couple its electromagnetic field with the Cu foil to induce an enormous electric field located solely at the position of the SiNP on the graphene. The coupled electromagnetic field can lead to hot spots of high electric field intensity (E2/E02 = 123.2) within the graphene. Even when we positioned only a few SiNPs upon the graphene/Cu foil, we obtained a Raman signal enhancement (ca. 206 times) much greater than that of graphene transferred onto a 300 nm oxide film (ca. 12 times). From a series of experiments comparing the Raman signals of graphene before and ...

In this study we developed a method, using a simple two-layer nanocavity structure, to significantly enhance light outcoupling from two-dimensional (2D) materials. Because the surface electric fields (E-fields) of the nanocavities were enhanced greatly over ultrabroadband regimes, the excitation of various 2D materials with laser light and their Raman and photoluminescence (PL) light emissions were all enhanced dramatically while maintaining band-to-band ratios and peak positions precisely. At the same time, the optical visibility of the 2D materials was also enhanced significantly over a broad spectral regime. Using a single type of Ag/SiO2 nanocavity structure, we obtained a 475-fold, equal enhancement in the intensities of the main Raman peaks of single-layer graphene (SLG) and more than a 350-fold increase in the intensities of both the Raman and PL signals of single-layer tungsten disulfide (WS2). Notably, the light outcouplings of these 2D materials were enhanced dramatically without any spectral di...

In this study we developed an approach to identify the surface polarity of silicon carbide (SiC) by using an excitation laser possessing a photon energy (2.33 eV) much lower than the band gap of 4H-SiC (3.30 eV). By gradually attenuating the intensity of the excitation laser, the effective depth that the laser could generate Raman signals could eventually be limited to within the ultrashallow region of the SiC wafer. Through three-dimensional finite-difference-time-domain (3D-FDTD) simulations, we found that the depth of the high electric field region could be limited from several micrometers below the surface to the near-surface region of 4H-SiC, merely by attenuating the power of the incident laser. Experimentally, we observed a clear trend in the Raman peak intensity ratio of the signals at 210 and 203 cm–1 in the FTA mode: the intensity ratio of the Si face was always higher than that of the C face regardless of the measurement position on the 4H-SiC wafer. Even through the carrier concentrations in t...

An investigation of speciated mercury transformation with the addition of hydrogen bromide (HBr) at elevated temperatures was conducted in a slipstream reactor with real flue gas atmospheres. A real flue gas atmosphere is composed of bituminous coal (with high sulfur and high chlorine contents) and Powder River Basin (PRB) coal (with lower sulfur and chlorine contents). The average sulfur, chlorine, and mercury contents in the tested bituminous coal were 1.31% and 1328 and 0.11 ppm and 0.61% and 170 and 0.08 ppm, respectively, for tested PRB coal. The average CaO, Fe2O3, and loss on ignition in collected fly ash contents of tested bituminous coal were 1.71, 17.51, and 7.13% and 22.95, 4.91, and 0.64%, respectively, for tested PRB coal. The different contents of coal chlorine, CaO, and Fe2O3 in fly ash can be attributed to the different mercury speciations at baseline tests for these two coals in this study. The addition of HBr concentrations into the flue gas was controlled in the 3−15 ppm range. Semi-con...

In this study we demonstrated that the improvement of detection capability of cadmium sulfide (CdS) photoconductors in the ultraviolet (UV) regime is much larger than that in the visible regime, suggesting that the deep UV laser treated CdS devices are very suitable for low-light detection in the UV regime. In addition, we determined that a nanocrystallized CdS photoconductor can behave as a picowatt-sensitive detector in the UV regime after ultra-shallow-region crystallization of the CdS film upon a single shot from a KrF laser. The strategy proposed herein appears to have great potential for application in the development of CdS photoconductors for picowatt-level detection of UV light with low power consumption.

We have used a direct imprint-in-metal method that is cheap and rapid to prepare incident angle-tuned, broadband, ultrahigh-sensitivity plasmonic antennas from nanoparticles (NPs) and imprinted metal mirrors. By changing the angle of incidence, the nanoparticle-imprinted mirror antennas (NIMAs) exhibited broadband electromagnetic enhancement from the visible to the near-infrared (NIR) regime, making them suitable for use as surface-enhanced Raman scattering (SERS)-active substrates. Unlike other SERS-active substrates that feature various structures with different periods or morphologies, the NIMAs achieved broadband electromagnetic enhancement from single configurations. The enhancement of the electric field intensity in the NIMAs originated from coupling between the localized surface plasmon resonance of the NPs and the periodic structure-excited surface plasmon resonance (SPR) of the imprinted mirror. Moreover, the coupling wavelengths could be modulated because the SPR wavelength was readily tuned by changing the angle of the incident light. Herein, we demonstrate that such NIMAs are robust substrates for visible and NIR surface-enhanced resonance Raman scattering under multiple laser lines (532, 633, and 785 nm) of excitation. In addition, we have found that NIMAs are ultrasensitive SERS-active substrates that can detect analytes (e.g., rhodamine 6G) at concentrations as low as 10(-15) M.

In this study, we demonstrated that the improvement of detection capability of cadmium sulfide (CdS) photoconductors in the ultraviolet (UV) regime is much larger than that in the visible regime, suggesting that the deep UV laser-treated CdS devices are very suitable for low-light detection in the UV regime. We determined that a nanocrystallized CdS photoconductor can behave as a picowatt-sensitive detector in the UV regime after ultra-shallow-region crystallization of the CdS film upon a single shot from a KrF laser. Photoluminescence and Raman spectra revealed that laser treatment increased the degree of crystallization of the CdS and led to the effective removal of defects in the region of a few tens nanometers beneath the surface of CdS, confirming the result by the transmission electron microscopy (TEM) images. Optical simulations suggested that UV light was almost completely absorbed in the shallow region beneath the surface of the CdS films, consistent with the observed region that underwent major crystal structure transformation. Accordingly, we noted a dramatic enhancement in responsivity of the CdS devices in the UV regime. Under a low bias voltage (1 mV), the treated CdS device provided a high responsivity of 74.7 A W(-1) and a detectivity of 1.0×10(14) Jones under illumination with a power density of 1.9 nW cm(-2). Even when the power of the UV irradiation on the device was only 3.5 pW, the device exhibited extremely high responsivity (7.3×10(5) A W(-1)) and detectivity (3.5×10(16) Jones) under a bias voltage of 1 V. Therefore, the strategy proposed in this study appears to have great potential for application in the development of CdS photoconductors for picowatt-level detection of UV light with low power consumption.

In this study we describe a low-cost cadmium sulfide (CdS) photoconductor that behaves as a highly sensitive and rapidly responding detector toward low-intensity light. Through the observation of TEM images and analysis of micro-Raman spectra, the degree of crystallization of CdS films increased and their dislocation defects were removed effectively after treatment with several shots from a KrF excimer laser. Such laser treatment of CdS photoconductors could be conducted in air and completed within a few seconds. At a very low bias voltage of 1 mV, the laser-treated CdS device provided a record high responsivity of 7200 A W−1 and a detectivity of 1015 Jones. In addition, at a normal bias voltage of 1 V, it displayed an extremely high responsivity of 7 × 106 A W−1 and a detectivity of 6 × 1016 Jones. The measured response time of the laser-annealed CdS device from the dark to illumination at 10−2 fW μm−2 was only 40 ms—much faster than the shutter speed or exposure time required for a professional digital camera for such low-light image detection. Accordingly, KrF laser annealing is a simple and rapid process that can significantly enhance the low-light detection properties of CdS, a commercial photoconductor. Our strategy proposed herein appears to hold great potential for ultralow-light image detection with ultralow power consumption.