Papers by Keyword: Light Absorption

Abstract: The zero-gap and low absorption in visible light spectrum has limited the potential of graphene potential in photoelectric applications. Two-dimensional (2D) heterostructures have grown up in recent years showing attractive prospects in making new materials with designed properties, and become a promising way to modulate properties of graphene. Recent research progress in 2D heterostructures, including the varieties and properties of van der waals and non-van der waals graphene-based 2D heterostructures separately, is reviewed in this paper. Then the photoelectric applications of graphene-based 2D heterostructures are summarized.

Abstract: Based on the Lorenz-Mie light scattering theory, we have calculated the light absorption of single silicon nanowire with Si₃N₄ coating, and compared with pure single silicon nanowire. The calculated result indicates that there exists an enhanced absorption in the Si₃N₄-coated silicon nanowire and shows a great photocurrent enhancement factor (~70%) for the coaxial NW with the shell thickness of ~70 nm. For a special shell thickness (175 nm) in the Si₃N₄-coated silicon nanowire for r = 150 nm, the enhancement comes up to ~98.45%.

Abstract: There are several oxygen concentration measurement methods applied in aircraft fuel tank inerting systems. In this work, an aircraft fuel tank inerting experiment system was built and oxygen concentration of the fuel tank ullage (fuel tank space above the surface of the fuel which is filled with fuel vapor and air) and the dissolved oxygen in the fuel was detected with the methods of light absorption and optical fluorescence. The experiment was conducted through different operating conditions and results has illustrated that the light absorption method as well as the optical fluorescence method has the same accuracy sensing calibration gases, but the suitable condition of the two methods are different. Results have shown that the method of light absorption is more suitable to test oxygen concentration of gas mixture, and the method of optical fluorescence is more suitable to detect the concentration of dissolved oxygen in liquid substance.

Abstract: Structural health monitoring systems are required for detecting damage in structures so as to facilitate their timely maintenance and repair and to prevent catastrophic structural failure. To date, a variety of different sensor platforms (e.g., piezoelectric materials, fiber optics, and wireless sensors) have been proposed for SHM. However, they still suffer from high energy demand, large form factors, and durability issues, particularly when applied for monitoring space structures and reusable spacecraft. In a previous study, a bio-inspired and photocurrent-based strain sensor has been developed. This poly(3-hexylthiophene) (P3HT)-based nanocomposite sensor has been shown to generate photocurrent whose magnitude varies in tandem with applied strain. However, the photocurrent generation performance of the sensor is quite low. In addition, the strain sensing mechanism is not fully understood. In this study, the performance of the photoactive thin films were enhanced, and its strain sensing characteristics were analyzed using ultraviolet-visible (UV-Vis) absorption spectroscopy. First, multilayered photoactive and P3HT-based thin films were assembled via spin coating. The photocurrent generation performance of the films was evaluated using two methodologies, namely its photocurrent time history and current-voltage (IV) response. Uniform coating of the photoactive layer and high purity aluminum electrodes were crucial for improving their photocurrent generation. Second, light absorption properties of the P3HT-based photoactive layer were investigated at different strain levels using a UV-Vis spectrophotometer. Light absorption was shown to vary linearly with applied tensile strains.

Abstract: Cu2S nanowire arrays with different morphologies were prepared by solid-gas reaction between Cu foil and mixture gas of H2S and O2. Their microstructures were observed with XRD, TEM, and the optical properties were measured by DRS, PL and Raman. The results showed that the nanowire were Cu2S single crystal with a thin layer CuxO (x=1, 2) over the surface. The optical properties of the Cu2S nanowire arrays are related to the diameter, length, and distribution density of nanowire arrays. The thinner is the nanowire’s diameter; the bigger is the absorption of the visible light, and the absorbance begun to descend within infrared band. The absorbance of nanowire arrays with bigger diameter to the infrared light was stronger than that with thinner diameter. The photoluminescence spectrum (PL) indicated that band gaps of Cu2S nanowire arrays also changed simultaneously with the nanowire arrays’ structure parameters. The research demonstrated the Cu2S nanowire arrays’ potential applications in the photovoltaic cell and solar-heat harvesting area.

Abstract: We have carried out detailed investigations into the light absorption in single Si (core)/SiO₂ (shell) coaxial nanowires (NWs) within the framework of the Lorenz-Mie light scattering theory. We have found that the light absorption in single coaxial NWs can be significantly enhanced as compared to in Si NWs, due to SiO₂ shells. We have also found that the photocurrent can be enhanced up to ~56% for the coaxial NW of the core radius of 150 nm by tuning the shell thickness.

Abstract: The main purpose of this paper is to investigate the optical properties of PTCDA and Alq3 films, prepared by two steps, vacuum evaporation and deposition processes on platelets of glass, quartz, and indium-tin-oxide (ITO) coated glass. We have emphasised the bands structure of the absorption spectra with peaks situated at 358 nm, 374 nm, 475 nm and 552 nm in PTCDA, respectively 232 nm, 261 nm and 380 nm in Alq3 that confirms the dominant presence of Alq3 meridianal molecular isomer. For PTCDA films deposited on glass coated with ITO, the structure of the weak double peak at low wavelength is partially modified, but the positions of the two important absorption peaks situated at 2.25 eV and 2.61 eV are unchanged. The two different luminescence emission peaks obtained in Alq3 for different excitation wavelengths (λ=360 nm and λ=520 nm) suggest the existence of the facial isomer beside the meridianal one. We have evidenced a significant Stocks shift in the spectra (EPTCDA=0.40 eV; EAlq3=0.9 eV) and a large Frank- Condon shift (0.40-2.3 eV), suggesting important effect associated respectively with the solid state structure and important conformational differences between the ground and excited state.