Topic
Absorption (electromagnetic radiation)
About: Absorption (electromagnetic radiation) is a research topic. Over the lifetime, 76674 publications have been published within this topic receiving 1381221 citations.
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TL;DR: Graphene-wrapped ZnO hollow spheres were synthesized by a two-step process, which combined a hydrothermal reaction with surface modification as discussed by the authors, which effectively decreases the density of the composite without sacrificing the contact between graphene and the nanoparticles.
Abstract: Graphene-wrapped ZnO hollow spheres were synthesized by a two-step process, which combined a hydrothermal reaction with surface modification. The experimental results show that reduced graphene oxide sheets adhere entirely to the surface of the ZnO hollow spheres consisting of nanoparticles. The unique structure effectively decreases the density of the composite without sacrificing the contact between graphene and the nanoparticles. Different mass ratios of graphene to ZnO hollow spheres mixed in a paraffin wax matrix (50 wt%) were prepared to investigate the electromagnetic wave absorption properties in the X-band region. When the mass ratio of graphene oxide to ZnO is 12 : 88, the composite exhibits a maximum absorption of −45.05 dB at 9.7 GHz with a sample thickness of only 2.2 mm. The fundamental mechanism based on electrical conductivity and the polarization between the graphene sheets and ZnO nanoparticles is discussed. The hierarchical structure of graphene-wrapped ZnO hollow spheres exhibits a promising designable approach to lightweight electromagnetic wave absorbing materials.
498 citations
TL;DR: In this article, a new technique was presented for obtaining the absorption spectra of small samples and low concentrations of gases, which makes use of currently available sources of wavelength-tunable intense coherent light such as the optical parametric oscillator, dye laser, or tunable diode laser.
Abstract: A new technique is presented for obtaining the absorption spectra of small samples and low concentrations of gases. The technique makes use of currently available sources of wavelength‐tunable intense coherent light such as the optical parametric oscillator, dye laser, or tunable diode laser. The absorbed power is detected by the heating and resultant pressure rise in the absorbing gas. An initial experiment with a 15‐mW He–Ne laser operating at 3.39 μ has shown a sensitivity adequate to measure the absorption of a concentration of 10−8 of methane in nitrogen. It is expected that, with higher‐power sources of tunable ir radiation, it may be possible in the future to detect concentrations of impurities as low as 10−13.
498 citations
TL;DR: Comparison of the results indicates the range of values of the scattering and absorption parameters where the computationally fast diffusion approach is applicable.
Abstract: To allow the determination of scattering and absorption parameters of a turbid material from reflection measurements the relation of these parameters to the reflection has been described by two theoretical approaches. One approach is based on the diffusion theory which has been extended to include anisotropic scattering. This results in a reflection formula in which the scattering and absorption are described by one parameter each. As a second more general approach a Monte Carlo model is applied. Comparison of the results indicates the range of values of the scattering and absorption parameters where the computationally fast diffusion approach is applicable.
498 citations
Journal Article•
496 citations
TL;DR: In this article, a model for the calculation of the absorption and emission spectra for GaAs at carrier concentrations in excess of 1×1018 cm−3 is described, which utilizes a Gaussian fit to Halperin-Lax band tails for the concentration-dependent density of states and also includes an energy-dependent matrix element.
Abstract: A model for the calculation of the absorption and emission spectra for GaAs at carrier concentrations in excess of 1×1018 cm−3 is described. This model utilizes a Gaussian fit to Halperin‐Lax band tails for the concentration‐dependent density of states and also includes an energy‐dependent matrix element. The calculated absorption and emission spectra are compared to previous experimental results. All results are for 297 K. For p‐type GaAs, the agreement is very good. The concentration dependence of the effective energy gap is obtained and can be expressed as Eg (eV) =1.424−1.6×10−8 [p (cm−3)]1/3. The concentration‐dependent thermal equilibrium electron‐hole density product n0p0 and the radiative lifetime τr are calculated for p‐type GaAs. The value of n0p0 increases from the low‐concentration value of 3.2×1012 cm−6 to 1.2×1013 cm−6 at p=1.6×1019 cm−3. This value of n0p0, together with the thermal generation rate obtained from the experimental absorption coefficient, gives τr as 0.37 nsec at p=1.6×1019 cm−3.
495 citations