The reduced graphene oxide (RGO)-based composites have attracted intensive attention in experiment due to its superior performance as photocatalysts, but still lacking is the theoretical understanding on the interactions between constituents, and the connection between such interaction and the enhanced photoactivity. Herein, the interaction between the g-C 3 N 4 and RGO sheets is systematically explored by using state-of-the-art hybrid density functional theory. We demonstrate that the O atom plays a crucial role in the RGO-based composites. Compared to the isolated g-C 3 N 4 monolayer, the band gap of composites obviously decreases, and at higher concentration, the levels in the vicinity of Fermi level are much more dispersive, indicating the smaller effective mass of the carrier. These changes are nonlinear on the O concentration.Interestingly, appropriate O concentration alters the direct-gap composite to indirect-gap one.Most importantly, at a higher O concentration, a type-II, staggered, band alignment can be obtained in the g-C 3 N 4 -RGO interface, and negatively charged O atoms in the RGO are active sites, leading to the high hydrogen-evolution activity. Furthermore, the calculated absorption spectra varying with the O concentration shed light on different experimental results. The findings pave the way for developing RGO-based composites for photocatalytic applications.
We present a new type of dual-band terahertz metamaterial absorber formed by a patterned metallic strip and a dielectric layer on top of a metallic ground plane. It is found that besides a strong absorption in the fundamental resonance, a prominent high-order resonance with near-unity absorption is also unveiled. The origin of the induced dual-band absorption was elucidated. Importantly, the quality factor (Q) and the figure of merit (FOM) of the high-order resonance are 8.4 and 22.7 times larger than that of the fundamental resonance, respectively, which makes the proposed absorber to have significant potential in biological monitoring and sensing. Moreover, we demonstrate a dual-band and insensitive for two orthogonal polarizations terahertz absorber based on a metallic cross and a metallic ground plane separated by a dielectric layer. The Q and FOM of the high-order resonance are still larger than that of the fundamental resonance. The proposed absorbers appear to be very promising for solar cells, detection, and imaging applications.
Compact wavelength-sensitive optical components are desirable for optical information processing and communication in photonic integrated system. In this work, optical waveguiding along single composition-graded CdS(x)Se(1-x) nanowires were systematically investigated. Under a focused laser excitation, the excited light can be guided passively along the bandgap-increased direction of the nanowire, keeping the photonic energy of the guided light almost unchanged during the whole propagation. In comparison, the excited light is guided actively through incessantly repeated band-to-band reabsorption and re-emitting processes along the bandgap-decreased direction, resulting in a gradual wavelength conversion during propagation. On the basis of this wavelength-converted waveguiding, a concept of nanoscale wavelength splitter is demonstrated by assembling a graded nanowire with several composition-uniform nanowires into branched nanowire structure. Our study indicates that composition-graded semiconductor nanowires would open new exciting opportunities in developing new wavelength-sensitive optical components for integrated nanophotonic devices.
We present a four-band and polarization insensitive terahertz metamaterial absorber formed by four square metallic rings and a metallic ground plane separated by a dielectric layer. It is found that the structure has four distinctive absorption bands whose peaks are average over 97%. The mechanism of the four-band absorber is attributed to the overlapping of four resonance frequencies, and the mechanism of the absorption is investigated by the distributions of the electric field. Particularly, the frequency of each absorption peak can be flexible controlled by varying the size of the corresponding metallic ring. The proposed concept is applicable to other types of absorber structure and can readily be scaled up to the structures that are working in the microwave frequency range. Moreover, the characteristic of the design can be used to design five-band metamaterial absorber by adding one more metallic ring. The proposed absorber has potential applications in detection, imaging and stealth technology.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.