Multifunctional graphene metamaterials based on polarization-insensitive plasmon-induced transparency.

In this paper, a 4L-shaped graphene patterned polarization-insensitive plasmon-induced transparency (PIT) metamaterial structure is proposed. The photoelectric switch based on this structure supports a variety of light sources, such as linearly polarized light with different polarization directions, left rotation circularly polarized light (LCP) and right rotation circularly polarized light (RCP). And the switch has excellent performance in the case of different light sources, the amplitude modulation is as high as 99.01%, and the insertion loss is as low as 0.04 dB. In addition, the PIT metamaterial has a high refractive index sensitivity of up to 49156 nm/RIU. The group index of the PIT metamaterial is as high as 980, which can achieve excellent slow light effect. This study provides a scheme and guidance for the design of optoelectronic devices.

Mpg-C3N4-ZIF-8 composites for the degradation of tetracycline hydrochloride using visible light.

It was found that mesoporous graphite carbon nitride (mpg-C3N4) prepared using melamine as the precursor and ammonium chloride as the bubble template, has good photocatalytic activity under visible light irradiation. In order to improve the photocatalytic performance of mpg-C3N4, it was combined with metal-organic framework ZIF-8. Taking tetracycline hydrochloride (TC) solution as a model pollutant, the photocatalytic activity of composites was studied to select the optimal composite ratio and pH value. The initial concentration of hydrogen peroxide and active oxidation species were also investigated. The results showed that when the loading of ZIF-8 was 40 wt%, the removal efficiency was the best and 74.8% of TC could be removed. The degradation efficiency of TC was negatively affected under extreme pH conditions, but the composite photocatalyst mpg-C3N4-ZIF-8 had a relatively higher degradation efficiency on TC at mild pH values (4-8). The removal efficiency was the best at pH 8, and 75.1% of TC could be removed; the adsorption capacity was 430.7 mg·g-1 and the photodegradation capacity was 548.6 mg·g-1. The order of active species affecting the photocatalytic degradation of TC by mpg-C3N4-ZIF-8 was hole > superoxide radical > hydroxyl radical.

Simulation Analysis on Photoelectric Conversion Characteristics of Silicon Nanowire Array Photoelectrodes.

Semiconductor nanowire photoelectrochemical cells have attracted extensive attention in the light-conversion field owing to the low-cost preparation, excellent optical absorption, and short distance of carrier collection. Although there are numbers of experimental investigations to improve the device performance, the understanding of the detailed process of photoelectric conversion needs to be further improved. In this work, a thorough optoelectronic simulation is employed to figure out how the nanowire diameter, doping concentration, and illumination wavelength affect the photoelectric conversion characteristics of the silicon nanowire array photoelectrodes. We find that two balances should be carefully weighted between optical absorption and photogenerated-carrier collection, along with between short-circuit photocurrent density and open-circuit voltage. For the small-diameter nanowire array photoelectrodes, the overall absorption is higher than that of the larger-diameter ones with the most contribution from the nanowires. However, the substrate shows increasing absorption with increasing illumination wavelength. Higher doping density leads to a larger open-circuit voltage; while lower doping density can guarantee a relatively higher short-circuit photocurrent. To obtain high-light-conversion-efficiency photoelectrodes, the doping density should be carefully chosen with considerations of illumination wavelength and surface recombination. Suppressing the surface recombination velocity can effectively enhance the short-circuit photocurrent (open-circuit voltage) for the lightly (heavily) doped nanowire array photoelectrodes. Our systematical results provide a theoretical guidance for the photoelectrochemical devices based on semiconductor nanostructures.

Tunable THz absorption in graphene-based heterostructures.

We investigate THz absorption properties of graphene-based heterostructures by using characteristics matrix method based on conductivity. We demonstrate that the proposed structure can lead to perfect THz absorption because of strong photon localization in the defect layer of the heterostructure. The THz absorption may be tuned continuously from 0 to 100% by controlling the chemical potential through a gate voltage. By adjusting the incident angle or the period number of the two PCs with respect to the graphene layer, one can tailor the maximum THz absorption value. The position of the THz absorption peaks can be tuned by changing either the center wavelength or the thicknesses ratio of the layers constituting the heterostructure. Our proposal may have potentially important applications in optoelectronic devices.