ABSTRACT
Aqueous CdTe quantum dots solar cells have been successfully fabricated by the blade coating method on the magnesium zinc oxide (Zn1-xMgxO or ZMO) window layer. Compared with the ZMO mono-window layer, the ZMO/CdS bi-window layer can decrease the interface recombination effectively due to the lower lattice mismatch and fast interdiffusion between CdS and CdTe. Moreover, the high temperature annealing of the CdTe quantum dots absorbed layer passivates the grain boundary of the CdTe crystalline via the replacement reaction of tellurium with sulfur. Finally, the conversion efficiency of our aqueous CdTe quantum dots solar device is improved from 3.21% to 8.06% with the introduction of the CdS interlayer and high temperature CdCl2 annealing. Our aqueous CdTe quantum dots solar devices show a large open circuit voltage and fill factor which are comparable with the conventional devices that are fabricated with organic CdTe quantum dots. We believe that it is the spike-like conduction band alignment between the ZMO and CdTe absorbed layer that reduces the majority carrier concentration, leading to the decrease in interface recombination probability.
ABSTRACT
Small organic molecules (SOMs) with fascinating chiroptical properties have received much attention for their potential applications in photoelectric and biological devices. As an important research tool, circularly polarized luminescence (CPL) provides information about the chiral structures of these molecules in their excited state, and has been an active area of research. With the development of the commercially available CPL instrumentation, currently, more and more research groups have attempted to enhance the CPL parameters (i.e., quantum yield and dissymmetry factor) of the chiral SOMs from all aspects. This review summarizes the latest five years progresses in research on the experimental techniques and theoretical calculations of CPL emitted from SOMs, as well as forecasting its trend of development.
Subject(s)
Luminescence , Luminescent Measurements/methods , StereoisomerismABSTRACT
A chiral metastructure composed of spatially separated double semi-periodic helices is proposed and investigated theoretically and experimentally in this Letter. Chirality-dependent electromagnetically induced transparency (EIT) and a slow light effect in the microwave region are observed from a numerical parameter study, while experimental results from the 3D printing sample yield good agreement with the theoretical findings. The studied EIT phenomenon arises as a result of destructive interference by coupled resonances, and the proposed chiral metastructure can be applied in areas such as polarization communication, pump-probe characterization, and quantum computing areas.
ABSTRACT
We present an effective surface-enhancement Raman scattering (SERS) substrate enabled by depositing metallic film on a liquid surface at room temperature. Thermal evaporation is used to deposit Au atoms on silicone oil surface and then form quasi-continuous films. Due to the isotropic characteristics of the liquid surface, this film consists of substantial nanoparticles with uniform diameter, which is different from films fabricated on solid substrates and can be served as an applicable substrate for SERS detection. With the assistance of this substrate, SERS signals of rhodamine 6G were significantly enhanced, the dependence between SERS spectra and film thickness was investigated. Analytical simulation results confirm the experimental observations and the superiorities of our proposed method for preparation of SERS substrate. This work provides a potential application of metallic film deposition on free-sustained surface and holds promise as an efficient sensor in rapid trace detection of small molecule analytes.
ABSTRACT
We have investigated numerically toroidal dipolar excitation at optical frequency in metamaterials whose unit cell consists of three identical Ag nanodisks and a SiO2 spacer on Ag substrate. The near-field plasmon hybridization between individual Ag nanodisks and substrate forms three magnetic dipolar resonances, at normal incidence of plane electromagnetic waves. The strong coupling among three magnetic dipolar resonances leads to the toroidal dipolar excitation, when space-inversion symmetry is broke along the polarization direction of incident light. The influences of some geometrical parameters on the resonance frequency and the excitation strength of toroidal dipolar mode are studied in detail. The radiated power from toroidal dipole is also compared with that from conventional electric and magnetic multipoles.
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We theoretically studied how to directly engineer the constitutive parameters of metamaterials for perfect absorbers of electromagnetic waves. As an example, we numerically investigated the necessary refractive index n and extinction coefficient k and the relative permittivity ε and permeability µ of a metamaterial anti-reflection layer, which could cancel the reflection from a hydrogenated amorphous silicon (α-Si:H) thin film on a metal substrate, within the visible wavelength range from 300 to 800 nm. We found that the metamaterial anti-reflection layer should have a negative refractive index (n < 0) for short-wavelength visible light but have a positive refractive index (n > 0) for long-wavelength visible light. The relative permittivity ε and permeability µ could be fitted by the Lorentz model, which exhibited electric and magnetic resonances, respectively.
ABSTRACT
A one-step graphene patterning method is developed in this paper. A phase shifting mask is used to modulate incident laser beam spatially and generate graphene patterns by laser heating. Periodic graphene nanoribbon and nanomesh structures are fabricated by employing 1D and 2D phase shifting masks, respectively. The noncontact, simple procedure, easy handling and economic properties of this method make it promising towards graphene-based device fabrication.
ABSTRACT
An efficient method based on the modified needle optimization technique is proposed to design high-power laser thin-film polarizers. In order to minimize the influence of the standing-wave electric field on the laser-induced damage threshold of the polarizers, a crucial optimization parameter, the maximum electric field intensity in the high-refractive-index layers, is included in the proposed merit function. The electric field distribution and optical performance obtained by the proposed method are studied. Improved electric field and identical optical characteristics are observed in comparison with those of the designs obtained by optimizing the traditional merit function without a standing-wave electric field term and by the analytical synthesis method.
ABSTRACT
We propose a novel method for the construction of multiwavelength narrowband high-reflection filters consisting of a reflection mirror, a middle structure, and an induced-reflection match stack (IRMS). The results show that the peak position of the proposed reflection filters is identical to that of the transmission filters consisting of the same middle structure and two flanking high-reflection dielectric film stacks. The range in which multiple reflection peaks occur is determined by the degree of overlapping of the forbidden band in the reflection mirror and the conducting band in the middle structure. This range can be extended by changing the dielectric coefficients of the dielectric film stack or by substituting the dielectric reflection mirror with a silver mirror.
ABSTRACT
Narrowband high-reflection filters with the structure sub|H(LH)(m1)alpha L(HL)(m2)Cr(beta)M|air are proposed. The effects of the Cr layer and the matching stack consisting of dielectric multilayer on the reflection characteristics of the filters are analyzed. The distribution of the internal electric field and the optical absorption is also calculated. The analysis indicates that the improvement of the sidebands could be reached by applying the matching stack without impairing the maximal reflectance and half-width of the reflection band. Wide and flat reflection sidebands could be realized by applying a relatively thicker metal layer. However, lowering the sideband reflection could only be achieved by adding appropriate matching stacks. Large m(1)-m(2) could increase the maximal reflectance, while large m(2) or n(H)/n(L) would reduce the width of the reflection band. In the Cr layer, the least average intense electric field occurred at the central wavelength, the relatively high electric field intensity exists at the wavelengths outside the central wavelength region. The optical absorption of the filter depends strongly on the electric field intensity inside the Cr layer.
