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A series of CoxAg1 - x nanostructured granular films have been prepared by ion beam sputtering and annealed at 100, 250, 400, 500°C. The optical constants, the complex dielectric function and magneto-optical Kerr parameters were measured at room temperature. For the samples having low Co compositions, the strong Kerr effect enhancement is observed around the Ag plasma edge. With an increase in annealing temperature, the resonance-like peaks appear in the Kerr rotation, and the peak positions are shifted toward the low photon energy region. From the analysis of the numerical calculations, it is concluded that the magneto-optical Kerr effect enhancement (MOKE) is due to the presence of the steep plasma edge. [ABSTRACT FROM AUTHOR]

Yttrium fluoride (YF3) columnar thin films (CTFs) were fabricated by electron beam evaporation with the glancing angle deposition method. The microstructures and optical properties of YF3 CTFs were studied systematically. The YF3 films grown at different deposition angles are all amorphous. As the deposition angle increases, the columns in YF3 CTFs become increasingly separated and inclined, and the volume fraction of YF3 decreases, resulting in lower refractive indices. This phenomenon is attributed to the self-shadowing effect and limited adatom diffusion. The YF3 CTFs are optically biaxial anisotropic with the long axis (c-axis) parallel to the columns, the short axis (b-axis) perpendicular to the columns, and the other axis (a-axis) parallel to the film interface. The principal refractive index along the b-axis for the 82°-deposited sample is approximately 1.233 at 550 nm. For the 78°-deposited sample, the differences of principal refractive indices between the c-axis and the b-axis and between the a-axis and the b-axis reach the maximum 0.056 and 0.029, respectively. The differences of principal refractive indices were affected by both the deposition angle and the volume fraction of YF3. [ABSTRACT FROM AUTHOR]

Abstract: Ultrafast third-order nonlinear optical responses of the as-deposited and annealed Cu:Bi2O3 nanocomposite films were investigated by using femtosecond Z-scan and time-resolved optical Kerr effect (OKE) techniques at the wavelength of 800nm. The Z-scan measurement showed that both the real and imaginary parts of the third-order nonlinear optical susceptibility were enhanced after thermal annealing treatment. The OKE response of the as-deposited film was instantaneous, and the enhanced OKE signal of the annealed film presented additional slow decay processes which imply the important contribution from photoinduced hot electrons in Cu nanoparticles. [Copyright &y& Elsevier]

Nanocrystalline CoFe2−xScxO4 (x=0–0.4) thin films were prepared on silicon substrates at reduced temperature by a sol–gel process, and the doping effects of scandium on the microstructure, magnetism and polar magneto-optical Kerr effects of the as-deposited films were examined. It was shown that the intensities of both of the Kerr rotation peaks increase with the doping content x of Sc3+. The increase for the peak at 540 nm is due to the decrease of the electrostatic polarization of O2− resulting from the relatively large radius of Sc3+, and that for the peak at 620 nm was a result of the migration of Co2+ from octahedral to tetrahedral sites in the presence of the dopant of Sc3+. [Copyright &y& Elsevier]

In this work, we analyze the performance of finite-size metal-dielectric nanoslits guided mode resonance metasurface optical filters by using finite-difference time-domain simulations and spatial Fourier transform analysis. It is shown that in the direction of the nanoslits period, the critical size required to maintain the performance of the corresponding infinite size filter is the product of the nanoslits period and the quality factor of the infinite size filter. Size reduction in this dimension below the critical dimension reduces the peak transmittance and broadens the spectral linewidth of the filter. In the dimension orthogonal to the nanoslits period direction, the critical dimension size required is not related to the quality factor of the corresponding infinite size filter. Our analysis shows that the critical size is 12 times the filter peak wavelength in the orthogonal dimension for maintaining the filter performance. The 12 times filter wavelength requirement corresponds to the second zero of the Fourier transform of the aperture function.

The electronic structures and optical properties of novel 2D biphenylene and hydrogen-terminated nanoribbons of different widths which are cut from a layer of biphenylene were explored via first-principles calculations. The findings of phonon computations demonstrate that such a biphenylene is dynamically stable and shows metallic properties. The crystal orbital Hamilton population analysis indicates that the tetra-ring local structure results in anisotropic mechanical properties. For 1D nanoribbons, their band gaps shrink, and a direct-indirect transition occurs in the band gap as the width increases, transforming the nanoribbon to endow them with metallic characteristics at a certain width. This is attributed to the weak coupling between the tetra-ring atoms, shrinking the direct band gap at the Y point in the Brillouin zone. Finally, the contribution of interband transitions to the dielectric function in 6-, 9-, and 12-armchair biphenylene nanoribbons (ABNRs) was identified. The lowest peak in the imaginary part of the dielectric function ε 2 spectrum was mainly a contribution of a Γ - Γ transition. As the width of ABNR increases, the transitions in the x direction become stronger while the transition strength in the y direction is not significantly altered. This investigation extends the understanding of the electronic and optical properties of 2D biphenylene and 1D nanoribbons, which will benefit the practical applications of these materials in optoelectronics and electronics.

Vertical van der Waals heterostructures have aroused great attention for their promising application in next-generation nanoelectronic and optoelectronic devices. The dielectric screening effect plays a key role in the properties of two-dimensional (2D) heterostructures. Here, we studied the dielectric screening effects on the excitonic properties and critical points (CPs) of the WS2/MoS2 heterostructure using spectroscopic ellipsometry (SE). Owing to the type-II band alignment of the WS2/MoS2 heterostructure, charged carriers spatially separated and created an interlayer exciton, and the transition energy and binding energy have been accurately found to be 1.58 ± 0.050 eV and 431.39 ± 127.818 meV by SE, respectively. We found that stacking the WS2/MoS2 vertical heterostructure increases the effective dielectric screening compared with the monolayer counterparts. The increased effective dielectric screening in the WS2/MoS2 heterostructure weakens the long-range Coulomb force between electrons and holes. Consequently, the quasi-particle band gap and the exciton binding energies are reduced, and because of the orbital overlap, more CPs are produced in the WS2/MoS2 heterostructure in the high photon energy range. Our results not only shed light on the interpretation of recent first-principles studies, but also provide important physical support for improving the performance of heterostructure-based optoelectronic devices with tunable functionalities.

Platinum diselenide (PtSe2) has attracted huge attention due to its intriguing physical properties for both fundamental research and promising applications in electronics and optoelectronics. Here, we explored the optical properties of chemical vapor deposition-grown PtSe2 thin films with varied thicknesses via spectroscopic ellipsometry. The dielectric function was extracted by using a Lorentz model over the spectral range of 1.25-6.0 eV. We firstly ascribed the resonant energies, extracted from the Lorentz model, to different interband electronic transitions between valence bands and conduction bands in the Brillouin zone. A predicted exciton is observed at 2.18 eV for the monolayer and the corresponding exciton binding energy is 0.65 eV, in line with previous theoretical calculation and the measured absorption spectra. Additionally, the exciton peak shows a red shift with the increase of thickness, which is the consequence of strong interlayer interaction. These results enrich the fundamental understanding of PtSe2 and are conducive to its potential applications.

Organic-inorganic perovskites were fabricated through a one-step procedure with different levels of hydration water in precursor solutions. The optical properties of CH 3 NH 3 PbI 3 films were investigated through spectroscopic ellipsometry and photoluminescence measurements. With the measured optical constants, the efficiency limit of perovskite solar cells is predicted with a detailed balance model. By comparing the optical measurement to that of planar heterojunction solar cells, we conclude that the radiative efficiency and porosity of the perovskite film significantly influence the performance of perovskite solar cells. An optimized hydration-water concentration is obtained for the 3CH 3 NH 3 I:1PbAc 2 •xH 2 O precursor solution. The results can provide guidance for further optimization of the device performance of perovskite solar cells by utilizing hydration water.