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Register a new userFabrication of plasmonic surface relief gratings for the application of band-pass filter in UV-Visible spectral range
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The measured experimental results of optical diffraction of 10, 5 and 3.4 micrometer period plasmonic surface relief grating are presented for the application of band-pass filter in visible spectral range. Conventional scanning electron microscopic (SEM) is used to fabricate the grating structures on the silver halide based film (substrate) by exposing the electron beam in raster scan fashion. Morphological characterization of the gratings is performed by atomic force microscopy (AFM) shows that the period, height and profile depends on the line per frame, beam spot, single line dwell time, beam current, and accelerating voltage of the electron beam. Optical transmission spectra of 10 micrometer period grating shows a well-defined localized surface plasmon resonance (LSPR) dip at ~366 nm wavelength corresponding to gelatin embedded silver nanoparticles of the grating structure. As the period of the grating reduces LSPR dip becomes prominent. The maximum first order diffraction efficiency (DE) and bandwidth for 10 micrometer period grating are observed as 4% and 400 nm in 350 nm to 800 nm wavelength range respectively. The DE and bandwidth are reduced up to 0.03% and 100 nm for 3.4 micrometer period grating. The profile of DE is significantly flat within the diffraction bandwidth for each of the gratings. An assessment of the particular role of LSPR absorption and varied grating period in the development of the profile of first order DE v/s wavelength are studied. Fabrication of such nano-scale structures in a large area using conventional SEM and silver halide based films may provide the simple and efficient technique for various optical devices applications.
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We report on the demonstration of MoS2/GaN UV-visible photodetectors with high spectral responsivity both in UV and in visible regions as well as the observation of MoS2 band-edge in spectral responsivity. Multi-layer MoS2 flakes of thickness ~ 200 nm were exfoliated on epitaxial GaN-on-sapphire, followed by fabrication of detectors in a lateral Metal-Semiconductor-Metal (MSM) geometry with Ni/Au contacts which were insulated from the GaN layer underneath by Al2O3 dielectric. Devices exhibited distinct steps in spectral responsivity at 365 nm and at ~ 685 nm with a corresponding photo-to-dark current ratio of ~4000 and ~ 100 respectively. Responsivity of 0.1 A/W (at 10 V) was measured at 365 nm corresponding to GaN band edge, while the second band edge at ~ 685 nm is characterized by a spectral responsivity (SR) of ~ 33 A/W when accounted for the flake size, corresponding to the direct band gap at K point of multi-layer MoS2.
Mostly forsaken, but revived after the emergence of all-dielectric nanophotonics, the Kerker effect can be observed in a variety of nanostructures from high-index constituents with strong electric and magnetic Mie resonances. Necessary requirement for the existence of a magnetic response limits the use of generally non-magnetic conventional plasmonic nanostructures for the Kerker effect. In spite of this, we demonstrate here for the first time the emergence of the lattice Kerker effect in regular plasmonic Al nanostructures. Collective lattice oscillations emerging from delicate interplay between Rayleigh anomalies and localized surface plasmon resonances both of electric and magnetic dipoles, and electric and magnetic quadrupoles result in suppression of the backscattering in a broad spectral range. Variation of geometrical parameters of Al arrays allows for tailoring lattice Kerker effect throughout UV and visible wavelength ranges, which is close to impossible to achieve using other plasmonic or all-dielectric materials. It is argued that our results set the ground for wide ramifications in the plasmonics and further application of the Kerker effect.
A robust and reproducible preparation of self-standing nanoporous gold leaves (NPGL) is presented, with optical characterization and plasmonic behaviour analysis. Nanoporous gold (NPG) layers are tipically prepared as thin films on a bulk substrate. Here we present an alternative approach consisting in the preparation of NPGL in the form of a self-standing film. This solution leads to a perfectly symmetric configuration where the metal is immersed in a homogeneous medium and in addition can support the propagation of symmetric and antisymmetric plasmonic modes. With respect to bulk gold, NPG shows metallic behaviour at higher wavelengths, suggesting possible plasmonic applications in the near / medium infrared range. In this work the plasmonic properties in the wide wavelength range from the ultraviolet up to the mid-infrared range have been investigated.
In this work, we present a detailed photophysical analysis of recently-discovered optically stable, single photon emitters (SPEs) in Gallium Nitride (GaN). Temperature-resolved photoluminescence measurements reveal that the emission lines at 4 K are three orders of magnitude broader than the transform-limited widths expected from excited state lifetime measurements. The broadening is ascribed to ultra-fast spectral diffusion. Continuing the photophysics study on several emitters at room temperature (RT), a maximum average brightness of ~427 kCounts/s is measured. Furthermore, by determining the decay rates of emitters undergoing three-level optical transitions, radiative and non-radiative lifetimes are calculated at RT. Finally, polarization measurements from 14 emitters are used to determine visibility as well as dipole orientation of defect systems within the GaN crystal. Our results underpin some of the fundamental properties of SPE in GaN both at cryogenic and RT, and define the benchmark for future work in GaN-based single-photon technologies.
We show that an azopolymer can be used to create a supramolecular architecture in a parallel process with patterned surface properties. By illuminating with an interference pattern, we created adhesion and charge patterns that reflect the molecular ordering. We studied the recording process in two limit situations. When birefringence dominates over mass transport, an adhesion pattern was recorded even in absence of a surface relief grating (SRG). When mass transport dominates, we measured a higher frequency adhesion and relief patterns on top of the SRG. We measured an increased negative charge in the regions where molecules are expected to be parallel aligned in trans conformational state.
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