Flat lenses when compared to curved surface lenses have the advantages of being aberration free, and they offer a compact design necessary for a myriad of electro-optical applications. In this paper we present flat and ultrathin lenses based on graphene, the world's thinnest known material. Monolayers and multilayers of graphene were fabricated into Fresnel zones to produce Fresnel zone plates, which utilize the reflection and transmission properties of graphene for their operation. The working of the lenses and their performance in the visible and terahertz regimes were analyzed computationally. Experimental measurements were also performed to characterize the lens in the visible regime, and a good agreement was obtained with the simulations. This work demonstrates the principle of atom-thick graphene-based lenses, with perspectives for ultracompact integration.
This paper presents a study on graphene platelet (GPL)-reinforced alumina (Al2O3) ceramic composites and the relationships between the loading of GPL and both mechanical properties and in vitro biocompatibility. Al2O3 powders with different GPL contents were prepared and sintered using a gas protected pressure-less furnace. The examination of the results shows the density of the composites varying from 99.2% to 95.6% with the loading of GPL from 0.75 to 1.48 vol %. Raman studies show that moderate agglomerations of GPLs occur during the ball milling process and graphitic defects were produced during the high temperature processing. Mechanical properties of the Al2O3 matrix are significantly improved by adding GPLs. A maximum increase of approximately 60% in flexural strength and 70% in fracture toughness are achieved by introducing 0.75 vol % GPLs. In the biocompatibility tests, it was found that cells directly seeding on top of GPL/Al2O3 samples showed better initial attachment (3 h after seeding) and viability (3 days after incubation) than the monolithic Al2O3, indicating that the GPL/Al2O3 composites have comparable or more favorable biocompatibility. The excellent mechanical and biomedical properties of the GPL/Al2O3 composites may enable them to be applied to a wide range of engineering and biomedical applications.
Highlights A new high resolution laser induced oxidation (colouring) method is proposed (single spot oxidation). The method is applied to control oxide films thicknesses and hence colours on titanium substrates in micro-scale. The method enable imprinting high resolution coloured image on Ti substrate Optical and morphological periodic surface structures are also produced by an array of oxide spots using the proposed method. Colour coding of two colours into one field is presented.
We computationally and experimentally demonstrate enhanced reflection effects displayed by silicon-based inverted nanocone arrays. A 3D finite element model is used to characterize the optical properties of the nanocone arrays with respect to the change in polarization and incident angles. The nanocone arrays are fabricated by e-beam lithography in hexagonal and triangular geometries with a lattice constant of 300 nm. The fabricated devices show a two-fold increase in reflection compared with bare silicon surface, as well as a strong diffraction within the visible and near-infrared spectra. The nanocone arrays may find a variety of applications from optical devices to energy conservation technologies.
In this work we studied tunable lensing effects of graphene Fresnel lens on different substrates with incident light of 850 nm and 1550 nm wavelengths.
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