Focused Ion Beam Processing for 3D Chiral Photonics Nanostructures

The focused ion beam (FIB) is a powerful piece of technology which has enabled scientific and technological advances in the realization and study of micro- and nano-systems in many research areas, such as nanotechnology, material science, and the microelectronic industry. Recently, its applications have been extended to the photonics field, owing to the possibility of developing systems with complex shapes, including 3D chiral shapes. Indeed, micro-/nano-structured elements with precise geometrical features at the nanoscale can be realized by FIB processing, with sizes that can be tailored in order to tune optical responses over a broad spectral region. In this review, we give an overview of recent efforts in this field which have involved FIB processing as a nanofabrication tool for photonics applications. In particular, we focus on FIB-induced deposition and FIB milling, employed to build 3D nanostructures and metasurfaces exhibiting intrinsic chirality. We describe the fabrication strategies present in the literature and the chiro-optical behavior of the developed structures. The achieved results pave the way for the creation of novel and advanced nanophotonic devices for many fields of application, ranging from polarization control to integration in photonic circuits to subwavelength imaging

Symmetry Breaking in Oligomer Surface Plasmon Lattice Resonances

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Atomic layer deposited α−MoO3 thin films as a promising solid-state hydrogen storage material

Hydrogen has the potential to become a crucial energy storage vector, allowing to maximise the advantages of renewable and sustainable energy sources. Hydrogen is usually stored as compressed hydrogen gas, or liquid hydrogen. However, the former requires high pressure, the latter cryogenic temperatures, being a huge limit to the widespread adoption of these storage methods. Thus, new materials for solid-state hydrogen storage shall be developed. Here we show that a α−MoO3 thin film, grown via atomic layer deposition, is a promising material for reversibly storing hydrogen. We found that hydrogen plasma is a convenient way to hydrogenise − at room temperature and relatively low pressures (500 or 1000 mTorr) − layered monocrystalline α−MoO3 thin films. Hydrogen has been shown to locate itself in the van der Waals gap along the [010] oriented α−MoO3 film. The process has been found to be totally reversible in air. Our essay could be a starting point to a transition from conventional (gas and liquid) to more advantageous solid-state hydrogen storage materials

Mid-Infrared Plasmonic Excitation in Indium Tin Oxide Microhole Arrays

Transparent conducting oxides (TCOs) are emerging as possible alternative constituent materials to replace noble metals such as silver and gold for low-loss plasmonic applications in the near-infrared (NIR) and mid-infrared (MIR) regimes. In particular, TCO-based nanostructures are extensively investigated for biospectroscopy exploiting their surface enhanced infrared absorption (SEIRA). The latter enhances the absorption from vibrational and rotational modes of nearby biomolecules, making TCO nanostructures a promising candidate for IR sensing applications. Nevertheless, in order to produce inexpensive devices for lab-on-a-chip diagnostics, it would be favorable to achieve surface-enhanced infrared absorption with very simple microstructures not requiring nanosize control. In this work, we attempt to demonstrate a SEIRA effect with the least challenging fabrication, gm-scale instead of nm-scale, by tailoring both device design and charge density of the indium tin oxide (ITO) film. We show that microperiodic hole arrays in a ITO film are able to produce SEIRA via grating coupling. Such a study opens the way for innovative and disrupting biosensing devices

AlN interlayer-induced reduction of dislocation density in the AlGaN epilayer

The emerging ultrawide-bandgap AlGaN alloy system holds promise for the development of advanced materials in the next generation of power semiconductor and UV optoelectronic devices. Within this context, heterostructures based on III-nitrides are very popular in view of their applications as electronics and optoelectronics components. AlGaN-based deep UV emitters are gaining visibility for their disinfection capabilities. Likewise, high electron mobility transistors are attracting increasing attention owing to their superior electron transport which yields high-speed and high-power applications. Those devices are conventionally made of AlGaN/GaN heterostructures grown on foreign substrate. However, structural defects, including stress induced by a mismatch in unit cell parameters and the presence of dislocations, can not only decrease the efficiency of the light emitters (by facilitating the non-radiative recombination of electron-hole pairs), but also impede electron mobility within the two-dimensional electron gas at the AlGaN/GaN interface. Therefore, the significance of obtaining high-quality AlGaN layers becomes evident. Including a thin AlN interlayer between the GaN buffer layer and AlGaN is a possible answer to address these drawbacks. Not only we show that a thin AlN layer, approximately ≤ 3 nm in thickness, between the GaN buffer and AlGaN layers, is effective in decreasing the dislocation densities in the AlGaN layer. Still, this is responsible of an increase in the electron mobility of the resulting heterostructure compared to a classical AlGaN/GaN heterostructure

Exploiting Photo- and Electroluminescence Properties of FIrpic Organic Crystals

none14In this work, we investigate the optical and structural properties of the well-known triplet emitter bis(4',6'-difluorophenylpyridinato)-iridium(III) picolinate (FIrpic), showing that its ability to pack in two different ordered crystal structures promotes attractive photophysical properties that are useful for solid-state lighting applications. This approach allows the detrimental effects of the nonradiative pathways on the luminescence performance in highly concentrated organic active materials to be weakened. The remarkable electro-optical behavior of sky-blue phosphorescent organic light-emitting diodes incorporating crystal domains of FIrpic, dispersed into an appropriate matrix as an active layer, has also been reported as well as the X-ray diffraction, nuclear magnetic resonance, electro-ionization mass spectrometry, and scanning electron microscopy analyses of the crystalline samples. We consider this result as a crucial starting point for further research aimed at the use of a crystal triplet emitter in optoelectronic devices to overcome the long-standing issue of luminescence self-quenching.restrictedMaggiore, Antonio; Pugliese, Marco; Di Maria, Francesca; Accorsi, Gianluca; Gazzano, Massimo; Fabiano, Eduardo; Tasco, Vittorianna; Esposito, Marco; Cuscunà, Massimo; Blasi, Laura; Capodilupo, Agostina; Ciccarella, Giuseppe; Gigli, Giuseppe; Maiorano, VincenzoMaggiore, Antonio; Pugliese, Marco; DI MARIA, FRANCESCA GIULIA; Accorsi, Gianluca; Gazzano, Massimo; Fabiano, Eduardo; Tasco, Vittorianna; Esposito, Marco; Cuscuna', Massimo; Blasi, Laura; Capodilupo, Agostina; Ciccarella, Giuseppe; Gigli, Giuseppe; Maiorano, Vincenz

Dry synthesis of bi-layer nanoporous metal films as plasmonic metamaterial

Nanoporous metals are a class of nanostructured materials finding extensive applications in multiple fields thanks to their unique properties attributed to their high surface area and interconnected nanoscale ligaments. They can be prepared following different strategies, but the deposition of an arbitrary pure porous metal is still challenging. Recently, a dry synthesis of nanoporous films based on the plasma treatment of metal thin layers deposited by physical vapour deposition has been demonstrated, as a general route to form pure nanoporous films from a large set of metals. An interesting aspect related to this approach is the possibility to apply the same methodology to deposit the porous films as a multilayer. In this way, it is possible to explore the properties of different porous metals in close contact. As demonstrated in this paper, interesting plasmonic properties emerge in a nanoporous Au–Ag bi-layer. The versatility of the method coupled with the possibility to include many different metals, provides an opportunity to tailor their optical resonances and to exploit the chemical and mechanical properties of components, which is of great interest to applications ranging from sensing, to photochemistry and photocatalysis