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The evolution of GaN growth on AlN and GaN nucleation layers is compared through morphological and structural analyses, including ion beam analysis. By using AlN nucleation layer grown at high temperature, improved crystalline quality is exhibited by 300 nm thin GaN epilayers. GaN (002) x-ray rocking curve as narrow as 168 arc sec and atomic-step surface morphology characterize such a thin GaN film on AlN. Defects are strongly confined into the first 50 nm of growth, whereas a fast laterally coherent growth is observed when increasing thickness, as an effect of high temperature AlN surface morphology and Ga adatom dynamics over this template. [ABSTRACT FROM AUTHOR]

We have studied the radiative and structural properties of identical In[sub x]Ga[sub (1-x)]As quantum dot laser structures grown by metalorganic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE). Despite the comparable emission properties found in the two devices by photoluminescence, electroluminescence, and photocurrent spectroscopy, efficient lasing from the ground state is achieved only in the MBE sample, whereas excited state lasing is obtained in the MOCVD device. Such a difference is ascribed to the existence of the internal dipole field in the MOCVD structure, induced by the strong faceting of the dots, as observed by high-resolution transmission electron microscopy. [ABSTRACT FROM AUTHOR]

This work explores the conditions to obtain the extension of the PL emission beyond 1.3 μm in InGaAs quantum dot (QD) structures growth by MOCVD. We found that, by controlling the In incorporation in the barrier embedding the QDs, the wavelength emission can be continuously tuned from 1.25 μm up to 1.4 μm at room temperature. However, the increase in the overall strain of the structures limits the possibility to increase the maximum gain in the QD active device, where an optical density as high as possible is required. By exploring the kinetics of QD surface reconstruction during the GaAs overgrowth, we are able to obtain, for the first time, emission beyond 1.3 μm from InGaAs QDs grown on GaAs matrix. The wavelength is tuned from 1.26 μm up to 1.33 μm and significant improvements in terms of line shape narrowing and room temperature efficiency are obtained. The temperature-dependent quenching of the emission efficiency is reduced down to a factor of 3, the best value ever reported for QD structures emitting at 1.3 μm. [Copyright &y& Elsevier]

We investigated the design and characterization of a Lab-On-a-Chip (LoC) cell detection system primarily designed to support immunotherapy in cancer treatment. Immunotherapy uses Chimeric Antigen Receptors (CARs) and T Cell Receptors (TCRs) to fight cancer, engineering the response of the immune system. In recent years, it has emerged as a promising strategy for personalized cancer treatment. However, it requires bioreactor-based cell culture expansion and manual quality control (QC) of the modified cells, which is time-consuming, labour-intensive, and prone to errors. The miniaturized LoC device for automated QC demonstrated here is simple, has a low cost, and is reliable. Its final target is to become one of the building blocks of an LoC for immunotherapy, which would take the place of present labs and manual procedures to the benefit of throughput and affordability. The core of the system is a commercial, on-chip-integrated capacitive sensor managed by a microcontroller capable of sensing cells as accurately measured charge variations. The hardware is based on standardized components, which makes it suitable for mass manufacturing. Moreover, unlike in other cell detection solutions, no external AC source is required. The device has been characterized with a cell line model selectively labelled with gold nanoparticles to simulate its future use in bioreactors in which labelling can apply to successfully engineered CAR-T-cells. Experiments were run both in the air-free drop with no microfluidics-and in the channel, where the fluid volume was considerably lower than in the drop. The device showed good sensitivity even with a low number of cells-around 120, compared with the 10 7 to 10 8 needed per kilogram of body weight-which is desirable for a good outcome of the expansion process. Since cell detection is needed in several contexts other than immunotherapy, the usefulness of this LoC goes potentially beyond the scope considered here.

Chiral lattice modes are hybrid states arising from the chiral plasmonic particles assembled in ordered arrays with opportune periodicity. These resonances exhibit dependence on excitation handedness, and their observation in plasmonic lattices is strictly related to the chiroptical features of the fundamental plasmonic unit. Here, the emergence of chiral surface lattice resonances (c-SLRs) is shown in properly engineered arrays of nanohelices (NHs), fully three dimensional (3D) chiral nano-objects fabricated by focused ion beam processing. By tuning the relative weight of plasmonic and photonic components in the hybrid mode, the physical mechanism of strong diffractive coupling leading to the emergence of the lattice modes is analyzed, opening the way to the engineering of chiral plasmonic systems for sensing applications. In particular, a coupling regime is identified where the combination of a large intrinsic circular dichroism (CD) of the plasmonic resonance with a well-defined balance between the photonic quality factor (Q factor) and the plasmonic field enhancement (M) maximizes the capability of the system to discriminate refractive index (RI) changes in the surrounding medium. The results lay the foundation for exploiting CD in plasmonic lattices to high performance refractometric sensing., (© 2022 The Authors. Advanced Science published by Wiley-VCH GmbH.)

Micromixers are essential components in lab-on-a-chip devices, of which the low efficiency can limit many bio-application studies. Effective mixing with automation capabilities is still a crucial requirement. In this paper, we present a method to fabricate a three-dimensional (3D) poly(methyl methacrylate) (PMMA) fluidic mixer by combining computer-aided design (CAD), micromilling technology, and experimental application via manipulating fluids and nanoparticles. The entire platform consists of three microfabricated layers with a bottom reservoir-shaped microchannel, a central serpentine channel, and a through-hole for interconnection and an upper layer containing inlets and outlet. The sealing process of the three layers and the high-precision and customizable methods used for fabrication ensure the realization of the monolithic 3D architecture. This provides buried running channels able to perform passive chaotic mixing and dilution functions, thanks to a portion of the pathway in common between the reservoir and serpentine layers. The possibility to plug-and-play micropumping systems allows us to easily demonstrate the feasibility and working features of our device for tracking the mixing and dilution performances of the micromixer by using colored fluids and fluorescent nanoparticles as the proof of concept. Exploiting the good transparency of the PMMA, spatial liquid composition and better control over reaction variables are possible, and the real-time monitoring of experiments under a fluorescence microscope is also allowed. The tools shown in this paper are easily integrable in more complex lab-on-chip platforms.

In this work we report the local growth of ordered arrays of 3D core-shell chiral nanohelices based on plasmonic gallium metal. The structures can be engineered in a single step using focused ion beam induced deposition, where a Ga + ion source is used to shape the metallic nanohelix core, while the dielectric precursor is dissociated to create dielectric shells. The solubility of gallium in the different investigated dielectric matrices controls the core-shell thickness ratio of the nanohelices. The chiral plasmonic behaviour of these gallium-based nanostructures is experimentally measured by circularly polarized light transmission through nanostructure arrays and compared with numerical simulations. Large chiroptical effects in the visible range are demonstrated due to the plasmonic effects arising from gallium nanoclusters in the core.

We describe a novel plasmonic-mode engineering, enabled by the structural symmetry of a plasmonic crystal with a metallic oligomer as unit cell. We show how the oligomer symmetry can tailor the scattering directions to spatially overlap with the diffractive orders directions of a plasmonic array. Applied to the color generation field, the presented approach enables the challenging achievement of a broad spectrum of angle-dependent colors since smooth and continuous generation of transmitted vibrant colors, covering both the cyan-magenta-yellow and the red-green-blue color spaces, is demonstrated by scattering angle- and polarization-dependent optical response. The addition of a symmetry driven level of control multiplies the possibility of optical information storage, being of potential interest for secured optical information encoding but also for nanophotonic applications, from demultiplexers or signal processing devices to on-chip optical nanocircuitry.

In this work, we experimentally investigate the chiro-optical properties of 3D metallic helical systems at optical frequencies. Both single and triple-nanowire geometries have been studied. In particular, we found that in single-helical nanostructures, the enhancement of chiro-optical effects achievable by geometrical design is limited, especially with respect to the operation wavelength and the circular polarization conversion purity. Conversely, in the triple-helical nanowire configuration, the dominant interaction is the coupling among the intertwined coaxial helices which is driven by a symmetric spatial arrangement. Consequently, a general improvement in the g-factor, extinction ratio and signal-to-noise-ratio is achieved in a broad spectral range. Moreover, while in single-helical nanowires a mixed linear and circular birefringence results in an optical activity strongly dependent on the sample orientation and wavelength, in the triple-helical nanowire configuration, the obtained purely circular birefringence leads to a large optical activity up to 8°, independent of the sample angle, and extending in a broad band of 500 nm in the visible range. These results demonstrate a strong correlation between the configurational internal interactions and the chiral feature designation, which can be effectively exploited for nanoscale chiral device engineering.

In this paper, we report on the effect of metal oxidation on strong coupling interactions between silver nanostructures and a J-aggregated cyanine dye. We show that metal oxidation can sensibly affect the plexcitonic system, inducing a change in the coupling strength. In particular, we demonstrate that the presence of oxide prevents the appearance of Rabi splitting in the extinction spectra for thick spacers. In contrast, below a threshold percentage, the oxide layer results in an higher coupling strength between the plasmon and the Frenkel exciton. Contrary to common belief, a thin oxide layer seems thus to act, under certain conditions, as a coupling mediator between an emitter and a localized surface plasmon excited in a metallic nanostructure. This suggests that metal oxidation can be exploited as a means to enhance light-matter interactions in strong coupling applications.