Optoelectronic properties of octahedral molybdenum cluster-based materials at a single crystal level.

Octahedral molybdenum (Mo6) clusters constitute suitable building blocks for the design of promising single crystal materials in the field of optoelectronics. Here, we prepared single crystals composed of hydroxo Mo6X8 (X = Br, Cl) cluster complexes interconnected by H-bonding interactions with water molecules and protons. The optoelectronic responses and the absorption and emission spectra of these cluster-based single crystals were acquired upon light irradiation, and they show dependency on the nature of the halogens, with the brominated cluster being the most conductive. A fast photoelectrical response was recorded and it showed remarkable stability after multiple illumination on/off cycles. The results obtained provide relevant information for the development of photonic and optoelectronic devices, sensors and photocatalysts.

Scanning Photocurrent Microscopy in Single Crystal Multidimensional Hybrid Lead Bromide Perovskites.

We investigated solution-grown single crystals of multidimensional 2D-3D hybrid lead bromide perovskites using spatially resolved photocurrent and photoluminescence. Scanning photocurrent microscopy (SPCM) measurements where the electrodes consisted of a dip probe contact and a back contact. The crystals revealed significant differences between 3D and multidimensional 2D-3D perovskites under biased detection, not only in terms of photocarrier decay length values but also in the spatial dynamics across the crystal. In general, the photocurrent maps indicate that the closer the border proximity, the shorter the effective decay length, thus suggesting a determinant role of the border recombination centers in monocrystalline samples. In this case, multidimensional 2D-3D perovskites exhibited a simple fitting model consisting of a single exponential, while 3D perovskites demonstrated two distinct charge carrier migration dynamics within the crystal: fast and slow. Although the first one matches that of the 2D-3D perovskite, the long decay of the 3D sample exhibits a value two orders of magnitude larger. This difference could be attributed to the presence of interlayer screening and a larger exciton binding energy of the multidimensional 2D-3D perovskites with respect to their 3D counterparts.

Optical properties of organic/inorganic perovskite microcrystals through the characterization of Fabry-Pérot resonances.

A precise knowledge of the optical properties, specifically the refractive index, of organic/inorganic perovskites, is essential for pushing forward the performance of the current photovoltaic devices that are being developed from these materials. Here we show a robust method for determining the real and the imaginary part of the refractive index of MAPbBr3 thin films and micrometer size single crystals with planar geometry. The simultaneous fit of both the optical transmittance and the photoluminescence spectra to theoretical models defines unambiguously the refractive index and the crystal thickness. Because the method relies on the optical resonance phenomenon occurring in these microstructures, it can be used to further develop optical microcavities from perovskites or from other optical materials.

Single Crystal Growth of Hybrid Lead Bromide Perovskites Using a Spin-Coating Method.

Synthesis and studies of single crystals of hybrid perovskite are important for achieving a better understanding of the optoelectronic phenomena occurring in this material and for improving ongoing applications. Here, we report on the growth of micrometer-size single crystals of methylammonium lead bromide (MAPbBr3) using the spin coating deposition method on a quartz substrate. We studied the influence of the rotation speed and the use of three different additives N-cyclohexyl-2-pyrrolidone, dimethyl sulfoxide, and 4-tert-butylpyridine on the crystal size and shape. The introduction of an additive in the precursor solution is revealed to be very useful for obtaining crystals with well-defined geometries and for decreasing the amount of defects. In this way, high-quality single crystals that sustain optical resonating modes were obtained and characterized by transmittance and photoluminescence measurements.

Silicon particles as trojan horses for potential cancer therapy.

BACKGROUND: Porous silicon particles (PSiPs) have been used extensively as drug delivery systems, loaded with chemical species for disease treatment. It is well known from silicon producers that silicon is characterized by a low reduction potential, which in the case of PSiPs promotes explosive oxidation reactions with energy yields exceeding that of trinitrotoluene (TNT). The functionalization of the silica layer with sugars prevents its solubilization, while further functionalization with an appropriate antibody enables increased bioaccumulation inside selected cells. RESULTS: We present here an immunotherapy approach for potential cancer treatment. Our platform comprises the use of engineered silicon particles conjugated with a selective antibody. The conceptual advantage of our system is that after reaction, the particles are degraded into soluble and excretable biocomponents. CONCLUSIONS: In our study, we demonstrate in particular, specific targeting and destruction of cancer cells in vitro. The fact that the LD50 value of PSiPs-HER-2 for tumor cells was 15-fold lower than the LD50 value for control cells demonstrates very high in vitro specificity. This is the first important step on a long road towards the design and development of novel chemotherapeutic agents against cancer in general, and breast cancer in particular.

Monodisperse silicon nanocavities and photonic crystals with magnetic response in the optical region.

It is generally accepted that the magnetic component of light has a minor role in the light-matter interaction. The recent discovery of metamaterials has broken this traditional understanding, as both the electric and the magnetic field are key ingredients in metamaterials. The top-down technology used so far employs noble metals with large intrinsic losses. Here we report on a bottom-up approach for processing metamaterials based on suspensions of monodisperse full dielectric silicon nanocavities with a large magnetic response in the near-infrared region. Experimental results and theory show that silicon-colloid-based liquid suspensions and photonic crystals made of two-dimensional arrays of particles have strong magnetic response in the near-infrared region with small optical losses. Our findings might have important implications in the bottom-up processing of large-area low-loss metamaterials working in the near-infrared region.

Mirror-image-induced magnetic modes.

Reflection in a mirror changes the handedness of the real world, and right-handed objects turn left-handed and vice versa (M. Gardner, The Ambidextrous Universe, Penguin Books, 1964). Also, we learn from electromagnetism textbooks that a flat metallic mirror transforms an electric charge into a virtual opposite charge. Consequently, the mirror image of a magnet is another parallel virtual magnet as the mirror image changes both the charge sign and the curl handedness. Here we report the dramatic modification in the optical response of a silicon nanocavity induced by the interaction with its image through a flat metallic mirror. The system of real and virtual dipoles can be interpreted as an effective magnetic dipole responsible for a strong enhancement of the cavity scattering cross section.

Porous silicon microcavities: synthesis, characterization, and application to photonic barcode devices.

We have recently developed a new type of porous silicon we name as porous silicon colloids. They consist of almost perfect spherical silicon nanoparticles with a very smooth surface, able to scatter (and also trap) light very efficiently in a large-span frequency range. Porous silicon colloids have unique properties because of the following: (a) they behave as optical microcavities with a high refractive index, and (b) the intrinsic photoluminescence (PL) emission is coupled to the optical modes of the microcavity resulting in a unique luminescence spectrum profile. The PL spectrum constitutes an optical fingerprint identifying each particle, with application for biosensing.In this paper, we review the synthesis of silicon colloids for developing porous nanoparticles. We also report on the optical properties with special emphasis in the PL emission of porous silicon microcavities. Finally, we present the photonic barcode concept.

A new dielectric metamaterial building block with a strong magnetic response in the sub-1.5-micrometer region: silicon colloid nanocavities.

A new dielectric metamaterial building block based on high refractive index silicon spherical nanocavities with Mie resonances appearing in the near infrared optical region is prepared and characterized. It is demonstrated both experimentally and theoretically that a single silicon nanocavity supports well-defined and robust magnetic resonances, even in a liquid medium environment, at wavelength values up to six times larger than the cavity radius.