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With the purpose of designing active patches for photodynamic therapy of melanoma, transparent and soft hydrogel membranes (HMs) have been fabricated by cation-induced gelation of rod-like cellulose nanocrystals (CNCs) bearing negatively charged carboxylic groups. Na+ , Ca2+ , Mg2+ have been used as cross-linkers of cellulose nanocrystal (CNC). The biosafety of this material and of its precursors has been evaluated in vitro in cell cultures. Morphological changes, cell organelles integrity, and cell survival with the tetrazolium salt reduction (MTT) assay were utilized as tests of cytotoxicity. Preliminary investigation was performed by addition of the hydrogel components to the cell culture medium and by incubations of the CNC-HM in direct and indirect contact with a confluent monolayer of A375 melanoma cells. Direct contact assays suffered from interference of physical stress. Careful evaluation of cytotoxicity was obtained considering the overall picture provided by microscopy and biochemical tests performed with the CNC-HM in indirect contact with two melanoma cell lines (A375, M14) and human fibroblasts. CNCs have been demonstrated to be a safe precursor material and CNC-HMs have a good biocompatibility provided that the excess of cations, in particular of Ca2+ is removed. These results indicate that CNC and can be safely used to fabricate biomedical devices such as transparent hydrogel patches, although attention must be paid to the fabrication procedure.

During the last years, organometallic lead halide perovskites (LHP) have been widely studied as outstanding materials for photovoltaics and photonics applications [1] . These emerging semiconductors are fabricated by cheap and straightforward solution process techniques on polycrystalline film of the compound CH 3 NH 3 PbX 3 (X=Cl, Br, I). Their outstanding properties of these films include large absorption coefficients above the bandgap, high electronic mobilities, high quantum yield of emission at room temperature or tunable band-gap with the composition [1] . In this work, we exploit the excellent light emitting and photodetection properties of CH 3 NH 3 PbI 3 thin films to integrate a waveguide amplifier and a photodetector within the same LHP thin film deposited in both rigid (SiO 2 /Si) and flexible (nanocellulose) substrates. As illustrated in Figure 1a , the device is based on the refractive index contrast between the LHP, a poly(methyl methacrylate) capping layer the substrate to engineer the number of propagating modes and their propagation constant [1] . In particular, the geometrical parameters of the structure were carefully designed to propagate an excitation beam injected at the input edge of the structure together with the photoluminescence (PL) emitted by the LHP through a mode that is extremely confined in the semiconductor film (see Fig. 1a ). As a result, this bilayer structure demonstrates amplified the spontaneous emission (ASE) with extraordinary low thresholds (2 nJ) [2] . Moreover, the incorporation of electrodes on the top of the LHP allows us to study a photocurrent dependent on the excitation light ( Fig. 1b ), and with it to monitor electrically the generation of PL and ASE ( Fig. 1c ). Experimental results (symbols in Fig. 3c) are properly reproduced with the simulations carried out with a rate equation model (solid lines in Fig. 3c). Here, we carefully compare the generation of optical gain and photocurrent in rigid and flexible substrates and demonstrate that the choice flexible substrate does not significantly alter the performances of the device [3] . Therefore, this approach illustrates a new amplifier-photodetector device that can pave the road towards a flexible and wearable technology LHP based technology.

The influence of the physical, rheological, and process parameters on the cellulose nanocrystal (CNC) drops before and after external gelation in a CaCl2 solution was investigated. The dominant role of the CNC’s colloidal suspension properties, such as the viscous force, inertial, and surface tension forces in the fluid dynamics was quantitatively evaluated in the formation of drops and jellified beads. The similarity and difference between the behavior of carbohydrate polymers and rod-like crystallites such as CNC were enlightened. Pump-driven and centrifugally-driven external gelation approaches were followed to obtain CNC hydrogel beads with tunable size and regular shape. A superior morphological control—that is, a more regular shape and smaller dimension of the beads—were obtained by centrifugal force-driven gelation. These results suggest that even by using a simple set-up and a low-speed centrifuge device, the extrusion of a colloidal solution through a small nozzle under a centrifugal field is an efficient approach for the production of CNC hydrogel beads with good reproducibility, control over the bead morphology and size monodispersion.

A ceramic composite was produced by mixing cubic zirconia with graphene nano-platelets. The samples were consolidated by flash sintering in argon atmosphere to avoid the oxidation of graphene at high temperature. The applied electrical field ranged between 50 V cm and 500 V cm, while the current density limit was set between 35 mA mm and 175 mA mm. The presence of the conductor filler reduced the onset flash temperature, and a good densification of the composite was obtained. Remarkably, the same level of densification was not possible on pure cubic zirconia samples (possessing the same geometry) as they got physically damaged at the flash ignition (likely due to internal temperature gradients). After sintering, part of the conductive filler was still partially present within the ceramic matrix although some zirconium carbide was also formed., V.M. Sglavo and M. Biesuz kindly acknowledge the support from the Italian Ministry of University and Research (MIUR) within the programs PRIN2017 - 2017FCFYHK“DIRECTBIOPOWER” and Departments of Excellence 2018–2022 (DII-UNITN). M. Biesuz kindly acknowledge thesupport from MIUR within the programs PRIN2017 - 2017PMR932 “Nanostructured Porous Ceramics for Environmental and EnergyApplications”

Porous silicon micro-particles (micro-pSi) with size in the range of 1–10 μm are obtained by etching of silicon wafers followed by sonication. The derivatization of the micro-pSi surface by wet chemistry (silylation and coupling with a diamine) yields an interface, which exposes negative (carboxylic) or positive (amine) groups at pH 7.4. The surface modification, beyond the introduction of groups for the drug loading by covalent or electrostatic interactions, stabilizes the intense orange luminescence characteristic of the silicon nano-crystallites. Derivatization by amines introduces also a second emission in the blue region, which follows a different excitation pathway and can be attributed to the interface defects. The micro-pSi are efficiently internalized by human dendritic cells and do not show any toxic effect even at a concentration of 1 mg mL−1. The intrinsic luminescence of the differently functionalized micro-pSi is preserved inside the cells and permits the selective and efficient tracking of the microparticles without using molecular tags and thus leaving the organic coating available for the interaction with the drug. The results obtained suggest that the functionalized micro-pSi are an efficient platform for simultaneous imaging and delivery of therapeutic agents to the disease site.

We demonstrate that the release of a poorly soluble molecule from nanoporous carriers is a complex process that undergoes heterogeneous surface nucleation events even under significantly diluted release conditions, and that those events heavily affect the dynamics of release. Using beta-carotene and porous silicon as loaded molecule and carrier model, respectively, we show that the cargo easily nucleates at the pore surface during the release, forming micro- to macroscopic solid particles at the pores surface. These particles dissolve at a much slower pace, compared to the rate of dissolution of pure beta-carotene in the same solvent, and they negatively affect the reproducibility of the release experiments, possibly because their solubility depends on their size distribution. We propose to exploit this aspect to use release kinetics as a better alternative to the induction time method, and to thereby detect heterogenous nucleation during release experiments. In fact, release dynamics provide much higher sensitivity and reproducibility as they average over the entire sample surface instead of depending on statistical analysis over a small area to find clusters.

Here were report a study of picene nano-cristalline thin films doped with pentacene molecules. The thin films were grown by supersonic molecular beam deposition with a doping concentration that ranges between less than one molecules of pentacene every 104 picene molecules up to about one molecule of pentacene every 102 of picene. Morphology and opto-electronic properties of the films were studied as a function of the concentration of dopants. The optical response of the picene films, characterized by absorption, steady-state and time-resolved photoluminescence measurements, changes dramatically after the doping with pentacene. An efficient energy transfer from the picene host matrix to the pentacene guest molecules was observed giving rise to an intense photoluminescence coming out from pentacene. This efficient mechanism opens the possibility to exploit applications where the excitonic states of the guest component, pentacene, are of major interest such as MASER. The observed mechanism could also serve as prototypical system for the study of the photophysics of host guest systems based on different phenacenes and acenes., Comment: 15 pages, 6 figures

Bilayer membranes for food packaging applications were prepared by depositing on polylactic acid (PLA) substrates pure cellulose nanofibers' (CNF) coatings and nanocomposite coatings made of CNF with dispersed TiO2 nanoparticles. The gas barrier properties of the bilayer membranes were studied by gas phase permeation technique using CO2, N2, D2, He and ambient air as test gases. Few micrometer thick pure and nanocomposite CNF coatings act as effective gas permeation barriers impeding the CO2, N2 and O2 transport and reducing the He and D2 transport rates by 3 orders of magnitude when compared with the PLA substrate. Gas transport through the coatings obeys the solution-diffusion mechanism: D2 permeation process shows activation energy values of 44 ± 6 kJ/mol and 40 ± 6 kJ/mol in the pure and nanocomposite CNF coating, respectively. The addition of the TiO2 nanoparticles reduces the penetrant diffusivity by increasing the tortuosity of the penetrant migration path but does not affect the gas barrier performances. UV–Vis spectroscopy analyses show that the optical transparency of the PLA support is slightly decreased by the CNF coating: at 600 nm the optical transmittance decreases, in fact, from 95% to 91%. TiO2 nanoparticles strongly absorb UV radiation and slightly reduce the PLA transparency in the optical range due to light scattering effects.

Graphene laminated (GL) coatings formed by stacked few layer graphene (FLG) nanocrystals were deposited on low-density polyethylene (PE) films by the mechanical rubbing technique. Molecular transport through the bilayer membrane was studied by the gas phase permeation technique by monitoring the CO2, N-2 and H-2(2) transport fluxes in transient conditions. The results evidenced that the transport exhibited anomalous character. The experimental data could be reproduced assuming that the penetrant concentration in the GL coating, c(int)(t), reached a saturation value c(s) following compressed exponential kinetics c(int)(t) = c(s)[1 - e(-(lambda relt)beta)]. The relaxation time tau(rel) = 1/lambda(rel) showed thermally activated behavior, and its value increased with the kinetic diameter of the penetrant molecules. The critical exponent beta = 1.5 +/- 0.1 for CO2 and N-2 and beta = 2.0 +/- 0.1 for H-2(2) did not change with temperature. Positron annihilation lifetime spectroscopy (PALS) analysis indicated that the average cross-section (h(g)) of the cavities in the GL coating exhibited comparable size to the kinetic diameter (sigma(k)) of the penetrant molecules. The results could be explained by assuming that the molecular infiltration in the GL structure occurred in nano-channels having distributed path lengths where the penetrant transport obeyed a configurational diffusion mechanism.

The interest towards aptamer-based surfaces in the field of bioaffinity assays is constantly growing. A crucial aspect is related to the ability of maintaining the high specificity of these molecules once immobilized on the surface. In this article we compare the immobilization of aptamers on a silanized silicon nitride surface as well as on a soft polymeric layer. An innovative immobilization approach, based on a copolymer, N-dimethylacrylamide-N-acryloyloxysuccinimide-3-(trimethoxysilyl)propylmethacrylate (DMA-NAS-MAPS) coating, able to crosslink itself to the substrate and to bind amino-modified biomolecules is proposed. Comparing this coating with a more classical functionalization process based on silane chemistry, we propose that the better results obtained on the polymeric layer are due to an increased binding efficiency of the aptamers bound to a soft material. The high specificity of immobilized DNA-aptamers is demonstrated using two sequences specific for thrombin detection and a non-sense sequence as negative control. The coating provides higher sensitivity compared to classical self-assembled silane coatings, probably due to a better mobility of bound aptamers. The aptamer immobilization on both surfaces was characterized and optimized using atomic force microscopy, X-ray photoelectron spectroscopy, contact angle and fluorescence microscopy. The comparison between the two different functionalizations highlights the better performances of the copolymer coating in terms of protein recognition, demonstrating thrombin detection down to 0.011 nM in buffer solution and 4.9 nM in complete human serum. Moreover, the localized immobilization of the aptameric sequences, utilized in this work, suggests the possibility of employing this platform also for multianalyte detection.

We have studied the kinetics of gas transport through films made of self-assembled cellulose nanofibrils (CNF) by a time-resolved mass spectroscopy technique. Few micrometers thick films deposited on polylactic acid (PLA) substrates act as impermeable barriers for CO2, O2, and N2 and reduce the 2H2 (deuterium) and He permeation flux by a factor of ∼103 with respect to the uncoated substrate. Penetrant transport is controlled by the solution-diffusion mechanism and the coating acts as a diffusive barrier. 2H2 and He diffusivity values are in the 10–10 and 10–9 cm2 s–1 range, respectively, and their migration occurs by thermally activated process with 39 ± 1 and 33 ± 2 kJ mol–1 activation energy. Positron annihilation lifetime spectroscopy analysis indicates that the diffusive path between the packed nanofibrils consists of elongated cavities with cross-sectional size ∼ 0.31 nm. Results evidence that the selective transport of the small size penetrants is due to sieving effects and that small penetrant tran...

Selective functionalization of the external/internal pore surface of porous silicon is of interest for the numerous potential applications of this material, in particular in pharmacology. With the aim of obtaining porous silicon platforms compatible with the aqueous environment and providing hydrophobic pores to load poorly water soluble molecules, we set-up a three step functionalization procedure consisting in two hydrosilylation reactions separated by the selective etching of the external surface. This procedure was applied both, to porous layers and porous microparticles. The characterization of the functionalized material by conventional techniques such as contact angle and FTIR showed a change of the properties of porous structures in line with the expected surface modifications. However, these techniques do not permit to clearly distinguish between internally and externally grafted functional groups. For this reason, an innovative procedure based on angle-resolved XPS was set-up and applied to differently functionalized pSi layers. By this technique, we obtained indications of prevalent grafting of hydrophilic moieties on the external surface and hydrophobic ones inside the pores.

A functionalization strategy, consisting of a silylation reaction by acrylic acid followed by diamine coupling, preserves and stabilizes the photoluminescence (PL) of porous silicon (pSi) microparticles suspended in ethanol. We found that under the condition of efficient amine coupling, besides the orange emission typical of the native pSi, an emission band in the blue region appears. The investigation of the interaction between pSi and diamine shows that diamine quenches and shifts the orange band meanwhile it induces an increase of the intensity of the blue one. PL lifetimes of the orange and blue bands are in the micro and nano second range, respectively. These values and their wavelength dependence clearly prove that the two bands have different origin: quantum confinement and nitrogen impurities introduced at silicon/silicon oxide interface, respectively. Thus, they can be used to discriminate between the pSi microparticles obtained by silylation, which expose carboxylic groups and the pSi microparticles after the diamine coupling, which bear amine functionalities at the surface. The increase in the stability of the PL emission of pSi in aqueous solution after functionalization, with quantum yields of the order of 1–2%, supports the use in biological systems of these brightly emitting, largely porous microparticles, bearing positive or negative surface charge.

In this study we investigated the fabrication of small hydrogel objects by the coordination-driven assembly of supramolecular rod-like crystallites of nanocellulose, using ionotropic gelation as a methodological approach and Ca2+ as a gelling agent. We proved that the gelation process is diffusion-mediated and fitting the equations modelling this process to the profile of the Ca2+ front, a Ca2+ diffusion coefficient in the incipient hydrogel of (4.5 ± 1.1) × 10−6 cm2 s−1 was calculated. At the steady-state a spatially homogeneous distribution of Ca2+-crosslinked sites in the hydrogel network was observed. External ionotropic gelation produced beads, wires or disks, while core–shell capsules were obtained by inverse ionotropic gelation. We demonstrated that equilibrium and dynamics of the distribution of Ca2+ offer the opportunity to design precisely the size and shape of these small hydrogel objects. In particular, the core size and the shell thickness of the capsules can be tailored under kinetic controlled conditions. The proposed approach, with supramolecular structures of the natural source as assembling components and the water-in-water fabrication process, is fast, simple, and requires only sustainable chemistry and is easily implementable in automatic microfluidic platforms.

International audience; We report the first synthesis of silicon nanocrystals embedded in a silicon nitride matrix through a direct pyrolysis of a preceramic polymer (perhydropolysilazane). Structural analysis carried out by XRD, XPS, Raman and TEM reveals the formation of silicon quantum dots and correlates the microstructures with the annealing temperature. The photoluminescence of the nanocomposites was investigated by both linear and nonlinear measurements. Furthermore we demonstrate an enhanced chemical resistance of the nitride matrix, compared to the typical oxide one, in both strongly acidic and basic environments. The proposed synthesis via polymer pyrolysis is a striking innovation potentially allowing a mass-scale production nitride embedded Si nanocrystals.

Biosensing analytical platforms rely on the intimate structure–function relationship of immobilized probes. In this context, hydrogels are appealing semi-wet systems to locally confine biomolecules while preserving their structural integrity and function. Yet, limitations imposed by biomolecule diffusion rates or fabrication difficulties still hamper their broad application. Here, using a self-assembling peptide, a printable and self-adhesive hydrogel was obtained and applied to fabricate arrays of localized bio-functional 3D microenvironments on analytical interfaces. This soft matrix represents a robust and versatile material, allowing fast and selective tuning of analyte diffusion, which is exploited here to run in-gel immunoassays under solution-like conditions in an unprecedented (

Silicon is the most common semiconductor in technology. Its main limit is the lacking of efficient light emission properties. Here quantum effects are exploited to fabricate optically active silicon photonics elements. The manuscript reports recent results obtained in different research fields spanning from bio- to integrated-photonics and nonlinear optics.

Silicon nanocrystals (Si-nc) are reviewed here for their interesting optical applications. On the one hand, they do exhibit quantum confinement effects. This allows turning silicon into a light-emitting material where luminescence can be excited by electrical injection. On the other hand, small sizes, large surfaces, and dielectric mismatch between the core and the surrounding matrix increase dramatically the nonlinear optical coefficients. This allows using Si-nc as a nonlinear material in different waveguide configurations. In this paper, we discuss specifically two different applications of Si-nc: (i) as a nonlinear material in various devices, e.g., in bistable optical cavities, in waveguide optical mode monitors that are based on two-photon excited luminescence detection, and in wavelength shifters by using four-wave mixing (FWM); (ii) as an entropy source for quantum random number generation, the key device for cryptography. (a) Top view optical image of a Si-nc-based whispering-gallery mode (WGM) microdisk resonator, vertically coupled with a bus waveguide. (b) Detail of the coupling zone. (c) Normalized waveguide transmission spectrum over a wide spectral range. The inset shows a blow up of a resonance with the radial and azimuthal mode orders and the Q factor value indicated.

Matrix Assisted Laser Desorption Ionization (MALDI) is a soft ionization method with widespread analytical applications. One of its limits is the spurious signal in the low mass region, due to the required use of matrices to desorb and ionize the analytes. The possibility to avoid their use will ease both sample preparation and mass spectrum interpretation because the low mass region will not be crowded by peaks of the matrix. In recent years, nanostructured materials have been proposed as matrix-free substrates, but their use is limited to specific combination of nanostructures and analytes, while no general matrix-free approach has yet been demonstrated. Here we propose a radically new type of transducer and we demonstrate that fluorosilanized bulk surfaces achieve similar detection limit of nanostructured substrates. The results of our work suggest that desorption/ionization (D/I) is a purely interfacial effect, with negligible contribution from the chemical nature of the underlying substrate, provided that the substrate contains fluorine species, is an electrical conductor and a good UV absorber.

Sol-gel transition of carboxylated cellulose nanocrystals has been investigated using rheology, SAXS, NMR and optical spectroscopies to unveil the distinctive roles of ultrasound treatments and addition of various cations. Besides cellulose fiber fragmentation, sonication treatment induces fast gelling of the solution. The gelation is independent of the addition of cations, while the final rheological properties are highly influenced by the type, concentration and sequence of the operations since the cations must be added prior to sonication to produce stiff gels. The gel elastic modulus was found to increase proportionally to the ionic charge rather than the cationic size. In cases where ions were added after sonication, SAXS analysis of the Na+ hydrogel and Ca2+ hydrogel indicated the presence of structurally ordered domains in which water is confined, and 1H-NMR investigation showed the dynamics of water exchange within the hydrogels. Conversely, separated phases containing essentially free water were characteristic of the hydrogels obtained by sonication after Ca2+ addition, confirming that this ion induces irreversible fiber aggregation. The rheological properties of the hydrogels depend on the duration of the ultrasound treatments, enabling the design of programmed materials with tailored energy dissipation response.

In this review materials and technologies of the hybrid approach to integrated photonics (IP) are addressed. IP is nowadays a mature technology and is the most promising candidate to overcome the main limitations that electronics is facing due to the extreme level of integration it has achieved. IP will be based on silicon photonics in order to exploit the CMOS compatibility and the large infrastructures already available for the fabrication of devices. But silicon has severe limits especially concerning the development of active photonics: its low efficiency in photons emission and the limited capability to be used as modulator require finding suitable materials able to fulfill these fundamental tasks. Furthermore there is the need to define standardized processes to render these materials compatible with the CMOS process and to fully exploit their capabilities. This review describes the most promising materials and technological approaches that are either currently implemented or may be used in the coming future to develop next generations of hybrid IP devices.

SiOCN ceramics have been prepared by the polymer pyrolysis method. The preceramic polymers were synthesized from a polysiloxane cross-linked with two different N-containing compounds: a silazane or a ternary amine. The corresponding SiOCN ceramics were obtained by pyrolysis in nitrogen atmosphere at five different temperatures from 1000°C to 1400°C. The electrical conductivity of the powdered SiOCN ceramic samples was determined by the powder-solution-composite technique. The results show an increase in room temperature AC conductivity of three orders of magnitude, from ≈10−5 (S/cm) to ≈10−2 (S/cm), with increasing pyrolysis temperature from 1000°C to 1400°C. Furthermore, the electrical conductivity of the amine-derived SiOCN is three to five times higher than that of the silazane-derived ceramic at each pyrolysis temperature. The combined structural study by Raman spectroscopy and chemical analysis suggests that the increase of electrical conductivity with the pyrolysis temperature is due to the sp3-to-sp2 transition of the amorphous carbon phase. The higher conductivity of the amine-derived SiOCN is also discussed considering features like the volume% of the free-carbon phase and its possible N-doping.

In this article we describe a reliable etching method to fabricate porous silicon free-standing membranes (FSMs) based on a self detachment of the porous layer in moderately doped n-type silicon substrates. We found that stable growth of smooth and straight pores is restricted to a narrow range of etching conditions and, unlike p-type substrates, the lift-off of the membrane is a self-limited process that does not require a large burst of current. The detachment of the porous membrane is independent of the structure of the already porosified layer, meaning that the average pore diameter can be tuned from nano to macro size within the same membrane. We also demonstrate that, despite their limited thickness, FSMs are quite robust and can sustained further processing. Thus, the etching receipt we are proposing here extends the range of sensors and filters that can be fabricated using porous silicon technology.

We propose an optical method to quantify the level of fabrication imperfections in a Silicon On Insulator wafer. The method is based on the use of Side Coupled Integrated Spaced Sequence of Resonators (SCISSOR) as test devices. Fabrication induced fluctuations of the effective index and of the coupling coefficient are mapped by comparing different spectral responses of nominally identical samples taken from different dies in the wafer. Random variations of the resonator's optical path are quantified in terms of standard deviations of normally distribuited variables by finding a statistical correlation with the coupled resonator induced transparency (CRIT) phenomena. We found a strong correlation between CRIT and fabrication errors. This led us to design a SCISSOR based test structure that allows to quantify the degree of local structural imperfections in a fast, accurate and non invasive way. Performances, possible applications and limitations are investigated with the help of transfer matrix simulations.

We report on a photonic sensor with an ultralow limit of detection (LoD) based on a phase interrogation readout scheme together with an anisotropic porous silicon (PSi) membrane. First, the fabrication of porous free-standing membranes from medium doped (100) surface oriented silicon, with pore diameters suitable for the infiltration of biomolecules, around 50 nm, is reported. Then, the phase interrogation scheme for characterizing the PSi membranes is presented whose results show that while volumetric sensitivity increases with the membrane thickness, the resolution in the birefringence measurements decrease dramatically due to depolarization effects. The best LoD was found to be equal to 6.25 ×10-6 RIU, from the thinnest 10-μm-thick membrane. Finally, the thermooptic coefficient of the 10 μm membrane was measured in an aqueous environment and shown to be equal to 8×10-4 rad/°C.

Flexible optoelectronics has emerged as an outstanding platform to pave the road toward vanguard technology advancements. As compared to conventional rigid substrates, a flexible technology enables mechanical deformation while maintaining stable performance. The advantages include not only the development to novel applications, but also the implementation of a wearable technology directly in contact with a curved surface. Here the monolithic integration of a perovskite‐based optical waveguide amplifier together with a photodetector on a nanocellulose substrate is shown to demonstrate the feasibility of a stretchable signal manipulation and receptor system fabricated on a biodegradable material. An integrated optical amplifier–photodetector is developed in which the photocurrent is exploited that is generated in the organic–inorganic lead halide perovskite under an applied bias. Such photocurrent does not minimally perturb the amplifier operation and is used to monitor the light signal propagating along the waveguide, opening a broad range of applications for example to regulate the operation temperature.

Ferroelectric polarization switching of high aspect ratio (80:1) PbZr(0.52)Ti(0.48)O(3) (PZT) microtubes with a wall thickness of ~200 nm was investigated. A charge-based technique was used to assess the dielectric and ferroelectric properties of individual mechanically-unconstrained PZT microtubes with interdigitated electrodes. An enhancement in the degree of ferroelastic (non-180 degrees ) domain wall motion was observed in the tubes relative to films of similar thickness on rigid substrates. The dielectric response of the tubes showed a Rayleigh-like ac field dependence over a wide temperature range; the extent of the extrinsic contribution to the dielectric response dropped as the temperature approached 10K, but remained finite. This work demonstrates a general methodology for directly electrically addressing small, unconstrained ferroelectric devices, extending the range of driving fields and temperatures over which these materials can be probed.

Porous silicon solid supports with pore diameter 0.5–1 μm, infiltrated with Ag nanostructures for surface enhanced Raman scattering (SERS) were prepared according to two procedures: spontaneous Ag+ reduction on the surface of freshly etched porous silicon immersed in Ag+ aqueous solutions, or anchoring colloidal Ag nanoparticles on the surface previously functionalized by aminosilane. Using Rhodamine 6G (RH6G) as analyte the detection limits were of the order of 20 μM and 20 nM with porous silicon metalized by the first and second procedure, respectively. This large increase of sensitivity notwithstanding a reduced surface density of Rhodamine 6G obtained on porous silicon metalized by the second procedure is discussed in terms of better hot spot efficiency and reduced aspecific binding out of the hot regions obtained depositing the colloids on the aminosilane functionalized surface.

Polymer pyrolysis to nanoceramics is employed for the production of photo-luminescent thin film samples, consisting of Si-nanocrystals dispersed in silica matrix. Thin films were deposited on Si wafer by spin-coating technique from a triethoxysilane-derived sol–gel solution. This is a fast process and a low cost technique. Samples were annealed at different temperatures between 600 °C and 1300 °C, under N 2 gas atmosphere. Structural evolution and luminescence from Si-ncs vs. temperature were investigated by FT-IR absorption spectroscopy and photo-luminescence. Absorption spectrum of As-Prep sample shows several vibrational bands due to Si–H, C–H x , and Si–O–Si structural units, without any appreciable luminescence. Silica phase segregation and intense PL (790 nm) due to Si-ncs were observed on annealing at T > 1000 °C.

Silicon oxycarbide samples were prepared by polymer pyrolysis using a methyltriethoxysilane-derived precursor. Transparent crack-free gel samples were obtained from the alkoxide by the sol–gel process. The dried gel samples were pyrolysed at different temperatures in the range between 400 and 1500 °C in Ar atmosphere. The chemical and microstructural evolution during pyrolysis were followed by FT-IR absorption, Raman scattering and photoluminescence (PL). The FT-IR spectra show the change in Si–O–Si asymmetric stretching, C–H x , Si–CH 3 stretching vibrational bands. The peak position and shape of these bands were found stable up to 600 °C. Above this temperature, a remarkable change in shape and peak position of Si–O–Si related vibration, reduction in C–H x and Si–CH 3 stretching absorption bands have been observed. Degradation of Si–CH 3 and the simultaneous formation of Si–CH 2 –Si via Si–CH 2 –CH 2 –Si is explicitly observed, experimentally. Annealing the sample at 800 °C starts to show the clear presence of D and G bands, related to the free carbon precipitation and its segregation with the temperature. The broad PL spectra centered at around 670 nm for the samples pyrolysed at 1500 °C shows an important information regarding the presence of crystalline SiC.

We present a post-processing free quantum random number generator (QRNG) based on silicon nanocrystals (Si-NCs) LEDs as a source of randomness. The relatively simple setup for data extraction, a negligible bias measured from the datasets and applying no post-processing operations to the raw data are the main advantages of this QRNG . The obtained bit sequences pass all the NIST tests and the highest bit-rate achieved is 0.6 Mbps.

Nanoporous materials are ideal candidates to fabricate sensors with high sensitivities. Using nanoporous materials both the strength and the type of interactions between analytes and host matrix can be tuned at will, and their large surface area permit to achieve ultralow detection limit and to keep high loading capacity and, thus, large dynamic range. Despite these intriguing possibilities their use in sensing technology is still limited because several fundamental aspects are not fully understood. By comparing supported and free standing Porous Silicon membranes, we demonstrate that sensor’s sensitivity is clearly overestimated if the sample is not properly washed. Moreover we underline the fact that, despite the reduced Q-factor of the resonant cavities, the strong interaction between the analyte and the optical modes in porous materials produces a large net sensitivity of the sensor. Finally, we show that the non-specific signal may have a linear response with the analyte concentration and it thus extremely difficult to separate it from the specific one. The work presented here is of importance in the design of nanoporous materials for sensing application. In fact it demonstrates that the final sensitivity of the device is not defined by its optical quality alone and that several other effects have to be considered to fabricate a reliable sensor.

We report measurements of angle-resolved light scattering in porous silicon films. Scattering rings were observed, and their aperture allowed to measure optical birefringence. These values are confirmed with other techniques. We study birefringence changes when pores are filled with liquids, after thermal annealing, and when the porous silicon layer is chemically etched in HF for different times. A decrease of optical anisotropy was observed in all cases.

Macroporous silicon with two-dimensional periodicity has been produced by electrochemical etching, using a p-type doped silicon substrate. The structure shows photonic energy gaps in the infrared region, as demonstrated by variable angle reflectance measurements. The agreement between measurement and band calculations confirms the high quality of the samples. The use of an optimized electrolyte allows the fabrication of very high quality samples, with high aspect ratio and low roughness both at the surface and on the pore walls. The best results are obtained with aprotic and protophilic solvents.

In this article we describe the fabrication of free standing n-type porous silicon microcavity (MC) and their properties as liquid sensors. We have optimized the etching recipe to keep both large pore size and high quality factor (Q-factor). Thus the fabricated porous layers have pore size in the range of 40 to 110 nm and are thus compatible with mass transport across the porous layer. We found that MC with a Q-factor of 60 can measure down to 1.1*10 -5 refractive index variations. Furthermore we analyze the role of non specific binding by comparing flow through versus flow over geometries. We compare these two approaches using different techniques and we show that flow over assay systematically overestimates the sensitivity of the device because of an inefficient rinse of the sample. Our work clearly indicates a limit in the reliability of measurements performed in flow over geometry unless specific controls are taken into account. Keywords: Porous silicon, Free standing membrane, Microcavity, Non specific signal, flow through, mass transport, electrochemical etching

Porous materials are ideal hosts to fabricate high sensitivity devices. Their large specific area and the possibility to modify the type and the strength of the matrix–analyte interactions allow the realization of sensors with finely tailored characteristics. In this article, we investigate how mass transport across the nanoporous structure influences the response due to the non-specific signal by comparing flow-through versus flow-over geometries. We observed a systematic overestimation of the sensitivity for porous substrate devices made of closed-ended pores compared with open-ended pore ones. Our analysis shows that such an effect is due to (unbound) analytes or contaminants that remain trapped within the pores and are not removed by rinsing of the sample. This result was verified by measuring similar samples in both flow through and flow over configurations, as well as their residual response after blockage of all their active sites. We also notice that sensors based on free-standing membranes show similar results independent of the fact that mass transport is induced by either an external pressure source or simply by Brownian motions.

The effect of surface roughness on the optical absorption of a porous material is numerically investigated. We performed a comparative study among different porous geometries and we demonstrate that the presence of the roughness significantly increases the optical absorption of light. This effect is optimized by using a proper matching layer that minimizes losses and maximizes absorption. Enhanced absorption is achieved over a broad range of wavelengths in these simple bilayered structures. The results of this work can be used to design more effective light trapping devices, e.g., third-generation photovoltaic backreflector exploiting the bandgap incident radiation.

A polarimetric sensor with state of the art sensitivity is developed using free standing porous silicon membranes. The use of an optimized etching receipt greatly reduces the pore roughness. Depolarization factors are thus limited and material birefringence is increased. Free standing membranes are fabricated in n-type substrates and characterized both from the optical and structural point of view. The proposed approach is fully CMOS compatible and can therefore pave the way to the development of cheap microarray that exploits multiplexing capabilities while keeping the amount of analyte required by the analysis down to the microliter level.

The modeling, fabrication and characterization of PSi fabricated from both (110) and (100) surface oriented silicon for optical sensing is thoroughly reported. First, based on the generalized Bruggeman method, the birefringence and sensitivity of the fabricated membranes were calculated as a function of the fabrication parameters such as porosity and pore sizes; and external effects, such as the pores surface oxidation. Thereafter we report on the fabrication of PSi membranes from (110) and (100) surface oriented silicon with pore sizes in the range of 50 - 80 nm, and the characterization of their birefringence using a polarimetric setup. Their sensitivities were determined by filling the pores with several liquids having different refractive index. As a result, sensitivities as high as 1407 nm/RIU were obtained for the (110) samples at a 1500 nm wavelength and 382 nm/RIU for the (100) samples at the same wavelength.

We present low temperature transfer bonding of porous silicon membranes to polymeric microfluidic devices, using neither adhesives nor bond surface treatment. The transfer is enabled by a novel dual cure ternary monomer system containing thiolene and epoxy. The ability of the epoxy to react with almost any dry substrate provides a very versatile fabrication method. We characterize the two stage curing mechanism, describe the device fabrication, and evaluate the bond strength.

In this work anisotropic porous silicon is investigated as a material for optical sensing. Birefringence and sensitivity of the anisotropic porous silicon membranes are thoroughly studied in the framework of Bruggeman model which is extended to incorporate the influence of environment effects, such as silicon oxidation. The membranes were also characterized optically demonstrating sensitivity as high as 1245 nm/RIU at 1500 nm. This experimental value only agrees with the theory when it takes into consideration the effect of silicon oxidation. Furthermore we demonstrate that oxidized porous silicon membranes have optical parameters with long term stability. Finally, we developed a new model to determine the contribution of the main depolarization sources to the overall depolarization process, and how it influences the measured spectra and the resolution of birefringence measurements.

Tensile strained-silicon waveguides were produced by LPCVD (780 °C) by depositing a 150 nm-thick Si 3 N 4 overlayer. Nonlinear nanosecond and femtosecond transmission experiments indicated the presence of a significant χ(2) in the bulk silicon.

Slot waveguides are very promising for optical sensing applications because of their peculiar spatial mode profile. In this paper we have carried out a detailed analysis of mode confinement properties in slot waveguides realized in very low refractive index materials. We show that the sensitivity of a slot waveguide is not directly related to the refractive index contrast of high and low materials forming the waveguide. Thus, a careful design of the structures allows the realization of high sensitivity devices even in very low refractive index materials (e.g., polymers) to be achieved. Advantages of low index dielectrics in terms of cost, functionalization and ease of fabrication are discussed while keeping both CMOS compatibility and integrable design schemes. Finally, applications of low index slot waveguides as substitute of bulky fiber capillary sensors or in ring resonator architectures are addressed. Theoretical results of this work are relevant to well established polymer technologies.

Silicon photonics has produced the first all-optical components intergrated into systems available already on the market. Nanosilicon, where low dimensional silicon allows new phenomena and devices, is a way to expand the

Here, we report on the design, fabrication and characterization of single-channel (SC-) and dual-channel (DC-) side-coupled integrated spaced sequences of optical resonators (SCISSOR) with a finite number (eight) of microring resonators using submicron silicon photonic wires on a silicon-on-insulator (SOI) wafer. We present results on the observation of multiple resonances in the through and the drop port signals of DC-SCISSOR. These result from the coupled resonator induced transparency (CRIT) which appears when the resonator band (RB) and the Bragg band (BB) are nearly coincident. We also observe the formation of high-Q (> 23000) quasi-localized modes in the RB of the drop transmission which appear when the RB and BB are well separated from each other. These multiple resonances and quasi-localized modes are induced by nanometer-scale structural disorders in the dimension of one or more rings. Finally, we demonstrate the tunability of RB (and BB) and localized modes in the DC-SCISSOR by thermo-optical or free-carrier refraction.

Optical characterization of complex coupled microring system is performed. Advanced optical effects as optical equivalent of electromagnetic induced transparency and all-optical tuning of single cavity are achieved and complex data transformation processes are envisaged.