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The azobenzene chromophore is used as a functional dye for the development of smart microfluidic devices. A single layer microfluidic channel is produced, exploiting the potential of a dye doped PDMS formulation. The key advantage of this approach is the possibility to control the fluid flow by means of a simple light stimulus. Furthermore, the deformation can be controlled in time, space and intensity, giving rise to several degrees of freedom in the actuation of the channel squeezing. A future perspective will be the implementation of the microfluidic platform with structured light, to have the possibility to control the flow in a parallel and reversible manner at several points, modifying the pattern in real time.

In this work, we performed a systematic study on the effect of the geometry of pre-patterned templates and spin-coating conditions on the self-assembling process of colloidal nanospheres. To achieve this goal, large-scale templates, with different size and shape, were generated by direct laser-writer lithography over square millimetre areas. When deposited over patterned templates, the ordering dynamics of the self-assembled nanospheres exhibits an inverse trend with respect to that observed for the maximisation of the correlation length &xi, on a flat surface. Furthermore, the self-assembly process was found to be strongly dependent on the height (H) of the template sidewalls. In particular, we observed that, when H is 0.6 times the nanospheres diameter and spinning speed 2500 rpm, the formation of a confined and well ordered monolayer is promoted. To unveil the defects generation inside the templates, a systematic assessment of the directed self-assembly quality was performed by a novel method based on Delaunay triangulation. As a result of this study, we found that, in the best deposition conditions, the self-assembly process leads to well-ordered monolayer that extended for tens of micrometres within the linear templates, where 96.2% of them is aligned with the template sidewalls.

We exploit directed self-assembly of di-block copolymers to obtain metal-dielectric nano-patterns over large area acting as hyperbolic meta-surface at visible wavelengths. We show that decay rate can be enhanced when spontaneous emitters are thereon located.

Controlling the location and the distribution of hot spots is a crucial aspect in the fabrication of surface-enhanced Raman spectroscopy (SERS) substrates for bio-analytical applications. The choice of a suitable method to tailor the dimensions and the position of plasmonic nanostructures becomes fundamental to provide SERS substrates with significant signal enhancement, homogeneity and reproducibility. In the present work, we studied the influence of the long-range ordering of different flexible gold-coated Si nanowires arrays on the SERS activity. The substrates are made by nanosphere lithography and metal-assisted chemical etching. The degree of order is quantitatively evaluated through the correlation length (ξ) as a function of the nanosphere spin-coating speed. Our findings showed a linear increase of the SERS signal for increasing values of ξ, coherently with a more ordered and dense distribution of hot spots on the surface. The substrate with the largest ξ of 1100 nm showed an enhancement factor of 2.6 · 103 and remarkable homogeneity over square-millimetres area. The variability of the signal across the substrate was also investigated by means of a 2D chemical imaging approach and a standard methodology for its practical calculation is proposed for a coherent comparison among the data reported in literature.

In recent years, the ability to pattern large areas at the micro- and nano-scale with stimuli-responsive materials has opened the opportunity to engineer surface structures and trigger peculiar properties such as complex optical functionalities or surface properties by laser-matter interactions. The use of light-sensitive materials, such as azobenzene compounds, can open the opportunity to active manipulate in terms of morphology, physical and mechanical properties a pre-patterned architectures, which are intrinsically static once fabricated. We employ azopolymers, in which the rapid and reversible photoisomerization reaction of azobenzene molecules can actuate mass transport phenomena typically parallel to the light polarization. The azopolymeric film is patterned by soft-imprinting as an array of micro-holes showing a well-defined isotropic round pores. Upon a linearly polarized illumination (365 nm, 150 W/cm2), we observe a deformation of the initial holes along the polarization direction, in such a way that the circular pores are transformed into long closed slits. A rotation of the polarization by 90° triggers a reconfiguration of the pristine round shape, with a good degree of control of the photo-induced pore reshaping. Due to the polarized-directionality of the photo-manipulation we demonstrate the possibility to tune the pristine morphology and properties along specific directions, providing a smart engineered platform with different reshaped micro-patterns. The light-induced contraction and expansion reshaping strategy of a porous polymeric structures shows exciting potential for a number of applications including microfluidics, lithography and tissue engineering. Tuning cells behavior in response to material manipulation cues is a promising goal in biology

A successful realisation of sub-20 nm features on silicon (Si) is becoming the focus of many technological studies, strongly influencing the future performance of modern integrated circuits. Although reactive ion etching (RIE), at both micrometric and nanometric scale has already been the target of many studies, a better understanding of the different mechanisms involved at sub-20 nm size etching is still required. In this work, we investigated the influence of the feature size on the etch rate of Si, performed by a cryogenic RIE process through cylinder-forming polystyrene-block-polymethylmethacrylate (PS-b-PMMA) diblock copolymer (DBC) masks with diameter ranging between 19-13 nm. A sensible decrease of the etch depth and etch rate was observed in the mask with the smallest feature size. For all the DBCs under investigation, we determined the process window useful for the correct transfer of the nanometric cylindrical pattern into a Si substrate. A structural and physicochemical investigation of the resulting nanostructured Si is reported in order to delineate the influence of various RIE pattern effects. Feature-size-dependent etch, or RIE-lag, is proved to significantly affect the obtained results.

The self-assembly (SA) of diblock copolymers (DBCs) based on phase separation into different morphologies of small and high-density features is widely investigated as a patterning and nanofabrication technique. The integration of conventional top-down approaches with the bottom-up SA of DBCs enables the possibility to address the gap in nanostructured lateral length standards for nanometrology, consequently supporting miniaturization processes in device fabrication. On this topic, we studied the pattern characteristic dimensions (i.e., center-to-center distance L0 and diameter D) of a cylinder-forming polystyrene-b-poly( methyl methacrylate) PS-b-PMMA (54 kg mol–1, styrene fraction 70%) DBC when confined within periodic SiO2 trenches of different widths (W, ranging between 75 and 600 nm) and fixed length (l, 5.7 μm). The characteristic dimensions of the PMMA cylinder structure in the confined configurations were compared with those obtained on a flat surface (L0 = 27.8 ± 0.5 nm, D = 13.0 ± 1.0 nm). The an...

In this work we investigate new degrees of freedom in controlling the physical properties of structured photo-sensitive materials that can be usefully exploited in many application fields. We employ azopolymers, a class of light responsive materials, which are structured in micro-pillar array. A reversible and controlled change in morphology of a pre-patterned polymeric film under properly polarized illumination is demonstrated to provide the opportunity to engineer surface structures and dynamically tune their properties. We exploit the laser process taking advantage of the light-induced deformation of a micro-textured azopolymeric film in order to modify the surface hydrophobicity along specific direction.

Block copolymer (BCP) self-assembly is expected to complement conventional optical lithography for the fabrication of next-generation microelectronic devices. In this regard, silicon-containing BCPs with a high Flory-Huggins interaction parameter (χ) are extremely appealing because they form high-resolution nanostructures with characteristic dimensions below 10 nm. However, due to their slow self-assembly kinetics and low thermal stability, these silicon-containing high-χ BCPs are usually processed by solvent vapor annealing or in solvent-rich ambient at a low annealing temperature, significantly increasing the complexity of the facilities and of the procedures. In this work, the self-assembly of cylinder-forming polystyrene-block-poly(dimethylsiloxane-random-vinylmethylsiloxane) (PS-b-P(DMS-r-VMS)) BCP on flat substrates is promoted by means of a simple thermal treatment at high temperatures. Homogeneous PS-b-P(DMS-r-VMS) thin films covering the entire sample surface are obtained without any evidence of dewetting phenomena. The BCP arranges in a single layer of cylindrical P(DMS-r-VMS) nanostructures parallel-oriented with respect to the substrate. By properly adjusting the surface functionalization, the heating rate, the annealing temperature, and the processing time, one can obtain correlation length values larger than 1 μm in a time scale fully compatible with the stringent requirements of the microelectronic industry.

We demonstrate the high potential of an optical integrated sensor which monitors the changes of the effective refractive index of the resonant optical modes induced by variations of the refractive index of the surrounding material. The detection system is a CMOS compatible structure based on a visible light emitting Si-rich Si3N4 μ-disk coupled to a passive Si3N4 waveguide placed underneath. We present a complete optical characterization of the active material in the isolated (μ-disk) and combined (plus coupled waveguide) photonic systems. The material has been optimized to obtain bright cavities with high quality factors. As a final result, we demonstrate that the sensor can achieve a sensitivity of 36 nm/RIU for small refractive index changes (Δ n = 0.002) and a minimum detection limit of 1.6 ×10-3 RIU. This structure can be used as a building block for detection systems with increased complexity, in which demultiplexing and detection could be readily integrated on the same chip.

In this work we will give an overview of the optical properties of Si nanoclusters coupled to Er 3+ ions in SiO 2 matrices produced by reactive magnetron co-sputtering. We have divided the work into two separate studies realised on the same samples, which are the result of a thorough optimisation work. The first one have been realised in order to get a clear picture of the interaction mechanism. On the second we will show a quantitative evaluation of the potential performances from a material point of view (determination of the whole optically active Er 3+ content, excitable by direct or indirect means) and actual performance in a waveguide device (determination of internal gain values).

We report on the morphological and emission properties of microdisk resonators with an optically active disk material made of luminescent substoichiometric Si3N4 matrix. We demonstrate the importance of optimising the material by finding a compromise between the photoluminesce properties and optical losses. A careful design of the cavities for optimising the radiative quality factors has been also performed, enabling us to produce active disks with low intrinsic losses. Subnanometer whispering gallery mode (WGM) resonances have been experimentally detected, showing quality factors as high as 1200 around the wavelength of 719 nm. These values are among the highest previously reported values in Si-nanocluster-based systems and are actually limited by the spectral resolution of our experimental setup. In addition, an increasing of the pumping flux is not generating a spectral widening of the resonances, thus not affecting the quality of the cavities. This is in contrast to what observed in other reports of Si-nc based microcavities, where significant enlargements are observed associated to carrier absorption losses. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Bipolar resistive switching memories based on metal oxides offer a great potential in terms of simple process integration, memory performance, and scalability. In view of ultrahigh density memory applications, a reduced device size is not the only requirement, as the distance between different devices is a key parameter. By exploiting a bottom-up fabrication approach based on block copolymer self-assembling, we obtained the parallel production of bilayer Pt/Ti top electrodes arranged in periodic arrays over the HfO2/TiN surface, building memory devices with a diameter of 28 nm and a density of 5 × 10(10) devices/cm(2). For an electrical characterization, the sharp conducting tip of an atomic force microscope was adopted for a selective addressing of the nanodevices. The presence of devices showing high conductance in the initial state was directly connected with scattered leakage current paths in the bare oxide film, while with bipolar voltage operations we obtained reversible set/reset transitions irrespective of the conductance variability in the initial state. Finally, we disclosed a scalability limit for ultrahigh density memory arrays based on continuous HfO2 thin films, in which a cross-talk between distinct nanodevices can occur during both set and reset transitions.

Optoelectronic properties of Er 3+ -doped slot waveguides electrically driven are presented. The active waveguides have been coupled to a Si photonic circuit for the on-chip distribution of the electroluminescence (EL) signal at 1.54 μm. The Si photonic circuit was composed by an adiabatic taper, a bus waveguide and a grating coupler for vertical light extraction. The EL intensity at 1.54 μm was detected and successfully guided throughout the Si photonic circuit. Different waveguide lengths were studied, finding no dependence between the waveguide length and the EL signal due to the high propagation losses measured. In addition, carrier injection losses have been observed and quantified by means of time-resolved measurements, obtaining variable optical attenuation of the probe signal as a function of the applied voltage in the waveguide electrodes. An electro-optical modulator could be envisaged if taking advantage of the carrier recombination time, as it is much faster than the Er emission lifetime.

In this work, the optoelectronic properties of silicon light emitting field-effect transistors (LEFETs) have been investigated. The devices have been fabricated with silicon nanocrystals in the gate oxide and a semitransparent polycrystalline silicon gate. We compare the properties of LEFET with a more conventional MOS-LED (two-terminal light-emitting capacitor) with the same active material. The ~45 nm thick gate siliconrich oxide is deposited in a size-controlled multilayer geometry by low pressure chemical vapor deposition using standard microelectronic processes in a CMOS line. The multilayer stack is formed by layers of silicon oxide and silicon rich silicon oxide. The nanocrystal size and the tunneling barrier width are controlled by the thickness of silicon-rich silicon oxide and stochiometric silicon oxide layers, respectively. The silicon nanocrystals have been characterized by means of spectrally and time resolved photoluminescence, high resolution TEM, and x-ray photoelectron spectroscopy. Resistivity of the devices, capacitance, and electroluminescence under direct and pulsed injection current scheme have been studied and here reported. The optical power density and the external quantum efficiency of the LEFETs will be compared with the MOSLED results. This study will help to develop practical optoelectronic and photonic devices via accurate modeling and engineering of charge transport and exciton recombination in silicon nanocrystal arrays.

An integrated erbium-based light emitting diode has been realized in a waveguide configuration allowing 1.54 μm light signal routing in silicon photonic circuits. This injection device is based on an asymmetric horizontal slot waveguide where the active slot material is Er3+ in SiO 2 or Er3+ in Si-rich oxide. The active horizontal slot waveguide allows optical confinement, guiding and lateral extraction of the light for on-chip distribution. Light is then coupled through a taper section to a passive Si waveguide terminated by a grating which extracts (or inserts) the light signal for measuring purposes. We measured an optical power density in the range of tens of μW/cm2 which follows a super-linear dependence on injected current density. When the device is biased at high current density, upon a voltage pulse (pump signal), free-carrier and space charge absorption losses become large, attenuating a probe signal by more than 60 dB/cm and thus behaving conceptually as an electro-optical modulator. The integrated device reported here is the first example, still to be optimized, of a fundamental block to realize an integrated silicon photonic circuit with monolithic integration of the light emitter. © 2013 IOP Publishing Ltd., This work was supported by the Spanish Ministry of Science through the project LASSI (TEC2009-08359), by the EC through the project ICT-FP7-224312 HELIOS and by Italy–Spain integrated actions. D N-U is grateful for the financial support of AGAUR through the Beatriu de Pinòs program.

In this paper, we report on the first attempt to design, fabricate, and test an on-chip optical amplifier which works at 1540 nm and can be electrically driven. It is based on an asymmetric silicon slot waveguide which embeds the active material. This is based on erbium-doped silicon rich silicon oxide. We describe the horizontal asymmetric slot waveguide design which allows us to get a high field confinement in a nanometer thick active layer. In addition, we detail the complex process needed to fabricate the structure. The waveguides have been characterized both electrically as well as optically. Electroluminescence can be excited by hot carrier injection, due to impact excitation of the Er ions. Propagation losses have been measured and high values have been found due to processing defects. Pump and probe measurements show a voltage dependent strong attenuation of the probe signal due to free carrier accumulation and absorption in the slot waveguide region. At the maximum electrical pumping level, electroluminescence signal is in the range of tens of μW/cm 2 and the overall loss of the device is only -6 dB. Despite not demonstrating optical amplification, this study shines some light on the path to achieve an all-silicon electrically driven optical amplifier. © 2012 IEEE., This work was supported by the European Commission, through the Project ICTFP7-224312 HELIOS and by Italy–Spain integrated actions.

The design, optical characterization and sensoristic capability provided by a complementary metal-oxide-semiconductor (CMOS) compatible integrated sensor based on a μ-disk resonator cavity are reported. The working principle of the presented device consists in monitoring the changes in the effective refractive index of the supported optical modes induced by variations of the refractive index of the surrounding material. The detection system has been designed on the base of a high quality factor (Q=1.4×10 4 ) Si-rich Si 3 N 4 (SRSN) μ-disk - emitting in the VIS under optical pumping - bottom coupled to a low loss passive stoichiometric Si 3 N 4 waveguide (WG), with losses values under 1 dB/cm measured in the same spectral region. The PL emission in the VIS range provided by the SRSN enable the use of Si-based detectors, easily integrable using the current CMOS standard technology. Proof of concept measurements performed on the coupled device revealed a good sensitivity of 51.79 nm/RIU (Refractive Index Unit), in accordance with the simulated data, and a minimum detection limit of 1.1 × 10 -3 RIU.

The convergence of photonics and microelectronics within a single chip is still lacking of a monolithical on-chip optical amplifier. Rare-earth doped slot waveguides show a large potential as on-chip source. Slot waveguides with silicon nanocrystals embedded in a dielectric host matrix can increase the light confinement in the active layer and allow electrical injection. In this work, horizontal slot waveguides formed by two thick silicon layers separated by a thin erbium doped silicon rich silicon oxide layer are studied as on-chip optical amplifiers. The waveguides are grown in a CMOS line with the active material grown by low-pressure chemical vapor deposition. Optical tests are performed and light propagation in the slot waveguides is observed. Using the cut-back technique, spectra propagation losses are evaluated. Room temperature electroluminescence is observed at 1.54 μm. Transmitted optical signal resonant with Er absorption is studied as a function of the injected current for different probing laser wavelengths.

Electrically driven Er(3+) doped Si slot waveguides emitting at 1530 nm are demonstrated. Two different Er(3+) doped active layers were fabricated in the slot region: a pure SiO(2) and a Si-rich oxide. Pulsed polarization driving of the waveguides was used to characterize the time response of the electroluminescence (EL) and of the signal probe transmission in 1 mm long waveguides. Injected carrier absorption losses modulate the EL signal and, since the carrier lifetime is much smaller than that of Er(3+) ions, a sharp EL peak was observed when the polarization was switched off. A time-resolved electrical pumpprobe measurement in combination with lock-in amplifier techniques allowed to quantify the injected carrier absorption losses. We found an extinction ratio of 6 dB, passive propagation losses of about 4 dB/mm, and a spectral bandwidth25 nm at an effective d.c. power consumption of 120 μW. All these performances suggest the usage of these devices as electro-optical modulators.

The electroluminescence (EL) at 1.54νm of metaloxidesemiconductor (MOS) devices with Er 3+ ions embedded in the silicon-rich silicon oxide (SRSO) layer has been investigated under different polarization conditions and compared with that of erbium doped SiO 2 layers. EL time-resolved measurements allowed us to distinguish between two different excitation mechanisms responsible for the Er 3+ emission under an alternate pulsed voltage signal (APV). Energy transfer from silicon nanoclusters (Si-ncs) to Er 3+ is clearly observed at low-field APV excitation. We demonstrate that sequential electron and hole injection at the edges of the pulses creates excited states in Si-ncs which upon recombination transfer their energy to Er 3+ ions. On the contrary, direct impact excitation of Er 3+ by hot injected carriers starts at the FowlerNordheim injection threshold (above 5MVcm 1) and dominates for high-field APV excitation.

One of the main drawbacks that explain why Si photonics is still not dominant with respect to compound semiconductors and Si microelectronics lies on the difficulties associated with making Si a host material for efficient light emission. Among the several alternatives to obtain highly efficient Si-based emitting materials, dielectric matrices with Silicon in excess have been probably the most investigated, since they can even provide optical gain in the visible region. [1] An interesting strategy has been to combine the light emission properties of those materials and the optical properties of circular microcavities (such as disks or rings). [2–5] In the present work, we report an experimental characterisation of the optical properties of active Si rich Si 3 N 4 µ-disk cavities in the visible range. In particular, we have studied the correlation between the quality factor (Q) of the cavities and the active material deposition parameters. Micro-photoluminescence (µ-PL) measurements have revealed subangstrom whispering galley modes (WGM) resonances and maximum Q of 104 around 760 nm. These values improve the best results reported so far for Si based light emitting circular resonators in the visible range. We have also quantified the on-plane emitted powers (hundreds of nW) and power efficiencies (10−6–10−5). In contrast to what reported on substoichiometric SiO 2 based microcavities, we demonstrate the absence of a spectral widening at high pump fluxes associated to carrier absorption (CA) mechanisms, which allows high emitted power without degrading the quality factor of the cavity.

Laser action using non-coupled excitation and detection of microspheres made of Nd3+ doped barium-titanium-silicate glass has been demonstrated and measured. The microspheres have also been successfully deposited over Si3N4 strip waveguides with a SiO2 separation layer, thus enabling the laser emission extraction onto a CMOS compatible photonic circuit. The dynamics of the lasing wavelength and intensity has been studied as a function of the pump power and interpreted in terms of thermal effects generated through non-radiative recombination of the excited ions. © 2013 Astro Ltd., The authors thank the Ministerio de Economía y Competitividad of Spain (MINECO) within the National Program of Materials (MAT2010-21270-C04-02/-03/-04), the Consolider-Ingenio 2010 Program (MALTA CSD2007-0045, www.malta-consolider.com), the EU-FEDER, the GICSERV NGG-268 for their financial support and ACIISI of Gobierno de Canarias for the project ID20100152 and FPI. DN-U acknowledges the financial support of Generalitat de Catalunya through the Beatriu de Pinòs program.

The sensitizing action of amorphous silicon nanoclusters on erbium ions in thin silica films has been studied under low-energy (long wavelength) optical excitation. Profound differences in fast visible and infrared emission dynamics have been found with respect to the high-energy (short wavelength) case. These findings point out to a strong dependence of the energy transfer process on the optical excitation energy. Total inhibition of energy transfer to erbium states higher than the first excited state (I-4(13/2)) has been demonstrated for excitation energy below 1.82 eV (excitation wavelength longer than 680 nm). Direct excitation of erbium ions to the first excited state (I-4(13/2)) has been confirmed to be the dominant energy transfer mechanism over the whole spectral range of optical excitation used (540 nm-680 nm). (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4712626]