Search

The dewetting and ordering characteristics of a lamellae-forming poly(styrene-block-methyl methacrylate) block copolymer (BCP) either alone or blended with low-molecular-weight polystyrene and poly...

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.

Nanoporous/nanocomposite thin films with controlled morphology at nanoscale were prepared onto transparent and conductive indium tin oxide (ITO) supports by exploiting the self-assembly of a lamellar polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA) block copolymer (BCP). A perpendicular orientation of PS and PMMA lamellar nanodomains was achieved by grafting a random PS-r-PMMA copolymer to the ITO supports and successive thermal annealing. Stable and reproducible nanoporous morphologies, characterized by PS lamellar nanodomains of width equal to ≈20 nm alternating to nanochannels of width equal to ≈8 nm, were obtained by irradiating the samples with an appropriate UV-C dose able to fix the relative arrangement of PS domains through activation of cross-linking reactions and selective removal of PMMA blocks. Nanoporous hybrid composites with a stable morphology were obtained either by applying the UV irradiation protocol to BCP nanocomposites characterized by selective inclusion of zinc oxide (ZnO) nanoparticles (NPs) in the PS domains (nanocomposite first/nanopores after) or by selective infiltration of cadmium selenide (CdSe) NPs in the nanochannels left free by PMMA removal through UV irradiation (nanopores first/nanocomposite after), demonstrating the strenght of the approach.

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.

The enhancement factor (EF) is an essential parameter in the field of surface-enhanced Raman spectroscopy (SERS), indicating the magnification of the Raman signal of molecules interacting with the surface of plasmonic nanostructures. The calculation of EF requires a careful evaluation of both the signal intensities and the number of molecules in SERS and normal Raman conditions. The determination of the surface density of molecules adsorbed on the plasmonic substrate is a challenging task, but essential for the estimation of the number of SERS-active molecules. This paper describes the determination of EF using 7-mercapto-4-methylcoumarin (MMC) as the probe molecule on gold-coated silicon nanowires, integrating SERS and normal Raman spectroscopy with X-ray fluorescence (RF-XRF) data that provide a reference-free quantitative measurement of the molecular surface density. In addition, the surface coverage of MMC on the substrate is modelled by molecular mechanics (MM) and molecular dynamics (MD) simulations.

We investigated the dewetting process on flat and chemically patterned surfaces of ultrathin films (thickness between 2 and 15 nm) of a cylinder forming polystyrene- block-poly(methyl methacrylate) (PS- b-PMMA) spin coated on poly(styrene- r-methyl methacrylate) random copolymers (RCPs). When the PS- b-PMMA film dewets on a 2 nm-thick RCP layer, the ordering of the hexagonally packed PMMA cylinders in the dewetted structures extends over distances far exceeding the correlation length obtained in continuous block copolymer (BCP) films. As a result, micrometer-sized circular droplets featuring defectless single grains of self-assembled PS- b-PMMA with PMMA cylinders perpendicularly oriented with respect to the substrate are generated and randomly distributed on the substrate. Additionally, alignment of the droplets along micrometric lines was achieved by performing the dewetting process on large-scale chemically patterned stripes of 2 nm thick RCP films by laser lithography. By properly adjusting the periodicity of the chemical pattern, it was possible to tune and select the geometrical characteristics of the dewetted droplets in terms of maximum thickness, contact angle and diameter while maintaining the defectless single grain perpendicular cylinder morphology of the circular droplets.

Block copolymers (BCPs) are emerging as a cost-effective nanofabrication tool to complement conventional optical lithography because they self-assemble in highly ordered polymeric templates with well-defined sub-20-nm periodic features. In this context, cylinder-forming polystyrene-block-poly(methyl methacrylate) BCPs are revealed as an interesting material of choice because the orientation of the nanostructures with respect to the underlying substrate can be effectively controlled by a poly(styrene-random-methyl methacrylate) random copolymer (RCP) brush layer grafted to the substrate prior to BCP deposition. In this work, we investigate the self-assembly process and lateral order evolution in RCP + BCP systems consisting of cylinder-forming PS-b-PMMA (67 kg mol–1, PS fraction of ∼70%) films with thicknesses of 30, 70, 100, and 130 nm deposited on RCP brush layers having thicknesses ranging from 2 to 20 nm. The self-assembly process is promoted by a rapid thermal processing machine operating at 250 °C fo...

Ordered magnetic nanodot arrays with extremely high density provide unique properties to the growing field of nanotechnology. To overcome the size limitations of conventional lithography, a fine-tuned sputtering deposition process on mesoporous polymeric template fabricated by diblock copolymer self-assembly is herein proposed to fabricate uniform and densely spaced nanometer-scale magnetic dot arrays. This process was successfully exploited to pattern, over a large area, sputtered Ni80Fe20 and Co thin films with thicknesses of 10 and 13 nm, respectively. Carefully tuned sputter-etching at a suitable glancing angle was performed to selectively remove the magnetic material deposited on top of the polymeric template, producing nanodot arrays (dot diameter about 17 nm). A detailed study of magnetization reversal at room temperature as a function of sputter-etching time, together with morphology investigations, was performed to confirm the synthesis of long-range ordered arrays displaying functional magnetic properties. Magnetic hysteresis loops of the obtained nanodot arrays were measured at different temperatures and interpreted via micromagnetic simulations to explore the role of dipole-dipole magnetostatic interactions between dots and the effect of magnetocrystalline anisotropy. The agreement between measurements and numerical modelling results indicates the use of the proposed synthesis technique as an innovative process in the design of large-area nanoscale arrays of functional magnetic elements.

Hydroxyl terminated poly(styrene-r-methyl methacrylate) (P(S-r-MMA)) random copolymers (RCPs), with molecular weight (Mn) spanning from 1700 to 69 000 g mol−1 and equal styrene unit content, were grafted at different temperatures onto a silicon oxide surface and subsequently used to study the orientation of nanodomains with respect to the substrate, in cylinder forming polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA) block copolymer thin films. When the grafting temperature increases from 250 to 310 °C, a substantial increase in the grafting rate is observed. In addition, an increase in the surface neutralization efficiency occurs thus resulting in an increase in the robustness of the surface neutralization step. These data revealed that the neutralization of the substrate is the result of a complex interplay between RCP film characteristics and underlying substrate properties that can be finely tuned by properly adjusting the temperature of the grafting process. © 2016 Society of Chemical Industry

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...

The morphological evolution of cylinder-forming poly(styrene)-b-poly(methyl methacrylate) block copolymer (BCP) thick films treated at high temperatures in the rapid thermal processing (RTP) machine was monitored by means of in-depth grazing-incidence small-angle X-ray scattering (GISAXS). The use of this nondisruptive technique allowed one to reveal the formation of buried layers composed of both parallel-and perpendicular-oriented cylinders as a function of the film thickness (24 700 nm, the two interfaces are completely decoupled, and the formation of a superficial layer of about 50 nm composed of perpendicular cylinders is observed. Furthermore, the through-film morphology affects the nanodomain long-range order, which substantially decreases in correspondence with the beginning of the decoupling process. When the thick samples are exposed to longer thermal treatments, an increase in the long-range order of the nanodomains occurs, without any sensible variation of the thickness of the superficial layer.

New low molar mass (M-n similar to 20 kg mol(-1)) polystyrene-b-poly(methyl methacrylate-co-perfluorohexylethyl acrylate) (PS-b-P(MMA-co-FA)) block copolymers were synthesized all consisting of similar to 70 mol% PS block and similar to 30 mol % P(MMA-co-FA) block. The amount of FA counits in the latter block was increased (0.5, 1, 3 and 4 mol%) in order to enhance the incompatibility between the two blocks and to form different self-assembled nanostructures. The block copolymers were thermally annealed by Rapid Thermal Processing (RTP) over wide ranges of temperatures and times. Complementary SEM and AFM analyses evidenced that the introduction of FA counits above a critical content (similar to 2 mol%) drove a self-assembly process through mixed morphologies. These were formed at a distance from the polymer-air interface and consisted of perpendicular cylinders of P(MMA-co-FA) in a PS matrix laying at the substrate- polymer interface, and surmounted PS stripes and PS dots. Modification by low amounts of FA produced block copolymer samples that self-assembled in new, mixed nanostructures, even though they possessed much lower molar masses than those of analogous well established PS-b-PMMA block copolymers.

Cylinder forming PS-b-PMMA block copolymer (BCP) thin films were deposited on pre-patterned surfaces with densely packed and nanometer wide trenches defined by conventional top down approaches and arranged to form a periodic grating. The films were subsequently annealed at 250 °C for times ranging from 30 s to 900 s in a rapid thermal processing device and their morphology evolution within the topographically defined structures was systematically investigated. Irrespective of the surface neutralization, an irreversible orientational flipping of the BCP microdomains inside the trenches was observed and attributed to de-swelling of the polymeric film as a consequence of a progressive desorption of the solvent retained inside the film. Systematic investigation of the annealing process indicates that the flipping is strongly dependent on the geometric parameters of the trenches and on the relative position of the analysed trench with respect to the periodic topographic structure. © 2014 The Royal Society of Chemistry.

The block copolymer self-assembly provides a reliable tool for the planar organization of materials at the nanoscale. In this paper, we review our recent achievements in the case of the polystyrene-b-poly(methyl-methacrylate) (PS-b-PMMA) polymeric mixture. By the proper choice of deposition and treatment parameters, one can adjust the thickness of the deposited material and transfer the block copolymer cylindrical organization to the material inclusions into the matrix. Silicon nanocrystals (Si-ncs) have been used as the active material to process, due to its interesting electrical and optical properties for electronic and photonic applications. This material has been fabricated in the form of well-defined arrays over a macroscopic surface, either by electron beam deposition or by ion beam synthesis. A further, crucial step toward the fabrication of the active area of the device is the formation of Si nanoparticle arrays onto sub-micrometric trenches defined by graphoepitaxy. The periodicity and the topography of the trenches highly affect the possibility of a conformal deposition of the ordered block polymeric mask, and consequently, of the reproduction of the patterned array of nanocrystals.

Two strategies are envisioned to improve the thermal stability of the grafted layer and to allow the processing of the random copolymer/block copolymer (RCP/BCP) system at high temperature. From one side, a high-temperature thermal treatment of a commercial a-hydroxyl omega-2,2,6,6-tetramethylpiperidinyloxy functional RCP, namely, TR58, leads to the formation of a stabilized layer able to induce the perpendicular orientation of a symmetric BCP to temperatures higher than 310 degrees C. On the other side, an alpha-hydroxyl omega-Br functional RCP, namely, BrR58, with the same molar mass and composition of TR58, was prepared by activator regenerated by electron transfer atom transfer radical polymerization. The resulting brush layer can sustain the self-assembly of the symmetric BCP for processing temperatures as high as 330 degrees C. In both systems, the disruption of the BCP film, deposited on the grafted RCP layer, occurs because of the formation of bubbles, due to a low-temperature evolution of monomers from the RCP layer. The extent of the low-temperature monomer evolution is higher for TR58 than it is for BrR58 and starts at lower temperatures. For both copolymers, the thermal treatment offsets the low-temperature monomer evolution while still maintaining surface characteristics suitable to induce the perpendicular orientation of the BCPs, thus ultimately extending the range of processing temperatures of the BCP film and consequently speeding the self-organization process.

The ordering process of asymmetric PS-b-PMMA block copolymers (BCPs) is investigated on flat SiO2 surfaces and on topographically patterned substrates. The topographic patterns consist of periodic gratings of 10 trenches defined by conventional top-down approaches and subsequently neutralized using a P(S-r-MIvIA) random copolymer (RCP). When the ordering process is accomplished on a flat surface at a temperature ranging between 180 and 230 degrees C, cylindrical microdomains perpendicularly oriented with respect to the substrate are observed irrespective of annealing temperature. In contrast, when the ordering process occurs on topographically patterned substrates, different phenomena have to be considered. The simultaneous effect of the flow around the gratings and the BCP flux from the zone located between adjacent trenches (mesa) into the inner part of the trenches results in significant thickness variations of the confined BCP film. Therefore, the amount of BCP inside the trenches depends on the width of the mesa region, which acts as a BCP reservoir. Moreover, within each trench group, the BCP thickness progressively decreases from the external to the central trenches composing the periodic grating. The thickness variation of the BCP film within the trenches strongly affects the ordering process, ultimately leading to different orientations of the microdomains within the trenches. In particular, when the annealing temperature is 190 degrees C a precise confinement of the BCP within the trenches featuring a perpendicular cylinder morphology is observed. At higher temperatures, mixed or parallel orientations of the microdomains are obtained depending on the width of the trenches in the periodic grating.

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)

Binary homopolymer blends of two hydroxyl-terminated polystyrene (PS-OH) and polymethylmethacrylate (PMMA-OH) homopolymers (Mn ~ 16000 g mol−1) were grafted on SiO2 substrates by high-temperature (T > 150 °C), short-time (t < 600 s) thermal treatments. The resulting brush layer was tested to screen preferential interactions of the SiO2 substrate with the different symmetric and asymmetric PS-b-PMMA block copolymers deposited on top of the grafted molecules. By properly adjusting the blend composition and the processing parameters, an efficient surface neutralization path was identified, enabling the formation, in the block copolymer film, of homogeneous textures of lamellae or cylinders perpendicularly oriented with respect to the substrate. A critical interplay between the phase segregation of the homopolymer blends and their grafting process on the SiO2 was observed. In fact, the polar SiO2 is preferential for the PMMA-rich phase that forms a homogeneous layer on the substrate, while the PS-rich phase i...

Hydroxyl-terminated P(S-r-MMA) random copolymers with molecular weight ranging from 1.7 to 69 kg/mol and a styrene unit fraction of 61% were grafted onto a silicon oxide surface and subsequently used to study the orientation of domains with respect to the substrate, in cylinder-forming PS-b-PMMA block copolymer thin films. When the thickness (H) of the grafted layer is greater than 5−6 nm, a perpendicular orientation is always observed because of the efficient decoupling of the BCP film from the polar SiO2 surface. Conversely, if H is less than 5 nm, the critical thickness of the grafted layer, which allows the neutralization of the substrate and promotion of the perpendicular orientation of the nanodomains in the BCP film, is found to depend on the Mn of the RCP. In particular, when Mn = 1700, a 2.0 nm thick grafted layer is sufficient to promote the perpendicular orientation of the PMMA cylinders in the PS-b-PMMA BCP film.

Synthesis of nanopatterned magnetic materials offers advanced capabilities in tailoring material structures and opens up new opportunities for engineering innovative devices (i.e. electronic and biomedical). In the frame of magnetic materials, the most demanding application consists in fabricating high-density arrays for use in data storage and magnetic sensors for spintronics [1]. In the last decade, many routes for the reliable fabrication of magnetic nanostructures have been extensively investigated, including top-down lithography and bottom-up self-assembly processes. Conventional electron beam lithography (EBL) soon turned out to be limited by low-speed and high costs while self-assembling emerged as a viable and handy alternative technique for designing nanostructures over a wide area on magnetic thin films.

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.

Hydroxyl-terminated P(S-r-MMA) random copolymers (RCPs) with molecular weights (M-n) from 1700 to 69000 and a styrene unit fraction of approximately 61% were grafted onto a silicon oxide surface and subsequently used to study the orientation of nanodomains with respect to the substrate, in cylinder-forming PS-b-PMMA block copolymer (BCP) thin films. When the thickness (H) of the grafted layer is greater than 5-6 nm, a perpendicular orientation is always observed because of the efficient decoupling of the BCP film from the polar SiO2 surface. Conversely, if H is less than 5 nm, the critical thickness of the grafted layer, which allows the neutralization of the substrate and promotion of the perpendicular orientation of the nanodomains in the BCP film, is found to depend on the M-n of the RCP. In particular, when Mn = 1700, a 2.0 nm thick grafted layer is sufficient to promote the perpendicular orientation of the PMMA cylinders in the PS-b-PMMA BCP film. A proximity shielding mechanism of the BCP molecules from the polar substrate surface, driven by chain stretching of the grafted RCP molecules, is proposed.

Binary homopolymer blends of two hydroxyl-terminated polystyrene (PS-OH) and polymethylmethacrylate (PMMA-OH) homopolymers (Mn similar to 16000 g mol(-1)) were grafted on SiO2 substrates by high-temperature (T > 150 degrees C), short-time (t < 600 s) thermal treatments. The resulting brush layer was tested to screen preferential interactions of the SiO2 substrate with the different symmetric and asymmetric PS-b-PMMA block copolymers deposited on top of the grafted molecules. By properly adjusting the blend composition and the processing parameters, an efficient surface neutralization path was identified, enabling the formation, in the block copolymer film, of homogeneous textures of lamellae or cylinders perpendicularly oriented with respect to the substrate. A critical interplay between the phase segregation of the homopolymer blends and their grafting process on the SiO2 was observed. In fact, the polar SiO2 is preferential for the PMMA-rich phase that forms a homogeneous layer on the substrate, while the PS-rich phase is located at the polymer-air interface. During the thermal treatment, phase segregation and grafting proceed simultaneously. Complete wetting of the PS rich phase on the PMMA rich phase leads to the formation of a PS/PMMA bilayer. In this case, the progressive diffusion of PS chains toward the polymer-SiO2 interface during the thermal treatment allows tuning of the brush layer composition.

Tailoring surface energies is the key factor to control the orientation of nanoscopic structures in thin block copolymer (BCP) films. In the general frame of the "grafting to" approach, this paper reports on the use of Rapid Thermal Processing (RTP) technology to perform flash grafting reactions of a hydroxyl terminated poly(styrene-r-methylmethacrylate) random copolymer to the activated silicon wafer surface. The perpendicular orientation of the cylindrical morphology of an asymmetric PS-b-PMMA block copolymer is achieved when the thickness of the random copolymer layer is higher than 6.0 nm. The grafting time to achieve this thickness reduces from about 750 s, when the RTP grafting process is performed at 230 °C, to 15 s at 310 °C. For a symmetric PS-b-PMMA block copolymer, the perpendicularly oriented lamellar morphology is obtained when the random layer thickness is higher than 3.5 nm, that is after 60 s RTP grafting time at 250 °C. In addition, TGA-GC-MS analysis indicates that a chain structural reorganization, which occurs during the RTP treatment at high temperature, affords a more stable film structure without changing its surface characteristics. In conclusion, the RTP technology allows the "grafting to" approach to be successfully integrated into the next generation lithographic processes and affords the unprecedented opportunity to study the grafting of macromolecules on time scales and in temperature ranges that have never been explored before, shedding new light on the early stages and on the dynamics of these processes. This journal is © the Partner Organisations 2014.

The self-assembly of asymmetric polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA) block copolymer based nanoporous thin films over a broad range of molar mass (M-n) between 39 kg.mol(-1) and 205 kg.mol(-1) is obtained by means of a simple thermal treatment. In the case of standard thermal treatments, the self-assembly process of block copolymers is hindered at small M-n by thermodynamic limitations and by a large kinetic barrier at high M-n. We demonstrate that a fine tuning of the annealing parameters, performed by a Rapid Thermal Processing (RTP) machine, permits us to overcome those limitations. Cylindrical features are obtained by varying M-n and properly changing the corresponding annealing temperature, while keeping constant the annealing time (900 s), the film thickness (similar to 30 nm), and the PS fraction (similar to 0.7). The morphology, the characteristic dimensions (i.e., the pore diameter d and the pore-to-pore distance L-0), and the order parameter (i.e., the lattice correlation length xi) of the samples are analyzed by scanning electron microscopy and grazing-incidence small-angle X-ray scattering, obtaining values of d ranging between 12 and 30 nm and L-0 ranging between 24 and 73 nm. The dependence of L-0 as a 0.67 power law of the number of segments places these systems inside the strong segregation limit regime. The experimental results evidence the capability to tailor the self-assembly processes of block copolymers over a wide range of molecular weights by a simple thermal process, fully compatible with the stringent constraints of lithographic applications and industrial manufacturing.

The control of the self-assembly (SA) process and nanostructure orientation in diblock copolymer (DBC) thick films is a crucial technological issue. Perpendicular orientation of the nanostructures in symmetric and asymmetric poly(styrene)-b-poly(methyl methacrylate) (PS-b-PMMA) block copolymer films obtained by means of simple thermal treatments was demonstrated to occur in well-defined thickness windows featuring modest maximum values, thus resulting in low aspect ratio (h/d < 2) of the final lithographic mask. In this manuscript, the thickness window corresponding to the perpendicular orientation of the cylindrical structures in asymmetric DBC is investigated at high temperatures (190 °C

This work reports experimental findings about the evolution of lateral ordering of lamellar microdomains in symmetric PS-b-PMMA thin films on featureless substrates. Phase separation and microdomain evolution are explored in a rather wide range of temperatures (190-340 degrees C) using a rapid thermal processing (RTP) system. The maximum processing temperature that enables the ordering of block copolymers without introducing any significant degradation of macromolecules is identified. The reported results clearly indicate that the range of accessible temperatures in the processing of these self-assembling materials is mainly limited by the thermal instability of the grafted random copolymer layer, which starts to degrade at T > 300 degrees C, inducing detachment of the block copolymer thin film. For T

The pattern coarsening dynamics in symmetric polystyrene-b-polymethylmethacrylate (PS-b-PMMA) block copolymer thin films under conventional thermal treatments is extremely slow, resulting in limited correlation length values even after prolonged annealing at relatively high temperatures. This study describes the kinetics of symmetric block copolymer microphase separation when subjected to a thermal treatment based on the use of a Rapid Thermal Processing (RTP) system. The proposed methodology allows self-organization of symmetric PS-b-PMMA thin films in few seconds, taking advantage of the amount of solvent naturally trapped within the film during the spinning process. Distinct and self-registered morphologies, coexisting along the sample thickness, are obtained in symmetric PS-b-PMMA samples, with periodic lamellae laying over a hexagonal pattern of PMMA cylinders embedded in the PS matrix and perpendicularly oriented with respect to the substrate. The ordering dynamics and morphological evolution of the coexisting dual structures are delineated and the intimate mechanism of the self-assembly and coarsening processes is discussed and elucidated.

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.

We perform a systematic study of the effect of adjacent nanostructures on the confinement of block copolymers (BCP) within pre-patterned trenches in 100 nm thick SiO2 films. Asymmetric PS-b-PMMA BCP with a styrene fraction of 0.71, Mn = 67100 are used. When deposited in the form of thin film, these BCP naturally self-organize upon annealing and form a PS matrix with hexagonally packed PMMA cylinders perpendicularly oriented with respect to the substrate. An accurate study of the confinement of this BCP thin film within isolated trenches is performed as a function of their width (80–260 nm). In this specific configuration the confinement of the BCP thin film within the pre-patterned structures has only been partially achieved. The effect of adjacent trenches on the arrangement of the BCP thin film is investigated using parallel trenches periodically distributed on the surface. The effective confinement of the BCP film is strongly modified by the periodicity of the pre-patterned structures.

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.

Self-assembling block copolymers generate nanostructured patterns which are useful for a wide range of applications. In this paper we demonstrate the capability to control the morphology of the self-assembling process of PS-b-PMMA diblock copolymer thin films on unpatterned surfaces by means of fast thermal treatment performed in a rapid thermal processing machine. The methodology involves the use of radiation sources in order to rapidly drive the polymeric film above the glass transition temperature. Highly ordered patterns were obtained for perpendicular-oriented cylindrical and lamellar PS-b-PMMA block copolymers in less than 60 s. This approach offers the unprecedented opportunity to investigate in detail the kinetics of the block copolymer self-assembly during the early stages of the process, providing a much deeper understanding of the chemical and physical phenomena governing these processes.

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.

This study addresses the thermal stability and degradation path of symmetric and asymmetric PS-b-PMMA block copolymers, widely employed to generate templates for nanopatterned materials, and of the associated P(S-r-MMA) random copolymers, through a combination of TGA and TGA-GC-MS techniques. The monomer evolution under isothermal and dynamic conditions was able to delineate the thermal degradation characteristics of all the copolymers. Although the temperature corresponding to the maximum of the main monomer loss is similar for the random and block copolymers, the onset of the main degradation for the random copolymers is observed at a temperature about 50 degrees C lower than the one for the block copolymers. In addition, the degradation profile of the random copolymers is highly asymmetrical in the low temperature side. This is partially due to the presence of TEMPO end groups, which behave as weak links. The successive evolution of the two monomers in the random copolymers occurs in a parallel fashion, indicating the occurrence of depolymerization via an unzipping process. In contrast, in case of the block copolymers, the two chemically different blocks depolymerize at different temperatures due to their distinct thermal stabilities and different end groups nature. Considering the overall system, comprising the block copolymer film on the grafted random copolymer layer, the monomer volatilization which occurs when the random copolymer is heated at temperatures equal or above 280 degrees C, leads to a reduced control of morphology orientation in the microdomains of the block copolymer film with an eventual local detachment of the block copolymer films. These results clearly indicate that the range of accessible temperature in the processing of these self-assembling materials is mainly limited by the instability of the grafted RCP layer.

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.