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The public sector, private firms, business community, and civil society are generating data that is high in volume, veracity, velocity and comes from a diversity of sources. This kind of data is known as big data. Public Administrations (PAs) pursue big data as “new oil” and implement data-centric policies to transform data into knowledge, to promote good governance, transparency, innovative digital services, and citizens’ engagement in public policy. From the above, the Government Big Data Ecosystem (GBDE) emerges. Managing big data throughout its lifecycle becomes a challenging task for governmental organizations. Despite the vast interest in this ecosystem, appropriate big data management is still a challenge. This study intends to fill the above-mentioned gap by proposing a data lifecycle framework for data-driven governments. Through a Systematic Literature Review, we identified and analysed 76 data lifecycles models to propose a data lifecycle framework for data-driven governments (DaliF). In this way, we contribute to the ongoing discussion around big data management, which attracts researchers’ and practitioners’ interest.

The implementation of dense, one-selector one-resistor (1S1R), resistive switching memory arrays, can be achieved with an appropriate selector for correct information storage and retrieval. Ovonic threshold switches (OTS) based on chalcogenide materials are a strong candidate, but their low thermal stability is one of the key factors that prevents rapid adoption by emerging resistive switching memory technologies. A previously developed map for phase change materials is expanded and improved for OTS materials. Selected materials from different areas of the map, belonging to binary Ge-Te and Si-Te systems, are explored. Several routes, including Si doping and reduction of Te amount, are used to increase the crystallization temperature. Selector devices, with areas as small as 55 × 55 nm2, were electrically assessed. Sub-threshold conduction models, based on Poole-Frenkel conduction mechanism, are applied to fresh samples in order to extract as-processed material parameters, such as trap height and density of defects, tailoring of which could be an important element for designing a suitable OTS material. Finally, a glass transition temperature estimation model is applied to Te-based materials in order to predict materials that might have the required thermal stability. A lower average number of p-electrons is correlated with a good thermal stability.

The large effects of moderate stresses on the crystal growth rate in Ge-doped Sb phase-change thin films are demonstrated using direct optical imaging. For Ge6Sb94 and Ge7Sb93 phase-change films, a large increase in crystallization temperature is found when using a polycarbonate substrate instead of a glass substrate. This increase is attributed to the tensile thermal stress induced in the phase-change film due to a difference in thermal expansion coefficient between the film and the polycarbonate substrate. By applying a uniaxial compressive stress to a phase-change film, we show and explain that isotropic crystal growth becomes unidirectional (perpendicular to the uniaxial stress) with a strongly enhanced growth rate. This is a direct proof that modest stresses can have large consequences for the amorphous phase stability and for the crystal growth rates, and these stresses are thus highly relevant for memories based on phase-change materials.

Chalcogenide-based nanostructured phase-change materials (PCMs) are considered promising building blocks for non-volatile memory due to their high write and read speeds, high data-storage density, and low power consumption. Top-down fabrication of PCM nanoparticles (NPs), however, often results in damage and deterioration of their useful properties. Gas-phase condensation based on magnetron sputtering offers an attractive and straightforward solution to continuously down-scale the PCMs into sub-lithographic sizes. Here we unprecedentedly present the size dependence of crystallization for Ge2Sb2Te5 (GST) NPs, whose production is currently highly challenging for chemical synthesis or top-down fabrication. Both amorphous and crystalline NPs have been produced with excellent size and composition control with average diameters varying between 8 and 17 nm. The size-dependent crystallization of these NPs was carefully analyzed through in-situ heating in a transmission electron microscope, where the crystallization temperatures (Tc) decrease when the NPs become smaller. Moreover, methane incorporation has been observed as an effective method to enhance the amorphous phase stability of the NPs. This work therefore elucidates that GST NPs synthesized by gas-phase condensation with tailored properties are promising alternatives in designing phase-change memories constrained by optical lithography limitations.

A long-standing question for avant-garde data storage technology concerns the nature of the ultrafast photoinduced phase transformations in the wide class of chalcogenide phase-change materials (PCMs). Overall, a comprehensive understanding of the microstructural evolution and the relevant kinetics mechanisms accompanying the out-of-equilibrium phases is still missing. Here, after overheating a phase-change chalcogenide superlattice by an ultrafast laser pulse, we indirectly track the lattice relaxation by time resolved x-ray absorption spectroscopy (tr-XAS) with a sub-ns time resolution. The approach to the tr-XAS experimental results reported in this work provides an atomistic insight of the mechanism that takes place during the cooling process; meanwhile a first-principles model mimicking the microscopic distortions accounts for a straightforward representation of the observed dynamics. Finally, we envisage that our approach can be applied in future studies addressing the role of dynamical structural strain in PCMs.

Phase change materials (PCMs) can be rapidly and reversibly switched between the amorphous and crystalline state. The structural transformation is accompanied by a significant change of optical and electronic properties rendering PCMs suitable for rewritable optical data storage and non-volatile electronic memories. The phase transformation is also accompanied by an increase of the Casimir force of 20 to 25% between gold and AIST (Ag5In5Sb60Te30) upon crystallization. Here the focus is on reproducing and understanding the observed change in Casimir force, which is shown to be related to a change of the dielectric function upon crystallization. The dielectric function changes in two separate frequency ranges: the increase of absorption in the visible range is due to resonance bonding, which is unique for the crystalline phase, while free carrier absorption is responsible for changes in the infrared regime. It is shown that free carriers contribute 50% to the force contrast, while the other half comes from resonance bonding. This helps to identify PCMs that maximize force contrast. Finally it is shown that if this concept of force control is to be employed in microelectromechanical devices, then protective capping layers of PCMs must be only a few nanometers thick to minimize reduction of the force contrast.

A computer-controlled procedure is outlined here that first determines the position of the amorphous-crystalline interface in an image. Subsequently, from a time series of these images, the velocity of the crystal growth front is quantified. The procedure presented here can be useful for a wide range of applications, and we apply the new approach to determine growth rates in a so-called fast-growth-type phase-change material. The growth rate (without nucleation) of this material is of interest for comparison with identical material used in phase-change random access memory cells. Crystal growth rates in the amorphous phase-change layers have been measured at various temperatures using in situ heating in a transmission electron microscope. Doped SbTe films (20 nm thick) were deposited on silicon nitride membranes, and samples with and without silicon oxide capping layer were studied. The activation energy for growth was found to be 3.0 eV. The samples without capping layer exhibit a nucleation rate that is an order of magnitude higher than the samples with a silicon oxide capping layer. This difference can be attributed to the partial oxidation of the phase-change layer in air. However, the growth rates of the samples with and without capping are quite comparable.

The technological success of phase-change materials in the field of data storage and functional systems stems from their distinctive electronic and structural peculiarities on the nanoscale. Recently, superlattice structures have been demonstrated to dramatically improve the optical and electrical performances of these chalcogenide based phase-change materials. In this perspective, unravelling the atomistic structure that originates the improvements in switching time and switching energy is paramount in order to design nanoscale structures with even enhanced functional properties. This study reveals a high-resolution atomistic insight of the [GeTe/Sb2Te3] interfacial structure by means of Extended X-Ray Absorption Fine Structure spectroscopy and Transmission Electron Microscopy. Based on our results we propose a consistent novel structure for this kind of chalcogenide superlattices.

peer-reviewed Cloud computing has now emerged as popular computing paradigm for data storage and computation for enterprises and individuals. Its major characteristics include the pay-per-use pricing model, where users pay only for the resources they consume with no upfront cost for hardware/software infrastructures, and the capability of providing scalable and unlimited storage and computation resources to meet changing business needs of enterprises with minimal management overhead [1]. The cloud, however, presents a major limitation to enterprises and individuals who move to public clouds: they lose control over the systems that manage their data and applications, leading to increased security and privacy concerns [2,3,4]. In this article, we examine cloud privacy concerns, and provide an overview of current and emerging solutions for protecting privacy of data and applications deployed in the cloud. Based on this, we suggest a set of recommendations for practitioners and researchers to improve privacy protection of cloud users.

Scientific reports 6, 22353 (2016). doi:10.1038/srep22353, Published by Nature Publishing Group, London

The electrical properties of amorphous-crystalline interfaces in phase change materials, which are important for rewritable optical data storage and for random access memory devices, have been investigated by surface scanning potential microscopy. Analysis of GeSb systems indicates that the surface potential of the crystalline phase is similar to 30-60 mV higher than that of the amorphous phase. This potential asymmetry is explained qualitatively by the presence of a Schottky barrier at the amorphous-crystalline interface and supported also by quantitative Schottky model calculations. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3691179]

With the recent exponential growth of applications using artificial intelligence (AI), the development of efficient and ultrafast brain-like (neuromorphic) systems is crucial for future information and communication technologies. While the implementation of AI systems using computer algorithms of neural networks is emerging rapidly, scientists are just taking the very first steps in the development of the hardware elements of an artificial brain, specifically neuromorphic microchips. In this review article, we present the current state of neuromorphic photonic circuits based on solid-state optoelectronic oscillators formed by nanoscale double barrier quantum well resonant tunneling diodes. We address, both experimentally and theoretically, the key dynamic properties of recently developed artificial solid-state neuron microchips with delayed perturbations and describe their role in the study of neural activity and regenerative memory. This review covers our recent research work on excitable and delay dynamic characteristics of both single and autaptic (delayed) artificial neurons including all-or-none response, spike-based data encoding, storage, signal regeneration and signal healing. Furthermore, the neural responses of these neuromorphic microchips display all the signatures of extended spatio-temporal localized structures (LSs) of light, which are reviewed here in detail. By taking advantage of the dissipative nature of LSs, we demonstrate potential applications in optical data reconfiguration and clock and timing at high-speeds and with short transients. The results reviewed in this article are a key enabler for the development of high-performance optoelectronic devices in future high-speed brain-inspired optical memories and neuromorphic computing., 26 pages, 18 figures, Accepted in Chaos special issue on Time-delay Dynamics

It has been suggested that a single photon can interfere with itself even if the difference between the two paths in the interferometer is larger than the “length” of the photon [Kessel’ and Moiseev, JETP Lett. 58, 81 (1993)]. The interference is regained by detecting the photons using a photon-echo process, where the absorbing atoms will, effectively, act as narrow-band filters. Such an experiment has several unique features. For example, single photons are used to carry out what is generally regarded as a multiphoton process; the absorption of a single photon can be regarded as separated into two different moments in time; the fact that the single-photon interference is regained using atoms acting as narrow-band filters as the detector means that the control of the detection process is quite different from cases where electronic (or possibly photographic) detection is used to register the interference etc. In general, interference and absorption are combined and intertwined in the experiment, which is discussed in this paper, in a way that has not been done before. In the present paper the possibility to carry out such an experiment in practice is investigated in some detail. The signal strength is explicitly calculated and the results are compared with our experimental data for the case of many interfering photons. We imply that this result can readily be extrapolated to the single-photon situation. We analyze the material parameters that are important for carrying out the experiment and give specific examples of some suitable materials.

Colloidal magnetic nanoparticles (MNPs) based on a nearly monodisperse iron oxide core and capped by oleic acid have been used as model systems for investigating the superparamagnetic spin dynamics by means of magnetometry measurements and nuclear magnetic resonance (H-1 NMR) relaxometry. The key magnetic properties (saturation magnetization, coercive field, and frequency dependent "blocking" temperature) of MNPs with different core size (3.5 nm, 8.5 nm, and 17.5 nm), shape (spherical and cubic), and dispersant (hexane and water-based formulation) have been determined. H-1 NMR dispersion profiles obtained by measuring the r(1) (longitudinal) and r(2) (transverse) nuclear relaxivities in the frequency range 0.01-60 MHz confirmed that in all samples the physical mechanisms that drive the nuclear relaxation are the Neel reversal at low temperature and the Curie relaxation at high frequency. The magnetization reversal time at room temperature extracted from the fitting of NMR data falls in the typical range of superparamagnetic systems (10(-9)-10(-10) s). Furthermore, from the distance of minimum approach we could conclude that water molecules do not arrive in close vicinity of the magnetic core. Our findings contribute to elucidate the local spin dynamics mechanisms in colloidal superparamagnetic nanoparticles which are useful in biomedical application as, e.g., contrast agents for magnetic resonance imaging.

Ferroelectric nanodomains can be created by the application of a bias voltage to the sharp conducting tip of a scanning force microscope (SFM) contacting the sample surface. Since an inhomogeneous electric field created by an SFM tip has maximum intensity along the surface normal, in multiaxial ferroelectrics the polarization inside these domains also tends to orient perpendicularly to the surface. Here we show theoretically that unusual domains can be created in uniaxial ferroelectrics when the SFM tip is applied to the crystal surface parallel to the polar axis. These 180 degrees nanodomains have polarization directed along the surface and should appear in LiNbO3 and LiTaO3 crystals at moderate tip voltages well below 100 V. Calculations of equilibrium domain dimensions demonstrate that subsurface domains have the shape of a needle oriented along the polar axis.

International audience; A Calvet-type differential scanning calorimeter has been implemented on a synchrotron beamline devoted to X-ray absorption spectroscopy. As a case study, the complex crystallization process in amorphous Ge(15)Sb(85) phase-change material is followed by simultaneous calorimetric and quick-EXAFS measurements. A first crystallization at 514(1) K is related to the crystallization of an Sb-rich phase accompanied by segregation of Ge atoms. Upon further heating, the as-formed amorphous Ge regions crystallize at 604(1) K. A quantitative analysis of the latent heat allows a Ge(11)Sb(89) stoichiometry to be proposed for the first crystallized phase.

The crystallization of amorphous GexTe1-x (x = 0.36,0.51, 0.63) films (50 nm) has been investigated by time resolved reflectivity, transmission electron microscopy, Raman spectroscopy and X-ray diffraction. The Ge-rich film has the highest crystallization temperature (354 degrees C) with respect to both GeTe (180 degrees C) and Te-rich samples(244 degrees C). In non-stoichiometric films, the precipitation of the excess atomic species is the first step during the crystallization process: amorphous Ge and crystalline Te precipitates were detected in Ge and Te rich alloys, respectively. The atomic interdiffusivity was estimated to be similar to 5x10(-15) cm(2)/s at 220 degrees C in the Te-rich alloy and similar to 4x(10-14) cm(2)/s in the Ge-rich film at 330 degrees C. In both cases Tellurium is likely to be the diffusing species. This description accounts for the presence of amorphous Ge precipitates at the initial stage of the crystallization of the Ge rich alloy. The GeTe crystalline grains subsequently act as a seed for Ge crystallization. Non stoichiometric crystalline alloys have been reamorphized by laser or ion irradiation. In laser irradiated samples, the crystallization is similar to that of as deposited film since the precipitates mix with GeTe during the melt duration. In ion implanted samples this mixing doesn't occur and GeTe crystallization temperature is close to that of stoichiometric film.

High diffraction efficiencies have been achieved with polarization gratings recorded in thin films of an azobenzene side-chain liquid crystalline polyester by means of biphotonic processes. Efficiency values up to 30% have been reached after an induction period of 300 s and subsequent evolution with the sample in darkness. These values are at least two orders of magnitude higher than those previously reported for biphotonic recording. The gratings can be erased with unpolarized blue light and partial recovery of the diffraction efficiency has been observed after the erasure process when the sample is kept in darkness. Red light illumination of the erased film increases the recovered efficiency value and the recovery rate.

In recent years, many nanophotonic devices have been developed. Much attention has been given to the waveguides carrying surface plasmon polariton modes with subwavelength confinement and long propagation length. However, coupling far field light into a nano structure is a significant challenge. In this work, we present an architecture that enables high efficiency excitation of nanoscale waveguides in the direction normal to the waveguide. Our approach employs a bowtie aperture to provide both field confinement and high transmission efficiency. More than six times the power incident on the open area of the bowtie aperture can be coupled into the waveguide. The intensity in the waveguide can be more than twenty times higher than that of the incident light, with mode localization better than lambda(2)/250. The vertical excitation of waveguide allows easy integration. The bowtie aperture/waveguide architecture presented in this work will open up numerous possibilities for the development of nanoscale optical systems for applications ranging from localized chemical sensing to compact communication devices.

The crystallization of amorphous Ge(2)Sb(2)Te(5) thin films has been studied by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The analysis has been performed on partially crystallized films, with a surface crystalline fraction (f(S)) ranging from 20% to 100%. XRD analysis indicates the presence, in the partially transformed layer, of grains with average lattice parameters higher than that of the equilibrium metastable cubic phase (from 6.06 angstrom at f(S)=20% to 6.01 angstrom at f(S)=100%). The amorphous to crystal transition, as shown by TEM analysis, occurs through the nucleation of face-centered-cubic crystal domains at the film surface. Local dimples appear in the crystallized areas, due to the higher atomic density of the crystal phase compared to the amorphous one. At the initial stage of the transformation, a fast bi-dimensional growth of Such crystalline nucleus occurs by the generation of transrotational grains in which the lattice bending gives rise to an average lattice parameter significantly larger than that of the face-centered-cubic phase in good agreement with the XRD data. As the crystallized fraction increases above 80%, dimples and transrotational structures start to disappear and the lattice parameter approaches the bulk value.

International audience; Phase-change materials are successfully employed in optical data storage and are becoming a promising candidate for future electronic storage applications. Despite the increasing technological interest, many fundamental properties of these materials remain poorly understood. However, in the last few years the understanding of the material properties of phase-change materials has increased significantly. At the same time, great advances have been achieved in technological applications in electronic as well as optical data storage. We review the latest scientific and technological developments in the field, focusing on the electronic, optical, and kinetic properties of phase-change materials.

Nanoscale ridge aperture antennas have been shown to have high transmission efficiency and confined nanoscale radiation in the near field region compared with regularly-shaped apertures. The radiation enhancement is attributed to the fundamental electric-magnetic field propagating in the TE(10) mode concentrated in the gap between the ridges. This paper reports experimental demonstration of field enhancement using such ridge antenna apertures in a bowtie shape for the manufacture of nanometer size structures using an NSOM (near field scanning optical microscopy) probe integrated with nanoscale bowtie aperture. Consistent lines with width of 59 nm and as small as 24 nm have be written on photoresist using such probes.

We derive the response of a volume grating to arbitrary small deformations, using a perturbative approach. This result is of interest for two applications: (a) when a deformation is undesirable and one seeks to minimize the diffracted field's sensitivity to it and (b) when the deformation itself is the quantity of interest and the diffracted field is used as a probe into the deformed volume where the hologram was originally recorded. We show that our result is consistent with previous derivations motivated by the phenomenon of shrinkage in photopolymer holographic materials. We also present the analysis of the grating's response to deformation due to a point indenter and present experimental results consistent with theory. (c) 2005 Optical Society of America.

We compare the system performances of two holographic recording geometries using iron-doped lithium niobate: the 90-degree and transmission geometry. We find that transmission geometry is better because the attainable dynamic range (M/#) is much higher. The only drawback of transmission geometry is the buildup of fanning, particularly during readout. Material solutions that reduce fanning such as doubly-doped photorefractive crystals make transmission geometry the clear winner. (C) 2003 Optical Society of America.

The reversible amorphous-crystalline phase change in a chalcogenide material, specifically the Se1-xTex alloy, has been investigated for the first time using ultrafast differential scanning calorimetry. Heating rates and cooling rates up to 5000 K/s were used. Repeated reversible amorphous-crystalline phase switching was achieved by consecutively melting, melt-quenching, and recrystallizing upon heating. Using a well-conditioned method, the composition of a single sample was allowed to shift slowly from 15 at. % Te to 60 at. % Te, eliminating sample-to-sample variability from the measurements. Using Energy Dispersive X-ray Spectroscopy composition analysis, the onset of melting for different Te-concentrations was confirmed to coincide with the literature solidus line, validating the use of the onset of melting T-m as a composition indicator. The glass transition T-g and crystallization temperature T-c could be determined accurately, allowing the construction of extended phase diagrams. It was found that T-m and T-g increase (but T-g/T-m decrease slightly) with increasing Te-concentration. Contrarily, the T-c decreases substantially, indicating that the amorphous phase becomes progressively unfavorable. This coincides well with the observation that the critical quench rate to prevent crystallization increases about three orders of magnitude with increasing Te concentration. Due to the employment of a large range of heating rates, non-Arrhenius behavior was detected, indicating that the undercooled liquid SeTe is a fragile liquid. The activation energy of crystallization was found to increase 0.5-0.6 eV when the Te concentration increases from 15 to 30 at. % Te, but it ceases to increase when approaching 50 at. % Te. (C) 2014 AIP Publishing LLC.

Data erasure is considered an essential requirement for a practical optical time-domain memory, and it requires that the laser used have very good frequency stability. Such a laser is developed for this work, and data erasure is demonstrated with a sample of YSiO5:Eu3+ for write/rewrite pulse sequences of up to a duration of 100 μs. This is two orders of magnitude longer than had been achieved previously. Phase-sensitive detection is introduced and is shown to be invaluable for monitoring the write, rewrite, and read processes.

The effect of random laser phase fluctuations on stimulated photon echoes (SPEs) and on coherently added SPEs was studied and evaluated both experimentally and analytically with statistical methods. The general concept of describing laser frequency fluctuations as a stationary stochastic process is presented and applied to three specific SPE configurations. The effect of phase fluctuations on erasing an SPE by coherently adding another SPE, phase-shifted by 180 degrees relative to the first, is presented.

We report results of parallel optical nanolithography using nanoscale bowtie aperture array. These nanoscale bowtie aperture arrays are used to focus a laser beam into multiple nanoscale light spots for parallel nano-lithography. Our work employed a frequency-tripled diode-pumped solid state (DPSS) laser (lambda = 355 nm) and Shipley S1805 photoresist. An interference-based optical alignment system was employed to position the bowtie aperture arrays with the photoresist surface. Nanoscale direct-writing of sub-100nm features in photoresist in parallel is demonstrated.

Ridge nanoscale aperture antennas have been shown to be a high transmission nanoscale light source. They provide a small, polarization-dependent near-field optical spot with much higher transmission efficiency than circularly-shaped apertures with similar field confinement. This provides significant motivations to understand the electromagnetic fields in the immediate proximity to the apertures. This paper describes an experimental three-dimensional optical near-field mapping of a bowtie nano-aperture. The measurements are performed using a home-built near-field scanning optical microscopy (NSOM) system. An aluminum coated Si(3)N(4) probe with a 150 nm hole at the tip is used to collect optical signals. Both contact and constant-height scan (CHS) modes are used to measure the optical intensity at different longitudinal distances. A force-displacement curve is used to determine the tip-sample separation distance allowing the optical intensities to be mapped at distances as small as 50 nm and up to micrometer level. The experimental results also demonstrate the polarization dependence of the transmission through the bowtie aperture. Numerical simulations are also performed to compute the aperture's electromagnetic near-field distribution and are shown to agree with the experimental results.

Isothermal crystallization of amorphous SbxTe films capped with ZnS-SiO2 or GeCrN layers was performed using in situ heating within a transmission electron microscope. The effect of the electron beam of the microscope on the crystallization process was investigated. It was found that electron irradiation during the crystallization process leads to a continuous increase in the crystal growth velocity. For SbxTe sandwiched between ZnS-SiO2 the effect of the electron beam was equivalent to a temperature rise of about 10 K, without affecting the activation energy for growth. However, for SbxTe sandwiched between GeCrN the activation energy for growth was also decreased due to electron beam exposure. The observed variations in the crystal growth rates are attributed to relaxations within the initial amorphous phase initiated by thermal energy and/or electron irradiation.

Fundamental aspects and state-of-the-art results of thermal scanning probe lithography (t-SPL) are reviewed here. t-SPL is an emerging direct-write nanolithography method with many unique properties which enable original or improved nano-patterning in application fields ranging from quantum technologies to material science. In particular, ultrafast and highly localized thermal processing of surfaces can be achieved through the sharp heated tip in t-SPL to generate high-resolution patterns. We investigate t-SPL as a means of generating three types of material interaction: removal, conversion, and addition. Each of these categories is illustrated with process parameters and application examples, as well as their respective opportunities and challenges. Our intention is to provide a knowledge base of t-SPL capabilities and current limitations and to guide nanoengineers to the best-fitting approach of t-SPL for their challenges in nanofabrication or material science. Many potential applications of nanoscale modifications with thermal probes still wait to be explored, in particular when one can utilize the inherently ultrahigh heating and cooling rates. Review: Thermal scanning probe lithographyThermal scanning probe lithography is reviewed in the context of material removal, conversion and deposition. Scanning probe lithography has long been a promising technique for direct-write nanoscale patterning on surfaces. However, while the technique is widely used in research labs, the slow write speed has limited its use in industrial settings. Instead, thermal scanning probe lithography has emerged, in which a heated tip is used to induce localized changes in the material, enabling write speeds limited by the speed of movement of the tip itself. A team from Ecole Polytechnique Federale de Lausanne led by Juergen Brugger now reviews the current state of play for thermal scanning probe lithography, focusing on whether material is removed, changed or deposited by the heated tip, and the types of materials that have been studied.

The prospect of massive parallelism of optics enabling fast and low energy cost operations is attracting interest for novel photonic circuits where 3-dimensional (3D) implementations have a high potential for scalability. Since the technology for data input-output channels is 2-dimensional (2D), there is an unavoidable need to take 2D-nD transformations into account. Similarly, the 3D-2D and its reverse transformations are also tackled in a variety of fields such as optical tomography, additive manufacturing, and 3D optical memories. Here, we review how these 3D-2D transformations are tackled using iterative techniques and neural networks. This high-level comparison across different, yet related fields could yield a useful perspective for 3D optical design.

WE examine the present state of holographic random access memory (HRAM) systems and address the primary challenges that face this technology, specifically size, speed, and cost. We show that a fast HRAM system can be implemented with a compact architecture by incorporating conjugate readout, a smart-pixel array, and a linear array of laser diodes. Preliminary experimental results support the feasibility of this architecture. Our analysis shows that in order for the HRAM to become competitive, the principal tasks will be to reduce spatial light modulator (SLM) and detector pixel sizes to I mu m, increase the output power of compact visible-wavelength lasers to several hundred milliwatts, and develop ways to raise the sensitivity of holographic media to the order of 1 cm/J.

We describe a two-center holographic recording method for the storage of persistent holograms in doubly doped lithium niobate crystals. We use a two-center model, and we show that our experimental observations can be explained by the model. We describe experimental methods for finding the unknown material parameters of LiNbO3:Fe:Mn crystals for the two-center model, and we discuss the optimization of two-center recording. (C) 2001 Optical Society of America.