Artificial intelligence (AI) is gaining strength, and materials science can both contribute to and profit from it. In a simultaneous progress race, new materials, systems, and processes can be ...devised and optimized thanks to machine learning (ML) techniques, and such progress can be turned into innovative computing platforms. Future materials scientists will profit from understanding how ML can boost the conception of advanced materials. This review covers aspects of computation from the fundamentals to directions taken and repercussions produced by computation to account for the origins, procedures, and applications of AI. ML and its methods are reviewed to provide basic knowledge of its implementation and its potential. The materials and systems used to implement AI with electric charges are finding serious competition from other information‐carrying and processing agents. The impact these techniques have on the inception of new advanced materials is so deep that a new paradigm is developing where implicit knowledge is being mined to conceive materials and systems for functions instead of finding applications to found materials. How far this trend can be carried is hard to fathom, as exemplified by the power to discover unheard of materials or physical laws buried in data.
Artificial intelligence in general and machine learning in particular are gaining ever more importance in science and technology. In materials science, they are taking over tedious screening tasks and helping design and discover materials based on both explicit and tacit previous knowledge possessed by the scientist. Social and humanistic aspects are acquiring tremendous importance, as power and explainability seem to grow at the expense of each other.
The True Value of Disorder López, Cefe
Advanced optical materials,
August 20, 2018, Volume:
6, Issue:
16
Journal Article
Border regions between areas where physical problems involve very few bodies with well‐described interactions or immensely many (amenable to statistical description) are prone to fall in the category ...usually associated with complexity. Disorder is an important factor to consider when examining complexity. Disordered optical materials per se would not qualify as complex but when disorder is partial or merely incipient or nonlinear interactions are included, an entirely new character is added. Here, attention is paid to three examples of these kinds of optical systems. The propagation of light through diffusive media and image formation behind an opaque screen is proposed as a problem where an exact computable solution can be expected but is impractical. Analysis shows that the problem is akin to condensed matter physics concepts related to narrow leads conductance. Another condensed matter related phenomenon brought to photonics is that of localization: disorder can induce a cessation of transport when interference of scattered fields is destructive in all directions forcing light to be exponentially confined. Finally, random lasers are a problem where a disordered, open, photonic system is governed by immensely many modes interacting nonlinearly.
From a proper definition or conceptual homogenization across disciplines to a practical measuring protocol, complexity remains a source of profound questions and a fertile ground of research. In most cases, complexity is accompanied by disorder but the most likely setting is a region where neither full order nor full disorder properly describes the problem. In this scenario, new tools and attitudes are wanted.
Photonic crystals have proven their potential and are nowadays a familiar concept. They have been approached from many scientific and technological flanks. Among the many techniques devised to ...implement this technology self‐assembly has always been one of great popularity surely due to its ease of access and the richness of results offered. Self‐assembly is also probably the approach entailing more materials aspects owing to the fact that they lend themselves to be fabricated by a great many, very different methods on a vast variety of materials and to multiple purposes. To these well‐known material systems a new sibling has been born (photonic glass) expanding the paradigm of optical materials inspired by solid state physics crystal concept. It is expected that they may become an important player in the near future not only because they complement the properties of photonic crystals but because they entice the researchers’ curiosity. In this review a panorama is presented of the state of the art in this field with the view to serve a broad community concerned with materials aspects of photonic structures and more so those interested in self‐assembly.
Photonic crystals and, more recently, photonic glasses embody concepts that capture the essence of solid state physics and many aspects of materials science, bringing them together in the field of photonic materials. Self‐assembly and colloidal techniques constitute proven bottom‐up methods that have spread and are very popular nowadays. Characterization and modelling techniques develop abreast of applications. The illustration is an optical microscope image of a self‐assembled photonic crystal where terraces of different thicknesses can be distinguished by their color. Near the terraces’ edges crystal orientation usually changes and can be appreciated by their color.
Self-assembly of colloidal particles into ordered superstructures is an important strategy to discover new materials, such as catalysts, plasmonic sensing materials, storage systems, and photonic ...crystals (PhCs). Here we show that porous covalent organic frameworks (COFs) can be used as colloidal building particles to fabricate porous PhCs with an underlying face-centered cubic (fcc) arrangement. We demonstrate that the Bragg reflection of these can be tuned by controlling the size of the COF particles and that species can be adsorbed within the pores of the COF particles, which in turn alters the Bragg reflection. Given the vast number of existing COFs, with their rich properties and broad modularity, we expect that our discovery will enable the development of colloidal PhCs with unprecedented functionality.
Electrically pumped random lasers with distributed feedback can be obtained by introducing random defects into the device active layer, modifying the epitaxial growth process and losing the ease of ...fabrication potentially offered by disordered structures. We recently demonstrated an alternative and more practical approach in which random lasing emission is obtained from a modified Fabry-Perot laser diode after pulsed laser ablation of its output mirror. Here, we improve our fabrication technique by sweeping the ablating laser beam along the output mirror at different speeds and with different pulse energies, obtaining control over the total energy delivered at each point. We optimize the ablation parameters by evaluating the device performances in terms of lasing threshold and output power and we present the device emission characteristics. The proposed technique is tunable, fast and reliable, allowing the fabrication of devices with different properties by proper selection of the ablation parameters.
Intensity fluctuations in lasers are commonly studied above threshold in some special configurations (especially when emission is fed back into the cavity or when two lasers are coupled) and related ...with their chaotic behaviour. Similar fluctuating instabilities are usually observed in random lasers, which are open systems with plenty of quasi-modes whose non orthogonality enables them to exchange energy and provides the sort of loss mechanism whose interplay with pumping leads to replica symmetry breaking. The latter however, had never been observed in plain cavity lasers where disorder is absent or not intentionally added. Here we show a fluctuating lasing behaviour at the lasing threshold both in solid and liquid dye lasers. Above and below a narrow range around the threshold the spectral line-shape is well correlated with the pump energy. At the threshold such correlation disappears, and the system enters a regime where emitted laser fluctuates between narrow, intense and broad, weak peaks. The immense number of modes and the reduced resonator quality favour the coupling of modes and prepares the system so that replica symmetry breaking occurs without added disorder.
Two major elements are required in a laser device: light confinement and light amplification. Light confinement is obtained in optical cavities by employing a pair of mirrors or by periodic spatial ...modulation of the refractive index as in photonic crystals and Bragg gratings. In random lasers, randomly placed nanoparticles embedded in the active material provide distributed optical feedback for lasing action. Recently, we demonstrated a novel architecture in which scattering nanoparticles and active element are spatially separated and random lasing is observed. Here we show that this approach can be extended to scattering media with macroscopic size, namely, a pair of sand grains, which act as feedback elements and output couplers, resulting in lasing emission. We demonstrate that the number of lasing modes depends on the surface roughness of the sand grains in use which affect the coherent feedback and thus the emission spectrum. Our findings offer a new perspective of material science and photonic structures, facilitating a novel and simple approach for the realization of new photonics devices based on natural scattering materials.
Self-assembly of particles into long-range, three-dimensional, ordered superstructures is crucial for the design of a variety of materials, including plasmonic sensing materials, energy or gas ...storage systems, catalysts and photonic crystals. Here, we have combined experimental and simulation data to show that truncated rhombic dodecahedral particles of the metal-organic framework (MOF) ZIF-8 can self-assemble into millimetre-sized superstructures with an underlying three-dimensional rhombohedral lattice that behave as photonic crystals. Those superstructures feature a photonic bandgap that can be tuned by controlling the size of the ZIF-8 particles and is also responsive to the adsorption of guest substances in the micropores of the ZIF-8 particles. In addition, superstructures with different lattices can also be assembled by tuning the truncation of ZIF-8 particles, or by using octahedral UiO-66 MOF particles instead. These well-ordered, sub-micrometre-sized superstructures might ultimately facilitate the design of three-dimensional photonic materials for applications in sensing.
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