Recent Submissions

  • Metal Contact and Carrier Transport in Single Crystalline CH3NH3PbBr3 Perovskite

    Lin, Chun-Ho; Li, Ting-You; Cheng, Bin; Liu, Changxu; Yang, Chih-Wen; Ke, Jr-Jian; Wei, Tzu-Chiao; Li, Lain-Jong; Fratalocchi, Andrea; He, Jr-Hau (Nano Energy, Elsevier BV, 2018-09-21) [Article]
    Organic-inorganic perovskites have arrived at the forefront of solar technology due to their impressive carrier lifetimes and superior optoelectronic properties. By having the cm-sized perovskite single crystal and employing device patterning techniques, and the transfer length method (TLM), we are able to get the insight into the metal contact and carrier transport behaviors, which is necessary for maximizing device performance and efficiency. In addition to the metal work function, we found that the image force and interface charge pinning effects also affect the metal contact, and the studied single crystal CH3NH3PbBr3 features Schottky barriers of 0.17 eV, 0.38 eV, and 0.47 eV for Au, Pt, and Ti electrodes, respectively. Furthermore, the surface charges lead to the thermally activated transport from 207 K to 300 K near the perovskite surface. In contrast, from 120 K to 207 K, the material exhibited three-dimensional (3D) variable range hopping (VRH) carrier transport behavior. Understanding these fundamental contact and transport properties of perovskite will enable future electronic and optoelectronic applications.
  • Photo-induced THz Plasmonics in Black Silicon

    Peters, L.; Gongora, J. S. Totero; Tunesi, J.; Pasquazi, A.; Fratalocchi, Andrea; Peccianti, M. (Advanced Photonics 2018 (BGPP, IPR, NP, NOMA, Sensors, Networks, SPPCom, SOF), The Optical Society, 2018-06-28) [Conference Paper]
    We experimentally investigated a novel form of photo-induced plasmonic response, in nanostructured silicon, at THz frequencies which can be employed to precisely control the full-wave properties, i.e. amplitude and phase, of the generated THz pulse.
  • X-ray created metamaterials: applications to metal-free structural colors with full chromaticity spectrum and 80 nm spatial resolution

    Bonifazi, Marcella; Mazzone, Valerio; Fratalocchi, Andrea (Conference on Lasers and Electro-Optics, The Optical Society, 2018-05-07) [Conference Paper]
    We created new types of metamaterials by hard X-rays possessing high fluency. We discuss applications in structural colors that show full spectrum of Cyan, Yellow, Magenta, Black (CYMK), realized in transparent dielectrics with 80 nm resolution.
  • Complex epsilon-near-zero metamaterials for broadband light harvesting systems

    Bonifazi, Marcella; Tian, Yi; Fratalocchi, Andrea (Physics, Simulation, and Photonic Engineering of Photovoltaic Devices VII, SPIE-Intl Soc Optical Eng, 2018-02-17) [Conference Paper]
    We engineered an epsilon-near-zero (ENZ) material from suitably disordered metallic nanostructures. We create a new class of dispersionless composite materials that efficiently harnesses white light. By means of Atomic Force Microscopy (AFM) and Photoluminescence (PLE) measurements we experimentally demonstrate that this nanomaterial increases up to a record value the absorption of ultra-thin light harvesting films at visible and infrared wavelengths. Moreover, we obtained a 170% broadband increase of the external quantum efficiency (EQE) when these ENZ materials are inserted in an energy-harvesting module. We developed an inexpensive electrochemical deposition process that enables large-scale production of this material for energy-harvesting applications.
  • High performance nanostructured Silicon heterojunction for water splitting on large scales

    Bonifazi, Marcella; Fu, Hui-Chun; He, Jr-Hau; Fratalocchi, Andrea (2017 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC), Institute of Electrical and Electronics Engineers (IEEE), 2017-11-02) [Presentation]
    In past years the global demand for energy has been increasing steeply, as well as the awareness that new sources of clean energy are essential. Photo-electrochemical devices (PEC) for water splitting applications have stirred great interest, and different approach has been explored to improve the efficiency of these devices and to avoid optical losses at the interfaces with water. These include engineering materials and nanostructuring the device's surfaces [1]-[2]. Despite the promising initial results, there are still many drawbacks that needs to be overcome to reach large scale production with optimized performances [3]. We present a new device that relies on the optimization of the nanostructuring process that exploits suitably disordered surfaces. Additionally, this device could harvest light on both sides to efficiently gain and store the energy to keep the photocatalytic reaction active.
  • Structural colours via metal free disordered nanostructures with nm resolution and full CYMK colour spectrum

    Mazzone, Valerio; Bonifazi, Marcella; Fratalocchi, Andrea (2017 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC), Institute of Electrical and Electronics Engineers (IEEE), 2017-11-02) [Presentation]
    Engineering colors through optical properties of nanostructures represents a research area of great interest, due to the many applications that can be enabled by this technology, from adaptive camouflage to micro-images for security and biomimetic materials [1-4].
  • Ultrafast pulse generation in integrated arrays of anapole nanolasers

    Gongora, J. S. Totero; Miroshnichenko, Andrey E.; Kivshar, Yuri S.; Fratalocchi, Andrea (2017 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC), Institute of Electrical and Electronics Engineers (IEEE), 2017-11-02) [Presentation]
    One of the main challenges in photonics is the integration of ultrafast coherent sources in silicon compatible platforms at the nanoscale [1]. Generally, the emission of ultra-short pulses is achieved by synchronizing the cavity modes of the system via external active components, such as, e.g., Q-switch or saturable absorbers. Consequently, the required optical setups are complex and difficult to integrate on-chip. To address these difficulties, we propose a novel type of integrated source based on the spontaneous synchronization of several near-field nanolasers. We design our near-field lasers by considering the nonlinear amplification of non-radiating Anapole modes [2]. Anapoles represent an intriguing non-conventional state of radiation, whose excitation is responsible for the formation of scattering suppression states in dielectric nanostructures [3]. Due to their inherent near-field emission properties, an ensemble of anapole-based nanolasers represent an ideal candidate to investigate and tailor spontaneous synchronization phenomena in a silicon-compatible framework. Additionally, their mutual non-linear interaction can be precisely controlled within standard nanofabrication tolerances.
  • Route to Photo-Enabled Random Terahertz Metasurfaces

    Peters, Luke; Gongora, J. S. Totero; Tunesi, Jacob D.; Fratalocchi, Andrea; Pasquazi, Alessia; Peccianti, Marco (Advanced Photonics 2017 (IPR, NOMA, Sensors, Networks, SPPCom, PS), The Optical Society, 2017-07-17) [Conference Paper]
    We experimentally investigate the enhancement and phase change of the THz emission from photo-excited randomly structured black silicon substrates mediated by an induced metallic state of the nanostructured surface.
  • Anapole nanolasers for mode-locking and ultrafast pulse generation

    Gongora, J. S. Totero; Miroshnichenko, Andrey E.; Kivshar, Yuri S.; Fratalocchi, Andrea (Nature Communications, Springer Nature, 2017-05-31) [Article]
    Nanophotonics is a rapidly developing field of research with many suggestions for a design of nanoantennas, sensors and miniature metadevices. Despite many proposals for passive nanophotonic devices, the efficient coupling of light to nanoscale optical structures remains a major challenge. In this article, we propose a nanoscale laser based on a tightly confined anapole mode. By harnessing the non-radiating nature of the anapole state, we show how to engineer nanolasers based on InGaAs nanodisks as on-chip sources with unique optical properties. Leveraging on the near-field character of anapole modes, we demonstrate a spontaneously polarized nanolaser able to couple light into waveguide channels with four orders of magnitude intensity than classical nanolasers, as well as the generation of ultrafast (of 100 fs) pulses via spontaneous mode locking of several anapoles. Anapole nanolasers offer an attractive platform for monolithically integrated, silicon photonics sources for advanced and efficient nanoscale circuitry.
  • Near-Field Coupling and Mode Competition in Multiple Anapole Systems

    Mazzone, Valerio; Gongora, J. S. Totero; Fratalocchi, Andrea (Applied Sciences, MDPI AG, 2017-05-24) [Article]
    All-dielectric metamaterials are a promising platform for the development of integrated photonics applications. In this work, we investigate the mutual coupling and interaction of an ensemble of anapole states in silicon nanoparticles. Anapoles are intriguing non-radiating states originated by the superposition of internal multipole components which cancel each other in the far-field. While the properties of anapole states in single nanoparticles have been extensively studied, the mutual interaction and coupling of several anapole states have not been characterized. By combining first-principles simulations and analytical results, we demonstrate the transferring of anapole states across an ensemble of nanoparticles, opening to the development of advanced integrated devices and robust waveguides relying on non-radiating modes.
  • On-chip Ultrafast Pulse Generator Based on Integrated Near-field Anapole Lasers

    Gongora, J. S. Totero; Miroshnichenko, Andrey; Kivshar, Yuri; Fratalocchi, Andrea (Conference on Lasers and Electro-Optics, The Optical Society, 2017-05-08) [Conference Paper]
    We developed an all-dielectric integrated source of ultrafast optical pulses by exploiting the mutual interaction and synchronization of near-field nanolasers emitting at the anapole frequency.
  • Enhanced Solar-to-Hydrogen Generation with Broadband Epsilon-Near-Zero Nanostructured Photocatalysts

    Tian, Yi; García de Arquer, Francisco Pelayo; Dinh, Cao-Thang; Favraud, Gael; Bonifazi, Marcella; Li, Jun; Liu, Min; Zhang, Xixiang; Zheng, Xueli; Kibria, Md. Golam; Hoogland, Sjoerd; Sinton, David; Sargent, Edward H.; Fratalocchi, Andrea (Advanced Materials, Wiley, 2017-05-08) [Article]
    The direct conversion of solar energy into fuels or feedstock is an attractive approach to address increasing demand of renewable energy sources. Photocatalytic systems relying on the direct photoexcitation of metals have been explored to this end, a strategy that exploits the decay of plasmonic resonances into hot carriers. An efficient hot carrier generation and collection requires, ideally, their generation to be enclosed within few tens of nanometers at the metal interface, but it is challenging to achieve this across the broadband solar spectrum. Here the authors demonstrate a new photocatalyst for hydrogen evolution based on metal epsilon-near-zero metamaterials. The authors have designed these to achieve broadband strong light confinement at the metal interface across the entire solar spectrum. Using electron energy loss spectroscopy, the authors prove that hot carriers are generated in a broadband fashion within 10 nm in this system. The resulting photocatalyst achieves a hydrogen production rate of 9.5 µmol h-1 cm-2 that exceeds, by a factor of 3.2, that of the best previously reported plasmonic-based photocatalysts for the dissociation of H2 with 50 h stable operation.
  • Ultrahigh Carrier Mobility Achieved in Photoresponsive Hybrid Perovskite Films via Coupling with Single-Walled Carbon Nanotubes

    Li, Feng; Wang, Hong; Kufer, Dominik; Liang, Liangliang; Yu, Weili; Alarousu, Erkki; Ma, Chun; Li, Yangyang; Liu, Zhixiong; Liu, Changxu; Wei, Nini; Wang, Fei; Chen, Lang; Mohammed, Omar F.; Fratalocchi, Andrea; Liu, Xiaogang; Konstantatos, Gerasimos; Wu, Tao (Advanced Materials, Wiley, 2017-02-22) [Article]
    Organolead trihalide perovskites have drawn substantial interest for photovoltaic and optoelectronic applications due to their remarkable physical properties and low processing cost. However, perovskite thin films suffer from low carrier mobility as a result of their structural imperfections such as grain boundaries and pinholes, limiting their device performance and application potential. Here we demonstrate a simple and straightforward synthetic strategy based on coupling perovskite films with embedded single-walled carbon nanotubes. We are able to significantly enhance the hole and electron mobilities of the perovskite film to record-high values of 595.3 and 108.7 cm(2) V(-1) s(-1) , respectively. Such a synergistic effect can be harnessed to construct ambipolar phototransistors with an ultrahigh detectivity of 3.7 × 10(14) Jones and a responsivity of 1 × 10(4) A W(-1) , on a par with the best devices available to date. The perovskite/carbon nanotube hybrids should provide a platform that is highly desirable for fields as diverse as optoelectronics, solar energy conversion, and molecular sensing.
  • Broadband Epsilon-near-Zero Reflectors Enhance the Quantum Efficiency of Thin Solar Cells at Visible and Infrared Wavelengths

    Labelle, A. J.; Bonifazi, Marcella; Tian, Y.; Wong, C.; Hoogland, S.; Favraud, Gael; Walters, G.; Sutherland, B.; Liu, M.; Li, Jun; Zhang, Xixiang; Kelley, Shana O.; Sargent, E. H.; Fratalocchi, Andrea (ACS Applied Materials & Interfaces, American Chemical Society (ACS), 2017-02-03) [Article]
    The engineering of broadband absorbers to harvest white light in thin-film semiconductors is a major challenge in developing renewable materials for energy harvesting. Many solution-processed materials with high manufacturability and low cost, such as semiconductor quantum dots, require the use of film structures with thicknesses on the order of 1 μm to absorb incoming photons completely. The electron transport lengths in these media, however, are 1 order of magnitude smaller than this length, hampering further progress with this platform. Herein, we show that, by engineering suitably disordered nanoplasmonic structures, we have created a new class of dispersionless epsilon-near-zero composite materials that efficiently harness white light. Our nanostructures localize light in the dielectric region outside the epsilon-near-zero material with characteristic lengths of 10-100 nm, resulting in an efficient system for harvesting broadband light when a thin absorptive film is deposited on top of the structure. By using a combination of theory and experiments, we demonstrate that ultrathin layers down to 50 nm of colloidal quantum dots deposited atop the epsilon-near-zero material show an increase in broadband absorption ranging from 200% to 500% compared to a planar structure of the same colloidal quantum-dot-absorber average thickness. When the epsilon-near-zero nanostructures were used in an energy-harvesting module, we observed a spectrally averaged 170% broadband increase in the external quantum efficiency of the device, measured at wavelengths between 400 and 1200 nm. Atomic force microscopy and photoluminescence excitation measurements demonstrate that the properties of these epsilon-near-zero structures apply to general metals and could be used to enhance the near-field absorption of semiconductor structures more widely. We have developed an inexpensive electrochemical deposition process that enables scaled-up production of this nanomaterial for large-scale energy-harvesting applications.
  • Fundamental and high-order anapoles in all-dielectric metamaterials via Fano–Feshbach modes competition

    Gongora, J. S. Totero; Favraud, Gael; Fratalocchi, Andrea (Nanotechnology, IOP Publishing, 2017-02-01) [Article]
    One of the most fascinating possibilities enabled by metamaterials is the strong reduction of the electromagnetic scattering from nanostructures. In dielectric nanoparticles, the formation of a minimal scattering state at specific wavelengths is associated with the excitation of photonic anapoles, which represent a peculiar type of radiationless state and whose existence has been demonstrated experimentally. In this work, we investigate the formation of anapole states in generic dielectric structures by applying a Fano-Feshbach projection scheme, a general technique widely used in the study of quantum mechanical open systems. By expressing the total scattering from the structure in terms of an orthogonal set of internal and external modes, defined in the interior and in the exterior of the dielectric structure, respectively, we show how anapole states are the result of a complex interaction among the resonances of the system and the surrounding environment. We apply our approach to a circular resonator, where we observe the formation of higher-order anapole states, which are originated by the superposition of several internal resonances of the system.
  • Light Manipulation in Metallic Nanowire Networks with Functional Connectivity

    Galinski, Henning; Fratalocchi, Andrea; Döbeli, Max; Capasso, Federico (Advanced Optical Materials, Wiley, 2016-12-27) [Article]
    Guided by ideas from complex systems, a new class of network metamaterials is introduced for light manipulation, which are based on the functional connectivity among heterogeneous subwavelength components arranged in complex networks. The model system is a nanonetwork formed by dealloying a metallic thin film. The connectivity of the network is deterministically controlled, enabling the formation of tunable absorbing states.
  • Harnessing Disorder at the Nanoscale

    Gongora, J. S. Totero; Fratalocchi, Andrea (Encyclopedia of Nanotechnology, Springer Nature, 2016-11-29) [Book Chapter]
  • Scalable, ultra-resistant structural colors based on network metamaterials

    Galinski, Henning; Favraud, Gael; Dong, Hao; Gongora, J. S. Totero; Favaro, Grégory; Döbeli, Max; Spolenak, Ralph; Fratalocchi, Andrea; Capasso, Federico (Light: Science & Applications, Springer Nature, 2016-09-27) [Article]
    Structural colors have drawn wide attention for their potential as a future printing technology for various applications, ranging from biomimetic tissues to adaptive camouflage materials. However, an efficient approach to realize robust colors with a scalable fabrication technique is still lacking, hampering the realization of practical applications with this platform. Here, we develop a new approach based on large-scale network metamaterials that combine dealloyed subwavelength structures at the nanoscale with lossless, ultra-thin dielectric coatings. By using theory and experiments, we show how subwavelength dielectric coatings control a mechanism of resonant light coupling with epsilon-near-zero regions generated in the metallic network, generating the formation of saturated structural colors that cover a wide portion of the spectrum. Ellipsometry measurements support the efficient observation of these colors, even at angles of 70°. The network-like architecture of these nanomaterials allows for high mechanical resistance, which is quantified in a series of nano-scratch tests. With such remarkable properties, these metastructures represent a robust design technology for real-world, large-scale commercial applications.
  • Ultrafast all-optical order-to-chaos transition in silicon photonic crystal chips

    Bruck, Roman; Liu, Changxu; Muskens, Otto L.; Fratalocchi, Andrea; Di  Falco, Andrea (Laser & Photonics Reviews, Wiley, 2016-06-08) [Article]
    The interaction of light with nanostructured materials provides exciting new opportunities for investigating classical wave analogies of quantum phenomena. A topic of particular interest forms the interplay between wave physics and chaos in systems where a small perturbation can drive the behavior from the classical to chaotic regime. Here, we report an all-optical laser-driven transition from order to chaos in integrated chips on a silicon photonics platform. A square photonic crystal microcavity at telecom wavelengths is tuned from an ordered into a chaotic regime through a perturbation induced by ultrafast laser pulses in the ultraviolet range. The chaotic dynamics of weak probe pulses in the near infrared is characterized for different pump-probe delay times and at various positions in the cavity, with high spatial accuracy. Our experimental analysis, confirmed by numerical modelling based on random matrices, demonstrates that nonlinear optics can be used to control reversibly the chaotic behavior of light in optical resonators. (Figure presented.) . © 2016 by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
  • Near-Field Nanolasers based on Nonradiating Anapole Modes

    Gongora, J. S. Totero; Miroshnichenko, Andrey E.; Kivshar, Yuri S.; Fratalocchi, Andrea (Conference on Lasers and Electro-Optics, The Optical Society, 2016-05-31) [Conference Paper]
    By employing ab-initio simulations of Maxwell-Bloch equations with a source of quantum noise, we study a new laser concept based on photonic dark-matter nanostructures that emit only in the near-field, with no far-field radiation pattern.

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