Davide Spirito

High performance bilayer-graphene terahertz detectors

We report bilayer-graphene field effect transistors operating as Terahertz (THz) broadband photodetectors based on plasma-waves excitation. By employing wide-gate geometries or buried gate configurations, we achieve a responsivity ∼1.2 V/W (1.3 mA/W) and a noise equivalent power ∼2 × 10−9 W/√Hz in the 0.29–0.38 THz range, in photovoltage and photocurrent mode. The potential of this technology for scalability to higher frequencies and the development of flexible devices makes our approach competitive for a future generation of THz detection systems.

Anomalous low-temperature Coulomb drag in graphene-GaAs heterostructures.

A. Gamucci, D. Spirito, M. Carrega, B. Karmakar, A. Lombardo, M. Bruna, A.C. Ferrari, L.N. Pfeiffer, K.W. West, M. Polini, ∗ and V. Pellegrini 1, † NEST, Istituto Nanoscienze-CNR and Scuola Normale Superiore, I-56126 Pisa, Italy Engineering Department, University of Cambridge, Cambridge, CB3 OFA, UK Department of Electrical Engineering, Princeton University, Princeton, NJ, USA Istituto Italiano di Tecnologia, Graphene labs, Via Morego 30, I-16163 Genova, ItalyVertical heterostructures combining different layered materials offer novel opportunities for applications and fundamental studies. Here we report a new class of heterostructures comprising a single-layer (or bilayer) graphene in close proximity to a quantum well created in GaAs and supporting a high-mobility two-dimensional electron gas. In our devices, graphene is naturally hole-doped, thereby allowing for the investigation of electron-hole interactions. We focus on the Coulomb drag transport measurements, which are sensitive to many-body effects, and find that the Coulomb drag resistivity significantly increases for temperatures <5-10 K. The low-temperature data follow a logarithmic law, therefore displaying a notable departure from the ordinary quadratic temperature dependence expected in a weakly correlated Fermi-liquid. This anomalous behaviour is consistent with the onset of strong interlayer correlations. Our heterostructures represent a new platform for the creation of coherent circuits and topologically protected quantum bits.

UV Light Detection from CdS Nanocrystal Sensitized Graphene Photodetectors at kHz Frequencies

We have fabricated UV-sensitive photodetectors based on colloidal CdS nanocrystals and graphene. The nanocrystals act as a sensitizer layer that improves light harvesting leading to high responsivity of the detector. Despite the slow relaxation of the photogenerated charges in the nanocrystal film, faster processes allowed to detect pulses up to a repetition rate of 2 kHz. We have performed time-resolved analysis of the processes occurring in our hybrid system and discuss possible photoinduced charge transfer mechanisms.

Bright-Emitting Perovskite Films by Large-Scale Synthesis and Photoinduced Solid-State Transformation of CsPbBr3 Nanoplatelets

Lead halide perovskite nanocrystals are an emerging class of materials that have gained wide interest due to their facile color tuning and high photoluminescence quantum yield. However, the lack of techniques to translate the high performance of nanocrystals into solid films restricts the successful exploitation of such materials in optoelectronics applications. Here, we report a heat-up and large-scale synthesis of quantum-confined, blue-emitting CsPbBr3 nanoplatelets (NPLs) that self-assemble into stacked lamellar structures. Spin-coated films fabricated from these NPLs show a stable blue emission with a photoluminescence quantum yield (PLQY) of 25%. The morphology and the optoelectronic properties of such films can be dramatically modified by UV-light irradiation under ambient conditions at a high power, which transforms the self-assembled stacks of NPLs into much larger structures, such as square-shaped disks and nanobelts. The emission from the transformed thin films falls within the green spectral region with a record PLQY of 65%, and they manifest an amplified spontaneous emission with a sharp line width of 4 nm at full-width at half-maximum under femtosecond-pulsed excitation. The transformed films show stable photocurrents with a responsivity of up to 15 mA/W and response times of tens of milliseconds and are robust under treatment with different solvents. We exploit their insolubility in ethanol to fabricate green-emitting, all-solution-processed light-emitting diodes with an external quantum efficiency of 1.1% and a luminance of 590 Cd/m2.

Multiband Plasmonic Sierpinski Carpet Fractal Antennas

Deterministic fractal antennas are employed to realize multimodal plasmonic devices. Such structures show strongly enhanced localized electromagnetic fields typically in the infrared range with a hierarchical spatial distribution. Realization of engineered fractal antennas operating in the optical regime would enable nanoplasmonic platforms for applications, such as energy harvesting, light sensing, and bio/chemical detection. Here, we introduce a novel plasmonic multiband metamaterial based on the Sierpinski carpet (SC) space-filling fractal, having a tunable and polarization-independent optical response, which exhibits multiple resonances from the visible to mid-infrared range. We investigate gold SCs fabricated by electron-beam lithography on CaF

Solution-processed silver sulphide nanocrystal film for resistive switching memories

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Thioethyl‐Porphyrazine/Nanocarbon Hybrids for Photoinduced Electron Transfer

and Si/SiO

Approaches for enhancing plasmon propagation in graphene waveguides

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Shape Approaches for Enhancing Plasmon Propagation in Graphene

substrates. Furthermore, we demonstrate that such resonances originate from diffraction-mediated localized surface plasmons, which can be tailored in deterministic fashion by tuning the shape, size, and position of the fractal elements. Moreover, our findings illustrate that SCs with high order of complexity present a strong and hierarchically distributed electromagnetic near-field of the plasmonic modes. Therefore, engineered plasmonic SCs provide an efficient strategy for the realization of compact active devices with a strong and broadband spectral response in the visible/mid-infrared range. We take advantage of such a technology by carrying out surface enhanced Raman spectroscopy (SERS) on Brilliant Cresyl Blue molecules deposited onto plasmonic SCs. We achieve a broadband SERS enhancement factor up to

Reduction of moisture sensitivity of PbS quantum dot solar cells by incorporation of reduced graphene oxide

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