[en] Graphene is a promising candidate for the development of detectors of Terahertz (THz) radiation. A well-known detection scheme due to Dyakonov and Shur exploits plasma waves in a field-effect transistor (FET), whereby a dc photovoltage is generated in response to a THz field. In the quest for devices with a better signal-to-noise ratio, we theoretically investigate a plasma-wave photodetector in which a dc photocurrent is generated in a graphene FET. The noise equivalent power of our device is shown to be much smaller than that of a Dyakonov-Shur detector in a wide spectral range

[en] The search for novel nanomaterials driving the development of high-performance electrodes in lithium ion batteries (LIBs) is at the cutting edge of research in the field of energy storage. Here, we report on the synthesis of single wall carbon nanotube (SWNT)-bridged molybdenum trioxide (MoO₃) nanosheets as anode material for LIBs. We exploit liquid phase exfoliation of layered MoO₃ crystallites to produce multilayer MoO₃ nanosheets dispersed in isopropanol, which are then mixed with solution processed SWNTs in the same solvent. The addition of SWNTs to the MoO₃ nanosheets provides the conductive framework for electron transport, as well as a bridge structure, which buffers the volume expansion upon lithiation/de-lithiation. We demonstrate that the hybrid SWNT-bridged MoO₃ structure is beneficial for both the mechanical stability and the electrochemical characteristics of the anodes leading to a specific capacity of 865 mAh g⁻¹ at 100 mA g⁻¹ after 100 cycles, with a columbic efficiency approaching 100% and a capacity fading of 0.02% per cycle. The low-cost, non-toxic, binder-free hybrid MoO₃/SWNT here developed represents a step forward for the applicability of exfoliated MoO₃ in LIB anodes, delivering high energy and power densities as well as long lifetime. (paper)

[en] Cold atoms in an optical lattice with brick-wall geometry have been used to mimic graphene, a two-dimensional material with characteristic Dirac excitations. Here we propose to bring such artificial graphene into the proximity of a second atomic layer with a square lattice geometry. For non-interacting fermions, we find that such bilayer system undergoes a phase transition from a graphene-like semi-metal phase, characterized by a band structure with Dirac points, to a gapped band insulator phase. In the presence of attractive interactions between fermions with pseudospin-1/2 degree of freedom, a competition between semi-metal and superfluid behavior is found at the mean-field level. Using the quantum Monte Carlo method, we also investigate the case of strong repulsive interactions. In the Mott phase, each layer exhibits a different amount of long-range magnetic order. Upon coupling both layers, a valence-bond crystal is formed at a critical coupling strength. Finally, we discuss how these bilayer systems could be realized in existing cold atom experiments. (paper)

[en] While silicon-based negative electrode materials have been extensively studied, to develop high capacity lithium-ion batteries (LIBs), implementing a large-scale production method that can be easily transferred to industry, has been a crucial challenge. Here, a scalable wet-jet milling method was developed to prepare a silicon-graphene hybrid material to be used as negative electrode in LIBs. This synthesized composite, when used as an anode in lithium cells, demonstrated high Li ion storage capacity, long cycling stability and high-rate capability. In particular, the electrode exhibited a reversible discharge capacity exceeding 1763 mAh g⁻¹ after 450 cycles with a capacity retention of 98% and a coulombic efficiency of 99.85% (with a current density of 358 mA g⁻¹). This significantly supersedes the performance of a Si-dominant electrode structures. The capacity fade rate after 450 cycles was only 0.005% per cycle in the 0.05–1 V range. This superior electrochemical performance is ascribed to the highly layered, silicon-graphene porous structure, as investigated via focused ion beam in conjunction with scanning electron microscopy tomography. The hybrid electrode could retain 89% of its porosity (under a current density of 358 mA g⁻¹) after 200 cycles compared with only 35% in a Si-dominant electrode. Moreover, this morphology can not only accommodate the large volume strains from active silicon particles, but also maintains robust electrical connectivity. This confers faster transportation of electrons and ions with significant permeation of electrolyte within the electrode. Physicochemical characterisations were performed to further correlate the electrochemical performance with the microstructural dynamics. The excellent performance of the hybrid material along with the scalability of the synthesizing process is a step forward to realize high capacity/energy density LIBs for multiple device applications. (paper)

[en] Highlights: • Unravelling the role of graphene nanoflakes as a new templating material for the preparation of LiFePO₄-graphene hybrid, exploited as cathode in a lithium ion battery. • Solution processing. • Hybrid electrodes. • 2D nanomaterials. • Environmentally-friendly. We have realized a Lithium Iron Phosphate (LFP)-graphene nanohybrid obtained by a direct LFP crystal colloidal synthesis on few-layer graphene (FLG) flakes produced by the liquid phase exfoliation (LPE) of pristine graphite. This hybrid material has been tested as a cathode in Li-ion batteries, achieving fast charge/discharge responses to high specific currents. We demonstrate a specific capacity exceeding 110 mAh g⁻¹ at 20 C, with no electrode damaging. Our LFP-FLG electrodes display a low charge transfer resistance, chemical stability and steady electrochemical behavior even under stressful conditions, such as impulsive charges at a high-rate (5 C) and long cycles at 1 C (> 700 cycles). The LFP colloidal synthesis combined with the FLG production by LPE allows for tuning both the LFP-platelets like and FLG flake morphologies in order to promote an optimal connection between the LFP and FLG flakes, ensuring fast charge transfers and consequently high-rate electrochemical performances. The method here proposed yields a scalable production path, which can be easily extended to silicate-, phosphate- and fluorophosphates-based cathode materials for the next generation of high-power lithium batteries.

[en] We demonstrate rapid deterministic (seeded) growth of large single-crystals of graphene by chemical vapour deposition (CVD) utilising pre-patterned copper substrates with chromium nucleation sites. Arrays of graphene single-crystals as large as several hundred microns are grown with a periodicity of up to 1 mm. The graphene is transferred to target substrates using aligned and contamination- free semi-dry transfer. The high quality of the synthesised graphene is confirmed by Raman spectroscopy and transport measurements, demonstrating room-temperature carrier mobility of 21 000 cm² V⁻¹ s⁻¹ when transferred on top of hexagonal boron nitride. By tailoring the nucleation of large single-crystals according to the desired device geometry, it will be possible to produce complex device architectures based on single-crystal graphene, thus paving the way to the adoption of CVD graphene in wafer-scale fabrication. (letter)

[en] The realization of a high-performance Li-ion full-cell with an anode prominently based on silicon, which can surpass the energy densities of commercial graphite-based Li-ion batteries and cyclability compatible for industrial applications, is still a challenge. Here, we report a Li-ion full-cell that combines a silicon/graphene/carbon (Si/G/C) nanocomposite anodic material, with a commercial LiNi_0.33Mn_0.33Co_0.33O₂ (NMC₁₁₁) cathode. Using a pre-lithiation technique, the proposed Li-ion full-cell exhibits an energy density of ∼400 Wh kg⁻¹ at the electrode material level, with a capacity >1.6 mAh cm⁻² and a capacity retention exceeding 90% after 300 cycles at C/2. These performances have been achieved by properly designing the anode material composed by Si nanoparticles wrapped by few-layer graphene flakes. An additional carbon coating is used to further improve the electron conductivity and mechanical integrity of the anodic structure upon charge/discharge cycles. The remarkable performance of the full-cell considering the scalability of the Si-based anode synthesis is a step forward towards the commercialization of high-capacity and high-energy density Li-ion batteries. (paper)

[en] Dilute arrays of GaAs/AlGaAs modulation-doped quantum dots with same sizes fabricated by electron beam lithography and low impact reactive ion etching exhibit highly uniform luminescence lines. Single quantum dots display spectral emission with peak energies and linewidths linked largely to the geometrical diameter of the dot and to the built-in electron population. Multicharged excitonic and biexcitonic emission intensities have activation energy of about 2 meV. These results highlight the potential of high quality nanofabricated quantum dots for applications in areas that require fine control of optical emission

[en] The use of graphene‐based electrodes is burgeoning in a wide range of applications, including solar cells, light emitting diodes, touch screens, field‐effect transistors, photodetectors, sensors and energy storage systems. The success of such electrodes strongly depends on the implementation of effective production and processing methods for graphene. In this work, we take advantage of two different graphene production methods to design an advanced, conductive oxide- and platinum-free, graphene-based counter electrode for dye-sensitized solar cells (DSSCs). In particular, we exploit the combination of a graphene film, produced by chemical vapor deposition (CVD) (CVD-graphene), with few-layer graphene (FLG) flakes, produced by liquid phase exfoliation. The CVD-graphene is used as charge collector, while the FLG flakes, deposited atop by spray coating, act as catalyst for the reduction of the electrolyte redox couple (i.e. - and Co^+2/+3). The as-produced counter electrodes are tested in both - and Co^+2/+3-based semitransparent DSSCs, showing power conversion efficiencies of 2.1% and 5.09%, respectively, under 1 SUN illumination. At 0.1 SUN, Co^+2/+3-based DSSCs achieve a power conversion efficiency as high as 6.87%. Our results demonstrate that the electrical, optical, chemical and catalytic properties of graphene-based dual films, designed by combining CVD-graphene and FLG flakes, are effective alternatives to FTO/Pt counter electrodes for DSSCs for both outdoor and indoor applications. (paper)

[en] Recently the possibility to exploit quantum-mechanical effects to increase the performance of energy storage has raised a great interest. It consists of N two-level systems coupled to a single photonic mode in a cavity. We demonstrate the emergence of a quantum advantage in the charging power on this collective model (Dicke Quantum Battery) with respect to the one in which each two-level system is coupled to its own separate cavity mode (Rabi Quantum Battery). Moreover, we discuss the model of a Quantum Supercapacitor. This consists of two chains, one containing electrons and the other one holes, hosted by arrays of double quantum dots. The two chains are in close proximity and embedded in the same photonic cavity, in the same spirit of the Dicke model. We find the phase diagram of this model showing that, when transitioning from the ferro/antiferromagnetic to the superradiant phase, the quantum capacitance of the model is greatly enhanced.