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  • Journal article
    Latham KG, Edathil AA, Rezaei B, Liu S, Nguyen S, Keller SS, Torrisi F, Greenhalgh ES, Titirici Met al., 2022,

    Challenges and opportunities in free-standing supercapacitors research

    , APL Materials, Vol: 10, Pages: 110903-110903

    <jats:p> The design of commercial supercapacitors has remained largely unchanged since the 1970s, comprising powdered electrodes housed in rigid metal cylinders or pouches. To power the next generation of integrated technologies, an evolution in supercapacitor materials and design is needed to create multifunctional materials that allow energy storage while imparting additional material properties (e.g., flexibility and strength). Conductive free-standing electrodes produced from fibers or 3D printed materials offer this opportunity as their intrinsic mechanical properties can be transferred to the supercapacitor. Additionally, their conductive nature allows for the removal of binders, conductive agents, and current collectors from the supercapacitor devices, lowering their economic and environmental cost. In this Perspective, we summarize the recent progress on free-standing supercapacitors from new methods to create free-standing electrodes to novel applications for these devices, together with a detailed discussion and analysis on their electrochemical performance and physicochemical and mechanical properties. Furthermore, the potential directions and prospects of future research in developing free-standing supercapacitors are proposed. </jats:p>

  • Journal article
    Kim H, Arbab A, Fenech Salerno B, Yao C, MacPherson R, Kim JM, Torrisi Fet al., 2022,

    Barium titanate-enhanced hexagonal boron nitride inks for printable high-performance dielectrics

    , Nanotechnology, Vol: 33, Pages: 1-8, ISSN: 0957-4484

    Printed electronics have been attracting significant interest for their potential to enable flexible and wearable electronic applications. Together with printable semiconductors, solution processed dielectric inks are key in enabling low-power and high-performance printed electronics. In the quest for suitable dielectrics inks, two-dimensional materials such as hexagonal boron nitride (h-BN) have emerged in the form of printable dielectrics. In this work, we report barium titanate (BaTiO3) nanoparticles as an effective additive for inkjet-printable h-BN inks. The resulting inkjet printed h-BN/BaTiO3 thin films reach a dielectric constant (εr) of ~ 16 by adding 10% of BaTiO3 nanoparticles (in their volume fraction to the exfoliated h-BN flakes) in water-based inks. This result enabled all-inkjet printed flexible capacitors with C ~ 10.39 nF cm-2, paving the way to future low power, printed and flexible electronics.

  • Journal article
    Spanu A, Mascia A, Baldazzi G, Fenech Salerno B, Torrisi F, Viola G, Bonfiglio A, Cosseddu P, Pani Det al., 2022,

    Parylene C-based, breathable tattoo electrode for high-quality biopotential measurements

    , Frontiers in Bioengineering and Biotechnology, Vol: 10, Pages: 1-15, ISSN: 2296-4185

    A breathable tattoo electrode for bio-potential recording based on a Parylene C nanofilm is presented in this study. The proposed approach allows for the fabrication of micro-perforated epidermal submicrometer-thick electrodes that conjugate the unobtrusiveness of Parylene C nanofilms and the very important feature of breathability. The electrodes were fully validated for electrocardiography (ECG) measurements showing performance comparable to that of conventional disposable gelled Ag/AgCl electrodes, with no visible negative effect on the skin even many hours after their application. This result introduces interesting perspectives in the field of epidermal electronics, particularly in applications where critical on-body measurements are involved.

  • Journal article
    Piatti E, Arbab A, Galanti F, Carey T, Anzi L, Spurling D, Roy A, Zhussupbekova A, Patel K, Kim JM, Daghero D, Sordan R, Nicolosi V, Gonnelli R, Torrisi Fet al., 2021,

    Charge transport mechanisms in inkjet-printed thin-film transistors based on two-dimensional materials

    , Nature Electronics, Vol: 4, Pages: 893-905, ISSN: 2520-1131

    Printed electronics using inks based on graphene and other two-dimensional materials can be used to create large-scale, flexible, and wearable devices. However, the complexity of the ink formulations, and the polycrystalline nature of the resulting thin films, have made it difficult to examine charge transport in such devices. Here we report the charge transport mechanisms of surfactant- and solvent-free inkjet-printed thin-film devices based on few-layer graphene (semi-metal), molybdenum disulfide (MoS2, semiconductor) and titanium carbide MXene (Ti3C2, metal) by investigating the temperature, gate and magnetic field dependencies of their electrical conductivity. We find that charge transport in printed few-layer MXene and MoS2 devices is dominated by the intrinsic transport mechanism of the constituent flakes: MXene exhibits a weakly-localized 2D metallic behaviour at any temperature, whereas MoS2 behaves as an insulator with a crossover from 3D-Mott variable-range hopping to nearest-neighbour hopping around 200 K. Charge transport in printed few-layer graphene devices is dominated by the transport mechanism between different flakes, which exhibit 3D-Mott variable range hopping conduction at any temperature.

  • Journal article
    Bohm S, Ingle A, Bohm M, Fenech Salerno B, Wu S, Torrisi Fet al., 2021,

    Graphene production by cracking

    , Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, Vol: 379, Pages: 1-14, ISSN: 1364-503X

    n recent years, graphene has found its use in numerous industrial applications due to its unique properties. While its impermeable and conductive nature can replace currently used anticorrosive toxic pigments in coating systems, due to its large strength to weight ratio, graphene can be an important component as a next-generation additive for automotive, aerospace & construction applications. The current bottlenecks in using graphene & graphene oxide and other 2D materials are the availability of cost-effective, high-quality materials and their effective incorporation (functionalisation and dispersion)into the product matrices. On overcoming these factors, graphene may attract significant demands in terms of volume consumption. Graphene can be produced on industrial scales and cost-effective top-down routes such as chemical, electro chemical, and/or high-pressure mechanical exfoliation. Graphene depending on end applications can be chemically tuned and modified via functionalisation so that easy incorporation into product matrices is possible. This paper discusses different production methods and their impact on the quality of graphene produced in terms of energy input. Graphene with an average thickness below five layers were produced by both methods with varied defects. However, a higher yield of graphene with a lower number of layers was produced by the high-pressure exfoliation route.

  • Journal article
    Seyedin S, Carey T, Arbab A, Eskandarian L, Bohm S, Kim JM, Torrisi Fet al., 2021,

    Fibre electronics: towards scaled-up manufacturing of integrated e-textile systems

    , Nanoscale, Vol: 13, Pages: 12818-12847, ISSN: 2040-3364

    The quest for a close human interaction with electronic devices for healthcare, safety, energy and security has driven giant leaps in portable and wearable technologies in recent years. Electronic textiles (e-textiles) are emerging as key enablers of wearable devices. Unlike conventional heavy, rigid, and hard-to-wear gadgets, e-textiles can lead to lightweight, flexible, soft, and breathable devices, which can be worn like everyday clothes. A new generation of fibre-based electronics is emerging which can be made into wearable e-textiles. A suite of start-of-the-art functional materials have been used to develop novel fibre-based devices (FBDs), which have shown excellent potential in creating wearable e-textiles. Recent research in this area has led to the development of fibre-based electronic, optoelectronic, energy harvesting, energy storage, and sensing devices, which have also been integrated into multifunctional e-textile systems. Here we review the key technological advancements in FBDs and provide an updated critical evaluation of the status of the research in this field. Focusing on various aspects of materials development, device fabrication, fibre processing, textile integration, and scaled-up manufacturing we discuss current limitations and present an outlook on how to address the future development of this field. The critical analysis of key challenges and existing opportunities in fibre electronics aims to define a roadmap for future applications in this area.

  • Journal article
    Hui F, Liu P, Hodge S, Carey T, Wen C, Torrisi F, Galhena T, Tomarchio F, Lin Y, Moreno E, Roldan J, Koren E, Ferrari A, Lanza Met al., 2021,

    In-situ observation of low-power nano-synaptic response in graphene oxide using conductive atomic force microscopy

    , Small, Vol: 17, ISSN: 1613-6810

    Multiple studies have reported the observation of electro-synaptic response in different metal/insulator/metal devices; however, most of them analysed large (>1 µm2) devices that do not meet the integration density required by the industry (1010 devices/mm2). Some studies employed a scanning tunnelling microscope (STM) to explore nano-synaptic response in different materials, but in this setup there is a nanogap between the insulator and one of the metallic electrodes (i.e. the STM tip), which is not present in real devices. Here we show how to use a conductive atomic force microscope (CAFM) to explore the presence and quality of nano-synaptic response in confined areas <500 nm2. For this study, we selected graphene oxide (GO) due to its easy fabrication and excellent electrical properties. Our experiments indicate that metal/GO/metal nano-synapses exhibit potentiation and paired pulse facilitation with low write current levels <1 µA (i.e. power consumption ~3 μW), controllable excitatory post-synaptic currents and long-term potentiation and depression. Our results provide a new method to explore nano-synaptic plasticity at the nanoscale, and point GO as an important candidate material for the fabrication of ultra-small (<500 nm2) electronic synapses fulfilling the integration density requirements of neuromorphic systems.

  • Journal article
    Lund A, Wu Y, Fenech-Salerno B, Torrisi F, Carmichael T, Mueller Cet al., 2021,

    Conducting materials as building blocks for electronic textiles

    , Materials Research Society (MRS) Bulletin, Vol: 46, Pages: 491-501, ISSN: 0883-7694

    To realize the full gamut of functions that are envisaged for electronic textiles (e-textiles) a range of semiconducting, conducting and electrochemically active materials are needed. This article will discuss how metals, conducting polymers, carbon nanotubes, and two-dimensional (2D) materials, including graphene and MXenes, can be used in concert to create e-textile materials, from fibers and yarns to patterned fabrics. Many of the most promising architectures utilize several classes of materials (e.g., elastic fibers composed of a conducting material and a stretchable polymer, or textile devices constructed with conducting polymers or 2D materials and metal electrodes). While an increasing number of materials and devices display a promising degree of wash and wear resistance, sustainability aspects of e-textiles will require greater attention.

  • Journal article
    Carey T, Arbab A, Anzi L, Bristow H, Hui F, Bohm S, Wyatt-Moon G, Flewitt A, Wadsworth A, Gasparini N, Kim JM, Lanza M, McCulloch I, Sordan R, Torrisi Fet al., 2021,

    Inkjet printed circuits with 2D semiconductor inks for high-performance electronics

    , Advanced Electronic Materials, ISSN: 2199-160X

    Air-stable semiconducting inks suitable for complementary logic are key to create low-power printed integrated circuits (ICs). High-performance printable electronic inks with 2D materials have the potential to enable the next generation of high performance low-cost printed digital electronics. Here, the authors demonstrate air-stable, low voltage (<5 V) operation of inkjet-printed n-type molybdenum disulfide (MoS2), and p-type indacenodithiophene-co-benzothiadiazole (IDT-BT) field-effect transistors (FETs), estimating an average switching time of τMoS2 ≈ 4.1 μs for the MoS2 FETs. They achieve this by engineering high-quality MoS2 and air-stable IDT-BT inks suitable for inkjet-printing complementary pairs of n-type MoS2 and p-type IDT-BT FETs. They then integrate MoS2 and IDT-BT FETs to realize inkjet-printed complementary logic inverters with a voltage gain |Av| ≈ 4 when in resistive load configuration and |Av| ≈ 1.4 in complementary configuration. These results represent a key enabling step towards ubiquitous long-term stable, low-cost printed digital ICs.

  • Journal article
    Sergioli G, Militello C, Rundo L, Minafra L, Torrisi F, Russo G, Chow KL, Giuntini Ret al., 2021,

    A quantum-inspired classifier for clonogenic assay evaluations

    , SCIENTIFIC REPORTS, Vol: 11, ISSN: 2045-2322
  • Journal article
    Mezzapesa FP, Garrasi K, Schmidt J, Salemi L, Pistore V, Li L, Davies GA, Linfield EH, Riesch M, Jirauschek C, Carey T, Torrisi F, Ferrari AC, Vitiello MSet al., 2020,

    Terahertz frequency combs exploiting an on-chip, solution-processed, graphene-quantum cascade laser coupled-cavity

    , ACS Photonics, Vol: 7, Pages: 3489-3498, ISSN: 2330-4022

    The ability to engineer quantum-cascade-lasers (QCLs) with ultrabroad gain spectra, and with a full compensation of the group velocity dispersion, at terahertz (THz) frequencies, is key for devising monolithic and miniaturized optical frequency-comb-synthesizers (FCSs) in the far-infrared. In THz QCLs four-wave mixing, driven by intrinsic third-order susceptibility of the intersubband gain medium, self-locks the optical modes in phase, allowing stable comb operation, albeit over a restricted dynamic range (∼20% of the laser operational range). Here, we engineer miniaturized THz FCSs, comprising a heterogeneous THz QCL, integrated with a tightly coupled, on-chip, solution-processed, graphene saturable-absorber reflector that preserves phase-coherence between lasing modes, even when four-wave mixing no longer provides dispersion compensation. This enables a high-power (8 mW) FCS with over 90 optical modes, through 55% of the laser operational range. We also achieve stable injection-locking, paving the way to a number of key applications, including high-precision tunable broadband-spectroscopy and quantum-metrology.

  • Journal article
    Ji X, Liu W, Yin Y, Wang C, Torrisi Fet al., 2020,

    A graphene-based electro-thermochromic textile display

    , Journal of Materials Chemistry C, Vol: 8, Pages: 15788-15794, ISSN: 2050-7526

    Electronic textiles (e textiles) are rapidly emerging as key enablers for wearable electronics. Graphene and 2D materials have played a major role in enabling truly wearable e-textiles. Here we demonstrate a textile-based display using the Joule's heating of a screen-printed, few-layer graphene ink to drive the colour switching of thermochromic polyurethane on a cotton fabric. The average temperature of the few-layer graphene ink on the fabric was voltage-controlled reaching about 43 °C in 45 s at a bias of 12 V and a recovery of <20 s with negligible degradation after several heating/cooling cycles. This is used to demonstrate several electro-thermochromic textile displays, thus representing a breakthrough in e-textiles technology.

  • Working paper
    Carey T, Arbab A, Anzi L, Bristow H, Hui F, Bohm S, Wyatt-Moon G, Flewitt A, Wadsworth A, Gasparini N, Kim JM, Lanza M, McCulloch I, Sordan R, Torrisi Fet al., 2020,

    Inkjet printed circuits with two-dimensional semiconductor inks for high-performance electronics

    , Publisher: arXiv

    Air-stable semiconducting inks suitable for complementary logic are key tocreate low-power printed integrated circuits (ICs). High-performance printableelectronic inks with two-dimensional materials have the potential to enable thenext generation of high performance, low-cost printed digital electronics. Herewe demonstrate air-stable, low voltage (< 5 V) operation of inkjet-printedn-type molybdenum disulfide (MoS2) and p-typeindacenodithiophene-co-benzothiadiazole (IDT-BT) field-effect transistors(FETs), estimating a switching time of {\tau} ~ 3.3 {\mu}s for the MoS2 FETs.We achieve this by engineering high-quality MoS2 and air-stable IDT-BT inkssuitable for inkjet-printing complementary pairs of n-type MoS2 and p-typeIDT-BT FETs. We then integrate MoS2 and IDT-BT FETs to realise inkjet-printedcomplementary logic inverters with a voltage gain |Av| ~ 4 when in resistiveload configuration and |Av| ~ 1.36 in complementary configuration. Theseresults represent a key enabling step towards ubiquitous long-term stable,low-cost printed digital ICs.

  • Journal article
    Schütt F, Zapf M, Signetti S, Strobel J, Krüger H, Röder R, Carstensen J, Wolff N, Marx J, Carey T, Schweichelt M, Ivo Terasa M, Siebert L, Hong H-K, Kaps S, Fiedler B, Kumar Mishra Y, Lee Z, Pugno N, Kienle L, Ferrari AC, Torrisi F, Ronning C, Adelung Ret al., 2020,

    Conversionless efficient and broadband laser light diffusers for high brightness illumination applications

    , Nature Communications, Vol: 11, Pages: 1-10, ISSN: 2041-1723

    Laser diodes (LDs) are considered the next generation of ultra-efficient light sources. However, state-of-the-art LD-based lighting systems rely on light-converting phosphorous materials, which strongly limit the efficiency, lifetime as well as the achievable light output due to energy losses, saturation, thermal degradation and low irradiance levels. Here, we demonstrate a macroscopically expanded, three-dimensional diffuser composed of interconnected hollow hexagonal boron nitride microtubes with nanoscopic wall-thickness, acting as an artificial solid fog, capable of withstanding ~10 times the irradiance level of remote phosphors. Indeed, in contrast to phosphors, no light conversion is required as the diffuser relies solely on strong broadband (full visible range) lossless multiple light scattering events, enabled by a highly porous (> 99.99%) non-absorbing nanoarchitecture, resulting in efficiencies of up to 98 %. This can unleash the potential of lasers for high-brightness lighting applications, such as automotive headlights, projection technology or lighting for large spaces.

  • Conference paper
    Mezzapesa FP, Garrasi K, Schmidt J, Salemi L, Li L, Davies AG, Linfield EH, Carey T, Torrisi F, Ferrari AC, Vitiello MSet al., 2020,

    Semiconductor THz frequency combs exploiting solution processed graphene

    , 45th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz), Publisher: IEEE, ISSN: 2162-2027
  • Journal article
    Qiang S, Carey T, Arbab A, Song W, Wang C, Torrisi Fet al., 2019,

    Wearable solid-state capacitors based on two-dimensional material all-textile heterostructures

    , Nanoscale, Vol: 11, Pages: 9912-9919, ISSN: 2040-3364

    Two dimensional (2D) materials are a rapidly growing area of interest for wearable electronics, due to their flexible and unique electrical properties. All-textile based wearable electronic components are key to enable future wearable electronics. Single component electrical elemements have been demonstrated however heterostructure-based assemblies, combining eletrically condutive and dieletric textiles such as all-textile capacitors are currently missing. Here we demonstrate a superhydrophobic conducting fabric with a sheet resistance ~2.16 kΩ □-1, and a pinhole-free dielectric fabric with a relative permittivity εr ~ 2.35 enabled by graphene and hexagonal boron nitride inks, respectively. The different fabrics are then integrated to engineer the first example of an all-textile-based capacitive heterostructure with an effective capacitance ~ 26 pF cm-2 and flexibility down to at least 1 cm bending radius. The capacitor sustains 20 cylces of repeated washing and more than 100 cycles of repeated bending. Finally, an AC low-pass filter with cutoff frequency ~ 15 kHz is integrated by combining the conductive polyester and the capacitor.These results pave the way toward all-textile vertically integrated electronic devices.

  • Journal article
    Taale M, Schütt F, Carey T, Marx J, Mishra YK, Stock N, Fiedler B, Torrisi F, Adelung R, Selhuber-Unkel Cet al., 2019,

    Biomimetic carbon fiber systems engineering: a modular design strategy to generate biofunctional Composites from Graphene and Carbon Nanofibers

    , ACS Applied Materials and Interfaces, Vol: 11, Pages: 5325-5335, ISSN: 1944-8244

    Carbon-based fibrous scaffolds are highly attractive for all biomaterial applications that require electrical conductivity. It is additionally advantageous if such materials resembled the structural and biochemical features of the natural extracellular environment. Here, we show a novel modular design strategy to engineer biomimetic carbon fiber-based scaffolds. Highly porous ceramic zinc oxide (ZnO) microstructures serve as three-dimensional (3D) sacrificial templates and are infiltrated with carbon nanotubes (CNTs) or graphene dispersions. Once the CNTs and graphene coat the ZnO template, the ZnO is either removed by hydrolysis or converted into carbon by chemical vapor deposition. The resulting 3D carbon scaffolds are both hierarchically ordered and free-standing. The properties of the microfibrous scaffolds were tailored with a high porosity (up to 93%), a high Young's modulus (ca. 0.027-22 MPa), and an electrical conductivity of ca. 0.1-330 S/m, as well as different surface compositions. Cell viability, fibroblast proliferation rate and protein adsorption rate assays have shown that the generated scaffolds are biocompatible and have a high protein adsorption capacity (up to 77.32 ± 6.95 mg/cm3) so that they are able to resemble the extracellular matrix not only structurally but also biochemically. The scaffolds also allow for the successful growth and adhesion of fibroblast cells, showing that we provide a novel, highly scalable modular design strategy to generate biocompatible carbon fiber systems that mimic the extracellular matrix with the additional feature of conductivity.

  • Journal article
    Torrisi F, Carey T, 2018,

    Graphene, related two-dimensional crystals, and hybrid systems for printed and wearable electronics

    , Nano Today, Vol: 23, Pages: 73-96, ISSN: 1748-0132

    Graphene and related two-dimensional crystals and hybrid systems showcase several key properties that can address emerging needs in the ever growing markets of printed, flexible and wearable electronic devices. Graphene's flexibility, large surface area, and chemical stability, combined with its excellent electrical and thermal conductivity, make it promising as a printed flexible electrodes in flexible and wearable electronic devices. Chemically functionalized graphene and self-assembly of graphene-organic molecule composites can also improve mobility and conductivity of organic semiconducting thin film transistors (TFT). Two-dimensional crystals and hybrid systems provide optical and electrical properties complementary to those of graphene, enabling the realization of printed an flexible ultrathin-film photodetectors or photovoltaic systems. Here, we review the use of graphene and related materials for printed and wearable electronics, defining the roadmap for future applications in these areas.

  • Book chapter
    Torrisi F, Carey T, 2018,

    Printing 2D Materials

    , Flexible Carbon-based Electronics, Publisher: Wiley-VCH Verlag GmbH & Co. KGaA, Pages: 131-205
  • Journal article
    Micallef FG, Shrestha PK, Chu D, McEwan K, Rughoobur G, Carey T, Coburn N, Torrisi F, Txoperena O, Zurutuza Aet al., 2018,

    Transparent conductors for Mid-infrared liquid crystal spatial light modulators

    , Thin Solid Films, Vol: 660, Pages: 411-420, ISSN: 0040-6090

    Transparent conductors (TCs) are required for liquid crystal spatial light modulators (LC-SLMs) in order to set up an electric field across the LC layer. In the middle infrared (Mid-IR) range (λ = 2 to 5 μm), LC-SLMs can offer a low-cost, non-mechanical, random-access and compact alternative to the gimbaled mirrors used currently for Mid-IR laser beam-steering. Indium tin oxide (ITO) is the industry standard for applications in the visible spectrum but it performs poorly in the IR, with a transmittance <20% for Mid-IR wavelengths. Little work has been done to develop a comparable material which fulfils the required properties in the Mid-IR: A sheet resistance allowing operation at typical frequencies (≈1 kHz) and, if patterned, with minimal voltage drop along the electrode, a transmittance >50% in the target range, chemical, thermal and mechanical robustness which can endure subsequent processing, and ability to be patterned at low-cost to a resolution comparable to the wavelengths investigated. Ni and Cu ultra thin metallic films (UTMFs), CuxO thin films (TFs), and chemical vapour deposition (CVD) grown mono-layer graphene were investigated. Ni UTMFs and graphene were found to have the best performance with sheet resistance values of 747±86Ω/□ and 360±34Ω/□ respectively for samples having a transmittance of 65% and 97% at λ = 2.3 μm. Both Ni UTMFs and CVD mono-layer graphene were found to be suitably stable with age. An increase of sheet resistance after baking was recorded due to oxidation and desorption of contaminating dopants respectively. Ni UTMFs were found to be patternable down to a 3 μm resolution, limited by the mask, using a standard photo-lithographic lift-off process. Transmissive LC cells with a maximum phase shift of 3π at λ = 2.3 μm were assembled with both Ni UTMFs and mono-layer graphene as TCs on sapphire, with the former having transmittance of 18.7% and contrast ratio of

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