Imperial College London


Faculty of Natural SciencesDepartment of Chemistry




+44 (0)20 7594 5818f.torrisi




401AMolecular Sciences Research HubWhite City Campus





Publication Type

86 results found

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

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, 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

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, 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

Torrisi F, Seyedin S, Carey T, Eskandarian L, Bohm S, Kim JMet al., 2021, Fibre electronics: towards scaled-up manufacturing of integrated e-textile systems, Nanoscale, 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

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.

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., 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.

Working paper

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 lightdiffusers for high brightness illuminationapplications, 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.

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.

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

Journal article

Viti L, Bianchi V, Carey T, Li L, Linfield EH, Davies AG, Tredicucci A, Yoon D, Karagiannidis PG, Lombardi Let al., 2018, Graphene Saturable Absorbers at Terahertz Frequency from Liquid Phase Exfoliation of Graphite

© 2018 OSA. We report on the development of terahertz (THz) saturable-absorbers exploiting printable graphene inks. The achieved 80% transparency modulation at 3.5 THz makes these devices potential candidates as passive components for THz solid-state lasers.

Conference paper

Carey T, Jones C, Le Moal F, Deganello D, Torrisi Fet al., 2018, Spray-coating thin films on three-dimensional surfaces for a semitransparent capacitive-touch device, ACS Applied Materials and Interfaces, Vol: 10, Pages: 19948-19956, ISSN: 1944-8244

Here, we formulate low surface tension (∼30 mN/m) and low boiling point (∼79 °C) inks of graphene, single-wall carbon nanotubes and conductive polymer poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and demonstrate their viability for spray-coating of morphologically uniform ( Sq ≈ 48 ± 3 nm), transparent conducting films (TCFs) at room temperature (∼20 °C), which conform to three dimensional curved surfaces. Large area (∼750 cm2) hybrid PEDOT:PSS/graphene films achieved an optical transmission of 67% in the UV and 64% in the near-infrared wavelengths with a conductivity of ∼104 S/m. Finally, we demonstrate the spray-coating of TCFs as an electrode on the inside of a poly(methyl methacrylate) sphere, enabling a semitransparent (around 360°) and spherical touch sensor for interactive devices.

Journal article

Viti L, Bianchi V, Carey T, Li L, Linfield EH, Davies AG, Tredicucci A, Yoon D, Karagiannidis PG, Lombardi L, Tomarchio F, Ferrari AC, Torrisi F, Vitiello MSet al., 2018, Graphene saturable absorbers at terahertz frequency from liquid phase exfoliation of graphite

© OSA 2018. We report on the development of terahertz (THz) saturable-absorbers exploiting printable graphene inks. The achieved 80% transparency modulation at 3.5 THz makes these devices potential candidates as passive components for THz solid-state lasers.

Conference paper

Call TP, Carey T, Bombelli P, Lea-Smith DJ, Hooper P, Howe CJ, Torrisi Fet al., 2017, Platinum-free, graphene based anodes and air cathodes for single chamber microbial fuel cells, Journal of Materials Chemistry A, Vol: 5, Pages: 23872-23886, ISSN: 2050-7496

Microbial fuel cells (MFCs) exploit the ability of microorganisms to generate electrical power during metabolism of substrates. However, the low efficiency of extracellular electron transfer from cells to the anode and the use of expensive rare metals as catalysts, such as platinum, limit their application and scalability. In this study we investigate the use of pristine graphene based electrodes at both the anode and the cathode of a MFC for efficient electrical energy production from the metabolically versatile bacterium Rhodopseudomonas palustris CGA009. We achieve a volumetric peak power output (PV) of up to 3.51 ± 0.50 W m-3 using graphene based aerogel anodes with a surface area of 8.2 m2 g-1. We demonstrate that enhanced MFC output arises from the interplay of the improved surface area, enhanced conductivity, and catalytic surface groups of the graphene based electrode. In addition, we show a 500-fold increase in PV to 1.3 ± 0.23 W m-3 when using a graphene coated stainless steel (SS) air cathode, compared to an uncoated SS cathode, demonstrating the feasibility of a platinum-free, graphene catalysed MFCs. Finally, we show a direct application for microwatt-consuming electronics by connecting several of these coin sized devices in series to power a digital clock.

Journal article

Carey T, Cacovich S, Divitini G, Ren J, Mansouri A, Kim JM, Wang C, Ducati C, Sordan R, Torrisi Fet al., 2017, Fully inkjet-printed two-dimensional material field-effect heterojunctions for wearable and textile electronics, Nature Communications, Vol: 8, Pages: 1-11, ISSN: 2041-1723

Fully printed wearable electronics based on two-dimensional (2D) material heterojunction structures also known as heterostructures, such as field-effect transistors, require robust and reproducible printed multi-layer stacks consisting of active channel, dielectric and conductive contact layers. Solution processing of graphite and other layered materials provides low-cost inks enabling printed electronic devices, for example by inkjet printing. However, the limited quality of the 2D-material inks, the complexity of the layered arrangement, and the lack of a dielectric 2D-material ink able to operate at room temperature, under strain and after several washing cycles has impeded the fabrication of electronic devices on textile with fully printed 2D heterostructures. Here we demonstrate fully inkjet-printed 2D-material active heterostructures with graphene and hexagonal-boron nitride (h-BN) inks, and use them to fabricate all inkjet-printed flexible and washable field-effect transistors on textile, reaching a field-effect mobility of ~91 cm2 V-1 s-1, at low voltage (<5 V). This enables fully inkjet-printed electronic circuits, such as reprogrammable volatile memory cells, complementary inverters and OR logic gates.

Journal article

Bianchi V, Carey T, Viti L, Li L, Linfield EH, Davies AG, Tredicucci A, Yoon D, Karagiannidis PG, Lombardi Let al., 2017, Terahertz saturable absorbers from liquid phase exfoliation of graphite, Nature Communications, Vol: 8, ISSN: 2041-1723

Saturable absorbers (SA) operating at terahertz (THz) frequencies can open new frontiers in the development of passively mode-locked THz micro-sources. Here we report the fabrication of THz SAs by transfer coating and inkjet printing single and few-layer graphene films prepared by liquid phase exfoliation of graphite. Open-aperture z-scan measurements with a 3.5 THz quantum cascade laser show a transparency modulation ∼80%, almost one order of magnitude larger than that reported to date at THz frequencies. Fourier-transform infrared spectroscopy provides evidence of intraband-controlled absorption bleaching. These results pave the way to the integration of graphene-based SA with electrically pumped THz semiconductor micro-sources, with prospects for applications where excitation of specific transitions on short time scales is essential, such as time-of-flight tomography, coherent manipulation of quantum systems, time-resolved spectroscopy of gases, complex molecules and cold samples and ultra-high speed communications, providing unprecedented compactness and resolution.

Journal article

Popa D, Jiang Z, Bonacchini GE, Zhao Z, Lombardi L, Torrisi F, Ott AK, Lidorikis E, Ferrari ACet al., 2017, A stable, power scaling, graphene-mode-locked all-fiber oscillator, Applied Physics Letters, Vol: 110, ISSN: 1077-3118

We report power tunability in a fiber laser mode-locked with a solution-processed filtered graphene film on a fiber connector. ∼370 fs pulses are generated with output power continuously tunable from ∼4 up to ∼52 mW. This is a simple, low-cost, compact, portable, all-fiber ultrafast source for applications requiring environmentally stable, portable sources, such as imaging.

Journal article

Karagiannidis PG, Hodge SA, Lombardi L, Tomarchio F, Decorde N, Milana S, Goykhman I, Su Y, Mesite SV, Johnstone DN, Leary RK, Midgley PA, Pugno NM, Torrisi F, Ferrari ACet al., 2017, Microfluidization of graphite and formulation of graphene-based conductive inks, ACS Nano, Vol: 11, Pages: 2742-2755, ISSN: 1936-0851

We report the exfoliation of graphite in aqueous solutions under high shear rate [∼ 108 s-1] turbulent flow conditions, with a 100% exfoliation yield. The material is stabilized without centrifugation at concentrations up to 100 g/L using carboxymethylcellulose sodium salt to formulate conductive printable inks. The sheet resistance of blade coated films is below ∼2Ω/□. This is a simple and scalable production route for conductive inks for large-area printing in flexible electronics.

Journal article

Ren J, Wang C, Zhang X, Carey T, Chen K, Yin Y, Torrisi Fet al., 2017, Environmentally-friendly conductive cotton fabric as flexible strain sensor based on hot press reduced graphene oxide, Carbon, Vol: 111, Pages: 622-630, ISSN: 0008-6223

A flexible conductive cotton fabric was demonstrated by formulation and deposition of a graphene oxide (GO) dispersion onto a cotton fabric by vacuum filtration. The deposited GO amount was controlled by the concentration and volume of the GO dispersion. The GO was reduced by a hot press method at 180 °C for 60 min, and no chemical reductant was needed in both the deposition and reduction processes. The carbon-oxygen ratio increased from 1.77 to 3.72 after the hot press reduction. The as-prepared flexible conductive cotton fabric showed a sheet resistance as low as 0.9 kΩ/sq. The sheet resistance of the conductive cotton fabric only increased from ∼0.9 kΩ/sq to ∼1.2 kΩ/sq after 10 washing cycles, exhibiting good washability. The conductive cotton fabric showed viability as a strain sensor even after 400 bending cycles, in which the stable change in the electrical resistance went from ∼3500 kΩ under tensile strain to ∼10 kΩ under compressive strain. This cost-effective and environmentally-friendly method can be easily extended to scalable production of reduced GO based flexible conductive cotton fabrics.

Journal article

Torrisi F, Popa D, Milana S, Jiang Z, Hasan T, Lidorikis E, Ferrari ACet al., 2016, Stable, surfactant-free graphene–styrene methylmethacrylate composite for ultrafast lasers, Advanced Optical Materials, Vol: 4, Pages: 1088-1097, ISSN: 2195-1071

Graphene–polymer composites play an increasing role in photonic and optoelectronic applications, from ultrafast pulse generation to solar cells. The fabrication of an optical quality surfactant-free graphene-styrene methyl methacrylate composite, stable to large humidity and temperature ranges is reported. The composite is tailored for photonic applications showing wavelength-independent linear absorption in the visible and near-infrared. When tested in a mode-locked laser, it allows the generation of stable ≈326 fs mode-locked pulses at 1550 nm, unperturbed by environmental conditions. The composite continues to operate as a saturable absorber even under complete water immersion at 60 °C. This confirms its stability against high-temperature and humidity.

Journal article

Fabbro A, Scaini D, León V, Vázquez E, Cellot G, Privitera G, Lombardi L, Torrisi F, Tomarchio F, Bonaccorso F, Bosi S, Ferrari AC, Ballerini L, Prato Met al., 2016, Graphene-Based Interfaces Do Not Alter Target Nerve Cells., ACS Nano, Vol: 10, Pages: 615-623, ISSN: 1936-086X

Neural-interfaces rely on the ability of electrodes to transduce stimuli into electrical patterns delivered to the brain. In addition to sensitivity to the stimuli, stability in the operating conditions and efficient charge transfer to neurons, the electrodes should not alter the physiological properties of the target tissue. Graphene is emerging as a promising material for neuro-interfacing applications, given its outstanding physico-chemical properties. Here, we use graphene-based substrates (GBSs) to interface neuronal growth. We test our GBSs on brain cell cultures by measuring functional and synaptic integrity of the emerging neuronal networks. We show that GBSs are permissive interfaces, even when uncoated by cell adhesion layers, retaining unaltered neuronal signaling properties, thus being suitable for carbon-based neural prosthetic devices.

Journal article

Woodward RI, Howe RCT, Runcorn TH, Hu G, Torrisi F, Kelleher EJR, Hasan Tet al., 2015, Wideband saturable absorption in few-layer molybdenum diselenide (MoSe₂) for Q-switching Yb-, Er- and Tm-doped fiber lasers., Opt Express, Vol: 23, Pages: 20051-20061, ISSN: 1094-4087

We fabricate a free-standing molybdenum diselenide (MoSe2) saturable absorber by embedding liquid-phase exfoliated few-layer MoSe2 flakes into a polymer film. The MoSe2-polymer composite is used to Q-switch fiber lasers based on ytterbium (Yb), erbium (Er) and thulium (Tm) gain fiber, producing trains of microsecond-duration pulses with kilohertz repetition rates at 1060 nm, 1566 nm and 1924 nm, respectively. Such operating wavelengths correspond to sub-bandgap saturable absorption in MoSe2, which is explained in the context of edge-states, building upon studies of other semiconducting transition metal dichalcogenide (TMD)-based saturable absorbers. Our work adds few-layer MoSe2 to the growing catalog of TMDs with remarkable optical properties, which offer new opportunities for photonic devices.

Journal article

Purdie DG, Popa D, Wittwer VJ, Jiang Z, Bonacchini G, Torrisi F, Milana S, Lidorikis E, Ferrari ACet al., 2015, Few-cycle pulses from a graphene mode-locked all-fiber laser, Applied Physics Letters, Vol: 106, ISSN: 0003-6951

© 2015 AIP Publishing LLC. We combine a graphene mode-locked oscillator with an external compressor and achieve ∼29-fs pulses with ∼52-mW average power. This is a simple, low-cost, and robust setup, entirely fiber based, with no free-space optics, for applications requiring high temporal resolution.

Journal article

Zhang M, Howe RCT, Woodward RI, Kelleher EJR, Torrisi F, Hu G, Popov SV, Taylor JR, Hasan Tet al., 2015, Solution processed MoS2-PVA composite for sub-bandgap mode-locking of a wideband tunable ultrafast Er:fiber laser, Nano Research, Vol: 8, Pages: 1522-1534, ISSN: 1998-0000

We fabricate a free-standing few-layer molybdenum disulfide (MoS2)-polymer composite by liquid phase exfoliation of chemically pristine MoS2 crystals and use this to demonstrate a wideband tunable, ultrafast mode-locked fiber laser. Stable, picosecond pulses, tunable from 1,535 nm to 1,565 nm, are generated, corresponding to photon energies below the MoS2 material bandgap. These results contribute to the growing body of work studying the nonlinear optical properties of transition metal dichalcogenides that present new opportunities for ultrafast photonic applications.

Journal article

Ren Y, Brown G, Mary R, Demetriou G, Popa D, Torrisi F, Ferrari AC, Chen F, Kar AKet al., 2015, 7.8-GHz Graphene-Based 2-μm Monolithic Waveguide Laser, IEEE Journal on Selected Topics in Quantum Electronics, Vol: 21, ISSN: 1077-260X

© 1995-2012 IEEE. We report a pulsed waveguide laser working at 1944 nm, mode-locked with a saturable absorber consisting of a graphene film deposited on an output coupler mirror. The waveguide is created into a ceramic Thulium-doped Yttrium Aluminium Garnet by ultrafast laser inscription. Q-switched mode-locking is achieved, with 6.5 mW average output power and ∼7.8 GHz pulse rate. This is a convenient, compact, high repetition rate laser for various applications, such as medical diagnostics and spectroscopy.

Journal article

Woodward RI, Howe RCT, Hu G, Torrisi F, Zhang M, Hasan T, Kelleher EJRet al., 2015, Few-layer MoS<inf>2</inf> saturable absorbers for short-pulse laser technology: Current status and future perspectives [Invited], Photonics Research, Vol: 3, Pages: A30-A41, ISSN: 2327-9125

© 2015 Chinese Laser Press. Few-layer molybdenum disulfide (MoS2) is emerging as a promising quasi-two-dimensional material for photonics and optoelectronics, further extending the library of suitable layered nanomaterials with exceptional optical properties for use in saturable absorber devices that enable short-pulse generation in laser systems. In this work, we catalog and review the nonlinear optical properties of few-layer MoS2, summarize recent progress in processing and integration into saturable absorber devices, and comment on the current status and future perspectives of MoS2-based pulsed lasers.

Journal article

Woodward RI, Kelleher EJR, Howe RCT, Hu G, Torrisi F, Hasan T, Popov SV, Taylor JRet al., 2014, Tunable Q-switched fiber laser based on saturable edge-state absorption in few-layer molybdenum disulfide (MoS₂)., Opt Express, Vol: 22, Pages: 31113-31122, ISSN: 1094-4087

We fabricate a few-layer molybdenum disulfide (MoS₂) polymer composite saturable absorber by liquid-phase exfoliation, and use this to passively Q-switch an ytterbium-doped fiber laser, tunable from 1030 to 1070 nm. Self-starting Q-switching generates 2.88 μs pulses at 74 kHz repetition rate, with over 100 nJ pulse energy. We propose a mechanism, based on edge states within the bandgap, responsible for the wideband nonlinear optical absorption exhibited by our few-layer MoS₂ sample, despite operating at photon energies lower than the material bandgap.

Journal article

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