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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 BaTiO3/h-BN thin films reach a dielectric constant (ε r) 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.

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 elements have been demonstrated; however heterostructure-based assemblies, combining electrically conductive and dielectric textiles such as all-textile capacitors are currently missing. Here we demonstrate a superhydrophobic conducting fabric with a sheet resistance Rs ∼ 2.16 kΩ □−1, and a pinhole-free dielectric fabric with a relative permittivity er ∼ 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 C ∼ 26 pF cm−2 and a flexibility of ∼1 cm bending radius. The capacitor sustains 20 cycles of repeated washing and more than 100 cycles of repeated bending. Finally, an AC low-pass filter with a cut-off frequency of ∼15 kHz is integrated by combining the conductive polyester and the capacitor. These results pave the way toward all-textile vertically integrated electronic devices.

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.

Ultrafast fiber lasers with short pulses and broad bandwidth are in great demand for a variety of applications, such as spectroscopy, biomedical diagnosis and optical communications. In particular sub-200fs pulses are required for ultrafast spectroscopy with high temporal resolution. Graphene is an ideal ultra-wide-band saturable absorber. We report the generation of 174fs pulses from a graphene-based fiber laser

We fabricate a saturable absorber mirror by coating a graphene- film on an output coupler mirror. This is then used to obtain Q-switched mode-locking from a diode-pumped linear cavity channel waveguide laser inscribed in Ytterbium-doped Bismuthate Glass. The laser produces 1.06 ps pulses at ~1039 nm, with a 1.5 GHz repetition rate, 48% slope efficiency and 202 mW average output power. This performance is due to the combination of the graphene saturable absorber and the high quality optical waveguides in the laser glass.

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.

Graphene, related two-dimensional crystals and hybrid systems showcase several key properties that can address emerging needs in electronics and optoelectronics, in particular for 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 and optoelectronics, defining the roadmap for future applications in this area.

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.

Fully-printed electronics based on two-dimensional (2d) material 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 for fully inkjet printed field effect heterostructures operating at room temperature and pressure, and the lack of a suitable dielectric 2d ink has impeded the fabrication of active field effect devices with fullyprinted 2d heterostructures. Moreover, electronic devices on textile (i.e. textile electronics) operate over a long time at room temperature, under strain and after several washing cycles. Exploiting the properties of inkjet printed electronics based on 2d materials for wearable and textile electronics requires robust, stable and washable printed devices. Here we demonstrate fully inkjet printed 2d material active heterostructures using graphene and hexagonal-boron nitride (h-BN) inks, and use them to fabricate all inkjet printed flexible and washable field effect transistors (FETs) on textile, reaching a field effect mobility of μ ~ 91 ± 29 cm2 V-1 s -1 on polyester fabric, at low operating voltages (< 5 V). The devices maintained their performance even under ∼ 4% strain and showed stable operation for periods up to 2 years, indicating the two-fold role of the h-BN layer as a flexible dielectric and encapsulant. Our graphene/h-BN FETs are washable up to 20 cycles, which is ideal for textile electronics. The viability of our process for printed and textile electronics is demonstrated by fully inkjet printing electronic circuits, such as reprogrammable volatile memory cells, complementary inverters, and OR logic gates with graphene/h-BN FETs., The authors are grateful for funding provided by the UK Engineering and Physical Sciences Research Council (EPSRC), T.C. acknowledges funding from the ERC grant Hetero2D. F.T. acknowledges funding from Trinity College, Cambridge and the Newton Trust. S.C., G.D. and C.D. acknowledge funding from ERC under grant number 259619 76 PHOTO EM and from the EU under grant number 77 312483 ESTEEM2. A.M. and R.S. acknowledge funding from the EU Graphene Flagship (grant No. 696656).

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., Graphene shows promise for saturable absorption, a key property for ultrafast lasing, yet graphene saturable absorbers operating in the terahertz region suffer from low absorption modulation. Here, the authors report terahertz saturable absorbers based on inkjet printed graphene with 80% transparency modulation.

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 confi rms its stability against high- temperature and humidity.

We report the exfoliation of graphite in aqueous solutions under high shear rate [∼ 10$^{8}$ 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., We acknowledge funding from EU Graphene Flagship, ERCs grants Hetero2D, HiGRAPHINK, 3DIMAGEEPSRC, ESTEEM2, BIHSNAM, KNOTOUGH, and SILKENE, EPSRC grants EP/K01711X/1, EP/K017144/1, and EP/N010345/1, a Vice Chancellor award from the University of Cambridge, a Junior Research Fellowship from Clare College and the Cambridge NanoCDT and Graphene Technology CDT. We thank Chris Jones for useful discussions, and Imerys Graphite and Carbon for graphite powders.

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.

Few-layer molybdenum disul de (MoS2) is emerging as a promising quasi-two-dimensional material, 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 article, 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.

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.

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.

We demonstrate wide-band ultrafast optical pulse generation at 1, 1.5, and 2 μm using a single-polymer composite saturable absorber based on double-wall carbon nanotubes (DWNTs). The freestanding optical quality polymer composite is prepared from nanotubes dispersed in water with poly(vinyl alcohol) as the host matrix. The composite is then integrated into ytterbium-, erbium-, and thulium-doped fiber laser cavities. Using this single DWNT polymer composite, we achieve 4.85 ps, 532 fs, and 1.6 ps mode-locked pulses at 1066, 1559, and 1883 nm, respectively, highlighting the potential of DWNTs for wide-band ultrafast photonics.

We demonstrate inkjet printing as a viable method for large-area fabrication of graphene devices. We produce a graphene-based ink by liquid phase exfoliation of graphite in N-methylpyrrolidone. We use it to print thin-film transistors, with mobilities up to ∼95 cm(2) V(-1) s(-1), as well as transparent and conductive patterns, with ∼80% transmittance and ∼30 kΩ/□ sheet resistance. This paves the way to all-printed, flexible, and transparent graphene devices on arbitrary substrates.

We demonstrate mode-locking of a thulium-doped fiber laser operating at 1.94 μm, using a graphene-polymer based saturable absorber. The laser outputs 3.6 ps pulses, with ~0.4 nJ energy and an amplitude fluctuation ~0.5%, at 6.46 MHz. This is a simple, low-cost, stable and convenient laser oscillator for applications where eye-safe and low-photon-energy light sources are required, such as sensing and biomedical diagnostics.

Felice Torrisi and Jonathan N. Coleman describe how graphene can be used in conductive inks to print electronic circuits.

Ultrafast passively mode-locked lasers with spectral tuning capability and high output power have widespread applications in biomedical research, spectroscopy and telecommunications [1,2]. Currently, the dominant technology is based on semiconductor saturable absorber mirrors (SESAMs) [2,3]. However, these typically have a narrow tuning range, and require complex fabrication and packaging [2,3]. A simple, cost-effective alternative is to use Single Wall Carbon Nanotubes (SWNTs) [4,10] and Graphene [10,14]. Wide-band operation is possible using SWNTs with a wide diameter distribution [5,10]. However, SWNTs not in resonance are not used and may contribute to unwanted insertion losses [10]. The linear dispersion of the Dirac electrons in graphene offers an ideal solution for wideband ultrafast pulse generation [10,15].

We demonstrate a wideband-tunable Q-switched fiber laser exploiting a graphene saturable absorber. We get ~2us pulses, tunable between 1522 and 1555nm with up to~40nJ energy. This is a simple and low-cost light source for metrology, environmental sensing and biomedical diagnostics.