Showing papers by "Cinzia Casiraghi published in 2019"

All-2D Material Inkjet-Printed Capacitors: Toward Fully Printed Integrated Circuits

Abstract: A well-defined insulating layer is of primary importance in the fabrication of passive (e.g., capacitors) and active (e.g., transistors) components in integrated circuits. One of the most widely known two-dimensional (2D) dielectric materials is hexagonal boron nitride (hBN). Solution-based techniques are cost-effective and allow simple methods to be used for device fabrication. In particular, inkjet printing is a low-cost, noncontact approach, which also allows for device design flexibility, produces no material wastage, and offers compatibility with almost any surface of interest, including flexible substrates. In this work, we use water-based and biocompatible graphene and hBN inks to fabricate all-2D material and inkjet-printed capacitors. We demonstrate an areal capacitance of 2.0 ± 0.3 nF cm–2 for a dielectric thickness of ∼3 μm and negligible leakage currents, averaged across more than 100 devices. This gives rise to a derived dielectric constant of 6.1 ± 1.7. The inkjet printed hBN dielectric has ...

Flexible, Print-in-Place 1D-2D Thin-Film Transistors Using Aerosol Jet Printing.

Abstract: Semiconducting carbon nanotubes (CNTs) printed into thin films offer high electrical performance, significant mechanical stability, and compatibility with low-temperature processing. Yet, the imple...

Low-voltage 2D materials-based printed field-effect transistors for integrated digital and analog electronics on paper

Abstract: Paper is the ideal substrate for the development of flexible and environmentally sustainable ubiquitous electronic systems, which, combined with two-dimensional materials, could be exploited in many Internet-of-Things applications, ranging from wearable electronics to smart packaging. Here we report high-performance MoS2 field-effect transistors on paper fabricated with a channel-array approach, combining the advantages of two large-area techniques: chemical vapor deposition and inkjet-printing.The first allows the pre-deposition of a pattern of MoS2; the second, the printing of dielectric layers, contacts, and connections to complete transistors and circuits fabrication. Average ION/IOFF of 8 x 10^3 (up to 5 x 10^4) and mobility of 5.5 cm2 V-1 s-1 (up to 26 cm2 V-1 s-1) are obtained. Fully functional integrated circuits of digital and analog building blocks, such as logic gates and current mirrors, are demonstrated, highlighting the potential of this approach for ubiquitous electronics on paper.

Charge-tunable graphene dispersions in water made with amphoteric pyrene derivatives

Abstract: Liquid-phase exfoliation (LPE) of graphite shows great potential as a mass scalable and low-cost method for production of solution-processed graphene, which can be used for a wide range of applications. Due to the hydrophobic nature of graphene, a stabilising agent is needed to exfoliate graphite in water – in particular, pyrene derivatives have been shown to be very effective in exfoliating graphite, by producing either positively or negatively charged dispersions, depending on the functional group used. In this work we have synthesised amphoteric pyrene derivatives, using amino acid-based functional groups (lysine and taurine), and tested them as exfoliating agents for LPE of graphene. Atomic force microscopy shows the flakes to have an average size between 100 and 300 nm, while qualitative Raman analysis shows the dispersion to be composed mainly of single and few-layer flakes, as also confirmed by transmission electron microscopy. Finally, we demonstrate that the surface charge of graphene can be adjusted by a systematic change of the pH level. Although both stabilisers demonstrated to be able to exfoliate graphite in water, pyrene-based lysine produces more concentrated and stable graphene dispersions, whose surface charge changes between positive and negative depending on the pH level. In contrast, sedimentation of the dispersed material was observed at extreme pH for graphene dispersions obtained with pyrene-substituted taurine. This is attributed to the low pKa value of the sulfonic group in taurine, which remains negatively charged even at very low pH.

Multiwavelength Raman spectroscopy of ultranarrow nanoribbons made by solution-mediated bottom-up approach

Abstract: Here we present a combined experimental and theoretical study of graphene nanoribbons (GNRs), where detailed multiwavelength Raman measurements are integrated by accurate ab initio simulations. Our study covers several ultranarrow GNRs, obtained by means of solution-based bottom-up synthetic approach, allowing to rationalize the effect of edge morphology, position and type of functional groups, as well as the length on the GNR Raman spectrum. We show that the low-energy region, especially in the presence of bulky functional groups, is populated by several modes, and a single radial breathinglike mode cannot be identified. In the Raman optical region, we find that, except for the fully brominated case, all GNRs functionalized at the edges with different side groups show a characteristic dispersion of the D peak (8--22 ${\mathrm{cm}}^{\ensuremath{-}1}$/eV). This has been attributed to the internal degrees of freedom of these functional groups, which act as dispersion-activating defects. The G peak shows small to negligible dispersion in most of the cases, with larger values only in the presence of poor control of the edge functionalization, exceeding the values reported for highly defective graphene. In conclusion, we have shown that the characteristic dispersion of the G and D peaks offers further insight into the GNR structure and functionalization, by making Raman spectroscopy an important tool for the characterization of GNRs.

Gas Blow Coating: a Deposition Technique to Control the Crystal Morphology in Thin Films of Organic Semiconductors

Abstract: Rapid, large-scale, and low-cost coating methods that enable precise control of the crystal growth of organic semiconductors are essential to deliver high-performance devices that are robust and re...

Enhanced Liquid Phase Exfoliation of Graphene in Water Using an Insoluble Bis-Pyrene Stabiliser

Abstract: Stabilisers, such as surfactants, polymers and polyaromatic molecules, offer an effective way to produce graphene dispersions in water by Liquid Phase Exfoliation (LPE) without degrading the properties of graphene. In particular, pyrene derivatives provide better exfoliation efficiency than traditional surfactants and polymers. A stabiliser is expected to be relatively soluble in order to disperse hydrophobic graphene in water. Here, we show that exfoliation can also be achieved with insoluble pyrene stabilisers if appropriately designed. In particular, bis-pyrene stabilisers (BPSs) functionalised with pyrrolidine provide a higher exfoliation efficiency and percentage of single layers compared to traditional pyrene derivatives under the same experimental conditions. This is attributed to the enhanced interactions between BPS and graphene, provided by the presence of two pyrene binding groups. This approach is therefore attractive not only to produce highly concentrated graphene, but also to use graphene to disperse insoluble molecules in water. The enhanced adsorption of BPS on graphene, however, is reflected in higher toxicity towards human epithelial bronchial immortalized cells, limiting the use of this material for biomedical applications.