Showing papers by "Cinzia Casiraghi published in 2018"

Intrinsic Properties of Single Graphene Nanoribbons in Solution: Synthetic and Spectroscopic Studies

Abstract: We report a novel type of structurally defined graphene nanoribbons (GNRs) with uniform width of 1.7 nm and average length up to 58 nm. These GNRs are decorated with pending Diels–Alder cycloadducts of anthracenyl units and N-n-hexadecyl maleimide. The resultant bulky side groups on GNRs afford excellent dispersibility with concentrations of up to 5 mg mL–1 in many organic solvents such as tetrahydrofuran (THF), two orders of magnitude higher than the previously reported GNRs. Multiple spectroscopic studies confirm that dilute dispersions in THF (<0.1 mg mL–1) consist mainly of nonaggregated ribbons, exhibiting near-infrared emission with high quantum yield (9.1%) and long lifetime (8.7 ns). This unprecedented dispersibility allows resolving in real-time ultrafast excited-state dynamics of the GNRs, which displays features of small isolated molecules in solution. This study achieves a breakthrough in the dispersion of GNRs, which opens the door for unveiling obstructed GNR-based physical properties and po...

Photocurrent study of all-printed photodetectors on paper made of different transition metal dichalcogenide nanosheets

Abstract: We have inkjet-printed in-plane 'metal–semiconductor–metal' type photodetectors on paper, one of the cheapest flexible substrates, which is also recyclable and foldable, in contrast to traditional plastic substrates The photodetectors are made by using graphene as electrodes and various transition metal dichalcogenides (TMDs) as photoactive component In particular, we have tested MoS2, WS2, MoSe2 and MoTe2 Large differences in responsivity and sensitivity were observed for all of the TMDs measured, with MoS2 showing the highest sensitivity and MoTe2 producing the largest response However, photodetectors made of MoTe2 show a large decrease in responsivity after one week of exposure to air The wavelength dependence of the responsivity in MoS2 based devices was further analyzed using a supercontinuum photocurrent spectroscopy setup, with the results suggesting a bolometric or photoelectric origin of the signal We also report some simple approaches to enhance the device performance and tune the energy range at which the maximum in responsivity or sensitivity is observed

Laser Ablation of Poly(lactic acid) Sheets for the Rapid Prototyping of Sustainable, Single-Use, Disposable Medical Microcomponents

Abstract: The employment of single-use, disposable medical equipment has increased the amount of medical waste produced and the advent of point-of-care diagnostics in lab-on-chip format is likely to add further volume. Current materials used for the manufacture of these devices are derived from petroleum sources and are, therefore, unsustainable. In addition, disposal of these plastics necessitates combustion to reduce infection risk, which has, depending on material composition, an undesirable environmental impact. To address these issues, we have developed a general approach for the rapid prototyping of single-use point-of-care cartridges prepared from poly(lactic acid), a sustainable material which can be milled and laser-cut as well as molded for translation to mass-market products. Here, the laser workability of poly(lactic acid) sheets is reported together with examples of microfluidic components. Furthermore, the low molecular adsorption in laser-ablated poly(lactic acid) channels and the compatibility of po...

Alpha particle irradiation of bulk and exfoliated MoS2 and WS2 membranes

Abstract: The properties of two-dimensional transition metal dichalcogenide (TMDC) nanosheets have been intensively studied in recent years as these compounds have emerged as promising materials for future electronic, photonic and sensor applications. Some of these applications may require the nanosheets to be exposed to radiation fields; therefore, an understanding of their interaction mechanisms with ionising radiation is required. In our experiment, we administer 1.66 MeV helium nuclei to bulk and liquid phase exfoliated MoS2 and WS2 membranes to two total absorbed doses. Raman spectroscopy shows small changes, within the spectrometer resolution, in all samples. Although small, some reproducible changes are observed such as a blueshift of the E 2 g 1 and A 1 g modes in the bulk MoS2 membrane irradiated to a high total absorbed dose; these shifts are accompanied by a small broadening of both peaks. In bulk WS2 membranes, He2+ irradiation induces a blueshift and monotonic mean peak width decrease of the 2LA(M) phonon mode with increasing fluence. The structural changes associated to these peak shifts are currently unknown. Raman spectroscopy, in agreement with energy dispersive x-ray spectroscopy, shows that amorphous carbon is present in the exfoliated MoS2 and WS2 membranes after irradiation. It is suggested that this amorphous carbon could be formed by radiolytic amorphisation of residual solvent, retained within the ripplocations of the exfoliated nanosheets. Due to the morphology of the liquid phase exfoliated nanosheets, they exhibit greater radiation stability than bulk TMDCs when exposed to heavy charged particle radiation. These results differ from those previously reported for monolayer and bulk MoS2 produced by mechanical exfoliation. The relative radiation stability of the liquid phase exfoliated nanosheets is expected to arise from attenuation and dissipation of the ion beam energy by the residual solvent and the amorphous carbon subsequently produced.

The roughening kinetics of hydrogenated graphene

Abstract: The roughness is a common property of all growing surfaces – however, the way the roughness of a growing surface changes with time and space is uniquely related to the underlying growth process, i.e. to how the atoms stick to the surface during the first stage of nucleation. This concept allows getting insights on the nucleation process of a growing surface by measuring two scaling exponents, α and β, known as roughness and growth exponents, respectively. In this work, we studied hydrogenation of graphene using the roughening kinetics. The coverage of graphene will depend on how the H ions stick on the surface, giving rise to a unique roughness evolution in time and space. We measured a roughness exponent of ~0.5 (derived from a Fourier index of ~3), and a growth exponent of ~0.3. The values of the growth and roughness exponents are close to those reported for clustered carbon, suggesting a roughening mechanism by clustering, in good agreement with the theory. We also compared our coverage data with a different model, used to describe the dynamics of graphene coverage, during chemical vapour deposition. Our data are in agreement with a nucleation-dominated growth, further confirming that hydrogenation is happening by clustering.