Ferlauto L.,CNR Institute for Microelectronics and Microsystems |
Liscio F.,CNR Institute for Microelectronics and Microsystems |
Orgiu E.,University of Strasbourg |
Masciocchi N.,University Dellinsubria And Toscalab |
And 4 more authors.
Advanced Functional Materials | Year: 2014
The introduction of side chains in π-conjugated molecules is a design strategy widely exploited to increase molecular solubility thus improving the processability, while directly influencing the self-assembly and consequently the electrical properties of thin films. Here, a multiscale structural analysis performed by X-ray diffraction, X-ray reflectivity, and atomic force microscopy on thin films of dicyanoperylene molecules decorated with either linear or branched side chains is reported. The substitution with asymmetric branched alkyl chains allows obtaining, upon thermal annealing, field-effect transistors with enhanced transport properties with respect to linear alkyl chains. Branched chains induce molecular disorder during the film growth from solution, effectively favouring 2D morphology. Post-deposition thermal annealing leads to a structural transition towards the bulk-phase for molecules with branched chains, still preserving the 2D morphology and allowing efficient charge transport between crystalline domains. Conversely, molecules with linear chains self-assemble into 3D islands exhibiting the bulk-phase structure. Upon thermal annealing, these 3D islands keep their size constant and no major changes are observed in the organic field effect transistor characteristics. These findings demonstrate that the disorder generated by the asymmetric branched chains when the molecule is physisorbed in thin film can be instrumental for enhancing charge transport via thermal annealing. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
PubMed | CNR Institute of Crystallography, University Dellinsubria And Toscalab, U.S. National Institute of Standards and Technology, Aix - Marseille University and 2 more.
Type: Journal Article | Journal: Nature | Year: 2015
As a cleaner, cheaper, and more globally evenly distributed fuel, natural gas has considerable environmental, economic, and political advantages over petroleum as a source of energy for the transportation sector. Despite these benefits, its low volumetric energy density at ambient temperature and pressure presents substantial challenges, particularly for light-duty vehicles with little space available for on-board fuel storage. Adsorbed natural gas systems have the potential to store high densities of methane (CH4, the principal component of natural gas) within a porous material at ambient temperature and moderate pressures. Although activated carbons, zeolites, and metal-organic frameworks have been investigated extensively for CH4 storage, there are practical challenges involved in designing systems with high capacities and in managing the thermal fluctuations associated with adsorbing and desorbing gas from the adsorbent. Here, we use a reversible phase transition in a metal-organic framework to maximize the deliverable capacity of CH4 while also providing internal heat management during adsorption and desorption. In particular, the flexible compounds Fe(bdp) and Co(bdp) (bdp(2-)=1,4-benzenedipyrazolate) are shown to undergo a structural phase transition in response to specific CH4 pressures, resulting in adsorption and desorption isotherms that feature a sharp step. Such behaviour enables greater storage capacities than have been achieved for classical adsorbents, while also reducing the amount of heat released during adsorption and the impact of cooling during desorption. The pressure and energy associated with the phase transition can be tuned either chemically or by application of mechanical pressure.