3 research outputs found
Assembly of the Intraskeletal Coral Organic Matrix during Calcium Carbonate Formation
Scleractinia coral skeleton formation occurs by a heterogeneous
process of nucleation and growth of aragonite in which intraskeletal
soluble organic matrix molecules, usually referred to as SOM, play
a key role. Several studies have demonstrated that they influence
the shape and polymorphic precipitation of calcium carbonate. However,
the structural aspects that occur during the growth of aragonite have
received less attention. In this research, we study the deposition
of calcium carbonate on a model substrate, silicon, in the presence
of SOM extracted from the skeleton of two coral species representative
of different living habitats and colonization strategies, which we
previously characterized. The study is performed mainly by grazing
incidence X-ray diffraction with the support of Raman spectroscopy
and electron and optical microscopies. The results show that SOM macromolecules
once adsorbed on the substrate self-assembled in a layered structure
and induced the oriented growth of calcite, inhibiting the formation
of vaterite. Differently, when SOM macromolecules were dispersed in
solution, they induced the deposition of amorphous calcium carbonate
(ACC), still preserving a layered structure. The entity of these effects
was species-dependent, in agreement with previous studies. In conclusion,
we observed that in the setup required by the experimental procedure,
the SOM from corals appears to present a 2D lamellar structure. This
structure is preserved when the SOM interacts with ACC but is lost
when the interaction occurs with calcite. This knowledge not only
is completely new for coral biomineralization but also has strong
relevance in the study of biomineralization on other organisms
Logic-Gate Devices Based on Printed Polymer Semiconducting Nanostripes
The applications of organic semiconductors
in complex circuitry
such as printed CMOS-like logic circuits demand miniaturization of
the active structures to the submicrometric and nanoscale level while
enhancing or at least preserving the charge transport properties upon
processing. Here, we addressed this issue by using a wet lithographic
technique, which exploits and enhances the molecular order in polymers
by spatial confinement, to fabricate ambipolar organic field effect
transistors and inverter circuits based on nanostructured single component
ambipolar polymeric semiconductor. In our devices, the current flows
through a precisely defined array of nanostripes made of a highly
ordered diketopyrrolopyrrole-benzothiadiazole copolymer with high
charge carrier mobility (1.45 cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup> for electrons and 0.70 cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup> for holes). Finally, we demonstrated
the functionality of the ambipolar nanostripe transistors by assembling
them into an inverter circuit that exhibits a gain (105) comparable
to inverters based on single crystal semiconductors
Molecular Reorganization in Organic Field-Effect Transistors and Its Effect on Two-Dimensional Charge Transport Pathways
Charge transport in organic thin film transistors takes place in the first few molecular layers in contact with the gate dielectric. Here we demonstrate that the charge transport pathways in these devices are extremely sensitive to the orientational defects of the first monolayers, which arise from specific growth conditions. Although these defects partially heal during the growth, they cause depletion of charge carriers in the first monolayer, and drive the current to flow in the monolayers above the first one. Moreover, the residual defects induce lower crystalline order and charge mobility. These results, which are not intuitively explained by electrostatics arguments, have been obtained by combining <i>in situ</i> real time structural and electrical characterization together with <i>ex situ</i> AFM measurements, on thin films of a relevant n-type organic semiconductor, <i>N</i>,<i>N</i>′-bis(<i>n</i>-octyl)-dicyanoperylene-3,4:9,10-bis dicarboximide grown by sublimation in a quasi-layer-by-layer mode at different substrate temperatures