Giampiero Ruani

A transparent organic transistor structure for bidirectional stimulation and recording of primary neurons

Real-time stimulation and recording of neural cell bioelectrical activity could provide an unprecedented insight in understanding the functions of the nervous system, and it is crucial for developing advanced in vitro drug screening approaches. Among organic materials, suitable candidates for cell interfacing can be found that combine long-term biocompatibility and mechanical flexibility. Here, we report on transparent organic cell stimulating and sensing transistors (O-CSTs), which provide bidirectional stimulation and recording of primary neurons. We demonstrate that the device enables depolarization and hyperpolarization of the primary neuron membrane potential. The transparency of the device also allows the optical imaging of the modulation of the neuron bioelectrical activity. The maximal amplitude-to-noise ratio of the extracellular recording achieved by the O-CST device exceeds that of a microelectrode array system on the same neuronal preparation by a factor of 16. Our organic cell stimulating and sensing device paves the way to a new generation of devices for stimulation, manipulation and recording of cell bioelectrical activity in vitro and in vivo.

Nanoimprint lithography for organic electronics

Thin films made of organic semiconductors (α-sexithiophene, PDAS and PBAS) have been printed and the impact on morphology studied by optical, atomic force and electron microscopy. Surfaces in contact with the stamp during printing undergo a change towards smoother and more ordered material at the macromolecular scale. Interdigitated nanoelectrodes to be used as source and drain in TFTs have been made and printed down to 100 nm. PDAS and PBAS can be printed at room temperature and preserve their printed feature provided they are cross-linked afterwards.

Weak intrinsic charge transfer complexes: A new route for developing wide spectrum organic photovoltaic cells

Solar emission extends in the near IR and one of the main issues in designing organic solar cells resides in extending the response into the near IR. Here we show that this may be achieved by making intimate interpenetrated networks of C60 and Zn–phthalocyanine (Zn–Pc) in the solid. Various spectroscopic investigations of co-sublimated thin films of C60 and Zn–phthalocyanine give indeed ample evidence of the existence of a weak charge transfer (CT) state at 1.4 eV, which quenches the photoluminescence of both molecules. The films produced by co-sublimation undergo to a spinodal decomposition producing domains prevalently constituted by Zn–Pc in contact with domain prevalently of C60. The domains size depends on the deposition conditions (rate, stoichiometry, and substrate temperature) forming a percolating 3D network. The separation in different domains is confirmed by the observation of two overlapping peaks, in the resonant Raman spectrum, that correspond to the Ag(2) pinch mode (C=C double bond stretch...

Multi-modal sensing in spin crossover compounds

We exploited the solvatochromic spin-state switching in a spin crossover (SCO) compound based on the FeII complex and the simultaneous change of spectroscopic properties for selective multimodal sensing of methanol and ethanol. We demonstrate that sensing capabilities are due to the inclusion of methanol or ethanol molecules into the crystalline structure, which tailors simultaneously the transition temperature, colour, birefringence and vibrational modes. We exploited this capability by integrating a neutral compound, switchable at room temperature, into a micrometric TAG sensitive to the colour and birefringence. The system was characterised by optical microscopy, magnetic susceptibility, Raman spectroscopy and X-ray diffraction.

Electronic levels ordering in α-sexithienyl

Abstract The electronic level ordering in a polycrystalline thin film of α-sexithienyl (T 6 ) has been determined by photoluminescence, one- and two-photon excitation, and photoconductivity measurements. The lowest 1 1 B u Frenkel exciton is located at 17 452 cm −1 . From site-selective photoluminescence we locate an extended inhomogeneous distribution of localized isolated T 6 levels (X-traps) below the 1 1 B u Frenkel exciton extending for 2000 cm −1 . The origin of the lowest 2 1 A g Frenkel exciton is located at 18 350 cm −1 , i.e. 898 cm −1 above the 1 1 B u . The photoconductivity action spectrum shows an onset at about the same energy of the 2 1 A g exciton band and reaches a maximum 1450 cm −1 above the 1 1 B u exciton band. T 6 is proposed as a good model compound for real polythiophene. The difference in energetics and photophysical properties due to different electronic correlation effects between polyenes and polythiophene is discussed.

The dynamics of the internal phonons tris(quinolin-8-olato) aluminum(III) in crystalline β-phase

A new approach to the analysis of the internal phonons of tris(quinolin-8-olato) aluminum(III) is presented, which enlightens the role played by the ligands in determining the vibrational properties of the organometallic compound and evidences the importance of the contributions arising from the coupling terms among the three quinolinato fragments. An accurate exam of the normal modes of the meridianal isomer evidences the role of the interactions among the fragments in the vibrational dynamics of the ground state. Due to the special attention paid to the quinolinato fragments, a preliminary investigation on the vibrational properties of 8-hydroxyquinoline, taken as a model fragment, was also performed. The vibrational properties of the polymorph species β of the organometallic molecule were obtained refining the calculated frequencies, the dipole moment derivative matrix, and the polarizability derivative tensor derived by the hybrid density functional B3LYP/6-31G* comparing with the frequencies and inte...

Carbon nanotube networks patterned from aqueous solutions of latex bead carriers

Patterning arrays of single walled carbon nanotubes (SWCNTs) is an important technological step for a range of applications of these materials in electronics, optics, electrochemistry and bio-sensing. Here, we demonstrate the fabrication of conductive networks of SWCNTs with controlled porosity on the mesoscopic scale by two dimensional assembly, from aqueous solutions, of monodisperse polystyrene (PS) beads carrying SWCNTs at their surface. SWCNTs are adsorbed onto the bead surface by non covalent hydrophobic interactions. Once the PS beads self-organize into ordered arrays, they are removed by an organic solvent, yielding a connected SWCNTs network that retains the geometrical structure of the bead assembly. The electrical properties of these ordered SWCNTs arrays exhibit a Mott-conducting behavior with RT conductivity of 100 S cm−1.

The polarized infrared and Raman spectra of α-T6 single crystal: An experimental and theoretical study

The polarized infrared absorption and Raman spectra on the bc plane of a single crystal of α-sexithienyl (α-T6) have been recorded in the range from 50 up to 3500 cm−1. The intermolecular interactions give rise to the Davydov splitting of the ungerade phonon energy levels originated by the molecular pyramidalization along with the CCH bending modes. A μ-Raman investigation on the crystal surface allows identification of the perturbed local packing of the molecules, which are spectroscopically crystal defects. The selective resonant enhancement of the scattering intensity of some Raman modes, obtained by exciting at λex=632.8 nm, indicates that these defects are associated with the lowering of the electronic excited states due to the increased π-orbital overlapping. Moreover, the resonant enhancement allows detection of some of the gerade intramolecular phonons not observed in the bulk. The comparison between the far-infrared absorption spectra recorded at room temperature and at 80 K evidences three latti...

Micro-Raman and Resistance Measurements of Epitaxial La0.7Sr0.3MnO3 Films

The Channel-Spark method was used for deposition of highly oriented ferromagnetic La0.7Sr0.3MnO3 films on NdGaO3 substrates. It was found that additional oxygen decreases the film quality suppressing the Curie temperature and metal–insulator transition below room temperature. To achieve the best quality of the films the samples were either annealed in high vacuum at deposition temperature or even deposited in argon atmosphere with no oxygen annealing. For such films the resistive measurements showed a metallic behaviour in the interval 10 to 300 K in accordance with the high Curie point (TC ≥ 350 K). Micro-Raman analysis indicates that the La0.7Sr0.3MnO3 films are well ordered, while some outgrowths show stoichiometrical deviations.

Eciency enhancement of P3HT:PCBM solar cells containing scattering Zn-Al hydrotalcite nanoparticles in the PEDOT:PSS layer

Abstract In this article we report on a new hybrid (organic-inorganic) composite material based on hydrophilic, electrically inert and semi-transparent hydrotalcite (HT) nanoparticles and a pHneutral formulation of PEDOT:PSS. The application of this composite material as electrically and optically active buffer layer in P3HT:PC61BM bulk heterojunction (BHJ) solar cells is reported. Two different synthetic routes are explored to obtain HTs having discoid shape, with a diameter of around 150- 200 nm and a thickness of ~20 nm, to be easily embedded in ~50 nm thick PEDOT:PSS films. The good affinity between HTs and the sulfonate groups of the PEDOT:PSS allows to obtain homogeneous HTs/PEDOT:PSS films, for HT concentrations of 0.25% and 0.50% by weight (vs. PEDOT:PSS). At these particle loads the electrical and morphological features of doped and undoped PEDOT:PSS films are nearly identical, while providing a significant effect on the visible light scattering properties of the composite films. We demonstrate ~12% improvement in power conversion efficiency (PCE) for P3HT:PC61BM solar cells incorporating HTs in the PEDOT: PSS layer, which mainly originates from increased shortcircuit current densities (JSC).