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Patterning PEDOT:PSS and tailoring its electronic properties by water-vapour-assisted nanoimprint lithography

In this article a new water-vapour-assisted nanoimprint lithography (NIL) process for the patterning and electronic property control, of the conducting poly-ethylenedioxythiophene : poly-styrenesulfonate (PEDOT:PSS) is presented. PEDOT:PSS is a conductive polymer, widely used for organic thin-film  transistors  (OTFTs), organic light-emitting diode (OLED) displays and in organic photovoltaic device (OPV). It has been also demonstrated as catalytically active anti-corrosion electrode in photoelectrochemical cells, in ionic charge storage medium for super capacitors, or as stable, biocompatible, implantable electrodes for in vivo neuronal activity recording. For most of those application nano structuration of the PEDOT:PSS layer is of key importance for device miniaturization and performance. 
 NIL process is a strong candidate for low cost high throughput technique for PEDOT:PSS nano structuration but with traditional NIL process results with limited aspect ratios were obtained (Max 0,86 AR for sub-100nm resolution). The process here presented was optimized with respect to relative humidity, applied pressure and temperature (RH, P, T). The control of environmental humidity was found to be crucial. 

High quality nanostructures were reproducibly obtained at high relative humidity values (RH >75%), with sub-100 nm resolution features attaining aspect ratios (AR) as high as ~6 at ~95% RH. The developed process of water-vapour-assisted NIL (WVA-NIL) strongly affects the electronic properties of PEDOT:PSS. 
By current-voltage measurements and ultraviolet photoemission spectroscopy we demonstrate that the process parameters p, T and RH are correlated with changes of PEDOT:PSS conductivity, work function and states of the valence band. In particular, an increase in the films conductivity by factors as high as 105 and a large decrease in the work function, up to 1.5 eV, upon WVA-NIL processing were observed. Moreover, it was found that workfunction shift can be reversed by a short oxygen plasma treatment, without altering significantly the layer's nano structure or conductivity. Employing the produced PEDOT:PSS nanostructured layers as anode buffer layer in P3HT:ICBA bulk heterojunction solar cells, a significant performance increase was obtained (60% relative increase of  efficiency respect to a not patterned reference cell).


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Patterning PEDOT:PSS and tailoring its electronic properties by water-vapour-assisted nanoimprint lithography

Andrea Radivo,ab   Enrico Sovernigo,ac   Marco Caputo,d  Simone Dal Zilio,a   Tsegaye Endale,e   Alessandro Pozzato,c  Andrea Goldonid and   Massimo Tormen*ac  
*Corresponding authors
a Istituto Officina dei Materiali-CNR, Laboratorio TASC, I-34149 Trieste, Italy
b University of Trieste, Piazzale Europa, I-34127 Trieste, Italia
c ThunderNIL srl, via Ugo Foscolo 8, 35131 Padova, Italy
d Sincrotrone Trieste SCpA, I-34149 Trieste, Italy
e Department of Chemistry, Addis Ababa University, P. O. Box: 1176, Addis Ababa, Ethiopia 

E-mail: tormen@iom.cnr.it ;Tel: +39 0403758416

RSC Adv., 2014,4, 34014-34025
DOI: 10.1039/C4RA04807E
Received 21 May 2014, Accepted 23 Jul 2014
First published online 23 Jul 2014

Alkali Metal Doped Picene Layers: Insulating Phase in Multilayer Doped Compounds

Since the discovery of superconductivity in 1911, one of the most interesting issue is to understand the mechanism of Cooper pair formation. New challenges arise also from the discovery of superconductivity  in C60 solid doped with alkali metals. Recently a polycyclic aromatic compound, the picene molecule, was discovered to have a superconducting phase transition when doped with alkali metals, with Tc around 18 K. 

Theoretical studies on K3picene showed that the superconductivity could be driven by electron−phonon (intramolecular) coupling, as in the case of K3C60. On the other hand, recent DFT calculations showed that K3picene turns into a Mott−Hubbard insulator when its unit cell experiences an enlargement of 5%, like observed in C60 compounds. Therefore, a fundamental question has to be addressed: do correlation effects and crystal arrangements play a decisive role in doped picene electronic structure and superconductivity as in the case of C60 compounds?
Figure 1 shows the K-doped picene multilayer valence bands at various doping stages, namely K0.5picene and K3picene.
A new state (C) near the Fermi level appears as a consequence of the LUMO − LUMO +1 derived picene bands filled by 4s electrons of K, however this new state is peaked at 0.8 eV of binding energy, and there is no DOS at the Fermi level showing, therefore, an insulating phase for the system.There is a possibility that the metallic state should appear by competing with a phonon-driven (and correlation-assisted) ground state, leading to an insulator−metal transition as a function of temperature.

Figure 2 shows the valence band spectra close to the Fermi level of K3picene as a function of temperature, but is evident that the LUMO − LUMO+1 peak remains below the Fermi level, and there is not any DOS appearing at EF.Therefore, the system is insulating also at low temperature. To understand if the observed insulating behaviour is related to correlation effects, we analyze the picene monolayer where possible correlation effects should be   screened by Ag substrate electrons. The evolution of the valence band for the pristine and K (Na) doped monolayers of picene is shown in figure3. The first observation is that in the pristine monolayer there is a Fermi level, and the HOMO-derived band is shifted from 3 to 2.7 eV in the undoped monolayer with respect to the multilayer.

The presence of the Fermi level in the monolayer/substrate system is mainly due to the underlying Ag, but it is evident that the DOS near EF changes as the alkali metals are added to the monolayer, as shown in figure4. Both the shift of the HOMO in the undoped system and the metallic phase for the doped monolayer can be ascribed to the screening effect of the metallic substrate. This behavior could be explained in close analogy to fullerides assuming that the HOMO−LUMO gap and the insulating state, observed in photoemission adding electrons to the LUMO − LUMO+1 bands, may have a strong Coulomb contribution.

However, it is worth noting that the UHV pristine films grown on Ag(111) have a peculiar adsorption geometry, which is different from the expectation based on crystal structure calculations and measurements for picene crystals. Due to strong correlation effects, small variations in the crystal structure (molecular arrangements) may be the reason for the observed insulating state in our doped picene multilayer.


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Experimental Study of Pristine and Alkali Metal Doped Picene Layers: Confirmation of the Insulating Phase in Multilayer Doped Compounds

M. Caputo , G. Di Santo , P. Parisse , L. Petaccia , L. Floreano §, A. Verdini §, M. Panighel , C. Struzzi , B. Taleatu , C. Lal , and A. Goldoni *

ST-INSTM Lab., Sincrotrone Trieste S.C.p.A., s.s. 14 km 163.5 in Area Science Park, 34149 Trieste, Italy
Department of Physics, Trieste University, Via Valerio 2, 34127 Trieste, Italy
§ Lab. TASC, IOM-CNR, s.s. 14 km 163.5 in Area Science Park, 34149 Trieste, Italy
Department of Physics, Obafemi Awolowo University Ile-Ife, Nigeria
Centre for Non-Conventional Energy Resources, University of Rajasthan, Jaipur, India
DOI: 10.1021/jp306640z
Publication Date (Web): September 4, 2012
Copyright © 2012 American Chemical Society

*E-mail: .


2H-TPP on Ag: carbon de-hydrogenation and geometrical adaptation

We observe a selective carbon de-hydrogenation, the formation of new aryl-aryl bonds between phenyl groups and the macrocycle, as well as the rotation of the phenyl rings in a flat conformation. Experiments and theoretical calculations prove this chemical reaction.

In our recent investigations we have demonstrated that one monolayer of 2H-TPP, prepared by thermal desorption of the corresponding multilayer at 550 K on Ag(111), adsorbs with the macrocycle and the phenyl flat. This information has been directly addressed by means of X-ray absorption and photoemission experiments.
 Theoretical calculations suggest a possible molecular reaction and modification of porphyrins, in order to explain this adsorption conformation: the de-hydrogenation of eight carbon atoms in the remaining monolayer after the multilayer desorption, with the formation of four new aryl-aryl carbon bonds.
While the reaction takes place also in the deposited monolayer annealed at 550 K, the initial presence of the multilayer favors a decrease of the aryl-aryl coupling barrier and the selection of a spiral conformation in the de-hydrogenated molecule. The chemical reaction produces a stable molecule that forms a patterned square lattice on Ag(111) and that can be further modified by the introduction of central metal atoms.


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Supramolecular Engineering through Temperature-Induced Chemical Modification of 2H-Tetraphenylporphyrin on Ag(111): Flat Phenyl Conformation and Possible Dehydrogenation Reactions

Giovanni Di Santo1, Stephan Blankenburg2, Carla Castellarin-Cudia1, Mattia Fanetti1, Patrizia Borghetti3, Luigi Sangaletti3, Luca Floreano4, Alberto Verdini4, Elena Magnano4, Federica Bondino4, Carlo A. Pignedoli2, Manh-Thuong Nguyen2, Roberto Gaspari2, Daniele Passerone2, Andrea Goldoni1,*

1INSTM—Micro & Nano-Carbon Laboratory, Sincrotrone Trieste S.C.p.A. s.s.14 km. 163.5, 34149 Trieste (Italy), Fax: +(39) 040-3758565Empa, Swiss Federal Laboratiories for 2Materials Science and Technology nanotech@surfaces Laboratory, Ueberlandstrasse 129, 8600 Dübendorf (Switzerland)
3Dipartimento di Matematica e Fisica and Interdisciplinary Laboratories for Advanced Materials Physics, Università Cattolica del Sacro Cuore, Brescia (Italy)
4Istituto Officina dei Materiali-CNR, Lab. TASC, s.s. 14 km 163.5, 34149 Trieste (Italy)


Chemistry - A European Journal vol 17, Issue 51, 14354, December 16, 2011
DOI: 10.1002/chem.201102268
Publication Date (Web): November 23, 2011
Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim


Metalation of tetraphenylporpyrin with Fe atoms and their conformational adaptation onto the Ag(111) surface.

In-situ metalation of porphyrin is of great interest for the characterization of pure species in a controlled environment. We have followed the formation of pure 2H-tetraphenylporphyrin and Fe- tetraphenylporphyrin layers on Ag(111) single crystal. G. Di Santo et al.J. Phys. Chem. C 115, 4155 (2011)

In this experiment we characterized the electronic states and the molecules' geometrical adaptation during the formation of pure 2H-5,10,15,20-tetraphenylporphyrin (2H-TPP) and Fe- tetraphenylporphyrin (Fe-TPP) layers on Ag(111) single crystal. Core level absorption spectra indicate the flat conformation of the monolayer suggesting an adatom hopping instead of a surface mediated dopant diffusion for the metalation process. Photoemission points out that the interaction between Fe dz-states and Ag bands increases the monolayer metallic character already induced by the charge transfer from the substrate. The NEXAFS spectra, taken in s and p light polarization at N and C K-edges, put in evidence the flat configuration for the macrocycle and showed that the phenyl groups lie flat in the case of the monolayer while having nonflat orientation in the multilayer.


   The multilayer Fe metalation favors a macrocycle N distortion, while in the monolayer, the conformation of the phenyl legs and the interaction with the substrate reduce the degrees of freedom of the macrocycle toward the already reached lowest energy situation. The influence of the Fe metallic center in the porphyrin core has only minor structural effects in the monolayer. Both core level and valence band photoemission results give evidence that the charge injection from the substrate is more likely confined to the first monolayer. The metallic state of the first layer evolves with Fe complexation because of d state hybridization with the s−p bands of the substrate.

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Conformational Adaptation and Electronic Structure of 2H-Tetraphenylporphyrin on Ag(111) during Fe Metalation

Giovanni Di Santo, Carla Castellarin-Cudia, Mattia Fanetti, Bidini Taleatu§||, Patrizia Borghetti, Luigi Sangaletti, Luca Floreano, Elena Magnano, Federica Bondino, and Andrea Goldoni*
Sincrotrone Trieste S.C.p.A. s.s.14 Km. 163.5, 34012 Trieste, Italy - Department of Physics, Università Cattolica del Sacro Cuore Brescia, Italy - Istituto Officina dei Materiali-CNR, Lab. TASC, s.s. 14 km 163,5, 34149 Trieste, Italy - § Department of Physics, Obafemi Awolowo University - Ile-Ife, Nigeria -  || International Center of Theoretical Physics, St. Costiera 11, 34151 Trieste, Italy

J. Phys. Chem. C, 2011, 115 (10), 4155
DOI: 10.1021/jp111151n
Publication Date (Web): February 22, 2011
Copyright © 2011 American Chemical Society


 Adsorption Geometry and Electron Transfer of Zn-tetraphenyl-porphyrin on different substrates

The importance of substrate and interfaces has been exploited in this experimental study on the interaction of one single layer of Zn-tetraphenyl-porphyrin with Ag(110) and Si(111). Photoemission, near-edge X-ray absorption, and resonant photoemission were used to investigate the bonding nature, the adsorption geometry as well as the dynamics of electron transfer between the molecules and the metal or semiconductor surfaces. ChemPhysChem, 11: 2248.

We report on the preparation of a conformationally controlled Zn-tetraphenyl-porphyrin (ZnTPP) single layer on two possible substrates, Ag(110) and Si(111).The ZnTPP molecule is characterized by four phenyl groups bonded to the macrocycle and a central Zn atom. As substrates we have chosen silver, normally used as contact in photovoltaic or transistor devices, and silicon, worldwide employed in semiconductor industry. The substrate can influence the thin film morphology, the distortion of the molecules and the electronic charge transfer as a consequence.

The molecular orientation with respect to the substrate was monitored using angular dependent near edge x-ray absorption fine-structure spectroscopy (NEXAFS), while the electronic properties of the filled states were investigated using x-ray and ultraviolet photoemission (XPS and UPS). 
Depending on the substrate, the adsorption orientation is mainly mastered by the coupling of the phenyl legs or the macrocycle with the surface. The ResPES behavior indicates that for the phenyl rings the charge transfer into the substrate is less favorable than on the Ag(110) case and comparable to the multilayer case. Core level photoemission indicates that the molecule is interacting with the substrate using a macrocycle pyrrole ring, while the phenyl rings are rotated in such a way to minimize the interaction with the substrate.

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Substrate Influence for the Zn-tetraphenyl-porphyrin Adsorption Geometry and the Interface-Induced Electron Transfer

Carla Castellarin-Cudia Dr.1, Patrizia Borghetti2, Giovanni Di Santo Dr.1, Mattia Fanetti Dr.1, Rosanna Larciprete Dr.1,3, Cinzia Cepek Dr.4, Paolo Vilmercati Dr.1, Luigi Sangaletti Prof.2, Alberto Verdini Dr.4, Albano Cossaro Dr.4, Luca Floreano Dr.4, Alberto Morgante Prof.4, Andrea Goldoni Dr.1

ChemPhysChem Volume 11, Issue 10, 2248, July 12, 2010
Article first published online: 10 JUN 2010
DOI: 10.1002/cphc.201000017

Structure and Molecule–Substrate Interaction in a Co-octaethyl Porphyrin Monolayer on the Ag(110) Surface

 The structure and the morphology of a highly ordered ultrathin film of Co-OEP is described in detail by means of STM images and NEXAFS spectroscopy, while the molecular interaction with the substrate and the electronic structure of the film are studied by means of UPS, NEXAFS at the Co 2p threshold, and DFT calculations. J. Phys. Chem. C 2011, 115, 11560

Ordered thin films of metallorganic magnetic molecules, e.g. metal porphyrins adsorbed on ferro- magnetic transition metal substrates, are potentially interesting in the fields of data storage and spintronics. Herein, we choose the octaethyl-porphyrins with the magnetic Co metal as the central atom, to investigate the possible realization of a long- range ordered 2D array of magnetic elements, by exploiting the self-organizing properties of porphyrins on Ag(110), a noncova- lently interactive and nonmagnetic substrate. The properties of this model system, which is prepared under highly controlled conditions and in ultra high vacuum, can be studied with the full capabilities of surface science techniques. In this work we present a combined experimental and theoretical study of the ultrathin film of Co-octaethylporphyrin (Co-OEP) molecules deposited on the Ag(110) surface. The morphological and electronic properties of this heterogeneous metallorganic interface were studied by means of scanning tunneling microscopy (STM), near-edge X-ray adsorption fine structure (NEXAFS) spectroscopy, ultraviolet photoemission spectroscopy (UPS), and density functional theory calculations (DFT). The long-range self-ordered single layer of Co-OEP was obtained by thermal desorption of the molecular multilayer. The single-layer molecules were arranged in a noncommensurate rectangular lattice aligned with the substrate high-symmetry directions.

The combination of experimental techniques and numerical simulations indicated that in this configuration each molecular macrocycle is tilted with respect to the metal surface of about 15°. The strong molecular interaction with the substrate leads to the electron transfer from the metal substrate to the molecule. The direct interaction with the substrate involves mostly the Co metal center, which modifies the valence state with respect to the free Co-OEP molecules due to the hybridization between Co states and Ag bands.

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Structure and Molecule–Substrate Interaction in a Co-octaethyl Porphyrin Monolayer on the Ag(110) Surface

Mattia Fanetti, Arrigo Calzolari§, Paolo Vilmercati, Carla Castellarin-Cudia, Patrizia Borghetti#, Giovanni Di Santo, Luca Floreano, Alberto Verdini, Albano Cossaro, Ivana Vobornik, Emilia Annese, Federica Bondino, Stefano Fabris§, and Andrea Goldoni
Sincrotrone Trieste S.C.p.A., S.S.14 Km. 163.5, Basovizza, I-34149 - Trieste, Italy - CNR-IOM, Laboratorio TASC, S.S. 14 km 163.5, Basovizza, I-34149 Trieste, Italy - § Theory@Elettra Group, CNR-IOM DEMOCRITOS Simulation Center, S.S. 14 km 163.5, Basovizza, I-34149 Trieste, Italy and SISSA-Scuola Internazionale Superiore di Studi Avanzati, via Bonomea 256, I-34136, Trieste, Italy -  || Dipartimento di Fisica, Universita' di Trieste, via Valerio 2, I-34127, Trieste, Italy  -
Department of Physics and Astronomy, University of Tennessee Knoxville, 1408 Circle Drive, Knoxville, Tennessee 37996, United States -  # Università Cattolica del Sacro Cuore, Dipartimento di Matematica e Fisica, via Musei 41, I-25121, Brescia, Italy

J. Phys. Chem. C, 2011, 115 (23), 11560
DOI: 10.1021/jp2011233
Publication Date (Web): May 23, 2011
Copyright © 2011 American Chemical Society

Last Updated on Monday, 29 September 2014 18:21