Suchergebnisse

By employing diverse surface sensitive synchrotron radiation spectroscopies we demonstrate that the fluorine content of initial C60F48 deposited at room temperature on Ag(111) varies with molecular coverage. At the very early stages of deposition, C60F48 fully de-fluorinates and transforms into C60. Strong indications of silver fluoride formation are provided. The chemical footprint of fluorinated fullerenes emerges at relatively low molecular coverage indicating that the degree of fullerene de-fluorination decreases (from total to partial de-fluorination) as molecules are deposited. De-fluorination stops well before the substrate surface is completely covered by fullerenes. At the molecular level, the fluorine loss observed by spectroscopic techniques are supported by scanning tunneling microscopy imaging. Both molecules and metal surface are importantly involved in the process. ; This work has been supported by the Spanish Government under the projects PID2019-110907GB-I00, MAT2017-85089- C2-1-R (AEI/FEDER, UE) and the ''Severo Ochoa'' Program for Centres of Excellence in R&D (CEX2019-000917-S). This project has received funding from the EU-H2020 research and innovation programme under grant agreement No 654360 having benefitted from the access provided by CNR-IOM in Trieste and Grenoble within the framework of the NFFA-Europe Transnational Access Activity (ID: 929). ; Peer reviewed

The present work assesses improved carrier injection in organic field-effect transistors by contact doping and provides fundamental insight into the multiple impacts that the dopant/semiconductor interface details have on the long-term and thermal stability of devices. We investigate donor [1]benzothieno[3,2-b]-[1]benzothiophene (BTBT) derivatives with one and two octyl side chains attached to the core, therefore constituting asymmetric (BTBT-C8) and symmetric (C8-BTBT-C8) molecules, respectively. Our results reveal that films formed out of the asymmetric BTBT-C8 expose the same alkyl-terminated surface as the C8-BTBT-C8 films do. In both cases, the consequence of depositing fluorinated fullerene (C60F48) as a molecular p-dopant is the formation of C60F48 crystalline islands decorating the step edges of the underlying semiconductor film surface. We demonstrate that local work function changes along with a peculiar nanomorphology lead to the double beneficial effect of lowering the contact resistance and providing long-term and enhanced thermal stability of the devices. ; This work has been supported by the Spanish Government under projects MAT2016-77852-C2-1-R (AEI/FEDER, UE), FANCY CTQ2016-80030-R, and "Severo Ochoa" Program for Centers of Excellence in R&D (SEV-2015-0496). We acknowledge the GC recognitions 2017-SGR668 and 2017- SGR918 and the Networking Research Center on Bioengineering, Biomaterials and Nanomedicine (CIBER-BBN). A.B. thanks the Spanish Government financial support through BES-2016-077519 FPI fellowship. This work has been carried out within the framework of the doctoral program (Ph.D.) of Material Science (Department of Physics) of the Universitat Autònoma de Barcelona (UAB). O.S. acknowledges the support of the Israel Ministry of Science, the Center for Absorption in Science of the Ministry of Immigrant Absorption, and the Committee for Planning and budgeting of the Council for Higher Education under the framework of the KAMEA Program. J.L. acknowledges the support of the Chinese Council for Ph.D. fellowship. We acknowledge The European Synchrotron Radiation Facility (ESRF) and CSIC for the provision of measurements using the BM25-SpLine beamline. ; Peer reviewed