Title: Structural and electrical properties of Indolocarbozole derivatives films: A scanning probe microscopy study

Authors: José Abad, Inés Nieto, Miriam Más-Montoya, David Curiel, Jaime Colchero.

Abstract: Organic conjugated compounds based on indolocarbazole derivatives have attracted much attention in view of the prospective applications of these conjugated materials in organic electronics. We have obtained very promising conductivity results (10 -2 S/cm). However, we have found a data variance from 10-2 to 10-8 S/cm for the same set of samples. These results point out the importance of the morphology in the conductivity properties. In the present work we apply scanning probe microscopy (SPM) techniques to study, on a nanometer scale, the morphology of these molecules prepared from different methods.

Title: Influence of Ultraviolet and Ozone degradation on the nanomorphology and electrical properties of P·OT thin films studied by Scanning Probe Microscopy and related techniques

Authors: J. Abad, N. Espinosa, R. García-Valverde, A. Urbina and J. Colchero

Abstract: In the field of organic solar cells the power conversion efficiency and the durability are issues that have to be addressed before this technology is competitive with traditional silicon solar cells1. One of the research lines of our group is devoted to a better understanding of how the nanoscale properties determine the macroscopic behavior of such devices2-5. In order to understand the degradation mechanisms of plastic solar cells, we investigate in the present work the modification of thin P3OT films by ultraviolet (UV) irradiation and O3 exposure. Films of 100 nm thickness have been prepared by spin-coating on conducting as well as insulating substrates. The samples were characterized by non-contact Scanning Force Microscopy (SFM), as well as by optical transmission measurements and macroscopic electronic transport measurements. Our experimental setup allows us to perform SFM nanoscale studies of the same region, even if the sample is taken out of the SFM system for different processes, and hence we can attribute the observed changes to the real effect of radiation and O3 as compared to possible statistical variations of surface properties.

Title: Nanoscale ultraviolet and ozone degradation of P3OT films studied by Scanning Probe Microscopy

Authors: J. Abad, A. Urbina, J. Colchero

Abstract: In the field of organic solar cells the power conversion efficiency and the durability are issues that have to be addressed before this technology is competitive with traditional silicon solar cells. To study the durability of plastic solar cells, in the present work we investigate the modification of thin P3OT films by ultraviolet (UV) radiation and ozone degradation. Films of about 100 nm thickness have been prepared by spin-coating on conducting as well as insulating substrates. The samples were analysed using Scanning Force Microscopy techniques (SFM) in particular Kelvin Probe Microscopy and local conductivity imaging and optical transmission measurements for every cycle of UV radiation and ozone exposure. Our experimental technique allowed us to perform a nanoscale study of the same area of the sample and therefore we can attribute the observed changes to the real effect of radiation as compared to possible statistical variations of surface properties.

Title: Structural and electrical properties of poly(3-octylthiophene) (P3OT) films: A scanning probe microscopy study

Authors: J. Abad, E. Palacios-Lidón, B. Pérez-García, A. Urbina, J. Colchero

Abstract: Poly-(3-octylthiophene) is one of the most promising materials for applications in organic opto-electronic devices such as field-effect transistors, light-emitting diodes or plastic solar cells due to its high hole mobility. Understanding the correlation between the morphological and electrical properties is of vital importance, since the structural arrangements of the molecules determines and limits the overall devices. In the present work we use scanning force microscopy techniques to study P3OT thin films, combining topographic, electrostatic, capacitance and electronic transport measurements.

Title: Gold-P3OT contact studied by Kelvin probe microscopy

Authors: Jose Abad and Jaime Colchero

Abstract: Poly-(3-octylthiophene) is one of the most promising materials for applications in organic opto-electronic devices such as field-effect transistors, light-emitting diodes and in particular plastic solar cells. In the field of organic solar cells a complete understanding of the metal-polymer interface is of vital importance in order to make this technology competitive with traditional silicon solar cells. In the present work we investigate the interaction between P3OT thin films and Au.

Title: Dynamic method for calibration of sensivity in Scanning Force Microscopy

Authors: J. F. González, J. Abellán, J. Colchero

Abstract: SFM has become a fundamental tool in many disciplines and fields. Among the different operation modes, the dynamic mode is without doubt the most important and versatile one. In this mode, the tip is oscillated at or near the resonance frequency of the supporting cantilever and the variation of resonance frequency or oscillation amplitude is used as feedback signal. For quantitative applications we believe that the calibration of the system is an issue that has not yet been resolved satisfactorily. In particular, most experiments are performed without a precise knowledge of oscillation amplitude, even though it has been shown [2] that due to the non-linearity of the SFM-system this amplitude can be a critical parameter for the behaviour of the total system.

Title: Precise measurement of electrostatic tip-sample interaction using 3D-SFM mode

Authors: I. Nieto, J. Abad and J. Colchero

Abstract: Interpretation of data obtained by ESFM or KPM is not an easy task. One of the main problems in this context is a precise knowledge not only of the state of the sample, but also of the precise behaviour of the tip. The latter is specially difficult, since, in contrast to the sample, the tip cannot be "seen" directly, that is, the tip cannot be imaged in order to study and infer its fundamental properties. In order to fully characterize with high precision the tip-sample system, in the present work we propose advanced spectroscopy methods based on multidimensional acquisition of "interaction images". As will be shown, careful processing of the force and, more importantly, the frequency shifts measured while tip sample voltage and tip-sample distance allow a precise and consistent evaluation of the tip behaviour.

Title: Measurement of adsorbed liquid films using Dynamic Force Spectroscopy

Authors: Jose Abad and Jaime Colchero

Abstract: Tip-sample interaction is measured in ambient conditions on gold and glass at different relative humidity. As compared to other spectroscopic experiments, very small oscillation amplitudes (<100pm) are used to keep the tip-sample system in the linear regime, this simplifies data processing and data interpretation. Very high signal to noise ratio is obtained in spite of the small oscillation amplitude. The force, the force gradient and the quality factor are determined simultaneously as a function of tip-sample distance. In the non-contact regime of the interaction, essentially no force and no variation of the quality factor is measured. Until the jump to contact point is reached, the force gradient perfectly follows the relation predicted by pure Van der Waals interaction. Since force and force gradient are measured simultaneously, the tip-sample position can be determined either from the force vs. distance (FvsD) curve, or from the pole of the Van der Waals interaction.

Title: Characterization of marble using Scanning Force Ficroscopy

Authors: M. F. Orihuela, J. Abad, J. F. González, J. Colchero

Abstract: Marble has been used as a building material since ancient times. The facades which use marble as cladding suffer from atmospheric agents and the effects of pollution, and their preservation is important in order to avoid their deterioration and to maintain their aesthetic appearance (colour, brightness,...). Red tone marbles, such as the Rojo Quípar variety, suffer from apparent colour variations and more marked brightness loss than other marbles when exposed to environmental conditions and pollution. Colour variations in marble materials have been attributed to the degree of chromophore oxidation the minerals responsible for colour (stone impurities). In addition to these changes, other physical changes could be the reason for the apparent variations in the colour and brightness of marble [1]. In particular roughness is an important parameter which conditions brightness. In the present work we investigate the nanoscale effect of atmospheric agents (ultraviolet radiation, UV) and pollution (acid rain, H 2SO4) on the Rojo Quípar marble variety.