Organic, Cluster Assembled and Nano-Hybrid Materials produced by Supersonic Beams: Growth and Applications to Prototype Device Development Salvatore Iannotta, Lucrezia Aversa, Andrea Boschetti, Silvia Chiarani, Nicola Coppedè, Marco Nardi, Alessia Pallaoro, Fabrizio Siviero, Tullio Toccoli, Roberto Verucchi Istituto di Fotonica e Nanotecnologie – Trento Division Via Sommarive, 18, 38050 Povo di Trento, iannotta@itc.it ABSTRACT An approach to the growth of films of π-conjugated organic materials, cluster assembled and nanohybrid materials combining supersonic free jets with a UHV deposition apparatus including surface characterization methods will be discussed. The unique control achievable with supersonic beams on initial kinetic energy, momentum and state of aggregation enables the growth of materials with controlled properties at different length scales. Results obtained with organic semiconductors and oligomers point out the crucial role of kinetic energy in growing organic crystalline films with well controlled morphologies and structures. By means of supersonic beams of clusters, nanocrystalline metal oxide films can be grown without annealing, so that grain size and morphology can be better controlled. In a co-deposition scheme these interesting features are combined in order to obtain a new class of hybrid functional materials with appealing properties for electronics, gas sensing and photovoltaic applications. Keywords: growth, organic semiconductors, nanophase metal oxides, nanohybrid materials, gas sensors. 1 INTRODUCTION The ability to synthesize nanostructured thin films with controlled structure and to tailor the needed interfaces is a key to develop new classes of devices. Indeed the properties of organic semiconductors as well as those of nanostructured metal oxides make them appealing for application in many fields, as electronics (Thin Film Transisitors, Organic Light Emitting Diodes), gas sensing (both air and Volatile Organic Compounds analysis) and solar energy conversion, nevertheless control on morphology and properties of thin films with thickness suitable for the use in real prototype devices is still hard to achieve. As to organic molecules, it has been proved that electronic transport and optical properties depend strongly on molecular orientation and packing. A supersonic molecular beam growth (SuMBE) technique has been developed that ensures a substantial improvement of quality and control of the properties of thin films. Very interesting results have been obtained with molecules such as thiophene-based oligomers, which can be considered the prototypes of π-conjugated systems for studying optical and electrical properties [1], and with pentacene [2]. With regard to metal oxides, the deposition from Supersonic Cluster Beams (SCBD) has proven to be a viable bottom- up approach to the synthesis of films with controlled structure at the nano-level [3]. It will be shown how the appropriate combination of these molecular beam methods opens new perspectives in the intriguing field of hybrid materials in which inorganic structures (metal oxides) are functionalized by means of organic species. The combination of nanophase TiO 2 and metal phthalocyanines will be used as a test case. 2 EXPERIMENTAL 2.1 Supersonic beams of organic molecules and clusters Supersonic free jets have been in the past largely exploited to prepare molecules in a well defined thermodynamic state for studies with time of flight methods [4]. Indeed molecules or clusters highly diluted in a supersonically expanding carrier gas exhibit a narrow velocity distribution, low divergence and, especially in the case of small molecules, alignment and a substantial relaxation of internal degrees of freedom. Therefore, when depositing species, control on the expansion’s parameters gives unprecedented control on the initial state of the precursors. The production of continuous supersonic beams of organic molecules is performed by means of a source consisting of a quartz tube in which a carrier gas (He, H 2 , Ar) is seeded with species sublimated by Joule heating (see Figure1). The mixture then expands into vacuum through a nozzle. Kinetic energy as well as the degree of clustering can be tuned by changing the carrier gas, the nozzle diameter and the seeding parameters (source temperature, gas inlet pressure). The deposition of clusters is performed via a Pulsed Microplasma Cluster Source (PMCS) [5], which has been developed in collaboration with the group directed by Prof. Milani at the University of Milan (Figure 1). Clusters are produced by quenching of the plasma in a buffer gas after a discharge between two electrodes hosted in a ceramic cavity. Virtually any conducting material can be vaporized, and the contamination of the gas with chemical species can NSTI-Nanotech 2005, www.nsti.org, ISBN 0-9767985-1-4 Vol. 2, 2005 127