Conduction mechanisms in organic / metal hybrid composites.

Hybrid organic:inorganic materials are nanocomposites with organic and inorganic components that are either homogeneous systems derived from monomers and miscible components, or heterogeneous systems where at least one of the component¿s domains has a dimension ranging from some angstrom to several nanometers. The hybridization of inorganic materials and conjugated organic molecules and polymers potentially combines the advantages of both kinds of materials, whose properties are not only limited to the sum of the individual contributions of both phases, but also the role of the inner interfaces could be predominant [1]. These new generations of hybrid materials offer a land of applications in many areas including electronics, ionics, mechanics, energy, environment, biology, optics, medicine, functional smart coatings, solar and fuel cells, catalysts, sensors, etc [2]. In particular, nanoparticles embedded in organic materials are being extensively used due to its potential for improving the performance of optoelectronic devices [3]. For instance, the use of semiconductor CdS nanoparticles doped with cupper within the polymer PMMA is intended for broader emission spectra of OLEDs with the structure ITO / PMMA / Al [4]. Semiconductor nanoparticles are being currently used not only for increasing the absorption spectra of polymer-based solar cells, but also for extending the active zone of charge separation trough the whole volume of the active layer using the concept of bulk heterostructures [5]. Metallic nanoparticles embedded in organic materials are widely used in single-layer organic memories due to the occurrence of the ¿switching effect¿. In this relatively simple heterostructure consisting of an organic layer mixed with metal nanoclusters, which is sandwiched between top and bottom electrodes, the conductivity of the device is abruptly changed for several orders of magnitude after a threshold voltage is applied. The high and low conductivity states are assigned to ¿ON¿ and ¿OFF¿ states of a memory, and due to these two possible states at a given voltage, the heterostructure is labelled as an ¿organic bistable device¿ OBD. Once either state is reached, the device remains in that state for a prolonged period of time. Depending on the device structure and materials involved, the switching behaviour is sometimes a reversible process which can be precisely controlled by the application of a positive voltage pulse (to write) or a negative voltage pulse (to erase). Device performance tests show that OBD is a promising candidate for high-density, low-cost electrically addressable data storage applications [6]. Organic memory devices consisting of a single layer offer advantages of low cost and simple fabrication and, due to its relatively simple structure, open the possibility of making an easier understanding of the switching process and conduction mechanisms. The carrier bistability in OBDs consisting of a single hybrid NP polymer layer largely depends on the structure, elements of the NPs, and electrical properties of the polymer matrix. For further understanding of carrier transport in OBDs, it is necessary to fabricate a simple OBD with a single hybrid polymer NP composite and carefully analyze the electrical behavior by fitting the current density¿voltage characteristics curve (J-V) [7], combined with the study of the electronic properties of the individual materials and their interfaces by photoemission spectroscopy (PES), and even complementary optical absorption measurements.