Summary of results
The core problem that DAFNEOX Project address is the controlled integration of nanoelements (as nanoparticles or nanochains) in regular patterns on top of self-organized materials, mainly oxide thin films for applications from spintronics and catalytics to optoelectronics. Beating the intrinsic limitations of lithographic methods for minituarization is one of highest nanoscience challenges. Our bottom-up approach take advantage of self-assembling phenomena occurring during the growth of thin films by physical methods.
By understanding the mechanisms controlling these phenomena we have prepared a wide variety of nanotemplated oxides with ordered arrays of nanoholes over a large surface. Furthermore, oxides being a large family of materials, they offer unique opportunities due to the wide range of reported functional properties. We have obtained nanotemplates with properties ranging from ferromagnetic or ferroelectric, metallic, semimetallic or insulating.
Later on, these nanotemplates have been used for the guided self-assembly of other nanoobjects as, for example, nanoparticles and nanochains. This has opened the possibility to study charge transport properties in individual nanoelements by the use of nanogap devices where new phenomena may be expected due to the reduced dimensions.
Expertise in studying optical, transport and magnetic properties has allowed us to establish the link between nanostructured materials and their functional properties as, for example, in the study of resistive switching phenomena, spin dynamics or magnetization reversal, all of them relevant in spintronic or optoelectronic applications
Our project brings together expertise in experimental and theoretical physics and a substantial effort was devoted to understand the properties of these nanoelements as model systems for the interpretation of complex nanoparticle/oxide behavior during self-assembling phenomena. Theoretical models have been used to explain self-assembling processes of magnetic nanoparticles into close-packed arrangements and into large macroscopic chains.
In summary, the advances that have been achieved through this interdisciplinary research will contribute to the design of a set of novel nanostructures of intelligent materials, which could be useful in variety of physical devices such as sensors, catalysts or magnetic storage media.
To achieve its goals, the project was structured in seven interlinked WPs that cover from fabrication, understanding and control of nanostructured materials to the advanced characterization of the physical and microstructural properties of both, the individual building blocks (nanoparticles and thin films) as well as the self-assembled nanostructures. Support from theoretical simulations was also needed for the design of novel configurations. An overview of the general progress of the project with a special emphasis in collaborative aspects may be summarized in the following subjects.
Preparation of nanotemplate oxide films with different properties (ferroelectric, ferromagnetic, …) was achieved at ICMAB-CSIC in close collaboration with ICN2. Furthermore, expertise in optical and local conductivity measurements from IPB allowed identifying novel phase segregation mechanisms for the formation of natural self-assembled nanocomposites or the unexpected behavior of resistive switching phenomena.
ICMAB-CSIC also was responsible for the preparation of oxide nanoelements, mainly magnetic nanoparticles. Theoretical simulations from IPB and in collaboration with UTFSM allowed to fully explain and understand the mechanisms governing the self-assembling of the nanoparticles into closed-packaged clusters or in large mesoscopic chains. The study of the dynamic magnetic properties of nanostructures was carried out by UTFSM. These studies open a new way for the exploitation of quasi-2D magnetic nanoparticles in several fields as storage devices, superlattices or magneto-rheological fluids
TUDelft and UChile developed a sound methodology to measure charge transport properties in devices consisting of single nanoelements prepared at ICMAB-CSIC. This milestone opens enormous possibilities in the field of nanoscale physics as new functionalities may be now envisaged for example through the control of interfacial effects in core/shell nanoparticles. Furthermore, the involvement of IPB in the theoretical approaches to explain the self-assembly mechanisms of nanoparticles into long..
Further nanoelements (metallic nanoparticles on GLAD structures) were prepared at KUL for studying their magnetic properties in UTFSM, particularly to study the influence of hydrogenation in the magnetic coupling.
Understanding magnetodynamic phenomena is critical for the realization of devices as magnetic memories and, in this respect, magnetization switching is a key parameter. The collaboration between ICN2, UTFSM and ICMAB-CSIC has already lead to interesting results (under publication) which will greatly contribute to the understanding of the relationship between growth parameters, microstructure and spin dynamics.
A fruitful exchange of knowledge between IPB and ICMAB-CSIC in the study of local properties through atomic force microscopy in nanostructured oxide films has allowed to identify different materials as potential candidates for the development of resistive-based memories.
Many of the results obtained by the consortium have been already published in specialized journals demonstrating their novelty.
Noticeable progress beyond the state of the art has been achieved in the study and preparation of self-organized oxide thin films. We have shown that formation of long-range ordered arrays of nanopits may be obtained at the surface of several oxide materials with a wide variety of properties. The origin of this phenomena lies at the competition between different growth modes. This result opens the possibility to design and generate templates of nanometric size over large surfaces and it has been already used for the guided self-assembly of nanoparticles. Different unexpected behaviors were observed in metallic or oxide nanoparticles and understanding this effect will be a challenge in the next period. Furthermore novel strategies for the nanostructuration of thin films based on phase segregation were identified.
Formation mechanisms of nanoparticle nanostructures, either close-packed arrays or nanochains, were elucidated by theoretical simulations. It was demonstrated the importance of size and shape of the nanoparticles in the magnetic dipolar interaction responsible for self-organization.
By achieving a good experimental knowledge of the parameters controlling self-organization we have been able to tune the deposition of nanoparticles on devices for studying its charge transport properties. The results were promising and open a new way to study charge transport in nanostructures. Such a research will give us the possibility of studying spin-dependent transport in nanodevices with reduced dimensions