DANYELA

He Diffraction and Nanostructure Growth

Prof. Juan José de Miguel Llorente

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DANYELA is an Ultra-High Vacuum (UHV) chamber basically dedicated to surface diffraction studies, and in particular to the detailed characterization of growth and structure in low-dimensional metallic and magnetic systems and nanostructures such as magnetic quantum dots.

The main experimental technique used here is Thermal Energy Atom Scattering (TEAS), although Low Energy Electron Diffraction (LEED), Medium Energy Electron Diffraction (MEED) and Auger Electron Spectroscopy (AES) are also available. An auxiliary chamber directly connected to the main one hosts the setup for Magneto-Optic Kerr Effect (MOKE) experiments, used to determine in-situ the magnetic status of the samples.

Activities

Taking advantage of the special characteristics of the TEAS technique, we concentrate on studies of epitaxial growth. Our emphasis is put on characterizing at the atomic level all the relevant elementary processes that influence the final system structure and morphology. TEAS is a extremely valuable tool for this purpose, given its high surface sensitivity and nil penetration depth. At the same time, this latter feature demands the use of other techniques with penetrating probes to analyze the subsurface structure of the growing material. To achieve this goal we usually employ LEED for the in-situ studies, and also Surface X-Ray Diffraction (S-XRD) for ex-situ research, performed either in-house or at the European Synchrotron ESRF .

Growth processes often display a high degree of complexity, due to the complicated interplay of many different processes (diffusion, nucleation, etc.) To help with the interpretation of the measured data and also with the design of new experiments, we resort to numeric simulations (Monte Carlo and Molecular Dynamics).

Our growth studies have dealt mostly with metals, and in particular with magnetic materials. The bottom line of our approach is not only to learn about the finest details of the growth process, but also to devise strategies (such as the use of surfactants) to steer it in a particular direction, in order to produce custom-designed, low-dimensional or nanostructured materials with specific properties for a given application. Our accurate control of the samples' morphology and atomic structure has lead us to several significative findings regarding the magnetic properties of these special types of materials.

Currently we are exploring some new lines of research related with the growth of magnetic materials on semiconductor substrates for spintronics , specific growth methods for the production of magnetic nanostructures (e.g., electrochemical deposition on patterned substrates) and self-assembled/self-organized systems.