Molecular Beam Epitaxy (MBE) is a technique for the growth of epitaxial thin films. In MBE the desired elements are sublimated evaporators (by thermal annealing) or introduced in the chamber in gas phase. In both cases the atoms stick on a substrate creating a solid solution in thin film form. The MBE can be performed only in Ultra High Vacuum (UHV) condition. The technique is characterized by a very small deposition rate (typically less than 1 nm per minute) that permit the deposition of thin film with the best possible thickness precision. Moreover this technique give rise to thin films with high purity stoichiometry and a high control on their crystal structure.
A cluster of UHV chambers that can exchange samples for growth and structural, chemical, magnetic and electronic analysis is available for users projects. The cluster is composed by 3 different chambers: 2 MBE chambers (Oxide and Mask) and 1 XPS station. The MBE cluster growth facility is located in the area of the APE beamline inside the experimental hall of Elettra, is not directly connected with the APE-NFFA end station but can exchange samples via a UHV shuttle chamber maintaining the samples in 10-10 mbar pressure.
The MBE-Oxide chamber is designed for the growth of complex oxides in pure ozone or oxygen as oxidizing ambient. The growth chamber is equipped with in-situ noninvasive measurement of atomic fluxes in real-time for single component materials (quartz crystal monitor) and for multi-component compound (atomic absorption spectroscopy). The deposition of individual monolayers is monitored by in situ reflection high energy electron diffraction (RHEED) system.
The MBE mask chamber allows for metal and simple rock-salt oxide depositions (masked or mask-less). The chamber is equipped for the standard tools for sample preparation in UHV conditions (sputtering with Ar ions, annealing stage by e-beam bombardment, quartz microbalance, leak valve for gas inlet and e-beam evaporators). Moreover the chamber is equipped with a shadow mask system that allows the direct evaporation of patterned film of micrometric size. In the chamber an AES/LEED system allows structural and chemical characterization. Together with the sample deposition tools, the MASK chamber is equipped with an in-situ MOKE apparatus (see MOKE section) for azymuthal Kerr magnetometry in UHV with fields up to 0.55T and temperatures in the range from 5 to 500 K. Finally, thanks to a 2 contact sample-holder, it is possible to measure transport properties (I vs V curve and magnetoresistance) of thin films and junctions.
The XPS analysis chamber is equipped with a double anode (Mg,Al) x-ray source and with a electrostatic hemispherical analyzer (mean radius 200 mm) to permit XPS measurements (see XPS section). The samples can be transferred in situ from the MBE chambers or can be directly introduced from the nearby load-lock chamber. In-situ with sputter/annealing surface treatments are available.
Complementary facilites at the co-located IOM-TASC clean-room are available for integrating lithography in the sample fabrication, in particular for "in-operando” type experiments.
The Oxide growth chamber is active in perovskite structure compounds deposition, like doped manganites, ferroelectric and multiferroic based thin films and heterostructures. The MASK chamber provides sample deposition and in-situ MOKE characterization in a wide range of temperatures. The two chambers are used in parallel, allowing the magnetic characterization of uncontaminated complex oxides. The sample can therefore be transferred in UHV environment with the shuttle chunk to APE-LE, APE-HE and SPRINT laboratories. Thanks to the clean room facility at TASC the 2D samples will be structured by lithography in order to obtain prototypes of functioning devices. The system also permits the characterization of the electrical transport properties of a device.
|Ultrathin Layers on Surfaces|
|3d,4d,4f metals||Ferromagnetic metals|
|organic molecules||Moleculer magnets|
|MgO, Al2O3, NiO||Insulationg Oxides|
|Metallization and masked deposition|
|Au, Pt||Conductive metals|
|Perovskite structure compounds ABO3|
|Spinel structure compound AB2O4|
|MBE Masked deposition|
|sample dimensions||5x5 mm|
|evaporation sources||up to 5 e-bombardment evaporators|
|annealing temperature||up to 950K|
|sample temperature control||5-500K|
|LEED / Auger spectroscopy||OCI BDL800IR|
|transport merasurements||Keithley 6487|
|MBE Oxide Growth|
|sample dimension||up to 10 mm x 10 mm|
|deposition temperature range||up to 800 K|
|deposition pressure in ozone/oxygen||up to 10^-5 mbar|
|deposition pressure without process gas||down to 10^-9 mbar|
|high temperature effusive cells (up to 1500°C)||3|
|conventional effusive cells||3|
|low temperature effusive cells||2|
|RHEED gun electron energy||10 kV|
|RHEED software analysis||KSA-400|
|RHEED spot size||100 micron diameter|
Piero Torelli is responsible of APE-HE endstation and MBE Cluster within CNR-IOM. He obtained his Ph.D. in physics from the University of Paris Sud (Paris XI) with a doctoral thesis on the magnetic properties of small systems. He worked as post-doc at the EU-STREP FOX Project at ESRF in Grenoble. His research activity is focused on the investigation of the magnetic properties of nanostructure and thin films. The class of material that I study comprises: metals, diluted magnetic semiconductors and oxides, multiferroics and new functional materials.
My research activity is mainly devoted to the study of the interplay between magnetic and electronic-structural properties in highly correlated systems on the Cluster Growth at APE beamline (buried interfaces, 2D electron gases, ferroelectric and magnetic oxides heterostructures). I do also local contact activity on APE-HE beamline.
Research activity concern to oxide thin films and heterostuctures growth by means of molecular beam epitaxy, and its magnetic, transport and structural properties study in dependence on interface and surface state and/or interaction (exchange bias and tunneling structures).
My research activities are essentially focused on multiferroic (ferroelectric/ferromagnetic) materials. From the MBE growths to characterization measurements, passing through micro or nano-patterning steps. My Ph.D consisted to observe dynamical effects in magnetic SAW devices and my post-doc will consist to observe static effects.