Magnetic and Semiconductor Nanostructures
Research focus
The Peer review has evaluated this group as Excellent
The group has been involved for more than twenty years in the study of the peculiar properties of materials spatially confined on a nanometric scale, in particular surfaces, interfaces, thin films and multilayers based on semiconductors and/or magnetic materials. Based on this expertise, in recent years the research has been focused towards the synthesis of new artificial materials for applications in the field of microelectronics, optoelectronics, photonics and spintronics. In this frame, a large part of the activity is devoted to the epitaxial growth of specimens nanostructured along the direction of growth (heterostructures, nanometric and subnanometric thin films and multilayers), and their characterization by means of several spectroscopy and microscopy techniques Two main lines can be identified on the basis of the materials investigated, either semiconductors or magnetic materials (sometimes both). The basic scope of the semiconductor activities is the synthesis and characterization of heterostructures and nanostructures on silicon substrates for microelectronic and optoelectronic applications. One of the strengths of the laboratory lies in the diversity of available deposition techniques, such as low-energy plasma enhanced chemical vapour deposition (LEPECVD), molecular beam epitaxy (MBE), and magnetron sputter epitaxy (MSE). These techniques are used for the fabrication of SiGe/Si heterostructures, such as self-assembled SiGe quantum dots, high-mobility strained-Ge quantum wells, and structures suitable for infrared photodetectors, modulators and waveguides. Besides epitaxial heterostructures nanocrystalline silicon films are grown for low-cost photovoltaic solar cells. Another area of major interest is monolithic integration of III-V semiconductors on Si substrates optoelectronic applications, especially high-efficiency solar cells. Epitaxial oxides grown by MBE provide an alternative route towards III-V integration, Formattato: Portoghese (Brasile) 48 besides novel devices based on thin oxide/Si combinations, and novel gate insulators. In the field of magnetism, the research is focused on magnetic materials spatially confined down to nanometric scale. Typical examples are ultrathin films with antiferromagnetic coupling, oxides thin films, ferromagnet/semiconductor interfaces, rare earths multilayers and transition metals multilayers. These innovative structures are synthesized by vacuum deposition on single crystal substrates, using either Pulsed Laser Deposition (PLD) or MBE. The samples are characterized in-situ by means of diagnostic tools such as diffraction of low/high energy electrons (LEED and RHEED, respectively), Auger spectroscopy (AES), x-ray photoemission spectroscopy (XPS). The electronic and magnetic properties are investigated in-situ by means of electron spectroscopies - also with spin resolution - and techniques based on the magneto-optical Kerr effect (MOKE). A specifically dedicated laboratory for ex-situ MOKE, is also available for vector magnetometry measurements from 10 K to 500 K. A further activity is devoted to the lateral definition of nanostructures and device fabrication by means of optical and electron beam lithography, and wet chemical or reactive ion etching. Transport properties are also investigated by performing measurements at low temperature by means of a helium cryostat with a superconducting magnet. Finally, dealing with micro- and nano-structures, it is certainly important to have access to microscopy techniques. In such a field, the activities deal both with well-established optical microscopies (confocal microscopy) and scanning probe techniques, such as Scanning Near-field Optical Microscopy (SNOM), Atomic and Magnetic Force Microscopy (AFM and MFM ), and Scanning Tunnel Microscopy. All the research lines are integrated within the activities of the Center of Excellence for NanoEngineered Materials and Surfaces (NEMAS), instituted by the Italian Ministry for University and Research (MIUR) at Politecnico di Milano, and of the Interuniversity Center (Politecnico di Milano and Università di Milano Bicocca) LNESS (Laboratory of Epitaxial Nanostructures on Silicon and for Spintronics).
Departments
Professors
Full Professors
Franco Ciccacci
Hans von Känel
Associate Professors
Lamberto Duò
Marco Finazzi
Riccardo Bertacco
Assistant Professors
Giovanni Isella