Section 1: ELECTRON MICROSCOPIES
The course aims at providing a picture of the electronic probe microscopy techniques as general as possible, starting from the basics of the major techniques and examples of prototypical applications up to state of the art scientific cases. The main goal is to provide the student with the ability of assessing the feasibility and effectiveness of microscopic measurements to tackle a given problem. The couse will focus on the information that can be obtained (morphology, chemical contrast, short-and long-range structure, spectroscopy) and on the choice of the microscopic techniques that can be effectively employed to investigate a system in a given environment.
- Probes with high spatial resolution and state of the art in research and applications.
- Interaction of free electrons and bound electrons with matter.
- Information obtained by using electronic probes.
a) Free-Electron Microscopy (electron beam)
- History (optical microscopy, spectroscopy).
- Charged particle optics (electron sources, electronic lenses, ray and wave optics: magnification; diffractive effects: resolution and Abbe criterion; aberrations, repulsion between beam charges).
- Transmission Electron Microscopy (TEM) and scanning (SEM)
- Microscope: structure, spatial resolution and typical numbers.
- Main modes of operation (direct and reciprocal space).
- Main information: dependencies on the beam kinetic energy, main detectors (morphology, structure, chemical sensitivity); energy-selective detectors (TEM: HEELS, SEM: XRF, SAM, EELS, energy scales and resolution); angularly selective detectors (diffraction, Kikuchi lines).
- Key applications (biology, structure of matter).
- Limitations and advantages (TEM sample preparation and damage; SEM: sample environment, conductivity and charging, depth of field, resolution, temporal resolution).
- Sample TEM and/or SEM studies.
b) Scanning probe microscopies
- History (profilometer).
- Scanning tunneling (STM) and scanning force (SFM) microscopies
- Tip-sample interaction models (STM: Wentzel-Kramers-Brillouin (WKB) tip-sample electron transport, SFM: van der Waals interactions).
- Microscope: structure; operation mode (STM: constant current, constant voltage; SFM: amplitude and phase, contact and non-contact); spatial resolution and typical numbers.
- Main information: morphology, structure, nano manipulation; STM: chemical sensitivity, local transport properties, scanning tunneling spectroscopy (STS): dependence on the bias voltage and on the spin polarization (magnetic STM tip); SFM: local interactions: tribology, mechanical properties and stress; MFM magnetic interactions.
- Key applications (the structure of matter: physics of surfaces and nanostructures with atomic resolution).
- Limitations and advantages (atomic spatial resolution; STM: conductivity and charging, field of view; SFM: environment).
- STM and/or SFM cases of study.
- Optical microscopy scanning near-field (SNOM), introduction
- Exceeding the diffraction limit by using the evanescent field.
- STM analogies.
Image analysis and practical testing of research instrumentation.
In the academic year 2015-2016 the couse will be held in the first half of the first term, from October 5th to the end of November 2014.
The range and detail of the course will be adapted to the level of the class during the course and may change significantly.
Section 2: SPINTRONICS
Nanomagentism is a modern discipline devoted to the study of magnetism in nanoscale objects. The "nano-world" opens unforeseen possibilities to develop new devices and paradigms exploiting the spin and orbital angular momentum of electrons and other quasi-particles (e.g. domain walls, magnons) propagating in engineered magnetic structures. Spintronics, in particular, is a branch of nanoelectronics aiming at developing new electronic devices taking advantage of the spin degree of freedom in addition to the charge of carriers.
The aim of this course is to present the fundamentals of micro and nanomagnetism necessary to understand the recent developments in the field of spintronics. A platform for micromagnetic simulation will be also presented, in order to provide the students with the essential tools for designing and analysing magnetic nano-devices. Finally, the lectures of the last part of the course are intended to review the recent advances in the field.
Outline of the program
The program will consist of lectures and exercises devoted to these topics:
Micro and NANO magnetism
Demagnetizing field, magnetostatic energy. Landau magnetic free energy and its contributions (exchange, anisotropies, magnetostrictions). Domain walls. Micromagnetic simulations (OOMMF). Coherent magnetization reversal (Stoner Wohlfart model) and reversal via propagation of domain walls. Magnetic nanoparticles. Domain wall conduits. Magnetic coupling in multilayers (Néel coupling, Exchange bias, Bilinear coupling).
Two currents model and spin dependent scattering. Giant magnetoresistance in CIP and CPP configurations. Spin accumulation and Valet-Fert model. Tunneling magnetoresistance and magnetic tunneling junctions. Non volatile magnetic memories (MRAMs) and magnetic sensors. Spin transfer torque. Magneto-electric coupling. Spin injection, manipulation and detection in semiconductors.
Rashba based devices and Spin-FET. Spin currents. Direct and inverse spin Hall effect. Antiferromagnet spintronics.
Laboratory instruction in specific techniques of magnetic characterization of materials and devices will be provided, at the laboratory of Nanomagnetism located within the facility Polifab.
Who should attend
The program is designed for students of the Engineering Physics course, but students from the electronic engineering, material science and nanotechnology courses may also benefit from this course. A good knowledge of the fundamentals of quantum mechanics and solid state physics is required.