Date: Monday December 16, 2019
Time: 12.00
Venue: S3 Seminar Room, Third Floor, Physics Building, FIM Department

Speaker: Sabina Spiga
Affiliation: CNR-IMM Agrate Brianza (IT)

Title: Memristive devices for brain inspired computing

Abstract: Memristive devices have been receiving an increasing interest for a wide range of applications, such as storage class memory, non-volatile logic switch, in-memory computing and neuromorphic computing. In particular, in bio-inspired systems, memristive devices can act as dispersed memory elements mimicking synapses in nervous systems, or as stochastic and non-linear elements in neuronal units. Among the proposed technologies, oxide-based memristors (also named resistance switching memory, RRAM) are based on redox reactions and electrochemical phenomena in oxides and are very promising because of low power consumption, fast switching times, scalability down to nm scale and CMOS compatibility. In our work, we focus on the switching dynamics of HfO2 RRAMs and on their implementation as electronic synapses in spiking neural networks (SNN).  Our results show that the device conductance can be tuned in an analog fashion by using train of identical pulses, to emulate the biological potentiation (conductance increase) and depression (conductance decrease) processes, over several cycles. The update of the conductance values can be achieved by a spike timing and rate dependent plasticity mechanism, which is demonstrated also at hardware level, and can be exploited as learning rule in a SNN. Finally, the experimental data sets are used to simulate a fully connected winner-take-all spiking neural network with leaky integrate and fire neurons equipped with circuitry emulating the temporal dynamics of biological synapses.

Host: Arrigo Calzolari arrigo.calzolari@nano.cnr.it

Date: Thursday November 14, 2019
Time: 12.00 CET
Venue: CNR Nano Modena, S3 Seminar room – FIM Department, III floor

Speaker: Dr. Alessandra Satta
Affiliation: CNR IOM (Cagliari IT)

Title: Towards modelling the degradation of pigments: Cd-yellow as a case study

Abstract: Several of the historical coloured pigments belonging to the paintings of the late 1800 and early 1900, are undergoing an irreversible degradation process, causes of which are still unclear. In the specific case of the brilliant yellow pigment that takes its colouration from cadmium sulfide (CdS), a II-VI wide-gap semiconducting compound, the role of structural defects is the subject of a still on-going research that aims to link the history of the material to the reactivity of the pigment surface.
The aforementioned study is carried out by means of a fully theoretical approach based on the density functional theory. As opposite to novel materials, in the field of Cultural Heritage where pigments already possess their long history, a theoretical method becomes secondary to the experimental analysis but still it represents a very good complementary tool extremely useful in the interpretation of complex mechanisms not easily accessible by experiments.  The interdisciplinary work takes advantage of various chemical and physical skills, both experimental and theoretical.

Host: Arrigo Calzolari arrigo.calzolari@nano.cnr.it