DQMP Forum - Ionic-gate Spectroscopy of Atomically Thin Semiconductors - Hydroborate Sodium Salts: an Emerging Class of Room-temperature Solid-state Electrolytes

02.06.2020 13:00 – 14:30

Ionic-gate Spectroscopy of Atomically Thin Semiconductors
Ignacio Gutirrez-Lezama (group of prof. Morpurgo)

Electronic devices operated with an ionic gate are best-known for their capability to accumulate
large electron densities (1014-1015 cm−2) at the surface of a wide range of materials, enabling theobservation of interesting physical phenomena, such as gate-induced superconductivity. There is however a lesser known yet important attribute of ionic gating: the possibility to extract the (single particle) band gap of a semiconductor directly from the I-V characteristics of the devices, a spectroscopic capability not present in transistors equipped with conventional solid state gate dielectrics.
In this forum presentation we will give an overview of ionic-gate spectroscopy, beginning by explaining the origin of the very large geometrical capacitance present in ionic-gated transistors and how it endows these devices with their spectroscopic capability. The possibility to accurately measure band gaps and even band offsets will be illustrated by a review of our work on 2D semiconductors and their heterostructures, including, when possible, comparisons to results obtained via other techniques. We will additionally show that ionic-gate spectroscopy serves as a complementary technique to optical probes, resulting in the extraction of additional information not accesible via each individual technique. Throughout the presentation we will also discuss the limitations of this spectroscopic technique and, when relevant, the technical challenges inherent to working with an ionic gate.


Hydroborate Sodium Salts: an Emerging Class of Room-temperature Solid-state Electrolytes
Matteo Brighi (group of Prof. Cerny)

To face the worldwide increasing energy demand, high voltage and large capacity storage systems are required. The next generation ion-batteries are the promising candidates to achieve this step forwards by means of solid-state electrolytes (SSE). In this context, the emerging family of hydroborates fulfil the necessary requirements as SSE. I will report six novel compounds featuring high Na+ conductivity and large electrochemical window to be employed as SSE for high voltage Na-ion batteries. The high ionic conductivity is not only consequence of the high symmetry crystal structure. A glass-like transition was observed in all cases related to an anomalous lattice thermal expansion. This peculiarity is explained by means of the Coupling Model that directly relates the Na-dynamics to the ion-ion interaction.

Lieu

Zoom Meeting

Please join us on Zoom, Meeting ID: 582 067 708
https://unige.zoom.us/j/582067708

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