Michele Failla

I obtained my BSc (2009) and MSc (2012) degrees in Physics at the University of Catania, Italy (Sicily), where I investigated the optical properties of two-dimensional (2D) arrays of germanium (Ge) quantum dots [Fig.1(a)].

During my PhD at the University of Warwick (UK, 2013-2017), I have been focused on the transport properties of holes - the counterpart of electrons in solids - in Ge quantum wells [Fig.2(b)]. The goal of the project was to quantify, by means of THz time-domain spectroscopy [4], their suitability for spintronics, a branch of electronics which aims to create transistors  which use the spin rather than the charge of carriers [Fig.1(c)].

Fig.1: (a) TEM of Germanium quantum dots multilayered samples [1]. (b) TEM of Germanium multiple QWs and [2]. (c) example of spintronic transistor [3].  

I joined the OM-group in October 2017. I am currently working on the optical characterization of Cd-, Pb-chalcogenides, as well as transition-metal-dichalcogenides-based nanostructures [nanoflakes or nanoplatelets, Fig.2(b)]. In comparison to “laterally extended” QWs, these can be produced in a cheap fashion from solutions processes [Fig.2(a)], a remarkable advantage that may lead to the creation of conductive, or photoconductive, cheap paint formed by a network of such nanostructures (NSs) [Fig.2(c)].

Fig.2: (a) Solution-dispersed MoS2, MoSe2, WS2, and WSe2 nanoflakes. (b) TEM image of nanoflakes. (c) SEM image of sprayed network of nanoflakes [6].  

By photoexciting these NSs with short light pulses (100-200 fs, 1 fs = 1^-15 s) in the wavelength range 200-2200 nm, the project investigates their suitability for optoelectronics applications. Optical-pump THz probe [4], as well as transient absorption experiments, are used to evaluate the ratio between photogenerated free carriers and excitons (bound electrons-holes pairs) and determine their formation-, decay-kinetic and mobility. This is fundamental as photovoltaics devices need free-carriers with high mobility, while LEDs use photons emission from excitons recombination.

[1] - S. Mirabella et al., Appl. Phys. Lett. 102, 193105 (2013)

[2] - Xue-Chao Liu et al., J. Phys. D: Appl. Phys. 44 (2011) 055102

[3] - I. Zutic and S. Das Sarma, Reviews of Modern Physics, 76

, 2004

[4] - www.youtube.com/watch for a video illustrating the principles of THz time-domain spectroscopy. -

[6] - Adam G. Kelly et al., Science 356, 69–73 (2017)