• characterization
• graphene
• inkjet prinying
• liquid phase exfoliation

During this Thesis work, I focused on the synthesis, characterization and ink-jet printing of Layered Material-based inks produced by liquid phase exfoliation (LPE), a top-down
approach for the production of LMs that has been receiving a great attention since it is particularly suitable for scaling-up and applications at the industrial levels.
I synthesized LPE-produced graphene-based inks in NMP and MoS2-based inks in IPA, that were then characterized morphologically using several techniques. First, the concentration of the as-produced inks was estimated by absorption spectroscopy; then, Raman spectroscopy was exploited to analyze the quality and the number of layers of the flakes dispersed in the ink, while transmission electron microscopy (TEM) was instead used to determine their lateral size. Finally, rheological analysis was carried out to measure the viscosity of the ink to be ink-jet printed.
Inkjet printing of the as-obtained inks was then performed on flexible Polyamide 6 on thin polyethylene terephthalate PET-foils.
Rectangular stripes were printed, that were then characterized both optically and electrically.
The surface topography was analyzed by means of optical and scanning electron microscopy (SEM). Atomic force microscopy (AFM) was exploited to measure the thickness of the
printed stripes, estimated as 500 nm for graphene (N=48 printing steps) and  800 nm for MoS2 (N=60 printing steps). Furthermore, Raman spectroscopy was carried out on the printed stripes to monitor the quality of the printed flakes, which were not affected by the printing process.
Before the electrical measurements, the printed stripes were first pressed and then annealed in order to remove residual solvent that may negatively affect the electrical conductivity of the as-prepared samples. 4-wire resistance measurements before and after such treatments have shown that this approach enabled to reduce the resistance of the printed stripes from hundred kOhm to few kOhm.
Finally, I have carried out some endurance tests on the printed stripes. The electrical resistance of the stripes easily recovers after mechanical stresses such as traction (up to a 5% normalized strain) or low-frequency protracted strain (registering a 0.4% and 0.7% increase in electric resistance after 36,000 and 72,000 bending cycles respectively). These preliminary results show the potentiality of this approach for the realization of fully-printed conductive components for flexible optoelectronics.
Photoconductivity tests with 532 nm laser excitation were then performed at different incident power. From the responsivity, an external quantum efficiency up to 0.001 was obtained.
Although there is plenty of room for optimization and the results can be considered preliminary,they may pave the way towards the development of printed heterostructures.