A crystallisation protocol was designed (sample set-up, control environmental conditions, concentration, volume , etc) using silicon as a reference substrate and glycine, as reference molecule. Glycine was selected because it has been widely used and its polymorphs can be easily distinguished by Raman spectroscopy. Both homogeneous and heterogenous nucleations were investigated.
-homogeneous nucleation was studied by performing acoustic levitation of graphene droplets. We observed formation of a liquid marble under specific conditions. The manuscript is currently ready to be submitted.
-heterogeneous nucleation was performed using graphene as impurity or surface. We show that graphene induces the preferential crystallization of the metastable α-polymorph compared to the unstable β-form at the contact region of an evaporating droplet. Computer modeling indicates the presence of a small amount of oxidized moieties on graphene to be responsible for the increased stabilization of the α-form. Our results show that the ability to finely tune the surface properties of graphene makes this material very attractive for polymorph screening. This work was published in ACS Nano 2020, 14, 8, 10394 and presented at Chem2D Mat conference in Dresden in 2019 and at the workshop: from 2Dto3D in 2021, Free University of Brussels.
-heterogenous nucleation was studied using different types of electrical readouts. First, an interdigitated electrode sensor has been used to monitor in real-time the crystallization process. We show that from the electrical signal, it is possible to easily and precisely extract the induction time and the supersaturation ratio. We observed characteristic fluctuations in the current after the induction time, which could be ascribed to the molecular assembly dynamics. The results were published in Nanoscale Horiz., 2021, 6, 468-473. In a second work, we demonstrated that electrolyte-gated organic field-effect transistors (EGOFETs) are able to monitor in real-time the crystallization process in an evaporating droplet. The high sensitivity of these devices at the solid–liquid interface, through the electrical double layer and signal amplification, enables the quantification of changes in solute concentration over time and the transport rate of molecules at the solid–liquid interface during crystallization. Our results show that EGOFETs offer a highly sensitive and powerful, yet simple approach to investigate the molecular dynamics of compounds crystallizing from water. The results were published in Nano Lett. 2022, 22, 7, 2643.
- we performed detailed Raman characterization of various types of graphene nanoribbons (GNRs), made by bottom up approach, showing that the low-energy region, especially in the presence of bulky functional groups, is populated by several modes, so a single radial breathing-like mode cannot be identified. However, we observed characteristic dispersions of the G and D peaks, which offer further insight into the GNR structure and functionalization, by making Raman spectroscopy a crucial tool for the characterization of these nanostructures. The results were published in Phys Rev B,100, 045406 (2019) and in JACS, 142, 18293 (2020); 139, 16454 (2017).
- we performed Raman characterization of graphene produced by electro-chemical exfoliation under different conditions showing that one can finely tune the surface chemistry of the material. The work was published in Nano Letters, 20 (5), 3411 (2020). The results were also used to develop a device based on this type of graphene, which has been funded with a ERC PoC.
- we developed a new way to deposit molecules on a surface, called the blow coating. The results are published in ACS Omega, 4, 11657 (2019).
