RESUMO
Organic/inorganic van der Waals heterojunctions formed by a combination of 2D materials with semiconductor polymer films enable the fabrication of new device architectures that are interesting for electronic and optoelectronic applications. Here, we investigated the charge-transfer dynamics at the interface between 2D layered franckeite (Fr) and two thiophene-based conjugated polymers (PFO-DBT and P3HT) from the resonantly core-excited electron. The unoccupied electronic states of PFO-DBT/Fr and P3HT/Fr heterojunctions were studied using near-edge X-ray absorption fine structure (NEXAFS) and resonant Auger (RAS) synchrotron-based spectroscopies. We found evidence of ultrafast (subfemtosecond charge-transfer times) interfacial electron delocalization pathways from specific electronic states. For the interface between the PFO-DBT polymer and exfoliated franckeite, the most efficient interfacial electron delocalization pathways were found through π*(S-N) and π*(S-C) electronic states corresponding to the benzothiadiazole and thiophene units. On the other hand, for the P3HT polymer, we found that electrons excited to π-π* and S1s-π*(C-C) electronic states of the P3HT polymer are the most affected by the presence of exfoliated franckeite and consequently are the main interfacial electron-transfer pathways in this heterojunction. Our results have important implications in understanding how ultrafast electron delocalization is taking place in organic/inorganic van der Waals heterojunctions, which is relevant information in designing new devices involving these systems.
RESUMO
We demonstrated a method to construct high efficiency saturable absorbers based on the evanescent light field interaction of CVD monolayer graphene deposited on side-polished D-shaped optical fiber. A set of samples was fabricated with two different core-graphene distances (0 and 1 µm), covered with graphene ranging between 10 and 25 mm length. The mode-locking was achieved and the best pulse duration was 256 fs, the shortest pulse reported in the literature with CVD monolayer graphene in EDFL. As result, we find a criterion between the polarization relative extinction ratio in the samples and the pulse duration, which relates the better mode-locking performance with the higher polarization extinction ratio of the samples. This criterion also provides a better understanding of the graphene distributed saturable absorbers and their reproducible performance as optoelectronic devices for optical applications.