Researchers from the University of Jyväskylä and Aalto University have developed a laser‑assisted area‑selective atomic/molecular layer deposition (AS‑ALD/MLD) method that grows europium‑organic thin films on graphene and other 2D materials with submicron precision, one molecular layer at a time. This resist‑free process turns chemically inert 2D surfaces into spatially defined growth templates, enabling patterned photoluminescent heterostructures and controllable electronic doping on a single chip.
The approach combines femtosecond laser two‑photon oxidation (TPO) with ALD/MLD to locally activate single‑layer graphene on a silicon chip. In selected regions, tightly focused fs‑laser pulses create hydroxyl and other oxygen‑containing functional groups, which act as nucleation sites for a europium‑organic Eu‑BDC network, while pristine graphene remains essentially non‑reactive. By tuning the laser dose, the researchers directly control nucleation density, achieving homogeneous Eu‑organic films up to about 11 nm thick with over 90% area selectivity and submicron feature sizes, without any resist or etching steps.
The graphene/Eu‑organic heterostructures show strong europium photoluminescence under continuous‑wave 532 nm excitation, with intense emission at 612 nm and additional lines at 579, 592, and 652 nm. A distinct green band around 566 nm appears only on graphene, not on Si/SiO₂, indicating a strong influence of the 2D substrate on the emission. Photoluminescence lifetimes are shorter on graphene, consistent with efficient energy and charge transfer across the graphene/Eu‑organic interface, which is further supported by Raman, I–V, work‑function, and time‑resolved PL measurements.
Deposition of the Eu‑organic layer lowers the graphene work function and shifts the Dirac point, producing controllable n‑type doping that is reversible: at moderate TPO doses (above about 160 pJ²s), post‑annealing restores graphene close to its initial electronic state. The same TPO‑assisted AS‑ALD/MLD strategy also works on MoS₂ and WS₂, where fs‑laser irradiation forms oxygen‑containing species and point defects that act as nucleation sites for Eu‑BDC.
With further optimization of transfer methods, laser doses, and precursor chemistry - and potentially combining TPO with near‑field patterning to push resolution below 10 nm - the method offers a versatile route to integrate dense, patterned emitters, photodetectors, and other functional metal‑organic films into 2D‑material‑based optoelectronic and energy‑harvesting devices.
