Deterministic Fabrication of Fluorescent Nanostructures Exhibiting Magnetic dipolar Transitions

The fabrication process, as shown in schematic Fig. 1A, includes spin-coating of a mixture of electron beam resist (ma-N2401) with 0.1 mass percentage of the fluorescent europium complex (Eu(TTFA)3) with a final thickness of ~80 nm. Then the film is exposed using electron beam lithography and developed. Crucially, this process gives precise control over the shape and size of the resulting fluorescent structures with a resolution of approx. 100 nm. Eu(TTFA)3 is a metal-organic coordination complex that has a well-established emission process. Specifically, the TTFA ligands absorb UV light $(\lambda=375\ \text{nm})$ and through energy transfer the central $\text{Eu}^{3+}$ ions ${}^{\text{5}}\text{Do}$ manifold is populated and photons are emitted in a decay transition to ${}^{7}\mathrm{F}_{\mathrm{j}}\ \{\mathrm{j}=0$, 1, 2,3,4,5,6 $\}. {}^{5}\mathrm{D}_{0}\rightarrow {}^{7}\mathrm{F}_{1}$ and ${}^{5}\mathrm{D}_{0}\rightarrow {}^{7}\mathrm{F}_{2}$ are magnetic dipole and electric dipole transitions, respectively [3]. This transition remains present after the fabrication process, for doses between 100 $\mu \mathrm{C}\cdot \text{cm}^{-2}$ and 500 $\mu \mathrm{C} \cdot \text{cm}^{-2}$, as shown in Fig. 1B.