Andrea, T., Rothermel, M., Reinert, T., Koal, T., & Butz, T. (2011). Creation of
3D microsculptures in PMMA by multiple angle proton irradiation. Nuclear Instruments and Methods in
Physics Research Section B: Beam Interactions with Materials and Atoms, 269(20),
2431-2434. doi:10.1142/S0129083512400244.