Helium-ion beam pattern imaging using irradiation-induced VB− centers in h-BN composite films

Spatially resolved characterization of helium-ion irradiation is important for beam profiling, irradiation-process control, and radiation-effects research. In this work, irradiation-induced color centers in hexagonal boron nitride (h-BN) were investigated for helium-ion beam-pattern imaging. Spherical h-BN/cycloolefin copolymer (Sh-BN/COC) composite films were irradiated with 50 keV He+ ions, while h-BN crystalline particles irradiated with 1.5 MeV Xe+ ions were examined as a comparative high-damage system. The irradiation fluence ranged from 1×1013 to 1 × 1016 ions cm−2. Following irradiation, a broad near-infrared photoluminescence (PL) band centered at approximately 820 nm was observed under 532 nm laser excitation. Room-temperature optically detected magnetic resonance features distributed around 3.45 GHz further supported the attribution of this emission to negatively charged boron-vacancy (VB−) centers. The PL intensity exhibited a non-monotonic dependence on irradiation fluence, while severe structural disorder and PL quenching occurred at the highest fluence. For beam-pattern imaging, the Sh-BN/COC composite film was irradiated through a five-slit mask and subsequently characterized by two-dimensional PL mapping. The reconstructed PL image reproduced the mask-defined irradiation pattern and resolved adjacent features separated by 40 μm. Using the conventional half-pitch definition, this feature size corresponds to a nominal equivalent spatial frequency of 12.5 line pairs per millimeter (lp/mm). These results demonstrate the feasibility of using irradiation-induced VB− centers in h-BN composite films as passive spatial recorders for post-irradiation helium-ion beam-pattern imaging.