Investigation of spitting effect in the boron target preparation using vapour deposition technique

Self-supported and carbon/aluminum-backed isotopically enriched thin boron targets were prepared by the vapour deposition technique using electron beam. To mitigate spitting effects observed during this process, boron powder was evaporated in both paste and pellet forms. Effective reduction of spitting was achieved by initially heating boron at low currents followed by its step-wise increase. Analysis of boron samples at various stages of evaporation was done by X-ray Diffraction (XRD) and Fourier-transform Infrared spectroscopy (FTIR). Direct exposure to high-energy electron beams contributed to a decrease in boron oxide and hydride compounds, thereby aiding in minimizing spitting. However, upon exposure to air, the evaporated film underwent surface oxidation, confirmed by Transmission Electron Microscopy (TEM), Energy Dispersive X-ray spectroscopy (EDX) and X-ray Photoelectron Spectroscopy (XPS) measurements. Further investigations into the longevity of the film (target) were conducted using optical microscopy and FTIR spectroscopy. These analyses revealed hydrogenation and oxidation of the film upon exposure to atmosphere, resulting in increased fragility and noticeable colour changes over time.