The study investigates the ambient degradation of exfoliated black phosphorus (BP) and its impact on field-effect transistors (FETs). Through a combination of microscopy and spectroscopy techniques, the researchers found that BP chemically degrades upon exposure to ambient conditions, forming oxidized phosphorus species. This degradation is accelerated on hydrophobic substrates like octadecyltrichlorosilane (OTS) and H-Si(111) compared to hydrophilic SiO2. The degradation causes significant increases in threshold voltage and decreases in FET current on/off ratio and mobility. However, atomic layer deposition (ALD) of aluminum oxide (AlOx) effectively suppresses this degradation, maintaining high FET performance for over two weeks. The findings highlight the importance of passivation in enhancing the environmental stability of BP, which could accelerate its implementation in electronic and optoelectronic applications.The study investigates the ambient degradation of exfoliated black phosphorus (BP) and its impact on field-effect transistors (FETs). Through a combination of microscopy and spectroscopy techniques, the researchers found that BP chemically degrades upon exposure to ambient conditions, forming oxidized phosphorus species. This degradation is accelerated on hydrophobic substrates like octadecyltrichlorosilane (OTS) and H-Si(111) compared to hydrophilic SiO2. The degradation causes significant increases in threshold voltage and decreases in FET current on/off ratio and mobility. However, atomic layer deposition (ALD) of aluminum oxide (AlOx) effectively suppresses this degradation, maintaining high FET performance for over two weeks. The findings highlight the importance of passivation in enhancing the environmental stability of BP, which could accelerate its implementation in electronic and optoelectronic applications.