Accurate detection of low-level radioactivity is critical in decommissioning. However, commercial sources used for calibration lack representativeness due to their flat surface. The objective of this work is to produce flexible and large area surface sources for alpha and beta emitters by functionalising aluminium foil. Functionalisation strategies were developed to provide these sources. The manganese oxide coated sample shows the highest fixation yield for $^{241}$Am: (70.0 ± 2.6)% and conforms to ISO 8769 for uniformity (92%).