The magnetization of a ferromagnetic layer can be controlled via spin-charge conversion (SCC) phenomena originating in an adjacent topological insulator (TI). Insertion of nonmagnetic interlayers between these materials has been demonstrated to enhance the SCC efficiency, as shown for Sb2Te3/Au/Co(Fe) heterostructures. The inert nature of the Sb2Te3/Au interface was assumed to preserve the topological surface state (TSS) of Sb2Te3, which mediates the SCC. Al is explored as an alternative to Au for its long spin diffusion length. Spin pumping experiments indicate the absence of SCC in the Sb2Te3/Al/Co heterostructure. Core level and valence band photoemission spectroscopies reveal that Al forms stable compounds with Te and Sb, thereby quenching the TSS of Sb2Te3, while the TSS is preserved upon the formation of the TI/Au interface. These results demonstrate directly the major influence of material …