Semiconductor-grade triethylboron (TEB) from SAFC Hitech was employed as the singlesource precursor and palladium membrane-purified hydrogen gas (H2) served as both a carrier gas and a co-reactant. To maintain stable precursor delivery, TEB was stored in a stainless-steel bubbler within a thermostat bath at 0°C, maintaining a vapor pressure of approximately 1.65 kPa. This stability was achieved by bubbling hydrogen gas through the liquid TEB.