We have investigated the performance and potential benefit of acoustic sensing for real-time monitoring and closed loop control of binary gas mixture compositions delivered from low vapor pressure metalorganic sources. Two solid phase sources were investigated in the presence of H 2 as a carrier gas: (1) trimethylindium (TMI) and (2) bis(cyclopentadienyl) magnesium ͑Cp 2 Mg͒, which have room temperature ͑25°C͒ vapor pressures of 2.5 and 0.04 Torr, respectively. An acoustic sensor was implemented on the gas feed line to measure the concentration-dependent speed of sound in the gas mixture. This enabled sensitivity and control at precursor levels as low as 0.6 ppm in H 2 . Closed loop process control was implemented to maintain TMI and Cp 2 Mg concentration target in the presence of intentionally introduced long term temperature drifts. Despite induced variations of the precursor vapor pressure up to 50%, the delivered composition was controlled to within ±0.15% for TMI (at 0.5 mol% set point) and ±0.3% for Cp 2 Mg (at 0.01 mol% set point). Short term variability could also be substantially reduced by the control scheme. This work demonstrates the feasibility of sensor-driven control systems for stable delivery of low vapor pressure, normally problematic precursor materials. In turn, this opens the door to utilization of a broader range of species which can be synthesized as chemical precursors
