Methods for depositing materials onto micro-device workpieces in a reaction chamber. One embodiment of such a method comprises providing a flow of a first precursor through the reaction chamber to deposit the first precursor onto the micro-device workpiece in the reaction chamber, and providing a flow of a purge gas through the reaction chamber to purge excess amounts of the first precursor. The method continues by monitoring a parameter correlated to a quantity of the first precursor and/or the purge gas in the reaction chamber as the first precursor and/or the purge gas flows through the reaction chamber. An additional aspect of this method is terminating the flow of the first precursor and/or the flow of the purge gas based on the monitored parameter of the quantity of the first precursor and/or the purge gas. The procedure of monitoring a parameter correlated to a quantity of the first precursor and/or the purge gas can comprise determining a concentration of the first precursor and/or the purge gas in the reaction chamber using a selected radiation.