A residual gas analyzer (RGA) is a small and usually rugged mass spectrometer, typically designed using quadrupole technology, used for process control and contamination monitoring in vacuum systems. The quadrupole consists of four parallel metal rods. Each opposing rod pair is connected together electrically, and a radio frequency (RF) voltage is applied between one pair of rods and the other. A direct current voltage is then superimposed on the RF voltage. Ions travel down the quadrupole between the rods. Only ions of a certain mass-to-charge ratio will reach the detector for a given ratio of voltages: other ions have unstable trajectories and will collide with the rods. This permits selection of an ion with a particular m/z or allows the operator to scan for a range of m/z-values by continuously varying the applied voltage. The QNC-MBE tool has at the moment two SRS 200 installed in the growth module, allowing for the study of many growth dynamics parameters (surface stoichiometry, sticking, incorporation, desorption, exchange, segregation).